Sliding bearing vibration fault diagnosis method

Update:2019-04-19

1. When the bearing bush works poorly or shows signs of friction, there may be no obvious reaction on the vibration, but the temperature of the bearing bush will increase significantly. You can observe the change of the local temperature gauge, cooling water temperature and oil temperature, and observe The color change of the lubricating oil.
2. When the vibration is caused by over- or looseness of the bearing top clearance assembly, the vertical vibration will increase significantly, and the ratio to the horizontal amplitude will shrink, approaching or even exceeding the horizontal amplitude. The vibration is generally only apparent on the bearing.
3. If the device is equipped with a non-contact sensor to measure the shaft vibration, the bearing wear is usually accompanied by a significant increase in the DC gap voltage, indicating the degree of wear of the bearing relative to the sensor position.
4. When the oil film whirls, the amplitude suddenly increases when the speed reaches a certain value, and the oil temperature vibration amplitude changes significantly.
5. The oil film oscillation fault will only appear on the flexible rotor, and its vibration frequency is close to the half frequency of the speed. Light-load bearings may first appear oil film whirl before this speed. Heavy-duty bearings may directly experience oil film oscillation during the speed increase process.
6. When the oil film whirls or the oil film oscillates, the lubricating oil pressure is increased, and sometimes the vibration changes more obviously.
7. The oil film oscillation speed lags. During the speed increase process, the oil film oscillates after the speed is greater than the instability threshold speed. However, after the oil film oscillation occurs, the vibration does not decrease when the unit is decelerated to the threshold speed. The vibration will only decrease when the speed is further reduced. There is a difference between the occurrence and the disappearing speed of the oil film oscillation during the speed increase and the speed reduction. This phenomenon is called the speed lag phenomenon.
8. Vibration has the dual characteristics of large amplitude and suddenness. When the oil film oscillates, an unstable low-frequency vibration component appears, and the amplitude is hidden. Once the oil film oscillates, the vibration amplitude will increase dramatically in a short time (a few seconds), and the vibration amplitude is much larger than the normal forced vibration.
9. The most effective method for defects such as microcracks and tire removal is the metal flaw detection method during shutdown.
10. Double- or multi-ring axial trajectory characteristics may occur when the oil film whirls, and the vibration waveforms of the sub-harmonics are characterized by enthalpy.
11. When the clearance is too large, the harmonic components of the frequency conversion are rich and significant, similar to the phenomenon of mechanical loosening. Sliding bearings with excessive clearance may cause small imbalances, misalignments, or other related forces to produce vibration spectra of many higher harmonics. In this case, the bearing is not the source of the fault. However, if the bearing clearance meets the specified requirements, the vibration amplitude does not increase.
12. When the oil film whirls, the half-frequency components in the spectrum increase significantly, but the amplitude is generally less than a octave amplitude. After the rotation speed increases, the order of the half-frequency and multi-frequency relationship remains.
13. Before the oil film oscillates, the vibration is dominated by the power frequency component. After the vibration is abrupt, the amplitude of the power frequency component will decrease, and the amplitude of the low frequency component will greatly exceed the power frequency component and become the main frequency component.
14. When the oil film oscillates, the vibration suddenly increases, which is no longer changed even if the speed amplitude continues to increase. The vibration frequency is always equal to the natural frequency of the rotor system and does not change with the change in speed. The vibration phases of the bearings at both ends of the rotor are basically the same.

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