A pair of carbon brushes
A brush or Evolution Brushes are a device, which conducts current among stationary wires and moving parts, most usually in a rotating shaft. Typical applications comprise electric motors, alternators along with electric generators.
Several types of generators or electric motors to function, the coils of the rotor must be connected to complete an electrical circuit. Formerly this was proficient by affixing a copper or brass commutator or ‘slip ring to the shaft, with springs pressing braided copper wire ‘brushes’ onto the rings which demeanour the current. Such brushes offer poor commutation as they moved from one commutator section to the next. The cure was the prologue of ‘high resistance brushes’ made from graphite (sometimes with added copper). Although the conflict was of the order of tens of milliohms, they were high conflict enough to provide a gradual shift of current from one commutator section to the next. The term brush is relics in use.
How the brushes are used?
Accurate work of the brush depends on the application. Graphite/carbon powder is commonly used. Einhell Carbon Brushes is used for better conductance (rare for AC applications and not on automotive fuel pumps that run on carbon commutators). In order to maximize electrical conductivity and green strength, highly dendritic (electrolytic) copper powder is used. Binders, mostly phenol or other resins or pitches, are mixed in so the powder holds its shape when compacted. Other additives comprise metal powders, and solid lubricants like MoS2, WS2. Much expertise and research is needed in order to define a brush grade mixture for each application or motor.
The brush compound is compressed in a tool consisting of upper and lower punch and die, on mechanical or hydraulic presses. In this step, depending on later processing, the copper-wire (called shunt wire) can be inserted repeatedly through a hole in the upper punch also fixed into the pressed brush block by the powder pressed around. This operation, called “tamping”, is usually performed using electrolytic copper powder, perhaps with silver coating for some high performance applications. After this progression, the brush is still very fragile and in professional jargon called a ‘green brush’.