Mechanism of the Sliding Contact of a Ag-Graphite Brush against a Au-plated Slip Ring for Varying Ag Content

Abstract

Brushes enable the transfer of electrical current between stationary and moving conductors. Typical contacting components are a brush and commutator in direct-current machines and a brush and slip ring in alternating-current machines. In recent years, Ag-graphite brushes and noble-metal-coated slip rings have often been applied. However, there are many aspects concerning the sliding contact of these components that require clarification. This paper focuses on characteristics relating to the brush wear and contact voltage drop of Ag-graphite brushes when the Ag content is varied for a Au-plated slip ring. In this study, we conducted sliding tests, using Ag-graphite brushes (coated with Ag contents of 50, 60, 70, 80, and 90wt%) and a Au-coated slip ring. The results showed the effects of the interposing layer on the brush wear and drop in contact voltage. In particular, there were three distinct compositional zones, namely a zone where the effect of graphite was dominant (Ag content of the brush of 50wt%), a zone where both the graphite and Ag powder had influence (60-80wt%), and a zone where the effect of Ag powder was dominant (90wt%).