Motor noise reduction. 2

[itsmoked]

I have a 56J 1/2hp 3Ph Baldor (CJM-3108) that seems to make a lot of noise spinning. I have it hooked to a VFD and when I turn off the VFD it terminates all drive, like a knife, and the motor coasts down to an eventual stop. During this coast the motor doesn't seem to make any failing bearing noises they just seem... like they are too mechanically connected to the motor end plates, and case, and that they're all sound-boarding the noise.

Or, am I wrong and there should be no noise other than fan fan noise?

Are there any techniques for remediating this? Can your get bearings that are resiliently mounted? Any other thoughts?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[electricpete]

Muthu – we could allow thermal expansion by providing room in housings without preload washer, right?

The purpose of wavey washer in electric motors imo is to provide axial preload to prevent skidding (in pumps and other equipment it can also be used to enhance radial centering). Yes, I agree not all motors have wavey washers.... What does it prove? Not really anything about the purpose of the wavey washers that I can tell... whatever their puprose is why wouldn't it apply to all motors. . I'd say it proves there are differences in factors related to skidding ( skidding is also dependent upon bearing size, speed, radial load, lubrication method) and also differences in motor design philosophy and quality.

http://www.skf.com/skf/support/html/dictionary/dictionary.jsp?dictPage=p&lang=en

Preload
Bearings should normally have a small residual internal clearance during operation. However, in applications such as work spindles of machine tools and pinion bearings in automotive axle drives, a preload is desirable to enhance stiffness or to increase running accuracy. For bearings under very light [radial] load, [axial] preload by springs is sometimes applied. Preload could be applied in radial direction, e.g. by drive up of a cylindrical roller bearing on tapered seat, or in axial direction by preloading two bearings against each other, e.g. single row angular contact ball bearings or taper roller bearings.

[FIGURE ON RHS] – Axial preload of deep groove ball bearings in a small electric motor to achieve low noise level. The preload is attained by a spring washer placed against the bearing at the non-drive end.

Note that light load is a contributor to skidding and noise is one consequence of skidding.
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Keith - some ideas on taking the bearing apart for inspection:

The toughest part is separating the outer ring from the rest of the bearing. Two ways (1A and 1B)
1A – take it to a machine shop and have them cut it with a Metabo cutting wheel.

1B – If you don't have access to a cutting wheel, drill out all the rivets in the cage, remove the two havles of the cage (one on each side, previously held together by rivets but now separable), move all the balls toward one half of the beairng, and pry between inner an douter race until beearing pops apart (have your safety glasses on). It sounds like you may have pried it apart with cage intact? That's hard to imagine.

2 – Once you have the outer ring removed, if not already done you need to remove the cage. Cut it with plyers at 2 points 180 degrees apart. Cage comes off in 2 pieces (with balls included) and you can inspect inner ring. You also have good inspection of balls without removing them from the cage, just spin them in the cage.

3 – Put solvent like paint thinner in a container enough to submerse your parts and rub the grease off.

It might seem like a hassle but if you've gone through this much trouble you might as well go the final mile to see exactly what the bearing surfaces look like imo because your corrective actions would be a lot different if you find bearing in good condition (not likely but possible) than bad.
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All – what exactly does it prove that youi can feel something when you touch the motor? I assume there is capacitive coupling of high frequency voltae components from stator winding to both stator core and rotor core. Stator core is obviously in intimate contact with stator frame regardless of what's going on with the beairngs. What conclusion do we draw from that tingle? Maybe it has something to do with grounding method used for the case?


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[itsmoked]

Thanks for the continued detailed discussion.

Looks like I should've hooked up an ammeter between the case and the shaft and run the motor with the VFD before I tore it down. If I saw current it would immediately justify something like Aegis.

And Jeff, the previous service was intermittent, and once it's put into service again it will be 24/7/365 running on a VFD, so, insulation or a current shunt makes a lot more sense.

But since I didn't measure the current I will inspect the bearings.

I love it. The VFD is about $120 and a single Aegis for the motor is $108.94 + tax.

Stay tuned.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

I cut the bearings open. It was actually really easy.

They are quite shiny with no apparent scratches. They weren't as clean as I thought, but, I think you can see the mirror finish. They are laying on a towel so you can see the scale of the magnification. Sorry for the file size - these were cut to less than 1/8th of the original dimensions.

Bearings in Repose:

Top lighted at about 200X magnification and very clean:

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

T'was the bearings.

I put in new bearings and ran it again.

World of difference.

The only noise was the fan. No rotational noise what-so-ever.

Some of the improvement was likely the double seals verse only the original shielded bearings.

Kudos.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

Kudos returned to you from someone just lurking.

It is good that some have the stamina to go through all steps sometimes.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

You have no idea..

Pressed the bearings on. Returned from the place with the press and found I'd left off a plate that had to go on before the DE bearing... Had to pull the bearing off and return to the press.

Got the motor all re-assembled, new seal in the pump, shaft extension on, pump housing, impeller, case on, and discovered the slinger lying on the bench. Back off with the pump case, impeller, pump housing.

Got that all reassembled and as I was basking in the success of it all, it was noticed the pump's output was pointing at least 10 degrees off vertical. Realized that I'd failed to line up the motor DE plate mark with the stator/mounting feet motor body..

Thanks Gunnar.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

Keith - Now you know the kinda hell we rewinders go through.

Muthu

http://www.edison.co.in