Centrifugal effects and free surface thin layer flow in roller bearings

Lubricant film thickness in EHL contacts is generally predicted by assuming ample lubricant supply. However, in many applications such as grease lubrication or at high speed, the lubricant supply may not be sufficient and starvation occurs. In order to predict the effects of starvation on film thickness and contact pressures, starved lubrication models have been developed. Input to these starved lubrication models is the thickness and the shape of the layer of lubricant on the track in the inlet region of the contact. In real bearing contacts the thickness and distribution of the supply layer is determined by many different effects, ranging from the impact of rolling elements, the supply rate of base oil bleeding from the grease, to redistribution of base oil due to surface tension and centrifugal effects. Such centrifugal effects play a role in e.g. spherical and tapered rolling element bearings. The influence of the centrifugal effects on the inlet layer is the topic of the presented research. A model for the free surface thin layer flow on a rotating axisymmetric surface has been developed. The model is applied to predict film thickness decay due to centrifugal effects in a spherical roller bearing. In the model it is assumed that in each roller-raceway contact the lubricant in the exit region equally partitions in two layers on the surfaces of a roller and the raceway . This so called equipartition assumption has been verified experimentally, measuring the lubricant layer thickness after separation of an oil layer between a plate and a cylinder.