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I'd like to get some opinions suggestions on what might be happening? The data is from a Kice centrifugal fan. Model Fc-33 The piece of equipment was never added to a standard route so longer history is not available. Maintenance history shows that the brgs were changed in 2004. I was able to capture data prior to bearing replacement and then after replacement. Bearings are Link-belt PB22463FH. Both brgs/housings were changed. What lead to the decision to have brgs replaced was the notice of a vibration in the floor. There was/ is a imbalance, but also what looked like brgs failing. Balancing is next on the list, but I believe there is still something going on . The attached file has screen shots of horz and vert directions of both brgs. G's look to be increasing daily. Temps are 147 deg F on both brgs. Fan speed is approx 817-819.

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Racer,

2.0 mil p-p displacement is less than 0.1 in/sec peak velocity. Here is your displacement data:

Drive-H = 2.2
Drive-V = 1.7
Non Drive-H = 6.1 ***
Non Drive-V = 1.6

Rotor balance is not too bad based on three of the fouur measurements. The 6.1 mils is either bad data or there must be resonant amplification or a loose bearing. Looks to be more than just a balance issue.

If the fan bearings are tapered rollers with adjustible expansion/locking collar, then perhaps the bearing interal clearance is not correct. Secondly the lubricant type and/or amount may be incorrect. Both can cause the high frequency acceleration (noise).

Walt
RM
Thank you for the quick replies. We did try the adding lube to the bearings while monitoring the spectrum, but the peaks did not drop at all. At first I thought that maybe I had something not set up correctly with my collector as this is new to me and I'm learning every day. Our contract service person was in after the brgs were replaced and we both collected data together to compare data, and he too had the same high peaks and raised floor. He uses a CSI collector and I have a Commtest. The replacement brgs were brand new still in the box. There is a adjustable locking collar on the one end of each brg assy, but they were not adjusted at all. Next available time to access this fan is next week. Now may I ask a question?. If there is excessive internal clearance, wouldn't that need to be corrected first before a proper balance could be performed? If the shaft was a tad undersized were the bearings are mounted, how would this reflect the spectrum?
RM
Ron's right. Just because a bearing is new, doesn't mean it's good. Had a split case pump with new bearings (flange type ball). After being put back in service, the OB bearing show some pretty good BPFO. The foreman, shop rebuild guy, and millwright all said "Can't be, that's a brand new bearings". The OB bearing was pulled and cut open. Found a 1/8" long spall on the outer race.....Everyone got real quiet!!!

How are these bearings held to the shaft? Set screws? Use a strobe light and see if the inner race collar and shaft are turning the exact same speed. Slipping?

I looked at your data after I posted. Like Danny said, get your new bearings ready and on hand!!!!
RM
I would post a picture of the brgs but for some reason I'm unable to grab the drawing from rexnord's site. I did see it the other day. But, there is set screws that lock the brgs to the shaft. I did use a strob light to check for slipping and did not notice any. Looking at the docs on these brgs,the internal clearance can be adjusted with the spanner nut that is on the one side of the brg housing. When these brgs were installed, the spanner nut adjustment was not adjusted.

I located a picture of the bearings used on this fan.

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  • brg
RM
Last edited by Registered Member
quote:
Originally posted by Walt Strong:
Racer,

2.0 mil p-p displacement is less than 0.1 in/sec peak velocity. Here is your displacement data:

Drive-H = 2.2
Drive-V = 1.7
Non Drive-H = 6.1 ***
Non Drive-V = 1.6

Rotor balance is not too bad based on three of the four measurements. The 6.1 mils is either bad data or there must be resonant amplification or a loose bearing. Looks to be more than just a balance issue.

If the fan bearings are tapered rollers with adjustable expansion/locking collar, then perhaps the bearing internal clearance is not correct. Secondly the lubricant type and/or amount may be incorrect. Both can cause the high frequency acceleration (noise).

Walt

On Friday, I was able to test out a brg adjustment for a short while. I have attached some spectrum before and after adjustment. From the results of the short time testing, and chance that a possible increase of failing may happen with the new settings, I had the adjustment turned back to original starting position. From what you suggested and what the spectrum looks like, I figured there was too much clearance, and by reducing clearance, the results would reduce the noise levels on the spectrum. At first, the g's went down a bit, but after 1hr 45min running, they were back up, and looked like some other peaks developed. I'm hoping that next week I may have a longer down time to try some other adjustments.

If the shaft diameter was a bit undersized, say .001-.002, would that cause the raised noise that I'm seeing?

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RM

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