Dear Members ,

We have a CT fan at our customer site with high Vibration Problem ,We dont have provision to take vibration data on CT Fan Gear Box ,we do take Vibration data on Motor .Please Verify the below attached data and General arrangement of the equipment and share your opinions.

Motor 37 K.W and Bearings D.E 6313 ,N.D.E 6213 C3 clearance running at 1475 R.P.M .CT


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Original Post

Vibration is possibly from fan blade passing frequency pulsation. What is fan shaft rpm? How many blades on fan?

The vibration could also be from intermediate stage tooth mesh frequency, assuming 2-stage gearbox (less likely). Get gearbox tooth counts and bearing information as part of your diagnostic investigation.

Inspect motor support and gearbox support for structural deterioration and looseness.


Kishore kumar posted:

Dear John ,

4420 c.p.m not a bearing frequency of this fan motor ,But the input from the intermittence team is , there is a backlash between the gears in Gearbox .

Why are you so certain the 4420 cpm is not a bearing frequency.  I see for the 6313 a BPFO of 3.07 which yields 4530 cpm.  That is for 9 elements and often depending on the bearing manufacturer you will find +/- 1 element.

Backlash can be normal, the lack of it is abnormal in most instances.  What are the tooth combinations, speeds, etc.  If you have the long spacer coupling as you've shown you are also not likely to get gearbox vibration at the motor which is your concern unless I'm misunderstanding things.





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With these type of CT fan arrangements when you only have the motor accessible the key parameter I look at is the motor inboard axial. this is where you can see the gearbox inboard shaft gear frequencies. I trend the amplitudes and look at the ratio of that parameter to the 1x motor speed.  

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