Effect of Rotation Speed on Electric Damage of Copper Tribo/Electric Rolling Pairs under Lubricated Single-Point Contact

Abstract

To investigate the detriment of oil lubrication on the tribo/electric contact, this paper has completed a series of experiments, with single-point disk-disk rollers lubricated Poly Alpha Olefin 4 (PAO 4) drips. The breakdown behaviors were monitored and the material damages were observed by Optical Metallograph Microscope (OMM), Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS) and White Light Interference Profilometer (WLIP). With the increase of voltage, the equivalent resistance of the contact pairs decreased rapidly at first and then towarded stability at finally. The voltage at the zero point of the derivative of the equivalent resistance was proposed as the breakdown voltage. Both the breakdown voltage and the final resistance increased with the rotation speed, which should be attributed to the thicker oil film at higher speed. Electric discharge erosion and the plastic flow of grains could be formed when the applied voltage exceeded the breakdown voltage. It was speculated that the transformation from the capacitive contact to ohmic contact during breaking should account to the conductive behaviors and the electric damages. The results could help to understand the failure of tribo/electric contact under oil-lubricated or oil-contaminated conditions such as shaft current damage in bearing.

Fig. 2 Synchronous data of friction coefficient, current and voltage during voltage rising.