High axial vibs on Gearbox-kiln main drive cement mill


Planning to visit cement mill day after to handle high axial vibs on a motor-gearbox driving the kiln mill. I made a visit to this site one month back for condition monitoring data collection. but during that time the motor was running at 1275 rpm less than its rated speed.attached is a 2 page report.

y'day i got a call from client saying that the axial vibs are high on the Gearbox assembly.

The vibs are high on the gearbox input bearings in the axial direction reaching 25-30 mm/sec when the speed was increased. Radial vibs are OK. But I have not got the data so far from the site.

The client says alignment was redone, gearbox internals, bearings were inspected and no damage found. Cleint says there is no change in the process parameters during raise in vibs. Can you send me your inputs?

I have planned for the following. please correct me if i am wrong,

1.Take the vib data at different speeds in HVA directions on the total system
2.Decouple and run the motor in the solo condition.
3.If unbalance induced vibs observed in the spectrum, balance the motor at site conditions at rated speed.
4.Check for any soft foot conditions.
5.Bump test on the motor bearings, coupling, gear internals
6.Study the gearbox drawings
7.Take data in load and no load conditions.

In your opinion and experience what may be the reason for high axial vibs on the gearbox input bearings while the radial vibs are OK.

Do gear internals (bull gear, pinion) natural frequency matching with the rated speed of motor...?? waiting for your valuable inputs.



Original Post

What is the trending level of the gearbox axial at the 1st place, i.e the data available before vibration goes high?

If from the trend it slowly increase, of course something might change.

If the vibration maintain at the level, just keep on monitor the vibration level.

The idea of decouple the kiln might help.

Good luck
Your description of the problem may hold your answer. You mention that the speed was only 1275 rpm, does the motor run faster normally? Is the axial vibration high when the motor runs closer to nameplate speed? It sounds like speed change is causing a rise in vibration?
IF you were take horz vert and axial at all bearing locations you can see what component is moving and in which direction (motor,gbx, pinion) Suggest you also collect phase data to better understand which component is moving and in what direction.
Is the axial vibes only high at a certain speed? I would think that if the motor was mis-aligned to the gearbox, both motor shaft end and gearbox input would both show high vibration in either the radial or axial direction at any operating speed.
I agree with taking data at different speeds, suggest looking the machine base very closely. Missing anchors, soft foot, broken welds, cracked beams.
Hope this helps
presently i m also facing same problem in gear box of kiln drive,
but my suggestion is to check bearing clearance of bearings are in gear box and also find out the life of each bearing.Next thing is advisable to make good chart of kiln shell expansion of that portion.Also find out girth gear attachment to the kiln shell.

Same problem we are facing in our plant. During start up when the kiln was starting. From 2.8 rpm to 3.5 rpm of kiln we found high vibrations in radial direction 11 mm/s . And when kiln rotates at full speed 4 rpm vibration comes down 2.8 mm/s.but the intersting fact is that  motor rpm is 1470 but in spectrum   First fundamental peak is at 600CPM at a amplitude 2.4.

And same frequency amplitude was increase during run-up.... Kindly suggest 

Does the 600 cpm dominant frequency change linearly with speed? Have you tried matching that frequency to other gear shaft speeds and bearing frequencies? Has there been any known structural issues with foundation, drive train, or kiln; such as cleaning, repairs or modifications? Have you tried any high frequency measurements such as PeakVue, demodulation, spike energy or ultrasound to locate source?


To go from 1470 RPM down to 4 RPM is likely a triple reduction of some sort.  1470/600 would be a ratio of about 2.45 which would be feasible in the 1st reduction.  You would need tooth counts to be sure.

If the gearbox has inspection ports, I'd be looking inside with particular attention directed to the condition of the 1st reduction mesh.   


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vishal sharma