An Analysis and Prediction of Lubricant Film Starvation in Rolling Contact Systems

Abstract

Optical EHD experiments in a ball-flat rig reveal that the degree of EHD fluid film starvation increases with both rolling speed and viscosity. Lubricant film starvation in rolling contacts is attributed to the insufficiency of fluid replenishment in the rolling path in the time interval between contacts. A film replenishment model is used to compute the film rebounding rate. The role of surface tension in contact lubrication is defined in terms of its effects on the rate of film replenishment. An analysis is presented using a depressed oil layer shape approximated by a deformed Hertzian point contact profile to predict the effect of upstream half-film height on the thickness of the plateau EHD film. A graph is obtained for the plateau film thickness as a function of the speed-viscosity parameter and a new starvation parameter proportional to oil-air surface tension and rolling element spacing. The result is in agreement with measured plateau film thickness in circular contact at different speeds for a realistic ambient layer thickness.