Fabrication and characterization of carbon brushes using Cu, Ag and CNT composites: Micro structural property correlation

Abstract

Carbon brush is widely used in electrical machines such as generators, automobile parts etc which is used to transfer charges from rotating part (shaft) to stationary part (battery). The important properties of carbon brushes includes (a) good electrical conductivity (b) sufficient wear rate and low hardness as compared to rotating shaft (c) less sparking. The Graphite is the major element used in carbon brushes due to its superior properties of high wear rate and electrical conductivity (5.2% IACS). However there are other elements such as silver (105% IACS), copper (100% IACS) and CNT (142% IACS) has high conductivity than graphite. This research work is focused on the development of carbon brushes using the graphite as the base metal and materials such as silver (105% IACS), copper (100% IACS) and CNT (142% IACS) used as composite materials. The carbon brushes were developed with variable wt. % of Cu, Ag and CNTs sintered at 800, 900 and 1000℃ in argon atmosphere.The hardness measurement were carried using Vickers micro hardness test, electrical conductivity measurement were done using four probe setup and wear test were performed using wear and friction Monitor machine. XRD (X-Ray diffraction) characterizations were done to observe the phases present in the composites. The results shows that as percentage of silver, copper and CNT increases, conductivity of the carbon brushes increases however wear rate does not follow any trend with composite wt. %.Carbon brush with 0.75 wt. % of CNT sintered at 900℃ shows the superior electrical properties comparing from the commercially available sample. Further a comparative study on the properties (electrical and wear) of market sample with sintered pure graphitic sample were done and correlated were done using XRD data.