Cylindrical bearing repair

The heating failure of rolling bearings is often accompanied by changes in vibration. The most prominent is that the acceleration value will increase and become larger. The reason why it is said to be different is that there are no other features to be found except the temperature increase.

1 Fever phenomenon

In the process of infrared thermal imaging monitoring, it was found that the temperature of the 3A sealed fan bearing box was too high (122 ° C) and the emergency shutdown was carried out. Then, the vibration test was carried out. It was found that the vibration was in good condition. There is no change, all within the excellent range (data omitted).

3A sealed fan, cantilever rotor, two supporting bearings are in the same bearing box, the temperature has been high (65-75 ℃) since the 168-hour trial operation;

The temperature of the two support bearings of the fan is almost the same;

There is no obvious temperature highlight;

The temperature rises faster after turning on.

2 Fault analysis

The reasons that cause the bearing temperature to be too high are generally: bearing damage, deterioration of lubricating oil, poor heat dissipation, lack of oil, improper adjustment of bearing clearance, etc.

1. After the sealed fan enters the 168-hour trial operation, the vibration monitoring is in good condition, and no bearing faults or other mechanical faults are found, so it can be ruled out that the bearing damage caused the bearing to heat up.

2. After the lubricating oil test, the oil quality is qualified.

3. Observed through the oil level mirror, the oil level is at 2/3 in the shutdown state, and the oil level is above 1/2 after the startup. Due to the rapid temperature rise after startup, there may be a lack of oil.

4. Since the temperature of the two support bearings of the fan is almost the same and there is no obvious temperature protrusion, it can be ruled out that the bearing axial clearance is improperly adjusted

5. After opening the bearing cover, it is found that the top clearance is tight and the interference is large (0.16mm)

6. Measure the actual position of the oil mirror and the bearing. It is found that when the oil level is at 2/3 in the shutdown state, the actual oil level is only less than 1/5 of the roller below the bearing, which is insufficient in design.

3 Analysis conclusion

1. Excessive tightening of the bearing top clearance may be one of the causes of heat generation, but it is not the main reason from the point of view of the rapid temperature rise after starting the machine.

2. When the oil level is at 2/3, it only covers 1/5 of the roller below the bearing. When the machine is turned on, after the oil has passed through the bearing, the oil level may have just passed the bottom of the roller below the bearing, so it is running without oil. is the main cause of fever.

4 Verification of Conclusions

Adjust the bearing top clearance to 0.02mm. In order to confirm whether there is a deficiency in the design of the oil mirror, add oil to 2/3 of the oil level mirror, start the test run, and find that the temperature rises rapidly, reaching 105 ℃ after 20 minutes, and then put the oil The oil level is increased to 5/6, which is close to the full oil level mirror.

This kind of failure has been encountered twice, both during the trial operation of the newly installed equipment, and the characteristic response is the same, and there is no obvious oil shortage in vibration. When I encountered it for the first time, I found this kind of problem after repeated disassembly and assembly twice.

Lubricating oil not only plays a role in lubricating, but also plays a role in heat dissipation and cooling of the bearing. As for why there is no response to vibration, I think it is probably due to insufficient lubrication, but no actual friction and lack of cooling.

For grease lubricated bearings, bearing heat is generally reflected in vibration. As for lubricated bearings, there is no phenomenon in vibration.