DOCSLIB.ORG

The Effect of Grease Composition on Fretting Wear

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Effect of Grease Composition on Fretting Wear © 2019 Alireza Saatchi ALL RIGHTS RESERVED THE EFFECT OF GREASE COMPOSITION ON FRETTING WEAR A Dissertation Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Alireza Saatchi May 2019 THE EFFECT OF GREASE COMPOSITION ON FRETTING WEAR Alireza Saatchi Dissertation Approved: Accepted: _____________________________ _____________________________ Advisor Department Chair Dr. Gary Doll Dr. H. Michael Cheung _____________________________ _____________________________ Committee Member Dean of the College Dr. Qixin Zhou Dr. Donald P. Visco, Jr. _____________________________ _____________________________ Committee Member Dean of the Graduate School Dr. Rajeev Gupta Dr. Chand Midha _____________________________ _____________________________ Committee Member Date Dr. Curtis Clemons _____________________________ Committee Member Dr. Gopal Nadkarni ii ABSTRACT This research studies the effects of composition and oil release mechanisms of greases on its performance properties, especially against a certain type of tribological damage called fretting. Grease is a complex lubricant that consists mainly of a base-oil and a thickener. Whereas the base oil is the primary lubricous component of the grease, the thickener gives the grease its consistency, or its ability to “stay put” wherever it is applied. Most thickeners are in the form of fibers dispersed colloidally in oil, entangled and connected together to form a three dimensional structure that traps the oil and prevents it from flowing freely. The oil needs to separate from the mixture and insert itself into the tribological contact in order to perform its function of preventing friction and wear. Therefore, the separation of oil from the grease, which is loosely referred to as the grease bleed, is an essential step in the protection mechanism of the grease. The “bleed rate” is a standard specification of the grease determined by a test in which the grease is put in a cone sieve under high temperature and the relative amount of oil which is “bled” out is measured. Despite the widespread application of greases, their oil release mechanism is not well understood. The theories that have been developed for oil lubrication have been applied to grease lubricated contacts, which fail to accurately account for the experimental observations. Therefore the grease bleed mechanism is the major topic in this study. We will focus on the oil release mechanism of the grease under fretting contact. Fretting is defined as a small oscillatory displacement of bodies in sliding or rolling contact and is often observed when a source of vibration or cyclic stress is present, causing excessive wear or premature fatigue failures in different applications and it is considered as a plague of the modern industry. In many of these applications, grease is iii employed as the lubricant. Another key motivation for this research is the fact that the term fretting in the literature and industrial standards fail to provide distinction between fretting under rolling and sliding contact. This is despite the fact that rolling and sliding fretting have been seen in numerous occasions to be two entirely different phenomena, especially as far as the performance of the grease is concerned, causing a great deal of confusion for both grease manufacturers and end-users. Finally, another motivation for this research is the investigation of non-soap thickened greases that unlike the more traditional soap thickened greases are not so well studied or understood especially their oil release mechanism which is for the most part, somewhat of a mystery. A good example of that is the calcium sulfonate grease that is among the newer grease types in the market and has exceptional properties. In grease making, this grease acts very differently than others in the way that it requires a lot more thickener to achieve the desired consistency. This is the reason for the extremely low bleed rate of the calcium sulfonate grease, however to the best of our knowledge, no one in the past had been able to explain the exceptionally good performance of this grease despite its nominal bleed rate being practically zero. This brings us back to the discussion of the grease bleed and points out the discrepancies in its definition. How can we define bleed as the oil release mechanism of the grease being responsible for its protection properties for the case of calcium sulfonate grease, where there is exceptional protective properties but zero bleed rate? Therefore, it seems to be necessary to redefine the bleed itself. To this end, three different grease types with soap and non-soap thickeners have been tested for their fretting wear performance. The soap thickener chosen was the lithium complex, which is one the most common grease thickener types of all times. We also tested non-soap, iv calcium sulfonate and polyurea thickened greases for comparison. Each grease was mixed with its own base