Thursday, May 9, 2019


A rubbing sound was observed from the compressor cooling fan motor. Vibration readings were collected only from the motor as the fan is directly mounted on the motor shaft. The obtained spectrum and waveform are given below.

An increased acceleration value in time signal indicates heavy impacts and asymmetrically shaped waveform (greater amplitude at positive side compared to the negative side) indicates restriction in rotor movement possibly created by rubbing. And also rubbing could happen only when there is increased clearance in bearings.
The highest peak is observed at approx. 5.4X orders and its harmonics also found in the spectrum. Since it is a non-synchronous peak, the possibility is bearing damage. Sidebands (sideband frequency is 18Hz, possibly from a damaged ball passing cage) also present with raised noise floor, confirming bearing damage.

Recommendations were provided to replace the bearings and inspect motor armature. The bearings were found having play and damage. Minor rubbing observed on the armature, following which winding resistance and other electrical healthiness checks were performed, ensuring the satisfactory condition of the motor. The bearings were replaced and the motor was reused.

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