The impact of water contamination on the performance failure of lithium grease

Abstract

The performance of grease is significantly influenced by water contamination in humid environments, such as those found in mines and offshore wind farms. In this study, the impact of water contamination on the physicochemical properties, rheological properties, film thickness and tribological properties of lithium greases was evaluated using a series of instruments and techniques, including rheometer, ball-on-disc contact test rig, UMT tribometer and others. Results show that the water content of 2% can enhance both the shear resistance and the extreme pressure capacity of lithium-based grease. The shear viscosity and the structural recoverability increase when water content is below 4%. However, when the water content reaches 8%, the equilibrium of the grease-water composite system is disrupted, resulting in the formation of soap fiber surface breakage notches and a notable reduction in shear viscosity. Furthermore, grease with a water content of 2% to 4% is capable of forming a thicker multi-phase mixed lubrication film, wherein soap fibers, base oil and water coexist. Conversely, the film thickness is observed to diminish rapidly when the water content reaches 6% to 10%. Moreover, the oil–water mixture exhibits inadequate lubricating oil film recovery ability in boundary lubrication. The coefficient of friction of water-contaminated grease increases significantly, reaching 2–3 times that of the initial fully lubricated state at a certain point with severe surface wear. These findings provide technical support for the utilization of lubricants in humid environments and highlight the potential impact of water contamination on lubricant performance.