The Effect of Cyclic Speed on the Wear Properties of Molybdenum Disulfide Greases under Extreme Pressure Loading Using 4 Balls Wear Tests

Authors: Gabi Nehme

Abstract:

The relationship between different types of Molybdenum disulfide greases under extreme pressure loading and different speed situations have been studied using Design of Experiment (DOE) under 1200rpm steady state rotational speed and cyclic frequencies between 2400 and 1200rpm using a Plint machine software to set up the different rotational speed situations.  Research described here is aimed at providing good friction and wear performance while optimizing cyclic frequencies and MoS2 concentration due to the recent concern about grease behavior in extreme pressure applications. Extreme load of 785 Newton was used in conjunction with different cyclic frequencies (2400rpm -3.75min, 1200rpm -7.5min, 2400rpm -3.75min, 1200rpm -7.5min), to examine lithium based grease with and without MoS2 for equal number of revolutions, and a total run of 36000 revolutions; then compared to 1200rpm steady speed for the same total number of revolutions. 4 Ball wear tester was utilized to run large number of experiments randomly selected by the DOE software. The grease was combined with fine grade MoS2 or technical grade then heated to 750C and the wear scar width was collected at the end of each test. DOE model validation results verify that the data were very significant and can be applied to a wide range of extreme pressure applications. Based on simulation results and Scanning Electron images (SEM), it has been found that wear was largely dependent on the cyclic frequency condition. It is believed that technical grade MoS2 greases under faster cyclic speeds perform better and provides antiwear film that can resist extreme pressure loadings. Figures showed reduced wear scars width and improved frictional values.

 

Keywords: MoS2 grease, wear, friction, extreme load, cyclic frequencies, aircraft grade bearing.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1088826

References:

[1] J. Gansheimer, R. Holinski “Study of Solid Lubricants in Oils and Greases under Boundary Lubrication”, Wear, 19(4), April 1972, pp. 439-339.
[2] A Misty, R. Bradbury “Investigation into the Effect of Molybdenum Disulphide and Graphite on the Load Bearing Capacity of Greases” NLGI Spokesman, 66(3), June 2002, pp. 25-29.
[3] A. Tamashuasky, “The effect of Graphite type, purity and concentration on the Performance of a Clay Filled Polyalpha Olefin Grease Based on four ball wear (ASTM 2266) with coefficient of friction and load wear index (ASTM D2596)”. NLGI Spokesman, 65(12), March 2002, pp. 10-25.
[4] Lansdown A.R. Molybdenum Disulphide Lubrication, Tribology Series, 35, Elsevier, p.380
[5] Kumar, A. Nagar, S.C., Mittal, B.D, et. al., "Titanium Complex Grease for Girth Gear Applications", NLGI Spokesman, 63, 6(1999)15-19
[6] Gabi Nehme and Micheline Dib, 2010, “Optimization of Mechanism of Boundary Lubrication in Fully Formulated Commercial Engine Oil Using Design of Experiment,” Tribology Transactions, 54(2), 208-226
[7] Gabi N. Nehme, The Effect of FeF3/TiF3 catalysts on the Thermal and Tribological performance of Plain Oil ZDDP under Extreme Pressure Loading. Wear, Volume 278-279 (2012): 1129-1147
[8] Gabi Nehme, Interactions of fluorinated catalyst and polutetrafluoroethylene in two different plain zinc dialkyldithiophosphate oils and one fully formulated oil using design of experiment. Lubrication Science (2011), Volume 23, Issue 4, pages 181-201
[9] Gabi Nehme, Performance Testing and Analysis of Anti-Wear Additives in Engine Oil for Reducing Phosphorus content and Improving Tail Pipe Emissions. University of Texas at Arlington, Ph.D Dissertation (2004).
[10] Gabi Nehme (2012), “The Importance of extreme pressure cyclic load in Molybdenum Disulfide greases using 4 balls wear tests” In Proceeding of IJTC2012, STLE/ASME International joint Tribology Conference, Denver, Colorado, Oct 7-10, IJTC-2012
[11] Gabi N. Nehme (2011), “The Tribological Performance of Plain and Fully Formulated Commercial Engine Oil under 2 Different Rotational Speeds and Extreme Pressure Contact Using Design of Experiment”, Tribology Transactions, 54(4), 568-588.
[12] G. Nehme and M. Dib (2011), “Fluorinated Mix in plain ZDDP oil and Commercial Oil Using Design of Experiment analysis of all Interactions and Fundamental Study of Fluorinated Mix in plain ZDDP Oils under 2 different r/min Test Cycles and Extreme Boundary Lubrication”, Proc. IMechE Vol. 225(4) Part J: J. Engineering Tribology, 193-201.
[13] Gabi Nehme (2010), “Interaction of Fluorinated catalyst with plain ZDDP oil and commercial oil using 2 rpm cycles testing and DOE analysis under extreme boundary lubrication” In Proceeding of IJTC2010, STLE/ASME International joint Tribology Conference, San Francisco, California, IJTC-2010-paper # 41044.
[14] R. L. Elsenbaumer, Pranesh B. Aswath, Gabi Nehme et al…University of Texas at Arlington and Platinum Research Cooperation. European Coating Conference: Smart Coatings II Berlin Germany: June 16, 2003. Sponsored by Vincentz Verlag KG. High Performance Lubricants and Coatings by Catalyzed PTFE Modification of the Metal Surfaces. Pg 1-10. (2003).
[15] P. Aswath, R. Mourhatch, K. Patel. S. Munot, A. Somayaji and R. Elsenbaumer, “ A Design of Experiments Approach to Develop a Better Grease”, NLGI Spokesman, 71(4), 2007, pp. 8-16.
[16] M. Kalin, J. Kogovsek, M. Remskar, “Mechanisms and improvements in the friction and wear behavior using MoS2 nanotubes as potential oil additives,” Wear 280– 281 (2012) 36– 45
[17] L. B. Barrentine, An introduction to Design of Experiment, ASQ Quality Press, Milwaukee, Wisconsin, 1999.