Experimental study of the impact of grease particle contaminants on wear and fatigue life of ball bearings

Ball bearings’ rating life is reduced when they are installed, operated and maintained under harsh environmental conditions as they suffer from excessive wear due to debris contaminants in the lubricant. This life reduction is taken into account when calculating the modified rating life but the impact of contaminant’s variables such as size, hardness and concentration level are not determined in detail. In this work, greases contaminated with particles of different sizes and hardness (steel and corundum) are tested to shed new light in the way these parameters and wear’s progress are related. A test rig is utilized and the most recent methods on vibration analysis regarding bearings’ condition and estimated residual life are assessed and evaluated. At the end of the tests, optical inspections using a stereoscope verify the vibration analyses results. It can be concluded that wear is more severe when harder particles are used, but regarding their size, it seems that wear progresses in a different manner depending on particle’s hardness and brittleness as soft ductile particles are rolled over and hard brittle particles are crushed down.