INFRARED AND VISUAL STUDY OF THE MECHANISMS OF SCUFFING

The development of a reliable models for predicting scuffing requires an understanding of the mechanism of scuffing initiation. This study e xamines the process of scuffing directly within a contact and thus tes ts some of the existing, proposed mechanisms. A lubricated steel ball is loaded and rotated against a sapphire flat and the load increased i n stages until scuffing occurs. Two methods of observation are employe d. In one, the temperature of the steel ball across the contact is map ped 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 maxi mum or at a critical inlet temperature. In the second approach, a soli d-state TV camera and video recorder are used to monitor the contact v isually up to and during scuffing. This work suggests that, for a rang e of different lubricants, the onset of scuffing is always immediately preceded by the buildup of fine wear debris in the contact inlet. Thi s then causes starvation followed by extremely rapid scuffing in the r ear of the contact. From these findings, an alternative method of scuf fing based upon the influence of wear debris on lubricant film thickne ss is proposed.