oil to obtain a range of bleed rates and then the mixtures were tested for their fretting performance under different rolling and sliding conditions to find a correlation between the grease bleed rate and its protective properties. The results showed that the fretting performance of the grease under rolling contact strongly depends on the grease bleed rate whereas it did not affect the sliding fretting performance of the grease. Furthermore, there had been instances of scuffing which is the result of metal-to-metal contact due to failure in lubrication, which gave us a chance to study the starvation and scuffing resistance of the greases as well. There were some observations that were rather unexpected or somewhat hard to explain at first glance. Firstly, the polyurea grease, which showed a comparatively high bleed rate, performed worse than others and especially showed the lowest resistance against scuffing. On the other hand, the calcium sulfonate grease showed the best performance on all fronts, even though for most of the calcium sulfonate mixtures, the standard bleed rate was zero. The calcium sulfonate grease raised more questions as it showed an extremely non-linear bleed rate trend with the addition of oil. The bleed rate results were interpreted within a model that correlated the bleed with the grease thickener geometries. To obtain the geometry of the actual thickeners, the greases were tested using Dynamic/Static Light Scattering (DLS/SLS) techniques. In the proposed model the grease thickeners were treated as particles suspended in a matrix of oil instead of the traditional view, in which the thickener structure was assumed to be a sponge that holds the oil and releases it into the tribological contact. In the present model, the “sponge” view is reserved only for the “static bleed” which simulates the oil flow v behavior of the standard bleed test. Within the tribological contact, however, the “dynamic bleed” should be viewed as the separation of oil from the loose and mobile thickener particles. In other words, the thickener particles are connected with each other and hold the oil, resulting in the consistency of the grease. However, at the same time, the thickener particles do not constitute a rigid body and can move independently in the oil matrix and are also capable of separating from each other if their attraction forces are overcome or in instances where they are diluted. Another significant difference between this model than those of the past is that a region surrounding each thickener particle, called the effective media, is assumed to have wholly immobilized the oil. In older models, the bleed was inaccurately assumed to occur from the viscous flow of oil through thickeners. In the current model, it was shown that the static bleed is indeed the viscous flow of only the unbound oil in a porous structure made of not only the thickeners but the entire effective media. Further to clarifying the differences between rolling fretting and sliding fretting, in conclusion of this work, three different types of bleed mechanisms are discussed, static bleed, dynamic bleed under sliding and dynamic bleed under rolling contact. The difference between the two dynamic bleed mechanisms was attributed to the direction of the motion of the particles with respect to the sliding/rolling direction. In the light of this model, many aspects of the observed phenomena were also explained such as the unusual protection and bleed behavior of the calcium sulfonate grease which was related to the spherical geometry of its thickener micelles. vi ACKNOWLEDGEMENTS This dissertation is a summary of my Ph.D work which would not have been possible without the help, guidance, encouragements and well wishes of great mentors, colleagues, friends and family members. At this moment of accomplishment, I wish to express my sincere gratitude to my advisor, Professor Gary Doll for his constant support, guidance, mentorship and encouragement throughout the five years of my research work. I would also like to thank Dr. Paul Shiller for his invaluable suggestions, support and mentorship in every step of the development of this project. I thank Professors Qixin Zhou, Rajeev Gupta, Curtis Clemons and Gopal Nadkarni for serving as my committee members and providing valuable insights to improve this research. I would like to thank Dr. S. Ali Eghtesadi for his guidance and contributions in microstructural characterizations and his advisor Professor Tianbo Liu for the support of this project. I thank Dr. Soroush Heidari Pahlavian for most of the artwork in this dissertation and his guidance regarding fluid dynamic problems. I sincerely thank Dr. Gareth Fish from the Lubrizol Corporation for his mentorship and guidance as well as providing most of the baseline grease samples for this study. I thank Dr. Barbara Fowler and Richard Fowler for their help and guidance in this project and William Wenzel and Brett Bell for technical support. I, along with our entire research team, acknowledge the Timken Company for providing funding for this work and Drs.
