The carbon brush stuff

We're talking about carbon brushes for power tools today. Carbon brush (Carbon brush), also called brush, as a sliding contact, is widely used in many electrical equipment. Carbon brush in the product application materials are mainly graphite, impregnated graphite, metal (containing copper, silver) graphite. Do you have enough carbon brushes to go through the box?

📍 When do I need to replace the carbon brush?
① The spark is large, the carbon brush burns the contact surface of the rotor, take it off and wipe it off with sandpaper. The spark situation may also be that the copper on the rotor converter is used up, the short-circuit spark is large, and the conductive performance is reduced.
② will not turn, carbon brush used up.
(3) Neither of the above two cases, that is, the spring type carbon brush, the single spring pressure is insufficient, resulting in the carbon brush and the rotor contact is not tight short circuit spark, need to pull out the carbon brush copper wire, add 2 springs.
(4) The copper sheet above the carbon brush, the copper sheet without card position is in use, the copper sheet rotation causes the copper wire above to tighten, the carbon brush can not be in close contact with the rotor, the spark is small, and the need to remove and shake.

📍 How the carbon brush works
Brush motor All motors are composed of stator and rotor, in the DC motor, in order to make the rotor turn up, you need to constantly change the direction of the current, otherwise the rotor can only turn half a circle, which is like pedaling a bicycle pedal, one foot can only pedal half a circle, so the DC motor needs to change the current in the rotor, that is, the direction of the current conductor in the need to reverse. The commutation of the commutator is that when a energized conductor is put into the electromagnetic field to cut off the magnetic field, the conductor will be pushed out of the static magnetic field, which is because the magnetic field line of the magnetic field is compressed and deformed by the electromagnetic field around the conductor, and the magnetic field line tries to bounce back to the straight shape, which is equivalent to producing attractive and repulsive forces to make the motor turn. The commutator consists of two semicircle segments separated by insulating material. The two segments rotate respectively to connect with the carbon brush, and the carbon brush is repeatedly connected to the segment of the commutator that meets the driving force, so that the repeating motor rotates.

📍 Problems encountered in replacing carbon brush and solutions
Problem: 1, carbon brush wear serious
The reason:
A. The influence of carbon brush material. Different manufacturers, different models of carbon brush composition structure is different, wear rate is also different. Therefore, when replacing the carbon brush, choose the same brand of carbon brush;
B. Surface finish of slip ring. The higher the surface finish of the slip ring, the smaller the friction coefficient and the lower the wear rate of the carbon brush.
C Effect of spring pressure. Excessive spring pressure will cause the mechanical wear of the carbon brush to increase; At the same time, the spring pressure is too small, although the friction between the carbon brush and the slip ring is small, but the poor contact is easy to produce sparks, which is also not desirable;
D. Effect of current. In general, for graphite carbon brushes, the current flowing through the positive carbon brush is larger than the current flowing through the negative carbon brush, so the wear of the positive carbon brush is larger than the wear of the negative carbon brush, and the wear of the positive slip ring is more than the negative slip ring.
The solution:
1, enhance the lubrication performance of the carbon brush, including the self-lubrication and surface lubrication of the carbon brush, the high temperature resistance of the added lubrication material;
2, enhance the quality stability of the carbon brush;
3, enhance the synergy of carbon brush and commutator (commutator);
4, ensure the performance stability of the spring.

Problem: 2, carbon brush fire
The reason:
A. Caused by excessive current flowing through the carbon brush;
B. Due to astringent carbon card, intermittent contact with the slip ring caused.
The solution:
1, pay attention to select the performance model matching carbon brush;
2, enhance the self-lubrication and surface lubrication of the carbon brush, and the high temperature resistance of the added wear reduction material.

Problem: 3, the carbon brush temperature is high
The reason:
A. overload of excitation system;
B. The contact surface between carbon brush and slip ring is small;
C. The quality of the carbon brush itself.
The solution:
1, pay attention to select the performance model matching carbon brush;
2, enhance the self-lubrication and surface lubrication of the carbon brush, and the high temperature resistance of the added wear reduction material.
3. Pay attention to the selection of carbon brushes with stable quality.

Problem: 4. The carbon brush is badly damaged
The reason:
A. High carbon brush temperature;
B. The carbon brush is not polished well;
C. The vibration of the unit is large, and the carbon brush is stuck in the brush grip;
D. Carbon brush quality is poor.
The solution:
1, pay attention to select the performance model matching carbon brush;
2, enhance the self-lubrication and surface lubrication of the carbon brush, and the high temperature resistance of the added wear reduction material.
3, choose reliable quality and stable carbon brush.

Problem: 5, carbon brush jumping
Cause: The carbon brush has broken fine pieces falling in the brush grip or other possible reasons
The solution:
1, pay attention to select the performance model matching carbon brush;
2, choose reliable quality and stable carbon brush.
3, enhance the self-lubrication and surface lubrication of the carbon brush, and the high temperature resistance of the added wear reduction material.