summary
Bearing is an important part of motor operation. According to years of maintenance experience, the author knows that whether the maintenance is standard or not will directly affect the service life of bearing and the safe and efficient operation of motor. Therefore, it is very necessary to do a good job in daily maintenance, according to the fault phenomenon, deal with it in time to avoid fault expansion, so as to avoid burning out the motor and causing greater economic losses.
1、 Causes of abnormal noise in rolling bearing and its treatment
1. When the motor is running, a screwdriver can be used, with the tip resting on the bearing cover and the ear close to the screwdriver wooden handle to monitor the bearing noise. If the rolling body has a faint rolling sound in the inner and outer rings, and the sound is monotonous and even, which makes people feel relaxed, it means that the bearing is good and the motor operates normally. If abnormal sound is heard, the cause shall be analyzed and handled.
1.1 hear obvious rolling and vibration sound of rolling body, indicating that the bearing clearance is too large or seriously worn, which needs to be replaced.
1.2 the sound of the rolling body is hoarse and the tone is heavy, which indicates that the bearing lubricating grease is too dirty and there is impurity invasion. The bearing shall be cleaned with kerosene and replaced with new lubricating oil.
1.3 the rolling element has irregular impact sound, which means that some of the bearings are broken and need to be replaced.
1.4 the sound similar to the whistle, mixed with the rolling sound of the rolling body, indicates that the bearing is lack of lubricating grease or the lubricating oil is improperly selected, and it is necessary to add clean lubricating oil or replace appropriate lubricating oil.
2. The reason of roller bearing heating and its treatment
2.1 if the motor has been used for a long time, the lubricating grease will deteriorate and harden; the new lubricating grease shall be replaced.
2.2 if too much or too little lubricating oil is added to the bearing chamber, 1 / 3-2 / 3 of the volume of the bearing chamber shall be added; and the lubricating oil of the same type and brand shall be added regularly and quantitatively according to the motor instructions.
2.3 if there are sundries in the bearing chamber, clean the bearing with kerosene and replace with new lubricating oil.
2.4 if the bearing is excessively worn or the inner ring and outer ring are broken, the new bearing of the same model shall be replaced.
2.5 bearing heating will be caused by motor running vibration, improper installation of coupling, too tight drive belt and bending of shaft; the cause shall be eliminated according to the situation.
2.6 if the bearing does not fit the shaft shoulder, disassemble the bearing cover, use a copper rod to hold the inner ring of the bearing and hammer it in symmetrically.
2.7 if the end cover or bearing cover is poorly assembled, it shall be reassembled to make the end cover at both ends and the stop of the machine seat fit well, and the fastening bolts of the bearing cover shall be tightened diagonally.
2.8 the working performance of the rolling bearing not only depends on the manufacturing accuracy of the bearing itself, but also relates to the dimensional accuracy, geometrical tolerance and surface roughness of the matching shaft and hole, the selected matching and the correct installation.
If the fit between the inner ring and the shaft is too tight, or the fit between the outer ring and the inner hole of the end cover bearing is too tight, i.e. the male 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 the bearing will be heated or even burnt during operation.
However, if the inner ring of the bearing is too loose with the shaft, or the outer ring of the bearing is too loose with the end cover, the inner ring of the bearing and the shaft, or the outer ring of the bearing and the end cover will move relative to each other during operation, causing friction and heating, resulting in overheating of the bearing. The proper interference fit between the inner ring and the shaft of the rolling bearing and the fit between the outer ring and the end cover of the rolling bearing generally adopt excessive fit. See the manual or instructions for their fit tolerance.
2、 How to clean rolling bearing
The bearing must be cleaned carefully before assembly, and the detergent is generally gasoline or kerosene. The purpose of cleaning is to:
1. Wash the rust inhibitor off the bearing.
2. Wash away the dirt and sundries that may enter the bearing due to carelessness. For bearings with dust cover or sealing ring on both sides, lubricant has been added before delivery. Do not clean them during installation.
Do not put the cleaned bearing directly on the workbench or in the unclean place. Use a clean cloth or paper pad under the bearing. Don't take it directly by hand. It's better to wear canvas gloves that are not easy to depilate.
3、 How to diagnose whether the rolling bearing is damaged and 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 movement 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 oil stains are found on the surface of the winding and iron core, it means that the bearing leaks oil, the seal is not tight or deformed.
3. After the bearing is removed, wipe off the grease in the bearing, and then clean the bearing with gasoline. Then shake the outer ring back and forth relative to the ball by hand, and the clearance of the good bearing is almost imperceptible. If the clearance between the ball and the inner and outer rings is large, it means that the bearing is seriously worn and needs to be replaced.
4、 Correct assembly of rolling bearing
There are two key problems in the assembly of rolling bearing, one is the cleaning method of bearing, the other is the installation method of bearing. Experience has proved that the cleaning and installation methods of bearings have a great influence on the noise and vibration of the motor. The correct cleaning and installation method can reduce the vibration and bearing noise of the motor. The incorrect cleaning and installation methods are often the main reasons for the vibration and noise of the motor, the damage of the bearing, or the reduction of its service life. Therefore, the rolling bearing cleaning and installation must be carefully carried out in accordance with the correct methods.
1. Preparation before assembly
1.1 the bearing assembly site shall be clean to avoid dust or small particles entering into the bearing.
1.2 check the form and position tolerance of the shaft, if it does not meet the requirements, it cannot be assembled. At the same time, check the fillet size at the root of the shoulder and the perpendicularity of the shoulder to the shaft. Generally, the fillet radius at the root of the shoulder should be smaller than that of the inner ring of the bearing to make the bearing close to the shoulder.
