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Abstract
The first aim of this work is to analyze the nature of the effective lubricating phase in grease lubricated contact. The second aim is to determine the shear rate experienced by lubricants in the inlet of the contact. A tribological investigation of four greases, their base oils and bleed products was conducted. The following composition parameters were varied: base oil, soap and the presence of additives.
By comparing effective viscosity, deduced from film thickness measurements of greases with base oils and bleed products, it could be seen that the lubricating phase of a grease does not always contain soap. A lithium fiber network does not appear to traverse the contact, whereas evidence is found in the contact of the presence of parts of an aluminum complex colloidal structure.
In contrast, polymer additives seem to go through the contact whatever the initial grease composition. Comparison with previous dynamic viscosity measurements on base oils as a function of shear rate allowed the determinationn of typical shear rates experienced by lubricants in the inlet of the contact to be about 50,000 s−1. The authors also conclude that in this work, the distance between the lubricating fluid meniscus and the center of the contact should be greater than two contact radii to ensure a well supplied contact and a thick lubricating film.
