Effect of Temperature on Lubricant Films

Abstract

THE friction apparatus developed by Bowden and Leben^1,2 has shown that when clean steel surfaces slide on one another, the motion is not smooth but proceeds in a series of irregular jerks. This apparatus has also been used for comparing the lubricating properties of various substances. With the high loads and low speeds employed, the conditions which obtain correspond to boundary lubrication. Experiments show that when a non-polar lubricant such as medicinal paraffin oil is used, the motion still proceeds in stick-slips, though the average value of the friction is lower than for the dry surfaces. Certain long-chain fatty acids and small quantities of these acids in a non-polar oil will, however, cause continuous sliding^1,3. This property has been used to detect the oxidation of non-polar oils on heating. The original oil gives a jerky motion; when a certain amount of oxidation has occurred the motion becomes smooth. The rate of this oxidation becomes appreciable with most oils at temperatures above 150° C. and the change in the frictional behaviour is irreversible on subsequent cooling³.