Bearing is an important part of the operation of the motor, the author based on many years of maintenance experience to know that its maintenance is standardized, directly affect the service life of the bearing, but also directly affect the safe and efficient operation of the motor. Therefore, it is necessary to do a good job of maintenance work on weekdays, and deal with it in a timely manner according to its fault phenomenon to avoid the expansion of the fault; So as to avoid burning out the motor and causing greater economic losses, it is very necessary.
Causes and treatment methods of abnormal noise in rolling bearings
►When the motor is running, you can use a screwdriver, the tip of which is against the outer cover of the bearing, and the ear is close to the wooden handle of the screwdriver to listen to the sound of the bearing. If there is a faint rolling sound in the inner and outer rings of the rolling element, and the sound is monotonous and uniform, which makes people feel relaxed, it means that the bearing is good and the motor is running normally. If you hear an abnormal noise, you should analyze the cause and deal with it.
1. Hearing obvious rolling and vibrating sounds of rolling elements means that the bearing clearance is too large or seriously worn and needs to be replaced.
2. The sound of the rolling element is hoarse and the tone is heavy, indicating that the lubricating grease of the bearing is too dirty and there are impurities invading, and the bearing needs to be cleaned with kerosene and replaced with new lubricating oil.
3. There is an irregular impact sound of the rolling element, indicating that the bearing has individual rolling elements that are broken and needs to be replaced.
4. The sound of a whistle, mixed with the rolling sound of the rolling element, indicates that the bearing lacks lubricating grease or the lubricating oil is not properly selected, and it is necessary to add clean lubricating oil or replace the appropriate lubricating oil.
► Causes and treatment methods of rolling bearing heating
1. If the motor is left for too long, the lubricating grease will deteriorate and harden; The grease should be replaced with a new one.
2. If the lubricating oil in the bearing chamber is too much or too little, it should be between 1/3 and 2/3 of the volume of the bearing chamber; And according to the requirements of the motor instructions, the same grade of lubricating oil should be added regularly and quantitatively.
3. There are debris in the bearing chamber, and the bearing needs to be cleaned with kerosene and replaced with new lubricating oil.
4. If the bearing is worn too much or the inner ring and the outer ring are broken, the new bearing of the same type should be replaced.
5. The vibration of the motor, the improper installation of the coupling, the tight transmission belt and the bending of the shaft will cause the bearing to heat up; Causes should be ruled out on a case-by-case basis.
6. If the bearing is not attached to the shaft shoulder, the bearing cover should be disassembled, and the inner ring of the bearing should be pressed against the copper rod and hammered in symmetrically.
7. If the end cover or bearing cover is not well assembled, it should be reassembled so that the end cover at both ends fits well with the base stop, and the fastening bolts of the bearing cover are tightened diagonally.
8. The working performance of the rolling bearing not only depends on the manufacturing accuracy of the bearing itself, but also depends on the dimensional accuracy, shape and position tolerance and surface roughness of the shaft and hole that it is mated with, the selected fit and the correct installation.
If the inner ring of the bearing fits too tightly with the shaft, or the outer ring of the bearing fits too tightly with the bore of the end cover bearing, that is, the interference is too large, the bearing clearance will become too small after assembly, sometimes even close to zero. In this way, the rotation of the bearing is not flexible, and it will heat up during operation, and even burn out the bearing.
However, if the inner ring of the bearing fits too loosely with the shaft, or the outer ring of the bearing fits too loosely with the end cover, then during operation, the inner ring of the bearing and the shaft, or the outer ring of the bearing and the end cover, will move relatively, and the friction will heat up, resulting in overheating of the bearing. The appropriate interference fit between the inner ring of the rolling bearing and the shaft and the fit between the outer ring of the rolling bearing and the end cover are generally overfitted, and their fitting tolerances are shown in the manual or instruction manual.
