Hi all,

 

Could you please help me with this high vibration belt driven fan, where

high predominant 1.59 X Motor speed (2363 CPM) @ 14 mm/s, with 1X Motor speed @ 6mm/s in Horizontal (Belt tension direction) and axial DE & NDE.

Motor speed: 1485

Speed ratio: 6

Fan speed: 247.5

Motor Pulley diameter: 142.6 mm

Fan pulley diameter: 855.6 mm

Center distance: 1082 mm

Belt length: 3850mm

Calculated belt RPM = 172.72

No of blades: 6

GE (enveloping) readings are very low

These readings was taken after replacing the belt with a new one and the two pulleys were checked, but the same high vibration with same pattern have not changed.

Any suggestion for the cause of this problem, and how I can check for structural or belt resonance

New belt could have same natural frequency as old one?

Even if the natural frequency for the belt or the system be around this frequency, shouldn’t be other forcing frequency to excite this natural frequency?

How far could be the calculated RPM from the actual (Unfortunately they don't have a stroboscope or working tachometer)

If someone still using SKF single microlog, how can I perform a bump test without bump test module?

 

Thanks

Original Post

Many questions.

 

 

"New belt could have same natural frequency as old one?"

 

Assuming new means in a good condition and old means partially damaged, the frequency can change.  The belt's properties (mainly length and stiffness) change.

 

I hope I'm right this time.

 

Regards- Ali M. Al-Shurafa

Originally Posted by Shurafa:

Many questions.

 

 

"New belt could have same natural frequency as old one?"

 

Assuming new means in a good condition and old means partially damaged, the frequency can change.  The belt's properties (mainly length and stiffness) change.

 

I hope I'm right this time.

 

Regards- Ali M. Al-Shurafa

Thanks for reply, do you suggest where this frequency @ 2363 cpm come from

change the new belt to the old one which was before and check the vibration predominant 1.59 X Motor speed present or not hope fully it will guide you the presence of problem exactly

1.59X showing on what bearing Fan DE...??? or Fan NDE.

Pls do the following

1. Check motor in solo condition (without belt). tabulate the readings and post it

2. Slightly reduce the belt tension and take one set of reading. Check if you still see 1.59X and if yes have the vibs reduced or increased..???

3. How does the time waveform look like...can you post it here..??

4. Do you see 1.59X even in vertical and axial...if yes what are the amplitude levels..??

Thanks

Dominant vibration looks to me like 2X "difference frequency" of motor and fan. Not sure what causes it, but shows up sometimes. Like has been said, I'd try reducing belt tension. Is the motor mounted down on the side of an A-frame pedestal that the fan bearings sit on?

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