Influence of topography on the running-in of water-lubricated silicon carbide journal bearings

The study summarizes an experimental investigation on the running-in of water-lubricated journal bearings and shaft sleeves made of 10 different commercial silicon carbide materials. In each test the sliding surfaces became polished and the sliding conditions were transformed from boundary or mixed lubrication to full film lubrication within a rather short sliding distance. The initial surface roughness strongly influenced on the initial dynamic coefficient of friction, and on the running-in distance required to reduce the coefficient of friction from a level typical of boundary or mixed lubrication to a level typical of full film lubrication. The initial surface roughness of the shaft sleeve was more slowly removed than that of the bearing, and therefore the surface quality of the shaft rather than that of the bearing governed the running-in distance required for the polishing. The initial surface roughness of the bearing practically only influenced the dynamic coefficient of friction at the beginning of the running-in procedure. In comparison with the influence of the surface roughness variations, the material properties of the silicon carbides studied has a limited influence on the running-in behaviour,which was principally related to a tribochemical surface polishing process.