Diagnosing slow speed bearing faults with ultrasound

November 8, 2011

Identifying faults on slow speed bearings can prove challenging with vibration analysis. Not to say it’s impossible… just challenging. For starters, it will require patience during data collection. For example capturing information about a possible defect on a hoist bearing turning at 14RPM would require at least 160 seconds, and preferably 320 seconds of data. What if the hoist never runs long enough to get sufficient data?

For this application, and hundreds more, we ask, “would it be easier or quicker to spot this defect with ultrasonic dynamic data collection?” The bearing in question, at 14RPM, would have an anticipated inner race defect frequency at 2.88 kHz (173CPM). Can ultrasound working at 36-40 KHz spot this defect?

Take a look at this 22 second (yes, twenty-two, not 160 or even 320) dynamic measurement displayed in the time domain.

The 14 RPM once-per-revolution can be seen as can a one-per-revolution packet of high amplitude impacts. If we zoom any one of those packets and apply a periodic cursor we find the impacts have a repetition frequency of 346 (2 x the inner race defect frequency).

In many industries slow speed vibration is considered an onerous or an impossible task. Who says ultrasound cannot be used to perform this otherwise difficult diagnostic? Learn more about bearing Monitoring.

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