Tribological behavior and wear prediction of molybdenum disulfide grease lubricated rolling bearings under variable loads and speeds via experimental and statistical approach

Abstract

Proper lubricants and lubrication methods for rolling bearings are essential for providing sufficient bearing performance in high pressure applications. Main roles of molybdenum disulfide (MoS2) grease lubricant in rolling bearing are reduction of friction and wear, removal of frictional heat, extension of fatigue life, and protection from corrosion. Traditional method to evaluate wear behaviour of grease is based on ASTM D2266 which evaluates the performance of grease at 75 °C, constant load and speed. However, actual applications may require bearings to be subjected to variable loading conditions where-in rotations per minute (rpm), load and duration of test are variables. 4 ball wear tests were conducted under these variable conditions using chrome-plated steel balls (Bearing-quality Aircraft Grade E52100), to examine the extent of wear and to predict its behaviour using 2 level design of experiment (DOE) factorial approach. In this paper wear and bearings grease deterioration with and without MoS2 are shown and statistical equations to predict wear with respect to speed, MoS2 concentration, and loads are calculated. Auger electron spectroscopy (AES), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) were used in order to highlight wear and friction for different lubricant blends and to understand the influence of MoS2 and variable loads on grease. Results indicated that wear depend largely on loading conditions. It is believed that MoS2 greases perform poorly under constant load and a reduced concentration of MoS2 is sufficient to provide the same improved wear characteristics under variable loads and speeds for extreme pressure applications.