A Proposed New Film Thickness-Roughness Ratio, Λz, in Rolling Bearings: Notes on an Engineer’s Experience with Surface Texture Parameters

The film thickness-roughness ratio Λ has been used since the mid-1960s as a simplified criterion for the lubrication conditions in rolling bearings. However, due to an assumed Gaussian distribution of the roughness height amplitudes of the functional surfaces of rolling bearings and other unsubstantiated assumptions regarding the mechanisms of contact interaction, concerns have arisen about the representability of Λ in terms of lubrication. In this study, a more objective Λ-type ratio that does not depend on the law of roughness height distribution and the peculiarities of contact mechanics is introduced and defined as Λz. The relevant range of the new Λ ratio is lower than that of its conventional counterpart, and it overlaps with contemporary theoretical and experimental results. The study exhibits unique profilometric data of the functional surfaces of the roller bearings, produced by the major bearing manufacturers. An extensive and precise inspection of the surface texture of a representative number of these bearings revealed a substantial deviation in their surface roughness height from the Gaussian distribution (especially evidenced by the large scatter of their kurtosis and skewness values beyond a normality tolerance).