Load more

Recommended publications
  • Bearing-Lube-Seals-Full-Report.Pdf
    Frictional Losses of Bearing Lubricants & Bearing Seals FULL REPORT Note: These tests involved the removal of the factory-installed bearing grease and replacement with aftermarket lubricants, and in some cases, removal of the factory bearing seals. These tests solely analyzed the effects of aftermarket lubricants on bearing efficiency, and did not evaluate the effects these lubricants might have on bearing longevity. Use of a lower viscosity or lighter lubricant in a bearing will most likely require more frequent re-lubrication to maintain proper life of the bearings. CONTENTS OVERVIEW ……………………………………………………………………….. 8 Lubricants Tested …………………………………………………….. 8 Bearings Tested ……………………………………………………….. 8 RESULTS- AVERAGE FRICTIONAL LOSSES …………………………… 9 RESULTS- FRICTIONAL LOSSES BY LUBRICANT …………………… 10 Specialty Grease Discussion …………………………………….. 11 EFFECTS OF FILL LEVEL ON LOSSES ……………………………………. 12 EFFECTS OF SEALS ON LOSSES …………………………………………… 13 With Slip Oil …………………………………………………………….. 14 With Standard Grease ……………………………………………… 16 RAW DATA / ALL DATA …………………………………………………….. 18 DISCUSSION- BALL SIZE & BALL COUNT …………………………….. 19 © CeramicSpeed 2018 1 LOSSES OF WHEEL BEARINGS- ESTIMATION ……………………… 22 Example calculation of BB + hub losses ……………......... 22 FULL PROCEDURE ………………………………………………………....... 24 BOTTOM BRACKET EFFICIENCY TEST EQUIPMENT …………….. 25 LOADING CALCULATIONS …………………………………………………. 26 © CeramicSpeed 2018 2 OVERVIEW Seven lubricants of various viscosities and chemical make-up were tested on three different makes/models of BB30 bottom bracket cartridge bearings to measure frictional losses (friction). The lubricants were selected to represent the categories of dry lubricant, low viscosity oil, medium viscosity oil, high viscosity oil, standard grease, and specialty grease. The sample lubricants were purchased by Friction Facts at retail outlets. Data presented is friction per pair (set) of bearings. Lubricants Tested: 1. Powdered sub-micron Molybdenum Disulfide (dry lubricant) 2. Avid Slip R/C Bearing Racing Oil (low viscosity oil) 3.
    [Show full text]
  • Two-Dimensional Fretting Contact of Piezoelectric Materials Under a Rigid Conducting Cylindrical Punch
    Journal of Mechanics of Materials and Structures TWO-DIMENSIONAL FRETTING CONTACT OF PIEZOELECTRIC MATERIALS UNDER A RIGID CONDUCTING CYLINDRICAL PUNCH Jie Su, Liao-Liang Ke and Yue-Sheng Wang Volume 11, No. 5 December 2016 msp JOURNAL OF MECHANICS OF MATERIALS AND STRUCTURES Vol. 11, No. 5, 2016 dx.doi.org/10.2140/jomms.2016.11.535 msp TWO-DIMENSIONAL FRETTING CONTACT OF PIEZOELECTRIC MATERIALS UNDER A RIGID CONDUCTING CYLINDRICAL PUNCH JIE SU, LIAO-LIANG KE AND YUE-SHENG WANG This paper investigates the fretting contact between a transversely isotropic piezoelectric half-plane and a rigid cylindrical punch in a plane strain state. It is assumed that the punch is a perfect conductor with a constant electric potential within the contact region. Since the fretting contact problem is frictional and history dependent, the two bodies are brought into contact first by a monotonically increasing normal load, and then by a cyclic tangential load, which is less than that necessary to cause complete sliding. It is assumed that the contact region contains an inner stick region and two outer slip regions in which Coulomb’s friction law is applied. With the use of the superposition principle and Fourier integral transform technique, the problem is reduced to a set of coupled Cauchy singular integral equations. An iterative method is used to determine the unknown stick/slip region, normal contact pressure, electric charge and tangential traction. The effects of the friction coefficient, electric load and conductivity of the punch on the surface electromechanical fields are discussed during different loading phases. 1. Introduction Piezoelectric materials are important smart materials and have been widely used in various electrome- chanical devices such as actuators, sensors, transducers and micropower generators.
