Control of friction

Abstract

In kinematically constrained sliding and/or rotating applications, the frictional force can reach very high values if surfaces cannot be lubricated with either liquid or solid lubricants. This situation arises in many bearings or machines where lubricant cannot be applied because of the unacceptability of airborne contaminants or because of the high operating temperature of machine components. When the lubricant is absent the frictional force increase is primarily due to the plowing of the interface by wear particles which eventually leads to seizure. Frictional force in bearings and sliding surfaces, even in the absence of lubricants, can be maintained at low values when the plowing by wear particles is eliminated by making the surface undulated to trap wear particles. Frictional force cannot be eliminated completely because of the presence of microscopic plowing that occurs even with the undulated surface. The friction coefficients obtained with the undulated surfaces without lubricants were as low as those found in boundary lubrication of flat surfaces. This indicates that the primary role of liquid lubricants is to reduce plowing through the elimination of wear particles from the interface and also through the minimization of particle agglomeration.