INFLUENCE OF SURFACE-ROUGHNESS ON NORMAL-SLIDING LUBRICATION

Contact between machine components can involve normal, sliding and rol ling motion, either singly or in combination. Combined normal and slid ing motion, which occur for example in the meshing of gear teeth and i n heavily-loaded rolling elements, can present problems for lubricatio n. The purpose of the present experimental study was to investigate ho w surface roughness affects the lubricant film characteristics under c onditions of combined normal and sliding motion. The experimental arra ngement consisted of a rotating roller which impacted a stationary bal l in the presence of a lubricant. Under the same conditions of normal surface approach, increasing the surface roughness significantly decre ased the level of roller sliding that could occur without breakdown of the lubricating film. This behaviour was similar to a step function. Of the several surface roughness parameters investigated, only those w hich involved the maximum peak-to-valley height correlated well with e xperimental results. In general, surface roughness had a greater effec t on oil film breakdown than did either viscosity or load.