The Measurement of Kinetic Boundary Friction, or the Experimental Investigation of “Oiliness”

Abstract

Considerations concerning the nature of sliding in friction-measuring instruments, in which friction is measured by the deflexion produced in an elastic system which presses one surface against another moving surface, have led to the design of an instrument which allows the variation of boundary friction with velocity to be determined at very low velocities.It is suggested that curves of the coefficient of boundary friction versus velocity constitute the correct form in which the results of measurements of kinetic boundary friction should be stated. Results are presented illustrating the influence of temperature, material nature of the surfaces, and surface finish on kinetic boundary friction for a variety of lubricants. These allow the boundary lubricating quality, or “oiliness”, of lubricants to be assessed in some measure. The results lend support to the original ideas of Sir William Hardy on boundary friction and lubrication.