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The premature aging of rolling bearings will cause equipment downtime. Now, combined with the author's motor maintenance practice, the experience of preventing premature aging of rolling bearings is introduced. The reasons for the premature aging of rolling bearings are: too tight fit, poor lubrication, misalignment of installation, strong vibration, material fatigue, pollution and corrosion, etc.
1. Too tight fit
When the inner ring of the bearing is forcibly inserted into the journal, the lighter one will produce a severely worn annular track at the bottom of the raceway, and the heavier one will have cracks or peeling on the inner and outer rings of the slideway and the balls. Reason: The gap between the ball and the slide is too small, the torque increases, the friction increases, and the working temperature of the bearing is too high, which makes the bearing wear and fatigue aggravate and fail.
Prevention method: restore the radial clearance of the bearing and reduce the amount of interference.
There are two ways to check the quality of bearing assembly:
Visual inspection method: After the bearing is installed in the bearing chamber of the motor end cover, when the end cover is rotated by hand, if the bearing rotates freely and flexibly, without vibration and shaking up and down, it is considered as qualified.
Feeler gauge inspection method: Assemble the motor end cover with bearing on the stop of the machine base, and use a 0.03mm thick feeler gauge to check the radial clearance around the bearing. If the maximum clearance is just above the center (the motor is installed horizontally) ), the assembly is correct and reliable, otherwise, it is a poor installation. The position of the end cap should be adjusted appropriately and reassembled until it is qualified.
2. Poor lubrication
The reason is a serious lack of grease or grease drying and aging. Due to the frictional heat generated by the high-speed operation of the motor, the bearing temperature is too high and oxidized and discolored, which is manifested as brown or blue in the balls, cage, inner ring and journal of the bearing.
Prevention method: Determine the oil replenishment and oil change time according to 4 factors such as the running time of the motor, the ambient temperature, the load condition, and the quality of the grease. Under normal circumstances, the motor should be replenished with oil once in 6000~10000h operation; the oil should be changed once in 10000~20000h operation. High-quality lithium-based grease (code ZL-2) should be used.
3. The installation is not aligned
If the installation is not centered, there will not only be bead marks on the bearing slideway, but also uneven wear marks of the balls, and deflection will occur. When checking the radial clearance on both sides of the bearing with a feeler gauge, it will be different, and the difference is large. The reason may be that the iron hammer directly hits the outer ring of the bearing; the transmission belt is pulled too tightly (gear engagement); the centerlines of the driving wheel and the driven wheel are not parallel. When the deflection is greater than 1/1000, the operating temperature of the bearing will be too high, the slideways and balls will be severely worn, the shaft will be bent and the end cover bolt pressing surface will not be perpendicular to the bolt axis.
Correct installation method: Use a steel tube sleeve with a smooth and flat end surface and almost the same thickness as the inner ring of the bearing to press the bearing on the correct position of the clean journal. When pressing in, the force should be even and not too strong. Then check the allowable deflection value in the radial direction of the shaft end according to the different speeds of the motor.
4. Strong vibration
When the motor iron core is faulty, the bearing will vibrate strongly. The reasons are: the iron core is heated and deformed; the motor bearing is aging; the bending deformation of the rotating shaft is large; the tightening bolts of the end cover stop are loose due to vibration; the foundation is not strong, which makes the bearing vibrate.
Prevention method: make the iron core small, soak the surface of the silicon steel sheet with silicone organic varnish 1052 and open the gap; replace the new bearing of the same type; withdraw the rotor core to straighten the bending part of the shaft; adopt the 180° symmetry method; tighten the end cap stopper Bolts; strengthen the foundation and tighten the anchor bolts.
5. Material fatigue
Due to the fatigue of the metal material, the irregular fragments falling off from the bearing raceway and the surface of the ball, if mixed in the grease, will increase the operating noise and the ball will be in a sliding state, resulting in an increase in the radial clearance of the bearing, and the allowable diameter of the shaft end. Increase the yaw value by 2~3 times. The determining factors of bearing fatigue degree include: motor load, speed, air gap, end cover type, toughness of material, grease quality and amount of grease added.
Prevention method: According to the motor operation record, when the light load working current is more than 60% of the rated value, run to 2000~25000h, the medium load working current is 60%~80% of the rated value, run to 15000~20000h, and the heavy load working current After running for 80%~100% of the rated value to 10000~15000h, the normal fatigue of the bearing material should be considered, and a new bearing of the same type should be replaced.
6. Pollution corrosion
At this time, red and brown speckled corrosion appeared on the surfaces of the raceways and balls, and the operating noise increased compared to the sound of new bearings.
The reason is that the assembly site is not clean, such as the presence of moisture, acid, alkali and toxic gases; contamination of tools and hands; the use of poor quality lubricating fingers.
Prevention methods: Assembling bearings must keep the environment, tools and tools clean; clean bearings thoroughly; replace high-quality lithium-based grease.
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