2X Pinion vibration problem: Motor-gear-compressor

Summary:

The root cause of the 2X pinion vibration issue in the motor-gear-compressor system was identified as hot/dynamic misalignment, which produced 2X excitation. Initial considerations included potential causes such as coupling misalignment, bearing looseness, and gear imbalance or alignment issues, but all were ruled out. Through testing, it was noted that 2X vibrations persisted even when the motor’s power was off, which further narrowed the cause to misalignment that only manifested dynamically, likely due to thermal expansion or alignment shift during operation.

Specifically, the system exhibited 2X vibration primarily due to parallel misalignment, which was consistent with literature findings that only parallel misalignment leads to this type of harmonic excitation. The coupling’s dynamic characteristics, combined with critical speed proximity and the interaction between the pinion and compressor, aggravated the vibration issue.

A solution was devised by modifying the coupling weight to shift the system's critical speed away from the problematic operating range, which resolved the vibration issue effectively.