Dear;

Please refer my attachment for details of a furnace fan.
The Fan NDE is always found to have high vibrations, paticularly in axial.
I hope it is some thing to be analysed along with the loadability of the fan << as it is running in parallel>>
1) Can you please help me with the axial load calculation for a radial flow fan.
2) any guess to pick the odd thing out

Blower_House_A.doc (74 Kb, 50 downloads) Fan details

helo prabhu, i am apparao,
FD fan looks over hung , and over hung fan vibration (always) seems more than horizontal and vertical what i observed in our plant .
Did you observed the same readings in other fans also?
Pls let me know your email address also to send message to you .

The peak you have marked at 12188 CPM (4.09x TS)matches a BPFO (outer race defect frequency) for several 6219 brgs with 10 rollers.

Is your diagram correct in stating there are 2 brgs at the NDE of this fan? If so, that's a new one on me.

Prabhu,

What is the rpm of the fan? It appears the peak is located around 12kcpm? BPF?? Is this a belt driven application?

I'm with Michael, looks like the BPFO on the 6219 bearing. And I've never heard of this dual bearing arrangement with these 2 bearings on one end. I thought NU cylindricals were mainly used for side loaded apps. like belt driven equipment.

Jason, the info is in the attached document.

I see sidebands around that peak. What is the spacing? Is the spectrum derived from the twf identified as fan NDE V? What is "A eff (mg) in the chart? Is this data really from August, 2007?

Can you post an autocorrelated time waveform?

I agree it sure looks like a bearing problem. If you label in orders, I'll be the big peak is 4.09 and just to the left of it is 4.00. Now move to the left a little ways and you should see 3.09 and 3.0. The 1x sideband around nonsync peak would tend to confirm the diagnosis. Also try log scale looking for further out harmonics of 4.09.

The magnitude 16 g's true pk/0 would suggest you will definitely see visible damage on the races if you pull it now.

I see you mention grease. All of the ball bearings and espeically roller bearings you have listed are waaaaaaaay too big to be greased and operating at 3000 rpm (unless perhaps this is a very limited intermitted duty machine). There are numerous references that give limits for grease lubrication based on bearing D*N number. They will all tell you these bearings are too big for grease lub at 3000rpm. I'll bet when you open up the bearings you will see at least localized discoloration of the grease near the rolling elements suggesting lubrication failure. I see this on many of our high D*N greased bearings, even when the bearing housings didn't seem how during operation. I believe the explanation for that paradox is that the grease lubrication is very transient. When lub conditions get bad, the bearing heats up, grease tends to flow and possibly release oil, and the lub conditions improve for awhile (changes over time). I am sorry to say it, but my prediciton is that you will see problems on these bearings forever (unless you replace the machine or retrofit with oil lube). Grease just doesn't work well at those high speeds on larger bearings.

To make the best of the situation, you need to pay very careful attention to all of your regreasing procedures on these machines. For example frequent addition of very small amounts (or better yet continuous) improves the situation (but still nowhere near as good as oil lube). Also these machines will not tolerate cavities getting full with grease (while slower machines will).

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