Electrical brushes are used in conjunction with slip rings, commutators, or other contact surfaces to maintain electrical connections in rotary and linear sliding contact applications. They require very good frictional characteristics combined with high to moderate conductivity.

Brush Types

Buyers of electrical brushes should consider materials of construction when selecting products.

• Graphite brushes are recommended for high power and sliding contact applications because graphite is a good lubricant and provides low friction contact. Some products combine graphite with other metals (such as copper) for improved electrical characteristics.
• Copper graphite brushes are generally more expensive, but provide excellent flexural strength and high electrical conductivity.  
• Silver graphite molybdenum disulfide brushes are recommended for slip ring mechanisms used in aerospace applications, and in solar power arrays.

The GlobalSpec SpecSearch database contains information about these and other types of graphite and metal brushes.

Configurations and Specifications

Electrical brushes are supplied as assemblies, leaf springs, plungers, contact tips or buttons, bar stock, brush pads, tamped or shunted brushes, and solid rock stock. Specifications for include current density, operating speed, outer diameter (OD) or width, length, thickness and conductivity.

Two performance specifications are especially important.

• Current density is the maximum current per unit area that the brush 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).

Applications for Electrical Brushes

There are many applications for electrical brushes. Some products are designed to avoid the material transfer and severe arc damage that can occur in DC applications. Brushes designed for sliding contact are recommended 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. Electrical brushes are also designed for re-tipping or replacement in various OEM units while maintaining or improving performance characteristics. Applications also include the transmission or pick-up of electrical signals in testing, probing or instrumentation applications.