The collector assembly of the electric motor is needed to transfer electricity to the armature windings. Since the anchor rotates during operation, transmission is through a special contact. For the organization of movable contact in all domestic and industrial engines do not use metal plates. This is due to high speeds, at which the friction of metal on metal would produce additional heating of the working surface and the rapid development of the collector. Therefore, graphite or coal was chosen as the contact. He got the name - electric brush.
Motor brushes
A sliding contact designed to supply and discharge electricity to collectors or ring contacts of all types of electric machines (electric motors and generators) is called an electric brush.
Electric motor brushes are produced both with metal conductors and without them. The wire is fixed in the brush by the method of expansion, pressing or by soldering. Brush current leads are of the following brands:
- MSC - a special type of stranded wire made of copper wire;
- - a flexible type of wire of copper wire weaving;
- PShchS - a universal wire with the increased indicator of flexibility.
Contact leads are provided on the lead wire. Using them, the wire is fixed with a bolt of the brush holder. Tips are forked, flagged, 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 filler in the form of soot and other substances. Designed brushes for easy switching in generators and engines. Grades EG61A and G20 are produced.
- Coal graphite type. Low strength brushes for low mechanical stress. Stamps G21, G22.
- Electrographic type. Carbon-enhanced brushes with enhanced mechanical strength. Perform switching of medium complexity. Withstand large current loads. There are grades 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. Different fillers go to them. Brushes have high durability, do not pass gas and liquid media. Applicable in high and medium complexity switching conditions. Provide the functioning of low voltage generators. The brands 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, brushes of the grades G33MI, G33, G30, G31 are produced.
Brush contact selection
The most important thing when selecting brushes for an electric motor is to know the parameters of the worn brushes. In addition to the geometric dimensions, the new brush should match the graphite brand, type and cross-section of the wire. It is not necessary to take the same brand as the original, but the hardness of the electric motor brush and the operating modes must match. The thickness of the wire should not be less than the original, and the flexibility to match. The main mistakes in selecting a brush contact:
- Establishment of stiffer graphite contact where softer ones were used. The result may be quick wear on the collector.
- Installation of "universal" brushes everywhere. This may interfere with the operation of the device.
- Orientation when buying a brush on the graphite marking on the side of the old electric motor brush. Graphite marking is not marking contact parameters!
Why do brushes sparkle
The sparking of brushes sliding across the collector is logical, because at the moment of transition from one lamella to another, an arc microdischarge occurs. With the proper functioning of the engine, serviceability and compliance of all elements, it is hardly perceptible to the eye. But if the electric motor brush sparks strongly, the reason indicates a malfunction. Ignoring this process is fraught with failure of the anchor.
The reasons why the brushes sparkle are as follows:
- The formation of soot or dirt on the collector. It is possible that during prolonged operation of the engine without maintenance, a thin film of carbon deposits formed on the collector contacts. It has increased resistance, which leads to sparking. You can fix the problem by treating the collector with sandpaper of zero grain size (in the direction the brushes rotate).
- Shorting 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.
- Wrong selection of brush parameters. As a result of the contact resistance mismatch, there will also be sparks on the collector. It is necessary to replace graphite brushes, based on the technical documentation of the engine.
- The production of brushes.
- Inter-turn circuit in the windings of the armature. Check anchor and replace in case of malfunction.
Replacing motor brushes
Changing brushes is necessary when at least a third of the working part is left, and also follow the rules:
- Choose brushes that match the previous settings.
- Visually inspect the manifold and clean if necessary.
- If the working surface of the brushes has a bevel, do not confuse its location.
- Allow the brushes to grind, including the motor without loads, and then remove the grinding dust from the collector.
Conclusion
In addition to all the listed brush care activities, there are also special lubricants for the collector assembly. They can reduce the mechanical load on the contact and prevent the formation of soot.