Infrared and Visual Study of the Mechanisms of Scuffing

The development of a reliable model for predicting scuffing requires an understanding of the mechanism of scuffing initiation. This study examines the process of scuffing directly within a contact and thus tests some of the existing, proposed mechanisms.

A lubricated steel ball is loaded and rotated against a sapphire flat and the load increased in stages until scuffing occurs. Two methods of observation are employed. In one, the temperature of the steel ball across the contact is mapped continuously using an infrared microscope. A novel, nodding mirror set-up enables temperature profiles to be taken many times a second. This work shows that scuffing does not occur at either a critical maximum or at a critical inlet temperature. In the second approach, a solid-slate TV camera and video recorder are used to monitor the contact visually up to and during scuffing. This work suggests that, for a range of different lubricants, the onset of scuffing is always immediately preceded by the buildup of fine wear debris in the contact inlet. This then causes starvation followed by extremely rapid scuffing in the rear of the contact.

From these findings, an alternative method of scuffing based upon the influence of wear debris on lubricant film thickness is proposed.