Oil film oscillation and sliding bearings
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The centrifugal compressors driven by turbines in our company have rotation speeds that are more than twice the critical speed; during operation, the shaft vibration often rises suddenly and exceeds the specified limit of 125 microns. This situation usually improves after reducing the speed by a few hundred revolutions, after which the speed is increased back to the rated level and the shaft vibration returns to normal. Sometimes reducing or increasing the oil temperature can also help resolve this issue. Replacing the rotor when there is a parking opportunity usually solves the problem. Could someone advise whether this is oil film oscillation, and whether replacing it with tilting pad bearings will solve the problem? Thank you! The shaft power is around 2500 KW.
I don’t know what the original poster means by “repeatedly appearing” Since the problem was solved by replacing the rotor, why has it appeared again? The problem was solved after raising the oil temperature, but it appeared again? Theoretically, there should be no oscillation when replacing tilting pads, but in practice it still occurs. It is recommended to examine the spectrum and holographic spectrum to determine whether it is oil film vortexing or oscillation. Additionally, observe the vibration behavior during the speed-up process to assess whether the critical speed has changed, or whether the speed range is too close to the critical value
Based on the description, it seems to be oil film oscillation; the sudden increase in vibration has nothing to do with critical resonance, and it can be completely resolved using tilting pad bearings.