One year ago during annual ispection we checkd DE journal bearing for FD fan, we found it is damaged.
Notethe damage was not from complete bearing but from the side which next to the fan). we changed the bearing and did alignment. BY approx. two months the motor was changed due to bearing problems. Then we started taking vibration readings and analysis two times aweak.
I'm sorry I don't have any plot analysis to post it but I will provide information:
RPM:1200
motor NDE BRG: 2.4 mm/s rms horizontal
motor DE BRG: 2.4 mm/s rms horizontal
fan DE BRG: 2.4 mm/s rms horizontal
fan NDE BRG: 1.8 mm/s rms horizontal
1x dominate on Fan DE BRG
vertical and axial are very low in all conventions.

This year we opened the same bearing we found the same problem.

Should I go for balancing?

Thanks

Imbalance occurs at running speed. But so does misalignment. It is a good idea to collect phase data throughout and also review what you have done previously.

Alignment: overhung! Did you graphically plot the fan's centerline of the shaft and the bearings (perform lift checks to do this)? If your motor was sitting basically in the bearing's bottom while the DE fan brg was at top and rotor end at bottom with how much over-hang from coupling to first bearing?????? Are you sure your alignment is good? Type of alignment measurements - sleeve bearings.

You may want to review and take a deep breath and not necessarily rule-out misalignment.

Please post spectral data if you can or list some frequency information and alignment techniques.

Alignment:
Axial
0
-0.06 -0.04
-0.10

Radial
0
0.25 0.15
0.40

Unit: mm

Sam, but other fans have the approx. same misalignment but are normal vib.
You can say I compare between them since the unit is shutdown.

Sorry, this is all I can say.

Thanks alot

Sam, where r u

AMJ,

I would definitely trim balance fan rotor in-place! If fan is a single inlet, then single plane balance method with weight on inlet shround is suggested. If fan is double inlet, then single plane balance with weight on center plate or 2-plane balance method with weights on inlet shrouds. Phase measurments on each bearing should reveal whether single or 2-plane balancing is needed. I would also check on lube oil type and condition.

Walt

Walt,

I will try single plane balancing.But, what do you mean by center plate

Thanks alot

AMJ,
Large FD and ID fan wheels that are double inlet often have a center plate (full disk or spider-like) that divides the wheel in half along the length.

Walt

From your explanation it appears that the bearing failure is something similar to edge loading. Request you to check the bearing shell and housing blue match once.Check for the dents or any high spots at bearing seating area which leads to internal misalignment.Due to misalignment within bearing housing, the bearing might be failing in Edge loading.
Bye