Effects of grease composition and structure on film thickness in rolling contact

The aim of this work is to show the correlation between the tribological behavior of grease and its composition and structure. A tribological investigation was conducted on various lubricants. The following parameters were varied: base oil, soap and presence of additives. To ensure efficient control of grease composition, greases containing the same type of soap were manufactured from the same concentrated soap sample. Film thickness measurements showed that the thickener microstructure (revealed by TEM observations) is not the determining factor for the formation of a thick lubricant film, i.e. a film following EHL equations. Nevertheless, the soap - base oil interaction is an essential parameter. The composition of a grease influences oil bleeding, mechanical stability, and rheological behavior. The elastic modulus G' seems to be the only parameter directly linked to tribological behavior. Greases with low G' have a greater capacity to form a thick EHD film compared to greases with large G'.