Grease flow based on a two-component mixture model

Abstract

Rolling element bearings are the most common type of bearings and about 90 % of them are lubricated with grease. In flow modeling grease has almost always been treated as a homogeneous single-component material described by a shear thinning rheological model. The present modeling paper attempts to incorporate key features not addressed by existing models: the two-component nature of the grease, and the fact that the thickener is a sort of delivery system of oil to the contact. In the present approach, the thickener is modeled as a medium containing the oil. Oil flows through the thickener according to the Darcy-Brinkman law. The thickener is regarded as a sort of porous medium, but the key feature is a linear interaction force between the two components. The model is conceptual and speculative but could provide inspiration for alternate ways of thinking about grease flow behavior. Three idealized cases are considered: flow in simple configurations of rheological devices, flow in a contact completely composed of grease, and flow in a contact with a layer of grease and a layer of oil. For illustrative purposes the rigid cylinder-plane contact is considered, and a beneficial effect of the grease is seen. Many extensions of the model itself are possible, and it can be applied to more realistic problems. Although validation is not provided, the conceptual framework could likely be tested by relatively straightforward experiments.