Bearings, as the main components of motor operation, have attracted more and more attention in recent years. The main reasons are: 1. The increase in recycled products. 2. The bearings are severely damaged, which affects the stable operation of the motor and even affects the full speed of the unit. 3. The labor intensity of workers is high and their technical ability is insufficient. Therefore, to improve the service life of bearings, we need to know and understand bearings, and we must start bit by bit in our daily work.

1. Overview of bearings

The working principle of rolling bearings developed based on sliding bearings is to replace sliding friction with rolling friction. They are generally composed of two rings, a set of rolling elements and a cage. They are highly versatile, standardized and highly serialized. High mechanical base parts. Since various machines have different working conditions, various requirements are put forward for rolling bearings in terms of load capacity, structure and performance. For this reason, rolling bearings need to have various structures. However, the most basic structure is composed of inner ring, outer ring, rolling elements and cage. Usually there are two rolling bearings installed on the motor shaft, usually a positioning bearing with a fixed axial position at the transmission end. The inner ring and the rotating shaft are tightly matched, and there is no gap between the outer ring and the inner and outer bearing caps. to prevent axial movement. Make it bear the axial force. At the non-transmission end, the inner ring of the directional bearing is tightly fitted with the shaft, and there is a gap of 0.5~1mm between the outer ring and the bearing cap. It is used to compensate for tolerances in manufacturing and parts assembly, and to prevent bearing clogging when the shaft expands and contracts due to temperature.

2. Bearing maintenance

(1) Bearing cleaning: When disassembling the bearing for maintenance, first record the appearance of the bearing, confirm the remaining amount of lubricant, and then clean the bearing after sampling the lubricant for inspection. As a cleaning agent, gasoline or kerosene is generally used. The disassembled bearings are cleaned, divided into coarse cleaning and fine cleaning. They are placed in containers respectively. First, put a metal mesh pad on the bottom to prevent the bearings from directly contacting the dirt in the container. During rough cleaning, if the bearing is rotated with dirt, it will damage the rolling surface of the bearing, so care should be taken. In the coarse cleaning oil, use a brush to remove grease and sticky matter. After it is roughly clean, switch to fine cleaning. Fine cleaning is to clean the bearing carefully while rotating it in the cleaning oil. In addition, the cleaning oil should also be kept clean frequently.

(2) Inspection and judgment of bearings: In order to judge whether the disassembled bearings can be used, the bearings should be inspected after cleaning. Check the condition of the raceway surface, rolling surface, and mating surface, the wear of the cage, the increase in bearing clearance, and the damage related to the decrease in dimensional accuracy, and abnormalities. For non-separable small ball bearings, use one hand to support the inner ring horizontally and rotate the outer ring to confirm whether it is smooth.

(3) The radial clearance and allowable wear values of rolling bearings are as follows:

3. Bearing operation inspection and failure analysis

(1) After the bearing is installed, an operation inspection is required to check whether the installation is correct. Small machines can be rotated by hand to confirm whether the rotation is smooth. Inspection items include: poor operation caused by foreign matter, scratches, and indentations; uneven rotational torque caused by poor installation and poor machining of the mounting base; excessive torque caused by too small clearance and installation errors, etc. wait. If there is no abnormality, the power operation can be started.

(2) Since large machinery cannot be rotated manually, you can turn off the power immediately after starting without load and perform inertia operation. Check whether there is vibration, sound, contact between rotating parts, etc. After confirming that there are no abnormalities, you can enter power operation. Power operation starts from no-load low speed and slowly increases to rated operation under specified conditions. The inspection items during the trial operation include: whether there are abnormal sounds, transfer of bearing temperature, leakage and discoloration of lubricant, etc. If any abnormality occurs during the trial operation, the operation should be stopped immediately, the machine should be inspected, and if necessary, it should be disassembled for inspection.

(3) Bearing temperature can generally be estimated from the outer surface of the shell. However, it is more accurate to use the oil hole to directly measure the temperature of the bearing outer ring. The bearing temperature gradually rises from the beginning of operation, and usually stabilizes within 1 to 2 hours. If the bearing or installation is poor, the bearing temperature will rise sharply and abnormally high temperatures will occur. The reasons include too much lubricant, too small bearing clearance, poor installation, excessive friction of sealing device, etc. In the case of high-speed rotation, check the rotation sound of the bearing with a sound detector or listening needle. Loud metal noise, abnormal sounds, irregular sounds, etc. indicate abnormalities. The reasons include poor lubrication, poor accuracy of the shaft housing, bearing damage and foreign matter intrusion.

(4) Please refer to the table below for the judgment and treatment methods of bearing faults during operation.

4. Assembly of bearings

The quality of bearing assembly directly affects the operating condition of the motor. Improper bearing assembly process will have many adverse effects on the motor, and in severe cases, the motor winding insulation will be burned. Therefore, as a maintenance worker, you must strictly implement the maintenance process regulations and the process requirements in the work instructions, and never be careless.

(1) The bearings were originally hot-set, but they are still hot-set during assembly. The original cold-set bearings still need to be cold-set when assembled. But in principle, it is better to use hot suit. The bearing assembly of motors below 7.5KW generally adopts the cold assembly method.

(2) For the cold pressing method, it is recommended to use the sleeve hitting method. The inner diameter of the sleeve is larger than the journal2~3mm. Its thickness should be smaller than the thickness of the bearing inner ring.

(3) The method of driving copper rods into bearings is not allowed. Because the uneven force on the inner ring of the bearing will cause the assembly quality to be low. It is easy to cause bearing failure. According to statistics, 35% of bearing failures are caused by improper maintenance operations.

(4) When the bearing is hot-packed, it should be heated with an eddy current heater. The heating temperature is generally controlled between 110℃~130℃.

(5) When installing the bearing, the bearing model should face outward.

(6) Check the matching tolerance between the bearing inner ring and the journal and the matching tolerance between the bearing outer ring and the broken cover bearing seat. See table below:

(7) The amount of grease in the bearing should be appropriate, generally no more than 1/3 to 2/3 of the bearing volume.

5. Precautions for bearing inspection

(1) There should be no abnormal sound and the temperature should be normal. The maximum temperature limit of rolling bearings is 95°C.

(2) Rolling bearings have poor impact load capacity, loud noise during operation, and short service life. Therefore, improper use and maintenance of bearings will cause the rolling bearings to overheat and even burn out.

(3) Bearings should be refueled and changed regularly. Generally, bearings need to be refueled once every 2,000 to 2,500 hours of operation. The oil should be changed once every 5,000 hours of operation. When changing the oil, remove the original grease and clean it thoroughly with gasoline, then add new grease.

(4) Cylindrical roller bearings and ball bearings must be lubricated with lubricants. Especially in winter, low temperature and other environments, there will be a problem of rolling noise. Generally, even if rolling noise occurs, the bearing temperature will not rise, fatigue life and lubrication life will not be affected, and the bearing can be used as usual.

(5) When purchasing bearings, the team must select responsible and technical personnel to inspect the quality of the bearings. Currently, there are many recycled bearings on the market. Only careful inspection can prevent inferior bearings from being used in equipment.

To sum up, it is not an easy task to do a good job in bearing maintenance. It touches every aspect. As long as we continue to strengthen our studies, continuously improve the quality of maintenance, strictly follow the rules at work, and constantly summarize the experience and lessons learned at work, we will definitely improve our ability to analyze and solve problems. Be sure to do a good job in bearing inspection and maintenance.