The influence of coatings on the oil-out performance of rolling bearings

The paper reports tests carried out using a high cycle rolling contact test facility based on a thrust ball bearing configuration. The test machine is instrumented for temperature, torque, and speed measurement. Our recent studies have focused on the "oil-out" performance using coated and uncoated counterfaces. The coatings tested were tungsten carbide amorphous hydrocarbon and chromium nitride. Also we have investigated the influence of surface finish on friction and wear performance. This work shows that the life of a thrust bearing, running under oil starvation conditions, can be extended by 50% by depositing a 1 μm thick tungsten carbide amorphous hydrocarbon coating on the rolling elements. The life can further improved to a 75% increase by depositing a 1 μm thick chromium nitride coating on the rolling elements. Data are presented illustrating the benefits provided by coatings under these extreme operating conditions, and their ability to delay the onset of catastrophic bearing damage.