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Bagi Uta 2502M 11920.Pdf (4.726Mb) EFFECT OF ADDITIVE MORPHOLOGY & CHEMISTRY ON WEAR & FRICTION OF GREASES UNDER SPECTRUM LOADING by SUJAY DILIP BAGI Presented to the Faculty of the Graduate School of The University of Texas at Arlington in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN MATERIALS SCIENCE AND ENGINEERING THE UNIVERSITY OF TEXAS AT ARLINGTON December 2012 Copyright © by Sujay Bagi 2012 All Rights Reserved ACKNOWLEDGEMENTS I would sincerely like to express the deepest appreciation and gratitude to my advisor and committee chair, Dr. Pranesh Aswath, who has continually encouraged me the with the spirit of independent thinking and instilled a research acumen in me throughout my time as a graduate student in the Department of Materials Science & Engineering at the University of Texas at Arlington. His fabulous knowledge of subject matter and meticulous way of guidance makes him the most remarkable mentor in the department. My sincere gratitude to the committee members, Dr. Yaowu Hao and Dr. Fuqiang Liu for being so encouraging and cordial; I am indebted to many of my colleagues and friends at UTA for making this time one of the most memorable moments in my life. I would like to whole-heartedly thank Dr Xin Chen for all the help regarding the chemistry formulations and Soxhlet apparatus. I would like to express my deepest gratitude to Dr. Mihir Patel for being a great friend and a mentor; I would like to acknowledge all my colleagues in the Tribology & Bio-materials group Megen Velten, Olumide Oruwajoye, Pradip Sairam, Vibhu Sharma, Ami Shah, Olusanmi Adeniran for all the help and the support I received. My sincere words of appreciation for Eray Erkan and Jei He for all the help and support in using the characterization equipment’s in CCMB; to Helen Hough, Libia Cuauhtli and Jennifer Standlee, for their help related to official matters, thesis writing and for all of their good wishes; My sincere acknowledgement to Dr. Jiechao Jiang and David Yen for the help and training with the CCMB characterization facility. I would also like to thank other grad students Dong Liu, Swathi Murthy, Amir Salehi, Manoucher Teimouri, Aida M Roshan, Zi Wei, Yishu Wang and Eric Yeh for their support. iii My sincere words of appreciation go to my family members and friends for their compassion and backings in completing this project. I would like to acknowledge my parents Dr. Dilip Bagi and Dr. Shraddha Bagi for their continual affection, love and support without which I wouldn’t have achieved all my dreams. I would like to thank my brother Sourabh Bagi for being an awesome person in my life with all his support & understanding. I would also like to acknowledge my family members Badal Bagi, Alhad Bagi, Preetam Bagi, Pradeep Bagi, Anil Manere, Yash Manere, Sheetal Manere, Sudhakar Manere, Gautam Killedar, Gomtesh Killedar for their unwavering support throughout my Master’s program. I would sincerely like to acknowledge Mr. Bharath Kamma who has been a source of inspiration and motivation to my throughout my career; all my friends and colleagues at John Deere, Albemarle Corporation and BMS College of Engineering. I would like to whole-heartedly thank Harsha Doreswamy, Sudeep Gangavathi, Avinash Bharadwaj, Sumanth Meda Jayaprakash, Bharat Venugopal, Abhishek Bangalore and Pavan Kanajar my friends and roommates at UTA, and I wish them all the very best & a marvelous life. December 4, 2012 iv ABSTRACT EFFECT OF SPECTRUM LOADING ON PERFORMANCE OF GREASES Sujay Bagi, M.S. The University of Texas at Arlington, 2012 Supervising Professor: Pranesh Aswath The primary focus of grease development is to minimize friction and improve on wear and load bearing capacity. Traditional method to evaluate wear behavior of grease is based on ASTM D2266 which evaluates the performance of grease at 75°C, 40Kg and 1200 rpm for 1 hour. However, actual applications may require bearings to be subjected to spectrum loading conditions where-in rotations per minute (rpm), load and duration of test are variables. A series of six tests were conducted for all the grease blends; load was treated as the variable in four of the tests while maintaining the frequency constant and in the other two tests frequency was treated as the variable while keeping the load constant. Four different blends of greases were formulated using techfine or unmilled MoS2, milled MoS2, the third one consisting of a combination of PTFE & ZDDP and the fourth one consisting of a combination of PTFE, ZDDP and MoDTC, which were then tested under spectrum loading conditions where loads, frequency and duration of the tests were treated as variables. MoS2 has long been considered as an Extreme Pressure (EP) additive; however untreated MoS2 at lower loads behaves as pro- abrasive agent leading