    [Show full text]
  • Removal of Grease from Wind Turbine Bearings by Supercritical Carbon
    1909 A publication of CHEMICAL ENGINEERING TRANSACTIONS The Italian Association VOL. 32, 2013 of Chemical Engineering Online at: www.aidic.it/cet Chief Editors: Sauro Pierucci, Jiří J. Klemeš Copyright © 2013, AIDIC Servizi S.r.l., ISBN 978-88-95608-23-5; ISSN 1974-9791 Removal of Grease from Wind Turbine Bearings by Supercritical Carbon Dioxide Javier Sanchez, Svetlana Rudyk*, Pavel Spirov Section of Chemical Engineering, Department of Biotechnology, Chemistry and Environmental Engineering, Aalborg University, Campus Esbjerg, Niels Bohrs vej 8, 6700 Esbjerg, Denmark [email protected] This work aims to test the ability of liquid carbon dioxide to remove grease from bearings in wind turbines. Currently, the removal of grease from wind turbines offshore in the North Sea is done by dismantling the bearing covers and scraping off the grease. This procedure is long, labour intensive and raises maintenance cost. Another issue is the environmental policy, the approval for newly introduced chemicals for flushing purposes are procedurally long. If the problems with grease removal could be solved in a different way other than manual removal or using chemicals, it will open many new market opportunities and would carved out a niche for the wind turbine maintenance industry. The solution of flushing grease could lower cost, time and reduce environmental impact by applying Supercritical Carbon Dioxide. The oil based grease SKF LGWM 1 was designed to handle extreme pressure and low temperature conditions. The grease covered the main bearing for 4 - 5 y in a wind turbine at Horns Rev 1 Offshore Wind Farm in the North Sea, 14 km from the west coast of Denmark.
    [Show full text]
  • Rolling Bearings and Seals in Electric Motors and Generators
    Rolling bearings and seals in electric motors and generators ® SKF, @PTITUDE, BAKER, CARB, DUOFLEX, DURATEMP, ICOS, INSOCOAT, MARLIN, MICROLOG, MONOFLEX, MULTILOG, SEAL JET, SKF EXPLORER, SYSTEM 24 and WAVE are registered trademarks of the SKF Group. © SKF Group 2013 The contents of this publication are the copyright of the publisher and may not be reproduced (even extracts) unless permission is granted. Every care has been taken to ensure the accuracy of the information contained in this publication but no liability can be accepted for any loss or damage whether direct, indirect or consequential arising out of the use of the information contained herein. PUB 54/P7 13459 EN · August 2013 This publication supersedes publication 5230 E and 6230 EN. Certain image(s) used under license from Shutterstock.com. 1 Rolling bearings in electric machines 1 2 Bearing systems 2 3 Seals in electric machines 3 4 Tolerances and fits 4 5 Lubrication 5 6 Bearing mounting, dis mounting and motor testing 6 7 Bearing damage and corrective actions 7 8 SKF solutions 8 Rolling bearings and seals in electric motors and generators A handbook for the industrial designer and end-user 2 Foreword This SKF applications, lubrication and maintenance handbook for bearings and seals in electric motors and generators has been devel oped with various industry specialists in mind. For designers of electric machines1), this handbook provides the information needed to optimize a variety of bearing arrangements. For specialists working in various industries using electric machines, there are recommendations on how to maximize bearing service life from appropriate mounting, mainten ance and lubrication.
