The original carbon brushes of Xi'an Simo Motor have good lubricity, a low friction coefficient, and excellent commutation performance. They are mainly suitable for the collector rings of large steam turbine generators, exciters, the collector rings of hydro-generators, and DC motors with normal commutation.
Carbon brushes are devices that transfer energy or signals between the fixed part and the rotating part of a motor, generator, or other rotating machinery. They are generally made of pure carbon with a setting agent. Their appearance is usually in the shape of a square block, which is stuck on a metal bracket, and there is a spring inside to press it tightly against the rotating shaft. For example, after an oil well drilling is completed and inspection is required, instruments need to be lowered into the wellbore. The signals are sent from the rotating part (the cable drum covered with steel wires) to the surface instruments through carbon brushes. The carbon brush looks a bit like an eraser for a pencil, with a wire lead at the top. Its volume varies in size. As a sliding contact part, carbon brushes are widely used in many electrical devices. The main materials of the products are electrographite, resin-impregnated graphite, and metal (containing copper and silver) graphite.
In a brushed motor, the carbon brush is placed on the surface of the commutator. When the motor rotates, it transmits electrical energy to the coil through the commutator. Since its main component is carbon, it is called a carbon brush, and it is prone to wear. It should be regularly maintained and replaced, and the carbon deposits should be cleaned.
Carbon brushes are classified into resin types, electrographite types, and non-ferrous metal types. They are used in different motors due to differences in materials and processes.
- A uniform, moderate, and stable oxide film can be quickly formed on the surface of the commutator or collector ring.
- The carbon brush has a long service life and does not wear the commutator or collector ring.
- The carbon brush has good commutation and current collection performance, suppresses sparks within the allowable range, and has low energy consumption.
- During the operation of the carbon brush, it does not overheat, makes little noise, is reliably assembled, and does not break.
- When the carbon brush is installed in the brush holder, it should be able to move up and down freely. The gap between the carbon brush and the inner wall of the brush holder is between 0.1 and 0.3 millimeters to avoid the swing caused by the excessive gap between the carbon brush and the brush holder. The distance between the lower edge of the brush holder and the surface of the commutator should be maintained at about 2 millimeters.
- On the same motor, in principle, the same type of carbon brush should be used. However, for some large and medium-sized motors with particularly difficult commutation, twin carbon brushes can be used. The sliding-in side uses carbon brushes with good lubrication performance, and the sliding-out side uses carbon brushes with strong spark suppression ability, so as to improve the operation of the carbon brushes.
- The unit pressure applied to each carbon brush of the same motor should strive to be uniform to avoid uneven current distribution, resulting in overheating and sparks in individual carbon brushes. The unit pressure of the carbon brush should be selected according to the "Technical Performance Table of Carbon Brushes". For motors with a higher rotational speed or motors operating under vibration conditions, the unit pressure should be appropriately increased to ensure normal operation. For example, the unit pressure of the carbon brush of a traction motor is 0.4-0.6kgf/cm2.
- Intuitively, the carbon brush should have an appropriate chamfer, be of the proper specification, have a standard structure, and the cross-section and length of the wire should meet the requirements. There should be no looseness, detachment, damage, edge chipping, corner chipping, or clamp problems.
- In terms of use, the main signs of good performance of the carbon brush are as follows:
(1) It has a long service life and does not wear the commutator or collector ring.
(2) It has good commutation and current collection performance, suppresses sparks within the allowable range, and has low energy consumption.
(3) During the operation of the carbon brush, it does not overheat, makes little noise, and does not break.
(4) During the operation process, a uniform, moderate, and stable oxide film can be quickly formed on the surface of the commutator or collector ring. - Detect the carbon brush through instruments. From a technical perspective, the carbon brush should comply with the national ministry-issued standards. The carbon brush can be tested according to the performance requirements in the "Technical Performance Table of Carbon Brushes" through instruments. Such as the resistivity of the carbon brush, Rockwell hardness, bulk density, current density, contact voltage drop, friction coefficient, wear in 50 hours, allowable circumferential speed, unit pressure, and even the size of the metal content, etc.
- On the same motor, carbon brushes of the same type and from the same manufacturer should be selected. Since the performance of carbon brushes produced by different manufacturers varies greatly, and even the performance of carbon brushes produced by the same manufacturer at different times may also vary. Therefore, for the same motor, carbon brushes of the same type, from the same manufacturer, and preferably produced at the same time should be selected as much as possible to prevent the uneven distribution of the current of the parallel carbon brushes caused by the performance differences of the carbon brushes from affecting the normal operation of the motor.
