Lubrication Mechanisms for Oil-in-Water Emulsions

Abstract

Numerous analyses and experiments regarding emulsions have been conducted, and seemingly contradictory notions of emulsion behavior claimed. Theoretical approaches include plate-out, dynamic concentration and mixture theory. Experimental observers report great disparities in film thicknesses and film thickness dependence on emulsion properties such as base oil characteristics and process variables such as rolling speed. This paper surveys the published research and attempts to reconcile apparent contradictions from different researchers. Different lubrication mechanisms of oil-in-water emulsions are identified and described, all of which are highly dependent on speed effects. At low speeds, plate-out is found to be the chief lubricating mechanism. As speed increases, the plated oil film is starved, leading to a decrease in film thickness. At even higher speeds, which are typical of most engineering applications, dynamic concentration of oil is the prevalent mechanism. Ultimately, mixture theory becomes useful at very high speeds.