An Experimental Study of Grease in Elastohydrodynamic Lubrication

The formation of a lubricating film by grease in conditions pertinent to elastohydrodynamic lubrication is studied in a disk machine, and the thickness measured by means of a magnetic reluctance technique. The greases examined are three lithium hydroxystearate greases, of different soap structures and soap contents, a low temperature sodium-based grease, and a high temperature clay-based grease, all in mineral oils. The film thickness of greases in EHL differs from that of pure mineral oils in one important aspect: with one charge of the lubricant the thickness decreases continuously with time. The time-dependent behavior of greases is examined in relation to the thickener structure, viscosity of the base oil, and the conditions of the inlet zone.