Free Surface Thin Layer Flow in Bearings Induced by Centrifugal Effects

To be able to predict service life of grease-lubricated bearings, it is of major importance to be able to predict the grease life; i.e., to predict when the lubricant film formation capability has decreased below a certain level. The objective of the present study is to develop theoretical models that can be used in practice to predict different aspects of grease life. As a first step, the influence of centrifugal forces on lubricant migration and the long-term film thickness decay rate due to this effect in a bearing is studied. The authors present a model that can be used to predict the decrease of oil-layer thickness due to centrifugal forces as a function of position across the track for different types of bearings. It is assumed that the oil layers in each of the roller raceway contacts separate equally between the diverging surfaces. To provide some justification for this hypothesis, a roller/plate experiment is carried out. As an example, the model is applied to the geometry of a spherical roller bearing. Two flow types are distinguished, depending on the shape of the lubricated surfaces. For various sizes and for different geometry parameter settings, similar central layer decreases are predicted. It is shown that the centrifugal effects can significantly reduce the layer thickness, within the service life of the bearing.