Influence of 'off-contact' electric potential on frictional behaviour of an agate-brass (SiO2-Cu) rubbing couple

The effect of 'off-contact' electric potentials on the frictional behaviour of an agate-brass rubbing couple was investigated using a commercial pin-o n-disc wear machine. The electric field was set to cover a large portion of the disc surface area but excluding the agate ball and brass contact. This is referred to as the 'off-contact' potential. A suspension of 1 wt% zinc stearate powder dispersed in deionized water was adopted as a lubricant in the experiments. Experimental results show that the coefficient of friction can be increased markedly by imposing a positive biased potential (disc wi th negative charge) when it exceeds a threshold value. For applying negativ e biased potentials, there are no obvious effects recorded. Furthermore, th e amount of increase in the coefficient of friction by imposing a fixed pot ential decreases with an increase in the applied load and the sliding speed , but the decreasing rate gradually becomes smaller. Experimental results u nder a.c. potentials in the frequency range from 0.1 to 100000 Hz were also presented and no obvious changes in the coefficient of friction for an aga te-brass rubbing couple were observed.