Analysis of abnormal noise of motor bearing and its countermeasures

1. Motor bearing sound is abnormal

A feed pump high-pressure (6kV) motor YKK400-2, power 450kW, speed 2975r / min. The shaft extension end uses deep groove column NU3E222 type bearing, non-load end uses deep groove ball 6222 type bearing. During operation, the sound of the shaft end is sharp and harsh, not like electromagnetic noise, nor the sound of dry grinding of the bearing. The noise lasts for about 2 minutes, then the interval is 2 min. The vibration amplitude of the bearing is measured with a vibrometer (VA-80A). When the value is 0.021 mm and the sound is abnormal, the measured vibration velocity is 53.6 m/s, sometimes even 97 m/s, far exceeding the standard value of 28 m/s, and the current fluctuates greatly.

Due to the clearance fit of the shaft extension, the axial positioning of the bearing cannot be adjusted. During the overhaul process, the inner oil cover was found to have uneven wear marks, and the bearing had two deep groove columns damaged. Measure the positioning dimensions of the bearing, the end cover and the inner and outer oil retaining caps, and after calculation, the allowable clearance of the bearing is 0.7mm. When the bearing temperature of the motor reaches 100°C, the expansion value of the bearing is about 0.9mm, which cannot meet the normal operation requirements of the motor. . After replacing the deep groove column bearing several times, the motor noise not only disappeared, but the abnormal sound cycle became 4min.

2. Failure analysis and processing

According to the characteristics of the bearing: Since the motor originally used NU type deep groove column bearings, the motor is allowed to move axially. The inner ring of the bearing has a rib on both sides, and the outer ring has no ribs, thus allowing the shaft to be displaced in two directions with respect to the bearing, and can withstand the elongation caused by thermal expansion of the shaft. At the same time, the clearance of the bearing is relatively large compared to the deep groove ball bearing, but the bearing force is linear, which is better than the point of the deep groove ball bearing. The bearing trajectory is not a circle but an ellipse. This is because there is a gap between the dry deep groove column (or deep groove ball) and the raceway, and the force is different during operation, so that the motion trajectory is elliptical. The bearing force is mainly in the lower part. For the deep groove column bearing, the force point is a straight line. During high-speed operation, due to the bearing clearance, the force point changes, and the force movement track becomes parabolic.

When the feed pump motor is running, it is mainly affected by the axial force, and the dragged load is stable. The necessity of the radial turbulence allowed by the deep groove column bearing is weakened. Therefore, the front bearing is replaced by a deep groove ball bearing, and the gap of the bearing is still C3. , about 0.04mm, can meet the operational requirements. At the same time, considering the expansion of the bearing, a spacer with a thickness of about 0.8 mm is added to the small cover of the oil retaining ring to overcome the turbulence caused by the temperature rise of the feed pump and the bearing.

The microscopic curvature of the rolling elements and raceways of the bearing is rough and uneven, and a certain impact will occur during the movement, but the pulse generated by this impact is high frequency, so the value of the high frequency interference of the motor running is measured by the vibrometer. Larger than the standard. The deep groove column bearing has more contact with the raceway, and the high frequency impact is large, and the contact between the deep groove ball bearing and the raceway is a point, and the high frequency impact generated is relatively small, so the motor of this example can be used deep. The groove ball bearing replaces the deep groove column bearing to solve the abnormal noise of the equipment.

After replacing the deep groove column bearing with a deep groove ball bearing, the bearing noise disappears. After running for a period of time, the noise does not reappear. The vibration amplitude of the motor is 0.013mm, the acceleration value is 2.8m/s2, the load performance is stable, and the current does not fluctuate greatly.

Complex Precision Turned Parts

Stand Dragon Industrial Co., Ltd. , https://www.standdragontw.com