4 stages of rolling bearing failure

The deterioration of rolling NSK bearings is not a linear process, but an exponential process. In different degradation stages, the fault information appears in different frequency bands, so different fault detection methods must be adopted. At present, the industry generally believes that the degradation process of rolling bearings can be divided into four stages.

Stage 1-Early stage of bearing failure

At this stage, the bearing will form microscopic cracks or lattice dislocations on the subsurface, while no cracks or micro-flaking can be seen on the bearing surface, and no obvious shock signal will be formed in the low frequency range of the vibration signal, which cannot be picked up by traditional acceleration sensors. To the fault signal, but the microscopic cracks on the subsurface or the dislocation of the crystal lattice will produce the acoustic emission signal or the stress wave signal. Therefore, the fault characteristics of the bearing at this stage are mainly reflected in the ultrasonic frequency range, which can be picked up by acoustic emission sensors or resonance-based acceleration sensors, which is mainly manifested as the measured signal peak value or energy value becomes larger. 

Phase 2-bearing failure development period

At this stage, the micro-deterioration of the bearing begins to expand from the subsurface to the surface, and damage points such as cracks or micro-flaking are generated on the contact surface of the bearing. When the surface of the bearing element is in contact with these damage points, a shock pulse of a certain frequency will be formed. According to the Fourier transform, the short-term shock signal is a broadband signal in the frequency domain, so this shock signal will inevitably arouse the bearing. The high-frequency natural frequency of the components resonates, so that the vibration is strengthened. This part of the signal can be picked up by the acceleration sensor, and then the characteristic frequency of the bearing fault can be observed by the envelope demodulation technology. At the end of the second stage The frequency multiplication of the characteristic frequency of the fault can also be observed.

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

Phase 3-a period of rapid development of bearing failure

At this stage, with the accelerated development of bearing damage, the impact of the damage point on the bearing contact surface becomes more and more intense. The frequency multiplier of the characteristic frequency of the bearing fault demodulated in the resonant frequency range is increasing, and its periodic impact The energy level of 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 multiplication has an increasing trend.

Stage 4-the end of bearing failure

At this stage, the rolling bearing has almost reached the end of its life, the damage point can be observed with the naked eye, the noise of the bearing movement has become particularly loud, and the temperature has risen rapidly. At this time, not only the fault characteristic frequency of the bearing and its multiplication frequency can be clearly seen on the direct power spectrum, if the damage point alternately enters the load area, you can also see obvious modulation side frequencies next to the fault characteristic frequency. At the end of the fourth stage, the spectral lines on the spectrum become not very clear, and a protruding "thatch" will be formed in the power spectrum. In addition, the energy of high-frequency vibration may not rise but fall at this time. If it is found to be high Frequent monitoring volume begins to decrease, not because the surface bearing condition is getting better, but because it indicates that the bearing has reached the end of its life.