Agricultural Engineering, Number 51 (2019)


Gabi Nehme, Sara El-Merhabi, Saeed Ghalambor
University of Balamand; University of Pittsburgh


The lamellar structure of MoS2 provides very good protecting layer that can be easily sheared under the application of extreme pressures and thus enhance the antiwear performance of the chromium steel bearing aircraft grade E52100. ASTM standard 2266 uses 4–ball testing by keeping the load at 393 Newton wherein the grease is heated to 75ºC and the test is conducted at a rotational speed of 1200 min-1 for 1 hour and the wear scar is measured at the end of the period. While this method is useful under fixed conditions it is not always representative of the fields where variable loads and speeds and different break in periods play a role and could change the results tremendously.

The goal of this study was to examine the loads and speeds conditions with and without break in period of 30 second at the start of the test and every 7.5 minutes thereafter. This will help explain their influences on the wear properties of lithium base grease under fixed 2% MoS2 concentrations. Results indicated that wear was largely dependent on the loading condition during specific break in period at a higher rotational speed. It is believed that MoS2 greases perform better under moderate loading when break in period is used as was optimized by Design Expert analysis (DOE). MoS2 is sufficient to improve the wear characteristics at different break in period for different speeds and loads for extreme pressure applications.

Keyword(s): Friction, Wear, Molybdenum disulfide, grease, Extreme pressure, load with break in period, Design of Experiment (DOE)


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, IJTC–2012.

Gabi N. Nehme, 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.

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.

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 181–20.

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).

J. Gansheimer, R. Holinski Study of Solid Lubricants in Oils and Greases under Boundary Lubrication, Wear, 19(4), April 1972, pp. 439–339.

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.

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.

G. Nehme and M. Dib. 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.

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.

Gabi Nehme (2011), Fluorinated FeF3 catalyst interactions in three different oil formulations using design of experiment optimization and chemistry characterization of tribofilms. Lubrication Science 23 (4), 153–179.

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.

Gabi Nehme (2013), The importance of variable speeds under extreme pressure loading in molybdenum disulfide greases using four-ball wear tests. Tribology Transactions 56 (6), 977–985.

Gabi Nehme (2017), Tribological behavior and wear prediction of molybdenum disulfide grease lubricated rolling bearings under variable loads and speeds via experimental and statistical approach. Wear 376, 876–884.

G Nehme. Tribological and thermal characteristics of reduced phosphorus plain ZDDP oil in the presence of PTFE/FeF3/TiF3 under optimized extreme loading condition and a break in period. Wear 301 (1–2), 747–752.

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Agricultural Engineering ISSN 1392-1134 / eISSN 2345-0371

This journal is published under the terms of the Creative Commons Attribution-Noncommercial 3.0 Unported License. Responsible editor: Dr A. Žunda.