1.3 the assembly surface of parts shall be cleaned with gasoline or kerosene. No rust, spots or solid particles are allowed.
2. Bearing suit technology
There are two assembly methods of bearing and shaft: Hot sleeve and cold sleeve. But generally, the hot sleeve is used, because the inner ring of the bearing and the journal are generally over matched, which is easy to be put on after heating.
2.1 oil heating method
The oil heating method is to put the inner ring of bearing or separable bearing into the oil tank containing transformer oil for heating. The temperature of oil is 80-100 ℃, and the heating time is 20-40min. In order to prevent the bearing from local heating and precipitated impurities entering the bearing, the oil surface shall be covered with no bearing, and there shall be a wire mesh 50-70mm from the bottom of the box, and the bearing shall be placed on the wire mesh. In addition, a thermometer must be hung in the oil tank to strictly control the oil temperature.
When heating the sleeve, 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, with both hands flat, align the shaft, and push it to the shaft shoulder. If the sleeve does not go in, the sleeve may be too slow, the bearing has cooled, or the bearing end is not equal by hand. At this time, use the copper sleeve to counter the inner ring of the bearing and tap it in gently with a hammer. After the bearing is sleeved, remove the transformer oil from the bearing, and then add the lubricating grease marked by the motor nameplate. Generally, it is between 1 / 3-2 / 3 of the bearing chamber volume, which should not be too much or too little. Too much will cause the bearing to heat and leak oil, too little will speed up the wear of the bearing and make a big noise.
2.2 cold press mounting method of bearing
Cold press is to press the bearing onto the shaft smoothly with a press at normal temperature. During press mounting, the center line of press shaft shall coincide with the axis line of bearing to prevent bearing deflection. And the pressure can only be applied on the inner ring of the bearing, not on the outer ring or the cage.
5、 The cause of the failure of the sliding bearing and its treatment
1. The causes and treatment methods of overheating of sliding bearing are as follows:
1.1 bearing overheating caused by oil ring damage
The oil ring is often used in the sliding bearing to bring the oil between the rotating shaft and the bearing bush. If the oil ring is deformed or worn seriously, it will cause the oil ring not to rotate or rotate slowly, thus reducing the oil amount between the shaft and the bearing bush and overheating. Open the bearing cover, check the oil ring and replace it in time.
1.2 bearing overheating caused by lubricating oil problems
There are many kinds of lubricating oil. If it is not selected properly, the oil is too dirty, and the amount of oil added is not enough, the bearing will overheat. The oil consumption of the sliding bearing is determined by the power and speed of the motor. Please refer to the relevant technical manual.
1.3 bearing overheating caused by poor processing of bearing bush
The poor scraping and grinding of the bearing bush results in the eccentricity of the bearing bush, which causes the partial wear of the bearing bush to be serious, so that the contact angle between the rotating shaft and the bearing bush is too large to form an oil wedge, which damages the friction of the oil body and causes the heating of the bearing bush; the bearing bush should be re grinded or replaced with a new one.
1.4 bearing heating caused by poor cooling
The bearing shell has oil pollution causing poor heat dissipation or the influence of water temperature and water quantity of the bearing cooling water. The bearing shell shall be kept clean and the cooling water pipes shall be unblocked, the scale shall be removed regularly, and the water quality and heat dissipation of the cooling water shall be ensured to be good.
1.5 bearing heating caused by oil circulation system fault
Pressure oil circulation lubrication of the sliding bearing, often due to oil pipeline blockage or oil pump failure and oil shortage, oil break, resulting in bearing heating. In addition, the water temperature of the circulating cooling water of the pressure oil is too high, which leads to the high temperature of the pressure oil as well as the bearing heating. The oil pipe should be dredged frequently and timely, especially in summer, to ensure that the temperature of circulating cooling water is not high.
2. Scraping and grinding of bearing bush of sliding bearing
2.1 generally, the bushing of bearing bush needs to be grinded and scraped. The purpose of scraping and grinding of bearing bush is to make the Bush form a certain geometric shape, so that there is a wedge-shaped gap between the Bush and the neck, 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 away from the Bush, and operates under the buoyancy of the oil film, so as to reduce the friction with the Bush, reduce its wear and power consumption.
2.2 the bearing shell shall be inspected by coloring method. When using the coloring method to check, first clean the bearing bush, and check that the bearing bush should be free of cracks, sand holes, shelling and other phenomena. Then evenly apply a thin layer of red lead on the journal, not too thick, which will affect the inspection effect. After the journal is coated with red lead, install the bearing bush and turn it for two turns; then take out the bearing bush, so that the protruding part of the bearing bush can be seen with red lead color. For the distribution of dyeing points, it is required to have 2-3 points per square centimeter within the angle of 60 ° - 70 ° of the bearing pad center, which should not be too much or too little; otherwise, it needs to be scratched.
2.3 the dry grinding method is adopted for the grinding and scraping of bearing bush. Use a triangular scraper to scrape the large points first, then the dense points are scraped thin, and then the general scraping is carried out along one direction, and the scraping can be carried out twice if necessary. The direction of the knife mark between each pass shall intersect to form network shape and fish scale shape. After scraping, clean the bearing surface and journal with white cloth stained with alcohol, repeat the above scraping method, so that the dyeing point of the bearing becomes finer and more scraping, until it meets the requirements.
2.4 no contact points are allowed outside the 70 ° angle of the bearing pad center, if any, they shall be scraped off, and the two sides of the bearing pad shall be gradually expanded into wedge-shaped clearance.
6、 Conclusion
The normal operation of the motor bearing is directly related to the safe and efficient operation of the motor. Only by strengthening the patrol inspection and properly maintaining the motor bearings can the safety of the motor be ensured.
