Starvation and Reflow in a Grease-Lubricated Elastohydrodynamic Contact

The lubrication mechanisms of a grease in a rolling-element bearing has been studied through the measurement of film thickness in a rolling point contact. To simulate bearing conditions the contact runs under fully starved conditions; there is no attempt to maintain bulk flow of the grease into the inlet using an external supply. In consequence the film thickness drops off rapidly as the contact progressively starves. After a few minutes rolling (at constant speed) an equilibrium film thickness is attained which has two components: a residual film (h_R) comprised of degraded grease thickener and a hydrodynamic component (h_EHD) due to the liquid phase from the grease. The hydrodynamic contribution represents a balance between lubricant lost from the contact and replenishment from the grease close to the track. The ability of the grease to replenish the rolling track has been inferred from measurements of lubricant reflow around the static contact. These results are discussed in light of current starvation and grease lubrication models.