Service life of lubricating grease in ball bearings (Part 2) analysis of service life based on infiltration characteristics of base oil

Abstract

The preceding paper Part 1 showed that the service life of urea grease in angular contact ball bearings, determined on FAG FE9 rolling bearing grease testers, considerably differed depending on the type of thickeners. Further, it reasoned that insufficient “Feed” of the base oil to the bearing raceway led to seizure limiting the service life on the basis of the results obtained by tracing infiltration of the base oil through re-distributed grease in the bearing. In order to provide a logical rationale for these findings, the present paper Part 2 analyzes the “Feed” behavior. The equivalent radius characterizing the infiltration rate of the base oil through grease with different thickener concentration is determined with a newly developed methodology using filter paper as the medium. A chart is introduced to show the change in the equivalent radius of grease during an operation and the limiting condition leading to the failure is discussed. Finally, the means to make relative comparison of the service life of grease without conducting bearing tests is proposed.