Motor Pedastal Axial Vibrations

What type of coupling is existing between motor and compressor?

Both side gear couplings. Axial vibrations on driven equipments are also within 3mm/sec.

My off the wall guess is that the bearing is skewed on the shaft.

Was the bearing pressed onto the shaft? How was it installed?

Thanks for the participation. Bearing outer shell is spherical in shape to take care of any skewness.

Bearing outer shell spherical in shape may take care of any skewness up to some extent only. I suggest to check following aspects also for high axial vibration:

1. Is the alignment within the norm after replacing the bearing?

2. Please check the gap between two thrust collars, whether sufficient space for expantion is ensured.

3. Some times gear couplings get locked and give rise to axial vibration. please check for freeness and proper lubrication.

4. Check the tightness of bearing housing and foundation bolts.

More ever, have you analysed the causes for failuare of the bearing. May be the same cause (if not removed) is responsible for this problem and it may leed to similar failure.

Pritam, Thanks for your participation. Please note the the following: 1) Skewness if more, bearing will have rubbing marks on cross ends 2) If gear coupling is locked, Motor rotor is heavier then compressor and the induced vibration will be reflected on compressors as well. 3) Further, we are having vibrations on one side pedestal only. Other pedestal is as smooth as if motor is not running. 4) Bearing failure reason has been analysed. This system tripped due to power failure. Due to power failure oil pump stops pumping immediately while due to momentum motor+compressor rotor keeps on rotating. Slight debri if comes during that period it will peel the bearing and same thing has happened in our case. Bearing got peeled off and without noticing, compressor was restarted resulting in bearing failure.

Mr Mukesh, You have not answered to the points 1,2 & 4 of my previvious post. Why do'nt you take vibration spectrum and analyse the causes?

The Bearing failure reason you have given is most common for turbomachines. You should install a small gravity oil tank to take care such evantuality.

In fact unkowingly these points got oversighted because no body will run tubo machinery without attending these three points.

Anyway, Yes Alignment is within norms, Thrust collar clerances are sufficient to take care of thermal expansion, and there is nothing left loose on the pedestal.

For your inf. problem is almost solved. We have added some weight to the pedestal to change its natural frequency and we got the positive results. Now Machine is running within normal limits.

Thanks a lot for all participants.

When gear coupling runs for long time in one particular set-up/position, the external gear works (digs) into internal gear a bit. For close observation, a tiny stamping could be noticed in the internal gear teeth. After an overhaul, the chance of these gears running in the same location is less likely. So a new position, the pair might, to start with, runs with a small linear contact. Of course, these pair of gears set-in more sooner than later. During this 'burning-in' period there could be high vibration, predominantly on the axial direction with one time rpm frequency.

Check the coupling gap is ser correctly. Also check that the couplinh halfs are put togther correctly. They can go togther backwards and break the tip off the location device.

How is the alignmnet of the two machines?

Was the oil, based on your quote, "The fan was scheduled for new lubrication and the vibration was observed 1 hour after start-up." of the correct viscosity.