What is Carbon Brush?
Carbon brush (Carbon brush) is also called electric brush, as a kind of sliding contact, it is widely used in many electrical equipment. Carbon brushes are mainly used in graphite, fat-impregnated graphite, and metal (copper, silver) graphite. A carbon brush is a device that transmits energy or signals between the fixed part and the rotating part of a motor or generator or other rotating machinery. It is generally made of pure carbon and a coagulant. A spring presses it tightly on the rotating shaft. When the motor rotates, the electric energy is transmitted to the coil through the commutator. Since its main component is carbon, it is called a carbon brush, which is easy to wear. It should be regularly maintained and replaced, and carbon deposits should be cleaned.
The carbon brush looks a bit like the rubber strip of a pencil, with wires leading out from the top. There are large and small volumes. As a sliding contact, carbon brushes are widely used in many electrical equipment. The main materials of the products are electrochemical graphite, fat-impregnated graphite, and metal (copper, silver) graphite.
Classification
Metal graphite
The main materials of this type of carbon brush are electrolytic copper and graphite. According to the needs of use, other metals such as silver powder (used in precision instruments, very expensive), aluminum powder, lead powder, etc. are sometimes used. These carbon brushes are divided into those with binders and those without binders. This type of carbon brush has both the friction characteristics of graphite and the high conductivity of metal, so it is suitable for low-voltage motors with high load and low commutation requirements (such as automobile starter motors, etc.). Its peripheral speed does not exceed 30 m/s.
natural graphite
Natural graphite is the main raw material of this type of carbon brush. The binder is made of pitch or resin, which is baked or sintered at 1000 degrees. This type of motor has good lubrication performance and current collection performance. Most of them are used for slip rings of small and medium-sized DC motors and high-speed turbogenerators with smooth operation.
Electrochemical graphite
The main components are carbon black, coke and graphite and other carbon powder materials, which are transformed into microcrystalline artificial graphite after high temperature treatment at 2500 degrees. This type of carbon brush has excellent commutation and self-lubricating properties, and is widely used in various AC and DC motors. It not only has a long life, but also has little wear on the commutator.
Features
The function of the carbon brush is mainly to conduct electricity while rubbing against the metal. It is not the same as the metal-to-metal friction; when the metal is frictionally conductive, the friction force may increase, and at the same time, the junction may be sintered together; and Carbon brushes don't because carbon and metal are two different elements. Most of its uses are used in motors, and the shapes are various, square and round, and so on.
Carbon brushes are suitable for all kinds of motors, generators, and axle machines. It has good reversing performance and long service life. The carbon brush is used on the commutator or slip ring of the motor. As a sliding contact body for leading and leading current, it has good electrical conductivity, thermal conductivity and lubricating performance, and has a certain mechanical strength and the instinct of commutating sparks. Almost all motors use carbon brushes, which are an important part of the motor. Widely used in various AC and DC generators, synchronous motors, battery DC motors, crane motor collector rings, various types of welding machines and so on. With the development of science and technology, the types of motors and the working conditions of use are becoming more and more diverse.
specific role
1. Add the external current (excitation current) to the rotating rotor (input current) through the carbon brush;
2. Introduce the static charge on the large shaft to the ground (grounded carbon brush) through the carbon brush (output current);
3. Lead the large shaft (ground) to the protection device for rotor grounding protection and measure the positive and negative ground voltage of the rotor;
4. Change the direction of the current (in the commutator motor, the brush also plays the role of commutation).
Except for induction AC asynchronous motors. There are other motors, as long as the rotor has a commutation ring.
The principle of power generation is that after the magnetic field cuts the wire, a current is generated in the wire. The generator cuts the wire by rotating a magnetic field. The rotating magnetic field is the rotor, and the cut wires are the stator.
Good Sign
In order to ensure the normal operation of the motor, the sign of good performance of the carbon brush should be:
1) A uniform, moderate and stable oxide film can be quickly formed on the surface of the commutator or collector ring.
2) The carbon brush has a long service life and does not wear the commutator or slip ring
3) The carbon brush has good commutation and current collection performance, which makes the spark suppressed within the allowable range, and the energy loss is small.
4) When the carbon brush is running, it is not overheated, the noise is small, the assembly is reliable, and it is not damaged.
