Double-row angular contact ball bearings are widely used in equipment, and the status of double-row angular contact ball bearings is directly related to the running status of rotating equipment, especially in continuous large production enterprises, which are widely used in important parts of large-scale rotating equipment. Therefore, the condition monitoring and fault diagnosis of double-row angular contact ball bearings in actual production is an important link to do a good job in equipment maintenance and management. After long-term practice and exploration, we have accumulated some practical skills for the actual fault diagnosis of double-row angular contact ball bearings.

1. Methods and main points of fault diagnosis of double row angular contact ball bearings

Vibration analysis is a practical method for condition monitoring and fault diagnosis of double row angular contact ball bearings.

In practice, it is necessary to select the location of the measuring point and the collection method. In order to truly and accurately reflect the vibration state of double-row angular contact ball bearings, it is necessary to pay attention to the accuracy and authenticity of the collected signal, so the measurement point should be arranged in the closest place to the bearing, the free end of the motor is generally a rear fan cover, and the measurement point is selected in the fan cover fixing screw to have a better monitoring effect. In addition, we must pay attention to multiple acquisition and analysis of vibration signals, and comprehensive comparison. To get an accurate conclusion.

2. Double row angular contact ball bearing normal operation characteristics and practical diagnostic skills

In our long-term production status monitoring, we found that double row angular contact ball bearings show strong regularity in their use process, and the repeatability is very good. When normal high-quality bearings start to use, the vibration and noise are relatively small, but the spectrum is somewhat scattered, and the amplitude is small, which may be due to some defects in the manufacturing process, such as surface burrs.

After a period of movement, vibration and noise maintain a certain level, and the spectrum is very single, only one or two times the frequency. Rarely appears more than three times the power frequency spectrum, the bearing state is very stable, into a stable working period.

After continued operation, the bearing vibration and noise begin to increase, and sometimes there are abnormal sounds, but the change of vibration increase is slow, at this time, the bearing kurtosis value suddenly begins to reach a certain value. We believe that at this time, the bearing is manifested as an initial failure.

At this time, it is required to closely monitor the bearing and pay close attention to its changes. Since then, the bearing kurtosis value begins to decline rapidly, and is close to the normal value, while the vibration and noise begin to increase significantly, and the increase amplitude begins to accelerate, when the vibration exceeds the vibration standard (such as ISO2372 standard), the bearing kurtosis value also begins to increase rapidly, when both the vibration standard and the kurtosis value exceed the normal value (available kurtosis relative standard), We believe that the bearing has entered the late stage of failure, it is necessary to timely repair the equipment and replace the double row angular contact ball bearing.

The bearing shows the characteristics of late failure to the occurrence of serious failure (generally bearing damage such as shaft holding, burn, sand frame spalling, raceway, bead wear, etc.) most of the time is not more than one week, the larger the equipment capacity, the faster the speed, the shorter the interval time. Therefore, in the actual double row angular contact ball bearing fault diagnosis, once the late fault characteristics are found, the bearing fault should be determined decisively and the maintenance should be arranged as soon as possible.

3. Double row angular contact ball bearing abnormal operation characteristics and diagnostic skills

Now due to fake and shoddy bearings will inevitably enter enterprises and equipment, and the serious failures caused by these mobile bearings are often sudden and catastrophic. Such as the sudden fracture of the bearing cage, the sudden burning fracture of the bearing inner and outer rings, etc., these faults will cause the rotor to hold the shaft, and the heavier will lead to the rotor or equipment scrap. In recent years, we have often encountered such situations in practice. Therefore, in the actual monitoring and diagnosis, it is necessary to diagnose the condition of double row angular contact ball bearings as soon as possible, and replace the shoddy bearings in time to avoid major accidents. In a large number of such accidents, we have also accumulated some practical skills, which is to monitor the vibration state of such bearings after installation and initial operation, and perform spectrum analysis. We found that in the early stage of operation, the bearing spectrum has its unique characteristics, that is, the equipment power frequency generally does not account for the main component. However, the total value of vibration is not large, and the vibration standard (such as ISO2372 standard) is qualified to judge the vibration.

At this time, it is necessary to cause us to be vigilant, this state is manifested in the presence of defects in bearing parts, etc., and its failure is often very fast and very sudden. In the above example, the rotor holds the shaft two hours after the diagram is measured.

When diagnosing the faults of these fake and shoddy bearings, it is necessary to pay attention to the accumulation of the frequency spectrum and vibration time domain of the normal operation of high-quality bearings on the equipment, so as to determine the bearing fault in time when such abnormal spectrum occurs and avoid equipment accidents.

4. Practical double-row angular contact ball bearing quick diagnosis skills

In the actual condition monitoring, we often only need to judge the quality of double-row angular contact ball bearings and how long they can be used, and it is often not practical to diagnose the fault of a certain part of the bearing in precise analysis and diagnosis. Due to the influence of working conditions and other factors, the characteristic frequency of double-row angular contact ball bearing can not be found out in practical precision diagnosis. Although the wavelet analysis and fast covibration demodulation analysis techniques developed in recent years are more accurate, they require large equipment investment and more analysis, and on-site fault diagnosis personnel are generally less applied. In practical diagnosis, we use the combination of dimensionless parameters and dimensionless parameters to make bearing fast fault diagnosis, that is, frequency vibration velocity in spectrum analysis and bearing kurtosis value to make comprehensive diagnosis. When both conditions exceed the standard, we judge that the bearing is faulty.

After three years of practice, this method proves to be very practical for the fault diagnosis of double row angular contact ball bearings. The judgment is fast and accurate, and the accuracy rate is more than 90%. The bearings diagnosed are basically in the late fault stage, with very good economic benefits.

In addition, when monitoring the low frequency vibration of double row angular contact ball bearings is very large, excluding the unit's misalignment, imbalance, structural loosening, and fundamental resonance structural factors, even if there is no double row angular contact ball bearing characteristic frequency, the double row angular contact ball bearing fault should be determined decisively for maintenance.

5. Practical spectrum analysis and diagnosis skills for double-row angular contact ball bearings

Now the use of data collectors has been relatively common. But pay attention to the practical tips. For vibration signals with small vibration, bearing kurtosis and complex spectrum, when it is difficult to judge whether there is a fault in the field, we collect the vibration signals back and send them to the computer for precise analysis. At this time, conventional analysis is carried out first to check whether the vibration velocity spectrum and bearing kurtosis are close to the standard, and then the power spectrum is used to investigate whether the vibration energy exceeds the standard. If the power spectrum is not large, various frequency components in the spectrum are observed. If the spectral line corresponds to the power frequency of the frequency, the fault of the unit structure should be found emphatically. If the power frequency fraction is multiple, there are more decimal frequency, you should focus on finding the bearing animal frequency, if there is, there is a fault in the bearing, if not, after eliminating the fault of other components, it is necessary to cause vigilance and strengthen monitoring. In fact, it is found that many cases of bearing failure occur when the vibration does not exceed the standard. Once there is a bearing characteristic frequency or close to the bearing characteristic frequency spectrum, it should be judged that there is a bearing fault, and then according to the amplitude, trend analysis or maintenance can be arranged.