Thin-film grease lubrication

One of the most important examples of the thin-film regime is in the grease lubrication of rolling element bearings. Grease lubrication is not usually considered in this context and yet there is considerable evidence that man y bearings operate under starved conditions where the film thickness drops to a fraction of the fully flooded value. Thus it is the mechanisms of lubr icant supply and film formation in the starved regime that are important in ensuring the successful operation of a bearing. The aim of this paper, the refore, was to explore grease lubrication from a thin-film perspective and to examine the many factors that could influence starved film formation. Mu ch of the current understanding in this area is derived from studies of sta rved fluid film lubrication and this provides a convenient starting point f or the discussion. Grease lubrication is considered as a replenishment prob lem and recent experimental work is presented illustrating some of the aspe cts discussed in the text. The effect of grease properties, bearing operati on and design on film formation is examined. Grease lubrication in the thin -film regime is a complex problem. It includes aspects of non-Newtonian rhe ology, surface chemistry, capillary flow and starved elastohydrodynamic lub rication (EHL). All of these aspects need to be resolved in any future mode l that will be capable of explaining and predicting grease lubricating beha viour in bearings.