How to clean rolling bearings
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Before the bearing is assembled, it must be carefully cleaned, usually with gasoline or kerosene. The purpose of cleaning is to:
1. Wash off the rust inhibitor on the bearing.
2. Wash away the stolen goods and sundries that may enter the bearing due to carelessness. Bearings with shields or seals on both sides should be lubricated before leaving the factory and should not be cleaned during installation.
Do not put the cleaned bearing directly on the workbench or in an unclean place, and use a clean cloth or paper to pad it under the bearing. Don't go straight to it with your hands, and it's best to wear canvas gloves that don't remove hair easily.
Diagnosing rolling bearings for damage and whether they can be used continuously
1. For small motors, move the shaft extension end of the rotor up and down by hand, if the shaft can have a large amount of activity at this time, it means that the bearing is seriously worn.
2. Disassemble the end covers at both ends of the motor for inspection, if there are oil stains on the surface of the winding and core, it means that the bearing is leaking, and the seal is not tight or deformed.
3. After the bearing is removed, wipe off the grease in the bearing, and then wash the bearing with gasoline. Then the outer ring is rocked back and forth by hand relative to the ball, and the clearance of a good bearing is almost imperceptible. If the gap between the ball and the inner and outer rings is large, it means that the bearing is seriously worn and needs to be replaced.
Rolling bearings are properly assembled
There are two key problems in the assembly of rolling bearings, one is the cleaning method of the bearing, and the other is the installation method of the bearing. Experience has shown that the method of cleaning and mounting bearings has a great impact on the noise and vibration generated by the motor. Proper cleaning and installation methods can reduce motor vibration and bearing noise. Incorrect cleaning and installation methods are often the main causes of vibration, noise, bearing damage, or reduced service life of motors. Therefore, the cleaning and installation of rolling bearings must be carried out carefully and carefully in accordance with the correct method.
► Preparation before assembly
1. The site where the bearing is assembled should be cleaned to prevent dust or small particles from entering the bearing.
2. Check the shape and position tolerance of the shaft, if it does not meet the requirements, it cannot be assembled. At the same time, the size of the fillet at the root of the shoulder and the perpendicularity of the shoulder to the shaft should be checked. Generally, the fillet radius of the root of the shoulder should be less than the fillet radius of the inner ring of the bearing, so that the bearing can be close to the shoulder.
3. The assembly surface of the parts needs to be cleaned with gasoline or kerosene. No rust, spots, or solid particles are allowed.
► Bearing assembly process
There are two ways to assemble the bearing and shaft: hot sleeve and cold sleeve. However, heat sleeves are generally used, because the inner ring of the bearing and the journal are generally over-fitted, and it is easy to fit after heating.
1. Oil heating method The oil heating method is to put the inner ring of the bearing or separable bearing into the oil tank containing transformer oil for heating, the temperature of the oil is 80-100 °C, and the heating time is 20-40min. In order to prevent the bearing from being heated locally and precipitating impurities into the bearing, the oil surface should cover the bearing, and there should be a wire mesh frame at 50-70mm away from the bottom of the box, and the bearing should be placed on the wire mesh frame. In addition, a thermometer must be hung in the tank so that the temperature of the oil can be strictly controlled. When the hot sleeve is heated, take the heated bearing out of the oil tank, and immediately wipe off the oil stains and attachments attached to the bearing surface with a lint-free white cloth, and then pad it with a cloth, and the two hands are flat, aligned with the rotating shaft, and pushed all the way to the shaft shoulder. If it doesn't fit in, it may be too slow, the bearing has cooled, or the hand is not leveling the bearing ends. At this time, the copper sleeve can be used to press against the inner ring of the bearing and gently hammer it in. After the bearing is sleeved, remove the transformer oil from the bearing, and then add the grease with the motor name tag. Generally, it is between 1/3-2/3 of the volume of the bearing chamber, and should not be too much or too little. Too much will cause the bearing to heat and leak oil, too little will accelerate the wear of the bearing and make loud noise.
