high vibration in horizontal plane

Dear experts

in our cement plant we have  eight cooler fan one of them has high vibration in only horizontal plane:

Motor NDE H-10MM/S

MOTOR DE H-11MM/S

FAN DE H-10MM/S

FAN NDE -11MM/S

motor kw-132 kw overhung fan

In all other direction vibration i.e in (vertically and axial) is below 2mm/s . in FFt spectrum only 1x with an amplitude of 9.2mm/s is dominated in all the direction i.e horizontal. i did cross phase analysis on motor and fan also for checking unbalance but cross phase in all direction is 180 degree.

wait but the story is not ended here sometime in whole day its vibration is recorded below 2mm/s in all the direction. this phenomenon of reduction in vibration confused me more.because we measured the fan in same parameters like same damper position same flow everything but still some time vibration is above 10mm/s and sometime below 3mm/s.

please suggest me whats going wrong here

Original Post

More details please, how about pics of the installation, moving hot or cold air, high vibes at warmest part of day? directional vibration, 0 and 180 degrees where there should be 90 degrees all sound like resonance. if the fans are all mounted on a common structure they could be sending vibes to each other. Thermal growth can put stresses on duct work and supporting structure. Have you identified if the process is changing during the high vibration events, vfd driven, all fans doing the same thing

Dave

Dear Akhil thanks for ur response 

1) yes I am noticing when this fan has high and low vibration symptoms are same I.e only 1x but amplitude will amplify 

2) No overhauling first I have doubt on alignment but when I check alignment by laser it was ok

3) motor is constant drive 1480 rpm

4) cross phase at FAn nde is 178 degree between H&V

cross phase at fan DE is 180 degree between H&V

please give ur precious comments 

The best practice to evaluate the envelope is not RMS or P-P, however I hope you analysed it well and there is no excessive clearance in the bearing or in the housing. It is always difficult to analyse the issue without any spectrum sent. So I will use a method of elimination and guessing  :

Resonance is the first thing that came to my mind according to your description (specially because of phase angles) but there is one big question there. You said there were days with the normal vibration level at the same speed and the same operating conditions. So basicaly there couldn't be resonance except you overlooked some influence of some nearby machine.

What could be left:

- your rotor/shaft/base may have a crack

- attachment problems

- some dirt sticks to the rotor and occasionally falls down.

 

 

 

 

vishal sharma posted:

Dear Akhil thanks for ur response 

1) yes I am noticing when this fan has high and low vibration symptoms are same I.e only 1x but amplitude will amplify 

2) No overhauling first I have doubt on alignment but when I check alignment by laser it was ok

3) motor is constant drive 1480 rpm

4) cross phase at Fan nde is 178 degree between H&V

cross phase at fan DE is 180 degree between H&V

please give ur precious comments 

Hi Vishal

Since how long this issue is going on. when did you first notice the change / increase  in vibrations?

Let us check the load variations.

  1. Can you share the motor amps during this high & low vibration condition occurs.
  2. How is the IGV opening adjusted & what % it is when this high & low vibration occurs.
  3. Also I would be interested in the Kiln feed & cooler load during these 2 conditions

Thanks

Akhil

Hi Vishal this is good.

By the pic I can see that you have the data for motor amps, flow in m3/h & load or damper opening in %.

Are these 3 parameters same during high & low vibration condition? I know by this time you would have done this comparison as you said this is a long pending issue.

I generally feel this can be due to 2 reasons

  1. Some dust or deposition gets accumulated on fan impeller increasing the vibration & later it falls down resulting in drop in vibration. But if so happens you don't get unbalance phase, secondly this is a FD fan, sucks fresh air. So we can eliminate this cause.
  2. I strongly feel this can be due to some operational change in the parameters. But that needs to be confirmed. If you have compared some data please let me know your workout on this

Thanks

Akhil

Hi Vishal,

Have you already check for any soft foot/looseness for motor and bearing block? I am not rooting for any process related cause and on the process, i believe the fan start in auto sequence then the igv will open gradually second after motor start and things like that. Mechanically, your problem is at horizontal plane for all bearings, and looseness will give contributing factors to affect whole machine component. if i were you, i would do phase reading on all bolt and determine the differences of phase.

regards,

RG 

Dear RG

thanks for ur reply 

Yes that fan is running in auto mode. Our problem is in only horizontal plane I did the following actions in last shit down

1) checking for motor soft foot not found 

2) retight the fan housing bolts which was already full tight

3) laser alignment done again 

4)coupling buffer change as one found in poor condition 

but when we run again same behaviour some time high vibration some time low. 

If you have any further recommendation please tell me I will do it

Akhil rathore posted:

Hi Vishal this is good.

By the pic I can see that you have the data for motor amps, flow in m3/h & load or damper opening in %.

Are these 3 parameters same during high & low vibration condition? I know by this time you would have done this comparison as you said this is a long pending issue.

I generally feel this can be due to 2 reasons

  1. Some dust or deposition gets accumulated on fan impeller increasing the vibration & later it falls down resulting in drop in vibration. But if so happens you don't get unbalance phase, secondly this is a FD fan, sucks fresh air. So we can eliminate this cause.
  2. I strongly feel this can be due to some operational change in the parameters. But that needs to be confirmed. If you have compared some data please let me know your workout on this

Thanks

Akhil

Hi Vishal

How much is the Motor amps when vib are high & low?

How much is the damper opening when vib are high & low?

How much is the flow in m3/hr when vib are high & low?

 

Thanks

Akhil

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