Case 1: In a production factory, the motor bearing model is NU319/C3. When the motor was started with the thick rubber pad placed on it, there was significant vibration. It was speculated that the abnormal noise originated from other components with greater vibration. There was no fixed testing platform on site. It was suggested to move the motor to the ground. After the vibration disappeared, the motor was operated on site for 40 minutes. The customer reported that it was normal. 

Case 2: A motor factory. Motor bearing model: 6226/C3 

In the frequency spectrum of the on-site motor acceleration envelope, a double-line frequency can be observed. There is unevenness in the air gap of the equipment. The motor manufacturer adjusted the alignment dimensions of the end covers on both sides and adjusted the air gap gap. After these adjustments, the motor noise disappeared. 

Case 3: A certain motor factory. Motor bearing model: 6208/C3 (iron cover) 

On-site verification revealed that the 6208/C3 bearing (with iron cover) was produced in 2021. By comparing the 2021 bearing with the newly released 2025 bearing, it was found that the grease of the 2021 bearing had somewhat dried out. The abnormal noise at the site was from the 2021 factory-borne bearing, while the 2025 factory-borne bearing was without any issues. The problem has been resolved. 

Case 4: A certain motor factory. Motor bearing model: 6306/C3 (iron cover) 

During the initial startup test of the motor bearings, abnormal noises were detected. After continued operation for 15 to 30 minutes, the noises disappeared. It is speculated that the bearings were not fully lubricated during the initial running, and the noises ceased after adequate lubrication. 

Case 5: A manufacturing factory. Motor bearing model: 6312/C3 (iron cover) 

The on-site fixed test bench produced a considerable noise. The noise from adding grease remained unchanged. With a 25um thickness of the pad paper and shim at the drive end, the noise decreased. Excessive bearing clearance resulted in increased bearing noise. Increasing the axial preload of the bearing can appropriately reduce the noise level of the bearing. 

Case 6: A manufacturing factory. Motor bearing model: NJ 2318/C4 

After testing the vibrating screen motor in the factory after maintenance, the maintenance workshop engineer noticed that the bearing made an abnormal noise. After conducting tests, it was found that the noise disappeared after adding lubricating oil, but it would reappear after a short period of time. The test was extended for 2 hours, but neither the vibration nor the temperature changed. Combined with the stethoscope, it was determined that this noise was the inherent noise of the bearing. Without optimizing any components, it was impossible to solve the problem. Considering the vibration condition of the motor, it was necessary to optimize the C4 clearance. However, on-site measurements of the sound decibel and infinite value were conducted. Finally, it was decided to put the motor into use. It has been running for one year without any abnormalities. 

Case 7: A manufacturing factory. Motor bearing model: NU 234/C3 

During the equipment inspection, the inspection engineer used a stethoscope to listen to the bearing sounds. Once an abnormality was detected, they used the recording function to record the sound. After returning to the office, they played it back on the computer to confirm the presence of regular abnormal sounds. Then, they went to the site again and conducted a vibration spectrum inspection and analysis to further confirm the fault spectrum of the outer ring. They immediately arranged for the motor to be shut down for maintenance, and after disassembly, they confirmed the fault of the bearing outer ring.