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Lubricants 2018, 6(2), 32; https://doi.org/10.3390/lubricants6020032

Effect of Base Oil Type in Grease Composition on the Lubricating Film Formation in EHD Contacts

Institute for Machine Elements and System Engineering, RWTH Aachen University, Schinkelstrasse 10, 52062 Aachen, Germany
This article is an extended version of the conference contribution published on GfT-Fachtagung 2017, 25–27 September 2017 in Göttingen, Germany.
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Received: 29 January 2018 / Revised: 15 March 2018 / Accepted: 23 March 2018 / Published: 9 April 2018
(This article belongs to the Special Issue Lubricating Greases 2017)
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Abstract

The service life of rolling bearings is significantly affected by the film formation in elastohydrodynamic (EHD) contacts, which depends on the operating conditions, like rotational speed or temperature. In grease lubricated EHD contacts, the film formation is determined by the grease consistency and composition, i.e., thickener and base oil type as well as properties of the bleed oil, which is released from the grease during operation. Thus, the film formation of grease lubricated contacts as compared to base oil lubricated contacts can be different. With increasing rolling speed, the film thickness of oil lubricated contacts usually grows. However, in case of grease lubricated contacts, which are not fully flooded, the film thickness remains constant or even decreases with further increasing rotational speed. This effect is referred to as starvation. Since the onset of starvation depends on the grease composition, the film formation of two different grease compositions is investigated in this study. The film thickness measurements are performed on a ball-on-disc tribometer for each grease, as well as the corresponding bleed and pure base oils. Thereby, the characteristic rotational speed leading to the onset of starvation has been identified in dependence of the grease composition and the differences in the lubricating film formation of base oil, bleed oil, and grease lubricated EHD contacts have been discussed. The investigations should help to establish an advanced understanding of the physical mechanisms leading to the onset of starvation to encourage future work with focus on a method to predict the film formation in grease lubricated EHD contacts. View Full-Text
Keywords: EHD contact; grease lubrication; starvation; bleed oil; lubricating film formation EHD contact; grease lubrication; starvation; bleed oil; lubricating film formation
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Fischer, D.; Jacobs, G.; Stratmann, A.; Burghardt, G. Effect of Base Oil Type in Grease Composition on the Lubricating Film Formation in EHD Contacts. Lubricants 2018, 6, 32.

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