Synthetics, Mineral Oils, and Bio-Based Lubricants Chemistry and Technology

Synthetics, Mineral Oils, and Bio-Based Lubricants Chemistry and Technology

Copyright 2006 by Taylor & Francis Group, LLC

CHEMICAL INDUSTRIES A Series of Reference Books and Textbooks

Consulting Editor HEINZ HEINEMANN

Berkeley, California

1. 2. 3. 4. 5. 6. 7. 8.

9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.

22. 23. 24. 25. 26. 27.

Fluid Catalytic Cracking with Zeolite Catalysts, Paul B. Venuto and E. Thomas Habib, Jr. Ethylene: Keystone to the Petrochemical Industry, Ludwig Kniel, Olaf Winter, and Karl Stork The Chemistry and Technology of Petroleum, James G. Speight The Desulfurization of Heavy Oils and Residua, James G. Speight Catalysis of Organic Reactions, edited by William R. Moser Acetylene-Based Chemicals from Coal and Other Natural Resources, Robert J. Tedeschi Chemically Resistant Masonry, Walter Lee Sheppard, Jr. Compressors and Expanders: Selection and Application for the Process Industry, Heinz P. Bloch, Joseph A. Cameron, Frank M. Danowski, Jr., Ralph James, Jr., Judson S. Swearingen, and Marilyn E. Weightman Metering Pumps: Selection and Application, James P. Poynton Hydrocarbons from Methanol, Clarence D. Chang Form Flotation: Theory and Applications, Ann N. Clarke and David J. Wilson The Chemistry and Technology of Coal, James G. Speight Pneumatic and Hydraulic Conveying of Solids, O. A. Williams Catalyst Manufacture: Laboratory and Commercial Preparations, Alvin B. Stiles Characterization of Heterogeneous Catalysts, edited by Francis Delannay BASIC Programs for Chemical Engineering Design, James H. Weber Catalyst Poisoning, L. Louis Hegedus and Robert W. McCabe Catalysis of Organic Reactions, edited by John R. Kosak Adsorption Technology: A Step-by-Step Approach to Process Evaluation and Application, edited by Frank L. Slejko Deactivation and Poisoning of Catalysts, edited by Jacques Oudar and Henry Wise Catalysis and Surface Science: Developments in Chemicals from Methanol, Hydrotreating of Hydrocarbons, Catalyst Preparation, Monomers and Polymers, Photocatalysis and Photovoltaics, edited by Heinz Heinemann and Gabor A. Somorjai Catalysis of Organic Reactions, edited by Robert L. Augustine Modern Control Techniques for the Processing Industries, T. H. Tsai, J. W. Lane, and C. S. Lin Temperature-Programmed Reduction for Solid Materials Characterization, Alan Jones and Brian McNichol Catalytic Cracking: Catalysts, Chemistry, and Kinetics, Bohdan W. Wojciechowski and Avelino Corma Chemical Reaction and Reactor Engineering, edited by J. J. Carberry and A. Varma Filtration: Principles and Practices: Second Edition, edited by Michael J. Matteson and Clyde Orr

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Corrosion Mechanisms, edited by Florian Mansfeld Catalysis and Surface Properties of Liquid Metals and Alloys, Yoshisada Ogino Catalyst Deactivation, edited by Eugene E. Petersen and Alexis T. Bell Hydrogen Effects in Catalysis: Fundamentals and Practical Applications, edited by Zoltán Paál and P. G. Menon Flow Management for Engineers and Scientists, Nicholas P. Cheremisinoff and Paul N. Cheremisinoff Catalysis of Organic Reactions, edited by Paul N. Rylander, Harold Greenfield, and Robert L. Augustine Powder and Bulk Solids Handling Processes: Instrumentation and Control, Koichi Iinoya, Hiroaki Masuda, and Kinnosuke Watanabe Reverse Osmosis Technology: Applications for High-Purity-Water Production, edited by Bipin S. Parekh Shape Selective Catalysis in Industrial Applications, N. Y. Chen, William E. Garwood, and Frank G. Dwyer Alpha Olefins Applications Handbook, edited by George R. Lappin and Joseph L. Sauer Process Modeling and Control in Chemical Industries, edited by Kaddour Najim Clathrate Hydrates of Natural Gases, E. Dendy Sloan, Jr. Catalysis of Organic Reactions, edited by Dale W. Blackburn Fuel Science and Technology Handbook, edited by James G. Speight Octane-Enhancing Zeolitic FCC Catalysts, Julius Scherzer Oxygen in Catalysis, Adam Bielanski and Jerzy Haber The Chemistry and Technology of Petroleum: Second Edition, Revised and Expanded, James G. Speight Industrial Drying Equipment: Selection and Application, C. M. van’t Land Novel Production Methods for Ethylene, Light Hydrocarbons, and Aromatics, edited by Lyle F. Albright, Billy L. Crynes, and Siegfried Nowak Catalysis of Organic Reactions, edited by William E. Pascoe Synthetic Lubricants and High-Performance Functional Fluids, edited by Ronald L. Shubkin Acetic Acid and Its Derivatives, edited by Victor H. Agreda and Joseph R. Zoeller Properties and Applications of Perovskite-Type Oxides, edited by L. G. Tejuca and J. L. G. Fierro Computer-Aided Design of Catalysts, edited by E. Robert Becker and Carmo J. Pereira Models for Thermodynamic and Phase Equilibria Calculations, edited by Stanley I. Sandler Catalysis of Organic Reactions, edited by John R. Kosak and Thomas A. Johnson Composition and Analysis of Heavy Petroleum Fractions, Klaus H. Altgelt and Mieczyslaw M. Boduszynski NMR Techniques in Catalysis, edited by Alexis T. Bell and Alexander Pines Upgrading Petroleum Residues and Heavy Oils, Murray R. Gray Methanol Production and Use, edited by Wu-Hsun Cheng and Harold H. Kung Catalytic Hydroprocessing of Petroleum and Distillates, edited by Michael C. Oballah and Stuart S. Shih The Chemistry and Technology of Coal: Second Edition, Revised and Expanded, James G. Speight Lubricant Base Oil and Wax Processing, Avilino Sequeira, Jr. Catalytic Naphtha Reforming: Science and Technology, edited by George J. Antos, Abdullah M. Aitani, and José M. Parera Catalysis of Organic Reactions, edited by Mike G. Scaros and Michael L. Prunier Catalyst Manufacture, Alvin B. Stiles and Theodore A. Koch Handbook of Grignard Reagents, edited by Gary S. Silverman and Philip E. Rakita Shape Selective Catalysis in Industrial Applications: Second Edition, Revised and Expanded, N. Y. Chen, William E. Garwood, and Francis G. Dwyer Hydrocracking Science and Technology, Julius Scherzer and A. J. Gruia

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67. Hydrotreating Technology for Pollution Control: Catalysts, Catalysis, and Processes, edited by Mario L. Occelli and Russell Chianelli 68. Catalysis of Organic Reactions, edited by Russell E. Malz, Jr. 69. Synthesis of Porous Materials: Zeolites, Clays, and Nanostructures, edited by Mario L. Occelli and Henri Kessler 70. Methane and Its Derivatives, Sunggyu Lee 71. Structured Catalysts and Reactors, edited by Andrzej Cybulski and Jacob A. Moulijn 72. Industrial Gases in Petrochemical Processing, Harold Gunardson 73. Clathrate Hydrates of Natural Gases: Second Edition, Revised and Expanded, E. Dendy Sloan, Jr. 74. Fluid Cracking Catalysts, edited by Mario L. Occelli and Paul O’Connor 75. Catalysis of Organic Reactions, edited by Frank E. Herkes 76. The Chemistry and Technology of Petroleum: Third Edition, Revised and Expanded, James G. Speight 77. Synthetic Lubricants and High-Performance Functional Fluids: Second Edition, Revised and Expanded, Leslie R. Rudnick and Ronald L. Shubkin 78. The Desulfurization of Heavy Oils and Residua, Second Edition, Revised and Expanded, James G. Speight 79. Reaction Kinetics and Reactor Design: Second Edition, Revised and Expanded, John B. Butt 80. Regulatory Chemicals Handbook, Jennifer M. Spero, Bella Devito, and Louis Theodore 81. Applied Parameter Estimation for Chemical Engineers, Peter Englezos and Nicolas Kalogerakis 82. Catalysis of Organic Reactions, edited by Michael E. Ford 83. The Chemical Process Industries Infrastructure: Function and Economics, James R. Couper, O. Thomas Beasley, and W. Roy Penney 84. Transport Phenomena Fundamentals, Joel L. Plawsky 85. Petroleum Refining Processes, James G. Speight and Baki Özüm 86. Health, Safety, and Accident Management in the Chemical Process Industries, Ann Marie Flynn and Louis Theodore 87. Plantwide Dynamic Simulators in Chemical Processing and Control, William L. Luyben 88. Chemical Reactor Design, Peter Harriott 89. Catalysis of Organic Reactions, edited by Dennis G. Morrell 90. Lubricant Additives: Chemistry and Applications, edited by Leslie R. Rudnick 91. Handbook of Fluidization and Fluid-Particle Systems, edited by Wen-Ching Yang 92. Conservation Equations and Modeling of Chemical and Biochemical Processes, Said S. E. H. Elnashaie and Parag Garhyan 93. Batch Fermentation: Modeling, Monitoring, and Control, Ali Çinar, Gülnur Birol, Satish J. Parulekar, and Cenk Ündey 94. Industrial Solvents Handbook, Second Edition, Nicholas P. Cheremisinoff 95. Petroleum and Gas Field Processing, H. K. Abdel-Aal, Mohamed Aggour, and M. Fahim 96. Chemical Process Engineering: Design and Economics, Harry Silla 97. Process Engineering Economics, James R. Couper 98. Re-Engineering the Chemical Processing Plant: Process Intensification, edited by Andrzej Stankiewicz and Jacob A. Moulijn 99. Thermodynamic Cycles: Computer-Aided Design and Optimization, Chih Wu 100. Catalytic Naphtha Reforming: Second Edition, Revised and Expanded, edited by George T. Antos and Abdullah M. Aitani 101. Handbook of MTBE and Other Gasoline Oxygenates, edited by S. Halim Hamid and Mohammad Ashraf Ali 102. Industrial Chemical Cresols and Downstream Derivatives, Asim Kumar Mukhopadhyay 103. Polymer Processing Instabilities: Control and Understanding, edited by Savvas Hatzikiriakos and Kalman B . Migler 104. Catalysis of Organic Reactions, John Sowa

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105. Gasification Technologies: A Primer for Engineers and Scientists, edited by John Rezaiyan and Nicholas P. Cheremisinoff 106. Batch Processes, edited by Ekaterini Korovessi and Andreas A. Linninger 107. Introduction to Process Control, Jose A. Romagnoli and Ahmet Palazoglu 108. Metal Oxides: Chemistry and Applications, edited by J. L. G. Fierro 109. Molecular Modeling in Heavy Hydrocarbon Conversions, Michael T. Klein, Ralph J. Bertolacini, Linda J. Broadbelt, Ankush Kumar and Gang Hou 110. Structured Catalysts and Reactors, Second Edition, edited by Andrzej Cybulski and Jacob A. Moulijn 111. Synthetics, Mineral Oils, and Bio-Based Lubricants: Chemistry and Technology, edited by Leslie R. Rudnick

Copyright 2006 by Taylor & Francis Group, LLC

Synthetics, Mineral Oils, and Bio-Based Lubricants Chemistry and Technology

Leslie R. Rudnick Pennsylvania State University State College, Pennsylvania

Boca Raton London New York

A CRC title, part of the Taylor & Francis imprint, a member of the Taylor & Francis Group, the academic division of T&F Informa plc.

Copyright 2006 by Taylor & Francis Group, LLC

Published in 2006 by CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2006 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group No claim to original U.S. Government works Printed in the United States of America on acid-free paper 10 9 8 7 6 5 4 3 2 1 International Standard Book Number-10: 1-57444-723-8 (Hardcover) International Standard Book Number-13: 978-1-57444-723-1 (Hardcover) Library of Congress Card Number 2005054272 This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. No part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright.com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC) 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data Synthetics, mineral oils, and bio based lubricants / edited by Leslie R. Rudnick. p. cm. -- (Chemical industries ; 111) Includes bibliographical references and index. ISBN 1-57444-723-8 (alk. paper) 1. Lubrication and lubricants. I. Rudnick, Leslie R., 1947- II. Chemical industries ; v. 111. TJ1077.S55 2005 621.8'9--dc22

2005054272

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Preface Lubricants are necessary for the efficient use of machinery. Because of this, the variety of lubricating fluids has grown to meet the demands of new machines having more stringent requirements due to their operation under more severe conditions or in challenging environments. This book is a collection of chapters on lubricating base fluids, applications and trends and provides detailed information on the chemical and physical properties and performance characteristics of all of the major areas of lubrication. An authority in their respective area has written each chapter. This book follows the format of Synthetic Lubricants and High-Performance Functional Fluids, Second Edition but has been greatly expanded to include new chapters on: cyclohydrocarbons, gas-to-liquids (GTL), natural oils as lubricants, chemically modified vegetable oils, the biotechnological enhancement of soybean oil, automatic and continuously variable transmission fluids, environmentally friendly hydraulic fluids, fire-resistant hydraulic fluids, vegetable oil-based engine oils, magnetizable fluids, lubricants for the disk drive industry, fluids for food-grade applications, the critical cleaning of advanced lubricants from surfaces, and diesel automotive trends. A new convention, first described by Stephen Godfree, publisher of the Journal of Synthetic Lubrication (Vol.17, Number 1, 2000) has been adopted for the description of upgraded mineral oil base fluids. This editorial has been included in Appendix 1 of this book. First and foremost I would like to acknowledge the assistance of Rita Lazazzaro throughout the several publishing projects we have worked on together. I have valued her input and suggestions in making the previous titles and this current project successful. I also want to thank

Copyright 2006 by Taylor & Francis Group, LLC

Marianne Russell and Laurie Passano for their help in early stages of this current project and to Russell Dekker for his support in publishing this and the previous books on lubricants and lubricant additives. I want to thank Anita Lekhwani, Fred Coppersmith, Michael Masiello, Vanessa Hodgkinson and Susan Fox-Greenberg of Taylor and Francis Books and K. Mohan Kemar of Newgen Imaging Systems for all of their efforts in bringing this book to completion. For this book, which includes over 60 contributing authors, I am very fortunate to have worked with colleagues who helped me to take this project to completion. I sincerely thank each and every one of you. The real credit goes to you individually and collectively. I dedicate this book to the memory of my father, Robert H. Rudnick, for encouraging me to follow my instincts to become a scientist, to my father-in-law, Sydney M. Miner for teaching me the need to describe the more theoretical and difficult aspects of my work in layman’s terms so as to promote the "useful" aspects of my work, and to two very close friends, Anne Arnstein Diamond and Becky Sidore Spitz who always shared their love of the written word and many other aspects of human endeavor. Finally, thank you to Paula, Eric and Rachel for your constant support and encouragement. In doing a project like this one gains experience, colleagues, friends, a deeper knowledge about the subject and even an appreciation for the process of publishing. I am constantly pleased to see each of you grow in the fields that you have chosen and to have you tell me of your experiences. Leslie R. Rudnick

Editor Leslie R. Rudnick is a Senior Scientist at The Energy Institute, The Pennsylvania State University, University Park. The author, coauthor, editor and coeditor of over 75 journal articles, book chapters, and books, including Synthetic Lubricants and High-Performance Functional Fluids, Second Edition (Marcel Dekker, Inc.) and Lubricant Additives: Chemistry and Applications (Marcel Dekker, Inc.), he holds 29 patents and is a member of the Society of Tribologists and Lubrication Engineers,

Copyright 2006 by Taylor & Francis Group, LLC

the American Chemical Society, the American Society for Testing Materials, and the Society of Automotive Engineers. Dr. Rudnick serves on the editorial board of the Journal of Synthetic Lubrication and received a B.S. degree (1969) in chemistry from the University of Iowa, Iowa City, and M.S. (1972) and Ph.D. (1975) degrees in chemistry from Rutgers University, New Brunswick, New Jersey.

Contributors Atanu Adhvaryu The Pennsylvania State University University Park, Pennsylvania

J. David Carlson Lord Corporation Cary, North Carolina

Garrett M. Grega Anderol Inc. East Hanover, New Jersey

Ewa A. Bardasz The Lubrizol Corporation Wickliffe, Ohio

Maryann Casserino Innovene Naperville, Illinois

Wilfried J. Bartz Technische Akademie Esslingen Ostfildern, Germany

Lois J. Gschwender Air Force Research Laboratory Wright-Patterson Air Force Base Ohio

Massimo Ciali (Retired) Sasol Italy S.p.A Milan, Italy

Gregory A. Bell E. I. DuPont de Nemours and Co., Inc. Deepwater, New Jersey

Roscoe R. Cooley Sasol North America Inc. Houston, Texas

Tom Black Ferrotec (USA) Corp. Nashua, New Hampshire

Serge Decroocq Innovene Lavéra, France

Lynnette Bowen Clarity Chemicals Limited Harrow, England

Kevin L. Dickey Quaker Chemical Corporation Conshohocken, Pennsylvania

Joseph F. Braza Nye Lubricants, Incorporated Fairhaven, Massachusetts

Charles R. Dietrich USDA-ARS Plant Genetics Research Unit Donald Danforth Plant Science Center St. Louis, Missouri

William L. Brown Union Carbide Corporation Tarrytown, New York Stephen A. Burian Santovac Fluids, Inc. Findett Corporation St. Charles, Missouri Richard G. Butler Chemtool Incorporated Crystal Lake, Illinois Edgar B. Cahoon USDA-ARS Plant Genetics Research Unit Donald Danforth Plant Science Center St. Louis, Missouri

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Ronald M. Epstein (Retired) Halocarbon Products Corporation River Edge, New Jersey Sevim Z. Erhan USDA, ARS, NCAUR Peoria, Illinois Louis L. Ferstandig Halocarbon Products Corporation River Edge, New Jersey Frank J. Gomba (Retired) United States Naval Academy Annapolis, Maryland

Sibtain Hamid Santovac Fluids, Inc. Findett Corporation St. Charles, Missouri H. Ernest Henderson Lithcon Petroleum USA Inc. Tulsa, Oklahoma Suzzy Ho ExxonMobil Chemical Company Edison, New Jersey Jon Howell E.I. DuPont de Nemours and Co., Inc. Deepwater, New Jersey Barbara F. Kanegsberg BFK Solutions, LLC Pacific Palisades, California Tom E. Karis Hitachi Global Storage Technologies San Jose, California John J. Kurosky Anderol Inc. Oakville, Ontario Stephen C. Lakes Cognis Corporation Cincinnati, Ohio Dennis A. Lauer Klüber Lubrication North America L.P. Londonderry, New Hampshire

Saurabh Lawate Lubrizol Corporation Wickliffe, Ohio

W. David Phillips Great Lakes Chemical Corp. Manchester, England

Simon Lawford Cognis Performance Chemicals UK Ltd Southampton, Hantz, UK

Douglas C. Placek Degussa-RohMax Oil Additives Horsham, Pennsylvania

Darren J. Lesinski Anderol Inc. East Hanover, New Jersey Kenneth C. Lilje CPI Engineering Services, Inc. Midland, Michigan Michael P. Marino Consultant Pocono Pines, Pennsylvania Michael L. McMillan General Motors Research & Development Warren, Michigan Kedar Murthy GE Silicones Waterford, New York Francesca Navarrini Sasol Italy S.p.A P. Dugnano, Italy

Clay Quinn GE Silicones Waterford, New York Michael John Raab Anderol Inc. East Hanover, New Jersey Steven James Randles Uniqema Redcar Cleveland England Blaine N. Rhodes Bellevue, Washington Leslie R. Rudnick The Energy Institute The Pennsylvania State University University Park, Pennsylvania Monica A. Schmidt USDA-ARS Plant Genetics Research Unit Donald Danforth Plant Science Center St. Louis, Missouri

Robert Perry GE Silicones Waterford, New York

Shirley E. Schwartz (Retired) General Motors Corporation

F. Alexander Pettigrew Ethyl Corporation Richmond, Virginia

Brajendra K. Sharma The Pennsylvania State University University Park, Pennsylvania

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Ronald L. Shubkin Baton Rouge, Louisiana Robert Silverstein The Orelube Corporation Plainview, New York Robert E. Singler Raytheon Material Engineering Lexington, Massachussets Carl E. Synder Air Force Research Laboratory Wright-Patterson Air Force Base Ohio Z. Ahmed Tahir Anderol Inc. East Hanover, New Jersey Frank Traver GE Silicones Waterford, New York Simon Tung General Motors Research & Development Warren, Michigan Clifford G. Venier (Retired) Shell Global Solutions US, Inc. Houston, Texas Uwe Wallfahrer Akzo Nobel Chemicals GmbH Dueren, Germany R. David Whitby Pathmaster Marketing Ltd Woking, England Margaret M. Wu ExxonMobil Research & Engineering Company Annandale, New Jersey

Contents

Part I

Fluids

Chapter 1

Polyalphaolefins Leslie R. Rudnick

Chapter 2

Polyinternalolefins Francesca Navarrini, Massimo Ciali, and Roscoe Cooley

Chapter 3

Esters Steven James Randles

Chapter 4

Neutral Phosphate Esters W. David Phillips, Douglas C. Placek, and Michael P. Marino

Chapter 5

Polymer Esters Uwe Wallfahrer and Lynnette Bowen

Chapter 6

Polyalkylene Glycols Simon Lawford

Chapter 7

Alkylated Aromatics Margaret M. Wu and Suzzy Ho

Chapter 8

Perfluoroalkylpolyethers Gregory A. Bell and Jon Howell

Chapter 9

Polyphenyl Ether Lubricants Sibtain Hamid and Stephen A. Burian

Chapter 10

Cyclohydrocarbons Sibtain Hamid

Chapter 11

Polychlorotrifluoroethylene Ronald M. Epstein and Louis L. Ferstandig

Chapter 12

Silicones Robert Perry, Clay Quinn, Frank Traver, and Kedar Murthy

Chapter 13

Silahydrocarbons Carl E. Snyder and F. Alexander Pettigrew

Chapter 14

Phosphazenes Robert E. Singler and Frank J. Gomba

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Chapter 15

Dialkyl Carbonates Leslie R. Rudnick

Chapter 16

Alkylcyclopentanes Clifford G. Venier

Chapter 17

Polybutenes Serge Decroocq and Maryann Casserino

Chapter 18

Chemically Modified Mineral Oils H. Ernest Henderson

Chapter 19

Gas to Liquids H. Ernest Henderson

Chapter 20

Comparison of Synthetic, Mineral Oil, and Bio-Based Lubricant Fluids Leslie R. Rudnick and Wilfried J. Bartz

Part II

Bio-Based Lubricants

Chapter 21

Natural Oils as Lubricants Leslie R. Rudnick and Sevim Z. Erhan

Chapter 22

Chemically Functionalized Vegetable Oils Sevim Z. Erhan, Atanu Adhvaryu, and Brajendra K. Sharma

Chapter 23

Biotechnological Enhancement of Soybean Oil for Lubricant Applications Monica A. Schmidt, Charles R. Dietrich, and Edgar B. Cahoon

Part III

Applications

Chapter 24

Automotive Crankcase Oils Stephen C. Lakes

Chapter 25

Fluids for Conventional Automatic and Continuously Variable Transmissionns (CVTs) Sibtain Hamid

Chapter 26

Automotive Gear Lubricants Stephen C. Lakes

Chapter 27

Industrial Gear Lubricants Dennis A. Lauer

Chapter 28

Synthetic Greases Joseph F. Braza

Chapter 29

Compressors and Pumps Kenneth C. Lilje

Chapter 30

Refrigeration Lubricants Steven James Randles

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Chapter 31

Hydraulics Douglas G. Placek

Chapter 32

Environmentally Friendly Hydraulic Fluids Saurabh Lawate

Chapter 33

Fire-Resistant Hydraulic Fluids Kevin L. Dickey

Chapter 34

Vegetable Oil Based Internal Combustion Engine Oil Blaine N. Rhodes

Chapter 35

Magnetizable Fluids Tom Black and J. David Carlson

Chapter 36

Metalworking Fluids William L. Brown and Richard G. Butler

Chapter 37

Lubricants for Near Dry Machining Robert Silverstein

Chapter 38

Lubricants for the Disk Drive Industry Tom E. Karis

Chapter 39

Synthetic-Based Food-Grade Lubricants and Greases Michael J. Raab

Chapter 40

Critical Cleaning of Advanced Lubricants from Surfaces Ronald L. Shubkin and Barbara F. Kanegsberg

Part IV

Trends

Chapter 41

Automotive Trends in Europe R. David Whitby

Chapter 42

Automotive Trends in North America Simon C. Tung, Michael L. McMillan, and Shirley E. Schwartz

Chapter 43

Diesel Automotive Trends Ewa A. Bardasz

Chapter 44

Automotive Trends in Asia R. David Whitby

Chapter 45

Automotive Trends in South America R. David Whitby

Chapter 46

Industrial Lubricant Trends Garrett M. Grega, John J. Kurosky, Darren J. Lesinski, Michael J. Raab, and Z. Ahmed Tahir

Chapter 47

Trends Toward Synthetic Fluids and Lubricants in Aerospace Carl E. Snyder, Jr. and Lois J. Gschwender

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Chapter 48

Part V

Commercial Developments R. David Whitby

Methods and Resources

Chapter 49

Lubricant Performance Test Methods and Some Product Specifications Leslie R. Rudnick

Chapter 50

Lubricant Industry Related Terms and Acronyms Leslie R. Rudnick

Chapter 51

Lubricant Industry Internet Resources Leslie R. Rudnick

Appendix

Publisher’s Note: The Meaning of “Synthetic”

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Part I Fluids

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1

Polyalphaolefins Leslie R. Rudnick CONTENTS 1.1 1.2

1.3 1.4

1.5

Introduction Historical Development 1.2.1 Technical 1.2.2 Commercial 1.2.2.1 AMSOIL, Inc. 1.2.2.2 Mobil Oil Corporation 1.2.2.3 Gulf Oil Company 1.2.2.4 Chevron Corporation 1.2.2.5 Amoco 1.2.2.6 Ethyl Corporation 1.2.2.7 Exxon Corporation 1.2.2.8 Quantum Chemical Corporation 1.2.2.9 Castrol Limited 1.2.2.10 Uniroyal Chemical Company 1.2.2.11 Neste Chemical 1.2.2.12 Texaco 1.2.2.13 Shell Chemical 1.2.2.14 Idemitsu Petrochemicals 1.2.2.15 Sasol Chemistry Properties 1.4.1 Physical Properties 1.4.1.1 Commercial PAOs 1.4.1.2 Comparison to Mineral Oils 1.4.1.3 Properties of Blends 1.4.2 Chemical Properties 1.4.2.1 Thermal Stability 1.4.2.2 Hydrolytic Stability 1.4.2.3 Oxidative Stability Applications and Performance Characteristics 1.5.1 Overview of Application Areas 1.5.2 Performance Testing for Automotive Applications 1.5.2.1 Crankcase 1.5.2.2 Transmissions 1.5.2.3 Gears 1.5.2.4 Seal Compatibility 1.5.2.5 Economy 1.5.3 Performance Testing for Industrial Applications 1.5.3.1 Refrigeration Compressors 1.5.3.2 Gear Oils 1.5.3.3 Turbines 1.5.3.4 Hydraulic Oil Performance 1.5.3.5 Metal Working Performance 1.5.3.6 Cost Savings

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1.5.4

Applications Sensitive to Health and Environmental Issues 1.5.4.1 Food contact 1.5.4.2 Cosmetics and Toiletries 1.5.4.3 Off-Shore Drilling 1.5.4.4 Miscellaneous 1.5.5 Military Applications 1.5.6 Space Applications 1.6 Markets and Production Capacities 1.6.1 Demand by Segment and Region 1.6.2 Emerging Markets 1.6.3 PAO Production Capacity 1.6.4 Competitive Products 1.6.4.1 Very High Viscosity Index Oils 1.6.4.2 High Viscosity Index Oils 1.6.4.3 Polyinternalolefins 1.7 Conclusion 1.7.1 Regulatory 1.7.2 Performance and Cost-Effectiveness 1.7.3 Original Equipment Manufacturers 1.7.4 Petroleum Companies and Blenders 1.7.5 Consumer 1.7.6 New Technology 1.7.6.1 Dodecene-Based PAOs 1.7.6.2 Mid-Viscosity PAOs Acknowledgements References

1.1 INTRODUCTION Further development in versatility and quality of Polyalphaolefins (PAOs) continues to improve this class of synthetic base fluids. In addition to synthetic esters, PAOs are the most commonly used synthetic base fluids in lubricants. PAOs are true synthetics since they are prepared under carefully controlled conditions from essentially pure alphaolefins, which are themselves synthesized. PAOs have been used in lubricants since the early 1950s and new versions are being introduced to provide lubricant formulators “mid-vis” properties, between the conventional 2 to 10 cSt fluids and the high-viscosity PAOs. For example, ExxonMobil Chemical has announced a planned upgrading of their plant in Beaumont, Texas that will make additional synthetic PAO. This will include new products expected to have lower volatility, better lowtemperature properties, and higher viscosity index (VI). ExxonMobil have a SpectraSyn™ line of PAOs ranging in viscosity from 2 to 100 cSt. They also offer a SpectraSyn™ Ultra line of PAOs with viscosities >100 cSt. The term “polyalphaolefin,” or PAO, is commonly used to designate these fluids, actually saturated olefin oligomers, and this designation will be used in this chapter. This class of synthetic high-performance functional fluids has been developed to meet the increasingly stringent demands placed on today’s working fluids. The term PAO

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was first used by Gulf Oil Company (later acquired by Chevron), but it has now become an accepted generic appellation for hydrocarbons manufactured by the catalytic oligomerization (polymerization to low molecular weight products) of linear-olefins having six or more (usually ten) carbon atoms [1]. Technological advances are often accompanied by a variety of problems and complications not previously anticipated. Advances in the function and efficient operation of modern machines and engines have brought new challenges relating to the satisfactory use and performance of existing functional fluids. Sum of these challenges are as follows: • Operation under increasingly severe conditions. • The need for more cost-effective and, hence, competitive

operations. • The need to reduce the dependence on the availability of

crude oil stocks. • The specialized performance requirements of emerging

end-use applications. • The necessity of accounting for the critically impor-

tant, but long-ignored, toxicological and biodegradable characteristics of the fluids being used. Today, mineral oil base stocks are being refined to give products that are certainly superior to those available a few years ago. But the limits to which mineral oils

can be economically refined are being strained. In order to satisfactorily address the challenge of solving the problems listed, industry is turning to synthetic alternatives. Polyalphaolefins are gaining rapid acceptance as highperformance lubricants and functional fluids because they exhibit certain inherent, and highly desirable, characteristics [1]. Some of these favorable properties are as follows: • • • • • • • • • • • •

A wide operational temperature range. Good viscometrics (high VI). Thermal stability. Oxidative stability. Hydrolytic stability. Biodegradability (for low viscosity grades). Shear stability. Low corrosivity. Compatibility with mineral oils. Compatibility with various materials of construction. Low toxicity. Manufacturing flexibility that allows “tailoring” products to specific end-use application requirements.

1.2 HISTORICAL DEVELOPMENT 1.2.1 Technical Synthetic oils consisting only of hydrocarbon molecules were first produced in 1877 by the prominent chemists Charles Friedel and James Mason Crafts [2]. Standard Oil Company of Indiana attempted to commercialize a synthetic hydrocarbon oil in 1929 but was unsuccessful because of a lack of demand. In 1931, Standard Oil in a paper by Sullivan et al. [3] disclosed a process for the polymerization of olefins to form liquid products. These workers used cationic polymerization catalysts such as aluminum chloride to polymerize olefin mixtures obtained from the thermal cracking of wax. At about the same time that this work was being carried out, H. Zorn of I.G. Farben Industries independently discovered the same process [4]. The first use of a linear α-olefin to synthesize an oil was disclosed by Montgomery et al. in a patent issued to Gulf Oil Company in 1951 [5]. Aluminum chloride was used in these experiments as it was in the earlier work with olefins from cracked wax. The use of free-radical initiators as α-olefin oligomerization catalysts was first patented by Garwood of SoconyMobil in 1960 [6]. Coordination complex catalysts such as the ethylaluminum sesquichloride/titanium tetrachloride system were disclosed in a patent issued to Southern et al. at Shell Research in 1961 [7]. The fluids produced by the various catalyst systems described earlier in this chapter contained oligomers with a wide range of molecular weights. The compositions and internal structures of these fluids resulted in viscosity/

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temperature characteristics that gave them no particular advantage over the readily available and significantly less expensive mineral oils of the day. In 1968, Brennan at Mobil Oil patented a process for the oligomerization of α-olefins using a BF3 catalyst system [8]. Prior to this, BF3 catalysis had given irreproducible results. Brennan showed that the reaction could be controlled if two streams of olefins were mixed in the reactor. The first stream contained the olefin plus a BF3 ·ROH complex, where ROH is an alcohol. The second stream contained the olefin saturated with gaseous BF3 . Of particular interest was the fact that this catalyst system produced a product consisting of a mixture of oligomers that was markedly peaked at the trimer. Shubkin of Ethyl Corporation showed that H2 O [9], as well as other protic cocatalysts such as alcohols and carboxylic acids [10], could be used in conjunction with BF3 to produce oligomers of uniform quality. The experimental technique employed a molar excess of BF3 in relation to the cocatalyst. The excess was achieved either by sparging the reaction medium with BF3 gas throughout the course of the reaction or by conducting the reaction under a slight pressure of BF3 . These studies showed that the oligomerization products exhibited pour points that were well below those anticipated for such compounds, even when dimeric products were allowed to remain in the final mixture. The molecular structure of the dimer was believed to consist of a straight carbon chain containing a single methyl group near the middle. Such branched structures were known to exhibit relatively high pour points. More pertinent to the current subject, these were the first patents to address the potential importance of PAOs derived from such BF3 · ROH catalyst systems as synthetic lubricants. Shubkin et al. later showed that the unique low-temperature properties could be attributed to a high degree of branching in the molecular structure [11].

1.2.2 Commercial The commercial development of PAO fluids as lubricants and high-performance functional fluids began in the early 1970s, but significant growth in markets and in the variety of end-use applications did not begin until the latter part of the 1980s. During this time, several companies played significant roles with both R&D and market development efforts [12]. 1.2.2.1 AMSOIL, Inc. AMSOIL, Inc. was apparently the first company to introduce a full synthetic API certified lubricant into the market in 1972. However, this product was 100% diester based. In 1973, AMSOIL introduced the first synthetic-based two-cycle oil. It was not until late 1977 that AMSOIL introduced full-synthetic 10W-40 motor oil based on PAO/ester [13]. AMSOIL has also introduced hydraulic

and compressor oils and a semisynthetic diesel engine oil, a full-synthetic gear oil based on PAO/ester, and PAObased greases. In 1996, they introduced a PAO/ester based 0W-30 motor oil. 1.2.2.2 Mobil Oil Corporation Mobil Oil Corporation was the first company to introduce a PAO-based synthetic lubricant. In 1973, Mobil began marketing a synthetic motor oil for use in automotive engines in overseas markets. Circulating oils and gear oils were added to the Mobil line in 1974. The first U.S. test marketing of Mobil 1 Synthesized Engine Lubricant began in the autumn of 1974. The test was expanded to eight cities in September 1975, and to all Mobil marketing areas in April 1976. Mobil 1 was initially an SAE 5W-20 product, but it was later replaced by a 5W-30 fluid based on PAO and a neopentyl polyol ester. The polyol ester improved additive solubility and increased seal swell. Mobil’s product distribution was extended to Canada, Japan, and several European countries in 1977. In the same year, Mobil introduced Delvac 1, a PAO-based product aimed at the truck fleet market. Mobil also pioneered PAObased industrial lubricants with its line of Mobil SHC products. Mobil’s PAO plant in the United States has an estimated annual capacity of 52,000 mt. A new plant at Notre Dame de Gravenchon, France, reportedly has an annual capacity of 50,000 mt. Mobil purchases 1-octene, 1-decene, and 1-dodecene for its PAO production. In addition to the low-viscosity PAOs, Mobil also produces two grades of high-viscosity PAO. The annual sales for these products is believed to be around 4000 mt. Mobil was purchased by Exxon that has created the world’s most versatile supplier and marketer of synthetic base fluids. These include PAOs from 2 to 1000 cSt. 1.2.2.3 Gulf Oil Company Gulf Oil Company appears to have had an interest in synthetic hydrocarbons in the 1940s. Developmental work at the Gulf laboratories in Harmarville, Pennsylvania, continued into the 1960s and 1970s. In 1974, Gulf built a semiworks plant with a capacity of 1125 mt/yr. The first commercial sale from this plant was in December 1974. During the years 1976–1980, Gulf introduced an arctic super duty 5W-20 CD/SE crankcase lubricant and an arctic universal oil/transmission oil. In Canada, Gulf began marketing PAO-based gear lubricants, synthetic greases, and a partial synthetic 5W-30 crankcase oil. Gulf began commercial production in their PAO plant in Cedar Bayou, Texas, in December 1980. The initial production capacity was 15,400 mt/yr, and the facility was strategically located next to Gulf’s olefin plant. In 1981– 1983, Gulf added several new PAO-based products to their line of synthetic fluids. These included Gulf Super

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Duty II, a full-synthetic 0W-30 crankcase oil, Gulf SL-H, a hydraulic fluid for high- and low-temperature operation, and Gulf Syngear, a 75W-90 gear oil for long life and fuel economy. In addition to their fully formulated products, Gulf marketed PAO to the merchant market under the trade name Synfluid Synthetic Fluids. Gulf Oil Corporation was acquired by Chevron Corporation in 1984. 1.2.2.4 Chevron Corporation Prior to 1984, Chevron marketed a single synlube-based product. That product was Chevron Sub Zero Fluid, a 7.5W-20 CD/SE crankcase oil for use in construction equipment and vehicles employed in the Alyeska pipeline project in Alaska. In June 1984, Chevron acquired Gulf Oil Company. In late 1985, the PAO manufacturing and marketing responsibilities were transferred to the Oronite Division of Chevron Chemical. Chevron continued to offer the PAO-based arctic oil plus Chevron Tegra PAO-based synthetic lubricants, which included the old Gulf Syngear and three grades of compressor oils. Unlike Mobil, who chose to market aggressively under their own name, Chevron decided to focus on the merchant market. The capacity of the Chevron plant has been increased to approximately 54,000 mt. Chevron, like Amoco Corporation, but unlike Mobil, is basic in the α-olefin raw material used to manufacture PAO fluids. In July 2001, Chevron Corporation merged their chemical assets (except for the Oronit Additives Division) with the chemicals part of Phillips Petroleum forming the joint venture Chevron Phillips Chemical Company LP. 1.2.2.5 Amoco Amoco, formerly Standard Oil Company (Indiana), was probably the first U.S. petroleum company to investigate synthetic hydrocarbon fluids. The pioneering work by Sullivan in the early 1930s has already been mentioned [3]. Those efforts led to a patent that described the aluminum chloride-catalyzed polymerization of olefins derived from cracked wax [14]. An attempt to commercialize a synthetic lubricating fluid in 1929 was abandoned because of lack of demand. In 1982, Amoco Oil Company began test marketing a 100% PAO-based lubricant. This venture was followed in April 1984 with the introduction of Amoco’s Ultimate line of crankcase oils for both gasoline and diesel oils. Amoco later expanded the product line to include gear oils and grease bases. All of the PAOs for the Ultimate products were purchased until 1996 when Amoco purchased both the alphaolefin and PAO technology plants from Albemarle Corporation. Amoco was purchased by BP (British Petroleum), however, BP has recently announced interest in selling its linear alphaolefins and PAOs business to adopt a new strategy for its petrochemicals business.

BP currently has the technology and resources to produce PAOs directly from its own ethylene. 1.2.2.6 Ethyl Corporation In 1970, Ethyl began conducting research on a process for the polymerization of linear α-olefins to form lowviscosity functional fluids. The concept was attractive since Ethyl was one of the world’s largest manufacturers of linear α-olefins. The target application was a hydraulic fluid specification for military jet aircraft. As it turned out, the specifications were written around an experimental fluid from Mobil, and the independent research at Ethyl led to a similar BF3 -catalyzed process and decene-based product as that developed by Mobil. Ethyl chose not to commercialize its findings because of the small potential market that existed at that time. Following the oil embargo of 1974, and the subsequent introduction of Mobil 1, Ethyl reinstituted a PAO research program. They entered the merchant market for PAO base fluids in the late 1970s through a toll manufacturing arrangement with Bray Oil in California. In 1981, Ethyl decided to build a Market Development Unit (MDU) to manufacture PAO in Baton Rouge, Louisiana. The 7000 mt MDU came on stream in mid-1982, and Ethyl intended that this plant would operate until the market had grown to a size that would justify a world-scale plant. Marketing of the PAO was handled by Ethyl’s Edwin Cooper Division, which was responsible for the manufacture and marketing of Ethyl’s lube oil additives, and the Division trade name HiTEC was used for the fluids. The division name was later changed to Ethyl Petroleum Additives Division (EPAD). Slow growth in the PAO market prompted Ethyl to shut down the MDU in 1985 and return to a toll arrangement. In 1987, Ethyl entered into an agreement with Quantum Chemical whereby Quantum would manufacture PAO from Ethyl’s decene. Ethyl’s PAO sales in Europe began to grow rapidly, and a decision was made to build a plant at Ethyl’s manufacturing site at Feluy, Belgium, where a large new α-olefin plant was also being planned. In early 1989, Ethyl transferred responsibility for the PAO project from the EPAD to the Industrial Chemicals Division. This decision reflected the philosophy that PAO is a base stock rather than a lube additive, and the action allowed Ethyl to expand the scope of the sales effort to include a broader potential market. In keeping with the philosophy of PAO being a base stock, the trade name for the bulk fluids was changed to ETHYLFLO PAO fluids, and an aggressive marketing campaign was launched in North America. In 1989, Quantum sold its Emery Division to Henkel, but retained its PAO plant at Deer Park, Texas, leaving Quantum in the difficult situation of having neither its own source of 1-decene nor its own marketing organization. In 1990, Ethyl purchased Quantum’s Deer Park plant, which

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is located only a few miles from Ethyl’s large α-olefin plant at Pasadena. The Deer Park facility has two PAO production trains and an annual capacity of 77,000 mt. Ethyl’s 36,000 mt Feluy plant came on stream in January 1991. Ethyl split off Albemarle as a separate company in 1994 that owned and operated the PAO business until March 1996 when Amoco purchased the alphaolefin and PAO business from Albemarle. BP now markets these PAOs under the DURASYN™ PAO trade name. 1.2.2.7 Exxon Corporation Exxon introduced Esso Ultra Oil in Europe in mid-1986. This lubricant is a partial synthetic oil containing PAO. Exxon has produced small quantities of PAO in its alkylation facility at its chemical plant in Port Jerome, France. Plans to convert that plant to full-scale PAO operation appear to have been shelved. ExxonMobil Chemical has recently announced a planned upgrading of their plant in Beaumont, Texas, that will increase capacity and provide additional synthetic PAO. The products are expected to have lower volatility, better low-temperature properties and a higher VI. ExxonMobil have a SpectraSyn™ line of PAOs ranging in viscosity from 2 to 100 cSt. They also offer a SpectraSyn™ Ultra line of PAOs with viscosities >100 cSt. 1.2.2.8 Quantum Chemical Corporation Quantum Chemical Corporation is the name adopted in 1988 by the former National Distillers and Chemical Corporation. National Distillers entered the synthetic lubricants business in 1978 with the purchase of Emery Industries, an important producer of ester-based synlubes. In December 1980, National Distillers announced the construction of a 15,400 mt PAO plant at their manufacturing facility in Deer Park, Texas. The plant did not actually come on stream until late 1983. In 1987, they entered into a manufacturing and marketing agreement with Ethyl Corporation, as described in Section 1.2.2.6. The 1-decene feedstock was supplied by Ethyl. By 1989, Quantum had debottlenecked the PAO plant and built a second, larger plant at the same location, bringing the total capacity to 77,000 mt. In 1990, they sold their PAO business and manufacturing site to Ethyl Corporation. In 1994, Ethyl spun off Albemarle Corporation. The PAO business and manufacturing site became part of Albemarle Corporation, but, as mentioned above, was sold to Amoco in March of 1996. 1.2.2.9 Castrol Limited Castrol, originally The Burmah Oil Public Limited Company, and then Burmah-Castrol, has historically been an innovator in automotive lubricant marketing. In 1981, they purchased Bray Oil Company, a small manufacturer of synthetic lubricants based in California. Bray Oil at that

time had been toll producing PAO for Ethyl Corporation. Although Castrol maintained a strong interest in marketing synthetic lubricants, they chose to close the PAO plant and purchase their PAO requirements. Castrol was an early marketer of synthetic automotive lubricants in Europe. They have introduced a full line of synthetic and semisynthetic gear lubes and compressor oils as well as higher-performance jet turbine oils, military hydraulic fluids, and jet lube products. They introduced Syntron X — a 5W-50 PAO-based automotive synlube — into the United Kingdom in 1988, and a new line of PAObased automotive products, under the trade names Syntorq and Transmax, was introduced into the United States in 1991. They introduced a 5W-50, Syntec PCMO in 1993 followed by a 10W-30 oil. They also introduced Syntec Blend, a part synthetic, in late 1995. 1.2.2.10 Uniroyal Chemical Company Uniroyal has produced high-viscosity PAOs (KV100◦ C = 40 and 100 cSt) since 1980 in a small plant at Elmira, Ontario, Canada. Uniroyal and ExxonMobil are the only two producers of these grades of PAO in the world. Total production capacity is about 2000 mt/yr. Uniroyal merged with Witco in September 1999 to become CK-Witco. This transitioned to Crompton Corporation in mid-2001 that now has the responsibility for the production and marketing of these heavy PAO products. 1.2.2.11 Neste Chemical Neste Chemical has a PAO plant in Berigen, Belgium. The facility came on stream in 1991 and is estimated to have a capacity of 28,000 mt. Neste have since changed their company name to Fortum and now manufacture and sell these products under the trade name NEXBASE™ 2000 series. 1.2.2.12 Texaco Texaco has conducted research on PAOs and holds several patents but has no commercial production. They do, however, market PAO-based lubricants under the trade name Havoline. 1.2.2.13 Shell Chemical Shell Chemical has conducted extensive research on PAOs but has never begun commercial manufacturing. Shell, along with Chevron and Amoco (now BP), is basic in the α-olefin raw material. 1.2.2.14 Idemitsu Petrochemicals Polyalphaolefins are not currently produced in Japan, however, Idemitsu Petrochemicals raised interest in plant construction several years ago. To date, they have not made

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any announcement to build a PAO plant on their own or with another company. 1.2.2.15 Sasol In South Africa, Sasol produces 1.4 million (MM) mt/yr of mixed alphaolefins from its coal to hydrocarbons process via Fischer-Tropsch (FT) chemistry. Making plans to produce PAOs and oxo alcohols in the future [15]. Sasol had previously announced plans to double its alphaolefins capacity at its coal to synthetic fluids facility in South Africa [16]. By the forth quarter of 1997, Sasol had a capacity of 110,000 mt/yr of hexane with further expansion planned in 1998–1999 that is expected to include pentene capacity. Sasol was expected to spend $50 MM to build a 50,000 mt/yr 1-octene unit at the facility that was expected to be on stream by 1999. They are considering licenses for China, with the objective of maximizing output of ultra-clean diesel fuel. Sasol has announced several gasto-liquids concepts including low-temperature FT that offers the potential to generate chemical products including C10 –C17 paraffins, waxes, and base fluids.

1.3 CHEMISTRY Polyalphaolefins are manufactured by a two-step reaction sequence from linear alpha-olefins, which are derived from ethylene. The first step is synthesis of a mixture of oligomers, that are polymers of relatively low-molecular weight. alpha-Olefin → Dimer + Trimer + Tetramer + Pentamer, etc. For the production of low-viscosity PAOs (2 to 10 cSt), the catalyst for the oligomerization reaction is usually boron trifluoride (PAOs are commonly classified according to their approximate kinematic viscosity (kV) at 100◦ C — this convention will be used throughout this chapter). The BF3 catalyst is used in conjunction with a protic cocatalyst such as water, an alcohol, or a weak carboxylic acid. It is necessary that the BF3 , a gas, be maintained in a molar excess relative to the protic cocatalyst. Although this stoichiometry may be accomplished by sparging the reaction mixture with a stream of BF3 , it is more practical, on a commercial basis, to conduct the reaction under a slight BF3 pressure (10 to 50 psig). For convenience, a general designation for the catalyst system is BF3 · ROH, where ROH represents any protic species such as those noted above, and the presence of excess BF3 is understood. The BF3 · ROH catalyst system is unique for two reasons. First, this catalyst combination produces an oligomer distribution that is markedly peaked at trimer. Figure 1.1 shows a gas chromatography (GC) trace indicating the

• • • • • • •

Trimers

Tetramers Dimers

Pentamers Hexamers

0

5

10

15

20

25

Time (min)

FIGURE 1.1 Gas chromatography of typical oligomer

oligomer distribution of a typical reaction product derived from 1-decene using a BF3 · n-C4 H9 OH catalyst combination at a reaction temperature of 30◦ C. The chromatogram indicates that only a relatively small amount of dimer is formed. The bulk of the product is the trimer, with only much smaller amounts of higher oligomers present. A second unique feature of the BF3 · ROH catalyst system is that it produces products that have exceptionally good low-temperature properties. The extremely low pour-point values were puzzling to the early workers in the field until it was shown that the resulting oligomers exhibit a greater degree of skeletal branching than would be predicted by a conventional cationic polymerization mechanism [11]. The reason that BF3 catalysis causes excess skeletal branching during the oligomerization process is unclear. The first researcher who recognized the phenomenon proposed a mechanism involving a skeletal rearrangement of the dimer [11]. A later paper proposed that the monomer undergoes rearrangement [17]. A third paper proposed that the excess branching arose from positional isomerization of the double bond in the monomer prior to oligomerization [18]. In fact, the large number of isomers that are formed cannot be explained by any single mechanism, and the role of BF3 · ROH in promoting the necessary rearrangements remains unexplained. Even though the mechanism of the BF3 · ROHcatalyzed oligomerization remains to be fully elucidated, researchers have learned how to advantageously control the composition of the final PAO product so as to tailor the oligomer distribution to fit the requirements of specialized end-use applications [19]. This customizing is done by manipulation of the reaction variables that include the following: • • • •

Chain length of olefin raw material Temperature Time Pressure

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Catalyst concentration Cocatalyst type and concentration Cocatalyst feed rate Olefin feed rate Reaction quench and recovery procedures Hydrogenation catalyst and conditions Distillation

In addition to controlling the relative distribution of the oligomers by manipulation of the reaction parameters, the PAO manufacturer can also make major alterations in the product properties by varying the choice of starting olefin. Today, the commercial PAO market is dominated by decene-derived material because these products have the broadest range of properties, but a knowledgeable producer has the option of choosing other starting olefins in order to better satisfy the requirements for a particular enduse application. For example, PAO based on C12 -olefin is manufactured commercially by Chevron and Mobil. Mobil also makes PAO material containing oligomers based on 1-octene, 1-decene, and 1-dodecene mixtures. More detail on the potential use of alternate olefin streams are discussed later. The crude reaction product is quenched with water or caustic, allowed to settle, and then washed again with more water to remove all traces of the BF3 catalyst. Gaseous BF3 can be recovered by concentration of the wash water and treating the solution with concentrated sulfuric acid. A second step in the manufacturing process entails hydrogenation of the unsaturated oligomer. The hydrogenation may be carried out before or after distillation. Distillation is required to remove any unreacted monomer, to separate the dimer, which is marketed as a 2.0 cSt product, and in some cases to coproduce a lighter and a heavier grade of PAO. The hydrogenation is typically performed over a supported metal catalyst such as nickel/kieselguhr or palladium/alumina. Hydrogenation is necessary to give the final product enhanced chemical inertness and added oxidative stability. The term PAO is used even though the fluid is saturated in a subsequent chemical hydrogenation. It is normally not possible to manufacture the higher viscosity PAO (40 and 100 cSt) products using the BF3 · ROH technology. However, several other catalyst systems are known that can give the desired products. One class of catalysts employs alkylaluminum compounds in conjunction with TiCI4 [7] or alkyl halides [20]. The latter system is preferred by Uniroyal, which uses ethylaluminum sesquichloride with allyl chloride. It has also been reported in a Mobil Oil European patent application that high-viscosity PAOs may be produced by dimerizing lower oligomers with peroxides [21]. The patent describes the use of stoichiometric quantities of di-tert-butyl peroxide, which would probably not be economically feasible. On the other hand, a system that

employs hydrogen peroxide directly or the regeneration of an active intermediate might be commercially attractive. Mobil has also obtained a large number of patents describing the use of supported chromium catalysts [22]. The system actually employed by Mobil for commercial manufacture has not been disclosed, but it is believed to employ an aluminum chloride catalyst. Recently, a 25 cSt PAO derived from 1-decene has been commercially produced through a patented process by Chevron Phillips. The catalyst system has not been disclosed but is not based on BF3 or the systems described for the 40 and 100 cSt PAOs. This is described in detail in Section 1.7.6.2.

with changes in temperature compared with the viscosity changes of a low-VI fluid. A practical consequence of this property is that PAOs do not require viscosity index improvers (VIIs) in many applications. The presence of a VII is often undesirable because many tend to be unstable toward shear. Once the VII begins to break down, the fully formulated fluid goes “out of grade” (i.e., fails to retain the original viscosity grade). Several other important physical properties of commercial PAOs are shown in Table 1.1. All products have extremely low pour points and have low viscosities at low temperatures. These properties make PAOs very attractive in the cold-climate applications for which they were first used. At the other end of the spectrum, all but the 2.0 cSt product have low volatilities as demonstrated by the low percentage loss of material at 250˚C in the standard NOACK volatility test. Low volatility is important in hightemperature operations to reduce the need for “topping up” and to prevent a fluid from losing its lighter components and thus becoming too viscous at low or ambient temperatures. Low volatility is also important as it relates to flash and fire points. The typical physical properties of conventional commercial high-viscosity PAO fluids are given in Table 1.2. The two grades available on the market today are the 40 and 100 cSt fluids. As with the low-viscosity PAOs, these fluids have a very broad temperature operating range.

1.4 PROPERTIES The physical and chemical properties of PAO fluids make them attractive for a variety of applications requiring a wider temperature operating range than can normally be achieved by petroleum-based products (mineral oils). An excellent review of PAO-based fluids as highperformance lubricants has recently been published [23]. A summary of the properties of commercially available PAOs is shown in Appendix I.

1.4.1 Physical Properties 1.4.1.1 Commercial PAOs Table 1.1 lists the typical physical properties of the five grades of commercial low-viscosity PAOs available today. These products are all manufactured using 1-decene as the starting material, and the final properties are determined by control of the reaction parameters and (depending on the manufacturer) selective distillation of the light oligomers. Table 1.1 shows that all commercial grades of lowviscosity PAOs have relatively high VIs of around 135 (Note: No VI is shown for PAO 2 because VI is undefined for fluids having a KV of less than 2.0 cSt at 100◦ C). The viscosity of a high-VI fluid changes less dramatically

1.4.1.2 Comparison to mineral oils The excellent physical properties of the commercial PAO fluids are most readily apparent when they are compared directly with those of petroleum-based mineral oils. The fairest comparison is to look at fluids with nearly identical KVs at 100◦ C. The differences in both low- and high-temperature properties can then be examined. Table 1.3 compares the physical properties of a commercial 4.0 cSt PAO with those of two 100N (neutral) mineral oils, a 100NLP (low pour) mineral oil, and

TABLE 1.1 Physical Properties of Commercial Low-Viscosity PAOs Parameter

Test method

KV at 100◦ C (cSt)

ASTM D 445 ASTM D 445 ASTM D 445 ASTM D 2270 ASTM D 97 ASTM D 92 DIN 51581

KV at 40◦ C (cSt) KV at −40◦ C (cSt) Viscosity index Pour point (◦ C) Flash point (◦ C) NOACKa (% loss)

PAO 2

PAO 4

PAO 6

PAO 8

PAO 10

1.80 5.54 306 — −63 165 99.5

3.84 16.68 2,390 124 −72 213 11.8

5.98 30.89 7,830 143 −64 235 6.1

7.74 46.30 18,200 136 −57 258 3.1

9.87 64.50 34,600 137 −53 270 1.8

a Volatility at 250◦ C after 1 h. Alternative procedure is ASTM D 5800.

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TABLE 1.2 Physical Properties of Commercial High-Viscosity PAOs Parameter

Test method

KV at 100◦ C (cSt)

ASTM D 445 ASTM D 445 ASTM D 445 ASTM D 2270 ASTM D 97 ASTM D 92 DIN 51581

KV at 40◦ C (cSt) KV at −18◦ C (cSt) Viscosity index Pour point (◦ C) Flash point (◦ C) NOACKa (% loss)

PAO 40 40–42 399–423 39,000–41,000 147 −36 to −45 275–280 0.8–1.4

PAO 100 103–110 1,260–1,390 176,000–203,000 170 −21 to −27 280–290 0.6–1.1

a Volatility at 250◦ C after 1 h. Alternative procedure is ASTM D 5800.

TABLE 1.3 4.0 cSt Fluids Parameter

Test method

PAO

100N

100N

100NLP

VHVI

VHVI

VHVI

ASTM D 445 ASTM D 445 ASTM D 445 ASTM D 2270 ASTM D 97 ASTM D 92 DIN 51581

IV 3.84 16.7 2390 124 −72 213 11.8

I 3.81 18.6 Solid 89 −15 200 37.2

I 4.06 20.2 Solid 98 −12 212 30.0

I 4.02 20.1 Solid 94 −15 197 29.5

III 3.75 16.2 Solid 121 −27 206 22.2

III 4.2 NRb Solid 127 −18 210 13

III 3.98 16.61 Solid 141 −38c 225 13.3

Base Oil Groupa

KV at 100◦ C (cSt) KV at 40◦ C (cSt) KV at −40◦ C (cSt) Viscosity index Pour point (◦ C) Flash point (◦ C) NOACKd (% loss)

a Base Stock Classification as defined by SAE Classification J357. b NR = Not Reported. c Probably pour point depressed. d Volatility at 250◦ C after 1 h. Alternative procedure is ASTM D 5800.

a hydrotreated HVI (high viscosity index) mineral oil. The PAO shows markedly better properties at both high and low temperatures. At high temperatures, the PAO has lower volatility and a higher flash point. A relatively high flash point is, of course, often important for safety considerations. At the low end of the temperature scale the differences are equally dramatic with the highest degree of difference occurring in the low-temperature low-shear regime as is the case with KV. However, similar differences have been observed in Brookfield viscosities. The pour point of the PAO is −72◦ C, while that of three 100N mineral oils and the HVI oil are −15, −12, −15, and −27◦ C, respectively. Table 1.4 compares a commercial 6.0 cSt PAO with a 160HT (hydrotreated) mineral oil, a 240N oil, a 200SN (solvent neutral) mineral oil, and a VHVI (very high viscosity index) mineral oil that is currently considered to be the best of the mineral oils on the market. The broader temperature range of the PAO is again apparent. Table 1.5 makes similar comparisons for 8.0 cSt fluids.

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The ability of PAO products to outperform petroleumbased products of similar viscosity at both ends of the temperature spectrum can be easily understood if one compares the GC traces. Figure 1.2 contains chromatograms run under identical conditions of a 4.0 cSt HVI oil and a 4.0 cSt PAO. The PAO product is essentially decene trimer with a small amount of tetramer present. The fine structure of the trimer peak is attributable to the presence of a variety of trimer isomers (same molecular weight, different structure). The HVI oil, on the other hand, has a broad spectrum of different molecular weight products. The oil contains low-molecular-weight materials that adversely affect the volatility and flash point characteristics. It also contains high molecular-weight components that increase the lowtemperature viscosity and linear paraffins that increase the pour point. Figure 1.3 compares the GC traces of a very highquality 6.0 cSt VHVI fluid with a PAO of similar viscosity. The PAO has a well-defined chemical composition consisting of decene trimer, tetramer, pentamer, and a small

TABLE 1.4 6.0 cSt Fluids Parameter

Test method

PAO

160HT

240N

200SN

VHVI

VHVI

ASTM D 445 ASTM D 445 ASTM D 445 ASTM D 2270 ASTM D 97 ASTM D 92 DIN 51581

IV 5.98 30.9 7830 143 −64 235 6.1

II 5.77 33.1 Solid 116 −15 220 16.6

I 6.98 47.4 Solid 103 −12 235 10.3

I 6.31 40.8 Solid 102 −6 212 18.8

III 5.14 24.1 Solid 149 −15 230 8.8

III 5.9

Base oil groupa

KV at 100◦ C (cSt) KV at 40◦ C (cSt) KV at −40◦ C (cSt) Viscosity index Pour point (◦ C) Flash point (◦ C) NOACKc (% loss)

NRb 127 −12 225 6

a Base Stock Classification as defined by SAE Classification J357. b NR = Not Reported.

c Volatility at 250◦ C after 1 h. Alternative procedure is ASTM D 5800.

VHVI

TABLE 1.5 8.0 cSt Fluids Parameter

Test method

PAO

ASTM D 445 ASTM D 445 ASTM D 445 ASTM D 2270 ASTM D 97 ASTM D 92 DIN 51581

IV 7.74 46.3 18.200 136 −57 258 3.1

Base Oil Groupa

KV at 100◦ C (cSt) KV at 40◦ C (cSt) KV at −40◦ C (cSt) Viscosity index Pour point (◦ C) Flash point (◦ C) NOACKb (% loss)

325SN

325N

I 8.30 63.7 Solid 99 −12 236 7.2

I 8.20 58.0 Solid 110 −12 250 5.1

5

10 15 20 25 30 35 40 45 PAO

a Base Stock Classification as defined by SAE Classification J357. b Volatility at 250◦ C after 1 h. Alternative procedure is ASTM D 5800.

5

10 15 20 25 30 35 40 45 Time (min)

FIGURE 1.3 Gas chromatography traces of 6.0 cSt fluids

HVI

amount of hexamer. The VHVI fluid, like the HVI fluid in the previous example, contains a wide range of components that degrade performance at both ends of the temperature scale. 5

10

15

20

25

30

35

PAO

5

10

15

20

25

30

35

Time (min)

FIGURE 1.2 Gas chromatography traces of 4.0 cSt fluids

Copyright 2006 by Taylor & Francis Group, LLC

1.4.1.3 Properties of blends The excellent combination of high- and low-temperature physical properties of PAOs, combined with their total miscibility with mineral oils, makes them attractive candidates for blending with certain base stocks in order to improve the base-stock quality and bring it into specification for a particular application. This practice has indeed become widespread (but little publicized) as refiners scramble to meet the newer and more stringent API classification requirements. Figure 1.4 shows the effect on volatility and viscosity upon blending 4.0 cSt PAO with a light (100N) mineral

6.5 6 Viscosity 5.5 5 4.5 4 3.5 80 100 Volatility

30 20 10 0 0

10

20

40

60

Viscosity at 100°C (cSt)

Volatility index (wt% loss)

40

PAO in blend, wt%

40

6.5 6 Viscosity 5.5 5 4.5 4 3.5 80 100 Volatility

30 20 10 0 0

10

20

40

60

Viscosity at 100°C (cSt)

Volatility index (wt% loss)

FIGURE 1.4 Effect of blending 4.0 cSt PAO with 100N mineral oil. (1) In-house test designed to give approximate correlation to ASTM D 972. (2) Weight percentage loss after 2.0 h at 204◦ C under flow of N2

PAO in blend, wt%

FIGURE 1.5 Effect of blending 4.0 cSt PAO with 200N mineral oil. (1) In-house test designed to give approximate correlation to ASTM D 972. (2) Weight percentage loss after 2 h at 204◦ C under flow of N2

oil [24]. The “Volatility Index” depicted in Figure 1.4 and the following Figure 1.5 is derived from an in-house test. A defined quantity of the test sample is placed in a small dish or “planchet,” that is placed in an oven for 2.0 h at 204◦ C. A constant flow of nitrogen is maintained over the sample throughout the test. The values are not the same as obtained in the standard ASTM D 972 or NOACK tests, but they have been shown to correlate well on a relative basis. Small amounts of PAO have a dramatic effect in reducing the volatility of the mineral oil, while having essentially no effect on viscosity. Figure 1.5 shows the effect of blending the same 4.0 cSt PAO with a heavy (200N) mineral oil. In this case, small amounts of the PAO have a large effect in reducing the viscosity of the mineral oil without increasing the volatility.

1.4.2 Chemical Properties In addition to the physical properties, the chemical properties of a functional fluid must be considered. The most important chemical property requirements are that the fluid must be thermally stable and chemically inert. Under normal operating conditions a working fluid must not thermally degrade nor react with the atmosphere, the materials of construction, seals, paints, varnishes, performance-enhancing additives, other fluids with which it is intentionally contacted, or inadvertent contaminants.

Copyright 2006 by Taylor & Francis Group, LLC

1.4.2.1 Thermal stability Many of the operations for which a functional fluid is required are carried out at elevated temperatures. For this reason it is important that the fluid employed not be degraded under the operating conditions. The choice of an appropriate bench test, however, is often difficult. It is important that the test differentiate between thermal and oxidative degradation while simulating real-world operating conditions. It is also important that the test differentiate between thermal degradation and volatility. Some evaluations based on oven-aging or thermogravimetric analysis (TGA) have led to erroneous conclusions because the loss in sample weight and increase in viscosity could be attributed to volatilization of the lighter components rather than chemical degradation. One test commonly employed that avoids the danger of misinterpreting volatility for thermal instability is the Panel Coker Thermal Stability Test. In this test, an aluminum panel heated to 310◦ C is alternately splashed by the test oil for 6 min and baked for 1.5 min. At the end of the test, the panels are rated for cleanliness. A completely clean panel has a rating of 10. Table 1.6 summarizes the results of one study that compared the performance characteristics of mineral oil and various synthetic base stocks for crankcase applications [25]. Under these severe conditions, the mineral oil panel was covered with deposits, indicating a lack of thermal stability. An alkylated aromatic also

1.4.2.2 Hydrolytic stability

performed poorly. By comparison, both a PAO of comparable viscosity and a dibasic ester performed well. The best performance was achieved using a mixture of PAO and a polyol ester. Dibasic and polyol esters are commonly used in conjunction with PAO in crankcase formulations. The thermal stability of PAOs was also investigated regarding use in aviation lubricants [26]. In this evaluation, thermal stability was determined by heating the fluid at 370◦ C under a nitrogen atmosphere for 6.0 h in a sealed autoclave. Thermal degradation was measured by the change in viscosity and by gas chromatographic analysis. The tests show that the thermal-stability of PAO products can be ranked as:

For a functional fluid, the importance of inertness to reaction with water is important for a variety of reasons. Hydrolytic degradation of many substances leads to acidic products which, in turn, promote corrosion. Hydrolysis may also materially change the physical and chemical properties of a base fluid, making it unsuitable for the intended use. Systems in which the working fluid may occasionally contact water or high levels of moisture are particularly at risk. Also at risk are systems that operate at low-temperature or cycle between high and low temperatures. The excellent hydrolytic stability of PAO fluids was reported as a result of tests conducted to find a replacement for 2-ethylbutyl silicate ester as an aircraft coolant/dielectric fluid used by the U.S. military in aircraft radar systems [27]. The test method required treating the fluids with 0.1% water (or 0.1% seawater) and maintaining the fluid at 170 or 250◦ F for up to 200 h. Samples were withdrawn at 20-h intervals, and the flash points were measured by the closed cup method. A decrease in flash point was interpreted as being indicative of hydrolytic breakdown to form lower molecular-weight products. The PAO showed no decrease in flash point under any of the test conditions, whereas the 2-ethylbutyl silicate ester showed marked decreases. Figure 1.6 shows the results for tests at 250◦ F.

Dimer > Trimer > Tetramer These findings are consistent with the molecular structures of the oligomers. The least thermally stable parts of the molecule are the tertiary carbon positions, that is, the points where there are branches in the carbon chains. The higher oligomers have more branches and are thus more subject to thermal degradation. Thermal stability as measured by Federal Test Method 791B (modified) shows that the thermal stability of PAOs is related to the amounts of dimer, trimer, tetramer, and pentamer present (Table 1.7).

TABLE 1.6 Panel Coker Thermal Stability Test Base fluid

1.4.2.3 Oxidative stability

Cleanliness

4.0 cSt mineral oil 4.0 cSt PAO 5.0 cSt Alkylated aromatic 5.4 cSt Dibasic ester 4.0 cSt PAO/(polyol ester)

0 8.0 2.0 8.0 9.5

Test conditions Panel temp. Sump temp. Operation Rating

310◦ C 121◦ C 6 min splash/1.5 min bake 10 = clean

A high level of oxidative stability is essential to the performance of a functional fluid. In many applications the fluid is required to perform at elevated temperatures and in contact with air. The results from attempts toward evaluation of fluids for oxidative stability, however, are often confusing. The results are dependent on the test methodology. Tests involving thin films tend to give different results than tests using bulk fluids. Not only the presence or absence of metals that catalyze oxidation is very important, but also the fact different metals interact differently with different fluids. In addition, oxidative stability may be enhanced

TABLE 1.7 Thermal Stability as a Function of Oligmer Viscosity loss at

2 cSt 4 cSt 6 cSt 8 cSt 10 cSt

Copyright 2006 by Taylor & Francis Group, LLC

Oligmer (%)

250◦ C

300◦ C

371◦ C

Dimer

Trimer

Tetramer

Pentamer

−0.2 −0.9 −2.4 −4.0 −4.4

−1.1 −5.3 −16.9 −22.4 −22.9

−49.9 −79.7 −88.4 −92.3 −94.3

90 0.6 0.1 — —

9.0 84.4 33.9 6.0 1.1

— 14.5 43.5 55.7 42.5

— 0.5 17.4 27.2 32.3

300

Flash point,°F

280 270

PAO Silicate ester

260 250 240 230

Induction time, min

180

290

Formulation: 100 SEN mineral oil 4.2 cSt PAO 13.7% DI 8.0% VII

170 160 150 140

220

0

210

10

20

30

Wt% PAO in oil 0

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 Time (h) at 250°F with 0.1% H2O

FIGURE 1.6 Hydrolytic stability

by the use of antioxidants, but different fluids respond differently to different antioxidants. One set of experiments that attempted to differentiate between PAOs and mineral oils entailed using Differential Scanning Calorimetry (DSC) [24]. In this test, the fluid is heated in a pan at a controlled rate, and the temperature at which there is an onset of oxidation is determined by the accompanying exotherm. All of the commercial PAO products (with the exception of 2.0 cSt fluid) were tested. The onset temperatures for the six viscosity grades fell in the very narrow range of 187.3 to 191.6◦ C. Two 6.0 cSt mineral oils gave values of 189.2 and 200.6◦ C, respectively. Quite a different result was reported for a laboratory oxidation test in which the fluid was heated at 163◦ C for 40 h in the presence of steel, aluminum, copper, and lead coupons [25]. In this test a 4.0 cSt mineral oil exhibited a 560% viscosity increase and a light sludge appearance, whereas a 4.0 cSt PAO showed only a 211% viscosity increase and no sludge. These results seem to indicate better performance for the PAO, but the loss of weight by the lead coupon in the PAO was 2.8 times that of the coupon in the mineral oil. The same paper reports better performance for mineral oils in a rotary bomb test that measures the time for a specific pressure drop, but better performance for PAOs in beaker oxidation tests in which the increase in viscosity is measured. It has been reported that the failure of unstabilized PAO to outperform unstabilized mineral oil in oxidative stability tests may be attributed to the presence of natural antioxidants in the latter [28]. The lack of inhibitors in the pure PAO is then given as the rationale for the greater responsiveness of the PAOs to the addition of small amounts of antioxidants. An interesting and somewhat similar rationale has been given for the unusually good responsiveness of PAOs to the addition of antiwear and other performance additives [29]. These researchers from the All-Union Scientific Institute of Oil Refining in Moscow conclude that the efficiency of small concentrations of additives in PAO oils is related to the fast adsorption of the additives on the

Copyright 2006 by Taylor & Francis Group, LLC

FIGURE 1.7 Thin-film oxygen uptake test (TFOUT)

metal surfaces, because there is little interference of the process in transportation from the bulk oil to the tribosurface. The low level of interference is a result of weak cohesive forces between the additive molecules and the PAO substrate. The arguments noted above are supported by results obtained from oxidative stability testing of fully formulated part-synthetic engine oils [30]. A thin film oxygen uptake test (TFOUT) was used for these studies. This test is a modified rotary bomb oxidation procedure in which the bomb is charged with sample, a small amount of water, a fuel catalyst, and a metal catalyst. The bomb is then pressurized with pure oxygen, placed in a bath at 160◦ C, and rotated axially at 100 rpm at a 30◦ angle from the horizontal. The time from the start of the test until a drop in pressure is noted and is defined as the oxidation induction time of the oil. The test oils each contained 13.7% of a detergent-inhibitor package (DI) and 8.0% of a VII. The base stock consisted of a 100 SN mineral oil blended with a 4.2 cSt PAO. Figure 1.7 shows that as the percentage of PAO in the sample was increased from 0 to 30%, the induction time for the onset of oxidation increased from 143 to 173 min. Two other papers of interest concerning the oxidative stability of PAOs are also referenced [31,32].

1.5 APPLICATIONS AND PERFORMANCE CHARACTERISTICS The use of PAO-based functional fluids is growing rapidly. Conventional applications, such as automotive crankcase, are being spurred on by tighter specifications and an increasing demand for higher performance. Nonconventional applications are also beginning to grow rapidly, especially where specific properties of PAO fluids give them particular advantages in performance, cost-effectiveness, or environmental acceptability. OEM confidence in PAObased synthetic formulations is demonstrated by factory fill crankcase use in expensive high-performance vehicles such as the Chevrolet Corvette, and the Dodge Viper. Porsche has also recently announced the approval of PAO-based full-synthetic SAE 5W-40 and SAE 10W-40

Mobil 1 for factory fill for all Porsche passenger cars. Audi uses PAO-based full-synthetic (0W-30) in larger automobiles. BMW factory fill full-synthetic gear oils are used for rear axle and manual transmission in passenger cars and Ford-Europe has a factory fill partial synthetic for its manual transmissions.

The Society of Automotive Engineers (SAE) [63]. In Appendix B of the SAE book, the editors summarize the “eight superior performance features of synthetic engine oils.” Their conclusions are based on a compilation of data in the various papers. The eight features which they identify are the following:

1.5.1 Overview of Application Areas

1. Improved engine cleanliness. This is based on a test using four taxicabs employing an SAE 5W-20 PAObased oil. Oil changes at 12,000 mi for 60,000 mi were followed by a 40,000 “no drain” period. 2. Improved fuel economy. The results of ten different test programs involving a total of 182 vehicles showed a weighted average fuel savings of 4.2%. 3. Improved oil economy. In ten different tests on oil consumption, the percentage of improvement in miles per quart ranged from 0% (for a military arctic lubricant) to 156%. The average improvement was 55.9%. 4. Excellent cold starting. Automobiles with 400 CID V-8 engines could be started at −39◦ F when the crankcase contained an SAE 5W-20 PAO-based synthetic oil. With a mineral oil of the same viscosity grade the lowest engine-starting temperature was −29◦ F. 5. Excellent low-temperature fluidity. For the two oils described in item 4, the PAO-based oil exhibited a pour point of −65◦ F, whereas the mineral oil had a pour point of −37◦ F. 6. Outstanding performance in extended oil drain. This conclusion was based on 100,000-mi tests using parkway police cruisers, which are normally operated at speeds ranging from 55 to 100 mi/h. The test vehicles used a PAO-based SAE 5W-20 “SE-CC” oil. Oil and filter changes were performed every 25,000 mi. The baseline consisted of a series of tests carried out in identical vehicles operated on SAE 10W-40 “SE” mineral oil with oil and filter changes every 5,000 mi. 7. High-temperature oxidation resistance. Viscosity increase was measured in a 2-l Renault after 64 h of operation with an oil-sump temperature of 302◦ F. The synthetic oil showed a 10% increase in viscosity and the mineral oil showed a 135% increase. Both samples were SAE 10W-50 oils. 8. Outstanding single- and double-length SAE-ASTMAPI “SE” performance tests. The results of all of these tests are presented in the reference. The PAO-based synthetic oils met or exceeded all of the requirements.

The following is a listing of both established and emerging application areas for PAOs. The list of applications has grown to such a degree in the last few years that a comprehensive review of the PAO performance attributes found advantageous in each and every application would require more space than is available here. Instead, where possible, a reference is cited so that the reader may refer to published information and data in the specific area of interest. Following this section, some performance data for areas of the broadest interest are presented. For detailed reviews of the most prominent areas of application, the reader is referred to the appropriate chapters in Part II of this book. Engine crankcase [33,34] Hydraulic fluids [35] Gear oils [36–39] Greases [4,40–42] Brake fluids [43] Shock absorbers [44] Automatic transmission fluids [45] Metal working fluids [46] Pumps [38] Mining and conveyor [47]

Compressor oils [38,48–50] Heat transfer media [51] Dielectric fluids [24,52] Gels for coating optical fibers [53] Off-shore drilling [54] Cosmetics and personal care products [55] Textiles [56–58] Polymers [59] Space applications [60] Turbine Oils [61,62]

1.5.2 Performance Testing for Automotive Applications Although physical properties are obviously important in choosing a fluid for a particular application, it is essential that the fluid be subjected to performance testing under conditions that simulate the limits to which the final product will be stressed. But, as indicated above, the list of applications for PAOs has grown to the point that it precludes a comprehensive discussion of performance testing for all applications. Because the requirements for the wide variety of automotive applications encompass much of the broader spectrum of applications, this section will focus on tests specifically designed and conducted by the automotive industry. An excellent summary of the automotive testing conducted in the 1970s and early 1980s may be found in a collection of 26 papers published in one volume by

Copyright 2006 by Taylor & Francis Group, LLC

More recent data show that PAO-based fluids continue to provide superior performance for the increasingly sophisticated cars being built today. Today’s automobiles tend to have smaller, more demanding engines. Increased emphasis on aerodynamics means less cooling under the hood, resulting in higher operating temperatures in both the engine and the transmission. In addition to the ability to meet this challenge with excellent thermal and oxidative

stability, PAOs offer another advantage over mineral oils under these severe operating conditions. Both the thermal conductivity and the heat capacity of PAO fluids are about 10% higher than values for the comparable mineral oils. The net result is that PAO-lubricated equipment tends to run cooler. Fully synthetic automotive lubricants for engine oils, automatic transmission fluids, gear oils, and grease applications provide improved protection of hardware [64]. The following sections examine, in somewhat greater detail, the results of testing for all the major areas of automotive applications. 1.5.2.1 Crankcase It is now widely accepted that synthesized fluids, such as PAOs and PAO/ester blends, offer inherent performance advantages over conventional petroleum — based fluids for the formulation of modern automotive and commercial engine oils. Proof-of-performance field testing is essential to validate bench test results and document oil quality reserve features [65–70]. The importance of oil quality as a major factor in its durability have been discussed in recent reports [71,72]. Quality differences in engine oil can account for differences of 2 to 3 times the levels of equipment wear. Tables 1.8–1.11 illustrate the results of tests related to the use of PAO in automotive crankcase applications [24]. Table 1.8 contains data relating to the hot oil oxidation test (HOOT), which is designed to measure the thermal and oxidative stability of the fluid inside an engine [73]. A PAO and a mineral oil were compared employing identical additive packages at identical concentrations. In this test, air is bubbled through 25 g of the test oil at a rate of 10 l/h for 5 days at 160◦ C. The oil contains 178 ppm iron(III) acetylacetonate and 17 ppm copper(II) acetylacetonate as oxidation catalysts. The significantly superior performance of the PAO has two possible implications. First, the PAO-based fluid can be used for longer drain intervals, resulting in less down-time and lower maintenance costs. Second, PAO can be used with lower levels of additives and other stabilizers, thus reducing the price differential between PAO and a comparable mineral oil. Table 1.9 contains the results of the Petter W1 Engine Test after 108 h. The test measures both the increase in viscosity of the fluid and the amount of wear, as determined by bearing weight loss. In this test, the advantages of employing a part-synthetic oil mixture are shown. When PAO is used as only 25% of the base oil, the percentage of viscosity increase is halved. The data in Table 1.10 was acquired from a Sequence IIIE Engine Test, which is commonly used in North America. Table 1.11 contains data relating to the VW Digiphant Test, which is more widely used in Europe. In both tests a 5W50 full-synthetic PAO-based oil is compared with a 15W-40 mineral oil. As indicated by the SAE

Copyright 2006 by Taylor & Francis Group, LLC

TABLE 1.8 Hot Oil Oxidation Crankcase)a Fluid

Test

(Automotive

Start (KV40◦ C , cSt)

Finish (KV40◦ C , cSt)

95 94

146.3 96.8

Mineral PAO

% Change 54.0 3.0

a Conditions: Same additive package at same concentration; temperature = 160◦ C; time = 5 days. Test described

in Shubkin, R.L. (1994). Lubrication Engineering 50, 196–201.

TABLE 1.9 Petter W1 Engine Testa Oil

Grade

KV40◦ C % increase

Mineral PAO-25% PAO-50% PAO-100%

15W-40 10W-40 10W-40 15W-40

108 54 45 20

Bearing weight loss, (mg) 14.1 9.7 11.5 14.5

a Conditions: Same additive package at same concentration;

time = 108 h.

TABLE 1.10 Sequence IIIE Engine (North America) Oil

Grade

Mineral PAO

15W-40 5W-50

Test

KV40◦ C % increase 167 62

TABLE 1.11 VW Digiphant Test (Europe)a Oil

Grade

KV40◦ C % increase

Mineral PAO

15W-40 5W-50

108 25

KV100◦ C % increase 62 9

a Time = 147 h.

classifications, the PAO-based oil is rated for operation at temperatures both lower and higher than the comparable mineral-oil-based fluid. Nevertheless, the PAO lubricant still out-performed the mineral oil by a wide margin.

The significant performance advantages of PAO-based synthetic engine oils compared with highly refined mineral oils has been reported [74]. Under the high-temperature conditions of a quadruple length (256 h) Sequence IIIE test, a PAO-based formulation resulted in excellent performance. Sequence VE sludge and wear testing is one of the most severe overall passenger car engine oil tests. This test simulates low temperature, stop and go driving conditions by measuring sludge, varnish and wear in a 2.3-L Ford engine. In double length tests, PAO-based formulations clearly outperformed oils blended with severely hydroprocessed mineral oil. In triple length CRC L-38 tests, PAO-based formulation showed exceptional wear and corrosion protection. In diesel engine testing a PAO-based formulation outperformed a commercial-oil-based on severely hydroprocessed mineral oil. Superior deposit and wear results were found for the PAO-based engine oil. Double length VW 1431 turbo diesel tests demonstrated the superior thermal/oxidative stability of the PAO-based formulation. Durability of an optimized PAO-based synthetic formulation compared with a commercial high-quality mineral oil was also measured. Chassie rolls testing was done at 55 mph and at 85 mph with 15,000 mi (24,123 km) oil drains intervals. Wear for the engine having the PAO-based formulation was essentially nil. The engine run on the commercial mineral oil formulation showed several wear parameters that exceeded factory limits. Final proof of performance was evaluated using over the road extended drain vehicle tests. In recent extended drain fleet testing studies, PAObased fully formulated full-synthetic oil outperformed mineral oil by having better viscosity control, less oil consumption, and better end-of-test vehicle engine ratings [75]. An added benefit from using synthetic oils over mineral oils (including hydrocracked oils) is the improved performance in regard to filter plugging. Goyal [76] has shown that overall filter life was improved using synthetic oils. The synthetic oils tested showed no filter plugging in extended drain up to 25,000 mi (40,000 km) over-the-road tests. Synthetic fluids, such as PAO/ester blends, offer a number of inherent performance advantages over conventional petroleum-based oils for the formulation of modern automotive engine oils. Another important feature that must be considered in automotive crankcase applications is low-temperature performance. The most widely recognized property benefit of PAO-based fluids is excellent low-temperature performance [77]. Table 1.12 and Table 1.13 compare the low-temperature characteristics of base fluid PAOs with HVI and VHVI mineral oils of comparable viscosity [24]. Highly refined mineral oil stocks are improved over conventional mineral oils, however, they suffer in

Copyright 2006 by Taylor & Francis Group, LLC

TABLE 1.12 Low-Temperature Performance (Crankcase)

Oil PAO VHVI HVI 100SN

KV100◦ C (cSt)

Pour point (◦ C)

Cold crank simulation −25◦ C (mPa sec)

3.90 3.79 4.50 3.79

−64 −27 −12 −21

490 580 1350 1280

Brookfield viscosity −25◦ C (cP) 600 1160 Solid Solid

TABLE 1.13 Low-Temperature Performance (Crankcase)

Oil PAO VHVI HVI HVI 150SN

KV100◦ C (cSt)

Pour point (◦ C)

Cold crank simulation −25◦ C (mPa sec)

5.86 5.38 5.84 5.79 5.17

−58 −9 −9 −9 −12

1300 1530 3250 2740 4600

Brookfield viscosity −25◦ C (cP) 1550 Solid Solid Solid Solid

low-temperature performance even with the addition of pour-point depressants. The Cold Crank Simulation Test is of vital interest to any car owner who has ever lived in a cold climate. The advantage of a PAO-based formulation in the crankcase is immediate and obvious on a cold winter morning – it is the difference of being able to start the car or not. The superior low-temperature operation of synthetic automotive lubricants in automotive engine oils, gear oils, and automatic transmission fluid formulations has been demonstrated [78]. Piston cleanliness is another important factor in choosing a crankcase oil. Table 1.14 presents the results of three different tests commonly used to rate piston cleanliness [24]. The PAO formulations performed well compared with the mineral oils, even when used (as in the Fiat test) at only a 15% level in a part-synthetic formulation. The results of a Caterpillar 1-G evaluation are given in Table 1.15 [24]. Both a part-synthetic and a full-synthetic PAO-based oil outperformed an equivalent 10W-40 mineral oil. The high performance of a new synthetic PAO-based SAE 5W-40 heavy duty oil has been recently demonstrated [79]. This oil exceeds API CG-4, CF-4, CF-2, CF, SH, and EC performance specifications. High performance levels were first measured in standard and extended length laboratory testing. On the road testing using greatly extended oil drain intervals validated high performance levels in Cummins engines. Field testing at extended

TABLE 1.14 Piston Cleanliness Test VW1431 Fiat TIPO MWM B

Base oil

Grade

Mineral PAO Mineral PAO (15%) Mineral PAO (50%)

15W-40 5W-50 15W-40 15W-40 15W-40 10W-40

Piston merit 63.7 72.6 6.4 7.6 73.0 82.8

KV100◦ C , cSt

TABLE 1.15 Caterpillar 1-G Tests Results for Mineral Oil and Synthetic Formulations

Oil

Grade

Total groove fill (80% maximum)

Mineral Part-synthetic Full-synthetic

10W-40 10W-40 10W-40

76 67 53

Total weighted demerits (300 maximum) 294 243 103

drain intervals demonstrated performance benefits compared with industry recognized mineral-oil-based 15W-40 diesel engine oils. The successful arctic experience of synthetic-based multi-viscosity engine oils by the U.S. Army has also been described [80]. 1.5.2.2 Transmissions The advantages of synthetic automotive transmission fluids based on PAO that have been recently reported are favorable low-temperature properties, lower volatility and better wear performance than non-PAO-based ATFs [81]. Synthetics have also been promoted as a way to improve bottomline operating performance by extending component service life and reliability [82]. Hot oil oxidation tests are used to screen oils for use in manual transmissions and rear axles. The test is conducted at a more severe temperature (200◦ C) than used in the evaluation of crankcase oils, and the KV at 100◦ C is measured at specified time intervals. A comparison of the performance of mineral- and PAO-based fully formulated oils is shown in Table 1.16 [24]. After 16 h, the viscosity of the PAO fluid increased only 19%, whereas the viscosity of the mineral oil fluid increased nearly 500%. After 24 h, the viscosity of the PAO fluid increased by only 21%, but that of the mineral oil product became too viscous to measure. The HOOT is also used as an indicator of performance for automatic transmission fluids. A less viscous oil is

Copyright 2006 by Taylor & Francis Group, LLC

TABLE 1.16 Hot Oil Oxidation Testa (Manual Transmission and Rear Axle Oils)

Time (h)

PAO

Mineral oil

0 4 8 16 24

10.00 10.45 11.54 11.92 12.10

10.50 12.60 12.90 51.24 TVTMb

a Temperature of test = 200◦ C. b TVTM = too viscous to measure.

Test described in Shubkin, R.L. (1994). Lubrication Engineering 50, 196–201.

used for automatic transmissions than for manual transmissions (7.5 vs. 10.0 cSt), but the test is still conducted at 200◦ C. The results of the test are presented graphically on Figure 1.8 [24]. The PAO-based formulation showed only an 8.6% increase in 100◦ C viscosity after 24 h. The viscosity of the mineral oil formulation increased 550% in the same time period. A 4 cSt full-synthetic ATF has been tested to demonstrate fuel economy potential and the ability to provide adequate transmission performance and protection. The PAO-based ATF demonstrated remarkable lubricant stability. Results showed adequate transmission performance over 20,000 cycles in the GM Dexron® IIE cycling test (THCT), light wear of applicable transmission parts, and trace sludge formation [83]. There was no shear down of the full-synthetic. The fluid remained in grade throughout the test. Although the tests described above indicate that PAObased transmission fluids show better durability and performance than mineral oils at a given temperature, another important phenomenon has been observed. Measurement of transmission lubricant temperatures under high-speed driving conditions shows that the synthetic-based oils run as much as 30◦ C cooler than their mineral oil counterparts [84]. The improved wear characteristics of PAO-based transmission fluid in ASTM D 4172 Shell Four ball testing over mineral-oil-based formulations has been reported [85]. Lower coefficients of friction were also reported for the PAO-based formulation. Lower temperature and lower coefficients of friction will result in less wear and fatigue failure. A lower rate of oxidation means that replacement of oil will also be reduced. These factors will result in more economical performance — less oil usage and lower maintenance.

KV 100 °C, cSt

62 48 44 40 36 32 28 24 20 16 12 8 4 0

Mineral oil PAO

0

4

8

12 Time (h)

16

20

24

FIGURE 1.8 Hot oil oxidation test (automatic transmission, 200◦ C)

TABLE 1.17 Mercedes Benz Gear Rig Performance Oil Mineral PAO

Grade 90 75W-90

Tensile strength (%)

Elongation (%)

Volume (%)

+1.80 −1.20 −50/0

−12.0 −13.0 −60/0

+1.0 +0.6 0/+5

0 0 0/+5

Acrylate 150SN PAO Limits

+5.40 −12.00 −15/+10

−7.70 −30.00 −35/+10

+3.40 −1.50 −5/+5

0 +4.0 −5/+5

Silicone 150SN PAO Limits

−66.0 −9.60 −30/+10

−60.0 −15.0 −20/+10

+14.80 +18.00 0/+30

−16.0 −13.0 −25/0

Nitrile 150SN PAO Limits

+11.0 +13.0 −20/0

−11.0 −19.0 −50/0

+2.40 −1.90 −5/+5

+1.00 +2.00 −5/+5

Time to tooth breakage (h) 85 135

1.5.2.3 Gears The Mercedes Benz Spur Gear Rig Performance Test is used to evaluate the performance of gear oils. In the test, the elapsed time to gear-tooth breakage is used as the indicator of performance. An SAE 75W-90 synthetic formulation showed a 60% improvement over an SAE 90 mineral oil [24]. The data are presented in Table 1.17. 1.5.2.4 Seal compatibility Seal compatibility is an important factor for any functional fluid. Unlike mineral oils, PAO does not have a tendency to swell elastomeric materials. Early commercial PAO products were not formulated properly to allow for this difference in behavior. Consequently, early PAOs gained an undeserved reputation for leakage. Extensive tests have since shown that the addition of small quantities of an ester to the formulation easily alleviates this problem. Recent work has indicated that the proper choice of other performance additives may eliminate the need to employ esters, but this approach is not yet in practice for crankcase applications. Table 1.18 shows the results obtained in the CCMC G5 Seal Compatibility Test for base fluids [24]. A 6.0 cSt PAO was compared with a 150SN mineral oil. The four seal materials studied were

Copyright 2006 by Taylor & Francis Group, LLC

TABLE 1.18 Seal Compatibility (CCMC G5 Specification)

Elastomer Fluoroelastomer 150SN PAO Limits

Hardness (points)

acrylate, silicone, nitrile, and fluoroelastomer. The seals were evaluated at the end of the test for changes in tensile strength, elongation, volume (seal swell) and hardness. The PAO performance fell within the specification limits for all four elastomers. The mineral oil failed with silicone. Similar tests have been carried out with fully formulated part- and full-synthetic PAO oils. In all cases the fluids met the specifications. Additional information on choosing the proper seal materials for use with PAO fluids may be found in References 86 and 87.

30

TABLE 1.19 Automotive Economy

Total savings Same oil drains ($) One drain for fullsynthetic

25.2(+5%) 595 714.00 36.00

.00 30.00

2.00 45.00

4.00 75.00

—

15.00

39.00

— —

3.00 3.00

−3.00 11.00

8.8

10

5 0

FIGURE 1.9 Volatility of fully formulated oils

1.5.2.5 Economy The performance benefits demonstrated by the various tests that have been described are meaningful to the automotive engineer or tribologist, but the average consumer is most interested in how much savings the use of a PAO-based product is going to generate. Table 1.19 describes the results of one study that considered both the increased fuel economy and the extended oil drain interval made possible with part- and fullsynthetic PAO crankcase oils. The original calculations [88] have been updated to reflect current prices for gasoline and oil in North America. The calculations are based on 15,000 mi of driving and a “do-it-yourself” oil change regimen. A pump price of $1.20/gal for gasoline has been chosen, and the oil has been priced at $1.00, $2.00, and $4.00/qt for the mineral oil, the part-synthetic, and the fullsynthetic, respectively. If the oil is changed every 5,000 mi, there is almost no cost differential for the three oils because of the improved fuel economy gained with the synthetics. For the 15,000 mi distance, the saving over the mineral oil formulation is $3.00 with the part-synthetic oil and a deficit of $3.00 is experienced with the full-synthetic. If, however, there is only one drain for the full-synthetic, the savings goes up to $11.00. In Europe, where gasoline is much more expensive and the differential in oil prices is less, the savings accrued by the use of synthetic crankcase oils will be much greater. The use of lighter grades of crankcase oil is one answer to the need for increased fuel economy. The possible downside to this strategy would be a concurrent increase in oil consumption and the loss of sufficient high-temperature viscosity for adequate engine protection. Studies show, however, that properly formulated PAO-based synthetic

Copyright 2006 by Taylor & Francis Group, LLC

10

Mineral 5W–30

24.6(+2.5%) 610 732.00 18.00

12.4

Mineral 10W–30

24 625 750.00 —

15.6 15

Mineral 10W–40

Fullsynthetic

Mineral 15W–40

Partsynthetic

Mineral 20W–50

Oil Cost ($/qt) Cost of 3 × 5 qt changes plus 3 × $5 filters ($) Additional cost ($)

Mineral oil

20

Synthetic 5W–50

Fuel Economy (miles/gal) Use (gal/15,000 mi) Cost ($1.20/gal) Savings ($/15,000 mi)

20.9 Volatility, %

Parameter

25.7 25

crankcase oils, with wide multigrade SAE performance classifications, can outperform mineral-oil-based formulations in both fuel and oil consumption, while maintaining superior engine protection [63]. Figures 1.9 to 1.12 from this study illustrate the point. Figure 1.9 shows the relative volatility of a 5W-50 full-synthetic formulation compared with five different mineral oil fluids. For European driving, a limit of 13% maximum volatility is specified for Association des Constructeurs Europiens d’Automobiles (ACEA) for top grade for passenger car and diesel engine passenger cars and commercial HDDO performance. It may be seen that a 15W-40 mineral-oil-based formulation is required to meet this specification. The 5W-30 mineral oil formulation, which is used in North America for fuel economy and cold-starting reasons, does not come close to meeting the volatility standard. Figure 1.10 compares the “high-temperature/highshear” viscosity at 150◦ C of the full-synthetic 5W-50 formulation and the mineral oil formulations. The viscosity of the synthetic oil is even higher than the 20W-50 mineral oil. The outstanding performance of the synthetic oil is attributable to the naturally high VI of the PAO in combination with a shear-stable VII. Figure 1.9 and Figure 1.10 indicate that oil consumption should be under control with a full-synthetic formulation because of the superior volatility and viscosity performance. Figure 1.11 shows the results of a 12-car field test in which the oil consumption for the 5W-50 synthetic oil was compared with a 15W-50 mineral oil. The oil consumption for the synthetic oil was 25% less than for the mineral oil. The data just presented for gasoline engines is equally valid for diesel engines. The CCMC D3 standard for super high-performance diesel (SHPD) engine oils can be met with a 5W-30 synthetic blend. Figure 1.12 shows that the full-synthetic SHPD oil gave approximately 2% increased fuel efficiency compared with the 15W-40 mineral oil SHPD across a range of typical driving modes.

4.9

5

Low load Med load High load

4.4 4.1

2.8

3 2

% fuel saving

4 3.7

4

3 2 1

1

0 1200

1500

1800

2200

Speed (rpm) Mineral 5W–30

Mineral 10W–40

Mineral 15W–40

Mineral 20W–50

0 Synthetic 5W–50

Volatility at 150 °C, cp* (*Shear Rate=106/S)

5

FIGURE 1.10 High-temperature/high-shear viscosity of fully formulated oils

FIGURE 1.12 Fuel efficiency: super-high-performance diesel formulation. Percentage fuel saving for 5W-30 full-synthetic vs. 15W-40 mineral oil • Packing seal lubricants for chemical injectors for oil and

gas field applications.

Miles per liter of oil

12,500

• Lubricant/coolant for double mechanical seals of cen10,800

10,000

trifugal pumps handling corrosive, abrasive chloride slurries. 8,600

Specific reports of performance advantages in industrial applications are discussed in the following sections.

7,000 6,000

1.5.3.1 Refrigeration compressors

2,500 0 Synthetic 5W-50

Mineral 16W-60

FIGURE 1.11 Average oil consumption for a range of modern cars

1.5.3 Performance Testing for Industrial Applications Industrial applications in which PAOs have served as the lubricant of choice have been known for over a decade [38]. Some of these include sealing fluids and lubricants for pumps handling polystyrene process liquid at 232.2◦ C (450◦ F) in nitrogen atmosphere. PAOs have also been used as a replacement for polyolester as a hightemperature bearing and gear lubricant in blowers used as steam booster compressors. Rotary and reciprocating mechanical vacuum pumps are lubricated using ISO 46 PAO formulations. The chemical inertness of PAOs has been demonstrated in chemical applications. PAOs give satisfactory performance as: • Lubricants for large conveyor chains with exposure to

sulfuric acid vapors. • Lubricants for reactor gearboxes handling nitric and

sulfuric acid mixtures.

Copyright 2006 by Taylor & Francis Group, LLC

Polyalphaolefins have also been used in ammonia and fluorocarbon refrigeration compressors because of their low pour points. Other performance advantages reported for PAO fluids include lower operating temperature and less equipment vibration. Bloch and Williams [39] discuss many benefits that high film strength synthetic lubricants offer over other lubricants. Using process plant applications as examples, these authors show that two significant advantages of using high film strength synthetic lubricants are lower operating temperatures (in excess of 20˚C) and reduced vibration. These two performance advantages increased the life of high torque worm speed reducers by 200 to 300% and extended oil replacement intervals by a factor of four in one application. In other applications, in addition to reduced operating temperature and vibration levels, the motor amperages were reduced when using the synthetic lubricant. Properly formulated high film strength synthetic lubricant based on diesters, PAOs, and combinations of these base stocks can result in reduced bearing and gear operating temperature. 1.5.3.2 Gear oils The use of PAO-based gear oils in industrial settings can lead to important savings in energy consumption, as well as decreased down-time and lower maintenance requirements. The wide range of operating temperatures allows the use of less viscous oils, which results in greater

energy efficiency. The relatively low coefficient of friction for PAOs reduces the amount of internal friction created by the normal shearing of an oil film during operation. Improved scuffing performance for gear/circulating oils has been demonstrated [89]. Jackson et al. have studied the influence of lubricant traction characteristics on the load at which scuffing occurs. The study compared low traction polyalphaolefin (PAO)-based lubricants with mineral oils in additive-free, antiwear, and extreme pressure (EP) formulations. Benefits of 25 to 220% were observed for the PAO-based synthetic lubricants over mineral oils. Among the conclusions reported, low traction PAO-based lubricants uniformly gave higher scuffing loads/unit width than the mineral-based fluids tested at both high and low specific film thickness. PAO-based gear and circulating oils outperformed mineral-oil-based gear and circulating oils, respectively. PAOs were also shown to be very responsive to additives. The advantages of PAOs as lubricants in conveyor applications has been demonstrated by Paton. Gear boxes lubricated with a fully synthetic PAO-based gear oil (75W-90) was studied. An all-season PAO-based fluid was chosen for pulley shaft bearing lubrication [47]. In wind turbine gear boxes the high VI of a synthetic fluid would insure that the change in viscosity with temperature would be less than with equiviscous mineral oils. A further advantage of a synthetic fluid for these types of applications is that synthetics have lower pour points than mineral oils [61]. Polyalpholefins provide both excellent VI and low pour point. These properties make PAOs a fluid of choice for an application where there will be a wide range of operating temperatures. Table 1.20 is a compilation of data from ten reports relating to the benefits of increased efficiency found when industrial transmissions were switched from a mineral-oilto PAO-based gear oils [90–99]. The increases ranged from 2.2 to 8.8%. It is interesting to note that the efficiency increase observed in worm gears has a close positive correlation with the reduction ratio. This correlation exists despite the fact that the data was reported by different companies and was collected on different types of equipment. 1.5.3.3 Turbines Wind turbine gear boxes are also subject to wear and pitting fatigue failure. Water contamination can also occur. Among the many lubricant related factors, film thickness under operating conditions must also be considered in the formulation of a wind turbine lubricant. Excellent low-temperature properties and high load performance is possible with a PAO-based wind turbine lubricant (Tribol 1510) [62]. Polyalphaolefins have been employed in larger General Electric (GE) and EGT industrial gas turbines. Oils used

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TABLE 1.20 Industrial Gear Oil Applications Transmission type Worm gear Worm gear Worm gear Worm gear Worm gear Worm gear Spur gear/chain Spur gear Series of nine worm gears Series of five worm gears

Reduction ratio

Power (hp)

Load Efficiency (% rated) increase (%)

10:1 15:1 25:1 30:1 50:1 50:1 — 24:1 15:1

3.0 1.55–2.0 6.5–8.1 3.2–3.9 3.0–6.0 0.5–1.0 35 200 122–142

100 100–130 100 96–117 100–200 50–100 — — 100–112

2.2 3.8 4.4 5.6 7.7 8.8 2 6 6

39:1

75

—

5.8

in these applications must have enhanced oxidation resistance to withstand journal heat soak temperatures that can go as high as 250 to 300◦ C. Mineral oils volatilize and form deposits whereas lubricants formulated with PAOs give cleaner running performance and extended useful life of the lubricant (from 4 to 5 yr up to 15 yr) [62]. Mobil Industrial Lubricants has developed Mobil SHC 800 for land-based gas turbines. This fluid, based on PAO, provides low maintenance and reliability over wide temperature ranges. 1.5.3.4 Hydraulic oil performance Polyalphaolefins offer a variety of property and performance features and benefits that cannot be achieved using alternative base fluids. PAOs have excellent lowtemperature fluidity and excellent VI when compared with all but the most expensive base fluids. They have very low volatility and excellent hydrolytic, thermal, and oxidative stability relative to many other oils. 1.5.3.5 Metal working performance Antiseizure properties of lubricants, as measured by their maximum workable die temperature (MWT), have been reported [46]. The MWT of lubricating oils reported were as follows: PAO oils: 160 to 170◦ C, polybutene oils: 150◦ C, mineral oils: 100 to 120◦ C, ester oils: 90◦ C. Addition of phosphorus containing extreme pressure (EP) agents to mineral oils or PAOs enhanced the workable die temperature to about 300◦ C. 1.5.3.6 Cost savings The open literature contains a number of reports of savings that have accrued to industrial concerns after they switched from a mineral oil to a PAO-based gear or bearing oil.

Table 1.21 is a short tabulation of some of these reports [100]. The table shows a diverse type of manufacturing for the companies included, and a diverse selection of applications for which the PAO-based lubricants were applied. The annual savings for these companies ranged from $12,000 to $98,000/yr. The largest reported savings on Table 1.21 was $98,000.00/yr when a PAO-based gear oil was used on the felt roll bearings in a paper mill. The high speed of the huge rolls in a paper mill is critical to their competitive operation, and the use of PAO-based fluids is becoming an important part of the over-all strategy for cost-effective operation.

1.5.4 Applications Sensitive to Health and Environmental Issues Results to demonstrate the favorable biodegradability of PAO fluids has recently been published [101–103]. In a comparison of PAOs with equiviscous mineral oils, PAOs were found to be significantly more biodegradable (Figure 1.13).

TABLE 1.21 Savings with PAO-Based Gear Oils Company type

Application

Soybean processing Plastics Copper wire Paper mill Steel mill

X Biodegradation (CEC-L33-A93)

Pharmaceutical Aluminum cans Manufacturing

100 90 80 70 60 50 40 30 20 10 0

Aeration blower Bearing circulation system Line gears Felt roll bearings Fly ash blower shaft thrust bearings Gear reducers Gear reducers Various

Annual savings $2100/unit $12,000 $19,000 $98,000 $77,000 $70,000 $35,000 $80,000

PAOs

Time extended CEC-L-33-A-94 testing has also shown that 2, 4, and 8 cSt PAOs continue to biodegrade well past the 21-day period prescribed in the standard method (Figure 1.14). PAO fluids are also considered to be nontoxic and nonirritating to mammals (Table 1.22). PAOs are not expected to be toxic to aquatic organisms. For example, in the Microtox test with bioluminescent bacteria, there were no effects for 49,500 ppm of the water-soluble fraction (Table 1.23). Results have also been presented that demonstrate that low viscosity (2 and 4 cSt) PAOs are significantly biodegradable (in the CEC L33 T82 biodegradability test) [104]. 1.5.4.1 Food contact Polyalphaolefin base stocks are pure, saturated hydrocarbons. They contain no aromatics (except for small amounts in the 40 and 100 cSt fluids produced by Mobil) and no functional groups. As such, the toxicity is expected to be as low or lower than the most highly refined white mineral oils. The PAOs have Food and Drug Administration (FDA) approval for use in both “indirect” and “incidental” foodcontact applications. They fall within the definition of a white mineral oil according to the Code of Federal Regulations, 21 CFR 178.3620, paragraph B. The applications for which FDA approval is required, and for which PAO is qualified, are listed in Table 1.24. In essence, PAO fluids may be used as a component of any material that contacts food or as a lubricant for any machinery that processes food. Direct food contact approval (i.e., as a component to be purposely ingested) has not yet been obtained in the United States, but probably could be obtained if there was an application that warranted the effort and expense of obtaining the approval. Fortum’s (previously named Neste) food grade PAO fulfills 21 CFR

Mineral oils 2 cSt

PAO2

MVI

4 cSt

HVI

PAO4

LVI

Bass stock

FIGURE 1.13 Biodegradability of base stocks poly(α-olefins) vs. equiviscous mineral oils: MVI, medium viscosity index (naphthenic base stock, aromatic content 1.9%); HVI, high viscosity index (paraffinic base stock, aromatic content 2.6%); LVI, low viscosity index (naphthenic base stock, aromatic content 12.3%)

Copyright 2006 by Taylor & Francis Group, LLC

% Blodegradation (Time-extended CEC L33 T82)

100 90 2 cSt

80 70

4 cSt

60 50 40 8 cSt

30 20 10 0 0

7

14

21

28

35

42

49

56

63

70

77

84

91

98

105

112

119

Days

FIGURE 1.14 Biodegradability vs. time for PAO fluids

TABLE 1.22 Acute Mammalian Toxicity of PAO Fluids PAO fluid Oral LD50 a Skin Eye (cSt) (g/kg) Irritationb Irritationc Comedogenicityd 2 4 6 8 10

>5 >5 >5 >5 >5

Negative Negative Negative Negative Negative

Negative Negative Negative Negative Negative

Negative Negative Negative Negative Negative

a Rat Oral LD (statistically calculated dose needed to kill 50% of the 50

rats in the study) is determined by single dose administration of undiluted test material. Rat oral LD50 values of >50 g/kg are considered nontoxic. b Where heated material or oil mists could be generated, consult the MSDS for recommended handling procedures. c According to criteria of Federal Hazardous Substance Act (FHSA, 16CFR 1500). d Comedogenicity refers to the ability of the test material to induce the enhanced collection of increased sebaceous material and keratin likened to acne blemishes.

TABLE 1.23 Acute Aquatic Toxicity of the Water Soluble Fraction of POA Fluids by the Microtox® Method PAO Fluid (cSt)

EC50 (5 min)

2 4 6 8 10 40 100

NR* NR NR NR NR NR NR

* NR — No observable effects at concentrations up to 49,500 ppm.

1.5.4.2 Cosmetics and toiletries 172.878 and 178.3620a for direct food contact. Fortum has approval for PAO 6 (Food Grade) as a food additive in Finland. Work is proceeding to get Europe-wide approval for PAO (Food Grade) as a food additive. Fortum has been selling PAO 6 (Food Grade) for use as a glazing agent for sweets in Finland since 1992. Polyalphaolefin specifications for food additive use in Finland are very strict on purity. There can be no oxygen containing components, and hydrogenation of the poly-1-decene must be complete. One test that is used to check purity is the “hot acid test” also referred to as the “readily carbonizable substances test,” described in the pharmacopoeias.

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Polyalphaolefin fluids are nontoxic when given orally to rats. The lethal dosage for 50% of the test subjects (LD50 ) is greater than 5 g/Kg of body weight. PAOs are also nonirritating to the eyes and skin of test animals, and they are not expected to induce sensitization reactions. They have low vapor pressures and therefore are not hazardous by inhalation. Subjectively, PAOs are said to have a better “feel” on human skin than white mineral oils. For all of these reasons, a small but growing market for PAO is developing in the cosmetics industry [55]. A national brand of lipstick contains PAO as a major component, and in Europe, PAOs (polydecene) can be found in a variety of cosmetic products such as make up removers, body oil, shampoos, lotions, shower and bath oils, and make up creams.

TABLE 1.24 FDA-Approved Applications for PAO Sectiona 175.105 176.200 176.210 177.2260 177.2600 177.2800 178.3570 178-3620 178.3910

Application Adhesives Defoaming agents used in coatings Defoaming agents used in the manufacture of paper and paperboard Production of resin-bonded filters Rubber articles (plasticizers) intended for repeated use Production of textiles and textile fibers Lubricants with incidental food contact Technical grade white mineral oil Surface lubricants used in the manufacture of metallic articles (e.g., metallic foil)

a Food and Drug Administration, HHS-21 CFR Ch. 1 (4-

1-88 edition).

1.5.4.3 Off-shore drilling Regulations on the marine toxicity of fluids used to lubricate the drill-head in off-shore drilling operations are becoming tighter, especially in the North Sea. PAO fluids have been used as a base stock for synthetic-based drilling fluids in off-shore applications. The purpose of these fluids is wellbore cleaning, bit cooling and lubrication, and shale stabilization. The discharge of cuttings using syntheticbased muds is considered less harmful to the marine environment. PAOs offer excellent marine toxicity. This technology was developed in the early 1990s [105,106]. This technology has been displaced by alternative technologies. Leading alternative technologies include linear alphaolefins [107] and isomerized olefins [108]. 1.5.4.4 Miscellaneous Other environmentally sensitive areas for which PAO fluids are being evaluated are: logging operations (chain saws), marine outboard engines, and hydraulic systems for large farm machinery. In addition to low toxicity, it is important that fluids used in these applications exhibit biodegradation and low levels of bioaccumulation. Preliminary evaluations indicate that PAOs do not bioaccumulate and that their rate of biodegradation is faster than that of mineral oils of comparable viscosity. On the other hand, the rate of biodegradation is slower than for some ester-based drilling muds that are also undergoing evaluations for this application. For a full discussion of this very complex issue, the reader is referred to Chapter 25 of this book.

1.5.5 Military Applications The earliest applications for PAO fluids were in the military. Mil-H-83282 is a specification for a hydraulic fluid

Copyright 2006 by Taylor & Francis Group, LLC

for jet aircraft. The specification was built around an experimental 4.0 cSt decene-based PAO produced by Mobil in the late 1960s. The requirements included extreme lowtemperature fluidity as well as high flash and fire point values. The latter requirement was to minimize the risk of loss due to fire in the event that a hydraulic line was severed by enemy gunfire. Mil-H-83282 remains an important military fluid today. An interesting, if not publicized, example of superior performance for PAO came to light as a result of the war in the Persian Gulf in January 1991. Under harsh desert conditions, the U.S. weapons that were lubricated and cleaned with PAO-based oils performed better than similar Allied weapons using conventional fluids, resulting in some rush orders to the lubricant formulators from Allied commanders. Table 1.25 contains a short summary of military specifications that either require or often use PAO fluids.

1.5.6 Space Applications Precision space craft mechanisms require critical selection of lubricants to maximize reliable performance in space where low or no maintenance situations exist. Communication, global surveillance, meteorological and navigational space craft contain a variety of moving mechanical assemblies (MMAs). These mechanical sub-systems have become life-limiting for many space craft [60]. Most problems have been lubricant related problems including loss of bearing contact and chemical degradation. Results of recent studies advocate the use of formulated PAO oils and greases for most high-cycle precision bearings [60].

1.6 MARKETS AND PRODUCTION CAPACITIES By the end of 1990, world PAO demand had grown to 188.4 MM lb [9]. This volume represents a remarkable 14-fold increase since 1975, but still represented less than 0.05% of the total world lubricant base-stock market at that time. By the end of 1993, world PAO demand had grown to 260 MM lb [109]. U.S. capacity as of June 1, 1993 has been reported to be 287 MM lb [110] and was predicted to grow to 458 MM lb/yr by the year 2000 [109]. The worldwide consumption of PAO in 1998 was 600 MM lb/yr. PAO global capacity was on the order of 700 MM lb/yr in 2002. During 1975–1980, demand for PAO grew at 33% per year. Synthetic engine oils were a novelty on the market during this period, and they were growing from a base near zero. Growth slowed during the 1980–1985 period to around 7%. Some early product entrants to the market were improperly formulated, and the resultant poor performance attached some stigma to the use of synthetics. The 1985–1990 time period saw a strong new interest in synthetic lubricants because of the enactment of stringent new specifications and governmental regulations that were

TABLE 1.25 Military Applications Specification number

Applications

Lubricant highlights

MIL-PRF-46170

Type I: Tank recoil and hydraulic systems

4 cSt PAO: ester: TCP PAO base stock specs Finished fluid specs

MIL-PRF-83282

Aircraft and missile hydraulic systems

4 cSt PAO: ester: TCP PAO base stock specs Finished fluid specs

MIL-PRF-(83282 low temperature)

Aircraft and missile hydraulic systems

Dimer/trimer ∼3 cSt PAO: ester: TCP No pour point or VII additives Finished fluid specs only

MIL-PRF-10924

Multipurpose grease for all ground vehicles, artillery, and equipment

Typically 6 cSt PAO base stock Finished grease specs only Formulation and constituents Confidential and proprietary

MIL-PRF-63460

Small large caliber weapons cleaner, lubricant, and preservative, −65◦ C to 150◦ F

Mineral oil and syntheticbased 2 and/or 3 cSt PAO Finished lube specs only

MIL-PRF-81322

Multipurpose grease for aircraft

Mixture of PAO fluids

MIL-PRF-32014

Multipurpose grease for aircraft

Mixture of PAO fluids

MIL-PRF-2104

I/C engine oil and power transmission fluids All types of military tactical/ combat ground equipment

Mineral oil, synthetic, or combination base stock

MIL-PRF-2105

Gear oil for units, heavy-duty industrial type gear units, steering gear units, and universal joints

Mineral oil, synthetic, or combination base stock Finished lube specs by grade only

MIL-PRF-87252

Dielectric coolant for electronic applications Hydrolytically stable Replacing silicate ester coolant

PAO base stock specified 2 cSt dimer ∼99.5% PAO Oxidation/corrosion inhibitor Finished fluid specs only

difficult to meet with mineral oil base stocks. The growth rate for PAO during this period was approximately 19% per year. Current growth rate is on the order of 7% per year.

1.6.1 Demand by Segment and Region Strong growth for the PAO market is predicted to continue in the foreseeable future. Table 1.26 shows the expected rate of growth for PAO into the automotive, industrial, military, and emerging market segments. The total market was expected to grow from 185 MM lb in 1990 to 450 MM lb in 1995 — an annual growth rate of about 20% per year [24,100]. Although the size of the PAO markets in 1990 were approximately the same in Europe and North America, the breakdown by segments was considerably different. The European market was driven primarily by the automotive demand whereas the North American market was more

Copyright 2006 by Taylor & Francis Group, LLC

balanced. In 1990 in Europe, 78% of the PAO demand was in the automotive sector, with the rest going into industrial applications. The PAO demand for the automotive sector in 1996 was 80%, little change from the early 1990s. In North America, the automotive and industrial markets each took about 38% of the PAO, while the military used 17%. The remainder went into “emerging” markets, which will be discussed in more detail Section 1.6.2. Table 1.27 is a breakdown of PAO market growth by both segment and region. It should be noted that the 1995 forecasts predict that the demand distributions by segment for PAO in Europe and North America will converge. North America in fact began catching up with Europe in the automotive applications area while Europe began catching up with North America in industrial applications. Both continents undertook vigorous development of the “emerging” segments. Overall market growth and trends are generally consistent with the predictions made earlier and the global

1.6.2 Emerging Markets

TABLE 1.26 PAO Market Segment 1990 (MM lb)

Predicted 1995 (MM lb)

Automotive Industrial Military Emerging

110 55 15 5

230 100 20 100

18 13 6 85

Total

185

450

20

Market segment

Predicted growth rate (% year)

1.6.3 PAO Production Capacity

TABLE 1.27 PAO Market Segment Growth by Region

Region and segment

1990 (MM lb)

1995 (MM lb)

Growth rate (% year)

1998 (MM lb)

North America Automotive Industrial Military Emerging Total

35 35 15 5 90

100 60 20 40 220

23 11 6 51 20

110

Europe Automotive Industrial Military Emerging Total

70 20 — — 90

110 40 — 60 210

10 15 — N/A 19

240 38 22 — 300

Far East Automotive Industrial Military Emerging Total

4 1 — — 5

15 5 — — 20

30 38 — — 32

230

80

PAO capacity is on the order of 350 kMT/yr. This means that there is strong PAO growth in terms of demand and production capacity. Furthermore, the fact that there are several new linear alphaolefin plants that have gone on stream during 2000–2002, means that there is adequate supply of precursor for the production of needed PAO for lubricant applications. The development of markets and applications for PAO has been generally confined to North America and Europe. In 1990, the Far East accounted for only 2.7% of the demand for PAO. Between 1990 and 1995, the consumption of PAO in the Far East grew at an annual rate of about 30% — reminiscent of the growth in the West during the 1975–1980 time frame. The non-European and U.S. consumption of PAO is on the order of 80 MM lb and is expected to grow.

Copyright 2006 by Taylor & Francis Group, LLC

A substantial portion of the growth being forecast for PAO has been described as “emerging” markets. The term “emerging” is used to designate application areas where there is a high potential for PAO to capture a part of the market now being serviced by other types of fluids. Table 1.28 lists seven areas where PAO fluids and formulations are continuing to be developed to fulfill specific requirements not being met by the fluids currently in use. The three driving forces for shifting from the current functional fluid to PAO are cost, performance, and toxicity.

At the end of 1990, the worldwide production capacity for PAO was 325 MM lb/yr. Sales for 1990 were 57% of production capacity, which represented a major reversal of the demand/supply situation of the mid-1980s. Because of the shortage of PAO available at that time, formulators were forced to seek alternative (if sometimes less satisfactory) solutions for their performance requirements. There was a strong and understandable hesitancy among equipment manufacturers, formulators, and end-users to place themselves in a precarious supply situation. As a result of the excellent supply situation that now exists, there is a new surge of activity in the development of new markets and applications for PAO fluids. Table 1.29 is a summary of the PAO producers and their capacities in 1990. Ethyl Corporation brought their 80 MM lb/yr plant in Feluy, Belgium, on-stream in January 1991. As mentioned earlier, Ethyl split off Albemarle as a separate company in 1994, which owned and operated the PAO business until March 1996 when Amoco purchased the alphaolefin and PAO business from Albemarle. BP announced in March 2004 that it was putting its linear alphaolefins and PAOs businesses up for sale. This is still pending at the time of this writing. Neste brought their 45 MM lb/yr plant in Berigen, Belgium, on-stream in 1991. Neste has now become Fortum. PAO production capacities are summarized in Table 1.29. A summary of synthetic lubricants including markets and consumption for PAOs has been published [111].

1.6.4 Competitive Products Chemically modified mineral oils (CMMOs) (highly refined mineral oils) approach PAO in some performance characteristics. These mineral oils fall into three categories. 1.6.4.1 Very high viscosity index oils The premier product derived from crude oil sources is Shell Oil’s patented extra high viscosity index (XHVI) oil. It is produced in France and Australia from a special cut of

TABLE 1.28 Emerging Markets

Product line

Current volume (MM lb)

Polymer Personal care Refrigeration Textile Dielectric fluids Brake fluid Shock absorbers Total

200 150 45 25 90 440 110 1060

Fluid type

Driving force

WMOa WMO/estersa Polyalkyl glycols Silicones/WMO Mineral/silicones/PCB Polyethylene glycol/silicones Mineral oil

Toxicity/performance Toxicity Performance Cost and performance Cost/performance/toxicity Cost and performance Performance

a White mineral oil.

TABLE 1.29 PAO Capacity (WorldWide) (Low and High Viscosity)

Manufacturer Amoco (BP)c Albemarle Ethyl Exxon-Mobila Mobil Chevron Exxon Neste Fortumb Uniroyal (Crompton) Total

1990 (MM lb/yr)

1993 (MM lb/yr) (109)

1996 (MM lb/yr) (112)

0 0 170

0 256 0

249 0 0

80 55 20 0

157 88 0 66

224

0 325

0 567

4.4 592.4

0 62

2002 (MM lb/yr) 260 0 0 275 0 90 0 0 70 5 695

a Formerly Exxon and Mobil separately. b Formerly Neste. c now innorene.

refinery slack wax by a severe hydrocracking procedure. Shell’s capacity is 150 MM lb/yr. Shell is apparently currently manufacturing XHVI base stocks from Syn Gas in Malaysia. The product exhibits very good performance characteristics, but it is deficient relative to PAO in both low-temperature properties and volatility (Table 1.4). Petro Canada has recently begun production of a 100 MM gal/yr base oil plant in Mississauga, Ontario, Canada [113]. This production includes a series of severely hydroprocessed mineral oils, one of which is a high VI line of API Group III VHVI Specialty Base Fluids under the name of Phoenix. These generally have higher pour points and higher NOACK volatility than the equiviscous PAOs, but are improved over conventional mineral oil base stocks.

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BP currently manufactures LaVera Hydrocracked Residue (LHC) fluids in LaVera, France. LHC fluids are available in 3, 4, 6, and 8 cSt grades. Processing consists of hydrocracking of a middle distillate stream, followed by vacuum distillation and a dewaxing step. These stocks are wax isomerates that are highly isoparaffinic. Chevron has also recently announced that it will produce unconventional base oils (UCBOs) at its lubricant base oil facility in Richmond, California. These new base oils are reported to be in the range of 115 to 135 VI [114]. Conoco and Pennzoil have announced a joint venture, Excel Paralubes, to produce 18,000 bbl/day base oil at Conoco’s plant in Lake Charles, Louisiana. These materials are processed (Chevron’s isodewaxing process)

to produce higher quality base stocks [113]. Conoco is marketing a new line of clear lube oils under the name Hydroclear™ produced using hydrocracking technology. SK Corporation (formerly Yukong) produce a slate of VHVI base stocks at its plant in Ulsan, South Korea using a combination of hydrocracking and catalytic dewaxing processes. This was developed with Raytheon Corporation. These materials are described in greater detail in Chapter 18 of this book.

1.6.4.2 High viscosity index oils High viscosity index (HVI) base stocks are intermediate in properties between the VHVI fluids and conventional solvent-refined oils (Table 1.3). HVI oils are manufactured by a process that involves hydrotreating, redistilling, and solvent refining. HVI fluids were first produced by BP in 1976 and are now produced by BP at LaVera and Dunkerque in France. HVIs are also produced by Modrica in Yugoslavia and DEA in Germany. HVI fluids are less costly than either PAO or VHVI fluids, but 1.4 to 2.0 times more material is generally required to blend with an off-specification mineral oil to bring a formulation into 10W-30 specifications. Exxon begun producing screening samples of its new EHC™ (Raffinate Hydroconversion) base stocks at its Baytown refinery in 1999. These high viscosity index oils are in the range of 105 to 119 VI. These materials are described in greater detail in Chapter 18 of this book.

1.6.4.3 Polyinternalolefins Polyinternalolefins (PIO) fluids are similar to PAO fluids in that they are both manufactured by the oligomerization of linear olefins. The olefins used for PIO manufacture, however, are derived from the cracking of paraffinic base stocks. The internal olefins are more difficult to oligomerize than the α-olefins derived from ethylene chain growth, and the products have VIs that are 10 to 20 units lower than comparable PAOs. These materials are described in greater detail in Chapter 2 of this book.

1.7 CONCLUSION A number of forces will drive the growth of highperformance functional fluids for the next decade and beyond. These forces derive from diverse societal needs, but they have a common goal rooted in the uniquely human belief that there must be a better way to do whatever it is that has to be done. Some of these forces and the consequences they imply for the growth of PAO fluids are discussed in the following sections.

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1.7.1 Regulatory U.S. regulations for Corporate Average Fuel Economy (CAFE) are having a significant effect in both the design of new automobiles and the lubricant requirements and recommendations for them. In order to meet the fuel economy standards, which will now include a cold-start cycle specification, the Original equipment manufacturers (OEMs) are being forced into recommending SAE 5W multigrade crankcase oils. In addition, increased emphasis on aerodynamics results in higher engine operating temperatures, which affects not only the crankcase lubricant but also the transmission fluid, the gear oils, and the greases. All these factors will require fluids with lower low-temperature viscosity coupled with lower volatility, higher thermal and oxidative stability, higher heat capacity, and higher heat conductivity. Consumer protection, worker safety, and environmental regulations are becoming increasingly stringent in their requirements for nontoxic, nonhazardous, environmentally friendly products. Regulatory agencies are beginning to recognize potential toxicological problems associated with white mineral oils. PAOs are being put forward as high-performance, safe substitutes.

1.7.2 Performance and Cost-Effectiveness The need for improved performance remains a critical factor in the drive toward increased usage of PAO-based lubricants and functional fluids. In many applications mineral-oil-based products either cannot meet the more stringent requirements or are only marginally satisfactory. The use of PAO for blending with marginal base stocks in order to bring them into specification is increasing. Fleet operators, who are much more sensitive to costeffectiveness than the general public, will continue to increase their usage of synthetics as they recognize the potential long-term savings. Operators of large industrial machinery are beginning to recognize the increased cost-effectiveness of lubrication with PAO-based products. Machines that operate at lower temperatures, are less subject to wear, require less maintenance and down-time, consume less oil, and operate longer between lubricant drain cycles. The value of PAObased products for the lubrication of heavy-duty, off-road mobile equipment is also being recognized, especially in situations where routine maintenance is difficult.

1.7.3 Original Equipment Manufacturers The diversity and regional availability of mineral oil base stocks make standardization based on mineral oils difficult. In those applications where performance requirements are exacting, there will be a shift by Original Equipment Manufacturers (OEMs) to require synthetic fluids in order to assure uniformity.

Industrial and automotive OEMs are under pressure from the consumer and from their competition to extend warranty periods. At the same time, OEMs are under pressure to reduce the required amount of maintenance and down-time. Both avenues may be addressed by switching from mineral oil to PAO-based fluids. General Motors used a full-synthetic, PAO-based oil as the factory fill and recommended crankcase fluid for the first time when it introduced the 1992 Chevrolet Corvette. Today, fullsynthetic PAO-based oil is still recommended for the highperformance vehicle. The latest trend to address consumer convenience as well as protection of equipment from inadvertent contamination of the working fluid is the “fill-for-life” concept. General Motors is studying a “fill-for-life” PAO-based automatic transmission fluid for its future models.

1.7.4 Petroleum Companies and Blenders Lubricant producers have historically had low profit margins. Base stock prices have been closely tied to crude oil prices, and the selling price for finished fluids has remained tied to base stock costs. Lubricant companies are beginning to recognize that high-performance, high-image products based on PAO afford the opportunity for higher selling prices and increased margins. European companies have been the leader in this regard, but North American companies are expected to catch up. While Mobil Oil has been the leader in the United States with Mobil 1 since the mid-1970s, most of the major lubricant producers have introduced, or plan to introduce, full-synthetic motor oils to the market in 1990s. Another large factor in the forecasted growth for PAO is the recognition that there are insufficient high-quality base fluids to meet new product requirements. PAOs will be used to blend mineral oil stocks into specification. Some of these products will be sold and marketed as “part-synthetic” oils at a price between the top-tier mineral oils and the “fullsynthetics.” In other cases, the blender or formulator will use PAO in an “in again–out again” basis, depending on the availability of mineral oil base stocks of sufficiently high quality. In these cases, the consumers will never know that they have purchased a “part-synthetic.”

1.7.5 Consumer The role of the consumer will be important to the growth of PAO fluids. Manufacturer’s recommendations will have little effect if the consumer does not pay attention to them. Studies show that the traditional attitude in the United States has been that all oils are “pretty much the same,” but this attitude is beginning to change. Consumers are becoming more aware of fuel economy, cleaner air, higher performance, lower maintenance, and longer vehicle life. All of these concerns, coupled with the increased availability of oils to meet the demand, will lead to a shift by a

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segment of the consumer population toward the premium synthetic oils.

1.7.6 New Technology The final area that will provide an impetus to the increased use of PAO fluids will be the development of new technology. Two areas are clearly important. The first is the development of new additives and formulation packages specifically designed for use with PAO fluids. Formulation development is being actively pursued by PAO producers, additive manufacturers, formulators, lubrication specialty companies, and OEMs. Some of this work is in the form of joint efforts, and much of the information being developed is proprietary. The second important area to be impacted by new technology is the development of new PAO fluids from new starting materials and with new catalyst systems. The objective in this research is to produce products with particular characteristics needed for specialty applications. The use of alternative (other than 1-decene) olefin streams as the starting olefin for PAO manufacture offers the opportunity to “tailor-make” products for niche markets [19]. Table 1.30 gives an indication of what happens when different linear α-olefins are reacted in an identical way. As mentioned earlier, decene was chosen as the raw material of choice by all of the PAO producers because it gives products with the broadest temperature operating range. But for many applications, properties exhibited at one end of the temperature range may be more important than those at the other. For instance, a piece of industrial machinery that runs continuously at high temperature may have few, if any, low-temperature requirements but may require a very stringent volatility or flash-point specification. In such a case, a PAO based on 1-dodecene or 1-tetradecene may be more appropriate. Performance characteristics that can be enhanced by the appropriate choice of starting olefin and reaction conditions include volatility, pour point, VI, low-temperature viscosity, flash and fire points, thermal and oxidative stability, and biodegradability [115]. The development of new catalyst systems for the production of olefin oligomers having specific isomer distributions also holds the potential for the development of new PAO products with enhanced characteristics [116]. 1.7.6.1 Dodecene-based PAOs Initially dodecene-based PAOs were investigated due to a shortage in decene during the mid-1990s but have now found a home due to their unique combination of properties. PAOs based on 1-dodecene are now being manufactured by Chevron Phillips Chemical Company in the same way as 1-decene based PAOs [117]. The products are distilled to different viscosities since the oligomers are multiples of dodecene rather than decene and the KV at

TABLE 1.30 Physical Properties: Effect of Olefin Chain Length Carbon number of initial olefin Property KV at 100◦ C (cSt)

KV at 40◦ C (cSt) KV at −18◦ C (cSt) Viscosity index Pour point (◦ C) Flash point (◦ C) NOACKa (% loss)

Test method

8

10

12

ASTM D 445 ASTM D 445 ASTM D 445 ASTM D 2270 ASTM D 97 ASTM D 92 DIN 51581

2.77 11.2 195 82 <−65 190 55.7

4.10 18.7 409 121 <−65 228 11.5

5.70 27.8 703 152 −45 256 3.5

14 7.59 41.3 1150 154 −18 272 2.3

a Volatility at 250◦ C after 1 h. An alternative procedure is ASTM D 5800.

100◦ C is principally a function of the molecular weight. Decene-based PAOs are known by their nominal viscosities at 100◦ C being 2, 4, 6, 8, and 10 cSt for the lower viscosity materials whereas the dodecene-based PAOs are distilled to 2.5, 5, 7, and 9 cSt. Typically, the decenebased and dodecene-based products are distinguished by referring to the “even” numbered viscosities and the “odd” numbered viscosities, respectively. The Chevron Phillips materials are prepared by process parameter modifications as well as the use of the different feedstock, that is, there is no on-purpose mixed-feedstockbased material at CPChem. There have, however, been attempts to imitate purely dodecene-based PAO products by using a mixed feedstock approach. The typical properties of the dodecene-based PAOs have been reported [118]. There are several performance advantages with the dodecene-based PAOs, namely, volatility, flash and fire points, low-temperature viscosity and VI. The pour point tends to be about 10◦ C higher than a decene-based PAO that is equiviscous at 100◦ C. Typically, this is not a problem for most applications as the pour point for PAOs is already quite low. However, for areas that require extreme low-temperature properties, the decene-based PAOs are still products of choice. One interesting observation that can be gleaned from comparing decene- and dodecene-based PAOs is that with a dodecene-based PAO the volatility is lower than the next highest viscosity grade of a decene-based PAO. That is, the PAO 5 (dodecene-based) has a NOACK volatility that is lower than the decene-based PAO 6. The PAO 7 has a lower NOACK than the PAO 8 and so on. Another interesting feature is that there is an apparent cross-over point that is observed when comparing the scanning brookfield traces for equiviscous decene- and dodecene-based PAOs. That is, the dodecene-based PAO will have a lower viscosity as the temperature decreases but as the pour point is approached the viscosity will cross-over the trace from the decenebased PAO. This seems to be an intrinsic property that is

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evident by the higher VI but also the higher pour point of the dodecene-based PAOs. The higher flash and fire points offer good advantages in higher temperature applications and can contribute to enhanced safety features for finished fluids. PAOs are used to address specific deficiencies of other, lower priced fluids. The dodecene-based PAOs simply provide a wider array of tools available to today’s formulators to address more demanding needs and tighter industry specifications. A new class of PAO fluids has been reported. These materials, referred to as HVI-PAO, have high VIs and good pour points [119]. These materials derive their properties from being prepared using a chromium on silica catalyst system. 1.7.6.2 Mid-viscosity PAOs For many years PAOs have been classified into low-vis and high-vis grades. The low-vis (2 through 10 cSt) are used in a wide variety of lubricant as well as nonlubricant applications. High-vis PAOs (40 and 100 cSt) offer unique blending opportunities for gear oils, greases, engine oils, and industrial lubricants. Often, the high-vis PAOs are blended with low-viscosity PAOs to achieve the necessary viscosity and other required properties for a desired product. Chevron Phillips has developed a new process [120] that utilizes a proprietary catalyst that produces Synfluid MVP, a mid-viscosity PAO. This material is designed to have a 25 cSt PAO at 100◦ C. The typical properties are shown in Table 1.31. Applications for this material are aimed at gear oils, greases, and industrial fluids as well as fiber-optic gels.

ACKNOWLEDGMENTS The author would like to acknowledge Ron Shubkin for his original chapter on PAOs in the first edition of Synthetic Lubricants and High-Performance Functional

TABLE 1.31 Synfluid MVP — Highly Branched Isoparaffinic PAO — Typical Properties KV@100◦ C (cSt) KV@40◦ C (cSt) Viscosity index Pour Point, [◦ C (◦ F)] Flash point (COC) [◦ C (◦ F)] Fire point (COC) [◦ C (◦ F)] NOACK volatility (wt %) Specific gravity, 15.6◦ /15.6◦ C (60◦ F/60◦ F) Density (lb/gal) Bromine index Appearance Odor Color (Saybolt)

25 208 155 −45 (−49) 270 (518) 310 (590) 1.5 0.85 7.03 50 Clear and bright No foreign odor +30

Fluids (Marcel Dekker) from which this chapter has been expanded, updated, and revised. The author would like to thank Dr H. Ernest Henderson, Tom Glenn, and Dr Ken Hope for providing information for this chapter and for many helpful discussions.

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68. Goldman, C. E. (1976). A synthesized engine oil providing fuel economy benefits, SAE Paper No. 760854, in Proceedings of the SAE Off-Highway Meeting, Milwaukee, WI, September. 69. Krulish, J. A. C., H. V. Lowther, and B. J. Miller (1977) An update of synthesized engine oil technology, SAE Paper No. 770634, in Proceedings of the SAE Fuels and Lubricants Meeting, Tulsa, OK, June. 70. Barton, D. B., J. A. Murphy, and K. W. Gardner (1978). Synthetic lubricants provide exceptional extended drain passenger car Performance, SAE Paper No. 780951, in Proceedings of the International Fuels and Lubricants Meeting, Toronto, Canada, November. 71. Thom, R., K. Kollman, and M. Frend (1995). Extended oil drain intervals: conservation of resources or reduction of engine life, in Proceedings of the SAE International Congress, Detroit, MI, February 27–March 2. 72. Lube Tech Report, (1995) Fuels & Lubes Int., July, p. 11–13. 73. Shubkin, R. L. (1994). Polyalphaolefins: meeting the challenge for high-performance lubrication, Lubr. Eng., 50, 196–201. 74. Mazzo-Skalski, S. L., W. L. Maxwell, W. H. Richman, and I. R. Morris (1995). Advances in high performance synthetic oil technology, Society of Automotive Engineers, in Proceedings of the SAE International Congress and Exposition, Detroit, MI, February 27–March 2, Paper No. 951026. 75. Rudnick, L. R. and E. F. Zaweski, unpublished results. 76. Goyal, A. and R. W. Willyoung (1985). Engine oil filter performance with synthetic and mineral oils, SAE Paper No. 850549, in Proceedings of the International Congress and Exposition, Detroit, MI, February 25–March 1. 77. Fuels & Lubes International (1995). The next generation of high performance synthetic oils, July, p. 10. 78. Aho, E., A. J. Harlow, and J. R. Lohuis. Synthetic automotive lubricants for superior low-temperature operation, SAE Paper 890053. 79. Kennedy, S., M. A. Ragamo, J. R. Lohuis, and W. H. Richman (1995). A synthetic diesel engine oil with extended laboratory test and field service performance, in Proceedings of the SAE Fuels and Lubricants Meeting, Toronto, October 16–19, SAE Special Publication N. SP-1121 193–203, Paper No. 952553. 80. Lestz, S. J., E. C. Owens, and T. C. Bowen (1989). Army arctic engine oil performance in high ambient temperatures, International Fuels and Lubricants Meeting and Exposition, Baltimore, MD, September 25–28. 81. Srinivasan, S. D. W., Smith, and J. P. Sunne (1995). Synthetic automatic transmission fluids, in Proceedings of the 50th STLE Meeting, Cincinnati, OH, May 19. 82. Eaton Corporation Brochure. Synthetic lubricant benefits, drive axle lubrication requirements, transmission lubrication Requirements. TCMT, Publication No. 0019 R3, 1996. 83. Zaweski, E. F. and D. G. Campbell, Amoco unpublished results, 1996. 84. Coffin, P. S., C. M. Lindsay, A. J. Mills, H. Lindenkamp, and J. Fuhrman (1990). The application of synthetic fluids

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87. 88.

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2

Polyinternalolefins Francesca Navarrini, Massimo Ciali, and Roscoe Cooley CONTENTS 2.1 2.2

Introduction Manufacturing 2.2.1 Reaction Step 2.2.2 Neutralization Step 2.2.3 Hydrogenation Step 2.2.4 Distillation Step 2.2.5 Fractionation Step 2.3 Analysis and Characteristics 2.4 Applications 2.4.1 Automotive Engine Oils 2.4.1.1 Synthetic 10W-40s Constitute One of the Most Widespread Grades on the European Market 2.4.1.2 Rheological Studies were Performed 2.4.1.3 Assessment of Results with PIOs 2.4.1.4 Assessment of Results of Replacing 30% PAOs by PIOs 2.4.2 Industrial Oils 2.5 Summary Acknowledgment References

2.1 INTRODUCTION Synthetic hydrocarbons, esters, and hydroisomerized or hydrocracked base stocks, the latter commonly classified as chemical modified mineral oils (CMMOs), are widely used to formulate multigrade, low viscosity, top tier engine oils suitable for modern vehicles. Furthermore, they are increasingly used in the production of high quality industrial lubricants. AgipPetroli and EniChem Augusta have developed a new synthetic component, polyinternalolefin (PIO), with a proprietary process that uses n-olefins as feedstock. This new component is excellent base oil for the formulation of high performance engine and industrial lubricants. This chapter describes the manufacturing process, the physical and chemical properties, and the performance of PIO in semi or fully synthetic multigrade engine oils and At the time of the development of PIO, AgipPetroli and EniChem Augusta were both units of the ENI Group. EniChem Augusta was subsequently acquired by the RWE DEA Group under the name of Condea Augusta and then acquired again by the Sasol group. Now the company is known by the name Sasol Italy S.p.A.

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synthetic industrial oils. Comparison with polyalphaolefins (PAOs) is included. There are two main reasons for replacing conventional base stocks, in part or completely, with synthetics or with CMMOs: 1. These products lower volatility and improve rheological behavior, particularly at low temperatures. 2. They improve the performance of finished products by virtue of this superior thermo-oxidative behavior and lower tendency to form deposits [1]. Synthetics and CMMOs differ widely in properties, levels of performance, additive response, and, last but not least, cost; the problem associated with their use in lubricants is, therefore, the optimization of the cost/performance ratio. Oil manufacturers have developed and are using different solutions depending on the availability of components, type of lubricant, and market strategy; PIOs represent a potential alternative. PIOs were evaluated in comparison to PAOs because the latter are the best-known and most widely used

Reaction

Catalyst recovery

Washing

Cruden pio storage

Alumina treat

Hydrogenation

Distillation

Off-gag Catalyst R-Olefins

CO-Catalyst

Water KON

Hydrogen make-up Solution to treatment

Pio to storage Light components

FIGURE 2.1 Plant flow sheet for PIO production

hydrocarbon-type synthetic base stocks. Moreover, a large amount of data is already available from the development of commercially available additive technologies. Additional data must be accumulated before CMMOs can be properly compared with PAOs. We nevertheless point out that in the field of hydrocracked base stocks in particular, different levels in terms of price, physical and chemical characteristics, performance, and quality consistency have been reported.

2.2 MANUFACTURING Polyinternalolefins are long-chain hydrocarbons, typically a linear backbone with some branching randomly attached; they are obtained by oligomerization of internal n-olefins. The catalyst is a BF3 complex with a proton source that leads to a cationic polymerization [2]. These systems were chosen for the easy removal of BF3 from reaction and because the cycle time is shorter than those of other polymerization reactions (free radical, Ziegler type, etc.) [3–5]. The process consists of four steps: reaction, neutralization/washing, hydrogenation, and distillation, as illustrated in Figure 2.1.

2.2.2 Neutralization Step The reaction product is neutralized with an alkaline solution. Then the heavy phase containing boron and fluorine salts is removed and sent to waste treatment, while the light phase (crude PIO) is sent to storage for further processing.

2.2.3 Hydrogenation Step Before hydrogenation, the crude PIO is treated over alumina beds to remove all organic fluorine; this treatment is necessary both to avoid poisoning of the hydrogenation catalyst and to prevent possible stress corrosion in the hydrogenation unit.

2.2.4 Distillation Step The hydrogenated product is distilled to remove all short paraffins, isoparaffins (by-products of the reaction), and light ends. The bottom product (finished PIO) is sent to storage or to fractionation. Typical yield in PIO is more than 85% based on feedstock.

2.2.5 Fractionation Step 2.2.1 Reaction Step Internal olefins (C15 –C16 blend, at an 80/20 ratio) and catalyst (BF3 and proton source) are fed continuously in loop reactors; the reactors are under BF3 pressure control, and at the end of the reaction, BF3 is stripped and recycled. Structural details are based on unpublished data from mass spectroscopic studies: desorption chemical ionization, desorption electron impact, ‘H NMR, and ‘3 C NMR.

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During this step, by further distillation, the finished PIO having a viscosity of 6 cSt at 100◦ C can be split into 4 and 8 cSt cuts. The flow sheet of this step is reported in Figure 2.2

2.3 ANALYSIS AND CHARACTERISTICS Table 2.1 summarizes the main physicochemical characteristics of PIOs and PAOs. To ensure meaningful

Cooling water Cooling water V-104 sealing system vessel

E-103 1st Pio 4 condenser

E-104 2nd Pio 4 condenser

P.L.C.

V-101

C-101 Heater Rich gas

Vapor separator

E-101 LUWA Evapor.

T.I.C.

V-105

P-104 hot oil pump

E-105 heat recovery

Bearings lubricant vessel

V-103 L.I.C.

Pio-8 to storage

V-102

Pio-4 recovery vessel

L.I.C.

K-101 vaccum unit

F.I.C.

Heavy pio recovery

Pio-6 from storage

Pio-4 to storage

P-101 Pio-6 loading pump

P-102 Pio-8 pump

P-103 Pio-4 pump

FIGURE 2.2 Plant flow sheet for PIO fractionation

TABLE 2.1 Polyolefin Characteristics Viscosity cuts 4 cSt Characteristic

8 cSt

PAO

PIO

PAO

PIO

PAO

Composition HPLC composition (% mass) Dimers Trimers Tetramers Higher NMR CH/CH3 ratio

100 Traces — — 4.8

— 85 15 — 5.1

66 34 — — 4.9

— 30 47 23 5.5

40.5 59.5 — — 5.1

5 5 56 35 5.4

Physical chemical characteristics Viscosity at 100◦ C (cSt) Viscosity at 40◦ C (cSt) VI Viscosity at −25◦ C (cP) Viscosity at −30◦ C (cP) Pour point (◦ C) Flash point (◦ C) NOACK (% wt mass)

4.33 20.35 122 750 1150 −51 230 15.3

3.84 16.7 124 — 850 −64 229 15.2

5.66 30.4 131 1550 2500 −48 234 9.0

5.83 30.5 137 1500 2300 <−51 235 7.8

7.72 48.2 127 3300

7.71 45.8 137 2800

−45 254 5.6

<−51 260 4.1

comparisons, data were generated in the same laboratory. Evaluation of high pressure liquid chromatographic (HPLC) data on PIOs and PAOs reflects the differences in the feedstock used in their production: n-olefin C15 –C16 for PIO and a-C10 for PAO. The differences in the chain length

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6 cSt

PIO

and in the double-bond position influence the branching, as can be seen from the NMR data. Thermal and oxidative stability is an important property for all base oils. PIO-6 demonstrates excellent thermal and oxidative stability as demonstrated by the results of

TABLE 2.2 Thermo-Oxidative Performances and Deposit-Forming Tendencya Test description

Source

Evaluation conditions

IP 48 MOT/E

In-house test

Gives information about oxidative oil thickening. Oil containing metal catalyst is oxidized at high temperature under airflow

MCT

GFC L 27T94

Evaluates the deposit-forming tendency. A small oil sample is put on a hot aluminum plate with a temperature gradient for 90 min; a merit rating (10 = clean) is given Viscosity cut 6 cSt

Test results IP 48 MOT/E 170◦ C, 100 ppm Fe (48 h) Viscosity increase at 40◦ C % Total acid number (mg KOH/g) IR at 1720 cm−1 A/cm IR at 1630 cm−1 A/cm MCT: temperature gradient 230 to 280◦ C Zone A merit Zone B merit Merit average

PIO

PAO

157 7.2 185 20

153 7.5 186 18

7.6 9.0 8.3

7.7 8.8 8.3

a GFC, Groupement François de Coordination (French national body in TAN, total acid number;

IR, infrared absorption).

TABLE 2.3 Tribology Test

TABLE 2.4 Elastomers Compatibility (% weight change) 6 cSt base stock

Elastomer type

PIO

ACM, Polyacrylate Elastomer (at 150◦ C)

PAO

Four-ball EP test: ASTM D-2783 Seizure load (kg) Welding load (kg) Scar diameter (mm) Pure product +0.10% ZTDP

40 120

40 100

3.98 0.88

4.04 0.95

Four-ball wear test: ASTM D-4172 Wear scar diameter (mm)

0.66

1.18

the microcoking test (MCT) and IP48 modified oxidation test/Euron (MOT/E) as illustrated in Table 2.2. It is important to note that the results of the bench tests show PIO-6 is equivalent to PAO. Table 2.3 reports the tribological behavior as measured in standard rig tests of the American Society for Testing and Materials (ASTM): PIOs perform somewhat better in the wear test. Table 2.4 reports the compatibility with elastomers measuring the weight change after 70 h. Performances

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VMQ, methyl vinyl Silicone (at 150◦ C) NBR, Acrylonitrile-butadiene rubber (at 125◦ C) FKM, Hydrofluorocarbon Elastomer (at 75◦ C)

PIO

PAO

XHVI

−1.18 2.51 −2.80

−1.31 2.00 −3.02

−1.01 1.84 −2.72

0.04

0.09

0.11

are comparable with PAO and hydrotreated reference mineral oil. The relative stability of PIO has been measured in presence of water with the Beverage Bottle Method. This test method requires a fluid treatment with 25% of water and a copper specimen under pressure for 48 h in an oven at 93◦ C. Weight change of copper is then measured. Viscosity and acid number of the fluid and acidity of water are determined. In Table 2.5, results of PIO are reported and compared with PAOs and a hydrotreated mineral oil. PIO fluids have very low toxicity since they are pure hydrocarbons with a very low content of aromatics. PIOs have the Food and DrugsAdministration (FDA) approval

TABLE 2.5 Hydrolytic Stability ASTM D-2619 Acidity of oil, mgKOH/g Before test After test Acidity of water mg KOH Copper specimen: mass change (mg) Viscosity change of fluid (cSt) Sludge in tested oil (% mass)

PIO

PAO

XHVI

0.01 0.19 <0.01 −0.3 +0.43 <0.01

0.02 0.10 <0.01 −0.2 +0.05 <0.01

0.02 0.17 <0.01 −0.3 +1.68 <0.01

for the following sections and applications: Regulation number §175.105 §175.210 §176.180

Title Adhesives Acrylate ester copolymer coating Components of paper and paperboard in contact with dry food §176.200 Defoaming agents used in coating §176.210 Defoaming agents used in the manufacture of paper and paperboard §177.1390 High temperatures laminates §177.1400 Water insoluble hydroxyethyl cellulose film §177.2600 Rubber articles intended for repeated use §177.2800 Textiles and textile fibers §178.3570 Lubricants with accidental food contact §178.3620(b) Technical white mineral oil §178.3910 Surface lubricants used in the manufacture of metal articles §178.3910(a) Substances employed in the rolling of metal foil or sheet §178.3910(b) Substances may be used to facilitate the drawing, stamping, or forming of metal articles from rolled foil or sheet by further processing §179.45 Packaging material for use during the irradiation of pre-packaged food Furthermore, PIOs are National Science Foundation (NSF) certified. According to this certification, these products may be used on food processing equipment as a protective antirust film, as a release agent on gaskets or seals of tank closures, and as a lubricant where there is a potential exposure of the lubricated part to food.

2.4 APPLICATIONS 2.4.1 Automotive Engine Oils Engine oil formulation is the main field in which PIOs can find their preferred field of application. This is because

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synthetic base stocks or NCBOs are needed to meet the current, more stringent requirements for finished lubricants from original equipment manufacturers (OEMs) and from European automakers (ACEA: Association des Constructeurs Européens d’Automobiles). AgipPetroli has collected an extensive series of data in order to assess PIO performance in this respect. More data are expected to be collected from new formulations being developed. An evaluation project was conducted to compare the efficacy of PIO in four main areas: 1. To compare partial synthetic 10W-40 formulations employing PAOs versus the same formulations containing PIOs. 2. To compare fully synthetic formulations employing PAOs with the same formulations containing PIOs. 3. To assess the absolute performance of fully synthetic formulations employing PIOs. 4. To compare fully synthetic formulations employing PAOs with 30% PAOs replaced by PIOs. The rationale was to gain performance evidence, taking primarily into account the opportunities constraints set by the current Base Oil Interchange Guidelines (BOIG) of API Engine Oil Licensing and Certification System (EOLCS) and Association Technique de l’Industrie European des lubricants, European Engine lubricant Quality Monitoring System (ATIEL EELQMS). According to the latter, PIOs are to be classified as “Group III” base stock, whereas PAOs constitute a specific “Group IV” base stock. 2.4.1.1 Synthetic 10W-40s constitute one of the most widespread grades on the European market An extensive series of blending tests was performed, using additive technologies from different sources with top performance credentials. Some significant data are given in Table 2.6. Rheology and volatility are usually to meet the ACEA limits (with possibly a more severe limit of 12% wt loss for the NOACK volatility, as set by one OEM). Optimization calls for keeping the synthetic (or nonconventional) base oil and viscosity index improver (VII) content to a minimum to meet these targets. The actual amount of these ingredients varies according to additive technology and the mineral base stock adopted. Therefore, in principle, it is not possible to give absolute figures. Experience has shown, however, that differences appear in the results of blending studies performed at different locations. The mineral base stock used is a typical solvent refined SN 150. The packages selected are commercially available products (A and B with API SJ/CF, ACEA A3/B3 credentials, whereas

TABLE 2.6 10W-40 Part Synthetic Engine Oils Commercial Additive Technology Oil 1 PIO 4 cSt (% mass) PAO 4 cSt (% mass) PIO 6 cSt (% mass) PAO 6 cSt (% mass) Mineral base stock (% mass) Package code % mass VII (n/d OCP) (% mass) PPD (% mass) Viscosity at 100◦ C (cSt) Viscosity at 20◦ C (cP) Viscosity index NOACK (% mass)

14.0

Oil 4

Oil 5

Oil 6

14.0 12.0 23.0

62.9 A 13.0 9.7 0.4 13.94 3350 153 10.9

Oil A

Oil B

47.2 27 — 3 12.8 10 15.4 92.7 176 3150 −25 −45 4.1 7.9 1.2 10

47.2 — 27 3 12.8 10 15.3 94.2 172 3300 −25 −42 4.2 7.9 1.2 10

C is a diesel-oriented technology with ACEA B3/E2 performance). Oil 1 through 4 was intentionally adjusted to tight, borderline rheology to illustrate possible differences in impact of the two base stocks. To compensate for the small differences in terms of low temperature viscosity between PAO and PIO with the packages A and B, slightly higher amounts of PIO were needed. The engine performance aspect was investigated, too, despite the fact that the current practical approach toward formulation testing and qualification is based on qualification of a fully mineral “core technology.” Thus 10W-40, part synthetic formulations (or mineral + NCBO), can be derived without the need of further engine testing on

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Oil 3

12.0

TABLE 2.7 SH Test Program Formulations and Typical Inspections

150 Solvent neutral PAO 6 cSt PIO 6 cSt Ester Package VI improver Viscosity at 100◦ C (cSt) Viscosity at 40◦ C (cSt) VI Viscosity at 20◦ C (cP) Borderline pumping temperature (BPT) (◦ C) Pour point (◦ C) Viscosity at 150◦ C (cP at 106 s−1 ) Total base number (TBN) (mg KOH/g) Sulfated ash (% mass) NOACK volatility (% mass)

Oil 2

64.9 A 13.0 9.7 0.4 13.99 3350 156 11.2

62.9 B 13.0 9.7 0.4 13.98 3350 153 11.0

64.9 B 13.0 9.7 0.4 13.92 3350 152 11.2

54.4 C 13.0 9.2 0.4 14.08 3300 145 10.4

23.0 54.4 C 13.0 9.2 0.4 14.05 3300 147 9.8

TABLE 2.8 SH Test Program Engine Test Results Oil A

Oil B

SH limits

Sequence II-D Average (merit)

8.6

8.5

8.5

Sequence III-E Viscosity increase at 64 h (%) Cam and lifter wear average (µm) Oil consumption (l)

70 6.8 1.4

93 3.2 0.4

375 maxa 30 max 5.1 max

Sequence V-E Average engine sludge (merit) Average engine varnish (merit) Cam wear average (mils)

9.3 7.2 3

9.2 6.8 0.85

9.0 min 5.0 min 5.0 max

CRC L-38 Bearing weight loss (BWL) (mg)

21

11.6

40 max

VW GOLF TDI Piston cleanliness (merit)

71

73

71

a Previous limit; ACEA A3 current limit is 100 max.

the basis of the BOIG, still retaining all the original qualifications. A performance comparison between part synthetic formulations with PIOs and the same with PAOs (or with NCBOs) could be, therefore, regarded as virtually unnecessary from the point of view of qualifications-related matters, nevertheless it is still of concern and significant from a “technical” (not to say “academic”) point of view. Tables 2.7 and 2.8 report a complete SH program implemented with a VW GOLF TDI test, carried out to compare engine performance of PIOs and PAOs. The two formulations contain the same amount of hydrocarbontype synthetic base stock and a small amount of ester. Comparison of the engine test results indicates that PIOs

TABLE 2.9 Composition and Main Characteristics and Sequence V-E Test Results

TABLE 2.10 Composition and Main Characteristics Composition (% wt)

SAE 5W-40 oil

Composition and characteristics

Oil A

PAO 6 cSt PIO 6 cSt Ester Package VI improver (disp. PMA) Viscosity at 100◦ C (cSt) Viscosity at −25◦ C (cP)

67.7 15 12.7 4.6 11.84 3300

74.9 8 12.7 4.4 11.85 3300

PIO 4 cSt PIO 6 cSt Package VI improver (n/d OCP)

14 62 14 10

Sequence V-E test results

Oil A

Oil B

SH/ACEA limits

Average engine sludge (merit) Rocker arm cover sludge (merit) Piston skirt varnish (merit) Average engine varnish (merit) Oil ring clogging (%) Oil screen clogging (%) Stock compression rings Cam wear average (mils) Cam wear max (mils)

9.5 9.24 7.63 7.5 2 2 None 0.5 0.5

9.5 9.43 7.67 7.5 1.5 3 None 1.1a 0.5

9 min 7 min 6 min 5 min 15 max 20 max None 5 max 15 max

Oil B

Main characteristics

a Correction factor applied.

and PAOs, in a given additive system, provide similar performance. 2.4.1.2 Rheological studies were performed Table 2.9 reports significant results relative to SAE 5W-30 formulations. A sequence V-E test, a key test for API SH/SJ compliance, was then performed on each sample formulation. This “back-to-back” comparison produced the same “pass” results. It was then decided not to proceed further with engine test comparison. Indeed, according to the BOI and OEM guidelines, this would involve rerunning all engine tests. Rather, it was decided to devote effort to the development of a new formulation (PIO + fully original additive package), in accordance with point 3 listed in Section 2.4.1. 2.4.1.3 Assessment of results with PIOs The API SJ engine tests were successfully completed; Composition and main characteristics of the formulation are reported in Table 2.10, and Table 2.11 gives the API SJ test results. The formulation exhibits excellent thermal-oxidative stability in terms of Sequence III-E viscosity increase. To obtain further evaluation of the thermal stability properties of PIO-based formulations as well as a more complete comparison with PAOs, double-length III-E tests are scheduled.

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Kinematic viscosity at 100◦ C (cSt) Kinematic viscosity at 40◦ C (cSt) Viscosity index Cold cranking simulator (CCS) dynamic viscosity at −25◦ C (cP) Mini rotary viscometer (MRV) dynamic viscosity at −35 (cP) Pour point (◦ C) Viscosity at 150◦ C (cP) at 106 s−1 TBN mg KOH/g Sulfated ash (% mass) NOACK (% mass)

14.39 94.06 158 3,200 11,700 −45 4 11 1.3 8.8

ACEA E4 and DC 228.5 qualification tests were performed according to Mercedes Benz OM441LA engine performance level for heavy duty diesel. In Table 2.12 and Table 2.13, composition and results are reported. 2.4.1.4 Assessment of results of replacing 30% PAOs by PIOs The PIO evaluation program was implemented with a fully synthetic formulation obtained replacing 30% of PAO with PIO. According to BOIG, all the original qualifications API SH and ACEA A3/B3 were retained after a Sequence V-E test had been rerun. Composition and Sequence V-E test results are reported in Table 2.14 and Table 2.l5. Further to the tests already shown, results relative to 0W-30 formulations were obtained in order to get PIO interchange with PAO. In fact, according to the latest news from the market, we’ll face an increase in demand for PIO 4 cSt in the next few years. In particular, new 0W-30 formulation will be required by the OEMs. Table 2.16 and Table 2.17 report the formulations with characteristics and test results. For the same purpose VW TDI and Peugeot XUD11BTE tests were performed to provide a comparison with PAO and also as requirement of ACEA B4/B5 engine oil specifications. The results, as reported in Table 2.18 and Table 2.19, indicate that the PIO based formulations satisfy ACEA B4/B5 requirements. Thanks to the above results, ATIEL agreed to include PIOs in a new category Group VI Base Oil. The action by ATIEL allows interchangeability between Groups IV and VI without further testing.

TABLE 2.11 API SJ Tests Results Engine/bench tests results Sequence II-D Average rust (merit) Sequence III-E Viscosity increase at 64 h (%) Hours to 375% viscosity increase Cam and lifter wear average (µm) Oil consumption (l) Sequence V-E Average engine sludge (merit) Average engine varnish (merit) Cam wear average (mils) CRC L-38 BWL (mg) Stripped viscosity at 100◦ C (cSt) Foam tendency (ml) Stage I Stage II Stage III Stage IV Homogeneity/misc. Federal test method (FTM) 791C

SJ limits

8.6

8.5 (ACEA A3 limit: 100 max)

1 (one) 85.5 4.7 1.1

64 30 max 5.1 max

9.4 6.6 1.7

9.0 min 5.0 min 5.0 max

10.2 13.77

40 max 12.5 min

0/0 0/0 0/0 120/10

10/0 50/0 10/0 200/50

Pass

Pass

GM Filterability: GM 9099P Flow reduction (%)

−3

50 max

TEOST (mg)

27.8

60 max

TABLE 2.12 Composition and Main Characteristics Composition (% wt) PIO 4 cSt PIO 6 cSt Mineral oil Package

Kinematic viscosity at 100◦ C (cSt) Kinematic viscosity at 40◦ C (cSt) Viscosity index Cold cranking simulator (CCS) dynamic viscosity at −25◦ C (cP) Pour point (◦ C) Viscosity at 150◦ C (cP at 106 s−1 )

TABLE 2.13 OM 441 LA Test Results

SAE 5W-40 oil 21 19 30 30

Main characteristics

Piston cleanliness (merit) Engine cleanliness (merit) Bore polishing (average %) Boost pressure loss at 400 (h %) Oil consumption (g/h) Deposit rating

PIO based oil

ACEA E4 limits

40.1 9.7 1.2 −2.3 86.67 1.4

40.0 min 9.0 min 2.0 max 4.0 max 100 max 3.0 max

11.96 74.01 158 3280

Source: Data reported in the table have been recently produced by Sasol Italy S.p.A.

−39 3.52

2.4.2 Industrial Oils

Source: Data reported in the table have been recently produced by Sasol Italy S.p.A.

Copyright 2006 by Taylor & Francis Group, LLC

SAE 5W-40 oil

The field of industrial lubricants, where the final customer is seldom aware of the costs associated with quality, is more difficult to approach. Some preliminary data on flooded rotary compressor oil formulations are reported in Table 2.20, where PIOs are again compared to PAOs. Oxidation stability was determined with the rotating compressor oxidation test (ROCOT) and overall performance

TABLE 2.14 Composition and Main Characteristics

TABLE 2.17 0W-30 Tests Results

Formulation and typical figures

Oil A

Oil B

ACEA A1 Engine/bench tests results PIO based oil ACEA limits

PAO 6 cSt PIO 6 cSt Packagea VI improver (n/d OCP) Viscosity at 100◦ C (cSt) Viscosity at −25◦ C (cP) Viscosity at 150◦ C (cP at 106 s−1 ) NOACK (volatility % mass)

76.4

46.3 30.0 12.7 11.0 15.1 3310 4.0 8.0

MB MIIIFE test Fuel economy improvement (%)a

12.6 11.0 14.6 2980 3.9 8.7

a Final formulations for both oil A and B involve

package at 13.0 wt%.

TABLE 2.15 Sequence V-E Test Results Sequence V-E

Oil A

Oil B

SH/ACEA limits

Average engine sludge (merit) Rocker arm cover sludge (merit) Piston skirt varnish (merit) Average engine varnish (merit) Oil ring clogging (%) Oil screen clogging (%) Stuck compression rings Cam wear average (mils) Cam wear max (mils)

9.4 9.5 7.8 7 0 3 None 1.1a 0.5

9.41 9.07 6.65 6.04 1 0 None 0.67 2.4

9 min 7 min 6 min 5 min 15 max 20 max None 5 max 15 max

2.2 (failed)

2.5 min

9 14.7

9 min 25.2 max

4.3 1.7

10 max

MB MIIIE SL test Average engine sludge (merit) Cam wear average (µm)

9.2 2.3

8.4 min —

MB OM602A KOMBI Cam wear average (µm) Viscosity increase at 40◦ C (%) Bore polish (%) Piston cleanliness (merit) Average engine sludge (merit) Average cylinder wear (µm) Oil consumption (kg)

34.8 33 3.7 18.1 9.4 12.1 7.4

85.1 max 90 max 7.0 max — — 15 max 10 max

Sequence VG Average engine sludge (merit) Cam cover sludge (merit) Piston skirt varnish (merit) Average engine varnish (merit) Oil screen clogging (%)

9.4 9.1 8.2 9.5 0

7.8 min 8 min 7.5 min 8.9 min 20.0 max

PSA TU3 tests Ring sticking (each part) (merit) Absolute viscosity increase at 40◦ C (cSt) Cam wear average (µm) Oil consumption (kg)

a An adjustment on formulation was done in order to pass this test.

A result of 2.9% was obtained. Source: Data reported in the table have been recently produced by Sasol Italy S.p.A.

a Correction factor applied.

TABLE 2.16 Composition and Main Characteristics Formulation and typical figures

SAE 0W-30 oil

PIO 4 cSt PIO 6 cSt Package Viscosity at 100◦ C (cSt) Viscosity at 40◦ C (cSt) Viscosity at −30◦ C (cP) Viscosity at 150◦ C (cP at 106 s−1 ) NOACK (volatility % mass)

44.3 36.3 15.4 9.83 60.4 3200 3.03 11.2

Source: Data reported in the table have been recently produced by Sasol Italy S.p.A.

Copyright 2006 by Taylor & Francis Group, LLC

TABLE 2.18 Composition and Main Characteristics 0W-30 Formulation and typical figures

Oil A

Oil B

PIO 4 cSt PIO 6 cSt PAO 4 cSt PAO 6 cSt Package Viscosity at 100◦ C (cSt) Viscosity at −35◦ C (cP) Viscosity at 150◦ C (cP at 106 s−1 ) Sulfated ash (% mass)

60 4 — — 26 10.7 6115 3.32 1.27

— — 60 4 26 10.7 5553 3.5 1.29

Source: Data reported in the table have been recently produced by Sasol Italy S.p.A.

TABLE 2.19 0W-30 Tests Results ACEA B4/B5 Engine tests results XUD11-BTE Viscosity increase at 100◦ C and 3% shoot Piston cleanliness VW TDi Viscosity increase at 40◦ C Average Ring sticking Piston cleanliness

Oil A

Oil B

27.46 (RL197 = 60) 53.9 (RL197 = 53.6)

19.1 (RL197 = 60) 51 (RL197 = 48.9)

9.3 0 73 (RL206 = 67)

5.77 0 98 (RL206 = 67)

ACEA limits

0.5 × RL197 max RL197 max — 1.2 max B4: RL206-3pts min B5: RL206 max

Source: Data reported in the table have been recently produced by Sasol Italy S.p.A.

TABLE 2.20 Synthetic Compressor Oil ISO VO 46 Formulations

Oil 1

PIO 6 PAO 6 Ester Package rust and oxidation (R&O) + antiwear/extreme pressure Viscosity at 100◦ C (cSt) Viscosity at 40◦ C (cSt) VI Neutralization number (NN) (mg) KOH/g Conradson carbon residue (CCR) (% wt)

85.5

Oil 2

12.5

85.5 12.5

2 7.3 42.8 133 0.13 0.03

2 7.3 42.6 137 0.15 0.03

0.22 2.2

0.42 2.4

1.91 9.6

2.13 9.6

Test results ROCOT Evaporative loss (% wt) Viscosity increase at 40◦ C (%) DIN 51352 Part 2 CCR (% wt) Evaporative loss (% wt)

was determined according to a German standard (DIN 51352 part 2).

2.5 SUMMARY PIOs have been extensively tested in both fully and partially synthetic formulations. This assessment has shown that

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PIOs can be formulated into top performance lubricants. Compared to PAOs, PIOs offer similar performances in bench and engine tests using the same additive and VII components. The excellent results obtained in both semi-synthetic and synthetic oils, together with a large variety of available raw material make PIOs an interesting new high quality base stock for modern lubricant formulations.

ACKNOWLEDGMENT I gratefully acknowledge the contributions of many whose talents and dedicated efforts have made this and the earlier chapter possible. I would especially like to thank G. Corsico, L. Mattei, and A. Roselli, EURON, Milan, Italy, and Carlo Gommellini, AgipPetroli, Rome, Italy.

REFERENCES 1. Kivosky, T. E. et al., SAE Technical Paper 922348, Society of Automotive Engineers, Warrendale, PA, 1992. 2. Shubkin, R.L., Baylerian, M.S., and Maler A.R., Ind. Eng. Chem. Res. Dev., 19, 15 (1980). 3. Priola, A. and Cesca, S., Italian Patent 017872 (1974). 4. Priola, A., Como, C., and Cesca, S., Italian Patent 24289A75 (1975). 5. Priola, A., Como, C., and Cesca, S., Italian Patent 20106A80 (1980).

3

Esters Steven James Randles CONTENTS 3.1

Introduction 3.1.1 History 3.2 Chemistry 3.2.1 Product Structure 3.2.1.1 Monoesters 3.2.1.2 Diesters 3.2.1.3 Phthalates 3.2.1.4 C36 dimerates 3.2.1.5 Trimellitates/Pyromellitates 3.2.1.6 Polyol Esters 3.2.1.7 Other Esters 3.2.2 Manufacture of Ester Lubricants 3.3 Properties and Performance Characteristics 3.3.1 Chemical Properties 3.3.1.1 Thermal and Oxidative Stability 3.3.1.2 Hydrolytic Stability 3.3.1.3 Environmental Performance 3.3.2 Physical Properties 3.3.2.1 Viscosity 3.3.2.2 Flow Properties 3.3.2.3 Lubricity 3.3.2.4 Energy Efficiency 3.3.2.5 Solvency 3.3.3 Application Areas 3.3.3.1 Engine Oils 3.3.3.2 Automotive Gear Oils 3.3.3.3 Two-stroke Oils 3.3.3.4 Aviation Turbine Lubricants 3.3.3.5 Hydraulic Fluids 3.3.3.6 Air Compressor Lubricant 3.3.3.7 Refrigeration Lubricants 3.3.3.8 High Temperature Chain Oils 3.3.3.9 Metalworking Fluids 3.3.3.10 Greases 3.3.3.11 Drilling Mud Lubricants 3.3.3.12 Transformer Fluids/Capacitor Fluids 3.4 Manufacturers, Marketing, and Economics 3.4.1 Manufacturers 3.4.2 Markets 3.5 Outlook Acknowledgment References

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3.1 INTRODUCTION 3.1.1 History Prior to the early Nineteenth century, one of the main classes of lubricants in use were natural esters contained in animal fats such as sperm, oil lard oil or in vegetable oils such as rapeseed or castor oil. The earliest recorded use of animal fats is 1400 b.c. when they were used to lubricate chariot axles. Around 1937, Dr Zorn of I.G. Faben in Germany began intensive work on synthetic lubricants. During World War II a range of synthetic oils were developed for commercial production. The great difficulty encountered in Russia in starting trucks and tanks in the winter of 1941 to 42 due to the cold provided an impetus to the development of synthetic ester lubricant. Among these, esters of long chain alcohols and acids proved to be excellent as low temperature lubricants. The production of 200 bbl/day of adipic and methyl adipic acid esters was planned in Germany, but the rate attained did not exceed 100 bbl/day [1]. Another ester research development in Germany meriting notice was one by the Deutsche Fettsaure Werke in Whitten (Ruhr). This company, which worked with fatty acids and produced synthetic butter and other esters, studied the use of esters as lubricants. They concluded that an ester of pentaerythritol and C6 to C10 fatty acids was well suited for such an application [1]. Following World War II, the further development of esters was closely linked to that of the aviation gas turbine. The U.S. military began the use of synthetic gas turbine lubricants in the 1950s following the publication of MIL-L-7808 specification for dibasic acid esters. In the early 1960s, neopentyl polyol esters were used in this application because of their low volatilities, high flashpoints, and good thermal stabilities. Esters are now used in many applications including automotive and marine engine oils, compressor oils, hydraulic fluids, gear oils, and grease formulations. The low toxicity and excellent biodegradability of ester molecules now afford added benefits to those of performance.

3.2 CHEMISTRY 3.2.1 Product Structure The polarity of the ester molecules causes them to be attracted to one another and other polar species. This has a direct impact on several performance criteria: • Low vapor pressures, low volatilities, and high flash-

points: The strong dipole moments of ester molecules causes them to be attracted to each other. Greater energy is therefore required to overcome these forces and transfer a lubricant molecule from the vapor liquid to the

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• • •

• •

gaseous state. Esters are therefore excellent vacuum pump lubricants. High solvency: High polarity makes esters excellent solvents. Hygroscopic: Water molecules are attracted to the polar ester bond. Lubricity: Esters’ high polarity attracts them to metal oxide layers making them good boundary lubricants and friction modifiers. Thermal stability: The ester linkage has excellent thermal stability. Hydrolytic stability: The reverse reaction of esterification is hydrolysis.

These properties are discussed at length later in the chapter. There are three main types of esters: • Acid/anhydride centered for example,

monoesters, diesters, phthalates, dimerates, and trimellitates • Alcohol centered for example, polyols • Polymeric esters for example, Polyalkyleneglycol (PAG) esters, complex esters, etc. Their physical properties are compared in Table 3.1. 3.2.1.1 Monoesters Monoesters are made by reacting a monofunctional acid (e.g., oleic, isostearic) with a monofunctional alcohol (usually between carbon chain C1 and C22 in length). Monoesters are characterized by their relatively low viscosity and high Viscosity indices (VIs). Examples of commercially available mono-oleate esters with their physical properties are given in Table 3.2. They are typically used in metalworking applications. Partial esters are also commonly used for example, Glycerol Mono-oleates (GMO) in applications such as friction modifiers. 3.2.1.2 Diesters Reacting a linear diacid with a linear, but more usually a branched, monofunctional alcohol makes a diester (Figure 3.1). Diesters have very good VIs and pour points. The reason for this is their “dumb-bell” configuration. The linear diacid portion of the diester contributes to the good VI, while the branched alcohol ends give the lubricant a good pour point. As the branched alcohols are at the end of a linear acid, the free rotation around the ester linkage is still good. This gives an excellent trade-off between VI and pour point. One disadvantage of diesters is their low molecular weight. This results in a limited ISO range (7 to 46) coverage. Examples of commercially available diesters are given in Table 3.3. Their small size combined with their high polarities makes them effective solvents. Diesters are often blended

TABLE 3.1 Typical Physical Properties of a Range of Ester Types Viscosity at 40◦ C (cSt)

Viscosity at 100◦ C (cSt) Viscosity index Pour point (◦ C) Flashpoint (◦ C) Oxidative stability Biodegradability

Monoester

Diesters

Phthalates

Trimellitates

Dimerates

Polyols

Complex polyols

4 to 30 1 to 6 150 to 230 −35 to +25 180 to 220 Fair Excellent

6 to 46 2 to 8 0 to 90 −70 to −40 200 to 260 Good Good

19 to 100 3 to 9 75 to 130 −50 to −30 200 to 270 Very good Fair

46 to 320 7 to 20 120 to 150 −55 to −25 270 to 300 Very good Poor

90 to 184 12 to 20 50 to 140 −50 to −5 240 to 310 Good Fair

7 to 320 2 to 30 40 to 170 −60 to +7 250 to 320 Excellent Excellent

32 to >10,000 7 130 to 230 −60 to −20 240 to 280 Fair Excellent

TABLE 3.2 Typical Physical Properties of Mono-Oleates Alcohol Methyl Iso-propyl Iso-butyl 2-Ethyl hexyl Iso-octyl Decyl Glycerol mono-oleate

Diesters

O C R

(CH2)n

O C

O

O

Viscosity at 40◦ C (cSt)

Viscosity at 100◦ C (cSt)

Viscosity index

4.5 5.3 6.0 8.0 9.1 10.2 100

1.8 2.0 2.2 2.8 2.9 3.4 10.4

— 221 219 238 192 246 83

n = 4 — Adipates n = 7 — Azelates n = 8 — Sebacates R n = 10 — Dodecanedioates

R = C7 to C18 linear or branched alkyl groups

FIGURE 3.1 Chemical structure of diesters

with poly alpha olefins (PAOs) to help additive solubility and to act as seal-swelling agents. Applications include: gear oils, engine oils, compressors oils, grease, metalworking, and biodegradable hydraulic fluids. Phthalates and dimerates are specific subgroups of diesters and are covered in separate sections. 3.2.1.3 Phthalates Phthalate esters are made by reacting phthalic anhydride with a monofunctional alcohol (Figure 3.2). Phthalates are a specific subgroup of diesters. Examples of commercially available phthalates and their physical properties are given in Table 3.4. Phthalic anhydride is used instead of phthalic acid for cost/availability reasons. Phthalate esters are one of the most cost-effective esters and as such they are often used in industrial applications, such as air compressors, to replace mineral oil. They may have either low pour points or good VIs but not both. The reason for this is the bulky “basket ball-like” shape to the molecule. In terms

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Pour point (◦ C) −12 −21 −50 −35 −29 −3 0

of viscosities they are available in the viscosity range of ISO 22 to 100. Applications include grease, compressor oils, and metalworking applications. 3.2.1.4 C36 dimerates Dimerates are made by reacting a C36 dimer acid and a monofunctional alcohol. The alcohol most widely used is 2-ethyl hexanol, making an ester that is usually referred to as 3608. It has the advantage of being an excellent lubricant and has good thermal and oxidative stability. In addition its stability can be further improved by hydrogenation of the double bonds. Because of the poor biodegradability of dimerates their use in marine two-stroke engines is decreasing and they are being replaced by polyol esters. Examples of commercially available dimerates and their physical properties are given in Table 3.5. Applications include chain oils and 2T and 4T oils. Higher viscosity can be made using dimer acids with higher trimer (C54) contents. The use of higher polymers, the so-called polymerized fatty acids (POFAs) can produce esters with very high viscosities (1000s of cSts at 40◦ C). 3.2.1.5 Trimellitates/pyromellitates Trimellitates are made by reacting trimellitic anhydride with a monofunctional alcohol (Figure 3.3). Reacting either pyromellitic anhydride or pyromelltic acid with

TABLE 3.3 Typical Physical Properties of Diesters

2-Ethyl hexyl Adipate Azelate Sebacate Dodecanedioate Iso-decyl Adipate Azelate Sebacate Dodecanedioate Iso-tridecyl Adipate Azelate Sebacate Dodecanedioate

Viscosity at 40◦ C (cSt)

Viscosity at 100◦ C (cSt)

Viscosity index

Pour point (◦ C)

Noak at 250◦ C/1 h (% loss)

CEC-L-33-A-93 % biodegradability

8.0 10.7 11.8 14.3

2.4 3.0 3.1 3.8

124 137 126 168

−68 −64 −60 −57

44.3 29.0 18.3 —

97 99 96 —

15.2 18.1 20.2 23.4

3.6 4.3 4.8 5.2

121 151 169 162

−62 −65 −60 −41

15.5 9.8 6.2 4.3

84 86 100 93

27.0 33.8 36.7 40.7

5.4 6.4 6.7 7.6

139 143 141 156

−51 −55 −52 −50

4.8 4.1 3.7 2.9

92 85 80 76

O C OR C

OR

O R = C7 to C18 linear or branched alkyl groups

FIGURE 3.2 Chemical structure of phthalates

a monofuctional alcohol makes pyromellitates. Examples of commercially available trimellitates and pyromellitates along with their physical properties are given in Table 3.6. Trimellitates are often used instead of phthalates if either enhanced performance (thermal, elastomer compatibility, and lubricity) or if higher viscosity is required. They are available in a wide range of viscosities (ISO 46 to 320). In terms of structure they are quite bulky and, like phthalates, have poor VI/pour point trade-offs. Trimellitates are very good lubricants and because of their high molecular weights have high flashpoints and low volatilities. Pyromellitates have excellent thermal and elastomeric compatibility properties. Unfortunately, due to the cost and poor availability of the raw materials pyromellitates tend to be very expensive. Trimellitates tend to be used in lubricants applications such as high-temperature chain oils, greases, and compressor oils. Pyromellitates tend to be used in high-temperature greases. 3.2.1.6 Polyol esters Polyols are made by reacting a multifunctional alcohol with a monofunctional acid (Figure 3.4).

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Examples of commercially available polyols and their physical properties are given in Table 3.7. They are available in a large range of viscosities (ISO 5 to 320). Neopentyl glycol and pentaerythritol esters are sometimes known as neopentyl polyols as their structures are based on the hydrocarbon neopentane. Polyols are also collectively referred to as “hindered esters” as they have no beta-hydrogens and are therefore beta-hindered. This is discussed further in Section 3.3.1.1. Polyols tend to have the same advantages and disadvantages as diesters. They are, however, more hydrolytically and thermally stable than diesters. A rule of thumb is that a polyol is 30 to 50◦ C more thermally stable than a diester of equivalent viscosity. Because of these performance advantages, sales of polyol esters are expected to grow at a faster rate than diesters. Polyols, however, tend to be more expensive than diesters. Polyol esters are used in a wide variety of applications, namely: refrigeration compressors, aviation, greases, air compressors, metalworking, fire resistant and biodegradable hydraulic fluids, and chain oils. 3.2.1.7 Other esters There are numerous other types of esters, namely: • Complex polyols are low molecular weight poly-

mers made from a polyalcohol (e.g., neopentylglycol, trimethyolpropane, or pentaerythritol), a diacid and end-capped with either an acid or an alcohol • PAG esters made from the reaction of a PAG hydroxyl group with an acid • Other polymeric esters (discussed in a separate chapter)

TABLE 3.4 Typical Properties of a Range of Phthalate Esters

Alcohol

Viscosity at 40◦ C (cSt)

Viscosity at 100◦ C (cSt)

Viscosity index

Pour point (◦ C)

Noak at 250◦ C/1 h (% loss)

19.0 28.8 26.4 38.5 45.5 80.5

2.8 4.5 4.2 5.3 5.8 8.2

— 39 21 50 49 56

−51 −42 −43 −44 −47 −43

21.1 17.5 19.0 11.7 9.2 2.6

Iso-heptyl Iso-octyl 2-Ethyl hexyl Iso-nonyl Iso-decyl Iso-tridecyl

CEC-L-33-A-93 % biodegradability 92 69 64 53 69 46

TABLE 3.5 Typical Physical Properties of Dimerate Esters

Alcohol 2-Ethyl hexyl 2-Ethyl hexyl (C36 hydrogenated) C9/C11 Iso-tridecyl

O C

Trimellitate

Viscosity index

Pour point (◦ C)

Noak at 250◦ C/1 h (% loss)

91.1 92.0

12.7 12.7

136 135

−50 −41

0.8 0.2

49 24

94.9 140.0

14.0 17.0

151 132

−15 −27

1.1 0.6

78 30

Pyromellitate

C

C OR C

Viscosity at 100◦ C (cSt)

O

O

RO

Viscosity at 40◦ C (cSt)

OR

C OR

RO RO

C

C

O O R = C7 to C18 linear or branched alkyl groups

FIGURE 3.3 Chemical pyromellitates

structure

O

of

OR

O

trimellitates

and

• Carbonate esters (discussed in a separate chapter) • Phosphate esters (discussed in a separate chapter) • Citrate esters

Complex polyols have great flexibility. Viscosity can be controlled by the degree of polymerization. Complex esters have the advantages of high biodegradabilities even at high viscosities. This makes them ideal bright stocks for two-stroke applications. Unfortunately, due to the high number of ester linkages they have a high polarity. If not properly optimized, this may cause problems with antiwear additives (see Section 3.3.3.2). The PAG esters have the advantage of high VIs and tend to be good lubricants. They do suffer from a similar

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CEC-L-33-A-93 % biodegradability

disadvantage as the complex polyol do in that being very polar they can have compatibility problems with antiwear additives. Highly ethoxylated PAG esters can be made to be water soluble and as such find application in metalworking fluids and fire-resistant hydraulic fluids. The PAG esters tend to be very hygroscopic and can suffer from poor hydrolytic stability. Polymeric esters can also be used to build a molecule to give a range of functionalities that can be optimized to deliver specific effects. Figure 3.5 shows a schematic of polymeric ester, which has three different functionalities built into it. By combining a polymeric alkyl chain, a carboxylic acid group, and an ethoxylate (EO) group in the same molecule a lubricant can be designed that simultaneously gives emulsification and lubricity properties [2]. The fact that the anionic emulsifier (carboxylic acid) is built into the molecular backbone means that the system does not suffer from anionic depletion. With conventional fluids, anionic depletion is likely to lead to emulsion instability and poor corrosion control. Further optimization of this design concept allows other features, such as low foam and hard- and soft-water stability to be built into the molecule. A range of other additive functionalities can also be built into the polymer backbone. Citrate esters are used as functional fluids for indirect/ direct food use applications.

TABLE 3.6 Typical Physical Properties of Trimellitate and Pyromellitate Esters Viscosity at 40◦ C (cSt)

Viscosity at 100◦ C (cSt)

Viscosity index

Pour point (◦ C)

Noak at 250◦ C/1 h (% loss)

Trimellitic anhydride + alcohol 7/9 8/10 9/11 2-Ethyl hexyl Iso-decyl Iso-tridecyl

48.8 51.9 72.5 90.2 144.2 305.2

7.3 8.1 9.8 9.7 13.0 20.4

108 126 116 82 79 76

−45 −45 −45 −36 −30 −9

0.9 0.4 1.7 1.6 1.0 1.6

69 61 3 14 0 9

Pyromellitic anhydride + alcohol 2-Ethyl hexyl

172.0

16.3

98

−27

0.4

3

CEC-L-33-A-93 % biodegradability

3.2.2 Manufacture of Ester Lubricants The reaction, acid + alcohol = ester + water, is the basis for the production of esters. The manufacturing process of esters consists of three distinct stages, namely:

Neopentlyglycol ester

O CH3

C CH2

C

• Esterification • Neutralization • Filtration

R

O

CH3 2

Trimethyolpropane ester

O C CH2

CH3

CH2

C

R

O

3

Pentaerythritol ester

O C CH2

C

R

O

4

Dipentaerythritol ester

O C

O

CH2

O

C

CH2

O

CH2

O

CH2

O

R C O

R

C R 2

R = A range of C5 to C18 linear or branched alkyl groups

FIGURE 3.4 Chemical structure of polyol esters

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For diesters, by using 5 to 10% alcohol in excess and by removing the water of reaction, the reaction can be driven to a high level of completion. This usually takes several hours, with the reaction being monitored by taking samples periodically for acid number determination. The use of an azeotroping agent such as xylene or toluene (to aid water removal) is optional. The acid and alcohol can be allowed to react directly or in the presence of a catalyst. Possible catalysts include: sulfuric acid, para-toluene sulfonic acid, tetra alkyl titanate, phosphorous oxides, and tin octanoate/oxides. After the ester has been formed, unreacted acid is neutralized using sodium carbonate or calcium hydroxide and is removed by filtration. Typical reaction conditions for titanium catalysts are 230◦ C in vacuum; acid catalysts require milder conditions since side reactions (e.g., color formation) become prominent at higher temperatures. Activated charcoal can be added to the reaction to improve the color of the ester. A significant amount of alcohol vaporizes along with the water and must be recovered. Condensing the reactor vapors and decanting the resulting two-phase liquid mixture accomplishes this. The alcohol is then refluxed and returned to the reactor. Polyol esters are made by reacting a polyhydric alcohol, such as neopentylglycol (NPG), trimethyolpropane (TMP), pentaerythritol (PE), or dipentaerythritol (diPE), with a monobasic acid to give a desired ester. A 5 to 10% acid

TABLE 3.7 Typical Physical Properties of Polyol Esters Viscosity at 40◦ C (cSt)

Viscosity at 100◦ C (cSt)

Viscosity index

Pour point (◦ C)

Noak at 250◦ C/1 h (% loss)

CEC-L-33-A-93 % biodegradability

NPG nC7 nC9 nC8/nC10 Oleic 2-Ethyl hexanoic 3,5,5-TMH

5.6 8.6 8.4 30.0 7.6 12.8

1.9 2.6 2.5 7.0 2.4 3.1

— 145 129 207 148 100

−64 −55 −33 −24 −54 −45

— 31.2 32.4 1.2 — —

100 97 100 100 — —

TMP nC7 nC9 nC8/nC10 Oleic 2-Ethyl hexanoic 3,5,5-TMH

13.9 21.0 20.4 46.8 24.8 51.7

3.4 4.6 4.5 9.4 4.4 7.2

120 139 137 190 75 98

−60 −51 −43 −39 −50 −32

11.8 2.3 2.9 — — 6.7

100 100 96 100 — 7

PE nC7 nC9 nC8/nC10 Oleic 2-Ethyl hexanoic 3,5,5-TMH

22.2 32.2 30.0 64.0 44.8 129.2

4.9 6.1 5.9 10.0 6.4 11.6

151 140 145 141 88 70

−40 −7 −4 −21 +8 +30

— 0.9 0.9 1.0 — —

100 100 100 98 — 8

Alcohol–acid

TMH = Trimethyl hexanoic = iso-C9.

Nonionic emulsifier EO COO-C8H17 Lubricity

COOH Anionic emulsifier

FIGURE 3.5 Idealized schematic of a multifunctional polymeric ester

is used in excess and the water removed as it forms. The acids are more volatile than the polyalcohols and can be recovered by distillation, carried out in vacuum. Residual acids are then neutralized with an alkaline compound (e.g., calcium or sodium hydroxide). Polyol esters can also be made via a transesterification (alcoholysis) route. Here, monoesters (usually methyl) are transesterified with a neopentyl alcohol in the presence of a catalyst. Catalysts that have been specifically designed to help the transesterification process are now available (e.g., anhydrous sodium sulfate).

Copyright 2006 by Taylor & Francis Group, LLC

Individual esters can be blended together to achieve a specific viscosity or other target. However, such blends can result in a meta-stable blend that can undergo further equilibration via transesterification at the elevated temperatures encountered in actual use. Variations in raw materials can have a major influence on the final physical properties of the ester. For example, the monofunctional alcohols used to make monoesters, diesters, phthalates, trimellitates, and pyromellitates are often mixtures of varying chain lengths and degrees of branching of isomers. Examples of this are: • Iso-tridecanol, which is a mixture of branched carbon

chain lengths in the range C11 to C14, rich in C13 alkyl chains. • Iso-decanol, which is a mixture of branched carbon chain lengths C9 to C11, rich in C10 alkyl chains. The degree of branching, chain length, and ratio of isomers is highly dependent on the feedstock and catalyst used to make the alcohol. The same alcohol purchased from different companies or from the same company made at different plants can be significantly different. Therefore, the typical properties of a given ester can vary from supplier to supplier. This can be seen in Table 3.8, which compares

TABLE 3.8 The Change in Physical Properties of a Trimellitate using Different Sources of Iso-Tridecanol Alcohol source Source 1 Source 2 Source 3 Source 4

Pour Viscosity at Viscosity at Viscosity Flashpoint point index (◦ C) (◦ C) 40◦ C (cSt) 100◦ C (cSt) 315 189 366 320

19.9 16.7 21.6 20.8

67 93 65 73

298 268 296 234

−7 −17 −23 −7

nominally the same ester trimellitate made from tridecanol but sourced from several different suppliers. A trimellitate was chosen, as it would differentiate the most between the different tridecanol sources. Marked differences between the esters from different sources can be seen. Variations also occur with naturally derived acids (e.g., C8/C10 acid is in fact a mixture of C6, C8, C10, and C12). The degree of unsaturation (iodine number) should also be checked. Even if exactly the same raw materials are used, the processing specification can have a major impact on the physical properties and hence the performance of the ester. The following properties of the ester should be tightly controlled: • • • • • •

Residual unreacted acid Hydroxyl number (degree of esterification) Residual unreacted alcohol Cross contamination from other esters made on plant Residual catalyst Residual neutralizing agents

Guidelines for the recommended levels of these ester properties are discussed in Table 3.9. It should be remembered that these are general guidelines and will need to be adjusted depending on the use.

3.3 PROPERTIES AND PERFORMANCE CHARACTERISTICS 3.3.1 Chemical Properties Mineral oil basestocks are derived from crude oil and consist of complex mixtures of naturally occurring hydrocarbons. Synthetic ester lubricants, on the other hand, are prepared from man-made raw materials having uniform molecular structures. This uniformity yields well-defined properties that can be tailored for specific applications. 3.3.1.1 Thermal and oxidative stability The ester linkage is an exceptionally stable one. Bond energy determinations predict that the ester linkage is more thermally stable than the C–C bond.

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TABLE 3.9 The Effect of Ester Specification on the Performance of an Ester Lubricant Property

Affects

Typical value

Total acid number

Hydrolytic stability Thermal stability Wear

<0.1 mg KOH/g

Hydroxyl number

Hydrolytic stability Deposit formation Volatility Foaming Flashpoint Viscosity Thermal stability Color stability Deposit formation Low temperature Flow Hydrolytic stability Thermal stability Deposit formation Hydrolytic stability Foaming All of the above

<4 mg KOH/g

Iodine number

Water content Process residuals (e.g., catalysts, neutralizing agents, azeotropes, etc.) Purity

As low as possible

<0.1% w/w <5 ppm metals

Oxidation tests sometimes reveal that pure esters have an oxidative stability similar or slightly worse than that of mineral oil. The reason for this is that mineral oil contains impurities that can act as antioxidants. Esters display their superior performance when formulated with antioxidants. Primarily, the oxidative and thermal stability of ester lubricants are dependent on the: • Presence of hydrogens on beta-carbons (avoided by use

of polyol esters). • Number and type of hydrogens present. In decreasing

order of stability –CH3 > –CH2 – > –CH–. Generally, therefore; • Linear acid esters are more stable than branched • Short-chain acidesters are more stable than long.

• Stability of the alcohol used for polyol esters. In decreas-

ing order of stability, PE > DiPE > TMP > NPG.

• Degree of aromaticity. • Degree of (un)saturation. • Type and dose rate of additives.

The advantages in thermal stability of polyol esters over diesters are well documented and have been investigated on a number of occasions [3–7]. It has been found that the absence of hydrogen atoms on the beta-carbon atom of the alcohol portion of the ester leads to superior thermal stabilities. The presence of such hydrogen atoms

H H

H

C C

H H

O

=

R H R H

R H R-C–C

R1

O

C

+

R

C

O

H

O

R H

H

=

H

. + .O - C - R .

HO C

H

(b)

R - C - C - O - C - R1

R

O=

C

=

R

R 1

H

O

=

O

R - C - C - O - C - R1

=

H H

=

(a)

C = C + HO - C - R1 R

R

FIGURE 3.6 Thermal decomposition mechanism of esters: (a) Ester with beta-hydrogens (e.g., diesters); (b) Esters without betahydrogens (e.g., polyols)

enables a more favorable decomposition mechanism to operate via a six-membered cyclic intermediate producing acids and alkenes, (Figure 3.6[a]). When beta-hydrogen atoms are replaced by alkyl groups this mechanism cannot operate and decomposition occurs via a less favorable free-radical pathway. This type of decomposition requires more energy and can only occur at higher temperatures, (see Figure 3.6[b]). Typical initial thermal degradation temperatures have been quoted for diesters as 275◦ C and for polyol esters as 315◦ C [5,7]. The presence of certain metals can reduce these stabilities by at least 50◦ C. For example, a significant reaction has been found with polyol esters with both cast iron and carbon valve steel at temperatures in excess of 200◦ C [8] (392◦ F). This reaction leads to a major increase in acid value of the oil and weight loss of the steel. The use of phosphate additives, which act to passivate iron surfaces, were found to markedly reduce the severity of this reaction. Pentaerythritol based polyols tend to be more thermally stable than polyols based on TMP, which in turn are more stable than those based on NPG. The number and type of hydrogen bonds has been shown to have a major effect on the oxidative stability of esters. The general rule is that the ease of oxidation of carbon–hydrogen bonds follows the order: primary (–CH3 ) > secondary (–CH2 –) > tertiary (–CH–) where primary are the most stable. Studies have shown that normal secondary hydrogens can be fifteen times less stable than primary hydrogens [9]. Tertiary hydrogens occur at positions of branching on the alkyl chains. Therefore, as a general rule, linear alkyl esters tend to be more thermally stable than branched. However, if the less stable tertiary hydrogens can be sterically hindered by adjoining methyl or ethyl groups, significant improvements in stability can be obtained [5,10]. Esters derived from geminal dimethyl acids are the most robust of the branched species, as they are incapable of supporting the beta-hydrogen elimination degradation pathway. The olefinic (C=C) bond in the oleate chain of polyoleates makes such molecules less stable to oxidation, especially at high temperatures. In several applications there is evidence of a direct link between the iodine number

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of the ester and sludge formation. Unfortunately, long chain molecules need to have some unsaturation for low temperature fluidity. It is important that the degree of unsaturation is minimized this is especially true for in conjugated double bonds. Aromatic molecules are very stable against oxidation. This stability is due to an energetically favorable atomic arrangement and a unique bonding system that make them slow to break apart and participate in free-radical reactions. When aromatic molecules do break down they often form soft carbonaceous deposits that can actually aid in lubricity. Various additives can be used to improve the oxidative stability of ester lubricants, namely: • Antioxidants for example, phenolics and aminics that act

as free radical scavengers • Antiwear additives for example, phosphites can act

as hydroperoxide scavengers and phosphates as metal passivators • Metal passivators for example, phosphates • Metal deactivators for example, thiadiazoles Mixtures of antioxidants, antiwear, and metal deactivators have been found to be synergistic. Additives, however, can markedly reduce the stability of an ester as well. Examples are: • Acidic additives (high acidity tends to catalyze ester

decomposition) • Anticorrosion additives • Antiwear additives • Metal deactivators (at temperatures above 130◦ C certain

metal deactivators will form decomposition products that will destabilize the ester) The deposit forming tendencies of lubricants are dependent on the following factors: • Oxidative stability of the lubricant • Polarity of the ester (which effects detergency and

dispersancy)

TABLE 3.10 Panel Coker Results on a Variety of Lubricants Addivated with 1% Aminic Antioxidant (275◦ C for 22 h in air) Lubricant Mineral oil PAO 6 Standard diester Standard phthalate Standard trimellitate Optimized trimellitate Standard TMP polyol ester Optimized TMP polyol ester

Visual demerit rating 3.95 >4.00 2.50 1.07 0.50 0.04 0.57 0.18

Visual rating system: >2.0 Thick carbonaceous deposits. 2.0 to 0.5 Low levels of deposits. <0.5 Virtually no deposits.

• Process residuals • Additives

The presence of air and metals can have a major effect on the deposit forming properties of esters [11]. The deposit forming tendencies of lubricants can be evaluated by the Panel Coker test. Here, where one litre of lubricant is dropped dripped continuously onto a steel plate at 275◦ C for 22 hrs in air. The lubricant is collected at the bottom of the plate and recirculated for repeated application on the steel plate. At the end of the test the deposits are visually analyzed and given a demerit rating. Several lubricants addivated with 1% aminic antioxidant have been evaluated (Table 3.10). The results clearly show the effects described earlier. Aromatic phthalates give superior results to diesters and polyol esters give superior performance to diesters, phthalates, and trimellitates. The ester can be further optimized by structural and process modifications to give outstanding performance. The effect of process residuals (catalysts, neutralizing agents, etc.) can be seen in Table 3.11. It is clear that even small levels of certain contaminants can make a huge difference to the deposit-forming tendency of an ester. This re-emphasizes the need for a tight specification. Lubricant oxidation reactions resulting in sludge formation can be catalyzed by metal surfaces. The role of metal catalysis in ester oxidation is twofold: it promotes the degradation of ester molecules by accelerating hydroperoxide decomposition and it affects condenstation of oxidation products to form sludge and varnish. The rate of catalytic activity on oxidation rate in decreasig order of activity was found to be: low-carbon steel > stainless steel > lead > aluminium > brass > copper. The rate of

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TABLE 3.11 The effect of Process Residuals on the Deposits Formation of a Trimellitate in the Panel Coker test (275◦ C for 22 h in air) Residual metals in ppm 0 to 5 6 to 10 11 to 15

Visual demerit rating 0.5 1.01 1.33

catalytic activity on the deposit formation in decreasing order of activity was found to be: low-carbon steel > stainless steel > aluminium > brass > copper > lead [11]. Esters made from linear acids generally have higher flashpoints than those made from branched chains or a mixture of linear and branched chains. Increasing molecular weight also increases the flashpoints. The volatility of esters depends on several parameters: • • • •

Increasing molecular weight decreases volatility Increasing the degree of branching increases volatility Increasing polarity decreases volatility Oxidative stability: Esters with low oxidative stability break down to form molecules of low molecular weight

3.3.1.2 Hydrolytic stability Ester lubricant base fluids are manufactured by the reaction of acids and alcohols, with the elimination of water. This reaction is reversible and the ester products can undergo hydrolysis, that is, reaction with water to regenerate the starting materials. The reaction between pure ester and water is very slow. Ester lubricants containing less than 500-ppm water can be stored for several years at ambient temperature and undergo essentially no reaction. For hydrolysis to occur at a significant rate the following are required: some form of heat (>60◦ C), the presence of a catalyst (metal or acid), and a source of water (>100 ppm). Ester hydrolysis reactions have been widely used as model reactions for studying factors affecting the rates of organic reactions, and a wide variety of measurement techniques have been used to study them and to elucidate the reaction kinetics. This work has shown that under ideal conditions, the rate of acid-catalyzed ester hydrolysis is proportional to the concentration of the reagents, ester and water, and to the concentration of the hydrogen-ion catalyst. However, real-life systems are more complex than the ideal systems studied in the laboratory. In the field, the rate of hydrolysis is dependent on several factors, namely the: • Temperature • Presence of contaminants (particularly water or acidic

species)

250

10

0.7

0.5

150

0.4 100

0.3 0.2

5

50

0.1 0

0 0

2

4

6

8

Time (days) Water value

Linear acid

1 0.5 Branched acid

0.2 0.1 0.05

0.01

2500

1

10

100

1000

Time (hours)

7 2000

6 5

1500

4 1000

3 2

Water value (ppm)

Acid value (mg KOH/g)

2

0.02

Acid value

8

500

1 0

Change in acid value (mg KOH/g)

200

0.6

Water value (ppm)

Acid value (mg KOH/g)

0.8

0

10

20

30

40

0

Time (days) Water value

Acid value

FIGURE 3.7 Polyol ester tested at 2000 and 200 ppm water at 150◦ C in a sealed tube containing a metal coupon • Presence of metals (which can act as catalysts) • Chemical structure of the lubricant (degree of branching) • Specification of the ester (low acid and hydroxyl value,

no residual catalysts) • Presence, dose rate, and type of additives

Hydrolysis occurs via an acid-catalyzed mechanism. A hydrogen ion adds to the carboxyl oxygen of the ester linkage, converting it transiently to a carbonium ion, which rapidly adds on water to form a positively charged tetrahedral intermediate. This tetrahedral intermediate then separates into carboxylic acid and alcohol, regenerating a proton that can then catalyze further reaction. The reaction is therefore autocatalytic. The more the acid that forms the faster the breakdown, which in turn creates more acid. Low initial acid values are therefore important and acidic contaminants should be avoided. From Figure 3.7 it can be clearly seen that as water is consumed the acid value of the polyol ester increases. When the water is completely consumed the acid value reaches a plateau. This degree of “de-esterification” or

Copyright 2006 by Taylor & Francis Group, LLC

FIGURE 3.8 Hydrolytic stability of a linear acid vs. a branched acid polyol ester tested at 2000 ppm water at 150◦ C in a sealed tube containing a metal coupon

hydrolysis is primarily related to the amount of water present. The reaction rate constants typically show temperature dependence consistent with an activation process following the Arrhenius equation (roughly the rate doubles for every 10◦ C increase in temperature). The first step in hydrolysis is cleavage at the ester linkage. As such, if the cleavage at the ester linkage can be hindered, hydrolysis will occur at a much slower rate. One obvious way of causing hindrance is to use a branched acid, especially those branched near the ester linkage (e.g., 2-ethyl hexyl or neo acids). Branching will have an effect on the rate of hydrolysis, but ultimately the degree of hydrolysis will be determined by the total amount of water present, that is, given time both linear and branched esters will equilibrate to similar levels (Figure 3.8). Also, there are penalties to be paid when using these branched feedstocks, namely very long reaction times to achieve complete esterification. This of course may translate into more expensive products. The hydrolytic stability of the polyols is generally regarded as superior to that of the diesters. Aromatic diesters, due to the higher degree of steric hindrance, are more stable than alkyl diesters. Metals, such as lead [12], can have a major impact on the rate of reaction. The acids produced by hydrolysis can react with metals to form soluble metal salts, thereby reducing the acid value and limiting the rate of reaction. On the other hand, the dissolved metal salts and to a lesser extent metal surfaces can act as hydrolysis catalysts and increase the rate of reaction. Phosphate esters, typically used as antiwear additives, are known to be less hydrolytically stable than ester lubricants. It is therefore vital that additives have the greatest

possible stability. Although the phosphates are not the best additive at reducing wear, they do process posses an excellent trade-off between stability and lubricity. Acidic additives (e.g., certain anticorrosion and antiwear additives) can have a major negative effect on the stability of the ester. High levels of acidity can autocatalyze the breakdown of the ester (organic acids can act as a catalyst). Phosphate ester antiwear agents, such as Tricresyl Phosphate (TCP), are less hydrolytically stable than most esters. These additives can break down to produce acid that can again autocatalyze the breakdown of the ester. The best way to avoid hydrolysis is to keep the level of water in the system low, avoid high temperatures, and avoid contact with certain metals that can act as catalysts. 3.3.1.3 Environmental performance 3.3.1.3.1 Esters from renewable resources Renewable raw materials can be used in ester lubricants through the hydrolysis of fats and oils to produce the constituent fatty acids as raw materials for chemical synthesis. A wide variety of natural sources, including solid fats and low-grade or waste materials such as tallow from rendering of animal carcasses or tall oil from wood pulp processing, can be converted through controlled chemical processing into pure fatty acids of consistent quality. Fatty acids of appropriate chain lengths and degree of unsaturation are used in the manufacture of synthetic ester base fluids with molecular structures designed for optimum application performance. Synthetic esters therefore represent an overlap between the synthetic and biolubricant product categories, since they can be designed to be readily biodegradable and to incorporate renewable raw materials, although they are not normally derived exclusively from renewables and indeed many of their useful properties depend on the use of raw materials that are (currently) derived from petrochemical sources. For example, replacement of the glycerol component of a triglyceride by a petrochemically derived neopentyl polyol ester such as TMP substantially increases the thermal and hydrolytic stability [13]. Saturated short-chain (C8 to C10) fatty acids are used to make high stability polyol esters that are used in high performance synthetic car engine oils, jet engine lubricants, and compressor oils. Esters of longer chain cis-unsaturated acids for example, trimethyolpropane trioleate (TMPO) are used in applications such as biodegradable hydraulic fluids and cutting fluids, where oxidative stability is less critical. (Esters of longer chain saturated acids are normally too high melting for use as lubricant basefluids tend to be waxy solids.) Unsaturated long-chain acids are oligomerized and isomerized to give dimer and isostearic acids. Esters of these acids are used in two-stroke oils, car engine oils, and chain oils. Unsaturated long-chain acids are also converted to

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short-chain diacids that are used to make ester base fluids for aviation engine oils and automotive gear oils. In addition to their use in lubricant ester base fluids, fatty acids from renewable sources are also used extensively in manufacture of lubricant additives. Both saturated and unsaturated longer chain fatty acids, and their derivatives such as amides and glycerol monoesters, are used as friction modifiers. Although they have good low temperature fluidity, polyunsaturated acids are not preferred for use in lubricant applications because of their poor oxidative stability. However, with oleic acid, they can be converted by acid catalyzed oligomerisation and isomerisation, followed by hydrogenation, to give branched C18 monoacid (isostearic), C36 diacid (dimer acid), and C52C54 triacid (trimer acid), which are useful raw materials for the synthesis of high-viscosity ester fluids [13]. The double bond in the unsaturated acids offers many obvious possibilities for chemical derivatization, some of which are already commercially exploited. For example, the linear diacids azelaic acid (C9) and sebacic acid (C10) are manufactured industrially by oxidation of oleic acid and alkali fusion of ricinoleic acid, respectively. These diacids are raw materials for synthetic ester base fluids such as the respective diesters of 2-ethyl hexanol. The production of azelaic acid gives the C-odd numbered monoacid nonanoic acid as coproduct. Another C-odd monoacid, heptanoic acid, is derived from ricinoleic acid by pyrolysis, as a coproduct in the manufacture of undecenoic acid. Nonanoic and heptanoic acids are used in the same way as their C-even homologues in manufacture of neopentyl polyol esters, where the C-odd chain lengths confers some low-temperature fluidity benefits. Manufacture of these C-odd monoacids from renewable resources is economically competitive with petrochemical routes, although the supply from the renewable route is limited by the demand for the more valuable coproduct, in each case [13]. 3.3.1.3.2 Biodegradability The biochemistry of microbial attack on esters is well known in general outline and has been well reviewed [14–17]. The main steps are: • Ester hydrolysis • beta-Oxidation of long chain hydrocarbons • Oxygenase attack on aromatic nuclei

The main features that slow or reduce microbial breakdown are the: • • • •

Position and degree of branching Degree of saturation in the molecule Presence of aromatic groups High molecular weight

Table 3.12 gives biodegradabilities for a range of esters measured by two types of tests. Generally, linear polyol

Ester type Monoesters Diesters Phthalates Dimerates Trimellitates Linear polyols Branched polyol Complex polyols

% Biodegradability CEC-L-33-A-95 (21 days) 70 to 100 70 to 100 40 to 100 20 to 80 20 to 80 80 to 100 20 to 50 0 to 90

% Biodegradability OECD 301B (28 days) 30 to 95 10 to 80 5 to 70 10 to 50 0 to 40 50 to 99 5 to 40 10 to 90

esters tend to be used if high biodegradabilities are required. The biodegradability of esters is discussed in greater length in the chapter on environment, Chapter 34. 3.3.1.3.3 Toxicity and ecotoxicity Considerable environmental testing has been carried out on ester fluids. It is clear from this work that these substances are of a low order of toxicity. 3.3.1.3.4 Handling In general, esters cause minimal acute toxicity by ingestion and skin absorption. Neither mineral oils nor esters show significant skin irritancy response. However, mineral oils have been known to cause skin problems with people who are constantly exposed and who take inadequate precautions. The solvency of the mineral oils can remove some of the fat from the skin. This defatting can lead to mild dermatitis after prolonged contact. Esters are polar and therefore tend to be superior solvents to mineral oil. There is potential, therefore, to give such responses more quickly. Where contact with esters is likely to be high, gloves should be worn. Due to the hygroscopic nature of esters and their potential for hydrolysis, wherever possible, they should be stored in a dry sealed drum and contact with moist air should be minimized. 3.3.1.3.5 Recycling and reuse Energy recovery is the most common form of lubricant waste disposal. The major environmental issue when disposing of used esters by incineration is the other possible components/contaminants of the waste. Predominant among these are contamination by polychlorobiphenyls (PCBs), halogens (especially chlorine), and metals. Many countries have limits on the maximum total halocarbon, PCB, and metal allowable in the lubricant that can be used as fuel supplement. No PCBs are present in the raw materials or production process used to synthesize esters, nor do esters decompose to form such products.

Copyright 2006 by Taylor & Francis Group, LLC

Viscosity at 100°C in cSt

TABLE 3.12 Biodegradabilities of Various Ester Lubricant Groups

7 6 5 4 3 2 1 0

NPG

4

TMP

5

6

PE

7

8

9

10

11

Linear acid chain length

FIGURE 3.9 The effect of chain length on the viscosity of linear acid polyol esters

Waste ester is not a fuel in the strict technical sense because its volatility and viscosity are unlikely to conform to fuel oil standards. In conventional combustion plants, waste oil is burned in an admixture of lubricant to diesel fuel or coal in proportions that promote efficient combustion and that allow the overall level of contamination to be controlled. Trials on the combustion of used ester oils in concentrations of 5 to 20% have been carried out. In comparison with diesel oil, no differences were noted when burning such mixtures and all the emission readings were the same order of magnitude. Used ester oils are currently being recycled and reused in the same applications as their original use in several areas (e.g., hydraulic, metalworking, and transformer fluids, etc.). Recycling trials on polyol ester using a thin-film evaporator have shown great promise.

3.3.2 Physical Properties Much of the early work correlating the structure of esters with their physical properties was conducted by scientists such as: Zorn [18], Barnes and Fainman [4], McTurk [19], and Niedzielski [20,21]. 3.3.2.1 Viscosity The viscosity of ester lubricants can be increased by: • Increasing the molecular weight of the molecule by

increasing the • • • • • • • •

Chain length of the acid Chain length of the alcohol Degree of polymerization Functionality of the ester

Increasing the size and the degree of branching Including cyclic groups in the molecular backbone Maximizing dipolar interactions Decreasing the flexibility of the molecule

Figure 3.9 shows the change in viscosity at 100◦ C with acid chain length for a range of polyol esters.

TABLE 3.13 The Effect of Branching on Viscosity Polyol ester

Viscosity at 100◦ C in cSt

PE linear octanoate PE 2-ethyl hexanoate PE isooctanoate

5.58 6.36 8.35

Branching can also have a marked effect on viscosity: For very viscous molecules, branched aromatic esters, branched diPE polyols, or polymeric esters tend to be used. For low viscosity esters, short-chain diesters, NPG polyols, or monoesters are used. 3.3.2.2 Flow properties The VI of an ester can be improved by: • Increasing the acid or alcohol carbon chain length • Increasing the linearity of the molecule: Branching

restricts the rotational freedom around the ester linkage and also decreases the ratio of length to cross-section. Both effects contribute to lowering the VI. • Not using cyclic groups in the backbone, which tend to lower VI even more than aliphatic branches • Molecular configuration: Viscosity indices of polyol esters tend to be somewhat lower than their diester analogues, due to the more compact configuration of the polyol molecule. The pour point of the lubricant can be improved by: • Increasing the level of unsaturation (e.g., TMP oleate,

−51◦ C

• •

• •

an unsaturated C18 has a pour point and TMP Stearate, a saturated C18 has a pour point +45◦ C) Increasing the amount of branching (e.g., TMP isostearate has a pour point of −30◦ C) The positioning of the branch: Branching in the center of the molecule gives better pour points than branches near the end. Decreasing the acid or alcohol carbon chain length Decreasing the internal symmetry of the molecule (e.g., NPG oleate has a pour point of −24◦ C, TMP oleate −51◦ C, and PE oleate −21◦ C)

Esters made from mixtures of linear and branched chains have VIs between those of linear and branched, but have lower pour points than the esters obtained from either branched or linear chains. Pour-point depressants can also be used, but they tend to be much less effective in esters than they are in mineral oil. Clearly, there is a trade-off between VI and pour point. For instance, by increasing the linearity of the ester, the VI improves but the pour point deteriorates.

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TABLE 3.14 Viscosity-Pressure Coefficients for a Variety of Lubricants Lubricant

Viscosity-pressure coefficient Gpa−1

ISO 32 alkyl benzene ISO 32 napthenic mineral oil ISO 32 PE polyol ester ISO 68 PE polyol ester ISO 68 trimellitate

30.2 26.1 15.2 19.3 16.6

22.0 19.0 12.8 14.9 13.9

3.3.2.3 Lubricity To understand how an ester lubricates, it is first important to understand its behavior in the different lubrication regimes. 3.3.2.3.1 Hydrodynamic lubrication The viscosity of a lubricant has a marked effect on wear (viscosity being related to film thickness). Viscosities of lubricating oils are often quoted at 40◦ C (ISO grade) or 100◦ C. In reality the viscosity under operating conditions is the controlling factor. For systems experiencing hydrodynamic and elastrohydrodynamic lubrication (EHL), the viscosity of the lubricant is a key requirement. The viscosity of the lubricant is dependent on the: • Viscosity at 40◦ C • Temperature (which is related to the VI) • Pressure (which is related to viscosity pressure coeffi-

cient) • Dilution of the lubricant by absorbed gases (which is

related to vapor liquid equilibrium, VLE) • Effect of shear rate on viscosity

The viscosity of an ester at 40◦ C can be modified by the factors discussed in 3.3.3.1. The VI of the lubricant is dependent primarily on the degree of linearity and the length of the acid chain. Wholly linear acid polyol esters (POE) tend to have indices in the region of 110 to 130 while wholly branched POEs have VIs in the region 55 to 65. Esters generally have poorer viscosity-pressure coefficients than mineral oil but this is somewhat offset by the esters’ superior VI and boundary lubricity. The pressure-viscosity coefficients of various lubricants have been measured at various temperatures. These are listed in Table 3.14. These compare well with literature values at 40◦ C [22– 25] for TMP ester (8.4 to 9.8 GPa−1 ), PE esters (7.5 to 12.2 GPa−1 ), phthalates (13.6 GPa−1 ), and diesters (6.6 to 7.6 GPa−1 ).

The viscosity-pressure coefficient of a lubricant is influenced by: • The length of the side chains in branched esters (the

longer the better) • The degree of branching (the more the better) • Aromaticity (the more the better)

Large, inflexible, unsymmetrical esters have large free volume and are much harder to pack together under pressure. This explains their superior viscosity-pressure coefficients. As the temperature increases, the pressure-viscosity coefficient decreases due to an increase in the free volume of the molecules. This results in less interaction between the molecules. Inter- and intra-molecular bonding will also play a role but this area has not yet been sufficiently explored to comment. Dissolved gases in the lubricant can seriously reduce the viscosity of lubricants and causes wear by removing protective lubricant films, for example, on the cylinder walls in reciprocating compressors. For certain types of gases, synthetics are much better at resisting this dilution effect. This area is discussed at greater length in the Chapter on refrigeration lubricants. 3.3.2.3.2 Elastrohydrodynamic lubrication As the lubrication regime passes from hydrodynamic into EHL, the materials of construction become more and more important. EHL films are thin and require smooth surfaces to prevent asperity contact. The hardness and surface treatment of materials used is therefore important. As the contact pressures increase, the viscosity-pressure coefficient of the lubricant will become increasingly important. The polarity of the ester can also be very important. Recent work suggests that when a small amount of a highviscosity polar ester is added to a low-viscosity nonpolar base fluid (e.g., PAO) the ester will preferentially stick to the surface. When the two metal surfaces are far apart the bulk viscosity is controlled by the PAO. When the surfaces come closer together the PAO is squeezed out of the contact zone. The polar ester sticks to the surface and stays in the contact area. As the ester has high viscosity the bulk viscosity of the oil will increase as the surfaces come closer together. Finally, a point will be reached where only the more viscous polar ester remains [26]. Such an effect can be very beneficial in EHD lubrication. Low levels of polymeric esters have been used as additives. This has allowed the reduction in dose rate of certain types of active antiwear additives (chloroparafins, zinc diaryl dithiophosphates [ZDDPs], etc.) in several industrial applications. 3.3.2.3.3 Mixed film Mixed film lubrication, as the term implies, is actually a combination of boundary, hydrodynamic, and EHL regimes. In the mixed lubrication regime the contact characteristics are determined by varying combinations of

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fluid film and boundary lubrication effects. Some asperity contact may occur and interaction takes place between mono- and multi-layer boundary lubricating films while a partial fluid-film lubrication action develops in the bulk of the space between the metal surfaces. It follows that both the physical properties of the lubricant (as per EHL) and the chemical properties of the lubricant (as per boundary) are important. 3.3.2.3.4 Boundary lubrication The properties of the bulk lubricant, (e.g., viscosity), are of minor importance in boundary lubrication. The surface phenomena that determines the behavior of boundary lubricants can be described in the following terms: • Physically absorbed layers of gas, liquid, or solid

lubricants • Chemically absorbed layers • Films formed by chemical reaction

Esters have a high degree of polarity due to the lone pair of electrons on the oxygen atom of the ester linkage. Polar molecules are very effective boundary lubricants as they tend to form physical bonds with metal surfaces (i.e., they stick to the surface better than mineral oil). Most metal oxide surfaces are partially hydroxylated in the presence of water vapor. This hydroxylated surface can participate in hydrogen bonding either as a hydrogen-atom donor or as an acceptor. Thus, absorption of hydrogen-atom acceptors such as ester lubricants (or decomposition by-products such as alcohols and carboxylic acids) leads to wear protection and friction reduction [27]. Esters therefore tend to be more effective lubricants than nonpolar mineral oils. Hydrogen bonds tend to be quite weak and as loads and temperature increase they will break down. However, at higher loads esters will tend to form chemisorbed films. As viscosity is reduced, or if shear rate or load is increased, the chance of boundary lubrication occurring increases. This is especially true under conditions of compressor start-up where the lubricant film may not yet have formed. The properties of the lubricant that affect boundary lubrication are the: • • • •

Degree of branching Molecular weight Polarity Additives present in the lubricant

Figure 3.10 shows a simplistic model of a monoester on a metal surface. As the chain length of the acid increases the film thickness of the lubricant increases. Linear chains also increase the degree an ester can pack together on the metal surface. As discussed in Section 3.3.2.1, branched chains give a higher viscosity than linear ones of the same length. Therefore, for a given ISO grade linear esters will have a longer

Linear

Branched Acid chain Polar ester head Oxide layer

Bulk metal

Bulk metal

FIGURE 3.10 Schematic of a surface packing of a monoester

chain and therefore potentially a thicker film. Surface force apparatus experiments on linear and branched alkanes have shown that even a small amount a of branching (a methyl side chain) can significantly reduce the ability of molecules to form discrete layers between solid surfaces [28]. Chemisorbed films are produced by the formation of soaps. Soaps tend to act as a friction modifier. The effectiveness of these films is limited by the melting point of the soap. Many metal soaps have melting points in the range 120 to 200◦ C, when reached they desorb and the boundary lubricating properties are lost. Under extreme boundary conditions esters tend to break down to form acids. Preliminary work suggests these acids further react to form metal carboxylate soaps. Metal carboxylates have been shown to convey good extreme pressure (EP) protection. A form of boundary lubrication can be given at higher temperatures by the incorporation of EP or load carrying (antiwear) agents. Sulfur, for instance, will start to react with metals at about 100◦ C to form sulfides with melting points in excess of 1000◦ C. It is worth noting that oxygen from the atmosphere, or free oxygen in the lubricant, is a valuable EP lubricant. It forms oxide layers that generally provide a low shear strength film capable of reducing friction and wear between bearing materials. Mineral oil contains small but important quantities of more reactive substances like sulfur, nitrogen, and oxygen. These chemicals readily react with newly exposed metal surfaces to provide boundary lubrication. Because of these different interactions, the lubricity of an ester in a fully formulated fluid is not always easy to predict. As ester groups are polar, they can compete with antiwear or EP agent for the metal surface. When a very polar base fluid is used, it can cover the metal surfaces instead of the antiwear additives. This can result in higher wear characteristics because, although esters have superior lubricity properties to mineral oil, under high load conditions they are certainly less efficient than antiwear additives. It is therefore very important to choose the correct additive and to optimize its concentration to get the full lubricity benefit of using ester basestocks. Often, more polar antiwear agents or the same antiwear agent at a higher dose rate are used to offset this factor. Alternatively, the ester can be modified to decrease its polarity.

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Esters can be classified in terms of their polarity, or non-polarity by using the formulae below [29]: Non polarity index (NPI) =

Total no of C atoms × RMM No of carboxylate groups × 100

where RMM is the Relative Molecular Mass. As a rule, the higher the NPI of the ester the lower its affinity for the metal surface. Esters with high NPI will therefore compete less with the antiwear package. For a particular additive package there will be a trade-off between dose rate and the NPI of the ester that is, esters with high NPI can generally be used at higher dose rates before competition at the surface becomes an issue. NPI does not allow for structural effects that is, the degree of branching, unsaturation, etc. More sophisticated spectrophometric based techniques are now being developed that allow for polarity measurements to be taken directly [30]. 3.3.2.4 Energy efficiency Under hydrodynamic lubrication conditions, the only energy lost is that required to overcome viscous drag in the lubricant film at key bearing surfaces. The energy losses in hydrodynamic lubrication have a linear dependence on the fluid kinematic viscosity at the operating conditions. Many applications (e.g., engine oils, compressor lubricants, etc.) have therefore moved to lower viscosity oils. Under boundary conditions the relative velocity is insufficient to entrain a load-supporting hydrodynamic film. There is asperity contact between the surfaces, and the load is mainly carried through these solid contacts. Under boundary lubrication a range of physical mechanisms that may contribute to frictional losses come into play. Although a partial fluid film is present that undergoes viscous shearing, this is only a minor contribution to the overall friction coefficient, and boundary friction coefficients generally show little dependence on lubricant viscosity. In the boundary regime, the major contribution to the frictional force is the energy required for deformation of contacting asperities. Lubricant base fluids or additives that form an adsorbed surface layer can modify the boundary friction coefficient. In particular, components that form a

coherent chemisorbed or physisorbed layer that deforms more readily than the underlying metal or metal oxide surface may reduce the boundary friction coefficients. Lubricants having a high polarity or affinity for metal oxide surfaces, such as esters, have a greater tendency to form such adsorbed layers than less polar fluids, such as mineral oils or synthetic hydrocarbons, and therefore have lower boundary friction coefficients. Esters containing predominantly linear alkyl substituents can form a more coherently packed adsorbed film, and consequently show lower boundary friction coefficients, than those with branched alkyl substituents. This principle can be extended to use of components with longer linear alkyl chains and polar head-groups that are widely used as friction modifying additives in a range of lubrication applications, particularly in low polarity base fluids such as hydrocarbons. Organic friction modifiers act predominantly by absorption to the metal surface with the formation of absorbed layers due to the polar nature of the molecules. Friction modifiers dissolved in oil are attracted to metal surfaces by strong adhesive forces, which can be as high as 13 kcal/mol [31]. The polar head is anchored to the metal surface and the hydrocarbon tail is left solubilized in the oil, perpendicular to the metal surface. Other frictionmodifier molecules have their polar heads attracted to each other by hydrogen bonding and Debye orientation forces resulting in dimer clusters. Forces are about 15 kcal/mol in strength [31]. Cohesive Van der Waal’s forces will cause the molecules to align themselves such that they form multimolecular clusters that are parallel to each other. The orienting field of the absorbed layer induces further clusters to position themselves with their methyl groups stacking on to the methyl groups of the tails of the absorbed monolayer. An overview of these forces can be seen in Figure 3.11. Volumetric efficiency also plays an important role in the energy efficiency of reciprocating compressors and engines. If the viscosity of the lubricant is reduced to too low a level, piston blow-by occurs. Excessive foaming can also reduce volumetric efficiency. On the down-stroke of the piston the foamy layer is compacted. This compaction absorbs energy and can thereby further reduce energy efficiency. 3.3.2.5 Solvency 3.3.2.5.1 Compatibility with additives and other lubricants Esters have excellent compatibility with most types of lubricants. This results in a number of advantages:

Van der Waals forces

Long, nonpolar chains

Polar heads O

Van der Waals forces

Dipole–dipole interactions

O

Adhesive hydrogen bonding

Oxidized and hydroxylated metal surface

FIGURE 3.11 Overview of molecular interactions affecting ester FMs

• Most additive technology is based on mineral oil and it

is therefore usually directly applicable to esters. • Esters can be blended with mineral oil or natural oils

(semisynthetics) to boost their performance. • Esters can be blended with other synthetics such as;

PAOs, PAGs and PIBs. This gives esters great flexibility and unrivalled opportunities to balance the cost of different lubricant blends against performance. Solubility problems can often result from the use of additives with PAOs due to their low polarity. This is especially true for VI Improvers (VII). In many applications esters are often combined with PAOs to overcome these solubility problems. As PAOs shrink seals and esters swell them an optimum combination of the two can therefore be used to obtain a desired seal-swell target. The low friction of the ester component also compensates the poor fictional properties of the PAO. Ester/PAO combinations are therefore used in many applications (e.g., engine oils, air compressor lubricants, gear oils, etc.). 3.3.2.5.2 Materials compatibility Elastomers that are brought into contact with liquid lubricants will undergo an interaction with the liquid via diffusion through the polymer network. There are two possible kinds of interaction: • Chemical interactions • Physical interactions

Chemical interactions of elastomers with esters are rare. During a physical interaction of an ester lubricant and an elastomer two different processes occur: • Absorption of the lubricant by the elastomer causing

• There are no contamination problems, esters can be used

in machinery that previously used mineral oil, PAO, PIBs, and in most cases PAGs.

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swelling. • Extraction of soluble components out of the elastomer

causing shrinkage.

The degree of swelling of elastomeric material can depend on the: • Molecular size of the lubricant component (generally the

larger the lubricant the smaller the swelling). • Closeness of the solubility parameters of the lubricant

and the elastomer. Generally, the “like-dissolves-like” rule is obeyed. • Molecular dynamics of the lubricant: Linear molecules containing flexible linkages allowing rotation can diffuse into elastomers more easily than branched or cyclic ones. • Polarity of the lubricant: It is known that several elastomers are sensitive to polar lubricants.

It is important to note that the processing of the elastomer can have a major impact on its performance. As esters can be efficient solvents they have the potential to extract any substances used during the manufacture of the elastomer. Elastomers from different suppliers can be highly different in terms of the degree of cross-linking, fillers and process residuals in the elastomer. Therefore, any information on ester compatibility with elastomers in general should be confirmed by tests on the specific material. The data in the Table 3.15 that follows are only to be used as rough guidelines. Compatibility will be highly dependent on the specific ester used, end application, and environment.

TABLE 3.15 Compatibility Data for Esters Suitable Elastomers Nitrile rubber (buna-N, NBR) only if nitrile exceeds 36% Fluorosilicone rubber Fluorocarbon (viton, teflon)

Marginal

Unsuitable

Nitrile rubber (buna-N, NBR) with nitrile content 30 to 36% Polyurethane Ethyl propylene terpolymer (EPDM) Polyacrylate rubber Ethylenepropylene co-polymer (EPR) Silicone rubber Polysulfide (thiokol)

Nitrile rubber (Buna-N, NBR) with nitrile content below 30% Natural rubber Styrene-butadiene rubber (SBR) Butyl rubber Chlorosulfonated polyethylene (very marginal?) Polychloroprene (neoprene) (very marginal?) Ethylene/acrylic (EAE)

Paints Epoxy Baked phenolic Two-component urethane Moisture-cured urethane

Oil resistant alkyds Phenolic Single-component urethane Industrial latex

Acrylic Household latex Polyvinyl chloride (PVC) Varnish Lacquer

Plastics Nylon Fluorocarbon Polyacetal (delrin) Acrynitrile-butadiene (celcon) Acetals Polyamides

Polyurethane Polyethylene Polyproylene Polysulfone Melamine Phenylene oxide (Noryl)

Polystyrene PVC Styrene (ABS) Styrene acrylonitrile (SAN) Polysulfones Acrylic (lucite, plexiglas) (very marginal?) Polycarbonate (lexan) (very marginal?) Polyphenyloxide

Cadmium Zinc Magnesium

Lead

Polyester (hytrel)

Metals Steel and alloys Aluminium and alloys Copper and alloys Nickel and alloys Titanium Silver Chromium Tin Iconel

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3.3.3 Application Areas 3.3.3.1 Engine oils The main automotive lubricant market trends are: • Reduced emissions which requires

• • • •

Lower volatility Improved wear protection Deposit control Reduced sulphated ash, phosphorus, and sulfur (SAPS) to meet OEMs’ concerns on catalyst system durability

• Extended drain which requires

• Increased oxidation stability • Lower deposit forming tendency • Improvements in fuel economy and fuel economy reten-

tion which requires • Lower viscosity oils • Improved oxidation stability Esters’ low volatility, highs VIs, clean burn, and excellent frictional properties make them excellent basestocks for automotive applications. In 1969, the first semisynthetic 10W-50 engine oil based on diester was put on the market. In 1977, this was followed by a fully synthetic crankcase oil containing a PAO blended with a diester. A typical 5W-40 engine oil formulation can be seen in Table 3.16. 3.3.3.1.1 Lubricant Low temperature viscosity is perhaps the single most important technical feature of a modern crankcase lubricant. Cold starts are a prime cause of engine wear and can be mitigated only by immediately effective lubricant circulation. Low temperature viscosity can also have the benefit

TABLE 3.16 Typical Synthetic Formulation Component

Passenger % Dose rate

Ester basestock

5 to 20

Friction modifier (FM)

0 to 3

Hydrocarbon Oil

40 to 70

VI improver Additive pack

8 to 15 10 to 20

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Car

Motor

Oil

Chemistry Diesters or TMP polyol esters Amide/ester organic FM Mo based inorganic FM PAO, hydrocracked, alkyl napthalene — Antiwear, detergent inhibition pack, etc.

of reducing start-up load and stresses, reduce battery current drain and making starting easier [32]. Oils are moving to lower viscosity specifications (5W and 0W) to meet the new energy fuel efficiency requirements. As lower viscosity oils tend to be more volatile, this has created the need to move increasingly towards synthetics. Low volatility is especially important in the context of the modern trend towards smaller sump capacities and longer oil-change intervals. The superior thermal stability of ester allows the use of low-viscosity oils while at the same time offering the benefits of low deposits (extended drain, cleaner systems) and low-temperature fluidity (reduced wear on engine startup). As the requirements placed on the engine oil increase there is a growing trend to higher synthetic contents in engine oils. It is now widely accepted that synthetic fluids, such as PAO/ester blends, offer a number of inherent performance advantages over conventional petroleum-based oils for the formulation of modern automotive engine oils. Practical benefits that may derive from their use include improved cold starting, better fuel and oil economy plus improved engine cleanliness, wear protection, and viscosity retention during service. Initial formulations were based on PAOs with a small amount of a phthalate (to act as a seal swellant). These formulations were followed by PAO/adipate ester blends where the diester was used at between 5 and 20%. Here, the ester acted as a seal swellant and as an additive solubilizer and made an important contribution to the desired deposit/volatility targets. Adipates can also be used with mineral oil to produce semisynthetics. With the increased needs for superior thermal stability, TMP esters have substituted for adipate esters. For reason of cost, hydrocracked oils are increasingly being substituted for the PAO. 3.3.3.1.2 Friction modifier Friction modifiers have been around for many years. Their first use in automotive applications was during the world’s oil crisis in the 70s, to reduce crude oil consumption. Since fuel economy became an international issue, FMs have also been introduced into automotive crankcase lubricants to improve fuel efficiency via the lubricant. Currently, FMs are applied in engine oils both to reduce fuel consumption and to reduce exhaust emissions. In the US, additional pressure was imposed on OEM’s by legislation covering corporate average fuel economy (CAFE), a federal regulation putting requirements on average production model car fuel consumption as well as substantial fines if these requirements are not met. Reduction of emissions is driven by a number of factors, of which the Kyoto agreement is the most recent one. This agreement urges governments to reduce the emission of carbon dioxide into the atmosphere and the OEM’s have to face a part of this challenge. Consequently, the interest

in using FMs has further increased. Both reduction of fuel consumption and reduction of emissions can be achieved by reduction of engine friction. In practice, the friction-reducing additives applied in automotive engine oils are selected from two specific groups: 1. Organic friction modifiers: These are long and slim molecules with a hydrocarbon chain consisting of at least ten carbon atoms and a polar group at one end. The hydrocarbon chain provides oil solubility whilst the polar group is one of the crucial factors with regard to the effectiveness of the molecule as a friction modifier. Chemically, organic friction modifiers can be based on: carboxylic acids and their ester, imides, amines, and their derivatives. 2. Organo-metallic compounds: These compounds are products that contain molybdenum especially such as molybdenum dithiophosphate, -dithiocarbamate, and -dithiolate. Out of the above group, molybdenum dithiocarbamate seems to be almost exclusively recommended for use as FM. Esters (e.g., Glycerol mono oleate [GMO]) are typically used in combination with organo-metallic modifiers. Improvements have been made to ester based friction modifiers to decrease their friction while at the same time increasing their retention of friction reducing properties. 3.3.3.2 Automotive gear oils

the superior shear stability of ester based oils give major performance advantages. Like engine oils, diester and polyol ester blended with PAO at between 15 and 30% are favored. A typical ester based 75 W gear oil can be found in Table 3.17. Low polarity polymeric esters are under evaluation as a potential replacement for PAO 100. 3.3.3.3 Two-stroke oils Ester lubricants offer a number of advantages over mineral oils as the lubricant component of two-stroke engine mixtures. The clean-burn characteristics result in less engine fouling with much reduced ring stick and lower levels of dirt build-up on ring grooves, skirts, and undercrowns. Ignition performance and plug life are also enhanced. Owing to the presence of polar ester groups in the molecule, giving increased adhesiveness to metal surfaces, esters have much better lubricity than hydrocarbons. This removes the need to use bright stock and simultaneously permits the use of leaner burn ratios. In turn, this significantly reduces smoke levels. About 95% of the particulates in the exhaust fumes were found to be from the unburnt lubricant [33]. The excellent solubility of esters also allows them to be used without solvents (which are usually added to conventional two-stroke oil to help miscibility with the fuel and low temperature fluidity). A typical ester based formulation can be seen in Table 3.18. The leaner burn ratios result in reduced oil emissions, which is a benefit in environmentally sensitive applications such as marine outboard engines and chainsaw motors.

The following market trends are present: • Filled for life which requires

• Improved thermal and oxidative stability • Increased shear stability • Improved fuel efficiency which requires

• Lower oil viscosities • New transmission designs (CVT)

TABLE 3.17 Typical Synthetic Gear Oil Formulation for Example, 75 W Component

% Dose rate

Ester PAO Additive pack

15 to 30 60 to 85 7 to 13

Chemistry Diesters polyols Blends of PAO 4, 6, 40, and 100 —

• Smooth shifting which requires

• Improved lubricity • Smaller and lighter units which requires

• Improved thermal and oxidative stability • Improved lubricity The main advantages of esters in this sector are their excellent oxidative stability, VIs, and low temperature flow properties. This allows synthetic gear oils to operate over a much wider temperature range than conventional oils. Also

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TABLE 3.18 Typical Ester based Two-Stroke Formulation Component

% Dose rate

Ester basestock

50 to 60

Bright stock

10 to 30

Add pack Solvent

10 to 15 15 to 20

Chemistry Dimerate NPG and TMP Polyol esters PIB (low smoke) trimellitate or polymeric ester — White spirit Low viscosity ester

The high biodegradabilities of esters and low ecotoxicity and clean burn characteristics of ester formulations make them excellent candidates for “environmental considerate” labeling such as Blue Angel in Germany. Where biodegradability is an important factor NPG and TMP based polyols have replaced dimerates. Biodegradable polyol ester formulations (>70% OECD 301B) for use in chainsaw and Jet Ski applications are in commercial use. PIBs are commonly used as a bright stock in many formulations to achieve low smoke. Trimellitates and complex esters gave have also been used as brightstocks. Low temperature performance is important in some applications, such as engines used to power snowmobile type vehicles. Therefore, esters with low pour points of down to −56◦ C are very suitable for these applications. 3.3.3.4 Aviation turbine lubricants The bulk of aviation lubricant demand is for gas turbine lubricants for both military and civilian use. Hydrocarbon oils cannot meet the requirements placed on the jet engine lubricant in terms of thermal stresses. The first generation of oils (Type I) were diesters, but these have slowly lost ground over the last 25 years to the more expensive but more thermally stable Type II and Type III polyol esters. Diesters are still used in less demanding applications such as small private aircraft or turbo-prop engines. Type II aviation gas turbine lubricants are produced to a viscosity of 5 cSt (at 100◦ C). For some military applications, where operability at low temperatures is vital, the corresponding viscosity is reduced to 3 cSt. Type III oils are available at 4 and 5 cSts at 100◦ C. With increasing jet engine capabilities the need for more thermally stable oils has increased. The additive package usually consists of an antiwear package (e.g., TCP) and an aminic antioxidant. There has been some concern over the potential reaction of TMP polyols and TCP to form TMP-P a potent neurotoxin [34,35]. 3.3.3.5 Hydraulic fluids 3.3.3.5.1 Biohydraulics Hydraulic fluids represent a major growth area for biolubricants. The specific application is in mobile hydraulic equipment used in environmentally sensitive areas. In such equipment, pumping hydraulic fluid at high pressure through flexible hoses transmits power. Any damage to the hoses results in loss of fluid to the environment. Hydraulic fluids should therefore be biodegradable and there are also increasing demands for the lubricant to have a high renewability content (i.e., to use natural based feedstocks). Table 3.19 compares the biodegradability vs. renewable content for a range of lubricants [36]. It can

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TABLE 3.19 Comparison of Renewability

Vegetable oil Mineral oil PAO Alkyl benzene Diesters Aromatic ester Polyol ester Complex ester Polyalkylene glycol

Lubricant

Biodegradability

and

% OECD 301B biodegradability

% Renewability

70 to 100 20 to 40 20 to 60 5 to 20 40 to 80 5 to 70 20 to 99 20 to 90 10 to 70

100 0 0 0 0 to 80 0 0 to 85 0 to 100 0

be clearly seen that esters allow for the development of high biodegradability and renewable and high performance hydraulic fluids. There are three market segments for biohydraulics, defined by type of equipment and operating temperature. For low severity, high-loss equipment operating up to 60◦ C, mainly farming equipment, vegetable oils may be used. For medium severity, medium-loss applications up to 100◦ C, mainly in forestry operations, synthetic esters with a high content of renewable raw materials for example, TMP oleates are used. However, some applications, particularly in the construction industry, require fluids capable of extended lifetimes at operating temperatures in excess of 100◦ C. Development of biodegradable fluids with the necessary high oxidative and thermal stability has been a major challenge for the industry. It is also essential for hydraulic fluids intended for outdoor use in mobile equipment to possess satisfactory pumpability at the prevailing ambient temperatures during the initial period of operation with cold fluid. Unfortunately, starting procedures using too viscous a hydraulic fluid may easily cause excessively high pressures that pressure control valves are incapable of handling satisfactorily, and hence result in expensive repair costs. All types of hydraulic fluids increase in viscosity and eventually solidify as temperature decreases. An understanding of structure–property relationships has been used to develop two distinct approaches to higher performing biodegradable hydraulic fluids. The first route is to improve TMP Oleate type products by modifying the fatty acid raw material composition so as to increase the degree of saturation, reduce the average alkyl chain length, and to decrease molecular symmetry. Using this approach it has been possible to design products containing 85% renewable raw materials, but with oxidative stability and low temperature fluidity greatly superior to standard TMP Oleate products. Figure 3.12 compares the change in viscosity with time during storage at −30◦ C for standard TMP Oleate and new generation product [36,37].

Viscosity (cSt)

Viscosity vs. storage time at – 30°C 18,000 16,000 14,000 12,000 10,000 8000 6000 4000 2000 0

TABLE 3.21 Typical Ester based HFDU Fluid TMPO Modified

0

50

100

150

Component

% Dose rate

Ester basestock

>96

VII Additive pack

1 to 2 1 to 2

200

Chemistry NPG, TMP, PE, Polyol ester (e.g., TMP oleate) Droplet modifier Antiwear, antioxidant, anticorrosion, etc.

Time (h)

FIGURE 3.12 Low temperature storage stability of standard TMP oleate vs. modified

TABLE 3.20 Typical Ester based Biodegradable Hydraulic Fluid Component Ester basestock

Antioxidant Metal decativator Antiwear Antifoam

% Dose rate >95

1 to 2 0.2 to 0.5 0.4 to 1.0 <50 ppm

Chemistry TMP oleate ester Modified TMP oleates Diesters Polyols Complex polyols Phenolic + aminic Metal free Metal free Metal free, usually non silicone

The alternative route is to redesign the molecular structure more fundamentally, using neopentyl polyol alcohols and saturated acids to optimize thermo-oxidative stability and biodegradability. This approach significantly reduces the renewable raw material content but has lead to development of products, which combine ready biodegradability with thermo-oxidative stability, superior to that of mineral oil based formulations. In terms of hydrolytic and oxidative stability the base fluids show the following trend (decreasing order of stability): Saturated polyols > Diesters > Modified TMP oleates > TMP oleates > High oleic sunflower oil > Rapeseed. Table 3.20 gives a typical formulation for an ester based biohydraulic fluid. The ester selected will be dependent on the trade-off between cost, renewability, oxidative stability, biodegradability, and low temperature pumpability. 3.3.3.5.2 Fire resistant hydraulic fluids Diesters blended with PAOs have been used for a number of years in military application as fire resistant hydraulic fluids (MIL-H-83288C spec). However, polyol esters now tend to be used, especially esters of oleic acid and most commonly the TMP ester of this acid. Polyol esters are classified as HFDU fluids. They compete in this market sector with phosphate ester technology.

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There are increasing concerns about the toxicity aspects around phosphate esters and the fact that their thermal decomposition products are highly noxious. Polyol esters are therefore beginning to replace phosphate esters in certain areas. Polyols have several advantages over phosphate esters: • • • • •

They are more cost effective Have better flow properties Are easier to recover from water Are less aggressive to seals They are better lubricants

Phosphate esters, however, are superior in their fire resistance. To enable polyol esters to pass certain fire resistance tests, for example, the factory spray test, <0.5% of a VII may be added. This additive helps modify the spray pattern of the fluid pumped through the nozzle by increasing the droplet size. Larger droplets of lubricant are much more difficult to ignite. A typical HFDU fluid formulation can be seen in Table 3.21. Esters (e.g., isooctyl oleate) can also be used in HFA synthetic emulsion (SE) fire resistant fluids as well. 3.3.3.6 Air compressor lubricant This application area covers a wide range of compressor types, used for a number of different gases. The three basic functions of compressor oils are to: • Lubricate (reducing friction between moving parts) • Act as an oil seal at rings, vanes or rotary screws • To cool critical bearings and points of constant

friction Esters have the following advantages in compressor applications: • Compressors that use esters can be less expensive to run • Have safety and ecological benefits • They are excellent lubricants

From the user’s standpoint the main reason for choosing a synthetic over conventional hydrocarbons is to save money.

This goal can be accomplished, in part through extended drain intervals (up to eight- or ten-fold) and other associated cost savings, such as less frequent replacements of oil filters and air/oil separators. Esters can have better lubricity, which can mean reduced wear and fewer replacements of mechanical parts such as piston rings, seals, and bearings. Power cost saving is another factor, which can range from 1 to 7% [38–40]. Resistance to breakdown means less sludge and varnish in the compressor and compressed gas system. There is also improved performance of newer compressors operating at higher speeds, temperatures, and pressures. From a safety performance standpoint there are reduced fire and explosion hazards for compressors handling air and chemical gases. High outlet temperatures in modern reciprocating air compressor installations cause carbon build-up on compressor outlet/discharge valves. These carbon deposits can glow and cause fires and in some cases explosion. This problem is intensified in environments where air filtration is less than ideal and dust contributes to a build-up of dangerous deposits. Esters, especially trimellitates and polyol esters have improved oxidation resistance and low volatility compared to those of mineral oils of similar viscosity. Esters therefore minimize build-up of deposits on the hot pistons and discharge valves. The high temperature stability and solvency action of esters therefore minimize the risks of fire and explosion [40]. The low volatility of esters results in reduced carryover. These properties, coupled with their higher flashand autoignition temperatures and low order of toxicity for vapor inhalation and ingestion make them considerably safer lubricants to use than mineral oil. Their low ecotoxicity and high biodegradability can also lessen their environmental impact. The excellent lubricity, thermal stability, and conductivity of esters allow them to be used in high-performance compressor oils that cannot be formulated using traditional hydrocarbon lubricants. Diesters and phthalates have found their major application in air-compressor lubricants, but they are also used in compressors handling natural gas, propane, iso-butane, and carbon dioxide. Diesters generally have higher VIs, giving them a wide temperature range without the use of VIIs which can shear in this application. In reciprocating compressors, where significantly higher viscosity oils are preferred, trimellitates can be used. The solvency characteristics of esters are such that care has to be taken in the selection of elastomeric sealing materials: the use of Viton is usually recommended. A typical ester based air-compressor formulation can be seen in Table 3.22. Diesters and polyol esters can also be blended with PAOs and hydrocracked oils for use in various compressor types. When blended with PAOs, esters (diesters, phthalates, trimellitates, and polyol esters) are typically used at between 5 and 25%.

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TABLE 3.22 Typical Ester based Air-Compressor Formulation Component

% Dose rate

Ester basestock

5 to 98

Other basestock Additive

0 to 93 1 to 5

Chemistry Diester Aromatic esters Polyol esters PAO or PAG Antioxidant, antiwear, anticorrosion, antifoam

TABLE 3.23 Typical Polyol Ester based Refrigeration Lubricant Component

% Dose rate

Ester Antioxidant Antiwear Foaming agent

>95 0 to 1000 ppm 0 to 5 0 to 1000 ppm

Chemistry Polyol ester (e.g., NPG, PE, DiPE) Storage stabilizer To reduce wear To reduce noise

3.3.3.7 Refrigeration lubricants For the past 50 years, lubricants produced from naphthenic and paraffinic mineral oils have been used in refrigerator compressor systems. These oils were fully compatible with the traditional chloro fluoro carbon (CFC) refrigerants for example, R12 and fully met system requirements. Due to the chemical differences between CFCs and the new alternative refrigerants for example, R134a, traditional mineral oils are not capable of meeting these requirements. Ester lubricants based on polyol ester chemistry have been developed that achieve the key characteristics of this application, namely good [41]: • • • • • •

Lubricity Materials compatibility Energy efficiency Resistance to copper plating Chemical, thermal, and hydrolytic stability Solubility with R134a, mineral oil, and additives

A typical based polyol ester formulation can be seen in Table 3. 23. Low-viscosity oils (ISO 150) are based on diPE polyols. Viscosities in between are based on pure PE polyol themselves or blended with NPG or DiPE polyols. TMP polyols are usually avoided mainly due to the TMP-P problem mention in the aviation turbine section. 3.3.3.8 High temperature chain oils Many manufacturing products today require extreme heat, either in the manufacturing, finishing, curing, or drying

TABLE 3.24 Typical Ester based Chain Oil Formulation Component Ester

% Dose rate >75

Tackifier/thickener

2 to 20

Additive pack

2 to 8

Chemistry Dimerate Trimellitate ester Polyol ester VII (PIB, PMMA) Polymeric esters Antioxidant, antiwear, and anticorrosion

process. Application areas such as: textile factories, car plants and pottery/glass kilns use roller chains, stenter chains, and sliding chains. Lubricants for these chains see temperatures above 150◦ C, and sometimes as high as a 1000◦ C. Esters that have high oxidative stabilities, low volatilities, and excellent clean burn properties are required. A typical ester based chain oil formulation can be seen in Table 3.24. Dimerates tend to be used in cost effective formulations. For higher temperatures trimellitates and PE/diPE polyol esters tend to be favored. Trimellitates tend to a poorer stability than POEs but decompose to leave a soft (easy to remove) deposit. Polyol esters decompose at higher temperature but can leave behind a harder deposit (varnish). Often blends of trimellitates and polyols are used to obtain the correct balance. VIIs are often used as tackifiers/thickeners. For very oxidative stable formulations high viscosity polymeric esters have been used as a tackifier. 3.3.3.9 Metalworking fluids Esters have the following advantages in this application area: • Environmentally considerate (biodegradable, low eco-

toxicity, etc.). • Good boundary lubricants. • Act as FMs. • Have good surface wetting ability letting them penetrate

between the work tool and workpiece. This has led to their use in steel rolling, aluminum drawing, and cutting oils. Esters are starting to see some use as quenching fluids as well. Most esters have poor solubility with water. However, complex polyalkylene glycol esters that are ethoxylated are fully water soluble. These esters show synergism with many types of corrosion inhibitors. Natural and synthetic esters are considered an integral part of today’s high performance and neat oil and water miscible metalworking fluids. The primary reason for using an ester is to reduce the friction between tool and work

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piece, with the specific aims of improving surface finish and extending tool life. The use of esters is set to increase as machining techniques develop and as greater consideration is given to the environmental and health aspects of metalworking formulations. The normal function of an ester, be it used in a neat (straight) oil or in a water-miscible formulation, is to reduce the friction between a tool and component or roller and metal strip in order to minimize tool or roller wear and to improve surface finish. A wide range of esters is used in neat oils, which can include esters such as monoesters (e.g., methyl oleate or isopropyl palmitate), diesters (e.g., propylene glycol dioleate), and polyol esters (e.g., trimethylolpropane trioleate). In water-miscible fluids, the most commonly used esters are isopropyl oleate, isobutyl stearate, neopentylglycol dioleate, and a number of trimethylolpropane derivatives. A common feature of the esters used in water-miscible formulations is their greater resistance to hydrolysis. Esters can be used either as additives (typically used at a treat-rate of 5 to 15%) or as the base oil. When used as an additive, the ester will improve the lubrication performance of a given formulation with the specific intention of improving surface finish and increasing tool life. Their use as base oils is usually the result of some additional requirement, such as higher lubricity, minimizing misting or a desire for a high level of biodegradability. Natural oils and fats, such as coconut and palm oils, and synthetic esters, for example, esters of NPG, TMP, and PE, are widely used in many rolling formulations. Following a recent development, low-viscosity complex esters are now a very interesting addition to the range of products suitable for use in rolling applications, particularly steel rolling [42]. With the restricted use of some additives, for example, chlorinated paraffins, formulators are being forced to develop new formulations of similar or higher performance but exclude the use of such additives. As discussed in Section 3.3.2.3.2, high viscosity complex esters (e.g., 1,000 to 45,000 cSt) are particularly suited for use as EP additives either alone or in combination with other performance additives, such as phosphate esters and sulfurized esters or olefins. 3.3.3.10 Greases Esters are commonly used as basestocks for greases when one or more of the following properties are required: • • • •

Low temperature flow (e.g., aircraft wheel bearings) High temperature applications Biodegradability Low toxicity (e.g., food use applications)

A range of ester types: diesters, phthalates, trimellitates, pyromellitates, and polyols are used in this application. 3.3.3.11 Drilling mud lubricants Ester based organic compounds are one type of synthetic base fluid (SBF) added to drilling muds used during offshore oil-drilling operations. Since 1990, the oil and gas extraction industry developed SBFs with synthetic and nonsynthetic oil-like materials as the base fluid to provide the drilling performance characteristics of traditional oilbased fluids (OBFs) based on diesel and mineral oil. Ester SBFs are needed to cool and lubricate the drill bit, and to help bring rock cuttings to the surface. Ester based drilling fluids have the following advantages over OBFs: • Faster and deeper drilling • Greater worker safety through lower toxicity • Elimination of polynuclear aromatic hydrocarbons

(PAHs) • Excellent biodegradability and lower bioaccumulation

potential

3.3.3.12 Transformer fluids/capacitor fluids Synthetic ester dielectric fluids, most commonly pentaerythritol polyol esters, have suitable dielectric properties and are significantly more biodegradable then mineral oil. Their use in electrical equipment is governed by IEC Standard 1099 and IEC standard 1203. Esters have been used as PCB substitutes in compact railroad traction transformers since 1984, and in klystron modulators where their low viscosity, high lubricity, and very low pour points justify their higher costs. Failure rates of traction transformers have significantly decreased since the replacement of PCBs with synthetic POEs [44]. Transformers require a highly efficient heat-transfer fluid. The fluid should also maintain a high dielectric integrity. In the case of capacitors, in addition to low cost, non-toxicity, and biodegradability the fluid should have a low viscosity, a low power factor, and exceptional resistance to discharge and in certain cases, a high permittivity. Trimellitate esters have been found to be suitable for this application [45]. To prevent a decrease in electrical strength it is vital that the moisture content of ester dielectric fluids remains low.

3.4 MANUFACTURERS, MARKETING, AND ECONOMICS

• Potentially less drilling waste volume • Reduced drilling costs

3.4.1 Manufacturers

Drilling engineers have published numerous technical papers that describe the successful application of substitute drilling fluids. In many instances, this substitution has resulted in significant cost savings. Government and industry research found that several synthetic-based fluids used in mud formulations exhibited similar biodegradation profiles to mineral oils offering no apparent benefits. As a result the UK government decided to reduce the discharge of a number of synthetic fluids. Esters were not subjected to the same reduction program because of their rapid biodegradation [43]. A typical ester based drilling formulation can be seen in Table 3.25.

A list of current ester lubricant suppliers and the type of esters they make are given in Table 3.26. Typically, these plants will produce esters not only for lubricant use but other applications as well (cosmetics, plasticizers, biodiesel, etc.). Several of these ester plants are large (>100,000 t), which means there is no shortage of ester lubricant capacity. In recent years several acquisitions have occurred: • Uniqema, ICI (formed from ICI, Unichema, and Mona.

Great Lakes ester business then acquired) • Exxon acquired Mobil • Fuchs acquired DEA

Table 3.26 does not include companies who produce esters only for internal use. TABLE 3.25 Typical Ester based Drilling Lubricant Formulation Component Ester Water Calcium chloride brine Viscosifier Emulsifiers/wetting agent Fluid loss control Lime Weighting agent

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% Dose rate

Chemistry

28 14 5.6 1 2 0.4 1 48

— — Alkalinity — — — Alkalinity —

3.4.2 Markets One difficulty in deciding the size of the ester lubricant market is deciding exactly what market segments should be included. For instance should dielectric fluids, fuel additives, mould release, biodiesel, plasticizers, or hydraulic fluids be included even though they are not lubricants? It is also very difficult to differentiate between the amounts of ester produced in Europe vs. the amount consumed (Europe is a net exporter of ester). For several application (e.g., metalworking) formulators may also produce much of their ester requirements internally.

Other industrial 8%

TABLE 3.26 Ester Lubricant Manufacturers Company

Esters produced

Uniqema, ICI Cognis

1, 2, 3, 4, 5, 6, 7 1, 2, 3, 4, 5, 6, 7

Oleofina Nyco Hatco Oleon Degussa Nippon oil and fat Exxon/mobil Aqualon Union camp ADK KAO

7 1, 2, 3, 7 2, 3, 4, 5, 6, 7 7 2, 7 6, 7 2, 3, 4, 7 7 1, 2, 6, 7 5, 6, 7 2, 4, 5, 6, 7

Witco BASF Akzo Inolex

— 2 3 2, 3, 6, 7

Trademark Emkarate ProEco, Edenor, Emery, EMgaurd — Nycobase Hatcol Radialube Drivolan Unister Esterex Hercolube Uniflex Adeka Kaolube, Exceparl, Vinycizer, Trimex Witcosyne Glissofluid Ketjenlube Lexolube

Figure 3.13 shows the size of the Western European ester market and its growth rate. The Americas ester market is probably in the region of 100 Kt with Asia being considerably smaller. In several application areas, polyol esters are expected to replace diesters because of their superior thermal and chemical stability. Therefore, polyols will have a higher growth rate than diesters.

3.5 OUTLOOK Modern lubricants are complex formulations, which are continually developing to meet increasing requirements for performance and durability. Taken as a whole, over the last decade, several general trends in lubricant properties have been seen, namely: Higher thermal stability Improved environmental performance Longer lubricant life Improved cost effectiveness

Esters have performance characteristics to meet all these developing trends. Major areas for growth will be the industrial refrigeration sector (Phase out of R-22), biodegradable hydraulic fluids, engine oils (fuel efficiency), and gear oils (CVT, windmills, etc.).

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Air compressor 4% Refrigeration 12%

Esters produced key: 1 = C36 Dimerates; 2 = Diesters; 3 = Complex Esters; 4 = Phthalates; 5 = Trimellitates; 6 = Monoesters; and 7 = Polyols.

• • • •

Aviation 5%

HF 32%

MWF 20%

2T 3%

4T 16%

Total market size 125 Kt (5 to 6% CAGR)

FIGURE 3.13 2002 Western Europe ester sales split by application; MWF = metal working fluids = includes roling, drawing, cutting, etc. HF = hydraulic fluids = Bio HF + fire resistant HF

As companies get larger and developing markets takeoff, new lubricants will be expected to be available globally. New environmental legislation and toxicity registration schemes are being generated at an ever-increasing pace. The cost of registering a brand new lubricant globally could potentially cost several hundred thousand dollars. Such costs can potentially curtail work on radically different chemistries. One way to minimize costs is to work on polymeric materials, which either have exemption or reduced toxicity costs under many nations’ registration programs. Polymers also allow a great deal of chemical flexibility. This has led to considerable ester research in the areas of: complex polyols, PAG esters, polycarbonates, etc. Research is also continuing in the more traditional diester, phthalate, and polyol ester areas as new raw materials or production routes are developed. The area of renewable resource materials is particularly fertile as it offers not only the advantage of improved environmental performance but also reduced costs as well. Sustained development of ester chemistry can therefore be expected to continue for at least the foreseeable future.

ACKNOWLEDGMENTS I would like to acknowledge Steven Stephen Boyde and Ron Pearce (Uniqema) whose help was very useful invaluable in putting this chapter together.

REFERENCES 1. Spaght, M.E. (July 1945). The Manufacture and Application of Lubricants in Germany. Combined Intelligence Objectives Sub-Committee. Nav Tec Miseu, CIOS TARGET NO. 30.303, Fuels and Lubricants. (http://www.fischertropsch.org/primary_documents/gvt_reports/CIOSC/ cios_30_32_68.htm). Report PB-110034. Tables of physical characteristics of a wide range of esters. I.G.Farenindustrie, Library of Congress. 2. Hoogendoorn, R. (June 1999). Field test results of self emulsifying ester based metalworking fluids demonstrate: reduced

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19. McTurk, W.E. (October 1953). Synthetic Lubricants. Wright Air Development Centre, Air Research and Development Command, United States Air force, Wright-Patterson Air Force Base, Ohio, WADC Technical Report, pp. 53–88. Contract AF 33(038)-14593, RDO No. 613–15. 20. Niedzielski, E.L. (1976). Neopentyl polyol ester lubricants – bulk property optimisation, Ind. Eng. Chem. Prod. Res. Dev. 15, 54–58. 21. Niedzielski, E.L. (1977). Neopently Polyol ester lubricants – boundary composition limits, Presented at 173rd National Meeting of the AIChE, Div, Petroleum Chem., Chicago, Illinois, USA. 22. Chang, H.S., Spikes, H.A., and Bunemann, T.F. (1991). The shear stress properties of ester lubricants in elastrohydrodynamic contacts. Journal of synthetic lubricants, 9, pp. 91–114. 23. Anderin, M., Johnston, G.J., Spikes, H.A., and Caporiccio, G. (1992). The elastrohydrodynamic properties of some advanced non hydrocarbon-based lubricants. Lubrication Engineering, 48, pp. 633–638. 24. Gunsel, S, Spikes, H.A., and Anderin, M. (1993). Tribology transactions, 36, pp. 276–282. 25. Guangteng, G. and Spikes, H.A. (May 1995). Boundary film formation by lubricant base fluids. Presented at 50th STLE meeting, Chicago, USA. Presentation 95-NP-7D-3. 26. Smeeth, M. and Spikes, H.A. (May 1995). The formation of viscous surface films by polymer solutions: boundary or elastrodynamic lubrication? Presented at 50th STLE Meeting, Chicago, USA. Presentation 95-NP-7D-2. 27. Bovington, C.H. (1997). Friction, wear and the role of additives. Chapter? Chemistry and Technology of Lubricant, R.M. Mortier, and S.T. Orzulik, (Eds), 2nd edn, Blackie Academic and Professional, London. 28. Wang.Y., Hill, K., and Harris, J.G. (1993). Comparison of branched and linear octanes in the surface force apparatus: a molecular dynamics study. Langmuir, 9, p. 1983. 29. Van der Waal, G. (1985). The relationship between chemical structure of ester base fluids and their influence on elastomers seals and wear characteristics. Journal of Synthetic Lubricants, 1, p. 281. 30. Ter Haar, R. (January 2004). A new polarity measurements technique for lubricants and some of its applications. In Proceedings of the 14th International Colloquium Tribology, Esslingen, Germany, pp. 1869–1873. 31. Bunemann, T., Kenbeek, D., Koen, P., and Wald, W. (October 2002). Friction modifiers for automotive applications. In Proceedings of the International Symposium on Fuels and Lubricants, New Delhi, India. 32. Coffin, P.S., Lindsay, C.M., Mills, A.J., Lindencamp, H., and Fuhrmann, J. (1979). The application of synthetic fluids to automotive lubricant development trends today and tomorrow. Journal of synthetic lubricants, 7, p. 123. 33. Suigura, K. and M.Kagaya. (June 1977). A Study of Visible Smoke Reduction from a Small Two-Stroke Engine Using Various Lubricants, SAE paper 770623. 34. Wright, L. (May 1996). Formation of the neurotoxin TMPP from TMPE-phosphate formulations. In Proceedings of the 51st STLE Meeting, Cincinnati, preprint No. 96-AM-7A-1.

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40. Witts, J.J. (1989). Diester lubricants in petroleum and chemical plant service. Journal of synthetic Lubricants, 5, p. 321. 41. Corr, S., Randles, S.J., and Stewart, A. (October 1993). Synthetic lubricants for freon replacement gases, The petroleum industry faces the environmental problems, Brussels, Belgium. 42. Eastwood, J. (October 2002). High Performance Components for Use in the Machining of Aluminium and Steel: An Evaluation of Ester Lubricant Properties. VII Giornata Europea del Lubrorefrigerante, Milan. 43. Spencer, S.J. (September 2000). Governments, operators eyeing effects of synthetic-based drilling fluids. Oil and Gas Journal, pp. 88–89. 44. McShane, C.P. (May/June 2000). New safety dielectric coolants for distribution and power transformers. IEEE Industry Application Magazine, pp. 24–32. 45. Waddington, F.B. (1983). High temperature esters: new dielectric fluids for power engineering applications. GEC Journal of Science and Technology, 49, pp. 18–22.

4

Neutral Phosphate Esters W. David Phillips, Douglas C. Placek, and Michael P. Marino CONTENTS 4.1

Introduction 4.1.1 Historical Development 4.2 Chemistry 4.2.1 Structure 4.2.2 Production 4.2.2.1 Triaryl Phosphates 4.2.2.2 Trialkyl Phosphates 4.2.2.3 Alkyl Aryl Phosphates 4.3 Properties and Performance Characteristics 4.3.1 Chemical Properties 4.3.1.1 Thermal Stability 4.3.1.2 Oxidative Stability 4.3.1.3 Hydrolytic Stability 4.3.2 Physical Properties 4.3.2.1 Vapor Pressure and Boiling Point 4.3.2.2 Viscosity 4.3.2.3 Other Properties 4.3.3 Performance Properties 4.3.3.1 Flammability 4.3.3.2 Lubricity 4.3.3.3 Corrosion and Rust Inhibition 4.3.3.4 Solvent Properties 4.3.3.5 Additive Response 4.3.3.6 Foaming and Air Release 4.3.3.7 Toxicology 4.3.4 Maintenance of Systems 4.4 Manufacture, Marketing, and Economics 4.4.1 Manufacturers 4.4.2 Suppliers 4.4.3 Economics 4.5 Outlook References

4.1 INTRODUCTION Since the discovery of their excellent antiwear and fire-resistance properties in the 1940s, the use of phosphate esters by the lubricants industry has steadily increased. As a result of many years of research and practical experience, M.P. Marino and D.G. Placek originally authored this chapter when working for FMC Corp, Philadelphia.

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industry has learnt to manufacture and formulate these versatile chemicals to satisfy a wide variety of demanding applications. Although the basic composition of products currently in commercial use has remained unchanged for over 30 yr, new applications continue to be found and the products are, today, regarded as cost-effective lubricant additives and safe, non-hazardous, hydraulic fluids and lubricants.

Phosphate esters are the most fire resistant of the nonaqueous synthetic basestocks in common use. Their high ignition temperatures, good oxidation stability, and very low vapor pressures make them difficult to burn while their low heats of combustion result in self-extinguishing fluids. Over 60 yr of use have shown them to be excellent lubricating additives and fluids with early shortcomings, for example, hydrolytic instability and neurotoxicity overcome by optimizing manufacturing techniques, raw materials, and stabilizer systems. This chapter describes the chemistry and manufacture of neutral esters of phosphoric acid. It outlines the physical and chemical properties that make them practical and useful industrial chemicals. The formulation of phosphate esters into lubricants and hydraulic fluids, with emphasis on commercial applications, is reviewed. Finally, the practical methods of managing systems employing phosphate esters to achieve optimum working life and costeffective performance in the industrial environment are indicated.

4.1.1 Historical Development Although thousands of organophosphorus compounds have been synthesized, only those classified as neutral, metal free, phosphate esters, or fully substituted esters of orthophosphoric acid (H3 PO4 ), have been used as synthetic lubricants or fire-resistant fluids. By contrast mono-, di-, and trisubstituted esters have all found commercial use as lubricant additives, but only neutral tertiary esters are the subjects of this study. Tertiary orthophosphate esters have been known for about 150 yr, the trialkyls having been synthesized in about 1849 [1] and the triaryls in about 1854 [2]. The development, after World War I, of less flammable nitrocellulose lacquers plasticized with tricresyl phosphate (TCP) as industrial and automotive coatings [3], led to the investigation of phosphate esters as safer hydraulic fluids and lubricants. Principally during the early 1940s, a number of investigators [4–7] examined the lubricating properties of phosphate esters, especially their usefulness as antiwear agents. During World War II and the years that followed immediately following, the development of increasingly sophisticated military and commercial aircraft, which used hydraulic rather than mechanical control systems, created a need for safe, nonflammable hydraulic fluids. Patents were awarded to J.D. Morgan, at the Cities Service Oil Company, in 1944 and 1946 [8,9], on lubricant and hydraulic fluid compositions having wide operating temperature ranges (−40 to 200◦ F) based on tributyl and other trialkyl phosphates. Also in 1946, W.F. Hamilton and coworkers at the Lockheed Aircraft Corporation [10] were awarded a patent on what can be considered the forerunner of today’s commercial aircraft hydraulic fluids.

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The use of both trialkyl and triaryl phosphates as synthetic basestocks was more thoroughly defined and developed in a major program jointly sponsored by the U.S. Navy and Air Force at the Shell Development Company between 1949 and 1953 [11]. As a result of this work, F.J. Watson was awarded several patents for fluid compositions based on tributyl phosphate and TCP [12–14]. At about the same time, the Douglas Aircraft Company and Monsanto Chemical Company helped pioneer the use of phosphate esters in commercial jet aircraft [15–18]. By the late 1950s, such planes as the Douglas DC-8, Boeing 707, and Convair 880 were flying on Monsanto’s Skydrol® 500A fluid, which was based on a mixed alkyl aryl phosphate. Concurrent with the use in aircraft, other commercial uses developed. TCP and other esters became widely used during the l950s as deposit modifiers in leaded gasoline. By the late 1950s, Monsanto, Celanese Corporation of America, and the E.F. Houghton Company had complete lines of phosphate ester-based industrial hydraulic fluids, which were readily adopted by the steel, aluminum, foundry, and casting industries. Each company also marketed phosphate-ester products for use as fireresistant compressor lubricants. The U.S. Navy, in 1961, adopted specification MIL-H-19457, a fire-resistant fluid then based on trixylenyl phosphate (TXP), for use in aircraft carrier elevators. Some of the early industrial fluids developed both in the United States and Europe were based on blends of alkyl aryl phosphates and chlorinated aromatic hydrocarbons (chlorinated biphenyls). However, the environmental and toxicological problems that subsequently arose with chlorinated biphenyls resulted in their complete disappearance from commercial use in the 1970s. The industrial phosphateester fluids in use today as lubricant additives or synthetic basestocks, therefore, are all based on triaryl phosphates free from halogenated components. Commercially available phosphate-ester hydraulic fluids for general industrial applications are categorized as type HFDR fluids according to ISO standard 6743, Part 4: Lubricants, industrial oils, and related products (class L) — Classification.

4.2 CHEMISTRY 4.2.1 Structure Numerous organic phosphorus compounds including phosphites, phosphonates, and phosphates have found application as additives in a variety of lubricant formulations as stabilizers, antiwear additives, antioxidants, metal passivators, and extreme pressure additives. Of these, the zinc dialkyl dithiophosphates, found in virtually all automotive engine lubricants, are the most widely used. Only one group of phosphates, the trisubstituted (tertiary), neutral esters of H3 PO4 , has found significant use as

synthetic basestocks. These compounds have the general structure: O R⬘

O

P

O

R⬙

O R⵮ 





where R , R , and R are the same or different and are alkyl C4 –C12 , aryl C6 or alkylaryl C7 –C14 . None of the commercially important basestocks contains nitrogen, sulfur, chlorine, or other elements substituted in the R groups. Although metallic or amide derivatives of the partial esters have found use as lubricant additives, all the significant commercial synthetic lubricant basestocks are compounds in which all three R groups are alkyl or aryl moieties containing four or more carbon atoms, hydrogen, and oxygen. Thus, the important phosphate-ester basestocks fall into three broad classes: triaryl, trialkyl, and alkyl aryl phosphates, and the rest of this chapter focuses on these compounds. The triaryl phosphates are the most commercially important products. The earliest products of significance, TCP and TXP, were often referred to as “natural” esters because the cresol and xylenol raw materials came from the distillation of coal. In this group of compounds all three organic groups are usually the same:

of different xylenol isomers, principally 2,4-; 3,4-; and 3,5-xylenol, together with ethyl phenols, etc. The trend toward products with improved hydrolytic stability has led to the use of feedstocks containing increased amounts of 3,5-xylenol [19]. Cresol, xylenol, and phenol can be blended and used to produce mixed esters; cresyl diphenyl phosphate (CDP) is the most significant of these but XDP, etc. have also been produced commercially. During the l960s, “synthetic” analogues of the natural esters were developed from the alkylation of phenol, which reduced both toxicological concerns and production costs. Isopropylphenyl and tertiarybutylphenyl phosphates are now commercially available in a variety of viscosity grades. Because these products are always made from a mixed feedstock of phenol and the respective alkyl phenol, they are also referred to as triphenyl phosphate (TPP), propylated or isopropylphenyl phenyl phosphate (IPPP), and TPP, butylated or tert-butylphenyl phenyl phosphate (TBPP). The structure of diphenyl-para-t-butylphenyl phosphate, the dominant species in a widely used ISO 46 basestock, is as follows:

Diphenyl-para-t-butylphenyl phosphate

Today, commercial production of TCP usually starts with the mixed meta/para isomer feedstock. This is because the presence of the ortho isomer can lead to the production of the highly neurotoxic triorthocresyl phosphate (TOCP). As a consequence the level of the ortho isomer in the feedstock has been significantly reduced over the years and is now normally well below 0.2%. The raw materials for the manufacture of TXP also contain a complex mixture

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All commercial synthetic triaryl phosphate fluid basestocks are mixtures of varying molecular weights. The location of substituents on the phenyl ring can vary between the ortho, meta, and para positions. In the lower viscosity synthetic products, unsubstituted TPP is usually the most significant component species. Increasing the proportion of alkyl phenol in the feedstock increases average molecular weight, viscosity, and the complexity of the mixture but lowers the phosphorus content and specific gravity of the final product. Commercially available trialkyl phosphates are typically symmetrical (R = R = R ). Tri-n-butyl phosphate (TBP) and triisobutyl phosphate (TiBP) are widely used in aircraft hydraulic fluids while tributoxyethyl phosphate (TBEP) and trioctyl phosphate (TOP) are currently of interest as phenol-free antiwear additives. Dibutyl phenyl phosphate (DBPP), also used in aircraft fluids, is the most common alkyl aryl ester. Although a significant patent estate developed on alkyl aryl esters and several of them were used widely at one time as industrial fluid basestocks, there is little significant commercial use of these esters today other than the dibutyl phenyl and the isodecyl diphenyl esters because of their good low temperature properties. Most alkyl aryl esters find

use as flame-retardant plasticizers in the thermoplastics industry.

4.2.2 Production Although the tertiary phosphates are described as esters of H3 PO4 , preparation from the acid gives poor yields because the water produced readily hydrolyzes the ester in the acidic conditions of the reaction. Because of the differences in the reactivity of starting materials and the chemistry of the products, distinct commercial routes have developed to produce triaryl, trialkyl, and alkyl aryl esters.

4.2.2.1 Triaryl phosphates The simplest laboratory preparation of triaryl esters and the most important commercial route is the phosphorylation of an aromatic alcohol — that is, a phenolic compound — with phosphorus oxychloride in the presence of magnesium or aluminum chloride [20]: 3ROH + POCl3

100–200◦ C

−→

(RO)3 P=O + 3HCl

(4.1)

An excess of the phenolic compound is maintained to avoid the presence of the intermediate chloridates, (RO)(Cl)2 P=O and (RO)2 (Cl)P=O, which would reduce yields and produce acidic partial esters during subsequent processing. Prior to the early 1960s, cresylic acids were the phenolic raw materials used in this preparation. The common cresylic acids (cresol, xylenol, and mesitol) have one, two, and three methyl groups on the ring, respectively, in any of the ortho, meta, and para positions. TXP became the most commonly used industrial fluid basestock of the triaryl esters. The range of viscosities required for industrial applications could be achieved by carefully selecting the xylenol isomers used as the starting material. For example, an isomer mixture consisting of mostly 3,5-xylenol gives a higher viscosity than a mixture rich in the 2,6-isomer. Work by the Albright & Wilson Company [21] and the Ciba-Geigy Corporation [22] in the United Kingdom in the 1960s resulted in the development of a more easily controlled and less expensive route to the range of products desired. Work at both companies involved the catalytic alkylation of phenol with propylene or butylene and the subsequent reaction of this “synthetic alkylate” with phosphorus oxychloride. In the synthetic process, the viscosity of the final product can be controlled in either or both of two ways: by the degree of alkylation of the phenol (i.e., by the number of alkyl groups on the phenol ring) and by using a variable, mixed feed of phenol and alkyl phenol to the phosphorylation reaction [23]. As the degree of alkylation increases,

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or the proportion of unalkylated phenol decreases, the viscosity of the product increases. Thermodynamics and steric hindrance determine the order in which the phenols react (phenol is fastest) and thus determine the molecular weight and isomer distribution in the final product. The commercial process is therefore more appropriately described as follows: xROH + (3 − x)R OH + POCl3 → (RO)3 P=O + (RO)2 (R O)P=O + (RO)(R O)2 P=O +(R O)3 P=O + 3HCl

(4.2)

For both the natural and synthetic esters, a variety of refining steps are used to produce the final product. By-product hydrogen chloride (HCl) can be removed from the reaction by heating, use of a partial vacuum, sweeping with an inert gas, or reaction with an organic base such as pyridine. The most common method combines heating and vacuum followed by washing with water to recover the HCl as a by-product in the form of a dilute acid solution. Following the HCl extraction, the crude product is refined. A series of distillation steps removes the unreacted phenols and alkyl phenols for recycling, isolates the refined product, and leaves the catalyst and high-boiling by-products in the still residue [24,25]. The crude product can, if necessary, be re-distilled to remove unreacted raw materials then, in order to remove residual acid and water, either washed with aqueous alkali and dried under vacuum [20] or treated with an adsorbent solid and dried. The foregoing discussion of the production chemistry and raw materials indicates that most commercial triaryl esters are not symmetrical products. The asymmetry in the phosphate-ester molecule is a significant determinant of its physical properties. Symmetrical products are crystalline or waxy solids. Indeed, the only truly symmetrical, pure triaryl phosphate of commercial importance is TPP, which melts at about 49◦ C and is therefore not useful as a fluid basestock. Conversely, controlling the degree of asymmetry produces liquids with varying physical properties, which can be tailored to a variety of application conditions. As implied by Equation (4.2), the asymmetry can be introduced into the molecule by using a mixed feed to the reaction. As long as the reactivity of the phenolic compounds is reasonably close, this method is acceptable, as is the case in the production of cresyldiphenyl phosphate, isopropylphenyl, and t-butylphenyl phenyl phosphates. Also with TCP or TXP, the similar reactivity of the ortho, meta, and para isomers makes the preparative reaction straightforward. Asymmetry can also be introduced into the triaryl phosphate molecule by stepwise reaction of the sodium salt of a phenol with an intermediate chloridate [13]. The following

reaction scheme is one of several possible alternatives: 2ROH + POCl3 → (RO)2 (Cl)P=O + 2HCl

(4.3)

R ONa + (RO)2 (Cl)P=O → (RO)2 (R O)P=O + NaCl (4.4) The properties of the mixtures prepared by these reactions can be quite similar to those of symmetrical triaryl phosphates with similar alkylaryl content. 4.2.2.2 Trialkyl phosphates Trialkyl phosphates can be prepared using reactions similar to those used for triaryl compounds. However, because trialkyls are generally less stable than triaryls, the reaction (Equation [4.1], phosphorylation of an alcohol) is usually carried out at more moderate temperatures. To drive the reaction to completion, greater excesses of alcohol are needed, and the by-product HCl must be removed as rapidly as possible. The higher molecular weight trialkyl phosphates can be purified by stripping the unreacted alcohol, alkaline washing, and distillation drying, in steps similar to those used for the triaryl processes. The lower molecular weight esters, below tripropyl phosphate, can be isolated only by dry techniques because they are soluble in water. Because of the inefficiencies of the aliphatic alcohol phosphorylation process, trialkyl phosphates are commercially produced by the reaction of sodium alkoxide with phosphorus oxychloride: 3RONa + POCl3 → (RO)3 P=O + 3NaCl

(4.5)

In this process, commonly referred to as the alkoxide process, the chloride is rapidly converted to sodium chloride, NaCl, which can then be removed by water washing, with further purification of the phosphate accomplished by distillation under vacuum. Mixed or unsymmetrical trialkyl phosphates can be produced by using mixed alcohol feeds or by stepwise reaction of the intermediate chloridate with an alkoxide as in Equations (4.3) and (4.4). 4.2.2.3 Alkyl aryl phosphates The alkyl aryl phosphates, either alkyl diaryl or dialkyl aryl esters, can be produced by the reaction of the appropriate purified intermediate alkyl or aryl phosphochloridate with the desired alcohol or phenol under reactions and purification techniques similar to those described above. The lower molecular weight dialkyl aryl phosphate esters (e.g., DBPP) are apparently best obtained [26] by the preparation of the dialkyl phosphoryl chloride (dialkyl phosphorochloridate) as in Equation (4.6), which is purified by distillation under reduced pressure. The chloridate

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is then reacted with the sodium arylate in water: (RO)2 (Cl)P=O + R ONa → (RO)2 (R O)P=O + NaCl (4.6) The dialkyl aryl esters can then be isolated and purified by the techniques already described. In the interest of economics, actual commercial processes often vary in some degree from the preceding relatively simple reaction schemes. Such variations often produce mixtures rather than pure products. For example, commercial DBPP may be a mixture containing TPP, TBP, monobutyl, diphenyl phosphate as well as DBPP. These factors need to be kept in mind in the evaluation of a variety of performance characteristics. Much of the process development in recent years on the production of the triaryl phosphate esters has involved improvements in process efficiency [23–28], including development of continuous process steps [29], which have replaced the batchwise operations of some earlier processes. Another focus has been on reducing the level of TPP in synthetic phosphates. TPP, while very oxidatively stable, has poor hydrolytic stability and its presence accelerates the rate of degradation of the fluid in the presence of moisture. In order, therefore, to reduce the TPP content two procedures have been developed. One distills the phosphate ester to reduce the TPP down to ∼2% [30] while the other is a two-step reaction in which pure alkylated phenol is first reacted with phosphorous oxychloride followed by reaction with phenol. This avoids the presence of significant amounts (>5%) of TPP [31].

4.3 PROPERTIES AND PERFORMANCE CHARACTERISTICS 4.3.1 Chemical Properties Chemical inertness is one of the primary attributes of any lubricant or fluid basestock. The fluid should not react with the metals or other materials from which the mechanical system is constructed. Since additives are commonly used, the basestockshould not be reactive with or attacked by other classes of chemical compounds. The trisubstituted phosphate esters, being neutral, have proven chemical stability over a wide temperature range through many years of industrial service. They are generally unreactive with organic compounds and are excellent solvents for most commonly-used lubricant additives. Other aspects of chemical stability for synthetic basestocks — their thermal, oxidative, and hydrolytic stability — are more significant. The following section discusses these latter properties. As noted above, most of the commercially important phosphate-ester fluids are actually mixtures in which asymmetry plays an important role in determining their useful properties. (The alkyl phosphates are exceptions to this rule.) To provide the most practical applications data,

the most commercially important products are emphasized. To facilitate the presentation, the following abbreviations are used for commonly occurring fluid/lubricant products: Triaryl phosphate esters: CDP IPPP

Cresyl diphenyl phosphate Isopropylphenyl phenyl phosphates (TPP, propylated) TBPP t-Butylphenyl phenyl phosphates (TPP, butylated) TCP Tricresyl phosphate TPP Triphenyl phosphate TXP Trixylenyl phosphate (trixylyl phosphate) Trialkyl phosphate esters: TBP Tributyl phosphate (tri-n-butyl phosphate) TBEP Tributoxyethyl phosphate TiBP Triisobutyl phosphate TOP Trioctyl phosphate (tri-2-ethylhexyl phosphate unless otherwise noted) Alkyl aryl phosphate esters: DBPP Dibutyl phenyl phosphate EHDPP 2-Ethylhexyl diphenyl phosphate IDDPP Isodecyl diphenyl phosphate Where appropriate, to further describe the product if it is used commercially as a basestock, the ISO viscosity grade number follows the ester designation. For example, IPPP 46 defines an ISO VG 46 phosphate-ester basestock derived from isopropyl phenol; TBPP 32 defines an ISO VG 32 basestock made from t-butyl phenol. The information presented below attempts to give a concise and accurate summary of the properties and usefulness of commercial phosphate esters. For information on the early technical development of phosphates see reference [18] while the properties of TBP have been thoroughly reported in [32]. Additional physical and chemical data, directed more toward field use of fluids, are contained in several volumes edited by Booser [33,34]. A further in-depth review of the physical and chemical properties, handling, and operating procedures directed toward practical use of phosphate-ester fluids and lubricants is also available [35]. 4.3.1.1 Thermal stability Thermal stability will generally define the temperatures at which a fluid can be used. Although in practice some oxygen is always present in the system, a study of the thermal stability in the absence of oxygen gives a clearer picture of the effect of temperature alone. It is also dependent on both temperature and time, that is, the shorter the time of exposure at a given temperature, the higher the temperature that can be tolerated.

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Over the years, a number of studies [18,36,37] have attempted to define and rank the relative thermal stability of phosphate esters. The general conclusions from these studies indicate that the triaryls are the most stable and the trialkyls the least, with the alkyl aryls intermediate. A more recent attempt to evaluate thermal stability [38] employed thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC). ASTM Methods D-3850 and E-537 respectively, were used, except that the samples were tested under nitrogen to eliminate oxidation effects. The DSC method estimates the “onset of decomposition” as the temperature at which an endotherm occurs when the sample is heated at a constant rate of 10◦ C/min. The TGA method measures the decomposition by determining the weight loss as the sample is heated, and the data are recorded as the temperature at which a given percent weight loss is reached. In both DSC and TGA techniques, the temperature recorded as the “onset of decomposition” could be influenced by evaporation of the most volatile component if the test fluid is a mixture. Evaporation is endothermic in DSC and will result in weight loss in TGA. This is especially true for compounds such as IPPP and TBPP, which are mixtures of monomeric compounds and can contain appreciable amounts of TPP. The DSC data in Table 4.1 show that commercially used triaryl phosphates begin to show an endotherm, whether decomposition or evaporation, over 300◦ C, well above common operating temperatures. TPP content apparently

TABLE 4.1 Relative Thermal Stability of Phosphate Esters Under a Nitrogen Atmosphere (ASTM E-537) by DSC

Phosphate ester TPP TCP TXP CDP TBPP 22–46 IPPP 22–46 EHDPP IDDPP TBP TOP TBEP

Initiation of decomposition (endotherm) temperature (◦ C) —a 333 311 306 338–347 311–314 252 264 283 281 276

a Does not decompose under these conditions. Source: From Shankwalkar, S.G. and Cruz, C., Ind. Eng. Chem. Res., 33, 740–743 (1994). With permission.

has little influence on the data, since it did not decompose below 360◦ C in a similar test conducted in a sealed tube. The three common trialkyls begin to decompose in the 275 to 285◦ C range. The TGA data in Table 4.2 also show that significant weight loss does not begin to occur until well above common system operating temperatures. The data on the commercial IPPP and TBPP fluids show the influence of evaporation of TPP, currently a significant component and the most volatile present in these basestocks. The data in Tables 4.1 and 4.2 support the prior studies regarding the relative stability as well as the practical experience developed over the years, namely, that the triaryl esters are more stable than the alkyl aryl esters and significantly more so than the trialkyl esters. Several studies [18,39–41] of the pyrolysis of phosphate esters have shown that the decomposition products are mainly unsaturated hydrocarbons and acidic phosphate esters. Results are similar with both the trialkyl

and alkyl aryl esters, indicating that the weakest link in the decomposition is the aliphatic carbon–oxygen bond. Again, the triaryl esters are the more stable. Alkylation of the ring in the triaryls tends to reduce the thermal stability but this, in turn, can be affected by the length and branching of the alkyl chain. Overall, all three classes of phosphate esters exhibit sufficient thermal stability for most commercial applications, although the triaryls have achieved the widest use. 4.3.1.2 Oxidative stability The oxidative stability of phosphate esters has proven to be quite high and has therefore encouraged their commercial use. Cho and Klaus [42] investigated the oxidative degradation of trialkyl and triaryl phosphates using the apparatus known as the Penn State Micro-Oxidation Tester. The results of this study (Table 4.3) confirmed again that the triaryl esters are more stable than the trialkyl esters

TABLE 4.2 Relative Thermal Stability of Phosphate Esters Under Nitrogen by TGA (ASTM D-3850) Temperature (◦ C) for

Weight loss (%)

TPP

IPPP 22

IPPP 32

IPPP 46

TBPP 46

TCP

TBP

TBEP

TOP

10 20 30 50 75

261 281 294 310 323

274 292 304 320 334

272 294 307 324 339

265 285 297 313 327

301 320 333 350 365

278 298 310 325 325

154 173 183 196 207

221 242 254 269 279

208 231 242 257 268

Source: From Shankwalkar, S.G. and Cruz, C., Ind. Eng. Chem. Res., 33, 740–743 (1994). With permission.

TABLE 4.3 Oxidative Stability of Phosphate Estersa Phosphate ester TBP TCP TCP TXP TCP TXP DBPP

Time (min) 5 10 30 60 30 30 15 15 360 180

Percent of original product

Temperature (◦ C)

Unoxidized

Oxidized

Evaporated

225 225 225 225 250 250 270 270 250 270

13 19 85 67 57 65 60 55 77 81

6 8 1 2 3 4 5 6 <1 <1

51 73 14 31 40 31 35 39 22 15

a As determined in the Peru State Micro-Oxidation Test apparatus (From Cho, L. and

Klaus, E.E., ALSE Trans, 4, 119–124, (1979). With permission.)

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and that both types, without additives, were more stable than a formulated organic ester aircraft engine lubricant (MIL-PRF-7808). The study showed no evidence of oxidation of the P–O–C bond, but rather that degradation was dependent on the structure of the alcohol/phenol from which the phosphate ester was derived. The higher molecular weight products of the oxidation were shown to be condensation products of the oxidized hydrocarbons. Some commercially available phosphate-ester fluids and basestocks were compared using DSC (ASTM E-537) and TGA (ASTM D-3850) methods in an oxygen atmosphere [43]. These data (Table 4.4) are consistent with

TABLE 4.4 Oxidative Stability of Phosphate Esters Under ASTM E-537 (DSC) and D-3850 (TGA) Methodsa Temperature (◦ C) at

Phosphate ester

Oxidation onset (◦ C)

1% wt loss

5% wt loss

10% wt loss

TBP TiBP TOP TBEP EHDPP IDDPP Triphenyl Tricresyl Trixylenyl IPPP 22c IPPP 32c IPPP 46c IPPP 68c IPPP 100c TBPP 22c TBPP 32c TBPP 46c TBPP 68c TBPP 100c Mineral oild

175 192 160 155 200 165 —b 215 210 215 215 210 210 180 295 290 300 300 305 167

65 84 60 35 90 93 185 170 225 200 201 202 218 224 213 222 227 230 234 155

100 116 169 145 220 213 220 230 260 239 252 265 265 243 262 268 272 275 277 205

115 130 191 170 229 235 235 260 280 263 272 287 288 258 280 286 292 293 295 225

a Oxygen flow, 75 mL/min; temperature 30 to 400◦ C; aluminum sample

container. The data represent the range of values obtained on samples of fluids or basestocks of various suppliers. b Does not oxidize under these conditions. c All these products are complex mixtures containing TPP and the respective alkylphenyl phenyl phosphates. Oxidation onset temperature will depend on the weakest alkyl phenol isomer present; the authors found that the data could be expected to vary by 10◦ C. d ISO 22 solvent-refined paraffinic neutral oil. Source: From Booser, E.R., Ed., Handbook of Lubrication and Tribology, Vol. III: Monitoring, Materials, Synthetic Lubricants, and Applications, CRC Press, Boca Raton, FL, 1994, pp. 269–286; Shankwalkar, S.G. and Placek, D.G., Ind. Eng. Chem. Res., 31, 1810–1813 (1992). With premission.

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earlier studies. In addition to confirming the superior stability of the triaryl esters, the results show the resistance of TPP to oxidation. Since the onset of oxidation depends on the weakest alkyl chain in the mixture, and commercial mixtures will vary, the authors indicate that a 15 to 20◦ C variation in onset temperature could be expected. In the ASTM E-537 test, TPP evaporates before oxidation occurs. Although alkylation of the ring tends to lower the oxidative stability, there appears to be little difference between adding one or two methyl groups, as in tricresyl and trixylenyl esters. On moving to isopropyl groups the situation depends very much on the position of the isopropyl group in the ring with the ortho isomer being the most stable followed by the meta isomer and, much less stable, the para derivatives [35]. The esters derived from butyl phenol are generally the most stable of all to oxidation. Based on the thermal stability and vapor pressure data (see Section 4.3.2), and other practical operating experience, the triaryl phosphates can be confidently used in systems operating at temperatures up to 135◦ C for extended periods, and up to 230◦ C for short periods. 4.3.1.3 Hydrolytic stability Phosphate esters can be considered to be the reaction products of an organic alcohol or phenol and inorganic phosphoric acid. As with most, if not all, esterifications, the preparative reaction can be reversed in the presence of water. That is, hydrolysis will occur. In fact, hydrolysis is the most important consideration in the commercial application of phosphate and other organic esters. As in the thermal and oxidative degradation processes, the hydrolysis reaction will produce acidic products, since it is the –O–C– bond that is attacked: (RO)3 P=O + H2 O → (RO)2 (OH)P=O + ROH (4.7) This hydrolysis reaction proceeds stepwise, first yielding the starting alcohol, phenol, or alkyl phenol and the disubstituted phosphoric acid ester. If the reaction is driven to completion, phosphoric acid and the starting alcohol/phenol will be generated, although lubricant/fluid-operating conditions are rarely severe enough to allow this to occur to any significant extent. Hydrolysis reactions are acid catalyzed, and thus the hydrolytic degradation can be considered autocatalytic: that is, the acid products of hydrolysis further catalyze the decomposition. As hydrolysis is so important in determining both product and system performance, numerous studies have been reported. A variety of factors mitigate the ability to compare different studies as well as to evaluate specific results. Test methods often were designed for mineral oils and employ large excesses of water, which may exaggerate and accelerate the hydrolysis of the ester if the water is

dispersed throughout. Where the water forms a separate, discrete phase there is less contact, and phase transfer of the acid into the aqueous layer may reduce the rate of hydrolysis. Proper attention should be given to the precision of the tests as well as the meaning of the results when applying the tests to chemical compounds of different types. As an example, calculations would show that simply extracting the acidity from a typical phosphate-ester fluid base stock (0.1 to 0.3 mg KOH/g), with no hydrolysis, will yield a water layer acid value high enough to fail the typical criteria of 5 mg KOH in the widely used ASTM D-26l9 “beverage bottle” test. Gamrath et al. [18] studied the relationship of hydrolytic stability to the structure of phosphate esters, with emphasis on alkyl diaryl esters, for 24 h under reflux with distilled water. The authors concluded that the trialkyl and triaryl esters were generally more stable than the alkyl diaryl esters, although structure had a considerable effect. The data showed that higher molecular weight alkyl chains are more stable than chains of lower molecular weight, that branched chains are more stable than straight chains, and that the alkyl dicresyl esters are more stable than the corresponding alkyl diphenyl esters (Table 4.5). While esters of all three types have been successfully used as fluid basestocks, only the TBPP and IPPP esters are important today in industrial uses. In the ASTM D2619 hydrolytic stability test, fluid and water are sealed with a copper strip in a beverage bottle which is rotated slowly at 93◦ C for 48 h. The acidity of both the fluid and water layer is determined and the weight loss of the copper strip is then measured. Producers’ literature [44–46] shows (Table 4.6) that unstabilized phosphates, especially

TXP and the higher viscosity TBPPs, can come very close to passing the requirements. When properly formulated, fluids made from TXP, IPPP, and TBPP readily pass the industry limits. In the practical application and use of phosphate esters, management of hydrolysis becomes the most important control element. While thermal and oxidative degradations can and do occur, hydrolysis from moisture contamination, accelerated by heat and acidic by-products, is the dominant cause of deterioration of phosphate-ester fluids. Conversely, if hydrolysis is kept under control, the phosphate-ester fluid or lubricant can remain useful in commercial equipment for many years without replacement (see Section 4.3.5,). Reports have, for example, been published of the benefits of vacuum dehydration in reducing the water content of phosphates with a very positive effect on the rate of acidity generation and hence on fluid life [47]. Perhaps more useful criteria are shown by previously unpublished data [48] generated using ASTM D-2619 on multiple samples of commercial products and repeated test runs on each sample. The study showed that broad variation in the data could be expected among different operators, and within samples with the same operator from slight procedure variations within the test protocol. However, the summarized and averaged data shown in Table 4.7 provided a clear ranking of the various esters and confirmed

TABLE 4.6 Hydrolytic Stability of Some Commercial Phosphate-Ester Hydraulic Fluids and basestocks (ASTM D-2619)

TABLE 4.5 Hydrolytic Stability of Selected Phosphate Esters

Phosphate ester Tributyl Tri-2-ethylhexyl Tricresyl n-Butyl dipheny] t-Butyl diphenyl n-Octyl diphenyl 6-Methylheptyl diphenyl 2-Ethylhexyl diphenyl n-Octyl dicresyl 2-Ethylhexyl dicresyl

Acid released per mole of phosphate estera 4.0 0.2 1.2 27.8 7.3 14.6 7.6 3.6 4.4 1.7

a Expressed as moles of monobasic acid equivalents.

Source: From Gamrath, H.R., Hatton, R.E., and Weesner, W.E., Ind. Eng. Chem., 46, 208 (1954). With permission.

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Phosphate-ester fluid TCP TXP TBPP 46 TBPP 68 TBPP 100 TBPP 32 gas turbine oil TBPP 46 MIL-PERF-19457D fluid IPPP 46 industrial fluid IPPP 100 compressor oil Standard criteria

Increase Increase Copper in fluid in water weight acidity acidity loss (mg KOH/g) (mg KOH) (mg/cm2 ) 0.10 Nil 0.05 0.09 0.20 0.0 0.03

9.1 Nil 6.17 8.98 11.2 4.21 2.71

0.30 0.03 0.18 0.34 0.45 0.0 0.05

0.05 0.12 0.2 max

1.4 1.3 5.0 max

0.05 0.04 0.3 max

Source: From Great Lakes Chemical Corp., Technical bulletin, REOLUBE® HYD Fire Resistant Fluids, Trafford Park, U.K., 2000; Akzo Nobel Chemicals Inc., Technical bulletin, 88-151 Fyrquel® Fire Resistant Hydraulic Fluids, Chicago, 1995; E.F. Houghton Co., Technical bulletin, Houghto-Safe® 1000 Series Phosphate Ester Fluids, no. 2-276-F 2M, Valley Forge, PA, 1990. With permission.

TABLE 4.7 Hydrolytic Stability of Phosphate Esters (ASTM D-2619) Average water acidity (mg KOH)

Copper weight loss (mg/cm2 )

Unformulated esters TCP TXP IPPP 22 IPPP 32 IPPP 46 IPPP 68 TBPP 22 TBPP 46 TBPP 100 TBEP TBP TOP

12 7 37 24 14 9 25 10 3 250 85 8

1.1 0.5 12 2 0.4 0.1 0.7 0.6 0.5 0.3 1 >0.1

Formulated fluids TXP TBPP 32 TBPP 46 Standard criteria

1 8 3 5.0

0.1 0.1 0.1 0.3

Phosphate ester

trixylenyl, and most other alkylphenyl phenyl phosphates are liquids. Within each series of liquids, the fluid characteristics are as predicted; that is, viscosity, pour point, and boiling point increase as molecular weight increases. The following sections emphasize the properties of the important fluid and lubricant basestocks, with other compounds included to illustrate trends or changes. 4.3.2.1 Vapor pressure and boiling point Vapor pressure and boiling point (or range) play a significant role in the useful operating temperature range of a fluid. Phosphate-ester basestocks generally have very high boiling points as shown in Table 4.8. The trialkyls have the lowest boiling points; TBP, used in aircraft and low temperature formulations, boils at about 284◦ C. The triaryl esters most widely used in industrial fluids have boiling points about 400◦ C and above at atmospheric pressure and over 250◦ C at 10 mmHg. All the triaryl basestocks, except for the ISO 100 grades, contain a significant amount of TPP, and all are mixtures of isomers. Commercial products are more correctly described as having boiling ranges, which are generally between 220 and 270◦ C at 4 mmHg. The vapor pressure of phosphate esters can be calculated from the Clausius–Clapeyron equation [49]:

Source: Placek, D.G., FMC Corp Rept. 6. PAD/T94-016

(a) the relative stability of the ‘cresylic acid’ esters TCP and TXP, (b) the instability of TPP and the consequent improvement in stability of the IPPP and TBPP series as the degree of alkylation and molecular weight increases, and (c) the positive response of phosphate esters to standard additives.

4.3.2 Physical Properties The phosphate esters commonly used as fluid and lubricant basestocks are monomeric molecules and all contain the phosphorus–oxygen–carbon (P–O–C) bond system as the central skeletal structure. While this P–O–C bond structure influences the basic properties, the organic moiety will determine most of the variation in physical properties exhibited by this class of compounds. Manufacturers achieve the range of properties by varying the size and number of the alkyl chains involved, whether alone in the trialkyl esters or attached to the aryl ring in the triaryl esters. In trialkyl esters, as the molecular weight increases, viscosity, boiling point, and pour points or freezing points increase. The triaryl esters present a somewhat different situation, in that the simplest molecule, TPP, is a solid at ambient temperature. As alkyl side chains are introduced, often introducing asymmetry at the same time, the melting point at first declines, giving useful liquids under ambient conditions; for example, cresyl diphenyl, tricresyl,

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log P =

A +B T

(4.8)

where P is the vapor pressure, T is the temperature, and A and B are constants. Table 4.9 contains values for A and B along with the vapor pressures calculated from several forms of Equation (4.8). The commercial triaryl phosphate basestocks (i.e., the IPPP and TBPP esters, ISO grades 22–100) generally have vapor pressures below 1 mmHg at 210◦ C — extremely low for monomeric materials. The phosphate-ester basestocks used commercially are less volatile than mineral oils of similar viscosity and, when properly chosen, will provide excellent performance under most ambient working conditions as well as some low pressure applications. 4.3.2.2 Viscosity Viscosity and its variation with temperature significantly influence the design of equipment the choice and performance of a lubricant/fluid. So much has been written on this subject that additional discussion is not presented here. Among numerous books and articles, The Handbook of Lubrication, Theory and Practice of Tribology [50] is an excellent source. The viscosity of the commercially important phosphate esters covers a wide and useful range (Table 4.10). The triaryl esters are marketed in ISO grades ranging from ISO 22 to ISO 100. Pour points of the triaryl esters generally fall

TABLE 4.8 Boiling Point and Heat of Vaporization of Phosphate Esters Boiling point (◦ C)

Latent heat of vaporization (kJ/mol)

At 760 (mmHg)

At 10 (mmHg)

Trialkyls Methyl Ethyl n-Propyl n-Butyl Isobutyl 2-Ethylhexyl Butoxyethyl

196 215 252 284 264 384 320

155 137 211 220

61.4 62.9 66.6

Triaryls TPP TCP TXP CDP IPPP 22 IPPP 32 IPPP 46 IPPP 68 IPPP 100 TBPP 32 TBPP 46 TBPP 68 TBPP 100

413 427 402 414 365 385 396 407 415 402 416 424 435

254 271 276 265 255 258 262 267 272 260 269 270 271

81.5 86.6–110.8

69.3

325

240 249 185

Alkyl aryls EHDPP IDDPP DBPP

66.2 90–110 90–110 90–110 90–110 90–110 90–110 90–110 90–110 90–110

93.8

Source: From Gunderson, R.C. and Hart, A.W., Synthetic Lubricants, Reinhold, 1962; Booser, E.R., Ed., Handbook of Lubrication and Tribology, Vol. III: Monitoring, Materials, Synthetic Lubricants, and Applications, CRC Press, Boca Raton, FL, 1994, pp. 269–286; Placek, D. and Marino M., in Booser, E.R., Ed., Tribology Data Handbook, Synthetic Oil Properties, CRC Press, Boca Raton, FL, 1997; Great Lakes Chemical Corp., Technical bulletin, REOLUBE® HYD Fire Resistant Fluids, Trafford Park, U.K., 2000; Akzo Nobel Chemicals Inc., Technical bulletin, 88-151 Fyrquel® Fire Resistant Hydraulic Fluids, Chicago, 1995. With permission.

between −20 and 10◦ C. Viscosity index (VI) of the triaryl esters is relatively poor, generally well below 100 and often near zero. The trialkyl esters have lower viscosity and pour points, but superior VIs, compared to the triaryls. The VIs of some trialkyl esters are close to 100, comparable to paraffinic mineral oils. Figure 4.1 summarizes the viscosity/temperature profiles of commercial phosphate-ester hydraulic fluids. The IPPP and TBPP triaryl phosphates products are combined for the purpose of simplifying the figure. The individual

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ISO grades of each class behave quite similarly as temperature changes, and are represented approximately by the lines shown. Suppliers’ literature [44–46] and Table 4.10 provide more specific data points. The useful operating range of either the alkyl or aryl family of esters can be extended by blending chemically or physically. That is, alkyl aryl esters (chemical “blends”) can be prepared by mixing aliphatic alcohols and phenols before phosphorylation, or a trialkyl and a triaryl ester can be physically mixed, to give viscosities, pour points, and VIs better than those of the individual components. Commercially available polymers also can be used to improve the VI of phosphates. The aircraft hydraulic fluid products [51–53] are primary example of the practical application of these techniques. These fluids (Table 4.11), which are 100% phosphate ester-based with a VI improver, have pour points typical of a trialkyl phosphates and high temperature viscosities similar to the triaryl esters. The VI of straight triaryl esters can also be improved with typical polymeric VI improvers. Acrylic, styrenic, and other polymers have been used successfully [33,53,54]. Although they normally have a low VI, phosphate esters possess excellent viscosity stability. The products are monomeric rather than polymeric, and they are based on stable aromatic rings and/or relatively short alkyl chains. Thus, there is little in the molecular structure susceptible to the shearing forces normally found in hydraulic systems and in service phosphate esters can remain without significant changes in viscosity for many years. Phosphate esters can also be blended with other basestocks, synthetic or petroleum, to provide a still broader range of properties [56,57] although aryl phosphates have limited solubility in highly paraffinic basestocks. As equipment is designed to operate at higher pressures, the variation of viscosity with pressure can become important. Table 4.12 shows the variation of viscosity with pressure of an IPPP VG 46 commercial fluid [44]. 4.3.2.3 Other properties A variety of other physical properties must be considered in the use of lubricants and the design of equipment. Tables 4.13 to 4.15 summarize data from a variety of sources, including suppliers’ technical literature [19,33,44–46]. Density and specific gravity (Table 4.13). The unit weight of a fluid influences flow characteristics, the weight of a system, and other factors considered in equipment design. Triaryl phosphates are denser than the trialkyl esters. Within both families, the density and specific gravity decrease as the molecular weight increases, that is, with decreasing phosphorus content. The alkyl aryl esters have intermediate values. Phosphate esters are denser than water and most mineral oils. In a wastewater treatment system, for example,

TABLE 4.9 Calculated Vapor Pressure of Phosphate Estersa Vapor pressure (mm Hg)

Constants

70◦ C

110◦ C

210◦ C

310◦ C

A

B

Equationb

3.02 × 10−6 3.05 × l0–5 7.77 × 10−6 4.25 × l0–5

2.4 × 10−4 1.0 × 10−3 4.0 × l0–4 1.0 × 10−3

0.562 0.921 0.441 0.743

92.14 70.34 43.84 45.09 33 56.15 41.25 45.1 31.2 59.9 35.12 37.4 52.85

14,369.5 12,217.2 12,962.0 11,569.1

29.164 25.203 26.008 23.647

x x x x

11,038.1 11,000.8

22.956 22.584

x x

4,253.0 10,771.2 12,874.3 10,258.7

9.07 22.029 25.687 21.559

y x x x

20.53 8.995 12.51 8.16

x y y y

11.151

z

Triaryl phosphates IPPP 22 IPPP 32 IPPP 46 IPPP 68 IPPP 100 TBPP 32 TBPP 46 TBPP 68 TBPP 10 TPP TCP TXP CDP

1.0 × 10−4 7.69 × 10−5

3.0 × 10−3 2.0 × 10−3

4.68 × 10−4 8.62 × l0–5 7.05 × 10−6 2.4 × 10−4

9.2 × 10−3 2.0 × 10−3 3.6 × 10−4 5.4 × 10−3

1.12 0.831 0.06 0.02 1.8 0.768 0.38 1.39

Trialkyl phosphates TBP TiBP TBEP TOP

0.1325 0.256 6.2 × 10−5 1.1 × 102

1.398 2.648 3.4 × 10−3 0.1251

91.42 157.6 4.35 9.41

472.8 160.8

7,735.0 3,283.1 5,734 3,471.0

0.2698

0.2c <0.1c 26.17

1.6d 0.5d 528.2

3,674.80

Alkyl aryl phosphates EHDPP IDDPP DBPP

0.0205

a Calculated from the Clausius–Clapeyron equation form in the right-most column. b Equation x: ln P = [−A/T ] + B (where T = K, P = mmHg); Equation y: log P = [−A/T ] + B (where T = K, P = mmHg); 10

Equation z: log10 P = [−A/T ] + B (where T = K, P = pascals) (133.3 mmHg Pa).

c At 150◦ C. d At 200◦ C.

Source: From Schulz. W.W. and Navratil, 3. D., Science and Technology of Tributyl Phosphate, Vols. I, IIa, and IIb, CRC Press, Boca Raton, FL, 1984; Booser, E.R., Ed., Handbook of Lubrication and Tribology, Vol. III: Monitoring, Materials, Synthetic Lubricants, and Applications, CRC Press, Boca Raton, FL, 1994, pp. 269–286; Placek, D. and Marino M., in Booser, E.R., Ed., Tribology Data Handbook, Synthetic Oil Properties, CRC Press, Boca Raton, FL, 1997; Shankwalkar, S.G. and Placek, D.G., Ind. Eng. Chem. Res., 31, 1810–1813 (1992); Akzo Nobel Chemicals Inc., Technical bulletin, 88-151 Fyrquel® Fire Resistant Hydraulic Fluids, Chicago, 1995; Placek, D.G. and Keltz, C.J., FMC Corp. Research & Development report PAD/T-94-016, 1995. With permission.

petroleum oil, being less dense than water, rises to the surface and can be skimmed off. Phosphate esters, being denser than either media, fall to the bottom of tanks, collection pits, etc. where arrangements for their removal can be made. In a hydraulic or lubricant system operating on a triaryl phosphate-ester fluid, any significant contamination by water, for example, from a cooler leak, collects on the surface of the fluid (usually in the reservoir) and can be removed by heat or vacuum. Thermal properties. As with density, specific heat (Cp ) is a characteristic property of a material and is important in the design of the heating or cooling requirements of a system. While the specific heat value

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of a phosphate ester varies with temperature, the values lie within a relatively narrow band over a broad temperature range, as shown in Table 4.14. The thermal conductivity of most triaryl phosphate fluids is approximately 0.46 kJ/h/m/◦ C in the temperature range 40 to 90◦ C. The coefficient of thermal expansion between 25 and 75◦ C of these fluids is 6.9×10−4 /◦ C. While some variation may exist between laboratories and among the various esters, the values above are representative of the entire class of commercial triaryl phosphate fluids. Compressibility and bulk modulus. The compressibility of a fluid, or its reciprocal, bulk modulus, is an important factor in hydraulic system performance. A compressible

TABLE 4.10 Viscometric Properties of Phosphate Esters Viscosity (cSt) Phosphate ester TBP TiBP TBEP TOP, tri-2-ethylhexyl Tri-n-octyl DBPP Di-2-ethylhexyl, phenyl EHDPP IDDPP CDP Tri(3-isopropylphenyl) Tri(4-isopropylphenyl) TCP TXP IPPP 22 IPPP 32 IPPP 46 IPPP 68 IPPP 100 TBPP 22 TBPP 32 TBPP 46 TBPP 68 TBPP 100 Aircraft fluid

0◦ C

20◦ C

40◦ C

100◦ C

7 10 26 36

3.9 4.9 12 16

61 220

25.6 19.6 44

2.6 3.0 6.7 7.9 8.4 4.45 8.6 8.6

1,000 1,700 400 990 1,600 7,600 14,400 450 1,500 2,500 9,000 18,000 36

76 170 65 76 140 280 550 72 90 160 290 700 18

1.05 1.12 2.0 2.0 2.5 1.2 2.2 2.25 3.0 3.2 5.53 6.14 3.8 5.2 3.8 4.3 5.2 6.3 6.6 4.0 4.6 5.3 6.3 7.8 3.0

16.5 42.7 53.6 24 43 22 31 43 65 103 24 31 43 65 100 10

Viscosity index 118 90 145 148

Pour point (◦ C) <–90 <–90 –90 –90 –1 <–70

67

35

0 <0 25 20 10 0 <0 35 25 15 5 <0 260

–54 −50 –34 59 50 –28 –20 –28 –22 –18 –11 –8 –30 –23 –18 –11 –5 <−62

Source: From Gamrath, H.R., Hatton, R.E., and Weesner, W.E., Ind. Eng. Chem., 46, 208 (1954); Schulz, W.W. and Navratil, 3. D., Science and Technology of Tributyl Phosphate, Vols. I, IIa, and IIb, CRC Press, Boca Raton, FL, 1984; Placek, D. and Marino M., in Booser, E.R., Ed., Tribology Data Handbook, Synthetic Oil Properties, CRC Press, Boca Raton, FL, 1997; Great Lakes Chemical Corp., Technical bulletin, REOLUBE® HYD Fire Resistant Fluids, Trafford Park, U.K., 2000; Akzo Nobel Chemicals Inc., Technical bulletin, 88-151 Fyrquel® Fire Resistant Hydraulic Fluids, Chicago, 1995; E.F. Houghton Co., Technical bulletin, Houghto-Safe® 1000 Series Phosphate Ester Fluids, no. 2-276-F 2M, Valley Forge, PA, 1990; Exxon Company USA, Technical bulletin HyJet® IV-Aplus Phosphate Ester Aviation Hydraulic Fluid, Houston, TX, 1996. With permission.

fluid will result in sluggish operation, greater energy consumption, and heat build-up. Phosphate esters are less compressible than petroleum oils (Table 4.15) and thereby provide a rapid hydraulic response and efficient operation. Conversely the operation is somewhat ‘harder’ or less elastic and noisier.

4.3.3 Performance Properties Fire resistance and lubrication characteristics are the most important performance parameters associated with phosphate esters and are responsible for their wide use in industrial applications. Although there is variation within the different families of phosphates, these two critical

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properties are inherent in the phosphate-ester structure: phosphate esters are excellent lubricants and the aryl phosphates are the most fire resistant of the moderately priced synthetic anhydrous fluids/lubricants. 4.3.3.1 Flammability Combustion, or fire, is the rapid vapor phase reaction of a fuel with oxygen. Ignition and subsequent burning of any given material depend on a variety of chemical and physical properties of the material and the environment surrounding it. Ease of ignition is influenced by thermal and oxidative stability, vapor pressure, molecular weight, heat of vaporization, and similar factors related to the molecular content and structure. To maintain combustion after

100,000 Triaryl phosphates ISO 100 10,000 ISO 68

Aircraft

ISO 40

hydraulic 1,000

ISO 32

fluid

ISO 22

TOP

100

TBEP

TBP 10 ISO 100 ISO 22 AHF 1 –60

–40

–20

0

40

20

60

80

100

120

Temperature, °C

FIGURE 4.1 Viscosity–temperature relationship for some commercial phosphate esters

ignition, there must be sufficient oxygen and enough heat released to vaporize the fuel. The resistance to ignition and burning, normally termed fire resistance in the fluids/lubricants field, can be measured by a wide variety of methods. Techniques have been developed to provide laboratory screening procedures as well as simulation of practical industrial hazards. These and many other tests fall into one of four categories that attempt to measure either bulk fluid ignition, ignition on a hot surface, ignition of sprays, or ignition when adsorbed on a substrate. Table 4.16 lists the most important tests that have been developed and accepted worldwide. Unfortunately, good performance under one test condition does not automatically mean a similar rating in another and to obtain an overall assessment of fire resistance it is necessary to evaluate fluids under a variety of test conditions, preferably those that are representative of the hazard [58]. Typical flash, fire point, and autoignition temperatures are presented in Table 4.17. It is clear from fire resistance

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data reported in suppliers’ technical literature, as presented in Table 4.18, that phosphate esters readily pass all the commonly specified tests. An important distinguishing characteristic of phosphate esters, which is derived from the presence of phosphorus in the molecule as well as the bond structure, is their heat of combustion. The triaryl phosphates have heats of combustion below 7800 kcal/kg [34,45], whereas mineral oils and other synthetic hydrocarbons are in the area of 9500 kcal/kg. The lower heat release does not support combustion, and phosphate esters are self-extinguishing when the source of ignition is removed. The fluids and lubricants industry has recognized shortcomings in certain fire resistance tests [58], many of which were designed to measure the properties of specific fluids and often failed to adequately discriminate among an ever-widening array of products. Recently, in both the United States and Europe, tests have been developed [59–61] in order attempts to more clearly define

TABLE 4.11 Typical Physical Properties of Phosphate-Ester Aircraft Hydraulic Fluids

Viscosity (ASTM D-445) (cSt) At –65◦ C At 38◦ C At 99◦ C VI Specific gravity 25/25◦ C Pour point (ASTM D-97) (◦ C) Acid. no. (ASTM D-974) Flash point (ASTM D-92) (◦ C) Fire point (ASTM D-92) (◦ C) Autoignition temperature (ASTM D-2155) (◦ C) Vapor pressure at l00◦ C (mmHg) Bulk modulus Coefficient of thermal expansion (per ◦ F)

Type IV [51]

Type V [52]

1363 10.6 3.3 260 0.995 <–62 0.03 178 185 427

1911 9.19 3.13 0.977 –62 0.04 164 183 482

262,000 4.97 × 10−4

7.7 211,000 4.6 × 10−4

TABLE 4.12 Viscosity/Pressure Relationship of a Phosphate-Ester ISO V 46 (IPPP 46) Hydraulic Fluid Pressure (bar) 0 138 276 414 552a 689a 827a

Viscosity (cP) at 37.8◦ C

71◦ C

104◦ C

51.8 70.8 96.8 132 185 260 350

11.7 14.6 18.2 22.7 29 36 45

4.9 5.9 7 8.4 10.5 12 15

a Extrapolated data.

Source: From Great Lakes Chemical Corp., Technical bulletin, REOLUBE® HYD Fire Resistant Fluids, Trafford Park, U.K., 2000, except as noted. With permission.

the differences in fluid spray ignition behaviour. The new methods measure the heat released during combustion and therefore ability to sustain a flame under typical spray conditions. Under the new test conditions, Factory Mutual classifies fluids according to a calculated spray flammability parameter (SFP) based on the heat release values and the critical heat flux to ignition — normally derived from the

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TABLE 4.13 Specific Gravity of Phosphate Esters Phosphate ester

Specific gravity at 20/20◦ C

Trialkyls TOP n-Octyl TBP TiBP TBEP

0.92 0.915a 0.980 0.965 1.020

Alkyl aryls DBPP EHDPP IDDPP

1.04 1.09 1.07

Triaryls CDP TCPb TXPb IPPP 22 IPPP 32 IPPP 46 IPPP 68 IPPP 100 TBPP 22 TBPP 32 TBPP 46 TBPP 68 TBPP 100

1.195 1.172 1.142 1.175 1.151 1.130 1.121 1.140 1.180 1.165 1.155 1.145 1.135

a At 25/25◦ C. b Typical commercial

product,

mixed

isomers. Source: From Gunderson, R.C. and Hart, A.W., Synthetic Lubricants Reinhold, (1962). Booser, E.R., Ed., Handbook of Lubrication and Tribology, Vol. III: Monitoring, Materials, Synthetic Lubricants, and Applications, CRC Press, Boca Raton, FL, 1994, Phosphate esters, pp. 269–286; Great Lakes Chemical Corp., Technical bulletin, REOLUBE® HYD Fire Resistant Fluids, Trafford Park, U.K., 2000; Akzo Nobel Chemicals Inc., Technical bulletin, 88-151 Fyrquel® Fire Resistant Hydraulic Fluids, Chicago, 1995; E.F. Houghton Co., Technical bulletin, HoughtoSafc® 1000 Series Phosphate Ester Fluids, no. 2-276-F 2M, Valley Forge, PA, 1990. With permission.

fire point. Phosphate esters and water glycol fluids are classified as Group 1, the least flammable, with an SFP <5 × 104 . The draft ISO 15029 Part 2 method measures an ignitibility factor and classifies fluids from A (=least flammable: e.g., oil-in-water emulsions) to H (= most

TABLE 4.14 Specific Heat of Phosphate Estersa Between 60 and 150◦ C Specific heat Cp (J/g/K) Phosphate ester

25◦ C

60◦ C

150◦ C

TBP TiBP TBEP TOP EHDPP TPP TCP TXP CDP IPPP 22 IPPP 32 IPPP 46 IPPP 68 IPPP 100 TBPP 22 TBPP 32 TBPP 46 TBPP 68 TBPP 100

1.4 —2.0 –– –– 1.7 1.45 1.5 1.45 1.5 1.5 1.6 1.6 1.6 1.5 1.5 1.6 1.6 1.7

1.58 2.23 2.17 1.97 1.76 1.98 1.85 1.66 1.89 1.93 1.75 1.70 1.84 1.85 1.78 1.78 1.87 1.69 1.94

2.04 –– 2.2 2.2 –– 2.25 2.13 1.88 2.6 2.33 1.99 1.97 2.09 2.10 2.10 1.85 2.11 1.86 2.09

TABLE 4.16 Standard Fire Resistance Test Methods Test Fire point Flash point Autoignition temperature Spray ignition tests Persistence of burning Spray flammability parameter Stabilized flame heat release Spray test–large scale method Manifold ignition Molten metal Wick ignition Linear flame propagation Compression ignition

Method and source ASTM D-92 ASTM D-92 ASTM E-659a ISO 15029 Part 1 Factory Mutual Research Corp. Standard 6930 (2001) ISO/DIS 15029 Part 2 ISO/DIS 15029, Part 3 ISO 20823, Federal test method FTMS 791C, Method 6053.1 Several proprietary tests on lead, aluminum, etc. ISO 14935 ASTM D-5306 U.S. Navy Specn. MIL-PRF-19457D

a Data developed using earlier versions of ASTM D-286 and D-2155

continue to be quoted in trade and other literature. Both these methods give values that arc 25 to 50◦ C higher than the current method (E-659) because of different test vessel geometry and volume.

a Determined by DSC in an unpurged atmosphere under ASTM

D-3947-80. Source: From Booser, E.R., Ed., Handbook of Lubrication and Tribology, Vol. III: Monitoring, Materials, Synthetic Lubricants, and Applications, CRC Press, Boca Raton, FL, 1994, pp. 269–286. With permission.

TABLE 4.15 Bulk Modulus and Compressibility of an IPPP 46 Phosphate-Ester Hydraulic Fluid at 37.8◦ C

flammable: e.g., mineral oil). Triaryl phosphate-ester fluids fall into Group D or E in this system. The third spray test [61] currently being standardized is another large-scale method with fluid pressures up to 200 bar and ignition sources up to 200 kW. This method (ISO 15029 Part 3) measures heat release rates and uses them to calculate combustion efficiency. Reasonable correlation was established between methods DIS/15029-2 and DIS/15029-3 as can be seen in Table 4.19 [61]. Where the methods do differ slightly in their assessment of flammability is with the most flammable fluids as a result of deteriorating precision.

Pressure (bar)

4.3.3.2 Lubricity

69 103 138 207 276 344 689 1034

Bulk modulus (bar × 104 )

Compressibility (bar–1 × 10−5 )

1.95 1.97 1.99 2.03 2.09 2.12 2.34 2.53

5.13 5.08 5.02 4.93 4.78 4.71 4.27 3.95

Source: From Great Lakes Chemical Corp., Technical bulletin, REOLUBE® HYD Fire Resistant Fluids, Trafford Park, U.K., 2000. With permission.

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Phosphate esters have proved to be excellent lubricants in practical applications over many years. A number of early studies of phosphate esters [4–6,63–65] led to their use as antiwear additives in both mineral and synthetic oils, a role that they still play today. Phosphate esters provide boundary lubrication by reacting with ferrous metal surfaces to form iron phosphides and/or iron (poly)phosphates. The actual mechanism is complex and likely to be affected by a number of variables such as the composition of the surface, availability of oxygen, temperature, etc. The latest studies suggest that in addition to the formation of a polyphosphate a carbonaceous layer is formed and this may be providing the lubrication [66].

TABLE 4.17 Flash Point, Fire Point, and Autoignition Temperature of Phosphate Esters Temperature data (◦ C)a Autoignition Flash point (COC)b Fire point temperature Phosphate ester ASTM D-92 ASTM D-92 ASTM E-659 TBP TiBP TOP TBEP DEPP EHDPP IDDPP TPP CDP TCP TXP IPPP 22 IPPP 32 IPPP 46 IPPP 68 IPPP 100 TBPP 22 TBPP 32 TBPP 46 TBPP 68 TBPP 100

165 155 190 190 170 224 240 224 255 225 255 255 255 255 255 255 240 255 255 255 255

182 170 240 230 238 260 310 340 340 340 335 335 335 335 335 340 350 350 350 350

400 476 375 260 >430

635 620 600 540 570 545 500 490 490 590 545 535 525 520

a The data can vary as follows: flash point ±5◦ C fire point and autoignition temperature, 10◦ C. The range can represent differences resulting

from reproducibility and repeatability of the test as well as differences in product tested such as isomer mixture and supplier. b COC Cleveland Open Cup. Source: From Schulz, W.W. and Navratil, 3. D., Science and Technology of Tributyl Phosphate, Vols. I, IIa, and IIb, CRC Press, Boca Raton, FL, 1984; Great Lakes Chemical Corp., Technical bulletin, REOLUBE® HYD Fire Resistant Fluids, Trafford Park, U.K., 2000; Akzo Nobel Chemicals Inc., Technical bulletin, 88-151 Fyrquel® Fire Resistant Hydraulic Fluids, Chicago, 1995; E.F. Houghton Co., Technical bulletin, Houghto-Safc® 1000 Series Phosphate Ester Fluids, no. 2-276-F 2M, Valley Forge, PA, 1990. With permission.

Laboratory data developed on commercial fluids, such as those presented in Table 4.20 (four-ball wear) and Table 4.21 (vane pump test), corroborate the practical lubricant performance. The laboratory data show equal or lower rates of wear than those obtained with petroleum oils and other synthetic fluids. 4.3.3.3 Corrosion and rust inhibition Phosphate esters are not normally corrosive to the metals commonly used in hydraulic and other systems. This is best illustrated by the performance of a number of

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commercial fluids and lubricants in the oxidation/corrosion test, Federal Test Method Standard VV-L-791C, method 5308. Performance data on several phosphate-ester products are presented in Table 4.22 and Table 4.23. However, the decomposition products of oxidation or hydrolysis are “strong” acids and, if allowed to rise uncontrolled, can result in corrosion. Copper and copper-based alloys as well as “soft” metals such as zinc, magnesium, etc. are most susceptible to attack. In order to minimize attack on copper and its alloys, “metal-passivators” such as benzotriazole, can be included in the phosphate-fluid formulation. Maintenance of acid number (TAN) at recommended levels (<0.3 mg KOH/g) can, of course, help to avoid such problems. The rust-inhibiting properties of phosphates can be favorably affected by the presence of acidic impurities; however, in order to provide a consistent level of performance, conventional rust inhibitors are incorporated where necessary. 4.3.3.4 Solvent properties Most phosphate esters are good solvents for other organic compounds including hydrocarbons, alcohols, esters, ketones, and other relatively nonpolar materials. Aryl phosphates are widely used as plasticizers for vinyl, cellulosic, and other resins. This strong solvency can be beneficial in that phosphates can be easily formulated with additives and other basestocks. In addition, phosphate esters used as a co-solvent can improve the solubility of additives, such as metal passivators and antioxidants, in mineral oil and poly (alphaolefin) basestocks [67] while providing antiwear and seal swell performance. Alkyl phosphates are also used as solvents in a variety of applications outside the oil industry, for example, in the extraction of uranium ore, the production of phosphoric acid and in surface coatings, etc. Solvent power also can be a source of problems, as demonstrated by the poor compatibility with a number of common coatings, seals, and hose materials. Care is required in choosing materials of construction (see Section 4.3.5). In systems where phosphate esters replace other fluids, phosphates can be very effective in removing residual sludge and other deposits from internal equipment parts. Preflushing the system or the proper use of filters should be considered in such cases. 4.3.3.5 Additive response Being good solvents, phosphate esters are compatible with a wide variety of commonly used lubricant additives such as metal passivators, antioxidants, corrosion inhibitors, etc. [53,54,68–73]. Although additives are generally beneficial in extending product life they are not always essential and at least one major supplier of hydraulic fluids claims excellent

TABLE 4.18 Performance of Commercial Phosphate-Ester Hydraulic Fluids in Fire Resistance Test Test Fire point (COC) (◦ C)

IPPP 32–68 fluids

TBPP 32–68 fluids

TXP 46 fluid

325—345 250—260 490-–570

330—360 250—260 515—595

340 255 540–590

None None None Self-extinguishes <60 sec No flashing or burning on tube Class I = SPF <5 × 104

Test criteria

Flash point (COC) (◦ C) Autoignition temperature (◦ C) (ASTM D-2155) Spray flammability (ISO 15029-1) Manifold ignition at 704◦ C (ISO 20823) Spray flammability parameter (Factory Mutual 6930) Ignitability factor (ISO/DIS 15029-2) Wick ignition (ISO 14935)

Pass

Pass

Pass

Pass

Pass

Pass

Class I

Class I

Class I

Group E Pass

Group E Pass

Group D Pass

Molten metal at 815◦ C Spark ignition Compression ignition ratio (MIL-PRF- l9457D)

No ignition No ignition 41:1

No ignition No ignition 47:1

No ignition No ignition 42:1

Self-extinguishes in <60 sec No ignition No ignition >42:1

Source: From Placek, D. and Marino M., in Booser, E.R., Ed., Tribology Data Handbook, Synthetic Oil Properties, CRC Press, Boca Raton, FL, 1997; Totten, G.E., Ed., Handbook of Hydraulic Fluid Technology (see Phosphate ester hydraulic fluids by W.D. Phillips), Marcel Dekker, New York, 1997; Great Lakes Chemical Corp., Technical bulletin, REOLUBE® HYD Fire Resistant Fluids, Trafford Park, U.K., 2000; Akzo Nobel Chemicals Inc., Technical bulletin, 88-151 Fyrquel® Fire Resistant Hydraulic Fluids, Chicago, 1995. With permission.

TABLE 4.19 A Comparison of the Relative Fire-Resistance of Different Fluids Types in European Spray Ignition Tests ISO 15029-2 Ignit. Index

Least flammable

ISO 15029-3

HFA

HFC (48% water)

HFC (34% water)

HFDR

HFDU (PGE)

HFDU (POE)

SHC-(PAO)

Min oil

Grp A

Grp B

Grp C

Grp E

Grp H

Grp H

Grp H

Grp H

HFA (a)

HFC (48%) (a)

HFC (34%) (a)

HFDR (b)

HFDU (POE) (c)

Min oil (c)

HFDU (PGE) (c)

SHC (PAO) (c)

Most flammable

Note: (a) Those fluids with no ignition; (b) those fluids with unstable ignition; (c) fluids which readily ignited. PGE = polyglycolether; POE = polyol ester; PAO = polyalphaolefin.

performance in typical industrial applications for additivefree products. In some specialized applications, such as aircraft hydraulic fluids (Table 4.22) and steam turbine lubricants [71–73], additives are frequently used to good effect due to the severity of the application. Where additives are required, hindered phenols and/or aromatic amines act as antioxidants, triazoles are effective metal passivators while corrosion inhibitors in the form of organic acids, their esters and amides are used. Silicones can be used as antifoam agents. Phosphate esters are also

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responsive to acrylate and methacrylate VI improvers but these are only added in cases where the fluid is not conditioned in situ by adsorbent media as the media can remove the polymer. 4.3.3.6 Foaming and air release Foaming tendency and air release can be issues in all hydraulic systems. Commercial phosphate-ester fluids pass frequently specified tests, such as ASTM D-892, which determine the maximum foam height generated under

TABLE 4.20 Four-Ball Wear Tests (ASTM D-4172) of PhosphateEster Fluidsa Fluid Formulated fluids IPPP 46 industrial fluid IPPP 100 compressor lube TBPP 32 gas turbine oil TBPP 46 MIL-PERF-19457D fluid Low temperature hydraulic fluid (alkyl aryl blend) Aircraft hydraulic fluid Unformulated basestocks TBP TiBP TOP TBEP TCP TXP CDP IPPP 22 IPPP 46 IPPP 100 TBPP 22 TBPP 46 TBPP 100

Wear scar diameter (mm) 0.58–0.64 0.54–0.60 0.58–0.64 0.54–0.60 0.60–0.70 0.60–0.70 0.80–0.85 0.95–1.10 0.90–0.94 0.80–0.85 0.58–0.64 0.58–0.64 0.58–0.64 0.64–0.68 0.58–0.64 0.54–0.60 0.60–0.64 0.54–0.60 0.52–0.58

a At 40-kg load, 1200 rpm, for 1 h at 75◦ C.

Source: From Placek, D. and Marino M., in Booser, E.R., Ed., Tribology Data Handbook, Synthetic Oil Properties, CRC Press, Boca Raton, FL, 1997; Totten, G.E., Ed., Handbook of Hydraulic Fluid Technology (see Phosphate ester hydraulic fluids by W.D. Phillips), Marcel Dekker, New York, 1997; Great Lakes Chemical Corp., Technical bulletin, REOLUBE® HYD Fire Resistant Fluids, Trafford Park, U.K., 2000; Akzo Nobel Chemicals Inc., Technical bulletin, 88-151 Fyrquel® Fire Resistant Hydraulic Fluids, Chicago, 1995; Exxon Company USA, Technical bulletin HyJet® IV-Aplus Phosphate Ester Aviation Hydraulic Fluid, Houston, TX, 1996. With permission.

standard air introduction rates as well as the rate of collapse of the foam. Suppliers’ literature [44–46] indicates that there is little difference between the IPPP and TBPP basestocks over the ISO 22 to 100 grade range. All fluids generate less than 50 mL of foam, and complete collapse normally occurs rapidly. Some suppliers may use an antifoam additive to meet this specification. Silicones are effective, but other agents have been employed as well. However silicones must be used with care as they can have an adverse affect on air release (see below). Air release, which is a related phenomenon to foaming, is of increasing concern in the performance of most hydraulic fluids. In this condition the bubbles of air rise

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TABLE 4.21 Performance of Phosphate-Ester Fluids in a V104C Vane Pump Wear Test (ASTM Standard Practice D???) Fluid IPPP 22 IPPP 32 IPPP 46 IPPP 68 TBPP 32 TBPP 46

Weight loss (mg)

Duration (h)

Temperature (◦ C)

Ring

Vane

Total

100 250 100 250 250 100 250 100 100

53 53 60 60 66 72 72 66 66

3.6 6.5 2.5 2.6 8.2 3.7 5.4 2.0 4.3

14.5 15.6 34.8 36.7 8.5 2.0 3.3 5.4 8.5

18.1 22.1 37.3 39.3 16.7 5.7 8.7 7.4 12.8

Source: From Placek, D. and Marino, M., in Booser, E.R., Ed., Tribology Data Handbook, Synthetic Oil Properties, CRC Press, Boca Raton, FL, 1997; Totten, G.E., Ed., Handbook of Hydraulic Fluid Technology (see Phosphate ester hydraulic fluids by W.D. Phillips), Marcel Dekker, New York, 1997; Great Lakes Chemical Corp., Technical bulletin, REOLUBE® HYD Fire Resistant Fluids, Trafford Park, U.K., 2000; Akzo Nobel Chemicals Inc., Technical bulletin, 88-151 Fyrquel® Fire Resistant Hydraulic Fluids, Chicago, 1995. With permission.

very slowly to the surface — or not at all. The problem is greatest when the bubbles are small, when insufficient time is available for them to rise to the surface of the liquid (inadequate tank residence time) or no provision is made inside the tank in the form of baffles, etc. to collect air bubbles. Any surface-active compounds present, for example, oil degradation products, can stabilize the rate of bubble rise. The problem can be exacerbated by the incorporation of antifoams that slow down even further the rate of bubble rise. The presence of air bubbles will obviously increase the rate of oxidation of the fluid and, in the worst conditions, will result in “dieseling” where the bubbles of air, unable to escape from the fluid, are rapidly compressed in the pump. During this process, the temperature of the interior wall of the bubble can increase to very high levels, possibly over 700◦ C, at which level the molecule undergoes complete destruction leading to carbon formation [74] and acid development. The air release behavior of phosphate esters varies from significantly better than mineral oil to inferior depending on the chemistry involved and is highly temperature dependent. This latter effect is demonstrated in Figure 4.2 for the different types of phosphates available. 4.3.3.7 Toxicology Much has been written about the toxicology of phosphate esters over the years. Nevertheless, misconceptions and

TABLE 4.22 Performance of Phosphate-Ester Aircraft Hydraulic Fluid in Standard Tests Results

Industry standard

Thermal stability at l2l◦ C, 168 h, 0.2–0.3% water (Boeing Material Spec. BMS 3-11K) Metal weight change (mg/cm2 ) Steel –0.06 +0.3 max Magnesium 0.54 +5.0 max Copper 0.05 +0.5 max Cadmium-plated steel 0.05 +0.3 max Aluminum 0.02 +0.2 max Total acid number change (mg KOH/g) −0.03 +0.l max Viscosity change (cSt) At 38◦ C 0.53 +1.0 max 0.10 +0.3 max At 99◦ C Corrosion, hydrolysis, and oxidation stability at 82◦ C, 168 h, 0.8% water (Boeing Material Spec. BS 3-11K) Metal weight change (mg/cm2 ) Steel 0.01 Magnesium 0.00 Copper −0.02 Cadmium-plated steel −0.01 Aluminum −0.015 Total acid number change (mg KOH/g) 0.065 Viscosity change (cSt) At 38◦ C 0.08 At 99◦ C 0.07 Four-ball wear test scar diameter (mm) (ASTM D-4172) At 4 kg load 0.21 At 10 kg load 0.34 At 40 kg load 0.65 Flammability tests Pipe wick (cycles) –– VV-L-791, method 352 34 Hot manifold at 704◦ C, VV-L-791, method 6053 No flame Low pressure spray — AMS 3150C Self-extinguishing

+0.1 max +0.2 max +0.4 max +0.4 max +0.l max +0.3 max +3.0 max +l.0 max 0.45 max 0.50 max 0.55-–0.75 25 min No flame Self-extinguishing

Source: From Exxon Company USA, Technical bulletin HyJet® IV-Aplus Phosphate Ester Aviation Hydraulic Fluid, Houston, TX, 1996. With permission.

confusion still prevail. The current situation will therefore be briefly outlined but, as data continue to be produced, the user or potential user of phosphate esters should evaluate the most recent data available. A summary of much of the data available on different phosphates was published in 1998 [75] but more recent studies are referred to below. These will enable correct conclusions to be reached about the appropriate level of concern and the care required in handling and use. There is no doubt that products made today are much safer than those manufactured in the early years when most problems occurred. The use of recent data needs to be emphasized, since much of the early information (about triaryl phosphates in particular) was developed well before toxicological expertise and testing techniques reached today’s level of

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sophistication. Often the purity of a compound or compounds involved in reported investigations was unknown, poorly defined, or incorrect. As will be seen below, one specific cresol isomer has been identified as the source of the most toxic of the triaryl phosphates. Its elimination results in a reduction of toxicity by several orders of magnitude. Assurance of, and confidence in, the composition of compounds being tested is thus a critical factor when assessing the resulting toxicity data of the product, and the appropriateness of its use in an industrial application. It has been known since the early 1900s that exposure to organophosphate compounds can cause toxic effects in animals and humans. This phenomenon has been noted in a variety of compounds including phosphates, phosphites, phosphonates, and others. The effects can be noted visually

TABLE 4.23 Performance of Industrial Phosphate-Ester Hydraulic Fluids in Corrosion/Oxidation Test (Federal Test Method Standard VV-L-591 Method 5308.6)

Properties Conditions Hours ◦C Total acid number increase (mg KOH/g) Viscosity change (%) Metal weight change (mg/cm2 ) Copper Steel Magnesium Aluminum Silver Pass/fail

Limits

IPPP 32 Gas turbine oil

IPPP 46 Industrial hydraulic fluid

TBPP 46 MIL-PRF19457D fluid

IPPP 100 Compressor oil

Low temperature hydraulic fluida

2.0 max

72 175 0.4

72 175 0.16

72 175 1.8

168 150 1.0

72 175 0.14

–5 to +10%

2.3

1.7

13

8.1

7.4

±0.4 ±0.2 ±0.2 ±0.2 ±0.2

–0.007 0.029 0.015 0.015 Nil Pass

0.015 −0.036 −0.029 −0.029 −0.022 Pass

0.051 0.007 0.015 Nil –0.095 Pass

0.01 Nil 0.02 −0.02 0.02 Pass

−0.015 −0.007 Nil Nil –0.007 Pass

a Alkyl aryl blended product.

Source: From Booser, E.R., Ed., Handbook of Lubrication and Tribology, Vol. III: Monitoring, Materials, Synthetic Lubricants, and Applications, CRC Press, Boca Raton, FL, 1994, pp. 269–286; Placek, D. and Marino, M., in Booser, E.R., Ed., Tribology Data Handbook, Synthetic Oil Properties, CRC Press, Boca Raton, FL, 1997; Great Lakes Chemical Corp., Technical bulletin, REOLUBE® HYD Fire Resistant Fluids, Trafford Park, U.K., 2000; Akzo Nobel Chemicals Inc., Technical bulletin, 88-151 Fyrquel® Fire Resistant Hydraulic Fluids, Chicago, 1995. With permission.

60 TBPP TXP IPPP

Air release (mm)

50

40

30

20

10

0 20

35

50

75

95

Temperature (°C)

FIGURE 4.2 Change in air release value with temperature for different arly phosphate types

in a deterioration of motor skills, which develops long after the exposure. Because of this, the effect has generally become known as organo-phosphate-induced delayed neurotoxicity (OPIDN). Neither carcinogenicity nor mutagenicity is involved in the observed effects.

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Johnson [76,77] and Abou-Donia and Lapadulla [78] have reported and reviewed the history, symptoms, and mechanics of OPIDN. The major visible consequence of the delayed neurotoxicity is motor dysfunction, predominantly in the limbs. Triorthocresyl phosphate TOCP has been defined as the one of the more potent OPIDN neurotoxins in humans. The attack generally begins with the inhibition of enzyme activity in the nervous system, leading to eventual damage to the system and impairment of neural transmissions. The degree of recovery, according to these authors, can often be related to the severity of the exposure. Mild exposure does not appear to result in permanent damage. As evidence of OPIDN and the role of TOCP became better defined, industry took extensive steps to reduce or eliminate this isomer from commercial products. For example, TCP is available today with very low levels (<0.2%) of total ortho isomer content and virtually zero TOCP. As a result this material has extremely low levels of neurotoxicity and readily meets industry standards. The IPPP and TBPP esters, widely used as fluid basestocks, exhibit far less OPIDN than the TCP and TXP available through the l960s. The trialkyl and alkyl aryl esters

TABLE 4.24 Results of OECD 301F Manometric Respirometer Biodegradability Tests on Different Types of Triaryl Phosphates

Phosphate chemistry Isopropylphenyl phosphate Tertiarybutylphenyl phosphate Trixylyl phosphate

Degradation after 28 days (%)

Time to reach 60% degradation (days)

Classification (ASTM D-6046)

47 62 29

42 27 54

Pw2 Pw1 Pw2

commercially used today also show little to no neurotoxic effects [79–82]. Any effect seen is often at extremely high “limit” doses. The synthetic triaryl phosphates are practically nontoxic by oral, dermal, and inhalation routes of exposure. Moreover, they are neither irritating to the skin or eyes nor mutagenic [83]. Several trialkyl esters, specifically TBP, TIBP, and TOP, however, are classed as skin irritants. Detailed data are readily available from the Material Safety Data Sheets published by all the various producers and other sources. The perception of phosphate esters is that they are eco-toxic and persistent in the environment. However, both aryl and alkyl esters are either readily or inherently biodegradable. Speed and extent of biodegradation are related partly to the susceptibility to hydrolysis of the individual compounds. Recent biodegradablity data obtained under OECD 301F test conditions using manometric respirometry are shown in Table 4.24. The three different aryl phosphate chemistries were evaluated viz. IPPP, TBPP, and TXP, and the samples chosen were of the same viscosity grade (ISO VG 46). Results show that the TBPP product is classified as readily biodegradable and the other two types as inherently biodegradable. Other eco-toxicological data obtained on an ISO VG 68 IPPP product have demonstrated that this product and others of similar or higher viscosity pose no significant risk to the environment. These data were obtained under water accommodated fraction test conditions, that is, on a saturated solution of the phosphate in water. This is because of the very low solubility of aryl phosphates in water. The results are given in Table 4.25. The excellent performance has resulted in the German Environmental Agency (Umweltbundesamt) approving the use of this material as an additive for rapidly biodegradable hydraulic fluids and chain oils. In Europe, the German water authorities have instituted a water hazard classification scheme based on the toxicity and eco-toxicity performance of the product in an attempt to classify its pollution potential. This system, commonly known as the WGK value, rates products as possessing no hazard to water, a low hazard (WGK 1 rating), a hazard to water (WGK 2) and a severe hazard to water (WGK 3).

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TABLE 4.25 Ecotoxicological Data on an IPPP 68 triaryl phosphate ester Ecotoxicity test LC50 acute fish toxicity EL50 acute toxicity to daphnia IC50 algal growth inhibition EC50 activated sludge inhibition LC50 (emergence) and EC50 (growth) — terrestrial plant growth test

Test method

Results

OECD 203 OECD 202 Pt.1 OECD 201 OECD 2099

>1000 mg/L >1000 mg/L >1000 mg/L >1000 mg/L

OECD 208

Both >100 mg/kg (highest concentration tested)

Phosphate esters, to which these criteria can be applied, will normally be rated WGK I. Some trialkyls (e.g., TBP, TOP), and the lower viscosity triaryl phosphate basestocks (TCP, IPPP/22, TBPP/22, etc.), require certain European Union hazard labels. In the case of synthetic aryl products this regulatory attention appears due to their high TPP content. Products such as TXP and the higher viscosity IPPP and TBPP fluids do not require such labels. The high TPP content of the lower viscosity phosphates causes fish toxicity. This is the reason for all triaryl phosphates (including products that are not fish toxic) being classified as marine pollutants under the International Maritime Organisation regulations. None of the triaryl phosphates that find significant use as basestocks is listed under the regulations of the International Agency for Research on Cancer (JARC), the U.S. Occupational Health and Safety Administration (OSHA), the American Conference of Governmental Industrial Hygienists (ACGIH), or the 1989 U.S. Superfund Amendment and Reauthorization Act Title III (SARA). TBP is not listed by JARC, OSHA, or SARA but does have a threshold limit value (TLV) of 2.5 mg/m3 under ACGIH standards. With correct handling procedures and good industrial hygiene, phosphate esters can be safely used in industrial applications without any significant adverse effect on worker safety, or on the environment.

4.3.4 Maintenance of Systems Some of the performance data discussed above indicate that proper maintenance and control of the mechanical systems can ensure excellent performance and result in exceptionally long fluid or lubricant life. The system maintenance program should involve three broad areas: 1. Design and preparation of the equipment and its components 2. Maintenance programs to preserve the mechanical integrity of the system and prevent contamination of the fluid 3. Operating procedures that include fluid conditioning and periodic chemical analysis of the fluid Good system design is critical to the performance of the fluid as it determines the thermal and oxidative stress levels imposed on the fluid. Poor design will significantly reduce fluid life and increase maintenance costs and downtime [84]. Since phosphate esters are excellent solvents for many organic compounds, supplier recommendations regarding suitable seals, hoses, filters, paints, and other accessory equipment should be followed carefully. Generally [33,36], seals and hoses should be made of a fluoroelastomer, ethylene/propylene, or butyl rubber. Epoxy coatings can be used, but painting of internal surfaces is not recommended. Most common metals can be used to fabricate parts and operating components. Suppliers of phosphate-ester fluids and lubricants normally have detailed recommendations on materials of construction and should be consulted early in the design stage of new equipment or when conversion of older equipment to phosphates is being planned. Hydrolysis presents the greatest risk to fluid stability, so maintenance of low water levels is important. Further, since hydrolysis results in the formation of acidic compounds, which can catalyze further hydrolysis, acid number can be used as an excellent control parameter both to determine the condition of the fluid and the need for in situ purification. Maintenance of low water and acid levels is an operation known as fluid conditioning. This can be most readily accomplished by the use of bypass filters containing fuller’s earth, activated alumina or, most recently, ion exchange resin media [85,86]. Properly designed and maintained, conditioning systems will maintain moisture levels in the fluid below the recommended 0.1% by weight and the acid number below 0.2 mg KOH/g, with only periodic change of the filter medium. The latest of these systems using ion exchange resins has also regenerated degraded fluid to satisfactory condition without removal of the fluid from the system [87–90]. As a result of the water content of the resins it is advantageous to use this type of treatment in conjunction with a means for removing excess. This is normally achieved by either chemical means (molecular sieves) or by the application of a vacuum to the fluid, preferably immediately after the resin treatment. The use

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of a vacuum dehydrator is also beneficial for removing excess air and volatile degradation products from the fluid. Such is the efficiency of this treatment that the first power station (in Switzerland) to try this form of conditioning is still using the initial charge of fluid filled into the turbine hydraulic system in 1979 [91]! In addition to reducing acid levels the resin is also able to remove the metal salts formed in the fluid by the previous use of fullers earth or activated alumina. Figure 4.3 shows the rapid improvement effected by resin on degraded fluid [91]. A number of equipment manufactures have now introduced this technology and widespread use in the power generation industry is being followed by application in the steel and aluminium industries. A number of reports have been published describing practical operating experience with phosphate-ester fluids and lubricants and ways of ensuring trouble-free operation [92,93] while The Handbook of Hydraulic Fluid Technology [35] contains a thorough review of currently recommended operating and maintenance procedures for systems using phosphate-ester lubricants and fluids.

4.4 MANUFACTURE, MARKETING, AND ECONOMICS 4.4.1 Manufacturers Estimated world production capacity for mono- and bisphosphates currently totals about 160,000 metric tones per year (MTPY). Since most companies produce a variety of products at the same plant location and sometimes in common equipment, capacity figures are difficult to assess accurately, but it is estimated that the capacity for the triaryl and alkyl aryl esters approaches 110,000 MTPY or more and about 50,000 tonnes for bisphosphates. Over 80,000 metric tons per year (MTPY) of monophosphate esters are sold worldwide (Table 4.26). Of this total, the triaryl and alkyl aryl esters represent 70,000–78,000 MTPY, with the major trialkyls (TBP, TBEP, and TOP) representing 10,000–15,000 MTPY. The largest use (Table 4.27), consuming 50,000–52,000 MTPY, is as a flame-retardant for plastics, chiefly polyvinyl chloride and polyurethane. Bisphosphates, for example, resorcinol diphenyl phosphate are currently used exclusively as flame-retardants for plastics (about 50,000 MTPY), in this case principally for engineering resins. (Their use as a hydraulic fluid or lubricant basestock is unlikely in view of their very high viscosity and sensitivity to moisture.) The lubricants industry is the next largest consumer of mono-phosphates. It uses about 20,000–26,000 MTPY, mostly as a base stock for industrial and aircraft hydraulic fluids. Other specialty applications include gas and steam turbine lubricants, and compressor lubricants; hydraulic fluids in mining operations and in hydraulic lifts, etc. on aircraft carriers. The isopropylphenyl and t-butylphenyl

NN

Water

0.6

0.12

Ca Mg 12 60 Neutralization No. mgKOH/g

Water %

Ca ppm

Mg ppm

0.5

0.10

0.4

0.08

8 40

0.3

0.06

6 30

0.2

0.04

4 20

0.1

0.02

2 10

10 50

0

0 Dec

Jan

Feb

Mar

Apr

May

1984

FIGURE 4.3 Change in fluid properties at a Swiss power station during early stages of resin treatment

TABLE 4.26 Estimated Worldwide Consumption of Phosphate Esters in 2003 (Thousands of Metric Tons) Region North and South America Europe and Africa Asia Total estimate

Triaryls/ Alkyl aryl

Trialkyls

Bisphosphates

Total

32–34 24–27 14–17 70–78

6–8 3–5 1–2 10–15

7–8 7–9 33–35 47–52

45–50 34–41 48–54 127–145

Source: Authors’ estimates.

TABLE 4.27 Estimated World Market for Phosphate Esters in 2003 (Thousands of Metric Tons) Use Flame retardant for plastics Lubricants/fluids Lubricant additives Other Total estimate

Triaryls/ Alkyl aryl

Trialkyls

Bisphosphates

Total

50–52 16–18 3–6 1–2 70–78

0–1 2–3 0–1 8–10 10–15

47–52 — — — 47–52

97–105 18–21 3–7 9–12 127–145

Source: Authors’ estimates.

phosphates also find wide use as antiwear additives in petroleum and synthetic-based hydraulic fluids, tractor fluids, circulatory oils, and aircraft piston engine lubricants. TCP (1500–2000 MTPY) is used mainly as an antiwear additive in aviation gas turbine lubricants but also by the plastics industry in Japan.

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The largest consumption of tralkyl phosphates outside the aviation industry is in floor polishes as a leveling agent. Smaller volumes are used as antifoam agents (TBP), as process solvents in phosphoric acid manufacture (TOP), and the extraction of uranium and other rare earth metal (TBP) [32].

TABLE 4.28 Major World Producers of Phosphate Esters (All Types) and Their Production Capacity (Thousands of Metric Tons per Year) Producer Chemtura Corp. (previously) Akzo-Nobel Bayer AG Daihachi Chemical Co. Ferro

Location Trafford Park Gallipolis Ferry, WV Bitterfeld Leverkusen Handa, Aichi and Higashi, Osaka Bridgeport, NJ Newport

U.K. U.S. Germany Germany Japan Japan U.S. U.K.

Production capacitya

Productsb

40–50 35–45 8–12 10–20 30–40

1,4 1,2,3,4 1 1,2,3 1,2,4

4–5 3–4

3 3

a Authors’ estimates. b 1, Triaryl phosphates; 2, trialkyls; 3, alkyl aryl phosphates; 4, bisphosphates.

Data on the haloalkyl phosphates, used almost exclusively as flame retardants for textiles, are not included in the above figures. This class is now under threat as an environmental pollutant.

4.4.2 Suppliers Phosphate esters are sold commercially by chemical manufacturers and fluid suppliers/distributors under a variety of trade names in both the fluid/lubricant and lubricant additive markets. Table 4.28 lists the major suppliers and their manufacturing locations. In addition to the companies listed there are also other smaller producers in Russia, Poland, India, and China. A list of commercial product names appears in Table 4.29, which includes fluids that are pure phosphate esters, as well as those in which the phosphate is blended with either petroleum or other synthetic basestocks. Except for the aircraft fluids in which TBP or an alkyl diaryl ester is the major component and power generation, where TXP is widely used, most of the important fluids and lubricants are based on the synthetic IPPP and TBPP triaryl phosphates.

4.4.3 Economics Phosphate-ester hydraulic fluids are more expensive to produce than those based on mineral oil and some of the other more common synthetic basestocks. Costs depend largely on petrochemical raw materials, such as butylene and phenol, and the relatively complex processing and purification procedures. Industrial fluids, such as those commonly used in primary metal refining and fabricating mills, generally sell for three to five times the price of petroleum oils: that is, in the (U.S.) $10 to $15/US gallon range. Other specialized fluids and lubricants are priced up to $26/gallon; the highly

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refined products such as the aircraft and electrohydraulic control fluids can reach over $30/gallon in small quantities. At these prices, phosphate-ester fluids are among the higher priced of the more common synthetic fluids such as organic acid esters and polyalphaolefins. However, they are not as expensive as silicone and fluorocarbon fluids and their price has to be compared against the cost of alternative (mechanical) fire protection and their low life-cycle costs. Phosphate esters provide the highest level of fire resistance and safety when all the moderately priced anhydrous fluids rated as “less hazardous” are considered. Their high resistance to ignition, and their low heat of combustion make them the only self-extinguishing fluids in their price range. Therefore, when personal safety factors and equipment preservation are of paramount importance, phosphate esters are arguably the most cost-effective fluid basestocks currently available. Cost effectiveness is also dependent on the life of the fluid or the frequency of replacement. Phosphate esters can be readily maintained and/or regenerated by on-line conditioning systems. Thus, a user can comply with environmental issues dictating the need to reduce leakage from systems and to minimize disposal quantities. Proper care and maintenance of the system and fluid minimizes top-up costs and virtually eliminates disposal costs, while allowing operation for many thousands of hours (>100,000 h in some instances) between fluid changes.

4.5 OUTLOOK Phosphate esters were among the earliest synthetic basestocks developed and are relatively mature products in many of their market segments. Pressure on operating costs, especially in applications with high fluid leakage, for example, the steel industry, has led to the use of lower cost alternative fluids in many market segments pioneered

TABLE 4.29 Suppliers of Phosphate-Ester Hydraulic Fluids, Lubricants, and Additives Company Supresta (previously Akzo Nobel)

Albright & Wilson, Inc. Bayer AG BPCastrol ChevronTexaco Daihachi Chemical Industry Co. D.A. Stuart Co. ExxonMobil Corp.

Chemtura Corp. (previously)

Fuchs Mineraloelwerke GmbH Houghton International, Inc. Metal Working Lubricants Co. Solutia Pacer Lubricants, Inc. Shell Global Lubricants

Trade namea Fyrquel Syn-O-Ad Fyrtek Fyrlube Duraphos Disflammol Enersyn SFD Anvol PE Phostex –– Dasco HyJet Pyrogard Pyrotec HFD Durad Reolube HYD Reolube Turbofluid Fosfocent Houghto-Safe Metsafe Skydrol Pyro-Safe PE Irus Fluid DR Turbo DR

Types of product Fluids Additives Fluids Fluids Additives Additives Fluids Fluids Fluids Fluids, Additives Fluids Aircraft fluid Fluids Fluids Additives Fluids Fluids Fluids Fluids Fluids Aircraft fluid Fluids Fluids Fluids

a Names listed are trademarks or trade names of the respective com-

panies. A number or letter designation often follows the trade name to further define the product. Some suppliers use the same trade name for fluids made from basestocks other than phosphate esters. Source: From Factory Mutual Research Corp., Factory Mutual System Approval Guide: Equipment, Materials and Services for Property Conservation, Norwood, MA, 2004 and private communication. With permission.

by phosphate esters. In other uses, such as in the aircraft and power generation (electrohydraulic control) markets, where safety is critical and high operating pressures and temperatures are common, use of phosphates as hydraulic fluids has continued to grow. With excellent lubrication performance as well as being fire resistant, phosphate esters have always held promise in other industrial applications. Extensive laboratory and field development effort has, for example, been directed at their use as main bearing lubricants for steam and gas turbines [94–96]. This is as a result of an increased risk of fire as turbine-operating temperatures have increased in the search for greater operating efficiency. Major steam turbine fires, while not common, still occur at a rate of about 1 to 2 per country per year and the repair/outage costs can total millions of dollars. The risk of fire has been further

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increased by the effects of privatization which has caused a major reduction in skilled operators at power stations; an increased use of older units; longer times between overhauls and the outsourcing of maintenance to organizations that may not necessarily have the requisite expertise. In the former USSR the occurrence of fires resulted in the development of phosphates as lubricants for large steam turbines [95]. About 500,000 h of operation on phosphates as bearing lubricants have now accumulated since the 1970s in the CIS in turbines of 220 to 1000 MW. 800 MW units designed to use these fluids are now being installed elsewhere in Asia. A report by the Electric Power Research Institute [97] presents an excellent review of worldwide operating experience with phosphate esters as lubricants for steam turbines. Experience in gas turbines is even more extensive than in steam turbines. The replacement of mineral oil by phosphate esters in combustion turbines started in 1958 in gas pipeline applications [96]. Today, fire-resistant lubricants are used in over 150 pipeline turbo-compressors and the market is set for significant expansion. Although phosphates are more expensive fluids than mineral oil, with the latest on-line conditioning techniques it is now possible to keep the same charge of fluid in the turbine for life and, there are savings to be made on the fitting of mechanical fire protection around the turbine. Insurance companies are also starting to actively promote the concept with their customers. Another concept that may develop over the next few decades is the use of phosphate esters as vapor-delivered lubricants for low heat rejection (adiabatic) engines or the expendable aero-gasturtrine in military applications. This work, pioneered by E.E. Klaus, E.E. Graham, J.L. Duda, and others at Pennsylvania State University and supported by the U.S. Department of Energy and other agencies [98–100], continues to be the subject of active research efforts [101–106] Low heat rejection engines, while expected to achieve high fuel efficiencies with reduced emissions, will place exceptional strain on the thermal stability of the lubricants both in the combustion chamber and in the lubricant sump. Vapor delivery of the lubricant avoids the latter problem, since the bulk of the lubricant can be kept at moderate temperatures until it is delivered to high temperature frictional contact zones (piston ring or turbine bearing). Work to date has shown that triaryl and/or trialkyl phosphate vapors can be delivered directly to the walls of the combustion chamber in very low concentration which, while providing adequate lubrication, will not result in excessive engine exhaust emissions or harmful deposit formation. The concept has been demonstrated on a laboratory diesel engine [103] and on a jet turbine engine at Wright Patterson Air Force Base. Next-generation engine development work is planned by both the U.S. Air Force and several commercial engine manufacturers [107,108] and is of particular interest in aviation because of the potential weight saving.

Phosphate esters may also play an important role as co-components with other synthetics in the lubrication of low-heat-rejection diesel engines being developed as intermediates or alternates to the truly adiabatic engine [101]. This work has been sponsored in part by the U.S. Department of Energy and several industrial companies. When used as quench oils in metal-forming operations, phosphate esters [109,110] can provide health, safety, and performance advantages. Compared to mineral oils, phosphates offer better oxidative stability and longer bath life; lower volatility and lower VI reduce evaporation, misting, and drag-out; superior ignition and fire resistance reduce spattering, fire hazards, and smoke generation. In addition, the phosphate quench oil applies a wear- and corrosion-resistant coating to ferrous surfaces. Another new metal working application involves the use of neutral alkyl phosphates as synergists for sulfurcarriers in cutting fluids. The addition of a relatively small amount of phosphorus has been shown to substantially increase the drill life performance of both neat oil and aqueous-based cutting fluids. This is thought due to the ease of degradation and release of phosphorus to the metal surface. Acid phosphates have traditionally been used in cutting fluids. These are difficult to handle, interact with other additives and, in aqueous applications, are sensitive to hard water. The use of neutral phosphates therefore offers significant technical advantages. In summary, increased emphasis on safety has become a driving force for renewed interest in phosphate esters as the operating conditions of many industrial processes become more severe. The possibility of a long life due to excellent stability and the capacity to be regenerated is an advantage that results in a significant reduction in the quantity released to the environment or being sent for incineration or waste treatment. Ironically, some of the weaknesses noted in the past about phosphates are becoming advantages in the environmental sphere. Esters, such as the trialkyls, which have been dismissed for poor stability, may have advantages in rapid biodegradability and less persistence in the environment. As more is learned of their toxicology and eco-toxicology, phosphates appear to be far less of a health and environmental hazard than has been the perception in the past. Even after more than 50 yr of use in which neutral phosphate esters have contributed significantly toward the safe and efficient operation of industry, research and development is still revealing new potential for these products. Clearly they will remain an important class of industrial chemicals for many years to come.

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32. Schulz, W.W. and Navratil, J.D., Science and Technology of Tributyl Phosphate, Vols. I, ha, and JIb, CRC Press, Boca Raton, FL (1984). 33. Booser, E.R., Ed., Handbook of Lubrication and Tribology, Vol. III: Monitoring, Materials, Synthetic Lubricants, and Applications, CRC Press, Boca Raton, FL, pp. 269–286 (1994). Phosphate esters. 34. Placek, D. and Marino, M., Phosphate esters, in Booser, E.R., Ed., Tribology Data Handbook, Synthetic Oil Properties, CRC Press, Boca Raton, FL (1997). 35. Phillips, W.D., Phosphate ester hydraulic fluids, in Totten, G.E., Ed., Handbook of Hydraulic Fluid Technology, Marcel Dekker, New York (1997). 36. Blake, E.S., Hammann, W.C., Edwards, J.W., Richards, T.E., and Oak, M.R., in Proceedings of the American Chemical Society Division of Petroleum Chemistry Symposium, Cleveland, April 5–14 (1960). 37. Raley, C.F., Jr., Wright Air Development Center, Technical Report 53-337 (1955). 38. Shankwalkar, S.G. and Cruz, C., Thermal degradation and weight loss characteristics of commercial phosphate esters, Ind. Eng. Chem. Res., 33, 740–743 (1994). 39. Barrington, H.E. and Setterquist, R.A., Pyrolsis of Alkyl Phosphates, J. Am. Chem. Soc., 79, 2605–2608 (1957). 40. Noone, I.M., Chem. Ind., 46, 1512 (1958). 41. Lhomme, V., Bruneau, C., Soyer, N., and Brault, A., Ind. Eng. Prod. Rec. Dev., 23, 98–102 (1984). 42. Cho, L. and Klaus, E.E., Oxidative degradation of phosphate esters, ASLE Trans., 4, 119–124 (1979). 43. Shankwalkar, S.G. and Placek, D.G., Oxidation and weight loss characteristics of commercial phosphate esters, Ind. Eng. Chem. Res., 31, 1810–1813 (1992). 44. Great Lakes Chemical Corp., Technical bulletin, REOLUBE® HYD Fire Resistant Fluids, Trafford Park, U.K., 2000. 45. Akzo Nobel Chemicals Inc., Technical bulletin, 88-151 Fyrquel® Fire Resistant Hydraulic Fluids, Chicago, 1995. 46. E.F. Houghton Co., Technical bulletin, Houghto-Safe® 1000 Series Phosphate Ester Fluids, no. 2-276-F 2M, Valley Forge, PA, 1990. 47. Duchowski, J.K., The use of a hydraulic purifier for the conditioning of phosphate ester hydraulic fluids, Lubr. Eng., 52, 817–825 (1996). 48. Placek, D.G. and Keltz, C.J., FMC Corp. Research & Development Report PAD/T-94-016, 1995. 49. Dolby, A. and Keller, R., Vapor pressure of some phosphate and phosphonate esters, J. Phys. Chem., 61, 1448 (1957). 50. Booser, E.R., Ed., Handbook of Lubrication. Theory and Practice of Tribology Vol. 11, CRC Press, Boca Raton, FL (1984). 51. Exxon Company USA, Technical bulletin HyJet® IV-Aplus Phosphate Ester Aviation Hydraulic Fluid, Houston, TX (1996). 52. Solutia Co., Technical bulletin Skydrol® 5 High Temperature Hydraulic Fluid, St. Louis, MO (1996). 53. Deetman, G., U.S. Patent 5,464,551 to Monsanto Co. (1995). 54. Okazaki, M.F., Chan, J.H., Abernathy, S.M., and D’ Souza, A., International Application Number WO 96/17517 to Chevron USA, Inc. (1996).

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55. Phillips, W.D., STLE Synthetic Lubricants Education Course, Phosphate esters presentation, Toronto, May 17–20 (2004). 56. Finger, H.C.S., Stage, C., von Schumann, H., Stack, R., and Fischer, R., East German Patent 324,326 (1991). 57. Akzo Nobel Chemicals Inc., Technical bulletin: Fyrtek® Fire Resistant Hydraulic Fluids, Chicago (1995). 58. Phillips, W.D., Fire resistance tests for fluids and lubricants — their limitations and misapplication, in Reichel, J.R. and Totten, G. E., Eds., Fire Resistance of Industrial Fluids, ASTM STP 1284, ASTM, Philadelphia (1996). 59. Kahn, M.M. and Brandao, A.V., Spray flammability of hydraulic fluids and development of a test method, Factory Mutual Research Corp., Technical Report FMRC 3.1. OTOW3.RC, Norwood, MA, May (1991). 60. Yule, A.J. and Moodie, K., A method for testing the flammability of sprays of hydraulic fluid, Fire Safety J., 18, 273–302 (1992). 61. Simonson, M., Milovancevic, M., and Persson, H., Hydraulic fluids in hot industry: fire characteristics and fluid choice, SP Report 1998:38, Swedish National Testing Institute (1998). 62. Factory Mutual Research Corp., Factory Mutual System Approval Guide. Equipment, Materials and Services for Property Conservation, Norwood, MA (2004). 63. Klaus, E.E. and Fenske, M.R., Fluids, lubricants, fuels and related materials, Wright Air Development Center, Technical Report 55-30, Part 3, November (1954). 64. Bieber, H.F., Klaus, F.E., and Tewksbury, E.J., A study of tricresyl phosphate as an additive for boundary lubrication, ASLE Trans., 11, 155–161 (1968). 65. Godfrey, D., The lubrication mechanism of tricresyl phosphate on steel, ASLE Trans., 8, 1–11 (1965). 66. Saba, C.S. and Forster, N.H., Reactions of aromatic phosphate esters with metals and their oxides, Tribol hett., 12, 2, 135–146, 2002. 67. Placek, D.G. and Rao, A., Enhancing the solubility of lubricant additives with phosphate esters, Society of Tribologists and Lubricating Engineers Annual Meeting, Cincinnati, May 20–23 (1996). 68. Miles, P., U.S. Patent 4,919,833 to Ciba-Geigy Corp. (1988). 69. Mitsui Petrochemical Industries KK, Japan Patent 870,328 (1987). 70. Wright, R.M., U.S. Patent 4,171,272 to FMC Corp. (1979). 71. Dounchis, H., U.S. Patent 4,169,800 to FMC Corp. (1979). 72. Stauffer Chemical Co., U.S. Patent 3,956,154 (1976). 73. Stauffer Chemical Co., U.S. Patents 3,707,500 and 3,674,697 (1972). 74. Roberton, R.S. and Allen, J.M., A study of oil performance in numerically controlled hydraulic systems, Proc. 30th Natl Conf. Fluid Power, 28, 435 (1974). 75. Goode, M.J., Phillips, W.D., and Placek, D.C., Triaryl phosphate ester hydraulic fluids — a reassessment of their toxicity and environmental behaviour, SAE Paper 982004, Milwaukee (1998). 76. Johnson, M.K., Arch. Toxicol., 34, 259 (1995).

77. Johnson, M.K., Organophosphates and delayed neuropathy Is NTE alive and well? Toxicol. Appl. Pharmacol., 102, 385–399 (1990). 78. Abou-Donia, M.B. and Lapadulla, D.M., Mechanisms of organophosphorus ester-induced delayed neurotoxicity: Type I and Type II. Ann. Rev. Pharmacol. Toxicol., 30, 405–410 (1990). 79. Camington, C.D., Lapadulla, D.M., Othman, M., Farr, C., Nair, R.S., Johannsen, F., and AbouDonia, M.B., Assessment of the delayed neurotoxicity of tributyl phosphate, tributoxyethyl phosphate and dibutylphenyl phosphate, Toxicol. Ind. Health, 6, 415–423 (1989). 80. World Health Organization, Environmental Health Criterion 112: Tributyl Phosphate, Geneva, (1991). 81. European Chemical Industry Ecology and Toxicology Center, Joint Assessment of Commodity Chemicals 20: Tris (2-ethylhexyl) phosphate, Brussels, May 1992. 82. European Chemical Industry Ecology and Toxicology Center, Joint Assessment of Commodity Chemicals 21: Tris (2-butoxyethyl) phosphate, Brussels, March 1992. 83. FMC Corp., Technical bulletin: Safety Profiles for FMC Triaryl Phosphate Esters, Report CPG/S/93-020 (1993). 84. Staniewski, J.W.G., The influence of mechanical design of electrohydraulic control systems on fire resistant fluid condition, Lubr. Eng., 52, 255–258 (1996). 85. Brown, K.J. and Staniewski, J.W., Condition monitoring and maintenance of steam turbine generator fire-resistant triaryl phosphate control fluids, Society of Tribologists and Lubricating Engineers Special Publication 27, pp. 91–96 (1989). 86. White, L.R., The care and filtration of a phosphate ester gas turbine lube system, in Advances in Filtration and Separation Technology, Vol. 2, Filtration and Separation in Environmental Control Technology, Gulf Publishing, Houston, TX, pp. 157–168 (1990). 87. Phillips, W.D., U.S. Patent 6, 358, 895, to FMC Corp. (1995). 88. Austin, E.M., Gauthier, C., and Staniewski, J.W.G., Operating experience with ion exchange purification systems for steam turbine control fluids, in Proceedings of the Society of Tribologists and Lubricating Engineers Annual Meeting, Cincinnati, 1996. 89. Phillips, W.D. and Sutton, D.I., Improved maintenance and life extension of phosphate esters using ion exchange treatment, in Proceedings of the 10th International Tribology Colloquium, Technische Akademie, Esslingen, January 9–11, 1996. 90. Duchowski, J.D. et al., Ion exchange/vacuum dehydration treatment: an improved approach for conditioning and reclamation of phosphate ester fluids, Lubr. Eng., 57, 29–34 (2001). 91. Brandt, F.C.J., Braun, D., and Trost, R., Erste Erfahrunden mit einem neuen Reinigungsverfahren für synthetische schwerbrennbarer Flüssigkeiten als Hydraulik und Schmieröle in Turbinenanlagen, Der Maschinenschaden, 57, 194–196 (1984). 92. Anzenberger, J.F., Evaluation of phosphate ester fluids to determine stability and suitability for continued use in gas turbines, Lubr. Eng., 43, 528–532 (1987).

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93. Shade, W.N., Field experience with degraded synthetic phosphate ester lubricants, Lubr. Eng., 43, 176–182 (1987). 94. Hartwig, J., Operating experience with difficultly flammable lubricants in a 10MW back-pressure turbine, VGB Kraftwerktech, 71, 905–911 (1991). 95. Phillips, W.D., Lysko, V.V., and Vilyanskaya, G.D., Recent operating experience in Europe and the Soviet Union with fire-resistant turbine lubricants, in Proceedings of the American Power Conference, Chicago, 1990. 96. Phillips, W.D., Triaryl phosphates: the next generation of lubricants for steam and gas turbines, ASME paper 94-JPGCPWR-64 (1994). 97. Electric Power Research Institute, Evaluation of fire retardant fluids for turbine bearing lubricants, Final Report NP-6542, Project 2969-2, September (1989). 98. Klaus, E.E., Jeng, G.S., and Duda, J.L., A study of tricresyl phosphate as a vapor delivered lubricant, Lubr. Eng., 45, 717–723 (1989). 99. Gunsel, S., Klaus, F.F., and Bruce, R.W., Friction characteristics of vapor-deposited lubricant films, SAE Paper 890148, SP 785, Worldwide Progress on Adiabatic Engines International Congress, Detroit, February 27–March 3, 1989. 100. Klaus, F.F., Duda, J.L., Jeng, J.S., Hakim, N.S., Groeneweg, M.A., and Belnaves, M.A., Vapor phase tribology for advanced diesel engines, in Proceeding of the Coatings for Advanced Heat Engines Workshop, U.S. Department of Energy, Castine, ME, 1987. 101. Weber, K.F., Advanced low heat rejection diesel technology development, in Proceeding of the Annual Automotive Technology Development Contractors Coordinating Meeting, U.S. Department of Energy, Dearborn, MI, October 22–23, 1990. 102. Hanyaloglu, B. and Graham, F.E., Effect of surface condition on the formation of solid lubricating films at high temperatures, Tribol. Trans., 1, 77–82 (1991). 103. Makki, J.F. and Graham, F.E., Vapor phase deposition on high temperature surfaces, Tribol. Trans., 33, 595–603 (1990). 104. Placek, D.G. and Freiheit, T., Progress in vapor phase lubrication technology, 1. Eng. Gas Turbines Power, Trans. ASME, 115, 4 (1993). 105. Graham, E.F., Nesarikar, A.R., Foster, N., and Gavin, J., Vapor phase lubrication of high temperature bearings, Lubr. Eng., 49, 13–718 (1993). 106. Forster, N.H., Jam, V.K., and Trivedi, H.K., Rolling contact testing of vapor phase lubricants, Part I and Part II, Society of Tribologists and Lubricating Engineers Annual Meeting, Cincinnati, May 20–23, 1996. 107. Saunders, J., Vapor phase lubricants take the heat, Lubr. World, 6, 33–36 (1996). 108. Rao, A.M., Vapor phase lubrication: application oriented development, Lubr. Eng., 12, 857– 862 (1996). 109. Placek, D.G., Quenching performance of synthetic phosphate esters as determined by cooling curve analysis, ASM 2nd International Conference on Quenching and Control of Distortion, Cleveland, November 4–7, 1996. 110. Placek, D.G., The use of phosphate ester quench oils for improved antiwear properties and safety considerations, Lubr. Eng., 51, 611–616 (1995).

5

Polymer Esters U. Wallfahrer and Lynnette Bowen CONTENTS 5.1

Introduction 5.1.1 Definition 5.1.2 History 5.2 Chemistry 5.2.1 Chemical Structure of the Polymer Esters 5.2.2 Manufacturing Routes 5.3 Physicochemical Properties of the Polymer Esters 5.3.1 Rheology 5.3.1.1 Viscosity 5.3.1.2 Elastohydrodynamic Film Thickness; Viscosity–Pressure Coefficients 5.3.1.3 Viscosity–Temperature Behavior; Pour Point 5.3.1.4 Viscosity Behavior in Blends 5.3.1.5 Viscosity Under High Shear Rates 5.3.2 Lubricity of the Polymer Esters 5.3.2.1 Inherent Lubricity 5.3.2.2 Synergy with Antiwear/Extreme Pressure Additives 5.3.3 Stability of the Polymer Esters 5.3.3.1 Thermal Stability 5.3.3.2 Oxidative Stability 5.3.3.3 Hydrolytic Stability 5.3.4 Compatibility of the Polymer Esters 5.3.4.1 Compatibility with Other Lubricating Oil Base Fluids and Additives 5.3.4.2 Compatibility with Elastomers 5.3.4.3 Compatibility with Metals and Paints 5.3.5 Health, Safety, and Environmental (HSE) Aspects 5.3.5.1 Biodegradability 5.3.5.2 Toxicology 5.4 Application Areas 5.4.1 Four-Stroke Engine Oils 5.4.2 Two-Stroke Engine Oils 5.4.3 Gear Oils 5.4.4 Metalworking Fluids 5.4.5 Greases 5.4.6 Lubricants with Incidental Food Contact 5.5 Manufacture, Marketing, and Economics 5.5.1 Manufacture of Polymer Esters 5.5.2 Cost-Effectiveness of Polymer Esters 5.6 The Future of Polymer Esters 5.6.1 Four-Stroke Engine Oils 5.6.2 Two-Stroke Engine Oils 5.6.3 Gear Oils; Other Industrial Oils References

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5.1 INTRODUCTION 5.1.1 Definition The name “Polymer Ester” is usually linked to copolymers derived from α-olefins and unsaturated diesters as monomeric units (Figure 5.1). From a chemical point of view they are positioned between typical “monomeric” esters (diesters, polyol esters) and synthetic hydrocarbons such as poly α-olefins (PAOs). There are other polymeric ester-type materials that sometimes are referred to as polymer esters (Figure 5.2): • Condensation products of bi- or polyvalent alcohols with

diacids. These products are correctly named complex esters or complex polyols. They do not have an all-carbon backbone and can be hydrolized back to their monomeric entities in the presence of water. • Copolymers of α-olefins with unsaturated monoesters (acrylate copolymers). These polymers are usually of a much higher molecular weight and are used for instance as viscosity modifiers. In this chapter, the term “polymer ester” solely refers to copolymers of α-olefins and unsaturated diesters.

5.1.2 History The roots of the polymer esters lie in the 1970s, when α-olefins became an ever cheaper raw material by virtue of the polymerization of ethylene, and the chemical industry started to investigate the potential of α-olefin derivatives in various markets. Originally aimed at the application of release agents for thermoplastics, the class of polymer

esters was soon seen to exhibit high load-carrying capacity (unsurpassed at that time), which made them predestined for use as lubricating oil base fluids. During the early 1980s, the first commercial products appeared on the market [1]. They were originally offered as a replacement for brightstock; their high viscosity (15 to 65 mm2 /sec at 100◦ C), relative to typical monomeric esters available at that time, gave two-stroke engine oils an enhanced lubricity. Subsequently, polymer esters were found to give an antiwear boost in four-stroke engine oils. At that time, however, the relatively high price of the polymer esters vs. other synthetic components, together with the oil formulators’ inexperience with optimized blending of these new compounds, prohibited their use on a larger scale. The first major breakthrough of this technology occurred in the late 1980s in the metalworking fluid market, when the use of chloroparaffins was virtually banned in Germany by the German legislation. The high inherent lubricity of the polymer esters in combination with their ability to form powerful synergies with antiwear additives often made these compounds the only viable alternative to chloroparaffins. With the requirements for lubricating oils in combustion engines also becoming more and more stringent, polymer esters started to penetrate this market as well, though initially restricted to premium and racing oils. Today, they are successfully established as a synthetic component for reducing wear in automotive and industrial fluids worldwide.

5.2 CHEMISTRY 5.2.1 Chemical Structure of the Polymer Esters

Hydrocarbon blocks Carbon backbone Ester side groups

FIGURE 5.1 Idealized molecular structure of polymer esters

Complex polyol (alcohol = Neopentylglycole) Hydrocarbon block

Ester group

Acrylate copolymer

FIGURE 5.2 Idealized structures of other polymeric ester-type products

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Polymer esters are copolymers of α-olefins and maleic or fumaric acid esterified with short or medium chain length alcohols. Polymer ester types with long ester side chains (coco, tallow esters) are also commercially available, however these products are solids at room temperature and typically used as wax lubricants or as protective coating for steel rather than as lubricating oil base fluids. The idealized chemical structure of a polymer ester is shown in Figure 5.1. Attached to the hydrocarbon backbone are hydrocarbon side chains and pairs of ester side groups. The ester pairs do interact, imparting to the polymer esters special properties (e.g., high thermal and hydrolytic stability) that differentiate polymer esters for instance from α-olefin–acrylic acid ester copolymers. α-Olefins and unsaturated diesters tend to form alternating copolymers, but not strictly so. By careful choice of reaction conditions and raw materials, it is possible to prepare polymer esters with a very broad polarity range, for instance products with an excess of hydrocarbon units and longer ester side chains that are compatible even with

E-CH = CH-E + In

CH-CH-In E

R-CH = CH2 R-CH-CH2-CH-CH-In

E

E

1

R In

R-CH = CH2 + O

E

O O

2

R

R E-CH = CH-E 2

R-CH = CH2

CH-CH2-CH-CH E

1

+

R⬘-OH

CH-CH2-CH-CH

n

E

E

high viscosity polyalphaolefins, or polymer esters that are water soluble (containing an excess of ethoxylated ester side chains).

5.2.2 Manufacturing Routes Polymer esters are usually produced from α-olefins and maleic or fumaric esters [2,3]. The reaction is a radically induced polymerization process as outlined in Figure 5.3. The unique properties of the polymer esters are achieved by choice of the radical initiator and by adjustment of reaction conditions (e.g., polymerization temperature, dosing rate of monomers). As with PAOs, after the polymerization step the polymer esters contain residual double bonds, which sometimes makes it necessary to hydrogenate the polymer to improve the final stability of the fluid, particularly for the lower molecular weight copolymers. Also unsaturated hydrocarbon monomers like low molecular weight polyisobuenes (PIBs) or even nonhydrogenated low viscosity PAOs can be used. However, yields are usually unacceptably low with these raw materials from an economic standpoint, and as the resulting copolymers do not offer any significant performance advantage over the typical polymer esters, there are no commercial products in the market based on these starting monomers. Another route used to manufacture polymer esters is to begin by reacting an α-olefin with maleic anhydride and subsequently esterifying the intermediate polymeric anhydride with the desired alcohol (Figure 5.4). Polymer esters produced by this method are usually higher in molecular weight or product viscosity [4]. As it is difficult to achieve a complete esterification of the polymeric anhydride these reaction products always have a residual acidity that can be neutralized with amines to give polymer esters with added anti-corrosion properties. For this reason polymer esters based on this manufacturing route are mainly used as additives in metal working fluids.

CH = CH O

O

: maleic anhydride

O

R⬘-OH

: short-, medium chain alcohol

FIGURE 5.4 Alternative synthetic route to the manufacture of polymer esters

Mol. weight

FIGURE 5.3 The chemical reaction mechanism of polymer ester formation

n

E

R-CH = CH2 : a-olefin

E-CH = CH-E: Maleate, Fumarate R-CH = CH2 : a-olefin In : Initiator

Copyright 2006 by Taylor & Francis Group, LLC

CH-CH2-CH-CH O O n O 1

6000 4000 2000 0 5

16 34 70 230 Kinematic viscosity 100°C (mm2/sec)

700

FIGURE 5.5 Average molecular weight vs. kinematic viscosity for the polymer esters

5.3 PHYSICOCHEMICAL PROPERTIES OF THE POLYMER ESTERS 5.3.1 Rheology Rheology is probably the most important property of any lubricating oil base fluid. The viscosity behavior of a lubricant, depending on oil temperature, pressure, and shear rate, is crucial for its ability to form oil films that reduce friction and wear. 5.3.1.1 Viscosity Polymer esters typically are colorless to yellowish viscous liquids. A wide range of viscosities is currently available to the commercial lubricating oil market, ranging from 6 mm2 /sec to more than 700 mm2 /sec at 100◦ C. The average molecular weights Mn range from 700 to in excess of 7000 Da. Figure 5.5 shows the relative molecular weights vs. kinematic viscosities of the polymer esters. The chain lengths of the monomers used to produce polymer esters determine their reactivity toward polymerization and thus the final molecular weight of the polymer esters at given reaction conditions, but they do otherwise have only a limited influence on the final viscosity of the fluid, which is contrary to the case of diesters or

polyol esters, where product viscosity can be significantly influenced by choice of appropriate acids and alcohols. 5.3.1.2 Elastohydrodynamic film thickness; viscosity–pressure coefficients Elastohydrodynamic lubrication occurs between loaded, rubbing nonconforming surfaces as found in systems such as cams and rolling element bearings. In such systems, very high pressures are produced at the rubbing point of the contacts, and these have two important effects. First, they result in local elastic deformation of the surfaces, to produce a small, flattened contact zone, typically 0.1 to 1 mm2 for steel surfaces. Second, the high pressure causes the viscosity of the oil in the contact inlet to increase to many times its normal, atmospheric pressure value. These two effects couple and result in the formation of an “elastohydrodynamic” oil film (EHD film) between the surfaces. The ability of an oil to build an efficient EHD film is a prerequisite to control wear rates and sliding contact fatigue lives [5]. The central film thickness of an oil at very high pressures is proportional to its viscosity–pressure coefficient α [6]. The higher the value of α, the more efficient is the oil under high pressure. Naphthenic mineral oils exhibit a relatively high α value, whereas most synthetic base fluids (e.g., PAOs or diesters) are significantly inferior in this respect. As shown in Figure 5.6, the α-values of polymer esters are more or less equivalent to that of mineral oil. 5.3.1.3 Viscosity–temperature behavior; pour point The viscosity indices (VI) of the polymer esters range from 140 to more than 250, correlating closely to the average molecular weight (i.e., viscosity) of the polymer ester types. Polymer esters, like other synthetic lubricating oil base fluids, show a general trend to higher VIs with increasing molecular weights. The VI of both monomeric esters and polymer esters can be improved by choosing straight chain raw materials (e.g., no branched ester side groups).

