How to carry out correct condition monitoring and diagnosis of rolling bearings?
Many failures of machinery are related to rolling bearings in rotation. The working quality of bearings has a great influence on the working state of machinery. Its defects will cause abnormal vibration and noise of equipment, and even damage equipment in severe cases. Correct condition monitoring and diagnosis of rolling bearings is an important aspect of equipment optimization management and predictive maintenance in modern enterprises
Four early warning stages of rolling bearing failure:
Corresponding to the structure of the rolling bearing, there are four common faults in the rolling bearing: the cage, the rolling element, the bearing outer ring, and the bearing inner ring. There are special mathematical calculation formulas for the calculation of the fault frequency of these bearings, but it is more troublesome to calculate in actual work. In daily use, the four problem stages that can be distinguished by experience and testing are:
The first stage is the embryonic stage when the bearing begins to fail.
At this time, the temperature is normal, the noise is normal, the total amount of vibration velocity and frequency spectrum are normal, but the total amount of peak energy and frequency spectrum have some symptoms, reflecting the initial stage of bearing failure. At this time, the real bearing failure frequency appears in the range of about 20-60khz in the ultrasonic section.
In the second stage, the temperature is normal, the noise is slightly increased, the total vibration speed is slightly increased, and the vibration spectrum does not change significantly, but the peak energy is greatly increased, and the spectrum is more prominent. The bearing failure frequency at this time appears in the range of about 500hz-2khz.
In the third stage, the temperature is slightly increased, the noise can be heard, the total vibration speed has greatly increased, and the bearing fault frequency and its harmonics and sidebands are clearly visible on the vibration speed spectrum, and the noise level on the vibration speed spectrum is obvious. As it increases, the total amount of peak energy becomes larger and the spectrum is more prominent compared to the second stage. The bearing failure frequency at this time occurs in the range of about 0-1khz. It is recommended to replace the bearing in the later stage of the third stage, then the rolling bearing failure characteristics such as wear that can be seen with the naked eye should have already appeared.
In the fourth stage, the temperature increases significantly, the noise intensity changes significantly, the total vibration velocity and the total vibration displacement increase significantly, and the bearing fault frequency on the vibration velocity spectrum begins to disappear and is replaced by a larger random broadband high-frequency noise horizon; The total amount of peak energy increases rapidly, and there may be some erratic changes. Bearings must never be allowed to operate in the fourth stage of failure development, or catastrophic failure could occur.
According to the research results, in general, if the entire service life of the rolling bearing is from the time the bearing is installed and put into use, in the first 80% of its life time, the bearing is all normal. Then, corresponding to the development of rolling bearing failures, the remaining life is 10% to >20% L10 in the first stage, 5%-10% L10 in the second stage, 1% ~ 5% L10 in the third stage, and about 5% in the fourth stage. For 1h or 1%L10.
Therefore, when faced with bearing problems in actual work, considering that the fourth stage of the development of bearing failures has unpredictable sudden hazards, it is recommended to replace the bearings in the later stage of the third stage, which can avoid the expansion of failures and more serious accidents. It is more convincing according to the characteristics of rolling bearing failures such as wear and parts damage that can be seen on the bearing at this time.
As for the identification of the later stage of the third stage of bearing fault development, it needs to be comprehensively considered based on the above theoretical characteristics and combined with the actual temperature, noise, speed spectrum, peak energy spectrum, total trend of speed and peak energy, and practical experience
