Film Thickness Evolution Behavior and Mechanism of Lubricating Grease at High Speeds

In most cases, lubricating grease serves as the primary lubricating medium for rolling bearings, ensuring normal operation by facilitating lubrication between bearing components. Current experimental research on grease lubrication predominantly focuses on low-speed conditions (below 2 m/s), which no longer aligns with the increasingly high operational speeds of rolling bearings. To address this gap, we conduct the high-speed lubrication experiments with a maximum speed up to 10.68 m/s using a ball-on-ring test rig under a certain amount of grease supply. The results reveal a clear distinction in film thickness evolution between high-speed and low-speed stages: at low speed, the film thickness gradually decreases with the number of ring revolutions until it stabilizes after the grease reservoir reformation; however, at high speed, a significant recovery in film thickness occurs following reservoir reformation. Observations of grease distribution further indicate that, under shear forces, the thickener on both sides of the track undergoes shear-induced breakdown and becomes uniformly distributed. This intensified shear promotes the formation of larger grease reservoirs along the contact sides and leads to the recovery of film thickness under high-speed conditions. The amount of effectively sheared grease that ultimately participates in lubrication can be characterized by the width of the grease ridge.