2. Cold pressing method of bearings Cold pressing is to press the bearing smoothly onto the shaft with a press at room temperature. When pressing, the centerline of the press shaft should coincide with the shaft line of the bearing to prevent the bearing from skewing. And the pressure can only be applied to the inner ring of the bearing, not to the outer ring or cage.
Causes and solutions of sliding bearing failures
►The causes and treatment methods of overheating of sliding bearings are as follows:
1. Oil ring damage causes bearing overheating The oil ring is often used in the sliding bearing to bring oil into the rotating shaft and the bearing, if the oil ring is deformed or worn seriously, it will cause the oil ring to not rotate or rotate slowly, so that the oil volume between the shaft and the bearing is reduced, and overheating occurs. Open the housing cover, inspect the oil ring and replace it in time.
2. There are many types of lubricating oil, if the choice is improper, the oil is too dirty, and the amount of oil is not enough, it can cause the bearing to overheat. The oil consumption of the plain bearing depends on the power and speed of the motor and other parameters, which can be found in the relevant technical manual.
3. Bearing overheating caused by poor bearing processing Poor scraping of the bearing leads to eccentricity of the bearing, which makes the part of the bearing wear serious, so that the contact angle between the rotating shaft and the bearing is too large, and the oil wedge cannot be formed, which destroys the oil friction and causes the bearing to heat up; The bearings should be scraped again or replaced with new ones.
4. Bearing heating caused by poor cooling The bearing shell is overheated due to poor heat dissipation caused by oil pollution or the influence of water temperature and water volume of the cooling water of the bearing. Keep the bearing housing clean and the cooling water pipeline unblocked, and descale regularly; And ensure that the water quality and heat dissipation of the cooling water are good.
5. Bearing heating caused by oil circulation system failure Bearing lubricated by pressure oil circulation often causes oil shortage and oil cut-off due to oil pipeline blockage or oil pump failure, causing bearing heating. In addition, the water temperature of the circulating cooling water of the pressure oil is too high, resulting in a high pressure oil temperature; It can also cause the bearing to heat up. The tubing should be dredged frequently and in time, especially in summer, to ensure that the water temperature of the circulating cooling water is not high.
► Scraping of bearings for plain bearings
1. The tile lining of the bearing generally needs to be scraped. The purpose of the bearing scraping is to make the bearing lining form a certain geometric shape, so that there is a wedge-shaped gap between the bearing and the journal, so as to ensure that when the journal rotates, a wedge-shaped oil film can be formed between the friction surfaces, so that the journal rises and leaves the tile lining, and operates under the buoyancy of the oil film, so as to reduce the friction with the tile lining, reduce its wear and power consumption.
2. The bearing is inspected using the coloring method. When inspecting by coloring method, the bearing should be cleaned first, and the bearing should be free of cracks, sand holes, shelling, etc. Then apply a thin layer of red pill evenly on the journal, not too thick, which will affect the inspection effect. After the journal is coated with red dan, the bearing is installed and rotated twice; Then remove the bearing so that you can see that the protrusion on the bearing has the color of red dan. The distribution of dyeing points is required to have 2-3 points per square centimeter within the angle of 60°-70° in the center of the bearing, and should not be too much or too little; Otherwise, scraping is required.
3. The grinding and scraping of the bearing adopts the dry grinding method. Use a triangular scraper to first scrape the large point, scrape the dense point, and then scrape it once in one direction, and if necessary, you can scrape it twice. The direction of the knife marks should intersect between each pass to form a network and fish scale. After scraping, clean the tile surface and journal with a white cloth dipped in alcohol, and repeat the above scraping method to make the bearing dyeing point scrape finer and finer until it meets the requirements.
4. No contact points are allowed outside the 70° angle of the bearing center, if there is, they should be scraped off, and the two sides of the bearing are gradually expanded into wedge-shaped clearances.
Whether the motor bearing can operate normally is directly related to the safe and efficient operation of the motor. Only strengthen the inspection and correct maintenance of the motor bearing; In order to ensure the safe operation of the motor.
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