Apart from the nonhydrogenated types, the pour point of polymer esters is usually higher than for typical ester base fluids of lower viscosity. The pour points range from approximately −45◦ C for the lower viscosity polymer esters to about −15◦ C for the very high viscous types. Using branched raw materials improve the pour point of the base fluids as against a detrimental effect on the viscosity index. The distribution of the monomers in the ester copolymer (more randomly distributed or more alternating) has an influence on the pour point as well. In practice, this calls for a very careful selection of starting materials and maintenance of reaction conditions to achieve the optimum balance between high viscosity index and low pour point. Hydrogenation always significantly increases the pour point of the fluid. Viscosity data and pour points of some typical polymer esters together with those of other synthetic base fluids are given in Table 5.1. 5.3.1.4 Viscosity behavior in blends In blends with polyalphaolefins or mineral oils, polymer esters exhibit a unique property, namely, a surprisingly low thickening effect, as is demonstrated in Figure 5.7. Other base fluids of comparable viscosity usually result in partly significantly higher viscosities in similar blends. In formulating, this physical benefit also allows the use of higher viscosity polymer ester types (15 to 65 mm2 /sec at 100◦ C) in substantial for example, 5W, or 10W automotive engine oil formulations. With the very high viscosity polymer ester types (300 mm2 /sec and above at 100◦ C), this low thickening effect is even more pronounced: A 40% solution of a 700 mm2 /sec polymer ester in PAO 6 has a lower viscosity than a similar solution of PAO 100 in PAO 6 despite the sevenfold viscosity of the polymer ester compared to that of PAO 100 (Figure 5.8). For this reason, in addition to other performance credits, high viscosity polymer esters have found their use in multigrade automotive gear oils as a successful

Viscosity–pressure coefficient (a)

25 20 15 10 5 0 Polymer ester 15 mm2/sec

Polymer ester 65 mm2/sec

Diester (adipate)

PAO 6

FIGURE 5.6 The viscosity–pressure coefficients of the polymer esters vs. those of other fluids

Copyright 2006 by Taylor & Francis Group, LLC

150 N mineral oil

TABLE 5.1 Viscosity Data and Flow Properties of Some Polymer Esters Compared to Other Synthetic Base Fluids Kinematic Viscosity (mm2 /sec) Base fluid Polymer ester, 6 mm2 /sec Polymer ester, 34 mm2 /sec Polymer ester, 300 mm2 /sec PAO 6 PAO 40 Diisodecyladipate (DIDA) Trimethylolpropane triheptanoate Pentaerythritol tetraisostearate

At 40◦ C

At 100◦ C

Viscosity index

27 340 4300 33 403 15.1 15.0 75.9

5.6 34 300 6.0 40 3.6 3.5 8.4

138 139 225 140 151 136 124 75

Pour point (◦ C) −42 −32 −18 −57 −40 <−70 −60 −55

Pure base fluid Polymer ester blend

Polymer ester 700 mm2/sec

Polyalphaolefin blend

PAO 100

6

6.5 7 7.5 Viscosity 100°C (mm2/sec)

8

0

200

400

600

800

Viscosity 100°C (mm2/sec) 40% in PAO 6

Polymer ester blend

Polymer ester 700 mm2/sec Polyalphaolefin blend

PAO 100

1000

1500

2000 2500 3000 Viscosity –20°C (mPas)

3500 0

5000

10,000

15,000

Viscosity –25°C (mPas)

FIGURE 5.7 The low and high temperature viscosities of a 40 mm2 /sec polymer ester vs. those of PAO 40 in 150 N mineral oil (20% solutions)

replacement for high viscosity PAOs. On the other hand, this low thickening effect restricts the use of very high viscosity polymer esters as viscosity modifiers. Acrylate copolymers of similar viscosities are more efficient in this respect. 5.3.1.5 Viscosity under high shear rates Typical monomeric esters do not change their viscosity under high shear rates; they exhibit Newtonian behavior which means they are shear stable. However, most polymers used in lubricants are non-Newtonian fluids, which means that their viscosity drops under high shear rates either temporarily (i.e., followed by a return to the original viscosity at low shear rates) or permanently (i.e., the viscosity remains lower because the polymer chains have

Copyright 2006 by Taylor & Francis Group, LLC

FIGURE 5.8 The low temperature viscosity of a 700 mm2 /sec polymer ester vs. PAO 100 in PAO 6

experienced physical cleavage under the shear stress). A permanent drop in viscosity is usually not desired in lubricating oils, particularly not in automotive engine oils or gear oils. In spite of their polymeric nature, polymer esters are both temporarily and permanently shear-stable. Even a 700 mm2 /sec polymer ester exhibits a shear loss of less than 1% after 20 h in the taper roller bearing shear test (CEC L-45-T-93).

5.3.2 Lubricity of the Polymer Esters 5.3.2.1 Inherent lubricity All ester-type compounds are known to be good lubricants as a result of their molecular structure; the lone electron pairs of the oxygen atoms of the ester linkages tend to

1 3 4

1 Spinning steel wheel 2 Metal specimen 3 Test fluid 4 Load

FIGURE 5.9 Operation principle of the Reichert Friction and Wear Tester

form electrostatic bonds with the metal surface. The more ester groups present at a given molecular weight, the more polar the ester molecule, and the higher generally the affinity of the ester to metals. Within the field of esters, the class of polymer esters exhibits the highest inherent loadcarrying capacity currently known, because of two special effects: • Their polymeric nature in conjunction with the presence

of many ester side groups in each polymer chain.

Reichert wear scar (150 N oil = 100)

120

2

1 Polymer esters 3 PAOs

100

2 Mineral oils 4 Esters

80 60

2

4 3

40 20

1

0 5

10

20

40

45

50

55

60

65

70

Viscosity 100°C (mm2/sec)

FIGURE 5.10 Reichert test results of some polymer esters compared to other base fluids

P RO

S

S

RO

P

Zn S

OR

S

OR

R = n-or iso-alkyl, aryl

FIGURE 5.11 Chemical structure of zinc dialkyldithiophosphate (ZDDP)

• The ester side groups occur in pairs.

These two effects together are responsible for a very high affinity to metal surfaces, sometimes described as the “caterpillar effect.” The superior inherent lubricity of the polymer esters can be demonstrated in the Reichert Friction and Wear Tester, which offers a simple, quick means of evaluating lubricating oil base fluids. The test machine consists of a rigidly mounted test roll, which is pressed against a revolving friction wheel by means of leverage. The friction wheel is immersed with its lower third in the test fluid, so that there is always sufficient fluid at the contact surface of test roll and friction wheel (Figure 5.9). The crosswise arrangement of the axles of the test roll and the friction wheel results in the formation of an elliptically shaped wear scar; its size indicating the load-carrying capacity of the test fluid. To be able to compare test results, the wear scar of the test fluid is usually reported as a percentage of the wear scar to a reference fluid set to 100%. For oil soluble candidates, the reference fluid is 150 N mineral oil. Figure 5.10 compares the Reichert wear results of the polymer esters to those of other mineral oil and synthetic base fluids. Because product viscosity significantly influences load-carrying capacity (the higher the viscosity, the better the lubricity of a base fluid), the lubricity vs. viscosity of the base fluids is given. As with typical esters, within the class of polymer esters (apart from product viscosity) the lubricity is also dependent on the polarity of the polymer ester types. The greater the number of ester groups incorporated in the ester copolymers, the higher their inherent lubricity.

Copyright 2006 by Taylor & Francis Group, LLC

5.3.2.2 Synergy with antiwear/extreme pressure additives Although the inherent lubricity is an important feature of every lubricating oil base fluid, their synergy with antiwear/extreme pressure (AW/EP) additives is even more important. It is the AW/EP additives in a lubricating oil that are used to prevent detrimental metal–metal contacts under severe conditions of high loads or low speeds of the moving parts, under “extreme pressure” or boundary lubricating conditions. A typical and probably still the most widely used AW/EP additive is zinc dialkyldithiophosphate (ZDDP; Figure 5.11). It is known that many diesters and polyol esters act synergistically with the various ZDDP types, derived from primary, secondary, or aryl alcohols. The resulting lubricity of the combination ester/ZDDP is higher than the sum of the performances of the two single components. The reason for this beneficial behavior of esters has been found to be a complex formation of the esters with ZDDP, resulting in a decrease of the decomposition temperature of the ZDDPs [7]. It is not the ZDDP but rather its in situ created phosphorus- and sulfur-containing decomposition products that are the true wear reducing agents, and thus the formation of these decomposition products at lower temperature means a wider temperature range of AW/EP activity of the ZDDP. The efficient synergy of polymer esters with ZDDP has been explained in terms of the drastic reduction of the decomposition temperature of the ZDDP, which permits

the wear protection of the ZDDP degradation products to start at even lower oil temperatures. This beneficial effect can be demonstrated in the Falex Pin & Vee Wear Test according to ASTM D-2670, as shown in Figure 5.12. In this test, a rotating steel pin is immersed in the test oil and subject to a constant pressure between two Vee-shaped blocks in a “nutcracker” device. The wear is expressed in so-called wear teeth, which is the number of teeth by which the ratchet wheel must be turned to maintain the constant pressure of the Vee-blocks on the pin during the test. If the wear becomes too excessive, a safety pin breaks and stops the test. The synergistic effect of the polymer esters with ZDDPs is efficiently demonstrated in this test. Whereas solutions of ZDDPs or polymer esters alone in mineral oil do not survive the test duration, the synergistic combination ZDDP/polymer ester results in a very low number of wear teeth. Diesters and polyol esters also show this synergy, but not to the same extent (Figure 5.13). Polymer esters display a synergy not only to ZDDPs. Similar boosts in lubricity are found with all kinds of sulfur containing AW/EP additives [8]. Front view

5

5

1 Steel pin Bottom view 2 Holdr 3 Safety pin 4 Vee-blocks 5“Nutcracker” device 5 6 Test fluid

3 2

5.3.3 Stability of the Polymer Esters 5.3.3.1 Thermal stability Typical monomeric esters are known to exhibit a superior thermal stability over mineral oils. Owing to the absence of hydrogen atoms in β-position to the ester linkages, the polyol esters are extraordinarily stable, which makes them suitable for use in jet engine lubricants, where the extremely high requirements with respect to thermal stability can be met only to a limited extent by diesters, and not at all by mineral oils. A gross indication for the thermal stability of a lubricating oil base fluid is its flash point and NOACK volatility (ASTM D-5800). The latter is measured by heating an oil sample at 250◦ C and determining the weight loss in percentage after 1 h. Some typical flash points and NOACK volatilities of polymer esters compared to other synthetic base fluids are shown in Table 5.2. A more precise method than the NOACK volatility test is the thermogravimetric analysis (TGA), where the weight loss of the candidate is recorded vs. time and temperature. The TGA curves of a typical polymer ester together with the curves of other lubricating oil base fluids are shown in Figure 5.14. Most polymer ester types exhibit a thermal stability similar to that of typical diesters or PAOs, however they do not reach the superior stability of polyol esters. For this reason polymer esters are usually not found in jet engine lubricants.

4 4 4

6

5.3.3.2 Oxidative stability 1

1

FIGURE 5.12 Two schematic views of the Falex Pin & Vee wear tester

One of the most important properties of an oil, especially for engine oils, oxidative stability gives a measure of the oil’s ageing characteristics in an oxidative environment. Oil oxidation, which results in a viscosity increase

1% ZDDP in mineral oil

Safety pin breaks before end of test

10% polymer ester in mineral oil 1% ZDDP + 10% polymer ester in mineral oil 1% ZDDP + 10% diester in mineral oil 1% ZDDP + 10% polyol ester in mineral oil 0

20

40

60

80

100

120

Number of wear teeth

FIGURE 5.13 Synergy of a 34 mm2 /sec polymer ester and other esters with a short chain secondary ZDDP demonstrated in the Falex Pin & Vee wear tester (ASTM D 2670)

Copyright 2006 by Taylor & Francis Group, LLC

and sludge/varnish formation on the engine parts by radically induced polymerization processes, is a major limiting factor of the lifetime of an oil. There are many tests available to describe the oxidation characteristics of an oil. Usually the oil is heated to a specified temperature while air is bubbled through the sample at a specified rate. After the test, acid number increase, viscosity increase, and weight loss are determined. Without the addition of antioxidants, diesters as well as polyol esters show inferior oxidation stability to that of mineral oils (group I base stocks), which inherently contain nitrogen- and sulfur-bearing compounds that act as natural radical scavengers. The polymer esters are

TABLE 5.2 Flash Points and NOACK Volatilities (ASTM D 5800) of Some Polymer Esters Compared to Other Synthetic Base Fluids Flash point (◦ C)

Base fluid Polymer ester, 6 mm2 /sec Polymer ester, 34 mm2 /sec Polymer ester, 300 mm2 /sec PAO 6 PAO 40 Diisodecyladipate (DIDA) Trimethylolpropane triheptanoate Pentaerythritol tetraisostearate

5.3.3.3 Hydrolytic stability Hydrolytic stability is a special feature of ester-type base fluids. It is part of the chemical nature of all esters to tend to hydrolyze, to cleave back into their acid and alcohol components, in the presence of water. This reaction is catalyzed be free acids that are formed during the reaction; the hydrolysis is an autocatalytic process. Thus esters should have the lowest acid number possible. Compared to diesters and polyol esters (which usually have acid numbers below 0.1 mg KOH/g), the polymer esters exhibit rather high acid numbers typically around 0.3 mg KOH/g. Nevertheless they are superior to most of the “conventional” esters in terms of hydrolytic stability owing to the special molecular geometry of the polymer ester chains. In a lipophilic environment (e.g., a solution in mineral oil), the ester linkages are “buried” inside hydrocarbon coils derived from the polymer backbone and side chains; the steric hindrance thus imparted protects

NOACK volatility (%)

230

12

250

3

280

0.7

235 272 245 220 250

7 0.8 15 8 1.5

inferior to diesters in this respect, as is demonstrated in the thermo-oxidative stability test according to IP 48 (Figure 5.15). In practice no lubricating oil base fluid is used without the addition of an antioxidant. When blended with antioxidants, polymer esters, like diesters and polyol esters, exhibit oxidative stability superior to that of mineral oils (Figure 5.16). Residual double bonds in the polymer ester chains have a negative effect on their oxidative stability that cannot be completely compensated for by the use of antioxidants. For this reason the lower molecular weight polymer esters are hydrogenated to give the oxidation stability required for their use in automotive engine oils.

100 90

Weight (wt(%))

80 70 60 50 40 30 20 10 0 0

50

100

150

200

250

300

350

400

Temperature Temperature increase: 5 k/min Polyisobutene Polymer ester

Mineral oil Diester

450

Atmosphere: N2

Flow rate: 75 mL/min Polyol ester

FIGURE 5.14 Thermogravimetric analysis of polymer esters and some other lubricating oil base fluids

Copyright 2006 by Taylor & Francis Group, LLC

500

140

Viscosity increase (%)

120 100 80 60 40 20 0 Polymer ester (34 mm2/sec)

Diester

polyol ester

Mineral oil

Conditions: 200°C, 12 h, air flow rate 15 L/h

FIGURE 5.15 Thermo-oxidative stability data according to IP 48 of some lubricating oil base fluids

Viscosity increase (%)

10

5

0 Polymer ester (34 mm2/sec)

Diester

Polyol ester

Mineral oil

Conditions: 200°C, 12 h, air flow rate 15 L/h

FIGURE 5.16 Thermo-oxidative stability data according to IP 48 of base oils in the presence of suitable antioxidants

them from attack by water. This special geometry also stays essentially in place in aqueous emulsions (soluble oils), thus making the polymer esters feasible components of soluble cutting fluids. The hydrolytic stability of a typical polymer ester compared to other esters is shown in Figure 5.17. Hydrolytic stability improves as molecular weight increases. The resistance of polymer esters to hydrolysis is so high that it is not possible to determine a saponification number for these compounds. Even after reflux in alcoholic potassium hydroxide for several hours, no more than approximately two-thirds of the ester bonds present in the polymer ester chains are cleaved.

Copyright 2006 by Taylor & Francis Group, LLC

5.3.4 Compatibility of the Polymer Esters 5.3.4.1 Compatibility with other lubricating oil base fluids and additives As mentioned earlier, polymer esters exist in a wide range of polarities. Most polymer esters based on nonethoxylated alcohols are compatible with mineral oils and commonly used lubricating oil additives. With the very low polarity poly(α-olefins), especially the higher viscosity PAOs, polymer esters with a high degree of ester side groups can cause compatibility problems, in particular at low temperatures. For this reason,

Acid number (mgKOH/g) Polyol ester 3 Diester 2

Polymer ester (34 mm2/sec)

1

0 0h

and tend to become absorbed in the elastomer, swelling the seals. The effect of polymer esters on oil seals is closely related to their polarity and molecular weight. Lower molecular weight types of higher polarity have a sealswelling effect, whereas high molecular weight polymer esters of low polarity may have even a slight seal-shrinking effect. Most polymer ester types however are more or less neutral to the seal materials in use today. 5.3.4.3 Compatibility with metals and paints

48 h

96 h Test duration

144 h

19 2h

FIGURE 5.17 Comparison of a polymer ester and two other esters for hydrolytic stability (total acid number according to ASTM D 2619)

only polymer esters of lower polarity, with a low degree of ester side groups in the polymer chains, are used as blend components with high viscosity PAOs. The polarity of a polymer ester is measured by an infrared (IR) method and is expressed by the ratio of the absorption intensities of the ester carbonyl bond and the hydrocarbon bond (νC=O/C−H ); that is, the higher this ratio, the more polar the polymer ester. Usually all polymer esters with a νC=O/C−H of less than 1.1 are compatible with PAOs. Remark: The nonpolarity index NI (= [total number of C-atoms × molecular weight]/[number of ester groups × 100]), a common formula for calculation of the polarity of a monomeric ester [9], is not applicable to polymer esters. According to this formula, all polymer esters would be extremely low in polarity (which is not the case) because of their very high molecular weight compared to monomeric esters. Apart from the polarity, the molecular weight of the polymer esters as well as the distribution of the hydrocarbon and ester side chains within the polymer chain can influence compatibility. The lower the molecular weight, the better the compatibility of the polymer ester at a given νC=O/C−H with low polarity base fluids. 5.3.4.2 Compatibility with elastomers A lubricating oil base fluid should not chemically or physically attack the elastomer materials used in the manufacture of oil seals designed to prevent leakages. Mineral oil base stocks are almost ideal in their neutral behavior toward seals. Usually synthetic base fluids with a polarity lower than that of mineral oils (e.g., PAOs) tend to exert a sealshrinking/hardening effect on elastomers that results from the extraction of soluble additives from the elastomer. Esters are partly much higher in polarity than mineral oils

Copyright 2006 by Taylor & Francis Group, LLC

Polymer esters like diesters or polyol esters exhibit excellent compatibility with the metals typically used in the manufacture of engine parts, metalworking tools, machined parts, and so on; there are no corrosive or leaching effects. Unlike, for instance, polyalkylene glycols, they do not dissolve paints or coatings of operating machines or shop floors.

5.3.5 Health, Safety, and Environmental (HSE) Aspects In addition to such performance aspects as lubricity or stability, the HSE requirements of a lubricating oil base fluid have become increasingly more important during the recent years. Specifically, lubricating oils should not affect human health or the environment. Particular attention is paid to the effects base oils can have on aquatic media or soils. Major criteria in this respect are the biodegradability of the base fluid as well as its toxicity to fish and bacteria. 5.3.5.1 Biodegradability Biodegradability of a lubricating oil base fluid is usually understood in terms of degradation by bacteria in an aqueous environment, because virtually all the common biodegradability tests are carried out in aqueous media. One of the most widely used tests for lubricating oils still is the CEC L-33-A-94 test, which originally was meant to determine the biodegradability of two-stroke outboard engine oils in lakes. Principally the test is based on measuring the disappearance of organic carbon by monitoring the infrared absorption of the carbon–hydrogen bonds after 21 days. Another frequently used biodegradability test is ASTM D-5864 (Aerobic Aquatic Biodegradation of Lubricants), which measures the ultimate biodegradability by carbon dioxide evolution. This test usually gives lower biodegradability figures than the CEC test. Various monomeric esters show good to excellent biodegradability in these tests; natural esters for example are often completely degraded within a few days. Lack of biodegradability is one of the weak points of the majority of compounds in the polymer ester range. Apart from the very low viscosity types, they usually

Polymer ester 6 mm 2/sec

Polymer ester 16 mm 2/sec

Polymer ester 65 mm 2/sec

PAO 40

Mineral oil (150 N)

Diisodecyl adipate (DIDA)

0

10

20

30

40

50

60

70

80

90

Biodegradability (%), according to CEC L-33-A-94

FIGURE 5.18 Biodegradability of polymer esters compared to other base fluids

exhibit an inherent but limited biodegradability, comparable to that of PAOs or mineral oils. As one would expect, the biodegradability rapidly decreases with increasing viscosity or molecular weight, respectively (Figure 5.18). However, in combination with other base fluids a surprisingly high biodegradability of the whole system is sometimes found [10]. 5.3.5.2 Toxicology The polymer esters, like most diesters and polyol esters, are regarded as harmless to man and the environment. They have very high LD50 figures. Actually it was not possible during the LD50 tests to induce any clinical symptoms on the test animals even at very high feeding rates of polymer esters [11]. Based on these results various polymer esters are approved by FDA for use in lubricating oils with incidental food contact in certain applications [12]. Polymer esters do not irritate skin or eyes and show no mutagenic activity. According to tests with selected polymer ester types, they are not skin sensitizing. Their toxicity to fish, daphnia, and bacteria is low. The whole class of polymer esters received a ranking of 1 in the German water-endangering class system (WGK), which is the lowest possible ranking in this system.

their costs. Included are all types of automotive lubricants as well as industrial fluids and greases. In less demanding areas (e.g., hydraulic fluids, compressor oils), polymer esters are usually not used.

5.4.1 Four-Stroke Engine Oils Due to their powerful synergy with AW/EP agents, the polymer esters are proven to give especially efficient wear reduction in four-stroke engine oils, which in practice results, for instance, in very low cam nose wear. Based on their special comb-like structure with unpolar as well as polar side groups, they also assist in keeping engines clean, an effect that is appreciated in particular in diesel engine oils. However, polymer esters like all other esters belong to the API Base Oil Group V which does not allow any base fluid interchangeability or read-across into other viscosity grades. This is thought to be one of the reasons why esters in general today are less frequently used in synthetic fourstroke engine oils. There are also limited wear issues with current state-of-the-art four-stroke engine oils (which however might change in future, see Section 5.6.1) . For this reasons polymer esters are more usually applied in racing oils or niche oils without API or ACEA approval.

5.4.2 Two-Stroke Engine Oils 5.4 APPLICATION AREAS Polymer esters are used in areas calling for high lubricity and stability, where their performance benefits outweigh

Copyright 2006 by Taylor & Francis Group, LLC

Their inherently high load-carrying capacity makes the polymer esters a favored base fluid for semi-synthetic and synthetic two-stroke motorbike engine oils fulfilling JASO

FC or ISO-L-EGD specifications. Another benefit is their especially clean burning without giving rise to smoke or hazardous fumes that enables the formulation of two-stroke engine oils with exceptionally high smoke indices. On the other hand, due to the lack of biodegradability of the polymer esters they find only limited application in two-stroke oils meant for use in environmentally sensitive areas, like in oils for lawnmowers and other garden equipment or in outboard engine oils, especially in Germany or Scandinavia where these oils must be readily biodegradable by legislation.

5.4.3 Gear Oils The performance requirements for multigrade automotive gear oils (in particular in the heavy-duty sector) have become more stringent over the past years, especially with respect to oil stability (to achieve fill-for-life). In this respect, high viscosity polymer esters are comparable to high viscosity PAOs that are commonly used in this application, and offer a better compatibility with lubricating oil additives. In addition they impart an improved lubricity enabling gear oils running at lower peak temperatures [13]. As a consequence in recent years the high viscosity polymer ester types have gained an increased market share in both automotive and industrial gear oils.

soluble oils (emulsions), and on the other hand in fluids that are less hazardous to operators and the environment (substitution of chloroparaffins, secondary amines etc.). Other driving forces have been the need for better performing fluids for more demanding operation conditions, to ensure extended tool life, and to accommodate higher cutting/forming speeds (i.e., better productivity), and more stringent requirements on the machined parts (e.g., narrower tolerance, better surface finish). Polymer esters are widely used in high performance, heavy-duty metalworking fluids. In this area, their biostability is an advantage. In soluble oils, this property of the polymer esters together with their resistance to hydrolysis, which prevents salt formation, assists in achieving increased fluid life in use with emulsions. The key advantage of polymer esters however again is their inherent load-carrying capacity that results in very low tool wear and, therefore, longer tool life ([14], Figure 5.19). These performance benefits are not accompanied by the disadvantages other traditional AW/EP additives impart, like for instance sulfurized compounds (lack of thermal stability → smell; copper corrosion), chloroparaffins (HCl formation → rust; waste disposal costs), passive extreme pressure (PEP) agents (high alkalinity, difficult metal degreasing), or ZDDP (salt/residue formation).

5.4.4 Metalworking Fluids

5.4.5 Greases

The quality of metalworking fluids has improved dramatically over the past years, which has resulted on the one hand in longer fluid lifetimes of both neat oils and

Polymer esters find an extended use in high performance greases, yielding homomorphic greases with good Newtonian behavior. In this respect they perform more like

Tool wear vs. running time Drilling 250

200

mm

150

without ester

100

0.5% TMP-oleate 0.5% polymer ester

50

0 0

0.5

specimen: tool: HC/TiN (DIN)

1

1.5 2 Running time (m)

2.5

3

3.5

4

Drilling conditions : 1170 rpm 25 m/min

FIGURE 5.19 Tool wear results obtained on a CNC cutting machine of some finished soluble oils. Apart from esters no other AW/EP additives were present

Copyright 2006 by Taylor & Francis Group, LLC

a polyalphaolefin rather than an ester, especially in aluminum complex greases where the incorporation of esters can pose problems. The main reason for using polymer esters again is their synergistic effect in boundary lubrication with thickeners as well as AW/EP additives, providing significant improvements of AW/EP properties in heavy load formulations [15].

5.6 THE FUTURE OF POLYMER ESTERS

5.4.6 Lubricants with Incidental Food Contact

5.6.1 Four-Stroke Engine Oils

The United States Food and Drug Administration (FDA) is maintaining a list of substances that are approved as components for lubricants likely to have incidental food contact. This list is published in the “Code of Federal Regulations” CFR 21, Act 178,3570. Also outside the United States most lubricants meant for incidental food contact are based only on components that are part of this list. The finished lubricating oil formulations (so-called H1 oils) today are certified by the National Sanitary Foundation (NSF). There are hardly any esters listed in CCR 21, Act 178,3570. Also polymer esters are not included; however there is an exemption letter from FDA allowing the use of several polymer esters in lubricating oils with incidental food contact in certain applications [12]. Based on this exemption letter these polymer esters are registered by NSF in the category HX [16] and thus are increasingly used in food-grade oil applications, mainly industrial gear oils and greases.

The current use of polymer esters in four-stroke engine oils is restricted to racing oils and niche oils without API or ACEA approval, for reasons explained in Section 5.4.1. However, due to the concern of poisoning of automotive catalysts, phosphorus, and sulfur levels are predicted to come further down in future engine oil specifications (e.g., ILSAC GF 5), making it necessary to find a replacement for ZDDPs which are ubiquitous in engine oils because of their antioxidancy and AW/EP-performance, but unfortunately being a major phosphorus source. Combinations of polymer esters with low levels of ZDDPs or phosporus-free additives (e.g., molybdenum dithiocarbamates) are proven to work well both in terms of antioxidancy and wear protection [8]. This could make polymer esters attractive also for future mass market engine oils.

5.5 MANUFACTURE, MARKETING, and ECONOMICS 5.5.1 Manufacture of Polymer Esters The only supplier of the polymer esters is Akzo Nobel bv, a multinational chemical company with headquarters in The Netherlands. Since the technology for making polymer esters is covered by patents [3,4], no other supplier is expected to emerge on the market in the foreseeable future.

The market for polymer esters has constantly increased during the last decade. With performance requirements especially for automotive engine oils becoming more and more stringent, the justification for the use of expensive synthetic polymer esters is likely to increase further. The outlook for the future, given by application is as follows:

5.6.2 Two-Stroke Engine Oils Polymer esters are base fluids of choice for two-stroke engine oils, however, as explained in Section 5.4.2, restricted to motorbike oils. For several years now there is a trend away from two-stroke motorbikes toward bikes with four-stroke engines. Apart from special friction requirements the engine oil specifications for these engines are similar to typical four-stroke gasoline engine oils. Thus there is currently no need to use polymer esters in these oils and it is expected that their use in two-stroke motorbike oils will come down in line with the slowly declining two-stroke engine oil market.

5.5.2 Cost-Effectiveness of Polymer Esters Polymer esters are at the top end of the market compared to other synthetic lubricating oil base fluids (Table 5.3). However, their outstanding properties justify their use, either by allowing the substitution of other components by polymer esters at a lower treat rate without losing performance, or by acting as a problem solver, especially in demanding areas like heavy-duty metalworking fluids.

5.6.3 Gear Oils; Other Industrial Oils Both automotive and industrial gear oils are applications where synthetic fluids will more and more dominate over mineral oil based fluids. Accordingly, the existing use of polymer esters (especially of the higher viscous types) will grow further. Another growing market should be the use in industrial gear oils and greases for food processing.

TABLE 5.3 Relative Prices of Lubricating Oil Base Fluids Fluid

Mineral oil

Polyisobutenes

Polyalkylene glycols

PAOs

Diesters

Polyol esters

Polymer esters

1

2–3

2–4

2–7

2–5

3–7

5–10

Relative price

Copyright 2006 by Taylor & Francis Group, LLC

The market share of polymer esters in metalworking fluids is flat to slowly growing in most European countries, as the replacement of chloroparaffins in these areas is largely concluded. In the United States and the Far East the market should further grow, depending whether and when chloroparaffins will be phased out.

REFERENCES 1. Akzo Chemicals bv, brochure, Ketjenlube 115, 135, 165 (1984). 2. Beck, H. and Frassek, K.-H., Copolymers of β-unsaturated dicarboxylic acid esters, processes for their preparation and their use, Canadian Patent 411,264 (1982). 3. Beck, H. and Frassek, K.-H., Liquid copolymers from αolefins and α, β-unsaturated dicarboxylic acid esters, German Patent DE 3,223,694 (1981). 4. Beck, H., Frassek, K.-H., and Holtvoigt, W., Olefin-maleic copolymers, German Patent DE 2,727,329 (1977). 5. Johnston, G.J., Wayte, R., and Spikes, H.A., The measurement and study of very thin lubricant films in concentrated contacts, STLE Trans., 34, 187–194 (1991). 6. Adenin, M., Johnston, G.J., and Spikes, H.A., The elastohydrodynamic properties of some advanced non-hydrocarbon based lubricants, Lubr. Eng., 48, 633–638 (1991).

Copyright 2006 by Taylor & Francis Group, LLC

7. Rumpf, T. and Schindlbauer, H., Some remarks to the function of additives in ester-containing lubricating oils, Tribol. Schmierungstechnik, 32, 29–33 (1992). 8. Bowen, L. and Wallfahrer, U., Low ZDDP high performance semisynthetic automotive engine oils using polymer esters as an antiwear booster, Lubr. Eng., 54, 23–28 (1997). 9. Van der Waal, G., Esters: synthetic base oils for lubricants, in Proceedings of the 2nd International Congress on Lubricants of the Future and Environment, Brussel (1991). 10. Platteau, C., Biodegradable lubricants and functional fluids, European Patent Application 0558835A1 (1992). 11. Test report 1-4-253-84, IBR Forschungs GmbH (1984). 12. Coleman, E.C., Food and Drug Administration, Department of Health & Human Services, Exemption letter for use of polymer esters in can seaming equipment (1995). 13. Wallfahrer, U., High viscous polymer esters as an alternative to PAO 100, in Proceedings of the 5th International Congress on Lubricants of the Future and Environment, Brussel (1995). 14. Walther, M., Untersuchung der Werkzeugstandzeit zur Leistungsbeurteilung von Kühlschmierstoffadditiven, test report (2002). 15. Holweger, W., Studies on polymer esters in greases, in Proceedings of the ELGI Annual General Meeting (1998). 16. http://www.nsf.org/usda.

6

Polyalkylene Glycols S. Lawford CONTENTS 6.1 6.2 6.3 6.4

Introduction History Polyalkylene Glycol Chemistry Base Fluids 6.4.1 Capped PAGs 6.5 Practical Application of PAG Based Lubricants 6.5.1 Compatibility with Mineral Oil and PAO 6.5.2 Paint Compatibility 6.5.3 Elastomer Compatibility 6.5.4 Oxidative and Thermal Stability 6.5.5 Viscosity Index 6.5.6 Lubricity 6.6 Applications 6.6.1 Refrigeration 6.6.2 Fire Resistant Hydraulic Fluids 6.6.3 Compressor Lubricants 6.6.4 Gear Lubricants 6.6.5 Automotive Applications 6.6.6 Textile Lubricants 6.6.7 Metalworking Fluids 6.6.8 Food Approved Lubricants 6.7 Market Size 6.8 Toxicity and Environmental Effects 6.9 Summary and Conclusion References

6.1 INTRODUCTION Polyalkylene glycol (PAG) based lubricants have for many years seen use in a number of industrial applications including compressor lubrication, hydraulic fluids (aqueous [HF-C] and nonaqueous), metalworking fluids, and of course gearbox lubricants. Although it is widely accepted that PAG has all of the attributes required of a good lubricant, for example, high viscosity index, low pour point, good shear stability, good cleanliness, and if formulated correctly, good oxidation and corrosion resistance; PAG use has been restricted to (approximately) 10% of the total industrial lubricant market. Although some valid reasoning can be attributed to this (perceived price penalty, incompatibility with other common lubricants, etc.) it could be argued that the traditional thinking of some within the

Copyright 2006 by Taylor & Francis Group, LLC

industry and the resulting “stigma” or reputation assigned to these products has made widespread market introduction challenging and hence was detrimental to their total market share to date. PAGs, if understood, can provide the end user or formulator with several degrees of freedom to solve lubrication problems. PAG lubricants are unique among synthetic lubricants due to their high oxygen content and inherent polarity, a facet that makes them largely insoluble in petroleum or polyolefin based fluids (another perceived disadvantage). Polarity of the molecule can be adjusted according to monomer choice which in turn adjusts solubility in water and hydrocarbon lubricants. PAGs offer the only opportunity to develop truly water soluble lubricants.

6.2 HISTORY The history of PAG is a long one. Early reports of the polymerization of ethylene oxide (EO) date back to the 1860s [1]. Commercialization of this class of product came much later, just prior to World War II [1]. The war years saw acceleration in the development of PAG based products where obvious performance requirements were fulfilled. One such application was the development (by the Union Carbide and Carbon Corporation) of water based, fire resistant hydraulic fluids. These were adopted by the military for use on ships and in aircraft. Such fluids are formulated to contain typically >40% of water (to confer a high degree of flammability resistance), ethylene glycol, and a high molecular weight PAG based thickener (as lubricant) are all used as components. The use of this class of fluid reduces the risk of intense fires that can be generated by mineral based hydraulics if line rupture occurs. Civilian application of this type of fluid includes deep mining and steel manufacture. The high viscosity indices and low pour points achievable within PAG based systems were quickly identified as two of the major advantages over mineral and latterly, polyolefin based lubricants [3]. These two combined properties were identified as being particularly advantageous where cold weather performance was a prerequisite; early developments were based around brake fluids and aircraft engine lubricants. PAG use in brake fluids is still a major business where small amounts of water will dissolve in the fluid and thus cause no detrimental effect on performance. Since the early development of PAGs the performance flexibility offered has meant that application uses have become increasingly diverse. PAGs are now used in applications such as compressor lubricants, gearboxes, chain oils, textile lubricants, etc. A detailed study of these applications will follow later in this chapter.

6.3 POLYALKYLENE GLYCOL CHEMISTRY Polyglycols are manufactured via the continued polymerization of alkaline oxide monomer units onto a starting molecule containing a labile or acidic hydrogen atom in the presence of catalysts (Figure 6.1). There are a number of catalysts available to the alkoxylator when considering the manufacture of PAGs. These include alkali–metal hydroxides, alkaline earth–metal

O

∆T

O

Catalyst

FIGURE 6.1 Polyglycol manufacture

Copyright 2006 by Taylor & Francis Group, LLC

O O

OH

hydroxides, Lewis acids, and double metal–cyanide complexes. Within this list, alkali–metal hydroxides (sodium or potassium) are, by far, the most preferred. The manufacture of PAGs can be essentially split into three phases, (1) catalysis of the initiator, (2) polymer build (alkoxylation), and (3) treatment (catalyst removal) (Figure 6.2). Initiator molecules must have labile hydrogen atoms available in order to generate a nucleophilic species on addition of catalyst. Traditionally therefore, alcohols have been seen as the best choice for initiators, however, amines, carboxylic acids, etc. are also suitable. After the initial reaction between initiator and catalyst, a stoichiometric equivalent of alkylene oxide (compared to OM+ functionality) will react with this species to afford an alkoxide derivative of a new alcohol. At this stage an equilibrium between metal alkoxide and the other alcohols present within the reaction system is generated, such that the next reaction of an alkylene oxide monomer unit can occur with either the molecule that has already reacted or with a different alcohol. This equilibrium between alcohol and alkoxide determines the molecular weight distribution of the product. The alkylene oxide monomers react with the metal salts of the alcohol at much faster rates than with the remaining unreacted alcohols. Thus molecular weight build and resultant distribution tends to be small until all free alcohol has reacted with at least one unit of alkylene oxide, when all molecules in the system have approximately the same reactivity. Therefore, a Poisson distribution of molecular weight, a much narrower distribution than the most probable or Gaussian distribution, results. This narrow distribution is critical as it means that there is no significant fraction of low molecular weight, volatile or low boiling components and in addition, a narrow molecular weight distribution leads to a high viscosity index [1]. Of importance is the fact that the functionality of the initiator will dictate the functionality of the final PAG. Thus, molecular weight, polydispersity, polarity, etc., can all be controlled via the correct selection of initiator. Water, for instance, when used as initiator results in the generation of a di-functional PAG. For the purposes of lubricant manufacture, starter molecules usually consist of relatively reactive, short chain mono-functional alcohols (typically C4). In some cases, where a high molecular weight is required water or alternatively, a polyfunctional initiator (greater than 2 labile hydrogens) can be used. Oxide addition will take place under elevated temperature and pressure using a stainless steel pressure vessel. Temperatures and pressures of reaction vary according to reactor design however, as a rule of thumb pressures of between 5 and 15 bar and a temperature range of 100 to 120◦ C are typically employed. The rate of reaction in this instance is a function of temperature and not pressure.

Step 1 Catalysis of initiator MOH

– + RO M

ROH

Step 2 Alkoxylation

–

+

RO M

R'

O +

M+

O O

R

R'

–

R'

R' O O

R

–

M+

O

+

O O R'

O

–

R'

R

M+ n

R′ = H — Ethylene Oxide R′ = CH3 — Propylene Oxide R′ = CH2CH3 — Butylene Oxide Step 3 Treatment R'

R' O O– M +

O R

R'

H+

O O

OH

n

R

n

R'

FIGURE 6.2 PAG manufacturing steps

Post reaction, the PAG will undergo some form of treatment to either remove or neutralize the catalyst. In the case of alkali–metal hydroxides, three types of treatments are available for commercial production:

homo-polymer

co-polymer (random)

• Acid neutralization • Ion exchange • Adsorption of metals using magnesium silicate (de-ash)

“De-ashing” is the most common form of treatment, since the PAG can be treated dry (nonaqueous) with good results (less than 5 ppm of Na/K) in a relatively simple system. Essentially two types of alkylene oxide are used to manufacture lubricant PAGs, ethylene oxide (EO), and propylene oxide (PO). Butylene oxide (BO) can also be used, but few products have been commercialized using this raw material, DOW currently being the only manufacturer [1]. Obviously, the nature of the alkylene oxide used will greatly affect the performance attributes of the final fluid. For example, a homo-polymer consisting of only PO will exhibit water insolubility. By introducing a quantity of EO into the polymer chain, varying degrees of water solubility can be achieved (as measured by cloud point).

Copyright 2006 by Taylor & Francis Group, LLC

co-polymer (block)

FIGURE 6.3 PAG structures

6.4 BASE FLUIDS The ability to manufacture both homo and co-polymers of EO and or PO oxide introduces the ability to change or control the structural conformation of these monomer units within the PAG chain. Practically this means that broadly, the following three distinct structural types are possible, these being; homo-polymer, co-polymer (random), and co-polymer (block) (Figure 6.3). Of the three structures represented above homo and random co-polymers play the largest roles in PAG based lubricants.

O

–

+

RO M

O

+

+ CH2O

CH3 O

–

M

ROH

+

O– M + CH2O

–

M

H2C

+

O + ROH CH2O –

M+

OH

+

RO – M +

H2C

FIGURE 6.4 Propylene oxide isomerisation

Lubricant homo-polymers are generally manufactured from propylene oxide (PPGs). Homo-polymers of EO (PEGs) suffer from relatively high freezing points (PEG 600 for instance will be solid at room temperature). Propoxylates suffer from broader molecular weight distributions (especially at higher growth factors) due to the isomerization of the propylene oxide monomer under base catalyzed conditions to produce allyl alcohol [4,5]. In this instance, the allyl alcohol formed reacts with PO to form new mono-allyl functional polypropylene glycol molecules (Figure 6.4). This effect can be minimized via the use of polyfunctional initiators but at the expense of properties such as viscosity indices (VI). The use of licensed ‘DMC’ (Double Metal Cyanide) catalysis is also reported to minimise allyl unsaturation. As a compromise for fluids with viscosities greater than ISO VG 150, poly-functional starters are employed allowing propoxylates to be manufactured up to viscosities of around 1000 cSt. These materials form the basis of marine gearbox lubricants, due to inherent demulsibility characteristics and high additive response. However, production costs are high relative to simple monols and therefore operate within niche markets only. Generally, block co-polymers find most use in applications such as antifoam agents, where surface activity is required. In this instance, the polarity differences between PO and EO provide a surfactant effect. If used as lubricant chemicals, block co-polymers can be incorporated in metalworking fluid formulations, where a combination of antifoam properties and some lubricity enhances the overall performance of the fluid. Other applications include nonaqueous hydraulic fluids and oil field chemicals (drilling muds). Of more significance is the random co-polymer class of PAG. By definition the flexibility offered to the alkoxylator when designing such a product is far higher than that achievable with a homo-polymer. Indeed the majority of modern developments in PAG lubrication, for example, gearbox lubricants are based

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around the use of this class of PAG (usually on a 50:50 EO:PO basis). For lower order viscosity grades (ISO VG 46–320) these materials are usually mono-functional. For reasons of aerosol toxicity, polyfunctional initiators can be used to manufacture PAGs with higher viscosities (>ISO VG 320). Due to the presence of EO, molecular weight restrictions do not generally apply and high percentages of allyl functionality do not occur. Random, EO containing molecules are therefore available at viscosity grades up to and surpassing 90,000 cSt (40◦ C) (∼30,000 Da). However, di- or polyfunctional initiators are used in order to reduce reactor batch times. Furthermore, FDA approved lubricants (21 CFR 178.3570 Incidental contact with food) can also be produced with these base stocks (as they can with monol [C4 ] initiated propoxylates). The increased load carrying capacity and superior EP performance of this class of fluid make them particularly useful when manufacturing fluids intended for use under high load conditions. Examples include wind turbine transmissions and large worm gears. The following tables detail some typical data for the major classes of PAG based fluid [6]. Tables 6.1 and 6.2 describe the general properties of random copolymers of EO and PO. These tables have two families of structurally related compounds. The mono-butyl ethers (Table 6.1) polymers are derived from a butyl starter and are formed from equal weights of EO and PO. These materials have very low pour points. A comparison with propoxylates (Table 6.3) shows the values to be very similar. PAGs containing higher percentages of EO (Table 6.2) however have much higher pour points (even taking into account molecular weight). Viscosity index increases with increasing EO content. The diol polymers (Table 6.2) are derived from water giving them two hydroxyl groups. The oxide incorporated in these is 75 wt% EO and 25 wt% PO.

TABLE 6.1 General Properties 50:50 wt% Mixed Oxide Random Co-Polymer — Monol Viscosity Viscosity Viscosity index Pour point, ◦ C Refractive index Specific gravity Flash point, ◦ C Vapor pressure Specific heat Surface tension, 20◦ C

cSt at 40◦ C cSt at 100◦ C ASTM D 2270 ASTM D 97 N20 D 20/20◦ C COC mm Hg 20◦ C kJ/kg K Dyn/cm

19 4.6 165 −58

52 11 212 −53

66 13.5 210 −50

133 25.5 230 −48

1.02 183

1.03 220

1.04 232

1.05 240

217 41 239 −42 1.46 1.06 240 <0.001 1.95 35–40

387 70 254 −42

477 83 262 −40

680 117 269 −39

1000 163 281 −39

1.06 240

1.06 241

1.06 230

1.06 230

TABLE 6.2 General Properties 75:25 wt% EO:PO Random Co-Polymer — Diol Viscosity Viscosity Viscosity index Pour point, ◦ C Refractive index Specific gravity Flash point, ◦ C Specific heat

cSt at 40◦ C cSt at 100◦ C ASTM D 2270 ASTM D 97 N20 D 20/20◦ C COC kJ/kg K

272 41 207 −1

2,025 300 335 6

250

252

18,000 2,540 414 6 1.45 1.10 245 1.95

30,000 4,200 430 6

55,000 7,900 430 6

240

240

TABLE 6.3 General Properties Monol Propoxylate Viscosity Viscosity Viscosity index Pour point, ◦ C Refractive index Specific gravity Flash point, ◦ C Vapor pressure Specific heat capacity Surface tension, 20◦ C

cSt at 40◦ C cSt at 100◦ C ASTM D 2270 ASTM D 97 N20 D 20/20◦ C COC mm Hg 20◦ C kJ/kg K Dyn/cm

16 3.8 151 −65

33 6.7 169 −60

56 10.7 184 −57

0.97 160

0.98 208

0.99 210

76 13.9 190 −52 1.45 0.99 211 <0.001 1.95 35–40

122 21.3 200 −48

224 36.7 214 −37

330 51.7 219 −32

1.0 215

1.0 219

1.0 225

6.4.1 Capped PAGs Capped polyalkylene glycols are becoming increasingly more apparent in the lubricant market sector. The process of capping involves the removal of terminal hydroxyl groups and replacement with a low order alkyl ether (Figure 6.5). This reaction follows that of the Williamson Ether Synthesis. Commercially, strong bases such as sodium or potassium methoxide [7] are used to metallate the PAG prior to the introduction of the alkyl chloride used to cap.

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Metal hydroxides can be used [8,10] but in this case, driving off the water of reaction is more difficult than removing methanol. Other techniques can be used, including phase transfer catalysis; however lower yields and or higher reaction times decrease the commercial viability of the process. Good capping efficiency is dependent on the degree to which the PAG is metallated. Sodium hydride [7,11] can be used within the laboratory environment but commercially wipe film evaporators (in conjunction

R⬘

R⬘

O

O

RO O

n

R⬘

OH

O

• Seal compatibility • Additive response • Questionable oxidative stability

R⬘ Strong base

O

O

RO

6.5.1 Compatibility with Mineral Oil and PAO

R⬘

R⬘ nO

O R⬘

OR⬙

R⬘

FIGURE 6.5 PAG ‘Capping’

with sodium methoxide) are used to drive the formation of methanol. Capped PAGs can be found in a number of applications, the most prominent being compressor lubricants in HFC and CO2 refrigeration and automotive air-conditioning systems. In this instance capping the PAG increases the miscibility of the oil with the refrigerant gas thus ensuring complete carry through and lubrication throughout the compressor system.

6.5 PRACTICAL APPLICATION OF PAG BASED LUBRICANTS It is widely known within the industry that PAGs do not exhibit the same characteristics as other lubricant base stocks. Therefore what follows are key areas for consideration. It is important when assessing the potential use of PAG that a generic approach is not taken to the performance of the fluid since the flexibility of PAG chemistry means that the performance of the fluid under test has to be assessed on an individual basis. For instance, due to polarity increases, a PAG with high EO content will exhibit extremely low mineral and PAO compatibility but high solubility in water. The performance advantages offered by PAG based lubricants are well defined and can be summarized as follows: • High viscosity index (typically >200) • Good temperature stability • Superior lubricity — reduced wear characteristics and

good EP performance • High hydrolytic stability Similarly, there are a number of disadvantages commonly reported (perceived or actual) that need to be taken into account when PAG use is being considered. These can be summarized as: • Poor compatibility with mineral and PAO based fluids • Paint compatibility

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The compatibility issues associated with PAG, mineral oil, and PAO are well documented. Essentially, these arise due to the high oxygen content of the PAG increasing the overall polarity of the molecule and thus reducing compatibility. Contamination of a PAG with a mineral oil or PAO (or vice versa) may create two phase systems and in severe cases gellation. The extent to which contamination becomes a problem is largely a function of the PAG, for example, by incorporating a long chain alcoholic starter into the molecule, maximizing PO content, and incorporating a terminal hydroxyl cap, oil compatible materials can be manufactured (Breox OSIL range) [16]. Compatibility of the OSIL range is a function of hydrocarbon base stock molecular weight. For instance PAO 2 is almost completely compatible in all respects. Limited compatibility at higher viscosities generally dictates that oil soluble PAGs be used as additives within mineral and PAO based formulations where performance boosts are required. Examples would be industrial lubes and automotive crankcase/drive train lubricants. Furthermore, this class of materials find use as flushing lubricants, increasing the ease of changeover between mineral/PAO fluids and PAG.

6.5.2 Paint Compatibility The compatibility of PAG fluids and alkyd paint has again been well documented. With the advent and use of Epoxy type paint systems however, occurrences where paint incompatibility occurs have now reduced dramatically. It should be noted, however, that the effect of a PAG fluid on paint should always be assessed before use. In this instance, factors such as EO content and molecular weight will affect the outcome of such assessments. Generally high EO containing polymers of relatively low molecular weight will potentially pose the greatest problem.

6.5.3 Elastomer Compatibility The aggressiveness of PAG toward elastomers can be regarded as low with most synthetic “rubbers.” As with paint compatibility, molecular weight and EO content play a significant role in the overall response of an elastomer toward PAG. Table 6.4 details some typical data [6].

6.5.4 Oxidative and Thermal Stability A simple comparison of bond strengths (C–C 84 Kcal/mol/ C–O 76 Kcal/mol) [11] suggests that the thermal stability

Structure III will then abstract another hydrogen atom to form structure IV.

TABLE 6.4 General Elastomer Response Elastomer

Response

SBR

Random co-polymer

Propoxylate

R

% Swell Hardness

0.8 −2

0 0

NBR

% Swell Hardness

−0.8 2

0 0

Isoprene

% Swell Hardness

0 2

0.4 2

Chloroprene

% Swell Hardness

1.9 −4

−1.1 4

Silicone

% Swell Hardness

0 2

3.3 −9

O

Initiation R⬘

R⬘

R

O

R2

O

.

R

R.

R⬘

O

R2

+ RH

R⬘

Propagation Structure II can then undergo reaction with oxygen to form a peroxy radical. R⬘ O R

.

R⬘ O

R2

R⬘

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O O2

R

R2

O R⬘

O R⬘

of a mineral or PAO based product would exhibit slightly better performance than PAG (ref). Differential scanning calorimetry (DSC) analysis suggests that a PAG (regardless of oxide structure) will decompose thermally at approximately 250◦ C, which is comparable to hydrocarbons. Under thermal decomposition PAGs undergo chain scission, producing low molecular weight species. These products of degradation are either volatile or soluble within the bulk fluid. Therefore, PAGs, unlike mineral oil or PAO, do not form sludges or varnish therefore maintaining the cleanliness of the lubricated system. All ethers are chemically susceptible to oxidative attack at the secondary or tertiary carbon atom adjacent to the oxygen atom. Since PAGs have an oxygen atom at every third position across the polymer chain it can be assumed that generally PAG will suffer under oxidative attack. The mechanism for oxidation is similar to that for mineral and PAO based oils, with the exception that the initial C radical is stabilized by the adjacent oxygen atom (Figure 6.6) [1].

O

O O

R⬘

R⬘ O

.

. O

R2 + RH

O

R

O R⬘

R2

+ R

.

O OH

It is the fate of structure IV (the hydroperoxide) that will ultimately determine the effect oxidation has on the lubricant [1]. In the case of hydrocarbon based lubricants hydroperoxide will rearrange to form aldehydes (Figure 6.7) which in turn undergo Aldol condensation to form high molecular weight, reactive α, β-unsaturated species [12]; which can react further to form high(er) molecular weight polar species that are not soluble within the unreacted base stock. Hence producing sludge and varnish [13]. In the case of PAG, since every third atom is oxygen, a high proportion of the chain cleavage products are esters, as illustrated in Figure 6.8 [1]. While esters can condensate, this type of reaction is difficult and much less likely to occur. Further cleavage can occur to produce a variety of complex carbonyl species, as described in Figure 6.9 [1]. As the majority of the above species are not simple aldehydes condensation reactions are not favored and therefore as oxidation progresses, the PAG chain will continue to degrade, ultimately to either a C2 species (EO) or C3 molecule (PO). The physical manifestation of PAG oxidation is the converse of hydrocarbon based fluids, with a reduction in overall kinematic viscosity. The low molecular weight and low polarity difference (between degredation product and base fluid) ultimately means that sludge and varnish are not produced. Due to the ever decreasing chain length during oxidation PAG degradation products are volatile resulting in clean burn off, an important property in applications such as oven chain lubricants. While the onset of oxidation is stabilized and therefore more likely to occur under oxidizing conditions, PAG lubricants are no more likely to oxidize than hydrocarbons. In terms of formulation and final use PAGs can be successfully inhibited against oxidation via the use of phenolic/aminic antioxidant combinations. Typical antioxidants in use include: butylated hydroxyl anisole, phenothiazine, hydroquinone monomethyl ether, and phenyl-alphanapthylamine [14,15]. The use of PAG based fluids in applications such as heat transfer fluids, gear lubricants, and compressor lubricants all demonstrate the success of oxidation inhibition.

OH O R2

R1

O

. R2

R1

O R1

CH2·

R2

+

FIGURE 6.7 Aldehyde formation R⬘

R⬘

O R

O R⬘

R2

O R

O

O

O.

R⬘

OH

R2

R O

O

R2 +

R⬘

.

R'

O

FIGURE 6.8 Chain cleavage O R

R

O

OH

O

Oxidation products

O O

R R

H3C

O

H3C

–

FIGURE 6.9 Final oxidation products

6.5.5 Viscosity Index At an average VI of greater than 200 the VI of PAG based lubricants are universally known to be the highest of all classes of lubricant base stock. Thus PAG based lubricants

Copyright 2006 by Taylor & Francis Group, LLC

are capable of operating within extremes of temperature without detrimentally effecting performance. High VI is an inherent property of PAG, therefore viscosity improvers are not required when formulating such products and as a direct result, the shear stability of PAGs is comparably higher than that of many formulated hydrocarbon based products. A simple comparison between the viscosity/temperature behavior of PAG/PAO and mineral oil based lubricants is demonstrated in Figure 6.10. Several factors affect VI. The major contributing factors being end group and oxide type/composition. For example, the data in Table 6.5 demonstrate the effect capping has on the overall VI of a PAG. The increase in VI with decreasing free OH is attributable to the effect hydrogen bonding has on the rheology and apparent molecular weight of the fluid. At low temperatures hydrogen bonding will artificially increase the molecular weight and viscosity of the fluid. As temperature increases a point occurs where the H-bond is broken and the viscosity drops dramatically, thus decreasing VI. This does not occur in a fully capped PAG. As a general rule

the viscosity of an uncapped PAG will be approximately 20% higher than its capped equivalent. The nature of oxide used to manufacture a PAG also affects VI, in the sense that with increasing carbon content the VI decreases, that is, a PEG > mixed oxide > PPG. This affect is demonstrated in the typical data tables presented earlier within this chapter.

TABLE 6.5 The Effect of Capping on VI Structure

VI

Viscosity (cSt) at 100◦ C

HO(CH2 CH(CH3 )O)x H HO(CH2 CH(CH3 )O)x Me MeCH2 CH(CH3 )O)x Me

137 179 214

9.607 9.816 9.760

6.5.6 Lubricity As well as VI, film-forming properties under extreme pressure and polarity all play a major role in the overall lubricity of a fluid. Under extreme pressure the tendency for a liquid to thicken and hence maintain a lubricating film is measured by the pressure viscosity co-efficient (α). Thus the higher the value of α the greater the likelihood of film maintenance under EP conditions. The α values of several PAGs can be seen in Table 6.6 [17].

These data suggest that when considering α alone, a PPG will exhibit greater lubricity than a PEG or mixed oxide PAG. Practically, however, this is not the case. Several institutions [18,19] have reported improved lubricant performance with EO containing polymers over and above propoxylates within the FZG scuffing test. This reiterates the complex nature of the processes involved during mixed 10,000

6,000 4,000 3,000

6,000 4,000 3,000

3,000

2,000

1,000

1,000

600 400

600 400

300

300

200

200

90 80 70 60

90 80 70 60

50

50

40

40

30

30

ISO VG 320PAG

20

20

ISO VG 220PAG

16

16

ISO VG 320PAO

10

ISO VG 320 MineralOil

10 –30

–20

–10

FIGURE 6.10

Copyright 2006 by Taylor & Francis Group, LLC

0

10

20

30 40 50 60 Temperature in °C

70

80

90 100 110 120 130

Kinematic viscosity in mm2/sec

Kinematic viscosity in mm2/sec

10,000

and boundary lubrication regimes. One factor that plays a major role in the performance of a PAG is polarity. All PAGs exhibit greater levels of polarity than hydrocarbon based lubricants. This polarity will inevitably increase the affinity of the lubricant to the metal surface, thus, potentially increasing boundary lubricity. Furthermore, this effect will increase with the inclusion of EO into the polymer backbone. EO is a highly polar molecule that when polymerized, produces a water soluble product. Conversely, the pendant methyl groups present in PO reduce the polarity of the polymer to the extent that above a molecular weight of approximately 400 Da, the product becomes almost completely water insoluble. Random co-polymers of EO and PO are generally manufactured via the addition of an oxide premix to the reactor. EO has a faster rate of reaction, thus the end of the molecule closest to the starter will be EO rich. This concentration gradient and resultant polarity ultimately increases the affinity of the molecule to the metal surface, thus imparting a pseudo EP activity. The depth of this activity is currently unknown, however, as described earlier the performance of this type of material is generally better than a PPG with the same additive system. Issues concerning additive induced micropitting and bearing damage can therefore be minimized by reducing

or even eliminating harmful EP/AW additives. Table 6.7 demonstrates the step changes in Falex seizure load and FZG scuffing performance found with random EO:PO co-polymers.

6.6 APPLICATIONS The application flexibility offered by PAG lubricants is an extremely diverse one, Figure 6.11 summarizes the major uses of PAGs.

6.6.1 Refrigeration The refrigeration industry has recently realized a number of significant changes due to problems associated with ozone depletion. Until relatively recently the main refrigerants in use were ozone depleting types such as R12, R22, and R502. The use of these refrigerants, with the exception of R22, is now prohibited in developed countries; plans are also developing to phase out R22 as a result of the ozone Textile lubes

MWF Drilling fluids

Drilling fluids

Compressor lubes

Gearlubes Random 50:50

Hydraulic

TABLE 6.6 α Values of Several Mixed Oxide PAGs Structure Monobutyl ether Monobutyl ether Diol Monobutyl ether Monobutyl ether Monobutyl ether Monobutyl ether Monobutyl ether

Refrigeration

%EO

%PO

%BO

Viscosity, cPs, 20◦ C

75 50 — — — — — —

25 50 100 100 100 100 100 100

— — — — — — — —

190 151 65 70 86 180 364 604

α (22◦ C)/ GPa−1

Block

9.1 9.9 14.8 14.8 13.5 13.9 14.3 14.6

MWF

PAG

Propoxylate

Random 75:25

Gear lubes Compressor lubes Textile lubes

Wire and tubedrawing

Water based

FIGURE 6.11 Application summary

TABLE 6.7 Basic Tribiological Data Starter

Oxide

Ave. MW

VI

4-ball wear scare

Falex seizure load

FZG test A/8.3/90)

Butanol Butanol Butanol Butanol Butanol Butanol Butanol Butanol Butanol

100% PO 100% PO 100% PO 100% PO 50:50 EO:PO random 50:50 EO:PO random 50:50 EO:PO random 50:50 EO:PO random 50:50 EO:PO random

1200 1400 1700 2100 1200 1700 2300 3200 4200

184 190 200 214 210 230 239 262 281

0.51 0.45 0.46 0.54 0.56 0.50 0.52 0.46 0.44

750 1000 1000 750 750 1000 1250 1250 1250

9 9 9 9 9 10 12 12 12

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depletion potential, albeit small, which is also associated with this gas. A number of significant alternative refrigerants have been established, including HFCs such as R134a, HFC blends such as R407c, R404a, and R410a. R134a is by far the most commonly used HFC refrigerant in use today. Halogen-free refrigerants also offer significant possibilities as long-term refrigerants, with single substances including NH3 (R717), propane (R290), iso-butane (R600a), and carbon dioxide (R744). In mobile A/C systems, the compressor lubricant travels through the system with the refrigerant. In order to ensure return to the compressor, the lubricant must have adequate miscibility in the refrigerant. The mineral oils that are used as lubricants with R12 are insoluble in R134a. PAG lubricants show good miscibility in R134a. Because of their good miscibility and lubricating characteristics, PAG lubricants are used in a major proportion of automotive A/C systems. Polyalkylene glycols have a number of physical properties that enable them to perform well as refrigeration lubricants when used in conjunction with R134a. These include their good miscibility and stability in R134a, excellent lubricity, and compatibility with many common elastomers. The good low temperature flow properties and low volatility of PAGs are also important in refrigeration applications. While PAGs have a number of physical properties that are desirable in a refrigeration lubricant, it is their good miscibility in R134a that has led to their use in mobile A/C systems. PAG refrigeration lubricants may be specifically structured so as to exhibit excellent low temperature miscibility. A high temperature immiscibility region

may be observed over certain low PAG concentrations (Figure 6.12) [20]. In general, the lower the viscosity of the PAG, the better the high temperature miscibility. In the high temperature immiscibility region the R134a/PAG mixture will separate into two layers. These two layers are not pure refrigerant and pure lubricant, but instead consist of a lubricant-rich phase and a refrigerant-rich phase. The composition of the two phases that form in the high temperature immiscibility region can be determined from the intersection of the horizontal temperature tie line with the PAG’s solubility curve (61). The excellent low temperature miscibility of PAGs and R134a, as well as their mutual solubility at elevated temperatures, ensures the circulation of the lubricant through the A/C system that is necessary for good compressor lubrication. In addition, by correct structural design of a PAG, the critical solubility line (with R134a) can be eliminated, Figure 6.13 describes this effect [21]. This is clearly an advantage for ensuring low temperature lubricant/refrigerant miscibility, exceeding the typical lubricant/refrigerant compatibility requirements of the industry. While lubricant miscibility in the refrigerant is necessary, it is also important for the refrigerant/lubricant pair to be chemically and thermally stable. PAG lubricants exhibit excellent stability in R134a. Sealed tube stability tests run at 350◦ F (175◦ C) for 14 days in the presence of steel, aluminum, and copper coupons show the PAG/ R134a combination to be at least as stable as mineral oils run under the same conditions in the presence of R12 [22,23].

90 80 70 60

Temperature (°C)

50 40 Temperature insolubility regions. Uncapped PAG.

30 20 10 0 –10 0

5

10

15

–20 –30 –40 –50 –60 Lubricant content (wt%)

FIGURE 6.12 CST Plot ‘single end capped PAG’

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20

25

30

100 80

Temperature (°C)

60 40 20 0 0

5

10

15

20

25

30

35

–20 –40 –60 Lubricant content (wt%)

FIGURE 6.13 CST Plot ‘Double End Capped PAG’

Polyalkylene glycols are excellent lubricants. Of particular importance in refrigeration applications is the high viscosity indices of PAGs, typically ranging from 180 to over 250. PAG refrigeration lubricants thus show significantly less change in viscosity with temperature than do mineral oils whose viscosity indices are typically less than 100. This means that when compared to mineral oils, PAGs are more fluid at low evaporator temperatures and still provide good lubricity in the hot compressor. Polyalkylene glycols are compatible with most common elastomers. It is important, however, to consider the effect of R134a in cases where both the refrigerant and lubricant are present. Owing to the variations that can exist between elastomers in the same generic family, it is important to test the compatibility of the refrigerant/lubricant pair with the specific elastomers that are to be used in critical applications. One of the major differences between PAGs and mineral oils is their affinity for water. PAGs are hygroscopic relative to mineral oil lubricants. PAG refrigeration lubricants usually have a maximum water specification of 500 ppm and normally contain between 400 and 200 ppm water. As they are hygroscopic, PAGs will pick up water when exposed to humid air. They will continue to pick up water until an equilibrium or saturation level is achieved. Typical saturation levels range from 1 to 5% depending on the humidity and the PAGs structure. It is important to realize that the water absorbed by PAGs is not free but is instead hydrogen bound to the PAG backbone. Therefore neither corrosion nor ice crystal formation has been a problem in refrigeration systems that are lubricated with PAGs.

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Because of their hygroscopicity, the exposure of PAG refrigeration lubricants to humid air during storage should be avoided. Bulk storage tanks and drums should be nitrogen blanketed or equipped with vent dryers. When stored in small containers, minimizing air exposure is usually sufficient to keep PAG refrigeration lubricants in satisfactory condition. There have been many questions asked regarding the proper handling of PAGs. PAG refrigeration lubricants are significantly less hygroscopic than DOT-3 brake fluids. If the same care is taken when handling PAG lubricants as when working with DOT-3 brake fluids, no performance problems should result. A challenge currently facing the refrigeration industry and in particular the automotive industry is how to service the vehicles on the road today that have been fitted with R12 powered air conditioners as the supply of this refrigerant becomes scarce. Much work has been done in the automotive industry to determine the best ways to convert, or retrofit, these R12 vehicles to R134a [24,25]. A retrofit lubricant must be compatible with residual R12 and its preferred lubricant (mineral oil) as well as soluble in R134a. Compressor makers, car manufacturers, and component suppliers have evaluated the use of PAGs as retrofit lubricants. Polyalkylene glycols have performed very well in these evaluations such that many major car companies have recommended PAG lubricants for use when retrofitting their vehicles. One of the major requirements of a retrofit lubricant is that it be stable in the presence of residual R12. Analysis of the refrigerant in retrofit vehicles shows that the residual concentration of R12 is typically about 1%. A worst-case retrofit would leave approximately 5% R12 in the A/C

system. Because of the ease with which the R12 concentration can be reduced to low levels, concerns about contamination of the refrigerant supply, and the higher pressures exerted by R12/R134a mixtures [24], SAEs position is that the concentration of R12 must be reduced to below 2% [25]. High temperature and long-term sealed tube tests show that PAG refrigeration lubricants are stable in the residual R12 concentrations that can be expected in retrofit vehicles [20]. Also, the analysis of lubricant samples from retrofit tests on compressor stands and from actual retrofit vehicles has shown no signs of PAG or R134a degradation. Polyalkylene glycols are compatible with used mineral oils in that they do not undergo any adverse physical or chemical reactions when they are mixed. While some PAGs exhibit limited solubility in mineral oils, this does not adversely affect their performance in retrofit applications. Since PAG lubricants are compatible with residual R12 and mineral oil, much work was done by the automotive industry to show that PAGs are good retrofit lubricants. As a result many major car manufacturers have decided to retrofit their vehicles with R134a and PAG lubricants. However, different procedures are recommended for different vehicles in order to achieve a reliable, cost efficient retrofit. It is important to follow the car makers’ specific recommendations when retrofitting a vehicle from refrigerant R12 to R134a. The refrigeration industry has now embarked on another technology “revolution.” Carbon dioxide has no ozone depleting potential (ODP), is nonflammable, and chemically very stable. It is only harmful to health in very high concentrations and is inexpensive, hence eliminating any need for recovery and disposal. Carbon dioxide as a refrigerant poses some very serious questions to the compressor designer, high discharge pressure, and a very low critical temperature of 31◦ C (74 bar). This requires sub and supercritical operating conditions in single stage systems with discharge pressure above 100 bars. However, in applications with potentially high leakage rates and where flammable (HC) refrigerants cannot be accepted for safety reasons (such as a car air conditioner), there exist opportunities for CO2 . A number of development projects, primarily in the area of vehicle air-conditioning, are underway, as well as the potential application of heat pumps for sanitary water heating. Initial work indicates that CO2 systems for automotive air-conditioning and heat pumps show improved efficiency over traditional R134a technology. For larger commercial and industrial refrigeration units, CO2 may be used as a secondary fluid in a cascade system and developments are also underway in this field. The majority of conventional lubricants such as mineral oils and alkylbenzenes are not soluble with CO2 . Polyol ester (POE) synthetic lubricants show very good

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miscibility properties, however this can result in a dramatic reduction in viscosity in the refrigerant condenser. Capped PAGs show partial miscibility with CO2 [26], however, the viscometric properties of PAGs remain unaffected and the decrease in viscosity observed with POEs is not observed for PAGs under CO2 dilution. Figure 6.14 describes the miscibility of Breox RFL 46-X with CO2 . The development of trans-critical CO2 systems requires speciality lubricants due to the high pressure and subsequently higher loading on bearings. The extreme pressure and antiwear properties of capped PAGs are superior to POEs and other synthetics such as PVEs, with such lubricating properties being retained under high pressure CO2 conditions. BREOX RFL lubricants, based on “capped PAG” technology, provide efficient lubrication for compression type refrigeration units and improved lubricating properties for CO2 systems; and enhanced thermal stability is achieved as a result of the capping technology.

6.6.2 Fire Resistant Hydraulic Fluids Fire resistant hydraulic fluids are used wherever the fire risk associated with the use of flammable hydraulic fluids cannot be tolerated. Fire resistant fluids are used in areas like foundries, die cast aluminum facilities, steel mills, and mines. The traditional classes of fire resistant hydraulic fluids are the PAG based water glycol fluids (HF-C), oil in water emulsions (HF-A/B), phosphate esters (HF-D), and polyol esters (HF-D). In order to formulate an HF-C type fluid a high molecular weight, water soluble PAG (or thickener) is required. It is the role of the thickener to provide lubricity to the fluid. A typical HF-C formulation would contain the following generic components and have a viscosity within the ISO46 category. Component

Purpose

Water Glycol

Fire protection Freeze protection and some thickening Lubricating component (typical molecular weight 20,000 Da) Provides mixed film and boundary lubrication Vapor phase and liquid corrosion protection

Polyalkylene glycol Antiwear additive Corrosion inhibitors

Essentially, two standards are available as performance indicators these being the 7th Luxemburg report and Factory Mutual approval. In both cases, tests such as “spray flammability” and the “hot channel test,” are used to evaluate fluids. The “spray flammability test” essentially requires an aerosol of the test fluid to be sprayed through a flame whereas the “hot channel test” requires the lubricant to be sprayed onto a channel

80.0

Temperature (°C)

60.0

40.0 30.9

Critical solution temperature 26.0 30.9

30.9

20.0 13.0 0.0

–20.0 –31 –40.0 0.0%

–31

–29.2

–31

Density inversion temperature 10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

Mass fraction lubricant (g/g)

4 Ball (mm)

Falex (failure load lb)

FZG Load stage (A/8.3/90)

VI

Monol propoxylate

0.54

750

9

214

Polyol propoxylate

0.47

750

11

210

Monol random co-polymer

0.52

1250

12

240

FIGURE 6.14 CST Plot of capped PAG in CO2

heated to ∼400◦ C, thus simulating a spillage onto a hot surface. In all cases water–glycol fluids exhibit the best resistance to ignition, fume generation, and continued to burn after removal of the source of ignition [27]. The reasons for the low propensity to burn or ignite are complex, however, these can be summarized as: • The high water content of the PAG increases the heat

capacity of the fluid (a comparison of the heat capacities of various hydraulic fluids can be seen in Table 6.8) [27]. • Polyglycols have low calorific values, since due to the polyether structure they are already partially oxidized. The requirement to evaporate water prior to the onset of burning also reduces flammability. Traditionally, the antiwear performance of HF-C type fluids has been criticized. Indeed these fluids are designed for use where safety is a must and not as high performance lubricants. As a general guide when using HF-C water glycol fluids, the pump lifetime is reduced between 25 and 60% of that of a mineral oil lubricated system. This

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TABLE 6.8 Fluid type Mineral oil Water-in-oil emulsion Phosphate ester Water–glycol

Heat content (Gross) kJ/g

Total heat output, kJ/g

44.9 25.7 45 13

14.1 8.5 6.7 2.7

is due to the high water content in water–glycol fluids. An example of a typical performance can be seen below. Rexroth Hydromatik A2V5S LD Axial Piston Pump A Rexroth Hydromatik axial piston pump (bent axis design) was tested to destruction with Breox Hydrolube NF46 2180 in collaboration with a major manufacturer of continuous casting equipment incorporating this pump design. Table 6.9 gives the complete test schedule. The equipment manufacturers wanted a pump bearing life of at least 4000 h with an HF-C fluid running at

TABLE 6.9 Pump Test Performance [15] Rexroth Hydromatik A2V55 LD Pump Test

Pump pressure (Bar) System pressure (Bar) High Low Pressure sequence Valves VICKERS REXROTH Flow rate (L/min) Piston wt. loss mg

First 1000 h

Second 1000 h

Third 1000 h

Fourth 1000 h

30–120

150.00

30–250

250.00

120.00 30.00 5 cycles/min

150.00 30.00 10 min–150 bar 2 min–30 bar

250.00 30.00 5 cycles/min

250.00 30.00 10 cycles/min

ECG 6

ECG 6

77.00 407.60

XCT 10 F 4WRZ 16E 126 75.00 260.60

50–77 52.50

ECG 6 4WRZ 16E 126 50–77 93.20

0.30

0.30

0.50

0.60

Barrel wt. loss mg

120 to 150 bars. The test indicated that it is practical to expect a minimum bearing life of 5000 h with Breox Hydrolube NF46 2180 at 150 bars and a pump speed of 1500 RPM [34]. Water–glycol based PAG thickened hydraulic fluids are usually formulated in the ISO 46 or ISO 68 viscosity regions. Their operating temperature is limited from about −30 to 65◦ C. The upper temperature limit is a result of the high vapor pressure of the contained water. Higher temperatures can lead to cavitation and premature pump failure. These fluids generally have good seal compatibility. In order to achieve optimal performance of water– glycol fluids, they must be properly maintained [28]. Water content must be controlled to the specification level. Too little water will significantly raise the viscosity. Too much water will thin viscosity and also result in significant increases in wear. Water content is easily measured by refractometry. The amine, or alkalinity, content must also be monitored. Higher wear can be experienced if the alkalinity is above the desired value. Greater wear will result if alkalinity is below the desired value. Alkalinity is easily monitored through acid–base titrations [1].

6.6.3 Compressor Lubricants Polyalkylene glycols are used in a variety of different compressor applications, the largest of which include, hydrocarbon gases (LPG and ethylene), hydrogen, inert process gases, and air. PAGs are suitable for use in both reciprocating and rotary screw compressor designs. The compression of petroleum derived gases such as methane, ethane, and ethylene (etc.) presents a severe lubrication challenge. These process gases dissolve in

Copyright 2006 by Taylor & Francis Group, LLC

Fifth 1000 h 350.00 310.00 100.00 10 cycles/min

DB20-2-41/350 4WRZ 16E 126 40–75 Damaged by fragments so that weight loss meaningless Damaged by fragments so that weight loss meaningless

petroleum and petroleum like lubricants, reducing viscosity and hence lubricity. Products such as white oils and viscous PIB based products have been used in the past but suffer from poor wear performance, difficult start-up, and product contamination. PAG, due to the inherent hydrocarbon incompatibility, does not suffer from these issues. Therefore low(er) viscosities can be used, reduced power consumption, lower degrees of product contamination, and increased lubrication performance can all be achieved. An example of an extreme application is that of low density polyethylene (LDPE) production. Ethylene is compressed within reciprocating hyper compressors to pressures exceeding 3000 bar. PAG performs outstandingly due in part to the reduced solubility in ethylene and the relatively flat pressure/viscosity curve maintaining a stable viscosity profile across the compressor stroke, thus increasing lubricity and reducing wear. In both LPG and ethylene compression, water soluble PAGs are used. The relative solubility of PAGs in various process gases can be seen in Table 6.10 [29]. Other process gases that can be compressed successfully include hydrogen, carbon dioxide, and helium. Low(er) viscosity PAGs (ISO 32–68) can be used as rotary screw compressor fluids. Due to the inherent lubrication property of PAG additives can be kept to a minimum or eliminated. Due to the degradation mechanisms of PAG these systems tend to be much cleaner than those lubricated with hydrocarbon based products. Due to the propensity of PAG to oxidize there have been few PAG based air compressor lubricants. Air compressor fluids are however commercialized which combine PAG

TABLE 6.10 Solubility of Process Gases in PAG Lubricant Polyalkylene glycol Polyalphaolefin Polyalkylene glycol Polyalphaolefine Polyalkylene glycol White oil Polybutene

Process gas

Solubility, wt.%

Methane Methane Nitrogen Nitrogen Ethylene Ethylene Ethylene

2.9 5.8 4.3 8.8 7.8 14.1 13.8

and polyol ester. The degradation pattern of PAG is used to advantage within these fluids since, unlike mineral or PAO fluids sludge is not produced, and therefore system cleanliness can be maintained [30].

6.6.4 Gear Lubricants There are essentially two types of PAG gearbox fluids; early technology centered around water insoluble PAGs or propoxylates. This class of PAG are used to formulate water demulsifying lubes, the excellent response of these fluids to corrosion inhibitors means that sea water corrosion can be eliminated. This class of lubricant is used, for example, in marine applications where water demulsibility and sea-water corrosion protection are a must [31]. Latterly, water soluble PAG gear lubricants (EO:PO homopolymers) have begun to enter the marketplace. These materials obviously cannot offer water demulsifying properties but take advantage of the inherent polarity gradient across the molecule to increase EP/boundary performance. Furthermore, H1 lubricants (21 CFR 178.3570 Incidental contact with food) can also be produced using water soluble base stocks (high viscosity insoluble grades based on polyol initiators are not H1 approved). The increased load carrying capacity and superior EP performance of this class of fluid make them particularly useful when manufacturing fluids intended to be used under high load conditions. Examples include wind turbine transmissions and large worm gears. A simple data comparison of EP lubrication properties between base stocks can be seen in Figure 6.14. The depth of this activity is currently unknown, however the performance of this type of material is better than a PPG with the same additive system. What is certain is that potentially corrosive or harmful EP/AW additives can be minimized when formulating products. Issues concerning additive induced micropitting and bearing damage can therefore be minimized by reducing or even eliminating harmful EP/AW additives [32]. The mineral or PAO formulator, who does not have this practical advantage, must therefore reach a balance between load carrying ability

Copyright 2006 by Taylor & Francis Group, LLC

Characteristics

Test results (ISO 320 H1 approved lubricant)

Paint compatibility P22-8050 Loctite compatibility 128068 Seals NBR Static FKM Static Dynamic Micropitting at 90˚C

Pass Pass Pass Pass Pass 10 pass Load stage/Endurance Ð High resistance

Micropitting at 60˚C

10 pass Load stage/Endurance Ð High resistance

FAG roller bearing test (80 Hr) FZG A/8.3/90 Failure A/16.6/90 Load A/16.6/140 Worm T59 Gear test T60 (Flender)

3 mg roller 7 mg cage >12 >12 12 L3/S2 L3/S5

Radicon worm gear efficiency test Flender 2% Tribol Foam 1390/320 test 4% Tribol 1390/320 2% Castrol Alphasyn SP 220

87%

4% Castrol Alphasyn SP 220

Good Good Acceptable

Acceptable

FIGURE 6.15 General performance attributes of a formulated PAG gear lubricant

(EP) or scuffing performance vs. micropitting and bearing longevity. This can be difficult since all drive trains will have a mixture of lubrication regimes. Hence, many formulators, will have different grade fluids, “standard” and “EP.” Polyalkylene glycol based gear lubricants, if formulated correctly can be manufactured as multipurpose grades, capable of operating across load or application demands with no detrimental effects. An example of this is the preparation of a food grade (H1) lubricant. Traditionally, these products have been assumed to perform to a lesser degree than their non-H1 counterparts. Cognis Performance Chemicals, however, have been able to develop a lubricant (using an H1 platform) that shows the performance attributes required to operate across application boundaries. An example of this can be seen in Figure 6.15. Traditional thinkers will question the use of PAG for several reasons. Hydrocarbon incompatability, elastomer, and paint performance have been tackled earlier in this chapter. Poor corrosion resistance and oxidation stability

may also be cited as potential disadvantages. As discussed earlier, it is more than possible to pass corrosion resistance tests such as ASTM D665 (A and B) using water insoluble PAGs. ASTM D665 (B) passes are harder to achieve with water soluble fluids, since a metal/oil/water barrier is not formed, but again with the correct combination of corrosion inhibiters passes can be achieved. Oxidation is, potentially, the Achilles heel of PAG gear lubes, however ASTM 2893 results of less than 3% Vk 100 increase 121◦ C can be achieved with innovative combinations of base fluid and antioxidants. Furthermore, as described earlier, oxidation of PAG does not form sludge and varnish. One example of the performance of PAGs as gear lubricant is that of the wind turbine industry. Wind turbine drive trains are susceptible to damage for a number of reasons. These include high loads, often above design limits in periods of high wind speeds, off axis loads due to the flexibility of the turbine tower, and exposure to the elements etc. Offshore turbines, cited in the sea, are particularly susceptible to damage. Maintenance, by definition, is also much harder to complete. The most complex part of a wind turbine is the gearbox and hence most failures are attributable to this equipment. Wind turbines are increasing in size at an extremely fast rate; five years ago, sub-megawatt power outputs were the norm. Five MW turbines are now under development. Performance lubrication is therefore becoming more and more important. PAG has been shown in several cases to provide the turbine builder with the performance attributes required to cut instances of gearbox failure and hence costs [33]. The changeover from hydrocarbon based lubricant to PAG can also provide cost advantages to the user. Trials performed by Cognis have proven that PAG can be retrofitted successfully such that damage like scuffing and micropitting can be arrested. Furthermore, friction induced high bearing and sump temperatures, originating either from damage and or manufacturing issues, can be reduced by replacing mineral and PAO oils with PAG. In order to facilitate retrofits, oil soluble PAGs are used as flushing fluids [26].

6.6.5 Automotive Applications The use of PAGs as passenger car motor oils was pursued in the mid-1940s [35]. These synthetic lubricants, based on polypropylene glycol monobutyl ethers, were evaluated in engine test stands and in extensive vehicle trials. Due to their very high viscosity indices and inherent good lubricity, wear of engine parts was comparable to that of the best petroleum oils of the time. The PAG lubricants demonstrated a number of advantages relative to petroleum based motor oils.

Copyright 2006 by Taylor & Francis Group, LLC

These included less sludge formation, reduced combustion chamber deposits and spark plug fouling, excellent detergency, and better low temperature properties. However, distribution problems, poor compatibility with conventional petroleum oils, and their high cost prevented PAG based automotive crankcase lubricants from being commercially successful. Work is continually being done to improve the performance properties of engine lubricants. Higher viscosity indices are needed to provide good low temperature flow properties while retaining sufficient lubricity at the high temperatures that exist in today’s engines. Good detergency reduces sludge formation. Better engine efficiencies, reduced emissions, and lower maintenance can be achieved by reducing the deposit forming tendencies on intake valves and in the combustion chamber. These requirements have renewed interest in the use of PAGs as engine crankcase lubricants because of their high viscosity indices, good detergency, and clean burn-off characteristics [36,37]. Oil soluble PAGs have recently been developed that reduce the oil compatibility problems associated with conventional PAGs while retaining the performance advantages provided by this class of synthetic lubricants. These new PAGs are made from the copolymerization of PO and an alpha-olefin epoxide onto a lipophilic alcohol starter. Engine trials and other motor oil evaluation tests showed that multigrade synthetic and semi-synthetic lubricants containing these oil soluble PAGs provided the benefits expected from similar formulations containing esters and polyalphaolefins. In addition, the formulations containing the oil soluble PAGs required less viscosity index improver and showed reduced volatility and improved engine cleanliness [37].

6.6.6 Textile Lubricants Water-soluble PAGs are widely used in the textile industry. They are nonstaining and can be washed from the finished yarn or fabric with water [1]. Polyalkylene glycol based lubricants also disperse static charge, thus allowing higher yarn speeds and increased throughput. Polyalkylene glycols, when they are oxidized at moderate temperature with an adequate oxygen supply, do not form colored by-products. This is particularly advantageous in the textile industry, where color is a critical quality consideration.

6.6.7 Metalworking Fluids Polyalkylene glycols are often used as lubricity additives in water based cutting and grinding fluids [39,40]. In addition, they have been utilized in drawing, forming, stamping, and rolling lubricants [40–42]. Because of their good water

solubility, PAGs are most often used in “synthetic” metalworking fluids. These fluids form true solutions in water. Synthetic metalworking fluids based on PAGs provide good lubricity and are excellent coolants. In general, they are also more resistant to microbial attack and easier to maintain than “soluble oil” metalworking fluids, which are actually oil-in-water emulsions [43]. Polyalkylene glycols provide good lubricity in synthetic metalworking fluids by taking advantage of their inverse solubility in water [38,39]. At ambient temperatures, PAGs are water soluble. At an elevated temperature, known as the “cloud point,” the PAG becomes insoluble and forms small polymer droplets. When a synthetic metalworking fluid containing a PAG is brought into contact with the hot die or cutting tool, it is heated to a temperature above the cloud point of the polymer; the PAG then comes out of solution, thus forming a lubricant film that provides excellent hydrodynamic lubricity. Synthetic metalworking fluid formulations often contain both PAGs and water soluble boundary or extreme pressure additives such as fatty acids or phosphate esters. Combinations of PAGs and fatty acids or phosphate esters have been shown to be synergistic, providing better lubricity than equivalent concentrations of either additive by itself [40]. As a result of this synergy, these aqueous metalworking fluids provide excellent lubricity as well as the good cooling properties of water [43]. Synthetic metalworking fluids will also contain other additives such as corrosion inhibitors, antifoams, and biocides. In general, those PAGs used in metalworking are of the block co-polymer type. As well as exhibiting shaper cloud points, these materials act as high temperature aqueous antifoams, thus reducing foam formation at the cutting operation.

6.6.8 Food Approved Lubricants Polyalkylene glycols, due to their low toxicity, offer a number of food approvals. Essentially, H1, incidental food contact (178.3570) is available for many grades at ISO viscosity grades of 150 and above. Direct food processing and therefore addition is also possible for many block co-polymer antifoams. Essentially all of the “standard” PAG grades listed in Tables 1, 2, and 3 are CFR 178.3570 approved (at 150 cSt and above).

6.7 MARKET SIZE Worldwide there are approximately ten PAG producers. The biggest five, producing PAGs for lubricant applications, as well as process intermediates are Cognis, DOW, BASF, Clariant, and Uniqema.

Copyright 2006 by Taylor & Francis Group, LLC

Geographically all of the above supply PAGs globally, however, Cognis, Uniqema, and Clariant are traditionally strong within Europe with DOW and BASF holding the North and South American markets. Manufacturing sites are present throughout western Europe, North America, and S.E. Asia. The exact global market size for PAGs is difficult to gauge accurately but a conservative estimate would be somewhere in the region of 150–200 thousand tonnes per year. The lubricant segment probably accounts for 20–30% of this figure.

6.8 TOXICITY AND ENVIRONMENTAL EFFECTS Generally, PAGs can be regarded as being of low toxicity. PAGs have been used safely for many years. Tests using various modes of contact, skin, ingestion, etc., have all corroborated the low toxicity of PAG. The one notable exception being Butanol started 50:50 random copolymers. ECOTOC report 55 [44] details the effect these materials have on the pulmonary system when ingested as aerosols. Tests (using UCON products) have shown that these grades above a MW of ∼2900 Da trigger a toxic pulmonary response. Further tests looking at different multifunctional starters, EO:PO ratios, and structural configuration all show that toxicity is limited to a very narrow band of products. It is therefore recommended that, in instances where inhalation of aerosols may occur, ventilation and respirators are used. Since the products of thermal and oxidative degradation, like many other organics (ketones, aldehydes, etc.) can be described as noxious, good ventilation should be used in cases where contact could result. Environmentally, PAGs can largely be classed as neutral. They are neither harmful to the environment nor do they biodegrade to any great extent. Therefore base fluids tend not to be labelled under European environmental legislation, where labels do occur this is due to individual or combinations of additives triggering labelling breakpoints. PAG producers have obviously tested their materials in a number of different ways and across species. In general, water soluble PAGs have high LC50 or EC50 thresholds. Water insoluble and low cloud point PAGs have the lowest figures. There is some evidence to suggest that this is not a toxic effect in the true sense of the word but more a physical, coating issue. The biodegradability of PAGs is a disputed topic. Some manufacturers claim biodegradability [1] whereas others do not make similar claims. This is due, in part, to the ambiguity of biodegradability testing, repeated tests for instance often produce a spread of results. Without the use of pre-conditioned or specially selected bacteria, PAG degradation is therefore low. Cognis do not make the claim that PAGs (as a class) are readily biodegradable. The factors that affect

biodegradability can be summarized as: • Molecular weight — Low MW PAGs are more likely to

biodegrade. • EO content — PO containing polymers are less likely to

biodegrade. • Co-polymer structure — Block co-polymers, with a high

EO content will promote biodegradation. • Water solubility.

Biodegradation can be enhanced via structural modification. Introduction of ester linkages, for example, across the PAG backbone can vastly increase the biodegradability of the product.

6.9 SUMMARY AND CONCLUSION The flexibility of this class of product provides tribologists with a vast array of potential solutions to lubrication problems. The inherent complexity of PAG chemistry can, if allowed to, confuse many outside of the industry to the point where incorrect generalizations and direct comparisons with hydrocarbons are made. Inevitably this approach will not do justice to the benefits of PAG lubricants. While the market share of PAG within the “Industrial” market will never overtake hydrocarbon based lubricants, more and more applications are demanding higher and higher performance levels, which can only be met by employing the virtues of PAGs.

REFERENCES 1. P.L. Matlock, W.L. Brown, and N.A. Clinton, Synthetics, Mineral Oils, and Bio-Based Lubricants: Chemistry and Technology 1st ed. this chapter. 2. G.E. Totten, S.R. Westbrook, and R.J. Shah, Fuels and Lubricants Handbook – Manuel 37, Polyalkylene Glycols. 3. Union Carbide, UCON Fluids and Lubricants, Union Carbide and Carbon Company, F-40134 (1956). 4. L.E. St. Pierre and C.C. Price, J. Amer. Chem. Soc., 78, 3432 (1956). 5. G.W. Gee, W.C.E. Higginson, P. Levesley, and K.J. Taylor, J. Chem. Soc., 1338 (1962). 6. Breox Fluids and lubricants guide, Cognis Performance Chemicals UK Ltd, No date. 7. M.J. Anchor, U.S. Patent 4,587,365 (1986). 8. B.G. Zupancic and M. Sopcic, Synthesis, 123 (1979). 9. T. Gibson, J. Org. Chem., 45, 1095 (1980). 10. N. Yoshimura and M. Tamura, U.S. Patent 4,301,083, November 17 (1981). 11. U.E. Diner, F. Sweet, and R.K. Brown, Canad. J. Chem., 44, 1591 (1966). 12. J. Igarashi, Jpn. J. Tribol., 35, 1095 (1990).

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13. S. Gunsel, E.E. Klaus, and J.L. Duda, Lubr. Eng., 44, 703 (1988). 14. Emkarox Polyalkylene Glycols, ICI Corp., No date. 15. D. Klamann, Lubricants and Related Properties, Verlag Chemie, Weinheim (1984). 16. BREOX OSIL 702/OSIL 220 OIL SOLUBLE LUBRICANTS, Cognis Performance Chemicals UK Ltd. 17. M.E. Aderin, G.J. Johnston, H.A. Spikes, T.G. Balson, and M.G. Emery, 8th International Colloquium on Tribology, Tribology 2000, Esslingen (January 1992). 18. S. Kussi, J. Syn. Lub., 2, 63 (1985). 19. Von P. Geymayer, Tribol. Schmierungstech, 31, 64 (1984). 20. W.L. Brown, SAE Technical Paper Series, 932904 (1993). 21. L. Dixon, S. Lawford, and G. Beckett, 13th International Colloquium Tribology, Esslingen (2002). 22. W.R. Finkenstadt, ASHRAE Transactions 1992, Vol. 98, Pt. 1 (1992). 23. SUVA Trans A/C (HFC-134a) for Mobile Air Conditioning, DuPont Chemicals, Wilmington, DE, ARDT-31. 24. Retrofit Guidelines for Conversion of CFC-12/R-12 Systems to HFC-134a/R-134a, A/C Action!, Mobile Air Conditioning Society, E. Greenville, PA (1993). 25. Procedure for Retrofitting CFC-12 (R-12) Mobile Air Conditioning Systems to HFC-134a (R-134a), SAE Standard J1661 (1993). 26. A. Hauk and E. Weidner, Ind. Eng. Chem. Res., 39, 4646–4651 (2000). 27. G.E. Totten, National Fluid Power Association, Technical Paper, No. I92-23.1 (March 1992). 28. G.E. Totten, R.J. Bishop, R.L. McDaniels, and D.A. Wachter, Iron Steel Engineer, 34 (1996). 29. D. Garg, 6th Annual Reciprocating Compressor Conference, Salt Lake City, September 23 (1991). 30. U.S. Patent #04302343, The Dow Chemical Company. 31. Technical Data Sheet Breox Industrial Lubricants IL SW grades, No date. 32. S. Lawford, 14th International Colloquium Tribology, Esslingen (2004). 33. H. Møller, Lubrication selection for the Horns Reef project, Technische Akademie Esslingen (2003). 34. Technical Data Sheet Breox Hydrolubes, No date. 35. D.K. Wilson, Society of Automotive Engineers — Quarterly Transactions, Vol. 2, No. 2, pages 242–254 (1948). 36. L. Imparato, F. Berti, and G. Mancini, Society of Automotive Engineers — Automotive Engineering Congress, paper #740118 (1974). 37. R. Cracknell, Lubr. Eng., 129 (1993). 38. E.R. Mueller and W.H. Martin, Lubr. Eng., 31, 348–356 (1975). 39. W.L. Brown, Lubr. Eng., 44, 168–171 (1988). 40. C.H. Sweat and T.W. Langer, Mech. Eng., 73, 469 (1951). 41. J. Marx, U.S. Patent No. 3,980,571 (1976). 42. G.F. Felton Jr., U.S. Patent No. 3,983,044 (1976). 43. R.E. Booser, CRC Handbook of Lubrication and Tribology, Vol. III, CRC Press, Boca Raton, FL (1994). 44. ECOTOC report 55, Pulmonary Toxicity of Polyalkylene Glycols (December 1997).

7

Alkylated Aromatics Margaret M. Wu and Suzzy Ho CONTENTS 7.1 7.2

Introduction General Chemistry for Product Synthesis and Structures 7.2.1 Reagents 7.2.2 Catalysts 7.2.3 Alkylation Chemistry and Product Compositions 7.3 Alkylnaphthalenes (AN) 7.3.1 Commercial Products 7.3.1.1 Manufacturer, Synthesis, Process, and Chemical Compositions 7.3.1.2 Chemical and Physical Properties of AN 7.3.2 Experimental Products 7.3.3 Applications 7.4 Alkylbenzenes (AB) 7.4.1 Commercial Processes and Products 7.4.1.1 Synthesis, Process, and Chemical Compositions 7.4.1.2 Commercial Manufacturers, Price, and Volume 7.4.1.3 Physical and Chemical Properties 7.4.2 Experimental Products — Synthesis and Properties 7.4.3 Applications 7.4.3.1 Historical Commercial Application 7.4.3.2 Current Application 7.5 Alkylated Aromatics Containing Heteroatoms Acknowledgments References

Since the last review of “Alkylated aromatics” in the 2nd edition of “Synthetic Lubricants and High Performance Functional Fluids” [1], new commercial alkylnaphthalene fluids with unique properties have become available and numerous papers and patents have reported unique performance features for alkylated aromatic fluids. In this chapter, we summarize these new developments together with key points discussed in the previous edition, to make this chapter a comprehensive review of this subject.

7.1 INTRODUCTION Aromatic components are known to be present in most petroleum-derived base stocks. Conventional solvent refined base stocks usually contain 20 to 40 wt% aromatics [2], depending on the crude source and refining process. The aromatic components in these base stocks are complex mixtures containing mono-, di-, and poly-nuclear

Copyright 2006 by Taylor & Francis Group, LLC

aromatic rings with paraffinic or cyclic substituents. Their presence usually imparts inferior lubricating properties, such as lower VI, reduced oxidative stability and storage stability problems. Advanced refining processes, especially severe hydroprocessing for the manufacturing of Group II plus or Group III base stocks, are designed to remove or convert most of these less desirable aromatic components into paraffins and to remove the associated heteroatoms. Although the naturally occurring aromatic components are not high performance components, some aromaticcontaining molecules with well-defined chemical structures were synthesized and found to have unique properties, such as low temperature fluidity, stability, and solvency [3]. Among all the aromatic-containing fluids, alkylated aromatics are the most common fluids. This is because the benzene or naphthalene aromatic cores are easily converted into alkyl aromatics that are large enough and have properties useful as lubricant base stocks or performance

fluids. This chapter will focus on alkylated aromatics. Other condensed aromatics as base stocks and functional fluids will be discussed in Chapter. Alkylated aromatics as lubricant base stocks were first developed in Germany during World War II [4]. These early developments were primarily motivated by a shortage of petroleum-derived base stock, not by any performance advantage offered by these fluids. Therefore, as soon as petroleum-based fluid became available after the war, the need to develop the alkylated aromatics quickly disappeared. During the late 1960s and early 1970s, engine oils formulated with Conoco alkylbenzene fluids were used by the construction crews on the trans-Alaskan pipeline project because of the excellent low temperature rheological properties of the lubricants [5]. In this application, the advantages of alkylbenzene fluids were clearly defined: better low temperature properties, better lubricity, lower oil consumption, and improved fuel economy. However, after the completion of the Alyeska Pipeline, the use of this type of fluid was never commercialized in large quantity, probably because they were by-products of the detergent alkylate process. In recent years, both fluid producers and lubricant formulators reported numerous activities in developing alkyl aromatic fluids for use in industrial or engine lubricants. Factors contributing to these activities are as follows: • Unique performance advantages of alkylated aromatics

were clearly identified for many special applications. • Extensive new developments in alkylation technology

improved the quality and supply of alkyl aromatics. • Alkylated aromatics are readily produced from readily

available raw materials. As a result, alkylated aromatic fluids re-emerged as costcompetitive, high performance base stocks. The term “alkylated aromatics” covers a wide range of fluids. Depending on the selection of the aromatic component, their properties varied widely, from oils with excellent viscometric properties, such as alkylbenzenes, to oils with superior thermal and oxidative stabilities, such as sulfur-containing alkylated aromatics. This chapter organizes the alkylated aromatics into three classes of fluids according to the aromatic components: • Alkylnaphthalenes • Alkylbenzenes • Alkylated aromatics containing heteroatoms

The production, properties, and applications of these fluids are reviewed in the following sections.

Copyright 2006 by Taylor & Francis Group, LLC

7.2 GENERAL CHEMISTRY FOR PRODUCT SYNTHESIS AND STRUCTURES 7.2.1 Reagents Most alkylated aromatic fluids are produced from a wellknown chemistry, the Friedel–Crafts alkylation of aromatic compounds [6]. In this reaction, an aromatic compound, such as benzene, naphthalene, or their substituted analogue, is alkylated by an olefin, alkyl halide, or alcohol over a Friedel–Crafts catalyst [6]. Olefins are the most often used alkylating agents because they are readily available at low cost and generate no by-products upon alkylation. In contrast, an alkyl halide or alcohol would generate hydrogen halide or water as by-products. The olefins can be alpha-olefins, internal olefins, or branched olefins typically with 8–18 carbons in the molecule. These large olefins are used because they produce alkylated aromatics with at least 25 carbons and with molecular weight greater than 300. Alkylaromatics of this range from benzene, naphthalene, or other aromatics have low volatilities and good viscometric properties as lubricant base stocks. Lighter alkyl aromatics of 15–20 carbons are used in special applications, such as refrigeration fluids or insulating oils.

7.2.2 Catalysts Many homogeneous [6,7] or heterogeneous, solid catalysts [8] are used to catalyze the alkylation of aromatic compounds. The choice of catalysts and reaction conditions depends on several factors including substrate reactivity and alkylate quality requirements. For example, strong acids, such as AlCl3 , BF3 , or HF are used to alkylate benzene that has relatively low alkylation reactivity. Milder Friedel Crafts catalysts, such as FeCl3 , SnCl4 , were claimed to be effective for the alkylation of highly reactive aromatics, such as ortho-xylenes or naphthalene. These halide-containing homogenous catalysts are usually corrosive and generate undesirable waste at the end of the reaction. Newer alkylation technology employs solid, heterogeneous catalysts, especially zeolites [9] or solid super acids [10]. Solid catalysts usually are non-corrosive and many can be regenerated and re-used. In addition to this process advantage, zeolites produce alkylaromatics with a unique isomer distribution that may contribute to unexpected performance advantages over products from conventional catalysts. The use of special catalysts or reaction conditions to favor the formation of specific isomer or monoalkylate, to give optimized lubricating properties has been widely reported. Examples of the synthesis of different alkylated aromatic fluids by using different catalysts are discussed later.

7.2.3 Alkylation Chemistry and Product Compositions Alkylated aromatics made from Friedel–Crafts alkylation reactions usually have very complex chemical compositions with many possible isomers. This complexity can be illustrated by the possible isomeric structures for a C30 H54 di-dodecylbenzene from benzene and 1-dodecene. There are two different schemes to produce the dialkylbenzene. In the first reaction sequence, the mono-alkylbenzene further reacts with the second olefin to give di-dodecylbenzene (Eq. 7.1). In this dialkylbenzene molecule, the aromatic ring may connect to either one of the two alkyl chains at any one of the six possible positions, creating a total of 21 possible isomers. Furthermore, the two alkyl substituents may occupy either ortho-, meta-, or para-position on the benzene ring. With these arrangements, 63 isomers are possible. Even discounting the unfavorable isomers, such as ortho-dialkylbenzene or 1-phenylalkane, we can easily have more than 30 possible isomers for this dialkylbenzene. In another possible scheme to create the C30 H54 alkylbenzene lube, two dodecenes first dimerize to give a C24 olefin, which then reacts with benzene to give a C30 , monoalkylbenzene lube (Eq. 7.2). The C12 dimer can have 21 possible isomers and each isomer may have many positional isomers for phenyl substitution. This results in an extremely complex mixture. If larger olefins are used as alkylating agents, or different olefins are used for the two alkylation steps, more isomers are possible for the final products. 1

3

5

9

7

4

2

6

11

10

8

1

12

2

3

4

5 6

+

6 isomers

1-dodecene 1

2 ortho

3

4

5 6

meta para 1

2

4

3

5

(7.1) 3

5

9

7

4

1

2

3

4

6

8

10

12 +

5

6

C24H49

C30 H54 alkylbenzene, > 100 isomers

(7.2)

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7.3.1 Commercial Products ExxonMobil Chemical Company has commercialized a new class of alkylated naphthalene (AN) fluids with the trade name Synesstic™ [11]. These AN fluids belong to API Group V category. Two viscosity grades with 100◦ C viscosity of 4.7 cSt and 12.4 cSt (Synesstic™ 5 and Synesstic™ 12 respectively) are available commercially. Their basic properties are summarized in Table 7.1. These ANs are made from well-defined chemical compositions. They have superior thermo-oxidative and hydrolytic stability compared to other fluids. When used as a blend stock, they can improve the performance of a variety of finished lubricants. 7.3.1.1 Manufacturer, synthesis, process, and chemical compositions AN can be synthesized by the alkylation of naphthalene with an olefin over a Friedel–Crafts catalyst (Eq. 7.3). Alkyl halides or alcohols can also be used as alkylating reagents. The basic chemistry for AN synthesis has many similar features as that for alkylbenzene synthesis as discussed in Section 7.2. Equation 7.3 shows, when naphthalene is alkylated with a 1-tetradecene, the naphthyl ring can be connected at the 2- to 7-positions of the C14-alkane chain. Also, the alkyl substituent can connect at either the α- or β-position of the naphthalene ring. The reaction product is usually a very complex mixture. By selecting proper

TABLE 7.1 Synesstic™ Alkylated Naphthalenes Product and Properties Synesstic™

11

2 2

7.3 ALKYLNAPHTHALENES (AN)

6

C30H54 di-alkylbenzene, 63 isomers

1

Among all the possible compositions, some structures have better lubricating properties than others. Therefore, a better alkylaromatic base stock can be produced by tailoring reaction conditions or alkylation catalysts to favor these special compositions. Much patent literature deals with this aspect of the technology. These structure–property correlations are discussed later in connection with each class of alkylated aromatic fluids.

Kinematic viscosity at 100◦ C, cSt Kinematic viscosity at 40◦ C, cSt Viscosity index Pour point, ◦ C Flash point, open cup, ◦ C Flash point, closed cup, ◦ C Kinematic viscosity at −40◦ C, cSt

5

12

4.7 29 74 −39 222 192 43,600

12.4 109 105 −36 258 240 392,500

catalyst and reaction conditions, one favors the desirable isomer composition and the amount of mono-, di-, and poly-alkylated naphthalenes in the final product.

2

3 4 5 6 7

Catalyst α

+

β

(7.3) In AN synthesis, naphthalene alkylation with one C12 or higher linear alpha-olefin is enough to produce a molecule with good viscosity and low volatility. In contrast, benzene alkylation usually will take at least two alkyl groups to make the molecule large enough to be a high quality base stock or functional fluid. This is because naphthalene itself is a larger and more polar aromatic core molecule. ExxonMobil’s Synesstic AN is produced by a proprietary technology based on the company’s proprietary zeolite catalyst. The company has been issued many patents covering the manufacturing of AN with optimized properties and at high yields [12,13].

7.3.1.2 Chemical and physical properties of AN The intrinsic properties of a base stock are important for the product to have a long and effective service live. Although additives can enhance the base stock performance, additives are used in very small quantities and they will be consumed or depleted during the oil service life. When that happens, the stability of the base oils provides the last defense from the attack of oxygen, water, or other agents. AN has many unique properties that are summarized below.

7.3.1.2.1 Oxidative stability of AN Lubricant formulators recognized that lubricants based on alkylnaphthalene fluid had excellent oxidative stability as early as the 1960s [14]. The electron-rich naphthalene rings in AN fluid can trap the oxy- or peroxy-radicals generated from hydrocarbon oxidation and thus, disrupt the oxidation chain process, preventing oxidative degradation [15,16]. Compared to poly-alpha-olefins (PAO) or dibasic ester, AN indeed has superior intrinsic oxidative stability without any antioxidants (Table 7.2) [17]. In the rotary bomb oxidation test (RBOT, ASTM D2272 method) at 150◦ C, 90 psi oxygen pressure and in the presence of water and copper catalyst, it takes 195 min for AN to react with a specific amount of oxygen. In contrast, it takes only 17 to 70 min for PAO or ester to react with the same amount of oxygen. In a high pressure DSC test (500 psi oxygen atmosphere and 180◦ C), the induction time before oxidation takes place is >60 min for AN, which is significantly longer than the 2.5 to 5 min for PAO or esters [18,19]. 7.3.1.2.2 Thermal stability of AN AN has superior thermal stability — the best among all the common synthetic base stocks (Table 7.3) [18,19]. In a thermal stability test, the base oil was heated to 550◦ F in nitrogen atmosphere for 72 h. During the test, thermal cracking of the oil molecules occurred resulting in viscosity loss, formation of acids, or weight loss from volatilization. Data in Table 7.3 demonstrate that AN fluids had the best thermal stability: 1. The low vis AN had no viscosity change — a 0.4% viscosity increase maybe due to volatility or within experimental error. The high vis AN had only 1.1% viscosity loss. This stability in viscosity change is comparable to that of the polyol ester, which is well documented to have extreme thermal stability and is used as base stock in high performance jet engine oil

TABLE 7.2 Comparison of Intrinsic Oxidative Stabilities — AN vs. PAO or Ester Base Stocksa

Viscosity at 100◦ C, cSt By D2272 method, at 150◦ C, minutes to breakdown Oxidative stability, DCS-IP min. Oxidation and corrosion test, TAN increase

Low viscosity AN

High viscosity AN

PAO

Adipate ester

Polyol ester

4.7 195

12.4 180

5.8 17

5.3 70

4.3 Not available

60+

60+

2.5

5.0

60+

0.092

0.089

NE

7.1

1.3

a All tests were conducted for the base stocks without any antioxidants.

Copyright 2006 by Taylor & Francis Group, LLC

TABLE 7.3 Thermal Stabilitya of AN Compared to Other Common Synthetic Base Stocks

Viscosity loss, % TAN, mg KOH/g Wt% loss

Low viscosity AN

High viscosity AN

PAO

Diester

Polyol ester

−0.4 0.32 0.51

−1.1 0.24 0.33

9.1 0.22 1.16

9.2 53.9 23.1

0.1 8.1 1.09

a Test conditions: oil sample was heated to 550◦ F under N atmosphere for 72 h. 2

TABLE 7.4 Hydrolytic Stabilitya of AN Compared to Other Common Synthetic Base Stocks

Viscosity at 100◦ C, cSt Hydrolytic stability, TAN increase

Low viscosity AN

High viscosity AN

PAO

Adipate ester

Polyol ester

4.7 0.02

12.4 0.02

5.8 nil

5.3 0.16

4.3 0.20

a By ASTM D 2619 method.

formulations [19]. In comparison, PAO and diester both lose more than 9% of the viscosity. 2. AN fluids had low total acid number (TAN) increase. In comparison, the diester and polyol ester had a significant increase in TAN, which leads to metal corrosion. 3. AN fluids had the lowest amount of weight loss during this thermal stability test, lower than the very thermally stable polyol ester. 7.3.1.2.3 Hydrolytic stability AN fluids are hydrocarbons and contain no functional groups that can react with water. Therefore, AN fluids are hydrolytically much more stable than the other commonly used Group V fluids — esters, which are reactive toward water to produce acids. Table 7.4 showed that AN generates very little change in total acid number (TAN) — about 8 to 10 times less than diesters or polyol esters in a typical hydrolysis test [18]. 7.3.1.2.4 Solvency and dispersancy One unique property of Group V base stocks is their relatively high polarity, high solubility, and dispersancy for the polar additives, sludge, and degradation products. AN has an electron-rich naphthalene core that contributes to the fluid’s polarity and solvency/dispersancy property. Traditionally, aniline point by ASTM D 611 method is used to measure the aromatic content of a mineral oil base stock. It is defined as the temperature when equal volume of

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aniline and the test hydrocarbon fluid become completely miscible into one phase. Because aniline is a very polar molecule, the aniline point can be used as a quantitative measure for the polarity of the test fluid. Higher aniline point indicates low polarity and lower aniline point indicates high polarity. Table 7.5 compares the aniline points of many common synthetic base stocks of comparable 100◦ C viscosities [18,19]. Synesstic™ 5 AN has very low aniline point, much lower than PAO, alkylbenzene (another alkylaromatic fluid discussed in the next section), and Group I mineral oil. This low aniline point is beneficial during formulation to help dissolve additives and to reduce deposit formation during service. AN fluids have higher aniline points than esters and are less polar than esters. This is advantageous because they are less likely to compete for metal surfaces, thus allowing surface-active additives to perform their functions without interference from the base stock. This advantage was reported in formulated products [20]. 7.3.1.2.5 Viscometrics AN fluids generally have very low pour points and excellent low-temperature viscosities, as shown in Table 7.6. For example a 4.7 cSt AN has a pour point of −39◦ C. AN fluids have lower VI than PAO or esters. In actual formulation, the VI of the AN fluids can be improved by blending with other base stocks or by using VI improvers. In many

TABLE 7.5 Aniline Point of AN Compared to Other Common Synthetic Fluids Fluid type

Low viscosity AN

High viscosity AN

PAO

Ester

Alkylbenzene

Group I base oil

4.7 32

12.4 90

5.5 119

5.2 20

4.2 77.8

4.0 100

Kv at 100◦ C, cSt Aniline point, ◦ C

TABLE 7.6 Viscometric Properties of AN and Other Synthetic Fluids Fluid type

Low viscosity AN

High viscosity AN

PAO

Diester

Group I base oil

4.7 74 −39

12.4 105 −36

5.5 130 −62

5.3 133 −57

4.0 90 −15

Kv at 100◦ C, cSt VI Pour point, ◦ C

300 250

RBOT, min

200 150 100 50 0 AN, wt% PAO, wt%

0% 100%

25% 75%

50% 50%

75% 25%

100% 0%

FIGURE 7.1 Different amount of Synesstic™ 5 AN in PAO show synergistic effect in improving oxidative stability of the blend stocks

applications, it is more critical for the fluid to have thermal oxidative stability and low pour point than higher VI. 7.3.1.2.6 Blend properties AN fluids have excellent solubility in all the hydrocarbon fluids (Groups I to VI) and many very polar fluids, such as polyalkylene glycols (PAG). This character makes AN superior blend stocks because with their intrinsic stability and solvency, they often create synergistic and unexpected improvements for the blends. For example, when different amounts of Synesstic™ 5 AN were blended with PAO, the oxidative stability of the blends by RBOT test were higher than the predicted RBOT from the pure component (Figure 7.1) [17]. In a modified oxidation and corrosion test, when the oil was heated to 93◦ C for 40 h with purging air in the presence of metal catalysts (similar to ASTM D 943 test), the addition of AN to PAO significantly improved the oxidative stability of the blends. Figure 7.2 showed the %viscosity increase and the TAN increase for the AN and PAO blends

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[17]. When 25% AN was added to PAO, the %viscosity increase was reduced from 91% for pure PAO to 28% for the blend. A similar decrease in TAN change was observed. This favorable synergistic trend continued when more AN was used in the blend. These data clearly demonstrated the synergistic improvement of oxidative stability by blending with AN. A similar synergistic improvement in oxidative stability was also observed with the blends containing AN with Groups I, II, and III mineral base stocks [18]. When 20% Synesstic™ 5 is used as blend stock in a typical mineral oil Groups I, II, and III base stocks, the blends have an almost fivefold increase in the DSC induction time in DSC oxidation test at 180◦ C and 500 psi oxygen atmosphere (Table 7.7). The improvement of oxidative stability for the blends containing AN fluids was also reported in the presence of an antioxidant [17]. Figure 7.3 shows that, in the presence of 0.25 wt% of a hindered phenolic antioxidant Ethyl 702, the oxidative stability of the AN/PAO blends by DSC induction

100

% Visc Increase

90

TAN Increase

80 70 60 50 40 30 20 10 0 0% AN

25% AN

50% AN

75% AN

100% AN

FIGURE 7.2 % Viscosity increase and TAN increase for blends containing different amounts of Synesstic™ 5 AN in PAO

TABLE 7.7 DSC Induction Time of Blends Containing Synesstic 5 AN with Different Groups I, II, and III Base Stocks DSC induction time of the blends, min Group I II III

DSC Induction Time, Min.

60

0% AN

10% AN

20% AN

28 26 27

34 30 31

150 151 48

50 40 30 20 10 0 25% AN

50% AN

75% AN

FIGURE 7.3 Improvement of oxidative stability of AN/PAO blends with or without 0.25 wt% Ethyl 702 antioxidant by DSC induction time measurement at 180◦ C and 500 psig oxygen pressure [17]

time measurement were significantly improved over pure PAO without any AN. The positive blending behavior for 5 cSt AN can be extended to the blends with the high viscosity 12 cSt AN.

7.3.2 Experimental Products Pure alkylnaphthalene has been used as a synthetic lubricant base stock occasionally since 1930. H. Dressler, etc. of Koppers Co. first reported the high oxidative stability of AN as lubricant base stocks in 1975 [21]. It is not

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• the chain length of the alkyl substituents decreases • the alpha/beta ratio of the alkyl substituent increases • the dialkyl AN content decreases

7.3.3 Applications

0% Antioxidant 0.25 wt% antioxidant

0% AN

clear if Koppers ever commercialized this fluid. Before the 1980s, reports about AN fluids were few [22]. Since then, many patents have claimed to produce fluids with significantly improved thermal oxidative stabilities by tailoring their molecular structures (Table 7.8) [23–25]. These data show that the useful service lifetime of AN fluid increases when:

AN fluids have intrinsic thermal, oxidative, and hydrolytic stability and excellent solubility and solvency. When used in combination with other base stocks, they synergistically improve the properties of the blends. In particular, AN fluids are superior for use in the formulation of synthetic or part-synthetic automotive engine and industrial lubricants. Major advantages are in longer and more stable oil service life, superior viscometrics, and better equipment protection [20]. A recent ExxonMobil patent application described that when AN was blended with Groups II to V base stocks, the blended base stocks had unexpected reduction of friction coefficients. Fully formulated automotive engine oils based on these AN-containing blends, showed significantly improved fuel economy in the standard Sequence VIB engine test [26]. In another patent, when a base fluid containing a small amount of AN in PAO or other hydrocarbon base stocks was used to formulate gear oil, circulating oil compressor oil, or other general industrial oils, the finished lubricants demonstrated an excellent balance of antiwear and antirust performance [27]. Nippon Oil Co. has marketed a long-drain synthetic lubricant based on AN fluid for rotary air compressors since 1991 [28]. This lubricant was formulated to take advantage

TABLE 7.8 Comparison of Relative Useful Service Life of AN of Different Chemical Compositions AN composition 1-Octene + naph. 1-Decene + naph. 1-Hexadecene + naph. 1-Octene + naph. 1-Decene + naph. Di-isopropylnaphthalene

Viscosity at 40◦ C, cSt

Pour point, ◦ C

α/β ratios

Service lifea , h

10.54 11.93 27.03 — — —

<−45 <−45 <−45 — — —

1.44 1.33 1.63 0.28 0.61 —

88 75 65 15 18 2

a Oxidation test was conducted at 170◦ C, oxygen flow rate of 3 L/h and in the presence

of copper wire catalyst. Useful lifetime was the time oil reached a total acid number of 1.0 mg KOH/g.

of the excellent thermal and oxidative stability of the AN fluid. This lubricant extended the oil change interval for rotary air compressor from the conventional 6 months or one year to up to 4 years or 12,000 h of continuous operation. This extended drain interval significantly reduced maintenance work and increased operational reliability. Alkylnaphthalene fluids were used in high temperature heat transfer fluid [29], in vacuum pump oil [30], in metalworking fluid [31], and in general high temperature applications [32]. No specific commercial applications in these areas were clearly documented. With the recent commercialization of AN fluids by ExxonMobil Chemical Co. and the identification of many performance features, it is expected that the use of AN fluids will expand and the volume growth will continue.

Scheme 7.1. Linear Alkylbenzene (LAB) Production Scheme (a) From n-paraffin dehydrogenation CH3(CH2)xCH3

n-alkanes, averaging C12

Dehydrogenation

CH3(CH2)yCH=CH(CH2)zCH3

linear internal olefins CH3(CH2)yCHCH2(CH2)zCH3

+

(7.4) (b) From n-paraffin chlorination

7.4 ALKYLBENZENES (AB) 7.4.1 Commercial Processes and Products 7.4.1.1 Synthesis, process, and chemical compositions Commercial AB fluids with 100◦ C kinematic viscosity of 2.5 to 10 cSt are available from detergent alkylate producers. Detergent alkylates, an intermediate for detergent manufacturing, are usually mono-alkylbenzenes. During the production of the detergent alkylate, some dialkylbenzene and heavier alkylbenzene are also produced. These heavier alkylates, unsuitable as detergent alkylates, are excellent lubricant base stocks. To discuss AB lubricant base stock manufacturing, we start with detergent alkylate manufacturing. There are two types of detergent alkylate — linear alkylbenzene (LAB) and branched alkylbenzene (BAB alkylates). Their production processes are summarized in Schemes 7.1 and 7.2 [33].

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CH3(CH2)xCH3 n-alkanes, averaging C12

CH3(CH2)yCH(CH2)zCH3 Chlorination Cl mono-chloroalkane CH3(CH2)yCH(CH2)zCH3

+

+ HCl

(7.5) (c) From alpha-olefins

+

CH3(CH2)yCH(CH2)zCH3

CH2 = CH(CH2)xCH3

(7.6)

Scheme 7.2 Scheme Branched Alkylbenzene (BAB) Production Scheme (a) From propylene oligomers (C3H6)x

+

(x = 3 to 5, averaging tetramer)

Propylene

Scheme 7.3 Production Scheme and Chemical Compositions for Heavier Alkylates CnH2n +1 CnH2n +1

2.

Diphenylalkanes R

(CH2)x

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R9

(CnH2n)2H

CH3

The common feature of these processes (Eqs. 7.4–7.7) is that an alkylating agent is reacted with benzene over a Friedel–Crafts catalyst, such as HF, BF3 , AlCl3 , or zeolites. These processes differ in that each alkylating agent is produced by a different reaction. The alkylating agent can be a linear internal olefin (Eq. 7.4), a mono-chloroalkane (Eq. 7.5), an alpha-olefin (Eq. 7.6), or a propylene oligomer (Eq. 7.7). The detergent alkylates produced in Eqs. 7.4–7.7 are C16 –C22 alkylbenzenes with an average of 18 carbons per molecule. They are too light and too volatile for most lubricant applications except in special cases, such as refrigeration lubricants. The alkylbenzenes useful as synthetic lubricant base stocks are usually the heavier alkylbenzenes that are produced from various side reactions in the detergent alkylate processes [34]. They usually amount to less than 10% of the total product. The chemical compositions of some of the heavier alkylates and the reactions that generate them are listed in Scheme 7.3.

Dialkylbenzenes (DAB)

Alkylbenzenes from olefin dimers

(C3H6)x - CH - CH2 - (C3H6)y

(7.7)

1.

3.

The detergent alkylates produced in Eqs. 7.4 to 7.7 can further react with the 2nd alkylating reagents to give dialkylbenzenes. One example was discussed in Eq. 7.1. The dialkylbenzenes are usually the major components in lube range alkylbenzene fluids. Di-olefins or di-chloroalkanes are produced as side reaction products from paraffin dehydrogenation or chlorination of Eqs. 7.4 or 7.5. These bi-functional alkylating reagents can react with two benzene molecules to give diphenyl alkanes as lubricant base stock components [35].

4.

Bi-cyclic alkanes R

The olefins in Eqs. 7.6 and 7.7 may dimerize first to give dimer olefins and then add to the benzene ring to give lube range molecules. The alkyl group in the detergent alkylates or the higher alkylbenzenes may cyclize over the Friedel–Crafts catalyst to these higher boiling bi-cyclic alkanes.

The chemical compositions of AB fluids vary significantly depending on the process. There are many other minor components and some of them are strong colored bodies, giving the fluid a deep color. 7.4.1.2 Commercial manufacturers, price, and volume In the United States, LABs are manufactured by Sasol (formerly Vista Chemical Co.) and Hunstman Chemical Corp. with a total 2003 production capacity of 852 million lb [33]. Only a very small fraction is used in lubricant and functional fluid applications and only Sasol offers lube range AB fluids produced from their LAB plant. The properties of these fluids and comparisons with other fluids are listed in Appendices 7.1 and 7.2. The early BAB-based detergents had poor biodegradability and were replaced quickly by LAB-based detergents. The last BAB producer in the United States, Monsanto, closed down its production in 1991. In the past, Chevron and Exxon Chemical Co. both produced BABs in Europe. In 2003, only Chevron Oronite still manufactured BAB in Europe as raw material for alkylbenzene sulfonates. It is not clear if any BABs are used as lubricant base stocks. The properties of some of these historical fluids are listed in Appendix 7.3. Table 7.9 summarizes the 1993 volume of alkylbenzene fluids together with all the producers in different regions and the estimated price of alkylbenzene fluids [36]. Obviously, these numbers have changed since 1993 and should be used only as a historical guide. Since all AB fluids are by-products from LAB or BAB detergent alkylate plant, the product quality and availability are not consistent. They are consistently priced lower than other common synthetic base stocks, such as PAO, esters, or PAG. Historically, the total volume for AB base stock has been very low compared to PAO, esters, or PAG. However, AB fluid can be produced readily on a large commercial scale if significant demand is developed because their raw materials are readily available and the manufacturing process is well documented [34].

TABLE 7.9 1993 AB Fluid Production Volume, Producers, and Price United States Volume, metric tons/yr Producers

Western Europe

Japan

3200

8100

3100

Vista Chem. Co. (now Sasol) Huntsman Chem. Co. Pilot Chem. Co.

Chevron Chem. Co. Exxon Chem. Co. Montedison SpA.

Nippon oil Co. Idemitsu Kosan Kyodo Oil Co. Showa Shell Sikiyu Cosmo Petrotech Co.

Estimated price, in $/Gal, and compared to other base stocks AB 3.8 3.2 PAO 4.8 5.3 Polyol ester 8.6 12.3 Dibasic ester 5.3 8.7 PAG 7.0 7.1

6.0 9.8 11.0 9.5 6.3

TABLE 7.10 Viscometrics of Alkylbenzene Fluids and Comparable Fluids Fluid trade name Company or source Fluid type

V-9050 Sasol Di-LAB

DN-600a Conoco Di-LAB

NALKYLENE 600a Conoco Mono-LAB

Zerol 150 Chevron BAB

Zerol 300 Chevron BAB

PAO —

Dibasic ester —

Mineral oil —

Properties Viscosity, cSt At 100◦ C At 40◦ C At −40◦ C VI Pour point, ◦ C Average molecular weight Flash point, ◦ Cb Specific Gr.

4.3 22.0 6,000 100 −60 397 215 0.89

5.1 29.1 8,600 115 −54 — 229 0.865

1.77 5.90 500 73 <−68 — 152 0.865

4.35 33.46 na 25 −40 na 170 0.87

5.8 57.0 na 14 −35 na 275 0.87

3.92 17.89 2,900 120 −68 na 218 0.82

5.3 28.2 16,100 134 −59 na 235 0.91

4.0 18.9 na 97 −15 na 194 0.86

a Data from Reference 5. b Measured by D 92 or Cleveland open cup method except that V9050 fluid was measured by D 93 or PM closed cup method.

7.4.1.3 Physical and chemical properties 7.4.1.3.1 Viscometrics Table 7.10 compares the typical viscometrics of the linear alkylbenzene (LAB) or branched alkylbenzene (BAB) base stocks with other common base stocks available commercially or reported in the literature. The LAB-based fluids usually have VI greater than 100, as well as very low pour points and very good low temperature viscosities. These properties are slightly inferior to a typical PAO or dibasic esters. They can be improved by careful choice of starting material and reaction conditions [37]. The BAB-based fluids usually have very poor VI and poor low temperature viscosities.

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7.4.1.3.2 Solvency The additive solvency of AB fluids is best measured by their aniline points (Table 7.11) [38]. As these data show, AB has a much lower aniline point than PAO or low viscosity mineral oil, indicating better solvency for additives or other polar components in the lubricants. Because of this excellent solvency, AB fluid may be used as ester substitute in many synthetic industrial or engine oil formulations [39]. 7.4.1.3.3 Volatility Generally, AB fluids have volatility lower than mineral oil and higher than PAO of comparable viscosity (Table 7.12) [38,39]. The alkylbenzene fluids produced as detergent alkylate bottoms have a wide distribution of molecular

weights because they are produced from olefins in the range of C10 to C15 . The lightest fraction of this broad molecular weight distribution contributes significantly to its volatility. If these light ends of the mixed alkylbenzene fluids can be removed by careful distillation, the volatility of AB fluid can be improved. AB fluids generally have flash points similar to those of PAO, another indicator for excellent volatility (Table 7.12). 7.4.1.3.4 Thermal and oxidative stability Commercial dialkylbenzene fluids have much better thermal stability than ester, and are similar in this regard to PAO [40]. Specialty AB fluids such as tri-n-alkylbenzene (discussed in Section IV.B) have outstanding thermal stability, as tested at 371◦ C under N2 (Table 7.13) [40]. At this testing condition, PAO loses 75% of its viscosity, whereas the tri-n-alkylbenzenes lose only 11 to 29% of their viscosities. Depending on test conditions, alkylbenzene fluids are comparable to or better than PAO in oxidative stability (Table 7.14) [38]. At higher temperature (such as 175◦ C), the AB fluids have similar oxidative stability as PAO when formulated with anti-oxidants [40].

7.4.2 Experimental Products — Synthesis and Properties Many experimental AB fluids prepared from benzenes or substituted benzenes are reported in the literature. Some examples are given in the following subsections.

1. Diphenyl alkane fluids. These were prepared from styrene or substituted styrene with alkylbenzenes over different types of Friedel–Crafts catalyst (Eq. 7.8) [35,41–43]. R Catalyst

+

(7.8) The diphenyl alkane fluids were reported to have high traction and good electrical insulating properties. 2. Among the several such fluids reported in the literature are the following:

7.4.1.3.5 Other Properties AB fluids were reported to have excellent elastomer compatibility, electrical insulating properties, refrigerant compatibility, and lubricity. These unique properties allow the fluids to be used in specialty applications.

(a) 1,3,5-Tri-n-alkylbenzene was prepared by reacting 1,3,5-trichlorobenzene with mixed alkyl magnesium chloride (Eq. 7.9) [44]. Cl +

Cl

TABLE 7.11 Comparison of Aniline Points of Base Stocks Linear Di-AB

PAO

Mineral oil

4.2 77.8

3.9 116.7

4.0 100

Viscosity at 100◦ C, cSt Aniline point, ◦ Ca a By ASTM D-611 method.

RMgCl + R⬘MgCl

Cl

R +

(7.9) (b) 1,3,5-Tri-n-alkylbenzene was prepared by reacting 1,3,5-trimethylbenzene with ethylene over butyllithium catalyst. Alkyl groups having 3 to 17 carbons with an average of 8 carbons per alkyl group

AB

PAO

100 SUS mineral oil

AB

PAO

200 SUS mineral oil

4.2 17.3 215a

3.9 14.4 215a

4.0 27.1 200a

6.55 10.8 230b

6.04 7.9 242b

6.21 10.1 224b

a Flash points measured by ASTM D 93 or PM closed cup method. b Flash points measured by ASTM D 92 or Cleveland open cup method.

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MgCl2

R⬘ R R,R⬘= n - C8H17 to C12H25

TABLE 7.12 Comparisons of Flash Point and Noack Volatility of Selected AB Fluids

Viscosity at 100◦ C, cSt Noack volatility, wt% Flash point, ◦ C

R

were generated (Eq. 7.10) [40]. CH3 +

H3C

CH2 = CH2

TABLE 7.15 Consumption Rate and Application Areas of AB Fluids in 1993

R

BuLi Catalyst

R⬘ ⬙R R,R⬘,R⬙ = n - C3H7 to C17H35

CH3

(7.10) (c) Mixed 1,3,5- and 1,2,4-tri-n-alkylbenzenes with excellent lubricant properties were prepared by cyclotrimetrization of 1-alkynes having 8 to 12 carbons over a solid chromium oxide on silica gel catalyst (Eq. 7.11) [45]. n-C8H17 Catalyst

n-C8H17

3 n-C8H17

(7.11) These tri-n-alkylbenzenes have excellent viscometrics (low pour points less than −40◦ C and high viscosity index VI >130) and superior thermal and oxidative stabilities compared to the TABLE 7.13 Thermal Stabilities of AB Fluids and Other Synthetic Base Stocks % Loss of 38◦ C viscositya

Fluid type PAO dimer Commercial C12 -dialkylbenzene 1,3,5-Tri-n-heptylbenzene 1,2,4-Tri-n-octylbenzene

75.3 72.7 11.2 29.1

Consumption rate, metric tons/yr

U.S.

Western Europe

Japan

Refrigeration lubricant Metalworking fluid Compressor oil Others

3.2 — — —

7.0 1.1 — —

— — 3.0 0.1

dialkylbenzenes prepared from Friedel–Crafts alkylation reaction. This is probably because the n-alkylbenzenes have fewer alkyl branches at the benzylic position and thus improved thermal and oxidative stabilities. 3. Dialkylbenzenes of 2–4 cSt. Fluids in this viscosity range can be produced from ethylbenzene and alphaolefins having 14–18 carbons over a silica-alumina catalyst. This type of AB fluid has VI greater than 95 and pour points less than −40◦ C [46]. The fully hydrogenated fluids with dialkylcylcohexane structures have higher viscosities and can be used as lubricant base stocks. 4. Other alkylbenzene fluids. Diisopropylbenzene (cumene bottom fraction) and 1-hexadecene over a catalyst of tantalum chloride (TaCl5 ) on silica gel produced alkylbenzene fluids [47]. The product lubricant had a kinematic viscosity of 3.6 cSt at 100◦ C and 89 VI. A similar fluid by conventional alkylation catalysts (e.g., AlCl3 ) had a kinematic viscosity of 3.97 cSt at 100◦ C and 79 VI.

7.4.3 Applications

a At 371◦ C, N atmosphere, 6 h, in 304 stainless steel 2

7.4.3.1 Historical commercial application

bombs.

In the late 1960s, Conoco, a linear alkylbenzene producer at that time, commercialized SAE 5W-20 and 10W-30 engine crankcase oil based on dialkylbenzene base fluid [5,48]. These products had very low pour points, (<−50◦ F), and provided satisfactory lubricating function at low temperatures. These early engine oils, introduced in 1969, served the equipment and machinery used during the search for oil in Alaska and Canada and during the construction of trans-Alaskan pipeline. Later, these engine oils were claimed to have the advantages of lower oil consumption, better fuel economy, extended drain interval, and excellent engine wear protection. Although these early products claimed many performance features, they were discontinued because they failed to meet overall marketing demand. In addition to the crankcase oils, several early synthetic industrial lubricants based on dialkylbenzene fluids

TABLE 7.14 Comparison of Oxidative Stability of Un-Additized Base Stocks — AB vs. PAO or Mineral Oil Fluid type RBOT, mina Turbine oil oxidative test, hb

Linear di-AB

PAO

100 Neutral mineral oil

23 109

17 39

20 23

a RBOT, rotary bomb oxidation test, ASTM D 2272, was conducted at 150◦ C in the presence of water and copper catalyst under 90 psi of oxygen atmosphere. b ASTM D 943 test was conducted at 95◦ C in the presence of water and iron–copper catalyst with constant air purge.

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TABLE 7.16 Physical Properties of Alkylated O- or S-Containing Aromatic Fluids

O-Containing fluids C16 -dibenzofuran C12 /C14 -diphenyl ether di-C12 /C14 -diphenyl ether C14 -phenoxanthin C16 -phenoxanthin S-Containing fluids C16 -benzothiophene C16 -dibenzothiophene C16 -thiophene C12 -diphenyl sulfide C16 -diphenyl sulfide

Viscosity at 100◦ C, cSt

VI

Pour point, ◦ C

Reference

7.1 3.6 9.7 7.8 7.9

78 78 118 41 62

−45 −57 −45 −35 −35

[59] [60] [60] [61] [61]

5.5 10.1 2.8 3.5 4.6

81 4.9 129 90 135

−58 −22 −13 −53 −43

[62] [62] [63] [64] [64]

were claimed to be usable in high and low temperature applications. Examples included: 1. Hydraulic fluids with improved low temperature pumpability and antiwear properties. 2. A heavy-duty extreme pressure synthetic gear oil with improved low temperature flow property (−65◦ F pour point). This oil was claimed to improve gear life at low temperature, to provide protection equivalent to a thicker SAE 90 grade gear lubricant and to provide improved energy saving compared to conventional gear oil. 3. A synthetic grease based on dialkylbenzene and bentonite or lithium soap as thickener. This type of grease was claimed to have good low temperature dispensability, high temperature adhesive property, and rust inhibiting property.

7.4.3.2 Current application The major applications of AB fluids in 1993 are summarized in Table 7.15 [36]. In 1993, more than 70% of the worldwide alkylbenzene was used as base fluids for synthetic refrigeration lubricants compatible with chlorofluorocarbons (CFCs) or hexachlorofluorocarbons (HCFCs) [49–51]. AB fluids have been used as synthetic substitutes for naphthenic mineral oils in the CFC- or HCFC-compatible refrigeration lubricants for the following reasons:

copper-lead bearing loss by ASTM L-38 single cylinder engine oxidation test.

1. They have excellent low temperature fluidity. 2. Compared to mineral oil or PAOs, either branched or linear alkylbenzenes have much better solubility with HCFC type refrigerants, such as R22 or R123, at temperatures below −60◦ C [50]. 3. Alkylbenzene fluids have better chemical stability toward the refrigerant than mineral oil because they contain no heteroatoms [51]. 4. Their seal compatibility and electrical insulating properties are comparable to those of mineral oil. 5. Alkylbenzenes can be blended with naphthenic mineral oils as semi-synthetics to reduce lubricant cost and still maintain some of their performance advantages. 6. Alkylbenzenes have excellent solvency to dissolve the antiwear, metal-passivating, and oxidation-inhibiting additive packages used to improve a lubricant’s long-term stability. 7. Compared to other synthetic base stocks, such as esters or polyalkylene glycols, AB fluids from the detergent alkylate process are relatively low cost.

These early synthetic and semi-synthetic lubricants failed to reach full-scale commercialization.

The Montreal Protocol required the discontinuation of CFC production by 1996 and the gradual phase-out of HCFC

The extra cost of synthetic dialkylbenzene fluid compared to conventional mineral oil was considered a disadvantage by early formulators. To reduce cost, formulators evaluated semi-synthetic lubricants using dialkylbenzene and conventional mineral oil [5]. Based on extensive testing, several semi-synthetic SAE 5W-30 motor oils were claimed to have the following improvements: • Lower oil consumption for the SAE 5W-30 oil • Higher oxidative stability by ASTM Sequence IIID test • Lower viscosity change, acid number change, and

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by 2020, to be replaced by more ozone-friendly HFC refrigerant. However, AB fluids have low solubilities in the ozone-friendly HFC refrigerants [36]. This poses a problem for AB because complete solubility of the lubricant fluids in refrigerant is critical for reliable operation in small hermetic refrigeration compressors. As a result, AB fluid may not compete effectively against the alternative refrigeration lubricants based on polyol ester (PE) or polyalkylene glycol (PAG), which are highly soluble in HFC refrigerant. However, PE- or PAG-based lubricants have other performance problems. Recently, many patents and much literature claimed their performance deficiencies of PE- or PAG-based lubricants can be improved by using alkylbenzene or by using blends of alkylbenzenes and PAO mixtures [52–55]. These multicomponent blends were claimed to have improved lubricity, wear protection, and hydrolytic stability or hydroscopicity, as well as better chemical stability and electrical insulating properties. Alkylbenzene fluids are used in metalworking fluids. For example, a low viscosity alkylbenzene fluid has shown advantages over highly refined paraffin oil in aluminum cold rolling to produce highly polished aluminum metal

surfaces [56]. Alkylaromatics, including alkylbenzenes, alkylated biphenyls, and diphenyl alkanes are used in electrical insulating oils because of their excellent electrical insulating properties and low water absorption [41,57,58].

7.5 ALKYLATED AROMATICS CONTAINING HETEROATOMS The properties of selected alkylated aromatic base stocks containing oxygen or sulfur atoms are summarized in Table 7.16. In general, these fluids have excellent viscometrics, with 100◦ C viscosities of 3 to 10 cSt, good VI, and excellent pour points. They are also claimed to have good thermal-oxidative stability and lubricity. Among oxygen-containing fluids, alkylated benzofuran, alkylated diphenyl ether, and alkylated anisole where reported to be excellent synthetic base stocks [59–61]. These alkylated aromatics can be produced by the alkylation of diphenyl ether with C6 –C18 alpha-olefins over either conventional Friedel-Crafts catalyst, AlCL3 [60], or solid acidic zeolite catalysts, such as Y-type zeolite [62]. Depending on reaction conditions, such as molar ratios of aromatics to olefins or catalyst employed, fluids with different amount

APPENDIX 7.1 Selected Alkylbenzene Fluids from Sasol and Their Properties Lube properties Average molecular weight Viscosity, cSt 100◦ C 40◦ C Pour point, ◦ C Flash point, ◦ C Boiling range, ◦ C Color, ASTM Appearance Aniline point, ◦ C

V-3050 310

V159L 340

V-8560L-H ∼380

3060L-B 450

2 to 4 11 to18 −42 to −58 >177 <330 to ∼420 — Varies ∼ 36

3 to 5 20 to 25 −50 >195 ∼ 320 to >500 1 to 2 Amber oily liquid ∼ 55

5 to 6 38 −40 to −45 >215 ∼350 to >525 2 to 3 Amber oily liquid 65 to 70

— 47 −40 to −45 226 ∼350 to >525 3 to 4 Dark yellow oily liquid 70 to 75

APPENDIX 7.2 Comparison of Dialkylbenzenes vs. Other Synthetic Base Stocks Oil Volatility Oxidative stability Viscosity index (actual) Pour point (actual, ◦ F) Additive solubility Sludge-forming tendency Seal compatibility Relative price

Dialkylbenzene

Olefin oligomers, PAO

Diester

Polyol ester

Mineral oil

2 2 4 (113) 2 (−70) 1 2 1 3–4

3 5 2 (137) 1 (−90) 5 2 3 4

2 4 1 (147) 1 (−96) 2 1 3 5

1 1 3 (130) 2 (−70) 1 2 3 7

5 2 5 (95) 5 (+5) 1 5 1 1

1 = Best, 5 = poorest or 1 = least expensive, 7 = most expensive.

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APPENDIX 7.3 Properties of Zerol Fluids from Chevron Chemical Co. Zerol 40◦ C viscosity, cSt 100◦ C viscosity, cSt Pour point, ◦ C Flash point, ◦ C Floc point/R12, ◦ C Floc point/R22, ◦ C Floc point/R502, ◦ C

55 5.5 1.6 <−60 134 — — —

150 30 4 −39 170 <−73 −72 −68

250 46 5 −40 190 <−73 −64 −68

350 68 6 −30 202 <−73 −60 −48

500 107 8 −28 212 <−73 −56 −34

Zerol fluids from Chevron are produced from alkylation of benzene with propylene tetramers. When used as refrigeration lubricant base stock with R12, R22, or R502 refrigerants, Zerol fluids have the following properties:

• • • • •

Excellent miscibility at low temperature Good oil return Low floc point Good lubricity Excellent compatibility with elastomers

of mono-, di-, or polyalkylated aromatics were produced. Generally, the alkylations take place either ortho or para to the oxygen substituent. Similarly to AN or AB fluids, the oxygen-containing aromatic components can attach to any carbon on the alkyl chain, creating a complex mixture. These subtle structural differences may have an influence on the lubricant performance. Many sulfur-containing aromatics, including diphenyl sulfide, benzothiopene, thiophene and phenoxathin, were alkylated to give lube range base stocks over acidic catalysts [62–65]. The chemistry for alkylation of sulfurcontaining aromatics is similar to that for the oxygencontaining aromatics. All these fluids remain as experimental products and little information is available about their actual application.

2.

3.

4. 5.

6. 7.

ACKNOWLEDGMENTS The authors would like to thank Gary Dudley of ExxonMobil Chemical Co in Edison, N.J. and Peter, A. Brown of ExxonMobil Chemical Co. in Houston, TX for providing valuable information about alkylnathalene fluids. We would also like to recognize our colleagues, especially Andy Jackson, Tom Degnan, Doug Deckman, and Bill Maxwell, for their helpful suggestions and comments. Appreciation also goes to ExxonMobil Research and Engineering Co. and the Synthetic Business Unit of ExxonMobil Chemical Co. for permission to publish this review.

8. 9.

10.

REFERENCES 1. Wu, M.M., Alkylated aromatics, in Synthetic Lubricants and High-Performance Functional Fluids, 2nd ed. (R.L.

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Shubkin and L.R. Rudnick, Eds.), Dekker, New York, 1999, pp. 195–213. Mang, T., Base oils, in Lubricants and Lubrication, (T. Mang and W. Dresel, Eds.), Wiley-VCH GmbH, Weinheim, 2001, pp. 33–60, 59 Properties of hydrocarbons of high molecular weight synthesized by Research Project 42 of The American Petroleum Institute, The Penn. State University, College of Science, University Park, PA. Koelbel, H., Synthesis of lubricants via the alkylation of naphthalene, Erdoel Kohle, 1, 308–318 (1948). Harlacher, E.A., Krenowics, R.A., and Putnik, C.F., Alkylbenzene based lubricants. Preprint 52D26P, 86th AICHE national meeting, Houston, April 1–5, 1979. Olah, G.A., Ed., Friedel–Crafts and Related Reaction, Vol. 1, Interscience Publishers, New York, 1963. Olah, G.A., Ed., Friedel–Crafts and Related Reaction, Vol. 2, Part 1, Interscience Publishers, New York, 1964, Chapters 14, 17, and 18. Young, L.B., Preparing phenylalkanes, U.S. Patent 4,301,316, to Mobil Oil Corp. (Nov. 17, 1981). (a) Huss, A., Jr., Le, Q.N., Tabak, S.A., and Wong, S.S., Process for preparing long chain alkyl aromatic compounds employing Lewis acid-promoted amorphous inorganic oxide, U.S. Patent 5,107,048 to Mobil Oil Corp. (April 21, 1992); (b) Le, Q.N., Marler, D.O., McWilliams, J.P., Rubin, M.K., Shim, J., and Wong, S.S., Process for preparing long chain alkyl aromatic compounds, U.S. Patent 4,962,256, to Mobil Corp. (October 9, 1990). Aufdembrink, B.A., Kresge, C.T., Le, Q.N., Shim, J., and Wong, S.S., Sulfated layered titanium oxide catalysts in process for preparing long chain alkyl aromatic compounds, U.S. Patent 5,105,042 to Mobil Oil Corp. (April 14, 1992). ExxonMobil Chemical Synthetics, P.O. Box 3272, Houston, TX 77253-3272.

12. Ashjian, H., Le, Q.N., Marler, D., Shim, J., and Wong, S., Naphthalene alkylation process, U.S. Patent 5,034,563, to Mobil Oil Corp. (July 23, 1991). 13. Ardito, S.C., Ashjian, H., Degnan, T.F., Helton, T.E., Le, A.N., and Quinones, A.R., Naphthalene alkylation with RE and Mixed H/NH3 form catalyst, U.S. Patent 5,629,463, to Mobil Oil Corp. (May 13, 1997). 14. Nichols, C.W., Jr., and Smith, M.I., Compositions of liquid paraffins containing mixtures of alkyl-substituted polynuclear aromatic hydrocarbons as swelling agents, U.S. Patent 3,498,920, to Mobil Oil Corp. (March 3, 1970). 15. Igarashi, J., Lusztyk, J., and Ingold, K.U., Auto-oxidation of alkylnaphthalenes. 1. Self-inhibition during the autooxidation of 1- and 2-methylnaphthalenes puts a limit on the maximum possible kinetic chain length, J. Am. Chem. Soc., 114, 7719–7726 (1992). 16. Igarashi, J., Jensen, R.K., Lusztyk, J., Korecek, S., and Ingold, K.U., Auto-oxidation of alkylnaphthalenes. 2. Inhibition of the auto-oxidation of n-hexadecane at 160◦ C, J. Am. Chem. Soc., 114, 7727–7736 (1992). 17. Le, Q.N. and Shim, J., Lubricant composition of polyalphaolefin and alkylated aromatic fluid, U.S. Patent 5,602,086, to Mobil Oil Corp. (Febuary 11, 1997). 18. Brown, P.A., Synthetic basestocks (Group IV and V) in lubricant applications. Lubrication Engineering, 59, CMF Plus, p. 20, 2003. 19. Proprietary data from ExxonMobil Chemical Co., Synthetic Business Unit. Synesstic™ 5 & 12 Alkylated Naphthalenes 20. Brown, P.A., Ho, S.C., and Dudley, G.K., Lubricant performance with alkylated naphthalene blendstocks, preprint of 14th International Colloquium Tribology in Esslingen, Germany, January 2004. 21. Dressler, H. and Meilus, A.A., Synthetic oils, U.S. Patent 4,604,491 to Koppers Co. (August 5, 1986). 22. (a) McGuire, S.W., Riddle, J.L., Nicks, G.E., Kerfoot, O.C., and Kennedy, C.D., Preparation of synthetic hydrocarbon lubricants, U.S. Patent 3,909,432, to Continental Oil Co. (September 30, 1975); (b) Bridwell, B.W. and Johnson, C.E., Mono-alkylation of naphthalene, to Nalco Chemical Co., U.S. Patent 3,959,399 (May 25, 1976). 23. Yoshida, T. and Watanbe, H., Synthetic oils, U.S. Patent 4,714,794, to Nippon Oil Co. Ltd. (December 22, 1987). 24. Yoshida, T. and Watanbe, H., Thermal medium oils, GB 2161176A to Nippon Oil Co. Ltd. (June 25, 1985). 25. Takei, M., Yoshida, T., Nagai, Y., and Masamizu, K., Lubricating oil composition and process for preparing the same, EP 0589107 A1, to Nippon Oil Co. Ltd. (September 24, 1992). 26. Winemiller, M.D., Deckman, D.E., Maxwell, W.L., Buck, W.H., and Baillargeon, D.J., Lubricating oil compositions with improved friction properties, U.S. Patent Application 20030166474A1, to ExxonMobil Research and Engineering Co. (September 4, 2003). 27. Nipe, R.N., High performance lubricating oil, U.S. Patent 6,180,575, to Mobil Oil Corp. (January 30, 2001).

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28. Takashima, H., Development of long drain rotary air compressor lubricants, Proceedings of the International Tribology Conference, Yokohama 1995, pp. 899–902. 29. Green, R.L., Larsen, A.H., and Pauls, A.C., 98 Get fluent about heat transfer fluids, Chemical Engineering, Febuary 1989, pp. 90–98. 30. Magerranmov, M.N., Tsvetkov, O.N., Lyutfaliev, A.G., and Chagina, M.A., Khimiya I Tekhnologiya Topliv I Masel N.4, pp. 15–16 (1992) Manufacture of vacuum pump oil via alkylation of naphthalene by alpha-olefins. 31. Yokoyama, N. and Imai, F., Heat treating oil — comprising mono-alkylnaphthalene with higher sec. or tert. alkyl group for quenching and tempering metals, EP 305114, to Nippon Oil Co. Ltd. (March 1, 1989). 32. JP 55073791, Lubricating oils for high temperature application, CA 93:170893, to Matsumura Petroleum Research Laboratory. 33. (a) Linear Alkylbenzene Product Focus, Chemical Week, January 28, 2004, p. 34; (b) Pujado’, R.R., Linear alkylbenzene (LAB) manufacture, in Handbook of Petroleum Refining Processes, 2nd ed. (Meyers, R.A., Ed.), 1997 McGraw-Hill Co., Chapter 1.5, p. 1.53. 34. (a) Cvengros, J., Faberova, A., and Lazar, L., Low pour point polyalkylbenzene oils for refrigeration compressors, J. Synth. Lubr., 10, pp. 273–284 (1993); (b) Berg, R.C., Malloy, T.P., and Vora, B.V., Production of dialkylated aromatics, U.S. Patent 4,520,218, to UPO Inc. (May 28, 1985). 35. Segnitz, A., Hovestadt, A., and Oppenlande, K., Di-phenyl alkane mixture useful as insulating oil. German Patent DE 3,432,746, to Chem Fab. Wibarco (March 13, 1986). 36. SRI Specialty Chemicals Update Program, Vol. 7, Synthetic Lubricants. October 1977. 37. Briot, P., Forestiere, A., Gautier, S., Benazzi, E., and Lew, L., Synthetic oil with a high viscosity number and a low pour point, U.S. Patent 6,491,809, to Institut Francais du Petrole Industrias Venoco C.A. (December 10, 2002). 38. Sowle, E.E. and Lachocki, T.M., Linear dialkylbenzenes as synthetic base oils, J. Soc. Trib. Lubr. Eng., 52, 116–120 (1966). 39. Willschke, A., Humbert, D., and Rossi, A., Synthetic base stocks for low viscosity motor oils, J. Synth. Lubr., 5, 31 (1988). 40. Gschwender, L.J., Snyder, C.E. Jr., and Driscoll, G.L., Alkylbenzenes — candidate high temperature hydraulic fluids, J. Soc. Trib. Lubr. Eng., 46, 377–381 (1990). 41. Kawakami, S., Endo, K., Dohi, H., and Sato, A., Electrical insulating oil, EP 336,133, to Nippon Petrochemicals Co. Ltd. (October 11, 1989). 42. Akatsu, K., Takayama, H., and Matsuoka, T., Di-arylalkane production from styrene and alkylbenzenes over HL-type zeolite catalyst, EP 421,340, to Kureha Kagaku Kogyo (April 10, 1991). 43. Aralkylation of alkylbenzenes with styrenes, to Mitsubishi Petroch, Japanese Patent J01193232 (August 3, 1989). 44. Eapen, K.C., Snyder, C.E. Jr., Gschwender, L., Dua, S.S., and Tamborski, C., Poly-n-Alkylbenzene Compounds.

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56. Shido, S., Onodera, K., and Kawanami, T., Influence of chemical structure of base stock on performance of aluminum cold rolling, Jpn. J. Tribol., 37, 895–905 (1992). 57. Sato, A., Endo, K., Kawakami, S., Yanagishita, H., and Hayashi, S., Refined electrical insulating oil and oil-filled electrical appliances, to Nippon Petrochemicals Co. Ltd., EP 0,150,252 A1 (December 30, 1983). 58. Sato, A., Endo, K., Kawakami, S., Yanagishita, H., and Hayashi, S., Electrical Insulating Oil Comprising Mixtures of Alkylbenzene Fluids, U.S. Patent 4,506,107, to Nippon Petrochemicals Co. Ltd. (March 19, 1985). 59. Rudnick, L.R., Alkylated benzofuran-derived lubricants, U.S. Patent 5,371,248, To Mobil Oil Corp. (December 6, 1994). 60. Yamamoto, T., Toyoda, J., and Yagi, T., Study of alkylated diphenyl ethers as synthetic lubricating oil, J. Jpn. Petrol. Inst., 22, 38–43 (1979). 61. Rudnick, L.R., Kremer, R.A., and Law, D.A., U.S. Patent 5,552,071, “Alkylated Diphenyl Ether Lubricants,” (September 3, 1996). 62. Rudnick, L.R., Rowe, C.N., Law, D.A., and Napier, A.G., Novel alkylated phenoxathin base stock for lubricants, U.S. Patent 5,286,396, To Mobil Oil Corp. (Febuary 15, 1994). 63. Rudnick, L.R., Rowe, C.N., and Law, D.A., Alkylated benzothiophene-derived lubricants, U.S. Patent 5,372,734, to Mobil Oil Corp. (December 13, 1994). 64. Rudnick, L.R. and Rowe, C.N., Alkylated thiophene lubricants, U.S. Patent 5,395,538, to Mobil Oil Corp. (March 7, 1995). 65. Kanie, T. and Yamamoto, T., Synthetic lubricating oil, Japanese Patent J58208392, to Matsumura Sekiyu K.K. Research Center (May 28, 1982).

8

Perfluoroalkylpolyethers Gregory A. Bell and Dr. Jon Howell CONTENTS 8.1 8.2

Development Chemistry 8.2.1 Product Structures 8.2.2 Preparation of PFPE Types 8.2.3 Functional Fluids and Soluble Additives 8.3 Properties 8.3.1 Chemical Properties 8.3.1.1 Thermal and Oxidative Stability 8.3.1.2 Lewis Acid Stability 8.3.1.3 Compatibility of PFPE Fluids with Metals and Metal Compounds. . 8.3.1.4 Hydrolytic and Chemical Stability 8.3.1.5 Solubility 8.3.1.6 Compatibility with Elastomers and Plastics 8.3.1.7 Flammability 8.3.1.8 Radiation Resistance 8.3.1.9 Shear Stability 8.3.1.10 Safety and Environmental 8.3.2 Physical Properties 8.3.2.1 Thermal Properties 8.3.2.2 Density 8.3.2.3 Electrical Properties 8.3.2.4 Vapor Pressure and Volatility 8.3.2.5 Viscosity 8.3.2.6 Compressibility 8.3.3 Lubrication Performance 8.3.3.1 Four-Ball Wear and Extreme Pressure Tests 8.3.3.2 Falex Extreme Pressure Tests 8.3.3.3 Bearing Fatigue Tests 8.3.3.4 Applications 8.3.3.5 PFPE Greases 8.4 Manufacturers, Marketing, Economics 8.4.1 Oil Producers 8.4.2 Marketing 8.4.3 Economics 8.5 Outlook References

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8.1 DEVELOPMENT Perfluoroalkylpolyether (PFPE) fluids were first synthesized by DuPont. The first applications were military/ aerospace in nature. Joint development efforts with the U.S. Military and NASA led to greases that were developed to take advantage of the high temperature lubricating abilities of the oils. Gumprecht [1] first disclosed the use of the perfluoroalkylpolyethers as lubricants in an ASLE/ASME lubrication conference in the fall of 1965. First applications took advantage of the chemical inertness, thermal stability, and nonflammability of the fluids. They are used as: 1. Valve and O-ring lubricants in oxygen service because of their nonflammability and stability in oxygen atmospheres. 2. Lubricants for aircraft instrument bearings because of their low vapor pressure. 3. Seal lubricants in reactive chemical environments, because they have chemical inertness, high temperature stability, and insolubility to chemicals. 4. Sealed for life electric motor bearing greases because of the good lubricity and the oil does not oxidize and fail. 5. High temperature greases because of the ability to withstand constant temperatures up to 550◦ F and intermittent temperatures up to 800◦ F or higher. Additional applications include base oils for specialty greases, antiseize, instrument oils, chlorine and oxygen service lubricants, valve greases, mechanical seal barrier fluids, nuclear industry, conveyor bearings, textile and plastics tenter frames, pressure relief valves, and as lubricants in many high temperature systems. They lubricate rocket nozzles, automotive antilock braking systems, gold contacts, and sintered bearings. The largest current use for PFPE fluids is in vacuum pumps. They are specified by vacuum pump manufacturers as a high vacuum, nonflammable fluid that can be safely used with the reactive chemicals found in computer chip manufacture.

8.2 CHEMISTRY Perfluoroalkylpolyether (PFPE) fluids are composed entirely of carbon, fluorine, and oxygen. They are colorless, odorless, completely inert to almost all chemical agents including oxygen, compatible with most other materials, and are liquids over a wide temperature range.

8.2.1 Product Structures Since the initial development, the following four distinct types of PFPE oils have become commercially available. Although all PFPE types exhibit similar physical

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and chemical properties, there are small and sometimes significant differences. PFPE-K CF3 CF2 CF2 O-[CF(CF3 )CF2 -O-]n CF2 CF3 PFPE-Y CF3 O-[CF(CF3 )CF2 -O-]y -[CF2 -O-]m CF3 PFPE-Z CF3 O-[CF2 CF2 -O-]z -[CF2 -O-] p CF3 PFPE-D CF3 CF2 CF2 -O-[CF2 CF2 CF2 -O-]q CF2 CF3 Both PFPE-K and PFPE-Y are nonlinear molecules, because the polymer chains contain pendent trifluoromethyl groups (–CF3 ). PFPE-D and PFPE-Z contain no pendent groups and are linear. The linear PFPE structures show less change of viscosity with temperature and pressure when compared to nonlinear PFPE. Pendant trifluoromethyl groups immediately adjacent to the ether, (–O–), linkage provide some shielding to protect that linkage from Lewis acid catalyzed cleavage. PFPE-K has a fully shielded polymer chain, because every ether linkage is adjacent to a carbon with a pendant trifluoromethyl group. PFPE-Y is not as stable to the presence of difluoroformyl segments in the polymer chain. PFPE-D and PFPE-Z have nonshielded polymer chains and are thus not protected from Lewis acid catalyzed cleavage. Perfluoroalkylpolyether-K and PFPE-D contain one type of ether group and are homopolymers while PFPE-Y and PFPE-Z contain two types of ether groups. PFPE-Y and PFPE-Z both contain the difluoroformyl, (–CF2 O–) linkage as well as the perfluoropropyl or perfluoroethyl group respectively. Even though PFPE-Y and PFPE-Z appear to be copolymers, they are prepared using only one monomer. A terpolmer containing all three linkages has also been reported.

8.2.2 Preparation of PFPE Types Perfluoroalkylpolyethers, PFPE-K, are prepared by anionic polymerization of hexafluoropropylene epoxide (HFPO) at low temperatures. The preparation of HFPO has been described in References 2 and 3. HFPO can be polymerized in solvents such as aliphatic hydrocarbon polyethers or nitriles using cesium fluoride as the source of fluoride ions. The reaction temperature is −5◦ C to −20◦ C, the boiling point of HFPO. The intermediate polymer contains an acid fluoride end group that is much too reactive for use in lubricants. The polymer is stabilized [4], by reaction: first with water, forming the carboxylic acid, and then with elemental fluorine. The polymer, as prepared, has molecular weight ranges of 435 to 13,500 and is fractionated into different viscosity grades by vacuum distillation. Perfluoroalkylpolyether-Y is prepared by the photochemical catalyzed polymerization of hexafluoropropylene in the presence of oxygen at low temperatures [5]. Treatment with UV light or thermally or both causes decomposition of the peroxide linkages. End groups include either OCOF or CF2 COF and are removed by high temperature

treatment with elemental fluorine, giving a polymer containing two types of perfluoroalkyl linkages in the polymer chain, [–OCF2 –] and [–OCF(CF3 )CF2 –]. The molecular weight range of this polymer is 1,000 to 10,000. An excellent review is found in Reference 6. Today, much of the PFPE-Y contains one chlorine atom on the terminal end due to the fact that trichloroethylene is used for molecular weight control. Perfluoroalkylpolyether-Z is produced when tetrafluoroethylene is used as the starting material instead of hexafluoropropylene [7] and the crude polymer is processed just as with PFPE-Y, but at lower temperatures. The PFPE-Z crude polymer has a higher molecular weight than PFPE-Y, ranging from 8,000 to 70,000. During the stabilization process, however, the molecular weight decreases because chains are cleaved into smaller pieces. This polymer contains a random distribution of perfluoroethylene oxide and perfluoromethylene oxide in roughly one to one ratio. The reaction mechanism and kinetic equation for the photo-oxidation of fluoro-olefins to PFPE-Y and PFPE-Z is described by Sianesi et al. [8]. Perfluoroalkylpolyether-D is obtained by Lewis acidcatalyzed or fluoride ion ring-opening polymerization reaction of 2,2,3,3-tetrafluorooxetane [8]. The hydrogen– carbon bonds are subsequently converted to fluorine– carbon bonds by direct fluorination with elemental fluorine. Ultraviolet light is used to catalyze the direct fluorination. The crude polymers of all types are usually purified by contact with absorbing agents to remove polar materials and distilled under reduced pressure. The reaction mass is fractionated by distillation into specific molecular weight and viscosity ranges. These ranges usually correspond to different grades or product types available commercially.

8.2.3 Functional Fluids and Soluble Additives Perfluoroalkylpolyether lubricants are not inherently good at preventing corrosion. They are not polar in nature and do not bond chemically with metal surfaces. Under extreme conditions of moisture and humidity, corrosion can occur on steel bearings and surfaces that are lubricated by these fluids. PFPE additives are typically formed with a PFPE oil backbone with one or two functional groups attached to the end of the chain. These functional groups allow the oil to bond more tightly to metal surfaces and to cause the oil molecules to align and pack more tightly on the surface. This packing effect fills voids in the oil barrier that could allow moisture to reach the surface of the metal and cause corrosion. Most commercial PFPE manufacturers today have at least one product containing an anti-corrosion additive. Conventional hydrocarbon based additives that are commonly used in most lubricants do not dissolve in PFPEs

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because of the PFPE’s extreme inertness and insolubility in chemicals. Because of this, the oils have not been used in some applications where anticorrosion additives or extreme pressure additives are needed. Solid additives have been added to greases since the thickener will hold them in place, but these additives cannot be used in oils. A number of soluble anticorrosion and wear reducing additives have been developed in the last few years to address the deficiencies of the oils. In addition to protecting the surfaces, they also raise the temperature that the oil decomposition reaction begins which allows the fluids to be used at higher temperatures [21]. These additives typically do not affect the oxygen stability of the PFPE lubricants. As with other additives, these have specific functions and there is no single additive to do everything. Rust prevention, high temperature anticorrosion, antiwear, and extreme pressure additives have all been developed. These additives usually have upper temperature limits that are typically not as high as the base oil. The shelf life of some of these additives is somewhat shorter than that of the oils. Special grades formulated for use in vacuum systems are manufactured to keep the vapor pressure constant and reduce back streaming in vacuum pumps. The typical treat rate is 1 to 10% and combinations of the additives can be used to improve overall functionality. They can also be used as pretreatment and for prevention of corrosion in storage by mixing with solvents and applying a thin coating that leaves a residual layer of protection. Special functional PFPE lubricants are used as computer disk lubricants. These linear fluid based lubricants are end capped with two functional groups that allow the lubricant layer to stay flat against the high speed disk surface while adhering tightly. This nearly monomolecular layer of lubricant has allowed the gap between the head and disk to be reduced to below 50 Å. Because of the ability of the lubricant to withstand the speed and temperatures, the storage efficiency and reliability of computers has increased significantly while the corresponding machine costs have gone down over the past few years. Functional fluids have been polymerized to handle specific applications and to allow the fluids to cover a broader range of applications. Both monofunctional and difunctional derivatives have been produced. These fluids can be incorporated into various polymer systems including polyurethanes, epoxies, polyesters, polyacrylates, polyamides, and polyimides to modify the polymers and to give performance typically associated with fluoropolymers such as surface protection and abrasion resistance. Monofunctional fluids include silanes, phosphates, hydroxyl, carboxylic acid, alcohol, and amines. Difunctional derivatives include dihydroxyl, ethoxy ether, isocyanate, aromatic, ester, and alcohols. The functionalities allow the various compounds to participate in a number of chemical reactions and to be used as surfactants and surface modifiers. The performance is obtained by having

reactive end groups that can interact with other chemicals and additives in a way that the inert PFPE molecule cannot. In addition, emulsions in water have been made that are mixtures of water, ammonia, and PFPE derivatives. Commercial quantities of these fluids are seen in the marketplace today.

8.3 PROPERTIES Polyfluoroalkylpolyether oils are colorless and odorless fluids. Physical properties that vary with molecular weight are density, pour point, viscosity, viscosity index, volatility, and vapor pressure. Chemical properties and stability usually depend more on chemical structure than on molecular weight, so they do not vary with changes in molecular weight or viscosity.

8.3.1 Chemical Properties 8.3.1.1 Thermal and oxidative stability The temperature at which thermal decomposition of the PFPE-K oils begins has been measured in our laboratory by differential thermal analysis. This method gives a value in excess of 470◦ C. PFPE impurities not removed during purification by the manufacturer can appreciably lower the temperature at which initial decomposition is observed. These impurities may be products of side or incomplete reactions during the manufacturing process. For this reason, a more useful value is obtained by determining the rate of degradation over a long period of time at a high temperature. Such an experiment was carried out by heating a sample of PFPE-K oil in an Inconel tube under an atmosphere of argon at 452◦ C for 31 days. The loss of oil averaged 1.1 wt% per day and the loss in viscosity was 3%. The oil as recovered was colorless and suffered little change in molecular weight. Table 8.1 summarizes available data on the temperature stability of PFPE by type. Perfluoroalkylpolyther oils are more stable in pure oxygen than they are in inert systems (Table 8.1). However,

TABLE 8.1 Stability of PFPE in Inert Atmosphere and Air PFPE Type PFPE-K PFPE-Y PFPE-Z PFPE-D

Stability limit (inert)

Stability limit (air)

>450◦ C <350◦ C NA NA

400◦ C <300◦ C <288◦ C 370◦ C

Source: Individual Manufacturer’s Reference literature. NA indicates that the data were not available.

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Sianesi et al. [9] showed that the decomposition temperature for PFPE-Y oils in air was very close to the thermal decomposition temperature in an inert atmosphere. Results of tests with PFPE-K shown in Table 8.2, under a variety of conditions, demonstrate the inertness of the PFPE oil to reaction with oxygen. Shock loading tests of PFPE-K with gaseous oxygen ranging from 93◦ C and 7500 psi to 277◦ C and 6000 psi showed no reaction. The thermal-oxidative stability of the PFPE polymer depends on its structure. The relative stability of each type of PFPE appears to be related to the degree of shielding of the ether linkage by pendant trifluoromethyl groups and to the presence of the difluoroformyl group on the polymer chain. Jones et al. [10] studied the effect of branching on the thermal oxidative stability of low-molecular-weight PFPE in the gas phase in glass ampoules. Oxidative stability measurements seemed to indicate that highly branched PFPE oils are much less stable than PFPE molecules containing a repeating, single trifluoromethyl pendant group. Impurities in the product can play an important role in the initial, apparent thermal-oxidative stability of the PFPE. Paciorek et al. [11] found that PFPE-K, PFPE-Y, or PFPE-Z (PFPE-D was not tested) oils that contained impurities initially appeared to have poor thermal-oxidative stability. However, once the impurities were removed or reacted away, the oil appeared significantly more stable until the upper temperature limit was reached. If these impurities are not removed during manufacturing, the apparent upper temperature limit of thermal-oxidative stability can be much lower than that expected. The decomposition products do not appear to promote or catalyze further degradation of the PFPE when the reaction is performed in glass. Gumprecht [12,13] reported that CF3 CF=CF2 , CF3 COF, and COF2 were the main products in the thermal decomposition of PFPE-K. Paciorek et al. [14] found SiF4 , CO2 , and some BF3 when oxygen was present. SiF4 and BF3 are formed by reaction with the glass ampoule walls in the presence of oxygen. Other studies confirm the effect of structure on the thermal oxidative stability of PFPE oils. Paciorek et al. [14] found PFPE-K to be stable in the presence of oxygen to the highest temperature tested, >340◦ C. However, Jones et al. [15] found that PFPE-Z is inherently unstable at 316◦ C in oxidizing atmospheres. Neither hydrogen end-capped polymer nor polymer with remaining peroxide linkages are the cause of this apparent instability. The instability has been attributed to the presence of the difluoroformyl (–CF2 O–) and tetrafluoroethylene oxide (–CF2 CF2 O–) units in the polymer chain. These same difluoroformyl, (–CF2 O–) groups are also present in PFPE-Y. In fact, Pearson et al. [16] reports that in the temperature range 325–405◦ C in a Monel vessel, PFPE-Y, which contains the difluoroformyl (–CF2 O–) group, decomposes 20–40 times

TABLE 8.2 Oxygen Compatibility Tests with PFPE-K

Test type

Temperature, ◦ C (◦ F)

Ignition in gaseous oxygena Pressure drop in gaseous oxygen bombb Mechanical impact in liquid oxygenc,d,e Mechanical impact in liquid oxygena Mechanical impact in liquid oxygenf

400◦ (752◦ ) 99◦ (210◦ ) Ambient Ambient Ambient

Oxygen pressure, MPa (psi)

Impact energy, Joules (ft-lb)

13 (1886) 0.7 (100) 98 (72) 122 (90) 736 (543)

Test result No ignition No pressure drop after 600 h No reaction in 20 trials No reaction in 10 trials No reaction in multiple trials

a British Specification 3100. b American Society for Testing and Materials, D-942. c Marshall Space Flight Center Specification 106B. d National Aeronautics and Space Administration Handbook, 8060.1B, Test 13, Part 1. e American Society for Testing and Materials, D-2512. f West German Federal Institute for Materials Testing (BAM), 8104-411.

8.3.1.2 Lewis acid stability Metal fluorides can catalyze the decomposition of PFPE oils, especially those PFPE oils that contain the difluoroformyl (–CF2 O–) group. PFPE lubricants will react with Lewis acids, such as aluminum trichloride, at temperatures normally considered safe for PFPE oils [17]. The apparent catalytic activity of the Lewis acid depends on the PFPE structure type. Polymers that contain the difluoroformyl group appear less stable than those without it [11]. PFPE-Z is stable up to 260◦ C in contact with metals but not stable at temperatures even less than 100◦ C in the presence of metal halide Lewis acids [18].

Copyright 2006 by Taylor & Francis Group, LLC

16

Weight loss at 120°C by ISOTGA

14

PFPE-Y

12 Wt. loss %

faster than PFPE-K. These observations are consistent with the theory that the difluoroformyl groups contribute to instability of the PFPE at higher temperatures. Perfluoroalkylpolyether oils leave no deposits when they volatilize. Even when PFPE molecules thermally decompose, tars or residues are not observed. Generally, the volatile decomposition products are removed as they are formed. PFPE decomposition products can react with the surface in contact with the PFPE, if the decomposition products are not removed. In contrast, hydrocarbon lubricants thermally form gums or oxidatively decompose or polymerize to form tars, or deposits. These hydrocarbonderived deposits then cause problems that can lead to apparent lubricant failure. The oxidation stability of PFPE oils is perhaps best demonstrated on a practical basis by the fact that samples of the oil contaminated with traces of hydrocarbon oils can be purified by blowing air through the mixture at high temperatures (300◦ C and up) for several hours. Under these conditions, the hydrocarbons are oxidized and the PFPE oils can be recovered in a pure state by filtration.

10 8

MIX 1:1

6 4 2

PFPE-K

0 0

5

10

20

30 40 50 Time, min

60

70

80

FIGURE 8.1 Effect of Lewis acids on PFPE degradation

Metal halides, such as AlCl3 , catalyze the decomposition of all types of PFPE oils. PFPE-Y and PFPE-Z, which contain the difluoroformyl (–CF2 O–) group decompose more rapidly than PFPE-K or PFPE-D, which do not contain that group. The effect of aluminum trichloride on the stability of different PFPE is shown in Figure 8.1. Sianesi et al. [9] show that metal oxides can also lower the decomposition temperature of PFPE-Y. Cuprous oxide had a small effect on the rate of decomposition at 360◦ C, whereas aluminum oxide had 100 times that rate. The data are summarized in Table 8.3. Carre and Markowitz [19] demonstrated that iron fluoride can form in the raceways of bearings lubricated with PFPE and that the presence of FeF3 can lower the temperature at which the polymer begins to decompose. Unfortunately, the PFPE type is not disclosed and the magnitude of this effect is difficult to evaluate.

8.3.1.3 Compatibility of PFPE fluids with metals and metal compounds A summary of metals compatible with PFPE oils at various temperatures is given in Table 8.4. In the presence of oxygen, oxidative-corrosion may occur with some metals. PFPE-K oils are inert to most metals at temperatures up to approximately 288◦ C in an oxygen atmosphere. Compatibility results of PFPE-K oils with a number of metals and

TABLE 8.3 Percent Weight Loss of PFPE-Y Per Minute, Exposure at 360◦ C Rate (%wt loss/min)

Metal oxide ZrO2 , CrO3 , SnO2 , WO3 , ThO2 , Al2 O3 CeO2 , TiO2 Fe2 O3 , NiO V2 O5 , MgO Cr2 O3 , Sb2 O3 , Co3 O4 , Ga2 O3 .12%H2 O CuO, MoO3 , HgO, ZnO, SnO, MnO2 , TeO2 , BaO, CaO, SiO2 , In2 O3 , GeO2 , Bi2 O3 , P2 O5 , PbO Cu2 O Inert gas, N2

>5 1–5 0.5–1.0 0.3–0.5 0.15–0.3 0.09–0.15

0.05 <0.02

TABLE 8.4 Metals and Alloys Suitable for Use with PFPE-K Oils at Elevated Temperatures 371◦ C (700◦ F)

343◦ C (650◦ F) 316◦ C (600◦ F)

288◦ C (550◦ F)

Below 288◦ C

8.3.1.4 Hydrolytic and chemical stability The Hydrolytic stability of PFPE oils is exceptional. Longterm contact with steam or boiling water produces no adverse effects on the PFPE fluids. All PFPE oils are essentially inert to most chemicals. No reaction is observed with boiling sulfuric acid, fluorine gas at 200◦ C, molten sodium hydroxide, chlorine trifluoride at 10–50◦ C , uranium hexafluoride gas at 50◦ C, or any of the following materials at room temperature: JP-4 turbine fuel, unsymmetrical dimethyl hydrazine, hydrazine, diethylenetriamine, ethyl alcohol, aniline, 90% hydrogen

Air Atmosphere Nickel alloys Cobalt alloys AMS-5547 steel AMS-5525 steel Titanium alloy Ti (6Al 6V 2Sn) Mg, Ag, Cr, V 301, 304, 310, 316, 321, 446 N-155 Titanium alloy Ti (13V -11Cr 3Al) Titanium alloy Ti (6Al 4V) Aluminum alloy Al (QQ-A-355) Bearing Bronze 405, 410, 440 stainless steels QQS-636, M-1, M-50, WB-49, 52100 steels Ti (8 Min) Copper Most metals and alloys show little or no evidence of corrosion

Test conditions: 72 h at 5 L dry gas/h, qualifying corrosion rate: <0.4 mg/cm-day. Note: Any metal or alloy suitable at one temperature is also suitable at all lower temperatures. Any metal suitable in air is also suitable in inert atmosphere. Source: DuPont literature.

Copyright 2006 by Taylor & Francis Group, LLC

+2.0

500

Temperature, °F 600

550

+1.0

0

700

650

6 S63 QQ EL E T S

52100 STEEL

Weight change, mg/cm2-day

Temperature

alloys, using the “Micro Oxidation-Corrosion Test” developed by the Air Force Materials Laboratory are shown in Figure 8.2. In general, nickel and cobalt alloys exhibit the greatest resistance to oxidative corrosion and are suitable for use with PFPE oils up to at least 370◦ C. Ordinary steels are not suitable above 288◦ C. Specific stainless steels are satisfactory at 316◦ C. Certain alloys cause catalytic depolymerization of PFPE oils at high temperatures. Titanium alloys that contain aluminum can decompose PFPE oils above 136◦ C. Aluminum 2024 appears to do the same thing at 370◦ C. These problems are greatly minimized in the absence of oxygen, indicating that the reactions involved are between the oil and oxide coating on the metals. Additives that markedly decrease the reaction rate of PFPE oils with many metals at high temperatures are under development [20,21]. Some offset the catalytic depolymerization of the oils caused by titanium alloys [15, 22–26].

STELLITE 25 ALUMINUM Ni INCONEL

NICKEL INCONEL

COPPER

–1.0 440 C

52100

–2.0

–3.0

–4.0 280

300

320

340

360

Temperature, °C

FIGURE 8.2 Corrosion of metals by PFPE-K at elevated temperatures

peroxide, inhibited red fuming nitric acid, and nitrogen tetroxide. PFPE-K oils are slightly soluble in hydrazine and have moderate (25–30%) solubility in nitrogen tetroxide. Again, there may be stability differences depending on the type and structure of the PFPE. PFPE-Y is reported to react with liquid (100%) and gaseous ammonia, alkaline metals, and finely divided powder of light metals such as aluminum, magnesium, and their alloys [27]. Table 8.5 summarizes PFPE-Y reactivity data. In comparison to the reactivity of PFPE-Y, PFPE-K has shown no reactivity

TABLE 8.5 Chemical Resistance of PFPE-Y Oils Chemical type

Chemical name

Organic solvents Organic acid Organic base Inorganic acid Inorganic base Inorganic salt Oxidizing agent Oxidizing agent Lewis acid Lewis acid

All common Carboxylic acids Tributyl amine HF, H2 SO4 , HCl KOH, NaOH, NaCl, KF Br2 , Cl2 , F2 KMnO4 , K2 CrO4 AlCl3 , FeCl3

Temperature, ◦ C 300 300 200 300 200 250 250 200 200 200

toward ammonia (personal observation). Although there are no available data on the reactivity of PFPE-K with alkaline metals, all PFPE molecules will probably react with nascent metal surfaces and unpassivated, high-surface-area metals. 8.3.1.5 Solubility Perfluoroalkylpolyether oils are not soluble in common solvents, acids, and bases, but some solvents will dissolve in PFPE oils. Solubility data for PFPE-Y is shown in Table 8.6. PFPE oils are completely miscible in highly fluorinated solvents such as trichlorotrifluoroethane, hexafluorobenzene, perfluorooctane, perfluorohexane, hexafluoropropylene dimer, 2,3-dihydrodecafluoropentane, perfluorodimethylcyclobutane isomers, and 1,1 dichloro-1-fluoroethane. PFPEs are also soluble in supercritical CO2 . Table 8.7 summarizes gas solubility data. 8.3.1.6 Compatibility with elastomers and plastics Elastomer compatibility with non-additized PFPE-K oil is summarized in Table 8.8 [28]. Most elastomers are affected only slightly by contact with the oil at 93◦ C. The inherent stability of the elastomers themselves, rather than incompatibility with PFPE, limits their use at higher temperatures. No significant changes in dimension, hardness, or color were noted when selected elastomers were

Source: Montedison literature

TABLE 8.6 Solubility of Common Solvents and PFPE-Y Oils Solvent Hexane n-heptane n-octane Cyclohexane Benzene Toluene Xylene Ethyl ether Tetrahydrofuran Ethyl acetate Methyl formate Dimethyl ketone Methylethyl ketone Trichloroethylene Monochlorobenzene Chloroform Carbon tetrachloride Perfluoroalkanes

Solubility of PFPE in solvent

Solubility of solvent in PFPE

SS PS I I I I I SS I I I I I I I SS SS miscible

PS SS I I SS I I PS SS I I I I PS I PS PS miscible

Gms solvent in 100 g PFPE 2.0 1.6 — — 1.3 — — 2.6 1.4 1.5 — — — 3.0 — 4.1 2.9 —

Source: Montedison literature SS = slightly soluble, PS = partially soluble, and I = practically insoluble.

Copyright 2006 by Taylor & Francis Group, LLC

TABLE 8.7 Gas Solubility in PFPE-Y at 20◦ C Type of gas

mL gas/mL PFPE-Y

ppm gas

0.08 0.09 0.290 0.190 1.30 3.189 0.197 0.806 0.04*

8 4 218 125 1344 5320 176 379 17

Helium Hydrogen Oxygen Nitrogen Carbon dioxide Chlorine Fluorine Hydrogen fluoride Water vapor

8.3.1.7 Flammability

a Estimated from water solubility.

Source: Montedison literature.

TABLE 8.8 Elastomer Compatibility with PFPE-K Oila Temperature Fluorosilicone Ethyl acrylate Methyl Silicone Viton® A fluoroelastomer Urethane Hypalon® synthetic rubber Butyl 325 VPA Natural rubber Neoprene® , WRT Hycar 100 (Buna N) Polysulfide (Thiokol) Cis-1, 4-polybutadiene Synpol 1013, 5BR EPT, sulfur cure EPT, peroxide cure Polypropyleneoxide XP-139 Cyanacryl, Acrylic rubber Teflon®

93◦ C

149◦ C

204◦ C

S S S S S S S S NG S S S NG NG S S — — S

S S S S — NG NG NG — NG — — — — — S NG S —

NG NG NG S — — — — — — — NG — — NG NG — NG S

a Based on 168 h tests at temperatures indicated.

Code: S = Only minor changes in elastomer properties. NG = Major, generally harmful, effect on elastomer properties. Source: Personal data and DuPont literature.

immersed in PFPE oil at 70◦ C for six months [29]. Elastomers used in this test were: neoprene, butyl, buna N, natural rubber, polyfluorosiloxane, polychlorotrifluoroethylene, and vinylidene fluoride–hexafluoropropylene copolymers. The new soluble additives can affect some materials and compatibility should be checked. Perfluoroalkylpolyether oils have no significant effect on plastics. The following showed no effect when

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treated with PFPE-Y for 1000 h at 70◦ C: acetal copolymer (POM), acrylonitrile–butadiene–styrene copolymer (ABS), phenylene-oxide based resins (PPO), polyamide 66 (NYLON 66), polybutylene terephthalate (PBT), polycarbonate (PC), high density polyethylene (HDPE), low density polyethylene (LDPE), polyethylene terephthalate (PET), polymethylmethacrylate (PMMA), polypropylene (PP), polystyrene (PS), polystyrene impact-resistant (HIPS), polyvinylchloride (PVC), polyvinylidenefluoride (PVDF), polyvinylidene sulfide (PVDS), and styreneacrylonitrile copolymer (SAN).

Perfluoroalkylpolyether-K oils are not flammable under any conditions likely to be encountered. They show no autogenous ignition, flash, or fire points up to 649◦ C (1200◦ F) in standard ASTM tests. A sample of PFPE-K did not flash or burn when contacting a manifold at temperatures in excess of 649◦ C (1200◦ F). In a high pressure spray ignition test (MIL-F-7100), PFPE-K oil did not flash or fire at up to two feet from the spray orifice. 8.3.1.8 Radiation resistance Perfluoroalkylpolyether-K oils are stable to radiation when compared with many materials used as lubricants or power fluids. In general, irradiation of PFPE-K oils causes only minor changes in its physical properties. No insoluble solids or sludge are formed, and the viscosity decreased 21% when a sample of PFPE-K was exposed to 108 rads of electron bombardment at ambient temperature in air. Mori and Morales [26] studied the effects of x-ray irradiation on the degradation of PFPE-D, PFPE-Z, and PFPE-K. They concluded that PFPE-D crosslinked more easily than the other fluids. 8.3.1.9 Shear stability Perfluoroalkylpolyether-K oil did not break down when subjected to high rates of shear. Exposure at 10 kHz in a sonic shear tester (ASTM D2603) at room temperature for 1 h resulted in viscosity changes of less than 0.5% . The sonic test is severe and is very effective in breaking-down polymers typically used as viscosity index improvers in various types of lubricating oils. 8.3.1.10 Safety and environmental Perfluoroalkylpolyether oils are not chlorofluorocarbons and have zero ozone depletion potential. They also do not contain any volatile organic chemicals so they are non-VOC materials and are not regulated as such. These materials will not biodegrade and can be regenerated indefinitely for reuse. If these fluids are pumped, they should be grounded well as they will generate high levels of static

TABLE 8.9 Typical Physical Properties of PFPE Oils Property Density, g/mL Refractive index Surface tension Isothermal secant Bulk modulus Coeff. Thermal Expansion, /◦ C Specific Heat, cal/g-C 38◦ C Thermal conductivity

PFPE-K

PFPE-Y

PFPE-Z

PFPE-D

1.86–1.91 at 24◦ C

1.86–1.91 at 20◦ C

1.82–1.85 at 20◦ C

1.29–1.301 nD24 16–20 mN/m 1034 MPa at 38◦ C, 34.5 MPa .00095–0.00109 0.23–0.24 0.0831–0.0934 W/m-K at 38◦ C 0.0692–0.0883 W/m-K at 260◦

1.29–1.304 nD20 18–21 mN/m 9650 Kg/cm2 at 25◦ C, 100 kg/cm2 .00092–.00109 0.24 No Data No Data

1.29–1.294 nD20 23–24 mN/m No Data

1.86–1.89 at 20◦ C 1.29–1.298 nD20 17.7–19.1 mN/m No Data

No Data 0.20–0.23 No Data No Data

No Data No Data No Data No Data

Source: DuPont, Montedison, Daiken Product literature.

Temperature, °F 200 300

400

500

12 Mol. wt = 3700 11

6

10 Mol. wt = 6250 9

5

Coefficient of cubical expansion/°F × 104

100

0

Coefficient of cubical expansion/°C × 104

electricity and if in a flammable atmosphere, the spark could cause ignition. The decomposition products of PFPE fluids contain COF2 , CF3 COF, perfluoroolefins, and volatile acid fluoride components, which can be highly toxic. The decomposition of these fluids proceeds at a slow rate so the evolution of these by-products does not occur all at once and normal ventilation will handle the fumes. Adequate ventilation is required when using these fluids above their decomposition temperature. Safety testing of non-additized PFPE fluids has shown excellent safety performance. Extensive biological testing has shown that these fluids have very low toxicity. In acute feeding studies, levels of 25 to 50 g/kg showed little effect. Eye and skin tests on animals and human skin patch tests show little effect. PFPE fluids have been used safely for years in cosmetics. Mutagenic and teratogenic testing have shown no issues. The fluids do not accumulate in animal tissue or organs. They do not support biological growth [35,36].

8 0

40

80 120 160 Temperature, °C

200

240

FIGURE 8.3 Thermal coefficient of expansion for PFPE-K oils

8.3.2 Physical Properties The physical properties of PFPE oils that show little change with molecular structure are summarized in Table 8.9. 8.3.2.1 Thermal properties Thermal conductivity of PFPE-K varies slightly over a wide temperature range. These values are a little lower than many hydrocarbon lubricants with similar viscosity. The specific heat of PFPE-K with number average molecular weight of 6000 amu is a linear function of temperature varying from 0.23–0.24 cal/(g.◦ C) at 38◦ C to 0.29–0.30 cal/ (g.◦ C) at 204◦ C. Thermal coefficient of expansion for two PFPE-K oils is given in Figure 8.3. The thermal coefficient of expansion and its change with temperature decrease with increasing molecular weight.

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8.3.2.2 Density The densities of PFPE fluids, are nearly twice that of hydrocarbon lubricants. Density increases slightly with increasing molecular weight and decreases linearly with temperature.

8.3.2.3 Electrical properties Electrical properties (Table 8.10) are affected by the presence of even trace amounts of moisture in the PFPE oil. The values will be lower for lower molecular weight/viscosity material and increase as molecular weight increases.

8.3.2.4 Vapor pressure and volatility

same viscosity have different vapor pressures. Commercial PFPE oils are composed of distributions of different molecular weight polymers, and the fraction of lower molecular weight polymer will determine the vapor pressure of that grade. Oils made specifically for vacuum systems are carefully distilled to remove low molecular weight fractions, which gives them superior vapor pressure. Volatility, as measured by ASTM D-972, is shown in Table 8.11. This test employs a steady stream of air blown across the surface of the hot oil and is useful in determining the light end content of the particular oil. As the lower molecular weight polymers evaporate, the viscosity of the oil will slightly increase.

The vapor pressure and volatility of PFPE oils at a specific temperature vary inversely with average molecular weights and thus, the higher viscosity oils generally have lower volatility losses. The vapor pressure of a PFPE fluid can be very sensitive to the presence of small amounts of impurities, such as very low molecular weight fractions or solvents. The Isoteniscope method is very sensitive to the presence of small amounts of high-vapor -pressure impurities whereas the Knudsen method is not. Comparing the vapor pressure obtained by each method indicates the level of these impurities. The Knudsen method is normally reported in the literature and manufacturer’s information bulletins. The vapor pressure and viscosity of specific homologues of PFPE will be dependent on its molecular weight. Commercial PFPE products may appear to contradict this correlation because different grades with the

8.3.2.5 Viscosity The viscosity of PFPE oils and their change with temperature for each type of PFPE are shown in Figure 8.4. The absolute or centipoise (mPa-sec) viscosity will be about 1.9 times higher than the kinematic viscosity because the density of PFPE oils is about 1.9 g/mL. The temperature dependence of viscosity (i.e., viscosity index) is similar to that of high grade petroleum oils with the exception of PFPE-Z, which is more favorable than petroleum oils. Polyfluoropolyether oil viscosity increases with an increase in the molecular weight. Commercial PFPE polymers are fractionated by distillation to produce a series of grades, based on viscosity. The viscosity is a function of average molecular weight, and the same viscosity can be obtained from a very narrow or a very broad molecular weight distribution. Cantow and Barrall [32] examined the dependence of the viscosities of PFPE fluids on temperature and pressure and found that differences could be attributed to structural differences. The bulky CF3 groups are responsible for the high pressure sensitivity of the nonlinear PFPE and the lower viscosity index.

TABLE 8.10 Electrical Properties of PFPE Oils at 25◦ C Property Dielectric breakdown voltage, ASTM D-877, KV/0.1 in. Specific resistivity, ASTM D-257, Ohm-cm Dielectric constant, ASTM D-150 at 102 to 105 Hz Dissipation factor, ASTM D-150 at 102 to 105 Hz

PFPE-K

PFPE-Y

PFPE-Z

38.8–41.1

40

30

6 × 1013 –4×1014

1015

4 × 1013

2.10–2.15

2.1–2.3

2.0

<0.003–<0.007

4 × 10−4

5 × 10−4

Source: Manufacturer’s literature.

TABLE 8.11 Evaporation of PFPE-K Oils (ASTM-D972) Wt% loss in 6 12 -h test MW

149◦ C

204◦ C

260◦ C

149◦ C

204◦ C

1850 2450 3000 3700 4800 6250 8250

<1 <1 <1 <0.1 <0.1 <0.1 <0.1

10 5 1 1 <1 <1 <1

60 30 10 5 1 1 <1

— — 45 30 15 4 2

20 5 3 1 — — —

80 40 20 5 2 1 —

Source: DuPont data.

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Wt % loss in 22-h test

99◦ C

260◦ C — — 60 40 20 6 3

8.3.2.6 Compressibility

8.3.3 Lubrication Performance

Perfluoropolyether oils are considerably more compressible, with lower bulk modulus, than conventional petroleum hydraulic fluids. Adiabatic tangent bulk modulus data (obtained by sonic methods) for PFPE-K are given in Figure 8.5 for pressures up to 34.5 MPa (5000 psig) and temperatures to 204◦ C (400◦ F). Figure 8.6 compares the compressibility of PFPE-K fluorinated oil with that of a typical hydrocarbon-based hydraulic fluid. At 38◦ C (100◦ F) and an applied pressure of 34.5 MPa (5000 psi), the hydrocarbon oil volume is reduced by about 2% while PFPE-K is compressed almost 3 21 %.

Perfluoropolyether oils are excellent lubricants under normal, severe, and starved operating conditions; under heavy loads; at high speeds; and at elevated temperatures. In general, when failure does occur, it occurs over a period of time, giving the operator warning of a failure. Test data in the following lubricity tests were obtained on PFPE-K oil that contained no additives.

5000 1000 200

8.3.3.1 Four-ball wear and extreme pressure tests Four-ball wear tests were conducted on PFPE-K at 75◦ C and 316◦ C and at loads of 1 to 40 kg using balls made of different alloys. Typical results at 620 and 1280 rpm are given in Figure 8.7. Table 8.12 shows the load carrying ability of PFPE oils in four-ball EP tests and how it increases with viscosity. 8.3.3.2 Falex extreme pressure tests

30 Z

15 7

D

5 Y

K

90 10 0 11 0 12 0 13 0 14 0 15 0

80

70

60

50

40

30

–1

0 0 10

3

20

Kinematic viscosity ASTM D445

Temperature, °C

FIGURE 8.4 Viscosity–temperature properties: comparison of different PFPE types

0

100

Extreme pressure tests with the Falex Pin & V-block tester, Table 8.13, using M-10 or 52100 steels with PFPE oils exceeded the limits of the test equipment. Using the standard shaft and V-block metals, the load at failure for PFPE oil far exceeded that of the non-PFPE test oils.

200

8.3.3.3 Bearing fatigue tests Fatigue test results in a rolling contact bearing rig in Table 8.14 showed PFPE oil to have excellent fatigue life at room temperature, 218◦ C, and 316◦ C. The test pieces

Temperature, °F 300

400

500

Adiabatic tangent bulk modulus (1000 psi)

240

1600

220 1400

200 180

1200

160

120

Applied Pressure psig Mpa 5000 34.5

100

4000

27.6

80

3000

20.7

60

2000

13.8

1000

6.9

0

0

140

40 50

100 150 Temperature, °C

FIGURE 8.5 Adiabatic tangent bulk modulus of PFPE-K fluorinated oil

Copyright 2006 by Taylor & Francis Group, LLC

200

800 600 400 200

20 0

1000

250

Adiabatic tangent bulk modulus (Mpa)

mm2 sec

100

were made from M-50 steel; the stress was 4826 MPa (700,000 psi) maximum Hertz and the speed was 25,000 stress cycles per minute. Oil was fed at the rate of 20 drops per minute.

8.3.3.4 Applications The chemical resistance of the PFPE lubricants (oils and greases) has led to their widespread use in many applications in the space programs where complete inertness to the fuels and oxidants is vital. Thus, both the oils and

70

10

Hydrocarbon Oil

Applied pressure (Mpa)

8 50

7

40

6 PFPE-1

5

30

4 3

20

2

Applied pressure (1000 psig)

9

60

10 1 0

0

1

2 3 4 5 Percent compressed

6

7

FIGURE 8.6 Compressibility of hydrocarbon oil and PFPE-K at 38◦ C

greases have been used to lubricate O-rings in many applications on the Apollo and other space projects. In general, a lighter oil is used if the O-rings are expected to operate after assembly. If the O-ring is static and a lubricant is required solely to assist in assembly, then a grease made from one of the heavier oils is preferred because of its lower volatility. Both oils and greases have been used as lubricants and antiseize compounds in the assembly of threaded fittings on spacecraft. Perfluoropolyether oil is used on the fasteners and moving parts of astronauts’ pressure suits, largely because of its nonflammability. This same oil has been used successfully on the bearings of antenna arrays on spacecraft. This oil has also proved satisfactory in lubricating bearings that permit extension of the paddle arms supporting solar cells on other spacecraft. PFPE is also used as the lubricant for the slide wire of potentiometers installed in spacecraft. The oil minimizes wear and does not migrate to other parts of the system. The most common use of the oils is in vacuum pumps in the semiconductor industry and in compressors and pumps handling reactive and hazardous gases. These fluids are used in rotary pumps, turbomolecular pumps, roots pumps, and diffusion pumps with adequate heating power. The higher molecular weight of the fluids can result in lower pumping speed in diffusion pumps. In nuclear power plants, PFPE was used as a bearing lubricant for pumps operating in an area where it was exposed to radiation. In this case, the radiation rapidly decomposed ordinary petroleum oils but the PFPE oil operated for long periods of time without appreciable decomposition. In one instance, after 900 h of operation

Four-ball wear test, 2 h at 620 rpm

Four-ball wear test, 2 h at 1280 rpm

316°C (600°F)

1.2

0.8

0.6 00

521

0.4

75°C (167°F)

10 M–

Average wear scar diameter, mm

10

0

1.0 52

Average wear scar diameter, mm

M –1

0

1.2

0 M–1

0.8

0 0

10

20 30 Load, kg

FIGURE 8.7 Wear characteristics of PFPE-K oil

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40

316°C (600°F)

0.6 00

521

0.4

0

75°C (167°F)

0 M–1

0.2

0.2

0

10

52

1.0

0

10

20 30 Load, kg

40

TABLE 8.12 Extreme Pressure Lubricating Characteristics of PFPE-K Oils, 4-Ball test Oil

Viscosity, 38◦ C

Mean Hertz load kga

Incipient seizure, kg

Weld point, kg

18.1 87.0 280.0 12.3 33.0 11.5 35.3

45.9 62.3 98.0 15.1 20.9 25.3 64.4

141 200 200 40 63 79 89

200 224 398 89 100 112 398

PFPE-MW = 1850 PFPE-MW = 3700 PFPE-MW = 6250 Di-2-ethylhexyl sebacate Silicate ester fluid Phosphate ester fluid EP petroleum gear oil

a Four-Ball Load Carrying Capacity Test (mean hertz load) by FTMS-791 Method

6503.1. Source: DuPont product literature.

TABLE 8.13 Extreme Pressure Characteristics of PFPE-K Oil, Pin and V-Block Test Specimen material Oil PFPE-K, MW = 6250 PFPE-K, MW = 6250 PFPE-K, MW = 6250 Deep dewaxed mineral oil

Maximum normal conditions

Shaft

V-Blocks

Loada , kg

Torque, J

SAE 3135 52100 M-10 SAE 3135

AISI 1137 52100 M-10 AISI 1137

1814 2041 2041 454

5.88 5.42 4.29 2.83

Failure load, kg 1928b No failure No failure 567c

Using the Falex Pin and V-Block Tester; Test Conditions: Load increased by 250 lb increments every minute. a 2041 kg capacity gauge b Load dropped c Shaft fractured Source: DuPont product literature

the viscosity had changed only 2%, and no sludge or gum had formed. The PFPE oils, because of their excellent stability to oxidation and the absence of gum formation, are used as lubricants for the bearings, jewels, and pivots of many different kinds of instruments. The shelf life for PFPE oils is nearly indefinite. PFPE-based lubricants have a very low static coefficient of friction compared to other lubricants. This eliminates the stick slip phenomenon and makes them exceptional lubricants for instruments and other devices such as surgical equipment that require precision control. Robots that are used for manufacturing use PFPE lubricants because of this ability to immediately and accurately respond without jerkiness.

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In an office machine a lightly loaded size R-6 bearing was placed near an electrical heating element and often reached temperatures greater than 260◦ C. This bearing, operating at 500 rpm, failed in less than 500 h with all MILG-25013 (dye-thickened, silicone-based) greases that were tested. This operating life was considered inadequate for the purpose. When PFPE grease was used as the lubricant, operating times in excess of 5000 h were obtained. Premature failure of the bearings of a synchronous electrical motor in a plant that produces synthetic textile fibers occurred when a dye-thickened silicone-based grease was used. The size 210 shielded cartridge-width ball bearings operating at 3200 rpm at a temperature of about 375◦ F failed in 2 to 6 months, for an average life of 2 21 months.

TABLE 8.14 Roller Contact Fatigue Tests Temperature

◦ C (◦ F)

32(90) 32(90) 218(425) 218(425) 316(600) 316(600)

Cycles

Bearing life

PFPE-K

B10 B50 B10 B50 B10 B50

3.3 × 106 10.1 × 106 7.2 × 106 13.5 × 106 8.4 × 106 18.1 × 106

MIL-L7808 oil 2.65 × 106 6.5 × 106 2.8 × 106 7.0 × 106 — —

Minimum 25,000 Stress Cycles, Maximum 700,000 psi (4,826 MPa) Hertz Stress, Air. Test Specimens: M-50 steel bars and rollers. 65,000 psi (448 MPa) maximum Hertz Load. Source: DuPont data.

When PFPE grease was substituted for the silicone grease, bearing life increased to an average exceeding 1 year. In a machine designed to orient polypropylene film at a temperature of 150◦ C, the film is held in position by studmounted, sealed roller bearings of 21 in. bore. When these bearings were lubricated with high quality diester type grease, the incidence of bearing failure reached an intolerable level, and production downtime became excessive. Introduction of a dye-thickened silicone grease improved but did not solve the problem. PFPE grease was then adopted with appreciable improvement in performance, and it has been in use at this plant for many years. The sealed rolling element bearings on a track and chain conveyor in another plant, one that manufactures polyester film, operate in an oven at 260◦ C. The use of a carbon black thickened silicone grease led to many premature bearing failures due to the tendency of the grease to run out of the bearings past the seal. This problem was solved by the use of PFPE grease, which has performed satisfactorily at this plant for many years. A battery of 7-hp electrical motors is used to drive centrifugal type blowers circulating hot air in a chemical drying process unit. The ambient air temperature in the vicinity of the motor bearings is about 250◦ C. The bearing nearest the blower is a size 310 shielded ball bearing and the one on the opposite side is a 35 MM (6207 size) bore roller bearing. When these bearings were lubricated with a premium quality high temperature bearing grease, bearing failures reduced motor life expectancy to less than 12 weeks. Bearing failure appeared to be due to lubrication starvation caused by the grease melting and running out of the bearing and by grease deterioration products forming within the bearing. When PFPE grease was adopted, average motor life increased to over 36 weeks, and any failures were due to mechanical parts, not the grease.

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There are several lower viscosity fluids available for use in vapor phase soldering, as heat transfer agents, and for reliability testing of equipment. They are used for liquid burn in, thermal shock testing, and leak detection in electronic equipment. In vapor phase soldering there is a range of fluids with different boiling points. These fluids create a vapor blanket that quickly transfers the heat to the component. The fluids are unaffected by the solder and flux and their low heat of vaporization allows them to quickly evaporate off the parts leaving no residue behind. 8.3.3.5 PFPE greases The PFPE oils can be used directly as lubricants, or they can be used as the base oils for making greases. The principal advantage of the greases over the oils is greases will “stay put” on surfaces where the oils might tend to run off or drain away rapidly. All of the oils are available for use in grease manufacture and are sold on the open market to many specialty grease manufacturers. There are hundreds of different greases available that are formulated for every imaginable application. Recently several grades of PFPE greases have received H-1 approval for use in food system applications. A large number of solids are suitable thickening agents for the formation of greases from the PFPE oils. Many of the thickening agents used for PFPE greases are the same as those used for hydrocarbon greases. Hydrocarbon soaps are typically not used because their thermal and chemical stability is poor. Thickening agents commonly used are finely divided silica, “Attapulgus clay,” montmorillonite, ammeline, boron nitride, copper phthalocyanine, metal-free phthalocyanine, PTFE family of polymers, fluorinated ethylene-propylene copolymers, and zinc oxide. Some thickeners or fillers have been described as imparting thermal conductivity to the grease. For instance, grease made with PFPE-Y and boron nitride has a coefficient of thermal conductivity of 0.68 and also possesses good heat and acid resistance [33]. Some of the PFPE greases thickened with fluorinated ethylene-propylene copolymer or PTFE contain antioxidants [34] such as tris(fluoroalkoxyphenyl)phosphine or corrosion inhibitors such as benzimidazole derivatives [35], perfluoroalkyl- and perfluoroalkyl ether-substituted benzoxazoles, benzothiazoles, bis-benzoxazoles, and bis-benzothiazoles [24]. Some PFPE greases are prepared by polymerizing tetrafluoroethylene in the perfluoroalkylpolyether [36]. The use of talc as a thickener will increase the BAM oxygen impact stability of the greases by as much as a threefold improvement. The different types of oils will also have an effect on the performance of the greases. Greases formulated with the linear types of fluids will have better

TABLE 8.15 Performance of PFPE-K Grease in Ball Bearings PFPE grease

Temperature ◦C

Speed rpm

Hours to failure

204 204 260 260 288

20,000 20,000 10,000 10,000 10,000

>500 >500 >500 >2, 000 >500

A B A B B

Source: DuPont product literature.

low temperature torque performance and can operate at lower temperatures. Greases made from shielded branched types of fluids will usually give better high temperature performance. Ball bearing performance tests on the PTFE thickened PFPE-K greases using FTMS-791, Method 333 show that PTFE thickened PFPE greases give excellent high temperature performance. Results in Table 8.15 are reported in hours to failure as evidenced by excessive running torque with a large increase in spindle input power, excessive bearing noise or screech, or increase of more than 20◦ F in bearing temperature.

brand names. Because soluble oil additives are relatively recent developments, the manufacturers have been the primary suppliers of formulated oils.

8.4.3 Economics The notion that these lubricants are prohibitively expensive or can only be used in very special situations is false. The lowest selling price is under US$100/lb and the highest is >US$3000/lb. Prices have been declining somewhat over the years as volumes increase. PFPE oils and greases can be used for general purpose lubrication, especially in the presence of severely harsh and demanding environments. These products are often the most cost effective solution even though the initial price is higher. They can significantly reduce costs by increasing the relubrication time interval and reducing the mechanical labor costs. The longer life and higher load carrying capability gives longer equipment life that reduces overall cost. The additional safety derived from a completely nonflammable lubricant that works at extremely high temperatures also increases its value. Because the oils can be regenerated by the manufacturers to new condition at a relatively low cost, the lifetime cost of the oils can be significantly reduced. The regenerated oils perform the same as new after regeneration, and regeneration eliminates the need to dispose of used oils.

8.4 MANUFACTURERS, MARKETING, ECONOMICS

8.5 OUTLOOK

8.4.1 Oil Producers

The use of these fluids is increasing. As designers reduce the size of components in automobiles, trucks, heavy equipment, computers, and other common devices, the internal temperatures increase and conventional lubricants that have been used for years begin to fail. Often, the only fluids with the capability to handle the temperatures are PFPEs. In many cases in the automotive/transportation business, manufacturers have increased warranties and now require lubricants with longer life than in the past. Additionally, new jet aircraft engines and stationary turbine electrical generating engines are being developed that run at temperatures above the capabilities of currently used turbine oils but are within the range of PFPE oils. These new turbines promise significantly enhanced fuel economy and performance. These fluids are in use or being tested in polymer modification and polymer curing, as magnetic fluids, electrorheological fluids, dielectric fluids, and as traction fluids. As new technology evolves, demands on conventional lubricants will continue to become more severe. This creates a continuing demand for the high temperature capabilities, non-reactivity, and long life of PFPE lubricants.

There are four primary companies that actually make most of the PFPE oils in the world: Du Pont in the United States, Solvay Solexis in Italy, Daikin in Japan, and NOK in Japan. The total capacity of PFPE oils is very difficult to determine, but should be more than 1000 tons/year. Information about the fraction that each company produces is not readily available. Within the last 10 years, Daikin reported a 60-metric tons per year fluorine oil plant, and Asahi Glass reported a 50-tons per year fluorinated oil plant. Appendix 8.1 lists standard commercially available fluids. The soluble and functional fluids are too complex to list here, but information about their properties is available from the manufacturers.

8.4.2 Marketing The manufacturers sell the oils directly and also produce their own brands of greases. Much of the oil goes directly into vacuum pump fluid use. In addition, the oils are often sold to specialty lubricant suppliers around the world who formulate the oils into greases that they sell under their own

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APPENDIX 8.1 Commercially Available Fluids and Properties Lubricating oils PFPE type

Average Molecular wt

Viscosity cSt at 20◦ C

Viscosity cSt at 40◦ C

Viscosity cSt at 100◦ C

Viscosity index

Pour point ◦C

1,350 1,500 1,750 2,300 3,100 5,000 6,250 8,250 8,600 9,400 11,600 2,500 3,500 5,000 7,000 8,200 10,500 1,500 1,800 3,200 4,100 6,250 6,600 7,250 4,500 5,800 7,200 7,400 4,000 8,000 9,800 12,500 12,500 4,000 8,000 9,500 13,000 2,700 4,500 5,600 8,400

7 16 36 80 180 550 810 1,600 1,712 2,560 3,500 31 70 150 233 350 540 38 60 250 470 1,200 1,500 1,850 153 240 543 800 30 150 280 550 1,300 30 160 263 600 53 150 250 500

4 8 15 30 60 160 240 440 500 740 1,023 15 32 65 99.9 150 220 15 22 80 147 345 420 510 72 111 208 277 17 85 159 310 700 18 92 157 355 25 65 100 200

— 2 3 5 9 18 25 42 46.4 64.5 88.5 3.7 7 12 18.5 26 40 3.2 3.9 10 16 33 40 47 16 24 34 41 5 22 45 86 200 5.6 28 49 98 5.9 (calculated) 12.6 (calculated) 16.7 (calculated) 31.6 (calculated)

— — 59 121 124 134 134 155 148 157 171 145 181 193 206 212 228 60 70 108 117 135 135 135 236 252 209 204 253 286 338 343 375 317 334 358 360 150 180 200 210

< −70 < −70 −63 −60 −51 −36 −36 −30 −25 −15 −5 < −75 < −70 −69 −67 −60 −60 −58 −50 −35 −30 −25 −25 −20 −65 −74 −54 −39 −85 −75 −65 −60 −50 −90 −80 −75 −63 −75 −65 −60 −53

Average molecular wt

Viscosity cSt at 20◦ C

Vapor pressure at 20◦ C, torr

Vapor pressure 100◦ C, torr

2,400 3,500 4,000 4,600 4,900 4,300

62 142 189 261 310 175

4 × 10−7 2 × 10−7 1 × 10−7 1 × 10−7 1 × 10−7 5 × 10−9

1 × 10−3 1 × 10−4 7 × 10−5 3 × 10−5 3 × 10−5 2 × 10−5

PFPE-K-100 PFPE-K-101 PFPE-K-102 PFPE-K-103 PFPE-K-104 PFPE-K-105 PFPE-K-106 PFPE-K-107 PFPE-K-XHT-500 PFPE-K-XHT-750 PFPE-K-XHT-1000 PFPE-K-L-15 PFPE-K-L-32 PFPE-K-L-65 PFPE-K-L-100 PFPE-K-L-150 PFPE-K-L-220 PFPE-Y-04 PFPE-Y-06 PFPE-Y-25 PFPE-Y-45 PFPE-YR PFPE-YR-1500 PFPE-YR-1800 PFPE-W-150 PFPE-W-200 PFPE-W-500 PFPE-W-800 PFPE-M-03 PFPE-M-15 PFPE-M-30 PFPE-M-60 PFPE-M-100 PFPE-Z-03 PFPE-Z-15 PFPE-Z-25 PFPE-Z-60 PFPE-D S-20 PFPE-D S-65 PFPE-D S-100 PFPE-D S-200 Vacuum pump fluids PFPE type PFPE-K-1506 PFPE-K-1514 PFPE-K-1520 PFPE-K-1525 PFPE-K-1531 PFPE-K-1618

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Density, g/mL 1.87 at 0◦ C 1.89 at 0◦ C 1.91 at 0◦ C 1.92 at 0◦ C 1.93 at 0◦ C 1.94 at 0◦ C 1.95 at 0◦ C 1.95 at 0◦ C 1.95 at 0◦ C 1.95 at 0◦ C 1.95 at 0◦ C 1.84 at 24◦ C 1.85 at 24◦ C 1.85 at 24◦ C 1.86 at 24◦ C 1.87 at 24◦ C 1.87 at 24◦ C 1.87 at 20◦ C 1.88 at 20◦ C 1.90 at 20◦ C 1.91 at 20◦ C 1.91 at 20◦ C 1.91 at 20◦ C 1.92 at 20◦ C 1.86 at 20◦ C 1.88 at 20◦ C 1.89 at 20◦ C 1.90 at 20◦ C 1.81 at 20◦ C .83 at 20◦ C 1.85 at 20◦ C 1.86 at 20◦ C 1.87 at 20◦ C 1.82 at 20◦ C 1.84 at 20◦ C 1.85 at 20◦ C 1.85 at 20◦ C 1.86 at 20◦ C 1.873 at 20◦ C 1.878 at 20◦ C 1.894 at 20◦ C

APPENDIX 8.1 Continued PFPE-K-16256 PFPE-Y-06/6 PFPE-Y-14/6 PFPE-Y-16/6 PFPE-Y-25/6 PFPE-Y-18/8 PFPE-Y-25/9 PFPE-Y-40/11 PFPE-Y-140/13 PFPE-D S-20 PFPE-D S-65 PFPE-K, L

PFPE -Y, Z, W, M,

PFPE - D Daikin,

11,000 1,800 2,500

2,717 64 140

3,300 2,800 3,400 4,100 6,600 2,700 4,500

270 190 285 474 1,508 53 150

3 × 10−14 8 × 10−7 at 25 C 1 × 10−7 at 25 C 2 × 10−6 at 25◦ C 5 × 10−8 at 25◦ C — — — — — —

1 × 10−9 5 × 10−3 2 × 10−3 2 × 10−4 2 × 10−3 — — — — — —

DuPont, Krytox® lubricants, USA, Deepwater, NJ 08023 800-424-7502, Europe 32-3-543-1267 www.krytox.com Solvay Solexis, Fomblin®lubricants, USA, 856-853-8119 www.solvaysolexis.com Europe, +39-02-3835-1 Demnum®lubricants Umeda-Center Bldg., 2-4-12, Nakazaki-Nishi, Kita-Ku, Osaka, 530-8323, Japan, +81-6-6373-4312 Daikin America, 20 Olympic Drive Orangeburg, N.Y.,10962, 1-845-365-9500 www.daikin.cc

REFERENCES 1. Gumprecht, W.H., “PR-143 — A new class of hightemperature fluids,” ASLE Transac., 9, 24–30 (1966). 2. Carlson, D.P. and Milian, A.S., Fourth International Symposium on Fluorine Chemistry, Estes Park, Colorado (July, 1967). 3. British Patent 904, 877 (September 5, 1962). 4. Gumprecht, W.H., “The Preparation and Thermal Behavior of Hexafluoropropylene Epoxide Polymers,” Fourth International Symposium on Fluorine Chemistry, Estes Park, Colorado (July, 1967). 5. US 3442942 (May 5, 1969). 6. US 3715378 (February 6, 1975). 7. Sianesi, D., Pasetti, A., Fontanelli, R., Bernardi, G.C., Caporiccio, G., and La Chimica E L’industria, Wear, 55, 208 (1973); US 4,451,646 (May 29, 1986). 8. Banks, R.E., Smart, B.E., and Tatlow, J.C., Organofluorine Chem. (1994). 9. Sianesi, D., Zamboni, V., Fontanelli, R., and Binaghi, M., Wear, 18, 85 (1971). 10. Jones, W.R., Bierschenk, T.R., Juhlke, T.J., Kawa, H., and Lagow, R.J., Ind. Eng. Chem. Res., 27/8, 1497 (1988). 11. Paciorek, K.J.L., Kratzer, J., Kaufman, J., and Nakahara, J.H., J. Appl. Polym. Sci., 24, 1397 (1979). 12. Gumprecht, W.H., “The Preparation and Thermal Behavior of Hexafluoropropylene Epoxide Polymers,” Fourth International Symposium on Fluorine Chemistry, Estes Park, Colorado (July, 1967).

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13. Gumprecht, W.H., “The Preparation, Chemistry and Some Properties of Hexafluoropropylene Epoxide Polymers,” Gordon fluorine Conference, New Hampshire (1968). 14. Paciorek, K.J.L., Kratzer, J., Kaufman, J., and Nakahara, J.H., J. Appl. Polym. Sci., 24, 1397 (1979). 15. Jones, W.R., Jr., Paciorek, K.J.L., Ito, T.I., and Kratzer, R.H., Thermal oxidative degradation reactions of linear perfluoroalkylethers, Ind. Eng. Chem. Prod. Res. Dev., 22, 166–170, (1983). 16. Pearson, R.K., Happe, J.A., and Barton G.W., Study of the degradation of two candidate diffusion pump oils, Krytox and Fomblin, Lawrence Livermore Laboratory report number UCID 19571 (1982). 17. Sianesi, D. and Fontanelli, R., Perfluoropolyethers, their structure and reaction with aluminum chloride, R. Makromol. Chem., 102, 115 (1967). 18. Montedison Brochure. 19. Carre, D.J. and Markowitz, J.A., The reaction of perfluoropolyalkyl oil with FeF3, AlF3, and AlCl3 at elevated temperatures, ASLE Trans., 28, 40 (1985). 20. Dolle, R.E. and Harasacky, F.J., “New High Temperature Additive Systems for PR*-143 Fluids,” U.S. Air Force Materials Laboratory Technical Report AFML-TR-65-349 (January, 1966). 21. Srinivasan, P., Corti, C., Montagna, L., and Savelli, P., Soluble additives for perfluorinated lubricants, J. Synth. Lubr., 10–12, 143 (1993). 22. Perfluoropolyether lubricants, Corti, C., and Savelli, P., Proceedings of the Conference on Synthetic Lubricants,

23.

24.

25.

26.

27. 28.

29.

pp. 128–55. Zakar, Andras, Ed., Hung. Hydrocarbon Inst., Szazhalombatta, Hungary (1989). Strepparola, E., Gavezotti, P., and Corti, C., Antirust additives for lubricants or greases based on perfluoropolyethers, Eur. Pat. Appl., p. 12, EP 337425 A1, CA111(26):236482v, (October 18, 1989). Christian, J.B. and Tamborski, C., Benzoxazole and benzothiazole antirust greases, Lubr. Eng., 36, 639–642 (1980). Snyder, C.E., Tamborski, C., Gopal, H., and Svisco, C.A., Synthesis and development of improved high-temperature additives for polyperfluoroalkylether lubricants and hydraulic fluid,” J. ASLE, 35, 451 (1978). Mori, S. and Morales, W., NASA Technical Paper 2910, “Degradation and Crosslinking of Perfluoroalkyl Polyethers in Ultra Vacuum,” (1989). PFPE manufacturer bulletin MA-816E, Montedison, USA. Dolle, R.E., Harasacky, F.J., Schwenker, H., Adamczak, R.L., “Chemical, Physical and Engineering Performance Characteristics of a New Family of Perfluorinated Fluids,” U.S. Air Force Materials Laboratory Technical Report AFML-TR-65-358 (September, 1965). Messina, J., “Perfluorinated Lubricants for Liquid Fueled Rocket Motor Systems,” ASLE Preprint No. 67 AM8A-4 (May 1, 1967).

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30. Ohsaka, Y., Perfluoropolyether Fluids (Demnum® ) Based on Oxetanes, Organofluorine Chemistry: Principles and Commercial Applications, New York, Plenum Press (1994), pp. 463–467. 31. Sianisi, D., Marchionni, G., De Pasquale, R.J., Perfluoropolyethers (PFPEs) from Perfluoroolefin Photooxidation, Fomblin® and Galden® Fluids, Organofluorine Chemistry: Principles and Commercial Applications, New York, Plenum Press, (1994), pp. 431–461. 32. Cantow, M.J.R., Barrall, E.M. II, Wolf, B.A., and Geerissen, H., Temperature and pressure dependence of the viscosities of perfluoropolyether fluids, J. Polym. Sci., Part B: Polym. Phys., 25, 603–609 (1987). 33. Mizushima, S., Nakahara, H., and Yamada, H., “Perfluoropolyether Compound Compositions With Excellent Thermal Conductivity,” JP 63251455 (October 18, 1988). 34. Christian, J.B., Oxidation Stable Polyfluoroalkyl Ether Grease Compositions, U. S. Pat. Appl., p. 14 Avail. NTIS Order No. PAT-APPL-6-418 106., US 418106 A, CA99(10):73640n (April 15, 1983). 35. Christian, J.B., Grease Compositions, U. S. Pat. Appl., 20 pp. Avail. NTIS Order No. PAT-APPL-225 546. US 225546 A0, CA96(4):22263x (July 31, 1981) 36. Tohzuka, T., Kataoka, Y., Ishikawa, S., and Fujiwara, K., Fluorine-Containing Grease and its Preparation, EP 341613 A1, CA112(12):101951x (November 15, 1989).

9

Polyphenyl Ether Lubricants Sibtain Hamid and Stephen A. Burian CONTENTS 9.1 9.2 9.3 9.4 9.5

Introduction Historical Development General Synthesis C-Ethers Properties and Performance Characteristics 9.5.1 Low-Temperature Properties 9.5.2 Thermal/Oxidation Stability 9.5.3 Surface Tension 9.5.4 Lubrication Characteristics 9.5.5 Vapor Pressure 9.6 Manufacture, Marketing, and Economics 9.7 Applications for PPEs 9.7.1 High-Vacuum Diffusion Pumps 9.7.2 Electronic Connectors 9.7.3 Optical Fluids and Gels 9.7.4 High Temperature Chain Lubricants 9.7.5 Heat Transfer Fluid/Thermal Compounds 9.7.6 Vibration Control Lubricants and Greases 9.7.7 Radiation Resistant Fluids and Greases 9.8 Outlook Acknowledgment References

9.1 INTRODUCTION A unique class of compounds known as polyphenyl ethers (PPEs) are mixed isomeric compounds ranging from tworing or phenyl groups to six-ring structures (Table 9.1) that were developed for use in extreme environments, including high-temperature hydraulic, lubricant/grease, heat transfer, and other fluid applications. The PPEs are viscous, clear, light yellow liquids that possess extraordinary resistance to degradation from heat, oxygen, radiation, hydrolysis, and chemical attack (Table 9.2). They are compatible with most metals and elastomers commonly used in high-temperature applications. In addition, PPEs respond well to antioxidants and preservative-type additives, and are soluble in many synthetic fluids such as esters, polyalphaolefins, and polyalkylene glycols. These fluids are nonhalogenated and are considered to be practically nontoxic and require no special handling or precautionary measures other than

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the normal hygienic practices employed with any industrial chemical. The PPEs were studied extensively in the mid-tolate 1950s as an outgrowth of U.S. Air Force work to develop high-temperature fluids and lubricants. Since that time, they have found application as high-temperature greases, jet engine/turbine lubricants, electrical contact lubricants, bearing lubricants, heat transfer agents, and as optical fluids. The unique properties of PPEs offer a myriad of use potentials. The PPEs may be considered an engineering design tool as system efficiencies (energy, speed, weight, temperature, and materials of construction) can be maximized using them. In addition, requirements for safety or fire-protection devices and noise or radiation shielding may be designed and engineered into such system efficiencies.

TABLE 9.1 Chemical Names for Polyphenyl Ethers (PPEs) Common and trade name

Chemical name

Six-ring polyphenyl ether (6P5E) Trade name: OS-138™ Five-ring polyphenyl ether (5P4E) Trade name: OS-124™ Four-ring polyphenyl ether (4P3E) Trade name: MCS-210™ Three- and four-ring oxy- and thioethers Trade name: MCS-293™ Three-ring polyphenyl ether (3P2E) Trade name: MCS-2167™ Two-ring polyphenyl ether (2P1E) Trade names: Monsanto or Dow DPO

Bis[m-(m-phenoxyphenoxy) phenyl] ether m-Bis(m-phenoxyphenoxy)benzene Bis(m-phenoxyphenyl) ether Thiobis[phenoxybenzene] and Bis(phenyl mercapto) benzene m-Diphenoxybenzene Diphenyl oxide, phenyl ether, phenoxybenzene, or diphenyl ether

TABLE 9.2 Properties of Base Stocks Property Viscosity, cSt At 37.8◦ C At 98.9◦ C At 260◦ C Thermal decomposition, ◦ C Autoignition temperature, ◦ C Pour point, ◦ C Evaporative loss, % (204◦ C, 6.5 h) Surface tension, dyn/cm at 24◦ C Isotherm secant bulk modulus, psi at 37.8◦ C

C-Ether

PPE [5P4E]

PPE (2PIE)

25.2 4.1 0.81 367

363 13.1 1.2 453

100 7.8 ca. 310

504

559

435

−29 10

+5 <1

−59 12

50

50

ca. 30

340,000 (0–7500 psi)

390,000 (0–6000 psi)

The PPEs are a class of lubricants having useful but rare properties, most significantly high thermal stability, radiation resistance, chemical inertness, high refractive index, and extremely low vapor pressure. Almost a century ago a German research chemist, Ullmann, first developed diphenyl ether by substituting an oxygen atom between the two benzene rings. At that time the need for such a compound simply did not exist, nor could Ullmann foresee that properties of such a compound would be in great demand in the 20th and 21st centuries when engineers would begin designing complex machinery — aircraft, automobile and space vehicles, and communications equipment that would be required to operate in harsh environments.

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The PPEs produced today still use the basic Ullmann synthesis process; however, more complex refining steps are utilized in order to increase further the stability and inertness of the molecule. A number of four- or five-ring PPEs are manufactured in multistep processing units. The position of the oxygen atoms on the benzene rings is critical to certain performance in low- and high-temperature regimes. The benzene rings tend to have high resonance energy. The bonds holding the molecule together by their resonance energy cause the PPEs to boil only at high temperatures (477◦ C, or 890◦ F, at atmospheric pressure). The temperature at which the molecule decomposes also tends to be very high.

9.2 HISTORICAL DEVELOPMENT The first synthesis of PPEs was reported in 1906 by Ullmann and Sponagel [1]. Their copper-catalyzed reaction of an alkali phenate with an aromatic halogen is the condensation reaction that is still referred to by Ullmann’s name. The first commercial interest in these fluids started in the 1950s, when the U.S. Air Force funded projects aimed at developing high-temperature hydraulic fluids [2]. Later, other Air Force contract work reported on the suitability of PPE materials as high-temperature lubricants [3]. The first large-scale application of a PPE lubricant was in the Pratt & Whitney J-58 engine on the U.S. Air Force SR-71 aircraft. Supersonic flight generates heat from friction that cannot be removed in the conventional manner of subsonic aircraft. The designed engine lubricant temperature in this plane was a continuous 316◦ C, much higher than any ester-based lubricant could withstand. A five-ring PPE base stock containing an antioxidant served as this plane’s engine lubricant from 1966 until the fleet was retired from active service in 1990. Occasionally this aircraft is put back into service for certain military maneuvers. Commercial PPE made today include higher performance fluids, lubricants, and greases. A very large application for PPEs is in high-vacuum diffusion pumps (Figure 9.1). These fluids are used where ultra high vacuums of 4 × 10−10 torr or higher at 25◦ C is required, such as electron microscopes, mass spectrometers, and equipment for various surface physics studies. Some of the common applications today for diffusion pumps are as follows: • • • • • • • • •

Decorative coatings Particle accelerators Semiconductor manufacture Electron tube manufacture Sputtering Mass spectrometry Metallurgy Leak detectors Deposition systems

Molecule capture

Coolant Vaporized oil

To forepump

Heater

FIGURE 9.1 High vacuum diffusion pump (Courtesy International Scientific Communications, Inc., Shelton, Connecticut)

• Electron microscopes • Space simulators • Optical coating

There are a number of specialty or niche applications for PPE materials. These include radiation resistant fluids and greases, connector lubricants, and vibration control lubricants. Another application of PPEs is in the area of vapor-phase lubricants for use in gas turbines and custom bearings. The vapor-phase lubrication is achieved by heating the lubricant above its boiling point. The resultant vapors are then transported to a bearing surface. The advantage of PPE is its high-temperature stability, since other lubricants in high-temperature regimes are either unstable or contain a halogenated compound that can produce toxic vapors.

9.3 GENERAL SYNTHESIS The following are possible PPE synthesis methods. The method of choice depends on whether an even or odd number of phenyl groups are desired in the product. By choosing the molecular weight and degree of substitution on the starting alkali phenate, a vast array of PPE products can be readily obtained. However, the PPEs with the most interesting physical properties contain four or more phenyl groups and are for the most part unsubstituted [4]. Most PPEs have been prepared by the Ullmann ether synthesis, which involves a copper-catalyzed coupling of

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2

OK + Br

Br

Ca ∆

O

O

FIGURE 9.2 Synthesis of polyphenyl ethers

an alkali phenate with an aromatic halogen compound as, outlined in Figure 9.2.

9.4 C-ETHERS Another class of PPEs is called C-Ethers or polyphenyl oxy/thio ethers. C-ether fluids have good oxidative stability up to 260◦ C (500◦ F) for a base stock blend of three- and four-ring components; the structures are presented in Figure 9.3. C-ethers are similar to the PPEs except that sulfur provides the link between some of the phenyl rings instead of oxygen [5]. Unformulated C-ethers have fair boundary lubricating ability and fair fire resistance. Like many other aromatic chemicals, the oxy- and thioethers possess inherent thermal and oxidative stability or great inertness. The oxyethers survive oxidation– corrosion tests up to 316◦ C. The thioethers survive tests up to 260◦ C and perform very well in the absence of copper up to 316◦ C. These aromatics also possess higher autoignition temperatures than aliphatic fluids. This property, together with their stability, allows their use at temperatures well above those of most other fluids, in applications such as high-temperature jet engines.

9.5 PROPERTIES AND PERFORMANCE CHARACTERISTICS The PPEs have outstanding thermal and oxidative stability. They also have reasonable lubricity and excellent resistance to nuclear radiation and chemical attack. The process for manufacturing these materials requires many steps and involves complex raw materials. This involved process, combined with a high pour point, particularly for the higher molecular weight compounds, has limited their use to very demanding specialty applications where cost and viscosity are minor considerations, and no other product or technology can do the job [4].

9.5.1 Low-Temperature Properties The four-ring PPE (4P3E) molecule described in Tables 9.3 and 9.4 is generally formulated as a blend to achieve a suitable material. The pure form has a +5◦ C pour point, which is an undesirable property in a lubricant. Blending the pure

S

S

1,3-Bis(phenylthio)benzene

O

S

O

1,1-Thiobis(3-phenoxybenzene)

O

S

S

1-Phenoxy-3-((3-(phenylthio)phenyl)thio)benzene

S

S

S

1,1-Thiobis(3-(phenylthio)benzene)

FIGURE 9.3 The C-ether family

molecule with other components, however, can eliminate the problem and produce mixtures with a pour point of −12◦ C. Below this pour point, the blended material will not crystallize, but rather becomes glassier as the temperature continues to drop. The pure substances will super cool and can remain in a liquid state for months at room temperature. The six-ring PPE (6P5E) differs from both the 4P3E and the five-ring PPE 5P4E in that it does not crystallize. This higher molecular weight molecule is used commercially as a pure isomer, which does not require formulating with other components. However, it generally must be heated slightly, since it has a pour point in the range of 10 to 15◦ C.

9.5.2 Thermal/Oxidation Stability The all-meta PPE structures have the highest thermal and oxidative stability of all other isomers of the same molecule. The differences between the isomers, however, are not large. For example, the thermal decomposition temperatures of the 4P3E isomers vary by about 8◦ C. Differences between the three-, four-, five-, and six-ring molecules are also small, as illustrated in Table 9.5. As these data show, the initial thermal-stability temperatures, as measured by isoteniscope, are very high. However, the temperatures at which these fluids perform as bulk lubricants are lower [6]. A more useful measure of thermal stability is to evaluate the increase in fluid viscosity over time while the fluid is held at a given temperature. Results are shown in Table 9.6 for a commercially available 5P4E product using Federal Test Method standard 791, Method 5308, where the fluid is held for 48 h at different temperatures using a 5 L/h airflow. The inhibited 5P4E fluid shows a 100◦ F viscosity increase of 23% after the 48-h test. The viscosity at operating temperature increases by a lower amount, but is not measured as a key property. The performance is considered acceptable for a bulk fluid high-temperature lubricant, given that this is an accelerated test. The viscosity increase is caused by high molecular weight

TABLE 9.3 Physical Properties of PPEs Polyphenyl ether (PPE) Six-ring 6P5E Five-ring 5P4E Four-ring 4P3E Three- and four-ring oxy/thio Three-ring 3P2E Two-ring 2P1E

Copyright 2006 by Taylor & Francis Group, LLC

Form at room temperature

Pour point (◦ F)

Specific gravity at 24◦ F

Viscosity (cSt) at 100◦ F

Viscosity (cSt) at 210◦ F

Clear liquid Clear liquid Clear liquid Hazy liquid

65 max. 45 max. 12 (−12 in mixture) −20

1.20 1.20 1.18 1.20

2550 max. 360 70 25

25 13 6 4

Solid Clear liquid

— —

1.20 1.07

12 100

3 7.8

TABLE 9.4 Additional Physical Properties of PPEs Polyphenyl ether (PPE)

TABLE 9.7 Shell Four-Ball Wear Test

Autoignition temperature

Thermal stability, by isoteniscope (◦ F)

Flash point (◦ F)

1170 1135 1095 935

836 847 825 693

600 550 465 440 min

1070 1144

800 —

380 365

Six-ring 6P5E Five-ring 5P4E Four-ring 4P3E Three- and four-ring oxy/thio Three-ring 3P2E Two-ring 2P1E

Load (kg)

Scar diameter (mm)

10 30 50

0.80 0.89 1.13

Conditions: 204◦ C, 600 rpm, 1 h, 52,100 steel balls.

TABLE 9.8 Ryder Gear Scuff Test Ryder Gear Scuff Test

TABLE 9.5 Thermal Decomposition Temperatures of PPEs

At 75◦ C

Polyphenyl ether (PPE)

ppi = pounds per inch.

Initial decomposition temperature, by isoteniscope (◦ C)

4P3E 5P4E 6P5E

445 465 447

TABLE 9.6 Thermal Stability of 5P4E Base fluid

Inhibited fluid

At 260◦ C At 288◦ C At 316◦ C At 316◦ C At 371◦ C Weight change (mg/cm2 ) Magnesium −0.01 Aluminium +0.01 Titanium 0.00 Steel +0.01 Copper −0.05 Silver +0.03

+0.04 +0.01 +0.01 +0.03 +0.03 +0.06

+0.25 +0.01 +0.02 +0.05 −0.95 +0.32

+0.02 +0.01 +0.02 +0.04 +0.29 −0.12

0.00 — — — −0.03 −0.02

Viscosity change (%) At 100◦ F 5 At 210◦ F 2

16 6

70 32

23 17

89 29

decomposition products. These by-products are large enough to allow distillation to economically separate them from the PPEs and therefore this reclamation process is commonly employed. The decomposition products are not large enough to precipitate out of solution, however. This explains why as long as PPEs are used at a temperature where viscosity increases are in the range of 25% their tendency to form coking deposits is low.

9.5.3 Surface Tension The surface tension of PPEs is high enough that these fluids tend not to wet metal surfaces. The surface tension

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At 204◦ C

2450 ± 300 ppi 1000 ± 150 ppi

of the commercially available 5R4E is 49.9 dyn/cm. This property is useful when the migration of a lubricant must be avoided, such as in the lubrication of certain types of electrical components. A thin film of PPE is not really a thin, contiguous film, but rather a field of tiny droplets. This property tends to keep the lubricant stationary, or at least causes it to remain in the area where the lubrication is needed, rather than migrating away by spreading and forming a new surface. As a result, contamination of other components or equipment that do not require a lubricant is avoided. There are no other known lubricants that have this property.

9.5.4 Lubrication Characteristics The PPEs have good wear characteristics in bearing and load-carrying ability, greater than mineral oils. However, these materials are not recommended for piston engine applications, since no additive package has been developed, to date, to lubricate the sliding wear of piston rings. Many of the additives commonly used for this purpose in other lubricant base stocks have solubility problems in PPEs. Tables 9.7 to 9.9 show the results of Shell four-ball wear tests, Ryder gear tests, and CRC bearing rig tests for the commercially available 5P4E fluid.

9.5.5 Vapor Pressure The vapor pressure of the 5P4E fluid, which is commercially sold as a vacuum pump fluid, is shown in Table 9.10. The PPEs have a very low vapor pressure, which is the major requirement for the working fluid in a diffusion pump. The PPEs have found their way into this application

TABLE 9.9 CRC Bearing Rig Test (Coordinating Research Council, United States) Fluid type Bearing temperature, ◦ C

Bulk oil temperature, ◦ C Oil inlet temperature, ◦ C Overall demerit rating Change in 100◦ F viscosity Acid number increase Consumption rate mL/h Sludge formation, g

Base 5P4E

Inhibited 5P4E

343 316 288 114 2000% (82 h) Nil 39 1.64

343 316 288 66 64% (100 h) Nil 50 3.11

The market price for PPEs is relatively high compared to other synthetics. This is due to expensive raw materials, a complex, multistep manufacturing process, and small markets, which are characterized as having extreme environments that require products with unique properties. In general, the price of the PPEs is only one factor that enters into the decision to use these products. PPEs are chosen either because they have properties that no other material possesses or because the benefits far outweigh the costs compared to alternative technologies in a specific application.

9.7 APPLICATIONS FOR PPES TABLE 9.10 Vapor Pressure of Blended 5P4E Pressure (mmHg) 0.0102 11.8 194 760

Temperature (◦ C) 260 343 427 476 (normal boiling point)

because of a combination of a number of properties, such as superior thermal stability, exceptionally low vapor pressure, and a tendency to wet surfaces less readily and “creep” to a lesser extent than is common with other fluids. The fluid is employed for the cleanest high vacuum and ultrahigh vacuum applications, where its excellent high vacuum performance and low tendency to migrate into the pump system are crucial. Since the fluid is chemically stable, noncorrosive, safe, nontoxic, and has excellent lubricating properties, it is also used to lubricate mechanisms in the overall vacuum system [7]. Since diffusion pumps work by boiling their fluid with an electric heating element, there are conditions under which the fluid will experience high surface temperatures. Another useful property of PPEs in this application is their ability to resist attack from other chemicals that may be introduced into the vacuum chamber. Acids, bases, and halogens have little effect on PPEs.

9.6 MANUFACTURE, MARKETING, AND ECONOMICS There continues to be only one producer of PPEs in the United States, Findett Corporation. A few other companies have attempted to manufacture PPEs in other countries. However, they either have abandoned their efforts or, apparently, are producing the compounds for captive use. The largest volume product continues to be the 5P4E, which is used as a jet lubricant and as a vacuum pump fluid. Smaller quantities of the other PPEs have been produced either under contract or for proprietary applications.

Copyright 2006 by Taylor & Francis Group, LLC

The first large-scale application for PPEs was in the Pratt & Whitney J-58 engines on the U.S. Air Force SR-71 aircraft. Supersonic flight generates heat from friction that cannot be removed in the conventional manner of subsonic aircraft. The designed engine lubricant temperature in this plane was a continuous 316◦ C, much higher than any ester-based lubricant could withstand. Other applications are in pumps where ultrahigh vacuums of 4 × 10−10 torr, and higher, at 25◦ C are required, such as in electron microscopes, mass spectrometers, and equipment used for studies in surface physics. There are also a number of other specialty or niche applications for the PPE materials. One of these exists in the formulation of radiation-resistant greases used in nuclear power plant mechanisms. PPEs are some of the most radiation-resistant fluids available. Tests have shown gamma- and associated neutron-radiation resistance at dosages up to 1010 erg/g at temperatures up to 600◦ F. Another application of PPEs and their derivates is in the area of vapor-phase lubricants for use in gas turbines and custom bearings, or where extreme environmental conditions exist. Vapor-phase lubrication is achieved by heating a liquid lubricant above its boiling point. The resultant vapors are then transported to a hot bearing surface. If temperatures are below the lubricant’s boiling point, the vapor condenses to provide liquid lubrication or vapor condensation. PPE technology can provide improved fire safety and fatigue life, depending on the specific bearing design. In addition, the PPEs have an advantage for this application, since they can lubricate both as a liquid at low temperatures and as a vapor at temperatures above 600◦ C.

9.7.1 High-Vacuum Diffusion Pumps Polyphenyl ethers offer unusually high thermal and oxidation stability. Isoteniscope tests show that 5P4E remains thermally stable at 870◦ F. PPEs may undergo a slight color change with use, but this does not effect the operation as a diffusion pump fluid. Oxidation and corrosion tests, as well as field experience, have shown that 5P4E has little

tendency to increase in viscosity during the standard testing. These results indicate that there is less change due to overheating and thermal degradation. The corrosion portion of the test indicates that 5P4E is generally compatible with the metallic materials most often used in diffusion pump manufacture. Absorbed films of 5P4E are easier to remove than silicone films. Santovac 5 can easily be baked off in vacuum or cleaned with standard solvents.

9.7.2 Electronic Connectors The PPE lubricants have a 30-yr history of commercial service for connectors with precious and base metal contacts in telecom, automotive, aerospace, instrumentation, and general-purpose applications. Many billions of contacts have been improved by the use of PPE-based lubricant formulations. A highly stable, nonspreading film is formed on connectors/terminals that affords long-term lubrication and protection even when the connectors are exposed to aggressive atmospheres. PPE connector lubricants reduce insertion force, minimize wear, and maintain low and stable contact resistance [1,8–10]. In addition these lubricants eliminate all forms of corrosion including “fretting corrosion.” These lubricants will last and continue to work for decades or for the life of the equipment. Most lubricants form a continuous film to create a protective layer between two surfaces. PPEs, though, lie on a surface not as a continuous film but as a field of microscopically small droplets. This unusual structure is a result of high surface tension; the surface tension of one commonly used PPE is 49.9 dyn/cm. Each tiny droplet vibrates constantly with something akin to Brownian movement, but the whole field of droplets remains where it was applied, even under mechanical pressure and even at high temperatures. No other known lubricants have this useful property of positional stability. Common problems in most systems are vibration, wear and abrasion, atmospheric contamination, temperature cycling, and corrosion. PPE could improve the performance and reliability of the systems. In cell phones, printers, and other electronic appliances, PPEs are applied to the electronic connectors usually of the multiple pinand-socket variety. Their purpose on electronic connectors is to protect against abrasion ( just as in a jet engine, but on a far smaller scale), and to protect against corrosion.

9.7.3 Optical Fluids and Gels Early in 2002 the search was expanding for new optical materials that could operate in extreme conditions. A test with PPE on advanced lasers and a diode laser, based on a gallium arsenate semiconductor, was carried out for use in welding and other similar applications (Figure 9.4).

Copyright 2006 by Taylor & Francis Group, LLC

FIGURE 9.4 Polyphenyl ethers can handle welding applications and may increase production speed for carbon composite parts (Courtesy of Nuvonyx Inc., Bridgeton, Missouri)

The degree to which the temperature increase effects phase is called the thermooptic coefficient. A high thermooptic coefficient permits the design of faster, smaller, and less power-consumptive switches. PPEs with their higher refractive index and high thermooptic coefficient are ideal materials for this application (Figure 9.5). Additionally, with the advent of high-power single-mode lightwave systems made possible by the recent invention of erbiumdoped fiber amplifiers (EDFAs) there is a further need for monitoring and switch elements that can handle intense near-infrared signal power [11].

9.7.4 High Temperature Chain Lubricants The PPE-based lubricants are used where extreme temperature conditions exist, such as kiln and high-temperature metal fabrication and molding. They have been used successfully in glass manufacturing. The advantages are low evaporation rate and no sludge or deposit formation on chains. The low-carbon residue leftover after excessive heat is a soft carbon deposit that can be removed easily by wiping it off of the metal surface.

Near UV

PPE based lubricants are therefore widely used in nuclear power plants, space satellites, nuclear submarines, food sterilization equipment, radiation chemistry systems, and medical imaging systems.

NEAR INFRARED WAVELENGTHS

VISIBLE

1064 nm

2.0

1300 nm

1550 nm

1.5

9.8 OUTLOOK 1.0

0.5

0.0

400

600

800

1000

1200

1400

1600

Wavelength (nm)

FIGURE 9.5 Optical absorption versus wavelength for a PPE optical fluid (Courtesy of Lightspan LLC, Wareham, Massachusetts)

9.7.5 Heat Transfer Fluid/Thermal Compounds The PPEs have good heat of vaporization (670◦ F 88.6 BTU/lb). The thermal conductivity of 0.1272 W/m and specific heat of 0.452 cal/g◦ C at 200◦ C makes it an excellent heat transfer fluid for many specialized applications. Polyphenyl ethers have also been used in heat sink compounds or thermal compounds. They offer low vapor pressure and high thermal stability. PPEs in these applications enhance the thermal conductivity of the overall compound.

9.7.6 Vibration Control Lubricants and Greases Many electrical connectors today are used on moving vehicles such as automobiles, aircraft, and space vehicles. These connectors experience shorter life due to vibration, and in some cases micromotion within the equipment. Both vibration and micromotion promote wear and consequently the connector fails. PPEs were found to absorb the micromotion and even vibration in these vehicles up to 80%. Aside from this damping function, they also provide protection from corrosion and reduce insertion forces. Overall, the use of PPEs increases the life of connectors manyfold.

9.7.7 Radiation Resistant Fluids and Greases In environments exposed to significant radiation the choice of lubricant becomes critical, particularly when the radiation consists of short-wavelength, highly energetic ionizing radiation such as gamma rays, x-rays, and subatomic charged particles. PPE based lubricants escape any damage by such radiation up to 10 ergs/g, while other hydrocarbonbased lubricants turn to viscous gels.

Copyright 2006 by Taylor & Francis Group, LLC

The outlook for the future of PPEs is promising, since there is a growing demand for lubricants, greases, and fluids that can function in extreme environments. The trend toward smaller and lighter automobiles will continue, and as a result, under-the-hood temperatures will rise beyond the useful operating range of standard hydrocarbon-type lubricants and greases. Therefore, PPEs and related materials that possess high-temperature withstanding properties will be a viable option. The same scenario exists in both the aircraft and industrial markets, where higher temperatures and pressure/vacuum environments will be influencing new and improved designs.

ACKNOWLEDGMENTS Authors would like to acknowledge valuable contributions made by Manuel Joaquim and Keith Van Pelt during the preparation of this chapter.

REFERENCES 1. M.E. Joaquim, Contact resistance and separation force at low temperature of polyphenyl ethers on lubricated connectors. 31st Annual Connector and Interconnection Symposium, October 19–21, 1998. 2. M.E. Joaquim, Advanced lubricants from a spy plane. Advanced Materials and Process, 35–37, November 2001. 3. M. Antler, Electronic connector contact lubricants: the polyphenyl ether. IEEE Transactions on CCHMT-10: 32–41, 1987. 4. R. Gunderson and A. Hart, Synthetic Lubricants, 1st ed. Reinhold Publishing Corporation, pp. 402–461. 5. L. Rudnick and R. Shubkin, Eds., Synthetic Lubricants and High-Performance Functional Fluids, 2nd ed. Marcel Dekker Inc., New York, 1999, pp. 239–248. 6. R.E. Booser, Ed., Handbook of Lubrication — Theory and Practice of Tribology, Vols 1 and 11, CRC Press, 1983. 7. M. Antler, Electronic connector contact lubricants: the polyphenyl fluids. IEEE Transactions on CHMT-10: 32–41, 1987. 8. M.E. Joaquim, Connector contact lubrication with polyphenyl ethers, a review. 30th Annual Connector and Interconnection Symposium, September 22–24, 1997. 9. N. Aukland and M.E. Joaquim, Lubricants extend the life of sensor connectors. Sensors, 78–81, May 2000. 10. M.E. Joaquim, Mussen Elektronische. Auto und Elektronik, 40–42, August 2002. 11. D.S. Stone and M.E. Joaquim, Polyphenyl ethers: old material has new benefits for photonics. Photonics Spectra, 90–92, April 2002.

10

Cyclohydrocarbons Sibtain Hamid CONTENTS 10.1 Introduction 10.2 Synthesis 10.3 Traction Theory 10.4 Traction Fluid Uses 10.5 Performance Characteristics of Cyclohydrocarbons 10.6 Lubricating Performance 10.7 Rust Protection 10.8 Gain in Fatigue Life of Rolling Elements 10.9 Conclusion Acknowledgment References

10.1 INTRODUCTION In recent years, the development of various methods for power transmission in automotive and truck applications has led to the need for fluids that can perform several essential functions within these transmissions. Production of continuously variable transmissions (CVTs) began a few years ago in automobiles and sport utility vehicles. The various existing transmission fluids, whether based on mineral oil or on synthetic hydrocarbons (PAO) have not to date demonstrated adequate performance in these transmissions, and especially in those CVTs that are based on full-toroidal or half-toroidal designs. Cyclohydrocarbons (Table 10.1 and Table 10.2; Figure 10.1 and Figure 10.2) are a new family of synthetic hydrocarbon oils and greases offering a series of unique performance advantages. In Table 10.1, CHC A is 100% dimerized alpha-methylstyrene, CHC B is 80% dimerized and 20% dimer alpha-methylstyrene, CHC C is 60%

TABLE 10.1 Cyclohydrocarbon Base Stock Properties CHC A Viscosity at 40◦ C

Viscosity at 100◦ C Pour point, ◦ C Flash point, ◦ C Coefficient of traction

14.6 3.1 −65 160 0.085

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CHC B

CHC C

CHC D

24.2 3.4 −45 165 0.09

37.2 5.2 −40 165 0.09

280 17.2 −15 172 0.09

dimerized and 40% trimer alpha-methylstyrene, and CHC D is 20% dimerized and 80% trimer alpha-methylstyrene. The numerals 30, 40, 50, and 70 in Table 10.2 represent formulated products containing both dimer and trimer moieties of alpha-methylstyrene, and performance additives such as antiwear agents, antioxidants, and corrosion inhibitors. The formulated cyclohydrocarbon contains both amine and phenolic type antioxidant, an antiwear additive such as tricrysl phosphate, which is very effective, a rust inhibitor such as calcium sulphonate and antifoam additive such as polysiloxane. They can also be formulated with extreme pressure additives containing sulfur and phosphorus. The lubrication action of these formulated products not only parallels or exceeds that of top quality petroleum oils, but at extremely high pressures a unique phenomenon occurs: the pressurized lubricant film acquires “grip.” This dynamic effect between rolling-contact surfaces results in a momentary transition of the lubricant’s mobile film to a rigid solid with immediate reversal when pressure is reduced. This effect is most dramatic in the greatly heightened power transfer between the smooth rolling surfaces. These traction lubricants meet the technological and economic demands made by machinery that must produce at high speeds, under heavy loads, with low noise levels, and perform precision operations with minimum maintenance. Such machinery employs rolling-contact elements for bearing and power transfer duties.

TABLE 10.2 Typical Values of Cyclohydrocarbon Lubricants Grades of cyclohydrocarbon lubricants Property

30

Kinematic viscosity (cs) At −40◦ F At −20◦ F At 0◦ F At 100◦ F At 210◦ F Pour point (◦ F) Density (g/cc) At 100◦ F At 200◦ F At 300◦ F Coefficient of expansion (1/◦ F) Bulk modulus (psi) Secant isothermal At 100◦ F At 200◦ F At 300◦ F

23,400 — — 14.7 3.10 −65 0.891 0.853 0.817 4.58 × 10−4

262,000 218,000 180,000

40

50

70

— 31,600 — 22.7 3.68 −45 0.853 0.886 0.850 0.814 4.42 × 10−4

— 41,500 5120 33.6 5.61 −35 0.853 0.889 0.855 0.820 4.42 × 10−4

— — 93,904 121 11.4 −10 0.885 0.850 0.815 4.19 × 10−4

292,000 230,000 190,000

294,000 230,000 185,000

294,000 237,000 191,000

O

Liquid

Solid

Liquid

HO

H2

H3C

H 3C 1, 3-Dicyclohexylbutan-1-0l HO

–H2O

FIGURE 10.1 Generalized cyclohydrocarbon structure H3C

Traction is the resistance to shear from external forces acting on a film that separates rolling elements, thereby allowing useful transfer of power. It is markedly different from internal frictional losses in such a film, or from force derived from sliding metal-to-metal contact. High traction and minimum slip, therefore, are most desirable properties for a lubricant that can be used in traction drives.

10.2 SYNTHESIS The dimerization of styrene has been known for many years. This has been described in U.S. patents No. 3,595,796 and 3,597,358 [1–6]. In general, dimeration produces cyclic linear products. These products are mainly alpha-methylstyrene, 1-cyclohexyl 1,3,3-trimethylhydrindane and other methylated styrene produce analogous products. Linear dimers of alpha-alkyl styrene can be prepared by polymerizing monomers of alpha-alkyl styrene. Preferred monomers include alpha-methylstyrene and alphaethylestyrene, and ring substituted monomers such as methyl-alpha-methylstyrene, ethyl-alpha-methylstyrene,

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H3C

H2 H3C

H3C (3-Cyclohexylbutyl)cyclohexane

FIGURE 10.2 Possible synthesis for a tractant drive fluid candidate. In this three-step process, an intermediate alcohol, 1,3-dicyclohexylbutan-1-ol, is prepared by the hydrogenation of the corresponding diaryl ketone. Dehydration of this intermediate followed by hydrogenation of the resulting olefin produces the desired cycloaliphatic end product, 3-cyclohexylbutyl cyclohexane

isopropyl-alpha-ethystyrene and the like. The catalyst material can be a mixture of phosphorus oxychloride and a strong mineral acid such as hydrochloric acid. The polymerization can be carried out by mixing a small amount of the catalyst material with the monomers and heating the mixture at a reaction temperature of 130◦ C and at atmospheric pressure.

The unsaturated dimers of alpha-alkylstyrene can then be hydrogenated in the presence of molecular hydrogenation catalyst. The reaction can take place at temperature from about 20 to 250◦ C and at pressures from about atmospheric to 2500 psig. The hydrogenation can be conducted in the presence of suitable organic solvents such as paraffins, naphthenes, and sterically hindered unsaturated hydrocarbons.

Torque transmitted

Driven member

10.3 TRACTION THEORY

Lubricant

Tangential force

Traction is broadly defined as the adhesive friction of a body on a surface on which it moves. A traction drive is a device in which torque is transmitted from an input element to an output element through nominal point or line contact typically with a rolling action by virtue of the traction between the contacting elements. While tractive elements are commonly spoken of as being in contact, it is generally accepted that a fluid film is present between them. Almost all traction drives require fluids to remove heat, to prevent wear at the contact surfaces, and to lubricate bearings and other moving parts of the drive. Thus, instead of metal-tometal rolling contact a film of fluid is introduced into the contact zone and interposed between the metal elements. The nature of this fluid determines to a large extent the limits in performance and the capacity of the drive. In transmitting power by rolling contact, as in a traction drive, the driver element acts on a slave (the driven element), transmitting force through the rolling contact. Thus, in traction drives the tangential force FT transferred in the rolling contact is proportional to the coefficient of traction (tangential force/normal force; Figure 10.3) and the normal load FN (force exerted perpendicular to contact) between the surfaces. It is obvious that the power transmission is most efficient when both traction coefficient (µ) and contact load are as high as possible. FT µ= FN

(10.1)

A high coefficient of traction is an inherent property of a lubricant. It is related to the shape and behavior of the molecules. Cyclohydrocarbon lubricants were chemically designed to have shaped molecular structures that produce high traction coefficients [7]. The traction phenomenon occurs in the elastohydrodynamic regime of lubrication, the regime in which contact pressures are too high for a thick hydrodynamic film to exist. It is this high pressure that can induce or give rise to the traction effect. In the elastohydrodynamic regime where traction drives operate, the metals are in elastic deflection of about 1,000 microinches; the film thickness between elements is on the order of 10 microinches, and the average diameter of the contact area is 100,000 microinches [8].

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Normal force

Torque applied Driving member

Traction coefficient =

Tangential force Normal force

FIGURE 10.3 Determination of traction coefficient

C

C

C

C

C

C

C

FIGURE 10.4 Liquid–solid transition of a synthetic cyclohydrocarbon under pressure

This concept suggests that under high contact stress (pressure) and high shear rates of rolling contact, the viscosity of the lubricant film in the contact area increases to a glassy solid state (Figure 10.4). Thus, this “pad” of solid film transmits the tangential force with a shear resistance far beyond the capability of a liquid film. The transitory solid “pad” protects parts by preventing metal-to-metal contact, and when compressed in surface cracks it inhibits fatigue and crack propagation. Freed from the rolling contact area, such a lubricant returns immediately to its liquid state and normal physical properties. The coefficient of traction has been shown to be independent of nominal viscosity, pressure viscosity, viscosity-index, specific gravity or other common physical properties. Thus, the more “solid” the film’s momentary “pad” can become under the pressure exerted, the higher will be its coefficient of traction and the more power it will transmit between rolling elements for a given normal contact load.

Hydrodynamic lubrication

Output speed change for a ball and disk traction drive (a)

id

45

Output torque (Lb-Ft)

40

Boundary lubrication

(b)

n tio

ac Tr

Formulation of lubricant

35

flu

eum

oil

rol Pet

(a)

30 (c) 25

Traction coefficient

50

Elasto-hydrodynamic lubrication

(b)

20 Increasing control pressure

15

5 0

FIGURE 10.6 Comparison of traction coefficients

(c) Thrust loads (a) 2000 lbs. (b) 1500 lbs. (c) 1000 lbs.

10

0

2

3

4

5 6 Slip %

7

8

9

• Adaptability to servo-control • Low maintenance requirements. 10

FIGURE 10.5 Variation of slip in speed with torque demand

The normal contact load in a traction drive determines the contact stress; it is limited by the yield point fatigue strengths of the metal parts. The power transmitted between the driver and driven elements is limited by the amount of traction force that can be transferred. The traction force can be increased at a given normal load up to the point where the elements would slip severely, overheat, and reach boundary contact that would result in seizure. The maximum torque obtainable before gross slip is governed primarily by the lubricant and the normal load — and to a lesser extent by system temperature, rolling speed, and the traction element geometry, materials, and surface finish (Figure 10.5).

10.4 TRACTION FLUID USES Traction drives are used for mechanical power transmission at fixed or variable speeds, like gear box trains, belt drives, hydrostatics, and variable speed electric motors. The established benefits of traction drives are • • • • •

Excellent power transmission at very high speeds Extremely low noise level in operation High efficiency Variable speed control operating under full load Stepless, infinitely-adjustable speed change within design range • Precision-set speeds • Low inertial elements that allow rapid speed change

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With the advent of these lubricants, three additional features can supplement existing advantages: 1. Higher power transmission can be achieved with increasing or variable loads. 2. Performance reliability and service life for parts are both extended. 3. Smaller, lighter-weight, lower-cost drives can be designed for a given level of output. Traction drives work on the principle that rotary motion, torque, and power are transferred by smooth rolling elements loaded against each other. A great variety of designs and transfer geometries is possible. These designs range from cone-on-ring to ball-on-disk, to disk-on-roller, roller-on-roller, toroidal disk-on-roller, etc. Moving the driver rolling contact position relative to the rotation axis of the elements is a common design principle used to vary speed [9]. In all designs, however, the transfer of torque takes place through the film of lubricant at the points of contact. The transferred torque in a traction drive is dependent on the normal contact loading between elements and the coefficient of traction of the lubricant. In most geometries tested, cyclohydrocarbon lubricants under adequately high normal loading form a film so resistant to shear that 50 to 100% more torque transferred before gross slip than with petroleum oil. The result is that existing traction drives can be lubricated with cyclohydrocarbon lubricant and will significantly, often dramatically, transfer more power and undergo less speed change with varying loads (Figure 10.6 and Figure 10.7). Instances of up-rating to 50% more power output are common. Fixed ratio drives, particularly, may up-rate to 100% more power [10].

and 10.3). In addition to their application in traction drives, they can be recommended for:

0.12 CHC-50 CHC-30

Traction coefficient

0.10

0.08

0.06

0.04 POE PAO

0.02

0 0

2

4

6

8

10

12

14

Slide-to-roll ratio

FIGURE 10.7 Coefficient of traction measurement

TABLE 10.3 Typical Values of Cyclohydrocarbon Lubricants

Vapor pressure (mmHg abs) at 350◦ F Specific heat (BTU/lb◦ F) At 100◦ F At 200◦ F At 300◦ F Thermal conductivity (BTU/h ft2 ◦ F) At 100◦ F At 200◦ F At 300◦ F Surface tension (dyn/cm) air interface At 100◦ F At 200◦ F At 300◦ F Flash point (◦ F) Fire point (◦ F) AIT (◦ F)

30

40

50

70

12

12

12

10

0.453 0.509 0.565

0.460 0.514 0.569

0.446 0.506 0.569

0.426 0.478 0.529

0.063 0.061 0.058

0.060 0.059 0.056

0.060 0.059 0.056

0.062 0.061 0.058

Rolling contact bearing lubricants Journal and sliding bearing lubricants Gear lubricants Hydraulic fluids Automatic transmission fluids.

Cyclohydrocarbon fluids — both oils and greases — are stable to high temperatures in the presence of air. They resist sludging, varnish formation, coking, and forming acidic degradation products at operating temperatures of 300◦ F and above for long periods of time. When overheated they leave no residue or hard carbonaceous deposits; the overheated surfaces remain clean. The higher thermal and oxidative stability of cyclohydrocarbon lubricants allows them to be used at higher temperatures and for much longer periods of time than petroleum oils (Table 10.4). They withstand protracted use at 300◦ F in air; higher temperatures in the absence of air. Because of their stability, these lubricants can extend drain periods and in many applications they can serve as a fill-for-life lubricant.

10.6 LUBRICATING PERFORMANCE When used in applications requiring hydrodynamic or boundary lubrication, cyclohydrocarbon lubricants perform like premium quality petroleum oils. CHC-50 and CHC-70 have been formulated to offer an optimum balance of antiwear and high load bearing properties. Although actual field performance in the specific application is the only true test, the standard laboratory ratings in Table 10.5 and 10.6 are suitable for initial comparisons.

10.7 RUST PROTECTION 24.4 21.4 18.4 325 340 605

31.6 27.0 22.4 300 325 600

23.0 20.7 18.4 325 345 620

25.4 22.1 18.8 335 350 675

10.5 PERFORMANCE CHARACTERISTICS OF CYCLOHYDROCARBONS The lubricating performance of cyclohydrocarbon lubricants is comparable to the highest quality petroleum oils of comparable viscosity used in automotive, aircraft, and industrial applications — with added oxidation resistance, chemical stability, vastly improved shear resistance, and greatly amplified traction coefficients (Tables 10.2

Copyright 2006 by Taylor & Francis Group, LLC

• • • • •

These lubricants are not corrosive. But, like petroleum oils, they do not prevent rust in the presence of moisture unless formulated with a rust-inhibiting additive. CHC 30, 50, and 70 have been rust inhibited and perform as shown in Table 10.7. Their elastomer compatibility is shown in Table 10.8.

10.8 GAIN IN FATIGUE LIFE OF ROLLING ELEMENTS The fatigue life of rolling elements operating on cyclohydrocarbon lubricants compared to mineral oil under the same loading and speed conditions is actually greater than predicted by calculation (Figure 10.8). This is because cyclohydrocarbon lubricants have an inherent property that prevents and/or forestalls fatigue failure. It is a phenomenon related to the chemical structure of the compounds.

TABLE 10.4 Oxidation Stability Oxidation stability and corrosion modified federal text method, Std. 791; Method 5308 350◦ F/72 h 5cc air/h Metal weight change (mg/cm2 ) Mg Al Fe Cu Final acid number (mg KOH/gm of fluid) Viscosity change at 100◦ F (%)

CHC 30

+0.01 +0.01 −0.03 −0.34 1.2

CHC 40

CHC 50

CHC 70

Naphthenic oil

ATF

−0.01 NCa +0.01 NC 0.31

NC −0.04 −0.03 −0.90 0.54

+0.01 NC +0.01 −0.41 1.86

+0.08 NC +0.02 −0.09 5.0

−0.02 +0.04 +0.06 −3.2 6.0

3.8

6.5

15.5

82

52

6.8

a No change.

TABLE 10.7 Rust Protection Properties

TABLE 10.5 Results of Wear Tests CHC lubricants Test Four ball weara LFWb

30 0.67 3.8

40

50

0.75 8.5

0.51 1.4

Petroleum oil 70

Naphthenic oil

0.54 0.9

1.10 21.8

CHC lubricants ATF

Test

0.45 0.7

Corrosion and rust (ASTM D 665A, distilled water)

a Scar dia. mm (200◦ F, 2 h 1260 rpm; 40 kg load; 12” AISI E52100 Rc

60 Steel Balls). b Wt. Loss of block, mg (Conforming bronze block sliding on hardened steel ring; 208◦ F, 24 h, 72 ft/min, 530 psi).

30

40

50

70

No rust or corrosion

No rust or corrosion

No rust or corrosion

No rust or corrosion

Cycloaliphatic hydrocarbon Mineral oil, paraffinic

TABLE 10.6 Shear Stability and Anti-Foam Properties CHC lubricants

Shear stabilitya Foam ASTM D 892b Sequence 1: 75◦ F Sequence 2: 200◦ F Sequence 3: 75◦ F

PAO

Petroleum oil

30

40

50

70

ATF

−5

0

−11

−24

−15

5/0 35/0 5/0

0/0 0/0 0/0

0/0 22/0 0/0

0/0 20/0 2/0

5/0 13/0 5/0

a Viscosity change at 100◦ F (%). ASTM Vol. 1, Oct. 1961, p. 1160. 100◦ F/120 m in sonic shearing. b ml foam after 5 min bubbling/ml foam 10 min after bubbling.

Hypothetically, the cyclohydrocarbon lubricant fills the surface cracks found in all polycrystalline metals and under heat and contact pressure turns solid, thus inhibiting the crack growth that leads to fatigue failure.

Copyright 2006 by Taylor & Francis Group, LLC

300°F 1200 rpm 700,000 psi Hertz stress

Diester 0

1

2 3 4 Stress cycle × 106 B10 fatigue life test conducted on twin disc machine

5

FIGURE 10.8 Results of B10 fatigue life test conducted on TWIN DISC machine. Courtesy of Machinery Lubrication, Tulsa, Oklahoma

The laboratory data from test samples in Table 10.9 indicate superior fatigue life.

10.9 CONCLUSION Cyclohydrocarbons can greatly improve the operating characteristics of traction drive systems and designs that were previously discounted as not feasible. This can be

TABLE 10.8 Elastomer Compatibility Elastomer compatibility, ASTM D 471 (7 h 300◦ F, immersion) Buna-N Durometer hardness (shore “A” points) Volumetric swell (%) Ultimate tensile strength (psi) Ultimate elongation (%) Polyacrylate Durometer hardness (shore “A” points) Volumetric swell (%) Ultimate tensile strength (psi) Ultimate elongation (%) Viton Aa Durometer hardness (shore “A” points) Volumetric swell (%) Ultimate tensile strength (psi) Ultimate elongation (%)

Elastomers CHC 30

CHC 40

CHC 50

CHC 70

Initial

Final

Initial

Final

Initial

Final

Initial

Final

64 — 1815 380

49 10 374 62

64 — 1815 380

58 6 521 81

63 — 1815 380

54 6 428 73

64 — 1815 380

48 39 297 131

66 — 1668 179

47 22 1261 181

66 — 1668 179

55 15 1508 185

66 — 1668 179

57 16 1467 197

66 — 1668 179

50 47 1045 183

58 — 2118 475

54 7 1535 458

59 — 2118 475

57 5 1625 445

58 — 2118 475

57 5 1695 477

59 — 2118 475

1647 472

a Trademark of DuPont de Nemours & Co.

TABLE 10.9 Rolling Contact Fatigue Test: Stress Cycles × 106 Pin 3/8 in. dia., Rc 60 hardness 52100 Steel, 12,500 rpm, 300◦ F 700,000 max. Hertz Stress CHC 30 CHC 40 CHC 50 CHC 70 Petroleum ATF Naphthenic oil Ester base MIL L 7808

B10 Life

B50 Life

3.2 4.2 4.9 6.1 2.7 2.2 1.3

6.4 7.0 8.9 12.7 4.5 2.7 2.7

seen today as new designs based on previous failures that relied on conventional lubricants becoming a reality in the automotive industry in CVTs (Continuously Variable Transmissions). This technology can be utilized in many industrial applications as well, such as planetrol gear systems where the ability to transfer torque because of the increase in the traction coefficient is highly desirable.

ACKNOWLEDGMENT The authors would like to acknowledge the valuable contributions made by Mr. Manuel Joaquim during the preparation of this chapter.

Copyright 2006 by Taylor & Francis Group, LLC

REFERENCES 1. R.L. Green, Grease Compositions Having High Tractive Coefficients. U.S. Patent 3,835,050 (9/10/1974) Monsanto Company. 2. W.C. Haummann and R. Schisla, Tractive Fluids and Method of Use. U.S. Patent 3,411,369 (11/19/1968) Monsanto Company. 3. G.L. Driscoll and M.W. Haseltine, Lubricant Comprising Gem-Structured Organo Compound. U.S. Patent 3,793,203 (2/18/1974). 4. D.E. Loeffler, G.D. Hussey, G. Smith, and J.M. Wortel, Synthetic Hydrocarbon Base Grease Compositions. U.S. Patent 3,712,864 (1/23/1973) Shell Oil Company. 5. W.P. Scott and W.W. Woods, Low Temperature Greases. U.S. Patent 3,730,896 (5/1/1973) Continental Oil Company. 6. E.L. Armstrong, R.A. Butcosk, and G.W. Murray, Greases Containing Hydrogenated Olefin Polymer Vehicle And Organophilic Clay Thickener. U.S. Patent 3,514,401 (5/26/1970) Mobil Oil Corporation. 7. J.H. Kraus, An automotive CVT, Mechanical Engineering, October 1976, 38–43. 8. M. Joaquim, Elastohydrodynamic lubricants for CVTs, Automotive Engineering International, July 2002, 45–47. 9. M. Joaquim and P.J. Milner, A robust CVT for heavy duty applications, Autotechnology, February 2003, 32–34. 10. N. Rose and S. Hamid, The race for a better CVT, Lubes ‘N’ Greases, May 2003, 22–27.

11

Polychlorotrifluoroethylene Ronald M. Epstein and Louis L. Ferstandig CONTENTS 11.1 Historical Development 11.2 Chemistry 11.3 Properties and Performance Characteristics 11.3.1 Chemical Properties 11.3.2 Physical Properties 11.3.3 PCTFE Interchangeability with Conventional Lubricants 11.3.4 Comparative Performance 11.4 Manufacture, Marketing, and Economics 11.5 Outlook References

Polychlorotrifluoroethylene (PCTFE) oils, greases, and waxes are halogen saturated lubricants that are chemically inert and nonflammable; they have high-thermal stability, good lubricity, high dielectric strength, high density, and low compressibility.

11.1 HISTORICAL DEVELOPMENT polychlorotrifluoroethylene lubricants were first synthesized in the 1940s by scientists looking for an inert lubricant for use in handling extremely reactive uranium hexafluoride in uranium isotope separation. Following World War II, the demand grew rapidly for aggressive industrial chemicals and gases such as chlorine, fluorine, oxygen, hydrogen peroxide, nitric acid, and sulfuric acid. Thus, a need for chemically inert lubricants grew and, again, PCTFEs were the materials of choice. New applications were found to exploit other unique characteristics of PCTFEs such as their high density (gyroscope flotation fluids), low compressibility (nonflammable hydraulic fluids), low vapor pressure (inert vacuum pump oils), and lubrication properties at extreme pressure. The most recent applications include metalworking lubricants for exotic metals such as tantalum, molybdenum, and tungsten, where PCTFEs appreciably extend the life of cutting tools and dies. In addition, the use of PCTFE oils leaves a smooth uniform finish on the metal surface. There is also an expanding use as inert low temperature bath fluids.

Copyright 2006 by Taylor & Francis Group, LLC

11.2 CHEMISTRY Chemically, PCTFE oils and waxes are saturated low molecular weight polymers of chlorotrifluoroethylene having the general formula (CF2 CFCl)n with n varying from 2 to about 10 units. They are made by a controlled polymerization technique. The product is then separated into various fractions from light oils to waxes, covering all the common lubricating grades.

11.3 PROPERTIES AND PERFORMANCE CHARACTERISTICS 11.3.1 Chemical Properties The most outstanding property of PCTFE lubricants is chemical inertness. This property, which includes nonflammability, is the basis for most of their usage. Specifically, PCTFE lubricants are nonreactive with the following chemicals and many others: Ammonium perchlorate Hydrogen sulfide Boron trichloride Muriatic acid Boron trifluoride Nitrogen oxides (all) Bromine Nitrogen trifluoride Bromine trifluoride Oleum (gaseous) Carbon dioxide Oxygen (liquid and gaseous) Calcium hypochlorite Ozone

Chlorinated cyanurates Chlorine Chlorine dioxide Chlorine trifluoride (gaseous) Fluorine (gaseous) Fuming nitric acid Hydrogen fluoride Hydrogen peroxide

Sodium chlorate Sodium hypochlorite Sulfur hexafluoride Sulfur trioxide Sulfuric acid Thionyl chloride Uranium hexafluoride

Fluorinated lubricants (PCTFEs and perfluoropolyethers) are not recommended for contact with sodium or potassium metal, amines that include amine additives, liquid fluorine, or liquid chlorine trifluoride. Caution should be used with aluminum and magnesium (and alloys of these metals) under conditions that may entail galling or seizing. PCTFE oils and greases are used routinely in aluminum and magnesium housings, tubing and containers where galling conditions do not exist. Greases thickened with silica, polytetrafluoroethylene (PTFE), and higher molecular weight PCTFE are produced commercially. The presence of silica as a thickener compromises the inertness to chemicals that react with silica, such as gaseous fluorine, halogen fluorides, hydrofluoric acid, and caustic solutions. The greases thickened with PTFE and higher molecular weight PCTFE exhibit the same chemical resistance as the base stock PCTFE oil. Oxygen compatibility is a major benefit of PCTFE lubricants. With the introduction of these products, many test procedures were developed to determine the safely of all lubricants in contact with oxygen. Several PCTFE oils and greases, including those with rust inhibitors, were tested using American Society for Testing and Materials (ASTM) method G-72-82 (Reapproved 1996), Standard Test Method for Autogenous Ignition Temperature of Liquids and Solids in a High Pressure Oxygen-Enriched Environment. None ignited throughout the entire testing range, which rose to 400◦ C (752◦ F) in the presence of 2000 psig (138 bar) oxygen. Another test with PCTFE oils and greases, including those with rust inhibitors, exceeded the energy limits of ASTM D-2512-95, Test for Compatibility of Materials with Liquid Oxygen (Impact Sensitivity Threshold Technique). None of the PCTFE lubricants tested showed any sensitivity at the highest impact loading of 114 ft lb (36.9 g cal). PCTFE oil and grease pass NASA testing at 8500 psi (586 bar) and 38.7◦ C (100◦ F). Some synthetic lubricants with low vapor pressures may have very high flash points, but they are still flammable and would explode with liquid oxygen and similar chemicals, whereas PCTFEsare completely nonreactive. The following U.S. government and international specifications are met or exceeded by PCTFE lubricants: • DoD-L-24574 (Mil), Lubricating Fluid for Low and

High Pressure Oxidizing Gas Systems

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• NASA 79K22280, Lubricant for 1000 GPM LO2 Pump

Bearings, Specification for EN ISO 4114-3 and EN 1797-1 The PCTFE oils decompose thermally to nonsludgeforming but toxic volatiles rapidly at 320◦ C (608◦ F), noticeably at 300◦ C (572◦ F) and to lesser extents at lower temperatures. The recommended long-term maximum operating temperature is 204◦ C (400◦ F) and the recommended short-term maximum temperature is 260◦ C (500◦ F) in scrupulously clean systems. Thermal stability is affected by the presence of metals and such exposure at temperatures above 177◦ C (350◦ F) should be evaluated before field application. Oils containing rust inhibitors may have lower operating temperatures as a result of the decomposition of the inhibitor even though the oil would not be affected at the lower temperature. PCTFE lubricants work well with many elastomer and plastic materials. However, most gaskets and O-rings have proprietary compositions with many ingredients, so the prudent approach to elastomer selection involves bench testing and, if possible, testing of the specific product under operating conditions. As a guide in the choice of materials, however, it can be stated that PCTFE oils have been found compatible with specific formulations of the following materials: • • • • • • • • • • • • • •

Ethylene propylene rubber Polyvinyl alcohol Neoprene Teflon Chlorinated polyethylene Rigid polyvinyl chloride (PVC) Rigid chlorinated polyvinyl chloride (CPVC) Viton, Fluorel Polyimides Polycarbonates Fluorosilicones Cured epoxies Urethanes Ethylene-propylene diene monomer (rubber EPDM)

In general, solvent-resistant elastomers and plastics are unaffected by PCTFE fluids but, at higher temperatures, the fluids may dissolve in and seriously weaken the following materials: • • • • • •

Buna-N(butadiene/acrylonitrile) Buna-S(butadiene/styrene) rubber Silicone rubbers Natural rubber Polymers or copolymers of chlorotrifluoroethylene PVC

The PCTFE lubricants wet metallic surfaces readily and form lubricating films similar to the more common

lubricants. Steel parts that have been lubricated with PCTFE oils and then disassembled for inspection appear to have benefited from the lubrication even in severe service. However, it has been reported that the disassembled, solvent-cleaned parts rust rapidly on exposure to air. Rusting can be inhibited by keeping a thin film of oil on the part and, where necessary, using oil with rust inhibitor. At temperatures up to about 177◦ C (350◦ F), PCTFE oils and greases are noncorrosive toward metals except for copper and some of its alloys, which will discolor at temperatures over 49◦ C (120◦ F). For applications above those temperatures, all metals should be pretested. The PCTFE light oils are soluble in most organic liquids, including aromatic and aliphatic hydrocarbon and chlorinated solvents, alcohols, ketones, and esters. The solubility decreases as the PCTFE molecular weight increases. All PCTFE fluids are insoluble in aqueous solutions, whether they are neutral, acidic, or alkaline. Typical organic materials with which various PCTFE fractions are miscible are Acetone Hexachlorobutadiene Amyl acetate Hexane Benzene Kerosene t-Butyl alcohol Methanol Carbon tetrachloride Methyl ethyl ketone Carbon disulfide Methyl isobutyl ketone Chloroform Methylene chloride Dibutyl phthalate Mineral oils Dioctyl phthalate Silicone oils Dioctyl sebacate Trichlorobenzene Ethanol Tetrachloroethylene Ether Trichloroethylene Glacial acetic acid The PCTFE fluids dissolve gases readily. Chlorine, for example, is soluble to the extent of several weight percent at ambient conditions. Air is soluble to about 15 vol%. Although both viscosity and density are changed by dissolved gas, most properties of the fluid itself are not affected. Tests performed by the Institut Francais de Pétrole indicate that PCTFE oils are excellent lubricants. On standard four-ball machines, seizure does not take place until 2.5 sec under as much as 200 kg load. This value compares favorably with that of “extreme pressure” oils intended for gear lubrication. Other extreme pressure tests using ASTM method D-2783, Standard Method for Measurement of Extreme-Pressure Properties of Lubricating fluids (FourBall Method), show that PCTFE oils exhibit no seizure even at the final applied load of 800 kg. Greases made with low viscosity base stock do show weld points, but only at the highest load. Even those greases and all the oils show load wear indices that are appreciably higher than those

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of hydrocarbon oils. The same data show reasonable scar diameters, increasing uniformly with load. PCTFE oils can be used interchangeably (see Section 11.3.3) with conventional lubricants for a wide range of standard equipment such as bearings, compressors, gearboxes, and oil pumps. However, if there is any question of direct interchangeability, a bench test in the piece of equipment may be advisable. Occasionally, some equipment modification may be required because of density, viscosity, and vapor pressure differences from hydrocarbon lubricants.

11.3.2 Physical Properties As the viscosity of the PCTFE oil increases, so does the density, pour point, and cloud point. Table 11.1 lists these and other physical properties. The vapor pressure decreases as the molecular weight of the oil increases, as shown in Figure 11.1. These data are helpful in the choice of the appropriate oil. The PCTFE polymers change from oils to waxes as the viscosity increases. All the waxes are white solids at room temperature and melt upon heating. They have initial boiling points above 260◦ C (500◦ F) and densities of about 1.89 g/ml at 99◦ C (210◦ F). Drop melting point and viscosity data are given in Table 11.2. The properties of PCTFE greases depend on the base oil used and how heavily they are gelled. Table 11.3 gives penetration, service temperature range, and drop melting point data. Various miscellaneous physical properties are listed in Table 11.4. Certain of these properties are especially noteworthy in comparison to conventional lubricants. The surface tension is very low, contributing to better wettability of most surfaces. The oils are not very compressible, which makes them useful as nonflammable hydraulic fluids with quick hydraulic response.

11.3.3 PCTFE Interchangeability with Conventional Lubricants When a conventional lubricant is to be replaced with a PCTFE oil, there are practical and theoretical approaches to choosing the appropriate grade. Through experience it has been found that the PCTFE viscosity at 38◦ C (100◦ F), expressed in centistokes, is numerically similar to the corresponding ISO viscosity grade. Table 11.5 shows the alignment of the commonly used viscosity systems. For example, Halocarbon 95 would be the choice to replace ISO 100 or other viscosity values in the same row. If there are reasons to be more precise, other factors should be considered. The high density of PCTFE oils (about twice that of water) means that the absolute

TABLE 11.1 Physical Properties of PCTFE Oils Viscosity1 (cSt at 100◦ F) 0.8 1.8 4.2 6.3 27 56 95 200 400 700 1000N Flash and fire points | − − − − − − − − − − − − − − − − − − − − None − − − − − − − − − − − − − − − − − − − − − − | Pour point2 Fahrenheit (±10◦ F) −200 −135 −100 −95 −40 −30 −15 10 15 40 50 Celsius (±5◦ C) Cloud point3 Fahrenheit (±10◦ F) Celsius (±5◦ C) Viscosity1 (±10%) At −65◦ F (−54◦ C) Centistokes Centipoises At 100◦ F (37.8◦ C) Centistokes Centipoises At 160◦ F (71.1◦ C) Centistokes Centipoises At 210◦ F (99◦ C) Centistokes Centipoises Density4 (±0.01 g/ml) 100◦ F (37.8◦ C) 160◦ F (71.1◦ C) 210◦ F (99◦ C) Refractive index 20 (typical) nD

−129

−93

−73

−71

−40

−34

−26

−12

−9

5

10

<−200 <−129

<−135 <−93

<−125 <−87

<−125 <−87

<−95 <−71

<−30 −34

−5 −21

35 2

50 10

55 13

65 18

5.7 10

143 271

— —

— —

— —

— —

— —

— —

— —

— —

— —

0.8 1.3

1.8 3.5

4.2 7.8

6.3 12

27 51

56 108

95 182

200 390

400 780

700 1365

1000 1950

0.54 0.89

1.1 1.9

1.9 3.4

2.6 4.7

6.8 13

11 21

16 30

26 49

40 75

62 118

83 158

— —

0.8 1.4

1.2 2.1

1.6 2.8

3.1 5.6

4.9 8.9

6.3 12

9 16

12 22

17 32

22 41

1.71 1.65 1.60

1.82 1.76 1.71

1.85 1.80 1.75

1.87 1.82 1.77

1.90 1.85 1.81

1.92 1.87 1.82

1.92 1.87 1.82

1.95 1.89 1.85

1.95 1.89 1.85

1.95 1.90 1.86

1.95 1.90 1.86

1.383

1.395

1.401

1.403

1.407

1.409

1.411

1.412

1.412

1.414

1.415

1. ASTM D-445. 2. ASTM D-97. 3. ASTM D-2500. 4. Gay–Lussac pycnometers or equivalent.

viscosity, expressed in centipoises, is about twice the kinematic viscosity, expressed in centistokes. When a change to a PCTFE oil is contemplated, the comparability of the viscosities of the two oils, in centipoises, should be verified. Table 11.1 gives values in both centipoises and centistokes. Another factor to be considered, if known, is the operating temperature. The viscosities of oils decrease as the temperature increases, as shown in Figure 11.2. If the viscosity of the conventional lubricant is known at the operating temperature for the specific application, this point can be located on Figure 11.2 using the appropriate unit of viscosity. Then, the closest PCTFE oil can be selected.

11.3.4 Comparative Performance The PCTFEs are chosen for many applications on the basis of comparative performance characteristics and

Copyright 2006 by Taylor & Francis Group, LLC

cost-effectiveness. A general listing follows:

1. Chemical industry • Chlorine (and bromine) service — as pump oils

(vacuum and pressure pump applications), oilinjected helical screw compressors, valve and plugcock grease, chlorine vaporizer lubrication, valve stem lubricant, assembly and repair of chlorine cylinder valves, tank car maintenance (chlorine valve and pressure relief valve lubricant), thread lubricant, and instrument fill fluid • Mechanical seal barrier fluid for the following operations: bromination, chlorination, fluorination, nitration, oxidation, and sulfonation • Lubricant for equipment used in the fluorination process for blow-molding polyethylene bottles and gasoline tanks

Temperature (°C) –10

0

10

20

30

40 50

60 70 80 90 100

120 140

160 180 200 220 240

500 400 300

500 400 300

200

200

100

100

50 40 30

50 40 30

20

20

10

10

5 4 3

5 4 3

Vapor pressure (millimeters of mercury)

1000

2

2

8

0.

1

1

0.5 0.4 0.3

0.5 0.4 0.3

0.2

0.2 8

1.

0.1

0.1 2 4.

0.05 0.04 0.03

3

6.

Vapor pressure (millimeters of mercury)

1000

0.05 0.04 0.03 0.02

0.01

0.01 56

27

0.02

0.001

0

20

40

60

80

10 00 N

0.002

0.005 0.004 0.003

40 0 70 0

95 20 0

0.005 0.004 0.003

100 120 140 160 180 200220 240 Temperature (°F)

0.002

280

0.001 320 360 400 450 500

FIGURE 11.1 Typical vapor.

• Sealant for flange faces • Sulfur trioxide spill control mixture (this mixture,

when spread over a sulfur trioxide spill, stops fuming completely and further cleanup can be done more easily on a nonemergency basis) • Compatible with chemicals listed above and many others that are not as widely used

Copyright 2006 by Taylor & Francis Group, LLC

2. Bulk gas industry • Oxygen service — lubricants for remote control

solenoid valves, thread lubricant, instrument fill fluid, rotary meter lubricant, diaphragm compressor oil, vacuum pump oils for evacuating oxygen cylinders and bulk storage tanks, vacuum pump

oils for oxygen plasma cleaning, bearing grease for liquid oxygen (LOX) pumps, and lubricant for compressors in portable oxygen plants • Welding gases — lubricants for bearings in LOX pumps and vacuum pump oils for evacuating oxygen cylinders

• Helium service — oil for helium compressors and

lubricants for helium regulators • carbon dioxide pump oil

3. Electronics industry • Vacuum pump oil for semiconductor manufacturing

TABLE 11.2 PCTFE Waxes

equipment • Vacuum pump oil for equipment used to plasma-

Wax Minimum drop melting point1 (◦ F) Celsius Viscosity2 Centistokes (±10%) at 160◦ F (71.1◦ C)

40 — — 190

600 135 57 1000

1200 230 110 —

1500 270 132 —

desmear multilayer printed circuit boards • Vacuum pump oil for equipment used to plasma-

clean electronic and medical devices • Inert grease for semiconductor processing equip-

ment • Instrument fill fluids (PCTFE fluids are used where

1. ASTM D-127. 2. ASTM D-445.

strong oxidizing agents such as oxygen, chlorine, fluorine, nitric acid, and hydrogen peroxidepreclude

TABLE 11.3 Physical Properties of PCTFE Greases Consistency Service temperature

Minimum drop melting point

NLGI1

ASTM penetration

Silica thickened greases 32

1

310–340

28

2

265–295

28LT

2

265–295

25-5S

3

220–250

19

4

175–205

−15 to 350◦ F −25 to 175◦ C

None

Polymer thickened greases 25-10M

1

310–340

X90-10M

1

310–340

25-20M

4

175–205

30 to 275◦ F 0 to 135◦ C −40 to 200◦ F −40 to 95◦ C 20 to 300◦ F −5 to 150◦ C

300◦ F 150◦ C 300◦ F 150◦ C 320◦ F 160◦ C

Grease

1. National Lubricating Grease Institute.

Copyright 2006 by Taylor & Francis Group, LLC

−15 to 350◦ F −25 to 175◦ C −15 to 350◦ F −25 to 175◦ F

None

−50 to 200◦ F −45 to 95◦ C 0 to 350◦ F −20 to 175◦ C

None

None

None

Description

Softest grease with broad temperature range This grease is also available with rust inhibitor (28I), which has a recommended service temperature of 0 to 250◦ F (−20 to 120◦ C). For low temperature use Also available with rust inhibitor (28LTI) Lowest vapor pressure. Also available with rust inhibitor (25-5SI, which has a recommended service temperature of 0 to 250◦ F (−20 to 120◦ C) Hardest grease with broad temperature range

Softest grease for wide temperature service For low temperature use Hardest grease with broad temperature range

the use of glycerine or silicone fill fluids) for:

TABLE 11.4 Miscellaneous Physical Properties Property Bulk modulus

Coefficient of cubic expansion Dielectric constant Distillation range

Heat of vaporization Specific heat Surface tension Vapor pressure

Volume resistivity

• • • • •

Value Over 200,000 psi [13.8 × 108 Pa at 100◦ F (37.8◦ C) with applied pressure of 10,000 psi (6.9 × 107 Pa)] 7.6–9.610−4 /◦ C 2.25–4.0, varies with frequency and oil temperature Initial boiling points at 1 atm (760 mmHg) range from 130◦ C (260◦ F) to above 300◦ C (572◦ F) 20–30 cal/g 0.2–0.25 cal/g 20–30 dynes/cm at 77◦ F (25◦ C) Regular oils: 0.004–40 mmHg at 122◦ F (50◦ C) Vacuum pump oils: <0.001–0.0035 mmHg at 122◦ F (50◦ C) 1013 –1014  cm

Diaphragm seals Pressure gauges Manometers Dead weight testers Sensors

4. Aerospace industry • Lubricant in oxygen delivery system to space shuttle

oxidizer tanks • Nonflammable hydraulic fluid for future aircraft

5. Life support systems (PCTFE oils and greases are used to lubricate life support systems where an oxygenenriched atmosphere (>23% O2 ) or high pressure air is required) • Diving gear — U.S. Navy • Hyperbaric oxygen chambers • Hospital oxygen and nitrous oxide systems

TABLE 11.5 Industrial Lubricant Viscosity Ratings PCTFE oil viscosity (cSt at 100◦ F)

AGMA1 grade no. (approximately)

SAE viscosity no. (approximately)

SAE gear lubricant no. (approximately)

Viscosity in SUS at 100◦ F (approximately)

2

—

—

—

29–35

5

—

—

—

36–44

10 15 22

— — —

— — —

— — —

54–66 68–82 95–115

32 46

— 1

10 W 10

75 W

135–165 194–236

68

2

20

80 W

284–346

100 150

3 4

30 40

— 85 W

419–511 630–770

220 320

5 6

50 60

90 —

900–1100 1350–1650

460 680

7 8

70 —

140 —

1935–2365 2835–3465

ISO grade

0.8 1.8 4.2 6.3

27

56 95

200

400

700 1000 1 American Gear Manufacturers Association.

Copyright 2006 by Taylor & Francis Group, LLC

FIGURE 11.2 Viscosity vs. temperature graph.

• • • • • •

Home oxygen units Liquid oxygen respiratory equipment Anesthesia machines Portable oxygen-generating plants Systems for evacuating and refilling oxygen bottles Breathing systems in airplanes and submarines

6. Lubricant industry • Base stock for specialty greases • Base stock for antiseize compounds and thread

sealants • Extreme pressure additive for lubricating oils

7. Metalworking industry • Cutting oil for machining tantalum, molybdenum,

and niobium • Drawing of tantalum wire and stainless steel tubing • Forming of tantalum parts • Manufacture of woven wire and cable for safe use

in aggressive services • Additive to other cutting oils for enhanced tool life • Machining of high nickel alloys

Copyright 2006 by Taylor & Francis Group, LLC

8. Nuclear industry • Lubricant for processing uranium hexafluoride • Hydrogen-free oil for use in nuclear service • Greases to lubricate controls for nuclear applications

9. Paper industry PCTFE lubricants are compatible with all the widely used pulp bleaching chemicals — chlorine, sodium chlorate, chlorine dioxide, oxygen, and hydrogen peroxide 10. Petroleum industry • Antiseize lubricant for drilling tools in hydrogen

sulfide environments • Alkylation lubricant (compatible with HF and sul-

furic acid) • Instrument fill fluid for oil exploration equipment

11. Steel industry Grease for swivel joints in oxygen delivery systems and oxygen heating systems

12. Water and wastewater treatment • PCTFE lubricants are compatible with water treat-

ment chemicals such as oxygen, ozone, hydrogen peroxide, chlorine, calcium hypochlorite, sodium hypochlorite, and chlorinated cyanurates that are used in chlorinators, pumps, valves, etc. • Swimming pool chemicals — lubricants for compacting equipment for calcium hypochlorite and chlorinated cyanurates and die release fluid for tableting swimming pool chemicals 13. Laboratory apparatus • • • •

Nonflammable low temperature bath fluid Stopcock lubricant Ground-glass joint lubricant Wax coating to protect glass from attack by aggressive species • Vacuum pump oil for mass spectrometers 14. Miscellaneous • • • • • • •

Refractive index matching fluids Potting and sealing waxes Damping fluids Inert heat transfer fluids Release agent for molding of plastics and elastomers Plasticizer for PCTFE and epoxy resins Immersion oil for insect embryo studies

11.4 MANUFACTURE, MARKETING, AND ECONOMICS Active companies in the PCTFE field are Halocarbon Products Corporation (River Edge, NJ, U.S.) [1], Atochem SA (Paris, France) [2], Daikin Industries, Ltd. (Osaka, Japan) [3], and Gabriel Performance Products (Ashtabula, Ohio, U.S.) [4]. All these companies market the oils and some formulated products such as greases, special waxes, vacuum pump oils, and oils and greases with performance enhancing additives such as rust inhibitors or PTFE. Many specialty lubricant producers, process equipment manufacturers, and government branches purchase the base stock oils and formulate their own finished products for sale or internal consumption. Even though they are more expensive than ordinary and synthetic hydrocarbon

Copyright 2006 by Taylor & Francis Group, LLC

oils, PCTFE oils are cost effective because of reduced downtime, increased equipment life, and reduced maintenance. Employee and plant safety concerns and efforts to reduce corporate liability often make the use of inert lubricants mandatory.

11.5 OUTLOOK Both the near- and long-term outlooks for these lubricants indicate growth along with industry in general. Although new applications are constantly developing and growing rapidly, their total volume is small compared with major applications. One use that is growing rapidly is the precision machining, drawing and forming of hightech metals. The use of inert lubricants in some major applications, such as the oxygen, chlorine, and electronics industries, is expected to show growth paralleling the growth of those industries. In recent years, many of the less cost-efficient chlorine and oxygen plants have been shut down, reducing the total amount of inert lubricants used in those industries. The following factors could significantly affect the long-term outlook for PCTFE lubricants: • Full development of nonflammable hydraulic fluids for

military aircraft and land applications. • Replacement of phosphate esters as vacuum pump fluids

in oxygen service. The U.S. Navy is already converting to PCTFE vacuum pump oils. • Replacement of environmentally unacceptable chlorinated solvent-based cutting oils with PCTFE oils. The ease of recycling PCTFE oil makes this an attractive alternative. • Many new customer-site noncryogenic oxygen plants use relatively low pressure compressed air and do not have much equipment that requires inert lubricants.

REFERENCES 1. Halocarbon Products Corporation, Polychlorotrifluoroethylene (PCTFE) Oils, Greases & Waxes brochure. 2. Atochem S.A., Voltalef® Oils and Greases brochure. 3. Daikin Industries Ltd., Daiflon® and Daiflon Grease technical information bulletin. 4. Gabriel Performance Products, Fluorolube® technical information bulletin.

12

Silicones Robert Perry, Clay Quinn, Frank Traver, and Kedar Murthy CONTENTS 12.1 Indroduction 12.2 Historical Development 12.3 Chemistry 12.3.1 Product Structure 12.3.2 Nomenclature 12.3.3 Synthetic Methods 12.3.4 Current Commercial Routes 12.4 Properties and Performance 12.4.1 Structural Considerations 12.4.2 Chemical and Related Properties 12.4.2.1 Chemical Inertness 12.4.2.2 Self-Extinguishing 12.4.2.3 Oxidation Stability 12.4.2.4 Thermal Stability 12.4.2.5 Hydrolytic Stability 12.4.2.6 Corrosion and Staining 12.4.2.7 Effect on Plastics and Rubber 12.4.3 Physical and Related Properties 12.4.3.1 Viscosity–Temperature Properties 12.4.3.2 Low-Temperature Properties 12.4.3.3 Shear Stability 12.4.3.4 Compressibility 12.4.3.5 Radiation Resistance 12.4.3.6 Surface Tension 12.4.3.7 Other: Flammability 12.4.4 Performance Data 12.4.4.1 Four-Ball Wear Test 12.4.4.2 Falex Test 12.4.4.3 Ryder Gear Test 12.4.5 Applications 12.5 Manufacture, Marketing, and Economics References

12.1 INDRODUCTION Silicones are a broad family of synthetic polymers that are partly inorganic and partly organic. Their structure consists of alternating silicon and oxygen atoms rather than the carbon-to-carbon backbone that characterizes organic materials. Typically, one or more organic side groups are attached to the silicon atoms, imparting properties such as chemical resistance, lubricity, improved thermal and oxidative stability, and reactivity with organic chemicals and polymers. Additionally, these materials are

Copyright 2006 by Taylor & Francis Group, LLC

characterized by chemical inertness, low surface tension, excellent water repellency, good electrical properties and weatherability, and a high degree of slip on most rubber or plastic surfaces. Silicones are grouped into three major categories: fluids, resins, and elastomers (Figure 12.1). Silicone fluids in commercial use often have side groups such as methyl, trifluoropropyl, phenyl, vinyl, longer aklyl, and other organic groups. In addition, they

Fluids

Resins

–

–

– O – Si – O –

–

– Si – O – Si –

Elastomers

R –

R –

–

R

R

R

R GUM REINFORCING FILLER CROSSLINK

FIGURE 12.1 The three major categories of silicones

may be modified with the use of fillers, solvents, antioxidants, or lubricity additives for use in a wide variety of applications.

O

O O Si

12.2 HISTORICAL DEVELOPMENT Organosilicone chemistry had its beginnings about 100 yr ago. Kipping of England was the first to name silicones. As early as 1904, he synthesized a number of R–Si–X compounds using Gridnard reagents. As scientific knowledge about the formation of large polymer molecules increased in the early 1930s, industrial development of silicones began [1]. Early work focused on resinous polymers for use as insulating materials that would withstand temperatures above the 105◦ C limit of Class A insulation. In 1940, through research done at its corporate research and development laboratory in Schenectady, New York, General Electric became the first company to successfully develop an economical procedure for silicone production. Both Dow Corning Corporation and General Electric began commercial development of silicone polymers during the 1940s. The Dow Corning plant opened in 1943; General Electric began commercial production in 1944 and completed the initial phase of its Waterford facility in 1947. Silicones were initially used for military applications during World War II, followed by use in the aerospace industry. Silicones’ success in meeting the demanding environmental conditions characteristic of these applications, together with their thermal and chemical stability, led to increased usage in the United States. Typical military applications for silicones include damping fluids for aircraft instruments, antifoams in petroleum oils, and greases used as ignition sealing compounds. After World War II, civilian uses expanded beyond these applications to include release agents for molding rubber, water repellents, and ingredients for paints, lubricants, and polishes. In recent years, silicones have grown from a chemical rarity into a widely use family of products. Silicone fluids have proved extremely versatile in solving many industrial

Copyright 2006 by Taylor & Francis Group, LLC

Si

H3C

CH3 CH3

H3C

FIGURE 12.2 The hybrid nature of the silicone polymer

problems and have been key ingredients in a number of new products. Probably no other synthetic fluid has found such a variety of uses in so many different industries.

12.3 CHEMISTRY 12.3.1 Product Structure Silicone fluids are unique polymers that combine an inorganic silicon–oxygen (siloxane) backbone with organic side chains: R groups such as methyl (CH3 ) and phenyl (C6 H5 ), as shown in Figure 12.2. This hybrid nature explains why silicones behave somewhat such as organic polymers, yet retain important inorganic properties such as heat resistance. Many of the unique properties of silicone fluids are due to the free rotation of molecules along the Si–O and Si–C bond axes and the flexible nature of the siloxane backbone. This freedom of motion leads to greater intermolecular distance and, therefore, to lower intermolecular forces. These factors explain the low modulus, low glasstransition temperatures (Tg ), and high permeability of silicones [2]. Structure also explains the slight temperature dependence of other properties, such as viscosity [3]. At lower temperatures, the siloxane has short chain extension and low molecular entanglement of the R groups. As the chain extends with higher temperatures, the backbone must shift to a higher-energy configuration where the R groups are closer together. The greater molecular mobility due to temperature is thus negated by increased molecular entanglement. Therefore, the viscosity of the flexible silicone

has much less temperature dependence than that of the stiff-chained hydrocarbon [4].

12.3.2 Nomenclature Silicone terminology is a blend of “official” International Union of Pure and Applied chemistry (IUPAC) rules, American Chemical Society (ACS) rules, and commonly used shorthand. The terminology borrows from organic chemistry nomenclature and defines SiH4 as silane, analogous to CH4 , methane. Hence, H3 SiCl is chlorosilane; (CH3 )2 SiCl2 is dimethyldichlorosilane; and H3 SiOH is silanol. The molecule H3 SiOSiH3 is disiloxane; polymers are polyorganosiloxanes (a more descriptive term than silicone). Polydimethylsiloxanes (PDMS) are the predominant commercial polymers. Strictly, proper nomenclature can be awkward to use, especially with polymer chemistry and in the spoken language. A useful shorthand has been developed, and it reflects the predominance of PDMS polymers. The letters, M, D, T, and Q are used to represent mono-, di-, tri-, and quadrifunctional monomer units, that is, monomer units

with the silicon bonded to one, two, three, and four oxygen atoms, respectively. (Keep in mind that each O is actually a bridge in the siloxane chain, and is “shared” by two Si atoms.) The remaining substituents are labeled with a prime, such as M [2]. Table 12.1 and Table 12.2 show common examples of this nomenclature and other common shorthand terms. The D chain-propagating units are used to build up the polymer, since they can form one Si–O bond to the growing chain and still have a bond site available to add the next monomer unit. The M units are used as chain terminators, since simply attaching to the chain uses their only Si–O bond site. The T and Q units are used to add branching and cross-linking, especially in resins.

12.3.3 Synthetic Methods Oxygen (50%) and silicon (25%) are the most abundant elements in the earth’s crust. Silicon is not found pure in nature, but rather in combination with oxygen in a wide variety of three-dimensional crystalline networks called silicates (Figure 12.3).

TABLE 12:1 Silozane Structures MDT formula

Common name

MM MDM MD2M

Mono Linear trimer Linear tetramer

D⬘4

Cyclic phenyltetramer

D⬘4

Cyclic methylphenyl-tetramer

(CH3)(C6H5)Si---O---Si(CH3)(C6H5) [(CH3)3SiO]3SiCH3

M3T

—

1,1,1,3,5,5,5,-Heptamethyltrisiloxane

(CH3)3SiOSi(H)(CH3)OSi(CH3)3

MD⬘M

—

1,1,3,5,5-Pentamethyl1,3,5-triphenyltrisiloxane

(CH3)2(C6H5)SiOSi(CH3)C6H5)

M⬘D⬘M⬘

—

Chemical name Hexamethyldisiloxane Octamethyltrisiloxane Decamethyltetrasiloxane Octamethylcyclotetrasiloxane

Structural formula (CH3)3SiOSi(CH3)3 (CH3)3SiOSi(CH3)2)Si(CH3)3 (CH3)SiO]Si(CH3)2O]Si(CH3)3 (CH3)2Si---O---Si(CH3)2 O

O

(CH3)2Si----O---Si(CH3)2 Octaphenylcyclotetrasiloxane

C6H5)2Si---)---Si(C6H5)2 O

O

(C6H5)2Si---O---Si(C6H5)2 2,4,6,8-Tetramethyl2,4,6,8-tetraphenlycyclotetrasiloxane Methyltris (trimethylsiloxy) silane

(CH3)(C6H5)Si---O---Si(CH3)(C6H5) O

O

OSi(C6H5)(CH3)2

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TABLE 12.2 Silicone Functionality Shorthand Notation Symbol

(CH3 )3 SiO0.5 (CH3 )2 SiO (CH3 )SiO1.5 (CH3 )(C6 H5 )SiO (C6 H5 )2 SiO (CH3 )(H)SiO SiO2

Mono Di Tri Di Di Di Quadri

M D T D D D Q

O

–

O

–

–

Functionality

–

Formula

– O

–

O

–

–

– O – Si – O – Si – O –

FIGURE 12.3 Structure of the silicate network

–

–

–

H H H

–

–

–

–C–C–C– H H H

2. Silicone has a tremendous affinity for (and is difficult to separate from) oxygen. In other words of looking at this, silicon builds polymers with oxygen, while oxygen tends to degrade hydrocarbons to single molecules (CO2 and CO). 3. Silicon does not form double bonds, while C=C and C=O bonds are important in organic chemistry. 4. Silicon compounds generally require higher energy (higher temperature) to react, making them more stable. The potential usefulness of the Si–O bond was not realized until the 1930s, when organic resins used for electrical insulation were found to be inadequate for new higher temperature applications. It was thought that a resin siloxane backbone with small organic side chains might have the proper temperature resistance [4]. Early synthetic schemes used Grignard reagents and silicon tetrachloride [7]. The Grignard reagent is prepared as follows: Mg + RBr → RMgBr The silicon tetrachloride is derived from quartzite rock, oil coke (carbon), and chlorine gas: SiO2 + 2C → Si + 2CO (electric furnace) Si + 2Cl2 + heat → SiCl4

FIGURE 12.4 Carbon bonding

The reactants are combined in an ethereal solvent: –

H H

–

–

H

–

–

–

– Si – Si – Si – H

H H

FIGURE 12.5 Polysilane

The substitution of atoms such as iron, aluminum, calcium, sodium, and potassium in the matrix gives rises to a wide variety of rocks and minerals. Through the craft of ceramics, humans have been using practical silicate chemistry for thousands of years [5,6]. However, due to the stable nature of silicates, silicon was not isolated and recognized as an element until 1824. Since silicon and carbon are both tetravalent (have four bonding electrons available), much of the research in the 1800s focused on synthesizing silicon analogs of organic compounds (Figure 12.4 and Figure 12.5). However, there was little success. Due to silicon’s more complex electron orbital structure, silicon chemistry differs from carbon (organic) chemistry in several important ways [5,6]: 1. Si–Si and Si–H bonds reach rapidly with oxygen and water, making them unstable under normal conditions (they will react with air).

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2RMgBr + SiCl4 → R2 SiCl2 + 2MgBrCl nR2 SiCl2+ (2n)H2 O → (2n)HCl + nR2 Si(OH)2 nR2 Si(OH)2 → n(H2 ) + (R2 SiO)n (linear and cyclic) This method proved costly and difficult on a production scale. Safety is also a concern with large quantities of reactive materials such as ether and magnesium. A direct process involving a catalyst mixture was developed by Rochow of General Electric Company that allowed the chlorosilane intermediates to be produced in one step [8,9]: Si + 2RCl → R2 SiCl2 nR2 SiCl2+ (2n)H2 O → (2n)HCl + nR2 Si(OH)2 nR2 Si(OH)2 → nH2 O + R2 SiO)n (linear and cyclic) This process made the commercialization of silicones possible, and it remains as the standard of the industry.

12.3.4 Current Commercial Routes Commercial silicone manufacture starts with the production of chlorosilane intermediates, especially methylchlorosilanes.

Bulk silicon

Methyltrichlorosilane

Unreacted methyl chloride to compression and distillation

Screens Copper catalyst

Crushing and grinding Fluid-bed reactor

Mixed chlorosilanes

Methyl chloride

Dimethyldichlorosilane

Vaporizer Higher boiling residue

Lower boiling chlorosilanes (bp < 65°C)

FIGURE 12.6 Conversion of bulk silicon

Typically, methyl chloride vapor is passed at high velocity through a fluid-bed reactor containing finely ground silicon metal and copper catalyst. The silicon is converted (at up to 90% efficiency) to a crude mix of dimethyldichloro-, methyltrichloro-, methyldichloro-, and trimethylchlorosilanes, as well as other monosilanes and higher-boiling residues [2] (Figure 12.6). Conditions are generally set to yield at least 50% dimethyldichlorosilanes. Fractional distillation columns are used to separate the desired components from the crude mix. The task is somewhat difficult since the boiling points of the chlorosilanes are similar (Table 12.3). Methylchlorosilanes are converted to silicone fluids in a two-step process. In the hydrolysis step, dimethyldichlorosilane is converted to cyclic and linear dimethylsiloxanes (D units):

[(CH3 )2 SiO]n + HO[CH3 )2 SiO]m H + HCl linear

Likewise, trimethylchlorosilane is converted to hexamethyldisiloxane, the source of chain-terminating M units: (CH3 )SiCl + H2 O → (CH3 )3 SiOSi(CH3 )3 + HCl

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Compound (CH3 )SiCl3 (CH3 )2 SiCl2 (CH3 )3 SiCl (CH3 )SiH(Cl)2 (CH3 )2 SiH(Cl)

Boiling point, ◦ C

Density d20 , g/cm3

Refractive 20 index, nD

Assay, %

66.4 70.0 57.9 41.0 35.0

1.273 1.067 0.854 1.110 0.854

1.4088 1.4023 1.3893 1.3982 1.3820

95 to 98 99 to 99.4 90 to 98 95 to 97 —

Siloxane polymer (MDx M) is formed in the equilibration reaction: H+ or OH− [CH3 )2 SiO]n + HO[CH3 )2 SiO]m H + (CH3 )3 SiOSi(CH3 )3 → [CH3 )2 SiO]n + (CH3 )3 SiO

(CH3 )2 SiCl2 + H2 O → cyclic

TABLE 12.3 Chlorosilane Properties

− [−CH3 )2 SiO−]p = Si(CH3 )3 + H2 O The average chain length can be controlled reliably by choosing the ratio of D to M. However, note that some cyclic siloxanes remain at equilibrium with the mix of polymer chains. The equilibrated fluid is washed with water to kill residual active groups, neutralized, dried, and devolatilized, to yield the final silicone fluid product. Commercial products can be pure or modified dimethylsilicone fluids. Fluids can be modified chemically

CH3

FIGURE 12.7 Structure of polymethylsiloxane

by copolymerization with methylalkyl, methylphenyl, diphenyl, methyltrifluoropropyl, or other organofunctional oligomers. The addition of silica fillers to fluids gives greaselike silicone compounds, used for electrical insulation and waterproofing or as antifoam compounds. The use of soap as a filler results in a lubricating grease.

Skin Ingestion Inhalation Eyes Patch testing

H

No reaction LD50 15 g/kg No injuries known (low vapor pressure) Transient irritation No skin irritation

H

H

–

m

–

–

–

–

CH3 CH3

TABLE 12.4 Physiological Properties of Dimethyl Silicone Oils

–

–

CH3

–

–

CH3 CH3

CH3 – SiO – SiO – Si – CH3

12.4 PROPERTIES AND PERFORMANCE

–

H

H

–

–

H–C– –C– –C–H X

H

FIGURE 12.8 Hydrocarbon fluid structure

12.4.1 Structural Considerations Silicones are used for lubrication in both critical (metalto-metal) and noncritical applications, such as plastic-toplastic. Critical lubrication conditions can be divided into three categories: hydrodynamic, boundary, and extreme pressure. These characteristics define the mechanisms whereby damage is prevented as one metal surface slides across another. Early application testing soon made it clear that the most basic silicone, polydimethylsiloxane fluid (Figure 12.7), in its unmodified and uncompounded state, lacked the ability to lubricate sliding metal-to-metal in any of the three categories outlined. Dimethyl fluids as well as molecular modifications with phenyl were ideal in thermal and oxidative stability. However, in viscosity and shear stability, they lacked the essential load-bearing characteristics necessary for critical lubricant use [10]. Molecular modifications utilizing phenylalkyl, fluoro, nitrile, methyl alkyl, and chlorophenyl functionalities, and compounding with fillers such as soaps, graphite, treated or untreated silicas, molybdenum disulfide, polyethylenes, carbon blacks, clays, or combinations of the preceding are used to achieve the variety of lubrication properties necessary for effective critical lubrication [11]. Compounding lubricating fluids produces either greases or compounds. A grease is a “semistructured lubricant that is utilized to lubricate or protect metal-tometal contact surfaces” [12]. A compound is a fluid that has been thickened and stabilized to a greaselike consistency. Compounds are used for applications other than metal-to-metal.

hydrolytically stable, nonstaining or noncorrosive, and, as a class of materials, very low in toxicity. The physiological properties of dimethyl silicone oils are presented in Table 12.4 [13]. It is the Si–O linkage that contributes to the outstanding high-temperature characteristics and general inertness of silicone fluids. The Si–O linkages are comparable to linkages found in similar high temperature materials (e.g., quartz, glass, and sand). The carbon-to-hydrogen bonds of hydrocarbon fluids (Figure 12.8) lack this relationship.

12.4.2 Chemical and Related Properties

12.4.2.3 Oxidation stability

Generally speaking, silicones are chemically inert, selfextinguishing, resistant to oxidation and thermal attack,

In oxidative breakdown, oxygen reacts with the organic groups of the molecules, causing the fluids to lose volatiles

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12.4.2.1 Chemical inertness Silicone fluids are inert to most common materials of construction. Generally, silicone polymers are unaffected by rubber, plastic, and most metals. However, the metals outlined in Table 12.5 either cause or inhibit gellation of silicones. Typically, water and ordinary aqueous solutions of inorganic acids or bases will not react with siloxanes intended for mechanical applications. However, strong acids or alkalis will cause molecular rearrangement and speedup gellation of silicone fluids under oxidative conditions. 12.4.2.2 Self-extinguishing Silicone polymers produce a white silica ash if burned and will eventually self-extinguish. See Section 12.4.3.7 (Flammability) for additional information.

TABLE 12.5 Effect of Metals on Silicone at High Temperaturesa Dimethyl (400◦ F)

Methyl phenyl (450◦ F)

Inhibits gellationb Inhibits gellationb Inhibits gellation Causes gellation Causes gellation Causes gellation

None None Volatilization None Causes gellation Causes gellation

Metal Copper Phosphor bronze Lead Yellow brass Selenium Tellurium

a Silicones S-9 Technical Data Book, Silicone Fluids,

General Electric Silicones, Waterford, NY.

b Cooper and phosphor bronze inhibit gellation up to 400◦ F.

At higher temperatures little effect is noted.

Thermal attack R

–

R

–

–

R

–

–

–

– Si – O – Si – O – Si – R

R

R

Oxidative attack

12.4.2.4 Thermal stability The best thermal stability for silicones is achieved in the absence of air or in an inert atmosphere such as nitrogen or carbon dioxide. Under strictly thermal conditions where oxidation is not a factor, the bonds linking silicon and oxygen can be broken at very high temperatures. The result is the forming of lower-molecular-weight, volatile silicones. Its activation temperature is approximately 316◦ C (600◦ F). 12.4.2.5 Hydrolytic stability When exposed to water at temperatures that will hydrolyze many other high-temperature hydraulic fluids, silicone lubricating or hydraulic fluids will remain unaffected. Problems such as gel precipitation and viscosity reduction will not be encountered. 12.4.2.6 Corrosion and staining Pure silicones contain no acid-producing chemicals to cause staining or corrosion. However, chlorophenyl polysiloxanes have been known to produce negligible to slight staining, with the exception of copper. For this reason, the use of pure copper is not recommended with chlorophenyl polysiloxane. Structural surfaces have been known to discolor at 204◦ C (400◦ F).

FIGURE 12.9 Thermal and oxidative attachment mechanisms

12.4.2.7 Effect on plastics and rubber TABLE 12.6 Oxidation Threshold Fluid Methyl phenyl siloxane (45 wt% MePh) Chlorophenyl polysiloxane Dimethyl polysiloxane Dibasic acid ester Petroleum oil

Oxidation threshold temperature, ◦ C (◦ F) 271 (520) 221 (430) 204 (400) 66 (150) 66 (150)

and increase in viscosity until gellation occurs. The reaction is dependent on the temperature and supply of air present (Figure 12.9). At the point called the oxidation threshold temperature, a significant amount of oxidation by-products starts to appear. Table 12.6 compares the oxidation thresholds of several silicone and organic fluids. Although silicone lubricants are characterized as having a high oxidation threshold, they have poor tolerance for oxygen. Antioxidants are sometimes added to silicone lubricants to extend their lives at high temperature.

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Although silicones are generally not affected by rubber or plastics, these materials can be affected by long immersion in silicone fluids. Very low-molecular-weight fluids (10 cSt or less) have been shown to have the most adverse effects, acting as solvents with plastics, and leaching out plasticizer in rubbers. Table 12.7 shows the effect on plastic after a 30-day immersion in dimethyl and methylphenyl silicones. Plastics, coatings, and resins are generally not affected by moderate-viscosity silicone lubricants at ambient temperatures. However, silicone fluids, like many organic materials, may cause stress cracking in polyethylene. Therefore, this plastic should be stress-relieved if it is to operate reliably in contact with silicone fluids for long periods of time. Cellulose acetate butyrate is stiffened and crazed by dimethyl fluids. Polyacetal (sold under the trade name Delrin) is stiffened and crazed by both dimethyl and methylphenyl fluids. When silicone fluids are used to provide surface coatings on rubber in order to impart slip to rubber parts, no effect is noted. Rubber containing little or no plasticizer compatible with silicone fluids is unaffected. Table 12.8 lists the temperature ranges recommended for various rubber uses with silicone. When silicones are used with these rubbers outside the recommended temperature range, the effect is usually

TABLE 12.7 Effect on Plastics after a 30-Day Immersion Plastica,b Nylon Polystyrene Methacrylics Modified methacrylics Polycarbonates (Lexan) Phenolics Cellulose acetate butyrate Polyacetal (Delrin) Polyethylene Linear polyethylene Linear polypropylene Polyvinyl chloride PTFE (Teflon)

Dimethyl SF96 (350 cSt)

Phenyl containing SF

No effect No effect No effect No effect

No effect No effect No effect No effect

No effect

No effect

No effect Stiffened

No effect No effect

Stiffened and crazed Some stress cracking Some stress cracking

Stiffened and crazed Some stress cracking Some stress cracking

Some stress cracking

Some stress cracking

Shrinks and hardens

Shrinks and hardens

No effect

No effect

a Linear polyethylene and linear polypropylene are not as susceptible to

stress cracking or crazing as ordinary polyethylene. b Teflon is a registered trademark of E.I. duPont de Nemours & Co.,

Inc.; Lexan is a registered trademark of GE Company; and Delrin is a registered trademark of Dow Chemical Co.

TABLE 12.8 Rubber in Silicone Fluid Systems Type Chloroprene Isobutylene isoprene Nitrile-butadiene Fluororubber

Producta Neoprene Butyl Nitrile Buna N Viton Fluorel

Recommended service temperature range, ◦ F −40 to 200 −40 to 200 −40 to 300 −20 to 450

a Neoprene and Viton are registered trademarks of E.I. duPont de

Nemours & Co., Inc., and Fluorel is a registered trademark of Minnesota Mining & Manufacturing Co.

a reduction of weight and volume and an increase in hardness caused by leaching of the plasticizer.

12.4.3 Physical and Related Properties Silicones’ excellent viscosity vs. temperature characteristics, low-temperature properties, and shear stability along with their high compressibility, good radiation resistance, and low surface tension are the physical properties that ensure their usefulness as lubricants [13].

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12.4.3.1 Viscosity–temperature properties Silicones experience a relatively small change in viscosity with regard to temperature. Other fluids such as petroleum oils and dibasic acid esters exhibit larger changes in viscosity with temperature than most silicones (Figure 12.10) [14]. The viscosity–temperature coefficient (VTC) is an indication of how much the viscosity changes with temperature. The lower the value, the less the viscosity changes with temperature. The VTC is defined as 1−

Viscosity at 99◦ C(210◦ F) Viscosity at 38◦ C (100◦ F)

Silicones generally have a VTC of only 0.6. This is different from organic fluids, which typically have a value of 0.8 or higher. Figure 12.10 shows the viscosity–temperature relationship of various fluids. 12.4.3.2 Low-temperature properties Low-temperature fluidity is an important advantage for silicones over conventional oils. It is measured by pour point: the temperature at which a fluid is so cold that it loses its ability to flow. Although analogous to the freezing point of a pure compound, the pour point of a polymeric fluid is not sharply defined and can vary with the test method. The most common method is ASTM D-97. Basic dimethyl polysiloxanes above 50 cSt have characteristic pour points of −50 to −54◦ C (−58 to −65◦ F). By specially formulating fluids, pour points down to extremely low values can be achieved. Typically, branched siloxanes remain pourable at the extremely low temperature of −84◦ C (−120◦ F). 12.4.3.3 Shear stability Low-molecular-weight or low-viscosity silicone fluids are essentially Newtonian in behavior. This means the measured viscosity does not change with different rates of shear. Dimethyl polysiloxanes of 40 to 1000 cSt at 25◦ C (77◦ F) are typical examples of this category. Fluids with viscosities above 1000 cSt at 25◦ C (77◦ F) exhibit pseudo-plastic flow. This means that there is deviation from linearity when the apparent viscosity is plotted against the rate of shear. Further, as the viscosity increases, the deviation becomes more pronounced (Figure 12.11) [15]. Additionally, the loss of viscosity is much smaller than that of organic fluids, and silicone fluids will return to their original absolute viscosity as long as the temperature remains below 316◦ C (600◦ F). Table 12.9 shows the stability of a methyl chlorophenyl siloxane in a pumping test. Compared with MIL-H-5606 in the same type of pump, the methyl chlorophenyl fluid

100,000 50,000 10,000 5,000 1×101

1,000 500

5 ×101 1 ×101

Kinematic viscosity, cSt

100

5 ×101

50

2 ×101 1 ×101 10 5 ×101 2 ×101

5.0

SAE 10 petroleum oil

MII-L-7808 Dlester 1.50 C F

–51 –60

–40 –40

–29 –20

–18 0

–7 20

4 40

16 60

27 80

38 100

49 120

60 140

71 82 93 104 115 126 137 148 160 171 182 193 204 215 23 150 160 200 220 240 260 280 300 320 340 360 380 400 420 450

Temperature, °C (°F)

FIGURE 12.10 Viscosity–temperature relationship of dimethyl fluids (20 to 10,000 cSt at 25◦ C) vs. selected hydrocarbon oils

1 × 102

m0 m

1.0 0.9 0.8 0.7 0.6

5 × 103

0.5 0.4 0.3 3 × 104

0.2

1 × 101 0.1 1 10

1.5

2

3

4

5 6 7 891 100

1.5

2

3

4

5 6 7 891 1.5 1000

2

3

4

Shear rate-seconds

FIGURE 12.11 Transitory viscosity of dimethylsiloxanes (1,000 to 100,000 cSt at 25◦ C) under shear conditions

.

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5 6 7 891 10,000

30

TABLE 12.9 Shear Stability in Pumping Testsa

Pressure, psig Temperature, ◦ F Test duration, h Recirculation, cycles Flow rate during test Fluid replaced Pump wear Viscosity change, cSt, at 38◦ C (100◦ F)

Mineral oil

25

Methyl chlorophenyl siloxane

MIL-H-5606

4,000 215 1,200 44,000 Constant None Nil −3.5%

4,000 175 500 20,000 Dropped, >18% >50% (Leakage) Serious −25%

Pressure–psl × 103

Fluid

Water

50 cStks & above

20

0.65 cStks

15 10 5

0

a Pump used: Lockheed MK 7 radial piston.

0

2

4

6

10

8

12

14

Percent compression

was pumped hotter and longer, resulting in a negligible viscosity change and pump wear. 12.4.3.4 Compressibility All fluids show some tendency to decrease in volume when subjected to high pressures. Silicone fluids are considerably more compressible than natural oils like petroleum products. It has been stated that a siloxane bond is like a ball and socket-free to move in any direction. When a load is applied to the “chain,” the linkage deflects, compressing the chain. The compression here is greater for siloxane because the spacing between the silicone and oxygen is greater than that of a hydrocarbon bond. Temperature has only a small effect over a range of −40–149◦ C (−40–300◦ F). The low-viscosity silicones have been found to be most compressible. For example, a dimethyl siloxane of 0.65 cSt was found to offer 19% volume reduction at 50,000 psig. However, the low volatility and effect on materials of construction make fluid of this viscosity inappropriate for many lubrication applications. A dimethyl siloxane of 1,000 cSt was found to offer only a 15% decrease in volume reduction under a pressure of 50,000 psig [16]. Figure 12.12 and Table 12.10 provide pressure vs. percent compressibility data for selected silicone fluids.

FIGURE 12.12 Compressibility of silicone fluids vs. mineral oil and water

TABLE 12.10 Percent Compressibility of Selected Silicone Fluids Fluid 100 cSt Polydimethylsiloxane 1,000 cSt Polydimethylsiloxane 12,500 cSt polydimethylsiloxane

7,100 psi

35,500 psi

284,000 psi

568,000 psi

4.5

12.7

28.6

34.0

4.6

12.7

28.2

33.5

4.5

12.5

28.1

33.5

roentgens will produce a large increase in the viscosity of dimethyl fluids. A dosage of 1 × 108 roentgens is usually sufficient to cause gellation. A methyl phenyl siloxane with 40–50 mol% phenyl would show minimum change at 1 × 108 roentgens. A methyl chlorophenyl siloxane of 8–13.5 mol% tetrachlorophenyl would demonstrate better resistance than a dimethyl siloxane, petroleum oil, dibasic acid ester, silicate, or disiloxane ester. Theoretical treatment of the effects of radiation on silicone can be found in References 17 and 18.

12.4.3.5 Radiation resistance It has been shown that radiation resistance is a function of aromatic content for both silicones and organic fluids. The dimethyl siloxanes contain no aromatic groups in their structure. Methyl and phenyl siloxanes and other aromatic siloxanes, therefore, demonstrate a much greater radiation resistance. Dimethyl silicone fluids show relatively poor resistance to gamma radiation. Tests have shown that a dose of 1×107

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12.4.3.6 Surface tension Surface tension of silicone fluids is usually low, making them appropriate for applications where high surface activity and great spreading power are necessary. Dimethyl silicones have the lowest surface tension values, and these are largely independent of viscosity [about 21 dyn/cm at 35◦ C (77◦ F) over a viscosity range of 20–100,000 centistokes]. Methyl phenyl fluids have

slightly higher surface tension values [about 24–25 dyn/cm at 25◦ C (77◦ F)], but these values are still much lower than those of organic materials. The surface tension of organic fluids is typically in the range of 30 to 40 dyn/cm. The value of water at room temperature is about 72 dyn/cm. 12.4.3.7 Other: flammability Characteristic of silicones are high flash, fire, and autoignition temperatures. Conventional silicone fluids of 50 cSt or more in viscosity have flash points of 238–302◦ C (460–575◦ F) when measured by the conventional “closed-cup method.” The fire points of silicones are significantly higher than their flash points. It has been estimated that their closedcup fire points can be as much as 93◦ C (200◦ F) higher than their flash points. The difference between the flash and fire points accounts for the self-extinguishing characteristics of nonvolatile, high-molecular-weight silicone fluids. Conventional nonsilicone fluids frequently have flash and fire points within a few degrees of each other, reducing the likelihood that they will self-extinguish. The autoignition temperatures for conventional silicones are estimated to be in the 438–460◦ C (820–860◦ F) range.

12.4.4 Performance Data Typically, silicones operate at temperatures between −73 and 232◦ C (−100 to 450◦ F). Specially formulated silicones like the chlorophenylmethyl silicones have been known to operate at temperatures up to 315◦ C (600◦ F). Other modified silicones like the methyl alkyls cannot operate continuously above 350◦ F because of the limited oxidative stability inherent in the fluid. In one of the most popular lubricating applications for high-performance silicones (ball bearing lubrication), the concept of “speed factor” or DN values (bearing bore diameter in mm, times speed in rpm) is used to define the operating capability of silicone and other bearing lubricants. Silicone fluids used as bearing lubricants are recommended for use between 200,000 and 350,000 DN at light to medium loads. This recommendation is also true for most silicone greases that were designed primarily for antifriction bearings. Silicone greases are known to provide extended bearing life over a wide operating temperature range. They are limited by the physical properties of the base silicone oil, in addition to the thickener chosen. While the DN value defines the operating capability of lubricants, tests like the Shell four-ball wear test, the Falex test, and the Ryder gear test are widely accepted screening and performance tests for lubricants. Others, like the Navy gear test, have poor reproducibility but have

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been used in the past to characterize the performance of lubricants. It has been demonstrated that chlorophenylmethyl siloxanes and methyl alkyl siloxanes, when properly formulated, compare favorably to traditional lubricants. Fluids or compounded methyl alkyl products have been known to perform even better than traditional lubricants in applications requiring aluminum-to-aluminum contact or lubrication of dissimilar metals. Conventional silicones compare poorly to traditional metal-to-metal lubricants in these tests. Other specialty formulations like trifluropropyl methyl fluids or even silicone glycol fluids have improved lubricating properties under certain conditions. However, physical properties or the inherent stability of the siloxane chain is often compromised. 12.4.4.1 Four-ball wear test Performance under sliding contact is measured by the fourball wear test. Table 12.11 compares typical wear scar data for a number of fluids in the temperature range of 25–75◦ C (77–167◦ F) in steel-to-steel applications. Methyl alkyl silicones are not included in the data in Table 12.11. However, in other studies, methyl alkyl fluids were compared to SAE 30, a traditional petroleum lubricant. The fluids were used to lubricate sliding aluminum S2 vs. stationary tool steel with a load of 40 kg. The test temperature is 75◦ C (167◦ F) at speeds of 600 rpm. The methyl alkyl siloxane were scar measured only 0.55 mm, as compared to a 0.70 mm scar for SAE 30 petroleum lubricant. The fluids were used to lubricate sliding aluminum S2 vs. stationary tool steel with a load of 40 kg. The test temperature is 75◦ C (167◦ F) at speeds of 600 rpm. The methyl alkyl siloxane wear scar measured only 0.55 mm, as compared to a 0.70 mm scar for SAE 30 petroleum lubricant. 12.4.4.2 Falex test This test is designed to measure the antiweld properties of lubricants and their resistance to wear under extreme pressure conditions. Table 12.12 shows data on various lubricants. 12.4.4.3 Ryder Gear Test The Ryder Gear Test (data generated using F.S. 791, method 6508) measures gross surface damage between case-hardened spur gears. Ratings are in terms of “scuff load,” the load at which 22.5% of the gear tooth area is scored. Methyl phenyl silicones show some advantages in these tests. Performance is primarily dependent on the lubricant’s “pressure–viscosity” properties: the greater the

TABLE 12.11 Shell Four-Ball Wear Test — Comparison of Typical Data Wear scars, mm at Test fluid

Test conditions

10 kg

Petroleum base Mineral oil Mil-H-5606 SAE 10 engine oil

167◦ F, 600 rpm Ambient, 600 rpm Ambient, 600 rpm

0.44 0.30 0.37

0.59 0.55 0.50

Dibasic acid esters Uncompounded Dibasic ester MilL-6085A Mil-L-7808

Ambient, 600 rpm Ambient, 600 rpm 167◦ F, 600 rpm

0.52 0.60 0.22

0.79 0.85 0.40

Orthosilicate ester Phosphate ester Polyphenyl ether

167◦ F, 600 rpm Ambient, 600 rpm 167◦ F, 600 rpm

0.71 0.46 0.56

1.10 0.57 1.25

Ambient, 600 rpm

0.39

0.53

Ambient, 600 rpm 400◦ F, 1200 rpm Ambient, 600 rpm

0.50 0.91 1.39

1.83 — 4.18

Ambient, 600 rpm 400◦ F, 1200 rpm 400◦ F, 1200 rpm

0.80 0.54 0.78

2.32 — —

Silicones Chlorophenylmethyl siloxane (8 to 13.5 mol% Cl4 PH) Dimethyl silicone Dimethyl silicone Methyl phenyl silicone (45 mol% MePH) Chlorinated methyl phenyl silicone Trifluoropropyl methyl silicone Trifluoropropyl methyl-dimethyl copolymer

50 kg

a Steel balls: AISI 52-100. Time: 1 h, except 400◦ F/1200 rpm tested fluids, which

are 2 h.

b Tests performed at ambient temperature are initiated at approximately 25◦ C (77◦ F) but no effort at temperature control is attempted. Temperatures will rise 10 to 50◦ F

(depending on the fluid); such data are roughly comparable to those that run at 75◦ C (167◦ F).

viscosity increases under pressure, the better the gear lubricant. Table 12.13 presents data on selected fluids.

12.4.5 Applications The applications of silicone fluids vary widely. They are used as base fluids for a variety of products such as emulsions, solutions, greases, and compounds. Although there are certain uses for silicone lubricating oils, more often the lubricant is in the form of grease. Silicone fluids have found limited use as lubricants in applications calling for a material that can withstand high temperatures and moderately loaded conditions, but are generally ineffective as lubricants for heavily loaded metal surfaces. For ferrous metals, silicones, and in particular dimethyl silicones, were especially poor in providing lubrication under boundary conditions [19–23]. It was

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concluded that oxidation of the dimethyl silicone created an oxygen starved contact between metal surfaces, which led to adhesive wear [24]. Using model systems, the highly varied wear protection effect at steel–steel contacts as a function of chemical composition was also examined [25]. However, advances in technology have improved the load carrying capabilities and lubricity of silicones: for example, fluorosilicone lubricants are effective in applications such as pumps and valves for fuel and solvent tanks in which the metal surface and the lubricant are exposed to hydrocarbon solvents. Some damping greases are also made of silicone components, especially where large temperature ranges are expected [26]. Another drawback of silicone fluids — their adverse effect on the adhesion of postdecorative coatings such as paint — has also been addressed by technology. Methyl

TABLE 12.12 Falex Test: Loads to Seizurea Dibasic acid ester Chlorophenylmethyl siloxane (8 to 13.5 mol% Cl4 PH) Petroleum oil Methyl alkyl silicone Methyl phenyl silicone Dimethyl silicone

1150–2000 1100–1200 600–900 To 750 50–100 60–80

a Pressure values are in psi.

TABLE 12.13 Ryder Gear Test: Scuff Loadsa Methyl phenyl silicone Dibasic acid ester Versilube F-50® Petroleum oil Dimethyl silicone

4000 2800 2400 1200 1000

a Pressure values are in psi.

alkyl-substituted polysiloxanes possess unique properties that allow them to be used in areas where soldering and painting are done. A number of silicone fluids have been blended successfully with synthetic, organic fluids to combine the best performance qualities of each. An example that has been marketed successfully is a diester–polysiloxane blend based on lithium soap. This product provides enhanced lubricating properties and lower cost compared with the polysiloxane equivalent. Silicone fluids are also used extensively as release agents in a variety of molding operations. They are desirable because of their resistance to high temperature, smoking, and fuming; and the small amount of product needed offsets their higher price. Other applications include personal care products, paper coatings, hydraulic fluids, damping fluids, and polishing fluids. Table 12.14 lists the various types of silicone fluid, their properties, and the applications in which they are used.

12.5 MANUFACTURE, MARKETING, AND ECONOMICS There are five fully integrated competitors in the global silicones market (Table 12.15). Although these producers vary widely in size, each has a fairly complete product line. This is a smaller number than that was several years ago

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as the trend toward globalization and consolidation continued. Bayer formed a joint venture with General Electric in Europe, and OSi was also acquired by GE Silicones in 2003. Huls sold its siloxanes business to Wacker and merged with Degussa and Th. Goldschmidt merged with SKW Trostberg. While not basic in hydrolyzate or fluids, Degussa–Huls and SKW Trostberg/Th. Goldschmidt are major players in the silanes market. There are also a number of specialty finishing companies, which purchase siloxane intermediates and process them into different elastomers, coatings, greases, compounds, and adhesives. In addition, there are also numerous small facilities in India, China, and other emerging countries in the Asia-Pacific region that are converting raw materials purchased from the global suppliers into finished silicone fluids. Overall demand for silicone fluids in the United Sates, Europe, and Japan grew at about 6% annually for the years 1995–1998 and only around 2% for the 1998–2002 time period. This is smaller than the 10–15% annual growth seen in the 1970s and reflected a maturing market for standard silicone materials. However, growth in personal care and electronics markets has sustained expansion in the area of specialty silicones. These include silicone elastomers, coating, and adhesives as well as organofunctional fluids. The anticipated annual growth rate is expected to rise to 5–8% for the next few years, fueled by the rapid growth in the Asia-Pacific region. Because the products are similar, there is generally a strong price competition among manufacturers of basic silicone fluids. In the case of more complex, specialty fluids, however, the issue is not competition, but rather price sensitivity on the part of consumers. Because they cost more than competing organic chemicals, silicones are considered high-end products and are selected for applications demanding their unique properties. Successful marketing and sales of these silicone fluids focus on the products’ special qualities or value-added economics. As was true a decade ago, an increasing share of silicone fluids production has been dedicated to specialty products. This trend continues to drive new technology and product development [27]. The highly engineered nature of specialty silicone products demands an investment in technology. The high cost of this technology has led to different product strategies among the producers. Some have bundled specialty silicones with organic specialties and targeted them at specific lubricant markets. Others have consolidated, formed joint ventures, or sold their interests to competitors. However, all these approaches are based on bringing value to the customer in specialty products like specialty lubricants. Within the past few years, an increasing share of silicone fluid production has been dedicated to specialty products. This trend drives new technology and product development.

TABLE 12.14 Applications for Common silicone Fluids Silicone type Dimethyl

Fluoro

Methyl phenyl

Methyl alkyl

Chlorophenylmethyl

Properties Excellent viscosity temperature characteristics, hydrolytic stability, reduces surface tension, imparts excellent slip to rubber and plastic, acts as a water repellent Good lubrication and resistance to chemicals and solvents, extended bearing life, excellent high-temperature properties, high load-carrying characteristics Increased thermal stability, good high- and low-temperatures stability, excellent radiation resistance, improved oxidation resistance Develops thick films under dynamic conditions, most compatible with organic materials, does not contaminate surfaces to be painted Greatly improved high-temperature lubricity; chlorine provides chemical reactivity with metal necessary for effective boundary lubrication, improved pour point

TABLE 12.15 Major Global Producers of Siloxane Fluids Company North America GE Silicones/OSi Specialties Dow Corning Corporation (a joint venture of Dow Chemical and Corning Glass Works) Wacker Chemical Company Europe GE Bayer Silicones (a joint venture with Bayer Corporation) Dow Corning, Ltd. Wacker Chemie, GmbH Rhodia Asia GE Toshiba Silicones (a joint venture with Toshiba Corporation) Dow Corning Toray Silicones Co., Inc. Shin–Etsu Chemical Company

GE Silicones/Shin–Etsu Joint Venture

Manufacturing Sites Waterford, NY Sistersville, WV Midland, MI Carrollton, KY Adrian, MI Leverkusen, Germany Barry, Wales Burghausen, Germany Nunchritz, Germany Saint Fons, France Ohta, Japan Ichihara, Japan Takefu, Japan Matsuida, Japan Naoetsu, Japan Thailand (expected 2004)

The highly engineered nature of specialty silicone products demands an investment in technology. The high cost of this technology has led to different product marketing strategies among the producers. Some have bundled

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Applications Plastic bearings, sheeting, cutting tools, molded and extruded parts, sewing thread, base fluid for compounds, hydraulic fluids, damping fluids Base fluid for greases, hydraulic fluids, bearings, chemical process compressors, vacuum pumps, other chemical and corrosive environments Base fluid for greases (maintenance and lube for life applications), impart slip to rubber and plastic, hydraulic fluid, thread, and fiber Base fluid for greases, difficult metal combinations, die casting, metalworking, cutting oils, penetrating oil Miniature bearings, base fluid for grease, bearings in high ambient temperature industries, clocks and timing devices, hydraulic systems, tape recorders, vacuum pumps

specialty silicone products with organic specialties and targeted them at specific lubricant markets. Others have consolidated, formed joint ventures, or sold their interests to competitors. However, all these approaches are based on bringing value to the customer in specialty products like specialty lubricants. The silicones industry has experienced a major shift from growth within traditional geographic boundaries to a global marketing approach. Silicone producers seek to improve existing product lines, develop new products, and enter new markets.

REFERENCES 1. Miller, J.W. (1984). Synthetic lubricants and their industrial applications, Appl. Rev. J. Syn. Lub. 1, pp. 136–152. 2. Hardman, B. and Torkelson, A. (1989). Silicones, Reprinted from Encyclopedia of Polymer Science and Engineering, Vol. 15, John Wiley & Sons, New York, pp. 204–303. 3. Awe, R.W. and Schiefer, H.M. in “Silicones”, Synthetic lubricants (1962), Reinhold Publishing Compant, New York; Gunderson, R.C. and Hart, A.W. (Eds.) pp. 264–319. 4. Liebhafsky, H.A. (1978). Silicones Under the Monogram, John Wiley & Sons, New York. 5. Noll, W. (1968). Chemistry and Technology of Silicones, Academic Press, New York. 6. Rochow, E.G. (1987). Silicon and Silicones, SpringerVerlag, Heidelberg, Berlin. 7. Burkhard, C.A., Rochow, E.G., Booth, H.S., and Hartt, J. (1947). “The present state of organosilicone chemistry” Chem. Rev., 41, pp. 97–149. 8. Rochow, E.G. U.S. Patent 2,380,995 (August 7, 1945), to General Electric Co.

9. Rochow, E.Gl. and Gilliam, W.F. (1945). “The district synthesis of organosilicon compounds” J. Am. Chem. Soc., 67, p. 963. 10. Smith, R.E. (1975). Silicone lubricants for the chemical processing industry, J. Am. Soc. Lub Eng., Presented at ASLE 30th Annual Meeting, Atlanta, GA (May 5–8). 11. Versilube Silicone Lubricants, Historical Technical Data Book S-10B, GE Silicones Products Department. 12. Barnes, J.E. and Wright, J.H. (1988). Silicone greases and compounds: their components, properties and applications, Presented at the 55th NCGI Meeting. 13. Lonsky, P. (1985). Some characteristics of silicones developed as lubricants, J. Syn. Lub., 1, pp. 302–313. 14. Wilcock, D.F. Silicone Oils Part II: Their Applications, General Electric Rev. Dec 1946, pp. 28–32. 15. Dugan, W.J. (1951). General Electric Viscasil Silicone Fluids for Mechanical Operations, Report No. CHSD-49, Waterford, NY. 16. Bridgman, P.W. (1949), Further Rough Compressions to 40,000 kg/cm2 , Especially Certain Liquids, Proc. Am. Acad. Sci., 77(4), pp. 115–146. 17. Miller, A.A. (1960). Radiation chemistry of polydimethylsiloxane: I. Crosslinking and gas yields, J. Am. Chem. Soc., 82, pp. 3519–3523. 18. Miller, A.A. (1964). Radiation stabilities of arylmethylsiloxanes, Ind. Eng. Chem. Prod. Res. Dev., 3, pp. 252–256.

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19. Moreton, D.H. (1964). Liquid Lubricants. In: E.E. Bisson and W.J. Anderson (Eds.), Advanced Bearing Technology, Washington, DC: NASA SP-38. 20. Vinogradov, G.V., Nametkin, N.S., and Nossov, M.I. (1965). Anti-wear and anti-friction properties of polyorganosiloxanes and their mixtures with hydrocarbons. Wear, 8, p. 93. 21. Fowle, T.I. (1967–1968). Lubricants for fluid film and hertzian contact conditions. Proc. Instn. Mech. Engrs., 182, p. 568. 22. Jemmett, A.E. (1969). Review of recent silicone work. Proc. Lubric. Symp., Paisley College of Technology, Paisley, U.K. 23–24 October. 23. Hatton, R.E. (1973). Synthetic Oils. In: Interdisciplinary Approach to Liquid Lubricant Technology, Washington, DC: NASA SP-318. 24. Lansdown, A.R. (1994). The effects of oxygen availability on the lubricating performance of a dimethyl silicone in the boundary regime, Wear, 175, pp. 25–38. 25. Dornhofer, G. (1998). Silikone zur Schmierung moderner Maschinenelemente. Tribologie und Schmierungstechnik, 45, pp. 8–15. 26. Montour, T. (2001). More than a lubricant. Machine Design, pp. 69–71, 23 August. 27. Smart, M. (2000). Silicones, Chemical Economics Handbook, SRI International, 583.0100A-283.0103O.

13

Silahydrocarbons Carl E. Snyder and F. Alexander Pettigrew CONTENTS 13.1 Introduction 13.2 Historical Development 13.3 Chemistry 13.3.1 Magnesium 13.3.2 Lithium 13.3.3 Zinc 13.3.4 Aluminum 13.3.5 Hydrosilation 13.4 Performance 13.4.1 Viscosity 13.4.2 Lubricity 13.4.3 Thermal Stability 13.4.4 Oxidative Stability 13.4.5 Hydrolytic Stability 13.4.6 Volatility and Flammability 13.4.7 Summary of Properties 13.5 Commercial Status References

13.1 INTRODUCTION Although there are currently no commercial applications for silahydrocarbons, this class of compounds has such unique properties that it remains interesting. The term “silahydrocarbons” is used here to describe a class of compounds that is more correctly termed tetraalkylsilanes (SiR4 ). The alkyl groups on silicon can be the same or different. Additionally, the alkyl groups can be straightchained (i.e., n-alkyl) or branched. For reasons discussed later, the silahydrocarbons of most interest have been those that contain n-alkyl groups. In this chapter, the term “silahydrocarbon” refers generically to the class of compounds; “tetraalkylsilane” is used as appropriate to clarify discussions of the chemistry.

13.2 HISTORICAL DEVELOPMENT While the history of silahydrocarbons goes back well over 100 years, it was in the 1950s that the modern history of their development as functional fluids began. The role of the U.S. Air Force, for the most part, defines that history This chapter is dedicated to the memory of Gunner E. Nelson.

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until the very recent past. The U.S. Air Force Materials Laboratories began a general investigation into the synthesis and properties of tetraalkylsilanes in the 1950s [1–3]. These fluids were called silahydrocarbons [4] to emphasize their hydrocarbon-like behavior. The driving force for the research was the recognition that new high performance aircraft would require lubricants and fluids capable of operating in a high temperature/high load environment. Over the years, the interest in silahydrocarbons rose and fell, finally reaching a peak in the 1980s. During this period, target specifications evolved for candidate fluids for use as hydraulic fluids in high performance aircraft. These target specifications eventually evolved to incorporate the low temperature requirements of MIL-H-5606 (mineral oil) [5] with the high temperature requirements of MIL-H-83282 [synthetic poly(α-olefins), PAO] [6]. Table 13.1, gives a partial listing of these hybrid target properties. Kinematic viscosity and most of the other properties were targeted to those of MIL-H-5606E fluid at low temperature and MIL-H-83282 at high temperature. The early front-runner was a PAO-based fluid. However, it was recognized that the flash point of this new fluid would be lower than the MIL-H-83282 specification (205◦ C minimum). The lower flash point was

TABLE 13.1 Original Target Properties of Military Hydraulic Fluids as Derived from MIL-H-83282 and MIL-H-5606 Fluid property

Target

MIL-H-5606

MIL-H-83282

Kinematic viscosity, cSt At −54◦ C, maximum At −40◦ C, maximum At 100◦ C, minimum Pour point, ◦ C, maximum Shear stability, MIL-H-5606D, % viscosity change Flash point, ◦ C (open cup), minimum Fire point, ◦ C, minimum

2500 500 3.5 −59.4 0 163 191

2500 600 4.9 −60 0 82 NA

NA 2600 3.5 −55 0 205 245

TABLE 13.2 Silahydrocarbon Performance vs. Target Properties for Low Temperature MIL-H-83282 Fluid property Kinematic viscosity, cSt At −54◦ C, maximum At −40◦ C, maximum At 100◦ C, minimum Pour point, ◦ C, maximum Shear stability, MIL-H-5606D, % viscosity change Flash point, ◦ C (open cup), minimum Fire point, ◦ C, minimum

Determined 2410 564 2.58 <−65 0

Target 2500 maximum 500 maximum 3.5 minimum −59.4 maximum 0

227

163 minimum

238

191 minimum

a consequence of the lower molecular weight required to obtain the desired kinematic viscosities at low temperatures. This compromise in flash point, in large part, spurred further development of silahydrocarbons as candidate hydraulic fluids. The inherent chemical structural differences between silahydrocarbons and PAOs made it possible to produce a silahydrocarbon-based fluid with a flash point matching MIL-H-83282 PAO and having the low temperature viscosity of the more volatile mineral oil. The subject of silahydrocarbon properties versus those of hydrocarbons is discussed later. By the late 1970s, the Air Force had successfully developed a silahydrocarbon composition nearly meeting these specifications [7]. It possessed excellent thermal stability, viscosity index, and low temperature flow characteristics. The properties of the Air Force silahydrocarbon fluid are compared to the target properties in Table 13.2. More recently, the silahydrocarbons have been developed and investigated as base fluids for candidate ultra-low volatility liquid and grease lubricants for space applications [8–10]. Their excellent viscosity index makes them ideal

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candidates because for a specific viscosity, the molecular weight of the silahydrocarbon fluid is significantly higher than mineral oil or other synthetic hydrocarbonbased fluids. This higher molecular weight results in their significantly lower volatility, an extremely important property for a lubricant in a space environment. This property continues to gain in importance as the mission lifetimes of the space-based systems continue to increase. Another advantage of the silahydrocarbons for space applications is that they can be prepared as unimolecular materials and still maintain excellent low temperature fluidity. This is an important property because as the lubricant slowly evaporates due to the high vacuums experienced in space-based applications, the viscosity of the fluid remains constant. This is contrasted to the behavior of lubricants that contain a range of molecular weight components, for example, mineral oils, PAO. As the lower molecular weight components evaporate, the viscosity of the remaining lubricant increases. This frequently results in the viscosity of the lubricant increasing to the point that the motors driving the mechanical assembly do not produce sufficient torque to overcome the high viscosity of the lubricant and the component fails. The comparative properties of three different silahydrocarbon base fluids (designated SiHC-1 to SiHC-3) are compared to some more commonly used hydrocarbonbased space lubricants in Table 13.3. The MAC designation is for multiply alkylated cyclopentane [11,12]. The comparative volatilities of these lubricants were determined using vacuum thermogravimetric analysis at 0.25 torr. This method provides information about the onset of volatility. It easily distinguishes the unimolecular fluids from the fluids that are mixtures by the shape of the curve. The relative volatilities are expressed as T0 and T1/2 values that correspond to the temperature at which the onset of volatility occurs and at which 50% of the lubricant has been lost, respectively. Candidate silahydrocarbonbased liquid and grease space lubricants are currently under test.

TABLE 13.3 Comparative Properties of Candidate Hydrocarbon-Based Space Lubricants Fluid Fluid property Kinematic viscosity, cSt at 100◦ C 40◦ C −18.7◦ C −40◦ C −54◦ C Viscosity index Volatility, TGA, T1/2 T0

PAO-1

PAO-2

MAC

SiHC-1

SiHC-2

SiHC-3

14.58 104 4860 — — 145

12.33 93.5 5030 — — 126

14.4 106 5138 77870 — 139

15.2 94.4 3051 34910 — 170

12.17 71.22 2059 20780 157300 169

9.98 56.5 1514 14870 110790 165

240 150

265 235

286 280

350 336

304 288

257 246

— No flow.

13.3 CHEMISTRY

with methyltrichlorosilane is:

The literature contains numerous reports on methods of preparation of silahydrocarbons, some dating back over a century. The types of reaction that appear to be useful include alkylation of silicon halides and hydrosilation of olefins. Alkylation can be affected by lithium, magnesium, zinc, and aluminum alkyl compounds. Each of these will be discussed in turn. A note regarding nomenclature is appropriate at this point. The valence of silicon in silane-type compounds is always four. When naming silanes, it is customary to leave out any hydrogens directly bonded to the silicon. Thus, methyldichlorosilane is CH3 Cl2 SiH.

RBr + R Br + 2Mg → RMgBr + R MgBr

13.3.1 Magnesium The first synthesis of tetraalkylsilanes (silahydrocarbon), reported by Friedel and Crafts in the mid-1800s [13,14] was the reaction of alkyl magnesium halides (Grignard reagent) with tetrachlorosilane to give low molecular weight symmetrical tetraalkylsilanes such as tetraethylsilane. 4RMgX + SiCl4 → R4 Si + 4MgXCl

CH3 SiCl3 + 3[RMgBr + R MgBr] → × [CH3 SiR3 + CH3 SiR2 R + CH3 SiRR2 + CH3 SiR3 ] + 3MgBrCl where R = n-octyl and R = n-decyl. A key to obtaining desirable low temperature properties in the final fluid was the fact that the product was a mixture of compounds similar in molecular weight. This suppressed solidification. For the fluid whose properties are reported in Table 13.2, R and R are 50:50 mixtures of n-octyl and n-decyl. Lennon at Monsanto developed two routes to methyltrialkylsilanes based on the catalyzed reaction of dialkyl magnesium with methyltrichlorosilane [17–19]. The preparation of magnesium hydride and its subsequent reaction with α-olefins to give dialkyl magnesium was previously known [20] Mg + H2 → MgH2 MgH2 + α-olefin → MgR2 heat

Since then, many workers have studied the preparation of tetraalkylsilanes via magnesium reagents. Gilman and Clark [15] studied the reaction of alkyl magnesium halides with alkyl trichlorosilane 3R MgX + RSiCl3 → RSiR3 + 3MgXCl Air Force researchers [4,16] developed a route based on the reaction of mixed alkyl magnesium halides or mixed alkyl lithium reagents with tetrachlorosilane or alkyltrichlorosilane. The case for the mixed magnesium reagent reaction

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3MgR2 + 2CH3 SiCl3 −→ 2CH3 SiR3 + 3MgCl2 Both cyanide compounds, such as cuprous cyanide [17] and thiocyanate salts [18] are used as catalysts. With either class of catalyst, Grignard reagents may take the place of the dialkyl magnesium. If a mixture, of α-olefins is used, a mixture of products, such as that described by the Air Force researchers, results.

13.3.2 Lithium Prior to the work by the Air Force discussed above, where an alkyl lithium was shown to be able to take the place

of an alkyl magnesium halide [15], Gruttner and Wiernik [21] reported the reaction of an alkyl lithium with a trialkylsilane to give the first unsymmetrically substituted tetraalkylsilane. R Li + R3 SiH → R3 SiR + LiH Gilman and Massie [22] reported the reaction of alkyl lithiums with tetrachlorosilane to give symmetrical tetraalkylsilanes 4RLi + SiCl4 → R4 Si + 4LiCl

13.3.3 Zinc There is a report by Bygden [23] of the reaction of dialkyl zinc with tetrachlorosilane to give symmetrical tetraalkylsilanes: 2ZnR2 + SiCl4 → R4 Si + 2ZnCl2

13.3.4 Aluminum Jenkner’s route [24,25] involves the reaction of trialkyl aluminum with methyltrichlorosilane catalyzed by a metal chloride to give low molecular weight tetraalkylsilanes: CH3 SiCl3 + AlR3 + MCl → CH3 SiR3 + MAlCl4 where R = CH3 or CH3 CH2 . Bakshi et al. [26] later developed a similar route that gave high molecular weight products. For example: CH3 SiCl3 + Al(C8 H17 )3 + NaCl → CH3 Si(C8 H17 )3 + NaAlCl4 Depending on the exact conditions, various levels of tetra-n-octylsilane and dimethyl-di-n-octyl silane could be produced as coproducts. The use of 0.5 equivalent of sodium chloride based on the tri-n-octyl aluminum was found to maximize the yield of the desired product, methyl-tri-n-octyl silane. Nelson and coworkers [27–31] at Ethyl developed a route to tetraalkylsilanes based on the alkylation of chlorosilanes with sodium aluminum tetraalkylates. The route first involves the preparation of the sodium aluminum tetraalkylate via the reaction of sodium aluminum hydride with α-olefins. The intermediate tetraalkylate is used next to alkylate a chlorosilane, such as methyltrichlorosilane: NaAlH4 + 4(C8 /C10 α-olefin) → NaAl(C8 H17 )x (C10 H20 )4−x 3NaAlR4 + 4CH3 SiCl3 → 4CH3 SiR3 + 3NaAlCl4 The product is a mixture of the four components described by the Air Force workers. Adjusting the C8 /C10 olefin ratio can readily alter product distribution, or, if another

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composition is required, olefins of other carbon numbers can be used. In an interesting modification of this process, olefin/aluminate interchange is used: NaAlR4 + 4(C8 α-olefin) → NaAl(C8 H17 )4 NaAl(C8 H17 )4 + C10 α-olefin + 4CH3 SiCl3 → 4CH3 Si(C8 H17 )4 (C10 H21 )3−x + NaAlCl4 Presumably, a rapid exchange of alkyl groups on the aluminate occurs during the alkylation process, yielding again the four-component mixture, with the relative mole fractions of each calculable on the basis of the C8 /C10 ratio as before. Such chemistry can be used to produce phenylalkylsilanes [32,33]. A similar route involves the treatment of a trialkyl aluminum with sodium followed by reaction with methyltrichlorosilane [34]. In an interesting extension of this chemistry, the sodium aluminum tetraalkylate can be prepared directly from sodium, aluminum, hydrogen, and α-olefins. This reaction product can then be reacted with a methyltrihalosilane [35]. Researchers at Shin-Etsu [36] reported the preparation of low molecular weight silahydrocarbons via the reaction of chlorosilanes with chlorinated hydrocarbons in the presence of metallic aluminum or aluminum alloys. A similar route was reported by researchers at Dow Coming [37].

13.3.5 Hydrosilation Hydrosilation has also been utilized in the preparation of tetraalkylsilanes. While it is likely not of preparatory significance, Austin et al. [38] reported an interesting route to tetraalkylsilanes. These investigators studied the photocatatyzed reaction of alkenes with alkylsilanes using tri-nuclear metal carbonyl catalyst precursors. Thus, irradiation of M3 (CO)2 (M=Fe, Ru, or Os) in the presence of 1-pentene and HSiEt3 gave n-C5 H11 SiEt3 . El-Durini and Jackson [39] studied another interesting approach. They reported the reaction of tripropylsilane with l-Octene in the presence of a free radical initiator. When the starting silane was present in excess, a high yield of the product, octyltripropylsilane, was obtained. Onopchenko and Sabourin [40,41] developed a route based on catalytic hydrosilation of α-olefins by mono-, di-, or triakylsilane. Various platinum-based catalysts are claimed. For example, (C8 α-olefin) + C6 H13 SiH3 + H2 PtCl6 · 6H2 O → (C8 H17 )3 (C6 H13 )Si A key to high conversion to the tetraalkylsilane is the exposure of the catalyst to oxygen. Under similar conditions, using a rhodium-based catalyst, the inventors were able to prepare mixtures of tetraalkylsilane that contained various levels of unsaturation in the side chains [42]. The mixture

can be hydrogenated to provide a saturated tetraalkylsilane. The unsaturation can also be sulfurized to provide a compound that can act as a lubrication additive. Onopchenko and Sabourin [43] developed another route to tetraalkylsilanes based on hydrosilation of α-olefins. The scheme involves hydrosilation of an α-olefin by methyldichlorosilane followed by reduction of the resultant methylalkyldichlorosilane to the methylalkylsilane by lithium aluminum hydride. This product is, in turn, reacted with another α-olefin via catalytic hydrosilation. This reaction scheme allows the synthesis of a series of methyldialkylalkylsilanes: CH3 SiCl2 H + α-olefin + catalyst → CH3 SiCl2 R CH3 SiCl2 R + LiAlH4 → 2CH3 SiH2 R + LiAlCl4 CH3 SiH2 R + α-olefin + catalyst → CH3 SiR2 R Malcolm et al. [31,44] developed a route to silahydrocarbons starting from silane (SiH4 ) itself. This route involves the partial alkylation of silane by sodium aluminum tetraalkylate. The olefin employed in the last step can be ethylene. The resulting product would thus be an ethyltrialkysilane, in contrast to the methyltrialkysilane produced by the methods starting from methyltrichlorsilane: SiH4 + NaAlR4 → R2 SiH2 + R3 SiH R2 SiH2 + R3 SiH + Co2 (CO8 ) → R3 SiH R3 SiH + α-olefin + catalyst → R3 SiR More recently, LaPointe et al. [45] reported studies of the palladium-catalyzed hydrosilation of alkenes by either triethyl- or triphenylsilane (R3 SiH).

13.4 PERFORMANCE As mentioned earlier, the term “silahydrocarbon” was chosen to describe the class of compounds under discussion because of their hydrocarbon-like character. Indeed, in many ways they are similar to hydrocarbons. It has been shown that silahydrocarbons are compatible with mineral oils and PAOs [43]. This compatibility is one aspect of the fluids that made them attractive to the Air Force as drainand-fill replacements for existing hydraulic fluids. There are, however, some inherent differences, and these form the basis for the interest in these materials. Most of the work on the properties of silahydrocarbons centers on their potential as hydraulic fluids. Therefore a property-by-property comparison to mineral oil and PAOs is warranted. Chapter 18 contains a more general discussion of the properties of a wider variety of fluids.

13.4.1 Viscosity As seen in the discussion of the chemistry, it is possible to synthesize a large number of tetraalkylsilanes of

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TABLE 13.4 Comparison of Melting Points of Silicon and Carbon Analogues Carbon analogue (CH3 )4 C (CH3 CH2 )4 C (n-C3 H7 )4 C (n-C4 H9 )4 C (n-C4 H9 )3 C(CH2 CH3 ) (n-C4 H9 )3 C(CH6 CH13 )

Melting point (◦ C)

Silicon analogue

Melting point (◦ C)

−16 −31 −26 −6 −66 −51

(CH3 )4 Si (CH3 CH2 )4 Si (n-C3 H7 )4 C (n-C4 H9 )4 C (n-C4 H9 )3 Si(CH2 CH3 ) (n-C4 H9 )3 Si(CH6 CH13 )

−95 −69 −46 −46 −91 −72

Source: Data from Snyder, C.E., Gschwender, L.J., Tamborski, C., Chan, G.J., and Anderson, D.R., ASLE Transactions, 25, 299–306, (1982).

the type SiR4 . Since R can be any hydrocarbon group from one carbon up, an enormous number of possibilities exist. A good starting point in understanding the difference between silahydrocarbons and hydrocarbons is a review of the physical properties of compounds with similar structure. The melting points of several tetraaIkylmethanes and tetraalkylsilanes are shown in Table 13.4. From the data, it is clear that for a given structure, the substitution of silicon for the quaternary carbon lowers the melting point dramatically. In practice, this translates to a beneficial decrease in pour point for fluids of similar molecular weight. There are reports in the literature of the synthesis of silahydrocarbons over a wide range of molecular weights [3,31,43,44,46]. A review of the data shows that the viscosity is a linear function of the molecular weight and is not influenced greatly by the molecular structure [47]. The linearity of the relationship is particularly impressive considering that some of the fluids are pure compounds and some are mixtures. Also, the fluids are composed of four classes of tetraalkylsilanes: dodecyltrialkysilanes, didodecyldialkylsilanes, methyltrialkylsilanes, and ethyltriakylsilanes. It is important to note that the viscosity correlation does not necessarily translate to low temperature. As the temperature is lowered, the fluids comprising single compounds suffer from the problem of crystallization (i.e., freezing). A fluid that is a mixture of compounds of similar but different molecular weights will have a pour point below that at which the single-component fluid would solidify. A discussion of viscosity is not complete without taking viscosity index and pour point into account. The viscosity indices of a mineral oil, a PAO, and a silahydrocarbon of the same 100◦ C viscosity are 94, 127, and 151, respectively [48]. A high viscosity index is favorable, indicating that the viscosity does not show large variations with temperature. The pour point of the mineral oil is only −15◦ C

while both the PAO and silahydrocarbon pour points are below −65◦ C.

13.4.2 Lubricity Silahydrocarbons were recently compared to a mineral oil and a PAO [48]. In the absence of additives, the lubricity of the mineral oil was found to be slightly better than that of the PAO, as measured by the size of the wear scar in the four-ball wear test. Both were better than the silahydrocarbon. In the presence of 1% antioxidant and 3% of an antiwear additive, the mineral oil and PAO were equivalent, and both were better than the silahydrocarbon. It is significant that the additives improved the performance of the silahydrocarbon, because this is not the case for some classes of fluids. It may be that an additive package developed specifically for silahydrocarbons would give better performance. Earlier work by the Air Force showed that the lubricities of the three fluids were equivalent in the presence of an antioxidant and an antiwear [49].

13.4.3 Thermal Stability The Air Force researchers reported the results of a systematic investigation into the relative performance of silahydrocarbons and several other candidate fluids as high temperature lubricants [49]. In regard to thermal stability, they found that silahydrocarbons were inherently more stable than mineral oil or PAO. Later work by Pettigrew and Nelson [47] at Ethyl confirmed this finding [47]. This difference in thermal stability is likely due to the different amounts of branching in the structures. The silahydrocarbon has the advantage of having a well-controlled structure with no branching other than the quaternary branch centered at silicon. It is well established that both mineral oils and PAOs used as hydraulic fluids contain considerable amounts of secondary and tertiary branch points. It has been argued that hydrocarbons of the same structure should be no less thermally stable than a given silahydrocarbon, provided both materials are pure [50]. Other works have shown that the situation may be more complex. Onopchenko and Sabourin [43] at Chevron found, as expected, that incorporation of tertiary hydrogen near the end of an alkyl chain in a silahydrocarbon decreased the thermal stability. However, incorporation of tertiary hydrogen on the carbon alpha to the silicon actually made the molecule more stable. Squicciarini et al. [51] at Pennzoil found that synthesized tetra(nalkyl)methanes and tri(n-alkyl)methylmethanes exhibited a good balance of properties compared to PAOs and tri(n-alkyl)methylsilanes.

13.4.4 Oxidative Stability Results cited by both the Air Force [48] and Ethyl [52] show that formulated silahydrocarbons and PAOs are equivalent

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TABLE 13.5 Sources of silahydrocarbons Huls America

80 Centennial avenue P.O. box 456, Piscataway, NJ 08855-0456 Tel: 908-980-6940 Fax: 908-560-6800 http://www.huls.com

Lancaster Synthesis Ltd.

P.O. box 1000 Windham. NH 03087-9777 Tel: 603-889-3306 Fax: 603-889-3326 http://www lancaster.co.uk

Aldrich Chemical Company, Inc.

940 West Saint Paul avenue Milwaukee, WI 53233 Tel: 414-273-3850 Fax: 414-273-4979 http://www.aldrich.sial.com/aldrich.html

in oxidative stability and that both are clearly superior to mineral oils. In further work the Air Force researchers studied the effect of side chain structure on the oxidative stability of a series of alkyltrioctylsilanes.

13.4.5 Hydrolytic Stability The hydrolytic stability of silahydrocarbons, silicate esters, and polysiloxanes was evaluated with regard to the possible use as dielectric coolants in military aircraft [54]. These studies showed silahydrocarbons to be resistant to hydrolysis.

13.4.6 Volatility and Flammability The volatility of nonpolar compounds is a function of molecular weight, as is the viscosity. A silahydrocarbon, mineral oil, and a PAO of the same viscosity at 100◦ C were measured by thermogravimetric analysis to determine their volatilities [47]. The temperature required to induce 5, 50, and 95% weight loss is cited for each fluid. These data clearly show that the silahydrocarbon is the least volatile. This difference in volatility translates to higher flash point as measured by ASTM D-92. The flash points are: silahydrocarbon, 234◦ C; PAO; 218◦ C; and mineral oil, 197◦ C.

13.4.7 Summary of Properties The key features of silahydrocarbons are low temperature fluidity, high thermal stability, low volatility (hence high flash point), and high viscosity index. In comparison to PAOs, the superior thermal stability, high viscosity index,

and low volatility (high flash point) seem to be the advantages that would lead one to consider a silahydrocarbon as a candidate fluid.

13. 14.

13.5 COMMERCIAL STATUS At present, there is no readily available information that indicates significant commercial applications for silahydrocarbons [55,56]. The patent literature discloses few uses for silahydrocarbons outside the hydraulic area. Milliken Research [57] and Ethyl Corporation [58] patented the use of silahydrocarbons as textile finish lubricants. Ferrofluidics [59,60] developed the use of silahydrocarbons in ferrofluid applications. Nippon Polyurethane [61] discloses the use of tetraoctadecylsilane as an internal mold release agent in the manufacture of polyurethane and polyurea articles. Sources of silahydrocarbon lubricants are listed in table 13.5. Several pure, low molecular weight tetraalkylsilanes are available from chemical supply companies. Some of these companies are listed in the appendix.

REFERENCES 1. Rosenberg, H., Groves, J.D., and Tamborski, C., J. Org. Chem., 25, 243, (1960). 2. Tamborski, C. and Rosenberg, H., J. Org. Chem., 25, 246, (1960). 3. Baum, G. and Tamborski, C., J. Chem. Eng. Data., 6, 142, (1961). 4. Snyder, C.E., Gschwender, L.J., Tamborski, C., Chen, G.J., and Anderson, D.R., ASLE Trans., 25, 299–306,(1982). 5. MIL-H-5606E, Hydraulic Fluid, Petroleum Base; Aircraft, Missile, and Ordnance, August 29, 1980. 6. MIL-H-83282C, Hydraulic Fluid, Fire Resistant, Synthetic Hydrocarbon Base, Aircraft, Metric, NATO Code Number H-537, March 25, 1986. 7. Gschwender, L.J., Snyder, C.E., Jr., and Fultz, G.M., Lub. Eng., 42, 485–490, (1986). 8. Snyder, Jr., C.E., Gschwender, L.J., Randolph, B.B., Paciorek, K.J.L., Shih, J.G., and Chen, G.J., “Research and development of low-volatility long life silahydrocarbonbased liquid lubricants for space,” Lubr. Eng., 48, 325–328, (1992). 9. Sharma, S.K., Snyder, Jr., C.E., and Gschwender, L.J., “Tribological behavior of some candidate advanced space lubricants,” Trib. Trans., 36, 321–325, (1993). 10. Gschwender, L.J., Snyder, Jr., C.E., Masse, M., and Peterangelo, S., “Improved liquid/grease lubricants for space mechanisms,” Lubr. Eng., 56, 12, 25–31, (2000). 11. Venier, C.G. and Casserly, E.W., “Lubricants Composing Novel Cyclopentanes, Cyclopentadienes, Cyclopentenes, and Mixtures Thereof and Methods of Manufacture,” U.S.Patent 4 721 823, January 26, (1988) and U.S. Patent 4 849 566, July 18, (1989). 12. Bessette, P.A., “The chemical and physical properties of aerospace grade lubricants,” Proceedings of the

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31st Aersopace Mechanism Symposium, NASA Conference, 3350, (1997). Friedel, C. and Crafts, J.M., Liebigs Ann. Chem., 127, 28, (1863). Friedel, C. and Crafts, J.M., Liebigs Ann. Chem., 259, 334, (1890). Gilman, H. and Clark, T.N., J. Am. Chem. Soc., 68, 1675, (1946). Tamborski, C., and Synder, C.E., U.S. Patent 4,367,343, to the United States of America represented by the Secretary of the Air Force (1983). Lennon, P.J., U.S. Patent 4,650,891, to Monsanto (1987). Lennon, P.J., U.S. Patent 4,672,135, to Monsanto (1987). Lennon, P.J., Mack, D.P., and Thompson, Q.E., Organometallics, 8, 1121–1122, (1989). Bogdanovic, B., U.S. Patent 4,329,310, (1982). Gruttner, G. and Wiernik, M., Beriehte, 48, 1474, (1915). Gilman, H. and Massie, S.P., J. Am. Chem. Soc., 68, 1128, (1946). Bygden, A., Berichte, 44, 2640, (1911). Jenkner, H., U.S. Patent 3,103,526, (1961). Jenkner, H., U.K. Patent 825,987 to Kali–Chemi (1957). Bakshi, K.R., Onopchenko, A., and Sabourin, E.T., U.S. Patent 4,595,777, to Gulf Research and Development Co. (1986). Nelson, G.E., U.S. Patent 4,711,965 to Ethyl Corp. (1987). Nelson, G.E., U.S. Patent 4,711,966 to Ethyl Corp. (1987). Nelson, G.E., U.S. Patent 4,845,260 to Ethyl Corp. (1989). Nelson, G.E., U.S. Patent 4,916,245 to Ethyl Corp. (1990). Pettigrew, F.A., Ploasker, L., Nelson, G.E., Malcolm. A.J., and Every, C.R., paper presented to the Society of Tribologists and Lubrication Engineers, Atlanta, May 4, 1989. Nelson, G.E. and Loop, J.G., U.S. Patent 5,124,502, to Ethyl Corp. (1992). Nelson, G.E. and Loop, J.G., U.S. Patent 5,120,458 to Ethyl Corp. (1992). Eisenberg, D.C. and Robinson, G.C., U.S. Patent 5,177,235, to Ethyl Corp. (1992). Nelson, G.E., U.S. Patent 4,973,724, to Ethyl Corp. (1990). Takeuchi, M., Yamamoto, A., and Endo, M., U.S. Patent 5,498,739, to Shin-Etsu Chemical Co. (1996). Halm, R.L., Chedwick, K.M., and Keyes, B.R., U.S. Patent 4,946,980 to Dow Corning Corp. (1990). Austin, R.G., Paonessa, R.S., Giordano, P.J., and Wrighton, M.S., U.S. National Technical Information Service report AD-A044506; available from Gov. Rep. Announce, Index, 77, 74–81, (1977); Chem. Abstr., 88, 14425/X (1977). El-Durini, N.M.K. and Jackson, R.A., J. Organomet. Chem., 232, 117–121, (1982). Onopchenko, A. and Sabourin, E.T., U.S. Patent 4,572,791, to Gulf Research and Development Co. (1996). Sabourin, E.T. and Onopchenko, A., Bull. Chem. Soc. Jpn., 62, 3691–3696, (1989). Onopchenko, A. and Sabourin, E.T., U.S. Patent 4,572,791, to Gulf Research and Development Co. (1986). Onopchenko, A. and Sabourin, E.T., J. Chem. Eng. Data, 33, 64–66, (1988). Malcolm, A.J., Evenly, C.R., and Nelson, G.E., U.S. Patent 4,670,574, to Ethyl Corp. (1987).

45. LaPoint, A.M., Rix, F.C., and Brookhart, M., J. Am. Chem. Soc., 119, 906–917, (1997). 46. Tamborski, D., Chen, G.J., Anderson, D.R., and Synder, C.E., Jr., Ind. Eng. Chem. Prod. Res. Dev., 22, 172–178, (1985). 47. Pettigrew, F.A. and Nelson, G.E., Silahydrocarbons, in Synthetic Lubricants and High-Performance Functional Fluids (R. L. Shubkin, ed.) Dekker, New York, 1993. 48. Thomas, S.G., Nelson, G.E., Lilje, K.C., Casserino, M.S., and Reid, R.C., Jr., Paper presented to the the Society of Tribologists and Lubrication Engineers, Montreal, Quebec, Canada, April 29, 1991. 49. Snyder, C.E. and Gschwender, L.J., Liquid lubricants for use at high temperature, US Air Force Report. 50. See the discussion by B. Cupples, following Reference 4. 51. Squicciarini, M.P., Hellman, W.J., and Bremmer, M.L., Lubr. Eng., 52, 111–114, (1996). 52. Thomas, S.G., Cambell, D.G., and Hsu, C.J., in Tribology 2000, Proceedings of the 8th Colloquium at the Technische Akademie in Esslingen, 2, 13.2.1–13.2.14, (1992).

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53. Gschwender, L.J., Snyder, C.E., Jr., Krawetz, A.A., Tovrong, T., Musif, G.J., and Chen, G.L., 46, 97–103, (1990). 54. Gupta, V.K., Stropki, M.A., Gehrke, T.J., Geshwender, L.J., and Snyder, C.E., Jr., Lubr. Eng., 46, 706–711, (1990). 55. Personal communication, Gschwender, L., Wright-Patterson Air Force Base. 56. Personal communication, Lilje, K.C., CPI Engineering. 57. Petrea, R.D. and Schuette, R.L., U.S. Patent 5,288,416, to Milliken Research Corp. (1994). 58. Plonsker, L., U.S. Patent 4,932,976, to Ethyl Corp. (1990). 59. Raj, K. and lonescu, C., U.S. Patent 5,452,520, to Ferrofluidics Corp. (1995). 60. Raj, K. and Moskowitz, R., U.S. Patent 5,462,685, to Ferrofluidics Corp. (1995). 61. Yokota, H., Ikemoto, M., Mitsunani, M., Sasaki, K., and Wada, H., Japanese Patent Application 5086161 A2, to Nippon Polyurethane Co. (1993).

14

Phosphazenes Robert E. Singler and Frank J. Gomba CONTENTS 14.1 Introduction 14.2 Chlorophosphazenes 14.2.1 Cyclic Chlorophosphazene Synthesis 14.2.2 Linear Chlorophosphazene Oligomer Fluids 14.3 Cyclic Phosphazene Fluids 14.3.1 Synthesis 14.3.2 Cyclic Phosphazene Fluids — Early Work 14.3.3 Cyclic Phosphazene Fluids — Further Developments 14.3.3.1 Fire-Resistant Hydraulic Fluids — Naval Ship Applications 14.3.3.2 Other Applications — Military and Commercial 14.4 Conclusions Acknowledgments References

14.1 INTRODUCTION Phosphazenes are ring or chain compounds consisting of alternating phosphorus–nitrogen atoms with two substituents attached to phosphorus. Representative structures are shown below. In these structures, R can be a halogen, organo, or organometallic substituent; X is generally a halide or metal halide counterion. The physical properties of phosphazenes vary considerably with molecular weight and choice of substituents (R). Many of the cyclic phosphazenes are either liquids or low-melting crystalline solids. As the molecular weight is increased, either by the size of the substituent or the number of P–N repeat units, one can obtain oils and greases; ultimately, elastomers and thermoplastics are formed. Historically, interest in phosphazenes has focused on applications where fire resistance and thermal stability were important factors. Due to the presence of phosphorus and nitrogen, phosphazenes are inherently fire resistant. Halogen-containing substituents further enhance fire resistance. With the proper selection of substituents, thermally and hydrolytically stable ring and chain compounds, including fluids with low pour points and good thermal stability, have been prepared. These properties have been the

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R R N R P

R P

N

R

R N R P

N P

R

R

P

N R P

R N

P N R

R

R 1

2 R

[R3P = N-PR2 = NPR3] (+) × (–)

[ P = N]n R

3

4

basis for many of the military and commercial applications, which are described in this chapter. Phosphazene fluids are based on structures 1, 2, and 3. Occasionally, these structures are referred to in the literature as “polymers”; however, we will reserve the term “polymer” for structure 4, n > 100. Although they are of interest in their own right, high polymers will not be discussed in this chapter. For a description of polyphosphazenes, the reader is referred to a recent symposium

on inorganic and organometallic polymers [1] and annual surveys of phosphazene chemistry [2].

14.2 CHLOROPHOSPHAZENES 14.2.1 Cyclic Chlorophosphazene Synthesis The chlorophosphazenes form the basis for the preparation of phosphazene fluids and lubricants. Ammonium chloride and phosphorus pentachloride react to form a mixture of hexachlorocyclotriphosphazene 5 and octachlorocyclotetraphosphazene 6, alongwith smaller amounts of higher cyclics and open-chain oligomers (Equation 14.1). This process has been known for over 100 years and has been extensively studied [3]. The chlorotrimer 5 and tetramer 6 are commercially available. Cl Cl N NH4Cl + PCl5

Cl P

Cl P

N

N P Cl

Cl

Cl N Cl P Cl +

P

N Cl P

Cl N

P Cl N Cl

Cl 5

and thus are limited in their applications. Replacement of hydrolytically unstable chlorine substituents with organic substituents might increase hydrolytic stability of these oligomers. Little additional progress has been made to develop stable fluids from the linear chlorophosphazene oligomers.

14.3 CYCLIC PHOSPHAZENE FLUIDS 14.3.1 Synthesis Most of the research and development of phosphazene fluids has centered on the alkoxy- and aryloxycyclophosphazenes, which are derived from the chlorotrimer and chlorotetramer. The cyclic chlorophosphazenes are versatile substrates for nucleophilic displacement processes [7]. Using the chlorotrimer as an example, both singleand mixed-substituent cyclophosphazenes can be obtained (e.g., 7, 8), depending on the selection of alcohols and phenols in the reaction (Equation 14.3). It should be noted that structure 8 represents only one of the possible isomeric products from a two-substituent process. Differences between 7 and 8 are discussed in the next section.

6

(14.1)

14.2.2 Linear Chlorophosphazene Oligomer Fluids One important modification of Equation 14.1 is the use of excess PCl5 with NH4 Cl or with chlorotrimer to obtain linear chloro–phosphazene oligomers. These open-chain oligomers are generally either oils or greases.

Cl N Cl P

Cl P

N

Cl

RO

N P

Cl

ROH

N

Base

RO P

RO H

OR

OR

se

9O H

OR9

RO P

N

N P

OR

OR9

RO

Trimer + PCl5

P

/R

Ba

R9O P

[PNCl2]nPCl5 (n=3–10)

N

7

N

NH4Cl + PCl5 (xs)

N

RO

Cl 5

OR P

8

(14.2)

(14.3)

Over a period of approximately 15 years, the Air Force Materials Laboratory sponsored the development of linear chlorophosphazenes for high-temperature fluid applications [4–6]. Oligomers such as [Cl(PCl2 =N)3 PCl3 ]PCl6 and [Cl(PCl2 =N)n PCl3 ]Cl (n ∼ 10) undergo further reactions above 300◦ C resulting in chain extension or cyclization. However, if these oligomers are end-capped with certain metal halides, the thermal stability is markedly enhanced. Oligomers, [Cl(PCl2 =N)3 PCl3 ]BCl4 and [Cl(PCl2 =N)3 PCl3 ]AlCl4 , are reported to be stable up to 400 and 700◦ C, respectively. The thermal stability of the products seems to depend on the stability of the metal halide anion, which effectively end-caps the reactive PNCl2 chain. Although these oligomers show excellent thermal stability, they are very sensitive to hydrolysis

A suitable base is required either to form the anion of the alcohol or phenol or to remove hydrogen chloride and thus drive the reaction to completion. A number of modifications of the process (Equation 14.3) have been described, including the use of sodium metal or sodium hydride in various inert organic solvents, using a tertiary organic amine or sodium carbonate as the hydrogen chloride acceptor, use of sodium hydroxide in xylene followed by azeotropic distillation of water, and phase-transfer catalysis [8–10]. In these reactions, it is important to obtain complete substitution of chlorine and to remove by-products in order to maximize the thermal and hydrolytic stability of the products. Partially substituted products, N3 P3 Clx (OR)6−x are generally thermally and hydrolytically less stable than fully substituted products [11].

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While nonfluorinated alkoxycyclophosphazenes are prone to rearrangement and decomposition below 200◦ C [12], fluoroalkoxy- and aryloxycyclophosphazenes are exceptionally stable to hydrolysis and heat [8,12]. They are also fire resistant, being self-extinguishing in a flame. While trifluoroethoxy and phenoxy-substituted trimers, N3 P3 (OCH2 CF3 )6 and N3 P3 (OC6 H5 )6 , are crystalline solids, using long-chain fluoroalcohols and substituted phenols can result in fluid products. Also, if mixtures of alcohols and phenols are used in the substitution reaction (Equation 14.3), mixed-substituent products 8 are formed, which often are fluids over a wider temperature range. The ability to attach an almost endless variety of side chains onto a phosphazene ring in a controlled fashion, to produce materials with a wide range of physical properties, has led to the development of several promising fluids, which are described below.

14.3.2 Cyclic Phosphazene Fluids — Early Work A number of references exist prior to 1980, mainly in the patent literature and in government reports, that describe the development of cyclic phosphazenes as fluids, lubricants, plasticizers, or as additives for lubricating oils and greases [3,13–20]. No attempt is made to describe all of the early work, but several of the reports are discussed in some detail, since they form the basis for current activity in this area. Structures given below are all derived from the same general reaction process shown in Equation 14.3. Nichols [14,15] synthesized a series of aryloxysubstituted cyclophosphazene trimers and tetramers, using m-trifluoromethyl-phenol, m-trifluoromethoxyphenol, and phenol combinations. Both single- and mixed-substituent trimers and higher cyclic oligomers were prepared and characterized. Both fluids and crystalline solids were obtained. Use of fluoro-substituted phenols tended to suppress crystallinity, lower pour points, and enhance thermal stability of the products. Fluid 9 had a pour point of −5◦ C, and was reported to be stable up to 400◦ C [14]. Other properties are listed in Table 14.1. NP(OC6 H4 –m–CF3 )2 ]3 9 During the 1960s, the U.S. Navy supported the development of cyclophosphazene as fire-resistant, compression– ignition-resistant hydraulic fluids to meet the requirements for MIL-H-19457A [21]. Selected examples are included in Table 14.1. Initial work [19] involved the preparation of fluoroalkoxycyclophosphazenes. Fluoroalcohols with terminal fluorine (e.g., CF3 CH2 OH, C3 F7 CH2 OH) generally gave crystalline products or had undesirably high vapor pressures. Hydrogen-terminated fluoroalcohols reduced the vapor pressure, but many of the derived fluids 10 were

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also crystalline. One notable exception, (10, x = 4) is shown in Table 14.1. [NP(OCH2 (CF2 )x H)2 ]y x = 2, 4, 6 or 8 y = 3 or 4 10 Attempts to eliminate crystallinity and improve other properties led to the synthesis of cyclophosphazenes with mixed fluoroalkoxy substituents such as 11. While a number of fluids were prepared, with pour points ranging from −23 to −48◦ C, the viscosities were too high for their intended use [21]. Most of the densities exceeded 1.8 g/mL. Tetramer products gave higher viscosities and lower, American Society for Testing Materials (ASTM) (viscosity–temperature) slopes [22] than the trimers. The effect of replacing the terminal hydrogen with fluorine can be seen with fluid 12 in Table 14.1. [NP(OCH2 (CF2 )2 H)a (OCH2 (CF2 )4 H)b ]3 11 a+b=2 [NP(OCH2 CF3 )a (OCH2 C3 F7 )b ]3 12 a+b=2 A series of mixed-substituent cyclophosphazenes with hydrogen-terminated fluoroalkoxy and aryloxy side chains was also prepared and characterized in this study [19]. Using both phenol and substituted phenols as the aryloxy group, some products were obtained that were liquid at room temperature. The properties of one fluid, 13, are shown in Table 14.1. Pour points and viscosities were higher, and the densities were lower, than for the mixed-fluoroalkoxyphosphazenes (11). [NP(OC6 H5 )a (OCH2 (CF2 )4 H)b ]3 13 a+b=2 In an attempt to obtain products with lower viscosities and densities than fluids such as 13, efforts were then directed toward the synthesis of mixed aryloxyfluoroalkoxycyclophosphazenes using fluorine-terminated fluoroalcohols [20]. Replacement of the terminal hydrogen on the fluoroalcohol reduced viscosity, and the use of shortchain fluoroalcohols reduced the density. Properties of the mixed-substituent derivatives were dependent on the length of the fluoroalkoxy chain, the aryloxy/fluoroalkoxy ratio (a/b), and the substituents on the benzene ring. Trends were, in general, independent of ring size. A direct comparison of the physical properties of the timer and tetramer products with identical a/b ratios showed that the tetramers generally had higher boiling points, viscosities, autogenous ignition temperatures (AITs), and thermal stabilities,

TABLE 14.1 Properties of Selected Cyclic Phosphazene Fluids: [NP(OR)(OR
)]3 Structure number, this chapter Property Substituentb Ar R R Viscosity, cStc At 38◦ C At 99◦ C Density at 25◦ C, g/mL Pour point, ◦ Ce S.I.T., ◦ Cf

9

13

14a

15a

–C6 H5 –CH2 (CF2 )4 H

–C6 H4 -m-Cl –CH2 CF3

–C6 H4 -m-CF3 –CH2 CF3

10.6 2.04 1.7

159 11.4 1.60

61.3 6.54 1.51

53.9 5.58 1.52

<−40 —

−23 635

−20 663

−20 677

10

11

12

–CH2 (CH2 )4 H

–CH2 (CF2 )2 H –CH2 (CF2 )4 H

–CH2 CF3 –CH2 C3 F7

44.3d 10.1 1.5

100.5 10.6 1.85

96.7 9.20 1.71

−5 —

−46 566

−48 538

–C6 H4 -m-CF3

a Synthesized from a commercial chlorotrimer–tetramer mixture (80:20).

b R, R , perfluoroalkyl groups, H or F terminated, structures 10–15; Ar, phenyl or substituted phenyls in structures 9 and 13–15. c MIL-H-19457 target goals [21]: 43–50 cSt at 38◦ C; 4.8 cSt minimum at 99◦ C. d Estimated based on Example 1, [15]. e MIL-H-19457 target goal (21): −18◦ C maximum. f S.I.T., spontaneous ignition temperature [19,20]. Modification of ASTM D-2155-66.

