Experimental Investigation of Effect of Surface Property on Film Shape and Friction in EHL

Considering that boundary slip effect may produce lower friction force, pure sliding EHL experiment was conducted using glass discs with different wettability. For steel ball against SiO₂-Cr-coated glass disc under lubrication of high viscosity lubricant PB2400, friction curve from EHL to HL had two inflection points and this was significantly different from traditional Stribeck curve. The two inflection points were related to the presence of dimple and disappearance of elastic deformation. Under lower load, two kinds of glass disc surfaces produced similar interference images and friction curves and the apparent slip of non-Newtonian effect of polybuttene might be the main cause of inlet dimple and abnormal friction curve. Under higher load, Cr-coated disc surface produced lower film thickness and friction force than SiO₂-coated disc surface and it is postulated lower surface energy of Cr surface lead to smaller friction and bigger contact slope.