Hello all,
I work in an industrial copper company as vibration analysis supervisor. This company started to work about 2 years ago. We have two Ball Mills and one Sag Mill. We had some visual inspection on pinion and ring gears, during these inspections we found some abnormal wear on this gears (pictures show this problem in enclosure).
After that we decided to do some tests as vibration and oil analysis. Result of the vibration and oil analysis tests are as a below:
Oil analysis: this shows amount of silica is very much.
Vibration analysis: These pictures are taken by VT60 (in enclosure).
I have some questions, I,d be glad to if somebody help me;
1- What is normal wear process of these gears?
2- Which vibration parameters are more suitable for this problem (displacement (rms, peak or …), velocity (rms, peak or …), or acceleration (rms, peak or …),)
3- What actions we can do?
Note: some technical specification is enclosed.

This message has been edited. Last edited by: afshar,

Doc1.doc (4,504 Kb, 74 downloads) pictures-vibration-technical data

Afshar,

High silica content in your lube oil, this is coming from the process, as you may be aware. Especially when there is a leak in the system and the air is polluted with fine pariculates. The only way to control this is fix (replace not repair) leaks in the pipe joints and bearing seals soon as it happens/ observed...daily walkaround/observations of the units will help identify this while in the early stages.
Q1...The gear damage is not regular wear, it is FOD (Foreign Object Damage) possibly bits of ball/rod could have passed thru the gears... I've seen this happen in these Mills. Also ensure the lubricant spray cover is returned to close position...from the picture there are signs of water ingress.
Q2...Velocity measurement gives you sufficient information to monitor gear/motor condition...possibly extend frequency of interest to 500 Hz. to see/capture GMF multiples and bearing faults.
Q3...Good housekeeping and vigilance will add value to your oil/vibration monitoring.

If your Mine is like others I've been to, it may be operating with lean manpower, controlled budget and pushing production, which results in time for 'fire-fighting' constantly and no time for PMs/CBM or even daily walkarounds. Hopefully it is different.
My two bits worth.

Cheers....Rajan Muthukrishnan

Hello Afshar,
I am vibration analyst and I’ve been working with 9 Ball mills which range from 3000 to 5000 Hp in an Iron ore pellet plants in northern Canada.
I’ll answer your question point by point.
1- Wear pattern should be even along the teeth and around the pinion. Side wear tend to suggest misalignment while specific tooth wear point to hunting tooth, load shock, natural frequency or torsion vibration. The pictures suggest superficial fatigue flaking that should be part of a normal service life depending on load, hardness, and lubricant. In case of a short life cycle any of those above and maybe some more should be investigated. Silica’s wear produce line perpendicular to the teeth while fatigues wear happen along the teeth on the loading zone or pitch line.
2- You need to monitor your pinion’s spectrum in velocity with fmax of 85 time turning speed or at least 3-gear mesh. Take at least one waveform in acc that contained 8 turns of the girth gear and perform waveform analysis. (James I Taylor gear analysis handbook)
3- Dig all reports made over the last 40 years and try to ensure you don’t have something in your hand that has been going on and addressed a long time ago. It could be part of a normal wear or something on pinion specification might have changed. Keep your mind open and refine you analysis technique it seem to be a good learning case in your hand!

Good luck and keep us posted.