I work at Cold Rolling Mill. There are several mill motors as big as 2 MW with 15 kW a blower. The blower is attached/suspended horizontally at motor outboard side and acts like a cantilever beam.

When I took the vibration for the first time, it was found unacceptable as per ISO 10816 mostly in vertical direction which is higher at outboard than inboard side. But spectrum was smooth and only 1X was observed appearing to me as structural resonance.

I feel that it should be normal as in case of cantilever, the side which is away from fixed support has most deflection, that is why we are seeing vibration in vertical direction.

What are your thoughts? How to reduce it?

 

 

 

 

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So, this looks like a motor cooling air fan/blower that is mounted to main motor upper air housing. I would not make any modifications without structural vibration test (impact-response), operating deflection shape test (ODS) or running impact test (with negative averaging). Possible corrections (if worthwhile) include adding vertical stiffeners close to motor on air housing, or adding mass to motor, or adding dynamic mass absorber (damper) to motor. Be aware that any change you make can have a negative impact by raising vibrations in other directions! If motor is still under warranty, then get OEM to evaluate and modify.

Walt

I have seen many situations like that, the solution is simple:

install base plate as a support  under the motor or the blower, the vertical vibration will drop.

2 days ago i have problem like that ,GB attached to motor, the vibration at MNDS vertical was 6.5 mm/s and after installing base plate under GB and weld it to fixed point on the structure, the vibration dropped from 6.5 mm/s to 0.9 mm/s

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Ayman Gamal posted:

I have seen many situations like that, the solution is simple:

install base plate as a support  under the motor or the blower, the vertical vibration will drop.

2 days ago i have problem like that ,GB attached to motor, the vibration at MNDS vertical was 6.5 mm/s and after installing base plate under GB and weld it to fixed point on the structure, the vibration dropped from 6.5 mm/s to 0.9 mm/s

Great. But in our case, I may not be able to perform similar activity. The management will kill me as modifying the motor design will make the warranty invalid. I just want to know whether this vertical vibration is enough to cause any damage?

Syed Huzaifa Ahmed posted:

I work at Cold Rolling Mill. There are several mill motors as big as 2 MW with 15 kW a blower. The blower is attached/suspended horizontally at motor outboard side and acts like a cantilever beam.

When I took the vibration for the first time, it was found unacceptable as per ISO 10816 mostly in vertical direction which is higher at outboard than inboard side. But spectrum was smooth and only 1X was observed appearing to me as structural resonance.

I feel that it should be normal as in case of cantilever, the side which is away from fixed support has most deflection, that is why we are seeing vibration in vertical direction.

What are your thoughts? How to reduce it?

 

 

 

 

Hi,

It cant be concluded that you have a structural resonance unless you test it. there's a lot of fault which to pertain in 1x dominant. I would suggest you to eliminate the point that causes of 1x. ea. unbalance, resonance and etc. Since your equipment is overhung, it is reasonable a structural issue, but if there is an unbalance, the resonance will be an amplificating factors of unbalance and cause a high vibration. so i suggest you to eliminate the possible cause.

For checking the unbalance, you can do static balance check. by rotating the fan and wait until it stop then mark the 270º angel and rotate it, if the mark portion are tangentially offset, your problem is not unbalance, but when the mark is again at 270º degree, you have unbalance.

For checking of resonance, you can do a simple bump test.

Please check also the phase for your further investigation.

Goodluck.

regards,

rg

"The management will kill me as modifying the motor design will make the warranty invalid. I just want to know whether this vertical vibration is enough to cause any damage?"

9 mm/sec would not likely cause structural fatigue damage. You could try to get an "extended warranty" if OEM says vibration level is "normal or okay". Corrective actions include: tightening motor base bolts (if loose), trim balance of fan/blower wheel, structural modifications to detune resonance (if present based on structural vibration tests).

You probably have more important problems in the plant than this machine!

Walt

You are 100% right guys. But since I only have Fluke 810 which is not an advanced vibration analysis tool, I cannot perform ODS, bump test, high resolution, balancing or phase analysis etc. Though I try my best to rule out possible causes by experience, chances, solo tests or visual inspections. And so far though time consuming, I have been very successful.

1X can correspond to the following faults:

Thermal rotor bow ---> Ruled out, no temp difference or abnormal temp

Unbalance ---> Ruled out, low probability. We have 14 similar config motors and all have same high 1x vertical. Not every 14 blowers would have unbalance. This is not a simple blower, it is mill motor, inside its box is blower, cannot be seen cannot be touched by outside.

So the chances of structural resonance is maximum and is visible visually.

I guess we should leave it as it is. Yes, we have more problems to deal with than this.

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