Common faults of the brush during operation include overheating, generating sparks, severe damage to the brush holder and the collector ring. From the causes of overheating faults, there are mainly the following aspects:
1. Overheating due to poor ventilation: Poor ventilation mainly results from blocked cooling air ducts, blocked ventilation grooves and holes on the collector ring surface, and reduced air volume of the circulating fan. Especially when the surface temperature of the collector ring is too high during operation, it leads to increased wear of the brush and accumulation of carbon powder, which may block the heat dissipation channels on the surface of the collector ring. Therefore, during major and minor overhauls, the ventilation grooves, holes on the collector ring surface, and the cooling air duct filters should be cleaned to keep them unobstructed. For collector rings that have undergone multiple reamings, if the height of the ventilation grooves on the surface of the collector ring is less than 5mm and has reached the radial limit hole, they should be replaced according to the instructions based on the small outer diameter for use to ensure the mechanical and heat dissipation reliability of the collector ring.
2. Overheating caused by excessive contact resistance or uneven distribution: The collector ring and the brush conduct current through mutual sliding contact. Depending on the capacity and model, each collector ring is approximately equipped with dozens of brushes. Due to different contact resistances and differences in current distribution, uneven heating occurs. There are the following reasons: (1) Excessive contact resistance between the brush and the surface of the slip ring, between the brush and the brush braid, and between the brush braid and the lead wire of the brush frame. This can be checked by comparing the total voltage drop of a single brush, the brush contact voltage drop, the brush body voltage drop, the connection voltage drop, and the brush braid voltage drop. At the same time, check whether all screws in the circuit are tightened. Check the cleanliness of the brush contact surface and whether there is oil contamination. (2) Uneven brush pressure or non-compliance with requirements may be due to short brushes, the spring becoming soft and aged due to overheating and losing elasticity. Use a spring scale to check the brush pressure. The constant pressure spring should be intact without mechanical damage, and the pressure should comply with the manufacturer’s specifications. The pressure deviation between the springs on the same pole should not exceed 5%. For non-constant pressure brushes, the pressure should comply with the manufacturer’s specifications when there are regulations. When there are no regulations, adjust the pressure to a low level that does not cause the brush to ignite. Generally, it is 140-250g/cm2. The pressure of each brush on the same brush frame should be uniform. (3) Excessive contact resistance between the collector ring and the rotor leads. This should reinforce the fastening screws between the collector ring and the rotor leads. (4) Poor brush material, poor conductivity, using a model that does not meet the requirements, or using different models of brushes. The same motor should use the same model and the same manufacturer’s brushes. For brushes with obvious differences in appearance, they should be replaced.
3. Overheating caused by mechanical and frictional reasons: In the overheating faults of the collector ring and brush, a large part is caused by mechanical and frictional reasons. If the collector ring and brush temperature is high before starting the machine or is too high during operation, and the temperature decreases after pulling out several brushes, it is basically certain that it is caused by mechanical and frictional reasons. The situation of overheating due to mechanical and frictional reasons is very complex, and there are the following aspects: (1) Poor grinding of the brush contact surface or excessive replacement of brushes during operation. During the same time, only 1-2 brushes on each brush frame are allowed to be replaced. The new brushes should be ground to the same diameter as the collector ring and have the same brand as the old ones. If many brushes are replaced during major overhauls, sufficient time should be left for the brush surface to form an oxide film before putting it into operation. (2) The contact area between the brush and the collector ring is too small, and the contact area should generally not be less than 75% of the cross-sectional area of a single brush. (3) The brush swings in the brush box or is stuck in motion. The brush should be able to move freely up and down within the brush holder, and the clearance should comply with the product specifications. If there are no specific specifications, the clearance can be 0.10 – 0.20mm. The shape of the brush should be square, and the size error of the upper and lower ends should not exceed 0.05mm. (4) The clearance between the brush holder and the collector ring is too large. Due to the brittle nature of the brush material, when the clearance between the brush holder and the surface of the collector ring is too large, during operation, the brush cannot come into full contact with the collector ring and will make a slanted contact with it, which is prone to causing the brush to break. The clearance between the surface of the brush holder and the collector ring should comply with the product technical requirements. If the product has no specific regulations, the clearance can be adjusted to 2 – 3mm. When adjusting the clearance, a layer of 2 – 3mm thick rubber pad can be attached to the surface of the collector ring, press the brush holder onto the rubber pad, then tighten the positioning screw, and remove the rubber pad.
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Post time: Feb-25-2026