High Vibration Ball Mill Duel Pinion Drive

[hugh62]

I have been out of the vibration field for awhile due to illness but had a request to give an opinion

A vibration survey was carried on this Ball Mill with a duel pinion drive. The vibration is high in all planes on both sides of the Mill or both pinion drives. The measurements were similar in velocity on the motor , gearbox and both pinion bearings.
The recommendations for repairs was close to exactly the same for both drives.

Gear mesh frequency is present at 1x to 3x and similar amplitudes on both sides. The Mill Trunion Bearings are at fair vibration

As with limited information at this time only the report with a few spectrums and a table of overall velocity reasons it is a bit difficult to get a handle on the issue.

It is believed the chances of both pinion drives to have similar vibration and similar faults is to me unlikely

I am trying to view this in a logic way. The girth gear is common to both pinion drives and could there be an issue here that is exciting the GMF the same on both drives.

I will look at adding the measurements to a drawing to give a picture of the vibration on both sides of the Mill

All thoughts and opinions would be appreciated

 

[Strong]

Hugh,

Look for sideband frequencies (spectrum or FFT) of tooth mesh frequency spaced at girth gear speed to indicate issue with girth gear. Consider demodulated spectrum as a good tool to isolate faults.

Walt

 

[MikeHalloran]

It's a ball mill, not a phono turntable.

Is it worse than when it was new?

Can you get a vibration survey with the ball chamber empty of balls and stuff?



Mike Halloran
Pembroke Pines, FL, USA

 

[hugh62]

I received some more information today. This is a ball mill in Gold Processing. The gearboxes for both drives are shaft mounted to the pinion shaft with an attached torsion arm. So the gearbox moves a bit during operation and would be a contributing factor to vibration by design.
The Mill was purchased second hand and the pinion and girth gear have pitting spalling and a 7deg C temperature differential across the pinion. So some misalignment but very close to acceptable limits

As suggested if I could get access to some high resolution data of the gear mesh frequency then see the spacing of the side bands. I would estimate the Mill would turning 11 CPM, ( attached a Mill layout)

From the report they have taken gSE but they have come to the conclusion replace motor bearings on both motors, replace all gear box bearings both gear boxes, check pinion bearing housing for looseness, inspect pinion girth gear replace as necessary

The gearboxes have been reconditioned in the past and bearings were reasonable and the gears looked ok.
They have had issues in the past with pinion bearing spinning on the shaft and looseness. This is one area critical to look at.

With both motors they have not taken gSE measurements but they have indicated BSF on all motor bearings and appears in the velocity spectrum. (not sure but believe these are grease lubricated bearings). I am not sure what other vibration data they have taken but to recommend to change bearing one would have a look at the acceleration spectrum and TWF, Gse Spectrum and TWF Gse if available and high resolution Velocity Spectrum

With this high vibration would bearing defects present be not as progressed as indicated in the vibration spectrum? This is where making a call can be difficult as we are not dealing with a machine with good vibration levels on a good foundation.
Has anyone been in this position and what was found, or was the final recommendation made on a visual assessment

All input and help appreciated. Will post additional information when I recieve