- For some large and medium-sized motors with particularly difficult commutation, braided carbon brushes can be selected. The purpose is to improve the commutation performance by increasing the short-circuit current inside the carbon brush. For motors with difficult commutation in a single-directional rotation, combined carbon brushes can be selected. That is, on the sliding-in side, low-resistance graphite-based electrographite carbon brushes with good lubrication performance and strong film-forming ability are selected, and on the sliding-out side, carbon black-based electrographite carbon brushes with good commutation performance and high resistivity are selected. In this way, it is easy to form an oxide film, and it also greatly improves the commutation performance. Carbon fiber composite carbon brushes can also be used on the sliding-out side, taking advantage of their strong arc extinguishing ability, so as to achieve the best operation effect of the motor.
- When the carbon brush is worn to a certain extent, it should be replaced with a new one. It is best to replace all the carbon brushes at once. If new and old carbon brushes are used together, uneven current distribution may occur. For large units, shutting down to replace the carbon brushes will inevitably affect production. It is possible to choose not to shut down. Our usual suggestion to customers is to replace 20% of the carbon brushes each time (that is, 20% of each brush rod of each motor), with an interval of 1-2 weeks each time. After running-in, the remaining carbon brushes can be gradually replaced to ensure the normal continuous operation of the unit.
- In order to ensure good contact between the carbon brush and the commutator, the new carbon brush should be arched. The arching is generally carried out on the motor. Place a piece of fine glass sandpaper between the carbon brush and the commutator. Under the normal spring pressure, grind the carbon brush along the rotation direction of the motor. The sandpaper should be tightly attached to the commutator as much as possible until the arc surface of the carbon brush fits. Then remove the sandpaper, blow off the dust with compressed air, and wipe it clean with a soft cloth. Emery sandpaper should not be used to grind the carbon brush to prevent the emery particles from being embedded in the grooves of the commutator, which may scratch the surfaces of the carbon brush and the commutator during the operation of the motor. After arching, the motor should be operated at a load of 20-30% for several hours to run in the carbon brush and the commutator and establish a uniform oxide film. Then gradually increase the current to the rated load.
The main function of the carbon brush is to conduct electricity while rubbing against the metal. It is different from the case of metal-to-metal friction for conducting electricity. When metal conducts electricity through metal-to-metal friction, the friction force may increase, and the contact area may be sintered together. However, the carbon brush will not have such problems because carbon and metal are two different elements. Its applications are mostly in motors, and its shapes are various, such as square, round, etc.
Carbon brushes are suitable for various motors, generators, and axle machines. They have good commutation performance and a long service life. Carbon brushes are used on the commutator or slip ring of the motor as sliding contact bodies for leading in and out the current. They have good electrical conductivity, thermal conductivity, and lubrication performance, and have a certain mechanical strength and the ability to suppress commutation sparks. Almost all motors use carbon brushes, and they are an important component of the motor. They are widely suitable for various AC and DC generators, synchronous motors, battery DC motors, the collector rings of crane motors, and various types of electric welding machines, etc.
With the development of science and technology, the types of motors and the operating conditions are becoming more and more diverse. Therefore, various grades of carbon brushes are required to meet these requirements, and the types of carbon brushes are also increasing with the development of the motor industry.
- Add the external current (excitation current) to the rotating rotor through the carbon brush (input current);
- Introduce the static charge on the shaft into the ground through the carbon brush (grounding carbon brush) (output current);
- Lead the shaft (ground) to the protection device for the rotor grounding protection and measurement of the positive and negative voltages of the rotor to the ground;
- Change the direction of the current (in a commutator motor, the carbon brush also plays a role in commutation);
Except for the induction AC asynchronous motor, other motors have carbon brushes, and as long as the rotor has a commutator ring, there are carbon brushes.
The principle of power generation is that after the magnetic field cuts the wire, current is generated in the wire. The generator cuts the wire by rotating the magnetic field. The rotating magnetic field is the rotor, and the cut wire is the stator.
In order to make the rotor generate a magnetic field, excitation current must be input into the rotor coil. The carbon brush is used to send the excitation current generated by the excitation generator into the rotor coil.
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