Sources: 9, Refs. 14 and 15; 10, 11, 13, Ref. 19, 12, R. E. Singler, G. L. Hagnauer, and C. E Snyder, unpublished results (1977): 14, 15, Ref. 20.

as well as lower ASTM slopes and frequently lower pour points [20]. Properties of selected examples, 14 and 15, are given in Table 14.1. [NP(OC6 H4 –m–Cl)a (OCH2 CF3 )b ]3 14 a+b=2 [NP(OC6 H4 –m–CF3 )a (OCH2 CF3 )b ]3 15 a+b=2

14.3.3 Cyclic Phosphazene Fluids — Further Developments 14.3.3.1 Fire-resistant hydraulic fluids — naval ship applications While some of the fluids prepared in the earlier Navy program [19,20] showed promise for MIL-H-19457, they did not have the requisite balance of physical properties and systems compatibility for sustained development. Some of the fluids crystallized in storage or failed more severe hydrolytic stability testing. Part of the problem may have been the result of the synthetic procedures employed in the early work or the difficulty in characterizing complex product mixtures [23]. Mixed-substituent products, such as 11–15, are complex mixtures with different chemical

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compositions and isomer distributions; this often made it difficult to determine if a given composition was inherently unacceptable, or perhaps there was a minor component in the mixture that adversely affected properties. These issues, as well as projected high costs of phosphazene fluids, also discouraged commercial development. In 1980, the Navy took a renewed interest in phosphazene fluids, after a consideration of alternate synthetic procedures that might be used to optimize fluid composition, and availability of modern characterization techniques that could more accurately analyze product composition. Singler [24,25], participating in a new program with the Navy to develop nontoxic, fire-resistant phosphazene hydraulic fluids, used a different process to synthesize aryloxy/trifluoroalkoxyphosphazenes. Unlike the earlier work [20], which used an azeotrope to remove water formed during the reaction, sodium salts of trifluoroethanol and the phenols were first formed with sodium hydride in anhydrous dioxane and tetrahydrofuran. The sodium salts were then added sequentially, starting with the least reactive nucleophile, to the PNCl2 trimer in an aromatic solvent. Both two-substituent and three-substituent cyclophosphazenes were prepared in order to optimize fluid properties (Equation 14.4). Of the various multisubstituent fluids prepared in this study [25], those that exhibited the best combination of properties were in the range of a + c = 1–4 for fluid 16.

TABLE 14.2 Cyclic Phosphazene Esters: Fluid Evaluationa N3P3(O

)a(OCH2CF3)b(O

)C CH3

Value of a: Value of b: Value of c: Viscosity, cSt At 40◦ C At 100◦ C Pour point, ◦ C Density, g/mL Total acid number (TAN), mg KOH/g High pressure AIT, ◦ Ca Flash point, ◦ C Demulsibility (40/40 in 30 min) Hydrolytic stability Change in TAN, mg KOH/g H2 O acidity, mg/cm2 Copper weight loss, mg/cm2 Cu appearance Insolubles, wt % Elastomer compatibility, % volume swell Buna-Nb Viton, class 1c Viton, class 2c EPRd Paint compatibilitye

2.2 3.8 —

3.3 2.7 —

1.4 3.2 1.4

MIL-H-19457C target properties

22.8 3.5 30 1.5 0.02 332 250 Pass

54.0 4.7 16 1.5 0.02 337 NDb Pass

42.9 4.8 21 1.4 0.01 280 245 Pass

43–50 4.8 minimum 18 maximum 2.0 maximum 0.1 maximum 235 275 Pass

0.01 0.58 0.02 Dark tarnish 0

0.01 1.11 0.03 Corrosion 0

0.01 0.42 0.03 Light tarnish 0

0.2 maximum 5.0 maximum 0.3 maximum No corrosion 0.5 maximum

0.8 18.9 15.0 0.1 No change

7.9 11.4 12.2 ND No change

ND 7.2 −3.3 −3.3 No change

None ±5 ±5 ±5 None

a Abbreviations: AIT, antogeneous ignition temperature (ASTM G-72-82); EPR, ethylene-propylene

copolymer rubber; ND, not determined; TAN, total acid number. b MIL-P-25732. c MIL-R-83248. d MIL-G-22050. e MIL-P-24441.

Source: From Singler, R.E., T.N. Koulouris, A.J. Deome, H. Lee, D.A. Dunn, P.J. Kane, and M.J. Bieberich (1982). Army Sci. Conf. Proc., 3, 297 (AD A117298).

The most promising fluids are listed in Table 14.2, alongwith property data and target property requirements for MIL-H-19457C hydraulic fluid replacements. While all of the fluids prepared in this study were not acceptable in every respect, this work demonstrated that trisubstituted aryloxy/fluoroalkoxyphosphazenes exhibit the best range of properties for hydraulic fluid performance, compatibility, and fire resistance [25]. Under Navy contract [26,27], Borg-Warner pursued the development multisubstituent aryloxy/fluoroalkoxycyclophosphazenes, using a synthetic process that involved phase-transfer catalysis (PTC). Patents were also filed by Borg-Warner [9,28]. Using PTC, Carr reacted both the trifluoroethanol and the phenolic constituents, in stoichiometric quantities, directly with the PNCl2 trimer

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in a medium comprising water, a base, a water-immiscible solvent, and a phase-transfer catalyst. Significant reductions were made in the preparation and reaction times, while achieving high yields of phosphazene esters. The PTC bulk addition process, which involved premixing the phenols and trifluoroethanol with caustic before addition of trimer in contrast to a PTC sequential addition process, gave a broader distribution of components in the product mixture. Carr also determined that crude or partially purified trimer, which contained a small amount of tetramer, could be used in place of pure trimer to yield fluids with a broader distribution of products and lower pour points. Of the many phosphazenes prepared by Carr, the most promising fluid, 17, was prepared using PTC, bulk addition, and a mixture of alkylphenols (m- and

p-methylphenol), phenol, and trifluoroethanol.

[29] has disclosed a lubricating grease composition based on a similar cyclic aryloxyphosphazene. Extensive toxicity evaluations, including acute toxicity tests, inhalation, skin absorption kinetic studies, and 21day repeated inhalation and dermal exposure testing of the Navy’s cyclic phosphazene hydraulic fluid, 17, were conducted by the Toxicology Detachment of the Naval Medical Research Institute [30]. The most significant routes of exposure to ship board hydraulic fluids are dermal, due to spills or leaks, and aerosol inhalation from pressurized system leaks. Tests that simulated these routes of exposure showed no evidence of toxicity when test animals were exposed to the phosphazene fluid. Test data clearly indicated that the phosphazene fluid is poorly absorbed into the body by any route and appears to produce little or no effect when artificially introduced into the body. Such

N3 P3 (OCH2 CF3 )3.5 (OC6 H5 )1.25 (OC6 H4 –m–CH3 )0.87 (OC6 H4 –p–CH3 )0.38 17 The aryloxy/fluoroalkoxy substituent ratio was established at 2.5:3.5 to achieve the required viscosity and pour point. A copper corrosion inhibitor, tolytriazole, was formulated into the fluid at a concentration of 100 ppm. Fluid analysis indicated better fire resistance, thermal and hydrolytic stability, and paint compatibility when compared with MIL-H-19457 phosphate ester. The lowtemperature properties, elastomer compatibility, and wear characteristics were comparable. The property data are listed in Table 14.3 for the phosphazene ester fluid representative of a 30-gal pilot plant production [27]. Nibert

TABLE 14.3 Evaluation of Fluid 17a N3 P3 (OCH2 CF3 )3.5 (OC6 H5 )1.25 (OC6 H4 m-CH3 )0.87 (O C6 H4 -p-CH3 )0.38 Properties Viscosity, cSt At 40◦ C At 100◦ C Density, g/mL Pour point, ◦ C TAN, mg KOH/g Demulsmility (40/40) Hydrolytic stability Change in TAN, mg KOH/g H2 O layer, mg KOH Cu weight loss, mg/cm2 Cu appearance Insoluble, wt % Flash point, ◦ C High pressure AIT, ◦ C Foam tendency Bulk modulus, isothermal secant at 10,000 psig Four-ball wear, mm (wear scar diameter) Material compatibility % Volume swelling Viton, class 1b Viton, class 2b EPRc Paint compatibilityc

PN fluids

Fluid acceptance criteria

35.2 (50.7 cP) 4.2 (6.1 cP) 1.45 −21 0.02 5 minimum

43–50 (50–58 cP) 4.8 minimum (5.5 cP) 1.5 maximum −18 maximum 0.1 maximum 5 minimum

0.83 0.03 0.02 Slight tarnish Nil 288 285 Nil 266,000

0.2 maximum 5.0 maximum 0.3 maximum No corrosion 0.5 maximum 275 maximum 235 maximum Nil Report

0.7

0.5–1.0

8.7 6.6 −1.7 No change

±5 ±5 ±5 No change

a Abbreviations: AIT autogenous ignition temperature (ASTM G72-82); TAN, total add number. b MIL-R-83248. c MIL-G-22050. d MIL-P-24441.

Source: Carr, L.J. and S.H. Rose (1984). Phosphazene Base Hydraulic Fluid Development, Navy contract N00167-82-C-0168, Phase II, DTNSRDC/SME-CR-18-84.

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materials are therefore unlikely to have more than minimal health consequences if used in shipboard hydraulic system applications. The advances made in the state of the art by Singler and Carr encouraged the Navy to continue their pursuit of phosphazene hydraulic fluids. In 1986, the Ethyl Corporation produced 280 gallons of the Navy’s phosphazene ester hydraulic fluid, 17, using a sodium salt procedure developed by Kolich [31]. The product met the Navy’s physical and chemical property specifications. The cyclophosphazene fluids prepared by Carr and Kolich via two distinctively different synthetic procedure were characterized and compared using GC/MS, HPLC, and 1 H-NMR [32]. Although the aryloxy/fluoroalkoxy ratio for both fluids was approximately the same (2.5:3.5) and the isomeric components were identical, the amounts of these components differed. Both fluids met the Navy’s target property requirements. The Navy conducted a 1000 h performance test of the Ethyl-produced cyclotriphosphazene fluid using a highpressure, variable-displacement piston pump (Sundstrand series 27) at simulated shipboard operating temperature, pressure, and flow rate to evaluate the lubricating ability of the phosphazene fluid [33]. Measured dimensional changes of critical pump parts showed no significant wear or unusual wear patterns. The volumetric efficiency remained fairly constant throughout the test and was in the expected range, indicating no degradation to the pumping components. The torque efficiency dropped from 89 to 78% within 100 h, but remained constant for the remainder of the test. The results of the analysis of fluid samples drawn at 100 h intervals during the test indicated that there was no physical or chemical degradation [33]. Although the phosphazene hydraulic fluid showed considerable promise as a replacement for the current MIL-H-19457 fluid, the Navy curtailed the program because of the projected cost ($12/lb, $144/gallon). This high cost is due to the limited demand for phosphazene fluids and the high cost of the starting materials, trifluoroethanol and chlorotrimer. The Navy hydraulic fluid has, however, been made available to other groups for testing purposes. 14.3.3.2 Other applications — military and commercial Other groups have continued to explore phosphazene functional fluids in the United States, Japan, and Europe. These developments are related to the earlier work in this field. Work on aryloxyphosphazene fluids as high-temperature lubricants for advanced engine requirements and lubricants for magnetic recording disc media are described, followed by a brief survey of other phosphazene fluids and greases and a program to evaluate fire-resistant phosphazenes as halon replacements.

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14.3.3.2.1 High-temperature lubricants Researchers at Dow Chemical Company have synthesized a series of single- and mixed-substituent aryloxycyclotriphosphazenes intended for use as high temperature lubricants [34–36]. One application was for aircraft gas turbine engines [36]. Through careful choice of substituents, the Dow group prepared an aryloxycyclotriphosphazene, bis(4-fluorophenoxy)tetrakis(3-trifluoromethylphenoxy)-cyclotriphosphazene, 18, with optimal low temperature properties, oxidative stability, lubricity, and low toxicity. Good antifriction- antiwear performance was observed for 18; this compound was superior to polyphenylene ether fluids in four-ball wear tests. Representative properties are shown for 18 in Table 14.4. This fluid, designated X-1P by Dow Chemical

TABLE 14.4 Selected Properties of X-IP N3P3(O

F)2(O

)4 CF3

Viscositya At 25◦ C At 100◦ C Pour pointb Low temperature fluidityc Specific gravity at 25◦ C Vapor pressure At 60◦ C At 330◦ C Antoignition temperatured Oxidative stabilitye Volatilityf 10% weight loss 50% weight loss Lubricity behaviorg Wear scar diameter Coefficient of friction Lubricity enhancement of commercial petroleum fluidh wear scar diameter 0% X-IP 1% X-IP Acute toxicityi

1.401 Pa s (934 cSt) 0.0156 Pa s (11.2 cSt) −15◦ C −11◦ C 1.50 1.17 × 10−7 Pa (10−9 mmHg) 2.66 × 103 Pa (27 mmHg) >650◦ C 429◦ C 314◦ C 355◦ C 0.51 mm 0.03

1.28 mm 0.45 mm Low

a ASTM D-445-88. b ASTM D-97-87. c Pumpability temperature for viscosity of 20,000 cP. d ASTM E-659-78. e Pressure differential scanning calorimetry. f Thermogravimetric analysis.

g Four-ball method: 300◦ C, 10 lb load, 1200 rpm, 1 h, steel balls. h Pentaerythritol tetraester. Same conditions as in note g except

200◦ C, 120 lb load. i LD in rats, 2000 mg/kg; dermal LD in rabbits, 2000 mg/kg. 50 50

[36], also improved the friction and wear properties of a commercial pentaerythritol tetraester (PET) fluid. N3 P3 (OC6 H4 –4–F)2 (OC6 H4 –3–CF3 )4 18 The chemical and tribological behavior of cyclophosphazene lubricants, including X-1P, on metal surfaces has also been studied by several other groups [37–40]. Investigations have included surface chemistry and friction behavior using x-ray photoelectron spectroscopy (XPS) and tribo-evaluation of several high-temperature fluids. Phosphazene, X-1P, gave excellent overall performance compared to several commercial fluids [38] and has also been used to develop an improved method to lubricate metal workpieces at elevated temperatures [40]. The oxidative stability and degradation mechanism of X-1P has been studied at elevated temperatures [41]. The oxidative stability of phosphazene fluids can be improved by incorporating inorganic metal salts, phosphines, or phosphine oxide into the fluid composition [42,43]. 14.3.3.2.2 Lubricants for magnetic recording disk media Cyclic aryloxyphosphazenes are being developed as advanced lubricants for both rigid and flexible thin film magnetic media [44–48]. Contact Start-Stop (CSS) test results with X-1P show that these lubricants have similar tribological performance to a standard perfluoropolyalkyl ether (PFPE), Fromblin Z-DOL, as a topical lubricant on carbon-overcoated thin film rigid disks under ambient conditions. However, X-1P significantly outperformed PFPE in CSS testing under hot/wet (30◦ C, 80% RH) conditions, thus demonstrating the excellent hydrolytic stability of X-1P in the presence of a typical slider material. Dow has proceeded with plans to commercialize X-1P as a lubricant on magnetic hard disks in conjunction with PFPE fluids [49]. 14.3.3.2.3 Other applications Other fluoroalkoxy, aryloxy, and mixed aryloxy– fluoroalkoxy cyclophosphazene fluids are under investigation. Applications include rotary pump lubricants, transmission oils, hydraulic fluids, electrical insulating media, electroviscous/electrorheological fluids, magnetic recording media, liquid cores for optical waveguides, chemical analysis, and as stabilizers for oils and greases [50–71]. Otsuka Chemical Company has introduced a series of fluoro-alkoxyphosphazene fluids, Phospharol NF fluids [50] that exhibit excellent lubricating ability, oxidative stability, chemical compatibility with plastics (particularly thermoplastics), and fire resistance [50–56]. Two examples, 19 and 20, have properties similar to that of the fluids described in Table 14.1. Phospharol fluids were developed for uses including electronic devices containing

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plastic components and in the manufacture of semiconductors. Fluid 19 was reported to be stable in the presence of AlCl3 [51,52]. Because of its low vapor pressure and fire resistance, 20 is claimed to be suitable for use as vacuum pump oil [53]. Phospharol fluids werealso reported as comprising the liquid phase of some electrorheological fluid compositions [55,56]. [NP(OCH2 (CF2 )4 H)2 ]3 19 [NP(OCH2 CF2 CF3 )(OCH2 (CF2 )4 H)]3 20 A different composition for a lubricating thin film for magnetic recording media is based on a cyclic phosphazene with perfluoro-polyether side chains [59]. The side chains in structure 21 have an average molecular weight of 2500, n = 14–15. Compositions based on 21 and similar perfluoroetheroxy-substituted phosphazenes were reported to have good lubricating properties when compared to conventional PFPE lubricants in these applications [59]. [NP(OCH2 C2 F4 (OC3 F6 )n F)2 ]3 21 Klobucar and Kolich [65] report on a series of mixedsubstituent cyclic phosphazene fluids with fluoroalkoxy, alkoxyalkyloxy, and alkoxy side chains [65]. Trisubstituted fluid 22 had a pour point of −42◦ C, a density of 1.391 g/mL, and a flash point >200◦ C. The viscosity range for 22 was similar to fluid 12 in Table 14.1. The incorporation of nonfluorinated side chains into the phosphazene structure has the potential of reducing the cost while maintaining the desired properties in the fluid. N3 P3 (OCH2 CF3 )3 (OC2 H4 OCH3 )1.6 (OC3 H6 OCH3 )1.4 22 The exceptional thermal stability of fluoroalkoxyphosphazenes has also found applications for chemical analysis. Ultramark® 1621 [68], a commercially available fluoroalkoxy cyclophosphazene, N3 P3 (OR)6 , R = −CH2 (CF2 CF2 )x H, x = 1–3, is a useful calibration standard/reference compound for mass spectrometry in the range of m/e 900 to 2200 [69]. Stabilizers for oils and greases Cyclic phosphazenes, substituted with aryloxy groups and perfluoropolyetheroxy chains, have been developed as stabilizers for oils and greases based on perfluoropolyethers [70]. The phosphazenes, such as 23, Rf = perfluoropolyetheroxy–, are claimed to inhibit the degradation process affecting the perfluoropolyethers when these are subjected to high temperatures in an oxidizing atmosphere and in the presence of metals, such as aluminum, titanium, vanadium and their alloys, or steels. Dekura [71] has prepared liquid and solid (greaselike) fluorine-containing phosphonitrile amides, 24, that exhibit

favorable lubricating ability, enhanced adsorption on metal surfaces, corrosion inhibition, and fire resistance. These fluorine-substituted aminophosphazenes can be used on their own as synthetic lubricants, or as lubricity additives in other oils. N3 P3 (OC6 H5 )3 (OCH2 Rf )3 23

[NP(NHRf )(NHRf )]3 24

The viscosity and lubricating properties of compounds having formula 24 are adjusted to suit different applications by selection of Rf and Rf radicals. For example, if Rf and Rf are fluoroalkylcarbonyl or fluoroalkylalkylcarbonyl radicals, the compounds tend to be solid with superior load-carrying capacity. In contrast, lower molecular weight products exhibit good low-temperature properties but poor load-carrying capacity. 14.3.3.2.4 Fire-resistant fluids — halon replacements Cyclic phosphazenes are being investigated as Halon substitutes at the New Mexico Engineering Research Institute [72,73]. The goals of the overall effort are to develop new chemical compounds that are highly efficient fire suppressants, are environmentally and toxicologically benign, have the same performance characteristics as Halon 1211, and are compatible with existing fire extinguishing equipment and aircraft materials. Fire extinguishing studies were conducted using both cup-burner and Laboratory Scale Discharge Extinguishing (LSDE) testing. Cup-burner testing has shown that a number of phosphazenes have extinguishing concentrations considerably lower than Halon 1211 or Halon 1301; such testing indicates a significant fire suppression potential for cyclic phosphazenes. Further testing and evaluation of cyclic phosphazenes, including some of the fluids cited in this chapter, is planned under this program [73].

14.4 CONCLUSIONS When one considers the rich chemistry of the phosphazenes, it is somewhat surprising that there are only a few phosphazene fluids that have reached the commercial stage [48,50,68]. Phosphazenes are inherently fire resistant, and they have other properties that are necessary for high-performance applications. The main factor that has discouraged extensive development of phosphazene fluids (and polyphosphazenes) is their high cost relative to commercial materials. Fluid 17, which was developed for the Navy, has been made available to other groups to evaluate for other applications [74]. The chemistry of phosphazene fluids and polyphosphazene is closely related, and large-scale development in one of these areas could be the stimulus for commercial development of all phosphazene technology.

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ACKNOWLEDGMENTS The authors would like to acknowledge Mary Jo Bieberich, Naval Surface Warfare Center; Ted Morgan, The Dow Chemical Company; Chris Allen, University of Vermont; Robert Tapscott, University of New Mexico, for assistance during the preparation of this manuscript.

REFERENCES 1. Wisian-Neilson, P., H.R. Allcock, and K.J. Wynne (1994). Inorganic and Organometallic Polymers II: Advanced Materials and Intermediates, ACS Symposium Series no. 572, American Chemical Society, Washington, D.C. 2. Allen, C.W. (1995). “Phosphazenes” in Organophosphorus Chemistry, Allen, D.W. and B.J. Walker, Eds., Royal Society of Chemistry, London, Chapter 7. 3. Allcock, H.R. (1972). Phosphorus–Nitrogen Compounds, Academic Press, New York, Chap. 4. 4. Nichols, G.M. (1962). “Synthesis of Inorganic High Temperature Fluids,” F33 616 7158, February, reported by C.D. Schmulbach in Progress in Inorganic Chemistry, F.A. Cotton, Ed., Vol. IV, p. 275, Wiley Interscience, New York. 5. Moran, E.F. (1968). J. Inorg. Nucl. Chem., 30, 1405; contract AF 657 10693 (AD 478112L), 1966. 6. Murch, R.M. (1969). “Thermally Stable Hydraulic Fluids,” AFML-TR-68-337 (AD 849 271). 7. Allcock, H.R. (1972). Phosphorus–Nitrogen Compounds, Academic Press, New York, Chaps. 6 and 7. 8. Allcock, H.R. (1972). Phosphorus–Nitrogen Compounds, Academic Press, New York, Chap. 6. 9. Carr, L.J. and G.M. Nichols (1986). U.S. Patent 4,600,791. 10. Wang, M.L. and H.S. Wu (1990). Ind. Eng. Chem. Res., 29, 2137. 11. Allcock, H.R. (1972). Phosphorus–Nitrogen Compounds, Academic Press, New York, Chap. 5. 12. Allcock, H.R. (1972). Phosphorus–Nitrogen Compounds, Academic Press, New York, Chap. 13. 13. Lipkin, D. (1940). U.S. Patent 2,192,921. 14. Nichols, G.M. (1966). U.S. Patent 3,234,304. 15. Nichols, G.M. (1967). U.S. Patent 3,316,330. 16. Kober, E.H., H.F. Lederle, and G.F. Ottmann (1966). U.S. Patent 3,291,865. 17. Kober, E.H., H.F. Lederle, and G.F. Ottmann (1967). U.S. Patent 3,304,350. 18. Drysdale, J.J., R.E. Le Bleu, and J.H. Fassnacht (1965). U.S. Patent 3,201,445. 19. Kober, E., H. Lederle, and G. Ottmann (1963). ASLE Trans., 7, 389; U.S. Navy Contract NObs-86482, AD 432,367. 20. Kober, E., H. Lederle, and G. Ottmann (1966). J. Chem. Eng. Data, 11, 221; U.S. Navy Contract NObs-90092, AD 608,144 (1964). 21. Military specification MIL-H-19457A (Ships) (1963). Superceded by MIL-H-19457D (Ships) (1989). 22. ASTM Standards (1967). Designation D-341-43, Viscosity Temperature Charts for Liquid Petroleum Products, American Society for Testing Materials, Philadelphia. Superceded by ASTM D-341-87 (1987).

23. Singler, R.E. (1976). Potential of Phosphazenes as Hydraulic Fluids, Conference on Hydraulic Fluids, NASA Ames Research Center, NASA TM X-73, p. 142. 24. Singler, R.E., T.N. Koulouris, A.J. Deome, H. Lee, D.A. Dunn, P.J. Kane, and M.J. Bieberich (1982). Preparation and Properties of Phosphazene Fire Resistant Fluids, Army Sci. Conf. Proc., 3, 297 (AD A117298). 25. Singler, R.E., A.J. Deome, D.A. Dunn, and M.J. Bieberich (1986). Ind. Eng. Chem. Prod. Res. Dev., 25, 46. 26. Carr, L.J., G.M. Nichols, and S.H. Rose (1983). Phosphazene Base Hydraulic Fluid Development, Navy contract N0016782-C-0168, Phase I, DTNSRDC/SME-CR-03-84. 27. Carr, L.J. and S.H. Rose (1984). Phosphazene Base Hydraulic Fluid Development, Navy contract N00167-82C-0168, Phase II, DTNSRDC/SME-CR-18-84. 28. Carr, L.J., G.M. Nichols, and S.H. Rose (1986). U.S. Patent 4,601,843. 29. Nibert, R.K. (1988). U.S. Patent Application 851,635; Chem. Abstr., 108, 8693. 30. Kinkhead, E., E. Kimmel, H. Wall, and J. Grabau (1990). Am. Ind. Hyg. Assoc. J., 51, 583. 31. Kolich, C.H. and W.D. Klobucar (1987). U.S. Patent 4,698,439. 32. Deome, A.J. and D.A. Bulpett (1986). Thermal Decomposition Product Analysis of Phosphazene and Phosphate Ester Fluids, U.S. Army Materials Technology Laboratory TR 86-35. 33. Barnes, R. (1988). Navy Test of Cyclotriphosphazene Hydraulic Oil in a 27 Series Pump. Sundstrand Sauer Letter Report to David Taylor Research Center. 34. Kar, K.K. and C.E. Pawloski (1991). U.S. Patent 5,015,405 35. Kar, K.K. and C.E. Pawloski (1992). U.S. Patent 5,099,055 36. Nader B.S., K.K. Kar, T.A. Morgan, C.E. Pawloski, and W.L. Dilling (1992). “Development and Tribological Properties of Cyclophosphazene High-Temperature Lubricants for Aircraft Gas Turbine Engines,” Tribol. Trans., 35, 37–44. 37. Dekoven B. M. and G.E. Mitchell (1992). “Chemical and Tribological Behavior of Thin Organic Lubricant Films on Surfaces,” ACS Symp. Ser., 485, 15–42. 38. Chao, K.K. and C.S. Saba (1995). “Tribo-Evaluation of High Temperature Candidate Fluids in a Sliding TBOD Bench Tester,” Tribol. Trans., 38, 63. 39. Choa S.H., K.C. Ludema, G.E. Potter, B.M. Dekoven, T.A. Morgan, and K.K. Kar (1995). “A Model for the Boundary Film Formation and Tribological Behavior of a Phosphazene Lubricant on Steel,” Tribol. Trans., 38, 757–768. 40. Graham, E.E. (1996). U.S. Patent 5,493,886. 41. Keller, M.A. and C.S. Saba (1996). Anal. Chem., 68, 3489–3492. 42. Nader, B.S. and M.N. Inbaskaran (1993). U.S. Patent 5,219,477. 43. Nader B.S. (1993). U.S. Patent 5,194,652. 44. Kar, K.K., C.E. Pawloski, and T.A. Morgan (1993). U.S. Patent 5,230,964. 45. Perrettie, D.J., W.D. Johnson, T.A. Morgan, K.K. Kar, G.E. Potter, B.M. DeKoven, J. Chao, Y.C. Lee, C. Gao, and Russak (1995). ISPS-vol. 1, Advances in Information

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15

Dialkyl Carbonates Leslie R. Rudnick CONTENTS 15.1 15.2 15.3 15.4

Introduction Historical Perspective Commercial Production Chemistry 15.4.1 Synthetic Methods 15.4.2 Synthesis by Transesterification 15.4.3 Current Commercial Routes 15.5 Production of Dimethyl Carbonate 15.5.1 Synthesis from Phosgene 15.5.2 Synthesis from Carbon Monoxide 15.5.3 Synthesis from Carbon Dioxide 15.6 Properties and Performance Characteristics 15.6.1 Physical Properties 15.6.2 Chemical Properties 15.6.3 Performance Characteristics 15.6.3.1 Tribology 15.6.3.2 Viscometrics 15.6.3.3 Oxidation and Thermal Stability 15.6.3.4 Elastomer Compatibility 15.6.3.5 Wear Protection 15.6.3.6 Sludge Protection 15.7 Toxicology, Biodegradability, and Handling Properties 15.7.1 Toxicology 15.7.2 Biodegradability 15.7.3 Handling Acknowledgments References

15.1 INTRODUCTION Dialkyl carbonates represent a class of functionalized synthetic fluids generally obtained by transesterification of dimethyl carbonate (DMC). The carbonate moiety represents the central core of either a symmetrical or asymmetrical compound depending on whether one or two alcohols are used. The physical properties and chemical reactivity of the dialkyl carbonates strongly depend on the size and shape of the alcohols. Alcohols can be chosen from a wide variety of natural and synthetic alcohols. Dialkyl carbonates have been used in various applications, both as lubricant base fluids and performance fluid

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components, due to their physical and chemical properties, performance characteristics, low toxicity, and favorable economics. Recently, the parent compound, DMC, has been reported to provide benefit as a gasoline additive and as a component in hydraulic fluids [1]. These authors report that the dialkyl carbonates are similar to conventional esters in terms of performance, with improved seal compatibility, the absence of acidic components on thermo-oxidative degradation and lower toxicity than esters [1]. Disubstituted carbonates containing aromatic and aliphatic structural components havebeen proposed as

lubricants for use with the newer refrigerants of the hydrofluorocarbon (HFC) type [2]. The aromatic portion of the structure provides good lubricity while the aliphatic portion provides stability. The quantity of dialkyl carbonates as base fluid in finished products ranges from 5 to 30% in automotive products and from a few percent to 100% in industrial applications.

15.2 HISTORICAL PERSPECTIVE Dialkyl carbonates have been reported to be used in lubricant applications since the early 1940s. In a 1941 patent, Fincke and Bartlett reported the use of small amount of carbonates (1 to 5%), mostly from low MW alcohols, to enhance the spreading and penetrability of mineral oilbased lubricants [3]. In 1945, Knutson and Graves reported on the use of minor proportion of dialkyl carbonates in mineral oil-based formulations to improve the loadcarrying capacity of the lubricant. Alkyl groups employed ranged from ethyl to lauryl alcohol and included the use of aromatic alcohols [4]. Dialkyl carbonates of alcohols C1–10 having low pour points and high viscosity index, were described by Mikeska and Eby in 1953 [5]. Bartlett described the use of polymers derived from monomers of carbonic ester as pour point depressants [6,7]. In 1956, Cottle et al. reported on the use of carbonates of alcohols C10–20 , which were obtained from oxosynthesis of branched olefins [8]. In 1982, Koch and Romano claimed that lubricant formulations containing dialkyl carbonates were obtained by transesterification of DMC with high molecular weight alcohols. The resulting products exhibit improved characteristics and performance [9]. A 1989 patent claims lubricant formulations containing organic carbonates as improved lubricants for the cold steel rolling [10]. Also in a 1990 patent, Fisicaro and Gerbaz claimed that lubricant formulations containing dialkyl carbonates were obtained by transesterification of DMC with high molecular weight branched alcohols. These alcohols were obtained by oxosynthesis of linear olefins, followed by cryogenic separation of the linear fraction [11]. The first commercial applications of dialkyl carbonates as lubricant components was in 1987, when AgipPetroli introduced dialkyl carbonates as a new synthetic base fluid in the formulation of semisynthetic, gasoline engine oils [12]. AgipPetroli extended the application of dialkyl carbonates to the formulation of other types of automotive lubricants, diesel and SHPD engine oils, and gear and 2-stroke oils. Dialkyl carbonates were also introduced in the field of industrial lubricants in the formulation of both molding and rolling oils.

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15.3 COMMERCIAL PRODUCTION The first commercial production of carbonates suitable for application in the lubricant field, was started in 1985 by Enichem Synthesis (Italy), with a capacity of 3000 t/yr. Starting raw materials were DMC and a mixture of synthetic alcohols in the C12–16 range. The process involves three main steps: • Transesterification of dimethyl carbonate • Purification of dialkyl carbonates • Methanol recovery

Currently, dialkyl carbonates are reported to be marketed by Polimeri Europa in Italy, and by Baoding Chemical Company, Shandong Province and Washong Chemical Company, Shanghai, China.

15.4 CHEMISTRY Dialkyl carbonates consist of a polar carbonate group with the carbon and three oxygen atoms in the same plane, and two alkyl chains bonded to two oxygen atoms. These alkyl groups are free to rotate about the axis of the carbon–oxygen bond: O O O

e.g., dimethyl carbonate. The chemical structure of the carbonate group and the pendant alkyl groups collectively determine the physical and chemical properties, and the tribological performance of dialkyl carbonates. Both the physical and chemical properties affect the performance of these materials when they are used as lubricant fluids. This includes the polarity of the dialkyl carbonate, which is affected by the ratio of carbon in the pendant alkyl groups to the carbonate functional group, and the reactivity of the pendant alkyl groups, which depend on the branching and degree of unsaturation present in these groups.

15.4.1 Synthetic Methods Dialkyl carbonates are diesters of carbonic acid and are derived from the condensation of carbonic acid with various alcohols: O O HO

ROH OH

–H20

O H

O O R

ROH –H20

O R

O R

Because carbonic acid has poor chemical stability under conditions necessary for the condensation of alcohols, this synthetic methodology is not practical. Furthermore, the half-ester formed in the first condensation step is also very unstable and cannot undergo the further condensation reaction necessary to prepare the dialkyl carbonate. Fortunately, alternative methods are available for the synthesis of dialkyl carbonates. One approach is that carboalkoxides can be directly obtained by reaction of carbon dioxide and the inorganic alcoholate in an alcohol solution:

From phosgene O

O

O

O

Me

R

+ R X 1

O

O

R1

R

–MeX

This reaction takes place in two separate steps:

O

O

O

(NaOH)

O

CO2 + ROMe

2 ROH

+

ROH

O Cl

Me

–2HCl

Cl

R

and subsequently converted to dialkyl carbonates. Carboalkoxides are quite unstable and can be readily hydrolyzed to inorganic carbonate and alcohol. Other laboratory and industrial routes have been investigated and developed for the synthesis of dialkyl carbonates having a wide range of physical and chemical properties and performance characteristics, starting from different raw materials. From a lubrication point of view, viscosity and oxidative stability are the main target specifications. The polarity of a dialkyl carbonate is dictated by the carbonate group, and stability is related to the branching and unsaturation present in the alcohol derived groups. This is discussed in greater detail in a later section. More feasible routes to dialkyl carbonates are described below:

O

O

R

R

This sequence provides asymmetrical diesters without any further separation if the starting reactant is an alkyl chloroformate instead of phosgene (Step 2) [13,14]. To recover high purity chlorine-free carbonates, the reaction product can be distilled in the presence of inorganic carbonates. From carbon dioxide With an adequate hydrophilic system as a catalyst, that is, ethylene oxide [15] or zeolites [16], the reaction proceeds as follows: O O

(NaOH) +

From alkyl halides

ROH –HCl

Cl

Cl

O

Cl

O

2

O Me

R O +

H2O

–CO2

Me2CO3 + 2ROH

O

O

R Cl

From carboalkoxides

R

O AgCO3 + 2C2H5I

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O

+

R1OH

(NaOH) –HCl

O

O

R1

R

O

O

From urea

C2H5

C2H5

Dialkyl carbonates can be prepared using high-boiling alcohols, at high temperature (>200◦ C) [17–19].

O

CO2

+

2ROH

agent:

catalyst

O O

–H2O

O

O O

R

R

–CH3OH

+ 2 ROH

O

O

O

R

R

From carbon monoxide Oxidation in the presence of complex palladium [20] or copper catalyst [21,22] provides the desired dialkyl carbonates. O

Me

15.5.1 Synthesis from Phosgene

O + 2ROH

H2N

Me

NH2

catalyst

O O

–2NH2

O

O + 2 CH3OH R

R

Cl

–HCl

15.4.2 Synthesis by Transesterification O 2 ROH +

CO + 12 O2

catalyst –H2O

O

O

R

R

In this equilibrium reaction, the more nucleophilic the alcohol, the easier the substitution with a less nucleophilic alcohol. Because of this, lower molecular weight alcohols are substituted by higher molecular weight alcohols, and aryl alcohols are substituted by aliphatic alcohols. Transesterification of asymmetric carbonates more easily leads to the substitution of the lower molecular weight alcohol.

15.4.3 Current Commercial Routes The most effective commercial route for the production of higher dialkyl carbonates is the transesterification of DMC consequently, the most important step of commercial routes is the synthesis of DMC. O

O

R

R

O

Me

Me

This synthesis route has been widely applied in the past to industrial scale production as the sole way to produce DMC. As in many transesterification syntheses, quantitative yields (>99%) are obtained by reaction of the ester with excess alcohol. The excess alcohol is subsequently recovered by distillation and reused. It is likely that environmental considerations and a generally more “green” approach to synthetic processes will replace this approach. The major problem with this process is in the handling and disposal of phosgene and chlorine compounds.

15.5.2 Synthesis from Carbon Monoxide An important industrial route to produce DMC begins with methanol and carbon monoxide, in presence of oxygen and a catalytic system based on Cu+ /Cu++ [23]. The reaction takes place in two separate steps: Step 1 (oxidation) OCH3 2 CH3OH + 2 CuCl + 12 O2

2 Cu –H2O

O O + 2 R1OH

O

Cl

O

O

R1

R1

+ 2ROH

Cl

Step 2 (reduction) O OCH3 Cu

15.5 PRODUCTION OF DIMETHYL CARBONATE There are three commercial routes for the production of DMC, all involving methanol as theirmethylating

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+ Cl

CO

O

O

Me

Me

–2 CuCl

The following reaction scheme summarizes the overall process:

Unsaturated dialkyl carbonates are widely used for the production of polycarbonates; however, these are beyond the scope of this chapter and will not be discussed.

O

2 CH3OH + 2 CuCl + 12 O2

15.6 PROPERTIES AND PERFORMANCE CHARACTERISTICS

catalyst O

O

Me

Me

–H2O

This synthetic route is increasing in importance because it utilizes readily available starting materials. The process is relatively economical and is generally “green” when compared to reactions involving phosgene.

15.5.3 Synthesis from Carbon Dioxide O O

catalyst

CO2 +

O

O

–H2O R R

By direct reaction of carbon dioxide and ethylene oxide, or propylene oxide, the corresponding cyclic fivemember carbonates are easily obtained in high yield. O HO O

O

4-hydroxy-1,3 dioxolane-2-one

R=H, CH3 In a second step, the cyclic carbonate can be transesterified with methanol, in a standard transesterification plant, to produce DMC. Synthesis from ethylene oxide is not economically competitive with that from carbon monoxide, described above [24] and has been used in the past by DOW Chemical in an industrial scale plant. The synthetic route from propylene oxide has not been equally investigated. It is likely to foresee that it could exhibit valuable economics related to the cost of raw materials (propylene oxide), and due to the value of the coproducts (propylene glycol). Dialkyl carbonates of high molecular weight alcohols can be obtained directly by transesterification of the cyclic carbonates. This route eliminates the need for DMC as an intermediate and can result in better overall production economics.

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The basic structure of the dialkyl carbonate molecule, the carbonic group, provides the polarity to the molecule. As a lubricant, this functional group is responsible for several important functions. It provides the potential for interaction with the tribological surface, which increases its tendency to remain on a metal surface relative to a nonpolar lubricant, such as mineral oils, polyalphaolefins (PAOs) and poly internal olefins. The polar functional group also provides an opportunity to improve the solubility of polar additives in a formulated lubricant. Most of the physical properties, such as viscosity, pour point, flash point, and fire point are a function of the size and shape of the alkyl groups. The isobaric vapor–liquid equilibria for alkyl carbonates and alcohols have been experimentally determined [25]. The isothermal vapor– liquid equilibria of dimethyl and diethyl carbonates with a variety of materials have been studied [26–30]. The thermal and oxidative stability are a function of the size and shape of the alkyl groups and also depend strongly on whether the alkyl groups are unsaturated. Generally unsaturated alkyl groups will lower the thermal and oxidative stability of a molecular structure. Tables 15.1 and 15.2 show some of the physical property data of several low and high molecular weight alkyl carbonates, respectively. From this data the effect of structure and molecular weight on viscosity and other properties can be observed. The viscosity of dialkyl carbonates produced by transesterification generally range from values less than 1 to 40 cSt at 100◦ C. Alcohols that impart this viscosity range to dialkyl carbonates are available from among the following structures: • Natural, linear, short chain (C6–8 ) and long chain

(C12–18 )

• Synthetic, branched, and long chain (C12–18 ) • Polyols, synthetic: trimethylol propane

(TMP), neopentylglycol (NPG), and neopentaerythritol (NPE)

This viscosity range can be expanded by suitable choice of alkyl group functionality and appropriate synthetic methodology. Several current commercial products in addition to DMC include diisooctyl carbonate (DIOC) and dibutyl carbonate (DBC). The physical and performance properties of these materials can be found in Tables 15.3 and 15.4, respectively. A comparison of the thermal stability of these materials is shown in Figure 15.1 [31]. This data shows that deposit formation is related to the molecular weight of the dialkyl carbonate.

TABLE 15.1 Physical Properties of Low Molecular Weight Dialkyl Carbonates

Carbonate Dimethyl Diethyl Di-n-propyl Di-isopropyl Diallyl Di-n-butyl Di-2-ethylhexyl Allyldiglycol Ethylene Propylene Methyl-isopropyl Methyl-n-propyl Methyl-n-butyl

a d20 4

Bp (◦ C)

Mp (◦ C)

Flash point (◦ C)b

1.073 0.976 0.941 0.920 0.994 0.924 0.897 1.143 1.322 (39◦ C) 1.207 0.969 0.983 0.964

90.2 125.8 166 147 — 208 100 (0.5 mm) — 248 242 120 131 162

4 −43 −40 −40 — −40 < −50 −4 39 −49 < −40 < −40 < −40

14 (c) 33 (c) 62 (c) 46 (c) — 92 (c) — 177 (o) — — 33 (c) 37 (c) 54 (c)

c n20 D

Viscosity at 25◦ C (cP)

CAS registration number

1.3687 1.3843 1.4022 — 1.4280 1.4099 1.1352 1.4503 1.4158 1.4189 — — —

0.66420 (at 20◦ C) 0.86815 (at 15◦ C) 1.27 1.14 — 1.72 4.4 cSt (40 C) 9.0 — — 0.77 0.84 1.01

616.38.6 105.58.8 623.96.1 6482.34.4 15022.08.9 542.52.9 14858.73.2 142.22.3 9649.1 108.32.7 — — —

a d20 density at 20◦ C referred to the density of water at 4◦ C 4 b data for closed-cup (c), and open-cup (o) test procedures. c n20 refractive index at 20◦ C of D line of sodium. D

TABLE 15.2 Physical Properties of High Molecular Weight Dialkyl Carbonates

Carbonate iso-C10 n-C12 iso-C13 oxo C12–15 oxo C12–15 /oxo i-C13 (1:1) oxo C14–15 branched iso-C8 /C6 diol oxo C12–15 /C4 diol (9:1) iso-C18 iso-C8 /TMP

Kinematic viscosity, cSt, at 100◦ C

Kinematic viscosity, cSt, at 40◦ C

Viscosity index

Pour point, ◦ C

NOACK volatility, %

2.5 3.4 3.9 3.8 3.9 4.1 4.7 5.2 11.0 12.4

9.4 12.2 19.8 15.7 17.2 18 24.5 23.9 180 151

86 169 81 144 115 126 110 153 <0 62

−57 +5 −42 +5 −21 −36 −34 0 −18 −30

— — — 15 16 12 — 10.8 — —

A higher molecular weight carbonate, C14–15 dialkyl carbonate is reported to have lubricant application in automotive and industrial engines and equipment, respectively. C14–15 dialkyl carbonate can be employed in gasoline and diesel engines and in gearbox applications [31]. Advantages of using C14–15 dialkyl carbonate include better engine protection, which results in longer engine life, extended drain periods are reported as are better cold starting performance [31]. In industrial applications these fluids serve in both compressors and metalworking fluids and in the textile industry. These materials are reported to provide better

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lubricity performance resulting in lower maintenance. The C14–15 dialkyl carbonate is also reported to have high biodegradability [31]. For metalworking in the aluminum industry, the use of C14–15 dialkyl carbonate results in less oil staining, less carbon residue, and a more uniform gloss sheet. This cleaner surface finishing results in higher productivity and application of C14–15 dialkyl carbonate uses less oil. Application of this material in the steel industry also results in a clean surface sheet, and low oil consumption resulting in overall high productivity. The fluids used form stable microemulsions. Application in the textile industry

is in the area of biodegradable softening agents for finishing without the need for silicon [32]. In general, the longer chain dialkyl carbonate provides a good viscosity index, good hydrolytic stability, and no acidic compounds formed due to thermooxidative degradation. From a performance point of view, the C14–15 dialkyl carbonate provides high lubricity, high biodegradability, and excellent antiwear performance. C14–15 dialkyl carbonate is completely compatible with other synthetic base fluids and with mineral oil base fluids [31].

TABLE 15.3 Physical Properties of Diisooctyl Carbonate Viscosity, cSt, at 40◦ C Viscosity, cSt, at 100◦ C Pour point, ◦ C Density, 25◦ C, g/L Flash point, ◦ C (COC) Boiling point, ◦ C (10 mm Hg) Biodegradability, MITI mod. Source: Personal Polimerieuropa.

4.45 1.512 −40 0.89 140 173 31% after 28 days

Communication

from

Carlo

Zecchini

TABLE 15.4 Physical Properties of Dibutyl Carbonate Boiling point, ◦ C Density at 20◦ C N20 D Molecular weight CAS Number

15.6.1 Physical Properties

207.5 0.9238 1.4117 174.237 542-52-9

All the industrially important dialkyl carbonates are colorless liquids and with only a few exceptions, a specific gravity less than one. Dialkyl carbonates generally possess high boiling points and some exhibit a pleasant odor. Residue after heating, 5 h/60 c

500

467

Numbers refer to molecular weight of dialkyl carbonate

450 400 Molecular weight

from

C14–15 dialkyl carbonate is a pure, odorless, colorless nonoily emollient that is stable to oxidation. Because of these features, it has also found application in the cosmetic industry having good feel and spreadability and compatibility with other oils and pigments. C14–15 dialkyl carbonate is able to form stable water in oil and oil in water emulsions. Its biodegradability makes it environment friendly. The physical properties for C14–15 dialkyl carbonate are shown in Table 15.5. Recently, oleochemical carbonates have been reviewed [33,34]. Glycerol carbonate is also referred to as glycerol cyclic 1,2-carbonate and 4-hydroxy-1,3 dioxolane-2-one and is a dialkyl carbonate that is formed by reaction of two of the three hydroxy groups of glycerol. The structure shown below has a free hydroxy group that contributes to its polarity and properties. There is the potential to modify the viscosity and polarity of the glycerol carbonate moiety by adding, for example, aliphatic or aromatic groups to the free hydroxyl group. For the aliphatic case, this would provide a long chain structure that is similar to fatty acids or fatty alcohols, which are known to impart improved tribological properties in lubricants. The main applications for glycerol carbonate are in moisturizers in cosmetic creams and in hair and skin conditioners. Although not generally considered lubricant applications, the lubricity imparted by these materials contributes to the overall performance [33,34]. The physical properties of glycerol carbonate can be found on Table 15.6.

350 300

286

250 200 174

150 100 50 0 0

20

40

60 Residue, %

FIGURE 15.1 Thermal stability of some dialkyl carbonates

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80

100

120

TABLE 15.5 Physical Properties of C14–15 Dialkyl Carbonate Viscosity, cSt 40◦ C Specific gravity Pour point, ◦ C Volatility Volatility, NOACK DIN 51581 CAS number ELINCS number INCI number CTFA number Source: Personal Polimerieuropa.

Communication

15–21 0.869–0.900 −40 5% at 242◦ C, 20% at 245◦ C, 40% at 250◦ C 16% 164907-75-9 401-240-2 C14-15 dialkyl carbonate 2541 from

Carle

Zecchini

from

In water, only the cyclic five-member carbonates (ethylene and propylene) present good solubility; other low molecular weight carbonates (dimethyl and diethyl) have very limited solubility; high molecular weight carbonates are essentially insoluble. Lower dialkyl carbonates generally form azeotropic mixtures with water and organic solvents. This aspect increases the number of operations related to the production of dialkyl carbonates via transesterification. Physical properties of the most important dialkyl carbonates are listed in Table 15.1 (low molecular weight carbonates) and in Table 15.2 (high molecular weight carbonates) and for other specific dialkyl carbonates in Tables 15.3 to 15.6.

15.6.2 Chemical Properties Dialkyl carbonates also represent an important class of starting materials and intermediates in organic chemistry because of their ability to undergo the following reactions:

TABLE 15.6 Properties of Glycerol Carbonate Viscosity, cP 100◦ C Viscosity, cP 38◦ C Density at 20◦ C, g/L Flash point, ◦ C Boiling point, ◦ C (0.1 mm Hg) Molecular weight CAS number EINECS number

3 26 1.4 212 125 to 135 118 931-40-8 213-235-0

Source: Personal Communication from Carle Zecchini from Polimerieuropa.

Notably, the physical state depends on the type and molecular weight of alcohols: high molecular weight (>C10 ) linear alcohols easily lead to solid products. Also low molecular weight carbonates with high symmetrical structure, for example, DMC and ethylene carbonate, exhibit melting points above 0◦ C. Dialkyl carbonates are generally soluble in organic solvents, mostly in polar solvents (alcohols, ethers, ketones, esters, etc.). Calculations have been made to determine the pressure dependence of dialkyl carbonates (DMC and diethyl carbonate) on density, isobaric thermal expansivity, and isothermal compressibility [1]. The dynamic viscosities and densities of dimethyl and diethyl carbonates have also been studied [35]. This work was done with potential application for the use of dialkyl carbonates in refrigeration systems, including automobile air conditioning systems. The viscometrics as a function of temperature are critical for this application since a vehicle will experience varying climates depending on country of origin and due to long-range travel through different climatic conditions.

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• To give urethanes and ureas with ammonia and amines • As alkylating agents for amines, phenols, and acids • As oxyalkylating agents, in the case of the five-

membered cyclic carbonates • To give malonates, by Claisen condensation • As carbonylating agents (DMC) for ketones, nitriles,

hydroxy amides, and amino alcohols • As methylating agents (DMC)

Apart from these synthetic uses, the structure of the carbonate group leads to the fact that dialkyl carbonates undergo thermal and catalytic decomposition to alcohols, carbon dioxide, and olefins, and therefore, in principle, decompose without acid formation. Similarly, in presence of water and of hydrolyzing agents, hydrolysis can lead back to formation of alcohols, carbonic acid, and, consequently, carbon dioxide. Dialkyl carbonates are generally stable to hydrolysis in acidic media, and hydrolyze at an appreciable rate in basic media. Since lubricant degradation (hydrocarbon oxidation) generally results in the formation of acidic species, this is a favorable property. In general, the hydrolytic stability of dialkyl carbonates increases with the molecular weight of the alkyl groups. The shape of the alkyl groups can also affect the rate of hydrolysis based on the steric effect of the alkyl group. The properties that most directly affect the use of these materials as lubricant fluids include: • • • • •

Stability to hydrolysis in acidic media No acid is formed on thermo-oxidation High biodegradability Low toxicity Moderate thermal stability

Coefficient of friction

SRV test results 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 C14-15 DAC

POE

Diesters

Alkyates

PAO

SN 150

FIGURE 15.2 SRV test results comparing the performance of iso-viscous (at 100◦ C) base fluids

Thermal stability is an important performance criterion for components of lubricant formulation. DBC, for example, is stable at 200◦ C for at least 20 h. Raising the temperature to 250◦ C, however, results in appreciable decomposition in 5 to 8 h.

satisfactory for dialkyl carbonates, even with respect to silicon elastomers, which are the most sensitive to the base fluid polarity. In particular, semisynthetic multigrade engine oils formulated with dialkyl carbonates exhibit better performance for silicon rubber swelling, than similar formulations made with polyalphaolefins or polyol esters.

15.6.3 Performance Characteristics The performance of dialkyl carbonates in engine oils applications has been reported elsewhere [12]. The main conclusions from that work can be summarized as follows. 15.6.3.1 Tribology The presence of the carbonic group in dialkyl carbonates imparts lubricity properties to these products, due to the interaction between the carbonic group and the metallic surfaces. A comparison of SRV data for C14–15 dialkyl carbonate with other mineral and synthetic base fluids having the same viscosity at 100◦ C, confirms the excellent lubricity properties of dialkyl carbonates (Figure 15.2). 15.6.3.2 Viscometrics Viscometrics data indicate that the amount of dialkyl carbonates necessary to meet the requirement of low viscosity multigrade engine oils (5W/XX, 10W/XX), is comparable with the amount of other synthetic base fluids (PAO, esters, etc.) of the same viscosity. 15.6.3.3 Oxidation and thermal stability Oxidation and thermal stability tests show an outstanding performance of dialkyl carbonates: the absence of acid products formed at the end of the tests, is an advantage. This aspect may affect the overall behavior of fully formulated lubricants in that corrosive wear phenomena can be positively controlled. 15.6.3.4 Elastomer compatibility Elastomer compatibility, a critical performance feature and specification for synthetic base fluids, is generally

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15.6.3.5 Wear protection The engine performance of multigrade oils containing dialkyl carbonates shows that the same excellent antiwear properties exhibited by this component as such are maintained in the finished oil formulation, without any interference with antiwear additives, as exhibited by other ester type basestocks. Results have been obtained on the OM 616 Kombi, CRC L-38, Petter W1 (extended to 144 h), and VW Cam & Tappet tests. 15.6.3.6 Sludge protection The formulations containing dialkyl carbonates give good sludge control, better than that exhibited by a pure mineralbased formulation containing the same package at the same concentration. Results were obtained from VE and M102E Black Sludge test. This performance can be related to the particular chemical structure of dialkyl carbonates, with a particularly strong polar group and a two alkyl chains in the same molecule, resulting in a synergistic effect with traditional dispersant additives in the control of sludge.

15.7 TOXICOLOGY, BIODEGRADABILITY, AND HANDLING PROPERTIES 15.7.1 Toxicology Dialkyl carbonates can be defined as not dangerous substances for the humans and for the environment, according to the relevant tests and experiments that have been carried on to assess this aspect. Among others, the effect of contact, ingestion, and inhalation, in acute, subacute, and chronic conditions has been investigated and tested indicating that dialkyl carbonates are not dangerous to humans.

TABLE 15.7 Biodegradability Test Results on Dialkyl Carbonates Carbonate of

Biodegradability, % (28 day)

–CH3 OH –oxo C12–15 /oxo i-C13 –oxo C14–15 branched –oxo i-C13 –TMP oxo C12–15 /i-C8 –i-C18

90 75 65 60 15 negligible

15.7.3 Handling No special procedure and care are required in handling dialkyl carbonates; only standard hygiene and safety procedures are recommended. Dialkyl carbonates are stable at ambient temperature and atmospheric pressure, do not require any special precautionary measure for storage, and can be safely stored in carbonsteel tanks, even for long periods.

ACKNOWLEDGMENT As far as the environment is concerned, dialkyl carbonates are not soluble in water, exhibit very low volatility, can be recollected from water and ground if any loss occurs, have a low degradation rate, and do not form harmful products by degradation. Based on these considerations, dialkyl carbonates can be considered not dangerous for the environment. Dibutyl carbonate exhibits good toxicological properties. Testing has shown that it is not an irritant to skin or eyes (rabbit test), and has an LD50 oral rate of >2000 mg/kg. C14–15 dialkyl carbonate has an LD50 oral rate of 10 mg/kg and an LD50 dermal rate of 5 mg/kg. Skin irritation, eye irritation, skin sensitization (rat), biological, ecotoxic, and subcutaneous effects are all reported as negative [31].

15.7.2 Biodegradability Biodegradability test data (Table 15.7) shows that, although for lower molecular weight dialkyl carbonates the polarity improves water solubility, which indirectly may improve biodegradability, the carbonate group does not insure biodegradability. Dibutyl carbonate exhibits the following performance in the MITI mod (OECD 301 C) test. COD (28 days) 68%, BOD (28 days) 72%. The biodegradability of dialkyl carbonates strongly depends on the biodegradability of the alkyl groups present in the molecule. There are several structures that can have an impact on the extent of biodegradability of various lubricant fluids. Some of these include the extent of branching of the hydrocarbon chains, the chain length, the proportion of oxygen in the structure, and olefinic content. Polarity is affected in dialkyl carbonates by the chain length, because there is already an oxygen functionality due to the carbonate group. In addition, any oxygen present in the alkyl chains further increases the polarity of the fluid. This can result in greater water solubility, which can impact the extent (and rate) of biodegradation since the test involves aqueous media.

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The author would like to acknowledge G. Fisicaro and G. Garbaz for their original chapter on dialkylcarbonates in the second edition of Synthetic Lubricants and HighPerformance Functional Fluids (Marcel Dekker) from which this chapter has been expanded, updated, and revised [36]. The author attempted via the internet and through professional colleagues to contact the original authors, without success, to update their chapter. The author (LRR) would also like to thank Carlo Zecchini of Polimeri Europa, Brajendra Scharma of USDA, Peoria, IL, and Chris Klumph of SNPE NA, Princeton, NJ USA for providing new data and helpful discussion for inclusion in this chapter.

REFERENCES 1. L. Lugo, V. Luna, J. Garcia, E.R. Lopez, M.J.P. Comunas, and J. Fernandez, Prediction of the pressure dependence on the thermodynamic properties of dialkyl carbonate + alkane mixtures using Nitta-Chao model, Fluid Phase Equilibria, Volume 217, Issue 2, pp. 165–173 (2004). 2. T. Takeno, K. Mizui, and K. Takahata, in Proceedings of the International Compressor Engineering Conference, Purdue, USA, pp. 1045–1054 (1992). 3. M.F. Fincke and J.H. Bartlett, Art of improving lubricating oils, U.S. Patent, 2, 263, 265 (1941). 4. A.T. Knutson and E.F. Graves, Lubrizol, U.S. Patent, 2, 387, 999 (1945). 5. L.A. Mikeska and L.T. Eby, Synthetic Cubricating oil, U.S. Patent, 2, 651, 657 (1953). 6. J.H. Bartlett, Polymerized carbonate ester lubricating oil additives, U.S. Patent, 2, 673, 185 (1954). 7. J.H. Bartlett, Oil solution of polymerized carbonate ester, U.S. Patent, 2, 718, 504 (1955). 8. D.L. Cottle, F. Knoth, and D.W. Young, Synthetic lubricants, U.S. Patent, 2, 758, 975 (1956). 9. P. Koch and U. Romano, Synthesis of higher alcohol carbonates and their use as synthetic lubricants, Italian Patent 20264 A/82 (1982). 10. E. Brandolese, Lubricant fluid for cold-rolling of steel, Italian Patent 20191 A/89 (1989). 11. G. Fisicaro and G.P. Gerbaz, Lubricant compositions for autotraction, Italian Patent 21812 A/90 (1990).

12. G. Fisicaro and S. Fattori, Conference on Synthetic Lubricants, Sopron, Hungary (1989). 13. J.R. Angle, U.D. Wagle, and D.C. Reid, Pennwalt Corporation, DE-OS 2926354 (1978). 14. M. Matzner, R.R. Kurkjy, and R.J. Cotter, Chem. Rev., 64, p. 645 (1964). 15. H.J. Buysch, H. Krimm, and H. Rudolph, DE 2748718, to Bayer (1977). 16. J. Genz and W. Heitz, Preparation of dialkyl carbonates, EP 85347, (1982). 17. W. Heitz and P. Ball, Process for the preparation of carbonic acid esters and its application to the preparation of polycarbonates, EP 13957, (1979). 18. W. Heitz and P. Ball, Process for the preparation of carbonic acid esters and polycarbonates, EP 13958, (1979). 19. W. Harder and F. Merger, Process for the preparation of carbonates, EP 41622, to BASF (1981). 20. F. Rivetti and U. Romano, Alcohol carbonylation with palladium (II) complex, effects of ligands, carbon monoxide, pressure and added bases, J. Organomet. Chem., 174, pp. 221–226 (1979). 21. E. Drent, Process for the preparation of carbonate esters, EP 71286, (1981). 22. G. Stammann, R. Becker, J. Grolig, and H. Waldmann, Process for the preparation of carbonic-acid esters, East European Patent, DE-05 3016187, (1981). 23. M. Massi, M. Mauri, U. Romano, and F. Rivetti, Ing. Chim. Ital., 21, pp. 1–3 (1985). 24. Y.R. Chin and N.F. Shih, SRI, PEP Review, 87, pp. 1–4 (1988). 25. H.-P. Luo, W.-D. Xiao, and K.-H. Zhu, Isobaric vapor-liquid equilibria of alkyl carbonates with alcohols, Fluid Phase Equilibria, 175, pp. 91–105 (2000). 26. F. Comelli and R. Francesconi, Isothermal vapor-liquid euillibria measurements, Excess molar enhalpies, and Excess molar volumes of dimethyl Carbonate + Methanol + Ethnol,

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27.

28.

29.

30.

31. 32. 33. 34. 35.

36.

and + Propan-1-ol at 313.15K, J. Chem. Eng. Data, 42, pp. 705–709 (1997). F. Comelli, R. Francesconi, S. Otani, Isothermal vaporliquid equilibria of dimethyl carbonate + diethyl carbonate in the Range (313.15 to 353.15) K, J. Chem. Eng. Data, 41, pp. 534–536 (1996). M.J. Cocero, F. Mato, I. Carcia, J.C. Cobos, and H.V. Kehiaian, Thermodynamics of binary mixtures containing organic carbonates. 2. Isothermal vapor-liquid equilibria for diethyl carbonate + cyclohexane + benzene, or + tetrachloromethane, J. Chem. Eng. Data, 34, pp. 73–76 (1989). M.J. Cocero, F. Mato, I. Carcia, and J.C. Cobos, Thermodynamics of binary mixtures contains organic carbonates, 3. Isothermal vapor-liquid equilibric for diethyl carbonate + cyclohexane + benzene, or + tetrachloromethane, J. Chem. Eng. Data, 34, pp. 443–445 (1989). M.J. Cocero, I. García, J.A. González, and J.C. Cobos, Thermodynamics of binary mixtures containing organic carbonates Part VI. Isothermal vapor-liquid equilibria for dimethyl carbonate + normal alkanes, Fluid Phase Equilibria, 68, pp. 151–161 (1991). Personal Communication from Carlo Zecchini from Polimerieuropa. C. Alberto, N. Corlo, Biodegradable compositions for use as textile softners. EP 507,973, (1992). M. Dierker, Lipid Technol., 16, pp. 130–134 (2004). J.A. Kenar, Inform, 15, pp. 580–582 (2004). A. Baylaucq, M.J.P. Comunas, C. Boned, A. Allal, and J. Fernandez, High pressure viscosity and density modeling of two polyethers and two dialkyl carbonates, Fluid Phase Equilibria, 199, pp. 249–263 (2002). G. Fisicaro and G. Garbaz, in L.R. Rudnick and R.L. Shubkin, Synthetic Lubricants and High-Performance Functional Fluids, 2nd ed, Marcel Dekker, New York, pp. 313–323 (1999).

16

Alkylcyclopentanes Clifford G. Venier CONTENTS 16.1 Introduction 16.2 Alkylcyclopentanes 16.2.1 Multiply Alkylated Cyclopentanes (MACs) 16.2.1.1 Preparation 16.2.1.2 Physical Properties 16.2.2 Alkanes with Cyclopentyl Substituents 16.3 Hydrindanes and other Fused Ring Compounds 16.4 Manufacture and Economics 16.5 Applications of Alkylcyclopentanes 16.5.1 Aerospace 16.5.1.1 Low Volatility 16.5.1.2 Good Lubricity (Friction and Wear) 16.5.1.3 Wear Additive Compatibility 16.5.1.4 High Viscosity Index 16.5.1.5 Low Temperature Fluidity 16.5.1.6 Low Infrared Absorbance 16.5.1.7 Chemical Stability 16.5.1.8 High Surface Tension 16.5.2 Greases Based on Alkylcyclopentanes 16.5.3 Computer Disks 16.6 Conclusions References

16.1 INTRODUCTION Naturally occurring cycloaliphatic materials have been generally recognized as important constituents of petroleum for a century [1–3]. “Naphthenes” [4] contain at least one ring while “paraffins” contain none. The different properties, both good and bad, of comparable products derived from naphthenic crude oil and paraffinic crude oil have been ascribed to the relative proportion of cyclic and acyclic molecules. Aromatic compounds also occur naturally in crude oils, and, in general, mineral oil base stocks contain all three classes of compounds in varying proportions. Synthetic hydrocarbon base materials can be classified into the same categories as conventional mineral oil: paraffinic, naphthenic, and aromatic. For example, polyalphaolefins (PAOs), the hydrogenated oligomers of 1-alkenes (see Chapter 1), are analogous to the paraffinic materials in petroleum. Dimers of internal olefins of the

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type used in detergent manufacture are also analogs of paraffinics and the commercial development of them under the name “polyinternalolefins” is under way in Europe. Polybutenes are a noncyclic aliphatic product with no analog in natural petroleum. The aromatic constituents of petroleum find analogy in synthetics as well. Synthetic alkylated aromatic compounds have found limited use as synthetic lubricating oil base stocks. Dialkylated aromatics have enjoyed the most commercial success. No example of a synthetic analog of the third major structural class of petroleum hydrocarbons, the naphthenes or cycloaliphatics, has yet been successfully commercialized on a large scale. The scope of this chapter is limited to a description of the preparation and properties of materials containing cyclopentane rings that may have potential use as lubricant

base stocks, and which have been reported in the literature and patent art. The related six-membered ring materials are treated in Chapter 10. Several general studies on structure–property relationships have included molecules containing saturated rings. The largest of these is the API Project 42 report [5], which compiles the physical properties of 321 pure hydrocarbons. The properties measured in the project include viscosities, densities, boiling and melting points, heat of vaporization, and light refraction properties. Other properties of selected sets of the compounds are also included: viscosities and densities at elevated pressures, vapor pressures, heats of combustion, heats of fusion, and thermal conductivities. No discussion of the relations of structure to properties is presented in the API Project 42 report, however. Since there is a larger body of data on pure alkylcyclohexanes than on pure alkylcyclopentanes, generalizations on the effects of alkyl groups on properties will sometimes be made on the basis of data on alkylcyclhexanes, even though they are not the subject of this chapter per se. Using some of the data from Project 42, Denis [6] has described the effect of five- and six-membered rings on tribologically relevant properties, in particular, the pour point and viscosity index (VI). He finds that rings centrally located within the longest chain, for example, in 1,4-dialkylcyclohexanes, have little effect on pour point or VI. On the other hand, rings have the same effect as other alkyl groups as side chains, namely the lowering of both the pour point and the VI. In general, the discussion of cyclopentanes in this chapter is limited to compounds with 20 or more carbon atoms. Compounds of lower molecular weight will, in general, have too low viscosities and too high volatilities for successful use as lubricants, but may be included to illustrate a special point or to discuss special applications.

ring, were reported by Venier and Casserly [7,8]. Multiply alkylated cyclopentanes (MACs) are available from the hydrogenation of the corresponding multiply alkylated cyclopentadienes, Equation (16.1). These, in turn, (CHR2)m +

2H2

Catalyst (CHR2)m

(16.1) are readily available by the alkylation of cyclopentadiene, methylcyclopentadiene, etc., by two fundamentally different routes [7,9,10]. Both preparative routes take advantage of the extraordinarily high acidity of simple cyclopentadienes. The very low pKa of cyclopentadiene (pKa = 18) compared to that of other simple hydrocarbons (pKa = 30 or greater) arises from the aromaticity of the cyclic six-electron periphery of the cyclopentadienide anion, Equation (16.2). H

H H

H

H H

Base

H

H

H H

H

(16.2) This relatively high acidity allows the cyclopentadienide anion to be usefully accessible using ordinary bases, such as alkoxides and hydroxides. The use of expensive air- and moisture-sensitive bases, such as alkyl lithium reagents, to generate the nucleophilic carbanion necessary for carbon–carbon bond formation, is easily avoided in the synthesis of higher molecular weight multiply alkylated cyclopentadienes. 16.2.1.1.1 Phase transfer alkylation In 1968, Makosza [11] reported that cyclopentadiene could be alkylated under phase transfer conditions using alkyl halides, Equation (16.3). Venier and Casserly [7,8,12] extended the earlier phase

16.2 ALKYLCYCLOPENTANES Two basic types of cycloaliphatics containing cyclopentane rings are discussed (1) compounds in which a single cyclopentane ring bears one or, more often, more than one alkyl substituent, and (2) compounds containing two or more terminal cyclopentane rings, that is, –C5 H9 substituents.

16.2.1 Multiply Alkylated Cyclopentanes (MACs) 16.2.1.1 Preparation The preparations of large number of examples of the first type of cycloaliphatics containing cyclopentane rings in which two or more alkyl groups are attached to a central

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+

mR2CH-X

Catalyst KOH (aq)

(CHR2)m + mKX

(16.3) transfer alkylation work to synthesize multiply alkylated cyclopentadienes and, subsequently, alkyl cyclopentanes in the useful lubrication oil range. Tris(t-butyl)cyclopentadiene can also be synthesized by phase transfer alkylation [10]. Multiple alkylations of cyclopentadiene, in which two to six alkyl groups are added to the cyclopentadiene ring, are easily carried out in a single pot using greater than 40% sodium or potassium hydroxide as the aqueous phase, an alkyl halide as both the alkylating agent and organic phase solvent, and a quaternary ammonium salt as the phase transfer catalyst. Unfortunately, the high cost of most

alkyl halides and the large excess of potassium hydroxide required may make this route prohibitively expensive, even though the reaction is virtually quantitative. 16.2.1.1.2 Alkylation with alcohols Hirsch and Bailey [13] and Fritz and Peck [14] reported the alkylation of cyclopentadiene using alcohols in the presence of base, Equation (16.4). Venier and Casserly [7,8,15] extended the alkylation of KOH 180N–250°C

cyclopentadiene by alcohols to the synthesis of products in the useful lubricating oil range. Cyclopentadiene is conveniently generated in situ by the efficient cracking of commercially available dimer, dicyclopentadiene, at the elevated reaction temperature (190 to 250◦ C). Alkoxide is conveniently generated by refluxing alcohols with KOH and using water separation via a Dean–Starke trap to drive the equilibrium to alkoxide. Because it suppresses the concentration of ions more basic than hydroxide ion, for example, alkoxide, water inhibits the reaction. The water produced in the reaction is, therefore, removed as it is formed during the course of the reaction. Multiple alkylations, in which two to five alkyl groups are added to the cyclopentadiene ring, are easily carried out in one step. Venier and Casserly [7] have used this reaction procedure to react alcohols with eight or more carbon atoms with cyclopentadiene. In principle, alcohols of lower molecular weight could be used; however, the high reaction temperature (190 to 250◦ C) would necessitate the use of an inert high boiling solvent or a closed system under the autogenous pressure of the alcohol. The reaction is virtually quantitative. This method has been used to produce one specialty lubricant marketed to the aerospace industry. 16.2.1.1.3 Friedel–Crafts oligomerization of 1-alkenes with halocyclopentanes The Friedel–Crafts oligomerization of 1-alkenes in the presence of halocyclopentanes gives products of lower viscosity and more uniform molecular weight than oligomerization in the absence of the halocyclopentane [16,17]. Yields were in the range of 40 to 60% based on starting 1-alkene. No structural data to suggest how much, if any, of the cyclopentyl derivative were incorporated into the product were presented in the 1961 patent. 16.2.1.2 Physical properties The discussion of cycloaliphatics containing cyclopentane rings is limited to compounds with 20 or more carbon atoms. Compounds of lower molecular weight will, in general, have low viscosities and high volatilities.


[(weight fraction of theith component) × (carbon number of the ith component)]

(CHR2)m + mH2O

(16.4)

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Cav =

16.2.1.2.1 Viscosity The viscosity of alkylcyclopentanes depends primarily on the molecular weight of the compound, increasing regularly as molecular weight increases. The kinematic viscosities (ASTM D-445) at 100◦ C for a variety of examples are given in Appendix 16.1 and Figure 16.1. Equations of the form log(vis) vs. log(Cav ) can be used to describe the dependence of viscosity on molecular weight. The equations relating log(vis) to log(Cav ) for MACs, 1-decene PAOs, and normal alkanes are: MACs log(vis) = 1.71 log(Cav ) − 1.92 PAOs log(vis) = 1.77 log(Cav ) − 2.06 n-alkanes log(vis) = 2.03 log(Cav ) − 2.36 Branching of the alkyl groups gives products that are more viscous than the products prepared from the corresponding linear alkyl groups of the same molecular weight. The viscosities of cyclopentanes prepared from the highly branched oxo alcohols, such as isodecanol and isotridecanol, lie above the regression line in Figure 16.1. This is to be expected since these alcohols are prepared from propene oligomers by hydroformylation. Isodecanol and isotridecanol are best characterized as mixtures of trimethylheptanols and tetramethylnonanol, respectively. Table 16.1 lists the properties of several cyclopentanes with a total of 29 carbon atoms. The alkyl groups vary from normal and branched octyls to normal decyls and normal 100 Viscosity (100˚C), cSt

+ mR2CH-OH

The reader should explicitly note that many of the examples used to illustrate physical properties are mixtures of two, and occasionally more, materials of different molecular weight. A weight average carbon number of a sample is defined to allow materials to be compared. The weight average carbon number of a sample, Cav , is defined as

0 n-Octyl n-Decyl n-Dodecyl 1 10

100 Carbon number, Cav

FIGURE 16.1 Kinematic viscosity as a function of carbon number for alkylated cyclopentanes

TABLE 16.1 Lubricant-Related Properties of MAC Synthesized Hydrocarbon Fluids of 29 Carbon Atoms

Alkyl, Ra n-Octyl 2-Octyl 2-Ethylhexyl n-Decyl n-Dodecyl

m, Number of groups 3 3 3 2,3 2

Cav b

Kinematic viscosity, 100◦ C, cSt

Kinematic viscosity, 40◦ C, cSt

Viscosity index

Pour point, ◦C

Reference

29 29 29 29 29

3.68 4.71 4.21 3.78 4.13

15.58 28.23 26.44 14.44 15.64

124 74 22 161 178

<−57 <−54 <−48 −9 +21

[7,8,15] [7] [72] [7,8] [7,8,15]

a R is the alkyl group in −R . m b C =  [(weight fraction) × (carbon number) ]. av i i i c Previously unpublished data.

TABLE 16.2 Viscosity Index of MAC Synthesized Hydrocarbon Fluids

Alkyl, Ra n-Octyl n-Octyl 2-Octyl 2-Ethylhexyl n-Decyl n-Decyl n-Decyl n-Decyl n-Dodecyl n-Dodecyl n-Octyl/n-decyl n-Octyl/n-decyl

m, Number of groups 3 3,4 3 3 2 2,3 3 4 2 3

Cav b

Kinematic viscosity, 100◦ C, cSt

Viscosity index

Pour point, ◦C

Reference

29 34 29 29 25 29 35 45 29 41 35c 41c

3.68 4.96 4.71 4.21 3.03 3.78 5.15 7.99 4.13 6.99 5.23 6.91

124 128 74 22 161 161 151 143 178 164 134 139

<−57 <−57 <−54 <−48 +6 −9 −27 <−60 +21 −9 <−50 <−50

[8] [8] [8] [8] [8] [8] [8] [8] [8] [8] [8] [8]

a R is the alkyl group in −R . m b C =  [(weight fraction) × (carbon number) ]. av i i i c Estimated from kinematic viscosity at 100◦ C.

dodecyls. Note that the branched alkyl cyclopentanes are more viscous than the normal alkyl cyclopentanes. Viscosities of a perfluoropolyether and tris(2octyldodecyl)cyclopentane at high pressures has been reported [18]. Rheological properties of both responded to changing pressure in similar ways.

16.2.1.2.2 Viscosity index Viscosity index (VI; ASTM D-2270) is the measure of the change of viscosity with temperature. The higher the viscosity index, the less the viscosity of the fluid changes with temperature. For lubricants, a high viscosity index is usually desirable.

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In the MACs in which two or more alkyl groups are attached to a single cyclopentane ring, the VI varies with both the number of substituents and the length of the alkyl groups. Therefore, a separate curve relating average carbon number to VI is generated for each alkyl group length. Representative examples are given in Table 16.2 and Figure 16.2. The VI depends strongest on the average length of the alkyl groups and less on the number of alkyl groups attached to the cyclopentane ring. For a given degree of substitution, the longer the average length of the alkyl groups, the higher the viscosity index. For example, tri(n-octyl)cyclopentane has an average alkyl length of 8 and a VI of 124. Tri(n-decyl)cyclopentane has an

average alkyl length of 10 and a VI of 151. Tri(ndodecyl)cyclopentane has an average alkyl length of 12 and a VI of 164. For a given average alkyl length, the greater the degree of substitution, the lower the viscosity index. For example, in progressing from di(n-decyl)cyclopentane to tri(n-decyl)cyclopentane to tetra(n-decyl)cyclopentane, the substitution increases from 2 to 3 to 4 alkyl groups, while the VI decreases from 161 to 151 to 143. For a given carbon number, the VI increases as the length of the alkyl groups increases or as the degree of substitution decreases. The following examples from Table 16.1 all have a total of 29 carbon atoms. Di(ndodecyl)cyclopentane has a VI of 178, the mixture of di- and tri(n-decyl)cyclopentanes has a VI of 161, and tri(n-octyl)cyclopentane has a VI of 124.

180

Viscosity index

× 160

n-Octyl n-Decyl n-Undecyl n-Dodecyl

Branching decreases the VI by effectively reducing the length of the longest alkyl group. In Table 16.1, examples of normal and branched octyl substituted cyclopentanes are given. The tri(n-octyl)cyclopentane has a VI of 124, while the tri(2-octyl)cyclopentane has a VI of 74, and the tri(2-ethylhexyl)cyclopentane has a VI of 22. The length of the longest uninterrupted alkyl chain decreases from eight to six to four carbon atoms in this series. The viscosity indices (VIs) of blends of MACs with different alkyl groups depend strongest on the length of the average alkyl group as well. Tri(n-octyl)cyclopentane has a VI of 124 and tri(n-dodecyl)cyclopentane has a VI of 164. A 50:50 mixture of the two has an average chain length of 10 and a VI of 140, which is between the VI of the components. Tri(n-decyl)cyclopentane has an average chain length of 10 by construction and exhibits a VI of 151. MACs that are prepared from mixtures of alcohols also exhibit VIs characterized by an average chain length. Two examples serve to illustrate this. For MACs with an average total carbon number of 35 the VIs are: n-octyl, 128; noctyl/n-decyl, 134; n-decyl, 151. For Cav = 41, the VIs are: n-octyl, 127; n-octyl/n-decyl, 139; n-decyl, 144.

×

140

120 20

30

40 Carbon number, Cav

50

60

FIGURE 16.2 Viscosity index as a function of alkyl group and carbon number for alkylated cyclopentanes

16.2.1.2.3 Low temperature properties The pour point (ASTM D-97) of cycloaliphatics with two or more alkyl groups attached to a single cyclopentane ring depends on a number of factors. First, for a given number of substituents, for example, di(n-alkyl)cyclopentanes, the pour point increases dramatically with increasing length of the alkyl group. Second, with a constant n-alkyl group, the pour point decreases as the number of substituents increases, that is, as the molecular weight increases.

TABLE 16.3 Low temperature properties of MAC synthesized hydrocarbon fluids

Alkyl, Ra n-Octyl n-Octyl n-Octyl n-Decyl n-Decyl n-Decyl n-Decyl n-Dodecyl n-Dodecyl 2-Octyldodecyl

m, Number of groups 2 3 4 2 2,3 3 4 2 3 2,3

Cav b 21 29 37 25 29 35 45 29 41 62

Kinematic viscosity, 100◦ C, cSt

Viscosity index

Dynamic Viscosity, −30◦ C, cP

Pour point, ◦C

Reference

2.18 3.68 5.99 3.03 3.78 5.15 7.99 4.13 6.99 14.56

158 124 125 161 161 151 143 178 164 137

— 700 3700 — — — 4500 — — 20,500

−24 <−57 <−57 +6 −9 −27 <−60 +21 −9 −57

[7,8,15] [7,8,15] [7,8,15] [7,8,15] [7,8] [7,8,15] [7,8,15] [7,8,15] [7,8,15] [7,8,15]

a R is the alkyl group in −R . m b C =  [(weight fraction) × (carbonnumber) ]. av i i i

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Finally, MACs with n-alkyl groups have higher pour points than cyclopentanes with branched alkyl groups. Representative data from Appendix 16.1 are given in Table 16.3 and illustrated in Figure 16.3. As with VI, a separate curve is generated for each alkyl group. For the di-substituted cyclopentanes, the pour point increases from −24◦ C to +6◦ C to +21◦ C as the alkyl group is changed from n-octyl to n-decyl to n-dodecyl. The same trend is clear in the tri(n-alkyl) series: tri(n-octyl), <−57◦ C; tri(n-decyl), −27◦ C; and tri(n-dodecyl), −9◦ C. All known examples of n-octyl substituted cyclopentanes with greater than 29 carbon atoms and n-decyl substituted cyclopentanes with greater than 41 carbon atoms have pour points less than −50◦ C. The molecular weight of cyclopentanes with n-decyl substituents increases 140 units for each n-decyl group. The pour point, however, decreases with each additional substituent, that is, each increase in molecular weight. Thus, di(n-decyl)cyclopentane has a molecular weight of 350 and a pour point of +6◦ C; tri(n-decyl)cyclopentane has a molecular weight of 490 and a pour point of −27◦ C; and tetra(n-decyl)cyclopentane has a molecular weight of 630 and a pour point of <−50◦ C. Since the molecular weight

correlates with the 100◦ C viscosity, the more viscous examples of this series have lower pour points. The effect of alkyl group chain length is greater than the effect of the number of substituents, as illustrated by the pour point of examples with the same molecular weight, that is, the same Cav . Tri(n-octyl)cyclopentane and di(n-dodecyl)cyclopentane each contain 29 carbon atoms. The tri(n-octyl)cyclopentane has a pour point of <−50◦ C whereas the di(n-dodecyl)cyclopentane has a pour point of +21◦ C. A mixture of di- and tri(n-decyl)cyclopentane, with an average of 29 carbon atoms has a pour point of −9◦ C. Thus, the pour point is very sensitive to the exact structure of the compound. Isoparaffins in the lubricating oil range are liquids, whereas the paraffins are solids. Thus, the pour point of MACs with branched side chains would be expected to be lower than for unbranched examples. One example in particular illustrates this point well. A mixture of diand tri(2-octyldodecyl)cyclopentane has an average carbon number of 62 and a pour point of −57◦ C. If the average carbon number vs. pour point curves in Figure 16.3 were extrapolated to alkyl chains of 20 carbon atoms, the series would all be solids. The introduction of a single branch in each alkyl group decreases the pour point dramatically.

Pour point, °C

30

10

–10 ×

–30

×

–50 20

30

40 Carbon number, Cav

n-Octyl n-Decyl n-Undecyl n-Dodecyl

50

60

FIGURE 16.3 Pour point as a function of alkyl group and carbon number for alkylated cyclopentanes

16.2.1.2.4 High temperature properties As is the case with most alkanes, the flash fire points are a function primarily of the molecular weight. Table 16.4 lists the flash and fire points of a number of MACs. The evaporation loss of representative MACs is also given in Table 16.4. Once again, as molecular weight increases, the evaporation loss goes down. The last entry in the table, tris(2-octyldodecyl)cyclopentane, is particularly noteworthy. Besides the low volatility and high flash and fire points, this material has a pour point of less than −55◦ C (see Table 16.3).

TABLE 16.4 High Temperature Properties of MAC Synthesized Hydrocarbon Fluids

Alkyl, Ra

m, Number of groups 3 4,5 3,4 2,3

n-Decyl n-Decyl n-Dodecyl 2-Octyldodecyl

Cav b

Kinematic viscosity, 100◦ C, cSt

Kinematic viscosity, 40◦ C, cSt

Viscosity index

Pour point, ◦C

Flash point, ◦C

Evaporation loss,c weight %

35 48 47 62

5.15 8.92 9.98 14.56

23.99 54.07 55.70 109.30

151 144 167 137

−27 <−45 −15 −57

260 288 294 307

6.1 1.3 0.4 0.1

a R is the alkyl group in −R . m b C =  [(weight fraction) × (carbon number) ]. av i i i c Modified ASTM D-972, 250◦ C for 6.5 h with a nitrogen flow of 2 L/min.

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Reference [15] [15] [15] [7,8]

TABLE 16.5 Selected Cyclopentanes from API Project 42 Report API Project 42 number

Carbon number

Viscosity, 100◦ C, cSt

Viscosity, 40◦ C, cSt

Viscosity index

Pour point, ◦ C

One cyclopentyl ring 9(3-Cyclopentylpropyl)heptadecane 11-Cyclopentylheneicosane 11-Cyclopentylmethylheneicosane

110 64 74

25 26 27

2.84 3.04 3.26

10.72 11.64 12.79

112 119 125

−21 −13 −21

Cyclopentylheneicosane isomers 1-Cyclopentylheneicosane 11-Cyclopentylmethylheneicosane

117 74

26 27

3.72 3.26

13.08 12.79

188 125

+45 −21

111

25

3.49

14.82

114

−40

202

26

3.81

16.12

130

+12

Compound name

Two cyclopentyl rings 1-Cyclopentyl-4(3-cyclopentylpropyl)dodecane 1,1-Dicyclopentylhexadecane

16.2.2 Alkanes with Cyclopentyl Substituents API Project 42 reported physical properties for 321 hydrocarbons, including paraffins, isoparaffins, cycloaliphatics, and aromatics. In the normal paraffin series, the greater the number of carbons, the higher the viscosity, the VI, and the pour point. Branching decreases the viscosity slightly, but the VI and the pour point for hydrocarbons with a given number of carbon atoms are markedly decreased by branching. The API Project 42 report includes data for several multi-ring compounds and several compounds in which a single alkyl group is attached to a single cyclopentane ring. All of these data are compiled in Appendix 16.2. The number of carbon atoms in these examples range from 22 to 27. Additional data for some of these compounds have been reported by Denis [6] and Reith [19]. Selected data from Appendix 16.2 are given in Table 16.5. The structure/property relationships, described above for the MACs, hold true for the alkanes with cyclopentyl substituents. The viscosity follows molecular weight. For example, the first three entries are structurally related, there is one branched alkyl group attached to one cyclopentane ring. As the molecular weight increases, the kinematic viscosity at 100◦ C increases from 2.84 to 3.26 cSt. The position of the cyclopentane ring on the alkyl group affects the VI and pour point. For example, the isomers 1-cyclopentylheneicosane and 11-cyclopentylheneicosane differ only by the placement of the cyclopentane ring. The one branch point reduces the length of the longest unbranched chain from 21 to 10. The VI is reduced from 188 for the 1-cyclopentylheneicosane to 119 for the 11cyclopentylheneicosane. In the same way, the pour point

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for the 1-isomer is +45◦ C and is −12.7◦ C for the 11isomer. 1-Cyclopentylheneicosane behaves more like the normal paraffin n-hexacosane [6] (kinematic viscosity at 100◦ C = 3.24 cSt, VI = 188, pourpoint = +56◦ C). In examples containing two cyclopentyl groups, 1,1dicyclopentylhexadecane has a higher molecular weight and a longer unbranched chain than 1-cyclopentyl4(3-cyclopentylpropyl)dodecane. Hence, it has a higher kinematic viscosity at 100◦ C, a higher viscosity index and a higher pour point.

16.3 HYDRINDANES AND OTHER FUSED RING COMPOUNDS Hydrindanes are two-ring compounds in which the a fiveand six-membered ring share two carbons in common. Appendix 16.3 shows data for compounds with two fused rings. Only a few examples of hydrindane are in the literature. A series of C19 hydrindanes with various distributions of the ten alkyl carbons have been reported (see Appendix 16.3). The data collected in Table 16.6 show the most interesting series. The relatively linear, 2-butyl5-hexylhydrindane has a VI of 87, closer to those of the decylhydrindanes (110 and 129), than to those of the other butylhexylhydrindanes (−2 and 25). Interruption of a chain by a ring, in which the resulting structure is still more or less linear, has minimal effect on the VI, whereas structures in which the ring structure biases the chain to a nonlinear conformation greatly reduce the VI. A limited number of other fused ring systems containing a five-membered ring are shown in Appendix 16.4.

TABLE 16.6 Properties of Cycloaliphatics with Two Fused Rings: Hydrindanesa

Compound Alkylhydrindanes 5-Decylhydrindane 2-Decylhydrindane 2-Butyl-5-hexylhydrindane 2-Butyl-1-hexylhydrindane 5-Butyl-6-hexylhydrindane

API Project 42 number

Number of R groups

Number of carbons

Viscosity, 100◦ C, cSt

Viscosity, 40◦ C, cSt

Viscosity index

Reference

598 596 603 601 605

1 1 2 2 2

19 19 19 19 19

2.32 2.46 2.24 2.32 2.14

7.84 8.23 7.91 10.18 8.43

110 129 87 −2 25

[5] [5] [5] [5] [5]

a Data in the range of room temperature to 150◦ C were extrapolated to 100◦ C and 40◦ C, temperatures more commonly

used today.

16.4 MANUFACTURE AND ECONOMICS Alkylated cyclopentanes represent an independent class of potential lubricant base materials that are derived from cheap starting materials in two high-yields steps [7,8]. Cyclopentadiene is a by-product of ethylene production, and the sources of the alkyl groups, primary alcohols, are readily available from ethylene oligomerization, hydroformylation, and from natural sources. MACs derived from 2-octyldodecanol have found utility in the aerospace applications. Bis(2-octyldodecyl) cyclopentane and tris(2-octyldodecyl)cyclopentane, has been commercialized as special lubricants for the aerospace industry under the names Pennzane® Synthesized Hydrocarbon Fluid X1000 and Pennzane® Synthesized Hydrocarbon Fluid X2000 (MAC X2000), respectively. They are low-volume, high-priced products that minimize volatility for a given kinematic viscosity. They have especially wide liquid ranges [7,9,20].

16.5 APPLICATIONS Of ALKYLCYCLOPENTANES 16.5.1 Aerospace The severe conditions of space and the difficulty in servicing spacecraft require that lubricants for spacecraft applications meet stringent filled for life service requirements. The lifetime of a spacecraft can be measured in days or years. The short-duration science experiment satellites released and captured by the Space Shuttle remain in orbit for only a few days. The majority of spacecraft remain in service for seven to ten years. The proposed International Space Station has a design life of 10 years with a goal of 20 years. The desired lubricant properties that result from the stringent service requirements are detailed below. Several types of liquid lubricants have been used for spacecraft lubrication [22,23]. These include super-refined mineral oils, perfluoropolyethers (PFPE), chloroarylalkylsiloxane (CAS), PAOs, esters, and one cycloaliphatic, the

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Lubricant property

Service requirement

Low volatility

Approximate vacuums in space are: deep space (10−14 torr), near earth orbit (10−8 torr), within spacecraft (10−7 torr) [21] Good lubricity Prevent friction and wear

Additive compatibility

Protect against wear under boundary lubrication conditions High viscosity index Maintain constant viscosity over wide temperature range Low temperature fluidity Maintain fluidity at temperature extremes Low infrared absorbance Reduce interferences in case of contamination Chemical stability No degradation products which interfere with performance High surface tension Low creep or migration

MACs. Each of the desired properties listed above are discussed in turn as they relate to the lubricant. 16.5.1.1 Low volatility Lubricants with high volatility can cause several problems in a spacecraft. As the oil evaporates, less oil is available for lubrication, leading to oil starvation and increased friction and wear. Also the viscosity of the lubricant will increase as the light ends evaporate and this could impact

the low temperature properties negatively. In order for the vapor pressure to improve significantly, approximately 20 to 30% must be volatilized [24]. The volatile components can also condense on cold surfaces and contaminate optical instruments or other critical surfaces. The vapor pressure of the MAC X2000, at 20◦ C, has been calculated to be 1 × 10−12 torr [25,26]. This is comparable to the Fomblin® Z25, a commonly used PFPE spacecraft lubricant with an extremely low vapor pressure, 3 × 10−12 torr at 20◦ C [27]. A comparison of vapor pressures of some materials relevant to space applications, including both bis- and tris(2-octyldodecyl)cyclopentane (Pennzane® SHF X1000 and X2000 respectively), has been published [28]. 16.5.1.2 Good lubricity (friction and wear) Low friction and wear are important lubricant considerations, especially for spacecraft. Power consumption increases with increasing torque, friction, and wear. The power supplies are limited on spacecraft since they are generated from solar cells and batteries. Momentum transfer mechanisms are used to control the attitude of the space vehicle. This can also be accomplished by spinning most of the vehicle. Changes in the friction at the de-spin interface bearings can cause the vehicle to wobble or tumble. The tight tolerances of the components can be increased by friction and wear. These increased tolerances can cause increased torque noise and/or variable torque levels, or outright mechanism failure [24]. Hydrocarbons are inherently good protectors of surfaces. The original engine lubricants for automotive applications were pure unadditized hydrocarbons, purified fractions of crude oil. For mild applications, hydrocarbon liquids provide wear protection. Vacuum four-ball tribometer data showed alkylcyclopentane (X2000) to exhibit lower wear than the PAO [29]. In testing new non-ozone-depleting solvents as cleaning solvents for oscillatory gimbal bearings, Loewenthal et al., found extraordinarily long lifetimes for bearings lubricated with Pennzane® SHF X2000 compared to those lubricated with PFPEs, orders of magnitude longer lifetimes [30,31]. Jones et al., reported similar results [32]. An evaluation of the successful use of Pennzane® SHF X2000 in the Moderate Resolution Imaging Spectroradiiometer (MODIS) instrument program has been described by VanDyk et al. [33,34]. In a bearing test apparatus designed to qualify lubricants for the geostationary operational environmental satellite (GOES) program, no degradation of Pennzane® SHF X2000 was observed under conditions in which Krytox® 143AB failed [35]. Recent studies in spiral orbit tribometers [36] showed the rate of degradation of tris(2-octyldodecyl)cyclopentane (Pennzane® SHFX2000) to be two orders of magnitude less

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than that of polytetrafluoroethylene (PTFE) [37]. Other studies have been reported [38,39].

16.5.1.3 Wear additive compatibility The amount of lubricant used in spacecraft is very limited. The lubricant must operate under all tribological conditions, from hydrodynamic lubrication to elastohydrodynamic lubrication to boundary lubrication. Boundary lubrication is encountered during low speeds, especially when the direction is reversed during oscillatory motions. Low speeds increase risk of wear problems. Additives that are effective against boundary lubrication must be incorporated into the lubricant. Lead naphthenate has been used as a boundary additive in MAC X2000 formulations. The lead naphthenate prevents wear during boundary lubrication by depositing a lead-containing layer on the surface. The lead layer protects the surface; however, the lead layer buildup can increase the torque of the system [40]. Bialke [41] reported that a “set of bearings lubricated with Pennzane SHF X2000 and 5% of lead naphthenate as an extreme pressure additive was found to be pristine after 8000 crossings through zero speed, and approximately 4 million revolutions in the boundary region.” More recent studies have been reported [38]. Another boundary additive used with MAC X2000 is tricresyl phosphate (TCP) or a less volatile anolog, trixylenyl phosphate (TXP). Formulating with 1% TXP in MAC X2000, increased the test life by an order of magnitude over the unformulated lubricant. The lubricants were tested under vacuum in an eccentric test fixture [40,42–44]. Almost all additives are designed for hydrocarbon lubricants and are not soluble in the nonpolar PFPE systems. The PFPE lubricants are generally used neat although research is in progress to develop additives for PFPE lubricants [45].

16.5.1.4 High viscosity index As described earlier, the VI is the measure of the change of viscosity with temperature. The higher the VI, the less the viscosity of the fluid changes with temperature. The VI has a direct impact on the low temperature viscosity. The PFPEs have extremely high VIs. Fomblin Z25 has a VI of 355 and as such the viscosity at low temperatures is relatively low. The MAC X2000 has a VI of 137. This VI is still considerably higher than the mineral oils which have been utilized. For example, Apiezon C has a VI of 100. Behavior under high pressure is also of interest in bearing design. Vergne et al., have looked at Pennzane® SHF X2000 and Fomblin® Z25 under high pressure and find the changes in rheological properties similar for both lubricants [18].

16.5.1.5 Low temperature fluidity Sicre and coworker [46–49] investigated the rheological properties of six liquid lubricants for space applications. These included the MAC X2000, two PFPE, and three PFPE greases. The Fomblin Z25 possesses an extremely high VI (VI = 355), low viscosity at low temperatures, and is useful for lubricating spacecraft over a wide temperature range (−40 to 100◦ C). However, the Fomblin Z25 is known to degrade under operating conditions. The Krytox 143AD has a relatively low VI (VI = 144) and a relatively high viscosity at low temperatures. It is not very useful for lubricating spacecraft except at higher temperatures (50 to 100◦ C). The synthetic hydrocarbon MAC X2000 has a relatively low VI (VI = 134) and moderate viscosity at low temperatures. Its useful temperature range is −20 to 60◦ C. Accordingly, in the view of Sicre and coworkers, there is not an oil that is satisfactory for all space applications. Fusaro [50] has tabulated the common spacecraft mechanisms and the tribological requirements. The temperatures encountered by the lubricants depend on the application. The solar arrays and antennae see the coldest temperatures, −60 to −80◦ C. Other mechanisms see more moderate temperatures of −40 to 65◦ C or even 0 to 20◦ C. The viscosity increases as the temperature decreases until the pour point is reached and the lubricant no longer flows. The MAC X2000 has a pour point of −57◦ C, the PFPE Fomblin Z25 has a pour point of −66◦ C, and the mineral oil Apeizon C has a pour point of −15◦ C. 16.5.1.6 Low infrared absorbance Optical instruments can operate in the infrared spectrum. For example, the Conical Earth Sensor uses infrared to detect the Earth’s horizon to determine the spacecraft’s pitch and roll attitude. Liquid lubricants can volatilize or migrate to optical surfaces. Molecular seals and vents into space away from the optical surface can minimize contamination. The lubricant should be transparent in the optical region of interest in the event of contamination. Bialke [41] has reported that the light transmission in the region of the horizon sensor’s infrared bandpass (14.2–15.6 µm) is higher for the MAC X2000 than for the Bray 815Z PFPE. Infrared spectral comparison of Pennzane® SHF X2000 to PFPEs has been published [25]. 16.5.1.7 Chemical stability The chemical stability of the lubricant and the additives enhance the lifetime of the lubricant. If the oil degrades, the degradation products can lead to reduced lubrication, increased friction and wear, and ultimately failure. The PFPE fluids are known to degrade in the presence of fresh stainless steel [23,46,50–54]. The oxide layer on metal surfaces enhances the chemical inertness of the metal surfaces.

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However, these protective oxide layers can be removed during normal operations. In vacuum environments, where the supply of oxygen is severely limited, the oxide layers will not readily reform, resulting in a fresh and active metal surface. The saturated hydrocarbons, such as the MAC X2000, are nonreactive under these conditions and do not generate decomposition products [41,48,55]. John et al., have suggested that hydrocarbons may undergo tribiologically initiated free radical decomposition under ultrahigh vacuum conditions [56]. 16.5.1.8 High surface tension Low surface tension (18 to 30 dyn/cm) is associated with creep or migration of the lubricant. As the lubricant migrates away from the region of contact, it can lead to oil starvation in the contact zone and increased friction and wear. Molecular seals incorporating a labyrinth geometry can prevent the oil from migrating away from the contact zone. Low surface tension, while promoting creep, is beneficial since it promotes wetting of the surface. Problems with creep have been encountered with PFPE oils due to their low surface tensions (18 dyn/cm). Sicre et al., reported surface tension data for Fromblin Z25 (21.1 dyn/cm) and MAC X2000 (30.7 dyn/cm) [47]. The migration of the lubricant can be mitigated by the use of a grease, which is a blend of the base oil and a thickener to form a semisolid liquid. The high viscosity of the grease immobilizes the oil so that it remains in place. The grease can supply additional lubricant to the contact since it can act as a lubricant reservoir [22]. Pentadecafluorooctylmethacrylate, an oleophobic polymer with a low surface tension (11 dyn/cm), can be coated on the surface to slow surface wetting and any associated creep. The film acts as an anti-creep barrier and can be beneficial in reducing oil loss especially where the mode of loss is creep and wetting. It cannot slow the loss of oil due to volatility [23,24,57].

16.5.2 Greases Based on Alkylcyclopentanes The alkylcyclopentane fluid, tris(2-octyl)cyclopentane (Pennzane® SHF X-2000) has been used as the base fluid for a number of greases, particularly for aerospace applications. Bessette describes greases using traditional soaps and PTFE as thickeners [58,59]. X-2000 based greases have shown excellent performance in ball-on-disk tests [60]. When thickened with PTFE, X-2000 greases were shown to be superior to those formulated with perfluoropolyalkylether in the spiral orbit tribometer [61–64]. X-2000 greases thickened with a variety of thickeners have been compared [65,66]. The performance of greases based on X-2000 to those based on PAOs and silanes have been reported [67].

A review has been written by Bessette comparing greases based on X-2000, polyphenyl ethers, and silanes [68,69].

16.5.3 Computer Disks Tris(2-octyldodecyl)cyclopentane and derivatives have been evaluated for use in the lubrication of computer disks [70,71].

16.6 CONCLUSIONS Alkylcyclopentanes with a wide variety of tribologically useful properties can be prepared by simple chemical reaction sequences. The facile alkylation of cyclopentadienide anion by alkyl halides and alcohols followed by hydrogenation of the intermediate alkylcyclopentadiene provides the products.

The properties of single-ring alkylcyclopentanes are determined by the number and nature of the substituents. Except for very compact or highly branched structures, the kinematic viscosity is determined almost exclusively by molecular weight. The other main viscometric properties, VI and pour point, are governed by the length of the average alkyl chain and by the extent of branching. As the average uninterrupted normal alkyl chain gets longer, the VI and the pour point will both get higher, all other things being equal. Branching drives both VI and pour point down. However, if a molecule is large enough to have both extensive branching and long uninterrupted alkyl chains, high VI and low pour point are achievable. For example, tris(2-octyldodecyl)cyclopentane has VI = 136 and a pour point of <−57◦ C. Although alkylcyclopentanes have not been commercialized in substantial quantities, a useful highly specialize set of hydrocarbon base oils, Pennzane®

APPENDIX 16.1 Lubricant-Related Properties of MAC Synthesized Hydrocarbon Fluids

Alkyl, Ra n-Octyl n-Octyl n-Octyl n-Octyl n-Octyl n-Decyl n-Decyl n-Decyl n-Decyl n-Decyl n-Decyl n-Dodecyl n-Dodecyl n-Dodecyl n-Dodecyl 2-Octyldodecyl 2-Ethylhexyl 2-Ethylhexyl Isononyl Isodecyl Isotridecyl 2-Octyl 2-Decyl n-Octyl/n-decyl n-Octyl/n-decyl

m, Number of groups 2 3 3,4 4 4,5 2 2,3 3 3,4 4 4,5 2 3 3,4 4,5 2,3 3 3,4 3,4 3,4,5 3,4,5 3 2,3

Cav b

Kinematic viscosity, 100◦ C, cSt

Kinematic viscosity, 40◦ C, cSt

Viscosity index

Pour point, ◦C

Reference

21 29 34 37 41 25 29 35 41 45 48 29 41 46 59 62 29 31 35.2 46 56 29 32 35c 41c

2.18 3.68 4.96 5.99 7.40 3.03 3.78 5.15 6.90 7.99 8.92 4.13 6.99 8.18 11.91 14.56 4.21 5.35 6.82 11.68 20.09 4.71 4.07 5.23 6.91

6.49 15.58 24.70 33.43 45.33 10.37 14.44 23.99 37.67 46.70 54.07 15.64 35.26 45.17 75.55 109.30 26.44 40.60 46.69 119.60 310.22 28.23 18.34 26.28 38.67

158 124 128 125 127 161 161 151 144 143 144 178 164 157 153 137 22 40 100 83 71 74 123 134 139

−24 <−57 <−57 <−48 <−54 +6 −9 −27 −45 <−60 <−45 +21 −9 −15 −9 −57 <−48 <−54 −46 −33 −27 <−54 — <−50 <−50

[7,8,15] [7,8,15] [7,8] [7,8,15] [7,8] [7,8,15] [7,8] [7,8,15] [7,8] [7,8,15] [7,8] [7,8,15] [7,8,15] [7,8] [7,8,15] [7,8] [72] [7,8] [72] [7,8,15] [7,8,15] [7] [7] [8] [8]

a R is the alkyl group in −R . m b C =  [(weight fraction) × (carbon number) ]. av i i i c Estimated from kinematic viscosity at 100◦ C. d Previously unpublished data.

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APPENDIX 16.2 Properties of Cyclopentanes from API Project 42 Report Compound name One cyclopentyl ring 9(3-Cyclopentylpropyl)heptadecane 11-Cyclopentylheneicosane 1-Cyclopentylheneicosane 11-Cyclopentylmethylheneicosane 11(2,4-Dimethylcyclopentylmethyl)heneicosane Two cyclopentyl rings 1-Cyclopentyl-4(3-cyclopentylpropyl)dodecane 1-Cyclopentyl-2-hexadecylcyclopentane 1,1-Dicyclopentylhexadecane 9[alpha(cis-0.3.3-Bicyclooctyl)methyl]heptadecane Three cyclopentyl rings 1,5-Dicyclopentyl-3(2-cyclopentylethyl)pentane 1,7-Dicyclopentyl-4(3-cyclopentylpropyl)heptane 1,3-Dicyclopentyl-2-dodecylcyclopentane

API Project 42 number

Carbon number

Viscosity, 100◦ C, cSt

Viscosity, 40◦ C, cSt

Viscosity index

Pour point, ◦ C

110 64 117 74 180

25 26 26 27 28

2.84 3.04 3.72 3.26 3.33

10.72 11.64 13.08 12.79 13.62

112 119 188 125 116

−21 −13 +45 −21 —

111

25

3.49

14.82

114

−40

15

26

3.74

14.21

162

+19

202 178

26 26

3.81 3.64

16.12 17.30

130 87

+12 —

553

22

3.88

20.84

58

—

113

25

4.52

23.43

105

−24

199

27

4.75

26.78

93

0

APPENDIX 16.3 Properties of Cyclopentanes with Two Fused Rings: Hydrindanesa

Compound 5-Decylhydrindane 2-Decylhydrindane 2-Butyl-5-hexylhydrindane 2-Butyl-1-hexylhydrindane 5-Butyl-6-hexylhydrindane 1-Hexadecylhydrindane 2-Hexadecylhydrindane 1,10-Di(5-hydrindanyl)decane

API Project 42 number

Number of R groups

Carbon number

Viscosity, 100◦ C, cSt

598 596 603 601 605 108 118 145

1 1 2 2 2 1 1 1

19 19 19 19 19 25 25 28

2.32 2.46 2.24 2.32 2.14 4.02 4.23 9.44

Viscosity, 40◦ C, cSt

7.84 8.23 7.91 10.18 8.43 16.33 17.27 4.68 (135◦ C)

Viscosity index

Pour point, ◦C

110 129 87 −2 25 151 157 102

— — — — — +2 — —

Reference [5] [5] [5] [5] [5] [5] [5] [5]

a Data in the range of room temperature to 150◦ C were extrapolated to 100◦ C and 40◦ C, temperatures more commonly used today.

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APPENDIX 16.4 Properties of Miscellaneous Ring Systems Containing a Five-Membered Ringa,b

Compound Perhydrodibenzo(a,i)fluorene 9-Dodecylperhydrofluorene 1,1-Di(5-perhydroacenaphthyl)ethane 5-Pentadecylperhydroacenaphthene 4(9-Heptadecyl)asperhydroindacene

API Project 42 number

Number of rings

587 237 200

5 3 3

193 177

3 3

Carbon number 21 25 26 (80◦ C) 27 29

Viscosity, 100◦ C, cSt

Viscosity, 40◦ C, cSt

Viscosity index

Pour point, ◦C

10.26 4.34 99.5

290.3 23.84 591.2

−199 81 <−200

— — —

5.59 6.44

28.55 48.42

138 75

— —

a All data are from American Petroleum Institute (1969). Properties of Hydrocarbons of High Molecular Weight Synthesized by Research Project 42 of the American Petroleum Institute, American Petroleum Institute, New York. b Data in the range of room temperature to 150◦ C were extrapolated to 100◦ C and 40◦ C, temperatures more commonly used today.

Synthesized Hydrocarbon Fluids, is available for aerospace uses. Other applications requiring low volatility and the chemical and tribological versatility of hydrocarbon might also be developed.

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17

Polybutenes Serge Decroocq and Maryann Casserino CONTENTS 17.1

Introduction 17.1.1 History 17.1.2 Manufacturing and Isobutylene Supply 17.1.3 Nomenclature 17.1.4 Applications 17.1.5 Synthetic Methods 17.2 Chemical and Physical Properties 17.2.1 Chemical Structure 17.2.2 Chemical Properties 17.2.3 Chemical Reactions 17.2.4 Physical Properties 17.2.4.1 Viscosity 17.2.4.2 Flash Point 17.2.4.3 Color and Appearance 17.2.4.4 Water Content 17.2.4.5 Total Acid Number 17.2.4.6 Bromine Number 17.2.4.7 Density 17.2.4.8 Molecular Weight and MWD 17.2.4.9 Volatility 17.2.4.10 Decomposition 17.2.4.11 Toxicity 17.2.4.12 Biodegradation 17.2.5 Very Low Viscosity Polybutenes 17.2.6 Polyisobutylene Rubbers 17.3 Performance Characteristics of Polybutenes as Synthetic Lubricant Additives 17.3.1 Polybutenes’ Advantages and Limitations 17.3.2 Tests for Deposit Formation 17.3.3 Applications 17.3.3.1 Polybutenes in Viscosity Adjustment 17.3.3.2 Polybutenes in Marine Diesel Cylinder Lubricants 17.3.3.3 Polybutenes in Two-Stroke Oils 17.3.3.4 Polybutenes as Compressor Lubricants 17.3.3.5 Polybutenes in Gear and Hydraulic Oils 17.3.3.6 Metalworking Fluids 17.3.3.7 Polybutenes in Grease Manufacture 17.3.3.8 Polybutenes as Wire Rope Lubricants 17.3.4 Summary 17.4 Manufacture and Economics 17.4.1 Manufacturers and Capacities 17.4.2 Market Price 17.5 Outlook References

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17.1 INTRODUCTION 17.1.1 History Butlerov and Gorianov are attributed with preparing the first polymers of isobutylene in the 1800’s. This followed work by Berthelot and others who studied the polymerisation of various olefins using Friedel-Crafts catalysis systems [1]. During the 1930’s commercial processes for the manufacture of solid polyisobutylene rubbers were introduced first in Germany [2] and then in the United States [3]. It was not until later, in the 1940’s and 1950s, that commercial routes were developed for the preparation of liquid polybutenes by Chevron [4], Standard Oil of Indiana [5], and the Cosden Petroleum Corporation [6] in the United States.

17.1.2 Manufacturing and Isobutylene Supply The current commercial routes to polyisobutenes are believed to be still very much based on the original technology developed by the likes of Cosden. However, improvements have been introduced and continue to be introduced by the producers to improve the manufacturing process, quality, and performance of the finished product. Specific details of the different manufacturing technologies that are in use are covered adequately and in some details in books [7,8] and in the patent literature [9,10]. Polybutenes are produced by the polymerisation of a hydrocarbon stream containing a high proportion of isobutylene. There are three main sources of isobutylene feedstock: • Refinery catalytic crackers producing gasoline • Steam crackers producing ethylene • Products of the dehydration of tertiary butyl alcohol,

which is a by-product in the manufacture of propylene oxide There can be competition for feedstock, since isobutylene is also used in the manufacture of several other important materials such as butyl rubber, methyl tertio-butyl ether (MTBE), alkylation products for gasoline antiknock properties, and polyisobutylene rubbers. The manufacturing process for polybutene using an isobutylene stream derived from the steam cracking of naphtha is shown in Figure 17.1. Crude oil is first separated by distillation into its many fractions. The naphtha cut is fed to a steam cracker, where it is broken down to ethylene, propylene, and a C4 olefin cut. The C4 cut is processed in a unit to extract the di-olefin butadiene. The butadiene raffinate, or raffinate 1 as it is often referred to following butadiene extraction, normally contains isobutylene (40–50 wt%), n-butenes, (20–30 wt%), and butanes (20–30 wt%). The raffinate 1 is then typically desulfurized and dried prior to being introduced into the reactor section.

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The isobutylene in the raffinate 1 stream is polymerised selectively using a Lewis acid catalyst to produce the polybutene polymers. The chain length or molecular weight of the polybutene polymer can be controlled by changing the reaction conditions (e.g., by changing the temperature of the polymerisation). The polymerisation is exothermic, and so cooling of the reactor is necessary to maintain the desired temperature of polymerisation. Upon completion of the polymerisation, catalyst residues, unreacted butenes, and the butanes are removed from the product. The remainder is then distilled to remove light polymer, leaving the final polybutene product. This is then transferred to storage. After quality control, it is sent out in bulk road cars, drums, or other suitable containers to the customer. The light polymer that is distilled can be further processed to yield useful low viscosity grades of polybutene. The unreacted butenes and the butanes (raffinate 2) can be used as a feed for processes requiring high levels of n-butenes or returned to the cracker for further processing.

17.1.3 Nomenclature As described, polyisobutenes or polyisobutenes are produced from a feed stream containing a mixture of butene monomers. The feed stream is rich in isobutylene but also contains proportions of butene-1 and butene-2 monomers. Polymerisation of this stream yields a polymer of essentially isobutylene that also contains a certain amount of the other monomer structures. The ratio of isobutylene to butene monomer incorporation increases as the molecular weight of the polybutene increases. That is, the higher molecular weight polybutenes contain less butene-1 or butene-2 structure in the polymer backbone. Nevertheless, to be strictly correct, these polymers should be described as copolymers of isobutylene/butene. Historically, for ease of reference, the term “isobutylene/butene copolymer” has been replaced by the shorter term, polyisobutenes (PiB), and this nomenclature has been retained throughout the chapter. Polyisobutenes are polymers that are liquid, although the higher molecular weight polybutenes possess some semisolid rubbery character. The term “polyisobutylenes” is usually reserved for polymers derived from a feed stream containing only the isobutylene monomer. Polyisobutylene polymers are normally high molecular weight (Mn > 10,000) rubbers. Another material that is sometimes confused with polybutenes is the thermoplastic polybutene-1. Polybutene-1 is produced by a transition metal (Ziegler-Natta) catalysed polymerisation of butene-1. Isotactic polybutene-1 has good high temperature properties and has found use in applications such as plastic hot water pipes and in heat-sealing plastic films [11]. Finally, the butyl rubbers, which are copolymers of isobutylene and isoprene, comprise another class of

Light polymer

Crude oil

Naphtha

Butadiene raffinate

C4 Cut

Treated raffinate

Isobutene 40–50% butenes 20–30% butanes 20–30%

polybutene

Polybutene raffinate

FIGURE 17.1 Schematic representation of the production of polybutene from crude oil.

material containing high levels of isobutylene monomer. The incorporation of isoprene at low levels introduces carbon-carbon double-bond functionality into the polymer structure, which allows butyl rubber to undergo conventional cross-linking reactions. From the foregoing discussion, it should be clear that the nomenclature “polybutenes” refers to liquid polymers made up predominantly of the isobutylene monomer. Polybutenes are available in a wide choice of viscosities or grades with appearance ranging from that of a free-flowing light oil to a semisolid rubber at 25˚C. There is little consensus among manufacturers on a standard system of nomenclature for grades of polybutene. An approach that has been used historically is to name the polybutene grade on the basis of its viscosity measured in SSU (Saybolt viscosity) at 100◦ C divided by 100. For example, using this system a polybutene with viscosity of 2960 SSU at 100◦ C would be defined after rounding to the nearest whole number as a 30 grade. Throughout this chapter though, the BP nomenclature system will be used to designate the various grades.

for lubricating oils and greases, and as components of explosives. Of the remaining 40% of world production, between 5 and 10% is used in cable applications, where the excellent insulating properties, high quality, and good consistency of polybutene are used to advantage to replace mineral oil in the formulation of filling compounds for electrical, telecommunication, and fibre optic cables, and for the impregnation of metallized paper capacitors. Industrial applications of polybutene that make use of the physical properties of the liquid polymers account for 30 to 35% of world production. In the period since their commercialisation, the range of physical properties of these polymers has led to their use in many everyday applications. Polybutenes are now widely used in oils and lubricants, adhesives, sealants, agrochemicals, tackified polyethylene, bitumen modification, concrete mould oils, mastic and putties, anticorrosion coatings, masonry coatings, paints, inks, and dispersion aids.

17.1.4 Applications

The cationic polymerisation of streams containing isobutylene is typically achieved using Lewis acid type catalyst systems. For example the Cosden process describes the use of anhydrous aluminium trichloride slurry with either gaseous HCl or chloroform as co catalyst [15]. Many other combinations of catalyst and co catalyst are capable of performing the polymerisation [16]. Cationic polymerisation remains an active field of research, as evidenced by the considerable quantity of scientific publications that deal with all aspects of the polymerisation process [17].

The major applications following commercialisation of liquid polybutenes made use of the many attractive physical properties of the polymers. Polybutenes found use as components of adhesives and sealants, as electrical oils, and as modifiers of rubbers [12]. Later the chemical reactivity of the polymer was recognized, with polybutenes being used as a starting material for the manufacture of ashless detergents [13]. Today about 60% of world production of polybutene is used in the manufacture of polybutene derivatives. The main class of derivatives are the polybutenyl succinimides, used as ashless detergent additives to combat wet sludge formation in crankcase engine oils, which are now also finding an important role as detergent additives for gasoline and diesel fuel to prevent carburettor fouling and engine deposits [14]. Derivatives of polybutene are also manufactured for use as corrosion inhibitors, as antiwear additives

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17.1.5 Synthetic Methods

17.2 CHEMICAL AND PHYSICAL PROPERTIES 17.2.1 Chemical Structure The structure of polybutenes as shown in Figure 17.2 is essentially that of the isobutylene repeat unit with incorporation of low levels of other butene structures. The majority of polybutene polymer molecules contain a carbon-carbon

CH3 CH3

C

CH2

CH3

CH3

C

C

CH3

CH3

CH.CH3

n –2

economics, or to satisfy customer end-use requirements, polybutenes of different viscosities can be blended to provide a polybutene grade with an intermediate viscosity range.

17.2.2 Chemical Properties CH2 .CH2 .CH CH3

CH2 .CH CH2 CH3

FIGURE 17.2 Typical structure of polybutene polymers. Backbone structure made up of predominantly the isobutene monomer unit, but there is low level incorporation of other butene structures; end group structure, mainly trisubstituted type. Polybutenes now available with high levels of vinylidene structure [PIB. CH = CH2 ].

double bond at the end of the polymer chains. A small minority of polymer chains are terminated with a carbonhalogen bond. The position of the double bond end group is important in determining the ease with which it may undergo chemical reaction. From “C NMR studies it has been shown that the positioning of the double bond in most polybutene grades gives rise to the cis- and transtrisubstituted end group structure. From studies of model compounds it has been shown that a number of other positions for the double bond at the end of the polymer chain are possible. An internal double bond may be present in some polymer chains, although these prove difficult to characterize. Polybutenes contain only one double bond per polymer molecule and therefore cannot undergo conventional cross-linking reactions. The composition of a given polybutene in terms of backbone structure and the positioning of the double bond at the end of the polymer chains can be influenced by the manufacturing conditions but is perhaps mostly dependent on feedstock composition and the overall manufacturing process. Polybutenes having the predominantly di-substituted vinylidene structure at the end of the polymer chains are now commercially available [18]. The preponderance of the vinylidene end group structure gives improved chemical reactivity to the polymer in, for example, the maleinization reaction with maleic anhydride to produce the important polybutenylsuccinic anhydride derivative. Polybutenes are available on the market as grades defined by a viscosity range. The nature of the polymerisation process results in each grade being made up of a distribution of polymer chains of different chain lengths or molecular weights Polybutenes produced by cationic polymerisation have relatively narrow molecular weight distributions. The shape of the distribution curve for a polybutene will to a good approximation approach that of a Gaussian distribution. For reasons of plant operation or

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Polybutenes are straight chain, aliphatic polymers made up of predominantly the isobutylene repeat unit. The main hydrogen types in the polymer are secondary and primary. Incorporation of other butene structural types in the polymer chain introduces a small proportion of the more reactive tertiary hydrogen type. However the main focus for any reactivity in the polybutene structure is the olefinic bond at the end of the polymer chain. Reaction of this olefinic group is normally achieved only under certain contrived conditions. Under normal storage conditions and for industrial applications, polybutenes can be considered to be stable products. The chemical stability of the polybutene polymers is well demonstrated by their retention of viscosity and tackiness, and by their failure to harden, to become waxy, or to show any deterioration in colour upon storage for many years at ambient temperatures. As produced, polybutenes are extremely pure materials containing extremely low levels of additional species such as water, chlorine, and metals such as iron. The polymers are also free from nitrogen and sulphur species at detectable levels. Sensitive tests recognized for the detection of polycyclic aromatic hydrocarbons have failed to detect the presence of aromatic compounds in polybutenes [19]. Polybutenes are constructed of carbon and hydrogen and are non polar in character. As such, they are normally soluble in non polar solvents and insoluble in polar solvents. Polybutenes are soluble in hydrocarbon solvents such as benzene, toluene, heptane, and kerosenes, in common halogenated hydrocarbons such as chloroform, methylene chloride, and carbon tetrachloride, and in certain oxygenated solvents such as tetrahydrofuran and diethyl ether. Polybutenes are insoluble in simple alcohols, esters, and ketones. Solubility does increase, however, with higher homologues and as the molecular weight of the polybutene decreases. Polybutenes are fully compatible at all concentrations with low, medium, and high viscosity mineral oils of varying aromatic, paraffinic, and naphthenic contents. Full compatibility has also been demonstrated with poly(αolefins) (PAOs) and alkyl benzenes. In most, but not all, cases polybutenes have been found to be compatible with synthetic ester oils. Incompatibility is found with silicone oils, except for some low viscosity polybutene grades, and with polyalkylene glycols. Polychloroprene and nitrile rubbers show good resistance to polybutenes, as do fluoroelastomers such as Teflon and Viton. These materials are most suitable for the pump packing and seals of equipment used to handle polybutenes.

17.2.4.1 Viscosity

Polybutene alcohol Phosphosulphurized polybutene

Hydrogenated polybutene

[24]

[23]

[20] Polybutene

Epoxidized polybutene

[22]

[21]

Halogenated polybutene

FIGURE 17.3 Some examples of the chemical reactions of polybutene.

17.2.3 Chemical Reactions The major end use for polybutenes takes advantage of the reactivity of the polymer afforded through the double bond at the end of the polymer chain. This involves reaction of a polybutene with maleic anhydride at elevated temperatures to produce a polybutenylsuccinic anhydride. Further reaction of the polybutenylsuccinic anhydride with a polyethylene polyamine forms the important imide derivatives used as ashless detergent additives in crankcase motor oils to disperse the sludge that forms in the engine at low engine temperatures. Polybutenylsuccinimides and polybutenylamines are used as gasoline additives. Their use at low concentration in the gasoline improves cleanliness in the carburettor, in valve ports, and on valve stems, helping, as well, to prevent of deposits on pistons. Under suitable conditions polybutenes can be made to take part in many of the typical reactions of simple olefins as indicated in Figure 17.3. In these reactions, the position of the olefin bond at the end of the polymer chain plays an important role in determining the course of the reaction and the yield that is possible. With the availability of polybutenes containing high levels of the vinylidene end group structure, which show improved reactivity compared with conventional polybutenes, routes to more effective and cleaner chemical reactions are expected to emerge.

The kinematic viscosity of polybutenes is normally measured using a suspended level viscometer under conditions set out in ASTM D-445. The viscosity of polybutenes increases with the molecular weight of the polymer. Polybutenes are available commercially with viscosity from about 1 to 45,000 cSt at 100◦ C, corresponding to a molecular weight range from 180 to 6000. The change in viscosity with temperature is illustrated in Figure 17.4. The rate of change in polybutene viscosity with temperature diminishes as the molecular weight of the polymer increases. To facilitate the handling and pumping of polybutene Indopol H-300 grade and above, the system is normally heated to between 60 and 100◦ C to lower the viscosity of the material. Polybutene Indopol H-100 grade and below offer viscosity index comparable to that available with mineral oil products. Viscosity index in excess of 170 and up to 380 are available from H-300 grade and above, but associated with these grades are relatively high viscosity and pour point. The viscosity of polybutenes up to H-300 grade show little dependence on shear rates and could be classed as near-Newtonian fluids. Above Indopol H-2100 grade, viscosity begins to show some dependence on shear rate, and at high shear rates, there is evidence to suggest some pseudoplastic behaviour.

17.2.4.2 Flash point The flash point of polybutenes is normally measured using Pensky Martin closed cup (PMCC) or Cleveland open cup (COC) apparatus under conditions set out in ASTM D-93 and D-92 methods. The flash point of polybutene indicates the proportion of low molecular weight polymer in the bulk material. The level of low molecular weight polymer present in the polybutene is influenced by the extent of light polymer stripping used by the manufacturer during production. Polybutene grades sold commercially are manufactured to a guaranteed flash point specification. In general, although it needs not be the case, flash points increase with the polybutene grade or molecular weight.

17.2.4 Physical Properties The main physical properties used routinely to characterize a polybutene are its viscosity and flash point. A typical product specification might also include properties such as colour, water content, and appearance. Other polymer properties such as density, molecular weight, and refractive index are used less frequently for product specifications. Polybutene grades representative of the range of polybutenes available on the market are given together with their typical physical properties in the appendix. The full range of grades from the low viscosity 03 grade to the high viscosity, semisolid 2000 grade find use in synthetic and semi synthetic lubricant applications.

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17.2.4.3 Colour and appearance The colour of polybutene is normally assessed by a visual examination in which a sample of polybutene is compared against a series of recognized colour standards. This forms the basis for the ASTM D-1209 method for determination of colour in Hazen (Platinum/Cobalt) units. Polybutenes are extremely low coloured materials and can be described as almost water-white products. Polybutenes should contain no particulate matter or other visible impurities. The bright, clear and water-white appearance of polybutene grades is a useful indicator to the quality of the material.

20,000,000 10,000,000 5,000,000 2,000,000 1,000,000 500,000 200,000 100,000 50,000 20,000 10,000 5,000 3,000 2,000 1,000

H-10000 H-6000

Viscosity (cSt)

500 400 300 200 150 100 75

H-1900 H-1500 H-1200

H-300

50 40 30

H-100

20

H-50

15

H-35 10 9 8 7 6

H-25 H-15

5 H-8 H-7

4

L-50 3 L-14 L-8

2.00 1.75

L-6

1.50 L-3 L-2

1.00 0

10

20

30

40

50

60

70

80

90 100 110 120 130 140 150 160 170 180 190 200

Temperature (°C)

FIGURE 17.4 Variation in viscosity with temperature for polybutene grades 03 to 2000.

17.2.4.4 Water content

17.2.4.5 Total acid number

The water content in polybutenes can be determined by a titrimetric technique using Karl Fisher reagent in accordance with ASTM D-1744. The water content of polybutenes is low, generally in the region of 20 to 40 ppm. Water levels in the region of 100 to 150 ppm cause a cloudiness to appear in the material; because polybutene is hydrophobic, higher levels of water are not tolerated, and the water separates to the bottom of the material as a discrete phase.

The total acid number for polybutenes can be determined using the ASTM D-974 method. Typically it is of the order of 0.02 mg KOH/g.

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17.2.4.6 Bromine number The bromine number determination by the IP 129 method gives a measure of the amount of carbon-carbon double-bond unsaturation per unit weight of material.

0.94 0.92 0.9

Density g/mL3

0.88 H-18000 H-6000 H-2100 H-300 H-100 H-50

0.86 0.84 0.82

H-25

0.8

H-7 L-8

0.78

L-6

0.76

10

30

40

50

60

70

80

90

100

110

130

Temperature (°C)

Polybutenes contain one double bond at the end of each polymer chain. The drop in bromine number with increasing molecular weight of polybutene reflects the lower level of double bonds per unit weight of material. 17.2.4.7 Density The density of a polybutene can be measured using a hydrometer, following the ASTM D-1298 procedure. The density of polybutene at 15.5◦ C increases with the polybutene grade or molecular weight and varies from 0.82 for L-6 grade up to 0.92 for H-18000 grade. The density of polybutene is a function of temperature and decreases with increasing temperature. The variation in density with temperature is shown for several grades of polybutene in Figure 17.5. 17.2.4.8 Molecular weight and molecular weight distribution The number-average molecular weight (Mn) of polybutene can be determined by vapour pressure osmometry (VPO) using ASTM D-2503 and by gel permeation chromatography (GPC) using the principles outlined in ASTM D-3593. GPC also gives information on the weight-average molecular weight (Mw) and the molecular weight distribution (MWD) of the polymer. The dispersion index (DI), which is a measure of the breadth of the molecular weight distribution, can be calculated from the quotient Mw/Mn Each polybutene grade contains a range of polymer molecules of different chain lengths spread around the number average. The shape of the MWD for polybutene from a manufacturing plant is normally unimodal and approximates that of a Gaussian distribution. Typical GPC traces for H-100 grade is shown in Figure 17.6. Intentional blending to form intermediate grades or poor manufacturing control can lead to polybutenes with relatively high dispersion indices and

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RI intensity

FIGURE 17.5 Variation in density with temperature for polybutene grades L-6 to H-18000. 19 18 17 16 15 14 13 12 11 10 9 2

2.5

3

3.5

4

4.5

Log MW (g/mol)

FIGURE 17.6 Typical molecular weight distribution curves for polyisobutene H-100 grade.

molecular weight distributions that contain shoulders or bimodal peaks. 17.2.4.9 Volatility Each polybutene grade is made up of a distribution of polymer chains of different molecular weight (Section II.D.8). As one consequence of this distribution, at temperatures in excess of about 80◦ C polybutenes can loose a proportion of their mass through evaporation of the lowest molecular weight polymer molecules. The rate of loss of material decreases with increasing polybutene molecular weight. The evaporation loss expressed as a percentage weight loss is shown for H-7 to H-18000 grade polybutene in Figure 17.7. Evaporation loss was determined on samples of polybutene held at various fixed temperatures for a 10-hours following ASTM D-972. 17.2.4.10 Decomposition Polybutenes differ from most other oils by decomposing at temperatures of 220–240 ◦ C through a depolymerisation or unzipping mechanism. The decomposition products are

120

100.0

TGA : Programmed heating at 3°C per min. in airflow rate at 25 ml/min.

10.0

Weight loss (%)

Weight loss (%)

100 H-7

1.0 H-100 H-300 H-2100 H-6000

0.1 90

100

110

120

140

150

60 40 Indopol H-300 20

H-18000 130

80

160

170

180

Temperature (°C)

FIGURE 17.7 Volatile loss for polybutenes when held at high temperature for 10 hours following ASTM D-972

of considerably lower molecular weight than the numberaverage molecular weight of the grade from which they are derived. Under conditions of rapid depolymerisation it has been shown that the main product of decomposition is isobutylene. Depolymerisation of the polymer chain does not proceed rapidly below temperatures of 180 to 200◦ C. At these temperatures, it is often difficult to distinguish between evaporation loss of low molecular weight polymer molecules and possible loss of polymer fragments through depolymerisation. Thermo gravimetric analysis results for several grades of polybutene are shown in Figure 17.8. The similarity in the curves for H-300 and H-6000 grades at temperatures above 230◦ C indicates the onset of depolymerisation in both polybutene grades. Polybutenes stored at high temperatures over a period of time are normally maintained under an inert gas atmosphere (nitrogen e.g.,). This prevents the formation of potentially explosive mixtures of low flash point material over the liquids and also avoids slow oxidation which can lead to discoloration of the polybutene. The depolymerisation mechanism of polybutenes is very valuable in allowing the higher molecular weight grades to volatilise before combustion takes place. This type of decomposition occurs cleanly and completely without the formation of carbon or carry materials and is in contrast to the behaviour of mineral oils, which decompose to leave carbon residues. However, if a polybutene is heated to above its flash point and then ignited, carbon and smoke will be generated as combustion products. In the case of the higher molecular weight grades, combustion is not selfsustaining unless the body of the liquid is raised to a temperature at which rapid depolymerisation also may occur.

Indopol H-6000

0 0

50

100

150 200 250 300 350 Temperature (°C)

400

FIGURE 17.8 Thermogravimetric analysis of polybutenes, heating at 180◦ C/h in dry air with flow rate 25 ml/min.

of extremely low oral toxicity. The acute oral toxicity of polybutenes is extremely low, with LD50 values quoted in the range of greater than 15.4 to 34.1 g/kg in rats, these being the maximum dose levels used. Long-term chronic oral studies employing 2 wt% polybutene in the diet of rats and up to 1000 mg/kg/day in dogs, for 2 years, produced no treatment-related effects [25,26]. These findings indicate that polybutenes can be considered to be practically nontoxic by ingestion, although intake of significant amounts may give rise to gastrointestinal disturbance. Polybutenes are virtually insoluble in water, and their bio toxicity in an aqueous medium is therefore difficult to assess. The International Marine Organisation (IMO) rates polybutenes as unlikely to bio accumulate and non hazardous to marine species. 17.2.4.12 Biodegradation In studies based on the European Community (EC) respirometric test for theoretical oxygen demand (ThOD), comparative tests revealed polybutene levels of biodegradation to be less than that for a poly(α-olefin) or mineral oil of similar viscosity. Under the test conditions, none of the materials attained the necessary level of ThOD to be regarded as readily biodegradable as accepted by the Organization for Economic Cooperation and Development (OECD) [27]. Under more favourable conditions, such as higher levels of active sludge acting for a longer period, however, it is clear that biodegradation of the oils including polybutene would be increased. The highly branched structure of the polybutene polymer is thought to be responsible for its resistance to biodegradation [28].

17.2.4.11 Toxicity

17.2.5 Very Low Viscosity Polybutenes

Polybutene polymers are materials of very low biological activity, as evidenced by their accepted use for many years as components of cosmetics, surgical adhesives, and pharmaceutical preparations. The polymers are products

In addition to the grades of polybutene described so far, there are polybutenes commercially available with viscosity below that of the L-6 grade. Commonly referred to as very light polybutenes, these grades are among the

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products isolated from the light polymer stream by distillation (Section LB). The very light polybutenes contain oligomers, which are mainly trimers and tetramers of mixed butenes. Grades are available with viscosity in the range 1 to 4 cSt at 20◦ C and flash points of 55◦ C to above 70◦ C, as determined by closed cup method. The very light polybutenes are solvent-like in character and find use in applications such as replacements for hydrocarbon solvents, in various industrial uses such as concrete mould release oils or 2-stroke oils.

17.2.6 Polyisobutylene Rubbers Polyisobutylene rubbers (Section LC.) are produced with molecular weights from 10,000 up to several million. They are used as components in adhesives and sealants, and in coatings. They also serve in oil and lubricant applications for thickening and for producing tacky or antithrow oils.

17.3 PERFORMANCE CHARACTERISTICS OF POLYBUTENES AS SYNTHETIC LUBRICANTS ADDITIVES 17.3.1 Polybutenes’ Advantages and Limitations Synthetic oils are used in applications in which mineral oils do not give the required level of performance for the lubricant or when a synthetic oil can provide a performance and cost advantage over a conventional mineral oil. Synthetic lubricants offer a number of advantages over mineral oil based products. These are well known and are summarized in Table 17.1. Poly(α-olefins) and esters will offer most or all of these benefits. In comparison, a polybutene with the same viscosity is more volatile and less resistant to oxidation. Polybutenes offer improvements in viscosity index only through use of more viscous and high pour point grades. Polybutenes therefore should not be considered to be true synthetic base oils in the same sense as PAOs and esters are for automotive engine oils. Polyisobutenes should really be considered as synthetic additives for lubricants applications. They find use where the special properties of the polymer such as very low deposit formation, low

TABLE 17.1 Performance Advantages Available from Synthetic Oils over Mineral Oils Reduced Pour point Volatility Toxicity Deposits

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Increased Oxidation stability Viscosity index Dispersancy Lubricity Flame resistance

TABLE 17.2 Properties of Polybutenes for Oil and Lubricant Applications Synthetic liquid organic polymers available in a wide range of viscosities Practically nontoxic Good lubricants Viscous grades have high viscosity index and are shear stable All grades depolymerize at elevated temperatures, leaving no residue Stable to UV radiation and, under moderate conditions, to oxidative degradation Medium and high viscosity grades provide tackiness and adhesiveness Clear and colourless Hydrophobic and non-corrosive

toxicity, thickening power, and polymer shear stability are of prime concern, and other properties such as volatility and high temperature oxidation resistance are of secondary importance. Properties offered by polybutenes for oil and lubricant applications are given in Table 17.2.

17.3.2 Tests for Deposit Formation The Conradson carbon residue test illustrates the tendency of polybutenes to form very low levels of deposits. In this test, oils are destructively heated in accordance with ASTM D-189 and the level of carbon deposits remaining is determined. The results of this test comparing polybutenes, esters, PAOs, and mineral oils are shown in Figure 17.9. It can be seen that both the low and high viscosity grades of polybutene give rise to extremely low levels of carbon deposits. In the test polybutenes gave better results than esters and mineral oils, with brightstock high viscosity mineral oil giving the most deposits of the oils tested. Poly(α-olefins) also give rise to low levels of carbon deposits, although slightly in excess of the amount given by polybutenes. Under oxidation conditions as measured by the total oxidation products (TOP) regimen following IP 280 and IP 306 test methods, the oxidation products of polybutenes are predominantly those of volatile acids (see Table 17.3). Oxidation products in the form of soluble acids or sludge, which would be expected to remain with the lubricant, are lower for polybutene than for esters, mineral oils, and PAOs. This again confirms the low deposit-forming tendencies of polybutene.

17.3.3 Applications 17.3.3.1 Polybutenes in Viscosity Adjustment Thickening agents are often required to achieve the correct viscosity characteristics for automotive and industrial oils. The high viscosity mineral oil grades of brightstock are the traditional products used for thickening low viscosity mineral oils. Normally large amounts are required to achieve

2.5 2.1

Weight carbon formation (%)

2.0

1.5

1.0 0.6

0.5 0.15 0.02

0.01

0.01

0.01

0.0 Bright/S

Ester 13

SN 500

Solvent

Indopol H-7

Indopol H-300

Indopol H-2100

FIGURE 17.9 Residue carbon conradson according to ASTM D 189.

TABLE 17.3 Comparison of Oxidative Breakdown Products of Polybutenes with those of other Oils. Following IP 280 and IP 300a Total acid number (mg KOH/g) Base oilb PAO, 4 cSt Ester, 13 cSt 150 SN Polybutene H-7 Polybutene H-50

Volatile acids

Soluble acids

Sludge (wt%)

Total oxidation products (%)

2.06 0.96 1.32 11.98 6.42

34.78 12.57 7.29 4.7 3.81

1.37 0.07 0.54 0.02 0.1

13.2 4.4 3.3 5.4 3.4

a Samples heated for 48 h under pure oxygen flow with copper catalyst. b PAO, poly(α-olefin); SN, solvent neutral.

the required viscosity adjustment. Polybutenes are very efficient synthetic alternatives to brightstock and have the advantage of raising the viscosity index of the thickened oil. In addition, the use of polybutenes improves the low temperature properties of the thickened oil by lowering the pour point and lowering the −18◦ C viscosity. The excellent shear stability of the polybutene polymer (Section III.C.4) ensures that the viscosity of the thickened oils is retained under normal service conditions. As an example, Figure 17.10 compares the thickening efficiency of polybutene with that of brightstock when

Copyright 2006 by Taylor & Francis Group, LLC

used to thicken solvent neutral 500 base oil. It can be seen that significantly less polybutene is required to give the same thickening effect as brightstock. The improvements in formulated oil viscosity index, pour point, and low temperature viscosity achieved through the use of polybutenes are clearly demonstrated for the oils blended to SAE 30, 40, 50 and ISO 32 viscosity specifications (Table 17.4 and 17.5). Polybutenes can be used in combination with esters and PAOs to provide partial or full synthetic blends for high performance lubricants. The use of polybutenes offers the formulator opportunities to achieve control of lubricant viscosity while imparting properties of low deposit formation, clean burning, and tackiness. If polybutene is used to replace a proportion of synthetic ester or high viscosity PAO, it should be possible to achieve savings in raw material costs while maintaining or benefiting lubricant performance. Polybutenes are fully compatible with PAOs and provide effective viscosity adjustment, as shown in Figure 17.11. With the higher viscosity polybutenes, a useful increase in the viscosity index of the blend is obtained at polybutene treat rates as low as 5–10%. Further investigation of lubricants meeting the ISO 32 specification reveals that polybutene/PAO blends provide superior viscometrics over the standard PAO product with only marginal changes in other physical properties (Table 17.5). Lubricant blends of polybutenes and PAO are of interest in high performance industrial oils, greases, and compressor lubricants.

Kinetic viscosity of blend at 40°C (cSt)

500 450 H-6000

400

H-2100

H-300

350 300 250 200 150

BRIGHT STOCK

100 50 0 0

5

10

15

20

25

30

35

40

45

50

Concentration of thickener in solvent 500 neutral (% Mass)

FIGURE 17.10 Viscosity adjustment of SN 500 mineral oil at 100◦ C comparing the efficiency of polybutene grades H-300, H-2100, and H-6000 with brightstock.

TABLE 17.4 Formulation for SAE 30, 40, and 50 Oils with Polybutenes and Brightstock Formulation Performance Polybutene 600 Polybutene 200 Polybutene 30 Brightstock 470/95 150 SN Kinematic viscosity, cSt At 100◦ C At 40◦ C Cold crank viscosity at –18◦ C, cP Viscosity index Flash point (PMCC), ◦ C Pour point, ◦ C

SAE 30

SAE 40

9.0 — — — 91.0

— 11.5 — — 88.5

— — 18.0 — 82.0

— — — 47.5 52.5

12.5 — — — 87.5

— 14.5 — — 85.5

— — 24.0 — 76.0

— — — 60.0 40.0

14.0 — — — 86.0

— 18.5 — — 81.5

— — 31.0 — 69.0

11.7 83.7 7,000 124 207 −15

10.8 78.5 6,000 124 205 −12

10.1 78 6,800 110 207 −12

11.3 98.3 12,000 101 213 −9

15.7 121 11,000 137 211 −15

13.1 101 7,600 126 200 −15

12.8 111 11,500 109 200 −15

14.2 140 21,000 98 221 −9

17.7 141 14,500 139 207 −15

16.7 141 12,400 128 196 −12

17 170 20,000 107 196 −15

In most cases there is good compatibility found for polybutenes and synthetic esters. Polybutene acts as an effective viscosity modifier for esters (Figure 17.12), with blends of interest in high performance two-stroke lubricants, industrial oils, greases, and chain lubricants. 17.3.3.2 Polyisobutenes in Marine Diesel Cylinder Lubricants In the last decade, marine diesel engines evolved on an unprecedented scale and this evolution placed even more severe technical demands on marine lubricants [29]. In this context, innovative additives technologies were developed to meet the new technical requirements. The use of bright stock as the thickener of choice has gradually become more problematic as the inherent

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SAE 50

drawbacks of bright stock were putting some limitations on the global performance of the lubricant. In addition, the quality of the bright stock has also become an important criteria to consider for use in Marine Diesel Cylinder Lubricants (MDCL) compositions. As described in previous chapter, polyisobutenes are very efficient synthetic thickeners with some demonstrated advantages. Hence the possibility to replace partially or totally the bright stock with a lighter oil/polyisobutene combination. The use of polyisobutenes in marine cross-head diesel engine cylinder oils has been first described in the patent literature in 1966 [30]. Marked improvements were demonstrated with compositions containing from 2 to 30% of polyisobutene, particularly in respect of the reduction of deposits in the grooves and on the inner part of the piston.

TABLE 17.5 Synthetic and Semi synthetic Blends with Polybutenes Showing Improvements in Viscosity Index and Low Temperature Viscometerics According to ISO 32 Full synthetic blends

Mineral oil: 100SN/500SN

Semi synthetic: 100SN/ PiB 600

PAO 6

PAO 4/ PiB 200

PAO 4/ PiB 600

62.5/37.5

96.0/4.0

100

92.5/7.5

94.0/6.0

31.3 5.18 3600 92 206 −10

31.5 5.82 1400 129 200 −16

31.1 5.88 870 136 224 −66

31.4 6.20 760 151 201 −52

31.0 6.23 710 155 203 −56

Blend/ratio Kinematic viscosity, cSt At 40◦ C At 100◦ C Cold crank viscosity at −25◦ C, cP Viscosity index Flash point, ◦ C Pour point, ◦ C

Viscosity of blend at 40°C (cSt)

a Mn 4200; b Mn 2500.

250 2000 200 150 600

100 50

200

0 0

5

10

15

20

Polybutene in PAO 4 cSt (wt%)

FIGURE 17.11 Viscosity adjustment at 40◦ C of a 4 cSt poly (α-olefin) with polybutene grades 200, 600, and 2000.

Viscosity of blend at 100°C (cSt)

90 80

10

70 60 50 40 5

30 20

07

10 0 0

20

40

50

60

Polybutene in ester 6 cSt (wt%)

FIGURE 17.12 Viscosity adjustment at 100◦ C of a 6 cSt diester with polybutene grades 07, 5, and 10.

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80

Likewise, a lubricating composition for low-speed, marine diesel engines was disclosed, comprising a mineral oil and a blend of two polyisobutenes, one of low molecular weight and the other with a higher MW [31]. In these lubricant compositions, polyisobutene has a positive effect on the deposits due to clean burn-off, but also on the wear performance. The incorporation of 3 to 10% of polyisobutene greatly reduces the wear on both ring and liner. This was also clearly evidenced in another patent describing the addition of 10 to 24% of polyisobutene with a molecular weight ranging from 250 to 950 that allows the reduction of premature wear on the piston and the cylinder walls [32]. 17.3.3.3 Polybutenes in Two-Stroke Oils Two-stroke engines power motorcycles, scooters, outboard motors for boats, snowmobiles, chain saws, and small agricultural equipment. The advantages of two-stroke engines over four-stroke crankcase engines lie in the high powerto-weight ratio of the former, which also offer simplicity of design and lower production costs. The market for two-stroke oil is very dependent on the fortunes of the motorcycle industry, which accounts for the majority of two-stroke oil consumption. White the market for twostroke oil in western Europe and Japan is seen as mature and in slow decline, growth in demand from the emerging countries in the Far East is increasing the size of the total market [33]. Unlike four-stroke crankcase lubricants, where the oil is held in the sump and pumped continuously to lubricate the engine, two-stroke oils are required to operate on a one-pass, total-loss basis. The oil is introduced into the engine either premixed with the fuel or by direct injection using a demand pump. The oil functions as a lubricant for the crank, bearings, and combustion cylinder and is then

consumed along with the fuel. Products of decomposition are lost through the exhaust system. Oil is therefore used continuously while the engine is in operation. Global specifications have been agreed for publication as an ISO standard classifying the performance of twostroke oils [34]. At the same time, the fitting of low cost catalytic converters to the exhaust system of motorcycles is becoming widespread. These steps have been driven largely by the dominant Japanese motorcycle producers, as they seek to assure the modern image of their product in the face of growing environmental pressures and concerns over engine reliability arising from the use of substandard oils. The global performance specifications, which build on those developed earlier by the Japanese Automotive Standards Organization (JASO) for oils used in Japan, benchmark the oil against a reference oil in the key performance areas of lubricity, detergency, exhaust smoke, and exhaust system blocking [35]. The JASO and global performance specifications are shown in Table 17.6. Traditional mineral oil based formulations can meet the requirements of the FB/EGB performance category shown in Table 17.6. It is, however, the FC/EGC performance level that is being widely adopted as the major type of oil used in Asian, European, and other markets. The original equipment manufacturers (OEMs) are promoting the use of improved quality oils by specifying FC/EGC in their handbooks. An FC/EGC oil provides low smoke, low exhaust system blocking, and good lubricity and detergency in the engine, and so addresses the environmental and performance concerns. The EGD level of performance was introduced to provide the European OEMs with oil having improved detergency in addition to low smoke and low exhaust system blocking. Polybutenes are recognized as an essential part of the oil formulation to meet the key FC/ EGC and EGD performance levels. Typically a minimum level of 30%

TABLE 17.6 Global and JASO Performance Classifications for Two-Stroke Engine Oil Performance requirementsa JASO specification: Global specification:

FB EGB

FC EGC

EGD

Engine

95 98 85

95 98 95

95 98 125

Piston skirt deposits

85

90

95

Exhaust smoke Exhaust system blocking

45 45

85 90

85 90

Honda Honda Honda Honda Honda Honda Suzuki Suzuki

Engine tests Lubricity Initial torque Detergency

Method JASO M340-92 JASO M340-92 JASO M341-92 (3-h test) JASO M341-92 (3-h test) JASO M342-92 JASO M343-92

a Reference oil Jatre-1 scores 100 in each test; performance indices are minimum requirements.

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polybutene is required to provide the low smoke and low blocking requirements for these oils. The oil blenders have largely consolidated on the use of a polybutene 10 grade, which provides a good overall balance of performance for the oil. Polybutene is normally combined with mineral oil, hydrocarbon diluent, and an additive pack to give a finished oil viscosity at 100◦ C in the 8 to 12 cSt range. An example of a minimum cost oil formulation meeting the FC/EGC performance level is shown in Figure 17.13. Even greater improvements in low smoke and low deposits in the engine and exhaust system are achieved through the use of polybutene up to levels of 55% in the oil formulation. At levels above 35% polybutene, formulators typically use combinations of high and low molecular weight polybutenes [36]. Inclusion of some synthetic ester in the oil formulation can improve lubricity, although care must be taken to ensure

that oil performance in smoke and exhaust system blocking is not compromised. An increased additive treat rate is normally employed to achieve the EGD performance level. Table 17.7 summarizes formulation options with polybutenes to meet JASO and global performance levels. A relationship has been proposed between the reaction energy of an oil and its tendency to produce visible smoke. Reaction energy is a measure of the energy involved in decomposing the oil [37]. Oils containing polybutene have been shown to have a low reaction energy and correspondingly low smoke-producing tendencies. The low value of reaction energy is clearly linked to the facile decomposition of the polybutene polymer at temperatures found in the two stroke engine. It has been reported that the structure of the polybutene used in the oil can influence the level of visible smoke

378 200 Polybutene 10 oil

JASO FC

180

Performance index

160 140 120 100

120 105 95

98 98

118 95

104 90

90

85

80 60 40 20 0 Lubricity

In.Torque Detergency P.Skirt

Blocking

Smoke

FIGURE 17.13 Example of a low cost two-stroke formulation based on polybutene 10 grade that meets JASO FC and global EGC performance requirements (P skirt, piston skirt deposits).

TABLE 17.7 Formulation Options with Polybutenes to Achieve Modern Performance Standards Polybutene function

Oil type Semi synthetic Semi synthetic Semi synthetic Semi synthetic Full synthetic

B/S replacement, lubricity additive Low smoke and low particulate base oil Low smoke and low exhaust blocking base oil Very low smoke and very low exhaust blocking base oil Low smoke component in combination with synthetic ester oils

PiB levels (wt%) 10–15 20–35 30–40

Typical polybutene grades

Expected performance levelsa JASO FB TISI JASO FC/global EGD

35–50

5, 10, 30 10 07, 5, 10, or combinations 07 and 5, 10, or 30

10–50

07, 5, 10

JASO FC/global EGD

JASO FC/global EGD

a JASO performance specifications for oils introduced by Japanese Automotive Standards Organization; global performance specifications for oils developed by the International Organization for Standardization (ISO); TISI performance specifications for oils introduced by the Thailand Industrial Standards Institute.

Copyright 2006 by Taylor & Francis Group, LLC

produced. Polybutenes that have low levels of butene-1 or which are free from butene-1 in the polymer backbone can undergo more complete depolymerisation and provide lower levels of smoke for the oil [38]. Very low viscosity polybutene (Section II.E) can be used to replace a proportion of the hydrocarbon diluent in the formulation. These low viscosity polybutene oligomers have a neutral effect on smoke and lubricity but appear to contribute positively to oil detergency and low exhaust system blocking [39]. Polybutenes are not readily biodegradable (Section II.D.12) by virtue of their highly branched structure, but have been shown to be essentially non-toxic in animals and non-photo-toxic in plants. Synthetic oils based on esters find application where legalization exists mandating the use of biodegradable oils.

17.3.3.4 Polybutenes as Compressor Lubricants Polybutenes are employed alone or in combination with other oils as lubricants for the barrels of compressors, which are used to generate the high pressures of ethylene gas required for reaction in the manufacture of low density polyethylene (LDPE). A simple scheme illustrating the steps involved in the production of LDPE is shown in Figure 17.14. Ethylene gas is supplied to a primary compressor, where it undergoes a first-stage compression to between 200 and 300 bar. It is then fed into the secondary compressor, where the ethylene gas is compressed to the final reaction pressure, which is normally between 2000 and 3000 bar. A peroxide initiator is pumped into the reactor where, at reactor temperatures 180 to 200◦ C, it undergoes a thermal decomposition to free radical species, which catalyse the polymerisation of the ethylene gas to LDPE. The unreacted ethylene gas that leaves the reactor is returned to the compressors for recycling, while the polyethylene passes to the polymer finishing section, where it is prepared for sale [40]. There are two designs of reactor: an autoclave reactor, which is a large stirred vessel, and a tubular reactor, which is basically a long high pressure pipe [41]. The reactor pressure employed in the autoclave reactor is generally 1500 to 2500 bar, while in the tubular

Initiator

Pure ethylene

Primary compressor

Secondary compressor

200–300 Bar

2000–3000 Bar

Reactor

Polymer

FIGURE 17.14 Schematic representation of the manufacture of low density polyethylene from ethylene gas.

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reactor the pressure is normally higher, at 2500 to 3000 bar. Conventional mineral oils are mostly used, and these are adequate for the lubrication of the compressor crankcase and bearings, and for the hydraulic and gear oils of the initiator pumps. However for the lubrication of the compressor barrels, and in particular the secondary compressor barrel, additional demands are made on the lubricant that cannot be satisfied by conventional mineral oil products. During the lubrication of the compressor barrel, the lubricant comes into contact with the compressed ethylene gas. Some of the lubricant is dissolved in the gas and is carried over continuously into the reactor area. A constant supply of lubricant to the cylinder is required to maintain adequate lubrication. After polymerisation, the lubricant is present at low levels as an intimate mix with the LDPE product. It is important therefore that the compressor barrel lubricant neither hinder the polymerisation reaction nor degrade the performance of the LDPE in its intended application due to its presence in the finished product. Table 8 lists properties required of the compressor lubricant. Polybutenes provide the necessary high pressure sealing, continuous film-forming, oxidation resistance, and limited volatility, and they meet in full the requirements regarding purity, low moisture content, low deposit formation, inertness, and food contact approval for lubricants in the application just described. Of importance in this application is the effect of pressure on the viscosity of the lubricant. Since the viscosity of the lubricant will increase with increasing pressure, its viscosity must not increase to the extent of compromising the operation of the lubricant delivery system for the compressor barrel, which would result in failure. Polybutenes thicken rapidly at high pressures, and for this reason their use tends to be found in the lower pressure autoclave LDPE manufacturing process. Thickening under pressure is a less serious problem if a blend of polybutene and a white

TABLE 17.8 Important Properties for the Lubricant Used in the Secondary Compressor Barrel for LDPE Manufacture Viscosity in the range 220–330 cSt at 38◦ C High pressure sealing capacity Low deposit formation Resistance to oxidation High purity Low volatility Low moisture content Inert to process gas and equipment No deleterious effect on end properties of LDPE Food contact approval

mineral oil is used. In the higher pressure tubular process, polyalkylene glycols are most often used to lubricate the secondary compressor barrel. Polyalkylene glycols thicken less than either polybutenes or polybutene/white mineral oil blends under pressure. In general, polyalkylene glycols are considered to offer better lubrication for the secondary compressor barrel. However polybutene lubricants are used in preference to polyalkylene glycols in the manufacture of ethylene/vinyl acetate copolymers, where the solubility of vinyl acetate in polyalkylene glycol precludes its use. Polybutene lubricants are also employed in the manufacture of LDPE destined for use either in electrical applications such as wire and cable or in coating applications such as card lamination. The residual low level of polyalkylene glycol in the LDPE appears to have a detrimental effect on the electrical properties of the polyethylene and also adversely affects the adhesion quality of coating grades. The use of polybutene has also been reported for lubricating compressors for other non-oxidizing gases such as hydrogen, nitrogen, and carbon dioxide [42]. 17.3.3.5 Polybutenes in Gear and Hydraulic Oils The selection of an oil for gear lubrication involves careful consideration of the gear design, the materials involved in the construction of the gears, and the likely conditions of operation. The viscosity of the oil has a key role in obtaining the correct thickness of oil to provide hydrodynamic lubrication of the gears, determine the load-carrying capabilities of the gears, control leakage at seals, and limit noise generation of the unit. The viscosity of the oil at low temperatures is important because the flow properties will determine the ease of start-up in cold climates and the ease of gear shifting. Gear systems are usually classified as automotive gears for cars and

commercial vehicles and industrial gears in manufacturing and processing industries. Automotive gear oils: For automotive gear oils, the SAE classification system has been adopted to define the performance of the oil in terms of viscosity at high and low temperature. Historically in Europe monograde oils have been used in cars and commercial vehicles. More recently, demands for improvements in the low temperature properties of gear oils and the realization that gear oil performance can make a contribution to fuel economy [43] have led to the development of multigrade gear oils. Multigrade oils are applicable for use over a wider temperature range than monograde oils, and the low temperature properties of the former are better defined. In 1998, the SAE classification system was reviewed and extended with the addition of 2 new grades and the requirement that all grades should remain “in grade” after the 20 h shear KRL test. Table 17.9 presents the complete new SAE 306 requirements. The first multigrade oils to be introduced, 80W-90 and 85W-140, could be formulated using conventional mineral oils. However, there is now a trend to even wider multigrade oils (e.g., 75W-90 for cars, 80W-140 for commercial vehicles), which require the use of synthetic base oils and viscosity index (VI) improvers. In Europe, where monograde oils still dominate the market, the use of multigrade oils should continue to grow as wider acceptance of advantages of synthetic oils is gained and the drive to improve fuel efficiency intensifies. Multigrade oils have found greater use in countries such as the United States, Canada, and Japan, where there is at present more emphasis on improving fuel economy and climatic conditions vary widely. As indicated, the viscometrics for 80W-90 and 85W140 oils can be met by blending brightstock oils with pour

TABLE 17.9 SAE J 306 Rev 1998 Requirements

SAE viscosity grade 70W 75W 80W 85W 80 85 90 140 250

Maximum temperature for viscosity of 150,000 mPa sec, ◦ C (Using ASTM D-2983)

Minimum

Maximum

−55 −40 −26 −12 — — — — —

4.1 4.1 7.0 11.0 7.0 11.0 13.5 24.0 41.0

— — — — <11.0 <13.5 <24.0 <41.0 —

Kinematic viscosity at 100◦ C, mm2 /sec (Using ASTM D-445)

Summer grades must stay-in-grade after shear in the KRL 20-h test (CEC L-45-T-53).

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point depressants and extreme pressure additives, although some companies include a VI improver to enhance the low or high temperature properties of the oil. The wider multigrade oils (75W-90 and 80W-140) cannot be blended using mineral oils alone, thus it is necessary to use synthetic base oils or blends of synthetic and mineral oils, or to add a VI improver in conjunction with synthetic or mineral oils. The selection of the correct VI improver is most important because of the severe mechanical shearing that exists in gear configurations. Clearly, the polymeric VI improver must be very shear stable in order to maintain effective viscosity contribution to the oil during service. Problems of VI improver breakdown were experienced during the initial stages of multigrade oil commercialisation. The early VI improvers, such as olefin copolymers or polymethacrylates with molecular weights in excess of 40,000, developed for crankcase engine oil, were found to undergo catastrophic mechanical breakdown when used in gear oils. It is now well recognized that much lower molecular weight polymers are required to withstand the greater demands made on polymer shear stability operating in a gearbox arrangement. Bench tests with diesel injector, FZG gear, roller bearings, and sonic equipment are now used routinely to assess the shear stability of prospective VI improvers and finished lubricant formulations. Polybutenes are shear-stable polymers that are effective as VI improvers in the formulation of high quality multigrade gear oils. Polybutenes are efficient oil thickeners at high temperatures and at the same time offer improved low temperature properties over oils thickened

with brightstock (Section III.C.1). The best combination of VI improvement and polymer shear stability has been found for polybutene grades 150, 200, and 600. The high viscosity of polybutenes at high molecular weight have led some manufacturers to offer special products in which the high viscosity polybutene is cut back with mineral oil to facilitate handling and blending [44]. Table 17.10 illustrates the excellent shear stability of the polybutene polymer when tested in diesel injector and FZG gear rigs. For comparison, the results of a commercial polymethacrylate VI improver are shown. The results show clearly the relationship between the molecular weight and the shear stability of the polymers. The trade-off that can be made between treat rate and cost (which favours the use of a relatively high molecular weight polymer) and the required polymer shear stability (which favours the use of a relatively low molecular weight polymer) will depend on the particular demands placed on the oil in the end application. For the wide multigrade 80W-140, the use of polybutene as a VI improver in combination with mineral oils is sufficient to achieve the viscosity specifications of the oil without recourse to special mineral oils or synthetic base oils. Polybutenes can be used as VI improvers in the formulation of 75W-90 oils. Without access to hydrocracked base oils, however, the use of a synthetic oil such as PAO or ester is required to achieve the viscosity specification. Also the quantity of synthetic oil in the formulation can be reduced by including low pour point base oil. An extended road car trial carried out with a 75W90 gear oil illustrates the excellent shear stability of the

TABLE 17.10 Shear Stability of Solvent Base Oil Thickened with Polybutene and Polymethacrylate (PAMA) Viscosity Index Improvers to Achieve a Similar Viscosity at 100◦ C SN base oil Property VI improver, polybutene grade/PAMA Molecular weight (Mn) Initial viscosity at 100◦ C, cSt Viscosity after diesel injector at 100◦ C, cSta Viscosity loss, % Initial viscosity at 100◦ C, cSt Viscosity after FZG shear at 100◦ C, cStb Viscosity loss, % Initial viscosity at 100◦ C, cSt Viscosity after FZG shear at 100◦ C, cStc Viscosity loss, %

PiB

PiB

PiB

PAMA

150 2300 19.12 19.00 0.60 19.12 17.57 8.10 18.44 16.40 11.00

200 2600 18.75 18.44 1.40 18.24 16.52 9.40 18.24 15.29 16.20

600 4200 17.72 17.35 2.10 17.72 15.65 11.70 17.72 14.39 18.90

— 9000 19.60 19.01 3 — — — 19.13 14.68 23.30

a Diesel injector rig IP294; 250 cycles. b FZG gear rig; proposed CEC TLPG7 conditions; load stage 5; extreme pressure

additive present. c FZG gear rig; IP351 (B); load stage 6; extreme pressure additive present.

Copyright 2006 by Taylor & Francis Group, LLC

TABLE 17.11 Examples of Wide Multigrade Gear Oil Specifications Using Polybutene as a Viscosity Index Improver Multigrade gear oil specifications 80W-140 SN100 SN300 Brightstock 470/95 PAO 6 Indopol H-6000 Indopol H-300 Indopol H-2100 Additive package Pour point depressant (ppd) Kinematic viscosity, cSt At 100◦ C At 40◦ C Viscosity index Pour point, ◦ C Cold crank viscosity, mPa sec (cP) At −18◦ C At −26◦ C At −40◦ C

polybutene VI improver, with the oil showing a loss of only 16.8% after 40,000 km service. The trial used a VW Passat with transaxle gear arrangement, which is known to provide a severe test of the shear stability of the VI improver. Industrial gear oils: Industrial gear units represent perhaps 60 to 75% of the total market for gear oils. Gears are classified as open and enclosed, with the enclosed gears gradually replacing open gears as the preferred design. The ISO viscosity system is used to specify industrial fluids. The requirements of an industrial gear oil are similar to those for an automotive gear oil. In addition, since water is often a contaminant in industrial processes, the oil must show good water separation characteristics. Polybutenes are polymers of high shear stability (Table 17.10) and can be used to adjust the viscosity of mineral base oils to the required viscosity specification for industrial gear lubricants. Polybutenes produce lubricants with superior viscosity index and low temperature properties over brightstock-thickened oils and can therefore be used to formulate more energy-efficient gear oils. In addition, the tacky nature of the high molecular weight polybutenes can improve the adhesiveness and antithrow properties of the oil, thereby increasing the retention lime of the lubricant on the gear surface. Polybutenes show good water separation, superior to solvent neutral fluids (SNI00 and SN500 mineral oils), but not as good as PAOs. The trend in the industrial sector is to the use of multipurpose and more energy-efficient oils. This suggests a

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75W-90

48.7 26.0 — — 17.8 — — 6.5 1.0

58.5 — 8.0 — — 4.5 21.5 6.5 1.0

23.5 — — 50.0 19.0 — — 6.5 1.0

18.3 — — 57.0 — 3.0 14.2 6.5 1.0

25.6 219 148 −27

25.2 245 131 −27

16.4 112 158 −39

15.3 110 145 −39

— 140,000 —

— 145,000 —

5,190 — 125,000

5,670 — 145,000

move to the use of more synthetic oils and an increased use of the cost-effective approach of employing shear-stable viscosity index improvers with conventional or special base oils. In addition, the demand for safer, non-toxic lubricants for use in the industrial sector will perhaps focus more attention on materials such as polybutenes, which are essentially non-toxic and are recognized as versatile materials for the formulation of lubricants. Hydraulic oils: The vast majority of hydraulic oils are based on mineral oils [45]. Polybutenes find use as viscosity adjusters and as shear-stable VI improvers in the formulation of mineral oil based hydraulic fluids. Polybutenes are especially useful where there is concern over contamination of the working area or the materials being handled by oil leakage from the hydraulic systems. This is the case, for example, with the lubricant used for the hydraulic system in an aluminium rolling plant discussed in the next section.

17.3.3.6 Metalworking Fluids In metalworking applications such as cutting, rolling, stamping, drawing, and pressing, a lubricant is used to maintain a protective film between the die or tool and the metal billet. Such a film acts to reduce the frictional heat generated during the operation. The lubricant is expected to prolong the life of the die or tool, reduce energy

requirements, and produce a smooth, stain-free surface on the metal article. Neat oils or soluble oils are suitable for applications where the loads between the die or tool and the metal being worked are light. High viscosity oils are preferred as these loads increase. In very demanding or severe operations, it is normal to include an extreme pressure additive in the oil. For example, fatty acid, fatty alcohol, or glycerine additives might be chosen, with sulfurized oils, chlorinated compounds, phosphates, or borates being reserved for the most severe operating conditions. If heat generation during the metalworking process is substantial, the use of a lubricant in the form of an emulsion can be advantageous. The larger volume of fluid that can be used, combined with the higher heat capacity of water compared to that for an oil, contributes to more efficient removal of heat. When used as lubricants in certain nonferrous metalworking applications, polybutenes have a number of advantages over mineral oil. The properties are summarized as follows : 1. Polybutenes do not contain aromatic compounds and are considered to be practically non-toxic by ail routes of exposure. Many metalworking operations position workers in close proximity with the lubricant. With the growing concern over the safety of the workplace the nature, composition, hence safety implications, for lubricants are being reassessed. 2. Polybutenes are pure aliphatic hydrocarbon polymers. They contain no sulphur or nitrogen species at detectable levels which, if present, could lead to staining of the metal. 3. Polybutenes on the surface of a metal will undergo a rapid and total decomposition if the metal is annealed or treated in excess of 300◦ C directly after forming. The decomposition of polybutene by depolymerisation of the polymer chain leaves no carbon deposits, which could be a source of corrosion problems. The clean decomposition also avoids the need to clean the metal prior to brazing, welding or additional processing. 4. Polybutenes are available with viscosities ranging from solvent like to semisolid at 25◦ C. There is often a polybutene of suitable viscosity to provide a lubricant of high film strength between the die or cool and metal, even under adverse operating conditions. 5. Polybutenes are typically more resistant to biodegradation than mineral oils. In emulsified form, polybutenes show extremely good resistance, superior to that shown by mineral oil, to microbial attack during storage. Subsections that follow illustrate the metalworking applications in which polybutenes are used to advantage over conventional mineral oil lubricants. Throughout, particular emphasis is placed on the ability of polybutene both

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to decompose cleanly and totally at high temperature and to avoid staining and leaving carbon deposits on the metal article. Metal rolling: In the rolling of aluminium sheet or foil, a lubricant is used to reduce the friction between the rollers and the metal sheet. This ensures a good surface finish. In the production of high quality sheet or foil, it is important that any lubricant remaining on the aluminium from the rolling process not give rise to surface staining or blemishes during the subsequent annealing of the aluminium. . In the cold rolling of aluminium, desulfurized gas oil or odourless kerosene are often used as the lubricant. However some manufacturers consider the staining that results from annealing the aluminium in the presence of residual mineral oil based lubricant to be unacceptable, and instead they choose to replace the mineral oil partly or totally with polybutene. A typical lubricant used for the cold rolling of aluminium might contain 0.5 to 2 wt% of oleic acid, lauryl alcohol, butyl stearate, or palm oil as a lubricity additive and a polybutene with viscosity in the range 2 to 4 cSt at 100◦ C [46–48]. In the hot rolling of aluminium the lubricant is often used in emulsified form at 5 to 10 wt % solids content. As in the cold rolling process, a fatty additive can be added to improve the lubrication. Polybutenes with viscosity in the range 2 to 4 cSt at 100◦ C can be used [49]. However the use of emulsified lubricants based on polybutenes of higher viscosity (e.g., 200 grade) has been reported for the hot rolling of aluminium [50]. In the rolling of aluminium, the need to produce strain-free sheet or foil also places certain demands on the lubricants that serve the bearing and hydraulic systems in the mill [51]. In normal operation there are frequent oil leaks from these systems, with the leaked oils entering the rolling oil or coming into contact with the metal sheet. If the bearing or hydraulic oils are formulated with mineral oils, staining of the aluminium sheet upon annealing can result. The problem of staining is overcome if a blend of polybutene in the rolling oil is used, together with the normal wear-reducing and viscosity-stabilizing additives. Oil leaks that contaminate the rolling oil or metal sheet do not then give rise to staining because polybutene decomposes cleanly at annealing temperatures [52–54]. A more viscous lubricant with higher film strength than the rolling oil is required for the bearings that support the rollers and for the hydraulics used to provide the movements on the millstand. In addition to its nonstaining properties, polybutene’s performance in bearing and hydraulic systems make use of the excellent shear stability and good viscosity index properties that are available from the polymers. In the production of aluminium foil or deepdrawn containers used to wrap or contain foodstuffs, the non-toxic nature of polybutene is also important if there is any concern over the possibility that residual lubricant could remain on the metal article [55].

In the rolling of steel, polybutenes are also used to eliminate discoloration or blemishes produced by the residual lubricant after tempering at high temperatures (540–980◦ C). Polybutenes with viscosity in the range of 13 to 225 cSt at 100◦ C have been employed either alone or in emulsified form, together with additives, to improve lubrication [56–58]. Tube drawing: Polybutenes with viscosity in the range 13 to 225 cSt at 100◦ C have been shown to be suitable lubricants for copper tube drawing when used either alone or in combination with an extreme pressure additive [59]. The use of polybutenes in place of mineral oil lubricants is found to give improved die life, and to eliminate the need for the cleaning stage that is required when mineral oils are used, another important advantage. At the annealing temperatures of 550 to 600◦ C used for copper tubing, the polybutene lubricant is removed quickly and completely from the surface of the metal [60]. Cutting oils: As neat oils, polybutenes are suitable only for light-duty cutting operations. Problems of fuming and misting prevent their use in heavy-duty cutting applications. The polybutenes of interest for use as neat oils are generally chose with viscosity in the range 4 to 13 cSt at 100◦ C. All grades of polybutenes can be emulsified to produce oil-in-water emulsions [61] and used as soluble oils for combined lubrication and cooling. Cutting fluids based on polybutene emulsions perform as well as conventional mineral oil products in terms of cutting requirements and in addition have a number of advantages. Since polybutenes are not readily biodegradable, an increased service life of the emulsion coupled with less severe problems of unpleasant odour from lubricant breakdown can be expected [62]. In addition, polybutenes are free from aromatic species and are recognized as being very low in toxicity, particularly following skin contact, which is a likely route of exposure for workers operating in close proximity to cutting fluids. In other metalworking applications such as forging, welding, casting, and ironing, polybutene can be used in the lubricant to provide improvements in nonstaining properties, die or tool life, and lubricant service life, as well as improving the safety of the lubricant in terms of toxicity [63–69]. Polybutenes can also be used in the temporary protection of metal articles while in storage or during shipment. The stable, adhesive, nonstaining, and water-resistant film of polybutene provides anticorrosion protection and prevents gum formation. These coatings can easily be removed if necessary by conventional solvent degreasing or by heating the metal piece to high temperature. 17.3.3.7 Polybutenes in Grease Manufacture A grease is a stable mixture of a base oil and a thickening agent. The manufacturing process and the quantity,

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dimensions, and distribution of the thickener in the oil largely dictate the nature and properties of the finished grease. As with lubricating oils, antioxidants, pour point depressants, rust inhibitors, antiwear additives, and other advantageous substances can be incorporated to enhance the properties or performance of the grease. The use of a grease is favoured when the lubricant is required to remain in position after application to a mechanism, since a lubricating oil might be lost through dripping or being flung during operation. The use of a grease is also preferred if physical opportunities to reintroduce a lubricant are limited by access or if the economics of relubrication are prohibitive. A grease is expected to perform ail the functions of a lubricating oil, with the exception perhaps of efficient cooling and cleaning of the contacting surfaces. A grease may often be expected to function as a sealant against dirt, water, or other contaminants and to be the primary means of preventing corrosion [70]. Polybutenes have particular properties as base oils and as modifiers of conventional mineral oils, which can help achieve the levels of performance demanded by automotive, industrial, and specialist greases. Table 17.12 gives an overview of these properties and lists the areas of current and potential interest for polybutene greases. Polybutenes of low viscosity (4 to 103 cSt at 100◦ C) can be used as the base oil for the manufacture of a grease. Traditional metal soaps such as aluminium, calcium, and lithium stearates, bentonite, and silica thickeners have been used to produce polybutene greases [71]. Some examples of these greases are given in Table 17.13. These results provide a general guide to the physical properties and performance levels that can be expected. The composition and manufacture of the polybutene greases illustrated has not been optimised, and performance-boosting additives have not been included. Polybutenes do not oxidize readily, but their resistance to oxidation can be improved by the addition of a proprietary antioxidant. Addition of antioxidants to polybutene greases is recommended if the grease is to be used at temperatures in excess of 100◦ C. More often, polybutenes of medium to high viscosity (4200 to 12,200 cSt at 100◦ C) are used in conjunction with a conventional mineral oil to produce a blended oil from which a grease can be manufactured [72]. The polybutene serves to adjust the viscosity and viscosity index of the mineral oil to modify and improve the properties of the finished grease. A number of advantages over grease manufacture from straight mineral oil have been claimed for grease manufactured with polybutene. These advantages relate to improvements in the viscosity-temperature properties, in adhesive and cohesive strength, in reduced oil bleeding [73–78], in physical and chemical integrity [79,80], and in the low temperature properties of the grease. In addition, polybutenes tan be used to manufacture greases for industries such as those involved in food processing

TABLE 17.12 Important Polybutene Properties for Grease Manufacture Property

Polybutene character

Applications

Pour point

Improved performance over mineral oils under low temperature conditions No detectable aromatic content and practically non-toxic White or transparent when thickened with light-coloured thickening agent Hydrophobic with good sealant proper for corrosion protection Good chemical and physical stability; permanently non-drying Wide range to modify adhesiveness and temperature response of grease Depolymerizes to volatile compounds above 250◦ C without residue or staining

Low temperature greases for automotive and industrial use Incidental food contact greases

Toxicity Colour Water resistance Inertness Viscosity Volatility

Food or medical greases Greases for bottling and canning ties Corrosion protection; wire rope lubricants; cable greases Heavy-duty gear operated over wide temperature range Graphite or molybdenum disulfide suspensions

TABLE 17.13 Physical and Performance Characteristics of Some Polybutene-Based Greases

Polybutene grade Polybutene 04 Polybutene 07 Polybutene 07 Polybutene 3

Compound

Wt%

Colour

Drop point ASTM D-566 (◦ C)

Al distearate Al distearate Li 12-OH stearate Bentonite 34.MeOH

10 10 11 5

Clear Clear White Light

105 108 197 >230

Thickener

Worked penetration, ASTM D-127 (mm/10) 281 313 267 293

NGLI number

Oil separation, IP121 (164 h/40◦ C)

Water washout (%wt)

Four-ball wear test, ASTM D-2266 (mm/mm)

2 1 2 2

7.2 4.25 0.95 0.5

7.0a 4.0a 6.0b <1.0b

0.53 0.48 0.32 0.44

a IP215 method; 38◦ C. b ASTM D-1264 method; 79◦ C.

[81] or in pharmaceutical production, which require lubricants approved for incidental food contact. Polybutenes in combination with light-coloured thickening agents produce white or even transparent greases, which are well placed to meet the exacting standards demanded in such industries. Polybutenes can also be used in high temperature specialty greases as carriers for suspensions of solid lubricants such as graphite or molybdenum disulfide. Lubricants of these types are normally applied to conveyor chains and roller bearings or used as release agents in the steel and glass industries. At the normal high temperature of operation in these applications, the polybutene decomposes by depolymerisation of the polymer chain, leaving the solid lubricant in position. In contrast to mineral oils, polybutenes that undergo thermal decomposition do not form deposits that could give rise to problems with wear, seizure, and corrosion.

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17.3.3.8 Polybutenes as Wire Rope Lubricants Wire ropes are used in a variety of industrial applications including cranes and, elevators, in mine haulage, as guy ropes, in drilling, and in bridge construction. In its simplest form a wire rope is made up of a collection of wires twisted together. In practice, wire ropes are produced to sophisticated designs to meet the performance requirements demanded of the rope in different end applications. The two major designs for a wire rope are the strand rope and the locked coil rope. In a strand rope, individual wires are wound into strands, which are then twisted around a central core. In locked coil ropes the individual wires are wound together, and specially shaped wires in the outer layers interlock to enclose the rope structure. The locked coil types have exceptional strength for a given rope thickness. When in use, a wire rope flexes and the wires and strands in its construction rub together. Also wire ropes

TABLE 17.14 Fatigue, Friction, and Corrosion Data for Polybutene. Mineral Oil, and Bitumen Based Wire Rope Protective Agents Friction testsa Lubricant base

Relative fatigue lifeb

Wear area (mm2 )

Coefficient of friction

Polybutened Polybutene/waxe Mineral oil Bitumen

263–303 188–230 163 —

0.07–0.16 0.22–0.27 0.07 4.12

0.10–0.12 0.09–0.11 0.07 0.54

Salt spray, ASTM B-117c Pass Pass

a Cameron–Plint machine; load 30 N, reciprocation rate 50 Hz, duration 2.5 × 105

cycles, stroke length 2.3 m. b 3 mm rope, l cycle/s, reverse bend under load, dry rope = 100. c Mild steel panel dip coated 20◦ C above drop point, 720 h at 35◦ C; no corrosion

for pass. d Polybutene grades 5 and 10. e Polybutene content in excess of 90%.

are often used in corrosive environments such as dockside cranes or undersea cables. Therefore a wire rope lubricant must not only minimize internal wear between the wires and strands and external wear between the rope and pulley or drum arrangement, it must also provide the rope with a high level of corrosion protection. The application of the wire rope lubricant is normally undertaken during the spinning or construction of the rope. Lubrication at the manufacturing stage is especially important for locked coil ropes, whose design makes relubrication difficult. The central core of the rope can also be impregnated with lubricant to provide a reservoir of lubricant to maintain the rope while in use. It is also common to relubricate a rope at regular intervals during its service life. Polybutenes exhibit the physical characteristics required of a wire rope lubricant. They are inert, nondrying, and adhesive materials that provide effective lubrication and corrosion protection for the wire rope. The medium to low viscosity polybutenes appear to have the best combination of properties for lubrication. However the use of a high viscosity polybutene has also been claimed in a lubricant formulation for a locked coil rope [82]. Paraffinic, microcrystalline, and polymer waxes can be used in a blend with polybutene to give control over the drop point of the lubricant. Wire ropes lubricated with polybutenes, polybutene/wax blends, mineral oil, and bitumen-based lubricants have been subjected to fatigue and friction testing. The results shown in Table 17.14 indicate that polybutene and polybutene/wax lubricants offer improved performance in rope life and give considerably higher coefficients of friction than mineral oil derived products. This set of properties is thought to be related to the branched structure of the polybutene polymer [83]. A high coefficient of friction or traction is desirable for applications

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TABLE 17.15 Summary of Key Property and Performance Benefits for Polybutenes in Oil and Lubricant Applications Application General Two-stroke oils

Metalworking lubricants Gear oils Compressor lubricants Grease/wire rope oils

Key property/performance benefit Base oil adjustment and viscosity control Low smoke JASO and global oils, low exhaust system blocking, low particulates, good lubricity Nonstaining, low deposits, low toxicity, low biodegradability Shear stable, VI improver, adhesiveness additive Good lubricity, inertness, low toxicity, good electrical properties Adhesiveness, hydrophobicity, inertness, good lubricity, non-hazardous

that rely on friction to drive the ropes. Polybutene lubricants have been claimed for use in friction-driven elevator ropes [84]. For general-purpose wire rope lubrication, bitumen, waxes, and high viscosity mineral oils are most often used. However, in higher performance applications such as in the lubrication of ropes for bridges, undersea cables, and elevator ropes, polybutenes are finding use. In addition, polybutenes are well positioned to replace bitumen or mineral oils in wire rope applications now demanding safer, non-toxic lubricants.

17.3.4 Summary Polybutenes combine effective viscosity control with the ability to deliver a number of key benefits and high

TABLE 17.16 Polybutene Grades Most Recommended for Each Lubricant Application Sector H-1900 Application/grade

03

Viscosity adjustment Two-stroke oils Metalworking Lubricants LDPE compressor oils Gear/hydraulic oils Greases Wire rope protective agents

TABLE 17.17 Estimated Worldwide Polybutene (Nameplate), 1984–2002

04

07

X

X X X

X

10

30

150

200

600

X X X

X X X X X X X

X

X

X

X

X

X X X

X

X

X X

X X

X X X

X

Capacities

1984

1987

1990

1993

1996

2003

North America Europe Japana South Americab India Others

380 160 30 10

350 165 30 15

355 180 40 25

405 205 45 30

10

10

25

30

405 315 50 45 44 50

305 310 35 50 29 81

Total

590

570

625

715

865

810

a Includes Idemitsu Petrochemical Company, Nippon Petrochemical

Company, and Nippon Oil and Fats. b Includes Polybutenous Argentinos and Polybutenos Industrios Quimicas.

performance characteristics to a wide range of automotive and industrial lubricants. The addition of polybutene to mineral oil based lubricants can result in a clean-burning, nonstaining product also having the properties of low smoke, adhesiveness, shear stability, very low toxicity, and low deposit formation. These properties bring tangible benefits to the performance of two-stroke oils, automotive and industrial oils, metalworking and compressor lubricants, grease, and wire rope protective agents. Similarly the use of polybutenes in combination with poly(α-olefins) and esters improves the cost and performance benefits of synthetic lubricants now finding increasing use as two-stroke oils, industrial oils, greases, and compressor lubricants. Tables 17.15 and 17.16, respectively, summarize the key performance benefits of polybutenes and indicate the grades most appropriate for use, divided by lubricant application sector.

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5

X X

Capacity (tons × 103 ) Location

3

X X

2000

TABLE 17.18 Major Manufacturers’ Estimated Capacities (Nameplate: tons ×103 ) for Europe and the United States in 2003 Europe

Capacity

Innovene Infineum Lubrizol BASF Russia/CIS

80 85 47 90 8

Total

310

United States Innovene Infineum Lubrizol Chevron TPC

Capacity 80 45 90 60 30 305

17.4 MANUFACTURE AND ECONOMICS 17.4.1 Manufacturers and Capacities The main centres for the production of polybutenes are in the United States and Europe. Production units also exist in Asia and in South America. There are small polybutene production units in South Korea, China, India, and possibly Russia. In 1996 there was an estimated worldwide nameplate capacity of polybutene of around 865,000 t. The nameplate capacity is, however, based on the production of a single grade of polybutene of 1000 molecular weight by a given manufacturer. Therefore, the actual production figure is considerably less for reasons of plant operation, plant reliability, and the practice of manufacturing a range of different polybutene grades. During the period 1984 to 1990 new production capacity for polybutene came on stream, but supply remained fairly constant as aged plants were closed by Cosden, Lubrizol, Chevron, and Petrofina in North America with Amoco-Fina closing their plant in Belgium in early 1989. Since 1990, there was initially some growth in the supply of polybutenes through plant debottlenecks and new production capacity from BASF in Belgium (Table 17.17). Since the late 1990s however, reduced demand for additives applications has led to some significant plant closures in both Europe and the USA.

In Europe, Innovene produces polybutenes at Lavéra in France. Infineum produces at Köln in Germany, Lubrizol at Le Havre in France, and BASF at Antwerp in Belgium and Ludwigshafen in Germany. The polybutene production of Lubrizol, like the majority of the production of both Infineum and BASF, is used in-house for the production of lubricant and fuel additives. Innovene is the major producer of polybutenes in Europe and supplies the open market. Innovene offers a wide range of polybutene grades under the Indopol trade name. Infineum markets a limited

TABLE 17.19 Guide to Cost of Synthetic Oils Relative to Mineral Oil Oil

number of polybutene grades under the trade name Parapol. BASF markets their product as Glissopal. In the United States, Lubrizol at Deer Park and Infineum at Bayway manufacture polybutenes and, as in Europe, the production is used in-house for additives manufacture. Innovene, the largest producer of polybutenes world wide, manufactures polybutenes at Whiting (Indiana), (Table 17.18).

17.4.2 Market Price It is difficult to be definitive about pricing. At the present time, polybutenes are less expensive than other synthetic additives such as esters or polyalkylmethacrylates. Table 17.19 has been proposed as a rough guide to the pricing of synthetic oils relative to mineral oil [85,86]. On this basis, polybutene would be priced in the range 3–4, depending on volume and grade of material requested.

Relative cost

Mineral oil Polyisobutene Poly(α-olefin) Diester Polyalkylene glycol Phosphate ester Silicone fluids

1 2.5–4 depending on the grade considered 2.5–3 4 3.5–4 5 10–50

17.5 OUTLOOK Demand for polybutene is expected to show reasonable growth over the next few years, as manufacturers look for clean-burning, low smoke, and low exhaust system blocking two-stroke oils to meet new global performance requirements. In addition, the use of polybutene is expected

TABLE 17.A.1 Indopol grade Polyisobutene gradea Unit Molecular weight weight Viscosity at 40◦ C Viscosity at 100◦ C Viscosity at 100◦ C Viscosity index Flash point (PMCC) Flash point (COC) Pour point Relative density Colour Refractive index Bromine number Acid number Water content Conradson residue

Method

L-6 03

L-8 04

H-7 H-25 H-50 H-100 H-300 H-1500 H-2100 H-6000 H-18000 07 3 5 10 30 150 200 600 2000

Mn

ASTM D-3593

260

310

440

cSt cSt SUS ◦C

ASTM D-445 ASTM D-445 ASTM D-445 ASTM 2270 ASTM D-93

6.6 2 32 90 105

15 3.4 39 92 120

126 13 70 95 130

◦C

ASTM D-92

110

135

145

◦C

20◦ C

Hazen

635

790

930

2300

2600

4200

5900

1,090 2,900 7,200 21,000 133,000 185.000 620,000 1,8000,000 55 103 225 635 3065 4250 12,200 40,500 270 480 1,050 2,960 14,300 20,000 57,000 190,000 98 100 125 181 246 264 306 378 140 155 165 170 175 175 180 190 240

250

270

275

280

−60 −60 −30 −21 −12 −7 0.815 0.833 0.852 0.874 0.882 0.891

4 0.895

18 0.904

24 0.91

35 0.914

50 0.917

ASTM D-1209 40 40 40 40 40 40 ASTM D-1747 1.461 1.467 1.474 1.487 1.490 1.494

40 1.498

40 1.503

40 1.504

40 1.505

40 1.508

12

8

6

4

3

0.03 40 <0.01

0.03 40 <0.01

0.03 40 <0.01

0.03 40 <0.01

0.03 40 <0.01

IP15/86 IP190/86

g Br/100 g IP129/87

40

155

27

190

20

210

16

mgKOH/g ASTM D-974 0.03 0.03 0.03 0.03 0.03 0.03 ppm ASTM A-1744 40 40 40 40 40 40 % residue ASTM D-189 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01

a Approximate grade number calculated by dividing the viscosity in SSU at 100◦ C by 100.

Source: BP Chemicals publications and internal documents, 1970–1997.

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1280

to increase in specialist metal-working lubricants, greases, and energy-efficient oils. In these applications, the special benefits and performance characteristics offered by polybutene will continue to provide cost and performance advantages over the use of other products. With lubricants under greater scrutiny for evidence of hazard, formulators will seek to employ sale, non hazardous, and cost-effective components for lubricants. As a result of this trend, synthetics, like polybutene, should come to play a greater role in the lubricants formulated for the future. The use of polybutene in blends with either poly(αolefins) or esters to provide high performance lubricants is expected to grow. Formulators will start to take advantage of combinations of different oils to achieve a synergistic response from the lubricant.

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20. (a) U.K. Patent 1,513,853, to Labrofina (1976). (b) U.S. Patent 3,100,808, to Cosden Petroleum Corporation (196.1). 21. (a) U.S. Patent 3,252,908, to Lubrizol (1963). (b) French Patent 1,446,344, to Esso (1965). 22. Japanese Patent 13,218, to Chisso Corp. (1968). 23. (a) U.S. Patent 847,339, to Esso (1958). (b) U.K. Patent 838,928, to Esso (1957). 24. U.S. Patent 3,429,936, to Monsanto (1965). 25. BP Chemicals technigram PB102, Polybutenes-Health, safety and environmental information, 92/500/GB (1995). 26. BP Chemicals Technigram PB103, Polybutenes-Food contact status, 96002/500 (1996). 27. Internal BP Chemicals correspondence, 1983. 28. Higgins, I.J. and Gilbert, P.D., in The Biodegradation of Hydrocarbons (H.J. Sometville, ed.), Heyden, London, 1978. 29. Insight Journal, Issue 13, March 2002. 30. GB Patent 1,162,172 to Labofina (1966). 31. US Patent 3,878,115 to Labofina (1973). 32. US Patent 3,852,204 to Cosden Oil (1974). 33. International Organization for Standardization, Draft International Standard ISO/DIS 13738 (1995). 34. (a) Noda, K., et al., Development of JASO 2-stroke engine oil standards, SAE paper 93–1938, Society of Automotive Engineers, Warrendale, PA, 1993. (b) Noda, K. and Inoue, N., Outline of engine oil standards for motorcycle, in Some Investigations on High Performance 2 Cycle Engine Oils in Next Generation. Fuels and Lubes Asia Conférence. M. Mitsumoto et al., (Eds.), Singapore, Jan. 29–31, 1996. 35. Sugiura, K. and Kagaya, M., A study of visible smoke reduction from a small two-stroke engine using various engine lubricants SAE paper, 770623, (1977). 36. (a) Mitsumoto, M., et al., eds., Some Investigations on High Performance 2 Cycle Engine Oils in Next Generation, Fuels and Lubes Asia Conférence, Singapore, Jan. 29–31, 1996. (b) Callis, G.E., et al., Development of engine oils for two-stroke motorcycles in the asian market, SAE paper 93–1568, Society of Automotive Engineers, Warrendale, PA, 1993. 37. (a) Yashiro, Y., Reduction of exhaust smoke and carbon deposits at exhaust port in two-stroke gasoline engines, SAE paper 871216, Society of Automotive Engineers, Warrendale, PA, 1993. (b) Pannoi, S., The effect of two-stroke oil reaction energy on white smoke, Fuels and Lubes Asia Conférence, Singapore, Jan. 19–22, 1997. 38. MacMahon, J. and Fotheringham, J., European Patent Application 0640680 (1993). 39. BP Chemical results, generated 1997. 40. Wikelski, K.W., J. ASLE, 37, 203 (1981). 41. Sittig, M., ed., Chemical Technology Review, No. 70, Noyes Data Corp., Park Ridge, NJ, 1981, p. 48. 42. Chevron Chemical Company, Chevron Polybutenes as Lubricants, technical data sheet, circa 1970. 43. O’Conner, B.M. and Ross, A.R., J. Synth. Lubr., 6, 31 (1989). 44. BP Chemicals technigram PB201, Polybutenes as viscosity index improvers, 203/500 (1992). 45. Me College of Petroleum Studies, Oxford, Synthetic Lubricants Course SP5 (1996).

46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65.

Japanese Patent 15,387, to Chisso Co. Ltd. (1963). U.S. Patent 2,899,390, to Standard Oil (1959). Bucsi, W.G., J. ASLE, 46, 186 (1990). European Patent Application 0048216, to Swiss Aluminium (1982). U.K. Patent, 1,052,652, to Aluminium Laboratories (1965). Schimon, W., J. ASLE, 40, 4371 (1984). U.K. Patent 964,268, to Aluminium Laboratories (1962). Guminski, R.D., U.S. Patent 3,298,951 (1966). U.S. Patent 4,488,979, to Swiss Aluminium Ltd. (1982). U.S. Patent 4,228,217, to Swiss Aluminium Ltd. (1977). Netherlands Patent Application 6503934, to Standard Oil Indiana (1965). U.K. Patent 1,109,304, to Standard Oil (1965). European Patent Application 0375412, to W.R. Grace and Co. (1990). Akzo Chemicals Technical bulletin 4/I, Chemicals for Metalworking. U.S. Patent 2,990,943, to Armour Industrial Chemical Co. (1956). BP Chemicals Technigram PB 107, Polybutene emulsions, 215/2000 (1989). Japanese Patent 184,375, to Toho Chemical Industries Ltd. (1984). Belgian Patent 678,683, to C.G. du Duralumin (1965). U.K. Patent 1,060,114, to Société de Produits Chimiques et de Synthèse (1963). U.K. Patent 2,185,996, to Smallman Lubricants Ltd. (1986).

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66. European Patent Application 0206280, to National Distillers and Chemical Co. (1986). 67. U.S. Patent 3,397,734, to Standard Oil Company (1966). 68. U.S. Patent 4,260,502, to Nalco Chemical Co. (1979). 69. U.S. Patent 4,758,358, to Van Straaten Corp. (1987). 70. SAE Information report J310a on Automotive Lubricating Grease, Society of Automotive Engineers, Warrendale, PA, 1985. 71. BP Chemicals Technigram PB204, Polybutene greases, 218/500 (1989). 72. Belgian Patent 779,526, to Labofina S.A. (1972). 73. U.S. Patent 3,663,726, to Cities Service Oil Co. (1969). 74. French Patent 2,045,577, to Cato Oil and Grease Co. (1969). 75. German Patent 1,955,951, to Chemische Fabrik Rhenus (1969). 76. U.S. Patent 3,472,770, to Chevron Research Co. (1967). 77. Canadian Patent 936,33, to Cato Oil and Grease Co. (1971). 78. U.S. Patent 3,379,972, to Southwest Petroleum Chemicals, Inc. (1972). 79. Japanese Patent 7,232,873, to Suwa Sickosha (1968). 80. U.K. Patent 853,751, to Esso Research and Engineering Co. (1960). 81. U.S. Patent 4,828,727, to Birko Corp. (1987). 82. U.K. Patent 2,095,696, to Shell International Research (1981). 83. Muraki, M., Tribol Int., 20, 347 (1987). 84. U.K. Patent 2,118,195, to Mitsubishi Denki Kabushiki Kasisha (1982). 85. Anon., Ind. Lubr. Tribol., p. 17, November/December 1989. 86. The College of Petroleum Studies, Oxford, Synthetic Lubricants Course SPS, Section 3, 1989.

18

Chemically Modified Mineral Oils H. Ernest Henderson CONTENTS 18.1 Introduction and Historical Development 18.1.1 Classification of Lubricant Base Stocks 18.1.2 Performance Requirements for Lubricants 18.1.3 Lubricant Performance Advancements and Impact on Lubricant Base Stocks 18.1.4 Evolution of Chemically Modified Mineral Oils 18.1.5 Manufacturing Schemes 18.2 Performance Features of Chemically Modified Mineral Oils 18.2.1 Composition 18.2.2 The Synthetic Nature of Chemically Modified Mineral Oils 18.2.3 Volatility 18.2.4 Low-Temperature Viscometrics 18.2.5 Oxidation Stability 18.2.6 Engine and Field Performance 18.2.7 Energy Efficiency 18.2.8 Environmental Friendliness 18.3 Applications for API Group III Chemically Modified Mineral Oils References

18.1 INTRODUCTION AND HISTORICAL DEVELOPMENT Petroleum refining has continuously evolved over the decades in response to changing performance demands, government regulatory requirements, and customer needs for different and improved products. The original demands from the early refineries in the 1860s and 1870s were to maximize the production of kerosene as a cheaper and more efficient source of light than provided by whale oil [1]. The next important product was paraffin wax for the production of candles. Lubricating oils did not have a place in the early refineries and were often considered to be an unwelcome by-product of the production of wax. Despite the opportunity to use lubricating oils as a replacement for lard oil and sperm oil for heavy machinery, the industry did not welcome lubricating oils with the same enthusiasm as they did kerosene. With the significant growth of industries in North America created by industrial expansion during the late 1800s, the interest in lubricating oils finally grew to such a level that it was able to displace animal and vegetable

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oils as the preferred option for machinery lubrication. And as refinery processing improved, the quality of lubricating oils also improved. The introduction of the internal combustion engine created a key demand for new products and refinery processing shifted toward the production of gasoline and diesel fuels. The evolution of the aviation industry created a further need for higher quality aviation gasoline and later jet fuels. These advancements created a further and significant demand for lubricating oils. Throughout the majority of the 20th century, the performance demand for lubricants has been fairly straightforward. Prior to the 1930s, straight mineral oils (i.e., lubricant base stocks) were used for most applications, including high temperature conditions where the potential for oxidation would occur. As engines and equipment underwent design changes to operate at higher speeds, loads, and operating temperatures, the technical demands on the lubricants increased dramatically. Unfortunately, straight mineral oils or base stocks were not capable of

meeting these new performance demands on their own. The result was the development of the chemical additives industry to compliment the base stock and provide the following features: • Improve the normal properties of the base stock. • Provide additional performance properties that were not

associated with the base stock itself. • Replace natural oxidation inhibitors (e.g., sulfur compounds), for example, and other chemical structures that were present in the base stock but removed to some degree during the refining process. • Provide additional protection to the equipment in which the base stock was used. Base stocks did undergo a fundamental change beginning in the 1930s when a shift from naphthenic to paraffinic base stocks occurred following the introduction of solvent dewaxing. Paraffinic base stock quality would range from 80 to 105 Viscosity Index (VI) with a typical VI of 95. Variations in base stock quality would be influenced by crude selection, process severity, and application demands. Continued improvements in base stock manufacturing did occur over the next several decades. However, these advancements were more focused on improving unit efficiency, product yields, feed flexibility, and unit safety. Throughout the latter half of the 20th century, solvent refining or separation processing has been adequate to produce high volumes of quality base stocks for most applications. Special small-volume or “niche” products were formulated, when required, to address severe operating conditions (e.g., high/low temperatures, high pressures, etc.) with high quality synthetic base stocks like polyalphaolefins (PAOs) and esters that have outstanding VI, pour point, volatility, and stability. Another key advancement in base stock manufacturing occurred in the early 1970s when lube hydrocracking or conversion technology was introduced as an alternative to solvent processing. The first commercial facility was commissioned by Gulf Canada (now Petro-Conada) in 1979 in Mississauga, Ontario, Canada. This was followed by investments by Sunoco in Yabucoa, Puerto Rico (1980), and Chevron at Richmond, California (1984), although the Sun facility has recently discontinued to produce base stocks. The benefits of hydrocracking included increased crude flexibility and the opportunity to produce higher VI base stocks. However, the higher cost to operate lube hydrocrackers combined with reduced unit reliability and lack of demand for premium products limited North American investment to only 10% of capacity as late as 1995 with no significant capacity in other regions of the world.

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TABLE 18.1 American Petroleum Institute Base Stock Categories Base oil group

Sulfur wt%

Group I Group II Group III Group IV Group V

>0.03 ≤0.03 ≤0.03

Saturates wt%

Viscosity index

And/or <90 80–119 And ≥90 80–119 And ≥90 ≥120 All polyalphaolefins (PAO) All base stocks not included in groups I–IV

Source: From American Petroleum Institute, Industry Services Department, Engine Oil Licensing and Certification System, API Publication 1509,15th ed., April 2002.

18.1.1 Classification of Lubricant Base Stocks The American Petroleum Institute (API, Table 18.1) presently categorizes base stocks into five groups depending on physical and compositional properties. This is included in API 1509 that is the Engine Oil Licensing and Certification System (EOLCS) and represents “a voluntary licensing and certification program designed to define, certify, and monitor engine oil performance deemed necessary for satisfactory equipment life and performance by vehicle manufacturers” [2]. The original standard was introduced in the early 1980s in an effort to capture the differing qualities of lubricant base stocks that could be used in the formulation of engine oils. API Groups I, II, and III represent base stocks typically refined from crude oil and are differentiated by Viscosity Index (VI), saturates content, and sulfur content. API Group I is achieved through solvent refining or separation processing, whereas, API Group II and III are produced either directly from conversion or hydroprocessing technology or from an integration of solvent and hydroprocessing technologies. The original set of API base oil groupings included three categories, with only one category reserved for hydroprocessed base stocks. This was due to the limited number of hydroprocessed base stocks that were available to the North American market. However, in the early 1990s an effort was made to position a new group of higher VI base stocks within the API Group II category as equivalent to PAO. This included, but was not limited to, base stocks produced, (i) through slack wax isomerization (e.g., Shell, Petit Courone France, and ExxonMobil at Fawley UK) where VIs in the 140+ range were obtained or (ii) through the upgrading of hydrocracker bottoms (e.g., BP, Lavera France) where VI’s in excess of 120 were produced. Although the API did not support the equivalency of these base stocks with PAO, due in part to a lack of comparative engine data, they did recognize the quality difference with North American API Group II base stocks

that were commercially produced at that time. These had VI properties in the 95 to 105 range. As a result, an API Group III category was created for severely processed base stocks where the minimum VI was established at 120. API Category IV was also introduced for PAOs. This class of lubricant base stock has been recognized by the petroleum industry and by the consumer as the pinnacle in base stock quality where the best in lubrication performance can usually be achieved. It is not surprising, therefore, that PAOs are traditionally referred to as synthetic. Because of the uniqueness of the PAO process and the consistency with its quality and compositional properties, all PAOs are considered equivalent and interchangeable provided they meet the same specifications regardless of the manufacturer. API Group V, finally, is a collection pot for all base stocks not covered by the Group I–IV guidelines, including but not limited to such materials as naphthenic base stocks, esters, silicones, glycols, polyglycols, etc. A new category for polyinternalolefins (PIOs) was introduced in Europe by the Association Des Constructeurs Europeans D’Automobiles (ACEA) in 2003 [3], and designated as Group VI, although the base stocks themselves have been produced for several years. The ACEA organization has established some interchange guidelines with PAO, however, the category has yet to be considered by the API for the North American marketplace.

18.1.2 Performance Requirements for Lubricants Throughout the past two decades, the demand for automotive and to a lesser extent industrial lubricants to meet the growing environmental and equipment performance demands has been rapid paced. The passenger car market has been the most active in this area with specification changes now occurring every 2 to 4 years. These new categories have addressed such features as reduced emissions, extended drain intervals, equipment reliability, and improved fuel economy. The effect has been the ongoing advancement and balance of both additive technology and lubricant base stock quality to work synergistically to deliver the required performance levels in each application. A summary of the key drivers for each of the passenger car engine oil performance changes that have occurred since the introduction of API SE quality in 1972 are provided in Figure 18.1 [4]. Performance improvements will continue to occur in the passenger car market in response to consumer and governmental pressures. Federal drivers include Corporate Average Fuel Economy (CAFE) and compliance to the Federal Clean Air Act Amendments (FCAAA). Consumer needs include reduction in number of oil changes and overall maintenance, reduced oil consumption, and a desire to have larger vehicles with more powerful engines.

IMPROVED PERFORMANCE

ILSAC GF-4 GF-3: + Emission Compatibility (Low P) + Fuel Economy + Fuel Economy Retention + Oxidation Control (2 X GF-3) + High Temp Wear Control + High Temp Deposit Control + Low Temp Pumpability

ILSAC GF-3 GF-2: + Fuel Economy Retention + Oxidation Control + Volatility + Foam + Ball Rust + Oil Seal Compatibility ILSAC GF-2 GF-1: + Fuel Economy + Oil Volatility + Foaming + Catalyst Compatibility + High TempDeposits

2001 Alliance 27-Jan-04

2002

2003

2004

FIGURE 18.1 Technical developments with PCEO performance upgrades

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2005

2006 5

Heavy-duty engine oils (HDEOs) have also seen significant and frequent performance upgrades as manufacturers demand lubricants to perform under higher temperatures. This, in turn, creates an increased level of thermal stress, resulting in a greater level of emissions. The impact of these changes on emissions, unfortunately, has been in conflict with the drive by the Environmental Protection Agency (EPA) to lower emissions. As a result, engine manufacturers have made several modifications and advancements to their engines, including the introduction of exhaust gas recirculation (EGR). EGR has provided further stress to the engine oil by increasing the level of carbonaceous soot particles caused by the incomplete combustion of the fuel. Two advancements have been made to HDEO formulations as a result of the increasing soot levels, namely (i) an increase in dispersancy to suspend soot molecules and (ii) a shift from solvent refined to hydroprocessed base stocks. Consequently, engine oils on the whole (i.e., passenger car engine oil (PCEO), HDEO) are now required to provide improved high and low temperature fluidity, thermal and oxidation stability, volatility control, and in selected instances energy efficiency in both a fresh and used oil state. Automatic transmission fluids (ATF) represent another automotive product line where performance changes and the approach to formulation have occurred. Today, Original Equipment Manufacturers (OEM) are searching for a solution to provide optimum efficiency, reliability, and ease of operation, either in terms of equipment or fluid selection. One of the consequences has been the introduction of an electronically controlled transmission where the oil passages have been drastically reduced. As a result, both the appearance of wax at reduced temperatures and the products of oxidation that are created at elevated temperatures and extended periods cannot be tolerated as each one of these can cause blockage to these narrow oil passages. Some manufacturers have now begun to specify the use of chemically modified base oils in their automatic transmission fluid (ATF) standards to provide long lubricant life, high shear stability, and improved low temperature fluidity. One of the first companies to incorporate this requirement was Daimler-Chrysler who stated in its MS-9602 Materials Characteristics “The fluid is designed as a fill-for-life application defined by improved oxidation stability, low temperature viscosity, friction durability/retention, fluid shear stability and anti-wear. ∗∗∗ This fluid will be formulated with a specific additive system and extra high viscosity index (XHVI) Group III base oil.∗∗∗ ” [5]. Ford was quick to follow with its MERCON® -V and MERCON® -SP standards [6] and has been a strong supporter in the use of chemically modified base stocks with its service fill (SF) and factory fill (FF) fluids. General Motors has recently recognized the advantages that can be achieved with hydroprocessed base stocks and have

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upgraded its DEXRON® -III standard to the DEXRON® IIIH performance level to utilize higher quality and in some instances chemically modified base stocks [7]. Industrial lubricants are also changing, albeit at a much slower pace compared to the automotive industry. However, a common theme remains as environmental concerns combined with the need to run smaller, more efficient equipment at faster rates to maximize productivity and extend maintenance schedules has led to an increased stress on the lubricant. One consequence has been a slow but gradual shift toward the use of chemically modified mineral oils, including API Group II and III [8].

18.1.3 Lubricant Performance Advancements and Impact on Lubricant Base Stocks As the industry has moved toward the use of premium products, there has emerged a growing interest toward the economic production of chemically modified mineral oils in acceptable quantities and qualities to meet these changing demands. This is the result of two key factors, namely: • The lower concentration of saturated vs. aromatic and

cyclic structures in solvent refined API Group I base stocks prevents formulators from achieving both current and future performance levels in some product areas, even when complimented with a strong additive system. This includes, but is not limited to, such performance features as oxidation stability, volatility, and fuel economy capability, both in a fresh and used oil state. • Solvent processing cannot produce the required yield of high quality base stocks due to an insufficient concentration of these higher quality molecules in the initial feed. Figure 18.2 [9] illustrates as to why solvent processing is limited in its ability to produce sufficient quantities of higher quality base stocks to meet increasing performance requirements. In a solvent processing operation, the yield and quality of a base stock is dependent on the quality of the crude to be processed and the efficiency of the operation to separate the desirable from the undesirable lubricant molecules. In a lubes refinery, volatility improvements with a constant feed is normally achieved by taking a narrower “distillate slice.” This reduces the concentration of low boiling components, which is desirable for improved volatility, but at the same time is countered by the removal of some of the heavier boiling components. This is required to maintain a constant kinematic viscosity with the finished base stock. During the past three PCEO performance upgrades, the typical GCD properties (i.e., Gas Chromatographic Distillation, by American Society for Testing and Materials Method (ASTM) D2887) for the finished engine

PREVIOUS — e.g., ILSAC GF-2 Distillation

Extraction

Dewaxing

Hydrofinishing

(10%)

(60%)

(75%)

(95%) 1.0

23.4 FUTURE — Low volatility, high saturates, low pour point (e.g., ILSAC GF-3, GF-4)

Distillation

Extraction

Dewaxing

Hydrofinishing

(4%)

(40%)

(70%)

(95%) 1.0

94.0

FIGURE 18.2 Limitations of solvent processing with regards to high-quality base stocks

oils (and the corresponding blended base oil) have changed as follows: • International Lubricant Standardization and Approval

Committee (ILSAC) GF-1 at 20% off at 371◦ C (ASTM D2887) • ILSAC GF-2 at 17% off at 371◦ C (ASTM D2887E) • ILSAC GF-3 at 9% off at 371◦ C (ASTM D5480) • ILSAC GF-4 at 10% off at 371C (ASTM D6417) This has led to a considerable reduction in lube distillate yields, particularly for the S100N-S130N viscosity grade that is preferred for low Society of Automotive Engineers (SAE) 5W-XX automotive grades. It is further impacted by the additional need for Noack volatility limits for ILSAC GF-3 and ILSAC GF-4, which are more stringent than the GCD limits. The net result has been the need for 100N130N base stocks to have a much lower GCD volatility than required by the finished oil specifications. For the former ILSAC GF-3 and recently introduced ILSAC GF-4 specifications, a 15 wt% Noack would equate to a GCD of approximately 3% off at 371◦ C, or 700◦ F. As a general rule of thumb, solvent extraction (API Group I) is economic for distillates where a solvent dewaxed VI of ≥ 50 is observed. These “lube crudes” can be very expensive when used to produce both lube and fuel products and refiners therefore continue to search for lower cost feed alternatives as this represents one of the major expenses in a refinery lube operation. Lower VI feeds can be more severely extracted but the raffinate yields become unattractively low and hence uneconomic. The same applies to the dewaxing operation where additional

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TABLE 18.2 Dewaxed Viscosity Index and Wax Contents of Domestic and International Crudes Crude Alaska North Slope (ANS) Arab light Arab heavy Brent California light Isthmus Kuwait Maya Pennsylvania West Texas Intermediate (WTI)

Dewaxed VI VGO Wax (−12◦ C pour point) content, LV% 15 60 55 65 8 40 50 40 100 55

7 9 9 19 5 10 7 16 0 12.5

Source: Wilson, M.W., Eiden, K.L., Muller, T.A., Case, S.D., and Kraft, G.W., Commercialization of Isodewaxing — A New Technology For Dewaxing to Manufacture High Quality Lube Base Stocks, National Petroleum Refiners Association, Paper FL-94-112, Fall Meeting, November 1994.

levels of residual wax will need to be removed with premium base stocks to provide the appropriate pour point and low temperature fluidity characteristics. A comparison of VI and wax contents of several domestic and international crudes is provided in Table 18.2 [10]. In the past, a low viscosity S100N-S130N base stock has typically been used as the major blending component to formulate low viscosity SAE 5W-XX and 10W-XX engine oils. Given the typical yield profile in Figure 18.1 for the

2 S

1,3

2 Step #1: Desulfurization and denitrogenation to remove sulfur and nitrogen Step #2: Saturation of the aromatic rings to naphthenes and residual double bonds into paraffins Step #3: A ring-opening step to convert naphthenes into paraffins

FIGURE 18.3 Processing steps and chemical modifications in a hydroprocessing operation

former ILSAC GF-2 performance specification (i.e., 1996– 2000), roughly 25 barrels of a good lube crude would be required to produce 1 barrel of an S100N-S130N base stock for this application. However, with tighter volatility specifications observed with the former ILSAC GF-3 and recently introduced ILSAC GF-4 performance categories, narrow fractionation is required, which has a dramatic effect on distillate yields. To maintain a high VI for oxidation, high temperature rheology, and volatility, more aromatics and cyclic compounds must be removed in the extraction step, limiting yields further. For improved low temperature fluidity, more wax in the base stock must be removed. The overall impact is a significant drop in processing yields for this example, such that it now requires almost 95 barrels of the same crude that was used for formulating GF-2 quality PCEO lubes to produce 1 barrel of the higher quality S100N-S130N to formulate at the ILSAC GF-3 and ILSAC GF-4 performance levels. This is unacceptable to refiners and has led to a search for better feedstock and process options to provide higher base stock qualities in acceptable yields.

18.1.4 Evolution of Chemically Modified Mineral Oils Hydrocracking is a conversion process that allows refiners to convert low VI components, which would normally be rejected in the solvent refining process, into higher quality materials. Low VI components are typically composed of multi-ring aromatics, some of which may contain sulfur and nitrogen. The basic process involves four steps, namely: • Step #1: Desulfurization and denitrogenation to remove

sulfur and nitrogen • Step #2: Saturation of the aromatic rings to naphthenes

and residual double bonds to paraffins • Step #3: A ring-opening step to convert naphthenes into

paraffins • Step #4: Isomerization of paraffins into isoparaffins

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4 Step #4: Isomerization to convert naphthenes into paraffins and more preferably isoparaffins

FIGURE 18.4 Processing steps and chemical modifications in an isomerization operation

Steps #1 thru #3 are shown in Figure 18.3, while Step #4 is shown in Figure 18.4. Although hydrocracking was seen as a novel approach to upgrade lower quality and hence more economic crudes into lubricant base stocks, the North American market was restricted to only three manufacturing facilities through the mid-1990s. These included: • Petro-Canada: Mississauga, Ontario Canada • Chevron: Richmond, California • Sun: Yabacoa, Puerto Rico

For nearly two decades, these three facilities accounted for only 10% of the paraffinic base stock production in North America. This was because during this period the process was considered to be an expensive capital investment for the quality of base stock that was required in the marketplace. At the same time, the long-term reliability of the process was questioned due to the severe reactor temperatures and pressures, as well as the limited operating experience in the production of lubricant base stocks. The increase in performance demands has led refiners to seek economical means to produce larger volumes of higher quality base stocks. The result has been a

160 API Group I

140

API Group II, III

Capacity, KBD

120

100

80

60

40

20

0 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 Year

FIGURE 18.5 North American API Group I, II, III Capacity — 1990 to January 1, 2005

significant investment in hydroprocessing technology and several breakthroughs in catalyst development and utilization to maximize feed flexibility and VI retention [11–13]. Today, several options are available to produce hydroprocessed base stocks at one or more of the following quality levels, that is, • API Group II with a nominal VI of 100. • API Group II+ with a VI in the upper portion of the API

Group II category, that is, 110–119. Some formulators would further restrict this unofficial category to 115– 119 VI. • API Group III with a VI of ≥ 120. The growth in hydroprocessing in North America for the production of lubricant base stocks is shown in Figure 18.5. Based on statistics reported by the National Petrochemical & Refiners Association or NPRA [14,15], the ratio of API Group I to API Group II/III as of January 1, 2005 for the United States and Canada was 85.4 KBD to 100.6 KBD or approximately 46:54. Today, base stock refiners have access to the knowledge and capability to produce chemically modified base stocks through variations in feed selection and processing schemes [16,17]. This is summarized in Table 18.3 [15]. The result has been the development and marketing of several base stock qualities within the hydroprocessed categories (i.e., API Group II, II+ , III, and III+ ) that, in turn, can significantly impact finished oil properties.

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18.1.5 Manufacturing Schemes The primary method to produce chemically modified base oils is through the use of hydroprocessing. This can be accomplished in a single stage or two-stage hydrocracker and results in considerable ring saturation and ring opening to produce higher VI molecules (Figures 18.3 and Figure 18.4). In the past, lube hydrocrackers were considered to be the sole source for high VI feedstocks. However, over the years it has been learned that many fuels hydrocrackers can be used to produce hydrocracker bottoms (HCB) that have the correct viscosity range and carbon:hydrogen ratio to produce high yields of chemically modified base oils. Figure 18.6 provides a schematic profile of a hydroprocessing operation to produce high VI API Group III base stocks [18]. The HCB feed can either be produced on site or obtained externally and fed into the plant operation. This may require a pretreatment step (e.g., guard reactor) to reduce the level of sulfur and nitrogen components in the feed as many hydrotreating catalysts are sensitive to these poisons. Dewaxing can be conducted in either a traditional solvent dewaxing or hydrodewaxing mode, the latter has been shown to enhance the overall VI of the finished base stock while contributing to outstanding low temperature properties in selected finished oil applications. Hydrodewaxing is a generic term where hydrogen is used in the presence of a catalyst to convert the waxy components in the feed. This would include catalytic dewaxing

TABLE 18.3 North American Producers of Hydroprocessed Base Stocks — January 1, 2005

Refiner

Location

American Refining Calumet Lubricants Co. ChevronTexaco Corp. Ergon Refining Excel Paralubes ExxonMobil Corp. ExxonMobil Corp. Evergreen oil Inc. Motiva Enterprises LLC Valero Energy Corp. Imperial Oil Ltd. Petro-Canada Lubricants

Group–Bradford, PA Shreveport, LA Richmond, CA Newell, WV Westlake, LA Baytown, TX Baton Rouge, LA Newyork, CA Port Arthur, TX Paulsboro, NJ Sarnia, Ontario, Canada Mississauga, Ontario, Canada

Total

Hydroprocessed capacity KBD

API Group II+ capablea

API Group III capablea

0.3 7.6 15.0 2.8 21.9 11.5 2.0 0.7 22.0 0.5 3.8

No Yes Yes No No Yes No No Yes No Yes

No No Yes No No No No No Yes No No

12.5

Yes

Yes

100.6

—

—

a Represents chemically modified base oils that are presently marketed commercially. Source: From National Petrochemical and Refiners Association, Lubricating Oil and Wax Capacities of Refiners and Re-Refiners in the Western Hemisphere, 2004 Annual Report, Washington, D.C., January 2005.

H2 Crude Vacuum Distillation Tower

LVGO

1st Stage Hydrotreater

HVGO

Fuel Gas Naphtha Distillate Gas Oil

Vacuum Resid

Propane

Propane Deasphalting

H2

External HCB

Asphalt H2 H 2

Plant

Fractionator

Fuel Gas

Guard Reactor H2 or Solvent

Finished Base Oils

Intermediate Storage (optional) Slack Wax

H2S

2nd Stage Hydrotreater

Distillation or Vacuum Stripper & Dehydrator

FIGURE 18.6 Schematic for process upgrading of hydrocracker bottoms into high VI base stocks

as licensed, for example, by ExxonMobil while isodewaxing is an alternative process that is licensed by Chevron. Both of these processes have rapidly grown in popularity with the recent shift in the North American market from solvent processing to hydroprocessing. As of January 1, 2005, it is estimated that 65.4 KBD or 35.2% of the total North American paraffinic base oil production

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(i.e., note that re-refined base oils are not included in this analysis) included hydrodewaxing as a key processing step [15]. After the initial hydrocracking step, the feed can either be separated and stored in intermediate tankage or blocked through the remainder of the operation as a total feed. This will normally determine the complexity of the post

Yield of Waxy Lube, LV% Increasing 95

100

105

110

115

120

125

130

135

Product SDW VI

FIGURE 18.7 Process tradeoff between VI and yield for hydrocracking operation

fractionation step and the overall yield profile for the lube operation. Hydrocrackers can operate in several modes, however, as the severity of the operation is increased to produce a higher base oil VI the yield of waxy lube decreases as shown in Figure 18.7 [10]. As a general rule of thumb, increasing the quality of a hydroprocessed base stock from the normal API Group II level of ∼100VI to the API Group II+ level of 115–119 can result in a yield loss of between 25LV% to 30LV%, depending on feedstock, catalyst, and operating conditions. An additional yield loss would be realized by further increasing severity to produce an API Group III chemically modified base oil where the VI is ≥120. Some refiners have evaluated the use of higher quality feedstocks when producing an API Group III slate. Although the feedstock may be more expensive, the improved yields and higher thruput of key viscosity grades can offset the feedstock premium. Hydrocrackers have evolved over the past decade as a multifunctional processing unit that can be optimized for both fuel and lube operations. As most refineries are driven by fuel and fuel based economics, hydrocracker demands must generally satisfy first the fuel requirements and, where practical, be optimized with lube production. As a result, hydrocrackers will vary in their modes of operation and their ability to produce a feed that is suitable to produce lubes of differing grades. This will become a growing concern in the future as regulations on fuel quality with reduced levels of sulfur content will challenge the use of hydrocrackers in either fuel or lubricants mode. Although hydrocracker bottoms have been the predominant feed source of chemically modified base oils, wax or wax based feeds have also become an alternative option to produce higher VI base stocks. As previously discussed, one can overcrack a feed to achieve a higher VI. But by beginning with a higher VI feed, one can then reduce the severity of the operation and still produce the same (or higher) VI base stock with a higher lube yield. At the same time, several advances in hydrodewaxing catalysts have provided an opportunity to produce high VI base stocks with limited, and in some cases negligible, VI loss.

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In the end, the final choice of feed or process severity to achieve the desired base stock VI will reside with the producer. However, the availability of wax or waxy feeds has provided an alternative approach to produce chemically modified mineral oils. Shell was one of the first to utilize wax as a valuable feed for lube production when it introduced its premium line of XHVI® base stocks from its Petit Couronne refinery in France [19,20]. The wax isomerization process was complimented with a solvent dewaxing operation to produce a slate of base stocks whose VI exceeded 140. Exxon, now ExxonMobil, also developed a wax isomerization process and commercialized its Exxsyn™ base stocks at the Fawley, U.K. refinery in 1993–1994 [21]. Again, solvent dewaxing was the complimentary process and base stock qualities were equivalent to Shell XHVI® at 140+ . Although the Fawley production was short lived, it has since been upgraded and complimented with a hydrodewaxing step to improve low temperature viscometrics for automotive crankcase and driveline applications. A new slate of Visom™ base stocks was introduced at Fawley in 4Q’03 [22]. Although the processing of wax as a pure feedstock has been limited to investments in Europe, North American refiners have also realized the value of waxy feeds and in selected instances have modified their internal refinery operations to accommodate the upgrading of wax and waxy feeds as a supplement into high VI base stocks on an opportunity basis. As the North American market has continued to upgrade base stock quality, the biggest concern has been the fate of the conventional solvent refinery. As solvent processing is limited in recovering high VI molecules, refiners have searched for a means to maximize the use of its solvent refinery to produce higher VI base stocks in appreciable yields. A breakthrough occurred during the 1990s when a new processing technology provided the means to integrate a medium severity hydroprocessing operation into an existing solvent process refinery. This allows the refiner to maintain its extraction section to remove a portion of the very low VI aromatic and cyclic components and provide a suitable feed for an optimized hydroprocessing step. The dewaxing operation can either be solvent dewaxing or hydrodewaxing depending on VI requirements as well as the demand for wax as a marketable product. This processing provides a lower cost approach to the production of conventional and chemically modified base stocks. ExxonMobil introduced Raffinate Hydroconversion (i.e., RHC™) in 1996 at its Baytown, Texas refinery and the methodology of this approach is shown in Figure 18.8 [23]. A comparison of the yield and VI impacts from an integrated solvent and hydroprocessing operation with and without wax hydrodewaxing is summarized in Table 18.4 [23].

Lubes Vacuum Solvent Pipestill Extraction

Solvent Dewaxing

Vacuum Fractionator EHC™ 45

Finishing Reactor

Conversion Reactor

Conversion Reactor

Raffinate Hydroconversion

Light Neutral

EHC™ 60

Heavy Neutral Aromatic Extract

Wax

FIGURE 18.8 Integration of raffinate hydroconversion with solvent processing lube plant Source: From Gallagher, E., Cody, I.A., and Claxton, A.A., Development and Commercialization of Raffinate Hydroconversion — A New Technology to Manufacture High Performance Basestocks for Crankcase and Other Applications, National Petroleum Refiners Association, Paper LW-99-121, Fall Meeting, November 1999.

TABLE 18.4 Comparison of Yield and VI Gains in Various Base Stock Process Operations Refinery process

Typical yield, LV%

Predicted VI uplifta

50–70 80–98 85–97

10–35 5–20 4–10

Solvent extraction RHC™ (or similar) Hydroisomerization

a Variations in process yields and VI reflect crude differences. Source: From Gallagher, E., Cody, I.A., and Claxton, A.A., Development and Commercialization of Raffinate Hydroconversion — A New Technology to Manufacture High Performance Basestocks for Crankcase and Other Applications, National Petroleum Refiners Association, Paper LW-99-121, Fall Meeting, November 1999.

18.2 PERFORMANCE FEATURES OF CHEMICALLY MODIFIED MINERAL OILS 18.2.1 Composition The composition of a lubricant base stock is directly related to its feed and processing history. Unlike PAOs which have a very specific and consistent composition, base stocks are composed of thousands of chemical components and can be grouped into the following bulk categories: • Paraffins, including n-paraffins and isoparaffins. • Cycloparaffins, or naphthenes, most commonly mono

and dicycloparaffins, however, polycycloparaffins with 3-, 4-, 5- and higher saturated rings might exist in smaller concentrations.

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• Aromatics, again with ring structures that are similar

to cycloparaffins. These components may also contain sulfur and nitrogen within its complex structure. Conventional processing tries to separate the most desirable molecules from crude oil (e.g., paraffins and small-ring cycloparaffins). This however is a limiting process that is incapable in producing high yields of very high VI base stocks. Hydroprocessing, either as an exclusive process or in combination with solvent processing has quickly evolved as an important advancement in the production of higher VI and in some instances chemically modified mineral oils. These are typically highlighted with an absence of aromatic components and a high concentration of paraffins and small-ring cycloparaffins. Table 18.5 [24,25] provides a compositional comparison of a series of API Group I, II, II+ , and III base stocks using a series of processing approaches. All of the base stocks have a kinematic viscosity at 100◦ C of roughly 4 cSt, consistent with a 100N designation. These are frequently considered for the formulation of low viscosity SAE passenger car engine oils (e.g., SAE 5W-XX). Although the analytical method is proprietary, it is based on mass spectrometry. For solvent processed API Group I base stocks that have a wider range of base stock components, including aromatics and thiophenes, the high-resolution mass spectrometry procedure assigns fragment ions into thirty-eight (38) hydrocarbon types, including: • Paraffins (iso- and n-) • Monocycloparaffins • Noncondensed polycycloparaffins

TABLE 18.5 Chemical Composition of Lubricant Base Oilsa Base stock A I

B I

C II

D II

E II

F II+

G III

Processing

Solvent refined

Solvent refined

Hydrocracked

Hydrocracked

Dewaxing HRMS, mass% Alkanes (n- & isoparaffins) Mono-cycloparaffins Polycycloparaffins Aromatics Thiophenes Paraffins + Monocycloparaffins

Solvent

Solvent

Solvent

Iso-

Severely Hydrocracked Solvent

Severely Hydrocracked Iso-

Severely Hydrocracked Iso-

25.7 20.8 27.9 24.9 0.7 46.5

29.0 25.0 31.7 14.2 0.1 54.0

23.7 30.8 39.1 6.4 0.0 54.5

30.2 30.5 35.3 4.0 0.0 60.7

32.6 34.2 32.9 0.6 0.0 66.7

51.4 24.4 23.9 0.3 0.0 75.8

76.1 14.7 9.2 0.0 0.0 90.8

API category

a Base oil kinematic viscosity approximately 4 cSt at 100◦ C.

Sources: From Henderson, H.E., Mack, P.D., Steckle, W.M., and Swinney, B., Higher Quality Base Oils for Tomorrow’s Engine Oil Performance Categories, SAE Paper 98252, October 1998; Henderson, H.E., Fefer, M., Legzdins, A., Michaluk, P., and Ruo, T., Compositional Features of New High Performance Specialty Base Fluids, Symposium: Worldwide Perspectives on the Manufacture, Characterization and Application of Lubricant Base Oils: IV, ACS National Meeting, New Orleans, Louisiana, August 1999.

• Condensed polycycloparaffins • Aromatic types (16 classes) having 1- to 7-condensed

aromatic or saturated rings • Aromatic types (16 classes) containing sulfur • Aromatic types (3 classes) containing oxygen

For highly saturated base stocks where there is an absence or minimal level of aromatic components (e.g., API Group II, II+ , III, IV), a modified hydrocarbon matrix of 13 classes is used. Solvent processed base stocks have a wide range in chemical composition, due to variations in feedstock quality and extraction severity. This is reflected by the range in compositional quality between base stocks A and B. With the introduction of hydoprocessing or conversion technology (e.g., base stocks C, D), aromatics are converted into cycloparaffins through ring saturation whereas thiophenes are eliminated. This is consistent with the limited concentration of sulfur and nitrogen containing species in API Group II and III base stocks. As hydroprocessing severity is increased (e.g., base stock E, F, G), there is a further shift toward the production of paraffins and small-ring (i.e., 1- and 2-ring) cycloparaffins. It should also be noted that the paraffin fraction is predominately composed of isoparaffins, although a small concentration (i.e., <5%) of n-paraffins may appear. Since n-paraffins have very poor pour point properties, they are normally removed during the dewaxing step. However, n-paraffin residual wax molecules (i.e., those waxy molecules whose pour point exceeds that of the finished

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base stock and hence remain in solution after the dewaxing step) may be present in the finished base stock, particularly when solvent dewaxing is used as the processing step. When hydrodewaxing is used, the presence of n-paraffins is significantly reduced as they are either cracked to lower boiling paraffins that are outside of the lube boiling range or converted to isoparaffins. This is very important when low-temperature fluidity is required. Base stock G represents a chemically modified mineral oil, whose composition is rapidly approaching that of PAOs whose isoparaffin concentration is reported at 100% [24,25]. In a separate analysis [26], a comparison of the physical, chemical, and compositional properties of an API Group I, II, III, and IV base stock was conducted to again show the significant changes in properties across lube processing (Table 18.6). The level of sulfur and nitrogen containing components are significantly reduced as the processing shifts from solvent refining to lube hydrocracking to severe hydroprocessing in combination with isodewaxing (i.e., VHVI). Detailed compositional properties were determined by initially separating the aromatic and nonaromatic components using elution chromatography (ASTM D2549). The nonaromatic fractions were then analyzed for their compositional properties using high ionizing voltage mass spectrometry (ASTM D2786). It can be seen that the compositional features of very high VI base stocks will vary depending on the processing approach but, more importantly, on the type of

TABLE 18.6 Comparison of 150N Grade API Group I, II, III, and IV Base Stocks API Group I Solvent Refined

II Lube Hydro Cracking

III VHVI (very high viscosity Index)

Physical characteristics KV at 40◦ C, cSt KV at 100◦ C, cSt Viscosity index Flash point, ◦ C Pour point, ◦ C CCS viscosity at −20◦ C, cP Noack volatility, wt%

30.1 5.1 95 216 −12 2100 17.0

29.6 5.1 99 222 −12 2000 16.5

32.5 6.0 133 234 −15 1230 7.8

31.3 5.9 135 240 −60 900 7.0

Chemical characteristics Sulfur, ppm Nitrogen, ppm

5800 12

300 4

<10 <1

<10 <1

Composition, wt%a Paraffins 1-Ring naphthenes 2-Ring naphthenes 3-Ring naphthenes 4-Ring naphthenes 5-Ring naphthenes Aromatics

27.6 20.8 25.9 2.9 0.3 0.0 22.5

33.4 30.2 17.2 9.3 5.1 1.1 3.5

55.5 20.4 12.1 9.1 2.1 0.0 0.8

100.0 0.0 0.0 0.0 0.0 0.0 0.0

Processing

IV Synthetic PAO

a Composition determined by ASTM D2549 and ASTM 2786 methods. Source: From Moon, W.S., Cho Y.R., Yoon, C.B., and Park, Y.M., VHVI Base Oils from Fuels Hydrocracker Bottoms, China Lube Oil Conference ‘98, Beijing, China, June 1998.

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135 Viscosity Index

analytical methodology that is used. Regardless of the approach, the end result is a reduction in the level of condensed multi-ring paraffins and aromatics [27] as shown in Figure 18.9 with a corresponding increase in the concentration of paraffins [28] as shown in Figure 18.10 as one shifts toward the production of API Group III chemically modified mineral oils. It is also apparent that the composition of chemically modified mineral oils will vary depending on feedstock selection, processing options, and base stock manufacturing targets. Wax, for example, will provide a higher concentration of paraffins since wax itself is a highly paraffinic material where VI can reach as high as 200. HCBs will also vary in composition depending on feed selection and processing severity. The dewaxing step will also influence composition as hydrodewaxing will crack and convert n-paraffins into isoparaffins (or nonlube components), whereas, solvent dewaxing is not selective and will remove a proportionate amount of waxy n-paraffin, isoparaffin and cycloparaffin components. Table 18.7 compares the compositional features of a number of chemically modified mineral oils using a constant high-resolution mass spectral procedure [25].

R2 = 0.93

125 115 105 95 0

5

10

15

20

25

[CNRP], wt%

FIGURE 18.9 Relationship between base stock VI and condensed multi-ring paraffins

Base stocks K and M have the highest concentration of isoparaffins and are consistent with the use of wax as a feedstock. The remaining base stocks use HCBs as a feedstock and have a noticeably lower concentration of isoparaffins. At the same time, their VI values are appreciably lower as wax isomerized base stocks will typically have VI values that exceed 140. Interestingly, there can also be variability in the concentration of polycycloparaffins

(e.g., 3 and 4+ condensed rings) and the presence of trace aromatics. These variations will impact the overall performance of the base stock in automotive, industrial, and other applications. Mass spectrometry can be a powerful tool when evaluating the compositional features of chemically modified mineral oils. Unfortunately, most procedures are internal proprietary methods where operating conditions and peak assignments vary considerably. The API through the Base Oil Interchange and Viscosity Grade Read across Task Force (API BOI/VGRA) conducted an analysis of the compositional features of six hydroprocessed base stocks that had similar saturates contents as measured

Viscosity index

140

R 2 = 0.91

by ASTM D2007 (i.e., Clay Gel saturates method) but significantly different VI properties. These are shown in Table 18.8 [29]. The results from the mass spectral study is shown in Figure 18.11 [29] and it is quite apparent that the reproducibility of detailed compositional properties is not an exact science and is highly dependent on the analytical procedure and peak assignments. However, although the variability was quite wide, the study did demonstrate that each of the participating laboratories was able to successfully rank base stocks according to their VI properties. This further confirms the relationship between base stock compositional properties with VI and the presence of a high percentage of isoparaffins with chemically modified mineral oils, that is, API Group III.

120

18.2.2 The Synthetic Nature of Chemically Modified Mineral Oils

100

During the latter half of the 1990s, considerable effort was made to demonstrate that chemically modified mineral oils were indeed different than conventionally processed API Group I and II base stocks and more in line with synthetically produced base stocks like PAOs. Both Petro-Canada and Chevron were very active in this area, including studies that involved the chemical composition of chemically modified mineral oils and their resultant performance in automotive and industrial products.

80 0

20

40

60

80

Isoparaffin content, wt %

FIGURE 18.10 Relationship between base stock VI and paraffin content

TABLE 18.7 Considerable Variability Observed in the Composition of High Quality API Group III Chemically Modified Mineral Oils SBF ID

H

I

J

K

L

M

N

O

P

Q

Viscosity index

5.6 131

6.0 122

6.2 128

7.0 143

6.0 127

5.9 143

5.3 128

4.7 126

5.0 143

6.0 131

Composition, HRMS (Mass%)a Paraffin, n- & isoMonocycloparaffin Dicycloparaffin Tricycloparaffin Polycycloparaffin Monoaromatic Polyaromatic Paraffin + monocycloparaffin Polycycloparaffin + aromatic

51.1 27.5 11.1 3.4 2.3 3.7 0.9 78.6 6.9

49.3 30.2 12.6 4.4 3.4 0.0 0.1 79.5 3.5

54.7 26.7 9.8 3.7 2.8 2.0 0.3 81.4 5.1

64.9 26.3 7.4 1.3 0.0 0.1 0.0 91.2 0.1

57.5 27.7 9.9 3.0 1.9 0.0 0.0 85.2 1.9

73.7 21.0 5.1 0.0 0.0 0.1 0.1 94.7 0.2

45.5 32.5 12.8 4.9 3.1 0.9 0.3 78.0 4.3

59.1 22.8 8.3 3.2 4.9 1.2 0.5 81.9 6.6

73.4 20.0 5.1 0.7 0.0 0.8 0.0 93.4 0.8

60.1 23.1 9.9 3.9 2.7 0.4 0.0 83.2 3.1

KV at 100◦ C, cSt

a HRMS described in Reference 23.

Source: From Henderson, H.E., Fefer, M., Legzdins, A., Michaluk, P., and Ruo, T., Compositional Features of New High Performance Specialty Base Fluids, Symposium: Worldwide Perspectives on the Manufacture, Characterization and Application of Lubricant Base Oils: IV, ACS National Meeting, New Orleans, Louisiana, August 1999.

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TABLE 18.8 Profile of API Group II, II+ , and III Base Stocks Included in API BOI/VGRA Task Force Study of Mass Spectral Analysis Base stock Viscosity Index Saturates, wt%, ASTM D2007 Isoparaffin, wt%, HRMSa

1 101 96.3 28.5

2 116 96.1 36.3

3 120 96.1 37.2

4 122 95.3 50.1

5 126 97.4 61.6

6 143 99.0 80.9

a HRMS procedure as discussed in Reference 17. Source of HRMS data. Source: From Henderson, H.E., American Petroleum Institute, Base Oil Interchange and Viscosity Grade Readacross Task Force, Report from Base Oil Characterization Work Group, July 11, 2002.

100.0 90.0 Lab A

Lab B

Lab C

Lab D

Lab E

Lab F

Alkane content, wt %

80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0 0.0 1

2

3

4

5

6

Oil code

FIGURE 18.11 Laboratory variability in base stock alkane content for a series of API Group II, II+ , and III base stocks

One of the key studies [30] looked at the compositional changes that occur during an all hydroprocessing threestage operation, including: • Step #1: Hydrocracking where the majority of sulfur,

nitrogen and other nonhydrocarbon impurities are removed. During this processing step, aromatics are essentially converted into cycloparaffins through the saturation of aromatic rings with hydrogen. At the same time, “molecular reshaping” of the remaining saturated species occurs through ring-opening reactions. • Step #2: Hydroisomerization where n-paraffins and molecules that contain waxy side chains are isomerized into branched components. During this step, residual amounts of aromatic components are saturated while trace impurities (i.e., sulfur and nitrogen) are removed as well.

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• Step #3: Hydrofinishing where any remaining impurities

are removed or reduced to trace levels. Several analytical procedures were used to fully understand the compositional changes that occur during the all-hydroprocessing three-stage operation of a standard vacuum gas oil feed (VGO) into an API Group III chemically modified mineral oil [30]. A summary of the steps and conclusions are provided in Table 18.9. The results from this study [30] showed that at least 80% of the components in the original VGO feedstock are catalytically transformed during an all-hydroprocessing three-stage operation. It is also suggested that the remaining 20% of the lube molecules are also chemically altered when semiquantitative NMR analysis and thermodynamic considerations are included. It is therefore quite possible that a full compositional transformation (i.e., synthetic alteration) of a VGO feedstock would occur during full

TABLE 18.9 Chemical Alteration of VGO Feedstock Using All-Hydroprocessing Three-Stage Operation Analytical Technique Solvent Dewaxing Preparative High Performance Liquid Chromotography (HPLC)

Gas Chromatography–Mass Spectrometry (GC Mass Spec) Field Ionization Mass Spectrometry (FIMS)

Chemical changes • • • • • • • • • • • •

Nuclear Magnetic Resonance Spectroscopy (NMR)

• •

• •

Conversion (%)

Solvent dewaxing to –10◦ C pour point produced 34% wax

34

Wax would be catalytically altered during lube manufacturing Dewaxed oil (i.e., 66% of VGO feed) separated into components 59% saturates, 38% aromatics, 3% polars Hydrocracking and hydrofinishing steps to convert aromatic and polar components Molecular alteration = 0.66 × [0.38 + 0.03] Analysis of saturates fraction shows 10% n-paraffins Hydroisomerization will convert all n-paraffins to isoparaffins Molecular alteration = 0.66 × 0.59 × 0.10 Significant shift in MW distribution and ring-content between VGO and finished base oil Spectral subtraction shows significant conversion of multi-ring naphthenes into isoparaffins and 1-ring naphthenes Estimate 43% of molecules in the dewaxed saturates fraction (e.g., n-paraffin components) are altered by MW distribution and ring number Molecular alteration = 0.90 × 0.59 × 0.67 1H and 13C NMR shows significant molecular rearrangement and transformation within the saturates fraction with more interior methyl branches than expected Reflects redistribution of isomers and some transformation from other species Molecular alteration not quantified but suggests that 80% conversion from dewaxing, HPLC, GCMS, and FIMS steps may be understated

27

4

15

>0%

Source: From Kramer, D.C., Sztenderowicz, Lok, B.K., Cheng, M., Rechsteiner, C.E., and Wilson, D.M., The Synthetic Nature of Group III Base Oils, NPRA Paper LW-99-124, November 1999.

hydroprocessing that is utilized by many API Group III producers, both in North America and globally.

18.2.3 Volatility The volatility of a lubricant base stock is directly related to its chemical composition and the fractionation efficiency of the distillation operation. As the volatility of a base stock improves, the distillation process is adjusted such that “narrower” slices from the common feed occur. This is shown in Table 18.10 for a commercially available API Group III chemically modified mineral oil where the relationship between Noack volatility and the distillation cut width is compared [24]. Although Noack volatility is a measured property (i.e., ASTM D5800), there have been predictive tools that have been developed based on gas chromatography (GC). The most notable method has been developed by BP Petroleum (i.e., DIN 51581 Part 2) where a gas chromatogram is sectioned into 10◦ C intervals and a weighting scheme is used to calculate the degree to which fraction would volatilize under Noack testing conditions (i.e., 250◦ C for

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TABLE 18.10 Effect of Base Oil Cut Width on Predicted Noack Volatility Cut width, ◦ C (50 to 5% GCD) 70 60 50 42.8a 40 30 20

Predicted Noack volatility, wt% 16.9 15.5 14.3 13.5 13.2 12.1 11.1

a Actual sample cut width. Measured Noack

volatility 13.1 wt% ±0.8 wt% based on 22 laboratory round robin study. Source: From Henderson, H.E., Mack, P.D., Steckle, W.M., and Swinney, B., Higher Quality Base Oils for Tommorrow’s Engine Oil Performance Categories, SAE Paper 98252, October 1998.

Kinematic viscosity at 100°C

20 95 VI 120 VI 140 VI 10

96

5 122

1 300

400

500

Mid boiling point, °C (ASTM D2887E)

144

FIGURE 18.12 Relationship between mid boiling point and kinematic viscosity for a series of API Group II, II+ , and III base stocks

1 h). Further simplifications to this method have been pursued and include an estimate based on the 5% and 50% points of a GC distillation curve, that is, its cut width. The reference base stock in Table 18.10 has a measured Noack volatility of 13.1 wt% and a predicted Noack using the 5% and 50% GCD points of 13.5 wt%. These results are well within the repeatability of this test and therefore considered to be similar. One can therefore use the 5% and 50% GCD points to estimate the effect of cut width on Noack volatility. The results suggest that the Noack volatility of a base stock can be improved by approximately 1 wt% for each 10◦ C reduction in the distillation cut width of the base stock. However, the ability to reduce Noack volatility is limited as a point will be reached where the fractionation efficiency and concentration of lube molecules in the correct boiling range are limited. To overcome this, refiners need to shift additional molecules into the desired boiling range. This can be achieved by increasing the VI and hence chemical composition of the base stock. Figure 18.12 [24,31] shows the relationship between mid boiling point and kinematic viscosity at 100◦ C for a series of base stocks of differing VI. Trend lines have been estimated from the data to reflect a VI of 95 that is typical of conventional solvent refined (API Group I) and hydroprocessed (API Group II) base stocks. Two additional trend lines are shown for chemically modified mineral oils consistent with the lower and upper end of the API Group III category. From a processing standpoint, one might consider that the 120 VI line is representative of chemically modified mineral oils produced from hydrocracker bottoms (HCBs), whereas, the 140 VI line might reflect an operation where wax is used as a feedstock. It should be noted that many chemically modified mineral

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oils that are produced from HCBs have VI properties that can extend into the 130+ range, depending on kinematic viscosity. Hence the 120 VI line is a reflection of the lower end of the API Group III category. It is apparent that as the VI of a base stock increases at a constant kinematic viscosity that its mid boiling point will also increase. For low SAE 5W-20/30 PCEO products, a base stock with a kinematic viscosity of ∼4.5 cSt at 100◦ C would be considered. As the VI increases from 95 to 120 to 140, the MBP, or mid boiling point increases from 405◦ C to ∼430◦ C. The increase in MBP is significant as it increases the number of higher boiling components at the correct kinematic viscosity. This higher yielding distillate can then be effectively fractionated to produce an acceptable yield of a low volatility base stock. When the VI reaches the 140 level, the MBP is further increased to ∼460◦ C. This provides an even higher yield of lube molecules in the correct boiling range and is one reason why wax and wax based feeds are being considered for the production of high VI chemically modified mineral oils for the automotive industry. Representations of the chemical structures that are associated with VI are included with Figure 18.12. These are model compounds that were analyzed as part of the API Research Project 42 [32] where the number of carbon atoms is 26, consistent with low-viscosity lube base stock that would be used to formulate low viscosity SAE passenger car engine oils. As the VI of the base stock is increased, the number of cycloparaffin ring structures is reduced from an average of two (2) with the 95 VI base stock, to one (1) with the 120 VI base stock to zero (0) with the 140 VI base stock. This further demonstrates the relationship between chemical structure and volatility and the improvements that are achievable with chemically modified mineral base oils.

The viscometric properties of a base stock are affected by many properties, including: • Kinematic viscosity (KV), where an inverse relationship

exists between KV and low-temperature fluidity. • Viscosity Index (VI), where a direct relationship exists

between VI and low temperature fluidity. • The levels of trace waxes or wax-like components that remain in a base stock following its dewaxing step. The property that is produced following dewaxing is referred to as pour point and is expressed as the temperature at which a fluid maintains its viscous flow. The difference between pour point and solid point (i.e., the temperature at which a fluid becomes solid) is normally 3◦ C or 5◦ F. • The types of residual wax or wax-like components that remain in a base stock following the dewaxing process. This is usually a reflection of the distillate feed and the type of dewaxing process as hydrodewaxing is a very selective process and essentially removes all n-paraffin waxes that exhibit very poor flow characteristics under slow (e.g., Brookfield viscosity) and some rapid cool (e.g., Cold Cranking Simulator, or CCS) conditions. Solvent dewaxing, meanwhile, is a nonselective process that removes a proportionate amount of n-paraffin, isoparaffin and cycloparaffin waxy components but is unable to specifically remove all traces of n-paraffin residual waxes. Chemically modified mineral oils have a high VI and should therefore provide improved viscometrics under both low-temperature and high-temperature regimes. The property itself represents the change in viscosity over a temperature range from 40◦ C to 100◦ C. The higher the VI, the lesser will be the change in the oil’s viscometric properties thus providing a “flatter” profile over the temperature range. This, in turn, can be extended to higher and lower temperatures, provided wax effects are not considered. More importantly, the dewaxing operation can have a more dramatic effect on base stock fluidity as it can influence the types of residual waxes that remain in the finished base stock. As previously discussed, n-paraffin residual waxes have a detrimental effect on low-temperature fluidity and their removal via hydrodewaxing can significantly improve the performance of chemically modified mineral oils. This is shown in Figure 18.13 [24] where the CCS viscosity of a series of solvent and hydrodewaxed base stocks is plotted against their predicted values, based on VI properties and not including secondary wax effects. Results show that the hydrodewaxed base stocks consistently have CCS viscosities that are lower than their theoretical predicted values. Since hydrodewaxing is normally associated with API Group III chemically modified

Copyright 2006 by Taylor & Francis Group, LLC

Measured CCS, cP at –25°C

18.2.4 Low-Temperature Viscometrics

2500

Solvent dewaxed Hydro-isomerized

1:1

2000 1500 1000 500 750

1000

1250 1500 1750 2000 Predicted CCS, cP at –25°C

2250 2500

FIGURE 18.13 Relationship between predicted and measured CCS viscosity for a series of solvent and hydrodewaxed base stocks

mineral oils that are produced in North America and AsiaPacific, this will provide excellent fluidity characteristics when formulating crankcase engine oils. Alternatively, solvent dewaxed base stocks exhibit a higher than predicted CCS viscosity. Hence an advantage in low-temperature fluidity under CCS conditions will occur when the base stock is hydrodewaxed rather than solvent dewaxed. Multigraded automotive oils are composed of three main ingredients, namely: • A lubricant base stock or base oil blend. • A detergent inhibitor package, or DI, that provides

the required performance benefits to a finished fluid that cannot be achieved from the base stock alone. Depending on the application, this could include but not be limited to such additive components as dispersants, detergents, antiwear and antirust agents, oxidation inhibitors, friction modifiers, demulsibility and antifoam agents, etc. • A Viscosity Modifier (VM) with or without a supplemental pour point depressant (PPD) to ensure adequate viscometrics under both high- and low-temperature conditions. Low-temperature viscometrics will be influenced by each of the components that are used in the finished blend. Because the DI is fixed for each product, the low- (and high) temperature properties will be influenced by the balanced contributions from the base stock and VM/PPD components. Chemically modified mineral oils, particularly those that are hydrodewaxed, have excellent low-temperature characteristics under both slow cool and rapid-cool procedures. The result is the ability to use a heavier viscosity base stock than normally required, which then provides an opportunity to use a lower VM treat to achieve the same product viscometrics. This leads to a formulation that is more cost effective since VM components can be very expensive.

TABLE 18.11 Comparison of Base Oil Effects on Viscometrics of Multigrade HDMO Formulations with Constant API CH-4 Treat Rate Formulation

Test method

SAE Viscosity grade API base oil group Dewaxing VM treat, Mass% Physical properties KV at 40◦ C, cSt KV at 100◦ C, cSt Viscosity Index HTHS, cP at 150◦ C and 106 sec−1 CCS viscosity at −15◦ C, cP CCS viscosity at −20◦ C, cP

ASTM D0445 ASTM D0445 ASTM D2270 ASTM D4683 ASTM D5293 ASTM D5293

A

B

C

15W-40 I Solvent 8.5

15W-40 II+ Hydro 6.8

10W-40 III Hydro 8.7

107 14.8 142 4.15 2,670 —

112 15.1 140 4.33 2,980 —

95.8 14.6 154 4.18 1,810a 2,920

a Estimated from measured CCS at −20◦ C.

Source: Henderson, H.E., Mack, P.D., Steckle, W.M., and Swinney, B., Higher Quality Base Oils for Tommorrow’s Engine Oil Performance Categories, SAE Paper 98252, October 1998.

Table 18.11 [24] provides an example of the benefits of using a chemically modified mineral oil in an API CH-4 performance heavy-duty engine oil. By comparing formulations A and B, it can be seen that by increasing the VI of the base stock from a nominal 95–100 VI with API Group I to 115–119 VI with API Group II+ , that a 20% reduction in the VM treat is realized. The reduced level of VM also results in an improvement in high temperature and high shear viscosity (HTHS), which is very important in heavy-duty engine oil (HDEO) applications. Formulation C, meanwhile, is produced from an API Group III chemically modified mineral oil that has been hydrodewaxed. Despite using the same treat rate of DI and VM/PPD components, the overall improvements in low temperature viscometrics allows a one (1) SAE grade drop from SAE 15W-40 to SAE 10W-40 with the chemically modified mineral oil. And the improved low temperature CCS properties with formulation C could provide additional opportunities to increase the KV of the base oil with a corresponding reduction in VM consistent with the comparison between formulations A and B. The effects of chemically modified mineral oils that are hydrodewaxed is more dramatic when slow-cool lowtemperature tests are considered as with driveline fluids, that is, ATF and automotive gear oils (AGO). Figure 18.14 [31] compares the low temperature Brookfield viscosity at −40◦ C for a series of API Group I, II, III, and IV base stocks that have been formulated with the same treat rate of a commercial Ford MERCON® -V performance system (i.e., DI + VM/PPD). Each data point of the graph represents a different commercial base stock and it can be seen

Copyright 2006 by Taylor & Francis Group, LLC

that viscosity profiles can be developed for the various API groupings. The previous Ford MERCON® specification required a finished oil Brookfield viscosity of 20,000 cP at −40◦ C. This could normally be achieved with a solvent refined API Group I base stock with a KV at 40◦ C of approximately 14.0 cSt (i.e., 78 SUS at 100◦ F). However, the current MERCON® -V specification has a more stringent Brookfield requirement of 9,000 ± 4,000 cP at −40◦ C. To meet this specification with a solvent refined API Group I base stock would require a significantly lower KV of roughly 8.5 cSt at 40◦ C (i.e., 56 SUS at 100◦ F). This is unacceptable for today’s transmissions as the use of such a low-viscosity fluid would negatively influence such finished oil properties as shear stability, oxidation stability, and volatility. One can use a slightly higher VI API Group II base stock, however, the fact that many of these are solvent dewaxed will again lead to similar low temperature deficiencies as with the API Group I base stocks. By shifting to a chemically modified API Group III base stock that has been hydrodewaxed, a step change in low-temperature performance is realized that rapidly approaches that for PAOs (API Group IV). From Figure 18.14, it can be seen that not only can the more severe low-temperature requirement be achieved with the chemically modified mineral oil but the kinematic viscosity of the base stock is actually higher than the API Group I solvent dewaxed base stock and the older MERCON® performance limit, that is, 17.5 cSt at 40◦ C or 94 SUS at 100◦ F [33]. The availability of high VI and hydrodewaxed chemically modified base oils has become a major advance

Finished Oil Brookfield Viscosity, cP at –40°C

50,000

Ford MERCON V Performance Package Commercial API Group I, II, III Severely Hydro-Treated/Solvent Dewaxed Severely Hydro-Treated/Hydro-Isodewaxed PAO

40,000 30,000

20,000

MERCON Specification

MERCON V 10,000 Specification

0 0.0

5.0

10.0

15.0

20.0

25.0

Base Stock Kinematic Viscosity, cSt at 40°C

FIGURE 18.14 Relationship between base oil kinematic viscosity and finished ATF brookfield viscosity for a series of API Group I, II, III, and IV base stocks

TABLE 18.12 Base Oil Effects on Low-Temperature Brookfield Viscosity Base oil I.D. Dewaxing Base oil properties KV at 40◦ C, cSt KV at 100◦ C, cSt Viscosity index Pour point, ◦ C Cloud point, ◦ C Finished oil propertiesa Brookfield at −40◦ C, cP

A Hydro

B Hydro

C Solvent

D Solvent

E Solvent

19.61 4.245 123 −24 −16

22.01 4.619 128 −21 −19

14.18 3.556 136 −15 −13

16.39 3.990 146 −18 −12

18.43 4.132 128 −27 −20

15,720

19,280

22,650

Solid

38,150

a Formulated with a constant treat of a commercial Ford MERCON®-V additive

system. Source: Henderson, H.E. and Swenney, B., Higher Quality Base Oils for Next Generation Automatic Transmission Fluids, SAE Paper 982666, October 1998.

in the development of “fill-for-life” ATFs. However, the dewaxing step remains a key as shown for a series of chemically modified API Group III base stocks in Table 18.12 [33]. Each of the base stocks was formulated with the same treat rate of a commercial Ford MERCON® -V additive system and the Brookfield viscosity measured at −40◦ C. The wide variation in low-temperature properties cannot be explained simply from the bulk base oil properties, such as KV, VI, and pour point. The formulations that used Base Oil A and B were both hydrodewaxed and, in general, provide low-temperature Brookfield viscosities that are consistent with the slight variations in base oil KV, VI and pour/cloud point properties. Interestingly, the formulations that were

Copyright 2006 by Taylor & Francis Group, LLC

blended with Base Oils C and D would be expected to deliver outstanding Brookfield performance as they have a significantly lower base oil KV, a significantly higher VI, and similar pour/cloud properties (i.e., within test reproducibility). However, their Brookfield performance is considerably poorer than the hydrodewaxed formulations and for Blend D is actually solid at −40◦ C. The same is true when Blends A and E are compared as the comparative base oil properties would suggest a slight advantage for Blend E, however, it’s Brookfield viscosity exceeds that of Blend A by a factor of two. The reason for differences in low temperature performance resides with the type of dewaxing operation. Solvent dewaxing does not completely remove n-paraffin

residual waxes that have a propensity to thicken an oil rapidly under slow-cooling conditions. When these waxy molecules are removed from the base oil via a hydrodewaxing process, the rapid thickening effect is removed and excellent low-temperature fluidity is observed [33,34]. This has been observed with most notably ATF fluids but has also been extended to the AGO area where the same concern for improved Brookfield performance is required.

18.2.5 Oxidation Stability The compositional properties of a lubricant base stock have become increasingly important in the past decade as new performance requirements in the automotive area, including improved oxidation, fuel economy retention, and “fill-for-life” requirements combined with higher performance demands in the industrial sector have created a technical need for base stocks that contain a higher concentration of saturated components. Chemically modified mineral oils have a higher concentration of saturated molecules as the hydroprocessing steps effectively maximize isoparaffins or cycloparaffins. In the passenger car engine oil area, this has been a growing requirement as the new ILSAC GF-4 performance category has introduced a new Sequence IIIG engine test that has a strong requirement for highly saturated formulations. For the lower SAE 5W-20 and SAE 5W-30 grades, this has resulted in an increased demand for chemically modified API Group III and API Group II+ base stocks, while, the appearance of these highly saturated base stocks into the SAE 10W-30 and SAE 10W-40 grades is growing. In the past, the heavier PCEO grades could be formulated with 100% API Group I or II base stocks, however, with ILSAC GF-4 this is no longer the preferred option. In the HDEO area, the introduction of EGR and retarded fuel injection to address U.S. EPA emission limits have resulted in a reduction in the combustion efficiency of

an engine, an increased level of unburned fuel referred to as soot, and an engine that is now operating under higher levels of thermal and oxidative stress. Several papers have been written on the role of lubricant base stocks in the heavy-duty area [35–38]. Most recently, Lubrizol have investigated the relationship of base stock composition with oil thickening under high soot loadings [37]. They have observed that HDEO formulations produced with highly saturated base stocks retard rapid thickening in a high soot environment. Conversely, rapid thickening is observed with formulations based on solvent processed API Group I base stocks where a higher concentration of aromatic and polar molecules is observed. Through an analysis of the electrical properties of both model compounds and used oils that were obtained from engine and field testing under various levels of soot loadings, Lubrizol have postulated that the rapid thickening from API Group I based formulations is due to the particle interactions of the soot molecules with the ionic and electrostatic effects caused by the aromatic and polar components with the base stock. This leads to a premature agglomeration of the soot particles, rapid viscosity growth and an abrasive material that can produce increased levels of wear. This is illustrated in Figure 18.15 [37,39]. The effect of base stock composition on soot-induced viscosity increase can be observed in Figure 18.16 for a Mack T-8 screener test [37,39]. Results show that as the composition of the base stock increases to higher levels of saturated vs. aromatic levels, there is a significant improvement in soot-induced viscosity control. Although minimal difference is observed between API Group II and API Group III based formulations, the results suggest that the highly saturated blends can perform in a similar manner to synthetic products that are formulated with PAO. General Motors (GM) recently upgraded its ATF standard to a new DEXRON® -H performance level [40].

165 mm Agglomerates

Agglomerates

201 nm

Agglomerates

FIGURE 18.15 Electron microscope picture of agglomerated and unagglomerated soot particles

Copyright 2006 by Taylor & Francis Group, LLC

Rotational Viscosity (cP) at 10 s−1

100 Base Oil M Group I

90

Base Oil N Group II

80

Base Oil O Group III

70

Base Oil P Group IV

60

Base Oil Q Group V

50 40 30 20 10 0 0.0

1.0

2.0

3.0

4.0

5.0

6.0

Soot (%)

FIGURE 18.16 Base oil effects in Mack T-8 screener test

4.5

DEXRON-IIIH 450 Hour Oxidation Test

API Group I

TAN, mg KOH/gm

4.0

API Group II

H Test

G Test

3.5 3.0

API Group III

Limit 3.25 Max

2.5 2.0 1.5 1.0 0.5 0.0 0

10

100

150 200 250 Test Hours

300

350

400

450

FIGURE 18.17 Base oil effects in the GM oxidation test

Bomb Life (min), 150°C

1000 Group III - A PAO Group III - B

800 600 400 200 0

0 0

100 0

90 10

75 25

50 50

25 75

10 90

0 100

Ratio of Antioxidant CC : DD(0.5 wt% treat)

FIGURE 18.18 Comparison of API Group III chemically modified mineral oils and PAO in RBOT bench oxidation test

Copyright 2006 by Taylor & Francis Group, LLC

The change has been triggered by the fact that some products that were formulated with API Group I base stocks were considered to be inadequate for their respective applications. Because API Group II and higher base stocks provide an increased level of stability and oxidation performance, GM has adopted a similar approach toward the use of highly saturated base stocks, including chemically modified mineral oils with its premium ATF products. A representation of the effect of base stock quality on oxidation performance in the GM oxidation test for a constant additive package is observed in Figure 18.17 [34]. The new DEXRON® -IIIH specification requires a maintenance of the oxidation limits that were observed with the former DEXRON® -IIIG performance specification, however, at an extended test period that is 50% longer than the previous limit. The results shown in Figure 18.17 demonstrate that as a formulation is upgraded from API Group I to API Group II a dramatic improvement in oxidation performance is observed. At the same time, a further improvement in quality can be observed with an API Group III chemically modified mineral oil where excellent control of viscosity is observed when complimented with the correct additive system. It is therefore not uncommon for chemically modified mineral oils to be utilized in premium ATF fluids, particularly where multiple performance demands are required (e.g., MERCON® , MERCON-V® , DEXRON-IIIH® , Allison C-4, DaimlerChrysler ATF+ 4, etc.). As was observed with low-temperature properties, subtle differences in the compositional properties of chemically modified mineral oils can be highlighted in oxidation tests where the synergistic interaction of the base stock and antioxidant components are critical. This is particularly evident in the industrial oil area where the concentration of lubricant additives is limited and the performance contributions from the base stock enhanced. Figure 18.18 shows the response of two chemically modified mineral oils with a mixed antioxidant in the rotating bomb oxidation test (RBOT, ASTM D2272) that was run at 150◦ C [28]. RBOT testing was conducted in duplicate with a varying ratio of two commercial antioxidants, including a phosphite and hindered phenol. No other additives were included in the study and the combined antioxidant treat was fixed at 0.5 wt%. The RBOT performance of the chemically modified mineral oil A was observed to provide a consistent performance to a similar series of blends using a PAO base stock (i.e., API Group IV) across each of the antioxidant combinations. However, a significantly different result was observed with chemically modified base oil B. The differences were associated with the compositional differences between the two API Group III base stocks where API Group III-A had a higher concentration of isoparaffins and small-ring cycloparaffins with minimal levels

Copyright 2006 by Taylor & Francis Group, LLC

TABLE 18.13 Compositional Features of API Group III Chemically Modified Mineral Oils Used in Industrial Oil Studies Group III ID

A

B

Composition, HRMS (Mass%)a Paraffin, n- & isoMonocycloparaffin Dicycloparaffin Tricycloparaffin Polycycloparaffin Aromatics Paraffin + monocycloparaffin Polycycloparaffin + aromatic

67.7 22.7 6.8 2.8 0.0 0.0 90.8 0.0

47.3 28.3 10.8 3.8 3.4 1.1 75.6 3.5

Sources: From Henderson, H.E., Fefer, M., Legzdins, A., Michaluk, P., and Ruo, T., Compositional Features of New High Performance Specialty Base Fluids, Symposium: Worldwide Perspectives on the Manufacture, Characterization and Application of Lubricant Base Oils: IV, ACS National Meeting, New Orleans, Louisiana, August 1999: Henderson, H.E., Swinney, B., and Steckle, W.M., Delivering Synthetic performance with VHVI Specialty Base Fluids, J. Synth. Lubr., 18, 136–153, July 2001.

of polycycloparaffins and aromatics. This is shown in Table 18.13. Several other studies have been conducted to assess the oxidation performance of industrial oil products using both Universal Oxidation Test (UOT ASTM D4871) and RBOT (ASTM D2272) procedures [30,41]. In two analysis involving hydraulic oil formulations (Table 18.14), the API Group III chemically modified mineral oil gave superior performance to both the API Group I and API Group II formulations based on the same comparative additive systems. In the UOT study [30], the performance also approached that of a PAO based blend. This has also been observed in other industrial oil studies [42] where a direct comparison of API Group III and PAO was made in hydraulic (i.e., ashless and antiwear), compressor, circulating, industrial gear, and grease formulations (Figure 18.19). In each of the comparisons, the overall performance of the API Group III chemically modified mineral oil based formulations was equivalent to the PAO based reference.

18.2.6 Engine and Field Performance Following the NAD (National Advertising Division) ruling in 1999 on the use of API Group III chemically

TABLE 18.14 Oxidation Performance of API Group III Chemically Modified Mineral Oil and PAO Based ISO 32 Hydraulic Oil Formulations Study API Group UOT oxidation at 170◦ C Hours to 2 mg KOH RBOT oxidation, Min

A I

A II

A III

A IV

B I

B II

B III

100 —

115 —

145 —

148 —

— 105

— 400

— 620

Sources: From Henderson, H.E., Fefer, M., Legzdins, A., Michaluk, P., and Ruo, T., Compositional Features of New High Performance Specialty Base Fluids, Symposium: Worldwide Perspectives on the Manufacture, Characterization and Application of Lubricant Base Oils: IV, ACS National Meeting, New Orleans, Louisiana, August 1999 (Study A); McGeehan, J. and Eiden, K.L., Low Temperature Oil Pumpability in Emission Controlled Diesel Engines, SAE Paper 2000-01-1989, October 2000 (Study B).

RBOT Oxidation, Min at 150°C

1800 VHVI

1600

PAO

1400 1200 1000 800 600 400 200 0 HYD A

HYD B

CIRC OIL A

CIRC OIL B

COMP OIL B

COMP OIL C

COMP OIL D

FIGURE 18.19 Comparison of API Group III chemically modified mineral oils and PAO in industrial oil products

modified mineral oils in synthetic applications, the growth and utilization of these high VI base stocks in both automotive and industrial products has grown dramatically. Today, most synthetic and partial synthetic formulations in North America, particularly PCEO, at the ILSAC GF-3 (and pending ILSAC GF-4) performance levels are formulated with API Group III chemically modified mineral oils. In support of this, extensive engine testing has been conducted to fully qualify formulations using various API Group III suppliers and additive technology combinations. This has since been extended into the HDEO area where synthetic products (e.g., SAE 5W-40 and SAE 10W-30) based on API Group III chemically modified mineral oils have been fully approved and are actively marketed. There are now several studies where the performance of API Group III chemically modified mineral oils have been compared to PAOs in both bench engine and field-test trials.

Copyright 2006 by Taylor & Francis Group, LLC

One series of studies focused on the development of a full synthetic PCEO based on a blend of an API Group III chemically modified mineral oil and a complimentary amount of a synthetic ester. This was fully tested at the API GF2/API SJ and ILSAC GF-3/API SL performance levels and was achieved through a direct substitution of the PAO component in the original formulation with the API Group III fluid [43,44]. Table 18.15 compares the results of Sequence IIIE engine tests under single length and double length conditions for a commercial PCEO formulation where the PAO component was directly replaced with an API Group III chemically modified mineral oil [43]. Statistical analysis of the comparative engine results by an outside laboratory for the single length 64-h test showed no differences in terms of oil thickening control and engine cleanliness.

TABLE 18.15 Statistical T-Test Analysisa of Single and Double Length Sequence IIIE Bench Engine Tests for Synthetic Commercial PCMO formulated with API Group III Chemically Modified Mineral Oil and PAOb Standard deviation 5.03 — 0.17c 0.16 0.54 0.32c 0.61c 0.38

Test parameter

Statistical significance at 64 h

Statistical significance at 128 h

Hours to 375% Vis. Inc. Vis. Inc. at 64 Avg. sludge Piston skirt varnish Oil ring land deposits Avg. (C + L) wear Max. (C + L) wear Oil consumption

Not significant N/A Not significant Not significant Significantly differentd Significantly differentd Significantly differentd Not significant

N/A N/A N/A N/A N/A Most likely not significant Most likely not significant Most likely significantd

a The Standard used for statistical T-test for each parameter came from either TMC LTMS or

calculated from TMC Sequence IIIE reference database. b Commercial formulation where API Group III chemically modified formulation used the

exact same additives and teat rate as the reference PAO based formulation (i.e., only change is substitution of API Group III for PAO. c Improved performance observed statistically for API Group III based formulation. d The standard deviation for these parameters is in transformed units. Source: Henderson, H.E. and Braid, R.A., Advanced Performance Products from VHVI Specialty Base Fluids, Presented at ICIS-LOR World Base Oil Conference, London UK, February 1999.

Max.Spec. (1 × IIIE) 375%

15 10 5 0

10.0

1x 2x Group III

1x 2x Group IV

Min. Spec. (1 × IIIE) - 9.2

9.8 9.6 9.4 9.2 9.0

Group III

Group IV

C+L Wear, µm

20

75 Max. Spec. (1 × IIIE) - 30.5 Avg./64 Max. 60 45 30 15 0

Average Engine Varnish

Average Engine Sludge

% Viscosity Increase

(SAE 5W-30, API SJ/EC/ILSAC GF-2 Quality)

10.0

Avg. Max. Group III

Avg. Max. Group IV

Min. Spec. (1 × IIIE) - 8.9

9.5 9.0 8.5 8.0 Group III

Group IV

FIGURE 18.20 Comparison of double length Sequence IIIE performance between commercial PAO and candidate API Group III chemically modified mineral oil based formulation

The same two SAE 5W-30 formulations were subsequently evaluated in a chassis dynamometer program utilizing a programmed driving cycle over a 50,000-mile simulation. A final evaluation involved taxi fleet testing over a 100,000-mile period where oil drain intervals

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were extended to 12,500 miles. The site was considered to be severe as it was conducted over hilly terrain and stop and go conditions in San Francisco, California. Results [44] showed that the formulation based on the API Group III chemically modified mineral oil provided

150 Group III Based (SAE 5W-40)

Iron (by IPC), ppm

Group IV/V Based (SAE 5W-40) 100 90

Condemning Limit

50

0

0

100

200

300

400

500 600 Hours on Oil

700

800

900

1000

FIGURE 18.21 Comparison of iron wear vs. test hours for SAE 5W-40 synthetic HDMO based on PAO/ester and API Group III chemically modified mineral oil — 1994/1996 Volvo VDE-12 in dump truck haulage

equivalent performance to the reference PAO formulation in terms of oil thickening control, wear protection, and engine deposit control. An advantage was observed in terms of improved oil consumption. An extension to this study involved the development of a premium PCEO product where extended length Sequence IIIE performance consistent with a premium full synthetic commercial PCEO based on a mixture of PAO and ester components was conducted [43]. Results are provided in Figure 18.20 and show that overall, the two formulations provide outstanding performance over both single length and double length test conditions. Oil thickening control was consistent for the two formulations, while minor differences were observed for average engine sludge (AES) and average engine varnish (AEV). However, the overall performance of the two formulations was equally balanced and was considered, for these parameters, to be equivalent. The only measurable difference was in terms of wear protection where the API Group III chemically modified based formulation provided improved performance. Considerable work has been done in the HDEO area to promote the benefits of API Group III chemically modified mineral oils in both synthetic and part-synthetic applications [44,45]. Petro-Canada has been very active in this area and has since introduced a series of premium products based in part on field studies in both stationary and mobile service, the latter including highway and off-highway operations. Field trials usually involve the analysis of used oil samples to compare oil thickening and wear metal control. One approach [45] was to compare the quality of a low-viscosity SAE 5W-40 formulation based on an API Group III chemically modified mineral oil with a series of commercially

Copyright 2006 by Taylor & Francis Group, LLC

available SAE 15W-40 reference oils. Engine types that were incorporated into the study included: • Site #1: Steel & Lumber Haulage — On-Highway

Service • 1996 Detroit Diesel Series 60 engines with 140,000 lb loads • Mack E7-400 engines with 140,000 lb loads • Site #2: Miscellaneous Off-Highway Service

• Caterpillar 3412 engine driving a crusher unit • Caterpillar 3406 unit driving a generator set • Caterpillar 3406 unit driving a front-end loader In each of these test sites and engine models, no operational problems were experienced with the SAE 5W-40 HDEO based on the API Group III chemically modified mineral oil. Excellent control of KV was observed with the synthetic SAE 5W-40 in most instances, such that oil drain intervals were extended by as much as a factor of two in some instances. Figure 18.21 compares the performance of two synthetic SAE 5W-40 HDEO formulations in 1994 and 1996 model Volvo VDE-12 units hauling 85,000 and 110,000 lb loads, respectively, in dump truck off-highway service. The oils included a commercial synthetic fluid based on a PAO/ester blend and the same candidate formulation based on an API Group III chemically modified mineral oil as tested in the other field studies. Oil drains were scheduled when the used oil analysis properties approached the recommended condemning limits for the specified Volvo units. The synthetic SAE

18.2.7 Energy Efficiency The drive for energy efficiency over the past has been driven by the passenger car engine oil (PCEO) market and its efforts to comply with the EPA Corporate Average Fuel Economy requirements (CAFE). This has led to both automobile design changes as well as considerable changes to the engine oil chemistry and viscometrics, most notably a continued shift toward lower SAE grades. Since the highest level of friction occurs at engine start up before full film lubrication is formed, the ability to effectively lubricate metal surfaces during engine start up is critical. At the same time, new fuel economy standards include a measurement of the fuel economy after an aging period to ensure that fuel economy is retained [47]. This requires that the engine oil must retain its stability during the aging process as oxidation will negatively impact fuel economy performance. Considerable work has been conducted to evaluate the relationship between engine oil chemistry and fuel economy [47–49]. One study by Honda, Nippon Oil, and Idemitsu Kosan [48] demonstrated that a PCEO that was formulated with an API Group III chemically modified mineral oil provided a lower coefficient of friction vs. a reference oil that was formulated with an API Group I base stock blend. In a second study [49], the fuel economy credits of an SAE 5W-30 formulation based on API Group III chemically modified mineral oils provided an excellent level of fuel economy retention when compared to a similar formulation based on API Group II and III base stocks (Figure 18.22). For ILSAC GF-3 and more recently ILSAC GF-4, there has been a continued shift toward the use of lower SAE grade engine oils. The most popular “fuel economy” grade is SAE 5W-30 that in 2003 represented 25% of total PCEO

Copyright 2006 by Taylor & Francis Group, LLC

1.8 Fuel Economy Improvement, %

5W-40 formulation based on the API Group III chemically modified mineral oil gave excellent oil viscosity control and was unaffected by the increased soot loading levels. Iron wear was significantly better than that observed with the reference PAO/ester blend and in one comparison (i.e., Unit 342, Figure 18.21) was still acceptable after 900 h of service, whereas, the reference blend reached the 90 ppm condemning limit at just over 600 h of operation [45]. Similar results have been observed in Mack T-8 and Caterpillar equipment when an API CG-4/SH HDEO that was formulated with an API chemically modified mineral oil as an SAE 10W-40 grade was compared to a similar SAE 15W-40 formulation based on conventional API Group I base stocks [46]. Both formulations incorporated the same DI and olefin co-polymer (OCP VM) components and the ability to drop an SAE grade by shifting from an API Group I to API Group III base stock blend was again observed. Overall performance of the synthetic formulation was superior to the conventional blend in terms of viscosity increase, filter plugging, and wear metal control.

1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 API Group III

API Group II/III

FIGURE 18.22 Comparison of sequence VIB fuel economy improvement for ILSAC GF-3 SAE 5W-30 formulations based on API Group III and API Group II/III formulations

sales in the United States that was estimated at 800 MGal [50]. The other key grade is SAE 5W-20 that represented only 3% of US PCEO sales in 2003 but is a viscosity grade that is being actively promoted by Ford for its fuel economy benefits. These SAE grades demand the use of chemically modified mineral oils, either an API Group II+ base stock with a VI range of 115 to 119, or a blend of an API Group III chemically modified mineral oil in combination with either an API Group I or II base stock.

18.2.8 Environmental Friendliness The emergence of chemically modified mineral oils has had a positive impact on environmental properties and related applications. The improved volatility and oxidation stability provides an opportunity for extended drains, thus reducing the frequency of oil changes and its associated disposal. At the same time, continued improvements in fuel economy and the reduction in emissions have also provided key environmental credits. From a compositional standpoint, the conversion of aromatics and multi-ring cycloparaffins into isoparaffins and small-ring cycloparaffins is environmentally favored. Aromatics and polars are materials that under high temperature conditions will form undesirable polynuclear aromatics, that is, PNAs. API Group III chemically modified mineral oils are essentially free of aromatic and polar components and are frequently produced to technical white oil quality. This is an interesting observation and had led to the evaluation of these stocks in sensitive food-grade applications. The biodegradability performance of chemically modified mineral oils have been compared with PAO and observed to provide equivalent performance for the same Kinematic Viscosity (KV) (Figure 18.23) [42]. One of the new developments with chemically modified mineral oils is its application into the metalworking industry [51]. An analysis of the influence of base stock properties on the formation of mist during drilling and milling tests on aluminum and steel plates has shown that

Biodegradability (CEC-L-33-T-82/A-93)

API Group III API Group IV

80 70 60 50 40 30 20 10 0

2.0

8.0

4.0 Viscosity, cSt at100°C

FIGURE 18.23 Comparison of biodegradability properties of API Group III chemically modified mineral oils and PAO

TABLE 18.16 Applications for Chemically Modified Mineral Oils Automotive oils Passenger car engine oils Heavy-duty engine oils Automotive gear oils Automatic transmission fluids Tractor fluids Shock absorber fluids Power steering fluids 2-Stroke oils Racing oils

Industrial oils Hydraulic fluids Turbine oils Compressor oils Vacuum pump oils Rolling oils

Specialties Heat transfer fluids Quenching oils Cutting oils Process oils Spray oils White oils Textile oils Transformer oils

Source: Park, Y.M. VHVI Base Oils, Profitability, Supply and Demand, NPRA Paper LW-98-127, November 1998, Kramer, D.C. Sztenderowicz, M.L. Lok, B.K. Cheng, M. and Rechsteiner, C.E. The Synthetic Nature of Group III Base Oils, NPRA Paper LW-99-124, November 1999.

mist generation is the lowest when a straight metalworking fluid is formulated with an API Group III chemically modified mineral oil. This is directly related to the lower volatility of the API Group III fluid, based on its higher VI properties and isoparaffinic compositional properties. During an aluminum milling study, the API Group III based fluid reduced misting by 81% relative to a reference formulation based on naphthenic base stock. During the milling of steel, the benefit was significant albeit lower at 36%. This provides an opportunity where the drive to improvements in the work environment can lead to a growth in API Group III chemically modified mineral oils in place of equipment modifications when straight oil metalworking fluids are used.

18.3 APPLICATIONS FOR API GROUP III CHEMICALLY MODIFIED MINERAL OILS Although the utilization of API Group III chemically modified mineral oils was originally focused in the PCEO area, its unique physical, chemical, and compositional features

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has provided an opportunity to formulators to expand its application into other product areas. Table 18.16 provides a summary of some of the potential applications of chemically modified mineral oils [52]. The application will depend on the KV properties of the individual base stock as slates will range from a 2 to a 8 cSt fluid at 100◦ C. Automotive applications will continue to drive the higher viscosity grades, while the lower viscosity grades will receive considerable interest in ATF and specialty applications.

REFERENCES 1. Purdy, G.A., Petroleum Prehistoric to Petrochemicals, Copp Clark Publishing, Canada, pp. 223–248, 1957. 2. American Petroleum Institute, Industry Services Department, Engine Oil Licensing and Certification System, API Publication 1509, 15th ed. April 2002. 3. The ATIEL Code of Practice for Developing Engine Oils Meeting the Requirements of the ACEA Oil Sequences, Issue Number 9, June 2003. 4. ILSAC GF-4, Alliance of Automotive Manufacturers, EPA/Stakeholders Meeting, Detroit MI, January 27, 2004.

5. Daimler Chrysler Corporation Material Standard No. MS9602, Change E, August 2, 2002. 6. Ford Motor Company, MERCON® -V Automatic Transmission Fluid Specification Trademarked for Service, January 1, 1999. 7. Linden, J., Changes in Automatic Transmission Fluids, ICISLOR/ILMA, New York, December 2003. 8. Irvine, D.J., Performance Advantages of Turbine Oils Using Group II and Group III Basestocks, STLE Annual Meeting, May 2000, Nashville, TN. 9. Henderson, H.E., Steckle, W.M., Mack, P.D., and Simmons, R., Advanced Performance Products for VHVI Specialty Base Fluids, National Petroleum Refiners Association, Paper LW-98-133, Fall Meeting, November 1998. 10. Wilson, M.W., Eiden, K.L., Mueller, T.A., Case, S.D., and Kraft, G.W., Commercialization of Isodewaxing — A New Technology for Dewaxing to Manufacture High Quality Lube Base Stocks, National Petroleum Refiners Association, Paper FL-94-112, Fall Meeting, November 1994. 11. Mayer, J., Brossard, D., Krishna, K., and Srinivasan, B., The All-Hydroprocessing Route Group II and Group III Base Oils: One Company’s Experience, National Petroleum Refiners Association, Paper AM-04-68, Spring Meeting, March 2004. 12. Zakarian, J.A., Robson, R.J., and Farrell, T.R., AllHydroprocessing Route for High-V.I. Lubes, Energy Progress, 7, 1987, p. 59. 13. Habib, M.M., Bezman, R.D., Dahlberg, A.J., and Mayer, J.F., New Generation of Isocracking® Catalysts, National Petroleum Refiners Association, Paper AM-00-32, Spring Meeting, March 2000. 14. National Petrochemical & Refiners Association, Lubricating Oil and Wax Capacities of Refiners and Re-Refiners in the Western Hemisphere, Annual Reports for 1990 to 2002, Washington, D.C., January 1990 to 2002. 15. National Petrochemical & Refiners Association, Lubricating Oil and Wax Capacities of Refiners and Re-Refiners in the Western Hemisphere, 2004 Annual Report, Washington, D.C., January 2005. 16. Process Options for Producing Higher Quality Basestocks, National Petroleum Refiners Association, Paper LW-01-128, Fall Meeting, November 2001. 17. Arnold, V.E. and Chum, K., Processing Strategies for the Production of Group II Base Oils from a Conventional Lube Plant, National Petroleum Refiners Association, Paper LW99-122, Fall Meeting, November 1999. 18. Cashmore, K., Moyle, M., and Sullivan, P.J., Hydrotreated Lube Oil Base Stocks, SAE Paper 821235, October 1982. 19. Wedlock, D.J., Changes in the Quality of Base Oils, Presented at the 8th Annual Fuels & Lubes Asia Conference and Exhibition, Singapore, January 29–February 1, 2002. 20. Wedlock, D.J., Gas to Liquids — The Next Generation of Base Oils, Presented at the 10th Annual Fuels & Lubes Asia Conference and Exhibition, Shanghai, March 2–5, 2004. 21. Releford, T.T. and Ball, K.J., Exxon’s New Synthetic Basestocks — EXXSYN, National Petroleum Refiners Association, Paper FL-93-117. Fall Meeting, November 1993. 22. Cox, X.B., Designing Basestocks to Meet the Quality Challenge, Presented at ICIS-LOR World Base Oil Conference, London UK, February 2003.

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23. Gallagher, E., Cody, I.A., and Claxton, A.A., Development and Commercialization of Raffinate Hydroconversion — A New Technology to Manufacture High Performance Basestocks for Crankcase and Other Applications, National Petroleum Refiners Association, Paper LW-99-121, Fall Meeting, November 1999. 24. Henderson, H.E., Mack, P.D., Steckle, W.M., and Swinney, B., Higher Quality Base Oils for Tomorrow’s Engine Oil Performance Categories, SAE Paper 98252, October 1998. 25. Henderson, H.E., Fefer, M., Legzdins, A., Michaluk, P., and Ruo, T., Compositional Features of New High Performance Specialty Base Fluids, Symposium: Worldwide Perspectives on the Manufacture, Characterization and Application of Lubricant Base Oils: IV, ACS National Meeting, New Orleans, Louisiana, August 1999. 26. Moon, W.S., Cho, Y.R., Yoon, C.B., and Park, Y.M., VHVI Base Oils from Fuels Hydrocracker Bottoms, China Lube Oil Conference ‘98, Beijing, China, June 1998. 27. Gatto, V.J., Grina, M.A., and Ryan, H.T., The Influence of Chemical Structure on the Physical and Performance Properties of Hydrocracked Base Stocks and Polyalphaolefins, Proc. 12th Int. Colloq. Tribol., Technische Akademie Esslingen, Germany, January 2000. 28. Henderson, H.E., Swinney, B., and Steckle, W.M., Delivering Synthetic performance with VHVI Specialty Base Fluids, J. Synth. Lubr., 18, 136–153, 2001. 29. Henderson, H.E., American Petroleum Institute, Base Oil Interchange and Viscosity Grade Readacross Task Force, Report from Base Oil Characterization Work Group, July 11, 2002. 30. Kramer, D.C., Sztenderowicz, Lok, B.K., Cheng, M., Rechsteiner, C.E., and Wilson, D.M., The Synthetic Nature of Group III Base Oils, NPRA Paper LW-99-124, November 1999. 31. Freerks, R., and Henderson, H.E., Fischer-Tropsch Base Stocks — Performance Beyond Current Synthetics, ICISLOR World Base Oil Conference, London UK, February 2002. 32. American Petroleum Institute, Properties of Hydrocarbons of High Molecular Weight, API research Project 42, pp. 1940–1966. 33. Henderson, H.E. and Swinney, B., High Quality Base Oils for Next Generation Automatic Transmission Fluids, SAE Paper 982666, October 1998. 34. Henderson, H.E., Olavesen, C., Alexander, A.G., and Ozubko, R.S., A New High Quality 100 Neutral Base Stock for Automotive and Industrial Oil Products, Lubr. Eng., 48, 777–781, 1992. 35. McGeehan, J. and Eiden, K.L., Low Temperature Oil Pumpability in Emission Controlled Diesel Engines, SAE Paper 2000-01-1989, October 2000. 36. Kelly, K.J. and Kennedy, S., Spagnoli, J.E., Performance of an Advanced Synthetic Diesel Engine Oil, SAE Paper 2000-01-1993, October 2000. 37. Kornbrekke, R.E., Patrzyk-Semanik, P., Kirchner-Jean, T., Raguz, M.G., and Bardasz, E.A., Understanding Soot Mediated Oil Thickening Part 6: Base Oil Effects, SAE Paper 982665, October 1998.

38. Cherrillo, R.A. and Huang, A., The Increasing Significance of base Oils in the Evolution of Heavy-Duty Diesel Engine Oils, NPRA Paper LW-99-130, November 1999. 39. Henderson, H.E. and Moon, W.S., API Group III Base Stocks: A Global Perspective, Presented at the 3rd ICIS-LOR ILMA Conference, New York, December 2003. 40. General Motors DEXRON® -III Specification Standard 41. Lok, B.K., Sztenderowicz, M.L., and Kleiser, W.M., Global Base Oil Product Trends, ICIS-LOR World base Oil Conference, London UK, February 2000. 42. Henderson, H.E. and Legzdins, A., Evaluation of Severely Hydro-treated and Isodewaxed Specialty Base Fluids in Industrial Oil Applications, 54th STLE Annual Meeting, Las Vegas, Nevada, May 1999. 43. Henderson, H.E. and Braid, R.A., Advanced Performance Products from VHVI Specialty Base Fluids, Presented at ICIS-LOR World Base Oil Conference, London UK, February 1999. 44. Henderson, H.E., Steckle, W.M., and Swinney, B., Formulation Capabilities with API Group III Synthetic Fluids, SAE Paper 2000-01-2920, October 2000. 45. Henderson, H.E., Quality Base Fluids to Deliver Next Generation Heavy Duty Engine Oil Performance, NPRA Paper LW-00-135, November 2000.

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46. Moon, W.S., Lee, J.H., and Kahn, S.K., Performance of High VI Basestock Produced from a Fuel Hydrocracker Unconverted Oil Stream, Proceedings of the International Tribology Conference, Yokohama, pp. 679–684, 1995. 47. Boffa, A.B. and Hirano, S., Oil Impacts on Sequence VIB Fuel Economy, SAE Paper 2001-01-1903, October 2001. 48. Nagashima, T., Saka, T., Tanaka, H., Satoh, Yaguchi, A., and Tamoto, Y., “Research on Low-Friction Properties of High Viscosity Index Petroleum Base Stock and Development of Upgraded Engine Oil,” SAE Paper 951036, February 27– March 2, 1995. 49. Ryoo, J.K. and Moon, W.S., The Effects of Different Base Oil on the Performance of GF-3 Engine Oil, Presented at the 8th Annual Fuels & Lubes Asia Conference and Exhibition, Singapore, February 2002. 50. 2003 Report on U.S. Lubricating Oil & Wax Sales, National Petrochemical & Refiners Association, November 2004. 51. Dasch, J.M., Ang., C.C., Wei, L., and Rossrucker, T., The Influence of the Base Oil on Misting in Metal Removal Fluids, 55th STLE Annual Meeting, Nashville, Tennessee, May 2000. 52. Moon, W.S., Cho, Y.R. and Chun, J.S., “Application of High Quality (Group II, III) Base Oils to Specialty Lubricants”, Presented at the 6th Annual Fuels and Lubes Asia Conference and Exhibition, Singapore, January 2000.

19

Gas to Liquids H. Ernest Henderson CONTENTS 19.1 Introduction 19.2 GTL Process and Historical Development 19.3 Performance Features 19.3.1 Composition 19.3.2 Volatility 19.3.3 Low Temperature Properties 19.3.4 Benchmarking with API Group III 19.3.5 Oxidation Performance 19.3.6 Engine Performance References

19.1 INTRODUCTION

19.2 GTL PROCESS AND HISTORICAL DEVELOPMENT

The use of wax and waxy feedstocks as a high VI feed source has grown in interest over the past several decades as refiners continue their search to produce lubricant base stocks with high Viscosity Index (VI) and associated properties. Shell has been a pioneer in this area with their use of slack wax, typically produced from a solvent dewaxing operation as a feed for their slate of Very High VI base stocks, known as Shell XHVI® at the Petit-Couronne Refinery in France [1,2]. ExxonMobil have also used slack wax as a source for high VI base stocks, initially with Exxsyn™ that was commercialized and produced for a short period of time at Fawley UK in the early 1990s [3], and more recently Visom™ that was reintroduced at Fawley in late 2003 [4]. During this period of development, wax produced from Fischer–Tropsch (F–T) synthesis has reemerged as a future source for high-performance base stock production. F–T is a key intermediate step in the overall process referred to as Gas to Liquids, or GTL technology. GTL is recognized as a technology of the future as it provides the opportunity to convert “stranded” natural gas or other feeds into high-quality fuel, chemical, and lube products [5–8]. Shell, again have been the leader in the commercial use of GTL to produce lubricant base stocks as it has used F–T wax produced from its refinery in Bintulu, Malaysia to manufacture its XHVI® base stocks at Yokkaichi in Japan and Petit-Courrone in France. The Yokkaichi manufacturing facility has been based on 100% GTL wax since 1994 [2].

Gas to Liquids technology represents a three-step process that has been researched, in one form or another, for nearly a century. A schematic of GTL is shown in Figure 19.1 [8] and represents the following steps [9], that is:

Copyright 2006 by Taylor & Francis Group, LLC

• Step #1 — The production of hydrogen and carbon

monoxide, known as syngas. This can be produced from a number of feedstocks of which coal and natural gas are the most commonly used. However, syngas can also be produced from petroleum coke, visbreaker residue, deasphalting pitch biomass, or other wastes and refuse. The technology that is used in the syngas step is well advanced, based on years of engineering design and operating experience. It is based on a conversion process using steam, oxygen, or in selected cases air in the presence of a catalyst. Equation (19.1) demonstrates the chemical process. CHn + 21 O2 → CO + 21 nH2

(19.1)

• Step #2 — Creation of long chain paraffinic wax from

syngas. This is referred to as the F–T step and is described with Equations (19.2)–(19.4). The reaction can occur in either a slurry or fixed bed system, again with a suitable catalyst, with the products of reaction including paraffins (i.e., Equation [19.2]), olefins (i.e., Equation 19.3), and alcohols (i.e., Equation [19.4]). The olefin and alcohol components can either be separated at

Hydrogen

Wax Natural gas Heat recovery

Oxygen Steam

Clear liquids

Syngas 1. Syngas generation

2. Hydrocarbon synthesis • Syngas is converted into a mixture of liquids and wax.

• Natural gas, or methane, is converted into a mixture of hydrogen and carbon monoxide.This mixture is called synthesis gas,or syngas.

3. Product upgrading • Process tailored to meet desired fuel, lube, and specialty product objectives.

FIGURE 19.1 Schematic overview of the GTL process

0.045 0.90 0.94

0.04

0.92 0.96

0.035 0.03 0.025 0.02 0.015 0.01 0.005 0 1

11

21

31

41

51

60

71

81

91

FIGURE 19.2 Carbon number profile for F–T process in lubricants range as defined by Anderson–Shultz–Flory equation

this time and diverted to a chemicals upgrading process or hydrogenated and processed further into fuels and/or lubes. (2n + 1)H2 + nCO → Cn H2n+2 + nH2 O

(19.2)

2nH2 + nCO → Cn H2n + nH2 O

(19.3)

2nH2 + nCO → Cn H2n+1 OH + (n − 1)H2 O (19.4) • Step #3 — Upgrading of the F–T wax into isoparaf-

fins, using conventional upgrading technology, namely hydroprocessing and hydrodewaxing. This is discussed in Chapter 18 under chemically modified mineral oils and shown in Equation (19.5). –(CH2 –)n – → Fuels, lubricants, etc.

(19.5)

An overview of GTL processing is shown in Figure 19.1 [8].

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The efficiency of the F–T process is defined by the Anderson–Schulz–Flory equation. The resultant profile of wax products for a lubricants F–T operation is shown in Figure 19.2 [10]. In a lubricants mode, a high alpha number is required, typically in excess of 0.90. For a fuels mode, alpha numbers would typically range from 0.75 to 0.90. With the Shell Middle Distillate Synthesis II process (i.e., SMDS), carbon numbers up to 200 in length can be produced, providing the opportunity to produce chemically modified mineral oils of both low and high viscosity. The ability to produce higher viscosity base stocks is a breakthrough as the production of chemically modified mineral oils from hydroprocessing of hydrocracker bottoms has an upper viscosity limit of 7 to 8 cSt at 100◦ C (i.e., approximately 250 SUS at 100◦ F). However, with advanced processing of F–T waxes, kinematic viscosities

TABLE 19.1 Properties of High Viscosity Chemically Modified Mineral Oils Produced from F–T Wax

TABLE 19.2 Commercialization of F–T Technology During 19th Century

KV at 40◦ C, cSt

Country

101.7 77.2 94.5 110.5 104.0 111.0 119.2

KV at 100◦ C, cSt

SUS at 100◦ F, cSt

Viscosity index

15.95 11.95 13.77 14.99 14.25 15.11 14.86

518.4 394.5 484.3 568.5 534.9 570.9 616.5

168 150 148 141 140 142 128

Pour point, ◦C −42 −15 −15 −27 −27 −30 −30

Source: From Wedlock, D.J., Gas to Liquid — The Next Generation of Base Oils, Presented at the 10th Annual Fuels & Lubes Asia Conference and Exhibition, Shanghai, March 2–5, 2004.

reaching 16 cSt at 100◦ C can be achieved (Table 19.1), providing an excellent opportunity to blend heavy SAE 40 engine oil products and/or ISO 460 industrial oil grades [2]. Initial research focused on the production of syngas through various processes and catalyst systems. Having the capability to process the key starting materials, the F–T process itself was developed during the 1920s by Franz Fischer and Hans Tropsch who successfully converted syngas in the laboratory into a series of oxygenated and liquid hydrocarbons. The F–T process involved the use of cobalt and nickel catalysts at atmospheric pressures and assumed that hydrocarbons were produced at low pressures, while oxygenates were produced at high pressures [11]. This was subsequently commercialized during the 1930s and played a key role during World War II when 9 plants in Germany produced some 12,000 B/D of F–T based products to support the German economy and military efforts. During the 20th century, several plants have been commercialized using the F–T process. This is summarized in Table 19.2. Today, there are three companies who are actively involved commercially in the use of F–T technology for the production of hydrocarbons. Schumann SASOL have the most extensive experience as they have successfully converted the vast coal reserves of South Africa into a series of commercial products including, but not limited to, diesel and jet fuels, solvents, and wax. Today, SASOL uses three plants to produce 175 KBD of F–T based products. MossGas, now PetroSA, is also using SASOL technology to produce a series of fuel and specialty products in South Africa. Production is estimated at 30 KBD and they have elected to use natural gas as a feedstock instead of coal. Shell began research into F–T technology during the early 1970s following the oil crisis in the Middle East. This has led to the commercialization of a 12.5 KBD plant in Bintulu, Malaysia in 1993–94 that uses natural gas as a feed

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Germany France Japan China United States South Africa Malaysia

Number of plants 9 1 4 1 1 3a 1a

Time period 1936–40 1937 1938–42 1942 1949 1954–Present 1994

a Plants are still in commercial operation.

and F–T technology via the Shell Middle Distillate Synthesis (SMDS) process to produce a slate of hydrocarbons, including fuels, solvents, and waxes. Approximately 10% of the overall production (i.e., 1250 BPD) is then shipped to upgrading plants in Japan and/or France to produce a series of high VI base stocks. Today, Shell is the only company that is producing chemically modified mineral oils from F–T wax. A summary of the current GTL plants at both the commercial and pilot plant scale is provided in Table 19.3 [12]. ExxonMobil have also been extensively involved with GTL research through its Advanced Gas Conversion for the 21st Century project, that is, AGC-21 [8,13–15]. The technology is well advanced and can also be adapted to produce API Group III chemically modified mineral oils. AGC-21 utilizes a cobalt based catalyst and slurry reactor system and has been successfully demonstrated in both small-scale pilot plant and larger-scale development units ranging in size from 2 to 200 B/D. Scale up capability has been confirmed and the process is protected by over 450 U.S. patents and 2300+ patents worldwide. In January 2004, Gas-to-Liquid News reported some 50 GTL projects that were under construction, development, or feasibility studies [12]. This is shown in Figure 19.3 and represents no less than 1.7 billion B/D of GTL potential to produce fuel, chemical, lube, and/or specialty products. The most active area is the Middle East and in particular Qatar where to date there have been 5 projects announced representing a total production of 554 million B/D of GTL products. These include SASOL/Qatar Petroleum (34 KBD), Shell (140 KBD), Conoco/Qatar Petroleum (160 KBD), ExxonMobil (100 KBD), and Marathon/Qatar Petroleum (120 KBD). The technology is also expanding as there are projects under study to mount a small commercial GTL plant onto a floating platform to access natural gas offshore. Presently there are three projects under study in

TABLE 19.3 Summary of Existing GTL Plants and GTL Pilot Plant Facilities — January 2004 Owner/Developer

Location

Product

Capacity, B/D

Feed

Process

Start date

Existing plants PetroSA SASOL I-III Shell Bintulu

S. Africa S. Africa Malaysia

Fuel/Specialty Fuel/Specialty Specialty

30,000 175,000 12,500

Nat Gas Coal Nat Gas

SASOL SASOL Shell SMDS

1992 1955–82 1993

Pilot/Demonstration plants BP JNOC Rentech Synergy technologies Synfuels Texas A&M Syntroleum Conoco JNOC Nippon Oil Corp. PetroSA/Statoil Syntroleum/MAP

Alaska Japan Colorado Calgary, AB Texas Oklahoma Oklahoma Japan Japan S. Africa Oklahoma

Syncrude Fuels Syncrude Syncrude Fuels Fuel/Specialty Fuels Fuels Diesel Fuel/Specialty Fuels

300 10 <1 4 12 2 400 7 N/A 1000 ∼90

Nat Gas Nat Gas Sim Syngas Nat Gas Nat Gas Nat Gas Nat Gas Nat Gas Nat Gas Nat Gas Nat Gas

BP/Kvaemer JNOC/JAPEX Rentech Synergy Tech Synfuels Int’l Syntroleum Conoco N/A N/A Statoil Syntroleum

2002 2002 1983 2000 2001 1990 2002 2002 2003 2003 2003

Source: Gas-to-Liquids News, January 2004, Published by Hart Downstream Energy Services, A division of chemical week, Publishing, LLC, Potomac, MD.

TABLE 19.4 Properties from a Slate of Chemically Modified Mineral Oils Produced from F–T Wax Total capacity 1.7 billion B/D

Existing plants (9) Under development (8)

Under construction (7) Under discussion (35)

FIGURE 19.3 Summary of GTL plants — commercial and proposed — January 2004. Source: Gas-to-Liquids News, January 2004, Published by Hart Downstream Energy Services, A division of chemical week, Publishing, LLC, Potomac, MD.

this area, including Mogal Marine, PetroSA/Transworld Exploration, and Syntroleum/PGS. The first two projects would focus on the production of methanol, whereas the Syntroleum/PGS project would focus on the production of fuels and potentially specialty products. A summary of the GTL projects that are presently under construction, development, and/or discussion/feasibility is provided in Appendix 19.1 [12]. A summary of the properties of a slate of chemically modified mineral oils produced by hydroprocessing F–T wax produced from a fixed bed reactor is provided in Table 19.4 [9].

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Base oil properties Density at 15◦ C, kg/L KV at 40◦ C, cSt KV at 100◦ C, cSt Viscosity index Pour point, ◦ C CCS at −30◦ C, cP CCS at −25◦ C, cP Flash point, ◦ C Noack volatility, wt% Composition, % iso-paraffins

GTL-2

GTL-3

GTL-5

GTL-7

0.795 5.0 1.7 — −59 — — 159 — 100

0.805 10.4 2.84 122 −45 — — 207 28.8 100

0.818 20.1 4.5 144 −21 1320 816 238 7.8 100

0.820 38.4 7.0 147 −21 — 2661 260 2.0 100

Source: From Henderson, H.E., Fischer–Tropsch Gas to Liquids Fluids, Performance Beyond Current Synthetics, Presented at the ICIS-LOR World Base Oil Conference, London, UK, February 2002.

19.3 PERFORMANCE FEATURES 19.3.1 Composition Lubricant base stocks are composed of thousands of chemical structures, including paraffins and iso-paraffins, cyclo-paraffins or naphthenes, aromatics, and aromatics where sulfur, nitrogen, and in limited cases oxygen can appear. The quality of the original feedstock and the resultant processing are key ingredients in determining

the overall properties of a base stock and in particular its composition. The highest-quality component in a lubricant base stock is normally associated with iso-paraffins. Previous studies [16,17] have discussed the composition of lubricant base stocks and the shift to higher concentrations of iso-paraffins with an associated increase in process severity. The highest concentration of iso-paraffins has been observed in API Group III chemically modified mineral oils produced from slack wax. A further increase in iso-paraffin content, however, can be observed when a higher-quality F–T wax is used as a feed [18]. Mass spectral analysis has shown that the concentration of iso-paraffins can reach 100%, consistent with poly-alphaolefins (PAOs). However this is dependent on the analytical procedure that is used and the relative peak assignments from the mass spectrometer. In a separate study, the composition of chemically modified mineral oils has been studied based on hydrocracker bottoms, slack wax, and F–T wax as feedstocks [1]. The procedure was based on an initial separation of the saturates fraction from the aromatics fraction using preparative chromatography followed by field ionization mass spectrometry (FIMS) of the saturates fraction. This allows identification of chemical structures from molecular ions produced from FIMS and not from molecular fragments. For hydroprocessed mineral oils, the concentration of saturated vs. aromatic components from the initial chromatography is very high, typically in excess of 95%. Hence, in many cases, chemical analysis is determined on only the saturates fraction. Figure 19.4 provides a comparison of the normal and iso-paraffin contents from the saturates fraction of three API Group III [1] chemically modified mineral oils produced from different feedstocks. Since API Group III chemically modified mineral oils have been determined to be synthetic in many regions

100 Mass % N & iso-paraffins in saturates fraction

90 80 70 60 50

of the world, it is not surprising that F–T based mineral oils are also synthetic in nature and provide the closest compositional match to PAOs. This will be dependent on the type of F–T process (i.e., fixed bed vs. slurry) and the resultant efficiency of the F–T reaction as determined from its Anderson–Shultz–Flory alpha number. Despite these factors, GTL-produced mineral oils will be positioned in the upper portion of the API Group III category and most likely marketed as API Group III+ .

19.3.2 Volatility The volatility of a base stock is directly linked to its compositional properties, with iso-paraffins having the highest mid boiling point (MBP) for a given kinematic viscosity [9,16]. It is therefore not surprising that chemically modified mineral oils that have been produced from F–T wax have the highest boiling compositional components for a given carbon number, and accordingly, excellent volatility characteristics. This is important for formulators of passenger car engine oils (PCEO) as the trend toward improved volatility characteristics for emission control is complicated by a similar shift to lower SAE viscosity grades for improved fuel economy properties. This requires low viscosity base stocks and to achieve the required volatility characteristics, a high VI and MBP, the latter as defined by the 50% point in a gas chromatography distillation (i.e., GCD, measured by ASTM D2887). This is a key element for both North American and European engine oils where the new Sequence IIIG (North America) and the Volkswagen T-4 (Europe) engine tests are highly sensitive to the volatility characteristics of the base stock components. Previous studies have shown that with chemically modified mineral oils produced from F–T wax that low SAE 0W-20 and 0W-30 PCMO products can be routinely formulated without the need for synthetic components such as PAOs and/or esters [10,18,19]. With Noack volatilities continuing to move toward lower levels, the role of F–T produced chemically modified mineral oils will continue to increase in importance with future performance upgrades, both in passenger car and heavy-duty applications. Figure 19.5 compares the MBP for a series of base stocks of equivalent kinematic viscosity at 100◦ C, that is: • API Group I (or II) with a nominal VI of ∼95 • API Group III with a VI of 120 that represents the lowest

40 30

level for this category

20

• API Group III with a typical VI for a chemically modified

10

mineral oil produced from hydrocracker bottoms (HCB) of 128 • API Group III produced from F–T wax in a pilot plant fixed bed reactor

0 Vacuum gas oil derived

Slack wax derived

Fischer– Tropsch derived

FIGURE 19.4 Comparison of normal and iso-paraffinic content for several API Group III chemically modified mineral oils

Copyright 2006 by Taylor & Francis Group, LLC

The naturally high VI of the F–T chemically modified mineral oil leads to a significantly higher VI for the

same kinematic viscosity. This increases the concentration, or yield, of molecules in the correct viscosity range and allows one to fractionate at an efficient level to achieve the desired volatility in acceptable yields. This provides a significant advantage for F–T processing and is a reflection of the significant level of interest in GTL processing for both fuel and lube applications.

19.3.3 Low Temperature Properties The fluidity of a base stock is directly related to its VI, its pour point, and the compositional features of the residual wax that remains in the base stock following its dewaxing operation. Since GTL chemically modified mineral oils are highly iso-paraffinic, they exhibit an extremely high VI that should provide excellent viscometrics over a wide temperature range. The key with low temperature fluidity, however,

450 445 Mid boiling point, °C

440 435 430 425 420 415 410 405 400 API Group I/II, ~95 VI

API Group III, 120 VI

API Group III, 128 VI

API Group III, 147 VI

FIGURE 19.5 Comparison of MBP by GC distillation for a series of conventional and chemically modified mineral oils

is the response of the base stock at temperatures below its pour point where secondary effects from the residual wax become very important. In the past, the low temperature properties of API Group III chemically modified mineral oils that were produced from slack wax were not particularly good when compared with other API Group III fluids produced from hydrocracker bottoms. This was due to the solvent dewaxing step with wax isomerized base stocks that was incapable of removing the trace levels of n-paraffin residual waxes that are detrimental toward good low temperature fluidity. Solvent dewaxing is not a selective process and therefore is not an effective tool for the removal of these n-paraffin residual waxes. Hydrodewaxing, however, is an excellent method to either isomerize these waxes and/or convert them into shorter fuel type products. The effect of dewaxing on low temperature fluidity has been discussed in many studies, particularly with passenger car engine oils and automatic transmission fluids (ATF) [9,16,20,21]. Figure 19.6 compares the low temperature brookfield performance of a series of base stocks that were formulated with a constant treat rate of a commercial GM DEXRON® -III ATF performance package [9,18]. The key requirements for an automatic transmission is to combine a high kinematic viscosity for improved shear stability and volatility control with excellent low temperature fluidity. The API Group I and II based formulations have a fairly low kinematic viscosity and a high brookfield viscosity when compared with the API Group III chemically modified mineral oil. This is not surprising as the API Group III fluid was hydrodewaxed, thus removing the n-paraffin residual wax components that are detrimental toward low temperature fluidity. The level of low temperature improvement would be further highlighted if the kinematic viscosity for the API Group I and II based formulations were increased to that of the

*Blended with constant treat rate of a commercial DEXRON-III ATF performance package.

40,000 30,000

7.5 7.4 7.3

20,000

7.2

10,000

Blended KV at 100°C, cSt

600,000cP

Brookfield viscosity at – 40°C, cP

7.6

! Brookfield@–40°C ! KV @100°C Data range

50,000

7.1

0 GTL-5

PAO-4

API GPI

API GPII

API GPIII

API GPIII (SWI)

FIGURE 19.6 Comparison of Low Temperature Brookfield Performance for a series of conventional and chemically modified mineral oils

Copyright 2006 by Taylor & Francis Group, LLC

API Group III formulation (i.e., low temperature brookfield viscosity is directly related to kinematic viscosity for a given base stock). An additional API Group III chemically modified fluid produced from slack wax isomerization (SWI) was also tested and showed an extremely high brookfield viscosity and a low kinematic viscosity. The brookfield result is linked to the base stock that was solvent dewaxed (SWI). The combination of wax isomerization and solvent dewaxing produces a base stock with a very high VI but with poor response to pour point depressants. In fact, with the early commercial SWI stocks, pour points in finished oils could not be reduced to the −40◦ C level, even with excessive levels of pour point depressants. This is a problem with automatic transmission fluids as the brookfield test temperature is −40◦ C. Hence the inability to pour depress a SWI based formulation to the −40◦ C level, combined with the presence of n-paraffin residual wax leads to an ATF formulation that is typically solid at the brookfield test temperature. This is shown in Figure 19.6. Alternatively, one can hydrodewax a SWI base stock to improve its response to pour point depressants and its low temperature viscometric properties. The GTL-based formulation demonstrates this improvement as the sample that was tested in Figure 19.6 was also hydrodewaxed. The overall performance is better than each of the API Group I, II, and III based formulations and comparable to the PAO-based formulation. This is very important as it shows that chemically modified mineral oils based on GTL can provide “PAO-like” performance when properly dewaxed and complimented with an appropriate additive system. The relationship between GTL and PAO base stocks is further compared in Table 19.5. A slate of chemically

modified GTL-based mineral oils produced from a fixed bed F–T reactor was compared with a corresponding slate of PAO base stocks that were blended to the same kinematic viscosity as the GTL slate [22]. The overall properties of the GTL and PAO slates match up extremely well, with pour point the only significantly differing feature. However, the pour point deficiency with the GTL slate can be easily improved with a small amount of a commercial poly-methacrylate pour point depressant. Conversely, an improved pour point can also be achieved with a more efficient hydro-dewaxing operation. Previous work [1,2,6] has shown that GTL chemically modified mineral oils can be routinely dewaxed catalytically to pour points that are fully competitive with PAOs. This is particularly true for the heavier viscosity base stocks that would typically be used in crankcase applications, as shown in Table 19.6 [1]. Results from Table 19.5, meanwhile, show that under routine dewaxing operations typical for normal base stock operations that the lower viscosity base stocks (i.e., GTL-2) can have an extremely low pour point consistent with PAOs [22]. The importance of excellent low temperature fluidity becomes very important when formulating passenger car engine oils. The continued shift toward improved fuel economy under both fresh and aged conditions has shifted the viscosity grades that are recommended for new automobiles to lower SAE grades. With the pending ILSAC GF-4 performance standard, the SAE 5W-20, and SAE 5W-30 grades will continue in popularity while an SAE 0W-20 grade will now be formally recognized. Today, SAE 0W-20 and SAE 0W-30 grades are typically formulated with PAOs and in some instances, a small amount of an ester base stock for seal compatibility. The use of API Group III chemically modified mineral oils is typically limited with these

TABLE 19.5 Comparison of Chemical, Physical, and Compositional Properties of GTL and PAO Base Stocks Sample

GTL 2

PAO 2

GTL 3

PAO 3

GTL 5

PAO 5

GTL 7

PAO 7

Base oil properties Density at 15◦ C, kg/L KV at 40◦ C, cSt KV at 100◦ C, cSt Viscosity index Pour point, ◦ C CCS at −30◦ C, cP CCS at −25◦ C, cP Flash point, ◦ C Noack volatility, wt% Composition, % iso-paraffins

0.795 5.0 1.7 — −59 — — 159 — 100

0.792 5.2 1.7 — −63 — — 159 — 100

0.805 9.6 2.7 117 −57a — — 199 34 100

0.801 9.8 2.7 114 −66 — — 173 51 100

0.818 20.1 4.5 144 −39a 1320 — 238 8 100

0.815 21.3 4.6 132 −67 1250 — 221 13 100

0.820 38.4 7.0 147 −39a — 2660 260 2 100

0.831 40.3 7.0 134 −54 — 2340 251 5 100

a Includes 0.1 wt% pour point depressant.

Source: From Henderson, H.E., Hydrocarbon Eng., August 2002.

Copyright 2006 by Taylor & Francis Group, LLC

ultra low SAE grades, however, severely hydrodewaxed GTL base stocks can be used to blend a full range of lowand high-viscosity PCEO and HDEO products because of their highly iso-paraffinic nature and excellent low temperature fluidity. Table 19.7 compares the base stock and formulated properties for a SAE 0W-30 passenger car engine oil using a hydrodewaxed API Group III chemically modified mineral oil and a corresponding GTL-based formulation that was also hydrodewaxed [2].

TABLE 19.6 Comparison of VI and Pour Point Properties for GTL Derived Catalytically Dewaxed Mineral Oils with PAO Source GTL GTL GTL PAO PAO

KV at 100◦ C, cSt

VI

Pour point, ◦C

5.1 5.2 5.5 3.9 5.1

130 136 144 121 148

−66 −59 −40 <−66 −45

Source: From Wedlock, D.J., Changes in the Quality of Base Oils, Presented at the 8th Annual Fuels & Lubes Asia Conference and Exhibition, Singapore, January 29–February 1, 2002.

This can be further extended to the SAE 0W-20 grade and in one study was achievable with a minimal level of Viscosity Modifier (VM). This is particularly interesting as the lack of VM will further provide improved shear stability performance.

19.3.4 Benchmarking with API Group III The high iso-paraffinic content of GTL-based chemically modified mineral oils provides several advantages in terms of VI, Noack volatility and oxidation, and thermal stability. When hydrodewaxed, these base stocks will also provide outstanding low temperature properties, in some instances consistent with PAOs. According to the definitions from API 1509 [23], chemically modified mineral oils produced from F–T waxes would fall under category API Group III as noted in Table 19.8. This category also includes high and very high VI base stocks produced from hydrocracker bottoms and slack wax. Previous studies [16,17] have evaluated the compositional and performance features of API Group III chemically modified mineral oils and found that there are subtle variations within the group that, in turn, impact their ability to be interchanged within a given additive system. This is due to several factors, including feedstock variation, manufacturing approaches, catalyst selection, and the finished base stock specifications that the refiner will target. Base stocks produced from slack wax have been shown

TABLE 19.7 Blend Study Comparison of API Group III and GTL Based Chemically Modified Mineral Oils — SAE 0W-30 PCEO Base stocks Gp III base oil Base oil properties KV at 100◦ C Viscosity index Pour point Blend components Group III base oil Additive package Pour point depressant VM concentrate Blend physicals SAE 0W-30 KV at 100◦ C CCS at −35◦ C MRV at −40◦ C Noack volatility

Unit

SHC Gp III A

SHC Gp III B

SMDS GTL

SMDS GTL

% m/m

83.6

83.1

82.6

63.9

cSt — ◦C

4.56 121 −21

4.44 130 −21

4.23 126 −45

4.24 128 −43

% m/m % m/m % m/m % m/m

83.6 10 0.2 6.2

83.1 10 0.2 6.7

82.6 10 0.2 7.2

63.9 15 0.2 21

cSt cP cP wt%

10.24 — 34,100 12.0

10.27 — 36,100 13.4

10.05 4297 16,400 10.3

11.74 5623 19,000 10.5

Source: From Wedlock, D.J., Gas to Liquids — The Next Generation of Base Oils, Presented at the 10th Annual Fuels & Lubes Asia Conference and Exhibition, Shanghai, March 2–5, 2004.

Copyright 2006 by Taylor & Francis Group, LLC

1400

TABLE 19.8 American Petroleum Institute Base Stock Categories Sulfur wt%

Group I Group II Group III Group IV Group V

>0.03 ≤0.03 ≤0.03

Saturates wt%

1000

Viscosity index

And/or <90 80–119 And ≥90 80–119 And ≥90 ≥120 All polyalphaolefins (PAOs) All base stocks not included in Groups I–IV

TOST life, h

Base oil group

1200

800 600 400 200

Source: From Reference 23. 0 VGO derived Gp III-B

TABLE 19.9 Comparison of Physical and Compositional Properties of API Group III Chemically Modified Mineral Oils and Hydrodewaxed GTL Based Fluids Industry range

Ideal fluid

Base stock properties

GTL-5

Min

Max

(Best of Industry)

KV at 100◦ C, cSt Viscosity index Pour point, ◦ C CCS at −25◦ C, cP Noack volatility, wt%

4.5 144 −21 816 (639)b 7.8

4.0 120 −24 729 10.4

5.0 141 −12 2239 14.8

High (141) Low (−24) Low (729) Low (10.4)

Composition, mass% Alkanes Mono-cycloparaffins Poly-cycloparaffins Aromatics Sample base

100 0 0 0 —

47.3 18.7 5.3 0.0

80.9 28.8 22.2 12 17

a

High (80.9) Low (28.8)c Low (5.3) Low (0.0) —

a CCS and Noack provide higher assessment of base stock quality than KV. b Predicted CCS viscosity at equivalent KV to “Best in Industry.” c Alkanes (i.e., iso-paraffins) preferred to mono-cycloparaffins.

Source: From Henderson, H.E., Hydrocarbon Eng., August 2002.

to provide the highest VI characteristics, hence one would anticipate that base stocks produced from F–T wax would be further up the quality ladder. Table 19.9 provides a comparison of the physical and compositional properties of a GTL produced base stock that has been hydrodewaxed with a series of commercial API Group III chemically modified mineral oils [22]. The base stocks represent global supply and a range in manufacturing approaches. The viscosity range of 4 to 5 cSt at 100◦ C represents the typical viscosity grade that is used in the formulation of low SAE engine oils. The range in properties represents the minimum and maximum values from the 17 base stocks that were

Copyright 2006 by Taylor & Francis Group, LLC

VGO derived Slack wax Gp III-C derived GP III

SMDS GTL

FIGURE 19.7 Comparison of predicted TOST life for a selection of commercial API Group III and GTL chemically modified mineral oils

included in the API Group III data set. An additional column represents the ideal fluid, namely the best features from each of the physical and compositional properties. One would therefore target a base stock with the highest VI and iso-paraffinic content, and the lowest pour point, CCS viscosity, and Noack volatility. Interestingly, the GTL produced base stock provided the highest quality in most of the measured properties when compared against the best that API Group III could provide. The pour point was slightly higher than the industry best, however, with a test repeatability and reproducibility of 3 and 6◦ C respectively, this result could be considered to be equivalent to the best of the API Group III fluids. Cold cranking simulator viscosity was only exceeded by one sample from the industry data set. However, when these two base stocks were compared at an equivalent kinematic viscosity, the GTL-produced base stock exhibited a lower CCS viscosity than the “industry best.” Similar observations occurred when a comparison was made with a 3 and 7 cSt base stock produced from hydrodewaxing a F–T wax [9]. This clearly demonstrates the capabilities of base stocks produced from GTL processing and how they will play an important role in premium product applications.

19.3.5 Oxidation Performance The composition of a base stock is important in determining its oxidation performance. A high concentration of iso-paraffins is preferred with an absence of multiring paraffins and aromatics as they can lead to premature decomposition to form products of oxidation, sludge, and varnish, depending on the operating environment. Base stocks produced from F–T wax have the highest level of iso-paraffins and should, therefore, provide outstanding oxidation performance when complimented with the correct additive system.

6

Max limit 275% Oil consumption, quarts

Viscosity increase, %

300 250 200 150 100 50 0

GTL 0W-20

5 4 3 2 1 0

PAO 0W-40

GTL 0W-20 10

Min limit 9.0 Weighted piston deposits

Average piston varnish

10

Max limit 5.2 quarts

9 8 7 6

PAO 0W-40

Min limit 4.0

9 8 7 6 5 4 3

5 GTL 0W-20

GTL 0W-20

PAO 0W-40

PAO 0W-40

FIGURE 19.8 Comparison of Sequence IIIF engine performance for a SAE 0W-20/40 PCEO formulation based on PAO and GTL base stocks

Fuel economy, % 3.0

ILSAC GF-3 test limits

Fuel economy, total EF1 & EF2

EF1

EF-1

OW-20 2.0

5W-20 10W-40 1.6 0.9

EF-2

1.7

1.3

0.6

Total

—

3.0

1.6

6.0

EF2 2.0

4.0 EF1 & EF2

EF1 EF2

EF1 1.0

EF1 & EF2 2.0

EF2 0

0 GTL SAE 0W-20

API Group II SAE 5W-30

API Group I SAE 10W-40

FIGURE 19.9 Sequence VIB fuel economy performance for a GTL-based PCEO formulation

Figure 19.7 compares the predicted TOST life (turbine oxidation stability test) for a series of API Group III chemically modified mineral oils produced from hydrocracker bottoms, slack wax, and GTL wax [6]. The GTL wax formulation provided the highest TOST life, consistent with its highest level of iso-paraffinic components. This response is not unexpected and should lead to outstanding performance in both industrial and automotive applications.

Copyright 2006 by Taylor & Francis Group, LLC

19.3.6 Engine Performance Shell have used F–T wax produced from its refinery in Bintulu, Malaysia to manufacture its XHVI® base stocks at Yokkaichi in Japan and Petit-Courrone in France, with Yokkaichi being based on 100% GTL wax since 1994. It is therefore not surprising that base stocks produced from GTL wax have been tested in many products, applications and engines.

One study looked at the performance of a GTL base stock slate that was produced from a fixed bed F–T reactor and hydrodewaxed in a North American PCEO formulation at the ILSAC GF-3 performance level. A Sequence IIIF and VIB engine test was conducted on a SAE 0W-20 formulation, reflecting the capabilities of these high-quality base stocks to produce low SAE grades. The formulation included a friction modifier and was compared against a similar product that was formulated with PAOs as a SAE 0W-40 grade [9,22]. Results from the Sequence IIIF bench engine test are shown in Figure 19.8. Excellent performance was observed with the GTLbased formulation and was consistent to the reference fluid formulated with PAOs. Oxidation control was outstanding and consistent with a high-quality base stock combined with an appropriate antioxidant system. Piston cleanliness was also considered to be equivalent, despite some variability with the individual results. The oil consumption was outstanding for a formulation with such a low SAE grade and is a refection of the excellent Noack volatility with the GTL base stocks that were used in the study. Fuel economy was compared against a SAE 5W-30 and SAE 10W-40 blend formulated, respectively, with an

API Group II and I base stock slate. This is summarized in Figure 19.9 [9,22]. The initial observation is the limited viscosity grades that can be produced with an API Group I or II base stock. Although SAE 5W-XX is achievable, this is dependent on the volatility and CCS properties of the individual base stocks. Because GTL base stocks have an excellent combination of CCS viscosity and Noack volatility, one is able to formulate an SAE 5W-XX product without difficulty and extend this to the lower SAE 0W-XX grade. The improved viscometrics is reflected by the fuel economy results as a step change in improvement is observed as one progresses to lower SAE grades. The GTL-based formulation provided the best fuel economy result and was consistent with the levels that have been proposed for ILSAC GF-4. The “aged fuel economy” result (i.e., EF2) was also outstanding and consistent with both the ILSAC GF-3 and proposed ILSAC GF-4 limits. This is reflective of the excellent volatility and oxidation stability of the GTL-based formulation and its highly iso-paraffinic nature. These results further confirm the capability of chemically modified mineral oils that are produced from GTL and their future use in premium products and extreme operating conditions.

APPENDIX 19.1 Summary of GTL Plants Under Construction, Development, and Discussion/Feasibility — January 2004 Owner/Developer

Location

Product

Capacity, B/D

Feed

Process

Start date

Under construction Sasol/Chevron Statoil Synfuels Int’l Sasol/Qatar Pet

Nigeria S. Africa Houston Qatar

Fuels Fuels Fuels Fuels

34,000 1,000 1,000–1,200 34,000

Nat Gas Nat Gas Nat Gas Nat Gas

Sasol Statoil Synfuels Sasol

2005–6 2003 2003–4 2005

Under development Conoco/Qatar Pet Oman–India Fertilizer Oman–India Fertilizer Statoil Syntroleum Shell

Qatar Oman Oman Mossel Bay Australia Qatar

Diesel/Naphtha/LPG Ammonia (2 plants) Urea (2 plants) Fuels Specialty Diesel/Naphtha/LPG

160,000 17,501 13,501 1,000 11,500 140,000

Nat Gas Nat Gas Nat Gas Nat Gas Nat Gas Nat Gas

Conoco Haldor Topsoe Snamprogetti Statoil Syntroleum Shell SMDS II

2009–10 2006 2006 2003 2005 2008–10

Fuels Syngas Fuels Fuels Fuels Diesel/lubes N/A NGLs/Diesel/Naphtha Fuels Fuels Diesel/Naphtha

50,000 8,000–10,000 50,000 20,000 10,000 100,000 10,000 90,000 45,000 45,000 120,000

Nat Gas Coal/gas Coal/gas Nat Gas Nat Gas Nat Gas Nat Gas Nat Gas Nat Gas Nat Gas Nat Gas

N/A N/A Syntroleum Synergy Rentech Slurry Exxon AGC-21 Rentech Syntroleum Syntroleum Syntroleum Marathon

2006 2006 2007 N/A N/A N/A N/A N/A N/A N/A 2008

Under discussion/feasibility study stage ANGTL Prudhoe Bay, AK ANGTL Cook Inlet, AK Australia Power & Energy Australia Drake Synergy Nigeria GTL Bolivia N/A ExxonMobil Qatar Forest Oil S. Africa Ivanhoe/Syntroleum/Repsol Bolivia Ivanhoe Energy Egypt Ivanhoe Energy Oman Marathon/Qatar Pet. Qatar

Copyright 2006 by Taylor & Francis Group, LLC

APPENDIX 19.1 Continued Owner/Developer

Location

Product

Capacity, B/D

Feed

Process

Narkanan GTL Int’l PDVSA Rentech Rentech Sasol/Chevron Sasol Shell Shell Shell Shell Shell Shell Shell Syntroleum Syntroleum Syntroleum/Ivanhoe/CITIC Syntroleum/Repsol-YPF Syntroleum/Repsol-YPF Syntroleum/APEL Syntroleum/EurOil Syntroleum/Yakutgazprom

Iran Venezuela N/A Indonesia Australia China Argentina Australia Egypt Indonesia Iran Malaysia Trinidad Chile Peru China Bolivia Bolivia Australia Cameroon Russia

N/A Syncrude N/A Fuels Fuels Fuels Mid Distillate Mid Distillate Mid Distillate Mid Distillate Mid Distillate Mid Distillate Mid Distillate Fuels Fuels N/A Diesel Fuels Mid Distillate N/A Diesel

35,000 15,000 N/A 15,000 30,000–45,000 N/A 75,000 75,000 75,000 75,000 75,000 75,000 75,000 10,000 5,000 N/A 13,500 90,000 52,000 N/A 13,000

Nat Gas Nat Gas Ind. Offgas Nat Gas Nat Gas Coal/Gas Nat Gas Nat Gas Nat Gas Nat Gas Nat Gas Nat Gas Nat Gas Nat Gas Nat Gas Nat Gas Nat Gas Nat Gas Coal Nat Gas Nat Gas

N/A N/A Rentech Slurry Rentech Slurry Sasol Sasol Shell SMDS II Shell SMDS II Shell SMDS II Shell SMDS II Shell SMDS II Shell SMDS II Shell SMDS II Syntroleum Syntroleum Syntroleum Syntroleum Syntroleum Syntroleum Syntroleum Syntroleum

Start date N/A 2004 2002 N/A N/A N/A 2006–7 2006–7 2006–7 2006–7 2006–7 2006–7 2006–7 N/A N/A N/A N/A N/A N/A N/A N/A

Source: Gas-to-Liquids News, January 2004, Published by Hart Downstream Energy Services, A division of chemical week, Publishing, LLC, Potomac, MD.

REFERENCES 1. Wedlock, D.J., Changes in the Quality of Base Oils, Presented at the 8th Annual Fuels & Lubes Asia Conference and Exhibition, Singapore, January 29–February 1, 2002. 2. Wedlock, D.J., Gas to Liquids — The Next Generation of Base Oils, Presented at the 10th Annual Fuels & Lubes Asia Conference and Exhibition, Shanghai, March 2–5, 2004. 3. Releford, T.T. and Ball, K.J., Exxon’s New Synthetic Basestocks — EXXSYN, National Petroleum Refiners Association, Paper FL-93-117, Fall Meeting, November 1993. 4. Cox, X.B., Designing Basestocks to Meet the Quality Challenge, Presented at ICIS-LOR World Base Oil Conference, London, U.K., February 2003. 5. Snyder, P.V., GTL Lubricants: The Next Step, National Petroleum Refiners Association, Paper LW-99-125, Fall Meeting, November 1999. 6. Wedlock, D.J. and Adams, N., High Performance Base Oils from Unconventional Feedstocks, Presented at the 9th Annual Fuels & Lubes Asia Conference and Exhibition, Singapore, January 21–24, 2003. 7. Glenn, T.F., A US Market Space Analysis of GTL Lubricants, National Petroleum Refiners Association, Paper LW-01-137, Fall Meeting, November 2001. 8. Cox, X.B., Burbach, E.R., and Lahn, G.C., The Outlook for GTL and Other High Quality Lube Basestocks, National

Copyright 2006 by Taylor & Francis Group, LLC

9.

10.

11.

12.

13.

14.

15.

Petroleum Refiners Association, Paper AM-01-64, Spring Meeting, March 2001. Henderson, H.E., Fischer–Tropsch Gas to Liquids Fluids, Performance Beyond Current Synthetics, Presented at the ICIS-LOR World Base Oil Conference, London, U.K., February 2002. Glenn, T.F. and Henderson, H.E., Properties, Performance and Market Opportunities for Gas-to-Liquids Produced Base Stocks, EUROFORUM France Gas-to-Liquids Conference, Paris, France, February 2003. Rockwell, J., History of GTL Technology, National Petroleum Refiners Association, Paper LW-01-131, Fall Meeting, November 2001. Gas-to-Liquids News, January 2004, Published by Hart Downstream Energy Services, A division of Chemical Week Publishing, LLC, Potomac, MD. Eisenberg, B., Fiato, R.A., Mauldin, C.H., Say, G.R., and Soled, S.L., Exxon’s Gas-to-Liquids Technology for Natural Gas Development, AIC Conference on Gas-to-Liquids Conversion, Singapore, March 1998. Eisenberg, B., Lahn, G.C., Fiato, R.A., and Say, G.R., Exxon’s AGC-21 Advanced Gas Conversion Technology, Presented at Alternate Energy ’93, Council on Alternate Fuels, April 1993. Kaufman, T.G., Fiato, R.A., Lahn, G.C., and Bauman, R.F., Gas-to-Liquids Technology Provides New Hope for Remote Fields, Lubricants World, pp. 30–33, October 2000.

16. Henderson, H.E., Mack, P.D., Steckle, W.M., and Swinney, B., Higher Quality Base Oils for Tomorrow’s Engine Oil Performance Categories, SAE Paper 98252, October 1998. 17. Henderson, H.E., Fefer, M., Legzdins, A., Michaluk, P., and Ruo, T., Compositional Features of New High Performance Specialty Base Fluids, Symposium: Worldwide Perspectives on the Manufacture, Characterization and Application of Lubricant Base Oils: IV, ACS National Meeting, New Orleans, Louisiana, August 1999. 18. Freerks, R. and Henderson, H.E., Fischer–Tropsch Base Stocks — Performance Beyond Current Synthetics, 1st ICISLOR/ILMA Base Oils and Petroleum Additives Conference — The Americas, New York, December 2001. 19. Freerks, R., Henderson, H.E., and D’Onofrio, M., Fischer– Tropsch Base Stocks — Performance Beyond Current

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20.

21.

22.

23.

Synthetics, Presented at the 8th Annual Fuels & Lubes Asia Conference and Exhibition, Singapore, January 29– February 1, 2002. Henderson, H.E. and Swinney, B., High Quality Base Oils for Next Generation Automatic Transmission Fluids, SAE Paper 982666, October 1998. Henderson, H.E., Olavesen, C., Alexander, A.G., and Ozubko, R.S., A new high quality 100 neutral base stock for automotive and industrial oil products, Lubr. Eng., 48, 777–781, October 1992. Henderson, H.E., Fischer–Tropsch gas to liquids base stocks — performance beyond current synthetics, Hydrocarbon Eng., Vol. 7, No. 8, pp. 13–18, August 2002. American Petroleum Institute, Industry Services Department, Engine Oil Licensing and Certification System, API Publication 1509, 15th ed. April 2002.

20

Comparison of Synthetic, Mineral Oil, and Bio-Based Lubricant Fluids Leslie R. Rudnick and Wilfried J. Bartz CONTENTS 20.1 Introduction 20.2 Reasons for Choosing Synthetic Fluids 20.3 Fields of Application and Market Share 20.4 Classification of Synthetic Fluids 20.5 Advantages and Disadvantages of Synthetic Fluids 20.6 Comparison of Some Chemical, Physical, and Technological Properties 20.7 Comparison of Certain Temperature Related Properties 20.8 Comparison of Some Property Groups 20.9 Overall Comparison of Synthetic Fluids 20.10 Allocation of Properties to Fields of Application 20.11 Conclusion Acknowledgments References

20.1 INTRODUCTION From a practical point of view, it is the selection of a particular lubricant fluid by the engineer or user that results in successful operation of a particular piece of equipment. The decision driving the selection process includes a number of important factors: • • • • •

Physical properties Chemical properties Lubrication properties Environmental friendliness Cost

The performance of a lubricant fluid is dependent on all of the property and performance features of the fluid, but will generally be selected based on certain critical parameters; the other features can be improved by the incorporation of additives into the fully formulated oil to make up for some or all of the deficiencies of that fluid for the particular application. In the discussion that follows, it should be kept in mind that there is no lubricant fluid perfect for all applications. Variation of properties and performance can differ as much within a lubricant type as between lubricant types. The practitioner in this field needs to select a lubricant fluid after considering all of the application requirements. For example, when considering mineral oils, Group I

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or II oils are significantly different from chemically modified mineral oils (CMMOs) of Group III that have seen severe hydrotreating. The performance features of a polyalphaolefin (PAO) and a Group III oil are closer than those of a Group I and Group III mineral oil. Biodegradability for a 2 cSt PAO is as good as for most esters and better than in most other base fluids; however, an 8 cSt PAO biodegrades at a very slow rate and is not considered readily biodegradable. At that viscosity it is virtually equivalent to most mineral oil lubricants. The conditions of the specific frictional contacts as well as those of the environment have to be taken into account for the application of lubricants. Both influencing factors result in the total complex of requirements to which the lubricants are exposed and those that have to be met in considering an adequate service life. Ranges and limitations of lubricants are controlled by the extent and importance of the single requirements. If a single requirement exceeds the limits of application of a certain fluid, its use will be generally questionable, regardless of whether all other requirements are met easily.

20.2 REASONS FOR CHOOSING SYNTHETIC FLUIDS Regarding the limits of application of fluids, physical and chemical effects have to be distinguished. The physical

Two reasons to select a synthetic fluid are:

Melting of glass 500

• The desired or required chemical or physical property or Metalworking

300 Aviation

Temperature, °C

400

200 Space

100

Automobiles Ocean

0 –100

10–17

10–9 100

–160

105 Pressure, atm Human beings

Refrigeration

FIGURE 20.1 Temperature and pressure ranges for several applications of lubricants and operational fluids

Radiation, 108 erg/g h

Nuclear reactors

Space and aviation 0 Inert

Air

100

°C e, 200 ur t General ra 300 pe industry m 400 Te

Oxidation, O2

Range for human beings

500 Glass industry

FIGURE 20.2 Oxidation, radiation, and temperature ranges for several applications of lubricants and operational fluids

effects are characterized by temperature and pressure. Figure 20.1 shows temperature and pressure ranges for certain fields of application for lubricants and operational fluids. Both factors particularly control the so-called “liquid range.” The solidification of a fluid at low temperatures and high pressures limits its application, as does its evaporation at high temperatures and low pressures. The chemical effects are characterized by oxidation and radiation influences, both affected by temperature. Figure 20.2 shows the oxidation, radiation, and temperature ranges for some fields of application for lubricants and operational fluids. We cannot expect one special or single fluid, such as a mineral oil, to meet the ranges of requirements shown in Figure 20.1 and Figure 20.2. Therefore, it becomes a technical necessity to use synthetic or bio-based fluids as lubricants and operational fluids.

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performance feature cannot be obtained by mineral oils, or by fully formulated mineral oils containing additives. • The extent or quality of the desired or required property or performance features cannot be obtained by mineral oils, or by a mineral oil containing additives. Mineral oils can be inferior to certain synthetic fluids in terms of the following properties or performance features: • • • • • • • • •

Thermal stability Oxidation stability Viscosity temperature behavior Flow behavior at low temperatures Volatility at high temperatures Temperature range of application Radiation stability Ignition resistance Biodegradability

No synthetic or bio-based fluid combines all properties in a superior manner to mineral oils. In general, some inferior properties have to be taken into account. Certain synthetic fluids may have properties or performance features that are inferior when compared with mineral oils. These will generally be a consequence of the chemical structure of the synthetic fluid: • • • • • • • • •

Hydrolytic behavior Corrosion behavior Toxicological behavior Compatibility with other design materials Miscibility with mineral oil Compatibility with seal materials Additive solubility Availability, in general or in certain viscosity grades Price

Certain of these features may not have significant consequence. For example, if one is selecting a synthetic fluid that had certain performance features over a mineral oil, and the equipment is used only with that oil and it is flushed with a solvent prior to use, then mineral oil miscibility may not be a negative feature of the synthetic. Additive solubility, for example, with PAOs was at first thought to be a problem and continues to be reported as a problem by mineral oil suppliers. However, the introduction of a small amount of ester to a formulation has made the use of PAOs very reliable in most areas of lubrication which has become a reality for several decades. Development of high oleic acid containing bio-based fluids has resulted in significant improvement in oxidative stability of these oils, and has resulted in the application of these vegetable oils as base fluids in several areas.

TABLE 20.1 Application Areas for Synthetic Lubricants

TABLE 20.2 Demand in Western Europe for Synthetic Lubricants, 1000 t/a

Automotive Engine oils Four-stroke oils Two-stroke oils Gear oils Brake fluids Lubricating greases

Area of application

Aviation Turbine oils Piston engine oils Hydraulic fluids Lubricating greases Industry Gas turbine oils Gear oils Bearing and circulation oils Compressor oils (gas, air, refrigeration) Hydraulic oils Metalworking fluids Heat transfer and isolating oils Lubricating greases

Price has always been higher for synthetic fluids, very expensive in some cases; however, if the performance features can only be met with the synthetic fluids and they are needed for the application, then this should be the fluid of choice. Many factors go into the calculation of overall cost for the use of a lubricating fluid. The cost per kilogram or liter of the lubricant is only a part of the equation. The oil replacement interval, downtime, and inconvenience to perform the replacement need to be factored into the decision to select a particular fluid. For CMMOs, the greater the degree of hydroprocessing, the “cleaner” these fluids become in terms of having lower amounts of heteroatoms and aromatics. This, in turn, reduces the quantity of natural antioxidants and also the lubricity properties of these highly refined fluids, which requires the use of additive technology similar to that used for other nonpolar synthetics such as PAOs and poly internal olefins. Again, it must be stated that no mineral, synthetic, or bio-based fluid combines all properties to be the perfect lubricating fluid. These fluids might exhibit inferior performance in some applications, while they have superior performance in other specific application areas. Therefore, the following point of view must also be considered. Certain advantageous properties may be linked inevitably with less sufficient properties. For instance, the behavior under mixed film lubrication conditions is strongly controlled by mutual interactions between the

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Automotive Four-stroke engine oils Two-stroke engine oils Gear oils Lubricating greases

Aviation Turbine oils Piston engine oils Hydraulic oils Lubricating greases

Industry Gas turbine oils Gear, bearing and circulating oils Compressor oils Hydraulic oils Metalworking fluids Lubricating greases Heat transfer and isolating oils

Total

1985

1990

1995

2000

45 3 2 6 — 56

90 7 4 4 — 105

130 10 6 4 — 150

166 10 8 6 — 190

9 1 1 — — 11

10 2 1 — — 13

11 2 2 — — 15

13 2 3 — — 18

1 8

1 15

1 21

2 27

5 23 25 2 1

10 25 35 4 2

15 29 40 6 3

15 34 43 7 4

— 65

— 92

— 115

— 132

132

210

280

340

2002

450

TABLE 20.3 Synthetic Lubricants Proportion of Total Lubricants Market for Western Europe 1985 −2.0%

1990 3.5%

1995 5.0%

2000 7.0–8.0%

2002 8.0–10%

lubricant molecules and the surfaces of the frictional contact, characterized by the chemical and physical properties of the fluid. But many synthetic fluids stand out for good chemical and physical stability resulting in good oxidation and thermal stability. Rather moderate or even poor behavior at mixed film lubrication conditions can be the result.

20.3 FIELDS OF APPLICATION AND MARKET SHARE Synthetic and partly synthetic lubricants are used for automotive, aviation, and industry applications. Table 20.1

shows some main fields of application where synthetic lubricants exhibit advantages against mineral oil-based lubricants. Table 20.2 reveals the consumption, for Western Europe, of synthetic and partly synthetic lubricants in the past and the estimated demand for these lubricants in the future. From Table 20.3 it becomes obvious that the market share of synthetic fluid-based lubricants probably will not exceed 7 to 8% of the total lubricants market.

TABLE 20.4 Classification of Synthetic and Bio-Based Fluids According to Chemical Composition Synthetic fluids

Composition

Synthetic hydrocarbons Poly(α-olefins) Poly internal olefins Alkyl cyclopentanes Alkylated aromatics Monoalkylbenzenes Dialkylbenzenes Polyalkylene glycols Carboxylic acid esters Dicarboxylic acid esters Neopentyl polyesters Vegetable oils Phosphoric acid esters (phosphate esters) Silicone oils Silicone oils Polysilicone oils (siloxanes) Silicate esters Polyphenyl ether Polymethacrylate/poly(α-olefin) co-oligomers Polyfluoroalkyl ether (alkyoxyfluoro oils) Chlorofluorocarbons, chlorotrifluoroethylenes

C, H

C, H, O C, H, O

C, H, O, P C, H, O, Si

C, H, O C, H, O C, F, O C, F, Cl

20.4 CLASSIFICATION OF SYNTHETIC FLUIDS Synthetic fluids may be classified based on their chemical composition. As Table 20.4 reveals, the following basic types of synthetic fluids can be distinguished [1]: • • • • • •

C, H C, H, O C, H, O, Si C, H, O, P C, F, O C, F, Cl

Bio-based fluids, which are generally triglycerides, are composed of C, H, and O. Another criterion of classification, especially for the distinction between mineral oils and synthetic fluids, might be the production process [1]. Mineral oils are produced by distillation and raffination, and are upgraded to different extents to produce Group II+ and III CMMOs, whereas synthetic fluids are obtained by specific chemical reactions of smaller molecules (Table 20.5). A third possibility for the systematic classification of synthetic fluids is based on their chemical structure [2] (Table 20.6).

20.5 ADVANTAGES AND DISADVANTAGES OF SYNTHETIC FLUIDS The advantages and disadvantages of some important synthetic fluids are summarized in Tables 20.7 to 20.16. 1.

Synthetic hydrocarbons Polyisobutenes PAOs

(Table 20.7) (Table 20.8)

TABLE 20.5 Classification of Mineral, Synthetic, and Bio-Based Fluids According to Production Process Mineral oils, produced by distillation and refining

Synthetic fluids, produced by chemical reactions

Conventional technologies

Modern technologies

Synthetic hydrocarbons

Other synthetic fluids

Acid refining Solvent extraction Dewaxing

Hydrotreating Hydrocracking

PAOs Poly internal olefins Polyisobutenes Dialkylbenzenes Alkyl aromatics Cyclo aliphatics

Dicarboxylic esters Neopentyl polyesters Polyalkylene glycols Phosphate esters Silicone oils Polyphenyl ethers Perfluoroalkyl ethers Chlorofluoroalkyl ethers PMA/PAO co-oligomers

Bio-based fluids, produced by isolation from plants.

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TABLE 20.6 Classification of Fluids According to Chemical Structure

TABLE 20.7 Advantages and Disadvantages of Polyisobutenes

1. Synthetic hydrocarbons 1.1. Polymers (of olefins) 1.1.1. Ethylene polymers 1.1.2. Propylene polymers 1.1.3. Polybutenes (e.g., polyisobutenes) 1.1.4. Polymers of higher olefins (e.g., PAOs) 1.2. Chlorinated hydrocarbons 1.3. Condensation products (of aromatic compounds with olefins) (e.g., polyalkyl and dialkyl aromatics) 1.4. CMMOs

Advantages Available in many viscosity grades Good corrosion behavior Nontoxic Clean burning without residues Good lubricating properties Miscible in mineral oils and in synthetic hydrocarbons Disadvantages Moderate oxidation stability Higher volatility Moderate cold flow behavior Poor viscosity temperature behavior

2. Polyether oils 2.1. Aliphatic polyether (e.g., polyalkylene glycols) 2.2. Perfluoroalkyl ether 2.3. Polythio ether 2.4. Polyphenyl ether 3. Esters, carboxylic acid ester 3.1. Ordinary and complex esters (e.g., dicarboxylic acid esters, complex esters) 3.2. Esters of neopentyl polyols (e.g., neopentyl polyesters) 3.3. Fluorine-containing esters (e.g., fluoroesters, perfluorodialkyl ether) 4. Phosphoric acid esters, phosphate esters 5. Oils containing silicon 5.1. Silicone oils, siloxanes 5.2. Silicic acid esters (e.g., silicate esters) 5.3. Silahydrocarbons (e.g., tetraalkylsilanes) 6. Halogen hydrocarbons, halogen carbons 6.1. Chlorohydrocarbons (e.g., chlorodiphenyls, polychloroparaffins) 6.2. Aliphatic fluoro- and chlorofluorocarbons (e.g., chlorofluoroethylene) 6.3. Hexafluorobenzene 7. Others 7.1. Ferrocene derivatives 7.2. Aromatic amines (e.g., triarylamines) 7.3. Heterocyclic N, B, and P compositions 7.4. Urea derivatives 7.5. PMA/PAO co-oligomers

2.

3. 4. 5. 6. 7

Polyether oils Polyalkyleneglycols (Table 20.9) Perfluoroalkylether (Table 20.10) Polyphenylether (Table 20.11) Ester oils, carboxylic acid esters Diesters and polyolesters (Table 20.12) Vegetable oils (Table 20.13) Phosphate esters (Table 20.14) Oils containing silicone Silicone oils (Table 20.15) Polymoleic anhydride (PMA)/PAO — C-oligomers (Table 20.16)

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TABLE 20.8 Advantages and Disadvantages of PAOs Advantages Available in many viscosity grades Very good cold flow behavior, pour points <−60◦ C Very low volatility up to +160◦ C, even at low viscosities High oxidative and thermal stability with oxidation inhibitors Very good viscosity–temperature behavior Compatible with mineral oil-resistant paints Higher viscous types compatible with mineral-oil-resistant seal materials Good friction behavior Unlimited miscibility with mineral oils and esters Good hydrolytic stability Good corrosion behavior No toxic potential owing to absence of aromatic contained in mineral oils Moderate costs Disadvantages Low viscous types have moderate compatibility with a lot of seal materials; compatible with fluorine rubber (FPM) materials Scuffing and wear protection properties not as good as mineral oils, polyglycols, and ester Moderate solubility of extreme pressure and antiwear additives Biological degradation moderate for low viscosity grades, poor for higher viscosity fluids

20.6 COMPARISON OF SOME CHEMICAL, PHYSICAL, AND TECHNOLOGICAL PROPERTIES An overall review of several chemical and physical properties and some selected technological properties (e.g., indications regarding toxicology, behavior against seal materials and metals, and stability against chemicals) is summarized in Table 20.17 [3].

TABLE 20.9 Advantages and Disadvantages of Polyalkylene Glycols Advantages Extraordinary high thermal and oxidative stability Highest chemical stability of all lubricating oils Very wide service temperature range Very low volatility Very good cold flow behavior Compatible with seal materials, plastics, and paints Fire resistant High radiation stability Good wear and scuffing protecting behavior Low surface tension; good wetting properties Disadvantages Moderate viscosity temperature behavior Low corrosion protection No solubility for additives Not miscible with any other oil Nontoxic up to decomposition temperature (280 to 350◦ C); at higher temperatures toxic decomposition vapors are formed Extraordinarily high costs

TABLE 20.10 Advantages and Disadvantages of Perfluoroalkyl Ethers Advantages Producible in all viscosity grades desired Very good viscosity–temperature behavior, high viscosity index High load-carrying capacity (i.e., good scuffing and wear-protecting properties) Excellent friction behavior, especially with steel/phosphor bronze contacts With inhibitors, very good oxidation stability High service temperatures up to 250◦ C Good cold flow properties, low pour point Good corrosion behavior Nontoxic Unbranched polymers with molecular weights up to 1500 Biologically degradable Disadvantages In general not miscible with mineral oils, esters, and synthetic hydrocarbons (but some more expensive types are miscible with mineral oils) Moderate solubility and response for additives Less pronounced viscosity–pressure behavior compared to mineral oils Fire resistant only in water solutions Compatible only with paints based on epoxy resin and polyurea Compatible only with seal materials based on fluorine rubber (FPM) and polytetraethylene (PTFE) materials Limited compatibility with acrylonitrile-butadiene rubber (NBR) and methyl vinyl silicone rubber (MVQ) materials

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TABLE 20.11 Advantages and Disadvantages of Polyphenyl Ethers Advantages Containing inhibitors: better oxidative and thermal stability compared with mineral oils High service temperatures Low pour point, good cold flow behavior Good viscosity temperature behavior Unlimited miscibility with mineral oils and most other synthetic oils Good wear and scuffing protection and friction behavior Low volatility Nontoxic Many types biologically degradable Mean costs Disadvantages Available only in low viscosity grades Problematical compatibility with seal materials; compatible only with FPM, PTFE, and MFQ materials No compatibility with paints Poor hydrolytical stability Moderate corrosion protection

TABLE 20.12 Advantages and Disadvantages of Diesters and Polyol Esters Advantages Highest thermal and oxidative stability of all lubricating oils Highest stability against high energy radiation High chemical stability; highest stability against acids Excellent lubricating properties, even at mixed-film conditions Low volatility Excellent hydrolytical stability Good miscibility for mineral oils and additives Disadvantages Available only in limited viscosity grades Poorest cold flow behavior of all lubricating oils Poorest viscosity temperature behavior (negative VI values) Moderate compatibility with paints Moderate compatibility with seal materials Not miscible with perfluoroalkyl ethers, silicone oils, and polyalkylene glycols Moderate corrosion protection properties High costs

20.7 COMPARISON OF CERTAIN TEMPERATURE RELATED PROPERTIES Figure 20.3 reveals the temperature limits of mineral oils, which are between 100 and 150◦ C for oxidation and between 350 and 400◦ C considering the thermal stability. The comparatively small influence of oxidation inhibitors in order to increase the service temperatures can

TABLE 20.13 Advantages and Disadvantages of Vegetable Oil-Based Fluids Advantages Biodegradable Renewable Low toxicity Low health and safety risks Easy disposal Low volatility Good lubricity Disadvantages Higher cost than mineral oils Poor low-temperature properties Reduced operating temperature range Available in limited viscosity grades Moderate oxidative stability

TABLE 20.14 Advantages and Disadvantages of Phosphoric Acid Esters (Phosphate Esters) Advantages Fire resistant Containing inhibitors: good oxidation stability Good cold flow behavior Excellent scuffing and wear protection, good friction behavior Good radiation stability Triaryl ester types not toxic Biologically degradable Disadvantages Poor viscosity–temperature behavior Poor hydrolytical stability Moderate corrosion protection Compatible only with FPM seal materials Not miscible with mineral oil

clearly be recognized. If oxidation were avoided, much higher service temperatures could be applied to mineral oils. The limiting temperatures are characterized by the limited thermal stability of the oxidation inhibitors. The temperature limits of some synthetic fluids are listed in Figure 20.4. The temperature limiting the oxidation and the thermal stability was plotted against the service life of the fluid. Obviously, the higher oxidation limit and thermal stability limit of some synthetic fluids result in a better high-temperature behavior compared to mineral oils. Comparing the behavior of polyphenyl ether with silicone and ester oils illustrates the problematic nature of a situation that can combine excellent hightemperature properties with insufficient low-temperature

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TABLE 20.15 Advantages and Disadvantages of Silicone Oils Advantages Available in many viscosity grades Best viscosity–temperature behavior of all lubricating oils Very good oxidative and thermal stability Excellent cold flow behavior Low volatility, even at low viscosities High flash points Compatible with seal materials, plastics, and paints Corrosion protection properties and hydrolytical stability similar to mineral oil Good cold flow properties High chemical stability Good electrical properties, such as high specific resistance and high dielectric strength (electronic insulation value) Water insoluble Disadvantages Low surface tension, good wetting capacity Very poor lubricating properties at mixed-film conditions Lowest load-carrying capacity (wear and scuffing protection), which cannot be improved by additives Not miscible with mineral oils, synthetic hydrocarbons, esters, polyphenylethers, and perfluoroalkyl ethers High costs

TABLE 20.16 Advantages and Co-Oligomers

Disadvantages

Advantages High viscosity index Low evaporation losses Excellent low-temperature behavior Good viscosity–temperature behavior Good oxidation stability Excellent compatibility with seal material Good miscibility with mineral oils and additives Nontoxic

of

PMA/PAO

Disadvantages Low fire resistance Not biologically degradable Limited viscosity grades Higher costs

behavior. The extraordinary high-temperature performance of polyphenyl ether becomes obvious, whereas the very low pour points of silicone oils and certain esters dedicate these fluids for low-temperature application. These relations result in a maximum service temperature for endurance and temporary service periods according to Table 20.18, and it becomes obvious that some synthetic fluids are superior to mineral oils. In principle, the same statement is valid with regard to low service temperatures

TABLE 20.17 Comparison of Properties of Synthetic Lubricating Oils Neopentyl

Property Maximum

polyol (complex)

Typical phosphate

esters

ester

Diester 250

300

120

Typical methyl silicone 220

Typical

Chlorinated

phenyl methyl silicone

phenyl methyl silicone

320

305

Polyglycol (inhibited) 260

Chlorinated diphenyl 315

Silicate ester or disiloxane 300

Polyphenyl ether 450

Mineral oil Fluorocarbon 300

(for comparison) 200

temperature in absence of oxygen, ◦ C Maximum

temperature will be higher in the absence of metal 210

240

120

180

250

230

200

145

200

320

300

150

temperature in presence of oxygen, ◦C Maximum

oxygen concentration is low and life is short 150

180

100

200

250

280

200

100

240

150

140

200

Minimum

−35

−65

−55

−50

−30

−65

−20

−10

−60

0

50

0 to −50

temperature due to increase in viscosity, ◦ C Density, g/mL Viscosity

0.91 145

1.01

1.12

0.97

1.06

1.04

1.02

0

200

175

195

160

1.42 −200 to +25

1.02

140

150

1.19 −60

1.95 25

0.88 0 to 140

index Resistance to

Good

Good

Fair

Very good

Very good

Good

Good

Excellent

Poor

Very good

Excellent

Excellent

Attacked

Attacked by

Attacked by

Attacked by

Attacked by

Attacked by

Attacked by

Very

Generally

Resistant

many chemicals

strong alkali

strong alkali

alkali

oxidants

resistant

poor

Resistant but attacked by alkalies and amines

Very

alkali

Noncorrosive

Noncorrosive

Noncorrosive, but unsafe with aluminum and magnesium

Noncorrosive

attack by water

chemicals

Effect on metals

This limit is arbitrary. It would be higher if

temperature due to decrease in viscosity, ◦ C

Resistance to

Remarks For esters, this

by alkali

Slightly corrosive to non-ferrous metals

Corrosive to some non-ferrous metals when hot

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Enhanced corrosion in the presence of water

Corrosive in the presence of water to ferrous metals

Noncorrosive

Some corrosion of copper alloys

Noncorrosive

Noncorrosive

resistant

when pure

With external pressurization temperature or low loads, this limit will be higher This limit depends on the power available to overcome the effect of increased viscosity

A high viscosity index is desirable This refers to breakdown of the fluid itself, not the effect of water on the system

Costs (relative

5

10

10

25

50

60

5

10

10

250

300

1

to mineral

approximations, and

oil) Flash point, ◦C

230

255

200

310

290

270

180

180

170

275

None

150 to 200

Spontaneous

Low

Medium

Very high

High

High

Very high

Medium

Very high

Medium

High

Very high

Low

ignition temperature Thermal

These are rough vary with quality and supply position Above this temperature, the vapor of the fluid may be ignited by an open flame Above this temperature, the fluid may ignite without any flame being present

0.15

0.14

0.13

0.16

0.15

0.15

0.15

0.12

0.15

0.14

0.13

0.13

conductivity, W/m/◦ C

A high thermal conductivity and high thermal capacity are desirable for effective cooling

Thermal

2000

1700

1600

1550

1550

1550

2000

1200

1700

1750

1350

2000

capacity, J/kg/◦ C Bulk modulus

Medium

Medium

Medium

Very low

Low

Low

Medium

Medium

Low

Medium

Low

Fairly high

Boundary

Good

Good

Very good

Fait but poor for steel on steel Nontoxic

Fair but

Good

Very good

Very good

Fair

Fair

Very good

Good

lubrication

Toxicity

Suitable

Slight

Nitrile,

rubbers

silicone

Effect on

May act as

plastics

plasticizers

Slight

Silicone

Powerful solvent

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Some toxicity Butyl, EPR

Slight, but may leach out plasticizers

poor for steel on steel Nontoxic

Nontoxic

Believed to be low

Neoprene, Viton

Neoprene,

Slight, but

Slight, but

may leach out plasticizers

Viton

may leach out plasticizers

Viton,

Nitrile

Irritant vapor when hot Viton

fluoro-silicone Generally mild

Powerful solvent

Generally mild

Slight

Believed to be low

Viton nitrile, fluoro-silicone Polyimides satisfactory

(None for very high temperatures) Some softening when hot

Nontoxic

Slight

unless over- heated Silicone

Nitrile

Generally slight

There are four different values of bulk modulus for each fluid, but the relative qualities are consistent. This refers primarily to antiwear properties when some metal contact is occurring Specialist advice should always be taken on toxic hazards.

600

Temperature, °C

500 Thermal stability limit (without oxygen)

400 Life in this region depends on oxygen amount and catalysts

300

With antioxidants

200

Oxidation stability limit (unlimited oxygen)

100 Without antioxidants 0 Low temperature limit by pourpoint (Depending on oil, viscosity, temperature, and additives) 2000

–100 1

2

4

10

20

40

100 200

400

1000

5000

3000 10000 Life, h

FIGURE 20.3 Temperature limits for mineral oils. Source: From Neale, M.J. (ed.), Tribology Handbook. Butterworth, London (1973)

600 Thermal stability limit polyphenyl ethers 500 Temperature, °C

Thermal stability limit for silicones 400

Oxidation stability limit for polyphenyl ethers

300 200 Oxidation stability limit for esters and silicones 100 Thermal and oxidation stability limit for phosphate esters 0

–100

Low temperature limit by pourpoint for silicones and esters 1

2

4

10

20

40

100 200

400

1000

2000

5000

3000 10000 Life, h

FIGURE 20.4 Temperature limits for some synthetic oils. Source: From Neale, M.J. (ed.), Tribology Handbook. Butterworth, London (1973)

(Table 20.19). Of course, any direct comparison of fluids of different classes can only be made for fluids having the same viscosity. These results can be summarized by comparing service temperature ranges of some synthetic fluids (Figure 20.5). Their superiority to mineral oils can clearly be recognized [4]. The temperatures that in general can be applied to synthetic fluids that contain adequate oxidation inhibitors are remarkably higher than those for mineral oils (Figure 20.6). The comparison of the viscosity–temperature behavior of some synthetic fluids and formulations based on mineral oil is shown in Figure 20.7. Comparing curves E and F reveals the extent of improvement by the usage of additives in mineral oils. For further improvements other fluids have to be selected, such as in curve B. It is obvious that

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the excellent viscosity temperature behavior of silicone oil cannot be realized with mineral oils, whether they contain VI improvers or not.

20.8 COMPARISON OF SOME PROPERTY GROUPS For application reasons a comparison of certain property groups seems to be most useful to select the optimum synthetic fluid to cover the requirements of special tribological contacts. This comparison is done for stability, viscosity, and lubricity properties. The simultaneous comparison of thermal, oxidation, hydrolytic, and volatility behavior of synthetic fluids and of mineral oil is shown in Table 20.20. There hardly exists

Typical mineral oils

TABLE 20.17 Maximum Service Temperatures for Synthetic Lubricating Oils

Polydecenes Alkyl benzenes

Temperature (◦ C)

Polyol esters Polyglycols

Continuous service

ab c d e f g

h

a Mineral oils b Alkyl phosphates

Fluid Mineral oils PAOs Polyalkylene glycols Perfluoroalkyl ether Polyphenyl ether Diesters Phosphate esters Vegetable oils Silicone oils Silahydrocarbons Silicate esters

Flash point

Pour point

200–300 200–350 200–260 — 230–350 200–270 100–260 300–350 230–330 270–290 180–280

0 to −60 −20 to −60 −30 to −50 −20 to −75 +20 to −20 −50 to −80 −10 to −60 −9 to −21 −10 to −100 −5 to −15 −50 to −70

Useful lifetime – hours

3.000

Temperature (◦ C)

350 °C

Intermittent service

Dependent on starting torque

FIGURE 20.5 Comparison of service temperature ranges of synthetic fluids. Source: From Neale, M.J. (ed.), Tribology Handbook. Butterworth, London (1973)

10.000

TABLE 20.18 Flash Points and Pour Points of Some Synthetic Lubricating Oils

300 °C

Phosphate esters 250 °C

130–150 310–340 220–230 80–90 200–220 420–480 120–150 200–230 260–280 310–340 310–340 280–310 400–450 280–340

200 °C

90–120 170–230 170–180 60–70 160–170 310–370 90–120 150–170 180–220 220–270 170–230 200–260 280–340 230–260

Dibasic acid esters

150 °C

Temporary

100 °C

Mineral oils Synthetic hydrocarbons Carboxylic acid esters Vegetable oils Polyalkylene glycols Polyphenyl ether Phosphoric acid esters (alkyl) Phosphoric acid esters (aryl) Silicic acid ester (silicate esters) Silicone oils, siloxanes Silahydrocarbons Halogenated polyphenyls Perfluorohydrocarbons Perfluoropolyglycols

Permanent

60 °C 50 °C 40 °C 30 °C 20 °C 10 °C

Fluid

c Alkyl silicates 1.000

d Polyglycols

300

e Synthetic hydrocarbons and diesters

100 30

f Polyol esters

10

g Silicones h Polyphenyl ethers

3 1 0

100 200 300 Temperature °C

400

FIGURE 20.6 Service life depending on temperature for different synthetic oils containing inhibitors. Source: From Neale, M.J. (ed.), Tribology Handbook. Butterworth, London (1973)

20.9 OVERALL COMPARISON OF SYNTHETIC FLUIDS

a single fluid exhibiting excellent, or at least very good behavior, regarding all four properties. A similar comparison of low-temperature fluidity, viscosity index, and pressure viscosity properties can be recognized from Table 20.21. PAOs, esters, and some silicon-containing fluids reveal very good or even excellent behavior regarding all properties compared. The comparison of wear protection properties, without and with additives, and fatigue life behavior is shown in Table 20.22. Again, it becomes obvious that no single fluid can cover all requirements simultaneously very well.

Copyright 2006 by Taylor & Francis Group, LLC

Table 20.23 shows an overall comparison of some important physical, chemical, and technological properties of the most important synthetic fluids [2,5–8]. Although desirable, the realization of such an overall comparison is difficult, considering the aim of a justified evaluation. Therefore, some introductory remarks seem to be necessary due to the fact that several fluids are commercial while some others are development fluids. Therefore, this type of comparison might be misleading at the present time. In addition, there are various subclasses within some general classes, a fact that is not considered in this chapter. The same restriction applies to the influence of additives on the changes of some properties [9]. Last

(A) Mineral oil + 10% fatty oil (B) Silicone oil (A) (C) Chlorinated silicone oil

10.000 Viscosity, mPos

1.000

(B)

200 100 30 15 10

(C)

50 20

5 4 3 –40

(F) (D)

(E) (D) Diester (E) Mineral oil + VI-Improver (F) Plain mineral oil –20

0

20

40

60

80

100 120 Temperature, °C

FIGURE 20.7 Viscosity–temperature behavior of some lubricating oils

TABLE 20.19 Relative Evaluation of Stability Properties of Different Synthetic and Bio-Based Fluids Product

Thermal

Oxidation

Hydrolytic

Volatility

Mineral oil (paraffinic) PAOs Alkyl benzenes Alkyl naphthalenes Diesters Polyol esters Vegetable oils Polyalkylene glycols Phosphate esters Silicones Fluorocarbons Polyphenyl ethers Silicate esters Silahydrocarbons

Good

Fair

Excellent

Poor/fair

Very good Good Excellent Good Good Fair/good Good Fair Very good Excellent Excellent Very good Excellent

Very good Good Excellent Very good Very good Fair/good Good Good Good Excellent Good Good Very good

Excellent Excellent Excellent Fair Fair Fair Good Fair Excellent Good Excellent Fair/poor Excellent

Very good Good Very good Good Good Excellent Good Fair/good Excellent Poor Good Good —

but not least, it should be mentioned that the ratings between “excellent” and “poor” need some explanation. For instance, a fluid was rated as “excellent” if it was nontoxic. To give another example, the cyclophosphazene fluids could not be rated regarding biodegradability. In most cases, the authors of the specific chapters of this book gave valuable assistance for the making of this table, which should be used to obtain a first impression of the properties of synthetic fluids relative to each other. The choice of a synthetic fluid is usually the result of the synthetic fluid having particular performance characteristics that are not obtainable with mineral oils. Lubricating fluids are chosen to achieve the requirements of specific applications. Therefore, the fluid of choice for one application may be totally inadequate for another. If certain cases of application require special properties that cannot be obtained by mineral oils, a certain synthetic

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fluid will have to be selected and applied in spite of some of its less good or even disadvantageous properties. Each property, therefore, has to be prioritized depending on the special application.

20.10 ALLOCATION OF PROPERTIES TO FIELDS OF APPLICATION The application of synthetic lubricants strongly depends on their specific properties, especially concerning those of mineral oils. Taking this point of view, the advantageous properties result in certain applications, the requirements of the frictional contacts of which cannot be covered by mineral oils. On the other hand, some predominant disadvantages of certain synthetic fluids will exclude them for specific fields of application. For the followingfluids this

TABLE 20.20 Relative Evaluation of Viscosity Properties of Different Synthetic Fluids Low-temperature fluidity

Product Mineral oil (paraffinic) PAOs Alkyl benzenes Alkyl naphthalenes Diesters Polyol esters Vegetable oils Polyalkylene glycols Phosphate esters Silicones Fluorocarbons Polyphenyl ethers Silicate esters Silahydrocarbons

VI

Pressure–viscosity

Fair/good

Good

Good

Excellent Good Excellent Very good Very good Poor Very good Faira /good Very good Fair Poor Excellent Excellent

Very good Very good Very good Very good Very good Very good Very good Faira /good Excellent Fair Fair Excellent Excellent

Good Good Good Very good Very good — Very good Very good Excellent Fair Poor Very good —

a Triarylphosphates have poorer VIs and low-temperature fluidity than trialkylphos-

phates.

TABLE 20.21 Relative Evaluation of Lubricity (Wear Protection and Fatigue) of Different Synthetic and Bio-Based Fluids Product Mineral oil (paraffinic) PAOs Alkyl benzenes Alkyl naphthalenes Diesters Polyol esters Vegetable oils Polyalkylene glycols Phosphate estersa Silicones Fluorocarbons Polyphenyl ethers Silicate esters

Natural lubricity and AW

AW with additives

Fatigue life

Good

Excellent

Fair/good

Good Good Good Fair Fair Excellent Good Excellent Poor Fair/good Good Good

Excellent Excellent Excellent Good Good Good Good Excellent Fair Good Good Very good

Good Good Good Fair Fair/good Fair/good Fair Fair Fair/good Fair/good Good Poor

a Acid phosphate esters have excellent AW properties but poor fatigue

life.

• • • • • •

Diesters and polyolesters (Figure 20.11) Phosphate esters (Figure 20.12) Perfluoralkylethers (Figure 20.13) Silicone oils (Figure 20.14) Polyphenylethers (Figure 20.15) Vegetable oils (Figure 20.16)

In order to summarize this allocation, Table 20.24 shows the main fields of applications for the most important synthetic lubricants.

20.11 CONCLUSION Mineral oils cannot meet all requirements of lubricants for frictional contacts or of operational fluids. As a result, certain synthetic fluids have gained significant importance. These fluids can be classified either by the production process, the composition, or the chemical structure. The chemical, physical, and technological properties of the synthetic fluids as well as the advantages and disadvantages of some important synthetic fluids are presented in a tabular form in this chapter.

ACKNOWLEDGMENTS allocation of properties to application is done: • PAOs (Figure 20.8) • Polybutenes (Figure 20.9) • Polyalkyleneglycols (Figure 20.10)

Copyright 2006 by Taylor & Francis Group, LLC

I (LRR) would like to acknowledge the original chapter on the comparison of lubricant base fluids by Wilfried J. Bartz published in Synthetic Lubricants and HighPerformance Functional Fluids, 2nd edition, Edited by L.R. Rudnick and R.L. Shubkin (Marcel Dekker) 1999.

TABLE 20.22 Comparison of Properties of Important Synthetic Fluids

Polyisobutenes

PAOs

Alkylated aromates

Polyalkylene glycols

Perfluoroalkyl ethers

Polyphenyl ethers

Dicarboxylic acid esters

Polyol esters

Neopentyl polyesters

Triaryl phosphate esters

Trialkyl phosphate esters

Silicone oils

Silicate esters

Silahydrocarbons

Chlorofluorocarbons

Cyclophosphazene fluids

Dialkylcarbonates

Alkylated cyclopentanes

PMA/PAO co-oligomers

Vegetable oils

HO vegetable oil

Viscosity–temperature behavior (VI) Low temperature behavior (pour point) Liquid range Oxidation stability Thermal stability Evaporation losses Volatility Fire resistance, Inflammability temperature Hydrolytical stability Corrosion protection Properties Seal material compatibility Paint and lacquer compatibility Miscibility with mineral oil Solubility of additives Lubricating properties load-carrying capacity Toxicity Bio-degradability Price compared with mineral oil

Mineral oils (Gp III)

Property

Mineral oils (Gp I, II)

Evaluationsa

4

4

5

2

4

2

4

5

2

2

2

5

1

1

1

2

4

5

3

3

2

2

2

5

5

4

1

3

3

3

5

1

1

2

4

1

1

2

3

3

3

3

3

2

3

3

4 4 4 4

4 4 4 4

5 4 4 4

2 2 4 2

3 4 4 3

3 3 3 3

1 1 1 1

5 2 1 3

2 2/3 3 1

2 2 3 1

2 2 2 1

2 2 2 2

3 4 3 2

1 2 2 2

1 2 3 3

2 3 2 2

5 1 2 3

4/5 3 3/4 3

2 2 3 4

1 2 4 1

2 2 3 1

3 5 4 1

3 3 3 1

5

5

5

5

5

4

1

4

4

4

4

1/2

1/2

3

4

4

1

1/2

3

5

4/5

5

5

1 1

1 1

1 1

1 1

1 1

3 3

1 5

1 4

4 4

3 4

4 4

4 4

3 4

3 3

4 5

1 1

2 5

3 3

3 1

1 1

2 2

5 1

5 1

3

3

3

2

3

3

1

3

4

4

4

5

5

3

3

2

4

3/4

3

2

1

4

4

1

1

1

1

1

4

2

4

4

4

4

5

5

3

4

1

3

3/4

2

1

1

4

4

—

1

1

1

1

5

5

3

2

2

2

4

4

5

4

1

5

5

2

1

1

1

1

1 3

2 4

1 3

2 3

1 3

4 2

5 1

2 1

2 2

2 2

2 2

1 1

1 3

5 5

3 4

3 3

5 1

4 2/3

2 2

3 3

1 2

3 1

3 1

3 4 —

3 4 1.5

1 5 3-5

1 5 3-5

5 5 3-5

3 1/2 6-10

1 5 500

3 5 200-500

3 1/2 4-10

3 1/2 4-10

3 1/2 4-10

4/5 2 5-10

4/5 2 5-10

1 5 30-100

4 4 20-30

2 5 30-70

2 5 300-400

2 — 30-50

1 1 4-10

1 5 3-8

1 4/5 5-10

1 1 2-3

1 1 2-3

a 1 = excellent, 2 = very good, 3 = good, 4 = moderate, 5 = poor

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Advantages • Good Flow Properties at low Temperatures • High Thermal and Oxidative Stability • Low Evaporation Losses at High Temperatures • High Viscosity Index • Good Friction Behavior (Mixed Film) • Miscibility with Mineral Oils and Esters • Good Hydrolytical Stability • Good Corrosion Protection • Not Toxic

Disadvantages • Limited Biodegradability • Limited Additive Miscibility

Especially Suited for

• Engine Oils • Compressor Oils • Hydraulic Oils • Gear Oils • Greases

Not Suited For • High Performance Gear Oils • Fast Biodegradable Oils

FIGURE 20.8 Poly(α-olefins)

Advantages

• Not Toxic • Clean Burning without Residues • Good Lubrication Properties • Good Corrosion Protection • Miscibility with Mineral Oils

Disadvantages

Low Oxidation Stability High evaporation Losses Bad Flow Properties at low Temperatures Low Viscosity Index

Especially Suited for

• Two Stroke Engine Oils (Base For Additives) • Ethylene Gas Compressor Oils • Metalworking Lubricants • Greases

Not Suited For

• Most Circulation System Lubricants

FIGURE 20.9 Polybutenes

Advantages

• High Viscosity Index • Excellent Wear and Scuffing Protection • Excellent Friction Behavior (Steel/Bronze) • Good Oxidation Stability • Good Cold Flow Properties • Not Toxic • Fast Biodegradable

Disadvantages • Not Miscible with Mineral Oils • Additives Hardly Miscible • Limited Seal Material and Paint Compatibility

FIGURE 20.10 Polyalkylene glycols

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Especially Suited for

• Worm Gear Oils • Fire Resistant Hydraulic Fluids • Compressor Oils • Fast Biodegradable Lubricants • Textile Oils • Automotive Refrigeration Oils • Metalworking Lubricants

Not Suited For • Engine Oils • High Performance Gear and Hydraulic Oils

Advantages

• Good Oxidation Stability • Good Low-Temperature Flow Behavior • High Viscosity Index • Low Evapo ration Losses at High Temperatures • Unlimited Miscibility with Mineral Oils • Good Scuffing and Wear Protection • Not Toxic • Fast Biodegradable

Disadvantages

• Low Viscosities • Limited Compatibility with Seal Materials and Paints • Bad Hydrolytical Stability • Moderate Corrosion Protection

Especially Suited for

• Aviation Turbine Oils • Engine Oils • Compressor Oils • Gear and Hydraulic Oils • Refrigeration Oils • Fast Biodegradable Lubricants

Not Suited For

• Application with Extreme Corrosion Protection Requirements • Application with High Viscosity Requirements

FIGURE 20.11 Diesters and polyolesters

Advantages • Fire Resistant • Good Oxidation Stability • Good Cold Flow Properties • Excellent Wear and Scuffing Protection • High Radiation Stability • Not Toxic • Fast Biodegradable Disadvantages • Moderate Hydrolytical Stability • Moderate Corrosion Protection • Low Viscosity Index • Limited Seal Material Compatibility • Not Miscible with Mineral Oils

FIGURE 20.12 Phosphate esters

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Especially Suited for

• Fire Resistant Hydraulic Fluids (Hydraulic Fluids and Bearing Lubricants in Power Stations) • Gas Turbine Oils

Not Suited For

• All Other Applications than Mentioned Above

Advantages • Extreme Thermal and Oxidative Stability • Highest Chemical Stability • Very Good Cold Flow Properties • Low Evaporation Losses • Extreme Temperature Range of Application • Excellent Compatibility with Seal Materials and Paints • High Radiation Stability • Good Wear and Scuffing Protection • Fire Resistant Disadvantages • Low Viscosity Index • Moderate Corrosion Protection • Not Miscible with Mineral Oils and Additives

Especially Suited for

• Extreme Fire Resistant Hydraulic Fluids • Nuclear Reactor Lubricants • Special Greases • Space Applications

Not Suited For

• Any Other Application Not Mentioned Above

FIGURE 20.13 Perfluoroalkyl ethers

Advantages

• Highest Viscosity Index • Very Good Thermal and Oxidative Stability • Excellent Cold Flow Properties • Low Evaporation Losses • High Chemical Stability • Excellent Compatibility with Seal Materials • Good Electrical Properties

Disadvantages

• Worst M ixed Film Lubrication Properties • Not Miscible with Mineral Oils and Additives

FIGURE 20.14 Silicone oils (siloxanes)

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Especially Suited for

• High Temperature Hydraulic Fluids • Greases • Special Lubricants with Contacts to chemicals and Electricity

Not Suited For

• Any Application in Mixed Film Conditions

Advantages

Especially Suited for

• Highest Thermal an d Oxidative Stability • Highest Radiation Stability • High Chemical Stability • High Hydrolytical Stability • Low Evaporation Losses • Good Miscibility with Mineral Oils and Additives

Disadvantages

• Special High Temperature Lubricants (Oils and Greases) • Nuclear Reactor Lubricants

Not Suited For

• Worst Cold Flow Properties • Lowest (Negative) Viscosity Index • Moderate Compatibility with Seal Materials and Paints • Moderate Corrosion Protection

• Subzero Temperature Applications • Other Applications Not Mentioned Above

FIGURE 20.15 Polyphenyl ethers

TABLE 20.23 Important Synthetic and Bio-Based Fluids and Their Applications Synthetic oil type

Main applications

Synthetic hydrocarbons PAOs Polyisobuthenes Alkylated aromatics Cycloaliphates

Engine oils, Industrial Lubricants (Compressor, Hydraulic & Bearing Oils) Metal Forming Oils, Two-Stroke engine oils, Electrical Isolation Oils Low-temperature Oils for Gears, Engines, Hydraulics Friction Gear Oils (Due to high friction coefficient)

Organic esters Diesters Polyolesters

Turbine Oils, Mixing Components for PAOs Turbine Oils, Compressor, Hydraulic, and Gear Oils

Vegetable oils

Two-Stroke engine oils, Hydraulic Fluids, Textile Oils, Chain Saw Oils. Mould Release Oils, Greases, Metalworking, Fluids

Polyglycols Water soluble Nonwater soluble

Brake Fluids, Metal Working Oils, Worm Gear Oils, Fire Resistent Hydraulic Fluids Worm Gear Oils

Others Phosphate esters Silicone oils Halogenated fluids Polyphenylethers

Fire Resistant Hydraulic Fluids, Gas Turbine Oils High-Temperature Hydraulic Fluids, Brake Fluids, Compressor Oils Extremely Fire Resistant Hydraulic Oils Radiation Resistent Lubricants, Heat Transfer Fluids

I have updated and expanded this chapter and included new information and data on bio-based fluids.

REFERENCES 1. Bartz, W.J., Notwendigkeiten für den Einsatz synthetischer Schmierstoffe und Betriebsflüssigkeiten (Necessities for the Application of Synthetic Lubricants and Functional Fluids). Tribologie und Schmierungstechnik 34: 262–269 (1987).

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2. Klamann, D., Schmierstoffe und verwandte Produkte (Lubricants and Related Products). Verlag Chemie, Weinheim (1982). 3. Neale, M.J. (ed.), Tribology Handbook. Butterworth, London (1973). 4. Williamson, G.I., Synthetic Lubricants — The State of Market Development and Inter-Product Competition. Course SP5, The College of Petroleum Studies, Oxford (5th and 6th Dec. 1988), 1988.

5. Schmid, W., Synthetische Industrieschmierstoffe (Synthetic Industrial Lubricants). Mobil Oil, Hamburg (1980). 6. Möller, U.J. and Boor, U., Schmierstoffe im Betrieb (Application of Lubricants). VDI-Verlag, Düsseldorf (1987). 7. Rudnick, L.R. and Shubkin, R.L., Synthetic Lubricants and High-Performance Functional Fluids, Marcel Dekker, 1999.

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8. Rudnick, L.R., “A comparison of synthetic and vegetable oil esters for use in environmentally friendly fluids,” in BioBased Industrial Fluids and Lubricants, S. Erhan and J. Perez (eds), AOCS Press, pp. 46–58, 2002. 9. Rudnick, L.R., Lubricant Additives: Chemistry and Applications. Marcel Dekker, 2003.

Part II Bio-Based Lubricants

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21

Natural Oils as Lubricants Leslie R. Rudnick and Sevim Z. Erhan CONTENTS 21.1 21.2 21.3 21.4 21.5

Introduction Chemical Structures of Vegetable Oils and Fatty Acids Effects of Structure on Physical Properties Effects of Structure on Chemical Properties Properties of Vegetable Oils 21.5.1 Viscosity 21.6 Effects of Structure on Performance 21.6.1 Stability 21.7 Lubrication, Friction, and Wear 21.8 Effects of Additives on the Performance of Natural Oils 21.9 Genetically Modified Vegetable Oils 21.10 Future Prospects References

21.1 INTRODUCTION The last decade has seen a slow but steady move toward the use of “environmentally friendly” or more readily biodegradable lubricant fluids. Biodegradability has become one of the most important design parameters both in the selection of the base fluid and in the overall formulation of the finished lubricant. By more readily biodegradable it is meant that the fluids, using standard methods and assays, are converted from the lubricating fluids to lower molecular weight components that have essentially no environmental impact. The rate at which lubricants, and other chemicals or additive components, biodegrade is related to their chemical structure. Their chemical structure affects their properties, many of which affect performance in the various tests for biodegradability. For example, water solubility is critical in some tests for biodegradability, and toxicity is very important, because if the lubricant is toxic and reduces the organism population, then this directly and negatively impacts the process of biodegradation. The demand for biodegradable lubricants is due to a growing concern for the impact that our technology is making to our environment. This concern is occurring both as the result of a combination of local and national regulations, and as well as a result of consumer influence. European countries, specifically Germany and Austria,

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and the Scandinavian countries have led the efforts in this region [1]. There are significant efforts within Europe to specifically exploit the benefits of agricultural materials. The Interactive Network for Industrial Crops and Applications (IENICA) is composed of 14 countries with the objectives of creating synergy with the European Union (EU) industrial crops industry, developing scientific, industrial, and marketing opportunities for crop applications, and to identify EU member strengths and to encourage collaboration [2]. One of the main application areas of this effort is in the area of lubricants. The environmentally friendly nature of vegetable oil-based lubricants and the marketing benefits of having such products have prompted several companies to become involved. For example, Mobil Chemical was preparing to implement a clean lubricants production line as part of the Agriculture for Chemicals and Energy (AGRICE) program. Shell Oil Company and British Petroleum were involved in a partnership with Societe Nationale des Chemins de fer Francais (SNCF) (French National Railways) to develop biodegradable lubricants for railway track grease. Additional efforts were in the application of vegetable oils as the mold release (lubricant) for construction casings for concrete. In 2002, the total Western European market for all lubricants was 5,020,000 tons/year, of which 50,000 tons/year were based on vegetable oils. The U.S. market for all lubricants is

8,250,000 tons/year and only 25,000 tons/year were based on vegetable oils [3]. It has been reported that more than half of the lubricants that are sold worldwide pollute the environment due to total-loss lubrication, spillage, and through evaporation [4,5]. The benefits of vegetable oils being both renewable and biodegradable have provided an incentive to find application for these fluids as chain-saw bar lubricants [6,7], outboard engine lubricants [8], drilling muds [9,10], and in partial loss applications such as hydraulic fluids [11–15] and greases [16–19]. The demand for outdoor power equipment has grown to $14 billion in 2002 [20]. Sales of gasoline-powered trimmers and brush cutters in 2002 had reached 5 million units, twice the number of units sold in 1997. This was also true of gasoline-powered blowers and chain-saws. This growth in equipment sales also included an increase in do-it-yourself volumes of replacement lubricant demand. A significant part of this came from the two-cycle industry, where the user mixes the lubricant and fuel to provide a mixture that fuels the equipment. The fate of much of this oil is unknown. If it is recycled, then the environmental impact can be minimal; however, if these oils are discarded at the site of use, or even in containers that will become landfill, then these fluids will eventually become pollutants. The shift to more bio-friendly fluids in these application areas has the potential to significantly reduce the impact of using this equipment on the environment. Efforts to develop biodegradable greases for the railroad industry have resulted in alternatives to nonbiodegradable petroleum-based greases. One example is the replacement by Norfolk Southern Railway of conventional petroleum-based rail grease to soybean oil-based biodegradable grease. These greases reduce wheel-flange and rail gauge face wear that are caused when trains go around curves [21]. Vegetable oils cost approximately twice that of mineral oils, are biodegradable, and renewable [1]. They are also able to provide biodegradable features, generally achievable by synthetic esters, but at substantial cost savings. Vegetable oils in general are deficient relative to mineral oils, chemically modified mineral oils (CMMOs), and most synthetic lubricants in terms of their thermal and oxidative stability. There are also, in some cases, serious limitations to the use of vegetable oils when used in applications requiring operation at low temperatures. Vegetable oils can be considered environmentally friendly because these materials are renewable, possess high levels of biodegradability, low aquatic toxicity, and do not accumulate in the environment. This chapter addresses the lubricating properties and performance of vegetable oils, that is, the triglycerides directly obtained from the plant, and the fatty acids directly obtained from the triglycerides. The concept of chemically

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modified or functionalized vegetable oils and fatty acids is the subject of Chapter 22.

