How to maintain DC motor daily

Motor dust, oil and dirt must be thoroughly removed. Any cleaning shall be carried out with the motor uncharged.

Trichloroethylene shall not be used to clean the inside of the motor, but anhydrous compressed air shall be used.

The maintenance of the motor is mainly to check the bearing, commutator, brush holder and brush. Special attention must be paid to the shiny and clean sliding surface of the commutator and good contact with the brush. The surface of the commutator is brown and normal, and the sparks in the brushes are generally caused by mechanical reasons. The deformation of the commutator is not round, the mica plate of the commutator protrudes, the brush in the brush holder is stuck, the rotor is not well balanced, or the installation is not correct, resulting in unstable operation of the motor. In all these cases, appropriate measures must be taken.

1. Bearing

When the motor leaves the factory, the inner cavity of the bearing has been filled with No. 3 lithium-based grease of 1/2 to 1/3, and the same or equivalent grease shall be used for re-lubrication as much as possible. There is a straight-through oil cup in the outer bearing cover. In order to prevent excessive grease filling in the bearing cavity, the waste oil should be removed after loosening the bearing cover screws.

2. commutator

The motor commutator has been ground by the manufacturer before leaving the factory. If no damage occurs during transportation, it is not necessary to grind it again during the first drive. Only in the case of external corrosive circulating air erosion and long-term low-load operation in dry circulating air, it is easy to be worn and must be reground. The brush must be lifted as far as possible when the motor is running and cold. Use silicon carbide emery cloth to stick on a concave wood board or rubber block (gold steel emery cloth is not allowed) that matches the outer circle of the commutator. For the out-of-round commutator, use a sharp turning tool to finish turning on the lathe. Mark the minimum allowable diameter of the commutator on the side of the commutator. After turning, use a file or a high-speed steel saw blade to carve 1 to 1.5mm the mica. Then manually chamfer to remove burrs, grind the surface again, taking care that the surface is not contaminated.

3. Brush

For low-power motors, the whole brush is used, and for motors under harsh electrical or mechanical conditions, split brushes with shockproof pads are used. The principle of brush selection is to obtain good commutation performance and operation reliability.

a, overload,

In the case of long-term overload, the brush wear will increase, the brush commutation performance will deteriorate, and the trend of uneven current distribution will increase.

B, low load, low load will often cause the formation of scratches, the base to cause extreme brush wear, this kind of situation in the motor operation should be paid attention.

C, brush pressure, for general medium-power and high-power motors, the correct pressure of the brush is (1.5-2)X 10 Pa when the vibration of the installation place is not great.

D, life, the life of the brush mainly depends on the load and air circulation. At air humidity of 6 to 12 grams of water per cubic meter, the normal wear and tear for 1000 working hours can be at most 5mm. Due to the air humidity or circulating humidity air pollution on the "carbon brush a commutator" characteristics have a great impact, so although the load is normal, the amount of wear will fluctuate by about 100.

E, the formation of scratches, brush cross-section is determined by the rated parameters, for a lighter load brush (I. e. long-term low load operation) may produce scratches, which can reduce the number of brush rod brushes, which can improve the current density of the working brush and prevent the formation of scratches. If the measure is impossible or ineffective. The manufacturer must be consulted. The brush on the original motor is ground, and it is usually not necessary to grind again in the motor debugging, but the movement of the brush in the brush holder and the spring force of the pressure finger (about [1.52]X 10 Pa) should be checked again before use. During operation, the wear rate of the brush shall be controlled and the lead wire of the brush shall be prevented from touching the surface of the commutator.

The brush material is D374N electrochemical graphite. The specifications are as follows (unit: mm)

10 (width) x 12.5 (length) x 32 (height),10x 16x 32,12.5x 16x 32,12.5x 20x 32,10x 25x 40,12.5x 25x 40,16x 25x 40,20x 25x 40.

For a certain specification of the motor with which specifications of the brush, you can open the cover on the end cover of the commutator to measure the width and length of the brush, or ask the factory.

For brushes 10 x 12.5,10 x 16.12.5 x 16,125 x 20, etc. Its height is as small as 17mm, for brushes

10 x 25,12.5 x 25,16 x 25,20 x 25, etc. When the height is as small as 25mm, consider replacing the brush. The brush material shall be D374N or equivalent. The same material brush must be used for the same motor.

