Experimental study of the effect of a contact conditioner on sliding electrical contacts

Abstract

This thesis documents research carried over the past two years, aimed at studying the tribology of sliding contacts subjected to high densities of current of the order is 422 --917A/mm2. The overall aim was the development of an experimental test bed for evaluating the effect of different solid lubricant conditioners on sliding electrical contacts. The experimental configuration consists of a flat ended copper tip pressed in contact with a flat copper disc. The copper plate is mounted on a spindle of a lathe which is operated at 550rpm, whereas the copper tip is mounted on a shaft which is instrumented with force sensing piezos to measure the forces during the test. A weak spring is used to compensate for wear of the tip during the experiment. The interface is subjected to high current densities of the order of 422 and 917A/mm2 to evaluate the effect of solid conditioner as contrast with the surface behavior when no interface lubrication was used. The key outputs of the experiments are a) Friction coefficient, b) Contact resistance, c) Amount of material transfer, d) number of passes to failure and e) Wear rate. Two types of tests, namely circular and spiral tests were carried out. The current density of 422A/mm2 would result in softening of the interface whereas current density of 917A/mm2 results in melting of the interface. In terms of contact voltages it is noted that Cu-Cu interface softens at 0.12V and melts at 0.43V. It has been noted that pre-application of SLIC leads to increase of contact resistance by approximately 20% when the interface is loaded statically. When the interface is tested for contact resistance, there is a significant effect of oxide layer on the surface of the plates. When contact resistance is measured these oxide layers contribute significantly, and increase the contact resistance substantially.