Industrial coal

The brush qualities are divided into the following groups:

Hard coals

have a bond of amorphous carbon materials (retort coal, soot, coke, etc.). This gives them a firm structure and greater hardness. They can be used on commutators with non-recessed lamella insulation. Due to the high coefficient of friction and the relatively low load capacity, these grades are almost only used in small motors.

Graphite carbons

are manufactured from various natural graphites. They are suitable for high peripheral speeds. The grinding effect is only slight. The vane insulation should be recessed.

Bakelite carbons

are synthetic resin-bonded graphite carbons with a high transition voltage. The transverse resistance is a multiple of the longitudinal resistance. This makes these grades suitable for particularly difficult commutation at not too high current densities.

Noble carbons

consist of carbon material that has been converted into electrographite at a temperature of 2,500 °C. This results in a significant improvement in electrical and thermal conductivity and burn-off resistance. High-grade carbons have excellent commutation properties. The lamella insulation should be recessed.

Bronze carbons

contain copper and other metals in addition to graphite and other carbons. They are characterized by significantly higher conductivity and lower contact resistance. They are used on slip rings and in low-voltage machines.

Silver carbons

are suitable for transmitting very low voltages in measuring currents, tachogenerators, contacts, etc. In the following list we have compiled the most important industrial carbon brushes.

Dimensions of the carbon brushes

The dimensions of the carbon brushes are normally specified according to DIN 43000 and IEC 1366 in the order txaxr.

t= tangential = width in the direction of the circumference of the commutator or slip ring
a = axial = length in the direction of the axis
r = radial = height in the direction of the diameter