Hello, i`m quite new in cbm world,could anyone give an advice ,what cause high 3Xfan speed on motor fan cooler that have 6 fan blade? motor rpm at 1480 and the fan rpm is 304,for info, this fan and motor are newly overhaul

Kiai
Start with simple checks.
3X is often attributed to looseness.
Misalignment and poor coupling setup are two others that come to mind.
One of the key statements you make is that it was recently overhauled. To me, thats a red flag.
Look closely at the work package that completed the O/H and particularly in those items noted above.
It would help if you could provide spectral and time waveform data.
Also, where on the machine do you see the highest readings?
More info needed to provide a more indepth response.
Regards
Jim P

quote:

Originally posted by kiai:
Hello, i`m quite new in cbm world,could anyone give an advice ,what cause high 3Xfan speed on motor fan cooler that have 6 fan blade? motor rpm at 1480 and the fan rpm is 304,for info, this fan and motor are newly overhaul

thanks, i already check all the possibility, looseness, alignment, it seems to within tolerance. one of my friend suggest 1/2 fan blade pass freq. it is possible??? by the way, the highest vibration is in axial dir only.

1/2 blade frequency?? --- I have not heard of that before. Maybe others in our forum can comment.
When you say high 3X...what does that mean?
Please post vib data or I'm just guessing

Jim P

if it's possible, could you post some spectrums up here? Is your fan belt driven?

Ok,,attached the spectrum as request. my unit consist of motor driver to a fan by a v belt. the sheave have 4 belt strand individually. I have done the bump test last week on the structure and the frequency match with the 3 X fan speed in the direction of the high vibration( axial). Suspected resonance. but what cause the 3X forcing freq???

3x_rpm.rtf (801 KB, 42 downloads) 3xrpm

quote:

Originally posted by kiai:
but what cause the 3X forcing freq???

The 3rd harmonic of running speed, which could result from looseness, is likely the forcing frequency.
And, yes, your case suggests a resonance at work.

Dave

everyone, i manage to reduce the vibration reading today. Thanks to everyone. what did i do is ,replace all the fan blade with a spare one. This fan is slightly different from the original one from it size and weight. Remember the high 3X fan RPM, the level reduce almost 80%, that amazing!!. Well it seems to be true resonance problem. but the question is what cause the amplification of the vibration and why 3X fan rpm?
My challenge right now is to find out what wrong with the old fan blade..if the blade are not balance properly, is it possible to have 3X fan rpm??

kcsa3_4_after2.rtf (878 KB, 20 downloads) after rectification