What causes irregular vibration fluctuations?
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In the TRT gas excess pressure generator set, the shaft vibration of the turbine bearings has recently shown irregular fluctuations, with a frequency of once every two days to once or twice a day. Mainly, the vibration of bearing 1# is too high, exceeding the alarm value at its peak. His spectrum is essentially at the power frequency, with no obvious clipping observed. The phase cannot be measured without a speed interface. The vibration of bearing 2# is low, with the power frequency being the dominant component; there are also 2nd to 10th harmonic frequencies. Two severe impact signals occur per cycle in the waveform, and these are suspected to be caused by grooves on the shaft. The generator vibration is excellent; there are no issues. Generally, such irregular fluctuations are caused by external factors. However, looking at the trend chart, these vibration fluctuations show no correlation with operating conditions – they appear suddenly and then resolve on their own after some time. During fluctuations, bearing 1# moves upward, while bearing 2# shows a basically opposite trend, indicating a change in load distribution? Additionally, when the machine is stopped for turning, the vibration of bearing 1# is slightly higher than that of the other bearings. I’m not sure which expert can help analyze this. Personally, I think the possible reasons are poor airflow, slight friction, or loose parts on the rotor – one of these three options – but none of them seem to fit perfectly. . .
It’s a bit like temporary thermal bending – heat bending is caused by friction from movement; vibration levels are high when there is friction, but they’re lower when there is no friction. It could also be due to loose air seal teeth or the presence of foreign objects!
Irregular vibrations are mainly caused by foreign objects scraping against the components, and bearings can also be inspected through vibration impact measurements. The 2# bearing is mainly loose. Personal opinion
However, the vibration of bearing 2# is relatively low. . . Moreover, on the time-domain plot, those two downward impulse signals are extremely large, exceeding the amplitude of the sine wave itself, which does not conform to physical laws; I think they are false signals caused by two depressions on the axis at the measurement point. Can excessive vibration during shaft turning be interpreted as shaft bending? Is it still a matter of focusing the mind?
Do you mean there is friction at the shaft seal? If a foreign object gets in, it should get worn away right away, right?
Could we compare the spectrum diagrams and axis trajectory for different periods, while also taking into account the velocity values in the time-domain diagrams? If the velocity increases, it indicates an inherent defect in the rotor, unrelated to the bearings. In your case, I believe the main issue is the abnormal vibration of bearing 1; my motor has the same problem and I am working on it
There’s a vibration expert in the forum; perhaps he can give you some advice. If you don’t know, you can ask the mechanical equipment moderator. Uh~ I realize that it seems like this is always the sentence I use whenever someone brings up the topic of vibration.
It is recommended to consider dynamic and static rubbing. The specific reason is the loss of teeth in the labyrinth steam seals on both sides of the impeller, which then leads to friction with the rotor. In our company, compressors have experienced the same issue described by the poster; upon disassembly for inspection, it was found that the problem was caused by friction between the moving and stationary parts.
Check if the anchor bolts are loose, and also check if the bearings are loose.
First, rule out the possibility that it’s a problem with the instrument.