Limits of Wear Protection for Grease Lubricated Rolling Bearings

More than 90 % of rolling bearings are operated with grease lubrication. Simultaneously, an insufficient lubrication is responsible for more than 80% of bearing failures. Hence, operation in the mixed and boundary friction regime requires additive-based wear protection. Polar AW/EP additives have the potential to form protecting tribofilms on the bearing surfaces. However, a prediction of wear protection of greases is not possible yet. Therefore, the objective of this project was to analyse the influences of the grease composition and temperature on the wear protection for rolling bearings. For this purpose, various greases were characterized, and extensive component tests were carried out on the FE8 test rig. Afterwards, the formation of additive-based tribofilms was examined with microanalysis. The wear protection is found to be strongly temperature-dependent, with higher wear masses occurring in the temperature range from 40 °C to 60 °C. The choice of lubricant significantly influences the wear protection of rolling bearings. Compared to a lithium thickener, the polyurea thickener promotes a more suitable additive-based boundary layer structure. The AW/EP additives provide different wear protection performances, whereby they do not increase wear protection significantly.

The IGF project (19279 N) of the research association DGMK Deutsche Wissenschaftliche Gesellschaft für Erdöl, Erdgas und Kohle e.V., Überseering 40, 22297 Hamburg was funded via the AiF within the framework of the programme for the funding of Industrial Collective Research (IGF) by the Federal Ministry for Economic Affairs and Energy on the basis of a resolution of the German Bundestag.