How to maintain the DC motor daily

The dust, oil and dirt of the motor must be completely removed. Any cleaning work must be done with the motor de-energized.

For cleaning inside the motor, trichloroethylene should not be used but anhydrous compressed air should be used for blowing.

The maintenance of the motor is mainly to check the bearings, commutators, brush holders and brushes. Special attention must be paid to the glossy and clean sliding surfaces of the commutator and good contact with the brushes. It is normal for the surface of the commutator to be brown, and the sparks on the brushes are generally caused by mechanical reasons. The commutator is deformed out of circle, the mica sheet of the commutator is protruding, the electric brush in the brush holder is stuck, the rotor balance is not good, or the installation is incorrect, 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 one-half to one-third of No. 3 lithium-based grease, and the same or equivalent grease should be used as far as possible for re-lubrication. There is a straight-through press-in oil cup in the outer bearing cover. In order to prevent the grease in the bearing cavity from being filled too much, 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 it is not damaged during transportation, it does not need to be ground again when the first drive is started. 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. Resharpening must lift the brush as far as possible with the motor running and cold. Use silicon carbide emery cloth to stick it on a concave wooden board or rubber block that matches the outer circle of the commutator (gold steel emery cloth is not allowed). For the out-of-round commutator, use a sharp turning tool on the lathe , The mark of the minimum allowable diameter of the commutator is given on the side of the commutator. After turning, use a file or a high-speed hacksaw blade to carve 1 to 1.5mm on the mica between the commutator segments, and then manually clean the chamfer, remove burrs and Impurities, polish the surface again, take care that the surface is not contaminated.

3. Brush

For low-power motors, one-piece brushes are used, and for motors with harsh electrical or mechanical conditions, split brushes with shock-proof pads are used. The principle of brush selection is to obtain good commutation performance and operational reliability.

a. Overload,

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

b. Low load, low load will often cause the formation of scratches, which will lead to extreme wear of the brushes. This kind of situation should be paid attention to when the motor is running.

c. Brush pressure, for general medium-power and high-power motors, where the vibration of the installation site is not large, the correct pressure of the brush is (1.5-2) X 10 Pa.

d. Life, the life of the brush mainly depends on the load and air circulation. When the air humidity is 6 to 12 grams of water per cubic meter, the normal wear of 1000 working hours can be 5mm at most. Due to the pollution of air humidity or circulating humidity air, it has a great influence on the characteristics of "carbon brush-commutator". Therefore, although the load is normal, the wear amount will fluctuate by about 100%.

e. For the formation of scratches, the cross-section of the brush is determined by the rated parameters. For a brush with a lighter load (ie, long-term operation at a low load), scratches may occur, and the number of brushes on the brush rod can be reduced. The current density of the working brush can be increased to prevent scratches from forming. If the measure is impossible or ineffective. The manufacturer's opinion must be consulted. The brushes on the original motor are ground, and usually do not need to be ground again during the motor debugging, but before use, check the movement of the brushes in the brush holder and the spring force of the pressing finger (about [1.52] X 10 Pa ). In: The brush wear rate must be mastered during operation, and the brush lead wire should be prevented from touching the surface of the commutator.

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

10 (W) X12.5 (L) X 32 (H), 10X16X32, 12.5X16X32, 12.5X20X32, 10X25X40, 12.5X25X40, 16X25X40, 20X25X40.

For the brush of a certain specification, 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. grind their heights down to 17mm, for brushes

When the height of 10 x 25, 12.5 x 25, 16 x 25, 20 x 25 is reduced to 25mm, you should consider replacing the brush. The brush material should be D374N, or the corresponding material. The same motor must use the same brush material.

When replacing the brush, keep the brush in good contact with the surface of the commutator. The brushes need to be ground for this purpose. The method is as follows: Wrap the abrasive cloth tightly on the surface of the commutator, the abrasive surface of the abrasive cloth is in contact with the brush, and rotate the armature back and forth to make the cylindrical abrasive cloth surface grind the brush until the sliding surface of the brush conforms to the circular shape of the commutator. until.. Choose a coarse emery cloth, and then grind it with a fine emery cloth and grind it several times in the direction of rotation. Finally, carefully remove the brush dust. The motor can be run under load after idling for several hours.

