Brush - definition

Brush is an electrical component used in rotating machines, such as commutator motors and generators, to provide electrical contact between the moving and stationary parts of the system, most commonly between the rotor and the external power or energy-receiving circuit. In the classical design, the brush takes the form of a carbon or graphite element pressed against the surface of the commutator or slip ring by a spring, allowing current to flow while the rotating part rotates.

The material used for brushes must provide an appropriate compromise between electrical conductivity, resistance to mechanical wear, and the ability to operate under friction and high temperature conditions. In practice, brushes made of pure graphite, metallised graphite (e.g. doped with copper) or specialised blends tailored to the characteristics of the machine are used. Depending on the type of machine, the current carried can be direct current (DC) or alternating current (AC), which also influences the choice of brush material and design.

Brushes are an essential component in DC commutator motors and in some synchronous and asynchronous machines with slip rings. Their function is to transmit energy without the need for additional mechanical connections, allowing the machine to run continuously. Over time, brushes wear out, requiring their periodic replacement to maintain the efficiency and reliability of the system. Failure of the brushes to work properly can lead to sparking, energy loss and damage to the commutator.

Today, in many applications, classic brush solutions are being replaced by brushless technologies (e.g. BLDC Motors), which eliminate the need for mechanical contact, increasing the durability and efficiency of drive systems. Nevertheless, brushes remain an essential component in many industrial, automotive and everyday appliance designs, where their simplicity and reliability are still valued.

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