1. Stable current transmission
The brush holder acts as, through constant pressure from the spring to the brush, keeping reliable sliding contact between the brush and high-speed rotating commutator or the slip ring. The current between the fixing part (the stator) and the rotating part (the rotator) is transmitted through the above-mentioned. Once instability of the brush holder, its contact resistance will be increased to cause the spark or even erosion the commutator.
2. Even if the excellent brush, its ineffective brush holder cannot operate well.
There is a saying that even if the excellent brush, its ineffective brush holder cannot reveal its qualified performances or even affect the performances and service life of the motor itself. The materials of the brush can be selected with high-qualified graphite, lubricated graphite or even metallic graphite composite materials. If inappropriate brush holder gap, unbalanced spring pressure and loose adaptability cooperation between the brush box and the brush, the brush will be abnormally worn, its vibration will be sped up and even its reversing will be worse.
3. Its accuracy determines its service life
The gap between the brush holder and the brush is generally controlled within 0.1-0.3mm, and the distance between the bottom edge of the brush box and the surface of the commutator is normally remained within 2mm. And, those impressive figures will directly determine the motor whether can operate within a long period. If excessive gap, the motor will be swaying in the brush box to cause unstable contact; and, if too narrow gap, the brush will be thermal expansion to cause jammed.
4. Double tests for heat dissipation and its insulation
In the process of the motor operation, a huge amount of heat will be generated owing to the sliding contact between the brush and the commutator. The materials of the brush holder (bronze casting, aluminium casting or synthetic resin) should be designed to meet the requirements for excellent heat dissipation and with sufficient insulation performance to protect the current against revealing to other components that should not be transmitted in the motor.
How severe if the brush holder cannot be qualified selected?
Operation experiences have revealed that, according to the heavy metallurgical industry, lots of the motors are destroyed due to the brush holder and the brush devices. Common problems are the facts that insufficient spring pressure will lead to excessive spark, abnormal brush holder will lead to dull and worn-out of the brush and the wear of inner cavity of the brush box will lead to swaying brush. For a large-scaled motor, the slip ring strikes the spark or generates the heat due to the conditions of the brush holders.
In conclusion, in spite of a small and impressive component, the brush holder plays multiple roles in fixing the brush, keeping the contact pressure, transmitting the current and auxiliary heat dissipation. It can be regarded as the bridge protector to connect between the "static world" and the "rotating world".
