Brushes are the most important part for transmission of electricity accomplished by sliding contacts in many electrical machines. Before, electrical motor brushes made from bundles of copper wires gave the name we still use today.
Today, we make brushes from carbon-based material that has good self-lubricating properties, relatively good electrical and thermal conductivity, high thermal and chemical resistance, and low density.
The manufacturing process is carried out by materials of raw carbon origin (petroleum coke, carbon black, graphite) milled into a fine powder and mixed in certain proportions with the addition of binders (tar, coal tar pitch, Bakelite resin). The mixed mass pressed into blocks gives desired size and shape. Blocks are heat treated in an inert atmosphere. When treated with heat, the binding is degraded, creating a further amount of carbon, which binds the block.
The final product is therefore entirely from carbon and does not depend on any other materials. By further heat treatment at temperatures above 2500 C, the structure changes into a form of graphite and, this is how we get electrical graphite materials. The described process refers to materials composed of carbon.
Production of metal graphite material takes place in a similar manner. By varying, the ratio of raw materials in the mix of each form makes these materials available in a wide range of desired combinations of physical properties. This occasion provides opportunity to manage a relatively large number of different materials, needed to cover entire areas of different electrical machines, each working in a variety of conditions.