    [Show full text]
  • Signature Redacted August 7, 2015 C Ifdb Y
    Scale-up of a High-Technology Manufacturing Startup: Improving Product Reliability Through Systematic Failure Analysis and Accelerated Life Testing MASSACHUSETTS INSTITUTE by OF TECHNOLOGY, All Shabbir OCT 0 12015 B.A.Sc. Mechanical Engineering, University of Waterloo (2014) LIBRARIES Submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Engineering in Manufacturing at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY September 2015 @ Ali Shabbir, MMXV. All rights reserved. The author hereby grants to MIT permission to reproduce and to distribute publicly paper and electronic copies of this thesis document in whole or in part in any medium now known or hereafter created. Signature redacted A uthor . ......... ........... Department of Mechanical Engineering Signature redacted August 7, 2015 C ifdb y...................------------ David E. Hardt Ralph E. and Eloise F. Cross Professor of echanical Engineering Accepted by ..... ............ Signature redacted ...... David E. Hardt Chairman, Department Committee on Graduate Theses Scale-up of a High-Technology Manufacturing Startup: Improving Product Reliability Through Systematic Failure Analysis and Accelerated Life Testing by Ali Shabbir Submitted to the Department of Mechanical Engineering on August 7, 2015, in partial fulfillment of the requirements for the degree of Master of Engineering in Manufacturing Abstract Ensuring product reliability is a key driver of success during the scale-up of a high- technology manufacturing startup. Reliability impacts the company image and its financial health, however most manufacturing startups do not have a solid under- standing of their product's reliability. The purpose of this thesis is to introduce systematic failure analysis to the engineering design process and to establish a frame- work for testing and analyzing product life so that imperative business decisions and design improvements could be made with regards to reliability.
    [Show full text]
  • Silicone Grease for Ground Glass Joints Lbsil 25 AUX Safety Data Sheet
    Silicone grease for ground glass joints LBSil 25 AUX Safety Data Sheet according to Regulation (EC) No. 1907/2006 (REACH) with its amendment Regulation (EU) 2015/830 Date of issue: 15/04/2011 Revision date: 21/11/2016 Supersedes: 15/07/2016 Version: 2.1 SECTION 1: Identification of the substance/mixture and of the company/undertaking 1.1. Product identifier Product form : Substance Trade name : Silicone grease for ground glass joints LBSil 25 AUX CAS No : 068083-14-7 Product code : S025-100 1.2. Relevant identified uses of the substance or mixture and uses advised against 1.2.1. Relevant identified uses Main use category : Laboratory use 1.2.2. Uses advised against No additional information available 1.3. Details of the supplier of the safety data sheet labbox labware s.l. Joan Peiró i Belis, 2 08339 Vilassar de Dalt - ES T +34 937 552 084 - F +34 937 909 532 [email protected] - www.labkem.com 1.4. Emergency telephone number Emergency number : +34 937 552 084 ( Office Hours) SECTION 2: Hazards identification 2.1. Classification of the substance or mixture Classification according to Regulation (EC) No. 1272/2008 [CLP]Mixtures/Substances: SDS EU 2015: According to Regulation (EU) 2015/830 (REACH Annex II) Not classified Adverse physicochemical, human health and environmental effects No additional information available 2.2. Label elements Labelling according to Regulation (EC) No. 1272/2008 [CLP] Extra labelling to displayExtra classification(s) to display No labelling applicable 2.3. Other hazards No additional information available SECTION 3: Composition/information on ingredients 3.1.
    [Show full text]
  • Influence of Surface Topography on Torsional Fretting Wear Under Flat-On-Flat Contact
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by University of Huddersfield Repository Influence of surface topography on torsional fretting wear under flat-on-flat contact Wenlong Lu1, Po Zhang1,*, Xiaojun Liu1,Wenzheng Zhai1,Mingzhuo Zhou1,Jian Luo1,Wenhan Zeng2,Xiangqian Jiang2 1The State Key Laboratory of Digital Manufacturing Equipment and Technology, School of Mechanical Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, PR China 2EPSRC Centre for Innovative Manufacturing in Advanced Metrology, University of Huddersfield, Huddersfield, HD1 3DH, UK Abstract: Influence of surface topography on torsional fretting under flat-on-flat contact were investigated. Contact surfaces of the lower specimens were prepared by milling with different initial surface roughness while the upper specimens were polished. Results indicate that with the increase of surface roughness, friction torque and accumulated dissipated energy present a first increase and then decrease tendency and are higher when the texture is perpendicular to the relative movement direction. The wear volume and wear rate present increasing and decreasing tendencies separately for textures parallel and perpendicular to the relative movement direction, and they are higher when the texture is parallel to the relative movement direction. The results can provide guidance for the initial surface design to reduce fretting wear. Keywords: surface roughness; texture direction; torsional fretting; friction and wear 1. Introduction Surface topography is the local deviation of a surface from a perfectly flat plane, and it has become increasingly important in many fields, such as materials, tribology and machine condition monitoring [1-2]. In many industrial applications the fretting degradation process is inevitable.