4. Brush holder

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

If the brush holder is slightly deviated from the neutral position in order to make the motor achieve a certain speed characteristic (or to make the generator achieve a certain voltage adjustment characteristic), the position of the brush holder must generally be readjusted. The neutral position must also be re-adjusted. The adjustment and inspection of the neutral position must be carried out when the brush is well ground and fully in contact with the commutator. The adjustment method is as follows: Connect a millivolt meter of about 600mv to the On the lead wires of the positive and negative brushes, use the series resistance to adjust the excitation current to 20-30% of the rated value, turn on and off the current when the armature is stationary, move the brush holder, and use the millivoltmeter according to the minimum value. The deflection value is used to find and determine the position, and then the magnetic field is cut off, so that the armature rotates in one direction in the direction of rotation of the brush grinding, which is suitable for

For motors that rotate in one direction, it is best to measure the neutral position through forward and reverse tests for reversible motors. When the armature voltage, current and excitation current are all unchanged, the forward and reverse speeds are measured respectively. , and move the brush holder to make the forward and reverse speeds equal, and this position is the neutral position.

The maintenance of the brush holder is mainly to keep the insulating 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 situation, otherwise it will affect the cooling of the motor and cause thermal damage to the motor.

To clean the coarse filter (metal filter), use compressed air to blow off dust particles, or use a solvent for cleaning, and clean the fine filter (fiber sandwich filter) with water. The water temperature does not exceed 40 °C, preferably It can be added with a commercially available cleaning agent, and it can also be beaten with hands, sucked out with a vacuum cleaner or blown off with compressed air. If the pollution is contact pollution, it needs to be washed with gasoline, but the filter should avoid twisting and strong jetting to eliminate dust. Filters are generally dried after washing.

6. Disassembly and Reassembly

Before disassembling the motor, consider carefully whether it is necessary to disassemble all or part of it. Before disassembling, cut off the power supply, then remove the shaft journal parts such as the coupling or belt pulley, and then open the commutator maintenance window. Lift the brush and clamp the brush in the guide box of the brush holder with the help of pressing fingers, so that the surface of the commutator is not damaged, and the outer circle of the commutator is preferably covered 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 bearing cover fastening screws and taking off the bearing, the end cover must be separated from the base after the screws are loosened. When separating, two large screwdrivers can be used to wedge the gap between the openings, slowly pry it open, and come out. The bearing chamber of the end cover should slide axially along the outer ring of the bearing. When using a ball bearing, it must be noted that the end cover cannot be inclined, and it should be kept as stable as possible. Separation, when removing the end cover of the motor end, the connecting wire must be marked on the brush holder in advance and then loosened. If a tachometer or other accessories are installed, they should also be removed before disassembly. Small motor armature can be used with bare hands. Take it out. If a hoisting cable and its auxiliary tools are required, it is not allowed to put the cable on the unprotected optical shaft extension, and it is not allowed to put it on the commutator or fan. The removed armature must be installed smoothly and must not be One end of itself can be cantilevered.

The steps of reassembly are basically the opposite of those of disassembly. The disassembled bearings are generally no longer used. For the integral lamination frame, the repair of the coil can be consulted or sent to the manufacturer for repair. The bearing chamber should be changed oil on schedule. After draining the original waste oil, the adjusting washer of the motor, especially the wave spring of the ball bearing chamber at the non-transmission end, must be re-installed in the original position according to the original quantity. Reassembly must pay attention to the following points: All insulation parts should be in good condition, there should be sufficient creepage distance between live parts, the brushes and commutators are in good contact, and all screw connections should be firm. The bearing movement accuracy is reliable, and on this basis, the insulation test and the running test are finally carried out.