21.2 CHEMICAL STRUCTURES OF VEGETABLE OILS AND FATTY ACIDS Fatty acids are primarily long chain unbranched aliphatic acids, with the carbon atoms attached to hydrogen and other groups and the chain terminating with a carboxylic acid. Most naturally occurring fatty acids contain an even number of carbon atoms in their backbone chains. These fatty acids have even-numbered chains with 14 to 22 carbon; those with either 16 or 18 carbons occur most frequently. The polar –COOH group is enough to make the shortest fatty acid chains water-soluble. As chain length increases, the fatty acid type becomes progressively less watersoluble and takes on oily or fatty characteristics. At points where hydrogen atoms are missing from adjacent carbon atoms, the carbons share a double instead of a single bond. If double bonds occur at multiple sites (up to a maximum of about six), the fatty acid is polyunsaturated. Unsaturated fatty acids have lower melting points than saturated fatty acids and are more abundant in living organisms. The carbon chain of a fully saturated fatty acid is more or less straight. An unsaturated fatty acid may take one or two forms at a double bond. In the cis form, both the hydrogen atoms of the double bond are positioned on the same side of the C–C bond. In the trans form (hydrogen atoms on opposite sides of the double bond), the chain is twice bent so that it continues in the same direction. Unsaturated trans fatty acids are thermodynamically more stable than the cis form and therefore melt at a higher temperature. If three fatty acids bind to each of the three –OH sites of the alcohol (glycerol; propane-1,2,3-triol), the resulting compound is known as triacylglycerol. They are the fully acylated derivative of glycerol. Similarly, when one and two of the –OH groups are esterified with alcohol, monoacylglycerols and diacylglycerols are formed, respectively. Seed-based oils constitute mostly of triacylglycerols (98%), with minor amounts of diglycerols (0.5%), free fatty acids (0.1%), sterols (0.3%), and tocopherols (0.1%) [22].

21.3 EFFECTS OF STRUCTURE ON PHYSICAL PROPERTIES There is a trade-off between the degree of linearity of the fatty acid structure and the properties and performance of that structure. It is a direct consequence of the bent structure of a fatty acid that contains unsaturation, and therefore that of the vegetable oil (triglyceride), that contributes to the liquid nature of the oil. A vegetable oil that contains only or a high percentage of linear, saturated fatty acids is generally solid at or near room temperature. A consequence of this is that these materials provide little benefit as lubricants

that need to be used in applications having a wide range of ambient temperature. This is not only true of vegetable oils and fatty acids. Other lubricants, such as polyalphaolefins (PAOs) derive their low-temperature properties and performance from the fact that these fluids are mixtures of various isoparaffins. A similar mixture of unbranched (linear) paraffins would not have good low-temperature properties because the waxlike paraffins would crystallize out or gel in solution at lower temperatures [23,24]. For example, if the predominant fatty acids in a particular vegetable oil are saturated, the low-temperature performance will be poor relative to a vegetable oil that contains predominantly mono- or polyunsaturated fatty acids.

FIGURE 21.2 The glycerol portion of triglycerides

21.4 EFFECTS OF STRUCTURE ON CHEMICAL PROPERTIES Why is vegetable oil source data varied in composition? Several factors contribute to the variation of fatty acid concentrations and the chemical composition of the fatty acids in vegetable oils. The climatic conditions, including the amount of sunlight and soil affect the concentrations of the various fatty acids. The chemical composition of the individual fatty acids within a particular vegetable oil is genetic. Most vegetable oils are triglycerides, which are composed of a glycerol molecule esterified with various fatty acids. A generalized structure is shown in Figure 21.1. The glycerol portion of the molecule has the structure shown in Figure 21.2. Fatty acids associated with vegetable oils can be classified as being saturated, mono-, di-, tri-unsaturated, etc. Figure 21.3 shows the structure of oleic acid, one of the most common fatty acids found in vegetable oils that are used as lubricants.

21.5 PROPERTIES OF VEGETABLE OILS A summary of some of the important lubricant-related properties of vegetable oils has been recently published that compares these properties with those of synthetic esters and

FIGURE 21.3 Oleic acid, COOH (CH2 )7 CH=CH(CH2 )7 CH3

PAO lubricants [25]. Detailed physical property data for many of the common vegetable oils, including American Society for Testing of Materials (ASTM) test results, have been reported by Lavate et al. [22].

21.5.1 Viscosity The viscosity of lubricating oils is one of their most important properties when specifying an oil for a particular application. The chemical structure of the vegetable oil affects the flow properties of the oil. For example, if a fluid oil that contains a significant quantity of oleic, linoleic, or linolenic acids or other unsaturated components is hydrogenated to produce a saturated version, the new material would have the properties of grease. The effect of this hydrogenation is to convert molecular structures that are bent at the double bond to molecular structures that are essentially linear in nature. Although this is discussed further in the next section, the effect of removing the double bonds improves the oxidative stability of the oil.

21.6 EFFECTS OF STRUCTURE ON PERFORMANCE 21.6.1 Stability

FIGURE 21.1 Triglyceride structure

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The key to the use of vegetable oil-based lubricants is that they cannot be used in every application. There is simply not enough vegetable oil produced globally on an annual basis. The entire production of vegetable oil does not go into lubricant application. Therefore, it is useful to consider the application of vegetable oils in lubricant applications where the properties and performance are best matched. For vegetable oils, this is in applications where

the maximum operating temperatures are on the order of less than 120◦ C. At the other end of the spectrum are the low-temperature properties of the vegetable oils relative to synthetic lubricants, mineral oils, and CMMOs. Many of these lubricants have excellent low-temperature properties and can be used under arctic conditions for extended periods of time. The limitations, described in the preceding section, show that vegetable oils should be employed in applications where the ambient temperatures remain above −40◦ C. Oxidative stability is dependent on the predominant fatty acids present in the vegetable oil. Oils containing mostly saturated fatty acids will have good oxidative stability compared to a vegetable oil containing oleic acid or other monounsaturated fatty acids. The vegetable oils that contain mostly polyunsaturated fatty acids exhibit poor oxidative stability. Performance properties of many of the common vegetable oils, including ASTM test results, have been reported by Lawate et al. [22]. Examples of the naturally occurring oils and their respective applications are summarized in Table 21.1. The application of selective plant breeding to provide more oxidatively stable vegetable oils is an alternative approach that is the subject of Chapter 23. There are also potential benefits to the transesterification of vegetable oils, thereby creating a variety of glycerol esters that are not necessarily found in plants but that have been

TABLE 21.1 Selected Applications for Various Vegetable Oils Canola oil

Castor oil Coconut oil Olive oil Palm oil Rapeseed oil

Safflower oil Linseed oil Soybean oil

Jojoba oil Crambe oil Sunflower oil Cuphea oil Tallow oil

Hydraulic oils, tractor transmission fluids, metal working fluids, food grade lubes, penetrating oils, chain bar lubes Gear lubricants, greases Gas engine oils Automotive lubricants Rolling lubricant–steel industry, grease Chain saw bar lubricants Air compressor — farm equipment Biodegradable greases Hydraulic fluid, fuel, soap Light-colored paints, diesel fuel, resins, enamels Coatings, paints, lacquers, varnishes, stains Lubricants, biodiesel fuel, metal casting/working Printing inks, paints, coatings, Soaps, shampoos, detergents, pesticides, disinfectants, plasticizers Grease, cosmetic industry, lubricant applications Grease, intermediate chemicals, surfactants Grease, diesel fuel substitute Cosmetics and motor oil Used in steam cylinder oils, soap, cosmetics, lubricants, plastics

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created entirely by rearranging natural fatty acids in the triglyceride. Rates of vegetable oxidation are directly related to the type and amount of unsaturation present in the fatty acids of the vegetable oil. The relative rates of oxidation of oleic acid, linoleic acid, and linolenic acids are 1, 10, and 100, respectively [26]. Vegetable oils, in general, are less volatile than isoviscous mineral oils and synthetics. Using thermogravimetric analysis, Rudnick has measured volatility in the absence of oxygen so that no oxidation affects the physical volatilization of oils [27] and has compared the volatility of hydrocarbon base fluids with vegetable oils and other esters [28]. The oxidative stabilization of vegetable oils has been reviewed [29]. In general, hydrocarbon oxidation rates are dependent on temperature, surface contact with metals, and irradiation sources such as sunlight or UV light [30,31]. The autoxidation process is known to involve free radicals, and therefore, approaches taken to retard the process of oxidation utilize free radical chain-breaking antioxidants (primary antioxidants) and hydroperoxide decomposers (secondary antioxidants) and combinations of both of these classes of antioxidants. The details of the application of antioxidants in the field of lubrication have been recently reviewed [32]. Vegetable oil oxidation has been described in terms of primary and secondary stages by Fox and Stachowiak [33]. The first stage involves the free-radical formation of hydroperoxides on the fatty acid portions of the molecule, while in the second stage, after sufficient buildup of the hydroperoxide concentration, there is decomposition to form alcohols, aldehydes, and ketones along with volatile decomposition products. Many tests of oxidative stability that previously included water, have been modified to better represent real operating environments. These tests are generally referred to as “dry.” The “dry” turbine oil stability test (TOST) provides discrimination between formulations or neat vegetable oils that more closely represents many of the applications where vegetable oil formulations would be used. For example, TOST (ASTM D943, DIN 51587) test with water is not used for lubricants that contain vegetable oils, such as HETG or HEES lubricants. An alternative test for oxidative stability that is used for vegetable oils is the Baader test (DIN 51554 Part 3). This test is run at 95◦ C for three days in a water-free environment. Vegetable oils, due to their structures, generally perform poorly in this test, even in the presence of some antioxidants. However, it was found that the appropriate antioxidant chemistry is effective in reducing the change in viscosity and Total Acid Number (TAN) under the test conditions [29]. The general consensus of vegetable oils oxidative stability is that vegetable oils degrade more rapidly than mineral oils, and in general, stability is inversely

proportional to the degree of unsaturation. This is due to the facility of reaction of the allylic hydrogens adjacent to multiple carbon–carbon double bonds in these structures [25]. Due to the necessary unsaturation in vegetable oils required by low-temperature properties, their oxidative stability will generally be lower than those of fully saturated synthetics such as PAOs, PIOs, synthetic esters, etc. This means that to provide comparable performance, vegetable oil formulations generally require higher doses of antioxidants. A representative selection of vegetable oils that contain phenolic and arylamine antioxidants has been evaluated using the RBOT test (ASTM D2272) and a modified IP 306 test [22,34,35].

21.7 LUBRICATION, FRICTION, AND WEAR The friction and load-bearing properties of several common vegetable oils have been reported by Lawate including 4-Ball wear, Shell 4-Ball EP, Falex, and Timken “OK” Load test results [22]. Vegetable oils have demonstrated to be potential as use for biodegradable lubricants in applications that include engine oils, hydraulic fluids, and transmission oils [36–41]. Erhan and Asadauskas [42] has reported on lubricant base stocks based on vegetable oils. Environmentally acceptable hydraulic fluids based on vegetable oil-base fluids have been reported by Rhee [43–45]. An extensive evaluation aimed at determining the suitability of rapeseed oil-based hydraulic fluids has been reported [46]. These studies included long-term testing using 37 agricultural machines that used a fully formulated hydraulic fluid. Several machines were monitored. Fluids were evaluated by measuring kinematic viscosity and neutralization number. The results of the investigation showed that hydraulic fluids based on rapeseed oil were suitable for use in agricultural machinery. Furthermore, it was reported that low ecotoxicity and high biodegradability was observed throughout the test program. A significant amount of heat is generated in the process of rolling metals. This heat is usually removed to some extent by lubricants called rolling fluids. These fluids not only reduce heat in the metal being deformed, but also serve to reduce friction between the cylinders that are employed in the process of rolling and the metal being shaped. This is important not only to protect the equipment but also to lower the rolling force by improving the lubricity of the rolling fluid. Vegetable oils are excellent lubricants and so have been successfully used in the formulation of rolling fluids. There are generally three types of lubricants used in cold-rolling: stable emulsions, metastable emulsions, and neat fluids [47]. Vegetable oils are used in the stable and metastable emulsions, whereas the neat fluids may contain fatty alcohols. Vegetable oils provide better

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antiwear performance and generally exhibit lower friction coefficients. The boundary lubrication properties of sunflower oil have been evaluated [48]. For oxidized samples, after aging for 28 days or more, the boundary lubrication performance of sunflower oil was degraded significantly. Since, during the process of oxidation there is a cleavage of the fatty acid chains, the triglyceride consists of three chains of different length. It is apparently the similar length of these three fatty acid chains that provides improved performance of vegetable oils as lubricants in boundary lubrication. Gangule and Dwivedi [49] have reported on the preparation and performance of a total vegetable oil-based grease. Normally, in conventional grease, the gellant is a vegetable oil-based soap and the lubricant can be mineral or synthetic in nature. The greases reported here consisted of a vegetable oil-based lubricant in addition to the conventional vegetable oil-based gellant. Most studies to date have investigated the friction and wear performance of vegetable oils neat or in the presence of certain additives in an environment of unidirectional motion. Vizintin and Arnsek [50] have also studied the performance of rapeseed oil under conditions of a highload oscillating movement. These studies included the evaluation of rapeseed oil-based formulations and mineral oil-based formulations with antiwear and extreme pressure (EP) additives. Six different fatty acids were tested as antiwear additives and a commercial S–P (sulfur–phosphorus) additive was evaluated for EP performance with the two types of oils.

21.8 EFFECTS OF ADDITIVES ON THE PERFORMANCE OF NATURAL OILS The variety of chemical structures used to improve the properties and performance of lubricants is immense [51]. The objective in designing fully formulated oils with biodegradable base fluids is to employ additive chemistries that are both compatible with the lubricants and are themselves nontoxic and biodegradable. Too often, the fate of the additive components in the environment is ignored and additive choices are based on past performance with mineral oil or synthetic formulations. Formulations using vegetable oils should be composed to the extent possible with the least toxicity, ready biodegradability, and best performance for the application. Becker and Knorr [52] have reported that synergistic mixtures of antioxidants improve the oxidative stability of a high oleic acid containing sunflower oil. ASTM D525, an oxygen uptake test has been applied to evaluate the response of rapeseed oil to oxygen under pressures at 100◦ C [53]. Pressure differential scanning calorimetry (PDSC) has also been used as an effective method for the evaluation of the oxidative stability of vegetable oils [54].

Miles has reported on the performance evaluation of several vegetable oils in combination with a variety of different commercially available antioxidant additives [1]. It was noted that both the antioxidant structure and the concentration of the antioxidant affects performance, and that vegetable oils performance is closer to that of mineral oils than synthetic esters despite the disparity in structure. It was suggested that this is due to the natural antioxidants present in mineral oils. The authors caution that the newer CMMOs have been hydrotreated severely and are essentially devoid of the structures that formerly provided inherent oxidative stability to mineral oils produced in the mid-1990s. Commercially available fully formulated hydraulic/ transmission lubricants based on rapeseed oil have been evaluated for friction and wear performance [39]. One of the three oils examined in this study was a Universal Tractor Transmission Oil (UTTO). Comparison was made with a mineral oil that was isoviscous with the bio-based oils at the test start temperature. When compared with mineral oil-based formulations, it was reported that in general, substantially lower coefficients of friction and better pitting resistance were observed for rapeseed-based formulations. These authors examined the scuffing load capacity of the test oils using the standard FZG A/8.3/90 test. Data was taken at 90◦ C. Operating temperatures were also reported to be lower for rapeseed-based oils due to lower shear stresses during contact and a higher viscosity index in the bio-based fluids [39]. This study showed that the scuffing load capacity of rapeseed-based hydraulic/transmission oils is equivalent to the isoviscous mineral oil-based oil. Chemical changes that occur during oxidation of sunflower oil samples are the most significant in terms of boundary lubrication properties. Oxidation of oil samples was shown by peroxide level determination and oxidative stability was measured using sealed capsule differential scanning calorimetry [33,55]. The tribological performance of a series of dialkyldithiophosphate ester additives, similar to zinc dithiophosphates, in rapeseed oil has been reported [56]. These dialkyldithiophosphate esters were prepared using standard synthetic approaches, and characterized by IR and thermogravimetric analysis (TGA). The tribological performance was evaluated using four-ball wear at loads of 200 to 400 N. Load-carrying capacity of the formulations was evaluated using ATM D2789. The new ester additives provided good load-carrying capacity as additives for rapeseed oil. One additive also showed good antiwear and low friction coefficient. In general, performance similar to that achieved with zinc dialkyldithiophosphate (ZDDP) was observed with the potential for lower ecotoxicity. The tribological performance of sulfur-containing borate esters has been studied in rapeseed oil. Using four-ball testing, the friction-reducing properties and antiwear performance of the borate esters were examined. At suitable concentrations, the additives were found to

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improve antiwear and lower friction in blends with rapeseed oil [57]. The tribological behavior of phosphate esters additives that contain the benzotriazole group in rapeseed oil blends has been investigated [58]. The studies included the evaluation of friction and wear using four-ball testing. The results of these studies showed that the phosphate esters gave good load-carrying capacity. Wear scar diameters of blends containing the additives were smaller than when the additives were not used. Wear scars were shown to be dependent on the additive concentration, as expected. Rapeseed oil was also investigated as a base fluid in combination with a series of phosphate esters, similar to an earlier report on dialkyldithiophosphate esters, only without the sulfur functionality [59]. These studies showed that phosphate esters also possess good load-carrying capacity and antiwear performance [56]. Although mostly related to synthetic esters and chemically modified esters, Hahn et al. [60] have evaluated the ecotoxicity and biodegradability of formulated lubricants. The norms and standards of biodegradability and toxicity are different in different countries [61], for example, the German specification for biodegradable lubricants is more rigid than the Swiss. Biodegradability results in self-decomposition by microorganism into nontoxic products (carbon dioxide and water). The ease with which organisms can accomplish this depends largely on their structures. Most of the bio-based hydraulic fluids are readily biodegradable. Relative biodegradability of lubricants is typically measured by CEC-L-33-A-94 test. Vegetable oils are typically 99% biodegradable and it usually drops to about 90 to 98% after blending with additives. In comparison, the biodegradability of mineral oils is around 20% [62,63]. Hamblin [29] has also summarized a variety of tests used to measure biodegradability. The use of suitable additive technology has the potential to provide a nearly equivalent performance to vegetable oil-based lubricants. This allows for the use of these oils as base fluids in the development of engine oils [64]. It should be noted that many classes of additives are themselves toxic and may bioaccumulate in the environment.

21.9 GENETICALLY MODIFIED VEGETABLE OILS Although this chapter is focused on naturally occurring vegetable oils, it is important to note that the performance of genetically modified vegetable oils has been the subject of several studies. This is the subject of Chapter 23. For example, high oleic sunflower oil, when improved by the addition of additives, provides excellent performance. Minami showed that at loads of 200 N, that certain acid, amine, and amide additives prevented wear, whereas a thiol-containing additive promoted wear under these conditions. When both wear volume and friction were considered, the order of lubricity for straight chain terminally functionalized additives was reported to be

“acid” > “amine” > “amide” = “base (unadditized oil)” > “thiol” [65]. Chemical changes that occur during the process of oxidation of vegetable oils have been reported to improve the lubricity of these oils [66,67].

21.10 FUTURE PROSPECTS The lubricant industry is in a constant state of change. Lubricants are continuously being developed with better properties for specific applications, and at the same time some lubricant formulations are finding wider applications than they might have been originally designed for. We are reaching a period in the development of the industry where a more holistic approach is being considered. An example of this can be seen in a recent advertisement for a bio-based hydraulic fluid where synthetic PAOs are being combined with bio-based oils and specially designed additives. This combination of renewable biodegradable vegetable oil and synthetic hydrocarbon base fluid represents the combination of products from two diverse disciplines to provide the benefits of each in a new product [68]. The author predicts that the future will bring more products of this type. The development of an industry centered on the technology of biologically designed antioxidants that are cost-equivalent to chemically derived additives will also occur. Some of this cost-leveling may be through efficient manufacturing methods or through economy of scale that companies cannot perceive yet. Alternatively or in combination, the cost of disposal of used lubricant that contains nonbiodegradable additive chemistry, or base fluids might tip the scales in favor of a cleaner environment for future generations. The U.S. Department of Agriculture (USDA) has proposed implementing a set of guidelines that would require federal agencies to use preferred procurement of bio-based products including lubricants. The USDA’s proposal has been published in the Federal Register (see www.biobased.oce.usda.gov). These efforts will help the United States become less dependent on foreign oil imports and at the same time provide environmentally friendly products to the consumer at both the industrial and consumer level. This approach will also help to grow the volumes of bio-based fluids so that they become even more cost-effective. The preferred procurement program, if implemented as proposed, will require federal agencies to significantly increase their use of bio-based products. It will require the federal agencies to purchase, whenever these products are available, if the cost to the agency is not significantly higher than a similar nonbio-based product. The products are also required to have similar performance features as the conventional product. The USDA is planning to ensure that each bio-based product contains a minimum quantity of bio-based components to be included in the proposed product categories. This proposed regulation would require government agencies to purchase lubricants,

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that include motor oils, metalworking fluids, and a variety of hydraulic fluids made using bio-based components.

REFERENCES 1. Miles, P., Synthetics vs. mineral oil: applications, options, and performance, J. Synth. Lubr., 15, 43–52, 1998. 2. David, O., Goss, G., and Gaouyer, J.P., Non-food industrial products from crops: example of biomolecular development in France, J. Synth. Lubr., 16, 333–337, 2000. 3. David Whitby, Market share of bio-lubricants in Europe and the USA, Lipid Technology, 16, 125–129, 2004. 4. Horner, D., Recent Trends in Environmentally Friendly Lubricants, J. Synth. Lubr., 18, 327–346, 2002. 5. Mang, Th. and Lingg, G. Rapidly biodegradable lubricants — current situation and outlook, Proceedings of the 3rd Annual Fuels and Lubes Asia Conference of Fuchs Petrolub AG OEL + Chemie, Singapore, pp. 1–2, January 1997. 6. Randles, S.J.; Wright, M. Environmentally considerate ester lubricants for the automotive and engineering industries. Synthetic Lubrication, 9(2), 145–161, 1992. 7. Battersby, N.S., Pack S.E., Watkinson R.J., A correlation between the biodegradability of oil products in the cec 1-33t-82 and modified sturm tests, Chemosphere 24(12): 1989– 2000 JUN 1992. 8. Beitelman, A.D., Time for a change? Assessing environmentally acceptable lubricants, Hydro Review, April 1998. 9. Addy, J.M. et al. 1978 Biological monitoring of sediments in the Ekofisk oilfield. In Proceedings of a Conference on the Assessment of the Ecological Effects of Oil Spills, American Institute of Biological Science, Washington D.C., pp. 515–539. 10. Addy, J.M., Harley, J.P., and Tibbetts, P.J., Ecological effects of low toxicity oil-based mud drilling in the beatrice oilfield. Marine Pollution Bulletin, 15, 429–436, 1984. 11. Bartz, W.J., Synthetic hydraulic fluids for high performance applications, STLE 55th Annual Meeting, Nashville, TN, 2000. 12. Mang, T., Proceedings ICIT-97, Calcutta, 639, 1997. 13. Kassfeldt, E. and Dave, G. Environmentally adapted hydraulic oils, WEAR 207 (1–2): 41–45 JUN 1997. 14. Kiovsky, T.E., Murr, T., and Voeltz, M., Biodegradable Hydraulic Fluids and Related Lubricants, International Truck and Bus Meeting and Exposition, Paper 942287, November 1994. 15. Cheng, V.M., Wessol, A.A., Baudouin, P.M., BenKinney, T., and Novick, N.J., Biodegradable and nontoxic hydraulic oils, 42nd Annual Society Automotive Engineers (SAE) Earthmoving Industry Conference, Paper 910964, April 1994. 16. Dwivedi, M.C.; Sapre, Smita. Total vegetable-oil based greases prepared from castor oil. Synthetic Lubrication 19(3), 229–241, 2002. 17. Dresel, W.H., Biologically degradable lubricating greases based on industrial crops, Ind. Crops Prod. 2, 281–288, 1994. 18. Hissa, R. and Monterio, J.C., Manufacture and evaluation of Li-greases made from alternate base oils. NLGI, 3, 426–432, 1983. 19. Stempfel, E.M. and Schmid, L.A., Biodegradable lubricating greases. NLGI, 55, 25–33, 1991.

20. Glenn, T.F., Lubes and Greases, October 2003, pp. 64–65. 21. Lubricants World, October 2003, p. 12. 22. Lavate, S.S., Lal, K., and Huang, C. Tribology Data Handbook, CRC Press, Boca Raton, FL, 1997, pp. 103–116. 23. Rudnick, L.R. and Shubkin, R.L., Polyalphaolefins, in Synthetic Lubricants and High-Performance Functional Fluids, 2nd ed, L.R. Rudnick and R.L. Shubkin, Eds., Marcel Dekker, New York, 1999. 24. Rudnick, L.R., Polyalphaolefins, in Synthetics, Mineral Oils and Bio-Based Fluids, L.R. Rudnick, Ed., Marcel Dekker, New York, 2005, Chapter 1. 25. Rudnick, L.R., in Bio-Based Industrial Fluids and Lubricants, S.Z. Erhan and J.M. Perez, Eds. AOCS Press, IL, pp. 46–58, 2002. 26. Sevim Z. Erhan, personal communication. 27. Rudnick, L.R., Buchanan, R.P., and Medina, F., Oxidationmediated volatility (OMV) of hydrocarbon lubricants, submitted for publication. 28. Rudnick, L.R., Buchanan, R.P., and Medina, F., Studies on the oxidation-mediated volatility (OMV) of vegetable oil lubricants (manuscript in preparation). 29. Hamblin, P. Oxidative stabilization of synthetic fluids and vegetable oils. Synthetic Lubrication, 16(2), 157–181, 1999. 30. Rasberger, M., Oxidative degradation and stabilization of mineral oil based lubricants, in Chemistry and Technology of Lubricants, R.M. Mortier and S.T. Orzulik, Eds., Blackie and Son Ltd., Glasgow, pp. 83–123, 1997. 31. Chasan, D., in Oxidation Inhibition in Organic Materials, Vol. 1, CRC Press Inc., Boca Raton, FL, 1990. 32. Migdal, C., in Lubricant Additives: Chemistry and Applications, L.R. Rudnick, Ed., Marcel Dekker, New York, pp. 1–27, 2003. 33. Fox, N.J. and Stachowiak, G.W., J. Soc. Tribol. Lubr. Eng., 59, 15–20, 2003. 34. Chasan, D., Oxidative Stabiization of Natural Oils, Presented at STLE Annual Meeting, May 1994. 35. Chasan, D. and Wilson, P.R., Stabilized lubricant compositions, Eur. Pat. Appl. EP0721979 A2, 1996. 36. Honary. Lou A.T., An investigation of the use of soybean oil in hydraulic systems. Bioresource Technology, 56(1), 41–47, 1996. 37. Honary, L.A., An investigation of the use of soybean oil in hydraulic systems, Bioresour. Tech., 56, 41–47. 38. Adamczewska, J.Z. and Wilson, D., Development of ecologically responsive lubricants, J. Synth. Lubr., 14, 129–142, 1997. 39. Arnsek, A.; Vizintin, J., Lubricating properties of rapeseedbased oils, Synthetic Lubrication 16, 281–296, 1999. 40. Arnsek, A.; Vizintin, J., Scuffing load capacity of rapeseedbased oils, Lubrication Engineering, 55(8), 11–18, 1999. 41. Arnsek, A.; Vizintin, J., Pitting resistance of rapeseed based oils, Lubrication Engineering, 57, 17–21, 2001. 42. Erhan, S.Z. and Asadauskas, S., Lubricant base stocks from vegetable oils, Ind. Crops Prod., 11, 277–282, 2000. 43. Rhee, I. Evaluation of environmentally acceptable hydraulic fluids, NLGI, 60, 28–35, 1996. 44. Bisht, R.P.S., Sivasankaran, G.A., and Bhatia, V.K., Vegetable oils as lubricants and additives, J. Sci. Ind. Res., 48, 174–180, 1989. 45. Lavate, S., Environmetally friendly hydraulic fluids, in Bio-Based Industrial Fluids and Lubricants, Sevim Z. Erhan

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22

Chemically Functionalized Vegetable Oils Sevim Z. Erhan, Atanu Adhvaryu, and Brajendra K. Sharma CONTENTS 22.1 22.2

22.3

22.4

Introduction Chemistry 22.2.1 Reactions at the Carboxyl Groups of VOs 22.2.1.1 Transesterification 22.2.1.2 Synthesis of Fatty Amines 22.2.2 Reactions Involving the Hydrocarbon Chain in VOs Triglycerides 22.2.2.1 Hydrogenation 22.2.2.2 Oxidative Scission 22.2.2.3 Epoxidation 22.2.2.4 Carboxylation 22.2.2.5 Cyclization 22.2.2.6 Alkarylation 22.2.2.7 Acetylation 22.2.2.8 Olefin Metathesis 22.2.2.9 Catalytic Cracking 22.2.2.10 Other Reactions 22.2.2.11 Polymerization Physicochemical and Performance Properties 22.3.1 Physical Properties 22.3.1.1 Viscosity and VI 22.3.1.2 Low Temperature Fluidity 22.3.2 Performance Properties 22.3.2.1 Lubricity, EP and Antiwear Behavior 22.3.2.2 Energy Efficiency 22.3.2.3 Corrosion and Foaming 22.3.2.4 Solvency/Compatibility 22.3.3 Chemical Properties 22.3.3.1 Thermal and Oxidative Stability 22.3.3.2 Hydrolytic Stability 22.3.4 Environmental Testing 22.3.4.1 Biodegradability 22.3.4.2 Toxicity 22.3.4.3 Pollution 22.4.4.4 Handling and Storage Application Areas 22.4.1 Automotive Engine Oils (Engine Oils, Crankcase) 22.4.2 Industrial Oils 22.4.2.1 Hydraulic Fluids 22.4.2.2 Machine Tool Lubricants 22.4.2.3 Total Loss Lubricants 22.4.2.4 Greases

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22.4.2.5 Additives 22.4.2.6 Biodiesel 22.5 Manufacturers, Marketing and Economics 22.5.1 Manufacturers 22.5.2 Markets 22.5.3 Economics 22.6 Conclusion Acknowledgment References

22.1 INTRODUCTION The depletion in world petroleum reserves and uncertainty in petroleum supply due to political and economical reasons stimulated the search for alternative energy sources. In recent years, pollution and environmental health concerns have become a major debatable topic due to deliberate and accidental lubricant losses to environment including evaporation, leakages, and spills [1]. Thus, strict specifications on various environmental matters such as biodegradability, toxicity, occupational health and safety, and emissions have become mandatory in certain specific areas of applications. It has been recognized for many years that vegetable oils (VO) can be used as fuel and lubricants. The use of VO as fuel has been demonstrated in 1900 at the Paris exposition, where a diesel engine was run wholly on groundnut oil [2]. Vegetable oils are already in use as lubricants [3] due to their superior lubricity, good anticorrosion, better viscosity–temperature characteristics, and low evaporation loss in industrial applications such as rolling [4], cutting [5], drawing [6], and quenching operations either alone or in combination with mineral oils. Moreover, these oils are readily biodegradable and environmentally safe compared to mineral oil as it contains readily biodegradable constituents such as Fatty Acids (FAs). Using the EPA Shake Flask test, soybean oil (SBO) degrades within 7 days, while mineral oil takes 28 days [7]. Some other advantages of VO-based lubricants include their naturally renewable resource and no dependence on foreign oils. From the environmental point of view, their importance is evident especially in areas of total loss lubrication, military applications, and in outdoor activities such as forestry, mining, railroads, dredging, fishing, and agriculture hydraulic systems. However, extensive VO use is restricted due to poor cold flow behavior, low thermo-oxidative and hydrolytic stability, which can be mitigated by suitable modifications of the oil structure. Recent environmental awareness has shifted the world’s attention toward the application of VOs as biodegradable lubricants. Synthetic lubricant base oils offer improved stability and performance characteristics over refined petroleum oils, but at a price. Most of the biodegradable synthetic oils are chemical esters that offer superior thermal and oxidative stability [8,9]. Prices for these niche

Copyright 2006 by Taylor & Francis Group, LLC

products are higher than VOs and significantly higher than petroleum-based lubricants. Synthetic oils are partly derived from petroleum products and therefore are dependent on petroleum crude oils. VO based lubricants cannot replace all synthetic and petroleum based lubricants, but play an important role among the alternate energy sources and contribute to the goal of energy independence and security. Although the cost of VO based lubricants is higher than conventional mineral oil based lubricants, still environmental advantages in short, medium, and long range can balance the difference in cost. Moreover, choice of biobased lubricant contributes to the public image of the company (ISO 14000), and with it opens up the possibility of conquering new markets. Two possible avenues are available for an improved biobased base oil: • Genetically modified oils: Oleic acids are more ther-

mally stable than polyunsaturated fats, and therefore are highly desired components in VOs. DuPont has developed a biotech soybean that contains higher level of oleic acid (C18:1) (CM:N signify: M = no. of carbon atoms, N = no. of double bonds) called high-oleic SBO, while Monsanto launched high-oleic canola oil. Some other specialty canola oil products that Monsanto expects to market include high stearate oil for food applications, high myristate for soap and detergent manufacturing, and medium-chain FAs for lubricants, nutritional, and high energy food products. The detail about this option is covered in Chapter 23. • Chemical modification: Modification of the oil through chemical processing to improve oxidation stability and low temperature fluidity is still a subject under active investigation. Different modification routes are covered in this chapter. The above two options in combination with chemical additive offer the greatest opportunity for achieving the ultimate goal.

22.2 CHEMISTRY Soybean oil ranks first in worldwide production of VOs (29%) and represents a tremendous renewable resource. The United States production is 2.5 billion gallons/year,

TABLE 22.1 Chemical Composition of Oils (FA Profiles) 16:0 SBO Rapeseed oil Canola oil Peanut oil Sunflower Safflower Linseed Olive Coconut Palm oil Palm kernel

11.8 3.5 2.5 10 6 5 5 14 9 42 7

18:0

18:1

18:2

18:3

22:1

3.2 0.9 1.0 3 3 1 3 2 2 5 2

23.3 19.4 64.4 50 28 15 22 64 7 41 15

55.5 22.3 22.2 30 61 79 17 16 1 10 1

6.3 8.2 8.2 —

45.0 1.0

other

3a

52 2 72b 2c 70d

a 20:1 (3%); b 10:0 (7%), 12:0 (48%), 14:0 (17%); c 14:0 (2%); d 10:0 (5%), 12:0 (50%), 14:0 (15%).

Note: The column heading “M:N” signify: M = no. of carbon atoms, N = no. of double bonds. C18 : 1 = oleic acid; C18 : 2 = linoleic acid; C22 : 1 = erucic acid.

with over 6.0 billion gallons/year produced worldwide. Other VOs include canola, primarily produced in Canada, rapeseed in Europe, and sunflower, peanuts, cottonseed, coconut, palm fruits, palm kernels, linseed, castor beans, olives, sesame, corn, safflower, etc. Crude SBO has a viscosity close to that of mineral oil (29 cSt at 40◦ C), a high flash point (325◦ C) and a high viscosity index(VI) (246). All crude VOs contain some natural elements such as unsaponifiable matter, gummy, and waxy matter that may interfere with the stability, hydrocarbon solubility, chemical transformation reactions, and freezing point, and so forth. Therefore, a purification step is required to obtain refined VOs that are completely miscible with hexane. Refined VOs are largely glycerides of the FAs. However, to modify the FA chain of the oil, it is necessary to know the exact composition of these oils and their thermal and oxidative properties. The chemical composition of some of these VOs is shown in Table 22.1. It gives indications of likely characteristics of the products formed after chemical modification and the most likely transformations, which are required to improve the physicochemical and performance characteristics of these VO derivatives. The triacylglycerol structure form the backbone of most VOs and these are associated with different FA chains. It is therefore a complex association of different FA molecules attached to a single triglycerol structure that constitutes VO matrix (Figure 22.1). The presence of unsaturation in triacylglycerol molecule due to C=C from oleic, linoleic, and linolenic acid moeties functions as the active sites for various oxidation reactions. Saturated FAs have relatively high oxidation stability. SBO has more polyunsaturation (more C18:2 and

Copyright 2006 by Taylor & Francis Group, LLC

FIGURE 22.1 Typical triacylglycerol molecule

C18:3) as compared to canola and rapeseed oil. Therefore, SBO needs chemical modification to reduce unsaturation in triacylglycerol molecule and suitable additives to bring its performance equal to or better than other commercial VOs. More than 90% of chemical modifications have been those occurring at the FA carboxy groups, while less than 10% have involved reactions at FA hydrocarbon chain [10]. Without sacrificing favorable viscosity–temperature characteristics and lubricity, unsaturated VOs can be converted into thermo-oxidatively stable products by saturation of the carbon–carbon double bonds using alkylation, arylation, cyclization, hydrogenation, epoxidation, and other reactions. Chemical modifications at the carboxyl group of VOs include transesterification, hydrolysis, etc. The reactions at double bond and carboxyl position of VOs are discussed in detail.

22.2.1 Reactions at the Carboxyl Groups of VOs 22.2.1.1 Transesterification Neat VOs pose some problems when subjected to extended use in internal combustion engine. These problems are attributed to high viscosity, low volatility, and polyunsaturated character of neat VOs. These problems are substantially reduced, by subjecting the VOs to the process of transesterification. Transesterification is the process of using an alcohol (e.g., methanol or ethanol) in the presence of a catalyst, such as sodium hydroxide or potassium hydroxide, to chemically break the molecule of the raw VO into their methyl or ethyl esters with glycerol as a by-product. This process was conducted by scientists E. Duffy and J. Patrick as early as 1853 (Production, 1995). One of the first uses of transesterified VO was powering heavy duty vehicles in South Africa before World War II. The name “biodiesel” has been given to the transesterified VO to describe its use as a diesel fuel. The methyl ester of VO, or biodiesel, is very similar to diesel fuel. Its viscosity is only twice that of diesel fuel and its molecular weight is roughly one-third of VO. Most Diesel engines were designed to use highly lubricating, high sulfur content fuel. Recent environmental legislature has forced diesel fuel to contain only a minimum amount of sulfur for lubricating purposes. Thus, the slightly higher viscosity of biodiesel

is helpful and provides good lubrication to most Diesel motors. A large number of transesterifications have been reported with lower alcohols such as methanol, ethanol, and isopropanol to obtain esters of commercial applications for use as biodiesel, plasticizer solvent, cosmetic base fluids, and lubricants [11]. Few transesterification reactions are reported with higher alcohols C8 to C14, for use as lubricants. However, glycerol is not desired in triacylglycerol structure because of the presence of one H atom on the carbon atom in the β-position of ester groups; this make esters more susceptible to elimination reaction leading to subsequent degradation of the molecule. The low stability of glycerol β-carbon may be eliminated by transesterification using more resistant polyhydric alcohols with a neopentyl structure without hydrogen at β-carbon, such as isosorbitol or neopentylpolyols, including pentaerythritol (PE), trimethylolpropane (TMP), or neopentylglycol (NPG) (Figure 22.2) for utilizing the transesterified products as lubricant base material [12–15]. Sodium alkoxide of the corresponding alcohol acts as best catalysts for transesterification with yields of monoesters ranging from 80 to 90% (Figure 22.3). Linseed has been transesterified with polyethylene glycol (molecular weight 300) using Na2 CO3 as a catalyst at 210◦ C. Sodium can be used as catalyst instead of NaOH or Na2 CO3 . Sulfuric acid is used for ringopening reaction at the epoxy group in epoxidized soybean oil (ESBO) followed by transesterification at the ester group [16]. Calcium oxide and lead oxide are also effective catalysts in the transesterification of VOs with monoand polyhydric alcohols [17]. Lead oleate acts as catalyst in transesterification of VOs such as linseed oil, olive oil, coconut oil, and castor oil with PE [18]. Mn(OAc)2 catalyzes formation of esters of higher alcohols from VOs

at 220◦ C [19]. Some other catalyst systems are shown in Figure 22.3. Most of the esters of higher alcohols have been prepared in a two-step process. In the first step, VO is hydrolyzed to corresponding FAs by a variety of methods. Most common being hydrolysis by steam [20] in continuously operating reaction columns at 250◦ C and pressures between 2×106 and 6×106 Pa (20 to 60 bar). In the countercurrent flow method, the glycerol that is formed is extracted continuously from the equilibrium mixture using water, yielding 98% hydrolysis in a single pass, without any catalyst. Other methods use acid hydrolysis at elevated temperature with hydrochloric or sulfuric acid–sulfonic acid mixtures. Alkaline hydrolysis (saponification) of VOs yield alkali soaps and glycerol, and is now of minor importance. Currently, soaps are made by neutralization of the FAs [21]. The FAs are then esterified in the second step with corresponding alcohol using sodium alkoxide formed in situ and p-toluene sulfonic acid/sulfonic acids and cation exchange resins as catalysts. Simultaneous transesterification and saponification of castor oil has been utilized to prepare completely VO based greases [22]. The alkali used as a catalyst for transesterification reaction serves as a reactant for the saponification reaction. The use of appropriate proportions of oil, alcohol, and alkali will thus form grease with desired composition and properties. Various commercial processes for producing alkyl esters, useful in biofuels and lubricants, are available. The alkali catalyzed transesterification of VOs with methanol to give fatty acid methyl esters (FAME) and glycerol (Scheme 22.1) is likewise carried out in continuously operating reaction columns, at 240◦ C and 107 Pa (100 bar) [23]. Transesterification of glycerides or esterification of free FAs is conducted in a single critical phase medium

CH2OH CH3

C

CH2OH CH3

H3CCH2

CH2OH

CH2OH Trimethylol propane

Neopentylglycol

CH2OH HOH2C

C

CH2OH CH2OH

CH2OH Pentaerythritol

HO

C

CH2OH

H2 C

O

H2 C

CH2OH

C CH2OH

Dipentaerythritol

FIGURE 22.2 Examples of polyols used for transesterified vegetable oil based lubricants

Copyright 2006 by Taylor & Francis Group, LLC

CH2OH

C

CH2OH

for increased reaction rates, decreased loss of catalyst or catalyst activity, and improved overall yield of the desired product [24]. In this method, glycerides or free FAs in VOs and restaurant grease are mixed with an alcohol stream or water stream and dissolved in a critical fluid medium, reacting the mixture in a reactor over either a solid or liquid acidic or basic catalyst. The product stream is separated from the critical fluid medium in a separator, where the critical fluid medium can be recycled to the process. Transesterification reactions of the partially hydrogenated and cyclized ester VOs are important because these reactions yield monoesters of VOs with better thermal stability and lower freezing points than the VOs as such. The glycerol obtained as a by-product, commands as much market value or more than the monohydric alcohols used for transesterification. Therefore, transesterification leads to value addition without much cost escalation. 22.2.1.2 Synthesis of fatty amines This class of compounds has an importance in biobased antioxidant/antiwear additives in lubricant formulations. The reaction proceeds by reacting FAs/VOs with ammonia, which gives amides and nitriles as intermediates. The nitriles are then hydrogenated with a nickel catalyst to the fatty amines. Type of fatty amine (primary, secondary, or Vegetable oils

KOH

Ethyl esters

(CH3ONa)

Methyl esters

KOH NPG esters KOH

H2O

pTSA Fatty acids

TMP esters Isopropyl esters

SnO

2-Ethylhexyl esters

SnO

Pentaerythritol esters

FIGURE 22.3 Different transesterification routes

tertiary) depends on the addition of ammonia or secondary amine during the hydrogenation [25–27].

22.2.2

Reactions Involving the Hydrocarbon Chain in VOs Triglycerides

The possible reactions involving the alkyl chains of the acyl groups in triacylglycerols is shown in Figure 22.4. Using these reactions, the most reactive double bonds can be eliminated leading to products with better oxidation stabilities. Most of these chemical transformations occur at the site of unsaturation because of high reactivity of double bonds. 22.2.2.1 Hydrogenation Some VOs such as SBO, linseed oil, and rapeseed oil have a high degree of unsaturation depending on the amount of linoleic and linolenic acid derivatives. As a result, the thermo-oxidative stability of these oils is poor and leads to polymerization resulting in gummy and resinous products at elevated temperatures. Their use as lubricants without reduction of unsaturation can cause deposit formation, corrosive action, and damage with relatively short useful service life. One of the several ways to reduce unsaturation is to partially hydrogenate and cyclize these VOs to improve their service lives without affecting the freezing points to a large extent. Complete hydrogenation used in industry with nickel catalyst is not desired, as it affects the low temperature properties. The problem of achieving selective hydrogenation has so far been only partly solved. An example is the conversion of linolenic and linoleic to oleic acid without unwanted positional or cis–trans isomerizations occurring at the same time. Even the use of heterogeneous metal catalysts, which are preferred in technical processes, have not yet led to satisfactory results [28]. Partial hydrogenation of cottonseed oil has been demonstrated using chromium-modified nickel catalyst [29]. Chromia has been found to suppress the stearate formation completely, although it retarded the overall hydrogenation activity of the nickel catalyst. Homogeneous catalysts based on complexes of precious metals could offer a solution to the problem, if a method could be found for

O H2C

O

C

R

HC

O

O C

R

H2C

O

C

R

Catalyst +

O

SCHEME 22.1 Transesterification with methanol

Copyright 2006 by Taylor & Francis Group, LLC

3CH3OH

3R - CO - OCH3

+

H2C

OH

HC

OH

H2C

OH

recovering and recycling these expensive catalysts. Possibilities that have been investigated are immobilization of the homogeneous catalyst on a support or the use of microdispersed catalyst systems such as colloids, clusters, or soluble polymer chelates; the last of these seems to offer good prospects [30]. Biotechnology may provide a solution to this problem. Catalytic hydrotreatment of VOs has been tested on a pilot scale to convert many types of biomass oil into a 60 to 90 cetane number middle distillate [31]. This bio-cetane product can be used neat as a diesel fuel or as a blending agent for ordinary diesel fuel. Laboratory emission testing of a transit bus has indicated that significantly lower emissions of particulates, carbon monoxide, and hydrocarbons can be achieved. A 10-month on-road test of six postal delivery vans has shown that the engine fuel economy was greatly improved by a blend of petrodiesel and the bio-cetane product. The Saskatchewan Research Council (SRC), in cooperation with Natural Resources, Canada and Agriculture and Agri-Food Canada, investigated the

Hydrogenation Olefin metathesis

Carboxylation

Epoxidation

Vegetable Oils/ Triglyceride

Oxidative scission

Alkylarylation

Cyclization Acetylation

FIGURE 22.4 Chemical modifications of hydrocarbon chain in triglycerides

use of conventional refinery technology to convert VOs into a product resembling diesel fuel [32]. SRC found that the use of a medium severity refinery hydroprocess yields a product (supercetane) in the diesel boiling range with a high cetane value (55 to 90). Preliminary engine testing by ORTECH (Canadian ORTECH Environmental Inc.) has shown that the impact of the “supercetane”/diesel mixture (green diesel) on engine emissions is similar to the impact of cetane enhancement via a nitrate additive when added to conventional diesel fuel. Advantages of hydroprocessing over esterification in the Canadian context include lower processing cost, compatibility with existing infrastructure, engines and fuel standards, and feedstock flexibility. In cooperation with a commercialization partner, Arbokem Inc., pilot testing of the hydroprocess was done and proven successful. A fleet demonstration and evaluation is currently underway.

22.2.2.2 Oxidative scission The double bond at unsaturation sites of VOs provides a point of attack for oxidative scission. Ozonides are formed initially in the ozonolysis reaction, which is a highly selective reaction [33] as shown in Scheme 22.2. These can undergo scission either reductively to mono- and dialdehydes or oxidatively to mono- and dicarboxylic acids. By the oxidative route, ester of oleic acid gives nonanoic acid (pelargonic acid) and ester of nonane-1,9-dioic acid (azelaic acid) (Scheme 22.2) [34]. The later can be converted to diester after esterification. This kind of oxidative scission in triacylglycerol molecule can improve their thermooxidative stability by removing the sites of unsaturation. Lubricants with optimal performance can be obtained by an alteration of the hydrocarbon chain (of transesterified product of more resistant polyols such as PE, TMP, or NPG) using ozonolysis reaction leading to short esters after combination with an alcohol [35]. The linear diacid portion of the diester contributes to good VI, while the branched ends give the lubricant a good pour point (PP). The only disadvantage of diesters is their low molecular weight, which makes them an attractive solvent because of their high polarity. It can be blended with VOs/CMVOs to make

H3C-(CH2)7-CH=CH-(CH2)7-COOR O3

H3C-(CH2)7-COOH

O (CH2)7–COOR

H3C–(H2C)7

+ HOOC-(CH2)7-COOR

O

O

SCHEME 22.2 Ozonolysis of unsaturated FA (Oleic) ester

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O H2C

O

C

HC

O

O C

H2C

O

C O

[H+]

H2O2/HCOOH

O O H2C

O

C

HC

O

O C

H2C

O

C

O

O

O

O

O

O

SCHEME 22.3 Epoxidation of a triacylglycerol molecule

different viscosity blends. Another solution is the esterification of these dicarboxylic acids with polyols, which can increase the viscosity of these products and as well have high shear stability [14]. Industrial application of ozonolysis is scarce, with only one reported for large scale production of azelaic acid from oleic acid [36]. Wider use of ozonolysis is still hindered by technical and economic problems. The process involving ruthenium complex catalyzed direct oxidation methods offer another possible approach to this problem [37]. 22.2.2.3 Epoxidation Epoxidation is one of the most convenient methods to improve the poor thermo-oxidative stability caused by the presence of unsaturated double bonds in VOs. Peracids such as performic acid or peracetic acid are the most common reagents, which results in the formation of oxirane rings at double bond sites in triacylglycerol molecule as shown in Scheme 22.3. Peracids are usually formed in situ with 50 to 60% hydrogen peroxide and the corresponding acid. Epoxidation is carried out at 40 to 80◦ C under various other reaction conditions. Approximately 15 to 45% hydroxyl acids are also formed as by-products depending upon the concentration of hydrogen peroxide. Extent of the reaction depends upon the temperature and time. The ratio of acid to hydrogen peroxide varies from 1:0.5 to 2. Various catalysts such as zeolites, Amberlite 120, anhydrous Na2 CO3 , (NH4 )2 SO4 , and SnCl2 have been used in increasing the extent of epoxidation. Acetylated castor oil can be epoxidized with acetic acid–acetic anhydride

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and hydrogen peroxide with sodium hydrogen phosphate as catalyst [38]. A very mild and effective epoxidation procedure can be performed utilizing methyltrioxorhenium (VII) and pyridine as the catalyst and H2 O2 as the oxidant with excellent yields of ESBO [39]. Stepwise oxidation in polyunsaturated esters can be affected by using H2 O2 and phthalic anhydride [40]. Continuous process has been developed for epoxidation of VOs using a battery of reactors in which hydrogen peroxide, acetic acid, and sulfuric acid are contacted with oil phase and aqueous phase of reactor in a cascade counter current system [41]. Metal (Ba and Cd) laurates can improve the stability of the epoxy derivatives. Epoxidized VOs show improved performance over VOs and some genetically modified oils in certain high temperature lubricant applications [42]. They have better thermal and oxidation stability compared to VOs and is largely due to the elimination of polyunsaturations and bis-allylic protons from VO triacylglycerol molecules. The oxirane groups in epoxidized VOs react readily with nucleophilic reagents. Possible reactions during epoxy ring opening leads to a large number of products (Table 22.2), which are interesting from the point of view of biodegradable lubricant formulations. One such example is conversion of epoxidized VOs to diesters (C2 to C10) using either a one- or two-step reaction with Boron trifluoride etherate or other suitable catalyst in an anhydrous solvent at 50◦ C for 3 h [43]. In the two-step modification, the epoxidized VO is first hydrolyzed to a dihydroxy intermediate, which is then reacted with the appropriate anhydride to yield the diester. The ester branching groups (R) not only serve to eliminate the sites of unsaturation, but

TABLE 22.2 Reactions Possible with Epoxidized Vegetable Oils H C

H C +

H C

X

OH

HX

O

Name

HX

H2

H C

Alcohols

Partial structure H H C C H OH

H2O

Diols

H H C C H O OH

ROH

Ether (or alkoxy) alcohols

H H C C H O OR

RCOOH

Ester alcohols or Hydroxy esters

H H C C H O OCOR

(RCO)2O

Diesters

H H C C ROCO OCOR

RCONH2

Hydroxy N-alkylamides

H H C C H O NHCOR

H2S

Hydroxy mercaptans

H H C C H O SH

R2NH

Hydroxy amines or Amino alcohols

H H C C H O NR2

HCN

Hydroxy nitriles

H H C C H O CN

HCl

Chlorohydrins

H H C C H O CI

NaHSO3

Hydroxy sodium sulfonates

H H C C H O SO3Na

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also impose spacing from other such molecules, thereby interfering with the formation of macro crystalline structures. The resultant modified VOs are thus characterized by enhanced fluidity. Triacylglycerols that are merely hydrogenated for the purpose of eliminating polyunsaturation in the molecule will tend to harden at room temperature due to alignment and stacking of adjacent molecules. For this reason, it is important that there be at least one site of unsaturation available for derivatization that will yield two branching sites. The ester side chains that are most effective for imposing the desired molecular spacing and for imparting the most desired PP properties are those having a chain length of at least C6. However, the PP and other functional properties of the derivatized oils are not significantly increased when the C7 to C10 branching chains are used. The resulting diesters are environmentally-friendly, have superior performance properties, and utility as hydraulic fluids, metalworking fluids, crankcase oils, drilling fluids, two-cycle engine oils, wear resistant fluids, greases, and the like.

22.2.2.4 Carboxylation Three types of carbon monoxide addition reaction at double bond sites in VOs are hydroformylation (oxosynthesis), hydrocarboxylation (Reppe reaction) [44,45], and the Koch synthesis as shown in Scheme 22.4 [46]. The formyl group obtained at unsaturation site in VOs after hydroformylation using transition metal complexes, can either be hydrogenated to give a hydroxyl group, or oxidized to a carboxy group. Hydroformylation and hydrocarboxylation are catalyzed by CO2 (CO)8 and carbonyl hydrides of metals of the eights subgroup. Hydrocarboxylation and Koch reaction both form esters at unsaturation site. Strong acids are used as catalyst in Koch synthesis, resulting in the formation of carbonium ions as the primary reaction products. The carbon chain undergoes rearrangement as a result of carbonium ion isomerization, yielding a mixture

(a)

H C

(b)

H C

H C H C

+

of isomers with high proportion of branched dicarboxylic esters [46].

22.2.2.5 Cyclization Another option to eliminate unsaturation is cyclization at unsaturation sites. Alkali catalyzed cyclization of linseed oil results in thermal ring closure leading to the formation of cis-monocyclic and some bicyclic compounds that have indaryl structure. Cyclization with Pd/C or Ni catalyst results in the formation of aromatic and monoenoic FAs [47]. The formation of aromatic cyclized structure is favored by low hydrogen supply, high temperature, and presence of sulfided catalysts [48]. Cis-configuration of fatty oils are converted into more thermo-oxidatively stable trans-configuration by hydrogenation with nickel sulfide and alumina as catalyst at 200◦ C and 20 atm pressure [49]. Dimerization by Diels–Alder reaction leads to the formation of cyclic structures. Addition reactions of isolated and conjugated double bond systems are often used for introducing ring or alkyl branching into the VO structure. Unsaturated fatty ester with two double bonds, first isomerize to a conjugated fatty ester and then undergo Diels–Alder reaction with appropriately substituted dienophiles. Thus isomerized linoleic ester, at temperatures above 100◦ C, forms adducts with maleic anhydride, fumaric acid, acrylic acid, and other dienophiles with activated double bonds as shown in Scheme 22.5 [50,51]. In order to synthesize Diels–Alder adducts, the conjugated double bonds must be in the trans-trans form. The desired configuration of the double bonds can be induced by means of an isomerization catalyst such as iodine or sulfur. This reaction results in the formation of cyclohexene derivatives. These adducts on appropriate hydrogenation give saturated cyclohexane ring derivatives of polycarboxylic acids, which on further esterification can give highly stable derivatives with low freezing points and relatively high viscosity indices. If the

CO + RO H

H2SO4 Co2(CO)8

+

CO + RO H

H2 C

H C COOR

O2 (c)

H C

H C

Where R=H, alkyl

+

CO + H2

Co2(CO)8

H2 C

H C CHO

SCHEME 22.4 Production of esters by carbonylation reaction. A: Koch reaction; B: hydrocarboxylation; and C: hydroformylation with oxidation

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cis cis H3C-(CH2)4-CH=CH-CH2-CH=CH-(CH2)7-COOR

H3C-(CH2)7-CH=CH-(CH2)7-COOR +

CH2=CH-COOH

H3C-(H2C)x

OH

Arylation

trans trans H3C-(CH2)x-CH=CH-CH=CH-(CH2)y-COOR

H3C-(H2C)7-H2C

H C

(CH2)7-COOR

(CH2)y-COOR OH

SCHEME 22.6 Addition of phenol to FA ester

HOOC x + y = 12

SCHEME 22.5 Acrylic adduct as a result of Diels–Alder reaction of isomerized linoleic ester and acrylic acid

viscosity of these derivatives is properly controlled, they can give hydrocarbon soluble derivatives in the lubricating oil range. Most of the Diels–Alder reactions have been carried out with highly unsaturated linseed oil, methyl esters, SBO, rapeseed oil, sunflower oil, and castor oil to give products that are base materials for alkyl resins, plasticizers, and stabilizers [52,53]. Cyclization to form cyclohexene ring takes place when maleic anhydride is added to sunflower oil FA methyl esters in the presence of silica–alumina support impregnated with phosphoric acid [54]. 22.2.2.6 Alkarylation Friedel Craft addition of phenols and alkylaromatics to the double bonds of VOs and FA ester to obtain alkylaryl derivatives result in improved thermo-oxidative stability and decreased freezing points of the resulting oil. VI of the oils is not greatly affected. This addition reaction also increases the viscosity of the FA monoesters. The possibility of side reactions such as polymerization of the acid and oils to dimer and trimer derivatives, limits the utility of Friedel Craft alkylarylation. The effects are more pronounced in castor oil and polyunsaturated monoesters while using anhydrous aluminium chloride as catalyst. Catalysts such as HF, BF3 , FeCl3 , and ZnCl2 minimize these polymerization side reactions. Alkanes add to olefins at 400◦ C in a thermally initiated free radical reaction. For example, addition of cyclohexane to 1-octene or to acrylic acid esters results in cyclohexane derivative [55]. Addition of toluene, xylene, anisole, naphthalene and phenol to castor oil, erucic acid, and FAs of tall oil using stannic chloride in the ratio of 1:1 with esters yield 40% phenyl derivatives of the esters (Scheme 22.6). Ethyl iodide on heating with linseed oil and refluxing with sodium ethylate in ethanol at 90◦ C gives an ethylated linseed oil derivative in 10 to

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15% yield. Compounds with substituted benzol ring have been added to double bonds of alkyl ester of VOs in the presence of cation exchange resin as catalyst at 120◦ C for 9 h, to form aryl derivative of alkyl esters [56]. The reaction is useful in partially saturating the double bonds in polyunsaturated VOs to improve stability and as well help in lowering the PP. VOs have been subjected to alkylation with a variety of organic groups with C1 to C8 carbon atoms, using an anhydrous AlCl3 catalyst, at 60 to 80◦ C; followed by esterification using alcohols with C1 to C10 carbon atoms with a sulfuric acid catalyst under reflux condition [57]. The products are obtained with wide viscosity range, have high VI, flash points, and low volatility. Such alkylated or arylated VOs can act as pour point depressants (PPDs), wax crystal modifiers, friction reducers, and flow improvers. If highly polar phenols are taken as alkylating groups, the resultant molecules will show oxidation inhibition activity. Amines, amides, salicylates, and the like can replace phenol. Color preservatives, low temperature oxidation inhibitors, rust preventives, and high temperature oxidation inhibitors can be prepared in increasing order of polarity of alkylating groups. 22.2.2.7 Acetylation This reaction has been used for natural VOs containing a hydroxy group or chemically modified VOs (CMVOs) with a hydroxyl group in their structure. The acetylation is accompanied by using acetic anhydride, acetic acid, and acetyl chloride as the reagents. The hydroxyl group present in the castor oil is converted into an acetate giving rise to a hydrocarbon soluble acetate glyceride. Acetylation of hydroxyl FA ester yield diesters of the octadecanoic FA (Scheme 22.7). These esters have high VI and low freezing points below −30 or −40◦ C. The thermo-oxidative stability is poor and can be improved by alkylarylation or some other method to saturate double bonds to yield a product of higher stability. Castor oil has been acetylated in quantitative yield with acetic anhydride using sulfuric acid as

H3C

H (CH2)9 C

(CH2)6-COOR

(CH2)6 COOR

H

OH

(CH2)6-COOR

H

X

+

Acetylation

CH3COOH/CH3COCl

H3C-(H2C)7

H3C-(H2C)7

X

SCHEME 22.9 Ene reaction of oleic ester H3C

H (CH2)9 C

(CH2)6COOR

OCOC H3

SCHEME 22.7 Acetylation of FA ester H3C-(CH2)7-CH=CH-(CH2)7-COOR + H2C=CH2 Catalyst H3C-(CH2)7-CH=CH2

+

H2C=CH-(CH2)7-COOR

SCHEME 22.8 Metathesis of oleic ester and ethane

catalyst. Acetylation with acetic acid gives a product containing free FA. Catalysts such as p-toluene sulfonic acid can be used, but they produce more free FAs that result from hydrolysis of castor oil. The hydrolysis can be reduced to minimum by continuous removal of water [58]. 22.2.2.8 Olefin metathesis The conversion of all the unsaturated acyls to saturated acyls in triacylglycerol will lead to solid products. The solution for this is to get saturated acyls of lower carbon number (C8 to C10). This can be obtained by olefin metathesis reaction followed by hydrogenation. Olefin metathesis is a bond rearrangement reaction catalyzed by certain transition metal (molybdenum, tungsten, and rhenium) compounds [59]. For example, cometathesis of oleic ester with short chain olefins such as ethene results in synthesis of unsaturated FA ester with chain lengths C10 and the corresponding olefin (Scheme 22.8). These metathesized VOs can be completely hydrogenated to the one with saturated acyl chain length of approx C10, in presence of 10% palladium on carbon in dichloromethane, or epoxidized to remove unsaturation [39]. Industrial application of this reaction path is hindered by the poor efficiency of the expensive catalyst. 22.2.2.9 Catalytic cracking The VOs are pretreated by catalytic cracking, whereby resinous and mucilaginous substances are converted to

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low-chain and gaseous hydrocarbons. The removal of resinous and mucilaginous substances is carried out in a cracking reactor at 42 to 220◦ C with a preheated catalyst bed, which consists of SiO2 , kaolin, and aluminum silicate serial connected in the direction of flow [60]. The residual gases are supplied to the intake air of an engine via heated storage tank. The pretreated oil is fed through a reactor containing an Sn alloy with above 90% Sn for metalation of the charge, and then a surfactant 0.01 to 1% is added to prevent separation of soaps and water in the injection pump. The product is filtered at above 30◦ C and forwarded to the engine of a power plant. The service life of engines and injection pumps is improved by pretreatment of the VO and fats. The alternative fuel is suitable for diesel engines of block-type thermal power stations.

22.2.2.10 Other reactions Dimerization by radical transfer polymerization accompanied by the transfer of hydrogen yields acyclic structures. Unsaturated fatty esters such as oleic acid can undergo an ene reaction at temperatures above 220◦ C with maleic anhydride or other compounds having activated double bonds as shown in Scheme 22.9 [61]. This reaction is suitable for introducing side chains containing heteroatom functional groups such as –COOR or –CN into unsaturated fatty ester with retention of double bond shifted across a carbon atom. Very few examples are known for use in VOs modification. The following reactions are a few examples, to indicate the enormous potential of VOs as a base material for synthesis of biobased additives. VOs can easily be chlorinated (up to 60%); beyond this they become too viscous and finally solidify [57]. Chlorination takes place by addition at double bonds and substitution at the end or middle of chain (Scheme 22.10). Monochlorination corresponds to about 10 to 12% chlorine. These chlorinated VOs can be used as EP additives and metal passivators in gear oils, straight metal cutting oils, and rust preventive formulations. The sulfonation of arylated VOs followed by careful manipulation of metal soap may lead to formation of excellent oxidation inhibitors, detergency additives, and dispersants (Figure 22.5). The sodium salt of this will be mild rust preventive, while the calcium salt will

H3C-(CH2)7-CH=CH-(CH2)7-COOR+Cl2 Chlorination by addition H3C-(CH2)7-CH-CH-(CH2)7-COOR Cl Cl + Cl2

Chlorination by substitution

Cl-H2C-(CH2)7-CH-CH-(CH2)7-COOR Cl Cl

SCHEME 22.10 Chlorination of FA ester H3C-(CH2)7-CH-CH2-(CH2)7-COOR

H3C-(CH2)7-CH-CH2-(CH2)7-COOR

SO3

HSO3 Sulfonic acid ester

Ca SO3 Calcium sulfonate

H3C-(CH2)7-CH-CH2-(CH2)7-COOR

FIGURE 22.5 Sulfonated product and calcium sulfonate

H3C-(CH2)15-CH2-COOR

+SO3/NaOH

H3C-(CH2)15-CH-COOR SO3Na +

(H3C-(CH2)15-CH-COONa+H3C-(CH2)15-CH2-COONa) SO3Na

SCHEME 22.11 Sulfoxidation of FA methyl ester

be high temperature antioxidants, detergents, and dispersants. Ashless products could be prepared by neutralizing the sulfonic acid with ammonia, triethanolamine, or other alkylamine, giving a wide variation in performance [57]. The ionic sulfonation of FA methyl esters using SO3 , lead to α-sulfonated esters, also called ester sulfonates (Scheme 22.11) [62]. They represent a surfactant class alternative to petrochemical based alkylbenzene sulfonate. Sulfurization results in saturation of double bonds and cross-linking (Scheme 22.12). Controlled sulfurization (S content 3 to 13%) can produce metal passivators, EP additives, and oiliness additives [57]. Sulfur could

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also be introduced as mercaptans or thio-alcohols to give thioesters, which could be then converted to disulfides (Scheme 22.12). These compounds have excellent EP and detergency characteristics. Oil-compatible phosphates (Figure 22.6) and phosphonates are well known for delivering excellent antiwear properties, and are used as EP agents and carbon dispersants. Phosphonates and phosphides can be prepared similarly; however, these do not have many functional applications [57]. The current area of interest is multifunctional additives, that is, compounds that incorporate all the functional groups in a multicomponent additive package. Every functional group should be in the right proportion and in right place. VOs can be used as base structure for such compounds, and one such derivative Zinc dialkyl dithiophosphate (ZDDP) (Figure 22.7) has been used extensively as an EP, detergent, and dispersant additives in engine oils. In this additive, the phosphate group provides detergency and dispersancy, sulfur gives EP characteristics, and zinc provides metal passivation and galvanization. Solubility in base oil and an antioxidant character could be introduced by incorporating Ca and a long-chain FA ester. VOs can be directly used as base material for a variety of multifunctional additives that could be designed based on the proper positioning of S, P, HSO3 , S2 , and metals such as Na, K, Ca, Ba, Zn, Ni, Mn, and Mg [57]. Specific substitution at the end carbon atom can be achieved by hydrozirconation [63]. In this reaction, zirconium hydrides in the form of complexes are added at the double bond position of unsaturated FAs, and then by a repeated process of elimination and reattachment of the zirconium hydride, the zirconium substituent migrates to the ω position where it can be replaced by any desired electrophilic reagent [64]. A cetane improver for diesel fuel consists of nitrated C1 to C4 FA esters derived from naturally occurring triglycerides, and is made by hydration of at least one double bond of the FA to form secondary alcohols, which are subsequently nitrated [65]. The unsaturated fatty esters are typically first epoxidized and then subjected to ringopening nitration to form C1 to C4 fatty esters with gem-dinitrate esters (Scheme 22.13). The process can include transesterification of VOs. When the product is added to a diesel fuel, the cetane can be improved by 90% lubricity and 50% detergency.

22.2.2.11 Polymerization The most reactive double bond can be eliminated by oxidation, polymerization, or oligomerization, resulting in lubricating base oils with different viscosities. Excessive branching of chains may decrease biodegradability and increase acidity.

H3C-(CH2)7-CH-CH-(CH2)7-COOR Sulfurization

S

H3C-(CH2)7-CH=CH-(CH2)7-COOR

S

H3C-(CH2)7-CH-CH-(CH2)7-COOR (Sulfurized fatty acid ester)

RS H H3C-(CH2)7-CH=CH-(CH2)7-COOH

H3C-(CH2)7-CH=CH-(CH2)7-CO-SR (Thioester)

H3C-(CH2)7-CH=CH-(CH2)7-CO-S-SR (Disulfide)

SCHEME 22.12 Reaction of FA ester with sulfur and thiol

H3C-(CH2)7-CH2-CH-(CH2)7-COOR H3C-(CH2)7-CH2-CH-(CH2)7-COOR

O HO

O HO

P

O

O

OH

O

P

OH

H3C-(CH2)7-CH2-CH-(CH2)7-CO-O

P

O

OH Monophosphate fatty acid ester

Dialkyl (fatty acid) diphosphate ester

FIGURE 22.6 Monophosphate and diphosphate vegetable oil esters

An interesting group of compounds is the estolides, which are the products of the inner esterification of unsaturated FAs when the carboxylic acid group of one acid is attached to the unsaturated carbon of another FA through an acid catalyzed process as shown in Scheme 22.14 [66,67]. Even a saturated FA can form an ester link with the unsaturated chain of other FAs. Polyestolides are formed by adding more FAs to the existing estolide unit. Because of elimination of unsaturation with more robust secondary ester linkage, the estolides have high VI, good biodegradability, good oxidation stability, superior low temperature properties, and are quite stable at temperatures up to 250◦ C even when exposed to air [68]. Oleic estolide esters have the lowest melting point (−31◦ C) of meadowfoam, crambe, and oleic derivatives. 2-ethylhexyl and C18-Guerbet esters of oleic estolides were found to have melting points of −34 and −43◦ C [69]. The extent of oligomerization (estolide number, EN) played a crucial role in the PP and viscosity. Higher EN gives higher PPs (e.g., EN of 2.96 has a PP of 0◦ C, EN of 1.1 has a PP of −27◦ C). Viscosities increase exponentially with increasing oligomerization. The estolides can be potentially used as base fluids in lubricants, greases, plastics, inks, cosmetics, and surfactants [70].

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R1O

S P

R2 O

OR4

S P

S

Zn

S

OR3

FIGURE 22.7 ZDDP. R1 to R4 are different alkyl groups of 3 to 12 carbons

Vegetable oils have been heat-bodied (thermal process) to improve their characteristics. Heat bodying is usually carried out in metal (copper, monel, and stainless steel) kettles at a temperature range of 232 to 330◦ C in an inert atmosphere (to prevent discoloration) [71]. At the temperature of heat bodying, the double bond migrates and conjugated dienes are formed, which is a reactive form for heat bodying. These conjugated dienes add readily to active double bonds to form a six-membered ring containing one double bond, which can further add to a conjugated group to form a second ring (Scheme 22.15). This ring formation leads to a bond between two triacylglycerols and results in the formation of bigger molecules as more and more triacylglycerols combine. This polymerization process often leads to an increase in oil viscosity.

H C

H C +

H C

H+

H C

H C

(CH3CO)2O

O+ H

O

H C

HNO3

ONO2OH Nitrato alcohol

HNO3 (CH3CO)2O H C

H C

ONO2 ONO2 Dinitrate

SCHEME 22.13 Nitration of epoxidized FA esters O OH Oleic acid H2SO4(65%) or p-Toluene sulfonic (45%) O O

O OH

Monoestolide O OH HClO4 (76%) O O

O O n

O OH

Estolide (n = 0 – 10)

SCHEME 22.14 Reaction for the formation of oleic estolides

Isomerization, intra- and intermolecular bond formations during heat bodying are crucial in designing products with appropriate characteristics. It has been found that thermal polymerization of VOs could be activated at lower temperatures (99 and 161◦ C compared to 232 and 330◦ C) under a dry-air purge in the presence of metal catalysts [72,73]. These heat-bodied oils are potential candidates for elevator fluids, hydraulic fluids, gear oils, and the like.

22.3 PHYSICOCHEMICAL AND PERFORMANCE PROPERTIES The main function of lubricants is to minimize friction, wear, corrosion, and deposit formation in various mechanical systems during operation. Thus, the quality of lubricant depends upon various physicochemical properties such as

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viscosity, flow behavior, lubricity, thermo-oxidative stability, hydrolytic stability, and solvency for additives. Base fluids usually comprise more than 80% of lubricant formulation and therefore control the physical properties of oil. VOs clearly exceed the functional properties of mineral oils in lubricity, volatility, viscosity–temperature characteristics, among others. On the other hand, parameters such as antiwear protection, load carrying capacity, corrosion prevention, foaming, demulsification are either similar to mineral oils or may be improved with suitable additive formulation [74]. The following characteristics are also considered critical depending on their intended applications: cleanliness, compatibility with other functional fluids (polyalphaolefin (PAO)/mineral oil/synthetic esters), homogeneity during long-term storage, hydrolytic stability, acidity, volatility, and elastomer compatibility, among others. It is a well-known fact that oxidative stability of VOs depend on their FA composition. More unsaturation

cis

cis

H3C-(CH2)4-CH=CH-CH2-CH=CH-(CH2)7-COOR trans H H C C

trans H C +

H C H C

H C

+

H C

H C

H C

H C

SCHEME 22.15 Formation of ring structures during heat bodying

sites make the chain, less stable (Table 22.3). Fully saturated FAs freeze most easily, and limit the low temperature capabilities of the oil. The diversification of FAs (length and unsaturation of the chain) and polyols allows many transesterified products to be obtained with suitable properties. Table 22.3 shows how length, branching, and unsaturation affect different properties. Another way of explaining this structure–property relationship of VO based lubricants is using the following approach: VO based lubricants and additives have similar structures. Both can be represented by a common basic chemical structures “R-P”, where “R” represents a nonpolar organic group, generally linear, and “P” represents a short and relatively polar group [57]. The organic group “R” determines the size and shape of the molecule and physical properties such as viscosity, density, VI, volatility, and freezing point. This also determines the solubility of the molecule in various liquids, particularly in those having similar molecular size and chemical structure. Any chemical modification made in “R” group will affect the above properties. The polar group “P” induces electronegativity in the molecule and determines the interaction of the molecule with other molecules, such as electropositive metal surfaces, and the interaction between similar molecules adsorbed onto colloidal particles, or relatively nonpolar wax crystals. In “R–P” structure, if the “P” group is slightly polar like amine, amide, sulfonate, etc., it can act as a detergent-dispersant additive. If the “P” is strongly polar in “R–P” structure and forms a strong bond with an electropositive metal surface, then it can act as a typical EP additive. Chemical modification of “P” group to a lesspolar group (e.g., ester of long chain or bulky branched alcohol) will make “R–P” structure function as lubricant,

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while to a more polar group (e.g., amine, amide, sulfonate) will help “R–P” structure function as additive.

22.3.1 Physical Properties 22.3.1.1 Viscosity and VI The viscometric behavior of fluids is characterized by viscosity, VI, low temperature fluidity, and compressibility. The viscosity–temperature dependence of CMVOs is more favorable, with the VI approaching 200. The production of lubricants over a wide range of viscosity is also possible with different alcohols and polyols, while maintaining a high VI (Table 22.4). CMVOs are superior to mineral oils as they would exhibit advantages with regard to fluidity in a fairly wide range of temperatures (VI in Table 22.4). Other reactions such as oxidation, polymerization, or oligomerization also enable the production of lubricants with wide viscosity range (10 to 10,000 cSt at 40◦ C). Besides the oxidation and oligomerization, an increase in viscosity can also be achieved by changing the chain length of the acyls and through branching. Viscosity increases with increase in acyl chain length. In isolated acyls, branching results in a viscosity decrease [16]; however, viscosity increases if cross-linking occurs in branched acyls. Cross-linking may occur via carbon, ether, or sulfide bonds. Viscosity also increases on increasing the molecular weight and chain length of the alcohol, as shown in Table 22.4 for methyl, ethyl, isopropyl, and 2-ethylhexyl esters of crambe oil. Viscosity of CMVO can be lowered by blending with biodegradable synthetic fluids such as adipates, oleates, PAOs, and mineral oils for desired applications [75].

TABLE 22.3 Effect of FA Unsaturation, Chain Length and Branching on Properties of Base Fluids Lubricity

VI

Low temperature fluidity

Oxidative stability

++ −− −

+ −− ±

− + +

− + −−

Chain length Chain branching Unsaturation

Volatility + − ±

++ very positive effect; + positive effect; ± without effect; − negative effect; −− very negative effect.

TABLE 22.4 Physical Properties of Esters

TABLE 22.5 PPs of SBO Chemical Modifications

Viscosity at 40◦ C (cSt)

Viscosity at 100◦ C (cSt)

VI

◦C

51.5 56.9 32.2 78.7 5.8 6.1 6.0 10.5

10.5 11.0 7.3 14.8 2.1 2.2 2.3 3.2

199 190 203 198 199 207 264 190

− 9 −12 − 6 0 − 6 3 −27 −18

Crambe oil Trimethylolpropane Neopentylglycol PE Methyl Ethyl Isopropyl 2-ethylhexyl

PP

Viscosity index increases with increasing FA and alcohol chain length used for VO transesterification (methyl and ethyl esters of crambe oil in Table 22.4). It decreases with the introduction of branching and cyclic groups in CMVO, resulting in a more compact molecular configuration. CMVOs also have higher specific gravity, there by resulting in higher density and weight per unit volume. 22.3.1.2 Low temperature fluidity A significant difference between mineral oil and VO is their PP (−20◦ C vs. −10◦ C, respectively) and is a result of nonbranched acyl groups in VO. Even with suitable PPDs, the lowest temperature for VO use is about −30◦ C. VOs typically solidify at −15◦ C upon long-term exposure and, therefore, chemical modifications are necessary to suppress or eliminate triacylglycerol crystallization. Transesterification with lower alcohols improve the cold flow properties with PPs reaching as low as −27◦ C for FA isopropyl ester, while with polyols, there is not much improvement in PPs (Table 22.4). Transesterification with branched chain alcohols dramatically reduce the PP. The position of branching is also critical, branching in the center decreases the PP more than that at the end of chain. Branching decreases the internal symmetry of the molecule, thereby resulting in decrease in PP. An example

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Test oils SBO ESBO Acetoxy-SBO Butoxy-SBO Hexanoyl-SBO

PP — ASTM D 97 (◦ C) − 6 0 − 3 − 3 −21

of branching effect on low temperature fluidity is through conversion of epoxidized VOs to diesters (C2 to C10). The resulting derivatives have excellent low temperature fluidity (Table 22.5) [43]. Increasing the chain length of acyl group at unsaturation site decreases the PP drastically (e.g., PP is −3◦ C for acetoxy VO and −21◦ C for hexanoyl VO). 45% toluene substitution at unsaturation sites of FA methyl ester decreases the PP by about 10◦ C, and 45% o-xylene substitution decreases PP by 20◦ C [11,56]. Pour point decreases with increasing number of double bonds in the molecule. Therefore, a fully saturated VO tends to be solid at room temperature. Unsaturation is, therefore, desirable for low temperature fluidity, while it is undesirable for oxidation stability. Degree of unsaturation is usually represented by iodine value, which is defined as the number of grams of iodine absorbed under standard condition by 100 g of VO and their derivatives. Chemical modification of VO by itself is not sufficient to meet all the low temperature criteria for use as crankcase oils. Therefore, they are blended with synthetic fluids such as adipate and oleate esters, PAOs, or mineral oils to achieve required low temperature flow behavior [76]. PPDs can also be used, but are less effective in VO base fluids than in mineral oils. These additives have very little effect on crystallization temperature; however, they restrict the process of crystal growth to lower the PP by 10 to 20◦ C. The PPD additives help in disrupting the stacking mechanism in VOs. An optimum PPD additive concentration of 1% in CMVO results in a PP of −30◦ C. Further addition

of PPD additives makes no significant improvement in the PP. With a combination of diluents (synthetic fluids) and PPD, the PP of CMVO (Hexanoyl-SBO) can go as low as −45◦ C. Low temperature storage stability of CMVO can be tested by keeping the samples at −25◦ C and visually inspecting every 24 h for 7 days for fluidity (similar to PP determination). The Hexanoyl-SBO formulated with PPD and biodegradable synthetic ester passed the 7-day storage stability test at −25◦ C.

22.3.2 Performance Properties 22.3.2.1 Lubricity, EP, and antiwear behavior These properties are characterized by wear and scuffing protection, friction behavior, and influence on fatigue life. In general, VOs show better lubricity than mineral oils. The ester linkage delivers inherent lubricity and helps sticking to metal surfaces. Lubricity of CMVO can be increased by increasing its viscosity (high molecular weight) [77], improving the flow of lubricant to the wear surface, by reducing degree of branching (more linear), and by using antiwear/EP additives. In hydrodynamic lubrication, viscosity, which is related to film thickness, has a noticeable effect on friction and wear. The viscosity of the lubricant, in turn, depends on the viscosity of base fluid at 40◦ C, temperature (VI), pressure (pressure viscosity coefficient), and the effect of shear rate on viscosity. Viscosity and VI of CMVO depends on various factors as described above. Pressure viscosity coefficient (PVC) can be increased by increasing the length of the branched chains, with a greater degree of branching and more aromaticity. As the distance between contact surface decreases, (i.e., toward elastohyrodynamic from hydrodynamic lubrication), the material of construction, PVC (because of pressure increase between contact surfaces) and polarity of CMVO become very important. The polar CMVO sticks to the surface and stays in the contact area, while the nonpolar material is squeezed out. In boundary lubrication, the physical properties of lubricants play a minor role. Surface phenomena, such as films formed by tribochemical reactions and physically and chemically absorbed layers of lubricants determine boundary lubrication. CMVOs have a high degree of polarity because of ester linkages in the molecules and it helps them to form physical bonds with metal surface using lone pairs of electrons on the oxygen atom of ester linkage, and are more efficient lubricants than nonpolar mineral oils. Another example where increased polarity helps reducing friction is the low coefficient of friction of ESBO compared to SBO when measured using a ball-on-disk configuration (load = 1778 N and speed = 6.22 mm/sec) [42]. At higher loads, CMVOs tend to produce chemisorbed films due to the formation of metal soaps. The soaps usually get desorbed, once their melting temperature is reached (120 to 200◦ C) whereby their boundary lubrication properties are

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lost. The incorporation of EP agents such as sulfur react at 100◦ C to form a sulfide (which are stable over 1000◦ C) film on the rubbing metal surface, and thus provides a high temperature boundary lubrication. The free oxygen in the lubricant or from the atmosphere also acts as EP lubricant by forming oxide layers. Fatty acid ethyl esters showed noticeable improvement compared to methyl esters in the wear properties tested using American Society for Testing Materials (ASTM) D 6079 method [78]. The esters of castor oil had improved lubricity over other oils with similar carbon chain length (C18) FAs, which can be ascribed to polarity. With a correct choice of ester base oils and additives, the inherently lower coefficient of friction (CoF) of ester can be adapted to meet the industrial requirements [79]. 22.3.2.2 Energy efficiency The energy efficiency of a system can be increased by decreasing viscosity, lower CoF, and PVC. Low viscosity is desired for high energy efficiency to reduce energy lost to viscous drag. CMVOs have low CoF and PVC compared to isoviscous mineral oils. PVC and CoF of polar long FA chains are lower than branched and mixed chains [80]. Some antiwear additives (such as molybdenum compounds) can be added to formulations, which are very effective in reducing CoF. Mechanical energy can be wasted if the lubrication film is too robust. Lower PVC of CMVO provides a much less viscous film compared to mineral oils. Therefore, use of CMVO in formulations of many engine oils, gear lubricants, and transmission fluids makes the system more energy conserving and leads to increased fuel economy. 22.3.2.3 Corrosion and foaming The anticorrosion properties of VOs are better than those of mineral oils, and they have a higher affinity to metal surfaces. Certain properties such as corrosion, foaming, and demulsibility are mostly additive dependent. The polar nature of triacylglycerols contributes to air entrainment and problems of foaming, compressibility, and bulk modulus. 22.3.2.4 Solvency/compatibility VOs have superior solubilizing power for contaminants and additive molecules than mineral base fluids. Most of the CMVOs are fully compatible with mineral oils and other functional fluids, thus most additives that were designed for mineral oils can be used for CMVOs as well. Better solvency and additive acceptability of CMVO permits application of even those additives, which are not soluble in mineral oils. Blending of CMVO with functional fluids such as PAOs, TMP esters, and others improve their low temperature performance and can also overcome solubility problem of additives in PAOs. Some of the disadvantages

with CMVO can be overcome using specially formulated additive packages. Tests have demonstrated that additive technology can be further applied to enable CMVOs to perform like polyol esters [81]. This is because the formulations for finished synthetic polyol ester and naturally occurring triacylglycerols are identical (with the exception of basestock). Both contain rust and oxidation inhibitors, EP additives, and defoamers. VO with the optimized additive package was found to provide overall performance (lubricity four-ball, Vickers 35VQ25 vane pump testing, RBOT oxidation stability, and fire-resistance) comparable to the synthetic fluid with greater biodegradability. When lubricants come in contact with seal materials, two different processes (swelling and shrinkage) can occur. Swelling is caused by absorption of the lubricant by seal, while shrinkage is caused by extraction of soluble components from seals. The degree of swelling decreases with increasing molecular size of the lubricant components, greater difference in solubility parameters of lubricant and seal material, more branched and cyclic structures (linear structures containing flexible linkages, which allow rotations can diffuse easily), and decreasing polarity. A very small swelling tendency is desired for seals to function properly. The more branched and less polar structures of certain CMVOs compared to VOs, make them more compatible with seal materials. This may be applicable for a large number of CMVOs, but not all. Therefore, seal compatibility of different CMVOs should be confirmed by testing.

22.3.3 Chemical Properties The chemical stability of fluids is characterized by thermal and oxidation stability, volatility, and hydrolytic stability. All stability criteria are strongly controlled by the temperatures of operation. 22.3.3.1 Thermal and oxidative stability While VOs are dependable lubricants, their tendency toward rapid oxidation at elevated temperatures has raised concerns about their performance. Pressurized differential scanning calorimetry (PDSC) is one of the methods of choice for measuring oxidative stability, among several benchtop oxidation tests (rotary bomb oxidation test, turbine oil oxidation test, peroxide estimation, active oxygen method, and Rancimat method) available [42]. The onset temperature (OT) is defined as the temperature when rapid increase in the rate of oxidation is observed in the system. By suitable chemical modification of VOs at their unsaturation sites and using specially formulated additive packages, these deficiencies can be overcome. Bis-allylic hydrogen in methylene-interrupted polyunsaturated FAs is very susceptible to free radical attacks, peroxide formation, and production of polar oxidation products. It has been shown that OT or oxidation stability increases with

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TABLE 22.6 Oxidation Stability (PDSC), Deposit Forming Tendencies, and Volatility (TFMO) of SBO Chemical Modifications

Test oils SBO ESBO Acetoxy-SBO Butoxy-SBO Hexanoyl-SBO

Onset temperature (PDSC), ◦ C

% volatile loss (TFMO)a

178 203 165 170 196

12.2 7.0 12.1 28.0 52.5

%Insoluble deposit (TFMO)a 65.8 9.5 9.1 15.1 22.1

PDSC at 10◦ C/min; a TFMO (Thin Film Micro Oxidation) conducted at 175◦ C for 1 h with 25 µL sample amount.

decrease in percentage of olefin carbons and bis-allylic CH2 [82], and decreasing unsaturation in oil samples [83]. In a way, oxidation instabilities are due to a high content of linoleic and linolenic FAs that are characterized by two and three double bonds, respectively. Therefore, oleic acid ester distribution in a naturally occurring ester basestock plays a major role in fluid performance. More double bonds make a material more prone to rapid oxidation and also lead to increase in viscosity, total acid number and metal corrosion, while some unsaturation (presence of oleic) is required to maintain low temperature fluidity. The viscosity increase after oxidation can be reduced by partial hydrogenation of the VOs [84]. Epoxidation of VOs improves their thermo-oxidative stability due to removal of multiple unsaturations in FA chains as shown by higher OT of ESBO compared to SBO in Table 22.6 [42]. Transesterification improves the oxidation stability of VOs. Bond energy calculations predict that the ester linkage is more thermally stable than the C–C bond. A lower thermo-oxidative stability of certain CMVO (obtained from modifications in FA chain of triacylglycerol molecule), is attributed to the hydrogen attached to glycerol β-carbon, which can be improved by the use of polyols. Linear FA chains are more thermally stable than branched chains because of relative stabilities of –CH3 >–CH2 >–CH, wherein –CH3 is most stable. Aromatic molecules are very stable to oxidative degradation. That is why, substitution of FA methyl ester double bonds at 45% with toluene increases the temperature of 5% destruction by 20◦ C, and substitution of 67% toluene increases the temperature by 30◦ C [56]. Toluene caused higher increase of stability than xylene. Anisole substituted products have even higher thermo-oxidative stability (60◦ C higher than original methyl ester). The deposit forming tendencies depend on oxidation stability of the lubricant, additives and polarity of the molecule, which affects detergency and dispersancy. One

of the methods to measure deposit forming tendencies of lubricants is thin film micro-oxidation (TFMO) method [42]. TFMO is usually carried out with low sample amount (25 to 50 µL) as thin film on high carbon steel catalyst surface at certain temperature for specific time duration under steady air flow (or nitrogen). The percent of insoluble deposit indicates the amount of insoluble oxidizable material in oil sample. For example, the percent insoluble deposit for SBO is approximately 65% and it decreases on addition of RCOO– group at double bond positions (Table 22.6). VOs have very low volatility due to the high molecular weight of the triacylglycerol structure and the narrow range of viscosity change with temperature. Volatility decreases with increasing molecular weight, increasing polarity, increasing oxidation stability, and decreasing degree of branching. VOs have high flash points (206◦ C vs. 170◦ C for the mineral oil); therefore, they are classified as nonflammable liquids. A higher flash point reduces potential fire hazard. Increasing molecular weight increases the flash point. VOs with branched FA chains have a low flash point compared with a similar VO with linear chains. The low oxidation stability of CMVO compared to mineral oil, requires a specific type of antioxidant, a selected mixture with synergistic properties, or large quantities (1 to 5 %) of antioxidants to inhibit oxidative degradation [85]. Most of the additives used for synthetic esters can be used for CMVO samples. Phenolic and aminic antioxidants function by scavenging free radicals, while phosphates scavenge hydroperoxides generated during oxidation processes. In general, hindered monophenols, sulfides, phosphites, aromatic amines, and zinc dithiophosphates were found less effective antioxidants, while hindered bisphenols, polyhydroxybenzenes, zinc, and bismuth dithiocarbamates were found remarkably effective antioxidants in VO based lubricants [86]. Mixtures of zinc dithiocarbamates, hindered bisphenol, and octylated diphenylamine exhibit a synergistic effect and provide more oxidation stability to VO based lubricants. In another study, butylated hydroxytoluene and ZDDP were found effective as antioxidants, while diphenylamine was found to be of limited use as antioxidant in VOs [83]. 22.3.3.2 Hydrolytic stability Hydrolytic stability can be measured by determining the acid number (number of milligrams of KOH required to neutralize 1 g of acid formed by hydrolysis due to water in the fluid). The low total acid number (TAN) of CMVOs, contribute to their good chemical and acceptable thermal stability. Mineral oils are superior to VOs and its chemical derivatives if hydrolytic stability is considered. The presence of ester functionalities makes CMVOs susceptible to hydrolysis when exposed to a humid atmosphere, or when

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in contact with water. In practice, hydrolysis has proven to be a less serious problem than expected. The resistance to hydrolysis is dependent on the type of alcohol in the ester (if it is transesterified product), the extent of acyl branching in the FA chains, molecular geometry, additives used, and operating conditions. Linear acyl groups are more susceptible to hydrolysis than branched acyl groups. The processing parameters (such as acid value, degree of esterification, removal of residual catalyst, neutralizing agent) of CMVO also have a major impact on their hydrolytic stability. A low acid value, very high degree of esterification, and low level of process residuals increases the hydrolytic stability of CMVOs. It is possible to retard hydrolysis by sterically hindering the ester linkage of the acid portion of triacylglycerol molecule. The hindrance of alcohol portion has little effect. Certain acidic additives (anticorrosion and antiwear) can have a major negative effect on hydrolytic stability of CMVOs.

22.3.4 Environmental Testing Biodegradability and microbial toxicity testing of lubricants has been well described elsewhere [87] with suitable approaches for generating this information under a variety of environmental conditions (aerobic, anaerobic, fresh water, and marine). The norms and standards of biodegradability and toxicity are different in different countries and are listed in Table 22.7 [79]. The German specification for biodegradable lubricants is more rigid than the Swiss. In Switzerland, the rate of biodegradation must not be less than 67% according to CEC (Coordinating European Council) specifications. Due to the variations and complexities of the applicable national norms, developing

TABLE 22.7 Standards Specifying Biodegradability and Ecotoxicity of Environment-Friendly Lubricants in Different Countries Country Austria Canada Germany Germany Germany Netherlands Scandinavia Sweden UK USA

Standard O-Norm C 2027 Environmental Choice Program Blauer Engel RAL-UZ 79 (Blue Angel Environmental Award) WGK (Water hazard/endangering class) VDMA 24568 (biodegradable hydraulic fluids) VAMIL (Regulations offers financial bonus for operators) White Swan SS 15 54 34 EA Standard ASTM D 6046-98a

and formulating biodegradable high-tech lubricants is significantly hindered. 22.3.4.1 Biodegradability Products based on VOs best meet the criteria for nonhazardous and environment-friendly lubricants. Their biodegradability results from the decomposition by microorganism into nontoxic products (carbon dioxide and water). The ease with which organisms can do this depends in a subtle way on the structure, particularly the extent of chain branching. The extent of biodegradability [88] is affected by the following: • Biological constituents (hydrocarbons, amino acids,

FAs, etc.) are generally readily biodegradable. • Aromatic compounds are generally resistant to biodegra-

dation; a benzene ring possessing –OH, –COOH, –NH2 , –CH, –CH3 , or –OCH3 is rather easily biodegraded, but structures possessing –X (halogen), –NO2 , and –SO3 H are resistant to biodegradation. • Biodegradation of linear hydrocarbon compounds occur more readily than branched hydrocarbon compounds. For example, erucic acid estolides, which are branched structures, degrade 84% compared to erucic acid, which degrades to 98% [89]. Biodegradability changes with the position and degree of chain branching. • Sterically hindered ester linkages in CMVOs, decreases the biodegradability to a greater extent. • Biodegradability of transesterified VO products decreases with the length of the acyl and alcohol chains. Three kinds of test methods are available according to the material’s biodegradability (susceptibility to aerobic or anaerobic microbial attack) as readily, inherently, and relative (primary) biodegradability [90]. Readily biodegradable is defined as degrading 80% in saltwater within 21 days. Most of the biobased hydraulic fluids are readily biodegradable. Inherently biodegradable are typically food-grade lubricants and white mineral oils and takes longer than VOs to degrade in the environment and are toxic over long periods. Relative biodegradability of lubricants is typically measured by CEC-L-33-A-94 test. The biodegradability of VOs is about 99% and it usually drops to about 90 to 98% after additivation, while the biodegradability of mineral oils is around 20% [12,90,91]. One of Mobil’s biobased grease and EAL 224H hydraulic fluid exceeds the Environmental Protection Agency (EPA) guideline of 60% minimum biodegradability in 28 days.

has now been passed in many parts of the world, which requires that before a new substance is marketed, certain eco-toxicological data must be submitted to the relevant authorities so that the hazards can be assessed [92]. The toxicity of a substance is the propensity of the substance to produce adverse biochemical or physiological effects in a living organism. Rainbow trouts are one of the forms of aquatic life most sensitive to pollutants and changes in environment. In a toxicity test of the VO based grease, 100% of a sample of rainbow trout survived exposure greater than 5000 ppm. In this test, if more than 50% of a sample of rainbow trout survives a minimum 1000 ppm dosage of a product for more than 96 h, this product is considered to be virtually nontoxic. Mobil’s EAL 224H hydraulic fluid also meets the same criteria for aquatic toxicity as grease. The U.S. Army Corps of Engineers are using both these products at their W. G. Huxtable Pumping Plant and meeting their goal of zero discharge of pollutants. It is clear that certain CMVO based lubricants are of a low order of toxicity. 22.3.4.3 Pollution Vegetable oils do not contribute to the greenhouse effect caused by increasing amounts of the carbon dioxide in the atmosphere. The CO2 balance is zero as these oils are the products of photosynthesis and when the oils undergo oxidation, there is no more CO2 created than is consumed in their synthesis. 22.3.4.4 Handling and storage Acute disorders can be associated with mineral oil-based metalworking fluid exposure, including skin irritation, contact dermatitis, eczema, defatting, drying of skin, sensitization and respiratory irritation, while no such effects on health were observed with VO based formulations [93]. The safety of VO based lubricants in terms of human health is evident from their use in foods. VOs in their native form are nonhazardous when in contact with skin, mucous membranes, respiratory, and digestive systems, but very little or no data is available on toxicity of CMVOs. Therefore, adequate precautions (e.g., wearing gloves during long exposures) should be taken, while using transesterified and other CMVOs. Due to high potential for hydrolysis of some of the CMVOs, they should be stored in dry sealed containers to minimize contact with moist air.

22.4 APPLICATION AREAS 22.3.4.2 Toxicity Since the 1970s, the need to gain a better understanding of the possible hazards of chemicals released in the environment has become widely accepted. As a result, legislation

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Lubricants can be classified into two main application categories: automotive and industrial lubricants. More than 70% of the total lubricant volume is used as motor oils for automotive engines with the remaining amount being

used as industrial lubricants. The outstanding physicochemical properties of some CMVOs, such as high VI, extremely low evaporation loss, good low temperature behavior, favorable boundary lubrication, and relatively harmless degradation products released during operation, make them strong candidates for use as lubricants. Due to their higher price, the best applications areas of VO based lubricants are those where their environmental advantages can be exploited to the maximum. Modified VOs can be used for loss lubrication of machinery, such as saw chains and blades, railway points, conveyors, and two-stroke engines. Further, they can be used for lubrication where the risk of oil leakage due to worn seals or other damage is involved, such as in hydraulic and transmission systems of agricultural and forestry equipment. Finally, they can be used as corrosion prevention agents and where petroleum products may contaminate the environment [94]. They are also used in engine oils and gear oils in addition to their increasing use as lubricants in hydraulic fluids, machine tool lubricants, metalworking lubricants, and total loss lubricants.

has been using corn oil formulations, developed in collaboration with Pennsylvania State University, as lubricants in their vehicles. Transesterified VOs are good candidates to be used in engine oils because of their superior thermal stability, low viscosity, low deposits (extended drain interval, cleaner systems), and better low temperature properties (reduce wear on engine start-up increasing engine life). Blends of ester based oils with PAOs/hydrocracked mineral oils, provides an excellent base fluid for the formulation of biobased engine oils [98,99]. Fuchs (Germany), BP, and Castrol introduced ester based rapidly biodegradable oils in 1996 and 1997 [95]. Transesterified triacylglycerol base oil together with a synthetic ester has been used in a lubricant formulation that is at least 60% biodegradable and has a gelation index of about 12 or less [100]. A combination of an ester based VI improver and an olefin copolymer VI improver can be added. The composition can be blended with high and low viscosities of mineral oils to lower the polarity in order to employ standard dispersant/inhibitor packages; and to prepare a full range of SAE grade engine oils for gasoline-fueled and diesel-fueled engines.

22.4.1 Automotive Engine Oils (Engine Oils, Crankcase)

22.4.2 Industrial Oils

The basic requirements for a good engine oil are as follows: • • • • • • • •

lower friction to improve fuel economy, lower engine oil consumption, cleaner overall emissions, more shear stable viscosity at high temperatures and speeds, good high temperature viscosity as well as good low temperature properties, increased performance levels with respect to cleanliness, reduce wear limit to increase engine life, and extended drain intervals to reduce maintenance times.

Low temperature viscosity is the most important technical feature of a modern crankcase lubricant. Cold starts result into engine wear and can be overcome by the use of products providing immediate effective lubrication. To meet these energy efficiency specifications, low viscosity 0W30, 5W-20, 5W-30 and extremely low evaporation loss oils (≤ 15%) will be introduced soon as per European ACEA specifications [95]. Low viscosity oils tend to be more volatile. There is a possibility of realizing 5% Noack evaporation for 5W oils [96]. VOs in native form can be used as motor oils, as shown by Duane Johnson (Colorado State University), where raw canola oil along with sunflower, soybean, and castor oil ran effectively in a Ford Mustang [97]. Similarly, Renewable Lubricants Inc., Hartsville, OH

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22.4.2.1 Hydraulic fluids Hydraulic fluids, under pressure, transmit power to moving parts of many machines, including cars, bulldozers, tractors, and most heavy equipments used to build roads and structures. A good hydraulic fluid has the following characteristics: power transmission with minimum loss, lubrication of surfaces moving against each other, and corrosion protection of metal surfaces [101]. They are an important group of industrial oils with a market share of 15% in Europe and 22% in the United States (222 Milliongallon) [95]. The trend toward rapidly growing use of biobased oils is most noticeable in this area because of their biodegradability, recyclability, reasonable level of fire-resistance, good thermal stability, good wear performance, and low and high temperature performance [102]. Natural VOs have most of the required properties as potential candidates for hydraulic applications, except that they have poor low temperature flow behavior, poor oxidation, and hydrolytic stability, which can be overcome by suitable chemical modifications. CMVO based hydraulic fluids will experience significant growth in future because of their improved thermo-oxidative and low temperature performance. These fluids will provide the extended protection of hydraulic pumps and the trouble-free operation of the plant. Biobased long chain esters, estolides blended with natural oil in presence of suitable PPD have also been found to improve oxidation stability and low temperature performance, enough to make their use as hydraulic fluids in countries such as Sweden and Norway a reality [103].

TMP Esters and Isooctyl oleate [79] also result in formulation of fire-resistant hydraulic fluids (MIL-H-83288C spec) when blended with PAOs. Hydraulic oil formulations based on saturated transesterified products can now be used in severe conditions (100◦ C and 300 bar) and drain intervals can exceed 8,000 to 10,000 h [104]. Fully formulated FA esters frequently serve as fire-resistant hydraulic fluids and will find growing application in areas such as mining, the steel industry, civil aviation, and as marine oils [105]. Blue Angel is an environmentally considerate eco-label in Germany and has defined ecological criteria for biobased hydraulic fluids. Gothenberg specifications Sweden 1995, Canadian environment choice program 1994, Environmental Agency England 1996, and an ISO 1997 draft to set international standards, show increasing concern toward the use of biobased hydraulic fluids. Even large international manufacturers, such as Caterpillar, Komatsu, and others are indicating their commitment with recommendation and specification for biobased hydraulic oil based on their technical feasibility. A German market survey report shows that share of biobased hydraulic fluids will increase to 50% by year 2005 [95]. Chemically modified SBO has been used in hydraulic fluid formulations along with an additive package by Agriculture-Based Industrial Lubricants (ABIL), University of Northern Iowa [106]. This formulation was successfully tested in laboratory and field trials in Curbtender, an automatic refuse collection truck, and rail car movers. Later, it was tested in 20 pieces of industrial equipment, maintained by Sandia National Laboratory, New Mexico. Even after 3000 h under normal operating conditions, no unusual hydraulic system failures, abnormal viscosity changes, or excessive wear was observed on any of the test equipments, and test results were within expected and industry limits. The performance level was at par with any high-grade mineral oil, and required no special equipment modification prior to their use. 22.4.2.2 Machine tool lubricants These lubricants include families of metalworking fluids, cutting fluids, open gear oils, sideway oils, spindle oils, compressor oils, and other machine lubricants. VO based esters are finding increasingly large use in these applications. The growing trend of biobased lubricants in this area is because of increasing awareness about safety at work and protecting health, environment, and in reducing disposal and system costs. Large machinery producers such as Diamler-Benz, General Motors, and Mitsubishi have shown trends toward change over from water miscible emulsion to neat oils with a 60% cost reduction. These companies have already shifted to WGK oils, which are rapidly biodegradable, have low evaporation, and are essentially nontoxic.

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VO derived esters have potential application in metalworking fluids. Chemically modified and heatmodified VOs are also used. Fine mists of existing metalworking fluids, which are used to continuously lubricate metal parts, can cause respiratory problems to workers. VO based fluids are preferred because of their superior performance (good boundary lubricants, friction modifiers), their environmentally considerate properties (biodegradable and nontoxic), easy handling, low disposal costs, low volatility (less mist formation), good surface wettability (which allow them to penetrate between the work tool and work piece), and no health concerns (pneumonia caused by inhalation of sprayed mineral oils can be eliminated). As a result of these properties, VO based fluids have started to be used in steel rolling, in aluminum drawing, as cutting oils, and as quenching fluids. Compressor oils can be formulated with CMVOs, such as esters and estolides because of their biodegradability, low ecotoxicity (ecological benefits), excellent lubricity, fire-resistance (safety), energy efficiency (less expensive to run), extended drains, and outstanding detergency. The three basic functions of compressor fluids are to lubricate, to cool critical bearings and points of constant friction, and to act as an oil seal at rings, vanes, or rotary screws. Cost benefit is a big driving factor in choosing CMVOs over mineral/synthetic oils, which is achievable because of extended drain interval, less frequent replacement of oil filters, longer periods between replacement of mechanical parts such as piston rings, seals, and bearings (reduced wear), and power cost saving (energy efficiency). Because of chances of shearing in these applications, their high VI helps them to be used over a wide temperature range without additional VI improvers. 22.4.2.3 Total loss lubricants This category of product covers 7 to 8% of total global lubricant demand and comprises of chain saw oils, mould release oils for the construction industry, two-stroke engine oils, drilling muds and oils, drip oils (oils for water and underground pumps), rail flange lubricants, agricultural equipment lubricants, and others. Mineral oil based lubricants of this type are being most rapidly replaced by readily biodegradable lubricants in most countries. Biobased lubricants offer the following advantages in this application area: readily biodegradable, low toxicity, higher stickiness, and reduced friction. Problems of skin irritation caused by the use of mineral oil can be eliminated. In the western world and industrialized Southeast Asian countries, the switch to VO and CMVO based lubricants will be complete in the next five years. The use of CMVO in formulating two-stroke engine oils is possible because of their clean-burn characteristics (low smoke), improved engine cleanliness, biodegradability, and low ecotoxicity. The presence of

polar ester groups in the molecule imparts increased adhesiveness to metal surfaces; thus, they have better lubricity than mineral based lubricants. The greatest advantage of using CMVO is the reduction in smoke level, especially reduction of the amount of PAHs in exhaust emission. The leaner burn ratios result in reduced oil emission, which is beneficial in environment sensitive applications such as marine outboard engines and chain saw motors. Drip oils are another strong opportunity for VOs. Many farmers use petroleum products as an irrigation pump lube, pouring 5 to 6 gallons each year down an estimated half million vertical shaft pumps. That is potentially 2.5 million gallons of petroleum products are being poured into the water table each year, all of which could be replaced by safer, nontoxic VOs. Historically, either water based mud (WBM) or oil based mud (OBM) have been used for offshore wells. VO based muds (VBM) offer pollution prevention advantages over OBM.

22.4.2.4 Greases Grease occupies 8% of the industrial lubricant market, and it corresponds to 18 million gallons of annual use in the United States. Greases are a mixture of two components: diluent oil and soap thickener/gellant. It is a solid or semisolid dispersion of a thickening agent in a liquid lubricant. In a conventional method, greases are formulated using VOs as diluent and preformed soap thickeners such as lithium hydroxystearate [107,108]. In another method, the soap thickener is formed via saponification of VOs with metal hydroxide in the absence of diluent oil [107]. The reaction process is traced to identify the point at which saponification and dehydration are completed. At this time the reaction is quenched by the addition of VOs. The soap concentrate is heated above the melting point, homogenized, cooled, mixed with the desired additives, and blended to give a product of desired penetration. A major shortcoming of such greases is that they also have the undesirable properties of the VOs, such as low chemical and oxidation stability due to presence of unsaturation and free acid groups. These shortcomings have been removed by making greases in which both the lubricants and gellant (soap) are formed from VOs [22]. Transesterification eliminates the acid group and gives higher chemical stability. It also decreases the PP and increases the VI. Biobased greases may have a real edge in lubricating rail tracks, as their impact on environment is enormous and conform to the requirements for high performance. For example, in Canada, over 50 million kg (50,000 metric tons) of grease has been completely lost to the environment over the course of a century, while in Russia, track lubricant consumption is said to be nearly 100 million kg (100,000 metric tons). These greases have the advantage of good biodegradability

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and are nontoxic; conform to the requirements for high performance and a wide range of application. 22.4.2.5

Additives

In order to maintain and enhance the performance standards, additives are added to lubricant formulations to improve wear, friction, EP characteristics, oxidative degradation, and so forth [109]. Use of antiwear additives that contain zinc, will not be used in future for formulations of hydraulic fluids, as zinc is considered a wastewater contaminant [95]. Due to environmental consideration, sulfurised olefins, toxic phosphorus derivatives will be phased out of the EP additive formulations for gear oils due to catalyst deactivation fitted in autogas exhaust [110]. Straight chain amines, sulfonates, and succinimides may replace current detergent additives [95]. Special additives for improving thermo-oxidative stability may gain increasing importance. Additives based on VOs (biobased additives) are biodegradable and, therefore, the resulting formulations, based on biobased additives, will be completely biodegradable. Apart from this, biobased additives retain the important physicochemical properties (such as high flash point, high VI, high molecular weight, high polarity, and excellent boundary lubrication properties) associated with the triacylglycerol structure. Addition of nitrated C1 to C4 FA esters, derived from naturally occurring triglycerides, to a diesel fuel, improved the cetane number by 90%, and lubricity and detergency by 50% [65]. FA methyl and ethyl esters of various VOs were also found to be very good fuel lubricity enhancers [78]. Ethyl esters of FA showed noticeable improvement compared to methyl esters in wear performance. 22.4.2.6 Biodiesel Although biodiesel contains a similar number of BTUs as petroleum diesel (118,000 vs. 130,500 BTUs per equivalent translating to similar engine performance in torque and horsepower), the chains are oxygenated and have a higher flash point. This makes biodiesel a much cleaner burning fuel while being safer to handle and store than petroleum diesel. In tests conducted at the Colorado Institute for Fuels and High Altitude Engine Research, a 20% blend was found to reduce particulate discharge by 14%, total hydrocarbons by 13%, and carbon monoxide by more than 7%. Biodiesel (including a B20 blend) is now recognized by both the EPA and Department of Energy as an alternative fuel, and it qualifies for mandated programs under the Clean Air Act Amendments (CAAA 90) and the Environmental Protection Act of 1992 (EPACT). In addition, biodiesel is nontoxic (its toxicity is less than 10% as that for ordinary table salt), biodegradable (degrades in about the same time as sugar), essentially free of sulfur and carcinogenic benzene, derived from renewable, recycled resources, which do not add significantly to the green house

TABLE 22.8 Suppliers of CMVO Based Lubricants Company Mobil Environmental Lubricants Manufacturing Inc., Iowa Texaco (now Chevron Texaco) E.F. Houghton Pennzoil (now part of Shell) Colorado Springs Renewable Lubricants, OH Bioblend Lubricants International Fuchs International Lubricants Inc. Raisio Chemical Karlshamns-Binol AB Moton Chemicals Cargill Industrial Oils & Lubricants

Biobased industrial fluids

Manufacturing location

Trade name

1, 2, 4 1, 2, 3, 6, 7, 8

Europe/USA USA

Mobil EAL SoyTrak, SoyEasy

2 2 2 8,11 1, 2, 5, 6, 7, 8, 9, 10, 11 1, 2, 6, 8 1, 2, 6, 8 2, 6, 7 2, 8 2, 7, 8 1, 8, 9 2, 3, 6, 7, 8

USA/Belgium USA USA USA USA USA/Europe USA/Europe USA/Europe

Biostar (Rando) Cosmolubric Ecolube

Europe/USA Europe USA/Europe/Japan

Biogrease/oil Bioblend Locolub eco Lubegard Raisio Biosafe Binol Biolube Novus

1. greases; 2. hydraulic fluids; 3. cutting oil; 4. refrigeration oil; 5. transmission oil; 6. gear oil; 7. metalworking oils; 8. bar and chain oils; 9. turbine drip oil; 10. vacuum pump oil; 11. crankcase oils.

gas accumulation associated with petroleum derived fuels. Direct benefits associated with the use of biodiesel in a 20% blend with petroleum diesel as opposed to using "straight" petroleum diesel include: • increasing the fuel’s cetane and lubricity for improved

engine life, • reducing substantially the emissions profile (including

CO, CO2 , SO2 ), particulate matter (PM), and volatile organic compounds (VOC), and • helping to clean injectors, fuel pumps, and fuel lines. These benefits occur while requiring virtually no engine modifications or costly infrastructural additions. In fact, with the addition of a catalytic converter, nitrous oxides (NOX ) can be reduced as well, allowing B20 fleets the flexibility to meet various air quality compliance criteria. Ultimately, biodiesel provides the diesel fleet operators and vehicle/equipment owners (including both on- and off-road use, stationary generation, and marine environments) the opportunity to comply seamlessly with Federal Clean Air and EPACT mandates without the burden of many of the high costs in capitalization associated with other alternative fuels. A number of independent studies have been conducted comparing the various alternative fuels. Included in this list were studies conducted by the U.S. Department of Agriculture and the U.S. Department of Energy’s National Renewable Energy Lab. In these, the life cycle costs and the projected cost per mile traveled were compared and biodiesel was substantially the most cost-competitive of the alternative fuels.

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22.5 MANUFACTURERS, MARKETING, AND ECONOMICS 22.5.1 Manufacturers Some of the manufacturers of biobased lubricants are listed in Table 22.8.

22.5.2 Markets The market for SBO lubricants will be driven by environmental concerns and controlled by economics and performance issues. Mineral oils will be cheaper and provide certain original equipment manufacturers (OEM)-desired performance characteristics in many uses. However, VOs show the ability to compete in this significant market. The need for biodegradable and nontoxic lubricants in environmentally sensitive areas has been recognized in Europe and by the U.S. government. Regulations have been adopted in some European countries, and both synthetic and VO lubricants have been developed to substitute for the offending mineral oils. In the United States, the Federal Executive Order 13010 (which set a goal that 25% of all government purchases be biobased) and the Bush Administration have recently been urging companies to make use of renewable, biodegradable basestocks, rather than petroleum basestocks, in many applications [81]. Achieving the U.S. federal government’s goal of tripling the use of biobased products and bioenergy by year 2010 could create $15 to 20 billion in new income for farmers in rural America and reduce fossil fuel emissions by an amount up to 100 million metric tons of carbon [111]. The U.S. government is working to develop 21st century biobased

industries that use trees, crops, and agricultural and forestry wastes to make fuels, chemicals, and electricity. The largest diesel fuel user in the world, the U.S. Navy, announced plans to produce its own cleaner burning biodeisel for use in its diesel vehicles, to reduce foreign dependence, to reduce emissions of potential cancer causing compounds (polyaromatic aromatic hydrocarbons) by 80 to 90%, unburned hydrocarbons (contributing factor to smog and ozone) by 68%, and carbon monoxide by 48% [112]. If the European model is followed, more regulatory efforts around biodegradable lubricants will be made in the United States in the next few years. Regulations are more likely to be passed at the state level than at the federal level, and in environmentally sensitive applications or locations. Therefore, the market for CMVO is poised to grow impressively as state and federal agencies look for ways to reduce vehicle emissions. According to Iowa Soybean Association estimate, lubricants could consume some 134 million gallons of soy oil, that is, filling about 10% of U.S. lube demand. High-grade esters (up to 30%) have been used for a number of years now in engine and gear oils. In 1996, 4% of all lubricants in European Union were rapidly biodegradable and this is likely to reach 18% by the year 2010 [93,95]. Vegetable oil will compete for a share of the emerging biodegradable lubricants market with synthetic base oils. VOs are lower in cost than synthetic oils and will be the product of choice when they can meet performance requirements. Development of a process to provide an economical and stable basestock is the key to the commercialization of biobased lubricants. SBO has a significant advantage in cost and availability in the United States over rapeseed or canola oil. This availability, coupled with the price advantages over most other VOs, makes it logical that SBO will find a place in the market as a substitute for mineral oils. These advantages make it possible that chemically modified SBO will capture a larger share of an emerging United States market for biodegradable lubricants, once the performance can be improved to the mineral oil standard.

22.5.3 Economics Chemically modified vegetable oil can be priced competitively when government subsidies are applied. The nonfood seed processor receives the raw material at a lower cost than the food processor. These unpredictable subsidized agricultural conditions and their time frames are the cause of delayed investment, which would not be financially sound under these aspects. The automotive industry has delayed engine clearances for vehicles fueled by VOs, causing further apprehension for potential consumers. A shortage of adequate filling stations is a final obstacle for vegetable fuel oil users. Mass production of VO-fueled special engines is restricted by their limited market potential.

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Annual consumption of oil-based lubricants in the United States is close to 10 million metric tons valued at more than $8 billion. This is well established and highly competitive market growing at an average rate of less than 1% per year [113]. World production of VOs in 2002 was about 93.2 million metric tons, which represents almost an eightfold increase since 1950. Out of total world production of oils and fats, only 14% was used for chemicals, 6% in animal feeds, and rest in foodstuffs. The prices of oils and fats fluctuate every day and are traded as commodities in international raw markets such as those in Chicago and Kuala Lumpur. The average annual rates of increase over a period of 25 years (1962 to 1987) for coconut (2.2%/year) and tallow (2.15%/year) are below the overall rate of inflation, and are much lower than petrochemical products (9.1%/year) [61]. By one industry estimate, at least 500,000 gallons of VO based hydraulic oils have been sold in a two-year period. This is one application where VOs have given good results, and the economics may be favorable wherever biodegradability is a requirement. Suitable marketing efforts can support this approach. For the time being, price considerations are not favorable for the wide use of VO based lubricants. However, differences between the prices of mineral and VOs are decreasing with the higher taxes imposed on petroleum products. The higher cost of VOs will be offset by engine improvements and reducing long-term environmental cleanup costs. The effect of pollution on the quality of life for people throughout the world is immeasurable.

22.6 CONCLUSION Chemically modified vegetable oils are becoming an important class of base fluid for lubricant formulations. With new strategies, policies, and subsidies, a tremendous demand for biobased lubes in lubricant sector is expected over the next few years and this will help reduce dependence on mineral oil, a nonrenewable natural source. The less stringent cleanup requirements in case of accidental spillage of biobased products will further promote their use as industrial lubricants. The share of biobased lubes is expected to grow to 15% of the total lubricants in European Union. VOs offer possibilities for providing with a wealth of chemically modified reaction products, which will be of great value in future for food and nonfood applications. The inherent problems (poor low temperature performance and oxidation stability) in VOs can be improved by a variety of reactions at either the FA carboxy groups or FA hydrocarbon chain depending on end use applications. Future progress will be along the lines of latter types of reactions with their potential for considerably extending the range of products with improved performance properties. Such progress is essential for a growth in the use of VOs as renewable raw materials. With improvements in their low temperature performance and oxidation stability, they can

be used in almost all automotive and industrial applications with additional advantage of being clean, biodegradable, nontoxic, and using lesser amounts of expensive additives (e.g., VI improvers are not required and lesser amounts of antiwear/antifriction additives are required). New applications of CMVO are constantly developing and growing rapidly in areas where environmental safety plays a major role, despite the higher costs involved. One such class of lubricants is total loss lubricants. The applications where lubricants are lost directly to the environment — as from railroad rails and switches, wire cables on cranes, the bars of chain saws and other power equipment — are the most likely application areas to initiate the use of biodegradable lubricants. In these limited-life applications, the stability of the lubricant is not a factor, giving SBO an advantage as the base oil. In spite of all these efforts that show increasing awareness, an appropriate strategy is needed to convince users of lubricants.

ACKNOWLEDGMENT One of the authors, Brajendra K Sharma acknowledges Dr. Sangrama K. Sahoo for assistance in the literature search and providing valuable comments during preparation of this manuscript.

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45. Roe, E.T. and Swern, D., JAOCS, 37, 661 (1960). 46. Falbe, J., New Synthesis with Carbon Monooxide, Springer, Berlin (1980). 47. Von Mikusch, J.D. and Sagidos, A.N., Fette Scifen Anstrichim, 73, 384 (1971). 48. Coenen, J.W.E., Wieske, T., Cross, R.S., and Rinke, H., JAOCS, 44, 344 (1967). 49. Balfas, J., Fatte Saifen Austrichem, 72, 425 (1970). 50. Powers, J.R. and Miller, C., U.S. Patent 4,081,462 to Westvaco Corp. (1976). 51. Ward, B.F., Force, C.G., and Bills, A.M., JAOCS, 52, 219 (1975). 52. Gruber, B., Hofer, R., Kluth, H., and Meffert, A., Fat Sci. Technol., 89, 147 (1987). 53. Suzuki, O. and Yamashina, T., Yukagaku, 27, 354 (1978). 54. Osami, S. and Takao, Y., Yukagaku, 27, 286 (1978). 55. Metzger, J.O., Hartmanns, J., and Koll, P., Tetrahedron Lett., 22, 1891 (1981). 56. Glavati, von O. and Glavati, L., Tribologie, 47, 19 (2000). 57. Patil, A.S., Pattanshetti, V.A., and Dwivedi, M.C., J. Synth. Lubr., 15, 193 (1999). 58. Grummitt, O. and Fleming, H., Ind. Eng. Chem., 37, 485 (1945). 59. Banks, R.L. and Bailey, G.C., Ind. Eng. Chem. Prod. Res. Dev., 3, 170 (1964). 60. Linden, W.-D., Koch, C., and Rudloff, M., Process for catalytic cracking of resinous and mucilaginous substances in vegetable oils and fats used as biodiesel in power plants, German Patent DE 19949342 (April 19, 2001). 61. Baumann, H., Buhler, M., Fochem, H., Hirsinger, F., Zoebelein, H., and Falbe, J., Angew. Chem. Int. Ed. Engl., 27, 41 (1988). 62. Stein, W. and Baumann, H., JAOCS, 52, 323 (1975). 63. Schwartz, T. and Labinger, J.A., Angew. Chem. Int. Ed. Engl., 15, 333 (1976). 64. Alvhall, J., Gronowitz, S., Hallberg, A., and Svenson, R., JAOCS, 61, 430 (1984). 65. Suppes, G.J., Heppert, J.A., and Mason, M.H., Nitrated C1–C4 fatty acid esters derived from naturally occurring triglycerides as cetane improvers for diesel fuel, U.S. Patent 20010037598 (November 08, 2001). 66. Isbell, T.A., Kleiman, R., and Plattner, B.A., JAOCS, 71, 169 (1994). 67. Isbell, T.A. and Kleiman, R., JAOCS, 71, 379 (1994). 68. Erhan, S.M. and Isbell, T.A., JAOCS, 74, 249 (1997). 69. Isbell, T.A., Edgcomb, M.R., and Lowery, B.A., Indust. Crops Products, 13, 11 (2001). 70. Erhan, S.M., Kleiman, R., and Isbell, T.A., JAOCS, 72, 671 (1995). 71. Powers, P.O., JAOCS, November, 468 (1950). 72. Erhan, S.Z. and Bagby, M.O., JAOCS, 71, 1223 (1994). 73. Wang, C. and Erhan, S.Z., JAOCS, 76, 1211 (1999). 74. Erhan, S.Z. and Asadauskas, S., Indust. Crops Products, 11, 277 (2000). 75. Erhan, S.Z., Asadauskas, S., and Adhvaryu, A., JAOCS, 79, 1157 (2002). 76. Asadauskas, S. and Erhan, S.Z., JAOCS, 76, 313 (1999). 77. Fox, N.J. and Stachowiak, G.W., Lubr. Eng., February, 15 (2003).

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78. Drown, D.C., Harper, K., and Frame, E., JAOCS, 78, 579 (2001). 79. Laemmle, P., SAE 2002-01-1455, NCFP I02-20.3 (2002). 80. Merchant, M.E., Lubr. Eng., 2, 56 (1946). 81. Patin, L.J. and James, D.K., Lubricants World, November, 26 (2002). 82. Adhvaryu, A., Erhan, S.Z., Liu, Z.S., and Perez, J.M., Thermochim. Acta, 364, 87 (2000). 83. Fox, N.J., Simpson, A.K., and Stachowiak, G.W., Lubr. Eng., October, 14 (2001). 84. Honary, L.A.T., Biores. Technol., 56, 41 (1996). 85. Adamczewska, J.Z. and Wilson, D., J. Synth. Lubr., 14, 129 (1998). 86. Becker, R. and Knorr, A., Lubr. Sci., 8, 95 (1996). 87. Battersby, N.S., Chemosphere, 41, 1011 (2000). 88. Kitamura, N., Biodegradable lubricants, Japanese J. Tribol., 38, 639 (1993). 89. Erhan, S.M. and Kleiman, R., JAOCS, 74, 605 (1997). 90. Product Review on Biodegradable fluids and lubricants, Ind. Lub. Tribol., 48, 17 (1996). 91. Makkonen, I., Environmentally Compatible Oils, FERI, Canada Pointe-Claire, Quebec, Canada (1994). 92. Randles, S.J. and Wright, M., J. Synth. Lubr., 9, 145 (1993). 93. Tocci, L., Lubes‘N’Greases, February, 24 (2003). 94. Gunstone, F.D. and Padley, F.B., Eds., Lipid Technologies and Applications (see pp. 737–757 by H. Mang), Marcel Dekker, New York, (1997). 95. Mang, T., Proceedings of ICIT-97, Calcutta, p. 639 (1997). 96. Saunders, J., Hart’s Lubricants World, May, 41 (1997). 97. Papanikolaw, J., Chem. Market Reporter, 255, 8 (1999). 98. Law, D.A. and Lohius, J.R., J. Synth. Lubr., 1, 6 (1972). 99. Mazzo-Skalszi, S.L., Maxwell, W.L., Richman, W.H., and Morris, I.R., Technical paper 951026, SAE International Congress and Exposition, Detroit, February 27–March 2, (1995). 100. Chiu, I.-C., Gunsel, S., and Lacey, P., Environmentally friendly lubricants containing modified vegetable oils, U.S. Patent WO 2003027212 (April 03, 2003). 101. Bartz, W.J., Synthetic Hydraulic Fluids for High Performance Applications, STLE 55th Annual Meeting, Nashville, TN (2000). 102. Pal, M. and Singhal, S., J. Synth. Lubr., 17, 219 (2000). 103. Kassfeldt, E. and Dave, G., Wear, 207, 41 (1997). 104. Legrand, J. and Durr, K., Agro-Food-Industry Hi-Tech., Sept./Oct., 16 (1998). 105. Yano, N., Japanese J. Tribol., 35, 957 (1990). 106. Honary, L.A.T., SAE Technical Paper # 95075, Warrandale, PA (1995). 107. Grives, P.R., NLGI Spokesman, 63, 25 (2000). 108. Silverstein, R.S. and Rudnick, L.R., Additives for greases, in Lubricant Additives: Chemistry and Applications, L.R. Rudnick, Ed., Marcel Dekker, New York (2003). 109. Rudnick, L.R., Ed., Additives: Chemistry and Applications, Marcel Dekker, New York (2003). 110. Wei, D., Lubr. Sci., 7, 365 (1995). 111. Soya & Oilseed Industry News, October 30 (2003). 112. Soya & Oilseed Industry News, October 31 (2003). 113. Padavich, R.A. and Honary, L., SAE Tech. Paper 952077, 13 (1995).

23

Biotechnological Enhancement of Soybean Oil for Lubricant Applications Monica A. Schmidt, Charles R. Dietrich, and Edgar B. Cahoon CONTENTS 23.1 23.2 23.3 23.4

Introduction Biotechnological Approaches for Soybean Oil Improvement Production of Transgenic Soybean Use of Biotechnology to Improve the Lubricant Properties of Soybean Oil 23.4.1 High Oleic Acid Soybean Oil 23.4.2 Production of Novel Fatty Acids for Improved Lubricant Performance of Soybean Oil 23.4.3 Development of Vegetable Oils with Increased Antioxidant Content 23.5 Conclusion References

23.1 INTRODUCTION Soybean oil is a potential low cost, renewable alternative to petroleum-derived chemicals for a number of lubricant applications. However, it is well recognized that soybean oil has a variety of physical properties that limit its use in lubricant formulations. These include low oxidative stability and the tendency of the oil to solidify at low temperatures [1–3]. Currently, less than 4% of the soybean oil produced in the United States is used for nonedible applications and only a small fraction of this is used for lubricants [4]. Assuming that the performance properties of soybean oil can be improved, the United Soybean Board has estimated that the potential demand for this oil in lubricant applications could result in the consumption of more than 100 million bushels of soybeans or over 3% of the current annual production in the United States [5]. The physical properties of soybean oil result largely from its fatty acid composition and antioxidant content. Biotechnology represents one approach for enhancement of the quality of soybean oil for lubricant applications. In this review, the underlying principles of soybean biotechnology will be described in context with past and ongoing efforts to modify the fatty acid composition and antioxidant content of soybean oil for improved lubricant performance.

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23.2 BIOTECHNOLOGICAL APPROACHES FOR SOYBEAN OIL IMPROVEMENT The term “biotechnology” in this review refers to the stable introduction of genes and associated genetic elements into a plant, such as soybean, that results in a desired trait. Plants derived from biotechnology are often referred to as “transgenic” plants. Nearly 80% of the soybeans grown in the United States contain a trait derived from biotechnology. This trait confers resistance to the herbicide glyphosate. This property improves weed control for farmers and prevents soil erosion by reducing the need for tillage. Apart from herbicide resistance, the only other transgenic trait in soybean that has received regulatory approval to date is the high oleic acid content in the high oleic acid soybean. As discussed later, the seed oil of these soybeans is enriched in oleic acid and contains very low amounts of less oxidatively stable polyunsaturated fatty acids. The fatty acid composition and antioxidant content are the primary determinants of the oxidative stability of soybean oil. The chemical composition of soybean oil is, in turn, regulated by the genes that are present in soybean. Genes are strings of DNA molecules that are transcribed into messenger RNA (mRNA), and the mRNA is translated into protein. Many of these proteins serve as enzymes that

catalyze specific biochemical reactions. Enzymes typically do not act alone but are part of a larger metabolic pathway that leads to the biosynthesis of a particular product. Metabolic pathways are often represented as maps listing all the substrates and enzymes involved in making a particular product. The flow of carbon through a pathway is referred to as the metabolic flux. The final product of a metabolic pathway can often be modified by changing the flux of the pathway. The flux through a pathway is altered by modifying the genes that encode the enzymes in the pathway. Thus by understanding the metabolic pathway and identifying the genes involved, it is often possible to modify the pathway in such a way that the product has enhanced value. In the case of oil improvement for lubricant applications, a major metabolic pathway that is often targeted is fatty acid desaturation that occurs in the endoplasmic reticulum of cells of the soybean seed. Five different fatty acids comprise soybean oil: the saturated fatty acids, palmitic acid (16:0) and stearic acid (18:0); the monounsaturated fatty acid, oleic acid (18:1); and the polyunsaturated fatty acids, linoleic acid (18:2) and linolenic acid (18:3). Polyunsaturated fatty acids are prone to oxidation and, therefore, decrease the value of soybean oil for lubricant applications. As shown in Figure 23.1, the conversion of oleic acid to linoleic acid is catalyzed by the enzyme
12 -oleic acid desaturase, which is encoded by FAD2 genes. By disrupting FAD2 genes or by blocking their transcription into mRNA, the ability of the cells of soybean seeds to produce polyunsaturated fatty acids is impaired [6]. Modification of a gene (e.g., by mutation) can results in: (a) changes in levels of gene expression or (b) production of an altered protein. Gene expression refers to when, where, and how often the gene is transcribed. The region of the gene that determines its expression is called the promoter. Promoters vary in both the rate and specificity at which they direct transcription. Some promoters are considered constitutive as they direct transcription at high levels in all cell types while other promoters allow transcription only in specific cells or tissues, as is the case with many seed specific promoters. Changes in the gene promoter can cause either up-regulation (increased transcription) or down-regulation (decreased transcription) of the gene. Second, mutations in the coding sequence of the gene can change the protein produced by that gene. These changes create new versions of the gene called alleles. Some alleles, referred to as nullalleles, do not produce any functional protein, while others produce altered version of the protein that may have a slightly different enzymatic function. Natural selection, plant breeding, and biotechnology all use genetic modifications to identify new and favorable traits. Natural selection relies on the occurrence of errors during DNA replication to create changes in the DNA sequence referred to as mutations. In addition, genes

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Conventional soybean

High oleic acid soybean

Oleic acid 18:1 (15–25%)

Oleic acid 18:1 (80%)

∆12-Oleic acid desaturase

FAD2

Linoleic acid 18:2 (50–60%) ∆15-Linoleic acid desaturase

FAD3

Linolenic acid 18:3 (10–15%)

∆12-Oleic acid desaturase

X

FAD2

Linoleic acid 18:2 (2–3%) ∆15-Linoleic acid desaturase

FAD3

Linolenic acid 18:3 (3–5%)

FIGURE 23.1 Metabolic pathway of fatty acid desaturation in the endoplasmic reticulum of cells of soybean seeds. The pathway in the left panel shows the conversion of oleic acid to linolenic acid in conventional soybean seeds by the successive activities of the
12 -oleic acid desaturase (encoded by the FAD2 gene) and the
15 -linoleic acid desaturase (encoded by the FAD3 gene). The relative content of each fatty acid in soybean oil is shown in parenthesis. The right panel shows the desaturation pathway in a high oleic acid soybean seed. As indicated, a block in the
12 -oleic acid desaturase-catalyzed step leads to a build up of oleic acid and a concomitant reduction in the content of the polyunsaturated fatty acids, linoleic and linolenic acids

undergo a natural process of recombination during the formation of egg cells and pollen that can create new combinations of promoters and genes and thus change gene expression. Natural selection occurs when these modifications result in a plant that has increased reproductive fitness and therefore passes the modified genes to more progeny than the plants with the unmodified genes. Natural selection has created tremendous biological and chemical diversity in the plant kingdom. The chemical diversity of plants is reflected in the wide variety of fatty acids that can be found in the seed oils of different species. Many of the novel fatty acids found in seed oils have properties that are valued for nutritional or industrial applications. In many cases, however, the plants that produce these oils are not well suited for large-scale agricultural production. For example, the meadowfoam plant produces a vegetable oil that is highly desired by the cosmetic and lubricant industries [7]. Though meadowfoam is grown as a winter crop in Oregon, it is not adapted for wide production in the United States and is not as productive as established agronomic crops such as soybean and corn.

Plant breeders use this same process of mutation followed by selection to enhance specific traits (e.g., seed oil composition) in crop species. Plant breeding differs from natural selection in that selection is based on enhancement of a particular trait and not necessarily on the reproductive fitness of the plant. The process relies heavily on mutations that either occur naturally or are induced by exposure to chemicals or radiation. Plant breeding techniques have been successful in modifying the oils from several crops including soybean. Perhaps the most notable achievement of plant breeding for improved soybean oil composition is the reduction of the content of linolenic acid, a polyunsaturated fatty acid, to as low as 1–3% of the total oil [8]. Linolenic acid normally makes up 10–15% of soybean oil and is a major contributor to the poor oxidative stability of conventional soybean oil. Biotechnology can be used to make the same modifications to gene expression that plant breeders select but in a more rapid and precise manner. Biotechnology works by directly introducing new genes, called “transgenes,” into a plant using a process referred to as transformation. The ease with which genes can be modified through biotechnology makes it possible to look at a metabolic pathway and make predictions regarding which genes should be targeted for increased or decreased expression in order to generate desired products from the pathway. The speed of biotechnology makes it possible to make changes and test the outcome of that change. Because the DNA sequence of the introduced gene is known, the effect of that gene can be more easily monitored in these plants than in plants derived from breeding techniques that rely on random changes. Transgenes are typically intended to have one of the following effects: (a) decreased or suppressed expression of a gene; (b) increased expression of a gene; or (c) expression of a gene that is novel to the host plant. Decreased expression of genes through biotechnology is achieved by use of methods such as sense or antisense suppression or more recently, RNA interference. Each of these methods results in reductions in the mRNA for only the targeted gene. The ability to selectively decrease or down-regulate the expression of a particular gene is a major advantage of biotechnology over traditional plant breeding methods. Plant breeding relies on generation of random mutations into the plants entire genome and then selecting for mutations that occur in the gene of interest. Multiple generations of backcrossing are then required to remove any mutations that may have occurred in other genes. This process can take several years and results in the same effect (i.e., down-regulation through decreased mRNA levels) as that which can be achieved through biotechnology in a single generation. A second advantage of biotechnology is that the expression of a gene can be down-regulated in a specific organ of the plant. This is accomplished by use of promoters that initiate expression of a gene in a confined organ, such as

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a seed. In the case of soybean oil modification, promoters for genes of seed storage proteins are often used. These genes are naturally expressed only in seeds and not in other organs of the plant such as leaves. When these promoters are linked to other genes, such as those engineered to shut off a step in fatty acid desaturation, the transgene is expressed only in seeds. This is in contrast to a mutation in a gene, which can often lead to the reduction or elimination of gene expression not only in seeds but also throughout the entire plant. In addition, biotechnology can be used to simultaneously reduce the expression of multiple genes. This is particularly useful for genes that have more than one copy present in the genome. For example, if a plant carries two copies of a gene, both copies can be downregulated by a single transgene, whereas plant breeding would require the generation of two mutations for both copies of the gene. Third, biotechnology can be used to increase the expression of a gene that is already present in the plant by introducing another copy of that gene. Typically, the introduced copy is placed under control of a strong promoter that confers high levels of expression. The use of organspecific promoters can make this technology even more powerful. For example, the expression of a gene involved in oil biosynthesis can be up-regulated specifically in the seeds so that there are no adverse effects on the vegetative parts of the plant. Conventional plant-breeding methods are limited in their ability to up-regulate the expression of a gene. Available methods involve crossing different varieties of a species, or closely related species, and selecting for offspring that may have a particular combination of genes that allows for increased expression of the gene of interest. Tracking these combinations of genes (referred to as quantitative trait loci or QTL) throughout populations is a difficult and time consuming process compared to the relative ease with which biotechnology can be used to directly modify traits. Another application of biotechnology involves the introduction of genes into crop plants that are derived from noncrop plant species or even from organisms such as viruses, bacteria, animals, or fungi. This is another application where biotechnology far exceeds what can be accomplished by traditional plant-breeding methods. While specialized techniques in plant breeding have broadened the range of species that can be cross hybridized there remain significant limitations. Biotechnology, however, is essentially limitless in regards to transferring genes across species. This is particularly useful in the applications of vegetable oils. As mentioned above, many of the highvalue oils are produced in noncrop plant species that are not easily amenable to large-scale agricultural production. Biotechnology offers the ability to transfer the genes from those species into a crop species, such as soybean. This enables soybean to produce oil with similar properties as the original species.

A further attribute of biotechnology is the ability to more rapidly “stack” traits. “Stacking” refers to the combination of more than one trait in a single plant. With regard to the improvement of soybean oil for lubricants, a stack could involve combining a high oleic acid oil trait with an enhanced antioxidant trait. Through the use of transformation methods described in the following sections, genes controlling two or more traits can be simultaneously introduced into a single soybean plant. This can save a number of years of crossing plants with different traits, as would be required by the use of conventional breeding methods. By modifying multiple genes in a single metabolic pathway or in multiple pathways, biotechnology has the potential to tailor the compounds produced by crops for use in specific applications, such as lubricants.

23.3 PRODUCTION OF TRANSGENIC SOYBEAN The initial hurdle in a biotechnology project is to identify the gene, or genes, governing the desired trait. Once the genes are known and the correct transgene has been prepared, the next step is the transformation and regeneration of a fertile soybean plant that has the desired trait. Simply, the transformation of a plant means to insert a gene into the plant’s genome. The two most widely used methods for soybean transformation are: (a) Agrobacterium-mediated transformation and (b) particle bombardment-mediated transformation. The first takes advantage of a naturally occurring soil microbe Agrobacterium tumefaciens. This microbe can infect most dicotyledonous or broad-leaved plants and causes a disease known as crown gall. The name of this disease is derived from the visual symptoms of the plant, namely a large tumor-like swelling, a gall, forms at the crown (stem area just above the soil) of the plant. In causing the disease, the bacterium transfers part of its DNA (referred to as transfer or T-DNA) to the plant and subsequently integrates its DNA into the plant’s genome. The genes that are transferred into the plant produce hormones that cause the plant cells to proliferate, resulting in tumor formation. Although the entire process by which Agrobacterium transfers its DNA into a plant cell is not fully understood, the basic components are known and have been effectively manipulated to transfer desired genes into a plant. In order for this to happen, the Agrobacterium strain used must first be “disarmed”; that is, the tumorcausing genes have to be deleted. Second, the genes of interest need to be placed under the appropriate regulatory elements and the resulting recombinant DNA placed into the bacterium’s T-DNA region. Since the transformation of a plant by Agrobacterium is dependent on the bacterium infecting the plant material, it is imperative that the plant species be susceptible to infection by this bacterium. Initially, soybean was believed not to be susceptible to Agrobacterium infection [9]. Further studies have found variations of Agrobacterium that in concert with certain

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soybean varieties have resulted in the successful production of transformed soybean plants [10,11]. The second commonly used plant transformation technique, microprojectile particle bombardment, is not dependent on a host–pathogen interaction. As a result, the range of plant species amenable to this transformation technique is broader than Agrobacterium-mediated transformation. In this technique, first described by Klein and colleagues [12], the recombinant DNA containing the gene of interest is literally shot (or propelled under high pressure) into the plant target tissue. Not surprisingly, the instrument used in this technique is commonly referred to as the “gene gun.” In brief, the recombinant DNA is precipitated onto microscopic gold particles and propelled into plant material through high pressure produced by helium gas. The gene gun is often criticized for its “randomness” or nondeliberate way of integrating foreign DNA into the genome of the plant. Agrobacterium-mediated transformation is touted as being a more precise and direct integration mechanism, albeit created by nature and not yet fully understood by scientists, while the gene gun relies on an apparent random integration of foreign DNA into the plant genome. Considering this, the ideal target tissue for a genegun experiment is a readily proliferating tissue so that when the pressure of the gene gun propels the recombinant DNA into the nucleus of the target cell, the plant mistakenly integrates and replicates the introduced DNA, while replicating its own DNA. Following transformation, the next step toward producing a genetically engineered plant is the regeneration of an intact fertile plant through tissue culture. Tissue culture is a phrase that encompasses the use of plant hormones and nutrients in order to produce desired developmental stages. In essence, successive hormone treatments are used to mimic the natural stages of plant development in order to regenerate a plant. The entire regeneration process would not be possible in soybean, or any plant, if individual plant cells did not have the ability to progress through development and ultimately give rise to a complete plant (Figure 23.2). This ability to dedifferentiate a cell type and give rise to all possible cell types necessary to form a plant is called totipotency. Because the result of a plant transformation event is a single cell, the daunting task is the regeneration of a whole plant from the single transformed cell. This process requires the identification of that single transformed cell from all the other surrounding nontransformed cells. This task can truly be paralleled to finding a needle in a haystack. To overcome this obstacle, a gene that confers some growth advantage to a transformed cell is placed in the DNA recombinant molecule along with the genes of interest that confers the desired trait. Genes that are often used to identify transformed cells encode for resistance to an antibiotic such as hygromycin [13–15] or to a herbicide such as glyphosate [16] or glufosinate [17]. In this case,

Promoter

Trait gene

Promoter

Selection marker (antibiotic or herbicide resistance gene)

Gene Gun Soybean embryos DNA-coated Particles

Integration of introduced DNA into soybean DNA

4–6 weeks Selection of transformed cells

X X

X

X X

X

~10 weeks

X

Plant regeneration

18 weeks Progeny (seeds)

FIGURE 23.2 Overview and timeline for the transformation of soybean embryos by particle bombardment. DNA vector containing the genes of interest and a selectable marker (i.e., antibiotic resistance gene) is coated onto gold particles and propelled into embryos that were induced from immature cotyledons. Embryos are then subjected to selection regiment at which point of time cells that were transformed will thrive and regenerate. Transgenic tissue is then regenerated into a plant through hormone treatments and the plant is subsequently matured to yield progeny

when a cell is transformed with a recombinant DNA containing the trait-conferring gene and a gene for antibiotic or herbicide resistance, the cell can readily be identified by growing all the plant cells on plant growth media that contains the corresponding antibiotic or herbicide. Only cells transformed with the antibiotic or herbicide resistance gene, and very likely the trait-conferring gene, will be able to thrive and regenerate. Genes, like the antibiotic or herbicide resistance gene that are used as a tool to identify the transformed cells are collectively referred to as “selectable markers” because they select for the desired transformed cell. Through the use of selectable markers, the plant researcher is able to drastically narrow down the pool of cells that likely will exhibit the desired trait and only those chosen cells are regenerated through tissue culture to produce a transformed plant. The ability to focus attention to only potentially transformed tissue greatly reduces the time needed to analyze tissue, especially in soybean where the successful transformation frequency is typically 1 to 2% [18], as opposed to other plant species, like tobacco, with upwards of an 80% success rate of transformation [19]. There are two general methodologies to regenerate soybean: organogenesis and embryogenesis. Organogenesis involves the production of a mass of undifferentiated cells,

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called callus tissue, from which organs, such as shoots, are induced through hormone treatments. Once transformed and newly regenerated shoots identified, root formation can then be induced by yet another hormone treatment. On the other hand, embryogenesis involves the formation of embryonic tissue, akin to the embryo naturally found in a seed, followed by the maturation of the embryo into a plant. Both regeneration methods rely heavily on starting with a cultivar of soybean amenable to tissue-culture techniques [18]. One cultivar of soybean, Jack, is often used in embryogenesis regeneration protocols [20] but another, Asgrow 3237, is often the cultivar of choice for organogenesis [21]. As has been implied earlier, the initial starting tissue type is of utmost importance in a soybean transformation procedure. What starting material is used largely depends on the transformation technique that will be employed. For instance, cotyledons isolated from newly germinated mature seeds are the ideal staring material in an Agrobacterium-mediated transformation of soybean. However, mature cotyledonary tissue has not proven effective for a biolistic transformation system, so the tissue of choice here is embryos that have been induced from immature cotyledons [20].

23.4 USE OF BIOTECHNOLOGY TO IMPROVE THE LUBRICANT PROPERTIES OF SOYBEAN OIL

18:2 a 18:1 (18%)

16:0

18:3

18:0 18:1 (80%)

16:0 Detector response

Using these methodologies, it is possible to selectively increase or decrease the expression of a gene that is native to soybean. Such genetic modifications can be targeted only to the soybean seed by the use of a promoter that initiates seed-specific expression of the introduced genes. These transformation techniques can also be used to express a gene in soybean seeds that originates from another plant species or even another organism. Overall, soybean transformation, combined with recombinant DNA technology, provides the basis for researchers to enhance the composition of soybean oil for lubricant applications, as well as a many other applications such as food processing.

b

18:0 18:2

18:2

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c 20:1∆5

20:0

20:1∆11

18:1 16:0

18:3 20:2

18:0

23.4.1 High Oleic Acid Soybean Oil The most significant achievement, to date, in the use of biotechnology for the improvement of soybean oil for lubricant applications is the production of the high oleic acid soybean by researchers at DuPont [6]. These soybeans were developed by suppressing the expression of FAD2 genes specifically in seeds (Figure 23.1). FAD2 genes encode the
12 -oleic acid desaturase, which catalyzes the conversion of the monounsaturated oleic acid to the polyunsaturated linoleic acid. The result of this biotechnological modification is an oil that is composed of about 80% oleic acid and <7% polyunsaturated fatty acids (linoleic + linolenic acids) (Figure 23.3[b]). By comparison, oleic acid normally constitutes 15–25% of soybean oil, and polyunsaturated fatty acids, largely in the form of linoleic acid, make up about 65% of the oil. More recently, soybean oil with oleic acid content approaching 90% has been generated by suppressing the expression of FAD2 genes along with the expression of FATB genes, which control the production of palmitic acid [22]. By comparison, the highest amount of oleic acid that has been obtained in soybean oil by conventional breeding is approximately 55–60% [23]. High oleic acid soybean oil displays considerably more oxidative stability relative to conventional soybean oil, as determined by several different methods. For example, using the rotating bomb oxidation test (RBOT), high oleic acid soybean oil supplemented with antioxidant and antiwear additives exhibited a fivefold greater RBOT time than conventional soybean oil that contained similar additives [24]. The longer RBOT time for the high oleic soybean oil was consistent with a higher degree of oxidative stability. The performance of high oleic acid soybean oil was in fact similar or better than some commercially available petroleum-based lubricants [24]. In addition, when examined by hydraulic pump testing, high oleic soybean oil with antiwear additives yielded >10-fold less cam ring and vane wear as compared to conventional soybean oil containing

18:3

Total C20 22%

18:2

d 12-Epoxy-18:2 (2%)

18:1 Vernolic (14%)

16:0 18:0 2

3

18:3 4

5

6

7

8

Retention time (min)

FIGURE 23.3 Fatty acid profiles from conventional soybean seeds (a), high oleic acid soybean seeds (b), soybean seeds coexpressing meadowfoam genes for a
5 fatty acid desaturase and fatty acid elongase (c), and soybean seeds co-expressing fatty acid epoxygenase genes from ironweed and Euphorbia lagascae (d). Shown are gas chromatograms of fatty acid methyl esters prepared from conventional soybean seeds (a) or from transgenic soybean seeds (b) to (d). The relative content of specific fatty acids is indicated in parentheses.

equivalent additives [24]. After 100-h of testing, the high oleic acid soybean oil, in contrast to conventional soybean oil, displayed little increase in viscosity from polymerization of the oil, which is further indicative of improved oxidative stability. Despite its superior performance, high oleic acid soybean oil has yet to be sold widely for lubricant applications. The commercial development of high oleic acid soybean oil as lubricants is currently being pursued by Environmental Lubricants Manufacturing, Inc.

23.4.2 Production of Novel Fatty Acids for Improved Lubricant Performance of Soybean Oil Through the use of standard biotechnological techniques, it is possible to engineer soybeans to produce fatty acids that are not normally found in its seed oil. A number of examples of the use of biotechnology to produce novel fatty acids in soybean seeds have been reported [13,25–27]. In many of these examples, soybean oil with improved properties

for industrial applications, including lubricants, have been developed. This research has involved the identification and isolation of genes associated with the biosynthetic pathways of novel fatty acids in seeds of plant species that typically have poor agronomic properties. These genes are then transferred to soybean using plant transformation techniques described earlier. The genes are engineered into soybean with promoter elements that result in their expression in seeds but not in other parts of the plant. The expression of these genes leads to the production of new types of fatty acids in soybean seeds, which are accumulated in the oil fraction. It should be noted that it is not possible to generate novel fatty acids in soybeans by conventional breeding, which underscores the benefit of biotechnology for the development of new, higher value soybean oils. One example of research directed toward the development of soybean oil with novel fatty acids for lubricant applications has involved the isolation and transfer of genes from meadowfoam (Limnanthes sp.). C20 and C22 fatty acids constitutes over 90% of the seed oil of meadowfoam, and approximately 60% of the oil is in the form of the C20 monounsaturated fatty acid
5 -eicosenoic acid (20:1
5 ) [13]. By comparison, C20 and C22 fatty acids typically make up <0.5% of conventional soybean oil. Meadowfoam oil has an oxidative stability that exceeds that of high oleic acid sunflower oil [28]. Meadowfoam oil also shares a limited amount of structural similarity with sperm whale oil, and it was envisioned that meadowfoam oil could serve as a replacement to sperm whale oil for high temperature lubricant applications. Meadowfoam, however, has yet to become a widely grown crop, due in part to its marginal agronomic properties and relatively low productivity compared to established crops such as soybean. As a result, meadowfoam oil sells for >$5.00/lb. Refined soybean oil, by comparison, sells for about $0.20/lb. The high price of meadowfoam oil has precluded its extensive use as an industrial lubricant. As an alternative to the agronomic improvement of meadowfoam as a crop, genes from this plant that are associated with the biosynthesis of 20:1
5 were identified and transferred to soybean [13]. These genes encode enzymes for: (a) a fatty acid elongase that initiates the extension of the carbon chains of C16 and C18 fatty acids to C20 and C22 chain lengths and (b) a fatty acid desaturase that catalyzes the introduction of the
5 double bond into C20 and C22 fatty acid substrates. Transgenic expression of the two genes from meadowfoam resulted in a soybean oil that was make up of >25% C20 and C22 fatty acids and also contained 10% of 20:1
5 (Figure 23.3[c]). Research is currently underway to identify additional genes from meadowfoam for the production of higher levels of C20 and C22 fatty acids in soybean seeds [13]. Another example of the use of biotechnology to produce soybean oil with improved lubricant properties

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involves the biological production of epoxy fatty acids in soybean seeds. The use of chemically epoxidized soybean oil as lubricants has been studied [29]. This modified oil was shown to have improved oxidative stability at high temperatures and was able to polymerize with metal surfaces, which resulted in reduced friction. In addition to the use of chemical methods to generate epoxidized fatty acids from conventional soybean oil, biotechnology also offers a means of producing similar types of oil in soybean seeds. Vernolic acid (12-epoxy-18:1
9 ) is a novel C18 fatty acid that contains
9 unsaturation and an epoxy group at the
12 position. This fatty acid is produced in high levels in seeds of plants such as ironweed (Vernonia sp.) and the spurge Euphorbia lagascae, neither of which is grown agronomically. Genes for enzymes that catalyze the formation of the epoxy group of vernolic acid have been identified from these species. The gene from ironweed encodes a structurally divergent form of the
12 -oleic acid desaturase [30], and the gene from E. Lagascae encodes a cytochrome P450-type enzyme [27]. Expression of either gene in soybean resulted in an oil that contains approximately 7% vernolic acid [27,30]. Furthermore, expression of both genes in soybean yielded an oil that contains approximately 14% vernolic acid and 2% of a novel epoxy fatty acid that contains unsaturation at the
9 and
15 positions as well a
12 epoxy group (Figure 23.3[d]). These examples illustrate the ability to produce novel fatty acids with potential value for lubricants in soybean oil through biotechnological approaches. In both cases, additional research is needed to increase novel fatty acid accumulation in soybean seed oil to levels that are commercially attractive to lubricant manufacturers.

23.4.3 Development of Vegetable Oils with Increased Antioxidant Content The oxidative stability of soybean oil is determined not only by its fatty acid composition but also by the content of oil-soluble antioxidants. The primary types of vegetable oil-soluble antioxidants in plants are tocopherols and tocotrienols. These closely related compounds comprise the Vitamin E family of antioxidants in plants and are co-extracted with vegetable oils during the commercial processing of oilseeds such as soybean. Tocopherols occur in seeds of all plants, while the occurrence of tocotrienols is limited primarily to seeds of monocotyledonous plants including palm, rice, wheat, and barley. These molecules scavenge reactive oxygen species generated from the oxidation of unsaturated fatty acids in vegetable oils and thus, function in a manner analogous to phenolic antioxidants that are added to petroleum-based lubricants. The content of tocopherols in soybean oil is approximately 1300 mg/kg oil [31]. This amount is about 1.4-fold higher than that of sunflower oil, which accounts in large part for the higher

levels of oxidative stability that are observed for soybean oil relative to sunflower oil [31]. Genes for enzymes that catalyze the rate-limiting reactions in the tocopherol and tocotrienol biosynthetic pathways in plants have recently been isolated. The enzyme that catalyzes this reaction in tocopherol biosynthesis is homogentisate phytyltransferase or HPT, and the related enzyme in the tocotrienol biosynthetic pathway is homogentisate geranylgeranyl transferase or HGGT [32,33]. Expression of the gene for HPT to high levels in seeds of transgenic Arabidopsis thaliana (a commonly used model plant) resulted in a nearly twofold increase in tocopherol content [34]. Similarly, expression of the gene for HGGT to high levels in seeds of transgenic corn was accompanied by a four- to sixfold increase in the total content of tocopherols and tocotrienols [33]. The effect of these increases in Vitamin E content on the oxidative stability of seed oils from these plants has not yet been examined. In addition, these biotechnological experiments have yet to be conducted with soybean, but a similar result (i.e., enhanced Vitamin E content of the seed oil) is expected. The combination of high oleic acid levels with high Vitamin E content should yield a soybean oil with a degree of oxidative stability that is higher than that of any currently available vegetable oil. Such an oil would be highly desired by the lubricant industry.

23.5 CONCLUSION Like conventional plant breeding, biotechnology is a tool that can be used to improve the properties of soybean oil for lubricant applications. The development of the high oleic acid soybean exemplifies the usefulness of this technology for enhancement of the lubricant performance of soybean oil. Potential biotechnology-derived traits for the lubricant industry include soybean oil with increased antioxidant content and soybean oil with novel fatty acids that have high oxidative stability or other desired properties such as extended carbon chain length. It should be stressed that biotechnology and conventional plant breeding are not exclusive approaches for soybean oil improvement. For example, a biotechnology-derived high oleic acid soybean line can be bred to a low linolenic acid mutant to achieve an additional increase in the oxidative stability of the oil. The future use of biotechnology for the improvement of soybean oil for lubricant applications, however, faces both technical and economic hurdles. For example, although it is now possible to produce a variety of novel fatty acids in soybean seeds [13,25–27], additional research is needed to identify metabolic processes that prevent these fatty acids from accumulating to commercially useful levels. It is also not clear if biotechnology-derived vegetable oils can be price competitive with petroleum-based lubricants. In addition to costs associated with research and development,

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transgenic plants with desired traits developed by biotechnology must receive regulatory approval before they can be grown commercially. Regulatory costs for a transgenic soybean line have been estimated to be in the one to ten million dollar range [18]. These costs must ultimately be recovered in the price charged for oils derived from the transgenic plants. As a result, the price of these oils will undoubtedly be higher than that of conventional soybean oil. However, in the long term, vegetable oils generated from biotechnological approaches may serve as an attractive alternative to petroleum-based lubricants as oil prices increase. The soybean oil traits with the highest chance for commercial success in the near term will likely be those that have value for multiple applications. For example, high oleic acid and high Vitamin E oils are not only desired for lubricant production but can also be used for food processing, which represents a much larger market. In conclusion, biotechnology is capable of providing a wide range of improved soybean oils for lubricant applicants. In addition, the rapid and targeted nature of biotechnological innovations will allow for the precise tailoring of soybean oil compositions for specific markets, including the lubricant industry.

REFERENCES 1. American Soybean Association. Soy Stats, A Reference Guide to Important Soybean Facts & Figures, (http://www.soystats.com/2003/Default-frames.htm), 2003. 2. L.A.T. Honary. An investigation of the use of soybean oil in hydraulic systems. Bioresource Tech. 56: 41–47, 1996. 3. S.Z. Erhan and S. Asadauskas. Lubricant basestocks from vegetable oils. Ind. Crops Prod. 11: 277–282, 2000. 4. S. Fernando and M. Hanna. Comparison of viscosity characteristics of soybean oils with a mineral oil two-stroke engine lubricant. Trans. ASAE 44: 1403–1407, 2001. 5. United Soybean Board. Market opportunity summary, soybased lubricants, January 2004. 6. A.J. Kinney. Development of genetically engineered soybean oils for food applications. J. Food Lipids 3: 273–292, 1996. 7. R.J. Roseberg. Underexploited temperate industrial and fiber crops. In: J. Janick, Ed. Progress in New Crops, Alexandria, VA, ASHS Press, 1996, pp. 60–84. 8. A.J. Ross, W.R. Fehr, G.A. Welke, and S.R. Cianzio. Agronomic and seed traits of 1%-linolenate soybean genotypes. Crop Sci. 40: 383–386, 2000. 9. M. DeCleene and J. DeLey. The host range of crown gall. Bot. Gaz. 42: 389–466, 1976. 10. M.A. Hinchee, D.C. Ward, C.A. Newell, R.E. McDonnell, S.J. Sato, C.S. Gasseer, D.A. Fischhoff, D.R. Re, R.T. Fraley, and R.B. Horsch. Production of transgenic soybean plants using Agrobacterium-mediated DNA transfer. Bio/Technology 6: 915–922, 1988. 11. R. Di, V. Purcell, G.B. Collins, and S.A. Chabrial. Production of transgenic soybean lines expressing the bean pod mottle virus coat protein precursor gene. Plant Cell Rep. 15: 746–750, 1996.

12. T.M. Klein, W.D. Wolf, R. Wu, and J.C. Sanford. High velocity microprojectiles for delivering nucleic acids into living cells. Nature 327: 70–73, 1987. 13. E.B. Cahoon, E.F. Marillia, K.L. Stecca, S.E. Hall, D.C. Taylor, and A.J. Kinney. Production of fatty acid components of meadowfoam oil in somatic soybean embryos. Plant Physiol. 124: 243–251, 2000. 14. J.M. Thomson, P.R. LaFayette, M.A. Schmidt, and W.A. Parrott. Artificial gene-clusters engineered into plants using a vector system based on intron- and intein-encoded endonucleases. In Vitro-Plant 38: 537–542, 2002. 15. E.M. Herman, R. Helm, R. Jung, and A.J. Kinney. Targeted gene silencing removes an immunodominant allergen from soybean seeds. Plant Physiol. 132: 36–43, 2003. 16. T. Clemente, B.J. LaValle, A.R. Howe, D.C. Ward, R.J. Rozman, P.E. Hunter, D.L. Broyles, D.S. Kasten, and M.A. Hinchee. Progeny analysis of glyphosate selected transgenic soybeans derived from Agrobacterium-mediated transformation. Crop Sci. 40: 797–803, 2000. 17. Z. Zhang, A. Xing, P. Staswick, and T.E. Clemente. The use of glufosinate as a selective agent in Agrobacteriummediated transformation of soybean. Plant Cell Tissue Organ. Cult. 56: 37–46, 1999. 18. W.A. Parrott and T.E. Clemente. Transgenic soybean. In: J.E. Specht and H.R. Boerma, Eds., Soybeans: Improvement, Production and Uses, 3rd ed., Agronomy Monograph No. 16. Madison, WI, ASA-CSA-SSSA, 2004. 19. Z. Svab and P. Maliga. High-frequency plastid transformation in tobacco by selection for a chimeric aadA gene. Proc. Natl. Acad. Sci. USA 90: 913–917, 1993. 20. H.N. Trick, R.D. Dinkins, E.R. Santarem, R. Di, V. Samoylov, C. Meurer, D. Walker, W.A. Parrott, J.J. Finer, and G.B. Collins. Recent advances in soybean transformation. Plant Tissue Cult. Biotech. 3: 9–26, 1997. 21. P. Staswick, Z. Zhang, T. Clemente, and J. Specht. Efficient down regulation of the major vegetative storage protein genes in transgenic soybean does not compromise plant productivity. Plant Physiol. 127: 1819–1826, 2001. 22. T. Buhr, S. Sato, F. Ebrahim, A. Xing, Y. Zhou, M. Mathiesen, B. Schweiger, A. Kinney, P. Staswick, and T. Clemente. Ribozyme termination of RNA transcripts down-regulate seed fatty acid genes in transgenic soybean. Plant J. 30: 155–63, 2002. 23. S.M. Rahman, T. Kinoshita, T. Anai, and Y. Takagi. Combining ability in loci for high oleic and low linolenic acids in soybean. Crop Sci. 41: 26–29, 2001.

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24. J.L. Glancey, S. Knowlton, and E.R. Benson. Development of a high oleic soybean oil-based hydraulic fluid. Feedstocks (United Soybean Board Publication) 4: 1–2, 1999. 25. E.B. Cahoon, T.J. Carlson, K.G. Ripp, B.J. Schweiger, G.A. Cook, S.E. Hall, and A.J. Kinney. Biosynthetic origin of conjugated double bonds: production of fatty acid components of high-value drying oils in transgenic soybean embryos. Proc. Natl. Acad. Sci. USA 96: 12395–12940, 1999. 26. E.B. Cahoon, K.G. Ripp, S.E. Hall, and A.J. Kinney. Formation of conjugated
8 ,
10 double bonds by
12 -oleic acid desaturase related enzymes: biosynthetic origin of calendic acid. J. Biol. Chem. 276: 2637–2643, 2001. 27. E.B. Cahoon, K.G. Ripp, S.E. Hall, and B. McGonigle. Transgenic production of epoxy fatty acids by expression of a cytochrome P450 enzyme from Euphorbia lagascae seed. Plant Physiol. 128: 615–624, 2002. 28. T.A. Isbell, T.P. Abbot, and K.D. Carlson. Oxidative stability index of vegetable oils in binary mixtures with meadowfoam oil. Ind. Crops Prod. 9: 115–123, 1999. 29. A. Adhvaryu and S.Z. Erhan. Epoxidized soybean oil as a potential source of high-temperature lubricants. Ind. Crops Prod. 15: 247–254, 2002. 30. W.D. Hitz. Fatty acid modifying enzymes from developing seeds of Vernonia galamensis. U.S. Patent No. 5,846,784, 1998. 31. F.J. Hidalgo, G. Gomez, J.L. Navarro, and R. Zamora. Oil stability prediction by high-resolution 13 C nuclear magnetic resonance spectroscopy. J. Agric. Food Chem. 50: 5825– 5831, 2002. 32. E. Collakova and D. DellaPenna. Isolation and functional analysis of homogentisate phytyltransferase from Synechocystis sp. PCC 6803 and Arabidopsis. Plant Physiol. 127: 1113–1124, 2001. 33. E.B. Cahoon, S.E. Hall, K.G. Ripp, T.S. Ganzke, W.D. Hitz, and S.J. Coughlan. Metabolic redesign of Vitamin E biosynthesis in plants for tocotrienol production and increased antioxidant content. Nature Biotechnol. 21: 1082–1087, 2003. 34. B. Savidge, J.D. Weiss, Y.-H.H. Wong, M.W. Lassner, T.A. Mitsky, C.K. Shewmaker, D. Post-Beittenmiller, and H.E. Valentin. Isolation and characterization of homogentisate phytyltransferase genes from Synechocystis sp. PCC 6803 and Arabidopsis. Plant Physiol. 129: 321–332, 2002.

Part III Applications

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24

Automotive Crankcase Oils Stephen C. Lakes CONTENTS 24.1 Introduction 24.1.1 Engine Oil Applications 24.1.2 Performance Requirements for Engine Oils 24.1.3 Requirements for Gasoline Engine Oils 24.1.4 Diesel Engine Oils 24.2 Historical Aspects of Synthetic Engine Oils 24.2.1 Early Fluids 24.2.2 Need for Synthetic Engine Oils 24.3 Types of Synthetics 24.3.1 Definition 24.3.2 Synthetic Basestocks 24.4 Comparative Performance Data 24.4.1 Bulk Physical Properties 24.4.2 High-Temperature Performance 24.4.3 Low-Temperature Characteristics 24.4.4 Antiwear Performance 24.4.5 Shear Stability 24.4.6 Oxidative/Thermal Stability 24.4.7 Hydrolytic Stability 24.4.8 Lubricity 24.4.9 Compatibility/Miscibility 24.4.10 Service Life of Synthetic Oils 24.5 Synthetics in the Marketplace 24.6 Summary References

24.1 INTRODUCTION Crankcase engine oils are the most recognizable lubricants in the automotive area. Both the individual and commercial consumer equate their vehicle lubrication with the engine oil. Millions in advertising budget are spent worldwide to promote specific brands in this area. The engines themselves and the crankcase lubricants protecting them have been upgraded over the last five decades such that engine life for gasoline passenger cars and heavy-duty diesel trucks are longer than ever before. Synthetic engine oils have been commercially marketed since the 1960s, but have taken only a small share of the large engine oil market worldwide. The European PCMO (passenger car motor oil), LDDO (light-duty diesel oil), and HDDO (heavy-duty diesel oil) market utilizes the highest proportion of full or partial synthetic engine oils,

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with the North American and Far Eastern areas lagging behind on synthetic use for this application. Synthetic based engine oils exhibit improved viscometric, volatility, and thermal stability properties over conventional petroleum based oils. Improved engine tolerances, governmental emission regulations, and fuel economy requirements are promoting improved performance engine oils and more stringent basestock requirements. Synthetics will play an important role in the future both in full synthetic formulations and as basestock or additive component in partial synthetic oils.

24.1.1 Engine Oil Applications There are several variations of internal combustion engines used as automotive power plants. Some use an oil sump or reservoir and others use an oil/fuel mix for lubrication.

Those engines with “crankcase fill” systems include four cycle gasoline engines, four and two cycle diesel engines, and unconventional fueled engines (natural gas, LP, alcohol, or vegetable oils). These internal combustion systems include both “direct drive” and “hybrid drive” vehicles. Hybrid vehicles are those in which an internal combustion engine runs a generator supplying power to electric motors that drive the wheels. This chapter will concentrate on lubricants used in crankcase oil sump lubrication systems. Two cycle motorcycle, outboard engines, and recreational vehicles, where the internal moving parts are lubricated by oil injection or oil/fuel mixtures are not included in this chapter. In crankcase fill engines, the lubricant is stored in the engine sump and is pumped or splashed onto the various moving parts during operation. The function of the engine oil encompasses friction reduction, wear reduction, cooling of internal components and collecting combustion by-products for removal. This by-product removal is accomplished by in-system filtration of the oil and a final drain of the used lubricant. Current automotive gasoline engines have an operating life of approximately 3,000 to 4,000 h and will use about 200 L of engine oil during that time. Most four cycle passenger car engines are scrapped for metal recycle, not rebuilt. On the other hand, heavyduty diesels for commercial over-the-road trucks will last approximately 15,000 h and use around 2,000 L of engine oil prior to rebuild. Preliminary studies of unconventional fueled engines have shown similar operating life and oil consumption compared to their gasoline or diesel fueled counterparts. Internal combustion engine life is measured as the operating hours before overhaul or engine replacement. The engine life is directly linked to the engine oil and whether it remains adequate to protect the critical moving parts. The primary areas for engine overhaul are the main bearings, the piston rings, and the cylinder walls. Excessive wear of the crankcase bearings will result in insufficient oil pressure in the internal galley and low oil delivery to the upper portion of the engine, resulting in accelerated wear and shortened life. Ring wear or sticking will result in power loss due to blowby and cylinder pressure leakage. Wear or glazing of the cylinder walls will result in excessive oil burning and subsequent power loss. The expectations for extended engine life by the individual or fleet operator are being reflected in increased awareness for engine oil performance. Improved cold weather starting, lower oil loss during operation and engine cleanliness are attributes that the consumer recognizes and demands of today’s oils. These combined with longer warranty protection from the equipment manufacturer are presenting an opportunity for synthetic basestock use. Synthetics can be added to improve mineral oil based formulations or used to make top tier full synthetic oils.

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TABLE 24.1 SAE Viscosity Grades for Engine Oils — SAE J300/Dec 99 Cold cranking viscosity (D-5293), cP

SAE viscosity grade 0W 5W 10W 15W 20W 25W 20 30 40 50 60

6200 at −35 6600 at −30 7000 at −25 7000 at −20 9500 at −15 13,000 at −10 — — — — —

Pumping viscosity max., cP (D-4684) 60,000 at −40 60,000 at −35 60,000 at −30 60,000 at −25 60,000 at −20 60,000 at −15 — — — — —

Kinematic 100◦ C viscosity (D-445), cSt Min. 3.8 3.8 4.1 5.6 5.6 9.3 5.6 9.3 12.5 16.3 21.9

Max. — — — — — — <9.3 <12.5 <16.3 <21.9 <26.1

TABLE 24.2 SAE J300 — Dec 99 High Temperature–High Shear Requirements (ASTM D-4683, ASTM D-4741, CEC L-36-90) SAE viscosity grade 20 30 40 40 40 50 60

HTHS at 150◦ C/106 sec−1 min. (cP) 2.6 2.9 2.9 2.9 (0W, 5W, 10W) 3.7 (15W, 20W, 25W) 3.7 3.7

24.1.2 Performance Requirements for Engine Oils The viscometric requirements for engine oils are categorized and defined in a group of viscosity grades defined under the “SAE Viscosity Grades for Engine Oils — SAE J300 Dec 1999” (Table 24.1). The predominant gasoline engine oils, in use, are the 5W30 through 10W40 multigrade oils. Passenger and heavy-duty diesel engine oils are mostly of 10W40 and 15W40 viscosity grades. After the viscosity grade has been defined, crankcase engine oils are classified into two major categories: Gasoline Engine Oils: API S, service category and A-96/02, European passenger car classifications.

Diesel Engine Oils: API C, commercial category, B-02 for European passenger diesel, and E-96/E-99/E-02, European heavy-duty diesel classifications. Alternative fuels are listed and defined in the “Alternative Automobile Fuels, SAE J1297, Mar93” and include LPG, ethanol, methanol, CNG, ethers (e.g., MTBE, TAME), and higher MW alcohols. No specified oil categories are available at this time for these fuels. It is currently under review by the SAE.

24.1.3 Requirements for Gasoline Engine Oils North American gasoline passenger car oils fall under the API and ILSAC categories. The API SL service category and ILSAC GF-3 (issued in 2001) comprise a set of engine tests for defining minimum oil performance: Sequence IIIF: Uses a 1996/1997 3800 CC General Motors V-block six cylinder commercial engine. This test evaluates an engine oil’s ability to resist oil thickening, piston deposits, sludge formation and cam lobe, lifter wear in the engine under high-temperature oxidation conditions. The used lubricant is analyzed for Kv40 increase and wear metals (Cu, Pb, Fe). Sequence IVA: Uses a KA-24E Nissan 2.4 L four cylinder in-line commercial engine. This 100 h test evaluates the lubricants to prevent camshaft lobe wear. The used lubricant is analyzed for Kv100, fuel dilution, and wear metals (Cu, Fe, Al). Sequence VG: Uses a 1994, 4.6 L Ford V-block 8 cylinder commercial engine. This test evaluates an engine oil’s performance to resist sludge/varnish formation and overhead valve wear in the engine and degradation/wear products in the lubricant (Kv100, Pb, Al, Fe, Cu, Si, Pentane insolubles, Fuel Dilution, TBN). Sequence VIB: Uses a 1993 4.6 L Ford eight cylinder commercial engine. This test evaluates the effect of the engine oil on gasoline fuel economy compared to a reference oil. Sequence VIII: Uses a 42.5 cubic inch, single cylinder test engine. This test evaluates a lubricant’s performance in preventing bearing corrosion under high-temperature conditions. The used engine oil is measured for viscous shear stability by Kv100 and fuel-dried viscosity. Ball Rust Test: Uses a laboratory test rig to simulate shortterm service conditions for rust formation. The equipment consists of a mixing container, which contains hydraulic lifter balls immersed in the engine test oil at a controlled temperature under shaking conditions. A solution of mineral and organic acids are injected into the oil. The metal lifter balls are rated for surface discoloration and the formation of rust. Other testing required for the API SL/ILSAC GF-3 include a filterability test, a water tolerance test, catalyst compatibility (phosphorus content), an ASTM D-892

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sequence I-III foam test, a TEOST oxidation test, a gelation test (ASTM D-5133), and an SS&C (FTM 791, 3470.1). The European ACEA gasoline oil categories were introduced in 1994 as replacements for the G-4 and G-5 oil categories. These were finalized in December of 1995 and became effective in early 1996. Since that time, there have been period reviews and several categories have been updated. Unlike North America, the European requirements address multiple grades or categories of service-fill gasoline engine oil [1]: A1-02: General purpose oil intended for gasoline engines capable of using low friction, low viscosity lubricants with an HTHS of 2.6 to 3.5 cP. A2-96: General purpose engine oil with standard drain intervals. A3-02: Higher tier, extended drain, stay-in-grade engine oil where specified by the engine manufacturer. A4: Not used at this time A5-02: Highest tier, extended drain, stay-in-grade engine oil for high performance gasoline engines and where specified by the engine manufacturer. These European categories and sequence tests are defined as minimal by the ACEA, "The sequences define the minimum quality level of a product for self-certification to EELQMS and presentation to ACEA members. Performance parameters other than those covered by the tests shown or more stringent limits may be indicated by individual ACEA member companies” [1]. Some European OEM’s require additional engine testing for specific usage, factory fill, or warranty application. Sequence laboratory and performance tests for ACEA include, but are not limited to: Peugeot TU5JP-L4 High Temperature Test: Uses a modified 1.5 L Peugeot TU5JP in-line four cylinder engine mounted on a dynamometer stand. This test evaluates an engine oil’s performance under high temperature, high speed conditions to resist ring sticking and piston deposits in the engine and viscosity increase in the lubricant (procedure listed as CEC L-88-T-xx). Peugeot TU3M Wear Test: Uses a 1.3 L Peugeot TU3M/KDX commercial four cylinder engine. This test evaluates an oil’s performance under slow and moderate speed/low temperature conditions to resist valve train wear (procedure listed as CEC L-38-A-94). Sequence VG: Same as API SL (please refer to previous API SL section). MB M111 Black Sludge Test: Uses a 2.0 L Mercedes Benz M111 E20 four cylinder commercial engine. This test evaluates an oil’s performance under varied driving conditions (urban to autobahn) to resist sludge formation in the cylinder head area, piston varnish and ring sticking in the engine. The lubricant is tested for viscosity change, fuel dilution,

TBN, sulfated ash, solids, and wear metals (procedure listed as CEC L-53-T-95). MB M111 Fuel Economy Test: Uses a modified 2.0 L Mercedes Benz M111 E20 four cylinder engine. This test evaluates the effect of the engine oil on gasoline fuel economy compared to a reference oil (procedure listed as CEC L-54-T-96).

measured for viscosity increase, soot loading, maximum oil pressure drop at the filter, and oil consumption. Mack T-9: Uses a 1994, 350 HP, in-line six cylinder commercial Mack engine. This engine test measures an engine oil’s capability to minimize piston cylinder liner and ring wear. The used oil is analyzed for Kv100, soot level, TAN, TBN, and Pb content.

The ACEA A series gasoline engine oil categories also include bench testing for shear stability, HTHS, NOACK volatility, sulfated ash limits, foaming properties, and elastomer compatibility limits.

The API CI-4 HDDO category was issued in 2002 to address the 2004 exhaust emission standards and uses the following engine tests:

24.1.4 Diesel Engine Oils North American diesel engine oils are predominately for heavy-duty commercial use. The API CG-4, CH-4, and CI-4 are the current HDDO categories and MIL-L-2104F military category use a set of engine tests for defining minimum oil performance. The API CH-4 was issued in 1998 and utilizes the following sequence testing: Sequence IIIE: Uses a 1986 231 cubic inch General Motors V-block six cylinder engine modified with an external oil sump cooler and jacketed rocker arm covers. This test evaluates a lubricant’s ability at inhibiting high-temperature oxidation and retarding cam and valve lifter wear. The used oil is evaluated for Kv100 increase. Roller Follower Wear: Uses a 6.5 L, 160 HP General Motors commercial diesel engine. This test is to evaluate an engine oil’s performance on the camshaft roller follower wear. Used oil analysis includes Kv100, Kv40, TBN, and wear metals taken on periodic samples. Caterpillar 1P: Uses a Caterpillar 1Y3700, 148.8 cubic inch, single cylinder test engine. This test measures an oil’s ability to resist formation of excess piston deposits, specifically related to ring sticking and inhibit piston, ring and liner scuffing. The oil consumption in g/kW-h is also measured. The used lubricant is analyzed for viscosity change, TBN, TAN, and wear metals. Caterpillar 1K: Uses a Caterpillar 1Y540, 148.8 cubic inch, single cylinder test engine. This test measures an oil’s ability to resist formation of excess piston deposits, specifically related to ring sticking and inhibit piston, ring and liner scuffing. The oil consumption in g/kW-h is also measured. The used lubricant is analyzed for viscosity change, TBN, and wear metals. Cummins M-11: Uses a modified 425 HP Cummins engine. This test measures the capabilities of an engine oil at moderating soot related wear of overhead components. Used oil analysis includes Kv100, Kv40, TAN, TBN and wear additives on periodic sampling. Mack T-8E: Uses an 11.93 L, six cylinder Mack E7-350 commercial diesel engine with exhaust gas recycle. This engine test measures an oil’s ability to resist viscosity increase due to excessive soot formation. The engine oil is

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Cummins M-11: Same as API CH-4 (see previous section). Mack T-8E: Same as API CH-4 (see previous section). Roller Follower Wear: Same as API CH-4 (see previous section). Sequence IIIF: Same as API SL/ILSAC GF-3 (see previous service-fill section). Caterpillar 1K or 1N: Uses a 148.8 CID single cylinder Caterpillar test engine. This test measures an oil’s ability to resist formation of excess piston deposits, specifically the top land and top groove areas of the piston. The oil consumption in g/kW-h is also measured. Caterpillar 1R: Uses a Caterpillar 1Y3700, 148.8 cubic inch, single cylinder test engine equipped with a two piece steel/aluminum piston. This test measures an oil’s ability to resist formation of excess piston deposits, specifically related to ring sticking and inhibit piston, ring, and liner scuffing for ferrous pistons. The used lubricant is analyzed for viscosity change, TBN, TAN, and wear metals. Mack T-10: Uses a modified, 460 HP, E7 Mack diesel engine. This test evaluates an oil’s performance for piston liner, ring and bearing wear in engines with exhaust gas recirculation. The used oil is analyzed for Kv100, soot level, TAN, TBN, Pb wear metal, and FTIR oxidation. The CI-4 test program also involves the ASTM D6594 Corrosion Bench Test, the ASTM D-4683 HTHS viscosity spec, the ASTM D-4684 used oil pumpability test, the ASTM D-5800 NOACK volatility, the ASTM D-6278 shear stability, the EOAT aeration test, elastomer compatibility, and the ASTM D-892 Foam Test (Seq I-III). Currently, the industry is laying the groundwork for the next generation diesel engine categories (API PC-10 and PC-11 in North America). The driving force for both the North American and European changes are the more stringent emission requirements (Figure 24.1). For North America, U.S. Federal Regulations are following the current trend. The engineering challenge during these changes are that the OEM and final end user will not readily accept shorter drain intervals or shortened engine overhaul life. The industry is pushing for both extended oil drains and maintaining engine life. European diesel engine oils are designated for lightduty use (passenger cars and light vans) or heavy-duty use (medium to heavy-duty trucks and vans). ACEA uses

Emission Requirements — Heavy Duty Diesel Engines (g/bhp-h) U.S. Federal Regulations Model HydroCarbon Oxides Fuel Year Carbons Monoxide of Nitrogen Particulate Sulfur 1985 1987 1988 1991 1994 1998 2002 2006 2007

1.9 37.1 1.3 15.5 1.3 15.5 1.3 15.5 1.3 15.5 1.3 15.5 1.3 15.5 1.3 15.5 (0.5)* 15.5

10.6 10.6 6.0 5.0 5.0 4.0 2.0 2.0

0.6 .28 0.6 .28 0.6 .28 0.25 .28 0.10 .05 0.10 .05 0.10 .05 0.10 (.0015) (0.5)* (0.01) (.0015)

FIGURE 24.1 Emission requirements — Heavy-duty diesel engines (From “Automotive Applications,” part of the STLE Synthetic Lubricants Education Course)

the B class designation for light-duty and E class designation for heavy-duty diesel. European OEMs may also require additional engine testing for specific usage and warranty applications. European Light-Duty Diesel (Passenger Cars/Vans): B1-02: General purpose diesel engine oil for those engines capable of using low friction, low viscosity oils with a HTHS of 2.5 to 3.5 cP B2-98: General purpose diesel engine oil for standard drain (primarily indirect injection) requirements B3-98: Diesel engine oil for use in high performance car and light van. May be extended drain under some circumstances B4-02: Higher tier, stable, stay-in-grade oil for cars and light vans with direct injection diesel engines. B5-02: Highest tier, stable, stay-in-grade oil for cars and light vans capable of using low friction, low viscosity oils with HTHS of 2.9 to 3.5 cP Sequence testing for these requirements include: MB OM 602A: Uses a 2.5 L Mercedes Benz commercial engine. This test is used for all three categories and measures an oil’s ability to resist cam wear, bore polishing, sludge formation, cylinder cleanliness, and excessive oil consumption in the engine. The engine oil is measured for viscosity increase and wear metals (procedure listed as CEC L-51-T-98). VW 1.6 L TC: Uses a 1.6 L TC Intercooled Volkswagen commercial diesel engine. This test measures an engine oil’s ability to resist ring sticking and piston cleanliness under high-temperature conditions (procedure listed as CEC L-46-T-93). XUD11BTE: Uses a 2.1 L Peugeot commercial diesel engine. This test measures an engine oil’s ability to resist ring sticking and piston cleanliness (merit system).

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The engine oil is measured for viscosity increase under soot loading conditions (procedure listed as CEC L-56-T-98). MB M111E: Uses a 2.0 L, four cylinder, M111 Mercedes Benz gasoline engine. This test measures the effect of the candidate oil on the fuel economy compared to a reference oil (procedure listed as CEC L-54-T-96). The B class category of diesel service-fill oils also include a CEC-L-14-A-93 shear stability, the CEC-L-36A-97 HTHS requirement, the CEC-L-40-A-93 NOACK volatility, the ASTM D-874 sulfated ash, the CEC-L-39T-96 seal compatibility, the ASTM D-892 Seq I–III foam test, and the ASTM D-6082 high-temperature foam test. European Heavy-Duty Diesel (Trucks/Off Road Equipment): E2-96: General purpose HDDO for naturally aspirated and turbocharged under standard drain intervals E3-96: General purpose HDDO for those diesel engines meeting Euro 1 and Euro 2 emission requirements. Some extended drain intervals are permissible according to manufacturers, recommendations E4-99: Higher tier HDDO, exhibiting stable, stay-ingrade capabilities for those diesel engines meeting Euro 1, 2, and 3 emission requirements. Extended drain capable according to manufacturers recommendations E5-02: Highest tier HDDO, with improved deposit control, soot handling and lubricant stability compared to E3. Recommended for use in highly rated diesel engines meeting Euro 1, 2, and 3 emission requirements. Extended drain capable according to manufacturers’ recommendations Sequence tests for these categories include: MB OM 602A: Same test platform and conditions as B category oils (see European light duty section). Mack T-8: Uses an 11.93 L, six cylinder Mack E7-350 commercial diesel engine. This engine test measures an oil’s ability to resist viscosity increase due to excessive soot formation. The engine oil is measured for viscosity increase, soot loading, maximum oil pressure drop at the filter, and oil consumption. Mack T-8E: Same test platform and conditions as API CH-4 and CI-4 (see North American diesel section). MB OM 364A: Uses a 3.97 L Mercedes Benz commercial diesel engine. This test is used in all three categories with different passing criteria. This test measures an oil’s ability to resist bore polishing, piston varnish/deposits, sludge formation, cylinder wear, and excessive oil consumption (procedure listed as CEC L-42-A-92). MB OM 441LA: Uses a 313 HP, 364 cubic inch Mercedes Benz commercial diesel engine. This test measures an engine oil’s ability to inhibit piston liner bore polishing,

piston carbon/varnish, and oil consumption (procedure listed as CEC L-52-T-97). The E class categories also utilize the CEC L-14-A-93 shear stability test, the CEC L-36-A-97 HTHS viscosity, the CEC L-40-A-93 NOACK volatility, the ASTM D-874 Sulfated Ash, the ASTM D-892 sequence I–III foaming properties, the CEC L-85-T-99 PDSC oxidation test, the ASTM D-5968 Pb corrosion test, and elastomer compatibility.

24.2 HISTORICAL ASPECTS OF SYNTHETIC ENGINE OILS 24.2.1 Early Fluids Synthetic hydrocarbons and esters for engine lubricants were initially researched in the 1920s and 30s. Both Sullivan et al. of Standard Oil in the United States [2,3] and Zorn of I.G. Farber in Germany [4] were investigating the polymerization of olefins to form improved engine oil basestocks. These were the first synthetic hydrocarbons comparable to the polyalphaolefins (PAOs) of today. Ester basestocks were also under development at the same time for improved low temperature properties. These synthetic basestocks never realized significant engine oil commercialization for economic and supply reasons. During the 1940s, with the development of the turboprop and jet turbine aircraft engines, ester lubricant development was renewed. However, it was not until the 1960s with the interest of military and the construction requirements for cold weather arctic conditions that synthetic engine lubricants had a resurgence. In the 70s with higher crude oil prices, interest developed in synthetic engine oils for the commercial market. These formulations used ester basestocks initially and later used PAO in full and partial synthetic formulations. In the 1970s, several engine oil producers in the United States marketed products for passenger car engine oils. Synthetic products were also developed and marketed in Europe and Japan during this time. Worldwide, synthetic engine oils were very slow to be accepted and they still comprise a small market share. Engine manufacturers are beginning to recognize the benefits of full and partial synthetic oils.

24.2.2 Need for Synthetic Engine Oils There are only three reasons for a consumer to use synthetic or partial synthetic engine oils. • It solves a technical problem • Improved economics in its use • Governmental regulations

Technical requirements may involve using synthetics to satisfy high or low temperature properties, improved oil

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durability, or improved engine test performance. In Europe, the addition of PAO and ester basestocks have allowed oil formulators to satisfy increased thermal/oxidative stability requirements, improved volatility specifications and better low temperature starting. In North America, OEMs are requiring more stringent lubricant performance in engine cleanliness, improved volatility, and low temperature pumping/starting. OEMs are starting to specify synthetic engine oils for some high performance applications (e.g., GM Chevrolet Corvette). Full synthetic arctic engine oils have been used by the U.S. military, NATO, and civilian companies since the early 1970s for use in extreme cold weather conditions (MIL-L-46167B and MIL-PRF-46167C). The use of synthetics in engine oils is just starting to involve economic justification in the marketplace. The consumer, whether it is an individual with a passenger car, a leasing company with return vehicles, or a business with a fleet of trucks, is beginning to recognize the economic advantage of increased engine life associated with higher performing oils. This can be shown for extended vehicle service or residuals on resale. High performance heavy-duty diesel engine oils are under development and testing to extend the oil drain interval and lower maintenance costs. This, while maintaining or increasing the engine operating life. Synthetic components (PAO, diester, polyol esters) are being evaluated in conjunction with high performance additive systems for this “next generation” HDDO. These components are being added at 5 to 30 wt.% with petroleum basestock for enhanced additive and by-product solubility, improved engine cleanliness, viscometric properties, and lower oil volatility. Worldwide, government regulations are starting to reflect concerns about vehicle fuel usage and the environmental impact of the products of the internal combustion engine. These regulations are affecting vehicle and engine design and formulations for the lubricants used in these vehicles. Fuel economy has been under government guideline since the 1970s (CAFE in the United States). Heavyduty diesel emissions guidelines in 1978, 1994, and 1998 in North America and corresponding requirements in Europe and the Far East are changing the engines and oils. All of these requirements are designed to promote more efficient energy usage and less environmental impact from these engines.

24.3 TYPES OF SYNTHETICS 24.3.1 Definition In no other area of lubrication has the definition of “synthetic” generated as much debate or confusion than for engine oils. Technical definitions are being combined with performance attributes to promote highly modified

petroleum oils as a “synthetic” or “synthetic performing” product. The reasons are economic and are related to business goals. The use of the label “synthetic” has a high performance connotation for the engine oil consumer and can justify a higher price. For this chapter, “synthetic” will be defined as a technical category. The ASTM definition is “synthetic lubricant is a product which consists of stocks manufactured by chemical synthesis and containing necessary performance additives.” To the chemical technologist, synthesis involves taking small chemical building blocks and combining them in a predictable, ordered reaction to form precise large molecules.

24.3.2 Synthetic Basestocks For engine oils, the term synthetic refers to the basestock portion of the compounded oil. The additives and any polymers present are usually considered synthetic, being synthesized for specific chemical purposes. The basestock constituent can be made from petroleum or synthesized structures or from a combination of the two. The predominant synthetic basestocks currently used in engine oils are PAO and carboxylic acid esters (diesters, polyol esters, or complex esters). Other synthetics include PIOs, PAGs, phosphate esters, silicones, alkylated aromatics, but these constitute only a small market share and if used are only present at additive levels in commercial engine oils. PAO and esters may be used at various levels in gasoline and diesel engine oils. Most oil formulators consider up to 10% as an additive level treat and 10% or higher as a basestock addition. Full synthetic gasoline engine oils are usually all PAO or a mixture of PAO/ester. Full synthetics using only ester basestock were developed and marketed in the 1970s. These oils showed good thermal stability and cleanliness,

but seal and petroleum oil compatibility questions relegated them to small niche, specific use areas. The all PAO and PAO/ester synthetic gasoline engine oils do not exhibit these deficiencies and are being successfully marketed throughout the world. Full synthetic diesel engine oils have been developed, but have attained little market share due to cost reasons. Partial synthetics utilize the addition of PAO, ester or PAO/ester combination to enhance the performance of a petroleum based engine oil. Typical levels are 5 to 30 wt.% in Group I or II base oils. Compared to conventional and unconventional petroleum oils (CBOs and UCBOs), PAO or ester contribute additional desirable performance properties to the formulated oil. Most additive systems for engine oils were developed for a petroleum based system and may not be suitable for synthetic oils. Additive selection for synthetics and partial synthetics are affected by the type and quantity of the basestock present. All PAO formulations usually show lower solubility for the polar additive packages compared to petroleum. These polar additives moderate detergent, dispersant, TBN, antiwear, and anticorrosion performance properties. For the engine oil formulator, the screening for acceptable additives or the incorporation of longer, alkyl chains on the additive molecules may have to be considered. Ester containing formulations usually show higher solubility for these polar additives compared to PAO or petroleum basestocks. A combination of both PAO and ester may be used to “dial in” a specific polarity index to the basestock to maximize additive and by-product solubility. Elastomer compatibility (seals, gaskets) may also be accurately defined with a mixed PAO/ester system without the use of a seal swell agent. Polymers used for viscosity index improvement or thickening can also be affected by the basestock type. The use of PAO or ester can alter the polarity of the oil sufficiently to impact compatibility of some oligomers. All

Automotive Lubricant Basestocks Basestock Changes to Gasoline/Diesel Engine Oils Addition of:

PETROLEUM

SYNTHETIC

API Group 1 thru 3 HighÐLow VI Neutral Oils Hydro-finished Oils

API Group 4 and 5 PAO Organic Esters - diesters - polyol esters

FIGURE 24.2 Automotive lubricant basestock types (From “Automotive Applications,” part of the STLE Synthetic Lubricants Education Course)

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Improved Viscometrics Improved Low Temp Properties Improved Volatility Improved High Temp Stability Detergent/Dispersant Credit Tailored Seal Swell Properties Improved Additive Solubility Improved Piston Cleanliness Improved Frictional Properties

Petroleum Synthetic UCBO PAO ESTER ! ! ! !

! ! ! ! ! ! !

! ! ! ! ! ! ! ! ! ! ! ! !

FIGURE 24.3 Effect of basestock addition to gasoline and diesel engine oils (From “Automotive Applications,” part of the STLE Synthetic Lubricants Education Course)

formulated oils, when evaluating an unknown system or polymer, should be fully tested for storage and high and low temperature compatibility as part of the testing regime.

24.4 COMPARATIVE PERFORMANCE DATA 24.4.1 Bulk Physical Properties The predominant viscosity grades for synthetic basestocks in engine oils are 4 to 6 cSt (at 100◦ C). This conforms to a 100 to 200 SN petroleum oil. PAO and ester (diester, polyol ester) usually show improved viscometrics, higher viscosity index, improved low temperature properties, and lower volatility compared to petroleum basestock.

4cSt Basestock Comparison Test Parameters

100 SN HC-4 PAO-4

100°C Visc, cSt 40°C Visc, cSt –18°C Visc, cSt –40°C Visc, cSt Viscosity index Pour Pt. °C Flash Pt. °C NOACK,% Loss

4.2 21.6 solid solid 95 –15 199 29.2

4.0 17.5 — solid 127 –22 236 16.0

3.9 16.9 314 2500 123 –69 225 13.0

Polyol Diester Ester 4.3 17.5 370 3500 161 <–65 232 7.7

4.1 18.1 — 3750 130 –69 250 3.8

FIGURE 24.4 cSt viscosity basestock comparison (From “Automotive Applications,” part of the STLE Synthetic Lubricants Education Course)

24.4.2 High-Temperature Performance Automotive synthetic basestocks (PAO and Ester) exhibit improved high-temperature properties compared to comparable viscosity petroleum oils. These improvements are characterized by viscosity retention at high temperature (due to a higher viscosity index), higher flash points, and lower volatility. Higher viscosity index basestocks, whether petroleum or synthetic, will exhibit lower viscosity loss at higher temperatures. This property will translate into higher film strength for hydrodynamic and elastohydrodynamic lubrication in the engine. At high temperatures this will equate into improved protection for bearings (sleeve, ball, or needle) and rotating seals. The High-Temperature High Shear (HTHS) is a test method for predicting viscosity effects for bearing wear for automotive engine [5]. Higher wear protection (boundary lubrication) will usually be handled by the antiwear additives present (i.e., cams, valve lifters, piston rings, and liners). Flash points are performed on engine oils to measure an oil’s flammability limits for storage and handling. DOT shipping requirements and OEM safety guidelines limit the flash points for commercial gasoline and diesel engine lubricants. The predominant test utilized for engine oils is the ASTM D-92 Cleveland Open Cup Method. Petroleum based oils are composed of a wide range of molecular weights within a distillation fraction. By contrast, synthetic basestocks are more highly controlled for structures and composition when compared with these refined basestocks. This results in tighter molecular weights and lower extraneous functional groups present that may impact flash points. As shown in Figure 24.4 and Figure 24.5, PAOs and Esters exhibit higher flash points over comparable viscosity petroleum basestocks. Esters, by containing polar functional groups, will exhibit higher flash points compared to similar molecular weight petroleum or PAO feeds. This is due to hydrogen bonding on the molecular level. Care must be exercised in the preparation and refining of esters to ensure low levels of

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6 cSt Basestock Comparison Test 200SN HC-6 Parameters 100°C Visc, cSt 40°C Visc, cSt –18°C Visc, cSt –40°C Visc, cSt Viscosity index Pour pt. °C Flash pt. °C NOACK, % loss

6.2 42.7 solid solid 97 –15 215 12.8

5.6 32.1 solid solid 130 –12 — 8.9

Polyol PAO-6 Diester 5.9 30.9 1200 8300 135 –60 243 7.5

Ester

6.4 5.6 33.8 32.4 1300 — 18700 30,000 145 114 –57 –54 243 254 4.7 3

FIGURE 24.5 cSt viscosity basestock comparison (From “Automotive Applications,” part of the STLE Synthetic Lubricants Education Course)

unreacted acids or alcohols. These low molecular weight components will have a significant impact on flash point. Addition of synthetic components to petroleum based engine oils will have minor impact on improving the flash point. Full synthetic engine oils usually exhibit better flash point properties than petroleum based oils. Fire points (temperature where an oil will sustain combustion) is similar for the same molecular weight petroleum, PAO, or ester based engine oils. Engine oil volatility is a measure of an oil’s resistance to evaporate under high-temperature operating conditions. This is important for an engine lubricant, because the loss of lower molecular weight components can significantly impact the viscosity properties. A 5W30 oil, which shows excessive volatility loss, may end up being a 10W40 or higher viscosity grade oil after several hundred miles’ service. A correlation has been established between NOACK volatility and oil consumption [6]. Several methods are used for measuring volatility including ASTM D2887 distillation method and the CEC L-40-T-87 NOACK volatility test. Synthetic basestocks have lower volatility losses by both methods [7]. (please refer to Figure 24.4 and Figure 24.5 for comparative

4000

! Diester

30

! Polyol Ester

20 10 0 0

20

40

60

80

100

Viscosity, cP (-25°C)

NOACK Vol., wt.%

40

2500

0

One of the strong areas for full synthetic engine lubricants is their low temperature flow and viscosity properties. PAO and ester basestocks show significantly lower pour points than their corresponding petroleum oils (please refer to Figure 24.4 and Figure 24.5). This is due to the molecular structure and lack of crystalline wax particles present in some refined petroleum oils. These lower pour points translate into better low temperature flow and protection in both gasoline and diesel engine oils. These low temperature flow properties may be measured in gasoline and diesel engine oils using laboratory viscosity methods (ASTM D-5293; Cold Crank Simulator, ASTM D-4684; MRV Pumping, Scanning Brookfield Viscosity), cold box simulation testing, and field conditions [9–13]. The low pour properties of the synthetic basestocks provide the formulator a tool for adjusting petroleum based engine oils for improved low temperature properties. Both PAO and ester may be used for this improvement. As an example, the addition of PAO (PAO-4) to a 5W-30 petroleum based engine oil showed improved low temperature viscosity and pour points. Typical petroleum based engine oils contain pour point depressants (ppds) which interrupt the crystal lattice formation of the wax content. The addition of synthetic basestock usually allows the removal of the pour point depressant from the additive package. Some low temperature compatibility problems have been experienced with the use of certain pour point depressants and synthetics. This may

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10

15

20

25

30

FIGURE 24.7 Low temperature cranking viscosity vs. PAO-4 addition in a petroleum 5W-30 gasoline engine oil [10]

–80 –70 –60 –50 –40 –30 –20 –10 0 0

24.4.3 Low-Temperature Characteristics

5

PAO-4 Addition (Wt %)

Pour Point, °C

NOACK volatility data). Unlike flash points, the addition of synthetic basestock can impact the overall volatility properties, even with small levels. The resulting final volatility will be approximately the algebraic calculation of the two components. Petroleum based engine lubricants can be topped off with PAO or ester to shift the volatility into the passing range. Both petroleum and synthetic low volatility basestocks have been investigated for formulating lower volatility engine lubricants [8].

3000

2000

% Ester In 100 Sn Basestock

FIGURE 24.6 NOACK volatility vs. ester type/ester content (From Cognis Corp./Synlubes Technology R&D, 1993, Internal Research)

3500

20

40

60

80

100

PAO-4 Addition, wt. %

FIGURE 24.8 ASTM D-97 pour point vs. PAO-4 addition in a petroleum 5W-30 gasoline engine oil [10]

cause slight hazing or precipitate floc of the ppd under low temperature, long-term storage. Specialty arctic engine oils have been developed for very low temperature usage, predominately for the military and the oil exploration industry. Full synthetics have been used for these applications since the mid-1970s and constitute the majority of these fluids for cold weather environments.

24.4.4 Antiwear Performance Engine oils require a certain level of antiwear capability. This antiwear requirement ensures the oil’s ability to protect those moving parts under boundary lubrication conditions. These may include rocker arm contacts, cams, and cylinder ring/wall contact areas. In modern engine oil formulations, this antiwear is predominately supplied by the additive package. The basestock portion, either petroleum or synthetic, has little antiwear capability. Petroleum oils may have a small amount of antiwear present as trace levels of sulfur, nitrogen, or phosphorus functionality from the crude petroleum source, but contain an insufficient amount to provide protection for modern engines. The use of PAO may require a higher uptreat of antiwear additive due to the absence of these “natural” additives.

PAO will be similar to petroleum for the treat level effect of most antiwear additive systems. Ester containing engine oils may also require an uptreat of antiwear additive to achieve the same level of protection as petroleum based systems. Esters are more polar than both petroleum and PAO and may compete at the metal surface with any polar additives (antiwear, corrosion inhibitors, etc.).

24.4.5 Shear Stability Most multigrade gasoline or diesel engine oils use a viscosity polymer for thickening the oil and improving the viscosity index. This allows the formulation of a cross-graded product that exhibits good viscometric profiles both at high temperatures under operating conditions and low temperatures during starting. The introduction of viscosity polymers required the industry to evaluate the properties of temporary and permanent viscosity loss under various shear conditions. HTHS (ASTM D4624 and D4683) is used to measure the temporary viscosity loss under high shear load, which simulates the condition of the oil in the crankshaft bearings. The use of synthetic basestocks may improve the HTHS slightly due to their higher viscosity index, but this effect is usually small compared to the contribution of the viscosity polymer. Permanent shear loss is measured by subjecting the motor oil to a sufficient shear force to cause breakage of the polymer structures resulting in viscosity loss. Several procedures are available for shear stability testing of engine oils. These include sonic shear (ASTM 2603), Orbahn Shear (D3945), and Bosch Injector (CEC L-14). Synthetic automotive basestocks (PAO, Esters) are similar to petroleum and show little or no viscosity loss under these tests. Some specialized esters used in biodegradable and two cycle applications exhibit some shear instability under high shear. These are not normally used for automotive “crankcase fill” engine oils. Care should be exercised in the selection of a viscosity polymer for use with partial or full synthetic engine oils. Some polymers show incompatibility with all PAO or PAO/esters systems. This incompatibility may manifest itself in immediate insolubility of the polymer in the basestock or separation in storage. Any formulation work involving new polymers or systems should include compatibility and storage testing under a variety of temperature conditions.

24.4.6 Oxidative/Thermal Stability PAO and ester basestocks show improved resistance to oxidative and thermal degradation compared to petroleum base oils. Oxidative stability of “inhibited” automotive

Copyright 2006 by Taylor & Francis Group, LLC

TABLE 24.3 Recommended Maximum Bulk Oil Temperatures for Various Inhibited Lubricant Basestocks Base fluid Petroleum PAO Diesters Polyol esters

Max. bulk oil temp. (◦ F) 250 250–350 300–350 350–425

basestocks shows the following progression: petroleum base oil < PAO < diesters < polyol esters Oxidative Stability This resistance of the synthetic basestocks is also shown in the recommended maximum bulk oil temperatures (Table 24.3). The service life of gasoline and diesel engine lubricants is a reflection of the basestock stability, the additive stability and holding capacity for by-products and wear metals. The oxidative and thermal stability of engine oils is measured by the increase in viscosity during engine testing (Sequence IIIF, Sequence VG, Peugeot TU3M High-Temperature Test, MB M111 Black Sludge Test and the MB OM 602A Diesel Test). Evaluations of a laboratory test (TEOST) to simulate the IIIE and of the IIIF test for high-temperature deposits are underway. The correlation of these tests is still under review [14,15]. The use of full synthetic engine oil formulations have shown some improvement in viscosity control and engine cleanliness over petroleum based oils [13,16,19,20,22,23]. These full synthetics have been all ester based, all PAO based, or a mixture of PAO/ester. The addition of PAO or ester to petroleum based engine oils for improved oxidative stability has shown mixed results. Laboratory work performed by Davis in the 1980s with PAO addition to petroleum 5W-30 gasoline engine oils showed oxidative improvement using the Thin Film Oxygen Uptake Test (TFOUT). Laboratory oxidation testing has shown improvement with the addition of either PAO or ester to petroleum formulations. There has been difficulty in translating laboratory thermal/oxidation tests to full-size engine tests. Most sequence engine tests show little or no improvement with the addition of lower levels of PAO or ester basestock (less than 5 wt.%). Field tests have shown mixed results in the success for synthetic addition in petroleum based formulations. Low levels of PAO addition (<15 wt.%) has not shown significant improvement in engine performance or cleanliness, but have shown improved oil consumption in heavy-duty diesel systems. Low level ester addition (<15 wt.%), has

Oxidation Induction Time, min.

220 200

TABLE 24.4 Examples of Typical Automotive Ester Basestocks

190

Diesters

210

180

di-2-ethylhexyl adipate di-isodecyl adipate di-isooctyl azelate di-isodecyl sebacate

170 160 150

Polyol esters Trimethylolpropane tri C9 Trimethylolpropane tri C8–10 Pentaerythritol tetra C9 Pentaerythritol tetra iso C9

140 0

10

20

30

40

50

60

70

80

90 100

PAO Addition, wt.%

FIGURE 24.9 Thin film oxygen uptake test (TFOUT) vs. PAO addition in a petroleum 5W-30 gasoline engine oil [17]

shown some ester basestocks to have improved engine cleanliness and oil consumption, whereas other ester types showed little or no improvement. Research tends to show this may be due to the bulk polarity of the final oil and its impact on the solubility of degradation product. During thermal, oxidative stressed conditions, both diester and polyol ester have shown improved basestock solubility over PAO and petroleum oil for retaining degradation by-products. This “detergency credit” helps to solubilize the more polar, oxidized hydrocarbon fragments, which would contribute to varnish and sludge formation. Some ester containing formulations have shown improved laboratory and field performance cleanliness in the piston and valve train areas.

24.4.7 Hydrolytic Stability Under normal operations, the internal combustion engine sees moisture in the engine oil from two sources. The first is from normal fuel combustion, which forms water vapor from the hydrogen present in the hydrocarbon fuels. Second, the oil sump is not a closed system and upon cool down will pull in outside, moisture laden air. In highway or extended driving conditions, both of these contribute small levels of water to the oil, usually less than 1000 ppm. When the engine reaches full operating temperature, the water is evaporated. Low mileage or stop-and-go driving conditions may show much higher levels of water in the oil due to insufficient oil temperature to properly evaporate out the water present. Engine oil must be able to handle these moisture cycles with no adverse reactivity or loss of performance. The predominant automotive synthetic basestocks (PAO, diesters, polyol esters) do not show any appreciable hydrolytic instability in engine oil applications. PAO is comparable to petroleum hydrocarbons in water solubility (insignificant) and hydrolytic reactivity (not detectable at automotive conditions). Esters, both diester and polyol esters, are the products from the reaction of a carboxylic acid and an alcohol. Under certain reaction conditions,

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esters can be hydrolyzed back to their reactants. Ester basestocks used for automotive engine oils have shown nondetectable or insignificant hydrolysis under automotive engine oil conditions.

24.4.8 Lubricity Lubricity is a measure of the effect of a lubricant on the coefficient of friction of a contacting part with a sliding surface. In engine oils, greater lubricity would impart improved fuel economy and lower frictional power loss. Fuel economy as measured in the Sequence VI, VIA, and MB M111 fuel economy tests is heavily influenced by the oil viscosity. Lubricity does have an effect with the addition of friction modifiers showing some improvement. Friction modifiers include some carboxylic acids, sulfurized fatty acids, glycerol mono-esters and oleate esters. Ester synthetic basestocks have shown some influence as friction modifiers in engine oils and in industrial applications. The esters, being more polar, are attracted to the metal surfaces and form monolayers. These thin layers reduce the coefficient of friction at the surface. Tests using a Low Velocity Friction Apparatus with ester containing engine oils have shown improved coefficient of frictions and corresponding fuel savings [18]. Caution should be exercised by the oil formulator, that this polar attraction does not adversely affect the surface active additives used and compete for antiwear and anticorrosion protection.

24.4.9 Compatibility/Miscibility The currently available, major brand, full, and partial synthetic engine oils in North America and Europe are fully compatible with the petroleum based engine oils. PAO and PAO/ester mixtures are soluble in most petroleum basestocks and present no problem for comixing in the engine with a conventional petroleum product. Most manufacturers do not recommend mixing engine oil brands due to the possible antagonism of the additive systems present. For the engine oil formulator, the additive solubility must be evaluated when introducing a synthetic basestock. Most engine oil additives are designed for petroleum systems and are polar in nature. All PAO full synthetic systems have shown some insolubility with certain additive packages. This is due to the lack of polar components

in the synthesized hydrocarbon, which would be normally present in most petroleum basestocks. Partial synthetic blends with PAO would be affected by the PAO/petroleum ratio. Any new formulation should be properly evaluated for additive solubility under both hot and cold storage conditions. Ester basestocks, being more polar than petroleum, show improved compatibility with most additive systems. A petroleum or PAO engine oil formulation with an additive insolubility can sometimes be corrected by the addition of diester or polyol ester.

24.4.10 Service Life of Synthetic Oils In the 1970s, the automobile manufacturers were promoting longer drain intervals. Some engine manufacturers were allowing up to 10,000 miles between oil changes for “standard” service. The introduction of full and partial synthetic engine oils had the potential for extending the drain even further with no loss in engine life. Several studies were performed on extended drain capabilities for synthetic engine oils [19–23]. The cost of the synthetic engine oil combined with a lowering of drain interval recommendations by the OEMs in the 1980s slowed the introduction and use of synthetics in North America. Currently, most manufacturers of synthetic gasoline engine oils recommend following the drain intervals as specified by the engine and vehicle manufacturer. In Europe the use of a tiered set of performance levels for gasoline engine lubricants allows extended drain for higher quality oils. In North American heavy-duty diesel engines, the oil sumps are much larger (32 to 44 L) and allow standard drain intervals of 10,000 to 25,000 miles. Work is underway in the industry to evaluate longer drain capable oils and self-draining oil systems for heavy-duty diesel engines. Synthetic basestocks will play a role in the formulation and development of these high tier, extended drain HDDOs. In Europe, mid- and heavy-duty diesel oils follow a similar tiered system as their gasoline engine oils. The higher tier diesel oils allow extended drain service for most manufacturers.

24.5 SYNTHETICS IN THE MARKETPLACE In North America, the use of full or partial synthetic gasoline engine oils are a small, niche market comprising less than 5% of the total engine oil consumption. The price of standard fill petroleum SL/ILSAC GF-3 quality oil remains at a low price. It is not uncommon to see name brand, petroleum oil advertised for less than $1.00 per quart in discount department stores. Market share is purchased over name brand loyalty by the consumer. Under these conditions, it is difficult to promote or sell the more expensive,

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Synthetics In Gasoline/Diesel Oils Market Projections Full Synthetics ¥ Small niche market, slow growth (gasoline) ¥ Insignificant market, low growth (diesel) ¥ Tied to new engine technology/problems Partial Synthetics ¥ Small niche market, slow growth (gasoline) ¥ small market, moderate growth (diesel) ¥ OEM/fleet driven Additive level ¥ Moderate market, potential strong growth (gasoline) ¥ Small market, potential strong growth (diesel)

FIGURE 24.10 Opportunities for synthetics in gasoline and diesel engine oils — market projections (From “Automotive Applications,” part of the STLE Synthetic Lubricants Education Course)

synthetic oil with similar credentials ($3.00 to $5.50 per quart). The use of synthetic basestock at lower levels in petroleum based engine oils is increasing. The more rigid test requirements and CMA rules for retesting are presenting an opportunity of additive level addition (<10%) of PAO and ester. Adjustments for passing volatility limits, fuel economy, engine cleanliness, and additive solubility are driving the use of synthetic addition. In North American markets, the use of synthetic heavyduty diesel oils is very small, comprising less than 1%. The economics of most truck operations and the price of petroleum CH-4 or CI-4 oils make the introduction of synthetic HDDOs very difficult. There are opportunities for synthetics with the increasing Federal Emissions requirements and desire for extended drain/extended engine life in the industry. As with gasoline engine oils, premium diesel oils are seeing the introduction of lower levels of synthetic components (<15%) for viscosity control and engine cleanliness under extended drain conditions. In Europe, the use of synthetic gasoline engine oils is much more acceptable. The prices for conventional, name brand engine oils are higher (3–5 Euro per liter) and the consumer is much more receptive for a premium product. In 1996, partial synthetics constituted approximately 15% of the PCMO market (at 5–7 Euro per liter) and full synthetic PCMOs at 3% market share (8–12 Euro per liter). The predominant synthetic components used in the European partial synthetic PCMOs are PAOs and polyol esters. In Europe, the introduction of the performance tier system for diesel engine oils (B and E categories) has improved the opportunity for synthetic use in high performance diesel engine oils. Full synthetic diesel oils were available in the marketplace, but have not gained much market share (<10%).

24.6 SUMMARY Automotive engines and engine oil requirements are changing at an increasing rate. Gasoline engine categories that were in effect for 7 to 8 years (SF, SG) are now being upgraded every 2 to 3 years. Each recent upgrade has introduced more stringent requirements and testing, along with a higher cost of development. Diesel engine manufacturers are being pressed to extend drain intervals with longer engine life while meeting ever increasing emission regulations. The engine manufacturers are recognizing that the engine lubricant is an integral part of a total system concept for these changes. Lubricant producers are working closer with OEMs, system suppliers, and truck fleets to develop these more advanced systems. Synthetic engine oils and basestocks have established a track record of high performance and protection over the last 25 years. More engine builders are considering synthetic oils or components as a technical solution for these upgraded oil requirements. Worldwide, the use of synthetic engine oils is increasing and will be a significant market influence in the 21st century.

REFERENCES 1. ACEA, “ACEA European Oil Sequences 2002, Service Fill oils for Gasoline, Light Duty Diesel and Heavy Duty Diesel Engines,” ACEA Publication (2002). 2. Sullivan, F.W. et al., Ind. Eng. Chem., 23, 604 (1931). 3. Sullivan, F.W. and Voorhees, V., U.S. Patent 1,955,260 (1934). 4. Gunderson, R.C. and Hart, A.W., Synthetic Lubricants, Reinhold Publishing Corp., New York, New York (1962), pp. 31–43. 5. Demmin, R.A., Girshick, F., and Schilowitz, A.W., “Engine Oil Viscosity and Bearing Wear: Field Test Results,” SAE Paper 922342. 6. Manni, M. and Ciocci, G., “An Experimental Study of Oil Consumption in Gasoline Engines,” SAE Paper 922374, 7. Ripple, D.E. and Fuhrmann, J.F., “Performance Comparisons of Synthetic and Mineral Oil Crankcase Lubricant Base Stocks,” Presented at the Fourth International Colloquium, Esslingen, Germany, (January 1984).

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8. Kiovsky, T.E., Yates, N.C., and Bales, J.R., “Use of LowViscosity, Low-Volatility Basestocks in Formulation of High Performance Motor Oils,” SAE Paper 922348. 9. Margeson, M.A. and Beimesch, B.J., “Cold Starting Capabilities of Petroleum and Synthetic Lubricants in Heavy-Duty Diesel Engines,” SAE Paper 890994. 10. Beimesch, B.J. and Davis, J.E., “Viscosity and Volatility Characteristics of Some Model SAE 5W-30 Engine Oil Formulations,” ASLE Preprint 85-AM-7C-1. 11. Boylan, J.B. and Davis, J.E., “Synthetic Basestocks for Partial Synthetic Motor Oils,” ASLE Preprint 83-AM-28-1. 12. Lestz, S.J. and Bowen, T.C., “Army Experience with Synthetic Engine Oils in Mixed Fleet Arctic Service,” ASE Paper 750685. 13. Frame, E.A., Montemayor, A.F., and Owens, E.C., “LowTemperature Pumpability of U.S. Army Diesel Engine Oils,” SAE Paper 892053. 14. Stipanovic, A.J. et al., “Base Oil and Additive Effects in the Thermo-Oxidation Engine Oil Simulation Test (TEOST),” SAE Paper 962038. 15. Selby, T.W., Richardson, J., and Florkowski, D.W., “Engine Oil Deposits and the TEOST — Protocol 33 and Beyond,” SAE Paper 962039. 16. Kennedy, S. et al., “A Synthetic Diesel Engine Oil with Extended Laboratory Test and Field Service Performance,” SAE Paper 952553. 17. Davis, J.E., “Oxidation Characteristics of some engine oil formulations containing petroleum and synthetic basestocks,” ASLE Lubr. Eng., 43, 199–202. 18. Lowther, H.V., Maxwell, W.L., and Rogers, T.W., “Improving the Fuel Saving Benefits of Synthetic Engine Oils,” SAE Paper 830166. 19. Boehringer, R.H., “Diester Synthetic Lubricants for Automotive and Diesel Applications,” ASE Paper 750686. 20. Hetrick, S.S., Keller, J.A., and Lowther, H.V., “Performance Advantages of Synthetized Commercial Engine Oils,” ASE Paper 780183. 21. Barton, D.B., Murphy, J.A., and Gardner, K.W., “Synthesized Lubricants Provide Exceptional Extended Drain Passenger Car Performance,” ASE Paper 780951. 22. Lohuis, J.R. and Harlow, A.J., “Synthetic Lubricants for Passenger Car Diesel Engines,” SAE Paper 850564. 23. Goyal, A.K. and Willyoung, R.W., “Engine Oil Filter Performance with Synthetic and Mineral Oils,” SAE Paper 850549.

25

Fluids for Conventional Automatic and Continuously Variable Transmissions (CVTs) Sibtain Hamid CONTENTS 25.1 25.2 25.3 25.4 25.5

Introduction Development of Automatic Transmissions and Fluids Partly Synthetic ATFs for Conventional Automatic Transmissions Fully Synthetic ATFs for Conventional Automatic Transmissions Comparative Performance 25.5.1 High-Temperature Viscosity 25.5.2 Low-Temperature Performance 25.5.3 Oxidative Stability 25.5.4 Antiwear Performance 25.5.5 Reduction of Operating Temperature 25.5.6 Friction Retention 25.6 Continuously Variable Transmissions and their Fluids 25.7 Rolling Traction Toroidal CVTs 25.8 Use of Cyclohydrocarbon Fluids in CVTs 25.9 Lenticular Planet Design 25.10 Traction Fluid Becomes Solid 25.11 Summary 25.12 Commercial Outlook References

25.1 INTRODUCTION Automatic transmissions for automotive applications fall into three main types: conventional automatic transmissions with multiple gears, belt-type continuously variable transmissions (belt-CVTs), and toroidal CVTs. Conventional automatic transmissions have been in production for more than 60 years. Belt-CVTs have been used in small-scale (e.g., small cars and snowmobile) applications for some time, while both belt- and toroidal CVTs have only in the last few years entered into automotive production. Initially, all fluids for conventional automatic transmissions were based on mineral oils but fluids based on synthetic bases were later developed. By contrast, only synthetic fluids were found to be more effective for CVTs.

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In each of these transmission types, the transmission fluid serves some or all of the following functions. First, the fluid has a role in the transfer of power within the transmission. The fluid serves additionally as a means of dissipating heat from the transmission. The fluid may also serve as a couplant for the torque converter in a conventional automatic transmission. It may also lubricate the fluid pump, operating valves, and motors associated with the transmission. There are numerous significant differences between conventional and CVTs in the demands they place on fluids. One example is the coefficient of traction. In conventional automatic transmissions, fluids having a low coefficient of traction are desirable and even a modestly elevated coefficient of traction may make a fluid unusable. CVTs, on the other hand, require a minimum coefficient of traction

and benefit from fluids having higher coefficients of traction.

25.2 DEVELOPMENT OF AUTOMATIC TRANSMISSIONS AND FLUIDS The development over time of transmissions for automotive applications is matched closely by the development of fluids to be used in those transmissions [1,2]. Initial automotive transmissions were all of the manual variety but it was recognized that the physical demands placed on the driver by the manual transmission and other required functions made driving a somewhat stressful endeavor. The logical solution to the problem was a transmission that would shift without driver intervention and the first commercially available automatic transmission was the Hydramatic model 180 in the 1940 Oldsmobile manufactured by General Motors (GM). Multi-gear automatic transmissions in use today retain many of the features of the Hydramatic, including fluids coupling (although without torque multiplication), three planetary gear sets, and torque transmission through multiplate clutch packs. In its early form, the multi-gear automatic transmission used a fluid much like the straight mineral oil used for engine lubrication at the time. For the transmission application, antioxidants and friction modifiers were added to the mineral oil base. Initially, the transmission fluid was sold only by GM, but within a few years GM had set up a qualification system that permitted wider production and availability of the transmission fluid. Further evolution of these transmission fluids followed. In 1949, GM and Ford introduced what was termed the Type A transmission fluid, which set minimum requirements in various bench, rig, and vehicle tests: viscosities, oxidative stability, and durability. In 1956, with the addition of further requirements, GM introduced Type A, suffix A. Ford and Chrysler in the meantime introduced separate oxidation tests, a move that resulted in some variation in standards. With further changes in specifications, GM introduced the DEXRON® trademark in 1967 [3]. Licensing was now a requirement to display the trademark. Changes in tests for oxidation and friction cycling, and the introduction of a wear test and a more strenuous friction retention test resulted in the upgrade to DEXRON® II in 1973 [4]. Ford introduced the MERCON® trademark, with accompanying specifications, in 1987 [5]. These specifications were modified in 1992 by requiring better fluidity at low temperatures, as well as by adding Viton and Vamac compatibility, improved pump wear, and improved oxidation and friction characteristics. In 1990 GM introduced DEXRON® IIE, with improvements in oxidation resistance and fluidity at low

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temperatures, reflecting the needs of electronically controlled automatic transmissions [6]. The introduction of DEXRON® III in 1993 involved improvements in several characteristics — higher oxidation resistance, longer retention of frictional characteristics, higher flash and fire points, and improved copper corrosion and foam protection. All of the many versions of automatic transmission fluid (ATF) to this point had used mineral oil as the base stock. This scenario changed abruptly in 1996 when Ford wrote the specifications for MERCON® V. These stringent requirements call for extremely low temperature performance, better shear stability, tighter foam and seal requirements, high temperature and high shear requirements, improved resistance to wear and extreme pressure, and improved friction characteristics. This requirement warranted introduction of some synthetic base fluid to the product to be able to meet this demanding schedule. Group lll based oils with better low temperature capability also are just as useful. The various tests required by the DEXRON® and MERCON® procedures are shown in Table 25.1.

25.3 PARTLY SYNTHETIC ATFS FOR CONVENTIONAL AUTOMATIC TRANSMISSIONS The addition of between 10 and 20% of polyalphaolefins (PAOs) to the fluid improves the fluidity of an ATF at low temperatures. Chiefly the action of the PAO is to inhibit the formation of a wax gel at temperatures below −40◦ C, but the addition of PAOs is relatively expensive compared to other methods, such as the addition of pour point depressants. The addition of PAOs may also result in a slight improvement in oxidative resistance or flash points [8,9].

25.4 FULLY SYNTHETIC ATFS FOR CONVENTIONAL AUTOMATIC TRANSMISSIONS The base stock of a conventional ATF such as DEXRON® III or MERCON® V is a high quality base mineral oil. In a conventional ATF, the base stock constitutes 75 to 90% of the formulation with the remainder consisting of various additives. The most significant additive is a viscosity index (VI) improver that increases fluid viscosity at higher temperatures and improves fluidity at lower temperatures. Other additives include dispersants to suspend carbonaceous oxidation products, antioxidants, antiwear components, agents to resist rust and corrosion of metals, antifoaming components, and additives to adjust friction levels on the wet clutches. By contrast, a synthetic ATF contains around 20% of an ester base oil, 70% of a PAO base oil, and 10% additives. The characteristics of the base fluid may make a viscosity improver unnecessary. Additional additives have functions similar to the additives in conventional ATFs, although

TABLE 25.1 Test Requirements for Conventional ATFs Testa Miscibility Kinematic viscosity, D-445 Brookfield viscosity, D-2983 Flash point, D-92 Copper corrosion, D-130 Rust, D-665-A Rust, D-1748 Mod. West test, D-2882 modified Color, D-1500 Foaming Elastomer compatibility Oxidation Friction durability Transmission cycling

Shift-feel

DEXRON® III Miscible with reference fluid At 40◦ C Report At 00◦ C 6.8 1,500 cP max at −20◦ C 20,000 cP max at −40◦ C 170◦ C min 1b No rust No rust 15 mg max 6.0–8.0 (red) No foam (GM method) 6 Materials GM oxidation test Clutch plate test, 100 h Band clutch test, 100 h THOTa , 20,000 cycles Stable shift times, fluid and parts analysis, in-vehicle test vs. reference fluid In-vehicle test vs. reference fluid

MERCON® V Miscible with reference fluid 6.8 1,500 cP max at −18◦ C 9,000 ± 4000 cP at −40◦ C 180◦ C min 1b No rust — 10 mg max 6.0–8.0 (red) D-892 foam 7 Materials Aluminum beaker oxidation text (ABOT) Clutch plate test, 20,000 cycles THOT, 20,000 cycles Stable shift times, fluid and parts analysis, in-vehicle test vs. reference fluid In-vehicle test vs. reference fluid

a THOT: Turbohydronamic oxidation test.

the formulator may adjust some additives to accommodate the change in base fluid. Antioxidant response often changes with base fluid, for example. Effects on elastomeric seal materials by different types of synthetic base fluids become critical if used alone. PAOs often cause seal shrinkage and can be poor solvents for some additives. However, at 3 to 5%, the seal-swelling additives will achieve the required seal compatibility with PAOs. Esters of various classes (adipates, azelates, sebacates, dimarates, and phthalates) range from being too highly swelling to being swell-neutral but few have viscometric properties appropriate for ATFs. The additives, developed for mineral oils, perform nicely in the even less polar PAOs. However, esters can disrupt the delicate balancing of surface activities required to deal simultaneously with wear, corrosion, and friction issues [8]. A PAO/ester mixture often provides the best combination in terms of seal compatibility, antagonism toward surface-active agents, and cost.

25.5 COMPARATIVE PERFORMANCE 25.5.1 High-Temperature Viscosity Synthetic ATFs are clearly superior to their mineral oil counterparts in the area of viscometric behavior. If a single

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fluid is to meet both the DEXRON® III and MERCON® V specifications, it must have a kinematic viscosity at 100◦ C of at least 6.8 cSt and a −40◦ C Brookfield viscosity of about 9000 cP. Synthetic and mineral oil based fluids achieve these requirements in different ways. High-temperature viscosity is dictated by the specific application. Where hydrodynamic mechanisms control wear, higher viscosities are preferred. In an automatic transmission, an excessively low-viscosity level leads to leakage around vanes and other surfaces. Shear heating and viscous drag on cold start-ups place an upper limit on viscosity. The VI improvers in ATFs are generally mixed polymethacrylates or styrene/maleic ester copolymers. These act as thickeners at operating temperatures and as pour point depressants at low temperatures. Synthetic based fluids need no pour point depressant, although olefin copolymers or styrene/butadiene copolymers can be useful. Polymethacrylates or styrene/maleic ester copolymers vary in their resistance to mechanical shearing. A high molecular weight polymer loses viscosity faster than one with a lower molecular weight. MERCON® V fluids, along with some European and Japanese ATFs, have markedly high shear stabilities. Table 25.2 shows the permanent and temporary viscosity loss for some ATFs.

TABLE 25.2 Comparison of Synthetic ATF and Mineral Oil ATF Before FISSTa ATF Synthetic A, no VI improver Synthetic B, no VI improver Synthetic C, VI improver Mineral oil D Mineral oil E

TABLE 25.3 Viscosities of Commercial PAOs used in ATFs

After FISSTa

KV 100

HTHSb

KV 100

HTHSb

7.19

2.39

7.16

2.39

5.68

1.9

5.69

1.93

7.55

2.12

5.83

1.97

7.19 7.32

2.11 2.1

5.67 5.5

1.97 1.9

PAO or 50:50 blend PAO 4 PAO 4/6 PAO 6 PAO 6/8 PAO 8 PAO 8/10 PAO 10

Kinematic viscosity at 100◦ C (cSt)

Brookfield viscosity at −40◦ C (cP)

4.06 4.82 5.91 6.79 7.78 8.72 9.87

2,042 3,680 6,538 10,550 15,105 21,440

a Fuel injector shear stability test ASTM D-3945B. b Tapered bearing simulator ASTM D-4683.

Temporary viscosity loss may occur with fluids containing viscosity improvers, although the base mineral oil stock alone may have high shear stability. Low molecular weight polymers that suffer less permanent viscosity loss from shearing also suffer less temporary viscosity loss [15].

25.5.2 Low-Temperature Performance The wax content of the mineral oil base controls the low temperature properties of a conventional ATF. The additives to counteract wax formation are polymers called pour point depressants, which limit the size of the wax crystals and suspend micro crystals in a separate liquid phase. The apparent viscosity of this mixture must be no more than 20,000 cP at −40◦ C to meet the DEXRON® III specification [17], and 9,000 ± 4,000 cP for MERCON® V. In contrast, PAOs and ester base fluids are wax free and easily meet the DEXRON® III and MERCON® V requirements. By using VI improvers, one obtains lower Brookfield viscosities and maintains high-temperature viscosities, but at the cost of shear stability. The impetus for better low-temperature performance is the requirement for reduced viscosity in electronically controlled transmissions. Low-temperature viscosity has two major effects. First, viscosity affects the viscous drag in the torque converter during starting and a more viscous fluid requires larger starter motor, batters, and cables [17]. Second, transmission operation is degraded by the sluggish flow of the ATF [18]. Table 25.3 shows the viscosities of commercial PAOs and blends useful for ATFs.

25.5.3 Oxidative Stability Polyalphaolefins and PAO/ester blends have markedly improved resistance to oxidation when compared to mineral oils [19–22]. Table 25.4 shows the results of the testing of two conventional transmission fluids based on mineral

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oils and a conventional synthetic PAO-containing transmission fluid, where the Turbohydronamic Oxidation Test (THOT) was used. The THOT is used for DEXRON® II and IIE fluids [23]. In this test, a model 4L60 transmission is driven in third gear at 1755 rpm by an electric motor, but with no other load applied. Excess heat, generated in the torque converter, is cooled through a standard in-radiator cooler, and the control system maintains a constant temperature of 163±1 ◦ . Air bubbled through the fluid at 90 mL/min for 300 h increases oxidation potential. During the test, the fluid is sampled at specified intervals. Indications of oxidation include increases in viscosity, total acid number (TAN). (ASTM D-664) and infrared absorbance (IR, R) in the carbonyl region at 1725 cm−1 . As Table 25.4 shows, there was also considerable variation in the −40◦ C Brookfield viscosities. The synthetic fluid was initially about 11,000 cP and increased only 3,000 cP during the test, even at 600 h. Mineral oil B started at 30,000 cP and suffered a 50% increase at 300 h. Mineral oil A was 35,000 cP when fresh, but exceeded 270,000 cP at −40◦ C after oxidation, beyond the point of usefulness. The MERCON® -required oxidation test is the aluminum beaker oxidation test (ABOT). This test is perhaps less severe than the THOT, but probably more reproducible, since the testing apparatus is less complex. A fluid sample of 300 mL is heated at 155 ± 1◦ for 300 h and aerated at 5 mL/min. A gear pump provides constant agitation of the fluid sample. Copper and aluminum strips immersed in the fluid promote sludge and deposit formation. The test is comparable to THOT if the shearing effect of THOT is ignored. Table 25.5 compares synthetic and mineral oil based ATFs in the ABOT. Mineral oil A is the reference fluid for this test and mineral oil B has the same additive package as the synthetic fluid A. The single-length test results show that the synthetic fluid has no peer among mineral oils in resisting oxidation. The synthetic ATF must go 600 h to have comparable results to the mineral oils in a 300-h

TABLE 25.4 Comparison of synthetic and mineral oil based ATFs in Dexron® IIE THOT DEXRON® IIE requirements

Parameter Pentane insolubles TAN IR Viscosity at 100◦ C, cSt: fresh Used −40◦ Brookfield Viscosity, cP

No limit 4.5 max 0.55 max — — Fresh Used

Mineral A 300 h (ref.)

Mineral B 300 h

Synthetic A 300 h

Synthetic A 600 h

0.57 4.2 0.5 7.05

0 1.78 0.41 7.22

0.05 0.73 0.14 7.18

0 2.35 0.38 7.18

6.8 35,000 >270,000

7.78 30,000 45,500

7.34 11,000 13,800

7.93 11,000 14,240

TABLE 25.5 Comparison of Synthetic and Mineral Oil Based ATFs in ABOT

Parameter Pentane insolubles TAN IR Viscosity increase at 40◦ C, %

MERCON® (1992) requirement 1% max at 200 h 5.0 max at 250 h 50 max at 250 h 50% max at 250 h

Mineral A single length (ref.)

Mineral B, single length

Synthetic A, single

Synthetic A, 600h

0.24 2.8 33.99 8.52

0.16 2.33 25.78 8.08

0.17 0.59 7.56 0.67

0.23 1.5 11.7 13.8

THOT test. The IR values are better for the synthetic fluid at 600 h than for the mineral oil based ATF at 250 h. The difference in oxidative stability is again attributable to the base fluid.

25.5.4 Antiwear Performance In conventional ATFs, wear of metal parts as they are exposed to the various lubrication regimes within the transmission may depend on additive chemistry or the fluid viscosity. One report demonstrates that a single ATF additive package in four different base fluids, including a synthetic base fluid with no VI improver, gave essentially identical results in both the FZG low-speed wear test and the MERCON® vane-pump wear test [14]. Other reports emphasize the importance of hightemperature high-shear (HTHS) viscosities as the factor controlling hydrodynamic film strength [17]. In one test used for both DEXRON® III and MERCON® V, the engine goes from idle to nearly full throttle 20,000 times within one minute. Wear on the pinion pins of the planetary gears showed differing amounts of wear depending on the HTHS viscosities of the ATFs that all contained the same additive package. The pins rotate between boundary and hydrodynamic lubrication. Greater film strength may

Copyright 2006 by Taylor & Francis Group, LLC

permit the pins to spend a greater fraction of their time in the hydrodynamic mode, leading to less wear.

25.5.5 Reduction of Operating Temperature Several reports have shown that operating temperature for synthetic based fluids is lower than for mineral oil fluids [24–26]. Multiple factors are probably at work to produce lower operating temperatures in synthetic base fluids. Among these is the fact that synthetic base fluids tend to have higher specific heats than mineral oil base fluids, that is, more heat must be applied to raise the temperature of the fluid.

25.5.6 Friction Retention Clutch engagement involves rotating clutch plates moving against stationary steel plates. As pressure is increased, torque increases until the stationary plates begin to rotate. At lock-up, the sliding speed differences between the mating plates approach zero and friction changes from dynamic to static. Since static fraction tends to be higher than dynamic friction, harsh or severe shift-feel can result. Additives can adjust the relative levels of static and dynamic friction in conventional ATFs; the base fluid plays little role. Additives developed for mineral oils work also

25.6 CONTINUOUSLY VARIABLE TRANSMISSIONS AND THEIR FLUIDS There are two major types of CVTs, and members of both types have already entered production to a limited extent. One type, the belt-driven CVT, uses a continuous belt or chain that is squeezed between two variable-ratio pulleys. Variation in the angle of contact between the pulley and the belt provides continuous variation in power ratio. The second type, toroidal CVTs, have no belt but transfer power between, for example, a curved planetary element and a cylindrical raceway. There are many toroidal CVT designs, but all depend on the continuously variable angle between two elements to change the power ratio. The strong interest in both types of CVTs stems from their overall efficiency, which in turns means better fuel economy. This efficiency, however, is derived from the interaction of the whole drivetrain, and is not generated by the CVT alone. A CVT whose efficiency is measured in isolation — that is, with the CVT mounted on a dynamometer test stand — generally achieves an efficiency between 85 and 90% — lower than the efficiency of a conventional automatic transmission subjected to the same test parameters. But when the efficiency of the whole powertrain (engine, transmission, axle) is measured, the powertrain employing a CVT demonstrates fuel savings that are generally between 7 and 12% when compared to a powertrain using a conventional automatic transmission. Belt-CVTs have, until recently, been restricted to relatively light-weight motor vehicles, while toroidal CVTs, whose development has lagged behind that of belt-CVTs, are suitable for both light and heavy automobiles and some designs may be suitable for heavy trucks. To some extent, the development of toroidal CVTs has been encouraged by the weight limitations of belt-CVTs. The fluid requirements are very different from the requirements for conventional automatic transmissions, in large part because of the increased role of the fluid in transferring power across relatively small areas of contact. Thus, the traction coefficient (tangential force divided by normal force) of fluids for CVTs becomes significant (Figure 25.1). As shown in Table 25.6 the physical properties and most other requirements of CVT’s are similar to those of conventional ATF fluids. A key difference between fluids for conventional automatic transmissions and fluids for CVTs is the relative importance of the base stock. In conventional fluids, the performance characteristics of the base stock play only a limited role in the performance characteristics of the finished fluid; key functionalities are derived largely from the additives. In CVT fluids, the base stock plays a far greater

Copyright 2006 by Taylor & Francis Group, LLC

0.10 Coefficient of traction

with PAO fluids. The frictional properties are retained until oxidation of the fluid reaches a critical level.

0.08 0.06 0.04 0.02 0.00

PMO

PAO

POE

S-Base

Coefficient of traction

FIGURE 25.1 Coefficient of traction, twin disk machine tests; PMO = Paraffinic Mineral Oil; PAO = Polyalphaolefins; POE = Polyol ester; S-Base = Proprietary base oil

TABLE 25.6 Properties of CVT Fluid A Properties Color Water content Chlorine (Cl) content Flash point Pour point Viscosity at +100◦ C (kV100) +40◦ C (kV40) −40◦ C (dV-40) Foaming characteristics New oil Oil after oxidation test Oil after storage Shear stability Viscosity at 100◦ C Change in viscosity at 100◦ C Elastomer compatibility (ACM, FPM, HNBR)

Requirement

CVT Fluid A

Colorless max 500 max 50 min 180 max −45

<4 50 35 169 −55

7.3–7.8 35–40 max 14,000

7.4 40.2 14,500

50/50/50 mL 100/100/100 mL 100/100/100 mL

0/0/5 Not determined Not determined

min 6.8 max 7.5

5.4 34 ASTMD 471 70 h at 150◦ C ACM/NBR/FPM ≥ 1

role and the influence of additives, while significant, is not nearly as pronounced. Part of the driving force behind the development of automotive CVTs has been the desire for improved fuel economy and the accompanying reduced emissions. Since both automotive CVT transmissions and electric/gasoline hybrid powered engines are now in production, a vehicle that combines both of these innovations has become a reality. Even without such a breakthrough, it seems likely that over the next several years belt-CVTs and toroidal CVTs will reach production status in more vehicle models and will to some degree replace conventional automatic and standard transmissions.

25.7 ROLLING TRACTION TOROIDAL CVTS Toroidal CVTs have gathered a great deal of attention for several reasons: they can be relatively cheap to manufacture; and they are smaller, lighter, and quieter in operation than conventional automatic transmissions. They work more smoothly than conventional transmissions, have long service lifetimes, and can increase fuel mileage substantially. The rolling traction versions of toroidal CVTs have the advantage of using an advanced “transmission fluid” that turns momentarily into a solid, permitting it to become “part of the machinery.” Not surprisingly, such advanced transmission fluids give important increases in efficiency and performance.

25.8 USE OF CYCLOHYDROCARBON FLUIDS IN CVTS Cyclohydrocarbons are a new family of synthetic hydrocarbon oils, which offer unique performance advantages. Their lubrication action not only parallels or exceeds top quality petroleum oils, but at extremely high pressures a unique phenomenon occurs: the pressurized lubricant film acquires “grip.” This dynamic effect between rollingcontact surfaces results in a momentary transition of the lubricant’s mobile film to rigid solid with immediate reversal when pressure is reduced. This effect is most dramatic in the greatly heightened power transfer between the smooth rolling surfaces. It has been discovered that these fluids provide advantages in CVT. The chemical structures of these new cyclohydrocarbons, along with their physical and chemical properties, are described in Chapter 10 of this book. Rolling traction CVT designs typically use a formulated cyclohydrocarbon transmission fluid [27]. These fluids are thermally stable and offer similar oxidative stability with antioxidant as do PAOs as shown in Figure 25.2 and Figure 25.3. In addition cyclohydrocarbon fluids are fortified with antiwear and extreme pressure (EP) additives and

are equal in performance to conventional ATF’s in antiwear properties as shown in Figure 25.4. A first-generation version of Milner CVT design (Orbital Traction Ltd., Hinckley, U.K.) has been recently licensed to an Asian motorcycle manufacturer, and a newer, larger design has been developed that is suitable for both autos and trucks [28]. In both of these designs, planetary elements roll between inner and outer raceways. As is typical in rolling traction CVTs, transfer of power takes place through the traction fluid in a small zone of contact where the two smooth surfaces of a planetary element and a raceway meet. The traction fluid, forming a thin film on the surfaces, prevents metal-to-metal contact and permits maximum power transfer. When the angle of contact between the raceways and the planetary elements are changed the operating radii are likewise changed. The result is a continuous range of ratios within the transmission, even under a load. The contact forces between the two smooth surfaces are quite high. In good CVT designs, these forces are developed and contained and do not consume significant amounts of power. The CVT must also have the ability to change ratio rapidly and smoothly in the presence of these

Cycloaliphatic hydrocarbon Mineral oil, paraffinic PAO Diester 0

1

2 3 4 Stress cycles × 106 B10 Fatigue Life Test Conducted on TWIN DSIC Machine

A 0

200

100

200

B 0

100

200

C 0

0.450

300

300

100

200

ATF 0

3

300

6

9

12

300 15

Oxidation stability ABOT Test (Viscosity increase) Viscosity increase%)

Wear scar diameter, mm

100

0.445 0.440 0.435 0.430 0.425 0.420

A

B

C

Four-ball wear test (30 kg load)

FIGURE 25.2 Comparison of oxidation properties of CVT oils with PAO based ATF

Copyright 2006 by Taylor & Francis Group, LLC

5

FIGURE 25.3 Comparison of CVT and conventional fluids

Limit 40% max at 250 h 0

300˚F 1,200 rpm 700,000 psi Hertz stress

FIGURE 25.4 Antiwear properties of CVT oils

D

Output Input

FIGURE 25.5 By using a three-part lenticular planet, the CVT achieves higher torque capacity without increasing the size of the transmission

torque capacity without making the transmission larger. The contact zones between the planets and the raceways also lie at a shallower angle to the rotation axis, resulting in smoother rolling, higher efficiency, and lower operating temperatures. Another consideration in successful CVT design is the balance between normal and tangential forces. These forces occur where a raceway makes contact with a lenticular planet. The two elements are squeezed together by normal (i.e., perpendicular) forces to transmit power. Tangential forces — meaning the tendency for the two elements to slip horizontally in relation to each other — are working at the same time.

25.10 TRACTION FLUID BECOMES SOLID

FIGURE 25.6 Layout of Heavy Duty Milner CVT

forces. Properly designed, a CVT accomplishes both of these objectives via an elegantly simple design, without the need for a high-pressure hydraulic control system.

25.9 LENTICULAR PLANET DESIGN Spherical planetary elements seem like a logical way to design a CVT, but in fact they are not the ideal. In auto and truck transmissions, spherical elements would be too large and too heavy to be practical. A better design is the threepart lenticular planet design employed in the Milner CVT (Figure 25.5 and Figure 25.6). In a lenticular planet, a central shaft separates two curved elements. This design permits a more compact power take-off system and permits a larger number of planets. One result is higher

Copyright 2006 by Taylor & Francis Group, LLC

A useful choice for CVTs is an elastohydrodynamic (EHD) traction fluid [29]. These fluids are cyclohydrocarbons and are generally considered the industry standard because of their exceptionally high traction coefficient (about 0.10). They also cause the transmission to operate far more quietly than is possible with any other fluid. But the most significant property of an EHD is its ability to turn into a solid during the brief period when it is between the two elements. As the planet and the raceway are squeezed together, and when the normal and tangential forces peak, the EHD fluid between the elements becomes a glassy solid for a few microseconds. When the fluid moves out of this zone, it immediately becomes a liquid again. Its brief solid state is the reason that EHDs have a traction coefficient (tangential force divided by normal force) of about 0.10, compared to 0.05 or 0.06 for other fluids. The use of EHD fluids in well-designed CVTs is expected to result in transmissions of exceptional performance and longevity. When EHD fluids are used in more conventional CVTs in demanding industrial applications such as high-speed printing machines that run 24 h a day, the EHD is typically replaced only after 5,000 continuous hours of use. The replacement is largely precautionary, since there is little or no degradation of the fluid. In autos, 5,000 h is roughly equal to 250,000 km of travel. It may be possible for both the CVT and the EHD fluid to outlast the rest of the vehicle. A close look into the interplay between the EHD and the element surfaces shows why such longevity is possible. A phenomenon that routinely kills transmissions and similar mechanisms is the formation and growth of micro-cracks at surfaces. Typically these cracks grow until failure takes place. A transmission fluid that is always a liquid would be forced under pressure into these microcracks and would accelerate their growth. But an EHD fluid becomes a solid when the elements are under pressure. It has far less ability to grow micro-cracks and greatly increases transmission longevity.

25.11 SUMMARY Conventional ATFs made with PAO’s offer advantages and performance benefits compared to mineral oil base fluids. Although in some formulations Group lll mineral oils may satisfy all original equipment manufacturer (OEM) requirements. The low-temperature viscosity after oxidation test may require PAOs to enhance the evaporation rate of the finished product. CVT fluids made with cyclohydrocarbon base fluid have demonstrated performance benefits in both CVTbelt/chain as well as in toroidal designs, as these fluids offer better coefficient of traction and other properties similar to PAO base fluids.

25.12 COMMERCIAL OUTLOOK Market projections by major OEMs suggest that over the next decade the installation rate of various types of CVT will continue to grow at the expense of the conventional automatic and manual transmissions. The driving force for this change is demand for increased fuel economy and vehicle emission reductions. The market is now well established with the belt-CVT in large number of transmissions. The next growth potential is toroidal traction drive transmissions, which is positioned to meet the market niche for light trucks and SUVs [30].

REFERENCES 1. Gott, P.G., Changing Gears: The Development of the Automotive Transmission, Society of Automotive Engineers, Warrendale, PA, Chapters 1–6, 1991. 2. Dean. H.E. and Sykowski, J.P., The evolution of today’s versatile, multifunctional automatic transmission fluids. Technical paper Fl-84-82, National Petroleum Refiners Association, 1982. 3. General Motors Corporation, General Motors Passenger Car Automatic Transmission Bulletin, GM, Ypsilanti, MI, 1967. 4. General Motors Corporation, DEXRON® -II Automatic Transmission Fluid Specification, GM 6137-M. GM, Ypsilanti, MI, 1973. 5. Ford Motor Company, WSP-M2C185-A, FMC, MERCON® Automatic Transmission Fluid Specification, Livonia, MI, 1987. 6. General Motors Corporation, DEXRON® Automatic Transmission Fluid Specification, GM 6137-M. GM, Ypsilanti, MI, 1990. 7. Kemp, S.P. and Linden, J.L., Physical and chemical properties of a typical automatic transmission fluid. SAE Technical paper 902148, Society of Automotive Engineers, Warrendale, PA, 1990. 8. Boylan, J.B. and Davis, J.E., Synthetic basestocks for partially synthetic motor oils. Lubr. Eng., 40, 427–432, 1984.

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9. Wilermet, P.A., Haakana, C.C., and Sever, A.W., A laboratory evaluation of partial synthetic automatic transmission fluids. J. Synth. Lubr., 2, 22–38, 1985. 10. Flory, P.J., Principles of Polymer Chemistry, Cornell University Press, Ithaca, NY, 1953. 11. Pori, W.S., O’Brien, J.W., Hensen, J.E., and Swern, D., Viscosity index improvers for lubricating oils. Ind. Eng. Chem., 43, 2105, 1951. 12. Alfrey, T., Bartovicx, A., and Mark, H., The effect of temperature and solvent type on the intrinsic viscosity of high polymer solutions. J. Am. Chem. Soc., 64, 1557, 1942. 13. Evans, H.C. and Young, D.W., Polymers and viscosity index. Ind. Eng. Chem., 39, 1676, 1947. 14. Hartley, T.J., Sunne, J.P., and Chrisope, D.R., The design of automatic transmission fluid to meet the requirements of electronically controlled transmissions. SAE Technical paper 902151, Society of Automotive Engineers, Warrendale, PA, 1990. 15. Alexander, D.L. and Rein, S.W., Temporary viscosity loss in shear stability testing, SAE Technical paper 801390, Society of Automotive Engineers, Warrendale, PA, 1980. 16. Chrisope, D.R., Ethyl Petroleum Additives, Inc., unpublished results, 1991. 17. Watts, R.F. and Szykowski, J.P., Formulating automatic transmission fluids with improved low temperature fluidity, SAE Technical paper 902144, Society of Automotive Engineers, Warrendale, PA, 1990. 18. Linden, J.L. and Kemp, S.P., Improving transaxle performance at low temperature with reduced viscosity automatic transmission fluids. SAE Technical paper 870356, Society of Automotive Engineers, Warrendale, PA, 1987. 19. Blackwell, J.W., Bullen, J.V., and Shubkin, R., Current and future polyalphaolefins. J. Synth. Lubr., 7, 25–45, 1990. 20. van der Waal, G.B., Properties and application of ester base fluids and PAOs. NLGI Spokesman, 53, 359–368, 1989. 21. Gunsel, S., Klaus, E.E., and Bailey, J.L., Evaluation of some polyalphaolefins in a pressurized Penn State micro-oxidation text. Lubr. Eng., 43, 629–635, 1987. 22. Gunsel, S., Klaus, E.E., and Duda, J.L., High temperature deposition characteristics of mineral oil and synthetic lubricant basestocks. Lubr. Eng., 44, 703–708, 1988. 23. Chrisope, D.R., Ethyl Petroleum Additives, Inc., unpublished results, 1991. 24. Laukotka, E.M., Lubrication of gears with synthetic lubricants. J. Synth. Lubr., 2, 39–62, 1985. 25. Coffin, P.S., Lindsay, C.M., Mills, A.J., Linderkamp, H., and Fuhrmann, J., The application of synthetic fluids to automotive lubricant development: Trends today and tomorrow. J. Synth. Lubr., 7, 123–143, 1990. 26. Jordan, G.R., Electric bills and the traction fraction (synthetic vs. mineral lubricants). Lubr. Eng., 39, 491–495, 1983. 27. Joaquim, M., Elastohydrodynamic lubricants for CVTs. Auto. Eng. Int., July 2002, pp. 45–47. 28. Joaquim, M. and Milner, P.J., A robust CVT for heavy duty applications. Autotechnology, 2/2003, 32–34. 29. Rose, N. and Hamid, S., The race for a better CVT, Lubes ‘N’ Greases, May 2003, pp. 22–27. 30. Tipton, C.D. and Qureshi, F., SAE report 2000-01-2906.

26

Automotive Gear Lubricants Stephen C. Lakes CONTENTS 26.1

Introduction 26.1.1 Area of Application 26.1.2 General Performance Requirements 26.1.3 API Gear Lubricant Service Categories 26.1.4 Manual Transmission Fluids/API MT-1 26.1.5 API MT-1 Performance Requirements 26.1.6 API GL-5 Level EP Axle Lubricants (MIL-L-2105D/MIL-PRF-2105E/ SAE 2360) 26.1.7 MIL-L-2105D Performance Requirements 26.1.8 MIL-PRF-2105E/SAE 2360 Performance Requirements 26.2 Historical Development 26.2.1 Early Gear Oil Categories 26.2.2 Need for Synthetics in Gear Lubricants 26.3 Types of Synthetics 26.3.1 Definition of Synthetic 26.3.2 Synthetic Basestocks used in Gear Oils 26.4 Comparative Performance Data 26.4.1 Bulk Physical Properties 26.4.2 High Temperature Viscosity Characteristics 26.4.3 Low Temperature Viscosity Characteristics 26.4.4 Antiwear and Extreme Pressure Performance 26.4.5 Shear Stability 26.4.6 Thermal and Oxidative Stability 26.4.7 Hydrolytic Stability 26.4.8 Lubricity and Fuel Economy 26.4.9 Compatibility Characteristics 26.4.10 Miscibility Characteristics 26.4.11 Service Life 26.4.12 Field Performance 26.5 Synthetic Gear Lubricants in the Marketplace 26.6 Summary References

26.1 INTRODUCTION Gear oils are the unseen workhorses of the automotive lubricants. Lacking the advertising clout and consumer attention that engine oils command, they are the lubricants for the remainder of the automotive power train. The power train transfers the power from the engine to the drive wheels. This equipment consists of one or more gearbox assemblies that allow a smooth transfer of rotational energy through various speeds and torque ranges. In automotive vehicles these gearboxes consist of the transmission and

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differential or a combination transaxle. Today’s driver, whether passenger car or class 8 truck, is rarely concerned with these fluids or their effect in the equipment. For most vehicle owners and operators, both the power train hardware and lubricant go unnoticed through the vehicles life cycle. This is a result of a concerted effort by the industry over a 50-yr period to constantly monitor and improve the equipment and lubricants protecting them in this application. Starting in the 1980s, synthetic lubricants have played a prominent role in power train lubrication, specifically in

the heavy-duty over-the-road segment. Ongoing changes in the passenger car and light-duty truck gear oil requirements are presenting new opportunities for synthetics for these applications also. Worldwide, synthetic gear lubricants are being recognized as useful components in the area of low maintenance and long durability in transmissions and axles.

26.1.1 Area of Application The equipment utilizing automotive gear lubricants includes manual transmissions, drive axles (differentials), power takeoffs, and nondrive applications (steering, trailer axles, and rear axles in front wheel drive vehicles). Fluid drive automatic transmissions utilize a specialized type of gear lubricant (ATF) and will be covered in a separate chapter. Transmissions are gearboxes that are used to smoothly convert the variable torque loading from the engine into a usable speed for the drive wheels. Manual transmissions utilize a series of gears controlled by a hand shift or automated shift mechanism. The internal components consist of power shafts, gears, bearings, seals, and synchronizers, which are predominately lubricated by a sump/splash system. There are a few manual transmission designs that utilize a pump mechanism for oil delivery, but these do not constitute a significant number in automotive applications at the present time. There are two major types of manual automotive transmissions depending on the level of gear synchronization for shifting. These are usually termed “synchronized” or “nonsynchronized.” The difference resides in the design of the transmission shift mechanism. The synchronized type of transmission is synchronized between every gear range. This assists the driver by frictionally matching the RPMs for a smooth gear meshing or shift. In the nonsynchronized transmission, there may be none or partial synchronization. The driver must consciously match the RPMs within the transmission (double clutching) during gear shifting. Most of heavy-duty nonsynchronized transmissions are partially synchronized with plate friction systems between the high and low range of speeds. The high and low range of speeds may be changed by a switch or button, usually located on the shift rod. Most passenger cars, small and midsize trucks worldwide, utilize synchronized manual transmissions. The number of speeds varies from three to seven forward gears with power loading going up to around 650 ft.lbs. torque in the midsize vans/trucks [1]. Worldwide, there is a variety in the use of synchronized vs. nonsynchronized equipment for heavy-duty truck use. European and Japanese heavy-duty trucks predominately use synchronized transmissions. In these markets, over 90% of all over-the-road heavy trucks are of the fully synchronized type. In North America, 90%+ of

Copyright 2006 by Taylor & Francis Group, LLC

the heavy-duty class 8 trucks use the nonsynchronized type of transmission. Usage throughout the world is mixed, depending on the source of the truck manufactured. This difference is mainly related to the shift density requirements. In Europe and Japan, a normal delivery run will consist of much higher levels of gear shifting per kilometer than in North America. In this heavy-duty market the number of speeds varies from 9 to 18 with power loading going up to around 1650 ft.lbs. torque. Some current applications and higher horsepower engines are pushing the power loading over 2000 ft.lbs. torque [2]. In both synchronized and nonsynchronized designs, extensive work is underway by the transmission system suppliers to develop “assisted” shifting mechanisms that work with the manual design gearboxes. These utilize hydraulic, pneumatic, or electrical actuators, which shift automatically and mimic the performance of an automatic, hydrodynamic transmission. These automated manual transmissions may lead the way to permanently remove both the gear and the range friction synchronizers, leading to simpler, more fuel efficient transmissions. A new type of manual transmission is currently under development. This is the CVT, continuously variable transmission. There are two main types of CVT design, a belt/chain system riding on a set of cones or a toroidal design. The transition between the speed ranges would not be stepwise as in a current design transmission, but would be continuous over the entire range. Both designs utilize a gear lubricant. The belt/chain design uses a lubricant that is formulated for wear and cooling performance on the drive transfer components. Most belt/chain CVT systems utilize a light viscosity MTF (manual transmission fluid) or ATF (automatic transmission fluid). Design limitations related to the durability of the belt or chain material has limited its development and application areas. The toroidal CVT relies on the lubricant for not only wear and cooling, but also for the frictional properties (traction coefficient) of the lube for power transfer. Most toroidal designs use a specialized formulated lube (viscosity and traction coefficient) matched to the equipment design and power loading. The first applications of CVTs have been lightweight passenger cars and small vans. Higher torque loaded vehicle designs are in development at this time. A drive axle set is used with the transmission to change the rotational direction of the power for use by the drive wheels. This may be in the form of a transaxle or a freestanding gearbox (differential axle). This secondary gear set will usually further modify the speed and torque depending on the specific vehicle type and performance requirements. It usually consists of a planetary, spiral bevel, or hypoid gear set coupled with a differential slip mechanism. The slip mechanism allows the inboard drive wheel to turn more slowly than the outboard wheel in a turn.

The slip mechanism may be of full controlled slip, limited slip, or locking design. In front wheel vehicles, which are predominately passenger cars, this directional change is handled by a transaxle, an integrated transmission, and axle assembly located adjacent to the engine. In rear wheel vehicles, the differential is separated from the transmission by a power shaft and is usually part of the axle/wheel assembly. In passenger cars, small and midsize trucks, there is usually only one differential supplying two to four drive wheels. In heavy-duty trucks and some four wheel vehicles, there may be two differentials supplying from four to eight drive wheels. Other automotive applications using gear lubricants are front steer axles in rear drive vehicles, trailer axles being pulled or articulated with the drive tractor, power takeoff assemblies for transferring engine power to drive auxiliary equipment (i.e., cement mixers), and the rear bearing axle assemblies on front wheel drive vehicles. The function of these nondrive lubricants are predominately for cooling and wear protection for bearings and seals.

26.1.2 General Performance Requirements The major function of automotive gear lubricants, transmission, or axle oils, is to provide protection to the moving and mating parts. These parts include: • gears (spur, worm, herringbone, planetary, helical, spiral

bevel, and hypoid design) • bearings (sleeve, bushing, roller, and tapered design) • seals (input, output power shaft, and wheel type) • synchronizer friction materials (bronze, steel, carbon,

paper, molybdenum, etc.)

Current Trends in Transmission and Gear Lubricants Smaller oil reservoirs Higher temperatures Higher gear loading Fuel economy benefits requested Factory filled/sealed for life One oil for both applications Improved seal life

FIGURE 26.1 Current trends in manual transmission and axle lubricants (From “Automotive Application,” part of the STLE Synthetic Lubricants Education Course)

TABLE 26.1 Axle and Manual Transmission Lubricant Viscosity Classification — SAE J306 July 98 SAE viscosity grade 70W 75W 80W 85W 80 85 90 140 250

Brookfield viscosity, cP (D-2983)

Kinematic viscosity, 100◦ C (D-445, cst)

Max.

Min.

Max.

150,000 at −55◦ Ca

4.1 4.1 7.0 11.0 7.0 11.0 13.5 24.0 41.0

— — — — <11.0 <13.5 <24.0 <41.0 —

150,000 at −40◦ C 150,000 at −26◦ C 150,000 at −12◦ C — — — — —

a Precision of test has not been established at −55◦ C

Overall, gear lubricants satisfy several functions: • • • • • • •

Minimizing friction and wear for moving parts Acts as a heat transfer agent Inhibits corrosion Removes wear particles from contact areas Reduces noise Able to function over wide temperature range Improves power transfer efficiency

Currently, there are changes affecting both the equipment design and lubricant requirements for the automotive power train. These are being driven by an increasing demand for improved efficiency, lower cost, and lower weight for the vehicle (Figure 26.1). The first defining category for the design and formulation of an automotive gear lubricant is the viscosity. Part of the crucial protective mechanism is to provide a sufficient oil film between the moving contact surfaces. The bulk viscosity functions predominately by providing protection in the hydrodynamic or elastohydrodynamic mode

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Brookfield.

of lubrication. In these modes of lubrication, the metal surfaces are sufficiently apart so that metal to metal contact (boundary lubrication) is not present. The major factor that influences the gear lubricant in this lube environment is the bulk oil viscosity. In automotive gear lubricants, three viscosity classifications are used. The SAE J306 defines the “Axle and Manual Transmission Lubricant Viscosity Classification,” which has both original monogrades and winter grade classes. The MIL-PRF-2105E/SAE 2360 encompasses three of these viscosity grades combined with a channel point requirement. Some manual transmission fluids use the SAE J300 engine oil nomenclature, which defines “Viscosity Grades for Engine Oils” (Tables 26.1 to 26.3). The low-temperature viscosity properties of a gear oil are defined the SAE winter categories (70W, 75W, 80W, 85W) and the MIL-PRF-2105E/SAE J2360 channel points. Most automotive vehicles operate under cold weather

TABLE 26.2 U.S. Military Manual Transmission and Axle Lubricant Viscosity Classification — MIL-PRF-2105E/SAE J2360 April 2001

Gear oil viscosity grade 75W 80W-90 85W-140

Brookfield viscosity, cP (D-2983)

Kinematic viscosity, 100◦ C (D-445, cst)

Channel point (FTM 3456) ◦C

Max.

Min.

Max.

max.

150,000 at −40◦ C 150,000 at −26◦ C 150,000 at −12◦ C

4.1 13.5 24.0

— <24.0 <41.0

−45 −35 −20

TABLE 26.3 Typical SAE Manual Transmission Fluid Viscosity Grades (from SAE Viscosity Grades for Engine Oils — SAE J300 Dec 99) Kinematic 100◦ C viscosity (D-445)

SAE viscosity grade

Min.

Max.

20 30 40 50

5.6 9.3 12.5 16.3

<9.3 <12.5 <16.3 <21.9

conditions sometime in their life cycle. If the outside temperature is too low for the grade of gear lubricant used, there will be insufficient oil film and additive available to protect the moving parts and damage can result before the transmission or axle is warmed up. Most petroleum based gear oils have viscosity limited to 80W or 85W viscosity grades, whereas most synthetic gear lubricants are of 70W or 75W viscosity grades. Besides increased low temperature protection, the lower viscosity of the synthetic gear lubes shows improved fuel economy, especially in cold weather operation. Bulk lube viscosity alone is insufficient for some parts of the automotive power train for protection of gears and bearings. Boundary lubrication protection is also required in the automotive power train. This is the lubricant environment where there is sufficient power density or loading across the gear faces to cause metal to metal contact and where antiwear and EP (extreme pressure) additives are required. These additives produce protective films on the metal surfaces. These films range from weakly adsorbed thin layers (lubricity agents to antiwear additives) to thermally active, chemically deposited protective layering (active antiwear and extreme pressure additives).

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26.1.3 API Gear Lubricant Service Categories The API designates service categories for automotive gear oils based on the level of antiwear or EP protection required. These designations refer to the lubricant performance necessary for a specific type of automotive application. These applications include manual transmissions, drive axles, steering axles, automatic transmissions, semiautomatic transmissions, torque converters, power takeoffs, and hydraulic systems. Some lubricants may be suitable for more than one service classification (Table 26.4). Some of the test requirements for the GL-1 to GL-4 level of service are no longer available. The GL-4 category, which is used as both a manual transmission fluid and a light/moderate load axle lubricant, are under review by the SAE for possible separation and upgrade. The MTF requirement would become a synchronized manual transmission category (PT-2). The light/moderate axle requirement would be rolled into the API GL-5 level. The GL-5 category is similar to and corresponds to the MIL-L-2105D set of performance requirements. All of the API gear oil categories are for general service fill only. Factory fill oils or service fill oil for specific conditions, are defined by the system suppliers or vehicle manufacturers. These factory fill approvals usually consist of a lubricant that meets or exceeds the requirements for the API GL category, plus additional testing as specified by the equipment manufacturer. Some examples of factory fill specifications are shown in Table 26.5. Some factory and service fill specifications have been combined with extended drain service or extended warranty coverage by the equipment manufacturers. These require more extensive performance testing by the warrantee company (Table 26.6). The development of synthetic gear lubes and the upgrading of factory fill specifications by the system suppliers over the last 30 yr have worked together in improving the overall performance of all of the automotive lubricants. As equipment has gotten smaller and hotter, all of the lubes have been under evaluation for improved thermal stability and durability. Opportunities for synthetic basestocks are increasing for all of the lubricants used in a modern vehicle, not just engine and gear oils.

26.1.4 Manual Transmission Fluids/API MT-1 Manual transmissions have historically been lubricated by three types of automotive fluids. These were engine oils, ATFs, and gear oils [3]. Under API guidelines, the predominant categories for manual transmission applications have been GL-1 (North American Mid- and Heavy-Duty Market), GL-3 (Japan, Far East Market), GL-4 (European, South American, and midsize North American market), and GL-5 (European and North American Heavy-Duty Market).

TABLE 26.4 API Gear Lubricant Service Designations — 1996 GL-1

GL-2 GL-3

GL-4

GL-5

GL-6 MT-1

Lubricants for this service are considered to be equivalent to straight mineral oil for antiscoring properties. Inhibitors (oxidation, rust, foam) may be present in the oil. Designated for lubricant service for mild conditions and low unit pressures (automotive spiral and worm gear axles, low torque manual transmissions). The reference oil would be the CRC reference oil RGO-100 Lubricants for this service are lightly treated with antiwear or mild EP additives (usually fatty acids or esters) for improved antiscoring protection for automotive worm gears Lubricants for this service contain active antiwear or mild EP additives for improved antiscoring protection over the GL-2 level. Designated for manual transmissions (synchronized and nonsynchronized) and lightly loaded axles (spiral bevel gears). The GL-3 CRC reference oil is RGO-104 Lubricants for this service contain active EP additives for passenger car or moderately loaded hypoid axle gears. Designated for synchronized and nonsynchronized manual transmissions, spiral bevel axles, and moderate load hypoid axles. The GL-4 reference oil is the CRC RGO-105. Some test platforms are obsolete for the GL-4. The industry has allowed a half EP additive treat version of an approved GL-5 oil for this category Lubricants for this service contain highly active EP additives for moderately or heavily loaded hypoid gears in axles for passenger cars and trucks. Similar to MIL-L-2105D performance requirements. Combined with API MT-1 for nonsynchronized heavy-duty manual transmission service. The GL-5 uses a set of RGO reference oils for the various performance categories Lubricants for this service contain uptreated levels of highly active EP additive for severe service involving high offset hypoid gear axles. An obsolete category designed for a single application Lubricants for this service contain activeantiwear or EP additives for heavy-duty manual transmissions. Designated for nonsynchronized heavy-duty transmissions, it must have minimum resistance to thermal/oxidative degradation and exhibit satisfactory performance with plate type synchronizers. This category has been combined with the GL-5 (MIL-L-2105D) to define the MIL-PRF-2105E/SAE 2360 performance category

TABLE 26.5 Examples of Original Equipment Manufacturer (OEM) Gear Oil Factory or Service Fill Performance Specifications for Standard Drain Applications Clark MS 8 Ford EST-M2C108-C GM 9985182 Iveco 18-1805 Mack GO-J MAN 341 Arvin Meritor O-76-D

TABLE 26.6 Examples of OEM Gear Oil Performance Specification for Extended Drain Service Eaton PS-037, PS-081 Eaton PS-163, PS-164 Mack Go-J Plus Arvin Meritor O-81

Since the latter 1970s, the lubricant industry has developed and promoted MTF, ATF, and lower treat EP gear lubes as lubricants for use in manual transmissions (both synchronized and nonsynchronized). The MTFs have gained the widest market acceptance in heavy-duty transmission service and those light and midsize applications showing deficiencies with the existing recommended oils.

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Changes in the design, operation, and power loading have required either increased gear protection where engine oils were specified or improved cleanliness where EP gear oils have been used. Synthetic manual transmission fluids have gained a significant portion of the heavy-duty nonsynchronized market in North America. A majority of class 8 trucks in the United States and Canada contain transmissions that are factory filled with synthetic MTF. In 1995, the API introduced a new category and requirements for gear oils being used in nonsynchronized heavy-duty applications. During development this was the PG-1 category, which became API MT-1. The standard specification for “Performance of Manual Transmission Gear Lubricants” is ASTM D 5760 approved in 1995. This category was later incorporated in the MIL-L-2105D specifications for the upgraded MIL-PRF-2105E/SAE 2360 category.

26.1.5 API MT-1 Performance Requirements CRC L-60-1 Thermal Oxidation Stability Test, uses a specialized test rig using a spur gear set, ball bearing assembly, and copper catalyst to evaluate an oil resistance to thermal and oxidative degradation. The used gears are rated for carbon/varnish and sludge formation. The used oil is analyzed for viscosity increase, pentane, and toluene insolubles. This procedure is listed as ASTM D 5704. Elastomer Compatibility Test, uses an oil seal immersion procedure to evaluate an oil’s resistance to chemical or thermal degradation of seal elastomers, which could result in oil leakage. The used polyacrylate and fluoroelastomer

samples are evaluated for change in elongation, hardness, and volume. This procedure is listed as ASTM 5662. Cyclic Durability Transmission Test, uses a Mack T2180 stock transmission modified for this test procedure to evaluate an oil’s resistance to thermal and oxidative degradation, which would cause failure of synchronization during the high to low range shift cycle. The test is run relative to a reference oil. This procedure is listed as ASTM 5579. FZG Load Capacity Test, uses a standard FZG gear test machine under A/8.3/90 conditions to evaluate an oil’s resistance to scuffing under specific conditions. This test procedure assesses the load capacity of a mild additive treated oils for visual scoring or scuffing. This procedure is listed as ASTM 5182, DIN 51350, or CEC L-07-A-85. The API MT-1 requirements also measure foaming tendency by ASTM D 892 and compatibility with MILL-2105D reference oils under Federal test methods 791C, methods 3430.2 and 3440.1. Development is underway in Europe and Japan for high performance MTFs for synchronized heavy-duty applications.

26.1.6 API GL-5 Level EP Axle Lubricants (MIL-L-2105D/MIL-PRF-2105E/ SAE 2360) Differentials or drive axles have historically been lubricated by heavier EP treated GL-4 or GL-5 oils. The API GL-4 class is equivalent to the older, outdated MIL-L2105 defined in 1950. The API GL-5 is similar to the MIL-L-2105D U.S. military fill specifications.

26.1.7 MIL-L-2105D Performance Requirements CRC L-60 Thermal Stability Test, uses the precursor to the L-60-1 thermal oxidation test rig to evaluate an oil’s resistance to thermal/oxidative degradation under high temperature conditions. The used gears and parts are not evaluated. The used oil is measured for viscosity change, pentane, and toluene insolubles. The L-60 test was less severe than the upgraded L-60-1. CRC L-33 Water Corrosion Test, uses a Dana Model 30 hypoid differential assembly in a test stand to evaluate an oil’s rust and corrosion inhibiting properties when subjected to water contamination and elevated temperature. The disassembled axle is inspected for rust on moving parts and cover plates. CRC L-37 Axle Test, uses a Dana Model 60 hypoid differential assembly in a test stand to evaluate an oil’s load carrying, wear, and extreme pressure characteristics under high-speed/low torque and low-speed/high torque conditions. The disassembled ring and pinion gears are evaluated for gear distress. Variations of this test procedure

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are commonly run for different conditions and gear types. These include the Canadian running conditions and coated drive pinion gears (Lubrited). CRC L-42 Axle Shock Load Test, uses a Dana Spicer Model 44-1 hypoid differential assembly in a test stand to evaluate an oil’s antiscoring properties under highspeed/shock loading conditions. The disassembled ring and pinion gears are evaluated for gear distress. The MIL-L-2105D also includes testing for foaming properties by ASTM D 892, resistance to copper corrosion by ASTM D 130, and field performance by a minimum of three vehicles for over 100,000 miles service.

26.1.8 MIL-PRF-2105E/SAE 2360 Performance Requirements In 1996, the MIL-L-2105 was upgraded to a performance classification, MIL-PRF-2105E. This military gear oil specification required both the MIL-L-2105D and the API MT-1 performance tests. In 2001, the MIL-PRF2105E was incorporated into the SAE 2360. All of the sequence and rig testing remained the same under these two categories.

26.2 HISTORICAL DEVELOPMENT 26.2.1 Early Gear Oil Categories Prior to World War II, automotive gear lubricants were classified under general categories depending on application. These were termed mild, regular, heavy, or multipurpose, but only reflected the level of additive present with minimal testing. In the early 1940s, the U.S. Army started to develop a hypoid gear lubricant specification. This became the 2-105A gear oil specification. By 1946, this specification had been upgraded to the 2-105B incorporating rig testing to simulate high-speed and low-speed/high torque operation. The U.S. military gear oil specification was renamed MIL-L-2105 in 1950 (Table 26.7).

TABLE 26.7 Chronology for the MIL/API GL-5 Gear Oil Category MIL-L-2105 MIL-L-2105A MIL-L-2105B MIL-L-2105C MIL-L-2105D MIL-PRF-2105E SAE 2360

1950 1959 1962 1976 1987 1995a 2001a

a Concurrent requirements during

changeover.

Two specification upgrades laid the groundwork for synthetic automotive gear lubricants. The MIL-L-2105B introduced the L-60 T.O.S.T. thermal oxidation test. This spur gear test rig measured a lubricant’s resistance to viscosity increase and pentane and benzene insoluble components being formed during thermal/oxidative degradation. MIL-L-2105C encompassed the 75W, 80W-90, and 85W140 viscosity grades and incorporated the MIL-L-10324 low temperature category. Synthetic automotive gear lubricants were first commercialized during the early and mid-1970s. Work done with synthetic engine and industrial oils were used in developing transmission and axle oil formulas. Field tests performed in the 1970s showed clean, long drain capabilities with full synthetic gear lubricants. In the 1980s, OEMs and system suppliers used this information to develop requirements for extended drain oils for heavy-duty manual transmissions and differentials.

26.2.2 Need for Synthetics in Gear Lubricants There are only three reasons for an end user or system supplier to use synthetic or synthetic containing gear lubricants: • It solves a technical problem • Improved economics in its use • Governmental regulations

The first reason to consider synthetics is as a technical solution. These can be in an existing or development area. The automotive transmission and axle area has been going through rapid and significant change in the last two decades. These changes have been worldwide. Passenger cars are being downsized, with longer service life and lower maintenance. The trucking industry has also been pushing for changes. Fleets and end users have demanded more fuel efficient, higher payload, and longer lasting equipment. These changing technical requirements have introduced opportunities for synthetics to be used in the power train equipment. Synthetic gear and transmission oils have shown improved low and high temperature viscosity performance, superior thermal and oxidative stability, and improved cleanliness over petroleum oils in these more severe environments. Smaller and hotter running equipment is pushing the limits that petroleum oils can be used successfully to satisfy the lubricant and equipment service life that the consumer and operator requires. The manufacturers of transmission, axles, and transaxles have recognized that the lubricant is an integral part of the design of new equipment. Improved economics are the second reason for considering synthetic gear oils. Automotive synthetic basestocks (poly-alpha olefins [PAO], Diesters, Polyol Esters) are more expensive than petroleum base oils. This higher

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raw material cost translates into a higher cost, upper tier product in the gear oil marketplace. Synthetics have become commercially successful in the heavy-duty truck industry because they are able to save money for the fleet or end user. The higher initial fill cost of synthetic oil in the transmission and axles will be offset by several factors over the life of the vehicle. These include: 1. The cost of the replacement oil in a standard drain program 2. Maintenance cost for oil replacement 3. Loss of income from out-of-service maintenance related to the oil drain schedule 4. Lower repair costs for unscheduled power train maintenance 5. Extended warranty from the system supplier or truck builder 6. Lower disposal costs 7. Fuel Savings 8. Higher resale value on used equipment Those truck fleets that have accurate accounting for cost per mile have shown justified cost savings in using synthetics over the life of the vehicle. The third reason for considering synthetics is government requirements or guidelines. Worldwide, national regulations impact a significant portion of the transportation industry. Governmental regulations for the manufacturer, lubricant supplier, fleet operator, and passenger car owner are increasing. For gear lubricants, these national regulations impact the cost of fuel, disposal of used oil, guidelines on vehicle fuel economy, and pollution limits. High performance lubricants will play a large part in assisting the engineer with the design and operation of the automotive equipment to satisfy these requirements.

26.3 TYPES OF SYNTHETICS 26.3.1 Definition of Synthetic A typical compounded automotive transmission or axle lubricant is composed of basestock(s) and an additive system. The basestock type designates whether the fluid is a petroleum oil, partial, or full synthetic based lubricant. Refined mineral oil is still used in this application. Its formulations satisfy the API GL-5 requirements, which are the current minimum requirements for moderate or severe service in planetary, hypoid, or spiral bevel gears systems. Petroleum oil differs in paraffinic content and viscosity index. Recent advances in refining technology have produced unconventional base oils (UCBOs), some with viscosity indices of over 130. All petroleum based oils are refined and treated with distillate cuts and consist of a complex hydrocarbon mixture. The API establishes Base Oil guidelines, based on five categories (Table 26.8).

TABLE 26.8 API 1509 Base Oil Guidelines Category

Sulfur (%)

Saturates (%)

Viscosity index

Group I >0.03 <90% 80 to 120 Group II ≤0.03 And ≥90% 80 to 120 Group III ≤0.03 And ≥90% ≥120 Group IV All polyalphaolefins (PAOs) Group V All others not included in Groups I, II, III, or IV

Automotive Lubricant Basestocks

PETROLEUM

SYNTHETIC

API Group1 –3 High–Low VI Neutral Oils Hydrofinished Oils

PI Groups4 and 5 PAO Organic Esters – diesters – polyol esters

FIGURE 26.2 Automotive lubricant basestock types (From “Automotive Applications,” part of the STLE Synthetic Lubricants Education Course)

API 1509 is currently under review and may involve changes or additional categories in the future. Synthetic basestocks, by difference, are manufactured from lower weight components and comprise a predetermined molecular structure. Recent marketing attempts have been made to classify some of these highly refined and treated mineral oils as synthetic or “synthetic performing.” For this chapter, “synthetic” will be defined as a technical category. The ASTM definition is “a synthetic lubricant is a product which consists of stocks manufactured by chemical synthesis and containing necessary performance additives.” The key word is synthesis, which involves taking small chemical building blocks and combining them in an ordered, predictable reaction to form precise large molecules (Figure 26.2).

26.3.2 Synthetic Basestocks used in Gear Oils Synthetic basestocks used in the automotive lubricant area include silicone fluids, PAOs, PIOs, dialkylated benzenes, alkylated naphthalenes, dibasic acid esters, polyglycols, polyol esters, and phosphate esters. Only three are widely used in the automotive gear and transmission area. These are the PAOs, diesters, and polyol esters [4]. Synthetic transmission and axle oils may consist or all PAO, all ester (diester or polyol ester), or a mixture of PAO and ester.

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Most current full synthetic formulations are all PAO based or PAO/ester based. All ester formulations were developed and marketed in the 1970s, but now only constitute a small, niche market for specialty applications. All ester system gears oils are being reevaluated for biodegradable applications, but no significant market share has been gained by any commercial products. Partial synthetic gear oils usually consist of a petroleum base oil with the addition of PAO or ester. The synthetic portion usually constitutes 10 to 30% of the basestock portion. Lower levels of PAO or ester (less than 10%) are usually classified as additive treat and not as a basestock component. Partial synthetics fall into a “gray” area for definition and labeling, since there are no defined limits or ranges for these basestocks. Partial synthetic gear lubes fall in between petroleum oils and full synthetics for viscometric and volatility properties, but are more similar to petroleum based oils for low temperature properties, thermal/oxidative stability, and long service durability. The two main types of synthetic gear oils are PAO and PAO/ester based. A properly formulated all PAO gear oil will show improved properties over a comparable mineral oil based lubricant. These include better low temperature performance (pour point, viscosity, and channel point), increased high temperature bulk viscosity (higher viscosity index), and improved thermal and oxidative stability. The polarity of PAO is very similar to petroleum oil with PAO based gear oils requiring the addition of a seal swell agent for elastomer compatibility. Petroleum and PAO basestocks have a tendency to shrink and harden most automotive elastomers. Additive solubility is usually lower with PAO compared to petroleum. Petroleum oils are a complex mixture and contain low levels of polar functional groups (oxygenates, sulfur, nitrogen compounds) to assist in solubilizing polar additives. Most additive packages are very polar systems, which are limited in solubility in the nonpolar PAOs. Most additive systems for gear oils (automotive and industrial) were developed for a petroleum based system and may not be suitable for all synthetic formulations. Additive selection for synthetics and partial synthetics are affected by the type and quantity of the basestock present. The screening for acceptable additives or the incorporation of longer, alkyl chains on the additive molecules may have to be considered when formulating synthetic based lubricants. PAO and petroleum are similar for cleanliness properties in the latter stages of thermal degradation and oxidation. Both have a tendency to “break dirty” when the oils have been heavily oxidized. The thermal and oxidation products of these basestocks are polar molecules (i.e., varnish, sludge) and are insoluble in these nonpolar systems. Low levels will fall out of solution and coat the internal parts or fall to the bottom as sludge. Detergents and dispersants moderate this property, but only have limited effectiveness.

The addition of ester (diester, polyol ester, or mixtures) to PAO or petroleum gear oils imparts improvements in several areas. A properly formulated gear oil using ester as a basestock component usually does not require a seal swell agent for elastomer compatibility. Seal swell agents are highly aggressive compounds added in small amounts to affect the volume and elongation change in the elastomers in contact with the gear oils. The use of ester in lubricants changes the polarity of the entire basestock system, which moderates the normal shrinking and hardening tendencies of elastomers. The amount and type of ester and the ratio of PAO to ester are critical parts of a gear oil formulation to maximize elastomer life in long service applications. Ester addition to gear oil formulations also promotes the solubility of most additive systems. These polar additives moderate detergent, dispersant, foaming, acid neutralization, antiwear, anticorrosion, and EP performance properties. Ester containing formulations have a much higher basestock polarity and improved solubility to polar additives compared to PAO or petroleum basestocks. A combination of both PAO and ester may be used to “dial-in” a specific polarity index to the basestock to maximize these additive and by-product solubilities. The higher basestock polarity imparted by esters also improves the solubility of thermal degradation and oxidation products. Ester systems have a tendency to “break clean” under highly degraded or heavily oxidized conditions. Moderately high levels of degradation product (i.e., carbon, coke, varnish, sludge) can remain soluble in the more polar basestock yielding a much cleaner system.

26.4 COMPARATIVE PERFORMANCE DATA The use of synthetic basestocks in automotive transmission and axle lubricants will show improved performance properties over a comparable viscosity grade mineral oil based product. These properties include better low temperature characteristics, improved viscometrics at high temperature (higher VI), enhanced thermal and oxidative stability, lower volatility, improved solubility characteristics, and higher efficiency. For the transportation industry, these improvements translate into extended drain intervals, reduced maintenance costs, lower downtime, and less oil disposal. An overall lower operating cost and enhanced hardware protection is realized.

26.4.1 Bulk Physical Properties The predominant basestock viscosity grades used in partial or full synthetic gear lubes are 6 to 8 cSt. A comparison of the PAOs and esters with comparable petroleum base oils (solvent neutral or UCBOs) show improved low temperature, volatility, and thermal/oxidative stability properties.

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26.4.2 High Temperature Viscosity Characteristics Automotive synthetic basestocks exhibit improved high temperature properties compared to equivalent viscosity petroleum oils. For gear oils these improvements are characterized by viscosity retention vs. temperature increase (due to a higher viscosity index), improved flash points, and lower volatility. Higher flash and lower volatility properties are usually not a concern for the gear lube formulator or end user as long as the transmission or axle lubricant meets minimum limits. High temperature operation in the power train is becoming more of a concern due to the use of smaller gear box design, lower lubricant volumes, higher torque loading, and the use of airfoils and air dams. These aerodynamic improving devices have been introduced onto trucks and incorporated into the body design of passenger cars and vans to improve the fuel economy of the vehicle. These designs restrict the flow of air over the drive train and increase the temperatures of the transmissions, transaxles, and axles. The lubricants must maintain a minimal bulk viscosity to ensure sufficient film strength to maintain proper hydrodynamic lubrication for certain parts. Higher viscosity index basestocks, whether petroleum or synthetic, will exhibit lower viscosity loss vs. temperature increase. This property will translate into higher film strength for hydrodynamic lubrication in the gearbox. At high temperatures this will equate improved protection for bearings, rotating seals, and lightly loaded gears.

26.4.3 Low Temperature Viscosity Characteristics Part of the driving force for the introduction of full synthetic gear lubricants were the improved low temperature flow and viscosity properties. PAO and ester basestocks show significantly lower pour points than comparable petroleum oils (please refer to Figure 26.3 and Figure 26.4). This 6 cSt Base Stock Comparison Test Parameters

200SN HC-6

PAO-6

Diester

Polyol Ester

100°C Visc, cSt 40°C Visc, cSt –18°C Visc, cSt –40°C Visc, cSt Viscosity index Pour pt. °C Flash Pt. °C NOACK, % loss

6.2 42.7 Solid Solid 97 –15 215 12.8

5.9 30.9 1200 8300 135 –60 243 7.5

6.4 33.8 1,300 18,700 145 –57 243 4.7

5.6 32.4 — 30,000 114 –54 254 3

5.6 32.1 Solid Solid 130 –12 — 8.9

FIGURE 26.3 Six cSt viscosity basestock comparison (From “Automotive Applications,” part of the STLE Basic Synthetic Lubricants Education Course)

Antiwear/EP Level vs. Thermal/Oxidation Stability

8 cSt Base Stock Comparison Test Parameters

325 SN

HC-8

PAO-8

Polyol Ester

100°C Visc, cSt 40°C Visc, cSt Viscosity index Pour pt. °C Flash pt. °C NOACK, % loss

8.0 61.8 96 +5 232 <10

9.0 63.3 118 –9 235 3

7.9 48.5 132 –59 264 3

6.9 37.1 148 –37 265 2.2

Engine Oils

Automatic Transmission Fluid (ATF)

Manual Transmission Fluid (MTF)

EP Gear Lubricant

-----------Thermal/Oxidation Stability------------------------ Antiwear/EP Protection------------

FIGURE 26.4 Eight cSt viscosity basestock comparison (From “Synthetic Basestocks Presentation,” Synlubes Technology R&D, Cognis Corporation)

FIGURE 26.5 Trends for antiwear/EP protection vs. oxidative stability for gear oils (From “Synlubes Technology Training Presentation 2003,” Synlubes Technology R&D, Cognis Corporation)

is due to the molecular structure and lack of crystalline wax particles typically present in refined petroleum oils. These lower pour point oils exhibit better low temperature viscosity and flow characteristics, which translate into enhanced protection in both transmission and axles under cold startup and operating conditions. These low temperature properties may be measured in gear lubricants by using low temperature kinematic and dynamic viscosity methods (ASTM D-2983 Brookfield viscosity), channel point testing (Federal Test Method 3456), cold box simulation testing, and field testing [5–7]. The low pour properties of the synthetic basestocks allow the formulator a tool for adjusting petroleum based gear oils (automotive and industrial) for improved low temperature properties. Both PAO and ester may be used for this improvement. Typical petroleum based gear oils are treated with pour point depressants, which interrupt the crystal lattice formation of the wax content. The addition of synthetic basestock usually allows the removal of the pour point depressant from the additive package. Some low temperature compatibility problems have been experienced with the use of certain pour point depressants and synthetics. This may cause slight hazing or precipitate floc of the pp depressant at low temperature and long-term storage. Care should be exercised in using certain pour point depressants with synthetic basestocks in full or partial formulations. Cold temperature storage compatibility tests should be run with any formulation change.

any antiwear capability beyond the bulk viscosity properties. Ester may contribute a small amount of antiwear property, mostly as part of a lubricity increase due to a polar monolayer present at the metal surface. All of these basestocks, however, fall significantly short in antiwear and EP capabilities and must be supplemented by additives for automotive transmission and axle applications. The predominant type of antiwear additive for automotive gear lubricants are phosphorus based active or nonactive systems. The major types of gear oil EP additives are sulfur and phosphorus thermally activated compounds. Alternate EP additives have been evaluated for these automotive applications, but have shown insolubility problems (graphite, molybdenum disulfide) or thermal/hydrolytic stability deficiencies (borate esters). The majority of EP additive for automotive gear lubricants, worldwide, are based on S/P chemistry. The level of antiwear or EP additive required by the application may be affected by the bulk oil viscosity and type of basestock present. Higher SAE grades of gear oils usually require a lower additive treat for the same level of gear protection [8]. PAO and ester based gear oils usually require an antiwear or EP additive overtreat for the same level of gear wear protection compared to using higher viscosity petroleum oil basestocks. Esters, being more polar, may compete with the additives at the metal surface and may require a more active additive package or a higher concentration of antiwear or EP additive. Most manual transmissions require only antiwear additive or low levels of active or nonactive EP additive for gear protection. Planetary, spiral bevel, and hypoid gear axle systems require active EP, either at the GL-4 or GL-5 additive level. Formulators of extended service oils must balance the use of antiwear and EP additive performance with thermal and oxidative stability. Thermal stability and EP gear protection conflict and usually require compromise in the transmission or axle lubricant (Figure 26.5). The amount and activity of the EP additive will also negatively impact bearing life and elastomer durability in the transmission or axle [9,10]. A properly formulated, extended drain gear oil will balance the level of EP with

26.4.4 Antiwear and Extreme Pressure Performance Automotive gear oils require different levels of antiwear and EP performance capabilities depending on the application. In modern gear oil formulation, little antiwear and EP protection is contributed by the basestock, either petroleum or synthetic. The metal to metal contact in gears must be handled by an additive system. Petroleum oils have a small amount of antiwear present as trace levels of sulfur, nitrogen, or phosphorus functionality coming from the crude petroleum source. PAO has not been shown to contribute

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the other additives present, to ensure gear, bearing, and seal protection over the life of the vehicle. The level of antiwear or EP performance required in the automotive gear lubricants are measured by various test platforms including the FZG A/8.3/90 Load Capacity test, the CRC L-37 Load Carrying axle test, the CRC L-42 Shock Load Axle test, the Mercedes Benz HL-4 Spalling test, and the Volvo VTM 01-96 Pitting Test. Field performance with equipment tear down and inspection are also used. Increased thermal stability requirements by the OEMs in the late 1980s led to the development of thermally stable sulfur/phosphorus EP additives. These, when used in conjunction with thermally stable synthetic basestocks, have led to gear lubricants with exceptional thermal stability, thermal durability, and extended service capabilities.

26.4.5 Shear Stability Increased emphasis on low temperature performance, fuel economy, and improved thermal stability has led to the wider use of multigrade gear lubricants over the traditional mono grade lubricants. If not properly formulated, insufficient film strength can result from viscosity loss due to mechanical shear down of the gear oil. Historically, automotive gear lubricants have used engine oil shear methods (ASTM D-2603 Sonic Shear Method, ASTM D-3945 Orbahn shear test) or full-size vehicle field test results to measure shear loss. Recently, the FZG Shear and Tapered Roller Bearing Shear Tests have been used to predict gear lubricant field service [11]. Heavy-duty truck field performance on multigrade gear oils have shown satisfactory lubricant protection at up to 40% shear loss when the final viscosity of the 75W90 gear lubricant was maintained within grade (13.5 cSt minimum) [7]. Currently, most multigrade automotive gear lubricants do not exhibit over 10 to 15% viscosity shear loss in extended drain service (up to 1,000,000 miles).

26.4.6 Thermal and Oxidative Stability Automotive gear oil synthetic basestocks (PAO and ester) show improved resistance to thermal and oxidative degradation compared to petroleum basestocks. Of the basestocks currently used in automotive gear lubricants, polyol esters are the most thermally stable, followed by diesters, PAOs, and petroleum oils. This progression is applicable for “inhibited” systems where antioxidants are present during the oxidation testing. In a noninhibited system, petroleum oil may show a better ranking due to naturally occurring antioxidants present from the crude oil. Recommended bulk oil temperature for these basestocks in low additive treat formulations (low antiwear or EP additive levels) are shown in Table 26.9. The available service life for gear lubricants is a reflection of the basestock stability, additive stability

Copyright 2006 by Taylor & Francis Group, LLC

TABLE 26.9 Recommended Maximum Bulk Oil Temperatures for Various Antioxidant Inhibited Lubricant Basestocks Base fluid

Max. bulk oil temp. ◦ F

Petroleum PAO Diesters Polyol esters

250 250–350 300–350 350–425

L-60-1 Thermal Oxidation Stability Test Extended Duration Hours to Reach 100% Viscosity Increase Petroleum 90 Petroleum 80W/85W-90 Petroleum Trans SAE 50 Partial Synthetic 80W-90 Synthetic 75W-90 Synthetic 75W-90 (Therm Stable) Synthetic Trans SAE 50

50–100 50–100 50–100 75–150 100–200 300 >400

FIGURE 26.6 Extended duration L-60-1 thermal oxidation stability test comparison data (From “Automotive Applications,” part of the STLE Synthetic Lubricants Education Course)

(antiwear, EP), and solubility of thermal degradation products. Gear lubricants use several test platforms to evaluate an oil’s resistance to thermal and oxidative degradation. These include the L-60/L-60-1 thermal oxidation stability test, the Cycling Durability Transmission test, the European DKA and GFC tube oxidation tests, and the Aluminum Beaker Oxidation Test (ABOT). With the development of synthetic gear lubricants and thermally stable additive systems, extended versions of these methods are used to further differentiate these high performance oils. The standard L-60 and L-60-1 T.O.S.T. for MIL-L2105E is 50 h at 325◦ F. The viscosity change during the test is limited to 100% increase for a passing oil. The L-60 test was incorporated into the MIL-L-2105B in 1959 and has shown good correlation with field experience for extended service life and oil thermal degradation. Extended versions of the L-60 and L-60-1 tests have been developed to separate the higher performance oils, specifically as a measure for extended drain service. 100, 200, and 300 h versions of the L-60 or L-60-1 tests have been used as an oxidation test for some factory fill and extended service/extended warranty requirements. Examples of comparative extended L-60 testing for various gear oils are given in Figure 26.6. In field trials and selected fleet monitoring, in heavy-duty nonsynchronized manual transmission use

Copyright 2006 by Taylor & Francis Group, LLC

Fuel Efficiency Increase using EP 75W-90 Synthetic Gear Lubricant vs. SAE 90 Petroleum Baseline 5 % 4

Winter Operation

3

2

1

253K miles

Transmission and axle lubricants will typically exhibit periodic levels of minor water contamination (0.1 to 0.2%) during normal operation of the vehicle. This is due to normal “breathing” of the equipment through the vent or other openings. This moisture will be picked up by the oil during a cool down cycle with the vehicle parked, then evaporate it when the equipment reaches operating temperature. High water contents in the oil may result from submergence, overly vigorous washing, or improper venting and may result in significant water contents. Transmission and axle oils must be able to handle the periodic moisture from equipment “breathing” and reasonable levels of water from transient ingestion. Up to several % water (1 to 5%) will eventually dry out on class 8 trucks on over-the-road service. Continued water entrainment or levels greater than 5% should prompt draining the lubricant for drying or replacement. With moisture being present in the gearbox environments, the gear lubricant must maintain its lubricating capabilities and protect the metal components from rust and corrosion. Properly formulated gear lubricants must not show hydrolytic instability in either the basestock or additives present (antiwear, EP, anticorrosives). The predominant automotive synthetic basestocks (PAO, diesters, polyol esters) do not show any hydrolytic instability in gear oil applications. PAO is comparable to petroleum hydrocarbons in water solubility (insignificant) and hydrolytic reactivity (not detectable at automotive conditions). Esters, both diester and polyol esters, are the products from the reaction of a carboxylic acid and an alcohol. Under certain reaction conditions, esters can be hydrolyzed back to their reactant raw materials. Most ester basestocks used for automotive gear lubricants have shown nondetectable or insignificant hydrolysis under transmission and axle conditions. The CRC L-33 water corrosion test is used in the MILPRF-2105E/SAE 2360 requirements to evaluate an oil’s ability to resist corrosion under high temperature/moisture conditions. Several test methods are used under OEM factory fill and extended service requirements. These include running a CRC L-37 axle test with 3% water addition, a Mercedes Benz extended storage test, and a Fiat water resistance test.

Lubricity is a measure of the effect of a lubricant on the coefficient of friction of a contacting part over a sliding surface. In transmission and axle lubricants, greater lubricity would impart improved fuel economy and lower frictional power loss. Both fuel economy and power loss can also be influenced by the bulk oil viscosity. Lubricity can be affected by the addition of friction modifiers to the oil. Friction modifiers for automotive applications include some carboxylic acids, sulfurized fatty acids, glycerol monoesters, and oleate esters. Laboratory testing using a passenger car hypoid axle have shown synthetic basestocks (PAO, High Visc PAO, and Diesters) impart a positive influence on axle efficiency [12]. In one study of axle efficiency, full synthetic heavyduty truck and passenger car formulations were shown to give the highest increase in axle efficiency, followed by partial synthetic formulations and petroleum based gear lubricants. Part of this increased efficiency was related to the viscometric properties of the test lubricants, part due to increased lubricity. Fuel economy testing has also been run on heavy-duty drive trains on both dynamometer and field tests. Compared to a conventional petroleum based SAE 90 gear lube, a synthetic 75W90 multigrade showed increased axle efficiency for an average of 1% diesel fuel savings (Figure 26.7). In the competitive trucking industry, fuel costs have become of paramount concern. Trucks are being designed for improved aerodynamics, lighter weight cab, and trailer components are being developed and speed and fuel monitoring equipment are becoming standard equipment. Synthetic gear lubricants in the transmission and axle of

168K miles

26.4.7 Hydrolytic Stability

26.4.8 Lubricity and Fuel Economy

New

(350 HP engine, nine speed overdrive, no oil cooler, full cab fairings, air shields, 80,000+ lb. gvw) conventional, standard drain, petroleum based transmission, and gear oils will typically show a 100% viscosity increase at approximately 100,000 miles and sludging at approximately 150,000 miles. Properly formulated synthetic transmission oils have remained in acceptable viscosity range after 1,000,000 miles of continuous service.

0 Dynamometer Test

RCCC

ALI Canada Forest

FIGURE 26.7 Comparison of diesel fuel efficiency of synthetic 75W-90 vs. petroleum 90 gear lubricant (From “Automotive Applications,” part of the STLE Synthetic Lubricants Education Course)

Annual Diesel Fuel Savings for the Average User with 100 Vehicles 100 vehicles × 100,000 miles

= 10 million miles

10 million miles × 5 miles/gal

= 2.0 MM gals. fuel

10 million miles × 5.05 miles/gal

= 1.98 MM gals. fuel

Therefore a 1% fuel savings

= 20,000 gals. fuel

FIGURE 26.8 Potential annual diesel fuel savings at 1% increase in fuel economy (From “Automotive Applications,” part of the STLE Synthetic Lubricants Education Course)

a class 8 over-the-road truck showing a 1% increase in diesel fuel economy can significantly impact a truck fleet’s bottom line (Figure 26.8).

26.4.9 Compatibility Characteristics The currently available major brands of synthetic automotive transmission and gear oils based on PAO and PAO/ester are fully compatible with conventional petroleum based gear oils. Gear oils that meet the API MT-1, MIL-L-2105D, and MIL-PRF-2105E/SAE 2360 requirements have passed the SS&C Federal Test Std 791C, Methods 3430.2 and 3440.1. This test regime assures that a candidate oil is fully compatible with a set of designated reference gear oils and that its additive system remains soluble under varying temperature environments. A vehicle factory filled with synthetic lubricant in the transmission or axle can be topped off with petroleum based oils if a synthetic source is not available. Mixing of petroleum and synthetic gear oils is not recommended, however, because the addition of petroleum oil to a full synthetic system reduces its extended drain capabilities, specifically its low temperature and oxidation stability performance. No critical adverse reaction will occur with this mixing. Most OEMs and system suppliers who qualify extended service oils for their transmissions and axles, limit the amount of petroleum addition to less than 10%. Over this amount the recommended drain interval for standard petroleum fill should be followed. By the same account, a petroleum filled unit may be topped off with synthetic gear lube. There is little advantage to this except for a slight improvement in low temperature properties, since the standard drain interval must be maintained. Some alternative EP based gear oils are not recommended for comixing with the sulfur phosphorus EP oils, either synthetic or petroleum based, due to a possible adverse reaction of the additive systems.

26.4.10 Miscibility Characteristics Similar to the compatibility properties, synthetic gear lubricants are fully miscible with petroleum based gear lubes.

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The PAO based synthetic gear lubes show comparable additive and degradation product miscibility with the petroleum gear oils. Both are nonpolar systems and show limited solubility with polar additives and oxidation by-products. The ester containing synthetic gear lubes show improved miscibility with most additive systems and degradation products compared to petroleum oils. Caution should be used when formulating synthetic automotive oils. Some additives and thickening agents developed for petroleum oils may exhibit insolubility when used with synthetics.

26.4.11 Service Life Properly formulated synthetic transmission and EP gear lubricants have been shown to have the capabilities for extended service for most automotive vehicles. North American system suppliers and OEMs have established extended service/extended warranty gear oil categories for factory and service fill. European and Japanese manufacturers are overseeing evaluations of high performance and thermally stable gear oils for extended service. Many of these categories will have performance requirements that will require the use of full synthetic formulations or the addition of synthetic basestocks to petroleum oils. Worldwide, the potential for “filled for life” power train lubricants is being seen as achievable.

26.4.12 Field Performance Field testing of heavy-duty synthetic transmission and EP gear oils began in the early 1970s in North America. Millions of miles of field experience were collected over the next decade while these products were being commercialized. During the 1980s, the trucking industry, both manufacturers and fleets, were seeing rapid and significant changes. Equipment was being designed for longer life, lower maintenance, and all the while the temperatures in the drive train were rising. The trucking industry, pushed by the cost of fuel, was demanding more aerodynamic designs, lower weight, and more efficient vehicles. These factors were placing higher power loading through the transmissions and axles while restricting the flow of air cooling over the housings. During this time, the manufacturers and engineers of truck components were recognizing that the lubricant was an integral part of a total system concept. OEMs started to insist on more stringent gear lubricant requirements. Synthetics allowed extended drain intervals, lower maintenance costs, and the increased lubricant durability and cleanliness prompted extended warranty coverage. In extended field tests and typical North American fleet operations, high performance synthetic gear lubricants have shown improved performanceover conventional

petroleum oils in several areas: • • • • • • • •

Extended service life, up to 15X standard drain interval Cleaner equipment, less varnish and sludge Extended bearing life Improved seal life Lower repair maintenance Improved fuel efficiency Less in-shop downtime Less oil disposal

Most fleets maintain a lube sampling and analysis program to monitor the condition of the fluids and wear metals from the equipment. Service personnel and maintenance supervision should be aware that synthetic gear lubes exhibit different analysis patterns than conventional petroleum gear oils. Ester containing synthetic engine and gear oils may exhibit higher wear metal contents than that of all corresponding PAO synthetics or petroleum based oils. Field studies started in the 1970s and continuing on today as equipment has changed has shown these higher wear metal levels (predominately iron or copper in the drive train) do not correspond to higher wear in the equipment [7]. Esters, especially diesters, in contact with the steel and yellow metal components (copper, brass, bronze) form soluble metal salts. These soluble salts or soaps are totally miscible in the oil and are not detrimental to the equipment. They are not abrasive and cannot be filtered out, in this soluble form. Analysis laboratories need to be aware that synthetic gear oils are being used such that higher limits for these metals can be logged into the tolerance ranges for change-out.

26.5 SYNTHETIC GEAR LUBRICANTS IN THE MARKETPLACE In the automotive gear oil market, synthetics have been commercially successful in selected areas. Most of these have been in heavy-duty manual transmissions and drive axles. Transaxles are still predominately filled with petroleum engine oils, ATF, or GL-4 gear oils. In passenger cars and light trucks, synthetic transmission and axle lubricants constitute a small portion of the market. They have been limited to some specialty vehicles (4 wheel drive off-road sport vehicles, high performance cars) and high or low temperature problem applications (arctic construction and military equipment, excessively hot transmission applications, service fill for cold weather shift problems). In North America and Europe, synthetic MTFs and EP axle oils are filling increasing applications in these smaller vehicles. In midsize vehicles, class 3 to class 5, synthetic gear lubricants constitute a small, but growing market share. Starting with niche applications related to higher

Copyright 2006 by Taylor & Francis Group, LLC

temperatures, OEMs and system suppliers are now recognizing the benefits of high performance lubricants, gained from the heavy-duty vehicle experience. These oils may have application in the inner city, short haul delivery van market. In heavy-duty class 8 vehicles, synthetic transmission and EP axle lubricants constitute a major share of factory fill in North America (75%+). In Europe, South America, Australia, and the Far East, there is growing interest in extended drain gear lubricants, including synthetics, but currently only low market share in factory or service fill applications (less than 50%). Among the commercial synthetic gear oils worldwide, most are PAO or PAO/ester based formulations. A properly formulated synthetic MTF or EP axle lube will show improved performance over a conventional petroleum oil, but will be more expensive on initial purchase. Market penetration has been achieved in the heavy-duty applications because the truck fleets have shown that the cost savings achieved by using the synthetics offset higher initial cost. In midsize vehicle fleets, lower accrued annual mileage and smaller fleets make it more difficult to confirm cost savings with synthetics. For most passenger cars, petroleum based products are able to fulfill the requirements for the service life of the vehicle. Technical requirements and governmental regulations may impact the lubricants used in these vehicles.

26.6 SUMMARY Automotive gear lubricant requirements have been changing at an increasing rate. Lubricants for manual transmissions and axles are being developed for extended drain service and being coupled with extended warranty programs. Synthetic gear oils are being used extensively for these long drain applications and currently comprise a majority of the factory fill for heavy-duty trucks in North America. The transmission and axle manufacturers are recognizing that the gear lubricant is an integral part of a total system for equipment with long life and low maintenance. Lubricant producers are working in conjunction with the system suppliers, truck builders, and fleets to develop these advance systems. Synthetic gear lubricants have established a high performance reputation for the heavy-duty truck builders in North America. Worldwide, interest is growing in these advanced lubricant systems for both trucking and passenger car applications. Synthetics will continue to have a significant market influence in the 21st century.

REFERENCES 1. Sammut, V.P., “Market Trends in Manual Transmissions for Class 1–8 Vehicles,” SAE Paper 922468.

2. “Eaton Corp., Details on the Fuller FR 10-Speeds” and “Mack Trucks, Adds to T200 Transmission Series,” Transport Topics, June 10, 1996. 3. Graham, R., Cain, R.W., and Peal, S.N., “Fluid Development for Manual Transmission Applications,” SAE Paper. 4. Lakes, S.C., “Synthetic Gear and Transmission Lubricants,” NLGI Spokesman, 1991. 5. Olszewski, W.F. and Taylor, D.J., “Synthetic Automotive Gear Lubricants,” SAE Paper 881324. 6. Moats, N.M., “Canadian Experience with Multi-Grade Gear Oils,” SAE Paper 811204. 7. Beimesch, B.J., Margeson, M.A., and Davis, J.E., “Field Performance of Synthetic Automotive Gear Lubricants,” SAE Paper 831730.

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8. Schiemann, L.F. and Schwind, J.J., “Fundamentals of Automotive Gear Lubrication,” SAE Paper 841213. 9. Nixon, H.P. and Zantopulos, H., “Observations of the Impact of Lubricant Additives on the Fatigue Life Performance of Tapered Roller Bearings,” SAE Paper 952124. 10. Richardson, R.C. and Scinto, P.R., “The Effects of Gear Lubricant Components on Oil Seal Compatibility,” Presentation at the 1993 NLGI Annual Meeting. 11. Schnur, E.R., “Evaluating Gear Lubricant Shear Stability,” SAE Paper 961108. 12. O’Connor, B.M., Schiemann, L.F., and Johnson, R.L., “Axle Efficiency-Response to Synthetic Lubricant Components,” SAE Paper 821181.

27

Industrial Gear Lubricants Dennis A. Lauer CONTENTS 27.1 Introduction 27.2 Historical Developments 27.2.1 Industrial Gear Oils 27.2.2 Need For Synthetic Gear Lubricants 27.3 Types of Synthetic Gear Lubricants 27.3.1 Gear Lubricants Based on PAOs 27.3.2 Gear Lubricants Based on PAGs 27.3.3 Gear Lubricants Based on Ester Oils 27.4 Performance Properties 27.4.1 Viscosity 27.4.1.1 Viscosity–Temperature Behavior 27.4.1.2 Viscosity–Pressure Behavior 27.4.2 Oxidation Stability 27.4.3 Application Testing 27.4.3.1 Worm Gear Test Rig 27.4.3.2 Test Oils 27.4.3.3 Worm Gear Test Results 27.4.3.4 FZG Twin Disk Machine 27.4.3.5 Temperatures and Oil Service Life 27.4.3.6 Performance Comparisons 27.5 Current Commercial Practice 27.5.1 Synthetics in Use 27.5.2 Market for Synthetic Gear Lubricants 27.5.3 Industry Demands Higher Performance References

27.1 INTRODUCTION Wooden pegs set in a hub were the components of the first operational gears. Lubrication was not considered a necessity even though these wooden gears would have benefited from lubrication. Later, metal gear teeth replaced these wooden pegs and hubs. Originally, animal fats were smeared on the gearing to reduce excessive wear and minimize noise. During the industrial revolution many more demands were placed on gearing to transmit power reliably and to provide a relatively long service life for the equipment. Consequently, mineral oil gear lubricants were produced and additive packages were developed to meet these needs. Today the need for even higher productivity and greater efficiency in operation has placed severe demands on the lubricants that can no longer be met by mineral oil products in many of the applications. To meet

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these extreme demands on the lubricant synthetic gear oils were developed. The automotive industry was among the first to embrace synthetic lubricants as the solution to many automotive gearing problems. In the 1960s through the 1970s both semisynthetics and fully synthetic automotive gear oils became popular. Industrial gear operators did not realize the benefits of synthetic lubricants until much later and are still in the process of acceptance. The American Gear Manufacturers Association (AGMA) Lubricant Specification that includes synthetic gear oils was not published until 1994. Gears continue to be the most commonly used means of transmitting mechanical power and controlling motion, which increased their usage in many applications.

A diverse variety of designs and sizes of gears are manufactured to operate under widely varying conditions and environments. The lubrication requirements are determined by these many variables [1]. In order to understand the development and application of synthetics in gear lubrication, it is necessary to review general principles of gears, gear lubrication, and how and why the technology developed. Some of the basic types of gears include: 1. 2. 3. 4. 5.

Spur gears Helical gears Bevel gears Worm gears Hypoid gears

All the above gearing systems can benefit by the use of synthetic gear lubricants to varying degrees. These basic gear types are used to develop all gearing systems. They are described in Table 27.1 [2] and Figures 27.1 to 27.5. Gear systems may involve one or more types of the basic gear designs. Their speeds can range from very low to extremely high while transmitting light or heavy loads. Gearing systems may be enclosed in a gearbox or open to the elements of the environment. The operating temperature of a gearing system [3] is influenced by speed, load, and the operating environment.

Lubricants for gearing systems have to perform the general task of transferring forces, minimizing wear, and reducing friction. If fluid lubricants are used, they also dissipate heat and remove abrasive particles. Depending on the type of gear and the operating conditions, gear lubricants have to meet various requirements. A universal gear lubricant does not exist that can satisfy all these demands. Lubricant manufacturers have developed different types of gear lubricants such as gear oils, gear greases, and adhesive lubricants with properties satisfying the individual operating needs. Gear oils have to meet the following requirements: • • • •

Excellent resistance to aging and oxidation Low foaming tendency Good load-carrying capacity Neutral toward the materials involved (ferrous and nonferrous metals, seals, paints) • Suitable for high and low temperatures • Good viscosity temperature behavior Gear greases in contrast are required to ensure the following criteria: • Good adhesion • Low oil separation

TABLE 27.1 Basic Gear Types Gear type Spur gears (Figure 27.1)

Helical gears (Figure 27.2)

Bevel gears (Figure 27.3)

Worm gears (Figure 27.4)

Hypoid gears (Figure 27.5)

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Description Spur gears are characterized by their cylindrical shape and parallel shafts. The contact of the intermeshing teeth is linear over the entire flank width. Straight-toothed spur gears usually have one or two teeth in mesh at all times. Because of this, their load-carrying capacity is relatively low and they generate considerable noise. Helical gears have parallel shafts like the spur gear system, but the tooth shape is either curved or helix, double helix or herring bone. Helical gears have a higher contact ratio, as well as lower shock loading and noise, since the flanks mesh gradually. Shaft bearing design is more complicated as a result of the axial forces that are generated. These axial thrust loads can be eleminated by means of double-helical or herringbone designs. Bevel gears are characterized by intersecting axes at 90◦ and a cone-shaped gear body. The gear teeth mesh in a line contact. Each tooth can be either straight like the spur gear or curved like the helical gear (a spiral bevel gear). Worm gears consist of a worm, which resembles a screw, and a worm gear. These gears are characterized by shafts that cross at 90◦ and high transmission ratios (5:1 to 70:1 being common). Compared to the other gear systems, they have the best noise behavior, but their very high sliding forces result in frictional losses. Worm gears operate hotter and have lower efficiency than other gearing systems. Hypoid gears are a form of spiral bevel gears. The axis of the pinion is below the axis of the ring gear. Therefore, this type of gearing has better load-carrying capacity than the standard bevel gear. Because of the increased contact ratio and additional sliding, hypoid gears operate much smoother than bevel gears.

Gear

Pinion

FIGURE 27.1 Spur gears

Gear

FIGURE 27.5 Hypoid gears

Large open gear drives that are lubricated with adhesive lubricants must possess the following characteristics:

Pinion

• Excellent adhesion. • Optimum load-carrying and lubricating capacity under

mixed friction conditions.

FIGURE 27.2 Helical gears

• Good emergency running properties in case of starved

lubrication. • Good pumping characteristics in automatic spraying

equipment. Individual industries may also require gear lubricants to meet special conditions. These conditions include regulations such as those of the U.S. Department of Agriculture (USDA) that ensure safety of food products. These are the requirements identified by the USDA H1 and H2 lubricant categories. Governments and individuals are also becoming more aware of the impact of waste lubricants and lubricant contamination on the environment. New requirements for rapidly biodegradable gear lubricants are being identified now and will continue in the future. Modern industries, such as silicon chip and computer manufacturing, are also placing new requirements on gear lubricants. Diverse circumstances, such as clean-room environments or high vacuums, place explicit demands on the lubricant. The necessity to reduce out-gassing has placed special low-vapor pressure requirements on modern lubricants.

FIGURE 27.3 Straight tooth bevel gears

Wormgear Worm

27.2 HISTORICAL DEVELOPMENTS 27.2.1 Industrial Gear Oils

FIGURE 27.4 Worm gears

• Low starting torques • Compatibility with synthetic materials • Noise dampening

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Lubrication specifications for industrial gear lubricants have historically been less formal than for automotive lubricants [3]. Many different types of gears comprise industrial gear systems and are used under a vast number of different conditions. Under normal operating conditions, severe demands are not placed on the lubricant

TABLE 27.2 Minimum Performance Requirements for Inhibited (RO) Oils

Property Viscosity grade

3448/D2422

Viscosity @ 40°C, mm2/s Viscosity @ 100°C,

Test method: ISO/ASTM

mm2/s

Requirements 32

46

68

Bulk fluid dynamic viscosity @ cold start-up3), mPa·s, max.

None/D2983

Flash point, °C, min.

460

680

1000–3200

>3200 Report1)

85

90

Report1)

150 000

2592/D92

180

4263/D943

1500

Water content4), ppm, max.

12937/D6304

Foam suppression – Volume of foam (mL), max. after:

6247/D892

Copper corrosion prevention, 3 h @ 121°C, rating, max

320

Report1)

Resistance to aging – Hours @ 95°C to reach 2.0 acid number, min.

200 750

Report1)

500

Report1)

300

Seq.I Seq.II Seq.III None/None Visual None/D2711 (Procedure A)

220

See table 4

3104/D445 2909/D2270

Water separation 5) – % H2O in oil after 5 h test, max. – Cuff after centrifuging. mL, max. – Total free H2O collected during entire test, starting with 45 mL, H2O mL, min. Rust prevention, Part B

150

3104/D445

Viscosity index2), min.

Cleanliness

100

Temperature 24°C 93.5°C 24°C

5 min blow 10 min settle 50 0 50 0 0 50

5 min blow 75 75 75

10 min settle 10 10 10

Must be free of visible suspended or settled contaminants at the time it is installed for use 0.5

2.5

Report1)

2.0

4.0

Report1)

30.0

30.0

Report1)

7120/D665

Pass

2160/D130

1b

NOTES: 1) Lubricant supplier to report value in accordance with stated test method for informational purposes. 2) Viscosity indices less than the minimum values listed are acceptable if agreed upon by the end user and equipment manufacturer and/or lubricant supplier. 3) Start-up temperature to be specified by end user. Report temperature for 150 000 mPa·s. 4) Water content of virgin lubricant as packaged. Acceptable value may be greater for some full synthetics, e.g., polyglycols (PAG), synthetic blends, or blends of synthetic and mineral base fluids. Value may be agreed upon by the end user and equipment manufacturer and/or lubricant supplier. 5) Maximum values shown are for mineral oils. Acceptable values may be greater for some full synthetics, e.g., polyglycols (PAG), synthetic blends, or blends of synthetic and mineral base oils. Acceptable values may be agreed upon by the end user and equipment manufacturer and/or lubricant supplier.

in stationary applications. Currently, and as in the past, standards in North America for gear lubricants in industrial applications are written primarily by the AGMA. In Europe, as well as most of the rest of the world, industrial gear oil specifications are written by the Deutches Institut für Normung (DIN). The requirements for open and

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enclosed gear systems established by the AGMA are listed in Tables 27.2 to 27.5. The AGMA requirements define tests for measurement of extreme pressure characteristics, oxidation protection, corrosion characteristics, water separation, and a variety of chemical and physical properties of the proposed lubricant. Most of the test procedures used by

TABLE 27.3 Minimum Performance Requirements for Antiscuff/Antiwear (EP) Oils

Property

Test method: ISO/ASTM

Viscosity grade

3448/D2422

Viscosity @ 40°C, mm2/s

3104/D445

Viscosity @ 100°C, mm2/s

3104/D445

2),

Viscosity index

min.

None/D2983

Flash point, °C, min

2592/D92

Resistance to aging @ 121°C – max. % increase in kinematic viscosity @100°C Water content4), ppm, max.

None/D2893

Cleanliness Water separation 5) – % H2O in oil after 5 h test, max. – Cuff after centrifuging. mL, max. – Total free H2O collected during entire test, starting with 90 mL, H2O mL, min. Rust prevention, Part B Copper corrosion prevention, 3 h @ 100°C, rating, max. Scuffling load capacity, FZG visual method, A/8.3/90, fail stage, min

46

100

68

150

220

320

460

680

1000–3200

Report1)

150 000 180

200 6

8

10

15

Report1)

Report1)

300 5 min blow 75 75 75

6247/D892 Seq.I Seq.II Seq.III

Temperature 24°C 93.5°C 24°C

5 min blow 10 min settle 0 50 0 50 0 50

10 min settle 10 10 10

Must be free of visible suspended or settled contaminants at the time it is installed for use 2.0

2.0

Report1)

1.0

4.0

Report1)

80.0

50.0

Report1)

7120/D665

Pass

2160/D130

1b

14635-1/ D5182

Report1)

85

90

12937/D6304

None/None Visual None/D2711 (Procedure A)

>3200 Report1)

See table 4

2909/D2270

Bulk fluid dynamic viscosity @ cold start-up3), mPa·s, max.

Foam suppression– Volume of foam (mL), max after:

Requirements 32

10

12

>12

NOTES: 1) Lubricant supplier to report values in accordance with stated test method for informational purposes. 2) Viscosity indices less than the minimum values listed are acceptable if agreed upon by the end user and equipment manufacturer and/or lubricant supplier. 3) Start-up temperature to be specified by end user. Report temperature for 150 000 mPa·s. 4) Water content of virgin lubricant as packaged. Acceptable value may be greater for some full synthetics, e.g., polyglycols (PAG), synthetic blends, or blends of synthetic and mineral base fluids. Value may be agreed upon by the end user and equipment manufacturer and/or lubricant supplier. 5) Maximum values shown are for mineral oils. Acceptable values may be greater for some full synthetics, e.g., polyglycols (PAG), synthetic blends, or blends of synthetic and mineral base oils. Acceptable values may be agreed upon by the end user and equipment manufacturer and/or lubricant supplier.

the AGMA are defined by the American Society for Testing and Materials (ASTM). No specific specification existed prior to 1994 for industrial gear lubricants formulated with synthetic fluids. The current AGMA specification, ANSI/AGMA 9005-E02, is application driven instead of lubricant chemistry driven. The minimum physical and

Copyright 2006 by Taylor & Francis Group, LLC

performance requirements apply to synthetic lubricants as well as mineral oil lubricants. Both the AGMA standards in North America and the DIN standards in Europe only indicate the minimum requirements for gear lubricants. Modern products, especially synthetic gear oils and greases, exceed these

TABLE 27.4 Minimum Performance Requirements for Compounded (CP) Oils Property

Test method: ISO/ASTM

Viscosity grade

3448/D2422

Viscosity @ 40°C, mm2/s

3104/D445

Viscosity @ 100°C, mm2/s

3104/D445

index2)

2909/D2270

Viscosity

, min.

Bulk fluid dynamic viscosity @ cold start-up3), mPa·s, max.

None/D2983

Flash point, °C, min.

2592/D92

Resistance to aging @ 95°C – max. % increase in kinematic viscosity @ 100°C Water content4), ppm, max.

None/D2893

Requirements 100

150

320

220

460

680

1000–3200

See table 4 Report1) 90

85 150 000

200 Report1)

12937/D6304

Report1)

300

5 min blow 75 75 75

10 min settle 10 10 10

Foam suppression – Volume of foam (mL), max. after:

6247/D892

Content of fatty or synthetic fatty oil, mass %

None/None

Cleanliness

None/None Visual

Must be free of visible suspended or settled contaminants at the time it is installed for use

Rust prevention, Part B

7120/D665

Pass

Copper corrosion prevention, 3 h @ 100°C, rating, max.

2160/D130

1b

Seq.I Seq.II Seq.III

Temperature 24°C 93.5°C 24°C

5 min blow 10 min settle 50 0 50 0 0 50 3 to 10

NOTES: 1) Lubricant supplier to report value in accordance with stated test method for informational purposes. 2) Viscosity indices less than the minimum values listed are acceptable if agreed upon by the end user and equipment manufacturer and/or lubricant supplier. 3) Start-up temperature to be specified by end user. Report temperature for 150 000 mPa·s. 4) Water content of virgin lubricant as packaged. Acceptable values may be greater for some full synthetics, e.g., polyglycols (PAG), synthetic blends, or blends of synthetic and mineral base fluids. Value may be agreed upon by the end user and equipment manufacturer and/or lubricant supplier.

requirements. Similar to new technologies, new lubricant types are only included in standards if they have been used successfully for some time and have gained acceptance on a wide basis. State-of-the-art lubricant technology proves that lubricants have kept pace with the general technological development and are well ahead of standardization since they exceed most standard requirements. Table 27.6 summarizes the current gear lubricant standards published by DIN. You will notice that the DIN standards still do not specifically list synthetic lubricants as a category.

Copyright 2006 by Taylor & Francis Group, LLC

27.2.2 Need For Synthetic Gear Lubricants Synthetic gear lubricants are needed whenever mineral gear lubricants have reached their performance limit and can longer meet the requirements of the gearing system. These requirements include very low or high temperatures, extremely high loads, or extraordinary ambient conditions. Special requirements, such as low flammability, may also need to be met. Even though many properties of mineral oils can be improved by means of additives, it is not possible to exert an unlimited influence on all of the

TABLE 27.5 Viscosity Grade Requirements

ISO viscosity grade

Mid-point viscosity at 40°C mm2/s1)

Kinematic viscosity limits at 40°C mm2/s1) min

max

Former AGMA grade equivalent2)

ISO VG 32

32

28.8

35.2

0

ISO VG 46

46

41.4

50.6

1

ISO VG 68

68

61.4

74.8

2

ISO VG 100

100

90.0

110

3

ISO VG 150

150

135

165

4

ISO VG 220

220

198

242

5

ISO VG 320

320

288

352

6

ISO VG 460

460

414

506

7

ISO VG 680

680

612

748

8

ISO VG 1000

1000

900

1100

8A

ISO VG 1500

1500

1350

1650

9

ISO VG 2200

2200

1980

2420

10

ISO VG 3200

3200

2880

3520

11

NOTES: 1) The preferred unit for kinematic viscosity mm2/s, commonly referred to as centistoke (cSt). 2) With the change from AGMA viscosity grade equivalents to ISO viscosity grade classifications, the designations S, EP, R and COMP will no longer be used as part of the viscosity grade nomenclature.

TABLE 27.6 DIN Standard Requirements for Common Gear Lubricants Standardized lubricants

Requirements

Type of lubricant

CL lubricating oils

DIN 51517 Pt 2

Mineral oils with additives enhancing resistance to corrosion and aging

CLP lubricating oils

DIN 51517 Pt 3

L-TD lubricating and control oils

DIN 51515 Pt 1

HL hydraulic oils

DIN 51524 Pt 1

HLP hydraulic oils

DIN 51524 Pt 2

Lubricating greases type G

DIN 51526

Mineral oils with additives enhancing resistance to corrosion and aging, and reducing wear under mixed friction conditions; FZG scuffing load stage (A/8.3/ 90): 12 min Mineral oil base turbine oils with additives enhancing resistance to corrosion and aging Pressure fluids made of mineral oils containing additives to enhance resistance against corrosion and aging Pressure fluids made of mineral oils containing additives to enhance resistance against corrosion and aging and to reduce wear; FZG scuffing load stage (A/8.3/90): 10 min Fluid to very soft greases of NLGI grade 000 to 1, based on mineral and/or synthetic oil plus thickener

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Application Gears subject to low loads, with a peripheral speed less than 30 m/s and a permanent oil bath temperature up to 100◦ C Gears with high flank loads and/or a high sliding percentage; permanent oil bath temperature up to 100◦ C

Gears in steam and gas turbines

Combined application in hydraulic systems and gears Combined application in hydraulic systems and gears subject to a high degree of wear

Splash lubrication of enclosed gears (e.g., gear motors, drum motors, actuators)

properties. This applies especially to properties depending on the chemical structure of the lubricant, such as thermal resistance, low temperature properties, flash point, and evaporation losses. A number of advantages are provided by synthetic gear lubricants; however, they do not necessarily outperform mineral oils in all respects and may even result in some draw backs despite their advantages. The advantages of synthetic gear lubricants, depending on the base oil, are [5]: • Improved thermal and oxidation resistance • Improved viscosity–temperature behavior (higher vis• • • • • •

cosity index) Improved low temperature properties Lower evaporation losses Reduced flammability Improved lubricity Lower tendency to form residues Improved resistance to ambient media

Along with the above advantages, there are possible disadvantages that may be: • Higher price • Reaction in the presence of water (hydrolysis, corrosion) • Material compatibility problems (paints, elastomers,

certain metals) • Limited miscibility with mineral oils

Application related advantages usually prevail so that synthetic lubricants will be increasingly used for gear lubrication, especially under critical operating conditions. As stated earlier, Government regulations and Original Equipment Manufacturer (OEM) and end user specifications will also increase the need for synthetic lubricants. The current mineral oil products, used by the food processing industry that meet USDA H1 requirements, cannot perform to the same level as the new synthetic gear lubricants meeting the same food grade requirements. Currently vegetable based products are used for rapid biodegradability in marine environments and other outdoor environments. Vegetable based products cannot meet the same high application demands as synthetic gear lubricants that are also rapidly biodegradable. Both polyalphaolefin (PAO) and ester oils are sometimes blended with a certain percentage of mineral oil to create a semisynthetic combination that provides several advantages. Semisynthetic gear oils can provide performance near that of a pure synthetic, but at a considerably lower price. This combination also increases the solubility of certain additives that are required for high performance. Also, the negative impact on Nitrile Butadiene Rubber (NBR) seals can be reduced by adding a small amount of ester oil to a PAO gear oil. The blending of mineral oil and PAO oils is much more prevalent in automotive gear oil applications.

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27.3 TYPES OF SYNTHETIC GEAR LUBRICANTS Synthetic gear lubricants based on PAOs, polyalkylene glycols (PAGs), and ester oils have proven particularly efficient in gearing systems.

27.3.1 Gear Lubricants Based on PAOs Polyalphaolefins are similar to mineral oil hydrocarbons in their chemical structure and are therefore also known under the name of synthetic hydrocarbons. PAOs have similar compatibility with sealing materials, disposal, and reprocessing as mineral oils. The main advantages of PAOs are their excellent low-temperature behavior and oxidation stability. It is possible to manufacture food grade lubricants (USDA-H1) for the food processing and the pharmaceutical industries with PAO base oils and special additives. Lower viscosity PAOs are also rapidly biodegradable.

27.3.2 Gear Lubricants Based on PAGs Polyalkylene glycol gear lubricants provide an especially low coefficient of friction that makes them suitable for gears with a high sliding percentage, specifically, worm and hypoid gears. When PAG oils contain the appropriate additives, they have an excellent antiwear effect on steel/bronze worm gear systems and a very good pressure absorption capacity. A negative impact on sealing materials and the solubility of some paints are some of the possible disadvantages. At operating temperatures above 100◦ C, only seals made of fluorinated rubber or Polytetrafluroethylene (PTFE) are resistant to PAGs. Below 100◦ C, seals made of NBR are resistant to PAG lubricants. If the gearbox housings are to be coated on the interior with a paint system, it is recommended that epoxy or polyurethane resin paint systems be used. PAG miscibility with mineral oils is very limited and, therefore, mixtures should be avoided. To ferrous metals and almost all nonferrous metals, PAG lubricants are neutral. If the gearing system has one gear made from aluminum or an aluminum alloy, there may be increased wear when there is a combination of high load and high sliding.

27.3.3 Gear Lubricants Based on Ester Oils Ester oils are the result of a reaction of acids and alcohols with water being separated. There are many different types of ester structures and all of them have a different impact on the chemical and physical properties of the lubricant. In the past, ester oils were mainly used in aviation applications for the lubrication of aircraft engines and turbines as well as gear systems and pumps, starters, etc. Ester oils have a high thermal resistance and excellent low-temperature behavior. Rapidly biodegradable ester oils will gain importance in industrial applications since it is possible to achieve the same efficiency as with PAO gear lubricants by selecting an appropriate ester based oil.

TABLE 27.7 Gear Oil Properties Properties

Mineral oils

PAOs

Density at 20◦ C, g/mL

0.9 80–100 −40 to −10 <250 Moderate Moderate Good Good

0.85 130–160 −50 to −30 >200 Good Good Good Good

0.9–1.1 150–270 −56 to −23 150–300 Good Good Very good Insufficient to good

1

5–10

6–10

Viscosity index Pour point ◦ C Flash point ◦ C Oxidation resistance Thermal stability Lubricity Compatibility with elastomers, coatings, etc. Price relation

27.4 PERFORMANCE PROPERTIES In general the advantages of synthetic gear lubricants are their thermal and oxidation stability, favorable viscosity– temperature behavior, high flash point, and good low temperature behavior. PAOs and PAGs also provide lower frictional losses in the gear train. Table 27.7 shows the average values of the most important properties of mineral oil compared to PAGs and PAOs [4].

27.4.1 Viscosity Gear oils change their flow behavior depending on temperature and pressure. Their viscosity decreases with a rising temperature and increases with rising pressure. This crucial behavior of gear oils is, therefore, of primary importance when determining the required viscosity and selecting a suitable type of oil for a particular application. The gear oil’s viscosity has a significant impact on the gear lubrication function. Increased viscosity results in a thicker lubricant film thus improving antiwear and damping behavior and to a certain extent the oil scuffing load capacity. If the oil’s viscosity is too high, increased churning and shearing losses result in excess heat, especially at an increased peripheral speed. Mixed friction conditions will prevail and result in increased wear when the viscosity is too low. 27.4.1.1 Viscosity–temperature behavior All lubricating oils have a viscosity that varies inversely with temperature. Therefore, as temperature increases the viscosity of the oil decreases. The rate at which viscosity changes with temperature varies from oil to oil. The oils viscosity–temperature behavior is generally depicted on special graph paper published by the ASTM. This graph paper is designed to display the varying temperature– viscosity relationship of mineral oil as a straight line. Since a PAO is a synthetic hydrocarbon, it also is displayed as a straight line on this graph paper. Even though PAG oils

Copyright 2006 by Taylor & Francis Group, LLC

Polyglycol oils

are typically shown as a straight line on this graph paper, if more than two points were plotted, it would have a slight curve. Figure 27.6 shows the difference between the viscosity–temperature behavior of a mineral oil, PAO and PAG. Each of these products has an ISO viscosity grade of 460 [4]. The flatter the viscosity–temperature line, the less sensitive the viscosity is to temperature change. The viscosity index (VI) is used to describe the temperature related change of viscosity. It is a dimensionless number and a high VI indicates a small change in viscosity relative to the temperature change. A much greater sensitivity to temperature change is identified by a low VI number. Table 27.7 shows the VI range of several oils. In practice, a high VI means that a gear system will start smoothly at low temperature conditions and have only minimal power losses. A high VI can also mean that a load bearing lubricant film is formed at increased temperatures that provides good protection against wear. Synthetic gear oils clearly have a higher VI than mineral gear oils. 27.4.1.2 Viscosity–pressure behavior A lubricating oil’s viscosity increases when the pressure rises. Elastohydrodynamic (EHD) action occurring in the lubrication gap between the meshing gear teeth flanks can produce pressures greater than 10,000 bar. This results in an increase of viscosity that may be several powers of ten higher than the initial viscosity of the oil under atmospheric pressure conditions. Figure 27.7 shows the isothermal increase of absolute viscosity of an ISO viscosity grade 220 synthetic oil at 60◦ C and 100◦ C as pressure varies from one to 4,000 bar [2].

27.4.2 Oxidation Stability External impacts continuously change an oil’s chemical structure, thus causing it to oxidize or age. Changes mainly occur when the oil is subject to high temperatures, the oil mixes with air, or if the oil is in contact with a metal catalyst,

–30

–10

–10

0

10

20

30

40

50

Mineral oil

–20,000 10,000

60

70

80

90

100 110 120 130 140 150

ASTM STANDARD VISCOSITY–TEMPERATURE CHARTS FOR LIQUID PETROLEUM PRODUCTS (0341) CHART VII: AKINEMATIC VISCISITY, MODLE RANGE, DEGREES CELSTUS

PAO

2,000 2,000 2,000

10,000 5,000 3,000 2,000

Polyglycol

1,000

Kinematic viscosity, cSt

1,000 600 400 200 200 100

500 400 300 200 100

100 70

100 50

50 40

40 40

30

30

20

20

11

10

10 9.0 8.0 7.0

10 9.0 8.0 7.0

6.0

6.0

5.0

5.0

4.0

4.0

3.0 –40

–30

–10

–10

0

10

20

30

40

50

60

70

80

90

Kinematic viscosity, cSt

–40 200,000 100,000 50,000

3.0 100 110 120 130 140 150

Temperature, °C

FIGURE 27.6 Viscosity–temperature behavior

27.4.3 Application Testing There has been considerable testing to determine the influence of different lubricants on gear system performance. One of the major components of a lubricant that influences the pitting or micropitting resistance of gears is the coefficient of friction [6].Studies show that if the coefficient of friction could be cut in half, the micropitting load capacity

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5 2 104 5 h [MPa sec]

such as copper or iron. The speed of the aging process primarily depends on the oil structure and the amount and duration of heat to which the oil is subjected. Additives can be used to retard or stabilize the rate of oxidation. Contaminants such as water, rust, or dust also have a negative impact on oil oxidation. Oxidation is indicated by oil discoloration, increased viscosity, formation of acids enhancing corrosion, as well as residues in the form of lacquer, gum, or sludge clogging oil lines and filters. The oils demulsibility and antifoaming tendencies, as well as anticorrosion and antiwear properties, are impacted negatively by oil oxidation. When using a mineral oil, the permanent bath temperature should never exceed 80◦ C because the oxidation process doubles in speed with every 10 K temperature increase above 80◦ C. In comparison to mineral oils, synthetic gear oils in similar applications are much more resistant to oxidation.

2 103 5 2 102 =

5

60°C Isotherme

= 100°C Isotherme

2 101 0

1000

2000 P [bar]

3000

4000

FIGURE 27.7 Viscosity–pressure behavior of a synthetic oil ISO VG 220

could be increased 1.7 times. This testing was performed on the Forschungsstelle für Zahnräder und Getriebebau (FZG) gear test rig. The Institute for Vehicle Engineering and Gear Design of the Technical University of Munich used the FZG test rig to determine if the coefficient of friction for a PAO

and PAG gear oil is significantly less than the coefficient of friction of a similar viscosity mineral oil (Table 27.8). Further testing for the total power loss of gears using the FZG gear test rig shows that not only the viscosity of the gear lubricant but the type of lubricant too has a significant influence [7]. This study determined that the churning losses in a gear box depended mainly on the viscosity of the lubricant, not the lubricant type. As was shown earlier in the viscosity–temperature behavior of the synthetic gear lubricants, it is possible to have a lower viscosity lubricant at start-up in a gear box and still maintain the same viscosity at operating temperature, thus reducing churning losses. On the other hand, mesh power losses in the gear train depended mainly on the type of lubricant and not on the viscosity–temperature relationship or oil additives. Mesh power loss can be reduced by as much as 50% of the power loss of mineral oils by using PAG lubricants. Figure 27.8 summarizes the results of the investigation and shows a mean value of 80% for PAO gear oils and PAG gear oils have a mean value of 70% of the coefficient of friction for mineral oils.

TABLE 27.8 Comparison of Coefficients of Friction ISO viscosity grade

Product Mineral oil base EP gear oil Synthetic gear oil, PAO base Synthetic gear oil, polyglycol base

base oil type

Mean gear friction coefficient µmz

220 220 220

code

0.048 0.036 0.033

oil type C CLP CLP CLP CLP CLP PAD PAD PAD PG PG PG PG PSE

synthetic fluids

mineral oils

M1 M2 M3 M4 M5 M6 polyS1 alphaS2 olefines S3 S4 polyS5 glyS6 coles S7 special S8 fluids S9 coefficient of friction percentage

ISO 0 VG 0 100 100 150 220 150 220 46 68 220 220 150 220 460 32 38 mmx 0 In % 0

The above research has not only been performed by academia, but has been sponsored and even endorsed by OEM Gear Box Manufacturers. A product information sheet from SEW Eurodrive [8] states that tests conducted with PAG oils have shown a possible higher power rating when compared to those using the standard mineral based oils. At high reduction ratios for worm gear drives, a 20% increase in output power is possible when using PAG oils vs. mineral oils. This same performance increase is not possible with synthesized hydrocarbon synthetic oils (e.g., PAOs). Obviously with lower coefficient of friction and less energy consumed, temperatures would also have to be reduced when using synthetic gear lubricants. During testing it was determined that at 60% of rated power, a PAG gear oil was found to operate at a temperature approximately 10◦ C cooler in the worm drive gear box than mineral oil. Also the PAG gear lubricant, at 100% rated power for the gearbox, operated at the same temperature as mineral oil when the gearbox was only at 70% rated power [4]. (Figure 27.9) The significant influence of synthetic gear lubricants has also been demonstrated in actual field applications. A Texas power generator found that by switching to a synthetic oil, the casing temperatures for large-speed reducing gears in coal pulverizers dropped well in excess of 20◦ F [9]. Additionally, wear rates were cut to a level that is estimated to double or triple the life of the high-torque worm speed reducers and at the same time increase the oil change period four-fold. Another field experience documented by Willamette Industries showed that an external washer filter in a pulp

20 40 60 80 100 120 140 150 100 200 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10

20 40 60 80 100 120 140 150 100 200 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10

Operating conditions: load stage 7 (Pc = 1080 N/mm2), gear type C pitch line velocity Vt = 10 m/sec • spray lubrication with oil = 90° and Voil = 2l/min

FIGURE 27.8 Coefficient of friction of different lubricants

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mill had been operating well above 1.5 G shock pulse activity and 0.2 in./sec vibration [9]. After switching to a synthetic oil, the shock pulse activity dropped to 0.75 G and the vibration reduced to 0.15 in./sec. This change occurred immediately and continued for a month (Figure 27.10). Over the last ten years there has been considerable refinement in the development of lubricants for worm drive gearboxes. Typically, the development of new gear oils starts with basic investigations modeling the tribological contact. Therefore, test rigs such as the four-ball tester and the oscillation-friction and wear tester are helpful. The most effective method of testing a gear oil is in a 100

Mineral oil

∆T (°C)

90 80 70 Polyglycol

60 50

10

20 25

30 50

60

40 Torque (mkp) 50 75

100 Rated power (%)

Shock pulse activity

FIGURE 27.9 Comparison of polyglycol vs. mineral oil in a worm drive gearbox

Oil change

real gearbox, especially in terms of contact pressure and temperature. This is the only way to verify that a gear oil provides: • Low friction and high efficiency • Low operating temperatures to improve oil service life • Low wear and delayed fatigue of materials

An increase of the load-carrying capacity of a worm drive gearbox should be accomplished with a good gear oil. 27.4.3.1 Worm gear test rig The setup of the test rig [12] (Figure 27.11) makes it possible to measure speed and torque of the worm (input side). Combined with the output torque of the wheel, the overall efficiency of the gearbox can be calculated. The test rig provides the opportunity to determine the lubricating regime in the mesh (Figure 27.12). This continuous operating method permits determination of changes in lubrication regime during the test run. The wear of the wheel is determined using the following two methods: • Weight loss of the wheel after completion of the test run. • Abrasion of the wheel flank while running. The mea-

Vibration

Oil change

Time

Time

FIGURE 27.10 Switching to a synthetic oil immediately reduces shock pulse activity and vibration

• • • •

surement is based on a continuous measurement of the wheel tooth thickness. Thus, it can be assessed whether the wear is a result of running in or of the actual operating conditions. As mentioned, the measurement of different temperatures is part of the standard test. Bulk temperature of worm shaft Oil sump temperature Housing temperature Ambient temperature

Motor

Top view

Dynamometer

FIGURE 27.11 Test rig

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Bevel gear

Torque and speed sensor input

Slave gear

Torque and speed sensor output

Test worm gear

27.4.3.2 Test oils Table 27.9 shows some data of the tested lubricants. For the test a variety of different synthetic oils were chosen and compared to a mineral oil that is often used for lubricating all types of gearboxes including worm gear drives. The viscosity of each oil is 460 mm2 /sec at 40◦ C (ISO VG 460). All tested oils are fully formulated (R&O, AW, and EP packages) and meet or exceed the requirements made on CLP oils. Each oil used in the test passes the FZG scuffing test with load stage greater than 12. The M460 oil is based on a paraffinic mineral oil and meets the CLP requirements. It contains a sulfur/phosphor additive package. M460 oil was selected as reference oil, because it is widely used in common gearbox applications. The polyglycol PG460-1 was chosen as a typical modern high performance gear oil. The ratio of ethylene oxide to propylene oxide is 1:1. These types of base oils offer low friction coefficients. This means that low oil temperature and high efficiency can be expected, especially for gearboxes with a high sliding component in the mesh. PG460-2 (polyglycol) was designed as a food grade lubricant. The formulation of the oil meets the guidelines of Sec. 21 CFR 178.3570 of the Food and Drug Administration (FDA). Specifically, only raw materials meeting the food grade specifications are used. The base oil properties are comparable to PG460-1.

Housing temperature

Ambient temperature

Insulating AC voltage

Oil sump temperature

Worm temperature

FIGURE 27.12 Determination of temperature and lubrication regime

PAO460-1 is a polyalphaolefin. This oil contains a sulfur/phosphor additive package and was originally developed for application in spur, helical and bevel gears. PAO oils also show lower friction coefficients than mineral oils. The oil PAO460-2 (PAO) contains base oils and additives contained in the aforementioned FDA list. Again, the result is a “food grade lubricant” acceptable for use in the food and pharmaceutical industry. The E460 oil is rapidly biodegradable and, therefore, intended for use wherever rapid biodegradability is required. The CEC-L-33-A-94 standard states an oil is rapidly biodegradable when more than 70% of the lubricant is biodegradable within 21 days. E460 oil is based on a synthetic ester. With mineral oil as a baseline, it can be seen in Table 27.10 that all of the synthetic oils are higher performers in most properties. 27.4.3.3 Worm gear test results Figure 27.13 shows an example of a test run performed with the M460 oil. Most measurements were evaluated after 250 h of test run. Test results show a shaft temperature of approximately 115◦ C (239◦ F). The total efficiency of the gearbox is nearly 60%. Graph 13-C identifies the lubrication regime. When the curve is on top of the diagram, mainly mixed friction appears in the contact zone. A curve at the bottom means better lubricating conditions and a separating oil film. Using this method, it is not possible to measure the exact film thickness. In the case of oil M460, the test shows mixed friction, which produces continuous wear of the wheel. The apparent decrease of wear at approximately 200 h is actually due to a measuring error, not a weight gain. During run in and the test run, the weight loss of the wheel is 5.5 g. The test results for the PG460-1 (Figure 27.14) show lower temperatures. After 150 h, the bulk temperature of the worm shaft remains constant at 70◦ C (158◦ F) and the efficiency reaches 78%. Graph 14-C gives an explanation for this high efficiency. When the gear runs with full load, after a period of approximately 50 h the film thickness increases and the lubrication conditions become better. High efficiency is a product of a good lubricating regime

TABLE 27.9 Test Oils Oil M460 PG460-1 PG460-2 PAO460-1 PAO460-2 E460

Copyright 2006 by Taylor & Francis Group, LLC

Base oil Paraffinic mineral Polyglycol Polyglycol Polyalphaolefin Polyalphaolefin Ester

Viscosity index 95 >220 >220 >150 >160 >150

Notes CLP (A/8.3/90) >12 CLP (A/16.6/140) >12 CLP, “food grade lubricant” (A/16.6/90) >12 CLP A/16.6/140) >12 CLP, “food grade lubricant (A/8.3/90) >12 CLP, “rapidly biodegradable” (A/8.3/90) >12

TABLE 27.10 Properties of Gear Oils Properties Viscosity– temperature behavior Aging resistance Low-temperature characteristics Wear protection Friction coefficient Neutrality towards sealing materials and paints

Ester∗

Mineral oil 0

Polyalphaolefines +

Polyglycol ++

+

0 —

+ ++

++ +

+ +

0 0

+ +

++ ++

+ ++

++

+ + /−

−/+

—

++ = very good 0 = satisfactory + = good — = poor * = The properties of esters depend on the specific type of ester and may differ strongly.

(a)

Wear [g] 400 300 200 100 0 0

(c)

0

50 100 150 200 250 300 Running time [h] Contact

1

Temperatures [°C]

(b) 140 120 100 80 60 40 20 0

500

50 100 150 200 250 300 Running time [h]

(d)

Efficiency [%] 100 90 80 70 60 50 40

0 0

50 100 150 200 250 300 Running time [h] shaft sump

Test gear Flender CUW 63 i = 1: 39; a = 63 mm worm shaft 16MnCrS5 no.11 worm gear GC-CuSn12 Ni no.11a Test conditions Running-in input speed: 350 1/min output torque: 24 h 100 Nm 24 h 200 Nm 2 h 300 Nm Permanent running input speed: 350 1/min output torque: 300 Nm

0

50 100 150 200 250 300 Running time [h]

Worm gear wear weight loss: 5.54 g wear rate: 0.91 mm/h

housing environment

FIGURE 27.13 Test results for mineral oil M460

and low frictional losses. The measured weight loss of the wheel is very low. Weight loss primarily seems to be a result of running in wear. Graph 14-A indicates no reduction of teeth thickness during the entire test run. The measurements for PG460-2 show interesting results (Figure 27.15). While measured temperatures and efficiency are comparable to the results for PG460-1, a clear run in effect is recognizable. Also after finishing the run in procedure, the wear of the wheel continues. After 150 h the wear of the wheel stops. The size and orientation of the contact pattern accounts for the change in wear

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rate. When the contact pattern reaches a minimum required area, a separating oil film can be formed. This leads to a maximum of efficiency and minimum temperatures. The PAO460-1 has a shaft temperature of approximately 100◦ C. The measured efficiency becomes stable at approximately 67%. Wear rate is relatively low (0.07 µm/h) and after approximately 50 h, a separating oil film occurs. This PAO460-2 shows similar shaft temperatures and efficiencies as PAO460-1. Due to the lack of separating oil film the wear rate is higher (0.41 µm/h). Apparently the

(a)

Wear [g]

140 120 100 80 60 40 20 0

400 300 200 100 0 0

(c)

50 100 150 200 250 300 Running time (h)

0

50 100 150 200 250 300 Running time (h)

(d)

Contact

1

Temperatures (°C)

(b)

500

Efficiency (%) 100 90 80 70 60 50

0 0

40

50 100 150 200 250 300 Running time (h)

Test gear Flender CUW 63 i = 1: 39; a = 63 mm worm shaft 16MnCrS5 no.17 worm gear GC-CuSn12Ni no.17 Test conditions Running-in input speed: 350 1/min output torque: 24 h 100 Nm 24 h 200 Nm 2 h 300 Nm Permanent running input speed: 350 1/min output torque: 300 Nm

0

shaft

50 100 150 200 250 300 Running time (h)

Worm gear wear weight loss: 0.22 g wear rate: ---- mm/h

housing environment

sump

FIGURE 27.14 Test results for polyglycol PG460-1

(a) 500

Wear [g]

140 120 100 80 60 40 20 0

400 300 200 100 0 0

(c)

50 100 150 200 250 300 Running time (h) (d)

Contact

1

0 0

Temperatures (°C)

(b)

50 100 150 200 250 300 Running time (h) shaft sump

0

Efficiency (%)

100 90 80 70 60 50 40

50 100 150 200 250 300 Running time (h)

Test gear Flender CUW 63 i = 1: 39; a = 63 mm worm shaft 16MnCrS5 no.37 worm gear GC-CuSn12Ni no.37 Test conditions Running-in Input speed: 350 1/min Output torque: 24 h 100 Nm 24 h 200 Nm 2 h 300 Nm Permanent running Input speed: 350 1/min Output torque: 300 Nm

0

50 100 150 200 250 300 Running time (h) housing environment

Worm gear wear Weight loss: 3.22 g Wear rate: 0.117 mm/h

FIGURE 27.15 Test results for polyglycol PG460-2

additives in the PAO460-2 oil do not form a protective layer that is sufficient to prevent wear on the wheel flanks. Efficiencies for the E460 are nearly 70% and temperatures are around 100◦ C. The wear rate is approximately 0.44 µm/h. As with PAO460-2, no separating lubricating oil film is formed under the selected test conditions. 27.4.3.4 FZG twin disk machine The performance of a gear oil in a real application can be determined by using the worm gearbox test rig, but

Copyright 2006 by Taylor & Francis Group, LLC

it does not measure the coefficient of friction. The worm gearbox test rig only implies the frictional loses through the efficiency calculation. With the FZG twin disk machine, Figure 27.16, the coefficient of friction can be measured for the different oil chemistries at several sliding velocities. As the efficiency results of the worm gearbox test rig imply, mineral oil has the highest coefficient of friction of the oils tested. PAO and ester gear oils have essentially the same results and polyglycol had the lowest coefficient of friction at all three test velocities. A comparison of the results is displayed in Figure 27.17.

V1

Upper disk

160

Load cell Lower disk

150

V2

Spring

FIGURE 27.16 FZG twin disc machine

0.060 0.050 0.040 0.030 0.020 0.010 0.000

Hertzian stress PH Slip Oil temperatur yoil ISO VG

Oil sump temperature (°C)

Flat spring Oil injection Loading device

140 130

Polyglycol

120 110

PAO/ester

100 90 Mineral oil

80 70 300 500

= 1000 N/mm2 = 20% = 90°C = 150

1,000 5,000 10,000 Oil change interval (h)

30,000

FIGURE 27.18 Oil change intervals

Mineral oil PAO/ester oil Polyglycol oil

0.12

0.41

Mineral oil VΣ = 2 m/sec

PAO/Ester

Polyglycol oil (EO:PO 1:1) VΣ = 4 m/sec VΣ = 8 m/sec 0.91

FIGURE 27.17 Friction coefficient of different base oils 0

27.4.3.5 Temperatures and oil service life It is known that lower oil temperatures lead to a longer oil life. At higher temperatures, oxidative degradation occurs much faster than at lower temperatures. Figure 27.18 shows the expected oil service life of different base oils. The oil service life for the different chemistry base oils is published in several papers and studies. For the determination of an average oil service life, a large number of used oil analyses were checked. The oil samples were tested with respect to additive and base oil degradation, viscosity change, water, and solid particle content. The slope of the curves represents the so-called 10 K rule. A temperature increase of 10 K doubles the speed of chemical reaction. Gearbox oil sump temperature is the most important factor affecting the oil change interval. Sump temperature is influenced mainly by the ambient temperature and friction between the gears. Because of this, the expected oil change interval for synthetic oils is better than mineral oil due to their better aging and thermal resistance as well as the reduced coefficient of friction. It can be stated, that the oil service life for PAO oils is approximately three times longer than mineral oil and for polyglycol five times longer than mineral oil. Reduced wear also leads to an extension of oil service life because of the low solid particle content. Wear metals in the oil can act as a catalyst in the oxidation reaction.

Copyright 2006 by Taylor & Francis Group, LLC

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1

Wear rate (mm/h)

FIGURE 27.19 Reduction of wear rate

27.4.3.6 Performance comparisons Results show that synthetic oils, especially polyglycol oils, with low friction coefficients improve efficiency and reduce temperatures. A basic influence on the efficiency of a gearbox is given by the base oil friction behavior. The influence of additives on wear is important for lubricating conditions with low film thickness, such as during run in and low speed operation. When examining the wear rate, the PAO and ester oil is about half of mineral oil and polyglycol is about 1/8th the wear rate of mineral oil. Figure 27.19 shows that polyglycol oil can provide less wear in a worm gearbox. Improved efficiency can mean a lot to the end user as well as the OEM (Figure 27.20). The end user will save energy that will reduce operational cost or can operate at the same energy level and increase the output level and productivity. Whereas for the OEM improved efficiency can impact some of the design decisions. The gearbox output rating can be increased with the current design or the gearbox can be redesigned to be less expensive and maintain the current output rating. Polyglycol gear oil (i.e., PAG) provides a significant energy savings advantage or power output advantage over mineral oil (Figure 27.21).

Mineral oil PAO/ester oil Polyglycol oil

70

60 0

20

40 60 Efficiency (%)

80

Oil change interval (h)

2,000 78

15,000 10,000 5,000 0

FIGURE 27.20 Increase in efficiency

Mineral oil PAO/ester oil Polyglycol oil

20,000

80

100 Oil sump temperatre (°C)

120

FIGURE 27.22 Extension of service life il lo

ra

Total power (kW)

ine

10 8

M

3

G PA

2.1

oil G PA

oil

1.8

6 4 2 0

B2 A B1 Output power Power loss

FIGURE 27.21 Reduction in energy cost. B1 : 12.5% increase of output power and B2 : 11.5% reduction of energy costs

Another important aspect of using synthetic oils in worm gears is the reduction of operating temperatures. This means an extension of oil service life and is an important step in the direction to “fill for life” of industrial gearboxes for the OEM. For the end user, increased oil change intervals means lower cost for lubricant, labor, and waste disposal. Expected oil service life (oil change interval) at three different oil sump temperatures is shown in Figure 27.22. The above benefits of synthetic gear lubricants that have been documented for enclosed gear boxes can also be experienced when using gear greases made with synthetic base oils as well as synthetic adhesive lubricants for open gear drives.

27.5 CURRENT COMMERCIAL PRACTICE 27.5.1 Synthetics in Use Although there are many different synthetic base oils available to use as gear lubricants, only a few have proven to be cost effective. For industrial gear lubricants the primarily synthetic base oils are: • Polyalphaolefins (PAO) • Polyglycols (PAG) • Esters

In order of use in North America, it is predominately PAOs that are used, followed by PAGs and esters are used

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only in a few limited applications where the application parameters would require the special performance characteristics of the ester oil. In the European community and other parts of the world, there is a much larger use of PAGs as industrial gear oils. PAOs are used less and esters have limited use in Europe. Almost all lubricants suppliers today will have at least a few synthetic gear oils available and there are a few suppliers who have a significantly broad range of synthetic gear oils. Thomas Register provides the names of synthetic gear oil suppliers in North America. In addition to the Thomas Register, there are several trade magazines that also publish lists of synthetic lubricants available to their industry. Table 27.11 is an excerpt from Plant Engineering Magazine, which publishes a biannual synthetic lubricants buyer’s guide [10]. All international lubricant suppliers have synthetic gear oils.

27.5.2 Market for Synthetic Gear Lubricants The major growth markets for synthetic industrial gear lubricants are the mining, chemical, and food industries. It appears that the driving force for the food processing industry is an increased enforcement activity of the requirements for H1 food grade lubricants. For gear applications, synthetic H1 food grade lubricants far outperform the nonsynthetic versions. In all industries, as well as the industrial machine and equipment manufacturing industry, maintenance departments are looking for greater savings through higher performing lubricants, as well as longer life lubricants. The concept of total cost of operations is slowly replacing the initial price of lubricants syndrome. Also, environmental controls are forcing companies to use chemical management programs that are looking not only at operating costs, but disposal costs of lubricants. Again, the advantages of synthetic gear lubricants becomes more evident under these circumstances [11].

27.5.3 Industry Demands Higher Performance Needless to say all industries, especially in North America, are highly competitive and in order to survive in the market

place each industry must maximize their productivity. The easiest way to attain maximum productivity in a manufacturing operation is to reduce downtime and at the same time increase production. One way to reduce downtime for machinery is to increase gearbox drain intervals or use gearbox lubricants that are filled for life. Due to their oxidation stability, synthetic gear lubricants can fulfill this need. Another way to improve productivity is to increase the speed of the manufacturing process. This usually requires additional heat in the process or generates more heat in the gearboxes. Again, the thermal stability and the viscosity–temperature characteristics of synthetic gear lubricants allow the manufacturer to push the process beyond its current limits without seriously effecting the equipment. Along with productivity comes efficiency. If the manufacturer can reduce his operating costs, this will also allow him to be more competitive. Synthetic lubricants provide a lower coefficient of friction in most gearboxes, therefore reducing the energy required to manufacture the product. Also, since the synthetic gear lubricants last longer, less maintenance hours are needed to change oil, consequentially freeing up those man-hours to implement other productivity improvements. Gearbox manufacturers, OEMs, and end users are beginning to demand better gear lubricants to meet the tougher performance targets. These targets are [3]: • • • •

Better thermal stability Longer or no drain intervals (fill for life) Heavier loads Higher quality

Copyright 2006 by Taylor & Francis Group, LLC

• More efficiency • Extended warranty

Synthetic gear lubricants will play an increased roll in meeting the operating performance objectives of the future.

REFERENCES 1. Lubrication, Vol. 66, Texaco, Inc., 1980. 2. Die Schmierung von Zahnradgetrieben, 9.3/9.4 d, Ausgabe 03. 1995, Klüber Lubrication München KG. 3. Korosec, P.S., Gear Oils, Synthetic Lubricants and High Performance Functional Fluids, 1st ed. 4. Lauer, D.A. “Gear oil classification and specification,” Gear Technology, May–June 1995. 5. Transmission Engineering, Selection and Application of Gear Lubricants, Kluber Lubrication München KG, August 1995. 6. Winter, H. and Oster, P. “Influence of lubrication on pitting and micro-pitting resistance of gears,” Gear Technology, March/April 1990. 7. Michaelis, K. and Höhn, B.-R. “Influence of lubricants on power loss of cylindrical gears,” STLE, Preprint No. 93-AM4B-1, 1993. 8. Product Information S-002-01, SEW Eurodrive, April 1990. 9. Bloch, H.P. and Williams, J.B. “Synthetic lubricants measure up to claims,” Chemical Engineering, January 1995 10. Plant Engineering Magazines Exclusive Chart of Synthetic Lubricants, Plant Engineering, Cahners Publishing Company, Reed Elsevier, Inc. 11. Personal communication with Kline and Company, Bill Downey, February 1997. 12. Mann, U. “Synthetic oils for worm gear lubrication,” AGMA, Technical Paper 99FTM17, 1999.

28

Synthetic Greases Joseph F. Braza CONTENTS 28.1 28.2

Synthetic vs. Petroleum The Composition of Synthetic Grease 28.2.1 Synthetic Base Fluids 28.2.2 Thickening Systems 28.2.3 Additive Packages 28.2.4 Lubricant Selection and the Design Cycle 28.3 Grease Manufacture 28.4 Grease Chemistry 28.4.1 Preparation of Synthetic Ester Grease 28.4.2 Preparation of Aluminum Complex Grease 28.4.3 Polyurea Grease 28.4.4 Organomodified Clay Thickened Synthetics 28.4.5 PTFE-Thickened Synthetic Grease 28.5 Grease Testing 28.5.1 Industry Standard Test Methods 28.5.2 Analytical and Application-Specific Test Methods 28.6 Cost of Synthetic Greases 28.7 Examples of Applications for Synthetic Greases 28.7.1 Synthetic Greases in Stationary Electrical Connectors 28.7.2 Synthetic Greases in Rolling Element Bearings 28.8 Cleanliness of Synthetic Greases 28.9 Packaging, Dispensing, and Solvent Dispersions for Grease 28.9.1 Packaging and Dispensing Considerations 28.9.2 Solvent Dispersions of Greases 28.10 Future Synthetic Grease Applications References

28.1 SYNTHETIC VS. PETROLEUM What is synthetic grease? Before we can answer this question, we need to define what grease is. The classical definition of lubricating grease is “a solid-to-semifluid product of a thickening agent in a liquid lubricant [1],” or in lay terminology, grease can be thought of as a “sponge of oil.” All lubricating greases, including synthetics, consist of three fundamental components: a lubricating base fluid, a thickener, and usually performance-enhancing additives [2]. The concentration of thickener determines the consistency of the finished product; however, it is the nature

Copyright 2006 by Taylor & Francis Group, LLC

of the oil that determines whether the grease is classified as a synthetic. The oil, thickener, and additive combinations provide manufacturers with a great deal of flexibility in formulating products with many different physical and chemical attributes [3]. The basic building blocks of any lubricating oil come from nature. Animal, vegetable, and mineral oils, including petroleum, are harvested and refined. Synthetic oils undergo another step: They are manipulated at the molecular level to improve lubrication characteristics.

For example, synthetic hydrocarbon oil starts with ethylene, a petroleum product. The ethylene is resynthesized to purify the oil and to narrow its range of molecular weights. The result is a synthetic hydrocarbon that is much less volatile than any petroleum base stock or, in more practical terms, oil that has a longer operating life and a broader operating temperature range. In short, synthetic oils rely on nature for their raw materials but the unique properties of synthetic oils are the products of rigidly controlled chemical processes [4]. While different families of synthetic oils are better suited for specific types of applications, the molecular homogeneity of synthetic oils in general make them more consistent, more predictable, and more robust than petroleum products in several ways. Synthetic lubricants are engineered for improved thermooxidative stability. Compared to petroleum, synthetics survive hotter temperatures, last three to five times longer, and are not as likely to form carbon deposits (i.e., varnish or sludge), which create drag and wear. In broad terms, the thermooxidative stability of synthetic oils contributes directly to improved performance and extended life of the lubricated component. The majority of synthetic oils also have lower cold temperature service limits than petroleum. For example, a number of synthetic hydrocarbon oils remain fluid at −60◦ C, while others can withstand temperatures down to −90◦ C, whereas petroleum typically becomes intractable at −20◦ C. The molecular structure of many synthetic oils also gives them higher film strengths than petroleum. The oil film keeps two moving parts from rubbing against each other, and higher film strength enables synthetics oils to withstand heavier loads, faster speeds, and to better prevent wear. Furthermore, unlike petroleum, the viscosity of most synthetic oils does not undergo radical shifts with temperature. Viscosity is a critical property when matching oil to specific operating conditions. If the viscosity is too low, the contact surfaces will not be separated and excessive wear will occur. If viscosity is too high, excessive power will be required for relative motion. While both synthetic and petroleum oils come in a wide range of viscosities, the viscosity of any fluid gets thinner as temperatures increase and thicker as temperatures decrease. How much the viscosity changes with temperature is indicated by the “Viscosity Index” (VI), which is a standard (ASTM D-2270) dimensionless rating: A higher number indicates a lower rate of change, which is ideal from a lubrication standpoint. Synthetic oils generally have higher VIs than petroleum, that is, the viscosity of synthetic oils remains more consistent over temperature changes. Most petroleum oils have VIs well below 100; most synthetics have VIs well above 100. For example, the VI of synthetic hydrocarbon oils ranges from 125 to 250; the VI of silicone oils falls between 200 and 650. Higher VI means a more stable molecule, which translates to longer lubricant life.

Copyright 2006 by Taylor & Francis Group, LLC

28.2 THE COMPOSITION OF SYNTHETIC GREASE 28.2.1 Synthetic Base Fluids In all lubricating greases, including synthetics, the base fluid represents the principal ingredient. All lubricating oils must have the ability to separate adjoining, moving surfaces to prevent or at least minimize wear. Synthetic fluids that are chemically similar but vary in viscosity can be classified into families. Each family has different advantages and limitations as described in Table 28.1. Synthetic lubricating oils also provide a broader operating temperature range than petroleum lubricants as shown in Figure 28.1. An understanding of these differences helps an engineer choose the best possible lubricant for the job at hand. There are currently six families of synthetic oils as follows: Synthetic hydrocarbons, also known as polyalphaolefins (PAOs), are the most widely used and are also abbreviated as SCHs, or abbreviated as SHCs. Because they are generally compatible with mineral oils, paints, plastics, and elastomers, switching from a petroleum to a SHC is relatively easy. They offer excellent cold-temperature performance and oxidative stability. Compared to other synthetic oils, they are also relatively inexpensive. Synthetic esters, which are chemically similar to PAOs, have an inherent polarity that makes them even less volatile and more lubricious. They are often blended with PAOs or other synthetic oils in lubricant formulations. Due to their affinity for metal, especially steel and iron, esters provide maximum wear protection. They are ideal for loaded bearings, potentiometers, and cut-metal and powdered-metal gearing, if proper seals are used. Since esters can withstand temperatures as high as 180◦ C, they have become the choice for automotive supercharger gearing and other severe duty applications. The disadvantage of esters is that they attack certain plastics and elastomers. Polyglycols, like esters, have an affinity for specific metals, such as brass or phosphate bronze. They offer good lubricity and film strength. A “clean-burning” lubricant, they are commonly used in arcing switches where they leave little or no residue, which would act as an insulator. Because they offer good load-carrying ability, polyglycols are also particularly effective in large worm and planetary gears to reduce friction and improve efficiency. They are the only synthetic oils that include water-soluble versions. Like esters, however, they present compatibility problems with some plastics and elastomers, particularly polycarbonates, ABS resins, natural rubber, Buna S, and butyl rubber. Silicones and Perfluoropolyethers (PFPEs) are compatible with nearly all plastics. Both are suitable for broad temperature applications, and have shown exceptional lowtemperature torque characteristics. PFPEs are also resistant to chemically aggressive environments and are unaffected by sulfuric acid, hydrochloric acid, alkalis, halogens, and

TABLE 28.1 Comparison of Base Oils for Synthetic Greases Base oils

Advantages

Limitations

Petroleum hydrocarbon

• Very low cost

• Limited temperature range • Product variability

Synthetic hydrocarbons

• Excellent thermal stability • Good friction reduction and lubricity • Wide range of viscosities • Low-temperature serviceability • Good plastic and elastomer compatibility • Long and growing list of applications in many industries

• Not suitable above 125◦ C

Polyglycols/polyethers

• • • • • • • •

Non-carbonizing, no residue Good lubricity and film strength Wide range of viscosities Unusually good elastomer compatibility Good load carrying Only synthetic oils that include water-soluble versions Good high-temperature stability with proper antioxidant Commonly used in arcing switches, and particularly effective in large worm and planetary gears

•

Synthetic Esters

• • • • • • •

Excellent oxidative and thermal stability Low volatility Excellent antiwear properties Outstanding lubricity Good low-temperature properties Minimal viscosity change with temperature Excellent load-carrying ability for bearing applications

• Not compatible with some plastics and elastomers

Silicones

• • • • • • •

Excellent oxidative and thermal stability Low volatility Wide range of viscosities Minimal viscosity change with temperature Excellent plastic and elastomer compatibility Good wetting capability Commonly used with plastic and elastomer components, including gears, control cables, and seals. Higher viscosities provide mechanical damping

• Poor load carrying • Tendency to migrate

Perfluoropolyethers (PFPE)

• • • • • •

Excellent oxidative and thermal stability Low volatility and vapor pressure Nonflammable and chemically inert Excellent plastic and elastomer compatibility Resistant to aggressive chemicals and solvents Commonly used in extreme-temperature environments and applications that require chemical, fuel, or solvent resistance

• High cost • Reduced effectiveness under heavy loads

Polyphenylethers (PPE)

• • • • • •

Highest thermal and oxidative stability of all oils Excellent radiation, chemical, and acid resistance Excellent lubricity Excellent high-temperature stability Non-spreading even in thin film Traditional lubricant for noble metal connector applications; also used for high-temperature, specialty bearings

• Not suitable for temperatures below 10◦ C • Not compatible with some plastics and elastomers • High cost

Multiplyalkylated cyclopentane

• Proprietary fluid that combines the low vapor pressure of a PFPE with the lubricity and film strength of a synthetic hydrocarbon

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Not compatible with some plastics and elastomers • Poor volatility above 100◦ C

• Not suitable above 125◦ C • High cost

Petroleum Synthetic hydrocarbons Multiplyalkylated cyclopentanes (MACs) Silahydrocarbons Polyglycols Synthetic esters Silicones Polyphenylethers Perfluoropolyethers –100 –80 –60 –40 –20

0

20

40

60

80 100 120 140 160 180 200 220 240 260

FIGURE 28.1 Temperature range (◦ C) of commonly used synthetic oils

Copyright 2006 by Taylor & Francis Group, LLC

10000.00

Normalized lifetime (orbits/
g)

petroleum solvents. They do not react with oxygen — even at 250◦ C under 500 psi of pure oxygen. In addition, some PFPEs have very low vapor pressure, which is essential for vacuum chamber and aerospace applications where outgassing can be problematic. The major advantages of silicones are that they show little change in viscosity with temperature and resist evaporation at elevated temperatures. However, silicones have limited load-carrying capacity. Polyphenylethers (PPEs) are the traditional lubricants for noble metal connectors. With the highest thermal and oxidative stability of all oils, they are also used for high-temperature, specialty bearings. PPEs are radiationresistant, which make them candidates for medical or dental apparatus, where radiation sterilization is mandatory. PPEs are not suitable for temperatures below 10◦ C, nor are they compatible with some plastics and elastomers. Multiplyalkylated cyclopentane, a type of SHC, is one of the newest synthetic lubricants. Its uniqueness lies in the fact that its low vapor pressure, which can be in the range of 3.5 × 10−11 torr, rivals the vapor pressure of PFPEs, but its sturdier hydrocarbon backbone enables it to handle heavier loads better than a PFPE. Silahydrocarbons are a relatively new class of lubricating oils that contain only silicon, carbon, and hydrogen, which have been recently developed. Silahydrocarbons have low volatility, are thermally stable, and are available in a wide range of viscosities. There are three types: tri, tetra, and penta, based on the number of silicon atoms present in the molecule. Another added benefit of silahydrocarbons is that they can accept conventional lubricant additives and are miscible with PAOs. The bearing performance of silahydrocarbon oils for synthetic greases was evaluated at NASA [5] using a spiral orbit tribometer (SOT). The SOT simulates an angular contact bearing under boundary lubrication conditions, with similar stress levels, and rolling and pivoting motions at room temperature. The results of this test are shown in Figure 28.2, which shows that the pentasilahydrocarbon exhibits similar performance to a 100 cSt PAO,

1000.00

100.00

10.00

1.00 Multiplyalkylated cyclopentane

PAO-100 cSt

Pentasilahydrocarbon Linear PFPE

FIGURE 28.2 Relative lifetimes at a mean Hertzian stress of 1.5 GPa of several space lubricants [5]

but substantially better performance than a linear PFPE. Although the multiplyalkylated cyclopentane exhibited a longer lifetime than the silahydrocarbon, the advantage of the silahydracarbon is its high-temperature capability of 210◦ C.

28.2.2 Thickening Systems Although it is the oil that characterizes grease as synthetic, the thickener type completes the identity of the grease. For example, a lubricating grease prepared from a PAO oil thickened with lithium 12-hydroxystearate would be referred to as lithium-soap thickened SHC. An ester thickened with organomodified clay would be described as a clay-based synthetic ester. Synthetic greases are prepared from both organic and inorganic thickeners as listed in Table 28.2. Organic thickeners are prepared from the reaction of a suitable alkali metal with either high-molecular-weight carboxylic acids or fats. When the chemical reaction takes place in the oil used in formulating the grease, it is referred to as in situ neutralization or in situ saponification, depending

TABLE 28.2 Common Thickeners for Synthetic Grease Thickener Paraffin wax Alkali Soap

Organoclay Alkali Complex Soap

Polyurea

Silica

PTFE

Metal oxide

Advantages • • • • • • • • • • • • • • • • • • • • • • •

Disadvantages

Lower cost Lower cost Water resistance Pumpability High loads Melting temperature > +250◦ C Water resistant Pumpability Low oil separation Melting temperature > +250◦ C Water resistant Pumpability Low oil separation Melting temperature > +250◦ C Water resistant Low oil separation Very high melting temperature Lubricity Inertness Melting temperature >300◦ C Thermal conductivity Inertness Very high melting temperature

upon whether an acid or fat is the coreactant. Table 28.2 identifies some of the commonly employed alkali soaps used to make greases. The alkali soaps are usually reacted with stearic acid, myristic acid, 12-hydroxystearic acid, or hydrogenated castor oil, a triglyceride that liberates 12-hydroxystearic acid during saponification. Other thickeners, such as chemically modified clay, amorphous silica, and polytetrafluoroethylene (PTFE), can also be used to form grease, but without the need for a chemical reaction for grease formation to occur. The efficacy of a particular thickener to convert synthetic oil into grease is dependent on the ultimate surface area of the thickener, its ability to hydrogen bond, and its tendency to associate with the fluid on a molecular level. The thickener must have an affinity for the base fluid that is intermediate between the forces that lead to greater solubility and those forces tending to induce phase separation.

• Low melting point: low load/low friction only • Reacts with some oils and metals

• Limited oil content/oil separation • Reacts with some oils and metals

• Stability at low shear • Storage hardening

• Mechanical instability with some base oils

• Moderate loads only

• Limited oil content, oil separation

TABLE 28.3 Common Lubricant Additives Additives Antioxidant Antiwear Antirust Anticorrosion Filler Extreme pressure (EP) Lubricity Viscosity index (VI) Pour point Dye

Capabilities Prolongs life of base oil Chemically active protection of loaded metal surfaces Slows rusting of iron alloys Slows corrosion of non-noble metals Thermal/electrical conductivity, special physical properties Solids burnish into loaded surface under extreme pressure Reduces coefficient of friction, starting torque, or stick/slip Reduces rate of change of viscosity with temperature Improves lower temperature limit Visual/UV markers as inspection/assembly aids

28.2.3 Additive Packages The third component of grease is the performance enhancing additives, which are chemicals that allow base fluids to function in harsh environments [6]. A comprehensive analysis of the lubricant additives is given in Reference 7. In many cases, the synthetic oil does not possess the properties necessary to perform effectively in today’s demanding

Copyright 2006 by Taylor & Francis Group, LLC

lubricating environment. Additives provide grease manufacturers with the ability to formulate greases with specific physical and chemical characteristics. Common lubricant additives are listed in Table 28.3. The additives used in a lubricant provide even greater design flexibility. Additives

Heat flow (W/g)

Polyol Ester with amine-based antioxidant Polyol Ester with sulfur-containing bis-phenolic additive 477.91 min

2

TABLE 28.4 Materials Compatible with Synthetic Oils and Greasesa

1205.72 min 1 185°C 24 h 500 psi oxygen at 100 mL/min 0

200

400

600

800 1000 1200 1400 1600 Time, min

FIGURE 28.3 Effect of two antioxidants on the thermal-oxidative stability on a polyol ester oil [8]

are mixed in small concentrations with the oil and thickener — usually less than 5% by weight — to enhance critical performance properties of grease, such as low temperature torque, metal corrosion protection, or fluid oxidation resistance. The grease performance can be improved by the appropriate additive selection. As an example, the hightemperature stability of polyol ester base oils can be dramatically improved by using different antioxidants [8]. Figure 28.3 shows thermal curves from a Pressure Differential Scanning Calorimeter (test conditions are shown on plot). The oxidation induction time with the aminebased antioxidant occurs at 478 min, on the other hand, using a sulfur-containing bis-phenolic additive in the oil, the oxidation induction time is increased to 1206 min — a twofold increase. These test results indicate that the hightemperature capabilities of the lubricant can be increased from 150 to 175◦ C.

28.2.4 Lubricant Selection and the Design Cycle While the performance of a lubricant depends on many variables, early evaluation of key lubricant selection criteria can help avoid design pitfalls and shorten product development time. Operating temperature: The most important design variable is the operating temperature range of the device. At the high-temperature limit, the lubricant must be chemically stable and have sufficient film strength to adequately prevent wear. At the lowest expected temperature, it must remain sufficiently fluid. Material compatibility: Some lubricants can “attack” certain plastics and elastomers. The base oil can infiltrate the solid material or cause the solid’s components to leach into the lubricant (Table 28.4). Good design practice tests the compatibility of specific plastics and elastomers by evaluating physical properties such as tensile

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Plastics Acetals Polyamides Phenolics Terephthalates Polycarbonates ABS resins Polyphenylene oxide Polysulfones Polyethylenes Elastomers Natural rubbers Buna S Butyl Ethylene propylene Nitrile (Buna N) Neoprene Silicone Fluoroelastomers

Synthetic hydrocarbons

Esters and polyglycols

Silicones (all types)

Fluorinated ethers

A A A A A A A

A A A A C C C

A A A A A A A

A A A A A A A

A B

C B

A A

A A

C C C C

C C C B

A A A A

A A A A

A A B A

B C B A

A A C A

A A A A

Legend: A = usually OK; B = be careful; C = causes problems. a Caution: These compatibility ratings are intended to be guidelines for design engineers when selecting lubricants. High mechanical stress, high temperature, poor plastic/elastomer quality, or any combination of these conditions, can compromise compatibility. Any synthetic lubricant used with a plastic or elastomeric component should be tested to ensure compatibility in a specific application.

strength, dimensional stability, and gravimetric stability after immersion in the lubricant. Higher temperatures and lower base oil viscosities usually exacerbate chemical incompatibility. Certain metals that come in contact with the lubricant may exhibit accelerated corrosion or lead to undesirable polymerization or “varnishing” and failure of the lubricant base oil. These problems can be avoided by identifying early in the design process the metal alloys used in the device and analyzing and testing their compatibility with candidate lubricants and additives. Load and wear: For most applications, the prevention of wear caused by friction is the primary reason for the use of a lubricant. Thus the load at the interface is an obvious concern. In general, higher viscosity base oils support heavier loads. If the load in the contact zone is too great or the speed is too slow, asperities on the rubbing surfaces can collide, causing excessive wear. In this situation, which is referred to as boundary lubrication, extreme pressure (EP) additives may be necessary. Synthetic ester greases are particularly suited for preventing heavily loaded metal-on-metal wear. Under relatively light

loading, the outstanding viscosity properties of a silicone grease may be useful.

28.3 GREASE MANUFACTURE Organic greases are usually manufactured in kettles. The size of the vessels ranges from laboratory units capable of manufacturing only 2 to 5 kg (5 to 10 lb) per batch, to very large units capable of manufacturing 18,000 kg (40,000 lb) of grease in a single operation. Since heat is required to initiate the reaction of the ingredients used to manufacture soap-based grease, or in general to promote the solvency of lubricating fluids and additives, grease kettles are heated. Most are jacketed to accommodate either steam or hot oil. Steam is an advantageous thermal medium because cold water can be circulated through the same jacket to cool the batch on completion of the chemical reaction. The primary disadvantage of heating the grease mixture with steam is that high pressure is required to attain temperatures above 230◦ C (446◦ F). Aside from steam, oil, electricity, and direct heating are also used to heat grease kettles. Generally, a soap-thickened grease is manufactured by adding a small portion of base oil to the kettle along with all of the fatty acid. At this stage, only enough heat is applied to melt the mixture. Once the fatty acid has melted into the base oil, an aqueous solution of the alkali metal salt is added to the kettle incrementally so it does not boil over. The kettle contents are continuously stirred, usually with counter rotating stirrers, to facilitate the dehydration of the soap mass as the reaction proceeds. After dehydration, additional base oil is gradually added to the kettle. The addition of oil must proceed slowly in order to maximize proper mixing of the intractable soap mass and the oil being added. After the addition of the required quantity of oil, the kettle contents are heated to some predetermined temperature and maintained at that temperature for several hours. After the heating cycle, the grease is rapidly cooled to optimize the dispersion of the thickener. The rate at which the kettle contents are cooled has a pronounced effect on the finished consistency of the grease. Additives are usually added to the grease after the temperature of the batch has fallen below 100◦ C (212◦ F). When the kettle contents have reached room temperature, the grease may be either milled or homogenized. As a final step, the grease may be filtered to remove contaminates. Quality control testing usually occurs prior to discharging the grease from the kettle for packaging.

28.4 GREASE CHEMISTRY 28.4.1 Preparation of Synthetic Ester Grease The following batch workup illustrates the preparation of 100 kg (220 lb) of synthetic ester grease thickened

Copyright 2006 by Taylor & Francis Group, LLC

with sodium myristate. The finished product is to contain 12% thickener. The kilograms of thickener required equals the batch size multiplied by the desired thickener concentration, so that the amount of thickener required is given by: 100 kg × 0.12 = 12 kg The balanced chemical reaction is: NaOH + H3 C(CH2 )12 COOH = NaOOC(CH2 )12 CH3 + H2 O Because the molecular weight of the thickener, sodium myristate, is 226 g/mol and 12 kg of thickener is needed, the number of moles of each reactant is equal to the number of moles of thickener, as there is a one-to-one stoichiometry indicated by the balanced chemical reaction. Therefore, the numbers of moles of sodium hydroxide and myristic acid required are determined as follows: 12, 000 g = 53.09 mol 226 g/mol

Ingredient NaOH Myristic acid

Number of moles

g/mol

Amount needed, kg (lb)

53.09 53.09

23 204

1.221 (2.691) 10.83 (23.88)

The sodium hydroxide would be dissolved in sufficient deionized water to completely dissolve the base, and the myristic acid would be added to the reaction vessel along with a small portion of nonsaponifiable petroleum oil (the reaction cannot be conducted in the presence of the ester base oil due to the susceptibility of esters to deesterification in the presence of strong bases). After the neutralization reaction is completed and the soap mass has been adequately dehydrated, the thickener is then capable of absorbing the synthetic ester base fluid. The oil is added incrementally to effect proper mixing while maintaining the temperature of the kettle contents at approximately 150◦ C (302◦ F). When the total amount of oil has been added to the kettle, the temperature is reduced and the desired additives are added to the grease. The batch is further cooled and discharged from the kettle. A primary advantage of synthetic lubricants over petroleum-based products is their improved serviceability at elevated temperatures. However, the ability of a lubricating grease to resist excessive softening or melting at extreme temperatures is dictated by the nature of the thickening agent. Most organic soap thickeners melt at temperatures below 230◦ C (446◦ F). To overcome the apparent thermal deficiency, complex thickeners (that do not melt) are used. Dropping points for many complex greases are usually above 260◦ C (500◦ F).

28.4.2 Preparation of Aluminum Complex Grease The preparation of 100 kg (220 lb) of an aluminum complex grease [9] containing a SHC base oil can be illustrated as follows:

Batch size 100 kg Thickener content 7.5% Ratio of benzoic acid 0.8% to stearic acid Ratio of both acids 1.9% to aluminum Kilograms of thickener 7.5 kg required = 100 kg × 0.075 Balanced chemical equation: H2 OAl(OC3 H7 )3 + C17 H35 CO2 H + C6 H5 CO2 H = (C17 H35 CO2 )AlOH(C6 H5 CO2 ) + 3C3 H7 OH

28.4.4 Organomodified Clay Thickened Synthetics

The amount of each ingredient is determined based on the specified composition of the grease in molar ratios.

