Observation of Grease Film Behavior in Sliding-Rolling Concentrated Contacts

In sliding-rolling concentrated contacts, the grease film is subjected to shear action. In this study, grease film behaviors have been observed under different sliding-rolling ratios (SRRs) by measuring film thickness and friction coefficient simultaneously. The evolution patterns of the grease films with disc revolutions are affected by SRR, entrainment speed, and grease consistency. The severe starvation due to film decay at low shear and the film recovery at high shear has been recognized. The grease with low consistency is in a fully flooded state due to improvement in lubricant replenishment. In addition, the corresponding friction coefficient tends to increase or be constant in terms of contact states. The mechanisms of the grease behavior related to shear actions and grease properties are analyzed.