Electrostatic charge monitoring of unlubricated sliding wear of a bearing steel

Previous papers [O.D. Tasbaz, H.E.G. Powrie, R.J.K. Wood, Electrostatic monitoring of oil lubricated contacts for early detection of wear, in: Proceedings of the International Conference on Condition Monitoring, University of Wales Swansea, 12–15 April 1999; Wear 230 (1) (1999) 86; H.E.G. Powrie, O.D. Tasbaz, R.J.K Wood, C.E. Fisher, Performance of an electrostatic oil monitoring system during FZG Scuffing Test, in: Proceedings of the International Conference on Condition Monitoring, University of Wales Swansea, UK, 1999, pp. 155–174; Condition Monitor 177 (2001) 6] have shown that electrostatic sensing technology can be used to successfully monitor adhesive wear processes in oil-lubricated contacts. This work has shown that ‘precursor’ charge signals can be detected prior to the onset of adhesive wear. The possible charging mechanisms involved have been identified as tribocharging, surface charge variations, triboemission and debris generation. This paper details experimental work focused on monitoring the unlubricated wear performance of a bearing steel sliding against a bearing steel using electrostatic sensing technology. Tests were carried out using a modified and instrumented pin-on-disc wear test rig with conditions designed to produce sliding wear in the mild oxidational wear regime. Test results have shown that there is a direct correlation between both the wear rate and coefficient of friction with the magnitude of charge detected. The influence of the periodical formation and delamination of oxidation products is also presented. The charge detected was found to be predominantly negative. The dominant wear related charging mechanism was thought to be surface charging as a result of contact potential difference.