Ingredient Stearic acid Benzoic acid Aluminum Total

Molecular Moles weight 1.0 0.8 0.94

278.6 122.0 27.0

Batch Unit

kg

(lb)

278.6 97.6 25.4 401.6

5.20 1.82 0.474 7.49

(11.5) (4.01) (1.04) (16.5)

Since the aluminum (as the isopropoxide) is supplied as a 12.7% mixture in oil, the 0.474 kg (1.04 lb) of aluminum would be available in 3.73 kg (8.22 lb) of the commercial product. To manufacture the grease, the reaction of the ingredients would be carried out in a portion of the SHC fluid, after which the remaining oil and additives would be added. Kettles suitable for manufacturing complex aluminum greases must be designed to recover the alcohol liberated by the reaction.

28.4.3 Polyurea Grease Although many polyurea greases contain petroleum base oils, these greases deserve mention in a text dedicated to synthetics because of their unique thickener chemistry [10]. The polyurea thickening agent commonly used is a synthetic low molecular weight polymer that provides the following advantages: a dropping point of approximately 250◦ C (482◦ F), excellent water resistance, low

Copyright 2006 by Taylor & Francis Group, LLC

oil separation, and a high propensity toward shear thinning that renders polyurea grease ideally suited for many rolling-element bearing applications. The major disadvantage of this grease is the health hazard associated with the isocyanates and amines to form the urea grease. The manufacturing of these types of greases require heavy labeling, sophisticated equipment, and paramount concern for safety. Recently, a preformed polyurea thickener [11] became commercially available as a tetramer powder, which will allow grease manufacturers to take advantage of good characteristics of the polyurea, but eliminate the health and safety concerns.

The ability of clay to function as an effective thickener for lubricating fluids is dependent on its surface pretreatment. The addition of a suitable organic compound to the surface of individual clay platelets transforms the material from a hydrophile to an oil absorber. Clay is useful as a thickening agent for grease due to its dispersible lamellar-type structure and ability to hydrogen bond. Individual platelets are only angstroms thick and possess tremendous surface area when efficiently dispersed. Moreover, since a chemical reaction is not required to form a synthetic grease from a clay thickener, these greases can be easier to produce and require less energy to manufacture than soap-based greases. However, to achieve a viable product the grease formulator must optimize the amount of dispersant and water used to open the individual clay bundles and promote hydrogen bonding. Clays are suitable for thickening hydrocarbons, polyglycols, and some silicones. However, the suitability of the clay thickener in a particular lubricating medium is predicated on the polarity of the oil and the clay’s surface treatment. A clay-(alkylaryl ammonium hectorite) thickened polyglycol grease can be prepared by simply adding approximately 7% clay to the polyglycol, stirring the mixture, then adding to this mixture a blend of propylene carbonate in distilled water. Propylene carbonate, is one of several dispersants used to manufacture clay-based synthetic greases. Acetone and ethanol are also used. Although clay-based greases are nonmelting and often recommended for high-temperature applications, sustained usefulness at elevated temperature is limited in all greases by the thermooxidative stability of the base oil.

28.4.5 PTFE-Thickened Synthetic Grease PTFE is one of two thickening agents that can be classified as a universal gellant. PTFE is capable of forming grease from all of the synthetic fluids that are listed in Table 28.1 due to its low surface energy. Greases prepared from PTFE and synthetic fluids are serviceable at

TABLE 28.5 Common Synthetic Grease Properties Property

Method

Unworked penetration

ASTM D-217

Worked penetration, 60 strokes

ASTM D-217

Oil separation

FTM 791B Method 321.2

Evaporation

ASTM D-972

Dropping point

ASTM D-2265

extremely low temperatures and are capable of continuous service up to 250◦ C (480◦ F). Grease prepared from telomers of PTFE are probably the most suitable for long-term lubrication of rolling element bearings. An NLGI Grade 2 grease can be prepared from 20% PTFE derived from the telomer dispersion, compared to less expensive micropowders that require 40% PTFE. A grease with the greater oil reservoir will function long after the lubricant with the higher concentration of thickener becomes intractable due to oil loss. The efficacy of grease is dependent on a favorable balance between the amount of oil and thickener. As the oil to thickener ratio changes because of oil separation, oil evaporation, and oil oxidation, the grease is gradually transformed into an intractable mass that fails to lubricate.

28.5 GREASE TESTING 28.5.1 Industry Standard Test Methods The American Society of Testing and Materials (ASTM), along with its European and Japanese counterparts, have standardized a vast number of tests used to measure a specific chemical or physical property of grease. Some of these tests may be classified as those that measure characteristics particular to the composition, while other tests are more suitable for assessing batch-to-batch variability. Volatility per D-972, water washout per D-1264, and the four-ball wear test per D-2266 are examples of tests that measure properties of the grease inherent to the formulation. Some variation in these properties is possible, due to either the product or the test method, but the magnitude of the variation should be minor from one batch to the next. However, it is necessary and prudent to conduct tests that are sensitive to the composition of the synthetic grease at established intervals. The specific interval ought to be determined after consultation with customers.

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Purpose Measures the consistency of the grease prior to the input of mechanical energy. This is what the customer’s pump is required to transfer Measures the mechanical stability of the grease. Excessive change may signal problems in applications imparting high shear to the grease This test assesses the amount of oil released from the grease structure after 30 h at 100◦ C (212◦ F) Measures evaporation of any volatile ingredients in the grease or residual by-products generated during manufacture Determines the high temperature attainable before a drop of oil separates from the grease

Because grease manufacturers cannot exercise absolute control over the chemical reactions or processes that produce grease, certain physical tests should be conducted on each batch of grease to monitor important grease characteristics. These tests can be used to monitor the homogeneity of the product from batch to batch. Table 28.5 lists tests that should be conducted on a batch-to-batch basis. Properties that can be tested to qualify a new grease formulation are presented in Table 28.6. The tests and criteria listed in this section represent only a small number of methods and procedures that are routinely used to characterize lubricating greases. Other tests determine the water resistance, electrical properties, and extreme pressure properties of lubricating grease. These test methods and others are available through ASTM. The consistency of a grease measures its resistance to deformation under an applied force. Consistency attempts to quantify plastic behavior as viscosity tries to delineate fluidity. The National Lubrication Grease Institute (NLGI) has developed a numerical scale to classify the consistency of greases by measurement of a depth to which a metal cone penetrates a sample of the grease in free fall under defined test conditions. The NLGI defines nine distinct grades of grease, ranging from Grade 000 to 6, based on the sixty stroke worked penetration, P60 , as shown in Table 28.7. Each range is 30 penetration units wide and 15 units separate the grades. For instance, the worked penetration of an NLGI Grade 2 Grease, a common grade for many bearing applications, is 265 to 295, while a Grade 3 Grease is 220 to 250. Semifluid greases have a triplezero rating while the hardest greases would receive a rating six. Although the worked, 60X, penetration determines the grade, the unworked penetration, Po, of grease is a very useful parameter since it identifies the consistency of the lubricant that the dispensing equipment must deal with. Changes in Po and P60 with time may or may not be a manifestation of lubricant deterioration due to oxidation.

TABLE 28.6 Synthetic Grease Properties to Qualify a New Grease Formulation Property

Method

Oxidation stability

ASTM D-942

Wear preventive characteristics

ASTM D-2266

Water washout

ASTM D-1264

Purpose Measures the thermo-oxidative stability of the lubricant at elevated temperature under pure oxygen pressure. The reduction in pressure indicated oxidation In this test the boundary lubricating properties of the lubricant are determined. A loaded, rotating steel ball is forced against three stationary balls at some elevated temperature for 1 h. The resulting average wear scar is used to assess the effectiveness of the lubricant and its additives in the boundary regime This test is used to asses the resistance of a grease formulation to resist displacement from a rolling element bearing by fresh water under dynamic conditions. Theoretically, one would not expect a particular grease formulation to show deviation beyond the limits inherent in the tests. However, minor changes in grease consistency, within the NLGI grade, could affect results

TABLE 28.7 Measures of Grease “Stiffness” [12]

NLGI grade 000 00 0 1 2 3 4 5 6

ASTM worked penetration, 60× 445–475 400–430 355–385 310–340 265–295 220–250 175–205 130–160 85–115

Analogous consistency for household food item (unworked penetration) Ketchup Applesauce Brown mustard Tomato paste Peanut butter Vegetable shortening Frozen yogurt Smooth paté Cheese spread

These measurements are taken shortly after grease is manufactured and represent the state of the thickener dispersion at that time. The oil separating tendency of a lubricating grease under thermal stress is determined by the cone and beaker technique. The method consists of placing approximately ten grams of the test specimen in a metal cone made from a 60-mesh screen and suspending the fixture in a covered beaker. The grease sample is placed in a constant temperature oven for some specified time and temperature. The amount of oil that has been separated from the grease and captured in the beaker is determined gravimetrically at the completion of the test. Twenty-four hours at 100◦ C is a convenient duration and temperature to rate oil separation and make comparisons between different greases. Temperatures exceeding 150◦ C should be avoided to prevent false positives due to the likelihood of oil evaporation from the covered beaker following separation. The results of oil separation should not be used initially to judge the appropriateness of a lubricating grease for an application.

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Low oil separation is good for some applications while high oil separation is appropriate for others. After a grease has been selected based on performance merit, oil separation is a useful quality control check. Oil separation is determined in accordance with FTM 791 Method 321.2. The evaporation of volatile components in a lubricating grease is measured by ASTM Method D-972. In this test the grease sample is placed in a metal sample holder and the entire test fixture is immersed in an oil bath for the required time and temperature. Preheated air is blown across the surface of the grease to facilitate the removal from the test apparatus of volatile grease constituents. Sample weight loss is used to determine volatility. The dropping point of a lubricating grease is a useful parameter but less so today than years ago. Early thickening systems softened appreciably at temperatures approaching 100◦ C and melted before 150◦ C. As a result the dropping point of the grease, which is defined as the lowest temperature at which a drop of oil separates from grease, was used to determine the upper temperature performance limit. However, with the advent of high-melting thickener systems such as organo modified clay, complex soaps, PTFE, and others, the dropping point of grease no longer serves as a reliable indicator of high-temperature usefulness. Shortcomings include poor results in the test from thermal separation by relatively soft greases made from heat-resistant thickening systems. Today the suitability of a lubricating grease at elevated temperatures is predicated on the thermooxidative stability of the base oil, thickener, and additives rather than the grease’s dropping point. With modern grease, the dropping point should never be considered the operating temperature limit.

28.5.2 Analytical and Application-Specific Test Methods Modern analytical laboratory equipment with integrated computer software can provide key insights into the

Lbs./100,000 units Diameter mm.

High Density

Grease Cost per Device LD@$10/Lb. HD@$100/Lb.

Volume* ml.

Low Density

1

0.0003

0.06

0.12

.000006

.00012

2

0.0021

0.46

0.93

.00005

.0009

3

0.007

1.6

3.1

.00016

.0031

5

0.033

7.2

14.4

.0007

.014

10

0.26

57.8

115.5

.0058

.116

* Equivalent to weight of the hemisphere in grams for an LD grease would weigh twice as many grams.

FIGURE 28.4 The approximate unit cost of synthetic grease in U.S. dollars

makeup and function of synthetic lubricant formulations. Spectroscopic methods such as Fourier Transform Infrared (FTIR) spectroscopy can identify molecular signatures for various gellants, base oil species, and additives. A thermogravimetric analyzer (TGA) and pressure differential scanning calorimeter (PDSC) are used for detailed quantitative analysis of melting points, phase changes, and thermooxidative stability of lubricant formulations. Application-specific testing is often performed by lubricant formulators to prescreen product candidates for OEM customers prior to full-scale lubricant qualification tests in the actual OEM device. Prescreening can include measurement of special functional properties (electrical or thermal conductivity, viscosity vs. shear rate, etc.), material compatibility (lubricant vs. plastic, elastomer, or solvent), and the effects of low- and high-temperature extremes on the lubricant. An example of analytical testing is shown when comparing antioxidants to increase the high-temperature capabilities of a traditional ester from 150 to 175◦ C (see Figure 28.3). The PDSC was used to compare two ester greases, identical in formulation except that one contained the new antioxidant. The analysis showed that the grease with the antioxidant lasted more than twice as long as the traditional ester. Specifically, when placed in a test chamber at 185◦ C for 24 h under 500 psi of pure oxygen, continually replenished at 100 ml/min, the “hightemperature ester” took 1205.72 min or just over 20 h to burn, compared to the traditional ester that reached exotherm after 477.91 min or just under 8 h.

28.6 COST OF SYNTHETIC GREASES The principal disadvantage of synthetic greases over petroleum-based greases is cost, however, demands placed on modern devices have made the higher cost of synthetics palatable to many manufacturers. As an extreme

Copyright 2006 by Taylor & Francis Group, LLC

example, a popular sodium-complex, high-speed spindle bearing grease formulated from a petroleum oil is commercially available at less than $1.00 per pound. Most synthetic greases are typically priced between $5.00 (U.S.) and $50.00 (U.S.) per pound in 16 kg (35-lb) containers. Synthetic lubricants formulated from perfluoropolyether can approach $1,000.00 per pound. Low volumes of specialized formulations requiring a great deal of testing for aerospace, computer, or medical applications can command even higher prices. The good news, however, in many applications, as illustrated in Figure 28.4, is that the cost of the grease per device is negligible when compared to the value added of longer operating life, improved reliability, lower torque, lower acoustic noise, and other functional advantages.

28.7 EXAMPLES OF APPLICATIONS FOR SYNTHETIC GREASES 28.7.1 Synthetic Greases in Stationary Electrical Connectors Connectors play an especially vital role in cars and light trucks. A luxury car can have more than 400 connectors with 3000 individual terminals [13]. The automotive environment challenges connector integrity where engine connectors must survive rapid heating and cooling cycles, high levels of humidity, and vibration from the engine, drive train, suspension system, and related components. Furthermore, connector manufacturers face an additional challenge: the ergonomics of separable connector design. The force required to mate separable connectors is of particular concern. Connector quality depends on many factors, including materials, contact geometry, normal force, and design of springs, crimp mechanisms, and housings. Lubrication also plays an important role, especially for low-voltage

connectors (0.1 to 0.5 W). A properly selected lubricant lowers insertion force by decreasing the coefficient of friction between mating surfaces. It reduces mechanical wear by placing a film of oil between the mating surfaces. With additives, a lubricant minimizes corrosion. Lubricants also reduce fretting corrosion, a special type of mechanical wear caused by low amplitude vibration, typical with tin-plated contacts. The vibration may be caused by vehicular motion in general, motion of nearby components, such as fans or small motors, and thermal expansion and contraction of connector components. Fretting corrosion continually exposes fresh layers of metal to oxidation. An anti-fretting lubricant reduces mechanical wear, provides an oxygen barrier, and helps to move any oxide debris away from the contact area. Generally, a lubricant’s ability to reduce wear and retard oxidative resistance extends connector life. To capture the benefits of lubricated contacts, some automotive connector manufacturers began lubricating female terminals with a petroleum-based, lithium-soap grease with a zinc oxide fortification. Over time, the grease attacked connector housings, which started falling off wire harnesses — an obvious safety, quality, and warranty problem. A silica thickened, high-viscosity SHC grease offered plastic and elastomer compatibility, an operating temperature range of −40 to 125◦ C, and solved the problem caused by the petroleum connector grease. The physical properties of this grease are shown in Table 28.8. Further improvements occurred with a stiffer version of this synthetic grease to improve production line injection capabilities, higher temperature capabilities, and lower oil separation. Its stiffer consistency enabled presses to run 30 to 50% faster and much cleaner. A new antioxidant boosted its temperature limit to 135◦ C, a copper passivator minimized corrosion of exposed copper substrate, and the addition of a UV dye facilitated quality inspections. Research in the late 1980s and early 1990s suggested that fretting corrosion could be controlled by connector design by adding an elastic element inside a separable connection to compensate for movement between mated

TABLE 28.8 Physical Properties of a Synthetic Grease for Stationary Electrical Connectors Physical property

Typical value

Viscosity of base oil at 100◦ C Viscosity of base oil at 40◦ C Pour point Flash point Grease dropping point Unworked penetration Worked penetration

39.4 cSt 390 cSt −30◦ C 300◦ C 260◦ C 310–340 317

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pin and socket at the contact point [14]. This elastic element increased the normal force on the female portion of the mated contacts. Furthermore, the proliferation of connections on or near the engine block limited the synthetic grease listed in Table 28.8, which has an upper temperature limit of 125◦ C. OEMs needed a high-temperature connector grease that could reduce mating force for high normal force connectors. Fluorinated base oils and thickeners were selected due to their excellent thermal stability and chemical inertness. As shown in Figure 28.5, a linear PFPE thickened with either sub-micron size PTFE particles or micronsize urea particles reduced insertion force approximately three times over dry contacts or contacts with the SHC grease listed in Table 28.8. Furthermore, the fluorinated oil provided a thermal operability to 250◦ C or above. As a note, the disadvantage of the PTFE thickener is that the particles have a tendency to “burnish” during the mating process, leaving an insulative polymer on the contact surface, whereas the urea thickener does not detrimentally increase resistance.

28.7.2 Synthetic Greases in Rolling Element Bearings Rolling element bearings represent a major market for synthetic greases. Bearings today are expected to operate over temperatures that may range from −54◦ C to over 200◦ C. The application may dictate that during the entire life of the device there is no opportunity for relubrication. Precision bearings also require synthetic greases with minimum particulate contamination. For example, ball bearings used for computer spindle applications require greases that minimize viscous drag, are oxidatively stable, and are free from particulate matter that may jeopardize or damage the bearing. Bearings used for computer disc drive applications must also be lubricated with greases that have low vapor pressures. If the lubricant is volatile, lubricant contamination of the storage media could occur with disastrous results. The vapor pressure of lubricating grease is determined by the molecular weight and molecular weight distribution of its base oil, the specific additives it contains, and its ability to resist degradation by oxygen. Under vacuum conditions, thermoooxidative stability becomes irrelevant due to the absence of oxygen. However, in the presence of oxygen at elevated temperatures, lubricants are susceptible to degradation, which during the initial stages liberates low-molecular-weight fragments that are highly volatile. If thermooxidative stability can be ignored, vapor pressure as defined by the Langmuir equation is proportional to surface area, temperature in degrees Kelvin, and molecular weight. Vapor pressure in torr can be expressed as follows: P = 17.41G(T /M)1/2 ,

90.00 80.00

Average peak force (oz)

70.00 60.00 50.00 PAO/Silica PFPE/PTFE PFPE/urea Dry

40.00 30.00 20.00 10.00 0.00 1

2

3

4

5

6

7

8

9

10

Insertion number

FIGURE 28.5 Insertion force data on various connector greases [15]

TABLE 28.9 Physical Properties of a PFPE Grease Physical property Color Appearance Unworked penetration Worked penetration, 60× Evaporation, 24 h at 204◦ C Oil separation, 24 h at 204◦ C Four-ball wear test Conditions Wear scar at 75◦ C Wear scar at 204◦ C Low-temperature torque at −73.3◦ C Starting After 1 h Solubility in fuel

Typical value White Smooth 241 269 0.79% 13% 1200 rpm, 40 kg for 1 h 0.85 mm 1.26 mm 2714 g cm 590 g cm None

where G is the rate of evaporation in grams per centimeter squared per second, T is the temperature in Kelvin, and M is the molecular weight of the material. Clearly, under vacuum conditions, the molecular weight of the ingredients in the lubricating grease determines its tendency to volatilize. At 100◦ C, SHC greases made from base oils with a viscosity of 5.8 cSt at 100◦ C possess vapor pressures that approximate 10−6 torr. Synthetic greases made from PFPEs and thickened with PTFE have vapor pressure below 10−10 torr at room temperature. For continuous duty at temperatures above 260◦ C, applications requiring a nonflammable grease, or chemical resistance toward aggressive chemicals like fuming sulfuric acid,

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only synthetic greases based on PFPEs and thickened with PTFE will suffice. Table 28.9 lists typical physical properties of a PFPE grease.

28.8 CLEANLINESS OF SYNTHETIC GREASES Dirt or contamination in synthetic lubricating grease is undesirable. Greases employed as lubricants for miniature precision bearings should contain a minimum of particulate contaminants to prevent race or ball damage caused by contaminant-induced rupture of the lubricating film. The sources of lubricating grease contamination are numerous. However, ultrafiltration is quite effective in removing contaminants greater than 35 µm from most synthetic greases. Some contamination in the 10 to 34 µm range is usually present in the grease after ultrafiltration, and is not usually removed because of concern for the technical merit and cost of doing so. Aside from removing contamination, ultrafiltration improves the homogeneity of grease by increasing dispersion of the thickener. Ultrafiltration makes some grease slightly firmer and tends to reduce oil separation. Not long ago it was a popular misconception that micrometer-sized filters removed some of the thickener. However, hundreds of grease types have been ultrafiltered in the author’s laboratory without a single incident of gross removal of the thickener. The benefits of ultraclean greases in prolonging bearing life and improving performance is well substantiated. Federal standards define cleanliness for filtered oil. MIL-STD 1246 includes five cleanliness levels: 50, 25, 10, 5, and 1, where each number refers to the largest particle (in microns) allowed in oil. A rating of Cleanliness Level 1, for example, means that there are no particles

larger than 1 micron in that oil. (For a sense of scale, the diameter of one grain of beach sand is approximately 600 µm.) Methods to measure the cleanliness levels are also standardized. Similar to cleanliness ratings for oils, there are three cleanliness levels for grease: unfiltered, filtered, and ultrafiltered [16]. Unfiltered grease can contain particles larger than 75 µm. Filtered grease cannot have any particulate matter larger than 75 µm and there must be less than 1000 particles per cubic centimeter between 24 and 74 µm in size (MIL-G-8l322, Aircraft Grease). Ultrafiltered or “ultraclean grease” must not have any particles larger than 35 µm, nor it may have more than 1000 particles per cubic centimeter between 10 and 34 µm in size (MIL-G-81937, Ultraclean Instrument Grease). Ultraclean grease with very low vapor pressure is made by mixing ultraclean oils and additives with a gellant in a vacuum kettle. Vapor given off during the mixing process is removed, which helps to reduce the vapor pressure of the finished product. Once the grease is mixed, it is ultrafiltered, which requires a controlled environment and a vast arsenal of filters. Generally, grease filters are either nylon or stainless steel, starting at a rating of three microns. At the author’s company, once a set of filters is selected, the grease is forced through them with customdesigned, high-pressure equipment in an ISO 5 (Class 100) mini-environment. This ultrafiltration system deposits the ultrafiltered grease directly into end-use containers, which range from 1 cc syringes to 35 pound pails. Before filling, each container undergoes a multi-cycle cleaning with filtered de-ionized water. They are then dried with HEPAfiltered hot air. Care is also taken in the selection of containers. Metal and fiber containers are avoided. Plastic is a good choice as long as there are no pressure plug openings. The friction from such openings releases contaminants. Glass is an excellent choice, but must be examined before use. A rough molding flash along the bottle threads can create contaminants when the caps are screwed on and off. Most important, once an ultraclean oil or grease is made to a customer’s specifications, the process is fully documented to ensure repeatability from batch to batch.

28.9 PACKAGING, DISPENSING, AND SOLVENT DISPERSIONS FOR GREASE 28.9.1 Packaging and Dispensing Considerations The consistency of grease and its oil separation performance can have a significant effect on choice of dispensing equipment in a manufacturing environment. On highthroughput manufacturing lines, greases with a consistency of NLGI Grade 2 or lower can be handled as a quasi-liquid and piped under pressure from the point of storage on a

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manufacturing line to the point of application. Push-plate style pumps can be used directly on the delivered grease containers to force heavier consistency greases directly into dispensing machinery at the point of use; long piping runs with greases of NLGI Grade 3 or greater are not usually feasible due to the extreme pressure drops encountered in the lines. In any pressurized delivery system, care must be taken to remove static pressure from grease lines when flow is stopped over long periods in order to avoid unintended oil separation. In small-quantity precision dispensing applications, several equipment suppliers have developed excellent metering and dispensing technology for grease. The grease can be applied at precise locations in precisely metered quantities from dollops of fractions of a gram to continuously applied beads of grease. Multiaxis robotic dispensers with custom-designed multihead dispensing needles allow the manufacturing engineer a number of options for incorporating automated grease dispensing into a high-speed automated assembly line. Grease dispensing equipment of this type requires appropriate grease packaging to allow proper interfacing to the automated machinery. Grease customers usually specify cartridge containers in industry standard styles such as Semco® cartridges or EFD® syringes. Cartridges should be properly filled by the grease manufacturer, using appropriate filtration and deaerating techniques, in order to avoid particulate contaminants and voids which might cause metering errors or cavitation faults in the dispensing machinery.

28.9.2 Solvent Dispersions of Greases Solvent dispersions provide a convenient means for application of a thin coating of grease in a precise manner. Solvents are employed with lubricants as: (a) a carrier for the lubricant or (b) as a cleaning agent. As a carrier, a solvent allows application of a controlled, thin layer of a lubricant. This approach is commonly used in lubricating separable electrical contacts [17]; insufficient coating thickness will permit corrosion and oxidation of the contact surfaces while excessive lubricant deposition can lead to contact resistance. As a lubricant carrier, high solubility of the solvent with the lubricant base oil is required in order to ensure uniformity in the applied lubricant film. For cleaning mechanism parts, during the manufacturing and assembly process, at least partial solubility of the solvent with the base oil is desired. The grease is dissolved, partially dissolved, or suspended in an appropriate solvent usually to a concentration by weight of 2 to 20%. The percentage concentration, the solvent evaporation rate, and other factors affect the coating thickness. The choice of solvent is critical in these applications. Until recently, when chlorofluorocarbons (CFCs) were restricted in use due to their ozone depletion potential, CFCs (e.g., Freon® ) were often the grease dispersion

TABLE 28.10 Properties of Solvents Used in Grease Dispersions Property Performance Solubility

Boiling point/evaporation rate

Plastic and elastomer compatibility Cost Safety/environmental Flammability

Toxicity

Desired characteristics Solubility with base oils, additives, and organic thickeners desired. If total solubility not achieved, stable (non-agglomerating) dispersion is desired. Best solubility using new halogenated solvents often achieved with solvent blend tailored to dissolve all grease components “Freon-like” is the most common requirement. Low evaporation rates (e.g., isopropanol (IPA), mineral spirits) do not allow uniform coating thickness in many applications. Very high rates (e.g., HCFC-141b) cause excessive depletion of solvent baths, caking of lubricant on applicators, and safety issues with respect to excessive vapor pressures Some hydrofluorocarbons (HFCs) and hydrochlorfluorocarbons (HCFCs) can attack ester-vulnerable materials. Not usually a concern unless dip-coating an entire assembly is being considered Hydrocarbon solvents and Freon in the $1/lb range. New halogenated solvents in the $10–$50/pound range. Higher costs driving a trend toward solvent vapor recovery Defined in the United States as having a flash point below 38◦ C (100◦ F). Nonflammability is required by customers in a significant portion of grease dispersion applications. This effectively eliminates many hydrocarbon solvents Suspected carcinogens (e.g., ketones) are not viable choices for most industrial customers. New halogenated solvents have generally low toxicity and are being designed with low GWP

solvent of choice. They exhibited excellent solubility with nearly all lubricant base oils, high volatility (important for laying down a uniform grease coating), low toxicity, nonflammability, and reasonably low cost. With the departure of Freon from the scene, other familiar solvents in most cases represent poor performance by comparison with Freon. In addition, “the bar” was continually being raised in the areas of toxicity, ozone-friendliness, and a second environmental parameter: global warming potential. A summary of properties required for these solvents is given in Table 28.10. There has been a great deal of product development effort carried out at some of the major chemical companies over the last ten years in the synthesis of new classes of solvents that will satisfy the requirements listed in Table 28.10. Although the primary focus of these efforts has been a replacement for CFCs for industrial cleaning applications, new halogenated solvents that are suitable for grease dispersions are now reaching the marketplace. As yet, there is no new panacea to replace Freon, and grease formulators have instead developed solvent blends that can dissolve certain classes of base oils, thickeners, and additives. Even so, except for the absence of a single universal solvent, these solvent blends have all the requisite properties.

28.10 FUTURE SYNTHETIC GREASE APPLICATIONS A trend across many industries is to develop products that perform at higher operating temperature and greater speeds. Products are also packaged smaller and contain lighter weight materials. This combination of

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heat, speed, and engineering plastics in mechanical and electromechanical components generally calls for some type of synthetic lubricant. Further, certain industries often drive new technological developments. For example, in the aerospace arena extended mission lifetimes have placed increased burdens on components, and reliability of a spacecraft’s moving mechanical assemblies depends upon the lubricant and greases employed [18]. In the media storage industry, disk drives are operating at ever-increasing precision and speeds. They require ultraclean lubricants with extremely low vapor pressure. Even the disks require the protection of a unique synthetic fluid coating. Semiconductor manufacturing equipment and other precision equipment in cleanroom environments need lubricants that do not outgas — a characteristic found only in a select group of synthetic fluids. The automotive industry has generally established a −40 to 120◦ C temperature range for all auto and truck components, a condition satisfied only by synthetic lubricants. The drive to reduce component cost is also generating interest in synthetics — regardless of temperature requirements. Plastic gear trains used in printers, scanners, copiers, and fax machines, for example, are generally fabricated from economical polycarbonates to keep product costs down. And manufacturers are discovering that synthetic lubricants do not cause the compatibility problems that come with petroleum-based lubricants. Synthetic will never replace petroleum as a universal lubricant. But design and industry trends are creating an ever-widening role for synthetic lubricants, especially in areas where material compatibility, operating life, and

quality performance in demanding environments is critical to success in the marketplace.

REFERENCES 1. (1996), Lubricating Grease Guide, National Lubricating Grease Institute, Kansas City, MO, 4th ed., p. 1.01. 2. Vendura, T.M., Brunette, G., and Shah, R. (2003) “Lubricating greases,” Fuels and Lubricants Handbook: Technology, Properties, Performance, and Testing, Totten, G.E., ed., ASTM International, West Conshohocken, PA, p. 557. 3. Bessette, P.A. and Stone, D.S. (1999) “Synthetic grease,” Synthetic Lubricants and High-Performance Functional Fluids, 2nd ed., Rudnick, L.R. and Shubkin, R.L., eds., Marcel Dekker, pp. 519–538. 4. Lay, J. and Weikel, J. (2001) “Gaining a competitive advantage with synthetic lubricants,” Appliance, 56–60. 5. Jones, Jr., W.R., Jansen, M.J., Gschwender, L.J., Snyder, Jr., C.E., Sharma, S.K., Predmore, R.E., and Dube, M.J. (2001) “The Tribological Properties of Several Silahydrocarbons for Use in Space Mechanisms,” Proceedings of 9th European Space Mechanisms and Tribology Symposium, Liege, Belgium. 6. Rizvi, S.Q.A. (2003) “Additives and additive chemistry,” Fuels and Lubricants Handbook: Technology, Properties, Performance, and Testing, Totten, G.E., ed., ASTM International, West Conshohocken, PA, p. 199. 7. Rudnick, L.R. (2003) Lubricant Additives Chemistry and Applications, Marcel Dekker.

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8. Holley, B. (2001) “Next-generation ester grease survives higher temps,” Lubricants World, 11, 13–17. 9. Kruschwitz, H. (1990) Thickener Systems for Aluminum Complex Greases, National Lubricating Grease Institute Education Course, Kansas City, MO. 10. Fagan, G. (1989) Polyurea and Complex Soap Greases, National Lubricating Grease Institute Education Course, Kansas City, MO. 11. Christiano, A. and Fessenbecker, A. (2004) Polyurea Grease Safe and Simple, Lubes-n-Greases, 10, 30–34. 12. Nye Lubricants, Inc. (1997) Synthetic Lubricants Engineering Reference Card, Nye Lubricants Inc., Fairhaven, MA. 13. Swingler, J. and McBride, J.W. (1999) “The Degradation of Road Tested Automotive Connectors,” IEEE Holm Conf. on Electrical Contacts. 14. Horn, J. et al. (1995) “Avoiding fretting corrosion by design,” AMP Journal of Technology, 4, 4–7. 15. Sparks, G. and Akin, K. (2003) “Evolution, development, and testing of automotive electrical terminal interface greases,” Proceedings of 36th Annual IICIT Connector & Interconnection Symposium, Orlando, FL. 16. Galary, W. (1999) “Ultraclean grease? No, It’s not an oxymoron!” Journal of Advancing Applications in Contamination Control, 2. 17. Antler, M. (1987) “Sliding studies of new connector contact lubricants,” IEEE Transactions, CHMT-10, 35–44. 18. Marchetti, M., Jones, Jr., W.R., and Sicre, J. (2003) “Relative lifetimes of MAPLUB greases for space applications,” Lubrication Engineering, 59, 11–15.

29

Compressors and Pumps Kenneth C. Lilje CONTENTS 29.1 29.2

Introduction Compressors 29.2.1 Dynamic Compressors 29.2.2 Positive-Displacement Compressors 29.2.2.1 Reciprocating Compressors 29.2.2.2 Rotary-Screw Compressors 29.2.2.3 Other Rotary Compressors 29.2.3 Compressor Applications for Synthetic Lubricants 29.2.3.1 Air Compressors 29.2.3.2 Gas Compressors 29.2.3.3 Refrigeration 29.3 Vacuum Pumps 29.4 Liquid Pumps References

29.1 INTRODUCTION Compressors and pumps are used to move materials for a large variety of purposes. Applications for these machines are in industries such as steel, petroleum, chemical, mining, food, gas, production and storage, energy conversion (refrigeration), etc. Their shutdown means loss in production. Compressors and pumps transfer gases, liquids, or sometimes slurries of liquid-solid mixtures. Lubricants in these applications lubricate moving parts such as bearings and gears, provide a liquid seal, and remove heat. This can be a difficult task as the lubricant often operates in a hostile environment. There are many reasons for using a synthetic lubricant in almost any type of machine. An individual synthetic may have specific advantages but none is superior in all respects. Typically compressor and pump applications have some characteristic or group of desirable properties that contributes to a synthetic’s performance advantages over mineral oils. Synthetic fluids can operate at higher temperatures, exhibit better low-temperature fluidity and pour points, and are less volatile than equiviscous mineral oil counterparts. Similarities exist between the design of compressors and the design of pumps. Two classifications for compressors are dynamic and positive-displacement compressor.

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Dynamic machines include centrifugal compressors and axial compressors. These types of compressors develop pressure by the action of a rotating blade, which imparts velocity and pressure to the flowing medium. Examples of positive-displacement compressors include reciprocating, rotary screw, rotary vane, lobe, and scroll. Positivedisplacement compressors confine successive volumes of gas in a closed space and elevate them to a higher pressure. Vacuum pumps are compressors that operate using suction pressure to create vacuum. Classifications for liquid pumps are similar to compressors (e.g., centrifugal and positive displacement). The latter includes vane, screw, reciprocating, gear, and lobe.

29.2 COMPRESSORS A detailed discussion of compressors is beyond the scope of this chapter but is available [1,2]. A brief description of these machines and their lubrication requirements helps to provide an understanding of how synthetic lubricants improve their performance. Examples of these compressors appear in Figure 29.1.

29.2.1 Dynamic Compressors Dynamic compressors handle significant flows at relatively high speeds. Multistage compressors are required for

Dynamic Axial

Radial

Rotary Single screw

Liquid ring

Screw

Rotary lobe

Vane

Displacement

Reciprocating Trunk

Crosshead

Diaphragm

Diaphragm “Oil free”

FIGURE 29.1 Various compressor types

higher pressures. A speed-increasing gear usually drives these machines. The lubricant reduces friction and prevents wear in bearings and gears. Oil is not meant to pass into the gas stream. Various methods of shaft sealing are used due to the variety of gases used and applications. These include labyrinths, carbon rings, contact seals, and bushings. The lubricant may act as a sealing fluid or otherwise aid in the operation of these seals (i.e., hydraulic action). Small amounts of lubricant may enter the gas stream through seal leakage. Conversely, gas may enter into the lubricant system. In some cases the gas provides a positive pressure to the lubricant reservoir to prevent leakage of air into the system (as with refrigeration and some chemical applications).

29.2.2 Positive-Displacement Compressors 29.2.2.1 Reciprocating compressors There are several types of reciprocating compressors. Lubrication points include cylinders, valves, pistons, piston rings, crankshafts, connecting rods, main and crank pin bearings, and other associated parts. Double-acting machines use crossheads and crosshead guides with connecting pins to join the crosshead to connecting rods. Most single-acting compressors use connecting rods attached directly to the pistons with wrist pins or piston pins. “Oil-free” machines do not require lubrication in the compression area.

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Cylinder lubrication includes cylinder parts, pistons, rings, valves, and rod packings. Crankcase parts include main and crank pin, crosshead (or wrist pin) bearings, and crossheads and crosshead guides. Additionally, the lubricant may help the efficiency of seals and minimize their wear. The crankcase on reciprocating compressors may either be open to the cylinders (as in many vertical, Vtype, and radial compressors) or sealed from the cylinder by a bulkhead and exposed to air (horizontal compressors). Bearing and other crankcase components require relatively large amounts of lubricant, which is usually supplied from the crankcase. Supply methods include “splash” (utilizing dippers in the oil), “flooded” (devices to lift the oil such as disks, screws, groves, or oil ring gears), and “forced-feed” systems. Cylinder lubrication is either “splash” from the crankcase or “force-feed” from either the crankcase or a separate reservoir. Ideally, the minimum amount of lubricant that is used must provide a strong lubricant film (to minimize wear and friction, to seal piston rings, valves, and rod packings), remove heat, and prevent corrosion. Machines with the crankcase open to the cylinder may experience gas leaks past the oil control rings and into the oil. Oil is fed to the cylinder walls and piston rod packings with a force-feed lubrication system in systems where the crankcase is not open to the cylinder. In the latter case, essentially all the oil fed to the cylinder eventually leaves the compressor with the gas.

29.2.2.2 Rotary-screw compressors Screw compressors [3] are constant-volume and have a built-in compression ratio. Compression in the single-stage double-helical type occurs through the meshing of two rotors in a one-piece, dual-bore cylinder. The cylinder has air inlet passages, oil injection, a compression area, and discharge ports. Rotors are designated as male, with helical lobes, and female, with corresponding helical grooves. In oil-flooded machines, the lubricant is injected into the compression area affording sealing via an oil film between the intermeshing screws and removal of the heat of compression. Oil separators are used to remove the oil from the discharge gas. “Dry-screw” machines utilize timing gears to position the screws so that no internal lubrication is required. Liquid-injected single-screw compressors are constantvolume, variable-pressure machines. Compression results from the intermeshing of a single screw with one or two gate rotors. The screw and casing combine to act as a cylinder. The gate rotor acts as a piston. The screw also provides the action of a rotary valve, the screw and gate act as a suction valve, and the screw and casing (port) serve as a discharge valve. There is a relatively low amount of friction between the screw and gate as the screw supplies nearly all the compression. Bearings may be lubricated by grease or fluid depending upon design.

29.2.2.3 Other rotary compressors There are two common types of small vane compressors, fixed-vane and rotating-vane compressors. Both types of compressors provide positive-displacement, nonreversing compression. The fixed-vane type uses a ring or roller, which rotates around an eccentric shaft. A single vane is mounted in a nonrotating cylinder housing. The rotatingvane compressor has a rotor concentric with the shaft and off-center with respect to the cylinder housing. The rotor is equipped with radially sliding vanes, which are forced against the cylinder walls by centrifugal force. Gas is trapped between the vanes and wall, where it is compressed due to a reduction in volume. The lubricant in rotary-vane compressors helps to provide a seal between the sliding vanes and the cylinder (or ring) wall. Larger systems may use oil pumps. Adequate lubrication should be provided to the vanes, vane slots, bearings, and seal faces. The oil to the cylinders may be supplied from the bearing lubricant discharge. The lubricant also prevents gas leakage in rotating-shaft seals. The basic compression unit in a scroll compressor is a set of two scrolls, one fixed and the other moving in a controlled orbit around a fixed point. Areas of lubrication include a short throw-crank mechanism, bearings, and the scroll tip. Sealing is achieved through very accurate machining, proper balancing of pressures between scrolls,

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linkage mechanisms, and sometimes a sealing element at the tip of the involute. Other types of rotary compressors include the lobe and liquid piston or liquid ring, which require no internal lubrication.

29.2.3 Compressor Applications for Synthetic Lubricants 29.2.3.1 Air compressors The major reason for selection of synthetic oils for air compressors is their stability in the presence of air and moisture. Air contains about 21% by volume oxygen, which reacts with hydrocarbon oils (oxidation) to form organic acids, carbon oxides, varnishes, sludge, and hard, carbon like deposits. Water vapor can condense as the compressed air is cooled. This water may cause corrosion, solubilize metals, or form emulsions. This not only interferes with compressor lubrication but also promotes more rapid deterioration of the oil. Certain metals such as iron and copper catalyze these reactions. The acids and sludge formed promote additional rapid deterioration of the oil [4]. Other considerations for selecting a synthetic lubricant are safety, reduced maintenance, and the potential to reduce energy requirements. Each type of compressor can take advantage of these benefits. 29.2.3.1.1 Reciprocating air compressors Conventional mineral oils produce carbonaceous deposits on valves, heads, discharge ports, and piping. The safety aspects of an air compressor lubricant are major areas of concern [5]. Explosions and fires in the compressor and piping of oil-lubricated air compressors have occurred. The following explanations for these explosions and fires have been developed over the past 50 years but remain essentially the same today [6]. The majority of these occurrences are the result of oxidized oil residuals (as carbon–oxygen complexes) on compressor discharge components and in the piping. The deposit continues to oxidize, in the presence of air and iron oxides, to eventually produce enough heat to ignite [7]. The temperature and oxygen partial pressure are also key factors. Fires and explosions are more common when oxidation of carbon and oily deposits are accompanied by temperatures above 300◦ F (149◦ C) and pressures above 100 psig (690 kPa) [8]. Deposits on discharge valves can lead to recompression of the gas due to valve sticking. This in turn can generate excessive discharge temperatures. Oil decomposition products in intercoolers and aftercoolers reduce their efficiency. Low volatility reduces the chance of a vapor fire and resulting explosion if excessive oil is present [9]. The ignition source is usually related to carbon deposits or valve failure. The low carbon-forming tendencies of

1100 1000 900 Temperature,°F

Phosphate Ester 800

Phosphate Ester W/Iron Oxldes Polyol Ester Diester, 100 ISO

700 600

Polyalphaolefin 500

Mineral Oil #1

400

Mineral Oil #2

A B

300 0

30

60

90

Mineral Oil #2 W/Iron Oxides

C 120 160 Pressure, PSIG

180

210

240

FIGURE 29.2 Autoignition of synthetic and mineral oils compared to discharge pressures and temperatures: (a) Single stage, (b) Two stage, (c) Three stage

many synthetics as well as their higher flash, fire, and autoignition temperatures reduce this hazard. Figure 29.2 illustrates higher autoignition temperatures for synthetic fluids at elevated air pressures. This information depicts common values for new, formulated compressor oils. Deterioration (through oxidation) will lower the autoignition temperature as exemplified by the lubricants containing iron oxides [10]. The discharge temperatures are for reciprocating compressors with inlet temperatures of 21◦ C (70◦ F) at all stages. Actual discharge temperatures will vary with cylinder size, degree of cylinder cooling, compression ratio, rpm, and other design variables [11]. Discharge temperatures for these reciprocating air compressors can easily reach 230◦ C (450◦ F), which is near the reduced autoignition of mineral oils at 135 psi (931 kPa) [12]. Excessive oil accumulation in the air system can propagate a fire. The special case of detonation, caused by the development and propagation of shock waves, is attributed to this type of fire. A simplified explanation follows. As the fuel burns, hot vapors evolve and expand, and pressure waves push into the unburned gas. These waves cause the unburned gas to develop extreme pressures and heat. The flame that follows affords an explosion in the piping, coolers, or receiver. Phosphate esters. Phosphate ester lubricants were originally selected for their fire-resistant nature [13]. Problems can occur when the lubricant degrades to form by-products that are aggressive toward paints and elastomers in older machines. Higher feed rates may be required than with mineral oils and there can be problems with close-tolerance lubrication between aluminum and cast iron cylinders. The high phosphorus content in these products can cause

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disposal problems. Even with these problems, phosphate esters continue to be used in high-pressure multistage machines and other selected applications [14]. Fires and explosions can occur even with the use of fire-resistant synthetic oils such as phosphate esters if they are allowed to accumulate in the air system [15]. Lower feed rates to compressor cylinders and oil/air separation equipment may be required to reduce this hazard. Devices have been developed to deliver smaller and more accurate amounts of lubricants [7]. Di-, tri-, and tetraesters and polyol esters. These fluids have low vapor pressures at elevated temperatures when compared to equiviscous mineral oils. This property, good oxidative stability, and an affinity to metal surfaces make it possible to use lower amounts of ester-type synthetics for cylinder lubrication. The feed rate for diester can be lowered to 50 to 65% of a conventional mineral oil [8,16]. Polyol esters with low volatility, excellent stability, and high viscosity index (VI) allow a feed rate of about 25% of a mineral oil. The actual feed rate will depend on the machine design and the specific ester’s properties. The lower carbon-forming tendency of esters helps to keep discharge valves, cylinder walls, intercoolers, aftercoolers, and piping clean. This reduces the fuel/ignition source for fires. Another obvious advantage of reduced feed rates to compressor cylinders is the reduction in lubricant usage. The cleanliness and good solvent action of the esters help to prolong the maintenance intervals of piston rings and valves. There have been several documented cases of prolonged maintenance intervals of two to four times that experienced with mineral oils [8,17,18]. At least one investigator reported superior results with diesters as opposed to triesters (trimellitate) [19].

There have been many commercial claims that synthetic lubricants are more efficient and afford lower energy consumption than petroleum oils. This has been attributed to the low coefficient of friction of esters, viscosity stability, and cleanliness. One study showed an average savings of 6.6% in kilowatt-hours consumed for a group of 23 reciprocating compressors ranging in size from 25 to 100 hp [20]. Polyalkylene glycols (PAG). Polyalkylene glycols are not generally accepted as lubricants for air compressor applications. This is due to their relatively poor volatility, their tendency to form volatile decomposition products, and their poor compatibility with mineral oils. Blends of polyalkylene glycols and esters overcome these difficulties [21]. Polyalphaolefins (PAO). These products have been formulated to have low volatility and low carbon-forming tendency. This has led to cleaner operation and reduction of fires in critical installations. Performance in a 120-hp two-stage reciprocating compressor operating at a discharge temperature of 392◦ F (200◦ C) and pressure of 100 psig (690 kPa) was still good after 16,000 h of operation [22]. Other fully formulated PAO based lubricants have surpassed the requirements of the ISO DP 6521 specifications [21]. PAOs have been blended with esters to improve their solvency and with oil-soluble silicones to reduce cylinder feed rates [7]. When deposits are formed they are either very sticky (polymers) or hard varnishes (as with paraffinic oils). Another benefit of PAO based

lubricants is their compatibility with elastomers and paints found in older machines that are designed for use with mineral oils. Other types. Other types of synthetic oils have been used for reciprocating air compressor applications. Fluorosilicone lubricants have been shown to reduce or eliminate air compressor explosions. Their high cost is offset by reduction in feed rates to 5% of that with mineral oils [23]. These oils have good lubricity with steel but may cause seizure with aluminum. 29.2.3.1.2 Rotary-screw air compressors The lubricant in a rotary-screw air compressor is circulated through a system that includes injection into the rotors. This design exposes the lubricant to high shear conditions. The oil also sees discharge conditions of high temperature, high moisture, high oxygen concentrations, and metal catalysts. Both thin-film and bulk oxidation conditions exist. The presence of moisture promotes hydrolysis and may promote the catalytic action of metals. Thermal stability is important as the lubricant is exposed to the heat of compression. Conventional mineral oils deteriorate in a relatively short time under these conditions. Table 29.1 lists the desirable and critical characteristics for these lubricants [24,25]. Most synthetic lubricants listed will provide drain intervals of 8000 h when operated in a normal environment and with discharge temperatures up to 180◦ F (or 90◦ C) and pressures below 690 kPa (100 psig). Use of the different lubricant classes is mainly

TABLE 29.1 Properties of Rotary-Screw Air Compressor Lubricantsa Property Oxidation resistance Flash point Poor point Volatility Lubricity Demulsibility Nonfoaming Rust and corrosion inhibited Hydrolytic stability Nontoxic Material compatibility

Diester

Polyol ester

Polyglycol and ester

PAO

Silicone

G VG VG VG G G VG G

E E E E V G V G

V V G G V P V G

V V V V G E V V

E E E V F E G F

Gb G Fd

Gb G Fd

G G Fe

E E E

E Gc Ef

a P, poor; F, fair; G, good; VG, very good; E, excellent. b Requires special additives. c Chlorinated additives. d Swells certain elastomers and may dissolve plastics. e Not compatible with certain plastics. f Silicone lost through separators may cause problems in painting operations.

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250

% Viscosity increase

100

Discharge 220-230°F Ambient 120-130°F Pressure 100 psi

Diester HVI R&O Turbine oil

90 80 ATF

70 60

PAO-1 PAO-2

50 40

Polyol Ester

30 20

Glycol/ Ester blend

10 0

200 400

800

1200

1600

2000

3000

3400

4800

5200

Hours of operation

FIGURE 29.3 High-temperature compressor test results

TABLE 29.2 Efficiency Loss in Rotary Screw Compressors Problem Viscosity increase or air-end varnish Blocked air/oil separator, P + 10 psi Excessive discharge temperature 18◦ F (10◦ C)

Penalty (%) 3–5 3–5 1–3

due to concerns with material compatibility, volatility, and operating life at higher temperatures or in high humidity. Figure 29.3 shows the effect of high discharge temperatures for various synthetic lubricants. Most of these tests were conducted by a major compressor manufacturer in a 25-hp compressor operating with discharge temperatures from 220 to 230◦ F (104 to 110◦ C) and were reported in earlier literature [24–28]. The expected life of these lubricants at standard temperatures of 180 to 190◦ F (or about 85◦ C) is about four times that shown for the elevated temperature. Energy savings are possible with synthetic lubricants. Conversations with original equipment manufacturers (OEM) suggest the penalties are attributable to using unstable oils (Table 29.2). Careful selection of a synthetic lubricant will prevent these penalties in a properly maintained compressor. Most of these fluids can reduce or eliminate separator blockage and varnish formation. Heavy varnish increases energy consumption and can restrict rotor movement. The result can be air-end failures through excessive wear of rotors and bearings. A stable viscosity and good lubricity can reduce friction and increase efficiency. Viscosity stability and cleanliness can improve oil-side heat transfer. Some of the synthetics have higher thermal conductivity, which can improve heat transfer. Diester and triester lubricants.Diester and triester based rotary-screw air compressor lubricants offer the

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advantages of being a natural detergent and of not producing insoluble varnishes or heavy polymers. This detergency does not always end problems with separator blockage. One study showed that coalescer blockage with a diester was only slightly better when compared to a mineral oil and significantly worse than a PAO compressor oil [29]. Esters dissolve varnishes leftover from mineral oils and thus can improve the efficiency of a dirty machine (vide supra). A study of 11 machines (40 to 300 hp) using diester lubricant showed that rotary-screw compressors might benefit from reduced energy requirements averaging 9.3% (kilowatt hours consumed) [20]. The study attributed energy saving to “friction reducing.” Esters, depending on the type (e.g., adipate, phthalate, trimellitate, etc.), usually increase the organic acid level and viscosity change during extended use at higher air compressor discharge temperatures (above 210◦ F). This could lead to mechanical failures or corrosion problems [19,24,25]. Both base fluid and additives must be carefully selected to avoid these problems. Diesters have a wide range of viscosity indices (VIs), depending on type and initial viscosity grade. They do not always meet rotary-screw compressor manufacturer minimum VI requirements (usually at least 90). A viscosity requirement at 210◦ F (or 100◦ C) is sometimes specified by the OEM. Diesters that have poor VIs may have too high a low-temperature viscosity for cold starting conditions. Adipate-type diester lubricants (or a blends) typically meet both requirements. Polyol esters. Polyol esters have not been used extensively for rotary-screw air compressors. This is typically due to their higher cost. These fluids have good oxidative and thermal stability [25]. Earlier formulations were limited by the availability of additives that would enhance the performance of these fluids. Long-term operation in

rotary-screw compressors at higher temperatures requires antioxidants and rust and corrosion inhibitors that are not volatile and do not deplete too rapidly. Newly developed additives and increased availability of these fluids (some improved) should result in their increased use. The polyol esters have low volatility for a given viscosity grade. This helps to limit their consumption through the use of highefficiency oil separators. They have excellent lubricity (elastohydrodynamic), VIs, and low-temperature properties. Many of these fluids are biodegradable, an important factor considering that water containing some lubricant is drained from aftercoolers and receivers. Polyalkylene glycols. Polypropylene glycols blended with polyol esters provide long life in compressors with discharge temperatures up to 230◦ F (110◦ C) [26]. Polypropylene glycols by themselves have deficiencies. They tend to wet metal poorly, which can lead to rust formation in humid conditions. The ester is added to compensate for this deficiency. Polypropylene glycol has excellent hydrolytic stability and less water absorption than other types of polyalkylene glycols. Good vapor pressure characteristics are achieved with the higher-viscosity fluid chosen for the blend (1200 molecular weight). Like the esters, the polyglycol/ester blend was reported to remain clean upon failure, producing “volatile components rather than cross-linking to viscous gums.” Phosphate esters. Phosphate esters, except as additives, are not normally used in rotary-screw compressors due to their rapid breakdown and formation of acids. The exception is critical applications that require the use of a “fire-safe” lubricant. In these instances the phosphate ester must be changed more frequently than other types of synthetics, usually every 500 to 1000 h. The alternative is an “oil-free” compressor where the phosphate ester may be used in anticipation of seal leakage. Polyalphaolefins. The PAO based synthetic hydrocarbon oils have been used extensively for rotary screw compressors. They are often preferred over esters for use in standard 100 psig (690 kPa), 180◦ F (90◦ C) applications. The PAOs have excellent hydrolytic stability as well as compatibility, not only with rubber and plastic materials in the compressor, but also in the compressed air system [27]. They are also compatible with mineral oils and common additives. These features make compressor conversions from mineral oils simple and help to prevent problems with materials and equipment used in the compressed air system. The PAOs have very little effect on swelling of rubber or elastomers. It is very common to add ester to increase seal swell and to help solubilize additives and contaminants. The PAO based compressor oils have longer drain intervals (ca. 30%) than do diesters. Their low water absorption and rapid water separation result in improved rust and corrosion protection and help water to be easily drained from the oil reservoir. PAO’s high VI and low volatility allow the

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use of lower viscosity grades. This combined with excellent low-temperature fluidity reduces power consumption during start-up in cold environments. The PAO based air compressor formulations that meet U.S. Department of Agriculture and Food and Drug Administration requirements for incidental food contact [30] are available. These lubricants may see increased use in Great Britain, where white mineral oils have been eliminated for food applications [31]. The PAOs are not considered mineral oils and thus have not been banned for use with food by that government. Most other areas of the world accept the U.S. regulations, especially where food is imported into their country. These lubricants are recommended for drain intervals of 4000 h for standard applications [27]. Dimethyl silicone based fluids have an excellent VI, thermal, oxidative and hydrolytic stability. Additives improve its otherwise poor lubricity with metals. A specially formulated dimethyl silicone rotary-screw air compressor lubricant has been marketed since the 1970s [24]. Several compressors have been in operation for 40,000 h. In most cases the results have been favorable [27]. Maintenance of the air–oil separator is critical as excessive oil carryover is expensive. In some cases, for example, painting operations, the dimethyl silicone can deposit on production parts and cause manufacturing problems. 29.2.3.1.3 Rotary-vane air compressors Flooded rotary-vane compressors benefit from the same synthetic lubricant properties described for rotary-screw compressor oils (vide supra). Many of these machines use a higher viscosity grade than the screw. An ISO 100 blend of PAO and phthalate esters was examined in two small (5.5 and 7.5 hp) air-cooled machines [32]. Severe test conditions were used: (a) High temperature (140◦ C), (b) High moisture, (c) Oxidants present, (d) Stop and Go operation, and (e) Caustic environment. The results were determined to be favorable after 3000 to 3500 h of operation as judged by relatively unchanged viscosity and acid number. The latter was considered important for maintaining a constant seal for stable air pressure. Exceptionally low oil consumption resulted in the lubricant not having a detrimental effect on ozone synthesis in a corona discharge process. Diester compressor oils are commonly used in vane compressors. The natural detergent action of these fluid helps to prevent sticking caused by deposits in the rotor slots of sliding-vane machines. Higher-viscosity polyol esters should be particularly useful in machines operating with high discharge temperatures. Some types of watercooled machines have discharge temperatures above 325◦ F (163◦ C). Some vane machines are equipped with plastic or composite vanes. The manufacturer should be consulted regarding the compatibility of these materials with esters (most are compatible).

29.2.3.1.4 Centrifugal and “oil-free” compressors Synthetic lubricants provide a wide operating temperature range, better heat transfer, lower energy requirements, and reduced hazard (if seal leakage occurs). Polyol esters are used for service in lobe compressors where high temperatures occur. One case involved the use of the lobe compressor as a blower for 600◦ F (315◦ C) air [27]. The polyol ester reduced bearing deposits (and failures), provided adequate viscosity for lubrication, and provided more efficient heat removal. The mixing of PAO with mineral acids results in, at most, very low exotherms. This is due to their saturated hydrocarbon structure. Because of this, the use of specially formulated PAO air compressor lubricants is permissible in chemical plant operations where leakage through seals could result in exothermic reactions. One such case is in ammunition plants where concentrated nitric and sulfuric acids are used. 29.2.3.2 Gas compressors The lubrication of gas compressors encompasses many different types of gas, which can be categorized as inert, highly soluble, or reactive. The International Standards Organization (ISO) has suggested further

classifications under ISO 6743/3 as shown in Table 29.3. It is recommended that these classifications be used for reference only and that the lubricant supplier and the equipment builder be consulted. In some cases these gases are divided into categories that relate to their industrial uses, for example, oil refinery, chemical, halogen, polymer, landfill, etc. (33). The use of synthetic lubricants in these varied applications requires a variation of the ISO method of categorization. The type of gas (hydrocarbon, carbon dioxide, etc.), the functionality of the lubricant, and performance of the compressor must all be considered. There are three distinct areas of concern in gas applications: solubility, reactivity, and effect of lubricant as a contaminant in the compressed gas. The first two affect the compressor performance and the latter the gas application. The solubility of a gas in the lubricant is a major concern. Excessive dilution may cause a reduction in viscosity and a loss of film thickness of the lubricant. The lubricant can be washed off wear surfaces by liquid components of the gas. Additional problems can occur when there is a reduction of pressure and degassing takes place (foaming, cavitation, and loss of lubricant film). The solubility of the lubricant in the gas can result in loss of lubricant by absorption of the lubricant into the gas

TABLE 29.3 Draft ISO DP 6743/3 B Gas Compressor Lubricants Symbol

Application

DGA

Inert gas

DGB DOC

Inert gas, moisture High solubility

DGD

Chemical reaction

DGE

Dry inert/reducing gas

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Application example <1500 psi Nitrogen Hydrogen Ammonia Carbon dioxide Argon All pressures Helium Sulfar dioxide Hydrogen sulfide <150 psi Carbon monoxide As for DGA Hydrocarbons >1500 psi Carbon dioxide Ammonia Hydrogen chloride Chlorine Oxygen >150 psi Carbon monoxide Nitrogen Hydrogen 1500 psi argon

Lubricant type Mineral oil or synthetic

As for DGA plus additives Synthetic

Nonhydrocarbon fluids

Synthetic

phase [34]. This can result in high lubricant feed rates and a source of contamination to the gas. Reactions of the gas with the lubricant can result in premature failure of the compressor or, in more severe cases, fires and explosions. The lubricant or additives may react with or inhibit catalysts, cause mechanical problems in the application (valves, etc.), or plug areas of gas flow. 29.2.3.2.1 Hydrocarbon gas applications Hydrocarbon gases are encountered in the collection and transmission of natural gas, in vapor recovery, landfill gas compression, and in the chemical industry (84). Synthetic oils are selected for their unique viscosity– temperature relationships or for their resistance to dilution by hydrocarbons. Compressed natural gas and other hydrocarbon gases are used to fuel gas turbines. The compressor supplies the gas at the flow rate and pressure needed for continuous operation of the turbine. Petroleum based lubricants carried in the gas may produce carbonaceous deposits in the gas inlet nozzles of the turbine, restricting flow and causing flameout. Hydrocarbon gases are often the feedstock for a chemical process. Examples include the manufacture of polyethylene and polypropylene. Synthetic oils are often used for these applications because they do not react with or inhibit the catalysts. Reciprocating compressors applications. For pressures below 1000 psig, ISO 100–150 mineral oils may be used. Problems occur when the gas is wet or at increased pressures. The addition of fatty oils is common. These additives are difficult to pump at low temperatures, can cause damage to discharge valves, accumulate in aftercoolers and piping, and emulsify with water. Detergent-type heavy-duty engine oils have been used in sour gas (H2 S) applications. High-pressure reciprocating compressors (5000 psig) are used to reinject natural gas into crude. Four basic problems have been identified [34]: 1. Loss of lubricant viscosity. 2. Increased cylinder surfaces by liquid components in the gas. 3. Loss of lubricant to the high-pressure gas stream. This resulted in feed rates to rod packings of 10 times normal rates or up to a barrel of lubricant per day per compressor. 4. Reaction of additives with well-bore fluids, leading to permanent impairment to the well and resulting in reduced gas-injection rates. The study showed that the use of an ISO 200 PAG would solve all of these problems. The higher VI of the PAG resulted in a higher initial viscosity (undiluted) at compressor discharge temperatures. Resistance to dilution by hydrocarbon gases resulted in a diluted viscosity in the

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cylinder of about twice that of the diluted ISO 680 mineral oil based cylinder lubricant. It was shown that the PAG did not adsorb in the gas phase, while the mineral and acidless tallow is nearly completely adsorbed. Field trails showed a 20-fold increase in the life of pressure packings and a reduction in overhaul maintenance from eight times per year to once per year. High feed rates with mineral oils can cause problems in natural-gas pipeline booster compressors. Excessive oil downstream reduces the volume within the pipeline and leads to a significant reduction in pipeline efficiency. Silicone “semisynthetic” blends with white oils (sometimes PAOs) are used in combination with microlubrication hardware to lower cylinder feed rates as much as 95% from that with mineral oils [35–37]. These systems have been in operation in more than 230 natural-gas pipeline booster compressors in the United States since 1981. The reduced feed rates and the use of the synthetic oil have resulted in longer life of the cylinder ring. One report showed no measurable wear after 2 years. Discharge valve life is improved by decreasing carbon buildup. The lower feed rates from microlubrication systems result in lower oil costs. The payback for the initial cost of the hardware and lubricant is less than 1 year and subsequent years show lower operating costs [38]. Rotary-screw compressors. Viscosity is the most critical lubricant requirement that must be met in the rotaryscrew compressors for hydrocarbon gases. Viscosity may be lowered as the hydrocarbon gas in the compressor and oil separator dilutes the lubricant. The final level of dilution is determined by the temperature and pressure in the separator, which is located on the discharge side of the compressor. Synthetic lubricants offer the advantage of very high viscosity and, in some cases, their resistance to dilution (lower solubility with hydrocarbon gases). The PAGs have reduced solubility with hydrocarbon gases. Different types of PAGs can offer unique solubility characteristics, depending on their chemical structure. Polypropylene glycols are used with lighter hydrocarbons. Advantages such as higher volumetric efficiency and energy savings have been proven and are often the main criteria in their selection. The inclusion of ethylene subunits in the PAGs structure reduces hydrocarbon solubility. A copolymer of ethylene and propylene oxide will afford 10 to 20 wt% hydrocarbon solubility before the fluid is saturated. Water solubility is increased but controllable, as these fluids exhibit inverse water solubility at temperatures above 140 to 160◦ F (60 to 70◦ C). Solubility with water at lower temperatures as well as the use of specifically designed additives helps control corrosion, particularly where H2 S is present, by reducing water on the metal surfaces. Essentially complete resistance to normal alkane dilution is possible with glycols based on ethylene oxide. Fallingball viscosities carried out at 13,790 kPa (2,000 psi) with a

typical wellhead gas proved no loss in viscosity. Although these fluids are water soluble, lubricity is not reduced (four-ball tests) with up to 7% water in the lubricant [39]. Propane compressors may gain up to 18% improvement in volumetric efficiency with certain PAGs [25]. The PAO lubricants also show efficiency improvements. A methane gas compression application at a cogeneration plant showed a 2% increase in volumetric efficiency, without increased power consumption [39]. The compressor was equipped with a slide valve allowing it to run in an unloaded mode when demand was less than output capacity. With the synthetic lubricant, less power was used to drive the compressor, with more frequent operation in the unloaded mode. The PAO was originally chosen for improved water separation and low-temperature fluidity, as the oil reservoir was located outdoors. 29.2.3.2.2 Reactive gases The use of “nonlubricated” compressors is common in the chemical industry. There may still be some chance of the gas contacting the lubricant (e.g., a seal leak). Each type of synthetic lubricant has a unique chemical functionality. This feature provides the opportunity to select a lubricant that will not chemically react with the gas. This property has led to the use of selected synthetics in lubricated compressors of reactive gasses. In some cases the lubricant must provide a barrier to corrosive attack on the compressor materials. The impact of the lubricant on the particular chemical process (e.g., catalyst interaction) must also be considered. A general overview of the use of synthetic lubricants with reactive gasses follows: 1. Oxygen compressors are usually the nonlubricated type. Highly fluorinated lubricants such as perfluoroethers are used. 2. Chlorine and hydrogen chloride compressors are usually nonlubricated types with halogenated lubricants used to lubricate mechanical parts. The lubricants are either the fluorinated (e.g., perfluoroethers or fluorosilicones) or may be chlorofluorocarbon lubricants. Some silicones have excellent chemical stability and protect metal surfaces from chemical corrosion. These have been combined with PAOs or with severely hydrotreated hydrocarbons or both together to provide the same metal protection as with the more expensive all-silicone fluids [25,40]. They are effective in many process gas applications involving chlorosilanes, methyl chloride, hydrogen chloride, and other chlorinated compounds. Applications involving vent gases (off gases) can contain water and can be extremely corrosive. Successful operation is achieved at temperatures above the dew point of water and purging with a dry, inert gas upon shutdown [39]. 3. Hydrogen sulfide, nitrous oxide, and sulfur dioxide all require lubricants that are dry. The later two are

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soluble in mineral oil and therefore reduce its viscosity. The PAOs have a low tendency to absorb moisture and are available in high-viscosity grades and are suitable for these applications. The blended silicone described above has also been used for its additional corrosion protection. 4. Ammonia compressors typically use hydrocarbon lubricants. Hydrotreated mineral oils give extended life compared to naphthenic oils. PAOs and polyglycols are also used is some applications. Ester lubricants cannot be used as they react with the ammonia [41]. 29.2.3.2.3 Inert gases . Inert gases are classified as such because they are typically chemically unreactive and do not lead to general lubrication problems. Only highly purified mineral oils are used, as polar contaminants lead to general lubrication problems. Synthetics are preferred for improved stability and for prevention of catalyst poisoning. Additives must also be carefully evaluated for similar reasons. The use of rotary-screw compressors with oil separators for these applications has resulted in the increased use of synthetics with low volatility. This helps reduce contamination of the gas. Food-grade PAOs are used in carbon dioxide (CO2 ) compressors where the gas is later used in food products. The PAGs are commonly used in both hydrogen and helium applications. PAGs of the oxyethylene/oxypropylene copolymer types have shown good lubricity in hydrogen applications with reciprocatingcompressor polytetrafluoroethylene (PTFE) packings and compression rings and are compatible with plant processes. PAOs have replaced PAGs in many hydrogen rotary-screw compressor applications for cost reasons as well as for their compatibility with equipment and processes. 29.2.3.3 Refrigeration The use of synthetic lubricants in refrigeration compressors has changed dramatically over the past 15 years. The main driver of this change has been the phase out of chlorofluorocarbon (CFC) refrigerants. This has led to the development of alternate refrigerants [42,43] with properties that preclude the use of traditional mineral oils (vide infra). The choice of refrigerant will influence the compressor system design and the characteristics required of the lubricant. Centrifugal compressors present a simple problem. There is little contact between the refrigerant and the lubricant. The lubricant in these machines may be selected to prevent problems associated with seal leakage (lubricant into the system) or where the refrigerant has contact with the oil reservoir. Reciprocating and rotary (screw, scroll, and vane) compressors present a more complicated situation because there is significant interaction between the refrigerant and the lubricant [44].

Q0

3

2

Condenser

Expansion valve

Motor

Compressor High-pressure side Low-pressure side

4

W

(Solubility)

(Miscibility)

Evaporator Qi (Refrigeration load)

1

FIGURE 29.4 Refrigeration cycle

Refrigeration lubricants may be required to provide many years of service without makeup and with a minimum of maintenance. Final compression temperatures may reach 320◦ F (160◦ C) for some applications and unsuitable oils may form carbonaceous deposits. In the special case of hermetic compressors the motor materials must not be adversely affected by the lubricant/refrigerant mixture or from by-products from its deterioration. This requires a lubricant that has excellent thermal and chemical stability and produces a minimum of deposits. Figure 29.4 shows a simplified diagram of the refrigeration process. A liquid refrigerant vaporizes in the evaporator to provide the required cooling. The vapors then proceed to the compressor where they are compressed to condensation pressure. The superheated gas is condensed to a liquid in the condenser using a cooling medium such as water or air. The liquid refrigerant then passes through an expansion valve (to reduce pressure, and thus boil) and returned to the evaporator where the cycle starts again. The lubricant in compression refrigeration systems has an influence on the operation and efficiency of the entire system [45]. Some lubricant is carried out of the compressor and into the system. The interactions of the refrigerant/lubricant pair will impact the return of this oil to the compressor. The lubricant must act as a compression sealing aid and reduce wear and friction in the compressor without adversely affecting the operation of the filter dryers, condenser, expansion valve, or evaporator. The lubricant must also be compatible with the materials of construction used in the entire system. The behavior of the oil/refrigerant pair is of major importance. The solubility of the refrigerant gas in the lubricant impacts compressor performance and the miscibility of the liquid refrigerant with the lubricant affect system performance. Dissolved gas in the lubricant reduces its viscosity. This can lead to excessive wear and inefficient compression. Miscibility is important for design of components and

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piping to allow uniform oil movement through the system and back to the compressor. Heat-transfer problems are more significant in systems where the oil is immiscible or partly miscible with the refrigerant. The lubricant has more effect on the performance of a screw compressor than with a reciprocating compressor, primarily due to the difference in design of their oil systems. The screw compressor injects oil at discharge pressure into the compression chamber. This oil is then removed from the compressed gas by the use of an oil separator and sump situated on the highpressure side of the system. The screw compressor needs a lubricant with limited solubility of the refrigerant gas at discharge conditions (at the oil separator) to achieve high performance. Limited solubility will reduce or eliminate bypass of refrigerant from discharge to suction or to a lower situated thread. External bypass caused by the refrigerant circulating with the oil is also reduced. This leads to both high volumetric efficiency and low torque. Most lubricants with low refrigerant solubility also have low miscibility. In some cases a synthetic lubricant can meet the requirement of low solubility while maintaining good miscibility. This combined with low volatility reduces oil in the system and improves heat transfer [46]. Synthetic lubricants offer a wide range of properties and the opportunity to customize a lubricant for a particular refrigeration system. They have been considered for refrigeration applications since 1929 [47] and have continued to show improvements in performance properties compared to mineral oils [48]. Properties of synthetic base stocks as they relate to refrigerant compression appear in Table 29.4. Of particular interest is the miscibility of these fluids with various refrigerants, as exemplified in Figure 29.5. Typical applications appear in Table 29.5. Polyalphaolefins. Polyalphaolefins (PAOs) have been extensively used in refrigeration compressor applications because of their high VI, low-temperature fluidity, and excellent thermal and chemical stability. The PAOs have good miscibility with R-12. Superior chemical and thermal stability have reduced the risk of carbonizing at high temperatures in heat pumps with R-12 and R-114 [25,49]. Superior adiabatic efficiency (3 to 10%) is achieved in rotary-screw compressors using these refrigerants with PAO compared to naphthenic refrigeration oils. This efficiency improvement is largely attributed to the higher viscosity of the PAOs at higher temperatures in the presence of the refrigerant. Superior performance and reliability have been achieved in reciprocating, twin-screw, and single-screw compressors [50]. Lower evaporator temperatures are permissible with PAOs than with mineral oils because PAOs are wax free and have good low-temperature fluidity. Low-temperature fluidity is the major reason PAOs have been used in the United States for relatively insoluble refrigerants such as R-13 and R-503. The lubricant viscosity, ISO 15 or 32, is selected by considering operating viscosity

TABLE 29.4 Properties of Synthetic Refrigeration Lubricantsa Synthetic hydrocarbons

Esters

Properties

PAO

Alkylbenzene

Polyalkylene glycol

Dibasic

Polyol

Chemical stability Thermal stability Miscibility (polar refrigerant) Volatility Low temperature Viscosity temperature Water adsorption Mineral oil compatibility

E VG P E VG VG E E

VG VG VG G G F G E

G Gd E G G E P P

Gb G VG VG VG G F VG

Gb VGe E E VG VG F G

Silicate Gc G E VG VG VG F P

a P, poor, F; fair; G, good; VG, very good; E, excellent. b Additives may be required; reacts with ammonia (R-717). c Hydrolyzes to form gels and solids. d Decomposes at 500◦ F; additives nay be required. e Additives required above 200◦ C.

Key One phase Two phases

20 PAO

Temperature,˚C

0

–20

PAO * Alkyl Bengone

*Complex ester critical solution temperature is below -68˚C

–40

Polyglycol

Mineral oil

–60 Alkyl benzene 0

20

40

60

80

100

% oil by weight

FIGURE 29.5 Miscibility characteristics for various fluids with HCFC-22

in the compressor as well as low-temperature fluidity below −73◦ C (−100◦ F) in the direct expansion dry-type evaporator system [51]. PAO applications with R-22 are limited, due to low miscibility, to systems that limit the amount of the oil leaving the compressor. Dry expansion type evaporators are used (similar to R-13 applications) or flooded evaporators with oil-skimming devises. Polyalphaolefins with low volatility have been used in very-low-temperature (−118◦ C [−180◦ F]) ethylene

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systems. Separators can effectively control the amount of lubricant in the low-temperature side of the system. Careful selection of oil viscosity provides sufficient lubricant film to lubricate compressor components in the presence of the gas. The small amount of miscible lubricant is diluted in the evaporator and can be easily returned. There are no problems of wax or viscous liquid formation as found with some mineral oils. The PAOs and “semisynthetic” hydrotreated isoparaffinic mineral oils have been found to provide several

TABLE 29.5 Typical Applications for Refrigeration Lubricants Refrigerant Chlorofluorocarbons (CFC) Hydrofluorochlorocarbons (HCFC) Highly fluorinated HCFC Hydrofluorocarbons (HFC)

Ammonia Propane/hydrocarbons

Synthetic product Poly(α-olefins) Alkylbenzenes Complex esters Polyol esters Polyalkyene glycols Polyalkyene glycols Polyol esters Other esters Poly(α-olefins) Hydrotreated “semisynthetic” Polyalkylene glycols Poly(α-olefins) Esters

performance advantages in ammonia systems [52,53]. Better thermal and chemical stability with ammonia results in reduced sludge and varnish and has resulted in extended drain intervals [54]. Lower solubility helps improve lubrication and reduces foaming. Lower volatility reduces oil consumption and improves heat transfer by limiting the amount of oil on heat-exchanger tubing. The excellent low-temperature fluidity and high VI of the PAO fluid allows for evaporator temperatures below −46◦ C (−50◦ F) and, at the same time, provides sufficient viscosity for higher compressor-operating temperatures. Good lowtemperature fluidity facilitates oil removal in most systems. These PAO and semisynthetic hydrocarbon ammonia lubricants can have materials compatibility issues with some elastomers. This problem is alleviated with appropriate additives [55]. The PAOs have only seen limited use in hydrofluorocarbon (HFC) applications due to their immiscibility with these refrigerants. They are being used in extremely low-temperature applications where their low-temperature fluidity affords sufficient oil return [56]. PAO lubricants are also used in carbon dioxide systems where miscibility is not required [57,58]. Alkyl benzenes. Alkyl benzene synthetic hydrocarbon oils have good chemical stability and good miscibility with R-22 and R-502. They have somewhat improved miscibility with more highly fluorinated CFC and HCFC refrigerants such as R-13 and R-503. Alkyl benzenes relatively low cost compared to other types of synthetics has made their use common with these moderately polar refrigerants. The improved miscibility of the alkyl benzenes has led to their use with more environmentally safe HCFCs such as R124 [59] and blends of HCFCs with HFCs [60]. Others have evaluated the use of alkylbenzenes with R-134a in rotary compressors [61].

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Alkyl benzenes are commercially available in ISO viscosity grades as high as 68 or 100. This has restricted their use where the solubility/viscosity relationships indicate a chance of overdilution. Compressors with oil reservoirs on the high-pressure side, such as rotary-screw types, are of particular concern. The viscosity–temperature relationship of the oil may be improved by increasing the carbon number of alkyl chains, at the expense of reduced miscibility. Formulations comprising blends of alkyl benzene with mineral oils or with a PAO may overcome these deficiencies. Private reports indicated that blends with PAO might separate in the liquid refrigerant in the evaporator [51]. Polyalkylene glycols. Polyalkylene glycols (PAGs) have excellent miscibility with polar refrigerants, good lubricity, and good low-temperature fluidity. Major drawbacks include their tendency to adsorb water, low compatibility with mineral oils, and the requirement of additives for good chemical and thermal stability. New developments with structural changes show promise in overcoming these deficiencies. Polypropylene glycols have been used in R-12 heat pump applications in rotary-screw compressors [47,62]. The PAGs have excellent viscosity–temperature characteristics and reduced solubility with R-12. Efficiencies achieved were similar to those with PAO. The PAGs have also been used with R-22. When carefully selected, these oils have complete miscibility to temperatures below −73◦ C (−100◦ F), even at concentrations over 50% by weight with R-22. Higher-viscosity-grade PAG fluids have low miscibility with some highly fluorinated CFCs such as R-13 (chlorotrifluoromethane). Polyalkylene glycols are miscible with HFC such as HFC-134a and also with blends of HFC and HCFCs. This has resulted in their initial use with HFC-134a in automotive air conditioners [63–65], rotary-screw compressors [64,46], and mobile refrigeration [66]. Increasing the viscosity of polyalkylene glycols reduces miscibility, especially at higher temperatures. There have been some lubricity problems with these highly fluorinated refrigerants, particularly with higher loads in reciprocating-type compressors and with aluminum surfaces. Problems associated with water and materials compatibility have limited their use in small hermetic machines. “Modified” polyglycols have provided somewhat better performance [54,67]. Rotary-screw compressors have shown improvements in volumetric efficiency (+2%), refrigeration capacity (+21%), and coefficient of performance (+12%) in constant-pressure-ratio comparisons with CFC-12 [46,68]. The CFC-12 data was obtained using an equivalent viscosity (at compressor discharge temperature) PAO as the lubricant. The polyglycol has excellent miscibility with R-134a at condenser and evaporator conditions but becomes less soluble within the compressor rotor bores. High viscosity

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60 45 30 Temperature,°C

during the compression cycle results in more efficient sealing between the rotors and between rotor and compression cylinder walls. The PAGs are used with hydrocarbon refrigerants for the properties described in the hydrocarbon gas section (vide supra). These lubricants are easily drained from the bottom of evaporators due to their higher density. Specially designed PAGs are also used in ammonia systems. Their structure is modified to provide partial [69] to complete [70] miscibility. The use of these type of lubricants improves system efficiency, particularly when DX type evaporators are used. The PAGs are also being evaluated for use in carbon dioxide refrigeration systems [57,58,71]. Diesters. Diesters have been recognized for their potential in R-22 applications, as they are widely available and have excellent miscibility. Major problems may exist with these materials due to poor stability with R-22 and a significant effect on the swelling of many elastomers [47]. An additional restriction for the use of these fluids in rotary-screw compressors with R-22 is their limited range of viscosity grades (up to ISO 100). Neopentylpolyol esters. Neopentylpolyol esters (POEs) were reported for use in low temperature (−80◦ C [−112◦ F] evaporator temperature) R-22 systems as long ago as 1968 [47,72]. Due to their polar nature these products tend to absorb more moisture than mineral oils. Additives may be used to enhance the performance of these lubricants [73]. Lower viscosity grades of neopentylpolyol esters, to 32 ISO, are miscible with the more polar refrigerant such as HFC-134a [74]. Higher-viscosity polyol esters with selected chemical structures have been described for HFC-134a [75,76]. Because of the variety of polyols and acids available, lubricant suppliers are able to provide equiviscous fluids with different miscibility characteristic. This can lead to optimized compressor and system performance. Figure 29.6 exemplifies this [77]. Considerable additional development of POEs for uses with HFC refrigerants has occurred over the last 12 years. Leading references are available [78–80]. High-viscosity, ISO 100-320, complex esters were found to improve adiabatic and volumetric efficiencies in twin-screw compressors using HCFC-22 [81]. These oils were developed to have moderate to low dilution effects due to solubility while maintaining good miscibility. Their good miscibility (to below −90◦ F) has also led to their use in low-temperature applications. Polyol esters have also seen significant use in carbon dioxide refrigeration [82–88]. Silicate esters. Silicate esters have been used at very low temperatures (with good miscibility) with highly fluorinated CFC refrigerants such as R-13. Problems have been reported that are associated with hydrolytic stability and the formation of varnishes or solids [89]. Different structures may solve these problems [47].

15 Miscible 0 –15 Immiscible

–30

Ester A Ester B

Immiscible

–45 –60 0

10

Immiscible 20 30 Weight % oil

Ester C 40

FIGURE 29.6 Miscibility of various ISO 32 polyol esters with HFC-134a

Phosphate esters. Phosphate esters, such as tricresyl phosphate, are used as lubricity additives. Their use as primary lubricants for refrigeration has been eliminated due to poor viscosity–temperature relationships and the formation of acids at higher temperatures [47]. Fluorinated lubricants. Fluorinated lubricants such as perfluoroethers and fluorosilicone fluids are extremely miscible with nearly all halocarbon refrigerants. Their high cost has been a limiting factor for use in refrigeration compressors. Fluorosilicone fluids are extremely miscible with HFC134a. Compressor tests with 100 ISO fluorosilicone lubricants in automotive air-conditioning applications resulted in bearing failures with aluminum components [90]. What is of current interest is the partial fluorination of at least one alkyl end-cap of polyalkylene glycols to improve their miscibility with HFC-134a [91]. Another approach has been to blend a chlorotrifluoroethylene polymer with PAGs [92]. Either method is said to result in miscibility with HFC-134a throughout the operating range for air-conditioning applications.

29.3 VACUUM PUMPS The same oils used for air compressors are suitable for most industrial vacuum pump applications. Synthetic oils with lower vapor pressures are used to achieve higher levels of vacuum without requiring a substantial increase in viscosity. These oils include the esters and PAOs previously described. Other types of synthetic fluids are used for their chemical compatibility with the gases being pumped. Diffusion pumps require lubricants that have been molecularly distilled for ultrahigh vacuum. Halogenated lubricants are used for their high chemical resistance to acids, alkalis, and corrosive gases, and their nonmiscibility with many common solvents. Perfluoroethers and CFCs are used extensively for plasma etching

in industries such as semiconductor manufacturing and for producing aluminum chloride. The perfluoroether can be used with pure oxygen and resist polymerization or the formation of nonvolatile residues when subjected to electron bombardment in sputter ion pump applications [93]. The perfluoroethers can breakdown in the presence of certain Lewis acids at temperatures above 210◦ F (100◦ C) to form toxic fragments [94]. Polyphenyl ethers and alkyl silicones have been used for high-vacuum applications as they are thermally and chemically stable [95]. Fluorosilicones have better chemical stability.

29.4 LIQUID PUMPS The use of synthetic lubricants for pump applications is limited to those applications either requiring compatibility with the material being pumped or having temperature requirements. The latter includes high-temperature applications where mineral oils may break down and applications where improved heat-transfer properties of selected synthetics help remove excess heat. A few examples of the variety of applications follow. The superior lubricity of some synthetic fluids provides better lubrication to seals and packings. One example is the reciprocating pump. The biggest maintenance problem with these pumps is the packing. There are many causes of short packing life, one of which is lack of lubrication. Mineral oils with tallow additives have been used to provide tenacity for the plunger surface to improve the lubricant film between plunger and packing. It was shown in previous sections that PAGs, silicones, and halogenated lubricants provide this same type of action in the presence of hydrocarbons that would wash away the tallow. Other synthetics are selected to resist washing away by the specific material being pumped. Centrifugal pumps are widely used in the chemical industry. Fluorosilicone lubricants have been applied successfully on several seal arrangements to eliminate product leakage and extend seal life. These lubricants are resistant to temperatures as high as 500◦ F and to many chemicals and solvents that attack mineral oils; however, they are not suitable with ketones [96]. Mineral oils and greases may break down at temperatures as low as 250◦ F (120◦ C), causing further temperature increases. Friction caused by packings rubbing on the shaft can easily generate these temperatures. The chemical being pumped is often at temperatures between 300 and 700◦ F (150 and 370◦ C). One method of heat removal is to use a double inside mechanical seal with a thermal convection lube system. The advantage of this system is that it normally requires very little attention. A molecular film of lube is maintained on the seal faces to provide lubrication. A low-viscosity PAO has been used as the sealing and lubricating fluid. The fluid heats up in the pump stuffing

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box, rises, flows back to the supply tank, and is replaced by cool fluid from the supply tank. This is a thermal convection circulation system. A thin fluid is used for good circulation and to prevent openings in the seal faces. Diaphragm pumps have been used for paint applications in the food industry. The fluid in one of these applications lubricates a reciprocating pump, which provides the pulsating action and acts against the diaphragm. There is the possibility that the diaphragm could develop a leak that could remain unnoticed for some time. Synthetic fluids provide a broad enough selection to insure that the fluid is compatible with the paint and also is “food grade.” A final example is the use of phosphate esters as lubricants for water-reactor coolant pump motors. Fires had occurred when the oils used to lubricate primary system pump motors leaked onto hot primary piping. The oil is pressurized in the oil lift, so it is sprayed on surrounding pipes if a leak occurs. Several lubricants were tested for the required fire-resistant properties and adequate stability, including radiation resistance. These included mineral oils, diesters, methyl alkyl silicones, and phosphate esters. It was found that mineral oils soaked in pipe insulation and maintained at temperatures above 375◦ F (190◦ C) eventually undergo exotherms to temperatures as high as 580◦ F (305◦ C). Storage temperatures for this type of exotherm to occur for other fluids were: diester, 425◦ F (218◦ C); silicone, 400◦ F (204◦ C); and phosphate ester, 575 to 625◦ F (301 to 329◦ C). The temperature at which exotherms occurred was higher than the 550◦ F (288◦ C) operating temperature for the reactor’s coolant pumps [97].

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30. Miller, J.W., “New synthetic food grade rotary screw compressor lubricant,” Lubr. Eng., 40, 433–436, 1984. 31. Ministry of Agriculture, Fisheries & Food. “Government to ban use of mineral hydrocarbons in food,” MAFF News Release, 53/89, February, 1989. 32. Legeeron, J.P. and Beslin, L., “Rotary-vane compressors: some technical aspects of long-life lubricants,” J. Synth. Lubr., 6, 229–309, 1989. 33. Compressed Air and Gas Institute. Compressed Air and Gas Handbook, 5th ed., Prentice-hall, Englewood Cliffs, NJ, 1973. 34. Matthews, P.H.D., “The lubrication of reciprocating compressor,” J. Synth. Lubr., 5, 271–290, 1989. 35. Lyons, R.L. and Van de Bogert, D.L., “A positive microlube technique for industry,” Lubr. Eng., 30, 648–650, 1983. 36. Miller, J.W., “Microlubrication of natural gas compressors with synthetic lubricants,” Fluids Lub. Ideas, September/October, 1980. 37. Van de Bogert, D.L., “Microlubrication control,” U.S. Patent 4,467,892, 1984. 38. Miller, J.W. and Krukowski, B.D., “Microlubrication cuts gas-transmission-line contaminants and improves flow,” Oil Gas J., July, 1989. 39. Tolfa, J.C., “Synthetic lubricants suitable for use in process and hydrocarbon gas compressors,” Lubr. Eng., 47, 289–295, 1991. 40. Miller, J.W., “Synthetic lubricants and their industrial applications,” J. Synth. Lubr., July, 1984. 41. Sumersmith, D., Selection of Oils and Lubricant System Design for Ammonia and Methanol Synthesis Plant Compressors, AMPO 78, Billingham Press Limited, Stockton, England, 1978. 42. Cohen, R. and Groll, E.A., “Update on refrigerant compressors in light of CFC substitutes,” IIR Bull., 96.5, 3–19, 1996. 43. Cavallini, A., “Working fluids for mechanical refrigeration,” Int. J. Refrig., 19, 485–496, 1996. 44. Short, G.D., “Refrigeration and Air Conditioning,” CRC Handbook of Lubrication and Tribology, Vol. III, CRC Press, Inc., Boca Raton, FL, pp. 387–408, 1994. 45. Hewitt, N.J., McMullan, J.T., Mongey, B., and Evans, R.H., “From pure fluids to zeotropic and azeotropic mixtures: the effects of refrigerant-oil solubility on system performance,” Int. J. Energy Res., 57–67, 1996. 46. Sjöholm, L.I. and Short, G.D., “Twin screw compressor performance and suitable lubricants with HFC-134a,” Proceedings of the International Compressor Engineering Conference, Purdue University, pp. 733–740, 1990. 47. Sanvordenker, K.S. and Larime, M.W., “A review of synthetic oils for refrigeration use,” ASHRAE Trans., 78, part 2, 1972. 48. Spauschus, H.O., “Evaluation of lubricants for refrigeration and air conditioning compressors,” ASHRAE J., 26, 59, 1984. 49. Kruse, H.H. and Schroeder, M., “Fundamentals of lubrication in refrigeration systems and heat pumps,” ASHRAE J., 26, 5–9, 1984. 50. Daniel, G., Anderson, M.J., Schmid, W., and Tokumitsu. M., “Performance of selected synthetic lubricants in industrial heat pumps,” J. Heat Recov. Sys., 2, 359–368, 1982.

51. Short, G.D., “Synthetic lubricants and their refrigeration applications,” Lubr. Eng., 46, 1990. 52. Short, G.D., “Hydrotreated oils for ammonia refrigeration,” Technical Papers, 7th Annual Meeting, International Institute of Ammonia Refrigeration, pp. 149–176, 1985. 53. Lilje, K.C. and Rajewski, T.E., “A review of lubricant chemistry for use in ammonia refrigeration systems,” 22nd Annual Meeting, International Institute of Ammonia Refrigeration, pp. 205–223, 2000. 54. Short, G.D., “Refrigeration lubricants update: synthetic and semi-synthetic oils are solving problems with ammonia and alternative refrigerants,” Technical Papers, 12th Annual Meeting, International Institute of Ammonia Refrigeration, pp. 19–53, 1990. 55. Watson, M.C., Lilje, K.C., Hayes, P., and Bellas, D.R., “Seal conditioning lubricants as part of a strategy for improved ammonia refrigeration performance,” Proceedings of the International Conference on Compressors and their Systems, ImechE, London, England, pp. 81–88, 2003. 56. Short, G.D. and Rajewski, T.E., “Refrigeration LubricantsCurrent Practice and Future Development,” Proceedings of Tsinghua-HVAC-95-Beijing, pp. 303–310, 1995. 57. Li, H. and Rajewski, T.E., “Experimental study of lubricant candidate for the CO2 refrigeration system,” Proceedings of the 4th IIR-Gustav Lorentzen Conference on Natural Working Fluids at Purdue, pp. 409–416, 2000. 58. Li, H., Lilje, K.C., and Watson M.C., “Field and laboratory evaluations of lubricant for CO2 refrigeration,” Proceedings of the 2002 International Refrigeration Conference at Purdue, R11-5, 2002. 59. Reed, P.R. and Spauchus, H.O., “HCFC-124: Applications, properties, and comparison with CFC-114,” ASHRAE J., 33, 40–41, 1991. 60. Bateman, D.J. et al., “Refrigeration blends for the automotive air conditioning aftermarket,” SAE technical paper 900216, International Congress and Exposition, Detroit, MI, 1990. 61. Sunami, M., Takigawa, K., and Suda, S., “New immiscible refrigeration lubricant for HFCs,” Proceedings of the International Refrigeration Conference at Purdue, pp. 129–134, 1994. 62. Shoemaker, B.H., “Symposium, synthetic lubricating oils,” Ind. End. Chem., 42, 2414, 1950. 63. El-Bourini, Hayahi, K., and Adachi, T., “Automotive air conditioning system performance with HFC-134a refrigerant,” SAE technical paper no. 900214, International Congress and Exposition, Detroit, MI, 1990. 64. Struss, R.A., Henkes, J.P., and Gabbey, L.W., “Performance comparison of HFC-134a and CFC-12 with various heat exchangers in automotive air conditioning systems,” SAE technical paper no. 900598, International Congress and Exposition, Detroit, MI, 1990. 65. Sundaresan, S.G., “Status report on polyalkylene glycol lubricants for use with HFC-134a in refrigeration compressors,” Proceedings of the ASHRAE/Purdue CFC Conference, pp. 138–144, 1990. 66. Bock, W. and Fahl, J., “Lubricating oils for use in mobile refrigerators,” DKV-Tagungsber, 25, 179–193, 1998. 67. Kaneko, M., Konishi, T., Kawaguchi, Y., and Takagi, M., “The Development of PAG Refrigeration Lubricants for

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84. O’Malley, S., “Applications of synthetic lubricants in process and hydrocarbon gas compressors,” IMechE Conf. Trans. (6, Compressor and Their Systems), 117–125, 1999. 85. Bock, W., “Compressor oils for natural refrigerants,” Ki LuftKaeltetech, 34, 337–341, 1998. 86. Fahl, J., “Lubricants for use with carbon dioxide as refrigerant,” Ki Luft-Kaeltetech, 34, 375–379, 1998. 87. Renz, H., “Semi-hermetic reciprocating and screw compressors for carbon dioxide cascade systems,” Proceedings of the 9th Annual Conference of the British Institute of Refrigeration, London, 2000. 88. Roth, R. and Konig, H., “Experimental studies on the operational behaviour of CO2 cascade refrigerating plant,” DKV-Tagungsbericht, 28(Vol. 2, Pt. 2), 33–43, 2001. 89. Downing, R. and Cooper, W.D., “Operation of the Three Stage Cascade System,” presented at ASHRAE Meeting, Nassau, 1972. 90. CPI Engineering Services, Inc. Internal correspondence on compressor testing with fluorosilicone lubricant and HFC134a with air conditioning compressor builder, Midland, MI, 1986.

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91. Short, G.D., “Rotary displacement compression heat transfer systems incorporating highly fluorinated refrigerantÄSynthetic oil compositions,” U.S. Patent no. 4,916,914, 1990. 92. McGraw, P.W. and Ward, E.L., “Lubricants for refrigeration compressors,” U.S. Patent no. 4,851,144, 1989. 93. Baker, M.A., Holland, L., and Laurenson, L., “The use of perfluoroalkyl ether fluids in vacuum pumps,” Vacuum, 21, 479, 1971. 94. Leybold-Heraeus Vacuum Products. Engineering Notes, Vacuum Pump Fluids, revised, Export, PA, 1986. 95. Holland, L. et al., “Pollution free high vacuum,” Physics, 23, 1972. 96. Miller, J.W., “Super-lube systems eliminate shaft-seal leakage,” Chem. Eng., 88–90, 1973. 97. Pietch, H., “Evaluation and test of improved fire resistant fluid lubricants for water reactor coolant pump motors, Fluid lubricants for water reactor coolant pump motors,” Fluid Evaluation, Bearing Model Tests, Motor Tests, and Fire Tests, prepared for Electric Power Research Institute, Vol. 1, EPRI NP-1447, 1980.

30

Refrigeration Lubricants Dr Steven James Randles CONTENTS 30.1 Intoduction 30.1.1 A Potted History of Refrigeration 30.1.2 The Move Away from CFCs 30.1.3 An Overview of a Basic Refrigeration System 30.1.3.1 The Compressor 30.1.3.2 The Condenser 30.1.3.3 The Filter Drier 30.1.3.4 The Expansion Device 30.1.3.5 The Evaporator 30.2 Desirable Properties of Refrigeration Lubricants 30.3 Historical Development 30.3.1 Earlier Uses of Synthetics in Refrigeration Lubricants 30.3.2 The Need for Synthetics 30.4 Types of Synthetic Used 30.4.1 Polyol Esters (POEs) 30.4.2 Polyalkylene glycols (PAGs) 30.4.3 Polyvinylether (PVEs) 30.4.4 Alkyl Benzenes (ABs) 30.4.5 Additives used in Refrigeration Applications 30.4.5.1 Storage Stabilizers (Typical Dose Rate 0.05 to 0.1%) 30.4.5.2 Antiwear Additives (Typical Dose Rate 0.1 to 5%) 30.4.5.3 Copper Deactivators (Typical Dose Rates 0.0001 to 0.3%) 30.4.5.4 Acid Catchers (Typical Dose Rates 0.1 to 1%) 30.4.5.5 Foaming/Defoaming (Noise Reducing) Agents (Typical Dose Rates 0.0001 to 0.3%) 30.5 Optimizing Performance Characteristics 30.5.1 HFC and HCFC 30.5.1.1 Reliability 30.5.1.2 Efficiency 30.5.1.3 Noise Reduction 30.5.2 Carbon Dioxide 30.5.2.1 Lubricant Transport 30.5.2.2 Wear 30.5.2.3 Stability 30.5.3 Ammonia (R-717) 30.5.4 Hydrocarbons (R-600a, R-290) 30.6 Current Commercial Practice 30.6.1 Synthetic Lubricants in Use 30.6.1.1 Domestic Appliance 30.6.1.2 Industrial and Commercial Refrigeration and Air-Conditioning 30.6.1.3 Automotive Air-Conditioning 30.6.1.4 List of Suppliers 30.6.2 Current Market Size 30.6.3 Incentives to Growth

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30.7

Future Market Trends 30.7.1 Market Drivers 30.7.2 Synthetics under Development 30.8 Conclusions References

30.1 INTODUCTION 30.1.1 A Potted History of Refrigeration Ancient Hebrews, Greeks, and Romans placed large amounts of snow into storage pits dug into the ground and insulated it with wood and straw. By 500 b.c. the Egyptians and Indians were using evaporative cooling. They filled earthen jars with boiled water and put them on their roofs, thus exposing the jars to the night’s cool air. By 1550, lower temperatures were achieved by adding chemicals such as sodium nitrate to water. In 1748, William Cullen was using volatile liquids such as ethyl ether boiling in a partial vacuum. Oliver Evans first proposed a closed cycle of refrigeration using volatile liquid in 1805. Jacob Perkin actually designed such a system and obtained a British Patent in 1835. Jacob Perkin’s vapor compression machine never advanced beyond the experimental, but his concept was developed into commercial use decades later. The earliest successful vapor compression system used ether. In 1869, ammonia refrigerants found their first successful commercial use. About the same time carbon dioxide was used commercially followed by sulfur dioxide in the 1880s, methyl chloride in 1884, ethyl chloride in 1870, and iso-butene in 1920 [1]. In the 1930s, scientists looking for a safe and effective refrigerant discovered a group of chemical compounds known as chlorofluorocarbons (CFCs). CFCs were found to have a number of properties that made them ideal for use as refrigerants and for a number of other purposes. They proved so useful that until very recently, thousands of tonnes of CFCs were manufactured and used throughout the world.

30.1.2 The Move Away from CFCs Conducting business in the 21st century will depend on the ability to create products and services that generate economic prosperity and contribute to environmental quality in a socially responsible and equitable manner. Over the last decade, industry has faced up to two pressing environmental challenges: 1. The need to move away from chemicals with high ozone depleting potential (ODP) and meet the targets outlined in the Montreal Protocol

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2. The need to move toward products that result in reduced global warming potential (GWP) and meet the targets outlined in the Kyoto Accord The Montreal Protocol led to the phaseout of ozone depleting CFC and hydrochlorofluorocarbon (HCFC) refrigerants and the introduction of refrigerants with zero ODP. Once it was realized that CFC usage needed to be phased out, other chemicals had to be found to replace them in essential applications. Many substances can be used as refrigerants. Most commonly used refrigerants are substances that can be changed easily from liquid to a gas and back again. These substances can be split into four main groups: 1. “Natural refrigerants” such as CO2 , iso-butane and ammonia. 2. CFCs, which are composed of the elements chlorine, fluorine, and carbon only, for example, R-12. 3. HCFCs, which contain hydrogen in addition to chlorine, fluorine, and carbon, for example, R-22. 4. Hydrofluorocarbons (HFCs), which contain hydrogen, fluorine, and carbon but no chlorine, are the newest group of compounds, for example, R-134a. Refrigerants that are used commercially are often denoted by the abbreviations such as HFC-, HCFC-, HFC-, R(for refrigerant), or a trade name (e.g., Klea-) followed by a standard number designated by the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE). The numbering system introduced by ASHRAE refers to the chemical structure of the refrigerant. Refrigeration equipment consumes electricity that is generally produced by burning fossil fuels that emits CO2 into the atmosphere. This gas is the main contributor to greenhouse gas emissions that can lead to global climate change. The GWP is an index that relates the potency of a greenhouse gas to that of CO2 over a time frame of 100 yr (Table 30.1). By the simple fact of consuming energy over its lifecycle, any refrigeration system contributes to climate change. This “indirect” effect can represent more than 84% of the impact. The remaining 16% are direct effects from refrigerant emissions [3]. To meet Kyoto Accord targets, effort has therefore been concentrated on improving the energy efficiency of refrigeration systems. Mandatory legislation

(e.g., EPA targets for the U.S. appliance industry) and voluntary schemes (e.g., eco labels such as “Energy Star”) have been used to ensure compliance to these targets.

30.1.3 An Overview of a Basic Refrigeration System

pressure, temperature, and boiling point of the refrigerant above that of the surrounding air. Compressors for domestic appliances are hermetically sealed. They are housed in a welded can and are therefore sealed-for-life. Compressors for other application areas can be hermetic, semihermetic, or open depending on the degree of access to the internal components of the compressor.

Figure 30.1 shows a simple schematic of the basic components contained within a refrigeration system.

30.1.3.2 The condenser

30.1.3.1 The compressor The refrigerant is drawn into the compressor and compressed into a smaller volume. In doing so, the refrigerant molecules are squeezed together causing their temperature and pressure to be increased. When the pressure of the refrigerant is increased, the boiling point also increases. The main purpose of the compressor is therefore to raise the

TABLE 30.1 ODP and GWP of Several Classes of Refrigerants [2] Chemistry

ODP

GWP (After 100 years)

Hydrocarbon (R-600a) Ammonia R-134a R-410A R-404A R407C R-22 R-12

0 0 0 0 0 0 0 0.055 1

1 3 2 1313 1739 3278 1538 1890 8500

Refrigerant Natural

HFC

HCFC CFC

CO2 1

HEAT

The refrigerant can then pass through an in-line filter drier. This removes contamination (water, acid, and wear debris) from the refrigerant liquid before it reaches the expansion device. Filter driers are typically molecular sieve, activated alumina or mixtures thereof.

The refrigerant enters the expansion device as a liquid at high pressure. The function of the expansion device is to regulate the flow of the liquid refrigerant into the evaporator and thereby reduce the pressure. The most common type of expansion device is a capillary tube that consists basically of a narrow bore copper Compressor

Low Pressure Side

IN

30.1.3.3 The filter drier

30.1.3.4 The expansion device

1 Carbon Dioxide produced from industry waste

4) Gas at Low EVAPORATOR Pressure

Basically, the condenser is like a radiator. The refrigerant gas enters the condenser at a relatively high temperature and pressure. The temperature of the refrigerant is reduced by the cooling medium (air for small units) until it begins to condense and form a liquid. This involves a change in state causing heat to be rejected. This explains why the back of a domestic refrigerator gets hot. The refrigerant then flows under the influence of gravity from the condenser as liquid at high pressure.

1) Gas at High CONDENSER Pressure

HEAT

High Pressure Side

OUT

IN-LINE DRIER 3) Liquid at Low Pressure

Expansion Device (capillary tube)

FIGURE 30.1 Schematic of a basic domestic appliance refrigerator

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2) Liquid at High Pressure

tube (typically 0.02

). Capillary tube restrictions operate on the principle that, by mass, liquid passes through them much more rapidly than vapor. System cleanliness is of critical importance so as to avoid any blockage in the capillary tube. A second type of expansion device is the thermal expansion valve (TXV). A thermal sensing device is used to exert a pressure on an internal diaphragm. As the superheat rises, the thermal load increases and the resultant force on the diaphragm is transmitted by a mechanical linkage to a variable office orifice, forcing it open to admit more refrigerant. Capillary-based expansion devices are used in domestic appliance application while TXVs are favored in the industrial commercial sector. 30.1.3.5 The evaporator There are two main types of evaporator. In dry evaporators, vapor occupies a considerable part of the volume. In flooded evaporators, the refrigerant space is largely filled with liquid. Flooded evaporators provide more rapid cooling, because the rate of heat transfer to liquid refrigerant is higher than that of a refrigerant vapor. Liquid refrigerant enters the evaporator at a pressure such that it will boil readily. This involves a change in state and heat is absorbed (latent heat of evaporation), hence it is cold inside the refrigerator. As the refrigerant passes through the evaporator, heat flows into it so that the boiling process continues. When the refrigerant reaches the outlet of the evaporator, it has completely vaporized and becomes a gas. Typically, the refrigerant is slightly superheated and the pipe to the compressor is lagged to ensure that no liquid reaches the compressor. The refrigerant now enters the compressor as gas at low pressure and the refrigeration cycle begins again.

• Have low hygroscopicity (low water uptake) • Have high thermal conductivity (good coolant) • Have good electrical resistivity and breakdown voltages

(for compressors with internal switches and motors) • Be environmentally acceptable (no handling problems), • Be compatible with materials of construction of the

compressor • Be soluble with the refrigeration gas, mineral oil, and

additives (no transport or heat transfer problems)

30.3 HISTORICAL DEVELOPMENT 30.3.1 Earlier Uses of Synthetics in Refrigeration Lubricants The first use of synthetic lubricants dates back to 1929 when the first synthetic oil manufactured was thought to be of use in ice making equipment. Fifteen years later polyalkylene glycols (PAGs) were considered for the same application. The mid-fifties saw the introduction of alkylbenzenes (ABs) [5]. Polyol esters (POEs) were used with R-22 systems, with evaporator systems of −80◦ C, in the late 60s [6]. The limited solubility of mineral oils with R-502 and R-13 initially led to the first in-depth investigation of synthetic oils for refrigeration use. As a result, ABs were found to give satisfactory performance in these systems [4]. Sanvordenker [5] was one of the first to characterize the suitability of a wide range of synthetics (diesters, polyols, PAGs, phosphate esters, and ABs) for use with R-22 and R-502. However, until the phaseout of CFCs, for reasons of cost, the use of synthetic lubricants has been limited.

30.3.2 The Need for Synthetics 30.2 DESIRABLE PROPERTIES OF REFRIGERATION LUBRICANTS The prime purpose of a refrigeration lubricant is to: 1. Act as an oil seal (at pistons, valves, gland seal, etc.) for compressed gas between suction and discharge sides in a compressor 2. Act as a coolant to remove heat from the crankcase to the compressor exterior 3. Reduce noise generated by moving parts in the compressor 4. Lubricate internal parts Other desirable properties of a refrigeration lubricant is to [4]: • Provide good energy efficiency • Be chemically stable

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In the past, compressors in refrigeration systems have been lubricated with mineral oils. However, they have poor performance with several classes of zero ODP refrigerants (e.g., HFCs and CO2 ). The main reason for this is their poor solubility. Poor solubility can give rise to several potential problems, namely: 1. Formation of lubricant-rich liquid plugs inside the condenser causing the system to splutter as they pass through the expansion device 2. Build-up of oil on the evaporator walls leading to reduced heat transfer and poorer energy efficiency 3. Poor oil transport resulting in the compressor being starved of oil Table 30.2 shows the compatibility of synthetic lubricants with a range of refrigerants.

O

TABLE 30.2 Suitability of Lubricants for a Variety of Refrigerants

H3C

CH2

CH2 CH2

C

Valeric (linear C5) acid CFC/HCFC HFC Hydrocarbon Ammonia CO2

MO

AB

PVE

PAG

POE

Yes No Yes Yes No

Yes No Possible Yes No

No RV No No No

No Auto Possible DX Yes

Possible Yes Possible No Yes

MO = Mineral oil; AB = Alkyl Benzene; PVE = Poly Vinyl Ether; PAG = Poly Alkylene Glycol; POE = Polyol Ester. Possible = Could be used but has relatively small market share; RV∗ = Primarily used in rotary-vane compressors; Auto = Primarily used in auto air-conditioning only; DX = Primarily used with systems containing direct exchange evaporators.

CH2OH

CH3 HO CH2 C

CH2OH

HO CH2 C

CH2OH

CH3

CH2OH

Neopentyl glycol (NPG)

Pentaerythritol (PE)

CH2 OH HO CH2 C

CH2

CH2OH O

CH2 C

CH2OH

CH2 OH

CH2OH

Dipentaerythritol (DiPE)

FIGURE 30.2 Schematic of alcohols used in refrigeration lubricants

30.4 TYPES OF SYNTHETIC USED 30.4.1 Polyol Esters (POEs) Neopentyl POEs are made by reacting a polyhydric alcohol and monobasic acid under conditions of elevated temperature and pressure to form an ester and water. The ester is neutralized to a low acid value, typically less than 0.04 mg KOH/g. The structures of the typical types of neopentyl polyol alcohols used in the refrigeration lubricants area are given in Figure 30.2. There are three main ways of modifying the performance of POEs. These are: • Changes in chemistry • Purity (e.g., tight manufacturing levels of water, acid,

degree of reaction, etc.) • Formulation with additives

The chemistry of the POE can be altered by changing: • The type of alcohol used Dipentaerythritol (DiPE),

Pentaerythritol (PE), Trimethyolpropane (TMP), or Neopentylglycol (NPG),

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OH

CH 3 CH2 H3C

CH2 CH2

CH2 CH2

O C OH

2-ethyl hexanoic (branched C8) acid

FIGURE 30.3 Schematic of typical acids used in refrigeration lubricants • The carbon chain length of the acid • The degree of branching of the acid

Figure 30.3 gives typical examples of the acids used in refrigeration lubricants. The chain length of the acids will typically range from five (C5) to ten (C10) carbons in length. Acids smaller than five carbons (C5) give concerns relating to their high corrosiveness while very long chains, greater than ten (C10), can lead to solubility problems and poor low temperature flow properties, which in turn can lead to oil transport difficulties. The viscosity of POE lubricants is related to their molecular weight, which is influenced by the selection of the polyfunctional alcohol. Typically, blends of NPG with PE are used for low viscosity esters (ISO 46). These alcohols are then reacted with a range of acids. These acids have a major impact on the performance of the ester. Two main types of esters are used commercially, these are: 1. HSPOEs: High Stability POEs based on completely branched acid esters, for example, 2-ethyl hexanoic, iso-heptanoic, and 3,5,5-trimethylhexanoic acid. 2. HOPOEs: Highly Optimized POEs based on a mixture of linear and branched esters. For low viscosity esters (
TABLE 30.3 Optimizing the Properties of Refrigeration Lubricant POE (Effect of Acid Moiety) Molecular weight

Degree of branching

Structural diversity

Polarity

+ + + +

− + − +

O O O +

+ O O O

− + − −

− + O +

O O + +

O O O +

Lubricity Viscosity Viscosity index (VI) Pressure–viscosity coeff. Thermal stability Hydrolytic stability Pour point Miscibility

Molecular weight = Increasing chain size; Degree of branching = Increased degree of branching; Structural diversity = Number of different acids used; Polarity = Number of ester linkages and size of ester.

TABLE 30.4 Physical Properties of POEs [7] Chemistry Viscosity at 40◦ C in cSt Viscosity at 100◦ C in cSt VIs Pour point in ◦ C Flashpoint in ◦ C Miscibility in 20% R-134a in ◦ C

Linear 9.9 2.7 125 −51 208 −40

Branched 10.4 2.6 56 −50 192 −50

Linear 18.9 4.2 128 −52 250 −42

Branched 23.1 4.2 70 < −50 210 −32

TABLE 30.5 Physical Properties of PAGs used in Mobile AirConditioning Viscosity Chemistry Viscosity at 40◦ C in cSt Viscosity at 100◦ C in cSt VI Miscibility in 20% R-134a in ◦ C

46 Single 44.1 9.1 193

46 Double 45.1 10.2 222 < −70

100 Single 102.5 18.9 206

100 Double 95.3 19.5 228 −43

R19(CH2 CH)n9(CH2 CH)m9R4 O

O

R2

R4

FIGURE 30.5 Chemical structure of PVEs

PAGs are said to be double end capped when X1 and X2 are both hydrocarbon groups (e.g., –CH3 ). When X1 is a hydroxyl group (–OH) and X2 is a hydrocarbon group, this is said to be single end-capped. Unend-capped PAGs (X1 and X2 are both –OH) are not used in automotive applications because of the high hygroscopicity and poor compatibility. The miscibility, wear performance, and hygrosopicity of PAGs can be modified by changing: the molecular weight (n + m), EO/PO ratio (n : m), and the type of end-caps (Figure 30.4). Much of the early work on lubricants for HFCs focused on PAGs. However, they were found to have several major drawbacks, namely: • Hygroscopic leading to absorption of between 3,000 to

X19(CH2 CH2 O)n9(CH2 CH9O)m9X2

high moisture affinity)

CH3 End-cap

EO

PO

• Copper plating (partly related to their high moisture End-cap

FIGURE 30.4 PAG lubricant chemistry

industrial usage has established HOPOEs as a commercially important class of POEs (Table 30.4).

30.4.2 Polyalkylene Glycols (PAGs) For refrigeration applications, PAGs are made from the polymerization of the monomers ethylene oxide (EO) and propylene oxide (PO). PAGs are synthesized by adding the oxide monomers to an alcohol initiator in the presence of a catalyst. The molecular weight, and thus the viscosity, of the PAG is controlled by the degree of polymerization (No. of oxide units).

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25,000 ppm of water depending on structure • Poor dielectric breakdown voltages (partly related to

affinity), • Poor stability with R-12 leading to potential retrofit

problems • Poor lubricants for aluminium contacts • Poor PET compatibility

In automotive air conditioning applications, many of the above issues were either not relevant or could be engineered around. PAGs are therefore the current lubricant of choice for original fill for this application. Most of the PAGs are doubled end-capped to improve thermal stability, reduce hygroscopicity, increase mineral oil miscibility and give superior lubricity (Table 30.5).

30.4.3 Polyvinylether (PVEs) The chemical structure of PVEs is shown in Figure 30.5 [8].

TABLE 30.6 Typical Properties of a Range of PVE Lubricants [8]

TABLE 30.7 Physical Properties of AB Refrigeration Lubricants [9]

ISO grades Viscosity at 40◦ C in cSt Viscosity at 100◦ C in cSt VI Pour point in ◦ C Flashpoint Miscibility in 20% R-134a in ◦ C

SUS viscosity Chemistry Viscosity at 40◦ in cSt Viscosity at 100◦ in cSt VI Pour point in ◦ C Flashpoint in ◦ C Miscibility in 20% R-134a in ◦ C

VG 32 32.4 5.12 78 −47 178

VG 68 64.4 7.68 77 −37 196 −24

CH3 CH39C H9CH29C CH3

(CH CH2)x9CH9 CH3 CH3

50 Branched 8.1 2.1 31 < −50 154 Immiscible

150 Branched 28 4.1 −24 −40 175 Immiscible

300 Branched 57 5.8 −14 −35 175 Immiscible

Note: Negative VIs merely indicate a poorer VI than the low reference standard oil

CH3

FIGURE 30.6 Chemical structure of ABs [9]

Viscosity can be adjusted by varying the degree of polymerization (m + n) and miscibility by changing the ratio of m to n. Typical properties for a range of PVEs are given in Table 30.6. PVEs have good HFC solubility and a high viscosity– pressure coefficient. High viscosity–pressure coefficients can be beneficial in elastohydrodynamic contacts. This has led to their use in rotary-vane compressors for air-conditioning applications. PVEs, like PAGs, have relatively poor electrical resistivities. Branching the substituents (R1 to R4 ) and keeping water levels low can compensate for this. Although their stability is generally poorer than POEs, it is adequate for most refrigeration purposes. Due to their polarity they are hygroscopic.

30.4.5 Additives used in Refrigeration Applications 30.4.5.1 Storage stabilizers (Typical dose rate 0.05 to 0.1%) Typically hindered phenolic antioxidants are used at a low dose rate. 30.4.5.2 Antiwear additives (Typical dose rate 0.1 to 5%) Antiwear additives can be very problematic in refrigeration systems. Poorly chosen additives can lead to stability problems resulting in blocked capillary tubes. Activated alumina driers can also effectively remove certain additives from the formulation. Great effort is therefore made to optimize the lubricant to totally remove, or at least reduce, the formulation’s antiwear content. The most common type of antiwear additive in the refrigeration sector is phosphate ester.

30.4.4 Alkyl Benzenes (ABs) The limited solubility of mineral oils with R-22 and R-502 initially led to the investigation of a number of synthetic oils. For refrigeration applications, branched alkyl benzenes (BAB), sometimes referred to as hard alkyl benzenes (HAB), tend to be used in. The general structure can be seen in Figure 30.6. Branched alkyl benzenes are used in preference to mineral oil in HCFC systems operating below −50◦ C due to their excellent miscibility and low temperature performance. BABs also have excellent viscosity–pressure coefficients, which make them good lubricants for rotaryvane compressors. The main disadvantage of ABs is their immiscibility with the new class of HFC refrigerants. Their typical properties can be seen in Table 30.7. AB viscosities in refrigeration applications are historically quoted in Saybolt units (SUS).

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30.4.5.3 Copper deactivators (Typical dose rates 0.0001 to 0.3%) Copper deactivators are used in some formulations to reduce the effect of copper plating. However, great care should be taken as many traditional copper deactivators can lead to capillary tube plugging issues. 30.4.5.4 Acid catchers (Typical dose rates 0.1 to 1%) Epoxide, carbamate, amide, or imide type acid catchers are added to some formulations to improve their hydrolytic stability. However, as the fear of hydrolysis has diminished over recent years, there has been a move away from adding these types of additives.

30.4.5.5 Foaming/defoaming (noise reducing) agents (Typical dose rates 0.0001 to 0.3%) Temperature

Polymeric silicone-based additives have been added at low dose rates in applications where foaming has been an issue. At higher dose rates, they can act as pro-foaming agents and this characteristic has been toused to reduce compressor noise.

Immiscible Region (Two phase)

30.5.1.1 Reliability 30.5.1.1.1 Miscibility and solubility (i) Terminology The major requirement for compressor lubricants is that they provide effective hydrodynamic, boundary, and mixed lubrication for compressor bearings and effective sealing of clearances. Dissolved refrigerant in the oil can influence not only these key criteria but several others as well, namely: 1. Vaporization of dissolved refrigerants can • Disrupt the oil film at bearings • Increase oil volume • Lead to excessive foaming causing flood-back prob-

lems in certain cases 2. Dissolved refrigerant can significantly reduce the viscosity of the pure lubricant. This in turn can impact • Sealing efficiency in certain compressor designs • Heat removal from the compressor • Wear performance

Solubility and miscibility data of the different refrigerant/lubricant mixtures are therefore vital in the selection of an effective lubricant. It is probably best to define clearly what is meant by the terms solubility and miscibility as they relate to refrigeration systems. Miscibility — the formation of a single, homogenous phase when two or more liquid phases are brought into physical contact. Solubility — the incorporation of material from a second phase to form a homogenous solution in the first phase when two or more phases are brought into physical contact. Miscibility is usually only applied to like-phases, for example, gas–gas, liquid–liquid, and solid–solid. Combinations of dissimilar phases, for example, gas–liquid, solid–liquid,

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Miscible Region (Single phase) Upper Critical Solution Temperature (UCST) Immiscible Region (Two phase)

30.5 OPTIMIZING PERFORMANCE CHARACTERISTICS 30.5.1 HFC and HCFC

Lower Critical Solution Temperature (LCST)

0

20

40

% Lubricant in refrigerant

FIGURE 30.7 Miscibility curve for a typical POE in HFC refrigerant

and gas–solid are covered by solubility. Solubility covers all combinations of phase types. Clearly, when we have a situation where there is initially a single liquid phase and a single gas phase, the property of interest is the solubility of the gas in the liquid. In a situation where there are initially two liquid phases and a gas phase, we have to consider both miscibility and solubility and the complexities that can result with variations in temperature, pressure, and composition. Refrigerant/lubricant combinations are classified as completely miscible, partially miscible, or immiscible. Completely miscible lubricants form a single liquid phase with the refrigerant in all proportions at any temperature. Partially miscible lubricants/refrigerant systems form a single phase over a limited temperaturerange. Figure 30.7 gives a typical example of a miscibility curve for a POE. The two critical solution temperatures are called the lower critical solution temperature (LCST) and upper critical solution temperature (UCST). The LCST is so named because it lies below a two-phase region, despite the fact it occurs at a higher temperature than the UCST. This situation is unusual in small molecule mixtures, but it is the normal behavior in polymer solutions. Such behavior has been explained using enthalpy and entropy of dilution theory and the use of free volume concepts. Above the UCST and below the LCST oil–refrigerant mixtures are completely miscible. Outside this temperature range, the liquid may separate into two phases. Such phase separation does not mean that the oil and the refrigerant are insoluble in each other. Each liquid phase is a solution; one is oil-rich and the other refrigerant-rich, depending on the predominant component. Each phase may contain substantial amounts of the minor component, although the two solutions themselves are immiscible. Figure 30.8 gives a visual depiction. It is generally agreed that the viscosity of the circulating liquid phase and the velocity of the driving gas are the two most important considerations from a lubricant return point

No solubility No miscibility .. ...... .... ...... .

Solubility No miscibility .. ...... .... ...... .

Vapor

Vapor

Solubility and miscibility .. ...... .... ...... .

Vapor

* * **** R-134a *** *** * **

x x ** x * Ester x*x * xx ** x x * ** ** x R-134a * x* * *x** *

** x* * * x*

x = Mineral oil * = R-134a

x = Ester * = R-134a

x = Ester * = R-134a

x x x x x x Mineral oil xx

x * * xx *x * x * R-134a/Ester *x *

FIGURE 30.8 Schematic of miscibility and solubility

of view with low liquid viscosity and high vapor velocity being desirable. Key areas of the system can be readily identified: Evaporator inlet

Evaporator outlet

the liquid viscosity is relatively low, approximately that of the liquid refrigerant. The vapor velocity is also relatively low. liquid viscosity is relatively high, tending toward that of the lubricant. The vapor velocity is also high.

For the vast majority of systems, the oil circulation rates are sufficiently low so that as a result of dilution by liquid refrigerant, within reasonable limits, the properties of the lubricant have very little influence on the evaporator inlet conditions; at least as far as oil circulation is concerned. At the evaporator outlet, however, the conditions are dominated by the properties of the lubricant. The majority of domestic appliance evaporators are designed such that insignificant quantities of liquid refrigerant remain at the end of the evaporator. It is therefore apparent that with either a miscible or an immiscible lubricant, there will still be only a single liquid phase at the end of the evaporator and that it is the physical properties (primarily viscosity) of this phase that govern oil return. The viscosity of this lubricantrich phase will depend to a first approximation on both the viscosity of the pure oil and the quantity of refrigerant dissolved in the oil phase, that is, the refrigerant solubility in the oil. The situation in practice is more complex since the chemical structure (e.g., polarity, H-bonding, etc.) of the oil can have an effect on the viscosity of the lubricant– refrigerant phase at lower temperatures. The excellent low temperature flow properties of synthetic oils can therefore markedly improve oil return. Historically, refined naphthenic mineral oils have been used for refrigeration applications [10]. These oils were highly dewaxed to remove refrigerant insolubles and refined further to improve chemical stability with CFC refrigerants. Users had therefore become accustomed to complete miscibility between R-12 and mineral oil. It was

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assumed that total miscibility was therefore a necessity. The main reason cited was poor oil return to the compressor from the evaporator (the evaporator is the coldest part of the system and the most likely part of the system for phase separation to occur). In dry-type evaporators for soluble/immiscible oils, there is usually enough turbulence to cause the phases to emulsify. Flooded evaporators are somewhat more problematic and care needs to be taken with immiscible oils. In practice, thousands of supermarket installations showed no problems of oil return even though the refrigerant (R-502) showed marked immiscibility with the mineral oil lubricant. Another reason cited was the possibility that the phase separated lubricant would coat the evaporator walls causing low heat transfer. A reduction in heat transfer would manifest itself as a reduction in energy efficiency. Experiments have shown that when the concentration of lubricant in the refrigerant phase is below 1%, lubricant miscibility does not appear to be a significant issue. Solubility is desirable, but miscibility is not a necessity. (ii) Viscosity dilution The degree of solubility of the refrigerant in the lubricant is a very important performance criterion. Refrigerants have very low viscosity. The viscosity of lubricants at a given pressure, as can be seen in the graphs below overleaf, can therefore be markedly affected by the presence of a dissolved refrigerant. For instance, it can be seen from Figure 30.9 that POEs can have a much higher solubility in R-22 than with R-134a. To give an equivalent working viscosity in R-22 to that of R-134a, the viscosity of the POE can be adjusted to counter the effects of the refrigerant dilution by using an ester one ISO grade or higher than used with R-134a. Such data are referred to under a variety of terms such as vapor liquid equilibria (VLE), vapor pressure temperature (VPT), or Daniel plots and they are vital to ensure that the correct lubricant viscosity is used. OEMs examine viscosity–solubility information at various temperatures and pressures to determine the optimum viscosity to lubricate and seal compressors, and to provide adequate fluidity to return entrained lubricant from the evaporator. (iii) Oil slugging and foaming Excessive solubility of the refrigerant in the lubricant can lead to oil slugging and foaming problems. This has been an issue with a variety of refrigerant/lubricant combinations such as: • POEs with CFCs and HCFCs (e.g., R-12, R-22) • POEs with CO2 (R-744) • Mineral oil with hydrocarbon refrigerants (e.g., R-600a,

R-290) These issues are highly system dependent and are only seen in certain system designs. Excessive foaming has led

1000

30

90% Oil

500 25 70% Oil

100% Oil 20 Pressure (bar)

Viscosity (cSt)

100

70% Oil

50

10

15

10

5 5 90% Oil

1 –40

–20

0

20 40 60 Temperature (°C)

80

100

0 –40

–20

0

20

40

60

80

100

Temperature (°C)

R-22

R-134a

Oil

FIGURE 30.9 Comparison of an ISO 68 POEs solubility in R-134a and R-22

to wear and energy efficiency issues. The problems have been avoided by the use of: • A sump heater • Antifoaming agents • Lubricants with lower refrigerant solubility (e.g., R-600a

has a lower solubility with POEs than mineral oil) (iv) Conclusion In conclusion, the important lubricant feature for most refrigeration situations is the solubility of refrigerant gas in the lubricant and not the miscibility. In general, lubricants that display miscibility with the refrigerant liquid over a wide range of conditions will also have good refrigerant gas solubilities; however, it is not true to say that, lubricants that display limited liquid refrigerant miscibilities will have poor refrigerant gas solubilities. Poor miscibility lubricants, which have been designed to have limited solubility combined with good low temperature flow properties, have shown excellent transport characteristics and no corresponding heat transfer problems. In several applications, they are in fact preferred to very miscible lubricants as they have excellent wear characteristics and avoid foaming and oil slugging issues. 30.5.1.1.2 Wear Early studies [11,12] have suggested that chlorinated refrigerants played a significant role in improving the

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antiwear performance of mineral oil. This was due to a contribution to boundary lubrication. R-12, for example, has been found to react with steel surfaces to form a protective film. The high temperatures and contact pressures developed under the conditions of metal-to-metal contact cause the refrigerant molecule to decompose, resulting in the formation of active chlorine products, which react chemically with metal surfaces to form protective chlorine containing boundary layers. Refrigerants with high levels of chlorine (e.g., R-12) have been found to be particularly effective. HFC refrigerants do not contain any chlorine and therefore contribute little to antiwear behavior. Lubricants for use with HFC refrigerants therefore have to be greatly superior in lubricity than their mineral oil equivalents. Linear acid HOPOE esters lubricate better than their branched HSPOE equivalents. This can be seen in Figure 30.10 where a Falex test was run under a R-134a atmosphere, 200 lbs, steel/aluminium contacts. The detailed reasons why linear acid esters lubricate better than their branched acid equivalents are given in Section 3.3.2.3.4. For a given carbon number (or molecular weight), branched acids give esters of higher viscosity than their linear counterparts, a property that is utilized in the design of higher viscosity products (>ISO 32). The readily available 3,5,5-trimethylhexanoic acid has particularly good thickening capability and is commonly used. Linear acid-based esters tend to have superior VIs when compared to their branched equivalents.

200 180 160

Wear in teeth

140 120 100 80 60 40 20 0 0

60

120

180

240

300

Time in minutes ISO10 HSPOE in R-134a (100% Branched)

ISO10 HOPOE in R-134a (100% Linear)

Mineral oil (3GS) + R-12

FIGURE 30.10 Falex wear test in R-134a for a wholly linear (HOPOE) and wholly branched (HSPOE) acid ISO 10 lubricant

(ppm) PAG

15,000

10,000 Modified PAG 5,000

Ester Cf. Mineral oil

0

0

10

20 Time (Hours)

30

40

FIGURE 30.11 Moisture uptake of a range of different refrigeration lubricants

30.5.1.1.3 Stability (i) Moisture Good refrigeration practice dictates that the moisture level in a refrigeration system should be carefully controlled. Effective measures for moisture control using POE lubricants have been developed and are in wide commercial use. Hygroscopicity is a term used to describe the affinity for moisture of a lubricant and refrigerant. HFC refrigerants and POE oils have a polar molecular structure, which attracts the polar water molecule. The solubility of water in HFCs such as R-134a is many times greater than in the CFCs they replace. POEs are also hygroscopic and

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can pick up more moisture from their surroundings and hold it much tighter than the previously used mineral oils. The most hygroscopic refrigeration lubricants in descending order are: PAGs, PVEs, POEs, ABs, and mineral oils (Figure 30.11). The rate at which POE lubricants pick up moisture is dependent on temperature, relative humidity (RH), exposure time, and relative surface area (Figure 30.12). Moisture can enter the refrigeration system by a number of routes: • Improper vacuuming of system • System leaks

Water level in ppm

3000 2500 2000 1500 1000 500 0 0

50

150 200 250 100 Exposure time in hours 50% RH 75% RH 80% RH

300

FIGURE 30.12 Typical moisture uptake curve of a typical POE lubricant at a range of RHs at ambient temperature • System components. At elevated temperatures, water

can leach out of elastomeric or plastic system components and be reabsorbed when the system cools down • Improper handling of refrigerant • Improper handling of POE lubricants • Saturated or malfunctioning drier It is important that the introduction of moisture into a system is minimized and the removal of the moisture takes place effectively. At high levels of moisture, the performance of the refrigeration system may be adversely affected. Water can interact with 1. Refrigerants forming clathrate hydrates. Clathrate hydrates are solids that are formed when water molecules are linked through hydrogen bonding creating cavities that can enclose various guest molecules also know as hydrate formers. The formation, nucleation, growth, decomposition, structures, properties, and thermodynamic phase equilibria have been reported for a number of hydrate formers, including HFC refrigerants such as R-32, R-125, R-134a, R-407C, and R-410A. 2. Polyethylene terephthalate (PET) leading to embrittlement and hydrolysis of polyester materials. 3. POE lubricant or refrigerant leading to acid formation. 4. Copper. One possible cause of copper plating is moisture reacting with the refrigerant to form an acidic solution. The acids then dissolve or leach copper from components in the air-conditioning system that are copper or contain copper-based alloys such as brass or bronze. However, copper plating can be caused by contaminants other than water. 5. Steel leading to corrosion. 6. Cold spots to form ice crystals. If these interactions take place they can lead to the following losses in system performance: • Reduction in effectiveness of the heat exchanger

(evaporator) due to ice deposition on the inside surface,

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• • • • • • • •

thus reducing the area of heat transfer, causing insufficient boiling. This results in a reduced refrigeration effect and eventually lowers the system coefficient of performance (COP). Expansion valve sticking. Corrosion of metallic materials inside the system. Blockage of the expansion devices due to ice formation. Copper plating. Poor lubrication. Degradation of wire coating and motor insulation material. Suction/discharge valve sticking. Plugging of liquid line filter drier, suction filter, or heat exchanger (clathrate formation).

POE lubricants below their moisture saturation limit (approximately <3000 ppm), contain no free water and therefore it is unlikely that ice crystals are formed. The degree of hydrolysis is driven by the amount of water present. A higher moisture level will lead to a higher degree of hydrolysis. The speed at which hydrolysis occurs is dependent on the temperature of the system and the acid value (acids can act as a catalyst). It has also been demonstrated that certain additives, high initial acid values and impurities inside the system can catalyze this reaction. For hydrolysis to occur, a sufficient amount of water must exist in the refrigeration system at an elevated temperature. Even at relatively high moisture contents, the rate of hydrolysis is insignificant at ambient temperatures. When the water content of the system is low, hydrolysis does not occur. The concern over hydrolysis has arisen as a result of several hydrolytic stability tests, which have been conducted at very high water levels (>2000 ppm) and highly elevated temperatures, orders of magnitude greater than expected or seen in the oil under normal operating conditions. While there is a theoretical potential for hydrolysis in refrigeration systems, this is severely restricted by the lack of available water. It is suggested that the level of water in the system after assembly be maintained below the equivalent of 50 ppm in the lubricant and preferably below the equivalent of 100 ppm in the system. Moisture can be removed from refrigeration systems by applying a vacuum. At ambient conditions, applying a vacuum of 0.2 mbar will reduce moisture levels to below 50 ppm. Moisture is harder to remove for higher viscosity lubricants and mild heat will significantly increase the drying rate. POEs hold moisture more tightly than mineral oil, but, in the case of R-134a, the refrigerant effectively competes with the ester lubricant in partitioning the water, that is, the water moves from the lubricant to the refrigerant (approximately 50 to 60% of the moisture injected into an air-conditioning system remains in the refrigerant and

Water content (ppm)

can reduce the decomposition temperature of the lubricant. These are the presence of:

240 200

• air • water (should be below 50 ppm in the POE and 100 ppm

160 120

for the system)

80

• contaminants • certain metals

40 0 0

40

80

120

160 200 Time (min)

240

260

320

FIGURE 30.13 Water pull-down rate for a molecular sieve drier in a hermetic system

the rest mixes with the compressor oil). R-134a removes moisture from the POE and then transports it to the drier where it is removed from the system. The inclusion of a drier in the refrigeration system reduces the equilibrium moisture content of both refrigerant and lubricant phase. Moisture is quickly and efficiently removed by the drier, which yields dramatic drying (pull-down) rates (Figure 30.13). The use of a fresh drier during servicing of the refrigeration system will reduce the chance of water contamination of various system components (in particular the expansion device and the evaporator). By minimizing the free water in the system, the propensity for acids to form, or hydrolysis to take place, is greatly reduced. Good housekeeping practices should eliminate most potential sources of moisture. • Avoid exposing the ester lubricant to air for an extended

period of time. • Keep containers of ester tightly closed except when the

oil is actually being dispensed. • Keep the compressor and refrigeration system com-

• • • •

ponents closed, except when work is actually being performed on the equipment. Never leave the equipment open during work breaks, overnight, or while doing other work. Make sure to keep esters in their original containers. Use the appropriate size container (try to ensure complete use of contents). Ensure that any vessel or equipment used to transfer the POE is thoroughly dried before used. The use of a fresh, appropriate sized drier, after servicing a refrigeration system, will reduce the impact of any water contamination.

(ii.) Thermal stability Lansdown [13] quotes that the initial temperatures for the thermal degradation (no air) of a POE to be around 315◦ C. A decomposition temperature of over 300◦ C for a POE cannot be guaranteed. There are several factors, which

Copyright 2006 by Taylor & Francis Group, LLC

Pulling a vacuum below 0.2 mm Hg at 25◦ C is usually sufficient to reduce the water content of the polyol ester below 50 ppm water and to remove residual air from the system. Certain metals can act as catalysts for thermal decompostion and are known to markedly reduce the stability of POEs. A significant reaction has been found with both cast iron and carbon valve steel at temperatures in excess of 200◦ C [14] (392◦ F). This reaction leads to a major increase in acid value of the oil and weight loss of the steel. The addition of water had little impact on the catalytic effect of the cast iron and steel [15]. The use of phosphate additives, which act to passivate iron surfaces, can greatly reduce the severity of this reaction [16]. Other metals that are known to adversely affect the stability of POEs are magnesium and cadmium. Data from the field show that the impact of iron/steel promoted thermal decomposition of POEs is not of concern in a correctly operated refrigeration system. Acidic (particularly inorganic) or chlorinated (e.g., chlorinated cleaning solvents) contaminants should be avoided, as such compounds can also markedly reduce the stability of the POEs. An oil that has a thermal stablity greater than 175◦ C has generally been shown to be of sufficient stability to work well in a refrigeration system. The glass sealed tube test, as described by ASHRAE standard 97, is widely used to assess the stability of refrigeration lubricants. It is thought of as the “standard” thermal stability screening test. Tubes are charged with lubricant, R-134a at 600 psi and copper, aluminium, and steel strips and heated at 175◦ C for 2 weeks. At the end of the test, acid number, colour, and the state of the plates are evaluated. Tests using this procedure show that POEs give excellent performance. Polyol esters have excellent thermal stability up to at least 175◦ C. For applications where oil temperatures are in excess of 200◦ C for long periods, an additized POE may be required. In summary, in a well constructed refrigeration system, operating under normal conditions, it is unlikely that the extremes of temperature sufficient to induce significant decomposition will be encountered. To put this temperature in perspective, system components such as PET slot liners show decomposition at temperatures in excess of 130◦ C. Therefore, other vital refrigeration system components will breakdown well before the lubricant does.

(iii) Materials compatibility It is well known that deposits, such as valve coking, have the potential to cause various problems in a compressor leading to reduced long-term reliability. Since the coldest point in most refrigeration systems is at the exit of the expansion device into the evaporator, materials that have a low solubility in the refrigerant–lubricant mixture will tend to precipitate here. Such deposition can result in flow restriction through the capillary tube or expansion valve orifice with materials of relatively high pour points such as waxes and gums resulting in a reduction in system performance, poor temperature control and, in extreme cases, system failure. Deposits or accumulation of insoluble materials can also be found in other system components — in particular in the evaporator. With sufficient material present, this can result in a reduction in heat transfer and a consequential drop in energy efficiency. Given the relatively small quantity of material required to influence the expansion device, the focus will be on factors influencing deposit formation in capillary tubes and expansion valves. It is also well known the deposits, such as valve coking, have the potential to cause various problems in a compressor leading to reduced long term reliability. There are a variety of mechanisms for the formation of deposits in (compressors and associated) refrigeration systems. These are summarized in Figure 30.14 [17]. There are several possible sources of system extractables. These include: 1. Process chemicals used in the production and assembly of compressors and compressor components (e.g., assembly fluids, wire winding lubricants, detergents, corrosion inhibitors, fluxes, etc.) 2. Extractables from the nonmetallic components used in the construction of the compressor (e.g., elastomers, plastics, insulating material for slot liners and wires, varnishes for motor windings, tying cords, etc.) 3. Lubricant components (e.g., additives, poorly soluble lubricant basestock components) 4. Inorganic components (e.g., machining debris, desiccant fines, copper plating) Tribopolymerization

Wear debris

Tribological debris Additive stability

SYSTEM DEPOSITS

System extractables

Chemical stability of POE Thermal decomposition

Hydrolytic decomposition

FIGURE 30.14 Schematic of deposit mechanisms

Copyright 2006 by Taylor & Francis Group, LLC

The mechanisms of deposition of material from each of the different sources are complex. An overview of the main mechanisms is set out in the following section. Process chemicals The solubility of the majority of the conventionally used process chemicals is different, in most cases lower, in HFCs compared to CFCs and HCFCs. Particular problems have been observed with low pour point paraffinic processing oils such as wire winding lubricants and assembly oils. In many hermetic systems, the copper motor windings are immersed to some extent in a lubricant-rich fluid at elevated temperatures (>60◦ C). The conventional paraffinic wire winding lubricants are soluble in esters at the low HFC levels encountered under lowpressure compressor sump conditions. It is well established that a small amount of lubricant is transported out of the compressor and into the system. It is therefore inevitable that the paraffinic wax dissolved in the ester/refrigerant mixture passes through the expansion device. The environment in the region of the expansion device is quite different to that encountered in the compressor sump — namely refrigerant-rich (>98%) and low temperature. The poor solubility of the paraffinic material under these conditions causes it to deposit in the expansion device as illustrated in Figure 30.15. The waxy surface of the paraffinic material deposited in the expansion device tends to entrap further system debris causing further build-up of deposit. This results in a heterogeneous deposit made up of many different phases. The relatively small amounts of material necessary to impair system performance coupled with the compositional complexity of the deposits requires a high degree of sophistication in analytical chemistry to understand the root cause of the problem. This is discussed in further detail below. Studies on field systems show that such deposits often have the appearance of a white waxy grease with included debris. Extensive field-testing has shown that this material can build up rapidly, in some instances only after running for hours and usually reaches saturation levels after running for several weeks. In industrial systems, there is often the possibility to clean deposits from a TXV. Following

Capillary tube

Desiccant fines Process chemicals

Sticky deposits (e.g., hydrocarbon wax)

Debris

Nonmetallic extractables

Mechanism

Lubricant extractables

Sticky waxy depoitsactsas “fly-paper” attracting other materials, for example, wear debris, and dessicant fines, and metal sulfides

FIGURE 30.15 Schematic of deposit formation inside a capillary tube

Flow rate (%)

100 80 60 40 20 0

0

2000

4000 Time (h)

Process oil No control on level controlled process oil

6000

8000

Oilbreakdown

FIGURE 30.16 Schematic of the effect of process oils on capillary blockage

a retrofit, any such deposited material can be removed by cleaning and, unless the system is heavily contaminated, is not likely to recur. In contrast, capillary tube systems cannot be cleaned easily and it is therefore important to address the issue at source, that is, by controlling the level and type of process chemicals in the equipment manufacturing/installation process. Because process oils are used in a finite quantity in any given system, the effects described above will eventually plateau at an equilibrium level. Figure 30.16 shows a schematic of a variety of typical behaviors of flow reduction in a capillary tube. The establishment of a steady-state restriction is a good indication that most of the restriction is because of process chemical contamination. If lubricant hydrolysis or thermal degradation occurred to any great degree, then capillary restriction would be expected to increase over time to the point of prohibitively large flow reduction (as exemplified in Figure 30.16). This type of degradative behavior has only been observed for lubricants that have been inappropriately formulated. Most appliance manufacturers have now introduced HFCcompatible assembly fluids, honing oils, and wire winding lubricants, and so forth. Where ester-based assembly fluids are used, they are typically one or two viscosity grades higher than the fill oil in order to minimize drainage from the surface during assembly. The use of higher viscosity assembly oils also provides some lubricity benefits during initial compressor break-in. Non-metallic components A wide variety of plastics and elastomers are used in refrigeration systems, particularly in hermetic and semihermetic compressors. These materials include wire enamels, various plastic components (e.g., mufflers, slot liners, etc.), o-rings, and gaskets. With the move to lighter compressors, the number, type, and amount of nonmetallic components within a compressor is likely to increase over the coming years. There are two major concerns with these types of materials. The first is the integrity of the material itself. The lubricant must not

Copyright 2006 by Taylor & Francis Group, LLC

deteriorate the properties of the various nonmetallic parts. The second concern is extraction or leaching of some of the plastics into the lubricant [18]. Unlike the mineral oils that they have replaced, lubricants that are compatible with HFCs tend to be polar by nature (e.g., PAGs, carbonates, and esters). This increased polarity results in a tendency to swell certain types of nonmetallic (plastic or elastomeric) materials. Besides causing swelling of the material, some components within the polymer (oligomers and processing additives) are soluble in the lubricant and can be leached out. A list of some of the components present in many nonmetallics, which can be identified in deposits in the expansion device, are listed below. • • • •

Processing aids (e.g., carboxylates, amines, esters) Fillers (e.g., carbonaceous compounds) Plasticizers (e.g., phthalates, diesters) Residual cross-linking compounds (e.g., sulfur-based compounds) • Mold release agents (e.g., esters, hydrocarbons) Transport of these materials to the expansion device is in the manner described above. Any particulate materials (desiccant fines, machining debris) are transported mechanically and are readily entrapped in the sticky primary deposits of organic material. Polyol esters are excellent solvents. In addition, HFC refrigerants are more polar than the traditional CFC/HCFCs refrigerants. HFC/POE mixtures can therefore respond in a different way to elastomers than CFC/mineral oil. It is well recognized that nominally identical materials obtained from different suppliers can give markedly different results when tested with refrigerant–lubricant mixtures. The precise recipe and processing conditions of the elastomer have a marked effect on a seal’s compatibility with POEs. POEs are good solvents and can leach-out processing residuals such as plasticizing agents, fillers, mould release agents, and cross-linking compounds. These chemicals may be HFC incompatible. The extraction of additives out of elastomeric seals can also cause an embrittlement of the elastomer. Any substance extracted could then lead to deposits or partake in chemical reactions that could lead to deposit formation. Experiments have shown that some elastomers can loose 20% by weight of such compounds. For refrigeration systems containing capillary tubes, particular care should be focused on the residual levels of sulfur containing compounds, fatty amides, and carboxylates. All of these compounds are known to cause flow restrictions. Table 30.8 gives a general outline on POE elastomer compatibility with a variety of refrigerants. It is recommended that elastomers from different suppliers be tested for compatibility before use and the

TABLE 30.8 Elastomer Recommendations for HFC/POE Combinations Typically compatible

Marginal

Teflon Nylon 6,6

EPDM CR/CF HNBR NBR

Typically incompatible Viton Natural rubber Butyl rubber

For NBR/HNBR it is recommended that the nitrile content be above 32% Typically Compatible = Acceptable; Marginal = Very dependent on supplier. Good passes to poor fails; Typically incompatible = Unacceptable.

TABLE 30.9 Pour Point of a Variety of Different POE Chemistries Ester ISO 32 HSPOE ISO 32 HOPOE ISO 32 linear POE ISO 46 branched POE PE branched C9 (solid)

Pour point in ◦ C −38 −48 −3 +8 +30

specification on its formulation be tightly controlled once approved. Lubricant components Poorly formulated lubricants can also produce deposits. If the ester lubricant is incorrectly formulated, components, which have poor low temperature flow performance, can precipitate leading to waxy or gummy deposits and poor performance at the expansion devices. Certain types of fully branched PE and DiPE POEs have very poor low temperature properties. The poor pour point of these esters can be seen in Table 30.9. Industrial grades of POE with a viscosity greater than 32 cSt, if not properly formulated, can contain significant concentrations of such materials and analysis of field units has shown these impurities to have formed deposits. This has led to many major compressor original equipment manufacturers (OEMs) setting maximum specifications for the amount of fully branched material permissible in the lubricant. This can happen even with lubricants that are miscible in the refrigerant to very low temperatures. Certain specific types of performance-enhancing additives can also cause problems. For example, certain silicone-based foaming agents have been found in expansion devices but it is unclear whether they are significant contributors to flow reduction. However, tests have shown that deposits of silicone-based foaming agents in the evaporator can lead to a marked drop in energy efficiency.

Copyright 2006 by Taylor & Francis Group, LLC

Inorganic components As described earlier, particulate debris (machining debris and desiccant fines) will adhere to the sticky organic layer laid down by the mechanism outlined in the processing oil section. (iv) Copper plating Copper plating on steel and iron parts has been a problem in air-conditioning and refrigeration systems for many years, first in the CFC/HCFC–Mineral Oil systems and now in the HFC–POE systems. The result of copper plating is reduced clearances between moving parts resulting in failed bearings, valves, oil pumps, and other moving parts. Under certain circumstances, copper can also deposit onto insulating films thereby leading to a reduction in their electrical properties. Copper plating seems to be associated with: • The presence of air • The use of certain chlorine and sulfur containing process

chemicals • High levels of acid • High levels of moisture • Certain types of chlorine and sulfur containing lubricant

additives The root causes of copper plating are varied and while the exact chemical mechanisms are unclear, there appears to be three major steps: 1. Oxidation of the copper metal to copper ions 2. Formation of an oil-soluble complex of copper ions that allows transfer to a site distant from the point of origin • Esters readily solubilize metal ions and complexes via

coordination with the carbonyl group 3. Deposition of the copper onto iron or steel • This electrochemical process is more likely to occur

on hot, clean iron or steel and is often seen on bearing surfaces One possible cause of copper plating is that an acidic solution is formed from decomposition of a system chemical (refrigerant, lubricant, or process chemical). The resultant acid may then dissolve or leach copper from other components in the refrigeration system, which are copper or contain copper-based alloys such as brass or bronze (e.g., heat exchangers, brass bearings, electric magnet wire, etc.). It has been postulated that this process may repeat over and over, resulting in formicary corrosion tunnels. Formicary or “ant-nest” corrosion is a particular form of localized corrosion of a submicroscopic nature. The morphology of the corrosion damage within the metal includes a series

of minute interconnecting tunnels, starting from the tube surface and propagating rapidly into the tube wall. The resulting corrosion product, copper oxide, is usually found in the micro-channels. The mechanism of formicary corrosion generally involves the presence of moisture, oxygen, and a corrosive agent such as an acid. Hydrolysis of an ester to form a carboxylic acid does not occur under normal operating conditions. Copper plating is also unlikely to occur even with carboxylic acids present. Tests that ran on esters with large water contents or acid values have not resulted in copper plating [15,18]. Tests carried out in the presence of inorganic acids, for example, HCl, usually result in severe copper plating. These results are consistent with the fact that strong acids are necessary for copper plating to occur. The most likely source of oxidizing agents is therefore from the decomposition of: 1. Oxygen • Entrapped air

2. Certain chlorine containing chemicals • • • •

CFC or HCFC refrigerants (e.g., R-12 and R-22) Chlorinated cleaning solvents Solder fluxes Chlorinated lubricant additives

3. Certain sulfur containing chemicals • Residual cross-linking agents from gaskets • Anticorrosion agents • Antiwear or extreme pressure lubricant additives

4. Strong acids • Decomposition of lubricant additives • Decomposition of refrigerants

The most likely causes of copper plating are high moisture content and contamination from chlorinated chemicals. Tight control of moisture and careful control of process chemicals is therefore vital. Tight control of water is especially important in HCFC-22 systems where copper plating can be problematic. In certain circumstances, copperdeactivating agents can help to reduce the effects of copper plating. However, extreme care is required. At elevated temperatures, these additives can result in deposits leading to capillary tube restrictions. Poorly formulated lubricants should be avoided and only OEM approved lubricants should be used. General field experience has shown that for well maintained refrigeration systems copper plating does not occur.

Copyright 2006 by Taylor & Francis Group, LLC

30.5.1.2 Efficiency Following the Kyoto conference on climate change, energy efficiency has become an important performance characteristic for all refrigeration and air-conditioning systems. Performance or labeling requirements are increasingly defined by legislation, such as the European Refrigerator Labeling Directive, the US DOE Energy Efficiency Standards, and the Japanese Energy Conservation Law. Correct selection of compressor lubricant can have a significant influence on the energy efficiency performance of a system. Lubricant selection can effect compressor energy efficiency in a number of ways. As discussed in the ester chapter (Section 3.3.2.4) two key lubricant performance criteria that affect efficiency are viscosity and friction coefficient. To examine these effects, commercially available freezer and refrigeration cabinets were filled with synthetic food packages to simulate an average loading and operated under controlled conditions over a 14-day period for each test lubricant. In each case, prior to testing, refrigerant was removed via the service port of the compressor, followed by removal of the original fill lubricant from the sump pipe. The discharged lubricant was weighed. The system was evacuated and recharged with the same weight of the first test lubricant, then reevacuated and charged with the required amount of refrigerant gas, as vapor. The cabinet was then restarted. This procedure was repeated for a range of HOPOE lubricants. Ambient temperature was controlled, and energy consumption of each unit was recorded. The results are presented in Figure 30.17. It is clear that viscous drag has a major impact on the energy efficiency of small reciprocating compressors. Energy efficiency is usually expressed in terms of the COP, which is the dimensionless ratio of the refrigeration effect to the heat of compression. The energy efficiency ratio (EER) is directly proportional to the COP and is expressed as follows: EER (Btu/h.watts) = COP × 3.412 Test experience on HOPOEs in a number of different systems indicates that typically an increase in COP of the order of 2% can be achieved for each step to a lower viscosity grade. These figures are presented only as a rough guide and approximate the test results from several different compressors. Actual values will be dependent on the system configuration and conditions of operation. For any specific compressor design and set of manufacturing tolerances, an optimum viscosity will exist. Beyond this, piston blow-by will increase leading to a decrease in volumetric efficiency and COP. As this limit is approached, the extent of energy efficiency gains with lower viscosity will be reduced. As the optimum viscosity is highly system dependent, it is very difficult to predict theoretically. Thus, direct system measurements are recommended.

Energy consumption kWh / 24h

1.2 Freezer 1.1 1.0 0.9 10% Improvement in efficiency 0.8 0.7

Refrigerator

0.6 0

5

10 15 Lubricant viscosity (cSt)

20

FIGURE 30.17 Energy efficiency vs. viscosity for a domestic refrigerator

30.5.1.3 Noise reduction Reducing noise and vibration is an increasingly important objective for designers and users of a wide range of mechanical systems. At home, low noise is an increasingly important performance requirement for all types of domestic appliance. Since lubricants are often the most easily changed component of a mechanical system, it is therefore not surprising that there is growing interest in controlling noise and vibration, in all types of machinery, by optimizing the lubrication. Transmission of vibration within a machine is significant because sound is typically radiated from the external casing of a machine, while the moving mechanical elements, which are the original source of the vibration, are enclosed within. For noise to be radiated, it is therefore necessary for acoustic vibrations to be transmitted from the source to the casing either through the solid, liquid, or gas phases. Lubricants can contribute to reduction of overall noise and vibration generated by machines, both by reducing generation of acoustic energy in lubricated contacts and by modulating the transmission of vibration through the lubricant. With most CFC/mineral oil mixtures, a slowly collapsing foam, consisting of a dense layer of small bubbles, is generated in the compressor leading to good noise suppression and little carry over to the condenser. The newer, more polar refrigerant/lubricant mixtures exhibit rapidly collapsing foam characterized by initial large bubble formation. Synthetic lubricants are very pure and tend not to foam. Mineral oil contained impurities that created a degree of foaming. This foam blanket tended to dampen the noise of a compressor. Certain OEMs have therefore found that the noise level of compressors that use unformulated synthetic lubricants is slightly higher than those using conventional mineral oil lubricants.

Copyright 2006 by Taylor & Francis Group, LLC

Foam generation and vapor entrainment depend partially on: • • • •

Viscosity Dynamic surface tension Gibbs elasticity and interfacial shear Dilational viscosities

Refrigeration lubricant formulations for improved noise and vibration performance must maintain stable, controllable levels of foam, and vapor entrainment in order to deliver improved acoustic performance without compromising reliability or efficiency. This can be achieved by controlling the chemical structure of highly optimized lubricant base fluids, formulated with surface-active additives (e.g., low levels of polyalkylsiloxanes) to control the interfacial properties. Each refrigeration compressor design has unique acoustic properties and characteristic lubricant flow and agitation patterns, and consequently requires a specifically tailored lubricant formulation in order to deliver optimum acoustic performance. Noise reduction via lubricant optimization has been found to be most effective for reciprocating compressors. Noise reduction of up to 3 dB can be achieved for the relatively quiet domestic appliance compressors and up to 9 dB for their larger, noisier industrial commercial counterparts (Figure 30.18).

30.5.2 Carbon Dioxide Carbon dioxide is an excellent refrigerant because it is nontoxic, nonflammable, has excellent heat transfer characteristics, is inexpensive, zero ODP, and has a net zero GWP when obtained from an industrial waste or byproduct source. It has therefore attracted attention in several applications such as automotive air-conditioning

Compressor noise

Noise dB

100

90

80

70 Recip.1

Recip. 1 with low noise lubricant

Recip. 2

Recip. 2 with low noise lubricant

Typical scroll

FIGURE 30.18 Noise reduction in industrial commercial reciprocating compressors

and heat pumps. However, there are several potential issues that will affect the selection of the lubricant, namely: 1. Lubricant Transport • To ensure good oil return to the compressor; in

refrigeration systems having liquid pools such as oil reservoirs, etc., the refrigerant oil needs to have either • A higher density than the CO2 refrigerant or • Good miscibility with it 2. Wear • CO2 is an excellent solvent and this solvency can

cause excessive lubricant dilution leading to potential wear and foaming problems • CO2 requires the use of higher operating pressures (e.g., in automotive air-conditioning, the working pressure becomes an order of magnitude higher when compared to HFCs [19]). High load increases stresses on bearings, which can lead to increased wear 3. Stability • CO2 can react with water to form carbonic acid that

can then accelerate potential hydrolysis processes 30.5.2.1 Lubricant transport Mineral oils have poor miscibility with CO2 . Table 30.10 gives a summary of the miscibility of CO2 with a range of lubricants. As can be seen in Figure 30.19, CO2 changes density very rapidly with temperature. This can result in a poorly miscible lubricant, at certain temperatures, floating on liquid refrigerant while sinking at other temperatures. This property is known as “phase inversion” and can be problematic in terms of oil separation. Fully miscible lubricants avoid this issue.

Copyright 2006 by Taylor & Francis Group, LLC

TABLE 30.10 Overview of Miscibility of CO2 with a Range of Synthetic Lubricants Lubricant

Miscibility

Mineral oil PAO AB Esters PAG

Immiscible Immiscible Immiscible Miscible Partially miscible

Due to their superior miscibility behavior when compared to mineral oils, POEs, diesters, and PAGs have undergone further studies.

30.5.2.2 Wear Since the viscosity of liquid CO2 is very low, the more the CO2 dissolves in the lubricant, the more it can dilute the viscosity of the mixture. CO2 is very soluble in POEs and this can lead to a marked viscosity reduction (markedly more than R-134a). This has to be compensated for by an increase in viscosity of the ester. The high solubility of CO2 in POE in certain systems can lead to foaming issues but this can be resolved, where required, by the use of conventional antifoaming agents. The high loads in certain systems may require the use of antiwear additives.

30.5.2.3 Stability Higher levels of moisture may also be present in the lubricants as water has less affinity for CO2 than it does for HFCs. Water can also react with CO2 to form carbonic acid. Therefore, there are legitimate concerns over possible stability and copper plating issues that could arise from these factors.

1.2

Density in g/cm3

1.1 PAG POE

1

MO AB

0.9 0.8 CO2 0.7 0.6 0.5 –30

–20

–10

0 10 Temperature in °C

20

30

40

FIGURE 30.19 Change in density vs. temperature for a range of lubricants [20]

In automotive applications, detailed testing has shown that double end-capped PAGs perform well [21]. Double end-capped lubricants are preferred as they do not possess terminal hydroxyl groups and thereby improve stability by: 1. Reducing the possibility of chemical reaction (residual hydroxyl groups can react with carbonic acid). 2. Reducing their affinity for moisture. Esters, due to their excellent solubility, have been used in heat pump applications. With esters, there is obvious concern around the potential for hydrolysis. The hydrolysis issue, as found with HFC systems, may not be as problematic as first thought. Provided correct handling procedures are followed, esters have been shown to work well. In fact, esters (and PAGs) have been used for a number of years as CO2 process gas lubricants without issue. Careful selection of antiwear additives is required, as they tend to be much more hydrolytically sensitive than the lubricant. As with HFC systems, copper deactivators can be used to alleviate copper plating where this is an issue. In summary, a range of lubricants can be used for CO2 applications. In certain systems, synthetic hydrocarbons such as PAOs and ABs can still be used even though they have poor solubility. The poor solubility of the synthetic hydrocarbons is compensated for by their excellent low temperature flow properties and can be improved still further by blending with more miscible lubricants (e.g., PAGs, esters, etc.). A range of individual components and blends of synthetic lubricants are therefore being evaluated to find the more cost effective solution for a particular application. Quite often, lubricant selection will be based on logistic factors, that is, a lubricant that can work with a variety of refrigerants.

Copyright 2006 by Taylor & Francis Group, LLC

30.5.3 Ammonia (R-717) Ammonia has zero ODP and GWP. However, limitations include its toxicity, strong odors and a limited range of flammability in air. Despite these limitations, ammonia is being considered for applications with limited exposure to dense populations (e.g., rooftop air-conditioning, water chillers, etc.). Mineral oil lubricants have poor solubility with ammonia. This is a benefit in flooded evaporator systems as these oils are heavier and can easily be removed by draining from the bottom of the evaporator vessels and returned to the compressor [22]. However, the poor solubility limits the use of mineral oil with systems that employ direct exchange (DX) evaporators. Here, the immiscible oil builds up in the evaporator reducing its efficiency and ultimately leading to oil starvation. This can be prevented by the installation of an oil separator but this results in additional materials costs, a larger system, and an increase in the amount of servicing the compressor requires. Other immiscible synthetic oils such as PAOs, ABs, and highly processed hydrocracked oils are used as alternatives to mineral oil in traditional ammonia systems where their excellent low temperature properties allow for operations at very low temperatures. Quite often, blends of several synthetic lubricants (e.g., AB/PAO) will be used to optimize performance [23]. PAGs are soluble in ammonia. This allows the use of ammonia in refrigeration systems with DX evaporators. The use of such systems has resulted in markedly reduced refrigerant charge (1/10th to 1/50th) when compared to that of conventional systems [6]. End-capped PAGs are again preferred due to their superior stability and lower affinity for moisture. Moisture can be reduced still further by the use of EO in the polymer chain. This produces the property of “inverse solubility.” Simply put, inverse solubility means that the hotter the lubricant becomes, the less soluble

the water becomes. Below 60 to 70◦ C (cloud point) water is completely absorbed into the lubricant. Above this temperature, it completely phase separates. By keeping the discharge temperature above the cloud point the moisture level in the PAG can be kept low. Polyol esters are known to react chemically with ammonia to form solids and are therefore avoided.

2. After-market (lubricants required for servicing existing equipment)

30.5.4 Hydrocarbons (R-600a, R-290)

Compressor types: Refrigerants used: Lubricant chemistry:

The utilization of hydrocarbon refrigerants such as propane and iso-butane in domestic appliances, air conditioning, and heat pumps has received a great deal of attention. ISO 10 to ISO 22 mineral oils are typically the lubricant of choice for R-600a domestic compressors. Generally, they have performed well except for a few issues connected with their high solubility. Mineral oils, being hydrocarbons, have high solubility in hydrocarbon refrigerants (like-dissolves-like). High solubility can lead to: • Foaming • Excessive lubricant dilution leading to potential wear

problems • High oil carryover leading to slugging

Foaming and wear have been overcome by the use of traditional antifoaming and antiwear additives. However, high oil carryover has led to oil slugging issues in certain systems and this can lead to markedly reduced energy efficiency over time. Esters and PAGs have lower solubility in R-600a refrigerants and can markedly reduce oil slugging. PAG lubricants tend not to be used due to difficulty in making them at very low viscosities (
30.6 CURRENT COMMERCIAL PRACTICE 30.6.1 Synthetic Lubricants in Use The refrigeration oil market consists of two main sectors: 1. Original fill oils sold to OEMs • Domestic Appliance (household refrigerators and

freezers) • Industrial and Commercial Refrigeration and Air-

Conditioning

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• Automotive Air-Conditioning

30.6.1.1 Domestic appliance

Lubricant viscosities:

Reciprocating R-134a and R-600a POEs for R-134a and mineral oil for R-600a ISO 7 to ISO 32

Domestic refrigerators relied heavily on CFC refrigerants and were the first area to convert to HFCs. This sector covers the domestic refrigerator and freezer market (appliance) and has the exact requirements for compressor lubricants. Refrigerators are designed to last 15 to 20 yrs making system reliability of paramount importance. The compressor lubricants affects not only compressor durability and wear but also noise, energy efficiency, and heat transfer. In the appliance sector, approvals by compressor manufacturers and cabinet manufacturers demand extensive testing. It is worth pointing out that only the compressor manufacturer and white goods producer consume lubricants. There is little to no after-market requirement for the appliance sector. Worldwide, over 65 80 million refrigerators are manufactured by this sector. 30.6.1.2 Industrial and commercial refrigeration and air-conditioning Compressor types: Refrigerants used: Lubricant chemistry: Lubricant viscosities:

Reciprocating, scroll, centrifugal, rotary-vane, and screw HCFC moving to HFC and natural refrigerants POEs for HFCs (some PVEs for rotary-vanes) ISO 22 to ISO 320

This sector covers lubricants used in the compressors of commercial and industrial refrigeration and freezing units. The sector can be further subsectioned into: 1. Commercial Refrigeration encompasses equipment and systems with a wide variety of applications in hotels, bars, corner shops, supermarkets, hospitals, and food industry. 2. Industrial Refrigeration is used in the chemical, petrochemical, and pharmaceutical industry, oil and gas industry, metallurgical industry, civil engineering, and industrial ice making. 3. Cold storage and food processing is one of the most important applications of modern refrigeration techniques. Dairy products, fish, meat, fruits, and vegetables are stored under chilled conditions.

4. Unitary air-conditioning systems and heat pumps: their main purpose is to provide a comfortable climate in private homes, shops, and supermarkets, as well as in several working environments. Water-cooled airconditioning systems are usually installed in large buildings. The cooling unit is the so called “water chiller.” 5. Heat pumps for heating-only purposes are used in residential, commercial, institutional, and industrial buildings. In industry, heat pumps are used to heat process streams for heat recovery and hot water production. 6. Mobile refrigeration systems are necessary to cool and chill products during transportation on ships, railcars, containers, and trucks.

The refrigeration systems used in these varied applications can range from relatively small units used in shop store display cases to sizable systems used in manufacturing industries. Generally, smaller units relied on CFCs while the larger systems were dependent on HCFCs. This sector is currently in the process of converting to HFCs. The after-market covers sales of lubricants for compressor oil changes in the industrial and commercial sectors. It is estimated that, when mature, four times as much lubricant will be consumed by this sector when compared to the original fill requirements of new equipment. Although original fill lubricants are supplied directly by the lubricant supplier, the after-market is much more fragmented and is usually supplied by a distribution network soured via a master distributor. Existing equipment using current CFC/HCFC mineral oil technology can be easily changed over to run on a HFC/POE combination using a well-established retrofit procedure.

30.6.1.3 Automotive air-conditioning Compressor types: Refrigerants used: Lubricant chemistry: Lubricant viscosities:

Reciprocating, scroll R-134a, possibly CO2 and R-152a in the longer term PAGs for original fill and POEs for the aftermarket ISO 46 to 150 for PAGs and ISO 68 to 100 for POEs

This sector covers lubricants used in automotive airconditioning compressors. This market traditionally used R-12 as a refrigerant. In developed markets, the transition to HFC has been completed. Polyol ester’s superior compatibility with R-12 and mineral oil makes them the oil of choice for retrofit market. Single and double end capped PAGs are used for the original fill.

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30.6.1.4 List of suppliers Over the last several years considerable market shake out has occurred, namely: • ICI acquired Unichema, which was combined with

existing ICI businesses to become Uniqema • Fuchs acquired the DEA refrigeration lubricant business • Lubrizol acquired CPI • Hatco acquired the Mobil refrigeration ester lubricant

business Table 30.11 lists the primary suppliers of refrigeration lubricants.

30.6.2 Current Market Size An approximation of the current global POE refrigeration market and its potential growth is given in Figure 30.20.

TABLE 30.11 List of Principal Refrigeration Lubricant Suppliers Chemistry

Company

POEs POEs POEs POEs POEs POEs

Uniqema, ICI Castrol, BP CPI, Lubrizol Japan Energy DEA (now Fuchs) Cognis, Henkel

ABs ABs ABs ABs ABs

Shrieve Chevron Soltex Infineum Nippon Oil Company

PAGs PAGs PAGs

Union Carbide Idemitsu Uniqema, ICI

PVEs

Idemitsu

1997 (30 K/t)

Automotive Industrial/Com.

2002 (40 K/t)

Appliance After-market

FIGURE 30.20 Sales of POEs into the refrigeration market

Consumption of R-22 as percentage of Montreal Protocol cap level

100 80

•

Canada – 2010 total ban on consumption

•

Japan – As Montreal protocol

•

USA – 2010 limited to use in refrigeration systems manufactured before 2010 – 2020 Total ban on consumption

60 40 20

0 2000 2005 2010 2015 2020 2025 2030 Year European union Montreal Protocol

FIGURE 30.21 Montreal Protocol phaseout dates

30.6.3 Incentives to Growth With the near completion of phaseout of CFCs, the growth rate of synthetic lubricants is highly dependent on targets set down for the phaseout of HCFCs as outlined in the Montreal Protocol (Figure 30.21). Western Europe, Japan, and USA have completed the phaseout of CFCs. HFCs and CO2 refrigerants will primarily use synthetic lubricants technology (POE and PAGs). Hydrocarbon refrigerants (R-600a, R-290) primarily use mineral oil lubricants. R-600a has gained some ground in the appliance sectors in Central Europe (60% 30% HFC, 40% 70% hydrocarbons), Japan (80% hydrocarbons) and China (50% HFC, 50% hydrocarbons). However, flammability concerns have led to its rejection by the USA. Due to flammability issues, the widespread use of hydrocarbons in larger industrial commercial refrigeration systems is unlikely. The automotive sector is primarily still using HFC refrigerants. However, in Europe, CO2 is a serious future candidate.

30.7 FUTURE MARKET TRENDS 30.7.1 Market Drivers The key technical market drivers in the refrigeration sector are: • Improved energy efficiency driven by the Kyoto Accord • Reduced noise • Improved reliability

The requirement to meet tighter efficiency targets has resulted in an: • Increase in the use of variable speed and linear compres-

sor technology. Improvements gains above 30% can be achieved • Increased interest in low GWP refrigerants (ammonia, CO2 , hydrocarbons, R-152a, etc.) • Shift to lower viscosity lubricants

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• Shift to screw and scroll compressors. In general, screw

and scroll compressors have the advantages of higher reliability, higher efficiency, and lower noise Modifications in compressor design, lubricant formulation (see Section 30.5.1.3), and compressor type are all being used in combination to reduce the noise of compressor and improve reliability.

30.7.2 Synthetics under Development Variations of POE and PAG technology to improve noise reduction, increase in efficiency, and increase in reliability will continue. As the sector moves toward maturity it seems unlikely that brand new lubricant chemistries will be successfully launched into this sector.

30.8 CONCLUSIONS Over the last ten years, the refrigeration sector has been a success for synthetic lubricants. They have brought considerable environmental benefits in terms of reduced global warming and allowed for the successful introduction of refrigerants that allowed for the strict targets as outlined in the Montreal Protocol to be met.

REFERENCES 1. Anon. (October 2003). Refrigeration history and from ice to refrigerator. Refrigeration Air Condition., October, 24–28. 2. Anon. (1995). Climate Change 1995, The Science of Climate Change: Summary for Policy Makers and Technical Summary of Working Group I Report, p. 26. 3. March Consulting Group (1998). Opportunities to minimize emissions of hydrofluorocarbons (HFCs) from the European Union. Final Report. Prepared by March Consulting Group, United Kingdom, for the European Commission. 4. ASHRAE Handbook (1990). Refrigeration Systems and Applications, SI ed. Chap. 8 — Lubricants in Refrigeration Systems. Printed in Mexico. ISBN 0-910110-70-0. 5. Sanvordenker, K.S. and Larime, M.W. (June 22–29, 1972). A Review of Synthetic Oils for Refrigeration Use. Symposium on Lubricants, Refrigerants and Systems — Some Interactions, ASHRAE Annual Meeting, Nassau, Bahamas. 6. Altman, S.S. et al. (April 22, 1969). Foreign Technology Division. Department of Commerce, Translation FTD-HT23-1489-68. 7. http://www.emkaraterl.com/. 8. http://www.idemitsu.co.jp/lube/english/topics/pve/pve.html. 9. Dressler, H. (1992). Alkylated aromatics. Synthetic Lubricants and High Performance Function Fluids. Chap. 5, R.L. Shubkin, Ed. Marcel Dekker, Inc., pp. 125–141. 10. Anon. (1980). Lubricants in refrigerant systems. ASHRAE Systems Handbook, Chap. 32. 11. Murray, S.F., Johnson, R.L., and Swikert, M.A. (1956). Dichloromethane as a boundary lubricant for steel and other metals. Mech. Eng., 78, 233.

12. Komatsuzaki, S. (March 1991). Antiseizure and antiwear properties of lubricating oils under refrigerant gas environments. Lubr. Eng., 47, 193–198. 13. Lansdown, A.R. (1994). High Temperature Lubrication. Mechanical Engineering Publications Limited, London, ISBN 0 85298 897 4. 14. Sanvordenker, K.S. (1991). Durability of R-134a compressors — the role of the lubricant. ASHRAE J., V, 33, 42. 15. Field, J.E. and Henderson, D.R. (1998). Corrosion of metals in contact with new refrigerants/lubricants at various moisture and organic acid levels. ASHRAE Trans., V, 104, Pt. 1. 210–220. 16. Jones, R.L, Ravner, H., and Cottington, R.L. (1970). Inhibition of iron-catalysed neopentyl polyol ester thermal degradation through passivation of active metal surfaces by tricresyl phosphate. ASLE Trans., 13, 1–10. 17. Randles, S.J, Whittaker, A.J, Nishizawa, T., and Corr, S. (November 1997). Field Experience with the Plugging of Capillary Tubes and TXVs using POE Lubricants. International Conference on Ozone Protection Technologies, Baltimore. 18. Lilje, K.C. (2000). The impact of chemistry of the use of polyol ester lubricants in refrigeration. ASHRAE Trans., V, 106, Pt. 2.

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19. Komatsu, S., Tsunoda M., and Yamamato, S. (December 2000). Development of Automotive Air Conidtioing System Using Carbon Dioxide. The International Symposium on HCFC Alternative Refrigerants and Environmental Technology 2000. The Japan Refrigeration and Air Conditioning Industry Association. Kobe. pp. 80–83. Paper 4.2. 20. Hagita, T., Kobayashi, H., Takeuti, M., Itiyanagi, T., Horaguti, N., and Ukai, T. (December 2000). The Development of CO2 Scroll Compressor for Automotive Air-Conditioning Systems. The International Symposium on HCFC Alternative Refrigerants and Environmental Technology 2000. The Japan Refrigeration and Air Conditioning Industry Assosiation. Kobe, pp. 48–51. Paper 2.4. 21. Kawaguchi, Y., Takesue, M., Kaneko, M., and Tazaeki, T. (July 2000). Performance study of refrigeration oils with CO2 . Society of Automotive Engineers. http://www.sae.org/misc/ac/presentations/idemitsu.pdf. 22. Takahashi, H. (February 2000). An introduction of miscible refrigeration oil for ammonia refrigerant. Refrigeration, 76, 111–114. 23. Oberle, J. and Rajewski, T. (March 1997). The development of lubricants for ammonia refrigeration systems. IIAR 19th Annual meeting. New Orleans, Lousiana, USA.

31

Hydraulics Douglas G. Placek CONTENTS 31.1

31.2

31.3

Introduction 31.1.1 Hydraulic Principles and Fluid Functions 31.1.2 Historical Development Synthetic Hydraulic Fluids and Properties 31.2.1 Why Synthetics? 31.2.2 Properties and Chemistry 31.2.2.1 Viscosity 31.2.2.2 Viscosity Index 31.2.2.3 Pump Efficiency 31.2.2.4 Low Temperature Fluidity 31.2.2.5 Viscosity–Pressure Characteristics 31.2.2.6 Compressibility 31.2.2.7 Air Release/Antifoam 31.2.2.8 Filterability 31.2.2.9 Hydrolytic Stability and Demulsibility 31.2.2.10 Thermal Stability 31.2.2.11 Oxidation Stability 31.2.2.12 Antiwear, Extreme Pressure, and Fatigue Life Properties 31.2.2.13 Friction Modification 31.2.2.14 Compatibility 31.2.2.15 Volatility 31.2.2.16 Radiation Resistance 31.2.2.17 Heat Transfer Properties 31.2.2.18 Contamination 31.2.2.19 Fire Resistance 31.2.2.20 Additive-Based Properties 31.2.2.21 Toxicity and the Environment 31.2.2.22 Biodegradability 31.2.2.23 Durability of Properties Comparative Performance 31.3.1 Viscometrics 31.3.1.1 Viscosity 31.3.1.2 Viscosity Index 31.3.1.3 Low Temperature Fluidity 31.3.1.4 Compressibility 31.3.2 Stability 31.3.2.1 Thermal Stability 31.3.2.2 Oxidation Stability 31.3.2.3 Hydrolytic Stability 31.3.2.4 Volatility 31.3.3 Lubricity and Wear Protection 31.3.3.1 Antiwear and Lubricity 31.3.3.2 Fatigue Life

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31.3.4

Compatibility 31.3.4.1 Seal Compatibility 31.3.4.2 Compatibility with Additives 31.3.5 Radiation Resistance 31.3.5.1 Nuclear Radiation 31.3.5.2 Sonic Radiation 31.3.6 Toxicity and Environment 31.4 Applications 31.4.1 Civil Aviation 31.4.1.1 Reasons for Use 31.4.1.2 Types of Fluid Used 31.4.2 Marine 31.4.3 Industry 31.4.3.1 Steel and Primary Metals 31.4.3.2 Mining 31.4.3.3 Manufacturing 31.4.3.4 Power Plants 31.4.3.5 Arctic Environment 31.4.3.6 Water Installations 31.4.4 Automotive 31.4.4.1 Mobile Equipment 31.4.4.2 Brake Fluids 31.4.5 Military 31.4.5.1 Military Aircraft 31.4.5.2 Missiles and Rockets 31.4.5.3 Navy Ships 31.4.6 Construction and Forestry 31.4.7 Servicing and Maintenance Acknowledgments References

31.1 INTRODUCTION 31.1.1 Hydraulic Principles and Fluid Functions Hydraulic systems are designed to transmit energy and apply large forces with a high degree of flexibility and control. Water and many other liquids can be utilized to make practical use of Pascal’s Law, which states that a fluid compressed in a closed container will transmit the resulting pressure throughout the system undiminished and equal in all directions. Hydraulic systems provide a significantly more accurate and adjustable means to transmit energy than electrical or mechanical systems. In general, hydraulic systems are reliable, efficient, and cost effective, leading to their wide use in the industrial world. They are part of a major technical discipline called fluid power technology. A typical hydraulic system includes the following components [1]: 1. A fluid flow or force-generating unit that converts mechanical energy into hydraulic energy, such as a pump. 2. Piping for transmitting fluid under pressure.

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3. A unit that converts the hydraulic energy of the fluid into mechanical work, such as an actuator or fluid motor. There are two types of motors, cylindrical and rotary [2]. 4. A control circuit with valves that regulate flow, pressure, direction of movement, and applied forces. 5. A fluid reservoir that allows for separation of water, foam, entrained air, or debris before the clean fluid is returned to the system through a filter. 6. A liquid with low compressibility capable of operating without degradation under the conditions of the application (temperature, pressure, and radiation). In this setup, the pump can be considered the heart of the system and the hydraulic fluid the lifeblood of the equipment. It is important to note that the pump does not generate pressure; it provides fluid flow into a system under pressure. The compression developed in the system is a result of the fluid flow restriction caused by control valves or a work load. The efficiency of the pump depends on proper viscosity selection and control, as well as protection against wear, cavitation, and corrosion. Wear or other deterioration of the sealing surfaces will allow internal leakage (or fluid recycle) from the high pressure side

back to the low pressure side of the pump. Internal leakage reduces the pump output, results in power loss, and increases the operating temperature of the fluid. Increased fluid temperature can cause higher levels of oxidation, and lead to deposits or varnish formation. These contaminants, as well as rust or dirt, can clog fine clearances and cause fluid flow or oil starvation problems. Since hydraulic fluids are transmitters of power through pressure and flow hydrostatics, they must be practically incompressible and must flow readily at all operating temperatures. They must also provide adequate seal, protect the working metal surfaces from wear and corrosion, and separate themselves easily from water and debris while in the sump, before being recirculated into the pump. Of all the components in a hydraulic system, the fluid is the most critical and multifunctional part [3]. The functions and requirements of a hydraulic fluid are summarized in Table 31.1. Many of these properties affect not only the function indicated but most of the other functions as well. A typical example is viscosity. If the fluid does not flow properly, heat transfer suffers, power transmission and control deteriorate, and all functions are put under stress. Synthetic hydraulic fluids are similar to mineral oil fluids in their functionality, with numerous performance

TABLE 31.1 Functions and Properties of Hydraulic Fluids Function

Property

Power transfer and control medium

Low compressibility (high bulk modulus) Fast air release Low foaming tendency Low volatility

Heat transfer medium

Good thermal capacity and conductivity

Sealing medium

Adequate viscosity and viscosity index Shear stability

Lubricant

Viscosity for film maintenance Low temperature fluidity Thermal and oxidative stability Hydrolytic stability/water tolerance Cleanliness and filterability Demulsibility Antiwear characteristics Corrosion control

Pump efficiency

Proper viscosity to minimize leakage High viscosity index

Special function

Fire resistance Friction modification Radiation resistance

Environmental impact

Low toxicity, when new or decomposed Biodegradability

Functioning life

Material compatibility

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advantages. In this chapter we will review how synthetic hydraulic fluids can be more durable under thermal/ oxidative stress, cleaner in operation, and span a broader spectrum of application. In the case of fire-resistant fluids, some synthetics are overwhelmingly superior to mineral hydraulic fluids, offering significant improvements in personal and property protection. Synthetic lubricants also justify their higher initial costs when used in severely oxidizing or high temperature environments [4].

31.1.2 Historical Development The earliest use of water hydraulic systems date back to the ancient Egyptians in 2000 b.c., and modern applications (hydraulic water press) are documented in the late 18th century. The availability of refined mineral oils in the early 20th century enabled the development of systems that could operate at higher temperatures and pressures, overcoming the limitations of water volatility. Pascal’s discovery of the fundamental law of physics (1664) on which hydraulic systems are based, enabled the development of fluid power on a scientific basis. One of the first documented uses of hydraulic power in industrial applications is credited to the London Hydraulic Power Company, which supplied power for the Tower Bridge, among other things. In 1906 oil based hydraulic systems were used in warships with heavy artillery. In the 1920s the use of water in hydraulic systems decreased and the use of oil increased. Synthetic hydraulic fluids were mentioned in the context of ester based lubricants in the 1937 Zurich Aviation Congress. The largest push for the development of synthetic hydraulic fluids came during World War II by the military establishments. The main driving force was the need for better low temperature fluidity and fire resistance. Aviation has been, perhaps, the most demanding application for synthetic hydraulic fluids. Overall, the U.S. military has played the leading role in opening the road to new and better lubricants and hydraulic fluids, and is generally given credit for the coordination of diverse industry efforts resulting in the advancement of the highest quality of lubricant and hydraulic fluid technology. An outgrowth of that effort is the development of a dynamic lubricant and hydraulic fluid additive industry that makes use of this technology worldwide.

31.2 SYNTHETIC HYDRAULIC FLUIDS AND PROPERTIES The specific conditions encountered in the application will define the type of product to be used. In the case of synthetic hydraulic fluids, there are more types and chemistries in use than in any other liquid lubricant category. A partial list includes poly-α-olefins (PAOs), dicarboxylic acid esters (diesters), polyol esters (POEs), phosphate esters, polyalkylene glycols (PAGs), alkylated

TABLE 31.2 Synthetic Fluid Advantages over Mineral Oils Fluid type Alkylated aromatics Diesters PAGs PAOs Perfluorocarbons Polyol esters Phosphate esters Polyphenyl ethers Silahydrocarbons Silicate esters Silicones

Primary advantage Low temperature fluidity, thermal and oxidative stability Low temperature fluidity, biodegradability, solvency Low deposit/sludge formation, water miscibility Thermal and oxidative stability, wide temperature operating range Chemically inert, nonflammable, thermal stability Environmentally friendly, fire resistance, wide temperature operating range Fire resistance, lubricity/antiwear Low vapor pressure, chemically inert, thermal stability, radiation resistance Low temperature fluidity, thermal stability, low volatility Low temperature fluidity, thermal stability, low volatility Chemically inert, hydrolytic stability, wide temperature operating range

aromatics, silicones, silicate esters, silahydrocarbons, perfluorocarbons, and polyphenyl ethers. A short summary of these fluid advantages can be found in Table 31.2.

31.2.1 Why Synthetics? The primary reason for selecting a synthetic hydraulic fluid in place of a lower priced and generally excellent quality mineral oil type of fluid is some extreme condition in a particular piece of equipment. Certain equipment is designed to run at high temperature, is undersized for space and weight considerations, cannot be adequately cooled, or is otherwise overstressed with respect to energy flow. The result is thermal and oxidative stress which can lead to accelerated breakdown of a mineral oil fluid. Others are subject to hazardous conditions, such as fire or radiation. Application trends toward higher power density dictate that hydraulic systems operate at higher pressures and temperatures. The hydraulic fluid in mobile construction equipment which currently operate at 3000–4000 psi (∼200–275 bar) and 70–80◦ C, will be challenged to operate at 4000–6000 psi (∼275–400 bar) and 100◦ C in the near future [5]. Synthetic fluids can offer longer life, a wider temperature operating window, and improved pump efficiency under these demanding conditions. To improve reliability, reduce costs, and extend maintenance-free operation of the equipment, a well-chosen synthetic fluid is recommended. The choice is based on specific properties that address the particular extreme in each system.

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31.2.2 Properties and Chemistry When choosing a certain type of chemistry for a hydraulic fluid base stock, one has to know how chemistry relates to each fundamental property of the fluid. A brief discussion of each property with respect to its performance in a hydraulic system is given in the following section. The comparative performance of each fluid type with regard to the various performance properties can be found in Section 31.3. 31.2.2.1 Viscosity Viscosity is one of the most important properties of any lubricant or hydraulic fluid, mineral oil or synthetic, and for systems and applications of all types. It is directly related to wear control (elastohydrodynamic lubrication film), liquid frictional losses, leakage, start-up ease, and efficiency. ISO 3448 (ASTM D 2422) is used to define viscosity grades, and there are three grades that represent over 80% of all fluid consumed: ISO VG 32, ISO VG 46, and ISO VG 68 [2]. In the 1980s, an effort was initiated by ASTM to develop a more informative classification system, which resulted in the approval of ASTM D 6080 [6]. The objective was to have a common, meaningful basis for classifying lubricants derived from viscosity measurements at a variety of temperatures. These combined viscometric properties have a direct relationship to hydraulic fluid performance. This practice was not intended to replace ISO 3448. Rather, it was an enhancement intended to provide a better description of the viscosity characteristics of lubricants used as hydraulic fluids. It includes factors related to low temperature viscosity, high temperature viscosity, and shear stability, which improve its relevance to actual in-service performance of hydraulic fluids. ASTM D 6080 utilizes ten low temperature viscosity grades which are defined by the temperature at which the oil reaches a viscosity of 750 mPa sec measured in the Brookfield viscometer (ASTM D 2983). This value corresponds to the maximum start-up viscosity specified by many oil equipment manufacturers (OEMs) for vane pumps. ASTM D 6080 includes a high temperature viscosity designation of the fluid corresponding to its rounded kinematic viscosity at 40◦ C (ASTM D 445) after it has been sheared in the 40 minute Sonic test (ASTM D 5621). For fluids containing a viscosity index improver, the ASTM D 6080 viscosity classification also includes a viscosity index designation (ASTM D 2270) after shearing the fluid in the 40 minute Sonic test. Proper viscosity grade selection is critical for optimizing equipment performance and operating costs. At low temperature, excessive viscosity may result in poor mechanical efficiency, difficulty in starting, and wear. At high temperature, low viscosity will result in low volumetric efficiency, overheating, and wear.

Pump manufacturers often provide in their documentation hydraulic fluid recommendations covering: • The maximum start-up viscosity under load • The range of optimum operating viscosity • The maximum and minimum operating viscosity

A system aimed at supporting equipment users in selecting hydraulic fluids with the appropriate viscosity was developed by the National Fluid Power Association (NFPA) [7]. It introduced the concept of the temperature operating window (TOW) for hydraulic fluids. The TOW corresponds to the difference between the temperatures at which an oil will reach the lowest acceptable operating viscosity and the maximum start-up viscosity for a given pump. The NFPA issued a recommended practice in which the acceptable operating viscosity for most pumps and motors was set from 13 to 860 mm2 /sec [8]. This system provides guidance to the equipment user in selecting the proper fluid for a given range of operating temperatures. Many synthetic fluids have higher viscosity indices than mineral oils, and thus offer a wider temperature operating window. 31.2.2.2 Viscosity index Viscosity index (VI) is a term which describes the viscosity–temperature relationship for a fluid, and is calculated using ASTM D 2270 knowing the viscosity at 40 and 100◦ C. API Group I and Group II mineral oils have VI’s in the range of 95–110. Higher VIs are a generally desirable property as it suggests that the fluid can function over a wider TOW. The TOW is defined as the temperature range over which a particular fluid can meet the maximum and minimum viscosity requirements defined by the equipment builder or pump manufacturer. Many synthetic fluids have VI’s that are higher than that of mineral oils and can be implemented to expand the TOW. If higher VI is desired, specially designed polymers called viscosity index improvers (VII) can be added to the formulation to raise the VI of a fluid and improve viscometric performance [9–11].

viscosity grade and VI is critical in order to obtain optimum system response and guarantee long-term performance [5]. The use of synthetic fluids can be a cost-effective technique that will allow equipment to start smoothly at low temperatures, and also deliver adequate oil flow rates needed for efficient operation at high temperatures. Mineral oils may not be satisfactory choices for challenging applications with wide TOW requirements, therefore synthetic fluids should be considered. The performance of hydraulic pumps and motors is a critical factor in overall hydraulic system reliability. There are two elements of hydraulic efficiency: volumetric efficiency and hydromechanical efficiency. Hydromechanical efficiency relates to the frictional losses within a hydraulic component and the amount of energy required to overcome viscous drag and generate fluid flow. Volumetric efficiency relates to the flow losses within a hydraulic component and the degree to which internal leakage occurs. Both of these properties are highly dependent on viscosity. Hydromechanical efficiency drops as fluid viscosity increases due to higher resistance to flow. Conversely, volumetric efficiency increases as fluid viscosity increases because of the reduction in fluid recycle or internal leakage. The overall efficiency of a hydraulic pump is the product of mechanical and volumetric efficiencies (Equation 31.1), and both factors must be considered together [5]. As can be seen in Figure 31.1, there is a range of hydraulic fluid viscosity that optimizes the overall efficiency. Overall efficiency = Hydromechanical efficiency × Volumetric efficiency

One of the essential functions of a hydraulic fluid is to provide a lubricating film between moving pump parts that reduces wear. The effectiveness of this film depends upon a balance between viscosity, sliding speeds, and loads within a hydraulic pump. As temperature increases and the fluid film becomes too thin, the lubricant film ruptures and metal-to-metal contact takes place. This results

Volumetric efficiency

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Efficiency

31.2.2.3 Pump efficiency Hard working hydraulic equipment must frequently operate at extreme temperatures, which can impact system response and reduce equipment life. Low temperature startup with high viscosity fluid can lead to delayed work schedules, sluggish operation, hydromechanical losses, and pump cavitation. At peak operating temperature the fluid viscosity is often too low, resulting in poor pump efficiency, inadequate oil flow, and system overheating. Mechanical solutions such as increased cooling capacity, or larger pumps and oil reservoirs are often not practical or too expensive. Selecting a hydraulic fluid with the proper

(31.1)

Mec

hanic

Optimum operating range

Over all ef

al ef

ficien

cy

ficien

cy

Viscosity

FIGURE 31.1 Relationship of viscosity to pump efficiency

in wear within the pump and additional fluid heating. Loss of volumetric efficiency causes the pump to work harder to produce the required flow to hydraulic actuators. At the same time, high temperatures compromise volumetric efficiency as the result of low viscosity fluid bypassing critical pump clearances. Thus, inadequate viscosity due to high temperatures creates a destructive cycle of rising temperatures, accelerated wear, and increased internal leakage. Synthetic hydraulic fluids with high VI are an excellent choice for equipment where the operating temperatures can vary widely. Synthetic hydraulic oils are also recommended to eliminate the downtime and maintenance costs associated with seasonal oil changes. A properly selected synthetic fluid will perform well at both winter and summer temperatures [12], compared to monograde mineral oil fluids. 31.2.2.4 Low temperature fluidity If fluid flow is insufficient at low temperature, cavitation can occur in the pump intake, or the cylinder operation can be impeded. Pump manufacturers have set limits for the maximum viscosity at cold start. The general limit recommended for vane pumps is 4000 SUS, or about 860 cSt. For piston pumps, the typical limit is 7500 SUS, or about 1600 cSt [8]. 31.2.2.5 Viscosity–pressure characteristics The measure of this property is the viscosity–pressure coefficient α. The higher the coefficient, the higher the viscosity increase with pressure. Lower coefficients allow wider ranges of operating pressures and reduced power losses possible. At pressures less than 700 bar (∼10,000 psi), the increase in viscosity due to pressure is not significant for mineral oil or synthetic fluids [10].

31.2.2.7 Air release/antifoam Fast air release and antifoaming properties are important for two reasons: to prevent “spongy” hydraulic controls and poor power transmission due to air entrainment, and also to avoid oil flow discontinuity, which can affect lubrication and wear protection. Antifoam additives, such as silicone oils, are often used, to modify the surface tension and inhibit bubble formation. However, certain additives can prove detrimental in some hydraulic fluid applications because they might weaken the air release properties. Foaming tendency is typically measured by ASTM D 892, and air release performance by ASTM D 3427 (DIN 51381 or IP 313). 31.2.2.8 Filterability Filterability is a measure of the ability of a fluid to pass through a standard filter without clogging or plugging. There are a wide variety of filterability test standards published by fluid suppliers and OEM’s, as well as industry standards from ISO and AFNOR. The filterability of clean base oils, either synthetic or mineral oil, is typically very good. Filterability is highly influenced by additive chemistry and the overall hydrolytic stability of the fluid [14]. Most test methods can be run dry, or with the addition of a prescribed amount of water contamination. Wet filterability tests are typically the most challenging to pass, as additive interactions with water can sometimes lead to the formation of gels that reduce fluid flow across the filter. A list of industry standard tests for filterability can be found below: • • • • •

AFNOR NF E 48690 (dry) AFNOR NF E 48691 (wet) ISO 13357 part 1 (wet) part 2 (dry) Denison TP 02100 (dry) Pall FIT-PMO Rev. 4

31.2.2.9 Hydrolytic stability and demulsibility 31.2.2.6 Compressibility As power transmitters, hydraulic fluids require very low compressibility (i.e., change in volume induced by a change in pressure) to be effective. A low compressibility ratio, which is the reciprocal of the volume elastic modulus (or bulk modulus), translates into fast response time, high pressure transmission velocity, and low power loss. Materials with high ratio or low bulk modulus act as damping fluids. The importance of high bulk modulus becomes greater when equipment size and weight are critical, as in aircraft. A poor bulk modulus will require increased line sizes and actuator cross-sectional areas to compensate for the lower stiffness or higher compressibility of the fluid. These increases will also mean larger fluid volume and weight in the system [13].

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A synthetic hydraulic fluid has to face the most important problem of most hydraulic oils, which is water. In this encounter, it must retain its chemical integrity (and not hydrolyze), and separate easily from the water soon after the encounter. Nonpolar fluids tend to demulsify well, with polar fluids showing a tendency to disperse or emulsify water. In general, highly polar additives such as corrosion inhibitors and antiwear additives are the source of most demulsibility problems. Formulators must select an additive package that balances all these performance requirements. The industry standard test for evaluating hydrolytic stability is ASTM D 2619, Hydrolytic Stability of Hydraulic Fluids (Beverage Bottle Method). In this test, a fluid is sealed in a rotating bottle containing water and a copper strip for 48 h at 93◦ C. Fluid decomposition,

by hydrolysis or oxidation, can produce acidic species which can possibly increase the tendency to emulsify water. Demulsibility performance of new fluids is typically evaluated by ASTM D 1401, in which 40 mL of oil and 40 mL of water are mixed at high speed, and then observed for separation. Fluids with good demulsibility will show complete separation in less than 30 min. 31.2.2.10 Thermal stability Synthetic hydraulic fluids require good thermal stability at high temperatures because they have to operate under severe conditions. Bond energies, position of an atom in a chain, and general molecular structure will determine thermal stability. This knowledge serves as a guide in designing molecules for use as synthetic hydraulic fluids. Thermal stability is frequently assessed by thermal degradation temperature (TDT). Since TDT is frequently adversely affected by the presence of metals, one can examine the impact of various metals using differential scanning calorimetry (DSC) in the presence of metals found in the hydraulic system (iron, copper, zinc, and magnesium). 31.2.2.11 Oxidation stability Good oxidation stability is a typical strength for a synthetic hydraulic fluid. There are a wide variety of oxidation stability tests applied to hydraulic fluids, a summary of which is provided in Table 31.3. Viscosity increase, total acid number (TAN), and sludge or deposit generation are the main criteria in such tests. 31.2.2.12 Antiwear, extreme pressure, and fatigue life properties The antiwear (AW) properties of a synthetic hydraulic fluid are not necessarily better than those of a mineral

type. However, formulation technology can boost the AW and extreme pressure (EP) performance of most synthetic hydraulic fluid types. Therefore, meaningful comparison can only be based on finished fluids. A wide variety of laboratory wear tests can be used to predict fluid AW capabilities, but hydraulic pump rig tests are preferred by most OEM’s as the best indication of fluid performance. Industry standard wear test protocols have been published by Denison (T6H20C hybrid pump) and Eaton–Vickers (35VQ25). The industry is currently evaluating replacements for the long standing ASTM D 2882 vane pump test, as production of the Vickers V-104C has been discontinued, and replacement parts are no longer available from the OEM. Extreme pressure performance is a performance requirement in European and Japanese specifications, and enables the fluid to carry higher loads. North American fluid specifications do not typically call for any particular level of EP performance. EP performance is usually assessed by the FZG load stage failure rating, according to DIN 51354. The fatigue life, such as the rolling fatigue life of bearings, is an important consideration in most systems. Generally, it appears that the more polar or reactive a fluid, the worse the expected fatigue life. AW, EP, and fatigue life are not always related and must be evaluated independently. 31.2.2.13 Friction modification The term “friction modification” usually implies a low static coefficient of friction or at least one that is not significantly higher than the dynamic coefficient of friction. Most hydraulic fluids, both synthetic and mineral based, do not require friction modification. Nevertheless, friction modification significantly reduces the “solid friction” (the one between boundary layers or solid surfaces) and increases efficiency in most mechanical systems.

TABLE 31.3 Hydraulic Fluid Oxidation Stability Tests Test method

Common test name

Conditions

ASTM D 2272 ASTM D 943 DIN 51587 ASTM D 4310 Cincinnati machine P-68, P-69, P-70 ASTM E 537 Penn state micro-oxidation test FTMS 3462 FTMS 5308.6

RBOT TOST Sludge Cincinnati machine

Oil + water + copper + oxygen at 150◦ C Oil + water + copper/iron + air at 95◦ C

DSC PSMO Panel coker Federal test method

Oil + air in metal pan Oil + air at 225◦ C Oil sprayed on steel surface at 300◦ C Oil + air + 5 metals at 175◦ C

DIN 51373 for fire-resistant heat transfer fluids DIN 51554

Oxidation test

Oil + air + copper/iron at 120◦ C

Baader test

Oil + air + metals at 110◦ C

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Oil + water + copper/iron + oxygen at 95◦ C Oil + copper/steel at 135◦ C

Measured Time for a 25 psi pressure drop Time to reach TAN of 2.0 Insoluble sludge generation Metals color change, sludge generation Time for oxidation onset Weight loss and deposits Deposit formation TAN increase, viscosity increase, metals corrosion TAN increase, viscosity increase, metals corrosion TAN increase, viscosity increase

Automatic transmission fluids and tractor fluids that also function as hydraulic oils in their respective systems are friction-modified, each within strict specifications. Those, however, are outside the scope of this chapter and are treated separately in this book (see Chapter 20). If a hydraulic fluid needs friction modification — to avoid, for example, stick-slip phenomena — special additives are used. These so-called friction modifiers are mainly long chain polar molecules [15]. 31.2.2.14 Compatibility Compatibility of the fluid with all materials of the system is always required, with seal compatibility a important consideration for synthetic fluids. To avoid leaks, a hydraulic fluid must slightly swell a seal, but never overswell, shrink, harden, depolymerize, or otherwise harm the integrity of the seal. Synthetics with highly polar groups act as plasticizers and can pose a difficult challenge in that they overswell and attack conventional nitrile (Buna-N) seals designed for use with mineral oils. Special seal and hose materials can solve this problem. Other materials that require fluid compatibility are packing, plastic parts, paints, and all types of metals in contact with the fluid. Manufacturers must be consulted when converting any hydraulic system from one fluid type to another. Most fluids types are not compatible with each other, and therefore thorough flushing techniques must be followed to avoid operational problems. 31.2.2.15 Volatility When choosing a hydraulic fluid for high temperature operation, one has to make sure that there will be no volatility problems. This measure is essential to avoid significant evaporation rates or low-flash-point-related situations, and also to avoid bubble formation at low pressure points, and thus pump cavitation. In homogeneous fluids, such as synthetic bases, no volatile components are expected. The volatility of the fluid will be determined mostly by the molecular weight and molecular cohesion forces. At low base oil viscosity, such as 2 cSt PAO (at 100◦ C) [16], the volatility factor must be examined before the application decision is made. 31.2.2.16 Radiation resistance Systems exposed to radiation must be serviced by hydraulic fluids that meet special requirements for radiation resistance. 31.2.2.17 Heat transfer properties The thermal capacity and conductivity of the fluid are design parameters in every hydraulic system. Fluids with a low coefficient of thermal expansion and low specific gravity are preferred.

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31.2.2.18 Contamination Contaminants from the environment can clog fine passages in the system and derate the flow and lubricating ability of the fluid, as well as negating several other desirable characteristics. A contaminated system will require costly downtime and repairs. Seals, when they retain their integrity and function, can protect the system from much of the outside contamination. Proper filtration and fluids sourced with appropriate cleanliness (according to ISO 4402) can insure good performance. 31.2.2.19 Fire resistance Fire resistance is a major performance requirement that has led large segments of industry and commerce to adopt the use of synthetic base stocks. Fires have been caused by accidental leakage of hydraulic fluid onto hot surfaces, resulting in combustion. Rupture or puncture of a high pressure hydraulic hose has been known to spray fluid up to 12 m away in the form of fine mist, which is highly combustible if it is made of mineral oil. Factories, ships, airplanes, military units, and other users have all experienced similar problems, and many have adopted special fire-resistant hydraulic fluids as the best practical solution. Fire resistance is a complex property measured by several different tests, and specification writers disagree about some of its aspects. Generally, values for spontaneous ignition, ignition point, heat of combustion, combustion persistence, and flame migration are among the criteria for fire resistance. Additional information on fire-resistant fluids can be found in Chapter 33. 31.2.2.20 Additive-based properties A functional fluid must, in addition to transmitting power, provide lubrication, heat transfer, corrosion resistance, and seal the system from contamination. The composition of the base stocks and additives contributes to each of these functions. Additives are required to reinforce or supply a large number of properties in synthetic hydraulic fluids, as they do in most lubricants and fluids. Hydraulic fluids generally contain a variety of additives having many different functions. Additive types frequently used include antioxidants, AW, and EP additives, antifoam agents, detergents, dispersants, demulsifiers, VII, pour point depressants, rust inhibitors, and corrosion inhibitors [17]. 31.2.2.21 Toxicity and the environment Environmental considerations, including the safety of people dealing with the hydraulic fluid through its operating life, are critical factors in the choice of a product. Although such matters can impose restrictions in selecting a fluid, they cannot be overridden by any performance or cost considerations. When use of a toxic fluid is seen as the only

practical answer, very severe system design safeguards are mandatory. Generally, a synthetic hydraulic fluid must be safe and benign to the environment, both when new and after decomposition. Reviews of current regulatory initiatives related to environmental aspects of hydraulic fluids have appeared [18–23]. Approximately three years ago, the fluids section of the Verband Deutscher Maschinen and Apparate Bauer (VDMA), which represents hydraulic oil formulators and OEMs in Germany, and the British Fluid Power Association (BFPA), issued guideline property and performance specifications for three distinct classes of environmentally acceptable hydraulic fluids. The three classes were differentiated by the base fluid type as follows: Class 1: vegetable oil based fluids, coded HETG Class 2: synthetic ester based fluids, coded HEES Class 3: polyglycol-based fluids, coded HEPG This classification is based on chemical type and not on performance. Two years later the classes were issued as a first draft of an ISO specification for environmentally acceptable hydraulic fluids (EAHFs). A new fourth class of EAHF based on PAO has recently been included in the most recent (third) draft issued by ISO, based on promotion of PAO-based EAHFs through the BFPA, the VDMA, the Svenska Mekanisters Rikssorenings (SMR), and German hydraulic equipment OEMs: Class 4: PAO-based fluids, coded HEPR (where PR = PAO-related) SMR has issued a specification for EAHFs that is based on performance criteria alone, without reference to base fluid chemistry. This is similar to the approach taken by the American Society for Testing and Materials (ASTM) in the United States. There are schemes in place in Germany which define the proper handling of fluids. The German Water Hazard Classification (WGK) regulates the handling of all fluids, including hydraulic (transportation and storage) fluids within Germany. The German Blue Angel scheme, initiated by the German Ministry of Environmental Affairs, has been recently extended to EAHFs. For example, the Blue Angel scheme already includes the requirement calling for the use of biodegradable chain saw oils. Toxicity is the inherent potential capacity of a substance to cause adverse effects on a living organism. Since a biodegradable substance could be or become ecotoxic, various tests have been designed to measure ecotoxicity [24]. Toxicity testing of hydraulic fluids has been surveyed [25]. In the United States, ASTM classification D-6046

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establishes categories of hydraulic fluids distinguished by their response to standardized laboratory procedures. The procedures indicate a possible response of certain environmental compartments to the added hydraulic fluid [26]. The classification consists of two test groups: one addresses the environmental persistence (aerobic aquatic biodegradability) and the other addresses the acute ecotoxicity of hydraulic fluids. 31.2.2.22 Biodegradability Biodegradable hydraulic fluids are becoming more and more important globally. The driving force for this trend seems to be coming from Europe; however, legislation on both sides of the Atlantic is forcing the formulation of more ecologically benign hydraulic fluids. Application areas include offshore uses such as offshore drilling and harbor maintenance activities such as dredging. Construction, forestry, and snow removal applications have also begun to use environmentally safe fluids. Three main criteria are used for the evaluation of the potential impact of a hydraulic fluid on the environment: biodegradability, toxicity, and bioaccumulation. Biodegradation is generally divided into primary and ultimate categories. Primary biodegradation is degradation to the minimum extent to change the identity of a substance [24]. Ultimate biodegradation refers to the complete conversion of the substance to carbon dioxide, water, inorganic salts, and biotic mass. Table 31.4 summarizes some of the biodegradation testing done in Europe on hydraulic fluids. In the United States, aerobic aquatic biodegradability testing is established by ASTM D-6046 [26], the standard classification of hydraulic fluids for environmental impact. Bioaccumulation has been defined as the process by which chemicals are taken up by aquatic organisms directly from water, or through consumption of food containing the chemical [24].

TABLE 31.4 Biodegradation Test Methods and Pass/Fail Criterion Method

Criterion

Primary

CEC-L-33-A-93 21-Day test Loss of hydrocarbon IR band

>67% (COMIA Standard) or >80% (German Blue Angel)

Ultimate

Modified Sturm (OECD 301B) 28-Day test Conversion to carbon dioxide

>60%

Ultimate

Modified AFNOR (OECD 301A) 28-Day test Loss of dissolved organic carbon

>70%

31.2.2.23 Durability of properties Quality performance starts with a fresh, high quality hydraulic fluid charge in a clean piece of equipment. It proceeds with the retention of all the good properties and performance attributes, over a long period of operation. A short-lived performance would necessitate frequent downtimes for fluid change, at the very least, and sometimes costly equipment repairs. To assure durability of properties, a carefully crafted additive package is fitted to the proper base fluid. Such additives as antioxidants, detergent/dispersants, stabilizers, corrosion inhibitors, lubricity or AW agents, and demulsifiers are among those chosen to build up and sustain desirable fluid properties. The fluid durability and useful life will depend heavily on the proper match of fluid properties to application demands.

31.3 COMPARATIVE PERFORMANCE Synthetic hydraulic fluids can provide the operator with a wide variety of performance improvements under challenging conditions. This section offers a comparison of the relative performance of the various classes of synthetic fluids. These ratings are averages, because each fluid category contains several grades or variations of molecular structures. Therefore, properties can vary widely within each category, and actual selection for an application needs more specific information than can be given here. Manufacturers should be consulted for specific information about commercial product performance.

31.3.1 Viscometrics Viscometrics includes high temperature viscosity, low temperature fluidity, VI, and pressure viscosity. Table 31.5

presents the relative performance in viscometrics for a variety of synthetic fluids. Clearly, some of the most expensive synthetics, such as fluorocarbons and polyphenyl ethers, show poorer viscometrics than paraffinic mineral oils. Conversely, PAOs, diesters, polyol esters, alkylbenzenes, polyglycols, silicones, and silicate esters are superior to mineral oil. This often holds true for pressure– viscosity relationships too [27]. Therefore, these synthetics would make good hydraulic fluids with regard to viscometrics in a fairly wide range of temperature and pressure conditions. The widest possible TOW is desirable in order to improve equipment performance and energy efficiency [5]. 31.3.1.1 Viscosity Most chemistries can provide products at low and medium range viscosities. Higher viscosities (above 100 cSt at 40◦ ) can be obtained with PAOs, polyglycols, silicones, and fluorocarbons in higher molecular weight forms. 31.3.1.2 Viscosity index Polyol esters, PAOs, diesters, polyglycols, trialkyl phosphates, silicate esters, and silicones usually have high VI, relative to paraffinic mineral oil. Polyaromatics, halogenated hydrocarbons, triaryl phosphate esters, and polyphenyl ethers have a lower VI, some of them even lower than mineral fluids. Compounds with alkyl structures will have higher viscosity index (>100) than those with aryl structures (<100). Selecting a fluid with high VI is important if a wide TOW is to be accommodated. All these fluids can be supplemented with viscosity index improver additives if necessary.

TABLE 31.5 Relative Performance in Viscometrics Product Mineral oil (paraffinic) PAOs Diesters POE PAG Phosphate esters Trialkyl phosphates Triaryl phosphates Silicones Alkylbenzenes Fluorocarbons Polyphenyl ethers Silicate esters Silahydrocarbons

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Low temperature fluidity

Viscosity index (VI)

Pressure–viscosity

Good Excellent Excellent Very good Very good

Good Very good Very good Very good Very good

Good Good Good Very good Very good

Excellent Fair Very good Excellent Fair Poor Excellent Excellent

Very good Poor Excellent Good Fair Poor Excellent Very good

Excellent Excellent Excellent Good Fair Poor Very good —

31.3.1.3 Low temperature fluidity Good low temperature fluidity is observed in synthetics having a large flexible molecular group or side chains. Fluorocarbons or polyphenyl ethers are rigid and therefore have poor low temperature fluidities. The PAOs and most organic esters have very good low temperature fluidity. Aryl phosphate esters are less flexible and only exhibit fairly low temperature properties. Pumping efficiency at low temperature is one area of superiority of some synthetics over mineral fluids. Thus, diesters, PAOs and other fluids with good low temperature fluidity offer significant improvements in hydromechanical pumping efficiency over mineral oil hydraulic fluids [28]. 31.3.1.4 Compressibility The compressibility or bulk modulus of polyphenyl ethers is excellent, which means that it has a very small compression ratio. It is followed by phosphate ester, which is superior to mineral oil. Generally, fluids with aromatic rings in their molecular structure have a smaller compression ratio, although the change in viscosity with temperature is quite large [29]. Silicate esters and silicones are worse than mineral oils. Perfluorinated fluids, like fluoroalkyl esters, show poor bulk modulus [13].

31.3.2 Stability Stability considerations important for hydraulic fluids include thermal stability, oxidation stability, hydrolytic stability, and volatility. Table 31.6 shows the relative performance in stability for several types of synthetic hydraulic fluids. These fluids are compared in their finished form, which means they are fully formulated with the proper additives. A comparison of the performance of hydraulic oils based on mineral oil (HLP), rapeseed oil (HETG), and

oleic acid esters (HEES) in a gear pump test has been reported [30]. The synthetic ester based hydraulic oil exhibited better viscosity control than the rapeseed oil based fluid, resulting in less frequent oil changes. 31.3.2.1 Thermal stability The thermal stability of polyphenyl ether, fluorocarbons, and silicones is superior to that of mineral oil and even exceeds that of the various carboxylic acid esters. Silahydrocarbons also show superior thermal and storage stability [31–34], especially the saturated ones [35]. 31.3.2.2 Oxidation stability While fluorocarbons and fluoroesters are top-rated in oxidation stability, PAOs and esters also perform very well. Silicones, polyphenyl ethers, and others achieve moderately good results. It is emphasized that antioxidants are practically always used in formulating synthetic hydraulic fluids, with the type of antioxidant frequently adapted to the chemistry and solubility/compatibility of the base fluid. The useful oxidation stability of a fluid depends on the temperature of application. Table 31.7 shows the tentatively recommended temperatures of operation for several synthetic hydraulic fluids [29]. The numbers are only approximations, since variations in grades and above all in formulation can make a very big difference in the actual operation. In recently reported studies on the stability and corrosion properties of eight commercial vegetable oil based biodegradable hydraulic oils [36], laboratory tests revealed that these oils exhibited generally poor oxidative stability. The oils were all derived from rapeseed oil and did not contain metallic additives. The eight oils all had large changes in viscosity, total acid number, and iodine values after oxidation. Vegetable oil based, environmentally

TABLE 31.6 Relative Stability of Formulated Synthetic Hydraulic Fluids Product

Thermal

Oxidation

Hydrolytic

Volatility

Mineral oil (paraffinic) PAOs Diesters POEs PAGs Trialkyl phosphate esters Triaryl phosphate esters Silicones Alkylbenzenes Fluorocarbons Polyphenyl ethers Silicate esters Silahydrocarbons

Good Very good Good Good Good Good Excellent Very good Good Excellent Excellent Very good Excellent

Fair Very good Very good Very good Good Good Excellent Good Good Excellent Good Good Very good

Excellent Excellent Good Good Good Fair Good Excellent Excellent Good Excellent Fair to poor Excellent

Poor to fair Very good Good Good Good Poor to fair Excellent Excellent Good Poor Excellent Good —

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TABLE 31.7 Recommended Operating Temperature Ranges Temperature (◦ C) Product

Long service

Mineral oil PAOs Polyglycols Diesters Polyol esters Triaryl phosphates Silahydrocarbons Silicate esters Silicone Polyphenyl ethers

93–121 149–232 163–177 177 191 204 149–232 191–204 218–288 316

Short service 135–149 288 191–204 204 218 274 288 246–274 288–329 427

acceptable hydraulic fluids have been shown to be limited in their useful range of operation (−10 to 90◦ C). This is due to poor thermal stability and limited low temperature performance [37]. In studies using pressurized differential scanning calorimetry, the vegetable oil based fluids were shown to have poorer oxidative stability than the fluids based on synthetic esters and petroleum. 31.3.2.3 Hydrolytic stability Hydrocarbon fluids exhibit excellent hydrolytic stability due to their hydrophobic nature. Top performers include PAOs, alkylbenzenes, polyphenyl ethers, and silicones. Silahydrocarbons are hydrolytically stable, whereas those with silicon alkoxy bonds and silicate esters are unstable [38,39]. However, hydrolytic stability of silicate fluids can be considerably improved if the silicon atoms are shielded by carbon moieties, as in certain silicone clusters [40]. All esters tend to succumb to hydrolysis, as they are more hydrophilic. Phosphate esters should be kept dry, as their decomposition by-products can be very corrosive. Traces of chlorine from chlorinated solvents accelerate the phosphate ester hydrolysis to form corrosive products [41]. Such hydrolysis problems can explain why esters in general are infrequently used as hydraulic fluids in areas where water can be found in close proximity. When fire resistance is of paramount importance, however, hydraulic systems designed to exclude water contamination can use fire-resistant fluids, such as phosphate esters. In the case of carboxylic acid esters, hydrolysis will also produce acids and alcohols or polyols. The organic acids produced are mild but can still lead to corrosion, deposits, and other problems. Some polyhydric alcohols from polyol esters, such as pentaerythritol, can form gels capable of clogging up the fine tolerances of a modem hydraulic system. This is one of the main reasons why carboxylic acid esters are not the leading choices for hydraulic fluids. Silicic acid esters can also hydrolyze and in the presence of acids form

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SiO2 , which is an abrasive similar to sand. Polyglycols are more stable, and water soluble versions demonstrate hydrolytic stability approaching that of hydrocarbon fluids. The effect of corrosion inhibitors on the hydrolytic stability of hydraulic fluids has been studied [42]. 31.3.2.4 Volatility Volatility depends not only on the chemistry but also on the grade of the synthetic fluid. Most fluids are available in a range of molecular weights or viscosities. Overall, polyphenyl ethers, silicones, and triaryl phosphates are excellent for higher temperature operations, or vacuum pump service, having very low volatility. The PAOs are also very good, followed by most of the esters. Fluorocarbons and trialkyl phosphate esters are no better than mineral oil. It is important to note that volatility is likely to be a concern for most fluid types in very low viscosity grades.

31.3.3 Lubricity and Wear Protection The frictional losses, rate of wear, and fatigue life of a system are also highly dependent on the fluid. Although all these properties can be strongly affected by the additive package in the formulation, the base fluid itself has a significant impact. Table 31.6 presents an approximation of the basic properties of several synthetic hydraulic fluid types. It is emphasized again that there can be wide variations within each type. 31.3.3.1 Antiwear and lubricity The natural lubricity or load-carrying ability of the hydrocarbons is exceeded by those compounds having higher polarity, especially esters. Phosphate esters can be strong AW and EP agents when used at additive treat rates in mineral oils or synthetic base stocks. They also demonstrate this performance advantage when used as base fluids. Carboxylic acid esters are also polar molecules that absorb onto metal surfaces, demonstrating natural lubricity and antiwear. However, polar base fluids will compete for metal surfaces with other polar compounds, such as lubricity and AW agents that are specifically included in the additive package. Therefore, additives for ester fluids must be carefully selected in order to achieve a proper balance. Silicones are very nonpolar and have poor absorbability on metal surfaces, as well as poor load-carrying characteristics. This set of inadequacies is attributed to the repelling interaction of the silicon atoms, and it is difficult to overcome with conventional additives [43]. 31.3.3.2 Fatigue life The fatigue life, or specifically the rolling fatigue life of bearing metal surfaces, varies among the different types

recognize that most types of synthetic fluids are chemically unique, and will not be miscible with each other. Manufacturers recommendations on system flushing and cleaning should be closely followed when changing from a mineral to a synthetic oil, or from one synthetic fluid to another.

TABLE 31.8 Relative Lubricity and Wear Protection

Product Mineral oil (paraffinic) PAOs Diesters Polyol esters PAGs Phosphate esters1 Silicones Alkylbenzenes Fluorocarbons Polyphenyl ethers Silicate esters

Natural lubricity and AW

AW with additives

Fatigue life

Good Good Fair Fair Good Excellent Poor Good Fair to good Good Good

Excellent Excellent Good Good Good Excellent Fair Excellent Good Good Very good

Fair to good Good Fair Fair to good Fair Fair Fair to good Good Fair to good Good Poor

1 Acid phosphate esters have excellent AW properties but poor fatigue

life. Acid phosphate esters are used as additives, not base fluids.

of synthetic fluids considered. As Table 31.8 suggests, the polarity or reactivity of a fluid can be detrimental to the expected metal surface fatigue life. Polyphenyl ether, PAOs, and alkylbenzenes have good fatigue lives. Most polar molecules like polyglycols and many esters, especially if they contain acidic species, or additives with reactive groups, exhibit a shorter fatigue life [29]. Therefore it is important to consider the degree of purity or the amount of decomposition products present in a fluid when estimating the fatigue life of a fluid. The phosphate esters constitute a prime example, as they tend to hydrolyze in the presence of moisture. Acid phosphate species are formed which are very polar and reactive, which will tend to shorten the fatigue life. This reaction sequence is more pronounced in the alkyl rather than the aryl phosphates. Therefore, in actual applications, the formulator of a phosphate fluid will incorporate acid neutralizers, such as epoxides, in the formulation. Maintenance engineers are encouraged to use filtration systems that absorb water and remove acidic degradation products, such as activated clay or ion exchange resins [44]. Finally, it is very important to note that the additive systems used will have the highest impact on fatigue life, as all of the base fluids considered are neutral. Highly reactive EP or corrosion inhibitor additives should be evaluated in order to avoid short fatigue life of hydraulic components.

31.3.4 Compatibility Compatibility with seals and other hydrocarbon components, must be determined in order to avoid fluid leakage, or damage to the equipment. When formulating a synthetic hydraulic fluid, care must also be taken is selecting additives with long-term solubility. It is also important to

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31.3.4.1 Seal compatibility All synthetic hydraulic fluids can be successfully used if the correct materials are selected for seals, hoses, and other system components. Most standard hydraulic equipment is designed for use with mineral oil, and therefore synthetic fluids can not always be utilized with common nitrile elastomers. Seal compatibility of PAOs is a concern in that these fluids cause shrinkage of many conventional types of seals. Formulation can correct this shortcoming through the incorporation of moderate amounts of seal swell additives, such as aromatics or esters. Conversely, esters, especially the more polar ones such as lower and medium molecular weight diesters, and certainly phosphate esters, tend to overswell the conventional nitrile seals. Many esters require the use of special elastomers. Some esters actually act as plasticizers, destroying the integrity of the seal or actually dissolving it. Fluorocarbons generally require special seals, such as phosphonitriles. Contrary to most other properties, there is no known additive that can correct overswelling at reasonable concentrations. Fluoroelastomers such as Viton® are compatible with a wide variety synthetic fluids over a wide temperature operating range, and are a good choice for specialty hydraulic systems that will use synthetic fluids. Table 31.9 reviews the seal compatibility of selected hydraulic fluids. The compatibility of conventional and biodegradable hydraulic fluids with elastomeric seal materials during long-term contact has been examined [45]. Elastomer swell properties have been reported to depend on the polarity and molecular weight of hydrocarbon in the oil [46]. Elastomer seal swell has caused problems in-service where mineral oil based hydraulic fluids have been replaced by ester based, EAHFs. Current manufacture of hydraulic equipment anticipates the specification of ester-based hydraulic fluids with respect to the selection of seal materials for full compatibility.

31.3.4.2 Compatibility with additives The majority of lubricant additive chemistries were originally developed for use in mineral oil fluids. Therefore, many of these additives are not optimized for use in synthetic base fluids, or possibly cannot be used at all. Additive compatibility is generally acceptable with all hydrocarbon bases, and is also fairly good with phosphate esters, polyphenyl ethers, carboxylic esters, and silicate esters.

TABLE 31.9 Seal Compatibility of Selected Hydraulic Fluids Seal Material

Mineral Oil

PAO

Water/glycol

Triaryl phosphate ester

Polyol ester

Buna-N Polychloroprene Fluoroelastomer PTFE Butyl rubber Ethylene/propylene

Yes Yes Yes Yes — —

Yes Yes Yes Yes — —

Yes Yes Yes Yes — —

— — Yes Yes Yes Yes

Yes Yes Yes Yes — —

Standard additive solubility is not as good with polyglycols, and it is truly poor with fluorocarbons and silicones. This breakdown imposes a limit on the AW capabilities and other desirable properties of the fluid, which in turn limits the equipment design parameters. The wear-reducing efforts of fluorinated sulfonamide AW additives in chlorotrifluoroethylene oligomer base fluids have been studied by means of a reciprocating tribometer [47,48]. Surface analysis techniques were used, and additives were shown to affect steel surfaces.

31.3.5 Radiation Resistance Radiation in all its forms is an energy input on the fluid and, like heat or oxidation, constitutes a shock to the molecular structures composing it. Resistance to radiation is one form of stability, although a special one. Most hydraulic fluids can skip this requirement because it pertains to a limited number of applications. Two of these are of special interest: nuclear radiation and sonic radiation environments. 31.3.5.1 Nuclear radiation Nuclear radiation can be destructive for many molecular structures. Of the synthetic hydraulic fluids, carboxylic acid esters, phosphate esters, and polyglycols are the most vulnerable. Hydrocarbon types, especially aromatic fluids, fare better. Polyphenyl ethers are among the best, perhaps ten times more resistant than mineral oil [49]. The explanation given is that when a neutron knocks out a hydrogen atom, the H+ carries the entire kinetic energy of the neutron and breaks C–C bonds until its energy is dissipated and the proton cools off. Polymerization occurs when paraffins are used. However, when aromatics are used, fewer fragments are formed and less polymerization takes place. Therefore, less viscosity increase is caused by radiation. With gamma radiation, bonding electrons are kicked out and the molecules decompose into radicals, which leads to polymerization. Again aromatic systems are able to convert the absorbed energy, to a large extent, into resonance energy of the aromatic ring systems without causing bond cleavage.

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31.3.5.2 Sonic radiation Sonic radiation is another form of energy that can attack molecular bonds and cause cracking of structures. There is a whole discipline of chemistry dealing with molecular changes (synthesis or decomposition) based on sonic energy input, which is called sonochemistry. In hydraulic fluids operating in a sonic energy environment, the first components to decompose are polymeric structures, such as the VII. The solution is to use low molecular weight, stable VII additives, or fluids containing no VII at all. Other additives are also subject to sonic shock. Many AW additives are known to decompose and precipitate out. Fluids used in the vicinity of submarine sonar systems must be properly selected to avoid premature fluid degradation problems.

31.3.6 Toxicity and Environment All synthetic hydraulic fluids should be handled with the same care as mineral oils, and operators should avoid extended skin contact as well as inhalation or ingestion. Paraffinic hydrocarbons and PAOs are practically nontoxic for humans who face acute exposure, with several types approved by the FDA for both indirect and incidental food contact. None of the synthetic fluids discussed in this chapter are considered to be acutely toxic. Biodegradability is a very desirable property if significant amounts of a hydraulic fluid leak into the environment. Low viscosity PAOs, especially the 2 cSt grade, and to a lesser extent the 4 cSt grade, are reported to be biodegradable [24,50–52]. Hydraulic fluids based on esters or vegetable oils are considered to be very biodegradable [15]. Rapeseed oil is now being used in many parts of Europe because of its good biodegradability, in applications where the equipment does not require the thermal stability of synthetic esters. Various fluid types have been compared in terms of primary and ultimate biodegradability [24,53]. The biodegradability of environmentally friendly synthetic ester (HEES type) hydraulic fluids has been examined before and after use in radial and axial pumps and in a gear pump [54]. In general it was found that biodegradability (CEC-L-33-A-93) of the synthetic ester based hydraulic

TABLE 31.10 Biodegradability of Base Fluids Typically Used in Ecologically Acceptable Hydraulic Fluids

Fluid type

Primary biodegradation CEC-L-3-A-93 (21 days)

Synthetic esters Vegetable oils PAO-2

>70% >80% 60 to 90%

Ultimate biodegradation (OECD 301B) >40% >70% 60 to 70%

the following: • Excellent low temperature fluidity, to operate in the •

•

• •

fluids was greater than 70% and varied depending on the formulation (see Table 31.10). Several classes of polyol ester fluids are based on acids derived from natural fats and oils, and are an excellent choice for use in equipment in environmentally sensitive areas. Refined vegetable oils are also commonly available, and are in fact natural polyol esters (glyceride tri-oleates) having an excellent environmentally friendly, nontoxic profile. Fluids based on aromatic ring structures tend to exhibit slow biodegradability. Certain triaryl phosphate esters and polyphenyl ethers have undesirable aquatic toxicity ratings as they decompose into phenolic compounds which are toxic to fish and other aquatic organisms.

31.4 APPLICATIONS The application of synthetic fluids covers the full range of technological activities. For easier treatment, these are divided into five main categories of application: civil aviation, industry, marine, automotive, and military. The latter could, to a certain extent, be distributed to the other categories, but that would not do justice to the special nature of many of the military uses. In addition, it must be kept in mind that most of the progress in the synthetic hydraulic fluid area came from the military, which continues to devote considerable resources and time toward further advances.

31.4.1 Civil Aviation 31.4.1.1 Reasons for use Synthetic hydraulic fluids find extensive use in aircraft applications. There is a necessity to function over a wide TOW with high power output utilizing compact and lightweight system design. There is also a requirement for fire-resistant fluids to reduce hazards in the vulnerable areas near the landing system, wheel brakes, and units proximate to the engine heat flow. The key properties that synthetic hydraulic fluids bring to the aircraft include

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coldest environments (−50 to −65◦ C). High viscosity index, to accommodate the rapid change in fluid temperatures from ground level to high altitude. High temperature stability — both thermal and oxidative — to allow prolonged full power operation without significant fluid degradation. Fire resistance, especially in commercial and military aviation to protect passengers and crew. Compatibility with all materials the fluid may contact, some of which are particular to aircraft systems.

31.4.1.2 Types of fluid used A large number of synthetic hydraulic fluid types are used in aviation. Among them are PAOs, phosphate esters (alkyl and aryl or mixed), silicate esters, silanes, fluorocarbons, fluorosilicones, fluoroglycols, and polyphenyl ethers. Many of those were developed for the military and bear military specification code numbers, as discussed in Section 31.4.5. Phosphate esters: Trialkyl phosphate esters are the primary base fluids used in commercial aircraft applications due to their combination of fire resistance and excellent low temperature fluidity. The finished formulation contains additives for improved oxidation and hydrolytic stability, VI boost, and lubricity. Special additives may also be frequently used to suppress valve erosion problems, reportedly due to complex electrochemical phenomena [55,56]. Contamination with chlorinated cleaning solvents or residual chlorine from the manufacturing process, can promote erosion of the metering edges of servovalves. The seals, hoses, packings, and O-rings must be made from special elastomers, because natural rubber, Buna-S, Buna-N, and Neoprene are unsuitable. Among the appropriate types of rubber are butyl, silicone, fluoroelastomers, polytetrafluoroethylene (PTFE), and ethylene propylene diene monomer (EPDM). Phosphate esters are highly polar and will dissolve standard paints and coatings, therefore, epoxy resins and silicone enamels are recommended [57]. Airlines frequently use recycled phosphate ester fluid which is filtered and reprocessed to meet new fluid specifications. Reprocessing of a used synthetic hydraulic fluid, of any type, is normal practice in many applications. Factors in the hydrolysis of phosphate ester based aviation hydraulic fluids have been discussed. A report on the effects of temperature, additive-related factors, and water concentration on thermal hydrolytic stability of phosphate ester based hydraulic fluids is available [58]. Silicate esters: They have been used in the Concorde Supersonic Transport, but such fluids are easily hydrolyzed; they also tend to gel at high temperatures,

and they are poor lubricants. More relevant information on aircraft fluids is given in Section 31.4.5 (military applications).

31.4.2 Marine Performance requirements found in aircraft applications are similar to those in marine applications, thus the need for synthetic fluids. Fires can be devastating on a ship at sea. Shipboard fires are caused by electrical equipment or oil and fuel ignition. Oil escaping through a pinhole in a pipe of hydraulic system at 207 bar, which is a normal operating pressure, can form a jet traveling over 10 m. Also, O-rings and flexible hoses can deteriorate with shock and vibration resulting in leaks. Two kinds of fire-resistant fluid are preferred: phosphate esters and water/glycol fluids. Triaryl phosphates are used, as there is no need for extreme low temperature performance. Poly(alpha-olefins) is extensively used in deck cranes of ships sailing between hot and cold climates. In such cases, PAO retains a useful level of viscosity, and the elastohydrodynamic lubrication factor remains satisfactory [59]. PAOs can also be treated with shear stable VII’s to increase the TOW if necessary. Fluids in marine vessels must be highly reliable, in order to reduce maintenance and costly port delays. The alternative to PAO would have been extensive and expensive equipment modifications. PAO also finds application in high line transfer equipment, which allows transfer of fluids between ships. Piston pumps are usually the problem area in this job. At least one ship operator has adapted a biodegradable nontoxic hydraulic fluid for steering gears on its roll on-roll off ferry [60].

31.4.3 Industry Synthetic hydraulic fluids are used extensively in nearly all sectors of industrial manufacturing. Steel [61] and primary metals, machining and manufacturing, energy, chemicals, and mining [62] are examples. Again, the main reasons for selecting a synthetic hydraulic fluid over a mineral oil are the same as those cited in connection with the other categories: severe operating conditions and safety concerns. 31.4.3.1 Steel and primary metals The steel industry, and generally the primary metals industry (steel processing, aluminum and zinc die casting, metal-forming processes, etc.) must deal with fire hazards. This is because molten or otherwise hot metal is being processed in close proximity to hydraulic control equipment. Because fluid leakage is always a distinct possibility, and the hot metal constitutes an available ignition source, the risk of fire must be reduced. Hence, fire-resistant hydraulic fluids are required, and synthetics or water-based

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fluids must be selected. Water-based fluids have excellent fire resistance but poor lubricity; they also have pitting tendencies and a restricted temperature range [63]. In modern systems operating below 2000 psig and 60◦ C, water-glycol fluids are the most widely selected products. Water-glycol fluids are used in the zinc and aluminum diecasting industries, coal mining, and automotive industry. These formulations, containing 40–50% water, 30–50% polyglycol thickeners, 0–20% propylene or ethylene glycol, and 1–2% additives, must be constantly monitored to ensure that the water content does not fall below 35%, which would eliminate their fire resistance capabilities. Phosphate ester hydraulic fluids, usually triaryl phosphates, are successfully used on a large scale in industry. Examples are hydraulic systems for the handling of hot metal ingots or stub, die casting, including continuous casting machines, furnace controls, rolling mills, shears, and ladles. The flame-retardant and fire resistance properties of a variety of phosphate ester containing mixtures have been reviewed [57]. Polyol ester based fluids are also widely used as fireresistant hydraulic fluids in some industrial applications. Polyol esters are a lower cost alternative to phosphate esters and are widely used in the steel and aluminum industries due to their high flash and fire points. Additional performance advantages include good lubricity, high temperature capabilities, low specific gravity, high VI, easier recovery from water, and the absence of a need to change the seals during conversion from mineral oil [64]. Polyol esters or other fire-resistant fluids are frequently used in the hydraulic systems of industrial robots, especially those used for welding. In such cases adequate filtration is of paramount importance because of the critical tolerances in servovalves and other intricate components. Polyol esters designed for high temperature operations and long life are based on fully saturated hydrocarbon chains. Another class of polyol esters are derived from natural fats and oils, having some degree of unsaturation and thus somewhat lower stability. A third class of fluids are vegetable or seed oils (glyceride polyol esters). Most polyol esters are readily biodegradable and environmentally friendly. The degree of unsaturation determines the oxidative stability and low temperature performance [20]. When attempting to change over from a mineral oil to a phosphate ester or polyol ester hydraulic fluid, care must be taken to flush out all mineral oil. Mineral oil contamination above 3% could make the fluid flammable. 31.4.3.2 Mining The mining industry, especially the below-ground section, is characterized by confined spaces, poor airflow for cooling, cold temperature start-up, water, dust, and dirt in the environment. Space constraints tend to minimize the size of the hydraulic fluid sump and the air space around it,

and to increase operating pressures, temperatures, and loading [65]. Cramped quarters also mean that servicing the hydraulic unit is very difficult at a time when maintenance is critical to deal with contamination factors at their worst. The biggest concern is fire, which, in an underground mine can mean many deaths. Therefore, most of the fluids used are fire-resistant hydraulic fluids [66]. Operational safety and human health reasons have resulted in the compulsory use of fire-resistant fluids in the hard coal mining industry in the European Community for over 30 yr [67]. Products such as phosphate esters and waterin-oil emulsions are not used in German mining because they are categorized as hazardous to watercourses. Mineral oil free aqueous solutions or microemulsions, aqueous polymeric solution (>35% water), and PAGs or synthetic esters are permitted in German mining. British mining, however, does allow phosphate esters and water-in-oil emulsions. Phosphate esters and water-glycol fluids are used extensively in the United States. Mining and associated equipment are examples. In coal mining, they are used in hydrokinetic transmissions (fluid coupling) driving coal conveyors and in coal-face machinery such as power loaders. PAO, used in many types of hydraulic mining equipment in areas where fire hazards are not great, as under severe conditions it is considered superior to mineral oil, requiring less downtime for servicing. 31.4.3.3 Manufacturing “Manufacturing” covers a long list of activities in which machines, crafts, equipment, tools, and numerous items of all kinds are fashioned. Production could be included here, ranging from commodities to offshore oil exploration platforms. This sector also uses large amounts of synthetic hydraulic fluids. Poly(alpha-olefin) is a fluid type that is gaining favor in many areas, including sealed-for-life units, critical servovalves, and machine tools. Phosphate esters are also popular in areas of fire hazard. Water-glycol fluids are widely used in plastic injection molding presses operating at lower pressures, as well as automotive assembly. PTFE finds use as hydraulic oil in vacuum pumps, due to extremely low vapor pressure and excellent chemical resistance. 31.4.3.4 Power plants Fire-resistant hydraulic fluids are used heavily in power plants. Specific examples are boiler control systems and hydraulic control circuits of steam turbines, including electrohydraulic control for throttle/governor mechanisms. Many large steam turbines are equipped with hydraulic circuits totally separate from the main bearing lubricant supply, and they use triaryl phosphate esters. This pair of measures both ensures the shutdown of the turbine in

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the event of a fire and eliminates the danger from contact with superheated steam pipes if a leak or burst occurs. The major manufacturer of steam turbine hydraulic systems has recommended aryl phosphate esters for the last 35 yr. Fluoroelastomer seals are used with those systems [68]. PAO is also used, when a fire-resistant fluid is not required, to improve efficiency and lengthen service intervals. In nuclear power plants, in areas with significant radiation exposure, polyphenyl ether is most frequently used. Unlike conventional hydraulic fluids, polyphenyl ethers are very radiation resistant and do not show large viscosity increase with time. This lengthens the useful life of the fluid and reduces downtime for service. In areas with no significant radiation exposure, such as the steam turbine hydraulic governor systems, triaryl phosphates are used to advantage for their fire resistance [69]. 31.4.3.5 Arctic environment Arctic conditions stress the importance of low temperature fluidity above everything else. This applies to both industrial and automotive applications. Only synthetic hydraulic fluids can meet this challenge. PAO is widely used, especially the lower viscosity grades. Also, diesters of low viscosity are used in selected areas where water is not present. 31.4.3.6 Water installations Critical areas of water installations have to take extra measures to avoid pollution and contamination. Hydraulic systems in those areas tend to use polyglycol hydraulic fluids. Examples of such applications are sluices, dams, dredging boats, water treatment plants, and swimming pools [70].

31.4.4 Automotive Automobiles, trucks, and construction of off-highway equipment also use hydraulic systems and may require the use of a synthetic fluid for optimum performance. 31.4.4.1 Mobile equipment Poly(alpha-olefin) has been found to improve significantly both efficiency and durability of the hydraulic systems in mobile equipment. Phosphate esters have also been used where fire resistance is a requirement. In those systems, however, one has to watch for wear problems that arise if the acidity of the phosphate ester is allowed to exceed a neutralization number (NN) of 2.0. It appears that in the presence of moist air, the metal surfaces catalyze the decomposition of the phosphate ester into acidic by-products. In case of axial displacement pumps, the acidity has been found to reach NN 3.0 in only 300 h of operation and to exceed NN 10.0 in

TABLE 31.11 Brake Fluids — Requirements and Composition Requirements Boiling point, ◦ C, minimum

DOT-3

DOT-4

DOT-5

Wet boiling point, ◦ C, minimum Ignition point, ◦ C, minimum

205 140 82

230 155 100

260 180 —

Viscosity, cSt, minimum At 100◦ C At 50◦ C

1.5 4.2

1.5 4.2

1.5 —

Low temperature fluidity, cSt, maximum At −40◦ C At −55◦ C

1500 —

1300 —

— 900

pH

7.0–11.5

7.0–11.5

—

Typical composition, base, by weight

Polyether, 10–20% Glycol ether, 80–90%

Boric ester of polyether, 30–40% Glycol ether, 60–70%

Silicone oil, 80–90%

Rubber seal swell Agent, by weight

—

—

1–2%

1–2%

Phosphate ester, 10–20% 0.1–1.2%

Additives, by weight

950 h. Acid pitting was then observed on the housing and the system showed an inability to maintain pressure [71]. 31.4.4.2 Brake fluids The brake fluid, which is a special hydraulic fluid, is purely synthetic. There are three main types of brake fluid as specified by the U.S. Department of Transportation (DOT) and essentially accepted worldwide [74]: type 3 (DOT-3), type 4 (DOT-4), and type 5 (DOT-5). Table 31.11 summarizes the requirements and typical compositions of those three types of brake fluid types [29,72,73]. The major danger for deterioration of the brake fluid is water pickup. The moisture drawn into the system is absorbed by the fluid. However, as the water content increases, the boiling point of the brake fluid decreases. After a few years of operation, a drop in the boiling point of over 90◦ C is possible. Low boiling point facilitates boiling or vapor generation, and at high temperatures (after a few stops) that can cause brake-fade problems. The accompanying loss of brake pedal effect results in a very dangerous situation. DOT-3, based on glycols and polyglycols, is very vulnerable to moisture. As a matter of fact, the higher the boiling point of the polyglycol, the more hydroscopic it can be. DOT-4, based on boric esters of polyglycol, was formulated to give greater in-service stability to water pickup. The boric acid ester consumes the moisture and denies it a chance to hydrolyze the polyglycol. DOT-5, based on silicone oil, has little fear of moisture and can operate at higher temperatures. It also exhibits

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excellent low temperature fluidity, as expected from the relative performances shown in Table 31.3. However, it is possible for unabsorbed water to collect at a low point, such as a steel cylinder or in the lines, where it can cause corrosion. In automobiles, silicone fluids can be a hindrance to adhesion, and they must be completely eliminated when painting is to be done. Also, they must be kept away from electrical contacts because silicone, which has a high spreadability, is a good insulator. The U.S. Postal Service and the military specify DOT-5 fluid in their vehicles, and large savings in maintenance costs are expected from it. Minor swelling problems of some elastomers by silicone fluids brought about improved formulations that utilize additives to make the DOT-5 fluid behave more like the glycol-based fluid. Seals compatible with glycol fluids are based on ethylene-propylene diene monomer (EPDM) and styrene– butadiene rubber. Fluoroelastomer seals are compatible with silicone fluids. The first brake fluids developed in the 1920s were a mixture based on castor oil, and the seals were made of leather. By the end of the 1930s, all automobiles in the United States had rubber seals in the brake hydraulic systems. The front wheel drive development caused a weight shift, and that considerably increased the braking torque requirements of the front units. Higher heat generation added to elevated brake line pressures. caused by vacuumassist power boosters, putting much stress on the parts of the system, including the seals and the fluid. To understand the magnitude of these stresses, one must remember that the capacity of a modern brake system

is very high. The thermal energy generated from one average deceleration within 61 m from 55 mph (89 kmh) to a complete stop is enough to boil off 450 g of water or to soften 16 cm3 of steel. Temperature in excess of 650◦ C can be expected at the front brake pads and the brake fluid itself. Adjacent rubber seals may be heated more than 150◦ C. In normal peak city traffic, temperatures of the system can exceed 200◦ C [72]. Therefore, the choice of the brake fluid chemistry is critical for safety.

31.4.5 Military The military, with its highly sophisticated requirements and willingness to finance new fluid development, is credited with the main advances in hydraulic fluid technology. Thus synthetic hydraulic fluids in the military constitute a higher section of the total hydraulic fluids volume than in any other industry. 31.4.5.1 Military aircraft The aircraft sector is dominated by synthetic fluids, and a wide variety of synthetic hydraulic fluids is available for use in military aircraft [74–76]. A critical survey of the aircraft hydraulic literature, with emphasis on flammability testing and flammability of existing and projected aircraft hydraulic fluids, has been made [77]. Hydraulic fluids are utilized both in primary flight controls and utility systems such as brakes, landing gears, and accessory doors. Military requirements are more stringent than those for commercial aviation because the performance requirements in military applications are more severe. Poly(alpha-olefins) is represented by the specification MIL-H-83282, and it is used in many applications with no imminent fire hazards. MIL-H-83282 (NATO designation H-536) has been used in navy carrier aircraft [78] with excellent results. PAO formulations can typically contain an AW agent, such as tricresyl phosphate (TCP) or other aryl phosphate ester, an antioxidant, such as a hindered phenol, and a rubber swell agent, such as an ester. They can also contain a VII (typically a polyalkylmethacrylate) to increase the TOW. However, their performance in modern aerospace hydraulic pumps appears to depend more on base stock viscosity than on the kinematic viscosity of the VII thickened fluid [79]. Poly(alpha-olefin) is typically specified for use in military aircraft. Properties such as excellent viscosity/fluidity over a wide temperature range, outstanding lubricity and AW characteristics (with the proper additives), good compatibility with conventional hydraulic seals, and a certain amount of fire resistance improvement over mineral oil give PAO a wide range of applications. Compatibility with other mineral oil fluids and lubricants used in military equipment is essential in case of cross-contamination due to accidental mixing. A finished PAO formulation usually contains

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a moderate amount of seal swell agent, such as diester, to bring its polarity up to that of a mineral oil. There has been continued interest in the use of low viscosity (2 cSt) PAO in various military applications, owing to its lower pour point and high flash point compared to other base oils. The major military applications for low viscosity fluids are dielectric coolants and hydraulic fluids [59]. Polyphenyl ethers: Polyphenyl ethers are used in some ultrahigh temperature hydraulic systems for advanced aircraft and spacecraft. These fluids are very stable thermally and oxidatively, and they are also radiation resistant. This stability is due to the delocalization of electrons in the aromatic hydrocarbon structure. The meta linkage yields medium viscosity liquids, which allows for the use of these ethers as hydraulic fluids. They also have good lubricity, as a result of “sandwich compounds” form on the metal surfaces. Aromatic ring systems and nonferrous metal ions are the building blocks of these compounds, in which d electrons of the metal interact with 7t electrons of the aromatic compounds [49]. Polyphenyl ethers swell nitrile rubber too much and, as with phosphate esters, they need special types of seal material. Fluorosilicones: Fluorosilicone fluids are used in aircraft high performance hydraulic systems. They possess excellent water resistance as well as resistance to chemicals. Thus, they can withstand the solvency of many solvents and do not get washed out. Actuating drives is one such area of application. Fluorosilicones also have good load-carrying ability, which is helpful in the design of efficient systems. Other fluid types: Chlorophenyl methyl silicone fluids are used in supersonic aircraft for high temperature, low flammability hydraulic fluids. Alkylbenzenes, of special structure, could be used as high temperature hydraulic fluids in air force applications if certain production problems are solved [80]. Silanes, both alkyl and aryl types, are also well represented. Silicate esters and disiloxanes are used for high temperature applications or as coolants for packaged electronic systems in aircraft and missiles. Silicones, including chloro derivatives, are also used. Phosphonitriles, fluorocarbons, and fluoroglycols are used in certain niches where special properties are important for performance. Phosphate esters, both the trialkyl and triaryl type, dominate the fire-resistant segment of application. Truly nonflammable hydraulic fluids can be based on fluorinated hydrocarbons or esters [81]. Table 31.12 shows the military designations and chemistry of a representative number of military specifications. Some of them are of the fire-resistant category and mainly, but not exclusively, intended for aircraft [82]. Several papers have been published concerning the application of nonflammable hydraulic fluids based on chlorotrifluoroethylene (CTFE). These include fluids for

TABLE 31.12 Synthetic Fluids Used to Formulate Military Specification Fluids U.S. military specification Air Force MIL-H-27601B

MIL-H-87257

MIL-H-83306 Army MIL-H-46170B MIL-H-53119 Navy MIL-H-83282C

Hydraulic application Fire-resistant, high temperature, flight vehicle Fire-resistant, low temperature, aircraft/missile Fire-resistant, aircraft

PAO

Fire-resistant, rust inhibited Nonflammable, armored vehicles

PAO

MIL-H-8446B (cancelled) General MLO-54-408C MLO-55-280

— —

MLO-56-578 MLO-54-540 MLO-54-856 MLO-59-287

— — — —

MIL-H-19457D

PAO

Phosphate ester

Chlorotrifluoroethylene

31.4.5.3 Navy ships Fire-resistant, aircraft Fire-resistant, catapult Fire-resistant, lifts Fire-resistant, wide TOW

MIL-H-22072C(AS)

Synthetic base fluid

the air friction on the missile skin can raise the temperature to 316◦ C. Disiloxane can meet the temperature range requirement. In storage, however, it has shown to form gelatinous precipitates. These unwanted products of hydrolysis can clog hydraulic in-line filters, causing pump cavitation and loss of hydraulic power. Disiloxane is also unstable in the presence of metals and corrodes steel. The PAO-based fluids or silahydrocarbon fluids can overcome storage stability problems and perform at the required temperature range [78]. Silahydrocarbons are used extensively in most rocket hydraulic systems for rocket control. In addition to the above-mentioned wide temperature range, they have good hydrolytic stability, good thermal conductivity and thermal capacity, and good AW properties when fortified with AW additives. Thus they are very dependable. However, silahydrocarbons are more expensive than PAO-based fluids.

PAO Water/glycol Phosphate ester Silicate ester

Tetradodecyl silane Diphenyl din-dodecyl silane Octadecyl trioctyl silane Silicate ester Silicate ester Chlorophenylmethyl silicone

use in advanced aircraft applications, as the hydraulic fluid for an armored vehicle turret-and-gun control system, and as the gun recoil fluid [83]. The interactions of metals [84] and alloys [85] with CTFE based fluids have been studied at elevated temperatures. The development of nonflammable hydraulic fluid based on CTFE with new additive chemistry has been reported [86]. The development of formulations containing surface active additives for CTFE oils was reported [87]. 31.4.5.2 Missiles and rockets Missile hydraulic systems are subjected to very severe temperature variations. In a bomb bay or on a missile launch platform at high altitude, temperatures can drop as low as −54◦ C. However, when the missile is deployed,

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The ships of the navy make extensive use of hydraulic systems, especially on aircraft carriers. A large hydraulic system powers the elevators that shuttle aircraft from on deck to below deck storage. A separate hydraulic system is also used for catapult launching of aircraft. The fluids can be phosphate ester types or water-glycol types [88,89]. Ships requirements include very low pour points (<−30◦ C), low toxicity, lubricity durability, corrosion protection, material compatibility (pipes, couplings, seals, etc.), adequately high operating temperatures, and contamination control. Phosphate esters require a well-designed system to prevent water contamination. Water/glycol fluids have a low-temperature ceiling of operation and very low lubricity, but they allow for seawater contamination. The latter is important for equipment that interfaces with water or is located outside the hull [89,90]. Fire resistance is such an important property for military applications that it generates a large number of technical publications and new products. A sample of the extensive work carried out on flammability of hydraulic fluids can be seen by scanning the pertinent literature [13,31,74,77,91–97].

31.4.6 Construction and Forestry Criteria for the choice of hydraulic lubricant for construction and forestry applications include biodegradability and low toxicity, especially in Europe where regulations mandate the use of environmentally friendly fluids. Fluids have been developed to replace petroleum-based fluids, based on natural esters (rapeseed and sunflower oils) [98]. Formulations can be made that are free of metallic sulfonates, zinc dialkyldithiophosphates, or phenolic antioxidants, which are all potentially hazardous to the environment. The use of

hydraulic fluids and lubricants in forestry applications has been reported [99]. The review included requirements for biodegradable chain saw lubricants and a discussion of forest soil contamination by these fluids.

High Performance Functional Fluids” (edited by Rudnick and Shubkin). This chapter is based on their original work, and contains a significant amount of their original text. We thank them for the opportunity to contribute to this edition by editing and updating their previous work.

31.4.7 Servicing and Maintenance All hydraulic fluid systems require servicing and maintenance. In the case of synthetic hydraulic fluids, prevention of contamination and purification is critical in order to protect the hardware and extend fluid life. Good maintenance pays well in cost savings and trouble-free performance. Avoidance and exclusion of water and dirt is the first basic rule, as this is the most common source of fluid problems. A well-designed filtration system and safeguards against water or humidity contamination are essential. A continuous monitoring program can identify problems before the fluid can be exchanged or the equipment replaced. Particle counting and viscosity, acidity, infrared spectrum, and spectroscopic analysis for wear metals are recommended for most hydraulic fluids [100]. For synthetic hydraulic fluids, such careful monitoring is even more important and cost effective. Phosphate ester fluids filtered through activated clay or activated alumina, are purified from acids created through hydrolysis. Attapulgus clay has been associated with production of deposits in turbine hydraulic systems [101–103], whereas alumina has not. Acidity, if left to increase, appears to allow foaming and promote corrosive attacks on the metals and other parts of the system. Worse yet, a degraded phosphate ester fluid accelerates further degradation [104]. The filters should be changed when the acidity reaches a TAN value of 1.0 and certainly before a TAN value of 2.0 is exceeded [105]. The latest and significantly improved bypass filtration techniques for phosphate esters make use of ion exchange resins [44]. In the conversion of a hydraulic system from a mineral to a synthetic, such as a fire-resistant fluid, great care should be taken to flush the equipment well and to pay attention to compatibility with seals and other parts of the system [64]. Even a small amount of residual mineral oil can greatly decrease the fire resistance of the new fluid [105]. Also, cleaning with chlorine-containing solvent should be discouraged. Contamination of a phosphate ester fluid with chlorinated solvents or salts can cause severe problems with corrosion or electrochemical erosion, as mentioned earlier. Similar problems can be introduced to many other types of synthetic hydraulic fluids through contamination.

ACKNOWLEDGMENTS The authors wishes to thank Mr Andrew Papay and Dr Leslie Rudnick for their significant efforts to prepare the original chapter on hydraulics found in the first and second editions of the book “Synthetic Lubricants and

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REFERENCES 1. Tessman, R., Melief, H., and Bishop, R.J. Jr., (Basic hydraulic pump and circuit design) Handbook of Hydraulic Fluid Technology, G.E. Totten (Ed.), Marcel Dekker, New York, p. 10 (2000). 2. Wamback, W.E., Hydraulic systems and fluid, Lubr. Eng., 39, 483–486 (1983). 3. Papay, A.G. and Harstick, C.S., Petroleum-based industrial hydraulic oils — present and future developments, Lubr. Eng., 31, 6–15 (1975). 4. Culpon, D.H. and Mead, T.C., Synthetic lubricants, Lubrication, 78, 1–16 (1992). 5. Herzog, S.N., Neveu, C.D., Placek, D.G., “Predicting the pump efficiency of hydraulic fluids to maximize system performance.” NCFP I02-10.8/SAE OH 2002-01-1430 presented at the IFPE/SAE Off-Highway Meeting, Las Vegas, NV, USA, March 19–23, 2002. 6. Stambaugh, R.L., Kopko, R.J., and Roland, T.R., “Hydraulic pump performance — a basis for fluid viscosity classification.” SAE paper 901633, presented at the SAE International Off-Highway and Powerplant Congress, Milwaukee, WI, September 10–13, 1990. 7. Michael, P.W., Herzog, S.N., and Marougy, T.E., “Fluid viscosity selection criteria for hydraulic pumps and motors.” NCFP paper I00-9.12 presented at the International Exposition for Power Transmission and Technical Conference, Chicago, IL, USA, April 4–6 (2000). 8. NFPA Recommended Practice T2.13.13-2002. “Fluid Viscosity Selection Criteria for Hydraulic Motors and Pumps.” (2002). www.nfpa.com. 9. Snyder, C.E., Jr., Gschwender, L.J., Paciorek, K., Kratzer, R., and Nakahara, J., Development of a shear stable viscosity index improver for use in hydrogenated polyalphaolefinbased fluids, Lubr. Eng., 42, 547–557 (1986). 10. Kinker, B.G., (Fluid viscosity and viscosity classification) Handbook of Hydraulic Fluid Technology, G.E. Totten (Ed.), Marcel Dekker, New York, p. 305 (2000). 11. Hamaguchi, H., Bartholomae, I., Kinker, B., Jelitte, R., and Dardin, A., Multi-graded lubricants — viscometrics, performance, economics, Proceedings of the 5th Annual Fuels and Lubes Asia Conference, Singapore, Jan. 26–29 1999. (www. flasia.info) 12. Makkonen, I., “Performance of Seasonal and Year-Round Hydraulic Oils in Forestry Machines,” FERIC Technical Note TN-251, Forest Engineering Technical Research Institute of Canada, 12/96. 13. Snyder, C.E., Jr., Gschwender, L.J., and Campbell, W.B., Development and mechanical evaluation of nonflammable aerospace (−54◦ C to 135◦ C) hydraulic fluids, Lubr. Eng., 38, 41–51 (1982). 14. Anon, Une autre conception du performance des huiles hydrauliques, Pet. Inf., 98, 27–31 (1987).

15. Papay, A.G., Oil-soluble friction reducers — theory and application, Lubr. Eng., 39, 419–426 (1983). 16. Hydraulic fluids based on two centistoke synthetic hydrocarbons, U.S. Patent 4,537,696 (1985). 17. Rizvi, S.Q.A., (Lubricant additives and their functions), ASM Handbook, Friction, Lubrication, and Wear Technology, Vol. 18, p. 98 (1990). 18. Cheng, V.M., Wessol, A.A., Baudouin, P., BenKinney, M.T., and Novick, N.J., Biodegradable and nontoxic hydraulic oils, Society of Automotive Engineers, 42nd Annual Earthmoving Industry Conference, April 9–10 (1991). 19. Eichenberger, H.F., Biodegradable hydraulic lubricant: an overview of current developments in central Europe, Society of Automotive Engineers, 42nd Annual Earthmoving Industry Conference, April 9–10 (1991). 20. Kitamura, N., A review of biodegradable lubricants, Jpn. J. Tribo., 38, 639–648 (1993). 21. Reichel, J. and Pelzer, E., Fast biodegradable hydraulic pressure fluids. Technical demands and operating behavior, Mineraloeltechnik, 40, 1–9 (1995). 22. Galvain, P., Cheng, V.M., Wessol, A.A., Baudouin, P., BenKinney, M.T., and Novick, N.J., Biodegradable and nontoxic hydraulic oils, Society des lngenieurs de 1’Automobile, Hydraulic Engineering in the Vehicle, Paris, May 4–6 (1994). 23. Buchser, W.J. and Jaeckle, H.W., Determination of the biodegradability of water-insoluble fluids (lubricating oils, etc.) using CEC L-33-A-94, Chimia, 48, 227–231 (1994). 24. Marougy, T., Presented at the Swedish Hydraulics Symposium on Ecologically Acceptable Hydraulic Fluids, June (1995). 25. Pelzer, E., Environmental standards and distribution guidelines for environmentally friendly hydraulic fluids, Technische Akademie Esslingen 9th International Colloquium, Ecological & EconomicAspects of Tribology, Proceedings, Vol. 2, pp. 1–17 (1994). 26. ASTM D-6046 Standard Classification of Hydraulic Fluids for Environmental Impact, American Society for Testing and Materials, Philadelphia. 27. Kussi, S., Eigenshaften von Basisflussigkeiten fur synthetische Schmierstoffe, Tribol. Schmierungstech., 33, 33– 39 (1986). 28. Law, D.A., Lohuis, J.R., Breau, J.Y., and Harlow, A.J., Development and performance advantages of industrial, automotive and aviation synthetic lubricants, J. Synth. Lubr., 1, 6–33 (1984). 29. Seki, H., Properties of hydraulic fluids and their application — synthetic type fluids, Junkatsu, 34, 587–593 (1989). 30. Riemann, U., Reichardt, H.U., Schuelert, G., Lindner, R., and Hollmann, A., Comparative studies of hydraulic oils based on mineral oil, rapeseed oil and esters in a gear pump test stand, Technische Akademie Esslingen 10th International Colloquium, Tribology-Solving Friction and Wear Problems, (119-11), Proceedings, Vol. 2, pp. 827–837 (1996). 31. Snyder, C.E., Gschwender, L.J., Tamborski, C., and Chen, G.J., Synthesis and characterization of silahydrocarbons — a class of thermally stable wide-liquid-range functional fluids, ASLE Trans., 25, 299–308 (1982).

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32. Tamborski, C., Chen, G.J., Anderson, D.R., and Snyder, C.E., Jr., Synthesis and properties of silahydrocarbon — a class of thermally stable wide liquid range fluids, Ind. Eng. Chem. Prod. Res. Dev., 22, l72–170 (1983). 33. Gupta, V.K, Snyder, C.E., Jr., Gschwender, L.J., and Fultz, G.W., Thermal decomposition investigations of candidate high temperature base fluids: Part l. Silahydrocarbons, STLE Trans., 32, 276–280 (1989). 34. Snyder, C.E., Jr., Tamborski, C., Gschwender, L.J., and Chen, G.J., Development of high-temperature (−40◦ C to 228◦ C) hydraulic fluids for advanced aerospace applications, Lubr. Eng., 38, 173–l78 (l982). 35. Paige, H.L., Snyder, C.E., Jr., Gschwender, L.J, and Chen, G.J., A systematic study of the oxidative stability of silahydrocarbons by pressure differential scanning calorimetry, Lubr. Eng., 46, 263–267 (1990). 36. Ohkawa, S., Konishi, A., Hatano, H., Ishihama, K., Tanaka, K., and Mikio, I., Oxidation and corrosion characteristics of vegetable-base biodegradable hydraulic oils, SAE Special publication SP-1069, Society of Automotive Engineers, Warrendale, PA, pp. 55–63 (1995). 37. Rhee, I.S., Evaluation of environmentally acceptable (EA) hydraulic fluids, NLGI Spokesman, 60, 28–35 (1996). 38. Gupta, V.K., Stropki, M.A., Gehrke, T.J., Gschwender, L.J., and Snyder, C.E., Jr., Hydrolytic studies of some siliconbased high temperature, Lubr. Eng., 46, 706–711 (1990). 39. Gschwender, L.J., Snyder, C.E., Jr., and Conte, A.A., Jr., Polyalphaolefln as candidate replacements for silicate ester dielectric coolants in military applications, Lubr. Eng., 41, 221–228 (1985). 40. Scott, R.N., Knollmueller, L.O., Milnes, F.J., Knowles, T.A., and Gavin, D.F., Silicate cluster fluids, Ind. Eng. Chem. Prod. Res. Dev., 19, 6–11 (1980). 41. Yagi, M., Synthetic lubricants — application to industrial use, Junkatsu, 32, 121–125 (1987). 42. Barabanova, G.V., Sheinina, S.Z., Gusev, V.K., Rudavets, L.N., and Larionova, T.A., The effects of corrosion inhibitors on the hydrolytic stability of the (Russian) erosion-resistant hydraulic fluid, Khim. Tekhnol. Topl. Masel, 1, 24–25, (l994). 43. Conte, A.A., The action of organo-phosphate additives in polysiloxane fluids, J. Synth. Lubr., 2, 95–120 (l985). 44. Phillips, W.D. and Sutton, D.I., “Improved maintenance and life extension of phosphate esters using ion exchange treatment,” Technische Akademie Esslingen, 10th International Tribology Colloquium (1996). 45. Peschk, G., Interaction of conventional and biologically degradable hydraulic pressure fluids with elastomeric materials, Technische Akademie Esslingen, 8th International Colloquium, Tribology 2000, Proceedings, Vol. 2, pp. 16.1-1–16.1-31 (1992). 46. Eguchi, R., Ohtake, Y., Ohkawa, S., Iwamura, M., and Konishi, A., Compatibility of hydraulic seal elastomers with biodegradable oils, SP-1148, SAE International Congress and Exposition, Detroit (1996). 47. Cavdar, B., Sharma, S.K., and Gschwender, L.J., Wearreducing surface films formed by a fluorinated sulfonamide additive in a chlorotrifluoroethylene-based fluid, Lubr. Eng., 50, 895 (1994).

48. Cavdar, B, Sharma, S.K., and Gschwender, L.J., Wearreducing surface films formed by a fluorinated sulfonamide additive in a chlorotrifluoroethylene-based fluid. STLE 49th Annual Meeting, Pittsburgh, Preprints N. 94-AM-3G-1, May (1994). 49. Plagge, A., Gebrauchsiegenschaften synthetischer Schmierstoffe und Arbeitsfluessigkeiten, Tribol. Schmierungstech., 32, 270–278 (1985). 50. Carpenter, J.F., The biodegradability of polyalphaolefin (PAO) base stocks, Jpn. J. Tribol., 39, 573–577 (1994). 51. Carpenter, J.F., Biodegradability and toxicity of polyalphaolefin (PAO) base stocks, Technische Akademie Esslingen, 9th International Colloquium, Ecological and Economic Aspects of Tribology, Proceedings, Vol. 1, pp. 4.6-1–4.6-6 (1994). 52. Carpenter, J.F., Biodegradability and toxicity of polyalphaolefin (PAO) base stocks, J. Synth. Lubr., 12, 13–20 (1995). 53. Harvey, D., Biodegradable fluids and lubricants, Ind. Lubr. Tribol., 48, 17–26 (1996). 54. Schuelert, G, Lindner, R., and Reichardt, H.U., Environmentally-friendly HEES-type [synthetic ester] hydraulic fluids. Testing and experience in practical use, Technische Akademie Esslingen 10th International Colloquium, Tribology-Solving Friction and Wear Problems, Proceedings, Vol. 2, pp. 821–826 (1996). 55. Phillips, W.D., The electrochemical erosion of servo valves by phosphate ester fire-resistant hydraulic fluids, Lubr. Eng., 44, 758–767 (1988). 56. Beck, T.R., Wear by generation of electrokinetic streaming current, ASLE Trans., 26, 144–150 (1983). 57. Snyder, C.E. and Gschwender, L.J., A survey of fire-resistant hydraulic fluids, Preprints N.95 AM-4D-1, STLE 50th Annual Meeting, Chicago, IL, p. 4 (1995). 58. Okazaki, M.E., Abernathy, S.M., and Laurent, J.W., Hydrolysis of phosphate-based aviation hydraulic fluids, Technische Akademie Esslingen 8th International Colloquium, Tribology 2000 Proceedings, Vol. 2, pp. 19.4-1–19.4-10 (1992). 59. Theriot, K.J. and Shubkin, R.L., A polyalphaolefin (PAO) with exceptional low-temperature properties, Technische Akademie Esslingen 8th International Colloquium, Tribology 2000, Proceedings, Vol. 2, pp. 19.7-1–19.7-8 (1992). 60. Anon., Sally [Line] steers a greener course, Mar. Eng. Rev., p. 19, July (1993). 61. Cichelli, A.E., Steel mill lubrication, Lubr. Eng., 39, 410–413 (1983). 62. Okon, L.W., Lubrication in the mining industries, Lubr. Eng., 39, 487–488 (1983). 63. Wilson, B. and Law, P., Water based hydraulic for the metals industry, Ind. Lubr. Tribol., 44, 21–23 (1992). 64. Wiggins, B.J., System conversions for fire-resistant hydraulic fluids, Lubr. Eng., 43, 467–472 (1987). 65. Young, K.J. and Kennedy, A., Development of an advanced oil-in-water emulsion hydraulic fluid, and its application as an alternative to mineral hydraulic oil in a high fire risk environment, Lubr. Eng., 49, 873 (1993).

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66. Bauer, K., Water-containing hydraulic fluids-requirements and properties, Kontakt Stud. (Hydraulikfluessigkeiten), 475, 342–358 (1995). 67. Reichel, J., Fluid power engineering with fire-resistant hydraulic fluids experiences with water containing hydraulic fluids, Lubr. Eng., 50, 947 (1994). 68. Phillips, W.D., The use of triaryl phosphates as fire-resistant lubricants for steam turbines, Lubr. Eng., 43, 228–235 (1986). 69. National Nuclear Risks Insurance Pools and Association, International Guidelines for the Fire Protection of Nuclear Plants, p. 10, September (1983). 70. Anon, Polyglykole-Technische Anwendungen, Erdol Kohle, 41, 229–230 (1988). 71. Perez, J.M., Hansen, R.C., and Klaus, E.E., Comparative evaluation of several hydraulic fluids in operational equipment — a full scale pump stand test and the four ball wear tester; Part II. Phosphate esters, glycols, and mineral oils, Lubr. Eng., 46, 249–255 (1990). 72. Car, J., Elastomer materials for automotive hydraulic brake systems, Lubr. Eng., 44, 22–27 (1988). 73. Yagi, M., Synthetic lubricants — application to industrial use, Junkatsu, 32, 121–125 (1987). 74. Coordinating Research Council, Inc., Flammability of Aircraft Hydraulic Fluids — A Bibliography, CRC Report 545, Atlanta (1986). 75. Snyder, C.E., Jr., Utilization of synthetic-based hydraulic fluids in aerospace applications, Int. Jahrb. Tribol., 1, 409–418 (1982). 76. Snyder, C.E., Jr., Aerospace applications of synthetic hydraulic fluids, Performance Testing of Hydraulic Fluids, International Symposium, London (1979). 77. Coordinating Research Council, Inc., Flammability of aircraft hydraulic fluids — a bibliography, Project CA-49-71, CRC, Atlanta (1986). 78. Gschwender, L.J., Snyder, C.E., Jr., Anderson, D.R., and Fultz, G.W., Determination of storage stability of hydraulic fluids for use in missiles, Lubr. Eng., 40, 659–663 (1984). 79. Gschwender, L.J. and Snyder, C.E., Jr., Pump evaluation of hydrogenated polyalphaolefin candidates for a −54◦ C to 135◦ C fire-resistant air force aircraft hydraulic fluid, Lubr. Eng., 44, 324–329 (1990). 80. Gschwender, L.J., Snyder, C.E., Jr., and Driscoll, G.L., Alkylbenzenes — candidate high temperature hydraulic fluids, Lubr. Eng., 46, 377–381 (1990). 81. Snyder, C.E., Jr. and Gschwender, L.J., Nonflammable hydraulic system development for aero space, J. Synth. Lubr., 1, 188–200 (1984). 82. McConnell, B.D. (Miltary specifications), Tribology Data Handbook, E.R. Booser (Ed.), CRC Press, New York (1997). 83. Van Brocklin, C.H., Campbell, W.B., Gschwender, L.J., Sharma, S.K., and Snyder, C.E., Chlorotrifluoroethylene oligomer-based nonflammable hydraulic fluid [(NFH)]. Two hydraulic components’ development, J. Synth. Lubr., 9, 299–309 (1993). 84. Gupta, V.K., Warren, O.L., and Eisentraut, K.J., Interaction of metals with chlorotrifluoroethylene fluid at elevated temperatures, Lubr. Eng., 47, 816 (1991).

85. Gupta, V.K. and Eisentraut, K.J., Interaction of alloys with chlorotrifluoroethylene fluid at 177◦ C, Lubr. Eng., 47, 6–12 (1991). 86. Gschwender, L., Snyder, C.E., and Sharma, S.K., Development of MIL-H-53119, −54◦ C to 175◦ C high-temperature nonflammable hydraulic fluid for Air Force systems, Lubr. Eng., 49, 621 (1993). 87. Cavdar, B., Sharma, S.K., and John, J., Wettability aspects of friction and wear reduction by a fluorinated sulfonamide additive in a chlorotrifluoroethylene-based fluid, Tribol. Int., 28, 501–506 (1995). 88. Eastaugh, P.R., Hargreaves, M.R.O., and Jones, H.J., Fire hazards associated with warship hydraulic equipment, Institute of Mechanical Engineers Conference on Naval Engineering Present and Future, Bath, September (1983). 89. Page, R.N.M., Selection of a fire-resistant fluid for hydraulic systems in Royal Navy ships, Trans. Inst. Mar. Eng., 10, 9–14 (1986). 90. Skinner, R.S., Synthetic lubricants — why their extra cost can be justified, Mar. Eng. Rev., 1821, August (1986). 91. Gupta, V.K., Gschwender, L.J., Snyder, C.E., Jr., and d Prazak, M., Thermal stability characteristics of a nonflammable chlorotrifluoroethylene CTFE base stock fluid, Lubr. Eng., 46, 601–605 (1990). 92. Snyder, C.E., Jr. and Gschwender, L.J., Nonflammable hydraulic fluid systems development for aerospace, J. Synth. Lubr., 1, 188–200 (1984). 93. Snyder, C.E., Jr. and Gschwender, L.J., Fluoropolymers in fluid and lubricant applications, Ind. Eng. Chem. Prod. Res. Dev., 22, 383–386 (1983). 94. Military Specification MIL-H-83282, Hydraulic fluid, fire resistant, synthetic hydrocarbon base, aircraft, NATO Code H-537 (Feb. 10, 1982).

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95. Military Specification MIL-H-46170B. Hydraulic fluid, rust inhibited, fire resistant, synthetic hydrocarbon base (Aug. 18, 1982). 96. Conte, A.A. and Hammond, J.L., Development of a high temperature silicone fire-resistant hydraulic fluid, Report NADC 79248-60, Naval Air Development Center, Warminster, PA, Feb. 5, 1980. 97. Raymond, E.T., Design guide for aircraft hydraulic systems and components for use with chlorotrifluoroethylene non-flammable fluids, AFWAL-TR-2111, Air Force Aero Propulsion Laboratory, Wright-Patterson Air Force Base, OH, March (1982). 98. Anon, A survey of lubrication news and equipment, Lubr. Eng., 52, 266–267 (1996). 99. Ruppert, D., Hydraulic fluids and lubricants in forestry. Fields of application and requirements, Technische Akademie Esslingen 9th International Colloquium, Ecological and Economic Aspects of Tribology Proceedings, Vol. 2, pp. 8.4-1–8.4-13 (1994). 100. Poley, J., Oil analysis for monitoring hydraulic oil systems, a step-stage approach, Lubr. Eng., 46, 41–47 (1990). 101. Phillips, W.D., The conditioning of phosphate ester fluids in turbine applications, Lubr. Eng., 39, 766–780 (1983). 102. Grupp, H., Aufban von schwer entflammbaren Hydraulikflussigkeiten auf phosphorsaure-esterbasis, Erfahrungen aus dem praktischen Einsatz in Kraftwerk, Masch, Schaden, 52, 73–77 (1979). 103. Tersiguel–Alcover, C., La Filtration des Esters Phosphates sur Alumine Activ6e, EDF Report P 331 4200/81-24 (June 1981). 104. Shade, W.N., Field experience with degraded synthetic phosphate ester lubricants, Lubr. Eng., 43, 176–182 (1987). 105. Stark, R., Anwendungstechnische Richtlinie fur schwerenflammbare Hydraulikfluessigkeiten HSD, Schmierungstechnik, 16, 285–286 (1985).

32

Environmentally Friendly Hydraulic Fluids Saurabh Lawate CONTENTS 32.1

Introduction 32.1.1 Background 32.2 Types of Hydraulic Systems 32.3 Environmentally Friendly Hydraulic Fluids 32.4 Hydraulic Fluid Specifications and Approvals 32.5 Environmentally Friendly Hydraulic Fluid Specifications 32.5.1 OEM Specifications for Environmentally Friendly Hydraulic Fluids 32.5.2 Environmental Label Specifications for Hydraulic Fluids 32.5.2.1 Blue Angel Label 32.5.2.2 Nordic Swan Label 32.5.2.3 Swedish Standard 32.5.2.4 EU Eco-Labeling Scheme 32.6 Formulation Considerations for Environmentally Friendly Hydraulic Fluids 32.7 Base Oil 32.8 Additives 32.8.1 Thickeners 32.8.2 Pour Point Depressants 32.8.3 Antioxidants 32.8.4 Anti-Wear Agents 32.8.5 Other Additives 32.9 Commercially Available Environmentally Friendly Hydraulic Fluids [29] 32.10 Future Outlook and Driving Forces for Environmentally Friendly Hydraulic Fluids Acknowledgments References

32.1 INTRODUCTION 32.1.1 Background Hydraulic fluids are one of the most commonly used industrial lubricants. The use of hydraulic fluids relative to other industrial lubricants is shown in Figure 32.1 [1]. The purpose of a hydraulic fluid is to transmit power from one location to another. The transmitted power is used for performing specific functions. In addition to transmitting power the hydraulic fluid must also lubricate moving parts and protect them from corrosion. A certain amount of load carrying capacity is also generally expected out of a hydraulic fluid. One of the earliest hydraulic fluids used was water. However, water was quickly replaced

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by mineral oils. Subsequently mineral oils evolved into R&O oils and then anti-wear hydraulic fluids. The fluids in current use are complex and highly formulated anti-wear hydraulic fluids [2]. Recently there is growing interest in environmentally friendly hydraulic fluids [3]. There is no universally accepted definition of “environmentally friendly hydraulic fluids” but over the years the technology related to these fluids has evolved around meeting some generally accepted criteria. These range from ecotoxicity and biodegradability in addition to certain performance specifications. This chapter is intended to provide an overview of these aspects as well as an overview of formulation strategies for the so-called “environmentally friendly hydraulic fluids.”

Other industrial fluids 38%

Feller buncher Mining truck Crawler Hydraulic fluids 49%

Backhoes Excavators 1

10

100

1000

10000

Hydraulic oil (Gallons) Other hydraulic fluids 11%

FIGURE 32.2 Hydraulic sump capacities for typical earthmoving equipment

Fire resistant hydraulic fluids 2%

FIGURE 32.1 Hydraulic fluid consumption in the United States

TABLE 32.1 Comparison of Hydraulic Sump Capacities of Mining Excavators [6]

OEM Japanese US and Japanese Japanese

Equipment type Hydraulic excavator Hydraulic excavator Hydraulic excavator

Operating weight (lbs.)

Hydraulic oil sump capacity

Engine oil sump capacity

1,600,000

3040

150

100,000

71

9

10,000

15

2

32.2 TYPES OF HYDRAULIC SYSTEMS There are numerous types of hydraulic systems [4]. The application and type of work that needs to be done dictates the type of hydraulic pump used, for example, vane vs. piston. Hydraulic systems can also vary from stationary systems mounted on the floor, such as in a steel mill, to systems equipped on a piece of off-highway earthmoving or mining equipment [5]. The size of a hydraulic system generally goes up as more power output is desired and the volume of the oil sump also goes up with higher power systems. The higher power is, of course, used to do more work (Table 32.1). The design and incorporation of hydraulic systems for any given application is a complex process that is undertaken by equipment manufacturers and a discussion on this topic is outside the scope of this review. The type of hydraulic system used is certainly the critical factor in determining the properties of the hydraulic fluid used. However, the end-use application also plays

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a critical role in determining fluid properties. This is discussed in the next two sections.

32.3 ENVIRONMENTALLY FRIENDLY HYDRAULIC FLUIDS In the case of loss lubricants such as chain bar oils and two stroke oils, the lubricant is continuously lost during use. In off-highway earthmoving, farming, and mining equipment, the lubricant and the equipment operate in close contact with the environment. Hence, the environmental impact of spills or leakage of oil occurring from this equipment is of great concern [7]. A report indicates that about 70,000 mt of lubricant was lost in Germany and Sweden [8]. When mineral oil-based lubricants are used in these applications there is concern about loss and spills and their impact on the environment. Mineral oils are not biodegradable and tend to persist in the environment leading to a negative impact on the ecosystem. The highest volume of lubricant used in off-highway equipment is the hydraulic fluid. A comparison of hydraulic fluid capacities in excavators is presented in Table 32.1. A broader comparison is provided for various types of off-highway equipment in Figure 32.2. It is obvious that with such large sump capacities, accidental leaks can cause significant amounts of fluid to leak into the environment. Moreover, if the fluid used in these systems is not biodegradable it will persist in the environment and thereby cause harm. These concerns have underscored the need for environmentally friendly lubricants. Consequently, there has been a lot of activity related to the development of “environmentally friendly hydraulic fluids” [9]. It is important to note that while engine oils and drivetrain lubricants account for the bulk of lubricant volume there is only limited interest in developing biodegradable oils for these applications. This is because the chance of accidental leakage in these applications is minimal. Even if a spill were to occur the volume of the spill from a passenger car is not likely to be more than a gallon. Recycling

Incidental food contact hydraulic fluids(NSF & H-1) Aviation hydraulic fluids Fire resistant hydraulic fluids Conventional hydraulic fluids (Baseline performance)

Eco-labeled hydraulic OEM branded biodegradable hydraulic fluids

TABLE 32.2 Hydraulic Fluids Requiring “Special” Approvals Hydraulic fluid category Incidental food contact hydraulic fluids (H1) Fire resistant hydraulic fluids [12] Aviation hydraulic fluids Military hydraulic fluids Biodegradable hydraulic fluids

Key conformance 21CFR Section 178.3570 Factory Mutual guidelines for non-flammability Airplane manufacturer specifications, non-flammability Military specifications OEM specifications; eco-label guidelines

FIGURE 32.3 Specialty hydraulic fluids

mechanisms are also well established for these oils and a significant amount of used oil is recycled.

32.4 HYDRAULIC FLUID SPECIFICATIONS AND APPROVALS An excellent summary of hydraulic fluid specifications is presented in a ready reference guide published by an additive supplier [10]. Typically, specifications for conventional hydraulic fluids are outlined by one of the following: • Original Equipment Manufacturers (OEMs) — Hydraulic

pump manufacturers OEMs — Off-highway equipment manufacturers • End-users — Steel mills and “Original Vehicle Manufacturers” • Equipment

In general, the major brands of hydraulic fluids on the market meet most of the criteria in the three categories indicated above. Additionally, special formulations are then tailored for meeting specific customer/OEM requirements. There is also a category of specialty hydraulic fluids. These hydraulic fluids are used in specialized applications as shown in Figure 32.3. These fluids generally meet baseline performance. In addition they must also meet certain requirements that are dictated by the end-use applications. Approvals beyond OEMs may also be required (Table 32.2). Generally the formulation of these hydraulic fluids is more challenging since formulation ingredient choices are often dictated by end use constraints, for example, compliance for fire resistance or Code of Federal Regulations (CFR) 21, Section 178.3750 (for incidental food contact hydraulic fluids). Technology is now commercially available for incidental food contact hydraulic fluids that are biodegradable [11]. Environmentally friendly hydraulic fluids belong to this special category and specifications for these fluids are discussed in the next section.

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32.5 ENVIRONMENTALLY FRIENDLY HYDRAULIC FLUID SPECIFICATIONS There is no universal specification for biodegradable or environmentally friendly hydraulic fluids. From a general standpoint these can be split into criteria that evaluate their operational and technical performance, and criteria that evaluate the impact of these fluids on the environment. From a practical standpoint there are three broad categories of specifications that marketers strive to meet in order to market or differentiate their products. • OEM specifications (e.g., Caterpillar, John Deere) • Environmental label specifications (e.g., Blue Angel,

Nordic Swan, and Swedish Standard) • Independent body specifications (e.g., Verband Deutscher

Maschinen- und Anlagenbau-German Engineering Federation (VDMA)) These specifications include technical performance criteria but may also include constraints on types of ingredients used. In most cases these also include environmental and toxicity guidelines that the product is expected to meet. Typical among these are: • Biodegradability: >60% after 28 days in the OECD

301B Test • Aquatic toxicity: LD 50 >1000 against aquatic organ-

isms like rainbow trout, daphnia, and algae • Limitations on the amount of additive used: Varies on

the basis of eco-labeling specifications Customers expect environmentally friendly hydraulic fluids to provide environmental benefits without significantly sacrificing base line performance. Some modifications to baseline specifications may be accepted in order to accommodate the fact that a significant portion of the base oil may not be mineral based. Such considerations also apply to the special categories of hydraulic fluids described earlier (Table 32.2).

TABLE 32.3 OEM Branded Biodegradable Hydraulic Fluids

TABLE 32.4 A Commercial Off-Highway Equipment OEM Branded Hydraulic Fluid

OEM

Requirements

Method

Flash point, ◦ C

ASTM D 92 ASTM D 97 ASTM D445 ASTM D445

220 −58 48.7 8.7

ASTM D2270 ASTM D943 (Dry TOST) ISO 4406 ASTM D892

160 100 h

Caterpillar John Deere

OEM product brand Cat Bio Hydo (HEES)a Bio HY-GARD

a Must meet Caterpillar BF-1 specification.

32.5.1 OEM Specifications for Environmentally Friendly Hydraulic Fluids Some off-highway equipment OEMs have set forth formal specifications for biodegradable fluids. These OEMs also market privately labeled hydraulic fluids which meet their own specification (Table 32.3). This OEM activity definitely heralds the first step in endorsement of this category of fluids. An example of a biodegradable hydraulic oil marketed by an equipment OEM is shown in Table 32.4.

32.5.2 Environmental Label Specifications for Hydraulic Fluids Another category of approvals is “environmental labels.” These are mostly European. The representative environmental labels are shown in Figure 32.4. Among these the German “Blue Angel,” [13] and products meeting the Swedish standard are the most prominent. An effort underway to develop a uniform European standard that will result in an environmental label for hydraulic fluids has been recently completed. 32.5.2.1 Blue Angel label The performance requirements for the German “Blue Angel Specification” are shown in Table 32.5. These are covered by the Blue Angel Hydraulic Fluid Specification RAL-UZ 79-1995. The German Blue Angel label was introduced in 1978. It now includes over 4000 products from 919 manufacturers in 77 product groups ranging from desktop printers to hydraulic fluids. Several commercial “blue angel” hydraulic fluids are now available [14]. (http://www.blauerengel.de/englisch/vergabe/vergabegrundlagen_download/ download_ral.php?id=83) 32.5.2.2 Nordic Swan label The Nordic Environmental Label or the “Swan label” is a multinational environmental labeling scheme in the Nordic countries (Sweden, Finland, Denmark, Iceland, and Norway). It covers hydraulic fluids. (http://www.nemko. no/s_environmental/swan.html)

Copyright 2006 by Taylor & Francis Group, LLC

Pour point, ◦ C Viscosity cSt at 40◦ C Viscosity at cSt 100◦ C Viscosiy index Oxidative stability Fluid cleanliness Foam test; Ml 25◦ C (∗ 24◦ C)

Pumps

35VQ-25

FZG rating 4-Ball wear test Biodegradability

ASTM D5182 ASTM D 4172 EPA 560/6-82-003

Biodegradability Toxicity water hazard Fish toxicity (Rainbow trout)

CEC-L–33-A-93 WGK rating OECD 203

Specification Range

15/13 max Without water: 25/0,50/0,25/0 With 0.1% water: 25/0,50/0,25/0 Ring wear 75 mg max; Cam wear 15 mg max Minimum 11 <0.4 mm 60% biodegradable in 28 days 83% Zero LC50 > 1000 ppm after 48 h

32.5.2.3 Swedish standard The Swedish Society for nature conservation (Bra Miljoval — good ecochoice) awards the “falcon” label. Hydraulic fluids meeting specification SS 15 54 34 qualify for approval. There are currently over 60 hydraulic fluids registered under this standard. For additional information please refer to the website (http://www.sp.se/km/en/tech_ser/ kmo/hydraul.htm)

32.5.2.4 EU Eco-labeling scheme In May 2003, the European Eco-label Board (EUEB) decided to work on establishing ecological criteria for the award of the European Eco-label to lubricants and published its initial findings in a report in November 2003 [15]. Based on the recommendations of this report, other work performance criteria have been established for hydraulic oils, chainsaw oils, greases, two-stroke oils, concrete release agents, and niche total loss in July 2004 [16]. Other lubricants, for example, motor oils, metalworking fluids, etc., will be excluded from environmental labeling guidelines. The grant of the eco-label will be subject to the product meeting seven criteria — no R phrase triggering materials, no materials at >1% of composition with aquatic toxicity >1 mg/L; >90% of

German Blue Angel Nordic Swan

Croatian

Austrian Umwelt

Swedish

European Union Norway

FrenchNF

Dutch

FIGURE 32.4 Representative “Eco-labels” in Europe

total composition should be readily aerobic biodegradable; no halogen or nitrite compounds or heavy metals; renewable carbon content >50%; impact on CO2 emission; ISO 15380 standards for technical performance criteria. Additional information can be found at the following website: (http://europa.eu.int/comm/environment/ecolabel/product/pg_lubricants_en.htm)

32.6 FORMULATION CONSIDERATIONS FOR ENVIRONMENTALLY FRIENDLY HYDRAULIC FLUIDS Hydraulic fluids are complex fluids. Wear protection, rust inhibition, and oxidation inhibition are key factors that the formulator must meet. Additionally, several other factors are also important to ensure that the fluid can be practically used over periods of time. For example, low temperature properties, demulsibility, foaming tendency, air entrapment, and viscosity grades are key considerations that affect fluid reliability. The formulation of environmentally friendly hydraulic fluid is further complicated by the biodegradability requirement (which limits the type of base stocks used) and ecotoxicity requirements (this limits the types of base stocks and additives) which can be used. Further, ecolabeling requirements may put limits on the amount of additives used. A typical formulation for an environmentally friendly hydraulic fluid is shown in Table 32.6. The table is only intended to provide general ranges of additives that may be effective. Every formulation must ultimately be tested for performance. A review of considerations for base oils and key additives shown in Table 32.7 is discussed below.

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32.7 BASE OIL The main considerations for base oils are: starting viscosity, low temperature properties, biodegradability and ecotoxicity, and responsiveness to antioxidants. Generally, in order to achieve biodegradability it becomes necessary to incorporate significant amounts of Group V base stocks, primarily vegetable oils or synthetic esters. However, it may be necessary to incorporate Group I, II, III, or IV base stocks in order to improve the cost/performance ratio of the finished fluid. The incorporation of these fluids is a “balancing act” in that large amounts of Group I, II, III fluids take away from the biodegradability and ecotoxicity. A good balance of properties can be achieved by balancing the formulation with the right combination of base oils. A comparison of base oils is shown in Table 32.7. A detailed compilation of vegetable oil properties is available [17]. A detailed review of various base stocks is found in the remaining chapters of this book as well as in a comprehensive book that was published earlier [18]. Highly unsaturated vegetable oils such as soybean, cottonseed, and corn oils are not very useful due to their poor oxidative stability. Canola oil has acceptable performance as long as the fluid is not subject to very high operating temperatures (>120◦ F). A good alternative to conventional vegetable oils is the use of high oleic oils [19, 20]. However, high oleic oils currently cost about twice as much as conventional vegetable oils. Various developments including the wide availability of high oleic canola and the proactive efforts of the United Soybean Board (USB) to develop a mid-oleic soybean under its “Better Bean Initiative” will help to reduce the cost differential and make this approach attractive.

TABLE 32.5 Technical Requirements for Various Hydraulic Fluid Specifications

Requirements Viscosity at −20◦ C at 0◦ C at 40◦ C at 100◦ C Low temperature fluidity after 7 Days Pour point, ◦ C (D97) Flash point, ◦ C (D92) % Insolubles Water content (mg/kg) Steel corrosion test; degree of corrosion Copper corrosion Baader oxidation test; 95◦ C/72 h; % Viscosity increase at 40◦ C Seal compatibility after 1000 h, 80◦ C HNBR: Change in Shore A hardness FPM: Rel. volume change; max % NBR1: Decr. in elongation; max % AU: Decrease in tensile strength; max % Air release at 50◦ C; max. min Foam test; Ml 25◦ C 95◦ C 25◦ C Demulsification; min at 54◦ C (∗ time to 3 mL) FZG; Load stage fail Pump test: Ring; max, mg Pump test: Vane; max, mg Density at 15◦ C; kg/m3 Ash content (oxides); % Neutralization value; mg KOH/g Color

TABLE 32.6 Typical Environmentally Friendly Hydraulic Fluid Formulation Component Base oil Pour point depressant Antiwear agent Antioxidant Rust inhibitor Demulsifier Thickener (if necessary to meet specific ISO grades) a Total amount to add to 100%.

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Typical amounta (%) >90 1–2 <1 ∼1 ∼0.5 <0.5 1–5

VDMA24 568/Blue Angel specification

VDMA24 568/Blue Angel test method

ISO HETG hydraulic fluid test method

NA 780 50.6–41.4 6.1 NA NA 185
NA DIN 51550 DIN 51561/62 DIN 51568 D 2532-93 DIN ISO 3016 DIN ISO 2592 DIN ISO 5884 DIN 51777 DIN 51585 DIN 51759 DIN 51554

ISO 3104 ISO 3104 ISO 3104 ISO 3104 D2532-93 DIN ISO 3016 DIN ISO 2592 DIN ISO 5884 ISO 12937 — ISO 2160 DIN 51554/3

— ±10 −3/+10 30 30 10

— DIN 53505 DIN 53521 DIN 53504 DIN 53504 DIN 51381

— ISO 6072 ISO 6072 ISO 6072 ISO 6072 ISO 9120

150/0 75/0 150/0 NA 10 120 30 NA NA NA NA

D 892-89 D 892-89 D 892-89 DIN 51599 DIN 51354 DIN 51389 DIN 51389 DIN 51757 DIN EN7 DIN 51558 —

ISO 6247 ISO 6247 ISO 6247 ISO 6614 DIN 51354 IP281/D2882 IP281/D2882 ISO 12185 ISO 6245 ISO 6618 ISO 2049

Synthetic esters and PAOs have excellent pour points and oxidative stability. However, in some cases they have lower base viscosities than are desired for most hydraulic fluids. Also, the biodegradability of PAOs goes down significantly as the viscosity increases. In such cases these base oils generally have most value as diluents — their main impact is on improvement of low temperature properties while improving oxidative stability in most cases. Among synthetic esters TMP trioleate is very useful since it has an ISO46 viscosity and a pour point that is about −50◦ C. The use of polyol esters with high oleic content is also described in a recently issued patent [21]. High oleate polyol esters are also commercially available [22]. Typically, esters serve as a very good blend component if they have lower biodegradability. Otherwise, they can be used without dilution. Overall, field experience has shown that

TABLE 32.7 Typical Properties of Base Oils [23] Base oil Soybean oil Canola oil High oleic canola oil (75% oleic) High oleic sunflower oil TMP trioleate TMP trioleate (high oleic) PAO-8 Mineral oil

Starting ISO grade 32/46 32/46 32/46 32/46 46 46 46 32 (150N)

Pour point, ◦C

Antioxidant response

Cost $/lb.a (price range)

−9 −21 −15

Poor Moderate Good

0.17–0.25 0.20–0.28 ∼0.35

100, >70 100, >70 100, >70

−12 −50 −45 −50 ∼−12

Good Moderate Good Good Excellent

0.45–0.55 ∼1.0 ∼1.25 ∼0.90 ∼0.16

100, >70 90, >60 90, >60 <50, ∼30 15, 5

Biodegradability (CEC, OECD)

hydrolytic stability is not as big an issue with biodegradable fluids based on vegetable oils and synthetic esters, as was originally felt.

32.8 ADDITIVES 32.8.1 Thickeners One of the primary considerations in hydraulic fluids is the ability to offer viscosity grades commonly ranging from ISO46 to ISO220. Vegetable oils generally are in the ISO32–46 range. Castor oil is the only vegetable oil which has an ISO 220 viscosity. Synthetic esters can vary from ISO 10 to ISO 220 or higher. However, not all these esters will be biodegradable. The formulator is left with two choices: blend higher viscosity oils or use thickeners. An interesting development underway is to genetically introduce a hydroxyl fatty acid in conventional vegetable oils [24]. Increasing hydroxyl content increases viscosity. Actual crop production from this technology is however several years away. Meanwhile, castor oil (or higher viscosity synthetic esters) can be blended into a vegetable oil. Alternatively, the use of styrene butadiene thickeners is also recommended. This technology is patented [25].

RBOT min to 25 lb oxygen pressure drop

a Price will vary based on quantity, customer supplier relationships, and market conditions.

300 250

0% Antioxidant 3% Antioxidant

200 150 100 50 0 Canola oil

High oleic canola oil

High oleic soybean oil

TMP trioleate

FIGURE 32.5 Performance of a commercial antioxidant package [28]

oils. This is because the solidification mechanisms for the two types of oils are different. However, for longer storage (including equipment sitting outside), it is also necessary to incorporate a co-solvent (an additional base stock). This enables vegetable oils to maintain a Brookfield viscosity of <25,000 cPs for extended periods.

32.8.3 Antioxidants 32.8.2 Pour Point Depressants Low temperature properties are very critical for offhighway equipment. Fortunately, many conventional pour point depressants used for mineral oils also work in vegetable oils. Maleic anhydride-styrene copolymers (MSC) and polymethacrylates (PMAs) are most effective. Typically the effective molecular weights for these polymers are about 40,000 for MSCs and about 40 to 70,000 form PMAs. Usually a higher percentage of pour point depressant is generally required than what is required for mineral

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It has been demonstrated that vegetable oils can be used as hydraulic fluids without additives. The problem is that after a short period of time (when the natural antioxidants are used up) there is a very dramatic increase in viscosity. The goal therefore, is to prolong the time taken to increase the viscosity as much as possible. Phenolic antioxidants are effective. Metal deactivators may also be employed. The results for an antioxidant package optimized for vegetable oils are shown in Figure 32.5. This and simulation technology is patented [26, 27].

32.8.4 Anti-Wear Agents Vegetable oils and synthetic esters have inherently good anti-wear properties. Typically, environmentally friendly hydraulic fluids are ash-less. This means that the use of ash containing anti-wear agents such as zinc dithiophosphate derivatives is replaced with other anti-wear additives. Phosphate esters or their salts are commonly used as anti-wear agents. Certain ash-less anti-wear agents such as lecithin can cause foaming and should be avoided.

32.8.5 Other Additives Other conventional additives typically used in hydraulic fluids are also used in environmentally friendly hydraulic fluids. These include rust inhibitors, demulsifiers, and antifoam agents. Vegetable oils and synthetic esters do not have a significant tendency to foam. Generally, many of the conventional additives are soluble in vegetable oils and synthetic esters.

32.9 COMMERCIALLY AVAILABLE ENVIRONMENTALLY FRIENDLY HYDRAULIC FLUIDS [29] A commercially available hydraulic fluid made using either vegetable oils or mixtures or vegetable oils has had a good history of usage. Results for this oil are shown in Table 32.8. Biodegradability/ecotoxicity of the formulations is shown in Table 32.9. A summary of pump test formulations is shown in Table 32.10.

32.10 FUTURE OUTLOOK AND DRIVING FORCES FOR ENVIRONMENTALLY FRIENDLY HYDRAULIC FLUIDS One of the philosophical issues in this area is that there is no standard definition for the term “environmentally friendly.” However, the development of eco-labels has enabled the crystallization of general criteria that environmentally friendly hydraulic fluids are expected to meet. This is a critical development since it makes it easier for the customer to understand the benefits that the term encompasses. It is expected that this will lead to a “customer pull.” Customer behavior may be reflected in the following statement on the Blue Angel website “Fifty percent of the population of the former West Germany and 33% in the former East Germany look for the “Blue Angel” when choosing environmentally friendly products, as was found in a survey commissioned last year by the Federal Environmental Agency.” Currently the market for these lubricants is growing at about 4–7% per year [30]. Environmentally friendly hydraulic fluids, as a class, now have a growing reputation of performance with added environmental benefits. This has been driven by the availability of additive technology and new base fluids. Since

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TABLE 32.8 Performance Summary for Commercial Hydraulic Fluids Base oil: Formulation identifier General performance Color (D1500) Viscosity at 40◦ C (D445) Viscosity at 100◦ C (D445) Viscosity index (D2270) Pour point, ◦ C (D97) Brookfield viscosity (D2983) −12.2/−25◦ C Foam (D-892), mL Seq. 1 Seq. 2 Seq. 3 Demulsibility (D-1401) Water/oil/ emulsion; mL Time, min Oxidation performance RBOT (D-2272) minutes to fail IGOT D-2893, %vis. increase, 312 h Rust and corrosion performance Copper strip (D130) (3 h at 100◦ C) Turbine oil rust (D-665) A-distilled water B-salt water Hydrolytic stability (D-2619) Cu loss, mg/cm2 /Cu appearance Acidity of water layer Wear and Extreme Pressure 4-Ball wear (D-4172) (1 h, 167◦ F, 1200 rpm, 40 kg); scar diam.; mm FZG load stage (D-5182)

HOSO:TMPTO 70:30

High oleic canola oil

Canola oil

A

C

D

L0.5 45.9

L1.0 42.4

L1.0 38.9

9.6

9.1

8.9

200

204

220

−33

−30

−36

750/3000

640/45,000

640/1920

0-0 10-0 0-0

10-0 40-0 20-0

20-0 90-0 30-0

40/40/0

40/38/2

40/38/0

10

10

10

197

76

3.4%

Not tested

1A

1A

Pass Pass

Pass Pass

0.0/1B

0.0/2B

0.21

0.21

0.36

0.40

12

11

marketplace the recently announced U.S. federal procurement initiative is a step in the right direction [31].

TABLE 32.9 Biodegradability and Ecotoxicity of Vegetable Formulation — Formulation “A” in Tables 32.7 and 32.8 Biodegradability CEC-L-33-T-82 Modified sturm, OECD 301B Ecotoxicity Fathead minnow, 96 h LC50, ppm Daphnia magna, 48 h, EC50, ppm

ACKNOWLEDGMENTS The author would like to acknowledge Mr. Patrick Lämmle, Executive Director, Panolin AG, PO Box 8322 Madetswil, Switzerland for general discussions on this topic.

95% 61% >10,000 ppm >10,000 WAF

REFERENCES TABLE 32.10 Pump Test Performance of Commercial Hydraulic Fluids HOSO:TMPTO 70:30 Formulation identifier Vickers 35VQ 25 Pump (3000 psi, 2400 rpm, 93.3◦ C) Standard duration First 50 h test (total 50 h) Second 50 h test (total 100 h) Third 50 h test (total 150 h) Extended duration 250 h on oil; 150 h on cartridge 350 h on oil; 250 h on cartridge 450 h on oil; 350 h on cartridge 550 h on oil; 450 h on cartridge Vickers V-104C Pumpb (2000 psi, 1200 rpm, 79.4◦ C; 100 h) Total ring and Vane weight loss (mg) Vickers 20VQ5 Total ring and Vane weight loss (mg) Denison T-5D vane (2000 psi, 93.3◦ C, 100 h)

Canola oil

A

D

8.0 11.0 10

17.0 16.0 22.0

NA 33a NA 174a

31 48 87 177

3.9

9.9

0.0

NA

25

NA

a Reading at 300 and 500 h. b Using the additive package in high oleic sunflower oil (HOSO) and high

oleic canola oil gave total cam and ring weight losses of 19.3 and 1.5 mg, respectively.

the base oil is the highest cost component, it is necessary that cheaper base oils are available with the desired oxidative stability. The United Soybean Board effort to develop a mid-oleic variety of soybean will be of great help. Overall, these developments and customer demand have prompted OEMs to establish their own specifications for environmentally friendly hydraulic fluids. While all these developments have led to a steady growth for this category of hydraulic fluids the real impetus for growth will be a mandated use of environmentally friendly fluids. While no mandate currently exists in the

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1. Report on U.S. Lubricating Oil and Wax Sales, National Petrochemical Refiners Association, 2002. 2. K.B. Grover and R.J. Perez, “The Evolution of Petroleum Based Hydraulic Fluids,” Lubr. Eng., 15–20, January 1990. 3. J.L. Glancey, S. Knowlton, and E.R. Benson, “Development of a High Oleic Soybean Oil Based Hydraulic Fluid,” Lubr. World, 49–50, January 1999. 4. R.M. Gresham, “Hydraulics: An Inside Look at Pumps,” Tribol. Lubr. Technol., 60, 18–20, 2004. 5. W.S. Evans, “The Modern Art of Lubricating Mining Equipment,” Machine. Lubr., 2003. 6. Obtained from websites of various companies using company provided specifications for the off-highway vehicles. 7. J. Nelson, The Carbohydrate Economy, Vol. 3, Issue 1, 2000. 8. P.W.J. Robotham and P. Gill, Input, Behavior, and Fates of Petroleum Hydrocarbons, Elsevier Applied Science, London, 1989. 9. S. Lawate, “Environmentally Friendly Hydraulic Fluids,” Chap. 3, Biobased Industrial Fluids and Lubes, S.Z. Erhan and J.M. Perez, Eds., AOCS Press, 2002. 10. Lubrizol Corporation, “Ready Reference for Lubricant and Fuel Performance,” Lubrizol Corporation, Cleveland, Ohio, Publication Number 240-94R4, 1998. 11. S. Lawate, P. Naegely, and V. Carrick, Environmental Friendly Food Grade Lubricants from Edible Triglycerides Containing FDA Approved Additives, U.S, Patent 5,538,654, 1996. 12. B. Lloyd, “Burning Controversy — Heated Debate Erupts Over Fire-Resistant Hydraulic Fluids,” Lubes’n’Greases, Vol. 9, Issue 5, p. 14, May 2003. 13. R. Navette and F. De Clercq, “The Development of Hydraulic Fluids for Earthmoving Machines Complying with Ecolabel Requirements,” SAE Technical Paper 981490, 1998. 14. www.panolin.com. 15. D. Theodori, R.J. Saft, H. Krop, and P.V. Broekhuizen, “Concept Background Document,” Development of Criteria for the award for the European Eco-label to Lubricants, report issued by IVAM Research and Consultancy on Sustainability, www.ivam.uva.nl, November 2003. 16. D. Theodori, R.J. Saft, H. Krop, and P.V. Broekhuizen, “Draft Criteria Document,” Criteria for the award for the European Eco-label to Lubricants, report issued by IVAM Research and Consultancy on Sustainability, www.ivam.uva.nl, July 2004. Also found at http://europa.eu.int/comm/environment/ecolabel/pdf/lubricants/draftcritera_040704.pdf.

17. S.S. Lawate, K. Lal, and C. Huang, “Vegetable Oil — Structure and Performance,” Tribilogy Data Handbook, E.R. Booser, Ed., CRC Press, 1997. 18. Synthetic Lubricants and High-Performance Functional Fluids, Leslie R. Rudnick and Ronald L. Shubkin, Eds., Marcel Dekker, Inc., New York, p. 881, 1999. 19. D. de Guzman, “High Oleic Oils Experience Rising Demand” — Oils, Fats and Waxes Overview, Chemical Marketing Reporter, August 11, 2003. 20. P. Corbett, “Research in the area of High Oleic Oils,” Plant Biotechnology Institute (PBI) Bulletin, 2002, Issue 1, p. 3, Published by the Canadian National Research council. Also found at http://pbi-ibp.nrc-cnrc. gc.ca/en/bulletin/2002issue1/page3.htm. 21. S.S. Lawate and K. Lal, High oleic polyol esters, compositions and lubricants, functional fluids and greases containing the same, U.S. Patent 5,773,391, 1998. 22. www.Cargill.com. 23. S. Lawate, “Environmentally Friendly Hydraulic Fluids,” Chap. 3, Biobased Industrial Fluids and Lubes, S.Z. Erhan and J.M. Perez, Eds., AOCS Press, 2002.

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24. www.linneaus.com. 25. K. Lal, Vegetable oils containing styrene/butadiene copolymers in combination with additional commercial polymers that have good low temperature and high temperature viscometrics, U.S. Patent 6,365,558, 2002. 26. S.S. Lawate, and K. Lal, High oleic polyol esters, compositions and lubricants, functional fluids and greases containing the same, U.S. Patent 5,773,391, 1998. 27. W.W. Garmier, Biodegradable lubricant composition from triglycerides and soluble copper, U.S. Patent 5,863,872, 1999. 28. Data using Lubrizol 7652 antioxidant package. 29. CP-24XX-46 Series of biodegradable hydraulic fluids available from CPI Engineering Services, 2300 James Savage Road, Midland, MI 48642 (989) 496 3780. 30. Private communication from Patrick Lämmle, Executive Director, Panolin, PO Box CH-8322, Madetswil, Zurich, Switzerland. 31. H.R.2646, Farm Security and Rural Investment Act of 2002; SEC. 9002. Federal Procurement of Biobased Products.

33

Fire-Resistant Hydraulic Fluids Kevin L. Dickey CONTENTS 33.1 Discussion 33.1.1 Fluid Classification, HFA 33.1.2 Fluid Classification, HFB 33.1.3 Fluid Classification, HFC 33.1.4 Fluid Classification, HFD References

The basic function of hydraulic fluid is to provide a method of power transfer within a hydraulic circuit. Hydraulic fluids must lubricate the pumps, valves, and other components of the system without negatively affecting the overall operation of the total hydraulic circuit. Considering the demands placed on hydraulic fluids, there are several areas that must be addressed when formulating these fluids. Hydraulic fluids must offer the following benefits to the end user of the fluids, at a minimum: • • • • •

Protection against corrosion Protection against rusting Provide thermal stability Provide anti-wear protection Provide oxidation stability

These are some of the key performance indicators used in evaluating hydraulic fluids. With this in mind, there are two primary classifications for hydraulic fluids once they have been developed. These are known as conventional mineral oils and fire resistant hydraulic fluids. In this chapter we review only the segment known as fire-resistant hydraulic fluids. Given the choice, most consumers would elect the usage of mineral oil based fluids for hydraulic applications due to cost and performance reasons. However, in many operations, such as mining and steel production, other needs are apparent in which a mineral oil cannot satisfy all of the requirements. These situations are operations that are subject to high risk of fire, which may result in significant equipment damage and more importantly a potential for loss of life. Fire resistancy of hydraulic fluids is achieved in two primary manners. The first would demonstrate that a hydraulic fluid is naturally fire resistant due to the chemical makeup of the fluid itself. In these fluids, the molecular structure

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of the fluid is such that it is inherently able to resist fire, but if it would somehow ignite, it would most likely selfextinguish. An example of this type of chemistry and fluid would be the polyol ester technology, which offers users significant advantages in these applications. The second type of fire-resistant fluid is developed by adding various levels of water into the finished hydraulic fluid. Under these types of fluids there are multiple subcategories, which are discussed in more detail later. With these types of the fluid, the water may be emulsified in the oil or oil may be emulsified in the water to provide fire-resistant hydraulic fluids in the emulsion phase. In this chapter, we evaluate all of the various types of fire-resistant hydraulics fluids that are readily available in the marketplace today. As an overview, we are discussing the groups, which are distinguished today as follows: HFA: High water containing fluids HFB: Invert emulsion fluids HFC: Water glycol fluids HFD: Synthetic fluids In the first section, we cover HFA, High water containing fluids.

33.1 DISCUSSION 33.1.1 Fluid Classification, HFA HFA fire-resistant hydraulic fluids are known in the industry as high water containing fluids. These fluids are typically 5% soluble oil emulsions (oil-in-water) offering a cloudy, milky white appearance. Other products could be classified as 5% solutions (vs. emulsions), which typically indicates some type of synthetic chemical additive placed

Water

External/continuous phase

Internal/dispersed phase

FIGURE 33.1 Typical emulsion

into solution within the water. These types of HFA fluids typically are clear or translucent in appearance. Emulsions are defined as a dispersion of liquid droplets in a second immiscible liquid. Dispersions may be formed temporarily through agitation of the two immiscible fluids, however, resolution of the emulsion is usually rapid and complete unless a stabilizing additive or emulsifier is used. Emulsions are composed of two phases; an internal or dispersed phase and an external or continuous phase (Figure 33.1). In the case of oil-in-water emulsions (Figure 33.2), these are designed such that the petroleum oil is dispersed into the water. In these emulsions, the water would be in the continuous phase and the fluid’s behavior is similar to water. When evaluating the soluble oil emulsions (macroemulsions), as noted above, these products have a milky white appearance. In the late 1970s new technology was introduced to the HFA category and this relates to the mention of solutions. These emulsions, also known as micro-emulsions, have much smaller droplet sizes. These droplets are also known as micelles. These emulsions have a translucent and sometimes transparent appearance. The dispersed internal phase in micro-emulsions is synthetic in nature as opposed to the mineral oil, soluble oil, and emulsions. The reason these products are labeled as microemulsions and macro-emulsions is directly correlated to their micelle sizes. Macro-emulsions have large micelle sizes, whereas the micro-emulsion has micelle size of 0.1 nm, which is less than a wavelength of light, hence they appear translucent. HFA fluids, whether a macro-emulsion or microemulsion, are extremely fire resistant. In addition to this they have exceptional cooling properties. When formulated properly, these fluids provide excellent protection against rust and corrosion and satisfactory lubrication of steel on steel. Other benefits of these fluids are very low applied costs and because of their high water content, they offer maximum fire protection. Some of the drawbacks of these fluids include the following. due to the fluids viscosity approaching that of water, pumps are typically derated in order to obtain service life. These products can put a significant strain on waste treatment facilities. If these products are not properly formulated or maintained in the field they can create bacteria and fungal growth. Typically mixing and control stations must be installed and finally, due to the high water content in these fluids, operation in colder climates requires winterizing of these fluids.

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Oil droplet

FIGURE 33.2 Oil-in-Water emulsion

Oil

Water

FIGURE 33.3 Water-in-Oil emulsion

For operation, the operating temperature of these fluids should be limited to a maximum of 120◦ F (50◦ C) in order to reduce the possibility of evaporation and deterioration of the fluids characteristics. Traditionally, this is not an issue because most of the systems operating on HFAs run cooler than oil systems. This is primarily due to the fact that they have higher specific heat and thermal conductivity properties. However, if these fluids are exposed to temperatures below freezing (32◦ F, 0◦ C) there may be separation of the phases, which will negatively affect the base fluid and additives. It is for this reason that these products require winterizing in cold climates.

33.1.2 Fluid Classification, HFB HFB fluids are similar to the HFA fluids in the fact that they are emulsion type fluids. Although this statement is true, they are significantly different. Whereas the HFA fluids are identified as Oil-in-Water emulsions, HFB fluids are known as Water-in-Oil emulsions (Figure 33.3). These types of fluids are typically known as invert emulsions. These products consist of water (35 to 45%), petroleum oil (40 to 50%), and an emulsifying additive stabilized by the emulsifier. Therefore, oil is the continuous phase and as such, maintains a very good viscosity for the hydraulic service. When compared to the various types of fire-resistant hydraulic fluids, these products have somewhat poor fire-resistant protection but a far superior to that offered by petroleum oils.

33.1.3 Fluid Classification, HFC HFC fluids are the next classification we will review. These fluids are known in the industry as water–glycol fluids. HFC fluids are composed of three primary components; water (typically 35 to 45%), glycol (a synthetic chemical of the same derivative as antifreeze), and some type of high molecular weight water-soluble thickener to improve viscosity. One additional component within these fluids can be an additive package, which is designed to improve corrosion protection, antiwear protection, and lubrication

Cost defined as $/gallon

Polyol ester Phosphate ester Mineral oil Water glycol Invert emulsion Vegetable oil

$0

$5

$10

$15

$20

$25

$30

FIGURE 33.4 Hydraulic fluid cost comparison Fire resistant tests and criteria Spray flammability

A spray of fluid is injected through an orifice under pressure and is contacted with a source of ignition (flame, molten metal, etc.)

Hot metal

Fluid is contacted with a hot metal surface heated to prescribed temperature

Molten metal

Same as hot metal, except the ignition source is molten metal

Wick test

Wick type tests are used to evaluate the effect of evaporation of volatile components of fluid flammability. The wick test involves soaking a wick with test fluid and passing it in and out of a flame until fluid ignition is sustained

Auto ignition temperature

Temperature at which fluid will burn in air without an additional ignition source

Flash point

Temperature at which fluid will burn, with an ignition source

FIGURE 33.5 Fire-resistant tests and criteria

properties of the finished product. Unlike the HFA and HFB fluids that are emulsions, the HFC category of products are solutions. Similar to the HFA and HFB fluids, the HFC products obtain their fire-resistant protection from their water content. When comparing the HFC fluids used in various industries, the primary component affecting the quality of the finished product is the additive package selected by the manufacturer. HFC fluids typically provide good lubrication protection, provided that high pressures and loads are not present. These fluids contain a high specific gravity, which can produce increased vacuums on the pump inlet ports. Other challenges present with the use of water glycol’s are metallurgical in nature. Some metal, such as zinc, cadmium, and magnesium may have an adverse reaction with water– glycol fluids. These reactions will result in the production

Copyright 2006 by Taylor & Francis Group, LLC

of sticky residues that can block lines, orifices, and filters causing valve spools to stick. This will result in erratic performance of the hydraulic system and a loss of hydraulic efficiency. Due to the potential problems noted above, it is recommended that hydraulic circuit components, which are alloyed or plated with any of the aforementioned metals, should not be used in conjunction with water–glycol fluids. Some areas where these items may be seen are; various fitting, galvanized piping, reservoir components, strainers, heat exchangers, and so on. Other areas of concern for water–glycol fluids, as well as with the HFD fluids covered in the next section, is the selection of seals for the hydraulic system. In general, most of the typical seal materials used with petroleum oils are suitable for use with water glycol’s. Older technology components such as leather and cork-impregnated seals should

(Comparison of fire resistant fluid properties) Performance category

Product Rankings

Fire resistance

WG>PH>PE>IE>VO>MO>PAO

Oxidation resistance

WG>PAO>MO>PE=PE>IE>VO

Lubrication

MO>PH=PE=PAO=VO>WG>IE

Biodegradability

PE=VO>WG>PH>IE>MO>PAO

Hydrolytic stability

WG>IE>MO=PAO>PE>VO>PH

Unit Cost ($/gal.)

PAO=PH>PE>VO>WG>MO>IE

Ease of disposal

PE=VO>WG>PH=IE=MN=PAO

Seal compatibility

MO>IE>WG>PE=VO=PAO>PH

Thermal stability

PAO=PH>MO>PE>VO>IE>WG

Legend PE = Polyol ester VO = Vegetable oil WG = Water glycol PH = Phosphate ester

IE = Invert emulsion MO = Mineral oil PAO = Polyalphaolefin

FIGURE 33.6 Comparison of fire-resistant fluid properties

Industry Blast furnace & Basic steel products Industrial machinery & equipment Iron & Steel foundries Motor vehicles & Equipment Fabricated metal products Non-ferrous rolling & Drawing Metal forging & Stamping Non-ferrous foundries & Die casting Aircraft & Parts Heavy construction Oil & Gas extraction Rubber & Plastic parts Electric, Gas & Sanitary services Lumber & Wood products Petroleum & Coal products Coal mining Railroad equipment Metal cans & Shipping containers Chemicals & Allied products Food & Kindred products Metal mining Space propulsion units & Parts Water transportation Pipelines (not natural gas) Ship & Boat building Paper & Allied products

SIC code 331 35 332 371 34 335 346 336 372 16 13 30 49 24 29 12 374 341 8 20 10 376 44 46 373 26

FIGURE 33.7 Summary of applications

not be used because these tend to absorb water. Some of the disadvantages of these fluids are noted below: • Due to the high molecular weight of HFCs, higher than

mineral oil, they do not float on water, therefore they will sink to the bottom making them extremely difficult to waste treat. • HFCs have restricted use in certain pumps. • HFCs systems must have operating temperatures kept low. • HFCs must be measured constantly to ensure that the water content is kept to acceptable levels. If water is evaporated, water must be added to maintain the proper viscosity and fire-resistant protection.

33.1.4 Fluid Classification, HFD The final section we will cover is HFD fluids. HFD fluids are known as synthetic fire-resistant hydraulic fluids. The majority of HFDs are formulated with organic esters as the base fluids. However, other base oils such as phosphate esters can be used in this class. The primary types of HFD fluids marketed are noted below: • • • •

Polyol esters Phosphate esters Halogenated hydrocarbons Mixtures of polyol esters or phosphate esters with mineral oils

Copyright 2006 by Taylor & Francis Group, LLC

Esters in general are described as compounds produced by the reactions between acids and alcohols. Naturally occurring esters (triglycerides) are a major component of all fats and vegetable oils. Synthetic esters can be construed from a variety of organic and inorganic acids and alcohols and the choices made determine the chemical properties and cost of the resultant ester. Reviewing polyol esters, this name is actually a derivative of neopentyl polyol esters, which are esters produced by reacting a monobasic fatty acid with polyhedric alcohol containing the neopentyl structure. One primary benefit of the neopentyl structure is that it does not contain hydrogen molecules. This is important because these hydrogen molecules are the first point of attack for thermal breakdown of the fluid. With this component eliminated, the thermal stability of the polyol ester is improved dramatically offering these products the ability to be used at much higher temperatures without sacrificing product quality or performance. In addition to this benefit, polyol esters have a high level of polarity, which reduces volatility as compared to other esters. Additionally, this high polarity enhances the lubrication properties of these fluids over other esters offered in the market today. Polyol ester relates to the base stock of the hydraulic fluid. Polyol ester hydraulic fluids, like most commercial hydraulic fluids, utilize performance enhancement additives that can make up to 10% of the finished product.

Polyol esters are typically derived from long-chain carboxylic fatty acids and polyhydric alcohols that contain two or more hydroxyl groups. As environmental awareness continues to rise to the forefront of product development, the polyol ester hydraulic fluid is the leading choice because they are readily biodegradable and have low aquatic toxicity. These products exhibit excellent lubrication, as noted above, and can be used in most all hydraulic applications. Considering all of the benefits of the polyol ester one may ask why it is not more widely utilized. One of the primary reasons, as with all of the HFD fluids, is described in Figure 33.4. As you can see from Figure 33.4, compared to mineral oil, polyol ester and phosphate ester hydraulic fluids are significantly more expensive than mineral oil on a cost/gallon evaluation. Phosphate ester fluids are comprised of triaryl phosphate esters along with performance-enhancing additives, which can make up 10% of the finished product. Although there may be differences in the chemical intermediates used in their manufacture, all of the triaryl phosphate esters in commercial use are nearly identical in chemical and physical properties as well as their performance characteristics. Close chemical control in their manufacture is maintained, in particular a low acid value is very important, low moisture content and low chloride residual is necessary to obtain good performance in application. Additives, up to 10%, are incorporated in order to provide rust and corrosion protection, antifoam characteristics, metal passivation, and oxidation resistance to improve performance of the finished fluid. Through selection of aryl intermediates of different average molecular weights, phosphate ester fluids can be supplied over a range of viscosities. Their fire resistance is derived from the phosphorous content, which gives snuffing action when exposed to a heat source. Phosphate ester fire-resistant fluids are used in various applications, similar to polyol ester fluids. There are also multiple trade names closely associated with these fluids. These fluids, as with polyol esters, will burn if sufficient heat and flame are applied, but they do not support combustion. Drawbacks of phosphate ester fluids are they can form very strong acids, such as phosphoric acid. These acids will attack and loosen commonly used paints and adhesives, deteriorate many types of insulations used in electrical cables,and deteriorate many gasket and

Copyright 2006 by Taylor & Francis Group, LLC

seal materials. Therefore, gaskets and seals for systems in which phosphate ester fluids are used are manufactured with specific materials. The only true viable seal material for use with phosphate esters is the viton seal. Most manufacturers, if they know a phosphate ester is going to be utilized, will specify paints to be used on exterior surfaces of hydraulic systems and components. When considering fire-resistant fluids, there are several tests and important criteria that are used to determine if a fluid is fire resistant. Figure 33.5 identifies some of the most important tests and criteria used in this determination. There are many other tests that are used and available but these are known as the most dominant. When a consumer is evaluating which type of fireresistant hydraulic fluid would be the most suitable for their particular application, many performance criteria should be considered. In Figure 33.6, various performance criteria are identified along with the appropriate ranking for each type of fire-resistant fluid. Considering the various industrial applications throughout the world today, it is important to understand where fireresistant hydraulic fluids are being utilized. In Figure 33.7, typical industries using fire-resistant fluids are identified through the Standard Industry Code (SIC).

REFERENCES 1. Quaker Chemical, U.S.A., Fire Resistant Hydraulic Fluids. 2. Quaker Chemical, U.S.A., Handbook of Polyol Ester Hydraulic Fluids. 3. Factory Mutual Research Corporation —Approval Standard. Less Hazardous Hydraulic Fluids, 26th August, 1969. 4. National Fluid Power Association (N.F.P.A.), U.S.A., Recommended Practice for the use of Fire Resistant Fluids for Hydraulic Fluid Power Systems, N.F.P.A. Standard T311.1 R1-1972. 5. Evanoff, T., “Selection of Hydraulic Fluids for a Rolling Mill.” 6. Khan, M.M., “Spray Flammability of Hydraulic Fluids,” Fire Resistance of Industrial Fluids, ASTM STP284, American Society for Testing Materials, Philadelphia, 1996. 7. Totten, E.T., Handbook of Hydraulic Fluid Technology, USA, 2000. 8. Staley, C. and McGuigan, B., Ciba Geigy (U.K.) Ltd. I. The European Use of Phosphate Esters in Steam and Gas Turbines,Lubr. Eng., 33, October 1977. 9. A.S.T.M. Annual Book of Standards, Part 17.

34

Vegetable Oil Based Internal Combustion Engine Oil Blaine N. Rhodes CONTENTS 34.1 34.2 34.3 34.4

The Function of Engine Oils The Lubrication of the Engine The Circulation of the Oil The Performance of Vegetable Based Oil 34.4.1 Friction and Power 34.4.2 Wear and Mileage 34.4.3 Viscosity and Mileage 34.4.4 Heat and Deposits 34.4.5 Emissions 34.5 The Conclusions at Present References.

34.1 THE FUNCTION OF ENGINE OILS This chapter concerns lubricants for internal combustion engines, which are gasoline or diesel fueled, as opposed to those with turbine or hydraulic drives. In these engines, fuel is combusted in the space above the piston, forcing the piston to move down a cylinder. This linear motion rotates a shaft through a crank mechanism, powering the valves used for air/fuel introduction, all the ancillary equipment on the modern vehicle, and finally the drive wheels or propeller. This mechanical daisy chain requires a number of functions from the engine oil, only one of which is lubrication. Inside the engine, combustion gases contain a high level of water, one of the major combustion products. The engine parts must be protected from corrosion by water (rust) or by the oil. Other products of combustion, when it is incomplete, are organic acids that can corrode metal parts. The oil must neutralize these acids. Incomplete combustion also produces a number of carbon compounds that can build to form deposits. It is another of the oil’s tasks to clean these compounds and transport them to the oil filter. All the time that the oil is saving the engine from its own friction, wear, and waste, it is being bombarded by its own greatest enemies: heat, oxygen, contaminants, and shear forces. Heat not only tears oil apart chemically, it increases the rate of all the degradation reactions that occur within the oil, such as viscosity change, oxidation, and additive removal. Oxygen attacks oil molecules

Copyright 2006 by Taylor & Francis Group, LLC

at any weak bond, inserting itself, further weakening the structure, and releasing hyper-reactive free radicals. This mechanism is actually slow-motion combustion of the oil. Contamination by wear metals, carbonaceous materials, combustion products, and even gasoline, changes the viscosity of the oil, increases wear rates of the parts, and starts corrosion. Shear, the forces that act on fluid layers in contact with rapidly moving adjacent currents, can be strong enough to tear molecules apart, especially the polymers used to improve viscosity in motor oils. The motor oil contains additives to combat the chemical attacks, to neutralize acids, and to segregate contaminants. Against the physical attacks of heat and shear, it relies only on its innate ability to persevere.

34.2 THE LUBRICATION OF THE ENGINE An internal combustion engine requires lubrication in distinct areas. All the bearings that hold spinning shafts, main, rod, and wrist pin bearings, need fluid to separate the journals and the races. The piston rings require lubrication when sliding against the cylinder walls. The contact between the cam lobes and the followers uses oil to minimize friction and wear. If the engine has pushrods, the ends that contact the rocker arms on the valves are protected by the oil. Similarly, the contact between the other end of the rocker arms and the valve stems needs oil. The mechanisms of engine lubrication fall into two regimes: hydrodynamic

100

Wide opening

Valve train 7%

Shaft spin

Fluid flow

Resultant force

Energy losses, % of total

90 80

FIGURE 34.1 Journal bearing cross-section

in the bearings, and boundary layer in the pistons and valves. Bearing lubrication is accomplished by maintenance of a fluid film between an outer stationary race and a closely sized, inner spinning journal, as shown in Figure 34.1. If the spinning shaft gets off center, the incompressible fluid it drags with it has to fit through a thin opening on one side, causing high pressure, and a wide opening on the other, causing low pressure. The resulting force is selfcorrecting, and the spinning shaft recenters itself. The inner and outer ring never touch each other when the engine is running. The effectiveness of oil in the journal bearings is entirely dependent on its viscosity. Since the surfaces never touch, there is no need for boundary layer additives. However, the higher the viscosity, the more energy is lost in a journal bearing due to viscous dissipation. Since the journal bearings in the main, rod, and cam shaft bearings are estimated to represent 40 to 60% of the energy losses within the engine that can be affected by lubrication, the viscosity of the oil is a key property. Boundary layer additives are needed at the surfaces of the cylinder walls and for the valve train components: pushrods, cam lobes, rocker arms, and valve stems. Parts that actually touch need better friction and wear control than are available in a base petroleum oil. Thus additives containing phosphorus, sulfur, and molybdenum are added to motor oil formulations. These additives protect the steel surfaces from long-term sliding wear, from pitting during contact, and from welding during impact. They also can affect the amount of frictional energy losses from the engine, estimated at 40 to 60% of lubricantrelated mechanical losses. The breakdown of losses and mechanisms is shown in Figure 34.2. The dominance of the viscosity or the boundary layer influence on fuel economy has been debated for some time. Repeatable testing has been the root of the problem. Whereas viscosity is a physical property of a lubricant,

Copyright 2006 by Taylor & Francis Group, LLC

Boundary and mixed lubrication, additives control

70 60

Piston rings 20%

50 Main bearings 11%

40 30 20

Narrow opening

Pistons 23%

10

Rod bearings 13%

Overlap in estimates Hydrodynamic lubrication: viscosity controls

Mechanical losses 26%

Mechanical losses 26%

Energy loss

Regime

0

FIGURE 34.2 Energy losses in internal combustion engine (From Bartz, Wilfried J., “Fuel Economy Improvement by Engine and Gear Oils,” Technische Akademie Esslingen, Ostfildern, Germany, 1995. With premission.)

and can be easily interchanged from one value to another with rapid results, boundary layer additives have chemical properties that affect metal surfaces for a prolonged period of time. Once an additive has been used in a test engine, the metal is conditioned for up to 50 h of use, even after the additive is removed from the lubricant. Thus, testing the effect of additives on fuel economy of actual engines is very time consuming and costly if several repetitions are going to be run on the same engine. No standard testing protocol for the engine testing of additives has been approved to date. The reader might have noticed that the viscosity grades of motor oils has been falling steadily since the days of SAE 30 weight and SAE 10W40. Replacement motor oils are now SAE 0W20, or two viscosity grades lower. Fuel economy testing has been the driver for this change. The Sequence VIA test weights viscosity over boundary layer improvements, as shown in Figure 34.3. The author has seen no analysis of the Sequence IVB test now in development. Lower viscosity means less viscous drag in the journal bearings of an engine, which shows up in the test as increased power. The viscosity effects are amplified by the Sequence IVA test. A return to high viscosity oil immediately returns the power of the engine to the lower levels previously recorded. Additives that lower the coefficient of friction of contact, however, do not disappear as soon as the oil is changed back to the standard. Once the metal surface is conditioned, it may remain that way for quite some time. Changing the oil back may not make a difference in the power output for hours. Since this is very difficult to predict from additive to additive, no engine testing of friction modifying oils has been standardized.

34.3 THE CIRCULATION OF THE OIL

pumped forcefully through a filter to remove solid particles, then it flows to the “top of the engine,” to the valve train through passages and through the hydraulic valve lifters and pushrods, if they are present. The pump also pushes the oil through passages in the block into the journal bearings. All the oil pumped, sprayed, or splashed onto surfaces in the engine drains by gravity back down to the bottom of the engine and the oil pan, to be picked up again by the pump. The dry path for the oil has not been under investigation until recently. Petroleum base oil is a mixture of petroleum molecules that range from 20 to 40 carbons long. The heat of the engine causes the smaller oil molecules to evaporate, filling the block with vapor. The majority of the oil is recirculated via the wet path. The vapors in the engine block, including oil fumes and gases that blow by the compression rings of the cylinders, are pumped into the intake manifold by the positive crankcase ventilation (PCV) system, where they join with the gas/air mix flowing to the combustion chamber as shown in Figure 34.4. The molecules in this vapor are much larger than those of gasoline. The combustion chamber is neither designed, nor is there time or sufficient heat, to burn all of the long carbon chains. The oil vapors continue from the combustion chamber as partially burned hydrocarbons (HC), increasing the load on the catalytic converter. Via the dry path through the engine, the oil is a contributor to the pollution from engine exhaust.

Oil takes two paths through an engine. The wet path is the lubrication design and a pump supplied. The oil is

100 90 Relative test weighting

80 70

Viscosity sensitive

Viscosity sensitive

60 50 40

Mixed

30 20 10

Mixed Additive sensitive

Additive sensitive

Sequence VI

Sequence VIA

0

FIGURE 34.3 Weights of the lubrication regimes in Sequence IV testing (From Kenbeek, D., Bünemann, T., and Reiffe, H., Uniqema Corporation, “Organic friction modifiers — contribution to fuel efficiency?,” Presented at the CEC/SAE International Spring Fuels and Lubricants Meeting, Paris, France, 20–22 June, 2000. With permission.)

Oil

Gasoline

Air Engine block

Intake manifold

PCV system

Combustion chamber

Exhaust manifold

Stable components

Rings blowby

Oxygen sensor

Engine control module

FIGURE 34.4 Dry path of oil within a gasoline engine

Copyright 2006 by Taylor & Francis Group, LLC

Volatile components

Wet path

Catalytic converter

Oxygen sensor

Exhaust

34.4 THE PERFORMANCE OF VEGETABLE BASED OIL 34.4.1 Friction and Power Vegetable based lubricants have improved frictional properties over petroleum oils, due to their mildly polar ester structure. Comparative motor oil formulations are no different, with the vegetable oil based motor oil showing reductions of coefficient of friction for steel-on-steel contact of 47% from petroleum motor oil and 26% from synthetic motor oil [5]. Over the relevant load range the comparison between motor oil friction modifications looks like Figure 34.5. The lowered friction of contact does not affect the viscous component of the energy losses, but it should affect engine power output and fuel economy by reducing boundary layer energy losses. Chassis dynamometer testing has confirmed an improvement in engine power output of an average of 6% over the standard RPM range of a production six-cylinder engine. These results are shown in Figure 34.6. Increased power corresponds to improved fuel economy depending on the drive train efficiency, the aerodynamics of the vehicle, the driver, and the type of driving done. Over the same driving routine, however, it should result in increased gas mileage.

34.4.2 Wear and Mileage The moving parts within an engine that contact other parts wear over time. Researchers who study the wear in engines follow the concentration of wear metals in the motor oil as an indication of the engine’s health. The major wear metal

Lubrication failure

160 150

Petroleum oil average coefficient under load

100

50 Bio-based Synthetic Petroleum 0 0

100 200 300 400 500 600 700 800 900 Load, Lb

FIGURE 34.5 Relative frictional properties of motor oil formulations by ASTM D 3233 (Printed with permission, Blaine N. Rhodes Consulting.)

Copyright 2006 by Taylor & Francis Group, LLC

Horsepower to the drive wheels

Percent of average petroleum oil coefficient of friction

200

observed in an engine oil is iron, from steel particles that have been scraped off contacting surfaces, or corroded off surfaces exposed to water and acids. There is no iron added to motor oils, so all iron in the oil at a check or change has come from these sources. High iron content means that some part of the engine is wearing or corroding at an unacceptable rate. Vegetable oil based engine oils have been shown to reduce the friction in metal-to-metal contact, but that does not necessarily mean that they prevent wear. Friction reduction denotes a slippery coating on the surface. Wear reduction denotes a tough coating. To verify wear protection, ASTM D 4172 four ball wear tests were performed and the vegetable oil based motor oil formulation resulted in an average wear scar diameter of 0.36 mm, compared to 0.42 mm for petroleum based formulations [5]. Results this close indicate that vegetable oil based motor oil is at least as effective as petroleum oil against wear. Wear metals analysis of the petroleum based, then the vegetable oil based, motor oils of gasoline engines during a three-year study undertaken with the United States Postal Service showed that the wear was reduced by the vegetable based oil under field conditions. These results are summarized in Figure 34.7. In the USPS four-cylinder engines, the slow driving and long idle periods (∼10 mi/h) kept the engines running cold, maximizing corrosive water, and minimizing the oil circulation rate. Under those conditions, iron levels climbed to over 300 ppm in the oil by the time the oil is changed, at about 1500 mi. In the same vehicles, the iron levels were approximately half when using a vegetable oil based motor oil. Considering the amount of research on vegetable oil based lubricants over the past several years, improvements in friction and wear over petroleum based oils should come as a small surprise.

140 120 100 80 60 40 1000

Petroleum Bio-based 2000

3000

4000

5000

RPM

FIGURE 34.6 Chassis dynamometer testing of a six-cylinder engine, consectutive runs with different oils (Printed with permission, Agro Management Group, Inc.)

350 Petroleum Bio-based

Viscosity at 100°C

300

14

Iron, ppm

250 200 150

12

10

8

100

Vegetable Petroleum

50

6 0

0 500 mi

Oil change

FIGURE 34.7 Iron levels in USPS vehicles over time [6] (From Rhodes, B.N., Reduction of emissions from U.S. Postal Service vehicles using vegetable-based engine oil, Proceedings of the United Soybean Board Lubricants and Fluids Technical Advisory Panel, Prepared by Omni Tech International, Ltd., Midland, MI, September, 2000, p. 4. With permission.)

34.4.3 Viscosity and Mileage The critical measure of viscosity has been previously discussed with regard to its role in fuel economy and testing. Its importance is greater than energy dissipation, however, because viscosity increase is the failure mode of vegetable oil based motor oils. Once the viscosity of the oil exceeds a critical level, which is different for each engine design, it fails to flow sufficiently to the places in the engine where it is needed, and wear-related problems ensue. The standard measure of the change of viscosity with temperature within the engine oil industry is the viscosity index (VI). The less the fluid viscosity changes with temperature, the higher the VI number, and the better engine oil it makes. Petroleum based oils contain polymeric liquids that thicken them at high temperatures, but do not interfere with low temperature properties. Petroleum oils have VIs of 90–110. The addition of polymers, called VI improvers, to the petroleum motor oil bring the VI of the finished oil to 150–160. The viscosity of an engine oil changes with operating engine hours, which can be measured as mileage in most vehicles. The trend is shown in Figure 34.8. The VI improver polymers in petroleum and synthetic base break down with shear during engine operation, causing petroleum oils to get thinner. Then, as the oil itself is exposed to heat and oxygen, its viscosity begins to rise in earnest. Vegetable oils have VIs of around 200, so they do not need any polymeric additives. This means, however, that the viscosity of a vegetable oil based motor oil does not drop in the first 2000 mi. Oxidation and heat cause the oil to thicken, however, and the reaction rate is exponential. The viscosity of the oil in Figure 34.8, based on USPS

Copyright 2006 by Taylor & Francis Group, LLC

1000

2000

3000 Miles

4000

5000

FIGURE 34.8 Viscosity of engine oil over mileage (Printed with permission, Agro Management Group, Inc.)

data, remains in specification for 4000 mi, but is out of specification at 5000 mi. The high VI of vegetable oil based motor oil means that it does not lose as much viscosity at higher temperatures as the petroleum oil does. Because of this, it can have a lower, fuel-saving viscosity at room temperature and then reach the same viscosity as the petroleum oil at higher engine operating temperatures.

34.4.4 Heat and Deposits At very high temperatures, without sufficient oxygen to burn, oils break down to carbon, forming deposits. Deposits occur on valves, pistons, injectors, and spark plugs, all places in contact with combustion temperatures. They can be affected by the gasoline additive as much or more than the motor oil packages. Still, deposits from carbonized oil can stick compression rings and obstruct the operation of valves in an engine. It is important to control the motor oil viscosity so that it does not rise above the point at which it flows through the clearances of the deposit-prone engine parts listed above. If it does, the oil will remain in those parts and form deposits. To avoid this, oil change intervals are shorter and stricter for vegetable oil based motor oils. Because of the relative simplicity of their formulations, deposit amounts are lower per unit weight for vegetable oil based than for petroleum oils. Deposit testing by thermooxidation engine oil simulation test (TEOST), Method 33, shows lower deposits from vegetable based formulations at the 800◦ F test temperatures (Figure 34.9).

34.4.5 Emissions Because of the dry path of the oil through the engine, emissions of unburned HC and carbon monoxide (CO) have the potential to be increased. The catalytic converter on gasoline-powered vehicles takes care of a large part of the

25

Maximum specified by OEMs Noack volatility % loss

60 50

% Deposits

40

30

20

15

10

5

20

0

10

5W30

0 Petroleum

Vegetable

FIGURE 34.9 Deposits testing of motor oils by TEOST Method 33 (From Rhodes, B.N., Reduction of emissions from U.S. Postal Service vehicles using vegetable-based engine oil, Proceedings of the United Soybean Board Lubricants and Fluids Technical Advisory Panel, Prepared by Omni Tech International, Ltd., Midland, MI, September, 2000, p. 6. With permission.)

extra emissions, but as the catalyst ages, the emissions of these pollutants rise. Oxides of nitrogen (NOx ) emissions from a modern vehicle are linked to the Dry Path of the oil by a less direct route. NOx is formed by high air/fuel ratios or increased spark advance by the engine control module (ECM). Input to the ECM comes from a number of sources, including oxygen sensors before and after the catalytic converter. Enough oxygen must be fed to the converter to react with the HC and CO to complete the oxidation, but too much means that the NOx will rise due to too high an air/fuel ratio (lean combustion conditions). The extra HC and CO from the oil fumes in the combustion chamber require the ECM to increase the oxygen to the catalytic converter, increasing the air/fuel ratio, and creating a lean burning condition that raises the output of NOx. Vegetable oils have very low volatility. In fact, they do not evaporate at atmospheric pressures, they thermally crack at extreme temperatures and the cracking products evaporate. The comparative Noack volatility, run at 250◦ C is shown in Figure 34.10. So, unless vegetable oil based motor oil reaches temperatures of 350◦ F or above for substantial periods of time, it will not take the dry path through the engine into the combustion chamber. The burn of the fuel is cleaner, deposits are reduced, and the load of HC and CO on the catalytic converter has been observed to be reduced. Also as a consequence, an NOx reduction has been measured due to a lower air/fuel ratio needed for the exhaust oxygen sensors. The size of the reduction has been dependent on the age of the vehicle and the condition of the catalyst, so a

Copyright 2006 by Taylor & Francis Group, LLC

10W30

15W40

Synthetic Bio-based

FIGURE 34.10 Noack volatility losses for motor oil formulations (Printed with permission, Agro Management Group, Inc.)

TABLE 34.1 Reduction in Pollutants from Gasoline Engines Compound

HC

CO

Reduction range Statistical significance

1–30% Established

1–50% Established

NOx 1 to 50% Not yet

Source: Printed with Permission, Agro Management Group, Inc.

range is presented in Table 34.1. However, the findings have been statistically significant when sufficient vehicles or repetitions of the tests have been performed. Testing of the effects of vegetable oil motor oils on diesel emissions has not been done to the level of statistical analysis as of yet, but preliminary testing has been positive. Other tests presented by a major diesel engine oil formulator did show a reduction in particulate emissions up to 30%, corresponding directly to the Noack Volatility of synthetic motor oils used in the engines [11]. As of this writing, more testing is pending on diesel engines.

34.5 THE CONCLUSIONS AT PRESENT Vegetable oil based motor oils have been successfully demonstrated in gasoline engine fleets. They show advantages and disadvantages when compared to present petroleum oil technology. The advantages include: • Improved friction reduction • Higher VI, leading to reduced viscous drag at cold

temperatures • Improved wear protection • Less tendency to create deposits • Higher volatility, leading to lower emissions

The disadvantages include: • Monotonic viscosity build, leading to decreased oil

change intervals • Incompatibility with existing petroleum motor oil, the

engine must be purged upon the initial change-over temperature fluidity limitations for some formulations

• Low

At present oil equipment manufacture (OEMs) are unlikely to accept an engine oil with shorter change intervals. Their thrust has been to claim intervals as long as possible, within limits. However, engines are now designed for petroleum based motor oils. Their pumps and passages are sized for oils that get thinner. Their oil capacities are calculated for minimum weight to save mileage, not for minimum friction. Considering the present and future work, it should not be long before someone designs an engine specifically for vegetable oil based motor oil. Then a true comparison of systems can be made.

REFERENCES 1. Bartz, Wilfried J., “Fuel Economy Improvement by Engine and Gear Oils,” Technische Akademie Esslingen, Ostfildern, Germany, 1995.

Copyright 2006 by Taylor & Francis Group, LLC

2. Kenbeek, D., Bünemann, T., and Reiffe, H., Uniqema Corporation, “Organic friction modifiers — contribution to fuel efficiency?,” Presented at the CEC/SAE International Spring Fuels and Lubricants Meeting, Paris, France, 20–22 June, 2000. 3. Printed with permission, Blaine N. Rhodes Consulting. 4. Printed with permission, Agro Management Group, Inc. 5. Printed with permission, Agro Management Group, Inc. 6. Rhodes, B.N., Reduction of emissions from U.S. postal service vehicles using vegetable-based engine oil, Proceedings of the United Soybean Board Lubricants and Fluids Technical Advisory Panel, Prepared by Omni Tech International, Ltd., Midland, MI, p. 4, September, 2000. 7. Printed with permission, Agro Management Group, Inc. 8. Rhodes, B.N., Reduction of emissions from U.S. postal service vehicles using vegetable-based engine oil, Proceedings of the United Soybean Board Lubricants and Fluids Technical Advisory Panel, Prepared by Omni Tech International, Ltd., Midland, MI, p. 6, September, 2000. 9. Schwartz, Shirley E., General motors powertrain, “Effects of the engine on oil and effects of degraded oil on the engine,” Presented to the Society of Tribologists and Lubricant Engineers Annual Meeting, Orlando, FL, 21–25 May, 2001. 10. Printed with permission, Agro Management Group, Inc. 11. Fotheringham, et al., BP Chemicals, U.K., “The effect of base oils in SAE 5W30 lubricants on the exhaust emissions of a heavy duty vehicle,” Presented at the Society of Tribologists and Lubricant Engineers Annual Meeting, Houston, TX, 19–23 May, 2002.

35

Magnetizable Fluids Tom Black and J. David Carlson CONTENTS 35.1 Introduction 35.2 Ferrofluid 35.2.1 History 35.2.2 Basic Constituents 35.2.2.1 Solid Phase 35.2.2.2 Liquid Phase 35.2.3 Engineering Properties 35.2.3.1 Saturation Magnetization 35.2.3.2 Viscosity 35.2.3.3 Volatility 35.2.3.4 Chemical Compatibility 35.2.4 Applications 35.2.4.1 Rotary Seal 35.2.4.2 Loudspeaker 35.2.4.3 Domain Detection 35.2.4.4 Magnetogravimetric Separation 35.2.5 Ferrofluid Economics 35.3 Magnetorheological Fluids 35.3.1 MR Fluid Description 35.3.2 History of MR Fluids 35.3.3 MR Fluid Composition 35.3.3.1 Liquid Vehicle 35.3.3.2 Polarizable Particles 35.3.3.3 Additives 35.3.4 Properties of MR Fluids 35.3.4.1 Off-state Plastic Viscosity 35.3.4.2 On-state Yield Strength 35.3.4.3 B-H Curve 35.3.4.4 Density 35.3.4.5 Volatility 35.3.4.6 Response Time 35.3.4.7 Compressibility 35.3.4.8 Figure of Merit 35.3.4.9 Characteristics of Typical MR Fluids 35.3.5 MR fluid Usage Constraints and Limitations 35.3.5.1 Temperature 35.3.5.2 Material Compatibility 35.3.5.3 MR Fluid Durability and in-Use-Thickening 35.3.5.4 MR Fluid Life 35.3.5.5 Centrifugal Effects 35.3.5.6 Component Wear

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35.3.6

Application of MR Fluid 35.3.6.1 Valve mode 35.3.6.2 Direct shear mode 35.3.7 MR Fluid Economics 35.4 Conclusion References

35.1 INTRODUCTION In nature, materials that exhibit magnetic properties are invariably solids. Magnetizable fluids, then, are not naturally occurring substances. They are man-made composite materials consisting mainly of a solid phase and a liquid phase. The solid phase is magnetic in nature, and the liquid phase is a functional fluid that imparts fluidity to the composite. The bulk properties of the composite are derived from the two main phases and their interaction with the environment. This chapter discusses two very different kinds of magnetic fluids that have found uses in engineering. These are ferrofluids and magnetorheological (MR) fluids. The two materials are distinguished most basically by the size of the individual particles that make up the solid, magnetic phase. In the case of ferrofluids, each particle of the solid phase is only a few nanometers in diameter. The individual particles are subdomain in size. As a consequence, each one has a permanent magnetic moment. The particles are suspended in the liquid phase by means of a surfactant, a coating that serves to physically separate the particles and couple them to the liquid phase. When properly prepared, the resulting composite appears to be a homogeneous, magnetically responsive liquid with no net magnetic moment, and no tendency to separate into its component phases. Ferrofluid is attracted to a magnetic field, but its flow properties are not materially affected by it. This property distinguishes ferrofluids from the other class of magnetic fluid, MR fluids. At a glance, MR fluids appear similar to ferrofluids. However, this similarity is superficial. The macroscopic behavior of a MR fluid in the presence of an external magnetic field differs dramatically from that of a ferrofluid. Instead of a body force that attracts the fluid to regions of high field strength, the most obvious reaction of MR fluid is an apparent change of state wherein the fluid appears to solidify into a semisolid. The essential rheological characteristic of MR fluid is the development of a shear yield strength that is more or less proportional to the applied magnetic field strength. Unlike the nano-sized particles found in a colloidal ferrofluid, the particles in an MR fluid are several orders of magnitude larger. Most typically, these particles are a few microns in size. Because of this relatively large particle size, the magnetic field-induced interaction between

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particles ends up being very much larger than any other competing forces on the particles. Most notably, the magnetic interaction energy between particles ends up being many orders of magnitude larger than thermal energy, kT. As a consequence, the applied magnetic field results in the formation of a very long range of particle structure in the fluid. The result is the development of a magnetic fielddependent yield strength. Because of the large particle size, MR fluids are not colloidally stable. Some explicit effort must always be made in formulating MR fluids so that they behave as relatively stable, homogeneous suspensions. Table 35.1 is a brief summary that compares and contrasts various features and properties of ferrofluids and MR fluids.

35.2 FERROFLUID 35.2.1 History Even though stable magnetic colloids were first described in 1938 (Elmore), it was not until the 1960s that they were successfully synthesized and became available to the engineering community. In 1965, S. Papell of NASA first disclosed a practical method for synthesizing ferrofluid in US Patent # 3,214,575. Papell had it in mind to magnetize liquid rocket fuel so that magnetic fields could be used to manage its flow in zero gravity. At about that time, AVCO Corp. was developing an Electric Arc Jet propulsion system for long-duration space flights. A nuclear power source was envisioned, and a method was needed to convert heat into electrical energy to power the Arc Jet engine. R. Rosensweig of AVCO and E. Resler, head of the Aerospace Department of Cornell University, worked to develop a Magnetocaloric Energy Conversion Cycle using metallic ferrofluid as the working fluid. The physics of such a cycle was worked out, but the necessary metallic ferrofluid could not be synthesized. The AVCO attempted to interest NASA in their propulsion system development without success. However, they did secure a contract to develop and characterize ferrofluid. Building on the work of Papell, Rosensweig’s team succeeded in increasing the magnetic strength of ferrofluid tenfold, synthesized ferrofluids based on a variety of new fluids, and identified the physiochemistry of the material. Rosensweig continues his research on ferrofluids until

TABLE 35.1 Two Types of Magnetizable Fluid Parameter

Ferrofluid

Magnetorheological Fluid

Typical particle size Basic magnetic response

5–10 nm Body force proportional to field gradient Colloidal Liquid
1–10 µm Induced yield strength proportional to magnetic field strength squared Non-colloidal Bingham plastic
kT 3–8, depending on particle volume fraction and magnetic field strength Electrorheological fluids Multi domain particles

Suspension type Rheological state under strong magnetic field Magnetic Interaction Energy Magnetic Permeability (relative) Electric Analog Domain structure

today. His 1985 book, Ferrohydrodynamics [4], is the defining text of the field. A large international research community has developed on the synthesis and characterization of ferrofluids. The First International Conference of Magnetic Fluids was held in 1977 under the jurisdiction of the European Physical Society. Ten such conferences have been held, the latest in 2005. The proceedings are published as special issues of the Journal of Magnets and Magnetic Materials (Elsevier Press). These journals represent a valuable archive of ferrofluid research. Commercial development of ferrofluid technology began in 1968 when Rosensweig and R. Moskowitz, another AVCO researcher, left and founded Ferrofluidics Corp. Ferrofluidic® rotary shaft seals were the first commercially viable product using ferrofluid.

N N

S S

S S

Magnatic particle N S

N

N

S

S Surfactant Carrier

FIGURE 35.1 Schematic representation of ferrofluid

35.2.2 Basic Constituents

35.2.2.1 Solid phase

Ferrofluid is a magnetically responsive liquid. Its magnetic properties arise from a stable suspension of magnetic particles in a liquid medium. Each particle is itself a permanent magnet. In order to achieve a stable suspension, the particles must remain far enough apart that their magnetic moments do not interact strongly. In this way, the particles are not attracted to each other, but are free to respond to an external magnetic force. This separation is normally accomplished by coating the particles with a surfactant. Figure 35.1 represents the ferrofluid system schematically. Surfactant molecules are long polymer chains of a type that is compatible with the liquid medium. They are provided with a functional group at one end that binds to the particle. With a proper surfactant formulation, and given the right conditions, a particular particle species can be suspended in a particular liquid medium [1]. Surfactant chemistry and processing conditions are generally proprietary, and are specific to a given end use application. The following is a discussion of the nature of the particles and liquid media that are most commonly found in commercial ferrofluids.

In principle, one has a wide choice of magnetic solids from which particles can be selected for ferrofluid synthesis. The common magnetic metals, iron and cobalt, would seem a natural choice because they have high magnetization. In fact, much work has gone into efforts to make ferrofluids from these substances. Ferrofluids with metallic particles have been synthesized and characterized [2,3], but to date none have proven robust enough for engineering use. Invariably, the particles are degraded by oxidation. Some metal oxides are sufficiently magnetic for use in ferrofluids. In fact, all commercially significant ferrofluids are made with metal oxide particles, most notably iron oxide Fe3 O4 (magnetite). Particle size is an important consideration in ferrofluid design. For magnetite ferrofluid, Rosensweig [4] showed the limiting particle size for physiochemical stability to be in the range of 8 nm. This agrees closely with practical experience, where approximately 10 nm is found to be the upper limit. A cubic centimeter of ferrofluid contains approximately 1017 such particles [5]. Within the

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practical range of particle size (0 to 10 nm), the smallest particles are avoided because they contribute very little to the magnetization of the finished ferrofluid. 35.2.2.2 Liquid phase A wide variety of liquids can be used to make ferrofluids for different end use applications, limited primarily by the ability to select a compatible surfactant. Some applications, notably rotary seals (see Section 35.2.4.1) require long service life and environmental stability. In these cases, high performance functional fluids are chosen. Synthetic and highly refined petroleum oils are commonly used, as are perfluoropolyether oils. Water- and solvent-based ferrofluids are used in applications where it is necessary to evaporate the liquid phase, such as magnetic domain detection. Between these extremes lies a range of applications with ferrofluid properties tailored for each.

35.2.3 Engineering Properties Ferrofluids are selected for a particular end use application based on four principal engineering properties — saturation magnetization, viscosity, volatility, and chemical compatibility. These properties are strongly interrelated. Achieving a desirable value for one often comes at the expense of another. Accordingly, an engineer selecting a ferrofluid for a particular use is called upon to carefully balance ferrofluid properties and device considerations to achieve an optimal design. Of the four engineering properties listed, the first two, magnetization and viscosity, are the ones that determine how the ferrofluid will behave in the application. The remaining two, volatility and chemical compatibility, speak of the durability of the ferrofluid.

field causes initially randomly oriented magnetic domains to become aligned. A full treatment of the theory of magnetism is beyond the scope of this chapter. In a ferrofluid, as in a ferromagnetic solid, this induced magnetization in a strong magnetizing field is termed Saturation Magnetization (Js) and has the units of Tesla or Gauss. 1 Tesla = 10,000 Gauss. In ferrofluid, the value of saturation magnetization depends on the particle concentration and the strength of the magnetic moment associated with each particle. In turn, the magnetic moment of each particle depends on its size and composition. Magnetitebased ferrofluids can have up to 0.1 T (1000 G) saturation magnetization. For most commercial applications, a value between 10 and 800 G is selected. For comparison, the value for pure iron is over 20,000 G. In most applications, ferrofluid is called upon to react to an applied magnetic field. The engineering property Js denotes the strength of the interaction. For example, in a ferrofluid rotary seal, the fluid resides in a sealing location surrounding a rotatable shaft. See Section 35.2.4.1. It is retained by a strong magnetic field in that location, just as the poles of a magnet retain iron filings. When pressure is applied to the seal, the ferrofluid is displaced from its initial position to the one where the magnetic field is lower. The fluid resists displacement. Accordingly, a ferrofluid seal has the capacity to resist pressure in proportion to its Ms and the strength of the magnetic field. The maximum pressure capacity (p) of such a seal is approximately p = µ0 JsH

(35.1)

where µ0 is the magnetic permeability of free space (a constant), and H is the field strength. See Reference 4 for the derivation of this relationship.

35.2.3.1 Saturation magnetization

35.2.3.2 Viscosity

In the introduction to this chapter, ferrofluid is described as a “homogeneous, magnetically responsive liquid with no net magnetic moment.” Ferrofluid responds to a magnetic field because it contains a large number of particles, each of which has a permanent magnetic moment. In the absence of an external magnetizing influence, the particles are randomly oriented. When a sample of ferrofluid is immersed in a weak magnetic field, some of the particles become aligned with the field. Others are prevented from doing so by thermal agitation, which tends to randomize their orientation. In a sufficiently large magnetic field, essentially all of the individual particles become oriented with the field. The ferrofluid is said to be saturated. In this state, the sample of ferrofluid has an induced magnetization arising from the magnetization of all of its constituent particles. This mechanism of induced magnetization is analogous to the behavior of ferromagnetic solids. When a ferromagnetic specimen is immersed in a magnetic field, the

Viscosity is defined as the resistance to flow. In a flowing fluid, shearing stress arises from friction between adjacent layers of fluid, which are thought of as sliding past each other. Sir Isaac Newton observed that for many common fluids, this shearing stress is linearly proportional to the rate of shearing strain at the interface between the layers [6]. The constant of proportionality in this relationship is called absolute viscosity, dynamic viscosity, or simply viscosity (as is done here). In the CGS system, the primary units of viscosity are dyne-seconds per square centimeter, or poise. Units of centipoise (= 10−2 poise) are normally given for convenience. It should be noted that an alternate definition of viscosity, arising from the measurement of flow through a tube or capillary driven by gravity, is termed kinematic viscosity and has units of centimeter2 per second or stoke. Kinematic viscosity is equal to (absolute) viscosity divided by the density of the fluid.

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The above discussion is founded on Newton’s observation of strict proportionality between shear stress and shear rate. As it happens, not all fluids obey Newton’s law. Those that do are referred to as Newtonian fluids or simple fluids. A discussion of non-Newtonian fluids is beyond the scope of the present discussion. Ferrofluids are somewhat non-Newtonian, but it is usually sufficient to treat them as Newtonian for engineering purposes. For an engineer contemplating an application for ferrofluid, viscosity is often an important consideration. For example, a very viscous ferrofluid might be undesirable in a ferrofluid seal operating on a large diameter shaft. The torque required to rotate the shaft at significant speed would be excessively high. In another ferrofluid application such as a loudspeaker (see Section 35.2.3.2), high viscosity might be desirable so that the device would have sufficient damping performance within a limited space. In ferrofluid, as in any colloid, the viscosity exceeds that of the liquid phase because of the presence of suspended particles [7]. As a result, a ferrofluid with high saturation magnetization has higher viscosity than the one with low Js, all other factors being equal. Further, the viscosity of most fluids (certainly all ferrofluids) is an inverse power function of temperature [8]. Accordingly, a ferrofluid at a high temperature will be less viscous than the same ferrofluid at a lower temperature. Commercial ferrofluids exhibit room temperature viscosity in the range of 10 to more than 100,000 cP. The low end of this range is occupied by ferrofluids that are intended to evaporate readily. At the high end are ferrofluids for viscous damping applications. The viscosity of sealing ferrofluids is normally between 100 and 10,000 cP. 35.2.3.3 Volatility In many engineering applications, a very small quantity of ferrofluid is required to survive for many years. For example, a typical ferrofluid rotary shaft seal may contain less than 0.1 mL of ferrofluid. Moreover, such a seal may be continuously exposed to high vacuum. A ferrofluid intended for this use should have low volatility so that it will not be lost to evaporation and it will not contaminate the vacuum environment it is intended to seal. Volatility of ferrofluids and other functional fluids is normally expressed in terms of evaporation rate, in units of grams per square centimeter-second. A fluid whose evaporation rate is 1 g/cm2 sec will evaporate 1 g from each cm2 of free surface per second. The evaporation rate of sealing ferrofluids is typically in the range of 10−9 g/cm2 sec or lower, measured at 100◦ C. Since volatility of ferrofluids is a power function of temperature, room temperature volatility is much lower. It is normally extrapolated from high temperature measurements. Volatility and viscosity are interrelated. Low volatility comes at the expense of increased viscosity.

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35.2.3.4 Chemical compatibility Ferrofluids are frequently exposed to environments such as ambient air, high vacuum, and high humidity. In addition, they are sometimes exposed to more aggressive environments that contain chemically reactive vapors. To be successful, a ferrofluid must be stable in its intended environment. Its liquid phase, solid phase, and surfactant must be compatible with the environment. High quality oils are exploited to serve as the liquid phase, including many of those discussed in detail in other chapters of this book. They are selected based on the needs of a particular application to have the optimal combination of volatility, viscosity, and chemical compatibility. As was mentioned earlier, there is an additional constraint; one must choose a substance for which a suitable surfactant is available.

35.2.4 Applications Ferrofluid has found use in a wide variety of applications. The most commercially important ones are described below. In addition to these, interesting applications or potential applications exist in diverse areas such as medicine, biotechnology, isotope separation, fluid transport, energy conversion, metrology, and submarine propulsion. 35.2.4.1 Rotary seal The commercialization of ferrofluid technology began with the introduction of ferrofluid-based rotary shaft seals. A ferrofluid rotary shaft seal (see Figure 35.2) consists of a permanent magnet, a magnetically permeable focusing structure, and ferrofluid as the sealant. The focusing structure, consisting of pole pieces and the shaft, serves to concentrate magnetic flux from the magnet into a number of narrow gap regions or “stages” surrounding the shaft. The stages strongly attract and retain the ferrofluid sealant, forming discrete, hermetic seal rings. Each seal ring has a certain pressure capacity (typically 1 to 10 PSI) and an arbitrary number of seal rings can be grouped together within a seal to provide any desired pressure capacity. Such seals have many desirable features. Because the sealing element is a liquid, it conforms perfectly to the shaft and pole piece surface, forming a leak-tight seal. It exhibits very low drag and no wear. One important limitation arises from the liquid nature of the seal element. Ferrofluid seals cannot be used to seal against liquids directly. Ferrofluid rotary shaft seals are used in a number of contamination-sensitive applications, either to retain or to exclude gases, vapors, and airborne particles. Some notable applications are: 35.2.4.1.1 Vacuum seal Multistage ferrofluid seals are the workhorses of the semiconductor industry, moving wafers into and out

O-rings provide Static seal

Magnet Pole pieces

Ferrofluid focussed between magnetic poles and shaft forms nonrubbing circular seal

O-ring

Polepiece Shaft

Magnet

Ferrofluid

FIGURE 35.2 Ferrofluid rotary shaft seal

of processing chambers and providing contamination-free, in-vacuum rotary motion. Many other applications rely on ferrofluid seals to provide motion in vacuum. Among these are: • Vacuum coating: Such as energy saving coatings for

architectural glass, hard coating of machine tool cutters and wear-resistant parts, and metallization of plastics for EMI/RFI shielding. • Optical coating: Ranging from antireflection coating of eyeglass lenses to precision multilayer optical filters for optical communications. • X-ray generators: Where high-energy electrons impinge on a rapidly rotating target (anode) to produce x-rays.

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• Energy storage flywheels: Mechanical “batteries” where

energy is stored in a flywheel rotated at high speed in vacuum. 35.2.4.1.2 Vacuum/pressure seals In many applications, ferrofluid seals are called upon to provide rotation and sealing in applications where a chamber or device is repeatedly evacuated and backfilled. Examples include the manufacture of light bulbs and the sterilization of medical devices. 35.2.4.1.3 Pressure seals Gas Lasers and equipment for the manufacture of optical waveguides are examples of applications where ferrofluid

Dust cap Air gap Diaphragm Flexible surround

Basket

Bobbin

Spider Front plate N S

N S

Magnet Back plate

Voice coil Pole piece

Ferrofluid

FIGURE 35.3 Ferrofluid cooled loudspeaker

seals are called upon to provide rotation while sealing pressurized gases. 35.2.4.1.4 Exclusion seals Certain electromechanical devices rely on ferrofluid seals to isolate and protect a contamination-sensitive environment. Computer disk drives and electro-optic devices such as airborne infrared cameras are examples. These applications are distinguished from pressure and vacuum applications in that their main purpose is isolation rather than pressure retention.

FIGURE 35.4 Demonstration of magnetogravimetric separation

35.2.4.4 Magnetogravimetric separation

Ferrofluid is commonly used in loudspeakers for high quality audio applications. In this application, ferrofluid’s magnetic nature is used simply to retain it in place within the voice coil gap of the speaker. There it serves to cool the voice coil, allowing a given speaker to operate at higher power. In addition, the fluid can provide damping, lubrication, and environmental protection, improving the sound quality and durability of the product. See Figure 35.3. The same technology is also applied to voice coil actuators used in digital videodisk players.

The body force developed within ferrofluid can be used to adjust its apparent density. One can expose a volume of ferrofluid to a magnetic field gradient. By varying the gradient, nonmagnetic bodies of varying density can be caused to float. Figure 35.4 shows a copper coin floating on the surface of ferrofluid, under the influence of a small magnet placed under the ferrofluid container. This principle is used in the mining industry to separate desirable minerals from a mixed feedstock. The same technology is used on a laboratory scale to separate materials for research purposes. Its applicability for solid waste recycling is under study at this time.

35.2.4.3 Domain detection

35.2.5 Ferrofluid Economics

Very dilute ferrofluids, formulated with volatile carriers, are used to visualize small-scale magnetic phenomena such as the magnetic domains of ferromagnetic materials and the data bits recorded on magnetic tapes and disks. The extremely small size of individual ferrofluid particles facilitates high-resolution imaging, exceeded only recently with the development of Magnetic Force Microscopy.

The first commercial application for ferrofluids remains the best-known one, ferrofluid rotary shaft sealing. The economic value of this application is best described in terms of device value as opposed to ferrofluid value because the amount of ferrofluid used in each seal is rather small. In fact, annual consumption of ferrofluid for sealing applications amounts to only about 750 L worldwide.

35.2.4.2 Loudspeaker

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This volume of ferrofluid supports a global seal industry valued at approximately $40 million per year. The loudspeaker application consumes approximately 800 L of ferrofluid annually, with a value of about $4 million. The Magnetogravimetric application is impossible to value directly. Mining interests, the largest practitioners, typically produce ferrofluid for their own use. The amount of ferrofluid used in this application is huge compared to all others. It is estimated to be approximately 10,000 L per year.

(a) t H2

tH2

G⬘

H1

Increasing H

g (b) H2 t

35.3 MAGNETORHEOLOGICAL FLUIDS

tH2

35.3.1 MR Fluid Description In the absence of an applied magnetic field, MR fluids behave approximately as simple, Newtonian liquids. An approximately constant, plastic viscosity characterizes this zero-field, “off-state” condition. In this context, plastic viscosity is defined as the slope of the shear stress vs. shear rate curve. Note, that at very low shear rates the detailed rheology of MR fluid in the off-state may depart significantly from that of a simple Newtonian liquid. This departure is most often characterized by the presence of a small, zerofield yield strength that is purposely created to inhibit or prevent particle settling. When an external magnetic field is applied to an MR fluid, the fluid develops a yield strength that is more or less proportional to the magnetic field strength. This yield strength arises from the internal structure that is formed when the largely iron particles polarize and chain together along the field lines. This yield strength adds linearly to the off-state shear stress such that the slope of the stress vs. shear rate curve, that is, plastic viscosity, remains largely unchanged. A simple, Bingham plastic model is effective at describing the basic field-dependent characteristics of MR fluid [9]. In this model, the total yield stress τtotal is given by: τtotal = τH sgn(γ˙ ) + ηp γ˙

(35.2)

where τH is the yield strength caused by the applied magnetic field H, γ˙ is the shear rate and ηp is the fieldindependent plastic viscosity defined as the slope of the shear stress vs. shear strain rate relationship. For applied stress values below the yield value (at strains on the order of 10−3 ), MR fluids behave viscoelastically [10] with a magnetic field-dependent shear modulus: τ = GH γ

(35.3)

where GH is the complex, field-dependent shear modulus and τ < τH . In this very low strain regime MR fluid behaves as a variable modulus viscoelastic solid. The real

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hp H1

Increasing H

H=0

g•

FIGURE 35.5 Pre- and postyield behavior of an idealized MR fluid in the presence of an applied magnetic field H as a function of shear strain and shear rate: (a) Preyield regime Characterized by variable modular γ˙ constant and (b) Postyield regime Characterized by variable yield strength

and imaginary parts of the modulus GH and GH both increase with the applied magnetic field while the loss ratio tan δ remains relatively field independent. The preand postyield behavior of an MR fluid is summarized by the graphs of τ vs. γ and γ˙ shown in Figure 35.5.

35.3.2 History of MR Fluids Magnetorheological fluids and their electric analogues electrorheological or ER fluids both have histories that date from the 1940s. ER fluids are suspensions of electrically polarizable particles in nonconductive liquids that develop a yield strength upon exposure to a high electric field. The initial discovery and development of MR fluids and devices can be credited to Jacob Rabinow at the U.S. National Bureau of Standards [now NIST] [11,12]. He applied for his first MR fluid patent in 1947 [13]. Interestingly, Rabinow was one of the most prolific inventors of the 20th century having been awarded 230 US patents on a wide range of electrical and mechanical devices [14]. These included the first magnetic disk memory and the magnetic particle clutch. Early MR fluids made by Rabinow for use in clutches were not dissimilar to many of those made today and exhibited comparable yield strength. Willis Winslow who is credited with inventing ER fluids in the 1940s also made early MR fluids [15].

Rabinow’s pioneering work led to a brief period of interest in MR fluids in the 1950s and early 1960s. However, by the late 1960s interest in MR fluids based on published papers had waned. It was at this time that a growing interest in ER fluids began to emerge. By the late 1980s, a large number of universities and companies around the world were actively pursuing research on ER fluids and devices [16]. Much of this work was motivated by potential automotive applications such as real-time controllable “smart” shock absorbers for improved ride and handling and controllable torque transfer devices [17]. In spite of great improvements in ER fluid formulations beginning in the late 1970s and continuing through the 1980s, ER fluid devices have failed to emerge in any practical way in the automotive world. Maximum yield strengths of ER fluids remain too low for most applications. Further, they require power supplies capable of outputting several kilovolts as well as expensive wires and connectors rated for such high voltages. The inherent temperature dependence of their electrical polarization mechanisms and a strong sensitivity to moisture and contamination makes their use outside of the laboratory difficult and costly. Beginning in the early 1990s a resurgence of interest in MR fluids and applications emerged as a way around the limitations of ER fluids [18,19]. MR fluids offered substantially higher yield stresses and the ability to operate at higher and lower temperatures. Moreover, the necessary magnetic fields could be achieved with electromagnetic powered by common, low-voltage power supplies, that is, 12 V systems. Groups at TRW, QED Corporation, and Lord Corporation demonstrated that practical MR fluids and devices could be made, which could actually enable many of the unrealized hopes for ER fluids [20–26]. Why did MR fluids remain in the background for so long? One answer seems to be the prevailing paradigm through much of the 1970s and 1980s that MR fluid devices with their electromagnets would be too slow, too bulky, and too cumbersome to be useful in real-time controlled systems compared to relatively sized ER fluid devices. It was not until the early 1990s that it was realized that the 10 to 20 times greater yield strength of MR fluids compared to ER fluids would enable MR fluid devices to have active fluid volumes that were as much as a factor of 100 smaller than those of ER fluids sized for relative mechanical performance. The volume of fluid in a device that needs to be activated by the applied field for a given level of mechanical performance actually scales as the inverse of the square of the maximum yield strength [19]. Thus, the necessary electromagnets do not need to be excessively large and slow. Magnetorheological fluids and devices have been successfully commercialized since the mid-1990s. A number of these applications are described later in the chapter. The holy grail of a mass-produced “smart” MR fluid automotive shock absorber system was finally realized in the

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early 2002, with the introduction of the MagneRide suspension system as the standard equipment on the Cadillac Seville STS with MR fluid made by Lord Corporation [27], and shock absorbers and struts made by Delphi Corporation [26,28].

35.3.3 MR Fluid Composition The composition of a typical MR fluid can be broken into three parts: a liquid vehicle, magnetically polarizable particles, and a variety of additives [29]. While it is possible to create a suspension that will display an MR response with just the first two of these parts, such suspensions are highly unstable and problematic in practical devices. A well-formulated additive package is necessary in order to achieve a stable, long-lived MR fluid. Much of the MR fluid research activity in recent years has focused on developing proprietary additive packages that enable the simultaneous realization of high on-state, low off-state forces in fluids that are highly stable and exhibit very long life [30]. 35.3.3.1 Liquid vehicle A wide variety of liquid vehicles or carrier liquids can be used to formulate MR fluids. By far, the most common vehicles are hydrocarbon oils. These can be mineral oils, synthetic oils, or mixtures of both. In general, hydrocarbon oils are the vehicle of choice because of their good lubricity, durability, and availability of a wide range of well-behaved and well-understood additives. Synthetic polyα-olefins or PAOs are often chosen because of their well-controlled properties over a broad range of temperatures. Other common liquid vehicles for MR fluids are silicone oils and water. While generally inferior to hydrocarbon oils in terms of lubricity, durability, and amenability to many additives, silicone oils do offer a somewhat broader temperature range with less variation in viscosity than synthetic hydrocarbons. Silicone oils are often chosen in situations where a hydrocarbon vehicle may not be compatible with other materials exposed to the MR fluid such as rubber seals and diaphragms. Care must be taken when using silicone oils to avoid conditions that might promote cross-linking of the oil leading to viscosity increase and gum formation. The high concentration of iron particle surface area can promote cross-linking of silicone oil-based MR fluids in high temperature, high shear rate environments. Water-based fluids offer the highest on-state yield strength and lowest off-state viscosity for a given particulate loading of any MR fluid. However, the high vapor pressure of water means that significant evaporative liquid loss must be considered. Water is only used as a vehicle for MR fluid in situations where evaporation is not a concern. In general, this means that water-based MR fluid is only used in systems that are absolutely sealed. Waterbased fluids are usually not appropriate for systems that

contain a dynamic, sliding seal such as a shock absorber, since the film of water invariably left on the surface of the exposed shaft will evaporate and lead to a progressive loss of fluid. Water-based MR fluids are commonly used in demonstration devices such as the “MR Syringe” toy (Lord Corporation RD-2013-1 MR Fluid Demonstration Device). Like water-based paints, water-based MR fluids are easier to clean and remove when inadvertently spilled. Waterbased MR fluids are generally formulated in combination with an antifreeze agent such as propylene glycol to extend their useful temperature range as well as an antioxidant to prevent rusting of the iron particles [31]. For extreme temperature ranges or other special situations, MR fluids can be formulated using more exotic vehicles such as perfluorinated polyethers, synthetic esters, or even liquid metals. The challenge with such vehicles is a far less well understood chemistry for creating appropriate additives. 35.3.3.2 Polarizable particles As in Ferrofluids, MR fluids have a high concentration of magnetizable particles dispersed in the liquid vehicle. Differences in particle size and composition however result in distinct behavioral differences. In particular, MR fluid particle sizes typically range from 10−6 to 10−5 m, two to three orders of magnitude larger than colloidal ferrofluid particles. The larger MR fluid particles allow for stable, highly magnetizable materials, and reversible particle aggregation. Typical micron-sized MR particles will support hundreds of magnetic domains. Domain dipole rotation in the presence of a field causes interparticle attraction. Maximum interparticle attraction and thus maximum MR effect is increased by choosing a particle material with high saturation magnetization Js . The magnetically polarizable particles in an MR fluid are usually nearly pure iron although any magnetically polarizable particle could be used. Powdered iron, water- or gas-atomized iron, nickel alloys, iron/cobalt alloys, magnetic stainless steels, and ferrites are all possible. The maximum yield strength of MR fluid scales as the square of the saturation magnetization Js of the particles. In this regard, the best particles one could use would be alloys of iron and cobalt such as Permendur with a saturation magnetization of 2.4 T [32–35]. Unfortunately, the cost of cobalt makes such alloys prohibitively expensive for most applications. The most cost effective MR fluid particle is pure elemental iron with a saturation magnetization of 2.1 T. Virtually all other metals, alloys, and oxides have saturation magnetizations significantly lower than that of iron resulting in substantially weaker MR fluids. The most widely used material for MR fluid particles is carbonyl iron. Carbonyl iron is the common name given to iron particles formed from the thermal decomposition of iron pentacarbonyl. Carbonyl iron powder is elemental iron

Copyright 2006 by Taylor & Francis Group, LLC

(Fe) with more than 98% iron content. Key physical properties of carbonyl iron powder are the very spherical shape of the particles and the fine particle size in the 1 to 10 µm range. Reduced grades of carbonyl iron powder in which most of the residual oxygen, carbon, and nitrogen resulting in mechanically soft particles having iron contents greater than 99.5% and having excellent magnetic properties are available [36,37]. Other forms of elemental iron powder, such as water atomized or electrolytic, are also possible. While generally less expensive than carbonyl iron powder, the larger size of these other forms (10 to 100 µm) and more irregular particle shape make them more difficult to use. On the other hand, while particles less than less than 1 µm would be easier to maintain in suspension, elemental iron particles smaller than 1 µm are not available as a commodity material. Magnetorheological fluids have a high volume fraction of particles. Typical volume fractions are between 20 and 45%. Choosing the ideal volume fraction for a particular application is always a trade-off. While the maximum onstate yield strength scales more or less proportionate to the iron particle volume fraction, the off-state viscosity also increases at an even faster rate with increasing particle content. The distribution of particle sizes also influences the performance of MR fluids. Particle size distributions that allow for higher particle packing densities give rise to MR fluids having higher yield strengths. Rather than monodisperse particles or a narrow Gaussian distribution of particle sizes, a bimodal or very broad distribution is generally preferred [38,39]. Such distributions have a mix of particle sizes that allows small particles to fill the interstitial spaces between the larger particles. The almost universal desire for an MR fluid to have low off-state viscosity generally means that spherical particles are preferred. Highly irregular particles or particles having a high aspect ratio such as platelets, rods, or whiskers invariably give rise to higher viscosity compared to spherical particles at the same volume fraction. 35.3.3.3 Additives A wide variety of proprietary additives similar to those found in commercial lubricants are formulated into MR fluids [29]. Such additives are used to discourage sedimentation, prevent agglomeration, enhance lubricity, prevent oxidation, modify viscosity, and inhibit wear. Unlike colloidal ferrofluids, the relatively large particle size and large difference between the specific gravity of the magnetic particles and the carrier liquid can cause rapid settling in an MR fluid. Sedimentation is typically controlled by the use of organic or inorganic thixotropic agents and surfactants. Organic agents include various metal soaps, metal soap complexes, organic metal salts, and nonmetallic agents such as polyureas. Other organic agents include

(a)

easily remixed. Attempting to make these MR fluids absolutely stable may actually compromise to the overall device performance [42].

H2

t

H1

35.3.4 Properties of MR Fluids H=0 t0

hp g•

(b) heffective = t/g•

H=0 hp g•

FIGURE 35.6 To inhibit particle sedimentation, additives are used to create a small, off-state yield strength (a) that results in a very large effective viscosity at low shear rate (b)

organoclays, associative polymers, phospholipids, and polycarboxylates. Inorganic agents include solids such as metal oxides, fumed and precipitated silica, clays, carbon black, talc, and graphite [40,41]. The thixotropic networks that form impart a small zero-field yield strength τ0 to the MR fluid that inhibits flow at ultralow shear rates. In essence, the effective viscosity of the MR fluid becomes nearly infinite. However, such thixotropic networks are very weak so that as the fluid is purposely sheared at higher rates, the network collapses causing the fluid to shear-thin to a desirable low off-state viscosity. See Figure 35.6. For most applications, it is usually not necessary to achieve complete suspension stability, that is, no supernatant clear layer formation [30]. Except for very special cases, such as dampers designed for seismic damage mitigation in civil engineering structures, complete suspension stability is not a necessity. MR fluid devices such as dampers and shock absorbers that are used in very dynamic applications are highly efficient mixing devices. When the piston in a MR fluid damper moves, MR fluid jets rapidly through the orifices causing it to swirl and eddy vigorously even at low piston speeds. Similarly, the shear motion that occurs in an MR brake or clutch causes vigorous fluid motion. As long as the MR fluid does not settle into a hard sediment, normal motion of these devices is usually adequate to remix any stratified MR fluid back to a homogeneous state. A typical MR fluid damper or shock absorber filled with MR fluid that is formulated to avoid hard sedimentation will remix itself in only one or two strokes. While the MR fluid in these dampers will stratify over time, the particle-rich sediment remains soft and

Copyright 2006 by Taylor & Francis Group, LLC

35.3.4.1 Off-state plastic viscosity The off-state property most critical for a dynamic mechanical application is the field-independent plastic viscosity ηp . This viscosity creates shear rate or velocity-dependent forces and torques that are always present in an MR device regardless of whether a magnetic field is applied or not. This viscosity is also responsible for most of the temperature dependence observed in the force output of a device. The magnitude of ηp is controlled by the viscosity of the liquid vehicle and the particle volume fraction. Plastic viscosities at room temperature typically range from 50 to 200 mPa sec although much higher values are easily possible with higher viscosity carrier liquids. The viscous off-state force in an MR device can become quite large at the shear rates (104 to >105 sec−1 ) routinely encountered in MR shock absorbers, clutches, and brakes. Additives used in the MR fluid may have some impact on ηp although most of their influence usually relates to the small off-state yield strength τ0 that creates a high effective viscosity at very low shear rates as described above. Typical off-state yield strengths are in the range of 5 to 20 Pa although much higher values might be created in special, highly stable gel-like fluids formulated for seismic dampers and other situations where the device may be required to sit quiescent for many years and then to perform instantly in response to a transient event. 35.3.4.2 On-state yield strength The most important on-state property is the magnetic fielddependent yield strength τH . This yield strength adds to the viscous-dependent stress at any given shear rate or speed. Maximum yield strengths τH (max) are typically in the range of 25 to 100 kPa and depend most strongly on the volume fraction of iron particles in the fluid. For magnetic field strengths up to about 100 kA/m, the developed yield strength is nearly linearly proportional to magnetic field. Above 100 kA/m, the increase in yield strength begins to roll-off and eventually saturates at a field strength of about 400 to 500 kA/m. 35.3.4.3 B-H curve The B-H curve for MR fluids throughout their useful range is nonlinear and of such a magnitudes as to place them into a unique category of materials intermediate between low susceptibility materials like aluminum and ferrous materials such as steel. MR fluids have initial (very low field) relative magnetic permeability in the range of 4 to 8.

As the MR fluid yield strength begins to saturate at higher magnetic fields, so also the slope of the B/H curves rolloff and approach a slope of 1 at fields in the range of 400 to 500 kA/m. The maximum magnetic field strength that is useful in a practical sense is typically about 250 kA/m. 35.3.4.4 Density Magnetorheological fluids are dense. Specific gravities range from about 2.2 for fluids with a 20% iron particle volume fraction to about 4 for heavily loaded (45% v/v) fluids. The high density of MR fluids needs to be a consideration when designing MR fluid devices for weight critical applications. Their high density also needs to be considered when making and transporting large quantities of MR fluid. A 160 L (∼42 gal) barrel of MR fluid weighs over half a ton. 35.3.4.5 Volatility Volatility and flash point are all largely dependent on the carrier liquid. Likewise, thermal expansion is due only to that of the liquid vehicle with virtually no significant contribution from the iron particle content. Thus, the total thermal expansion coefficient of MR fluid equals that of the liquid component times (1 − φ) where φ is the particle volume fraction. Thus, heavily loaded MR fluids show less thermal expansion than lightly loaded MR fluids. 35.3.4.6 Response time Response time is the time it takes for the MR fluid to respond to a change in magnetic field intensity. For all practical purposes, the response time of any MR device is purely controlled by the inductance of the electromagnet and the characteristics of the current amplifier [51], and not the inherent response time of the MR fluid. While there have been no good experimental measures of MR fluid response time apart from the associated device inductive response time, it has been estimated that this time is much less than 10−3 sec [43]. An upper limit for the actual MR fluid response time can be made by noting the time it takes for an element of the MR fluid to pass through the magnetic pole region of a valve in a MR damper operated at high speed. For example, the Lord RD-1005-03 damper has been operated at speeds up to 1 m/sec without any change in the magnetic field-induced force over and above the viscous force. At this speed the magnetic field dwell time of an element of MR fluid as it passes through the gap region in the piston is about 2 × 10−4 sec. The fact that no decrease in MR force is noted at high damper speed implies that the MR fluid is able to respond with a time characteristic even shorter than the fluid dwell time as it passes through the valve [42].

Copyright 2006 by Taylor & Francis Group, LLC

35.3.4.7 Compressibility MR fluid can exhibit significant volume compressibility depending on how well the fluid has been degassed. Ultimately, compressibility of an MR fluid equals that of the carrier oil scaled by the fluid volume fraction (1 − φ). The large surface area of the iron particles provides sites for adsorption of large quantities of air during the fluid mixing process. Fluids are routinely vacuum degassed prior to the fluid mixing process to eliminate as much of this air as possible [44]. 35.3.4.8 Figure of merit The factor τH2 /ηp is a figure of merit useful in estimating how large a given controllable fluid device must be in order to achieve a specified level of mechanical performance [26,45,46]. The minimum volume of active MR fluid in a device is inversely proportional to this figure of merit. A large figure of merit means a smaller device. This factor arises from the simultaneous need to have a large on-state to off-state force ratio as well as achieve a specified absolute on-state force in many MR fluid devices such as those widely used for real-time vibration control. 35.3.4.9 Characteristics of typical MR fluids While there are a number of “standard” MR fluids commercially available today, MR fluids for significant applications are generally tailored to meet the specific requirements of the application. The liquid type and viscosity, particle details and volume fraction, and additive package will all be chosen to optimize the MR fluid for the conditions and environment of the application. A summary of the normal ranges for various MR fluid properties along with specific values for several commercial MR fluids are given in Table 35.2. Graphs of the on-state yield strength vs. magnetic field; B-H curves and off-state shear stress vs. shear rate are given in Figures 35.7 to 35.9 for several “standard” MR fluids commercially available from Lord Corporation.

35.3.5 MR fluid Usage Constraints and Limitations 35.3.5.1 Temperature The temperature range over which MR fluids may be used is generally limited only by the flow and volatility characteristics of the carrier liquid. The viscosity of all carrier liquids increases as the temperature decreases. Eventually, a pour point limit is reached where the liquid will no longer flow. Additives can be used to improve, that is, lower, the pour point to some extent. This is particularly the case with water-based MR fluids where various antifreeze agents such as ethylene glycol or propylene glycol, can be used to lower the minimum operational temperature.

TABLE 35.2 Properties of Typical MR Fluids Property Carrier liquid Particle volume fraction, φ Particle weight fraction Density (g/cm3 ) Yield strength (kPa) at 100 kA/m Yield strength (kPa) at 200 kA/m Yield strength (kPa) at saturation Plastic viscosity (mPa sec) at 40◦ C, γ˙ > 500 sec−1 Temperature range (◦ C) Magnetic permeability, relative at low field 2 /η Figure of merit (Pa/sec) τsat p Response time (sec) Flash point (◦ C) Thermal conductivitya (W/m◦ C), at 25◦ C Specific heat (J/g◦ C), at 25◦ C Coefficient of thermal exp.b 0 to 50◦ C, (V /V )/◦ C

Normal range

MRF-122-2ES

MRF-132AD

MRF-336AG

MRF-241ES

— 0.20–0.45 0.70–0.90 2–4 10–55 20–80 25–100 50–200 — 3.5–10 1010 –1011 <0.001 — — 0.6–1.0 2–7 × 10−4

Hydrocarbon 0.22 0.72 2.38 13 23 ∼29 70 −40–130 ∼4 1.2 × 1010 <0.001 >150 0.21–0.81 0.94 6.5 × 10−4

Hydrocarbon 0.32 0.82 3.09 23 42 ∼45 90 −40–130 ∼6 2.2 × 1010 <0.001 >150 0.25–1.06 0.80 5.5 × 10−4

Silicone oil 0.36 0.82 3.45 29 46 ∼53 100 −40–150 ∼7 2.8 × 1010 <0.001 >150 0.20–1.88 0.94 5.8 × 10−4

Water 0.41 0.85 3.86 48 67 ∼80 88 at 25◦ C −10–70 ∼8 7.2 × 1010 <0.001 >93 0.85–3.77 0.65 2.2 × 10−4

a Values were calculated with and without magnetic field applied. Thermal conductivity of MR fluids is not strongly dependent on temperature. b Calculated values.

