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Lubricants 2015, 3(2), 197-221;

Grease Aging Effects on Film Formation under Fully-Flooded and Starved Lubrication

INEGI, Institute of Science and Innovation in Mechanical and Industrial Engineering, Dr. Roberto Frias Street, 400, 4200-465 Porto, Portugal
ISEP, Superior Engineering Institute of Oporto, Dr. António Bernardino de Almeida Street, 431, 4200-465 Porto, Portugal
FEUP, Faculty of Engineering of Porto University, Dr. Roberto Frias Street, 4200-465 Porto, Portugal
Author to whom correspondence should be addressed.
Academic Editors: Jose M. Franco and Jesus F. Arteaga
Received: 25 December 2014 / Revised: 5 February 2015 / Accepted: 25 February 2015 / Published: 9 April 2015
(This article belongs to the Special Issue Lubricating Greases)
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Several film thickness measurements were performed with three fresh and aged lubricating greases, their base and bled oils under a wide range of operating conditions using a ball-on-disc test rig with optical interferometry. The analysis of the film thickness measurements is in agreement with the observations of several authors and adds some important aspects regarding separate film properties in EHL contacts. At full film lubrication and moderate to high speeds, the bled oil showed a similar behavior of its lubricating greases. At fully-flooded condition, low speeds and thin films, it was observed that the thickener lumps play a major role on film formation, overcoming the bled oil effects. A relationship between thickener type and film formation was evidenced. The same trends were observed under starved lubrication, where the thickener type that contributes the most to locally increase the film thickness follows the order of PP > Ca > Li. The aging process of the greases was shown to change their rheological response in different manners—softening or hardening—depending on the grease formulation. Grease aging increased the film thickness under fully-flooded and starved lubrication, regardless of the level of degradation. View Full-Text
Keywords: aging; grease; bled oil; thickener; film formation aging; grease; bled oil; thickener; 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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Cousseau, T.; Graça, B.; Campos, A.; Seabra, J. Grease Aging Effects on Film Formation under Fully-Flooded and Starved Lubrication. Lubricants 2015, 3, 197-221.

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