Dear Sirs

I need help regarding high axial vibration in gear box of a blower. I have attached all the details. If any further data required kindly reply. 

High vibration observed after replacement of impeller. No maintenance was carried out on the motor-GB side.

 

S.P.Mishra

Attachments

Files (1)
Spectrum Phase & readings
Original Post

Dear Soumya

In your attachment it is mentioned that machine is of class-IV type. How is the machine mounted why it is considered flexible. 

In the machine train diagram blower is shown as directly mounted on Gear box shaft is it the case or there is a coupling in between.

Regards
Rohit Mishra

It is difficult for me to ascertain exactly what is going on with out wave-forms.

However if nothing but the impeller was changed, without even looking at the data,  I have to wonder about couple unbalance.  Any balance specs?  A picture of the impeller would help.  Any documentation on the shaft to impeller fit? 

Rohit02 posted:

Dear Soumya

In your attachment it is mentioned that machine is of class-IV type. How is the machine mounted why it is considered flexible. 

In the machine train diagram blower is shown as directly mounted on Gear box shaft is it the case or there is a coupling in between.

Regards
Rohit Mishra

The machine is mounted on rigid base. But the power consumed by the equipment is 2MW , so we have considered the  machine in Class IV (OEM recommended also) . 

Yes , there is a coupling between GB & impellor of Pin- bush type

Accelo1 posted:

It is difficult for me to ascertain exactly what is going on with out wave-forms.

However if nothing but the impeller was changed, without even looking at the data,  I have to wonder about couple unbalance.  Any balance specs?  A picture of the impeller would help.  Any documentation on the shaft to impeller fit? 

I will attach the time wave form & image of impeller shortly.

The impeller was vacuum balanced prior to installation. Impeller is coupled with shaft with a pin-bush type coupling. 

Does your phase measurements account for transducer orientation?  I am assuming no.  The obvious is the 2X blower speed.  Did they check alignment after impeller was installed?  Another liability is the 180° phase difference at position 2H and 2V.  This should be 90°.  This may indicate some eccentricity between the motor and reducer coupling.  Need to check phase axially between the motor and input shaft of reducer.  This would indicate misalignment between the motor and reducer.  I would also check the phase between axial directions between the blower and reducer.

The problem was finally solved. The base bolt vibration in a particular bolt was 8mm/sec as compared to others of 2-3mm/sec.

We went with suspecting soft foot & after blue matching of GB foot & base around 20% contact area was found. After improving surface condition the contact are was around 50-60%.

After the same , the vibrations reduced drastically to 3 mm/sec.

 

Thank you guys for your response.

Just a "general" precaution when working on a gearbox with a fabricated steel housing.  When installed by a knowledgeable technician, it is not that unusual to purposely shim the bottom of the gearbox casing unevenly in an effort to improve the tooth contact.  Later, a millwright then checks for soft foot and finds and corrects the apparent problem but the supposed corrective action then results in poor contact.  I always advise that when you find a fabricated housing shimmed in an unusual manner, check the service records to be certain this was not done on purpose and if possible, verify the tooth contact after the maintenance work.

The practice is often referred to as "racking the housing" and is not likely to be done on a cast housing because of the risk of breaking off a mounting foot.

 

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