Carbon brushes are important components in almost every electric motor and are used, among other things, in car windscreen wipers, gasoline pumps, starter systems as well as in washing machines and drills. With the help of slip rings or collectors, carbon brushes establish electrical contact with the rotating part of a drive system – a technology for the transmission of electricity that is more than a hundred years old yet still state of the art. This approach is still regarded as a reliable solution in demanding innovative industries, such as the automotive industry.
Many carbon brushes contain graphite as an additive in the sliding contact. As carbon brushes are subjected to high wear – carbon brushes in a car starter unit have to withstand up to 40,000 starting cycles, for example – so they are particularly resilient and resistant to oxidation. For this purpose, iron or copper powder is mixed with graphite, pressed into shape and sintered. In order to achieve the highest possible electrical conductivity with excellent lubricating properties, either high-purity vein graphite from Sri Lanka or specially refined natural graphite is used for carbon brushes.