On the film forming and friction behaviour of greases in rolling/sliding contacts

The film forming and friction properties of nine greases covering different thickener types, viscosities and NLGI grades have been investigated. Film thickness results are in agreement with previous work that all greases form a thicker film than the base oil counterpart at low speeds, suggesting that lambda ratio and kappa of greases can be much higher than their corresponding oils. The base oil viscosity appears to govern the grease film thickness at low speeds by a direct relationship for polyurea greases whereas by an inverse relationship for lithium and calcium complex greases. Grease friction results indicate that the shape of grease friction curves can differ quite significantly from that of oils. Possible underlying mechanisms that govern friction properties are discussed.