    [Show full text]
  • On Monitoring Physical and Chemical Degradation and Life Estimation Models for Lubricating Greases
    lubricants Review On Monitoring Physical and Chemical Degradation and Life Estimation Models for Lubricating Greases Asghar Rezasoltani and M. M. Khonsari * Department of Mechanical Engineering, Louisiana State University, Baton Rouge, LA 70803, USA; [email protected] * Correspondence: [email protected]; Tel.: +1-225-578-9192 Academic Editor: James E. Krzanowski Received: 19 June 2016; Accepted: 5 September 2016; Published: 13 September 2016 Abstract: Degradation mechanisms for lubricating grease are categorized and described. An extensive survey of the available empirical and analytical grease life estimation models including degradation monitoring standards and methods are presented. A summary of the important contributions on grease degradation is presented. Keywords: grease replenishment time estimation; grease degradation; oxidation; mechanical degradation; base oil evaporation; base oil separation 1. Introduction The lubricating effectiveness of grease is limited by both physical and chemical deteriorations caused by shear stresses, pressure, and the severity of operating conditions, particularly temperature. Degraded grease becomes inefficient and eventually loses its lubrication capacity such that it can adversely affect the machine’s performance and functionality. Proper monitoring of degradation and on-schedule replacement/replenishment of grease are important facets of machinery maintenance practices. Presently, grease replacement is performed periodically according to time schedules adapted from empirical models. Although some empirical relationships for estimating grease life are available, they tend to be restrictive. The drawback of empirical models is limited applicability when the working condition of grease is different from the operating conditions from which the empirical models were derived. In applications where the bearing element is lubricated and sealed for life, there are quality control standard procedures to measure the grease resistance to different degradation processes.
    [Show full text]
  • THE PAIN of FRETTING CORROSION by David P
    THE PAIN OF FRETTING CORROSION By David P. Scopelliti INTRODUCTION: The following paper is intended to inform on the subject at hand and is based on years of laboratory observations. Fretting motion, fretting wear, fretting corrosion … what does it all mean and can it be prevented or at least mitigated? WHAT IS FRETTING? Photo courtesy of Samtec Photo courtesy of Samtec Photo 1 Photo 2 The science is called Tribology, the study of moving, contacting surfaces, wear, friction, lubrication, etc. You may or may not remember studying Triboelectric charge in school (the electricity created by rubbing materials together). Our interest is in the phenomena known as Fretting Corrosion (and fretting motion, the driving force behind fretting corrosion). How is this different from normal plain old wear? The big difference is that fretting is a micro- motion issue typically less than 0.005” of movement. Just about any material that oxidizes is in danger of fretting corrosion under the right conditions. Everyone who has ever ridden a bicycle has seen the black residue on the chain and sprockets. It is not the macro-motion of the chain around the sprocket that causes fretting; it is the “jittering” of the chain against the sprocket and the rubbing of the individual chain components as well. The tiny vibrations set up by the chain/sprocket interaction along with the vibration generated as the bike travels is what we are talking about. As the surfaces of the chain and sprocket grind together, pulverized metal particles are frictionally heated and react with the moisture and oxygen in the air and any number of other corrosive gases or liquids in the ambient environment.
