LanYu Bearing teaches you 5 methods to judge the failure of double row angular contact ball bearings

Double-row angular contact ball bearings are widely used in equipment. The state of double-row angular contact ball bearings is directly related to the operating state of rotating equipment, especially in large-scale continuous production enterprises. They are widely used in important parts of large rotating equipment. Therefore, in actual production, double-row angular contact ball bearing state monitoring and fault diagnosis are important links in equipment maintenance and management. After long-term practice and exploration, we have accumulated some practical skills for actual fault diagnosis of double-row angular contact ball bearings.

1. Methods and key points for fault diagnosis of double-row angular contact ball bearings

The practical method for state monitoring and fault diagnosis of double-row angular contact ball bearings is vibration analysis.

In practice, attention should be paid to the location and collection method of the measuring point. In order to truly and accurately reflect the vibration state of the double-row angular contact ball bearing, it is necessary to pay attention to the accuracy and truthfulness of the collected signal. Therefore, the measuring point should be arranged at the place closest to the bearing. There is generally a rear fan cover at the free end of the motor. The measurement point is selected at the fan cover fixing screw for better monitoring effect. In addition, it is necessary to pay attention to multiple collection and analysis of vibration signals and make comprehensive comparisons. Only then can accurate conclusions be obtained.

2. Characteristics and practical diagnostic techniques of normal operation of double-row angular contact ball bearings

In long-term production status monitoring, we found that double-row angular contact ball bearings show strong regularity and very good repeatability during their use. When normal high-quality bearings are first used, 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, the vibration and noise maintain a certain level, the spectrum is very single, and only one or two times the frequency appear. It is rare to have a spectrum above three times the power frequency, and the bearing state is very stable and enters a stable working period.

After continuing to run and entering the later stage of use, the vibration and noise of the bearing begin to increase, and sometimes abnormal sounds appear, but the vibration increase changes slowly. At this time, the kurtosis value of the bearing begins to suddenly reach a certain value. We believe that the bearing is showing an initial fault at this time.

At this time, it is required to monitor the bearing closely and pay close attention to its changes. After that, the kurtosis value of the bearing began to drop rapidly again and approached the normal value, while the vibration and noise began to increase significantly, and the increase began to accelerate. When the vibration exceeded the vibration standard (such as ISO2372 standard), the kurtosis value of the bearing also began to increase rapidly. When it exceeded the vibration standard and the kurtosis value also exceeded the normal value (the relative standard of kurtosis can be used), we believe that the bearing has entered the late stage of failure production, and it is necessary to repair the equipment in time and replace the double-row angular contact ball bearing.

The time from the bearing showing late-stage failure characteristics to the occurrence of serious failure (generally bearing damage such as shaft seizure, burns, sand rack spalling, raceway, bead wear, etc.) is generally no more than one week. The larger the equipment capacity and the faster the speed, the shorter the interval time. Therefore, in the actual double-row angular contact ball bearing fault diagnosis, once the late-stage fault characteristics are found, it should be decisively judged that the bearing is faulty and maintenance should be arranged as soon as possible.

3. Abnormal operation characteristics and diagnostic techniques of double-row angular contact ball bearings

Nowadays, counterfeit and inferior 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 combustion and fracture of the inner and outer rings of the bearing, etc., these faults will cause the rotor to seize the shaft, and in severe cases, the rotor or equipment will be scrapped. In recent years, we have often encountered such situations in practice. Therefore, in actual monitoring and diagnosis, it is necessary to diagnose the condition of the double-row angular contact ball bearing as soon as possible, and replace the counterfeit bearings in time to avoid major accidents. We have also accumulated some practical skills in a large number of such accidents, that is, monitor the vibration state of such bearings in the early stage of operation after installation, and perform spectrum analysis. We found that the spectrum of the bearing has its unique characteristics in the early stage of operation, that is, the power frequency of the equipment is generally not the main component. However, the total vibration value is not large, and the vibration is qualified by using vibration standards (such as ISO2372 standard).

At this time, we must be vigilant. This state is manifested as defects in the bearing components, etc., and its failure is often very fast and very sudden. In the above example, the rotor seized the shaft two hours after the measurement of this figure.

When diagnosing these fake and inferior bearing failures, it is important to accumulate the spectrum and vibration time domain of the normal operation of high-quality bearings on the equipment, so that when such abnormal spectrum occurs, the bearing failure can be judged in time to avoid equipment accidents.

IV. Practical quick diagnosis techniques for double-row angular contact ball bearings

In actual condition monitoring, we often only need to judge whether the double-row angular contact ball bearings are good or bad and how long they can be used, while the diagnosis of a certain part of the bearing failure in precision analysis and diagnosis is often not very practical. In practical precision diagnosis, due to the influence of factors such as working conditions, it is often difficult to find the corresponding characteristic frequency of the double-row angular contact ball bearing. Although the wavelet analysis and fast resonance demodulation analysis technology developed in recent years are relatively accurate, the equipment investment required is large and more analysis is required. On-site fault diagnosis personnel generally use it less. In practical diagnosis, we use a combination of dimensional parameters and dimensionless parameters to make a quick diagnosis of bearing faults, that is, the frequency vibration speed in the spectrum analysis is combined with the bearing kurtosis value for comprehensive diagnosis. When both conditions exceed the standard, we judge that the bearing is faulty.

After three years of practice, this judgment method has been proven to be very practical for fault diagnosis of double-row angular contact ball bearings. The judgment is fast and accurate, with an accuracy rate of over 90%. The diagnosed bearings are basically in the late stage of failure, which has very good economic benefits.

In addition, when the low-frequency vibration of the double-row angular contact ball bearing is very large, after excluding the misalignment, imbalance, loose structure, and foundation resonance structural factors of the unit, even if there is no characteristic frequency of the double-row angular contact ball bearing, the double-row angular contact ball bearing fault should be decisively judged and repaired.

V. Practical spectrum analysis and diagnosis skills of double-row angular contact ball bearings

Data collectors are now widely used. But pay attention to the skills in practice. For vibration signals with small vibration, small bearing kurtosis, and complex spectrum, when it is difficult to judge whether there is a fault on site, we will collect the vibration signal and transmit it to the computer for precise analysis. At this time, first perform conventional analysis to check whether the vibration velocity spectrum and bearing kurtosis are close to the standard, and then use the power spectrum to examine whether the vibration energy exceeds the standard. If the power spectrum is not large, observe the various frequency components in the spectrum. If the frequency of the spectrum line is an integer multiple of the power frequency, the fault in the unit structure should be focused on; if it is a fractional multiple of the power frequency and there are many decimal frequencies, the bearing frequency should be focused on. If it exists, the bearing has a fault. If not, it is necessary to be vigilant and strengthen monitoring after eliminating other component faults. In fact, many cases of bearing failures have been found when the vibration does not exceed the standard. Once the bearing characteristic frequency or the spectrum close to the bearing characteristic frequency appears, it should be judged that the bearing has a fault, and then according to the amplitude, trend analysis or maintenance can be arranged.