We recently replaced one of the centrifuges here at a customer site with a rebuilt one. The #3 bearing (came from bird with the rebuild) gave an alarm in spike energy, but velocity looked good. The time waveform shows a pretty good hit also. We have strobed all that we could see, but found nothing out of the ordinary. the old yellow handled ultrasonic tool points to something within the bearing. The peaks are all awfully close to BPFO.

What do you all think??

Dave

This message has been edited. Last edited by: RRS_Dave,

Bird_Centrifuge.doc (74 Kb, 60 downloads)

For those with UE software, the TWF and spectrum looks just like the vibes one, with less sensitivity. Here is the .wav file. It doesn't sound bad when listening, but the tick is there, and so is the frequencies.

Dave

W227_030706095007.wav (459 Kb, 36 downloads)

From that spike energy spectrum, it looks like you nailed it.

A classic severe defect detected by Spike energy and TWF.

What is weird here, IMO, is the fact that in the normal spectrum the defect is barely visible.
I think it is because Fmax in not high enough.

Dave,
If you can take a normal spectrum with Fmax=180,000 CPM or even higher, BPOR may show up there well in a form of resonance with BPOR sidebands.

We'll going to try that tomorrow Dave, and see what we get. I use analog overall, and it is showing 0.252 ips Pk. My digital overall on the spectrum is showing 0.182 ips Pk, so there is something further out.
There was another thread about new bearings showing defects, and this is a new one. Pretty good size too. Of course, everyone here who had anything to do with it swears it was handled well, and no strikes anywhere as it was hoisted up the hole to the third floor, and then hopscotched over a couple of cranes to where it now resides. I guess it was bad out of the factory
I'll post the new spectrum tomorrow.

Dave

Here are the readings today. We're taking bets as to whether it will make it till Friday or not.

The increased velocity Fmax does show harmonics of BPOR. The sidebands are of ball spin.

Dave

Bird_Centrifuge2.doc (86 Kb, 28 downloads)

Dave--

For what it's worth, I've seen brand new bearings show defect frequencies which upon tear-down showed no visible indications. Further investigation / testing / tweaking found excess thrust on bearing races causing the bearing to "send out a distress signal." As soon as the thrust issue was dealt with, defect frequencies disappeared. HFE measurements are especially sensitive to this type of thing, but I've seen it in normal velocity data as well.

Tony

Tony,

Our axial readings are .105 ips Pk overall, with the radials being .3 something. It doesn't appear to be thrusting, but one can never tell until we put the eye ball on it. Thanks for the idea.

Dave

Dave--

By "thrust" I'm not necessarily talking about motion/vibration, but excessive (static) thrust load parallel to the shaft--or excessive radial preload (e.g. incorrect fit on shaft or in bearing housing).

Tony

OK. We have questoned the mechanic who put the bearings on, and he seems to feel that these were no different than the "1000 before" . However, the preload from fit has been discussed. But like you said, until we look at it, I'm not sure we can be sure of anything. The sidebands of roller and cage has me believeing they damaged the thing either during installation of the bearing itself, or during the transportation up to the unit. Hard preload due to it being in the wrong position on the shaft, and then crammed into the housing would probably give me the same thing though. It will be interesting to see.

Dave

Dave,

There is something else in the TWF plot still bothering me. Repetition rate of the big impact
is every 0.291569 sec ( 3.4 HZ or 206 CPM) and it looks periodic. (Is it?) You'll see it better in the spectrum if you take low Fmax readings. What is it? Does not look like something bearing related. May be bearing spinning or load related or ...?

Just like the "1000 before"!! How many of those did the mechanic plot the bearing fits to verify it is in tolerance? Do they supply a report of all the shaft and housing measurements as well as how square the housing boss is to the bearing. We have found bearings cocked when locked down that preloads them leading to failure. Also, how about true and/or false brinelling. Could happen at most any time during its life. A bearing autopsy will help determine, if there are enough remains left.

Gary B

David,

You mention that 'velocity looked good'. The spectrums you provided in velocity are being viewed on the .2 in/sec scale. Try looking at the same data on a scale of say .05 in/sec and see if you detect BPFO fault frequencies. I suspect you will.

Gary

Why hello Two Dogs!!

Yes, if you right click, drag, and explode you can see the BPFO. But it is not uncommon to see a very small OR freq on these things sometimes, but mostly on the #4 side (float). We always allude it to the fact of "pinching", as it is gone by the next survey.
The "Spike" really caught out eye. This unit was put in service on Feb. 16 I believe. I don't think they are in the mood to "stop and look", and certainly not change it out (don't know if they even have another one this size to replace it with). However, The reliability man on site, Frank, will be watching it and keeping them informed. What they do from there is anyones guess.
See ya,

Dave

quote:

Originally posted by David_G:
Dave,

Repetition rate of the big impact
is 0.291569 sec ( 3.4 HZ or 206 CPM). You'll see it better in the spectrum if you take low Fmax readings. What is it?

RRS_Dave,

In case if you missed the above question but find it worthwhile... I am personally interested to know why 3.4 HZ. Is there a way to find this out? Thanks.

David_G,

I am not on that site right now, and won't be back there until first week of April. I left a day early due to being sick (sick in amotel room 500 miles from home sucks).
However,
Frank, when you read this, send me a template of the bird and we'll figure something out on it.
I did not copy the database when I left.

Dave