    [Show full text]
  • Issue 18: the Difference Between True and False Brinelling
    Issue 18: The Difference Between True and False Brinelling Note from Author: I wrote this article back in 2012 and it was only seen by those receiving our mailings. Now that we have gone digital with email and posting on our website we felt it was time to roll out all of my older articles. They are still relevant and I hope you enjoy! --Bud In my years of dealing with bearing failure I have heard the term brinelling used over and over with the relationship of being true or false. It’s not a question of whether or not the dent mark exists; the word true or false is defining if the dent mark is a result of the materials elastic limit being exceeded. In this short article I will try my best using as few as possible engineering terms to explain. First we need to review what these terms mean: Brinell Mark is the mark left in metal which is created by another piece of metal (or hard object.) Brinell Hardness is a scale designed to define the hardness of a material. This is measured by pressing a hardnened ball into a material and measuring the brinell mark. Pic 1: Concept of Brinell Hardness Brinelling is the term that refers to the indentation caused by impact or contact with a hard object. So then what is True Brinelling? True brinelling is a dent or brinell mark caused by contact stress that is above the allowable material limit. The estimated amount of pressure to leave a dent that is 0.0001 times the size of the rolling element is 609,000 psi in ball bearings and 580,000 psi in roller bearings.
    [Show full text]
  • Film Thickness and Friction Relationship in Grease Lubricated Rough Contacts
    Article Film Thickness and Friction Relationship in Grease Lubricated Rough Contacts David Gonçalves 1,* , António Vieira 2, António Carneiro 2, Armando V. Campos 3 and Jorge H. O. Seabra 2 1 Instituto de Ciência e Inovação em Engenharia Mecânica e Engenharia Industrial, Universidade do Porto, Campus FEUP, Rua Dr. Roberto Frias 400, 4200-465 Porto, Portugal 2 Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal; [email protected] (A.V.); [email protected] (A.C.); [email protected] (J.H.O.S.) 3 Instituto Superior de Engenharia do Politécnico do Porto, Rua Dr. António Bernardino de Almeida 431, 4200-072 Porto, Portugal; [email protected] * Correspondence: [email protected]; Tel.: +351-229-578-710 Received: 30 June 2017; Accepted: 3 August 2017; Published: 17 August 2017 Abstract: The relationship between the film generation and the coefficient of friction in grease lubricated contacts was investigated. Ball-on-disc tests were performed under different operating conditions: entrainment speed, lubricant temperature and surface roughness. The tests were performed with fully formulated greases and their base oils. The greases were formulated with different thickener types and also different base oils natures and viscosities. Film thickness measurements were performed in ball-on-glass disc tests, and Stribeck curves were measured in ball-on-steel disc tests with discs of different roughness. The role of the thickener and the base oil nature/viscosity on the film thickness and coefficient of friction was addressed and the greases’ performance was compared based on their formulation.
    [Show full text]
  • Aviation Grease Color Color Is Not an Indicator of Grease Quality Or Suitability
    Tech topic Aviation grease color Color is not an indicator of grease quality or suitability Key insight Introduction Dyes and pigments impart Depending on the application, grease can present several benefits over fluid lubrication. Greases provide a physical seal preventing contamination color only ingress, resist the washing action of water and can stay in place in an application, even in vertically and have no effect on a grease’s mounted positions. Greases are manufactured by lubricating capability. combining three essential components: base oil, thickener and additives. Base oils Thickeners Base oil comprises up to 95 Thickeners for aviation greases percent (by weight) of grease. include soap — such as aluminum, Base oil may be mineral oil, calcium and lithium — clay, and any synthetic oil or any fluid that material that holds the base oil provides lubricating properties; or will produce the solid to 95% however, all aviation greases semifluid structure. use synthetic base oil. It is the base oil component that performs the actual lubrication, except in very slow or oscillating applications. Aviation grease color Additives Grease color spotlight Additives are required to protect the component against wear, rust, corrosion and oxidation. As in lubricating oil additives, grease additives and modifiers impart special properties or modify existing ones. Additives and modifiers commonly used in lubricating greases are oxidation or rust inhibitors, extreme pressure (EP) additives, antiwear agents, lubricity or friction-reducing agents, and dyes or pigments. Mobil™ Aviation Grease SHC™ 100 grease can have varying shades of red. Possible causes include: • Very minor variation in quantity of an amine antioxidant in the grease • Temperature variation during manufacturing The color of aviation greases depends on the requirement of the specifications, OEM (Original Equipment • Inappropriate product storage Manufacturer) qualifications and/or QPL (Qualified Product Lists).
    [Show full text]