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RustyCas

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We’ve had problems with the bearing below for years. This is a split roller bearing but the one they just took off was a standard SKF roller bearing with a tapered sleeve. Have been through a few of each the last 10 years or so. They call me in after the bearing is mounted, sometimes to help set clearance, and sometimes just align and baseline vibration. Got here a little early this evening and helped get the wheel back to where it was and then I noticed the gap under the center of the bearing (which is not bolted down). Gap is 0.040” at the center, and base is 15” wide. Sits solid at the ends where it bolts up.

Assuming that gap has always been there (that the bearing pad is bowed down), based on your experience, would this cause the kinds of problems we’ve seen?

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MarkL

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Reply with quote  #2 
Rusty,
What kind of problems have they been experiencing? you hadn't mentioned in detail the type of failures. My initial impression is their would be a degree of deformation on the housing with that sort of gap underneath. Are the split bearings Coopers? they can show high noise floor even when running ok.
electricpete

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I think that causes distortion, which can induce misalignment between the two bearings of the machine, which tends to create misalignment between shaft and each bearing, which can put stresses on the bearing if it is not tolerant of misalignment.  As you know cylindrical roller bearings are not tolerant of misalignment, spherical roller bearing or spherical seat bearings are tolerant of misalignement.

It is also possible that the bearing misalignment could translate to shaft-to-shaft misalignment at the coupling and generate reaction forces that way which could put stresses on any type of bearing. But that would be apparent during  runout checks.

Also there could be some stress put on the bearing from non-uniform housing support to the outer ring (if the housing tends to distort out of round). But  I think most bearing housings have a fairly beefy steel cylinder such that most of the distortion would occur elsewhere, not at the cylinder. 

That's just my thoughts, roughly in the order of swag-significance that I judge them fwiw.  I don't have any direct experience to rely on for this particular problem.
Danny Harvey

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Reply with quote  #4 
I had one case where there was significant soft foot in a Cooper 5-15/16" PB bearing. Correcting the shimming we went from new bearings about every 2 months to lasting years.  Someone removed the shims and we had another failure. We put them back and the bearings lasted until the fan was decommissioned.

But that was due to twisting the housings, not allowing it to sag or bow in the center.
fburgos

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Reply with quote  #5 
As other points out, out of roundness and misalignment, so if you have bpfo or harmonics you will know what's the problem
dnk

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Reply with quote  #6 
From what i see i would believe the problem was with mounting plate not the bearing hsg. Have seen this several times. I treat this like soft foot and shim bearing so it is supported across whole length of bearing hsg.  also check for level on machined part of bearing hsg. If machine is old and distorted i would check level in shaft. I have seen fan bases that distorted that both bearings need shimming and not always in sane direction.
electricpete

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Reply with quote  #7 
You could also try measuring shaft to bearing alignment if you have enough room/access to put an indicator base on the shaft indicating off the outer ring face.  If you find a problem there (or high shaft runout for that matter), it would provide more ammunition to fix this condition.

I don't know of any measurements to figure out if the housing is providing non-circular / non-uniform support to the outer ring.    As Tom from SKF showed us in this thread https://www.machineryanalysis.org/post/out-of-round-housing-visible-indication-on-bearing-9865262?highlight=tom+skf&trail=15 there might be some clues if you inspect a removed bearing outer ring (although if the outer ring creeps over time the evidence might not be so clear). 

RustyCas

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Reply with quote  #8 
dnk, I agree and I shimmed the housing of the bearing we just installed before we bolted it down.  It is a Timken "Revolvo" bearing, so is a split bearing. These always look and sound like hell compared to regular bearings.  I know they are easy to replace, but I still hate them, probably more than 2-pole motors or VFD machines.
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