Electrical Brushes

Electrical brushes and brush materials play an important role in electrical machines, including generators, motors, and other electrical equipment. These brushes are used for transmitting electrical current from a stationary to a rotating part of the machine, and therefore, require good frictional characteristics combined with high to moderate conductivity. Electrical brushes are made of various materials, including copper graphite, amorphous carbon, graphite and flake graphite, electro graphite, metal graphite, resin-bonded graphite, silver and silver alloys, silver graphite, and specialized or proprietary materials.
Carbon brushes made a major contribution to the industrial revolution in the 20th century, especially in the case of direct current motors. Even today, the production of steel sheets is not possible without big direct current drives with capacities of up to 10MW, and various other industries rely on electric drives with carbon brushes as well.

To improve the adjustment of carbon brush sliding contacts to specific electric and mechanical conditions, various designs have been developed in addition to the basic block brushes. Twin and triple carbon brushes are two designs in which the contacting conditions are improved by two or three partial brushes of equal size positioned behind each other in a tangential plane. This design is particularly useful for machines in reversing mode, as it helps to stabilize operations.

Split carbon brushes are a special form of twin brushes in which both partial brushes have a head area that is inclined towards the centre of the brush. This design is useful for operations that are susceptible to vibrations because the increased friction between the carbon brush and the inner wall of the holder pockets caused by the spreading (damping) results in better contacting on the commutator.

Sandwich type carbon brushes are designed for difficult commutation conditions, preventing 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.
The choice of brush material depends on the specific application requirements. Copper graphite brushes are commonly used in low-voltage motors, while electro-graphite brushes are suitable for high-voltage applications. Amorphous carbon brushes are often used in high-speed applications due to their low friction and low wear characteristics. Silver graphite brushes are used in applications requiring high current densities, while metal graphite brushes are often used in low-friction and high-temperature applications.

In conclusion, electrical brushes and brush materials are an essential component of electrical machines and play a crucial role in their performance. The use of appropriate brush materials and designs can help to improve efficiency, reduce wear and tear, and extend the life of the equipment. With advancements in technology, more specialized and innovative brush designs and materials are being developed, leading to improved performance and increased reliability in electrical machines.

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