The collector assembly of the electric motor is needed to transfer electricity to the armature windings. Since the armature produces a rotational movement during operation, the transmission is carried out through a special contact. To organize a moving contact in all household and industrial engines, metal plates are not used. This is due to high speeds, at which metal-to-metal friction would produce additional heating of the working surface and rapid exhaustion of the collector. Therefore, graphite or coal was chosen as the contact. He got the name - electric brush.
Motor brushes
Sliding type contact, designed for supplying and discharging electricity on collectors or ring contacts of all types of electrical machines (electric motors and generators), was called an electric brush.
Motor brushes are produced both with and without metal conductors. The wire is fixed in the brush by flaring, pressing or by soldering. Brush current leads are of the following brands:
- MPShch -special type of wire stranded, made of copper wire;
- PShch - flexible type of copper wire braid;
- PShchS - universal wire with increased flexibility.
Contact tips are provided on the lead wire. With the help of them, the wire is fixed with a brush holder bolt. Tips are fork, flag, double and plate type.
Types of brushes
There are several classes of brushes that satisfy different switching conditions:
- Graphite brushes. They are made on the basis of graphite with the addition of a filler in the form of soot and other substances. Brushes are intended for light commutation in generators and engines. EG61A and G20 grades are produced.
- Carbon-graphite type. Brushes of low strength for small mechanical loads. Grades G21, G22.
- Electrographite type. Brushes of increased mechanical strength, saturated with carbon. Perform switching of medium complexity. Withstand high current loads. There are brands EG2A, EG74, EG14, EG4, EG841.
- Metal-graphite type (copper-graphite brushes for electric motors). The main component of the brush is copper, tin and graphite powder. They come with different fillers. The brushes are highly durable and do not allow gas and liquid media to pass through. Applicable in high and medium complexity switching conditions. Ensure the operation of low voltage generators. Marks have MG, MGS, MGS 5, MGS 20, MGS 51, MGSOA, MGSO,MGSO1M, M1A, M1.
The described brush contacts are applicable in industry, for household equipment they produce brushes of the G33MI, G33, G30, G31 brands.
Brush contact selection
The most important thing when selecting motor brushes is to know the parameters of the worn out brushes. In addition to the geometric dimensions, the new brush must match the grade of graphite, type and cross section of the wire. It is not necessary to take the same brand as the original, but the hardness of the motor brush and the operating modes must match. The thickness of the wire should not be less than the original, and the flexibility should match. The main mistakes when selecting a brush contact:
- Installing a stiffer graphite contact where softer ones were used. The result can be rapid wear of the manifold.
- Installation of "universal" brushes everywhere. Doing so may disrupt the operation of the device.
- Orientation when buying a brush on the marking of graphite on the side of the old motor brush. Graphite marking is not contact parameter marking!
Why do brushes sparkle
The sparking of brushes sliding along the collector is natural, because at the moment of transition from one lamella to another, an arc microdischarge occurs. With the correct functioning of the engine, serviceability and compliance of all elements, it is barely perceptible to the eye. But if the brush of the electric motor sparks strongly, the reason indicates a malfunction. Ignoring this process is fraught with failureanchors.
The reasons why brushes spark are as follows:
- Formation of soot or dirt on the manifold. It is possible that during prolonged operation of the engine without maintenance, a thin film of soot has formed on the collector contacts. It has increased resistance, which leads to sparking. You can fix the problem by sanding the commutator with zero-grit sandpaper (in the direction the brushes rotate).
- Closing adjacent collector contacts with graphite dust or fine copper powder. In this case, currents increase in the circuits, which leads to strong sparking. Jumpers should be carefully removed with a sharp object.
- Incorrect selection of brush parameters. As a result of the contact resistance mismatch, there will also be sparks on the collector. Graphite brushes need to be replaced based on engine data sheet.
- Brush production.
- Interturn short circuit in armature windings. Check armature and replace if defective.
Replacing motor brushes
It is necessary to change the brushes when at least a third of the working part is left, and also follow the rules:
- Select brushes that match the parameters of the previous ones.
- Conduct a visual inspection of the collector and clean it if necessary.
- If the working surface of the brushes has a bevel, do not confuse its location.
- Give the brushes time to lap, running the motor with no load, and then remove the lapdust from the collector.
Conclusion
In addition to all the above measures for the care of brushes, there are also special lubricants for the collector assembly. They reduce the mechanical load on the contact and prevent the formation of deposits.
