Electrical Brushes and Brush Materials

Electrical brushes and brush materials are used in conjunction with slip rings, commutators or other contact surfaces to maintain an electrical connection in rotary and linear sliding contact applications. Electrical brushes and brush materials require very good frictional characteristics combined with high to moderate conductivity. Graphite brush materials are used for high power equipment. Metal brushes or sliding contacts are used for signal or low power applications.

Electrical brushes and brush materials are made from copper graphite, amorphous carbon, graphite and flake graphic, electrographite, metal graphite, resin-bonded graphite, silver and silver alloys, silver graphite, and specialized or proprietary materials. A carbon brush is typically constructed of carbon with an amorphous structure or graphite, which is an allotropic form of carbon. A graphite brush is useful in high power or sliding contact applications because the graphite is a good lubricant and provides low friction contact. Electrical brushes and brush materials also include combining graphite with metals. A metal graphite brush, such as a copper brush combined with graphite, provides the low friction capability of graphite with the high conductivity of copper to provide reliable contact. A copper graphite brush is an expensive option, but has excellent flexural strength and high conductivity. A silver graphite molybdenum disulfide brush is the most common used in slip ring mechanisms used in aerospace applications, such as solar power arrays.

An electrical brush can come in a variety of shapes and configurations, depending on the material used and the application. Shapes for electrical brushes and brush materials include assemblies, leaf springs, plungers, contact tips or buttons, bar stock, brush pads, tamped or shunted brushes, and solid rock stock. Specifications for electrical brushes and brush materials include current density, operating speed, outer diameter (OD) or width, length, thickness and conductivity. Current density is the maximum current per unit area that the contact, brush or electrode is designed to handle in continuous use without excessive overheating, erosion or sticking. Conductivity, the inverse of resistivity, is often given as percent of a copper standard, which is 100% IACS (International Annealed Copper Standard).

There are many applications for electrical brushes and brush materials. Electrical contact for direct current devices (DC) are designed to avoid the material transfer and severe arc damage that can occur in DC applications. Brushes designed for sliding contact are suitable for applications in which the contacting members provide the electrical connection or path for the transmission of power or signals across a rotary interface in motors or generators. Some electrical brushes and brush materials are designed for retipping or replacement in various OEM units while maintaining or improving performance characteristics. Others are designed for transmission or pick-up of electrical signals in testing, probing or instrumentation applications. 

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