Industrial Applications

Carbon Brushes for Industrial and Traction Use

Sliding contacts in the form of carbon brushes are an important component for current transmission in many electrical machines.

This is due to the particular material characteristics of carbon and graphite. These include good frictional properties, relatively good electrical and thermal conductivity and high resistance to elevated temperatures.

Carbon does not melt, but sublimes at temperatures above 3500 C degree. Thus, when switching sparks and arcing occur, the formation of beads of molten material, such as occur, for example, on metalic contacts, is prevented. Because of technological advances, the requirements, which are imposed on carbon brushes, have become vary extensive and diverse, In order to achieve an optimum result in every application, materials, sometimes with widely varying properties, are available.

Pantograph Carbons for Electric Traction Units

The excellent sliding properties of carbon have been exploited for decades to transmit power from overhead contact wires to electrically driven traction units. In addition to these sliding properties, carbon contact strips possess high mechanical strength, good damping properties, and are good conductors of heat and electricity.

Normally, overhead contact wires are made of copper which, upon contact with the carbon, forms a carboniferous surface layer which not only protects the contact wire but also produces a low coefficient of friction in the sliding contact. As a result, frictional vibrations and the contact interruptions associated with them are prevented, and the radio interference common to metal contact strip does not occur.

As a result of the advantages made in the design of electric traction units, greater demands have been placed on the contact material. The most important of these are:

• High currents must be transmitted. Operation in the critical load region is longer owing to higher speeds, increased drive power and the feedback of brake currents into the overhead wire.
• Reliable contacts must be assured over speed range from 0 km/h to 400 km/h.
• Contact wire and strip wear must be minimized to reduce operating and maintenance cost.