to an increase in the wear numbers. Milled MoS2 was primarily used to study the deteriorating role played by the sharp edges or corners of the MoS2. The third blend v which used a combination of PTFE (Polytetrafluoroethylene) & ZDDP (Zinc Dialkyldithiophosphate) was used as PTFE acts as a friction modifier and ZDDP as an anti-wear additive. The fourth blend which consisted of PTFE, ZDDP & MoDTC (Molybdenum Dithiocarbamate) was tested to study the effect of friction modifier on the combination of PTFE & ZDDP. With intent to replace the MoS2 based greases the combination of PTFE, ZDDP and the combination of PTFE, ZDDP & MoDTC were proven to be synergistic and reported very low wear and friction numbers. Four ball tribometer was used to carry out the wear tests. E52100 steel balls as specified by the ASTM D2266 standard were used. The role played by the test variables on wear and friction was examined; the tribofilm formed on the surface was analyzed using various characterization techniques like SEM, EDS and Stereo Optical Microscopy. This research is focused on understanding the interactions of various additive chemistries and milling conditions under the influence of load, temperature and rpm. Ball milling of MoS2 leads to significant changes in the morphology of the particles owing to which a significant improvement in the wear behavior and friction coefficient is seen. Functionalization of PTFE particles with electron beam irradiation makes the PTFE particles highly polar and increases the surface affinity of the particles leading to a better tribofilm resulting in significantly reduced wear. The addition of a friction modifier like MoDTC to a mixture of PTFE and ZDDP further reduces friction and wear due to its synergistic interaction with the additives. vi TABLE OF CONTENTS ACKNOWLEDGEMENTS ................................................................................................................iii ABSTRACT ...................................................................................................................................... v LIST OF ILLUSTRATIONS.............................................................................................................. xi LIST OF TABLES ...........................................................................................................................xiv Chapter Page 1. GENERAL OVERVIEW……………………………………..………..….. .......................... 1 1.1 Objectives and Drive for the Research work .................................................... 3 1.2 Outline of the Research work ........................................................................... 5 2. BACKGROUND............................................................................................................... 6 2.1 Tribology ........................................................................................................... 6 2.1.1 History of Tribology .......................................................................... 6 2.1.2 Interdisciplinary aspects ................................................................... 7 2.2 Friction................................................................................................................ 9 2.2.1 Laws of Friction .............................................................................. 10 2.2.2 Asperities and Stick-slip phenomenon ........................................... 12 2.2.3 Adhesion theory of friction.............................................................. 14 2.3 Wear ............................................................................................................... 15 2.3.1 Mechanisms of Wear ..................................................................... 16 2.3.1.1 Adhesive wear .................................................................... 16 2.3.1.2 Abrasive wear .................................................................... 17 2.3.1.3 Corrosive wear ................................................................... 17 2.3.1.4 Fatigue ............................................................................... 18 2.3.2 Stages of Wear .............................................................................. 20 2.4 Lubrication ...................................................................................................... 21 vii 2.4.1 Lubrication regimes ........................................................................ 23 2.4.2 Stribeck curve ................................................................................ 26 2.5 Greases .......................................................................................................... 28 2.5.1 Grease composition and properties ............................................... 29 2.5.2 Grease
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