Bearing grease deterioration

Abstract About 80% of bearing mountings are grease lubricated. This has many advantages, such as eliminating complicated oil cooling systems, and better organisation of the available space in machine tools and aircraft. However, the bearing service life is reduced by grease deterioration. Many papers give recommendations concerning regreasing intervals but information concerning grease deterioration and service life is poor. This paper presents theoretical and experimental work concerning grease film thickness estimation and its deterioration. An equation relating grease service life to the main influencing factors is proposed. We measured grease film thickness by the global electrical resistance method. Grease deterioration is illustrated by electron microscopy.