Pinion Gear Vibration At Bull Gear Frequency

[Franko]

A speed increasing gear has a shaft displacement probe on the pinion. During operation, there is subsynchronous vibration on the pinion that changes with load. Frequencies are at one times and two times bull gear frequency, with much smaller amplitudes at other harmonics of bull gear frequency. Gear ratio is close to five and there are no common factors in the tooth numbers (hunting tooth design).

Besides high pitch line runout of the bull gear, have there been other causes experienced and corrected?

 

[MachineryWatch]

Franko,

Some questions:

1) Is there more than 1 pinion meshing with the bull gear?
2) If so, do you see the same indications on these pinions?
3) Can you look at a Synchronous Time Average (STA)of the waveform from the pinion that is triggered by the bull gear speed?
4) Have you looked at amplitudes of gear mesh harmonics with an accelerometer mounted on the pinion bearing?

In the STA waveform it would be interesting to see if there are any spikes that standout indicating a bad tooth. It may take a lot of averages to develop a good picture of a bad tooth. Doing the STA of the enveloped waveform is another technique that may be worth trying. You would need to use an accelerometer on the casing near the pinion bearing for this to work. If you can't configure your analyzer to do STA on an enveloped waveform and you have a magnet mount or permanent mount ultrasound sensor (available from SDT and UE) you can take the output from the ultrasonic meter into your analyzer and do STA on it.

The high frequency range of the enveloped accelerometer signal or the heterodyned ultrasound signal give better response to any impact or stress waves generated by a cracked or broken gear tooth that will not influence the lower frequency response of the proximity probe. That said, I have seen some interesting results produced by high pass filtering a proximity probe signal, as well!

Hope this helps.

Skip Hartman

http://www.machinerywatch.com

 

[electricpete]

I don't have my gear notes handy.

One thought - How about damaged bull gear tooth. Gives a stronger impact every time it engages, giving 1x, 2x, 3x etc time bull gear.



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[sms]

Is the gear set single helical or double helical? Do you have shaft probes on the bull gear? If it is a small pinion, and you have a high bull gear shaft vibration it begins to look like pitch line runout. Do you have axial probes? You migh get some good info looking at the axial vibration. If the pinion is shuttling it is probably due to run out on the bull.

 

[sms]

You might also post this on the message board at

http://www.reliability-magazine.com.

There are a bunch of gear heads over there as well.