80 MRF-241ES (41%)

Yield stress (kPa)

70 60

MRF-336AG (36%)

50 40

MRF-132AD (32%)

30

MRF-122-2ED (22%)

20 10 0 0

50

100 150 200 250 300 350 Magnetic field intensity, H (kA/m)

400

FIGURE 35.7 Yield stress vs. magnetic field for several commercial MR fluids measured in parallel plate mode at a maximum shear rate of 262 sec−1

For most devices, if the temperature is above the freezing or pour point, any mechanical motion of the device heats the MR fluids very quickly and moves it even further above the limit. At the high temperature end, device operation is limited by the volatility or vapor pressure of the carrier liquid. The temperature ranges listed in Table 35.2 are conservative guidelines for a safe usage. As one approaches or exceeds the high temperature end of the range, the MR fluid does not catastrophically cease to function. Rather, the life of the device may be limited due to carrier fluid loss. This will depend on the specifics of the device design and specifics of the time–temperature profile. Very short excursions to much higher temperatures can likely be sustained without significant fluid degradation.

Copyright 2006 by Taylor & Francis Group, LLC

Apart from the minor change in particle volume fraction that occurs when MR fluid is heated or cooled due to thermal expansion of the oil, the magnetic-induced force is nearly independent of temperature. The only significant temperature-induced change is in the off-state force that is controlled by the off-state viscosity of the MR fluid. The off-state viscosity of MR fluid will vary with temperature as much as the viscosity of conventional hydraulic oil varies. Thus, it behooves the MR fluid device designer to choose configurations and geometries that minimize the off-state viscous contribution to the overall device force in order to minimize temperature sensitivity. It is also important to note that since the electrical resistance of an electromagnetic coil will change with temperature and that the magnetic field produced by such a coil is a function of current, it is important to utilize a current controlled source rather than a voltage controlled source to drive the MR device [44,51].

35.3.5.2 Material compatibility Some ingredients used to formulate MR fluid may swell or otherwise negatively affect rubber components. Likewise, some component materials may adversely affect certain MR fluid formulations. Table 35.3 is a compatibility list provided by Lord Corporation as a guide for selecting the appropriate fluid for a given environment. Lord recommends that users test the specific Lord Rheonetic™ MR fluid in their system, as specific rubber formulation ingredients may affect compatibility.

1.5

B (T)

MRF-241ES, 41% 1.0 MRF-132AD, 32% MRF-122-2ED, 22% 0.5

–800

–600

–400

–200 200

600

400

800

H (kA/m) –0.5

–1.0

–1.5

FIGURE 35.8 B-H curves for several commercial MR fluids

120

MRF-132AD at 40°C ~90mPa- sec

Shear stress (Pa)

100

MRF-241ES at 25°C ~90mPa- sec

80

MRF-122-2ED at 40°C ~70mPa- sec

60

40 s

20

0

0

200

400

600 Shear

800

1000

1200

rate(sec–1)

FIGURE 35.9 Off-state shear stress vs. shear rate and associated plastic viscosities for several commercial MR fluids

35.3.5.3 MR fluid durability and in-use-thickening During the development and early commercialization of MR fluid devices, problems with the MR fluid were discovered that were not anticipated during the early research phase of these projects. Specifically, this was a phenomenon called “In-Use-Thickening” or IUT [30]. If an ordinary MR fluid is subjected to high stress and high shear rate over a long period of time, it is observed that the fluid

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will thicken. Superficially, this process appears similar to the process of churning cream to make butter. An originally low-viscosity, that is, low off-state, MR fluid progressively thickens until it eventually turns into a thick, nonflowing paste having a waxlike consistency similar to shoe polish. This problem or limitation only becomes apparent when MR fluids or devices are subjected to heavy, long-term use.

TABLE 35.3 Compatibility of MR Fluids with Various Materials MR fluid Carrier liquid Buna-n Butyl EPDM, EPR Fluoro-elastomer Natural rubber Neoprene Nitrile Silicone Iron Stainless steel Aluminum

MRF-336AG

MRF-122-2ED

MRF-132AD

MRF-241ES

Silicone oil Good Good Good Good Good Good Good Poor Good Good Good

Hydrocarbon Poor Poor Poor Good Poor Good Good Fair Good Good Good

Hydrocarbon Poor Poor Poor Good Poor Good Good Fair Good Good Good

Water Good Good Good Good Good Good Good Fair Good Good Fair

In general, IUT manifests itself as a progressive increase in the off-state force due to an increase in the off-state viscosity of MR fluid subjected to long-term shear and stress. One cause of the IUT viscosity increase is believed to be spalling of the friable surface layer from the surface of the iron particles that comprise the particle component of MR fluid. This surface layer is composed of native oxides, carbides, and nitrides and can be rather brittle, particularly in the carbonyl iron particles, which are the most common form of iron particle, used in MR fluids. When subjected to high interparticle stress, this surface layer fractures and breaks into small pieces that separate from the primary particle. Compared to the primary iron particles, these nanometer-sized secondary particles have a very large surface area to weight ratio. Consequently, a very small weight fraction of these secondary particles is capable of significantly affecting the rheology of the overall MR fluid. Most early MR fluid formulations show significant IUT effects when subjected to long-term dynamic shear. Today, the IUT problem has been solved. Good, commercial MR fluids now show no measurable IUT after many millions of device cycles under very demanding conditions [30]. 35.3.5.4 MR fluid life Depending on the conditions of the specific application, all MR fluids will eventually show some degree of deterioration. Such deterioration is usually manifested as a thickening of the fluid as described above although other problems may occur as well. Silicone oil-based fluids, for instance, are prone to cross-linking if exposed to high temperatures for extended periods or to ionizing radiation, particularly when used in an environment rich with an iron catalyst as in an MR fluid. The amount of deterioration generally depends on the shear rate, temperature, and duration.

Copyright 2006 by Taylor & Francis Group, LLC

An ad hoc measure that has proven useful in estimating the expected life of an MR fluid in a particular application is the lifetime dissipated energy or LDE [30] defined in Equation (35.4): 1 LDE = V


life P · dt

(35.4)

0

P is the instantaneous mechanical power converted to heat in the MR device. V is the volume of MR fluid in the device. LDE is simply the total mechanical energy converted to heat per unit volume of MR fluid over the life of a device. It is our experience that the best MR fluids today can sustain an LDE on the order of 107 J/cm3 before they thicken to the point where device performance is compromised. Poor MR fluids, on the other hand, may become unusable with LDEs as low as 105 J/cm3 [42]. 35.3.5.5 Centrifugal effects Of concern in many rotary applications, for example, clutches, are centrifugal effects. Because of the large density difference between particles and liquid, centrifugal separation can occur at high rotational speeds. However, for brakes in which the housing is stationary, centrifugation is generally of less concern because of the continual shearinduced remixing. The commercial MR brakes described below are routinely operated for extended periods of time at centrifugal accelerations of 300 m/sec2 and appear to be capable of over 6000 m/sec2 . 35.3.5.6 Component wear Magnetorheological fluids have the potential of being very abrasive. In fact, one application of a special class of MR fluids is for use as a polishing media for very fine and highly

controlled figuring of optical components. Such MR fluids are actually formulated with highly abrasive additives such as cerium oxide powder that allows them to efficiently remove the surface material from glass optics under the control of a magnetic field. For most MR fluid devices, wear or abrasion of components is not desirable and the MR fluids are formulated to minimize such wear or abrasion. The choice of the specific iron particles has some influence in this regard. High purity, soft iron particles are less aggressive than nonreduced, hard varieties. Proprietary additives similar to those used in lubricating oils are also effective at mitigating wear. Of particular importance is wear of the dynamic elastomeric shaft seals that are necessary in all shock absorbers and dampers. In this regard, it is important to ensure that the surface finish of the shaft is fine enough so that no particles are stuck in surface imperfections such that they cannot be scraped off by the seal. If the particles are subsequently carried through the seal line, they can act like a rasp and rapidly degrade the effectiveness of the seal. The surface finish of the shaft used in MR fluid dampers is usually specified to be much finer than the minimum particle size of the MR fluid. If care is taken in this regard, it is possible to have dynamic devices that will sustain tens of millions of cycles or many more hundreds of kilometers of cumulative seal travel. Special classes of MR fluids that are intentionally designed to be abrasive have been developed by QED Technologies LLC for use in a highly controlled process for finishing fine optical components [23,53]. The MR fluids used in this application are water-based and contain an additional abrasive component such as cerium oxide particles. In traditional optical finishing, a work piece is rotated about its axis while a constant force is applied to a polishing lap whose geometry has been matched to that of the work piece, and the material removal rate is controlled by the lap geometry. In contrast, with MR finishing, a magnetically stiffened abrasive MR fluid flows through a preset region in contact with the work piece to create a precise material removal and polishing. MR fluid finishing is able to produce extremely precise optical surfaces with a surface roughness less than 1 nm with figure errors corrected to a fraction of a wavelength of light on a wide range of optical surface shapes including aspherics.

35.3.6 Application of MR Fluid Magnetorheological fluids are typically used in either a valve mode or a direct shear mode as illustrated in Figure 35.10 [26,32]. Examples of valve mode devices include servo-valves, dampers, shock absorbers, and actuators. Examples of direct shear mode devices include clutches, brakes, chucking and locking devices, some dampers, and structural composites. A less well known squeeze-film mode has been explored only minimally and will not be discussed here [29,54–56].

Copyright 2006 by Taylor & Francis Group, LLC

35.3.6.1 Valve mode In the valve mode (Figure 35.10[a]), MR fluid flows through a flow channel and a magnetic field is applied transverse to the flow direction. The yield strength that develops in the fluid establishes a pressure threshold for any fluid flow. Varying the magnetic field allows one to vary this pressure threshold thus creating a controllable and proportionate valve mechanism without the need for moving mechanical parts. A well-designed magnetic circuit with electromagnet and ancillary high magnetic permeability steel flux conduits and pole pieces defining the flow channel are all that is required. Valve mode operation is most commonly found in MR fluid dampers and shock absorbers. In these devices, a piston moves back and forth in a tubular housing that is filled with MR fluid. The MR fluid is forced to pass through an orifice in or around the piston. An electromagnet, fed by current passing though wires in the piston rod, is located in the piston and configured to apply a magnetic field to the MR fluid in the orifice region. The yield strength induced in the MR fluid by the field controls the amount of pressure required to cause the fluid to flow through the orifice and, hence, the amount of damping or resistive force created by the shock absorber. Examples of valve mode devices include controllable damper systems for heavy-duty vehicle seating [26,57,58], variable shock absorbers for race cars [26,28], real-time controllable suspension systems for consumer automobiles [26,28], special controllable dampers for prosthetic devices [59], and controllable dampers for damage mitigation in buildings and bridges subject to seismic or wind excitation [28]. 35.3.6.2 Direct shear mode In a direct shear mode device (Figure 35.10[b]), a layer of MR fluid is constrained between the poles and a force is applied that causes one pole to move laterally relative to the other, directly shearing the fluid layer. The amount of force needed to cause the fluid to shear then depends on the applied magnetic field strength and the developed shear strength in the MR fluid. Again, a welldesigned magnetic circuit with electromagnet and ancillary high magnetic permeability steel flux conduits and pole pieces are used to apply the magnetic field to the MR fluid. Direct shear devices are most commonly found in clutches and brakes. In these cases, the device is configured such that a layer of MR fluid resists shear when one member is rotated relative to another. Common arrangements are disk and drum types of clutches and brakes that produce a controllable amount of torque coupling. Current applications for such direct shear MR fluid devices include (a) haptic brakes used in steer-by-wire systems in order to provide tactile or force feedback to the

(a)

Valve mode

(b)

Direct shear mode

Force Velocity

Pressure flow

Applied magnetic field, H

Applied magnetic field, H

FIGURE 35.10 Two standard modes for using MR fluid — (a) valve mode and (b) direct shear mode

operator in vehicles that have no mechanical connection between the steering wheel and the drive wheels [26,28] and (b) controllable fan clutches for light duty trucks that enable more precise and more efficient temperature regulation of the engine [60]. Other possible applications include small linear controllable dampers for controlling passage through resonance in variable speed appliances such as washing machines [61].

35.3.7 MR Fluid Economics Magnetorheological fluids have been used commercially since the mid-1990s. The first application was a small controllable MR fluid brake in aerobic exercise equipment manufactured by Nautilus [62]. In retrospect, this was not a particularly good application for MR fluid owing to the inherent fickleness of the exercise equipment market and the extreme use to which some exercise equipments can be subjected. However, it did demonstrate the efficacy of MR fluids for providing real-time control in mechanical systems. In 1998, small, real-time controlled MR fluid damper systems were introduced commercially into the heavy-duty truck and off-highway vehicle market for suspended seat applications [26–28,57]. In 2000, Carrera [26] introduced a controllable MR fluid-based primary suspension shock absorber for use on NASCAR race vehicles. In January 2002, the Cadillac Seville STS automobile was introduced with a standard equipment MagneRide suspension system with controllable shock absorbers and struts made by Delphi Corporation, and MR fluid made by Lord Corporation as standard [28]. Similar, controllable MagneRide MR Fluid-based suspension systems on the Corvette, Cadillac STS, and Cadillac XLR models soon followed. In 2004, MR fluids in small, liter-sized quantities cost about $600 per liter. When purchased in larger quantities appropriate to automotive production volumes, MR fluids are priced in the range of 60 to $180 per liter depending on the details of the specific MR fluid formulation and the actual annual fluid production volume (L. Yanyo, Lord Corporation, personal communication, 2003).

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Magnetorheological fluid production levels in 2004 are on the order of hundreds of tons per year (or tens of thousands of liters) such that commercial applications on several automotive platforms are supported. A factor of ten or more increase in volume over the next ten years is anticipated. It is estimated that there are presently more than 105 MR dampers, shock absorbers, brakes, and clutches in use worldwide. This number is expected to rise into the millions over the next ten years as more automotive platforms adopt smart MR fluid suspensions and fan clutch systems.

35.4 CONCLUSION Ferrofluids and MR fluid exist as distinct and complimentary magnetizable liquids. While superficially similar, each exhibit its own unique set of physical properties and behaviors. While new developments and improvements continue to occur, both of these magnetic fluids have wellestablished commercial applications in a wide variety of devices. Owing to the ease with which they may be controlled or manipulated by easily achievable magnetic fields, they are among the most successful “smart materials” in use today.

REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9.

To Follow To Follow To Follow To Follow To Follow To Follow To Follow To Follow RW Phillips. Engineering Applications of Fluids with a Variable Yield Stress. PhD dissertation, University of California, Berkeley, CA, 1969. 10. KD Weiss, JD Carlson, and DA Nixon. Viscoelastic properties of magneto- and electro-rheological fluids. Journal of Intelligent Material Systems and Structures, 5: 772–227, 1994.

11. J Rabinow. The magnetic fluid clutch. American Institute of Electrical Engineers (AIEE) Transactions, 67: 1308–1315, 1948. 12. National Bureau of Standards. Magnetic fluid clutch. NBS Technical News Bulletin, 32: 54–60, 1948. 13. J Rabinow. Magnetic fluid torque and force transmitting device. U.S. Patent 2,575,360 (to United States of America) 1951. 14. JD Carlson. Rabinow memorial lecture. Proceedings of the 8th International Conference on Electrorheological Fluids and Magnetorheological Suspensions, July 2001, Nice. G Bossis, Ed. Singapore: World Scientific, 2002, p. 7. 15. WM Winslow. Induced fibration of suspensions. Journal of Applied Physics, 20: 1137–1140, 1949. 16. JD Carlson, AF Sprecher, and H Conrad. Electrorheological fluids. Lancaster: Technomic, 1990, pp. 1–454. 17. TG Duclos. Design of Devices using Electro-Rheological Fluids. Society of Automotive Engineers, Technical Paper Series, No. 881134, Warrendale, PA, 1988. 18. JD Carlson. The promise of controllable fluids. Proceedings of Actuator 94, Bremen, H Borgmann and K Lenz, Eds. Bremen: AXON Technologie, 1994, pp. 266–270. 19. JD Carlson, DM Catanzarite, and KA St. Clair. Commercial magneto-rheological fluid devices. Proceedings of the 5th International Conference on ER Fluids, MR Suspensions and Associated Technology, July 1995, Sheffield, WA Bullough, Ed. Singapore: World Scientific, 1996, pp. 20–28. 20. EM Shtarkman. Rotary shock absorber with a controlled damping rate. U.S. Patent 4,942,947 (to TRW) 1990. 21. EM Shtarkman. Fluid Responsive to a Magnetic Field. U.S. Patent 4,992,190 (to TRW) 1991. 22. WJ Kordonski. Magnetorheological effect as a base of new devices and technologies. Journal of Magnetism and Magnetic Materials, 122: 395–398, 1993. 23. WJ Kordonski and SD Jacobs. Magnetorheological finishing. Proceedings of the 5th International Conference on Electrorheological Fluids, Magnetorheological Suspensions and Associated Technology, July 1995, Sheffield, WA Bullough, Ed. Singapore: World Scientific, 1996, pp. 1–12. 24. JD Carlson and KD Weiss. A growing attraction to magnetic fluids. Machine Design, 8 August, 1994, pp. 61–66. 25. KD Weiss, TG Duclos, JD Carlson, MJ Chrzan, and AJ Margida. High Strength Magneto- and ElectroRheological Fluids. Society of Automotive Engineers Technical Paper Series, No. 932451, Warrendale, PA, 1993, pp. 1–6. 26. JD Carlson and JL Sproston. Controllable Fluids in 2000Status of ER and MR Fluid Technology. Actuator 2000, Proceedings of the 7th International Conference on New Actuators, Bremen, H Borgmann, Ed. Bremen: Messe Bremen GmbH, 2000, pp. 126–130. 27. Lord Corporation. Rheonetic Magnetic Fluid Systems. Publication No. PB8003, 1996, pp. 1–10. 28. JD Carlson. Innovative devices that enable semi-active control. Proceedings of the 3rd World Conference on Structural Control, Como, Italy, April 2002, F Casciati, Ed., Chichester: John Wiley, 2003, pp. 227–236.

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29. JD Carlson. Magnetorheological fluid actuators. In: H Janocha, Ed. Adaptronics and Smart Materials. Berlin: Springer Verlag, 1999, pp. 180–195. 30. JD Carlson. What makes a good MR fluid. Journal of Intelligent Material Systems and Structures, 13: 431–435, 2003. 31. JD Carlson and JC Jones–Guion. Aqueous Magnetorheological Fluids. U.S. Patent 5,670,077 (to Lord) 1997. 32. AJ Margida, KD Weiss, and JD Carlson. Magnetorheological materials based on iron alloy particles. International Journal of Modern Physics B, 10: 3335–3341, 1996. 33. JD Carlson and KD Weiss. Magnetorheological Materials Based on Alloy Particles. U.S. Patent 5,382,373 (to Lord) 1995. 34. JD Carlson, MR Jolly, and MR Fluid, Foam and elastomer devices. Mechatronics, 10: 555–569, 2000. 35. JM Ginder, LC Davis, and LD Elie. Rheology of magnetorheological fluids: models and measurements. Proceedings of the 5th International Conference on ER Fluids, MR Suspensions and Associated Technology, Sheffield, UK, 1995, WA Bullough, Ed. Singapore: World Scientific, 1996, pp. 504–514. 36. BASF. Carbonyl Iron Powder. Technical Leaflet, M5686e, Ludwigshafen, Germany, 1990. 37. ISP. Carbonyl Iron Powders. Publication No. 2302-301, Wayne, New Jersey, 1997. 38. KD Weiss, JD Carlson, and DA Nixon. Method and Magnetorheological Fluid Formulations for Increasing the Output of a Magnetorheological Fluid Device. U.S. Patent 6,027,664 (to Lord) 2000. 39. KD Weiss, JD Carlson, and DA Nixon. Method and Magnetorheological Fluid Formulations for Increasing the Output of a Magnetorheological Fluid Device. U.S. Patent 5,900,184 (to Lord) 1999. 40. KD Weiss, DA Nixon, JD Carlson, and AJ Margida. Thixotropic Magnetorheological Fluids. U.S. Patent 5,645,752 (to Lord) 1997. 41. KA Kintz, JD Carlson, BC Munoz, and JD Sessoms. Magnetorheological Fluid Grease Composition. U.S. Patent 6,547,986 (to Lord) 2003. 42. JD Carlson. Critical factors for MR fluids in vehicle systems. International Journal of Vehicle Design, 33: 207–217, 2003. 43. JM Ginder. Rheology controlled by magnetic fields. Encyclopedia of Applied Physics, 16: 487–503, 1996. 44. G Yang. Large-Scale Magnetorheological Fluid Damper for Vibration Mitigation: Modeling, Testing and Control. PhD dissertation, University of Notre Dame, South Bend, IN, 2001. 45. MR Jolly, JW Bender, and JD Carlson. Properties and applications of commercial magnetorheological fluids. Journal of Intelligent Material Systems and Structures, 10: 5–13, 1999. 46. MR Jolly and M Nakano. Properties and applications of commercial controllable fluids. Actuator 98, Proceedings of the 6th International Conference on New Actuators, H Borgmann, Ed. Bremen: Messe Bremen GmbH, 1998, pp. 411–416. 47. Lord Corporation. Rheonetic™ MRF-122-2ED. Product Bulletin No. 2002-41-0, 2002 48. Lord Corporation. Rheonetic™ MRF-132AD. Product Bulletin No. 2003-15-1, 2003.

49. Lord Corporation. Rheonetic™ MRF-241ES. Product Bulletin No. 2002-14-0, 2002. 50. Lord Corporation. Rheonetic™ MRF-336AG. Product Bulletin No. 2003-16-0, 2003. 51. G Yang, BF Spencer, Jr., JD Carlson, and MK Sain. Largescale MR fluid dampers: modeling and dynamic performance considerations. Engineering Structures, 24: 309–323, 2002. 52. Lord Corporation. Rheonetic™ magnetically responsive technology: magnetorheological fluid/material compatibility, Product Bulletin No. 2002-23-0, 2002. 53. W Kordonski and D Golini. Progress update in magnetorheological finishing. Proceedings of the 6th International Conference on ER Fluids, MR Fluids and Their Applications, Yonezawa, Japan, July 1997, M Nakano, Ed. Singapore: World Scientific, 1998, pp. 837–844. 54. MR Jolly and JD Carlson. Controllable squeeze film damping using magnetorheological fluid. Proceedings of Actuator 96, 5th International Conference on New Actuators, Bremen, H Borgmann and K Lenz, Eds., Bremen: AXON Technologie 1996, pp. 333–336. 55. ND Sims, R Stanway, A Johnson, and P Mellor. Design, testing and model validation of a MR fluid squeeze-flow vibration damper. Proceeding of the SPIE Smart Structures and Materials Conference pp. 4331–43312, Newport Beach, 2001.

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56. AK El Wahed, JL Sproston, and R Stanway. The rheology of electrorheological fluids in dynamic squeeze flow. Proceedings of Actuator 2002, 8th International Conference On New Actuators, Bremen, 2002, pp. 573–576. 57. SJ McManus and KA St. Clair. SAE Technical Paper Series — Ergonomics, Work Station and Driver Issues, 2000-01-3408, Truck and Bus Meeting and Exposition, 2000. 58. Lord Corporation. Motion Master Ride Management System. Publication No. MD-2001-21, 2001. 59. JD Carlson, W Matthis, and JR Toscano. Smart prosthetics based on magnetorheological fluids. Industrial and commercial applications of smart structures technologies, Proceedings of SPIE 8th Annual Symposium On Smart Structures and Materials, Newport Beach, 4332: pp. 308–316, 2001. 60. D Guilford and GM Finds. Broader use for magnetic fluid. Automotive News, 22 December, 2003, p. 10. 61. MJ Chrzan and JD Carlson. MR fluid sponge devices and their use in vibration control of washing machines. Smart structures and materials 2001 — damping and isolation, Proceedings of the SPIE 8th Annual Symposium On Smart Structures and Materials, Newport Beach, 4331: pp. 370–378, 2001. 62. Design News Editorial. Brake Cuts Exercise-Equipment Cost. Design News, 4 December, 1995, p. 28.

36

Metalworking Fluids William L. Brown and Richard G. Butler CONTENTS 36.1 36.2 36.3 36.4

Overview Definitions Historical Development Synthetic Lubricants 36.4.1 Polyalkylene Glycols 36.4.2 Esters 36.4.3 Phosphate Esters 36.4.4 Synthetic Hydrocarbons 36.4.5 Other Synthetic Lubricants 36.5 Synthetic Lubricants in Chemical MWFs 36.5.1 PAGs in Chemical MWFs 36.5.2 Laboratory Studies on PAGs in Chemical MWFs 36.5.2.1 Plain Strain Compression Test: The Effect of PAG Cloud Point on the Performance of Chemical MWFs 36.5.2.2 Lathe test: The Effect of PAG Cloud Point on the Performance of Chemical MWFs 36.5.2.3 Lathe test: The Synergy between PAGs and Fatty Acids, PAGs, and Phosphate Esters 36.5.3 Modified PAGs in Chemical MWFs 36.5.4 Applications of PAGs in Chemical MWFs 36.5.4.1 Grinding 36.5.4.2 Tapping 36.5.4.3 Hobbing 36.5.4.4 Machining and Rolling 36.5.4.5 Blanking and Drawing 36.5.4.6 Cold Forming 36.5.4.7 Drawing and Forming 36.6 Synthetic Lubricants in Semichemical MWFs 36.6.1 Polyalkylene Glycol Esters in Semichemical MWFs 36.6.2 Self-Emulsifying Esters in Semichemical MWFs 36.6.3 Laboratory Studies on SEEs in Semichemical MWFs 36.6.4 Complex Polymeric Esters in Semichemical MWFs 36.6.5 Synthetic Hydrocarbons in Semichemical MWFs 36.7 Synthetic Lubricants in Soluble-Oil MWFs 36.8 Synthetic Lubricants in Straight-Oil MWFs 36.9 Market Outlook 36.9.1 Market Size 36.9.2 Future of Synthetic Lubricants in MWFs 36.9.2.1 Waste Minimization and Disposal 36.9.2.2 Workpiece Quality 36.9.2.3 Toxicity 36.10 Conclusions References

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36.1 OVERVIEW Metalworking is a major industry in the United States today. Metalworking operations include rolling, forging, stamping, drawing, forming, cutting, and grinding. Practically all metal objects, from structural steel beams to screws, have undergone at least one metalworking operation. The success of most metalworking operations is dependent upon the use of good lubricants and coolants. There are a large variety of these metalworking fluids (MWFs). They include fatty acid based soaps, formulated hydrocarbons, emulsified oils, and aqueous solutions. These products are used in operations ranging from the drawing of wire to the tapping of nut threads. In each case, the MWF has been adapted to satisfy the needs of a specific application. This chapter reviews the uses of synthetic lubricants in various metalworking operations. It begins by defining metalworking and MWFs. A brief review of the history of MWFs is then presented, with particular attention being paid to the incorporation of synthetic lubricants. The synthetic lubricants currently being used in MWFs are defined. These products include PAGs, esters, and synthetic hydrocarbons. The generic structures of these synthetic lubricants are illustrated and the physical properties that have led to their incorporation in MWFs are described. This chapter focuses on the use of PAGs in MWFs. PAGs are of importance to the metalworking industry because of their unique solubility properties in water. The mechanism of how they work is described, and a number of applications are presented. The use of other synthetic lubricants in MWFs is then reviewed. The rest of this chapter examines the future of synthetic lubricants in the metalworking industry. The effect of health and disposal regulations and the need for improved workpiece quality on the use of synthetic lubricants in MWFs is discussed. It should be pointed out here that the metalworking industry is very large and diverse. The formulations of MWF are tailored to specific operations and locations. Formulations are affected by such factors as production speeds, inventory turnover, local water quality, ambient weather conditions, and effluent regulations. Therefore, this chapter will attempt only to give an overview of the uses of synthetic lubricants in the metalworking industry.

36.2 DEFINITIONS Metalworking is the shaping of a metallic workpiece to conform to a desired set of geometric specifications. Metalworking can be divided into two basic categories, cutting and forming. In cutting operations, the blank is shaped by removing unwanted metal in the form of discrete chips. Cutting operations include turning, tapping,

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milling, broaching, and grinding. Metal forming processes involve the plastic deformation of the workpiece into a desired shape. Drawing, hot and cold rolling, stamping, and forging are examples of metal forming operations. In both cutting and forming operations, the MWF plays a critical role. The two most important functions of the MWF are to provide adequate lubrication between the workpiece and the tool or die and to remove the heat that is generated [1]. Lubrication can be defined as the reduction of friction between two moving surfaces. In metalworking operations, lubrication can be divided into two types, hydrodynamic and boundary or extreme pressure (EP). In hydrodynamic lubrication, the moving surfaces are always separated by a film of fluid or lubricant. The film thickness and the coefficient of friction are both a function of the parameter ZN/P, where Z is the lubricant’s dynamic viscosity, N represents the relative velocity of the moving surfaces, and P is the applied load per unit area [2,3]. The faster the velocity or the more viscous the lubricant, the thicker the fluid film. The coefficient of friction will also increase because of an increase in viscous drag. Conversely, increasing the load or pressure will decrease the film thickness and the coefficient of friction as long as hydrodynamic conditions are maintained. Boundary or EP lubrication is necessary when the pressures experienced are great enough to cause contact between the moving metal surfaces. The purpose of boundary or EP additives is to minimize the wear experienced when the surfaces rub against each other. Boundary lubricant additives are polar compounds like fatty alcohols, acids, and esters that adsorb onto the metal surfaces forming thin, low shear strength films. These solid films help prevent metal–metal contact and reduce friction and wear [2,4]. The EP lubricity additives used in metalworking operations are usually organic compounds, which contain phosphorus, chlorine, or sulfur. During the metalworking process, these additives react with the metal surfaces forming organic or organometallic films [2,4]. These films then act to reduce the force necessary to slide the surfaces past one another, while at the same time minimizing wear [5]. Cooling is the other critical function of a MWF. The transfer of heat away from the tool or die is affected by the specific heat and the heat of vaporization of the MWF. The specific heat is the amount of heat required to raise the temperature of one gram of fluid one degree celsius. The larger this value, the more heat the fluid can absorb for an incremental temperature rise, resulting in more efficient cooling. The heat of vaporization is the amount of heat required to vaporize a gram of liquid. A fluid with a high heat of vaporization will also cool efficiently since it absorbs large amounts of energy as it transforms from a liquid to a gas. Heat transfer in metalworking can also be affected by the fluid’s boiling point, ambient

temperature [5], viscosity, surface energy, and application method. Good lubrication and cooling will prolong tool or die life, improve surface finishes, and permit higher production speeds. The cooling and lubricating properties of a MWF must be matched to the operation being performed. In high cutting speed operations like turning and grinding, cooling is of paramount importance. However, in lower speed operations that involve heavy cuts or large deformations, the lubricating properties of the MWF are critical [6]. In addition to providing adequate lubrication and cooling, MWFs must protect the machine and the workpiece from corrosion and remove chips from the cutting zone. It is also important that the MWF be benign and nonirritating to the operator. There are four major classes of MWFs. These different types are defined below: Straight oils: These products are derived primarily from petroleum fractions, although animal and vegetable oils are occasionally used [6]. Synthetic lubricants can also be employed as straight-oil base stocks. These base stocks, whether natural or synthetic, are usually compounded with various boundary and EP lubricity additives. Straight-oil MWFs contain no water and are sold “ready-to-use.” They are excellent lubricants but have limited cooling capacity. Soluble oils: Soluble oils are actually oil-in-water emulsions, which take advantage of the lubricity of oils and the cooling properties of water. This is a very versatile class of MWFs. In severe cutting or forming operations, they are usually formulated with chlorine and sulfur containing EP lubricity additives and diluted only 1 to 5 times with water [7]. However, in light cutting or grinding operations, the soluble-oil concentrate often contains only rust inhibitors and can be cut 20 to 100 times with water. Chemical solutions (synthetics): Chemical MWFs contain no petroleum oil and form true solutions when diluted with water. These MWFs are often referred to as “synthetics.” However, not all “synthetic” MWFs contain synthetic lubricants as is defined later in this chapter. Synthetic lubricants include PAGs, various esters, and polyolefins. Therefore, to avoid confusion in this chapter, these oil free, water-soluble products will be referred to as “chemical MWFs” or “chemical solutions.” Chemical solutions were originally formulated for grinding and light-duty cutting operations. However, the incorporation of synthetic lubricants and the development of improved water-soluble boundary and EP lubricity additives has greatly expanded the utility of this class of MWFs.

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Semichemical solutions (semisynthetics): Semichemical MWFs are an attempt to get the liquid to possess the best properties of both soluble oils and chemical solutions. The most common definition of a semichemical MWF is a product whose concentrate contains water-soluble additives, emulsifiers, and less than 20% petroleum oil [8].

36.3 HISTORICAL DEVELOPMENT The use of lubricants is known to date back to the times of the ancient Egyptians who used fats to grease chariot wheels [9]. However, the use of lubricants in metalworking operations is relatively recent. One of the earliest references to metalworking lubricants comes from the writings of Biringuccio in the early 1500s [10]. He observed that it is important to use wax when drawing high quality gold and silver wire. The widespread use of MWFs, however, coincided with the industrial revolution, which began in England in the late 18th century [2]. By the mid-19th century mineral oils were being widely used as metalworking lubricants [2]. W.H. Northcott observed in 1868 that the use of oils as MWFs greatly improved cutting speeds and tool life, reduced power consumption, and produced smoother cuts [11]. Northcott also described how soda–water worked well as a MWF despite some corrosion problems. The development of high-speed cutting tools and the increased use of grinding began to show the limitations of oils as metalworking lubricants [2]. Most of the energy used to cut or grind a metal workpiece is dissipated as heat [4,8,12]. Thus, as cutting speeds increased, the cooling properties of the MWF became more important. While oils are excellent lubricants, their cooling capacity is limited. The use of oil based MWFs in higher speed operations resulted in poor tool life and the generation of irritating smoke and fumes [13,14]. In 1883, Taylor demonstrated the importance of water as a base for MWFs [15]. He showed that by using water as a MWF, cutting speeds could be increased by 30 to 40%. The primary reason for this increase in speeds is the excellent cooling properties of water relative to hydrocarbon oils. Water has a higher specific heat and heat of vaporization than hydrocarbon oils, accounting for its superior cooling ability [16]. By the end of the 19th century, the use of water to flood the cutting tool was quite common [12]. However, as a MWF, water has two obvious drawbacks. First, water is a poor lubricant. Second, the use of water leads to the corrosion of both the tool and the workpiece [17]. The first attempts to solve these shortcomings occurred at the turn of the century. Sodium carbonate, or soda ash, was added to inhibit corrosion, and phosphates and soaps were included for lubricity enhancement [12,14]. However, over time the soda ash had a tendency to drop out of

solution, depositing on machinery and thereby preventing smooth operation [12]. Also, about the same time, mixtures of oils and water, loosely coupled by alkali, were being used to improve the performance of water as a MWF. Unfortunately, these systems did not adequately control corrosion and were inherently unstable [12]. Good quality soluble oils were first developed in the 1920s [12,14]. They quickly became the dominant form of water based MWF, although solutions containing sodium carbonate continued to be used in grinding operations through the 1950s [12,14]. Soluble oils effectively take advantage of the cooling properties of water while providing good lubricity and corrosion protection. The use of soluble oils instead of neat hydrocarbon based MWFs enabled manufacturers to increase their productions rates without significant sacrifices in surface finish or tool or die life. The use of soluble oils grew quickly at the expense of neat hydrocarbon MWFs during the middle of this century. Besides being better coolants, soluble oils offer a number of other advantages. Soluble oils are cleaner than straightoil MWFs. They do not fume or smoke significantly, and pose a greatly reduced risk as a fire hazard [7]. Also, it is easier to remove soluble-oil residues from the machinery and the workpiece. Another major factor that led to the growth of soluble oils is their versatility. The lubrication and cooling properties of soluble-oil MWFs can be adjusted by simply altering the dilution ratio or changing the type or amount of lubricity additives. In heavy-duty forming operations the soluble-oil concentrate can be formulated with high concentrations of chlorine, sulfur, or phosphorus containing EP lubricity additives and diluted only 1:1 or 1:2 with water prior to use [7]. However, soluble oils are also used in high speed, light-duty cutting and grinding operations after being diluted 20:1 to 100:1 with water. These light-duty products are often formulated only with rust inhibitors. A further advantage of soluble oils relative to neat hydrocarbon based MWFs is cost. Although the price of a soluble-oil concentrate is more expensive than an equivalent volume of straight-oil MWF, the actual cost is significantly reduced due to dilution with water. Also, soluble oils are less prone to losses from dragout than straight oils, which results in lower fluid makeup costs [14]. Despite their obvious advantages, soluble oils did present some new problems. The most significant drawback associated with soluble oils is their susceptibility to bacterial attack. Microorganisms living in the water quickly learn to metabolize the emulsified organic compounds. They rapidly multiply, releasing unpleasant odors and eventually splitting the emulsions by metabolizing the surfactants and lowering the fluid’s pH [12]. While the incorporation of biocides can reduce the magnitude of this deficiency, biological attack is still the biggest problem faced by the users of soluble oils.

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Soluble oils presented several other problems. Soluble oils tend to emulsify tramp gear lubricants or hydraulic fluids, which can adversely affect the performance of the metalworking lubricant. Also, soluble-oil MWFs are sensitive to water quality, especially pH and hardness [18]. In the early 1950s the users of grinding solutions containing soda ash began to find substitutes that provided good corrosion protection without forming troublesome deposits [12]. These alternative corrosion inhibitors were based mostly on alkali nitrites, organic amines, or amine neutralized organic acids [12,14,19]. These new solutions, referred to as chemical or synthetic MWFs because they contained no petroleum oil, were quite successful. They provided good corrosion protection, excellent cooling, and adequate lubricity. They were also clean, very stable, and more resistant to biological attack than soluble-oil MWFs [5]. Because of their initial success as grinding coolants, and the continuing search for cutting and forming lubricants that were more trouble free than soluble oils, chemical MWFs were tried in a number of more demanding cutting operations such as turning, milling, and tapping [14]. Their performance in these operations was promising enough to encourage further development. The inclusion of water-soluble lubricity additives such as fatty acids, phosphate acid esters [20], and PAGs significantly enhanced the lubricity of chemical MWFs. Chemical MWFs were soon being used in many cutting operations as well as applications involving light- and medium-duty drawing and forming [14,19]. Chemical MWFs offered a number of advantages over traditional soluble oils. These advantages, which still exist today, are summarized below. Biological stability: While biocides are still needed for optimum performance, chemical MWFs are generally more resistant to biological attack than soluble oils [5]. This increased biological stability results in less odor, better pH control, and longer sump life [5,12]. Longer fluid life means reduced raw material and disposal costs. Solution stability: Chemical MWFs can be formulated to have good hard-water stability and be resistant to pH variations [18]. They are also less prone to dragout than soluble oils, resulting in less coolant use and cleaner chips or swarf [12]. Cooling: Chemical MWFs are significantly better coolants than soluble oils [5,21]. Better cooling means longer tool life and higher production speeds. Cleanliness: The clarity of chemical MWFs is very good, resulting in excellent workpiece visibility [5,14]. Not only are these products clear initially, but their ability to reject tramp gear and hydraulic oils helps them remain transparent [18].

Chemical MWFs also produce less oily residues on the machines and floor, thereby greatly reducing the risk of a fall [14]. However, chemical MWFs were not a panacea. They presented the metalworking industry with the following problems: Slideway lubrication: Many chemical MWFs, because of their good detergency, have a tendency to wash away slideway lubricants. This results in significant operational problems. Also, some chemical MWFs can, over time, cause the machine’s moving parts to stick. This sticking can be the result of water evaporating from some isolated coolant leaving behind the more viscous corrosion inhibitors and lubricity additives. However, it can also be due to the deposition of additives that react with the calcium and magnesium ions in hard water to form insoluble residues (14). Gummy residues can also be formed when fluids containing amine borate corrosion inhibitors are used in hard water [22]. Over the years it has been found that slideway lubrication problems can be reduced by reformulating the concentrate with lower viscosity components that have good hard-water stability and less detergency. Also, the use of detergent resistant slideway lubricants and a more comprehensive machine lubrication program can help alleviate these problems [12]. Machine lubrication: Upon switching from soluble oils to chemical MWFs, some operators discover that their machinery is no longer being adequately lubricated. Because chemical metalworking lubricants by definition contain no hydrocarbons, they do not leave a residual oil film on the machine’s moving parts [5]. This problem can often be solved by following a routine machine lubrication program [12]. Paint and seal compatibility: Some of the components in chemical coolants can attack the seals and paints used in metalworking machinery. Resistant paints and seals are now available and can be found in much of the newer machinery [12]. Lubricity and corrosion: While insufficient lubricity and corrosion protection limited the use of early chemical MWFs, the development of improved water-soluble additives has greatly expanded the utility of these products. They can now be employed in many of the applications that are currently using soluble oils. The problems associated with chemical MWFs, especially those pertaining to machine and slideway lubrication, led to the development of semichemical MWFs. These products typically contain up to 20% hydrocarbon oil in

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their concentrate as well as surfactants, amines, and other water-soluble additives. Semichemical fluids were well established by the mid-1960s [5] and they are currently enjoying an increase in popularity. However, while they strive to incorporate the better machine lubrication of soluble oils, they also lose some of the bacterial resistance inherent in chemical MWFs [12]. In short, semichemical products, as their name suggests, are a compromise between soluble oils and chemical MWFs. By 1971, 33% of the MWFs sold into cutting and grinding applications were soluble oils, chemical fluids, or semichemical products [23]. However, these fluids are sold as concentrates that, on average, are diluted about 20 times with water. Thus, approximately 90% of all metal removal operations were using water based MWFs [24]. Both chemical and soluble-oil MWFs have undergone significant formulation changes over the past 20 years due to toxicity concerns. In the late 1960s the presence of nitrosamines in chemical MWFs was discovered. Nitrosamines can be formed by reactions between nitrites and monoethanolamine or diethanolamine. Particular attention was given to the discovery of N-nitroso-diethanolamine (NDELA) in MWFs. NDELA is a potent carcinogen in rats and hamsters [25], and it is known to be absorbed through human skin [26]. Because of concerns about the exposure of machinists to NDELA, much work was done during the mid 1970s to find replacements for sodium nitrite [22]. The best substitutes were found to be amine borates or the salts of organic acids and amines. By 1980 the use of nitrites in MWFs had been essentially eliminated. In the mid 1980s, oils containing polynuclear aromatics were identified as potential carcinogens. As a result, practically all oil containing MWFs were reformulated. These products now incorporate severely hydrotreated hydrocarbons as lubricant base stocks [27]. Toxicity continues to be a major issue affecting the use of the various types of MWFs. The other factors currently shaping the MWF industry are waste minimization, disposal, environmental regulations, and workpiece quality.

36.4 SYNTHETIC LUBRICANTS Synthetic lubricants are defined as products that are made from the controlled combination of discrete compounds. This distinguishes them from refined petroleum products. There are several major classes of synthetic lubricants that are used in metalworking operations. These lubricants are described below.

36.4.1 Polyalkylene Glycols This diverse class of synthetic lubricants is made from the polymerization of alkylene oxides as shown in Figure 36.1.

Polyalkylene glycols O R

OH

+

n

H2C

CH R'

alcohol starter

alkylene oxide

R

O

CH2

HC

O

H n

R' polyalkylene glycol R, R' = H, CH3, alkyl, aryl

FIGURE 36.1 Polyalkylene glycols

The starter is usually an alkyl alcohol or a diol, but branched polymers are also made by alkoxylating triols or polyols. The oxide feed can be all ethylene oxide (R
=H), all propylene oxide (R
=CH3 ), or mixtures of the two. Higher molecular weight monomers like butylene oxide can also be polymerized, but the commercial use of these products is very limited. The oxide feeds can be either mixed, resulting in a random PAG, or sequential, yielding a blocked structure. Blocked PAGs are more surface active than the random polymers, but they are also much more likely to foam. Polyalkylene glycols can be either soluble or insoluble in water, depending on the ratio of ethylene oxide to propylene oxide in the monomer feed. At room temperature, PAGs made from a monomer feed consisting of more than approximately 20% ethylene oxide are water soluble. PAGs that contain less than 20% polymerized ethylene oxide show good solubility in hydrocarbons. Water-soluble PAGs have been used extensively in chemical and semichemical MWFs [24,28–30]. Oil soluble PAGs have been employed in both semichemical and straight-oil MWFs as lubricity additives [31]. They have also been used neat in applications where their excellent water washability, resistance to staining or sludge formation, or clean burn-off characteristics are important [32–35].

36.4.2 Esters Esters are made from the condensation of organic acids and alcohols. This is a very diverse class of compounds, and the physical properties vary greatly depending on the acids and alcohols used. The most common classes of esters are monobasic acid esters, dibasic acid esters, polyol esters, and PAG esters. The generic structures of these compounds are shown in Figure 36.2. Monobasic acid esters and PAG esters are widely used in the metalworking industry. Monobasic acid esters such as methyl and butyl stearate and hexyl laurate have long been employed as lubricity additives in MWFs [2,32]. In hydrocarbon based products, these esters help reduce the interfacial tension between the oil and the metal surface, thereby increasing the ability of the fluid to penetrate between the workpiece and the tool or die [5]. In water

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based products, monobasic acid esters are most commonly used as additives in the hydrocarbon phase of soluble oil or semichemical MWFs where they serve as boundary lubricants and corrosion inhibitors. Polyalkylene glycol esters are used in chemical or semichemical MWFs because of their solubility or good dispersity in water [36,37]. They are usually made from PAG diols, but monol and polyol started PAGs can also be used. PAG esters provide good lubricity and are synergistic with many corrosion inhibitors. Two new polymeric esters have recently been commercialized for use in metalworking operations. One type, referred to as “complex polymeric esters,” is based on pentaerythritol and have high molecular weights, ranging from 150,000 to over 2 million [38]. These high molecular weight liquids have been designed to enable the replacement of sulfur and chlorine containing extreme pressure additives in soluble-oil MWF formulations. The second type of synthetic lubricants recently designed for use in MWFs are “double-comb polymer esters.” These esters are made by reacting butanol with alpha-olefin dicarboxcylic acid copolymers [39]. These molecules have a double-comb structure where the ester groups are in the form of short side chains off a long hydrocarbon backbone. These polymeric esters range in molecular weight from 1200 to 2500. They have been used as lubricity additives in both neat oil and soluble-oil systems.

36.4.3 Phosphate Esters Phosphate esters are formed by reacting alcohols with phosphoric acid as shown in Figure 36.3. Phosphate esters are used as synthetic lubricants in fire-resistant hydraulic fluids because of their resistance to burning [40]. However, these synthetic lubricant base stocks have not found any significant use in metalworking applications. Phosphate esters are widely used in MWFs as EP lubricity additives [2,5,6,32,41,42]. Oil soluble phosphate esters are well known lubricity additives and are commonly used in straight-oil and soluble-oil MWFs. Water-soluble phosphate esters can be made by reacting ethoxylated alcohols with phosphoric acid. These products are often used as lubricity additives in chemical MWFs [6,30].

Monobasic acid esters O

O R

C

HO

+

OH

acid

R⬘

R

C

alcohol

O

H2O

+

R⬘

ester

water

R, R⬘ = akyl, aryl Dibasic acid esters O

O HO

C

R

C

O

O + 2

OH

diacid

R⬘ OH

O

R'

C

R

C

R⬘ +

O

2 H2O

dibasic acid diester

alcohol

water

R, R⬘ = akyl, aryl Polyol esters R

OH

n

O

O

+

n R⬘

C

polyol

R

OH

acid

O

R⬘

C

n

n H2O

+

polyol ester R

OH

n

water

represents an alcohol with 3 or more hydroxyl groups R, R' = akyl, aryl

Polyalkylene glycol esters O

R HO

CH2HC

O

n

H + 2 R⬘

C

R

O OH

R⬘

C

O

acid

polyalkylene glycol

O

CH2 CH

O

C

R⬘ +

n

2 H2O water

PAG ester R = H, CH3,CH2–CH3 R⬘ = akyl, aryl

FIGURE 36.2 Structures of some esters that are used as synthetic lubricants

O

O HO

P

OH

+

alcohol(s)

R

O

P

O

OH

OH

phosphoric acid

phosphate ester

R⬘

R, R⬘ = H, alkyl, aryl, alkoxylate

FIGURE 36.3 Phosphate esters

36.4.4 Synthetic Hydrocarbons Synthetic hydrocarbons are made from the combination of olefins through their double bonds. The most common synthetic hydrocarbons are polyalphaolefins, dialkyl benzenes, and polyisobutylenes. The generic structures of these three types of synthetic hydrocarbons are shown in Figure 36.4.

Copyright 2006 by Taylor & Francis Group, LLC

Of these three classes of synthetic hydrocarbons, only polyisobutylenes have found significant use in the metalworking industry. Their primary applications have been as nonstaining thickeners [2], or as base oils for high temperature forming operations [32]. Recently, alpha olefins have used in a variety of metalworking operations in conjunction with paraffinic base

Polyalphaolefins R n

CH

R

HC

CH2

CH2

n

polyalphaolefin

alphaolefin Dialkyl benzenes

CH2

R

CH2 CH2

R

H2C

2

R

CH

CH2

+

benzene

alphaolefin

R = akyl Polyisobutylenes CH3

CH3 n

H2C

C CH3

isobutylene

H 2C

C

n

CH3 polyisobutylene

FIGURE 36.4 Structures of some common synthetic hydrocarbons

stocks. The MWFs containing an equal blend of paraffin and alpha-olefin base stocks provided better lubricity and improved surface finishes relative to tests run with the paraffinic based control [39].

of chemical MWFs and allows them to effectively compete with soluble oils in a variety of cutting and forming operations.

36.5.1 PAGs in Chemical MWFs 36.4.5 Other Synthetic Lubricants Other synthetic lubricants and polymers have found use in metalworking operations. Polyacrylonitriles [43], styrene– maleic anhydride copolymers [44,45], and polyacrylamides [46] have all been documented as providing good lubricity in water based MWFs. Polyvinylpyrrolidones, polyvinyl alcohols, and copolymers of acrylic acid or methacrylic acid and an acrylic ester, have also been cited as lubricity additives for use in chemical MWFs [47]. However, the commercial use of these synthetic polymers is small. Also, a number of thermoplastic polymers have been used as solid lubricants in forming operations. A review of these polymers is presented by Shey [2]. However, the use of solid lubricants is not covered in this chapter.

36.5 SYNTHETIC LUBRICANTS IN CHEMICAL MWFS The most significant use of synthetic lubricants in the metalworking industry is in chemical solutions. The use of PAGs in conjunction with water-soluble boundary or EP lubricity additives can significantly enhance the lubricity

Copyright 2006 by Taylor & Francis Group, LLC

Polyalkylene glycols have a number of characteristics that make them ideal for use in chemical MWFs. These properties include [24]: Water solubility: PAGs can be synthesized that are soluble in water in all proportions. They are hydrolytically stable and are essentially unaffected by water quality or hardness. Inverse solubility: PAGs exhibit a property that is referred to as “inverse solubility.” This property is characteristic of ethoxylated materials. As the temperature of an aqueous PAG solution increases, the solubility of the PAG in water decreases. Above a temperature known as the cloud point, the PAG will come out of solution, forming a hazy or cloudy dispersion. A 1% solution of a PAG below and above its cloud point is shown in Figure 36.5. The cloud point of a PAG is dependent on a number of factors. These include the polymer’s ethylene oxide to propylene oxide ratio, starter, end groups, and molecular weight. It is also affected by the

(a)

(b)

FIGURE 36.5 The inverse solubility (cloudpoint) of a 1% solution of PAG in water

PAG concentration and the presence of other watersoluble compounds. In particular, the cloud point of PAGs can be lowered by the presence of ionizing salts. The high temperature insolubility of PAGs can be used to greatly enhance the lubricating ability of chemical MWFs. Nonionic behavior: Because PAGs are nonionic, they can be used in combination with either cationic or anionic additives. Low reactivity: PAGs are noncorrosive to commonly used metals. Liquid residues: Because PAGs are stable and water soluble, their residues are liquid and, if necessary, easily removed from machinery [24]. Resistant to biological attack: While PAGs are biodegradable, their degradation rates are slow relative to those of fatty acids, phosphate esters, and many commonly used surfactants. This bioresistance leads to easier fluid maintenance and longer sump life and thus lower raw material and disposal costs. Low toxicity: PAGs exhibit low toxicity. However, as with all chemicals, the material safety data sheets should be studied before the product is used. A typical formulation for a MWF employing a PAG is shown in Table 36.1. This type of formulation is usually diluted 10:1 to 30:1 with water for typical cutting operations. It can also be used at much higher concentrations. For severe drawing operations, dilutions of 1:1 of 2:1 with water might be used. For light grinding, dilutions up to 50:1 have been employed. The purpose of the PAG is to provide hydrodynamic lubricity and inverse solubility. The fatty acid or phosphate ester provides enhanced wetting and boundary lubrication. The phosphate ester also has EP lubricating properties. In severe metalworking operations, a water-soluble

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TABLE 36.1 Typical Chemical MWF Formulation Component Polyalkylene glycol Phosphate ester (or fatty acid) Sulfurized fatty acid Nonnitrite corrosion inhibitor TEA Biocide Water

Amount (wt %) 10–15 5–10 0–5 15 10–15 —a 45–60

a Biocide added at concentrations recommended by the manufacturer.

sulfur containing compound may be necessary for added EP lubricity. The nonnitrite inhibitor is to protect both the machine and the workpiece from corrosion. Triethanolamine (TEA) serves as an inexpensive corrosion inhibitor by keeping the pH of the solution elevated, typically between 8.5 and 9.2. The ethanolamine also helps to solubilize some of the lubricity additives. Biological attack is retarded through the use of biocides. Other additives such as antifoams, dyes, and chelating agents can be added if needed. The key to the effectiveness of PAGs in chemical MWFs is their inverse solubility. The following mechanism has been used to describe the role of the inverse solubility of PAGs in MWFs [2,24,30,48]. This mechanism, is illustrated in Figure 36.6. Cloud point mechanism of PAG containing chemical MWFs: 1. At ambient temperatures, typical of those found in a machine sump, the MWFs is completely soluble in water, forming a clear, transparent solution.

MWF in solution at ambient temperature.

PAG comes out of solution at hot metal surface.

Emulsified PAG droplets wet out hot metal surface forming a polymer and additive-rich film that provides excellent lubricity.

Water soluble EP additives migrate to polymer–water interfaces.

FIGURE 36.6 The inverse solubility (cloud point) of chemical MWFs containing PAGs

2. The MWF is brought in contact with the hot tool or die. The temperature of the fluid is elevated above the cloud point of the PAG, causing the polymer to come out of solution and form small, oil-like drops. 3. The lubricity additives in the MWF are surface active and collect at the interface between the PAG and the water phases. 4. These PAG drops then preferentially wet the surfaces of the workpiece and the tool or die, much like the emulsified hydrocarbon droplets in a soluble-oil MWF. The result is the formation of a thin layer of concentrated PAG and lubricity additives. This PAG film has excellent lubricating properties. The ability of the PAG to concentrate the polar lubricity additives at the tool or die surface helps explain the synergy often noted between these products [6,24,30]. 5. The spent chips and excess MWF fall back into the relatively cool machine sump where the PAG goes back into solution. In contrast, the chips generated while using soluble oils are coated with a significant amount of hydrocarbon lubricant that does not reemulsify.

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As a result, less lubricant is lost due to dragout when a chemical MWF is used. Chemical MWFs that do not contain PAGs rely on their water-soluble additives coming in contact with the surface of the workpiece in order to achieve sufficient lubricity. The probability of this occurring is a function of the concentration of these lubricity additives. The addition of PAGs, because of their inverse solubility, serves to concentrate the lubricity additives at the point of cut, or in the case of a drawing or forming operations, at the hot surface of the die. Also, the PAG itself is an excellent hydrodynamic lubricant. Better lubricity can therefore be achieved at the same product dilution ratio when PAGs are used in conjunction with water-soluble boundary or EP additives. While the presence of PAGs improves the efficiency of lubricant delivery to the hot surfaces of the workpiece and the tool or die, it is important to remember that the mechanism of these chemical MWFs is temperature activated. At ambient temperatures the lubricity of chemical MWFs that contain PAGs is greatly reduced. Because they

contain no oil, these fluids do not coat the relatively cool machine parts with a film of lubricant. This can lead to problems on machines that rely on the MWF for slideway or other mechanical lubrication. The incorporation of a small amount of emulsified oil to form a semichemical MWF is currently a popular solution to this problem. The adoption of a more rigorous machine lubrication program is also effective in some cases. Since elevated temperatures are required in order for the PAG to come out of solution and coat the hot die surface, forming lubricants containing these polymers can have trouble during start-ups when the dies are cold. This problem is more severe when softer, nonferrous metals are being deformed. In these cases, unacceptable amounts of the softer workpiece material can transfer onto the die before operating temperatures can exceed the cloud point of the PAG. These cold start-up problems can sometimes be overcome by initially increasing the concentration of the MWF to the point where it provides sufficient lubricity at ambient temperatures. The incorporation of a polymeric thickener or the emulsification of small amounts of mineral oil are other possible solutions. Work is also being done to see if preheating the PAG containing MWF during the start-up can solve this problem.

36.5.2 Laboratory Studies on PAGs in Chemical MWFs There are many lubricity tests used to evaluate MWFs in the laboratory. The pin and V-block, four ball, and Timken wear tests are all commonly used. However, much

% reduction = 1 –

better correlations with actual metalworking operations are obtained when fluids are evaluated under cutting or deformation conditions. Three studies undertaken to examine the role of PAGs in chemical MWFs are presented in this section. The first utilizes a plain strain compression test in which a lubricated aluminum coupon is plastically deformed. The remaining two studies used an instrumented lathe to evaluate different MWFs while cutting a section of steel pipe. These studies provide strong evidence that supports the cloud point mechanism of PAG based chemical MWFs that was described earlier in this chapter.

36.5.2.1 Plane strain compression test: The effect of PAG cloud point on the performance of chemical MWFs A plain strain compression press [49] was used to verify the cloud point mechanism of chemical MWFs containing PAGs. The press consists of two rectangular male dies, their faces measuring 0.25 by 1.5 in. The dies were attached to a 10 t hydraulic press. Each die was equipped with thermostatically controlled heating elements so that the temperature of the dies’ surfaces could be controlled. A 1 in. wide coupon made from a 0.16 cm thick sheet of 5252 aluminum, H28 temper was thoroughly cleaned. A bead of lubricant was then placed on each side of the coupon. The lubricated coupon was then placed between the male dies of the plain strain-compression press as shown in Figure 36.7 [30]. The dies were then forced

final thicknes s intial thicknes s

× 100 %

Press

Die

Lubricant

Coupon

Before compression

After compression

FIGURE 36.7 The deformation of an aluminum coupon in a plane strain compression test. From Brown, W. L., Lubr. Eng., 44, 168–171 (1988)

Copyright 2006 by Taylor & Francis Group, LLC

100

TABLE 36.2 MWF Concentrate for Plane-Strain Compression Study

Polyalkylene glycol Fatty acid Ethanolamine Water

40 10 20 30

together under a predetermined pressure that was great enough to cause plastic deformation of the coupon. The thickness of the coupon after deformation was measured and the percent reduction calculated using the equation: % reduction = (1 − initial thickness/final thickness) × 100% The greater the percent reduction, the better the lubricant. Two chemical MWF concentrates were made up using the formulation shown in Table 36.2. The only difference between concentrates A and B was the PAG used. The PAG used in concentrate A had a 1% cloud point of 37◦ C, while the polymer in concentrate B had an inverse solubility temperature of 65◦ C. Concentrates A and B were tested for lubricity using the plain strain compression press, as were 5% solutions of each in water. Fluid C, a kerosene based aluminum cold-rolling fluid, was also tested. In this study a lubricated aluminum coupon was placed between the dies. The dies were then brought together and held for 5 sec at a pressure of 78,000 psig. The dies were then released and the percent reduction of the coupon determined. The lubricity of each fluid was tested at die temperatures ranging from 20 to 95◦ C. The results are plotted in Figure 36.8 [30]. The effect of the cloud point of the PAG is evident from the results shown in Figure 36.8. At all temperatures, concentrates A and B were excellent lubricants, giving percent reduction values of between 80 and 90%. This was to be expected, since the viscosities of concentrates A and B were quite high, 110 and 67 cSt (40◦ C) respectively. The slight improvement of lubricity with increasing temperature may have been due to the evaporation of water from the concentrate or from a mild cloud point effect. At low temperatures, below the cloud point of either polymer, the lubricity of the 5% aqueous solutions of concentrates A and B was quite low. The percent reductions achieved using these dilute solutions of concentrates A and B were 50 and 45% respectively. Between 30 and 50◦ C, there was a sudden rise in the measured percent reductions of solution A, indicating a significant improvement in lubricity. This improvement in lubricity was centered around the cloud point of the product’s PAG (37◦ C). Above

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80

Amount (wt %)

70 Percent reduction

Component

90

60 50 40 30 20 10 0 0

10

20

30

40

50

60

70

80

90

100

Temperature °C Fluid A (Neat) Fluid B (5%)

Fluid B (Neat) Fluid C

Fluid A (5%)

FIGURE 36.8 Demonstration of cloud point mechanism of chemical MWFs containing PAGs: data obtained from tests on a plane strain compression. From Brown, W. L., Lubr. Eng., 44, 168–171 (1988)

50◦ C, the 5% solution of fluid A provided lubricity equal to that of the concentrate. The lubricity of the 5% of solution of concentrate B showed the same behavior as the dilute concentrate A, only the increase in lubricity occurred between 60 and 75◦ C. As with the 5% solution of concentrate A, this improvement in lubricity bracketed the cloud point of the PAG used in concentrate B. Above 75◦ C, the dilute solution of fluid B provided the same lubricity as the concentrate. The kerosene based rolling lubricant showed poor lubricity at all temperatures primarily because of its low viscosity of 4 cSt (40◦ C). What is important is that its lubricity decreased with increasing temperature. This is because the product’s viscosity decreases as the temperature rises. While a more viscous hydrocarbon lubricant would provide much better lubricity, its performance would also be expected to decrease with increasing temperature due to a drop in viscosity. The results of this test support the cloud point mechanism of chemical MWFs that contain PAGs. It should be noted that this was a static test. When compared to a highspeed cutting operation, there was a relatively long time in this test for the PAG to come out of solution and form a lubricant film on the surfaces of the dies. However, while straight-oil lubricity is not achieved in many cutting and forming operations, the improvement in performance due to the use of PAGs in chemical MWFs is well documented [6,24,30,48].

36.5.2.2 Lathe test: The effect of PAG cloud point on the performance of chemical MWFs

cutting conditions 1 to 5, with condition 5 being the most severe. The results of this test are shown in Table 36.4. A good correlation exists between decreasing cloud point and enhanced performance. Fluids A and B, with cloud points of 37 and 52◦ C respectively, cut effectively under all five conditions. Fluid C, which contains a PAG with a cloud point of approximately 95◦ C, failed under condition 5. Fluids D and E, whose cloud points were both greater than 100◦ C, failed at condition 4. Fluid F, which contained no PAG, failed at condition 3. The results of this work demonstrate the cloud point mechanism of chemical MWFs in an actual metal removal operation.

A similar study was performed using a 16 in. Loge & Shipley single-point turning lathe. The lathe used in this study was instrumented with a strain gauge and a thermocouple. The thermocouple was inserted in the cutting tool. The tool holder was mounted on the strain gauge. A piece of 1026 steel pipe was end-cut while the MWF under evaluation was directed onto the rake face of the tool. The tool temperature and the vertical cutting force were monitored throughout the duration of the test. Both cutting force [2,50,51] and tool temperature [2,5,13,52] have been shown to correlate with tool life. The lower the tool temperature and the cutting force, the more effective the MWF. To show the effect of the inverse solubility of the PAG in a chemical MWF, five concentrates were made up differing only in the cloud point of the PAG used [53]. The concentrates tested are listed in Table 36.3. Each concentrate was diluted 20:1 with water and then tested under

36.5.2.3 Lathe test: The synergy between PAGs and fatty acids, PAGs, and phosphate esters The instrumented lathe was used to demonstrate the synergy that exists between PAGs and polar, water-soluble lubricity additives [30]. Five concentrates were made up

TABLE 36.3 MWF Concentrates for Cloud Point Study Using a Lathe PAG properties

Component (%)a Sample A B C D E F

TEA

H2 O

FA

PAG

Molecular weight

Viscosity at 40◦ C (cSt)

Cloud point, 1% solution (◦ C)

18 18 18 18 18 18

32 32 32 32 32 72

10 10 10 10 10 10

40 40 40 40 40 0

2700 2700 2700 2500 2000 —

400 400 400 280 —b —

37 52 100 >100 100 —

a TEA, Triethanolamine; FA, fatty acid b Product is a solid at room temperature due to high ethylene oxide content.

TABLE 36.4 Lathe Test Results for Cloud Point Studya Condition 1

Condition 2

Condition 3

Condition 4

Condition 5

Sample

T

F

T

F

T

F

T

F

T

F

A B

94 92

490 500

100 100

540 540

104 104

550 570

114 116

610 640

122 126

680 710

C

100

500

102

540

108

540

108

640

D E

96 96

500 510

102 106

540 540

108 102

570 580

F

100

520

186

500

Failure

Failure

Failure

a T, cutting tool temperature in Celsius; F, vertical cutting force in pounds-force; Failure

either severe vibration or tool breakage.

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PAG 40 30 20 10 0

Lubricity additive

TEA

Water

0 10 20 30 40

40 40 40 40 40

20 20 20 20 20

Cutting force (N × 10–3)

2.42

TABLE 36.5 MWF Concentrates (%) Used in the Lathe Synergy Study

2.40 2.38 2.36 2.34 2.32 2.30 0

10

20

30

40 Pag

40

30

20

10

0 Fatty acid

Percent lubricity additive in concentrate

104 102 100 98 0

10

20

30

40 Pag

40

30

20

10

0 Fatty acid

Percent lubricity additive in concentrate

FIGURE 36.9 Demonstration of the synergy between PAGs and fatty acids in chemical MWFs: data obtained from tests on an instrumented lathe. From Brown, W. L., Lubr. Eng., 44, 168–171 (1988) Cutting force (N × 10–3)

so that the sum of the PAG and the lubricity additive was equal to 40% by weight. The percentage of polymer ranged from 40 to 0 while the percentage of lubricity additive went from 0 to 40. The concentrates, shown in Table 36.5, were then diluted 20:1 with water and evaluated on the lathe. Two different studies were run. In the first, the lubricity additive was a fatty acid. The results from this study are shown in Figure 36.9. The minimum cutting force was achieved with PAG levels of between 20 and 30%. Maximum cooling, represented by the minimum tool temperature, occurred with between 10 and 20% polymer in the concentrate. These curves show that combinations of the PAG and fatty acid perform better than either additive by itself. In the second study, a water-soluble phosphate acid ester was employed as the EP lubricity additive. The data from this study are shown in Figure 36.10. In this case, minimum cutting force was achieved with PAG levels of between 10 and 20% in the concentrate. The minimum tool temperature occurred between 0 and 30% polymer. Again, combinations of PAG and lubricity additive performed better than either additive used individually. This synergy is further evidence supporting the cloud point mechanism of chemical MWFs containing PAGs.

Tool temerature °C

106

2.55 2.53 2.51 2.49 2.47 2.45 0 40

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20 20

30 10

40 Pag 0 Phosphate

Percent lubricity additive in concentrate

36.5.3 Modified PAGs in Chemical MWFs 105 Tool Temerature °C

Polyalkylene glycols provide good lubricating properties in a large number of metalworking operations. They are also very stable in hard water, low foaming, and resistant to biological attack. When used in combination with additives such as fatty acids or phosphate esters, the lubricating and cooling properties of the MWF are enhanced. Unfortunately, both fatty acids and phosphate esters are sensitive to hard water, prone to foaming, and susceptible to biodegradation. In an attempt to achieve the benefits of these combinations without the drawbacks, two types of modified PAGs have been commercialized. These modified PAGs are either esterified or grafted with organic acids. Polyalkylene glycol esters are made from the condensation reaction between organic acids and the terminal

10 30

104 103 102 101 100 0 40

10 30

20 20

30 10

40 Pag 0 Phosphate

Percent lubricity additive in concentrate

FIGURE 36.10 Demonstration of the synergy between PAG and phosphate esters in chemical MWFs: data obtained from tests on an instrumented lathe. From Brown, W. L., Lubr. Eng., 44, 168–171 (1988)

hydroxyl groups of the alkoxylated polymer. These products, like PAGs, exhibit inverse solubility in water and thus behave in an analogous manner. PAG esters exhibit good boundary lubricating properties [36,54], yet have better hard-water stability and are less likely to foam than blends of fatty acids and unmodified PAGs [22]. A second method of modifying PAGs that has gained commercial acceptance is the addition of organic acid functionalities through grafting technology. The result is an anionic PAG that has organic acid groups randomly attached to the polymer’s backbone with hydrolytically stable covalent bonds. These modified PAG polymers exhibit inverse solubility and excellent hydrodynamic and boundary lubricity. Because the acid groups are randomly attached to the polymer, the foaming tendencies of this type of product are significantly lower than those of blends of fatty acids and PAGs. Since the PAG itself is very water soluble at room temperature, the grafted polymer has excellent hard-water stability. Its resistance to biological attack is also very good [55].

36.5.4 Applications of PAGs in Chemical MWFs Polyalkylene glycols have been used in chemical MWFs for the past 40 yr. Because of their good lubricity and synergy with other water-soluble lubricity additives, they have helped expand the applications of chemical MWFs. Chemical MWFs containing PAGs have all of the advantages characteristic of this product class. These advantages include excellent cooling, good biological and hard-water stability, transparency, and cleanliness. The presence of the PAGs in chemical MWFs enables the formulation of products with enhanced lubricity properties, allowing them to compete directly with heavy-duty soluble oils in many applications. While PAGs or modified versions have been used in chemical MWFs for many years [19,24,37], performance data comparing these products to other types of MWFs is relatively scarce. Articles comparing different classes of MWFs to each other, like chemical solutions to soluble oils or soluble oils to straight oils are readily found in the literature. However, the specific formulation information needed to examine the effects of synthetic lubricants in these products is rarely included. The rest of this section reviews some of the documented work that demonstrates the effect of PAGs, both normal and modified, in chemical MWFs. The use of PAG based MWFs in grinding, tapping, hobbing, rolling, drawing, and forming operations is also described. 36.5.4.1 Grinding Levesque et al. [55] published a paper in 1983 describing their experience with an acid grafted PAG in three different grinding operations.

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In the first case a mineral seal oil fortified with approximately 5% of a fatty acid was used to grind hardened steel balls. Odor, general housekeeping problems, and a concern about the flammability of the oil caused them to switch to a water based MWF. A chemical MWF based on a mixture of caprylic acid and a PAG was selected for the ball grinding operation. Initially the product worked very well. During use, however, the effectiveness of this fluid gradually decreased. The addition of concentrate was necessary to return the coolant to acceptable performance levels. Analytical testing of the coolant during use showed that the drop in performance was due to the selective depletion or biodegradation of caprylic acid. Rather than continually monitor their fluid for acid concentration, the authors switched to a dilute solution of an amine neutralized, acid grafted PAG. This modified PAG performed well. The second case study involved a centerless roller grinding operation. A heavily fortified soluble oil was used in a 7000 gal central sump. The problem with the soluble oil was that it covered the regulatory wheels with a layer of oil and metal fines that prevented the achievement of the desired tolerances. The authors decided to switch to a chemical MWF because of the cleanliness that was possible with this type of product. The soluble oil was replaced with a chemical MWF containing a fatty acid ester, a boric acid corrosion inhibitor, and a biocide. Initially the product worked well, but within a month the surface finishes degraded to an unacceptable level. The depletion of the fatty ester was determined to be the problem. The authors then switched this system to the amine neutralized, acid grafted PAG fortified with a carboxylic acid based corrosion inhibitor. At the time the paper was written the roller grinding operation had been using this chemical MWFs for 16 months with essentially no problems due depletion or biodegradation. In the third study conducted by the authors, the same chemical MWF based on the acid grafted PAG was used in a double-disk surface grinding operation. The life of this coolant system was more than 8 months, whereas the life of the previously used soluble oil was only 2 to 3 months. 36.5.4.2 Tapping In 1984 Nash and Colakovic [54] published a study on the affect of a PAG ester and three other lubricity additives on the performance of chemical MWFs during the tapping of high silicone content aluminum blanks. The fluids were evaluated using a tapping torque test machine [56]. The taps employed were HSS, 3-flute, 10 to 15 mm. The tap surface speed was 0.508 m/sec. The nut blanks were made from high silicone A380.1 aluminum with a 16 to 25 mm nonheat-treated surface finish.

of a single component come from the addition of the PAG ester or the alkyl acid phosphate. Furthermore, the combination of the PAG ester and phosphate was synergistic, providing lower tapping torques and thus better efficiency than the sulfurized, chlorinated reference oil. The addition of the sulfurized oleic acid resulted in a small improvement over the base formulation and also showed synergy when combined with the PAG ester. The use of the chlorinated oleic acid had no significant affect on tapping efficiency.

The chemical MWFs were diluted to 10% of their original concentration with 140 ppm hard water. The torque required to tap the nut blanks was recorded and compared to that achieved when using a straight-oil MWF. This control oil was a neat cutting fluid fortified with chlorine and sulfur containing lubricity additives. The percent tapping efficiency was then calculated using the equation: % Efficiency = (Control oil torque/Test fluid torque) × 100%

36.5.4.3 Hobbing

The higher the % tapping efficiency, the better the MWF. A series of chemical MWFs was made up to determine the effects of four water-soluble lubricity additives on tapping efficiency. The additives tested were a PAG ester, which exhibits inverse solubility, an alkyl acid phosphate, a sulfurized oleic acid, and a chlorinated oleic acid. Each fluid also contained a carboxylate salt for corrosion protection and TEA to solubilize the lubricity additives and provide reserve alkalinity. The physical characteristics of the components used to make up the test concentrates are shown in Table 36.6. The compositions of the different fluids tested and their average percent tapping efficiency are shown in Table 36.7. It can be seen from these data that the largest positive effects

Katsuki et al. [57] described work that they had done to evaluate the performance of water based MWFs in a gear hobbing operation. In this study the durability of the hob was evaluated using a fly-tool cutting test on a milling machine. This fly-tool cutting evaluation was set up to correlate closely with an actual gear hobbing operation. The MWF concentrates were diluted with water. During the cutting operation, the face of the hob was flooded with the diluted MWF. Grooves were cut into the workpiece to correspond to the manufacture of 14.7 gears. The corner and center wear of the hob were then evaluated. The smaller the wear scars, the more effective the MWF. Four water-soluble PAGs of different molecular weights were evaluated and compared to a chlorinated fatty

TABLE 36.6 Physical Characteristics of Fluid Components Kinematic viscosity (cSt) Component

At 40◦ C

At 100◦ C

Total acid number

— 300 222 2750 95 190 150

— — 14 230 18 20 22

— 170 — 15 330 185 140

Water Carboxylate salt TEA PAG ester Alkyl acid phosphate Sulfurized oleic acid Chlorinated oleic acid

Miscellaneous properties 140 ppm hardness 140 ppm base number 1% cloud point, 77 ◦ C 11% phosphorous 8.5% sulfur 30% chlorine

TABLE 36.7 Test Fluid Concentrate Compositions and Aluminum Tapping Torque Efficiency Solution concentrates Component

Base

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Water Carboxylate salt TEA PAG ester Phosphate Sulfurized acid Chlorinated acid

84 8 8 — — — —

74 8 8 10 — — —

80 8 8 10 4 — —

70 8 8 10 4 — —

80 8 8 — — 4 —

70 8 8 10 — 4 —

76 8 8 — 4 4 —

66 8 8 10 4 4 —

80 8 8 — — — 4

70 8 8 10 — — 4

76 8 8 — 4 — 4

66 8 8 10 4 — 4

76 8 8 — — 4 4

66 8 8 10 — 4 4

72 8 8 — 4 4 4

62 8 8 10 4 4 4

% Efficiency, mean value

79

91

90

101

84

97

92

101

80

81

97

99

88

91

84

91

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oil that was considered an excellent gear cutting lubricant. The PAGs were all diluted ten times with water and then compared to the oil based standard. The PAGs evaluated are characterized in Table 36.8. The results are shown in Table 36.9. It can be seen from the data in Table 36.9 that the center wear of the chlorinated fatty oil control is lower than that of any of the PAGs. The differences are more extreme at the intermediate cutting speeds of 86 and 117 m/min. At these intermediate speeds, increasing the molecular weight of the PAG tends to decrease the center wear. However, at cutting speeds of 62 and 159 m/min, there was essentially no difference seen between the performance of the different molecular weight polymers. The corner wear experienced when using the PAGs was equivalent to that of the chlorinated fatty oil at a cutting speed of 62 m/min. As cutting speed increased, however, the corner wear seen when using the oil based control rose much more quickly than with the PAGs. There was no significant affect of PAG molecular weight on corner wear. A second study was performed to determine the affect of PAG concentration on hobbing performance. Polymer PAG-4 was tested over a wide range of dilutions and compared to water and the chlorinated fatty oil control at a cutting speed of 159 m/min. The results are shown in Table 36.10. From this study it can be seen that even at very low concentrations the presence of the PAG yields very low corner wear relative to water. At concentrations equal to or greater than 0.62%, the use of the PAG-4 solution also results in

TABLE 36.8 PAGs Evaluated in Hobbing Study

Sample

MW

Viscosity at 30◦ C (cSt)

PAG-1 PAG-2 PAG-3 PAG-4

1,675 2,430 4,750 11,800

205 276 1,590 27,500

VI

Diluted viscosity at 40◦ C (cSt)

203 210 290 427

1.29 1.41 2.16 5.26

lower corner wear than the chlorinated fatty oil control and equivalent center wear. It is interesting to note that while corner wear decreased with increasing PAG concentration, center wear increased. The authors of this study found that while the use of the PAGs provided superior performance as measured by lower wear, the corrosion protection provided by these solutions was insufficient. It was found that the addition of rust preventatives could significantly improve the corrosion protection provided by the PAG. However, the addition of these corrosion inhibitors did cause hob wear to increase at higher cutting speeds. 36.5.4.4 Machining and rolling A number of chemical MWF formulations based on PAGs and mixtures of these polymers with polyvinylpyrrolidone, polyvinyl alcohol, polyacrylates, and polymethacrylates were patented by Marx [47]. Several of these formulations and their applications are shown in Table 36.11. The formulations in this table were used successfully in a number of machining and sheet rolling operations. Marx also described how the replacement of soluble oils with chemical MWFs containing the aforementioned water-soluble polymers enabled cutting speeds to be increased in a number of sawing, planing, and drilling applications. These MWFs were also successful at replacing straight oils in deep-hole drilling operations. This resulted in significant cost savings. Marx then relates how aqueous solutions containing 15 to 20% PAG or mixtures of PAGs and some of the higher molecular weight polymers mentioned previously can be used for deep drawing steel and stainless steel parts. These solutions can also be used for the drawing of wire and tubing. An advantage of these polymers in drawing operations is that their residues can be easily washed off with water. 36.5.4.5 Blanking and drawing The early use of PAG solutions in blanking and drawing operations was documented by Sweatt and Langer in 1951 [37]. The properties of the PAG used in these chemical MWFs are shown in Table 36.12.

TABLE 36.9 Results from Hobbing Evaluation Cutting speed (m/min) 62 86 117 159

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Center wear (mm)

Corner wear (mm)

Control

PAG-1

PAG-2

PAG-3

PAG-4

Control

PAG-1

PAG-2

PAG-3

PAG-4

0.07 0.10 0.14 0.18

0.11 0.28 0.48 0.21

0.12 0.22 0.50 0.20

0.11 0.16 0.37 0.20

0.12 0.18 0.29 0.20

0.10 0.17 0.27 0.50

0.10 0.11 0.12 0.16

0.10 0.11 0.12 0.16

0.10 0.11 0.12 0.16

0.10 0.11 0.15 0.15

TABLE 36.10 Effect of Polyalkylene Dilution Ratio on Hobbing Performance PAG-4 concentration (%) 0.10 0.20 0.33 0.62 1.25 2.50 5.00 10.00

Center wear (mm)

Corner wear (mm)

PAG-4

Water

Control oil

PAG-4

Water

Control oil

0.11 0.11 0.12 0.16 0.17 0.18 0.16 0.20

0.11

0.18

0.60 0.48 0.60 0.22 0.21 0.20 0.11 0.11

1.02

0.50

TABLE 36.11 Formulations and Applications of Chemical MWFs Containing PAGs Concentrate formulations (%) Component

Fluid 1

Fluid 2

Fluid 3

Fluid 4

PAG Polyvinylpyrrolidone Polyvinyl alcohol Amine phosphate CIa TEA Water

20 — — — — 6 74

15 5 — — — 6 74

15 5 — — 46 — 24

20

Dilution ratio

20:1

20:1

20:1

10:1

Applications

Steel sheet rolling: brass and copper sheet formation

Rolling of thin (Cu, Sn, Au, brass)

Steel tapping: rod and channel formation

Steel planning, milling, and cutting

4 — 46 — 30

a Corrosion inhibitor package containing 16 parts of benzoic acid, 9 parts of TEA (tri-

ethanolamine), 15 parts of triethanolamine phosphate, and 6 parts of morpholine.

TABLE 36.12 PAG Characteristics Property

Value

Molecular weight Viscosity At 40◦ C At 100◦ C Specific gravity, 20/20◦ C Water solubility at 25◦ C 1% Cloud point, ◦ Ca

1600

a Inverse solubility temperature.

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132 26 1.05 Complete 50

A 25% solution of this PAG in water with a small amount of corrosion inhibitor was used to replace a petroleum oil based lubricant in a blanking and a drawing operation. The two applications are summarized in Table 36.13. While the good lubricity of the PAGs is evident from the increased tool life, their cleanliness and water washability was also important. 36.5.4.6 Cold forming A chemical MWF formulation for use in cold-forging operations was patented by Felton [48]. The formulation is shown in Table 36.14. This MWF was used neat to successfully form 3/4 in hexagonal nut blanks from a 3/4 in rod of AISI 1038 steel. The nuts were formed at a rate of 2 blanks each second. This operation took five separate

TABLE 36.13 Applications of Aqueous PAG Solutions Operation

Workpiece material

MWF

Number of pieces per die refinishing

Blanking and pressing

Annealed spring steel

Drawing shells

Nickel-plated steel

Oil PAG solutiona Oil PAG solutiona

35,000–50,000 100,000–120,000 25,000–30,000 >65,000

a Solutions contained 25% PAG.

TABLE 36.14 Cold-Forming Lubricant Formulation Component PAG

Sulfurized fatty acid Chlorinated fatty acid Glycerin Potassium nitrite Potassium hydroxide Silicone defoamer Water

Amount (vol %) 32

5 5 3 2 1.75 0.10 51.5

Component description Molecular weight, 2200 40 wt % ethylene oxide (EO) 60 wt % ethylene oxide (EO) 14 wt % sulfur 35 wt % chlorine

steps. The die used in each step was flooded with lubricant between hits. The trial was run without problems for 5 h, indicating good lubrication. The finished blanks were bright and shiny when the PAG based MWF was used, as opposed to the dull, scorched appearance that was achieved when employing a straight oil forming lubricant. Also, the smoke generated during this operation was greatly reduced when the forming lubricant was switched from the oil to the PAG based product.

36.5.4.7 Drawing and forming The use of a PAG based chemical MWF in a number of drawing and forming operations was described by Brown [58]. The formulation used is shown in Table 36.15. This formulation was used at various dilutions with water depending upon the severity of the operation. Up to 5% of a sulfurized fatty acid was added for additional extreme pressure lubrication when needed. The operations in which this formulation was used are summarized in Table 36.16. The first three operations are described in more detail in the following sections.

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TABLE 36.15 PAG Based drawing and Forming Lubricant Component PAG Phosphate acid ester Corrosion inhibitor (nonnitrite) TEA Sulfurized fatty acid Water

Amount (wt %) 15 6 15 10 0–5 49–54

36.5.4.7.1 Trailer hitches Trailer hitches were being drawn from HRPO AKDQ C 1008 (0.141 to 0.151 in. thick) drawing-quality steel using an 800 t press. Ten hitches were drawn each minute. Using a straight-oil metalworking lubricant that was fortified with a chlorinated paraffin, the dies had to be refinished every 15,000 to 20,000 parts. While the lubricity provided by the chlorinated oil was good, it was very difficult to completely remove the lubricant from the formed pieces. Also, the operators complained of skin irritation while using the chlorinated product. The straight oil was therefore replaced by the PAG based MWF shown in Table 36.15. This formulation was fortified with 5% of the sulfurized fatty acid and was used without further dilution with water. Die life remained unchanged at 15,000 to 20,000 hitches per refinishing. However, the PAG based lubricant provided excellent corrosion protection while the formed parts were stored and could be easily removed with aqueous cleaning systems prior to subsequent operations. More importantly, the operators found the product to be benign. 36.5.4.7.2 Water heater tops and bottoms A soluble-oil MWF formulated with rust inhibitors and diluted 20 times with water was being used to form water heater tops and bottoms. The operation involved a 4 in. draw of 9 to 10 gauge mild cold-rolled steel. The pieces were produced at a rate of ten per minute. The problem with

TABLE 36.16 Applications of PAG Based Forming Lubricant PAG/fluid dilution ratio, H2 O:lube

Previous producta

Application

Process description

Trailer hitches

Severe draw

Neat

Chlorinated paraffin

Water heater tops and bottoms

Blanking and one 2 in. draw

20:1

R&O sol oil (dil 20:1)

Water heater jacket tops Oven liners

Cone spinning, 40% elongation Five-stage operation (four 0.5 in. draw, one shear/punch) Blanking operation and one 4 in. draw

20:1

Chlorinated sol oil (dil 10–20:1)

2:1

Chlorinated sol oil (dil 2:1)

2:1

Chlorinated sol oil (dil 2:1)

Lawnmower bodies

Observations Nonstaining, nonirritating; good die life Water washable; good rust protection Good cooling and lubrication Water washable; no staining Excellent rust protection; good die life

a Rust and oxidation soluble-oil MWF.

the soluble oil was that it was very difficult to completely remove it from the formed pieces. The presence of residual oil caused defects in the enamel coating, which in turn led to the premature corrosion of the water heater. The chemical MWF shown in Table 36.15 with no sulfurized fatty acid was diluted 20 to 1 with water and used to replace the soluble oil. The PAG based MWF provided equivalent lubricity when compared to the soluble oil. More importantly, this chemical MWF was easily washed off of the formed parts, virtually eliminating defects in the enamel coatings.

both soluble oils and straight-oil MWFs. The PAG containing products have all of the beneficial properties of chemical MWFs including excellent cooling, ease of maintenance, and cleanliness. In addition, they exhibit enhanced lubricity that enables them to compete with heavy-duty soluble oils and, in some cases, straight-oil MWFs. The properties of polyalkylene based chemical MWFs make them especially desirable in applications where workpiece staining or water solubility are important.

36.5.4.7.3 Cone spinning of water heater jacket tops Tops for water heater jackets were made in a cone spinning operation. A 16 in. diameter disk made from mild cold-rolled steel was blanked in a separate step. During the cone-spinning operation, this disk was spun at 1500 to 1700 rpm and made to undergo a 40% elongation. The wheel of the cone spinning machine was flooded with a 20 to 1 dilution of a chlorinated soluble oil. This MWF provided insufficient cooling and lubricity, which resulted in the discoloration of the workpiece. The chlorinated soluble oil was replaced with the chemical MWF shown in Table 36.15 fortified with the sulfurized fatty acid. This product was also used as a 5% solution in water. The lubricity and cooling properties of this product were excellent. Also, this chemical MWF provided the spun workpiece with corrosion protection during storage for even more than 60 days. To summarize, PAG fortified chemical MWFs are effective coolants and lubricants in a wide range of metal removal and deformation operations. They have replaced

Semichemical MWFs are, as their name implies, a hybrid of soluble oils and chemical solutions. Their main advantage is that they are cleaner and better coolants than soluble oils but still contain emulsified hydrocarbons that provide good corrosion protection and lubricity to both the tool or die and the machinery. These advantages are pushing semichemical MWFs growth at the expense of soluble oils and to a lesser extent true synthetic MWFs. A typical formulation for a semichemical MWF concentrate is shown in Table 36.17. This concentrate will then be diluted 10:1 to 30:1 with water for most cutting or grinding operations. For more severe metalworking operations, higher concentrations are employed.

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36.6 SYNTHETIC LUBRICANTS IN SEMICHEMICAL MWFS

36.6.1 Polyalkylene Glycol Esters in Semichemical MWFs Synthetic lubricants in semichemical MWFs are used primarily as water-soluble lubricity additives. Canter et al. [36] described the use of PAG esters in semichemical MWF

Self-Emulsifying Esters

TABLE 36.17 Typical Semichemical Concentrate Formulation Component

H3C

Amount (wt %)

Mineral oil Emulsifiers Couplers Corrosion inhibitors EP additives Water-soluble lubricity additives Biocides Water

Hard water stability

5–20 5–20 0–5 5–10 0–10 0–20

EO

H3C COO–C8H17

—a

COOH

40–70

FIGURE 36.11 Generalized structure of self-emulsifying esters

TABLE 36.18 Semichemical Test and Reference Formulations Test formulation (% component)

Reference fluid (% component)

3–13 9–20 10 6 2 1.5

8 12 — 5 2 1.5

60.5

70.5

Naphthenic oil Emulsifier base PAG ester Amine borate Triazine Propylene glycol methyl ether Water

formulations. A number of esters were made up by reacting PAGs with either one or two equivalents of a fatty methyl ester. The PAGs used had ethylene oxide to propylene oxide ratios of 5:1, 3:1, and 1:1. The fatty groups evaluated were pelargonate, laurate, oleate, and stearate. Many of these compounds displayed inverse solubility properties in water. The PAG esters were incorporated into the base formulation shown in Table 36.18. The oil to emulsifier base ratios were adjusted to enable the formation of a stable microemulsion for each PAG ester tested. The reference semichemical fluid formulation is also shown in Table 36.18. All of the semichemical MWF formulations containing PAG esters provided significantly better lubricity on a pin and V-block wear test at a 10 to 1 dilution with water than the reference fluid at the same concentration. Two of the formulations containing dioleate esters as well as the product made with the dipelargonate ester were also low foaming and provided better corrosion protection than the reference fluid.

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Lubricity

Emulsification and waste treatability

a As recommended by the manufacturer.

Component

CH3

Another growing use for PAGs in semichemical MWFs is as coupling agents to help solubilize the corrosion inhibitor packages [34].

36.6.2 Self-Emulsifying Esters in Semichemical MWFs Two types of synthetic lubricants find use as chlorinated paraffin replacements. The first, self-emulsifying esters (SEE) are based upon a polymerized fatty acid backbone reacted with ethylene oxide forming polyethylene glycol esters. These polyethylene glycol (PEG) esters are further reacted with monoalcohols and carboxylic acids. The resulting SSE has a structure shown in Figure 36.11. Because SEE are large complex molecules containing ester, carboxylic acid and PEG ester functionality, they act as both emulsifiers and lubricants. As emulsifiers, they have been shown to decrease MWF consumption by up to 50% compared to a control MWF lacking SEE [83]. The carboxylic acid group on the SEE molecule can be reacted with both caustic and amines yielding versitile emulsifying soaps. Yet, their combination of nonionic (PEG) and anionic (acid) groups allows SEE to be both hardwater resistant and waste treatable. The nonionic (PEG) portion allows the carboxylic acid groups to form soaps with divalent cations such as calcium yet remain soluble in water. However, the carboxyl groups are not so stable as to be resistant to common waste-water treatment cationic coagulants like aluminum sulfate. After reacting with waste-treatment coagulants, SEEs migrate to the oil phase and lose the ability to hold a used MWF emulsion together. As lubricants, SEEs have a combination of a bulky polymerized fatty acid and ester functionality. They benefit from branched alkyl groups in the polymerized fatty acid backbone that provide steric hinderence. The hindered

Pentaerythritol

TABLE 36.19 SEE Micro-Tapping Evaluation Summary % Efficiency Formulation Control (average of 11 different coolants) 3% SEE 1% SSE

1018 Steel

6061 Aluminum

100

100

113 —

— 184

All tests run 300 ppm water.

structure provides biostability and helps prevent breakdown by water (hydrolysis).

36.6.3 Laboratory Studies on SEEs in Semichemical MWFs On ferrous materials such as 1018 steel, the addition of three percent SEE in moderately hard water improves the percent tapping efficiency on a micro-tapping test. The percent torque efficiency improvement was 113% compared to an average of 11 different metal working fluids. For 6061 aluminum the advantages of SEE are more substantial. Only one percent SSE in 300 ppm water shows significant micro-tapping efficiency gains compared to the same eleven fluids. The micro-tapping efficiency improvement ranged from a high of 225 to low of 140%. The average micro-tapping efficiency improvement was 184%. The results are summarized in Table 36.19. Other bench tests including Falex, tapping torque and Reichert Wear show the benefits of SEE lubricity [83]. SEEs dual roles as chlorine replacements and waste treatable emulsifiers prolonging coolant lifetimes can contribute to more environmentally friendly fluids.

36.6.4 Complex Polymeric Esters in Semichemical MWFs The second type of synthetic lubricants that are finding use in semichemical fluids as a chlorine replacement are complex polymeric synthetic esters. These complex polymeric esters (CPE) are both soluble in mineral oil and emulsifiable in water. In Figure 36.12, the pentaeythritol backbone of CPE is illustrated. Up to four different species may be reacted at each terminal hydroxyl group. Many different possiblities for forming different CPE are possible. Three major types are commercially availible; complex polymeric vegetable esters (CPVE), complex polymeric sulfurized esters (CPSE) and another form SSE based upon a pentaerythritol center.

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HO

HO O

H

OH Each-OH group is available to react with an acid, EO, PO, or another polymer

FIGURE 36.12 Structure of pentaerythritol that is used as a base for forming complex polymeric ester synthetic lubricants

Complex polymeric esters have molecular weight range typically between 15,000 and 50,000. The large size of CPE gives them the ability to hold up well under boundary conditions. They all exhibit high viscosity indexes and show good thermal stability. CPSE have sulfur levels between 10 and 20%. These light colored, low odor CPSE are synergistic with overbased calcium sulfonates and CPVE. The moderate sulfur levels in CPSE are considered inactive sulfurized additives. They do not give greater than a 1b ASTM D-130 copper corrosion stain [84]. Complex polymeric vegetable esters have inherent corrosion inhibition on ferrous materials. As shown in Figure 36.13, a cast iron chip test of at 5% concentration of CPVE in 200 ppm hardness water demonstrates almost no corrosion. On 6061 aluminum, a comparision of 5% CPVE and 5% SSE showed approximately equal tapping torque efficiency in semichemical fluids. However, CPVE had larger improvements over SSE in soluble-oil tapping torque comparisions [84].

36.6.5 Synthetic Hydrocarbons in Semichemical MWFs In theory, synthetic hydrocarbons like polyalphaolefins (PAOs) could be used in place of the emulsified mineral oil in a semichemical formulation. The cost of this substitution usually outweighs the benefits in most applications. However, there are a small number of cases where such formulations are marketed for use in operations where no mineral oils are allowed yet an emulsified lubricant phase is still desired. Polyalphaolefins are used more often as partial mineral oil replacement in semichemical fluids. The blending of more polar PAOs with mineral oil in a semichemical formulation provides some lubrication improvement and foam reduction while keeping the cost more reasonable. Other synthetic hydrocarbons such as polyisobutylenes and mineral oil blends are more difficult to work with in semichemical formulations and are less frequently used.

Complex polymeric vegetable ester IP 287: cast iron rust test Dilution in 200 ppm CaCO3 water

3%

4%

5%

FIGURE 36.13 Corrosion protection of CPVE

TABLE 36.20 Typical Soluble-Oil Concentrate Formulation Component Mineral Oil Emulsifiers Coupling agents Corrosion inhibitors EP additives Biocide Water

Amount (wt %) 70–80 10–20 1–5 5–10 0–10 —a 0–5

a As recommended by the manufacturer.

36.7 SYNTHETIC LUBRICANTS IN SOLUBLE-OIL MWFS Soluble-oil MWFs still make up a major portion of the water based lubricants used today. They are well accepted and the presence of a hydrocarbon oil provides many operators and machinists with a significant degree of comfort. A typical soluble-oil concentrate formulation is shown in Table 36.20. The use of synthetic lubricants in soluble-oil MWFs as oil replacements is very small. Water-soluble synthetic lubricants are not used in soluble-oil formulations. Synthetic hydrocarbons or esters could be emulsified along with or in place of the mineral oil, but the cost of such substitutions usually outweighs the benefits. However, as with semichemical MWFs, there are specialty applications where synthetic hydrocarbons are emulsified to make “synthetic” soluble oils. This is usually done to satisfy customers who require oil-free MWFs but still need an emulsified product. Such formulations can also be used in applications where the workpiece is susceptible to staining.

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Another application for synthetic lubricants is in rolling oils for steel. These products are usually soluble oils containing mineral oils and tallow fats. These natural fats are being replaced in some cases by synthetic esters made from the reaction between pentaerythritol or trimethylolpropane and C-12 to C-18 fatty acids [34]. Double-comb polymeric esters, made by reacting butanol with alpha-olefin dicarboxylic acid copolymers [39], have been used to formulate high-performance soluble-oil MWFs. The “double comb” structure is illustrated in Figure 36.14. Several concentrates were made up to determine the effectiveness of the double-comb polymeric esters as lubricity additives. The concentrates were diluted with water to give 10% solutions and then evaluated using a Reichert frictional wear tester, which is believed to correlate well with a number of metalworking operations [39]. The results of this work are shown in Table 36.21. The addition of the double-comb polymeric ester greatly improves the performance of soluble-oil formulations containing a variety of traditional phosphorus and sulfur containing extreme pressure lubricity additives. The development of lubricity additives that can replace chlorinated and sulfurized compounds is a goal of the metalworking industry. The elimination of chlorine is becoming increasingly desirable as the disposal of halogenated wastes becomes more difficult and costly. Sulfurized additives can promote microbial growth in the active MWF. Complex polymeric esters based on pentaerythritol have been used in soluble-oil formulations as lubricity additives to enable the replacement of chlorine and inactive sulfur in some applications [38]. Figure 36.15 shows how various lubricants compare under machining conditions. Several soluble-oil concentrates were blended using the complex polymeric ester in place of a sulfurized fat and a chlorinated paraffin that were used in the control formulation. All of the products were then diluted with

Double-comb polymer ester

Ester groups

Hydrophilic

Carbon “back bone”

Hydrophobic

Hydrocarbon side chains

FIGURE 36.14 Idealized structure of a double-comb polymer ester

TABLE 36.21 Lubricity of Soluble Oils Containing Complex Polymeric Ester Formulation Components

A

B

C

D

E

F

Double-comb polymeric ester, 357 cSt at 100◦ C Mineral oil Emulsifiera Dibutyl phosphite Sulfurized fat, 16% sulfur TPPTb Reichert Test results, % relative abrasionc

—

10

—

10

—

10

75 25 — —

65 25 — —

70 20 3 2

60 25 3 2

72 25 — —

62 25 — —

— 97

— 94

— 91

— 56

3 96

3 73

a Alkylbenzenesulfonate, soap, fatty acid alkanolamide. b Triphenylphosphorothionate. c Deionized water = 100% abrasion.

distilled water to form 5% solutions by weight. The diluted soluble-oil MWFs were then evaluated using the tapping torque test, ASTM D-5619. The evaluations were performed using high-speed taps and 1215 steel nuts at 400 rpm. The control sample containing the chlorinated paraffin and sulfurized fat was assumed to have a tapping efficiency of 100%. Higher tapping efficiencies mean better performance. Formulations A and C performed as well as or better than the control sample. The soluble-oil formulations and tapping torque test results are shown in Table 36.22 [38].

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36.8 SYNTHETIC LUBRICANTS IN STRAIGHT-OIL MWFS Straight-oil metalworking lubricants continue to be the products of choice in a large number of metalworking operations, particularly those involving drawing and forming or low speed, high severity metal removal. A typical straight-oil formulation is shown in Table 36.23. Straight-oil MWFs can be formulated with synthetic lubricants instead of mineral oils. The predominant synthetic lubricants used in straight-oil MWFs are PAGs, polyisobutylenes, and esters. The major advantages of these products is their low staining and clean burn-off characteristics. Several applications of straight-oil MWFs based on synthetic lubricants are described below. The use of neat PAGs in two drawing operations is described by Sweatt and Langer [37]. Their work is summarized in Table 36.24. In both operations die life was significantly increased by switching from an oil based product to a PAG. When using an oil soluble PAG to draw 85 to 15 brass, they also found that there was a significant reduction in tarnish. More importantly, it was possible to solder the brass pieces after drawing without first having to remove the lubricant. The use of a water-soluble PAG to draw sheet iron not only increased die life by a factor of five but also enabled the parts to be thoroughly cleaned using a water wash. Similar observations were noted by Russ (1951, private communication, Union Carbide Corp.) while making 3 in. bubble caps. The caps were made from 0.064 in. thick copper sheet. The operation involved a 2.5 in. draw of the copper blanks. The original lubricant was lard oil. The use of the lard oil led to the lubricant sticking between the die and the workpiece and discoloration of the finished caps. The lard oil was replaced by an 80 cSt (40◦ C)

Efficacy at operating temeratures

Lubricant type

Metal sulfides

Metal phosphides Metal chlorides Complex polymeric esters

Metal soaps

0

200

400

600 Temperature,°C

800

1200

1000

FIGURE 36.15 Activation temperatures for various lubricant additives formed at the tool–workpiece interface during machining

water-soluble PAG. The use of this synthetic lubricant eliminated workpiece sticking and discoloration and also improved the surface finish of the drawn caps. The addition of oil soluble PAGs to aluminum sheet and foil-rolling lubricants has also been explored. Whetzel et al. [31] described how the addition of PAGs to light mineral oils resulted in an increase in fluid performance. The percent reduction in thickness achieved when rolling 1100 aluminum alloy under a rolling load of 5500 lb/in. of strip width increased 10 to 15% when 4% PAG was added to the mineral oil base. Another application for oil-soluble PAGs is in vanishing oils. The PAGs are dissolved in low molecular hydrocarbons having flash points of less than 140◦ F. The vanishing oil is then applied to the workpiece where the volatile carrier evaporates, leaving a thin, uniform PAG film. This film provides excellent lubricity and is easy to remove from workpiece. In many cases the workpiece does not have to be cleaned. Polyalkylene glycols, polyisobutylenes, and alkyl benzenes are all finding use in wire drawing compounds as carriers of dispersed solid lubricants. The major advantage of these synthetic lubricants in wire drawing operations is their clean burn-off characteristics during annealing [32,34]. Polyisobutylenes are also used as mineral oil thickeners in a wide variety of metalworking applications. Their high molecular weight, low staining characteristics, and tendency to volatilize completely at high temperatures without leaving varnishes make them well suited for this use [32]. There is little indication that straight oils containing synthetic lubricants are being used in cutting applications. The benefits associated with synthetic lubricants do

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TABLE 36.22 Lubricity of Soluble Oils Containing Complex Polymeric Ester Formulation Components

Control

A

B

C

D

Soluble base Complex polymeric ester Amine phosphate TEA Sulfurized fat (10% inactive sulfur) Chlorinated paraffin (60% chlorine) Pale oil, 100 SUS

21 — — — 10

15 5 — 0.75 —

15 2 — 0.30 —

15 3.5 0.5 0.90 —

15 — — — —

4

—

—

—

—

65

79

83

79

85

Tapping torque test, % efficiency

100

106

96.8

100

93.5

TABLE 36.23 Typical Formulation of a Straight-Oil MWF Component Mineral oil Corrosion inhibitors EP additives Boundary lubricity additives Antioxidants

Amount (wt %) 75–100 0–5 5–20 0–10 0–2

not make up for the added cost in this segment of the metalworking industry. However, it is possible that PAOs could be used as cutting-oil base stocks in some specialty operations [34].

TABLE 36.24 Applications of Neat Polyalkylene Glycols as Forming Lubricants Workpiece material

Operation Drawing

85–15 Brass

Drawing

Sheet iron

Metalworking Lubricant

Number of pieces per die refinishing

Oil PAGa Oil PAGb

5,000 17,000 50 250

a Oil soluble; viscosity at 40◦ C, 27 cSt. b Water soluble; viscosity at 40◦ C, 130 cSt.

TABLE 36.25 Cutting Fluid Formulations Based on α-Olefins Amount of component in formulation (wt %) Component

Formulation A (control)

Formulation B (α-Olefin)

Paraffinsa α-Olefin 1-Dodecanol Butyl stearate

93 0 6 1

46.5 46.5 6 1

a Equal amounts of C and C components were used. 18 16

A relatively recent example of the use of synthetic lubricants in straight-oil cutting fluids is the application of alpha olefins containing 16 to 18 carbons as replacements for paraffin base stocks. Work has been done that shows that the replacement of 50% of the paraffinic base stock with an alpha olefin can increase the surface force of attraction to the metal surface by 10 to 40% [59,60]. This high surface attraction results in better surface finish and reduced tool wear. In some cases it has also enabled the reduction of sulfur containing extreme pressure lubricity additives [59]. In sheet and foil-rolling applications, increased thickness reductions, better surface finishes, and reductions in rolling force of up to 22% have been documented [59,61]. To demonstrate the advantages of using alpha olefins in conjunction with paraffins in straight-oil cutting fluids, the two test formulations shown in Table 36.25 were made up [60]. Formulations A and B were first evaluated by tapping predrilled holes in a piece of 1020 steel. The taps were then cleaned and examined for welding spots using a scanning electron microscope. The tap used with the paraffin based formulation A showed 207 weld spots. The tap used with Formulation B, where 50% of the paraffin base stock had been replaced with alpha olefins, exhibited only 76 weld

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TABLE 36.26 Surface Finishes of Milled Aluminum Alloys Cutting fluid

Aluminum alloy

Torn area (%)

Formulation A Formulation B Formulation A Formulation B

356 356 380 380

69.4 53.4 83.7 58.7

spots, a 63% reduction [62]. This reduction in welding results in longer tool life and better surface finish. These same two formulations were then used to mill 356 and 380 aluminum alloys. The alloys were milled at a feed rate of 0.38 m/min. The cutting depth was set at 3.56 × 10−4 m. After milling, the surfaces were examined for surface tares. The results are shown in Table 36.26 [60]. With both alloys, the use of Formulation B containing the alpha olefins resulted in significantly smoother surfaces that exhibited 20 to 30% less taring. Formulations A and B were also used to turn 304 stainless steel rods on a lathe. Three different cutting tools were used. The cutting conditions and test results are shown in Table 36.27 [60]. In all three cases, the use of the alpha olefins in Formulation B resulted in reduced surface roughness. A second example of the use of synthetic lubricants in straight-oil cutting fluids is the incorporation of the doublecomb polymeric esters has been shown to improve the lubricity off metal cutting fluids, thereby improving tool life and surface finish [39]. Several formulations were made to determine the effectiveness of the double-comb polymeric esters in cutting fluids. These straight-oil cutting fluids were evaluated using a tapping torque test machine. The effectiveness of the fluid can be determined by measuring the torque required to tap predrilled holes. The fluids were compared to a chloroparaffin based reference oil. A “torque difference” was then calculated. A positive torque difference means that the test fluid outperformed the chloroparaffin standard by requiring less torque to tap a given hole. A negative torque difference indicates poorer fluid performance relative to the standard. The results, summarized in Table 36.28, show the benefits achieved through the use of the double-comb polymeric ester [39].

36.9 MARKET OUTLOOK 36.9.1 Market Size The total annual consumption of MWFs in the United States is currently estimated to be between 100 and

TABLE 36.27 Surface Roughness of Turned 304 Stainless Steel Rod

Cutting fluid Formulation A Formulation B Formulation A Formulation B Formulation A Formulation B

Tool typea

Tool speed (m/sec)

Chip (µm)

Surface roughness (µm)

Standard deviation (nm)

0.172 0.172 2.34 2.34 2.24 2.24

178 178 152 152 152 152

41.5 21.9 63.3 46.4 32.9 25.4

19.5 7.0 26.4 13.7 13.7 18.4

HSS HSS CER CER CTD CTD

a HSS, high speed steel; CER, cermet; CTD, carbide insert coated with Ti nitride and Ti

carbonnitride.

TABLE 36.28 Cutting fluid Formulationsa Containing Double-Comb Polymeric Esters Formulation Chloroparaffin (reference) Formulation Q Formulation R Formulation S Formulation T Formulation U

Mineral oil (ISO VG 46)

TNPS∗

Polymeric ester

TMP ester∗∗

Torque difference

—

—

—

—

—

100 98 75 73 73

— 2

— — 25 25 —

— — — — 25

−3 −0.50 −0.25 +0.30 −1.15

2 2

a TNPS, di-tert-nonyl polysulfide (extreme pressure additives); TMP ester, C fatty acid ester of 9

trimethylolpropane.

140 million gallons of straight oils and water-dilutable concentrates [63,64]. Taking the dilution of the soluble oil, chemical, and semichemical concentrates into account, the total annual consumption of MWFs in the United States has been estimated to be 3.2 billion gallons [65]. Approximately 60 to 70% of the MWFs sold in the United States are used in metal removal operations, while the remaining MWFs and concentrates are employed in forming applications [66,67]. It is estimated that 30 to 40% of these MWFs sold in the United States are straight oils, while soluble oils, chemical, and semichemical fluid concentrates make up the remaining 60% [67]. The water-dilutable MWFs can be subdivided further. Approximately 60% of these products are soluble oils, while the remaining 40% are divided between chemical and semichemical MWF concentrates [67]. Over the last several years, semisynthetic MWFs have taken a greater share of this remaining 40% at the expense of true chemical solutions. The growth rate of the MWF market in the United States has been slow over the last decade. Depending upon the source, this market has grown at a rate of between

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0.1 and 1.3% per year [63,64,68]. It is expected that over the next five years the amount of MWFs consumed in the United States will remain constant or even decrease slightly [64]. Environmental concerns will lead to the formulation of longer life fluids, improved fluid maintenance, and increased recycling. All of these trends will contribute to decreased MWF consumption. While the growth of the MWF market in the USA is slow or flat, the global use of metalworking lubricants appears to be growing significantly faster. Over the last six years the total global consumption of straightoil MWFs and water-dilutable concentrates has grown from an estimated 474 million to 638 million gallons [67, unpublished data from Lubrizol Corp., 1996]. This represents a growth of 35%, or a growth rate of roughly 5% per year. Approximately 40 to 50% of this 638 million gallons is straight-oil MWFs. Two thirds of the remaining material is soluble oils, with semichemical fluids representing 10 to 20% of the total MWF market and chemical solutions only accounting for approximately 5% (unpublished data from Lubrizol Corp., 1996).

It is very difficult to determine the number of pounds of synthetic lubricants that go into each of the four segments of MWFs. There are two major reasons for this. First, formulators are hesitant to give out information regarding the amount of synthetic lubricants they use in order to protect their formulation strategies. Second, the producers of synthetic lubricants do not know what percent of their products sold to formulators go into MWFs. This is because the formulators of MWFs are also likely to compound and sell other products like hydraulic fluids, gear lubricants, quenchants, and compressor lubricants. All of these products can be formulated with synthetic lubricants, and it is therefore very difficult for the polymer suppliers to know in what applications their products are being used.

36.9.2 Future of Synthetic Lubricants in MWFs There are three major factors that will influence the shape of the MWF market over the next decade. The first involves waste minimization, disposal, and environmental impact. The second factor is workpiece quality. The third is MWF toxicity. 36.9.2.1 Waste minimization and disposal The most important factor influencing the MWF market today is waste minimization and disposal. Waste disposal regulations are regional and may vary considerably between different municipalities. The appropriate choice of MWF may be greatly affected by these local regulations. The advantages and disadvantages of the four classes of MWFs with respect to waste minimization and disposal are summarized below. Straight-oil MWFs are relatively easy to maintain. With the absence of water, and assuming the product does not contain large amounts of fatty compounds, bacterial activity is minimal when compared to water based products. Once the useful life of the straight-oil MWF is over, the used product can be burned for fuel value or recycled [69]. However, the disposal of straight-oil products can be made significantly more difficult by the presence of chlorinated paraffin lubricity additives. Also, stricter air quality standards are in some cases making it more difficult to use oil based MWFs because of mist formation, smoke generation, and the evolution of volatile hydrocarbons. Of the water based MWFs, soluble oils are the most difficult to maintain. They are very susceptible to attack from microorganisms. They also tend to emulsify tramp oils and can be sensitive to water quality. Because they are two phase systems, they are not always amenable to commonly used fluid maintenance techniques such as ion exchange, ultrafiltration, and centrifugation. From a disposal point of view, soluble oils are relatively easy to treat. Soluble oils can be split rather easily into an oil phase, which can be incinerated or reclaimed, and a

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water phase. Often this water phase can be sent directly to the local publicly owned treatment works (POTW). However, as water regulations become increasingly strict, the cases where this aqueous phase does not meet disposal regulations are increasing. In these cases, secondary treatment is required. Soluble oils that contain chlorinated paraffins are becoming more difficult to get rid of. It is becoming harder to incinerate chlorine containing compounds, and local POTWs are starting to closely regulate the amount of chlorinated organic products that they will accept in a waste stream. Chemical fluids are the easiest MWFs to maintain. They are much more resistant to biological attack than soluble oils. Because they form true solutions in water, they are amenable to a wide variety of treatment techniques. They can be ion exchanged to keep the water hardness under control, centrifuged to remove metal fines and tramp oils, and filtered to remove solids and emulsified oils. Large central systems containing chemical MWFs have been maintained for periods of several years. Because chemical MWFs are easier to maintain than soluble oils, they generally last longer. This significantly reduces the volume of waste MWF that is generated. However, because all of the components are water soluble, removing the organic components from the water is difficult. Whether or not this is a problem depends upon the local regulations. Often a POTW will accept a spent chemical MWF if it is found to be compatible with their treatment system. Sometimes a surcharge is levied. Semichemical MWFs fall somewhere between soluble oils and chemical products. They are usually easier to maintain than soluble oils. However, for disposal purposes, semichemical products often take on the worst characteristics of soluble-oil and chemical MWFs. Much of the development work currently being done in the field of metalworking involves minimizing the environmental impact of the lubricants and coolants used to aid in the processing of the metal workpiece. Minimizing the environmental impact of a MWF can be done by making formulation changes that extend its useful life or that aid in the product’s disposal. A technology that may enable the formulation of soluble oils and semisynthetic MWFs that exhibit both extended service life and cleaner, more efficient posttreatment and disposal has recently been commercialized. This technology is based on the development of a destructible, nonionic surfactant. Under basic conditions, this family of surfactants is stable and provides all of the advantages of conventional nonionic surfactants. However, under acidic conditions, these surfactants readily and irreversibly split into their hydrophobic and hydrophilic constituents [70]. Once split, the surfactant can no longer effectively emulsify the oil phase of the MWF. The hydrophobic component of the splittable surfactant then separates out along with the hydrocarbon portion of the MWF. Once separated, the

hydrophobic constituents of the MWF can be removed, resulting in a greatly reduced FOG (fats, oils, greases) content. The hydrophilic portion of the surfactant remains in the aqueous phase, which can be more easily handled due to the removal of the hydrophobic components. Additionally, the treated aqueous phase has less environmental impact because the hydrophilic portion of the surfactant has faster biodegradation and lower aquatic toxicity than most common nonionic surfactants. These splittable surfactants contain a pH-sensitive functionality [71,72] that serves to link the hydrophobic alkyl part of the surfactant to the hydrophilic alkoxylated portion. In a basic aqueous environment, such as that which exists in MWFs, these surfactants are stable. However, if the solution is acidified, the pH-sensitive link becomes unstable and the surfactant breaks down into a hydrophobic compound and hydrophilic alkoxylate. Since the surfactant is now destroyed, the emulsion separates. The hydrophobic segment of the surfactant separates out with the rest of the oil where it can be removed from the aqueous portion of the MWF. Surfactants are needed in soluble-oil and semisynthetic MWFs to emulsify hydrocarbon oils that help to increase lubricity and corrosion protection. Anionic surfactants such as soaps and petroleum sulfonates are often used. This class of surfactant bears a negatively charged ion that makes up the hydrophilic portion of the molecule. A commonly used treatment technology for used MWFs based on anionic surfactants involves the addition of acid and alum or a polyelectrolyte that neutralize the charge and thus remove the emulsifying properties of the surfactant [71]. The oil portion of the MWF then separates out and can be readily removed. The problem with anionic surfactants is that they are prone to foaming and are sensitive to hard water. Nonionic surfactants are often chosen over anionics for use in MWFs because they have better wetting properties and are less sensitive to hard water [73]. Nonionic surfactants also allow the creation of tighter emulsions and are lower foaming that anionic surfactants [71]. The major problem with nonionic surfactants is that they are not amenable to treatment techniques commonly used to separate emulsions made with anionic surfactants. The splittable nonionic surfactants provide the benefits of traditional nonionic surfactants while allowing the formulation of a soluble-oil or semisynthetic metalworking, which can be easily treated to enable the reduction of the FOG content prior to disposal. Treatment involves acidification of the MWF with sulfuric or hydrochloric acid to a pH of between 3 and 5. The splitting of the acetal based surfactant will increase in efficiency as the pH of the system decreases. The temperature of the system being treated should be between 20 and 50◦ C. Splitting efficiency will increase with increasing temperature. Deactivation time typically will range from 30 to 120 min, depending on the

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system and process conditions. Also, since the purpose of the splittable surfactant is to permit the coalescence of the FOGs into a readily removable form, the incorporation of other products which act as surfactants or dispersants into the MWF should be avoided. Products which could impede the separation of the oil component of the MWF include polyacrylates, some phosphates, and conventional nonionic surfactants [71]. The splittable surfactants, like conventional nonionic surfactants, biodegrade at a moderate rate before being split. However, after being split in an acidic environment, the hydrophilic and hydrophobic components both exhibit much higher biodegradation rates [73]. The aquatic toxicity of the splittable surfactants before destruction is also similar to other nonionic surfactants. After splitting, the resulting hydrophilic component of the surfactant is essentially nontoxic to aquatic life. Most of the hydrophobe should be removed with the hydrocarbon phase of the acid treatment. Bacterial inhibition tests indicate that neither the surfactant nor its associated hydrophilic and hydrophobic components should negatively impact conventional biological waste-water treatment facilities when discharged at normally expected concentrations [73]. The aquatic toxicity of a splittable surfactant before and after acid treatment is shown in Table 36.29 [73]. 36.9.2.2 Workpiece quality Product quality is becoming extremely important. As a result, tolerance of workpiece corrosion, staining, and coating defects is decreasing. Two major causes of staining and coating defects are the presence of corrosive additives in the MWF and the incomplete removal of the lubricant prior to the coating process. Chlorinated hydrocarbons are one of the most commonly used EP lubricity additives in straight-oil and soluble-oil MWFs. However, during storage, the residual chlorine can cause significant staining of the metal workpieces. Because of their staining tendencies and the fact that their disposal is becoming increasingly difficult, much work is underway to develop replacements. This work is providing significant opportunities for the use of synthetic lubricants in MWFs. The complete removal of residual MWFs from the workpiece can be difficult when either straight-oil or soluble-oil products are used. Residual lubricant can prevent the adherence of coatings, like paint or enamel, causing unacceptable defects. These problems are becoming more widespread as the use of vapor degreasers and solvent-cleaning processes are coming under pressure for various environmental reasons. The need for water washable MWFs should result in the increased use of chemical and semichemical products. It will also favor the use of neat PAGs in straight-oil applications where solvent-cleaning

TABLE 36.29 Aquatic Toxicitya of a Splittable Acetal Based Nonionic Surfactant (9 mol Ethoxylate)

Surfactant Before acid treatment After acid treatment Hydrophobe Hydrophile

Acute Daphnia magna, 48 h LC50 (mg/L)

Acute fathead minnow, 96 h LC50 (mg/L)

Bacterial inhibition, 16 h IC50 (mg/L)

Selenastrum algal, 96 h EC50 (mg/L)

15

5

>10,000

6

0.3 10,000

2 >10,000

970 >10,000

0.5 >20,000

a LC , median lethal concentration; IC , inhibition concentration; EC , calculated concentration with expected 50 50 50

algal cell counts at 50% of control cell counts.

operations can be omitted because of the polymer’s water solubility. The complete burn-off characteristics of PAGs, polyisobutylenes, and alkyl benzenes will become more important since they sometimes enable the elimination of a cleaning operation prior to various high-temperature operations. As the need for improved workpiece quality grows, the production of defective parts will become unacceptable. The resistance to the higher cost of synthetic lubricants should therefore decrease as the price of seconds due to inadequate cleaning increases.

36.9.2.3 Toxicity Health concerns are a major concern in the metalworking industry because of the high exposure of the operator to the MWFs. Potential carcinogens such as polycyclic aromatic hydrocarbons [74], nitrosamines, and specific short-chain chlorinated paraffins have been successfully eliminated from use in MWF formulations [75]. Studies are currently underway to better understand the health effects of other chemicals commonly used in MWFs, including biocides [76,77], formaldehyde [78], diethanolamine, o-phenylphenol, and oil mists [79]. Bacterial growth in MWFs and the resulting endotoxin production is also receiving attention, especially the role mycobacteria endotoxin concentrations in respiratory distress [75]. In general, synthetic lubricant base stocks are very pure relative to petroleum-oil base stocks and are therefore less likely to contain potentially undesirable impurities. Also, synthetic lubricant base stocks such as polyalphaolefins [80], PAGs [81], and polyolesters (82) exhibit low orders of toxicity via skin absorption or ingestion. Some polyalphaolefins and PAGs have FDA status for various applications [81]. The high purity and low toxicity of these synthetic lubricant base stocks could lead to the increased usage of these products as the effort to understand the health effects of MWFs is increased. However, it is difficult to foresee the next toxicity issue or to predict

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how it will affect the use of synthetic lubricants in the metalworking industry.

36.10 CONCLUSIONS Synthetic lubricants will continue to play a major role as water-soluble lubricity additives in chemical and semichemical MWFs. The synthetic lubricants most commonly used in these MWFs are PAGs and their ester or acid derivatives. MWFs based on these products are excellent coolants and lubricants. They are in general easy to maintain, low in toxicity and environmental impact, nonstaining, and easy to remove from the finished workpiece. As environmental issues become more important, the use of this class of synthetic lubricants in MWFs is likely to increase. In straight-oil MWFs, due to cost considerations, the use of synthetic lubricants is basically limited to specialty applications. Synthetic esters, polyisobutylenes, and PAGs are all used in applications where clean burn-off or nonstaining characteristics are important. In conclusion, the use of synthetic lubricants in MWFs will grow. Increasingly strict environmental regulations affecting the workplace and air and water quality will favor the use of water based products and therefore PAG lubricants. Environmental and disposal related concerns will also reduce the use of solvent cleaning systems and chlorinated lubricity additives. Both of these factors should also favor the use of synthetic lubricants. The emphasis on product quality and the increasing cost of seconds will also increase the consumption of synthetic lubricants. As the costs associated with waste disposal, fluid maintenance, and workpiece quality all increase, the performance advantages of synthetic lubricants will outweigh their higher initial costs and lead to their increased application in metalworking lubricants.

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49. Guminski, R.D. and Willis, J.J., Development of cold-rolling lubricants for aluminum alloys, J. Inst. Met., 88, 481–492 (1960). 50. Richter, J.P., Cutting oil performance — a significant new machining test, ASLE preprint 77-LC-2C-3 (1977). 51. DeChiffre, L., Lubrication in cutting — critical review and experiments with restricted contact tools, ASLE Trans., 24, 340–344 (1980). 52. Ham, I., Fundamentals of tool wear,American Society of Tool and Manufacturing Engineers, MR68-617 (1968). 53. Brown, W.L., Notebook 12811, Union Carbide Chemicals and Plastics Company, Inc., unpublished (1987). 54. Nash, J.C. and Colakovic, N., Effect of synthetic additives on the performance of aluminum tapping fluids, Lubr. Eng., 41, 721–724 (1985). 55. Levesque, A. and McCabe, M., Improved synthetic coolants using a modified polyalkylene glycol, Lubr. Eng., 40, 664–666 (1984). 56. Faville, W.A. and Voitik, R.M., The Falex tapping torque test machine, Lubr. Eng., 34, 193–197 (1978). 57. Katsuki, A., Ueno, T., Matsuoka, H., and Kohara, M., Research on soluble cutting fluids for gear cutting — the influence of dilution ratio and the effect of synthetic fluids, Jpn. Soc. Mech. Eng., 28, 735–743 (1985). 58. Brown, W.L., The use of polyalkylene glycols in metal forming and drawing lubricants, STLE Annual Meeting, Denver, 1990. 59. Shell, NEODENE alpha olefins for metalworking lubricants, Technical literature SC:1927-954R, Shell Chemical Company, Houston, TX, 1994. 60. Denley, D.R., York, G., and Haberman, L.M., Olefinic versus paraffinic based in metalworking applications probed by three different microscopic techniques, Technical bulletin SC:2208-94, Shell Chemical Company, Houston, TX, 1994. 61. Koyama, S., Shido, S., Onodera, X., Hara, S., Tomari, Y., Saito, T., and Nara, T., Lubricating oil composition, U.S. Patent 5,171,903 (1992). 62. Shell, NEODENE additives for metalworking fluids, Technical literature SC:2222-95, Shell Chemical Company, Houston, TX 1995. 63. ILMA, Report on the Volume of Lubricants Manufactured in the United States and Canada by Independent Lubricant Manufacturers in 1995, Independent Lubricant Manufacturers Association, Alexandria, VA, 1996. 64. The Fredonia Group, Inc., Marketing news — Demand for industrial lubricants reach 1.3 billion gallons in 2000, Lubr. Ing., 52, 391 (1996). 65. Anon., HWB fluid market seen ready for sharp growth, Chem. Marketing Rep. 227, 27 (1985). 66. National Petroleum Refiners Association, 1989 Report on U.S. Lubricating Oil Sales, NPRA, Washington, DC, 1989.

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67. The Lubrizol Corp.Metalworking Fluid Trends, Lubrizol document 491 404-7 (1991). 68. Steigerwald, J.C., Report on the Volume of Lubricants Manufactured by the Independent Lubricant Manufacturers in 1989, Independent Lubricant Manufacturers Association, Alexandria, VA, 1989. 69. Childers, J.C., Metalworking fluids — A geographical industry analysis, Metalwork. Topi., 1, 1–4 (1989). 70. Anon., Product report, EPA endorses Union Carbide surfactant, Chem. Eng. News, 75, 44 (1997). 71. Galante, D.C., Hoy, R.C., Joseph, A.F., King, S.W., Smith, C.A., and Wizda, C.M., Aldehyde-based surfactant and method for treating industrial, commercial, and institutional waste-water, European Patent Application EP 0742177-A1 (1996). 72. Galante, D.C., Hoy, R.C., Joseph, A.F., King, S.W., Smith, C.A., and Wizda, C.M., Ketone-based surfactant and method for treating industrial, commercial, and institutional wastewater, European Patent Application EP 0742178-A1 (1996). 73. Union Carbide, Triton®SP-series surfactants, Technical Literature UC-1492, Union Carbide Corp., Danbury, ST, 1996. 74. McKee, R.H. and O’Connor, D.J., Dermal carcinogenicity studies of metalworking fluids, Lubr. Eng., 52, 97–102 (1996). 75. Rossmore, H.W., Health and environment, Lubr. Eng., 52, 94–96 (1996). 76. Passman, F.J., Formaldehyde risk in perspective: A toxicological comparison of twelve biocides, Lubr. Eng., 52, 69–80 (1996). 77. Rossmore, H.W. and Rossmore, L.A., Factors affecting selection of metalworking fluid biocides, Lubr. Eng., 52, 23–28 (1996). 78. Brutto, P.E., Pohlman, J.L., Ryan, A.M., and Smith, R., Formaldehyde control in metalworking fluids preserved with triazine biocide, Lubr. Eng., 52, 8–14 (1996). 79. Lucke, W.E., Health and safety of metalworking fluids, Lubr. Eng., 52, 596–604 (1996). 80. Booser, R.E., CRC Handbook of Lubrication and Tribology, Vol. III, CRC Press, Boca Raton, FL, 1994. 81. Rudnick, L.R. and Shubkin, R.L., Ed., Synthetic Lubricants and High-Performance Functional Fluids, 2nd ed., Dekker, New York, 1999. 82. Henkel, Emery 2941-B ISO 46 synthetic lubricant (basestock), Material Safety Data Sheet (MSDS) 2941-B, Henkel Corp.-Emery Group, Cincinnati, OH, 1994. 83. Anon, Self-Emulsifying Esters for Metalworking Fluids, Tribology and Lubrication Technology, 44–46, (2004). 84. Ollinger, C., Self-Emulsifying, Bio-based Lubricant — Naturally Better, Tribology and Lubrication Technology, 40–42 (2004).

37

Lubricants for Near Dry Machining Robert Silverstein CONTENTS 37.1 Introduction 37.2 Friction and Wear 37.3 Metalworking Operations 37.4 Near Dry Machining References

37.1 INTRODUCTION Metalworking may be man’s earliest known technological occupation as gold, silver, and copper were hammered into thin sheets and shaped into jewelry and household utensils as early as 5000 b.c. [1]. Processes involving metal removal can be dated back into antiquity as hammered or cast objects were polished with a stone to a finish; whereas a process such as metal cutting may have been developed in the middle ages [2]. The onset of the industrial revolution, and with it the demand for greater machining accuracy, new machine tools, higher cutting speeds, and more widespread use of grinding saw the development of coolants [2]. The advantage of employing a coolant was first discovered in 1883 when F.W. Taylor directed a stream of water on the tool in a turning operation. The cutting speed and hence, production, could be increased as much as 40% by the cooling effect of the stream of water [3]. Because water has a higher specific heat and heat of vaporization compared to hydrocarbon oils, cutting speeds could be increased because of the excellent cooling properties of water [4]. As a result increased cutting speeds and decreased production time started the metalworking industry on the path to higher output at lower cost. With the evolution of metalworking fluid technology from its earliest beginnings, greater output, longer tool life, and better surface finish have occurred, all of which are of great economic importance. The basic functions of cutting fluid are: • Direct cooling and control of the heat generated in the

metal cutting operation • Lubrication and friction reduction • Prevent welding or adhesion of the tool and workpiece

at metal contacts

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There are other important requirements that a cutting fluid provides: • Move chips away from the work area • Protect finished workpieces, tools and machinery against

rust and corrosion Since it has been well documented that the use of metal removal fluid increases cutting tool life by friction reduction and heat removal, various forms of metal removal fluid have been used in the machining process by the metalworking industry. Metal removal fluids help increase the quantity of parts that can be produced before a tool needs to be replaced, or enable a machine tool to produce parts faster with the same cutting tool life increasing productivity [4]. According to survey results from the 2002 National Petrochemical & Refiners Association (NPRA) Lubricating Oil & Wax Sales Report, total reported U.S. sales of metalworking oils were 80 MM gal in 1999, 83 MM gal in 2000, 60 MM gal in 2001, and 55 MM gal in 2002 (Figure 37.1). Furthermore, from the same survey, total reported sales of metal removing oils were 22 MM gal in 1999, 21 MM gal in 2000, 13 MM gal in 2001, and 13 MM gal in 2002 (Figure 37.2) [5]. The main metalworking fluid types primarily manufactured include: straight oils, soluble oils, semi-synthetic fluids, and synthetic fluids. Straight or neat oils are nonaqueous lubricants used as is. Soluble oils contain mineral oil and emulsifiers enabling them to be mixed in water. Semi-synthetic fluids contain a lesser percentage of mineral oil with a larger percentage of emulsifiers blended with water to form a microemulsion. Synthetic fluids are true chemical solutions that contain a large percentage of water and no mineral oil.

Metalworking oils 100 1999

2000

80 MM gal

2001 60

2002

40 20 0

FIGURE 37.1 Total reported U.S. sales metalworking oils 1999 to 2002 Metal removing oils 25

1999

2000

MM gal

20 2001

15

2002

10 5 0

FIGURE 37.2 Total reported U.S. sales metal removing oils 1999 to 2002

37.2 FRICTION AND WEAR A metalworking fluid should impart sufficient lubricity between the tool and the workpiece to cause a significant reduction in friction to occur [6]. Friction is the resistance to the motion of one surface over another. Lubricants are used to reduce the frictional forces. High friction results in heat and because more force or power is necessary to move the parts relative to one another, this friction reduces operating efficiency, and in the case of metalworking, shortens tool life, affects surface finish, and increases production time. When the lubricant film is insufficient to protect the metal surfaces, there is wear on one or both components. Wear is material loss directly caused by the interaction of asperities on the two surfaces while in relative motion to each other. Thus, wear will directly affect tool life and the finish and quality of the workpiece. When a lubricant is applied between the contacting surfaces, the friction and wear can be minimized. Three lubrication regimes are defined depending on the amount of lubricant film separating the surfaces. These are: • Boundary lubrication • Elasto-hydrodynamic (mixed lubrication) • Hydrodynamic lubrication

Hydrodynamic lubrication is a regime where the moving surfaces are essentially separated from each other. In this regime the viscosity of the oil in combination with the movement of the tool can produce a fluid pressure high enough to completely separate the two surfaces.

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Elasto-hydrodynamic lubrication is a regime where the film thickness is insufficient to completely separate the surfaces. In this regime the surface asperities make contact, which leads to wear. Lubricant in the contact area is continually replenished at the front of the contact [7]. The film thickness in the elasto-hydrodynamic regime is larger than in boundary lubrication but smaller than the film thickness in the hydrodynamic regime. Boundary lubrication is a regime where film thickness between the moving surfaces is only a few molecules thick. In this regime, because of the closeness of the moving surfaces, friction and wear are determined by properties of both the surfaces and the lubricant. Boundary films form because they reduce the surface energy and, therefore, are thermodynamically favored [8]. These films are formed by molecules that contain polar functional groups. Because of this, they orient onto the surface by either chemical or physical adsorption. Boundary lubrication can range from mild to severe conditions. Physical adsorption is a reversible process where molecules adsorb and desorb from a surface without chemical change. Additives that provide protection by physical adsorption are polar structures. This is because at least two phenomena must occur: the molecule must have a preferential affinity for the surface and it should have a preferred orientation on the surface so that a more closely packed arrangement can be achieved. Alcohols, acids, and amines are examples of long-chain molecules with functional groups at the end. Molecules that can pack tightly and orient in a close packed arrangement relative to the surface provide improved film strength. Because the forces

involved in physical adsorption are relatively weak, these films are effective at low to moderate temperatures. New molecules from the bulk lubricant are constantly available to replace those that physically desorb or are mechanically removed from the surface. Chemical adsorption, however, is an irreversible process where a lubricant fluid molecule or additive component reacts with the surface to form a low shear strength protective layer. As this new low shear strength material is worn away, additional additive reacts to form a new protective layer. Protection from chemical adsorption occurs at higher temperatures because chemical reactions are required to generate the actual species that form the surface films. Wear protection and friction reduction over a wide temperature range can be achieved by combining additives that function by physical adsorption and chemical adsorption. Between the low-temperature physically adsorbed layer and the high-temperature chemically adsorbed layer can be a temperature range over which there is poorer wear protection. This has been experimentally demonstrated where oleic acid was used as the normal wear additive and a chlorinated additive provided extreme pressure protection at the higher temperatures [9].

37.3 METALWORKING OPERATIONS Metal machining involves the removal of metal to produce an item of precise form and dimension from its initial rough form. A machine tool removes material by using power to force one or more precisely shaped tools against the workpiece, moving the two in one or more directions relative to each other [10]. Drilling is one of the most widely used machining processes to produce circular holes in metallic and nonmetallic materials. A drill is a rotary end-cutting tool, with the most common type being the twist drill. The drill, attached to either a stationary machine or hand held, is used to originate or enlarge a hole in a solid material. A drill will have cutting edges and straight or helical grooves or flutes, which allow for movement of chips and cutting fluids/coolants. Drill wear is not proportional to the number of holes drilled, but occurs at an accelerated rate. A reamer is a rotary cutting tool (similar to a drill) with one or more cutting elements, used to enlarge to an exact size and impart a smooth finish to, a previously drilled hole. Drilling can be characterized as in a rough form, whereas reaming is the exact form. Tapping is a procedure by which a thread is formed (machined) on the interior of the metal. An example would be a bolt hole. This process is also called thread tapping. On the exterior part of the metal it is called threading. The threading tools are called dies and can be held in a stationary holder used in a drill press or lathe.

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Turning is a machining process for producing external cylindrical or tapered forms by removing metal, typically with a single-point cutting tool. The single-point tool is moved parallel to the machine spindle for straight or contour turning of the outside diameter and turning or boring of an internal surface. The most common turning machines include lathes, automatic screw machines, automatic bar and chucking machines, and CNC automatic turning centers. Boring is for the most part internal turning, in that usually a single-point cutting tool forms internal shapes. Most machines that will perform turning operations will also perform boring operations, although there are boring machines available that instead of turning, will do drilling, reaming, and other related processes. The simplicity of operations and of cutting tool design and application makes planers and shapers the most universal of all machine tools. Flat surfaces can be produced in horizontal, vertical, and angular planes; odd and irregular shapes as well as internal surfaces can be machined. By the use of special tools, these machines can form flat or curved surfaces, and surfaces located in deep pockets and other not readily accessible places. Planning and shaping operations involve a single-point cutting tool fed into a moving workpiece making parallel cuts to remove metal from flat surfaces. Shapers are generally used for smaller operations. Milling produces machined surfaces by removing a material from the workpiece using a rotating cutter containing a certain number of teeth, which is dependent on the application. A characteristic feature of the milling process is that each tooth of the cutting tool takes a portion of material in the form of small, individual chips [11]. Broaching is a precision machining operation where a broach can be pulled or pushed through a workpiece opening or over its surface to produce an exact shape. A broach can finish an entire surface in a single pass as opposed to milling. Internal or External shapes can be cut using broaches. Grinding is an abrasive machining operation, whether rough or precise, whereby material is removed from a workpiece by the mechanical action of abrasive particles of irregular shape, size, and hardness producing smooth surfaces, flat, cylindrical, or irregularly shaped.

37.4 NEAR DRY MACHINING Historically, the metalworking industry has used metal removal fluids by flood application in machining operations. But because the costs associated with use, management, and disposal of flood coolants has risen over the years, in part due to increasing federal, state, and local regulations aimed at worker safety and fluid disposal, there has been a growing trend to utilize methods requiring less

metalworking fluid to reduce cost, protect the environment, and improve and protect worker health, without sacrificing productivity and quality. The basic functions of a flood coolant are:

• Cool the tool and workpiece • Flush away chips • Lubricate the cutting tool

Guerbet alcohols have high molecular weight, low irritation properties, and low volatility. Since they are saturated they exhibit excellent oxidative stability at elevated temperatures, in addition to excellent color initially and at elevated temperatures [13]. They are clear, water white, essentially odor free, oily biodegradable liquids. R1 CH2 CH2 | R2 CH2 CH2 OH

Near dry machining can be described as a process by which a minimum quantity of lubricant mixed with air is continuously applied to the tool/workpiece interface during the machining operation. Thus, the application of near dry machining lubricants, which are for the most part consumed in the machining process, yields desirable economic, employee, and environmental benefits. One of the earlier examples of near dry machining lubrication could be seen in aircraft manufacturing. Freon® gas was used as a lubricant and coolant in three distinct areas of the riveting process — drilling, rivet insertion, and rivet-head milling. Because of the undesirable effects of Freon® gas on the ozone layer, manufacturing research and development engineers introduced an alternate method to cooling tools, using fatty alcohol lubricant compositions to efficiently lubricate tools preventing heat buildup while greatly reducing the reworking after drilling that had been necessary with Freon® because of exit burrs, oversized holes, and a rough finish on the inside surface of the holes. These lubricants were used in drilling, reaming, and coldworking of fastener holes in aircraft wing skins; installation of wedge-head lock bolts; lubrication of hand drills; and on machinery that automatically drill rivet holes and install rivets on large sections of airplanes. It was shown that the application of minimal quantities of lubricant could reduce friction, speed production, increase tool life, and improve surface finish and hole quality in a number of machining applications. Near dry machining lubricant compositions tend to be more expensive on a per unit basis compared to flood coolants, but when overall costs are calculated, they can cost considerably less. Near dry machining lubricant compositions may contain the following chemistries:

1. Guerbet alcohols via the Guerbet reaction are products of the condensation of alcohols at high temperature and pressure in the presence of sodium alkoxide or copper by a dehydrogenation, aldol condensation, and hydrogenation sequence [12]. Both natural and synthetic alcohols may be used as raw materials for Guerbet alcohol synthesis. The end products (2-alkyl alkanols) are linear straight chain alcohols with defined, not random branching. Because they are branched, they remain liquid at very low temperatures.

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where R1 and R2 are alkyls. 2. Fatty alcohols are long chain aliphatic or linear alcohols. Monohydric aliphatic alcohols of six or more carbon atoms are generally referred to as higher or fatty alcohols. Higher alcohols are generally nontoxic and cause no primary skin irritation. Hexadecanol and octadecanol are used extensively in the cosmetics and pharmaceuticals industries and in lubricants [14]. Cetyl alcohol (1-hexadecanol) is a waxy, white solid produced from natural feedstocks such as coconut and palm kernel oil. The refined oil is first converted to methyl ester, which is fractionated then hydrogenated to alcohol, which is further fractionally distilled [15]. RCH2 OH where R = C5 alkyl and higher. 3. Synthetic esters are chemical compounds typically derived from the reaction of an organic acid with an alcohol. The ester group is responsible for physical properties such as volatility and flash point, as well as other properties such as thermal stability, hydrolytic stability, solvency, lubricity, and biodegradability [16]. The main types of esters are acid/anhydride centered as exemplified by monoesters, diesters, phthalates, and trimellitates; alcohol centered such as polyols; and polymeric esters such as polyalkylene glycol esters [17]. R1 COOR2 4. Vegetable oils such as rapeseed, canola, or soybean oil, or the methyl esters of fatty acids from vegetable oil such as rape or soy methyl ester. The process of extracting and refining vegetable oils involves a number of steps [18]. Rapeseed oil contains a large percentage of unsaturated carbon chain lengths greater than C-18, while canola and soybean oil are composed predominantly of C-18 unsaturated carbon chain lengths. Vegetable oils are predominantly triglycerides, which are tri-esters where three fatty acid groups are esterified to a glycerol backbone [19]. The fatty acid groups in a triacylglycerol are mostly responsible for the physical and performance properties of a purified vegetable oil [20]. Most vegetable oils are mixed triglycerides because of the presence of more than one type

of fatty acid [21]. Additionally, triglycerides can be converted to methyl esters and glycerine via transesterification utilizing methanol [22]. The glycerine is concentrated and refined. The methyl esters are purified and separated into individual esters by fractional distillation.

TABLE 37.1 Examples of Commercially Available Near Dry Machining Lubricants Product

H2 COOCR1

Acculube Boelube® Coolube Tri-cool

| HCOOCR2 | H2 COOCR3

where R1 , R2 , R3 are fatty acids. In the near dry machining process, the liquid lubricant can be delivered as fine droplets or oil fog through one or more nozzles positioned accordingly around the cutting tool or through a rotating spindle and tool with internal channels, as with oil hole tools. Delivering the lubricant as fine droplets to the cutting edge is necessary in order to reduce friction between the chip, tool, and workpiece, and prevent the chips from adhering to the tool cutting edge. Because the chips have less contact with the tool, a larger percentage of the heat is transferred and carried away with the chip, allowing the tool to stay cooler [23]. The near dry machining process requires continual reapplication of lubricant to the tool cutting edge and wear surfaces. This can be accomplished externally on band and circular saws, milling cutters, broaches, etc., as well as on shallow drilling and tapping operations. Using a coaxial supply of compressed air and lubricant to the nozzle, the nozzle directs lubricant droplets in the compressed air directly to the cutting edge. The compressed air will help move chips from the tool cutting edge as the fine lubricant droplets form a thin film at the point of contact to reduce friction. Lubricant can also be delivered continually through tools with internal channels directly to the cutting edge in drilling, reaming, tapping, boring, gun drilling, etc. In near dry machining the goal is high efficiency, which is achieved as a result of using as little lubricant as possible. Although the lubricant generally has high film strength, it must be continually reapplied to the cutting edges of tools and wear surfaces. Typically, lubricants used in near dry machining are non water-soluble; they may comprise mineral or synthetic oils, ester or fatty alcohol, with ester or fatty alcohol being more common. Depending on the type of machining operation, tool, workpiece composition, etc., the amount of lubricant usage can range from less than 50 ml/h to more often less than 10 ml/hour. Because minimal amounts of lubricant are used, the near dry machining process yields nearly dry workpieces and dry chips [24].

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Supplier Illinois Tool Works Inc. The Orelube Corporation Unist, Inc. Trico Mfg. Corp.

Traditional metal removal fluids (oil and water miscible) can also be applied at reduced levels (0.08 l/min or 0.02 gal/min) in a process described by the authors as microlubrication, eliminating the need for a required collection system for the applied fluid [25]. Near dry machining lubricants, the majority of which are in liquid form, can be formulated into solid and paste forms too. Pastes are extremely cost effective in singlepoint work such as tapping, drilling, or reaming. A minimal amount of paste can be brushed on to the tool, or the tool can be dipped into the paste, in order to obtain highquality finish and increased tool life with little or no cleanup required. Solids come in a variety of shapes and sizes to accommodate ease of application in drilling, tapping, reaming, abrasive belts, files, deburring tools, grinding wheels, awls, chisels, band, circular and hand saw blades. They can improve tool life by reducing heat buildup in belt, disc, or wheel-grinding operations. Typically the solid form is applied to the tool before start-up. In a block form, it can be hand held and a drill bit can be touched to the block before drilling or the block may be swiped across the surface to be drilled. Only a minimal amount is required when drilling through thin material. There are a number of near dry machining lubricants of different composition in the marketplace, not all are priced similarly or perform equally (Table 37.1). But in principle, they all share common goals — improvement in tool life and surface finish, reduction in lubricant usage and subsequent cleaning and disposal costs, reduced environmental impact, improved housekeeping, and easier chip handling and recycling.

REFERENCES 1. John A. Schey, Tribology in Metalworking, American Society for Metals, Metals Park, Ohio, 1983, p. 1. 2. John A. Schey, Tribology in Metalworking, American Society for Metals, Metals Park, Ohio, 1983, p. 5. 3. William L. Brown, Synthetic Lubricants and HighPerformance Functional Fluids, 2nd ed., Leslie R. Rudnick and Ronald L. Shubkin (Eds.), Marcel Dekker, New York, 1999, p. 628.

4. T. McClure and M. Gugger, Microlubrication in metal machining operations. Lubr. Eng., Vol. 58, 2002, p. 15. 5. The National Petrochemical & Refiners Association 2002 Report on U.S. Lubricating Oil Sales (used by permission of NPRA). 6. Robert Silverstein and Leslie R. Rudnick, Lubricant Additives, Leslie R. Rudnick (Ed.), Marcel Dekker, New York, 2003, pp. 525–527. 7. J. Pemberton and A. Cameron, A mechanism of fluid replenishment in elastohydrodynamic contacts. Wear, Vol. 37, 1976, pp. 185–190. 8. Boundary Lubrication (Texaco Inc.), Vol. 57, 1971. 9. D.D. Fuller, Theory and Practice of Lubrication for Engineers, John Wiley & Sons, Inc., New York, 1984. 10. The Petro-Canada Guide to Metalworking. Petro-Canada, 1986, p. 2. 11. Ronald A. Walsh, McGraw-Hill Machining and Metalworking Handbook. McGraw-Hill, New York, 1994, pp. 580–596. 12. Hawley’s Condensed Chemical Dictionary, 13th ed., Revised by Richard J. Lewis, Sr. Van Nostrand Reinhold, 1997, p. 555. 13. Anthony J. O’Lenick Jr. and Raymond E. Bilbo, Guerbet Alcohols A Versatile Hydrophobe. Soap/Cosmetics/Chemical Specialties for April 1987, pp. 52–54. 14. Kirk-Othmer, Concise Encyclopedia of Chemical Technology, John Wiley & Sons, Inc., New York, 1985, pp. 52–53. 15. Procter & Gamble Chemicals Technical Data Sheet, CO1695 Cetyl Alcohol, 2001.

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16. Steven James Randles, Synthetic Lubricants and HighPerformance Functional Fluids, 2nd ed., Leslie R. Rudnick and Ronald L. Shubkin (Eds.), Marcel Dekker, New York, 1999, p. 63. 17. Steven James Randles, Synthetic Lubricants and HighPerformance Functional Fluids, 2nd ed., Leslie R. Rudnick and Ronald L. Shubkin (Eds.), Marcel Dekker, New York, 1999, p. 64. 18. Vegetable Oils and Fats, Goran Magnusson, Gunilla Hermansson, and Rita Leissner (Eds.), Karlshamns Oils and Fats AB, Halls Offset, Vaxjo, Sweden, 1989, p. 68. 19. S. Lawate, K. Lal, and C. Huang, Tribology Data Handbook, E.R. Booser (Ed.), CRC Press, Boca Raton, FL, 1997, p. 103. 20. S. Lawate, K. Lal, and C. Huang, Tribology Data Handbook, E.R. Booser (Ed.), CRC Press, Boca Raton, FL, 1997, p. 104. 21. Douglas M. Considine (Editor-In-Chief), Chemical and Process Technology Encyclopedia, McGraw-Hill Book Company, New York, 1974, p. 1129. 22. Morrison and Boyd, Organic Chemistry 3rd ed., Allyn and Bacon, Inc., Boston, 1973, p. 682. 23. Dierk Stabler, Basics of Minimal Lubrication Technology. Fraunhofer Institut ICT, Pfinztal, Germany, p. 1. 24. Dierk Stabler, Basics of Minimal Lubrication Technology. Fraunhofer Institut ICT, Pfinztal, Germany, p. 2. 25. T. McClure and M. Gugger, Microlubrication in metal machining operations. Lubr. Eng., Vol. 58, 2002, p. 16.

38

Lubricants for the Disk Drive Industry Tom E. Karis CONTENTS 38.1 Introduction 38.2 Recording Disk Lubricants 38.2.1 Properties 38.2.1.1 Viscoelastic (Rheological) 38.2.1.2 Dielectric 38.2.1.3 Thin Film Viscosity 38.2.1.4 Vapor Pressure 38.3 Spindle Motor Lubricants 38.3.1 Ball Bearing Spindle Motor Bearing Grease 38.3.1.1 Yield Stress at Temperature 38.3.1.2 Hydrodynamic Film Thickness 38.3.1.3 Grease Electrochemistry 38.3.2 Ball Bearing Spindle Motor Ferrofluid Seal 38.3.3 Fluid Bearing Motor Oil 38.3.3.1 Viscosity and Vapor Pressure 38.4 Conclusions and Future Outlook Acknowledgment References

38.1 INTRODUCTION When thinking of a disk drive, one picture that comes to mind is that of digital data bits stored on a spinning disk housed inside a device such as a computer, digital video recorder, or MP3 jukebox. The precision and reliability of these high speed rotating devices is, perhaps, one of the leading examples of micro electromechanical systems and nanotechnology at work today. For example, the magnetic recording read/write head floats on an air lubricated bearing just 10 nm away from the disk surface with a relative velocity, which is often about 10 m/sec. That is a shear rate of 1 billion m/sec, and, occasionally, the recording head contacts asperities on the disk surface. With the data track width decreasing below 200 nm, the tolerance of the spindle motor on which the disks are mounted must have increasing stiffness with vibration amplitudes that are well below the track width to minimize servo seek time and track following. Ball bearing spindle motors used in the past have reached their limit, and future high performance products are incorporating fluid dynamic bearing spindle motors. In addition, when there is a high relative velocity between metallic and insulating components, electrostatic charge generation and dissipation must be

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controlled. Lubricants play a key enabling role in all of the above vital requirements for the disk drive industry, and fundamental understanding of the lubrication requirements and the detailed physical chemistry of their performance are essential to the advancement of the technology. This chapter focuses on lubricants for the magnetic recording disk, and the spindle bearing motor. Throughout the chapter, much emphasis is placed on the analytical tools that are common to all of the lubricants. Similar techniques are applied to characterize the physical properties of lubricants that influence their performance. Rheological measurements are employed not only to characterize the viscosity, but to estimate the short time dynamic response of disk lubricants through time–temperature superposition. Shear rheometry is exploited to characterize the yield stress of grease, as well as the effect of blending on fluid dynamic bearing motor oils. Dielectric spectroscopy is widely utilized to explore the dipole relaxation of disk lubricant end groups. Dielectric permittivity and conductivity measurement are used for development of conductivity additives for ferrofluid used in motor seals, and to investigate the effects of contamination on ball bearing grease electrochemistry.

Another powerful technique that is highlighted in this chapter is Fourier transform infrared spectroscopy. This powerful technique can be used to study thin films in reflection or bulk samples in transmission. Examples are shown in which infrared spectroscopy is also applied to identify the reaction product formed during electrochemical oxidation of ball bearing grease. Thermal analysis is employed to measure the vapor pressure of disk lubricants, and a model is described that simulates evaporation of polydispersed lubricants based on molecular weight distributions measured by gel permeation chromatography. Surface energy from measured contact angles is combined with the chemical kinetic model for viscous flow and evaporation to predict the viscosity of molecularly thin films and to understand factors that limit lubricant spin-off from rotating disks. The chemical kinetic model is also employed to combine vapor pressure and viscosity data in the quest for the molecular structure of a fluid bearing motor oil that has both low viscosity and vapor pressure. Not only are the techniques illustrated here with examples from the disk drive industry applicable to the lubrication industry in general, but they also will be particularly useful in adapting these methodologies to the tribology of micro and nano electromechanical systems.

38.2 RECORDING DISK LUBRICANTS The soft magnetic layers on the magnetic recording disk substrate are typically overcoated with about 5 nm of amorphous carbon. Since the carbon has a relatively high surface energy, a low surface energy lubricant is applied on top of the overcoat. The most widely used perfluoropolyethers (PFPEs) are those having the Z type backbone chain. These are random copolymers with the linear backbone chain structure

TABLE 38.1 Molecular Structure for Some of PFPE End Groups on the Z Type PFPE Chain A20H has one Zdolend group. Name

Structure

Z

CF3

Zdol

CF2CH2OH OH CF2CH2OCH2CHCH2OH

Ztetraol Zdiac

CF2COOH

Zdeal

CF2COOCH3 CF2CH2(OCH2CH2)1.5OH

Zdol TX

O AM-3001

A20H

CH2

CF2CH2OCH2

P CF2CH2O N

ZDPA

N P

O CF3

P N

CF2CH2N

O 5 CH2CH2CH3 CH2CH2CH3

The molecular structures of the D and K series of PFPEs, also considered for magnetic recording disk lubricants, are shown in Table 38.2. The repeat unit of the D chain is perfluoro n-propylene oxide. The D series includes Demnum with nonpolar end groups, Demnum SA with a hydroxyl end group, and Demnum SH with a carboxylic acid end group. The repeat unit of the K chain is perfluoro isopropylene oxide. The K series includes Krytox with nonpolar end groups and Krytox COOH with a carboxylic acid end group.

X–[(O CF2 )m –(O CF2 CF2 )n –(O CF2 CF2 CF2 )p –(O CF2 CF2 CF2 CF2 )q ]x0 –O X, where X is the end group. A wide range of end groups is available to tailor the lubricant for optimum lubrication properties. The end groups for some of the commercially available lubricants are shown in Table 38.1. The adsorption energy of end groups (other than –CF3 ) on the carbon overcoat surface is higher than that of the backbone chain [1,2]. The X1P type end group on A20H [3,4] is sterically large in comparison to the chain monomers [5], and the X1P end group molecular weight of about 1000 Da is a significant contribution to the molecular weight of commonly used backbone chains of 2000 to 4000 Da [6]. Lower molecular weight end groups, also intended to passivate Lewis acid sites, are derived from Zdol with dipropylamine [7], and referred to as ZDPA.

Copyright 2006 by Taylor & Francis Group, LLC

38.2.1 Properties Perfluoropolyethers are attractive as magnetic recording disk lubricants because of their low surface energy, low vapor pressure, wide liquid range, transparency, and lack of odor. PFPEs are related to polytetrafluoroethylene, but they have lower glass transition temperatures [8–10]. The first commercially available PFPEs had perfluoromethyl end groups, and are referred to as nonpolar PFPEs. More recently, polar PFPEs with hydroxyl, carboxylic acid, and other polar end groups have come into widespread use. The polar end group provides an additional means to adjust the fluid properties and the interaction with surfaces. PFPEs with polar end groups are predominantly used to lubricate present day rigid magnetic recording media. Their versatility has motivated considerably the detailed study of PFPEs. The bulk viscosity and glass

TABLE 38.2 Molecular Structure for D and K Type PFPEs Name

Structure CF3CF2CF2O

Demnum S100

CF3CF2CF2O

Demnum SA

Demnum DPA

CF3CF2CF2O

CF2CF2CF2O

CF2CF2CF2O

CF2CF2CF2O

xo

xo

CF2CF3

CF2CF2CH2

CF2CF2CH2N xo

OH

CH2CH2CH3 CH2CH2CH3 O

Demnum SH

CF3CF2CF2O

CF2CF2CF2O

xo

CF2CF2C OH

CF3 Krytox 143AD

CF3CF2CF2O

CF

CF2O

xo

CF3 O

CF3 Krytox COOH

CF3CF2CF2O

transition temperature of the nonpolar PFPEs have been extensively characterized by Sianesi et al. [8], Ouano et al. [11], Cantow et al. [12], Marchionni et al. [13–16], Cotts [17], and Ajroldi et al. [18]. Subsequent investigations have begun reporting the properties of PFPEs with polar end groups, for example, Danusso et al. [19], Tieghi et al. [20], Ajroldi et al. [21], and Kono et al. [22]. The composition and molecular weight of several PFPE lubricants, measured by nuclear magnetic resonance (NMR) spectroscopy [23] is given in Table 38.3. 38.2.1.1 Viscoelastic (rheological) Oscillatory shear and creep measurements were done with a Carri-Med CSL 500 (now TA Instruments) Stress Rheometer with the extended temperature module and a 40 mm diameter parallel plate fixture. The dynamic strain amplitude was 5%, and this was within the range of linear viscoelasticity for these materials. The storage G and loss modulus, G , were measured between 1 and 100 rad/sec at each temperature. Typically, measurements were done each 20◦ C from −20 to −100◦ C. Low temperature measurements were performed to provide the high frequency properties that are required for calculations at the short timescales encountered in asperity contacts. The data measured at low temperature is transformed to high frequency through time–temperature superposition with Williams Landel Ferry (WLF) coefficients [24] that

Copyright 2006 by Taylor & Francis Group, LLC

CF

CF2CF3

CF2O

CF

C OH

xo

are derived from the rheological measurement data. The PFPEs were linearly viscoelastic at these test conditions. The dynamic properties were independent of strain amplitude, and no harmonic distortion of the sinusoidal angular displacement waveform was observed even at the lowest measurement temperatures. Time–temperature superposition was employed to obtain the master curves [25]. Viscosities for the lubricants at each temperature were calculated from the steady state creep compliance. The glass transition temperatures, Tg , were measured using a modulated differential scanning calorimeter manufactured by TA Instruments model number 2920 MDSC V2.5F. The samples were cooled to −150◦ C and heated to 20◦ C at 4◦ C/min with a 1.5◦ modulation over a period of 80 sec. The differential heat flow and temperature phase shift were measured to determine the reversible and nonreversible components of the heat flow. The glass transition temperatures of several PFPE lubricants are listed in Table 38.4. The temperature dependence of the viscosity is shown in Figures 38.1 through 38.3 as the ratio of the viscosity to the molecular weight η/Mn plotted as a function of distance from the glass transition temperature T − Tg . The ratio η/Mn is proportional to the segmental friction coefficient [25], and shifting the temperature by Tg takes into account the effect of Tg on the relaxation times. The smooth curves are from the regression fit of the shift factors in the WLF equation. A subset of the Z series showing the effects of different end groups are shown in Figure 38.1. Most

TABLE 38.3 The Composition of Several PFPEs Lubricant Z03 Zdiac Zdeal Ztetraol 2000 Ztetraol 1000 Ztx Zdol4KL819 Zdol4KL492 Zdol4KL990 Zdol4KBL598 Zdol4KL905 Zdol 2500 Demnum S100 Demnum SA2000 Demnum SA2 Demnum DPA Demnum SH Krytox 143 AD Krytox COOH

m

n

p

q

m/n

O/C

x

Mn (Da)

0.530 0.508 0.567 0.485 0.523 0.475 0.612 0.568 0.515 0.492 0.469 0.456 — — — — — — —

0.405 0.435 0.426 0.515 0.477 0.517 0.383 0.425 0.475 0.508 0.526 0.544 — — — — — — —

0.057 0.048 0.003 0 0 0.007 0.003 0.005 0.005 0 0.0025 0 — — — — — — —

0.008 0.008 0.004 0 0 0.001 0.0025 0.002 0.005 0 0.0025 0 — — — — — — —

1.31 1.17 1.33 0.94 1.10 0.92 1.60 1.34 1.08 0.97 0.89 0.84 — — — — — — —

0.754 0.744 0.782 0.743 0.762 0.736 0.720 0.693 0.666 0.658 0.650 0.728 0.333 0.333 0.333 0.333 0.333 0.333 0.333

73.4 24.4 22.8 23.2 14.2 22.7 46.5 39.1 39.2 47.2 41.5 26.1 31.7 12.6 18.6 48.4 18.3 39.8 32.3

6810 2310 2070 2300 1270 2230 4000 3600 3600 4300 3900 2420 5230 2080 3080 8100 3040 6580 5370

The degree of polymerization x = xo + 2. The Zdol4K series are different batches of Zdol 4000 from the manufacturer.

Z03 Zdiac Zdeal Ztetraol 2000 Ztx Zdol4KL 905 Zdol 2500

1.E+04

Lubricant Z03 Zdiac Zdeal Ztetraol 2000 Ztx Zdol4KL819 Zdol4KL492 Zdol4KL990 Zdol4KBL598 Zdol4KL905 Zdol 2500 Demnum S100 Demnum SA2000 Demnum SA2 Demnum DPA Demnum SH Krytox 143 AD Krytox COOH

Tg

C1

C2

−131.8 −118.4 −120.2 −112.2 −109.9 −126.7 −123.3 −119.7 −117.2 −115.6 −113.6 −111.2 −114.1 −110.2 −110.7 −110.1 −66.1 −61.4

14.13 18.14 17.25 23.22 15.67 11.73 16.27 15.98 16.66 10.54 13.62 13.06 13.75 13.77 12.13 13.27 12.22 11.97

24.51 25.90 23.64 45.81 42.75 38.46 49.82 52.22 37.14 38.05 59.72 62.76 43.89 62.11 78.52 63.56 31.65 40.79

The reference temperature for C1 and C2 is Tg .

Copyright 2006 by Taylor & Francis Group, LLC

1.E+02 h/Mn(Pa-sec/Da)

TABLE 38.4 The Glass Transition Temperature and the WLF Coefficients of Several PFPEs

1.E+00

1.E–02

1.E–04

1.E–06

0

25

50

75 T –Tgo

100

125

150

FIGURE 38.1 The ratio of viscosity to molecular weight as a function of distance from the glass transition temperature for the PFPE Z series

of the PFPEs shown in Figure 38.1 had an oxygen to carbon (O/C) ratio of about 0.65, except for the Zdeal, which had an O/C ratio of 0.694. The segmental friction coefficient was the lowest for nonpolar Z03 and the Zdol4KL905 (and Zdol4KL819 shown in Figure 38.2), and highest for

Zdol4KL819 Zdol4KL492 Zdol4KL990 Zdol4KL598 Zdol4KL905

1.E+04

1.E+02 h/Mn(Pa-sec/Da)

h/Mn(Pa-sec/Da)

1.E+02

1.E+00

1.E–02

Demnum S100 Demnum SA2000 Demnum SA2 Demnum DPA Demnum SH Krytox 143AD Krytox COOH

1.E+04

1.E+00

1.E–02

1.E–04 1.E–04 1.E–06

0

25

50

75 T–Tgo

100

125

150

FIGURE 38.2 The ratio of viscosity to molecular weight as a function of distance from the glass transition temperature for the PFPE Zdol4K series, showing the effect of O/C ratio. The smooth curves are from the WLF equation

the Ztetraol, with two hydroxyls on each end group. The segmental friction coefficients for Z chains with other types of end groups were in between the Z03 and Ztetraol. The friction coefficient for the Zdeal was slightly lower than the Zdiac, because the methyl ester probably blocks some of the hydrogen bonding. The Ztx, Zdiac, and Zdol2500 had nearly the same segmental friction coefficient as one another. The effect of the O/C ratio on the segmental friction coefficient for the Zdol 4K series is shown in Figure 38.2. The lots with intermediate O/C ratio, Zdol4K L492, 990, and 598, were above Zdol4K L819 with (high) O/C = 0.72 and Zdol4KL905 with (low) O/C = 0.65, which were about the same as one another, even though their Tg are 11◦ apart. This surprising relationship may arise from a dependence of the segmental friction coefficient on the chain flexibility and the cohesive energy density that is different from the dependence of Tg on these properties. The segmental friction coefficient for the D and K series, shown in Figure 38.3, was within the range of that observed for the Zdol4K series in Figure 38.2. The nonpolar Krytox and the Krytox COOH were nearly the same as one another, and were below the Demnum for most of the Demnum series. All of the Demnum series were nearly the same as one another. The addition of polar end groups had little effect on the segmental friction coefficient of the D and K. The storage and shear moduli, G and G , were measured and shifted along the temperature axis to obtain the master curves. The WLF coefficients [24] were calculated from the shift factors aTo (T ) by nonlinear regression

Copyright 2006 by Taylor & Francis Group, LLC

1.E–06 0

25

50

75 T–Tgo

100

125

150

FIGURE 38.3 The ratio of viscosity to molecular weight as a function of distance from the glass transition temperature for the PFPE Demnum and Krytox series. The smooth curves are from the WLF equation

analysis using the functional form log(aTo ) =

−C1 (T − To ) C2 + (T − To )

(38.1)

where the reference temperature To = Tg , and C1 and C2 are the WLF coefficients with respect to Tg . The WLF coefficients are listed in Table 38.4. Our 10.5 < C1 < 23.5, and 23.5 < C2 < 79 are consistent with those for nonpolar PFPEs Y and Z reported by Marchionni et al. [13]. Up to three Maxwell elements were derived from the master curves by nonlinear regression analysis from the linearly viscoelastic shear storage modulus, G , and loss modulus, G : G =


Gi (ωaT τi )2 o 1 + (ωaTo τi )2

(38.2)

i

and G =


i

Gi ωaTo τi 1 + (ωaTo τi )2

(38.3)

where ω is the shear strain sinusoidal oscillation frequency. The shear rigidities Gi and corresponding relaxation times τi are listed in Table 38.5. The WLF coefficients, the shear rigidities, and the relaxation times provide the solid curves in Figures 38.4 to 38.6. The dynamic response for the Z series with different end groups is shown in Figure 38.4. The polar end group increases the relaxation times. Two relaxation times are observed in the Zdiac, Zdeal, and Zdol4KL905. Three relaxation times are

TABLE 38.5 The Coefficients of the Maxwell Elements from the Master Curves at Reference Temperature Tg η(−20◦ C ) (Pa-sec) Lubricant

G1 (kPa)

τ1 (sec)

G2 (kPa)

τ2 (sec)

G3 (kPa)

τ3 (sec)

From creep

From dynamic

Z03 Zdiac Zdeal Ztetraol 2000 Ztx Zdol4KL819 Zdol4KL492 Zdol4KL990 Zdol4KBL598 Zdol4KL905 Zdol 2500 Demnum S100 Demnum SA2000 Demnum SA2 Demnum DPA Demnum SH Krytox 143 AD Krytox COOH

49.3 28.4 31.1 36.6 55.6 4.0 43.4 49.7 48.4 19.3 51.9 11.8 54.0 35.1 42.0 47.5 55.3 44.9

1.11E + 07 5.17E + 10 6.31E + 09 4.02E + 13 7.42E + 06 3.56E + 05 1.51E + 07 5.77E + 06 2.10E + 08 2.40E + 03 5.03E + 04 4.52E + 04 4.09E + 05 5.49E + 04 1.87E + 08 2.28E + 04 1.35E + 05 3.08E + 04

— 5.6 4.0 8.9 — 5.2 — — — 19.7 — 38.0 — 10.4 3.38 6.8 3.1 4.7

— 3.09E + 09 1.44E + 08 3.86E + 12 — 7.91E + 04 — — — 2.21E + 02 — 9.91E + 03 — 6.43E + 03 1.22E + 07 1.60E + 03 4.30E + 03 1.21E + 03

— — — 5.5 — 14.3 — — — — — 3.4 — — — — 1.0 2.3

— — — 3.16E + 11 — 8.13E + 03 — — — — — 2.84E + 02 — — — — 1.16E + 02 7.17E + 01

0.2 1.0 0.4 83 2.0 0.2 1.3 1.3 2.3 0.3 2.2 3.7 1.1 2.8 3.6 2.9 81 220

0.2 1.0 0.4 70 1.6 0.5 1.1 1.5 1.4 0.2 2.0 1.5 1.5 2.1 2.5 2.8 69 200

The steady shear viscosity measured in creep, and the zero shear viscosity calculated from the dynamic data at −20◦ C.

observed in the Ztetraol and Zdol4KLl819. At ambient temperature the Z03 has nearly the shortest characteristic time, τ1 , of all the PFPEs, even though it has the highest Mn . Ztetraol had the longest τ1 within the Z series. The response of the Zdol with a range of O/C ratio is shown in Figure 38.5. The O/C ratio had a significant effect on the dynamic response of the Zdol 4K series. The dynamic response of the Demnum and Krytox are shown in Figure 38.6. The τ1 for the Krytox is much longer than that for the Demnum. The linear viscoelastic properties, zero shear viscosity η = G1 τ1 and the equilibrium recoverable compliance Je0 = τ1 /η may be calculated from the dynamic properties listed in Table 38.5. The viscosity or relaxation time can be calculated at an arbitrary temperature T with the ratio of the shift factors from the WLF equation. For example, τ1 (T ) or η(T ) = η(Tg )aTg (T ). The relaxation times for the Z series of lubricants calculated at 50◦ C is shown in Figure 38.7.

dielectric analyzer (DEA) model 2970 with a single surface ceramic sensor. Measurements were taken at an applied voltage of 1 V. The frequency sweep ranged from 0.1 to 10,000 Hz. Measurements were done at temperatures ranging from −100 to 100◦ C. The data at the various temperatures were shifted relative to reference temperature T0 = 50◦ C to provide the dielectric master curves for several magnetic recording disk lubricants, shown in Figure 38.8. The dielectric properties are derived from the master curves with a discrete relaxation time (Debye) model [26] for the dielectric loss factor, ε , and the dielectric permittivity, ε : ε =


(εs,i − ε∞ )ωaT τi σ 0 + ε0 ωaT0 1 + (ωaT0 τi )2

and ε = ε∞ +


i

38.2.1.2 Dielectric The lubricant dielectric properties provide complementary information to the rheological data. The concept is similar in that both energy storage and dissipation are characterized in response to a sinusoidal application of an electric field. The permittivity and loss factor of the different lubricant samples were measured using a TA instruments

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(38.4)

i

εs,i − ε∞ 1 + (ωaT0 τi )2

(38.5)

where ω is the sinusoidal oscillation frequency of the applied voltage, τi are the dielectric relaxation times, and ε0 is the absolute permittivity of free space (8.85 × 10−12 F/m). The parameters in the discrete relaxation time series determined by a regression fit to the dielectric master curves. There are multiple dielectric relaxation times for the Zdol and Ztetraol. Four were employed to

(a) 1.E+06 Ztx

Ztetraol

G
(Pa)

1.E+04 1.E+02 Zdiac 1.E+00 Zdol 2500 Zdeal 1.E–02 Z 03 1.E–04 1.E–16 1.E–14 1.E–12 1.E–10 1.E–08 1.E–06 1.E–04 1.E–02 1.E+00 vaTg(rad/sec) (b) 1.E+06 Ztetraol 1.E+04

G  (Pa)

1.E+02 1.E+00 1.E–02

Zdiac

Z03

Zdol 2500 Ztx

Zdeal

1.E–04 1.E–16 1.E–14 1.E–12 1.E–10 1.E–08 1.E–06 1.E–04 1.E–02 1.E+00 vaTg(rad/sec)

FIGURE 38.4 Shear loss (a) and storage (b) modulus master curves for the Z series. The smooth curves are from the discrete relaxation time series fit to the frequency temperature shifted data. Reference temperature Tg

approximately fit the data in Figure 38.8. These provide estimates for theconductivity, σ , the dc relative permittivity, ε  (0) = i εs,i , and the limiting high frequency permittivity, ε∞ . Note that the capacitive energy storage is proportional to the dc relative permittivity, and the refractive index n is related to the high frequency relative √ permittivity by the Maxwell relation n ≈ ε∞ . For PFPEs, n ≈ 1.3 [23], which gives ε∞ ≈ 1.7. The dielectric properties, and the four relaxation times, and static relaxation amplitudes are listed in Table 38.6. 38.2.1.3 Thin film viscosity The above results have shown that in bulk PFPEs disk lubricants viscosity increases exponentially as the measurement temperature approaches the glass transition temperature. This is because chain motions are progressively “frozen out” as the thermal energy becomes less than their activation energy. The lubricant viscosity also increases as the lubricant film thickness decreases, which helps to prevent the lubricant from flowing completely off of the magnetic recording disks in the air shear [27].

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Viscosity enhancement of thin films arises from a different mechanism than that found with decreasing temperature. Dispersive interaction has a dramatic effect on the viscosity of the molecular layers closest to the surface, and can be explained in terms of the rate theory for viscous flow. Within the rate theory, a flow event comprises the transition of a flow unit from its normal or quiescent state, through a flow-activated state, to a region of lower free energy in an external stress field. For small molecules, the flow unit is the whole molecule, while for longer chains, the flow unit is a segment of the whole molecule. By analogy with chemical reaction rate theory, there is a flow-activation enthalpy, Hvis , and entropy, Svis , for transition into the flow-activated state. A flow unit is approximated by a particle in a box, with the energy being partitioned among rotational and translational degrees of freedom, which govern the transition probability. On this basis, the viscosity η = (Nhp /Vl ) exp( Gvis /RT ), where N is the Avogadro’s number, hp is the Planck constant, Vl is the molar volume, R is the universal gas constant, T is temperature, and

Gvis = Hvis − T Svis is the flow-activation Gibbs free

(a)) 1.E+06

Zdol4KL990

1.E+04

G
(Pa)

Zdol4KBL598 1.E+02 1.E+00 1.E–02

Zdol4KL905

Zdol4KL492 Zdol4KL819

1.E–04 1.E–16 1.E–14 1.E–12 1.E–10 1.E–08 1.E–06 1.E–04 1.E–02 1.E+00 vaTg (rad/sec) (b) 1.E+06 1.E+04

G (Pa)

Zdol4KBL598 1.E+02 1.E+00 1.E–02

Zdol4KL492

Zdol4KL819

Zdol4KL905

Zdol4KL990 1.E–04 1.E–16 1.E–14 1.E–12 1.E–10 1.E–08 1.E–06 1.E–04 1.E–02 1.E+00 vaTg (rad/sec)

FIGURE 38.5 Shear loss (a) and storage (b) modulus master curves for the Zdol4K series. The smooth curves are from the discrete relaxation time series fit to the frequency temperature shifted data. Reference temperature Tg

energy. The flow-activation enthalpy Hvis = Evis +

(pV )vis , where Evis is the flow-activation energy and

(pV )vis is the pressure–volume work. At constant pressure, (pV ) = p Vvis . For PFPE Z, the flow-activation volume Vvis ≈ 0.1 nm3 [12], which is equivalent to a spherical region ≈0.6 nm in diameter. At ambient pressure (100 kPa), (pV )vis ≈ 6.2 J/mol, so that near ambient conditions, Hvis ≈ Evis . Therefore, the viscosity is given by:     Nhp ( Evis − T Svis ) exp (38.6) η= Vl RT A regression fit to the bulk viscosity as a function of temperature [27], provided Evis = 34.7 kJ/mol and

Svis = 9.87 J/mol ◦ K. The flow-activation energy is close to that reported for bulk Zdol with a molecular weight of 3100 Da in References 28 and 29. A positive value for the flow-activation entropy of bulk Zdol means that the entropy of the flow unit increases on going into the flow-activated state. Changes in the lubricant flow-activation energy and entropy near the solid surface cause changes in the viscosity

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with decreasing film thickness. The flow-activation energy near a solid surface is estimated from the thin film vaporization energy as follows: In an ideal gas, the chemical potential µ (or partial molar Gibbs free energy) is given by: dµ = RTd ln P

(38.7)

where P is the partial pressure of the lubricant in the vapor phase. The chemical potential energy per unit volume in the lubricant film µ/Vl = . The ratio of the film surface vapor pressure to the vapor pressure of the bulk lubricant, Po (h)/Po (∞), is derived by integrating Equation (38.7). 

Po (h) µ(h) − µ(∞) = RT ln o P (∞)

 (38.8)

The reference state is taken to be the chemical potential and vapor pressure of the bulk lubricant: u(∞) = 0 and Po (∞) is the vapor pressure of the bulk liquid. In general, since the surface energy is defined as the free energy per unit area, the total disjoining pressure ( ) for these fluids can be derived from the experimental surface

(a) 1.E+06 Demnum S100 1.E+04

Krytox 143AD

G
(Pa)

1.E+02 1.E+00

Demnum SA2 Krytox COOH

1.E–02

1.E–04 1.E–16 1.E–14 1.E–12 1.E–10 1.E–08 1.E–06 1.E–04 1.E–02 1.E+00 vaTg(rad/sec) (b) 1.E+06 1.E+04

Krytox 143AD Demnum S100

G  (Pa)

1.E+02 1.E+00 1.E–02

Demnum SA2 Krtox COOH

1.E–04 1.E–16 1.E–14 1.E–12 1.E–10 1.E–08 1.E–06 1.E–04 1.E–02 1.E+00 vaTg(rad/sec)

FIGURE 38.6 Shear loss (a) and storage (b) modulus master curves for the Demnum and Krytox series. The smooth curves are from the discrete relaxation time series fit to the frequency temperature shifted data. Reference temperature Tg

energy (contact angle) data by: =−

∂ d (γ + γ p ) ∂h

(38.9)

Here, γ d and γ p are the dispersive and polar components of the surface energy, respectively, and h is the film thickness. The regression fit to the surface energy data, shown as the smooth curves in Figure 38.9(a) and Figure 38.9(b), were numerically differentiated to obtain the disjoining pressure [30]. The total disjoining pressure, as well as the individual contributions from the dispersive and polar components, is shown in Figure 38.10(a). Notice that γ d decreases monotonically with h, which is consistent with Equation (38.10). Below film thicknesses of approximately 0.5 nm, at each molecular weight is dominated by γ d , which increases rapidly with decreasing film thickness and is largely independent of molecular weight. The γ p , however, oscillates with film thickness and becomes larger in magnitude than γ d as h increases. Oscillations in γ p provide an additional contribution to for PFPE Zdol that produces alternating regions of stable and unstable film thickness [31]. The sum of the two contributions gives rise to oscillations in

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the total disjoining pressure. It may seem surprising, but given the disjoining pressure from the surface energies as a function of film thickness, and Equation (38.9) relating the disjoining pressure to the degree of saturation provides the adsorption isotherms for low molecular weight Zdols, according to P/P0 = exp(− Vl /RT ), which are shown in Figure 38.10(b). There are two thermodynamically stable regions of film thickness for degrees of saturation corresponding to regions where > 0 and ∂ /∂h < 0. For thicknesses in between these regions, condensing Zdol molecules will either reevaporate, or form islands at the next higher stable film thickness. For the purpose of explaining the viscosity increase of thin films, surface chemical potential is approximated by the unretarded atom–slab dispersive interaction energy: Vl A (38.10) 6π h3 The dispersive interaction coefficient A is also referred to as the Hamaker constant, and A = 10−19 J for Zdol. As mentioned, the vaporization energy is the energy required to remove a molecule from the liquid without leaving behind a hole and the flow-activation energy, which µ=−

Relaxation time (sec)

(a) 1.E-04

1.E-05

50

Zt e

t ra

Zd o

ol

l2

20

0

Zt x

00

al Zd e

ac Zd i

Z0 3

1.E-06

Relaxation time (sec)

(b) 1.E-04

1.E-05

1.E-06 0.8

1

1.2

1.4

1.6

1.8

m/n

FIGURE 38.7 Longest relaxation time at 50◦ C for the Z series of lubricants (a) and Z series with a range of monomer chain composition (b) calculated from the dynamic rheological measurements with time–temperature superposition

is the energy needed to form a hole of the size of a molecule in the liquid. The free volume needed for a flow unit to transition into the flow-activated state is less than the size of the entire molecule. It is found that the ratio n ≡ Evap,∞ / Evis,∞ > 3, where Evap,∞ and Evis,∞ are the vaporization and flow-activation energy of the bulk liquid, respectively. Thus, the flow-activation energy near the surface is approximately given by:

Evis = Evis,∞ −

µ n

(38.11)

For linear chains longer than 5 or 10 carbon atoms, n increases due to the onset of segmental flow. In practice, n is experimentally determined from the measured values of the vaporization and flow-activation energy. For PFPE Zdol 4000, Evap,∞ = 166 kJ/mol, giving n ≈ 4.8. This is consistent with segmental flow. In order to calculate the thin film viscosity with Equation (38.6), the flow-activation entropy near the surface is also needed. Experimental flow-activation entropy is calculated from the spin-off data [27] with Equations (38.6) and (38.11) as follows: The experimental η vs. h is determined from the dh/dt during air shear induced flow on a rotating disk. Equation (38.6) is then solved for Svis vs. h using Equation (38.11) for Evis .

Copyright 2006 by Taylor & Francis Group, LLC

The flow-activation entropy and entropy are shown in Figure 38.11(a). The flow- activation energy suddenly increases below about 0.8 nm due to the strong film thickness dependence of the dispersion force. The retarding effect of this increase on flow is compounded by the apparent effect of confinement on restricting the degrees of freedom in the flow transition state, as seen by the negative entropic contribution in Figure 38.11(a). Below 2.3 nm, T Svis ≈ −1.9 kJ/mol, which corresponds to the critical configurational entropy change for flow (−R ln 2 ≈ −5.76 J/mol ◦ K). The combined effects give rise to the observed increase in viscosity with film thickness shown in Figure 38.11(b), and enables extrapolation of the viscosity to even thinner films where the spin-off is so slow that it takes years to measure. The viscosity increases by a large amount with film thickness, which is much greater than the increase with temperatures that might normally be encountered in the disk drive. The bulk viscosity for several PE lubricants is shown in Figure 38.12. Since the increase in viscosity with thickness below about 0.8 nm is so much more than the increase with temperature between 0 and 60◦ C, the operating temperature of disk drives should have no significant effect on lubricant spin-off from the disk by air shear. That is, excluding air shear force due to the head suspension assembly and the air bearing. 38.2.1.4 Vapor pressure The vapor pressure of PFPE lubricants should be low to prevent evaporation from the disk. One method to measure the vapor pressure was developed as follows: A model was derived to calculate the vapor pressure from the measured Zdol molecular weight distribution and evaporation rate. Molecular weight distributions were measured by gel permeation chromatography (GPC), as described in Karis et al. [23]. The vapor pressure of discrete molecular masses was calculated from the evaporation rate measured by isothermal thermogravimetric analysis (TGA) with a stagnant film diffusion model as in Karis and Nagaraj, [32]. Polymers such as Zdol differ from the low molecular weight synthetic hydrocarbon oils in that polymers comprise a variety of different molecular weights. Further considerations must be taken into account in modeling the evaporation of polymers, as described below: A numerical model was developed to simulate the evaporation of a polymer from an initial molecular weight distribution measured by GPC. The evaporation simulation is written in terms of mass flux and the discrete form of the molecular weight distribution wi (t) as:   A + wi (t ) = wi (t) − fluxi (t)

t (38.12) m0 where A is the surface area of the evaporating lubricant, m0 is the initial mass of lubricant, and t is the time step

(a) 1.E+08 Ztetraol 1000





1.E+06 1.E+04

Ztetraol 2000

1.E+02

Zdol 4000

1.E+00 1.E–02 1.E–04 1.E–05

1.E–01

1.E+03

1.E+07

1.E+11

1.E+15

vaTo(rad/sec) (b) 1.E+08 Ztetraol 1000

1.E+06 Ztetraol 2000




1.E+04 1.E+02 Zdol 4000 1.E+00 1.E–02 1.E–05

1.E–01

1.E+03

1.E+07

1.E+11

1.E+15

vaTo(rad/sec)

FIGURE 38.8 Dielectric loss factor (a) and relative permittivity (b) master curves for the Ztetraol 1000, Ztetraol 2000, and Zdol 4000. The smooth curves are from the discrete relaxation time series fit to the frequency temperature shifted data. Reference temperature T0 = 50◦ C

TABLE 38.6 The Coefficients of the Debye Equation from the Dielectric Master Curves at Reference Temperature T0 = 50◦ C Lubricant Parameter ε  (0) σ (S/m) εs,1 τ1 (sec) εs,2 τ2 (sec) εs,3 τ3 (sec) εs,4 τ4 (sec)

Zdol 4000

Ztetraol 2000

Ztetraol 1000

3,330 1E-11 3,000 500 300 50 30 5 2 1E-8

11,100 4E-8 10,000 50 1,000 5 100 0.5 4 1E-8

11,100,000 6E-7 10,000,000 8 1,000,000 0.8 100,000 0.06 5 1E-8

The high frequency ε∞ ≈ 1.7 from the index of refraction.

Copyright 2006 by Taylor & Francis Group, LLC

in the simulation. The mass flux of the ith molecular weight fraction Mi is given by stagnant film diffusion:   Di Mi (38.13) Pi , fluxi (t) = δ RT where, Di is the vapor phase diffusion coefficient and δ is the diffusion length (calculated or measured with a liquid of known vapor pressure). The mass flux divided by the mass density yields the rate of film thickness change. The solution vapor pressure for the ith molecular fraction was approximated assuming an ideal solution according to Raoult’s law Pi = xi Pi0 where xi is the mole fraction of the ith molecular fraction. The Hirschfelder Approximation [33] is used for the vapor phase diffusion coefficient: Di = 1.858 × 10−4



1 1 + Mi Mgas

1/2

T 3/2 Pσi2 

(38.14)

where Mgas is the molecular weight of the ambient atmosphere (air or nitrogen to suppress oxidation), P is the

Dispersive (mN/m)

(a) 25 20 15 10 Zdol

5 0 0.0

Z

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

4.0

4.5

Thickness (nm) (b) 25

Polar (mN/m)

20 15 10 5 1100 Da 0 0.0

0.5

1.0

1600 Da

1.5

2.0

2.5

3100 Da 3.0

3.5

Zdol thickness (nm)

FIGURE 38.9 The components of the surface energy measured on CHx overcoated thin film magnetic recording media with fractionated Zdol of narrow polydispersity index. (a) The dispersive component of the surface energy for PFPE Z and Zdol, and (b) the polar component of the surface energy for PFPE Zdol [30] i i )/2 is the colambient pressure, and σi = (σlube + σgas i lision diameter. For nitrogen, σgas = 0.315 nm. The vapor phase molecular diameter of the ith molecular weight component employed in estimating the binary mass diffusion i coefficient √ is approximately given by σlube = 2 × Rg,i ≈ 0.05 × Mi , where the molecular weight Mi is in Da, and the radius of gyration Rg,i is in nanometer. This expression was derived from the radius of gyration for Zdol measured in Freon [34]. The molecular diameters from this approximation for a range of ideal monodisperse Zdol molecular weights are listed in Table 38.7. By analogy to hydrocarbon oils, the collision integral  for collision between molecules in the gas phase is a function of their binary Lennard–Jones interaction potential. The collision integral between Zdol molecules and nitrogen molecules was taken to be the same as that for collision between hydrocarbon molecules and nitrogen,  = 1.2. The Clapeyron equation is employed to calculate the pure component vapor pressure:

i

i − Evap

Svap 0 Pi = P exp exp{−1} exp (38.15) R RT i i − S is the = Svap where the vaporization entropy Svap liq difference between the entropy in the vapor state and that

Copyright 2006 by Taylor & Francis Group, LLC

in the liquid state. The Zdol liquid entropy is assumed to be independent of molecular weight. It was determined along with the activation energy by comparison of the simulated evaporation with isothermal TGA evaporation weight loss data. The liquid entropy for Zdol, Sliq = 107 J/mol ◦ K, is within the range obtained for the synthetic hydrocarbon oils. The vapor phase translational entropy for oils is approximated with the Sackur–Tetrode equation:

 3 (2π )3/2 (RT )5/2 5 i + ln(Mi ) + ln Svap,trans = R 2 2 hp3 N 4P (38.16) The vapor phase rotational entropy is given by [35]:       1 8π 3 IRT a/2  i  (38.17) = R 1 + ln Svap,rot πq  hp2 where a is the number of independent rotation axes, q is the degeneracy, and I is the moment of inertia. A useful i approximation for Svap,rot is given in Reference 32. The vaporization entropy also includes the vibrational entropy. The available vibrational states are comparable between liquid and vapor for these high molecular weight

(a) 80 60

50 ∆Evis

40 30

40 kJ/mol

Π(Mpa)

(a)

1100 Da 1600 Da 3100 Da

20

20 10

T∆Svis

0 0 –20

0

1

2

3

4

–10

5

0.1

Zdol thickness (nm) 5

1100 Da 1600 Da 3100 Da

4

1.0

100.0

(b) 1000

3

100

2 1 0

100.0

h/h`

Zdol thickness (nm)

(b)

1.0 10.0 Zdol thickness (nm)

10

0

0.2

0.4

0.6

0.8

1

P/P0

hydrocarbons, or polymeric oil, molecules, while the translational and rotational states are much more restricted in the liquid phase. Note that the ideal gas law is employed in deriving Equation (38.15) as follows: The vaporization enthalpy i i + (PV ) . The pressure volume expan Hvap = Evap i sion work term has been replaced by (PV )i = RT . The i , also depends on vaporization activation energy, Evap molecular weight because a longer molecule requires more energy to overcome the intermolecular interaction force between itself and its neighbors in the surrounding liquid. Polar end groups contribute a fixed contribution to the vaporization energy, which gives rise to the intercept in the plot of vaporization energy as a function of molecular weight. As one might expect, there seems to be a linear relation between the activation energy and molecui lar weight for Zdol [36], Evap ≈ Eint + Eslope × Mi . The slope, Eslope = 0.029 kJ/mol/Da, and intercept,

Eint = 50 kJ/mol, of the vaporization activation energy dependence on molecular weight for Zdol were determined by comparing of the simulated evaporation data with that measured by isothermal TGA. The thermodynamic properties, vapor phase diffusion coefficient, and vapor pressure for a range of ideal monodisperse Zdol molecular weights calculated as described above are listed in Table 38.8. The numerical values in Table 38.8 can be

Copyright 2006 by Taylor & Francis Group, LLC

10.0

Zdol thickness (nm)

FIGURE 38.11 (a) Flow-activation energy and the entropic component of the flow-activation free energy, and (b) dispersionenhanced viscosity as a function of film thickness. The filled symbols are from the spin-off measurements, and the dashed region of the curve was calculated with constant flow-activation entropy below 2.3 nm. Fractionated Zdol molecular weight 4500 Da, temperature 50◦ C [27] 0.5

0.4

h` (Pa–sec)

FIGURE 38.10 The disjoining pressure from the fractionated Zdol surface energies in Figure 38.9(a) and the corresponding Zdol adsorption isotherms at 60◦ C (b)

1 0.1

0.3 Ztetraol 2000 0.2 Zdol 4000 0.1 Z03 0.0 0

20

40

60

80

100

T (°C)

FIGURE 38.12 Bulk viscosity and flow-activation energy of several PFPE lubricants as a function of temperature

TABLE 38.7 The Gas Phase Molecular Diameter for Ideal Monodisperse Zdol Fractions Calculated from the Radius of Gyration in Theta Solvent √ d(nm) = 0.05 M(Da) Gas phase molecular diameter M (Da) 500 750 1000 1350 1500 2000 3000 4000 4300 5400

d (nm)

Degree of polymerization

Contour length (nm)

Equilibrium thickness (nm)

1.12 1.37 1.58 1.84 1.94 2.24 2.74 3.16 3.28 3.67

3.54 6.29 9.03 12.88 14.53 20.02 31.01 42.00 45.30 57.38

2.71 4.06 5.41 7.29 8.10 10.79 16.18 21.56 23.18 29.10

0.66 0.74 0.82 0.93 0.98 1.14 1.46 1.79 1.88 2.24

The degree of polymerization, the contour length measured along the chain from one end to the other, and the equilibrium thickness are also included. The equilibrium thickness is the maximum stable film thickness, or dewettting thickness, determined from the first zero crossing of the disjoining pressure with increasing film thickness.

used in Equation (38.15) to calculate the vapor pressure of perfectly monodispersed molecular weight fractions. Actual samples of commercial PFPE lubricant such as Zdol are polydisperse. Consequently, there is a wide range of partial pressures for a given sample, and the lowest molecular weight species in the distribution have the highest vapor pressure. In the case of Zdol 2000, since it is a copolymer of perfluoromethylene and perfluoroethylene oxide, the lowest molecular weight oligomers group together with similar molecular weights, hence similar vapor pressures. Figure 38.13(a) shows the molecular weight distribution of Zdol 2000 measured by GPC. The oscillations in the molecular weight distribution are visible up through 1000 Da. The mole fraction distribution is also shown, since it plays a key role in determining the actual vapor pressure. Qualitatively, the vapor pressure is increasing with decreasing molecular weight, but as the molecular weight becomes lower, there are fewer of these molecules in the solution, so Raoults’ law acts to partly offset the increase in vapor pressure, causing the vapor pressure to decrease in the limit of low molecular weight. Hence, the shape of the partial pressure distribution superimposed on the distribution in Figure 38.13(a), calculated at 50◦ C. The partial pressure distribution for Zdol is shown with units on an expanded scale in Figure 38.13(b). This shows the great detail provided by the GPC method, and also, the partial pressure peaks show the molecular weights that will evaporate with the highest rate, or distill out of the distribution. The total vapor pressure of polydisperse Zdol 2000 at 50◦ C is the sum of the partial pressures of each component, in this case, 0.2 Pa.

Copyright 2006 by Taylor & Francis Group, LLC

There are some other important properties of magnetic recording disk lubricants that will not be covered in this chapter, and several references on these are provided below. Lubricant spin-off and transfer to the slider is minimized by chemisorption to the overcoat [37]. Chemisorption [38], also referred to as bonding, is well described by Tyndall et al. [39]. Disk lubricants also serve to inhibit corrosion. The corrosion protection ability of Zol lubricants was related to surface energy by Tyndall et al. [39] The most successful disk lubricant additive has been cyclic phosphazines. However, cyclic phosphazine increases the lubricant mobility [40] and dewetting thickness [31]. More recently, an effort has been made to combine the desirable properties of both by incorporating cyclotrophosphazine end groups onto Zdol. This lubricant is referred to as A20H, and it is well described in a recent paper by Waltman et al. [4]. The A20H end group is shown in Table 38.1.

38.3 SPINDLE MOTOR LUBRICANTS There are ball bearing and fluid dynamic bearing spindle motors, see Reference 41 for a good overview. The arrangement of the spindle motor and types of spindle motor bearing are shown in Figure 38.14.

38.3.1 Ball Bearing Spindle Motor Bearing Grease Ball bearing spindle motor bearings are typically lubricated with an NLGI grade 2 lithium grease. The grease

TABLE 38.8 i , Binary Diffusion CoefVaporization Entropy Svap

(a)

i for Perficient Di , and Vapor Pressure Pvap fectly Monodispersed Zdol Fractions Evaporating into Nitrogen at Ambient Pressure (105 Pa) at Three Different Temperatures, Sliq = 107 J/mol ◦ K, i (kJ/mol) = 50 (kJ/mol) + 0.029 (kJ/mol) × Evap Mi (Da) i (J / mol ◦ K) Svap

Temperature 35◦ C 500 750 1000 1350 1500 2000 3000 4000 4300 5400 Temperature 45◦ C 500 750 1000 1350 1500 2000 3000 4000 4300 5400 Temperature 60◦ C 500 750 1000 1350 1500 2000 3000 4000 4300 5400

D (m2 /sec)

100

i Pvap (Pa)

1000 10,000 Molecular weight (Da)

100,000

(b) 0.0020 123 133 140 147 150 157 167 174 176 182

3.16E−06 2.27E−06 1.78E−06 1.38E−06 1.26E−06 9.79E−07 6.82E−07 5.25E−07 4.91E−07 3.98E−07

1.13E+00 2.26E−01 3.17E−02 1.48E−03 3.72E−04 3.07E−06 1.25E−10 3.61E−15 1.50E−16 1.16E−21

123 133 141 148 151 158 168 175 177 183

3.32E−06 2.38E−06 1.87E−06 1.44E−06 1.32E−06 1.02E−06 7.15E−07 5.51E−07 5.15E−07 4.18E−07

2.76E+00 6.01E−01 9.19E−02 4.87E−03 1.29E−03 1.27E−05 7.44E−10 3.05E−14 1.41E−15 1.61E−20

124 135 142 149 152 159 169 176 178 184

3.56E−06 2.55E−06 2.00E−06 1.55E−06 1.41E−06 1.10E−06 7.66E−07 5.90E−07 5.52E−07 4.48E−07

9.51E+00 2.34E+00 4.05E−01 2.55E−02 7.28E−03 9.19E−05 8.80E−09 5.91E−13 3.17E−14 6.26E−19

Partial pressure (Pa)

Mi (Da)

Weight fraction Mole fraction Partial pressure

0.0015

0.0010

0.0005

0.0000 0

Other parameters used are given in the text.

composition, referred to as SRL, is a lithium grease comprising approximately 10% Li 12-hydroxy stearate, 17% di 2-ethylhexyl sebacate, 70% pentaerythritol tetraesters, and the rest is a sulfonate rust inhibitor and an amine antioxidant. Lithium soap gel fibers thicken the grease [42]. The grease base oil viscosity at 40◦ C is 22 mPa-sec, and the worked penetration is 245. A great variety of greases could potentially be used in these bearings, but in practice, the

Copyright 2006 by Taylor & Francis Group, LLC

500

1000

1500

2000

Molecular weight (Da)

FIGURE 38.13 The molecular weight distribution, mole fraction distribution, and the calculated partial pressure distribution (a) and the partial pressure distribution on an expanded scale with units (b) for Zdol 2000 at 50◦ C

grease is limited by stringent requirements of low volatility, yield stress at temperature, low torque noise, and good thermal stability. 38.3.1.1 Yield stress at temperature Typical ball bearing spindle motor grease rheological properties and yield stress are described by Karis et al. [43]. For practical purposes, the yield stress is measured by gradually increasing the stress in a stress rheometer with a cone-plate fixture. The yield stress is detected when the cone begins to rotate. For example, the yield stress as a function of temperature for several grease candidates for use in ball bearing spindle motors is shown in Figure 38.15. There is a general trend of decrease with temperature, but all the greases maintain a measurable yield stress up through at least 80◦ C. The decrease of the yield stress with temperature is much less than that of the grease base oil, as will be shown later. Diluting the grease with additional base oil, or incorporation of contaminants in the grease, also affects the yield stress. Additional oil is often added to prelubricate the new bearing once it has been filled with grease. This is done to provide a lubrication film during initial startup of the new bearing, before the base oil from the gel thickener of the grease has had time to diffuse throughout the surfaces

Slider Suspension

(a)

Base grease +0.6% Zn (diacrylate) +12.5% Base oil +16% Prelube A +16% Prelube B +36% Prelube B + 0.03% Zn (diacrylate) + 0.01% Fe (octanoate)

Disk Spindle motor

800 700

Base casting

600

Ball bearing spindle motor Ferrofluid seal

Yield stress ( Pa)

(b)

Rotor

Ball Bearings

Stator

400 300 200

Fluid bearing spindle motor

(c)

500

Fluid

Rotor

bearings

Stator

100 0 0

FIGURE 38.14 The arrangement of the magnetic recording disks and head suspension assembly on the spindle motor (a), schematic ball bearing spindle motor (b), and schematic fluid bearing spindle motor (c) 800 F4 SRL L252 BQ 72-72 LY 716R

700

Yield stress (Pa)

600 500 400 300 200 100 0 0

20

40 60 Temperature (°C)

80

100

FIGURE 38.15 The yield stress of various candidate greases for ball bearing spindle motors as a function of temperature

of the balls and raceways. The prelube can either be the grease base oil itself, or specially formulated prelube oil. Results with two types of prelube are also described here. Prelube oil A is diester oil with a sulfonate rust inhibitor and a hindered phenol antioxidant. Prelube oil B is mostly

Copyright 2006 by Taylor & Francis Group, LLC

20

40 60 Temperature (°C)

80

100

FIGURE 38.16 The yield stress of base grease SRL showing the effect of additional base oil, prelube oils, and organometallic salt contamination on yield stress as a function of temperature

diester oil with several percent of a polyalphaolefin oil (PAO), a sulfonate rust inhibitor, and a Zn dialkyl dithiocarbamate antiwear additive. Grease may also be exposed to organometallic salts formed from various components within the bearing, bearing shields, or motor. Zn was incorporated as Zn(diacrylate), and Fe was incorporated as iron (III) 2-ethylhexanoate. The Zn(diacrylate) contaminant was intended to model products of bearing corrosion by the incomplete curing of a motor bearing adhesive [44]. Model grease containing prelube or contaminants was prepared in the laboratory by thoroughly mixing them in a custom-built lab scale grease mill. The grease mill capacity was about 10 g of grease. The mill comprised two 32 mm diameter disks perforated with 35 circular holes, each 460 µm in diameter, inside a stainless steel tube. The perforated disks were separated by a 3.8-mm wide cavity. Grease was forced back and forth through the holes in the perforated disks by the reciprocating action of two opposing pneumatic cylinders driving Teflon pistons against the perforated plate within the steel tube. Air pressure was alternately applied to the cylinders using a cam and follower arrangement driven by a variable speed gear motor. The yield stress of these model greases is shown in Figure 38.16. The yield stress was increased by Zn(diacrylate), while prelube oils decreased the yield stress. For comparison with the yield stress vs. temperature, the viscosity and density of the SRL grease base oil and

100.00 Base oil Prelube A Prelube B

1.0E+00 1.0E–01 1.0E–02

(b)

1000

Density (kg/m3)

1.0E–03 –40 –20

950

0

20 40 60 80 Temperature (°C)

100 120

Film thickness (nm)

Viscosity (Pa-sec)

(a) 1.0E+01

10.00

1.00 Base oil Prelube A Prelube B 0.10 0.001

0.010

0.100

1.000

Mean rolling speed (m/sec)

900

FIGURE 38.18 The film thickness as a function of rolling speed measured by ultrathin film interferometry (courtesy of H.A. Spikes, Imperial College, London)

850 800 –40 –20

0

20 40 60 80 Temperature (°C)

100 120

FIGURE 38.17 The viscosity (a) and density (b) of SRL grease base oil base grease and two prelube oils as a function of temperature

two prelube oils are shown as a function of temperature in Figure 38.17. The viscosity and density of the base oil are somewhat higher than that of the prelube oils. Blends between the base oil and the prelube oils A or B will have intermediate viscosities. The oil viscosities decrease much more than the yield stress with temperature. This implies that most of the yield stress change with temperature, Figure 38.16, is due to the gel network of the thickener. The reduction in yield stress on blending grease with prelube oil is probably due to dilution of a transient network in the gel thickener. 38.3.1.2 Hydrodynamic film thickness The hydrodynamic film thickness of the oil provided by the grease must be sufficient to clear the asperities on the balls and race during operation at the specified load and velocity. The hydrodynamic film thickness is given by: h = k(Uη0 )0.67 (αp )0.53

(38.18)

where h is the film thickness, k is a materials and geometry parameter, U is the entrainment velocity, η0 is the viscosity at atmospheric pressure, and αp is the pressure viscosity coefficient [45]. The film thickness between a steel ball and a plate by ultrathin film interferometry [46] was measured by Prof. H.A. Spikes, and his students, at Imperial College in London. The film thickness as a function of sliding speed for the grease base oil, and the prelube oils A and B,

Copyright 2006 by Taylor & Francis Group, LLC

is shown in Figure 38.18. There is some variation in the power law slope between the oils, which slightly varies from the coefficients used in Equation (38.18). By comparison of a fluid with a known pressure–viscosity coefficient, they estimated the pressure–viscosity coefficients over a limited speed range between 0.1 and 1 m/sec to be approximately 15 l/GPa for the base oil, 12 l/GPa for prelube oil A, and 10.5 l/GPa for prelube oil B. The difference between prelube oils A and B is probably due to the minor fraction of PAO in prelube oil B. 38.3.1.3 Grease electrochemistry Some types of high performance disk drive spindle motors incorporate ball bearings with silicon nitride ceramic balls for higher stiffness and lower vibration. It is critical that the bearings and grease provide smooth rotation so as not to excite resonances of the disk pack, Figure 38.14(a). Electrostatic potential generated by bearings can induce a small current flow through, with a return path through the ferrofluid seal, Figure 38.14(b). In order to investigate the effect of electrochemistry, grease containing various types of contaminants was sandwiched between two steel electrode plates. The plates were 25-mm diameter mirror polished 304 stainless steel electrode plates on 160-µm thick filter paper. The plates were subjected to 25 V to simulate the passage of electrical current through the grease in the bearing. After several hundred hours, the plate were separated and examined for degraded grease as deposits on the plates. Film deposits were characterized by optical microscopy, Fourier Transform Infrared (FTIR) spectroscopy in reflection, and x-ray photoelectron spectroscopy (XPS). Figure 38.19 shows the current through the electrode plates plotted as a function of the voltage applied across the

SRL grease alone 16% Prelube A 16% Prelube B 12.5% Base oil

300 ppm Zn 16% Prelube A+300 pm Zn 16% Prelube B+300 ppm Zn 12.5% Base oil+300 ppm Zn

10,000

Current (nA)

1000

Sample

100

10

1 0.1

TABLE 38.9 Grease Electrochemical Cell Test Results for Grease on 160 µm Thick Filter Paper between 1 in. Diameter Electrode Plates

1

10

100

Voltage

FIGURE 38.19 Initial current–voltage plot for SRL grease alone, and SRL grease with the indicated additives and contaminants measured in the electrochemical cells

grease film with fresh grease between the plates. The conductance of the ferrofluid seal in the motor was about 77 nS (13 M), so that the current through the bearing is typically 30 to 80 nA. In steady state, the electrochemical cells were operated at 25 V, or between 100 and 3000 nA, depending on the type of grease contamination. Higher voltage was employed in the electrochemical cells to increase the rate of any electrochemical reactions that might take place. The initial conductance of the electrochemical cells, calculated from the linear region of the current–voltage plot, is listed in the second column of Table 38.9. The lowest conductance was obtained with the SRL grease alone, and SRL grease combined only with an additional 12.5% more of its own base oil. The highest conductances were found with the grease containing 16% prelube oil B and 300 ppm Zn, and grease containing 16% prelube oil B. The grease conductance gradually varied with time during voltage application, as shown for several greases with and without contaminants in Figure 38.20. Pure grease, with no diluents or contaminants, maintained the lowest conductance. After several hundred hours, the plates were separated and washed with chloroform by squirting from a pipette. When present, films were observed on the negative electrode plate. Although there was sometimes minor film formation or slight pitting on the positive plate, there was too little to quantify. Micrographs of the film deposits on several of the negative electrode plates are shown in Figure 38.21. These show the fibrous appearance. The film

Copyright 2006 by Taylor & Francis Group, LLC

SRL Grease alone SRL grease +36% Prelube A +300 ppm Zn +100 ppm Fe SRL grease +300 ppm Zn, SRL grease +16% Prelube A SRL grease +16% Prelube A +300 ppm Zn SRL grease +16% Prelube B SRL grease +16% Prelube B +300 ppm Zn SRL grease +12.5% SRL base oil SRL grease +12.5% SRL base oil +300 ppm Zn

Initial conductance (ns)

Time (h)

Film deposit

4 28

960 336

light medium

7

336

heavy

8

576

heavy

20

336

light

52

576

light

93

336

heavy

9

336

light

16

336

heavy

The initial conductance was calculated from the linear region of the current–voltage data measured between 1 and 25 V (Figure 38.19). Prelube is defined in the text. The right-hand column gives the appearance of the film deposit on the negative electrode plate after application of 25 V for the amount of time listed in the third column.

deposits were highly viscous. Film deposits were qualitatively ranked in terms of their severity, which is referred to as light, medium, and heavy, after the indicated electrolysis time, in Table 38.9. The lightest deposits were observed with the virgin grease, and the grease diluted with its own base oil. The heaviest deposit coincided with the highest conductance. However, even though they had nearly the lowest conductance, grease contaminated by 300 ppm of Zn as acrylate, or with 16% of the prelube oil A, also formed heavy deposits. Reflection FTIR was performed on the residue on the plates after each test. Typical FTIR spectra are shown in Figure 38.22. The IR peaks were assigned to chemical groups according to the peak assignments in Table 38.10. The peak assignments, in conjunction with XPS measurements on the residue in Table 38.11 clearly show electrochemical oxidation of the grease. The ratio of carbonyl groups has clearly increased following the

SRL grease alone 36% Prelube A + 300 ppm Zn + 100ppm Fe 300 ppm Zn 16% Prelube A 16% Prelube B

Conductance (nS)

100

10

electrochemistry. For the pure thickener, the ratio of carbonyl to Li is 1.07, while aged grease and electrochemically oxidized grease have increased carbonyl due to oxidation. For black grease from a failed bearing, residue in a noisy bearing and a pin on disk wear test track also show increased carbonyl relative to the original thickener. In summary, for the longest lifetime and best performance under all conditions, lithium grease should be kept free of metallic impurities and diluents. When electrochemical oxidation does occur, it forms a residue from the soap thickener on the raceway.

38.3.2 Ball Bearing Spindle Motor Ferrofluid Seal

1 0

200

400 600 Time (h)

800

1000

FIGURE 38.20 Conductance-time plot for SRL grease alone, and SRL grease with additives and contaminants measured in the electrochemical cells

Composition

As mentioned above, the return path from the rotor to the stator for charge generated by the ball bearings is through the ferrofluid seal, Figure 38.14(b). The ferrofluid is held in place by magnets in the seal housing, and the primary function of the ferrofluid seal is to prevent airflow through the motor into the disk drive enclosure. The typical ferrofluid is a suspension of 10 to 30 wt% subdomain magnetite particles 10 nm in diameter in a trimellitic/trimethylolpropane

10 × Lens

20 × Lens

(a)

(b)

100 µm scale bar

FIGURE 38.21 Optical micrographs showing the film deposits on the negative electrode plate following electrochemical oxidation of contaminated grease at two different levels of magnification. The residue was insoluble in chloroform and isopropanol, while the initial grease was easily removed from the plates by rinsing with chloroform. SRL grease +300 ppm Zn for 336 h (a), and SRL grease +16% Prelube A for 576 h (b)

Copyright 2006 by Taylor & Francis Group, LLC

(a) Absorbance

1581

2921

4000

3500

1736

3000

2500

2000

1451

1500

1000

500

1000

500

1000

500

Wave numbers (cm–1)

(b) Absorbance

1587 2922 1456 1712

4000

3500

3000

2500

2000

1500

Wave numbers (cm–1)

(c) Absorbance

1587 2922

1718

4000

3500

3000

2500

2000

1456

1500

Wave numbers (cm–1)

FIGURE 38.22 Reflection FTIR spectra of residue deposited on the negative electrode plates from grease containing various contaminants (a) Prelube A, Zn, and Fe, (b) Zn, and (c) Prelube A. Oil was removed by washing with solvent before measurement

TABLE 38.10 FTIR Peak Assignments Absorbance Broad dimer hydrogen bonded carbonyl O–H stretch in 12-hydroxy stearic acid Hydrogen bonded O–H stretch in alcohol Asymmetrical methylene C–H stretch Aliphatic aldehyde or ester C=O stretch Aliphatic methyl ketone C=O stretch Aliphatic internal ketone C=O stretch carboxylic acid dimer C=O stretch in 12-hydroxy stearic acid C–O–H in-plane bend in 2-hydroxy stearic acid Carboxylate anion, asymmetrical stretch Carboxylate anion, symmetrical stretch Ester C–C(=O)–O in base oil

Wavenumber (cm−1 ) 3500–2500 3500–3200 2928–2917 1740 1730 1725 1695 1470 1589–1581 1456–1442 1166

The carboxylate anion is formed with Li or Zn and 12-hydroxy stearic acid. The ratio (C=O)salt /C(–H)2 was measured using the carboxylate anion, asymmetrical stretching, and the asymmetrical methylene C–H stretching.

Copyright 2006 by Taylor & Francis Group, LLC

ester oil with 10 to 20 wt% dispersing agent and up to 10 wt% antioxidant. Ferrofluid is a mature technology, and these fluids are highly stable. The most recent effort to modify the properties of the ferrofluid was intended to increase the electrical conductivity so as to reduce the electrical potential between the rotor and stator of the spindle motor. The development of conductivity additives for ferrofluids is described below. Additives to increase the conductivity of the carrier oil were investigated. A number of conductivity enhancing compounds were incorporated in a model carrier oil, trioctyltrimellitate (TOTM), and the conductivity was measured by DEA, as described in Section 38.2.1.2. The results of the initial screening are given in Table 38.12. Most of the additives reduced the conductivity. This probably indicates that the additives were associating with impurities, which were the primary charge carriers in the oil. The most promising initial results were obtained with a micellar solution of succinimide and dodecylbenzenesulfonic acid [47]. Variations of the organic acid, and the succinimide/acid ratio were explored to optimize the conductivity of the TOTM carrier oil. The results are shown in Table 38.13. The mixtures of succinimide and acid provided the highest conductivity to the oil. The most promising conductivity additives based on the tests in the model oil are shown in Figure 38.23. Even the best combination of conductivity additives TOTM still had lower conductivity than any of the ferrofluids. Dielectric spectroscopy was performed to determine the conductivity mechanism of the ferrofluid. The ferrofluid has three dielectric relaxation times, 260, 43, and 6.3 msec. These relaxation modes probably comprise the phoretic motion of the magnetite particles, phoretic motion of ions, and electronic hopping, respectively. The activation energy for conductivity is close to the viscous flow-activation energy, so the conductivity of the ferrofluid is mostly due to the phoretic motion of the magnetite particles. The relaxation times were unchanged by the conductivity additives. Since it became apparent that conventional additives used to enhance the conductivity of the carrier oil are of no benefit, or reduce the conductivity of the ferrofluid, a different approach was needed. Ferrofluid is significantly more conductive than the carrier oil, due to the presence of the magnetic particles. The conductivity of a ferrofluid can only be enhanced by improving the efficiency of charge transfer between the suspended magnetite particles. This may be done by incorporating particles coated with conducting polymer, conducting polymer oligomers, or nano-wires in the form of multiwall carbon nanotubes. Conducting polymer coated carbon black particles (Eeonomer, Eeonyx Corp., 750 Belmont Way, Pinole, CA 94564, USA [48]) and multiwall nanotubes (BU200, Bucky USA, 9402 Alberene Dr., Houston,

TABLE 38.11 The Ratio of Carboxylic Acid to Methylene from FTIR, the Ratio of Total Carbonyl Carbon to Methylene Carbon and to Li, and Atomic per cent of Li and Zn from XPS, in Model Compounds, Electrochemically Deposited Films, Inner Race Deposits, and Black Grease from Failed Motor Bearings FTIR Film

XPS

hydrogen bonded OH

(C=O)salt /C(–H)2

(C=O)total /C(–H)2

(C=O)total /Li

Li (at %)

Zn (at %)

Yes

0.067 (exact)

0.067

1.07

4.3

0.09

Yes —

0.035 —

0.079 0.063

1.5 —

3.6 <0.3

— 3.0

Yes

0.049

—

—

—

—

Yes

0.17, 0.05, 0.054

0.097

1.3

5.1

0.06

Yes

0.086, 0.082

0.11

1.4

4.7

0.12

Yes No No, Yes No

0.072, 0.077 0.076 0.10, 0.06 0.12, 0.20, 0.31, 0.13

0.11 0.14 — —

1.4 0.5 — —

5.3 15.8 — —

— 0.16 — —

Li 12-hydroxy stearate Li 12-hydroxy stearate from grease (brown, stored 8 yr) Zn (12-hydroxy stearate)2 Zn (12-hydroxy stearate)2 after 10 min at 130◦ C eChem SRL grease +36% Prelube A +300 ppm Zn +100 ppm Fe eChem SRL grease +300 ppm Zn eChem SRL grease +16% Prelube A Black grease In-plane residue Ball track residue

The extinction coefficient ratio, εC(–H)2 /εC=O = 0.0475, was calculated from FTIR spectra of methylene C(–H)2 asymmetric stretch and carboxylic acid (C=O–O) anion asymmetric stretch measured for Li 12-hydroxy stearate and Li stearate. Grease samples were rinsed with solvent to remove the oil. For Li 12-hydroxy stearate, the exact ratio of C=O/C(–H)2 is 1/15 = 0.067, and the exact ratio of C(=O)/Li is 1, the exact atomic per cent of Li = 4.8, and for Zn = 2.4. 300 ppm of Zn corresponds to 0.06 atomic per cent of the Lithium 12-hydroxy stearate. These results show evidence for electrochemical oxidation of the 12-hydroxy stearate thickener.

TABLE 38.12 Trial Matrix of Potential Conductivity Additives in TOTM Model Carrier Oil Additive None Disodium sebacate (Ciba DSSG) Succimide (2,5-pyrrolidenedione) Dodecylbenzenesulfonic acid Butylated hydroxy toluene (BHT or Ionol) Ciba irgamet 30 Dicyclohexylammonium benzoate PMC cobratec 911S Mellitic acid Mixtures Succimide (2,5-pyrrolidenedione) Dodecylbenzenesulfonic acid Succimide (2,5-pyrrolidenedione) Dodecylbenzenesulfonic acid Conductivity measured at 1 Hz and 50◦ C.

Copyright 2006 by Taylor & Francis Group, LLC

Concentration (wt%)

Comments

Conductivity (pS/m)

— 1 2 2 2 2 2 2 2

— Milky Mostly insoluble Clear solution Clear solution Clear solution Milky Clear solution Mostly insoluble

250–300 5–7 80–100 180–230 50–70 170–180 200–260 130–150 8–17

1.6 1 7.6 4.8

Hazy

860–990

Hazy/gel

3000–5000

TABLE 38.13 Optimization Matrix of Succinimide/Sulfonate Conductivity Additives in TOTM Model Carrier Oil Concentration wt%

Additive None Succinimide DDBSA Succinimide DDBSA Succinimide DDBSA Succinimide DNNSA Succinimide

— 2 2 1.6 1 7.6 4.8 1.5 1.4 1.5

DNNDSA

0.8

Comments

Permittivity, 1 Hz

Conductivity (pS/m)

— Mostly insoluble Clear solution Hazy

5◦ C 3.9 — — 4.9

50◦ C 6.3 4.0 4.0 6.5

5◦ C 15 — — 140

50◦ C 250–300 80–100 180–230 860–990

Hazy/gel

—

26.0

—

3000–5000

Brownish, hazy

3.0–3.2

4.8–5.6

160–220

4400

Whitish, hazy, looks good

—

2.9–3.2

—

5–8

Succinimide is 2,5-pyrrolidenedione (99.1 g/mol). DDBSA is dodecylbenzenesulfonic acid (326.5 g/mol). DNNSA is dinonyl naphthalenesulfonic acid (460.71 g/mol). DNNDSA is dinonyl naphthalene disulfonic acid (540.79 g/mol). Amounts of DNNSA and DNNDSA are adjusted for molecular weight and normality.

1.E–06

TABLE 38.14 Conductivity Evaluation of Multiwall Nanotubes and Eeonomers in TOTM Model Carrier Oil

Ferrofluid 1 Ferrofluid 2 Ferrofluid 3 Ferrofluid 4

Conductivity(S/m)

1.E–07 Ferrofluid 1 +3%succinimide +2%DDBSDA

1.E–08

Ferrofluid 2 particles Redispersed in DOS

TOTM +7.6%succinimide +4.8%DDBSDA

1.E–09 TOTM +1.6%succinimide +1%DDBSDA

1.E–10

Pure TOTM

Additive None 2% Eeonomer 200F 2% Eeonomer 610F 1% BS200 Multiwall Nanotubes 10% BU200 Multiwall Nanotubes

Conductivity, σ (S/m) 2.5−3.0E−10 6.1E−4 3.1E−4 2.0E−4 2.3E−4 9.0E−4 9.0E−4 8.8E−4 8.6E−4

1.E–11 0

10

20

30

40

50

60

70

Temperature (°C)

FIGURE 38.23 Conductivity of several types of ferrofluid, conductivity additives in model carrier oil, and Ferrofluid 1 combined with one of the most promising conductivity additives

TX 77074, USA) were evaluated in the TOTM model oil. As shown in Table 38.14, the Eeonomers and nanotubes increased the oil conductivity by about five orders of magnitude. A stable mixed suspension of the nanotubes could not be adequately dispersed in the ferrofluid.

Copyright 2006 by Taylor & Francis Group, LLC

The conductivity of the ferrofluid increased with the Eeonomer concentration, and was nearly independent of temperature between 5 and 50◦ C, as shown in Figure 38.24. The conductivity as a function of temperature for Ferrofluid 1 containing Eeonomers is shown in Figure 38.25(a). The conduction mechanism seems to be limited by electronic transport through the Eeonomers, rather than by diffusive contacts between the particles, since the product of the conductivity and the viscosity of the ferrofluid containing Eeonomers decreased with temperature, Figure 38.25(b). The metallic-like conductivity of the conducting polymer sheath is decreased by scattering due to lattice vibrations faster than the transport between

(a) Conductivity (S/m)

1.E–02

1.E–04

1.E–04 1.E–06 2% Eeonomer 610 F 0.5% Eeonomer 610 F 0.1% Eeonomer 610 F Ferrofluid 1 alone

1.E–08 1.E–10

1.E–05

0

10

20

30

40

50

60

Temperature (°C) (b) Eeonomer 610 F, 50°C Eeonomer 200 F, 50°C Eeonomer 610 F, 25°C Eeonomer 200 F, 50°C Eeonomer 610 F, 10°C Eeonomer 200 F, 10°C Eeonomer 610 F, 5°C Eeonomer 200 F, 5°C

1.E–06

1.E–07

1.E–08

0

0.5 1 1.5 2 2.5 Eeonomer concentration (wt%)

3

Viscosity ⫻ conductivity (Pa-sec-S/m)

Conductivity (S/m)

1.E–03

1.E–02

1.E–02 1.E–04 1.E–06

0

Many disk drives are now being built with fluid dynamic bearing motors. These replace ball bearing spindle motors, because their lower nonrepeatable runout allows the servomechanism to follow narrower data tracks. At the heart of a fluid dynamic bearing are a shaft in a sleeve for radial thrust and a thrust plate and a bushing for axial thrust. Embossed on one face of the radial and axial thrust members are grooves, which force the oil inward, creating the pressure internal that provides the bearing stiffness. The oil film thickness in high performance motors for 10 to 15 krpm is typically 5 to 10 µm. Two fundamental requirements of fluid dynamic bearing oil are low viscosity and low vapor pressure. The viscosity must be thin enough to allow for spin-up in a reasonably short period of time at temperatures approaching 0◦ C. For example, the spin-up time for prototype disk drives with fluid bearing motors is shown in Figure 38.26. The viscosity dominates the spin-up time when it is higher that about 25 mPa-sec. For lower viscosities, the spin-up

Copyright 2006 by Taylor & Francis Group, LLC

10

20

30

40

50

60

Temperature (°C)

FIGURE 38.25 Conductivity of Eeonomers in Ferrofluid 1 as a function of Eeonomer temperature (a), and the product of conductivity × viscosity as a function of temperature (b) with additives in Ferrofluid 1 25

Spin-up time (sec)

38.3.3 Fluid Bearing Motor Oil

2% Eeonomer 200 F 0.5 Eeonomer 200 F 0.1% Eeonomer 200 F

1.E–10

FIGURE 38.24 Conductivity of Eeonomers in Ferrofluid 1 as a function of Eeonomer concentration and temperature

particles is increased by Brownian motion with increasing temperature. While the Eeonomers appear to be the most effective means to increase the ferrofluid conductivity, the long-term stability may be degraded by reaction of the dodecylbenzenesulfonic acid with the ester carrier oil. Furthermore, the conducting polymer sheath may also be crushed off of the carbon black in milling during the initial dispersion phase of ferrofluid manufacturing.

2% Eeonomer 610 F 0.5% Eeonomer 610 F 0.1% Eeonomer 610 F Ferrofluid 1 alone

1.E–08

Base oil Base oil + Conductivity additive

20

15

10

5 0

10

20

30

40

50

60

Viscosity (mPa-sec)

FIGURE 38.26 Spin-up time for prototype disk drives as a function of fluid bearing oil viscosity measured between 1 and 25◦ C. The conductivity additive was mixed polymers, as described in Reference 41. The base oil is a commercially available diester

time is limited by inertia of the disk pack and peak motor power. The oil vapor pressure must be low enough so that there is no appreciable evaporation over the 5 to 7 yr lifetime of the motor at its maximum internal operating temperature of about 80◦ C. In addition, the fluid bearing oil must be sufficiently conductive to dissipate static charge accumulation

TABLE 38.15 Molecular Structures of the Diester Oils Investigated for Fluid Dynamic Bearing Motors Molecular Acronym weight (g/mol)

Structure O

DBS

314

O

O O O

DOA

O

371

O O

DOZ

413

O

O O

O O

DOS

427

O

O O O

DIA

427

O

C

C

O

O

due to air shear, electrical double layer shear [49], and work function difference between the slider and disk [50]. The oil must also have a low dc dielectric permittivity to minimize charge storage by ionic separation or dipole orientation. Finally, well formulated oil should contain antioxidants and other additives to inhibit oxidation and corrosion. Formulation and testing of antioxidants for fluid bearing oil is already described in Reference 41. 38.3.3.1 Viscosity and vapor pressure The oil viscosity and vapor pressure are thermodynamically interrelated by the dispersion and dipolar forces between the molecules. All of the intermolecular potential energy must be surmounted to evaporate a molecule from the liquid, and part of the intermolecular potential energy must be surmounted for flow. To first order, the dispersion force is proportional to the number and type of atoms, thus to molecular weight. For the relatively low molecular weight oils useful in fluid bearings, the flow is mostly by the whole molecule, rather than segments of the molecule. Thus, increasing the molecular weight, or polarity, to reduce the vapor pressure, the viscosity increases. The relationship between oil vapor pressure and viscosity is thoroughly investigated with Eyring’s chemical reaction rate theory of evaporation and flow in Karis and Nagaraj, [32]. The essence of their findings is summarized below: A variety of low molecular weight hydrocarbon oils were investigated with the goal in mind of providing guidelines for selection of the oil with the lowest possible viscosity and vapor pressure. The oils studied were diesters

Copyright 2006 by Taylor & Francis Group, LLC

(Table 38.15), triesters (Table 38.16), and nonpolar hydrocarbons (Table 38.17). Some of the oils are isomers, having the same molecular weight and composition, but differing only in molecular structure. More details of the oil properties are given in Reference 32. According to the Eyring Equation (38.6), a plot of ln(η) vs. 1/T is a straight line with slope, Evis /R and intercept ln(Nhp /Vl ) − Svis /R. The viscosity of several low molecular weight ester and hydrocarbon oils are shown plotted as ln(η) vs. 1/T in Figure 38.27. There is some systematic deviation from linearity, but overall the general trend is fit by the Eyring equation between −20 and 100◦ C. trans + S rot is The flow-activation entropy Svis = Svis vis approximately the sum of the translational and rotational contributions. The slope and intercept of the ln(η) vs. 1/T plot is then employed to calculate Svis , and Evis for each of the oils. These thermodynamic properties for flow are listed in Table 38.18. A similar analysis was performed for the vapor pressure of these oils. According to the Claperyron Equation (38.15), a plot of ln(P0 ) vs. 1/T is a straight line with slope − Evap /R, and intercept ln(P) − 1 + Svap /R. The vapor pressure of several low molecular weight ester and hydrocarbon oils are shown plotted as ln(P0 ) vs. 1/T in Figure 38.28. There is some systematic deviation from linearity, but overall the general trend is fit by the Eyring equation between −20 and 100◦ C. The vaporization trans + S rot is approximately the sum entropy Svap = Svap vap of the translational and rotational contributions. The intercept of the ln(P0 ) vs. 1/T plot is then employed to calculate

Svap and Evap for each of the oils. The translational

TABLE 38.16 Molecular Structures of the Triester Oils Investigated for Fluid Dynamic Bearing Motors Acronym

Molecular weight (g/mol)

Structure O

TRIB

H2C O O CH

302

H2C O

O O

O TRIH

387

H2C O O CH O H2C O O

O TRIO

471

H2C O O CH O H2C O O CH3

O O

C O

TMP

471

O O

O

TABLE 38.17 Molecular Structures of the Nonpolar Oils Investigated for Fluid Dynamic Bearing Motors Acronym

Molecular weight (g/mol)

2,2-DPP

196

1,3-DPP

196

PAO

240

PRS

269

SQL

423

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Structure

ln (Viscosity) (Pa–sec)

(a) –1 –2 –3 –4

DBS DOA DOZ DOS DIA

Diesters

–5 –6 –7 0.0025

0.0030

0.0035

0.0040

1/Temperature (1/ °K)

ln (Viscosity) (Pa–sec)

(b)

–1 –2 –3 –4

TRIB TRIH TRIO TMP

Triesters

–5 –6 –7 0.0025

0.003 0.0035 1/Temperature (1/ °K)

0.004

ln (Viscosity) (Pa–sec)

(c) 0 –2 –4

2,2–DPP 1,3–DPP PAO PRS SQL

Nonpolar

–6 –8 0.0025

0.003 0.0035 1/Temperature (1/ °K)

0.004

FIGURE 38.27 Natural logarithm of viscosity as a function of inverse temperature (a) diesters, (b) triesters, and (c) hydrocarbon oils, from Reference 32. The line is a fit to the Eyring equation

component of the vaporization is approximately equal to the vapor phase entropy given by Equation (38.16), and the rotational component is similarly calculated in the vapor phase with Equation (38.17) [32]. The vaporization entropy and the calculated vapor phase translational and rotational entropy are employed to estimate the liquid phase entropy as Sliq ≈ Svap − Svap . These thermodynamic flow properties for vaporization are listed in Table 38.18. Note that typographical errors in the units of Svap , Sliq , and Svis from the corresponding Table 38.5 in Karis and Nagaraj, [32] are correctly written here in Table 38.18. Further insight into the relationship between the evaporation and flow properties of the potential fluid bearing motor oils is obtained by combining the results together within the framework of thermodynamics and the reaction rate model for evaporation and flow [51,52]. The

Copyright 2006 by Taylor & Francis Group, LLC

ratio of the vaporization energy to the flow-activation energy n = Evap / Evis provides a measure of the partial decoupling of intermolecular forces between molecules during flow relative to the complete decoupling that takes place upon vaporization [53]. Another thermodynamic quantity that plays a key role in the flow process is the flow-activation rotational entropy. The flow-activation rot , was calculated from the comrotational entropy, Svis bined vapor pressure and viscosity vs. temperature in Karis and Nagaraj, [32]. If there is a way to lower the viscosity without increasing the vapor pressure, it seems that it can only be done by increasing the flow-activation entropy, Svis . For the oils shown here, Svis is proporrot , as shown in Figure 38.29(a). However, tional to Svis rot

Svis decreases with n, as shown in Figure 38.29(b). Thus, the flow-activation rotational entropy decreases with the

TABLE 38.18 Evaporation and Flow Thermodynamic Properties Calculated from Vapor Pressure and Viscosity Data for Low Molecular Weight Hydrocarbon Oils Evaporation

Oil DBS DOA DOZ DOS DIA TRIB TRIH TRIO TMP 2,2-DPP 1,3-DPP PAO PRS SQL

Flow

Evap (kJ/mol)

Svap (J/mol-◦ K)

Sliq (J/mol-◦ K)

Evis (kJ/mol)

Svis (J/mol-◦ K)

rot Svis (J/mol-◦ K)

n

90.7 94.4 84.5 108.6 94.1 81.8 93.3 116.3 81.0 59.1 74.2 89.6 78.5 82.8

160 160 125 175 143 154 156 185 110 120 159 188 166 124

114 117 154 105 137 163 167 143 218 144 105 80 104 156

20.6 24.7 26.7 26.7 28.9 25.1 23.2 26.2 28.9 25.5 22.3 22.7 22.8 32.9

−4.2 4.1 6.8 5.8 11.2 10.5 −1.5 3.5 10.4 17.0 8.4 4.5 4.6 21.2

−3.1 6.61 19.8 2.6 18.1 12.5 2.4 −1.4 30.3 30.4 6.6 −4.2 2.6 36.6

4.4 3.8 3.2 4.1 3.3 3.3 4.0 4.4 2.8 2.3 3.4 3.9 3.5 2.5

Evaporation properties are referenced to 100◦ C and atmospheric pressure (100 kPa). Flow properties are referenced to 40◦ C.

amount of decoupling, or asymmetry between vaporization and flow. For example, spherical molecules could become more freely rotating in the flow-activated state, while rodlike molecules rotation becomes less likely in the flow-activated state, as they surmount the energy barrier between adjacent molecules in the surrounding liquid. While the preceding discussion provides qualitative general guidelines for how the thermodynamic properties of vaporization and flow should differ in oil with improved vapor pressure and viscosity for an improved fluid bearing motor oil, little can be said about specifically what molecular structure and compositions can be synthesized to provide these benefits. Recent developments on molecular dynamic simulation promise to bridge this gap between molecular structure and thermodynamics. For example, Bair et al. [54] have demonstrated good agreement between high shear viscosity measurements and predictions from a molecular dynamics simulation. Yet, the model requires input of a particular molecular structure, in their case, squalane, and numerically intensive computations are required to predict the viscosity. Even more complexity is involved if one tries to similarly predict the viscosity of a more complex polar molecule such as diesters. Oil blends, or viscosity reducing additives have also been considered. Blending oils changes the pressure– viscosity coefficient [45] and provides an intermediate viscosity [55,56]. The vaporization energy and entropy, and flow-activation energy and entropy are shown for

Copyright 2006 by Taylor & Francis Group, LLC

a blend of polar diester oil in nonpolar PAO oil in Figure 38.30. In this case, the vaporization energy of the blend was less than that of the pure components. The entropy of the blend was higher than that of the pure components. The reduction in the vaporization energy outweighed the increase in liquid entropy, and the vapor pressure of the blend was higher than that of the pure components. There is, however, an interesting dip in the properties near 95% DOS, which was reproducible. The flow-activation energy and entropy of the blends are shown in Figures 38.30(c) and Figure 38.30(d). The flow-activation energy is approximately given by a linear combination of the weight fractions of blend components. There is some benefit in the flow-activation entropy near 50%. Taking the analysis one step further, the flow-activation rotational entropy has a sharp maximum near 95% DOS in Figure 38.31(a). The ratio n = Evap / Evis has a sharp minimum near 95% DOS, Figure 38.31(b). This unusual behavior near 95% DOS suggests that synergistic effects are possible in oil blends. These probably arise from clustering of the nonpolar oil with the aliphatic chains of the diester. Perhaps this type of effect could be exploited to develop viscosity reducing additives, which have a lower vapor pressure than the base oil. However, for a blend to be useful, it would also need to be capable of forming an azeotrope, and then it could only be used in motors at the azeotropic composition. Otherwise, the evaporation of the oil component

(a) 10 Diesters ln (P 0) (Pa)

5 DBS 0 DOA –5

DOZ

–10 –15 0.0020

DIA

DOS 0.0025 0.0030 1/Temperature (1/°K)

0.0035

(b) 10 Triesters ln (P 0) (Pa)

5

TRIB

0 TRIH

–5

TMP –10 –15 0.0020

TRIO 0.0025 0.0030 1/Temperature (1/°K)

0.0035

(c) 15 Nonpolar 2,2-DPP

ln (P 0) (Pa)

10

1,3-DPP

5 PRS

0

PAO

–5 –10 –15 0.0020

SQL 0.0025 0.0030 1/Temperature (1/°K)

0.0035

FIGURE 38.28 Natural logarithm of vapor pressure as a function of inverse temperature (a) diesters, (b) triesters, and (c) hydrocarbon oils from Reference 32. The line is a fit to the Clapeyron equation. Ambient pressure P = 100 kPa

with the highest vapor pressure would gradually change the oil blend viscosity and vapor pressure, leading to an unfavorable increase in the viscosity with age.

38.4 CONCLUSIONS AND FUTURE OUTLOOK Magnetic recording disk drives employ the state of the art lubrication in lubrication science and technology to achieve unparalleled reliability. Continued growth in storage capacity relies on ever more fundamental understanding to provide the required advancements in the key areas of lubrication, nanolubrication of the head disk interface, and fluid bearing motor lubricants. The key properties of the PFPE disk lubricants were described here. The bulk and thin film properties, in combination with polar end groups, provide many years of lubrication by virtue of viscosity enhancement and vapor pressure reduction of molecularly thin films. Advanced disk lubricants are being

Copyright 2006 by Taylor & Francis Group, LLC

designed to fulfill increasingly stringent requirements of environmental variations [57,58] and friction at low flying height [59]. Grease lubricated ball bearing spindle motors have reached their pinnacle with 10,000 rpm drives. Over the course of developing sophisticated channeling greases for these high performance, low vibration, long-life, bearings, much was learned about grease chemistry, physical properties, and the effects of contamination. Herein was described a comprehensive overview of grease yield stress and the effects of grease contamination on yield stress and electrochemical oxidation of an ester oil based grease with a lithium soap thickener. The same principles apply to precision greases in general; therefore, they may potentially be useful in wide ranging fields of application where smooth high speed rotation is needed. Spindle motors are rapidly evolving toward fluid dynamic bearings, which provide much smoother rotation

(a) 25

DSvis(J/mole–°K)

20 15 10 5 0 –5 –10 –10

0

10 20 30 ∆S rot vis (J/mol –°K)

40

50

(b) 50

rot (J/mole–°K) ∆S vis

40 30 20 10 Diesters Tristers Nonpolar

0 –10 2

3 4 ∆S rot vis (J/mol –°K)

5

FIGURE 38.29 Flow-activation entropy vs. flow-activation rotational entropy (a) and the flow-activation rotational entropy vs. the ratio of the vaporization energy to the flow-activation energy (b) for the oils listed in Tables 38.15 to 38.17, from Reference 32

95

(c) 30

90

28 ∆Evis (kJ/mol)

∆Evap (kJ/mol)

(a)

with comparable or better stiffness than ball bearings. Stiffness is provided by the relative motion between a shaft and a sleeve, one of which contains a pattern of grooves on its surface. The grooves pressurize a several micron thick film of oil. This chapter highlighted two key properties of the fluid bearing oil, its viscosity and vapor pressure. Present fluid bearing oils have a low enough vapor pressure so that the evaporation loss of oil is small over the lifetime of the drive. However, there is a trade-off between the vapor pressure and oil viscosity such that the lowest operating temperature of the drive is limited by the maximum power of the motor and the oil viscosity. Attempts to use lower viscosity oils result in oils with a higher vapor pressure, and this appears to be a physical constraint of oils in general. Detailed thermodynamic analysis of the relationship between oil vapor pressure and viscosity were reviewed in this chapter. It was shown the flow and vaporization activation energies are linked to one another by the dispersion and polar interaction between the oil molecules. There is, however, in principle, some chance of reducing the viscosity without altering the activation energies if a molecular structure could be found that has a large positive rotational component of the flow-activation entropy. Molecular structures examined so far provide limited insight into how this may be accomplished. Another approach is to develop a blend of two different oils, combining mixtures of polar and nonpolar molecules. There is the potential to develop an oil blend that forms an azeotrope and also has a lower viscosity and vapor pressure than the pure component oils.

85 80 75

26 24 22

70

20

65 0

20

40

60

80

100

0

20

wt% DOS in PAO (b) 180

60

80

100

80

100

(d) 10

160

∆Svis (J/mol-°K)

∆Svap (J/mol-°K)

40

wt% DOS in PAO

140 120 100

8 6 4 2

0

20

40

60

wt% DOS in PAO

80

100

0

20

40

60

wt% DOS in PAO

FIGURE 38.30 Vaporization activation energy and entropy (a) and flow-activation and entropy (b) for blends of DOS in PAO

Copyright 2006 by Taylor & Francis Group, LLC

(a) 30

rot ∆Svis (J/mol–°K)

25 20 15 10 5 0 –5 –10 0

20

40 60 wt% DOS in PAO

80

100

0

20

40 60 wt% DOS in PAO

80

100

(b) 4.0

3.5 n 3.0 2.5

polydisperse lubricant evaporation model. Many of the fractionated PFPE lubricants were graciously provided by R. Waltman in the Hitachi Global Storage Technologies San Jose Development Laboratory. Many thanks are due to the excellent summer students who contributed to this work, A. Brooks, J. Castro, A. Voss, and A. Greenfield. Much of the NMR characterization, viscosity, density measurement, and evaporation data analyses were performed by D. Hopper over about 5 yr working part time and in summers with us. H.S. Nagaraj first introduced me to ball bearing grease, and then fluid bearing oil for spindle motors. The grease mill was designed and built by J. Miller, who also prepared the modified grease samples, and performed the electrochemical measurements on the greases. Invaluable insight and technical discussions on surface energy were provided by G. Tyndall at the IBM Almaden Research Center. Finally, I thank my managers B. Marchon, J. Lyerla, O. Melroy, and J. Kaufman for their encouragement and support throughout this work. Special thanks are also due to A. Hanlon and C. Hignite for their guidance and advice.

2.0

FIGURE 38.31 The rotational component of the flow-activation entropy (a) and the ratio of the vaporization energy to the flowactivation energy, n, (b) for blends of DOS in PAO

Much fruitful work remains to be done here in the quest for a lower viscosity and vapor pressure fluid bearing motor oil. The reward for success will be a reduction in spin-up time at cold temperature, and a lower minimum operating temperature for drives with fluid bearing motors.

AKNOWLEDGMENTS Throughout the decade of work on drive industry lubricants, a substantial team effort enabled the progress described in this chapter. Thanks are due to P. Kasai at the IBM Almaden Research Center for technical discussions on lubricant end groups and NMR peak assignments. Thermal analysis, dielectric spectroscopy, and rheological and viscosity measurements were done by M. Carter, and NMR spectroscopy and interpretation were provided by J. Burns, in the Hitachi Global Storage Technologies San Jose Materials Analysis Laboratory. Also, in the Hitachi Global Storage Technologies San Jose Materials Analysis Laboratory, the author thanks D. Pocker for the XPS, and F. Eng for IR microscopy on grease residues. Thanks are due to R. Siemens, who carried out the GPC measurements on PFPE lubricants. The author is grateful to T. Gregory for invaluable advice and technical discussions on PFPE vapor pressure, and development of the

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39

Synthetic-Based Food-Grade Lubricants and Greases Michael J. Raab CONTENTS 39.1 39.2 39.3 39.4

Introduction Food-Grade Lubricants — What are They? Lubricant Additives Lubrication in Food Processing: A Brief Regulatory History(United States) . 39.4.1 White Mineral Oils 39.4.2 Dimethylpolysiloxane 39.4.3 Hydrogenated Polyalphaolefin Synthetic Fluids 39.4.4 Other Regulations and Laws 39.5 Food-Grade Lubricants Registration 39.6 Global Trends with Potential Influence on the Food-Grade Lubricant Market 39.6.1 Religious Organizations Influence Food-Grade Lubricant Composition 39.7 Opportunities for Synthetic-Based Food-Grade Lubricants 39.8 Conclusions References

39.1 INTRODUCTION Processing of foods and beverages into consumable products is an immense business enterprise. In the United States, $561 billion in sales revenue was generated in 2002 ($485 billion in 1997) by this industry (Table 39.1). This makes the food-processing industry comparable in size to the transportation equipment manufacturing industry, representing nearly 14.6% of all manufacturing in the United States (up from 13% in 1997). It is bigger than the entire USA chemical industry or its computer equipment market. Nearly 29,350 establishments utilized a total of 1.7 million employees to create $233 billion in value-added goods. Nearly $2.8 billion of food production machinery was sold to support this market. Over the last several years there has been a profound shift in the role of government regulations and inspections away from command and control strategies toward focus on food safety. For example, consider the impact that USDA has on meat and poultry supply; in 1996, 25 voluntary recall notices were issued. By 2000, that number grew to 76 recall notices. The total weight of meat (tons of product withdrawn from the market) affected by these recall notices follows a slightly different pattern: from virtually zero pounds in 1996 to over 45 million pounds in 1998,

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followed by a decline to under 22 million pounds in the year 2000. In other words, the increased scrutiny by the United States Department of Agriculture’s (USDA) Food Safety and Inspection Service (FSIS) appears to have caused a drop of over 50% in contaminated, diseased, or mislabeled meat products reaching the marketplace. It may be of interest to the members of the lubricants and grease industry that during this period, three of the recalls involved contamination of a meat product by a nonfood grade lubricant. While the percentage of all meat impacted by lubricants was small (0.5%), the recalls impacted 500,000 pounds of the product [2]. Food safety is not just an American concern. Certainly the widely published European cases of “mad-cow disease” or Bovine Spongiform Encephalopathy (BSE), plus worldwide cases of Escherichia coli O157:H7, Listeria, Salmonella, and other food borne bacteria support an argument for the global aspects of food safety. Yet, the areas of concern are much broader. In 1999 the Pan American Health Organization (PAHO) members, including the United States, pushed for “comprehensive inter-country food surveillance” [3]. Among the key elements of this plan was the implementation of Hazard Analysis and Critical

TABLE 39.1 2002 Economic Census Food, Beverage, and Tobacco Product Manufacturing: Advance Comparative Statistics for the United States 1997 NAISC Code 311 312

Number of establishments

Sales revenue

Annual payroll

Paid employees

26,374

$457,333,358

45,456,279

1,507,923

2,997

104,027,582

6,798,446

157,347

29,371

561,360,940

52,254,725

1,665,270

Food manufacturing, beverage and tobacco product manufacturing, Food, beverage, and Tobacco manufacturing

Totals

Control Point (HACCP). Since that time, the World Health Organization [4], the Food and Agriculture Organization of the United Nations, the Pan American Health Organization [5] and other global organizations have established food safety as a priority. Central to these food safety plans are the implementation of HACCP. Consider the supply and demand shifts of global food production. Escalating land value in the United States, Canada, and Europe are working to increase the cost of agricultural production in those regions. Lesser developed countries with easily abundant land stand ready to fill the production gap. Shifting attitudes regarding international trade and trade barriers are also abetting this change. To illustrate, since the ratification of the North American Free Trade Agreement (NAFTA), agriculture trade between the United States and Mexico has increased substantially: 34% of imports into the United States come from NAFTA partners; imports increased from $5 billion to $12 billion over the period from 1989 to 1999; NAFTA partners import 25% of all agricultural exports from the United States; and, U.S. exports to NAFTA partners grew from $5 billion to nearly $12 billion during the 1989 to 1999 period [6].

39.2 FOOD-GRADE LUBRICANTS — WHAT ARE THEY? “Food-Grade Lubricants” are compounded or uncompounded products acceptable for use in meat, poultry, and other food-processing equipment, applications, and plants. A distinction is drawn between products that may come into contact, those that will contact, and those that will never contact the foodstuff. The United States Department of Agriculture (USDA) originally established a rating system to control lubricants (nonfood compounds) [7] that is still used today: H1 for use as lubricants where incidental contact might occur generally on equipment above the edible product line H2 for use where no contact is possible or below the edible product line, and H3 for soluble oils. H3 lubricants are acceptable for hooks, trolleys, and similar equipment. In cases where the lubricant is used in intimate contact (say as a baking product release lubricant),

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the Food and Drug Administration (FDA) publishes a list of authorized ingredients in the Code of Federal Regulations [8]. An H1 food-grade Lubricant is generally composed of one or more approved base stocks and additives (“approval” is discussed below). The maximum allowable concentration of each additive is controlled. While the composition of H2 lubricants are not specifically controlled, they must exclude poisons, toxins, or other materials that cause a health risk. The following lubricant base stocks are in commercial use in or as H1 lubricants (other uses are included for reference): 1. White Mineral Oil (21 CFR 172.878) may be used as a release for confectionery, bakery, dehydrated fruit, or yeast; floatation aid; component of hot-melt coating for meat; and as a dust control agent. 2. Petrolatum (21 CFR 172.880) may also be used as a release aid and as a protective coating for raw fruits and vegetables. 3. Synthetic Isoparaffinic Petroleum Hydrocarbons (21 CFR 172.882) may be employed as a defoamer, component in insecticides, coating on shell egg, and as a floatation aid. 4. Technical White Oils (21 CFR 178.3620) are authorized for use as a coating on eggshells, defoamer, floatation aid, and insecticide component. Addition to food is limited to 10 parts per million. 5. Linear, random polyalkylene glycols, having an average molecular weight of 1500 or more are approved under 21 CFR 178.3570. Addition to food is limited to 10 parts per million [9]. 6. Dimethylpolysiloxane with a viscosity greater that 300 cSt or more is approved in 21 CFR 178.3570. Addition to food is limited to 1 part per million.

39.3 LUBRICANT ADDITIVES The base oils described above are sometimes used directly as lubricants on operating equipment in lightly loaded and

low speed applications. However, as operating conditions become more severe the demands on the lubricant are greatly increased. To perform under more severe conditions the lubricant is formulated using one or more “approved” additives: • “Generally Recognized as Safe” (GRAS) for use in food • Used in accordance with the provisions of a prior

sanction or approval. • Contained in paragraph (a) (3) of 21 CFR 178.3570 titled

“Lubricants with Incidental Food Contact.”

39.4.2 Dimethylpolysiloxane Prior to 1958 there were no regulations covering food contact substances, or food additives in general. Some substances were allowed by their common use in food prior to 1958 and prior sanction letters from the FDA allowed some. One producer, Dow Corning, holds prior sanction letters for the use of dimethylpolysiloxane fluids and emulsions as defoaming agents in food processing that dates back to 1953. Specific regulations covering the use of dimethylpolysiloxane in lubricants were allowed in 1965 as a result of a petition filed by General Electric (GE) [13].

39.4 LUBRICATION IN FOOD PROCESSING: A BRIEF REGULATORY HISTORY(UNITED STATES)

39.4.3 Hydrogenated Polyalphaolefin Synthetic Fluids

The processing of agricultural or animal substances into consumable food products is performed in a multifunctional manufacturing plant. Such processing includes one or more operations: cleansing, sterilizing, homogenizing, blending, mixing, stirring, baking, freezing, chilling, baking, frying, cooking, cutting, slicing, packaging, canning, or bottling. Large scale food-processing is often done with machinery and support components such as pumps, mixers, tanks, hoses and pipes, chain drives, and conveyer belts. Such machinery and associated support equipment contains mechanical or moving components. Hydraulic fluids, greases, gear and chain lubricants, and other oils are required to ensure reliable and efficient operation of these components. While good engineering design can reduce the likelihood of adulteration of the food by these lubricants, myriad operating constraints and tradeoffs (economic, engineering, logistics, hygienic practice, quality assurance, applicable regulations, and others) tend to increase the contamination risk. Therefore it is essential that those lubricants that may incidentally contact the food product be physiologically safe. As mentioned earlier, formulated lubricants are based on one of five FDA approved base-stock classes: white oil (various grades); synthesized hydrocarbons (polyalphaolefins, polyisobutenes); polyalkylene glycol; dimethylpolysiloxane; or natural oils.

Polyalphaolefin meet all the requirements of the FDA as a white mineral oil (21 CFR 172.878). They were introduced to the market in 1981 by Gulf Research and Development Company [14].

39.4.1 White Mineral Oils The United States Pharmacopoeia (USP) first listed “white mineral oils” in its tenth decennial revision of 1926 [10]. In 1935 an early paper presenting the general principles of white oil manufacturing can also be found. Other papers, including a text, were later published on the subject [11]. In 1950, National Formulary (NF) added, “white mineral oil” to its monographs [12]. In 1965, following enactment of the Food Additives Amendment, the FDA issued regulations covering the application of food-grade lubricants in industrial applications.

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39.4.4 Other Regulations and Laws The 1958 Food Additives Amendment to the Federal Food, Drug and Cosmetics Act created regulations covering food contact substances, or food additives in general. Two federal laws requiring the maintenance of safe and sanitary conditions in federally inspected meat and poultry plants were then enacted. These laws are the “Federal Meat Inspection Act” as amended by the “Wholesome Meat Act of 1967,” and the “Poultry Products Inspection Act” as amended by the “Wholesome Poultry Products Act of 1968.” These acts were placed for enforcement under the Food Safety and Quality Service through the Meat and Poultry Inspection Program (a part of USDA). The inspection program called for authorization of substances or compounds used in processing plants [15]. Lubricants used with equipment in the processing of foods and beverages require special selection and application in order to meet the unique toxicity and sanitation needs. Two U.S. government agencies, the United States Department of Agriculture (USDA) regulates meat and poultry plants and the Food and Drug Administration (FDA) monitors other food and pharmaceutical manufacturing operations. Until 1998 the USDA [16] maintained a system of oversight by granting “prior authorization” for lubricants intended for use in food-processing facilities. In September of that year, regulatory changes were imposed that affected the food-grade lubricant market of the future. The FSIS eliminated the preapproval program and implemented new regulations and procedures [17]. These regulations have shifted the burden of assessing risk. Implementation of those regulatory requirements is defined by HACCP procedures. They make the food processor (manufacturer) responsible for the proper selection of lubricants. However,

the lubricant manufacturer and/or the equipment supplier (or OEM), still remains responsible for the composition and effectiveness of the lubricant. HACCP requires the food processor to perform an assessment of each point in the operation where contamination might occur. Implicit in this assessment is the need for the food processor to know and understand the physiological risk that a lubricant may pose. Such an analysis may require the processor to review and approve the chemical composition of the lubricant. Prior to February 1998, the USDA performed that review role. This transfer of responsibility allows USDA and FSIS to redirect its resources to ensuring the implementation of HACCP regulations.

While current efforts of the third-party certifiers focus around adopting the former USDA guidelines, industry groups are at work to more rigorously define “Food-Grade lubricants.” These steps are the likely precursor to the development of an ISO standard; steps have already been initiated in Germany (DIN) and the USA (ANSI) in this regard. Groups such as the European Hygiene Equipment Design Group, seek to evolve standards that go well beyond the current “gate keeper” principles evolved through the former USDA guidelines. Thus, the reader can expect this area to remain in flux for the next several years.

39.5 FOOD-GRADE LUBRICANTS REGISTRATION

The importance of food safety is reflected in the decisions recently adopted by the 53rd World Health Assembly of WHO that issued Resolution WHA53.15 establishing food safety as a priority (May 2000). Several regional organizations are now developing plans supporting this objective. For instance, the Pan American Health Organization issued a draft of its plan on March 22, 2001 [20]. A joint committee of The Food and Agriculture Organization of the United Nations and The World Health Organization was established in 1963 (Codex Alimentarius Commission), but its role grew significantly in the 1990s:

Commercial organizations responded to the changes in registration procedures. Notably, NSF International [18] (see www.nsf.org) developed a program to offer “third party” or “external agency” certification programs. It may interest the reader to note that the USDA/FSIS anticipated the possibility of a third-party certifier when it originally issued its intention to change the regulations. “… FSIS specifically requests comments on whether an industry-recognized, nongovernment organization or laboratory could provide prior approval or a similar service to chemical manufacturers and distributors …” [19]. In concept, the approval process has changed little under the current “external agency” certification programs. These programs are based on the original USDA/FSIS “pre-authorization” system. Namely, the lubricant composition is submitted to NSF along with other supporting documentation. Each component in the composition is reviewed against the U.S. Food and Drug Administration list of permitted substances (see 21 CFR Title 178). Other documentation submitted to them includes certifications regarding raw material sourcing and manufacturing practice(s). Registration programs cover the original formulation by the manufacturer, amended formulation, and distributors (for authorized rebranding). Third-party registrars issue a “registration number” as a part of a “Registration Letter” for each formulation and/or rebrand. NSF offers an internet-based Web service available for checking the status of registrations. NSF maintains a listing on this Internet site of products reviewed and registered by NSF under its applicable guidelines. Not all countries accept a third-party certifier. For instance, the Canadian Food Inspection Agency operates a product registry for food-grade lubricants used in that country. A noninclusive list of other examples includes New Zealand, Australia, and Japan. Efforts are underway to bring about wider acceptance of the NSF program by these countries.

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39.6 GLOBAL TRENDS WITH POTENTIAL INFLUENCE ON THE FOOD-GRADE LUBRICANT MARKET

The Codex Alimentarius has relevance to the international food trade. With respect to the ever-increasing global market, in particular, the advantages of having universally uniform food standards for the protection of consumers are self-evident. It is not surprising, therefore, that the Agreement on the Application of Sanitary and Phytosanitary Measures (SPS) and the Agreement on Technical Barriers to Trade (TBT) both encourage the international harmonization of food standards. A product of the Uruguay Round of multinational trade negotiations, the SPS Agreement cites Codex standards, guidelines and recommendations as the preferred international measures for facilitating international trade in food. As such, Codex standards have become the benchmarks against which national food measures and regulations are evaluated within the legal parameters of the Uruguay Round Agreements [21].

Taken together these international efforts toward a global HACCP program will shape the acceptance of food-grade lubricants and greases in the future global marketplace.

39.6.1 Religious Organizations Influence Food-Grade Lubricant Composition Several major religions further restrict the formulation of food-grade lubricants. Two such are the Jewish and the Muslim religions. With nearly 16 million Jews and

TABLE 39.2 Toxicological Properties of Selected Synthetic Base Fluids Base stock designation Technical white oil Polyalphaolefin (Manufacturer’s data) Polyalkylene glycol (Handbooka )

Acute oral LD50, mg/kg

Acute dermal LD50, mg/kg

>5,000 >15,380 “Relatively Harmless” >15,700 “Relatively Harmless”

— >3,0 “Practically non-toxic” n/a

a N. Irving Sax, “Dangerous Properties of Industrial Materials.”

Sludge,mg TAN change

PAO, 204°C

Vis. change, %

Mineral oil,190°C

0

2

4

6

8

10

FIGURE 39.1 Oxidation–corrosion stability (24 h). Mineral oil vs. polyalphaolefin base food grade compressor lubricants (ISO 46) (By federal Test Method 5308)

1.4 billion Muslims worldwide, such laws have wide influence in the food-processing industry [22]. Under both religions strict rules cover all aspects of food processing. The following paragraphs list only the portions of those dietary laws applicable to lubricants. In both religions, the lubricant manufacturing plant is subject to supervision of the applicable organization. The Jewish dietary laws are generally termed “Kosher for Pareve” or simply Kosher. Approval under Kosher law is done by one of several rabbinic orders. In the United States, the Orthodox Union and the Organized Kashrus Laboratories, both in New York, are two major approval organizations known to this author to be active in the approval of food-grade lubricants. Essentially, Kosher laws prohibit the use of pork, pork by-products, and control or exclude various other materials and processes. This limitation precludes the use of lard oils and derivatives in lubricants intended for use in Kosher food processing. Kosher laws also prohibit contamination of meats with dairy and eggs. All equipment must be properly cleaned, “kosherized” and left idle for 24 h before and after making Kosher products. The Muslim faiths impose “Halal” laws (an Arabic term meaning lawful or permitted for Muslims) on their food products. In the Unitde States, the Islamic Food and Nutrition Council of America (Chicago) issues Halal Certificates. While differing in many aspects from Kosher, the practical implications on lubricant formulation and

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Sludge, mg TAN change Vis. change,%

PAO

Mineral oil

0

1

2

3

4

FIGURE 39.2 Oxidation stability comparison 160◦ C (24 h) (By Federal Test Method 5308)

production of Halal are similar. Halal excludes the use of alcohol in its products, a potential limitation for the manufacturing of some additives.

39.7 OPPORTUNITIES FOR SYNTHETIC-BASED FOOD-GRADE LUBRICANTS The toxicological properties of various base fluids (meeting the requirements as given in Section 39.2) available for the formulation of synthetic-based food-grade lubricants are superior to technical mineral oils, as illustrated in Table 39.2. Synthetic-based food grade lubricants offer improved oxidative stability as well as improved operating temperature properties as shown in Figures 39.1–39.3. Synthetic-based food-grade lubricants can be formulated to

Pour point,°C

TABLE 39.4 Typical Physical Properties of Fully Formulated Food-Grade (H1) ISO 320 Gear Lubricants Property

PAO PAG M/O

–40

–30

–20

–10

0

FIGURE 39.3 Comparison of low temperature properties ISO 320 gear lubricants, food grade

TABLE 39.3 Typical Physical Properties of Food-Grade (H1) ISO 46 Hydraulic Fluids Property Viscosity 40◦ C, cSt

Viscosity 100◦ C, cSt

Viscosity index Flash point, ◦ C Pour point, ◦ C Pump Test, 104◦ C

Mineral oil

PAO

PAG

47.8 6.67 85 204 −20 Pass

42.3 7.21 133 254 −50 Pass

46 6.8 102 185 −15 Pass

Source: ANDEROL Inc. published literature

exceed the performance capabilities of comparable mineral oil-based lubricants. As with other synthetic lubricants, food-grade synthetics offer extended maintenance intervals, high and wide temperature application, and operating cost reduction. To date, synthetic-based lubricants and greases tend to be used as “problem solvers” in food-processing applications; they remain a relatively minor player in the overall lubrication of equipment employed in the food and beverage industry. However, as original equipment manufacturers (OEM) and food processors struggle to meet the myriad regulatory and technical challenges, synthetic lubricants are likely to grow to satisfy critical applications in the food industry. Such areas are likely to include: baking chains in ovens; high temperature bearings and gears, including worm gears; conveyor systems that a wide temperature operating envelop; high performance hydraulic systems; and, sealed for life components.

Viscosity, 40◦ C, cSt Viscosity, 100◦ C, cSt Viscosity index Flash point, ◦ C Pour point, ◦ C FZG Gear test, pass

Mineral oil

PAO

PAG

327 24.8 98 220 −12 12

295 28 127 230 −35 12

285 40.7 198 221 −26 12

3. Third-party certifiers such as NSF International have replaced USDA in order to provide industry with needed documentation regarding the toxicity of proprietary substances for incidental contact of food. 4. Numerous international efforts are underway that will affect the food-grade lubricant of the future: • Efforts in Germany and the United States to develop

an ISO standard governing food-grade lubricants. • Efforts by the World Health Organization, Pan

American Health Organization, and Food and Agriculture Organization of the United Nations to develop and implement national and international food safety systems based on HACCP. 5. Food supply is undergoing rapid globalization. With that shift comes a myriad of national and international regulations and customs. 6. As the food supply continues to globalize, religious laws will have an even greater impact on the lubricants markets. 7. Synthetic-based lubricants offer performance advantage over conventional mineral oil-based products: • Additive systems are limited in both constituents and

dosage rates. • The inherent properties of synthetic base stocks,

such as superior oxidative stability, offer the lubricant formulator a unique opportunity to differentiate performance. The market for food products is operating under an increasingly global business environment. The regulatory and quasi-regulatory surroundings under which food-grade lubricants are controlled are changing rapidly.

39.8 CONCLUSIONS 1. The USDA has abandoned its former command and control programs in favor of HACCP. 2. Food-grade lubricants are no longer “pre-authorized” for incidental food contact.

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REFERENCES 1. 2002 Economic Census: Table 1, Advance Summary Statistics for the United States, 2002 NAICS Basis. http://www.census.gov/econ/census02/advance/ table1.htm.

2. Food Safety and Inspection Service, U.S. Department of Agriculture, Washington, D.C. 20250-3700: “Recall Information Center,” http://www.fsis.usda.gov/OA/recalls/. 3. “Comprehensive Intercountry Food Surveillance. A Guarantee of Quality and Hygiene for Imports,” By Dr. Catherine E. Woteki, Under Secretary for Food Safety, USDA (RIMSA 11/18, 9 April, 1999). 4. “Food Safety — Report by the Secretariat”: 108th Session of the Executive Board of the World Health Organization. EB108/7 dated 27 April, 2001. 5. “Health Ministers Seek Improved Food Protection Programs,” Press Release by the Pan American Health Organization, dated 27 September, 2000. 6. “Free Trade Area of the Americas: What are the Benefits to U.S. Agriculture?” Economic Research Service/USDA, Agricultural Outlook, April, 2000. 7. USDA, FSIS Miscellaneous Publication 1419 (updated yearly until 1998), “List of Proprietary Substances and Nonfood Compounds.” 8. Code of Federal Regulations, Vol. 21, Parts 170 to 199, revised annually, U.S. Government Printing Office, Washington, D.C. or on the WWW at //frwebgate.access.gpo.gov. 9. Code of Federal Regulations, Vol. 21, Parts 170 to 199, revised annually, U.S. Government Printing Office, Washington, D.C. or on the WWW at //frwebgate.access.gpo.gov. 10. A Private correspondence with USP. In it, USP traces the monogram of petrolatum, mineral oil, white mineral oil, and other items. 6 April, 2001. 11. Morawek, R., Tietze, P.G., and Rhodes, R.K., “Food Grade Lubricants and Their Applications.” Presented to American Society of Lubrication Engineers (now STLE), 33rd Annual Meeting in Dearborn, MI, 17–20 April, 1978. 12. Morawek, R., Tietze, P.G., and Rhodes, R.K., “Food Grade Lubricants and Their Applications.” Presented to American

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13. 14.

15.

16.

17.

18.

19.

20.

21.

22.

Society of Lubrication Engineers (now STLE), 33rd Annual Meeting in Dearborn, MI, 17–20 April, 1978. A Private Correspondence Between Dow Corning (D. Como and J. McCourt) and the author, April 23, 2001. Galli, R.D., Cupples, B.L., and Rutherford, R.E., “A New Synthetic Food Grade White Oil.” Presented at the 36th Annual Meeting of the Society of Tribologists and Lubrication Engineers (STLE) in Pittsburgh, PA, 11–14 May, 1981. USDA, Food Safety and Quality Service, Agriculture Handbook No. 562, September 1979. “Guidelines for Obtaining Authorization of Compounds to be used in Meat and Poultry Plants.” USDA, Food Safety and Quality Service, Agriculture Handbook No. 562, September 1979. “Guidelines for Obtaining Authorization of Compounds to be used in Meat and Poultry Plants.” Raab, M.J., “Assuring Food Safety in Food Processing: The Future Regulatory Environment for Food-Grade Lubricants.” Presented at the 55th Annual Meeting of STLE on 8 May, 2000. NSF Registration Program for Proprietary Substances and Nonfood Compounds used in USDA Meat and Poultry Facilities. Version 1.0, January 24, 2000. Elimination of Prior Approval for Proprietary Substances and Nonfood Compounds (Docket 91-007N), Fed. Regis., 63, (February 13, 1998), 7319–7322. XII Inter-American Meeting, at the Ministerial Level, on Health and Agriculture (Provisional Agenda Item 4.1 — RIMSA12/4 [eng.]). Understanding The Codex Alimentarius, Food And Agriculture Organization of the United Nations, World Health Organization, http://www.fao.org/. The Islamic Food and Nutrition Council of America, “Kosher vs. Halal — A Simplified Comparison for the Food Professionals,” (undated).

40

Critical Cleaning of Advanced Lubricants from Surfaces Ronald L. Shubkin and Barbara F. Kanegsberg CONTENTS 40.1

40.2

40.3

Introduction 40.1.1 Historical Perspective 40.1.2 Why is Cleaning Necessary? Overview of Cleaning Agents 40.2.1 Organic Solvents 40.2.1.1 Hydrocarbons and Oxygenated Hydrocarbons 40.2.1.2 Classic Chlorinated Solvents 40.2.1.3 trans-1,2-Dichloroethylene (Trans) 40.2.1.4 Chlorofluorocarbon Solvents (CFCs) 40.2.1.5 Hydrochlorofluorocarbons (HCFCs) 40.2.1.6 normal-Propyl Bromide (nPB) 40.2.1.7 Perfluorinated Compounds (PFCs) 40.2.1.8 Hydrofluoroethers (HFEs) and Hydrofluorocarbons (HFCs) 40.2.1.9 n-Methylpyrollidone (NMP) 40.2.1.10 Biobased Cleaning Agents 40.2.1.11 Volatile Methyl Siloxanes (VMSs) 40.2.1.12 Solvent Blends 40.2.2 Aqueous and Aqueous Blends 40.2.2.1 Cleaning Action 40.2.2.2 Temperature 40.2.2.3 Time of Exposure 40.2.2.4 Rinsing 40.2.2.5 Drying 40.2.2.6 Soils 40.2.2.7 Materials of Construction and Product Configuration 40.2.2.8 Holistic Process Design 40.2.2.9 Additives to Aqueous Cleaners 40.2.2.10 What is an Aqueous Cleaning Agent? 40.2.2.11 On-Board Cleaning Agent Recovery and Bioremediation 40.2.2.12 Process Change to Aqueous 40.2.3 Semi-Aqueous Systems 40.2.4 Co-Solvent Systems 40.2.5 “Nonchemical” or Limited Chemical Processes Physical and Chemical Properties of Cleaning Agents 40.3.1 Solubility 40.3.1.1 Kauri–Butanol Number 40.3.1.2 Hildebrand Parameters 40.3.1.3 Hansen Parameters 40.3.1.4 TEAS Diagram 40.3.2 Wetting Index 40.3.3 Boiling Point

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40.3.4 40.3.5 40.3.6 40.3.7

Flammability Hydrolytic Stability Specific Gravity Compatibility 40.3.7.1 Metals 40.3.7.2 Plastics Compatibility 40.4 Cleaning Processes 40.4.1 Vapor Degreasing 40.4.2 Aqueous Cleaning Lines 40.4.3 Ultrasonics 40.4.4 Hand Wipes 40.4.5 Aerosols 40.4.6 Sprays 40.4.7 Specialized Cleaning Systems 40.5 Comparison of Cleaning Efficiency for Selected Solvents 40.6 Benefiting from Case Studies 40.7 Environmental Considerations and Regulations 40.7.1 SNAP — Significant New Alternatives Policy 40.7.2 VOC — Volatile Organic Compound 40.7.3 ODP — Ozone Depleting Potential 40.7.4 GWP — Global Warming Potential 40.7.5 AL — Atmospheric Lifetimes 40.7.6 SARA — Superfund Amendments and Reauthorization Act 40.7.7 HAP — Hazardous Air Pollutant 40.7.8 NESHAP — National Emission Standard for HAP 40.7.9 RCRA — Resource Conservation Recovery Act 40.8 Conclusion References

40.1 INTRODUCTION Several recent volumes have been devoted to the use of, and advances in, synthetic and mineral oil based lubricants [1,2]. In addition, a comprehensive treatment of critical cleaning has recently been published [3]. This chapter, however, is the first time that the interdependent relationship of these two important areas of practical technology has been addressed as an independent topic.

40.1.1 Historical Perspective The utilization of fluids to perform functional tasks dates to antiquity. The earliest of these applications involved the use of natural oils for lubrication. Art decorations on the inner wall of the Egyptian tomb of Tehuti-Hetep (ca. 1650 b.c.) indicate that olive oil on wooden planks was used to facilitate the sliding of large stones, statues, and building materials. Egyptian chariots dating to 1400 b.c. have been uncovered that have small amounts of greasy materials, presumed to be beef or mutton tallow, on the axles. A millennium later, Herodotus (484 to 424 b.c.) described methods of producing bitumen and

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lighter oils from petroleum. It was not until the Industrial Revolution, however, that serious demands began to develop for stable fluids that could maintain their physical characteristics and chemical integrity over a wide range of temperatures and operating conditions. Charles Friedel and James Mason Crafts produced the first synthetic hydrocarbon oils in 1877, and an unsuccessful synthetic hydrocarbon was briefly commercialized in 1929. However, it was the German disaster at the Battle of Stalingrad in 1942 that showed the world that conventional petroleumbased products were inadequate to lubricate the modern machines of war in the sub-zero temperatures of the Russian winter. Since the mid-twentieth century, there has been a proliferation of advanced fluids. Some of these are highly refined mineral oils or other natural products, but many are synthetic fluids. Each of these fluids has been devised to meet rigorous performance criteria for specialized applications, including lubrication, heat transfer, power transmission, electrical insulation, corrosion inhibition, and others. As more and more chemically diverse functional fluids were introduced, a new problem began to surface. How do you remove these fluids in a rigorous fashion?

40.1.2 Why is Cleaning Necessary? Critical cleaning of parts contaminated with lubricants or other functional fluids is an essential part of many technologically advanced processes. There are several aspects of cleaning in relation to lubricants. All involve a consideration of both the individual process step and overall impact on the product. One aspect is appropriate surface preparation prior to the application of lubricants. Critical cleaning may be required to prepare surfaces for the next step in fabrication or for the application of a paint or coating. Preexisting contaminants on a surface have the potential to modify the lubricant and compromise immediate and/or long-term performance. Soil has been defined as matter out of place [4]. A lubricant or other metalworking fluid may perform a critical function at one stage of the build process, but it may have to be removed at subsequent steps. One issue is the question of exactly what constitutes a soil. Certainly, if surface material interferes with a subsequent operation, it would be considered soil. While critical cleaning or precision cleaning is often thought of as the removal of all extraneous materials from the surface, this is not necessarily the case. For example, in certain thermal spray and PVD applications, it is necessary to remove all organic lubricants. However, a visible fingerprint, if it is composed of inorganic material, is readily removed by aluminum oxide blast and does not interfere with the engineered coating [5]. Complex, multistep assembly processes are often conducted at multiple sites; sometimes job-shops or subvendors are involved. An assortment of oils, lubricants, and other metalworking fluids, as well as associated cleaning steps (or lack of cleaning steps), are permitted. Each option may have been evaluated in terms of appropriate physical, chemical, and overall performance properties. However, the fit in the overall process may not have been considered. For example, a series of metalworking fluids may be used — some classic, others synthetic, still others semi-synthetic. Each may be carefully formulated and subject to rigorous quality control requirements; each may meet exacting performance specifications. However, after a series of eight to ten assembly operations with as many metalworking fluids, some accompanied by heating, other by long-term storage, a complex, ill-defined residue is deposited. If the residue has been found to interfere with a subsequent processing operation, the application of a final coating or the end-use application, multiple and often complex cleaning steps are added. The argument could be made that a higher-quality surface with less total cleaning time and effort could be obtained were cleaning conducted at several steps in the fabrication process. The problem of contamination and soil residue is exacerbated by process changes. For example, an assembly operation may include specification-required solvent

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cleaning based on traditional usage of a petroleum-based lubricant. Other lubricants used in the same process might be more effectively removed with a different solvent or with water-based cleaning chemistries. Studies may have to be performed to qualify a replacement of the petroleumbased lubricant with a synthetic product. In such cases, it is not unknown to discover that the solvent-based cleaning is left in place. With a bit of planning in such cases cleaning steps could be reduced. Eliminating unnecessary cleaning is important. With cleaning, more is not necessarily better. Aside from increased time, labor, and capital costs, cleaning has the potential to do damage to the product. Rigorous cleaning may also be needed prior to a repair operation, especially if the contaminating lubricant is flammable or can be degraded to a baked on residue during the repair procedure. In fact, burnt-on, caramelized lubricant is a major issue in recovering or restoring parts. Lubricant stabilizers are helpful, but may not prevent all cases of field-related aging. Where additional soils are introduced during use, the problem of removal becomes even more complex. Sometimes a part is coated with a lubricant, grease, or wax to protect it during manufacture, shipping, or storage, but the coating must be removed before the part is used in the final application. Coating of optical lenses is an example of this practice. Cutting oils and other machine oils often contaminate parts during manufacture and must be removed prior to final use. Electronic assemblies and advanced aerospace equipment may be rendered inoperable by mere traces of contamination, and a final cleaning operation is critical to their successful operation.

40.2 OVERVIEW OF CLEANING AGENTS It is fallacious (and expensive) to assume that any arbitrarily selected cleaning agent will be effective for removing a particular lubricant. Both the cleaning agent and the cleaning process require careful, thoughtful selection. Choosing the appropriate cleaning process is an exacting, often traumatic experience. One could write a book about cleaning [3] and still not cover the entire topic. Some ascribe to the theory of first selecting the cleaning equipment and then choosing a cleaning agent that will work in the selected equipment. There is some logic to this approach. Such factors as temperature, cleaning action (spray in air, spray under immersion, agitation, rotation, and ultrasonics), rinsing, water preparation, recycling/waste management, drying, sizing, safety features, environmental controls, and throughput are all equipment-dependent. Others prefer to test various cleaning chemistries and then design cleaning equipment around the optimal chemistry. There is also some logic to this approach. The solvency properties must match the soils in question; the cleaning agent must not damage the part

or leave a significant residues. Physical properties must be such that adequate wetting is achieved to reach tightly spaced components and blind holes. To achieve optimal cleaning, both the cleaning agent and cleaning action must be considered. The cleaning agent and cleaning process have to be developed in parallel. As chemists, we will take the liberty to begin with an overview of cleaning chemistries. Where appropriate, we will also allude to the cleaning process. Some cleaning agents have been in use for a very long time, but a host of new cleaning agents and cleaning agent blends have been introduced in recent years to meet the challenges presented by today’s industrial cleaning requirements. Requirements can be broadly thought of as efficacy of cleaning and drying, compatibility with materials of construction, contamination issues, costs (including both cleaning agent cost and cleaning process cost), employee exposure considerations, and environmental/regulatory issues. The following is meant to provide a general, nonexhaustive overview of cleaning agents and cleaning agent blends, some new, others recently developed. In general, reference is made to aqueous, solvent, and so-called nonchemical or specialty approaches. While water is a solvent in the global sense, most industrial and governmental people, when discussing cleaning, use the term solvent to mean organic solvents and the term aqueous to refer to those systems based primarily on water (“primarily” being a somewhat loosely defined concept). Both aqueous and solvent-based chemistries (as well as advanced or “nonchemical” cleaning) offer advantages in specified niche applications. However, none are universally applicable. The question arises as to whether a water-based system or an organic chemical should be used. One might imagine that the answer would be based on technical considerations. Just as there are people oriented to cleaning equipment vs. cleaning agents, so are there hydrophilic vs. hydrophobic chemists, engineers, and employees of environmental regulatory agencies. In recent years, there has been intense polarization based less on technical considerations than on the judgment of environmental regulatory agencies. Those who actually need to prepare a highquality surface understand that selection of the cleaning agent involves technical, cost, and safety considerations as well as environmental concerns. Most, if not all, cleaning agents and cleaning processes can be managed safely, and with respect for the environment.

40.2.1 Organic Solvents 40.2.1.1 Hydrocarbons and oxygenated hydrocarbons Hydrocarbons and oxygenated hydrocarbons became readily available with the advent of petroleum refining in the mid-nineteenth century. They are very effective for the

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removal of hydrocarbon-based mineral oils, and they have the obvious historical advantage of low cost. The use of hydrocarbons and oxygenated hydrocarbons as cleaning solvents is very wide spread, but there are associated safety and environmental issues. Many are flammable and therefore dangerous when used in cleaning operations that are carried out in equipment that is not specifically designed for handling flammable liquids and vapors. Examples of hydrocarbons in use as solvents today include heptane, toluene, and mineral spirits. Examples of common oxygenated hydrocarbons include acetone, methyl ethyl ketone (MEK), isopropyl alcohol, and diethyl ether. Most hydrocarbons and oxygenated hydrocarbons are also listed as Volatile Organic Compounds (VOCs). The use of VOCs may be sharply restricted in areas of poor air quality. Some hydrocarbons also have toxicological problems. Benzene, which was once widely used, has been associated with certain cancers. Acetone deserves special consideration in that it is environmentally favored (and, in many cases effective) but requires careful management because it is flammable. Acetone has recently come into wider use as a cleaning solvent because it has been exempted at the Federal level as a VOC. The use of acetone is therefore favored or at least less regulated in many areas of poor air quality. This situation has led to the unfortunate proliferation in the use of acetone-based aerosols. Typically, the aerosol is primarily acetone with a small amount of a VOC solvent. Because acetone evaporates very rapidly and because it is an exceedingly aggressive solvent, there can be cleaning issues and/or compatibility problems. The use of acetone aerosols has led to the practice of continued spraying of parts until enough of a puddle of the VOC accumulates on the part so that cleaning can be accomplished. Properly contained and managed, acetone can be a useful cleaning agent. There are even liquid/vapor (degreaser) systems for low flashpoint solvents that can be used for acetone and various alcohols. While the initial capital costs are high and the solvent cost is typically low, the investment in a low flashpoint system may be recovered rapidly in solvent savings for some operations [6]. In addition, availability of such systems expands the range of solvent options. 40.2.1.2 Classic chlorinated solvents Chlorinated solvents were developed to overcome the flammability issues associated with hydrocarbons and oxygenated hydrocarbons. Most chlorinated solvents are nonflammable and are extremely effective cleaning agents. Perchloroethylene (PCE), trichloroethylene (TCE), methylene chloride (MC), and 1,1,1-trichloroethane (TCA) have a broad solvency range for an array of lubricants. They can be used in the liquid or vapor phase. Final cleaning in the vapor phase allows self-rinsing in freshly

distilled solvent. They do not leave significant residues. They were relatively low-cost and could be obtained at high levels of purity. However, the first three have relatively unfavorable worker exposure profiles. In addition, past inappropriate chemical management has resulted in groundwater problems and in worker and community health issues. 1,1,1-TCA was introduced as a replacement for TCE, but it was later found to be an Ozone Depleting Chemical (please see Section 4.2.1.3). Existing stockpiles are still in use for critical applications, primarily military. Chlorinated solvents must be used in relatively well-contained liquid/vapor cleaning systems (vapor degreasers) as specified in the Federal NESHAP (National Emission Standard for Hazardous Air Pollutants) rules. These solvents are useful for removal of many organic lubricants, and, even with the current restrictions, they can be used in a relatively nonemissive manner, particularly with some of the newer airless or airtight cleaning systems. Such systems, while requiring a high initial capital input, allow these very powerful solvents to be used in a manner that is responsible to both workers and to the surrounding community. 40.2.1.3 trans-1,2-Dichloroethylene (Trans) Trans is one of the few current chlorinated solvents that are relatively free of regulatory encumbrances. Trans is a chlorinated compound with moderate to aggressive solvency. Although it has a low flashpoint and has not been exempt as a VOC, it is not a hazardous air pollutant (HAP) and has a relatively favorable worker exposure profile. Until recently, Trans was not used neat for cleaning because it is flammable. It can be used in low flashpoint systems, albeit with a substantial initial capital outlay. It has, however, grown in importance recently because it is being used to blend with hydrofluorocarbons (HFCs) and hydrofluoroethers (HFEs). The blends are typically azeotropic and thus suitable for use in vapor degreasers. The Trans provides enhanced solvency for the blends while the HFCs or HFEs provide flashpoint suppression and lower VOC content. 40.2.1.4 Chlorofluorocarbon solvents (CFCs) 1,1,2-Trichloro-1,2,2-trifluoroethane (CFC-113) was a popular cleaning agent with a relatively favorable worker safety profile. CFC-113 and 1,1,1-TCA (see Classic Chlorinated Solvents) were widely used because they are nonflammable, self-rinsing, and are effective cleaning agents. They are low in both particulate and in thin-film residue. Cleaning agent residue is an important concern in contamination control. Both evaporate rapidly, and they can be used in both the liquid and vapor phase. Vapor phase cleaning and rinsing is important industrially in that such processes

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usually assure clean, uncontaminated solvent. By the midtwentieth century they had come into widespread use for critical cleaning. During the 1970s and 1980s, there was an increasing awareness of the role that many chlorocarbon and hydrochlorocarbon solvents play in the depletion of ozone in the upper atmosphere. In addition, 1,1,1-TCA was included in the list of NESHAP solvents, so that even where it is available, it must be used in relatively contained systems (please refer to Section 4.2.1.5). The phaseout of ozone depleting chemicals has prompted development of a host of new cleaning agents and cleaning processes. None possess the exact attributes of CFC-113 and 1,1,1-TCA. Many process engineers harbor the unrealistic expectation that new products with similar attributes will appear. This expectation is exceedingly unlikely for several reasons. For one thing, increasing technical specificity, stringent cleaning requirements, and a plethora of location-specific environmental regulations have produced a splintered market. In addition, regulatory scrutiny of potential new compounds has increased markedly. With a relatively small potential return, the costs of product development (including technical and regulatory approval) are so high that further development of new cleaning compounds is not likely. 40.2.1.5 Hydrochlorofluorocarbons (HCFCs) HCFCs were developed as cleaning agents to be replacements for CFCs (or, more realistically, adapted from other products that had wider uses in industry such as in foam blowing or refrigerants). The most widely used members of this class include HCFC-141b and HCFC-225. 40.2.1.5.1 HCFC-141b Unfortunately, the most popular and promising HCFC (HCFC-141b) was found to have not only similar performance properties to 1,1,1-TCA but also similar ozone depletion potential. In the United States, the potential for global environmental impact lead to a series of complex regulations at the Federal level restricting both the sale and allowable uses of the compound. However, because HCFC-141b was relatively inexpensive, showed moderate solvency, and reasonable performance properties, and most importantly because it was federally exempt as a VOC, it continued to be used and even to be favored by some local regulatory agencies in areas of poor air quality. In many instances, issues of smog (local air quality) superseded those of ozone depletion potential (global air quality). A Federal production ban was instituted at the beginning of 2003. The material is still used, and will continue to be used as long as sufficient stockpiles are available. One problem is that HCFC-141b is often blended with other solvents, in part to lower the VOC content, so those in industry are often not aware that they are managing

the process on borrowed time, perhaps without an appropriate replacement. The chemical may be described as CAS# 1717-00-6 or as 1,1-dichloro-1-fluoroethane or as dichlorofluoroethane. The challenge will be to find a product that is not too expensive, cleans, and evaporates in an acceptable manner, does not have a flashpoint, and is not too costly. Finding replacement processes for HCFC-141b promises to be challenging for some critical applications. In addition, in aerosol applications there have been trends toward accepting low flashpoint or flammable solvents as well as solvents with less favorable or even unknown worker exposure profiles [7]. Another approach to replacing HCFC-141b has been to develop blends of aggressive cleaners, such as nPB, with mild cleaners such as hydrofluorocarbons [8]. 40.2.1.5.2 HCFC-225 HCFC-225 has moderate solvency (similar to CFC-113). It will eventually be phased out of production because it is an Ozone Depleting Substance (ODS). However, it is used in the United States and throughout the world and is another valuable tool for removal of lubricants. HCFC-225 has a number of favorable properties. It does not have a flashpoint; it is VOC exempt; and it has a relatively favorable worker safety profile. It is available as blends and as constant boiling azeotropes. While these blends tend to increase the VOC content, the addition of stronger solvents serves to increase the solvency range for soils of interest. Less aggressive blends are useful where the substrate to be cleaned may be impacted by the solvents. For cost-effective use, products based on HCFC-225 are often most judiciously employed in relatively contained cleaning systems, with recycling to extend the life of the product. However, the products are sometimes used in bench top or even aerosol processes, particularly for high-value applications. 40.2.1.6 normal-Propyl bromide (nPB) nPB was introduced in the early 1990s as a direct replacement for TCA, which was being phased out. It has nearly identical physical properties to TCA, but it has a very low Ozone Depletion Potential (ODP). It is nonflammable and has proven to be a very effective cleaning solvent with a broad solvency range. It is an attractive option where organic lubricants must be removed. Because it can be obtained both in unblended (neat) and in blends and constant boiling azeotropes, it can be used with a range of substrates and in a number of different applications. Cleaning agents designed to replace CFCs must be deemed acceptable by the Significant New Alternatives Policy (SNAP) Program of the U.S. Environmental Protection Agency (EPA). After an unusually long and comprehensive evaluation period, the U.S. EPA published a

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Proposed SNAP Rule for nPB in the Federal Register on June 3, 2003. A SNAP Ruling is required for any solvent introduced to replace an ODS, and the EPA has made it clear that nPB should not be considered as an ozone depleting chemical when it is used within the continental United States. The ODP has been determined to be somewhat higher at equatorial latitudes. Controversy remains concerning the Allowable Exposure Limits (AEL) for personnel handling nPB. The EPA has recommended an AEL of 25 ppm for an 8-h time-weighted average. OSHA has not yet established a legally enforceable exposure limit. 40.2.1.7 Perfluorinated compounds (PFCs) PFCs are nontoxic, nonflammable, and tend to have very favorable worker exposure profiles. However, they tend to be expensive and have poor solvency for most soils, including most lubricants. The notable exception is their ability to solubilize highly fluorinated oils and greases. PFCs are exceedingly stable. Because of their long atmospheric lifetimes, there is regulatory concern about their contribution to global warming. In the United States, the Federal regulatory position is that PFCs should be used only where other approaches are not technically feasible. Development of HFCs and HFEs were in part prompted by expected restrictions on HCFCs. 40.2.1.8 Hydrofluoroethers (HFEs) and hydrofluorocarbons (HFCs) HFCs and HFEs include a range of compounds with variable solvency properties and variable costs. Some, such as HFC-43-10mee (2,3-dihydrodecafluoropentane) and nonafluorobutyl methyl ether (an HFE) have favorable employee exposure profiles, are not ODSs, have relatively short atmospheric lifetimes, and do not have a flashpoint. Perhaps most important for many manufacturing facilities, they are VOC exempt at the Federal level. HFEs and HFCs have limited solvency for most soils of interest. The VOC exemption and the absence of a flashpoint have contributed to their adoption in blends and azeotropes with more aggressive solvents. The above HFCs and HFEs are often blended with varying amounts of trans-1,2-dichloroethylene and/or alcohols. Specific performance properties and environmental attributes vary with the compound. For example, HFC-365mfc (1,1,1,3,3-pentafluorobutane) has a flash point. However, it can be blended with nonflammable solvents such as n-propyl bromide to moderate the solvency, increase wettability (desirable with ornate or closely spaced components), and decrease the VOC content [9]. 40.2.1.9 n-Methylpyrollidone (NMP) NMP has the advantage of removing polar and some nonpolar soils and has found utility in removing certain

lubricants. NMP is a high boiling (295◦ C), high flash point (91◦ C) solvent. NMP is not exempt as a VOC. It is miscible with water at elevated temperatures. At ambient temperatures it forms a distinct phase when mixed with water. This property, properly used, is economically and ecologically advantageous in industrial processes because the solvent can be recovered and reused. Because NMP is miscible in many organic solvents as well as in heated water, it can be used in multistep cleaning processes. Sometimes it must be rinsed off with a lower boiling solvent in order to reduce residues. It is also used in hand-wipe applications. 40.2.1.10 Biobased cleaning agents Biobased products, as the name implies, are derived from currently available plants or animals as opposed to fossil fuels. Such products are more likely to come from renewable resources. In fact many of them represent agricultural waste streams, including portions of plants that would be otherwise unusable. Support for biobased products includes agriculture and environmental regulatory organizations. A consequence of recent Federal legislation is that purchase of biobased products by U.S. federal agencies will be mandated with some exemptions (such as performance and cost issues) [10]. Increased use of biobased products, including biobased lubricants and biobased cleaning agents is also likely in the consumer market. Methyl soyate and d-limonene are two examples of biobased products that are described in more detail below. They are used alone or in blends. Additives can alter the cleaning capabilities and may also modify the worker exposure and environmental profile. Many of the biobased products are unknown quantities in terms of cleaning and toxicity. There is a perception that products derived from plants are inherently safe. However, in most cases, long-term toxicity studies have not been performed. As with all chemicals, prudent handling, including minimizing employee and environmental exposure, are appropriate. Other biobased products are based on palm oil and ethyl lactate. Ethyl lactate is promising in that it is fairly aggressive and has a broad solvency range. Assuming an ongoing emphasis on the reduction of dependence on fossil-based material, it seems likely that designed biobased products, perhaps based on lesser-known crops or other organisms, could be developed. 40.2.1.10.1 Methyl soyate Methyl soyate is an esterified soy product with reasonable solvency (KB value of about 60), similar to many hydrocarbon blends. Methyl soyate has not been exempted as a VOC. However, because it may not be detected in analytical determinations of VOC content, it is considered environmentally preferable in some areas of poor air quality (SCAQMD website [11]). Methyl soyate boils at

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over 600◦ F and leaves a residue that must be rinsed off for most applications. Blends containing surfactants can be rinsed with water in semi-aqueous processes. Other blends are more appropriately rinsed with an organic solvent (co-solvent processes). 40.2.1.10.2 d-Limonene d-Limonene is a cyclic hydrocarbon derived from citrus. It is flammable, but it is environmentally friendly. Like NMP, it has a high boiling point (178◦ C) and is therefore slow drying. d-Limonene has a moderately high KB value (in the mid-50s), and has a high solvency for some soils of interest. As with methyl soyate, d-limonene can be used alone, blended, and in semi-aqueous, and co-solvent applications. d-Limonene has been successfully used in removing heavy waxes in optics applications. It is promising for the removal of mixed lubricants and other soil mixtures. 40.2.1.11 Volatile methyl siloxanes (VMSs) VMSs, such as hexamethyldisiloxane, are low in toxicity and contain no halogen atoms. They are chemically very stable. On the other hand, they have flash points and only moderate solvency. They are useful for silicon-based materials and have unexpected solvency for some mixed soils. 40.2.1.12 Solvent blends An important thing to note about blends is that some are azeotropes and some are not. An azeotrope is a blend where the relative concentrations of the components are the same in the boiling liquid and the vapor. When two or more compounds are blended in the correct proportions to form an azeotrope, the resulting blend can be distilled at a constant temperature and the relative concentrations in the distillate will be the same as in the distillation pot. In an operation using a vapor degreaser, it is important to use an azeotropic blend. If a nonazeotropic blend is used, the vapor degreaser will act like a distillation unit. The higher boiling component will be concentrated in the boil-up sump while the lower boiling solvent will concentrate in the rinse sump. In cold cleaning operations, hand wipes, and aerosols, azeotropic performance is not needed. Blended cleaning agents have found applicability in bench-top cleaning as well as for larger batch, automated processes. Blends can increase the solvency range. At the same time, there is the problem of undisclosed composition and undefined toxicological properties of either the individual components or the blend as a whole. Very little is known about possible synergistic or antagonistic impacts of blends. Given the difficulties of conducting toxicological studies of blends, the assumption is that health effects are additive. This may or may not be accurate. The judicious approach is to obtain as much information as possible from the supplier and other sources and then handle the product in a conservative manner.

40.2.2 Aqueous and Aqueous Blends Water is an excellent solvent for inorganic materials. With additives, aqueous-based cleaning systems have also been adopted for removal of lubricants, including synthetic and semi-synthetic lubricants. Particularly with aqueous systems, it is not necessarily productive to consider the cleaning agent apart from the process context. The following are some important aspects of the process context to consider in addition to the cleaning chemistry. It must be emphasized that these factors are important for all systems, solvent and aqueous. They are introduced here because, in part for environmental reasons, aqueous systems are being adopted for removal of soils where solvency parameters are not favorable.

compatibility issues are exacerbated by longer exposure times. In addition, the process must be short enough to be economically feasible. 40.2.2.4 Rinsing

Examples of cleaning action (sometimes called cleaning force) include mechanical agitation (including elbow grease in hand-wipe applications), spray, spray under immersion, ultrasonics, and megasonics. Many techniques are line-of-site (spray and megasonics) whereas ultrasonics is not. Ultrasonics is therefore particularly useful for ornate components with blind holes. It should be emphasized that quantifiable metrics for ultrasonic performance have not been established, certainly not universally accepted. Exposure of standard (not heavy duty) aluminum foil to the ultrasonic system and noting the presence of a characteristic orange peel pattern remains the favored approach for assessing ultrasonic performance. The force of action must be moderated not only to maximize soil removal but also to avoid product damage. Further, particularly with ultrasonics, the cleaning technique can markedly contribute to the aggressiveness of the cleaning agent. On the positive side, this promotes soil removal. On the negative side, materials compatibility issues may be exacerbated.

Rinsing requirements depend on process requirements. For some general metals cleaning requirements and maintenance operations, it is not necessary to avoid cleaning agent residue. For more critical applications, cleaning agent residue itself can have a catastrophic impact on the product. In addition, the rinsing step may serve as an additional cleaning step. For example, in systems employing sequential use of organic solvents, termed co-solvent systems, a high-boiling solvent such as d-limonene may be rinsed with isopropyl alcohol (obviously, in a system designed for low flashpoint cleaning agents). Because the two have very different solvency parameters, such a system is useful for exceedingly adherent soils. Particularly with aqueous systems, it is important to take steps to avoid metal corrosion. Many aqueous cleaning agents contain rust preventatives (often referred to as RPs). RPs may be required at the rinse stage. The longevity of the corrosion protection, from hours to weeks or even months, varies with the RP. In addition, the RP itself leaves a residue. The significance for the specific process must be considered. When water is used to rinse aqueous cleaning agents (certainly a logical choice), it must be remembered that the rinsing agent has a higher surface tension than does the cleaning agent. For complex components, the consequence is that cleaning agent residue may be trapped, only to interfere in subsequent steps. This problem is exacerbated when the components are allowed to dry between steps. The problem may arise during the time it takes to move the component from the washing bath to the rinsing bath. To lessen the problem, some aqueous systems include a water spray between baths.

40.2.2.2 Temperature

40.2.2.5 Drying

In general, the rate of reaction doubles with each ten degrees increase in temperature. Aqueous systems often use heating to simply melt the soil from the surface. However, some substrates are temperature-sensitive. In addition, many aqueous cleaning agents that are designed for use in spray systems contain solvents that must be brought to an adequately high temperature to minimize excess foaming. However, cleaning agents, particularly in systems with ultrasonic action, show an optimal temperature beyond which efficacy of cleaning decreases.

It is amazing that production engineers purchase an aqueous cleaning system with a good design for the wash and rinse stages, neglect to include a drying stage, and then complain that the cleaned component is wet. Where corrosion is a concern, it is crucial to consider the drying step. There are a number of types of drying systems including centrifugal drying and forced air drying. Considerations include temperature optimization to maximize efficiency and avoid product damage as well as filtration and pump selection to avoid recontamination. In specialized applications, organic chemical drying is also used, both with aqueous and solvent systems. One might initially wonder why solvent cleaning is not adopted in these cases. Sometimes, the cleaning agent selected better removes the soil. In addition, chemical drying can

40.2.2.1 Cleaning action

40.2.2.3 Time of exposure Again a balance must be struck. Longer exposure times tend to result in greater soil removal. However, materials

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minimize the use of costly solvents. The chemical of choice depends on how dry the part needs to be. Alcohol drying is popular, and it probably also serves as a vapor phase rinse. Where extremely thorough drying is required, fluorinated materials have been used.

agent solely on the basis of coupon testing is often as not unsuccessful. Far from being unsophisticated, aqueous cleaning agents that are successful for critical applications are carefully formulated, sophisticated products containing a number of organic and inorganic additives [12–14].

40.2.2.6 Soils Soils can be particulate or thin film, organic compounds, inorganic compounds, living organisms, or cell debris. Mixtures of soils change the picture for soil removal in terms of both cleaning agents and cleaning action. In general, aqueous cleaning agents have a more narrow solvency range, or, more positively, more soil specificity than do organic solvents. Therefore, when the lubricant is changed or when any other soil is changed, it is prudent to reevaluate the cleaning process. 40.2.2.7 Materials of construction and product configuration There is no universal solvent. If you had one, how would you store it? Everyone would like to optimize cleaning. However, the more aggressive the solvent, the more likely is the occurrence of compatibility problems. Further, just as contamination control or cleaning is related to process, so is compatibility. With aqueous systems, corrosion is a particular materials compatibility issue both at the cleaning and the rinsing stage. Finally, because materials can interact as they degrade, materials of construction must be tested together, not separately. Static dip tests in a cleaning agent at ambient or even at elevated temperature does not tell the whole story. The product must be tested in the cleaning and drying sequence. With increasing miniaturization and greater sophistication of CAD/CAM programs, product configuration and product complexity add to the potential problems in cleaning and process control. It may be observed that many designers have the attitude that if the computer program indicates that the components will fit together, there is the assumption that the product can be successfully built. Potential problems of chemistries involved in the build, cleaning, and ultimate surface quality are not always considered. Therefore a change in product design may cascade into an array of changes in lubricants and metalworking fluids and therefore in cleaning. The tighter the spacing, the more difficult it is for cleaning agents to penetrate. 40.2.2.8 Holistic process design The above factors are important in both solvent and aqueous cleaning. However, traditional solvent cleaning is sometimes more forgiving. A nonoptimized process, therefore, may give at least marginally effective results. With aqueous cleaning, process optimization is far more critical. Attempting to simply adopt an aqueous cleaning

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40.2.2.9 Additives to aqueous cleaners The acidity or alkalinity of an aqueous cleaning agent is important for soil removal. Aqueous cleaning agents generally operate at pH ranges away from neutral (pH of 7). In general, acidic (low pH) cleaners are useful as brighteners and for removal of scale. Alkaline cleaners are useful for many soils of interest, including lubricants. As a guideline, acid cleaners have a pH range of 1–5; neutral, pH 7; low alkaline, pH 8–10; high alkaline, pH 10–13; and caustic, pH 12–14. Occasionally, water with either an acid or base is used as the cleaning agent. More often, additional additives are employed to increase efficacy of cleaning, extend the solvency range, control foaming, and protect the product. Surfactants reduce the surface tension or interfacial tension between water and the soil or substrate. Surfactants allow water to get into the smaller spaces and blind holes of ornate parts. Surfactants are classed as nonionic, anionic, cationic, or amphoteric (Zwitterionic). Neutral surfactants such as glycol esters are a frequent choice for industrial cleaning. They are bio-resistant, promote wetting, and many are low foaming. Negatively charged surfactants such as amine/metal salts and sulfonates are more common in high-foaming cleaners and in emulsified coolants. Positively charged surfactants such as ammonium salts serve as emulsifiers. Amphoterics such as sultaines and betaines, once rarely used industrially, are increasingly finding their way into high-performance cleaners. Of course, one must remove the cleaning agent by rinsing, and that generally involves water, which has the higher surface tension you were trying to get away from in the first place. Aqueous cleaning agents contain an array of additives referred to as builders. Builders help to establish the pH of alkaline cleaners, but they may also be multifunctional. For example, amines are used in high alkaline cleaners to promote detergency and to inhibit corrosion. Builders have their positives and negatives. For example, amines contribute to corrosion protection, but many are costly; and there may be odor issues. Phosphates were traditionally used for their detergency and sequestration properties; but there are increasing environmental restrictions and some compatibility problems. Silicates contribute to detergency and corrosion inhibition; but may leave an adherent residue and may mask the presence of cracks during nondestructive testing. Carbonates are low in cost and contribute to detergency and corrosion inhibition, but they are consumed during use.

Cleaning agents may also contain chemicals referred to as sequestrants, chelators, or water conditioners to prevent soap scum and avoid residue buildup on the component. Specific organic chemicals that liquefy at particular temperatures to assist in defoaming may also be added where the product will be used in a spray system. Corrosion inhibitors are important both in the wash and rinse chemistries. They act as barriers to oxidation or they may be sacrificial. Many may be used in a single product. The extent of corrosion protection required will influence the chemistry that is chosen, and this involves working with the cleaning agent vendor. Choosing a reliable vendor who offers good product support is crucial [15]. Because aqueous cleaning agents may have complex formulations, it is important to assure that the additives are safe for workers and for the environment. One issue is that if the toxic is below 1%, it does not have to be listed. If “families” of toxics having related toxicity issues are used, even if each is under 1%, they do have to be listed. However, because there could be a temptation to declare various additives as being at best distant cousins, it is very important to work with reliable cleaning agent suppliers [16].

40.2.2.10 What is an aqueous cleaning agent? Sometimes, the additives in the concentrate result in what is basically a blend of organic solvents with some inorganics. Depending on how dilute the mixture is when employed, one may still have basically an organic blend (perhaps of high boilers) that is then marketed as an aqueous product. One problem is that some U.S. regulations sharply restrict the level of organic compounds that are VOCs. A few organic compounds with low reactivity have been classed as VOC-exempt. In many areas, they can be used with few if any environmental restrictions. Relatively few of these, however, are useful in aqueous blends. To further complicate the situation, some regulatory agencies have programs to determine the VOC content by analytical detection rather than by actual content [17]. Even with gas chromatography/mass spectroscopy (GC/MS), depending on the sample preparation and transfer technique used in the test laboratory, high-boiling organics and complex mixtures may not show up. To maximize available options, it is necessary to consider all applicable environmental regulations, not just the complete list of components as provided by the manufacturer.

40.2.2.11 On-board cleaning agent recovery and bioremediation Maintaining the cleaning agent bath is crucial for ecological, economic, and performance considerations. With

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lower boiling organic solvents and azeotropic blends, on-board recovery by distillation is often feasible. With aqueous cleaners and higher boiling blends, filtration and oil separation are required to maintain the cleaning agent. Skimmers are often added to baths to remove oils and particulates and prevent redeposition on the part. Selection of the appropriate filter can be problematic. With aqueous cleaners, any filter will alter the chemistry. Formulators often strive to design the product so that it can be filtered with minimal impact on cleaning agent composition. Some aqueous systems use “oil-eating” bacteria to achieve on-board bioremediation. Such systems are typically “sink on a drum” or remote reservoir cleaners. There is a misconception that the bacteria are promoting the cleaning process. In a sense they are, but they are doing so indirectly by keeping the cleaning bath free of soil. With bacteria remediation systems, the bath temperature, type of soil, and soil loading must be considered. The cleaning chemistry is specific for the bacteria chosen. Because such systems are nearly neutral for appropriate applications, there has been good employee acceptance. 40.2.2.12 Process change to aqueous Success in conversion to aqueous cleaning has been mixed. Aqueous systems are very inexpensive in terms of detergent cost, but they are not suitable for all applications. Unfortunately, zealous, albeit well-intentioned, environmental restrictions have led some companies and locales to mandate adoption of a subset of aqueous technologies without consideration of process design, process cost, or required optimization. High capital investment, multistep processing, a large equipment footprint, and high-energy costs are often reported. Residuals on the clean parts and difficult drying are also problems. Corrosion of metal parts may become a factor. Finally, some critical components such as electrical and electronic applications often cannot tolerate the presence of remaining traces of water. At the same time, for the appropriate lubricants and other soils, aqueous cleaning can be the best approach.

40.2.3 Semi-Aqueous Systems A semi-aqueous system consists primarily of a solvent or solvent blend containing additives that allow rinsing with water. For example, a blend of esters combined with surfactants might be followed with a water rinse. Problems with semi-aqueous processes are typically associated with inadequate attention to process design. One problem with semi-aqueous systems is carryover; that is, the cleaning agent is trapped in the product and carried into the rinse tank. This makes rinsing and disposal more difficult. The problem of proper disposal of semi-aqueous systems is often overlooked. Because of the high organic content, it is not appropriate (or legal in many cases) to

dispose of these systems down the drain. In addition, an RP may be needed in the rinse tank to avoid corrosion. With good process design and ongoing process control, semi-aqueous systems are valid options.

40.2.4 Co-Solvent Systems In co-solvent systems, solvents are used sequentially, often with a high boiler used for washing and a lower boiler for rinsing and perhaps drying. A co-solvent process is particularly attractive where several metalworking fluids with varying solvency properties are used. A similar ester blend to the one described for semi-aqueous cleaning might be supplied without surfactants. The blend would then be rinsed with an HFC or with an alcohol depending on the soil mix, the environmental requirements, and the availability of low flashpoint cleaning systems. Aqueous, semi-aqueous, and co-solvent processes all share similar advantages as well as many of the same potential problems. Again, process control is the key to success.

40.2.5 “Nonchemical” or Limited Chemical Processes Processes such as CO2 snow, CO2 pellets, steam, and a vast array of abrasive materials alone or with liquids have been used for surface finishing or cleaning. CO2 snow is actually a combination of physical and chemical cleaning. Most are appropriate for final spot cleaning rather than removal of appreciable levels of lubricants. All are essentially line-of-sight techniques [18]. In addition, liquid and supercritical CO2 have been used for cleaning. The process time is typically significant as is the initial capital outlay. In addition, cleaning chamber size restricts the parts being cleaned to relatively small objects.

40.3 PHYSICAL AND CHEMICAL PROPERTIES OF CLEANING AGENTS The choice of a solvent for critical cleaning depends on a variety of physical and chemical properties. The most important of these characteristics are described below.

40.3.1 Solubility The underlying principle in both aqueous and solvent cleaning is that the contaminant to be removed must dissolve to some extent in the cleaning agent. Aqueous systems, however, tend to depend less on solvency and more on cleaning action, time of exposure, and temperature than do solvent systems. It is well-established conventional

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wisdom that “like dissolves like,” and that is a good starting point for choosing a cleaning solvent. This concept simply means that compounds of similar chemical structure are more likely to be miscible with each other than compounds whose molecules are very different. However, the average person facing a cleaning decision (engineer, shop foreman, etc.) needs a more straightforward way of ranking the solubilizing performance of candidate cleaning solvents toward the soil to be removed. For this reason, several different systems of assigning solubility parameters have come into common use. 40.3.1.1 Kauri–Butanol number The Kauri–Butanol number, or KB number, is widely quoted in reference to cleaning solvents. It is a measure of the ability of a solvent to dissolve a mixture of Kauri resin in butanol. As a practical guide, it is useful in predicting the ability of a solvent to dissolve heavy hydrocarbon oils and greases. The higher the KB number, the more effective the solvent will be. The test was designed for evaluating hydrocarbon solvents, but the range of use has been expanded to include halogenated solvents. It is not used for oxygenated solvents. Table 40.1 contains some representative KB numbers along with the corresponding boiling points. A relatively high boiling point can compensate for a somewhat lower KB number. Sometimes, materials are blended to enhance the KB number. In looking at HFEs alone and blended, it should be noted that blending increases the KB number fivefold but decreases the boiling point. In this case, the azeotrope, HFE-72DE, is desirable in that some of the solvency properties of trans-1,2-dichloroethylene are maintained, but the flashpoint of trans (36◦ F) is suppressed by the HFE. 40.3.1.2 Hildebrand Parameters Unlike the KB number, which is experimentally determined, the Hildebrand Parameters are calculated from several physical constants. Substances with similar Hildebrand solubility parameters tend to be soluble in each other. 40.3.1.3 Hansen Parameters The Hansen Parameters were developed to overcome certain inconsistencies in the Hildebrand Parameters. The Hansen Parameters are broken down into polar, nonpolar, and hydrogen bonding components. These are the three main types of intermolecular attraction. The more closely the three parameters for the solvent compare to the parameters for the lubricant to be removed, the more effective the solvent will be. Table 40.2 presents Hansen Parameters for a variety of solvents.

TABLE 40.1 KB Values and Boiling Points of Selected Solventsa Cleaning agent

KB number

CFC-113 1,1,1-Trichloroethane Methylene chloride Perchloroethylene Trichloroethylene HCFC-141b HCFC-225 HCFC-225 ATEb n-Propyl bromide (nPB) Blend, 1:1 nPB/HFC-365mfc trans-1,2-Dichloroethylene HFC 43-10 HFE-7100 HFE-7200 HFE-72DEc Methyl soyate Alkyl C16 –C18 methyl esters, soybean oil (CAS# 67784-80-9) Parachlorobenzotrifluoride d-Limonene Benzene Toluene Xylene Stoddard solvent (CAS# 8052-41-3)

TABLE 40.2 Hansen Parameters for Selected Solventsa,b

Boiling point, ◦ C

32 124 136 90 129 56 31 115 125 30 117 9 10 10 52 61

48 74 40 121 87 32 54 45 71 45 47 55 61 76 43 315

64 76 107 105 98 33

139 178 80 111 139 188

a KB values obtained from a variety of sources. Validation from suppliers

or by experiment may be advisable.

Compound CFC-113 1,1,1-Trichloroethane HCFC-141bc C6F14 (a perfluorocarbon) Trichloroethylene Methylene chloride Perchloroethylene n-Propyl bromide HFC 43-10mee C7-11 Hydrocarbons, 25% aromatics Parachlorobenzotrifluoride Isopropyl alcohol Acetone Butyl acetate Methyl acetate Ethyl acetate Methyl ethyl ketone Methyl isobutyl ketone Methyl propyl ketone n-Methylpyrollidone d-Limonene Water

Nonpolar (dispersive)

Polar

Hydrogen bonding

14.7 17.0 15.1 11.5 18.0 18.2 19.0 16.0 12.9 15.8

1.6 4.3 5.1 0 3.1 6.3 6.5 6.5 4.5 0

0 2.0 2.0 0 5.3 6.1 2.9 4.7 5.3 0

13.9 15.8 15.5 15.8 15.5 15.7 16.0 15.3 16.0 18.0 16.6 8.6

9.9 6.1 10.5 3.7 7.2 5.3 9.0 6.1 7.6 12.2 0.6 13.4

4.7 16.4 7.0 6.3 7.6 7.2 5.1 4.1 4.7 7.2 0 25.8

a Hansen Parameters obtained from a variety of sources. Validation may be advisable. b Data presented as δ/(MPa)1/2 . c HCFC-141b parameters estimated by Dr Ken Dishart.

b HCFC-225 blended with 55% trans-1,2-dichloroethylene, 3.3% ethyl

alcohol, and 5% nitromethane. c 10% HFE-7100, 20% HFE-7200, 70% trans-1,2-dichloroethylene.

physical properties of the solvent: Wetting Index = density × 1000/(surface tension

40.3.1.4 TEAS diagram The TEAS diagram, which is a measure of the ratios of the polar, hydrogen bonding, and nonpolar forces, provides an indication of solvency characteristics without indicating solvency strength. Thus, many HFCs have a similar solvency style to chlorinated solvents. However chlorinated solvents are more aggressive solvents. For a more comprehensive discussion of solvents and solubility, the reader is referred to a recent review of the topic [19].

40.3.2 Wetting Index The Wetting Index is sometimes used as an indication of the ability of a cleaning or rinsing agent to penetrate tightly spaced components or to reach into blind holes. The concept of the Wetting Index was originally proposed by W.G. Kenyon (Global Centre Consulting) as a guidance or teaching tool [20]. It is derived from three fundamental

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× viscosity) The Wetting Index has pragmatic value in understanding the behavior of cleaning and rinsing agents. In general, cleaning agents with a higher Wetting Index are favored for cleaning complex components and for rinsing any residue from complex or tightly spaced components. A few examples of the Wetting Index are provided in Table 40.3. The Wetting Index provides a guideline only; pragmatic testing with the substrates, soils, and product configuration are required. The Wetting Index does not indicate aggressiveness of a particular cleaning agent for the soil of interest. For example, HFE-7200 has a high Wetting Index but is an exceedingly mild solvent. In addition, both the Wetting Index and the component physical properties (density, surface tension, and viscosity) must be considered in evaluating potential cleaning agents. While such physical properties should be readily available, they are not always readily available, particularly for some of the newer biobased materials and for blended products. It should also

TABLE 40.3 Wetting Index of Selected Solvents Cleaning agents (source) HCFC-225a n-Propyl bromidea 1,1,1-Trichloroethanea HCFC-141ba Trichloroethylenea CFC-113a Parchlorobenzotrifluoridea HFC-43-10a HFE-7200b (HFE-569sf2) Acetonea Isopropyl alcohola Hexanea Volatile methyl siloxane (VMS OS-10)a d-Limoneneb H2 0a Saponifier solution, 6% ethanolamine-based saponifierc

Density, g/cm3 (25◦ C)

Surface tension, Dyn/cm3 (25◦ C)

Viscosity centipoises, (25◦ C)

Wetting Index

1.55 1.35 1.32 1.24 1.46 1.57 1.34 1.58 1.43 0.79 (20◦ C) 0.78 0.66 (20◦ C) 0.82

16.2 25.9 25.6 19.3 26.4 17.3 25.0 14.1 13.6 23.3 (20◦ C) 21.8 (15◦ C) 18 (25◦ C) 16.5

0.59 0.49 0.79 0.43 0.54 0.65 0.79 0.67 0.61 0.36 (20◦ C) 2.4 (20◦ C) 0.31 (20◦ C) 0.82

162 106 65 149 102 140 68 167 172 94 15 118 61

0.84 1.00 1.00

25 72.8 29.7

1.28 1.00 1.08

26 14 31

Sources: a Handbook for Critical Cleaning. b MSDS. c Estimates, W.G. Kenyon.

be noted that the wetting properties of water and of other organic solvents can be improved by blending. However, chemicals used for blending, particularly high-boilers, can leave a residue. For many applications, surfactants and other adherent additives must be removed by rinsing; care must be taken that the rinsing agent (water or organic solvent) has sufficient wetting capability to adequately remove the additives. A word of caution should be noted. The calculated Wetting Index has been found to be inconsistent with experimental drop spreading experiments with some blends of solvents. In particular, a 50:50 blend of n-propyl bromide and HFC-365 mfc has a calculated Wetting Index of 135. This is somewhat lower than HCFC-225 (162) or HCFC-141b (149). When several drops of the solvent are dropped on a smooth metal plate, however, the nPB/HFC-365 blend spreads over an area approximately 6.5 times that of either of the other two solvents [21]. In this case, the referenced authors believe that the large difference in the vapor pressures of the two solvents is responsible for the spreading behavior.

temperature, a high boiling solvent may evaporate from the cleaned surface too slowly. A low boiling solvent, on the other hand, may evaporate from the cleaning bath at an unacceptably high rate. The vapors from a solvent that boils at too low a temperature may also pose a worker safety hazard by increasing the risk of inhalation. The boiling temperature of the cleaning agent is also important in cleaning operations that are carried out hot, typically at the boiling point. The solubility of a substance in a cleaning agent (aqueous or solvent-based) is temperature-dependent, with solubility approximately doubling with every 10◦ C increase in temperature. However, higher temperatures are also more likely to damage sensitive substrate materials. In addition, significantly higher energy costs may be associated with maintaining a refluxing solvent bath or an aqueous system at a higher temperature. A solvent with too low a boiling temperature, on the other hand, may be too difficult to efficiently condense and recycle in an open vapor degreaser.

40.3.4 Flammability 40.3.3 Boiling Point The boiling point temperature is very important in choosing a cleaning agent. In cleaning operations performed at room

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The flammability of a cleaning solvent is a very important safety concern. Many hydrocarbons and oxygenated hydrocarbons are excellent solvents, but they are highly

flammable and therefore dangerous to use. Some chlorinated solvents and CFCs were developed to overcome this shortcoming. Some of these chlorinated materials have been banned or restricted as ODSs, and other nonflammable compounds have been developed to take their place. These include normal-propyl bromide (nPB), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), and hydrofluoroethers (HFEs). There are a variety of definitions of flammable liquids, and a variety of tests for determining flammability [22]. The most common test for flammability is the Flash Point Test. This may be carried out using the Tag Closed Cup apparatus (ASTM D56, low viscosity fluids), the Tag Open Cup apparatus, the Cleveland Open Cup apparatus, or the Pensky-Martens Closed Cup apparatus (ASTM D93, high viscosity fluids). Solvents tend to have very low viscosities, so ASTM D56 is usually the method of choice. If a solvent fails to show a flash point under the test conditions, it means that it is incapable of maintaining combustion on its own. Some solvents have no flash point, but they will burn in an external source of ignition. This is characteristic of nPB, most chlorinated solvents, and most HCFCs. These solvents should not be used in areas where the vapors may contact the flame from a welding torch or other source of ignition. Another aspect of flammability is the flammability limits of a solvent. Some solvents that do not have a flash point will burn within narrow concentration limits in air. The limits of flammability are reported as the Lower Explosive Limit (LEL) and the Upper Explosive Limit (UEL). The LEL and UEL are usually reported as the volume percent of the solvent vapor in the air. A solvent that has no flash point but does have flammability limits is still considered to be nonflammable. Once ignition takes place, the concentration of the solvent in the air rapidly goes outside the flammable range, and the combustion self extinguishes. Many chlorine containing solvents and nPB have no flash point but do have flammability limits. These solvents generally are not suitable for use where there may be direct contact with liquid or pure oxygen. HFCs and HFEs that have a sufficiently high ratio of fluorine to hydrogen will have no flash point or flammability limits. They are generally safe to use in the presence of oxygen.

40.3.5 Hydrolytic Stability Most chlorinated solvents and nPB hydrolyze to some extent in the presence of water. The result is the formation of hydrochloric acid in the case of the chlorinated solvents and hydrobromic acid for nPB. For this reason, formulations of these solvents for cleaning applications usually include a few percent of an acid acceptor, a compound that is added to neutralize any acid that is formed. Butylene oxide is the most commonly used acid

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acceptor. Hydrocarbons, HFCs, and HFEs are generally not susceptible to hydrolysis.

40.3.6 Specific Gravity During the operation of an open vapor degreaser, a certain amount of water is condensed on the cooling coils that are used to capture the solvent vapors. Water has very low solubility in most solvents used for cleaning with an open vapor degreaser. Oxygenated solvents such as low-boiling alcohols and ketones (acetone, for instance) are miscible with water, but these can be used only in closed vapor degreasers because they are also flammable. Hydrocarbons and oxygenated hydrocarbons have specific gravities (or densities) less than water. If they are used in a vapor degreaser, any water that separates from the solvent must be removed from the bottom of the water separator. Halogenated solvents, however, have specific gravities that are greater than water, and the water will float to the top. The design of the water separator must be consistent with the density of the cleaning solvent.

40.3.7 Compatibility Compatibility of cleaning agents with both the parts to be cleaned and the materials of construction of the cleaning equipment is a complex issue. The following sections cover compatibility issues of solvents with metals and with plastics and elastomers. Additional information may be found in the Aqueous section. 40.3.7.1 Metals Some metals chemically react with certain cleaning solvents. Aluminum is a very common material of construction, but it is also very reactive. Normally, a thin layer of inert aluminum oxide forms on the surface and protects the aluminum metal from chemical attack. An aluminum part that is freshly machined, however, may have surfaces that are not yet protected by an oxide coating. 1,1,1-TCA is an example of a solvent that reacts immediately with aluminum. If an aluminum coupon is scratched below the surface of liquid TCA at room temperature, an immediate reaction is visible to the eye. The entire coupon may be consumed in a very short period of time. Other metals, like silver and copper, are easily stained by a variety of solvents. Even carbon steel will react slowly with some solvents. Metal compatibility problems are most typical with chlorinated solvents and nPB. These solvents are formulated for cleaning applications with two or more metal passivators. Metal passivators commonly used include: 1,4-dioxane; 1,3dioxolane; 2,2-dimethoxypropane; acetonitrile, alcohols; and nitromethane.

As discussed earlier, metals compatibility may also be an issue with aqueous cleaning systems. This may be particularly true with iron or carbon steel parts where drying is inadequate to remove the water from blind holes or interior sections of a complex part. 40.3.7.2 Plastics compatibility The most aggressive cleaning agents are also the ones most likely to run into compatibility problems with plastic or elastomeric substrates on the materials being cleaned. The most common problem is absorption of the solvent with subsequent swelling of the plastic or elastomer. A more serious problem is encountered when the solvent actually dissolves part of the substrate. Polycarbonates are particularly vulnerable to dissolution by strong solvents. Among plastics, low-density polyethylene and polyether imides are marginal for use with aggressive solvents at elevated temperature. Among elastomers, butyl rubber and NBR nitrile rubber show marginal performance while EPDM-60 and silicones are unacceptable at elevated temperatures. Sometimes it is possible to solve compatibility problems by shortening the cleaning cycle. Other times, it may be necessary to switch to a less aggressive solvent. Many solvent manufacturers and formulators have solved compatibility problems by blending an aggressive solvent with a mild solvent. Several blends of nPB (a very aggressive solvent) with HFCs or HFEs have appeared on the market in an effort to address the compatibility issue.

40.4 CLEANING PROCESSES The cleaning process is an integration of the cleaning agent with the appropriate cleaning, rinsing, and drying equipment, sometimes referred to as the cleaning system. The process may also include devices for transporting and orienting parts and components. The cleaning process is sometimes incorporated directly into other aspects of the build process. For example, critical applications such as ion vapor deposition (IVD) may include plasma cleaning as an integral part of the IVD system. In addition, the cleaning system may include in-line process monitoring. For example, where particulate contamination is of critical concern, a particle counter may be linked to the process bath. The surface of the product may be monitored in-line. Water or solvent quality may also be continuously tested as an integral part of the process. Finally, the system may include on-board devices for achieving and maintaining appropriate qualities of the cleaning chemistry. Examples include filtration and distillation. Achieving and maintaining appropriate cleaning agent quality is important in order to minimize the costs and ecological consequences of waste generation. It is also crucial to assure that the cleaning and rinsing agents show minimal soil loading and do not themselves become sources of contamination.

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Given the number of possible variables, there are a wide array of cleaning methods and equipment available for critical cleaning. The choice of the appropriate cleaning system is application-specific and site-specific. A complete and detailed description of each is beyond the scope of this chapter, but a brief overview of the more important industrial processes follows.

40.4.1 Vapor Degreasing Vapor degreasing with an appropriate solvent or solvent blend is carried out in a specially designed piece of equipment called a vapor degreaser. A vapor degreaser shows some similarities to a reflux condenser, albeit on a larger scale. A vapor degreaser generally consists of a boil-up sump, a rinse sump, and a water separator. The solvent is heated to reflux in the boil-up sump and forms a vapor zone above the sump. The vapors are condensed on cooling coils and the condensate is sent to a water separator to remove any water that may have condensed. The clean solvent flows to the rinse sump. From the rinse sump, it flows back to the boil-up sump. One typical cleaning process is as follows. The parts to be cleaned are lowered into the hot vapor zone above the boiling solvent in the boil-up sump. The solvent vapors condense on the cold surfaces of the part being cleaned. The solvent dissolves the soils and drips back into the boilup sump where the nonvolatile soils remain. For stubborn soils, the parts may be lowered into the boil-up sump. Next the parts are placed in the rinse sump to remove any dirty solvent that may be adhering to the part. Finally, the parts are moved back to the vapor zone. When the parts reach the temperature of the hot vapor, they are dry (free of solvent) and are removed. The entire cleaning process may take as little as five to ten minutes. A number of types of cleaning are possible including vapor phase, hot or cold solvent spray in vapor, immersion, spray under immersion, and ultrasonics. Vapor degreasing is typically self-rinsing (a second cleaning chemistry is not needed). In most cleaning processes, the bath is contaminated as soon as the first part is cleaned. However, vapor phase cleaning provides cleaning in truly uncontaminated solvent. Vapor degreasers vary in size from small bench top models with a solvent capacity of a few gallons to large automated machines that may hold hundreds of gallons. Some are open top models, but there is a trend toward closed systems. The latter reduces solvent emissions into the air, and that may be important for both environmental and economic reasons. Some vapor degreasers are used for batch operations while others are set up for continuous operation as part of an assembly line situation. In addition, where costly or regulated solvents are the best choice, airless or airtight systems are becoming increasingly popular. In some locales, airless systems are considered to be the standard for solvent containment.

The parts to be cleaned are placed in the cleaning container, which is then sealed. Air is removed; and the cleaning and drying activities take place under vacuum. Such systems typically are capital-intensive. Because the chamber is sealed, the option of having large parts partly extending from the chamber is not possible; the equipment must be sized carefully. Airless processes are typically slower than classic vapor degreasing. However, airless provide superior process control with miniscule solvent loss; and they can be adopted successfully [5]. Low-flashpoint systems are specifically designed for use with flammable solvents. Such systems allow cleaning with heated solvent, vapor phase cleaning, and ultrasonics. The initial capital cost is high. However, where isopropyl alcohol, cyclohexane, or acetone is the preferred choice, investment in a low flashpoint systems is imperative. Further, although solvent containment typically does not match that of airless systems, the increased cleaning efficiency and reduction in solvent loss over benchtop cleaning very often results in sufficient savings to justify the initial capital expense.

40.4.2 Aqueous Cleaning Lines Even though aqueous cleaning dates to antiquity, modern critical cleaning with aqueous agents requires specialized equipment [23]. As indicated in the section describing aqueous cleaning agents, matching the appropriate cleaning system with the cleaning agent is crucial for optimizing aqueous performance. The actual cleaning operation may be carried out using a spray or by immersion in a tank. In the case of immersion, several methods of agitation may be employed. These may include ultrasonics, spray-under immersion or turbulation. Temperature is also a critical parameter in the cleaning operation. Foaming of aqueous agents can be a problem, and sometimes this can be controlled with the proper choice of cleaning agent. Sometimes two cleaning tanks are used in series. The first bath removes the bulk of the soil and then the second, cleaner, bath removes the rest. Rinsing is very important in cleaning with aqueous agents. Often, spray rinsing is more effective than immersion rinsing. Multiple rinsing steps are usually required, and care must be taken concerning the purity of the rinse water. Ordinary tap water may leave behind undesirable residues. Finally, the cleaned part must be dried. Water has a high surface tension, a high boiling point, and a high heat of vaporization. Parts wet with water dry slowly. Many aqueous cleaning lines use air knives to dry parts after they are rinsed. Many localities and organizations promote the use of aqueous cleaning over solvent cleaning on the basis that there are no emissions into the atmosphere. A problem with aqueous cleaning that is sometimes overlooked, however, is that while the aqueous cleaning agent itself may present

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few disposal problems, once the cleaning agent is contaminated with soils and traces of metal, local ordinances often prohibit disposal of the used streams into sewers. Issues involving disposal of rinse water may be overcome by closed cycle systems for water treatment, but a careful cost analysis should be done before implementing such a system. Because disposal of spent cleaning agent can be significant and because high soil-loading adversely impacts cleaning, oil-splitting chemistries and a filtration system that allows regeneration of the cleaning agent are highly desirable. Filtration that is appropriate for soil removal also tends to retain components of the cleaning chemistry. However, some formulations show minimal impact after filtration. Therefore, ability to be refiltered is yet another consideration in choosing the aqueous cleaning agent. Finally, oil and particles often float to the surface of the bath, only to resettle on the part during transfer. To minimize recontamination, such devices as weirs and carousel oil skimmers are often employed. Choices in configuration, size, and design of aqueous cleaning equipment are so numerous as to be overwhelming. Choices for small-scale applications include a remote reservoir (sink-on-a-drum), a dip tank with agitation (or with ultrasonics for critical processes), or a spray chamber. Such units often do not provide rinsing action and are used where some residue of cleaning agent is acceptable. A spray chamber with a glove box is often selected for low-throughput, high-diversity applications where parts must be individually cleaned and where line-of-sight cleaning is acceptable. Such semi-enclosed systems also have the advantage of minimizing employee exposure to both the cleaning agent and the soils. Aqueous systems that minimize employee involvement are preferable. Even though the cleaning agent may be environmentally preferred, minimizing employee exposure to any industrial process is preferable; and more automated systems allow use of higher temperatures, stronger cleaning forces, and provide better cleaning consistency. With enclosed cabinet washers, the part is placed on a turntable and sprayed with heated cleaning agent, and sometimes with heated rinse agent. Other systems look and act like industrial versions of home dishwashers. For more sophisticated processes, batch cleaning or in-line cleaning are preferable. In-line cleaning involves placing the product on a conveyor belt that then passes through chambers (typically spray chambers) that deliver the cleaning chemistry and rinsing agent. Such processes are therefore also line-ofsight cleaning and often depend on high-pressure spray for the cleaning action. Drying is usually accomplished with air knives. In most batch cleaning processes, the product is placed in baskets or fixtures, which are then transferred to various wash, rinse, and drying baths or chambers. Batch

processes, by the way, are also used with organic chemicals in co-solvent processes. Such chambers are typically heated. Cleaning action may include rotation of the basket as well as other typical cleaning forces. Consistent, acceptable process control is difficult to achieve without automation, usually overhead robotics. A fine spray of water is often introduced between the rinsing and drying tanks to prevent soils and cleaning agent from baking onto the surface. Batch processes are more flexible than in-line processes in that with in-line cleaning, the variables are the conveyor belt length and the conveyor belt speed. With batch processes, it is possible to custom-program the wash, rinse, and dry times to specific product requirements. Sometimes, several of the cleaning or rinsing agents may be sequentially introduced into a single tank to save space or conserve water. The importance of purchasing high-quality equipment cannot be overemphasized, particularly for aqueous applications. Given required heating and agitation, less costly but poorly insulated equipment costs money in the long run. Cutting costs in a way that results in inadequate exposure of the product to the cleaning chemistry can result in unacceptable performance. For example, in estimating equipment size and configuration for spray systems, it is important to remember that the product cannot be jumbled into a basket but must instead be arranged in “monolayers” that are exposed to the spray. It is worth investing the time and money up-front to achieve a consistent process.

40.4.3 Ultrasonics Ultrasonic cleaning may be employed in combination with either solvent or aqueous cleaning agents. In the case of solvent cleaning, the ultrasonic unit may be built into the boil-up sump of a vapor degreaser. Ultrasonic cavitation and implosion effectively displaces a saturated layer of cleaning agent on the surface of the part being cleaned, thus allowing fresh cleaning agent to come in contact with the contaminant being removed from the surface. An excellent review on the theory and application of ultrasonics for cleaning is available [24].

a repair being made in the field. As an example, aerosol cleaners are used for cleaning electronic parts that must be repaired on site and quickly placed back into service.

40.4.6 Sprays Spray cleaning can be carried out with either solvent or aqueous cleaning systems. In addition to the solvating effects of the cleaning agent, a spray provides a gentle agitation that helps to loosen and dissolve the soil. Sprays are sometimes used in combination with vapor degreasers. When a solvent is used in the spray, care should be taken to recover as much of the solvent as is possible and to provide proper ventilation. Spray cleaning is sometimes done in spray cabinets that are specifically designed for this application.

40.4.7 Specialized Cleaning Systems Additional specialized cleaning systems are utilized. Examples include abrasive cleaning with a variety of solid materials from bicarbonate to metal pellets, CO2 (steam, snow, liquid, and supercritical), steam, and plasma. Most are not used for the initial removal of lubricants. Many are used as a final or finishing cleaning, often before coating.

40.5 COMPARISON OF CLEANING EFFICIENCY FOR SELECTED SOLVENTS It is not possible in the limited space available to compare all cleaning agents for all types of cleaning applications. Instead, we have selected a limited number of solvents and will compare their solvency and cleaning efficiency in a very difficult cleaning job. The data presented in this section was obtained experimentally by one of the authors and has been previously published [25]. Figure 40.1 shows the relative solvating ability at room temperature of five halogenated solvents for four common lubricants. The solvents are n-propyl bromide (nPB), 1,1,1trichloroethane (1,1,1-TCA), trichloroethylene (Tric), perchloroethylene (Perc), and methylene chloride (MeCl2 ).

Hand wipe systems for cleaning have been around for a long time. For many applications, nothing is simpler and easier. New innovations in this area have to do with impregnation of the clean agent on a suitable cloth. Most hand wipes should be used with suitable gloves and in areas that are properly ventilated.

40.4.5 Aerosols Aerosols provide a convenient way of cleaning specific areas of otherwise large pieces of equipment. This may be particularly desirable where cleaning is essential prior to

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Relative ranking

40.4.4 Hand Wipes

1.4 1.2 1 0.8 0.6 0.4 0.2 0

nPB TCA TCE PCE MC

Mineral oil

Polyol ester

Grease

Silicone oil

Lubricants

FIGURE 40.1 Relative solvating abilities of five halogenated solvents for four lubricants

120 % Soil removed

nPB TCA TCE PCE MC

80 60 40 20

Relative ranking

1.2

100

1 nPB HCFC-225 HFC-43-10 HFE-Me

0.8 0.6 0.4 0.2 0

0 Polyol ester Lubricants

FIGURE 40.2 Cleaning efficiency of five halogenated solvents for difficult cleaning jobs. Metal coupons were coated with soil, heated at 250◦ C for 1 h, and submerged in boiling solvent for 5 min

The four lubricants are a mineral oil, a polyol ester, a mineral oil based grease, and a silicone oil. Thirty percent by weight solutions of each lubricant were prepared in a solvent. Steel wool wedges were weighed and then soaked in the contaminated solvent, drained, and dried at 100◦ C for 30 min. The wedges were reweighed and the weight of the retained lubricant recorded. The impregnated wedges were then placed in short glass tubes and washed with 3 mL of the test solvent. The wedges were then drained, dried, and weighed as before. The grams of soil lost per milliliter of test solvent gives a measure of the solvating power. The final data was normalized to nPB = 1.0. Figure 40.2 compares the same solvents in a much more difficult cleaning task. In this experiment, metal coupons were coated with approximately 0.1 g of the test soil. The soil was then baked on by placing the coupon in an oven at 250◦ C for 1 h. The coupon was then immersed in the boiling test solvent for 5 min, removed, dried, and weighed. The percent soil removal was recorded. Each experiment was run in triplicate and the results averaged. Similar tests were carried out in an effort to compare a halogenated solvent (nPB) to the three leading fluorinated solvent types. The three fluorinated solvents were dichloropentafluoropropane (HCFC-225), heptafluorodecane (HFC-43-10mee), and nonafluorobutyl methyl ether (HFE-Me). The test soils were mineral oil, silicone oil, and a standard soil designated ASTM 448. ASTM 448 contains kerosene (30.7%), mineral spirits (30.7%), mineral oil (2.6%), SAE 10 motor oil (2.6%), vegetable shortening (7.7%), olive oil (7.7%), linoleic oil (7.7%), and C16 /C18 olefin (7.7%). Figure 40.3 is a solvating test of the fluorinated solvents at ambient temperature as described for Figure 40.1. nPB is clearly superior for this task, while HCFC-225 is second best. These results are not surprising when one compares the KB values of the solvents. Figure 40.4 is a tough cleaning job for fluorinated solvents and was carried out in the same manner as the experiment in Figure 40.2. The HFC-43-10mee and the

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Mineral oil

Rosin flux

Silicone oil Lubricants

ASTM 448

FIGURE 40.3 Relating solvating ability of a halogenated solvent (nPB) compared to three fluorinated solvents

Wt% soil removed

Mineral oil

100 90 80 70 60 50 40 30 20 10 0

nPB HCFC-225 HFC-43-10 HFE-Me

Mineral oil

Polyol ester

Rosin solder flux

Lubricants

FIGURE 40.4 Cleaning efficiency of one halogenated solvent (nPB) and three fluorinated solvents for difficult cleaning jobs. Metal coupons were coated with soil, heated at 250◦ C for 1 h, and submerged in boiling solvent for 5 min

HFE-Me are somewhat effective on the baked on mineral oil and polyol ester, but are incapable of removing the rosin solder flux. The HCFC-225 did poorly on all three soils.

40.6 BENEFITING FROM CASE STUDIES A study recently published by the University of Dayton Research Institute in conjunction with the Materials Directorate of the U.S. Air Force Laboratory at Wright-Patterson Air Force Base looks at solvency and compatibility issues for a variety of solvents and aqueous cleaning agents under consideration as replacements for HCFC-141b and CFC-113 [26]. The Dayton study is an example of a published study that is valuable, not necessarily in terms of findings that might be copied in detail, but rather as food for thought for one’s own process considerations. A valuable study includes the underlying conditions and motivations for solvent and process selection. This includes such factors as solvency, process time, convenience, costs (capital and ongoing), worker safety, environmental concerns, and customer constraints. While this study is very disclosive in terms of motivations of the participants and in evaluating and comparing studies from a number of sources, given the number of possible variables, it is important to discern the basic motivation of the study. One might immediately see vendor-sponsored studies as requiring

extra consideration. However, even governmentally sponsored studies may in fact effectively represent advocacy for a particular subset of cleaning processes deemed to be environmentally preferred.

United States to have negligible impact on ozone depletion [27]. On the other hand, HCFC-225 with an ODP of 0.03 is scheduled for phase-out.

40.7.4 GWP — Global Warming Potential 40.7 ENVIRONMENTAL CONSIDERATIONS AND REGULATIONS There are many federal, state, and local regulations dealing with the use and disposal of industrial cleaning agents. All cleaning agents are not regulated by the same rules. All regulations do not apply to all applications. And, all rules do not apply in all localities. Suppliers of cleaning agents are usually able to supply information regarding which regulations may apply to their particular product, especially in regard to federal regulations and specific applications. It is always a good idea to check with local authorities to determine if additional regulations apply in your area. In addition to government-mandated rules and regulations, there are several health and environmental considerations when choosing a new cleaning agent. There follows a partial listing of the most important rules, regulations, and related issues.

40.7.1 SNAP — Significant New Alternatives Policy The U.S. EPA is charged under the Clean Air Act with evaluating all solvents introduced as replacements for ODSs. Once a substance has been submitted to the EPA for evaluation, it may be used commercially until the EPA promulgates a final rule. The primary basis for approval is the ODP of the substance, but worker exposure and toxicity issues also play a large role. The EPA may grant broad approval or they may grant approval only for certain applications.

40.7.2 VOC — Volatile Organic Compound All volatile organic compounds are classified as VOCs until the EPA specifically exempts a compound based on experimental evidence that it does not contribute to the formation of smog. The use of VOC exempt solvents is required in certain “nonattainment” areas where air pollution exceeds mandated federal or state levels.

GWP is a measure of the ability to a substance to contribute to global warming. This value is often linked to persistence in the atmosphere, or atmospheric lifetimes. Most HFCs and HFEs have very high GWPs.

40.7.5 AL — Atmospheric Lifetimes Some solvents decompose rapidly (a few weeks) in the atmosphere, while others are very stable and persist for years. Both the ODP and the GWP values are dependent on the atmospheric lifetime.

40.7.6 SARA — Superfund Amendments and Reauthorization Act This act requires reporting of inventories and emissions of listed chemicals and groups. SARA 313 is specific for cleaning solvents. Choosing a cleaning solvent listed in SARA 313 results in additional paperwork to meet the reporting requirements.

40.7.7 HAP — Hazardous Air Pollutant This is a listing of chemicals that the EPA has declared as hazardous.

40.7.8 NESHAP — National Emission Standard for HAP NESHAP sets standards for the use of materials listed as HAPs. Again, the choice of a solvent that is not on the HAP list will result in having fewer regulations that must be followed.

40.7.9 RCRA — Resource Conservation Recovery Act This act defines hazardous wastes and how to manage them. Once more, the choice of a cleaning agent that is not listed in RCRA allows a wider range of options in how to handle and dispose the waste materials produced by the cleaning operation.

40.7.3 ODP — Ozone Depleting Potential

40.8 CONCLUSION

ODP is a measure of the ability of a substance to deplete the ozone in the upper atmosphere. While no specific maximum ODP has been established, some guidance may be gleaned from rulings and statements by the EPA. The EPA, in their Proposed SNAP Rule for normal-propyl bromide, finds the ODP level of 0.013 to 0.018 in the continental

Critical cleaning of parts and assemblies is an essential element in the fabrication, repair, and/or operation of many products. One type of contaminant that may have to be removed is a functional or lubricating fluid. The necessity for critical cleaning has been confounded by the proliferation of new types of fluids, including synthetics, biobased,

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and highly refined mineral oils. Fortunately, many options for cleaning do exist. In this chapter we have attempted to present a broad view of the cleaning agents and methods available today. In addition, we have pointed out a variety of conditions that one must be aware of in making a satisfactory selection. Cleaning efficiency is only one aspect of the cleaning problem. Worker safety, regulatory compliance, and cost-effective performance must all be taken into consideration.

REFERENCES 1. Synthetic Lubricants and High-Performance Functional Fluids (R.L. Shubkin, Ed.), Dekker, New York, 1993. Synthetic Lubricants and High-Performance Functional Fluids, 2nd ed. (L.R. Rudnick and R.L. Shubkin, Eds.), Dekker, New York, 1999. 2. Lubricants and Related Products (D. Klamann, Ed.), Verlag Chemie, 1984. Chemistry and Technology of Lubricants, (R.M. Mortier and S.T. Orszulik, Eds.), Blackie Academic and Professional, 1997. 3. Handbook of Critical Cleaning (B.F. Kanegsberg and E. Kanegsberg, Eds.), CRC Press, Boca Raton, FL, 2001. 4. Petrulio, R., private communication. 5. Kanegsberg, B.F., B. Dowell, S. Norris, and J. Unmack, Compliance and performance: selecting and optimizing a contained cleaning system, Presented at the International Thermal Spray Association, Las Vegas, NV, October 31, 2003. 6. Kanegsberg, B.F., Impact on manufacturing and assembly resulting from exemption of acetone as a VOC, Study for Chemical Manufacturers Association, December, 1999. 7. Kanegsberg, B., Your workday without HCFC 141b, Presentation and Proceedings, Fourteenth Annual International Workshop on Alternative to Toxic Materials in Industrial Processes, Scottsdale, AZ, December 8–11, 2003. 8. Shubkin, R.L. and R.J. DeGroot, New SNAP favored azeotropic blends, Presentation and Proceedings, Fourteenth Annual International Workshop on Alternative to Toxic Materials in Industrial Processes, Scottsdale, AZ, December 8–11, 2003. 9. Shubkin, R.L. and R.J. DeGroot, Solvent Trends for 2003, CleanTech Mag., 3, 27–31, January 2003. 10. Duncan, M., Biobased products as hazardous material alternatives, Presentation and Proceedings, Fourteenth Annual International Workshop on Alternative to Toxic Materials in Industrial Processes, Scottsdale, AZ, December 8–11, 2003. 11. www.aqmd.gov.

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12. Kanegsberg, B., Cleaning is more than dipping and scrubbing, Presentation and Proceedings, CleanTech 2003, Chicago, IL, March 2003. 13. Quitmeyer, J., Cleaning challenges: chemistry, process, testing, and waste treatment, Proceedings, CleanTech 2002, pp. 353–360. 14. Bockhorst, R., M. Beeks, and D. Keller, Aqueous cleaning essentials, Chap. 1.3 in CRC Handbook of Critical Cleaning (B.F. Kanegsberg and E. Kanegsberg, Eds.), CRC Press, Boca Raton, FL, 2001, pp. 37–58. 15. Maluso, P. and B. Kanegsberg, Hydrostatic pump rebuild: implementing aqueous, steam and solvent free processes, Proceedings of the Tenth Annual Conference on Solvent Substitution and the Elimination of Toxic Substances and Emissions, Scottsdale, AZ, September 13–19, 1999. 16. O’Neill, E., A. Miremadi, R. Romo, A. Guzman, M. Shub, and B. Kanegsberg, Simplifying aqueous cleaning, IPAX, Products Finishing Magazine, August, 2000. 17. AQMD CAS Program, 2003, South Coast Air Quality Management District, Clean Air Solvent (CAS) Certification Program, http://www.aqmd.gov/rules/cas/cas.html. 18. Kanegsberg, E. and B. Kanegsberg, Critical cleaning by abrasive impact, A2C2 Mag., May, 2000. 19. Burke, J., Solvents and solubility, Chap. 1.2 in CRC Handbook of Critical Cleaning (B.F. Kanegsberg and E. Kanegsberg, Eds.), CRC Press, Boca Raton, FL, 2001. 20. Kenyon, W.G., New ways to select and use defluxing solvents, NEPCON West Proceedings, 1979, pp. 55–71. 21. Shubkin, R.L. and R.J. DeGroot, Newly Developed Advanced Solvent Systems for Critical Cleaning, Presented at CleanTech 2004, Chicago, IL, February 23, 2004. 22. Shubkin, R.L. and B.F. Kanegsberg, Solvent Flammability Basics, CleanTech Mag., 3, 17, October/November, 2003. 23. See Reference 13. 24. Fuchs, R. John, The fundamental theory and application of ultrasonics for cleaning, Chap. 2.2 in CRC Handbook of Critical Cleaning (B.F. Kanegsberg and E. Kanegsberg, Eds.), CRC Press, Boca Raton, FL, 2001. 25. Shubkin, Ronald L., normal-Propyl bromide, Chap. 1.7 in CRC Handbook of Critical Cleaning (B.F. Kanegsberg and E. Kanegsberg, Eds.), CRC Press, Boca Raton, FL, 2001. 26. Roberts, M.B., C.E. Snyder, Jr., L.J. Gschwender, J. Di Cocco, and S. Bryant, Lubricant cleaning and compatibility study for candidate chlorofluorocarbon and hydrochlorofluorocarbon solvent replacements, Tribol. Lubr. Technol., 60, 35–41, February, 2004. 27. U.S. Environmental Protection Agency, 40 CFR Part 82, “Protection of Statospheric Ozone: Listing of Substitutes for Ozone-Depleting Substances-n-Propyl Bromide; Proponed Rule”, Fed. Regist., 68, 33284–33316, June 3, 2003.

Part IV Trends

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41

Automotive Trends in Europe R. David Whitby CONTENTS 41.1 Introduction 41.2 Trends in the Automotive Industry in Europe 41.2.1 A Manufacturers and Competitive Forces 41.2.1.1 Production of Vehicles in Western Europe 41.2.1.2 Production of Vehicles in Central and Eastern Europe 41.2.1.3 Imports and Exports 41.2.1.4 European Vehicle Manufacturers’ Trends and Prospects 41.2.1.5 Suppliers of components to the European Automotive Industry 41.2.1.6 Consolidation of Vehicle Manufacturing in Europe 41.2.2 European Automotive Design and Engineering 41.2.3 European Automotive Vehicle Regulations 41.2.3.1 Safety 41.2.3.2 Environment 41.2.4 European Automotive Lubricant Specifications and Tests 41.2.4.1 ACEA 41.2.4.2 CEC 41.2.4.3 Vehicle Manufacturers Lubricant Specifications and Tests 41.3 Current Status of Automotive Fluids in Europe 41.3.1 Engine Oils 41.3.1.1 Gasoline Engine Oils 41.3.1.2 Passenger Car Diesel Engine Oils 41.3.1.3 Heavy Duty Diesel Engine Oils 41.3.1.4 Two-Stroke Engine Oils 41.3.1.5 Automotive Gears and Automatic Transmissions 41.3.1.6 Other Automotive Oils 41.4 Development of Markets for Synthetic and High Performance Automotive Fluids in Europe

41.1 INTRODUCTION Emissions legislation, fuel economy, and vehicle performance have continued to be the major driving forces behind the design and choice of automotive engines and transmissions in Europe. The regulations and market forces that affect vehicle manufacturers have major effects on oil and additive companies. As a result, fuel and lubricants suppliers continue to strive to meet the requirements of existing and advanced technologies emerging from the motor and transport industries. These forces look set to continue to dominate Europe in the foreseeable future.

Copyright 2006 by Taylor & Francis Group, LLC

Current engine oils are required to function effectively for much longer and under more severe operating conditions than ever before. Engines have become more complex, with a larger number of working parts engineered to finer tolerances and a greater mix of different materials. The aerodynamic styling of many car designs, with very few cars having appreciable radiator grilles, for example, has reduced sharply the amount air cooling around the engine. Front wheel drive and the increased use of powered equipment, such as power steering, servo-assisted

braking, and air conditioning, all driven from the engine, have also reduced free space under the bonnet to a minimum. As a result, engines typically run at higher temperatures. Engines are also required to run for much longer, due to extended maintenance intervals, so lubricants must keep engines clean and efficient for longer. As an environmental improvement, engine oils are required to volatilize (evaporate) less at higher temperatures, thereby contributing less to the quantity of part-burned hydrocarbons (from the fuel) emitted to the atmosphere through the exhaust system. The pressures driving the overall performance demands on engine lubricants will continue to grow in the foreseeable future. Some of these pressures for passenger car engines include smaller or flatter oil sumps, improved oil ring efficiency, and lower oil consumption levels and use of on-board oil sensors to give extended oil drain intervals. Pressures for commercial and off-highway diesel engines include use of on-board oil sensors and computers, again to allow extended oil drain intervals. The changes in the last 15 to 20 yr have been dramatic. In Europe, around 19,200 km (12,000 mi) is now a commonplace service interval for family cars and over 80,000 km (50,000 mi for trucks), compared with as little as 6,400 km (4,000 mi) for cars and 30,000 km (18,800 mi) for trucks in the early 1980s. At that time new oil was continually being added, to top-up the lubricant and partially replenish its properties. Nowadays, many car engines do not need to be topped-up with oil between services. Lubricant stress has therefore become much more of an issue. New baseoils, many of them synthetic or severely hydrocracked mineral oils, and additives have been developed to counter this problem and to ensure that lubricants can continue to function effectively under much more demanding operating conditions. During the last few years, the internal combustion engine has been singled out for a great deal of attention and regulation on environmental performance. While emissions from gasoline engines have been reduced by around 95% compared with 20 yr ago, the trend is likely to continue and more attention is now being paid to reducing emissions from diesel engines. There has been a general move by all the organizations concerned with automotive development to improve environmental performance. In the case of engine oils, this has been either accompanied or created by increased efficiency and economic performance. For example, the generation of waste oil has been reduced by the use of smaller sump sizes and extended drain intervals. The amount of lubricant consumed during use has been reduced by improved sealing, which eliminates leakage, and tighter engineering design and tolerances that reduce the amount of oil being burnt in the combustion chamber. Increased fuel efficiency is another area of improved environmental performance, achieved through the use of lower viscosity lubricants.

Copyright 2006 by Taylor & Francis Group, LLC

41.2 TRENDS IN THE AUTOMOTIVE INDUSTRY IN EUROPE 41.2.1 A Manufacturers and Competitive Forces 41.2.1.1 Production of vehicles in Western Europe Western Europe is the world’s largest car market, ahead of North America, and is the third largest truck and bus market in the world, as indicated by the global vehicle population data shown in Table 41.1. In terms of the total numbers of vehicles on the road, Western Europe had 33.6% of the world’s cars and 13.1% of the world’s trucks and buses in 2002. In addition, Central and Eastern Europe (including the former CIS) had 10.1% of the world’s cars and 7.6% of the world’s trucks and buses in 2002.

TABLE 41.1 World Vehicle Population, 1998 to 2002 Number of vehicles in use (million) Region

1998

1999

2000

2001

2002

Cars W Europe C & E Europe N America C & S America Middle East Asia Africa Oceania

169.0 49.2 147.9 26.4 12.6 74.1 10.1 9.8

171.4 51.4 148.4 26.4 12.6 78.8 10.2 10.1

176.9 54.6 150.1 26.9 13.0 81.6 10.2 10.3

181.9 55.7 156.7 27.1 13.2 84.9 10.4 10.4

187.0 56.8 163.1 27.7 13.7 87.7 10.5 10.5

Total cars

499.1

509.3

523.5

540.3

557.0

23.1 15.2 86.6 8.6 5.2 36.6 4.4 2.7

23.4 15.1 86.7 8.7 5.3 39.8 4.4 2.8

24.0 14.3 90.6 8.8 5.4 40.5 4.4 2.9

25.3 14.9 94.1 8.9 5.5 41.2 4.5 2.9

26.6 15.6 97.5 9.0 5.6 41.8 4.6 3.0

Total trucks and buses

182.42

186.2

190.9

197.3

203.6

All vehicles W Europe C & E Europe N America C & S America Middle East Asia Africa Oceania

192.1 64.4 234.5 35.1 17.76 110.63 14.5 12.6

194.8 66.5 235.1 35.1 17.9 118.6 14.6 12.9

200.9 68.9 240.6 35.7 18.4 122.2 14.6 13.1

207.2 70.6 250.8 35.9 18.7 126.1 14.9 13.3

213.7 72.4 260.6 36.7 19.2 129.6 15.0 13.5

Total vehicles

681.5

695.4

714.4

737.6

760.6

Trucks and buses W Europe C & E Europe N America C & S America Middle East Asia Africa Oceania

Source: Pathmaster Marketing, from various industry sources.

TABLE 41.2 Western European Vehicle Population, 1998 to 2002 Number of vehicles in use (million) 1998

2000

2002

Total

Cars

Trucks and buses

Country

Cars

Trucks and buses

Austria Belgium Denmark Finland France Germany Greece Ireland Italy Netherlands Norway Portugal Spain Sweden Switzerland UK Others

3.89 4.42 1.84 2.02 26.30 41.37 2.44 1.06 31.37 5.47 1.69 3.08 14.75 3.70 3.32 21.88 0.39

0.74 0.53 0.30 0.29 5.38 3.22 0.98 0.16 2.79 0.60 0.40 1.01 3.01 0.34 0.22 3.10 0.04

4.63 4.96 2.14 2.31 31.68 44.59 3.41 1.22 34.16 6.07 2.09 4.09 17.76 4.04 3.54 24.98 0.43

4.01 4.49 1.78 2.07 27.48 42.42 2.68 1.27 31.37 6.34 1.81 3.20 17.45 3.89 3.47 22.76 0.43

168.99

23.10

192.09

176.92

Total

Total

Cars

Trucks and buses

0.33 0.45 0.35 0.30 5.61 3.40 1.01 0.19 2.93 0.83 0.45 1.10 3.84 0.35 0.31 2.51 0.04

4.34 4.95 2.13 2.37 33.09 45.82 3.69 1.46 34.30 7.17 2.26 4.30 21.28 4.24 3.78 25.27 0.48

4.18 4.68 1.88 2.15 28.70 44.38 3.42 1.31 33.24 6.54 1.87 3.59 18.15 4.02 3.63 24.85 0.44

0.40 0.62 0.40 0.34 5.90 3.59 1.08 0.22 3.31 0.85 0.46 1.37 4.16 0.41 0.33 3.16 0.05

4.58 5.30 2.28 2.48 34.60 47.98 4.49 1.53 36.55 7.39 2.34 4.96 22.31 4.43 3.96 28.01 0.49

24.00

200.92

187.03

26.63

213.66

Total

Source: Pathmaster Marketing, from various industry sources.

The largest markets for vehicles in Western Europe are, not surprisingly, Germany, France, Italy, Spain, and the United Kingdom. Numbers of cars, trucks, and buses for each country in Western Europe are shown in Table 41.2. A number of surprising statistics are evident from the data. In 2002, Italy had 15.8% more cars than France, even though the respective populations of France and Italy were 59.4 and 58.4 million. Germany, the largest country in Western Europe with a population of 82.5 million in 2002, had fewer trucks and buses than either France or Spain, and only slightly more than either Italy or the United Kingdom. Both Greece and Portugal, which are highly agricultural economies, have relatively large numbers of trucks and buses compared to the numbers of cars in each country. Most countries in Western Europe have vehicle manufacturing plants, although the biggest manufacturers of cars, trucks, and buses are located in the five main markets for vehicles. Data for the production of cars in Western Europe is shown in Table 41.3, while the production of trucks and buses is shown in Table 41.4. In total, 14.8 million passenger cars and 2.1 million trucks and buses were manufactured in Western Europe in 2002. It is evident from both Tables that manufacturing of vehicles in Western Europe has been relatively static, or even declining slightly, over the past five or so years. This

Copyright 2006 by Taylor & Francis Group, LLC

TABLE 41.3 Production of Passenger Cars in Western Europe, 1998 to 2002 Number of vehicles manufactured (thousand) Country a Austriab Belgiumb Finland France Germanyb Italy Netherlands Portugal Spain Sweden UK Total

1998

1999

2000

2001

91.5 951.2 31.1 2582.3 5348.1 1402.4 243.0 181.4 2216.4 368.3 1748.3 15164.0

123.8 917.5 34.0 2784.5 5309.2 1410.3 262.2 187.0 2208.7 434.5 1786.6 15458.3

126.0 912.2 38.5 2879.8 5131.9 1422.3 215.1 190.9 2366.4 260.0 1628.5 15171.6

121.2 884.2 41.9 3181.5 5116.8 1271.8 189.3 177.4 2211.1 251.0 1492.4 14938.6

2002 120.4 786.7 39.0 3283.8 4960.9 1125.8 182.4 182.6 2266.9 234.0 1628.0 14810.5

a Cars are not manufactured or assembled in Denmark, Norway, or

Switzerland. b Figures may be slightly inaccurate, due to some double counting

between Germany and Austria and between Germany and Belgium, but the total figure is accurate. Source: Pathmaster Marketing, from various industry sources.

TABLE 41.4 Production of Vans, Trucks, and Buses in Western Europe, 1998 to 2002 Number of vehicles manufactured (thousand) Country a

1998

1999

2000

2001

2002

Austria Belgium Finland France Germany Italy Netherlands Portugal Spain Sweden UK

11.7 114.0 0.5 341.1 378.7 290.4 27.5 89.6 609.7 114.5 227.4

15.5 98.9 0.5 395.7 378.3 290.8 25.1 65.3 643.7 59.1 185.9

25.0 121.1 0.5 468.6 394.7 316.0 30.5 55.8 666.5 35.7 185.3

24.3 128.6 0.4 446.9 390.5 307.9 49.7 62.4 638.7 38.1 192.9

19.9 119.7 0.4 409.0 346.1 301.2 48.9 68.3 588.4 38.5 193.1

2205.1

2158.8

2299.7

2280.3

2133.2

Total

is despite the overall increase in the numbers of vehicles sold in all countries in Western Europe during the same period. The main reason for this is the increase in sales of vehicles in Western Europe that were manufactured in the new and upgraded plants in Central Europe, particularly the Czech Republic, Poland, Slovakia, and Slovenia. These plants have been established mainly as a result of the lower labor costs in these countries and their close proximity to the large markets for vehicles in Western Europe.

41.2.1.2 Production of vehicles in Central and Eastern Europe

a Vans, trucks, and buses are not manufactured or assembled in Denmark, Norway, or Switzerland.

Source: Pathmaster Marketing, from various industry sources.

Central and Eastern Europe is the world’s fourth largest market for cars, as well as trucks and buses, well behind Western Europe, North America, and Asia, as shown in Table 41.1. Numbers of vehicles for the larger countries in the region are summarized in Table 41.5. The largest market for vehicles in the region is Russia, which has about the same number of vehicles as the United Kingdom. Other important markets for vehicles are Poland, the Ukraine, and the Czech Republic. Most

TABLE 41.5 Central and Eastern European Vehicle Population, 1998 to 2002 Number of vehicles in use (million) 1998

2000

2002

Total

Cars

Trucks and buses

Total

Cars

Trucks and buses

Total

Country

Cars

Trucks and buses

Bulgaria Croatia Czech Rep Estonia Hungary Kazakhstan Latvia Lithuania Poland Romania Russia Slovakia Slovenia Ukraine Uzbekistan Yugoslavia Others

1.73 0.99 3.62 0.45 2.28 1.00 0.48 0.98 8.78 2.65 14.00 1.18 0.80 4.69 0.90 1.86 2.79

0.25 0.12 0.41 0.09 0.32 0.30 0.10 0.11 1.68 0.44 9.95 0.11 0.06 0.94 0.01 0.16 0.20

1.98 1.11 4.03 0.54 2.60 1.30 0.58 1.09 10.46 3.09 23.95 1.29 0.86 5.63 0.91 2.02 2.99

2.04 1.13 3.72 0.48 2.35 1.02 0.57 1.15 9.28 2.74 17.05 1.27 0.86 4.93 0.90 1.98 3.12

0.31 0.12 0.44 0.10 0.33 0.30 0.11 0.11 1.85 0.46 8.60 0.12 0.07 0.96 0.01 0.17 0.26

2.35 1.24 4.16 0.58 2.68 1.32 0.68 1.26 11.13 3.20 25.65 1.40 0.93 5.89 0.91 2.15 3.38

2.24 1.26 3.70 0.52 2.48 1.04 0.64 1.25 9.39 2.84 17.82 1.25 0.92 5.18 0.90 2.10 3.26

0.33 0.13 0.61 0.11 0.40 0.31 0.13 0.13 1.78 0.48 9.40 0.17 0.08 0.98 0.01 0.19 0.32

2.57 1.39 4.31 0.63 2.88 1.35 0.77 1.38 11.17 3.32 27.22 1.42 1.00 6.16 0.91 2.29 3.58

Total

49.19

15.24

64.42

54.59

14.32

68.91

56.79

15.56

72.35

Source: Pathmaster Marketing, from various industry sources.

Copyright 2006 by Taylor & Francis Group, LLC

of the other countries in the region have relatively small numbers of vehicles. The ratio of trucks and buses to cars is much higher in Central and Eastern Europe compared with Western Europe, reflecting the greater importance of commercial and public transport over private transport. Production of passenger cars in Central and Eastern Europe, summarized in Tables 41.6, has been increasing steadily over the past five years. Conversely, production of trucks and buses, summarized in Table 41.7, has been declining steadily. Car production has increased due to steadily reviving economies, which translates to increasing consumer wealth, and as a result of major investment in

TABLE 41.6 Production of Passenger Cars in Central and Eastern Europe, 1998 to 2002 Number of vehicles manufactured (thousand) Country

1998

1999

2000

2001

Belarus Bulgaria Czech Republic Hungary Poland Romania Russia Slovakia Slovenia Ukraine

— — 368.6 83.5 543.9 103.9 830.8 125.1 126.4 25.5

— — 349.2 119.9 474.9 88.3 954.8 126.5 118.2 8.7

— — 428.1 134.7 290.9 64.1 968.1 181.3 122.9 14.4

— — 456.9 140.4 376.1 56.8 1022.0 181.6 126.7 14.8

— — 441.3 138.2 298.1 65.3 980.7 225.4 125.9 36.7

2207.7

2240.5

2204.5

2375.3

2311.6

Total

2002

Source: Pathmaster Marketing, from various industry sources.

TABLE 41.7 Production of Vans, Trucks, and Buses in Central and Eastern Europe, 1998 to 2002 Number of vehicles manufactured (thousand) Country

1998

1999

2000

2001

2002

Belarus Bulgaria Czech Republic Hungary Poland Romania Russia Slovakia Slovenia Ukraine

12.7 0.4 44.2 9.3 46.5 23.0 188.6 0.8 — 5.8

12.8 0.5 28.5 8.3 36.9 18.6 221.4 0.3 — 7.4

14.7 0.5 29.5 5.5 23.7 14.0 233.3 0.4 — 2.5

16.8 — 9.5 3.9 19.8 12.0 235.3 0.4 — 2.6

16.5 — 7.2 3.3 18.6 14.1 177.2 0.3 — 1.5

Total

331.3

334.7

324.1

300.3

238.7

Source: Pathmaster Marketing, from various industry sources.

Copyright 2006 by Taylor & Francis Group, LLC

new and upgraded plants by international manufacturers. During the last ten years, Volkswagen has acquired Skoda and invested in plants in the Czech Republic, Hungary, and Poland, PSA Peugeot Citroen has built plants in the Czech Republic and Slovakia, Renault has invested in a plant in Slovenia and acquired Dacia in Romania, Daewoo built a plant in Poland (although production has been severely cut back recently), General Motors acquired a plant in Poland, and Suzuki invested in a plant in Hungary. The acquisition of production facilities in Central Europe by a number of international manufacturers has led to the closure of many old, inefficient, formerly stateowned plants. This means, for example, that all cars made now in the Czech Republic are either VW Skodas or PSA Peugeot Citroens, which are being exported all over Europe in addition to being purchased by Czech motorists. All other makes of cars sold in the Czech Republic are imported. Similarly, all cars made currently in Slovakia are VWs or PSA Peugeot Citroens and all cars made in Slovenia are Renaults. In Hungary, only VW Audi and Suzuki make cars. At the same time, production of trucks and buses has declined in Central and Eastern Europe over the last five years. International manufacturers have not yet acquired production facilities in the region and the comparatively poor quality and performance of locally manufactured vehicles has become increasingly evident. This has meant that more trucks and buses are being imported into the region, mainly from Western Europe (see next section). 41.2.1.3 Imports and exports The main vehicle producing countries in Western Europe are large importers as well as large exporters of cars, trucks, and buses. Data for 2001 and 2002 is shown in Table 41.8. The primary reason for this is the concentration of manufacturing by OEMs in each country, with Europe-wide sales of vehicles. For example, all BMW and MercedesBenz cars sold in Europe (Western, Central, and Eastern) are made in Germany. All Renault cars sold in Europe are made in France, Spain, Slovenia, or Turkey, while all PSA Peugeot Citroen cars are made in France, Spain, Italy, the United Kingdom, the Czech Republic, or Slovakia. All this leads to a huge trade in vehicles between countries in Western Europe. Of specific note are the large numbers of cars and trucks that are imported into and exported from Belgium. In 2002, 1.42 million cars were imported into Belgium, 787,000 were manufactured there, and 1.74 million were exported, compared with total sales of cars in Belgium of only 468,000 cars. Belgium appears to be the only country in Western Europe where the import/export/production/sales ratios are so large, suggesting that the country is a major transfer location for vehicles bought and sold throughout Europe.

TABLE 41.8 Import and Export of Vehicles in Western Europe, 2001 and 2002 Numbers of vehicles (thousand) Imports Cars

Exports

Trucks and buses

Cars

Trucks and buses

Country

2001

2002

2001

2002

2001

2002

2001

2002

Austria Belgium Denmark Finland France Germany Greece Ireland Italy Netherlands Norway Portugal Spain Sweden Switzerland UK

437.7 1447.4 96.2 67.6 2376.6 1864.8 280.2 164.7 1737.8 726.8 91.9 345.9 1005.8 349.1 316.6 1851.5

382.9 1417.7 116.6 77.9 2344.6 1915.3 268.5 156.1 1693.4 693.5 88.7 287.3 888.7 363.9 295.1 1999.4

100.3 343.1 36.4 17.8 528.8 182.0 22.8 42.9 182.9 102.6 37.4 112.4 233.0 102.8 31.6 224.1

79.0 291.5 40.7 20.3 529.1 224.4 21.1 40.6 237.7 107.4 31.3 84.3 248.1 104.8 30.2 354.6

265.4 1842.9 — — 3303.4 3639.9 — — 596.1 385.9 — 268.1 1791.3 353.3 — 885.1

223.8 1736.8 — — 3483.3 3623.3 — — 539.6 365.2 — 243.8 1823.7 343.5 — 1063.8

162.5 423.4 — — 479.4 275.9 — — 217.4 50.8 — 68.5 546.1 105.7 — 100.9

62.5 343.2 — — 433.3 251.8 — — 193.4 48.5 — 64.3 503.5 104.0 — 189.6

Source: Pathmaster Marketing, from various industry sources.

In 2002, 47% by value of exports of vehicles from Western Europe went to North America, 13% went to Central and Eastern Europe, and 19% went to Asia, of which Japan accounted for 7%. At the same time, 32% of the value of imports into Western Europe came from Japan, 10% came from South Korea, and 30% came from Central Europe. Imports into and exports from selected Central and Eastern European countries are shown in Table 41.9. The data confirms the increasing numbers of cars being exported from the Czech Republic, Hungary, Poland, Slovakia, and Slovenia and the increasing numbers of trucks and buses being imported into many countries in the region. It is also notable that Russia is importing increasing numbers of cars, trucks, and buses, but no longer appears to be exporting vehicles, even to former CIS states. 41.2.1.4 European vehicle manufacturers’ trends and prospects During 2002 and 2003, many European vehicle manufacturers reported falling profits (or increased losses) and generally gloomy prospects. The despondency was caused by falling sales, persistent overcapacity of 30% in manufacturing vehicles, and a dash to cut prices and offer special deals (such as free finance, insurance and/or servicing) just to “move metal.” Some dealers were offering discounts of

Copyright 2006 by Taylor & Francis Group, LLC

as much as 30% in 2003. Discounting on this scale can be a real problem, since it is almost impossible to stop once consumers perceive that future prices might be lower than current ones. Manufacturers of cars in Europe are now under such huge financial pressures that they have begun to realize over the last few years that more profits can be made by selling finance, insurance, parts, servicing, and even mobile “infotainment” than by making and selling cars. They have also been able to make significant savings in the costs of marketing, sales, and distribution of cars. Industry analysts have calculated that the cost of marketing support, advertising, and distribution of vehicles can account for 30% of the pre-tax retail price of a car in Europe. The percentage is higher for small cars and lower for bigger ones. Many European car manufacturers are seeking to rationalize their dealer networks in favor of larger, better-funded groups. Internet sales are now seen as a way of providing information about specific models and their availability to prospective customers and then directing them toward the most appropriate local dealer. In this way, the manufacturer does not by-pass its dealers and consequently does not upset them. Recent surveys have suggested that 50% of U.K. motorists and 39% of French motorists would consider buying a car through the Internet, compared with 49% in the United States and 29% in Japan.

TABLE 41.9 Imports and Exports of Vehicles in Central and Eastern Europe, 2000 and 2001 Numbers of vehicles (thousand) Imports Cars

Exports

Trucks and buses

Cars

Trucks and buses

Country

2001

2002

2001

2002

2001

2002

2001

2002

Czech Republic Hungary Poland Romania Russia Slovakia Slovenia

131.9 129.8 436.3 15.0 81.0 62.5 69.0

139.1 175.4 459.8 36.6 139.9 84.2 67.1

36.9 71.9 125.4 17.2 66.3 16.6 19.7

45.4 82.4 101.0 30.5 136.7 24.8 21.0

365.7 123.6 246.4 9.2 — 184.7 115.0

416.4 122.1 218.8 13.3 — 188.3 118.6

45.1 — 45.4 — — — —

23.8 — 33.1 — — — —

Source: Pathmaster Marketing, from various industry sources.

Car manufacturers and their franchised dealers are continuing to pay a high price for the widespread public perception, and in some cases reality, that servicing and repair charges, for both parts and labor, are higher at franchised dealerships. The perceptions vary from country to country in Europe, with German motorists being the least skeptical and U.K. motorists the most skeptical. French and Spanish motorists are somewhere in between. In practice, though, once a car’s three-year warranty expires or it is sold by its company fleet manager, it is not likely to be serviced in a franchised dealer’s service center again. A few car manufacturers in Europe, notably Ford, experimented with either buying or setting-up fast-fit service centers in an attempt to capture some of the lost profits. However, in most cases, the independent service centers tended to continue to offer quicker and better service at lower prices. Some industry analysts forecast that sales of cars in Europe in 2003 would be between 3 and 4% lower than in 2002, and another 2 to 3% lower in 2004. The decline has been biggest in France and Germany, where economic weakness has coincided with a cyclical pause in buying cars. In addition to these problems, DaimlerChrysler, BMW, and Volkswagen are heavily exposed to the U.S. market. PSA Peugeot Citroen and Renault have not been affected as badly, the former due to a number of successful new models and the latter due to a revival with Nissan, now 44% owned by Renault. But two of the biggest casualties in Europe have been General Motors and Ford, both of which have been forced to cut capacity and improve productivity to try to reduce losses. Europe’s weakest car manufacturer in 2002 and 2003 was Fiat, in which GM now has a 20% shareholding. European motorist’s demands for smaller vehicles will also reduce profitability. More motorists are buying smaller cars as a result of the tax benefits of better fuel efficiency.

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Small cars are less profitable to make than larger cars. At the same time, European car manufacturers are becoming more frustrated, because climate change is a global issue, not just a European one. In addition, less polluting cars cost more to manufacture. Direct injection gasoline engines (Mitsubishi) are 15% more efficient, but are 10% more expensive. Diesel engines are 20% more fuel efficient, but cost twice as much. Hybrid cars can do 60 mpg, but these cars are 8% more expensive. Car manufacturers also have gloomy prospects about countering low-cost competition from Asia, particularly China. European vehicle manufacturers believe that European governments are not sufficiently committed to manufacturing as a fundamental part of the economy. They forecast that there will be no growth in the European market beyond the current 45–£50 bn total sales. 70% of European vehicle manufacturers believe they can compete effectively within Europe, partly as a result of productivity and efficiency gains. But only 25% believe they are competitive with companies outside Europe. To become more competitive, more products will need to be imported and more manufacturing moved to lower-cost countries. During the last three, there has also been much debate in the United Kingdom about the effect of the £:e exchange rate on the production of vehicles and components in the United Kingdom vs. European countries in the “euro-zone.” For example, Nissan’s plant in Sunderland, United Kingdom, which makes more than 330,000 cars per year, is acknowledged to be the most efficient car plant in Europe. But its profitability has been severely undermined by the relative strength of the £ against the e from 2000 to 2003. Around 70% of the cars made in Sunderland are sold in the euro-zone. Nissan had planned to increase output from Sunderland to 500,000 cars per year, but has

postponed these plans until the £ is “stable” against the e. By “stability,” Nissan appears to mean “when the UK has joined the euro-zone countries.” At some time in the near future, Nissan may decide to expand production of cars in one of the Renault plants in France or Spain, since the French and Japanese companies have merged their operations in Europe. European and U.S. car manufacturers narrowed the productivity gap with leading Japanese manufacturers in Europe in 2002, as a new round of cost reductions improved worker productivity. Toyota, Honda, and Nissan increased labor efficiency in Europe by 5.4% in 2002, while European companies by 7%. This reversed the 2001 trend, when non-Japanese car plants saw productivity fall. However, an annual industry study found that the productivity lead of Toyota, Honda, and Nissan remained unassailable. The Japanese carmakers made an average 87.5 cars per worker at their European factories, against just 58.6 at rival European manufacturers’ plants. Industry observers believe the Japanese method of manufacturing is still viewed as the benchmark. Much of the productivity improvements at companies like General Motors and Ford was due to the adoption of “lean manufacturing” techniques pioneered by the Japanese. But, even the Japanese-owned factories in Europe lagged behind those in Japan itself, where productivity can reach almost double the best level in Europe. All four of the Japanese plants in Europe were in the top eight. However, the factories with the single biggest improvements in 2002 were IBC, the General Motors-owned van plant at Luton, United Kingdom, and Fiat’s Cassino plant in Italy. Toyota’s factory in Burnaston, Derbyshire, was the worst performer among the Japanese, dropping from third to eighth place. Burnaston’s productivity decline fits with accusations made this year by Kosuke Shiramizu, the company’s board member in charge of global production, that French workers work harder than British ones. Toyota’s new Valenciennes plant in Spain took third place, despite of only being one year old, when factories are usually struggling to overcome set-up problems. GM, Fiat, Honda, and PSA Peugeot Citroen all increased productivity by more than 10%. In mid-2002, DaimlerChrysler began a ten-year plan for closer integration of the company’s car brands, including Mercedes-Benz, Chrysler, and Mitsubishi Motors. The aim of the plan is to integrate parts distribution, dealer services, logistics, and salary payments across the group. It is the latest cost-cutting exercise and is being coordinated by the group’s “Executive automotive committee” that was created in 2001 to improve cooperation between brands. The committee had already agreed a ten-year plan to reduce the group’s number of different engines and transmissions, and is aiming to combine such activities as spare parts procurement and distribution and service workshops,

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while protecting the identities of DaimlerChrysler’s different marques. In July 2003, MG Rover, which was bought for £10 from BMW in 2000 by a venture capital-backed management team, began selling a new “small” Rover, built entirely by Tata Corporation in India; at least 100,000 “Roverized” versions of the Indica small car from 2003 to 2008. Rover hopes to sell between 35,000 and 40,000 of these cars per year. Selling price is below the Rover 25, due to Tata’s low-cost production base in India. Later in the year, however, a potential manufacturing alliance with China Brilliance, collapsed. Fiat’s share of the Italian car market fell to 27.0% in June 2003, from 34.2% in June 2001. In Italy, PSA Peugeot Citroen had a 10.9% market share in 2003, VW had 10.4%, Ford had 8.6%, GM had 8.1%, Renault had 7.7%, and other manufacturers had 27.3%. Fiat cut 12,300 jobs worldwide in June 2003 in an attempt to reduce losses, which were e4.3 bn in 2002. These job cuts were partially offset by the simultaneous creation of 5,400 new jobs. Fiat aims to increase operating income by e4.7 bn by 2006, allowing the group to break even at the operating level in 2004. Much of the cost savings are intended to come from a turnaround project for Fiat, accelerated restructurings for CNH (the U.S. farm and construction equipment manufacturer), and the Iveco truck division and stronger coordination of purchasing for Fiat Auto, CNH, and Iveco. Only one small plant was closed in Italy, where Fiat suffers from overcapacity, and only 12 of its 138 plants worldwide were closed. 2,800 job cuts in Italy were offset by 1,600 new jobs. Nissan, the Japanese carmaker approached PSA Peugeot Citroen in June 2003 about using its large diesel engine to power U.S. light trucks and to support a possible launch of luxury cars in Europe. The approach came despite Nissan being controlled by Renault, PSA’s main rival. Nissan is also considering developing its own diesel engine, working either with Renault or using a Suzuki diesel currently used by Renault. Nissan wants access to a large diesel engine for pick-up trucks and sports utility vehicles, in case U.S. motorists begin to switch from gasoline after new regulations helping diesel come into effect in 2006. Nissan is mainly interested in having access to a large diesel for the U.S. market. But Nissan also requires a large diesel engine for the launch of luxury vehicles in Europe, either under the Infiniti brand the company uses in the United States, or as Nissans or Renaults. Diesels make up around 40% of all car sales in Europe and sales have been held back at brands such as Honda and Jaguar, which lacked the more efficient engines. If Nissan uses a PSA diesel engine, it would be further confirmation for the French group’s partnership strategy. Unlike many car manufacturers, PSA did not join the rush to merge with another company, but sought to share costs through joint development projects. The company, which is

the world’s biggest manufacturer of diesel engines, already has a joint venture with Ford, to develop and produce 3m diesel engines. A new V6 engine, the one of interest to Nissan, was unveiled in mid-2003 to be used in the latest Jaguar S-type car. Separately, GM’s European subsidiaries, Opel and Vauxhall, are collaborating with Fiat and Isuzu (part of GM’s Japanese affiliate) to develop and use diesel engines in European cars. In July 2003, Toyota began selling cars in Japan that were made in the United Kingdom. The company aims to ship 20,000 Avensis cars and estates from the plant in Burnaston, Derbyshire. The plant manufactured 220,000 Avensis and Corolla models in 2003 and aims to make 270,000 in 2004, with three-shift working. Toyota’s engine plant in Deeside, North Wales made 450,000 engines in 2003, for plants in the United Kingdom, France, Turkey, and South Africa. A number of Western European vehicle manufacturers have either built new plants or completely upgraded old plants in Central European countries during the last six years. Volkswagen acquired a 70% share in the Skoda plant in Mlada Boleslav, the Czech Republic in 1991 and increased this stake to 100% in 2000, having expanded the operations and added an engine plant in 1998. The company also built a new engine plant in Lower Silesia, Poland in 1999 and expanded car manufacturing capacity at its plant in Bratislava, Slovakia, to 250,000 cars per year. Renault has a plant in Romania, following the acquisition of Romania’s biggest car manufacturer, Dacia, in 1999. In January 2003, PSA Peugeot Citroen decided to build a new e700m plant in Trnava, Slovakia, to manufacture up to 300,000 cars per year in 2006. However, the investment in new and upgraded facilities is expected to slow down once the Central European countries begin to join the EU in 2004, as tax benefits and incentives become smaller and workers’ wages grow. In September 2002, DaimlerChrysler paid $700m for a 43% stake in Fuso, the truck unit of Mitsubishi Motors, its Japanese partner, in which it has a 37.7% stake. Prior to the acquisition, DaimlerChrysler had only a 1% share of the Asian truck market, which accounts for 20.5% of the world’s trucks. Separately, DaimlerChrysler announced aggressive plans in December 2002, to share at least 75% of the cost of engines and axles between its truck manufacturing operations in Europe, the United States, and Asia. Analysts believe the company could save $500m to $l bn per year if it can make the plan work. Little effort has been made in the past to share parts among the company’s disparate truck businesses. An attempt to introduce Mercedes-Benz engines to the Freightliner business in North America in 2000 had little success as U.S. truck drivers proved reluctant to abandon traditional Detroit engine brands. The company is now pushing Freightliner to work more closely with Mercedes, the largest European heavy truck

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maker, and with Fuso and Hyundai, the company’s new partners in Japan and South Korea. DaimlerChrysler is the largest heavy truck maker, with a 21% share of the world market. But after 20 yr of owning Freightliner, DaimlerChrysler has been forced to find cost savings to stem heavy losses caused by promises to buy back trucks for too high a price in the United States. The company does not plan to build identical “world trucks” for sale everywhere, but intends to try to share more of the parts that buyers do not see. This could mean that at least 75% by value of the engine, axles, and gearbox, which comprise more than half the total cost of a truck, could be identical in all the company’s trucks. DaimlerChrysler is still identifying savings in truck chassis, with internal estimates ranging from 35 to 80% sharing. Very little of the cab is likely to use common parts, because of the different tastes of truck drivers in different regions. Scania and MAN announced a long-term collaboration on component parts in April 2003. The main parts involve gearboxes and axles, for which the companies claim to have substantial synergies. As a result of the announcement, industry observers began speculating about a possible merger of the two companies. MAN and Scania expect the Western European market for heavy trucks to decline by between 5 and 10%, to about 200,000 trucks in 2003. This compares with the North American market of about 172,000 trucks in 2003. However, in July 2003, Volkswagen began discussions to acquire MAN. The German insurance group Allianz holds a 14% stake in MAN and Commerzbank and Munich Re each hold 7%. VW and MAN together would be the world’s third largest truck maker. Currently, MAN is the third largest manufacturer of trucks in Europe, VW only has a light van business. Simultaneously, a European Commission ruling requires Volvo to sell its 31% voting stake (45% capital stake) in Scania before April 2004. VW has a 34% voting stake (18% capital stake) in Scania, so if VW acquired MAN, it may be forced by the European Commission to sell its stake in Scania.

41.2.1.5 Suppliers of components to the European Automotive Industry Vehicle manufacturers demand great commitment and involvement from suppliers, so suppliers are having to invest in high-quality staff, new production processes, and new technologies in order to compete. The more innovative or complex the component, the more closely the supplier and the manufacturer will have to cooperate. Suppliers have become increasingly involved at the earliest stages in the design of a new vehicle and are now required to run computer simulations of how their components will function in conjunction with parts from other suppliers. These simulations also need to model the efficiency

and cost-effectiveness of components in the complete new vehicle. Component suppliers are also doing more of the manufacturing and assembly work that was done previously by vehicle manufacturers. They are also having to exchange information constantly with their customers. The Internet has made the sharing of designs, computer simulations, and parts integration between suppliers and manufacturers and among suppliers, significantly easier and faster. These Internet links are expected to grow, not least because vehicle manufacturers are trying to shift more of the development work and costs to component suppliers. At the same time, European suppliers can reduce their cost bases by shifting some of the design and development work to engineering centers in places like India, again, using the Internet. For example, Valeo, the largest French manufacturer of car components, makes everything from clutch systems to windscreen wipers, supplies parts worldwide, has around 180 production sites and over 100 operating divisions. All the company’s sites are now linked to each other and to customers and suppliers via the Internet. The company now uses the Internet to provide web-catalogs to customers, to run online reverse auctions with its suppliers (using requests for quotation), to manage purchasing decisions, and for customer and supplier relationship management. Hundreds of companies supply parts and components to the main European vehicle manufacturers. Many more companies are subsuppliers. The larger European manufacturers of major components for vehicles include Bosch, Brose, Delphi, Denso, Doga, Dura Automotive, Getrag, GKN, Lear Automotive, Magna, Magneti Marelli, Meritor, TRW, TVR Engineering, and ZF. In another example of the increasing closeness of relationships between manufacturers and suppliers, Magna Kansei in the United Kingdom supplies BMW, Nissan, General Motors, Rover, Land Rover, and Jaguar with automotive interior parts. To boost manufacturing quality and productivity, Magna Kansei uses Six Sigma processimprovement statistical tools. The company is a synchronous supplier to Nissan, in that it has built a factory just a few minutes away from Nissan’s plant in Sunderland. This gives Magna Kansei a huge competitive advantage, because it can adjust production and delivery to match Nissan’s requirements precisely. Despite all this, suppliers remain under relentless cost pressures. Nissan, having completed a 30% cost reduction drive, now intends to reduce production costs by a further 15% by 2005. Faced with exchange rate variations caused by making vehicles outside the euro-zone for sale within it, Nissan’s Sunderland plant has placed only 30% of its components spend for the 2003 Micra with U.K. suppliers compared with 80% for the old model. To cut costs and raise quality and efficiency even further, Nissan is beginning to give suppliers the complex task of producing

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entire modules. Magna Kansei needs to build a new plant, because it will make the entire cockpit assembly for the new Micra. 41.2.1.6 Consolidation of vehicle manufacturing in Europe As a result of the cost pressures faced by manufacturers of vehicles in Europe, a significant number of alliances, joint ventures, and even mergers have occurred during the last five years. European vehicle manufacturers have begun to collaborate as never before. In March 1999, Renault acquired a 36.8% shareholding in Nissan. The deal suited both companies, as the cash boost enabled Nissan to overcome the severe financial difficulties experienced in 1998 and continue manufacturing cars, while Renault expanded from its mainly European market into Asia. The alliance between the two companies enabled both to achieve benefits without the costs of a full merger. The alliance was further strengthened in March 2002, when Nissan acquired a 15% stake in Renault and Renault increased its shareholding to 44.4%. At the same time, the French government reduced its shareholding in Renault to 25.9%. The alliance between Renault and Nissan has led to major benefits for both companies, including reduced purchasing costs, sharing of engineering designs, powertrains (engines and gearboxes) and vehicle platforms, cross-utilization of manufacturing sites, and a common European distribution policy. One result is that Renault cars and vans are now being manufactured at Nissan sites in Spain and Mexico and Nissan pick-up trucks are being made at Renault’s plant in Brazil. In March 2002, Nissan began selling Interstar, an adapted version of Renault’s Master van. In July 2002, BMW and PSA Peugeot Citroen initiated a e750m alliance to develop and assemble up to 1 million new engines per year. A common project team designs the engines at BMW’s research center in Munich and PSA oversees parts procurement and engineering. The engine production capacity is planned to meet the future needs of both companies’ small cars, including BMW’s new Mini. New gasoline engines produced under the alliance will reduce BMW’s reliance on its engine joint venture with DaimlerChrysler at Curitiba in southern Brazil. Initially, BMW sourced all engines for its Mini small cars from Brazil. However, the plant’s future was in doubt following a sharp reduction in output for Chrysler, which uses engines from there for its PT Cruiser and Neon models. Chrysler cut engines sourced from Curitiba to just 3,000 in 2002, compared with 100,000 for BMW’s Minis. The plant has a capacity of 250,000 engines a year. The new engines developed with PSA will be used in BMW’s next-generation Mini vehicles, due to be launched after 2007. With current Mini production running at about

250,000 per year, most of the engines from the alliance will initially go to PSA, although the costs of the plant are being split on a 50:50 basis. The alliance follows several other technical alliances by both BMW and PSA, which regard limited cooperation with other carmakers as one way to safeguard their future independence. PSA has a joint venture in diesel engines with Ford and is also developing a new small car with Toyota, to be produced at a new plant in the Czech Republic. BMW has also signed a deal with Toyota for the supply of diesel engines for the Mini. In April 2000, Renault and Volvo trucks announced plans to merge the two companies’ truck activities and, following clearance from the EU Commission competition authorities and the U.S. Federal Trade Commission, Renault became the main shareholder in Volvo Trucks, with a 20% stake, in January 2001. The two companies combined their truck manufacturing, to become Europe’s largest maker of trucks and the world’s second largest truck maker. Following the sale of Volvo cars to Ford in 1999, Volvo has focused on truck manufacturing. Volvo, Renault, and Mack have an alliance, Global Trucks, which now accounts for more than two-thirds of Volvo’s net revenues. Volvo’s other activities include construction equipment, buses, marine and industrial engines, and aerospace engine components.

