hello every body i have an electrical drive coupled on gearbox to rotate a kiln this motor and gearbox readings were fine before last shutdown then after start it goes high i took a phases reading between horizontal and vertical on motor inboard it give me 0 and monitor orbit it give the elipse shape but so compressed seems like line

Criticalspeed.doc (132 Kb, 76 downloads) the readings

can any one help me here ??

I may be able to help, we need some more information.
1) The plots you provided show 740 rpm as one time run speed of what. Is their other shafts or speeds associated with this machine? Do you have a photo of the machine?
2) All the trends you provided show the readings have increased. Was the increase primarily at 1X or did other frequencies increase?
3) Your frequency scale is too high, and you may need to increase lines of resolution to properly diagnose. Fmax should be about 30kcpm with 1600 to 3200 lines of resolution.
4) Do you have any vertical or axial axis data? All I see is horizontal information. The machine can move in three different axis. It is important to understand how each axis is moving.
5) I would also anticipate an increase in vibration until the kiln comes up to temperature?.
email is daver@thewallingcompany.com

Ahmed
Dave gives good advice. Here's one other:

Ask critical questions to your maintenance group about what maintenance was performed recently. Its obvious that there was a sudden change following Shutdown. Even small details are important. If you've followed a Kepnor-Tregoe thought process, it will help isolate possible causes. You can then test possible causes to concentrate on the likely root cause.
I didnt see the orbit but if it is as you described, something is preventing the shaft from moving in its normal motion. Keep this in mind as you ask about details

Hope this helps
Jim Powers

Is 748 the output speed of the gearbox? Was there any maintenance done during the shutdown? If any work was done on the coupling, perhaps it was not put back together in the same position causing imbalance.

actually the vertical and axial readings still the same. this is an electric motor drive gearbox to drive a kiln shell in cement plant the gearbox inlet speed was the 743 and the about very small and the last shutdown they perform a whole layer of the refractories inside the shell so any recommendation to make resonance tests ?? or how i can be assure thats is a critcal speed ?? i will thankful for reply