Carbon & Graphite

Electrical brushes & brush materials require very good frictional characteristics combined with high to moderate conductivity. Electrical brushes & brush materials are made of copper graphite, amorphous carbon, graphite and flake graphic, electro graphite, metal graphite, resin-bonded graphite, silver and silver alloys, silver graphite, and specialized or proprietary materials.

In the 20th century, direct current motors with carbon brushes made a major contribution to the industrial revolution, even today the production of steel sheets is not possible without big direct current drives with capacities of up to 10MW, moreover, paper, plastics, rubber, cement or power would also not be available without electric drives with carbon brushes either.
To improve the adjustment of carbon brush sliding contacts to specific electric and mechanical conditions further designs have been developed in addition to the block brushes over the years.

Most important basic forms include:

Twin and triple carbon brushes in which the contacting conditions are improved by two or three partial brushes of equal size positioned behind each other in a tangential plane. In particular, machines in reversing mode work more stably on account of this arrangement.

Split carbon brushes constitute a special form of the twin brushes in which both partial brushes have a head area which is inclined towards the centre of the brush. In case of operations which are susceptible to vibrations the bigger friction between the carbon brush and the inner wall of the holder pockets caused by this spreading (damping) results in better contacting on the commutator.

Sandwich type carbon brushes are designed for difficult commutation conditions. They prevent the strong formation of sparks, scorching of bars or high wear and tear. In addition to the conventional graphite materials copper/ graphite composites or impregnated graphite materials have proved to be best suited for the production of carbon brushes.