41.2.2 European Automotive Design and Engineering Europe has always been at the forefront of automotive vehicle design and engineering, and this has continued during the 1990s. Much of the successful automotive engineering carried out in Europe stems from the very heavy involvement in the United Kingdom, Germany, France, Italy, and other countries in the world’s racing car industry, particularly Formula 1 and Indy 500 racing. While these areas are highly specialized and involve comparatively few companies and people, the commercial spin-off from their innovations and developments cannot be overemphasized. European OEMs are currently doing a significant amount of engineering design and development work on gasoline engines. The aim of the work is to make significant further improvements in engine efficiency, to give enhanced fuel economy, and reduced exhaust emissions. Ford introduced a new series of Jaguar XJ cars with aluminum bodies toward the end of 2002. If the new cars prove popular and successful, Ford will consider using aluminum bodies for all its premium cars. Aluminum is becoming increasingly popular as a replacement for steel in cars, to reduce weight and hence gain better performance from the same engine and gearbox assembly. Its use in Europe is being encouraged by tax reductions for low emission cars. The aluminum body Jaguar XJ cars have a 10% better fuel efficiency compared with their previous

Copyright 2006 by Taylor & Francis Group, LLC

steel body equivalents. However, aluminum is more difficult and expensive to work with than steel, so aluminum is likely to be used only for more expensive cars. Cars made by VW’s Audi division have been using aluminum bodies for several years. In June 2003, Ford and PSA Peugeot Citroen announced the introduction of compacted graphite iron (CGI) for the blocks of turbo-charged diesel engines. CGI will replace conventional cast iron in a new 2.7 L V6 diesel engine to be used in Jaguar S-type cars in mid-2004. The strength of CGI means that less material is needed than for a conventional cast iron block, allowing the engine to have a relatively light weight of 202 kg and to occupy less space. This boosts its power-to-weight ratio and fuel economy characteristics. The use of CGI has required advances in manufacturing processes, including the development of machine tools to handle the material. The new engine is the first to be developed under the Ford/PSA collaboration agreement. It is aimed at the rapidly growing premium end of the diesel market, where customers are reluctant to compromise in areas such as performance, noise, and efficiency. Ford and PSA hope the V6 will allow them to compete with BMW and Mercedes, both of which have diesel engines designed for larger cars. After initial use in the Jaguar, the engine will appear in other premium models across the two companies’ ranges. The engine includes a number of technical innovations developed by Ford and PSA during their five-year collaboration. It has a compression ratio of 17.3:1, which is low for a diesel engine, giving quieter combustion and helping to reduce emissions. It also uses state-of-the-art common-rail fuel injection technology capable of achieving an operating pressure of 1650 bar, higher than previous systems. The quantity of fuel injected is controlled by a piezo actuator, while the injectors themselves deliver fuel from a hole 145 µm in diameter, providing a spray of fuel fine enough to achieve maximum uniformity of fuel/air mixture. Ford and PSA have also developed an advanced electronic control unit (ECU) to monitor and manage the new engine. The ECU draws data from 23 sensors and sends out instructions to 20 actuators. Most European car manufacturers currently provide three-year warranties on their vehicles, despite the introduction of five-year warranties by Hyundai in 2002. The change to longer warranties may have been prompted by changes in EU rules that govern car sales and repairs. From the end of 2003, independent service centers have been allowed to carry out service work within a car’s warranty period, without affecting the warranty, provided the service center demonstrates it meets the servicing standards set by the car manufacturer. Car manufacturers are also required to provide independent service centers with all relevant information required to service their cars. A five-year warranty appears to be a marketing plan to tempt car owners to have the servicing done by franchised Hyundai dealers.

However, other European car manufacturers have decided that three-year warranties are more appropriate, since many motorists buy a new car about every three years. One innovation is the use of electromagnetic inlet and exhaust valves. These use the force of a small springloaded armature to change the position of each valve and a magnetic field to hold the valve in the selected open or closed position. A very short electrical impulse switches the spring from one position to the other. These “digital binary valves” will be controlled by an electronic engine management system and will operate significantly faster than valves opened and closed by a mechanical camshaft and springs. Their operation can also be varied depending on the output torque required from the engine. Both developments are claimed to result in fuel savings of up to 20%. Another very important advantage of electronic engine valves is the resulting ability to separate the valve operation from the mechanics of the crankshaft and piston assembly. This, in turn, allows the lubrication of the crankshaft and piston rings to be separated from the lubrication of the valves, since there is no camshaft and tappets to be lubricated. The importance of this innovation lies in the significantly reduced antiwear requirements for engine oils used in these engines, allowing greatly reduced levels of zinc dialkyl dithiophosphate (ZDDP) antiwear additives. European OEMs are seeking engine oils with low (or even no) zinc (Zn) and phosphorous (P) contents, as these elements are accumulative poisons of exhaust system catalysts. OEMs believe that low Zn and P engine oils are likely to assist in maintaining exhaust emissions system durability for the 50,000 km required by European Auto Oil IV regulations due to be implemented in 2005. Another set of technologies that has been developed, and is now being introduced, by European (and Japanese) OEMs is gasoline direct injection (GDI). GDI was developed and implemented first by Mitsubishi in Japan, but requires the use of very low (<10 ppm) sulfur fuel. Since this fuel is now becoming available in Europe, more OEMs are planning to introduce cars with GDI engines. These engines give improvements in fuel economy of up to 35% and reductions in exhaust emissions of up to 40%. Two variations on GDI are “homogeneous direct injection” (early injection) and “stratified charge direct injection” (late injection). Other engine technologies are being developed in Europe for possible use in the future. One innovation is plastic engine casings, to shorten starting times from cold, which will improve fuel efficiency and reduce emissions. Starting from cold represents an engine’s hardest work. It usually takes 10 min for the coolant to reach its optimum working temperature, 20 min for the engine oils and even longer for the gear oil. Until then, the engine is operating well below its optimum efficiency. Encasing an engine in plastic enables better retention of heat during start-up

Copyright 2006 by Taylor & Francis Group, LLC

but does not affect heat dissipation, through the cooling system, during normal operation. Ford initiated a fuel cell test program in Europe toward the end of 2003. The programme involves demonstration Ford Focus FCV Hybrid vehicles. These cars use a Ballard Mk 902 fuel cell stack, which provides 68 kW (92 hp) of power. This power unit is supplemented by a 216 V hybrid battery to start the car and supply an additional 18 kW (25 hp) of thrust during acceleration. The battery is recharged by a regenerative braking system. The cars have a range is 180 to 200 mi and a top speed of 80 mph with a single speed transmission. Current gasoline engines convert about 30% of the energy potential of the fuel into power. The fuel cell efficiency is about 60%, with a peak of 90%. However, the Focus FCV Hybrid weighs 1600 kg, compared with about 1400 kg for the gasoline powered equivalent. About 150 “weight optimized” components have had to be used, to save around 300 kg of weight. Large segments of the underbody, together with the doors and bonnet, are made of aluminum. The windscreen is made of thin glass or polycarbonate. Springs are made of titanium, brackets are made of magnesium alloy and composites are used in the boot lid. The electric drive motor also acts as the generator brake, allowing 95% of braking to be used to produce electrical energy to be fed back into the battery. Ford and BP have set up a research-sharing partnership for fuel cell vehicles. As part of this collaboration, BP plans to open a number of pilot hydrogen filling stations in selected locations throughout Europe, as well as in the United States and Australia. Ford and DaimlerChrysler are working closely with Ballard Power Systems (Vancouver, Canada). DaimlerChrysler has 60 fuel cell powered A-Class cars, the “F-Cell,” on trial in Europe, the United States, and Singapore. The company also began trials of small fleets of fuel cell powered buses in each of ten European cities in late 2003 and early 2004, as part of an EU funded project. Three Mercedes buses began running in London in January 2004. They are powered by a Ballard 250 kW fuel cell, have a top speed of 80 kph and a range of 200 km. Liquid hydrogen, supplied by BP, is used as the fuel, although it is dispensed to the buses as a compressed gas. General Motors and BMW are jointly developing standardized hydrogen systems for cars, with the aim of producing commercial fuel cell powered vehicles by 2010. The work will focus on developing standards for suppliers to find the best technical solutions for handling and storing hydrogen. These are likely to include technical specifications developed by the European Commission’s Integrated Hydrogen Project. BMW expects there to be at least 10,000 hydrogen filling stations in Germany alone by 2010. Bosch has developed an advanced sensor system to measure the temperature, viscosity, and conductivity of the engine oils used in cars and trucks. Current oil change

intervals are based either on vehicle manufacturers’ experiences or on computer simulations that use algorithms derived from engine speeds, numbers of cold starts, fuel quality, and ambient temperatures. The new system is designed to allow drivers to make optimally timed oil changes. However, problems identified with the sensors include a reduction in accuracy of the tests caused by the presence of water in the oil and corrosion, silting and glazing of sensors that are in constant contact with oils. Dirty sensors are less sensitive, so a computational method has been developed to take account of the gradual reduction in sensitivity.

41.2.3 European Automotive Vehicle Regulations 41.2.3.1 Safety European vehicles are becoming more complex and sophisticated as a result of stricter safety and environmental laws and of increasing demands from customers. The trend has been captured by the automotive industry catch-phrase “more car per car.” The trend toward an increasing use of airbags and side-impact protection bars typifies the emphasis on greater safety. Both concepts were pioneered in Europe, with Mercedes-Benz inventing the original steering wheel airbag and Volvo inventing the side-impact protection system. However, the routine use of airbags was evident first in the United States. These trends are now becoming apparent in Asian markets, particularly on Japanese, South Korean, and Malaysian cars destined for export to the United States and Europe. Road traffic accidents are a major public health problem, both in industrialized countries, where roads are very busy, and in developing countries, where accident rates per kilometer are higher. Progress in vehicle design since 1980 has more than halved the risk of occupant injury in the event of an accident. Improvements in road infrastructures have also reduced the numbers of accidents. Renault and PSA Peugeot Citroen jointly fund the Laboratory for Accident Research, Biomechanics and Human Behavior (LAB), which was set up in 1969. The laboratory studies safety factors and has found that driver error contributes to 95% of fatal traffic accidents, 42% are caused by problems with road infrastructure, 27% arise from vehicle faults, and 20% result from traffic conditions. Human behavior is a contributing factor in almost 80% of all road accidents. European vehicle manufacturers have become very safety conscious over the last 20 yr, taking both vehicle parameters and driver reactions into account. Following on from automatic braking systems (ABS), new systems have been developed, including electronic stability program (ESP), to correct the difference between driver input and the desired vehicle trajectory.

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The French Ministry of Transport initiated the Lavia (Limiteur s’Adaptant à la Vitesse Autorisée) project to study the acceptability and effects on driving behavior of an on-board system that limits the vehicle speed to the maximum authorized on the road where the vehicle is traveling. In September 2002, senior executives from a number of European, U.S., and Japanese car manufacturers used the Paris Motor Show to call for governments and regulators worldwide to work together to allow common global designs for vehicle safety and emissions, thereby reducing development and manufacturing costs. They argued that different car safety and emissions regulations in different countries are impeding free trade and should be the same in the United States, EU, and Japan. A meeting of the heads of the biggest car manufacturers was the first time executives such as Rick Wagoner of General Motors, Hiroshi Okuda of Toyota, and Louis Schweitzer of Renault joined to form a global lobby. Jean-Martin Folz, chairman of the managing board of PSA Peugeot Citroen, who called the meeting, denied the industry was trying to water down safety or pollution standards. He is reported to have said that “We are not looking to counteract or to put pressure against the environmental concerns or safety issues.” The car manufacturers are concerned about the problems that are caused by governments acting in noncoordinated ways. The automotive industry is one of the most highly regulated, with rules covering everything from particle emissions to the maximum and minimum height of headlights. Many rules are different in each region. Attempts have been made through an international committee to bring standards into line, but little progress has been made so far. Planned new regulations on pedestrian safety has unnerved some executives. European car manufacturers appear to be losing the race to make vehicles lighter, to meet more demanding EU emissions limits, at the same time they are being made safer and with more features. While car manufacturers and their suppliers attempt to reduce weight as much as possible, safety improvements and consumer demand for bigger vehicles and state-of-the-art systems are pulling in the opposite direction. In January 2004, Volvo disclosed its Ultra Light Steel Auto Body (ULSAB) series of projects that aim to reduce the weight of car bodies by as much as 70% over the next few years. But, it is difficult to cut weight when you have to maintain a reputation for crashworthiness. High-strength steel was still little used by the car industry even in the late 1990s, although Volvo began to use it in the 740 model in 1984, where the proportion was about 15% by weight. With the new XC90 and S40 Volvos, that proportion had risen to just over 50%, but the body of the new S40 weighs 311 kg compared with 266 kg for the earlier 1996 model. Volvo has a reputation for safety to maintain, so the problem

of weight reduction is particularly difficult. And for any car manufacturer such reductions have to be cost-effective. Volvo acknowledges that there is a direct conflict between crash protection and reducing weight and there is also a conflict between reduced weight and cost. Aluminum alloys were once seen as a potential rival to steel, but it is now generally accepted that both can exist together, if used appropriately. However, aluminum is at a disadvantage to steel for use in the primary body structure of volume cars, because car manufacturers’ installed asset bases have a heavy investment in steel presses, assembly facilities, and paint shops. Others disadvantages for aluminum include its higher cost, that is compounded by price volatility, and its durability. Aluminum will always eventually fail due to fatigue if subjected to enough stress cycles, whereas at low, but repeated stresses, steel does not. There is more scope for aluminum’s use in bolt-on parts, such as suspension components, body closures, and skin panels, and aluminum has considerable promise. BMW’s new 5-Series is widely praised as an example of using aluminum appropriately. The entire structure forward of the dashboard is aluminum, benefiting both overall weight and contributing to a 50/50 front/rear weight distribution, which helps handling. Magnesium alloys are also being used in some niche applications, notably cross-car beams such as the instrument pack beam behind the dashboard. Magnesium alloys generally have to be cast, which limits them to components with open cross-sections and in places where they are not normally visible. The cross-car beam has to carry the weight of components mounted in the central console, such as the air-conditioning unit, and in a crash it takes loads from the steering column and airbags. In a side impact it has the important function of bracing the passenger safety cell. A fairly large, yet lightweight section in magnesium is well suited to these tasks. Seat frames and inner door structures are other possible applications. Stainless steel is another material with good potential. Its benefits include high strength, good formability, and durability. Cost is a disadvantage, but this is coming down. Because of its formability, stainless steel might be used in specific applications where extra high-strength steels, such as press-hardened boron steels, are now used. Sandwich materials can be used where noise or vibration is a problem. These typically consist of two sheets of steel of 0.2 to 0.5 mm thick with a layer of rubber sound-deadening material in between. For strength and welding the sandwich can be treated as a conventional steel sheet, but saves the weight of separate sound deadening material. To combine improved safety with reduced weight, the front body structure of the Volvo S40 is divided into several zones, each with a different task in the process of deformation through which crash forces are absorbed. To give each zone the relevant properties, four different grades of steel, from conventional mild steel to ultra high strength were

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used. The outer ones are responsible for most of the deformation; the closer the collision forces get to the passenger compartment, the less the materials used deform. The front bumper incorporates a rigid UHSS (boron steel) cross member. The straight sections of the side members are ductile high-strength steel, optimized for high energy absorption. This is where most of the deformation is in a collision. Further back, the member just before the A-post is designed to act as a barrier for the cabin space, and to help prevent the front wheel penetrating the interior. This section is extremely rigid and is made of extra highstrength steel. A rigid cross member connects the A-posts and lower side members, helping to maintain the cabin space in a bad crash. The patented technique allowed Volvo to achieve the same safety performance as the larger S80 saloon with a 200 mm shorter structure. For the XC90’s front crash structure Volvo improved its crash performance by designing it as a space-frame of members in direct compression or tension rather than relying on their strength as beams in bending. However, the body of a car is only about 25% of the total weight, so reductions in weight are also having to be made with the other components, particularly the engine, gearbox, and transmission assemblies. Other devices or systems to improve vehicle safety that might be adopted in the future include automatic collision detection, phone call and vehicle information management systems, headlights that bend when a vehicle is cornering and head-up displays. Some of these could be included in luxury cars by 2008. Video cameras will detect oncoming cars, management systems will divert incoming phone calls during cornering or overtaking maneuvers, and in-car displays will be laser-projected head-up types. Navigation systems could provide voice feedback for the last 5 mi of a journey, which is when drivers need it the most, according to recent market research. New design of starter alternator allows engines to be turned off when the car stops at traffic lights and then turned on immediately. Valeo has developed the novel headlight system and plans to supply it to Porsche for the next generation of cars. This is also an attempt by a component supplier to use exclusive technology in order to avoid price cuts being forced on suppliers by manufacturers. 41.2.3.2 Environment Emissions regulations in Europe (and the United States) have succeeded in reducing carbon monoxide (CO), unburnt hydrocarbons (HC), and nitrogen oxide (NOx ) emissions from cars, trucks, and buses by over 95% since the mid-1980s. Particulates from diesel engines have also been reduced, although emissions of ultra-fine particulates continue to be a concern. Research is in progress in the EU to determine if current limits for particulates need

revision to take particle surface area into account. Future EU emissions standards could include the number and size of particulates in addition to their total mass. Vehicles produce over 20% of the total CO2 emissions in the EU, a figure that will obviously increase with the vehicle population. CO2 can be limited only be reducing the amount of carbon-based fuel used, which is why in the long term, cutting frictional losses and raising thermal efficiency is so important. In Europe, the European Commission and ACEA have agreed a target new car fleet average (for the range of models and number of cars made by each manufacturer) for CO2 emissions of 140 g/km by 2008. To measure the effectiveness of this strategy, the Commission issued Directive 1999/94/EC, which requires all car manufacturers to publish information on CO2 emissions and fuel economy for each model of car and to display this information “on or near” each model in a car dealer’s showroom. The data must be included in all brochures and advertising material. A fuel economy guide must be produced at least once every year. EU Member States must notify the Commission of the competent body or bodies responsible for the implementation and functioning of the consumer information scheme. The regulations came into effect in January 2000 and were required to be implemented in all Member States by January 2001. Current discussions between the European Commission and car manufacturers appear to be aiming at a new car fleet average limit for CO2 emissions of 120 g/km by 2010. In the last ten years, European car manufacturers have invested in diesel technology as the main way to reduce fuel consumption. However, with a target of 120 g/km, diesel technology is unlikely to be enough. Hybrid gasoline/electric technology is not cheap, but it is probably the least costly method of reducing CO2 emissions. Examples are Honda’s Civic IMA (integrated motor assist) car. DaimlerChrysler’s Smart and A-Class cars and BMW’s Mini are helping to improve the average fuel consumption of these manufacturers of mainly big executive cars. Unfortunately, other trends are going in the opposite direction. Heavier 4 × 4 vehicles are becoming more popular in Europe, for the same reasons they have in the United States, and customer demands for equipment such as power steering and air-conditioning adds both to weight and fuel consumption. The U.K. average CO2 emissions for 2001 was 168 g/km, but in 2002 there was a marginal increase to 169 g/km. European car manufacturers have begun to realize that it is likely to be very difficult to achieve fleet CO2 emissions the targets by 2008. However, a number of European car manufacturers in addition to BMW and DaimlerChrysler (Mercedes-Benz) have made major steps toward achieving the reduced CO2 emissions goal. For example, more than 400,000 PSA Peugeot Citroen 206 and C3 HDi diesel-engined cars,

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emitting 114 and 110 g/km of CO2 respectively, have been sold so far. The company plans to manufacture and sell 1.7 million vehicles of this type by 2006. For gasoline engines, catalytic converters achieved the greatest reductions in vehicle emissions, more than any other engineering or design improvement so far. Particulates may prove to be a further challenge, if and when direct injection engines are used in a majority of gasoline cars. Diesel engines are being used in an ever greater number of passenger cars in Europe and the number of heavy duty diesel powered trucks sector is also growing, as more goods are transported by road. But the increase in diesel use is tempered by the need to reduce both NOx and particulates. Concern over particulate emissions has prompted the widespread use of oxidation catalysts (oxcats) on diesel passenger cars and some heavy duty vehicles. In all cases low-sulfur fuel is essential for effective operation. These catalysts cut CO2 and HC emissions effectively and oxidize the organic fraction of diesel particulate matter, lowering particulate mass by 50%. In addition, the use of particulate trap-based aftertreatment reduces the number of particles, including the ultra-fine ones, as well as achieving over 99.9% filtration efficiency over a wide range of operating conditions. The original oxidation catalysts in catalytic converters, which convert CO and unburnt HCs to CO2 and water, are being superseded by three-way catalysts (TWC), which simultaneously oxidize CO and HC to CO2 and water and reduced NOx to nitrogen. TWCs operate best at relatively high temperatures and catalytic converters only reach optimum temperatures a few minutes after the engine has started, so emissions immediately after start up account for a significant proportion of the total. The latest generation of converters use several methods to improve light-off time, defined as the time taken for 50% conversion of regulated emissions. Techniques include positioning the converter nearer to the exhaust manifold, preheating the catalyst, or using HC adsorber systems that trap HCs for release after light-off. GDI engines also pose a challenge to catalyst designers, as well as having an impact on piston ring design and lubricant formulation. Conventional TWCs prove less effective at reducing NOx under lean burn conditions, so alternative systems are being developed. Lean DeNOx catalysts use advanced structural properties in the catalytic coating to enable NOx reduction by HCs from the exhaust. NOx traps adsorb and store NOx under lean burn conditions, which is then desorbed during a brief return to “rich” operation and destroyed in a conventional TWC downstream. Particulate matter resulting from lean burn combustion may prove a further challenge should direct injection engines form a larger part of the gasoline passenger car parc. Work is also in progress to develop homogeneous charge compression ignition engines, which typically run

on natural gas or gasoline, and offer advantages in thermal efficiency, fuel economy, and NOx production compared with spark ignition engines. They also seem to offer a route to zero particulate matter, but may still pose a challenge to emissions catalysts. Other catalyst developments included plasma catalysts and plasma aftertreatments. EU emission regulations for new light duty vehicles (cars and light commercial vehicles) were originally specified in Directive 70/220/EEC. This regulation has been amended several times. Euro 1 and 2 limits were covered in Directives 93/59/EC and 96/69/EC respectively. Current (Euro 3) and future (Euro 4) limits were covered in Directive 98/69/EC. The Euro 3 and 4 standards, for 2000 and 2005, were accompanied by an introduction of more stringent fuel quality rules that require minimum diesel cetane number of 51 (2000), maximum diesel sulfur content of 350 ppm in 2000 and 50 ppm in 2005, and maximum petrol (gasoline) sulfur content of 150 ppm in 2000 and 50 ppm in 2005. The emission test cycle for these regulations is the ECE 15 + EUDC procedure. The Euro 2, 3, and 4 standards are different for diesel and gasoline vehicles. Diesels have lower CO standards but are allowed higher NOx . Gasoline vehicles are exempted from PM standards. The standards for new passenger cars are summarized in Table 41.10 and the standards for light commercial vehicles (vans) in Table 41.11. In addition, EU Member States may introduce tax incentives for the early introduction of 2005 (Euro IV) compliant vehicles. There is also a requirement for

on-board emission diagnostics systems (OBD) to be phased-in between 2000 and 2005. A low temperature emission test (7◦ C) for gasoline vehicles became effective in 2002. Most industry observers believe that fuel cell powered cars are unlikely to become more widely available from car manufacturers until a hydrogen distribution infrastructure is built. Currently, much discussion is in progress in Europe, and in North America, between the automotive and oil industries about the type of fuel distribution infrastructure that will be both technically and commercially practical for fuel cell vehicles. Some advocates are promoting hydrogen, in either liquid or gaseous form, while others are promoting methanol as an easily transported and delivered liquid. The Argonne National Laboratory in the United States is developing an autothermal reactor nozzle to convert methanol, natural gas, gasoline, or diesel into hydrogen to power a fuel cell. The device works on the same principles as those used to make syngas from natural gas, air, or steam. To produce hydrogen while avoiding the formation of particles of carbon, which would clog the catalyst and block the nozzle, the gasoline, or diesel, steam and air must be present in a very specific ratio and must be very finely mixed without being vaporized. But the researchers now need to demonstrate that the device is robust enough to work properly for several thousand hours in adverse driving conditions. In Europe, most of the major car manufacturers have fuel cell powered cars either undergoing field trials or in

TABLE 41.10 EU Passenger Car Emissions Limits Emissions limits, g/km, by year of introduction Fuel

Emissiona

Euro 1 1992

Euro 2 1996

Euro 3 2000

Euro 4 2005

CO HC HC + NOx NOx

2.72 — 0.97 —

2.20 — 0.50 —

2.30 0.20 — 0.15

1.00 0.10 — 0.08

CO HC + NOx NOx PM

2.72 0.97 — 0.14

1.00 0.70b — 0.08c

0.64 0.56 0.50 0.05

0.50 0.30 0.25 0.025

Gasoline

Diesel

a CO = carbon monoxide, HC = unburnt hydrocarbons, NO = nitrogen oxides, PM = x

particulates. b Limit for IDI engines. From 1996 to 1999, the limit for DI engines was 0.9 g/km. c Limit for IDI engines. From 1996 to 1999, the limit for DI engines was 0.10 g/km.

Source: European Commission.

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TABLE 41.11 EU Light Commercial Vehicle Emissions Limits Emissions limits, g/km, by year of introduction Fuel and vehicle weighta (kg)

Emissionb

Euro I 1994

Euro II 1998

Euro III 2000

CO HC + NOx HC NOx

2.72 0.97 — —

2.20 0.50 — —

2.30 — 0.20 0.15

1.00 — 0.10 0.08

1305–1760

CO HC + NOx HC NOx

5.17 1.40 — —

4.00 0.65 — —

4.17 — 0.25 0.18

1.81 — 0.13 0.10

>1760

CO HC + NOx HC NOx

6.90 1.70 — —

5.00 0.80 — —

5.22 — 0.29 0.21

2.27 — 0.16 0.11

CO HC + NOx NOx PM

2.72 0.97 — 0.14

1.00 0.90 — 0.10

0.64 0.56 0.50 0.05

0.50 0.30 0.25 0.025

1305–1760

CO HC + NOx NOx PM

5.17 1.40 — 0.19

1.25 1.30 — 0.14

0.80 0.72 0.65 0.07

0.63 0.39 0.33 0.04

>1760

CO HC + NOx NOx PM

6.90 1.70 — 0.25

1.50 1.60 — 0.20

0.95 0.86 0.78 0.10

0.74 0.46 0.39 0.06

Gasoline <1305

Diesel <1305

Euro IV 2005

a For Euro I and II, the weight classes were <1250, 1250 to 1700, and >1700 kg. b CO = Carbon monoxide, HC = unburnt hydrocarbons, NO = nitrogen oxides, x

PM = Particulates. Source: European Commission.

the later stages of engineering development, as noted earlier in this Chapter. However, some analysts believe that it is likely to be another 20 yr before mass-produced cars powered by fuel cells are widely available. The European regulations for new heavy duty diesel engines were introduced first in Directive 88/77/EEC. The Euro I standards for medium and heavy duty engines were introduced in 1992 and the Euro II regulations came were introduced in 1996. (The standards have different designations from those for passenger cars and light duty diesel engines, in order to distinguish the two sets of standards.) The medium and heavy duty diesel standards applied to both heavy duty highway diesel engines and urban buses, although the urban bus standards, however were voluntary.

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The Euro III, IV, and V standards, for implementation in 2000, 2005, and 2008 respectively, were defined in Directive 1999/96/EC. The standards also set specific, stricter values for extra low emission vehicles (also known as “enhanced environmentally friendly vehicles” or EEVs) in view of their contribution to reducing atmospheric pollution in cities. In April 2001, the Commission adopted Directive 2001/27/EC that introduced further amendments to Directive 88/77/EEC. The new Directive prohibits the use of emission “defeat devices” and “irrational” emission control strategies, which would be reducing the efficiency of emission control systems when vehicles operate under normal driving conditions to levels below those determined during the emission testing procedure. The limits are summarized in Table 41.12.

TABLE 41.12 EU Heavy Duty Diesel Emissions Limits Euro emissions limits, g/kWh, by year of introduction I

II

III

IV

V

2008

1999 Test cycle ECE R-49

Emissiona

1992

1996

1998

EEVs

2000

2005

CO HC NOx PM, <85 kW PM, >85 kW

4.5 1.1 8.0 0.612 0.36

4.0 1.1 7.0 0.25

4.0 1.1 7.0 0.15

— — — —

— —

— —

— —

—

—

—

CO HC NOx PM Smokeb

— — — — —

— — — — —

— — — — —

1.5 0.25 2.0 0.02 0.15

2.1 0.66 5.0 0.10c 0.8

1.5 0.46 3.5 0.02 0.5

1.5 0.46 2.0 0.02 0.5

CO NMHC CHd4 NOx PM e

— —

— —

— —

— —

— —

— —

3.0 0.40 0.65 2.0 0.02

5.45 0.78 1.6 5.0 0.16 f

4.0 0.55 1.1 3.5 0.03

4.0 0.55 1.1 2.0 0.03

ESC and ELR

ETC

a CO = carbon monoxide, NMHC = nonmethane unburnt hydrocarbons, CH = methane, NO = nitrogen oxides, PM = x 4

particulates.

b Limits for smoke are in m−1 . c For engines of <0.75 dm3 swept volume per cylinder and a rated power speed of >3000 min−1 , the limit is 0.13 g/kWh. d For natural gas engines only. e Not applicable for gas-fueled engines for Euro III and Euro IV. f For engines of <0.75 dm3 swept volume per cylinder and a rated power speed of >3000 min−1 , the limit is 0.21 g/kWh.

Source: European Commission.

It is expected that the emission limit values set for 2005 and 2008 will require all new diesel powered heavy duty vehicles to be fitted with exhaust gas aftertreatment devices, such as particulate traps, SCR, and DeNOx catalysts. The 2008 NOx standards were to have been reviewed by December 31, 2002, but they are still under discussion and need to be either confirmed or modified, depending on the availability of emission control technology. Changes in the engine test cycles were introduced in the Euro III standard. The steady-state engine test cycle ECE R-49 was replaced by two cycles: a stationary cycle ESC (European Stationary Cycle) and a transient cycle ETC (European Transient Cycle). Smoke opacity is measured on the ELR (European Load Response) test. For Euro III type approval of new diesel vehicles, manufacturers had a choice between either ETC and ESC/ELR tests. For Euro IV and IV type approvals and for EEVs, the emissions have to be determined on both the ETC and the ESC/ELR tests.

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As with gasoline and light duty diesel engines, EU Member States are allowed to use tax incentives to encourage the early launch of vehicles meeting the new standards. Such incentives have to comply with the following: • They apply to all new vehicles offered for sale on the

market of a Member State that comply in advance with the mandatory limit values set out by the Directive. • They cease when the new limit values come into effect, either 2005 or 2008. • For each type of vehicle they do not exceed the additional cost of the technical solutions introduced to ensure compliance with the limit values. Additional regulations are also being introduced progressively by the Commission. They include the introduction of an OBD for heavy duty vehicles from October 1, 2005 and provisions on the durability of emission control devices with effect from the same date, to ensure that they

operate correctly during the normal life of a vehicle. The Commission is also discussing provisions to ensure the conformity of in-service vehicles that are properly maintained and used, as well as appropriate limits for pollutants that are nonregulated currently, as a consequence of the introduction of new alternative fuels. The Fifth European Community Action Programme on the environment and sustainable development emphasized the need to modify methods of production and development and consumer behavior. The EU approach to waste management uses two strategies; to avoid generating waste by improving product design and to increase recycling and the reuse of waste. As part of this approach, EU Directive 2000/53/EC requires vehicle manufacturers, together with manufacturers of materials and equipment to: • Endeavor to reduce the use of hazardous substances

when designing vehicles. • Design and produce vehicles that facilitate the dis-

mantling, reuse, recovery, and recycling of end-of-use vehicles. • Increased the use of recycled materials in vehicle manufacture. • Ensure that components of vehicles marketed after July 1, 2003 do not contain mercury, hexavalent chromium, cadmium, or lead, except in cases listed in Annex II. The Commission must amend the Annex in the light of scientific and technical progress.

same periods. Less stringent objectives may be allowed for vehicles manufactured before 1980. Regulations for free take-back and manufacturers’ responsibilities were introduced in the Netherlands and Sweden even before the Directive came into force and in Germany and Austria in 2002. In the Netherlands, vehicle manufacturers have to pay a recycling fee when the vehicle is first sold and this fee is used to cover possible recycling costs. In the United Kingdom, from early in 2003 until early in 2007, motorists are being forced to pay an extra £50 to cover the costs of disposal of end-of-life cars. The EU Directive mandates that manufacturers must meet the cost by 2007. Analysts believe that the extra charge is likely to increase significantly the number of old cars that are simply abandoned every year in the United Kingdom. In 2003, 350,000 cars were abandoned by their owners. Another 2m cars are scrapped or dismantled every year in the United Kingdom. It has been estimated that the cost of the Directive to U.K. suppliers of cars manufactured before 2002 could be between £24 and £43m per year.

41.2.4 European Automotive Lubricant Specifications and Tests 41.2.4.1 ACEA

The Directive came into effect on October 21, 2000 and EU Member States had until April 21, 2003 to implement the Directive. An end-of life vehicle (ELV) is any type of vehicle that is waste, as defined in Directive 75/442/EEC. Vehicle manufacturers responded by redesigning vehicles to increase the percentages of recyclable materials and components and ensuring that these are more easily separable during dismantling. The Directive also requires EU Member States to set up collection systems for ELVs and for waste used parts, as well as a system of de-registration upon presentation of a certificate of destruction. An ELV must be sent to an authorized treatment facility where it can be dismantled, with as many parts as possible being recycled or reused. The regulations also specify that the last owner of an ELV built during or after 2002 should be able to dispose of it free of charge, called “free take-back.” Vehicle manufacturers are required to meet all, or a significant part of, the cost of meeting this requirement. By the end of 2002, about 75% of the metal content of old vehicles was being recycled in the European Union. The aim of the Directive is to increase the rate of recovery and reuse to 85% (by average weight per EVL and model year) by 2006 and to 95% by 2015 and to increase the rate of recycling to at least 80% and 85% respectively over the

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The Association des Constructeurs Européens d’Automobiles (ACEA) replaced the previous trade association, the Comité des Constructeurs du Marché Commun (CCMC, the Committee of Common Market Automobile Constructors) in 1991. ACEA is a differently structured organization. Historically in Europe, the automotive industry developed its plans in private and was not restricted by the need for consensus with the lubricant industry. However, in 1974, partially in anticipation of the formation of CCMC and the need for dialogue, the Technical Committee of Petroleum Additive Manufacturers (ATC) was formed. Similarly, in 1976, a lubricant marketers organization (Association Technique de 1’Industrie Européene des Lubrifiants, ATIEL) was formed, specifically to address the need for discussion with CCMC. The first CCMC sequences published in 1975 covered additional requirements to the existing API designations that were thought necessary to bridge shortfalls in operating small engines in a European environment. These sequences were extensively revised in 1984 and 1991. Performance parameters such as high-temperature/high-shear viscosity and volatility were recognized widely for the first time and had a significant and positive effect on quality in the European market. Most of the additional test

requirements were developed by the Coordinating European Council for the Development of Performance Tests for Transportation Fuels, Lubricants and Other Fluids (CEC) based on prototype tests recommended by engine manufacturers. CCMC sequences and API classifications had several important differences. Working groups that monitored test quality directly backed the U.S. classifications, while CCMC sequences were based (mostly) on CEC test procedures, but the links between the organizations were much less formal. The European classification acknowledged the separate passenger car diesel market, which did not exist in North America. CCMC also recognized the possibility of providing differently classified lubricants for the same equipment, depending on type of service or oil change interval. In the United States there is only one recommended minimum quality for a specific application at any one time. Although often encouraged to do so, CCMC never gave oil approvals, because it was reluctant to incur the financial costs of developing and maintaining the necessary infrastructure. Also, the association was not a legally established body with the power to enforce any such system. ACEA has objectives that are broadly similar to those of CCMC, but has a different organization. Unlike CCMC, ACEA includes U.S.-owned companies, which manufacture in Europe (General Motors and Ford) and European companies (Volvo, Saab-Scania) whose headquarters are outside the original Common Market. ACEA is likely to continue issuing lubricant “sequences” but not granting approvals. The organization also favors using multi-cylinder European engine tests developed by CEC wherever possible. The current ACEA specifications, which were reissued in November 2004, are available from ACEA’s website, www.acea.be. The first allowable use of the 2004 sequences was November 1, 2004. The previous 1999 sequences were withdrawn on February 1 , 2004 and the 2002 sequences will be withdrawn on November 1, 2006. The main reason for the new specifications is the introduction of Euro IV emissions limits for cars and vans in January 2005 and for heavy duty trucks in October 2005. Some manufacturers have introduced engines that meet the new limits early, so the ACEA specifications were prepared to ensure that suitable lubricants will be available when needed. The new limits are about 50% lower than the previous limits for emissions of carbon monoxide, unburnt hydrocarbons, nitrogen oxides and particulates (from diesel engines). For gasoline and small diesel engines, ACEA has replaced the A and B sequences with revised A/B categories and has introduced new C sequences, for “catalyst compatibility oils”. Only four A/B combinations

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are allowed: 1. A1/B1; Oil intended for use in gasoline car and light van diesel engines specifically capable of using low friction, low viscosity oils. 2. A3/B3; Stable, stay-in-grade oil intended for use in high performance gasoline car and light van diesel engines and/or for extended drain intervals and/or for year-round use of low viscosity oils and/or for severe operating conditions as defined by the engine manufacturer. 3. A3/B4; Stable, stay-in-grade oil intended for use in high performance gasoline and direct injection diesel engines. 4. A5/B5; Stable, stay-in-grade oil intended for use for extended drain intervals in high performance gasoline car and light van diesel engines designed to be capable of using low friction, low viscosity oils. All three catalyst compatibility (C) sequences are for stable, stay-in-grade oils intended for use in high performance car and light van diesel and gasoline engines with three way catalyst (TWC) and diesel particulate filters (DPFs). The C categories are: 1. C1; For engines requiring low friction, low viscosity, low SAPS oils. 2. C2; For engines requiring only low friction, low viscosity oils. 3. C3; For all other engines. The C sequences are roughly based on the performance criteria of the A5/B5 sequence, but with chemical limits. (For the definition of “low SAPS” oils, see my previous column in the January issue of TLT.) To meet Euro IV emissions regulations, manufacturers of heavy-duty diesel engines have introduced either exhaust gas recirculation (EGR) based systems, many of which include a diesel particulate filter (DPF), or selective catalytic reduction (SCR) systems. ACEA has deleted the E3 and E5 sequences and introduced a new E7 sequence, which is essentially an upgrade of E5. E4, E6 and E7 categories are for stable, stay-in-grade oil recommended for highly rated diesel engines meeting Euro I, II, III and IV emission requirements. The revised E sequences are: 1. E2; General purpose oil for naturally aspirated and turbocharged heavy-duty diesel engines, medium to heavy-duty cycles and mostly normal oil drain intervals. 2. E4; Suitable for engines without particulate filters and for some EGR engines and some engines fitted with SCR NOx reduction systems. 3. E6; Suitable for EGR engines with or without DPFs and for engines fitted with SCR NOx reduction systems. Strongly recommended for engines fitted with DPFs in combination with low sulphur diesel fuel.

4. E7; Suitable for engines without DPFs and for most EGR engines and most engines fitted with SCR NOx reduction systems.

ACEA notes that all the C category oils and the E4, E6 and E7 oils (all of which are for engines running under very severe conditions, such as significantly extended oil drain intervals) may be unsuitable for use in some engines and recommendations may differ between engine manufacturers, so driver manuals and/or dealers should be consulted if in doubt. Also, the car, truck, lubricant and additive companies in Europe have instigated a process for managing the development of new performance specifications. The European Engine Lubricants Quality Management System (EELQMS) has, where practicable, drawn on experience from North America. An ATC Code of Practice, which currently contains European tests, is aligned closely with the CMA Code of Practice described in Section 5.5.2. ATIEL has developed a Lubricant Code of Practice which is broadly based on the API Engine Oil Licensing and Certification System (EOLCS). One significant difference between practices in North America and Europe concerns the way in which the importance of auditing and quality monitoring is recognised. Europe has a larger number of smaller but more diverse laboratories, so relatively more emphasis is placed on “the laboratory” (using ISO 9000 quality systems and EN 45001 laboratory accreditation) rather than on “the test stand”, as happens in North America. With new lubricants costing as much as $1.5m to develop and test, with the costs having to be paid by lubricant and additives suppliers before product sales materialise, there is understandable concern that it may be difficult for these companies to recover their development costs if the specifications are driven higher too quickly. European lubricant manufacturers are keen to avoid the US experience where the ILSAC Sequences (set by US and Japanese motor manufacturers) went through a number of changes in very short succession, causing additives manufacturers to spend more and more money in an effort to keep up with the changing specifications. Future ACEA and OEM classifications in Europe are increasingly likely to recognise that that quality classifications cannot be built on poor test procedures. As a result, the focus is likely to be identifying the most important bench, rig and engine test parameters and to develop new tests or improve existing CEC tests to more precise standards. The new ACEA specifications keep Europe at the forefront of environmental regulatory compliance, while maintaining fuel economy, engine performance and long oil drain intervals for users.

Copyright 2006 by Taylor & Francis Group, LLC

41.2.4.2 CEC In Europe, CEC has a parallel but much more limited role than ASTM in North America. Its scope is limited to performance tests (essentially engine and rig-tests) and bench tests are generally left to other organizations such as the Institute of Petroleum (IP) or the German standardization organization Deutscher Normenausschuss, which awards DIN (Deutsche Industrie Normung) classifications. CEC develops tests but does not set limits on those tests, leaving it to commercial organizations to set limits. Until 2001, the CEC Council was composed of members elected from its ten constituent national European Organizations. Committees, including an Engine Lubricants Technical Committee (ELTC) and a Transmission Lubricants Technical Committee (TLTC), each with voting membership from national organizations, reported to the Council. The working groups that reported to the committees had members from individual companies and it was only at this working level that CEC really had much in common with the ASTM. Council meetings and Technical Committee meetings were held semi-annually and decision making tended to be slow. The CEC structure and voting by national organizations had strengths and weaknesses. Decisions were requested of people who lacked the detailed experience to make effective judgments. Many of the CEC lubricant engine test procedures were less rigorously defined and maintained than their U.S. equivalents. Work to determine the repeatability and reproducibility of new tests was assigned to volunteer laboratories of the working group member companies. To try to address some of these issues, CEC began cooperating closely with ACEA, ATIEL, and ATC during the early 1990s. However, since June 2001, the CEC has adopted a new management structure. A board of directors has replaced the Council, with members representing ACEA, CONCAWE, ATEIL, and ATC. Work to determine the repeatability and reproducibility of new tests will be contracted to test laboratories, and will be paid for from the subscriptions of member organizations. The CEC Board set a fee of e50,000 (∼$45,000) for a company to become a test sponsor. By 2003, 15 oil and additive companies and OEMs had paid to become sponsors. A test case for the new system was already waiting. It had been agreed earlier in 2001 that a test to measure fuel economy retention in light duty diesel engines was needed. Ford had agreed to provide the engine, so a formal protocol for the test was sent to all interested laboratories, with the indication that one laboratory would be chosen to develop the test. Seven proposals were received by CEC and the Board chose ISP Laboratories in Salzbergen, Germany. Development work started at ISP in August 2001, with CEC overseeing the project. The work was completed toward the end of 2003, but did not produce a repeatable

and reproducible test. Many lessons were learnt about fuel economy testing in engines and a technical paper summarizing the results is being prepared for a forthcoming SAE meeting in Toulouse, France. New tests being developed currently by CEC include a test for oil dispersion at medium temperature for passenger car direct injection diesel engines, using the Peugeot DV4TD engine (to replace the XUD11BTE test) and a test to determine asphaltenes in used engine oils, particularly for marine and large diesel engines. Investigations have also started to find replacement tests for the OM602A and M111 Sludge Test methods. As before, CEC will develop tests, but not classifications or limits, which will continue to be defined by ACEA and individual European OEMs. The major challenge for the future will be to combine speed with quality.

41.2.4.3 Vehicle manufacturers lubricant specifications and tests OEMs are keen to develop higher lubrication specifications to support advanced engine designs. The impact of this, however, is to reduce product life cycles dramatically. In the past, a relatively simple lubricant formulation might have a working life of up to ten years. Now, a much more complicated product may only be in use for two or three years before a higher specification renders it obsolete. A view began to emerge in Europe in the late 1990s that the speed with which CEC, ATEIL, and ACEA are able to plan, agree, and introduce specifications that meet the needs of the OEMs is too slow and does not allow sufficient competitive differentiation between each OEM’s range of cars, vans, and trucks. The response of some of the OEMs in Europe, notably VW, Mercedes-Benz, BMW, and Volvo, has been to develop their own specifications, which do not necessarily correspond with the ACEA specifications.

The three main OEMs that issue engine oil specifications and approvals in Europe are VW, Mercedes-Benz (DaimlerChrysler), and BMW. VW has been issuing specifications for many years and MB has begun reissuing passenger lubricant approvals after a break of several years. BMW is particularly significant in Germany. PSA (Peugeot Citroen) is also significant in France. Following the introduction of revised ACEA specifications in 1998, an important development in the European lubricants market was the introduction in late 1999 of new VW and Mercedes-Benz (DaimlerChrysler) service fill oil specifications. The VW passenger car service fill specifications are listed in Table 41.13. VW has indicated that it will only give Service Fill approvals in conjunction with Factory Fill approvals. However, since there are only two approved suppliers of factory fill oils at present, this VW policy is currently being challenged at the European Commission by UEIL (the European Union of Independent Lubricant Suppliers) in conjunction with several nonapproved suppliers of lubricants. The two new VW specifications, used for cars manufactured from 2000 onwards, are summarized in Table 41.14. Although Volkswagen does not specify the types of components (baseoils or additives) to be used to meet the new specifications, it is widely acknowledged in Europe that both can only be met at present by using PAO and/or Group III and Group III+ baseoils. It is also very instructive to note that the new specifications list only 0w, 5w, and 10w oils and do not refer to heavier viscosity levels. VW plans that all new cars from 2000 onwards will have low viscosity (preferably 0w or 5w) oils with extended drain capabilities. The new Mercedes-Benz service fill approvals are for 0w and 5w gasoline and passenger car diesel engines are summarized in Table 41.15. While the performance criteria for the Mercedes-Benz service fill oils are not as severe as those for the VW specifications, the trend toward ever higher performance is clear. Other European OEMs, including Volvo, Peugeot, and BMW are known to be

TABLE 41.13 VW Passenger Car Service Fill Specifications Specification number Gasoline engines Up to Model Year 1999 and beyond, without extended oil drain interval From Model Year 2000, with extended oil drain interval Unit injector engines, without extended oil drain interval Unit injector engines, with extended oil drain interval. Source: VAG.

Copyright 2006 by Taylor & Francis Group, LLC

Diesel engines

500.00, 501.01, 502.00

505.00, 505.01

503.00 — —

506.00 505.01 506.01

TABLE 41.14 VW 503.00 and 506.00 Specifications Test limits Performance or test ACEA quality High-temperature high-shear (HTHS) viscosity, cP Sulfated ash Oil drain interval Volatility (Noack) Viscosity Phosphorous content Seal swell Key tests

503.00

506.00

A3, except HTHS

B4, except HTHS 2.9–3.4

1.5% max 30,000 km or 2 yr

Engine tests if <1.5% 50,000 km or 2 yr

13% max 0w, 5w, 10w/20, 30, 40 0.08% max Numerous tests PV 1449 (T4) PV 1451 Audi FE PV 1452 (New TDI) PV 5106 (Cam and Tappet)

Source: VAG.

considering further improvements to the current ACEA specifications, along the lines of those enhancements required by VW and Mercedes-Benz. The new BMW Service Fill specification introduces a “BMW Longlife Oil,” that passes ACEA A3-98/B3-98 and the BMW M52 engine test and is suitable for oil drain intervals of 20,000 ± 5,000 km or 2 yr. The BMW Longlife approvals have been divided into two categories; LL98 is for oils approved via the M44 engine and LL01 is for oils approved against the more severe M52 engine. 2002 model year vehicles will require LL01 oils. Both Scania and Volvo Truck’s main lubricant specification requirements (Table 41.16) also use the Mercedes-Benz OM441LA and OM364LA tests for turbo-charger and piston deposit control and bore polish protection, the OM602A and M11 tests for sliding valve train wear protection, the Mack T8E test for soot control, and the Mack T9 test for ring and liner wear protection and copper and lead corrosion protection. Both Volvo and Scania require field trials that demonstrate extended oil drain interval performance. As in North America, the progression of CCMC and then ACEA specifications have required ever more demanding engine and bench tests, coupled with more stringent pass limits. Extending oil drain intervals (ODIs) has been one of the key trends for European lubricant specifications. European OEMs have forecast that current ODIs, which averaged 15,000 to 20,000 km in 2000, could average 30,000 km by 2005. Mercedes-Benz, VW, and BMW are among the leading advocates of extended ODIs. In particular, the new VW specifications have an ODI of 30,000 km or two years for gasoline engine oils in model year 2000 cars onwards and 50,000 km or two years for diesel engine oils.

Copyright 2006 by Taylor & Francis Group, LLC

41.3 CURRENT STATUS OF AUTOMOTIVE FLUIDS IN EUROPE 41.3.1 Engine Oils 41.3.1.1 Gasoline engine oils The value chain for lubricants dictates that customers drive the performance properties of lubricants and, in turn, that the properties required of blended lubricants drive the performance properties of baseoils and additives. Customers include motorists, buyers of lubricants in industrial companies, ship-owners, airlines, government departments, and many other people. In Europe, the main drivers for automotive lubricants have been, and will continue to be: • Lower vehicle emissions, through improved fuel econ-

omy and enhanced engine performance, for both gasoline and diesel engines. • Longer drain intervals, now averaging 12,000 km for passenger cars and 30,000 km for heavy duty trucks. • Enhanced operability at both higher and lower temperatures, to give both better driveability and improved engine protection. • Tighter mechanical tolerances, leading to less lubricant leakage, lower top-up and hence higher lubricant stress. European cars and trucks have smaller, more fuel efficient and higher performance engines than vehicles in North America and Asia. Better fuel economy in cars can be achieved by aerodynamic design, improved engine design and control, and smaller engine size, as well as by reduced engine and gearbox friction, which is

TABLE 41.15 Passenger Car Motor Oil Requirements of Individual European OEMs OEM Mercedes-Benz

Specification or classification p229.1

p229.3

p229.5

BMW

Long life oil LL98

Long life oil LL01

Porsche

All season engine oil

Requirements and comments ACEA A3-98/B3-98/B4-98 M111E sludge test and M111E fuel economy test OM602A wear test Restrictions on phosphorous and dynamic viscosity ACEA A3-98/B3-98/B4-98, plus MB229.1 M111E sludge test and M111E fuel economy test OM602A wear test to MB228.3 level VW T4 and BMW M44 data (as a support) Chlorine content 100 ppm max, sulfur content 0.5% max and soluble acidity 1.5% max Oil drain interval of 15,000 to 30,000 km ACEA A3-98/B3-98/B4-98 High temperature high shear viscosity greater than 3.5 cSt NOACK volatility <10% DIN 50017 corrosion test Double duration M111E sludge test M111E fuel economy OM602A wear test to MB228.5 level VW T4 and VW TDI tests OM611, M113, M166 and M111E23ML tests Chlorine content 50 ppm max, sulfur content 0.5% max, phosphorous content 0.11% max and soluble acidity 0.5% max Oil drain interval of 15,000 to 30,000 km 3 yr Snail field test and 2 yr Barracuda field test 5w or 10w gasoline engine oils suitable for oil drain intervals of 20,000 ± 5,000 km or 2 years ACEA A3-98/B3-98 M44 engine test (225 h endurance): evaluate wear, piston cleanliness, oil consumption and used oil properties, relative to a reference oil 5w or 10w gasoline engine oils suitable for oil drain intervals of 20,000 ± 5,000 km or 2 years ACEA A3-98/B3-98 M52 engine test (225 h endurance): evaluate wear, piston cleanliness, oil consumption and used oil properties, relative to a reference oil For 2002 model year cars onwards 15w40 oils, 10w40, 5w40, 5w30, 0w40, and 0w30 oils Minimum quality API SL, ILSAC GF-3, ACEA A3 or ACEA A1, as appropriate Porsche Air Entrainment test required for 5w40 and 10w40 oils 120 h Porsche engine test required for 0w40 and Xw30 oils HTHS viscosity 3.5 cP min NOACK volatility 12% max Porsche engine test required for oils with KV100 below 11.0 cSt

Source: Pathmaster Marketing, from OEM and industry contacts.

Copyright 2006 by Taylor & Francis Group, LLC

TABLE 41.16 Heavy Duty Diesel Engine Oil Requirements of Individual European OEMs OEM Mercedes-Benz

Specification or classification p.227.0/.1

p.228.0/.1

p.228.2/.3

p.228.5

MAN

270/271

M3275

M3277

Volvo

VDS

VDS-2

VDS-2 + Euro III

VDS-3 + Euro III

Scania

ACEA E3-96

ACEA E5-02

Requirements and comments 15w40 oils OM441LA, OM364LA, and OM602A tests Oil drain interval 10,000 to 30,000 km 15w40 oils OM441LA, OM364LA, and OM602A tests; tighter limits than p.227.1 Oil drain interval 10,000 to 30,000 km 15w40 oils OM441LA, OM364LA, and OM602A tests; tighter limits than p.228.1 Oil drain interval 10,000 to 30,000 km 10w40 and 5wXX oils OM441LA, OM364LA, and OM602A tests; most severe limits Oil drain interval up to 100,000 km Generally 15w40 oils ACEA E2, MB p228.1 minimum performance Oil drain interval 20,000 to 45,000 km 15w40, 10w40 and 5w30 oils ACEA E3 minimum performance 5w oils must be 100% Group III or IV baseoils and 10w oils must be minimum 25% Group III baseoils Oil drain interval 20,000 to 60,000 km 10w40 and 5w30 oils ACEA E4 minimum performance OM441LA and OM602A at MB p288.5 severity Plus MAN/MTU turbocharger deposit test Oil drain interval 20,000 to 80,000 km 15w40 and 10w30 oils ACEA E2 minimum performance Oil drain interval 15,000 to 30,000 km 15w40 and 10w30 oils ACEA E3 minimum performance Oil drain interval 25,000 to 45,000 km 15w40 and 10w30 oils ACEA E5 minimum performance Oil drain interval 15,000 to 40,000 km 15w40 and 10w30 oils ACEA E5 minimum performance Oil drain interval up to 100,000 km Generally 10w30 and 15w40 oils OM441LA/OM364LA, OM602A, Mack T8E and Mack T9 tests Oil drain interval up to 60,000 km Generally 10w40 oils OM441LA/OM364LA, OM602A, Mack T8E, Mack T9 and extended drain (LDF) tests Oil drain interval up to 120,000 km

Source: Pathmaster Marketing, from OEM and industry contacts.

Copyright 2006 by Taylor & Francis Group, LLC

achieved using lower viscosity and friction modified lubricants. Emissions reduction can be achieved by improved combustion, exhaust gas recirculation, and better fuel quality. However, many of these changes will also impact the properties required of lubricants, and hence of the baseoils from which they are made. The impacts and associated requirements include: • Reduced engine friction: lower viscosity, higher viscos-

ity index. • Higher operating temperature: better detergency, better

oxidation stability. • Direct injection: Improved detergency, bore polishing,

increased soot formation, better dispersancy. • Exhaust gas recirculation: Increased soot formation, better dispersancy, improved wear control, better acid neutralization. • Emissions compliance: catalyst protection from low sulfur and phosphorous, low ash, lower volatility. • Extended oil drain: lower volatility, better oxidation stability, total base number (TBN) retention, viscosity control. The pressures that customers exert on lubricant suppliers are derived, in turn, from environmental concerns and regulations, from the desire for increased equipment productivity and performance, from lower maintenance, and from a desire to produce less waste. Customers require suppliers, including lubricant suppliers, to focus on helping to reduce their total operating costs. For example, extended ODIs contribute to lowering fleet owners’ operating costs, mainly by keeping trucks on the road for longer, hauling freight more productively, and lowering maintenance costs. However, extended ODIs are applicable only for specific operating conditions, which include the long distance and relative constant speed driving of truck haulage fleets. Stop-start driving and long periods of engine idling, such as in off-highway mining trucks, are unsuited to extended ODIs. During the last ten years, the Western European market for automotive engine oils has become clearly defined in terms of tiered product quality: “good, better, best.” These quality levels are most closely aligned with “standard”, “part-synthetic” and “synthetic” and with specific oil viscosities. In 1995, the viscosity levels were 20w50, 15w50, and 10w40. At the end of 2003 they are slightly different for each European country, as summarized in Table 41.17. In Germany, “synthetic” must, by law, refer to an engine oil that contains only synthesized baseoils, usually PAOs and/or esters. German law does not accept XHVI or VHVI to be “synthetic.” Outside Germany, these definitions have not been challenged in court, so many lubricant

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TABLE 41.17 Gasoline Engine Oil Viscosity Levels in Europe, 2003 Typical oil viscosities

Belgium France Germany Italy Netherlands Spain Sweden UK

Good

Better

15w40 15w40, 15w50 15w40 15w40 15w40 20w50 10w40 15w40

10w30, 10w40 10w30, 10w40 10w30, 5w30 10w40 10w30, 10w40 15w40 10w30, 5w30 10w40

Best 5w30 5w30 0w30 10w30, 5w30 0w30, 5w30 10w40 0w30 5w30, 0w30

Source: Pathmaster Marketing.

suppliers now promote their premium engine oils as “synthetic performance.” (This description is not allowed in Germany.) Western Europe is a much more quality conscious and diverse market for automotive lubricants than is North America, or other regions of the world.

41.3.1.2 Passenger car diesel engine oils During the 1970s, most passenger cars in Europe were gasoline powered. Diesel cars were regarded as dirty, smoky, slow, and noisy. Diesel engine technology at that time was based on indirect fuel injection. During the 1980s, diesel engined cars started to gain favor. Turbocharging meant that the performance of diesel engines began to approach that of gasoline engines. In addition, European country government tax incentives (notably in France) and the superior fuel economy of diesel engines compared with gasoline engines encouraged the use of diesel passenger cars. From the 1990s onwards, lower sulfur fuel and exhaust gas catalysts reduced smoke emissions greatly, while improved turbocharging, direct fuel injection, and common rail fuel injection meant even better fuel economy. European governments also kept diesel prices below those of gasoline prices (using lower tax rates), so even luxury marques (such as the Audi A8, BMW740d, Mercedes 320cdi, and new Jaguar S Class) began to use diesel engines. Common rail engines are viewed as the future by most OEMs for diesel passenger cars, and even for some truck diesel engines. Mercedes Benz (Daimler Chrysler), Alfa Romeo, and PSA introduced common rail diesel engines in the mid-1990s and BMW introduced their first common rail engine, a V8, to power their luxury 5 and 7 series cars, in 1998. The notable exception was VW, but even they announced an Audi developed 3.3L V8 common rail engine in 1999.

Some reports are emerging from the industry that there may be a problem with high pressure direct injection and common rail injection systems. Abnormal wear of injectors and some pump parts has been reported. It has been suggested this may be due to the water content of the fuels, although still at low levels, causing wear at injector tips etc. due to very high pressures and temperatures at these localized sites. 41.3.1.3 Heavy duty diesel engine oils

TABLE 41.18 Oil Drain Intervals for European Heavy Duty Diesel Engines, 2003 OEM

Specification

DAF MAN Mercedes-Benz

HP1 and HP2 M3277 p.228.3 p.228.5 LDF VDS-3

Oil drain interval (km) Up to 120,000 Up to 80,000 Up to 45,000 Up to 90,000 Up to 120,000 Up to 100,000 km, depending on fuel consumption

For heavy duty diesel engines in Europe, the main market drivers are:

Scania Volvo

• Emissions performance • Improved fuel economy • Longer oil drain intervals, to reduce down-time and

Source: Pathmaster Marketing, from industry contacts.

maintenance and to improve productivity The technology challenges for heavy duty diesel engines have been driven by public and regulatory concerns for the environment as well as by the desire of fleet operators to reduce costs and improve efficiencies. The list of engine technology challenges is long, and is increasing: • • • • • • • • • • •

Fuel injection pressures of 1600 bar and higher Common rail injection Unit injection Retarded injection Pilot injection Central injectors Raised top piston ring Articulated pistons Four valves per cylinder Cooled exhaust gas recirculation (EGR) Variable geometry turbochargers

Current ODIs for European heavy duty diesel engines are listed in Table 41.18. Extended ODIs minimize service costs over the lifetime of the truck and mean savings of up to $500 per day in improved truck productivity. However, using the newer engine technologies to assist with extending ODIs and improving fuel efficiencies is leading to problems for the engine oil in terms of: • Much higher soot loadings: From previous levels of 2%

to current levels of up to 8%wt. • Fuel dilution: With consequent reductions in lubricant

viscosity. • Engine wear: Due to higher soot content and to oil

viscosity loss. • Cost vs. performance: Twelve oil changes for an engine

operating life of 500,000 km vs. three oil changes for an engine operating life of 300,000 km.

Copyright 2006 by Taylor & Francis Group, LLC

Many European heavy duty diesel engines (and an increasing number of passenger car diesel engines) are either turbocharged or supercharged. These engines use forced induction of air in order to improve combustion efficiency. This is achieved by blowing air into the inlet manifold under pressure. A turbocharger is a turbo-pump that is driven by the engine’s exhaust gases, while a supercharger is a mechanical pump driven from the engine’s crankshaft. Larger diesel engines tend to be supercharged. Turbocharging and supercharging increase the specific power output of the engine by improving “breathing,” so that more oxygen is available for combustion. Intercoolers are also used to cool the air prior to induction. This increases the density of the air, making further oxygen available and an even larger increase in power output. Naturally aspirated engines achieve power outputs of around 15 kW/L of cylinder volume. Turbocharged engines can double this, to achieve power outputs of around 30 kW/L of cylinder volume, and turbocharged engines with intercooling can achieve power outputs of around 40 kW/L of cylinder volume. For European heavy duty diesel engines, engine power outputs have been increasing steadily and now average 400 to 450 bhp, with some trucks having 600 bhp engines. These increases in power have been coupled with decreases in engine size and weight, to gain more space (for more freight) and to further improve fuel economy. The consequences have been reductions in crankcase lubricant capacity, with yet more stress on the engine oil. Increased power densities through the transmission and axle have also meant higher lubricant loadings, both dynamically and thermally. In addition, the introduction of city diesel (low sulfur content) throughout Europe over the last three years has led to increases in fuel pump wear and to the introduction of a different type of soot loading into diesel engine oils. Both factors have led to higher fuel consumptions, so some

of the benefits of the reduced sulfur have been mitigated by increases in CO2 , NOx , and particulate emissions. Some European diesel engine manufacturers are concerned about ACEA E5 quality oils’ abilities to cope with EGR and soot over long drain intervals. Volvo has upgraded the VDS-2 specification for its new D9 and D12 engines. VDS-3 quality oils are designed for ODIs between 60,000 and 100,000 km. To meet the next Euro IV and V emissions limits, diesel engines will need to run on ultra-low-sulfur fuel and use new types of exhaust aftertreatments, including selective catalytic reduction (SCR) technologies. New diesel engine oils are likely to have to use some hydrocracked baseoils. In Europe, this means combinations of Group III and Group I baseoils, compared with North America where Group II baseoils are likely to be used. European lubricant formulators have over 30 yr experience of using combinations of Group I and Group III baseoils in gasoline engine oils, so the new formulations required for diesel engine oils should not prove too difficult. BP Castrol is claiming to have the most advanced heavy duty diesel engine oil, with the new Castrol Elixion 0w30 grades. It is the world’s first 0w viscosity HDDEO and has been formulated specifically to deliver fuel consumption benefits of between 4 and 6% compared with conventional 10w and 15w viscosity HDDEOs. ExxonMobil introduced the first full-synthetic HDDEO, Mobil Delvac 1, based on polyalphaolefins. Delvac 1 is available in a number of viscosity grades, including 5w40. 41.3.1.4 Two-stroke engine oils Two-stroke (2T) engines are enjoying continued global growth in nonautomotive sectors, including agriculture (chain saws and portable power generators) and recreation (jet skis, power boats, and off-road motorcycles). The efficiency of two-stroke engines is being enhanced through new lubricant, fuel, and injection technologies, as well as improved catalysers, but some environmental concerns remain about the biodegradability and toxicity of residual oils. Some European OEMs support the use of API TC specification oils for 2T engines, with JASO FB oils as a minimum quality standard and ISO-L-EGD (JASO FD) as the highest quality standard. Other OEMs believe that a higher performance level is needed, with improved lubricity and detergency to meet the ISO-L-EGE specification. The CEC is developing the Piaggio Hexagon test as part of the effort to improve quality levels toward full-synthetic 2T oils. Water-cooled 2T engines, used, for example, in boats and jet-skis on lakes and seas, are increasingly required to meet biodegradability and toxicity criteria. The National Marine Manufacturers Association (NMMA) supports only TC-W3-recertified oils, although TC-W and TC-WII

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products are still being marketed. The newly created International Council of Marine Industries Associations (ICOMIA) specification includes a Sturm-type biodegradability test, replacing the CEC-L-33 test.

41.3.1.5 Automotive gears and automatic transmissions The important performance requirements and trends in Europe for automotive gear oils are no leakage of oil from the gearbox, reduced gearbox noise, improved fuel economy, and low levels of chlorine. No gear oil leakage needs dynamic seal performance, no chemical attack by the oil on the seals and thermal stability of the oil. The EU introduced more stringent vehicle drive-by noise limits in October 1996 and is currently considering further legislation. Limits of chlorine in formulated gear lubricants of 50 to 100 ppm are preferred in Europe, particularly in Germany, Austria, Switzerland, Sweden, and Norway. More fuel efficient automotive gear oils have required a move to thinner and wider span viscosities. Another interesting industry consensus forecast for European passenger cars is that the use of automatic transmissions (and hence ATFs) is expected to grow rapidly. In 1995, automatic transmissions accounted for around 15% of demand in passenger cars. In 2002, it was around 20%. It is forecast to grow to 35% in 2005 and to 60% in 2015. The result for ATFs, and hence premium quality baseoils (particularly Group III), will be a significant increase in demand, at the expense of conventional automotive gear oils. With European manual synchromesh passenger car and light commercial vehicle gearboxes, shift quality and “feel” are of paramount importance to the owner and hence the OEM both at low, and to a lesser extent, high temperatures. Shift feel is heavily influenced by the viscometric and frictional properties of the gear oil. Durability of the syncromesh friction material, in terms of load and corrosion, is also important and is also influenced by gear oil properties and performance. Ideally, a manual transmission fluid (MTF) should be compatible with a wide range of synchronizer materials, including molybdenum, aluminum alloy, brass, sintered bronze, and various seal materials. The latest specifications for MTFs in Europe are typically for 75w80/90 viscosity oils. These assist the low temperature performance shift quality by minimizing oil drag on synchronized inertia, enhance fuel economy, and ensure an adequate lubricant film at higher gearbox temperatures. Specifications with multiple viscosity requirements are becoming more common in Europe. For example, the new PSA Norme Vehicule B71 specification requires viscosity measurements at 100, 40, 0, and −40◦ C.

Improved vehicle aerodynamics (for fuel efficiency), smaller gearboxes (to reduce weight and increase vehicle space), lower noise levels (to comply with legislation), and greater power densities require gear oils with significantly higher thermal stability and freedom from deposits and sludge. Lower oil viscosities are also demanded, to minimize friction losses within the gearbox and axle (driveline), as part of the drive for fuel efficiency, and to help lower gearbox temperatures. In turn, thinner gear oils also reduce the size of oil coolers required for gearboxes. Improved oxidation and thermal stability also helps to maintain lower operating temperatures and extend gear oil life. OEM factory fill-for-life is already a reality in Europe and dedicated MTF fluids are being individually designed for OEMs. MTF friction characteristics are being tailored for shift quality and there are different MTF viscometrics profiles for low temperature shift quality, for high temperature protection, and for fuel economy. European MTFs also have improved seal compatibility and greater oxidative and thermal stability. For automatic transmission fluids, of which 110,000 tonnes were sold in Europe in 2002, the key market drivers are • Extended, high-performance service, which requires

high oxidation resistance, viscosity stability, and retention of fluid friction characteristics. • Prevention of “shudder.” • Fill-for-life capability, usually translated to mean ∼150,000 km operation. • Improved cold-start, which requires lower resistance to pumping. In Europe, there are three types of automatic transmissions: • Conventional ATs, based on a continuously slipping

torque converter clutch (CSTCC). • Belt drive continuously variable transmissions (b-CVTs). • Traction drive continuously variable transmissions

(t-CVTs), also known as infinitely variable transmissions (IVTs). European AT OEMs, of which the most important are ZF, Voith, and Mercedes-Benz, tend to follow North American OEMs with regard to ATF performance properties. Revisions to General Motor’s DEXRON® III specifications were expected during 2000 but are now expected during 2004. Revisions to Ford’s MERCON® and MERCON® V specifications are anticipated in the future. Most European automotive manufacturers plan to implement CVTs. Those testing CVTs currently include BMW, Fiat, Ford, Honda, Nissan, Mercedes-Benz,

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Mitsubishi, Rover, Renault, Toyota, Volvo, VW (and Audi), and ZF. The b-CVT market is expected to grow sooner than the t-CVT market and, in the near term, Asia-Pacific (Japan) is likely to be an important market. However, it is expected that, in the longer term, Europe will be the larger market. CVTs are expected to replace other transmission types, such as manual gearboxes, in Europe. They will be applied to larger engine applications, and fluids with high metal– metal friction coefficients are desired to provide high push belt torque capacity. Traction drive CVTs are being evaluated, but their future depends on their economics compared with conventional AT and b-CVT. High quality, shear stable fluids based on hydrocracked, part-synthetic, and synthetic baseoils will be required for ATFs and b-CVTFs. Although it is desirable to have one transmission fluid to meet all types of transmission performance, the performances required for ATF, b-CVTF, and t-CVTF applications is likely to lead to separate unique fluids. Traction coefficient is critical to the success of t-CVTs, so t-CVTFs have evolved from different lubricant types with precisely controlled coefficients of friction. Current ATFs have very low coefficients of friction and are completely unsuitable for use in t-CVTs. The older designs of automatic transmissions are, in general, less fuel efficient than manual transmissions. The newer CVTs and IVTs provide much better fuel efficiency than conventional ATs, in some cases approaching that of manual transmissions. Another way of gaining the fuel efficiency of a manual transmission is the use of an automated manual transmission (AMT). The most fuel efficient design currently is a double clutch transmission (DCT), which provides full automation of the gear changing process while delivering better fuel efficiency than a manual transmission. AMTs make use of current technology and gear oils, and requires no major change to existing production lines. DCTs started to be used in European cars in 2003 and are forecast to achieve a market share of 20% by 2010. Borg-Warner’s Dualtronic DCT is one example of the new AMTs. With European truck transmissions, enhancements in vehicle aerodynamics to improve fuel efficiencies have led to reduced airflows around the gearbox and differentials. This, in turn, has led to increases in transmission oil operating temperatures of up to 20◦ C. Although the use of wide span multigrade gear oils has mitigated the effects of the increases in operating temperature, oxidation and thermal stresses on truck gear oils have more than doubled in the last ten years. Transcontinental European trucks are typically driven 130,000 to 180,000 km/year and the driving force is extended warranty in a very competitive market. The performance considerations for truck transmissions are surface fatigue, seal life, temperature reduction, and gear oil thermal and shear stability.

In Europe, around 95% of manual truck transmissions are synchronized, whereas in North America, only 5% are. Also, currently in Europe, around 75% of truck gear oils sold are for service fill, while a number of lubricant and additive companies believe that by 2010, around 75% will be for factory fill. Synchronizer performance is a balance of frictional and load carrying characteristics. Materials commonly used in synchronizers are aluminum, silicon, nylon, molybdenum, sintered bronze, and pyrolytic carbon. The synchronizer affects on gear shift characteristics are very important, particularly at low temperatures, so the low temperature flow properties of gear oils are under increasing scrutiny. Tests for pitting resistance are being incorporated into gear oil specifications. Most importantly, the drive for improved fuel economy has led to a move toward 75wXX gear oil viscosities. Retarders are being used increasingly in European trucks. They act as a brake on the transmission, increase the overall efficiency of the vehicle, and reduce the biggest vehicle service cost, which is brake pad replacement. They also assist with meeting braking distance legislations. Their design is similar to that of a hydraulic coupling and they are fitted either internally or externally to the transmission. A retarder has the potential to generate coast side gear teeth scoring and to increase the gear oil temperature. In 1994 only 15% of new European heavy trucks were fitted with a retarder, but it is expected that this year the number will be 50%. The European bus market for ATFs is also important. 99% of citybuses, 20 to 30% of intercity buses, and 20 to 30% of mini/midi buses are equipped with automatic transmissions in Europe. Only around 5% of coaches are equipped with automatic transmissions, though. While passenger car ATs are filled-for-life, bus ATs are not, and OEMs are demanding extended drain intervals for the service filling of bus ATFs. Drain intervals are being extended to 120,000 km, for which full synthetic Dexron IIE and III ATFs are required. The important manufacturers of bus ATs in Europe are ZF, Mercedes-Benz, Voith, and Allison. 41.3.1.6 Other automotive oils Comparatively small volumes of hydraulic fluids, brake fluids, shock absorber oils (both of which are specialized types of hydraulic fluid), refrigeration compressor oils (for use in either air-conditioning systems or on refrigerated trucks), and greases are used in vehicles. Nowadays, most of these systems are designed to be “filled-for-life,” with the exception of brake fluids, which are required by most OEMs to be replaced at least every two years. Brake fluids have been continually improved, especially in terms of boiling point, starting from the SAE J 7OR3 specification of the 1960s. It is now being widely recognized that brake fluids deteriorate in service after two

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to three years, due to water absorption. Due to the compactness of European cars, brake temperatures have been steadily trending upwards for the last 20 yr, so boiling points for brake fluids have had to follow suit. Typical boiling points in use in Europe are now 220 to 250◦ C, which are too high for the previous DOT 3 (U.S. Department of Transportation) specification. 220◦ C is the minimum requirement to meet the later DOT 4 specification. DOT 4 fluids are formulated to give greater “in service” stability, especially as regards water absorption. There has been a major swing to DOT 4 fluids in the last five years in Europe, but not in the United States. With air-conditioning and refrigeration systems, some of the newer refrigerants, R134A and R125B introduced as replacement for CFCs, are causing difficulties for previously used refrigerator oils, such as naphthenic mineral oils, alkyl benzenes, and polyalphaolefins, which are not compatible. Since the early 1990s, vehicle manufacturers have progressively switched to polyalkylene glycol or esters type fluids. The types of hydraulic fluids, shock absorber oils, and greases used in European vehicles has changed little in the last few years, except for some of the chassis lubricants used on European trucks. Some OEMs and users, particularly in the more environmentally sensitive countries, are now using ester-based biodegradable chassis lubricants, to allow for the inevitable wash-off while driving through rain and heavy spray.

41.4 DEVELOPMENT OF MARKETS FOR SYNTHETIC AND HIGH PERFORMANCE AUTOMOTIVE FLUIDS IN EUROPE Europe is already the world’s largest market for synthetic and part-synthetic automotive lubricants. Overall, around 8% of gasoline engine oils are fully-synthetic, between 18 and 20% of gasoline engine oils are part-synthetic and almost 15% of heavy duty diesel engine oils are part-synthetic in Europe. These figures, however, mask some wide differences between different European countries. Sales of synthetic and part-synthetic engine oils are highest in Germany, France, the United Kingdom, Sweden, Austria, and Finland and very much lower in Spain and Portugal. Italy, Belgium, and the Netherlands are intermediate. Sales of synthetic and part-synthetic engine oils have been rising steadily across Europe for the last 20 yr. The trend started in Germany, Switzerland, Sweden, and Finland, spread to Austria, Denmark, Belgium, the Netherlands, France, and the United Kingdom, and has now reached Italy, Spain, and Portugal. Consumer resistance to the higher cost of synthetic oils was overcome several years ago in Europe, when discerning motorists recognized the performance and total cost benefits of

the higher quality level. The increased sales of full and partsynthetic oils have led to significant increases in demand for Group III baseoils, polyalphaolefins, and esters from lubricants blenders. With the introduction of 0w30 and 0w40 viscosity grades in many countries, these volumes have continued to rise. European consumers’ technical understanding of the quality and benefits of synthetic oils has been increasing for several years. Where demonstrable cost-performance advantages can be assessed, for example, in highperformance gasoline engine oils, there is a solid acceptance by OEMs, lubricant and additive companies and customers. The use of synthetic and part-synthetic automotive lubricants in Europe received a major boost in the 1980s from the introduction of the NOACK volatility test and received a second boost in the mid-1990s from environmental regulations for lower emissions and improved

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fuel efficiency. With the introductions of Euro IV and V regulations in 2005 and 2008 respectively, this boost is set to continue. The European market for automotive engine oils has been through a period of unprecedented change over the last 20 yr, in terms of industry specifications, product development, and customer expectations at a time of low overall growth in demand for products. This has caused problems of profitability for additive manufacturers, baseoil producers, and lubricant suppliers, but opportunities for companies with marketing and service support skills. The primary observation is that suppliers with higher performance products, better marketing, and attention to service support are more likely to take market share from suppliers that lack one or more of these customer-driven attributes.

42

Automotive Engine Oil Trends in North America Simon C. Tung, Michael L. McMillan, and Shirley E. Schwartz CONTENTS 42.1 Introduction 42.1.1 Automotive Engine Operation 42.1.2 Issues Related to Energy Consumption in an Engine 42.2 Engine Oil Characteristics 42.2.1 Engine Oil Composition and Functions of its Additives 42.2.2 Engine Oil Viscosity Effects 42.2.3 Engine Oil Quality and Oil Degradation During Vehicle Use 42.2.4 Fluid Film Lubrication 42.3 Gasoline Engine Oil Performance Categories and Associated Test Methods 42.3.1 Introduction of Gasoline Engine Oil Performance 42.3.2 ILSAC GF-4 and API SM Standard Tests 42.4 Diesel Engine Oil Performance Categories and Associated Test Methods 42.4.1 Service Effects of Diesel Engines Related to Engine Oil Degradation 42.4.2 Examples of Test Methods for Diesel Engine Oils 42.4.3 A Model for the Rate of Engine Oil Degradation in Diesel Engines 42.4.4 Future Concerns of Diesel Exhaust Emissions 42.5 Current Issues and Future Trends 42.5.1 Issues Related to Conservation of Fuel 42.5.2 Effects at the Molecular Level 42.5.3 Insights Gained from Tests with an Alternative Fuel 42.5.4 Prolonging the Working Life of Engine Oil 42.5.5 Minimizing Emissions and Pollutants and Ensuring Backward Compatibility 42.5.6 Future Trends and Research Directions Acknowledgment References

42.1 INTRODUCTION The automotive industry is facing tough international competition, government regulations, and rapid technological changes. Ever increasing government regulations require improved fuel economy and lower emissions from the automotive fuel and lubricant systems. Higher energyconserving engine oils and better fuel-efficient vehicles will become increasingly important in the face of both the saving of natural resources and the lowering of engine friction. Recently, industry research needs for reducing friction and wear in transportation are critical for saving fuel economy and extended vehicle reliability. There are many hundreds of tribological components, from bearings, pistons, transmissions, and clutches, to gears and drivetrain

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components. The application of tribological principles is essential for the reliability of the motor vehicle, and the energy conservation of our environment. This chapter will provide a comprehensive overview of various lubrication aspects of a typical power train system including the engine, transmission, driveline, and other components, as well as the major issues and the current development status for automotive engine lubricants in North America. This chapter also describes the major functions of typical engines (gasoline and diesel), engine oil characteristics, and test methods. Included are descriptions of the tribological concerns associated with various engine components, service effects on engine oil, standard automotive tests for

Rockers Valve springs Piston rings

Camshaft Valve Piston

Oil filter Cylinder block Con rod Journal bearings Crankshaft Oil pump Oil consumption Oil

Sump

FIGURE 42.1 Diagram of the main components in an internal combustion engine

engine oil and the types of service they represent, and an overview of the current issues and future trends that need to be addressed. FIGURE 42.2 Cross-section view of a V-6 engine

42.1.1 Automotive Engine Operation An internal combustion engine, such as illustrated in Figure 42.1, is the predominant power source for most types of cars and trucks. Various conditions influence engine development, such as the desire for high power output, legislative requirements for reduced emissions, increased fuel economy, and minimal generation of hazardous substances. Many technical and environmental challenges await those who attempt to address these concerns [1–4]. The following discussions contain examples of current conditions (and in some cases, the evolution up to current conditions), to provide insight into the types of issues that must be understood and actions that are desirable to successfully meet future concerns. Directions in which future developments may evolve are included. Passenger car engines in North America typically use a “four stroke” cycle, which represents the number of times a piston changes direction before the events in the process of powering the engine are repeated. Some diesel and spark-ignited engines use a “two stroke” cycle, but this is not common for passenger car applications because two stroke engines may provide relatively higher emissions of unburned fuel. Some engines locate the camshaft and valves above the engine, and others locate the valves within the engine block. Engines also differ with regard to the number of cylinders and the orientation of those cylinders, such as in-line or V shaped. Figure 42.2 provides an example of a typical V-6 (6 cylinder) engine.

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42.1.2 Issues Related to Energy Consumption in an Engine The fuel provides the energy to maintain vehicle motion. However, the magnitude of the fuel consumption depends on a great number of factors. The extent to which energy is lost during operation of a given vehicle will vary with characteristics such as vehicle weight, engine type, component design, operating conditions, outside temperatures, type of terrain (flat or hilly), the number of below-freezing starts in which the engine oil never warms completely before shutdown, the viscosity of the engine oil at various operating temperatures, service history and age of the vehicle, and extent of component wear [3,4]. According to the information of Figure 42.3 (derived from an automotive database), friction in the engine, transmission, and axles represents approximately 11% of the energy consumed by a light-duty vehicle such as a gasoline-fueled passenger car. Within this 11% portion of energy usage, the piston skirt and piston rings contribute significantly to energy loss. Cooling and exhaust also represent a significant fraction of the energy loss. The severity of surface interactions between the moving components in an engine is reduced, to a greater or lesser extent, by the presence of engine oil. The oil provides different functions in different regions of the engine. Lubrication conditions are often subdivided into boundary, mixed, and hydrodynamic domains, according to the Stribeck curve (Figure 42.4), which also shows the

DISTRIBUTION OF ENERGY LOSSES IN A TYPICAL LIGHT-DUTY VEHICLE

Wheels 12%

Exhaust 33%

Axle & Transmission 22.5%

Air Pumping 6% Braking & Coasting 7.5%

}

Engine Friction 7.5% Axle & Transmission Friction 3% Accessories 4% Cooling 29%

Piston Skirt Friction 25%

Crankshaft 5% Piston Rings 19%

Valvetrain 6% Bearings 22.5%

Research and Development Center

FIGURE 42.3 Typical values for energy loss in a light-duty vehicle

Coefficient of friction

Boundary 1.0

Hydrodynamic Mixed Piston rings

0.1 Valve train 0.01

Piston skirt Engine bearings

0.001 Viscosity × speed Unit load

FIGURE 42.4 Stribeck diagram, including the operating regions of several engine components

lubrication regimes in which various engine components usually operate. Figure 42.4 indicates the relationship between the coefficient of friction (vertical axis) and a term consisting of the viscosity of the oil at a given operating temperature, times the relative difference in speed between the two surfaces, divided by the load that one surface exerts on the other. The range over which various engine components operate is indicated by the horizontal arrows. It should be noted that the vertical axis is drawn on a logarithmic scale, so that the differences in friction would be greater if drawn on a linear scale. The low point on Figure 42.4 indicates

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the condition under which friction is a minimum (and thus fuel consumption will be minimized for a given vehicle). Engines do not operate at a constant temperature, vehicles sometimes drive on rough roads, and various additional conditions influence vehicle operation, and so Figure 42.4 represents a highly idealized assessment of friction effects. In the hydrodynamic region, the sliding surfaces are completely separated by an oil film, and friction is essentially due to shearing of the fluid. As sliding speed and viscosity of the engine oil decrease and loads increase, the two opposing solid surfaces begin to interact. Moving to the left on the Stribeck curve, the coefficient of friction rises sharply as the load is shared between the fluid and the solid surfaces in the region identified as mixed lubrication. At some sufficiently low value of viscosity and component speed and at an adequately high load, the contact zone moves into the domain of boundary lubrication [5,6].

42.2 ENGINE OIL CHARACTERISTICS 42.2.1 Engine Oil Composition and Functions of its Additives The major component of engine oil is its base stock (i.e., the oil itself). Various additives are placed in the engine oil, each of which provides a highly specific mode of action

to protect the engine and reduce the rate at which the engine oil degrades. Zinc dialkyl-dithiophosphate (known as ZDP) is an essential additive in engine oil, and it has two functions: inhibition of oil oxidation and protection against wear. To protect the oil against oxidation, ZDP tends to react faster with oxygen, compared to the rate of attack by oxygen on the oil’s base stock. In this way, the oil’s base stock and its other additives are less likely to be oxidized. In addition, ZDP reacts with iron on an engine’s surface (particularly in a heavily loaded contact) by laying down a phosphorus and sulfur coating that is resistant to wear. The phosphorous in ZDP can poison catalytic converters, which has contributed to a trend in recent years to reduce ZDP concentrations in engine oil. Thus, additional compounds that provide supplemental oxidation protection are also generally incorporated into an engine oil’s formulation. A detergent in the engine oil behaves somewhat like a soap, in that it reduces the tendency of partially oxidized oil to form tar-like deposits on a hot surface. A dispersant helps keep degraded oil from coagulating, so that the coagulated oil will not be able to block narrow lubricant passageways. A pour-point depressant allows the oil to flow at low temperature.

42.2.2 Engine Oil Viscosity Effects Appropriate engine oil viscosity is essential for satisfactory engine performance, but maintaining suitable viscosity over a temperature range that can extend well below 0◦ C and well above 100◦ C requires an additive in the engine oil (viscosity index improver, typically called “VI” improver) that helps to minimize the adverse consequences of large temperature fluctuations. A VI improver is a long-chain polymer that is less soluble in cold oil, but is more soluble in warm oil. When cold, the VI improver folds in upon itself and offers less resistance to oil flow. Thus, the VI improver facilitates cold starting of an engine. When the oil is hot, the VI improver expands into a loose coil, so that the viscosity of the engine oil increases over what it would otherwise be at an elevated temperature. This expansion and contraction effect may diminish as the VI improver ages and is broken down by high-shear conditions that are likely to be experienced whenever engine oil passes through narrow, hot contact points, such as in a heavily loaded bearing or underneath the piston rings. The oil container will display a term such as SAE 5W30, in which the “5W” signifies the oil viscosity when the oil is cold; the “30” indicates the viscosity at normal operating temperatures. Viscosity requirements under various shear conditions for the different viscosity grades are established by SAE and are included in SAE J300 [7], “Engine Oil Viscosity Classification.” The latest requirements are summarized in Table 42.1.

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Oil containers usually also display something relating to the performance capabilities of the oil. The two most common symbols indicating that engine oil satisfies a particular performance standard for gasoline engines in the United States are the API Certification Mark (Starburst) and the API Service Symbol (donut).

42.2.3 Engine Oil Quality and Oil Degradation During Vehicle Use A container of engine oil, such as one would buy in a store or at a service station, should have a symbol that indicates whether the oil meets current standards (as indicated above). Unfortunately, some stores also carry engine oils that do not have a current designation, and an unaware purchaser is at risk for buying an inappropriate grade of engine oil. In addition, overly degraded engine oil also puts an engine at risk of damage. Examples of oil analysis tests that are helpful in documenting the extent of engine oil degradation during use include changes in viscosity as described in various standard tests such as American Society for Testing Materials (ASTM) D 445, D 446, D 4683, and D 4684. (Note: All ASTM Standards cited in this paper can be found in the Annual Book of ASTM Standards, available from ASTM International, West Conshohocken, PA.) Loss of antioxidant/antiwear protection as a consequence of exposure of engine oil to the exceedingly high heat and pressure of combustion processes can be measured using ASTM D 5483. Remaining oil alkalinity (including remaining corrosion protection) can be measured using ASTM D 2896 or D 4739. (Note: the authors have observed that ASTM D 2896 was particularly useful when attempting to compare the rates of engine oil degradation in a broad range of service types.) Accumulation of acids in the engine oil (due to incomplete combustion of the fuel or oil oxidation in hot spots) can be measured using ASTM D 664. The extent to which wear debris or corrosion residues have entered the engine oil (e.g., measurements of iron, copper, lead, aluminum, etc.) can be determined via analysis of the chemical elements in the oil. This type of analysis is particularly beneficial when one uses a nontraditional fuel or a new material in an engine application. That is, whenever engines are modified to meet new conditions, it becomes important to determine whether the engine oil degrades differently than was the case before the modification. If there are different mechanisms of oil degradation, tactics will have to be developed to understand those mechanisms and to find techniques to reduce adverse consequences, if any. Engine operating conditions can be particularly harsh on the engine oil, compared to conditions experienced by most other types of automotive lubricants. An operating engine produces nitrogen compounds and partially burned oil or fuel, which then become pollutants, as well as carbon

TABLE 42.1 SAE Viscosity Grades for Engine Oilsa,b Low-temperature (◦ C) cranking viscosityc , mPa sec max

Low-temperature (◦ C) pumping viscosityd , mPa sec, max with no yield stressd

Low-shear-rate kinematic viscositye , (−mm2 /s) at 100◦ C min

Low-shear-rate kinematic viscositye , (mm2 /s) at 100◦ C max

High-shear-rate kinematic viscosityf , (mPa sec) at 150◦ C min

6200 at −35 6600 at −30 7000 at −25 7000 at −20 9500 at −15 13,000 at −10 — — —

60,000 at −40 60,000 at −35 60,000 at −30 60,000 at −25 60,000 at −20 60,000 at −15 — — —

3.8 3.8 4.1 5.6 5.6 9.3 5.6 9.3 12.5

— — — — — — <9.3 <12.5 <16.3

40

—

—

12.5

<16.3

50 60

— —

— —

16.3 21.9

<21.9 <26.1

— — — — — — 2.6 2.9 2.9 (0W-40, 5W-40, and 10W-40 grades) 3.7 (15W-40, 20W-40, 25W-40, 40 grades) 3.7 3.7

SAE viscosity grade 0W 5W 10W 15W 20W 25W 20 30 40

a Notes: 1 mPa sec = 1 cP; 1 mm2 /s = 1 cSt. b All values are critical specifications as defined by ASTM D 3244 (see text, Section 42.3). c ASTM D 5293. d ASTM D 4684: Note that the presence of any yield stress detectable by this method constitutes a failure regardless of viscosity. e ASTM D 445. f ASTM D 4683, CEC L-36-A-90 (ASTM D 4741), or ASTM D 5481.

dioxide and water vapor. The amounts of pollutants can be minimized by exhaust after-treatment. In reality, service effects can be more complex than the above description. The complexities arise from differences between one type of engine and another, the type of service that the engine is experiencing at a given instant, the nature of the fuel, severity of the terrain, weather conditions during use, and the extent to which the driver uses rapid accelerations. Service effects can be roughly categorized under four headings: easy freeway, high-temperature high-load service, taxi service, and extreme short-trip service at low outside temperatures [8,9]. Even though one or another of these service conditions may predominate for a given driver, in reality, most vehicles, at some point, are driven under each of these conditions. The sequence of events that engine oil experiences in freeway service is approximately as follows: An adequate supply of oil is pulled up from the oil pan, filtered through an oil filter, and is distributed to those engine components that require lubrication. Sufficient oil pressure needs to be available to permit bearings to ride on a fluid film. Engine oil is moved along an engine cylinder bore by the motion of the piston rings. The conditions within the cylinder are extremely harsh, since the fuel typically explodes

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several times a second, creating extreme heat, high pressures, and the fuel sometimes creates corrosive chemicals whenever combustion is not complete. The heat of combustion would be strong enough to partially oxidize the engine oil and form organic acids (i.e., oxidized hydrocarbons), except that the oil’s antioxidant (as long as it has not degraded) blocks oxidation and acid formation [9–12]. Once an oil’s antioxidant has degraded, the second line of defense against acid attack is the oil’s detergent, which is an alkaline agent that neutralizes acids that form during exposure of the engine oil to heat in the presence of oxygen. Thus, the detergent reduces the rate at which polar reaction products accumulate on engine surfaces, and therefore the detergent helps keep the engine’s surfaces clean. When the oil’s detergent has become inactivated during long-term vehicle use without an oil change and without oil refreshing via addition of makeup oil, engine corrosion (from acid attack) becomes more likely, and excessive deposits may form on engine surfaces. Since the oil’s antioxidant is also its antiwear agent, once the antioxidant is largely degraded, the wear rate in an engine can then accelerate. These harmful effects are highly unlikely in freeway service, except under conditions in which the engine oil has not been changed for far greater distances than recommended in

owners’ manuals or when a driver has installed an engine oil of inferior quality. In many ways, high-load service is similar to freeway service, except that oil temperatures and engine speeds are higher, and thus the rate of engine oil aging will be faster. In addition, oil viscosity is lower at high temperature, which means weaker oil films are present in high-temperature contact points. An increase in engine speed also means that a flame front will impinge on the cylinder bore more frequently than during service at slower engine speeds. Thus, higher engine speeds promote higher oil temperatures, faster oil degradation, and increased stress on an oil film [13]. These effects accelerate the wear rate, though use of an oil cooler can reduce some of the adverse consequences of high-temperature service. If the engine oil has not been changed soon enough in high-load service, so that the oil’s protective additives have become overly degraded and ineffective, various ill effects are likely to be observed. For example, the lighter ends of the engine oil will boil away faster than in freeway service, so that the engine oil’s viscosity increases. The antioxidant/antiwear agent in the oil will experience faster thermal degradation, which means that an increase in the engine wear rate may occur as soon as the oil’s antiwear agent is no longer effective. Oil thickening will increase due to chemical interactions within the oil. If high-load service continues long enough without an oil change or if an inappropriate engine oil has been used (e.g., an engine oil that has not passed the standard tests, but which is easily available to the public), the oil can become viscous enough that engine failure becomes a concern [13]. Chemical and physical effects of city driving (such as taxi service, where the oil is completely warm, but severe accelerations may occur) differ from those found during freeway or high-load service. For example, if a taxi is attempting to move through a large, congested city during rush hour, the taxi’s engine will be at idle when the vehicle is at a red light. When the light turns green, the taxi will accelerate, but will move slowly whenever traffic is again blocked. A sudden acceleration tends to produce incomplete combustion of the fuel and formation of both organic acids and additional harsh chemicals. Periods at idle or at slow vehicle speed (so that the engine receives very little cooling from the wind) also promote formation of aggressive chemicals that can condense in or be formed in the engine oil. The effects resulting from extreme short-trip service during cold weather (e.g., all trips lasting only 5 or 10 min with outside temperatures below freezing) can be particularly harsh [13]. On start-up, the oil and the engine are cold. Once the engine has started, fuel condenses in the engine oil. Even if the weather warms or a longer trip is taken, so that the lighter ends of the fuel evaporate, the heavier ends of the fuel are likely to remain in the oil and cause the oil to have a lower-than-normal viscosity.

Copyright 2006 by Taylor & Francis Group, LLC

Partially burned fuel (including organic acids and other reactive chemicals) also condenses in the oil. These fuelderived agents can degrade protective oil additives, attack the oil’s base stock, and attack some engine materials [9]. For example, organic acids derived from the fuel begin to neutralize the oil’s detergent and cause the oil’s antioxidant to become less effective. Acids can also modify an engine’s surface properties, so that engine materials are more easily removed by mechanical action (i.e., rubbing) than would normally be the case. Thus, these corrosive wear conditions accelerate removal of metal from rubbing surfaces during short-trip winter driving. Water-in-oil emulsions form a “white sludge” that also contains fuel, partially burned fuel, and oil additives. If an engine has not been turned on for several weeks in winter (after having been used in extended short-trip service), a layer of “white sludge” (containing measurable amounts of polar oil additives and water) may form and drop to the bottom of an oil pan. This condition of water-in-oil occurred during a test in which vehicles that had been driven exclusively in 3-km trips for 2 years (without having changed the engine oil) were left parked for 2 weeks in midwinter [10,11]. By the end of the 2 weeks, water and polar oil additives had settled to the bottom of the oil pan and had frozen. The oil uptake in the oil pan was totally blocked by the frozen water. Thus, the engine oil did not flow when the engine was started. The driver immediately turned off the engine when he noted a lack of oil pressure. Warmth applied to the bottom of the oil pan resolved the problem. However, such a scenario poses a risk of severe engine problems if a vehicle is driven very far under conditions in which the engine oil cannot flow up from the oil pan to lubricate the engine.

42.2.4 Fluid Film Lubrication The thickness of a fluid film, in many cases, plays a crucial role in the durability of an engine component. The film thickness and the oil film’s capacity to protect against wear, corrosion, and excessive friction are related to the viscosity of the bulk of the oil at the operating temperature, the oil temperature increase in a heavily loaded contact, the roughness of each of the surfaces in the contact zone, the speed at which one surface is moving relative to the adjacent surface, the presence or absence of any debris (such as honing burrs on the cylinder of a newly manufactured engine or dust in the engine oil), and the extent to which the lubricant has degraded. The “fluid film ratio” is a useful measurement determined by comparing the oil film thickness to a term representing the roughness of each of the mating surfaces. If the oil film thickness is of the order of magnitude of the surface roughness, undesirable wear may result. To avoid this possibility, a designer can modify the surface roughness, increase the viscosity of the lubricant, change engine design to supply more oil to the contact zone, reduce load, or upgrade the oil’s additive package

(all of which may be difficult to modify and at the same time still provide acceptable lubrication to other regions in the complex engine structure). The above assessment assumes that the lubricant wets the surface of interest. If a surface material and its lubricant are not mutually attractive (i.e., the fluid beads up on a surface, rather than spreads spontaneously over it), a mating surface has the potential to wipe away the lubricant rather than use the lubricant to form a lubricating film. An accelerated wear rate then occurs. A simple test can determine the wetting characteristics of a surface and any fluid that may come in contact with that surface, as follows: A drop of lubricant is placed on a level portion of the surface. If the drop beads up, especially if the edge of the drop forms a steep angle with the surface (such as 80 or 90◦ ), one can assume that the contact is nonwetting, or nearly so. An even more surprising effect related to a nonwetting surface can sometimes be identified. A drop of lubricant is smeared to form a thin film over a clean sample of the surface of interest. Next, the point of a pin is lightly dragged a distance of a centimeter or more over the middle of the thin layer of fluid on the surface. If the fluid is not attracted to the surface, the fluid can recoil from the path over which the tip of the pin has moved, so that a hole forms in the fluid film. This nonwetting condition is not desirable in a lubricated contact. Such concerns must be addressed whenever one considers utilizing fuels other than hydrocarbons. Simple compatibility tests can often be conducted in advance to determine whether alternative fuels may influence the durability of engine components (seals in particular) or diminish the ability of the engine oil to provide suitable lubricating films. These examples illustrate that it is not always easy to replace one automotive material or fluid with an alternative substance. Unexpected consequences may result.

42.3 GASOLINE ENGINE OIL PERFORMANCE CATEGORIES AND ASSOCIATED TEST METHODS 42.3.1 Introduction of Gasoline Engine Oil Performance In the early years of automobile use, engine oil had to be added or changed at an exceedingly brief interval. In addition, oils were not standardized. An individual vehicle operator could be at the mercy of his intuition with regard to the purchase of an appropriate automotive lubricant for his car. With time, people began to realize that something had to be done to avoid the possibility of serious adverse consequences if a driver had used the wrong kind of oil for his engine. Thus, there was strong motivation to look for chemical agents that both provided protection to an engine and promoted long life of the engine oil. This trend (toward improving engine and oil durability

Copyright 2006 by Taylor & Francis Group, LLC

and placing additives in the oil to provide specific beneficial attributes) is an ongoing process. Currently, promoting environmental acceptability has also become an essential ingredient of responsible engine oil formulation. Throughout these developments, it has been essential to create and conduct appropriate engine oil test methods that ensure oils available to the public produce appropriate engine protection. Various classes of standard tests are available to confirm that current automotive engine oils provide the desired protection, including long oil life, corrosion and wear protection, resistance to the formation of sludge and deposits, ability to remain within an appropriate viscosity range, and so forth. International Lubricant Standardization and Approval Committee (ILSAC) and American Petroleum Institute (API) are two organizations that play a major role in overseeing availability of standard engine oil-related test methods. The ASTM is typically one of the organizations that publish standard procedures to be used when conducting an automotive test. Such standard tests are prepared in painstaking detail, so that there will essentially be no chance of conducting a standard test incorrectly if one has followed the written directions. Automotive companies tend to be the ones who develop such tests. In general, different tests are used for gasoline-fueled engines than those used for diesel engines. Tests typically need to be updated periodically, for various reasons. In some cases, test components, such as a specific type of engine, may no longer be available. Changes in the chemical nature of the fuel, such as the transition from leaded to unleaded fuel, may mean that a former test is no longer pertinent to current engine wear, corrosion, and sludge characteristics. Future engine designs that differ from current test engines mean that standard tests will have to be created using the newer types of engines, since the older engines may not be predictive of current performance. If it is possible to legitimately substitute a bench test for an engine test (such that the fundamental mechanisms of oil and engine damage correlate strongly with the results from the bench test), the bench test becomes far less labor intensive and expensive. A brief overview of the evolution of standard engine oil test methods and the status of current automotive engine oil test method development is provided in the following paragraphs. Early test methods for engine oils were far less sophisticated and less specialized than those of today. It can be anticipated that the tests of the future may be even more specialized. Wherever possible, bench tests will be substituted for engine dynamometer tests, such as was the case for development of the Ball Rust Test, a bench test that replaced the Sequence IID (i.e., Sequence 2D) engine test, which measured the ability of an engine oil to protect against the kind of corrosive damage that can occur during extended short-trip winter service in which water and corrosive chemicals (derived from the partial combustion

TABLE 42.2 Current Emission Standards Emission level

Vehicles starting Limits, g/mi NMHC 50k mi 100/120k mi CO 50k mi 100/120k mi NOx 50k mi 100/120k mi

LEV

LEV

ULEV

ULEV

LEVII

ULEVII

cars and LDT1

LDT2

cars and LDT1

LDT2

cars = trucks 2004

cars = trucks 2004

0.075 0.090

0.100 0.130

0.040 0.055

0.050 0.070

0.75 0.090

0.04 0.055

3.4 4.2

4.4 5.5

1.7 2.1

2.2 2.8

3.4 4.2

1.7 2.1

0.20 0.30

0.40 0.50

0.20 0.30

0.40 0.50

0.05 0.07

0.05 0.07

of the fuel) enter and remain in the engine oil for extended periods, and cause engine corrosion. At the fundamental level, oil analyses can determine whether a given engine oil has all the required additives in its formulation (and thus is not deficient, such as an “SA” quality oil would be). Such information can be pertinent to engine durability field problems, since most vehicle warranties are invalidated if the wrong grade of engine oil has been used in an engine. As of early 2004, the only two designations widely used to describe light-duty, gasoline engine oil performance were API SL and ILSAC GF-3. Later in 2004, API SM and ILSAC GF-4 oils became available in the marketplace. The engine test and bench test performance requirements for API SL are similar to those for ILSAC GF-3, but in addition, ILSAC GF-3 oils must also meet energy-conserving requirements. Similarly, API SM requirements as well as energy-conserving requirements must be passed before an engine oil can be designated as ILSAC GF-4. The appropriate test methods for engine oils must be conducted in accordance with the requirements outlined in the American Chemistry Council (ACC) Product Approval Code of Practice. These requirements include test registration of all tests, use of only calibrated equipment and facilities, and guidelines for acceptable modifications during program development. These requirements were implemented when API SH and ILSAC GF-1 designations for engine oil were adopted in 1993, and the requirements have been continued as new performance categories have evolved.

42.3.2 ILSAC GF-4 and API SM Standard Tests In January 2004, ILSAC issued its latest Minimum Performance Standard for Engine Oils, ILSAC GF-4 [18]. Compared to GF-3 (the previous engine oil category), oils

Copyright 2006 by Taylor & Francis Group, LLC

meeting GF-4 requirements [18] provide improved oxidation resistance, improved high-temperature deposit control, better cam and lifter wear discrimination, improved low-temperature wear protection, and improved lowtemperature used-oil pumpability. ILSAC GF-4 oils have also reduced phosphorus and sulfur contents to provide enhanced emissions system protection and to help vehicles meet the stringent Tier 2 Bin 5 emissions standards as shown in Table 42.2, which require, among other things, that vehicles emit no more than 0.07 g/mi (0.045 g/km) of nitrogen oxides over 120,000 mi (190,000 km) of driving. GF-4 oils also provide improved fuel efficiency for both new and used oils, compared to GF-3 oils. GF-4 oils began to marked during the second half of 2004, and all oils licensed to display the API Certification Mark (Starburst) must meet GF-4 requirements. The companion S category to GF-4 engine oils, designated API SM, was defined by the API Lubricants Committee. The API SM category includes the same performance requirements (except for fuel efficiency) as ILSAC GF4, for those viscosity grades defined by GF-4 (i.e., SAE 0W-20, SAE 5W-20, SAE 5W-30, and SAE 10W-30). For other non-ILSAC viscosity grades, some other differences between API SM and ILSAC PGF-4 requirements exist, as outlined in API 1509, “Engine Oil Licensing and Certification System”, Latest Edition. Descriptions of the standard tests for ILSAC GF-4 and API SM engine oils are as follows: Although the performance limits in many of the engine and bench tests in ILSAC GF-4, as well as the chemical compositional requirements, were modified to achieve the benefits described earlier, there was only one new engine performance test developed for GF-4 (the Sequence IIIG Test as shown in Table 42.3, which replaced the Sequence IIIF Test, ASTM D 6984). The IIIG Test utilizes the same General Motors 3800 Series II engine used in the IIIF Test,

TABLE 42.3 Sequence IIIG Performance Test Standard for Pass or Fail [18] Parameter Viscosity increase Weighted piston deposits Average cam plus lifter wear Stuck rings Hot oil consumption interpretability MRV at EOT

Pass limit 150% 3.5 minimum 60 mm maximum None 4.6 L, maximum 60,000 cP max

but the IIIG Test has different operating conditions and uses retrofitted valve train metallurgy. The measured parameters in the IIIG Test as shown in Table 42.3 include average cam plus lifter wear, end-of-test kinematic viscosity increase, and a composite assessment of piston deposits. An endof-test oil sample from the IIIG Test is also evaluated for its low-temperature engine oil pumpability characteristics (ASTM D 4684). In addition, the test length was increased to 100 h (from 80 h in the IIIF Test), engine load was increased from 200 to 250 N m, and sampling and additions of makeup oil were minimized to increase the severity of the IIIG Test. Oil sump temperature was actually decreased from 155 to 150◦ C in IIIG (a decrease in test severity), because of concerns over abnormal depletion (degradation) of the engine oil’s antioxidant/antiwear agent, ZDP, at temperatures above 150◦ C. The Sequence IIIG Test retains the same alloy-cast-iron lifters used in the IIIF Test, but in the Sequence IIIG Test, the camshaft is phosphated (with a manganese phosphate coating) to minimize scuffing during break-in of the test engines. Thus, the Sequence IIIG Test addresses the issues that were of concern at the time of its inception. As conditions and issues evolve, it can be anticipated that this test (and other test methods) will evolve to meet future needs. The Sequence IVA (i.e., 4A) Test mimics city service and determines whether the engine oil provides sufficient wear protection to an overhead cam and slider followers. The Sequence VIII (i.e., Sequence 8) Test measures the extent of shear of the VI improver. In addition, the Sequence VIII Test determines whether the engine oil provides sufficient protection to copper–lead bearings when using unleaded fuel. The previously available test (L-38) used leaded fuel, and thus the L-38 test is no longer appropriate for vehicles using the current unleaded fuels. The Sequence VG Test (i.e., 5G) addresses some of the issues related to partial replacement for the Sequence VE Test (ASTM D 5302). Sequence VG measures the sludge and deposit control tendency of engine oils under engine conditions that simulate stop-and-go city service in vehicles.

Copyright 2006 by Taylor & Francis Group, LLC

The Sequence VIB (i.e., 6B) Test replaces the Sequence VIA Test (ASTM D 6202) for measuring the fuel-efficient properties of an engine oil. Like its predecessor, the Sequence VIB Test measures the improvement in fuel efficiency of a test oil compared to an ASTM standard reference oil. Unlike its predecessor, however, the Sequence VIB Test not only measures the fuel efficiency of the oil when it is relatively new (after only 16 h of aging in the engine), but also the fuel efficiency after 96 h of aging, which corresponds to about 4000 to 5000 mi (6400 to 8000 km) of vehicle operation. Different levels of fuel efficiency improvement are required, depending upon the SAE viscosity grade of the engine oil (the same groupings of viscosity grade as were defined in the ILSAC GF-2 requirements for the Sequence VIA Test). Sequence VIB fuel efficiency requirements apply only to ILSAC GF-3 and GF-4 oils, not to API SL or SM oils. All engine performance test standards for ILSAC GF-4 engine oils are listed in Table 42.4 [18]. The Ball Rust Test is a bench test that mimics the effects of extreme short-trip winter driving. It replaced a previously used engine dynamometer test, and thereby saves considerable expense, time, and effort in the testing process. In the test, an engine component (ball) is immersed in a fluid that contains engine oil to which the kinds of corrosive chemicals has been added that are generated from incomplete combustion of the fuel when the oil and the engine are very cold (e.g., organic acids and other oxidized compounds). At the end of the test, the extent of rust formation is evaluated electronically. As can be seen, test methods for engine oils can be complex, time consuming to develop, expensive to run, and they need to be revised whenever engine designs have changed (e.g., as a consequence of environmental issues, including modifications to fuels, lubricants, or engine materials). Thus, upgrading of standard tests is an essential and ongoing effort to ensure that new materials, engine design, fuels, and government mandates related to vehicle operation are adequately addressed.

42.4 DIESEL ENGINE OIL PERFORMANCE CATEGORIES AND ASSOCIATED TEST METHODS 42.4.1 Service Effects of Diesel Engines Related to Engine Oil Degradation An overview of service effects on engine oils used in diesel engines includes the following: Under freeway driving conditions, in the absence of hilly terrain, a modern diesel engine operating under a light load will move along the freeway with no (or very little) visible evidence of generation of soot. The rate of engine oil oxidation is influenced primarily by the engine oil volume, oil temperature, engine characteristics, engine speed, and load. Thus, under lightduty freeway conditions, engine oil life will be a maximum

TABLE 42.4 ILSAC GF-4 Engine Test Requirements [18] 1. 1.a

1.f

Engine Test Requirements Engine Rusting: ASTM Ball Rust Test • Average Gray Value Wear and Oil Thickening: ASTM Sequence IIIG Test • Viscosity Increase (kV 40◦ C) • Weighted Piston Deposit Rating • Hot Stuck Piston Rings • Cam plus Lifter Wear Wear, Sludge, and Varnish: ASTM Sequence VG Test • Average Engine Sludge Rating • Rocker Cover Sludge Rating • Average Engine Varnish Rating • Average Piston Skirt Varnish Rating • Oil Screen Clogging, % • Oil Screen Debris, % • Hot Stuck Compression Rings • Cold Stuck Rings • Oil Ring Clogging • Follower Pin Wear, Avg, µm • Ring Wear, Avg, µm Valve train Wear: Sequence IVA • Average cam wear (7 position average), µm Bearing Corrosion: Sequence VIII • Bearing Weight Loss, mg Fuel Efficiency: ASTM Sequence VI-B Test

1.f.1

• SAE 0W-20 and 5W-20 viscosity grades

1.f.2

• SAE 0W-30 and 5W-30 viscosity grades

1.f.3

• SAE 10W-30 and all other viscosity grades not listed above

1.b 1.b.1 1.b.2 1.b.3 1.c 1.c.1 1.c.2 1.c.3 1.c.4 1.c.5 1.c.6 1.c.7 1.c.8 1.c.9 1.c.10 1.c.11 1.d 1.e

for a given engine design, oil sump volume, and engine oil temperature, as was the case for gasoline-fueled vehicles. In contrast, if the same diesel vehicle is heavily loaded and driving up a long, steep incline (such as can be found in mountainous regions) or experiencing stop-andgo city driving with frequent stops followed by heavy accelerations, the rate and extent of engine oil degradation will increase, and soot may form during an acceleration. The harder and hotter an engine works, the faster the engine oil’s antioxidant degrades, the engine oil alkalinity decreases, and the engine oil acidity increases. City driving produces lower vehicle speeds with frequent stops and starts, which generate the potential for both soot formation and an increased rate of engine oil degradation. Thus, two major differences between service with gasoline and service with diesel fuel are the generation of soot in diesel engines and the fact that diesel engines in North America do not normally experience short-trip cold-start driving [14,15].

Copyright 2006 by Taylor & Francis Group, LLC

100 minimum 150% maximum after correction for oil consumption 3.5 minimum None allowed 60 maximum 7.8 minimum 8.0 minimum 8.9 minimum 7.5 minimum 20.0 maximum Rate and report None Rate and report Rate and report Rate and report with statistics annually Rate and report with statistics annually 90 maximum 26 maximum All FEI 1 and FEI 2 values determined relative to ASTM Reference Oil BC 2.3% FEI 1 minimum after 16 h aging 2.0% FEI 2 minimum after 96 h aging 1.8% FEI 1 minimum after 16 h aging 1.5% FEI 2 minimum after 96 h aging 1.1% FEI 1 minimum after 16 h aging 0.8% FEI 2 minimum after 96 h aging

Mandates for the reduction of sulfur in diesel fuel, starting in 2006, should help promote longer engine oil life, since fewer acidic reaction products should be generated from the fuel.

42.4.2 Examples of Test Methods for Diesel Engine Oils Both the physical and chemical properties of diesel engine oil change during use. Standard tests for engine oils used in diesel service focus on those conditions that may produce damage to the engine or the oil, or may cause oil-related engine failure, as was also the case with gasoline fuel. The various active diesel engine oil performance categories include at least two (and typically more than two) engine performance tests that must be conducted to demonstrate compliance with category requirements. Various bench tests are also included. A description of the standard tests for diesel engine oils can be obtained from

such organizations as ASTM or the American Petroleum Institute. Examples of test methods that determine the physical and chemical properties of engine oils used in diesel applications include the following: The volatility of the engine oil should not exceed 15% in the Noack Volatility Test (ASTM D 5800). Shear stability of the engine oil is measured using ASTM D 6278, and the limiting values for shear stability depend on the initial viscosity designation of the engine oil (e.g., a 15W-30 engine oil will be compared to a standard 15W-30 and a 15W-40 engine oil will be compared to a 15W-40 standard oil). The low-temperature pumpability of used diesel engine oil is measured in a minirotary viscometer at −20◦ C, using a test that is a modified version of ASTM D 4684. High-temperature, high-shear characteristics of the engine oil can be determined using ASTM D 4683. The ability of the engine oil to resist forming foam is determined by ASTM D 892. The oil’s capability to control aeration (i.e., ability to allow bubbles in the oil to escape at a sufficiently fast rate) is confirmed with the Engine Oil Aeration Test (EOAT). The extent of engine oil thickening due to the accumulation of soot in the engine oil can be measured by the Mack T-8E test, ASTM D 5967. The engine oil’s capability to inhibit corrosion of bearings is measured by ASTM D 6594, in which metals of interest include copper, tin, and lead. Bench tests that are much simpler than standard engine tests can provide useful insights into the nature of interactions between contaminated engine oil and wear of engine surfaces. For example, bench wear tests have documented the role that diesel soot can play in increasing the wear rate of engine materials [14]. Since vehicle service modifies the properties of engine oil in a variety of ways, bench tests with fresh oil do not necessarily provide useful information about the characteristics of used engine oil. Measurements of the changes in physical and chemical characteristics of diesel engine oil tend to be a reflection of both the nature of the service as well as the characteristics of the engine. Engine tests related to performance of engine oils in diesel service look for stress or failure of the engine or its components, such as extent of protection against wear in both sliding and rolling contacts, the extent to which corrosive wear occurs, and unacceptable changes in oil properties during severe service such as soot loading, acid formation, viscosity increase, etc. Several brief descriptions of standard tests that have been used in currently active API performance categories for diesel engine oils (i.e., API CG-4, CH-4, CI-4, CF, and CF-2) are as follows: The Detroit Diesel 6V92TA test lasts 100 h and measures oil volatility, wear, and protection to the engine. Various 8-h segments are interspersed with 3-h shutdowns. The engine speed and load are specified for the different segments of the test. Scuffing of cylinder liners is noted, and pistons and rings are inspected for wear or other forms

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of damage. Limiting values for various measurements are provided to determine whether the engine oil has exceeded its ability to adequately lubricate and protect the engine. For example, the maximum allowed port plugging in a given cylinder is 5%, and the overall average port plugging should be no more than 2%. Required engine oil analyses include a measurement of wear metals as well as additive metals. If the concentration of additive metals has increased, this provides a direct measure of the amount of oil volatility that has taken place. That is, if a metallic element such as calcium, which is part of the engine oil formulation, has increased in concentration by 5%, that means approximately 5% of the oil’s base stock has evaporated. The Caterpillar 1M-PC Test is conducted using a Caterpillar 1Y73 single cylinder indirect injection engine and measures scuffing of rings, pistons, and cylinder liner, piston deposit formation, and piston ring sticking. The test is part of the requirements for API CF and API CF-2. The Cummins M11 exhaust gas recirculation (EGR) Test is part of the API CI-4 category and measures ring and overhead wear, extent of filter plugging, and sludge formation, as related to exhaust gas recirculation (i.e., EGR). Fifty hour segments of the test are conducted overfueled (i.e., using more fuel than is required during the service conditions of the test) at an engine speed of 1600 rpm and alternated with 50-h segments at 1800 rpm overfueled with retarded timing. The total test duration is 300 h. Engine measurements include ring and overhead wear, filter plugging, sludge formation, weight loss of engine crossheads, and sludge formation on the engine valve covers and in the oil pan. Oil analysis measurements include viscosity, base number and acid number, concentration of additive elements in the engine oil, and accumulation of wear metals in the engine oil. For example, under high-temperature operation, zinc concentration in the engine oil (from ZDP) will increase when the more volatile engine oil hydrocarbons have evaporated. Under severe service conditions, once the engine oil’s additives are no longer effective, concentration of wear metals such as iron will also increase. The Engine Oil Aeration Test uses a 1994 7.3 L V-8 engine. The test is conducted at 215 brake horsepower at 3000 rpm. The amount of air in the engine oil is determined at 1, 5, and 20 h during the test. Wear metals are determined at the start of the test and at 20 h. No more than 10% air is allowed for API CG-4 oils. Additional standard tests measure characteristics such as roller follower wear and the influence of soot in the engine oil on engine wear. The Roller Follower Wear Test (for categories API CG4, CH-4, and CI-4) uses a General Motors 6.5 L, indirect injected diesel engine. The engine speed during the test is 1000 rpm at near-maximum load. The test duration is 50 h, and makeup oil is added at 25 h. Oil gallery and coolant-out temperatures are controlled at 120◦ C. New roller followers are installed at the beginning of each test. At the end of the test, roller followers are removed and the extent of

Particulates (g/HP-hr)

0.60

Diesel Emissions Requirements North America

EGR recirculation Duct

(a)

1988

Intake manifold 0.25 0.10

2002 (NOx + HC)

1998 1994 0.05 EPA Plan 1 2 2.5 3 4 5 for 2007: NOx :0.2 g/hph NOx (g/HP-h) Part. : 0.01 g/hph

N 6

FIGURE 42.5 Emissions requirements for diesel engines

wear is measured. Oil analyses are conducted at 40 and 100◦ C. The alkalinity (total base number) of the engine oil is determined, as are wear metals and additive elements. The maximum allowed wear on the roller follower axle is 11.4 µm for CG-4 oils and 7.6 µm for CH-4 and CI-4 engine oils. Various additional tests for engine oils used in diesel service are also available. The above discussions document most of the test methods currently deemed necessary for ensuring acceptable engine oil performance in diesel engines. Proposed future regulations regarding emissions of nitrogen oxides and particulates (such as soot) as shown in Figure 42.5 for future diesel engines mean that current engines will need to be modified to meet requirements for the near future. The necessary modifications may include catalysts and particulate traps. A very low sulfur concentration in the fuel will also be required. An exhaust gas recirculation system, as shown in Figure 42.6, has the potential to increase the temperature of an engine and its engine oil. Higher engine and engine oil temperatures mean greater susceptibility to increased wear and a faster rate of engine oil degradation. Faster oil degradation has the potential to accelerate the reduction of the corrosion-inhibition capabilities of the engine oil. In addition, engine oils that provide benefits for 2007 year model engines may not necessarily provide the desired benefits for previous engines. Thus, it becomes worthwhile to explore any areas in which uncertainties exist.

42.4.3 A Model for the Rate of Engine Oil Degradation in Diesel Engines To investigate the fundamental mechanisms of engine oil degradation in diesel engines, a number of tests were conducted with a vehicle having a medium-duty diesel engine, covering a full range of service conditions. An extensive amount of computerized measurements were taken, and oil samples were collected and analyzed, including soot generation, remaining antioxidant in the engine oil, oil acidity, and alkalinity, etc. Then, when attempting to generate a

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Exhaust manifold

1991

(b) 15% cooled exhaust gas

Potential corrosion 25-35% More heat to coolant Potential bearing wear

FIGURE 42.6 Lower nitrogen oxide emissions and better volumetric efficiency when using a cooled EGR system (a) Exhaust gas recirculation (b) EGR wear control challenges

mathematical model for the rate of engine oil degradation in diesel engines, it became necessary to include a term for both soot generation and a term for the rate of degradation of the engine oil’s antioxidant, since these two measurements interacted with each other, according to the results of the testing that had been conducted. Thus, to provide the desired statistical correlation, the two terms had to be multiplied together, which strongly confirmed an interaction between the effects of soot generation and engine oil degradation. The results of this testing are described in U.S. Patent 6327900 [15].

42.4.4 Future Concerns of Diesel Exhaust Emissions Ongoing engine-related concerns include such issues as reduction in exhaust emissions, expense and effort required in the development of standard tests for engine oils, creativity needed to envision zero-pollution vehicles of the future, etc. Examples are shown in Figures 42.5 to 42.7. Figure 42.5 illustrates the current diesel engine emission standards that designate the allowed values for nitrogen oxide and particulates emissions up to the year 2007. Limits on particulate emissions are also shown in Figure 42.5. Figure 42.6 describes some of the consequences of EGR. Besides the implementation of the EGR system, diesel particulate filter has been widely used in reducing particulates as shown in Figure 42.7(a). To meet with stringent emission

(a)

pollution, and exploring various alternatives to gasoline and diesel fuel.

Insulation

X

Inlet

Exhaust

42.5 CURRENT ISSUES AND FUTURE TRENDS

Steel Canister

42.5.1 Issues Related to Conservation of Fuel Croos section X-X

Exhaust flow (b) Number of tests to qualify products

16

15 12

12

0 API:

lity

Qua

8

ea

Incr

8 4

Oil sing

5

5

CE

CF-4

2

CD

CG-4

CH-4

CI-4

FIGURE 42.7 Improved engine protection when using diesel particulate filter and EGR in diesel engines with CI-4 lubricants

regulations, the increase in the number of required standard tests for certifying high performance of engine oils in diesel engines was also shown in Figure 42.7(b). In addition, engine protection can be improved when using both EGR and diesel particulate filter along with the CI-4 diesel lubricants. Each additional test represents increased expense to the lubricant manufacturer. In addition to efforts making engine oils more environmentally friendly, many automobile manufacturers have now incorporated devices in their vehicles that indicate the point at which engine oil should be changed. In some cases, sensors of various types are used (e.g., acid, base, or temperature sensors, along with a computer assessment of the point at which a given reading has become excessive). In other cases, a microprocessor determines the rate at which the engine oil has degraded, and a signal is given to the driver to “change oil soon,” and at a slightly later date the driver will be provided with a “change oil now” warning. Such systems can reduce both the chance of harm to the engine, and, for a driver who spends most of the time on the freeway, can greatly extend the point at which the engine oil needs to be changed. Examples presented in this chapter indicate the complexity of simultaneously attempting to reduce energy consumption, reduce friction, prolong the life of the engine oil, minimize wear and corrosion in an engine, identify environmentally friendly power sources, and reduce the amount of polluting substances that enter the environment after lubricant disposal, but at the same time still retain personal mobility. Insight, continuing effort, and creativity are required in these domains. One can assume that efforts will continue to be aimed at enhancing fuel economy, reducing

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In several countries, government regulations mandate improvements in fuel economy. Vehicle weight reduction is one way to address this mandate. If aluminum components are used in an engine or in any automotive wearing surface, it becomes important to identify a design such that aluminum oxide (which can form on an aluminum surface) is not rubbed off and allowed to enter the lubricant, since aluminum oxide is abrasive and can act as a severe polishing agent, which will increase the wear rate. Lubricant additives that are optimum for use with an iron surface do not necessarily provide the same wear and scuffing protection for an aluminum surface. Aluminum engine blocks with cast iron cylinder bores must be designed such that differences in the rate and magnitude of thermal expansion of these metals do not cause unacceptable gaps to open between contacting surfaces.

42.5.2 Effects at the Molecular Level When considering interactions between one material and another, or between materials and their lubricants, conventional lubrication wisdom does not necessarily provide a complete understanding of interactions at the molecular level. Investigators believe that it may be feasible to create a number of beneficial effects if nano-materials can be optimized for specific applications. Desired applications include materials optimized for such attributes as friction reduction, optimum hardness, scuffing resistance, enhanced strength, thermal stability, and so forth.

42.5.3 Insights Gained from Tests with an Alternative Fuel Hydrocarbon fuel supplies from fossil sources are finite. To ensure future mobility capability, various alternatives to hydrocarbon fuels have been tested, such as solar power, batteries, hydrogen, alcohol fuel (such as methanol or ethanol), and “flexible fuels,” which may contain up to 85% alcohol, but which also incorporate enough hydrocarbon (at least 15%) to permit a cold start. Suitable performance has been obtained in most cases. However, each type of alternative fuel may also have its unique disadvantages. In addition, the transition from one fuel to another often requires important modifications to any automotive materials that touch the fuel or its reaction products, in order to avoid incompatibility problems. Thus, utilization of alternatives to hydrocarbon fuel typically requires a significant development effort to ensure appropriate durability of materials.

A number of years ago, at a time of heightened interest in finding a substitute for gasoline, experiments using methanol-containing fuel were carried out by various car companies. The fuel (termed M85) consisted of 85% methanol and 15% unleaded gasoline. City and freeway driving tests were conducted on a chassis dynamometer, so that each vehicle on test experienced exactly the same road and weather conditions as the other test vehicles [16]. A flexible-fuel vehicle that ran on gasoline was also part of the test, so that a quantitative assessment of the effects caused solely by differences in the fuel could be obtained. The findings from that test were as follows: In freeway service there was no difference in the rate of engine oil degradation or engine damage between the methanol fuel and unleaded gasoline. This suggested that, under conditions in which the combustion of the fuel is complete, the nature of the fuel was not a factor in the extent of engine oil degradation. In city service, the engine oil used with gasoline degraded approximately two and a half times faster than oil in the methanol-fueled vehicles that had been tested under identical conditions. That is, methanol was significantly milder to the oil than gasoline during city driving. The reason for this difference in severity was because the molecular weight of methanol is considerably lower than that of gasoline, so that the products of partial combustion of methanol boiled out of the oil and thus were not available to inactivate the engine oil’s additives. The investigators were surprised by this result, since at that time it was assumed that alcohol’s effects on engine oil would be more aggressive than those of gasoline under all types of service conditions. In extremely cold short-trip winter service, methanol was harsher to the oil than was gasoline, since combustion of methanol produces approximately twice as much water per kilometer of service than does gasoline. Toward the end of short-trip testing with methanol fuel, the engines were being lubricated with a mixture that contained less than 50% engine oil and slightly more than 50% contamination (water, fuel, and fuel reaction products). When gasoline fuel entered the engine oil during short-trip winter service, the viscosity of the engine oil decreased. When methanol fuel entered the engine oil, the methanol formed an emulsion, which caused the viscosity of the oil to increase. Even though extreme short-trip driving in a winter climate is not representative of most trips, it is desirable to learn about any potential problems before the vehicles are in the hands of the general public. These results indicate that, when using a nontraditional fuel, an investigator must confirm that engine materials are not endangered. An additional concern that needs to be explored when using alternatives to gasoline is to make sure that engine and seal materials are compatible with the alternative fuel of interest. For example, in studies conducted by exposing polyacrylate, silicone, and nitrile seals to methanol fuel, it

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was found that methanol was able to extract beneficial protective additives out of some seals, so that the susceptible seals might become prone to hardening [17]. To conduct such a seal test, a thin segment of the elastomer of interest is immersed in the desired test fluid (here, M85 fuel) and allowed to remain in contact with the fluid at a temperature of interest for whatever duration the investigator deems important. Analyses can determine whether beneficial additives have been extracted out of the elastomer by the test fuel. In addition, an alternative fuel may enter a seal and soften it. Thus, any seal that had become softened by an alternative fuel would be at risk of accelerated wear or failure. Even though some types of seals had become soft in the short-trip study with methanol fuel, seal failure did not occur. Solubility relationships between engine materials and engine fluids can usually be identified in handbooks or tables incorporating titles such as “solubility parameters” or “cohesion parameters.” The solubility parameters include three numerical terms. One of the terms indicates the extent to which the substance of interest is soluble in hydrocarbons such as gasoline. A second term indicates the extent to which the substance of interest is soluble in mildly polar materials such as a compound that has a chain of several carbon atoms linked to a polar atom such as chlorine at one end of the hydrocarbon chain. A third term indicates the extent to which the molecule of interest is soluble in a hydrogen-bonding fluid such as water. If any engine material interacts adversely with a fuel of interest, either the engine material needs to be replaced or the material needs to be coated or in some way protected. Use of these solubility parameters to determine material compatibility before attempting a vehicle test with an alternative fuel can sometimes allow an investigator to avoid an engine failure. If piston rings have a molybdenum fill (or another kind of potentially removable fill), it is worthwhile to conduct a bench test to determine whether the fuel interacts with the fill material. In the case study cited above, M85 fuel was capable of removing the molybdenum fill in piston rings, which caused the rings to contact the cylinder bore on the sharp edges at the center of the rings. The sharp edges of the rings (where the molybdenum was removed) contacted and abraded the cylinder bore. It is also important to determine that bearings are not damaged in the presence of an alternative fuel. A simple immersion of the material of interest in the alternative fuel, followed by analysis of the elements that have entered the fuel by being extracted from the engine component, provides an assessment of compatibility. In addition, the amount of fuel in an elastomer sample should be measured. If analysis indicates a problem, it becomes prudent to identify an alternative material composition for the component that exhibited the incompatibility. These driving tests with an alternative fuel provided results that were sometimes at odds with conventional

automotive wisdom. Because of this divergence, the investigators were able to gain an enhanced understanding of several mechanisms of oil degradation and their relationship to engine wear and corrosion for both gasoline and alcohol fuels. In addition, these results highlighted the fact that it may be risky to make assumptions about durability of engine materials in both city and short-trip service, when using an alternative fuel, since the alternative fuel may behave differently than hydrocarbons when in contact with engine materials. The kinds of issues related to alternative fuels, as described above, need to be investigated, understood, and resolved before alternative fuels and the engines in which they are used are placed in the public domain. Useful information in this regard can sometimes be gained from bench tests (e.g., wear tests), but unanticipated interactions between the fuel and engine oil may occur under actual operating conditions that may be outside the domain of a simplified or single parameter bench test. In addition, valuable insights regarding fundamental causes of various engine effects may be derived when comparing test results from different kinds of fuels. These tests indicate that, by paying attention to material compatibility and recognizing the needs that are specific to a given fuel, alternatives to gasoline can become highly successful automotive power sources. If at some future date supplies of hydrocarbon fuels begin to dwindle significantly, many major automobile companies already have test results in their archives that will permit them to successfully utilize alternative fuels.

42.5.4 Prolonging the Working Life of Engine Oil A decade or two ago, many North American vehicles’ owners’ manuals indicated that a driver should change engine oil at 5,000 km (3,000 mi) under most driving conditions other than freeway service. 12,000 km (7,500 mi) was a recommended North American oil-change interval for freeway or longer-distance service, but possibly only 10 or 20% of the drivers drove under conditions that met the criteria for the longer oil-change interval. Oil-change intervals for vehicles that were developed to use “synthetic” engine oil were approximately two times longer during freeway or autobahn service than was the case for a normal mineral oil. Even though it was well known that oil quality and service type greatly influenced the rate of engine oil degradation, it has only been within the last two or three decades that automobile manufacturers have begun to provide an in-vehicle warning to the driver that an oil change is needed. Such a warning system is now available on a significant fraction of current-model vehicles. Some of these warning systems include a sensor that may determine whether an engine oil has become excessively acidic or if

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the engine or oil has exceeded a reasonable value for some other parameter such as oil temperature or viscosity. Other systems incorporate a computer model that calculates the rate of engine oil degradation based on measurements that the vehicle manufacturer believes are important. Examples include such values as the temperature of the engine oil and the number of times the oil has been exposed to a combustion event. No matter which technique has been used as part of an oil-change indicator system, the end result is that, in general, the oil-change interval indicated by the warning system often is longer than the values that had previously been listed in an owner’s manual, since the presence of a sensor or a model eliminates much of the uncertainty that a driver might have, regarding the appropriate point at which to change engine oil. It also reduces the probability that a driver may completely neglect to change the engine oil [13,15]. Computer monitoring of all aspects of vehicle operation is likely to continue expanding in the future, and is expected to extend oil drain intervals and prolong the availability of oil supplies.

42.5.5 Minimizing Emissions and Pollutants and Ensuring Backward Compatibility Two important approaches toward minimizing automotive emissions include (1) improving the efficiency of the engine so that fewer pollutants are produced during the combustion process and (2) reducing the amount and type of chemicals in the fuel, engine, and engine oil that can adversely influence the effectiveness of a catalytic converter [18]. A tactic that is useful to improve the efficiency of an engine is to adjust engine parameters on an instantaneous basis during vehicle operation, so that combustion will be optimized immediately, and engine efficiency will be maximized [19]. Another issue of great importance for engine oils is the concept of backward compatibility. Current engine oil formulations must provide adequate protection to older engines for which previous engine oil formulations were designed, otherwise there is potential for generating engine problems and causing customer confusion.

42.5.6 Future Trends and Research Directions Techniques such as solar energy, batteries, and various types of alternative fuels have been developed to power vehicles, but only a few alternatives to hydrocarbon-fueled vehicles have remained available to the public for more than a relatively short interval of time. Hybrid-electric vehicles represent a positive step toward reducing consumption of hydrocarbon fuels, but such vehicles do not fall within the domain of “completely renewable”. Addressing mobility issues, including reliability and utilization of renewable resources (from manufacture, to use, to environmentally acceptable recycling or disposal), will

provide challenges to future generations of lubrication engineers. For example, automotive lubricants in the future may have to differ measurably from those of today to meet the demands of advanced vehicles. The information needed to lubricate hybrid vehicles, fuel cell-powered vehicles, or whatever other type of automobile will be in use in the year 2050 or 2100 will have to be gained experimentally. Automotive engine oils will have to be formulated using base oils and additives, which do not cause deterioration of emission control system components, since it is important to move in the direction of reducing pollution to the extent that it is possible. At the same time, customers are demanding more maintenance-free vehicles, so that fillfor-life lubricant systems will be a preferred development. These desires will require novel approaches to lubricant formulation and revolutionary, as opposed to evolutionary, advances in additive chemistry. Whereas we are currently pursuing low sulfated ash, phosphorus, sulfur (SAPS) oils to enable current and near-term emission requirements to be met, zero SAPS oils will likely be required in the longer term. Innovation in both the lubricant industry and the automotive sector is desirable, such as designing lubricating systems that automatically sense the amount and condition of the lubricant, adjust fluid levels accordingly, replenish additives when necessary, and regenerate the oil by removing contaminants. Such innovations represent significant challenges to industries that have become accustomed to small, stepwise increases in performance over the years.

ACKNOWLEDGMENT The authors thank James Spearot of General Motors Research and Development Center, Robert Olree and Edward Becker of General Motors Powertrain, Thomas Boschert of Afton Chemical Corporation, Larry Smith of Infineum, Ben Weber of Southwest Research Institute, Ewa Bardasz of Lubrizol, and George Schwartz of Electromechanical Associates for providing information relative to the completion of this chapter.

REFERENCES 1. R.I. Taylor, “Improved Fuel Efficiency by Lubricant Design,” Proc. Instn. Mech. Engrs., 214 (Part J.), 1–15, 2000.

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2. H.A. Spikes, “The Behavior of Lubricants in Contact: Current Understanding and Future Possibilities,” Proc. Instn. Mech. Engrs., 208, 3–15, 1994. 3. S.E. Schwartz, S.C. Tung, and M.L. McMillan, “Automotive Lubricants,” Chap. 17, ASTM Manual 37 on Fuels and Lubricants, pp. 465–495, 2003. 4. A. Kapoor et al., “Materials, Coatings, and Industrial Applications,” in Modern Tribology Handbook, Vol. 2, Chap. 32, CRC Press, Automotive Tribol., pp. 1187–1229, 2003. 5. C.M. Taylor, The Internal Combustion Engine in Theory and Practice, Cambridge, MA, The MIT Press, 1985. 6. K.C. Ludema, Friction, Wear, Lubrication — A Textbook in Tribology, CRC Press, Boca Raton, FL, 1996. 7. SAE Engine Oil Viscosity Classification, SAEJ300 Standard, SAE, 2001. 8. S.C. Tung and M.L. McMillan, “Automotive Tribology Overview of Current Advances and Challenges for the Future,” Tribol. Int., 37, 517–536, 2004. 9. S.E. Schwartz and D.J. Smolenski, “Development of an Automatic Engine Oil-Change Indicator System,” SAE International (Society of Automotive Engineers) Paper No. 870403, 1987. 10. S.E. Schwartz, “A Model for the Loss of Oxidative Stability of Engine Oil during Long-Trip Service. Part 1. Theoretical Considerations,” STLE Tribol. Trans., 35, 235–244, 1992. 11. S.E. Schwartz, “A Model for the Loss of Oxidative Stability of Engine Oil during Long-Trip Service. Part 2. Vehicle Measurements,” STLE Tribol. Trans., 35, 237–244, 1992. 12. P.J. Younggren and S.E. Schwartz, “The Effects of Trip Length and Oil Type (Synthetic Versus Mineral Oil) on Engine Damage and Engine-Oil Degradation in a Driving Test of a Vehicle with a 5.7L Engine,” SAE International Paper No. 932838, 1993. 13. D.J. Smolenski and S.E. Schwartz, “Automotive Engine Oil Condition Monitoring,” Lubr. Eng., 50, 716–722, 1994. 14. F.G. Rounds, “Effect of Lubricant Additives on Pro-Wear Characteristics of Synthetic Diesel Soots,” Lubr. Eng., 43, 273–282, 1987. 15. J.E. McDonald et al., “Oil Life Monitor for Diesel Engines,” U.S. Patent 6327900, December 11, 2001. 16. S.E. Schwartz, “An Analysis of Upper-Cylinder Wear with Fuels Containing Methanol,” Lubr. Eng., 42, 292–299, 1986. 17. S.E. Schwartz, “Effects of Methanol, Water, and Engine Oil on Engine Lubrication System Elastomers,” Lubr. Eng., 44, 201–205, 1986. 18. ILSAC GF-4 and Sequence IIIG Performance Test Standard, ILSAC GF-4 Specification, 2004. 19. N. Canter, “Development of a Lean, Green Automobile,” Tribol. Lubr. Technol., 60, 15–16, 2004.

43

Diesel Automotive Trends Ewa A. Bardasz CONTENTS 43.1 Introduction — Historical Perspective 43.2 Diesel Benefits 43.3 Diesel Engines in Europe 43.3.1 Current Perspective 43.3.2 Emissions Legislation 43.3.2.1 Euro 3 Emission Standards: Passenger Cars (2000) 43.3.2.2 Euro 3 Emission Standards: Light Commercial Vehicles (2000) 43.3.2.3 Euro 4 Emission Standards: Passenger Cars (2005) 43.3.2.4 Euro 5 Emission Standards (2008?) 43.3.3 Lubricants for Future Diesel Engines 43.4 Diesel Engines in North America 43.4.1 Historical Perspective 43.4.2 Public Perception 43.4.3 Legislation — Federal and California Standards 43.4.4 Future Perspective 43.5 Diesel Barriers in North America 43.6 Summary References

43.1 INTRODUCTION — HISTORICAL PERSPECTIVE Diesel fuel combustion technology started just over 100 yr ago in Germany. In 1893, Dr Rudolf Diesel succeeded in creating spontaneous ignition by blowing fuel into a chamber containing highly compressed air [1] (Figure 43.1). The diesel engine achieves its high performance and excellent fuel economy by compressing air to much higher pressures (14:1 to 25:1) than in a gasoline-fueled engine, and then injecting a small amount of fuel into the compressed air. In the combustion chamber, the highly atomized fuel evaporates quickly while it is being mixed with this hot surrounding air. At the fuel’s auto-ignition temperature, rapid combustion occurs and it is then followed by rapid energy release. The diesel engine is designed to combust a wide variety of fuels from semisolid slurries (coal or shale derived), to commercial diesel fuel (including biodiesel), through compressed natural gas and hydrogen. Since their development over a 100 yr ago, diesel engines continue to play a vital role in the global economy due to their wide range of attributes, such as safety, higher energy content, excellent efficiency, and outstanding

performance in conjunction with the implementation of various electronic controls. They are also recognized for certain performance characteristics such as excellent torque and durability, which have enabled these engines to become key power makers for heavy-duty applications in the marine, power generation, bus, and heavy-duty trucking industries, etc. Application in the area of personal transportation caught on relatively fast in Europe, but at a much slower rate in North America. However, diesel technology has continued to evolve throughout the years and Table 43.1 provides a comprehensive list of the major technological improvements including both light-duty (passenger car) and heavy-duty (bus, truck) applications.

43.2 DIESEL BENEFITS Why is the diesel engine the number one choice for European car buyers? Table 43.2 lists numerous advantages and disadvantages of owning a vehicle equipped with a diesel 733

Copyright 2006 by Taylor & Francis Group, LLC

FIGURE 43.1 Rudolph Diesel Patent and first diesel engine

TABLE 43.1 Chronology of Diesel-Related Technology Developments [2] Year

Event

1893

Rudolph Diesel’s paper (“the theory and construction of a rational heat engines”), Diesel awarded the patent and built the first compression-ignition engine Alfred Buchi patent for practical turbocharger Buchi’s prototype: first turbocharged diesel engine Robert Bosch developed the first fuel injection system, allowing metering of fuel First turbocharged diesel heavy-duty truck engine First production high-pressure diesel fuel injection equipment (FIE) Rate shaping with FIE, including pilot injection (reduced noise and NOx ) Emission reduction aftertreatment: Diesel oxidation catalysts (DOC), Diesel particulate filters (DPF), Selective catalyst reduction (SCR), NOx traps, NOx catalysts First electronic diesel control (EDC) Computer controlled FIE pioneered by DDC Homogeneous Charge Combustion Ignition (HCCI) and low-temperature regime combustion advances Waste heat utilization: turbocompounding and bulk semiconductor thermoelectrics Beltless engines or more electric trucks Integrated starter, alternator/motor developments Common rail FIE for passenger cars DOE contract for high-efficiency thermoelectric waste heat recovery BMW introduces electric water pump (Series 5)

1905 1915 1927 1957 1980s–Present

1983 1990s Late-1990s to Mid-2000s

1999 2004 2005

engine. The diesel engine’s much higher compression ratio, lean burn operation, and direct injection make it not only more energy efficient, but also creates more torque (i.e., power) than a spark-ignition gasoline engine of the same displacement. In addition, diesel fuel is less flammable and less explosive than gasoline, and also contains up to 30% more energy per gallon of fuel. However, on the negative side, diesel engines tend to be more expensive and produce combustion by-products

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containing high levels of smog-causing chemicals (NOx ) and particulate matter (PM, soot). Therefore, future clean diesel engines will need to be equipped with various types of exhaust gas emission control devices, such as Diesel Oxidation Catalysts (DOC), Particulate filters (DPF), Selective Catalyst Reduction (SCR), NOx traps, and NOx catalysts. In Europe, the popular approaches to reducing particulates include refinements in engine control combined with very clean burning fuels, like a synthetic

TABLE 43.2 Advantages and Disadvantages of Diesel Engines [3,4] Advantages

Disadvantages

Fuel economy Durability High torque Reliability Lower fuel cost Low maintenance costa Low hydrocarbonsa Low COa

Weight Noisea Low speed Low air utilization High engine cost Low exhaust temperatureb High NOx High PM

a regulated. b significant for exhaust aftertreatment and turbocharger efficiency.

have not been able to boost the average mileage that their fleets get, because public demand for more powerful trucks and sport utility vehicles (SUVs) have escalated and actually exceeded the percent of car sales (Figure 43.3) in 2001. However, the steady increase in oil prices may one day make Americans reconsider their choice of buying gas-guzzlers powered by gasoline engines. The most recent data reported by the Department of Energy (DOE) indicates significant fuel economy benefits for North American SUV type engines. (Table 43.3). The Dodge Durango and Dodge Ram are both equipped with the same size diesel powertrains.

43.3 DIESEL ENGINES IN EUROPE 43.3.1 Current Perspective

Co2 Emissions, g/km

280

Gasoline Diesel

240 200 19% 160 120 700

900

1100 1300 Vehicle weight, kg

1500

FIGURE 43.2 Diesel vs. gasoline vehicles: improvements in CO2 emissions [6]

diesel fuel (made via Fischer–Tropsch synthesis from natural gas) or even a biodiesel fuel. DPF or traps are also under consideration and there is much discussion in this area with respect to their need, cost/benefit ratio and type, such as passive or active regeneration schemes, frequency of ash deposits removal, etc. NOx reduction is frequently addressed through the use of NOx adsorbers or SCR utilizing urea or ammonia as a reductant. The fuel-saving potential of diesels engines has been well documented, especially in European powertrains (Figure 43.2). Furthermore, it needs to be stressed that today’s diesel engines get 10 to 30% better fuel economy than those built over ten years ago [5,6]. Primarily this is due to improvements in the higher-pressure fuel injection systems, redesigned turbochargers, and introduction of advanced electronic controls. In North America, although the diesel engine is not popular in the passenger car motor oil (PCMO) market segment, diesel engine technology may enable light trucks to meet a proposed increase in the 2007 Corporate Average Fuel Economy (CAFÉ) requirements, where the limits to 22.2 mpg will be modified from the current level of 20.7 mpg. Over the last decade, American car manufacturers

Copyright 2006 by Taylor & Francis Group, LLC

The modern turbo-charged, high-speed, direct-injection, high-pressure common rail light-duty diesel engines are well established and are becoming increasingly the power train of choice in Europe [7]. Diesel penetration for all of Europe is currently exceeding 40% and in some countries such as Austria the figure is about 70%. Whereas diesels were traditionally selected solely on the fuelsaving potential, the new generation of engines offer fuel economy and refinement as well as increased driving pleasure due to the high torque/power available. This market growth for the diesel engine is even more exceptional when one considers that legislation over the same period has called for a 90% reduction in NOx and PM emissions. A recent report [8] also indicates a rapid upward trend in the sales of diesel cars, despite some reduction in the total number of vehicles sold (Figure 43.4). During 2002, a total of 14,518,000 vehicles were sold, whereas in 2003 only 14,323,000 vehicles were purchased. However, in 2003, diesel sales increased by 6.5% to a total of 6,300,000. This record level growth resulted in an increase of diesel penetration from 35.9% in 2001 to 44% in 2003. Some companies such as Bosch are anticipating this diesel penetration to hit 50% within the next three to four years in Western Europe. Geographically, France has for many years been by far the largest market for diesel passenger cars in Western Europe, followed by Germany, Italy, Spain, United Kingdom, and Belgium. This European drivers’ preference for smaller diesel cars is driven to some degree by economic incentives. Low taxes on diesel fuel make diesel vehicles particularly attractive to the citizens of the European Union. Diesel fuel is also substantially less expensive than gasoline in this region. For example, the current US equivalent price for regular unleaded gasoline in France is $4.78/gallon, $5.01/gallon in Germany, $5.38 in the United Kingdom, and $5.69 in Netherlands, whereas the price of diesel fuel is at least 25% lower.

80 70 % of vehicles sold

Cars 60 54%

50 40 30

Light trucks

20 10 '03

'04/7

'02

'01

99

'00

98

97

96

95

94

93

92

91

90

89

88

87

86

85

84

0

FIGURE 43.3 US passenger car and light truck market [2]

TABLE 43.3 Fuel Consumption Comparison Between Diesel and Spark Ignited Engines [2] City mpg

Highway mpg

Combined mpg

Combined gal/miles

CO2 reduction

Dodge Durango Gasoline Diesel

12 20.3

17 25.0

13.8 22.1 +60% Better

0.072 0.045 37% Reduced

— — 27%

Dodge Ram 1500 Gasoline Diesel

12 19.8

16 24.6

13.5 21.7 +61% Better

0.074 0.046 38% Reduced

— — 28%

16,000,000 2002

14,000,000 Car sales

2003 12,000,000

Hyundai, 2% Toyota, 4% BMW group, 4%

Others, 5%

VW group, 22%

Fiat group, 6% GM group, 7%

10,000,000 8,000,000

PSA group, 18%

DC group, 8%

6,000,000 4,000,000 Total car sales

Diesel car sales

Ford group, 11%

Renault,13%

FIGURE 43.4 Recent trends in vehicle sales in Western Europe

FIGURE 43.5 Share of European diesel car sales, 2003 [5]

Thus, it is not surprising that all major automakers are steadily increasing their diesel to gasoline sales ratio. In particular, French automakers PSA Peugeot Citroen and Renault have now joined their German counterparts, Volkswagen Group and DaimlerChrysler in selling more diesel than gasoline-powered cars in Europe [8].

As shown in Figure 43.5, Volkswagen is currently the top producer of diesel passenger cars in Western Europe with production of nearly 1,500,000 vehicles in 2003, followed by PSA Peugeot Citroen with 1,100,000 vehicles, Renault, Ford, DaimlerChrysler, GM, FIAT, BMW, and the Japanese manufacturers [8,9].

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TABLE 43.4 Euro 3: Emission Standards for Passenger Cars Mass CO (g/km)

Mass HC + NOx (g/km)

Mass HC (g/km)

Mass NOx (g/km)

Mass PM (g/km)

Vehicle class category

G

D

G

D

G

D

G

D

D

M

2.3

0.64

0.20

—

—

0.56

0.15

0.50

0.05

G = gasoline powered; D = diesel. Type approval: January 1, 2000 for vehicles up to 2500 kg maximum mass, January 1, 2001 for vehicles of maximum mass above 2500 kg; All production: January 1, 2001 for vehicles up to 2500 kg maximum mass, January 1, 2002 for vehicles of maximum mass above 2500 kg.

TABLE 43.5 Euro 3: Emission Standards for LCVs

Vehicle class category N1 I N1 II N1 III

Mass CO (g/km)

Mass HC + NOx (g/km)

Mass HC (g/km)

Mass NOx (g/km)

Mass PM (g/km)

Ref. weight rw (kg)

G

D

G

D

G

D

G

D

D

rw ≤ 1305 1305 < rw ≤ 1760 1760 < rw

2.3 4.17 5.22

0.64 0.80 0.95

0.20 0.25 0.29

— — —

— — —

0.56 0.72 0.86

0.15 0.18 0.21

0.50 0.65 0.78

0.05 0.07 0.10

G = gasoline powered; D = diesel. Values in the above table also apply to passenger cars of maximum mass greater than 2500 kg. Type approval: January 1, 2000 for Class I vehicles, January 1, 2001 for Class II and Class III vehicles; All production: January 1, 2001 for Class I vehicles, January 1, 2002 for Class II and Class III vehicles.

43.3.2 Emissions Legislation The European Economic Community (EEC), now the European Union (EU), issued its first directive (Directive 70/220/EEC) detailing the measures to be taken against air pollution by gasses from passenger cars and light commercial vehicles (LCVs) in 1970. All member states of the EEC adopted this directive from 1971, either in replacement or addition to any existing national regulation of vehicle emissions. Although amended considerably since its introduction, Directive 70/220/EEC remains the basis for the current EU passenger car and LCV emissions laws, known as Euro 3, which are currently detailed in directive 98/69/EC. Regulation of the emissions from heavy-duty diesel vehicles and buses was introduced in 1988 (Directive 88/77/EEC). This legislation has also been amended a number of times and the current set of laws, also known as Euro 3, are detailed in Directive 199/96/EC. The legislation for passenger cars, light commercial vehicles, and heavy-duty diesel vehicles has been aligned

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since 1992 into a series of standards known as Euro 1, 2, 3, 4, and 5. Let us concentrate only on the most recent standards, starting with Euro 3. 43.3.2.1 Euro 3 emission standards: passenger cars (2000) The current legislation mandated by Directive 98/69/EC and known as “Euro 3” is shown in Table 43.4. The provisions of this directive started to take effect on January 1, 2000, as those of Directive 94/12/EC (“Euro 2”) were phased out. 43.3.2.2 Euro 3 emission standards: light commercial vehicles (2000) The current legislation is shown in Table 43.5. For LCVs, its provisions were phased-in between January 1, 2000 and

TABLE 43.6 Euro 4: Emission Standards for Passenger Cars Mass CO (g/km) G 1.00

Mass HC + NOx (g/km)

Mass HC (g/km)

Mass NOx (g/km)

Mass PM (g/km)

D

G

D

G

D

G

D

G

D

0.50

0.10

—

—

0.30

0.08

0.25

—

0.025

Type approval: January 1, 2005 for vehicles up to 2500 kg maximum mass, January 1, 2006 for vehicles of above 2500 kg maximum mass. All production: January 1, 2006 for vehicles up to 2500 kg maximum mass, January 1, 2007 for vehicles of above 2500 kg maximum mass.

TABLE 43.7 Emission Standards for LCVs

Vehicle class category N1 I N1 II N1 III

Mass CO (g/km)

Mass HC + NOx (g/km)

Mass HC (g/km)

Mass NOx (g/km)

Mass PM (g/km)

Ref. weight rw (kg)

G

D

G

D

G

D

G

D

D

rw ≤ 1305 1305 < rw ≤ 1760 1760 < rw

1.0 1.81 2.27

0.50 0.63 0.74

0.10 0.13 0.16

— — —

— — —

0.30 0.39 0.46

0.08 0.10 0.11

0.25 0.33 0.39

0.025 0.04 0.06

Values in the above table also apply to passenger cars of maximum mass greater than 2500 kg. Type approval: January 1, 2005 for Class I vehicles, January 1, 2006 for Class II and Class III vehicles; All production: January 1, 2006 for Class I vehicles, January 1, 2007 for Class II and Class III vehicles.

January 1, 2002. Directive 96/69/EC also sets standards of increased severity for introduction in 2005. 43.3.2.3 Euro 4 emission standards: passenger cars (2005) In addition to Euro 3, above, Directive 98/69/EC includes passenger car and LCV exhaust emissions standards for introduction from 2005. These are shown in Tables 43.6 and 43.7. 43.3.2.4 Euro 5 emission standards (2008?) The Euro 5 emissions limits possibly for promulgation in 2008 have not been finalized at the time of writing. The most stringent proposals were set by UBA (the German Federal Environment Agency) at the Diesel Engine Emissions Reduction (DEER) Conference — San Diego, California, August 2002 and are listed in Table 43.8. Although these proposals appear to allow a relaxation in diesel CO levels, the significant intentions are to bring

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diesel NOx and PM levels in line with gasoline engines, effectively forcing the use of DPFs.

43.3.3 Lubricants for Future Diesel Engines Over the last five years there has been a growing pressure for engine lubricants to function over extended oil drain intervals and to provide a measure of fuel economy improvements and to be compatible with various aftertreatment devices that has resulted in the development of new engine lubricant technologies. In order to enable extension in drain interval the engine lubricant must provide increased resistance to thermal and oxidative degradation, lower oil consumption rates, and greater Total Base Number (TBN) retention. To achieve these performance increases, engine lubricant formulations have evolved to use unconventional base oils (API Group III and API Group IV) rather than mineral base oils (API Group I) and new additive technology that is formulated for use in conjunction with these unconventional base oils. The use of unconventional base oils has also led to a move away from higher viscosity grades (20W-50 and

TABLE 43.8 UBA Draft Proposal: Emission Standards for Passenger Cars Mass CO (g/km)

Mass HC (g/km)

Mass NOx (g/km)

Mass PM (g/km)

Vehicle class category

G

D

G

D

G

D

GDI

D

M

1.0

1.0

0.1

0.1

0.08

0.08

.0025

.0025

G = gasoline powered; D = diesel.

15W-40) to lower viscosity grades (OW-30, 5W-30, and 5W-40). In order to assist in the EU’s strategy to reduce greenhouse gas emissions, ACEA made a voluntary commitment to reduce the level of CO2 emissions from vehicles by 25% over the period 1995 to 2008. To achieve this reduction in CO2 , ACEA members have begun to increase the fuel efficiency of their vehicles through introduction of new engine designs and technology, for example, direct injection diesel engines in passenger cars. These changes in engine design have resulted in both an increase in the performance demanded from the engine lubricant in conjunction with an increasing requirement for the engine lubricant to deliver a measure of fuel economy itself. To meet these new requirements there has been an increase in the use of lower viscosity grade engine lubricants (0W-30 and 5W-30 for passenger cars) and an increase in the use of friction modifier technology in conjunction with new additive technology. As EU emissions legislation changes from Euro 3 to Euro 4, it brings further reduction in the levels of carbon monoxide, hydrocarbons, oxide of nitrogen, and PMs of between 20 and 50% depending on the vehicle type. The levels set are intended to force widespread introduction of new aftertreatment systems such as DPFs and SCR. The introduction of these new aftertreatment systems is also creating a demand for new engine lubricant technology. EU legislation defines the maximum permissible emissions of a range of substances. The current legislation that is in force is known as Euro 4, will become mandatory from October 2005 for passenger cars and LCVs and January 2006 for heavy-duty diesel trucks. However, various EU member states are introducing national legislation to encourage the early adoption of the standard during 2004. The move to Euro 4 is fundamentally changing the formulation of engine lubricants, demanding the development of new components that are optimized to deliver the required engine performance, but with less impact on the efficiency of the aftertreatment system. New specifications are beginning to be introduced that restrict the level of sulfated Ash, Phosphorous, and Sulfur currently present in lubricating fluid as a way of minimizing the impact on the

Copyright 2006 by Taylor & Francis Group, LLC

S

S S

S P

P

Zn

RO

OR OR

RO

FIGURE 43.6 Structure of ZDDP

efficiency of the aftertreatment system. Extensive research and development is underway to create these new components that provide the required engine performance as well as meeting the challenge of formulating at lower Sulfated Ash, Phosphorous, and Sulfur. Some vehicle manufacturers are beginning to set limits on the levels of Sulfated Ash, Phosphorous, and Sulfur, which are significantly lower than the levels seen in existing engine lubricants. As Sulfated Ash, Phosphorous, and Sulfur relate to some of the most fundamental building blocks of engine lubricant formulations, reductions in these are resulting in the development of new technology for additives and may restrict the types of base oils used to formulate engine lubricants. Lowering the Sulfated Ash of a lubricant impacts the level of metal-containing detergents that can be used and lowering its overall TBN value. Therefore, in order to neutralize corrosive combustion by-products, novel lubricants have the detergency levels compensated with alternative detergent and dispersant technologies. The key lubricant component that contains phosphorous is zinc dialkyl dithio phosphate (ZDDP) and its structure is shown in Figure 43.6. ZDDP has been used since the 1950s as a very effective antiwear and antioxidation additive. As the levels of phosphorous are reduced to avoid poisoning effects on catalysts, ZDDP will need to be reduced and replaced with alternative phosphorous-free antiwear and antioxidant technology. ZDDP also contains sulfur and whilst the level of sulfur in the engine lubricant will be reduced as the level of ZDDP is reduced, the main contributor to sulfur is the lubricant basestock. API Group I basestocks can contain between 0.2 and 1wt% sulfur. Consequently, in lower sulfur lubricants the mineral basestocks will need to be replaced by sulfur-free basestocks, such as API Group III

40 35 30 25 20 15 10 5 0

Series 1

Not a problem, available 37.4

Somewhat of a problem 20.8

Problem but would still buy 8.2

Serious problem might not 6.5

Serious problem would not 20.6

Don't know 9.2

FIGURE 43.7 Public’s impression of diesel fuel availability [9]

and Group IV. The majority of viscosity modifiers contain mineral basestocks that will also be replaced by sulfur-free basestocks. In other groups of additives, some detergents (sulfonates, phenates) and antioxidants also contain sulfur and these will need to be kept to a minimum and replaced with sulfur-free chemistries. The convergence of trends is resulting in a demand for engine lubricants that deliver an extension of a drain interval and a measure of fuel economy at a lower level of Sulfated Ash, Phosphorous, and Sulfur. This is presenting a challenge for oil formulators as the extended drains and fuel economy are driving higher levels of chemistry and consequently higher levels of Sulfated Ash, Phosphorous, and Sulfur, while emissions trends are driving the levels down for aftertreatment compatibility.

43.4 DIESEL ENGINES IN NORTH AMERICA The situation in the United States is very different. Diesel vehicles in this region currently represent less than 1% (0.4%) of all new car sales, with an additional 2% of the market share, if pick-up trucks are included in the mix.

43.4.1 Historical Perspective Historically, diesel engine technology for the light-duty (passenger car) vehicle market never caught interest in North America. The poor image for this technology was first initiated by the introduction of a diesel-powered Volkswagen Rabbit (1.5-L, 50 hp, 62-lb-ft four cylinder), which was the Golf’s predecessor in 1976 [10]. In addition, an American-made diesel version of the Cadillac was created and introduced in 1979. Unfortunately, these cars

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ran poorly, were unreliable, required frequent service, and tended to emit smelly, black smoke. “This year marks a comeback of the diesel in North America,” said Allen Schaeffer, executive director of the Diesel Technology Forum, a lobby group representing diesel engine makers and others [11]. Unfortunately, this prediction has not yet come to fruition in the United States.

43.4.2 Public Perception In a recent Opinion Research Corporation survey [12], 35% of respondents said diesel fuel availability would be of no concern if they were considering buying a diesel vehicle (Figure 43.7). Another 20.8% considered it somewhat of a problem, but not a big deal, while another 8.2% viewed it as a problem, but not one that would prevent them from buying a diesel. On the other hand, only 27% said it was a serious enough problem that they either might not (7%) or would not (21%) buy a diesel because of it. In summary, almost two thirds of respondents did not consider fuel availability to be a show stopper for purchasing a diesel vehicle. Owners of gasoline vehicles generally still believe that diesel-powered cars are noisy, smelly, and underpowered, relative to gasoline vehicles. In large part, this is due to their unfamiliarity with modern diesel engine technology. For example, when compared with 1998 technology, modern diesel engines have 100% more torque, produce 60% less noise, emit 90% lower emissions, and are 30% more fuel efficient [13]. Thus, modern diesel engines are not noisier than gasoline engines, they do not produce odor, and their acceleration is comparable to that of gasoline-powered vehicles.

100

80

60

40

20

0 Better Equal Worse

Reliability 70 25 5

Power 65 25 10

Acceleration 30 45 25

Fuel economy 95 5 0

Emissions 50 35 15

Price 15 25 60

FIGURE 43.8 Diesel vehicle owners views: diesel vs. gasoline

80 70 60 50 40 30 20 10 0 Better Equal Worse

Reliability 30 40 30

Power 55 30 15

Acceleration 20 45 35

Fuel economy 75 20 5

Emissions 60 20 20

Price 5 20 75

FIGURE 43.9 Gasoline vehicle owners views: diesel vs. gasoline

Surveys of owners of gasoline vehicles and diesel vehicles conducted by J.D. Power and Associates [14] revealed two key insights about the potential market for diesel vehicles. First, diesel vehicles owners have strong, positive perceptions of their vehicles, except for their higher price (Figure 43.8). Secondly, owners of gasoline vehicles have generally positive perceptions of diesel vehicles, but they are still more negative than those perceptions held by of the diesel vehicle owners (Figure 43.9). Diesel owners perceive their vehicles to be much more reliable, powerful, and fuel-efficient than gasoline vehicles, and they see their vehicles as having comparable acceleration performance. More than half, however, consider the price of a diesel to be undesirable. More than half of gasoline vehicle owners believe diesels are more powerful and have cleaner emissions, and about three quarters consider them to be more fuel efficient. At the same time, they rate diesels as being equally reliable, but slower and more expensive. These survey results thus suggest that diesels should

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be potentially acceptable as a mass-market technology in the United States, provided that their price can be held at an acceptable level.

43.4.3 Legislation — Federal and California Standards Diesel-powered vehicles face various challenges for achieving future market success in the United States. A critical stumbling block for increased penetration of the diesel engine in the U.S. market is the Environmental Protection Agency’s two-phase strategy to reduce tailpipe diesel emissions [15]. The first phase adopts engine standards originally drafted in 1997 for all trucks and SUVs larger than 8500 lb. These standards are set to apply to all trucks in 2004 and require a 40% reduction in emissions for all diesel-powered vehicles. The second phase, scheduled to begin in 2007, will require further reduction of NOx emissions for both large and small trucks by 75 to 90% beyond

TABLE 43.9 Tier 2 Emission Standards for all Pollutants (Certification Bins), FTP 75, g/mile 50,000 miles Bin#

NMOG

Temporary bins MDPVd 0.125 10b,c,e,g (0.160) 9b,c,f 0.075 (0.140) Permanent bins 8c 0.100 (0.125) 7 0.075 6 0.075 5 0.075 4 — 3 — 2 — 1 —

120,000 miles

CO

NOx

PM

HCHO

3.4 (4.4) 3.4

0.4 0.2

— (0.018) —

0.015 (0.230) 0.015 (0.180)

3.4

0.14

—

0.015

3.4 3.4 3.4 — — — —

0.11 0.08 0.05 — — — —

— — — — — — —

0.015 0.015 0.015 — — — —

NMOG

CO

NOx a

PM

HCHO

0.280 0.156 (6.4) 0.090

7.3 4.2

0.9 0.6

0.032 0.018

4.2

0.3

0.12 0.08 (0.027) 0.06

0.125 (0.156) 0.090 0.090 0.090 0.070 0.055 0.010 0.000

4.2

0.20

0.02

0.018

4.2 4.2 4.2 2.1 2.1 2.1 0.0

0.15 0.10 0.07 0.04 0.03 0.02 0.00

0.02 0.01 0.01 0.01 0.01 0.01 0.00

0.018 0.018 0.018 0.011 0.011 0.004 0.000

0.018

a average manufacturer fleet NO standard is 0.07 g/miles. b Bin deleted at end of 2006 model year (2008 for HLDTs). x c The higher temporary NMOG, CO, and HCHO values apply only to HLDTs and expire after 2008. d An additional temporary bin restricted to MDPVs, expires after model year 2008. e Optional temporary NMOG standard of 0.195 g/miles (50,000) and 0.280 g/miles (120,000) applies for qualifying LDT4s and MDPVs only. f Optional temporary NMOG standard of 0.100 g/miles (50,000) and 0.130 g/miles (120,000) applies for qualifying LDT2s only. g 50,000 mile standard optional for diesels certified to bin 10.

Phase 1 requirements, and the PM emissions will need to be reduced by an additional 90%. Two set of standards, Tier 1 and Tier 2, have been defined for light-duty vehicles in the Clean Air Act Amendments (CAAA) of 1990 [15,16]. The Tier 1 regulations were fully implemented in 1997. The Tier 2 standards were phased-in in 2004. Tier 1 light-duty standards apply to all new light-duty vehicles (LDVs), such as passenger cars, light-duty trucks, SUVs, minivans, and pick-up trucks. Depending upon the vehicle weight class, diesel-equipped passenger car vehicles can be certified either as a vehicle on a chassis dyno (light duty-FTP 75), or as an engine (heavy duty- US HDDTC). Light-duty emission limits are measured in g/mile whereas heavy-duty emission measurements are in g/bhph. The break point for vehicle class is greater than 8500 lb GVWR. Under Tier 2, the applicability of light-duty emission standards is extended to cars, minivans, light-duty trucks, and SUVs. Since light-duty emission standards are expressed in grams of pollutants per mile, larger engines (such as those used in light trucks or SUVs) will have to utilize more advanced emission control systems than smaller engines in order to meet the required standards (Table 43.9). These same emission limits apply to all engines regardless of the fuel they use. Thus, vehicles

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fueled by gasoline, diesel, or alternative fuels will all be required to meet the same emission standards. The Tier 2 tailpipe standards are structured into eight certification levels, called “certification bins” and an average fleet standard for NOx emissions. Vehicle manufacturers have a choice to certify particular vehicle to any of the eight bins. At the same time, the average NOx emissions of the entire vehicle fleet sold by each manufacturer will have to meet the average NOx standard of 0.05 g/mile. From a light-duty perspective the majority of OEMs are targeting Bin 5 emissions, due to the fact that achievement of this bin matches the corporate average NOx requirement, and hence no penalties would be associated with the sale of diesels. A diesel vehicle’s “full useful life” span has been extended to 120,000 miles. Light-duty emissions legislation is further confounded by differing classes of vehicles. The main effect of the vehicle class is a change in their effective emissions’ life. This leads to a longer life requirement for the heavier vehicles, which will result in the requirement for longer service life expectancy 435,000 miles vs.150,000 miles. The current California emission standards are expressed through the following emissions categories: Tier 1, Transitional Low Emission Vehicles (TLEV),

TABLE 43.10 Tier 1/LEV California Emission Standards for LDVs, FTP 75, g/miles 50,000 miles/5 yr Category

NMOGa

Passenger cars Tier 1 0.25 TLEV 0.125 LEV 0.075 ULEV 0.040 LDT1, LVW < 3750 lbs Tier 1 0.25 TLEV 0.125 LEV 0.075 ULEV 0.040 LDT2, LVW > 3750 lbs Tier 1 0.32 TLEV 0.160 LEV 0.100 ULEV 0.050

100,000 miles/10 yr

CO

NOx

PM

HCHO

NMOGa

3.4 3.4 3.4 1.7

0.4 0.4 0.2 0.2

0.08 — — —

— 0.015 0.015 0.008

0.31 0.156 0.090 0.055

4.2 4.2 4.2 2.1

0.6 0.6 0.3 0.3

— 0.08 0.08 0.04

— 0.018 0.018 0.011

3.4 3.4 3.4 1.7

0.4 0.4 0.2 0.2

0.08 — — —

— 0.015 0.015 0.008

0.31 0.156 0.090 0.055

4.2 4.2 4.2 2.1

0.6 0.6 0.3 0.3

— 0.08 0.08 0.04

— 0.018 0.018 0.011

4.4 4.4 4.4 2.2

0.7 0.7 0.4 0.4

0.08 — — —

— 0.018 0.018 0.009

0.40 0.200 0.130 0.070

5.5 5.5 5.5 2.8

0.97 0.9 0.5 0.5

— 0.10 0.10 0.05

— 0.023 0.023 0.013

CO

NOx

PM

HCHO

a NMHC for all Tier 1 standards.

Abbreviations: LVW — loaded vehicle weight (curb weight + 300 lbs), LDT — light-duty truck, NMOG — nonmethane organic gases, HCHO — formaldehyde.

Low Emission Vehicles (LEV), Ultra Low Emission Vehicles (ULEV), Super Ultra Low Emission Vehicles (SULEV), and Zero Emission Vehicles (ZEV). Table 43.10 and Table 43.11 summarize the Tier 1/LEV standards applicable through year 2003. Future California emission standards LEV II will extend from 2004 to 2010 and are listed in Table 43.12 (passenger cars, light-duty vehicles) and Table 43.13 (medium-duty vehicles).

43.4.4 Future Perspective Diesels can have a future as mainstream power train technologies for light-duty vehicles in the United States. However, in order to do so, diesels will need to meet Tier 2 Bin 5 emissions standards to capture up to 7% of the U.S. light-duty vehicle market by 2008 and 15% by 2010 [17]. Currently diesel vehicles can be sold in only 45 states, with the exception of California, New York, Massachusetts, Connecticut, and Vermont. In addition, California, New York, Massachusetts and Vermont have stricter emission regulations than federally mandated guidelines. In 2003 only one vehicle manufacturer, Volkswagen, offered diesel passenger cars to the U.S. market. This situation will change in the near future as diesel passenger cars are offered by Daimler Chrysler, Toyota, and

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Volkswagen. Currently, all of these vehicles are undergoing testing to show that they can meet the 2007 emission standards [18,19]. Aftertreatment technologies needed to meet new emission regulations are also available. Current testing is being conducted using a low sulfur diesel fuel that is used in Europe, but is not yet widely available in the United States. This fuel will be made available starting in August of 2006. The sulfur content of this fuel is 15 parts per million (ppm), which is down from the current level of 300 ppm. The emissions systems of these prototype aftertreatment technologies must also show that they can maintain the emissions levels for 10 yr or 150,000 miles before they can be certified. A comparison of the newest diesel vs. gasoline counterparts’ vehicles introduced in the United States is shown in Table 43.14. The cost comparison between 2007 diesel technology and current U.S. gasoline technology is not encouraging [21,22]. Diesel engine production might even increase to several thousands dollars higher if aftertreatment systems need to be incorporated. However, if fuel consumption reduction becomes mandated for the gasoline engine, because of future CAFÉ or CO2 standard’s the equation may become a little more palatable. The addition of variable valve train (VVT), gasoline direct injection (GDI), and turbocharging technology to gasoline engines to improve fuel consumption will increase the base engine cost considerably. Perhaps in its ultimate form, with fully flexible

TABLE 43.11 California Emission Standards for Medium-Duty Vehicles, FTP 75, g/miles 50,000 miles/5 yr Category

NMOGa

MDV1, 0–3,750 lbs Tier 1 0.25 LEV 0.125 ULEV 0.075 MDV2, 3,751–5,750 lbs Tier 1 0.32 LEV 0.160 ULEV 0.100 SULEV 0.050 MDV3, 5,751–8,500 lbs Tier 1 0.39 LEV 0.195 ULEV 0.117 SULEV 0.059 MDV4, 8,501–10,000 lbs Tier 1 0.46 LEV 0.230 ULEV 0.138 SULEV 0.069 MDV5, 10,001–14,000 lbs Tier 1 0.60 LEV 0.300 ULEV 0.180 SULEV 0.090

120,000 miles/11 yr

CO

NOx

PM

HCHO

NMOGa

3.4 3.4 1.7

0.4 0.4 0.2

— — —

— 0.015 0.008

0.36 0.180 0.107

5.0 5.0 2.5

0.55 0.6 0.3

0.08 0.08 0.04

— 0.022 0.012

4.4 4.4 4.4 2.2

0.7 0.4 0.4 0.2

— — — —

— 0.018 0.009 0.004

0.46 0.230 0.143 0.072

6.4 6.4 6.4 3.2

0.98 0.6 0.6 0.3

0.10 0.10 0.05 0.05

— 0.027 0.013 0.006

5.0 5.0 5.0 2.5

1.1 0.6 0.6 0.3

— — — —

— 0.022 0.011 0.006

0.56 0.280 0.167 0.084

7.3 7.3 7.3 3.7

1.53 0.9 0.9 0.45

0.12 0.12 0.06 0.06

— 0.032 0.016 0.008

5.5 5.5 5.5 2.8

1.3 0.7 0.7 0.35

— — — —

0.028 0.028 0.014 0.007

0.66 0.330 0.197 0.100

8.1 8.1 8.1 4.1

1.81 1.0 1.0 0.5

0.12 0.12 0.06 0.06

— 0.040 0.021 0.010

7.0 7.0 7.0 3.5

2.0 1.0 1.0 0.5

— — — —

— 0.036 0.018 0.009

0.86 0.430 0.257 0.130

10.3 10.3 10.3 5.2

2.77 1.5 1.5 0.7

0.12 0.12 0.06 0.06

— 0.052 0.026 0.013

CO

NOx

PM

HCHO

a NMHC for all Tier 1 standards.

Abbreviations: MDV — medium-duty vehicle (the maximum GVWR from 8,500 to 14,000 lbs). The MDV category is divided into five classes, MDV1 . . . MDV5, based on vehicle test weight. The definition of “test weight” in California is identical to the Federal ALVW, NMOG — nonmethane organic gases, HCHO — formaldehyde.

TABLE 43.12 California LEV II Emission Standards, Passenger Cars, and LDVs < 8500 lbs, g/miles 50,000 miles/5 yr Category LEV ULEV SULEV

120,000 miles/11 yr

NMOG

CO

NOx

PM

HCHO

NMOG

CO

NOx

PM

HCHO

0.075 0.040 —

3.4 1.7 —

0.05 0.05 —

— — —

0.015 0.008 —

0.090 0.055 0.010

4.2 2.1 1.0

0.07 0.07 0.02

0.01 0.01 0.01

0.018 0.011 0.004

valve train system, the gasoline engine may be able to compete with a light-duty diesel engine, but the cost and complexity are significant and the diesel then becomes an attractive option. The challenge is reducing the cost of the powertrain to a reasonable level that will meet the needs of the customer. The majority of the diesel engines in the United States are currently fitted into pick-up trucks where the market

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penetration is expected to be nearly 6%. In these applications, consumers clearly appreciate the added utility of diesel and are willing to pay premiums of up to $5000 for the diesel-powered vehicles. Hence, in order to fully exploit the potential for diesels in the United States, particularly for the very significant SUV and light truck market, the diesel engines are likely to be custom designs for the United States, rather than

transplanted European technology. These custom designs will allow the cost gap to be narrowed between gasoline and diesel while still offering all the benefits of drivability, reduced fuel consumption, low noise, etc. For smaller passenger car applications where four cylinder engines are likely to dominate, applying European engines into U.S. vehicles is considered more feasible. The additional volume for this class of engine will also reduce the cost of the European engines.

43.5 DIESEL BARRIERS IN NORTH AMERICA There are several reasons for the currently limited diesel growth in the United States. They are as follows: 1. Emission legislation. Future Tier 2 and US 2007/2010 emissions legislation presents a technical challenge to diesel engines, which will require the use of advanced combustion and durable aftertreatment systems. While this required technology will be available in the required timeframe, cost issues will remain. 2. Product cost. The level of technology required to meet the future emissions legislation may result in engines that are significantly more expensive to produce than gasoline engines of today. The major cost contributors of the advanced diesel engine are the fuel injection, turbo machinery, exhaust gas recirculation (EGR), and aftertreatment systems.

TABLE 43.13 California LEV II Emission Standards, Medium-Duty Vehicles, Durability 120,000 miles, g/miles Weight (GVWR), lbs. 8,500–10,000

10,001–14,000

3. Diesel perception. Many consumers still regard diesel as “dirty, noisy, smelly, and slow” even though advanced diesel technologies available today are very different from engines in the early 1980s. The main challenge is to educate the consumer and to convince them to test drive a modern diesel-powered vehicle. The diesel engine’s performance benefits would rapidly win over these skeptics. 4. Fuel economy pressure. There is currently little pressure to improve fuel consumption of passenger car motor vehicles. CAFÉ legislation has been relatively ineffective at promoting a reduction in fuel consumption; in fact, average fuel consumption has actually increased in the United States which is in large contrast to the trend in many European countries [23,24]. The cost of fuel is a large driver for the reduction of fuel consumption in Europe where typical fuel costs can be three times that of the United States. All car companies are also committed to the voluntary reduction of CO2 emissions under the ACEA agreement. The situation in the United States may change in the near future due to the government’s stated desire to reduce the U.S. dependency on foreign oil. This may either promote more interest in the reduction of foreign oil consumption or a change to alternative fuels such as hydrogen. 5. Fuel infrastructure. Only around 30% of filling stations in the United States currently offer diesel fuel [25]. Many of these locations are truck stops, where the pumps are located in nonuser friendly locations. However, the investment required to increase the availability is probably relatively low and this process could be completed quickly, should diesel market penetration increase significantly.

43.6 SUMMARY Category

NMOG

CO

NOx

PM

HCHO

0.195 0.143 0.100 0.230 0.167 0.117

6.4 6.4 3.2 7.3 7.3 3.7

0.2 0.2 0.1 0.4 0.4 0.2

0.12 0.06 0.06 0.12 0.06 0.06

0.032 0.016 0.008 0.040 0.021 0.010

LEV ULEV SULEV LEV ULEV SULEV

The biggest factors determining the fate of diesel engines in the U.S. passenger car motor vehicle market is not technical, but more a blend of economic, regulatory, and social. Currently, there is no significant driver to reduce fuel consumption and until this situation changes, there is correspondingly little consumer pressure to change this.

TABLE 43.14 Side-by-side Comparison — Gasoline /Diesel N. American vehicles [20]

Fuel delivery system EPA (mpg) city/hwy Horsepower/torque (lbs. ft.) Price ($)

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VW Golf GL, 1.9L (gasoline)

VW Golf GLTDI, 1.9L (diesel)

VW Touareg, 5L, V8 (gasoline)

VW Touareg 5L, V-10 TDI (diesel)

Mercedes-Benz E 320 (gasoline)

Mercedes-Benz E 320 CDI (diesel)

24/31 115/122 16,355

Unit injectors 38/46 100/177 17,775

14/18 310/302 43,255

Unit injectors 17/23 310/553 58,415

19/27 221/232 48,795

Common rail 27/37 201/369 49,795

The desire by the U.S. government to reduce foreign oil dependency may stimulate a change in this direction, but legislation will probably be required. Whether taxation on fuel is a politically acceptable means to drive down fuel consumption is still an unanswered question. Technology is available today to achieve light-duty Tier 2 Bin 5 emissions levels in vehicles up to at least 6000 lb of inertia test weight. The approach required to meet these levels includes increased engine flexibility via the use of advanced air and fuel systems. These systems allow the optimization of low engine out NOx and soot, as well as the flexibility to control aftertreatment devices. From an aftertreatment DPFs will be mandatory for all engine classes. DPF application is now commonplace in Europe and the technology is relatively mature. NOx aftertreatment is much less mature and will still present many technical challenges. For passenger cars under ∼4000 lbs the achievement of Tier 2 Bin 5 appears feasible without the need for NOx aftertreatment. This approach is possible due to the reduced emissions of the lighter vehicles and the fact that alternative combustion can be applied for a wider range of the emission relevant speeds and loads. For heavier vehicles NOx aftertreatment is required and the development of suitable systems is still underway. However, it is likely that suitable NOx aftertreatment devices will be available in the Tier 2 timeframe. Future DPF and NOx aftertreatment devices are likely to be integrated into “4 way catalysts” such as the Toyota DPNR system, which may have the added benefit of reducing overall costs and improved performance. From a larger displacement passenger car motor vehicle perspective, the 2007 emissions levels appear achievable without the need for NOx aftertreatment, but with the application of a DPF. These engines will have a similar cylinder displacement to the light-duty engines, although displacements in the 5.5 to 6.5 L range are expected. However the 2010 regulations are a different matter and at present these will require significant developments in both NOx aftertreatment and combustion technology to ensure emissions compliance. The consumers’ perception of diesel engine technology is also an issue, since perceptions are often not based on facts, but rather feelings. Modern diesels are fuel efficient, clean, quiet, and offer the end user improved drivability over the gasoline engine. Once end users experience these engines, their negative perceptions should quickly be eliminated. The major challenge will be in getting consumers to test drive the vehicles in the first place. This then represents a marketing, rather than a technical challenge, which must be addressed by the auto manufacturers. Lastly, and very significantly, the increased cost of the diesel engine must be considered. Unless the OEMs can convince the end user of the added benefits of diesel technology, it will be difficult to charge a premium for these vehicles and even more difficult to retain a profit from their

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sale. As aftertreatment system development and production volumes increase, the overall costs to implement these systems should be reduced. In addition, fuel system costs, which account for around 40% of the total diesel cost, should also be reduced as competitive forces and production volumes increase. If value is placed on fuel economy, either via fuel taxation or future legislation, then gasoline production costs will climb based on the added technology needed to achieve fuel savings. Under this scenario it is possible that the cost associated with diesel technology will become acceptable. In addition to the fuel economy benefit, it is important that the performance aspect be highlighted, which would then allow further justification for any price premiums. With the amount of miles driven by the average U.S. consumer rising, coupled with a decrease in vehicle fuel economy, the usage of fossil fuels is at an all time high in North America. A number of alternative propulsion systems are being evaluated by vehicle OEMs, Government bodies, and research establishments. Fuel cells, Hybrid Electric Vehicles, and Hydrogen IC engines are all being presented as possible solutions to help reduce U.S. dependency on oil. In Europe, where reductions in fuel consumption have been accepted voluntarily by the car companies, the diesel engine is currently the main solution to the fuel equation. In the United States, one or more major drivers will be needed to pull (or push) this technology through, in order for it to become more readily adopted for use in passenger car motor vehicles.

REFERENCES 1. Diesel, R. German Patent No. 67207,“Working Method and Design for Combustion Engines,” February 23, 1893. 2. 10th Diesel Engine Emissions Reduction Conference, August 2004. 3. Heywood, J.B. Internal Combustion Engine Fundamentals McGraw-Hill, New York, 1988. 4. Holt, D.J. “The Diesel Engine,” Society of Automotive Engineers, Warrendale, PA, 2004. 5. Greene, D.L. and Liu, J.T. “Automotive Fuel Economy and Consumers’ Surplus,” Transportation Research A, 22A, 203–218, 1998. 6. Burke, A. and Abeles, E. “Feasible CAFE Standard Increases Using Emerging Diesel and Hybrid-Electric Technologies for Light-Duty Vehicles in the United States,” UCD-ITSRR-04-9, Institute of Transportation Studies, University of California at Davis, Davis, CA, April, 2004. 7. Birch, S. “Ricardo’s Diesel Future,” Automotive Engineering International, 111, 78–79, 2003. 8. Ricardo, “Diesel Passenger Car & Light Commercial Vehicle Markets in Western Europe,” 2004. 9. Brown, W. “Europe’s diesel vehicle market is healthy, growing,” The Washington Post, 2 April 2004. 10. Hart R. “Two more for the road; VW’s take on ‘alternative vehicles increases,’ ” Auto Week, 28 June 2004.

11. Incantalupo, T. Stepping on the diesel with gasoline prices soaring, the economy of this alternative fuel sparks renewed interest among carmakers and the public. Newsday, 30 May 2004. 12. Caravan, “ORC Study #713228” conducted for National Renewable Energy Laboratory by Opinion Research Corporation, Princeton, NJ, May 27, 2004. 13. Duleep, K.G. “Diesel Technology and Product Plan Review,” presentation to the U.S. Department of Energy, Office of Policy, prepared by Energy and Environmental Analysis, Inc., Arlington, Virginia, April 2004. 14. McManus, W. “Hybrids and Clean Diesels: If You Build It, Will They Come?” J.D. Power and Associates, Detroit, Michigan, 2004. 15. www.epa.gov 16. www.dieselnet.com 17. Davis, S.C. and Diegel, S.W. Transportation Energy Data Book, ed 23, ORNL-6970, Oak Ridge National Laboratory, Oak Ridge, Tennessee, October 2003. 18. White, J.B. A New Crop of Diesel Cars Hits the Market Amid Rising Gas Prices, Dow Jones & Co., 27 May 2004.

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19. Volkswagen, Mercedes, Jeep Roll Out Fuel-Efficient Models. Wall Street Journal, 27 May 2004. 20. Kranz, R. Gasoline price spike will boost sales of diesel cars, VW predicts; Passat, Touareg join diesel lineup. Automotive News, 26. June 2004 21. Energy Information Administration. Annual Energy Outlook 2004,DOE/EIA-0383-04, U.S. Department of Energy, Washington, DC, January 2004. 22. Diesel Car Perspectives to 2009, May 17, 2003, www.eagleaid.com/dsltext.htm. 23. Kleit, A.N. “The Effect of Annual Changes in Automobile Fuel Economy Standards,” Journal of Regulatory Economics, 2, 515–572, 1990. 24. Motor News — National Research Council (NRC). Effectiveness and Impact of Corporate Average Fuel Economy (CAFÉ) Standards, National Academy Press, Washington, DC, 2002. 25. Hadder, G.R. “High Quality Diesel Fuel Production, Logistics and Consumer Costs,” Engineering Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, May 2004.

44

Automotive Trends in Asia R. David Whitby CONTENTS 44.1 Introduction 44.2 Trends in the Automotive Industry in Asia 44.2.1 A Manufacturers and Competitive Forces 44.2.1.1 Production of Vehicles in Asia 44.2.1.2 Exports and Imports 44.2.1.3 Asian Vehicle Manufacturers’ Trends and Prospects 44.2.1.4 Suppliers of Components to the Asian Automotive Industry 44.2.2 Asian Automotive Design and Engineering 44.2.3 Asian Automotive Vehicle Regulations 44.2.3.1 Safety 44.2.3.2 Environment 44.3 Current Status of Automotive Fluids in Asia 44.3.1 Engine Oils 44.3.1.1 Gasoline Engine Oils 44.3.1.2 Diesel Engine Oils 44.3.1.3 Two-Stroke Engine Oils 44.3.2 Transmission and Gear Oils 44.3.3 Other Automotive Oils 44.4 Development of Markets for Synthetic Automotive Fluids in Asia

44.1 INTRODUCTION Asia is the most populous region on earth, with more than half the world’s people. Asia contains the world’s two most populated countries, China and India, together with Japan, Indonesia, Bangladesh, and Pakistan, all of which have large populations. During most of the 20th century, the population of Asia grew at a faster rate than the world average. Asia was the fastest growing region in the world for more than 10 yr prior to the 1997/1998 financial crisis, with an average annual growth rate of over 7%, compared with around 2% in Europe, 2.5% in the United States, 1.5% in Japan, and a global average of close to 2.5%. Many of the countries that experienced low or even negative growth rates in 1998 and 1999 have now recovered, despite countries such as Hong Kong, Singapore, and Thailand facing further problems in 2001. However, average growth rates in 2002 and 2003 were slightly lower than before, at around 5% per year. Asian countries have experienced widely differing economic circumstances over the last ten years. Japan began to

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emerge in mid-2003 from one of the longest recessionary periods in its history. The growth in GDP that began in the second quarter resulted from stronger exports, mainly to the United States, China, South Korea, and Taiwan. Export growth countered the ongoing deflation in the Japanese economy, although some inflation is now starting to reappear. The growth in Japanese GDP is forecast to be 17% in 2005 and the same in 2006. Meanwhile, the economies of China and India have continued to steam ahead. China was finally admitted to the World Trade Organization (WTO) in September 2001, and a new era in Chinese politics and economics began in 2003 with the transfer of the post of state president from Jiang Zemin to Hu Jintao. Chinese GDP growth was 7.9% in 2002 and 9.2% in 2003, following a period of similar annual increases from 1996 onwards. Many analysts believe that this inexorable rate of growth is unsustainable and that the rate will have to slow to around 5 or 6% per year. This is the kind of growth that India has experienced from 1997 onwards, with increases in GDP of 4.8% in 2002 and 6.1% in 2003. Singapore and South Korea struggled a little in 2003, with increases in GDP of 0.8 and 2.5%

respectively, although 2004 was better, with increases of 8.2 and 4.6% respectively. Malaysia, Indonesia, Thailand, and Taiwan experienced respectable increases in GDP of between 3.8 and 7.1% per year during 2003 and 2004. Forecast increase in GDP for 2005 are between 4.4 and 5.1%. Three billion people live in Asia. Half of these people are under 25 yr of age. By 2010, it has been forecast that there could be 120 million cars on the road in Asia, compared with around 62 million in 1996. There could be almost 180 million motorcycles, of which China will account for 40%. Asia is now the largest market for lubricants, having consumed around 11.15 million mt in 2003 and overtaken North America. The growth rate for lubricant demand in the region as a whole has averaged about 3.8% per year for the last 20 yr. In 1997, when consumption was 9.22 million tonnes, Asia looked set to start challenging North America as the largest total market for lubricants, but this changed in 1998 as the economic turmoil in the region spread. Since then, growth in both GDP and lubricants consumption has resumed, although at slightly lower rates. Both China and Japan are not only large consumers of lubricants in their own rights, but are also large producers. Japan is a net exporter of lubricants, mainly to other countries in Asia. China is a large importer of lubricants, as are many of the other countries in the region, with the exception of Singapore, which produces more than it consumes. South Korea is also an exporter of lubricants.

44.2 TRENDS IN THE AUTOMOTIVE INDUSTRY IN ASIA 44.2.1 A Manufacturers and Competitive Forces 44.2.1.1 Production of vehicles in Asia Asia is not only the world’s third largest market for cars after Western Europe and North America, but is also the second largest market for trucks and buses after North America. This is shown by the data in Table 44.1. Asia accounts for 16.1% of the world’s cars and 20.5% of its trucks and buses. As indicated in the Introduction (Section 44.1) to this chapter, the market for cars in Asia has been the fastest growing in the world over the last ten years and is set to keep growing, as more people acquire the finance to purchase a car. From 1998 to 2002, the number of cars in Asia increased by 18%, compared with increases of 11% in Western Europe and 10% in North America. The number of trucks and buses in Asia increased by 14% in the same period, slightly lower than in Western Europe (15%) and slightly higher than in North America (12%). The largest markets for cars in Asia are in Japan, China, Taiwan, and India, as shown by the numbers of vehicles in

Copyright 2006 by Taylor & Francis Group, LLC

TABLE 44.1 World Vehicle Population, 1998 to 2002 Number of vehicles in use (million) Region

1998

1999

2000

2001

2002

Cars W Europe C and E Europe N America C and S America Middle East Asia Africa Oceania

169.0 49.2 147.9 26.4 12.6 74.1 10.1 9.8

171.4 51.4 148.4 26.4 12.6 78.8 10.2 10.1

176.9 54.6 150.1 26.9 13.0 81.6 10.2 10.3

181.9 55.7 156.7 27.1 13.2 84.9 10.4 10.4

187.0 56.8 163.1 27.7 13.7 87.7 10.5 10.5

Total cars

499.1

509.3

523.5

540.3

557.0

23.1 15.2 86.6 8.6 5.2 36.6 4.4 2.7

23.4 15.1 86.7 8.7 5.3 39.8 4.4 2.8

24.0 14.3 90.6 8.8 5.4 40.5 4.4 2.9

25.3 14.9 94.1 8.9 5.5 41.2 4.5 2.9

26.6 15.6 97.5 9.0 5.6 41.8 4.6 3.0

Trucks and buses W Europe C and E Europe N America C and S America Middle East Asia Africa Oceania Total trucks and buses

182.42

186.2

190.9

197.3

203.6

All vehicles W Europe C and E Europe N America C and S America Middle East Asia Africa Oceania

192.1 64.4 234.5 35.1 17.76 110.63 14.5 12.6

194.8 66.5 235.1 35.1 17.9 118.6 14.6 12.9

200.9 68.9 240.6 35.7 18.4 122.2 14.6 13.1

207.2 70.6 250.8 35.9 18.7 126.1 14.9 13.3

213.7 72.4 260.6 36.7 19.2 129.6 15.0 13.5

Total vehicles

681.5

695.4

714.4

737.6

760.6

Source: Pathmaster Marketing, from various industry sources.

the main countries in the region, in Table 44.2. The largest markets for trucks and buses are in Japan, China, Thailand, and South Korea. There are more cars, trucks, and buses in Japan than in the rest of the Asian countries put together. The fastest growing vehicle market in Asia, by far, is China. The number of vehicles in other countries in the region has been increasing steadily over the last 20 yr. Passenger cars still account for less than half the Chinese market for vehicles, which is still dominated by trucks and buses. The total number of cars that was sold in China in 2002 was 1.2 million. VW/SAIC had a 23% share, VW/FAW had an 18% share, and GM/SAIC had a 9% share, as did Toyota/TAIC. The Chinese vehicle market has maintained its pace of growth in 2003. In the nine months to September, total vehicle sales were 1,454,522, up 69% for the same period in 2002.

TABLE 44.2 Asia-Pacific Vehicle Population, 1998 to 2002 Number of vehicles in use (million) 1998

2000

2002

Total

Cars

Trucks and buses

Total

Cars

Trucks and buses

Total

Country

Cars

Trucks and buses

Asia China India Indonesia Japan S Korea Malaysia Pakistan Philippines Singapore Taiwan Thailand Others

3.33 4.70 2.73 45.86 6.69 2.30 0.80 0.67 0.37 4.20 1.51 0.91

5.34 2.79 1.74 18.62 2.52 0.61 0.37 0.26 0.13 0.70 3.10 0.36

8.67 7.49 4.48 64.49 9.22 2.91 1.17 0.93 0.50 4.90 4.60 1.27

3.49 4.79 2.85 51.16 7.58 2.57 0.88 0.76 0.40 4.67 1.53 0.94

5.98 2.98 2.28 20.56 2.95 0.65 0.36 0.28 0.14 0.83 3.14 0.38

9.47 7.77 5.13 71.72 10.53 3.22 1.24 1.04 0.54 5.50 4.67 1.32

7.12 4.98 2.95 53.45 8.61 2.65 0.97 0.81 0.41 4.70 2.19 0.96

6.36 3.12 2.32 19.87 3.65 0.71 0.40 0.31 0.15 0.89 3.66 0.40

13.48 8.10 5.27 73.32 12.26 3.36 1.37 1.12 0.56 5.59 5.85 1.36

Total Asia

74.08

36.55

110.63

81.62

40.53

122.15

89.80

41.83

131.63

Pacific Australia New Zealand Others

7.79 1.79 0.27

2.07 0.46 0.20

9.86 2.25 0.47

8.26 1.78 0.24

2.21 0.45 0.20

10.47 2.23 0.44

8.45 1.84 0.24

2.30 0.48 0.20

10.75 2.32 0.44

Total Pacific

9.84

2.73

12.57

10.27

2.86

13.13

10.53

2.98

13.51

83.92

39.28

123.20

91.89

43.39

135.28

100.33

44.81

145.14

Total

Source: Pathmaster Marketing, from various industry sources.

Production of cars in Asia from 1998 to 2002 is shown in Table 44.3. Production of trucks and buses is shown in Table 44.4. Data for the Pacific region (Australia and New Zealand) has been included for completeness, since some of the cars manufactured in Japan, South Korea, Malaysia, and most recently China are being sold in the Pacific region. As with vehicle sales, China has experienced the fastest growth in the production of vehicles, particularly cars, over the last decade. In 1995, 290,000 cars and 1.05 million trucks and buses were manufactured in China. By 2002, these figures had increased to 1.10 million and 2.16 million respectively, a total of 3.26 million vehicles. China’s vehicle production was 4.4 million in 2003, with cars reaching 1.9 million, 70% more than in 2002. By 2004, China became the world’s third largest market for vehicles, after the United States and Japan. Some planners expect the Chinese vehicle market to overtake that of United States, to become the world’s biggest in 2025. China has a draft policy for automotive manufacturing, which aims to ensure that local car manufacturers, with their own intellectual property rights (IPR), account for more than half of domestic sales by 2010. Some

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TABLE 44.3 Production of Passenger Cars in Asia-Pacific, 1998 to 2002 Number of vehicles manufactured (thousand) Country

1998

1999

2000

2001

2002

Australia China India Indonesia Japan Malaysia New Zealand South Korea Taiwan Thailand

298.2 507.1 498.4 8.4 8,055.8 132.7 8.2 1,625.1 292.1 32.0

322.6 565.4 646.6 5.9 8,100.1 241.4 — 2,361.7 246.0 72.7

329.7 604.7 645.6 37.3 8,363.5 275.3 — 2,602.0 263.0 97.1

304.1 703.5 676.2 32.2 8,117.6 329.0 — 2,471.4 195.1 288.9

328.6 1,090.8 706.1 23.8 8,618.7 350.5 — 2,651.3 231.5 270.1

11,458.0

12,562.4

13,218.2

13,118.0

14,271.4

Total

Source: Pathmaster Marketing, from various industry sources.

international manufacturers have expressed concern about this, but others are not so worried. Independent Chinese vehicle companies currently have a share of less than 10% of the market for cars, but dominate sales of trucks and buses.

and smaller numbers of Malaysian and Indian cars being exported to North America and Europe. The scale of the imports and exports is highlighted in Table 44.5. All developing countries in Asia import cars, trucks, and buses, many from Japan and South Korea. A comparatively small number of luxury cars are imported into Japan, Hong Kong, Singapore, Taiwan, and China from Germany, France, the United Kingdom, and Sweden. Japan exported 4.01 million cars and 686,000 trucks in 2002. The United States imported 1.82 million cars and another 233,000 were sent to Canada. Another major destination for Japanese cars was Australia, which imported 268,000 in 2002. Germany imported 193,000 Japanese cars and China imported 78,000 in 2002. South Korea exported 1.41 million cars and 94,000 trucks in 2002. As with Japan, the majority of cars were sent to the United States (629,000) and Canada (98,000), with 76,000 being exported to Italy and 58,000 to the United Kingdom. Conversely, comparatively few cars and almost no trucks and buses are imported into Asia from other regions. These cars that are imported tend to be limited to higher priced luxury cars such as Mercedes-Benz, BMW, Jaguar, and Rolls Royce. There is also a large regional internal trade in cars, trucks, and buses within Asia, with the principal producing countries, particularly Japan, South Korea, and Malaysia exporting relatively small numbers of vehicles of all types to the nonproducing countries of Singapore, Hong Kong, the Philippines, Vietnam, Myanmar, and Cambodia. How the current patterns of exports and regional trade will change in the next few years remains unclear at the time

44.2.1.2 Exports and imports Asia is the world’s largest regional exporter of cars, with huge numbers of Japanese and South Korean cars

TABLE 44.4 Production of Vans, Trucks, and Buses in Asia-Pacific, 1998 to 2002 Number of vehicles manufactured (thousand) Country

1998

1999

2000

2001

2002

Australia China India Indonesia Japan Malaysia New Zealand South Korea Taiwan Thailand

22.0 1120.7 129.3 49.7 1994.0 — — 329.4 109.6 125.5

23.5 1259.3 169.8 117.3 1795.3 — — 481.4 104.3 132.1

25.0 1464.4 155.8 308.1 1781.4 14.9 — 513.0 109.6 242.0

33.4 1630.9 148.7 296.0 1659.6 20.0 — 474.9 76.6 244.1

34.3 2160.4 186.2 275.1 1639.0 14.4 — 496.3 102.2 253.6

Total

3880.2

4083.0

4614.2

4584.2

5161.5

Source: Pathmaster Marketing, from various industry sources.

TABLE 44.5 Import and Export of Vehicles in Asia, 2000 and 2001 Number of vehicles (thousand) Imports

Exports Trucks and buses

Cars

Trucks and buses

Cars

Country

2000

2001

2000

2001

2000

2001

2000

2001

Australia China Hong Kong India Indonesia Japan Malaysia Singapore South Korea Taiwan Thailand

294.7 101.7 25.9 35.8 25.6 283.6 26.2 53.9 2.0 45.1 111.4

302.3 116.2 26.8 27.9 28.1 287.1 28.4 54.6 2.2 48.2 74.5

112.7 46.7 17.9 0.6 52.3 14.5 21.2 28.9 0.4 22.4 —

88.9 49.1 18.8 0.5 64.2 15.2 23.8 29.2 0.5 24.4 —

169.2 217.4 — 103.2 — 3737.0 252.5 — 1437.2 ND 94.0

204.7 185.6 — 131.8 — 3568.7 299.8 — 1397.0 ND 278.9

— 913.1 — 25.5 81.4 697.5 — — 265.3 ND 242.0

— 949.2 — 27.6 79.2 597.4 — — 251.2 ND 214.1

ND = No data. Source: Pathmaster Marketing, from various industry sources.

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of writing. Many Japanese and Korean car makers have been building production plants in Europe and North America during the last decade in an effort to minimize trade disputes and exchange rate fluctuations. Although these facilities were intended to reduce exports from Asia, recent economic turmoil could prompt a possible return to exporting as a way of countering reduced domestic demand and maximizing foreign currency inflows. 44.2.1.3 Asian vehicle manufacturers’ trends and prospects The alliance between Nissan and Renault, which was agreed in March 1999 has given both companies the benefits of a merger without having to create a merged company. When Nissan experienced severe financial difficulties in 1998, Renault agreed to take a 36.8% shareholding as part of a deal to inject the much needed interim cash. The alliance was further strengthened in March 2002, when Nissan acquired a 15% stake in Renault and Renault increased its shareholding to 44.4%. At the same time, the French government reduced its shareholding in Renault to 25.9%. The deal in 1999 suited both companies, as the cash boost enabled Nissan to continue manufacturing cars and Renault expanded from its mainly European market into Asia. Nissan has had three successive years of increasing profits and has almost eliminated its debt. The company achieved a dramatic turnaround between mid2000 and mid-2003, turning a net debt of ¥2100 billion ($17.4 billion), which threatened the company with bankruptcy, into a net cash position of ¥8 billion ($7 million). (The company’s operating profit in 2002 was ¥737 billion.) The recovery has been due to a combination of severe cost reductions, new and improved models, and increases in market share in all Nissan’s main markets. Renault and Nissan each own 50% of Renault– Nissan BV, a Dutch based strategic management company, which in turn owns Renault–Nissan Purchasing Organisation (RNPO) and Renault–Nissan Information Services (RNIS). Most of the purchasing of components for both companies is supposed to go through RNPO, as in Europe and South America, although the regional Nissan teams in Japan and North America are still very independent. Nissan and Renault have also adopted a common quality system for suppliers. RNPO was created in 2001 to maximize the benefits of developing common platforms and sharing engineering costs for new vehicle development. The new Nissan Almera and Renault Megane/Scenic models share around 60% of their components. Toyota has now become an established competitor to Mercedes-Benz, BMW, and Jaguar in the luxury segment of the car market through the company’s Lexus brand, which was introduced first in North America and has proved to be a strong seller. Lexus cars have been available

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in Western Europe for a number of years and Toyota is planning to introduce the brand into the Japanese market in 2005. The aim is to make Lexus a truly global, top-class brand. At the same time, Toyota has recognized that the Japanese car market has changed in recent years, with economic stagnation leading to a shift in market demand toward smaller cars. The company has acknowledged that it cannot rely on bigger production volumes or higher market shares to increase revenues. As a result, Toyota is planning to build “a balanced, global operating platform that enhances our ability to respond quickly and flexibly to changes in the business climate.” This means increasing product development and production capabilities outside Japan. The company has established a joint venture with PSA Peugeot Citroen to manufacture cars in Central and Eastern Europe. A new plant is being built in the Czech Republic, to manufacture up to 300,000 small cars per year for sale throughout Europe, and production is scheduled to start towards the end of 2005. In April 2002, Toyota’s plant in Poland began producing manual transmissions (MTs) for Toyota vehicles manufactured in the United Kingdom and France. Toward the end of 2004, the Polish plant will begin producing gasoline engines for use in the new Czech small car plant. Another plant in Poland will begin producing up to 150,000 diesel engines a year, to be used in cars manufactured in the United Kingdom and France. Mitsubishi and Mazda are two of Japan’s car manufacturers that have struggled in recent years. Mitsubishi Motors (MMC) had DaimlerChrysler as a 37% shareholder until April 2004, when the German company decided that it could not provide any further financial aid to its loss making Japanese affiliate. DaimlerChrysler had been expected to buy several billion euros worth of new shares in addition to the e2.5 billion ($2.95 billion) it had already spent since 1999 to build up the 37% stake. However, the company decided it could not justify further investments in MMC. Following the decision, the Mitsubishi Group (which includes financial, engineering, and shipbuilding companies) indicated it would support MMC’s bail-out plan. DaimlerChrysler is now seeking to sell its shareholding in MMC, although industry analysts have cautioned that, even if MMC survives, it faces severe operational problems as a result of its damaged reputation, ageing models, slow sales, and lack of profitability. As part of the refinancing plans, MMC was forced early in 2004 to sell its 42% shareholding in truck maker Mitsubishi Fuso, which has a 20% share of the southeast Asian market for commercial vehicles. The shareholding was bought by DaimlerChrysler. MMC’s problems in the U.S. market may be due to its “zero, zero, zero” marketing campaign in 2003. A new range of smaller cars, targeted at young, low income buyers, were sold on the basis of no deposit, no interest, and

no repayments for the first year. The company accumulated large losses when a number of the young buyers failed to start making payments after the first year; a problem that DaimlerChrysler might have prevented in a market that Chrysler should have understood. In other markets, including Japan, MMC was forced in 2000 to recall 2.5 million faulty vehicles and admit that it had covered up customer complaints during the previous three decades. Mazda, which is 33% owned by Ford, raised profits by a little in 2003 after several tough years both in Japan and North America. However, industry analysts believe that it is likely to be mid-2005 before new Mazda models will have had a chance to revive the company’s position. Intense competition means that Mazda has lost money in Japan. Although Mazda’s rotary engines and sporty cars sell well in Europe, the company struggles in North America, mainly due to a lack of global integration. To compete on both cost and marketing, car manufacturers have to build a range of models using ever fewer basic chassis and engine designs. Coordinating design, manufacturing, and marketing profitably is a huge challenge. While Mazda’s excellent product development and manufacturing skills have helped Ford, the bigger company has provided little help with marketing to its affiliate in North America. The main theme of vehicle manufacturing in Asia during the last five years has been China. It appears likely that China will continue to be the dominant theme of vehicle manufacturing in Asia for the next five years, since China looks set to overtake Japan as the world’s second largest market for cars. Toyota agreed to establish a joint venture with First Automotive Works (FAW), China’s largest car manufacturer in August 2002 to make up to 400,000 cars per year by 2010. As part of the deal, FAW will acquire a controlling stake in Tainjin Automotive Xiali, Toyota’s other Chinese partner, which manufactures buses. The joint venture started making small cars in FAW’s Tianjin plant in mid-2003, with an annual production target of 100,000 vehicles. Manufacture of between 10,000 and 20,000 sports utility vehicles (SUVs) also started in 2003, at FAW’s Changchun plant. The joint venture plans to start making medium and luxury cars in 2005, with an annual target of 50,000. Toyota’s overall aim is to achieve a 10% share of the Chinese market by around 2010. One difficulty for the new joint venture could be FAW’s relationship with its other partner in China, Volkswagen (VW). Because Toyota and VW will be in direct competition, FAW’s loyalty to one or both of them could be tested at some time in the next few years. Another complication is VW’s partnership with SIAC. Indigenous Chinese vehicle manufacturers are allowed to form joint ventures with more than one foreign partner. China’s top four main car manufacturers (First Automotive Works [FAW], Shanghai Automotive Industry Corp [SAIC], Guangzhou Auto, and Dongfeng Automobile)

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have links with at least two international partners. This is a potential source of friction in an industry in which technology and design innovations are guarded closely. To try to counteract this potential conflict, international car manufacturers are starting to form alliances with more than one Chinese partner. Toyota has also initiated discussions with Guangzhou Auto. In mid-2003, Honda and Dongfeng agreed to make a small off-road vehicle, even though Honda already had a joint venture with Guangzhou. Dongfeng also has a joint venture with Nissan and FAW has a technical agreement with Mazda. Volkswagen, the market leader in China with about 35% share of the car market in 2003, is also planning to double its capacity to 1.36 million vehicles per year by 2007, to try to protect its dominant position. The cost of the e6 billion project will be financed entirely from the revenues of the current Chinese plants. VW has a joint venture with FAW in Changchun, northeast China. Production of FAW vehicles will be increased to 33,000 per year, as will the production of VW Golf, Bora, and Jetta models and Audi A4 and A6 models. At the same time, Shanghai Volkswagen Automotive, will increase capacity to 700,000 cars by 2007. VW sold around 600,000 cars in China in 2003, an increase of 17% over 2002. However, VW has experienced a rapid decline in its share of the Chinese car market in recent years. Its share of the car market was over 50% in 2002, declined to around 35% in 2003 and is forecast to be below 20% in 2004. While VW has continued to sell about the same number of cars per year, other manufacturers, particularly Toyota/FAW, GM/SAIC, Nissan, Hyundai, and BMW, have all begun to sell cars in even bigger numbers. VW has responded by announcing the plans to expand capacity still further, by shifting some office jobs from Germany to China, to be closer to customers, and by increasing the local sourcing of components, including engines and transmissions, to cut costs. The company is also considering making Skoda branded cars in China, as recent sales of the VW Polo have been only 65% of planned sales. The Skoda Octavia is a low-cost large family car, while the VW Polo is a complex small car. BMW signed an agreement in March 2003 to establish its first car manufacturing plant in China, as a 50:50 joint venture with Brilliance China Automotive Holdings. The plant started to manufacture 3-series cars towards the end of 2003 and 5-series cars towards the end of 2004. BMW hope to use the joint venture to increase its sales of cars in Asia from about 80,000 in 2003 to more than 150,000 in 2008. Already, China is BMW’s second largest market for 7-series cars, after the United States. Total sales of BMWs in China in 2003 were 15,260 cars. General Motors (GM) announced a further expansion of vehicle manufacturing in China in November 2003, including an extension of its main Shanghai plant and

plans to make and import cars bearing the Cadillac brand. The company is planning to expand capacity from just above 500,000 vehicles per year to about 760,000 by 2006. GM is increasing capacity to meet the demand in the fastest growing car market and to prepare for the fully fledged entry into the market over the next two years of Toyota and Nissan. The company’s Shanghai plant, a joint venture with state-owned SAIC, which went to three-shift production in August 2003, will increase capacity from 200,000 to 300,000 units by the end of 2005. GM’s joint venture in Guangxi making light trucks will increase capacity by 150,000 units to 336,000 by 2006. GM’s joint ventures, which manufacture cars, SUVs, and small trucks, have a market share in China of about 9.1%, having sold a total of 386,710 vehicles in China in 2003. MG Rover, the United Kingdom’s last indigenous volume manufacturer of cars, has been considering a strategic collaboration with SAIC for most of 2004. MG Rover has been struggling to sell cars since it was sold by BMW to a management buy-in team in 2000, so it has had difficulties in developing new models. It is expected that nearly all of MG Rover’s new models would be developed and manufactured under the new venture, which is currently in the final stages of being approved by the Chinese government. The new models would be built in both the United Kingdom and China and the deal is reported to allow SAIC access to MG Rover’s dealer networks in Europe and other countries. This would fit with the Chinese government’s goal of creating a fully integrated car industry capable of exporting to the world’s highly competitive markets. Ford announced at the end of 2003 that it is considering building Land Rovers or Volvos in China, to participate in the growing market for luxury vehicles. The company is currently studying which brand would be most suited to the Chinese market, although the study is unlikely to be completed before the end of 2004 and Ford might still decide not to proceed. Ford believes that Land Rover could benefit from its off-road image, as China still has a lot of rough roads. Theft or abuse of IPR, a problem that is endemic in many Chinese industries, is another source of tension for international vehicle manufacturers. In 2001, VW (which has a partnership with SAIC) found that the main car produced by Chery (a Chinese company part-owned by SAIC) was a direct copy of the Jetta and used original VW parts. The dispute was resolved amicably through discussions, to VW’s satisfaction, even though it had not been possible for VW to sue Chery, because of the difficulty of proving culpability. However, Toyota sued Geely in August 2003, alleging that it had copied Toyota’s logo on its Merrie saloon. Later in 2003, GM began an investigation of Chery’s QQ small car, claiming that its design was copied from the Chevrolet Spark, which is a rebranded version of Daewoo’s Matiz small car. (GM now owns Daewoo.) Although GM has

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found solid evidence that Chery copied the design, it faces formidable legal and political obstacles if it decides to try to sue Chery. GM has taken the case to the Chinese government to seek a resolution. Now that China has joined the WTO, all manufacturers expect copyright and trademark laws to be strengthened and counterfeiting to be reduced. In November 2003, VW announced that it will make cars in China for sale in Australia and aiming to make the company’s manufacturing costs low enough to use China as an export base. The initial production run for export to Australia will consist of right-hand drive versions of VW’s Polo model and will be tiny, at about 600 cars in 2004. The symbolic significance is not in the number of cars but in the hoped for political benefits from the export decision. VW made the announcement to reporters brought to one of its Shanghai joint venture plants from around the country to ensure it received wide publicity domestically. Exporting cars from China had not been considered much until recently because costs and quality levels were not internationally competitive and the local market was growing so quickly. VW now believes that some of its Chinese point venture plants, which initially had higher costs than even the company’s German plants, could now manufacture competitively enough to sell in Australia. The Polo sells for Rmb120,000 ($14,498) in China and will be priced similarly in Australia, where import tariff for cars have reduced significantly over the last decade. Of the 43,000 “vehicles” exported from China in 2002, half were leisure vehicles, such as golf carts and snowmobiles. With so many companies either having increased or planning to increase vehicle production in China, some analysts are concerned that international manufacturers could be creating a large over-capacity problem, similar to those that exist now in Europe and the United States. Consensus estimates suggest that total manufacturing capacity for cars, with both local and international companies, could be 7 million by 2008, compared with a projected demand of 5.7 million cars. Although car manufacturers appear to be aware of the potential dangers, similar to the recent problems in Brazil, the severe competition between the global car makers combined with the apparently huge longterm potential of the Chinese market is likely to ensure that the industry marches inexorably toward a short- to medium-term over-capacity position. To complicate the situation even further, the Chinese government is currently trying to engineer a slowdown in the overheated economy. Such a slowdown will affect demand for all goods and services, including cars, vans, trucks, and buses. Indeed, there was a significant reduction in the rate of increase of car production in the first eight months of 2004 compared with 2003. The Chinese car market grew at annualized rates of between 40 and 80% during 2002 and 2003, but is now growing at rates of around 20%. The government put new restrictions on

loans to buy cars, which require consumers to post substantial collateral in order to qualify for a loan, thereby cooling demand. Another factor contributing to slowing demand is the expectation of further price cuts, as some car manufacturers have reduced prices in a battle for market share. Volvo Trucks has signed a joint venture agreement with China National Heavy Truck Corporation (CNHTC) in July 2003 to manufacture Volvo FL, FM9, and FM12 models. The new company, called Jinan Huawo Truck Company, started production toward the end of 2003 in CNHTC’s plant in Jinan. The initial capacity of 2,000 trucks per year is planned to be raised to 10,000 per year by 2010. Later, in March 2004, Volvo Trucks announced plans for a $200 million joint venture with CNHTC and FAW to manufacture engines for trucks, buses, construction equipments, and boats. At the same time, Caterpillar disclosed that it is considering taking stakes in several state-owned Chinese construction equipment companies that could eventually lead to full acquisitions. This is part of a plan to raise Caterpillar’s sales in China from $500 million in 2003 to more than $2 billion by 2010. It has been reported that the Chinese government would like to see some consolidation among national construction equipment manufacturers, because many are inefficient and unprofitable. Caterpillar already has four Chinese joint ventures in excavators, tractors, castings, and small diesel engines, in addition to two wholly owned projects in compactors and generator sets. The South Korean market for passenger cars expanded by 16% in 2002, as a result of government tax incentives for car purchases that continued until September 2002, to boost the indigenous production of vehicles following the financial problems with Daewoo. In October 2002, GM finally acquired a 42% stake in Daewoo, the bankrupt South Korean vehicle manufacturer, after two years of difficult negotiations with the company, union representatives, and the South Korean government. Before Daewoo’s bankruptcy, it had a 26% share of car sales in South Korea, but by the time of the creation of GM Daewoo, this share had fallen to less than 10%. Shortly after the launch of GM Daewoo, it was announced that GM would begin selling Daewoo cars in China and that SAIC would take a 10% stake in GM Daewoo. In 2000, Renault acquired Samsung Motors in South Korea. Initially, the new company, called Renault Samsung Motors, manufactured only one model of car, the “SM5,” which gained popularity steadily. The car was derived from the Nissan “Maxima.” In September 2002, the “SM3” that was developed using the Renault–Nissan alliance was introduced. The second car shares the platform of Nissan’s “Bluebird Sylphy.” In addition to its problems with MMC, DaimlerChrysler has also had problems with its South Korean affiliate Hyundai, in which it had a 10% shareholding, which

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it decided to sell in May 2004. Following four years of rapid growth and the improving quality and popularity of Hyundai cars throughout the world, the South Korean company decided it no longer needed the support of the European–U.S. partner. The two companies found that they were increasingly competing with each other, particularly in the United States. When DaimlerChrysler purchased the stake in 2000, Hyundai was going through an upheaval resulting from the break-up of its parent Hyundai Group following the Asian financial crisis of 1997/1998. Since then, exports have grown to 61% of sales in 2003 and net profits have quadrupled. The growth is due, in part, to heavy investment in overseas production, including a plant in the United States, coupled with improvements in quality, design, and branding. At the same time, DaimlerChrysler’s activities in Asia, particularly in China, began to clash with Hyundai’s plans. The two companies’ strategic objectives began to diverge, so the rationale behind the alliance became more tenuous. However, both companies have agreed to continue working together on a project-by-project basis, including the three-way passenger car alliance with MMC. Tata Motors, India’s second largest vehicle manufacturer and a subsidiary of India’s second largest private sector group of companies, returned to profitability in 2003 by reducing its workforce from 26,500 to 21,500 and by intensely focusing on operational cost-efficiency. The company is also negotiating to purchase a Daewoo truck manufacturing plant in South Korea, for US$118 million. Tata is investigating building or acquiring vehicle manufacturing facilities in China, Russia, and South Africa. In addition, the company is exporting its Indica small car to the United Kingdom, to be sold throughout Europe by MG Rover. However, in September 2004, Tata announced that it could consider ending its agreement with MG Rover if current talks fail to resolve differences over the price and positioning of the Indica/CityRover car. MG Rover wants to reduce the price of the car or add free equipment to make it more competitive and has proposed that Tata should bear some of the cost. Sales of the CityRover have been so poor that Tata suspended exports earlier in 2004, when it had planned to sell 100,000 cars over five years. Superficial changes for the U.K. market, such as trim, make the cars unsuitable for sale in India. Tata’s suspicions about MG Rover’s intentions have been heightened by the U.K. company’s ambitions in China. Tata has indicated that it is committed to expansion in South Africa, as a stepping-stone to other markets in Southern Africa. Tata already builds buses and light trucks in Johannesburg with Imperial Holdings, would like to sell its Indigo and Indica cars there too, and is bidding to become one of the main suppliers of minibus taxis. Nissan announced in July 2004 that it plans to invest $246 million in its car plant in Thailand over the next

five years, to increase production of an expanded product range, some of which will be exported to Australia, South America, and Africa. Thailand is Nissan’s third largest manufacturing base in Asia, after Japan and China, and the company views Thailand as an important expanding market and a base to export to other countries in the ASEAN (Association of South East Asian Nations) free trade area. While the current capacity of the plant is 130,000 units a year, production was only slightly over 40,000 in 2003. Nissan plans to expand the capacity to 200,000 units a year by 2008 and to double the workforce. Surprisingly, Thailand is the world’s second largest manufacturer of pick-up trucks, after the United States. Toyota, Isuzu, Mitsubishi, Nissan, Mazda, Ford, and GM all manufacture pick-up trucks in Thailand; total production in 2003 was 470,000 vehicles, most of which were exported. Ford has announced plans to spend $500 million to expand production of both pick-ups and cars, Toyota is spending $750 million to increase capacity and establish a research and development center and Mitsubishi, although struggling elsewhere, is spending $525 million to expand operations in Thailand. Thailand has attracted this investment as a result of innovative government industrial policy and very supportive excise-tax incentives. The government set excise tax on pick-ups at just 3%, compared with as much as 50% for cars, many years ago, thereby guaranteeing sales of pick-ups. The growing local production has become a natural base for exports throughout Asia and more recently for most other regions. The country hopes to be exporting more than 800,000 vehicles by 2011. BMW, for example, is now making 3-, 5-, and 7- series cars in its Thai plant and is exporting them throughout Asia. During 2004, MG Rover and Proton, Malaysia’s national car manufacturer, briefly explored a collaboration on “a number of projects,” although only an intention to collaborate has been signed so far. Proton has investigated a number of strategic partnerships with several unnamed foreign car manufacturers, to help it face the stiffer competition that will arise when Malaysia is forced to abolish import tariffs on cars made in other ASEAN countries, primarily Thailand. Malaysia had agreed to phase out the tariffs in 2005, but decided to extend the deadline until 2008 and impose excise taxes on cars entering the country. The delay is seen as giving Proton more time to adjust to a more competitive market, as Toyota, Nissan, Honda, and Ford all have car plants in Thailand, so are expected to begin exporting to Malaysia as soon as the import tariffs are abolished. The Malaysian market accounts for more than half the 1 million new cars sold each year in southeast Asia and Proton’s share has already fallen from 49% in 2002 to 39% in 2003, as foreign competitors reduced prices and local consumers delayed purchases in the expectation of the abolition of tariffs in 2005.

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Although Proton’s cars can be up to 45% cheaper than similar sized Toyota or Honda cars, they have the worst record on quality and reliability in Malaysia. Proton’s latest model, the “Gen.2,” has a waiting list of more than five months because of a shortage of engine components and has a roof that is too low to allow adults in the rear seats to sit comfortably. Proton has begun a drive to become more competitive, by building an automated car plant, cutting staff, and planning to introduce new models based on technology from Lotus, the company’s U.K. subsidiary. Even so, the company is reported to be seeking to sell a 20% shareholding to a foreign partner, although this could be difficult to achieve. 44.2.1.4 Suppliers of components to the Asian automotive industry Companies that supply components to vehicle manufacturers in Asia include both large multinationals and small local suppliers. Those companies that supply to the major international vehicle manufacturers, such as GM, Ford, VW, Renault, Toyota, Nissan, BMW, and DaimlerChrysler, are required to meet the same specifications and quality levels as in Western Europe and North America. Denso, the world’s third largest components supplier that was originally part of Toyota, now has manufacturing plants in 28 countries outside Japan, including most countries in Asia, the United States, Mexico, Brazil, Argentina, most countries in Western Europe, Hungary, Poland, the Czech Republic, Saudi Arabia, and Turkey. The company supplies engine cooling systems, air-conditioning systems, diesel common rail systems, alternators, starter motors, spark plugs, anti-lock brakes, power steering, and navigation systems. Denso plans to build 15 million vehicle air-conditioning units by 2005, which represents 30% of the world market, as a result of expansion in Europe. Aisin Seiki manufactures a wide range of automotive components, from brakes, chassis, body parts, powertrains to information technology. Drivetrain systems, including automatic transmissions (ATs), accounts for almost half of the company’s sales. Aisin Seiki developed powered sliding door systems for vehicles, in conjunction with Toyota. The company purchased Nissan’s 23% shareholding in Exedy Corporation, the specialist manufacturer of clutches and torque converters. Calsonic Kansei, created by the merger of Calsonic and Kansei in 1999, is Nissan’s largest supplier of components, mainly engine cooling and air-conditioning systems. Although Nissan accounts for 60% of the company’s sales, other buyers of components include Honda, Isuzu, Mazda, Mitsubishi, GM, Ford, and DaimlerChrysler. Stanley Electric focuses on automotive lighting, including headlamp and rear combination lamp assemblies, as well as automotive electronic components.

GKN, the U.K. automotive and aerospace company, has been working to expand in Japan for many years. As the world’s largest supplier of constant velocity joints, GKN acquired plants owned by Nissan and formed a joint venture with a Toyota Subsidiary. GKN has also had a long-term alliance with Tochigi Fuji Sangyo (TFS), the world leader in torque management systems, devices that give a smoother and safer ride. GKN acquired a 33% stake in TFS in 2002 and acquired the remaining shares in May 2004. Other major suppliers to vehicle manufacturers in Japan, China, and other countries in Asia include Borg-Warner (gearboxes, transmissions), Bosch (spark plugs, injectors, electronics, wipers), Delphi (brakes, clutches, indicators, controls, sensors, injectors), Federal-Mogul (camshafts, seals, gaskets), Getrag (gearboxes, transmissions), INA (bearings), Magneti Marelli (electronics, injectors), Mahle (pistons), Siemens (motors, relays, sensors, controls), SKF (bearings), Valeo (brakes, clutches, switches), and ZF (gearboxes, transmissions). Many of these companies supply a wide range of components in addition to those listed. Additionally, there are hundreds of other companies that supply all the other components, such as glass, plastic, wiring, hoses, and lights. During 2002, Toyota challenged itself to redouble its cost reduction program, aiming to achieve world-class competitiveness for around 170 major components that account for more than 90% of overall parts purchasing costs. The company has initiated focused collaborations between its component suppliers and engineering, production engineering, production, and purchasing divisions. Toyota claims that it has almost achieved the target, but is continuing to pursue manufacturing innovations aimed at achieving substantial cost reductions. This inevitably squeezes the company’s suppliers. Ford initiated plans at the end of 2003 to source about $1 billion worth of components per year from Chinese suppliers, for use in making vehicles in other countries, including plants in Thailand, Malaysia, and the Philippines. This includes many of the metal castings and plastic moldings supplied by local Chinese manufacturers to car plants, including Ford’s competitors in China. Surprisingly, although labor costs are low in China, vehicle manufacturing costs are among the highest in the world. This is caused by fragmented and expensive supply chains, the comparatively high cost of local components, and the need to import many high-technology components from Europe and North America. The result is total manufacturing costs that can be up to 30% higher than in the United States. Prices for some Chinese made components have been set artificially high, to the benefit of state-owned companies. Fortunately, competitive market pressures and reduced government protection has been forcing prices down over the past couple of years.

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Indian manufacturers of automotive parts could export components valued at $100 million per year to Ford’s manufacturing plants worldwide, according to Ford. The company has developed a large supplier base in India because the cost of parts is lower, which helps to boost volumes. Industry analysts indicate that Indian automotive parts are between 15 and 20% cheaper than equivalent quality components from European or U.S. suppliers. Ford makes about 40,000 Ikon cars per year at its plant in Chennai. Bharat Forge, a family-controlled company based in Pune, India, close to Tata Motor’s headquarters, is the world’s third largest forging business. In addition to supplying to Tata Motors, the company supplies to international manufacturers such as Ford and DaimlerChrysler. Bharat Forge acquired Carl Dan Peddinghaus in Germany toward the end of 2003, for US$35 million, giving the company an annual production of almost 300,000 of forgings and forecast sales in 2004 of US$350 million. The company is now pursuing ventures in China and North America, which, if successful, will make it the world’s largest supplier of forging, ahead of ThyssenKrupp of Germany.

44.2.2 Asian Automotive Design and Engineering Toyota launched the world’s first mass-produced hybrid car, the Prius, which featured the Toyota Hybrid System (THS), in 1997. Hybrid vehicles have both a combustion engine and a battery system for providing motive power. Up to the end of 2003, the company had sold a total of 130,000 Prius Mark 1 hybrid cars worldwide. The second generation Prius was launched in Japan in April 2003 and in Europe in November 2003. The Mark 2 car is larger than the Mark 1, with an improved shape to appeal to more mainstream consumers. The electric components remain the same, with a traction motor, separate generator, and Panasonic NiMH (nickel metal-hydride) battery pack, but the traction motor’s voltage has been increased from 274 to 500 V. Since the current is the same, the motor’s power has increased from 33 kW (44 bhp) to 50 kW (67 bhp) between 1040 and 5600 rpm. This makes the car’s performance slightly better than the average 1.0 or 1.2 L gasoline engine. The Panasonic battery pack is 15% smaller and 25% lighter, with 35% higher output density. The traction motor’s torque is 400 Nm from 0 to 1200 rpm, which equates to a 0 to 62 mi/h time of 11 sec. The new Prius was named “Car of the Year” at the 2004 Detroit Motor Show. The earlier version was considered to have comparatively slow acceleration, a bland appearance, and a high price. The new five-door version is faster, better looking, and is highly fuel efficient, averaging 66 mi/gal. The new Prius, with THS II, is fully compliant with California’s Advanced Technology Partial Zero

Emission Vehicle (AT-PZEV) regulations that came into effect in 2003. Toyota has begun to expand production in Japan, after receiving orders for more than 10,000 cars from the United States. Toyota was also the first to introduce a commercial fuel cell hybrid vehicle (FCHV), through a limited sales launch in Japan and the United States in December 2002. The company has also been testing a fuel cell hybrid bus, developed jointly with Hino Motors, on Japanese roads, since October 2002. In January 2003, Toyota and Hino were selected by the Tokyo Metropolitan Government to provide vehicles for a pilot scheme for fuel cell hybrid buses operating in Tokyo. Nissan and Toyota announced in September 2002 that they will collaborate on designing and developing hybrid cars. The collaboration, which is expected to last for ten years, involves Toyota supplying Nissan with hybrid vehicle technology, for vehicles to be sold in the United States in 2006. It is planned that sales of these cars in the United States will reach 100,000 per year by 2011. Nissan’s decision to use Toyota’s technology, first developed for the Prius, appears to be another of the pragmatic tactics used by the company to limit costs and avoid expensive development programs. Industry analysts believe that Toyota continues to incur losses of a few thousand dollars on each Prius it sells. It is understood that Nissan has agreed with Toyota to pay only for the hybrid units it needs, on a royalty basis. This may be an indication that Nissan believes sales of hybrid cars may not grow as rapidly as some observers have forecast. However, sales of hybrid vehicles are expected to grow in the United States, from a small base, as a result of forthcoming emissions limits and favorable tax benefits for environmentally friendly vehicles. Sales of hybrid cars have begun to increase in Japan, North America, and Western Europe, albeit from a low base. The main reason for this is fuel economy in an era of high prices for crude oil, and therefore gasoline. Globally, the Honda and Toyota hybrid cars take the first and second places in a list of the ten most fuel efficient vehicles being sold at present. The Honda Insight has a CO2 emissions value of 80 g/km while the Toyota Prius has a CO2 emissions value of 104 g/km. The list is shown in Table 44.6. It is worth noting that the average CO2 emissions value for all new cars sold in the United Kingdom in 2003 was 174 g/km. Honda’s Insight hybrid was launched in 2000, but has met with only limited sales success as a result of it being a two-seater coupe with minimal luggage capacity. Also, the Insight’s gasoline engine and electric unit always ran together, offering no all-electric mode. Honda introduced the Civic IMA hybrid in December 2003, as a hatchback car with luggage space and comparatively little price premium over a conventional gasoline powered car. Honda’s chief R&D engineer, Kenichi Nagahire, is reported to have said

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TABLE 44.6 Top Ten Vehicles for Emissions of CO2 , 2004 Rank

Manufacturer and vehicle model

1 2 3 =4 =4 =6 =6 =6 =9 =9

Honda Insight Toyota Prius Citroen C2 Citroen C3 Renault Clio Peugeot 206 Toyota Yaris Smart Daihatsu Charade Ford Fiesta

Engine type Hybrid Hybrid Diesel Diesel Diesel Diesel Diesel Gasoline Gasoline Diesel

CO2 Emissions, g/km 80 104 108 110 110 113 113 113 114 114

Source: ACEA.

that 40% of the company’s sales are likely to be hybrids by the end of this decade. Ford plans to launch a four-wheel-drive hybrid, the Escape, toward the end of 2004 and Nissan and GM are developing hybrid vehicles. Industry analysts forecast that annual sales of hybrid cars in the United States will be 400,000, or about 1 hybrid for every 40 conventional car. In September 2004, Toyota announced that it plans to join forces with China’s FAW to sell Prius hybrids in China. The cars will be assembled from kits made in Japan and will only be available for sale in China and not for export. However, while environmental protection is high on the agenda for Chinese policymakers, there is little evidence, at present, of a consumer base for products that are environmentally friendly.

44.2.3 Asian Automotive Vehicle Regulations 44.2.3.1 Safety Cars are becoming more complex and sophisticated as a result of stricter safety and environmental laws and increasing demands from customers. Many of the safety features in cars are developed initially in Western Europe, North America, or Japan and are then applied to vehicles made and sold in other regions. The trend toward an increasing use of airbags and side-impact protection bars typifies the emphasis on greater safety. Both concepts were pioneered in Europe, with Mercedes-Benz inventing the original steering wheel airbag and Volvo inventing the side-impact protection system. However, the routine use of airbags was evident first in the United States. These trends are now becoming apparent in Asian markets, particularly on Japanese, South Korean, and Malaysian cars destined for export to the United States and Europe.

In Japan, Toyota has been working on vehicle safety for many years. The company developed the anti-lock braking system (ABS) in 1971 and adopted the traction control (TRC) system in 1987. In 1995, Toyota commercialized the steering-assisted vehicle stability control (VSC) system. Toyota engineers believe that the ultimate goal of achieving no accidents and no deaths involves people, vehicles, and the traffic environment being viewed as three pillars of an interrelated whole in which each pillar should complement and support the others. It is essential that countermeasures toward each of these areas are implemented comprehensively. According to Toyota, preventive safety and collision safety are the two target areas that come into play before and after an accident. Within these target areas, the roles that people, automobiles, and the traffic environment play are ever changing. Toyota’s ambition is to continually effect evolutions in safety technology so that the automobile can continue to play a greater role toward safety regardless of the stage of accident occurrence. The basic theme of preventive safety is ensuring a high level of vehicle stability. Toyota has been engaged in the development of visibility support technology, such as the blind-spot monitor. Toyota uses a rigid process to analyze and evaluate its safety technology, examining and recreating accidents to find their causes and then assessing safety technology by incorporating it into its vehicles and examining and confirming its effectiveness in real circumstances. The company seeks to learn from actual accidents that occur within the marketplace. An important conclusion from Toyota’s analyzes is that, even if car manufacturers were to maximize the incorporation of various safety measures, the reduction in fatalities is expected to reach no higher than 60% by 2030. Toyota believes the “zero injuries and fatalities” target can be achieved only from a combination of driver training and experience, the traffic environment and vehicle safety countermeasures. In March 2004, Toyota announced the development of a radar-based cruise control system that can be used in slowmoving traffic to make driving less stressful. The system is an improved version of one introduced in 1997 for Toyota’s Celsior luxury car. The first system was designed for use at speeds of 25 to 60 mi/h (40 to 100 km/h), but with advances in laser sensors and smoother braking, the new system can be used at much lower speeds. The system keeps track of the vehicle in front at speeds of 20 mi/h (∼30 km/h) or lower. When the vehicle in front stops or slows down, the system gives visual and audio warnings urging the driver to apply the brakes. If the driver does not respond in time, the system slows the vehicle to a complete stop. As a result, it can assist the driver in stop-go traffic by reducing pedal work. Toyota estimates that the system’s low speed and conventional modes cover around 90% of driving speeds during a typical weekday on

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the Tokyo Metropolitan Expressway. The system will be fitted to a new vehicle to be launched by Toyota later in 2004. Traffic accident statistics in Japan show that rear-end impacts account for almost 50% of all injury-causing accidents and that over 90% of the injuries sustained by occupants whose vehicles are struck in rear-end collisions are to the neck region. More than 200,000 people suffer such injuries annually. Rear-end collisions, even at relatively low impact speeds, can result in back or neck injuries and in some cases lead to subsequent discomfort such as whiplash injuries. Nissan investigated actual traffic accidents thoroughly and has used the data to develop of a safety system based on actual human body movement. Nissan’s Active Head Restraint system uses the force of the occupant’s body against the seatback in a rear-end collision to move the head restraint forward instantaneously to support the head, thereby helping to reduce the impact to the neck of a front-seat occupant. The mechanism of whiplash injuries closely involves two factors resulting from the impact: the force acting to bend the neck backward and the force that causes the head to tilt rearward. Because the Active Head Restraint is effective in controlling these two factors, it can help reduce the load on the neck at the moment of the collision, reducing the resultant bending force by approximately 45%. Nissan started to provide Active Head Restraints as standard equipment in all its cars, wagons, mini-vans, and SUVs in Japan during 2004. Nissan has also developed a number of safety technologies to help protect occupants in side collisions. Typical examples include the high-strength Zone Body construction, SRS side airbag systems for the driver and front passenger (also available in the rear seat on some models), and interior trim materials with high energy-absorbing capabilities. As a further measure, Nissan is continually expanding the application of SRS curtain airbag systems to help minimize head and neck injuries in side collisions. When the vehicle is impacted from the side, the SRS curtain airbag system instantly inflates the airbags built into the sides of the ceiling to help protect front- and rearseat occupants. These airbags help cushion the impact when an occupant’s head strikes a pillar or a side window. They also help to mitigate neck injuries by helping control excessive twisting of the neck. Though SRS curtain airbag systems are often thought to be safety features found on luxury models, Nissan has adopted these systems also on the new generation of its March small passenger car. Nearly all Nissan cars, wagons, mini-vans, and SUVs for the Japanese market were available with SRS curtain airbag systems from early in 2005. In September 2004, Honda announced plans to introduce an in-car warning system that alerts drivers on dark roads when there is a person or animal is ahead of them. The Intelligent Night Vision System uses two far-infra-red

cameras, mounted on a vehicle’s front bumper, to detect warm objects up to 80 m away. The incoming image data is analyzed using software that recognizes the characteristic shapes of pedestrians and calculates how far they are from the car. The system projects an image of the roadway ahead onto a mirror on the vehicle’s dashboard and adds a glowing orange outline of any pedestrians when they are detected. It also sounds an alarm to alert the driver. Honda plans to launch the system later in 2004 in the new version of its Legend car. The Japanese Institute of Traffic Accident Research and Data Analysis has reported that 70% of pedestrian fatalities occur at night. According to MMC, in the event of a collision, reducing the impact to the occupant and maintaining the available survival space within the body are essential. MMC introduced its Reinforced Impact Safety Evolution (RISE) body construction in the 1996 Galant, claiming to set a new standard for improved collision safety performance. In May 2003, MMC launched the Grandis, which uses further refined RISE technology, such as “straight frame construction,” “octangular front side member,” and “three-way input distribution cross-dash pillar braces” to minimize cabin deformation while effectively absorbing and distributing impact energy. In addition, the Grandis incorporates “tailored blank” technology whereby welds are formed between steel materials of varying thickness for improvements in both impact safety performance and weight reduction due to the optimal allocation of material. In MMC vehicles, special construction is used to reduce contact between the foot and the brake pedal and the foot-actuated parking brake in an impact forward of the vehicle. This reduces injury to the driver’s ankle area. In a frontal impact, the backward movement of the engine may cause the brake booster to get pushed in toward the vehicle interior, but this construction allows the brake pedal to withdraw where it is attached at its upper end, allowing it to move down along the stopper plate, thus reducing pedal interference. This safety system is now being fitted to all MMC eK Wagon, Airtrek, Colt, and Grandis vehicles. 44.2.3.2 Environment While the rapid growth of vehicles in Asia has contributed to economic development and welfare, it has become clear that it presents three main problems: congestion (roads in Asian cities are becoming increasingly congested), pollution (air quality in Asian cities are among the worst in the world), and road safety (the Asia/Pacific region accounts for almost half of all accident deaths in the world). These problems have a negative impact on the economic and social development of countries in Asia as they result in significant costs for medical expenses and lost productivity. Tackling these problems requires a comprehensive approach, involving policies, legislation, enforcement, institutional coordination, monitoring, and training.

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With specific regard to pollution, a comprehensive strategy includes increasingly stringent emissions standards for new vehicles, specifications for clean fuels, programs to insure proper maintenance of vehicles, and traffic and demand management. The Asian Development Bank issued a report in May 1997 warning that pollution problems in the region pose an economic as well as an environmental threat. The report noted that 13 of the 15 most polluted cities in the world were in Asia and concluded that the region’s environmental crisis is in large part the result of failed policies and neglect. It also emphasized that economic growth itself is not directly to blame. Estimates of the economic costs of environmental degradation in Asia were as high as 9% of GNP. The ADB believed that continuing rapid urbanization was likely to make the situation worse, so it urged governments in the region to change their environmental policies. The report warned that a “pollute now, pay later, approach to the environment increasingly makes little economic or ecological sense.” It is estimated that road transport contributes about 14% to global CO2 and that about 30% of this is from vehicles in the less developed countries (LDCs). LDC contribution is higher than its vehicle share because of higher fuel consumption of older, poorly maintained vehicles, which also emit more pollutants because few of them are fitted with emission control devices. Although buses and trucks are the main contributors, their shares in terms of passenger km or tonne km are relatively low. Poorly maintained diesel engines in buses and trucks produce almost 50% of the world’s output of particulate matter. A large number of two-stroke engines emit high levels of hydrocarbons and smoke. In India it is estimated that they are responsible for about 33% of emissions. Vehicle emission control began in Japan in 1966 under the administrative guidance of the Ministry of Transport. Carbon monoxide (CO) emissions from gasoline vehicles was the first air pollutant to be regulated. Particulate, unburnt hydrocarbon (HC), and NOx emissions were regulated from 1975 onwards. Japan’s Central Environment Council issued Motor Vehicle Exhaust Emission Regulations, which comprehensively set the standards for NOx, HC, and CO for both gasoline and diesel vehicles in 1976. New emission limits with short-term and long-term targets were further set in December 1989. As in Europe and the United States, Japan developed its own environmental program, called the Japan Clean Air Program (JCAP). Although significant reductions in emissions from individual vehicles were achieved from 1975 to 1995, the increasing number of vehicles, particularly diesels, meant that total emissions were still trending upward. As a result, the Ministry of International Trade and Industry (MITI) started a program in 1996 to study possible future fuel and vehicle technology to improve air quality. The first step was started as a Petroleum Energy Centre

(PEC) project, with invited participation by the Japan Automobile Manufacturers Association (JAMA) and the Petroleum Association of Japan (PAJ). The PEC determined that it would not be possible to simply follow the United States and European leads because of the differing air pollution conditions in Japan, differences in automotive technology and, the prevalence of high quality fuel with low sulfur levels and high cetane numbers. Japan imposed more stringent emissions limits on new cars, trucks, buses, and motorcycles in 1998. The standards, which are shown in Tables 44.7 to 44.9, are similar to those in the United States and the European Union (EU). The Central Environmental Council also introduced emissions regulations for special vehicles such as bulldozers, power shovels, and farm tractors, which are estimated to be responsible for around one third of total transport-related NOx emissions. China first introduced laws on the prevention and control of air pollution in 1988, focusing on stationary sources of emissions. Vehicle emission regulations for all new vehicles were adopted in 1995 and were revised in 2000. In addition to the national standards, local standards that are more stringent can be set by the governments of provinces, autonomous regions, or municipalities, after agreement with the State Council. The latest regulations also contain provisions for testing motor vehicles annually to check whether they continue to comply with emissions limits. During 1997, the Chinese government initiated a technical review of the best method to tackle vehicle emissions. The review concluded that the gradual introduction of EU vehicle emissions limits, starting in the major cities, would be best, so Euro 1 limits for gasoline engines in passenger cars became mandatory in Beijing and Shanghai in January 1999. These limits were extended to the whole of China for new cars manufactured from October 2001 onwards. Euro 2 limits were mandated in the main cities during 2002 and became mandatory for new cars throughout China in July 2004. Dates for the introduction of Euro 3 and Euro 4 limits are shown in Table 44.10. The Chinese vehicle emissions standards are planned to be at the “advanced international level” standards by 2010. While the standards currently cover cars, vans, trucks, buses, and motorcycles, the Chinese government is proposing to add agricultural vehicles and LPG and liquefied natural gas (LNG) vehicles. Liquefied natural gas is being promoted in China as the answer to deteriorating urban air quality. LPG and LNG powered vehicles, particularly buses and taxis, have been introduced progressively in many Chinese cities, including Beijing, Shanghai, Shenzen, and Haikou. Shanghai opened its first LNG refueling facility to serve the city’s growing fleet of LNG-powered taxis in 1998 and by 2004 all mass transit vehicles in the city were operating on the gas. Leaded gasoline was finally replaced by LRP (lead replacement petrol) in China in 2003.

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The Chinese government announced early in 2004 that it was about to issue the first standards on car fuel efficiency, but at the time of writing the limits had not been decided. However, it is clear that China plans to catch up to international standards for both fuel efficiency and emissions by 2010. As a result, much cleaner gasoline and diesel fuels will have to be available in China, requiring investment in either upgrading existing or building new refineries to meet both quality levels and increasing volume demands. The Chinese government has forecast that annual gasoline consumption could double to 80 million tonnes between 2003 and 2010. India’s government also took a step toward cleaner fuels when it approved proposals to set up diesel hydrodesulphurization units at nine refineries, at a total cost of $1.56 billion. The units enable lower sulfur diesel fuel to be produced, thereby allowing the fitment of more effective catalytic aftertreatment devices to vehicles. The refineries are in Gujarat, Haldia, Mathura, Panipat, Visakapatnam, and Mumbai. Unleaded gasoline has been available throughout India since the beginning of 2000. Progressively during 2000 and 2001, lower sulfur gasoline and diesel (0.05%) has been mandated, first in the main cities (New Delhi, Mumbai, Kolkata, and Chennai) and then in other cities. 0.05% sulfur fuels will be mandated throughout India during 2005. The effectiveness of vehicle emissions inspection programs in reducing pollution in India was brought into doubt by the initial results, reported during 1997, of a crackdown in the Indian capital New Delhi. More than 200,000 motorists had visited pollution control stations to have their vehicles checked and to obtain the certificate required to continue driving in the city. The limited number of stations available meant a familiar problem for such schemes; delays of up to 3 h for motorists requiring a test. From April 15, 1997 onwards, vehicles without a certificate have been unable to purchase petrol. Regulations to control vehicle emissions in India started in 1991, with the introduction of the “Mass Emission Regulation,” which covered CO and HC emissions from gasoline vehicles. Diesel vehicles were added in 1992. The regulations were tightened in 1996 and NOx, evaporative, and crankcase emissions were added. In 1998, 50% tighter limits were applied to vehicles that are fitted with catalytic converters, which were mandated in 42 major cities for gasoline powered cars. “India 2000” limits (equivalent to Euro I standards) were introduced in 2000. In April 2000, the Society of Indian Automotive Manufacturers (SIAM) proposed skipping the Euro III emissions limits for new trucks and buses and adopting the Euro IV limits for these vehicles in 2006/2007. SIAM proposed adopting Euro III limits for new passenger cars in 2004 and two- and three-wheelers in 2005 and Euro IV limits for these vehicles in 2005/2006 and 2009 respectively.

TABLE 44.7 Japanese Gasoline and LPG Motor Vehicle Emissions Standards Vehicle type Passenger cars

Engine typea 2- and 4-cycle

Test modeb 10.15M (g/km)

11M (g/test)

Trucks and buses

4-Cycle mini-sized

10.15M (g/km)

11M (g/test)

2-Cycle mini-sized

10.15M (g/km)

11M (g/test)

Light-duty, GVW 71.7 t

10.15M (g/km)

11M (g/test)

Medium-duty, 1.7t < GVW 71.7 t

10.15M (g/km)

11M (g/test)

Heavy-duty, 71.7 tGVW > 2.5 t

G13M (g/kWh)

Emission typec

Limite Yeard

Maximum

Average

CO HC NOx CO HC NOx

1975 1975 1978 1975 1975 1978

2.70 0.39 0.48 85.0 9.50 6.00

2.10 0.25 0.25 60.0 7.00 4.40

CO HC NOx CO HC NOx CO HC NOx CO HC NOx CO HC NOx CO HC NOx CO HC NOx CO HC NOx CO HC NOx

1998 1998 1998 1998 1998 1998 1975 1975 1975 1975 1975 1975 1988 1988 1988 1988 1988 1988 1998 1998 1994 1998 1998 1994 1998 1998 1995

8.42 0.39 0.48 104 9.50 6.00 17.0 15.0 0.50 130 70.0 4.00 2.70 0.39 0.48 85.0 9.50 6.00 8.42 0.39 0.63 104 9.50 6.60 68.0f 2.29 5.90

6.50 0.25 0.25 76 7.00 4.40 13.0 12.0 0.30 100 50.0 2.50 2.10 0.25 0.25 60.0 7.00 4.40 6.50 0.25 0.40 76 7.00 5.00 51.0g 1.80 4.50

Notes: a 2-Cycle passenger cars, trucks, and buses are no longer in production. GVW = gross vehicle weight. b 10.15-mode (10.15M) represents a typical driving pattern in urban areas. 11-mode (11M) is a typical driving pattern of a

cold-started vehicle traveling from the suburbs to an urban center. c CO = Carbon monoxide, HC = unburnt hydrocarbons, NOx = nitrogen oxides. d Year of first enforcement. e Maximum is the maximum permissible value for the vehicle type; average is the average value for vehicles of that type. f 105 for LPG vehicles. g 76 for LPG vehicles. Source: Japanese Ministry of the Environment.

Currently, emissions from new cars, trucks, and buses have to meet “Bharat Stage II” air quality standards (equivalent to Euro II limits on NOx and particulate emissions) in all major cities. An Indian Inter-Ministerial Task Force recommended in March 2001 that by April 2005, Bharat Stage II emissions will be mandatory across

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India and “Bharat Stage III” requirements will have to be met in eleven major cities, including New Delhi, Mumbai, Chennai, and Kolkata. New two- and threewheeled vehicles have had to meet Euro II standards since April 2005 they will have to meet Euro II limits. Vehicle emissions limits for India are shown in Table 44.11.

TABLE 44.8 Japanese Diesel Motor Vehicle Emissions Standards

Vehicle type

Test modea

Engine type

Passenger cars

Trucks and buses

Emission typeb

Limitd Yearc

Maximum

Average

10.15M (g/km)

CO HC NOx PM

1986 1986 1997e 1997e

2.70 0.62 0.55 0.14

2.10 0.40 0.40 0.08

Light-duty, GVW 71.7 t

10.15M (g/km)

CO HC NOx PM

1988 1988 1997 1997

2.70 0.62 0.55 0.14

2.10 0.40 0.40 0.08

Medium-duty, 1.7 t < GVW 71.7 t

10.15M (g/km)

CO HC NOx PM

1993 1993 1997f 1997f

2.70 0.62 0.97 0.18

2.10 0.40 0.70 0.09

Heavy-duty, GVW > 2.5 t

G13M (g/kWh)

CO HC NOx PM

1994 1994 1997g 1997g

9.20 3.80 5.80 0.49

7.40 2.90 4.50 0.25

Notes: a 10.15-mode (10.15M) represents a typical driving pattern in urban areas. 11-mode (11M) is a typical driving pattern of a cold-started vehicle traveling from the suburbs to an urban center. b CO = carbon monoxide, HC = unburnt hydrocarbons, NOx = nitrogen oxides, PM = particulates. c Year of first enforcement. d Maximum is the maximum permissible value for the vehicle type; average is the average value for vehicles of that type. e 1997 for small cars, EIW 71.25 t, and 1998 for medium cars, EIW > 1.25 t. EIW = equivalent inertia weight. f 6 1997 for MT vehicles, 1998 for AT vehicles. g 1997 for GVW 73.5 t, 1998 for GVW 712 t, and 1999 for GVW > 12 t. Source: Japanese Ministry of the Environment.

TABLE 44.9 Japanese Motor Cycle Emissions Standards Engine type Test mode

Emission typea

Limitc Yearb Maximum Average

4-Cycle

2-Wheel test (g/km)

CO HC NOx

1998 1998 1998

20.0 2.93 0.51

13.0 2.00 0.30

2-Cycle

2-Wheel test (g/km)

CO HC NOx

1998 1998 1998

14.4 5.26 0.14

8.00 3.00 0.10

Notes: a CO = Carbon monoxide, HC = unburnt hydrocarbons, NOx = nitrogen oxides, PM = particulates. b Year of first enforcement. 1998 for small motorcycles (Type I), 1999 for larger motorcycles (Type II). c Maximum is the maximum permissible value for the vehicle type; average is the average value for vehicles of that type. Source: Japanese Ministry of the Environment.

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“Bharat Stage IV” standards are currently under discussion. All commercial vehicles (buses, taxis, auto-rickshaws, and trucks) in India now have to pass an annual “fitness” check, for emissions, safety, and roadworthiness. The inspection and certification tests are performed by government authorized agencies (RTOs). PUC centers at fuel stations and repair garages are also authorized to perform periodic (three or six monthly) emissions checks on commercial vehicles. SIAM has recommended that “fitness” tests are extended to include cars and two- and threewheelers, using rigorously accredited private test centers. The number of test centers would need to be expanded significantly, as there were more than 40 million two- and three-wheeled vehicles in India in 2002. However, SIAM has recognized that the current PUC system in India is not achieving the objective of reducing pollution, because the independent centers do not follow rigorous procedures (due to inadequate training), the test equipment is not calibrated periodically by independent

TABLE 44.10 Chinese Emissions Limits for Passenger Car Gasoline Engines Emissiona and limits (g/km)

Mandated byb

Emissions standard

CO

HC + NOx

HC

NOx

Beijing

Shanghai

All China

Euro 1 Euro 2 Euro 3 Euro 4

2.72 2.20 2.30 1.00

0.97 0.5 — —

— — 0.2 0.1

— — 0.15 0.08

Jan 1999 Jan 2002 Jan 2005 Jan 2010

Jan 1999 Mar 2002 TBD Jan 2010

Oct 2001 July 2004 TBD TBD

Notes: a CO = Carbon monoxide, HC = unburnt hydrocarbons, NOx = nitrogen oxides. b TBD = To be decided. Source: Pathmaster Marketing, from various industry contacts.

authorities, a lack of professionalism has led to malpractices, and there is no system to monitor vehicles that have failed the tests. To help overcome these difficulties, SIAM has designed an automated emission test device for gasoline vehicles that is as tamper-proof as possible. Other Asian countries have also been active in introducing vehicle emission standards. EU limits have been in place in Singapore and Hong Kong for some years. Malaysia introduced pollution emissions standards based on EU limits in January 1997, aimed at reducing emissions from cars and trucks. In June 2004, the Thai Ministries of Industry and Finance agreed to offer tax incentives to encourage the production and sale of energy-efficient vehicles in Thailand. At the same time, car makers urged the government to cut tariffs on imported hybrid cars. The tax incentives aim to encourage manufacturers to produce vehicles that consume less fuel under the government’s “Best Little Car” project, formerly known as “Eco Car” and would also be provided for fuel cell or hybrid cars as well as models that use ethanol-blended gasohol. New light-duty diesel vehicles sold in Thailand have been required to meet Euro III standards from July 2004 and heavy-duty diesel vehicles currently have to meet Euro II limits. The timing of adopting Euro III limits for heavy-duty diesels and Euro IV limits for all diesel vehicles is currently being discussed. Low sulfur diesel (350 ppm) is now mandated in Thailand and it is proposed that 50 ppm sulfur diesel should be mandated by 2010. In addition, the Thai government has encouraged initiatives to evaluate LPG, dual-fuel (CNG/gasoline and CNG/diesel), and bio-fuel engines for buses and taxis in Bangkok. Motorcycle manufacturers in Asia reacted to pressure to reduce emissions of pollution and noise. In early 1997, an alliance was formed between Honda, Suzuki, Yamaha, and Kawasaki to examine ways to meet the challenges. The Nippon Motorcycle Association, which coordinates the alliance, also invited membership from motorcycle retailers and distributors, and has organized activities

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for motorcycle owners, in addition to the environmental research. Worldwide, as the disproportionate contribution to ground level ozone and hydrocarbon pollution from motorcycles became apparent, ways to curb emissions were investigated and developed. The levels of pollution have encouraged some countries, such as Taiwan, to enforce the sale of low emission scooters. From 1998, 5% of scooters sold in Taiwan must offer zero emissions. It might be difficult to see why two-stroke engines should be encouraged from the perspective of emissions alone. Conventional two-stroke engines must pass the fuel– air mixture through the crankcase then into and (as exhaust) out of the cylinder through fixed ports opened and closed by piston movement. Even at their most efficient, combustion temperature is high and so, consequently, are NOx emissions. Wet sump lubrication is not possible, so oil must be carried in the fuel-air mixture, burning with it and contributing to HC emissions. Because of the fixed porting, the engine is at its most efficient only rarely; at other speeds and loads a proportion of the mixture passes straight through the combustion chamber unburned, so fuel consumption is high and HC emissions are increased further. A measure of the challenge to a lean-burn compact two-stroke is that current EU legislation tolerates around ten times the emissions from a small two-stroke scooter than it does from a car. However, with twice as many power strokes in its operating cycle as a four-stroke engine, a much smaller capacity engine can produce the same power, and even more torque. The two-stroke is cheap and simple to produce and maintain. The more these virtues are preserved while emissions and consumption are brought down, the more environmentally (and commercially) friendly they become through the indirect advantages of low weight and compactness. Asian companies known to be working on the development of improved two-stroke engines include Yamaha-Shansin, Honda, Subaru (which has close links to

TABLE 44.11 Indian Vehicle Emissions Limits Fuel type

Vehicle type

Gasoline

2-Wheelers

3-Wheelers

Passenger cars

Diesel

Passenger cars Light vehicles, GVW 73.5 t

Heavy vehicles, GVW > 3.5 t

Emission and limits (g/km or g/kWh)a

Year mandated

CO

HC

HC + NOx

PM

1991 1996 2000 2005 1991 1996 2000 2005 1991 1996 1998b 2000 2004/05

12–30 4.50 2.00 1.50 12–30 6.75 4.00 3.00 14.3–27.0 8.68–12.4 4.34–6.20 2.72 2.20c

8–12 — — — 8–12 — — — 2.0–2.9 — — — —

— 3.00 2.00 1.50 — 5.40 2.00 1.50 — 3.00–4.36 1.50–2.10 0.97 0.50d

— — — — — — — — — — — — —

2004/05e 2004/05f 1992 1996 2000 2004/05 1992 1996 2000 2004/05

1.0 1.0–1.5 14 11.2 4.5 4.0 17.3–32.6 11.2 4.5 4.0

— — 3.5 2.4 1.1 1.1 2.7–3.7 2.4 1.1 1.1

0.7 0.7–1.2 21.5 16.8 9.1 8.1 — 16.8 9.1 8.1

0.08 0.08–0.17 — — 0.36g 0.15 — — 0.36 0.15

Notes: a CO = carbon monoxide, HC = unburnt hydrocarbons, NOx = nitrogen oxides. Values for 2-wheelers, 3-wheelers, and gasoline and diesel passenger cars are g/km and values for diesel engines are g/kWh. b For cars fitted with catalytic converters. c For vehicles up to six seats and GVW up to 2.5 t. 2.2–5.0 for vehicles with more than six seats and GVW up to 3.5 t. d For vehicles up to six seats and GVW up to 2.5 t. 0.5–0.7 for vehicles with more than six seats and GVW up to 3.5 t. e For vehicles up to six seats and GVW up to 2.5 t. f For vehicles with more than six seats and GVW up to 3.5 t. g For engines exceeding 85 kW power. 0.61 for engines less than 85 kW power. Source: Society of Indian Automobile Manufacturers.

Nissan), Toyota, Suzuki, and Daihatsu. The most active in publishing patents in this field have been Yamaha-Shanshin and Honda.

44.3 CURRENT STATUS OF AUTOMOTIVE FLUIDS IN ASIA 44.3.1 Engine Oils 44.3.1.1 Gasoline engine oils An extremely wide range of gasoline engine oil qualities is available in Asia currently, ranging from low quality

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mineral oils to fully synthetic oils. The pattern has begun to change over the past five or more years, as many of the countries in the region become more wealthy and more aware of the value of goods and services. High quality automotive lubricants have been available in Japan, Singapore, Hong Kong, South Korea, Taiwan, and Malaysia for over ten years. Other countries in Asia have started to catch up. Within Japan, OEMs have generally developed proprietary factory fill specifications and then selected oil companies to develop the required engine oils using proprietary engine tests. These oils are also marketed by the OEMs as so-called genuine oils. They are mainly SAE

10w30 viscosity grades. There is reluctance to reformulate these oils until there is an engine change and virtually no formulation modifications are accepted without extensive testing. In other countries, Japanese vehicle manufacturers have relied generally on the API classification system to recommend engine oils for service fill applications in passenger cars. The Japanese Automobile Standards Organisation (JASO) is similar in many ways to the Co-ordinating European Council in Europe, in developing engine test procedures that do not have pass/fail limits. The parallel is not complete, however, because Japanese vehicle manufacturers often do not require these tests for their own in-house specifications. The JASO engine tests have an unofficial parallel with the tests used in the API “S” sequences and are used to evaluate oils of different quality levels. In 1993, JASO modified its previous policy and quoted limits for a Japanese industry standard (JIS K2215), which includes a specification for the minimum quality engine oil for Japanese automotive gasoline engines. Since 1990, the JAMA has worked with the Motor Vehicle Manufacturers Association of the United States (MVMA, now the Alliance of Automobile Manufacturers [AAM]) to develop a new performance standard called ILSAC, the International Lubricants Standardisation and Approvals Committee. It is intended that the ILSAC specifications will eventually include at least one Japanese engine test. As a result the Nissan KA24E low temperature valve train wear test has been developed and round robin testing has been completed by JASO. The result is that, in addition to the OEM “genuine oils,” typical gasoline engine oils available in Japan currently meet the API SL, ACEA A1/A3, and ILSAC GF-3 specifications, with API SM and ILSAC GF-4 quality oils about to be introduced before the end of 2004. Some API SG and SH quality oils are still available, although only recommended for use in older model cars and vans. In China, the typical quality level available currently is API SE or SF, made from lower quality baseoils and additive packages no longer available in North America or Western Europe. However, some API SC and SD quality oils are still sold and API SH and SJ quality oils have been marketed for the past few years. Automotive oils accounted for 54% of all lubricants sold in China in 2003. High quality refers to gasoline engine oils that meet API SG or better. Many oils are still monograde SAE 30 or 40 viscosity, although an increasing number of 20w50 and 15w50 multigrade oils are being sold. PetroChina (“Kunlun,” “Feitian,” and “Qixing” brands) and Sinopec (“Great Wall” brand) are the main indigenous suppliers, although there are hundreds of smaller lubricant blending and marketing companies in China. Most of the major international lubricant marketers, including Shell, Esso (ExxonMobil), BP/Castrol,

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and Caltex (ChevronTexaco) are active in China. Together, foreign brands accounted for 78% of the high quality gasoline engine oil market in 2003. China’s import tariffs on lubricants have been reduced from 9 to 6% following the country’s entry into the WTO in 2001. PetroChina aims to capture a 35% share of the high quality automotive engine oil market by 2005 and is working hard to improve the recognition and reputation of its main Kunlun brand. Sinopec is now accredited to ISO 9000 and ISO 14000 quality standards and has lubricants that meet international standards (API, ACEA, SAE, ISO) as well as being “approved” by international OEMs such as VW, BMW, DaimlerChrysler, Renault, Volvo, Cummins, Dennison, and ZF. Sinopec’s Great Wall brand now sells a fully synthetic 5w50 gasoline engine oil that meets the API SJ specification. Great Wall also offers API SE, SF, SG, and SJ mineral oil grades. Toward the end of 2003, Jiffy Lube (Shell) and SAIC announced a $30 million joint venture to build a chain of quick lube centers across China. The plan is to build a number of pilot centers in Shanghai during 2004 and then branch out into other cities in China. The centers will be modeled on the U.S. Jiffy Lube chain, providing oil changes and radiator, transmission, filter, and other services in 15 min. Shell and SAIC believe there will be a strong and growing demand for this type of convenience service in China, as a result of the rapid growth in car ownership. Automotive lubricants account for 65% of the market in India. Of this, only 5% is for passenger car gasoline engine oils. Most products are currently API SF or SG quality and generally 20w40 viscosity grade. Over the next five years, gasoline engine oils available in India are forecast to move toward API SH, SL (GF-3), and even SM (GF-4) quality, with fuel-conserving 15w40 and possibly 10w30 viscosity grades becoming available. These newer oils will have higher viscosity index (VI), lower cold cranking simulator viscosity, and lower NOACK volatility than the current products. From mid-2003 onwards, API Group II baseoils became more widely available in India, as a result of the commissioning of a new 140,000 tonne per year hydroprocessing plant at Indian Oil’s Haldia refinery. These baseoils are being used in the higher performance gasoline engine oils, as well as higher performance diesel engine oils and industrial oils, that will be introduced to the market gradually. Additional supplies of Group II baseoils will become available from the beginning of 2006, when Bharat Petroleum commissions a new 180,000 tonne per year plant at its Mumbai refinery. Although many countries in Asia still have lower quality gasoline engine oils on sale, high quality API SL/ACEA A3/ILSAC GF-3 synthetic 5w40 and part-synthetic 10w40 oils have been available in Singapore, Hong Kong, and South Korea for many years. As more motorists begin to

buy more expensive cars in other countries, the current tiny market share of the premium quality oils will begin to grow. 44.3.1.2 Diesel engine oils The pattern for diesel engine oils, both light-duty and heavy-duty, in Asia mirrors the pattern for gasoline engine oils; wide variations in both quality and viscosity. In Japan, JAMA requested a new API category for heavy-duty oils, for use in diesel engines operated in southeast Asia. JAMA’s concern with the CH-4 and CI-4 requirements is that it could lead to low ash oils, counter to their desires for higher ash oils. The requested category would be PC-8 and would be aimed at diesel engines with lower piston temperatures, greater use of slider followers, and hence greater need for wear protection. This specification was dropped, however, in favor of the new DHD-1 specification. The JAMA, ILSAC, and ACEA worked hard to develop the first global specification for heavy-duty diesel engine oils, DHD-1, which was introduced in 2001. The DHD-1 specification not only includes elements of both API CH-4 and ACEA E5 specifications, but also includes the Mitsubishi 4D34T4 engine test for soot-related valve train wear. This aims to overcome JAMA’s concerns about low ash oils. Inevitably, the DHD-1 is more restrictive that either the API or ACEA specifications, as it is intended to provide a very high performance oil that can be used in any heavy duty diesel engine from any OEM used anywhere in the world. Following the introduction of the API CI-4 specification in 2003 and the revised ACEA E5 specification at the end of 2004, JAMA and ILSAC plan to introduce an updated DHD-2 specification during 2005. Shortly after the introduction of DHD-1, the same OEMs recommended guidelines for the development of a set of global specifications for light-duty diesel engine performance. The DLD-1, DLD-2, and DLD-3 specifications are intended for high-speed, four cycle diesel engines. Unlike DHD-1, there are three performance levels. DLD-1 provides a basic level of quality for markets with highsulfur fuels. DLD-2 provides a higher level of performance, while requiring lower oil viscosities to assist with fuel efficiency. DLD-3 provides the highest level of performance, with both long drain and severe operating condition capabilities, as defined by engine manufacturers. All three specifications contain tests developed by CEC, JAMA, and ASTM. The three specifications were introduced, primarily in Asia, in 2003. Although there have been no Japanese industry diesel specifications developed to date, JAMA has been heavily involved in the development of the new DHD-1 and DLD-1, 2, and 3 specifications. As a result, operators of mixed fleets of diesel vehicles anywhere in the world now have the option of using the same quality of oil in either light-duty

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or heavy-duty engines irrespective of the OEMs that built the engines. In China, API CD and CE quality diesel engine oils are the most common products, although API CC oils can still be purchased from many of the smaller, local lubricant blenders and marketers. Great Wall (Sinopec) now markets an API CI-4 quality oil that is claimed to also meet ACEA E3, E5, and B4 specifications as well as MB228.3, MB229.1, Volvo VDS-3, Cummins CES20071/72/76/77/78, MAN 3275, and Mack EOM+MTU specifications. Great Wall also offers API CH-4, CF-4, CF, and CD diesel engine oils. Diesel engine oils account currently for 65% of the automotive lubricants market in India. Many of the oils being sold at present are API CC or CD quality and 20w40 viscosity grade. The main manufacturers of trucks in India, such as Tata Motors and Ashok Leyland, began to recommend API CH-4 or CI-4 quality oils for new vehicles from 2005 onwards. It is forecast that the higher performance oils are also likely to be 15w40 viscosity grade. The market drivers for these changes are reductions in emissions limits (see later), which focus on lower NOx and particulates, together with extended drain intervals and reduced oil consumption. Similar qualities of diesel engine oils are available in all other countries in Asia, including Singapore, Hong Kong, South Korea, Taiwan, Malaysia, Thailand, Indonesia, and the Philippines. 44.3.1.3 Two-stroke engine oils Globally, 70% of all motorcycles have two-stroke engines and a large percentage of these motorcycles are found in Asian countries. It is not surprising, therefore, that the current standards for two-stroke engine oils are based on JASO standards. The current JASO specifications for two-stroke engine oils, FB, and FC, incorporate tests for lubricity, initial engine torque, oil detergency, piston skirt deposits (varnish), exhaust smoke levels, and exhaust system blocking performance. The first four tests use a Honda engine, while the last two tests use a Suzuki engine. The FC performance level is more severe than the older FB performance level, particularly with respect to exhaust smoke and exhaust system blocking. Global performance specifications that are based on the types of performance criteria and tests used in the JASO specifications are now being introduced for two-stroke oils. These newer specifications are aimed at improving the image of two-stroke engines and at allowing for continued improvements in engine performance. The specifications are a response by the engine manufacturers, working with specification setting organization such as JASO, ASTM, and CEC, to the growing environmental pressure to reduce smoke emission from exhaust systems and to standardize the quality of lubricant available for use

TABLE 44.12 Japanese and Global Specifications for Two-Stroke Engine Oils JASO specification Global specification Performance criterion

FB EGB

FC EGC

EGD

Requirements

Lubricity Initial torque Detergency

95 98 85

95 98 95

95 98 125

Piston skirt deposits

85

90

95

Exhaust smoke Exhaust system blocking

45 45

85 90

85 90

Test engine Honda Honda Honda Honda Honda Honda Suzuki Suzuki

Test method JASO M340-92 JASO M340-92 JASO M341-92 3 h test JASO M341-92 3 h test JASO M342-92 JASO M343-92

Source: JASO.

worldwide. The specifications cover oils used for motorcycles, scooters, chainsaws, snowmobiles, and agricultural equipment. A summary of the specifications is shown in Table 44.12. Polybutene synthetic oils, which have the ability to depolymerize cleanly in the two-stroke engine, are increasingly being used in the formulation of oils that meet the smoke, exhaust blocking, and lubricity requirements of the major oil types being specified by engine manufacturers. However, polybutenes are not classed as biodegradable and synthetic esters are chosen to meet biodegradability requirements when this is needed for outboard, two-stroke oils. While two-stroke engines have definite advantages, such as reduced weight and size, higher power to weight ratio, fuel efficiency, fewer parts, and lower cost to manufacture, compared with four-stroke engines, their main disadvantage is higher emissions. While a large number of Japanese engine manufacturers, notably Mazda, Subaru, Nissan, and Toyota, were very interested in developing low emission two-stroke engines in the late 1980s, this interest has declined markedly in recent years, due to the problem of overcoming the high emissions levels. However, the work to lower two-stroke emissions led to the development of direct gasoline injection for four-stroke engines, so the research has had a positive outcome. In 2002, India had more than 42 million two- and three-wheeled vehicles with two-stroke engines, so it is not surprising that 13% of Indian automotive lubricants are two-stroke oils. The increasing severity of emissions limits in India mean that many of these vehicles will need to use EGC or EGD specification two-stroke oils by 2005. Other countries in Asia with large numbers of twostroke motor cycles, notably Thailand, Vietnam, Myanmar, and Cambodia, are likely to have to follow India’s example.

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44.3.2 Transmission and Gear Oils The majority of developments with automotive gear and transmission fluids occur in North America, primarily because of the huge use of ATs in this market. These developments have impacted the market in Europe, and are starting to impact the Asian market. The overwhelming majority of transmissions in Asia are manual gearboxes and conventional hypoid rear axles, which use standard API classes of gear lubricants. The majority of conventional automotive gear oils in Asia are API GL-4 or GL-5 quality. Fully synthetic SAE 75w90 and 75w140 viscosity grade gear oils are now being sold in China and India. These products have been available in Japan, Singapore, and South Korea for many years. The Japanese automotive transmission market is markedly different from the rest of Asia, in that 63% of transmissions were ATs in 2001. Continuously variable transmissions (CVTs) accounted for 18% of the market and MTs accounted for the other 19%. The market is forecast to change further by 2010, with ATs declining to 50% of the market, CVTs increasing to 38%, and MTs declining to 10%. The remaining 2% is forecast to be dual clutch transmissions (DCTs). The world’s largest manufacturer of ATs is Aisin Seiki. Most car manufacturers are now promoting the concept of “filled-for-life” ATs, to increase customer satisfaction, and to assist with further improving vehicle fuel economy. This is derived from “shudder-free” torque converter clutches and stable automatic transmission fluid (ATF) friction characteristics. The demand for “filledfor-life” will require significant improvements to ATFs. Anti-wear requirements will need to last for 100,000 to 150,000 mi, the oils will need to have exceptional high temperature viscosity properties combined with good low temperature fluidity properties and high shear stability in pump and clutch tests. Obviously, foaming resistance, air

entrainment, and material compatibility (elastomers, bearing materials, and friction materials) will need to be at least as good or better than how it is currently. As a result, there will be a heavy dependence on baseoil properties, which probably means the use of Group II or III baseoils, PAOs, and esters. Ford’s activities toward a MERCON-V specification have continued. ATFs to meet the requirements were trialed in Europe in 1996 and in 1997 in North America. Primary service fill of MERCON-V began at the end of 1997. Although Chrysler has delayed work to develop a new ATF, they are now recommending against the use of any fluids that do not meet their MS7176D specification. It is possible that Chrysler’s new MS9602 specification will be introduced later this year. Following the expenditure of around $3 million by GM and the additive companies on new DEXRON-IV oils, this development has been suspended due to the cost of the ATFs that met the target performance levels. New, lower performance, targets were prepared in 2001 and GM announced the start of DEXRON-III “H” licensing in April 2003. The new performance limits require ATF formulators to use Group II and/or II+ baseoils in the new fluids. The requirements for the next GM ATF are broadly the same as those demanded by Ford and GM’s main service fill will continue to be DEXRON-III until DEXRON-IV is ready, which may now be quite some time in the future. The AAM and JAMA are working toward the standardization of ATF tests. However, it appears that there will not be an ILSAC ATF specification, due to differing friction properties required by different OEMs. One aspect of the current activities is a program to assure customers that they are using the correct ATF in their transmission. Fluids for use in CVTs were developed using factory fill ATFs as a starting point, although a standardized friction test, for determining traction coefficients, still has to be agreed. Many CVTs now use specialized traction fluids, of which Santotrac and Shell are the main suppliers. In Japan, Honda, Toyota, and Mitsubishi have developed CVTs and fluids for use in them. Advanced CVTs, which usually incorporate a lock-up torque converter, appear to be the favored new transmission system solution in Japan for engine sizes up to 2 L. Nissan also claimed to have made significant progress with a split-path toroidal transmission for more powerful vehicles. Engineering opinion is that a CVT coupled with an integrated engine/transmission electronic control unit will become essential if the engine is to be run at high efficiency most of the time, thus reducing fuel consumption and CO2 emissions.

44.3.3 Other Automotive Oils Developments in Asia with other automotive oils, such as brake fluids, shock absorber oils, and air-conditioning

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system oils, are influenced mainly by developments in the United States and Europe. The majority of specifications are those recommended by the SAE and API. Even now, brake fluids that meet the DOT 3 specification tend to be marketed rather than those meeting the newer DOT 4 and DOT 5.1 specifications, although the latter are available in the more progressive markets in Japan, Korea, Hong Kong, Singapore, Australia, and New Zealand. Air-conditioning in cars is relatively rare, but is increasing in Australia and Japan.

44.4 DEVELOPMENT OF MARKETS FOR SYNTHETIC AUTOMOTIVE FLUIDS IN ASIA As in all markets, the growth in lubricant demand in Asia follows the general pattern of economic development. In 1995, lubricant demand growth in Asia averaged 5.0%, but by 1997 it had slowed to 4.1%. It picked up to average 4.5% in 2000, but in 2003 it had slowed again, to an average of 3.8%. Even so, this demand growth was considerably higher in 2003 than in Western Europe and North America, which both recorded declines of 0.1% in lubricant consumption. Asia overtook North America in 1999 to become the largest lubricants market. Asia’s share of the global lubricants market was 29.7% in 2003, compared with North America’s share of 23.8% and Western Europe’s share of 13.3%. At present, although synthetic lubricants represent only around 1% of the total market in Asia, the prospects for synthetic automotive lubricants remain optimistic. There are several reasons for this optimism: • Increasingly stringent emissions regulations and envi-

ronmental concerns will promote the use of greater fuel efficiency and higher equipment performance, particularly with gasoline and diesel engines. Many of the recent improvements seen in Europe and North America have been contingent upon higher performance lubricants, including synthetics, so these are also likely to be required in Asia and other developing regions. • Global competition in all industries is likely to promote the adoption of global standards of best practice in manufacturing and services. In order for Asian companies to continue to compete in global markets, their use of the latest technologies will need to grow. This includes the use of synthetic and part-synthetic lubricants in those applications in which mineral oils have demonstrated performance limitations. • The emerging speciality chemicals industries in Asia are likely to identify and exploit opportunities to produce and export synthetic lubricants to other markets in both developed and developing regions. • Even following the economic turmoil experienced in 1997/1998, the majority of people in Asia still aspire to the living standards and mobility of the developed

countries, so development will continue. As a result, the progressive adoption of European and North American patterns of goods and services, including synthetic lubricants, is likely to continue, albeit possibly at a slower pace than in recent years.

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Indeed, the most positive outcome of the events of recent years in Asia has been the increasing realization by governments, companies and individuals of the global nature of the world economy and the need to develop and adopt global standards and practices.

45

Automotive Trends in South America R. David Whitby CONTENTS 45.1 Introduction 45.2 Trends in the Automotive Industry in South America 45.2.1 Manufacturers and Competitive Forces 45.2.1.1 Production of Vehicles in South America 45.2.1.2 Imports and Exports 45.2.1.3 South American Vehicle Manufacturers’ Trends and Prospects 45.2.1.4 Suppliers of Components to the South American Automotive Industry 45.2.2 South American Automotive Design and Engineering 45.2.3 South American Automotive Vehicle Regulations 45.2.3.1 Safety 45.2.3.2 Environment 45.3 Current Status of Automotive Fluids in South America 45.3.1 Gasoline and Diesel Engine Oils 45.3.2 Two-Stroke Oils 45.3.3 Transmission and Gear Oils 45.4 Development of Markets for Synthetic Automotive Fluids in South America

45.1 INTRODUCTION Following a period of good economic stability and growth in the mid-1990s, many countries in Central and South America have experienced relative economic instability and low or negative growth over the last four or five years. The previous growth had been due to much stronger structural foundations, demonstrated by progressive economic growth before the Mexican financial crisis in the early 1990s and relatively rapid stabilization following it. Structural reforms, such as reduced public spending, privatization, increased foreign investment and reduced tariffs, stimulated strong economic growth between 1991 and 1994. The benefits were reduced inflation, increased foreign capital inflows, decreased national debt, and rising value-added exports. Unfortunately, the previous economic growth in many countries in Central and South America had been financed with high, and in some cases unsustainable, levels of foreign debt. In the aftermath of the financial crisis in Asia in 1997 and 1998, attention inevitably turned to debt levels in other countries. The countries most affected in South America were Argentina and Brazil.

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Growth started to slow in Argentina in 1998 and unemployment started to rise, mainly due to the effects on export markets following the Asian crisis. The situation worsened in 1999, with deflation around 2%. There were frequent violations of the Mercosur trade rules in 1999 by both Argentina and Brazil, the two largest members of the trading block. In 2000, the Argentinean recession continued and unemployment reached more than 15%. Toward the end of 2001, the government suspended repayments of Argentina’s $132 billion foreign debt and in 2002, the economy collapsed, with unemployment reaching 22%, gross domestic product (GDP) down by 11.5%, inflation at 50%, and the $:Peso exchange rate going from 1 to 0.27. Although debt restructuring talks were held with the International Monetary Fund (IMF), the banking system collapsed and the government and most companies were unable to repay any debts. Personal savings fell by an average of between 30 and 40%. The economic situation was stabilized by the government during 2003, after much political and social upheaval, and the Argentinean economy began to grow again.

While the economic situation in Brazil was not as bad as in Argentina, it was not that much better either. By 1998, the country had built-up a large budget deficit and the danger of a financial meltdown became apparent in 1999. The Real was allowed to float after one of the State governments initiated a moratorium on debt repayment and the resulting currency devaluation required taxes to be raised, expenditure to be cut, credit to be tightened, and interest rates to be increased. The political and economic problems escalated during 2000, with average per capita income falling by 5.5%. Brazil has had much lower growth rates than previously during 2001, 2002, and 2003, although the austerity measures now appear to be working. There was considerable uncertainty among foreign investors in Brazil’s abilities to repay debt and with the volatile exchange rate during most of 2001 and 2002. Central and South America’s problems were compounded further by the ongoing insurgency and war on drugs barons in Colombia, political turmoil in Venezuela, recessions in Chile in 1999 and in Peru in 2000 and 2001, and severe economic problems in Paraguay and Uruguay from 1999 to 2002. Peru also experienced severe political turmoil in 2000, when riots led to the (eventually) peaceful overthrow of the government. Chile largely weathered the economic crises in neighboring Argentina and Brazil, but has had lower than normal growth rates in 2001 and 2002. While several countries were poised to provide growth opportunities for vehicle manufacturers and lubricants suppliers, this did not occur between 1999 and 2003. With economies in recession, uncertainty about employment prospects, higher taxes, and tighter credit, the last thing consumers wanted to do was buy new cars and companies were reluctant to spend money on new trucks. Some of the economic pain was mitigated by the two important trading blocks; Mercosur (Brazil, Argentina, Paraguay, Uruguay, and Chile) and the Andean Pact (Venezuela, Colombia, Bolivia, Peru, and Ecuador) are the major trade alliances. Both blocks offered some support foundation industries and dampened short-term disruptions in a number of countries. The intraregional trade agreements gave way to a more balanced common market structure modeled after Europe and reduced tariffs helped to minimize marketers’ supply costs. With the economic, political, and social problems in Central and South America, it is not very surprising that the region had the slowest growth of all regions from 1998 to 2002 in the numbers of cars, trucks, and buses in use. Data for the region, together with those of other regions for comparison, is shown in Table 45.1. While global growth in the number of cars was 11.6% during the period, in Central and South America it was only 4.9% compared with 18.4% in Asia. Growth in the number of trucks and buses in Central and South America was only 4.7% during the period. The total numbers of cars, trucks, and buses in

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TABLE 45.1 World Vehicle Population, 1998 to 2002 Number of vehicles in use (million) Region Cars W. Europe C. & E. Europe N. America C. & S. America Middle East Asia Africa Oceania

1998

1999

2000

2001

2002

169.0 49.2 147.9 26.4 12.6 74.1 10.1 9.8

171.4 51.4 148.4 26.4 12.6 78.8 10.2 10.1

176.9 54.6 150.1 26.9 13.0 81.6 10.2 10.3

181.9 55.7 156.7 27.1 13.2 84.9 10.4 10.4

187.0 56.8 163.1 27.7 13.7 87.7 10.5 10.5

Total cars Trucks and buses W. Europe C. & E. Europe N. America C. & S. America Middle East Asia Africa Oceania

499.1

509.3

523.5

540.3

557.0

23.1 15.2 86.6 8.6 5.2 36.6 4.4 2.7

23.4 15.1 86.7 8.7 5.3 39.8 4.4 2.8

24.0 14.3 90.6 8.8 5.4 40.5 4.4 2.9

25.3 14.9 94.1 8.9 5.5 41.2 4.5 2.9

26.6 15.6 97.5 9.0 5.6 41.8 4.6 3.0

Total trucks and buses All vehicles W. Europe C. & E. Europe N. America C. & S. America Middle East Asia Africa Oceania

182.42

186.2

190.9

197.3

203.6

192.1 64.4 234.5 35.1 17.76 110.63 14.5 12.6

194.8 66.5 235.1 35.1 17.9 118.6 14.6 12.9

200.9 68.9 240.6 35.7 18.4 122.2 14.6 13.1

207.2 70.6 250.8 35.9 18.7 126.1 14.9 13.3

213.7 72.4 260.6 36.7 19.2 129.6 15.0 13.5

Total vehicles

681.5

695.4

714.4

737.6

760.6

Source: Pathmaster Marketing, from various industry sources.

each of the major countries in the region, in 1998, 2000, and 2002 are shown in Table 45.2.

45.2 TRENDS IN THE AUTOMOTIVE INDUSTRY IN SOUTH AMERICA 45.2.1 Manufacturers and Competitive Forces 45.2.1.1 Production of vehicles in South America Brazil and Argentina dominate the production of cars, trucks, and buses in Central and South America, as shown by the data summarized in Tables 45.3 and 45.4. Between 1998 and 2002, the production of cars in Central and South America (Table 45.3) changed very little. There was a sharp fall in 1999, followed by a recovery in 2000 and 2001. However, total production in 2002 was again below that in

TABLE 45.2 Central and South American Vehicle Population, 1998 to 2002 Number of vehicles in use (million) 1998

2000

2002

Total

Cars

Trucks and buses

Total

Cars

Trucks and buses

Country

Cars

Trucks and buses

Argentina Brazil Chile Colombia Ecuador Panama Peru Puerto Rico Uruguay Venezuela Others

5.05 12.70 1.28 0.78 0.47 0.21 0.68 0.88 0.50 1.53 2.35

1.50 2.89 0.67 0.66 0.05 0.08 0.39 0.19 0.05 0.55 1.60

6.55 15.59 1.95 1.44 0.52 0.29 1.07 1.07 0.55 2.08 3.95

5.15 12.90 1.34 0.76 0.46 0.22 0.70 0.89 0.51 1.56 2.40

1.55 2.90 0.72 0.67 0.06 0.08 0.41 0.20 0.06 0.56 1.62

6.70 15.80 2.06 1.43 0.52 0.30 1.11 1.09 0.57 2.12 4.02

5.31 13.40 1.40 0.77 0.46 0.23 0.72 0.89 0.51 1.60 2.45

1.59 2.91 0.74 0.68 0.06 0.08 0.42 0.20 0.06 0.58 1.64

6.90 16.31 2.14 1.45 0.52 0.31 1.14 1.09 0.57 2.18 4.09

Total

26.43

8.63

35.06

26.89

8.83

35.73

27.74

8.96

36.70

Total

Source: Pathmaster Marketing, from various industry sources.

TABLE 45.3 Production of Passenger Cars in Central and South America, 1998 to 2002

TABLE 45.4 Production of Vans, Trucks, and Buses in Central and South America, 1998 to 2002

Number of vehicles manufactured (thousand)

Number of vehicles manufactured (thousand)

Country

1998

1999

2000

2001

2002

Country

1998

1999

2000

2001

2002

Argentina Brazil Chile Colombia Ecuador Peru Venezuela Total

353.1 1254.0 2.8 17.8 — — 127.8 1755.5

224.7 1109.5 1.5 20.8 3.8 — 74.2 1434.5

238.7 1361.7 5.2 33.4 1.2 — 72.9 1713.1

169.6 1483.5 4.4 50.8 13.4 — 114.4 1836.1

111.3 1521.4 6.3 57.1 12.4 — 81.6 1790.1

Argentina Brazil Chile Colombia Ecuador Peru Venezuela

104.9 331.6 16.2 18.9 — 0.3 58.2

80.1 247.2 12.5 13.1 8.7 0.2 33.0

100.5 329.5 14.0 16.5 16.8 0.3 30.4

66.0 315.5 10.5 24.1 14.9 0.3 22.4

48.1 271.2 11.7 21.6 14.8 — 15.1

Total

530.1

394.8

508.0

453.7

382.5

Source: Pathmaster Marketing, from various industry sources.

Source: Pathmaster Marketing, from various industry sources.

2001. The pattern for manufacturing trucks and buses was even worse (Table 45.4), with a relatively steady decline from 1998 to 2002. Predictably, production of cars in Argentina fell dramatically during the period, while production of cars in Venezuela also declined, but not by as much. Production of cars in Brazil held up reasonably well, mainly due to a significant devaluation of the Real in 1999. This allowed exports of cars (and trucks) to be maintained from Brazil to other South American countries. The main manufacturers of cars in Argentina in 2003 were General Motors (GM; Chevrolet), Fiat, Ford,

Renault, Peugeot Citroen (PSA), Toyota, and Volkswagen. GM manufactures Chevrolet pickups in Argentina, both for the internal market and for export to other South American Countries. Toyota produces Hilux vans in Argentina, Mercedes-Benz produces light and heavy trucks, Chrysler manufactures pickups and Ford, Iveco and Renault also manufacture vans and trucks. Renault manufactures Clio, Kangoo cars and vans, and Megane cars in Argentina. The main manufacturers of cars in Brazil in 2003 were Volkswagen (VW), Fiat, GM, Renault, Honda, and Toyota. GM manufactures Celta, Corsa, Kadett, Ipanema, Vectra, and Omega cars, Corsa pickups and Crew Cab and Blazer

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trucks in Brazil. Most of these are sold within South America, although some are exported to the Middle East, South Africa and, most recently, Russia. The company has an assembly plant in Colombia, which imports complete vehicles and completely knocked down (CKD) kits from Japan, Brazil, Canada, the United States, Venezuela, and Chile. Cars are also assembled in Venezuela, for sale in the local market and for export to Colombia and Ecuador. Toyota sold 161 thousand cars and vans in Central and South America in 2003. The company manufactures Corolla cars and assembles engines in Brazil, manufactures Hilux vans and Land Cruisers in Colombia, and manufactures Corolla and Dyna cars, and Daihatsu Terios and Land Cruisers in Venezuela. PSA sold 108 thousand cars and vans in Central and South America in 2003, down 1% on sales in 2002. PSA is now producing Peugeot the 307 in Argentina and the 206W in Brazil. Honda now manufactures the Civic and the Fit, a new small car, in Brazil. Renault manufactures Clio and Megane cars in Brazil and Twingo, Clio and Megane cars in Colombia. The company also manufactures engines, engine subframes, disc hubs, and rear corner modules in Brazil and gearboxes in Chile, some of which are exported to Europe and Asia. Renault stopped making cars in Chile in 1999, having produced only 1100 vehicles in 1998. Sales of Renault vehicles, including Nissan and Samsung, in Central and South America amounted to 129 thousand in 2003, down from 131 thousand in 2002. Ford currently produces Fiesta and Ka cars in Brazil and Escort cars and Ranger vehicles in Argentina for the South American market. Ford has been struggling in Brazil for some time, having seen its market share decline from over 20% in 1985 to less than 5% in 2002. Until 1994, Ford had a manufacturing alliance, called Autolatina, with VW. The European company was the stronger partner and managed to weather the breakup, but Ford had uncompetitive products and an inferior dealer network. So far, only one vehicle manufacturer has attempted to integrate operations across the region as a whole. Fiat’s Project 178, the “world car” platform for its Palio, Weekend, and Siena models, is produced in Brazil, Argentina, and Venezuela, with assembly in Venezuela from kits exported from Brazil and Argentina. Development was carried out with local suppliers. For example, Cofap, a Brazilian maker of shock absorbers, piston rings, and exhaust systems, helped develop the models’ suspension units. Brazil, with a population of 174.6 million, has only one car per 13.0 people, compared with one car per 2.1 people in the United States. The main reason for the lower ownership level is Brazil’s relative poverty; GDP per head was $3,070 in 2001, compared with $34,280 in the United States. This should mean increasing car ownership as the economy recovers and consumers become wealthier. Argentina is

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almost as promising. Although its population is less than a quarter of Brazil’s, GDP per head was $7,460 in 2002 and the number of cars per person is 6.8. The largest truck and bus manufacturing countries in Central and South America are Brazil and Argentina, with smaller numbers of vehicles produced in Colombia, Venezuela, Ecuador, and Chile. Volkswagen, GM, Fiat, and Mercedes-Benz are the main manufacturers of commercial vehicles in Brazil. Scania and Volvo also manufacture heavy trucks in Brazil, for both internal sales and exports throughout South America, but Navistar decided at the end of 2002 to pull out of the Brazilian market, due to poor sales. VW’s newest truck and bus factory at Resende, near Rio de Janeiro, has had a capacity to make 40,000 vehicles a year from its start at the beginning of 1997, but is still not fully utilized. Scania launched its Series 4 range in South America in 1998, following its launch in Europe in 1997. MercedesBenz spent $20 million developing its Brazil Series of four trucks, introduced early in 1997 and designed to replace 14 older models. Production and sales of agricultural equipment in South America, which fell sharply in 1996, has not really recovered since, due to the economic problems that have plagued the region. Looking further ahead, it is possible that growth will be led by the economic stabilization program in Brazil and Argentina and long-term economic expansion. Only ten years ago, Brazil’s automotive market was the great hope of a global car industry experiencing painful downturns in Europe and North America. Sales of cars in Brazil increased by 51% in 1993 and by 24% in 1994. By 1997, 1.57 million cars were sold in Brazil, import tariffs were falling, foreign investment was being encouraged by the government, and many of the biggest car companies were racing to build more manufacturing capacity. According to Brazil’s motor industry trade association, more than $30 billion has been invested in car plants since 1995. In 2003, many Brazilian car plants were operating at less than half capacity and thousands of employees were either on compulsory holidays to keep production down or had been made redundant. In August 2003, VW announced plans to lay off almost one in six of its 25,000 employees in Brazil. GM had earlier laid off 650 of its 18,800 employees. Total car manufacturing capacity in Brazil is currently 3.2 million units, but only 1.52 million were produced in 2002, fewer than in 1997. However, the beginnings of a recovery have started to appear. More than 1.42 million vehicles were produced in Brazil the first 8 months of 2004, up 21.3% on the same period in 2003. The Brazilian National Association of Automotive Manufacturers said August 2004 was also a record month for automotive exports, defined as parts, cars, light trucks, and farm tractors. They totaled more than $773 million for August and $5.14 billion since the beginning of the year, up 54%. Only time will tell whether

these trends continue and spread to other countries in the region. 45.2.1.2 Imports and exports In 1995, members of the Mercosur free trade area set duties of 70% for vehicles imported from outside the area and duties of 2% for imported parts as part of an agreement on policies for the motor industries in Brazil and Argentina. Vehicle manufacturers operating in the two countries, however, are allowed to import vehicles at half the set rate. Since 1995, duties on imported vehicles have fallen to the target of 20% in 2000 and duties on components have risen to the Mercosur common external tariff of about 14%. Dual vehicle manufacturing in Brazil and Argentina has become the industry norm, with Argentina tending to be used for higher value, lower volume products and Brazil for bigger volume, “popular” models. A similar regime was agreed in 1993 between Colombia, Venezuela, and Ecuador. Duties on vehicle imports from outside the three countries were set at 35% for passenger cars and light commercial vehicles and at 15% for trucks. Duties on CKD components and kits were set at 3%. Local content requirements were fixed at an initial 30% for cars and light commercial vehicles, rising to 33% in 1998, and of 13%, rising to 18%, for heavy trucks. Components manufactured inside the bloc are treated as local content in all three countries. Intracountry trade in vehicles and components has become a standard practice throughout South America in the last 5 years. The primary driver is to achieve economies of scale in manufacturing, so as to provide lower cost components despite the higher distribution costs. Fiat’s Palio models produced in Brazil are designed primarily to meet the demand of the markets of Central and South American countries. However, the three-door Palio is also exported from Brazil to Italy. Since the Palio range is part of Fiat’s World Car Program, although Brazil is the initial and major hub of Palio production, specific models and parts belonging to the range are also produced in Argentina, Poland, Turkey, Egypt, Morocco, South Africa, India, and Vietnam. According to Fiat, certain Palio models are also to be manufactured in China and Russia in the near future. While the Betim plant manufactures all models within the Palio range, India’s Palio production, for example, focuses entirely on the hatchback and sedan varieties, while Palio production in Vietnam concentrates on just the sedan model. Since all elements of the Palio range produced in Brazil are interchangeable with those produced in Fiat’s other global Palio plants, there is a continual flow of products between Palio facilities worldwide. This therefore gives Fiat do Brasil the opportunity to expand its export potential by producing additional units of certain Palio elements to be fitted to Palio vehicles produced elsewhere.

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For example, extra units of parts belonging to the estate car version of the Palio, known as the Palio Weekend, are produced at Fiat’s Betim plant to then be fitted to the Weekend produced in Poland. From Poland, the model is then exported to Italy, France, Germany, and Spain. General Motor’s Celta model is aimed specifically at the South American market, with its major export destinations being Argentina, Bolivia, and Venezuela. In October 2001, GM began to export the Celta to El Salvador, placing the car on the Central American market for the first time. The car is now being exported to other Central American countries, including Guatemala and Honduras. General Motor imports Isuzu light trucks into South America from Japan. GM also transfers cars, pickups and medium-sized trucks from Brazil to Argentina and Chile and imports CKD kits and cars from the United States, Japan, and Europe. The company imports engine parts and other components from the United States, Germany, and Spain into Brazil, for use in the production of cars, pickups, and trucks. Transmissions are imported from Japan and Austria. The company also exports engines from Brazil to Germany and the United Kingdom. Brazil exported $1.29 billion worth of automotive products, which cover both vehicles and component parts, to the United States in 2002, and another $1.16 billion worth to Mexico. Argentina also exported $270 million of automotive products to Mexico in 2002. In total, Central and South America exported automotive products to other regions of the world to a value of $4.93 billion in 2002. In July 2004, the Argentinean government approved an agreement made between local car manufacturers and automotive parts suppliers to limit the value of imported components used to assemble vehicles in Argentina to no more than 40% of the value of the vehicle. 45.2.1.3 South American vehicle manufacturers’ trends and prospects 1996 was a record year for automotive industry spending in South America. VW, the largest car manufacturer in the region, opened two new car plants in Brazil in the last quarter of the year. The company commenced construction in November 1997 of a new $650 million factory in southern Brazil to produce the Audi A3, the new Golf, and Passat. Production of cars, which started in 1999, was planned to rise to a total of 250,000 units, but has not exceeded even half of that to date. Fiat, the second biggest car manufacturer in South America, invested about $1 billion to increase car production in Brazil and to launch the company’s Palio “world car.” It also spent $600 million on a new car factory in Argentina. General Motor, which ranks third behind VW and Fiat in Brazil, spent $1.25 billion on three new plants for cars, components, and engines. The company built a $600 million plant at Grazatai, in Rio Grande do Sul state.

At the same time, Ford invested about $800 million to manufacture its European Fiesta in Brazil, $300 million on a new engine plant in Brazil, and $150 million to modernize its truck plant. Mercedes-Benz announced in July 1997 a 70,000-unit capacity $400 million plant in the state of Minas Gerais to build its A-class model subcompact car. The plant started production towards the end of 1999. General Motors opened its new Brazilian car manufacturing plant, designed to be a benchmark for GM plants elsewhere, in Gravatai in July 2000. The factory manufactures it’s new compact car, the Chevrolet Celta, which competes against VW’s Polo and Fiat’s Mille Smart in the 1-L-engine car market, which accounts for about 65% of Brazilian-made domestic car sales. The Celta is several inches smaller than the lowest-priced GM model, the Opel Corsa. GM plans to also export the car to Europe, Mexico, and Brazil’s Mercosur trading partners Argentina, Paraguay, and Uruguay. General Motor aims to use the plant and the Celta as guinea pigs to test the new factory model, which cuts expenses through ultraswift deliveries of components and increased automation. The plant, located in a new industrial park in the southernmost state of Rio Grande do Sul, is flanked by 16 car-part suppliers who can move their brake and light fittings, air filters, or security systems to GM’s assembly floor in a matter of minutes, slashing storage and inventory costs. The Gravatai industrial park arrangement reduces the number of suppliers GM needs to put a car together by 60%. Gravatai is also GM’s most automated plant in the world with 120 robots and an installed capacity to produce 120,000 vehicles. If the project is successful, GM plans to take the factory model elsewhere, although the company recognizes that it will be difficult to copy and apply to already-existing manufacturing plants. In May 2000, Renault and Nissan announced a broad cooperation agreement in South America’s Mercosur trade bloc, which includes Nissan vehicle production at Renault’s plant in Brazil. Nissan will invest a total of $300 million in the region by 2005 to manufacture five Nissan models with Renault support. Manufacturing, sales, and purchasing operations in Mercosur will be linked, with hopes of gaining a 15% market share in the world’s third largest trade bloc in the next 10 years. Nissan invested $90 million in the first project involving the production, starting early in 2002, of new Frontier pickups at Renault’s existing plant in southern Parana state. In 2003, Nissan started producing Xterra sports utility vehicles at the Brazilian plant. Three other products to be launched are still in the development stages. The two companies want to sell a minimum 150,000 Nissan vehicles by the year 2010 with Renault support. The Nissan–Renault alliance created 600 jobs directly and another 3,000 indirectly through its new operations, mainly in Brazil. Renault’s plant already had a production capacity of 200,000 vehicles per year, producing Clio and Scenic

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models since 1998. The plant also makes 280,000 engines a year. The alliance’s plant also makes Renault’s light commercial vehicles. It should produce 50,000 vehicles a year. In Argentina, Renault is producing a wide range of vehicles at its Santa Isabel plant with an annual capacity of 130,000 units. In Uruguay, Renault makes 10,000 cars a year. As part of Fiat’s global car strategy, it has focused heavily on the development of the small, economy car. Since the Brazilian market is primarily concerned with entry-level passenger cars, and Fiat is one of the main manufacturers in South America, Brazil was chosen by Fiat as the launch pad for the Palio range of vehicles. Fiat has been manufacturing vehicles in Brazil since 1972 and began manufacturing the Palio in 1996, when the company redeveloped its existing factory in Betim. The plant’s programming and logistics computer is central to the way in which the facility is controlled, enabling the plant to be operated on a just-in-time delivery basis. Of the top ten cars sold in Brazil, four of them are of the Fiat brand. Of these, three are from the Palio family; the standard Palio, the Palio Weekend, and the Palio Siena. The range is managing to weather the storm due to the extent of its popularity on the domestic market. Fiat’s Betim plant has the capacity to produce approximately 30,000 units of the Palio range per year. The qualities of the Palio in terms of auto parts, technology, and design, are said to be regarded by Brazilian consumers as superior to those of other models. Fiat was forced to suspend 1300 employees in Argentina in 2000, following a decline in sales of over 25% compared with 1999. Fiat, which had to make the suspensions permanent in 2001, blamed the currency devaluation in Brazil, which is Argentina’s main trading partner and buyer of 90% of its vehicle exports. However, the company announced in March 2004 that it plans to invest heavily in Brazil in 2005 and 2006. Ford’s new assembly plant, Complexo Amazon, started production of its Amazon range of cars in April 2002 and the commercial launch of the five new models started later in the year. The new plant has the capacity to produce 250,000 passenger cars per year. The Amazon range of small, compact cars, is based on Ford’s global Fiesta platform. The cars have a Brazilian content of 90%, with 13 of the 23 major components suppliers working within Ford’s assembly plant itself, and the remaining 10 based in the adjoining supplier park. However, despite the economic problems endured by Brazil toward the end of 2001, GM still managed to increase its production of the Celta and continued to do so during 2002. The Celta model is GM’s best-selling car in Brazil, accounting for approximately 25% of the company’s Brazilian sales. According to GM do Brasil, the company is likely to begin producing another economy-sized car in the country within the next 2 or 3 years. The company is also set to

increase its exporting operations for other economy cars that it produces in Brazil. For example, GM has recently started exporting Corsas from Brazil to Egypt, in the form of CKD kits. The devaluation of the Real in 1999 served to encourage GM and Ford to invest in Brazil. The country’s financial crisis helped to lure investment, as international manufacturers recognized the opportunity to benefit from the relative strength of their currencies. Manufacturers chose Brazil as the major production base for economy models over other countries in the region partly as a result of its comparatively cheap production costs. GM’s Gravatai and Ford’s Camacari plants were established when the Argentine Peso was still pegged to the U.S. dollar, making Argentine production far more expensive. Both Ford and GM appear to be willing to be patient about their investments in South America, prepared to wait several years if necessary for their manufacturing plants to become profitable. However, some industry analysts have begun to question whether Ford may eventually be forced to quit production in Brazil if profitability does not return soon. By the time GM’s Gravatai plant opened in September 2000, Brazil’s economy had made a comeback and, as the largest economy within Mercosur, prospects were excellent for vehicle makers to experiment with new manufacturing techniques. Since Brazil has a much longer history as a vehicle manufacturer than some of the other Latin American countries, such as Chile and Venezuela, it has the infrastructure in place to aid the transportation of vehicles to market, and it also has a ready supply of components suppliers. Moreover, Brazil has remained accessible to car manufacturers looking to test new methods, since its industry has greater freedom to absorb change than the more mature industries of Europe. Union opposition to new working arrangements is, although currently on the increase, still far lower in Brazil than it is in countries such as the United States and Mexico. With Brazilian demand tending toward the small, economy passenger car, Brazil has been a logical place for automakers to test new entries to this segment of the market. Since the rate of auto tax that consumers pay depends on the size of the car, vehicle makers such as Ford, Fiat, and GM have better prospects at the smaller end of the market. While Brazilian vehicle demand does focus heavily on small, compact cars, this may become less noticeable over time, for the fashions of the affluent classes tend to be guided by U.S. and European trends. The number of SUVs purchased for private use in Brazil increased slightly in 2005, but only amongst the rich minority. Volkswagen has been manufacturing cars in Brazil since 1953 and the country is VW’s second largest market, after Germany. Brazil accounts for almost 10% of VW’s worldwide production of cars and trucks. The history of its cars and its industrial plant in São Bernardo do Campo

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meshes with Brazil’s modern history, with a good part of the economy of the State of São Paulo over the last decades driven by its presence. In the last decade, VW opened new plants in Brazil and Argentina. In November 1995, the company opened the General Pacheco Industrial Centre in Argentina. A year later, in November 1996, it opened a new truck plant in Resende and an engine plant in São Carlos, the latter being enlarged some months later for the production of engines for the Golf and Audi A3 models. In January 1999, the company opened the plant in São José dos Pinhais, in the State of Paraná, with a total investment of 1.2 billion Reals. Over a history of almost 50 years in Brazil, VW has always pursued technological evolution and improvement of its products. The company’s Product Engineering and Development Department has some 1500 engineers, designers, and specialists capable of designing and producing world-class vehicles. The engineering facilities include a vehicle impact center where all of its vehicles manufactured in Brazil are crash-tested. With a total of around 28,000 employees, VW is one of the largest private companies in Brazil and one of the largest employers. The average production capacity is 3,200 vehicles and 2,850 engines everyday in its five manufacturing plants in Brazil. In 2002, VW entered a new stage of production, with its new Nova Anchieta plant, one of the world’s most modern manufacturing centers. Located in the city of São Bernardo do Campo, the plant has undergone a full refurbishing as a requirement for the production of the new Polo. The manufacturing line has 400 new robots and is fully computerized. However, VW took a charge of e120 million in 2003 to cut 4000 jobs in Brazil. The company had initially indicated that it would retrain the employees, but later decided to offer a voluntary redundancy program. Other car manufacturers have also lost substantial amounts of money after rapid building of car plants left the country with massive overcapacity. Then, in September 2004, VW announced plans to manufacture a van derived from the Fox car, in Argentina, with sales starting in 2006. The Fox van marks VW’s entry into a new market segment, to compete with GM’s Meriva and Fiat’s Idea vans. Honda started production of the Fit, a new subcompact car, in Brazil in 2004. The company is promoting the new car as offering innovative safety and environmental features, in addition to excellent power and fuel consumption, excellent driving performance, and outstanding comfort. Peugeot Citroen is seeking to expand sales in the Mercosur markets, particularly Brazil and Argentina, in addition to plans for expansion in Central Europe, Turkey, and China. The company started manufacturing Peugeot 307 cars in Argentina in 2004 and in September 2004, it announced plans to produce Citroen C4 cars in Argentina by 2007.

Toyota forecasts steady demand for vehicles in Brazil for the foreseeable future. In May 2004, the company announced that it is to start selling the Corolla-based Fielder station wagon in Brazil. The model is produced at the company’s Indaiatuba plant in São Paulo state, where the Corolla sedan has been manufactured since 1998. There is no doubt that the last 5 years have been very tough for all automotive manufacturers in South America. In addition to the economic, political, and social turmoil, the overcapacity to produce both vehicles and components has meant that almost every company has lost money. The next 5 years may prove to be equally tough, until the economies of each of the countries, particularly Brazil and Argentina, continue to stabilize and rebound. The weaknesses in vehicle manufacturing in North America and Western Europe are unlikely to help either. 45.2.1.4 Suppliers of components to the South American automotive industry As manufacturing methods in South America become more similar to those in the rest of the world, factories there can supply parts and vehicles to ever wider markets. Brazil is already the industry’s main, though not only, manufacturing base for South America. Manufacturers already swap some parts between factories in Brazil and Europe, for example. As this trend continues, Brazil’s role in the region should be strengthened. Several vehicle manufacturers believe Brazil is the precise choice for manufacturers setting up in the region, simply because it offers the biggest single market. The development of the Mercosur customs union between Brazil, Argentina, Paraguay, and Uruguay should also strengthen Brazil’s role, although the union will take time to mature. Brazil has been used as an experimental zone by several major vehicle manufacturers in recent years, specifically with regard to the development of small-car manufacturing techniques. GM, Ford, and Fiat Auto have all established notable small-car production facilities in Brazil and all three have promising prospects, despite the country’s economic difficulties. The efficiency of the plants in terms of manufacturing looks set to boost the market share of these three automakers within Brazil, while at the same time giving Brazil the opportunity to expand its export markets. This, in the longer term, should set Brazil up as a specialist in small-car production. Ford’s experimental Amazon project and GM’s Gravatai complex have led major manufacturers of both vehicles and components to look to Brazil with interest. Projects such as these have demonstrated how components suppliers can play a far greater role in the vehicle manufacturing process than they do in traditional assembly arrangements. The proportion of components that can be manufactured on-site has reached unprecedented levels and therefore far fewer suppliers are required now. Meanwhile,

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Fiat’s Betim plant, although built some 23 years before the others, has captured the world’s attention in recent years, for the way in which the automaker used Brazil as a test-bed to produce its Palio models in 1996. At each of these plants, the focus is on the cost-effective production of small, entry-level passenger cars. General Motor’s Gravatai plant has changed the relationship between vehicle makers and components suppliers, since the role of the supplier has been wholly integrated into the design of the car plant itself. The model currently produced at Gravatai is the Celta, produced since September 2000, with as much as 85% of its components manufactured on-site. In most assembly plants, only 40% of components (in terms of value) are sourced from within the factory. This gives GM greater flexibility, enabling it to adapt certain features of the Celta according to customer preference. As a result of the close integration between manufacturers and components suppliers and the proximity of major suppliers to the assembly lines, these three plants are highly efficient and have the potential to reduce the cost of manufacturing small cars in Brazil significantly. This in turn enables the cars produced to be competitively priced on the domestic market, giving the car makers the opportunity to boost domestic market share. Through the launch of the Amazon line of cars, for example, Ford intends to increase its market share in Brazil from 9 to 14%. With Brazil’s interest rates being characteristically high, it is expensive for automakers based there to obtain credit and this subsequently pushes up the price charged to the consumer for the finished vehicle. If car manufacturers are able to cut production costs, as they are able to do at these new, innovative plants, their ability to price the cars competitively increases. GM claims that the GM Celta is sold at approximately US$500–1000 cheaper than many other small cars sold on the Brazilian market. Since GM itself covers all freight costs within Brazil with regard to the Celta model, the car can be sold for the same price throughout the country, boosting sales in the northeast, for example, far from the industrial center of Sao Paulo. In a climate of intense global competition, increasing car prices and falling sales, a reduction in output costs also gives these automakers the opportunity to increase their share of the small-car export market. Supported by the availability of a relatively cheap labor force, as well as infrastructure that is sufficiently developed to allow vehicles to be easily exported, these new plants in Brazil are able to stand as major low-cost production centers, from which vehicles can be directed primarily toward the markets of other developing countries. Small-car manufacturing is likely to take off further in Brazil in 2002 and to an even greater extent in the long term, since the country has already gone some way toward gaining a reputation as a global small-car specialist. Not only does Brazil look set to build on this reputation

in the coming year, with the production of the Amazon car, but also some of the manufacturing systems used at plants such as Gravatai are likely to be emulated elsewhere. There are already signs that the less controversial aspects of GM’s Gravatai methods have influenced the style of GM’s new Lansing River Plant in Michigan (US). The T-shaped assembly line of Gravatai is to be replicated and the components produced at the Michigan plant are to be codesigned by GM and the components suppliers. Aside from boosting its position as a small-car expert during 2002, Brazil is likely to witness an increase in the role played by components suppliers in the production of larger vehicles in the long term. VW has already demonstrated that this is possible, through its innovative truck plant in Resende. Although the parts are manufactured offsite, they are installed into the trucks by the components suppliers themselves, rather than by VW. The influence to be had by the small-car test-beds has only just begun. Many of the world’s largest suppliers of automotive components have plants and operations in Brazil, Argentina, Chile, Colombia, and Venezuela. Dana operates a new axle-housing manufacturing plant in Sorocaba, Brazil, which recently received a best in class award for technical innovation from DaimlerChrysler Brazil. The plant also houses Dana’s Traction Technology Group, which produces axles for manufacturers of small and fullsize pickups and light trucks, including GM, Ford, and VW. Dana’s Commercial Vehicle Systems, part of Heavy Vehicle Technology and Systems Group, designs, manufactures, and markets front-steer, rear-drive, trailer, and auxiliary axles; driveshafts; steering shafts; brakes; suspensions; and related systems, modules, and services for the commercial vehicle market. Major components and modules are marketed under the Spicer® brand name. Eaton has three plants in Brazil that supply transmissions, axles, and engine air management systems. The company’s Brazilian Transmission Division resulted from the acquisition of Equipamentos Clark, an automotive transmissions manufacturer with a 90% share of the domestic market, in 1996. Components manufactured by Eaton in Brazil are also exported to the United States, Argentina, Mexico, and Turkey. Denso, the world’s third largest components supplier that was originally part of Toyota, now has manufacturing plants in 28 countries outside Japan, including most countries in Asia, the United States, Mexico, Brazil, Argentina, most countries in Western Europe, Hungary, Poland, the Czech Republic, Saudi Arabia, and Turkey. The company supplies engine cooling systems, air-conditioning systems, diesel common rail systems, alternators, starter motors, spark plugs, antilock brakes, power steering and navigation systems. Denso plans to build 15 million vehicle air-conditioning units by 2005, which represents 30% of the world market, as a result of expansion in Europe.

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Delphi has a manufacturing plant in Brazil to supply the South American market with systems and modules. The company is one of the world’s major suppliers of automotive components, with 171 plants located in North America, South America, Europe, Asia, the Middle East, and Africa. Delphi designs, engineers, and manufactures a wide variety of components, integrated systems, and modules on a worldwide basis and claims to be the largest and most diversified supplier of parts for cars, trucks, and buses. The company aims to provide vehicle manufacturers with a global, single-point sourcing capability, tailored to meet specific customer’s needs. Visteon has a total of six manufacturing facilities in Brazil and Argentina, making chassis components, power train components, electronics, heating and air-conditioning systems, glass, and vehicle interior and exterior components. The company has 205 facilities in 25 countries worldwide. Visteon is one of the key suppliers to Ford’s Amazon Project in Brazil, where it supplies electronics systems. Valeo is another global automotive components supplier with manufacturing facilities in Brazil and Argentina, as well as in 23 other countries. The company manufactures electrical and electronic systems (lights, wipers, switches, motors, actuators, connectors, sensors, and security systems) as well as air-conditioning and engine cooling systems, friction materials, and clutch systems. Other major suppliers to vehicle manufacturers in South America include Borg-Warner (gearboxes, transmissions), Bosch (spark plugs, injectors, electronics, wipers), Delphi (brakes, clutches, indicators, controls, sensors, injectors), Federal-Mogul (camshafts, seals, gaskets), Getrag (gearboxes, transmissions), INA (bearings), Magneti Marelli (electronics, injectors), Mahle (pistons), Siemens (motors, relays, sensors, controls), SKF (bearings), Valeo (brakes, clutches, switches), and ZF (gearboxes, transmissions). Several of these companies supply a wide range of components in addition to those listed. Additionally, there are hundreds of other companies that supply all the other components, such as glass, plastic, wiring, hoses, and lights.

45.2.2 South American Automotive Design and Engineering Design and engineering for vehicles manufactured and assembled in Central and South America is supplied primarily by parent companies in the United States, Europe, and Japan. While many car and truck design and engineering centers are located in Detroit, Frankfurt, Munich, Tokyo, and other major cities, the trend toward “global” vehicles by most vehicle manufacturers means that inputs to design and production specifications are also being made by local subsidiaries and component suppliers.

Additionally, because many of the bigger manufacturing plants now make vehicles for export as well as local consumption, there is a great deal of more emphasis than before on common design and engineering practices. Brazil and Argentina are no exception to these trends. When visiting most of the larger cities in Central and South America, it is relatively easy to see that the vehicle populations are a blend of comparatively up-to-date European and North American models, with a smaller proportion of Japanese and Asian models. Designs and engineering standards have become global and interchangeable. Since the South American car market is focused on smaller, entry-level cars, such as Fiat’s Palio and GM’s Celta, it is not surprising that some of the design and engineering concepts for these cars have been conceived and developed in Brazil. The result has been that Brazilian engineers and designers have worked with U.S. and European designers to refine and adapt some of the global influences to meet South American consumers’ needs. Another feature of the Brazilian market for cars is the need for vehicles that can run on either gasoline, diesel, natural gas, or ethanol. The Brazilian gasohol (ethanol fuel) program of the 1970s was dropped, but has recently been revived again. Alcohol-fueled cars conquered the Brazilian market in the 1980s, and represented more than 90% of car manufacturing within a few years. Cheap alcohol and expensive gasoline pushed this trend, but alcohol shortages in 1989 and 1990, together with cheaper gasoline, sharply undermined the popularity of ethanol. Sales of alcoholpowered cars plummeted to less than 1% of total vehicle sales. In 2002, VW and GM developed “bi-fuel” vehicles that can run on either gasoline or ethanol, or a mixture of the two. The bi-fuel car emerged because crude oil prices went up to over $25 per barrel, more than twice that of 1988. Dual fuel vehicles are also aimed at helping consumers to get past their hesitations about alcohol-only cars. Drivers are no longer subject to shortages or high prices of one fuel or the other, because they can always use the cheaper one. Additionally, the use of ethanol as a fuel or fuel component is being promoted as more environmentally responsible, since overall emissions of carbon dioxide are lower with the renewable fuel. There are no major differences in the emissions of unburnt hydrocarbons or nitrogen oxide from either fuel. The bi-fuel car may also allow Brazil opportunities to export vehicles, alcohol, and automotive technology. Several countries, including the United States, China, and Canada, already consume gasoline with alcohol added. There are nearly 2 million “flex fuel” cars in the United States, but they have to use a mix with a maximum of 85% alcohol, which means adding 15% gasoline. The bifuel engineering, which VW started developing in 1998, changes that restriction.

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Most recently, in October 2004, VW announced the development of a “tri-fuel” polo for the Brazilian market. This car can run on gasoline, ethanol, a blend of the two, or natural gas. The prototype model was presented to the São Paulo Auto Show at the end of October 2004.

45.2.3 South American Automotive Vehicle Regulations 45.2.3.1 Safety The safety standards applied to vehicles manufactured in South America are derived from those developed in North America, Western Europe, and Japan. The main reason for this arises from the export of vehicles, particularly cars, vans, and light trucks to countries outside South America and the manufacturing cost savings that result from having uniform designs and components irrespective of whether the vehicle is destined for the local or international market. There appear to be few South American government regulations that directly govern vehicle safety. Most governments appear content to follow U.S., Japanese, and Western European vehicle safety standards, assuming that manufacturers will adopt uniform standards for economic and business reasons. This approach gained momentum in October 2003 when executives from the world’s main carmakers agreed, at an automotive industry meeting in Japan, to push for global safety and environmental standards. 45.2.3.2 Environment Many of the countries in Central and South America are adopting either U.S. or European standards on the control of emissions of gases from vehicles, albeit more slowly than in the more developed regions of the world. Brazil and Chile have adopted U.S. regulations, while Argentina has opted for European regulations. The majority of regulations were adopted between 1992 and 1995, with slightly less stringent emissions limits being progressively tightened up to 2000. Since then, there has been little further tightening of the regulations in South America, due to the more pressing needs of stabilizing the regions’ economies, reducing unemployment and encouraging saving and investment. Catalytic converters became mandatory for new cars in Chile in 1992. Currently, well over half of all cars in Santiago, the capital city, are fitted with these emissions control devices. On days with “preemergency” pollution alerts, 40% of all cars without catalytic converters are banned from Santiago roads. It is, however, very unclear how this ban is enforced. Levels of air pollution required to trigger a “preemergency” alert include 285 µg/m3 for particulates. This compares with the current limit of 50 µg/m3 in the United Kingdom. Santiago was the first South American city to join the U.S. Department of the Environment “Clean Cities”

program in April 1997. The city authorities are working with their counterparts in Chicago, which has been a member of the program since 1994, to promote greater environmental responsibility. In Chile, the program, which is voluntary, focuses on increasing the use of alternative fuels such as LPG, LNG, and oxygenates. The Argentinean Secretariat of Natural Resources and Environment started a $4.5 million program in January 1997 to establish the precise nature of the pollution problems in Buenos Aires and other urban areas. The project involves a number of mobile air pollution monitors being used in both the capital and in the provincial cities of Cordoba and Rosario. Data from the monitors, together with data from a number of other sources, has been used to establish a national database on air quality. A local Argentinean environmental group, Fundacion Siglo 21, which has monitored air pollution in Buenos Aires, claims that carbon monoxide levels are double the acceptable WHO levels for more than half the time. These claims are dismissed by the authorities, although they do acknowledge that current controls on industrial and transport emissions are few and far between. The air quality problems of Buenos Aires are undoubtedly fewer than those of many other South American cities, such as Santiago and Sao Paulo, even though levels of emissions appear to be little different from these cities, because Buenos Aires enjoys favorable winds and rains that regularly sweep atmospheric pollutants out to sea. In Colombia, it was a requirement for all new cars to have catalytic converters be fitted to them from the beginning of 1998 onward. Although the government expected the total level of emissions from vehicles to decline rapidly, the reality of North American and European experience demonstrated that it has taken at least 5 years for the increasing number of vehicles fitted with catalytic converters to have a significant impact of total emissions, particularly when diesel engines continue to not be fitted with these devices. However, the Colombian government introduced regulations that require all inspection equipment for monitoring emissions and maintaining vehicles to be equivalent to current U.S. and European equipment from 1999 onward. It was reported at the end of 1996 that, at the time when compelling evidence of the damaging effects of excess lead on human health was being submitted to the first World Congress on Air Pollution in Developing Countries, a number of Central American governments were extending the use of unleaded petrol in their countries. A number of doctors had submitted detailed scientific evidence to the Congress of the deleterious effects of lead in the human body, and the degree to which high lead concentrations are transmitted from pregnant women to their unborn children. The evidence that lead poisoning is transmitted from mother to child was particularly worrying,

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because a child’s tolerance of high lead levels is far less than that of an adult. In response to the increasing evidence of the damage done by lead poisoning, most Central American governments introduced a formal prohibition on the use of leaded petrol in vehicles. Guatemala imposed a total ban on the use of leaded petrol in 1991, with the full support of the motor industry. Honduras banned leaded petrol in January 1996, Costa Rica in March 1996, and El Salvador and Nicaragua in July 1996. Evidence collected in the City of Tegucigalpa in Guatemala, indicated that within months of banning leaded petrol the amount of lead in the atmosphere dropped from 1.2 mg to just 0.2 mg/m3 . The small amount of lead still remaining in the atmosphere was attributable to the presence of a smelter. In areas without smelters, lead pollution has fallen almost to zero. Guatemala became the first country in the world to make a total change to unleaded petrol and, according to the government, there has been no evidence that any damage has resulted to vehicles in the country. Everyday in most of the larger cities in South America, millions of motorists are held up for hours in traffic jams caused by too many vehicles trying to squeeze onto too little space on the roads. The World Health Organization estimates that 100 million people in Central and South America have health problems related to the emissions. In response, in 1998, the World Bank established the Clean Air Initiative, creating a forum for politicians, environmental organizations, local businesses, and international companies to discuss the issues, identify the problems and causes of air pollution, decide on measures to combat it, and use money from development loans to implement practical measures. The main reason for the dirty air is that 70% of the air pollution is caused by vehicle emissions, which explains why the primary goals of the Clean Air Initiative include cleaner fuels, environment-friendly engines, and promoting public transportation. In Brazil, DaimlerChrysler has set up a Center of Competence for the production of gas engines. The exhaust emissions from these engines are up to 50% lower than those of the diesel engines currently in use. In addition, over 300 DaimlerChrysler gas-powered buses are being used in São Paulo, the largest city in Brazil. Since the subway network in São Paulo is not very extensive, buses are the most important means of getting around. The fastest route from A to B is via the corredores in the middle of the road, which are allowed for the use of only express buses. To keep all the other 5 million vehicles out, the corredores are fenced off. As a result, the express buses run faster than the city’s average of 9 mi/h, which is why so many of the local people, the Paulistanos, prefer to ride them. The line that connects São Mateus and Jabaquara, for example, carries over 6 million passengers per month.

The problem facing Central and South American cities is more than just a matter of the numbers of vehicles on the road. The average age of the vehicles is also a problem. In São Paulo the average car is 10 years old, the average bus 7, and the average truck has been around for 12 years. Along with São Paulo, other cities that take part in the Clean Air Initiative include Lima-Callao, Rio de Janeiro, Buenos Aires, Santiago, and Bogotá. The cities have also decided to cooperate in controlling emissions and coordinate their activities. Even before the Clean Air Initiative was founded, São Paulo had begun working on ways of managing the chaotic traffic and dangerous emissions levels. Since 1996, a system has been in place that requires cars to take turns staying off the roads. They rotate based on the last number on the license plate. On Mondays, for example, all vehicles with license plates ending with a 1 or 2 may not be used. In the past, the Paulistanos cheerfully ignored this regulation, but now the police have started imposing heavy fines on offenders. Environmental emissions are still being taken seriously by most governments in Central and South America, although current evidence suggests that most attention is being paid to levels of pollution, in both air and water, from large mining, power generation, metal processing, and industrial manufacturing plants, rather than from vehicles. As in many other regions, politicians have probably decided that it is easier and more productive to control business than to upset voters.

45.3 CURRENT STATUS OF AUTOMOTIVE FLUIDS IN SOUTH AMERICA 45.3.1 Gasoline and Diesel Engine Oils Demand for all lubricants in Central and South America totaled 2.70 million metric tons in 2002 and 2.73 million metric tonnes in 2003. Of this, around 72% was for the transportation sector and 28% for the industrial sector. Gasoline and diesel engine oils accounted for 69% of all transportation lubricants. Latin Americans prefer passenger cars and minibuses. Motorcycle lubricant consumption is relatively low, reflecting consumer preference for passenger cars as first affordable vehicles. Demand for natural gas engine oils is relatively high, as is the case for automatic transmission fluids. Demand for transportation lubricants is likely to be constrained by low consumer purchasing power, urban congestion, and underdeveloped infrastructure. Lower quality oils will still account for a substantial part of the Latin American market in 2005. In 2002, about 50% of the market for gasoline engine oil used American Petroleum Institute (API) SF quality oils or lower. Monogrades filled about half of the demand and multigrades the other half. The most popular multigrade oils are 20w40 and 20w50, although 15w40 viscosity oils are available in

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most countries. Full and partial synthetics, usually 5w40 viscosity, currently command less than 3% of the market. The highest quality levels available currently are API SJ and SL, which also meet the ACEA A3-98 requirements. Lubrax Sinético from Petrobras, for example is a 5w40 oil that meets API SJ/CF, ACEA A3-98/B3-98, VW 502.00/505/00, and MB 229.1 specifications. Many companies have plans to introduce API SM quality oils in the near future. ILSAC GF-2 and GF-3 quality oils do not appear as being sold in South America yet. For diesel engine oils, the average quality level currently is API CF-4, although monograde SAE 30, 40, and 50 API CC oils are still sold in many countries. The highest quality heavy duty diesel engine oils are API CH-4/ACEA E5-99, although API CI-4 oils are now being introduced in Brazil, Argentina, and Chile. Multigrade diesel engine oils are generally 20w50, although the newer, “top of the range” oils are 15w40 viscosity oils. State oil companies control 30% of the lubricants market in Central and South America. Included in this group are Brazil’s Petrobras and Venezuela’s PDVSA affiliate Maraven, both of which are trying to maintain their domestic share and build a position in nearby countries. (Petrobras has been partially, but not fully, privatized.) In 2002, for example, Petrobras acquired Argentina’s EG3 brand. Multinational oil companies, which now control 55% of the lubricants market, entered Central and South America while state-owned oil companies privatized and relinquished control of retail marketing. In 1996, Petroperu privatized and sold Petrolube to Mobil, Brazil prepared for the partial privatization of Petrobras, Bolivia delayed privatization of YPFB, and Venezuela liberalized its retail market and formed a domestic refining company Deltaven. Argentina’s YPF was privatized in 1994, but was acquired by Spain’s Repsol in 1999. It remains to be seen how much market share or control can be retained by previously state-owned companies after markets are opened and downstream operations are privatized. The remaining 15% of the Central and South American petroleum market is controlled by domestic independents. As a whole, the region is in the relatively early stages of market maturity for automotive engine oils. Gasoline service stations account for between 30 and 50% of transportation lubricant sales, depending on the country. Distributors handle around 50% of transportation and 80% of industrial lubricant sales. Indirect distribution channels, such as franchised workshops and mass merchandisers, have yet to achieve the grow associated with more mature markets. Channel structures differ due to market development and the channel preferences of marketing companies. The Mexican financial crisis led to the rapid growth of the “changarro”, or sidewalk peddler, in Mexico, Venezuela, and other South American countries. The changarro are urban and mobile, purchasing lower quality, branded, and

counterfeit products from distributors and reselling them after a severe discount. This channel accounted for roughly 60% of engine oil sales in Mexico and 35% in Venezuela during the Mexican crisis. As a result, Mexican lubricant quality in 1995 fell due to NAFTA’s removal of minimum quality limits and considerable margin volatility. Governments will need to reduce the activities of changarro significantly and encourage more disciplined markets. In Brazil, Petrobras currently controls around 22% of the lubricants market. Petrobras Distribuidora, is responsible for blending, packaging, distribution, and marketing of Lubrax branded lubricants. Although the company’s countrywide logistics and retail network of about 7200 service stations provided a competitive advantage in a protected market environment, it is unlikely that Petrobras will be able to maintain this position in the face of open market competition. Texaco is the leading multinational lubricant marketer in Brazil, followed closely by Shell. Other majors such as Esso, Mobil, and Castrol each have less than a 10% share. Both Texaco and Shell have benefited from a long-term commitment to the marketplace and strong brand management. Texaco’s corporate image building was achieved by support of municipal-level environmental initiatives and community development issues. Texaco has about 2900 service stations, 40 of which are convenience store Star Shops. Texaco has aggressive plans to build an additional 1250 convenience store stations by 2000. Shell has taken a high profile position in Brazil, leveraging its corporate image as a leading edge technology company with appeal to consumers’ European tastes. Shell opened its first convenience store station in 1987 under the name Express, and now has 4500 service stations across the country. In addition, Shell’s local operating company has been given considerable independence to grow as the Brazilian market permits. Castrol has had a number of difficulties in Brazil. Parallel importing and brand management issues led to a weakening of Castrol’s high-end corporate image. In the mid-1980s, Castrol had 20% share of the consumer automotive segment of the market. By 1995, this had fallen to 8%. Castrol is attempting to rebuild its image through promotions of select products. Brazilian refiner Ipiranga controls 18% of the lubricants market. Ipiranga acquired Atlantic in 1995 and now has three blending and packaging facilities and 5588 service stations throughout the country. It has aggressive objectives to expand its retail network through convenience store stations and quick-lube centers. Ipiranga is in the process of unifying its brands from multiple acquisitions and developing commercial ventures that will provide it with product technology and supply to maintain competitiveness. Quaker State, Pennzoil, and Valvoline also have entered Brazil’s market. As market conditions improve,

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these companies are expected to expand distribution and establish manufacturing operations. Others are waiting in the wings. Although this is a large market, low market prices and high costs were a significant hurdle that pushed margin performance into the red during 1996 and 1997. The end of Petrobras monopoly in the Brazilian oil industry during 1997 lead to a drop in lubricant prices of between 6 and 12%, due to the liberation of imports. Prior to 1997, importation of lubricants needed a previous authorization from the fuels agency, DNC. The Argentinean petroleum market, and with it the market for lubricants, was deregulated in 1992, and the process to privatize the state-owned oil company YPF was started in 1993. Following the deregulation of the lubricants market, the number of suppliers has dropped from 128 to 42, because most of them were either too small, too inefficient, or unable to restructure and had to merge or be acquired by bigger competitors. At present, about 85% of the lubricant’s market in Argentina is controlled by four companies; Repsol-YPF, Shell, ExxonMobil, and Petrobras (Eg3). In Chile, the leading suppliers of lubricants are Copec (ExxonMobil), Shell, and Texaco, with Repsol-YPF becoming more active. Copec’s current market share is a little over 50%. In 1996, Copec assumed responsibility for sales of lubricants to industrial customers previously supplied by Lubricants de Chile. In 1997, the company took over the operation of a lubricants blending plant and the distribution of Mobil lubricants. Shell Chile currently has a network of 440 service stations in the country and plans to build a lubricants blending plant in Quinteros during 1998. The plant is scheduled to begin its operations in 2000 or 2001. Although Texaco Chile has only around 40 service stations and a 2% share of the fuels market, the company is reported to have a 10% share of the Chilean lubricants market. Lubricant quality levels are similar to those found in Brazil and Argentina. Castrol reported that the trading environment for lubricants intensified in parts of South America in 1996, as new competitors entered these markets and some old ones returned. Major marketing initiatives by Castrol included the launches of Castrol Formula SLX and GTX Magnatec. Supply chain initiatives brought benefits, while harmonization of brands and advertising are bringing scale efficiencies.

45.3.2 Two-Stroke Oils Motorcycles make up only a tiny fraction of transportation vehicles in Central and South America, so demand for two-stroke engine oils is comparatively small. Specifications and performance levels are similar to those in Japan and North America, with almost all motorcycles being imported into Central and South America from Japan. Although there are no plans at present to adopt the latest ECG global two-stroke engine oil standards, it is likely

that Brazil, Argentina, Chile, and Peru will progressively introduce these oils over the next few years. The JASO FC quality oils are used most generally for motorcycles, although API TC oils are also available in many countries. Multigrade 20w50 API SF and SG oils are also sold for four-stroke motorcycles. For outboard twostroke engines, NMMA TCW-3 oils are sold in Brazil and Argentina.

45.3.3 Transmission and Gear Oils The majority of developments with automotive gear and transmission fluids are occurring in North America, primarily because of the huge use of automatic transmissions in this market. These developments have started to impact the market in Europe, and are slowly starting to filter through to South America. The overwhelming majority of automotive transmissions in South America are manual gearboxes and conventional hypoid rear axles, which use standard API classes of gear lubricants, most usually GL-4 and GL-5, but also GL-1. Monograde SAE 90 and 140 oils are commonly available, although they are being replaced slowly by multigrade 85w140, 80w90, and even 75w90 gear oils. Because the majority of South American cars have manual transmissions, the use of automatic transmission fluids is much lower than it is in North America, although it is growing, particularly in the larger cities in Brazil and Argentina. Most ATFs are marketed with U.S. specification performance levels, most usually GM Dexron III, Ford Mercon, and Allison C4 specifications. Petrobras also markets Lubrax OH-50-TA, an ATF that meets the GM Type A Suffix A specification, for use in automatic transmissions fitted to Mercedes-Benz vehicles.

45.4 DEVELOPMENT OF MARKETS FOR SYNTHETIC AUTOMOTIVE FLUIDS IN SOUTH AMERICA In the mid-1990s, vehicle manufacturers looking for double-digit growth rates, as opposed to the much slower growth found in mature markets, turned to South America, Eastern Europe, and South-East Asia, the three regions where demand appeared to be flourishing. Prospects in Brazil and Argentina, the two biggest South American car markets, looked buoyant after a downturn brought about by government economic tightening. The optimist outlook for both markets, linked via the Mercosur trade bloc, was reflected in the series of decisions to build new car plants. Markets in other Central and South American countries were similarly optimistic. The prospects from 1999 onward took a sharp downward turn in Central and South America. They may have started to brighten again more recently, but still do not appear to be anywhere near as optimistic as they appeared in 1998. As a consequence, sales of new vehicles that would

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benefit from using synthetic or part-synthetic lubricants have slowed dramatically over the last few years, and so has the growth in demand for higher performance lubricants. South American consumers generally consider a new passenger car “like a valued member of the family, deserving appropriate treatment.” Strong brand image and service provider recommendations highly influence the consumer’s engine oil purchasing decisions. As a result, South Americans place value on brands when seeking high quality lubricants. Marketers should capitalize on this by enhancing the perceived value of their product, price accordingly, and minimize costs. Achieving profit in Central and South America will depend on a marketer’s perception of the customer in terms of price, performance, brand, service, channel, and market linkage. Lubricant sales channels for market entry will continue to be limited until fuel prices reach international levels. In the transportation sector, about 80% of consumer passenger car sales and 50% of commercial truck sales are through service stations, of which there are more than 60,000 throughout South America, many of which are old. Profits from complementary convenience store operations have effectively subsidized these outlets. These will eventually consolidate. New, high-volume, efficient stations have already been built in Brazil, Argentina, Chile, and Peru. As channels evolve, the presence of dealer service centers, franchise workshops, and quick-lube centers are likely to increase. Hypermarkets may come to urban centers, but generally South American consumers are not accustomed to these points-of-sale for lubricants. Imports of high quality lubricant baseoils and synthetic fluids will continue to grow over the coming years, due to the market’s shift to multigrades and multinational penetration, but at a much slower rate of growth than in the mid-1990s. Major regional baseoil suppliers, such as Petrobras, Maraven, Echopetrol, and Repsol-YPF, have not announced firm plans to upgrade their baseoil production facilities. Consequently, the trade deficit will increase unless the local producers improve the quality of their baseoils. New passenger cars and the original equipment manufacturer (OEM) “push” for higher quality oils are likely to reduce the monograde level further. Brazil accounts for around 38% of the South American lubricants market, representing a necessary keystone for building a regional position. Brazilian lubricant demand has been increasing steadily since 1996 and is now slightly more than 1 million tonnes per year. While the transportation sector contracted, the industrial sector enjoyed modest expansion due to the growth of the automotive production, mining, and agricultural processing industries. Most industry analysts forecast that demand for lubricants in Brazil is likely to grow at around 2% annually until 2008. The largest market segments, automotive engine oils (representing 49% of demand), industrial hydraulic oils (14%), and industrial greases and metalworking fluids

(11%), will be moving toward higher quality standards. If the pace of reform slows, demand growth will be relatively flat, but progress toward higher quality should continue. High operating costs have limited the attractiveness of Brazil compared to other South American countries. Although government price controls for lubricants were removed about 3 years ago, the government has imposed a 53% fund unification price (FUP) tax. In 1996, the import duty for finished lubricants was 12% and for baseoils it was 5%. With the implementation of the new petroleum regulation law, these barriers appear to be falling. Other important South and Central American markets for automotive lubricants include Argentina, Venezuela,

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Chile, Colombia, and Puerto Rico. In 2002, the total market for lubricants in Argentina was around 270,000 mt, while in Venezuela it was around 200,000 t. All other individual South American lubricants markets are less than 200,000 t annually, with several less than 100,000 t annually. Forecasting future demand for synthetic and partsynthetic lubricants in Central and South America is fraught with difficulty. The region has always had great promise, but in recent years has suffered political, social, and economic turmoil. Until steady and uninterrupted economic growth and social stability returns, demand for higher value products, including automotive lubricants, is unlikely to resume at earlier rates.

46

Industrial Lubricant Trends Garrett M. Grega, John J. Kurosky, Darren J. Lesinski, Michael J. Raab, and Z. Ahmed Tahir CONTENTS 46.1 46.2 46.3 46.4 46.5 46.6

46.7

46.8

Introduction Future Growth Markets General Market Drivers Biodegradable Lubricants Metalworking Trends Gear Lubricant Trends 46.6.1 Original Equipment Manufacturers Trends 46.6.2 Gear Manufacturing Trends 46.6.2.1 Higher Accuracy Hobbing 46.6.2.2 Gear Grinding 46.6.2.3 Superfinishing 46.6.3 Mechanical Trends in Gear Manufacturing 46.6.3.1 Improving Surface Finish. 46.6.3.2 Surface Modification 46.6.3.3 Failure Mechanisms 46.6.4 New Materials in Gear Manufacturing 46.6.4.1 Powder Metallurgy 46.6.4.2 Ceramics 46.6.4.3 Plastics 46.6.5 Trends in Gear Lubrication 46.6.6 Higher Energy Efficiency with Synthetic Gear Lubricants 46.6.6.1 Lubrication Modeling 46.6.7 Gear Lubricant Formulation Trends 46.6.8 Gear Lubricant Specification Trends 46.6.8.1 Bearing Specification Requirements 46.6.9 Specific Synthetic Gear Lubricant Applications 46.6.9.1 Wind Turbines 46.6.9.2 Pumpjack Gearbox 46.6.9.3 Open Gear Sets 46.6.10 Gear Lubricant Summary Compressor Oil Trends 46.7.1 Air Compression 46.7.2 Industrial Gas Compression 46.7.2.1 Rotary Screw 46.7.2.2 Reciprocating 46.7.2.3 Future Trends 46.7.3 Refrigerant Gas Compression 46.7.4 Compressor Lubricants Summar Hydraulic Oil Trends 46.8.1 Types of Hydraulic Systems 46.8.2 Hydraulic Fluid Classification 46.8.3 OEM and End User Future Trends

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46.8.3.1 Ecologically Sensitive Fluids 46.8.3.2 Crop Derived Fluids 46.8.3.3 Synthetic Hydraulic Fluids 46.8.3.4 Improved Cleanliness 46.8.3.5 Improved Fire Resistance 46.8.3.6 Products for Use in Food and Pharmaceutical Plants 46.8.3.7 High Pressure Systems 46.8.3.8 Increased Specifier Sophistication 46.8.3.9 Shrinking Market for Low Pressure Systems 46.8.3.10 Fluid and Supplier Rationalization 46.8.3.11 Multigrade Fluids 46.8.3.12 Elastomer and Material Versatility 46.8.3.13 Fluid Monitoring and Trend Analysis 46.8.3.14 Ashless Formulations 46.9 Grease Trends 46.9.1 Grease Overview 46.9.2 Grease Manufacturing Trends 46.9.2.1 Batch Processing 46.9.2.2 Manufacturing for Low Noise 46.9.3 Application Trends 46.9.4 Environmental Trends 46.9.5 Grease Market Trends 46.10 Effects of Base Oils on Industrial Lubricants 46.11 Summary References

46.1 INTRODUCTION This chapter focuses on general trends in industrial lubricants. Industrial lubricants refer to a broad category of lubricants and the trends cannot all be addressed within a single chapter. Therefore we will narrow our focus to the following topics: • • • • • • • • •

Future growth markets General market drivers Biodegradable lubricants Metalworking trends Gear oil trends Compressor oil trends Hydraulic oil trends Grease trends Effects of base oils on industrial lubricants

Over the last three years industrial lubricant sales have seen flat to no-growth. Sales of lubricating oils and greases totaled 2.46 billion gal in 2002, the lowest since 1992, according to the National Petrochemical and Refiners Association. This follows a 3.3% drop in 2001 and flat sales in 2000 [1]. The third-quarter of 2003 showed a 19% decline in U.S. lubricant sales when compared to the same third-quarter of 1997. Many factors contributed to this decline including the global recession, closure of

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steel and paper mills, as well as the increased performance of synthetic lubricants.

46.2 FUTURE GROWTH MARKETS With declines in the United States and European lubricant market, growth will need to come from other geographic areas. Asia, particularly Malaysia and China, as well as India represent prime growth areas for industrial lubricants. Frost & Sullivan estimates that the total synthetic lubricant market for Southeast Asia was worth $819 million in 2001 with a compound annual growth rate of 3.5%. At this rate, the region is forecast to reach $1 billion in synthetic lubricant sales by 2008 [2]. Why is the region so ripe for growth? One primary reason is the increase in the standard of living that has increased the number of consumers of automobiles [3]. Malaysia represents one of the largest automobile markets in Southeast Asia. While much of the synthetic growth will be in automotive engine oils, this author believes that synthetic lubricants will be needed in the industrial sector to maintain the production efficiencies required to grow the automotive market. In general, machinery in this region is considered valuable capital that must be maintained. The timely availability of replacement from other areas of the world increases the emphasis

on preventive maintenance practices. Therefore, synthetic lubricants offer more value to operators who need to keep downtime to a minimum and protect the value of the asset. India is another country with projected increases in industrial demand. At the ICIS-LOR World Base Oils Conference, Ramesh V. Rao, general manger and executive director of Gulf Oil Corp. Ltd. projected a 3% sales growth in 2004 and 5% in 2005. India went through some major declines in lubricant sales between 2000 and 2002. However, the growth in India’s vehicle population will create a rise in sales of both automotive lubricants and industrial lubricants. By 2005 India is expected to have over 59 million vehicles on the road compared with only 44 million in 2000. However, the current tax structure could hamper industrial lubricant sales by requiring storage and billing facilities within each state. Some states may also demand entry permits and lube licenses. Mr. Rao states that some trucks can “go through 21 check points to make a delivery” [4]. China clearly represents the growth engine for industrial lubricants in the world. Currently China’s lubricant demand accounts for nearly 30% of the world’s total, according to Harland Bulow of Tri.Zen International [5]. According to Hugh Peman, president of Shanghai-based research company Research-Works, China is 18 months into an “unprecendented economic growth spurt which may last a total of three to five years.” Peman compares China’s growth spurt to the United States in the 1950s when highways and infrastructure were being built [6]. Clearly, if China maintains this pace, industrial lubricant consumption will increase. Within the established markets of Europe and North America, we can expect to see increases in synthetic and specialty lubricants. As equipment manufacturers tighten specifications and increase equipment performance, more specialty lubricants and greases will be needed to meet the expanding performance levels. We are already seeing this in the United States with a reported jump in synthetic lubricants sold by 5.2% in 2002 while conventional lubricants declined during that same period [7]. In addition, with the recent inclusion of ten more member states into the European Union, Europe should see an increase in industrial lubricant growth as these ten economies benefit from the increased trade that a full member of the European Union offers. Industrial lubricant growth will be directly tied to the economic forces within a given region of the world. As the regional economy improves, so will the sales of industrial lubricants. Specialty lubricants and greases should see an increase as both regulations and equipment specifications force lubricant users to consider the advantages of synthetic lubricants. The following sections of this chapter will address direct trends seen within specific lubricant applications.

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46.3 GENERAL MARKET DRIVERS Although there are many applications for industrial lubricants, a few common drivers have significant influence on the growth of synthetic lubricants. • Operational improvements • Efficiency gains • Environmental impact

General industrial facilities are under increased pressure to improve productivity while minimizing the cost of operations. Maintenance budgets are constrained while output targets are increased. Therefore, equipment reliability and capital preservation are critical to the success of any manufacturing business. Utility costs represent a significant portion of any manufacturing budget. Reducing energy consumption, particularly with the volatile trend of energy prices, has become even more critical to the cost competitiveness of an operation. Manufacturing companies must incorporate environmental responsibility into each aspect of their business as a result of consumer awareness and legislative pressures. Synthetic lubricants offer an opportunity to be a solution. Typical applications discussed further in this chapter illustrate the impact that synthetics have in meeting these industrial challenges.

46.4 BIODEGRADABLE LUBRICANTS Biodegradable lubricants are receiving increased attention by consumers, regulators, and equipment manufacturers. While there is increased focus on using biodegradable fluids in construction and mining, only 2% of the hydraulic fluids used in bulldozers, tractors, and heavy equipment are considered biodegradable [8]. This gives room for growth. Cargill in particular would like to capitalize on this potential growth. It has announced plans to double the capacity of its Chicago plant-based esters plant [9]. In a separate announcement, Cargill announced plans with Kaufman Holdings Corporation to construct a renewable base oils esterification facility in Brazil [10]. Industries face a range of environmental risks these days. In recent years, legislation has phased out ozonedepleting gases under the Montreal Protocol and other similar initiatives. Additional environmentally targeted legislation, which will directly affect the lubricant market, is currently being debated and may eventually be mandated. As with any formal legislation this is a slow process. However, once implemented the impact on industry can be substantial. Current activity includes the evolution of the Montreal Protocol to incorporate industrial air conditioning and refrigeration equipment, the Farm Bill for the use of renewable resources, and waterway protection programs amongst others. Tough environmental targets and environmental group pressures in addition to current and

TABLE 46.1 Uses of Typical Biodegradable Chemistries Biodegradable chemistries Vegetable oils PAOs Esters and polyolesters PAGs

Typical applications Sawmill lubricants, chain drive lubricants, hydraulic oils Hydraulic oils (low temperature, high pressure applications) Compressor oils, turbine oils, hydraulic oils, and marine based fluids Compressor oils, gear oils

future legislation have placed greater emphasis on effectively managing the risks associated with lubricant use and application. One result of these pressures was the evolution of International Environmental Standard ISO 14001. A number of certification labels signifying compliance with certain norms have been devised in several countries. These include the German “Blue Angel,” the “White Swan” of Nordic countries and the Canadian “Environmental Choice” maple leaf. Certification activities have also been initiated in China, Thailand, Japan, and India. Discussions among several countries have been initiated to create Global Eco-Labeling Network (GEN) [11]. These and other initiatives are specifically targeted at reducing the potential impact of lubricants on the environment and human health. As Table 46.1 shows, biodegradable oils can be classified by their chemistries: Vegetable oils, Biodegradable polyalphaolefins (PAOs), Diesters, Biodegradable polyolesters, and Polyalkyleneglycol (PAGs). Vegetable oils have shown positive performance as sawmill lubricants and chain drive lubricants where the “once-through” aspect of the applications requires a low toxicity lubricant. (Kržan and Vižintin [12] demonstrate that a formulated vegetable-based, and synthetic esterbased Universal Tractor Transmission Oils have high lubricity, high viscosity index, and provide equivalent or, in some respects, superior gear protection performance compared to a mineral-based UTTO fluid [12].) By contrast, Biodegradable PAOs are used in high-pressure and lowtemperature environments as both hydraulic and engine oils. However, biodegradable PAOs are limited to low viscosity grades. Diesters and Polyolesters have historically been used as lubricants for compressors and turbines. However advances in chemistries have identified uses in hydraulics and marine applications. Finally, although PAGs have been known to be biodegradable, they are still poorly miscible with mineral oils. As a result, one must thoroughly flush a system before using a PAG [13]. One of the more demanding areas for biodegradable lubricants includes the marine and inland waterway industries. Shipbuilders, barge operators, and locks and dam owners are seeking biodegradable lubricants that are

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nontoxic to the environment and produce no visible sheen on the waterways. Technology advances in this area will satisfy a latent need of industrial lubricant users. Today’s environmentally friendly lubricants, although biodegradable and nontoxic, still provide a visible sheen when inadvertently released into a waterway. To demonstrate the economic incentive to develop a lubricant to meet the requirements of incorporating biodegradability, low toxicity, and no-sheen properties consider the following example: If one assumes an average sump size of 525 gal (2,000 L) per ocean going vessel and a 10% acceptance rate for 20,000 vessels, the estimated market size for biodegradable lubricants is on the order of $15 to 30 million.

46.5 METALWORKING TRENDS Over the years metalworking fluids have been one of constant changing chemistries. As new worker-safety rules that limit particulates, chlorinated paraffins, and exposure levels have taken effect, lubricant providers have had to significantly modify formulations. Today’s focus in the metalworking industry has been in the area of mist control. In March 2004, a three-judge panel for the U.S. Court of Appeals in Philadelphia unanimously ruled that although oil mist does appear to cause health problems, Occupational Safety and Health Administration (OSHA) could focus on materials that pose bigger health risks [14]. As a result, the United Auto Workers Union and the United Steelworkers of America are unlikely to realize legislation that lowers the permissible level of mist exposure for their workers. The regulation battle is not the full story for mist control. Private industry has focused on this as an opportunity and developed new nozzle designs and new lubricants that reduce misting in the workplace. Misting is caused when the air/lubricant stream exiting a nozzle shears and causes a fog or mist to form. Older nozzle designs have been proven to suspend 70% of the lubricant in the air as fog with only 30% reaching the machining surface [15]. Therefore, it was imperative to develop a nozzle where 90% of the lubricant can reach the surface. By changing the nozzle design so that the air flows around the outside of the nozzle (causing laminar air flow) and the lubricant flows through (inside) the nozzle, one can increase the nozzle velocity without inducing a mist. In addition, to the mechanical design improvements, lubricant formulators have designed new products to increase the lubricity of the lubricants to eliminate components with potential health risks and to decrease the misting tendencies of the lubricant. As a result, operators now have the option of installing a nozzle–lubricant combination that delivers over 90% of the lubricant to the machine surface with reduced health risk impact [16]. This design, although proven, has not been adopted throughout the metalworking industry. As the new

technology is implemented, one can see significant decreases in metalworking fluid demand. With 60% more lubricant hitting the active surface, the total lubricant consumption in a metalworking plant will decrease. One other trend occurring in the metalworking industry is the increase of “Dry” cutting operations. Europe, particularly Germany, has led the revolution in “Dry” cutting operations, where no lubricant or coolant is used. As costs for cutting-fluid disposal increase more metalworking shops will opt to use “Dry” technology that includes ceramic and cermet cutting tools that do not require cutting fluids. Although reaming, broaching, and grinding may be the last subsegments to convert, milling and turning operations may go “Dry” [17].

46.6 GEAR LUBRICANT TRENDS Gears systems are employed widely in industrial applications to transmit power or to change speed, torque, or direction of motion. Gears are renowned for their high mechanical efficiency in power transmission with values exceeding 90% routinely obtained in a single mesh design. Competitive pressure to improve energy efficiency of machinery leads the demand for better gearing. As gear teeth mesh, they roll and slide in relation to oneanother. While rolling is continuous throughout the mesh, sliding varies from a maximum velocity in one direction at the start of the mesh, through zero velocity at the pitch line, and back to maximum velocity in the opposite direction at the end of the mesh. In general, it is friction at the rolling/sliding contact that accounts for the majority of losses. Friction can be reduced through effective lubrication strategies. The manufacturing processes for gears have historically left relatively rough surfaces such that oil films are generally on the same scale as the average roughness. It is generally understood that contact between two such surfaces and the enclosed oil film occurs under elastrohydrodynamic conditions. In this section we will examine the mechanical, manufacturing, and energy efficiency, as well as chemistry trends that may drive future lubrication requirements and formulations. Examples are given of successful synthetic-based gear lubricant applications.

46.6.1 Original Equipment Manufacturers Trends The global market for nonautomotive gear manufacturing is estimated to be $10.0 billion dollar with 54% of that manufacture carried out in Europe, 27% in the USA, and 19% in Japan. Unfortunately, there are no readily available data for market activity in such countries as India, China, Australia, Czech Republic, Poland, etc. Each of these countries has a growing industry that is important to world production and consumption of geared products [18].

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In the coming years Gear Manufacturers (Original Equipment Manufacturer, OEM) will face increased worldwide competition. Modern, high-speed communication systems will only exacerbate this pressure. Trade restrictions and customs duty have all but been abolished by political pressure. There is a strong movement toward specialization; bigger companies are reducing the number of their product lines. Gear manufacturing will continue to consolidate and move where there is a strong and vibrant steel industry along with the availability of energy and labor at reasonable costs. Specialization will drive OEMs to increase reliability in order to create product differentiation. Additional forces driving reliability are coming from the insurance industry and from Legislative bodies. For example, in the globalization of the wind energy market, the Insurance Industry coupled with the Danish authority, have pushed the wind turbine OEM, gear box manufacturers, and the lubricants industry to international standardization of manufacturing specs (e.g., AGMA 6006). Gearbox OEM’s are coming together with bearing and seal manufacturers to create cross-functional standards (i.e., gear, bearing, seals, and lubricants). Emerging countries and regions will need power plants, transportation systems, water supply, and medical care. These emerging areas will create new opportunities for gear manufacturers. These developing areas have a ready source of low-priced labor but they have little capital; these areas will need to use this cheap labor to pay for their expansion.

46.6.2 Gear Manufacturing Trends Tighter tolerances for equipment and improved processes and techniques are driving improvements in gear manufacturing. Demands driving gearbox design and manufacturing include: increased power density, lower noise, higher reliability, extended warranty, and lower cost. 46.6.2.1 Higher accuracy hobbing Load-carrying capacity of gears, especially the surface durability, is influenced by tooth surface finish (roughness) and the tooth profile. Smoother tooth surfaces, harder gears, and more accurate tooth profiles are needed in order to achieve high load-carrying capabilities. Ariura and Umezaki [19] tell us of advances in the design and materials involved in hobbing of gears. Included is the use of finished hobs, finished hob process is used to remove distortion following the heat treatment process. Finished hobs are required to give good wear and chip resistance, smooth finishing of tooth surfaces, and high accurate hobbing. 46.6.2.2 Gear grinding Hazelton [20] teaches, “the benefits of ground gears are well known. They create less noise, transmit more power

and have longer lives than non-ground gears. But grinding has always been thought of as an expensive process, one that was necessary only for aerospace or other hightech gear manufacturing.” As gear-grinding machinery has become more productive, the grinding wheels are better and the overall cost of grinding has gone down. Gear grinding is now incorporated in a wide variety of industries including makers of automobiles, trucks and motorcycles. It is also commonly used in textile, printing, power generation, and motion control industries. Many standard gearboxes use ground gears to improve control over backlash and noise. 46.6.2.3 Superfinishing Superfinishing the working surfaces of gears and their root fillet regions results in performance benefits. Initially developed to increase surface durability, it has since been found that superfinishing to a low surface roughness can reduce friction, pitting fatigue, noise, operating temperature, bending fatigue, metal debris, and wear. Superfinishing techniques include grinding and honing, or chemically accelerated vibratory finishing. Such techniques have been used to achieve high quality gears with a roughness average of between 1.0 and 3.0 µin [21].

46.6.3 Mechanical Trends in Gear Manufacturing 46.6.3.1 Improving surface finish Improving the surface finish of gear teeth is a highly profitable way of reducing friction and consequently increasing efficiency. For instance, Britton et al. [22], examined the effect of surface finish in a special four-gear test rig using gear tooth frictional losses at loads and speeds representative of those employed in a gas-turbine engine. He found that superfinishing resulted in reducing friction typically by 30% with correspondingly lower tooth surface temperatures. Further, the behavior of friction-torque with increasing loads and speeds indicates a transition from “mixed” to hydrodynamic gear friction occurred with both when ground to a super finish. AGMA 9006-A94 “Gear Tooth Surface Texture with Functional Considerations” teaches that typical surface roughness (Ra ) can range from 0.3 to 6 µm (12 to 250 µin.) for commercial quality gears with some gears as low as 0.2 µm. In one application — gear boxes for wind turbine AGMA 6006-A03 (Table 7) recommends (Ra ) values of 0.5 µm on the low speed sun and planet gears up to 0.7 µm on intermediate and high speed pinions and gears. Krantz and Kahraman [23] studied the influence of lubricant viscosity and additives on the wear rate of spur gear pairs. Their work demonstrated that wear rate is strongly related to the viscosity of a lubricant. Lubricants with higher viscosity exhibit larger lambda ratios and lower

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wear rates. In their testing, doubling lambda decreased wear rate by a factor of 3. Since lambda is the ratio of lubricant viscosity to Ra , it is clear that improving surface finish has a strong influence on wear and fatigue life. It should also be noted that increasing the viscosity under the operating condition has an equivalent effect. 46.6.3.2 Surface modification The use of solid lubricants will likely impact the development and manufacturing of gears in the future. While the use of solid lubricants is not new in itself, recent developments in materials and in application methods offer interesting new possibilities. For instance, lamellar solid lubricants or transition metal dichalcogenides MX2 (where M is Mo, W, Nb, Ta, etc. and X is sulfur, selenium, or tellurium) are among the lowest-friction materials known in dry and vacuum environments. MoS2 and WS2 are standard lubricants for vacuum and aerospace applications. However, by themselves the lubricity of these materials are affected by moisture and other environmental effects. Development is occurring in “smart coatings” and nanocomposite and layered solid lubricants that offer longer wear life and lower friction coupled with less sensitivity to variations in the operating environment. Very low coefficient of friction materials such as boric acid, diamond-like carbon, and other advanced materials for solid lubricant application are also being developed [24]. Modern methods of application — such as physical and chemical vapor deposition by sputtering, ion platting, ionbeam deposition, and ion implantation — enable use of the advanced materials on a practical basis. Work by Weck et al. [25] discusses physical vapor deposition coatings of hard materials such as CrAlN, TiAlN, WC/C (amorphous metal carbon coating) and ZrC on gear flanks, coating thickness being 1 to 4 µm. The basic aim of this study is to transfer the functions of individual lubricant additives to the surface of the material via the application of wear-protection coatings in order to be able to reduce the additive content of gear lubricants. The report shows that the use of metal–carbon layers enables the omission of surfactant additives. One coating showed significant difference, particularly in the FZG scuffing test, with regard to wear on the tooth flanks (2.5 fold less mass loss under the specified test conditions). Engineered or “Textured Surfaces” offers yet another possibility for improving gear teeth friction properties. One technique under development is termed “Laser Surface Texturing” (LST) or “Micro Dimpling.” LST creates micropores on surfaces that act as miniature hydrodynamic bearings, improving mechanical seal performance, reducing friction, lowering wear, and face temperature. In summary, surface modifications such as deposited solid lubricants and LST offers significant improvements

by lower coefficient of friction and in improving surface durability of metals. These or similar developments will likely lead to reduced costs making such techniques viable in high performance gearing. 46.6.3.3 Failure mechanisms As highly loaded, case or through-hardened gears have found their way into industrial application researchers have found a new failure mechanism, namely “micropitting.” Micropitting is a surface fatigue occurring in Hertzian contacts caused by cyclic contact stresses and plastic flow on the asperity scale. It is most often found in the dedendum area of gear teeth and represents a large total damage area that results in loss of the tooth profile. It is manifested as a large number of small, shallow pits with a characteristic length of 10 µm. Micropitting has been identified as a key issue in the operation of highly loaded, case or through-hardened gears such as found in wind turbine application. It can be minimized by proper selection of lubricant, improving surface finish, decrease in the corrosiveness of the lubricant to the metallic surface, and decreasing the boundary friction between the metallic surfaces. While testing by FZG gear test rig is the preferred method, other techniques have been used to replicate micropitting in laboratory equipment. Errichello [26] instructs that micropitting occurs after an initial incubation period from 104 to 106 cycles. Micropits originate at surface asperities where maximum peakto-valley roughness of a ground tooth surface may be about 2 to 4 µm. Micropits occur at peaks of asperities and are typically smaller than 1 µm. Therefore, scanning electron microscopy (SEM) is needed to study micropitting, especially in the early stages. Micropitting occurs under elastrohydrodynamic lubrication (EHL) oil films where the oil film thickness is on the same order as the surface roughness (Ra ), and load is borne by surface asperities and lubricant. When a significant portion of load is carried by asperities, collisions between asperities on opposing surfaces cause elastic or plastic deformation depending on local loads. Li and Devlin et al. [27], present a model based on boundary friction coefficient, oil film thickness, oil corrosiveness (measured as average gray value), and surface roughness of the gear tooth applicable to predicting fatigue pitting life in an FZG test for gear oils. The authors show that surface roughness is the dominant contribute to characteristic micropitting giving a 22% relative contribution. They also found that when a macropit or spall formed, it was always observed on the upper edge of a micropitting band, which had formed earlier in the sequence. From a lubrication point of view, Li and Devlin’s empirical expression says that increasing film thickness and decreasing oil corrosiveness has the potentials of changing the hours to pitting [28]. Incorporating additives capable of

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modifying the boundary friction (friction modifiers, antiwear, and EP properties) can have a 2051 times greater impact of hours to pitting. From a mechanical point of view, decreasing surface roughness has a 1224 to one impact. Devlin also shows that temperature has an affect on micropitting. When the test temperature was raised from 90 to 120◦ C, the mode of failure changed from micropitting with mild wear (at 90◦ C) to scuffing wear with essentially no micropitting at 120◦ C. Thus, reducing the oil film thickness in the contact zone promotes asperity-to-asperity interactions. Ueno et al. [29] found that antiscuffing additives or EP additives in a GL-5 type gear lubricant could cause micropitting to increase. Following up on this work, Cardis and Webster [30] investigated the impact on lubricant additives on micropitting. They also demonstrated that gear oils could be formulated using new additive systems balanced to meet the combination of providing antiscuffing performance while reducing the risk of micropitting.

46.6.4 New Materials in Gear Manufacturing 46.6.4.1 Powder metallurgy Powder metallurgy (P/M) is a highly developed method of manufacturing reliable ferrous and nonferrous parts. Made by mixing elemental or alloy powders and compacting the mixture in a die, the resultant shapes are then sintered or heated in a controlled-atmosphere furnace to bond the particles metallurgically. Basically this is a “chip less” metalworking process; P/M typically uses more than 97% of the starting raw material in the finished part. Because of this, P/M is both an energy and a materials conserving process. Many of the early P/M parts, were very simple shapes such as bushings and bearings. Today, complex contours and multiple levels are often produced economically. In recent years processes and techniques, including compaction, have evolved to a point were gears are now manufactured by P/M. For example, the 2003 Metal Powder Industries Federation “Overseas Grand Prize” was awarded for a P/M spiral bevel gear used in a reciprocal power saw. While P/M manufactured gears remain on the small size, use of this technology is expected to increase in the foreseeable future. 46.6.4.2 Ceramics Bearings based on ceramic materials such as Silicon Nitride (Si3 N4 )are being manufactured today for gear applications in aerospace. Silicon nitride, being nearly twice as hard as bearing steels, offers improved wearresistance and reduced damage due to the effects of repeated surface contact. The use of ceramic rolling elements reduces lubricant degradation and significantly

increase bearing life in many applications. Silicon nitride can operate at temperatures up to 980◦ C, exceeding the best high temperature bearing steels by a factor of two. Because it is essentially inert, Si3 N4 represents an advance in the effort to improve bearing performance in corrosive environments [31]. Lightweight Si3 N4 balls have a superfine surface finish and high hardness (Rc78) that can help to extend service life up to five times that of standard steel bearings. Low-friction characteristics enhance operation under minimal lubrication conditions and increase both life and speed capabilities of lubricants. Farther into the future, ceramic materials may be employed in gear manufacturing as well. Researchers have demonstrated that including carbon nanotubes into a ceramic material can nearly triple the resistance to fracturing. “Such durable materials could eventually replace conventional ceramics or even metals in countless products,” says Joshua D. Kuntz [32] of the University of California, Davis. “For instance, engineers might use the toughened ceramic to make gears, bearings, or other parts for everything from racecars to industrial food-processing equipment.” 46.6.4.3 Plastics Plastic gears are a powerful means of reducing drive cost, weight, noise, and wear. Plastic gears also open new opportunities for smaller, more efficient transmissions in many products. Historically, they were limited to very-lowpower transmissions, such as clocks, printers, and lawn sprinklers. Today’s stronger, more consistent engineering polymers, and better control of the molding process, now make it possible to produce larger, more precise gears that are compatible with higher horsepower. Thermoplastic and thermosetting polymers have long provided alternatives to metals in low-powered, nonlubricated gear trains. Gears machined from phenolics and other thermoset plastics can be used at higher operating temperatures and they are more resistant to lubricants that are generally required. However, injection-molded thermoplastic gears have better fatigue performance and, unlike those manufactured from thermoset materials, can cut manufacturing costs significantly compared with metal gears. Thermoplastics are now finding their way into applications demanding lubricated drives, higher horsepower, and higher American Gear Manufacturers Association (AGMA) quality standards [33].

46.6.5 Trends in Gear Lubrication Competitive forces will continue to drive design toward smaller gearboxes. Coupled with smaller gearbox designs is the effort to increase transmitted power. This trend means increased gearbox temperature and less oil in the system. Ultimately this will drive the lubricant requirements for higher thermal and oxidative stability.

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The OEMs will continue to move away from maintaining lubricant approvals and are turning instead to national and international bodies such as ASTM, AGMA, ISO, DIN to develop and maintain gearbox standards and specifications. As consolidation and internationalization of gear manufacturers continues, look for global standardization to occur as regional design criteria are accepted worldwide. This all means OEM approval lists in the future may disappear; but this will be at the expense of commoditization of lubricant specifications. Differentiation will need to occur at the end user level whereby product performance attributes that directly effect the consumer (such as increased energy efficiency, reduced wear, and other value-added features) will need to be demonstrated in field operations. There is increasing awareness by the gearbox OEM and by the user community that expected life and performance of the gear set, the associated bearings, and the gear lubricant are highly interrelated. For instance, a roller element test developed by FAG OEM und Handel AG, A company of Kugelfischer Group (FE-8) (DIN 51517 Part III) is required by all gearbox OEMs [34]. Additionally, gearbox approvals now require approval by bearing and seal manufacturers in addition to the gearbox OEM. Acceptance of synthetic gear lubricants has been quite impressive in the heavy-duty truck market. Most notably the Eaton Corporation has driven this acceptance. A flavor for the attraction to synthetics is given in a European Patent Specification [35], which documents that oil change intervals of 80,000 km with a petroleum-based lubricant can be extended five fold to 400,000 km with a synthetic gear lubricant. “Until recently, petroleum based oils were used for lubrication in heavy duty truck transmissions even though they were susceptible to oxidation when operating the transmissions at oil sump temperatures above 110◦ C. Many of the mineral gear oils break down above 110◦ C and oxidize, and thereby deposit carbonaceous coatings onto seals, bearings and gears that may cause premature failures. Consequently, regular oil changes were required in order to minimize oxidation and these deposits, to assure maximum component life and to maintain the warranties with the transmission manufacturers. The lower temperature limit and requirements for a transmission oil cooler restricted the success of the mineral gear oils to milder applications. The new synthetic lubricants which are currently available can be operated at temperatures up to 120◦ C, with intermittent operating temperatures up to 150◦ C, without harming the transmission . . . .” New or improved synthetic lubricant base stocks are coming into the market, including higher viscosity PAO and poly internal olefins (PIO). Certain esters and PAG base stocks are gaining interest due to their biodegradability and eco-friendly properties. These new materials allow the lubricant manufacturer to extend the market reach of synthetic based gear lubricants. These new materials give rise

to the possibility of achieving high viscosity indices (VIs) without the use of polymeric VI improvers. The potential benefits include higher film thickness and little or no viscous shearing.

46.6.6 Higher Energy Efficiency with Synthetic Gear Lubricants The literature is replete with energy saving improvements through the use of synthetic lubricants, but energy improvement claims have had minimal impact in most industrial markets. Perhaps as newer demands are imposed on the gearbox this potential benefit will be more fully realized in the marketplace. As early as 1983, Facchiano and Johnson [36] examined the impact of synthetic vs. mineral oil based gear lubricants for their effect on energy efficiency. There results showed a 1.8 to 2.4% increase in energy efficiency depending upon temperature under prescribed load and test conditions in a double enveloping worm gear. Bronshteyn and Kreiner [37] examine the energy efficiency of industrial lubricants in some detail. They claim “lubricants influence energy efficiency mainly through reducing energy losses, which include churning losses and friction losses in hydrodynamic, elastrohydrodynamic and boundary lubrication regimes. The total energy loss depends on lubricant viscosity and chemical composition. Different sources of lubricant-related power losses in industrial systems are described. The dependence of churning and friction losses on oil properties is analyzed.” Among their conclusions is that “. . . a minimal pressure–viscosity dependence, as shown for PAOs, is most beneficial for energy conservation as well as for antiwear performance.” Naruse et al. [38] examined the influence of chemical structure of various lubricant compositions, based on mineral oils and various synthetics, on friction loss in spur gears. They conclude that: “generally, friction loss decreases with increasing viscosity and with increasing rotational speed at relatively high loads. Furthermore it becomes evident that the values of friction loss in high load range are quite dependent on the kind of lubricating base oil, that is, mineral oil and synthetic oils. The temperature rise of gear teeth has a close relationship with friction power loss of spur gear.” Michaelis and H˝ohn measured the churning losses and showed that by using low viscosity lubricants, reduced mesh power losses of as much as 50% of the power loss of mineral oils could be achieved by using Polyglycol-type lubricants. Besides this energy saving effect, the oil temperature in the gear box was reduced by up to 20◦ C [39]. Moore and his coworkers [40] performed a number of studies in process equipment in use in petrochemical operations and showed improved equipment reliability, energy efficiency, and reduced overall costs. Blahey et al. [41] showed

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a 3.7% energy savings vs. a mineral oil using an FZG gear test rig. This study then looked at energy efficiency in gearboxes used in a coal crushing operation. Depending upon load, 8.5 to 9.6% of increases in energy efficiency were obtained vs. a comparable mineral oil-based lubricant. 46.6.6.1 Lubrication modeling In 2003 a large body of information had been assembled in understanding the effect of lubrication and its effects on gear surfaces. AGMA published an information sheet (AGMA 925-A03) “designed to provide currently available tribological information pertaining to oil lubrication of industrial gears for power transmission applications. It is intended to serve as a general guideline and source of information about gear oils, their properties, and their general tribological behavior in gear contacts . . . . The equations provided allow the user to calculate specific film thickness and instantaneous contact (flash) temperatures for gears in service. These two parameters are considered critical in defining areas of operation that may lead to unwanted surface distress. Surface distress may be scuffing (adhesive wear), fatigue (micropitting and macropitting), or excessive abrasive wear (scoring). Each of these forms of surface distress may be influenced by the lubricant; the calculations are offered to help assess the potential risk involved with a given lubricant choice [42].”

46.6.7 Gear Lubricant Formulation Trends PAO manufacturers have improved both quality and product range. For instance in 2001 Hope and Twomey [43] of ChevronPhillips showed that improving the degree of hydrogenation (by modifying the order of processing steps) improved oxidation stability of commercial PAO by 30 to 50% (as measured by ASTM D-2272 and other techniques) depending upon viscosity grade. ExxonMobil has several patents in the field. Wu of that company claims low-viscosity fluids with low volatility compared to commercially available PAO [44]. In a separate patent by Wu, novel PAOs with high VIs and low pour points are disclosed. The resultant materials are C30 to C1300 liquid lubricants [45]. Goze et al. [46] also of ExxonMobil claims lower volatility and low pour points achieved through various catalysts. Several higher viscosity polymeric materials have recently been introduced into the market. These new materials extend upward the range of viscosities now available for gear lubricant formulation. Opportunities of greater film thickness under elastrohydrodynamic conditions are possible, helping to reduce friction, increase efficiency, and reduce wear: • Improved wear protection in many lubricating regimes. • A VI that is 35 to 40 units higher compared to conven-

tional PAO of the same viscosity grade.

• A pour point that is 10 to 20◦ C lower than conventional

PAO of the same viscosity grade. • An increase of synergistic VI when blended with mineral and synthetic base stocks. • A high viscosity with good ambient fluidity. Alkylated napthalene: According to Wu and Trotto [47] Alkylated napthalene offers improved solubility, oxidative stability, hydrolytic stability, and additive efficacy compared to esters. The alkylated naphthalene molecule has a lower affinity to metal surfaces compared to esters; it is less likely to form a lubricant film compared to highly polar esters. Alkylated Naphthalene materials offer superior thermal and oxidative properties.

46.6.8 Gear Lubricant Specification Trends Synthetic-based gear lubricants are coming of age as national and international specifications and standards recognize them as equal to or superior to traditional petroleumbased lubricants. For instance, in 2002 the American Gear Manufacturers Association issued ANSI/AGMA 9005E02. This version of the specification titled “Industrial Gear Lubrication” incorporates several changes compared to AGMA 9005-E94 (1994). For one, the distinction between synthetic (S) and mineral oil-based EP mineral oils was removed. Now, the specification treats all EP oils without exception for base oil type (although there are certain exceptions for water separation properties). Further, the oxidative stability requirement was tightened. Gone are the Timken OK load requirement, and 4 ball and 4-ball EP requirements. The newer version of the spec now requires FZG pass of 10, 12 or 12+ depending upon viscosity. The later spec now requires a determination of the temperature for bulk fluid dynamic viscosity at cold start-up.

TABLE 46.2 Selected Properties of ‘High VI PAO’ ISO VG 320 Synthetic Based Gear Lubricant EP (Synthetic Hydrocarbon Blend, no VI Improver) Property Kinematic viscosity at 40◦ Kinematic viscosity at 100◦ Viscosity index Pour point Shear stability, 20 h Flash point NOACK volatility, procedure ‘B’ Four ball load wear index (LWI) Four ball weld load Oxidation induction time

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Method

Unit

ASTM D-445 ASTM D-445 ASTM D-2270 ASTM D-97 CEC-L-45 ASTM D-92 ASTM D-5800 ASTM D-2596 ASTM D-2596 PDSC

cSt cSt — ◦

% ◦

% — kg min

Typical value 330 40 175 <−36 <5 >250 <3 >140 >700 >180

Finally, the new-E02 eliminates the AGMA viscosity grade requirements in deference to the ISO VG system. 46.6.8.1 Bearing specification requirements Gearbox OEMs are recognizing the importance of the lubricant and its impact on bearing life as a critical requirement. For instance, OEMs require the FAG FE 8 bearing test, which is part of DIN Standard 51517 Part III is required by all gearbox manufacturers in wind turbine applications. Other bearing tests are under evaluation for inclusion in the new oil specification as well. Additionally, the SKF Emcor rust test is being evaluated to include testing with salt water [48].

46.6.9 Specific Synthetic Gear Lubricant Applications This section discusses just some of the many examples of successful applications of synthetics in industrial gear application. 46.6.9.1 Wind turbines Wind turbines are machines that take the energy from wind and translate it into electrical energy. Such turbines range from less than 0.4 to well above 2.5 MW. Rotor blades for newer designs are on the order of 75 to 80 m in diameter. Gears connect a low-speed shaft to a high-speed shaft by increasing the rotational speed from about 30 up to 1800 rpm. Wind turbines are expected to last a minimum of 20 yr. Gears are generally spur, helical, sun and planetary, or combinations in order to achieve minimum weight and physical size. Typically 3 to 4 stages are employed with gear ratios on the order of 4 : 1. The loads on a wind turbine are directly related to the site and the design of the turbine. Load fluctuations may occur as a result of any of the following conditions: • Turbulent wind fluctuations due to terrain, boundary

• • • • • • • • • • • •

layer and atmospheric effects, and wakes from other turbines Vertical and horizontal wind shear Gravity loads on overhung components Yawing motion of the rotor Off-axis yawed operation Unsteady loading due to the blades passing through the tower wake Transient starting loads due to generation controls Loads due to monitoring Transient stopping loads from aerodynamic or mechanical brakes Rotor mass imbalance Buffeting during parked rotor conditions Transportation and assembly Fault-induced control actions [49]

The gearbox is subjected to periodic extreme and shock load conditions. A wind turbine gearbox is susceptible to fretting wear. For instance with the high-speed pinion stopped by a brake and the rotor buffeted by the wind, the mating gear rocks back and forth through small amplitude motion. False brinelling can occur when the wind turbine is parked for a short time under light winds. Fretting corrosion can occur when the wind turbine is parked for an extended period under heavy winds. Moreover, fretting corrosion and false brinelling are not merely restricted to gear tooth damage; roller-element bearings can also suffer these effects when the wind turbine is parked. Fretting corrosion can also occur when a wind turbine is rotating, occurring on components such as splines or blade pitch bearings that are subjected to small-amplitude vibratory motion [50] The gear Lubricant must function in an EHD regime; must cope with high incidence of boundary friction; and deal with the potential for generated debris and wear particles. Film thickness is extremely important. New advances in lubricant technology are going to increase film thickness. Examples include PAG-based fluids and high VI PAO fluids. Bearing failures account for nearly 90% of all wind turbine gearbox breakdowns. Wind turbine gearboxes subjected to wide extremes in ambient temperatures and moisture conditions: for example, High Desert, offshore platform, or North Sea cold temperatures. Its’ efficiency is extremely weight sensitive so that eliminating or downsize lubricant coolers and preheaters can offer a big weight savings and can lower costs to manufacture. Periodic maintenance and oil changes are quite costly and problematical. All these factors drive the demand for very-high-performance gear lubricants. 46.6.9.2 Pumpjack gearbox Oil and Gas industry pumpjacks can be subjected to extreme weather application. While petroleum oils are by far the favored lubricants in this application, in lowtemperature application, a synthetic-based EP gear lubricant offers significant performance advantages compared to petroleum type oils. In a multiyear field trial in Alberta Canada, testing demonstrated reduced start-up torques, an average 14.4% lower input energy, and improved pumpability for critical production applications at temperatures as low as −51◦ C. The synthetic gear lubricant maintained a favorable VI and pour point. Assuming that proper fluid condition monitoring and maintenance practices are employed, and given the lowered wear rates, these pumpjacks will require change-outs only once every five years [51]. 46.6.9.3 Open gear sets A nonasphaltic synthetic open gear lubricant can reduce downtime and scheduled maintenance when performing at

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extreme temperatures compared to a traditional asphalticbased, solvent-cutback lubricant. Developed to eliminate the use of solvents, this open gear lubricant allows for rapid set-up on gear teeth helping to prevent metal loss and reduces volatile organic carbon (VOC) emissions. The synthetic lubricant is a transparent amber color that can make clean up, inspection, and maintenance simple [52]. Improvements gained from the synthetic lubricant also included excellent cold-weather pumpability, negligible maintenance, and alleviation of excessive spare-part inventory previously required in anticipation of equipment failure [53].

46.6.10 Gear Lubricant Summary Synthetic gear lubricants will play an increasing role in the future lubrication of high performance gears as new processes, materials, and techniques allow for increased power density while at the same time serving extended periods in demanding environments. Competitive pressures of globalization and consolidation as well as mechanical, manufacturing, and environmental factors including energy efficiency will continue to drive future lubrication requirements and formulations.

