Twin disc micropitting tests

Gears are important power transmission components and their efficiency and durability strongly depend on their tribological performance. The demand for higher efficiency has further increased the requirements for controlled tribological performance of gear contacts. One of the typical tribological failures that gears experience is micropitting, which is a fatigue failure of the surface strongly associated with low lubricant film thickness. Micropitting is claimed to be the dominant life limitation for ground hardened gears operating under modest conditions. In this work the factors affecting micropitting performance of gears were studied. Twin disc experiments were carried out to investigate the effect of surface roughness, lubricant type and surface treatment on micropitting performance of two case hardening steels. The test results showed that the roughness of the gear has a major impact on the micropitting performance. Also the use of DLC coating or carbonitriding surface treatment and the use of ester type lubricant had a beneficial effect compared to untreated or mineral oil lubricated surfaces.