Effect of over rolling frequency on the film formation in grease lubricated EHD contacts under starved conditions

The service life of rolling bearings is significantly affected by the lubricating film formation in elastohydrodynamic (EHD) contacts. Grease lubricated EHD contacts show a film thickness decay from a characteristic rolling speed, which is referred to as starvation. Thus, the film thickness differs from that of oil lubricated contacts under fully flooded conditions. However, base oil properties under fully flooded conditions are commonly assumed to estimate the service life of grease lubricated bearings, which are usually not fully flooded. However, this assumption results in an overestimation of the film thickness for rotational speeds in the range of starvation, which can lead to uncertainties in the bearing design. The onset of starvation can be related to high rolling speeds, i.e. high over rolling frequencies, when the lubricant does not replenish entirely, so that the contact starves due to insufficient lubricant supply. Therefore, the focus of this contribution is to investigate the effect of over rolling frequency on the lubricating film formation in starved, grease lubricated EHD contacts. The investigations should help to establish an advanced understanding of the mechanisms of grease lubrication, to encourage future work with focus on a method to predict the film formation in grease lubricated EHD contacts. © 2019 Expert Verlag. All rights reserved.