Influence of free water droplets on film formation under point contact grease lubrication

Abstract The influence of the grease-water two-phase emulsion on the bearing track on the film formation has been studied by carrying out optical interferometry experiments on a ball disk test rig to observe the dynamic film-forming behavior of lubricating grease under steady-state and micro-oscillation conditions. It is found that free water cause a brief rise in the grease film under steady-state conditions, specifically due to the grease-water phase connecting the oil band on both sides of the oil reservoir. The experiment determines that the state of the phase before entering the elastohydrodynamic lubrication (EHL) contact is water-in-oil. For the reciprocating motion and oscillation, the effects of the amount of free water and the length of the motion stroke are discussed in detail. It is found that for reciprocating movements with long stroke lengths, the effect of free water is summarized to enhance the fluidity of the fibrous mass of the grease thickener in the first few cycles of the movement. For shorter stroke lengths, the effect of free water is a scouring effect on the contact zone grease after 100 cycles. This paper provides new insights into the effects that causes water pollution to the point contact lubrication during the transformation from reciprocating motion to fretting.