The causes and solutions of common faults in brushes and collector rings:

The causes and solutions of common faults in brushes and collector rings:

The most common faults of electric brushes during operation are heating, generating sparks, and severe burning of the brush holder and collector ring. From the causes of overheating faults, there are mainly the following aspects:

1. Heating caused by poor ventilation: Poor ventilation is mainly due to blockage of the cooling air duct, ventilation channels and holes on the surface of the collector ring, and a decrease in the air volume of the circulating fan. Especially when the surface temperature of the collector ring is too high during operation, it leads to intensified brush wear and increased carbon powder accumulation, which may block the heat dissipation channels on the surface of the collector ring mentioned above. Therefore, during major and minor repairs, the ventilation channels, holes, and cooling air ducts on the surface of the collector ring should be cleaned and kept unobstructed. For the collector ring that has been turned multiple times, if the height of the ventilation ditch on the surface of the collector ring is less than 5mm and it has been turned to the radial limit hole, it should be replaced according to the manual according to the minimum operating diameter to ensure the mechanical and heat dissipation reliability of the collector ring.

2. Heating caused by excessive contact resistance or uneven distribution: The collector ring and brush conduct excitation current through sliding contact with each other. Depending on the capacity and model, there are about ten brushes distributed on each collector ring. Due to differences in contact resistance and current distribution, uneven heating can be caused by the following reasons: (1) The contact resistance between the brush and the sliding ring surface, the contact resistance between the brush and the brush braid, and the contact resistance between the brush braid and the brush holder lead are too high. It can be checked by comparing the total voltage drop of a single brush, brush contact voltage drop, brush body voltage drop, connection voltage drop, and brush braid voltage drop with each other. At the same time, check whether all screws in the circuit are tightened. Check the cleanliness of the brush contact surface for oil contamination. (2) Uneven or unsatisfactory brush pressure may be caused by the brush being too short, the spring becoming soft due to overheating, aging, and losing elasticity. Spring scale should be used to check the brush pressure. The constant pressure spring should be intact without mechanical damage, and the pressure should comply with the regulations of its product. The pressure deviation of the spring on the same pole should not exceed 5%; For non constant pressure brush springs, the pressure should comply with the regulations of the product when specified. When there are no regulations, the pressure should be adjusted to the lowest pressure that does not cause the brush to catch fire, generally 140-250g/cm2. The pressure of each brush on the same brush holder should be uniform. (3) The contact resistance between the collector ring and the rotor lead is too high. In this case, the fastening screws between the collector ring and the rotor lead should be reinforced. (4) The material of the electric brush is poor, the conductivity is poor, the model used does not meet the requirements, or different models of electric brushes are used. Brushes of the same model and manufacturer should be used on the same motor. Brushes with significant differences in appearance should be replaced.

3. Overheating caused by mechanical and friction reasons: A large part of the overheating faults of the collector ring and brush are caused by mechanical and friction reasons. If the temperature of the collector ring and brush is found to be high before excitation is applied during startup, or if the temperature is too high during operation, and a few brushes are removed, the temperature will actually decrease. It can be basically confirmed that it is caused by mechanical and friction reasons.

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