Hello sir

I am facing a problem of vibration in overhung fan, 

Fan is mounted in concrete base , in all point ie motor bearings and fan DE bearing vibration is good in both direction ( axial & radial) but in Fan NDE bearing vibration is high in horizontal direction, 

Vibration in fan NDE bearing vibration is 8 mm/s and vertical and axial is less than 2 mm/s 

Sir i can't understand what is the problem in fan ...can anybody help me ??

Original Post

Once check the pedestal fixing bolts .The high vibration at horizontal and vertical causes unbalance but vibration high in axial direction in overhung fans (directed coupled fans) the unbalance forces acted on shaft to create shaft bending moment causing the bearing house to move axially

The series of harmonics on  FFT indicate non linear response results from rotating looseness , you can check internal bearing clearance,wear in bearing housing ,shaft wear under bearing and worn or loose sleeves .

Replacing the bearing or check aforementioned point might solve the problem. 

I don't believe that you have imbalance problem unless you have high  axial vibration specially you have overhung fan.

I wish you all the best.

Mukesh Chandrawanshi posted:

Sir,

Bearing & housing is newly installed......

And i have already checked bearing clearance....

 

You might already checked this but make sure NDE bearing is floating and DE is fixed. Spectrum is clearing showing looseness though not much noise floor. More info about bearing and installation would be useful like Islam mentioned. 

I assume NDE is the fan bearing bearing next to the fan wheel? Is this a direct drive or belt drive fan? What is the fan operating speed?

Any phase data?

Have you balanced the fan? Have seen this vibration pattern be pure imbalance due to weak bearing supports. See anything around the bearing supports that looks rusty in color like metal to metal contact or metal to concrete contact. 

Could the fan bearings not be in proper alignment with each other? Either side to side or vertically? Is something rubbing, maybe infrared could prove this.

Dave

This would be my approach:

  • What maintenance was done.
  • What were vibration before and after maintenance.
  • how do the FFT compare before and after.
  • Scan all bolted flanges with FRF and check phase across.
  • It would not hurt to do impact test to identify structural natural frequencies.
  • Do phase analysis across entire train especially coupling to check for any misalignment.

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