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Effect of Over Rolling Frequency on the Film Formation in Grease Lubricated EHD Contacts under Starved Conditions

Institute for Machine Elements and Systems Engineering, RWTH Aachen University, Schinkelstrasse 10, 52062 Aachen, Germany
Author to whom correspondence should be addressed.
This article is an extended version of the conference contribution published on the GETLUB Tribology and Lubricant Conference organized by FVA, 6–7 November 2018 in Hamburg, Germany.
Lubricants 2019, 7(2), 19;
Received: 30 November 2018 / Revised: 8 February 2019 / Accepted: 13 February 2019 / Published: 21 February 2019
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 rotational speed, which is referred to as starvation. Thus, the film thickness of grease lubricated contacts differs from that of oil lubricated contacts. However, the base oil properties under fully flooded conditions are commonly assumed to estimate the operating lifetime of grease lubricated bearings, which are usually not fully flooded. Hence, 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. At high rotational speeds, i.e., high over rolling frequencies, starvation is likely to occur, due to insufficient lubricant supply by replenishment behind the rolling element. Therefore, the focus of this contribution is to investigate the effect of over rolling frequency, and thus replenishment time, on the lubricating film formation in starved, grease lubricated EHD contacts. The film thickness measurements were performed on a ball-on-disc tribometer, which was extended by adding a second ball specimen in front of the measuring ball. By varying the angular distance between the two contacts, the lubricant displacement can be controlled, such that the effect of replenishment time on the film formation can be determined. These investigations should help to establish an advanced understanding of the mechanisms of grease lubrication, and encourage future work with a focus on developing a method to predict the film formation in grease lubricated EHD contacts. View Full-Text
Keywords: EHD contact; grease lubrication; starvation; replenishment; thickener layer EHD contact; grease lubrication; starvation; replenishment; thickener layer
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MDPI and ACS Style

Fischer, D.; Mues, H.; Jacobs, G.; Stratmann, A. Effect of Over Rolling Frequency on the Film Formation in Grease Lubricated EHD Contacts under Starved Conditions. Lubricants 2019, 7, 19.

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