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Shanghai Shang Shaft Bearing Quality Inspection Institute Co., Ltd.

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Four stages of rolling bearing failure

2020-09-30 13:39

Deterioration development of rolling bearings is not a linear process, but an exponential process. In different degradation stages, fault information appears in different frequency bands, so different fault detection methods are used. At present, it is generally believed in the industrial field that the deterioration process of rolling bearings can be divided into four stages.

Stage 1-Initial stage of bearing failure

At this stage, the bearing is the first to form micro-cracks or lattice dislocation on the secondary surface, while the bearing surface can not see cracks or tiny spalling, and no obvious impact signal will be formed in the low frequency band of the vibration signal. The traditional acceleration sensor cannot pick up the fault signal, but the micro-cracks or lattice dislocation on the secondary surface will produce acoustic emission signal or stress wave signal. Therefore, the fault characteristics of the bearing at this stage are mainly reflected in the ultrasonic frequency band, which can be picked up by an acoustic emission sensor or a resonance-based acceleration sensor, which is mainly manifested as the measured signal peak value or energy value becomes larger.

Stage 2-Development period of bearing failure

 

At this stage, the microscopic deterioration of the bearing begins to expand from the secondary surface to the surface, and the contact surface of the bearing produces damage points such as cracks or tiny spalling. When the surface of the bearing component contacts with these damage points, an impact pulse with a certain frequency will be formed. According to the Fourier transform, the short-term impact signal is a broadband signal in the frequency domain, so this impact signal will inevitably arouse the high-frequency natural frequency of the bearing component to resonate, thus strengthening its vibration. This part of the signal can be picked up by the acceleration sensor, the fault characteristic frequency of the bearing can be observed by using the envelope demodulation technology, and the double frequency of the fault characteristic frequency can be observed at the end of the second stage.

 

At this stage, the fault characteristic frequency of the bearing is temporarily submerged in the high noise of the low frequency band, so no clear fault characteristic frequency is observed in the fault characteristic frequency band.

Stage 3-Rapid Development Period of Bearing Failure

 

At this stage, with the accelerated development of bearing damage, the impact of the damage point on the bearing contact surface is more and more intense, and the frequency doubling of the bearing fault characteristic frequency demodulated in the resonance frequency band is more and more, and the energy of its periodic impact is enough to be directly observed through the power spectrum of the vibration signal. At this time, the fault characteristic frequency of the bearing can be clearly seen directly on the power spectrum of the vibration signal, and its frequency doubling has an increasing trend.

Stage 4-End of bearing failure

At this stage, the rolling bearing has almost reached the end of life, the damage point can be observed by the naked eye, the noise of the bearing movement becomes particularly large, and the temperature rises rapidly. At this time, the direct power spectrum can not only clearly see the fault characteristic frequency of the bearing and its frequency multiplier, if the damage point alternately enters the load zone, but also see the obvious modulation edge frequency next to the fault characteristic frequency. At the end of the fourth stage, the spectral line on the spectrum becomes not very clear, and a protruding "thatch pile" will be formed on the power spectrum. In addition, the energy of high-frequency vibration may not rise but fall at this time. If the monitoring amount of high-frequency vibration is found to begin to decline, it is not that the surface bearing condition is getting better, but that the bearing is approaching the end of its life.

Summary

To sum up, from the four stages of bearing deterioration, it can be seen that the frequency range of bearing fault characteristic frequency, whether there is frequency doubling and edge frequency of bearing fault characteristic frequency, all reflect the deterioration information of bearing to a certain extent. From the relationship between frequency and time, the deterioration of bearing has the trend of moving from high frequency to low frequency. First, the signal measured in ultrasonic frequency range changes. With the development of bearing deterioration, the fault characteristic frequency of the bearing can be observed by a certain analysis method for the signal of the resonance frequency band, and finally the fault characteristic frequency is observed on the power spectrum of the low frequency band signal within 1KHz. This shows that with the development of bearing fault, the fault characteristics will gradually move from high frequency band to low frequency band.