Wear Rate vs Dynamic and Material Properties at Elevated Temperatures for a Copper-Graphite Brush

Abstract

A copper-graphite brush is used as a sliding part in the electrical contacts of electrical machines and usually operates at elevated temperatures. This experimental research relates the dynamic properties of the copper-graphite brush to its INTRODUCTIONSliding electrical contacts are necessary whenever an electrical current needs to be transferred between a stationary and a rotating part, like in alternators or DC motors. A brush and a slip-ring or commutator, which form the contact, are the primary components that affect the lifetime of electrical machines. Therefore, a lot of attention has been given to the prediction of wear in electrical contacts [1] The wear rate and dynamics of a copper-graphite brush are highly dependent on the properties of the brush material [1]. The material properties can be researched by differential thermal analysis (DTA) or by thermogravimetric (TG) analyses, e.g., Kuz'mina et al. [22]. They observed that an increase in the copper content in the composite leads to a change in the shape of the TG curves, while the binder properties, an ordinary compound of the brush composite, can be tested with differential scanning calorimetry (DSC) [23]. In addition to the DSC analyses, the material properties were also studied using hardness tests [24].The effect of temperature on the dynamic properties of the brush is not commonly referred to as an influencing wear parameter, and only a few studies have paid attention to these properties separately [17], [20], [22] and [25].The aim of this study was to analyse the effect of temperature on the dynamic properties of the copper-graphite brush and to compare it to the wear rate.The dynamic properties were investigated through the natural frequencies, the hysteretic damping ratio and evaluated through the material's properties, i.e., hardness tests and DSC, while the wear rate was measured previously, see, e.g., [26].This research is organised as follows: in Section 1 the experimental methodology is introduced, in Section 2 the experimental results with a discussion are presented, and in Section 3 the conclusions are given. EXPERIMENTAL RESEARCHIn the experimental research section the methods and conditions for the dynamic response analyses, DSC, hardness and wear rate are presented. The dynamic properties were researched using dynamic response analyses, compared to the wear rate of the copper-graphite brush. For an additional insight into the effect of temperature on the brush material's