Effect of PV factor on the wear of carbon brushes for micromotors

In this paper the effect of the PV factor (product of contact pressure and peripheral speed) on the wear of carbon brushes was investigated in detail. The wear tests were done on an alternate current (ac) motor. The results show that the wear rate of brushes is proportional to PV factor when PV factor is less than 0.5 MW/m2, but it increases exponentially when PV factor is greater than 0.5 MW/m2. SEM (scanning electron microscope) and EDS (energy dispersive X-ray analysis) were adopted to analyze the worn surface of brushes for different PV factors and a thermocouple was used to measure the temperature of the surface of brushes. These characterizations infer that the mechanical wear of brushes is proportional to PV factor and the electrical wear is mainly caused by damaging the lubricating film, oxidizing the resin binder, weakening the structure of brushes and a low “relative humidity” due to a high temperature on the surface of brushes.