When replacing the brush, it is necessary to keep the brush in good contact with the surface of the commutator. For this purpose, the brush shall be ground. The method is as follows: the emery cloth is tightly wrapped on the surface of the commutator, the sand surface of the emery cloth is in contact with the brush, and the armature is rotated back and forth to grind the brush on the cylindrical emery cloth surface until the sliding surface of the brush conforms to the circle of the commutator.. Use coarse emery cloth, and then grind it several times in the direction of rotation after grinding with fine emery cloth. Finally to brush dust carefully removed. The motor can run with load after idling for several hours.

4. Brush holder

The brush holder with brush holder has been adjusted to the best position in line with the operating conditions in the manufacturer, I .e. neutral position. It is opened at the window of the near end cover and marked on the brush holder. Attention should be paid to ensure this position when reinstalling after disassembly, otherwise it will affect the commutation performance and cause brush sparks.

If the brush holder slightly deviates from the neutral position in order to make the motor reach a certain speed characteristic (or to make the generator reach a certain voltage adjustment characteristic), the position of the brush holder shall be readjusted generally. When replacing the armature, the neutral position shall also be readjusted. The adjustment and inspection of the neutral position can only be carried out when the brush is well ground and completely contacted with the commutator. The adjustment method is as follows: connect a millivolt meter of about 600mv to the lead wires of the positive and negative brushes, adjust the excitation current to 20-30% of the rated value with a series resistor, turn on and off the current when the armature is stationary, move the brush holder, find and determine the position on the millivolt meter according to the minimum deflection value, then cut off the magnetic field, and make the armature rotate unidirectionally along the rotation direction of brush grinding, which is suitable

For motors with single-direction rotation, it is best to measure the neutral position of motors with reversible operation through positive and reverse tests. Under the condition that the armature voltage, current and excitation current are unchanged, the positive and reverse rotation speeds are measured respectively, and the brush holder is moved to make the positive and reverse rotation speeds equal. This position is the neutral position.

The maintenance of the brush holder is mainly to keep the insulation part clean.

5. Filter device

If the motor has a filter, it should be thoroughly cleaned after a certain period of time according to the pollution, otherwise it will affect the cooling of the motor and cause thermal damage to the motor.

The coarse filter (metal filter) can be cleaned by blowing off dust particles with compressed air or cleaning with solvent. The fine filter (fiber sandwich filter) can be cleaned with water. The water temperature should not exceed 40 ℃. It is better to add commercial cleaning agents, or to beat with hands, suck out with vacuum cleaner or blow off dust with compressed air. If the pollution is contact pollution, it needs to be washed with gasoline, however, the filter should avoid wringing and strong spraying, and the filter should be dried after washing.

6. Disassembly and reassembly

Before disassembling the motor, it must be carefully considered whether it is necessary to disassemble it completely or partially. Before disassembling, cut off the power supply first, then remove the journal parts such as coupling or belt reel, and then open the commutator maintenance window. Lift up the brush, clamp the brush in the brush holder guide box with the help of the pressure finger, so that the surface of the commutator is not damaged, and the outer circle of the commutator is preferably coated with cardboard as a protective layer. To prevent the armature from falling onto the poles below it, the air gap between the armature and the poles must be filled with cardboard. After removing the fastening screws of the bearing cover and removing the bearing, the end cover must be separated from the machine base after loosening the screws. When separating, two large screwdrivers can be used to wedge into the matching gap of the stop and slowly pry it apart. When taking out the end cover bearing chamber, it should slide along the axial direction of the outer ring of the bearing. When using ball bearings, it should be noted that the end cover cannot be tilted and kept as stable as far as possible. Under special circumstances, separate the end cover from the machine base. When removing the end cover of the motor end, mark the connecting line on the brush holder in advance and then loosen it. If it is equipped with tachometer or other accessories, it should also be removed before removal. For small motor armature, it can be taken out with bare hands. If lifting cable and its auxiliary tools are required, the cable shall not be sleeved on the unprotected optical axis extension, let alone on the commutator or fan, the removed armature must be installed smoothly and must not be cantilevered to one end of itself.

The steps of reassembly are basically opposite to those during disassembly. The disassembled bearings are generally no longer used. For the integral laminated machine base, the repair of the coil can be consulted or sent to the manufacturer for repair. The bearing chamber should be changed on schedule. The original waste oil must be drained during oil change. The adjusting washer of the motor, especially the wave spring of the non-transmission end ball bearing chamber, must be reinstalled to the original position according to the original quantity. The following points must be noted for reassembly: all insulation parts should be in good condition, there should be sufficient creepage distance between live parts, the brush and the commutator should be in good contact, and all screws should be firmly connected. The bearing movement accuracy is reliable, and on this basis, the insulation test and operation test are finally carried out.