Investigation of electrostatic charging mechanisms in oil lubricated tribo-contacts

Fundamental studies using a spinning disc tribocharging rig have shown that disc surface roughness, oil temperature and oil composition have an effect on the charging ability of lubricating oils. Further investigations into the effect of oil composition on the charging nature have employed the oil droplet rig to investigate a range of base and formulated oils. Experimental results indicated that charging in base oils is controlled by levels of impurities, such as sulphur, and aromatic content. For formulated oils it has been determined that the additives are the major contributor to the charging nature and any effect that impurities and aromatics have is negligible. Studies into the sensitivity of the electrostatic sensor system to surface charge has shown that surface transformations that occur during scuffing in tribocontacts can lead to contact potential differences detectable by this system.