Effects of break in period on the 4-ball wear tests using molybdenum disulphide (MoSշ) as EP additives in lithium based grease

The lamellar structure of MoS 2 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% MoS 2 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 MoS 2 greases perform better under moderate loading when break in period is used as was optimized by Design Expert analysis (DOE). MoS 2 is sufficient to improve the wear characteristics at different break in period for different speeds and loads for extreme pressure applications.