46.7 COMPRESSOR OIL TRENDS The compressor lubricant industry can be segmented into three primary categories: industrial air compression, industrial gas compression, and refrigerant gas compression. Contrary to most industrial applications synthetics have been generally accepted and utilized with great success in the compressor industry. The primary reasons for their use and acceptance are directly related to the value-added benefits realized by end users including extended lubricant and equipment life, safer operations, environmental responsibility, and energy efficiency. Building on these attributes in addition to satisfactorily addressing new market requirements will contribute to the continuing use of synthetics in compressor applications. The general equipment/market trends influencing the lubricant utilized in each defined segment will be detailed in the following sections

46.7.1 Air Compression The former industry workhorse reciprocating compressors have been and will continue to be replaced by rotary screw designs for most air compressor applications. The traditional diester-based lubricants utilized in most reciprocating designs will remain the lubricant of choice. As the reciprocating design are replaced a decline in the diester lubricant consumption will follow. Rotary screw compressors enjoy the largest market share of the air compressor segment. PAO, Group III, and PAG/ester blend-based products are the current synthetic

base fluids of choice for many OEM’s. Group III products are gaining ground based on comparable performance to PAO at significantly lower costs. End users demands and local legislations are driving future design considerations, which include smaller, quieter, reduced environmental impact, and lower cost of operation compressors. The lubricant selection amongst other engineering considerations plays a significant role in the design process to satisfactorily address each of these emerging market requirements. The leading OEM’s are gradually upgrading their engineering technologies in addition to employing advanced synthetic lubricant technologies to meet these market challenges. In particular there is a trend toward utilizing Polyolester lubricant technology as part of the solution. The applicability of Polyolesters to meet these market requirements is driven by the following attributes. • • • • • •

Extended drain intervals of 10,000 h or more Excellent thermal-oxidative stability Biodegradability Low order of toxicity Inherent lubricity properties Good elastomer/seal compatibility

At present, polyolester technology is the leading chemistry to address the current trends; however, the current synthetic fluids are expected to continue to hold the majority market share for the immediate future. As the demand increases new performance attributes the trend toward higher performing synthetic fluids will accelerate.

46.7.2 Industrial Gas Compression The preferred lubricants for hydrocarbon gas compressors are generally based on PAGs although any of the common types of mineral oil or synthetic lubricants suffice in many applications. The overriding consideration in selecting which lubricant to use is the degree of solubility of the particular gas being compressed in the compressor lubricant, that is, minimizing gas solubility in the oil results in less oil dilution and subsequent loss of oil viscosity. This is the foremost consideration and the reason that PAG’s have found a niche in this market. As in the compression of air, the two main types of compressors utilized in the process and hydrocarbon gas industry are reciprocating and rotary screw. 46.7.2.1 Rotary screw The trend in the process gas industry is toward achieving ever increasing pressures by means of rotary compression. Formulated PAG compressor oils from ISO 68 to 150 are commonly employed. Since the lubricant in rotary screw compressors is recirculated, it is important that the effects of oil dilution by the gas are minimized. Rotary screw compressors are found mainly in various types of gas gathering operations.

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There is also a trend toward multistage rotary screw compressors, which permit greater efficiencies than the typical rotary/reciprocating combination. This makes the choice of lubricant even more critical. 46.7.2.2 Reciprocating Again, the trend is toward very high discharge pressures in reciprocating compressors lubricated with PAG-based fluids. For example, the compression of hydrocarbons, nitrogen, and carbon dioxide by hyper-compressors used in enhanced oil recovery operations typically discharge at 5,000 psi with some multistage compressors approaching discharge pressures of 10,000 psi. The trend toward higher discharge pressures exacerbates the loss of oil viscosity due to dilution, resulting in a lubricant requirement for oils of higher ISO grades, for example, ISO 220 to ISO 460. 46.7.2.3 Future trends Environmental awareness and increasing efficiencies in fuel conservation and ultra low emission vehicles (ULEV) has lead to developments in compression of natural gas and hydrogen for consumer-type-fueling systems. Hybrid and natural gas fueled vehicles will require the use of small natural gas compressors, which must operate under standards of safety and reliability more stringent than current industrial standards. Fuel cell powered engines will require the same standards of safety. These standards are not achievable with traditional mineral oil-based lubricants. PAG-based fluids and other types of synthetic fluids such as silicate esters and polyethers will most likely dominate these applications [54–57]. Experimental research efforts by several lubricant base stock manufacturers are attempting to incorporate multifunctional chemical groups to impart improved antiwear, thermal oxidative resistance, and other desirable enhancements into the synthetic base. If successful, these efforts will result in greatly improved lubricant life, improved compressor performance and reliability, and subsequent reduction in waste oil disposal costs [58].

46.7.3 Refrigerant Gas Compression The refrigeration and air conditioning industry is in the process of experiencing dramatic changes, which will have significant impact on the growth of synthetic lubricants. The Montreal protocol’s initiatives are well documented with regard to the phase out of ozone depleting chlorinated refrigerants principally R-22 [59,60] Over the past ten years or more a conversion of both automotive air-conditioning systems and small appliances have been converted to hydrofluorocarbon (HFC) nonchlorine containing gas (R-134A). PAGs became the product of choice for mobile air-conditioning systems while polyolesters dominated the small appliance market.

The market is now experiencing significant changes in several market segments. Europe and Asia are moving toward the use of hydrocarbons refrigerants such as isobutene (R-600), which utilizes mineral oil as the lubricant in small appliance applications [61]. The primary driver for the change is cost. The system design and associated cost of the refrigerant and lubricant are significantly lower compared to the traditional designs. North America is resisting the change due to flammability/fire concerns. The typical appliances in the North American market are much larger than those found in Europe or Asia. As a result the amount of flammable hydrocarbon gas is larger [62]. The larger industrial air-conditioning systems continue to utilize primarily R-22 type gases. Although not certain, the expected trend is that R-22 refrigerant gases will be replaced by R-407/R-410 (chlorine free materials). Significant pressures are being placed on air-conditioning OEM’s to increase the efficiency of their units by as much as 30% as reflected in the proposed 13 SEER standard [63]. This in itself is not the reason for a change to HFC refrigerants. Legislation requires the phase out of chlorofluorocarbon (CFC) refrigerants in industrial air conditioning systems by 2010. This will positively affect the growth of polyolesters (POEs) as the lubricant of choice for miscibility with the chosen gas. Polyvinylether technology remains a viable technology for select applications; however, it is expected to experience minimal growth relative to the general market [64]. The market for refrigeration lubricants is uncertain and will depend largely on government actions, environmental/health concerns, and cost constraints. The future growth of synthetic lubricants, principally PAGs and POEs in the refrigeration market is directly related to the refrigerant technology employed.

46.7.4 Compressor Lubricants Summary The market for synthetic lubricants in compressor applications is changing with the dynamics of each subsegment. Synthetic lubricants have been widely accepted as superior value-added products in most compressor applications and this will continue. Energy savings, longer life, and environmental considerations will continue to influence the choice of the lubricant employed. Environmental and legislative factors are leading factors that necessitate additional potential changes, which in most cases will require higher performing synthetic technologies to meet emerging market requirements.

46.8 HYDRAULIC OIL TRENDS Hydraulic fluids represent the largest market share of industrial lubricants in the world. A tremendous variety of equipment and applications utilize hydraulic fluids. The next sections briefly define the types of hydraulic

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Hydraulic fluids

Hydrostatic applications

Hydrokinetic applications

ATF DIN 51502

Mobile systems

HA HN ISO 6743/4

UTTO STOU

FIGURE 46.1 General classification of hydraulic fluids

pumps and classification of different fluids. The primary focus of this section is to discuss future trends in the hydraulic oil segment.

46.8.1 Types of Hydraulic Systems Hydraulic pumps can be classified into three main categories: Gear pumps: Gear pumps are relative to other pump designs and inexpensive to manufacture. A Design News study [65] in 2002 reported that 71% of engineers specify a fixed displacement gear hydraulic pump in their systems. The main market for this type of pump is within the mobile hydraulic segment such as construction equipment. Vane pumps: Vane pumps are a low cost alternative to piston pumps. Vane pumps operate up to about 4500 psi and thus fall into the mid-performance range. A wide variety of applications use vane pumps. Piston pumps: Piston pumps are gaining increasing importance as they offer significant control at low speeds. Operating pressures approach 6000 psi and several pump manufacturers are pushing for even higher pressures primarily by incorporating superior valve technology. Again a wide variety of application use piston pumps to take advantage of the higher efficiencies.

46.8.2 Hydraulic Fluid Classification Mang and Dresel [66] offer a detailed look at the various classification schemes (Figure 46.1 and Figure 46.2) to enable users to select a suitable fluid. It is interesting to note that along with classic fluid property specifications Mang and Dresel add application-derived classifications as well, such as food grade lubricants.

46.8.3 OEM and End User Future Trends Some of the key trends are listed below: A brief description of each trend follows the list: • Ecologically sensitive fluids • Crop derived fluids

Hydrostatic apps

Food grade

Environmentally friendly ISO 15380

Mineral oil based ISO 6743/4, DIN51502 ISO 6743/4 DIN 51524

Water soluble

ISO 11158

Water insoluble

HEPG

NSFH1 and H2

HETG, HEES, HEPR

Fire resistant 7th Lux, ISO 6743/4. Water containing

Water free

HFAE, HFAS, HFB, HFC

HFDR, HFDS, HFDT, HFDU

HH, HL, HM, HR, HV, HS, HG

DIN 51524

HL, HLP, HLPD, HVLP, HVLPD

FIGURE 46.2 Classification of hydraulic fluids for hydrostatic applications • • • • • • • • • • • •

Synthetic hydraulic fluids Improved cleanliness Improved fire resistance Products for use in food and pharmaceutical plants High-pressure systems Increased specifier sophistication Shrinking market for low-pressure systems Fluid and supplier rationalization Multigrade fluids Elastomer versatility Fluid monitoring and trend analysis Ashless formulations

46.8.3.1 Ecologically sensitive fluids The trend to utilize more ecologically sensitive fluids is set to continue both for novel applications and for replacing mineral oil-based fluids in sensitive applications. It is envisaged that the legislative and consumer focus will change from simply requiring a biodegradable fluid to one that takes account of other factors as well. Norrby [67] suggests that for environmentally acceptable lubricants (EALs) in addition to biodegradability, renewability, toxicity, bioaccumulability, life cycle assessment, and energy savings should be considered to determine the overall impact to the environment. He also reports that future trends in the development of EALs include increasing use of renewable raw materials and re-refined base oils. Denison has published data indicating that some biodegradable fluids perform better than mineral oil in vane pumps. As the costs come down for ecologically sensitive fluids, a significant increase in volume is expected. Norrby et al. [68] report that the European “Environmentally Acceptable Lubricants” (EALs) market is expected to

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grow by 15% per annum to 2006 and suggest that the next strong market for EALs is in mobile hydraulics such as off-highway equipment and construction. They also suggest that there is a strong downward pressure on price attributed to the economic downturn and that the legislation and global agreements are not moving at sufficient pace for rapid EAL development. This however is expected to change as the global economy is now beginning to show signs of recovery. 46.8.3.2 Crop derived fluids Bevard [69] reports that hydraulic fluids leaking from Triplex mowers, tractors, and aerators with hydraulic lift cylinders and other machinery utilizing hydraulic systems can kill putting green turf on a golf course. Bevard suggests that the vegetable oil-based fluids are just as damaging to the turf as mineral oil-based fluids as primarily damage occurs due to the high temperature of the oil; however, the recovery of the grass is much faster with vegetable oil-based fluids. 46.8.3.3 Synthetic hydraulic fluids Pressure to deliver services in all climatic conditions is putting pressure on users to choose synthetic fluids that typically offer a wider temperature tolerance. Cullen [70] reports one such application in Montreal, Canada where significant reduction in repair and maintenance was achieved by switching a fleet of garbage collection trucks from mineral to synthetic hydraulic fluids. Ehrenman [71] reports that in the United States the demand for synthetic functional fluids is expected to grow by 5% per year to 2006 to $2.8 billion.

46.8.3.4 Improved cleanliness Improved cleanliness of the hydraulic system is a critical element in extending equipment life. This has implication for formulators, system designers, filter manufacturers, and operators alike. From the formulator’s perspective with some filter manufacturers recommending a 3 µm filtration there are implications for keeping additives such as siliconbased antifoam in solution. Stewart [72] reports that filter manufacturers are concerned about filter fibers breaking away due to ever increasing drain intervals without a filter change. He reports a maximum of 325 to 400 h filter lifetime in mining off-road equipment. Stewart also reports that a change from a 13 to a 2 µm fuel filter resulted in a doubling of pump life. Similarly, Anderson [73], reports that in a trial at the Port of Tacoma, USA, maintenance costs were reduced by up to 97% on a straddle carrier by improving the oil cleanliness. Among “extended service” technologies suggested by Stewart are upgraded cellulose, cellulose–synthetic blends, microglass, and meltblown polyester filter media.

dimensions. Redpath [76] reports that for the earth moving segment current systems are operating above 6,000 psi with fuel system pressures approaching 40,000 psi. 46.8.3.8 Increased specifier sophistication End users are knowledgable about different types of fluids and their use in various applications. This trend is expected to continue with sophisticated selection, purchase, and use criterion established end-users. System designers are also critically evaluating various hydraulic fluids on a range of measures that not only include the traditional fluid properties but also field application demands such as corrosive environments, usage in eco-sensitive areas and logistic and technical support. Technical articles on selection and use of hydraulic fluids are now to be found in virtually all industry publications on a regular basis. As an example, Zink [77] suggests evaluating fluids on safety and environmental concerns along with the performance characteristics such as antiwear performance, oxidation resistance, and elastomer compatibility. 46.8.3.9 Shrinking market for low pressure systems

46.8.3.5 Improved fire resistance Fire resistance of hydraulic fluids has also come under the spotlight with several commentators indicating a rapidly developing market. Hitchcox [74], writes that the mere existence of fire resistant and environmentally friendly hydraulic fluids is a liability for nonusers and suggests that litigation prevention may be an important driving force for the development of such fluids.

46.8.3.6 Products for use in food and pharmaceutical plants In many countries, food processing or preparation areas require the use of “food grade” lubricants [75]. This market segment is expected to enlarge rapidly. Food grade lubricants are generally considered those that have been formulated with approved ingredients found in the Food and Drug Administration (FDA) document 21 CFR178.3570 and the Generally Recognized as Safe (GRAS) list within 21 Code of Federal Regulations (CFR). Development of food grade products became stagnant around 1998 by the departure of U.S. Department of Agriculture (USDA) from approving food grade lubricants. National Sanitory Foundation (NSF) International and the Dutch Nederlandse Organisatie Voor toegepast-natuurwetenschappelijk Onderzoek (TNO) among others have since filled this void.

46.8.3.7 High pressure systems The hydraulic fluid market is steadily moving toward ever increasing pressures and smaller overall system

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Electromechanical systems are grabbing market share from low-pressure systems. Gear pump systems are particularly affected. Vehicle assembly robots and injection molding machines are examples of segments where this migration is the strongest [78]. 46.8.3.10 Fluid and supplier rationalization There is an increasing trend among the end users toward consolidating products and suppliers. Economic pressures primarily drive this trend. Although in some market segments, such as food grade lubricants, this is partly to avoid cross contamination mistakes. Several lubricant suppliers now offer “total fluid management” programs, however in most cases it is found that savings are achieved in the first two years after which the program becomes unattractive for the fluid suppliers and the customers. An additional concern with such programs is the heavy reliance on a single source and the potential loss of not capitalizing on new developments by another supplier. 46.8.3.11 Multigrade fluids Placek [79] has documented the benefits of using multigrade hydraulic fluids in the forestry segment and includes purchase, maintenance, downtime, and disposal costs in the economic evaluation. Lost production time and machine life reduction is suggested as additional costs to be assessed. He concludes that the use of multigrade hydraulic fluids was a significant factor in keeping the machinery operating at the optimum level and that these fluids were the preferred option when wide operating temperature ranges are encountered.

46.8.3.12 Elastomer and material versatility The applications using hydraulic fluids are widespread with limitless variations in operating environments and demands on the system. A critical aspect in improving system versatility is in improving the versatility of the elastomers, coatings, and hoses used in the system. This is becoming increasingly important as users switch from one fluid type to another due to legislative or other operating demands. As an example, Wangsgaard [80] reports on new urethane seals that are resistant to hydrolysis and thus are suitable for use in vegetable-based fluids and other esters that have a tendency to absorb water. 46.8.3.13 Fluid monitoring and trend analysis Biamonte [81] calls for a rigorous check of the health of the hydraulic fluid at least on a quarterly basis. He suggests the monitoring of viscosity, water, wear metals, and contaminant levels as a minimum and that trending is an effective technique to avoid field failures. Routine fluid monitoring and trending is expected to grow significantly as pressures on system reliability increase. 46.8.3.14 Ashless formulations Legislation, particularly in Western Europe and environmental concerns in other applications is forcing formulators to deliver ashless formulations that is, not containing any metal containing additives. ZDDPs, which are common antiwear additives used in hydraulic fluids, have seen their use decline and this is expected to continue. Duncan et al. [82], report on ashless additives in synthetic POE fluids that meet the performance of several conventional fluids and exceed the performance of vegetable-based oils.

46.9 GREASE TRENDS 46.9.1 Grease Overview In general, grease provides a better mechanical cushion for extreme conditions, resists the washing action of water while sealing out contaminants, and stays where it has been applied compared to liquid lubricants. Lubricating greases utilized in heavy industrial, food processing, automotive, and automotive after-market applications tend to be based primarily on conventional base oil technology. These market segments have incorporated the use of new thickener technologies almost as soon as the technology has become available. On the other hand, commercial and military aviation applications have and will continue to rely on synthetic base oil technologies for lubricating grease requirements. The military aviation market has not readily incorporated advanced grease thickener compositions. The changing needs of these market segments have resulted in new manufacturing methods and equipment as well as utilization of

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components that lubricating grease manufacturers have, as a rule, avoided. Consumer demand, regulatory pressure plus advancements made in materials and mechanical engineering provide machinery and components that require lubricating grease products that conform to more stringent specifications. Grease manufacturing must supply product that consistently meet these stringent quality and performance demands, while providing a greater variety of products at the same time [83].

46.9.2 Grease Manufacturing Trends Understanding grease trends requires basic knowledge of the manufacturing process and associated challenges. Production techniques and chemical nature of the components utilized in lubricating grease formulations dictate the processing equipment that manufacturing facilities employ. Lubricating grease production can be described as the formation of a thickener component in a reaction vessel followed by heat to promote the reaction or gel formation. After the thickener has been properly formed the manufacturer cools the product and then mills the grease while adding more base oil, followed by additive addition and filtration, see Figure 46.3. Lubricating greases of a commodity stature tend to be supplied by major petroleum refining companies. These products tend to be lower cost materials that are made in continuous saponification or grease making units. Continuous grease making units produce about 4,000 to 10,000 lbs of grease an hour and need to make large quantities of the same grease formulation per production run to maintain product consistency and cost efficiency. One of the drawbacks to continuous grease making units is that all the components required to manufacture a particular formulation must be liquid, excepting when product is diverted to finishing vessels for the incorporation of lubricating solids [84]. Noncommodity grease formulations tend to be produced in batch processes, which are capable of producing large quantities of lubricating grease, but batch size is constrained by processing vessel capacity. 46.9.2.1 Batch processing Batch processing methods and equipment are more suited to producing specialty greases, especially those based on synthetic fluids other than the synthetic hydrocarbon types. Batch processing equipment is based on pressure reactors like STRATCO® Contactors and autoclaves or open to the atmosphere vessels with proper mist elimination systems. Stratco contactors are very efficient batch processing equipment due to grease saponification times taking approximately 21 to 23 the amount required with open to atmosphere vessels and autoclaves [85]. Grease manufacturers with batch processing equipment for synthetic oil based greases are becoming more important to supply

the demand of consumers for these specialty lubricants. This demand for specialty greases with synthetic base oils is a result of the longer life, improved performance in applications of extreme thermal or oxidizing conditions, and additional lubricity and film forming ability provided by these types of products. Batch processing techniques lend the lubricating grease manufacturer the ability to produce products with mixed thickener systems. Generally, during application the intermixing of greases with differing thickeners can show compatibility issues. The performance of the intermixed blend may be affected in such a way as to influence the performance of the lubricated part. For example, sodium stearate thickened greases find utility as moderately high temperature lubricants in food machinery applications in the Asian marketplace. Sodium stearate thickeners are not approved components for greases that may have incidental food contact. NSF International, a not-for-profit consumer advocate and public health standards group, has approved some aluminum complex thickened greases with United States Pharmacopeia (USP) white oil or PAO fluids for incidental food contact. Compatibility testing between these two types of grease as per American Society for Testing and Materials (ASTM) D 6185 — Standard Practice for Evaluating Compatibility of Binary Mixtures of Lubricating Greases can provide an indication where potential problems could arise in application upon the change from one grease to another. In the future, the intermixing of different grease thickeners to achieve specific performance enhancements will be employed for the lubrication of critical machines operating in adverse conditions. For example, the intermixing of calcium complex greases with polyurea thickened greases has been described as providing a lubricating grease with improved fretting wear performance and additional loadcarrying capacity for automotive bearings in front wheel drive applications [86]. The polyurea described in the invention would not have exhibited improved load-carrying capability without the calcium complex component nor would the polyurea have had a dropping point in excess of 500◦ F. Reduced wear due to fretting would not have been achieved in the calcium complex grease without the polyurea component. Note that the calcium complex grease typically exhibits dropping points in excess of 550◦ F, but the patent describes the invention with a substantially lower dropping point. The dropping point given for the invention is great enough to provide adequate performance in under-the-hood automotive applications. 46.9.2.2 Manufacturing for low noise The manufacturing procedures employed by grease producers can be modified to further enhance the performance of specialty greases in fulfilling the needs of bearing manufactures, such as “low noise” greases. The result of

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performance enhancement made by bearing manufacturers for automotive, precision, and electronic/electrical equipment has shown that the noise arising from these types of applications are attributable to the lubricating grease [87]. Filtration of grease components and the finished product take on additional importance due to the substantial influence associated with contamination of foreign materials such as dirt. Because grease is a semifluid to solid product of a dispersion of finely divided particles (thickener) in a liquid lubricant there is a need to control the particle size of the thickening agent. Some lubricating grease manufacturers have dedicated the time and capital to develop manufacturing processes to utilize “clean” raw materials in modified processing equipment that generate grease thickening particles of less than 500 µm in size. An ingenious method of grease production developed by a major oil company was to incorporate milling during the thickener formation. In particular, during the production of low-noise lithium complex thickened grease (with and without synthetic fluids) the grease components were filtered in liquid form prior to addition to the batch. The lithium complex thickener was milled during the saponification process in a SUPRATON® model S400 milling apparatus (available from Krupp Industrietechnik GmbH) with a gap setting of 100 to 500 µm [88]. Another major oil company known for “low noise” polyurea thickened grease employed a facility with prior filtration of grease components and a clean-room environment dedicated to producing one grease formulation.

46.9.3 Application Trends The commercial and military aviation industry has been designing new aircraft and specifying military qualified lubricating greases that had not been reformulated for decades. Lubricating greases qualified to a military or commercial aviation specification cannot be changed without qualifying the new formulation. The qualification of a lubricating grease product can be time consuming and expensive. The subsequent lack of product innovation by lubricant manufactures is not looked upon as entirely inappropriate. A result of decades without major changes to specifications or lubricant technology upgrades are a plethora of qualified suppliers to a given specification. Many of these specifications have performance overlap and in the mid-1990s resulted in a request from commercial aviation companies for the airframe manufacturers and lubricant industry to develop a single-grease specification that could be used on the entire plane [89]. The product initially developed reduced the number of different grease products specified to lubricate a single aircraft from 99 to less than 10. The Boeing Company issued a material specification designated BMS3-33A in 1995 that dictates the lubricating

grease qualified to this specification will be composed of a lithium complex thickener. Other descriptive requirements of this specification are an operating temperature range for the grease of −73 to 121◦ , high load-carrying capability, must prevent corrosion in harsh environments, and resist the washing action of water. The specific requirements of the Boeing specification are more stringent than any military specification written with similar testing procedures (examples would be MIL-PRF-23827C, MIL-G-21164D). A number of lubricant manufacturers designed a mixed grease thickener system (albeit primarily lithium complex) that would allow the qualified greases to perform at low temperatures, possess high load-carrying capability, and prevent corrosion of iron containing metals exposed to salt water solutions of 3% sodium chloride. This mixed grease thickener system incorporated a significant portion of calcium sulfonate complex that is added to the lithium complex during the manufacturing process. During the manufacturing process of lithium complex grease formulators can incorporate low temperature synthetic diesters, which is needed for low temperature performance. The manufacturing of calcium sulfonate complex cannot incorporate synthetic diesters without hydrolyzing these base oils. The calcium sulfonate complex portion allows the qualified grease to prevent corrosion. This portion of the lubricating grease contributes to reducing water washout tendencies and contributes to the load carrying capability of the product. The significance of utilizing a mixed thickener system is that the aviation industry forced lubricant designers to combine the benefits of one thickener type and incorporate the benefits of another to solve difficult lubricating conditions. Powder metallurgy processing techniques produce micrograin high-speed steels with improved wear resistance. These specialty steels are impregnated with oil or semifluid greases and then expected to function in operating conditions reflective of a starved lubrication regime. Theoretically, impregnation of P/M materials with semifluid grease provides lubricating films with a mixed composition of lubricating oil and thickener. The composition of the lubricating film is dependent upon the grease type and speed of the rolling or sliding contacts. Experimental evidence for the makeup of the mixed composition has been investigated with infrared spectroscopic techniques [90]. Lubricating grease thickeners are thought to form thin residual films on metal surfaces. Under starved conditions the lubricating film thickness will depend on the efficiency of the base oil to flow from the thickener into areas of Hertzian contact [91,92]. In these studies greases with thickeners of lithium 12-hydroxystearate (14% by weight) and tetraurea (7 and 14% by weight) showed that the lubricating film was comprised mostly of base oil. Thickeners at low concentration and of lower shear stability, in this case the tetraurea thickener, provided greater lubricating film thickness [9]. Impregnation of P/M steels

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with synthetic diester based lithium 12-hydroxystearate thickened semifluid greases work exceptionally well in prolonging the life of these bearings and tools. Reason being that a shear stable thickener like12-hydroxystearate at low concentration (typically less than 7% by weight) releases the diester base oil at rates sufficient to prolong the life of the part. The polar nature of the diester base oil forms a more stable lubricating film, thus providing a larger film thickness than products based on conventional mineral oils.

46.9.4 Environmental Trends Environmental legislation and consumer awareness are impacting the design of and application of grease. Industries operating in eco-sensitive environments are looking to minimize the risk of adversely impacting the environment. The marine and inland waterways are particularly interested in eco-friendly grease products. Ocean going vessel applications include wire rope dressings and vessel stern tubes. Water treatment facilities and hydroelectric facilities are also under pressure to be more environmentally focused. The offshore oil explorations and drilling industry is moving toward greener grease applications. Grease trends in these applications require biodegradability, low toxicity, and the absence of sheen on the water in the event of a release. Formulators employ ester and vegetable-based products to meet the environmental requirements of these applications. Emphasis on environmentally friendly greases, has influenced formulators to consider calcium sulfonate thickener systems. Depending on the chain length, some calcium sulfonates are considered environmentally friendly. One of the challenges facing grease formulators is to find ecologically sensitive additives for rust inhibition, antiwear, and long operating life (The EC Dangerous Preparations Directive attempts to codify additives and thickener systems into broad categories) [93]. For example, amino-based rust inhibitors do not function effectively in the presence of salts. Therefore, finding additives that will work in salt water, brackish water, or hard water environments is difficult.

46.9.5 Grease Market Trends From the above examples, the direction in developing new lubricating greases can be summarized into several specific aspects. In general, users of lithium thickened greases are moving to lithium complex greases, while users of lithium complex greases see increased need for the performance benefits of calcium sulfonate complex thickeners. Calcium sulfonate complex greases offer some inherent lubricating properties with respect to wear and rust inhibition as well as water resistance. Manufacturing equipment and methodology are evolving to produce products that have measurable differences in grease thickener property, such as particle size needed

to sustain the increasing desire for “low noise” greases. A move is seen from mass producing large quantities of the same grease formulation to fulfill commodity supply and demand rules of major petroleum refining operations to the production of batch quantities of specialty lubricating greases to satisfy the more stringent demands imposed by the lubricant consumer. The demand by industry for higher performance greases continues to increase. To achieve the performance requirements formulators are intermixing thickener systems and incorporating new synthetic base fluids to optimize the final formulation. Environmental pressures are also changing the selection and formulation of greases with the requirement of more eco-friendly solutions to meet local and global legislative requirements. To address these industry trends grease marketers/manufacturers will need to be flexible and provide tailored solutions for specific applications.

46.10 EFFECTS OF BASE OILS ON INDUSTRIAL LUBRICANTS With the expected increases in industrial lubricant demand from Asia, North America, and Europe, one can expect tight base oil supplies. Already, Asia is seeing a shortage of base oil for its projected demand [94]. The advent of Group II and Group III production will create further shortages as refiners meet the demands for these new base oil qualities while sacrificing Group I production. Within the next 10 yr, gas-to-liquids (GTL) technology will enter lubricant oil formulations [95]. GTL technology gives refiners the opportunity to tailor molecules to meet exact specifications such as viscosity, VI, and pour point. The new technology products will come the closest to approaching the performance of PAOs and PIBs. In the short term, one can expect new base oil stocks from Russian refiners. Already, Europe and Asia are importing Russian base stocks for use in finished lubricants [96]. If Russia can supply the world with additional base oils, this will mitigate the global tightening that we are experiencing in Group I stocks as more refiners move to Group II and Group III production. So what does all this mean for finished industrial lubricant marketers? In general, Group II and Group III products are not widely used within industrial lubricants. Group II stocks can be found in gas engine oils, compressor oils, and turbine oils. Over the next few years, industry should see a shift toward more Group II and Group III stocks in hydraulic and gear oils. Industrial users will insist upon the additional quality offered by Group II and III stocks. The automotive sector has already adopted this standard. It is now progressing into commercial vehicle lubricants as well as construction and mining. As Group II and Group III stocks increase industrial market share, conventional Group I stocks will decrease.

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Industrial synthetics formulated with PAO, PAG, or Polyolester technology should continue a steady growth [97]. Polyolester technology will continue to develop in compressor and aviation turbine technology. As the biodegradable market expands, polyolester base stocks will play a pivotal role in achieving extended life and high temperature performance. Polyalkylene glycol base oils will offer niche performance attributes particularly within the oil and gas segment where gas and liquid solubility is crucial. Compatibility with PAOs, mineral oils, and POEs, will hinder growth of PAGs. PAOs have already been widely accepted within the industrial lubricant segment. Hydraulic, gear, and circulating oils that require high or low temperature performance will typically use PAOs.

46.11 SUMMARY There are many trends happening within industrial lubricants. Some trends, such as biodegradability, are directly influenced by legislation. Demands for biodegradable lubricants are clearly increasing. Within the gear, compressor, and hydraulic markets, manufacturers are reducing the size of equipment. With smaller sump sizes, there are more thermal and oxidative stresses on the lubricant. As a result, future products will incorporate advanced additive technology and synthetic technology to improve lubricant performance characteristics. Some of the same trends affecting oils are also influencing greases. Specialty greases incorporating the benefits of mixed base oil and thickener technologies will emerge to meet the needs of critical equipment. All of these trends are requiring the development of new advanced products, which in many instances are satisfied by employing synthetic lubricant and grease technologies. The growth of synthetics will be directly related to the requirements for improved industrial productivity, efficiency, and environmental concerns. In addition, the cost/performance ratio compared to conventional technologies will have significant influence on the next generation of synthetic fluids.

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23. Krantz, T.L. and Kahraman, A., “An experimental investigation of the influence of the lubricant viscosity and additives on gear wear,” Tribology Transactions, Volume 47, pp. 138–148. 24. Ali Erdemir, “Dry Film Lubrication,” STLE Chicago Section Lube School, 17–18 March, 2004, Argonne National Laboratory. 25. Weck, Hurasky-Schònwerth, and Bugiel, “Service behavior of PVD-coated gearing lubricated with biodegradable synthetic ester oils,” Gear Technology, November/December 2003, pp. 34–40. 26. Errichello, R., “Micropitting of gear teeth-a review of the literature, description of morphology and mechanism, and recommendation for prevention,” Copyright Geartech, 3/26/02. 27. Li, S., Devlin, M., Milner, J., Iyer, R., and Tze-Chi Jao, “Investigation of pitting mechanism in the FZG pitting test,” SAE Technical Paper Series, 2003-01-3233, Powertrain & Fluid Systems Conference Pittsburgh, PA, 27–30 October 2003. 28. Li, S., Devlin, M., et al., “Investigation of pitting mechanism in the FZG Pitting Test,” SAE 2003-01-3233, Powertrain and Fluid Systems Conference and Exhibition, Pittsburgh, PA, 27–30 October 2003. 29. Uneo, T., Ariura, Y., and Nakanishi, T., “Surface durability of case-carburized gears — on a phenomenon of gray-staining of tooth surfaces,” ASME paper, No. 80-C2/DET-27, The American Society of Mechanical Engineers, New York, 1980. 30. Cardis, A.B. and Webster, M.N., “Gear oil micropitting evaluation,” Gear Technology, September/October 2000, pp. 30–33. 31. Anon “Ceramic Bearings-an Engineered Solution”, http://www.timken.com/industries/superprecision/ceramics/. Copyright © 2004 The Timken Company. 32. Jessica Gorman, “Fracture protection: nanotubes toughen up ceramics,” Science News Online, Week, 2003, Volume 163, p. 3, Anon “Ceramic Bearings-an Engineered Solution”, http://www.sciencenews.org/articles/20030104/ fob1.asp. 33. Smith, Z. and Fletcher, M., “Gearing up with plastic,” Mechanical Engineering, Copyright 1998 by The American Society of Mechanical Engineers, http://www.memagazine. org/backissues/september98/. 34. Deirdra Barr and Ethyl Petroleum Additives Ltd., “Modern wind turbines: a lubrication challenge,” Machinery Lubrication Magazine, September 2002. 35. “Procedure for Qualifying Synthetic Base Gear Lubricant,” European Patent No. AU7709191, by Muyskens D.E., Newkirk J.E., Published 1991-11-28. 36. Facchiano, D.L. and Johnson, R.L., “An examination of synthetic and mineral based gear lubricants and their effect on energy efficiency,” Presented at the National Lubricating Grease Institute, 23–26 October 1983. 37. Bronshteyn, Lev A. and Kreiner, Jesa H., “Energy efficiency of industrial oils,” Preprint no. 99-AM-2. Presented at the 54th Annual Meeting, Las Vegas, NV. 23–27 May 1999. 38. Naruse, Chotaro., Nemoto, Ryozo., Haizuka, Shoui., and Yoshizaki, Masatoshi., “Influence of oil viscosity, chemical

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59. United Nations Environment Program, “Montreal protocol on substances that deplete the ozone layer,” Final Act, United Nations, 1987. 60. London meeting of the parties to the Montreal Protocol, June 1990. 61. Greg Mazuikiewicz, “Adding up the costs of higher SEER,” The Air Conditioning, Heating & Refrigeration News, 19 November 2001. http://www.achrnews.com/ CDA/ArticleInformation/coverstory/BNPCoverStoryItem/ 0,6152,67439,00.html 62. Richard A. Kelley, Business Manager, Hatco Corporation, Personal Interview, 6 May 2004. 63. Danfoss Compressors, “Practical application of refrigerant R 600a isobutane in domestic refrigerator systems,” Technical Bulletin CN.60.E2.02, November 2000. 64. Richard A. Kelley, Business Manager, Hatco Corporation, Personal Interview, 6 May 2004. 65. “Fluid power,” Design News, 4/7/2003, Volume 58, p. 44. 66. Mang, Theo, Dresel, Wilfried (eds). Lubricants and Lubrication. Vch Verlagsgesellschaft Mbh; 2001. 67. Norrby, Thomas, Environmentally adapted lubricants — where are the opportunities? Industrial Lubrication and Tribology, 2003, Volume 55, pp. 268–274. 68. Norrby Torbacke, T. and Kopp, M., Environmentally adapted lubricants in the Nordic marketplace — recent developments. Industrial Lubrication and Tribology, 2002, Volume 54, pp. 109–126. 69. Bevard, Darin S., “After the spill,” Grounds Maintenance, 2002, Volume 37, pp. G33–G36. 70. Cullen, David, “Cold comfort,” Fleet Owner, 2004, Volume 99, pp. 54–55. 71. Ehrenman, Gayle, “Use of synthetic fluid to spread,” Mechanical Engineering, 2003, Volume 125, pp. 22. 72. Stewart, Larry, “Filter innovations clean today’s fluids,” Construction Equipment, 1999, Volume 100, pp. 72–77. 73. Anderson, B., “Fluid analysis pays big dividends,” Hydraulics and Pneumatics, 2002, Volume 55, pp. 41–43. 74. Hitchcox, A.L., “Fluid formulations continue evolutionary improvements,” Hydraulics and Pneumatics, 1999, Volume 52, pp. 35–38. 75. Rajewski, T., Fokens, J., and Watson, M. “Development and application of synthetic food grade lubricants,” Industrial Lubrication and Tribology, 2000, Volume 52, pp. 110–116. 76. Redpath, Jim, “Keep it clean,” Construction, 2004, Volume 71, pp. 29–32. 77. Zink, M., “Match characteristics to application needs,” Hydraulics and Pneumatics, 2002, Volume 55, pp. 31–36. 78. Anon, Fluid Power “A plan for reliability data,” Design News, 2003, Volume 59, p. 44. 79. Placek, D., “Study examines multi-grade fluids for forestry equipment,” Hydraulics and Pneumatics, 2001, Volume 54, pp. 39–41. 80. Wangsgaard, M.F., “Keeping environmentally safe hydraulic fluids in their place,” Hydraulics and Pneumatics, 1999, Volume 52, pp. 39–44. 81. Biamonte, Jeffrey, “Selecting quality fluids,” Hydraulics and Pneumatics, 2003, Volume 56, pp. 52–54.

82. Duncan, C, Reyes-Gavilan, J, Costantini, D., and Oshode, S.J., “Ashless additives and new polyol ester base oils formulated for use in biodegradable hydraulic fluid applications,” STLE, 2002, pp. 18–29. 83. Duringhof, R., “Grease manufacturing by means of high concentrate saponification,” NLGI Spokesman, 1990, Volume 54, pp. 7–321 to 9–323. 84. Witte, A.C. and Colemann, R.L., “Method for continuous grease manufacture,” U.S. Patent 4,297,227, 18 January 1980. 85. Kay, J., “Stratco® contactor reactor economic analysis,” NLGI Spokesman, 2003, Volume 66, pp. 8–17. 86. Waynick, J.A., “Polyurea and calcium soap lubricating grease thickness system,” U.S. Patent 5,084,193, 28 January 1992. 87. Wunsch, F., “Noise characteristics of lubricating greases used for anti-friction bearings,” NLGI Spokesman, 1992, Volume 56. 88. Moehr, S., “Lubricating grease composition and preparation,” U.S. Patent 6,407,043, 18 June 2002. 89. Sullivan, Tim, “Airframe lubrication fit for service?,” Lubesn-Greases, 2002, Volume 8, pp. 20–23. 90. Hurley, S. and Cann, P.M., “Infrared spectroscopic characterization of grease lubricant films on metal surfaces,” NLGI Spokesman, 7 October 2000, Volume 64, pp. 13–21.

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91. Hurley, S. and Cann, P.M., “Infrared spectroscopic analysis of a grease-lubricated rolling contact,” NLGI Spokesman, 2003, Volume 67. 92. Cann, P.M., “Friction properties of grease in elastohydrodynamic lubrication,” NLGI Spokesman, 2002, Volume 66, pp. 6–15. 93. John Eastwood, Martina Williams, Hans Ridderikhoff, and Uniqema Lubricants UK, “EC dangerous preparations directive application to greases and ingredients,” ELGI Eurogrease, July/August 2002, pp. 15–21. 94. Tim Sullivan, “Asia’s indpendents face dim outlook,” Lube Report, 16 March 2004, 25 March 2004, http://www.lubereport.com/e_article000239251.cfm? x=a2HdhY7,aW0j1gs. 95. Nancy DeMarco, “Shell: GTL taps will gush in 5 years,” Lube Report, 24 February 2004, 25 March 2004, http://www.lubereport.com/e_article000231367.cfm? x=a2DjWJL,aW0j1gs. 96. Nancy DeMarco, “Russia earmarks more oils for export,” Lube Report, 24 February 2004, 25 March 2004, http://www.lubereport.com/e_article000231377.cfm?x=a2 DjWJL,aW0j1gs. 97. Tim Sullivan, “U.S. lubes dipped in 2002,” Lube Report, 18 September 2003, 25 March 2004, http://www.lubereport. com/e_article000202976.cfm?x=a2mM17t,aW0j1gs, aW0j1gs.

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Trends Toward Synthetic Fluids and Lubricants in Aerospace Carl E. Snyder, Jr. and Lois J. Gschwender CONTENTS 47.1 Liquid Lubricants 47.2 Hydraulic Fluids 47.3 Other 47.4 Developmental Synthetic Fluids and Lubricants References

Synthetic fluids and lubricants have been used in aerospace equipment for many years. Aerospace applications are very demanding on fluids and lubricants. The major reason that aerospace applications are so demanding is that there is such a concern about the weight associated with aerospace systems. Since significant costs are incurred with flying every pound of an aerospace system, all elements of every system are the smallest, lightest available. This results in minimum volumes of fluids and lubricants used, the smallest heat exchangers possible, smaller reservoirs, smaller pumps, actuators, etc. The result is that fluids and lubricants in aerospace applications are required to withstand extremely severe levels of stress since small volumes are used and must operate at high temperatures generated in the application as well as at extremely low temperatures in which aerospace equipment is required to operate. In general, the synthetic fluids and lubricants are required for aerospace applications due to the wide temperature range over which they must operate. In comparison, nonaerospace applications, which are generally not so concerned about the amount of fluid used or the overall weight of the system, which permits the use of large heat exchangers, if required, do not put as much demand on fluids and lubricants. However, as nonaerospace applications become more sophisticated and the synthetic fluids and lubricants become less exotic and more readily available at lower costs, synthetics will be more widely used. Different classes of synthetics have been used for different aerospace application areas. To better define the scope of aerospace applications, it must be recognized that the largest volume applications are in aircraft equipment. Although the excellent performance characteristics of synthetic fluids and lubricants have also resulted in their use in spacecraft, missiles, and satellites,

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these volumes are significantly smaller and, therefore, not as well known or defined. The arrangement of the fluid classes discussed in this chapter will be based on the larger volume applications of the class of synthetics as a primary method of grouping. Lower volume applications will be mentioned as appropriate as they are being discussed. Most of the classes of synthetic lubricants covered in this chapter have been covered in detail in earlier chapters of this book. Therefore, references will be cited only when a specific class of synthetic lubricants is not covered elsewhere in this book or because the information is extremely important. The two major areas of application of synthetic fluids and lubricants are liquid lubricants, primarily as gas turbine engine lubricants, and hydraulic fluids. Applications involving synthetics that are of lower volume are greases, coolants, and inertial guidance damping fluids. This method of grouping is not meant to indicate that a critical, low volume application where a synthetic lubricant is the only choice is not equally, if not more, important.

47.1 LIQUID LUBRICANTS The application area in which the largest volume of liquid lubricants used in aerospace is gas turbine engine oils. The most widely used class of synthetic lubricants used as gas turbine engine oils is the ester class. Selection of esters is driven by their wide usable temperature range and their excellent thermo-oxidative stability in the presence of metals. The environment in which they are required to operate includes extremely low temperatures (down to −54◦ C), at which their viscosity must be low enough to permit the engines to start, as well as high bulk fluid temperatures (over to 200◦ C), at which they must provide lubrication

for the main shaft bearings in the engine. The ester-based lubricants used for the engine lubrication application are described in military specifications MIL-PRF-7808 [1] and MIL-PRF-23699 [2]. The MIL-PRF-7808 revision K describes Grade 3, a −54 to 177◦ C fluid, and Grade 4, a −51 to 204◦ C fluid [3]. MIL-PRF-23699 contains a 175◦ C standard grade (STD) oil, a 175◦ C corrosion inhibited (CI) oil and a 204◦ C higher temperature (HTS) grade. Materials conforming to these specifications are adequate to meet the lubrication requirements for most current aerospace gas turbine engines. However, in an attempt to improve the fuel efficiency of turbine engines and to meet the more severe operational requirements, higher operational temperatures are predicted for near-term advanced engines. It is anticipated that these requirements can be met by the successful development of improved ester-based lubricant formulations that will increase their upper temperature capability to 230◦ C. An on-going research program is underway to develop that “optimal ester”-based gas turbine engine oil. The term “optimal ester” was coined as it is the consensus of the aerospace fluid and lubricant community that it represents the widest temperature operational lubricant that can be developed from the ester chemistry. It will probably necessitate a relaxation of the lower temperature operational capability from −54 to approximately −40◦ C. This will require a careful balance of ester base stocks and improved additives to achieve the balance of viscosity– temperature properties and excellent thermo-oxidative stability as well as other requirements for a gas turbine engine lubricant. As discussed later, further advanced engine concepts will require utilization of different classes of synthetic lubricants. In addition to turbine engine lubrication, the esters are used in aerospace applications as low temperature greases, for example, MIL-PRF-23827 [4] gear oils, for example, DOD-L-85734 [5], and to some degree as instrument lubricants, for example, MIL-PRF-6085 [6]. When SR-71 aircraft engine operational temperatures exceeded the limits of ester-based lubricants, another class of synthetic lubricants with significantly higher high temperature stability was utilized. This class of synthetic lubricants is the polyphenylethers [7]. The liquid lubricant described in military specification MIL-PRF-87100 [8] has an upper operational temperature of 300◦ C. An improved version of MIL-PRF-87100 with an extension of the upper operational temperature to 320◦ C has been developed but not implemented. In addition, MIL-PRF-87100 has excellent fire resistance as demonstrated by a flash point in excess of 450◦ C and autogenous ignition temperature of 450◦ C. The major deficiency of the polyphenylether class of liquid lubricants is that they have extremely poor low temperature operational capability as they have pour points of +5◦ C and higher, limiting their lower temperature use temperature to +15◦ C. In addition, the current formulation described by the specification of these fluids has relatively poor lubricity characteristics compared with other classes

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of liquid lubricants. These limitations, coupled with their high cost ($1000+ per gallon), have limited their use to applications in which no other liquid lubricants would function. As more efficient gas turbine engines operating at higher temperatures are developed, the polyphenylethers, either as MIL-PRF-87100 or as an advanced version of the specification, will find increased applications. When the capabilities of the polyphenylethers are exceeded or when liquid lubricants capable of operating not only at the elevated temperatures at which polyphenylethers operate but also at the more typically required low temperatures of −40◦ C and below, it is anticipated that the liquid lubricant of choice will be based on a perfluoropolyalkylether (PFPAE) [9]. Commercial versions of this class of synthetic lubricants that have the potential for providing a liquid lubricant capable operating over a −55 to 300◦ C temperature range are currently available. Research and development programs are currently underway to increase the upper temperature to at least 330◦ C. The major drawback of this class of synthetic lubricants is the lack of suitable additive technology. The chemical behavior of the PFPAE fluids is so different from other nonperfluorinated lubricants that the additives used to enhance the properties of other lubricants are not even soluble in PFPAE fluids. Up until a few years ago there were very limited examples of additives that are soluble in PFPAE fluids, and these were all specifically synthesized to be soluble in PFPAE fluids [10–12]. Although this class of fluids has very attractive and impressive properties as unformulated fluids, their true potential cannot be realized until a supporting technology base of performance improving additives has been developed. The types of additives required for PFPAE fluids to have properties appropriate for their use as liquid lubricants in aerospace applications are (1) metal deactivator/stability additive; (2) rust inhibitor additive; and (3) lubricity additive. Significant advances in additive technology for PFPAEs have been made in the last few years. A number of soluble, effective performance improving additives have been recently developed that will significantly improve their capabilities in the lubrication of mechanical equipment [13]. The PFPAE synthetics are used in oxidatively stable greases as described in military specification MIL-PRF-27617 [14]. Other potential aerospace applications for formulated PFPAE fluids include long life lubricants for space, instrument lubricants, and high temperature nonflammable hydraulic fluids.

47.2 HYDRAULIC FLUIDS Synthetic-based hydraulic fluids are widely used in aerospace. The nonsynthetic hydraulic fluid that the synthetics replaced in both commercial and military aircraft is described in specification MIL-PRF-5606 [15]. The reason

synthetic hydraulic fluids were developed to replace MILPRF-5606 was to provide increased fire safety. MIL-PRF5606 is a naphthenic mineral-oil-based hydraulic fluid that has proved to be an adequate aerospace hydraulic fluid from an operational aspect. However, the high flammability hazard associated with its use is well known [16]. The commercial aircraft industry recognized this hazard first and, in conjunction with the fluid industry, developed a fire resistant hydraulic system around the phosphate ester class of synthetics. It was necessary to develop an entirely new hydraulic system because the phosphate esters are not compatible with the same seals, paints, wiring insulation, etc. that are used in aircraft using a hydrocarbonbased hydraulic system. In addition, hydraulic system components had to be modified to provide optimum performance with the new phosphate ester-based hydraulic fluids. The phosphate ester hydraulic fluids are described in AS1241 [17]. The military community did not follow the commercial industry in the switch from MIL-PRF-5606 to phosphate esters. This decision was driven primarily by the noncompatibility of the phosphate esters with the aircraft systems and ground service equipment originally designed to use the hydrocarbon-based MIL-PRF-5606. In fact, mixing MIL-PRF-5606 and AS1241 hydraulic fluids resulted in gel formation causing excessive maintenance to correct the problem. In addition, the aggressive solvency of the phosphate esters toward seals, paints, and wiring insulation used in aircraft with hydrocarbon-oilbased hydraulic systems prevented their consideration as a retrofit option. The military conversion from MIL-PRF5606 to a fire resistant synthetic-based hydraulic fluid required that another new class of synthetic fluids be developed, that is, synthetic hydrocarbon fluids based on polyalphaolefins (PAOs). The synthetic hydraulic fluids based on PAOs are described in military specifications MIL-PRF-83282 [18] and MIL-PRF-87257 [19]. MILPRF-83282 was developed to replace MIL-PRF-5606 as a no-retrofit, drain and fill replacement. This required total compatibility with the materials used in MIL-PRF-5606 systems and with the MIL-PRF-5606 system designs. Most military aircraft were converted to MIL-PRF-83282 by the year 1985. The only aircraft for which the conversion was not approved were those for which acceptable operation at −54◦ C would be compromised by the higher viscosity of MIL-PRF-83282 at lower temperatures. MILPRF-83282 is described as a −40 to 204◦ C hydraulic fluid compared with −54 to 135◦ C for MIL-PRF-5606. MIL-PRF-87257, a −54 to 200◦ C PAO-based fire resistant hydraulic fluid with equivalent −54◦ C viscosity to MIL-PRF-5606, was developed to provide a fire resistant hydraulic fluid that would not compromise the low temperature operational use at −54◦ C. The successful validation of MIL-PRF-87257 has led to its use in U.S. Air Force aircraft [20,21] and small commercial aircraft.

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MIL-PRF-87257, like MIL-PRF-83282, was designed to serve as a no-retrofit, direct replacement hydraulic fluid for MIL-PRF-5606. It is totally miscible with MIL-PRF-5606 and is compatible with MIL-PRF-5606 hydraulic system materials and design. A similar PAO-based hydraulic fluid containing rust inhibitors has been developed for use in ground vehicles [22]. The improved fire resistant properties of MIL-PRF-83282 and MIL-PRF-87257 over MIL-PRF5606, which have resulted in significant reductions in hydraulic fluid fire damage, include (1) higher flash and fire points; (2) higher autogenous ignition temperature; (3) lower flame propagation rate; and (4) improved resistance to gunfire ignition [16]. The conversion of aircraft from MIL-PRF-5606 to MIL-PRF-83282 was accomplished by both drain and fill and attrition methods, both of which were equally successful and without problem. The conversion of aircraft from MIL-PRF-5606 to MILPRF-87257 has been by attrition. Recent introduction of JP-8 fuel into the military to replace JP-4 has lessened the need for a −54◦ C hydraulic fluid since JP-8 is significantly inferior to JP-4 in low temperature flow characteristics. However a low temperature hydraulic fluid may still be required because of long, small diameter lines used in current aircraft hydraulic systems. Long, small diameter lines require relatively low viscosity fluids to permit flow and circulation, which is needed for hydraulic actuation. Other quite important but smaller volume applications of PAO are as greases, for example, MIL-PRF-81322 [23] and MIL-PRF-3204 [24], instrument lubricants, and liquid coolants [25]. The PAO-based greases provide excellent usable temperature range and good reliability with low maintainability requirements. MIL-PRF-32014 is superior to MIL-PRF-81322 because it is lithium soap thickened rather than clay thickened and has many corrosion resisting additives. The newer, MIL-PRF-32014 was recently developed to meet the operational requirements of the #1 bearing in the F-107 cruise missile engine. This grease is covered by the military specification MIL-PRF-32014. This grease has proven to be an excellent grease that has enabled the overhaul interval for the engine to be extended from 12 months, which was limited primarily by the poor hydrolytic stability of the previously used grease, to 60 months. Additionally, the engine overhaul depot reported that in most cases, at the 60-month overhaul period, the #1 engine bearing is cleaned, inspected, and relubricated with MIL-PRF-32014 and put back into service for an additional 60 months. In response to the excellent overall properties of MIL-PRF-32014, it is being considered as a multipurpose grease, which could potentially replace a number of older, outdated greases in the DoD inventory. This would be a significant improvement in our logistic situation, which now requires the availability of a wide number of greases for aircraft maintenance. It was sucessfully test flown for over two years on a C-5 aircraft and is being evaluated by the Navy for several aircraft with

wear and corrosion problems. Instrument lubricants based on PAO have successfully replaced the difficult to obtain paraffin-based mineral oil instrument lubricants previously used. A PAO-based coolant meeting the properties defined in MIL-PRF-87252 [26] has essentially replaced another class of synthetic fluids, the ortho-silicate esters, described in MIL-C-47220 as dielectric and liquid coolants in military electronic systems. MIL-PRF-87252 is also finding use in cooling mainframe computers and in other applications. In this case, it is replacing water–glycol coolants, eliminating the algae problem, and fluorinated coolants, greatly reducing cost and weight. The PAOs have excellent properties as lubricants and hydraulic fluids. Their compatibility with mineral oils and systems designed to use mineral-oil-based lubricants and fluids makes them excellent candidates for use in newly emerging aerospace systems. Replacing mineral oils is especially important when mineral-oil-based products are either difficult to obtain or no longer provide adequate performance. Both phosphate ester and PAO hydraulic fluids have been excellent hydraulic fluids, which, due to their fire resistant properties, have significantly reduced the hydraulic fluid fire hazards in both commercial and military aircraft. However, they are not nonflammable, but are capable of ignition if sufficient energy (temperature, flame, etc.) is available. With regard to current and future aircraft, high fire hazard areas where hydraulic fluids are used exist in brake systems, in which brake temperatures can approach 1600◦ C on an aborted take-off and around engine nacelles where the temperatures exceed 800◦ C. Both these conditions exceed the autogenous ignition temperatures and flash and fire points of both phosphate ester- and PAObased hydraulic fluids. As the costs of our aircraft and other aerospace systems continue to increase, it becomes even more important to minimize the possibility of losing these aircraft to hydraulic fluid fires. The development and validation of a completely nonflammable hydraulic fluid and compatible seals has been completed [27,28]. The synthetic hydraulic fluid is based on chlorotrifluoroethylene (CTFE) oligomers and is described in military specification MIL-H-53119 [29]. The CTFE-based hydraulic fluid is not compatible with hydraulic systems designed for use with other hydraulic fluids and therefore requires that hydraulic systems be designed around its unique properties. MIL-H-53119 is specified for use from −54 to 175◦ C and is compatible with a number of elastomeric seals. One of the major disadvantages of MIL-H-53119 is that it has significantly higher density, which results in a serious weight penalty for use in aerospace applications. In order to overcome this penalty, higher-pressure hydraulic components were developed and systems were designed and validated. At higher pressures, 55.2 MPa (8000 psi), the penalties associated with the higher density are minimized due to the extremely small volumes of hydraulic fluid required. If the weight penalty were not important,

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MIL-H-53119 could be used at lower pressures and provide nonflammable hydraulic systems for a variety of application areas. MIL-H-53119, although fully demonstrated, has not yet been used. However, because it is essentially nonflammable and has been demonstrated to be a good operational hydraulic fluid, it will find applications in the future. Another important, but small volume, application for higher molecular weight versions of CTFE as well as for polymers of bromotrifluororethylene (BTFE) is as high density flotation/damping fluids for inertial guidance systems.

47.3 OTHER The only class of synthetic fluids that has been developed for quite some time and has not been discussed in this chapter is the silicones. The silicone class of synthetics has some very interesting properties, which would make it a serious candidate for a wide number of aerospace applications. The most important of those is the extremely good viscosity–temperature properties that silicone fluids possess, especially the polydimethylsiloxanes. However, the silicones also possess two less desirable properties that make them less useful for the two major volume applications in aerospace, that is, gas turbine engine lubricants and hydraulic fluids. The more significant deficiency is their inability to provide lubrication for steel-on-steel rubbing surfaces. Lubricity additives are generally not effective in silicones. This deficiency has limited their use as both liquid lubricants and hydraulic fluids, but in addition, another deficiency that limits their use as hydraulic fluids is their low bulk modulus, or high propensity for compressibility. This requires compensation in hydraulic system design in the form of larger actuators than would be required for less compressible fluids. The larger actuator would compensate for the “sponginess” of the fluid and would provide satisfactory service, but the weight of the hydraulic system would be significantly increased, which is unacceptable for aerospace applications. However, silicones have been used in a variety of greases [30] that are widely used in aerospace applications. Another member of the silicon containing class of synthetic fluids is the silicate ester class [7]. This class of synthetic fluids has had two areas of application, that is, wide temperature range hydraulic fluids and coolants. The original application of the silicate esters as a hydraulic fluid was as described in military specification MIL-PH-8446 [31]. This specification, which has been canceled due to lack of current systems requiring the fluid, described a hydraulic fluid for use over the temperature range of −54 to 204◦ C. The silicate esters were the most acceptable class of hydraulic fluids for that requirement. Silicate ester-based hydraulic fluids were used in the now retired B-58 and in the B-1 test aircraft and in the retired commercial supersonic aircraft, the Concorde. Their major deficiency was

their propensity to hydrolyze with moisture that got into the hydraulic system. The resulting hydrolysis products were an alcohol, which degraded the fire resistance of the fluid, and a gelatinous precipitate, that clogged system filters and the small orifices that exist in hydraulic systems, resulting in the need for high levels of maintenance. Similar hydrolysis problems were experienced with the silicate ester-based coolants, described in military specification MIL-C-47220 [32]. This problem with hydrolysis that resulted in a high level of maintenance has led to the substitution of the PAO-based coolant MIL-PRF-87252 for MIL-C-47220 in nearly all military aerospace applications.

47.4 DEVELOPMENTAL SYNTHETIC FLUIDS AND LUBRICANTS The synthetic fluids and lubricants discussed previously in this chapter have either found significant application in the aerospace industry or there is a significant production capability and potential applications have been identified. In this section, classes of newly emerging synthetic lubricants and fluids will be discussed as well as the properties that make them so promising. The first class of newly emerging synthetics is the silahydrocarbon, or tetralkylsilane, class. While this class of synthetics has been known for quite some time, their potential application in the aerospace industry had not been significantly advanced until recently [33]. The largest volume application for the silahydrocarbons is as wide temperature range, high temperature, and fire resistant hydraulic fluids. Their excellent viscosity–temperature properties make them excellent candidates as they can be used down to −54◦ C while still maintaining adequate viscosity at elevated temperatures to provide adequate film thickness for lubrication. Their excellent stability at temperatures up to 370◦ C permits their extended use at elevated temperatures. Since these fluids contain aliphatic carbon–hydrogen bonds, oxygen must be excluded at these elevated temperatures. Another very important aerospace application is liquid space lubricants [34–36]. Their excellent viscosity–temperature characteristics permit the selection of extremely high molecular weight (1000 to 1500 amu) silahydrocarbon fluids to be used. These fluids have extremely low volatility, which makes them excellent candidates for long life, noncontaminating liquid and grease lubricants for space. A third potential application of the silahydrocarbons is as a cryogenic coolant with a −150◦ C or lower low temperature capability. As with the other potential applications, silahydrocarbons are yet to be used for this application. Another class of synthetic fluids and lubricants, which are still in the stages of development, are the n-alkyl benzenes [37]. These fluids have excellent thermal stability and very good viscosity–temperature properties. One of

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the advantages these fluids have over the PAO and silahydrocarbon classes for use at high temperature is their improved solubility for performance improving additives. The benzene ring appears to provide significant solubility enhancement for the typically polar performance improving additives, which are essential to provide the required performance. Their most promising aerospace application is as a wide temperature range, high temperature hydraulic fluid. The major obstacle in reducing them to the application is lowering the cost of production, while maintaining the wide liquid range stability. Future trends in aerospace synthetic fluid and lubricant development will be the development of more environmentally acceptable lubricants and fluids. There is significant interest in biodegradable hydraulic fluids and nontoxic rust inhibited fluids. Aerospace lubricants are generally more stable materials, which is usually contrary to good biodegradability. Because hydraulic fluids especially compose a significant percentage of the waste stream from operational bases and airports, emphasis has been placed on reduction of this waste stream. Fortunately MIL-PRF87252 and MIL-PRF-83282 are biodegradable to some extent. Military systems have long depended on rust inhibited hydraulic fluids for storage of aerospace hydraulic system components and as functional hydraulic fluids in military ground vehicles. MIL-PRF-6083 and MIL-PRF46170 are the rust inhibited versions of MIL-PRF-5606 and MIL-PRF-83282, respectively. Both of these fluids currently use a barium-based rust inhibitor and, since barium is now considered a toxic material, used MIL-PRF-6083 and MIL-PRF-46170 must be disposed of at great expense. Recently a study concluded operational fluid could be used for aircraft component storage in place of rust inhibited versions. Technical documents are being changed to reflect this finding.

REFERENCES 1. MIL-PRF-7808L Military Specification, Lubricating Oil, Aircraft Turbine Engine, Synthetic Base, NATO Code Numbers 0-148 (Grade 3) and 0-163 (Grade 4) (2 May 1997). 2. MIL-PRF-23699F, Military Specification, Lubricating Oil, Aircraft Turbine Engine, Synthetic Base, NATO Code Number 0-156 (21 May 1997). 3. Gschwender, L.J., Snyder, C.E., Jr., and Beane,G.A., IV, “Military Aircraft 4-cSt Gas Turbine Engine Oil Development,” Lubr. Eng., 43, 654–659 (1987). 4. MIL-PRF-23827C(1) Military Specification, Grease, Aircraft and Instrument, Gear and Actuator Screw, NATO Code Number G-354 (19 June 2002). 5. DOD-PRF-85734, Lubricating Oil, Helicopter Transmission System, Synthetic Base (29 June 2004). 6. MIL-PRF-6085D Military Specification, Lubricating Oil: Instrument, Aircraft, Low Volatility (20 February 1998). 7. Gunderson, R.C. and Hart, A.W., Eds., Synthetic Lubricants, Reinhold Publishing Co., New York (1962); Joaquim, M.,

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“Polyphenyl Ether Lubricants,” in Synthetic Lubricants and High-Performance Functional Fluids, L.R. Rudnick and R.L. Shubkin, Eds., Marcel Dekker (1999); Hamid, S., “Polyphenyl Ether Lubricants,” in Synthetics, Mineral Oils and Bio-Based Lubricants: Chemistry and Technology, L.R. Rudnick, Ed., Marcel Dekker, 2005 (this volume). MIL-PRF-87100A, Military Specification, Lubricating Oil, Aircraft Turbine Engine, Polyphenyl Ether Base (28 November 1997). Snyder, C.E., Jr. and Gschwender, L.J., “Fluoropolymers in Fluids and Lubricant Applications,” I & EC Prod. R & D, 22, 383–386 (1983). Tamborski, C. and Snyder, C.E., Jr., “Perfluoroalkylether Substituted Aryl Phosphines and Their Synthesis,” U.S. Patent 4,011,267 (8 March 1977). Tamborski, C. and Snyder, C.E., Jr., “Perfluoroalkylether Substituted Phenyl Phosphines,” U.S. Patent 4,454,349 (12 June 1984). Sharma, S.K., Gschwender, L.J., and Snyder, C.E., Jr., “Development of a Soluble Lubricity Additive for Perfluoropolyalkylether Fluids,” J. Synth. Lubr., 7, 15–23 (1990). Gschwender, L.J., Snyder, C.E., and Fultz, G.W., “Soluble Additives for Perfluoropolyalkylether Liquid Lubricants,” Lubr. Eng., 49, 702–708 (1993). MIL-PRF-27617F, Military Specification Grease, Aircraft and Instrument, Fuel and Oxidizer Resistant (17 February 1998). MIL-PRF-5606H(1), Military Specification, Hydraulic Fluid, Petroleum Base; Aircraft, Missile and Ordnance, NATO Code Number H-515 (23 July 2003). Snyder, C.E., Jr., Krawetz, A.A., and Tovrog, T., “Determination of the Flammability Characteristics of Aerospace Hydraulic Fluids,” Lubr. Eng., 37, 705–714 (1981). AS 1241B, “Fire Resistant Phosphate Ester Hydraulic Fluid for Aircraft,” Society of Automotive Engineers, 400 Commonwealth Dr., Warrendale PA 15096 (18 February 1992). MIL-PRF-83282D(1) Military Specification, Hydraulic Fluid, Fire Resistant, Synthetic Hydrocarbon Base, Aircraft, Metric, NATO Code Number H-537 (1 December 1997). MIL-PRF-87257B Military Specification, Hydraulic Fluid, Fire Resistant; Low Temperature, Synthetic Hydrocarbon Base, Aircraft and Missile, NATO Code Number H-538 (22 April 2004). Gschwender, L.J., Snyder, C.E., and Fultz, G.W., “Development of a −54◦ to 135◦ C Synthetic Hydrocarbon-Based, Fire-Resistant Hydraulic Fluid,” Lubr. Eng., 42, 485–490 (1986). Gschwender, L.J., Snyder, C.E., and Sharma, S.K., “Pump Evaluation of Hydrogenated Polyalphaolefin Candidates for a −54◦ C to 135◦ C Fire-Resistant Air Force Aircraft Hydraulic Fluid,” Lubr. Eng., 44, 324–329 (1988). Alvarez, R.A., Wright, B.R., and Phillips, G.L., “Final Report on Technology Demonstration of Single Hydraulic

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31. 32. 33.

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Fluid for Armored Ground Vehicle Systems,” U.S. Army Interim Report, TFLRF No. 306, AD A312088 (1996). MIL-PRF-81322G Military Specification, Grease, Aircraft, General Purpose, Wide Temperature Range (24 January 2005). MIL-PRF-32014 Grease, Water Resistant, High Speed, Aircraft and Missile (29 September 1997). Gschwender, L.J., Snyder, C.E., Jr., and Conte, A.A., Jr., “Polyalphaolefins as Candidate Replacements for Silicate Ester Dielectric Coolants in Military Applications,” Lubr. Eng., 41, 221–228 (1985). MIL-PRF-87252C Military Specification, Coolant Fluid, Hydrolytically Stable, Dielectric, NATO Code No. S-1748 (24 October 97). Gschwender, L.J., Snyder, C.E., Jr., VanBrocklin, C.H., and Warner, W.E., “Chlorotrifluoroethylene Oligomer Based Nonflammable Hydraulic Fluid, I Fluid, Additive and Elastomer Development,” J. Syn. Lubr., 9, 188–203 (1992). VanBrocklin, C.H., Gschwender, L.J., Snyder, C.E., Sharma, S.K., and Campbell, W.B., “Chlorotrifluoroethylene Oligomer Based Nonflammable Hydraulic Fluid, II Hydraulic Component Development,” J. Syn. Lubr. 9, 299–309 (1992). MIL-H-53119 Military Specification, US Army, Hydraulic Fluid, Nonflammable, Chlorotrifluoroethylene Base (1 March 1991). MIL-G-25013E Military Specification, Grease, Aircraft, Ball and Roller Bearing, NATO Code Number G-372 (28 October 1991). MIL-H-8446B Military Specification, (Canceled) Hydraulic Fluid, Nonpetroleum Base, Aircraft (16 July 1959). MIL-C-47220B Military Specification, (cancelled) USAF, Coolant Fluid, Dielectric (13 January 1995). Snyder, C.E., Gschwender, L.J., Tamborski, C., Chen, G., and Anderson, D.R., “Synthesis and Characterization of Silahydrocarbons — A Class of Thermally Stable Wide Liquid Range Functional Fluids,” ASLE Trans., 25, 299–308 (1982). Paciorek, K.J.L., Shih, J.G., Kratzer, R.H., Randolph, B.B., and Snyder, C.E., Jr., “Polysilahydrocarbon Synthetic Fluids I. Synthesis and Characterization of Trisilahydrocarbons,” I & EC Prod. R & D, 29, 1855–1858 (1990). Snyder, C.E., Jr, Gschwender, L.J., Randolph, B.B., Paciorek, K.J.L., Shih, J.G., and Chen, G.J., “Research and Development of Low Volatility Long Life Silahydrocarbon Based Liquid Lubricants for Space,” Lubr. Eng., 48, 325–328 (1992). Gschwender, L.J., Snyder, C.E., Jr., Massey, M., and Peterangelo, S., “Improved Liquid/Grease Lubrication for Space Mechanisms,” Lubr. Eng., 12, 25–31 (2000). Gschwender, L.J., Snyder, C.E., Jr., and Driscoll, G., “Alkyl Benzenes — Candidate High-Temperature Hydraulic Fluids,” Lubr. Eng., 46, 377–381 (1990).

48

Commercial Developments R. David Whitby CONTENTS 48.1 Introduction 48.2 Demand for Synthetic Lubricants 48.3 Economic Comparison of Synthetic Lubricants 48.3.1 Advantages and Disadvantages of Different Synthetic Oils 48.3.2 Balancing Conflicting Performance Requirements 48.3.3 Costs and Cost Comparisons 48.4 Developments in the Synthetic Lubricants Business 48.5 End-Use Markets for Synthetic Lubricants 48.5.1 Automotive Lubricants 48.5.1.1 Gasoline and Diesel Engine Oils 48.5.1.2 Motorcycles and Outboard Engines 48.5.1.3 Transmissions and Gearboxes 48.5.1.4 Automatic Transmissions 48.5.1.5 Brake Fluids 48.5.1.6 Automotive Air-Conditioning 48.5.1.7 Automotive Greases 48.5.2 Compressor Oils 48.5.2.1 Air and Gas Compressors 48.5.2.2 Natural Gas Compressors 48.5.2.3 Refrigeration Compressors 48.5.3 Turbine and Hydraulic Oils 48.5.3.1 Steam Turbine Oils 48.5.3.2 Gas Turbines Oils 48.5.3.3 Hydraulic Fluids 48.5.4 Gear, Circulating, Process, and Functional Oils 48.5.4.1 Circulation Systems 48.5.4.2 Gears 48.5.4.3 Bearings 48.5.4.4 Heat Transfer Oils and Solar Fluids . 48.5.4.5 Electrical and Insulating Oils 48.5.4.6 Cable Compounds 48.5.4.7 Oil-Based Drilling Fluids 48.5.4.8 Circuit Board Fluxes 48.5.4.9 Mould Release Agents 48.5.5 Metalworking Fluids 48.5.5.1 Water-Miscible Cutting Fluids 48.5.5.2 Neat Cutting Oils 48.5.5.3 Steel, Aluminium, and Copper Rolling Oils 48.5.5.4 Stamping, Pressing, and Forming Oils 48.5.5.5 Wire and Tube Drawing Lubricants 48.5.5.6 Aluminium Can Stock and Can Drawing Fluids 48.5.5.7 Heat Treatment (Quenching) Fluids 48.5.6 Other Industrial Lubricants 48.5.6.1 Textile Lubricants

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48.6

48.5.6.2 Wire Rope, Chain, and Chainsaw Lubricants 48.5.6.3 Food Grade Oils 48.5.7 Greases 48.5.8 Aviation Lubricants 48.5.8.1 Civil Aviation Lubricants 48.5.8.2 Military Aviation Lubricants Future Trends

48.1 INTRODUCTION

48.2 DEMAND FOR SYNTHETIC LUBRICANTS

The last 15 yr has witnessed the transition of synthetic lubricants from a niche segment of some industrial applications to a mainstream segment of the whole lubricants industry. It has now become impossible to discuss the international lubricants business without including a discussion of synthetic lubricants. The first commercially used synthetic lubricants were silicones, developed by Dow Corning and General Electric in 1943. Then followed polyalkylene glycols, in 1945, developed by Union Carbide, diesters in 1951, phosphate esters in 1953, and polyol esters in 1963. Many of the early applications for synthetic fluids were in U.S. military equipment, notably gas turbines, hydraulic systems and instruments. Demanding service conditions required higher levels of performance than were possible using conventional mineral oils, even with performance enhancing additives. Amsoil Corporation introduced the first API-rated fully synthetic engine oil in 1972, although Agip had launched a part-synthetic motor oil, Sint 2000, in Italy in 1969. Mobil 1 was launched as the first worldwide fully synthetic engine oil in 1977. When it was launched, Mobil claimed that the oil improved fuel economy, reduced oil consumption, allowed faster cold-weather starting, kept engines cleaner, and provided better engine protection. Synthetic lubricants are now used in more than 70 applications, in gasoline and diesel engines, aviation and industrial gas turbines, gear and transmission systems, compressors, hydraulic systems, heat transfer systems, air conditioning, metalworking fluids, food contact industries, and greases. While the higher cost of synthetic fluids has previously been perceived as a barrier to their wider use, it is now more generally accepted that the performance benefits provided often outweigh the higher cost, particularly in applications for which higher lubricity, lower volatility, better biodegradability, lower toxicity, or wider operating range are important factors. As a result, it is now recognized that, while overall worldwide demand for lubricants is likely to remain relatively static, demand for synthetic lubricants is likely to increase at between 5 and 7% per year. This inevitably means that demand for mineral oil-based lubricants is likely to fall over the next five to ten years.

The conventional definition of a synthetic baseoil is one that has been chemically synthesized from distinct discrete chemical components. It is, therefore, easy to see that polyalphaolefins (PAOs) are synthetic because they have been synthesized from ethylene via 1-decene and that polyalkylene glycols (PAGs) are also synthetic because they have been synthesized from ethylene or propylene and alcohols via ethylene oxide and/or propylene oxide. Mineral baseoils, on the other hand, are made by physically removing or chemically altering the undesirable components present in vacuum distillation residues derived from crude oil. These definitions of synthetic have, however, been thrown into considerable confusion by Shell’s development of the Middle Distillate Synthesis Process, now being used commercially in Bintulu in Malaysia. The process makes paraffin waxes, as part of a process to make very clean diesel, kerosene, and other distillates from natural gas, which Malaysia has in abundance. Some of the paraffin wax is now being shipped to Shell’s lubricants refinery in Yokkaichi, Japan, where it is converted into very high viscosity index (VHVI, API Group III) baseoils using the company’s wax isomerization process. The composition and properties of these VHVI baseoils are identical to those of the VHVI baseoils produced from crude oil by Shell at Petit Courrone. But, according to the conventional definitions, the Yokkaichi VHVI baseoils are synthetic, because they have been synthesized from natural gas. Much discussion between oil, chemical, additive, and lubricant end-user companies, about what is synthetic and what is not, over the last five years has yet to reach a definitive conclusion. However, a consensus is beginning to emerge that, for lubricants, “synthetic” is a marketing term that helps to define a level of lubricant performance. In the United States, the API and the SAE have decided not to technically define the term synthetic, but to define the properties, performance, and manufacturing processes of each type of baseoil. For users of lubricants, what is important is the performance and suitability of the lubricant, not whether it has been made by one process or another. According to some industry analysts, synthetic lubricants, however they are defined, were forecast to account

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for more than 5% of the total lubricants market by 2000. In reality, by the beginning of 2003, fully synthetic lubricants accounted for around 7.8% of the market in Western Europe and part-synthetic lubricants accounted for another 21.4%. (Total synthetic baseoil demand was almost 19% of the Western European lubricants market.) Synthetic and VHVI (API Group III)-based lubricants already accounted for almost 5% of the North American lubricants market and around 3% of the lubricants market in other regions of the world. Total worldwide demand for synthetic and VHVI/Group III baseoils amounted to over 1.8 million tonnes in 2002, or around 4.9% of global lubricant demand. Other chapters in this book have described and reviewed the main types of synthetic fluids, and have summarized the volumes of each type of fluid sold each year, so a comprehensive breakdown of the volumes of each type of fluid sold is not attempted in this section. However, the main types of “synthetic” fluids, by market volume, are polyalphaolefins (PAOs), esters (of all types), polyalkylene glycols (PAGs), polybutenes (PIBs) and, of course, VHVI/Group III mineral oils. Pathmaster Marketing’s estimates of the volumes of synthetic baseoils used in lubricants in Western Europe are shown in Table 48.1.

48.3 ECONOMIC COMPARISON OF SYNTHETIC LUBRICANTS 48.3.1 Advantages and Disadvantages of Different Synthetic Oils Each of the different synthetic oils described in this book have their good points and their poor points. Some good

points are better than others, some worse. A number of the more important advantages and disadvantages of each type of synthetic oil are described in their respective chapters. Whether any specific advantage or disadvantage is important will depend on the application for which the lubricant is to be used. In general, highly desirable lubricant properties that are generally advantageous are: • • • • • • •

Good inherent lubrication properties Good low-temperature properties Good high-temperature properties Good viscosity/temperature properties Low volatility Good stability Low toxicity

In some applications, an apparently inferior performance might turn out to be a positive advantage. Examples include: • The incompatibility of some PAGs with mineral hydro-

carbons enables them to be used in natural gas compressors. • The thermal depolymerization of polyisobutenes enables them to be used in clean-burning two-stroke oils. • The chemical structure of diesters that gives them poor hydrolytic stability also means that they are readily biodegradable. The most important consideration in assessing comparative advantages and disadvantages is that, if a specific application does not require a particular performance property, then a synthetic oil that performs well in that

TABLE 48.1 Estimated Consumption of Synthetic Baseoils in Western Europe, 1990 to 2002 Estimated consumption (000 tonnes) Synthetic type Polyalphaolefins Esters Polyisobutenes Polyalkylene glycolsa Phosphate esters Alkyl benzenes Others Total

1990

1996

1998

2000

2001

2002

45 45 22 15 4 8 6

90 55 28 18 4 9 8

125 90 38 23 5 11 9

190 110 46 25 5 11 10

220 120 50 25 5 11 11

220 125 52 26 5 11 11

145

212

301

397

442

450

a PAG content only.

Source: Pathmaster Marketing.

Copyright 2006 by Taylor & Francis Group, LLC

respect will not have any added value for that application. Conversely, if the synthetic oil performs poorly, then, for that application, it will not matter anyway.

Successfully determining the correct level of costeffective performance is usually achieved by obtaining realistic answers to the following questions:

48.3.2 Balancing Conflicting Performance Requirements

• • • • •

The lubrication chemist’s task in formulating a costeffective lubricant to perform a specific function is not easy. In many cases, a large number of performance requirements, some of which may conflict, will need to be satisfied. Previous chapters have described the range of tests available, both standard and specific, under: • • • • •

User specifications Laboratory tests Rig and bench tests Quality control tests Quality assurance and acceptance tests

There are literally hundreds of examples of potentially conflicting requirements that need to be balanced when formulating a lubricant. A few illustrations will suffice to explain the problem: • Blending a diester with a PAO to improve the latter’s

•

•

•

•

seal swell properties in automotive engine oil tests is likely to detract from the excellent hydrolytic stability characteristics. Polyisobutenes are very shear stable and can be used to make very good gear oils, but their low-temperature properties make them unsuitable for use in outdoor gearboxes in cold climates. Using VI improvers in conventional mineral oils can be a cheap way to enhance the viscosity/temperature properties, but at the expense of overall shear stability properties. Water-based hydraulic fluids generally have excellent fire-resistant properties, but cannot be used at operating temperatures much above 60◦ C or much below about 5◦ C. Water-miscible cutting fluids that contain soluble polymer load-carrying and extreme-pressure additives can have lubricating properties close to those of mineral oil cutting fluids, but at the expense of significantly higher monitoring and maintenance costs.

Many users of experience have shown that the task of formulating a finished lubricant is analogous to producing a perfectly round inflated balloon; if you try to push in any small bump on one part of the balloon’s surface, another bump is likely to appear somewhere else on the surface! Push too hard and the result might not be the desired one.

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What performance does my customer want? What performance will satisfy my customer’s needs? How much is my customer willing and able to pay? Can this performance be achieved at this cost? What aspects of performance can be sacrificed to meet a cost limit? • Will I still be able to make a profit? Finding these answers is not always easy. Often, it requires a genuine partnership between lubricant supplier and user. Fortunately, with original equipment manufacturers (OEMs), industrial and military users, such partnerships are becoming more usual. It is particularly important to remember at all times that the only true test of a lubricant’s performance is whether it functions satisfactorily for several years in the machinery for which it was formulated. Lubricant specifications, laboratory tests, rig tests, and field trials are only useful as a guide or prediction of likely performance in service. Ultimately, there is no universal short-cut to the dilemma of balancing the conflicting requirements. This is where the expertise, experience, and dedication of the lubricant supplier provides a great deal of added value.

48.3.3 Costs and Cost Comparisons The current costs of various types of mineral and synthetic baseoils are listed in Table 48.2, which also lists their relative costs compared with 150 solvent neutral Group I mineral baseoil. We should emphasize strongly that these prices are averaged list prices in Europe for unformulated baseoils only, and do not reflect the volume discounts that some suppliers are able to offer their long-term customers. Also, the prices and their comparisons change from month to month, particularly with changes in the prices of Group I baseoils. The prices of synthetic oils tend to vary less with time than those of mineral oils, which are more directly dependent on the price of crude oil. When comparing the costs of different fluids, will a user of a PAG get six times the performance compared to a mineral oil? Is a polyol ester about nine times better than a mineral oil or a PAO almost twice as good as a Group III baseoil? Fortunately, these comparisons are highly misleading. First, for many applications, large quantities of additives need to be added to mineral oils to bring their performance to a satisfactory level. This adds significantly to the total cost. Second, there are a number of other costs that need to be considered when attempting to compare performance.

TABLE 48.2 Western European List Prices for Lubricant Baseoils, March 2004 Fluid Group I baseoils Group III (VHVI) baseoils Group III+ (XHVIa ) baseoils Polyalphaolefins Polyalkylene glycols Polybutenes Diesters Polyol esters Phosphate esters Alkyl benzenes

List price ($/ton) 370 600–700 900–1000 1400–1500 2200–2450 950–1750 2300–3500 3000–4000 3750–5250 1350–1450

Price relative to 150 SN 1.0 1.6–1.9 2.4–2.7 3.8–4.1 6.0–6.6 2.6–4.7 6.2–9.5 8.1–10.8 10.1–14.2 3.6–3.9

a XHVI is a registered Shell trademark.

Source: Pathmaster Marketing, from industry discussions.

These include: Immediate costs

Baseoils Additives and components Blending and storage Transportation and distribution Field trials Sales Marketing

Hidden costs

Formulation Laboratory testing Rig and specification testing Monitoring Servicing Collection Disposal

A more realistic comparison of cost as regard performance would be in the price paid by the user. Although this depends on all the factors that we identified earlier, it is likely to be a more accurate guide to comparative performance. In these terms, the most readily obtainable price comparisons are those for retail motor oils sold on garage forecourts and DIY shops. Currently, average price comparisons for a number of automotive oil types on sale from the major oil companies in the United Kingdom and Germany are shown in Table 48.3. Clearly, the U.K. market believes that a fully synthetic 0w40 gasoline engine oil will be able to provide 7.1 times the performance of a 20w50 mineral oil product for certain demanding applications in high-performance cars. Conversely, in Germany, the market is only willing to pay 2.9 times the price for the fully synthetic 0w40 oil, although the basic product is a 15w40 grade in Germany, while it is still a 20w50 grade in the United Kingdom. Many manufacturers of synthetic oils produce tables that attempt to compare the performances of various types of oils in a range of tests. These tables, too, can be misleading. The quoted tests are usually selected very carefully to

Copyright 2006 by Taylor & Francis Group, LLC

TABLE 48.3 Motor Oil Price Comparisons in the United Kingdom and Germany, May 2004 Price ratio compared to lowest cost product Product

UK

Germany

Gasoline engines 20w50 Mineral oil 15w40 Mineral oil 10w40 Part-synthetic 5w40 Synthetic 0w40 Synthetic

1.0 2.6 3.8 5.9 7.1

— 1.0 1.8 2.5 2.9

Diesel engines 15w40 Mineral oil 10w40 Part-synthetic

2.0 4.1

1.2 1.8

Source: Pathmaster Marketing.

show the particular manufacturer’s product(s) in the best possible light. The use of ticks, crosses, plus signs, and minus signs to indicate good or poor performance is an oversimplification that does not provide qualitative comparisons. Even replacing ticks and crosses with relative numbers does not help much. Is a mineral oil’s hydrolytic stability five times better than that of a diester? Does a PAG lubricate 2.5 times better than a silicone oil? The answer usually depends on which test you do and how you measure the result. In any case, the proper answer is the comparative overall performance of each of the lubricants in the practical application. Attention to what the customer needs is the key to assessing comparative performance.

48.4 DEVELOPMENTS IN THE SYNTHETIC LUBRICANTS BUSINESS The synthetic lubricants business has been progressing steadily since the late 1970s and early 1980s, when chemical companies became interested in the commercial potential of speciality products that could command high prices. At that time, it was not well recognized that the costs of most synthetic lubricants are tied to the prices of bulk chemical feedstocks such as ethylene, propylene, and naphtha, which in turn are linked to the price of crude oil and natural gas. It was an unfortunate coincidence that shortages of chemical feedstocks occurred in 1987 and 1988, pushing ethylene and some derivative prices to very high levels and bulk PAOs to nearly $2000 per ton. As a result of pricing swings, the price ratio of PAOs to mineral baseoils, for example, has varied between 3.5 and 7.0 to 1 during the 1990s. The lesson has been that the lubricants industry

need to understand the driving forces in synthetic lubricant production and pricing, while the chemical industry needs to understand the economics of the baseoil industry, which has remained linked to crude pricing for 30 yr. Only the VHVI/Group III baseoils have been able to break this pattern. Automotive lubricants have seen by far the biggest increase in synthetic fluid use in the 1990s. Increased sales of part-synthetic oils has lead to significant increases in demand for both PAOs and diesters from lubricants blenders. Sales of Group III baseoils are booming. The pattern started in Europe in the mid-1980s and has now spread to all regions of the world, as lubricant marketers recognized the commercial gains possible from a “good/better/best” range of automotive engine oils. Although synthetics have been used for many years in the industrial markets, steady growth is still being experienced for PAOs, PIBs, PAGs, and esters, particularly in compressors, bearings, gears, and circulation systems and for fire-resistant hydraulics and metalworking applications. Esters are emerging as the dominant technology for biodegradable lubricants, as used in forestry, waterways, and construction. Phosphate esters are making a comeback against polyol esters in fire-resistant hydraulic fluids, but the long-term position of polyglycols in brake fluids is uncertain, with the introduction of DOT 4 and DOT 5.1 fluids. The technical understanding of the properties of synthetic lubricants has been increasing for some years. Some applications have been lost by one synthetic, but gained by another. Where demonstrable advantages can be assessed, for example, in high-performance compressors, there is a solid acceptance at all levels, from OEMs, lubricant companies, and customers. This is the key to success. If any of the three elements of consensus are missing, there is only disappointment and frustration. The market penetration of synthetic fluids received a major boost in the 1980s from the introduction of the NOACK volatility test and is now receiving a second boost from biodegradability and toxicity issues, generally summarized as environmental benefits. Consolidation and focus has also begun to emerge in the synthetic lubricants business. Hatco purchased the industrial synthetic lubricants business of Hüls, including the Anderol, PQ, and Aosyn brand names, in September 1996. The company then purchased Royal Lubricants, the aviation and military lubricants business of Shell Oil, in November 1996. Hatco, which has manufactured and marketed ester fluids for many years, has announced that it will operate its synthetic industrial lubricants business under the Anderol brand and its aviation and military synthetic lubricants business under the Royal brand, for the foreseeable future. Amoco Chemicals purchased the PAOs business of Albemarle Corporation in January 1996. Albemarle had

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decided to focus on its core α-olefins business, while Amoco had recognized that PAOs would be a strategic fit with its lubricants business. In the early 1990s, no oil company that manufactured VHVI oils had a chemical division that made PAOs or esters, while no chemical company that manufactured PAOs or esters was owned by an oil company that made VHVI baseoils. By the end of 1997, this situation had begun to change radically. BP purchased Amoco, then Arco, then Castrol and merged all the lubricants activities under the BP and Castrol brands. ExxonMobil Oil makes Groups II and III baseoils and ExxonMobil Chemical makes PAOs and esters, as does Fortum Oil/Fortum Chemical and ChevronTexaco Oil/ChevronTexaco Chemical. Crompton (previously Uniroyal) also announced a progressive 50% increase in its high viscosity PAO manufacturing capacity in July 1996, in response to increasing market demand. It has become evident that the performance advantages of synthetic lubricants are becoming understood and accepted by the market, and that synthetic fluids are becoming integrated into the strategic business plans of the majority of lubricants manufacturers and marketers. This is a significant commercial advance from the situation only 20 yr ago, and is unlikely to stop now.

48.5 END-USE MARKETS FOR SYNTHETIC LUBRICANTS The range of current and potential applications for synthetic lubricants is huge. In order to cover the subject in some systematic way, we will group the applications into the following areas: • • • • • • • •

Automotive lubricants Compressor oils Turbine and hydraulic oils Gear, circulating, and process oils Metalworking fluids Other industrial lubricants Greases Aviation lubricants

In total, within these sectors, some 70 end uses for synthetic oils have been identified. In some applications, only synthetic fluids are used, primarily due to some performance limitation or other demonstrated by conventional mineral oils. These applications include automotive air conditioning units, brake fluids, a number of different types of gas compressor lubricants, fire-resistant hydraulic fluids, electro-hydraulic fluids, aviation gas turbine oils, electrical cable oils, chain lubricants, and aviation greases. In most other markets, synthetic fluids are used for the demanding, high-performance applications in which the performance of mineral oils is inadequate.

48.5.1 Automotive Lubricants 48.5.1.1 Gasoline and diesel engine oils The drivers for changes to engines are government regulations, on fuel economy, emissions, noise, and recycling, coupled with consumer needs for affordability, performance, driveability, durability, and styling. These drivers lead to changes in engine, fuel, lubricant and other material technologies. Regulatory compliance is now regarded as an entry price for vehicle manufacturers, while meeting consumer’s desires is seen as the way to product differentiation, increased market share, and higher profits. The changes in engine design technology are typified by General Motors’ “World Engine,” introduced in 2000. About 800,000 of these engines are being built in both North America and Europe, in multiple configurations of four cylinder, double overhead camshaft, with 2 and 4 valve per cylinder variants in 1.8, 2.0, and 2.2 L capacities. The development costs were around $1.3 billion. At the same time, the Toyota D-4 engine was engineered for improved performance with ultra-low fuel consumption, higher output, quicker response, and lower emissions. It has high pressure, fuel swirl, direct injection, helical intake ports, variable valve timing, exhaust gas recirculation, and NOx storage reduction catalysts. The replacement of current tests for proof of performance testing and the development of the next engine oil specifications (ILSAC GF-4, API PC-10, and ACEA 04) are the main issues at present. The GF-4 requirements were proposed toward the end of 2001, as a follow-on to the GF-3 specification, to reduce emissions, to protect emission control systems, to further improve fuel economy, and to give protection during extended drain intervals. GF-4 oils are required to be backwards compatible with GF-3 and earlier oils, to have maximum phosphorous and sulfur contents, to have even lower viscosities (5w20) and to provide better wear performance in roller cam followers. GF-4 oils were originally required for 2004 model year cars and the specification definition, tests and test limits were the first trial of a new system of cooperation between OEMs, oil companies and additive manufacturers. Although matrix testing started in June 2002, it was quickly realized that the time schedule was too tight, so the target introduction was revised to 2005 model year cars. Agreement on test limits was achieved in July 2003 and the final GF-4 specification was released in January this year. Product formulation, development, and testing has been done since then and the date for first API licensing has been set for July 31, 2004, so that oils will be available for motorists toward the end of the year. Licensing of GF-3 oils in the United States will cease in June 2005.

Copyright 2006 by Taylor & Francis Group, LLC

In Europe, the ACEA specifications were introduced in January 1996. These replaced the CCMC specifications and included five new tests. ACEA has now replaced the initial specifications with updated ACEA-02 specifications having significant changes and improved product performance. ATEIL and ATC are, however, questioning the need and timing for the changes, as well as the process to be used for the new categories. The new categories are A5 for fuel economy and higher oxidation resistance, B4 for direct injection passenger car diesel engines with 30,000 km oil drain, B5 as the passenger car diesel equivalent of A5, E4 for super high-performance diesel engine oils, to meet the MB 441LA test requirements and E5 for longer drain intervals. Other new ACEA tests could include some of those proposed for GF-4, including fuel economy retention, OPEST (oil protection of emissions system test), BRT (ball rust test), and Cummins M11. The latest North American heavy duty diesel engine specification is CI-4 (developed as provisional classification nine, PC-9), which was introduced in mid-2002. The main reason for the new specification is that mandated reductions on NOx emissions from diesel engines cause an increase in soot in the engine oil. As a result, the CI-4 specification has three new engine tests, Caterpillar 1R for steel and aluminium piston deposits, oil consumption and oil oxidation, Mack T-10 for ring and liner wear and Cummins M11 for crosshead wear, oil sludge and oil filter pressure drop. To these have been added tests for shear stability, low-temperature pumpability, elastomer compatibility, volatility, corrosion, and foaming. The CI-4 category was defined during 1999, when reference oils were also selected. Precision testing was completed in June 2001, as was the ASTM ballot, and test limits were decided in October 2001. API licensing began in December 2001 and the first products began to appear in the North American market in April 2002. The development cost for CI-4 was $5.7 million. In addition to the industry standards, other OEMspecific approvals such as Mack, will continue. Mack plans to issue a new approval list, EO-M, and Cummins is reported to be considering the introduction of a new list of approved premium specification HDD oils. In Japan, JAMA has requested a new API category for HDD oils, for use in diesel engines operated in South-East Asia. JAMA’s concern with the CH-4 and CI-4 requirements is that it could lead to low ash oils, counter to their desires for higher ash oils. The requested category would be PC-8 and would be aimed at diesel engines with lower piston temperatures, greater use of slider followers, and hence greater need for wear protection. This specification has now been dropped, however, in favor of the new DHD-1 specification. The next HDDEO for the North American market is PC-10, which will be required for 2007 model year

trucks equipped with EGR engines and particulate traps and emissions control catalysts. The first request for a PC-10 specification was made in June 2001, although it was only confirmed in September 2002. Development of new engine tests began in October 2002, but the decision to develop the specification was delayed until February 2003. Matrix testing started in May of this year. The API committee responsible for PC-10 plans to issue the final specification by June 2005 and to begin first licensing of the new classification (which will be CJ-4) in July 2006. The performance demands of the current and emerging engine oil specifications means that PAOs, esters, Group III and Group II baseoils feature heavily and are likely to continue to do so in the formulation of many of the higher-performance products. 48.5.1.2 Motorcycles and outboard engines The development of global standards for oils for air-cooled two-stroke (2T) engines continues to progress. At present, 70% of all motorcycles worldwide are 2T and the current standards for oils are based on the JASO FA, FB, and FC specifications. These are now being developed further by ASTM, CEC, and JASO working groups. By the early 1990s, requirements for improved engine durability and reduced maintenance led European OEMs to look for even better detergency and higher-temperature performance than that specified by the JASO FC, now ISO-L-EGC, category. As a result, a higher detergency EGD category has been added, together with a piston skirt deposit index. A draft international standard was issued in 1998 and final approval of the new EGD category was agreed at the beginning of 1999. Because consumers are demanding more performance, better durability, and reduced maintenance, the latest generation of increased complexity two-stroke engines are smaller, lighter, and equipped with refinements such as fuel and oil injection, variable exhaust valves and catalytic converters. As a result, demands on the lubricant are continuing to increase and even higher levels of lubricant performance are being sought. This has led Piaggio in Europe to develop a test method, using their liquid-cooled single-cylinder 150 cc Hexagon engine running at high speed (7000 rpm) and maximum load for 20 h, to really differentiate between the highest-performing oils. At the end of the test, candidate oils are rated for ring sticking and cleanliness of the aluminium piston, together with exhaust port blocking. The Hexagon test proposed by Piaggio is likely to become the basis for the next level of specification, ISO-L-EGE. North American motorcycles are mainly four-stroke (4T), with the oil system common to the engine and transmission. Worldwide, around 30% of motorcycles are 4T, and this percentage is continuing to grow. The main growth

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factors are emissions and noise levels. Most 4T motorcycles use conventional PCMOs (passenger car motor oils), but some ILSAC GF-2 oils have been found to cause problems of one-way clutch slipping, due to low viscosity and low friction properties. Transmission gear durability problems have also been observed, so clutch and gear durability tests are being developed. As a result, many motorcycle manufacturers are developing 4T oils specifically for motorcycles. Emissions standards have now been developed for recreational marine 2T engines. These were introduced in the United States and Europe from 1997 onwards, with the aim of being fully implemented by 2006. The emissions levels are 75% lower than those permitted in 1991, and are mainly related to reductions in levels of volatile organic carbons (VOCs). While manufacturers of outboard marine engines would like to continue to sell 2T engines, it is likely that new technologies will need to be introduced to meet increasingly tighter emissions standards. The next stage in the development of outboard engine oils, particularly in the United States, will be in more environmentally friendly oils. This is being built into the revised TC-W3© specification. The biodegradability test for this standard will be based on the ASTM D5864 28-day test method. The proposed minimum level of biodegradability will be 60%, whereas current TC-W3 oils fall mainly between 10 and 25%. In the United States, the current Federal Trade Commission guidelines for environmental claims indicate that to claim biodegradability, “. . . the entire product will completely break down and return to nature . . . .” The need to be able to support such statements may inhibit the marketing of improved outboard engine oils and is almost certain to make them more expensive, since they will have to be based on synthetic or natural esters. 48.5.1.3 Transmissions and gearboxes Automotive manual transmission and axle oils are increasingly multigrade in Western Europe and North America, with SAE 80w140 and 75w90 viscosity grades replacing EP80 and EP90 viscosity grades. The use of SAE 75w90 or 80w140 gear oils is reputed to save between 4 and 10% on fuel consumption. The use of these grades, when based entirely on mineral oils, has reportedly led to rear axle wear problems. This problem has been eliminated by the incorporation of from 20 to 25% of esters into the formulation of 75w90 or the use of combinations of PAOs and PIBs, particularly in fully synthetic 75w90 formulations. Some of the latest formulations also contain up to 20% wt of 4 cSt Group III baseoil. According to Castrol, lubricant oil temperatures at high speeds can be 30◦ C cooler with a synthetic oil. In the United States Eaton Axles issued new “Road-Ranger” specifications for full synthetics in July 1996. In the heavy duty

gear and transmission systems of class 8 trucks, after the first oil change (3,000 to 5,000 mi) the fluids can be run for up to 500,000 mi without changing, giving real cost-benefits to users. Eaton regards these systems as “filled-for-life” and believes that the next improvement will be “sealed-for-life,” which will definitely require synthetic oils. Part-synthetic 80w90 heavy duty gear oils were also introduced in North America. Texaco launched “Multigear SS” early in 1996, followed by Century Lubricants “Unigear SS.” A number of other companies are selling similar products. Peterbilt Motors, a large U.S. builder of trucks, began using fully synthetic gear and transmission oils as factory fill in all its trucks in April 1996. Peterbilt uses mainly Eaton and Rockwell gear and transmission components, and has been a major supporter of Eaton’s extended drain and fill-for-life policies associated with the use of synthetic lubricants. Demand for SAE 75w90 rear axle oils is expected to grow. The attitude of the OEMs is critical, as the majority of vehicles now have filled-for-life transmissions. The market for 75w90 is strong in Scandinavia, with their severe winters. In the past axle oils have been frozen solid, when engines were still able to start. The annual demand in the United States for automotive axle and gearbox fluids is currently around 125,000 t, for both cars and trucks. At present, sales of synthetic gear oils are between 5,000 and 6,000 t per year, mainly 75w90 for trucks, but also cars. In Western Europe, demand for automotive manual transmission gear and axle oils was 189,000 t in 2002, of which around 10,000 t was fully synthetic oils. 48.5.1.4 Automatic transmissions Most car manufacturers are now promoting the concept of “filled-for-life” automatic transmissions, to increase customer satisfaction and to assist with further improving vehicle fuel economy. This is derived from “shudder-free” torque converter clutches and stable ATF friction characteristics. The demand for “filled-for-life” will require significant improvements to ATFs. Antiwear requirements will need to last for 100 to 150 thousand miles, the oils will need to have exceptional high-temperature viscosity properties combined with good low-temperature fluidity properties and high shear stability in pump and clutch tests. Obviously, foaming resistance, air entrainment, and material compatibility (elastomers, bearing materials, and friction materials) will need to be at least as good or better than currently. As a result, there will be a heavy dependence on baseoil properties, which probably means the use of Group II or III baseoils, PAOs, and/or esters. Ford’s activities toward a MERCON-V specification have continued. ATFs to meet the requirements were trialed in Europe in 1996 and in 1997 in North America.

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Primary service fill of MERCON-V began at the end of 1997. Although Chrysler has delayed work to develop a new ATF, they are now recommending against the use of any fluids that do not meet their MS7176D specification. It is possible that Chrysler’s new MS9602 specification will be introduced later this year. Following the expenditure of around $3m by General Motors and the additive companies on new DEXRON-IV oils, this development has been suspended, due to the cost of the ATFs that met the target performance levels. New, lower performance, targets were prepared in 2001 and GM announced the start of DEXRON-III “H” licensing in April 2003. The new performance limits require ATF formulators to use Group II and/or II+ baseoils in the new fluids. The requirements for the next GM ATF are broadly the same as those demanded by Ford and GM’s main service fill will continue to be DEXRON-III until DEXRON-IV is ready, which may now be quite some time in the future. 48.5.1.5 Brake fluids Brake fluids used to represent one of the major outlets for PAGs when DOT 3 fluids were used widely. Now, the two main brake fluid formulations in use in Western Europe and North America are based on specifications issued by the U.S. Department of Transportation (DOT). They are DOT 4 and DOT 5.1. The former fluids use comparatively little PAG, which has been replaced by mixed glycol ether borates. The latter fluids are based almost entirely on mixed glycol ethers and mixed glycol ether borates. As a result, the amount of PAGs used in brake fluids has been decreasing for some time. Brake fluids have been continually improved, especially in terms of boiling point, starting from the SAE J 7OR3 specification of the 1960s. However, brake fluid has largely become a filled-for-life fluid and is rarely changed. It is now being widely recognized that brake fluids deteriorate in service after two to three years, due to water absorption. In general, the higher the boiling point of the brake fluid, the more hygroscopic the glycols are. Boiling points are still trending slightly upwards. Typical boiling points in use in Europe are now 220 to 250◦ C. 220◦ C is the minimum requirement to meet DOT 4. DOT 5.1 fluids have typical boiling points of 240 to 260◦ C. The DOT 4 fluids are formulated to give greater “in service” stability, especially as regard water absorption. The formulation of DOT 4 blocks the ether linkage and hydroxyl group, which are vulnerable to moisture pickup. These properties are further improved in the DOT 5.1 fluids. There has been a major swing toward DOT 4 fluids in the last five years in Europe and in the United States. Naturally this has been reflected in lower sales of PAGs to the formulators. This trend will of course continue to work its way through the car “fleet” over the next five to ten years.

At the peak, in the mid-1980s, PAG sales were about 12,000 t for consumption in Europe, but had declined to about 6,000 t by 1996. DOT 5 fluids have also been introduced in Western Europe and North America. These are silicone-based brake fluids, with performance properties comparable to DOT5.1 fluids. However, the two fluids are completely incompatible and severe problems could result if they are inadvertently mixed in an automotive braking system. 48.5.1.6 Automotive air-conditioning This market is much larger in the United States than anywhere else in the world, although there has been a big increase in the number of new vehicles being sold with airconditioning in many countries, notably in Europe. As a result of the chlorofluorocarbon (CFC) controversy and the Montreal Protocol, new hydrofluorocarbon (HFC) refrigerants have been introduced, notably R134A for automotive air-conditioning systems. Air-conditioning (refrigeration) systems that use HFC refrigerants cannot be lubricated with mineral oils or PAOs, because of their higher miscibility with the refrigerant. Consequently, polyol ester or PAG-based refrigerator oils are used with HFC systems. Both fluids have well-defined viscosity/temperature/pressure relationships with each of the most widely used HFCs, including R134a. They provide excellent evaporator cleanliness, reduced compressor wear, excellent low-temperature fluidity, and improved evaporator efficiency. At present, PAGs appear to be more widely used than polyol esters in automotive air-conditioning systems. Recently, a number of suppliers of these fluids have developed “capped PAGs,” which have even better compatibility with HFC refrigerants. 48.5.1.7 Automotive greases PAO and ester-based greases are being used for automotive purposes, but the bulk of the market remains with conventional products, such as lithium-based greases. However, in Western Europe, concern expressed for the environment, with particular emphasis on buses and trucks with automatic grease applicators, is leading to the adoption of polyol ester-based greases, using long chain (such as C18 oleic acid) technology. At present this market for biodegradable greases is in its infancy, having really begun in 1990, but it is growing.

48.5.2 Compressor Oils This is a complex market, because of the wide range of gases and compressors in service. The main gases, types

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of compressor, the competing synthetic products being sold into each end-use are described below, or those uses where only one synthetic has proved satisfactory. The total demand for compressor lubricants in Western Europe is around 40,000 tons. As an order of magnitude estimate, it is estimated that total synthetics sales are currently in the range of 20,000 tons. There is now competition from VHVI (API Group III) mineral oils. At least a similar volume is used in the United States, where Group III baseoil competition is not so strong. A volume of 4,000 tons of PAGs is known to be used in chemical, natural gas, and helium compressors. The United States of course has a large network of natural gas pipelines and gas production. 48.5.2.1 Air and gas compressors Stability in the presence of combinations of air and moisture is the most important reason for selecting a synthetic fluid to lubricate an air compressor. Oxygen in the air reacts with hydrocarbon oils (oxidation) to form organic acids, carbon oxides, varnishes, sludge and hard, carbonlike deposits. Water can condense as air is compressed and later cooled. This may cause corrosion, solubilize, or form emulsions. This not only interferes with compressor lubrication but also promotes more rapid deterioration of the oil. These reactions are catalyzed by certain metals such as iron and copper. The acids and sludge formed promote rapid deterioration of the oil. Other considerations for selecting a synthetic lubricant are safety, maintenance, and the potential to reduce energy requirements. Each type of compressor can take advantage of the these properties. VHVI and PAO-based reciprocating compressor oils have been formulated with low volatility and low carbonforming tendency. This has led to cleaner operation and reduction of fires in critical installations. Performance was good, with discharge temperatures at 392◦ F (200◦ C) and pressures at 100 psi (68 kPa) in a 120-hp two-stage reciprocating compressor after 16,000 h of operation. PAOs have to be blended with esters to improve their solvency and seal swell properties, and with oil-soluble silicones to reduce cylinder feed rates. When deposits are formed they are either very sticky (polymers) or hard varnishes (as with paraffinic oils). The major benefit of VHVIs and PAOs is their compatibility with elastomers and paints found in older compressors, which were designed for use with mineral oils. VHVIs and PAOs are used extensively and increasingly in rotary screw air compressors. They are often preferred over esters for use in standard 100 psi (68 kPa), 90◦ C applications. The excellent hydrolytic stability and compatibility, not only with rubber and plastic in the compressor, but also in the compressed air system. They are also compatible with mineral oils and common additives.

This makes compressor conversions from mineral oils simple and helps to prevent problems with materials and equipment used in the compressed air system. The PAOs have very little effect on swelling of rubber or elastomers. It is very common to add from 8 to 15% of a diester (or polyol ester) to increase seal swell and to help solubilize contaminants. PAO-based compressor oils have longer drain intervals than do diesters (usually about 30% longer). Their low water adsorption and rapid water separation result in improved rust and corrosion protection and help water to be easily drained from the oil reservoir during long periods of shut down. A high viscosity index and low volatility allow the use of lower-viscosity grades. This combined with excellent low-temperature fluidity reduces power consumption during start-up in cold environments. 48.5.2.2 Natural gas compressors The problems associated with the compression of gases have been known for a long time but in specific areas these problems have now become critical with the need to compress gases to much higher pressures. These problems are particularly relevant in oil fields where it is now the practice to reinject surplus natural gas into a suitable formation rather than flare off surplus gas, which was the practice in the past. Gas injection pressures, can be in the region of 400 bar and to achieve these high pressures, reciprocating compressors are normally used. The combination of the nature of the gas, its rate of flow, and the high pressures involved have caused problems with these compressors resulting in scoring and high rates of wear of piston rings and pressure packings. There are four basic problems involved when using mineral oil cylinder lubricants. The first problem, reduction in viscosity caused by dissolution of the gas into the oil, can be overcome by increasing the viscosity of the oil used, although with very rich gases the highest viscosity oils could be reduced to an unsatisfactory level. Difficulty could also be experienced with pumping of these heavy oils, particularly in low-temperature installations. The second problem, which can be experienced with low pressure gas as well as with high pressure gas, is high rates of wear resulting from the lubricant being washed off the cylinder surfaces by liquid components in the gas. An investigation into the cause of premature failure of a high pressure natural gas compressor highlighted the third problem, which was an unexpected loss of lubricant into the high pressure gas. To compensate for this loss under typical reinjection conditions, the lubricant supply to the cylinders and packings would have to be increased to at least ten times the manufacturer’s recommended feed rates. This would mean that a typical reinjection compressor might consume a barrel of lubricant per day.

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The fourth problem is associated with production rather than lubrication but is still related to the type of cylinder lubricant used. It has been found that certain additives used in the cylinder lubricants, which are necessary to ensure adequate lubrication and to prevent excessive wear, can react with the wellbore fluids being used and can cause well impairment (blocking of the porous rock structure) resulting in reduced gas injection rates, or in some cases, permanent impairment. The cumulative effect of these problems is to severely restrict the operating period of the compressors, often as low as 600 h, before complete stripdown and replacement of piston components and pressure packings is necessary, each overhaul taking approximately two days. In addition to the cost of replacement components, there is also the loss of oil production during the frequent downtime periods. Most gases are soluble in lubricating oils and the degree of solubility will depend on the gas temperature and pressure, gas composition, and the type of lubricating oil. In general the effect of gas solubility is to reduce the viscosity of the oil, thereby reducing the effective oil film thickness and limiting the protection it affords, particularly under boundary conditions. Since absorption or solubility of gas into the oil increases with pressure it could be considered that the viscosity of gas saturated oils decreases with increasing pressure. However, it is also known that oils increase their viscosity with increasing pressure and it is therefore necessary to determine the resultant effect taking these two opposing factors into account. In addition, solubility will decrease with increase in temperature. The way in which these problems have been overcome has been to use oil insoluble PAG-based lubricants in natural gas compressors. The viscosity of a PAG lubricant is approximately double that of a mineral oil when subjected to a pressure of 340 bar and saturated with methane. With an increasingly large gas pipeline transmission network in North America, in Europe, and in South America, the trend toward PAG lubricants is expected to accelerate. 48.5.2.3 Refrigeration compressors Refrigeration lubricants may be required to provide many years of service without makeup and with a minimum of maintenance. Final compression temperatures may reach 160◦ C for some applications, at which temperatures unsuitable oils form carbonaceous deposits. In the special case of hermetic compressors, the motor materials must not be adversely affected by the lubricant/refrigerant mixture or by-products from its deterioration. This requires a lubricant that has excellent thermal and chemical stability and produces a minimum of deposits. The lubricant in compression refrigeration systems has an influence on the operation and efficiency of the entire system. Some lubricant is carried out of the compressor

and into the system. The lubricant must act as a compression sealing aid and reduce wear and friction in the compressor without adversely affecting the operation of the filter dryers, condenser, expansion valve, or evaporator. The behavior of the oil/refrigerant pair is of major importance. Refrigerants can be carbon dioxide (CO2 ), ammonia (NH3 ), chlorofluorocarbons (CFCs; R11, R12, R113, or R502), hydrochlorofluorocarbons (HCFCs; R22, R123, or R124), or hydrochlorocarbons (HFCs; R23, R134a, R404a, R407c, R410a, or R507). The solubility of the refrigerant gas in the lubricant and the miscibility of the liquid refrigerant with the lubricant respectively affect compressor performance and system performance. Dissolved gas has the effect of reducing lubricant viscosity. Miscibility is considered for design of components and piping to promote uniform oil movement through the system and back to the compressor. Heattransfer problems are more significant in systems where the oil is immiscible or partly miscible with the refrigerant. The main differences between screw compressors and reciprocating compressors for refrigerating systems, with respect to the oil system, are that a screw compressor has an oil separator and an oil sump situated on the high-pressure side and the compression chamber is flooded with oil, to seal the threads that are under compression. In refrigerating screw compressors, the lubricant has more effect on performance than it does with the reciprocating compressor. To reach high performance, the screw compressor needs a lubricant with limited solubility of the refrigerant gas at discharge conditions (at the oil separator). Limited solubility will reduce or eliminate by-passing of refrigerant from discharge to suction or to a lower situated thread. External by-pass caused by the refrigerant circulating with the oil is also reduced. This leads to both high volumetric efficiency and low torque. Most lubricants with low solubility also have low miscibility (liquid refrigerant in oil). In some cases a synthetic lubricant can meet the requirement of low solubility while maintaining good miscibility. This, combined with low volatility, reduces oil in the system to improve heat transfer. Mineral oils were used extensively in refrigeration compressors, due to their good miscibility with R-12 refrigerant. Superior chemical and thermal stability of HVI and VHVI oils have reduced the risk of carbonizing at high temperatures in heat pumps with R-12 and R-114. Superior adiabatic efficiency of 3 to 10% is achieved in rotary-screw compressors using these refrigerants when compared to naphthenic refrigeration oils. Further efficiency improvements can be obtained with PAOs, largely due to their higher viscosity at higher temperatures in the presence of the refrigerant. Superior performance and reliability have been achieved in reciprocating, twin-screw, and single-screw compressors. The Montreal Protocol banned the used of CFCs and these refrigerants are now being phased out and replaced

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with HFCs. HCFCs are also being phased out progressively, although many marine refrigeration systems still use these refrigerants. Lower evaporator temperatures are permissible with PAOs than with mineral oils because PAOs are wax-free and have good low-temperature fluidity for oil return. Low-temperature fluidity is the major reason why PAOs have been used in the United States for relatively insoluble refrigerants such as R-13 and R-503. The lubricant viscosity, ISO 15 or 32, is selected by considering operating viscosity in the compressor as well as low-temperature fluidity below −73◦ C in the direct expansion dry-type evaporator system. PAOs and VHVI oils have been found to provide several performance advantages in ammonia refrigerating systems. Better thermal and chemical stability with ammonia results in reduced sludge and varnish and has resulted in extended drain intervals. Lower solubility helps improve lubrication and reduces foaming. Lower volatility reduces oil consumption and improves heat transfer by limiting the amount of oil in the system and on heat-exchanger tubing. The excellent low-temperature fluidity and HVI of the PAO fluids allow evaporator temperatures below −46◦ C and maintain viscosity for higher compressor operating temperatures. Good low-temperature fluidity facilitates oil removal in most systems. Refrigeration systems and heat pumps that use CO2 , NH3 , CFCs, or HCFCs as refrigerants can be lubricated with mineral oils or PAOs. In general, refrigerator lubricant suppliers and users have increasingly tended to use PAO-based fluids, because they have better low- and hightemperature properties. As a result, they can be used in compressors operating at high discharge temperatures in refrigeration systems with low evaporator temperatures. Additionally, PAOs have much lower volatilities than mineral oils, so are less prone to “light end stripping,” thus minimizing viscosity buildup and giving lower oil consumption. The solubility of most of the refrigerants in PAOs is low, resulting in higher film thickness in the presence of refrigerants under pressure and lower shaft seal leakage. Refrigeration systems that use HFC refrigerants cannot be lubricated with mineral oils or PAOs, because of their higher miscibility. Consequently, polyol ester and PAGbased refrigerator oils are used with HFC systems. Both fluids have well-defined viscosity–temperature–pressure relationships with each of the most widely used HFCs. They provide excellent evaporator cleanliness, reduced compressor wear, excellent low-temperature fluidity, and improved evaporator efficiency. When changing from a CFC or HCFC refrigerant to an HFC refrigerant, the compressor oil must also be changed. This necessitates a complete clean and flush of the lubrication and refrigeration systems. All refrigerator compressor manufacturers issue recommended procedures for changing both the refrigerant and the lubricant.

48.5.3 Turbine and Hydraulic Oils 48.5.3.1 Steam turbine oils In general, the properties required of a steam turbine lubricant are not extreme, but they need to be maintained for many thousands of hours of continuous service. The oils are expected to remain in service for between 10 and 20 yr without any oil change. These requirements are adequately met by specially refined baseoils from selected crude oils, inhibited with rust and oxidation inhibitors. Regular topping-up of the system with new oil contributes to achieving the long oil life. If improved oil seals are developed, which reduce the oil top-up rate, or if oil system temperatures are increased, the life of the current turbine oils could be considerably reduced. Under these operating conditions there would be a need for a more oxidatively stable oil. This could be achieved by using PAOs but, since the systems are large, the cost could be prohibitive and it is more likely that a blend of PAO and mineral oil would be used. On the smaller steam turbines it is usual to use the main system oil as the fluid for the hydraulically controlled governor systems. Larger turbines now tend to use electro-hydraulic governor control systems that operate at relatively high pressures and this, combined with higher steam temperatures, increases the risk of a fire if a leak develops in a hydraulic line. For this reason the trend is to use phosphate ester fire-resistant hydraulic fluids in these systems, operated from a separate supply. Phosphate esters have also been used successfully as a combined hydraulic fluid and system lubricant in a turbo generator. It is envisaged that the use of these lubricants could be an economical way of reducing the fire risks associated with steam turbines in hazardous environments such as oil refineries, sugar and paper mills, and chemical plants.

48.5.3.2 Gas turbines oils Industrial gas turbines fall into two main types: • The direct use of aero-derived turbines for electricity

generation and mechanical drive applications (compressors and pumps). • Specially developed gas turbines, pioneered by General Electric (GE), but also now developed by ABB, GEC, and Siemens. These are also used for electricity and cogeneration but are now on a much larger scale than the aero engines. For example, while the RollsRoyce RB211 aero-engine generates 25 MW, the latest industrial GE Frame “9 F” produces 210 MW of electricity. Almost all aero-derived engines operating on oil rigs in the North Sea, or on Soviet gas pipelines for pumping,

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use aero-engine oils, for example, diesters for Rolls-Royce “Avons” and polyol esters for RB211s. On the other hand, the large industrial gas turbines have tended to use highperformance mineral turbine oils. Now, however, there are examples of some using synthetics, based on PAO/ester mixes. In the 1990s the market outlook for heavy-duty industrial gas turbines was exceptionally good, as natural gas fired combined cycle power stations of high efficiency and moderate capital cost are built in large numbers, in response to environmental pressures. Since privatization, in the United Kingdom alone, about 25 new power stations of 300 to 900 MW each have been either built or proposed, mainly using combinations of at least two industrial gas turbines and one steam turbine. Since 1960, GE, the market leader, has shipped over 5000 units of industrial gas turbines. The current world market for industrial turbine lubricants of all types (steam and gas) is around 285,000 t per year. Of this, only about 20,000 t is represented by the toptier VHVI, ester-, and PAO-based products. Around 5,000 t per year of PAOs are used currently, mainly in PAO/mineral oil blends for larger gas turbines in combined cycle power generation plants. 48.5.3.3 Hydraulic fluids Increasingly, hydraulic systems have become smaller and are required to operate at higher pressures. This has demanded the use of more thermally, oxidatively, and hydrolytically stable oils, particularly in those systems that use high-pressure rotary vane pumps to deliver fluid pressure and flow. Demands for multi-metal compatible, superior antiwear and enhanced corrosion protection fluids has increased since 1980. Fortunately, most of these demand can be achieved using correctly formulated HVI-based oils. Simultaneously, demands for increased workplace safety, especially in places involving hot surfaces or explosion hazards, such as foundries, steel and aluminium rolling mills, casting workshops, and coal mines, has lead to an increase in the use of fire-resistant hydraulic fluids. Most hydraulic fluids are either mineral oils, or one of the four types of fire-resistant fluids, which are oil-inwater emulsions, water-in-oil (invert) emulsions, waterglycol solutions, or phosphate esters. During the 1980s, PAOs and polyol esters were promoted as “fire-resistant” fluids, but it has now been demonstrated clearly that the fire retardancy properties of these synthetics is very limited. In general, VHVI oils do not show any useful performance advantages over HVI oils for hydraulic fluid applications. The one notable exception is in the formulation of “multigrade” hydraulic oils, for use in machines operated outdoors in colder climates. In these applications, the hydraulic oil must be pumpable at low temperatures (from 0 to −30◦ C) when the machines are first started

each morning, but must also have all the required hydraulic fluid attributes of good oxidation, thermal, and hydrolytic stabilities, together with excellent antiwear and corrosioninhibiting properties. Hydraulic oils with the correct viscometric and pour point properties can be formulated from HVI baseoils, by the use of appropriate amounts of viscosity index improvers and pour point depressants, as well as the normal antiwear, oxidation inhibitor, and corrosion inhibitor additives. However, the use of viscosity index improvers does increase the level of shear instability of the hydraulic oil, particularly under the high fluid shear conditions found in many hydraulic pumps and motors. One way of overcoming the shear problem found with some HVI hydraulic oils is to use a VHVI baseoil, so that the amount of viscosity index improver is either eliminated or reduced significantly. Unfortunately, the cost penalty of using this formulation route is quite high. As a result, shear stable “multigrade” hydraulic oils based on VHVI oils are marketed for only a relatively few critical applications in which the high fluid shear conditions or the extremes of temperature experienced in the hydraulic equipment justifies the additional cost. The majority of these applications are found in Scandinavia, northern Europe, Canada, and northern U.S. states, particularly in outdoor timber and construction machinery and agricultural equipment. PAOs have begun to find a small niche as central system hydraulic fluids in a few designs of passenger cars. These central systems combine the suspension, shock absorber, clutch, and brake systems, for which a universal system, preferably mineral oil compatible is required. This is a very small market, which is unlikely to grow much in the next few years. Another recent trend has been an increase in the demand for environmentally friendly or biodegradable hydraulic fluids for use in outdoor and mobile equipment. These systems include those on logging and forestry machinery, excavators and mechanical handling machinery in open-cast mining, hydraulically operated rock-drills, and road construction machinery. Demands for ester-based and vegetable oil-based hydraulic fluids have been greatest in Canada, Sweden, Switzerland, Austria, Germany, Norway, and Finland. Initially, many of these biodegradable hydraulic oils were based on vegetable oils. However, problems were encountered in many applications with oxidation stability, thermal stability, and low-temperature performance, so more of these applications are now using synthetic ester hydraulic oils. In 2002, the International Standards Organisation (ISO) issued a new global standard for biodegradable hydraulic fluids, ISO 15380. This standard contains specifications for four new categories of “environmentally acceptable” hydraulic fluids:

• HEES: Synthetic esters • HEPR: Polyalphaolefins and related hydrocarbons

• HETG: Triglycerides (Vegetable oils) • HEPG: Polyglycols

Gear oils are used to lubricate various types of “gears” designed to transmit power from one point to another

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(Specifications for mineral oil [classification H] hydraulic fluids are contained in ISO 11158 and specifications for fire-resistant [classification HF] hydraulic fluids are contained in ISO 12922.) Development of the ISO standard was based on the experiences of suppliers and users of biodegradable hydraulic fluids in a number European countries, including Sweden, Germany, Austria, and Switzerland. In addition to the usual tests for viscosity, pour point, flash point, rust prevention, copper corrosion, oxidation stability, foaming tendency, air release, demulsibility, and antiwear performance, ISO 15380 contains limits for biodegradability, acute fish toxicity, acute daphnia toxicity, and bacterial inhibition, using standard ISO test methods. The technical and marketing approaches to health, safety, and environmental issues are intended to promote lubricants that are more friendly to the general environment, including people. Either they are more compatible, have reduced ecological impact, reduce pollution, or are more environmentally responsive or responsible. The current annual world market for all hydraulic fluids is around 1.35 million metric tons, of which mineral oils represent over 85%. The other 15% are mainly fireresistant products, including oil-in-water emulsion fluids, water-glycol fluids, and synthetic phosphate esters. The Western European market for biodegradable hydraulic oils was around 35,000 t in 2002, of which around 20,000 t was synthetic esters.

48.5.4 Gear, Circulating, Process, and Functional Oils 48.5.4.1 Circulation systems Some circulation systems, such as those feeding lubricant to gearboxes operating paper mill drying cylinders, run at high bulk oil temperatures. Particularly in Scandinavia and the United States, it has been found that PAG lubricants enable the mills to be run faster and at higher temperatures, without deterioration of the lubricant through oxidation. Higher paper output has been achieved. Large paper mill manufacturers are now recommending synthetics at startup. Polypropylene glycol is the most commonly used synthetic base for this application, but PAOs are also being introduced. In low-temperature conditions, found in cold storage applications and occasionally in steel works and opencast mining, alkyl benzenes and PAOs are being used as circulation lubricants. 48.5.4.2 Gears

in order to do work. The primary function of a gear lubricant is to provide a high degree of reliability and durability in the service life of gear equipment. Use of gear lubricants dates back to the early days of the industrial revolution when ways were being sought to generate and transmit more power, more efficiently and at higher loads than could normally be handled. Nowadays, the technology associated with gears, their function, and their lubrication has become very sophisticated. The basic types of gears include spur and helical, bevel, hypoid, and worm, from which all gear “systems” are developed. A system, whether automotive or industrial, may contain only one type of gear or it may involve a combination of gears. However, most automotive applications use hypoid and spur gearing, while most industrial applications use bevel and worm gearing. The speeds may range from very low to very high under both light and heavy loads, depending on the type of work required from the gear system. These gear systems may be enclosed or open and exposed to the atmosphere. Speed, load, and climatic conditions all have an effect on the operating temperature of the particular gear system. Proper lubrication is essential to ensure optimum life of the gears. The gear lubricant should be of the type, grade, and quality to provide proper protection for the gears to function effectively for the intended application. Such lubricants should provide the following general performance characteristics: • • • • • • • • •

Extreme pressure and antiwear protection Thermal and oxidative stability Foam suppression Ability to demulsify water Proper working viscosity Good low-temperature flow properties Seal compatibility Environmental acceptability Cost-effectiveness

Synthetic gear lubricants operate over a different temperature range in terms of viscosity than do conventional mineral oil-based gear lubricants. This range is important to the user, enabling the use of one lubricant for a variety of applications. The viscometrics for a PAO, for example, enable gear lubricants to be formulated for both low- and high-temperature performance without the use of polymeric viscosity index improvers, since the PAOs have a high “natural” viscosity index. PAGs have similar properties. Among the most important factors of synthetics are their low-temperature viscosity properties. When oils are cold their viscosity may be many times higher than at ambient temperature. This changes the lubricity of the lubricant and in extreme cases can cause damage to the gears.

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Synthetic gear lubricants have better low-temperature pumpability. In general, PAO-based multigrade gear oils have much greater shear stability than conventional mineral oil-based formulations, since they use less or no viscosity index improver. Also, multigrade mineral oil based gear lubricants tend to shear out of grade, a problem that does not affect fully synthetic formulations. This can be very important to the service life and durability of modern gearboxes and gear oils. Most industrial gear oil specifications are based on performance criteria easily met by conventional gear lubricants. These, mineral oil-based gear oils are very costeffective, so there is little incentive to change. However, there is a growing volume of evidence to suggest that significant energy savings can be made by using synthetic gear lubricants. The use of PAOs and PAGs in industrial gearboxes can lead to important savings in energy consumption, as well decreased down-time and lower maintenance requirements. The wide range of operating temperatures allows the use of less viscous oils, which results in greater energy efficiency. The relatively low coefficient of friction for PAGs and PAOs reduces the amount of internal friction created by the normal shearing of an oil film during operation. 48.5.4.3 Bearings The high pressures encountered on large calender machines producing rubber or plastics, can result in bulk oil temperatures of over 200◦ C. Up to about 150◦ C mineral oils are still used, but for higher temperatures the PAGs have been accepted as the solution. Again, PAOs have also been introduced for this application and even some PAO/ester blends in the United States. 48.5.4.4 Heat transfer oils and solar fluids Heat transfer systems and the fluids used in them are complex and highly specialized. The largest volumes are in major circulation systems at chemical or process plants. This business is usually awarded at the initial-fill stage, with sales thereafter only as top-up or infrequent change. It is important to offer technical support at the design and commissioning stage of these large “one-off” systems. The fluid used is dependent on the heat transfer temperature required. About 45% of the overall heat transfer fluid market is met with mineral oils. The total worldwide market is 50,000 t per annum, and synthetics represent about 9,000 t (20% of the total) per annum. Thus liquids represent 65% of the market. The balance are high-temperature vapor-phase systems (25%) and intermediate temperature systems (10%). The main synthetic fluids are polyglycols, silicones, and specialized hydrocarbons. Mineral oils have a tendency

to foul, and also have a relatively narrow operating range (up to 300◦ C) and poor thermal stability. PAGs also have some problems of thermal stability and narrow operating range (165–250◦ C). However, they are in wide use in smaller systems, such as plastic injection molding machines, mobile heat exchangers (for composites), or small chemical reactors. Silicones have high thermal stability and wide operating range, but poor heat transfer properties. The specialized hydrocarbons, such as hydrogenated polyphenyls (−10–345◦ C), alkyl aromatics (50–300◦ C), or polyphenyls (75–400◦ C) are offered to provide the right balance of properties. Monsanto and Dow Chemical are leaders, with the widest range of specialist products on offer. BP/Castrol, Bayer, Hüls, ChevronTexaco, Nippon Steel, and Wibarco (with alkyl aromatics) are suppliers with narrower ranges of products. These well-established aromatic compounds, phenyls and diphenyl oxide type materials, are coming under increasing government pressure for control and restriction in the United States. Crompton (Uniroyal) and BP have been actively promoting PAOs in this market sector, as potential replacements. Solar fluids for roof-type water heaters are another heat transfer market, which although already in wide use in countries like the United States, Italy, Cyprus, and Israel, is likely to grow, in an energy-conscious and “green” world. Low viscosity PAOs (2 cSt), with metal deactivators, are finding outlets as solar fluids.

dependent on electricity-related properties, where the main function is as a heat transfer medium; whereas high-voltage capacitor uses have required a range of other products. Silicones and other speciality type products have probably gained the biggest share of the PCB replacement market. They are particularly suitable for new equipment, which can be designed around the dielectric. Dow Corning has been marketing a polymethylsiloxane product and silicone-based products are also offered by Bayer and Rhone Poulenc for transformers. Other developments in this field came from GEC Alsthom in the United Kingdom, which completed work on natural fatty acid-based esters, which are marketed under the name of Midel. GEC Alsthom believes the main market is for retrofilling existing equipment, where silicone-based products are less suitable. Another ester product has been developed by Rhone Poulenc, in cooperation with the Swedish cable company, Asea Kabel. The fluid is a nonchlorinated ester, benzyl neocaprate. Further possibilities for PCB replacement exist with PAOs. Crompton introduced a range of high molecular weight PAO fluids, which it claims are less costly than silicones and which have been approved by the fire authorities. The demand for insulating oils of all types, including mineral oils, is estimated at 150,000 t in Western Europe, covering both the initial-fill and top-up and replacement markets. The expected demand for synthetics, of all types, is thought to be in the 2,000 t range.

48.5.4.5 Electrical and insulating oils

48.5.4.6 Cable compounds

Naphthenic baseoils have traditionally been used in transformers and capacitors, for those applications where fire risk was not being considered, that is to say, outdoors. The naphthenics were believed to have higher oxidation stability than paraffinics and, with their lower wax contents, the pour points were suitable, on average, for transformers operating outdoors down to −35◦ C (pour points of −45◦ C). In fact, special naphthenics have been refined with pour points down to −60◦ C, but for applications with potential operating temperatures below −50◦ C, synthetics have generally been used. In the past, transformers operating indoors tended to use fire-resistant insulating fluids, such as polychlorinated biphenyls (PCBs). However, under EU regulations, end users have been prohibited from using PCBs for more than 30 yr. The EU regulations have led to the total replacement of PCBs in all applications. The environmental persistence of PCBs was first recorded in Sweden in the late 1960s. The excellent range of properties exhibited by PCBs as dielectrics is illustrated by the number of products that has been necessary to introduce to cover the same field adequately. In general, silicone-based products have been found satisfactory for those transformer applications less

“Cable compound” is a term concerned with those compounds used for the impregnation of paper-insulated electric power cables and for filling interstitial spaces in plastic-insulated telecommunication cables. It includes blends of oils (which may be mineral oil or synthetic), and formulations of such blends with additives to achieve particular characteristics, such as higher viscosity and a nonmigratory performance during service. Even in this limited and specialized field there is a wide diversity of compound types. The primary differentiation is between power cables and telephone cables, as follows:

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• Power cables:

• “Self contained” hollow core cable • “Pipe” type cable • “Solid” cable (mass impregnated; non-draining or viscous liquid) • Telephone cables:

• “Fully filled” plastic-insulated cables • Optical fiber cables

It is important to distinguish between the terms “impregnating,” as applied to power cables, and “filling,” as applied to telephone cables. In a power cable, the compound and the paper together form a composite dielectric, which has greatly superior properties of insulation than could be achieved with either component separately. The compound forms an integral part of the cable insulation, and in the manufacture of the cable every effort is made to ensure that no air or vacuous spaces remain in the dielectric, following the process of impregnation. In a telephone cable it is the extruded plastic around the conductors that forms the primary insulation. The “filling” compound has a secondary insulating function, but is primarily introduced to prevent the penetration of water into and along the length of the cable, in the event of rupture of the cable oversheath. Pockets of air can be tolerated within the interstitial spaces of the cable core, provided a continuous channel does not exist along a significant length of the cable. Nationally or internationally agreed quality control tests are applied to manufactured cable lengths, to ensure compliance with specification requirements. Cables of the hollow fiber type require oils of the lowest possible viscosity, compatible with the need for an acceptably high flash or fire point, to minimize the possibility of fire hazard. Naphthenic mineral oils having a carefully controlled degree of aromaticity are still used for this application, but currently alkyl benzenes are more often specified. Pipe type cables utilize a fairly low viscosity oil to transmit the hydraulic pressure within the pipe, but a considerably higher viscosity compound to impregnate the cable cores. Polybutenes have replaced mineral oils to a very great extent in this design. Solid type cables were traditionally impregnated with blends of viscous oils, to which refined natural resin (colophonium) had been added. This addition resulted in a very greatly increased viscosity at ambient temperature, without unduly increasing the viscosity at cable impregnating temperatures (commonly between 115 and 135◦ C). In this way problems resulting from compound drainage in service were reduced, while processing times during manufacture could be kept down, in the interests of economics. PIBs of approximately 900 to 1200 molecular weight have been widely used in the past two decades for the same purpose; their disadvantage of HVI has been made good by improved cable manufacturing techniques. However, since the 1960s, by far the greater proportion of solid cables have been impregnated with Mass Impregnated Non-Draining (MIND) compounds. These can be based either on mineral oils or on PIBs, to which are added suitable waxes, which result in a high melting point. In optical fiber cables used for telecommunications, the tube or slot filling formulations are based on low viscosity technical white oils/PIBs or high molecular weight

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PAOs, gelled with micronized silica. Interstitial spaces are filled with wax/mineral oil or wax/PIBs. Technical white oils and waxes are used to prepare thixotropic gels that are hydrophobic, are stable over a wide range of temperatures and can be pumped into the cable tube at room temperature. They are non-melting, with no phase or structural changes, and have a substantially constant viscosity over a wide range of temperatures. These cable jellies act as water blocking and buffering materials. Metallic (usually copper) conductor telecommunications cables use compounds made from either white oil/wax blends, PIB/wax blends, technical white oils, or block copolymers. Cable compounds for power and telephone usage are usually formulated by specialists such as DussekCampbell, BP Chemicals, ExxonMobil Chemicals, Crompton (previously Witco), or Sasol (previously Schumann). 48.5.4.7 Oil-based drilling fluids Due to high temperatures and pressures, there are significant advantages to the use of oil-based drilling muds, including good lubricity coefficients, easier drilling through salt, potash, or gypsum, reduced drill point torque and drag, plus corrosion protection of the drill pipe. In general, faster drilling, longer bit life, and higher working temperatures are possible. The range of possible viscosities used on drilling fluids is quite wide, and varies from light mineral process oils through nontoxic gas oils to odorless kerosene. Although oil-based muds use less additives and are reusable, there have been concerns about harm to marine life if muds are disposed of at sea. (Muds are not deliberately disposed of, but some fluid adheres to the drill cuttings that are disposed and accumulate on the sea bed.) Hence the development of the shrimp test or Krangen–Krangen test, used in the North Sea, to assess the effects of mud oils on sea life. At its height the North Sea was using about 50,000 t of mineral oil bases for drilling muds annually. In the mid1990s, oil-based muds were banned in the North Sea as a consequence of their poor biodegradability compared to water-based muds. Biodegradable ester-based muds were, however, permitted. As a result, the drilling industry switched to ester or water-based muds in the North Sea, while continuing to use mineral oils and low viscosity PAOs in other offshore regions, as well as for onshore drilling. More recently, the disposal of drill cuttings in the North Sea has also been banned, so all drill cuttings (and thus drilling mud) must be returned onshore for disposal, adding significantly to the costs of drilling. Oil-based muds have begun to make a comeback, although many are mineral oil based.

48.5.4.8 Circuit board fluxes A new end use for synthetics has been developed in printed circuit board fluxes, where clean burn-off is an essential requirement. PAGs dominate this market. Potential sales are around 5000 t per annum worldwide, with of course strong demand from the Pacific Rim.

cutting fluids. The Law on Water sets limits on the concentration of pollutants routed into sewers. Also, the law on the handling of water-polluting substances, Water Pollution Categories and storage and/or volumes define the Water Pollution stages which, in turn, govern the cost-relevant monitoring and investment-intensive protection measures necessary when handling water-polluting fluids.

48.5.4.9 Mould release agents

48.5.5.1 Water-miscible cutting fluids

This is another hard-to-define market. Mineral oil emulsions have been used as concrete mold release agents for many years. The end use identified here is for mold release in the plastics and rubber industries, where clean lift-off and noncompatibility with the rubber or plastic are essential characteristics. PAGs are the most popular product on a price/performance basis, with silicones also competing in this sector, although at much higher prices. Since the early 1990s, the use of environmentally friendly, biodegradable concrete mold release oils has been encouraged in Western Europe, particularly in Scandinavia, Germany, Austria, France, Belgium, and the Netherlands. Many of the products are based on vegetable oils, but some of the products are based on biodegradable synthetic esters. The market for biodegradable mould release oils was estimated to be around 13,000 t in 2002, of which 10,000 t were vegetable oils and 3,000 t were synthetic esters.

With water-mix cutting fluids, change is constant, and the current situation is that the main favored product is semi-synthetic, that is, it retains a mineral oil content, but contains an array of other products, mainly based around a corrosion inhibitor (CI) additive package. Some of the semi-synthetic cutting oils contain up to 20 components and it is very difficult to persuade formulators to confirm what is being used in the final product. In the 1970s polyglycols were introduced as components for cutting fluids, but suffered technical drawbacks from paint stripping and the removal of lubricants from machine slideways. As a result, synthetics received a “poor press” in the cutting oil business. The move to semi-synthetics in the 1980s was an attempt to rebalance the situation, by again adding mineral oils to the formulation. Nevertheless, it appears that cutting oils are still a target for the synthetics suppliers, with primarily PAGs trying and gaining success, especially for very hard or exotic metals. PAGs have also been used by formulators as the lubricity base for water-soluble cutting and grinding fluids. They work by taking advantage of the phenomenon of inverse solubility, which means that a material becomes less soluble in water as the solution temperature increases, as it does at the metalworking workface, between tool and piece. The PAG comes out of solution and coats/protects the metal surfaces at the critical time. A recent development was the introduction of longchain polyol esters as “neo-synthetics.” These are used at high levels (30 to 50%) in the emulsion concentrates, to replace the EP additive, sulfur, or chlorine. Such formulations are used for machining hard alloys, like silicone aluminium, and for deep hole or gun drilling applications. Another development has been the development, by Uniqema, of self-emulsifying esters specifically for watermix fluids. These fluids combine lubrication and emulsification in one molecule that allows a single formulation to be suitable for use in all types of water hardness. Self-emulsifying esters do not suffer problems with the formation of calcium soaps in hard waters or the development of excessive foam in soft waters. Also, no depletion of anionic emulsifiers or corrosion inhibitors occurs. The overall result is more stable emulsions that have longer service lives compared to conventional water-mix emulsions. Self-emulsifying esters can also be used in neat forming oils, to allow water washability after forming, in copper

48.5.5 Metalworking Fluids During the early 1980s, neat (mineral oil-based) cutting oils were increasingly replaced by water-based emulsion and solution cutting fluids, due to problems with faster cutting speeds, generation of oil mists, health and safety issues associated with MVI mineral oils and chlorinated additives and the risk of fires. It was soon recognized, however, that water-based cutting fluids suffered equally serious problems of microbial degradation, shorter operating lifetimes, corrosion, sticky deposits after evaporation from workpieces and machine tool surfaces, and requirements for much greater monitoring and control. In 1995 and 1996, several European initiatives caused machine tool workshop staff to ask for replacements for water-soluble metalworking fluids. Health and disposal issues have exposed these fluids to considerable study and monitoring. Adverse health effects related to watermiscible fluids involve the presence of benzoic acid derivatives, alkaline nitrites, the danger of nitrosamine formation and germicidal contamination. Germany’s Waste Water Levy and Law on Water have considerable influence on the splitting and reconditioning of water-miscible cutting fluid. Waste Water Levy charges for pollutants with high chemical oxygen demand (COD, CSB) that are routed into public sewers are of particular relevance to water-miscible

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wire drawing oils, to reduce copper soap formation, and in low-foaming grinding fluids. Overall, however, volumes of synthetics sold into this sector remain small, and the bulk of the market remains either with traditional mineral oil emulsions or the multicomponent “semisynthetics,” which are mainly complex chemicals, rather than the synthetic base fluids under review. 48.5.5.2 Neat cutting oils As a result, neat mineral oils containing replacements for chlorinated additives have been developed to eliminate these concerns, while maintaining the advantages of water-miscible fluids. When making the switch back to neat cutting fluids, the favorable properties that water imparts (good cooling, good chip flushing, and fire resistance) need to be considered. Low viscosity fluids are needed to retain these qualities. Drag-out losses on workpieces and chips is also dependent on viscosity. But low viscosity mineral oils traditionally display relatively high evaporation rates and low flash points, which conflict with worker safety and ecological considerations. Such problems can be solved with low-viscosity, esterbased cutting fluids, which have rapid biodegradability, low evaporation, low misting, and high flash point properties. High-performing synthetic esters are obtained by the chemical/physical modification/refining of either natural vegetable or animal oils (oleochemical products) or mineral oil. In metalworking, the first machining trials with ester-based oils took place in the 1980s. The priorities then were technical requirements for high-speed grinding and the avoidance of additives containing chlorine. Ester oils performed well under high speeds, producing good surface finishes. Since then, and with a view to the “machine tool” system, it has been possible to develop an ester-based fluid family of cutting fluids, gear oils, slideway oil, hydraulic fluids, and greases. These are all compatible with one another, so leakages from machine parts do not, or only slightly, alter the properties of the cutting fluid. This results in longer cutting fluid life and the elimination of tramp oil problems (including costs). 48.5.5.3 Steel, aluminium, and copper rolling oils In steel rolling oils, the move toward long-chain polyol esters has continued and they now have a dominant share of the steel market in Western Europe. These products are based on trimethylol propane (TMP) or pentaerythritol esters. Earlier formulations were based on emulsifiable oils (70% mineral oil, 25% tallow fats, 5% emulsifiers). The TMP esters were originally developed by Quaker Chemical, but this technology has now been adopted by other specialist suppliers in both Europe and the United States.

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However, while these esters now have an estimated 90% of the European market, development in the United States has been much slower, and only about 35% of the steel market is currently using long-chain esters. In cold rolling of aluminium foil, where all products used must be nontoxic, because the foil is used for food wrapping, the main fluid used for the rolling process is a nontoxic gas oil, mainly produced by solvents companies. Also in wide use are iso-paraffinic solvents such as Exxon’s “Norpar.” A single large mill can use 3000 t of solvents per year. Rolling is at 200 to 300 meters per minute at 675◦ C. The base solvent has a viscosity of 1.8 cSt at 40◦ C and a boiling range of 200 to 250◦ C. Load carrying and lubricity additives are incorporated, which enable increased reductions to be taken, before breakdown of the lubricants. It is known that PIB is in use as an additive, because of its ability to depolymerize and evaporate. Similarly there is evidence in the United States that PAGs are used as an additive/rolling aid at a ratio of 5% of the total solvent. Additionally, from 1988 to 1991, in foil rolling plants in Europe, PIB-formulated machinery lubricants increased their share of the business, to ensure compatibility and nontoxicity in the event of cross-leakage to the foil. For copper rolling, the annual demand for fluids is about 15,000 t in Western Europe. Emulsifiable mineral oil/fatty acid blends are used, to avoid staining problems due to water, and metal passivators are also added. Fatty acid esters are replacing straight fatty acids. PIBs have been used for hot rolling of copper, but it is not known if the products are yet established. 48.5.5.4 Stamping, pressing, and forming oils In hot stamping the primary products that are used are mixtures of graphite and water, from companies such as Acheson Colloids. The concern of the hot stamping companies is that, if they use any kind of mineral product or chemical product, there will be a “fire-flash,” before the product actually serves its purpose, as a carrier of the graphite to the point of contact. Nevertheless, there is still interest in the possibility of using polyglycols or PIBs for these applications. More technical work is needed before progress will be made, as this is a very conservative industry. In cold pressing lubricants for sheet metal, it is believed that the traditional special semifluid pastes are still the dominant products, coming from organizations such as the Houghton Group. BP confirms that they are selling PIBs for stainless steel pressing, again presumably because of the clean burn-off and non-staining nature of the PIB. PAGs and PIBs are also being used in automatic cold stamping of components, such as spark plug bodies. The clean burn-off of the products during annealing is a major advantage. Several suppliers have been trying synthetics in recent years for these applications.

In the stamping and forging of aluminium in the United States, the industry has recently been replacing chlorinated paraffins, for environmental reasons. Removal of stamping fluid is of course needed, and here PAGs, which can be water-rinsed, are finding an outlet in preference to products needing washing off with 1,1,1-trichloroethane. 48.5.5.5 Wire and tube drawing lubricants In the drawing of wire, the products that were used for many years were based on soaps and fats. Clearly these are now being replaced by more modern and environmentally acceptable products. It has been reported that some 2500 t of polyglycols are being sold into the wire drawing sector in Europe, and this usage for PAGs has also been confirmed in the United States. BP Chemicals also advise that PIBs are being used in stainless steel wire drawing and also in copper tube drawing. On the other hand, in the production of shaped aluminium extrusions, such as for window frames or patio doors, it appears that water-graphite mixtures are still the norm. These are swabbed onto the ram area of the extruder, and not used as a die lubricant. 48.5.5.6 Aluminium can stock and can drawing fluids These are specialized markets, where a number of companies, like ExxonMobil, have strong positions. Additionally, specialized formulators like Nalco and Ferro in the United States compete, and some aluminium companies make up their own formulations on site. Nontoxicity and FDA approval are, of course, mandatory requirements. It is known that PAGs are in use in small amounts, as are PIBs. Similarly, long-chain polyol esters, which are emulsified at consuming plants, are used for aluminium can stock drawing in the United States. 48.5.5.7 Heat treatment (quenching) fluids In the quenching fluids sector, attempts by producers of synthetic quenchants to push up their market share continue without abatement. Union Carbide (now Dow Chemical) was the first company active in this sector, with their “Quenchant A,” and subsequently Uniqema (ICI) and others moved into the market. Polymer quenchants are much better than mineral oils in environmental terms, because of the elimination of fire hazards and the need for less protection equipment. They also improve working conditions, due to the elimination of smoke and fumes. Additionally, because they are diluted with water to an average of 15% (range 10 to 20%), there are lower initial costs and reduced “drag-out.” The main products competing in this market are PAGs, polyvinyl alcohols (PVA), polyvinyl pyrrolidone (PVP), and polyacrylates. The two leaders at present are PAGs and polyacrylates, there having been a number of problems with PVA and PVP.

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48.5.6 Other Industrial Lubricants 48.5.6.1 Textile lubricants Synthetic fibers are polymers of very high molecular weight. The nature of polymers is such that they have very little inherent lubricity. In every stage of their manufacture, from polymerization to production of finished consumer articles, it is necessary to provide lubrication to aid the control of friction. This lubrication is provided as a “spin finish” for primary fiber production. Depending on the end use, this finish may be removed and secondary textile mill finishes provided for subsequent processing and even for point-of-sale handling. The demands of the textile industry for processing aids to control the fiber friction at different stages of processing are infinite. This has led to a supporting industry providing the necessary expertise, often integrating chemical manufacture, textile evaluation, and blending facilities. For simplicity the requirements can be classified into two main groups: 1. Spin finishes • Provide the correct balance of fiber-to-fiber and fiber-

to-guide friction. • Provide static control during polymer spinning and

subsequent processing. • Seek to provide a product that has optimal thermal

stability and volatility characteristics. • Give rapid fiber surface wet out; Have good anticor-

rosive properties. • Have good stability at high and low temperatures;

Have minimal effect on the fastness of dyes and pigments. • Are easy to remove in washing off baths. 2. Textile mill finishes • Provide correct frictional and static control as with

spin finishes. • Provide effective control for a full range of natural

and synthetic fibers and blends. • Provide efficient performance in a range of textile

operations. • Are compatible with other processing aids both within

the system and with spin finishes. • Can be easily removed and have no adverse effect on

the dyeing or dye fastness ratings. • Do not leave deposits that are difficult to remove, or

interfere with machine performance. • Are stable over a wide range of temperatures and have

an extended shelf life. Originally white mineral oils were widely used for this application. PAGs have now taken over from white oils

almost completely, due to their controllability (via molecular weight) and water solubility. PAGs are used mainly in nylon and polyester finishes. Probably 90% of PAG consumption is in this area rather than in wool or natural fibers. There are no figures available on actual PAG consumption within the many finish formulations. 48.5.6.2 Wire rope, chain, and chainsaw lubricants Industrial chains are often working under severe conditions of heat, in textile works (stenter chains) in car factories or in pottery and glass kilns. Large chains are mainly used in conveyor systems, but the difficult applications are mainly those involving severe heat from ovens. Such hightemperature conveyor bearings have always been a difficult lubrication problem. Often molybdenum disulphide carrying products have been used. PAOs, PIBs, and trimellitates have proved successful for temperatures up to 200◦ C. Some manufacturers in the United States also market ester-based products for this application, for use up to 280◦ C. One major supplier estimates a total of 1000 t of sales of synthetics into “hot” applications in the United States, such as ovens, glassworks, stenters, and conveyors. Although the PAGs enjoy a broad industrial market, increased usage of synthetic alternatives is expected in future. PAOs and PAO/ester blends are the most likely competitors. It is believed that sales of synthetics into these sectors of the industrial market have increased significantly over the past few years, as a result of major sales efforts, especially by ExxonMobil, and total sales in Western Europe could now be around 10,000 t per annum. Similarly, for forestry chainsaw oils, long-chain esters are used together with diester-based two-stroke oils, for the chainsaw engine. PIB based products are available for “high tackiness” applications on overhead conveyors in car plants, where drip-off would be unacceptable. PIBbased products are also now in use in wire rope lubricant formulations, traditionally bitumen based. Since the late 1990s, vegetable oil-based biodegradable chainsaw oils are being used increasingly in Scandinavia, Germany, Austria, and Switzerland. The total Western European market for chainsaw oils was estimated to be around 40,000 t in 2002, of which about 15,000 t were vegetable oil-based and about 2,000 t were synthetic esters. 48.5.6.3 Food grade oils For many years white mineral oils have been used for direct food contact applications. A high volume example is dough-knife lubricants in bakeries; a large bakery can use 50 to 100 t/yr of white oil. There are numerous applications for medicinal white oils used in direct contact with foods. These include release agent and lubricant for bakery products, release agent for dehydrated fruits,

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vegetables, and egg white solids, release agent, binder and lubricant in the manufacture of yeast for bakery and brewing, release agent and as sealing and polishing agent in the manufacture of confectionery and release agent, binder and lubricant in or on capsules or tablets containing concentrates of flavorings, spices, condiments, or nutrients intended for addition to foods, excluding confectionery, and in or on capsules or tablets containing food for special dietary use. Other applications include protective float on fermentation fluids in the manufacture of wine or vinegar, to prevent or retard access of air, evaporation of water or alcohol and wild yeast contamination during fermentation, protective float on brine used in the curing of pickles, protective coating on raw fruits and vegetables, component of hot-melt coating applied when freezing meats, dust control agent for wheat, corn, soybean, barley, rye, oats, sorghum, and rice. Protective coatings applied to fruits and vegetables are also used to provide “glossing,” to give the products a more appealing look for consumers. Antidusting sprays used for grains are used mainly in storage silos, conveyors, and bulk grain transporters (trucks, rail tank cars, and ships) to minimize the risks of explosions associated with static buildup during movement of the grains. In addition to the use of medicinal white oils in or on foods, all lubricants used in machinery for preparation or handling foods must be food (medicinal) grade quality. This applies whether the lubricants are oils or greases. Food machinery lubricants include: • • • • • • • • • • • • •

Hydraulic oils Gear oils Air compressor oils Refrigerator compressor oils Vacuum pump oils Heat transfer oils Rotary cooker and sterilizer oils and greases Dryer and over oils and greases Chain oils and greases Conveyor oils and greases Plastic packaging machine oils and greases Bottle, crate, and keg washing machine oils and greases Bottle filling and capping machine oils and greases

Lubricants based on PAGs, PAO, and PIB can be formulated to pass FDA tests. Dow Chemical offers a range of fully formulated PAG-based extreme pressure lubricants for food machinery, where accidental contact can occur. All components can be identified in the FDA Regulations 21CFR 178.3570(a). In addition to providing nontoxicity, better lubricity, higher VI, oxidation and thermal stability, the lower pour points and viscosities have led to energy saving of up to 8%, compared to white oils or mineral oils, in food machinery gearboxes. As discussed earlier under aluminium rolling, lubricants for machinery rolling foil is

a growing outlet for PIB-formulated lubricants. PAO producers are also selling into the “food-grade” markets at present. Many food grade oils and greases now use either Group III (VHVI), PAO, diester, polyol ester, polyalkylene glycol, or silicone baseoils. Formulations are very similar to those of standard industrial oils, but using only FDA approved additives. A number of newer formulations do not use technical or medicinal mineral white oils, which require higher concentrations of oxidation inhibitors to achieve satisfactory stability.

48.5.7 Greases All lubricating greases, whether mineral oil or synthetic fluid based, consist of two fundamental components: a base fluid representing the principal ingredient in the formulation and a thickening agent that is used to immobilize the fluid. The concentration of thickener determines the consistency of the finished product. However, it is the nature of the oil that determines whether the grease will be classified as a synthetic. Although all greases contain oil and thickener, the possible oil, thickener, antioxidant, antiwear, extreme pressure, and anticorrosion additive combinations that can be used provide manufacturers with a great deal of flexibility in formulating products with many different physical and chemical attributes. The primary advantages of synthetic greases are improved thermo-oxidative stability, wide temperature serviceability, and less change in apparent viscosity as a function of temperature. Since oils used to formulate synthetic greases are virtually free of unsaturation and are synthesized to be resistant to oxidative attack, synthetic greases, as a class, greatly outperform their non-synthetic rivals under severe oxidizing conditions. With selected oils, synthetic grease can be formulated with unsurpassed ability to remain pliable at −54◦ C while not deteriorating or excessively evaporating at temperatures above 177◦ C. Adequate viscosity under operating conditions is the most important property any lubricant can possess. Without it, moving surfaces are destined for self-destruction regardless of how well the grease is fortified with special additives. Greases made from synthetic oils maintain their apparent viscosity as a function of temperature better than non-synthetics. Higher-performance greases, based on synthetics of all types, PAO, PAG, PIB, and polyol esters (all chain lengths), are now being promoted widely. Polyurea greases are ideally suited for rolling bearings operating in hightemperature and high-speed conditions, particularly if the grease is ester based. Kluber has developed both fullsynthetic and part-synthetic ester-based polyurea greases, specifically for bearings operating under arduous conditions. Lithium soaps can also be used for synthetic greases, as can PAOs, PAO/VHVI blends, and PAO/ester blends. Hatco has a polyol ester grease (HATCO 3000) for use

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on stenter frames, and other applications with operating temperatures of up to 280◦ C. Many grease manufacturers believe that the total market for greases will remain static, with increasing demand in some industries and regions being offset by the ever expanding use of sealed-for-life bearings and longer life products that substantially decrease relubrication intervals. These trends inevitably mean the use of greater amounts of synthetic fluids in grease manufacture, which has been confirmed in the latest worldwide surveys conducted by the U.S. National Lubricating Grease Institute (NLGI). Synthetic, highly water-resistant greases have also been introduced. Environmental issues are also having an increasing influence on grease users. Biodegradable greases are now being supplied for a number of environmentally sensitive applications, including agriculture, forestry, railroad, mining, and central lubrication systems for trucks and buses. These are applications in which the grease can leak into the environment, be washed off exposed surfaces, or may be spilled accidentally. The trends are most evident in Scandinavia, Germany, Austria, Switzerland, and the Netherlands, although biodegradable greases are also being used in France, the United Kingdom, Belgium, and Italy. In 1998, environmental criteria for lubricating greases were included in the Gothenburg “Ren Smörja” (“Clean Lubrication”) project. These criteria have been further refined and are now a part of the Swedish Standard “Lubricating Grease — Requirements and Test Methods — SS 15 54 70.” Following international consultation, the Standard was issued in 2002 and the official English version will be issued during 2004. The environmental requirements, as given in Section 4.2 in the Standard, are rigorous. They require that a lubricating grease should be biodegradable and have minimal aquatic toxicity. Also, an assessment is required of chemical compounds that have sensitizing properties. A grease conforming to SS 15 54 70 is classified in one of three classes; A, B, or C. These are differentiated by the levels of substances allowed in the product. Class A greases must have a minimum content of components from renewable resources of 65% by weight. The content of renewable resources in Class B greases should be more than 45%. For Class C greases, there is no requirement to include components form renewable resources. Greases are examined by SP (Swedish National Testing and Research Institute), on behalf of the producer or supplier. Each assessment requires access to the formulation, including the chemical composition of the base fluid(s) and the additives. All information about the product and the test results is supplied to SP under a written personal confidentiality agreement. The required performance properties are set by the Standard and the test results are certified by the manufacturer.

As of March 2004, only Class B greases had been assessed. A number of European marketers of greases now supply biodegradable products, including Agro Oil, Binol, BP/Castrol, Cargo Oil, Fortum, Kuwait, Preem, Shell, and Statoil. Automotive greases were covered in Section 4.7.5.1 and aviation greases will be covered in the next section.

48.5.8 Aviation Lubricants 48.5.8.1 Civil aviation lubricants The bulk of civilian aviation lubricant demand is for gas turbines in jet aircraft, followed by aviation piston engine oils. Development costs for jet lubricants are extremely high, as are the costs of flight tests. In 1998, only Castrol, Esso, Mobil, Nyco, and Shell remained in the aviation gas turbine business, even BP having withdrawn in 1980, as others did in the 1970s. Now, following the merger of Exxon and Mobil at the end of 1999, the situation has changed as a consequence of conditions attached to the merger by the U.S. Securities and Exchange Commission (SEC) and the European Commission (EC) Competition Directorate. Exxon’s aviation lubricants business was sold to BP, which is now back in the business as BP/Castrol. Mobil’s activities became the basis for ExxonMobil’s new aviation lubricants business, so there are now only four main suppliers: BP/Castrol, ExxonMobil, Nyco, and Hatco (Royal). The first generation of gas turbine lubricants, known as Type I oils, were of 3 cSt viscosity, mainly based on diesters, principally azealates and sebacates. One other earlier type of lubricant (the Type I, 7.5 cSt oil) was thickened with a PAG. This product was used primarily in turboprops, to combat the heavier loadings. The civil turboprop aircraft that used Type I oils are now mainly phased out, except for a few Viscounts, plus of course HS748s and Fokker F27s, used on regional routes. In Western Europe most aircrafts now use Type II or Type III oils, which are all based on polyol esters and are of 5 cSt viscosity. The accompanying slide shows the various lubricant specifications. Diester-based Type I oils are still in use, at a level of about 1500 t per annum in Europe, for both civil aircraft as mentioned and for aircraft retained by the military (such as the VC10 or Buccaneer). Additionally a good proportion of diesters are used in jet engines for generating, gas pumping, or industrial use, such as the Rolls-Royce Avon. Almost no diesters are in use now in the United States. ExxonMobil have their major blending plant at Bayway (New Jersey) and Shell, Nyco, and BP/Castrol blend in Europe. The leading base ester suppliers in the United States are Hatco and ExxonMobil, followed by Emery (now Henkel), while in Europe, Uniqema, Ciba, and Nyco are the main producers of esters approved for aviation usage. Nyco is a major

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supplier to the French Air Force, and also a significant exporter of synthetics to the USSR. In the piston engine aviation market, which is of course dominated by engine lubricants for small light aircraft, high-quality single-grade mineral oils have been the preferred choice for many years. However, Shell introduced a PAO/mineral oil multigrade (Aeroshell Oil W 15w50), and it is understood that this is enjoying increasing popularity. In the field of aircraft hydraulics, civilian aircraft are using specially developed types of fire-resistant phosphate esters in their hydraulic systems. Monsanto and Chevron of the United States are the two suppliers to this market sector on a global basis. The requirement is for phosphate esters capable of operating at very low temperatures. Monsanto makes alkyl-aryl esters “in-house” at Bridgeport, New Jersey, and possibly in St Louis. Chevron offers mixed triaryl/trialkyl esters. Total demand for phosphate esters is believed to be about 3000 to 4000 t. Military aircraft tend not to use fire-resistant hydraulic fluids, but more recently have been switching from naphthenic mineral oils to PAO/ester blends, following losses in action in Vietnam, through fires from hydraulic leakages. The overall demand for “aviation” hydraulic fluids worldwide is estimated at about 15,000 t, including the former CPE countries. About half this demand is mineral oil, and it should also not be overlooked that “aviation quality” or “superclean” and military specification fluids are demanded for ground equipment, and even in earthmoving equipment, by nonmilitary organizations. Aviation greases are of course made to the same stringent standards as other products for the aircraft industry, and have to withstand the same extremes of temperature. A number of companies are offering greases using PAOs or esters as bases, and these are proving to be increasingly successful in this demanding market. Despite its intrinsic appeal, the aviation business does not utilize large volumes of lubricants. The lubricants in gas turbines are rarely changed, but are simply topped up at the end of long flights, so that there is a continual renewal of the charge. Additionally, one company in the United Kingdom has Rolls-Royce approval to recondition gas turbine lubricants. A small but steady business exists in recycling and reconstituting used gas turbine lubricants and returning them to their owners, all over the world. It is estimated that the total consumption for both military and civilian aviation is in the order of 70,000 t per annum, split as follows: 45% for gas turbine oils, 25% for piston engines, 25% for hydraulic fluids, and the balance of 5% for greases, compounds, and miscellaneous uses. 48.5.8.2 Military aviation lubricants Practically all military lubricant applications are covered by specifications, issued by the United States (Mil-L-etc.),

the United Kingdom (DEng), France (AIR), or Russia, with NATO codes also available as a cross-reference. Obviously many synthetic products, such as gas turbine lubricants, are common to both civilian and military uses. However there are differences in specifications and usage, in that, for example, the U.S. Air Force prefers to use a 3 cSt polyol ester, while most civilian aircraft and the U.S. Navy prefer 5 cSt. There are now signs of change here, and a new 4 cSt polyol ester specification is being introduced soon. So far, BP/Castrol (with Castrol 4000) is the only approved supplier. The U.S. Army has a tank, the M1 Abrams, which is the only one in the world with a gas turbine engine. This has a requirement for a polyol ester lubricant meeting the Mil-L-23699D specification. A further long-standing but small U.S. Army requirement has been for an Arctic engine oil (spec. Mil-L-46167). A product meeting this specification was in great demand by oil companies in the Alaskan oil fields, during their development, but since then sales have dropped sharply. The predominant formulation used was a dialkyl benzenebased lubricant, supplied by ConocoPhillips; however, the specification can also be met with a 70% PAO/30% ester formulation. PAO-based formulations have also been in use for several years in military hydraulic fluids for aircraft (MilH-83282) and ground equipment (Mil-H-46170). Sales of these fluids were around 12,000 t in 1996, worldwide. The 83282 specification replaces the naphthenic mineral oil specification. (Mil-H-5606) and is known to be used in F14, F16, and F/A18 fighters of the U.S. Air Force, Navy, and Marines. The formulation is a mixed 65% PAO/35% diester, but it is believed that a polyol ester may be introduced soon. The 46170 specification formulation includes rust inhibitors, for tanks and other ground equipment hydraulics, used when in storage. Additionally, PAO and esters have been introduced for instrument applications, where the recognized specification is Mil-L-6085A. Avionics uses include dielectric heat transfer fluids, used in closed systems for radars and ECM systems. A U.S. Air Force specification Mil-C-87252 calls for a 2 cSt PAO for these applications. A wide range of military greases for aviation has been specified, including those with NATO codes such as G382 based on mineral oils (−40 to 120◦ C operating range), or silicones and perfluorosilicones (G372 and G398). As far as synthetics are concerned, G354 is a diester-based grease (−75 to 120◦ C operating range), G395 is a non-soap PAO-based grease (−55 to 175◦ C operating range), and G363 is a complex ester-based grease that is hydrocarbonresistant. Finally, mention should be made of the CIS, which surprisingly has used large volumes of naphthenic mineral oils for aircraft gas turbine lubrication for many years. However, the CIS also has a polyol ester specification, B-3V for

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a 5 Kinematic Viscosity (100◦ C) lubricant, and VNII NP50-1-4-U for a 3.2 KV diester-based lubricant, as well as IPM-10 for a 3 KV diester/synthetic hydrocarbon blended product.

48.6 FUTURE TRENDS The market for automotive engine oils has been through a period of unprecedented change in terms of industry specifications, product development, and customer expectations at a time of low overall growth in demand for products. This has caused problems of profitability for additive manufacturers and baseoil producers, in addition to opportunities for companies with marketing and service support skills. The primary observation is that suppliers with higherperformance products, better marketing, and attention to service support are more likely to take market share from suppliers that lack one or more of these customer-driven attributes. Overall growth in markets for industrial lubricants is likely to continue to be relatively slow for the foreseeable future. World GDP and inflation rates are becoming lower, so increases in demand for industrial lubricants in Asia, South America, and Central Europe are likely to be substantially offset by decreases in demand in Western Europe and North America. Quality and performance are likely to be the key to higher prices and product differentiation in industrial lubricants. Unfortunately, higher quality and performance are likely to lead to further increases in product lifetimes, extended drain intervals, lower maintenance, and downtime and reductions in lubricant volumes. The dominant environmental issues for automotive and industrial lubricants over the next five years are likely to be: • • • • •

Fuel efficiency Emissions limits and emissions durability Biodegradability and bioaccumulation Toxicity Waste, disposal, and recyclability

There is likely to be a greater use of PAOs and PAO/mineral oil blends in land-based gas turbines. Larger, heavy-duty power generating gas turbines will be favored in many parts of the world in which natural gas is readily available. This includes large parts of Western and Central Europe, Asia, and South America, particularly Chile and Argentina. The trend toward higher gas temperatures for greater thermal efficiency is likely to continue. In industrial gearboxes, there is likely to be an increasing use of synthetic lubricants, but PAOs are unlikely to grow as fast as PAGs. The main reason for this, despite the favorable reductions in operating temperatures and power consumptions for both types of fluids, is the sludge problems experience by PAO-based fluids in gear systems exposed to moist operating conditions.

With rotary screw air compressors, the use of PAOs is likely to increase, although the competition from VHVI oils is likely to increase. Unfortunately, this is not a large market in total. There is unlikely to be any significant change in the use of PAOs in refrigerating compressors. Last, but by no means least, it is likely that lubricant suppliers will pay more attention in future to customer needs and improved marketing methods. Benefit selling is likely to be a key factor in determining success, whereby genuine partnerships between lubricant suppliers and lubricant users will allow both to share in the financial rewards obtained from using higher-quality and performance industrial lubricants. The synthetic lubricants business is no longer a pioneering industry. However, it remains competitive, tough, and “slow-going.” Some of the promised benefits have not been demonstrated and education of the market has taken much longer than many people anticipated. Expertise, experience, and confidence have grown among users and suppliers throughout the 1980s. Identifying user benefits and technology-oriented marketing remain the key to commercial success. More specifications are being introduced that favor the use of synthetic oils. The situation with U.S. automotive specifications is worth watching. Relationships between price and performance for conventional baseoils, Group III baseoils, and synthetic oils are better understood. Suppliers of all types of lubricants have learnt to adopt user-sensitive pricing strategies. Health, safety, and environmental issues have opened up new opportunities for synthetic lubricants. Some examples are the growth in demand for esters and rapeseed/ester blends in biodegradable lubricants, the substitution of PAGs, or polymer esters for chlorinated paraffins, in the forging and stamping of aluminium, or the increasing use of long-chain polyol esters in plants such as paper converters, where there may be a fire risk. Ease of disposal will grow as an issue in the lubricants business, as it is in the plastics business today, which may help some synthetics. The synthetic lubricants business is entering an exciting new phase of potential development. A growing number of OEMs and customers have begun to accept that synthetics offer improved cost/performance compared to mineral oils. This trend is likely to continue. More specifications are being issued, like VW503, Mercedes-Benz p229.5, or “Road Ranger” from Eaton, which can only be met with synthetics or unconventional baseoils. This opens up wider opportunities. There will be an increased commitment to the use of Group III, synthetics and/or part-synthetics, as know-how is acquired.

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However, due to the likely continuing overcapacity in conventional lubricants markets, the market for synthetics is likely to remain competitive. There will be growing inter-product competition, especially in automotive, twostroke, compressor, bearing, circulation, and hydraulic applications. The result is likely to be a constant stream of reformulated, improved, and new products based on cost-benefit analyses of customers’ needs. The dynamism of the synthetics business is reflected in the many sectors that have been opened up in the last decade or so. Examples are two-stroke engine, auto airconditioners, aircraft piston engines, military hydraulics and instruments, extensions in the usage of fire-resistant fluids, offshore compensators, solar fluids, electrostatic precipitator, fiber optic gels, circuit board fluxes, and metalworking applications, especially rolling, drawing, stamping, and pressing operations. Pricing relationships between the synthetics and between mineral oils, unconventional baseoils, and synthetics are now more widely understood, together with product performance advantages or limitations. This is now leading to more careful and accurate formulation choices, especially in those areas where confusion reigned in the early 1980s, such as motor oils, where PAOs, esters, and their new competition from VHVI baseoils are now the preferred blending stocks for advanced formulations, involving 0w/5w-based motor oils with low volatility. However despite all these efforts, synthetic lubricants remain (except perhaps in European motor oils) a conglomeration of niche markets. As a result, the forecasts in the early 1980s are likely to prove to be optimistic, unless there is, in particular, a more rapid swing to 0w motor oils and even lower NOACK volatility limits for U.S. automobile and truck engine oils. Considering that most of the market in the United States is already on 5w/10w oils, this is of significant importance for synthetic lubricant volume, as it has been in Europe. The future for synthetics remains interesting, but not spectacular. Success will come from hard work and the dedication of efforts to meeting real customer needs and solving technical problems. Structurally, the suppliers of synthetic baseoils are particularly chemical companies, whilst the bulk of lubricants are sold by oil companies. To succeed, chemical company know-how about end users and performance, needs to match that of the oil companies. The lubricants business has in general been dominated by engineers, not chemists, and the blending of these two disciplines, or their partnership, is the key to the future of synthetics.

Part V Methods and Resources

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49

Lubricant Performance Test Methods and Some Product Specifications Leslie R. Rudnick

This chapter contains a selection of many of the most commonly used test methods and specifications selected from the United States, Europe, and Japanese Lubricant Testing Methods. These include methods, standards, and specifications from ASTM, FTM, MIL, CEC, DIN, JPI, as well as Federal Supply Class 9150 commodities. Some cross-references are also given.

The American Society for Testing and Materials publishes an Annual Book of ASTM Standards: Petroleum Products, Lubricants, and Fossil Fuels, Volumes 5.01–5.04, where a complete list of ASTM methods pertaining to lubricants may be found.

Summary of Standard Test Methods and Specifications ASTM D 86 D 88 D 92 D 93 D 95 D 97 D 130 D 150-98 (2004) D 156 D 189 D 217 D 257-99 D 287 D 445 D 482 D 524 D 525-05 D 566 D 567 D 611 D 664 D 665 D 877-02e1 D 874 D 892

Standard Test Method for Distillation of Petroleum Products Standard Test Method for Viscosity Saybolt Seconds Universal Standard Test Method for Flash and Fire Points by Cleveland Open Cup Standard Test Method for Flash Point by Pensky-Martens Closed Tester Standard Test Method for Water in Petroleum Products and Bituminous Materials by Distillation Standard Test Method for Pour Point of Petroleum Products Standard Test Method for Detection of Copper Corrosion from Petroleum Products by the Copper Strip Tarnish Test Standard Test Methods for AC Loss Characteristics and Permittivity (Dielectric Constant) of Solid Electrical Insulation Standard Test Method for Saybolt Color of Petroleum Products (Saybolt Chromometer Method) Standard Test Method for Conradson Carbon Residue of Petroleum Products Standard Test Method for Cone Penetration of Lubricating Grease Standard Test Methods for DC Resistance or Conductance of Insulating Materials Standard Test Method for API Gravity of Crude Petroleum and Petroleum Products (Hygrometer Method) Standard Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and the Calculation of Dynamic Viscosity) Standard Test Method for Ash from Petroleum Products Standard Test Method for Ramsbottom Carbon Residue of Petroleum Products Standard Test Method for Oxidation Stability of Gasoline (Induction Period Method) Standard Test Method for Dropping Point of Lubricating Grease Standard Test Method for Calculating Viscosity Index Standard Test Method for (1993)el Aniline Point and Mixed Aniline Point of Petroleum Products and Hydrocarbon Solvents Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration Standard Test Method for Rust-Preventing Characteristics of Inhibited Mineral Oil in the Presence of Water Standard Test Method for Dielectric Breakdown Voltage of Insulating Liquids Using Disk Electrodes Standard Test Method for Sulfated Ash from Lubricating Oils and Additives Standard Test Method for Foaming Characteristics of Lubricating Oils

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ASTM (Continued) D 893 D 942 D 943 D 972 D 974 D 1091 D 1092 D 1093 D 1159 D 1160 D 1209 D 1238 D 1264 D 1296 D 1298 D 1331 D 1358 D 1401 D 1403 D 1478 D 1500 D 1646 D 1662 D 1742 D 1743 D 1744 D 1748 D 1831 D 2007 D 2070 D 2155 D 2161 D 2265 D 2266 D 2270 D 2272 D 2273 D 2500 D 2509 D 2512-95 (2002)

Standard Test Method for Insolubles in Used Lubricating Oils Standard Test Method for Oxidation Stability of Lubricating Grease by the Oxygen Bomb Method Standard Test Method for Oxidation Characteristics of Inhibited Mineral Oils Standard Test Method for Evaporation Loss of Lubricating Greases and Oils Standard Test Method for Acid and Base Number by Color-Indicator Titration Standard Test Methods for Phosphorus in Lubricating Oils and Additives Standard Test Method for Measuring Apparent Viscosity of Lubricating Greases Standard Test Method for Acidity of Hydrocarbon Liquids and Their Distillation Residues Standard Test Method for Bromine Numbers of Petroleum Distillates and Commercial Aliphatic Olefins by Electrometric Titration Standard Test Method for Distillation of Petroleum Products at Reduced Pressure Standard Test Method for Color of Clear Liquids (Platinum Cobalt Scale) (APHA Color) Standard Test Method for Flow Rates of Thermoplastics by Extrusion Plastimeter (Melt Index) (or ISO 1133–1991) Standard Test Method for Determining the Water Washout Characteristics of Lubricating Greases Standard Test Method for Odor of Volatile Solvents and Diluents Standard Test Method for (1990)el Density, Relative Density (Specific Gravity), or API Gravity of Crude Petroleum and Liquid Petroleum Products by Hydrometer Method Standard Test Method for Surface and Interfacial Tension of Solutions of Surface Active Agents Standard Test Method for (1995)el Spectrophotometric Diene Value of Dehydrated Castor Oil and Its Derivatives Standard Test Method for Water Separability of Petroleum Oils and Synthetic Fluids Standard Test Methods for Cone Penetration of Lubricating Grease Using One-Quarter and One-Half Scale Cone Equipment Standard Test Methods for Low-Temperature Torque of Ball Bearing Grease Standard Test Method for Color of Petroleum Products (ASTM Color Scale) Standard Test Method for Rubber Viscosity, Stress Relaxation, and Pre-Vulcanization Characteristics (Mooney Viscometer) Standard Test Method for Active Sulfur in Cutting Oils Standard Test Method for Oil Separation from Lubricating Grease During Storage Standard Test Method for Corrosion Preventive Properties of Lubricating Greases Standard Test Method for Determination of Water in Liquid Petroleum Products by Karl Fischer Reagent Standard Test Method for Rust Protection by Metal Preservatives in the Humidity Cabinet Standard Test Method for Roll Stability of Lubricating Grease Standard Test Method for Characteristic Groups in Rubber Extender and Processing Oils and Other Petroleum Derived Oils by the Clay-Gel Absorption Chromatographic Method Standard Test Method for Thermal Stability of Hydraulic Oils (discontinued 1981, replaced by E 659) Standard Practice for Conversion of Kinematic Viscosity to Saybolt Universal Viscosity or to Saybolt Furol Viscosity Standard Test Method for Dropping Point of Lubricating Grease over Wide Temperature Range Standard Test Method for Wear Preventive Characteristics of Lubricating Grease (Four Ball Method) Standard Test Method for Standard Practice for Calculating Viscosity Index from Kinematic Viscosity at 40 and 100◦ C Standard Test Method for Oxidation Stability of Steam Turbine Oils by Rotating Bomb Standard Test Method for Trace Sediment in Lubricating Oils Standard Test Method for Cloud Point of Petroleum Oils Standard Test Method for Measurement of Load Carrying Capacity of Lubricating Grease (Timken Method) Standard Test Method for Compatibility of Materials with Liquid Oxygen (Impact Sensitivity Threshold and Pass-Fail Techniques)

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ASTM (Continued) D 2549-02 D 2595 D 2596 D 2602 D 2603-01 D 2619-95 (2002)e1 D 2620 D 2622 D 2625 D 2670 D 2710 D 2711 D 2766 D 2782 D 2783 D 2786-91 (2001)e1 D 2879 D 2882 D 2887 D 2893 D 2896 D 2982 D 2983 D 3120 D 3228 D 3232 D 3233 D 3238 D 3244 D 3336 D 3427-03 D 3525 D 3527 D 3704 D 3705

Standard Test Method for Separation of Representative Aromatics and Nonaromatics Fractions of High-Boiling Oils by Elution Chromatography Standard Test Method for Evaporation Loss of Lubricating Greases over Wide Temperature Range Standard Test Method for Measurement of Extreme-Pressure Properties of Lubricating Grease (Four Ball Method) (replaced by D 5293), Standard Test Method for Apparent Viscosity of Engine Oils at Low Temperature Using the Cold-Cranking Simulator Test Method for Sonic Shear Stability of Polymer-Containing Oils Standard Test Method for Hydrolytic Stability of Hydraulic Fluids (Beverage Bottle Method) (discontinued 1993, replaced by D 5293) Standard Test Method for Sulfur in Petroleum Products by X-Ray Spectrometry Standard Test Method for Determining Endurance Life and Load Carrying Capacity of Dry Solid Film Lubricants (Falex Method) Standard Test Method for Measuring Wear Properties of Fluid Lubricants (Falex Method) Standard Test Method for Bromine Index of Petroleum Hydrocarbons by Electrometric Titration Standard Test Method for Demulsibility Characteristics of Lubricating Oils Standard Test Method for Specific Heat of Liquids and Solids Standard Test Method for Measurement of Extreme-Pressure Properties of Lubricating Fluids (Timken Method) Standard Test Method for Measurement of Extreme-Pressure Properties of Lubricating Fluids (Four-Ball Method) (Load Wear Index) Standard Test Method for Hydrocarbon Types Analysis of Gas-Oil Saturates Fractions by High Ionizing Voltage Mass Spectrometry Standard Test Method for Vapor Pressure–Temperature Relationship and Initial Decomposition Temperature of Liquids by Isoteniscope Standard Test Method for Indicating the Wear Characteristics of Petroleum and Non-Petroleum Hydraulic Fluids in a Constant Volume Vane Pump Standard Test Method for Boiling Range Distribution of Petroleum Fractions by Gas Chromatography Standard Test Method for Oxidation Characteristics of Extreme-Pressure Lubricating Oils Standard Test Method for Base Number of Petroleum Products by Potentiometric Perchloric Acid Titration Standard Test Method for Detecting Glycol-Base Antifreeze in Used Lubricating Oil Standard Test Method for Low-Temperature Viscosity of Automotive Fluid Lubricants Measured by Brookfield Viscometer Standard Test Method for Trace Quantities of Sulfur in Light Liquid Petroleum Hydrocarbons by Oxidative Microcoulometry Standard Test Method for Total Nitrogen, in Lubricating Oils and Fuel Oils by Modified Kjeldahl Method Standard Test Method for Measurement of Consistency of Lubricating Greases at High Temperatures Standard Test Method for Measurement of Extreme Pressure of Fluid Lubricants (Falex Method) Standard Test Method for Carbon Distribution and Structural Group Analysis of Petroleum Oils by the ndM Method Standard Test Method for Standard Practice for Utilization of Test Data to Determine Conformance with Specifications Standard Test Method for Life of Lubricating Greases in Ball Bearings at Elevated Temperatures Standard Test Method for Air Release Properties of Petroleum Oils Standard Test Method for Gasoline Diluent in Used Gasoline Engine Oils by Gas Chromatography Standard Test Method for Life Performance of Automotive Wheel Bearing Grease Standard Test Method for Wear Preventative Properties of Lubricating Grease Using the (Falex) Block on Ring Test Machine in Oscillating Motion Standard Test Method for Misting Properties of Lubricating Fluids

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ASTM (Continued) D 3711 D 3829 D 3850-94 (2000) D 3945 D 4047 D 4048 D 4049 D 4057 D 4172 D 4294 D 4310 D 4485 D 4624 D 4628 D 4629 D 4636 D 4683 D 4684 D 4693 D 4739 D 4741 D 4742 D 4781-03 D 4857 D 4927 D 4950 D 4951 D 5119 D 5133

D 5182 D 5183

Standard Test Method for Deposition Tendencies of Liquids in Thin Films Standard Test Method for Predicting the Borderline Pumping Temperature of Engine Oil Standard Test Method for Rapid Thermal Degradation of Solid Electrical Insulating Materials By Thermogravimetric Method (TGA) Standard Test Method for Shear Stability of Polymer-Containing Fluids Using Diesel Injector Nozzle (Deactivated 1998, replaced by D6278) Standard Test Method for Phosphorus in Lubricating Oils and Additives by Quinoline Phosphomolybdate Method Standard Test Method for Detection of Copper Corrosion from Lubricating Greases Standard Test Method for Determining the Resistance of Lubricating Grease of Water Spray Standard Test Method for Standard Practice for Manual Sampling of Petroleum and Petroleum Products Standard Test Method for Wear Preventive Characteristics of Lubricating Fluid (Four-Ball Method) Standard Test Method for Sulfur in Petroleum Products by Energy-Dispersive X-Ray Fluorescence Spectroscopy Standard Test Method for Determination of the Sludging and Corrosion Tendencies of the Inhibited Mineral Oils Standard Test Method for Standard Specification Performance of Automotive Engine Oils Standard Test Method for Measuring Apparent Viscosity by Capillary Viscometer at High-Temperature and High Shear Rates Standard Test Method for Analysis of Barium, Calcium, Magnesium, and Zinc in Unused Lubricating Oils by Atomic Absorption Spectrometry Standard Test Method for Trace Nitrogen in Liquid Petroleum Hydrocarbons by Syringe/Inlet Oxidative Combustion and Chemiluminescence Detection Standard Test Method for Corrosion and Oxidative Stability of Hydraulic Oils, Aircraft Turbine Engine Lubricants, and Other Highly Refined Oils Standard Test Method for Measuring Viscosity at High Shear Rate and High Temperature by Tapered Bearing Simulator Standard Test Method for Determination of Yield Stress and Apparent Viscosity of Engine Oils at Low Temperature (MRV TP-1 Cycle) Standard Test Method for Low Temperature Torque of Grease-Lubricated Wheel Bearings Standard Test Method for Base Number Determination by Potentiometric Titration Standard Test Method for Measuring Viscosity at High Temperature and High Shear Rate by Tapered-Plug Viscometer Standard Test Method for Oxidation Stability of Gasoline Automotive Engine Oils by Thin-Film Oxygen Uptake (TFOUT) Standard Test Method for Mechanically Tapped Packing Density of Fine Catalyst Particles and Catalyst Carrier Particles Standard Test Method for Determination of Coefficient of Friction of Lubricants Using the Four-Ball Wear Test Machine Standard Test Method for Elemental Analysis of Lubricant and Additive Components, Barium, Calcium, Phosphorus, Sulfur, and Zinc, by Wavelength-Dispersive X-Ray Fluorescence Spectroscopy Standard Classification and Specification for Automotive Service Greases Standard Test Method for Determination of Additive Elements in Lubricating Oils by Inductively Coupled Plasma Atomic Emission Spectrometry Standard Test Method for Evaluation of Automotive Engine Oils in CRC L-38 Spark Ignition Engine Standard Test Method for Low Temperature, Low Shear Rate, Viscosity/Temperature Dependence of Lubricating Oils Using a Temperature-Scanning Technique (Scanning Brookfield Test with Gelation Index Calculation) Standard Test Method for Evaluating the Scuffing Load Capacity of Oils (FZG Visual Method) Standard Test Method for Evaluating Coefficient of Friction of Lubricants Using the Four-Ball Wear Test Machine

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ASTM (Continued) D 5185

D 5293 D 5302 D 5306-92 (2002)e1 D 5480 D 5483 D 5533 D 5570 D 5621 D 5704 D 5706 D 5707 D 5800 D 5862 D 5864 D 5949 D 5968-04 D 5969 D 6006 D 6022 D 6046 D 607904e1 D 608097(2002) D 6081 D 6082 D 6121 D 6138 D 6158 D 6186 D 6278

Standard Test Method for Determination of Additive Elements, Wear Metals, and Contaminants in Used Lubricating Oils and Determination of Selected Elements in Base Oils by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) Standard Test Method for Apparent Viscosity of Engine Oils between −5 and −30◦ C Using the Cold-Cranking Simulator Standard Test Method for Evaluation of Automotive Engine Oils in the Sequence VE Spark Ignition Engine Standard Test Method for Linear Flame Propagation Rate of Lubricating Oils and Hydraulic Fluids Standard Test Method for Engine Oil Volatility by Gas Chromatography Standard Test Method for Oxidation Induction Time of Lubricating Greases by Pressure Differential Scanning Calorimetry Standard Test Method for Evaluation of Automotive Engine Oils in the Sequence IIIE Spark Ignition Engine Standard Test Method for Evaluating the Thermal Stability of Manual Transmission Lubricants in a Cycle Durability Test Standard Test Method for Sonic Shear Stability of Hydraulic Fluids Standard Test Method for Evaluation of Thermal and Oxidative Stability of Lubricating Oils Used for Manual Transmissions and Final Drive Axles Standard Test Method for Determining Extreme-Pressure Properties of Lubricating Greases Using a High-Frequency, Linear-Oscillation (SRV) Test Machine Standard Test Method for Measuring Friction and Wear Properties of Lubricating Grease Using a High Frequency, Linear-Oscillating (SRV) Test Machine Standard Test Method for Evaporation Loss of Lubricating Oils by the NOACK Method Standard Test Method for Evaluation of Engine Oils in Two-Stroke Cycle Turbo-Supercharged 6V92TA Diesel Engine Standard Test Method for Determining the Aerobic Aquatic Biodegradation of Lubricants or Their Components Standard Test Method for Pour Point of Petroleum Products Standard Test Method for Evaluation of Corrosiveness of Diesel Engine Oil at 121◦ C Standard Test Method for Corrosion Preventive Properties of Lubricating Greases in the Presence of Dilute Synthetic Sea Water Environments Standard Guide for Assessing Biodegradability of Hydraulic Fluids Standard Test Method for Calculation of Permanent Shear Stability Index Standard Classification of Hydraulic Fluids for Environmental Impact Standard Test Method for Evaluating Lubricity of Diesel Fuels by the High-Frequency Reciprocating Rig (HFRR) Standard Practice for Defining the Viscosity Characteristics of Hydraulic Fluids Standard Practice for Aquatic Toxicity Testing of Lubricants: Sample Preparation and Results Interpretation Standard Test Method for High Temperature Foaming Characteristics of Lubricating Oils Standard Test Method for Evaluation of Load Carrying Capacity of Lubricants Under Conditions of Low Speed and High Torque Used for Final Hypoid Drive Axles Standard Test Method for Determination of Corrosion Preventive Properties of Lubricating Greases Under Dynamic Wet Conditions (Emcor Test) Standard Specification for Mineral Oil Hydraulic Oils Standard Test Method for Oxidation Induction Time of Lubricating Oils by Pressure Differential Scanning Calorimetry (PDSC) Standard Test Method for Shear Stability of Polymer-Containing Fluids Using a European Diesel Injector Apparatus (see also D 3945)

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ASTM (Continued) D 6278

Standard Test Method for Shear Stability of Polymer Containing Fluids Using a European Diesel Injector Apparatus D 6417 Standard Test Method for Estimation of Oil Volatility by Capillary Gas Chromatography D 6425 Standard Test Method for Measuring Friction and Wear Properties of Extreme-Pressure (EP) Lubricating Oils Using SRV Test Machine D 6557 Standard Test Method for Evaluation of Rust Preventative Characteristics of Automotive Engine Oils D 6594-04a Standard Test Method for Evaluation of Corrosiveness of Diesel Engine Oil at 135◦ C D 6595 Standard Test Method for Determination of Wear Metals and Contaminants in Used Lubricating Oils or Used Hydraulic Fluids by Rotating Disk Electrode Atomic Emission Spectrometry E 537-02 Standard Test Method for The Thermal Stability Of Chemicals By Differential Scanning Calorimetry E 659 Standard Test Method for (1994)el Autoignition Temperature of Liquid Chemicals E 1064 Standard Test Method for Water in Organic Liquids by Coulometric Karl Fischer Titration G72Standard Test Method for Autogenous Ignition Temperature of Liquids and Solids in a High-Pressure 82(1996)e1 Oxygen-Enriched Environment G133/95 Standard Test Method for Linearly Reciprocating Ball-on-Flat Sliding Wear STP 315H Multicylinder Test Sequence for Evaluating Automotive Engine Oils STP 509A Single Cylinder Engine Test for Evaluating the Performance of Crankcase Lubricants CEC Test Methods L-01-A-79 L-02-A-78 L-07-A-85 L-11-T-72 L-12-A-76 L-14-A-93 L-18-A-80 L-19-T-77 L-20-A-79 L-21-T-77

L-24-A-78 L-25-A-78 L-28-T-79 L-29-T-81 L-30-T-81 L-31-T-81 L-33-A-93 L-33-A-94 L-34-T-82 L-35-T-84 L-36-96 L-36-A-90 L-36-A-97 L-37-T-85

Test for diesel engine crankcase oils using the Petter AVI single cylinder laboratory diesel engine Oil oxidation and bearing corrosion test using the Petter W1 single cylinder gasoline engine Load carrying capacity test for transmission lubricants using the FZG testrig The coefficient of friction of automatic transmission fluids using the DKA friction machine Evaluation of piston cleanliness in the MWM KD 12 E test tengine (Method B more severe) Evaluation of the shear stability of lubricating oils containing polymers using the Bosch diesel fuel injector pump rig Procedure for measurement of low temperature apparent viscosity by means of the Brookfield viscometer (liquid bath method) Evaluation of the lubricity of two-stroke engine oils (using the Motobecane engine AV7L 50 cm3 ) Evaluation of two-stroke engine lubricants with respect to engine deposit formation oils (using the Motobecane engine AV7L 50 cm3 ) The evaluation of two-stroke engine lubricants: Sequence I — Piston antiseizure Seqeunce II — General performance Sequence III — Preignition (using a Piaggio Vespa 180 SS engine) Engine cleanliness under severe conditions using the Petter AVB supercharge diesel engine Engine oil viscosity stability test (using a Peugeot 204 engine) The evaluation of outboard engine lubricant performance (using Johnson and Evinrude marine outboard engines) Ford Kent test procedure for evaluating the influence of the lubricating oil on piston ring sticking and deposit formation (using a Ford Kent engine) Cam and tappet pitting test procedure (using MIRA cam and tappet test machine) Predicting the borderline pumping temperature of engine oils using the Brookfield viscometer Biodegradability of Two-Stroke Cycle Outboard Engine Oils in Water Biodegradability of two-stroke cycle outboard engine oils in water Preignition tendencies of engine lubricants (using a Fiat 132C engine) Motor oil evaluation in a turbocharged passenger car diesel engine (using a VW ATL 1.6 litre). The Evaluation of Oil-Elastomer Compatibility (Laboratory Test) The measurement of lubricant dynamic viscosity under conditions of high shear (using a Ravensfield viscometer) HTHS Shear stability test for polymer-containing oils (using the FZG test rig)

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CEC Test Methods (Continued) L-38-A-94 L-39-T-87 L-40-A-93 L-41-T-88 L-42-A-92 L-46-T-93 L-51-T-95 L-51-T-98

L-53-T-95 L-54-T-96 L-55-T-95 L-56-T-95 L-56-T-98

Valve train scuffing (using a PSA TU3 engine) wear test Oil/elastomer compatibility test Lubricating oil evaporative losses (using NOACK evaporative tester). Evaluation of sludge-inhibition qualities of motor oils in a gasoline engine (using a Mercedes-Benz M102E engine) Evaluation of bore polish, piston cleanliness, liner wear, and sludge in a DI turbo-charged diesel engine (using Mercedes-Benz OM364A engine) VW Intercooled turbo-Diesel ring stiching and Piston cleanliness test OM 602A neon test The Evaluation of Engine Crankcase Lubricants with Respect to Low Temperature Lubricant Thickening & Wear under Severe Operating Conditions (MB-OM602A engine) ‘A’ Status granted basis cam-wear only M111 black sludge test Fuel Economy Effects of Engine Lubricants (MB M111 E20) TU3 MH high temperature deposits, ring stiching, and oil thickening test XUD11 ATE medium temperature dispensarity test Oil Dispersion Test at Medium Temperature for Automobile Diesel Engines (XUD11BTE engine)

GM 9099P

Engine Oil Filterability Test (EOFT) (to be modified for GF-3)

SAE J183 J300 J357 J1423

Engine Oil Performance and Engine Service Classification (Other Than "Energy-Conserving") Engine Oil Viscosity Classification Standard Physical and Chemical Properties of Engine Oils Classification of Energy-Conserving Engine Oil for Passenger Cars, Vans, and Light-Duty Trucks

Miscellaneous Test Methods CEM Electric Motor Test (grease) DIN 51350 Part 2 Weld Load DIN 51350 Part 3 Wear Scar DIN 51352-1 Testing of lubricants; determination of ageing characteristics of lubricating oils; increase in Conradson carbon residue after ageing by passing air through the lubricating oil DIN 51554-1 Testing of mineral oils; Test of susceptibility to ageing according to Baader; Purpose, sampling, ageing DIN 51587 Testing of Lubricants; Determination of the Ageing Behaviour of Steam Turbine Oils and Hydraulic Oils Containing Additives DIN 51802 (IP-220) Emcor Rust Test DIN 51851 (ASTM-D 5100 NOACK Volatility) Emcor Rust Test (grease) FE-8 Test (grease) FTM-350 Evaporation Loss FTM-791B Cone Bleed FTM-791C (Method 3470.1) Homogeneity and Miscibility FTM-3009 Contamination, Particulate (oils) FTM-3411 Thermal Stability and Corrosivity FTM-5309 Corrosion, Copper, 24 Hours FTM-5322 Corrosiveness (bimetallic couple) GE Electric Motor Test (grease) JPI-55-55-99 Hot Tube Test MIL-G-22050 Gasket and Packing Material, Rubber, for Use With Polar Fluids, Steam, and Air at Moderately High Temperatures

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Miscellaneous Test Methods (Continued) MIL-G-81322 Grease, Aircraft Wide Temperature Range MIL-H-22072C(AS) Hydraulic Fluid Catapult MIL-H-27601B Hydraulic Fluid, Petroleum Base, High Temperature, Flight Vehicle MIL-H-46170, Water Sensitivity MIL-H-46170B Hydraulic Fluid, Rust Inhibited, Fire Resistant, Synthetic Hydrocarbon Base MIL-H-53119 Corrosion Rate Evaluation Procedure (CREP) for CTFE Hydraulic Fluids MIL-H-83282 High-Temperature Stability (sealed ampule) MIL-H-83282 Linear Flame Propagation Rate MIL-H-83282C Hydraulic Fluid, Fire Resistant, Synthetic Hydrocarbon Base, Aircraft MIL-H-83306 Hydraulic Fluid, Fire Resistant, Phosphate Ester Base, Aircraft MIL-H-87257 High Temperature Stability (Purged with Nitrogen) MIL-P-25732 Cold resistant acrylonitrile-butadiene rubber MIL-PRF-2104 Lubricating Oil, Internal Combustion Engine, Combat/Tactical Service MIL-PRF-2105 Lubricating Oil, Gear Multi-purpose MIL-PRF-10924 Grease, Automotive and Atrillery MIL-PRF-46170 Hydraulic Fluid, Rust Inhibited, Fire Resistant, Synthetic Hydrocarbon Base MIL-PRF-63460 Lubricant, Cleaner and Preservative for Weapons and Weapons Systems (Metric) MIL-PRF-81322 Grease, Aircraft, General Purpose, Wide Temperature Range MIL-PRF-83282 Hydraulic Fluid, Fire Resistant, Synthetic Hydrocarbon Base, Metric, NATO CODE NUMBER H-537 MIL-PRF-87252 Coolant Fluid, Hydrolytically Stable, Dielectric MIL-R-83248 Rubber, Fluorocarbon Elastomer, High-Performance Fluid and Compression Set Resistant MIL-STD-1246 Cleanliness Levels SKF R2F Test (simulates paper mill applications) USS Low-Temperature Mobility Test (grease)

Federal Supply Class 9150 Product Commodities Document MIL-PRF-23699F MIL-PRF-23827C MIL-PRF-81322F MIL-PRF-81329D MIL-PRF-83282D MIL-PRF-85336B MIL-L-19701B MIL-G-21164D MIL-L-23398D MIL-G-23549C MIL-G-25013E MIL-G-25537C MIL-H-81019D MIL-S-81087C a MIL-G-81827A MIL-L-81846 MIL-G-81937A DOD-L-85645Aa DOD-G-85733 DOD-L-85734

Summarized title and description Synthetic Aircraft Turbine Engine Oil Aircraft and Instrument Grease Aircraft Wide Temperature Range Grease Solid Film Lubricant Synthetic Fire Resistant Hydraulic Fluid All Weather Lubricant for Weapons Semi-Fluid Lubricant for Weapons Molybdenum Disulfide Grease Solid Film Lubricant, Air-Cure General Purpose Grease Aircraft Bearing Grease Aircraft Helicopter Bearing Grease Hydraulic Fluid for Ultra Low Temperatures Silicone Fluid Anti-Wear Grease Aircraft High Loading and Anti-Wear Grease Instrument Ball Bearing Lubricating Oil Ultra Clean Instrument Grease Dry Thin Film Lubricant High Temperature Catapult Grease Synthetic Helicopter Transmission Lubricant

Copyright 2006 by Taylor & Francis Group, LLC

QPL Yes Yes Yes No (FAT) Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes No Yes Yes

Custodian Navy/AS

NATO code O-156/O-154 G-354 G-395 S-1737 H-537

G-353 S-748 G-372 G-366 H-536

Federal Supply Class 9150 Product Commodities (Continued) Document VV-D-1078B SAE J1899 SAE J1966 SAE AMS-G-4343 SAE AMS-G-6032 MIL-H-22072C A-A-59290 MIL-PRF-9000H MIL-PRF-17331H MIL-PRF-17672D MIL-PRF-24139A DOD-PRF-24574 MIL-L-15719A MIL-T-17128C MIL-G-18458B MIL-H-19457D MIL-L-24131B MIL-L-24478C DOD-G-24508A DOD-G-24650 DOD-G-24651 VV-L-825C A-A-50433 A-A-50634 A-A-59004A MIL-PRF-6081D MIL-PRF-6085D MIL-PRF-6086E MIL-PRF-7808L MIL-PRF-7870C MIL-PRF-8188D MIL-PRF-27601C MIL-PRF-27617F MIL-PRF-32014 MIL-PRF-83261B MIL-PRF-83363C MIL-PRF-87100A MIL-PRF-87252C MIL-PRF-87257A MIL-H-5606Ga DOD-L-25681D MIL-L-87177A MIL-PRF-2104G MIL-PRF-2105E MIL-PRF-3150D MIL-PRF-6083F MIL-PRF-10924G MIL-PRF-12070E MIL-PRF-21260E

Summarized title and description Silicone Fluid Damping Fluid Aircraft Piston Engine Oil, Ashless Dispersant Aircraft Piston Engine Oil, Non Dispersant Pneumatic Systems Grease Plug Valve Grease Hydraulic Fluid for Catapults Arresting Gear Hydraulic Fluid Diesel Engine Oil Steam Turbine Lubricating Oil Hydraulic Fluid Multipurpose Grease Lubricating Fluid for Oxidizing Mixtures High Temperature Electrical Bearing Grease Transducer Fluid Exposed Gear and Rope Grease Fire Resistant Hydraulic Fluid Graphite and Alcohol Lubricant Molybdenum Disulfide and Alcohol Lubricant Multipurpose Grease Food Processing Equipment Grease Food Processing Equipment Lubricating Oil Lubricating Oil for Refrigerant Compressors Sea Water Resistant Grease Lubricating Oil for Compressors Using HFC-134A Anti-Galling Compound Jet Engine Lubricating Oil Aircraft Instrument Lubricating Oil Aircraft Gear Petroleum Lubricating Oil Aircraft Turbine Synthetic Engine Oil Low Temperature Lubricating Oil Corrosion Preventive Engine Oil [FSC 6850] Hydraulic Fluid Aircraft and Instrument Grease Aircraft and Missile High Speed Grease Aircraft Extreme Pressure Grease Helicopter Transmission Grease Aircraft Turbine Synthetic Engine Oil Dielectric Coolant Fluid [FSC 9160] Synthetic Fire Resistant Hydraulic Fluid Petroleum Hydraulic Fluid for Aircraft/Ordnance Silicone Fluid with Molybdenum Disulfide Synthetic Corrosion Preventive Lubricant Combat/Tactical Diesel Engine Oil Multipurpose Gear Oil Preservative Oil Operational and Preservative Hydraulic Fluid Automotive/Artillery Grease Fog Oil Preservative and Break-in Engine Oil

Copyright 2006 by Taylor & Francis Group, LLC

QPL No Yes Yes No Yes Yes No Yes Yes Yes Yes Yes Yes No Yes No (FAT) Yes No Yes No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes No No No Yes Yes Yes Yes No No (FAT) Yes Yes Yes Yes Yes No Yes

Custodian

Navy/AS2 Navy/AS2 Navy/SH

NATO code S-1714 to 1732 O-123/O-128 O-113/O-117 G-392 G-363 H-579 O-278 O-250 H-573

H-580

O-282/O-290

Air Force/11

O-132/O-133 O-147 O-153/O-155 O-148/O-163 O-142 C-638 G-397-399/-1350

G-396 S-1748 H-538 H-515 Air Force/68 Air Force/70 Army/AT

S-1735 O-236/-237/-1236 O-186/-226/-228 O-192 C-635 G-403 F-62 C-640/C-642

Federal Supply Class 9150 Product Commodities (Continued) Document MIL-PRF-32033 MIL-PRF-46002C MIL-PRF-46010F MIL-PRF-46147C MIL-PRF-46167C MIL-PRF-46170C MIL-PRF-46176B MIL-PRF-53074A MIL-PRF-53131A VV-G-632B VV-G-671F A-A-52039B A-A-52036A A-A-59354 SAE J1703 MIL-PRF-63460D MIL-L-11734C MIL-L-14107C MIL-L-45983 MIL-L-46000C MIL-G-46003A MIL-L-46150 MIL-PRF-3572B MIL-DTL-17111C MIL-PRF-26087C MIL-L-3918Aa MIL-L-46014a MIL-L-83767Ba VV-C-846B A-A-50493A A-A-59113 A-A-59137 A-A-59173 A-A-59197 SAE AS1241C

Summarized title and description

QPL

Preservative and Water-Displacing Oil Vapor Corrosion Inhibitor (VCI) Preservative Oil Solid Film Lubricant Solid Film Lubricant Arctic Engine Oil Synthetic Fire Resistant Hydraulic Fluid Silicon Brake Fluid Steam Cylinder Lubricating Oil Precision Bearing Synthetic Lubricating Oil General Purpose Industrial Grease Graphite Grease Automotive Engine Oil API Service SH Commercial Heavy Duty Diesel Engine Oil Hydraulic Fluid for Machines Conventional Brake Fluid Cleaner-Lubricant-Preservative for Weapons Synthetic Lubricant for Mechanical Fuse Systems Low Temperature Weapons Lubricant Heat-Cured Solid Film Lubricant Semi-Fluid Weapons Lubricant Rifle Grease Semi-Fluid High Loading Weapons Lubricant Colloidal Graphite in Oil Power Transmission Fluid Reciprocating Compressor Lubricating Oil Instrument Lubricating Oil for Jewel Bearings Spindle Lubricating Oil Vacuum Pump Lubricating Oil Emulsifiable Oil Type Cutting Fluids Penetrating Oil Machine Tools/Slideways Lubricating Oil Breech Block Lubricating Oil (Naval Ordnance) Silicone Grease Fatty Oil for Metal Working Lubricants Fire Resistant Phosphate Ester Hydraulic Fluid

Yes No (FAT)

0-190

Yes Yes Yes Yes Yes No Yes No No No No No No Yes No

S-1738

Yes No Yes Yes Yes No No (FAT) No No No No No No No No No No No

Custodian

NATO code

O-183 H-544 H-547 O-258

G-412

Army/AR

H-542 S-758

O-157 O-158

DSCR/GS H-575

a

Those specifications in bold italics had been designated as “Inactive for New Design” and no longer used except for replacement purpose. Their QPLs will be maintained until the products are no longer required. b See Navy/AS2 under Abbreviations used below.

Specifications having Cross-Reference between, JIS, ASTM, and Others ASTM or others

JIS

F 312

B 9930

F 313 D 117 D 923 D 4559

B 9931 C 2101

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Title and contents Hydraulic Fluid — Determination of Particulate Contamination by the Particle Count Method Fluid Contamination — Determination of Contaminants by the Gravimetric Method Testing method of electrical insulating oils Sampling Evaporation

Specifications having Cross-Reference between, JIS, ASTM, and Others (Continued) ASTM or others

JIS

D 1218/21807 D 974 D 1275 D 1533 D 2112/2440 D 877/1816 D 924 D 1169 K 2249 D 1298/E100 D 4052/5002 ISO 3833 D 941 D 70 D 1250 D 140/4057/4177 D 1093

K 2251 K 2252 K 2254

D 86, E133 D 1160 D 2287 K 2255 D 3341 D 3237 D 661 D 323 D 381

K 2256 K 2258 K 2261 K 2265

D 56 D 3828/3278 D 93 D 92 K 2269 D 97 D 2500 K 2270 D 189 D 4530 K 2272 D 482 D 874 K 2275 D 95/4006 D 4377/1744 DIN 9114 K 2276 D 873 D 2386

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Title and contents Refractive index and specific dispersion Total acid number Corrosive sulfur Water content Oxidation stability Dielectric strength Dielectric loss tangent and relative dielectric constant Volume resistivity Crude petroleum and petroleum products — Determination of the density and petroleum measurement tables based on a reference temperature (15◦ C) I-shaped float method Oscillating method Wardon picnometer method I-shaped picnometer method Hubbard picnometer method Density, mass, and volume conversion table Crude Petroleum and Petroleum Products — Sampling Testing Method for Reaction of Petroleum Products Petroleum products — Determination of distillation characteristics Test method for distillation of petroleum products at atmospheric pressure Test method for distillation of petroleum products at reduced pressure Test method for boiling range distillation of petroleum products by gas chromatography Petroleum products — Gasoline — Determination of lead content Iodine monochloride method Atomic absorption spectroscopy method Testing Methods for Aniline Point and Mixed Aniline Point of Petroleum Products Testing Method for Vapor Pressure of Crude Oil and Petroleum Products (Reid Method) Petroleum products — Motor gasoline and aviation fuels — Determination of existent gum — Jet evaporation method Crude oil and petroleum products — Determination of flash point Tag closed test Small scale closed test Pensky–Martens closed cup test Cleveland open cup test Testing methods for pour point and cloud point of crude oil and petroleum products Pour point Cloud point Crude Petroleum and Petroleum products — Determination of carbon residue Conradson method Micro method Testing methods for ash and sulfated ash of crude oil and petroleum products Ash Sulfated ash Crude oil and petroleum products — Determination of water content Distillation method Karl-Fischer volumetric method Karl-Fischer coulometric method Hydride reaction method Petroleum products — Testing methods for aviation fuels Oxidation stability (potential residue) Freezing point

Specifications having Cross-Reference between, JIS, ASTM, and Others (Continued) ASTM or others

JIS

D 1094 D 235/4952 D 3227 D 1740 D 1840 FS 1151.2 D 3242 D 3948 D 2550 D 3241 D 2276/5452 IP 227 D 2624 D 3343 K 2279 D 4529/4868 D 4868 K 2280 D 2699 D 2700 D 909 D 613 D 4737 D 1368 D 2268 K 2283 D 445/446 D 2270 D 341 D 525 IP 309 D 1145 D 1945/1946 ISO 6326-1 ISO 6326-1 ISO 6327 D 900/1826 D 3588 D 1070 D 3588 D 4057

K 2287 K 2288 K 2301

K 2420 K 2501

D 974 D 664 D 4739 D 2896 K 2503 D 91/2273

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Title and contents Water tolerance Doctor test Determination of mercaptan sulfur (potentiometric method) Luminometer number test Determination of naphthalene (ultraviolet spectroscopy) Explosive vapor test Total acid number Water separation index (micro separometer) Water separation index (water separometer) Thermal stability (JFTOT) Particulate contaminant Copper corrosion Electric conductivity Hydrogen content Crude petroleum and petroleum products — Determination and estimation of heat of combustion Net heat of combustion Gloss heat of combustion Petroleum products — Fuels — Determination of octane number, cetane number, and calculation of cetane index Research octane number Motor octane number Supercharge octane number Cetane number Calculation method for cetane index using four variable equation Small amount of lead in n-heptane and isooctane (dithizone method) Purity of n-heptane and isooctane (capillary gas chromatography) Crude petroleum and petroleum products — Determination of kinematic viscosity and calculation of viscosity index from kinematic viscosity Kinematic viscosity Viscosity index Estimated relation between kinematic viscosity and temperature Testing Methods for Oxidation Stability of Gasoline (Induction Period Method) Gas oil — Determination of cold filter plugging point Fuel gas and natural gas — Methods for chemical analysis and testing Sampling of gas sample Chemical analysis (gas chromatography) Analysis of total sulfur Analysis of hydrogen sulfide Analysis of water (dew point method) Heat of combustion (Junkers gas calorimeter) Heat of combustion (calculation method) Specific gravity (picnometer method) Specific gravity (calculation method) Method of Sampling for Aromatic Hydrocarbon and Tar Products Petroleum products and lubricants — Determination of neutralization number Color indicator titration (TAN, strong acid number, strong base number) Potentiometric titration (TAN, strong acid number) Potentiometric titration (TBN, strong base number) Potentiometer titration (TBN, perchloric acid method) Testing method of lubricating oil for aircraft Precipitation number

Specifications having Cross-Reference between, JIS, ASTM, and Others (Continued) ASTM or others D 94 FS 3006.3 FS 204.1 ISO 6617 FS 5308.7 D 665 D 130 ISOTa D 943 D 2272 D 3397 IP 280 D 892

JIS

K 2510 K 2513 K 2514

K 2518 K 2619

D 2619 D 2782 K 2520 D 1401 IP 19 K 2536 D 1319/2001/2427 D 2267/4420/5580 D 1322

K 2537 K 2540 K 2541

D 2785/ISO 4260 D 3120 D 1551 D 4294/ISO 8754 D 129 D 1266 D 2622 K 2580 D 156 D 1500 K 2601 D 3828 D 96/4007/1796 IP 77 D 3230 D 2892 D 1159/2710

K 2605 K 2609

D 3228 D 3431 D 4629/5762

Title and contents Saponification number Contamination Diluted pour point Oxidation stability Corrosiveness and oxidation stability Testing Method for Rust-Preventing Characteristics of Lubricating Oil Petroleum Products — Corrosiveness to Copper — Copper Strip Test Lubricating oils — Determination of oxidation stability Oxidation stability of lubricants for internal combustion engine Turbine oil oxidation stability test (TOST) Rotating pressure vessel oxidation test (RBOT) Total acid number (semimicro method) Turbine oil oxidation stability (oil soluble catalyst method) Petroleum products — Lubricating Oils — Determination of Foaming Characteristics Lubricating oils — Testing methods for load carrying capacity Soda four ball (4 ball test modified by Dr. Soda) Timken Petroleum products — Lubricating oils — Determination of demulsibility characteristics Demulsibility test Steam emulsion number Liquid petroleum products — Testing method of components Fluorescent indicator adsorption analysis (FIA) Determination of aromatics by gas chromatography Petroleum Product — Aviation Turbine Fuels and Kerosene — Determination of Smoke Point Testing method for thermal stability of lubricating oils Crude oil and petroleum products — Determination of sulfur content Oxy-hydrogen combustion method Microcoulometric titration Quartz tube test Energy dispersive x-ray fluoroscence spectroscopy General bomb method Lamp method Wavelength dispersive x-ray fluoroscence spectroscopy Petroleum products — Determination of color Saybolt ASTM Testing methods for crude petroleum Flash point Water and sediment Salt content (titration) Salt content (coulometric) Distillation at atmospheric pressure Petroleum distillates and commercial aliphatic olefins — Determination of bromine number — Electrometric method Crude petroleum and petroleum products — Determination of nitrogen content Macro-Kjerdahl method Microcoulometric titration Chemiluminescence method

Note: a ISOT stands for Indiana Stirring Oxidation Test.

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ABBREVIATIONS USED QPL FAT Navy/AS Navy/AS2 Navy/SH Navy/YD Air Force/11 Air Force/68 Air Force/70 Army/AT Army/AR DSCR/GS

Qualified Products Listing No QPL exists, but a First Article Test (FAT) is required or may be optional Naval Air Systems Command (NAVAIR), Patuxent River, MD Naval Air Systems Command (NAVAIR), Lakehurst, NJ Naval Sea Systems Command (NAVSEA), Arlington, VA Naval Facilities Engineering Command (NAVFAC), Alexandria, VA Air Force Aeronautical Systems Center (ASC), Wright-Patterson AFB, OH Air Force San Antonio Air Logistics Center (SAALC), Kelly AFB, TX Hill Air Force Base Logistics Center, UT Army Tank-Automotive and Armaments Command, Tank-Automotive Research Development and Engineering Center (TARDEC), Warren, MI Army Tank-Automotive and Armaments Command, Armaments Research Development and Engineering Center (ARDEC), Picatinny, NJ Defense Logistics Agency’s Defense Supply Center Richmond (DSCR), Richmond, VA

ACKNOWLEDGMENTS This chapter was compiled with the generous help of several colleagues in the lubricant community. The author thanks Piet Purmer (Shell Chemical Company), Dick Kuhlman (Ethyl Corporation), Don Campbell,

Copyright 2006 by Taylor & Francis Group, LLC

Ed Zaweski, and Hiroshi Yamaochi (Amoco Chemicals — retired), Alan Plomer (BP — Belgium), Darryl Spivey (BP — Analytical), Ed Snyder (AFRL/MLBT), and Bob Rhodes.

50

Lubricant Industry Related Terms and Acronyms Leslie R. Rudnick

The plethora of acronyms related to the field of lubrication continues to grow. These acronyms and abbreviations come from a variety of diverse industries and disciplines, including original equipment manufacturers, component suppliers, lubricant additive and fluid suppliers and producers, and professional societies directly and peripherally involved in the lubricants industry. Each class of lubricants, synthetic and conventional, has its set of abbreviations reserved to describe differences in structure or performance characteristics. Terms and acronyms for lubricant

3P2E 4P3E 4T 5P4E 6P5E AAM AAMA AAR AB ABIL ABMA

ABOT ACC ACIL ACEA ACERT ACS AEL AEOT AES AEV A/F AFNOR AFR AFV AGELFI

additives are numerous and generally reflect the chemical structure or type of additive. In some cases the acronym reflects the function of the additive. Acronyms created at different times by different industries have resulted in identical abbreviations that refer to different things. This chapter collects in one place many of the important terms generally used in the lubricants industry. A complete list would require far more space than can be devoted in this book.

three-ring polyphenyl ether four-ring polyphenyl ether A term applied to lubricants for four-cycle engines five-ring polyphenyl ether six-ring polyphenyl ether Alliance of Automobile Manufactures American Automobile Manufactures Association American Association of Railroads alkylbenzene agriculture-based industrial lubricants American Bearing Manufacturers Association — a nonprofit association of American manufacturers of antifriction bearings, spherical plain bearings, or major components thereof. The purpose of ABMA is to define national and international standards for bearing products and maintain bearing industry statistics aluminum beaker oxidation test American Chemistry Council American Council of Independent Laboratories, ACIL is the national trade association representing independent, commercial engineering, and scientific laboratory, testing, consulting, and R&D firms Association des Constructeurs Europeens d‚Automobiles Advanced Combustion Emission Reduction Technology (Caterpillar) American Chemical Society allowable exposure limits Engine Oil Aeration Test Average engine sludge Average engine varnish air to fuel ratio Association Francais de Normalisation Air/fuel ratio alternative fuel vehicle Co-operative Research Organization of AGIP, ELF, and FINA oil companies

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AGO AGMA AHEM AIAM AIChE AL ALTNER Anti-oxidant Anti-wear additive ANFAVEA ANIQ ANSI AO AOCA AOCS API ARB ASEAN ASLE ASME ASTM A/T ATF ATIEL AT-PZEV AW BFPA Bhp-hr BHRA BLF Block grease

Automotive gas oil, automotive gear oil American Gear Manufacturers Association Association of Hydraulic Equipment Manufacturers Association of International Automobile Manufacturers American Institute of Chemical Engineers atmospheric lifetimes Alternative Energy Programs of the European Commision A chemical component added to lubricants to reduce the tendency for oxidation-related degradation of the oil Additives that can deposit multilayer films thick enough to supplement marginal hydrodynamic films and prevent asperity contact, or preferentially wear rather than allow contact between asperities that result in wear Associação Nacional dos Fabricantes de Veículos Automotores Asociación Nacional de la Industria Química, AC American National Standards Institute anti-oxidant American Oil Change Association, provides a link between the motoring public and auto maintenance specialists American Oil Chemists Society, a global forum for the science and technology of fats, oils, surfactants, and related materials American Petroleum Institute Air Resources Board (California) Association of South East Asian Nations American Society of Lubrication Engineers American Society of Mechanical Engineers American Society of Testing and Materials Conventional shifting automatic transmission Automatic transmission fluid Association Technique de l‚Industrie Europeenne des Lubrifants Advanced Technology Partial Zero Emission Vehicle anti-wear

BOCLE BOI BOIG BOTD Boundary lubrication BSFC BTU

British Fluid Power Association brake horsepower hour British Hydromechanics Research Association British Lubricants Federation A very firm grease produced as a block that is applied to large open plain bearings that operate at low speed and high temperatures Ball on cylinder lubricity evaluator Base oil interchange Base Oil Interchange Guidelines Ball on three disks A regime of lubrication where there is partial contact between the metal components and partial separation of the surfaces by the lubricant fluid film brake specific fuel consumption British Thermal Units

CAA CAAA CAFÉ CARB CBO CCD CCR CCS CDP

Clean Air Act Clean air act amendment (1990) Corporate average fuel economy California Air Resources Board Conventional base oil Combustion chamber deposits Conradson carbon residue Cold cranking simulator cresyl diphenyl phosphate

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CEC CEN CFC CFR CFV CGSB CIDI CMA CMMO CMVO CNG CNHTC CO CO2 CONCAWE Corrosion inhibitor CPPI CRC CVMA CVS CVT b-CVT t-CVT DAP DASMIN DBC DBPP DCT DDC DEC DEER Demulsibility DEO DEOAP DETA DEXTRON DFA DH-1 DHYCA DI DI DI DII DIN DIOC DiPE DMC DME DOA

Co-ordinating European Council Europeen de Normalization Chlorofluorocarbon Coordinating Fuel and Equipment Research Committee clean fuel vehicle Canadian General Standards Board — a consensus organization of producers, users, and general interest groups that develops standards for test methods and products for Canada Compression ignition direct injection (diesel) Chemical Manufacturers Association Chemically modified mineral oil chemically modified vegetable oils Compressed natural gas China National Heavy Truck Corporation Carbon monoxide Carbon dioxide Conservation of Clean Air and Water-Europe A lubricant additive used to protect surfaces against chemical attack from contaminants in the lubricating fluid or grease. These additives generally operate by reacting chemically and forming a film on the metal surfaces Canadian Petroleum Product Institute Co-ordinating Research Council, Incorporated Canadian Vehicle Manufacturers Association Constant volume sampling Continuously variable transmission Belt-CVT Toroidal-CVT Detroit Advisory Panel (API) Deutsche Akkreditierungastelle Mineralol (German) Dibutyl carbonate dibutyl phenyl phosphate dual clutch transmission Detroit Diesel Corporation Diethyl carbonate diesel engine emissions reduction A measure of the ability of an oil to separate from water as measured by the test time required for a specified oil–water emulsion to break using ASTM D-1401 Diesel engine oil Detroit Engine Oil Advisory Panel (API/EMA) Diethylene triamine General Motors ATF specification Diesel fuel additive A JASO diesel engine oil category — a category mainly for Japanese-made heavy duty diesel engines providing wear, soot handling properties, and thermal-oxidative stability Direction des Hydrocarbares et Carburants (French Ministry of Industry) detergent inhibitor direct injection drivability index Diesel injection improver Deutsche Industrie Normung Diisooctyl carbonate dipentaerythritol Dimethyl carbonate Dimethyl ether Dioctyl adipate

Copyright 2006 by Taylor & Francis Group, LLC

DOC DOCP DOD DOE DOHC DOP DOS DOT DPF DPMA Dropping point DSC DTBP

Diesel oxidation catalysts dispersant olefin copolymer Department of Defense Department of Energy Double overhead cam Di 2-ethylhexylphthalate Di 2-ethylhexylsebacate Department of Transport Diesel particulate filters dispersant polymethacrylate The temperature at which a grease changes from a semisolid to a fluid under the test conditions. This temperature can be considered to be a measure of the upper use limit for the grease differential scanning calorimetry Di-tert-butyl phenol

EC ECCC EDC EEC EFI EGR EHDPP EHEDG ELGI ELTC ELV EMA EMPA Emulsion

EPACT EPACT EPDM EPM ESCS ESI ETC EU EUC EUDC EUROPIA EV EVA

European Community Electronically controlled computer clutch Electronic diesel contro European Economic Community Electronic fuel injection Exhaust gas recirculation 2-ethylhexyl diphenyl phosphate European Hygiene and Equipment Design Group European Lubricating grease Institute Engine Lubricant Technical Committee (CEC) end-of-life vehicle Engine Manufacturers Association Swiss Federal Laboratories for Materials Testing and Research A mechanical mixture of two mutually insoluble fluids. Some metalworking fluids are designed to remain as a stable emulsion by incorporation of an emulsifier European Natural Gas Vehicle Association Engine Oil Licensing and Certification System(API) Extreme pressure — an additive designed to prevent metal–metal adhesion or welding when the degree of surface contact is sufficiently high that the normal protective (oxide) films are removed and other surface active species in the oil are not reactive enough to deposit a protective film. EP additives function by reacting with the metal surface to form a metal compound, for example, iron sulfide Environmental Protection Act of 1992 Energy Policy and Conservation Act Ethylenepropylene diene-based elastomeric seal material Ethylene propylene-based elastomeric seal material Engine Service Classification System extended service interval European Transient Test Cycle European Union Elementary Urban Cycle Extra Urban Driving Cycle European Petroleum Industry Association electric vehicle Ethyl vinyl alcohol

FATG FBP FCAAA FCC FDA FE

Fuel Additive Task Group (CMA) final boiling point Federal Clean Air Act Amendments fluid catalytic cracker Food and Drug Administration Fuel economy

ENGVA EOLCS EP additive

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FEI FF FFV FIE FIMS FSIS FT FTC FTIR FZG

Fuel economy improvement (fuel efficiency increase) Factory fill flexible fueled vehicle Fuel injection equipment Field ionization mass spectrometry Food Safety Inspection Service Fischer-Trophsch Federal Trade Commision (US) Fourier-transform infrared Forschungstelle fur Zahnrader und Getriebau

GATC GC

Gross additive treat cost In the ASTM D-4950 Standard Classification and Specification for Automotive Service Greases, the letters GC designate service typical of the lubrication of wheel bearings operating in passenger cars, trucks, and other vehicles under mild to severe duty gasoline direct injection Gross delivered treating cost Group des Experts pour la Pollution et l’Energie (group of experts for pollution and energy) Gear service characteristics (API) glycerol monoleate generally recognized as safe Gas-to-liquids global warming potential

GDI GDTC GEPE GL-4/5 GMO GRAS GTL GWP HACCP HAP HC HCB HCCI HCFC HDD HDDEO HDEO HDMO HEUI HFC HFE HOOT HOPOE HRMS HSPOE HTHSRV HVI Hydrodynamic lubrication

Hazard and Critical Control Point implement procedures for USDA regulators requirements hazardous air pollutant Hydrocarbon Hydrocracker bottoms Homogeneous charge combustion ignition Hydrochlorofluorocarbon heavy-duty diesel Heavy duty diesel engine oil Heavy duty engine oil Heavy duty motor oil Hydraulically operated electronically controlled unit injectors Hydrofluorocarbon hydrofluoroethers Hot Oil Oxidation Test highly optimized POE High-resolution mass spectrocopy high-stability POE High-temperature high-shear rate viscosity high viscosity index oil A lubrication regime characterized by a full fluid film between two moving surfaces. As oil is moved between the moving parts the action causes a high pressure in the lubricant fluid and this separates the moving parts

IBP IC IDDPP IDI IEA IENICA IFP ILMA ILSAC IOP

initial boiling point internal combustion isodecyl diphenyl phosphate indirect injection International Energy Agency Interactive Network for Industrial Crops and Applications Institut Franciais du Petrole Independent Lubricant Manufacturers Association Internation Lubricant Standardization and Approval Committee Industries Institute of Physics — Tribology group

Copyright 2006 by Taylor & Francis Group, LLC

IP IPPP IR ISO IVD

Institute of Petroleum (UK) isopropylphenyl phenyl phosphate infrared International Organization for Standardization Intake valve deposit

JALOS JAMA JASO JAST JIS

Japanese Lubricating Oil Society Japan Automobile Manufacturers Association Japanese Automotive Standards Organization Japanese Society of Tribologist Japanese Industrial Standard

KTH KV

Royal Institute of Technology, Sweden Kinematic viscosity

LB

LCO LCST LDV LEV LeRC LMOA LNG LOFI LPG LSC LSD

In the ASTM D-4950 Standard Classification and Specification for Automotive Service Greases, the letters LB designate service typical of lubrication of chassis components and universal joints in passenger cars, trucks, and other vehicles under mild to severe duty light cycle oil lower critical solution temperature Light duty vehicles Low emission vehicles Lewis Research Center — NASA Locomotive Maintenance Officers Association Liquefied natural gas Lubricant Oil Flow Improver Liquid petroleum gas Lubricant Standards Committee Low sulfur diesel

MERCON MIL MITI MOD MOE MON MOT MSDS MT MTAC MTBE MTF MVMA MWF MWT

Ford ATF specification Military Specification Ministry of International Trade and Industry (Japan) Ministry of Defence (British) Ministry of Energy (UK) Motor octane number Ministry of Transport (UK) material safety data sheet manual transmissions Multiple Test Acceptance Criteria Methyl t-butyl ether Manual transmission fluid Motor Vehicle Manufacturer’s Association Metal working fluid(s) maximum workable die temperature

NAFTA NAAQS NATC NDTC NEDO NEFI NESHAP NFPA NI NLGI NMR

North American Free Trade Agreement National Ambient Air Quality Standards Net additive treat rate Net delivered treat rate New Energy and Technology Development Organization (Japan) New England Fuel Institute National Emission Standard for Hazardous Air Pollutants National Fluid Power Association nonpolarity index National Lubricating Grease Institute (US) Nuclear magnetic resonance (spectroscopy)

Copyright 2006 by Taylor & Francis Group, LLC

NOX NPG NPI NPRA NRCC NREL NRL

Nitrogen oxides Neopentylglycol non-polarity index National Petrochemical & Refiners Association National Research Council of Canada National Renewable Energy Laboratory Naval Research Laboratory

OCP ODI ODP ODS OEM OPEC OPEST ORD ORNL OSHA OTA Oxidation

olefin copolymer Oil drain interval ozone depleting potential ozone depleting substance original equipment manufacturer Organization of Petroleum Exporting Countries Oil Protection of Emission Systems Test Octane requirement decrease Oak Ridge National Laboratory Occupational Safety and Health Administration Office of Technology Assessment (DOE) One of several modes of oil degradation. The process generally involves the addition of oxygen to the lubricant structure, followed by cleavage or polymerization resulting in unfavorable oil properties and performance

PAG PAH PAHO PAJ PAO PAPTG PC PCD PCEO PCMO PCTFE PDSC PDVSA PE PEA PEC PFPAE PFPE PIB PIO PM2.5 PM10 PM PMA PMAA PNA PNGV POFA Poise

polyalkylene glycol polycyclic aromatic hydrocarbons Pan American Health Organization Petroleum Association of Japan polyalphaolefin Product Approval Protocol Task Group (CMA) Proposed classification Passenger car diesel passenger car engine oil passenger car motor oil polychlorotrifluoroethylene pressure differential scanning calorimetry Petroleos de Venezuela pentaerythritol Polyether amine Petroleum Energy Centre perfluoropolyalkylether Perfluoropolyether polyisobutylene polyinternalolefins particulate matter less than 2.5 microns diameter particulate matter less than 10 microns diameter Particulate matte polymethacrylate Petroleum Marketers Association of America polynuclear aromatic Partnership for a New Generation of Vehicles (US) polymerized fatty acids The CGS unit of absolute viscosity (dyne-sec/cm2 ) as measured by the shear stress required to move one layer of fluid along another over a total thickness of one centimeter at a shear rate of one centimeter per second. Absolute viscosity values are independent of density and are directly related to the resistance to flow A conventional measure of the lower temperature limit for low-temperature flow of a lubricating fluid

Pour point

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PPD PPE ppm PTFE PVC PVE

Pour point depressant polyphenyl ether Parts per million Polytetrafluoroethylene pressure viscosity coefficient polyvinyl ethers

QPL

Qualified Products List (US Military)

RBOT RCRA RME ROCOT RON ROSE RVP

rotary bomb oxidation test Resource Conservation Recovery Act Rapeseed methyl ester rotating compressor oxidation test Research octane number Rose Foundation — Recovery of Oil Saves the Environment Reid vapor pressure

SAE SAIC SAIT SARA SCR Scuffing SF SHC SHPD SIAM SIB SIP SMDS SME SMM&T SMR SMRP SNAP SNCF SOF SOT SSI STLE SULEV SUS SUV SwRI

Society of Automotive Engineers Shanghai Automotive Industry Group South African Institute of Tribologists Superfund Amendments and Reauthorization Act Selective catalyst reduction Wear caused by the localized welding and fracture of rubbing surfaces Service fill Synthetic hydrocarbon Super high-performance diesel Society of Indian Automotive Manufacturers sulfurized isobutylene Styrene-isoprene copolymer Shell Middle Distillate Synthesis Society of Manufacturing Engineers Society of Motor Manufacturers and Traders Ltd. (UK) Svenska Mechanisters Rikssorenings Society for Maintenance and Reliability Professionals Significant New Alternatives Policy Societe Nationale des Chemins de fer Francais soluble organiz fraction Spin orbit tribometer Shear stability index Society of Tribologists and Lubrication Engineers Super ultra low emission vehicle Saybolt Universal Second (same as SSU) Sport utility vehicle Southwest Research Institute

TAN TBEP TBN TBP TBPP TCP TEOST TFMO TFOUT tga ThOD THOT

total acid number tributoxyethyl phosphate total base number tributyl phosphate tert-butylphenyl phenyl phosphate tricresyl phosphate thermal-oxidation engine oil simulation test Thin Film Micro Oxidation Test thin film oxygen uptake test Thermogravimetric analysis Theoretical oxygen demand turbohydrodynamic oxidation test

Copyright 2006 by Taylor & Francis Group, LLC

TiBP TISI TLEV TLTC TMP TOCP TOP TOST TOTM TPP TXP

triisobutyl phosphate Thailand Industrial Standards Institute Transitional low emission vehicles Transmission Lubricants Technical Committee Trimethylolpropane triorthocresyl phosphate trioctyl phosphate turbine oxidation stability test trioctyl trimellitate triphenyl phosphate trixylenyl phosphate

UCBO UCST UEIL UFIP ULEV ULSD USB USCAR USDA UTTO

Unconventional base oil upper critical solution temperature European Union of Independent Lubricant Manufacturers Union Francaise des Industries Petrolieres Ultra low emission vehicles ultra low sulfur diesel United Soybean Board United States Council for Automotive Research United States Department of Agriculture universal tractor transmission oil

VDS, VDS2 VGO VGRA VHVI VI VII VM VOC VOF Volatility VTC VVT

Volvo Long Drain Lubricant Specification Vacuum gas oil viscosity-grade read across very high viscosity index viscosity index viscosity index improver Viscosity modifier volatile organic compound volatile organic fraction A measure of the amount of material evaporated from a sample under a particular set of conditions, usually expressed as a percentage of original sample viscosity-temperature coefficient variable valve train

WAFI WASA WCM WSPA

Wax antisettling flow improver Wax antisettling additive Wax crystal modifier Western States Petroleum Association

XDP

xylenyl diphenyl phosphate

ZDDP ZDP/ZDTP ZEV

zinc dialkyldithiophosphate zinc dithiophosphate Zero emission vehicle

Copyright 2006 by Taylor & Francis Group, LLC

51

Lubricant Industry Internet Resources Leslie R. Rudnick CONTENTS 51.1 Alphabetical Listing 51.2 Internet Listings by Category 51.2.1 Lubricant Fluids (Base Oils, Greases, Biodegradable, Synthetics, Packaged Oils, and Solid Lubricants) 51.2.2 Additives 51.2.3 Oil Companies 51.2.4 University Sites 51.2.5 Government Sites/Industry Sites 51.2.6 Testing Labs/Equipment/Packaging 51.2.7 Car/Truck MFG 51.2.8 Publications/References/Recruiting/Search Tools, etc.

51.1 ALPHABETICAL LISTING 2V Industries Inc., www.2vindustries.com 49 North, www.49northlubricants.com 76 Lubricants Company, www.tosco.com A.W. Chesterton Company, www.chesterton.com A/R Packaging Corporation, www.arpackaging.com Acculube, www.acculube.com Accumetric LLC, www.accumetric.com Accurate Lubricants & Metalworking Fluids Inc. (dba Acculube), www.acculube.com Acheson Colloids Company, www.achesonindustries.com Acme Refining, Division of Mar-Mor Inc., www.acmerefining.com Acme-Hardesty Company, www.acme-hardesty.com Adco Petrol Katkilari San Ve. Tic. AS, www.adco.com.tr Advanced Ceramics Corporation, www.advceramics.com Advanced Lubrication Technology Inc. (ALT), www.altboron.com Aerospace Lubricants Inc., www.aerospacelubricants.com AFD Technologies, www.afdt.com African Lubricants Industry, www.mbendi.co.za/aflu.htm AG Fluoropolymers USA Inc., www.fluoropolymers.com Airflow Systems Inc., www.airflowsystems.com Airosol Company, Inc., www.airosol.com Akzo Nobel, www.akzonobel.com Alco-Metalube Company, www.alco-metalube.com Alfa Laval Separation, www.alfalaval.com Alfa Romeo, www.alfaromeo.com

Copyright 2006 by Taylor & Francis Group, LLC

Alithicon Lubricants, Division of Southeast Oil & Grease Company, Inc., www.alithicon.com Allegheny Petroleum Products Company, www.oils.com Allen Filters Inc., www.allenfilters.com Allen Oil Company, www.allenoil.com Allied Oil & Supply Inc., www.allied-oil.com Allied Washoe, www.alliedwashoe.com Alpha Grease & Oil Inc., www.alphagrease. thomasregister.com/olc/alphagrease/ ALT Inc., www.altboron.com Amalie Oil Company, www.amalie.com Amber Division of Nidera, Inc., www.nidera-us.com Amcar Inc., www.amcarinc.com Amerada Hess Corporation, www.hess.com American Agip Company, Inc., www.americanagip.com American Bearing Manufacturers Association, www.abma-dc.org American Board of Industrial Hygiene, www.abih.org American Carbon Society, www.americancarbonsociety.org American Chemical Society (ACS), www.acs.org American Council of Independent Laboratories (ACIL), www.acil.org American Eagle Technologies Inc., www.frictionrelief.com American Gear Manufacturers Association (AGMA), www.agma.org American International Chemical, Inc., www.aicma.com/ American Lubricants Inc., www.americanlubricantsbflo.com

American Lubricating Company, www.alcooil.com American Machinist, www.penton.com/cgi-bin/ superdirectory/details.pl?id=317 American National Standards Institute (ANSI), www.ansi.org American Oil & Supply Company, www.aosco.com American Oil Chemists Society (AOCS), www.aocs.org American Petroleum Institute (API), www.api.org American Petroleum Products, www.americanpetroleum.com American Refining Group Inc., www.amref.com American Society of Agricultural Engineering (ASAE), www.asae.org American Society of Agronomy (ASA), www.agronomy.org American Society for Horticultural Science (ASHS), www.ashs.org American Society for Testing and Materials (ASTM), www.astm.org American Society of Mechanical Engineers International (ASME), www.asme.org American Synthol Inc., www.americansynthol.com Amoco, www.amoco.com Amptron Corporation, www.superslipperystuff.com/ organisation.htm Amrep Inc., www.amrep.com AMSOIL Inc., www.amsoil.com Ana Laboratories Inc., www.analaboratories.com Analysts Inc., www.analystinc.com Anderol Specialty Lubricants, www.anderol.com Andpak Inc., www.andpak.com ANGUS Chemical Company, www.dowchemical.com Anti Wear 1, www.dynamicdevelopment.com API Links, www.api.org/links Apollo America Corporation, www.apolloamerica.com Applied Energy Company, www.appliedenergyco.com Aral International, www.Aral.com Arch Chemicals, Inc., www.archbiocides.com ARCO, www.arco.com Argonne National Laboratory, www.et.anl.gov Arizona Chemical, www.arizonachemical.com Asbury Carbons, Inc.—Dixon Lubricants, www.asbury.com Asbury Carbons, Inc.—Dixon Lubricants, www.dixonlube.com Asbury Graphite Mills Inc., www.asbury.com Asheville Oil Company, Inc., www.ashevilleoil.com Ashia Denka, www.adk.co.jp/eng.htm Ashland Chemical, www.ashchem.com Ashland Distribution Company, www.ashland.com Asian Oil Company, www.nilagems.com/asianoil/ Aspen Chemical Company, www.aspenchemical.com Aspen Technology, www.aspentech.com/ Associated Petroleum Products, www.associatedpetroleum.com

Copyright 2006 by Taylor & Francis Group, LLC

Associates of Cape Cod Inc., www.acciusa.com ASTM, www.astm.org Atlantis International Inc., www.atlantis-usa.com Atlas Oil Company, www.atlasoil.com ATOFINA Canada Inc., www.atofinacanada.com Audi, www.audi.com Ausimont, www.ausiusa.com Automotive & Industrial Lubricants Guide, www.wearcheck.com Automotive Aftermarket Industry Association (AAIA), www.aftermarket.org Automotive and Industrial Lubricants Guide by David Bradbury, www.escape.ca/∼dbrad/index.htm Automotive and Industrial Lubricants Tutorial, www.escape.ca/∼dbrad/index.htm Automotive News, www.autonews.com Automotive Oil Change Association (AOCA), www.aoca.org Automotive Parts and Accessories Association (APAA), www.apaa.org Automotive Service Industry Association (ASIA), www.aftmkt.com Automotive Services Retailer, www.gcipub.com AutoWeb, www.autoweb.com AutoWeek Online, www.autoweek.com Avatar Corporation, www.avatarcorp.com

Badger Lubrication Technologies Inc., www.badgerlubrication.com Baker Petrolite, www.bakerhughes.com/bakerpetrolite/ BALLISTOL USA, www.ballistol.com Bardahl Manufacturing Corporation, www.bardahl.com Baron USA Inc., www.baronusa.com BASF Corp., www.basf.com Battenfeld Grease and Oil Corporation of New York, www.battenfeld-grease.com Bayer Corp., www.bayer.com Bearing.Net, www.wearcheck.com Behnke Lubricants/JAX, www.jaxusa.com Behnke Lubricants Inc./JAX, www.jax.com Bell Additives Inc., www.belladditives.com Bel-Ray Company Inc., www.belray.com Benz Oil Inc., www.benz.com Berenfield Containers, www.berenfield.com Bericap NA, www.bericap.com Berry Hinckley Industries, www.berry-hinckley.com Bestolife Corporation, www.bestolife.com BF Goodrich, www.bfgoodrich.com BG Products Inc., www.bgprod.com Bharat Petroleum, www.bharatpetroleum.com Bianco Enterprises Inc., www.bianco.net Big East Lubricants Inc., www.bigeastlubricants.com Bijur Lubricating Corporation, www.bijur.com Bio-Rad Laboratories, www.bio-rad.com

BioTech International Inc., [email protected] Bismuth Institute, www.bismuth.be Blackstone Laboratories, www.blackstone-labs.com/ Blaser Swisslube, www.blaser.com BMW (International), www.bmw.com/bmwe BMW (USA), www.bmwusa.com BMW Motorcycles, www.bmw-motorrad.com Bodie-Hoover Petroleum Corporation, www.bodie-hoover.com Boehme Filatex Inc., www.boehmefilatex.com BoMac Lubricant Technologies Inc., www.bomaclubetech.com Boncosky Oil Company, www.boncosky.com Boswell Oil Company, www.boswelloil.com BP, www.bp.com BP, www.bptechchoice.com BP, www.bppetrochemicals.com BP Amoco Chemicals, www.bpamocochemicals.com BP Lubricants, www.bplubricants.com Brascorp North America Ltd., www.brascorp.on.ca Brenntag Northeast, Inc., www.brenntag.com/ Brenntag, www.brenntag.com Briner Oil Company, www.brineroil.com British Lubricants Federation Ltd., www.blf.org.uk British Petroleum (BP), www.bp.com Britsch Inc., www.britschoil.com Brno University of Technology, Faculty of Mechanical Engineering, Elastohydrodynamic Lubrication Research Group, http://fyzika.fme.vutbr.cz/ehd/ Brugarolas SA, www.brugarolas.com/english.htm Buckley Oil Company, www.buckleyoil.com Buckman Laboratories Inc., www.buckman.com Buick (GM), www.buick.com Burlington Chemical, www.burco.com BVA Oils, www.bvaoils.com Cabot Corporation (fumed metal oxides), www.cabot-corp.com/cabosil Cadillac (GM), www.cadillac.com California Air Resources Board, www.arb.ca.gov Callahan Chemical Company, www.calchem.com Caltex Petroleum Corporation, www.caltex.com Calumet Lubricants Company, www.calumetlub.com Calvary Industries Inc., www.calvaryindustries.com CAM2 Oil Products Company, www.cam2.com Cambridge, http://chemfinder.camsoft.com Cambridge Universirty, Department of Materials Science and Metallurgy, Tribology, www.msm.cam.ac.uk/tribo/ tribol.htm Cambridge University, Department of Engineering, Tribology, www-mech.eng.cam.ac.uk/Tribology/ Canner Associates, Inc., www.canner.com Cannon Instrument Company, www.cannon-ins.com Capital Enterprises (Power-Up Lubricants), www.NNL690.com

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Car and Driver Magazine Online, www.caranddriver.com Cargill—Industrial Oil & Lubricants, www.techoils. cargill.com Car-Stuff, www.car-stuff.com Cary Company, www.thecarycompany.com CasChem, Inc., www.cambrex.com Castle Products Inc., www.castle-comply.com Castrol Heavy Duty Lubricants, Inc., www.castrolhdl.com Castrol Industrial North America, Inc., www.castrolindustrialna.com Castrol International, www.castrol.com Castrol North America, www.castrolusa.com CAT Products Inc., www.run-rite.com Caterpillar, www.cat.com Caterpillar, www.caterpillar.com Center for Innovation Inc., www.centerforinnovation.com Center for Tribology, Inc. (CETR), www.cetr.com Centurion Lubricants, www.centurionlubes.com CEPSA (Spain), www.cepsa.es Certified Laboratories, www.certifiedlaboratories.com Champion Brands LLC, www.championbrands.com Charles Manufacturing Company, www.tsmoly.com Chart Automotive Group Inc., www.chartauto.com Chattem Chemicals, Inc., www.chattemchemicals.com Chem Connect, www.chemconnect.com Chem-EcoI Ltd., www.chem-ecol.com Chemetall Foote Corporation, www.chemetall.com/ Chemical Abstracts Service, www.cas.org Chemical Resources, www.chemcenter.org Chemical Week Magazine, www.chemweek.com Chemicolloid Laboratories Inc., www.colloidmill.com Chemlube International Inc., www.chemlube.com Chempet Corp., www.rockvalleyoil.com/chempet.htm Chemsearch Lubricants, www.chemsearch.com Chemtool Inc./Metalcote, www.chemtool.com Chevrolet (GM), www.chevrolet.com Chevron Chemical Company, www.chevron.com Chevron Oronite, www.chevron.com Chevron Phillips Chemical Company LP, www.cpchem.com Chevron Phillips Chemical Company, www.chevron.com Chevron Products Co. Lubricants & Specialties Products, www.chevron.com/lubricants Chevron Products Company, www.chevron.com Chevron Texaco, www.chevrontexaco.com Chevron, www.chevron.com Christenson Oil, www.christensonoil.com Chrysler (Mercedes Benz), www.chrysler.com Ciba Specialty Chemicals Corporation, www.cibasc.com CITGO Petroleum Corporation, www.citgo.com Citroen (France), www.citroen.com Citroen (UK), www.citroen.co.uk/fleet Clariant Corporation, www.clariant.com Clark Refining and Marketing, www.clarkusa.com

Clarkson & Ford Company, www.clarkson-ford.com CLC Lubricants Company, www.clclubricants.com Climax Molybdenum Company, www.climaxmolybdenum.com Coastal Corporation, www.elpaso.com Coastal Unilube Inc., www.coastalunilube.com Cognis, www.cognislubechem.com Cognis, www.cognis-us.com Cognis, www.cognis.com Cognis, www.na.cognis.com College of Petroleum and Energy Studies CPS Home Page, www.colpet.ac.uk/index.html College of Petroleum and Energy Studies, www.colpet.ac.uk Colorado Petroleum Products Company, www.colopetro.com Colorado School of Mines Advanced Coating and Surface Engineering Laboratory (ACSEL), www.mines.edu/ research/acsel/acsel.html Commercial Lubricants Inc., www.comlube.com Commercial Oil Company Inc., www.commercialoilcompany.com Commercial Ullman Lubricants Company, www.culc.com Commonwealth Oil Corporation, www.commonwealthoil.com Como Industrial Equipment Inc., www.comoindustrial.com Como Lube & Supplies Inc., www.comolube.com Computational Systems, Inc., www.compsys.com/ index.html Concord Consulting Group Inc., www.concordcg.com Condat Corporation, www.condatcorp.com Conklin Company, Inc., www.conklin.com Conoco, www.conoco.com Containment Solutions Inc., www.containmentsolutions.com Coolants Plus Inc., www.coolantsplus.com Co-ordinating European Council (CEC), www.cectests.org Coordinating Research Council (CRC), www.crcao.com Cortec Corporation, www.cortecvci.com Cosby Oil Company, www.cosbyoil.com Cosmo Oil, www.cosmo-oil.co.jp Country Energy, www.countryenergy.com CPI Engineering Services, www.cpieng.com CRC Industries, Inc., www.crcindustries.com Creanova, Inc., www.creanovainc.com/ Crescent Manufacturing, www.crescentmfg.net Croda Inc., www.croda.com Crompton Corporation, www.cromptoncorp.com Crop Science Society of America (CSSA), www.crops.org Cross Oil Refining and Marketing Inc., www.crossoil.com Crowley Chemical Company Inc., www.crowleychemical.com Crown Chemical Corporation, www.brenntag.com Crystal Inc-PMC, www.pmc-group.com/ CSI, www.compsys.com

Copyright 2006 by Taylor & Francis Group, LLC

Cummings-Moore Graphite Company, www.cumograph.com Cummins Engine Company, www.cummins.com Custom Metalcraft Inc., www.custom-metalcraft.com Cyclo Industries LLC, www.cyclo.com

D & D Oil Company, Inc., www.amref.com D. A. Stuart Company, www.d-a-stuart.com D. B. Becker Company, Inc., www.dbbecker.com D. W. Davies & Company Inc., www.dwdavies.com D-A Lubricant Company, www.dalube.com Daimler Chrysler, www.daimlerchrysler.com Danish Technological Institute (DTI) Tribology Centre, www.tribology.dti.dk/ Darmex Corporation, www.darmex.com Darsey Oil Company Inc., www.darseyoil.com David Weber Oil Company, www.weberoil.com Davison Oil Company, Inc., www.davisonoil.com Dayco Inc., www.dayco.com DeForest Enterprises Inc., www.deforest.net Degen Oil and Chemical Company, www.eclipse. net/∼degen Delkol, www.delkol.co.il Delphi Automotive Systems, www.delphiauto.com Dennis Petroleum Company, Inc., www.dennispetroleum.com Department of Defense (DOD), www.dodssp.daps.mil/ dodssp.htm Departments of Mechanical Engineering Luleå Technical University, Sweden, www.luth.se/depts/mt/me/me.html Des-Case Corporation, www.des-case.com Detroit Diesel, www.detroitdiesel.com Deutsches Institute Fur Normung e. V. (DIN), www.din.de Dexsil Corporation, www.dexsil.com Diagnetics, www.entek.com Dialog, www.dialog.com Diamond Head petroleum Inc., www.diamondheadpetroleum.com Diamond Shamrock Refining Company, LP, www.udscorp.com Diesel Progress, www.dieselpub.com Digilube Systems Inc., www.digilube.com Dingo Maintenance Systems, www.dingos.com/ Dion & Sons Inc., www.dionandsons.com Diversified Petrochemical Services, www.chemhelp.com Division of Machine Elements Home Page Niigata University, Japan, http://tmtribo1.eng.niigata-u.ac.jp/ index_e.html Dixon Lubricants & Special Products Group, Div. of Asbury Carbons, www.dixonlube.com Dodge, www.dodge.com Don Weese Inc., www.schaefferoil.com Dover Chemical, www.doverchem.com Dow Chemical Company, www.dow.com

Dow Corning Corporation, www.dowcorning.com Dryden Oil Company, Inc., www.castrol.com Dyson Oil Company, www.synergynracing.com DSI Fluids, www.dsifluids.com DSP Technology Inc., www.dspt.com Dumas Oil Company, www.esn.net/dumasoil DuPont-Dow Elastomers, www.dupont-dow.com DuPont Krytox Lubricants, www.lubricants.dupont.com DuPont, www.dupont.com/intermediates Duro Manufacturing Inc., www.duromanufacturing.com Dutton-Lainson Company, www.dutton-lainson.com Dylon Industries Inc., www.dylon.com

E. I. DuPont de Nemours and Company, www.dupont.com/intermediates Eagle, www.eaglecars.com Eastech Chemical Inc., www.eastechchemical.com Eastern Oil Company, www.easternoil.com Easy Vac Inc., www.easyvac.com Ecole Centrale de Lyon, France Laboratoire de Tribologie et Dynamique des Systèmes, www.ec-lyon.fr/recherche/ltds/index.html Ecole Polytechnique Federale de Lausanne, Switzerland, http://igahpse.epfl.ch Ecopetrol (Columbian Petroleum Company), www.ecopetrol.com.co Ecotech Div., Blaster Chemical Companies, www.pbblaster.com Edjean Technical Services Inc., www.edjetech.com Eidgenössische Technische Hochschule (ETH), Zurich Laboratory for Surface Science and Technology (LSST), www.surface.mat.ethz.ch/ EKO, www.eko.gr El Paso Corporation, www.elpaso.com Elco Corporation, The, www.elcocorp.com Elementis Specialties-Rheox, www.rheox.com Elf Atochem Canada, www.atofinachemicals.com Elf Lubricants North America Inc., www.keystonelubricants.com Eljay Oil Company, Inc., www.eljayoil.com ELM Environmental Lubricants Manufacturing Company, www.elmusa.com EMERA Fuels Company, Inc., www.emerafuels.com Emerson Oil Company, Inc.www.emersonoil.com Energy Connection, The, www.energyconnect.com Engel Metallurgical Ltd., www.engelmet.com Engen Petroleum Ltd., www.engen.co.za Engineered Composites Inc., www.engineeredcomposites.net ENI, www.eni.it Environmental and Power Technologies Ltd., www.cleanoil.com Environmental Lubricants Manufacturing, Inc. (ELM), www.elmusa.com

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Environmental Protection Agency (EPA), www.fedworld.gov Equilon Enterprises LLC, www.equilon.com Equilon Enterprises LLC-Lubricants, www.equilonmotivaequiva.com Equilon Enterprises LLC-Lubricants, www.shellus.com Equilon Enterprises LLC-Lubricants, www.texaco.com Ergon Inc., www.ergon.com Esco Products Inc., www.escopro.com Esslingen, Technische Akademie, www.tae.de Ethyl Corporation, www.ethyl.com Ethyl Petroleum Additives, www.ethyl.com ETNA Products Inc., www.etna.com Etna-Bechem Lubricants Ltd., www.etna.com European Automobile Manufacturers Association (ACEA), www.acea.be European Oil Companies Organization of E. H. and S. (CONCAWE), www.concawe.be European Patent Office, www.epo.co.at/epo/ EV1, www.gmev.com Evans Industries Inc., www.evansind.com Evergreen Oil, www.evergreenoil.com Exxon, www.exxon.com ExxonMobil Chemical Company, www.exxonmobilchemical.com ExxonMobil Corp., www.exxonmobil.com ExxonMobil Lubricants & Petroleum Specialties Company, www.exxonmobil.com

F&R Oil Company, Inc., www.froil.com F. Bacon Industriel Inc., www.f-bacon.com F.L.A.G. (Fuel, Lubricant, Additives, Grease) Recruiting, www.flagsearch.com/ Fachhochschule Hamburg, Germany, www.haw-hamburg. de/fh/forum/f12/indexf.html/tribologie/etribology.html Falex Corporation, www.falex.com Falex Tribology NV, www.falexint.com/ FAMM (Fuel and Marine Marketing), www.fammllc.com Fanning Corporation, The, www.fanncorp.com Far West Oil Company Inc., www.farwestoil.com Farmland Industries Inc., www.farmland.com Federal World, www.fedworld.gov Ferrari, www.ferrari.com Ferro/Keil Chemical, www.ferro.com FEV Engine Technology, Inc., www.fev-et.com/ Fiat, www.fiat.com Fina Oil and Chemical Company, www.fina.com Findett Corporation, www.findett.com Finish Line Technologies Inc., www.finishlineusa.com FINKE Mineralolwerk, www.finke-mineraloel.de Finnish Oil and Gas Federation, www.oil.fi Flamingo Oil Company, www.pinkbird.com Flo Components Ltd., www.flocomponents.com Flowtronex International, www.flowtronex.com

Fluid Life Corporation, www.fluidlife.com Fluid Systems Partners US Inc., www.fsp-us.com Fluid Technologies Inc., www.Fluidtechnologies.com Fluids Analysis Lab, www.butler-machinery.com/oil.html Fluidtec International, www.fluidtec.com Fluitec International, www.fluitec.com/ FMC Blending & Transfer, www.fmcblending-transfer.com FMC Lithium, www.fmclithium.com FMC, www.fmc.com Ford Motor Company, www.ford.com Fortum (Finland), www.fortum.com Forward Corporation, www.forwardcorp.com Freightliner, www.freightliner.com Frontier Performance Lubricants Inc., www.frontierlubricants.com Fuchs Lubricants Company, www.fuchs.com Fuchs, www.fuchs-oil.de Fuels and Lubes Asia Publications, Inc., www.flasia.com.ph Fuki America Corporation, www.fukiamerica.com Functional Products, www.functionalproducts.com

G-C Lubricants Company, www.gclube.com G & G Oil Co. of Indiana Inc., www.ggoil.com G. R. O’Shea Company, www.groshea.com G. T. Autochemilube Ltd., www.gta-oil.co.uk Galactic, www.galactic.com Gamse Lithographing Company, www.gamse.com Gard Corporation, www.gardcorp.com Gas Tops Ltd., www.gastops.com Gasco Energy, www.gascoenergy.com Gateway Additives, www.lubrizol.com Gear Technology Magazine, www.geartechnology.com/ mag/gt-index.html General Motors (GM), www.gm.com Generation Systems Inc., www.generationsystems.com Geo. Pfau’s Sons Company, Inc., www.pfauoil.com Georgia Tech Tribology, www.me.gatech.edu/research/ tribology.html Georgia-Pacific Resins, Inc.—Actrachem Division, www.gapac.com Georgia-Pacific Resins, Inc.—Actrachem Division, www.gp.com Gerhardt Inc., www.gerhardths.com Global Electric Motor Cars, LLC, www.gemcar.com Globetech Services Inc., www.globetech-services.com Glover Oil Company, www.gloversales.com GMC, www.gmc.com GOA Ce., www.goanorthcoastoil.com Gold Eagle Company, www.goldeagle.com Golden Bear Oil Specialties, www.goldenbearoil.com Golden Gate Petroleum, www.ggpetrol.com Goldenwest Lubricants, www.goldenwestlubricants.com

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Goldschmidt Chemical Corporation, www.goldschmidt.com Gordon Technical Service Company, www.gtscofpa.com Goulston Technologies, Inc., www.goulston.com Graco Inc., www.graco.com Granitize Products Inc., www.granitize.com Greenland Corporation, www.greenpluslubes.com Grignard Company LLC, www.purelube.com Groeneveld Pacific West, www.groeneveldpacificwest.com Gulf Oil, www.gulfoil.com

H & W Petroleum Company, Inc., www.hwpetro.com H. L. Blachford Ltd., www.blachford.ca H.N. Funkhouser & Company, www.hnfunkhouser.com Haas Corp., www.haascorp.com Hall Technologies Inc., www.halltechinc.com Halocarbon Products Corporation, www.halocarbon.com Halron Oil Company, Inc., www.halron.com Hammonds Fuel Additives, Inc., www.hammondscos.com Hampel Oil Distributors, www.hampeloil.com Hangsterfer’s Laboratories Inc., www.hangsterfers.com Harry Miller Corporation, www.harrymillercorp.com Hasco Oil Company, Inc., www.hascooil.com Hatco Corporation, www.hatcocorporation.com Haynes Manufacturing Company, www.haynesmfg.com HCI/Worth Chemical Corporation, www.hollandchemical.com Hedwin Corporation, www.hedwin.com HEF, France, www.hef.fr/ Henkel Surface Technologies, www.henkel.com Henkel Surface Technologies, www.thomasregister.com/ henkelsurftech Hercules, Inc., Aqualon Division, www.herc.com Herguth Laboratories Inc., www.herguth.com Heveatex, www.heveatex.com Hexol Lubricants, www.hexol.com Hindustan Petroleum Corporation, Ltd., www.hindpetro.com Hino Motor Ltd., www.hino.co.jp Hi-Port Inc., www.hiport.com Hi-Tech Industries, Inc., www.hi-techind.com Holland Applied Technologies, www.hollandapt.com Honda (Japan), www.worldhonda.com Honda (USA), www.honda.com Hoosier Penn Oil Company, www.hpoil.com Hoover Materials Handling Group, Inc., www.hooveribcs.com Horix Manufacturing Company, www.sgi.net/horix Houghton International Inc., www.houghtonintl.com How Stuff Works, www.howstuffworks.com/engine.htm Howes Lubricator, www.howeslube.thomasregister.com Huls America, www.CreanovaInc.com/ Huls America, www.huls.com

Huntsman Corporation, www.huntsman.com Huskey Specialty Lubricants, www.huskey.com Hydraulic Repair & Design, Inc., www.h-r-d.com Hydrocarbon Asia, www.hcasia.safan.com Hydrocarbon Online, www.wearcheck.com/ publications.html Hydrocarbon Processing Magazine, www.hydrocarbonprocessing.com/ Hydrosol Inc., www.hydrosol.com Hydrotex Inc., www.hydrotexlube.com Hy-Per Lube Corporation, www.hyperlube.com Hysitron Incorporated: Nanomechanics, www.hysitron.com/ Hyundai, www.hyundai-motor.com

I.S.E.L. Inc., www.americansynthol.com ICIS-LOR Base Oils Pricing Information, www.icislor.com/ Idemitsu, www.idemitsu.co.jp ILC/Spectro Oils of America, www.spectro-oils.com Illinois Oil Products Inc., www.illinoisoilproducts.com Imperial College, London ME Tribology Section, www.me.ic.ac.uk/tribology/ Imperial Oil Company, Inc., www.imperialoil.com Imperial Oil Ltd., www.imperialoil.ca Imperial Oil Products and Chemicals Division, www.imperialoil.ca Independent Lubricant Manufacturers Association (ILMA), www.ilma.org Indian Institute of Science, Bangalore, India, Department of Mechanical Engineering, www.mecheng.iisc.ernet.in Indian Oil Corporation, www.indianoilcorp.com Indiana Bottle Company, www.indianabottle.com Industrial Lubrication and Tribology Journal, www.mcb.co.uk/ilt.htm Industrial Maintainence and Engineering Links (PLI, LLC), www.memolub.com/link.htm Industrial Maintenance & Plant Operation (IMPO), www.mcb.co.uk/cgi-bin/mcb_serve/ table1.txt&ilt&stanleaf.htm Industrial Packing Inc., www.industrialpacking.com Infineum USA LP, www.infineum.com Infiniti, www.infiniti.com Ingenieria Sales SA de CV, www.isalub.com Inolex Chemical Company, www.inolex.com Innovene, www.innovene.com Insight Services, www.testoil.com/ Institut National des Sciences Appliquees de Lyon, France, Laboratoire de Mechanique des Contacts, www.insa-lyon.fr/Laboratoires/LMC/index.html Institute of Materials Inc. (IOM), www.savantgroup.com Institute of Materials, www.savantgroup.com Institute of Mechanical Engineers (ImechE), www.imeche.org.uk

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Institute of Petroleum (IP), http://212.78.70.142 Institute of Physics (IOP), Tribology Group, www.iop.org Instruments for Surface Science, www.omicroninstruments.com/index.html Interline Resources Corporation, www.interlineresources.com Internal Energy Agency (IEA), www.iea.org International Group Inc., The (IGI), www.igiwax.com International Lubricants Inc., www.lubegard.com International Organization for Standardization (ISO), www.iso.ch International Products Corp., www.ipcol.com Intertek Testing Services-Caleb Brett, www.itscb.com Intl. Tribology Conf. Yokohama 1995, www.mep.titech.ac. jp/Nakahara/jast/itc/itc-home.htm Invicta a.s., www.testoil.com/ Iowa State University, Tribology Laboratory, www.eng. iastate.edu/coe/me/research/labs/tribology_lab.html IQA Lube Corporation, www.iqalube.com Irving Oil Corporation, www.irvingoil.com ISO Translated into Plain English, http://connect.ab.ca/ ∼praxiom Israel Institute of Technology (Technion), http://meeng. technion.ac.il/Labs/energy.htm#tribology Isuzu, www.isuzu.com ITW Fluid Products Group, www.itwfpg.com

J & H Oil Company, www.jhoil.com J & S Chemical Corporation, www.jschemical.com J.H. Calo Company, Inc., www.jhcalo.com J.R. Schneider Company, Inc., www.jrschneider.com J.A.M. Distributing Company, www.jamdistributing.com J.A.M.Distributing, www.jamdistributing.com J.B. Chemical Company, Inc., www.jbchemical.com J.B. Dewar Inc., www.jbdewar.com J.D. Streett & Company, Inc., www.jdstreett.com J.N. Abbott Distributor Inc., www.jnabbottdist.com Jack Rich Inc., www.jackrich.com Jaguar, www.jaguarcars.com Japan Association of Petroleum Technology (JAPT), www.japt.org Japan Automobile Manufacturers Association (JAMA), www.japanauto.com Japan Energy Corporation, www.j-energy.co.jp/eng/ index.html Japan Energy, www.j-energy.co.jp Japanese Society of Tribologists (JAST) (in Japanese), www.jast.or.jp Jarchem Industries Inc., www.jarchem.com Jasper Engineering & Equipment, www.jaspereng.com JAX-Behnke Lubricants Inc., www.jax.com Jeep, www.jeep.com Jenkin-Guerin Inc., www.jenkin-guerin.com Jet-Lube (UK) Ltd., www.jetlube.com

John Deere, www.deere.com Johnson Packings & Industrial Products Inc., www.johnsonpackings.com Journal of Fluids Engineering, http://borg.lib.vt.edu/ ejournals/JFE/jfe.html Journal of Tribology, http://engineering.dartmouth.edu/ thayer/research/index.html K.C. Engineering Ltd., www.kceng.com/ K.l.S.S. Packaging Systems, www.kisspkg.com Kafko International Ltd., www.kafkointl.com Kanazawa University, Japan, Tribology Laboratory, http://web.kanazawa-u.ac.jp/∼tribo/labo5e.html Kath Fuel Oil Service, www.kathfuel.com Kawasaki, www.kawasaki.com Kawasaki, www.khi.co.jp Keck Oil Company, www.keckoil.com Keil Chemical, www.ferro.com Kelsan Lubricants USA LLC, www.kelsan.com Kem-A-Trix Specialty Lubricants & Compounds, www.kematrix.com Kendall Motor Oil, www.kendallmotoroil.com Kennedy Group. The, www.kennedygrp.com King Industries Specialty Chemicals, www.kingindustries.com Kittiwake Developments Limited, www.kittiwake.com Kleenoil Filtration Inc., www.kleenoilfiltrationinc.com Kleentek-United Air Specialists Inc., www.uasinc.com Kline & Company Inc., www.klinegroup.com Kluber Lubrication North America LP, www.kluber.com Koehler Instrument Company, www.koehlerinstrument.com KOST Group Inc., www.kostusa.com Kruss USA, www.krussusa.com Kuwait National Petroleum Company, www.knpc.com.kw Kyodo Yushi USA Inc., www.kyodoyushi.co.jp Kyushu University, Japan, Lubrication Engineering Home Page, www.mech.kyushu-u.ac.jp/index.html Lambent Technologies, www.petroferm.com Lambourghini, www.lamborghini.com Laub/Hunt Packaging Systems, www.laubhunt.com Lawler Manufacturing Corporation, www.lawler-mfg.com Leander Lubricants, www.leanderlube.com Leding Lubricants Inc., www.automatic-lubrication.com Lee Helms Inc., www.leehelms.com Leffert Oil Company, www.leffertoil.com Leffler Energy Company, www.leffler.com Legacy Manufacturing, www.legacymfg.com Les Industries Sinto Racing Inc., www.sintoracing.com Lexus, www.lexususa.com Liftomtic Inc., www.liftomatic.com Lilyblad Petroleum, Inc., www.lilyblad.com Lincoln-Mercury, www.lincolnmercury.com Linpac Matls. Handling, www.linpacmh.com

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Liqua-Tek Inc., www.hdpluslubricants.com Liqua-Tek/Moraine Packaging, www.globaldialog.com/∼mpi Liquid Controls Inc., A Unit of IDEX Corporation, www.lcmeter.com Liquid Horsepower, www.holeshot.com/chemicals/ additives.html LithChem International, www.lithchem.com Lockhart Chemical Company, www.lockhartchem.com Loos & Dilworth Inc. — Automotive Division, www.loosanddilworth.com Loos & Dilworth Inc. — Chemical Division, www.loosanddilworth.com Lormar Reclamation Service, www.lormar.com Los Alomos National Laboratory, www.lanl.gov/ worldview/ Lowe Oil Co./Champion Brands LLC, www.championbrands.com LPS Laboratories, www.lpslabs.com LSST Tribology and Surface Forces, http://bittburg.ethz. ch/LSST/Tribology/default.html LSST Tribology Letters, http://bittburg.ethz.ch/LSST/ Tribology/letters.html Lube Net, www.lubenet.com LubeCon Systems Inc., www.lubecon.com Lubelink, www.lubelink.com Lubemaster Corporation, www.lubemaster.com LubeNet, www.lubenet.com LubeRos—A Division of Burlington Chemical Company Inc., www.luberos.com Lubes and Greases, www.lngpublishing.com LuBest, Division of Momar Inc., www.momar.com Lubricant Additives Research, www.silverseries.com Lubricant Technologies, www.lubricanttechnologies.com Lubricants Network Inc., www.lubricantsnetwork.com Lubricants USA, www.finalube.com Lubricants World, www.lubricantsworld.com Lubrication Engineering Magazine, www.stle.org/ le_magazine/le_index.htm Lubrication Engineers Inc., www.le-inc.com Lubrication Engineers of Canada, www.lubeng.com Lubrication Systems, www.lsc.com Lubrication Technologies Inc., www.lube-tech.com Lubrication Technology Inc., www.lubricationtechnology.com Lubrichem International Corporation, www.lubrichem.net Lubrifiants Distac Inc., www.inspection.gc.ca/english/ ppc/reference/n2e.shtml Lubri-Lab Inc., www.lubrilab.com LUBRIPLATE Div., Fiske Bros. Refining Company, www.lubriplate.com Lubriport Labs, www.ultralabs.com/lubriport Lubriquip Inc, www.lubriquip.com Lubritec, www.ensenada.net/lubritec/ Lubrizol Corporation, The, www.lubrizol.com

Lubromation Inc., www.lubromation.com Lub-Tek Petroleum Products Corporation, www.lubtek.com Lucas Oil Products Inc., www.lucasoil.com LukOil (Russian Oil Company), www.lukoil.com Lulea University of Technology, Department of Mechanical Engineering, www.luth.se/depts/mt/me/ Lyondell Lubricants, www.lyondelllubricants.com Machines Production Web Site, www.machpro.fr/ Mack Trucks, www.macktrucks.com MagChem Inc., www.magchem.com Magnalube, www.magnalube.com Maine Lubrication Service Inc., www.mainelube.com MaintenanceWorld, www.wearcheck.com Manor Technology, www.manortec.co.uk/ Manor Trade Development Corporation, www.amref.com Mantek Lubricants, www.mantek.com Marathon Ashland Petroleum LLC, www.mapllc.com Marathon Oil Company, www.marathon.com MARC-IV, www.marciv.com Marcus Oil and Chemical, www.marcusoil.com Markee International Corporation, www.markee.com Marly, www.marly.com Maryn International Ltd., www.maryngroup.com Maryn International, www.poweruplubricants.com Master Chemical Corporation, www.masterchemical.com Master Lubricants Company, www.lubriko.com Maxco Lubricants Company, www.maxcolubricants.com Maxim Industrial Metalworking Lubricants, www.maximoil.com Maxima Racing Lubricants, www.maximausa.com Mays Chemical Company, www.mayschem.com Mazda, www.mazda.com McCollister & Company, www.mccollister.com McGean-Rohco Inc., www.mcgean-rohco.com McGee Industries Inc., www.888teammclube.com McIntyre Group Ltd., www.mcintyregroup.com McLube Divisionl/McGee Industries Inc., www.888teammclube.com Mechanical Engineering Magazine, www.memagazine.org/index.html Mechanical Engineering Tribology Web Site, http://widget.ecn.purdue.edu/∼metrib/ Mega Power Inc., www.megapowerinc.com Mercedes-Benz (Germany), www.mercedes-benz.de Metal Forming Lubricants Inc., www.mflube.com Metal Mates Inc., www.metalmates.net Metalcote/Chemtool Inc., www.metalcote.com Metalworking Lubricants Company, www.metalworkinglubricants.com Metalworking Lubricants, www.maximoil.com Metorex Inc., www.metorex.fi Mettler Toledo, www.mt.com MFA Oil Compny, www.mfaoil.com

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Michel Murphy Enterprises Inc., www.michelmurphy.com Micro Photonics Inc., www.microphotonics.com/ Mid-Michigan Testing Inc., www.tribologytesting.com Mid-South Sales Inc., www.mid-southsales.com Mid-Town Petroleum Inc., www.midtownoil.com Migdal’s Lubricant Web Page, http://members.aol.com/ sirmigs/lub.htm Milacron Consumable Products Division, www.milacron.com Milatec Corporation, www.militec.com Millennium Lubricants, www.millenniumlubricants.com Miller Oil of Indiana, Inc., www.milleroilinc.com Mitsubishi Motors, www.mitsubishi-motors.co.jp Mobil, www.mobil.com Mohawk Lubricants Ltd., www.mohawklubes.com MOL Hungarian Oil & Gas, www.mol.hu Molyduval, www.molyduval.com Molyslip Atlantic Ltd., www.molyslip.co.uk Monlan Group, www.monlangroup.com Monroe Fluid Technology Inc., www.monroefluid.com Moore Oil Company, www.mooreoil.com Moraine Packaging Inc., www.hdpluslubricants.com Morey’s Oil Products Company, www.moreysonline.com Moroil Technologies, www.moroil.com Motiva Enterprises LLC, www.motivaenterprises.com Motor Fuels/Combustibles Testing, www.empa.ch/ englisch/fachber/abt133/index.htm Motorol Lubricants, www.motorolgroup.com Motul USA Inc., www.motul.com Mozel Inc., www.mozel.com Mr. Good Chem, Inc., www.mrgoodchem.com Murphy Oil Corporation, www.murphyoilcorp.com/ Muscle Products Corporation, www.mpc-home.com Muse, Stancil & Company, www.musestancil.com Nalco Chemical Company, www.nalco.com Nanomechanics and Tribology Swiss Tribology Online, http://dmxwww.epfl.ch/WWWTRIBO/home.html NanoTribometer System, www.ume.maine.edu/LASST Naptec Corporation, www.satec.com NASA Lewis Research Center (LeRC) Tribology & Surface Science Branch, www.lerc.nasa.gov/ Other_Groups/SurfSci National Centre of Tribology, UK, www.aeat.com/nct/ National Fluid Power Association (NFPA), www.nfpa.com National Institute for Occupational Safety and Health, www.cdc.gov/homepage.html National Institute of Standards and Technology, http://webbook.nist.gov/chemistry National Lubricating Grease Institute (NLGI), www.nlgi.org National Metal Finishing Resource Center, www.nmfrc.org National Oil Recyclers Association (NORA), www.recycle.net/Associations/rs000141.html

National Petrochemical & Refiners Association, www.npradc.org National Petrochemical Refiners Association (NPRA) www.npradc.org National Petroleum News, www.petroretail.net/npn National Petroleum Refiners Association (NPRA), www.npra.org National Research Council of Canada Lubrication Tribology Services, http://132.246.196.24/en/fsp/ service/lubrication_trib.htm National Resource for Global Standards, www.nssn.org National Tribology Services, www.natrib.com Naval Research Lab Tribology Section — NRL Code 6176, http://stm2.nrl.navy.mil/∼wahl/6176.htm NCH, www.nch.com Neale Consulting Engineers Limited, www.tribology.co.uk/ Neo Synthetic Oil Company Inc., www.neosyntheticoil.com Newcomb Oil Company, www.newcomboil.com Niagara Lubricant Company, Inc., www.niagaralubricant.com Nissan (Japan), www.nissan.co.jp Nissan (USA), www.nissandriven.com Nissan (USA), www.nissanmotors.com NOCO Energy Corporation, www.noco.com Noco Lubricants, www.noco corn Nordstrom Valves Inc., www.nordstromaudco.com Noria-OilAnalysis.Com, www.oilanalysis.com/ Northern Technologies International Corporation, www.ntic.com Northwestern University, Tribology Lab, http://cset.mech.northwestern.edu/member.htm Nyco SA, www.nyco.fr Nye Lubricants, www.nyelubricants.com Nynas Naphthenics, www.nynas.com

O’Rourke Petroleum, www.orpp.com Oak Ridge National Laboratory (ORNL) Tribology Test Systems, www.ms.ornl.gov/htmlhome Oakite Products, Inc., www.oakite.com OATS (Oil Advisory Technical Services), www.oats.co.uk Occidental Chemical Corporation, www.oxychem.com Occupational Safety and Health Administration (OSHA), www.osha.gov Ocean State Oil Inc., www.oceanstateoil.com Oden Corporation, www.oden.thomasregister.com Oden Corporation, www.odencorp.com Ohio State University, Center for Surface Engineering and Tribology, Gear Dynamics and Gear Noise Research Laboratory, http://gearlab.eng.ohio-state.edu/ Oil Analysis (Noria), www.oilanalysis.com Oil Center Research Inc., www.oilcenter.com Oil Depot, www.oildepot.com

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Oil Directory.com, www.oildirectory.com Oil Distributing Company, www.oildistributing.com Oil Online, www.oilonline.com/ Oil-Chem Research Corporation, www.avblend.com Oilkey Corporation, www.oilkey.com Oil-Link Oil & Gas Online, www.oilandgasonline.com Oilpure Technologies Inc., www.oilpure.com Oilspot.com, www.oilspot.com OKS Speciality Lubricants, www.oks-india.com OMGI, www.omgi.com OMICRON Vakuumphysik GmbH, www.omicroninstruments.com/index.html Omni Specialty Packaging, www.nuvo.cc OMO Petroleum Company, Inc., www.omoenergy.com OMS Laboratories, Inc., http://members.aol.com/ labOMS/index.html Opel, www.opel.com Orelube Corporation, www.orelube.com Oronite, www.oronite.com O’Rourke Petroleum Products, www.orpp.com Ottsen Oil Company, Inc., www.ottsen.com Owens-Illinois Inc., www.o-i.com Oxford Instruments Inc., www.oxinst.com Paper Systems Inc., www.paper-systems.com Paramount Products, www.paramountproducts.com PARC Technical Services Inc., www.parctech.com Parent Petroleum, www.parentpetroleum.com PATCO Additives Division — American Ingredients Company, www.patco-additives.com Pathfinder Lubricants, www.pathfinderlubricants.ca/ Patterson Industries Ltd. (Canada), www.pattersonindustries.com PBM Services Company, www.pbmsc.com PdMA Corporation, www.pdma.com PDVSA (Venezuela), www.pdvsa.com PED Inc., www.ped.vianet.ca Pedroni Fuel Company, www.pedronifuel.com PEMEX (Mexico), www.pemex.com Pennine Lubricants, www.penninelubricants.co.uk Pennsylvania State University, The, www.me.psu.edu/ research/tribology.html Pennwell Publications, www.pennwell.com Pennzoil Industrial Lubricants, www.pennzoil.com/ prdsmktg/products/industrial/default.htm Pennzoil, www.pennzoil.com Pennzoil-Quaker State Company, www.pennzoilquakerstate.com PENRECO, www.penreco.com Penta Manufacturing Company/Division of Penta International Corporation, www.pentamfg.com Performance Lubricants & Race Fuels Inc., www.performanceracefuels.com Perkin Elmer Automotive Research, www.perkinelmer.com/ar

Perkins Products Inc., www.perkinsproducts.com Pertamina (Indonesia), www.pertamina.com Petro Star Lubricants, www.petrostar.com PetroBlend Corporation, www.petroblend.com Petrobras (Brazil), www.petrobras.com.br Petro-Canada Lubricants, www.htlubricants.com Petrofind.com, www.petrofind.com Petrogal (Portugal), www.galpenergia.com/ Galp+Energia/home.htm Petrogal (Portugal), www.petrogal.pt Petrolab Corporation, www.petrolab.com Petrolabs Inc., http://pages.prodigy.net/petrolabsinc Petroleum Analyzer Company LP (PAC), www.Petroleum-Analyzer.com Petroleum Marketers Association of America (PMAA), www.pmaa.org Petroleum Packers Inc., www.pepac.com Petroleum Products Research, www.swri.org/4org/ d08/petprod/ PetroleumWorld.com, www.petroleumworld.com Petro-Lubricants Testing Laboratories, Inc., www.pltlab.com PetroMin Magazine, www.petromin.safan.com PetroMoly, Inc., www.petromoly.com Petron Corporation, www.petroncorp.com Petroperu (Peru), www.petroperu.com Petrotest, www.petrotest.net Peugeot, www.peugeot.com Pfaus Sons Company Inc., www.pfauoil.com Pflaumer Brothers Inc., www.pflaumer.com Philips Industrial Electronics Deutschland, www.philips-tkb.com Phillips Petroleum Company/Phillips 66, www.phillips66.com/phi11ips66.asp Phoenix Petroleum Company, www.phoenixpetroleum.com Pico Chemical Corporation, www.picochemical.com Pilot Chemical Company, www.pilotchemical.com Pinnacle Oil Inc., www.pinnoil.com Pipeguard of Texas, www.pipeguard-texas.com Pitt Penn Oil Company, www.pittpenn.com Plastic Bottle Corporation, www.plasticbottle.com Plastican Inc., www.plastican.com Plews/Edelmann Division, Stant Corporation, www.stant.com PLI LLC, www.memolub.com Plint and Partners: Tribology Division, www.plint.co.uk/trib.htm Plymouth, www.plymouthcars.com PMC Specialties Inc., www.pmcsg.com PolimeriEuropa, www.polimerieuropa.com PoIySi Technologies Inc., www.polysi.com Polaris Laboratories, LLC, www.polarislabs.com Polar Company, www.polarcompanies.com Polartech Ltd., www.polartech.co.uk

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PolySi Technologies, www.polysi.com Pontiac (GM), www.pontiac.com Power Chemical, www.warcopro.com Power-Up Lubricants, www.mayngroup.com Practicing Oil Analysis Magazine, www.practicingoilanalysis.com Precision Fluids Inc., www.precisionfluids.com Precision Industries, www.precisionind.com Precision Lubricants, www.precisionlubricants.com PREDICT/DLI—Innovative Predictive Maintenance, www.predict-dli.com Predictive Maintenance Corporation, www.pmaint.com/ Predictive Maintenance Corporation: Tribology and the Information Highway, www.pmaint.com/tribo/docs/ oil_anal/tribo_www.html Predictive Maintenance Services, www.theoillab.com Premo Lubricant Technologies, www.premolube.com Prime Materials, www.primematerials.com Primrose Oil Company, Inc., www.primrose.com Probex Corporation, www.probex.com Products Development Manufacturing Company, www.veloil.com ProLab TechnoLub Inc., www.prolab-technologies.com ProLab-Bio Inc., www.prolab-lub.com Prolong Super Lubricants, www.prolong.com ProTec International Inc., www.proteclubricants.com Pulsair Systems Inc., www.pulsair.com Purac America, Inc., www.purac.com Purdue University Materials Processing and Tribology Research Group, www.ecn.purdue.edu/∼farrist/lab.html Pure Power Lubricants, www.gopurepower.com QMI, www.qminet.com Quaker Chemical Corporation, www.quakerchem.com Quaker State, www.qlube.com Quorpak, www.quorpak.com R & D/Fountain Industries, www.fountainindustries.com R.A. Miller & Company, Inc., www.ramiller.on.ca R.T. Vanderbilt Company, Inc., www.rtvanderbilt.com R.E. Carroll Inc., www.recarroll.com R.E.A.L. Services, www.realservices.com R.H. Foster Energy LLC, www.rhfoster.com R.T. Vanderbilt Company, www.rtvanderbilt.com Radian Inc., www.radianinc.com Radio Oil Company, Inc., www.radiooil.com Ramos Oil Company, Inc., www.ramosoil.com Rams-Head Company, www.doall.com Ransome CAT, www.ransome.com Ravenfield Designs Ltd., www.ravenfield.com Reade Advanced Materials, www.reade.com Red Giant Oil Company, www.redgiantoil.com Red Line Oil, www.redlineoil.com Reed Oil Company, www.reedoil.com

Reelcraft Industries Inc., www.realcraft.com Reit Lubricants Company, www.reitlube.com Reitway Enterprises Inc., www.reitway.com Reliability Magazine, www.pmaint.com/tribo/docs/ oil_anal/tribo_www.html Renewable Lubricants, Inc., www.renewablelube.com Renite Company, www.renite.com Renite Company-Lubrication Engineers, www.renite.com Renkert Oil, www.renkertoil.com Rensberger Oil Company, Inc., www.rensbergeroil.com Rexam Closures, www.closures.com Rhein Chemie Corporation, www.bayer.com Rhein Chemie Rheinau GmbH, www.rheinchemie.com Rheotek (PSL SeaMark), www.rheotek.com Rheox Inc., www.rheox.com Rhodia, www.rhodia.com Rhone-Poulenc Surfactants & Specialties, www.rpsurfactants.com Ribelin, www.ribelin.com RiceChem, A Division of Stilling Enterprises Inc., www.ricechem.com RichardsApex Inc., www.richardsapex.com Riley Oil Company, www.rileyoil.com RO-59 Inc., http://members.aol.com/ro59inc Rock Valley Oil & Chemical Company, www.rockvalleyoil.com Rocol Ltd., www.rocol.com Rohm & Haas Company, www.rohmhaas.com RohMax Additives GmbH, www.rohmax.com Ross Chem Inc., www.rosschem.com Rowleys Wholesale, www.rowleys.com Royal Institute of Technology (KTH), Sweden Machine Elements Home Page, www.damek.kth.se/mme Royal Lubricants Inc., www.royallube.com Royal Manufacturing Company, Inc., www.royalube.com Royal Purple, Inc., www.royalpurple.com Russell-Stanley Corportion, www.russell-stanley.com RWE-DEA (Germany), www.rwe-dea.de RyDol Products, www.rydol.com

Saab Cars USA, www.saabusa.com Saab, www.saab.com Safety Information Resources on the Internet, www.siri.org/links1.html Safety-Kleen Corporation, www.safety-kleen.com Safety-Kleen Oil Recovery, www.ac-rerefined.com Saftek: Machinery Maintenance Index, www.saftek.com/boiler/machine/mmain.htm Saitama University, Japan Home Page of Machine Element Laboratory, www.mech.saitama-u.ac.jp/ youso/home.html San Joaquin Refining Company, www.sjr.com Sandia National Laboratories Tribology, www.sandia.gov/ materials/sciences/

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Sandstrom Products Company, www.sandstromproducts.com Sandy Brae Laboratories Inc., www.sandy/brae.com Santie Oil Company, www.santiemidwest.com Santotrac Traction Lubricants, www.santotrac.com Santovac Fluids Inc., www.santovac.com Sasol (South Africa), www.sasol.com SATEC Inc., www.satec.com Saturn (GM), www.saturncars.com Savant Group of Companies, www.savantgroup.com Savant Inc., www.savantgroup.com Saxton Industries Inc., www.saxton.thomasregister.com Saxton Industries Inc., www.schaefferoil.com Scania, www.scania.se Schaeffer Manufacturing, www.schaefferoil.com Schaeffer Oil and Grease, www.schaefferoil.com Schaeffer Specialized Lubricants, www.schaefferoil.com Scully Signal Company, www.scully.com Sea-Land Chemical Company, www.sealandchem.com Selco Synthetic Lubricants, www.synthetic-lubes.com Senior Flexonics, www.flexonics-hose.com Sentry Solutions Ltd., www.sentrysolutions.com Service Supply Lubricants LLC, www.servicelubricants.com Sexton & Peake Inc., www.sexton.qpg.com SFR Corporation, www.sfrcorp.com SGS Control Services Inc., www.sgsgroup.com Shamban Tribology Laboratory Kanazawa University, Japan, http://web.kanazawa-u.ac.jp/∼tribo/labo5e.html Shamrock Technologies, Inc., www.shamrocktechnologies.com Share Corp., www.sharecorp.com Shell (USA), www.shellus.com Shell Chemicals, www.shellchemical.com Shell Global Solutions, www.shellglobalsolutions.com Shell International, www.shell.com/royal-en Shell Lubricants (USA), www.shell-lubricants.com Shell Oil Products US, www.shelloilproductsus.com/ Shell, www.shellus.com Shepherd Chemical Company, www.shepchem.com Shrieve Chemical Company, www.shrieve.com Silvas Oil Company, Inc., www.silvasoil.com Silverson Machines Inc., www.silverson.com Simons Petroleum Inc., www.simonspetroleum.com Sinclair Oil Corporation, www.sinclairoil.com Sinopec (China Petrochemical Corporation), www.sinopec.com.cn SK Corporation (Houston Office) www.skcorp.com SKF Quality Technology Centre, www.qtc.skf.com Sleeveco Inc., www.sleeveco.com Slick 50 Corporation, www.slick50.com Smooth Move Company, www.theprojectsthatsave.com Snyder Industries, www.snydernet.com Sobit International, Inc., www.sobitinc.com Society of Automotive Engineers (SAE), www.sae.org

Society of Environmental Toxicology and Chemistry (SETAC), www.setac.org Society of Manufacturing Engineers (SME), www.sme.org Society of Manufacturing Engineers, www.sme.org Society of Tribologists and Lubrication Engineers (STLE), www.stle.org Soltex, www.soltexinc.com Sourdough Fuel, www.petrostar.com Southern Illinois University, Carbondale Center for Advanced Friction Studies, www.frictioncenter.com Southwest Grease Products, www.stant.com/ brochure.cfm?brochure=155&location_id=119 Southwest Research Institute (SwRI) Engine Technology Section, www.swri.org/4org/d03/engres/engtech/ Southwest Research Institute, www.swri.org Southwest Spectro-Chem Labs, www.swsclabs.com Southwestern Graphite, www.asbury.com Southwestern Petroleum Corporation (SWEPCO), www.swepco.com Southwestern Petroleum Corporation, www.swepcousa.com SP Morell & Company, www.spmorell.com Spacekraft Packaging, www.spacekraft.com Spartan Chemical Company Inc. Industrial Products Group Division, www.spartanchemical.com Spartan Oil Company, www.spartanonline.com Specialty Silicone Products Inc., www.sspinc.com Spectro Oils of America, www.goldenspectro.com Spectro Oils of America, www.spectro-oils.com SpectroInc. Industrial Tribology Systems, www.spectroinc.com/ Spectronics Corporation, www.spectroline.com Spectrum Corp., www.spectrumcorporation.com Spencer Oil Company, www.spenceroil.com Spex CertiPrep Inc., www.spexcsp.com SQM North America Corporation, www.sqmna.com St. Lawrence Chemicals, www.stlawrencechem.com Star Brite, www.starbrite.com State University of New York, Binghamton Mechanical Engineering Laboratory, www.me.binghamton.edu/ me_labs.html Statoil (Norway), www.statoil.com Steel Shipping Containers Institute, www.steelcontainers.com Steelco Industrial Lubricants, Inc., www.steelcolubricants.com Steelco Northwest Distributors, www.steelcolubricants.com Stochem, Inc., www.stochem.com STP Products Inc., www.stp.com Stratco Inc., www.stratco.com SubTech (Petroleum Service & Supply Information), www.subtech.no/petrlink.htm Suburban Oil Company, Inc., www.suburbanoil.com Summit Industrial Products Inc., www.klsummit.com

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Summit Technical Solutions, www.lubemanagement.com Sunnyside Corporation, www.sunnysidecorp.com Sunoco Inc., www.sunocoinc.com Sunohio, Division of ENSR, www.sunohio.com Superior Graphite Company, www.superiorgraphite.com/ sgc.nsf Superior Lubricants Company, Inc., www.superiorlubricants.com Superior Lubrication Products, www.s-l-p.com Surtec International Inc., www.surtecinternational.com Swiss Federal Laboratories for Materials Testing and Research (EMPA) Centre for Surface Technology and Tribology, www.empa.ch Synco Chemical Corporation, www.super-lube.com SynLube Inc., www.synlube.com Synthetic Lubricants Inc., www.synlube-mi.com Syntroleum Corporation, www.syntroleum.com

T.S. MoIy-Lubricants Inc., www.tsmoly.com T.W. Brown Oil Company, Inc, www.brownoil.com/ soypower.html Taber Industries, www.taberindustries.com TAI Lubricants, www.lubekits.com Tannas Company, www.savantgroup.com Tannis Company, www.savantgroup.com/tannas.sht TCC, www.technicalchemical.com Technical Chemical Company, www.technicalchemical.com Technical University of Delft, Netherlands Laboratory for Tribology, www.ocp.tudelft.nl/tribo/ Technical University, Munich, Germany, www.fzg.mw. tu-muenchen.de Technische Universitat Ilmenau, Faculty of Mathematics and Natural Sciences, www.physik.tu-ilmenau.de/ index_e.html Tek-5 Inc., www.tek-5.com Terrresolve Technologies, www.terresolve.com Test Engineering Inc., www.testeng.com Texaco Inc., www.texaco.com Texas Refinery Corporation, www.texasrefinery.com Texas Tech University, Tribology, www.osci.ttu.edu/ ME_Dept/Research/tribology.htmld/ Textile Chemical Company, Inc., www.textilechem.com Thailand, Petroleum Authority of, www.nectec.or.th/ users/htk/SciAm/12PTT.html Thailand, Petroleum Authority, www.nectec.or.th The Maintenance Council, www.trucking.org Thermal-Lube Inc., www.thermal-lube.com Thermo Elemental, www.thermoelemental.com Thomas Petroleum, www.thomaspetro.com Thornley Company, www.thornleycompany.com Thoughtventions Unlimited Home Page, www.tvu.com/ %7Ethought/ Tiodize Company, Inc., www.tiodize.com

Titan Laboratories, www.titanlab.com TMC, www.truckline.com Tokyo Institute of Technology, Japan Nakahara Lab. Home Page, www.mep.titech.ac.jp/Nakahara/home.html Tomah Products, Inc., www.tomah3.com Tom-Pac Inc., www.tom-pac.com Top Oil Products Company Ltd., www.topoil.com Torco International Corporation, www.torcoracingoils.com Tosco, www.tosco.com Total, www.total.com Total, www.totalfinaelf.com/ho/fr/index.htm Totalfina Oleo Chemicals, www.totalfina.com Tower Oil & Technology Company, www.toweroil.com Toyo Grease Manufacturing (M) SND BHD, www.toyogrease.com Toyota (Japan), www.toyota.co.jp Toyota (USA), www.toyota.com TransMontaigne, www.transmontaigne.com Transmountain Oil Company, www.transmountainoil.com TriboLogic Lubricants Inc., www.dynamaxx.com TriboLogic Lubricants Inc., www.tribologic.com Tribologist.com, www.wearcheck.com/sites.html Tribology Consultant, http://hometown.aol.com/ wearconsul/wear/wear.htm Tribology Group, www.msm.cam.ac.uk/tribo/tribol.htm Tribology International, www.elsevier.nl/inca/ publications/store/3/0/4/7/4/ Tribology Letters, www.kluweronline.com/issn/ 1023-8883 Tribology Research Review 1992-1994, www.me.ic.ac.uk/ department/review94/trib/tribreview.html Tribology Research Review 1995-1997, www.me.ic.ac.uk/ department/review97/trib/tribreview.html Tribology/Tech-Lube, www.tribology.com Tribos Technologies, www.tribostech.com Trico Manufacturing Corporation, www.tricomfg.com Tricon Specialty Lubricants, www.tristrat.com Trilla Steel Drum Corporation, www.trilla.com Trinity College, Dublin Tribology and Surface Engineering, www.mme.tcd.ie/Groups/Tribology/ Troy Corporation, www.troycorp.com Truklink (Truck fleet information), www.truklink.com Tsinghua University, China, State Key Laboratory of Tribology, www.pim.tsinghua.edu.cn/index_cn.html TTi’s Home Page, www.tti-us.com/ Turmo Lubrication Inc., www.lubecon.com TXS Lubricants Inc., www.txsinc.com U.S. Department of Energy (DOE), www.energy.gov U.S. Department of Transportation (DOT), www.dot.gov U.S. Energy Information Administration, www.eia.doe.gov U.S. Patent Office, www.uspto.gov U.S. Data Exchange, www.usde.com U.S. Industrial Lubricants Inc., www.usil.cc

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U.S. Oil Company, Inc., www.usoil.com UEC Fuels and Lubrication Laboratories, www.uec-usx.com Ultimate Lubes, www.ultimatelubes.com Ultra Additives, Inc., www.ultraadditives.com Ultrachem Inc., www.ultracheminc.com Unilube Systems Ltd., www.unilube.com Unimark Oil Company, www.gardcorp.com Union Carbide Corporation, www.unioncarbide.com Uniqema, www.uniqema.com Uniroyal Chemical Company Inc., www.uniroyalchemical.com UniSource Energy Inc., www.unisource-energy.com Unist, Inc., www.unist.com Unit Pack Company, Inc., www.unitpack.com United Color Manufacturing Inc., www.unitedcolor.com United Lubricants, www.unitedlubricants.com United Oil Company, Inc., www.duralene.com United Oil Products Ltd., http://ourworld. compuserve.com/homepages/Ferndale_UK United Soybean Board, www.unitedsoybean.org Universal Lubricants Inc., www.universallubes.com University of Akron Tribology Laboratory, www.ecgf. uakron.edu/∼mech University of Applied Sciences (FH-Hamburg), Germany Dept of Mech. Eng Tribology, www.fh-hamburg.de/fh/fb/m/tribologie/e_index.html University of Applied Sciences, Hamburg, Germany, www.haw-hamburg.de/fh/fb/m/tribologie/e_index.html University of California, Berkeley Bogey’s Tribology Group, http://cml.berkeley.edu/tribo.html University of California, San Diego Center for Magnetic Recording Research, http://orpheus.ucsd.edu/cmrr/ University of Florida, Mechanical Engineering Department, Tribology Laboratory, http://grove.ufl.edu/ ∼wgsawyer/ University of Illinois, Urbana-Champaign Tribology Laboratory, www.mie.uiuc.edu University of Kaiserslautern, Germany Sektion Tribologie, www.uni-kl.de/en/ University of Leeds, M.Sc. (Eng.) Course in Surface Engineering and Tribology, http://leva.leeds.ac.uk/ tribology/msc/tribmsc.html University of Leeds, UK Research in Tribology, http://leva.leeds.ac.uk/tribology/research.html University of Ljubljana, Faculty of Mechanical Engineering, Center for Tribology and Technical Diagnostics, www.ctd.uni-lj.si/eng/ctdeng.htm University of Maine Laboratory for Surface Science and Technology (LASST), www.ume.maine.edu/LASST/ University of Newcastle upon Tyne, UK Ceramics Tribology Research Group, www.ncl.ac.uk/materials/ materials/resgrps/certrib.html University of Northern Iowa, www.uni.edu/abil

University of Notre Dame Tribology/Manufacturing Laboratory, www.nd.edu/∼ame University of Pittsburg, School of Engineering, Mechanical Engineering Department, www.engrng.pitt.edu/∼mewww University of Sheffield, UK Tribology Research Group, http://www.shef.ac.uk/mecheng/tribology/ University of Southern Florida. Tribology, www.eng.usf.edu/∼hess/ University of Texas at Austin, Petroleum & Geosystems Engineering, Reading Room, www.pe.utexas.edu/Dept/ Reading/petroleum.html University of Tokyo, Japan, Mechanical Engineering Department, www.mech.t.u-tokyo.ac.jp/english/ index.html University of Twente, Netherlands Tribology Group, http://www.wb.utwente.nl/vakgroep/tr/tribeng.htm University of Western Australia Department of Mechanical and Material Engineering, http://www.mech.uwa.edu.au/tribology/ University of Western Ontario, Canada Tribology Research Centre, http://www.engga.uwo.ca/research/tribology/ Default.htm University of Windsor, Canada Tribology and Wear Research Group, http://zeus.uwindsor.ca/research/wtrg/ index.html University of Windsor, Canada, Tribology Research Group, http://venus.uwindsor.ca/research/wtrg/ index.html Unocal Corporation, www.unocal.com Uppsala University, Sweden Tribology Group, http://www.angstrom.uu.se/materials/index.htm U.S. Department of Agriculture (USDA), www.usda.gov U.S. Department of Energy (DOE), www.energy.gov U.S. Department of Defense (DOD), www.dod.gov USX Engineers & Consultants, www.uec.com/labs/ctns USX Engineers and Consultants: Laboratory Services, www.uec.com/labs/ Vacudyne Inc., www.vacudyne.com Valero Mktg. & Supply, www.valero.com Valhalla Chemical, www.valhallachem.com Valvoline Canada, www.valvoline.com Valvoline, www.valvoline.com Van Horn, Metz & Company, Inc., www.vanhornmetz.com Vauxhall, www.vauxhall.co.uk Vesco Oil Corporation, www.vesco-oil.com Victoria Group Inc., The, www.victoriagroup.com Viking Pump Inc., A Unit of IDEX Corporation, www.vikingpump.com Vikjay Industries Inc., www.vikjay.com Virtual Oil Inc., www.virtualoilinc.com Viswa Lab Corporation, www.viswalab.com Vogel Lubrication System of America, www.vogel-lube.com

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Volkswagen (Germany), www.vw-online.de Volkswagen (USA), www.vw.com Volvo (Sweden), www.volvo.se Volvo Cars of North America, www.volvocars.com Volvo Group, www.volvo.com Vortex International LLC, www.vortexfilter.com VP Racing Fuels Inc., www.vpracingfuels.com Vulcan Oil & Chemical Products Inc., www.vulcanoil.com Vulsay Industries Ltd., www.vulsay.com

Wallace, www.wallace.com Wallover Oil Company, www.walloveroil.com Walthall Oil Company, www.walthall-oil.com Warren Distribution, www.wd-wpp.com Waugh Controls Corporation, www.waughcontrols.com WD-40 Company, www.wd40.com Wear Chat: WearCheck Newsletter, www.wearcheck.com/publications.html Wear, www.elsevier.nl/inca/publications/ store/5/0/4/1/0/7/ Wearcheck International, www.wearcheck.com/ Web-Valu Intl.www.webvalu.com Wedeven Associates, Inc., http://members.aol.com/ wedeven/ West Central Soy, www.soypower.net West Penn Oil Company, Inc., www.westpenn.com Western Michigan University Tribology Laboratory, www.mae.wmich.edu/labs/Tribology/Tribology.html Western Michigan University, Department of Mechanical and Aeeronautical Engineering, www.mae.wmich.edu/ Western States Oil, www.lubeoil.com Western States Petroleum Association, www.wspa.org Whitaker Oil Company, Inc., www.whitakeroil.com Whitmore Manufacturing Company, www.whitmores.com Whitmore Manufacturing Company, The, www.whitmore.com Wilcox and FIegel Oil Company, www.wilcoxandflegel.com Wilks Enterprise Inc., www.wilksir.com Winfield Brooks Company, Inc., www.tapfree.com Winzer Corp., www.winzerusa.com Witco (Crompton Corporation), www.witco.com Wolf Lake Terminals Inc., www.wolflakeinc.com Worcester Polytechnic Institute, Department of Mechanical Engineering, www.me.wpi.edu/Research/ labs.html World Tribologists Database, http://greenfield. fortunecity.com/fish/182/tribologists.htm Worldwide PetroMoly, Inc., www.petromoly.com WSI Chemical Inc., www.wsi-chem-sys.com WWW Tribology Information Service, www.shef.ac.uk/ ∼mpe/tribology/

WWW Virtual Library: Mechanical Engineering, www.vlme.com/ Wynn Oil Company, www.wynnsusa.com X-1R Corporation, The, www.x1r.com Yahoo Lubricants, http://dir.yahoo.com/business_ and_economy/shopping_and_services/automotive/ supplies/lubricants/ Yahoo Tribology, http://ca.yahoo.com/Science/ Engineering/Mechanical_Engineering/Tribology/ Yocum Oil Company, Inc., www.yocumoil.com YPF (Argentina), www.ypf.com.ar Yuma Industries Inc., www.yumaind.com Zimmark Inc., www.zimmark.com Zinc Corporation of America, www.zinccorp.com

51.2 INTERNET LISTINGS BY CATEGORY 51.2.1 Lubricant Fluids (Base Oils, Greases, Biodegradable, Synthetics, Packaged Oils, and Solid Lubricants) 2V Industries Inc., www.2vindustries.com 49 North, www.49northlubricants.com 76 Lubricants Company, www.tosco.com A/R Packaging Corporation, www.arpackaging.com Acculube, www.acculube.com Accurate Lubricants & Metalworking Fluids Inc. (dba Acculube), www.acculube.com Acheson Colloids Company, www.achesonindustries.com Acme Refining, Division of Mar-Mor Inc., www.acmerefining.com Acme-Hardesty Company, www.acme-hardesty.com Advanced Ceramics Corporation, www.advceramics.com Advanced Lubrication Specialties Inc., www.advancedlubes.com/ Aerospace Lubricants Inc., www.aerospacelubricants.com African Lubricants Industry, www.mbendi.co.za/aflu.htm AG Fluiropolymers USA Inc., www.fluoropolymers.com Airosol Company Inc., www.airosol.com Akzo Nobel, www.akzonobel.com Alco-Metalube Co., www.alco-metalube.com Alithicon Lubricants, Div: Southeast Oil & Grease Co. Inc., www.alithicon.com Allegheny Petroleum Products Company, www.oils.com Allen Oil Company, www.allenoil.com Allied Oil & Supply Inc., www.allied-oil.com Allied Washoe, www.alliedwashoe.com Alpha Grease & Oil Inc., www.alphagrease. thomasregister.com/olc/alphagrease/

Copyright 2006 by Taylor & Francis Group, LLC

ALT Inc., www.altboron.com Amalie Oil Company, www.amalie.com Amber Division of Nidera, Inc., www.nidera-us.com Amcar Inc., www.amcarinc.com Amerada Hess Corporation, www.hess.com American Agip Company Inc., www.americanagip.com American Eagle Technologies Inc., www.frictionrelief.com American Lubricants Inc., www.americanlubricantsbflo.com American Lubricating Company, www.alcooil.com American Oil & Supply Company, www.aosco.com American Petroleum Products, www.americanpetroleum.com American Refining Group Inc., www.amref.com American Synthol Inc., www.americansynthol.com Amptron Corporation, www.superslipperystuff.com/ organisation.htm Amrep Inc., www.amrep.com AMSOIL Inc., www.amsoil.com Anderol Specialty Lubricants, www.anderol.com Anti Wear 1, www.dynamicdevelopment.com Apollo America Corporation, www.apolloamerica.com Aral International, www.Aral.com Arch Chemicals, Inc., www.archbiocides.com ARCO, www.arco.com Arizona Chemical, www.arizonachemical.com Asbury Carbons, Inc.—Dixon Lubricants, www.asbury.com Asbury Carbons, Inc.—Dixon Lubricants, www.dixonlube.com Asbury Graphite Mills Inc., www.asbury.com Asheville Oil Company Inc., www.ashevilleoil.com Ashia Denka, www.adk.co.jp/eng.htm Ashland Chemical, www.ashchem.com Ashland Distribution Company, www.ashland.com Aspen Chemical Company, www.aspenchemical.com Associated Petroleum products, www.associatedpetroleum.com Atlantis International Inc., www.atlantis-usa.com Atlas Oil Company, www.atlasoil.com ATOFINA Canada Inc., www.atofinacanada.com Ausimont, www.ausiusa.com Avatar Corporation, www.avatarcorp.com

Badger Lubrication Technologies Inc., www.badgerlubrication.com BALLISTOL USA, www.ballistol.com Battenfeld Grease and Oil Corporation of New York, www.battenfeld-grease.com Behnke Lubricants/JAX, www.jaxusa.com Behnke Lubricants Inc./JAX, www.jax.com Bell Additives Inc., www.belladditives.com Bel-Ray Company Inc., www.belray.com

Benz Oil Inc., www.benz.com Berry Hinckley Industries, www.berry-hinckley.com Bestolife Corporation, www.bestolife.com BG Products Inc., www.bgprod.com Big East Lubricants Inc., www.bigeastlubricants.com Blaser Swisslube, www.blaser.com Bodie-Hoover Petroleum Corp., www.bodie-hoover.com Boehme Filatex Inc., www.boehmefilatex.com BoMac Lubricant Technologies Inc., www.bomaclubetech.com Boncosky Oil Company, www.boncosky.com Boswell Oil Company, www.boswelloil.com BP Amoco Chemicals, www.bpamocochemicals.com BP Lubricants, www.bplubricants.com BP, www.bptechchoice.com BP, www.bppetrochemicals.com Brascorp North America Ltd., www.brascorp.on.ca Brenntag Northeast, Inc., www.brenntag.com/ Brenntag, www.brenntag.com Briner Oil Company, www.brineroil.com British Petroleum (BP), www.bp.com Britsch Inc., www.britschoil.com Brugarolas SA, www.brugarolas.com/english.htm Buckley Oil Company, www.buckleyoil.com BVA Oils, www.bvaoils.com

Callahan Chemical Company, www.calchem.com Caltex Petroleum Corporation, www.caltex.com Calumet Lubricants Company, www.calumetlub.com Calvary Industries Inc., www.calvaryindustries.com CAM2 Oil Products Company, www.cam2.com Canner Associates, Inc., www.canner.com Capital Enterprises (Power-Up Lubricants), www.NNL690.com Cargill- Industrial Oil & Lubricants, www.techoils.cargill.com Cary Company, www.thecarycompany.com CasChem, Inc., www.cambrex.com Castle Products Inc., www.castle-comply.com Castrol Heavy Duty Lubricants, Inc., www.castrolhdl.com Castrol Industrial North America Inc., www.castrolindustrialna.com Castrol International, www.castrol.com Castrol North America, www.castrolusa.com CAT Products Inc., www.run-rite.com Centurion Lubricants, www.centurionlubes.com Champion Brands LLC, www.championbrands.com Charles Manufacturing Company, www.tsmoly.com Chart Automotive Group Inc., www.chartauto.com Chem-EcoI Ltd., www.chem-ecol.com Chemlube International Inc., www.chemlube.com Chempet Corporation, www.rockvalleyoil.com/ chempet.htm Chemsearch Lubricants, www.chemsearch.com

Copyright 2006 by Taylor & Francis Group, LLC

Chemtool Inc./Metalcote, www.chemtool.com Chevron Chemical Company, www.chevron.com Chevron Oronite, www.chevron.com Chevron Phillips Chemical Company LP, www.cpchem.com Chevron Phillips Chemical Company, www.chevron.com Chevron Products Company, Lubricants & Specialties Products, www.chevron.com/lubricants Chevron Products Company, www.chevron.com Christenson Oil, www.christensonoil.com Ciba Specialty Chemicals Corporation, www.cibasc.com Clariant Corporation, www.clariant.com Clark Refining and Marketing, www.clarkusa.com Clarkson & Ford Company, www.clarkson-ford.com CLC Lubricants Company, www.clclubricants.com Climax Molybdenum Company, www.climaxmolybdenum.com Coastal Unilube Inc., www.coastalunilube.com Cognis, www.cognislubechem.com Cognis, www.cognis-us.com Cognis, www.cognis.com Cognis, www.na.cognis.com Colorado Petroleum Products Company, www.colopetro.com Commercial Lubricants Inc., www.comlube.com Commercial Oil Company, Inc., www.commercialoilcompany.com Commercial Ullman Lubricants Company, www.culc.com Commonwealth Oil Corporation, swww.commonwealthoil.com Como Lube & Supplies Inc., www.comolube.com Condat Corporation, www.condatcorp.com Conklin Company Inc., www.cnklino.com Coolants Plus Inc., www.coolantsplus.com Cortec Corporation, www.cortecvci.com Cosby Oil Company, www.cosbyoil.com Country Energy, www.countryenergy.com CPI Engineering Services, www.cpieng.com CRC Industries, Inc., www.crcindustries.com Crescent Manufacturing, www.crescentmfg.net Crompton Petroleum Additives Corporation, www.cromptoncorp.com Crown Chemical Corporation, www.brenntag.com Cyclo Industries LLC, www.cyclo.com

D & D Oil Company, Inc., www.amref.com D. A. Stuart Company, www.d-a-stuart.com D. W. Davies & Company, Inc., www.dwdavies.com D-A Lubricant Company, www.dalube.com Darmex Corporation, www.darmex.com Darsey Oil Company Inc., www.darseyoil.com David Weber Oil Company, www.weberoil.com Davison Oil Company, Inc., www.davisonoil.com Dayco Inc., www.dayco.com

DB Becker Co. Inc., www.dbbecker.com Degen Oil and Chemical Company, www.eclipse.net/∼degen Delkol, www.delkol.co.il Dennis Petroleum Company, Inc., www.dennispetroleum.com Diamond Head Petroleum Inc., www.diamondheadpetroleum.com Diamond Shamrock Refining Company LP, www.udscorp.com Digilube Systems Inc., www.digilube.com Dion & Sons Inc., www.dionandsons.com Dixon Lubricants & Special Products Group, Div. of Asbury Carbons, www.dixonlube.com Don Weese Inc., www.schaefferoil.com Dow Chemical Company, www.dow.com Dow Corning Corp., www.dowcorning.com Dryden Oil Company, Inc., www.castrol.com Dryson Oil Company, www.synergynracing.com DSI Fluids, www.dsifluids.com Dumas Oil Company, www.esn.net/dumasoil DuPont Krytox Lubricants, www.lubricants.dupont.com DuPont, www.dupont.com/intermediates

E.I. DuPont de Nemours and Company, www.dupont.com/ intermediates Eastech Chemical Inc., www.eastechchemical.com Eastern Oil Company, www.easternoil.com Ecotech Div., Blaster Chemical Companies, www.pbblaster.com EKO, www.eko.gr El Paso Corporation, www.elpaso.com Elf Lubricants North America Inc., www.keystonelubricants.com Eljay Oil Company, Inc., www.eljayoil.com ELM Environmental Lubricants Manufacturing Company, www.elmusa.com EMERA Fuels Company Inc., www.emerafuels.com Emerson Oil Company, Inc.www.emersonoil.com Engen Petroleum Ltd., www.engen.co.za Enichem Americas, Inc., www.eni.it/english/mondo/ americhe/usa.html Environmental Lubricants Manufacturing, Inc. (ELM), www.elmusa.com Equilon Enterprises LLC, www.equilon.com Equilon Enterprises LLC-Lubricants, www.equilonmotivaequiva.com Equilon Enterprises LLC-Lubricants, www.shellus.com Equilon Enterprises LLC-Lubricants, www.texaco.com Esco Products Inc., www.escopro.com ETNA Products Inc., www.etna.com Etna-Bechem Lubricants Ltd., www.etna.com Evergreen Oil, www.evergreenoil.com Exxon, www.exxon.com

Copyright 2006 by Taylor & Francis Group, LLC

ExxonMobil Chemical Company, www.exxonmobilchemical.com ExxonMobil Lubricants & Petroleum Specialties Company, www.exxonmobil.com F&R Oil Company, Inc., www.froil.com F. Bacon Industriel Inc., www.f-bacon.com FAMM (Fuel and Marine Marketing), www.fammllc.com Far West Oil Company Inc., www.farwestoil.com Fina Oil and Chemical Company, www.fina.com Findett Corp., www.findett.com Finish Line Technologies Inc., www.finishlineusa.com FINKE Mineralolwerk, www.finke-mineraloel.de Finnish Oil and Gas Federation, www.oil.fi Flamingo Oil Company, www.pinkbird.com Forward Corporation, www.forwardcorp.com Frontier Performance Lubricants Inc., www.frontierlubricants.com Fuchs Lubricants Company, www.fuchs.com Fuchs, www.fuchs-oil.de Fuki America Corporation, www.fukiamerica.com G-C Lubricants Company, www.gclube.com G & G Oil Co. of Indiana Inc., www.ggoil.com G.T. Autochemilube Ltd., www.gta-oil.co.uk Gard Corp., www.gardcorp.com Geo. Pfau’s Sons Company, Inc., www.pfauoil.com Georgia-Pacific Pine Chemicals, www.gapac.com Glover Oil Company, www.gloversales.com GOA Company., www.goanorthcoastoil.com Gold Eagle Company, www.goldeagle.com Golden Bear Oil Specialties, www.goldenbearoil.com Golden Gate Petroleum, www.ggpetrol.com Goldenwest Lubricants, www.goldenwestlubricants.com Goldschmidt Chemical Corporation, www.goldschmidt.com Goulston Technologies, Inc., www.goulston.com Great Lakes Chemical Corporation, www.glcc.com Granitize Products Inc., www.granitize.com Greenland Corporation, www.greenpluslubes.com Grignard Company LLC, www.purelube.com Groeneveld Pacific West, www.groeneveldpacificwest.com Gulf Oil, www.gulfoil.com H & W Petroleum Company, Inc., www.hwpetro.com H.L. Blachford Ltd., www.blachford.ca H.N. Funkhouser & Company, www.hnfunkhouser.com Halocarbon Products Corporation, www.halocarbon.com Halron Oil Company, Inc., www.halron.com Hampel Oil Distributors, www.hampeloil.com Hangsterfer’s Laboratories Inc., www.hangsterfers.com Harry Miller Corp., www.harrymillercorp.com Hasco Oil Co. Inc., www.hascooil.com

Hatco Corporation, www.hatcocorporation.com Haynes Manufacturing Company, www.haynesmfg.com HCI/Worth Chemical Corp., www.hollandchemical.com Henkel Surface Technologies, www.henkel.com Henkel Surface Technologies, www.thomasregister.com/ henkelsurftech Hexol Canada Ltd., www.hexol.com Hexol Lubricants, www.hexol.com Holland Applied Technologies, www.hollandapt.com Hoosier Penn Oil Company, www.hpoil.com Houghton International Inc., www.houghtonintl.com Howes Lubricator, www.howeslube.thomasregister.com Huls America, www.CreanovaInc.com/ Huls America, www.huls.com Huskey Specialty Lubricants, www.huskey.com Hydrosol Inc., www.hydrosol.com Hydrotex Inc., www.hydrotexlube.com/ Hy-Per Lube Corporation, www.hyperlube.com I.S.E.L. Inc., www.americansynthol.com ILC/Spectro Oils of America, www.spectro-oils.com Illinois Oil Products, Inc., www.illinoisoilproducts.com Imperial Oil Company, Inc., www.imperialoil.com Imperial Oil Ltd., www.imperialoil.ca Imperial Oil Products and Chemicals Division, www.imperialoil.ca Ingenieria Sales SA de CV, www.isalub.com Innovene, www.innovene.com Inolex Chemical Company, www.inolex.com International Lubricants Inc., www.lubegard.com International Products Corporation, www.ipcol.com IQA Lube Corporation, www.iqalube.com Irving Oil Corp, www.irvingoil.com ITW Fluid Products Group, www.itwfpg.com J & H Oil Company, www.jhoil.com J & S Chemical Corporation, www.jschemical.com J.A.M.Distributing, www.jamdistributing.com J.B. Chemical Company, Inc., www.jbchemical.com J.B. Dewar Inc., www.jbdewar.com J.D. Streett & Company, Inc., www.jdstreett.com J.N. Abbott Distributor Inc., www.jnabbottdist.com Jack Rich Inc., www.jackrich.com Jarchem Industries Inc., www.jarchem.com Jasper Engineering & Equipment, www.jaspereng.com JAX-Behnke Lubricants Inc., www.jax.com Jenkin-Guerin Inc., www.jenkin-guerin.com Jet-Lube (UK) Ltd., www.jetlube.com Johnson Packings & Industrial Products Inc., www.johnsonpackings.com Kath Fuel Oil Service, www.kathfuel.com Keck Oil Company, www.keckoil.com Kelsan Lubricants USA LLC, www.kelsan.com

Copyright 2006 by Taylor & Francis Group, LLC

Kem-A-Trix Specialty Lubricants & Compounds, www.kematrix.com Kendall Motor Oil, www.kendallmotoroil.com Kluber Lubrication North America LP, www.kluber.com KOST Group Inc., www.kostusa.com Kyodo Yushi USA Inc., www.kyodoyushi.co.jp Lambent Technologies, www.petroferm.com LaPorte, www.laporteplc.com Leander Lubricants, www.leanderlube.com Lee Helms Inc., www.leehelms.com Leffert Oil Company, www.leffertoil.com Les Industries Sinto Racing Inc., www.sintoracing.com Lilyblad Petroleum, Inc., www.lilyblad.com Liqua-Tek Inc., www.hdpluslubricants.com Liquid Horsepower, www.holeshot.com/chemicals/ additives.html LithChem International, www.lithchem.com Loos & Dilworth Inc.-Automotive Division, www.loosanddilworth.com Loos & Dilworth Inc.-Chemical Division, www.loosanddilworth.com Lowe Oil Company./Champion Brands LLC, www.championbrands.com LPS Laboratories, www.lpslabs.com LubeCon Systems Inc., www.lubecon.com Lubemaster Corporation, www.lubemaster.com LubeRos — A Division of Burlington Chemical Company, Inc., www.luberos.com LuBest, Division of Momar Inc., www.momar.com Lubricant Technologies, www.lubricanttechnologies.com Lubricants USA, www.finalube.com Lubrication Engineers Inc., www.le-inc.com Lubrication Engineers of Canada, www.lubeng.com Lubrication Technologies Inc., www.lube-tech.com Lubrication Technology Inc., www.lubricationtechnology.com Lubrichem International Corporation, www.lubrichem.net Lubrifiants Distac Inc., www.inspection.gc.ca/english/ ppc/reference/n2e.shtml Lubri-Lab Inc., www.lubrilab.com LUBRIPLATE Div., Fiske Bros. Refining Company, www.lubriplate.com Lubritec, www.ensenada.net/lubritec/ Lucas Oil Products Inc., www.lucasoil.com Lyondell Lubricants, www.lyondelllubricants.com MagChem Inc., www.magchem.com Magnalube, www.magnalube.com Maine Lubrication Service Inc., www.mainelube.com Manor Trade Development Corporation, www.amref.com Mantek Lubricants, www.mantek.com Markee International Corporation, www.markee.com Marly, www.marly.com

Maryn International Ltd., www.maryngroup.com Maryn International, www.poweruplubricants.com Master Chemical Corporation, www.masterchemical.com Master Lubricants Company, www.lubriko.com Maxco Lubricants Company, www.maxcolubricants.com Maxim Industrial Metalworking Lubricants, www.maximoil.com Maxima Racing Lubricants, www.maximausa.com McCollister & Company, www.mccollister.com McGean-Rohco Inc., www.mcgean-rohco.com McGee Industries Inc., www.888teammclube.com McLube Divisionl/McGee Industries Inc., www.888teammclube.com Mega Power Inc., www.megapowerinc.com Metal Forming Lubricants Inc., www.mflbeu.com Metal Mates Inc., www.metalmates.net Metalcote/Chemtool Inc., www.metalcote.com Metalworking Lubricants Company, www.metalworkinglubricants.com Metalworking Lubricants, www.maximoil.com MFA Oil Company, www.mfaoil.com Mid-South Sales Inc., www.mid-southsales.com Mid-Town Petroleum Inc., www.midtownoil.com Milacron Consumable Products Division, www.milacron.com Millennium Lubricants, www.millenniumlubricants.com Miller Oil of Indiana, Inc., www.milleroilinc.com Mohawk Lubricants Ltd., www.mohawklubes.com Molyduval, www.molyduval.com Molyslip Atlantic Ltd., www.molyslip.co.uk Monroe Fluid Technology Inc., www.monroefluid.com Moore Oil Company, www.mooreoil.com Moraine Packaging Inc., www.hdpluslubricants.com Morey’s Oil Products Company, www.moreysonline.com Moroil Technologies, www.moroil.com Motiva Enterprises LLC, www.motivaenterprises.com Motorol Lubricants, www.motorolgroup.com Motul USA Inc., www.motul.com Mr. Good Chem, Inc., www.mrgoodchem.com Muscle Products Corporation, www.mpc-home.com NCH, www.nc.com Neo Synthetic Oil Company, Inc., www.neosyntheticoil.com Niagara Lubricant Company, Inc., www.niagaralubricant.com NOCO Energy Corporation, www.noco.com Noco Lubricants, www.noco.com Nyco SA, www.nyco.fr Nye Lubricants, www.nyelubricants.com Nynas Naphthenics, www.nynas.com O’Rourke Petroleum, www.orpp.com Oakite Products, Inc., www.oakite.com

Copyright 2006 by Taylor & Francis Group, LLC

OATS (Oil Advisory Technical Services), www.oats.co.uk Occidental Chemical Corporation, www.oxychem.com Ocean State Oil Inc., www.oceanstateoil.com Oil Center Research Inc., www.oilcenter.com Oil Center Research International LLC, www.oilcenter.com Oil Depot, www.oildepot.com Oil Distributing Company, www.oildistributing.com Oil-Chem Research Corporation, www.avblend.com Oilkey Corporation, www.oilkey.com Oilpure Technologies Inc., www.oilpure.com OKS Speciality Lubricants, www.oks-india.com Omega Specialties, www.omegachemicalsinc.com Omni Specialty Packaging, www.nuvo.cc OMO Petroleum Company Inc., www.omoenergy.com Orelube Corp., www.orelube.com Oronite, www.oronite.com O’Rourke Petroleum Products, www.orpp.com Ottsen Oil Company, Inc., www.ottsen.com

Paramount Products, www.paramountproducts.com Parent Petroleum, www.parentpetroleum.com PATCO Additives Division-American Ingredients Company, www.patco-additives.com Pathfinder Lubricants, www.pathfinderlubricants.ca/ PBM Services Company, www.pbmsc.com Pedroni Fuel Company, www.pedronifuel.com Pennine Lubricants, www.penninelubricants.co.uk Pennzoil Industrial Lubricants, www.pennzoil.com/ prdsmktg/products/industrial/default.htm Pennzoil, www.pennzoil.com Pennzoil-Quaker State Company, www.pennzoil-quakerstate.com PENRECO, www.penreco.com Penta Manufacturing Company/Division of Penta International Corporation, www.pentamfg.com Performance Lubricants & Race Fuels Inc., www.perforanceracefuelsm.com Perkins Products Inc., www.perkinsproducts.com Petro Star Lubricants, www.petrostar.com PetroBlend Corporation, www.petroblend.com Petro-Canada Lubricants, www.htlubricants.com Petroleum Packers Inc., www.pepac.com PetroMoly, Inc., www.petromoly.com Petron Corp., www.petroncorp.com Pfaus Sons Company Inc., www.pfauoil.com Pflaumer Brothers Inc., www.pflaumer.com Phoenix Petroleum Company, www.phoenixpetroleum.com Pico Chemical Corporation, www.picochemical.com Pinnacle Oil Inc., www.pinnoil.com Pitt Penn Oil Company, www.pittpenn.com Plews/Edelmann Div., Stant Corp., www.stant.com PoIySi Technologies Inc., www.polysi.com

Polar Company, www.polarcompanies.com PolimeriEuropa, www.polimerieuropa.com PolySi Technologies, www.polysi.com Power Chemical, www.warcopro.com Power-Up Lubricants, www.mayngroup.com Precision Fluids Inc., www.precisionfluids.com Precision Industries, www.precisionind.com Precision Lubricants Inc., www.precisionlubricants.com Prime Materials, www.primematerials.com Primrose Oil Company Inc., www.primrose.com Probex Corporation, www.prob.com Products Development Manufacturing Company, www.veloil.com ProLab TechnoLub Inc., www.prolab-technologies.com ProLab-Bio Inc., www.prolab-lub.com Prolong Super Lubricants, www.prolong.com ProTec International Inc., www.proteclubricants.com Pure Power Lubricants, www.gopurepower.com QMI, www.qminet.com Quaker Chemical Corporation, www.quakerchem.com Quaker State, www.qlube.com R.E. Carroll Inc., www.recarroll.com Radio Oil Company Inc., www.radiooil.com Ramos Oil Company, Inc., www.ramosoil.com Rams-Head Company, www.doall.com Ransome CAT, www.ransome.com Red Giant Oil Company, www.rediantoilg.com Red Line Oil, www.redlineoil.com Reed Oil Company, www.reedoil.com Reit Lubricants Company, www.reitlube.com Reitway Enterprises Inc., www.reitway.com Renewable Lubricants, Inc., www.renewablelube.com Renite Company, www.renite.com Renite Company-Lubrication Engineers, www.renite.com Renkert Oil, www.renkertoil.com Rensberger Oil Company, Inc., www.rensbergeroil.com RichardsApex Inc., www.richardsapex.com Riley Oil Company, www.rileyoil.com RO-59 Inc., http://members.aol.com/ro59inc Rock Valley Oil & Chemical Company, www.rockvalleyoil.com Rocol Ltd., www.rocol.com Rowleys Wholesale, www.rowleys.com Royal Lubricants Inc., www.royallube.com Royal Manufacturing Company Inc., www.royalube.com Royal Purple, Inc., www.royalpurple.com RyDol Products, www.rydol.com

Safety-Kleen Oil Recovery, www.ac-rerefined.com Sandstrom Products Company, www.sandstromproducts.com

Copyright 2006 by Taylor & Francis Group, LLC

Santie Oil Company, www.santiemidwest.com Santotrac Traction Lubricants, www.santotrac.com Santovac Fluids Inc., www.santovac.com Saxton Industries Inc., www.saxton.thomasregister.com Saxton Industries Inc., www.schaefferoil.com Schaeffer Manufacturing, www.schaefferoil.com Schaeffer Oil and Grease, www.schaefferoil.com Schaeffer Specialized Lubricants, www.schaefferoil.com Selco Synthetic Lubricants, www.synthetic-lubes.com Sentry Solutions Ltd., www.sentrysolutions.com Service Supply Lubricants LLC, www.servicelubricants.com SFR Corporation, www.sfrcorp.com Share Corporation, www.sharecorp.com Shell Global Solutions, www.shellglobalsolutions.com Shell Lubricants (USA), www.shell-lubricants.com Shrieve Chemical Company, www.shrieve.com Simons Petroleum Inc., www.simonspetroleum.com SK Corporation (Houston Office) www.skcorp.com Slick 50 Corporation, www.slick50.com Smooth Move Company, www.theprojectsthatsave.com Sobit International, Inc., www.sobitinc.com Soltex, www.soltexinc.com Sourdough Fuel, www.petrostar.com Southwest Grease Products, www.stant.com/ brochure.cfm?brochure=155&location_id=119 Southwestern Graphite, www.asbury.com Southwestern Petroleum Corporation, www.swepcousa.com Spartan Chemical Company Inc. Industrial Products Group Division, www.spartanchemical.com Spartan Oil Company, www.spartanonline.com Specialty Silicone Products Inc., www.sspinc.com Spectro Oils of America, www.goldenspectro.com Spectro Oils of America, www.spectro-oils.com Spectrum Corporation, www.spectrumcorporation.com Spencer Oil Company, www.spenceroil.com St. Lawrence Chemicals, www.stlawrencechem.com Steelco Industrial Lubricants Inc., www.steelcolubricants.com Steelco Northwest Distributors, www.steelcolubricants.com STP Products Inc., www.stp.com Suburban Oil Company, Inc., www.suburbanoil.com Summit Industrial Products, Inc., www.klsummit.com Sunnyside Corporation, www.sunnysidecorp.com Superior Graphite Company, www.superiorgraphite.com/sgc.nsf Superior Lubricants Company, Inc., www.superiorlubricants.com Superior Lubrication Products, www.s-l-p.com Surtec International Inc., www.surtecinternational.com Synco Chemical Corporation, www.super-lube.com SynLube Inc., www.synlube.com

Synthetic Lubricants Inc., www.synlube-mi.com Syntroleum Corporation, www.syntroleum.com T.S. MoIy-Lubricants Inc., www.tsmoly.com T.W. Brown Oil Company, Inc, www.brownoil.com/ soypower.html TAI Lubricants, www.lubekits.com TCC, www.technicalchemical.com Technical Chemical Company, www.technicalchemical.com Tek-5 Inc., www.tek-5.com Terrresolve Technologies, www.terresolve.com Texas Refinery Corporation, www.texasrefinery.com Textile Chemical Company, Inc., www.textilechem.com Thermal-Lube Inc., www.thermal-lube.com Thornley Company, www.thonleycompanyr.com Tiodize Co. Inc., www.tiodize.com Tom-Pac Inc., www.tom-pac.com Top Oil Products Company, Ltd., www.topoil.com Torco International Corporation, www.torcoracingoils.com Totalfina Oleo Chemicals, www.totalfina.com Tower Oil & Technology Company, www.toweroil.com Toyo Grease Manufacturing (M) SND BHD, www.toyogrease.com TransMontaigne, www.transmontaigne.com Transmountain Oil Company, www.transmountainoil.com TriboLogic Lubricants Inc., www.dynamaxx.com TriboLogic Lubricants Inc., www.tribologic.com Tribos Technologies, www.tribostech.com Trico Manufacturing Corporation, www.tricomfg.com Tricon Specialty Lubricants, www.tristrat.com Turmo Lubrication Inc., www.lubecon.com TXS Lubricants Inc., www.txsinc.com U.S. Industrial Lubricants Inc., www.usil.cc U.S. Oil Company, Inc., www.usoil.com Ultrachem Inc., www.ultracheminc.com Unimark Oil Company, www.gardcorp.com Union Carbide Corporation, www.unioncarbide.com Uniqema, www.uniqema.com Uniroyal Chemical Company Inc., www.uniroyalchemical.com UniSource Energy Inc., www.unisource-energy.com Unist, Inc., www.unist.com United Lubricants, www.unitedlubricants.com United Oil Company, Inc., www.duralene.com United Oil Products Ltd., http://ourworld. compuserve.com/homepages/Ferndale_UK United Soybean Board, www.unitedsoybean.org Universal Lubricants Inc., www.universallubes.com Unocal Corporation, www.unocal.com Valero Mktg. & Supply, www.valero.com Valvoline Canada, www.valvoline.com

Copyright 2006 by Taylor & Francis Group, LLC

Valvoline, www.valvoline.com Vesco Oil Corporation, www.vesco-oil.com Vikjay Industries Inc., www.vikjay.com Virtual Oil Inc., www.virtualoilinc.com Vogel Lubrication System of America, www.vogel-lube.com VP Racing Fuels Inc., www.vpracingfuels.com Vulcan Oil & Chemical Products Inc., www.vulcanoil.com Wallover Oil Company, www.walloveroil.com Walthall Oil Company, www.walthall-oil.com Warren Distribution, www.wd-wpp.com WD-40 Company, www.wd40.com West Central Soy, www.soypower.net Western States Oil, www.lubeoil.com Whitaker Oil Company, Inc., www.whitakeroil.com Whitmore Manufacturing Company, www.whitmores.com Wilcox and FIegel Oil Company, www.wilcoxandflegel.com Winfield Brooks Company, Inc., www.tapfree.com Winzer Corporation, www.winzerusa.com Witco (Crompton Corporation), www.witco.com Wolf Lake Terminals Inc., www.wolflakeinc.com Worldwide PetroMoly, Inc., www.petromoly.com Wynn Oil Company, www.wynnsusa.com X-1R Corp., The, www.x1r.com Yocum Oil Company, Inc., www.yocumoil.com Yuma Industries Inc., www.yumaind.com

51.2.2 Additives Acheson Colloids Company, www.achesonindustries.com Acme-Hardesty Company, www.acme-hardesty.com Advanced Lubrication Technology Inc (ALT), www.altboron.com AFD Technologies, www.afdt.com AG Fluoropolymers USA Inc., www.fluoropolymers.com Akzo Nobel, www.akzonobel.com Amalie Oil Company, www.amalie.com Amber Division of Nidera, Inc., www.nidera-us.com American International Chemical, www.aicma.com/ Amitech, www.amitech-usa.com ANGUS Chemical Company, www.dowchemical.com Anti Wear 1 www.dynamicdevelopment.com Arch Chemicals, Inc., www.archbiocides.com Arizona Chemical, www.arizonachemical.com Asbury Carbons, Inc.—Dixon Lubricants, www.asbury.com Asbury Carbons, Inc.—Dixon Lubricants, www.dixonlube.com Ashland Distribution Company, www.ashland.com Aspen Chemical Company, www.aspenchemical.com

ATOFINA Chemicals, Inc., www.atofina.com ATOFINA Canada Inc., www.atofinacanada.com

Baker Petrolite, www.bakerhughes.com/bakerpetrolite/ Bardahl Manufacturing Corporation, www.bardahl.com BASF Corporation, www.basf.com Bayer Corporation, www.bayer.com Bismuth Institute, www.bismuth.be BoMac Lubricant Technologies Inc., www.bomaclubetech.com BP, www.bp.com BP Amoco Chemicals, www.bpamocochemicals.com Brascorp North America Ltd., www.brascorp.on.ca Brascorp North America Ltd., www.brascorp.on.ca British Petroleum (BP), www.bp.com Buckman Laboratories Inc., www.buckman.com Burlington Chemical, www.burco.com Cabot Corporation, (fumed metal oxides), www.cabot-corp.com/cabosil Callahan Chemical Company, www.calchem.com Calumet Lubricants Company, www.calumetlub.com Cargill-Industrial Oil & Lubricants, www.techoils. cargill.com Cary Company, www.thecarycompany.com CasChem, Inc., www.cambrex.com Center for Innovation Inc., www.centerforinnovation.com Certified Laboratories, www.certifiedlaboratories.com Chattem Chemicals, Inc., www.chattemchemicals.com Chemetall Foote Corporation, www.chemetall.com/ Chemsearch Lubricants, www.chemsearch.com Chevron Oronite, www.chevron.com Ciba Specialty Chemicals Corporation, www.cibasc.com Clariant Corp., www.clariant.com Climax Molybdenum Company, www.climaxmolybdenum.com Cognis, www.cognislubechem.com Cognis, www.cognis-us.com Cognis, www.cognis.com Cognis, www.na.cognis.com Commonwealth Oil Corporation, www.commonwealthoil.com Cortec Corporation, www.cortecvci.com Creanova, Inc., www.creanovainc.com/ Croda Inc., www.croda.com Crompton Petroleum Additives Corporation, www.cromptoncorp.com Crowley Chemical Company Inc., www.crowleychemical.com Crown Chemical Corporation, www.brenntag.com Crystal Inc.-PMC, www.pmc-group.com Cummings-Moore Graphite Company, www.cumograph.com

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D.A. Stuart Company, www.d-a-stuart.com D.B. Becker Company, Inc., www.dbbecker.com DeForest Enterprises Inc., www.deforest.net Degen Oil and Chemical Company, www.eclipse. net/∼degen Dover Chemical, www.doverchem.com Dow Chemical Company, www.dow.com Dow Corning Corporation, www.dowcorning.com DuPont — Dow Elastomers, www.dupont-dow.com Dylon Industries Inc., www.dylon.com E.I. DuPont de Nemours and Company, www.dupont.com/intermediates E.W. Kaufmann Company, www.ewkaufmann.com Elco Corporation, The, www.elcocorp.com Elementis Specialties, www.elementis-na.com Elementis Specialties-Rheox, www.rheox.com Elf Atochem Canada, www.atofinachemicals.com Environmental Lubricants Manufacturing, Inc. (ELM), www.elmusa.com Ethyl Corporation, www.ethyl.com Ethyl Petroleum Additives, www.ethyl.com Fanning Corporation, The, www.fanncorp.com Ferro/Keil Chemical, www.ferro.com FMC Lithium, www.fmclithium.com FMC, www.fmc.com Functional Products, www.functionalproducts.com G.R. O’Shea Company, www.groshea.com Gateway Additives, www.lubrizol.com Geo. Pfau’s Sons Company., Inc., www.pfauoil.com Georgia-Pacific Pine Chemicals, www.gapac.com Georgia-Pacific Resins, Inc.—Actrachem Division, www.gapac.com Georgia-Pacific Resins, Inc.—Actrachem Division, www.gp.com Goldschmidt Chemical Corporation, www.goldschmidt.com Great Lakes Chemical Corporation, www.glcc.com Grignard Company LLC, www.purelube.com Hall Technologies Inc., www.halltechinc.com Hammonds Fuel Additives, Inc., www.hammondscos.com Heveatex, www.heveatex.com Holland Applied Technologies, www.hollandapt.com Huntsman Corporation, www.huntsman.com Infineum USA LP, www.infineum.com International Lubricants Inc., www.lubegard.com J.H. Calo Company, Inc., www.jhcalo.com J.B. Chemical Company, Inc., www.jbchemical.com Jarchem Industries Inc., www.jarchem.com

Keil Chemical Division; Ferro Corporation, www.ferro.com King Industries Specialty Chemicals, www.kingindustries.com Lambent Technologies, www.petroferm.com LaPorte, www.laporteplc.com Lockhart Chemical Company, www.lockhartchem.com Loos & Dilworth Inc.—Chemical Division, www.loosanddilworth.com LubeRos— A Division of Burlington Chemical Company Inc., www.luberos.com Lubricant Additives Research, www.silverseries.com Lubricants Network Inc., www.lubricantsnetwork.com Lubri-Lab Inc., www.lubrilab.com Lubrizol Corporation, The, www.lubrizol.com Lubrizol Metalworking Additive Company, www.lubrizol.com Mantek Lubricants, www.mantek.com Marcus Oil and Chemical, www.marcusoil.com Master Chemical Corporation, www.masterchemical.com Mays Chemical Company, www.mayschem.com McIntyre Group Ltd., www.mcintyregroup.com Mega Power Inc., www.megapowerinc.com Metal Mates Inc., www.metalmates.net Metalworking Lubricants Company, www.metalworkinglubricants.com Milatec Corporation, www.militec.com

R.T. Vanderbilt Company Inc., www.rtvanderbilt.com R.H. Foster Energy LLC, www.rhfoster.com R.T. Vanderbilt Company, www.rtvanderbilt.com Reade Advanced Materials, www.reade.com Rhein Chemie Corporation, www.bayer.com Rhein Chemie Rheinau GmbH., www.rheinchemie.com Rheox Inc., www.rheox.com Rhodia, www.rhodia.com Rhone-Poulenc Surfactants & Specialties, www.rpsurfactants.com RiceChem, A Division of Stilling Enterprises Inc., www.ricechem.com Rohm & Haas Company, www.rohmhaas.com RohMax Additives GmbH, www.rohmax.com Ross Chem Inc., www.rosschem.com Santotrac Traction Lubricants, www.santotrac.com Santovac Fluids Inc., www.santovac.com Sea-Land Chemical Company, www.sealandchem.com Sea-Land Chemical Company, www.sealandchem.com Shamrock Technologies, Inc., www.shamrocktechnologies.com Shell Chemicals, www.shellchemical.com Shepherd Chemical Company, www.shepchem.com Soltex, www.soltexinc.com SP Morell & Company, www.spmorell.com Spartan Chemical Company Inc. Industrial Products Group Division, www.spartanchemical.com SQM North America Corporation, www.sqmna.com St. Lawrence Chemicals, www.stlawrencechem.com Stochem, Inc., www.stochem.com

Nagase America Corporation, www.nagase.com Naptec Corporation, www.satec.com NC’eed Enterprises, www.backtosebacics.com Northern Technologies International Corporation, www.ntic.com

Thornley Company, www.thornleycompany.com Tiodize Company, Inc., www.tiodize.com Tomah Products, Inc., www.tomah3.com Troy Corporation, www.troycorp.com

Oil Center Research Inc., www.oilcenter.com OKS Specialty Lubricants, www.oks-india.com Omega Specialties, www.omegachemicalsinc.com OMG Americas Inc., www.omgi.com OMGI, www.omgi.com Oronite, www.oronite.com

Ultra Additives Inc., www.ultraadditives.com Uniqema, www.uniqema.com Uniroyal Chemical Company Inc., www.uniroyalchemical.com United Color Manufacturing Inc., www.unitedcolor.com United Lubricants, www.unitedlubricants.com

PATCO Additives Division-American Ingredients Company, www.patco-additives.com Pflaumer Brothers Inc., www.pflaumer.com Pilot Chemical Company, www.pilotchemical.com PMC Specialties Inc., www.pmcsg.com Polartech Ltd.., www.polartech.co.uk Precision Fluids Inc., www.precisionfluids.com Purac America, Inc., www.purac.com

Valhalla Chemical, www.valhallachem.com Van Horn, Metz & Company, Inc., www.vanhornmetz.com Virtual Oil Inc., www.virtualoilinc.com

Copyright 2006 by Taylor & Francis Group, LLC

Wynn Oil Company, www.wynnsusa.com Zinc Corporation of America, www.zinccorp.com

51.2.3 Oil Companies Adco Petrol Katkilari San Ve. Tic. AS, www.adco.com.tr Amoco, www.amoco.com Aral International, www.Aral.com/ Asian Oil Company, www.nilagems.com/asianoil/ Bharat Petroleum, www.bharatpetroleum.com BP, www.bp.com CEPSA (Spain), www.cepsa.es Chevron Texaco, www.chevrontexaco.com Chevron, www.chevron.com CITGO Petroleum Corporation, www.citgo.com Coastal Corporation, www.elpaso.com Conoco, www.conoco.com Cosmo Oil, www.cosmo-oil.co.jp Cross Oil Refining and Marketing Inc., www.crossoil.com Ecopetrol (Columbian Petroleum Company), www.ecopetrol.com.co ENI, www.eni.it Ergon Inc., www.ergon.com ExxonMobil Corp., www.exxonmobil.com

MOL Hungarian Oil & Gas, www.mol.hu Murphy Oil Corporation, www.murphyoilcorp.com/ PDVSA (Venezuela), www.pdvsa.com PEMEX (Mexico), www.pemex.com Pertamina (Indonesia), www.pertamina.com Petrobras (Brazil), www.petrobras.com.br Petrogal (Portugal), www.galpenergia.com/ Galp+Energia/home.htm Petrogal (Portugal), www.petrogal.pt Petroperu (Peru), www.petroperu.com Phillips Petroleum Company/Phillips 66, www.phillips66.com/phi11ips66.asp RWE-DEA (Germany), www.rwe-dea.de San Joaquin Refining Company, www.sjr.com Sasol (South Africa), www.sasol.com Shell (USA), www.shellus.com Shell International, www.shell.com/royal-en Shell Oil Products US, www.shelloilproductsus.com/ Sinclair Oil Corp., www.sinclairoil.com Sinopec (China Petrochemical Corporation), www.sinopec.com.cn Statoil (Norway), www.statoil.com Sunoco Inc., www.sunocoinc.com

Fortum (Finland), www.fortum.com Gasco Energy, www.gascoenergy.com Hindustan Petroleum Corporation, Ltd., www.hindpetro.com Idemitsu, www.idemitsu.co.jp Indian Oil Corporation, www.indianoilcorp.com Interline Resources Corporation, www.interlineresources.com/

Texaco Inc., www.texaco.com Thailand, Petroleum Authority, www.nectec.or.th/ users/htk/SciAm/12PTT.html Tosco, www.tosco.com Total, www.total.com Total, www.totalfinaelf.com/ho/fr/index.htm YPF (Argentina), www.ypf.com.ar

51.2.4 University Sites

Japan Energy Corporation, www.j-energy.co.jp/eng/ index.html Japan Energy, www.j-energy.co.jp

Brno University of Technology, Faculty of Mechanical Engineering, Elastohydrodynamic Lubrication Research Group, http://fyzika.fme.vutbr.cz/ehd/

Kuwait National Petroleum Company K. S. C., www.knpc.com.kw/

Cambridge Universirty, Department of Materials Science and Metallurgy, Tribology, www.msm.cam.ac.uk/ tribo/tribol.htm Cambridge University, Department of Engineering, Tribology, www-mech.eng.cam.ac.uk/Tribology/ College of Petroleum and Energy Studies CPS Home Page, www.oxfordprinceton.com College of Petroleum and Energy Studies, www.colpet.ac.uk

LukOil (Russian Oil Company), www.lukoil.com Marathon Ashland Petroleum LLC, www.mapllc.com Marathon Oil Company, www.marathon.com Mobil, www.mobil.com

Copyright 2006 by Taylor & Francis Group, LLC

Colorado School of Mines Advanced Coating and Surface Engineering Laboratory (ACSEL), www.mines.edu/ research/acsel/acsel.html

Ohio State University, Center for Surface Engineering and Tribology, Gear Dynamics and Gear Noise Research Laboratory, http://gearlab.eng.ohio-state.edu/

Danish Technological Institute (DTI) Tribology Centre, www.tribology.dti.dk/ Departments of Mechanical Engineering Luleå Technical University, Sweden, http://www.luth.se/depts/mt/me/ Division of Machine Elements Home Page Niigata University, Japan, http://tmtribo1.eng.niigata-u.ac.jp/ index_e.html

Pennsylvania State University, The, www.me.psu.edu/ research/tribology.html Purdue University, Materials Processing and Tribology Research Group, www.ecn.purdue.edu/∼farrist/lab.html Purdue University, Mechanical Engineering Tribology Web Site, http://widget.ecn.purdue.edu/∼metrib/

Ecole Centrale de Lyon, France Laboratoire de Tribologie et Dynamique des Systèmes, www.ec-lyon.fr/recherche/ltds/index.html Ecole Polytechnique Federale de Lausanne, Switzerland, http://igahpse.epfl.ch Eidgenössische Technische Hochschule (ETH), Zurich Laboratory for Surface Science and Technology (LSST), www.surface.mat.ethz.ch/ Esslingen, Technische Akademie, www.tae.de Fachhochschule Hamburg, Germany, www.haw-hamburg.de/fh/forum/f12/indexf.html/ tribologie/etribology.html Georgia Tech Tribology, www.me.gatech.edu/research/ tribology.html Imperial College, London ME Tribology Section, www.me.ic.ac.uk/tribology/ Indian Institute of Science, Bangalore, India, Department of Mechanical Engineering, www.mecheng.iisc.ernet.in Institut National des Sciences Appliquées de Lyon, France, Laboratoire de Mécanique des Contacts, www.isan-lyon.fr/Laboratoires/LMC/index.html Iowa State University, Tribology Laboratory, www.eng.iastate.edu/coe/me/research/labs/ tribology_lab.html Israel Institute of Technology (Technion), http://meeng. technion.ac.il/Labs/energy.htm#tribology Kanazawa University, Japan, Tribology Laboratory, http://web.kanazawa-u.ac.jp/∼tribo/labo5e.html Kyushu University, Japan, Lubrication Engineering Home Page, www.mech.kyushu-u.ac.jp/index.html Lulea University of Technology, Department of Mechanical Engineering, www.luth.se/depts/mt/me/ Northwestern University, Tribology Lab, http://cset.mech. northwestern.edu/member.htm

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Royal Institute of Technology (KTH), Sweden Machine Elements Home Page, www.damek.kth.se/mme Saitama University, Japan Home Page of Machine Element Laboratory, www.mech.saitama-u.ac.jp/ youso/home.html Sandia National Laboratories Tribology, www.sandia.gov/materials/sciences/ Shamban Tribology Laboratory Kanazawa University, Japan, http://web.kanazawa-u.ac.jp/∼tribo/labo5e.html Southern Illinois University, Carbondale Center for Advanced Friction Studies, www.frictioncenter.com State University of New York, Binghamton Mechanical Engineering Laboratory, www.me.binghamton.edu/ me_labs.html Swiss Federal Laboratories for Materials Testing and Research (EMPA) Centre for Surface Technology and Tribology, www.empa.ch Swiss Tribology Online, Nanomechanics and Tribology, http://dmxwww.epfl.ch/WWWTRIBO/home.html Technical University of Delft, Netherlands Laboratory for Tribology, www.ocp.tudelft.nl/tribo/ Technical University, Munich, Germany, www.fzg.mw.tu-muenchen.de Technische Universitat Ilmenau, Faculty of Mathematics and Natural Sciences, www.physik.tu-ilmenau.de/ index_e.html Texas Tech University, Tribology, www.osci.ttu.edu/ ME_Dept/Research/tribology.htmld/ Tokyo Institute of Technology, Japan Nakahara Lab. Home Page, www.mep.titech.ac.jp/Nakahara/home.html Trinity College, Dublin Tribology and Surface Engineering, www.mme.tcd.ie/Groups/Tribology/ Tsinghua University, China, State Key Laboratory of Tribology, www.pim.tsinghua.edu.cn/index_cn.html University of Akron Tribology Laboratory, www.ecgf.uakron.edu/∼mech University of Applied Sciences, Hamburg, Germany Dept of Mech. Eng Tribology, www.fh-hamburg.de/fh/fb/m/tribologie/e_index.html

University of Applied Sciences, Hamburg, Germany, www.haw-hamburg.de/fh/fb/m/tribologie/e_index.html University of California, Berkeley Bogey’s Tribology Group, http://cml.berkeley.edu/tribo.html University of California, San Diego, Center for Magnetic Recording Research, http://orpheus.ucsd.edu/cmrr/ University of Florida, Mechanical Engineering Department, Tribology Laboratory, http://grove.ufl.edu/ ∼wgsawyer/ University of Illinois, Urbana-Champaign Tribology Laboratory, www.mie.uiuc.edu University of Kaiserslautern, Germany Sektion Tribologie, www.uni-kl.de/en/ University of Leeds, M.Sc. (Eng.) Course in Surface Engineering and Tribology, http://leva.leeds.ac.uk/ tribology/msc/tribmsc.html University of Leeds, UK Research in Tribology, http://leva.leeds.ac.uk/tribology/research.html University of Ljubljana, Faculty of Mechanical Engineering, Center for Tribology and Technical Diagnostics, www.ctd.uni-lj.si/eng/ctdeng.htm University of Maine Laboratory for Surface Science and Technology (LASST), www.ume.maine.edu/LASST/ University of Maine, NanoTribometer System, www.ume.maine.edu/LASST University of Newcastle upon Tyne, UK Ceramics Tribology Research Group, www.ncl.ac.uk/materials/ materials/resgrps/certrib.html University of Northern Iowa, www.uni.edu/abil University of Notre Dame Tribology/Manufacturing Laboratory, www.nd.edu/∼ame University of Pittsburg, School of Engineering, Mechanical Engineering Department, www.engrng.pitt. edu/∼mewww University of Sheffield, UK Tribology Research Group, http://www.shef.ac.uk/mecheng/tribology/ University of Southern Florida. Tribology, www.eng.usf.edu/∼hess/ University of Texas at Austin, Petroleum & Geosystems Engineering, Reading Room, www.pe.utexas.edu/Dept/ Reading/petroleum.html University of Tokyo, Japan, Mechanical Engineering Department, www.mech.t.u-tokyo.ac.jp/english/ index.html University of Twente, Netherlands Tribology Group, http://www.wb.utwente.nl/vakgroep/tr/tribeng.htm University of Western Australia Department of Mechanical and Material Engineering, http://www.mech.uwa.edu.au/tribology/ University of Western Ontario, Canada Tribology Research Centre, http://www.engga.uwo.ca/research/tribology/ Default.htm University of Windsor, Canada Tribology and Wear Research Group, http://zeus.uwindsor.ca/research/ wtrg/index.html

Copyright 2006 by Taylor & Francis Group, LLC

University of Windsor, Canada, Tribology Research Group, http://venus.uwindsor.ca/research/wtrg/ index.html Uppsala University, Sweden Tribology Group, http://www.angstrom.uu.se/materials/index.htm Western Michigan University Tribology Laboratory, www.mae.wmich.edu/labs/Tribology/Tribology.html Western Michigan University, Department of Mechanical and Aeeronautical Engineering, www.mae.wmich.edu/ Worcester Polytechnic Institute, Department of Mechanical Engineering, www.me.wpi.edu/ Research/labs.html

51.2.5 Government Sites/Industry Sites American Bearing Manufacturers Association, www.abma-dc.org American Board of Industrial Hygiene, www.abih.org American Carbon Society, www.americancarbonsociety.org American Chemical Society (ACS), www.acs.org American Council of Independent Laboratories (ACIL), www.acil.org American Gear Manufacturers Association (AGMA), www.agma.org American National Standards Institute (ANSI), www.ansi.org American Oil Chemists Society (AOCS), www.aocs.org American Petroleum Institute (API), www.api.org American Society of Agricultural Engineering (ASAE), www.asae.org American Society of Agronomy (ASA), www.agronomy.org American Society for Horticultural Science (ASHS), www.ashs.org American Society for Testing and Materials (ASTM), www.astm.org American Society of Mechanical Engineers International (ASME), www.asme.org Argonne National Laboratory, www.et.anl.gov ASTM, www.astm.org Automotive Aftermarket Industry Association (AAIA), www.aftermarket.org Automotive Oil Change Association (AOCA), www.aoca.org Automotive Parts and Accessories Association (APAA), www.apaa.org Automotive Service Industry Association (ASIA), www.aftmkt.com British Lubricants Federation Ltd., www.blf.org.uk California Air Resources Board, www.arb.ca.gov Center for Tribology, Inc. (CETR), www.cetr.com

Co-ordinating European Council (CEC), www.cectests.org Coordinating Research Council (CRC), www.crcao.com Crop Science Society of America (CSSA), www.crops.org Department of Defense (DOD), www.dodssp.daps. mil/dodssp.htm Deutsches Institute Fur Normung e. V. (DIN), www.din.de Environmental Protection Agency (EPA), www.fedworld.gov European Automobile Manufacturers Association (ACEA), www.acea.be European Oil Companies Organization of E. H. and S. (CONCAWE), www.concawe.be Federal World, www.fedworld.gov Independent Lubricant Manufacturers Association (ILMA), www.ilma.org Industrial Maintenance & Plant Operation (IMPO), www.mcb.co.uk/cgi-bin/mcb_serve/table1. txt&ilt&stanleaf.htm Institute of Materials Inc. (IOM), www.savantgroup.com Institute of Mechanical Engineers (ImechE), www.imeche.org.uk Institute of Petroleum (IP), http://212.78.70.142 Institute of Physics (IOP), Tribology Group, www.iop.org Internal Energy Agency (IEA), www.iea.org International Organization for Standardization (ISO), www.iso.ch Japan Association of Petroleum Technology (JAPT), www.japt.org Japan Automobile Manufacturers Association (JAMA), www.japanauto.com Japanese Society of Tribologists (JAST) (in Japanese), www.jast.or.jp Los Alomos National Laboratory, www.lanl. gov/worldview/ NASA Lewis Research Center (LeRC) Tribology & Surface Science Branch, www.lerc.nasa.gov/ Other_Groups/SurfSci National Centre of Tribology, UK, www.aeat.com/nct/ National Fluid Power Association (NFPA), www.nfpa.com National Institute for Occupational Safety and Health, www.cdc.gov/homepage.html National Institute of Standards and Technology, http://webbook.nist.gov/chemistry National Lubricating Grease Institute (NLGI), www.nlgi.org National Metal Finishing Resource Center, www.nmfrc.org

Copyright 2006 by Taylor & Francis Group, LLC

National Oil Recyclers Association (NORA), www.recycle.net/Associations/rs000141.html National Petrochemical & Refiners Association, www.npradc.org National Petrochemical Refiners Association (NPRA), www.npradc.org National Petroleum Refiners Association (NPRA), www.npra.org National Research Council of Canada Lubrication Tribology Services, http://132.246.196.24/en/fsp/service/ lubrication_trib.htm Naval Research Lab Tribology Section—NRL Code 6176, http://stm2.nrl.navy.mil/∼wahl/6176.htm Oak Ridge National Laboratory (ORNL) Tribology Test Systems, www.ms.ornl.gov/htmlhome Occupational Safety and Health Administration (OSHA), www.osha.gov Petroleum Marketers Association of America (PMAA), www.pmaa.org Society of Automotive Engineers (SAE), www.sae.org Society of Environmental Toxicology and Chemistry (SETAC), www.setac.org Society of Manufacturing Engineers (SME), www.sme.org Society of Tribologists and Lubrication Engineers (STLE), www.stle.org Southwest Research Institute (SwRI) Engine Technology Section, www.swri.org/4org/d03/engres/engtech/ Southwestern Petroleum Corporation (SWEPCO), www.swepco.com Thailand, Petroleum Authority (PTT), www.nectec.or.th U.S. Department of Agriculture (USDA), www.usda.gov U.S. Department of Defense (DOD), www.dod.gov U.S. Department of Energy (DOE), www.energy.gov U.S. Department of Transportation (DOT), www.dot.gov U.S. Energy Information Administration, www.eia.doe.gov U.S. Patent Office, www.uspto.gov U.S. Data Exchange, www.usde.com Western States Petroleum Association, www.wspa.org

51.2.6 Testing Labs/Equipment/Packaging A.W. Chesterton Company, www.chesterton.com A/R Packaging Corporation, www.arpackaging.com Accumetric LLC, www.accumetric.com

Airflow Systems Inc., www.airflowsystems.com Alfa Laval Separation, www.alfalaval.com Allen Filters Inc., www.allenfilters.com Ana Laboratories Inc., www.analaboratories.com Analysts Inc., www.analystinc.com Anatech Ltd., www.anatechltd.com Andpak Inc., www.andpak.com Applied Energy Company, www.appliedenergyco.com Aspen Technology, www.aspentech.com/ Associates of Cape Cod Inc., www.acciusa.com Atico-Internormen-Filter, www.atico-internormen.com Baron USA Inc., www.baronusa.com Berenfield Containers, www.berenfield.com Bericap NA, www.bericap.com BF Goodrich, www.bfgoodrich.com Bianco Enterprises Inc., www.bianco.net Bijur Lubricating Corporation, www.bijur.com Biosan Laboratories, Inc., www.biosan.com Bio-Rad Labroatories, www.bio-rad.com BioTech International Inc., [email protected] Blackstone Laboratories, www.blackstone-labs.com/ Cannon Instrument Company, www.cannon-ins.com Certified Laboratories Lubricants, www.certifiedlaboratories.com Chemicolloid Laboratories Inc., www.colloidmill.com Como Industrial Equipment Inc., www.comoindustrial.com Computational Systems, Inc., www.compsys.com/ index.html Containment Solutions Inc., www.containmentsolutions.com CSI, www.compsys.com Custom Metalcraft Inc., www.custom-metalcraft.com Delphi Automotive Systems, www.delphiauto.com Des-Case Corporation, www.des-case.com Dexsil Corporation, www.dexsil.com Diagnetics, www.entek.com Digilube Systems Inc., www.digilube.com Dingo Maintenance Systems, www.dingos.com/ DSP Technology Inc., www.dspt.com Duro Manufacturing Inc., www.duromanufacturing.com Dutton-Lainson Company, www.dutton-lainson.com Dylon Industries Inc., www.dylon.com Easy Vac Inc., www.easyvac.com Edjean Technical Services Inc., www.edjetech.com Engel Metallurgical Ltd., www.engelmet.com Engineered Composites Inc., www.engineeredcomposites.net

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Environmental and Power Technologies Ltd., www.cleanoil.com Evans Industries Inc., www.evansind.com Falex Corporation, www.falex.com Falex Tribology NV, www.falexint.com/ FEV Engine Technology, Inc., www.fev-et.com/ Flo Components Ltd., www.flocomponents.com Flowtronex International, www.flowtronex.com Fluid Life Corporation, www.fluidlife.com Fluid Systems Partners US Inc., www.fsp-us.com Fluid Technologies Inc., www.Fluidtechnologies.com Fluids Analysis Lab, www.butler-machinery.com/oil.html Fluidtec International, www.fluidtec.com Fluitec International, www.fluitec.com/ FMC Blending & Transfer, www.fmcblending-transfer.com Framatome ANP, www.framatech.com Fuel Quality Services Inc., www.fqsgroup.com G.R. O’Shea Company, www.groshea.com G.T. Autochemilube Ltd., www.gta-oil.co.uk Galactic, www.galactic.com Gamse Lithographing Company, www.gamse.com Gas Tops Ltd., www.gastops.com Generation Systems Inc., www.generationsystems.com Georgia-Pacific Resins, Inc.—Actrachem Division, www.gapac.com Gerhardt Inc., www.gerhardths.com Globetech Services Inc., www.globetech-services.com Graco Inc., www.graco.com Gulfgate Equipment, Inc., www.gulfgateequipment.com Hedwin Corporation, www.hedwin.com Hercules, Inc., Aqualon Division, www.herc.com Herguth Laboratories Inc., www.herguth.com Hi-Port Inc., www.hiport.com Hi-Tech Industries, Inc., www.hi-techind.com Hoover Materials Handling Group Inc., www.hooveribcs.com Horix Manufacturing Company, www.sgi.net/horix Hydraulic Repair & Design, Inc., www.h-r-d.com Hysitron Incorporated: Nanomechanics, www.hysitron.com/ Indiana Bottle Company, www.indianabottle.com Industrial Packing Inc., www.industrialpacking.com Insight Services, www.testoil.com/ Instruments for Surface Science, www.omicron-instruments.com/index.html Interline Resources Corporation, www.interlineresources.com International Group Inc., The (IGI), www.igiwax.com

Intertek Testing Services-Caleb Brett, www.itscb.com Invicta a.s., www.testoil.com/ J & S Chemical Corporation, www.jschemical.com J.R. Schneider Company, Inc., www.jrschneider.com JAX-Behnke Lubricants Inc., www.jax.com Johnson Packings & Industrial Products Inc., www.johnsonpackings.com K.C. Engineering, Ltd., www.kceng.com/ K.l.S.S. Packaging Systems, www.kisspkg.com Kafko International Ltd., www.kafkointl.com Kennedy Group, The, www.kennedygrp.com Kittiwake Developments Limited, www.kittiwake.com Kleenoil Filtration Inc., www.kleenoilfiltrationinc.com Kleentek-United Air Specialists Inc., www.uasinc.com Koehler Instrument Company, www.koehlerinstrument.com Koehler Instrument Company, www.koehlerinstrument.com Kruss USA, www.krussusa.com Laub/Hunt Packaging Systems, www.laubhunt.com Lawler Manufacturing Corporation, www.lawler-mfg.com Leding Lubricants Inc., www.automatic-lubrication.com Legacy Manufacturing, www.legacymfg.com Liftomtic Inc., www.liftomatic.com Lilyblad Petroleum, Inc., www.lilyblad.com Linpac Matls. Handling, www.linpacmh.com Liqua-Tek/Moraine Packaging, www.globaldialog.com/∼mpi Liquid Controls Inc., A Unit of IDEX Corporation, www.lcmeter.com Lormar Reclamation Service, www.lormar.com LubeCon Systems Inc., www.lubecon.com Lubricant Technologies, www.lubricanttechnologies.com Lubrication Engineers of Canada, www.lubeng.com Lubrication Systems, www.lsc.com Lubrication Systems, www.lsc.com Lubrication Technologies Inc., www.lube-tech.com Lubriport Labs, www.ultralabs.com/lubriport Lubriquip Inc, www.lubriquip.com Lubrizol Corporation, The, www.lubrizol.com Lubromation Inc., www.lubromation.com Lub-Tek Petroleum Products Corporation, www.lubtek.com Machines Production Web Site, www.machpro.fr/ Manor Technology, www.manortec.co.uk/ Metalcote/Chemtool Inc., www.metalcote.com Metorex Inc., www.metorex.fi Mettler Toledo, www.mt.com Michel Murphy Enterprises Inc., www.michelmurphy.com

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Micro Photonics Inc., www.microphotonics.com/ Micro Photonics Inc., www.microphotonics.com/ Mid-Michigan Testing Inc., www.tribologytesting.com Monlan Group, www.monlangroup.com Motor Fuels/Combustibles Testing, www.empa.ch/ englisch/fachber/abt133/index.htm Mozel Inc., www.mozel.com Nalco Chemical Company, www.nalco.com Naptec Corporation, www.satec.com National Tribology Services, www.natrib.com NC’eed Enterprises, www.backtosebacics.com NCH, www.nc.com Newcomb Oil Company, www.newcomboil.com Nordstrom Valves Inc., www.nordstromaudco.com Oden Corporation, www.oden.thomasregister.com Oden Corporation, www.odencorp.com Oil Analysis (Noria), www.oilanalysis.com OMICRON Vakuumphysik GmbH, www.omicron-instruments.com/index.html OMS Laboratories, Inc. http://members.aol.com/ labOMS/index.html Owens-Illinois Inc., www.o-i.com Oxford Instruments Inc., www.oxinst.com Paper Systems Inc., www.paper-systems.com PARC Technical Services Inc., www.parctech.com Patterson Industries Ltd. (Canada), www.pattersonindustries.com PCS Instruments, www.pcs-instruments.com PdMA Corporation, www.pdma.com PED Inc., www.ped.vianet.ca Perkin Elmer Automotive Research, www.perkinelmer.com/ar Perkins Products Inc., www.perkinsproducts.com Perma USA, www.permausa.com Petrolab Corporation, www.petrolab.com Petrolabs Inc., http://pages.prodigy.net/petrolabsinc Petroleum Analyzer Company LP (PAC), www.Petroleum-Analyzer.com Petroleum Products Research, www.swri.org/4org/d08/petprod/ Petro-Lubricants Testing Laboratories, Inc., www.pltlab.com Petrotest, www.petrotest.net Pflaumer Brothers Inc., www.pflaumer.com Philips Industrial Electronics Deutschland, www.philips-tkb.com Pipeguard of Texas, www.pipeguard-texas.com Plastic Bottle Corporation, www.plasticbottle.com Plastican Inc., www.plastican.com Plews/Edelmann Division, Stant Corporation, www.stant.com

PLI LLC, www.memolub.com Plint and Partners: Tribology Division, www.plint.co.uk/trib.htm Polaris Laboratories, LLC, www.polarislabs.com PREDICT/DLI—Innovative Predictive Maintenance, www.predict-dli.com Predictive Maintenance Corporation, www.pmaint.com/ Predictive Maintenance Services, www.theoillab.com Premo Lubricant Technologies, exwww.premolube.com Pulsair Systems Inc., www.pulsair.com Quorpak, www.quorpak.com R & D/Fountain Industries, www.fountainindustries.com R.A. Miller & Company Inc., www.ramiller.on.ca R.E.A.L. Services, www.realservices.com Radian Inc., www.radianinc.com Ramos Oil Co. Inc., www.ramosoil.com Ravenfield Designs Ltd., www.ravenfield.com Ravenfield Designs Ltd., www.ravenfield.com Reelcraft Industries Inc., www.realcraft.com Rexam Closures, www.closures.com Rheotek (PSL SeaMark), www.rheotek.com Ribelin, www.ribelin.com Russell-Stanley Corportion, www.russell-stanley.com Safety-Kleen Corporation, www.safety-kleen.com Saftek: Machinery Maintenance Index, www.saftek.com/ boiler/machine/mmain.htm Sandy Brae Laboratories Inc., www.sandy/brae.com SATEC Inc., www.satec.com Savant Group of Companies, www.savantgroup.com Savant Inc., www.savantgroup.com Saxton Industries, www.saxton.thomasregister.com Scully Signal Company, www.scully.com Senior Flexonics, www.flexonics-hose.com Service Supply Lubricants LLC, www.servicelubricants.com Sexton & Peake Inc., www.sexton.qpg.com Silvas Oil Co. Inc., www.silvasoil.com Silverson Machines Inc., www.silverson.com Sinclair Oil Corporatoin, www.sinclairoil.com SKF Quality Technology Centre, www.qtc.skf.com Sleeveco Inc., www.sleeveco.com Snyder Industries, www.snydernet.com Southwest Research Institute, www.swri.org Southwest Spectro-Chem Labs, www.swsclabs.com Spacekraft Packaging, www.spacekraft.com Specialty Silicone Products Inc., www.sspinc.com SpectroInc. Industrial Tribology Systems, www.spectroinc.com/ Spectronics Corporation, www.spectroline.com

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Spex CertiPrep Inc., www.spexcsp.com Star Brite, www.starbrite.com Steel Shipping Containers Institute, www.steelcontainers.com Stratco Inc., www.stratco.com Sunohio, Division of ENSR, www.sunohio.com Superior Lubricants Company, Inc., www.superiorlubricants.com Taber Industries, www.taberindustries.com Tannas Company, www.savantgroup.com Tannis Company, www.savantgroup.com/tannas.sht Thermo Elemental, www.thermoelemental.com Thomas Petroleum, www.thomaspetro.com Thoughtventions Unlimited Home Page, www.tvu.com/ %7Ethought/ Titan Laboratories, www.titanlab.com TriboLogic Lubricants Inc., www.dynamaxx.com TriboLogic Lubricants Inc., www.tribologic.com Trico Manufacturing Corporation, www.tricomfg.com Trilla Steel Drum Corporation, www.trilla.com TTi’s Home Page, www.tti-us.com/ UEC Fuels and Lubrication Laboratories, www.uec-usx.com Ultimate Lubes, www.ultimatelubes.com Unilube Systems Ltd., www.unilube.com Unit Pack Company Inc., www.unitpack.com USX Engineers & Consultants, www.uec.com/labs/ctns USX Engineers and Consultants: Laboratory Services, www.uec.com/labs/ Vacudyne Inc., www.vacudyne.com Van Horn, Metz & Company, Inc., www.vanhornmetz.com Viking Pump Inc., A Unit of IDEX Corporation, www.vikingpump.com Viswa Lab Corporation, www.viswalab.com Vortex International LLC, www.vortexfilter.com Vulsay Industries Ltd., www.vulsay.com

Wallace, www.wallace.com Waugh Controls Corporation, www.waughcontrols.com Wearcheck International, www.wearcheck.com/ Wedeven Associates, Inc., http://members. aol.com/wedeven/ West Penn Oil Company Inc., www.westpenn.com Western States Oil, www.lubeoil.com Wilks Enterprise Inc., www.wilksir.com WSI Chemical Inc., www.wsi-chem-sys.com Zimmark Inc., www.zimmark.com

51.2.7 Car/Truck MFG Alfa Romeo, www.alfaromeo.com Audi, www.audi.com BMW (International), www.bmw.com/bmwe BMW (USA), www.bmwusa.com BMW Motorcycles, www.bmw-motorrad.com Buick (GM), www.buick.com Cadillac (GM), www.cadillac.com Caterpillar, www.cat.com Caterpillar, www.caterpillar.com Chevrolet (GM), www.chevrolet.com Chrysler (Mercedes Benz), www.chrysler.com Citroen (France), www.citroen.com Citroen (UK), www.citroen.co.uk/fleet Cummins Engine Company, www.cummins.com Daimler Chrysler, www.daimlerchrysler.com Detroit Diesel, www.detroitdiesel.com Dodge, www.dodge.com Eagle, www.eaglecars.com EV1, www.gmev.com Ferrari, www.ferrari.com Fiat, www.fiat.com Ford Motor Company, www.ford.com General Motors (GM), www.gm.com Global Electric Motor Cars, LLC, www.gemcar.com Hyundai, www.hyundai-motor.com Infiniti, www.infiniti.com Isuzu, www.isuzu.com Jaguar, www.jaguarcars.com Jeep, www.jeep.com John Deere, www.deere.com Kawasaki, www.kawasaki.com Kawasaki, www.khi.co.jp Lambourghini, www.lamborghini.com Lexus, www.lexususa.com Lincoln-Mercury, www.lincolnmercury.com Mack Trucks, www.macktrucks.com Mazda, www.mazda.com

Copyright 2006 by Taylor & Francis Group, LLC

Mercedes-Benz (Germany), www.mercedes-benz.de Mitsubishi Motors, www.mitsubishi-motors.co.jp Nissan (Japan), www.nissan.co.jp Nissan (USA), www.nissandriven.com Nissan (USA), www.nissanmotors.com Opel, www.opel.com Peugeot, www.peugeot.com Plymouth, www.plymouthcars.com Pontiac (GM), www.pontiac.com Saab Cars USA, www.saabusa.com Saab, www.saab.com Saturn (GM), www.saturncars.com Scania, www.scania.se Toyota (Japan), www.toyota.co.jp Toyota (USA), www.toyota.com Vauxhall, www.vauxhall.co.uk Volkswagen (Germany), www.vw-online.de Volkswagen (USA), www.vw.com Volvo (Sweden), www.volvo.se Volvo Cars of North America, www.volvocars.com Volvo Group, www.volvo.com

51.2.8 Publications/References/Recruiting/ Search Tools, etc. American Machinist, www.penton.com/cgi-bin/ superdirectory/details.pl?id=317 API Links, www.api.org/links Automotive & Industrial Lubricants Guide, www.wearcheck.com Automotive and Industrial Lubricants Guide by David Bradbury, www.escape.ca/∼dbrad/index.htm Automotive and Industrial Lubricants Tutorial, www.escape.ca/∼dbrad/index.htm Automotive News, www.autonews.com Automotive Service Industry Association, www.aftmkt.com/asia Automotive Services Retailer, www.gcipub.com AutoWeb, www.autoweb.com AutoWeek Online, www.autoweek.com Bearing.Net, www.wearcheck.com Cambridge, http://chemfinder.camsoft.com Car and Driver Magazine Online, www.caranddriver.com Car-Stuff, www.car-stuff.com Center for Innovation Inc., www.centerforinnovation.com

Chem Connect, www.chemconnect.com Chemical Abstracts Service, www.cas.org Chemical Resources, www.chemcenter.org Chemical Week Magazine, www.chemweek.com Concord Consulting Group Inc., www.concordcg.com Dialog, www.dialog.com Diesel Progress, www.dieselpub.com Diversified Petrochemical Services, www.chemhelp.com Energy Connection, The, www.energyconnect.com European Patent Office, www.epo.co.at/epo/ F.L.A.G. (Fuel, Lubricant, Additives, Grease) Recruiting, www.flagsearch.com/ Farmland Industries Inc., www.farmland.com Fuel Quest, www.fuelquest.com/cgi-bin/fuelqst/ corporate/fq_index.jsp Fuels and Lubes Asia Publications, Inc., www.flasia.com.ph Gear Technology Magazine, www.geartechnology.com/ mag/gt-index.html Haas Corporation, www.haascorp.com HEF, France, www.hef.fr/ How Stuff Works, www.howstuffworks.com/engine.htm Hydrocarbon Asia, www.hcasia.safan.com Hydrocarbon Online, www.wearcheck.com Hydrocarbon Processing Magazine, www.hydrocarbonprocessing.com/ ICIS-LOR Base Oils Pricing Information, www.icislor.com/ Industrial Lubrication and Tribology Journal, www.mcb.co.uk/ilt.htm Industrial Maintainence and Engineering Links (PLI, LLC), www.memolub.com/link.htm Intl. Tribology Conf. Yokohama 1995, www.mep.titech. ac.jp/Nakahara/jast/itc/itc-home.htm ISO Translated into Plain English, http://connect.ab.ca/∼praxiom Journal of Fluids Engineering, http://borg.lib.vt.edu/ ejournals/JFE/jfe.html Journal of Tribology, http://engineering.dartmouth.edu/ thayer/research/index.html Kline & Comphany Inc., www.klinegroup.com LSST Tribology and Surface Forces, http://bittburg. ethz.ch/LSST/Tribology/default.html

Copyright 2006 by Taylor & Francis Group, LLC

LSST Tribology Letters, http://bittburg.ethz.ch/LSST/ Tribology/letters.html Lube Net, www.lubenet.com Lubelink, www.lubelink.com Lubes and Greases, www.lngpublishing.com Lubricants Network Inc., www.lubricantsnetwork.com Lubricants World, www.lubricantsworld.com Lubrication Engineering Magazine, www.stle.org/ le_magazine/le_index.htm

MaintenanceWorld, www.wearcheck.com MARC-IV, www.marciv.com Mechanical Engineering Magazine, www.memagazine. org/index.html Migdal’s Lubricant Web Page, http://members.aol.com/ sirmigs/lub.htm Muse, Stancil & Company, www.musestancil.com

National Petroleum News, www.petroretail.net/npn National Resource for Global Standards, www.nssn.org Neale Consulting Engineers Limited, www.tribology.co.uk/ Noria—OilAnalysis.Com, www.oilanalysis.com/

Oil Directory.com, www.oildirectory.com Oil Online, www.oilonline.com/ Oil-Link Oil & Gas Online, www.oilandgasonline.com Oilspot.com, www.oilspot.com

Pennwell Publications, www.pennwell.com Petrofind.com, www.petrofind.com PetroleumWorld.com, www.petroleumworld.com PetroMin Magazine, www.petromin.safan.com Practicing Oil Analysis Magazine, www.practicingoilanalysis.com Predictive Maintenance Corporation: Tribology and the Information Highway, www.pmaint.com/tribo/docs/ oil_anal/tribo_www.html ref

Reliability Magazine, www.pmaint.com/tribo/docs/ oil_anal/tribo_www.html Safety Information Resources on the Internet, www.siri.org/links1.html Savant Group of Companies, www.savantgroup.com SGS Control Services Inc., www.sgsgroup.com Shell Global Solutions, www.shellglobalsolutions.com SubTech (Petroleum Service & Supply Information), www.subtech.no/petrlink.htm

Summit Technical Solutions, www.lubemanagement.com Sunohio, Division of ENSR, www.sunohio.com

United Soybean Board, www.unitedsoybean.org Victoria Group Inc., The, www.victoriagroup.com

Tannas Company, www.savantgroup.com Test Engineering Inc., www.testeng.com The Maintenance Council, www.trucking.org TMC, www.truckline.com Tribologist.com, www.wearcheck.com Tribology Consultant, http://hometown.aol.com/ wearconsul/wear/wear.htm Tribology International, www.elsevier.nl/inca/ publications/store/3/0/4/7/4/ Tribology Letters, www.kluweronline.com/ issn/1023-8883 Tribology Research Review 1992-1994, www.me.ic.ac.uk/ department/review94/trib/tribreview.html Tribology Research Review 1995-1997, www.me.ic.ac.uk/ department/review97/trib/tribreview.html Tribology/Tech-Lube, www.tribology.com Truklink (truck fleet information), www.truklink.com

Copyright 2006 by Taylor & Francis Group, LLC

Wear Chat: WearCheck Newsletter, www.wearcheck.com Wear, www.elsevier.nl/inca/publications/ store/5/0/4/1/0/7/ World Tribologists Database, http://greenfield. fortunecity.com/fish/182/tribologists.htm WWW Tribology Information Service, www.shef.ac.uk/ ∼mpe/tribology/ WWW Virtual Library: Mechanical Engineering, www.vlme.com/ Yahoo Lubricants, http://dir.yahoo.com/ business_and_economy/shopping_and_services/ automotive/supplies/lubricants/ Yahoo Tribology, http://ca.yahoo.com/Science/ Engineering/Mechanical_Engineering/Tribology/

Appendix. Publisher’s Note: The Meaning of “Synthetic” This note appeared in the Journal of Synthetic Lubrication, Vol 17, #1, april 2000 and is reprinted by permission of Stephen Godfree, publisher. Readers of this journal, particularly in the United States, will no doubt be aware of the decision by the National Advertising Division (NAD) of the Council of Better Business Bureaux, made in April 1999, concerning the use of the word “synthetic” as a description of certain lubricants on the market. Its attempt to widen the use of the term to cover hydroprocessed oils would seem to have raised more questions than it has solved. The original Castrol–Mobil tussle that led to the NAD’s adjudication was over an advertising claim within the United States. Mobil objected (despite allegedly having itself marketed hydroisomerized base stocks as “synthetic” in Europe and elsewhere∗ ) that Castrol’s hydroprocessed Syntec® was not synthetic. The NAD did not agree, arguing that Castrol’s evidence, although not demonstrating its product’s superiority, constituted a reasonable basis for the claim that Castrol Syntec, as currently formulated, is a synthetic motor oil. Perhaps the first thing to realize is that the NAD is a powerless body outside the USA. Its jurisdiction is advertising claims on its home territory. It would not be unreasonable to say that it was out of its depth here, where the issues would seem to be: (1) what does “synthetic” mean in the context of lubricant make-up? (2) what is the importance of performance? and (3) why does anyone need to define mineral hydroprocessed oils as “synthetic?”

A.1 “SYNTHETIC” AS A TERM The normal scientific or technological definition is of “synthesis,” not of “synthetic.” “Synthesis,” in the context of chemistry, means the “artificial production of compounds from their constituents as distinct from extraction from plants, etc.” (The Concise Oxford Dictionary.) In practice, this involves taking two or more defined molecular species and synthesizing from them a product that is a predictable and defined compound. While Group III base oils are the result not simply of refining but also of a sophisticated process wherein ∗ Katherine Bui, “A defining moment for synthetics, Part 1,” Lubricant’s World, October 1999.

Copyright 2006 by Taylor & Francis Group, LLC

a smaller or larger proportion of the molecules are chemically converted, there remain, in every case, elements of the oil that are unknown and that can only be identified by analysis. This process would seem to be almost the opposite of synthesis. Herein lies the first error in the NAD ruling. It seemingly failed or was unable to define “synthetic,” the adjective from “synthesis,” in terms of its technical use, even ignoring the industry definition found in the base oil groupings in API Publication 1509, where Groups I, II, and III are identified by saturates, VI, and sulfur, while Group IV oils are simply defined as polyalphaolefins. In other words, a distinction is made between refined (I, II, and III) and synthetic (IV) oils. Instead, the NAD concerned itself exclusively with the word in the marketing context. This is intimately connected with the question of performance.

A.2 THE IMPORTANCE OF PERFORMANCE One of the central themes of the Castrol–Mobile dispute was performance. Performance is a concept that has, in a wider context, taken on more importance of late. Certain research and testing establishments are now told to judge products on performance, in a possibly ill-informed, if not downright dangerous, attempt to sweep away old methods and open up competition. As a result, it seems, lubricant and fluid evaluations can no longer relate to chemical class. Thus, when choosing blindly, between fluid A and fluid B, the selector will be unable to take into account the hydrolysis problem associated with fluid A, since hydrolysis tests are not normally used to evaluate fluids in the application in question and so have not hitherto been included in performance tests. This disadvantage will not be apparent until it is too late. Considerations of safety are liable to become secondary to those of price where performance is made the sole criterion. Conversely, in the limited, in terms of performance, popular automotive market, a hydroprocessed oil will easily perform within the specifications of a normal engine oil. These are not very demanding: pour points of −30◦ C, flash points of 225◦ C, and drain intervals of up to 10,000 miles (16,000 km), usually define their use and life.

In some ways, synthetics in this market are unnecessary, an overkill, as the automotive manufacturers have not yet commercialized cars and trucks that are guaranteed to run on the same oil for, say, 500,000 to a million miles (800,000–1.6 m km), that is, in sealed-for-life engines. Instead, automotive engines still usually demand services including oil changes every 4,500 or 6,000 miles, thus never giving synthetic oils a chance to show their real mettle. However, in the extreme conditions imposed by a jet engine or the climate in the Antarctic, for instance, only a synthetic oil has all the properties required. So, here the NAD ruling really falls down. Having concluded from the performance criteria that hydroprocessing produces a synthetic oil, it had to admit that Castrol was unable to show that their enhanced mineral oil was superior to a synthetic and effectively ignored the fact that specific synthetic oils can always outperform mineral oils. Herein lies the second, major, difference concerning performance: since true “synthetics” are chemically designed, their properties can be varied at will — pour points, flash points, VIs, kinematic viscosities, within much greater ranges than enhanced mineral oils — according to their end purpose. This can be done to a certain extent with hydroprocessed mineral oils by additivation. But is “additivation” the same as synthesis? Does additivating an oil make it “synthetic?” Is a vegetable oil that has its properties altered “synthetic?” The risk is that by extending the term to cover any oil that has had its chemistry tampered with, it loses all meaning.

Copyright 2006 by Taylor & Francis Group, LLC

A.3 DEFINING MINERAL HYDROPROCESSED OIL AS “SYNTHETIC” Why does anyone need to define mineral hydroprocessed oil as “Synthetic?” This is, perhaps, one of the most interesting, and unconsidered, aspects of the whole question. If a hydroprocessed mineral oil has certain performance advantages over a normal refined mineral oil, why not define it, marketwise, as “hydroprocessed” and let the products and their performance stand on their merits in that category? Why bother to try to borrow a term previously used for something else? The answer must inevitably be marketing related. It has been perceived, rightly or wrongly, that “synthetic” oils, as normally defined, possess some consumer cachet, some commercial magic, that mineral oils do not. This decision may come back to haunt the advertisers, should they ever have a product that they really want to distinguish as synthetic. The manufacturers and marketers of “real” synthetics could react by saying what their synthetic is, for example, a PAO or an ester. The image creators could surely have a field day with the terminology, the chemical makeup, and the futuristic mystery of these chemically synthesized products. So there it is: “synthetic” as a term has been redefined and watered down by the NAD decision. It obscures questions of the ultimate performance and application of synthetics. And all because of what? A marketing ploy? Perhaps that was all the Castrol–Mobil dispute was about.