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

 

[MikeHalloran]

There shouldn't be much noise.

If someone has disassembled the motor, there may be chips or dirt between the shell and the end caps. Or there may be dirt on the bearing that's supposed to float axially in its housing, typically the NDE. Or they may have reassembled it with too-cheap bearings, or without good bearing install practices.

Or they may have made 'improvements'.

Or it may be undamaged and just not 'inverter duty'.



Mike Halloran
Pembroke Pines, FL, USA

 

[DickDV]

It may be all inverter-related noise. If you can, temporarily shift the PWM carrier frequency up as high as it will go. That will probably be 8khz or higher.

Run the motor then and see if the noise mostly went away. If so, its due to the inverter pulses making the motor magnetic material resonate.

If the motor has to be quiet, operate it on the lowest carrier frequency where the noise is still not too high. The higher the carrier frequency, the more heat losses in the VFD and the more stress on the motor insulation so, less is better.

 

[itsmoked]

The motor was purchased new a decade ago and run by VFD since day one for a total of only about 400hrs. I have disassembled the motor and found that the sealed bearings felt good. No catching or roughness and a little drag, not dry endless spinning. I did not remove the bearings from the shafts. The drive end bearing is clamped into its hole with a little plate with two screws. The NDE just has a spring wavy washer dropped into the end bell hole it slides into.

Reiterating: The drive is OFF and not modulating at all as the motor coasts down. "Cut off like a knife." All noise I'm referring too is coming from an electrically inert motor's spinning only.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[electricpete]

I'm assuming it makes noise during running and coasting, right?

Does it make noise consistently during coasting, or only certain speeds?

Regarding rolling a bearing in your hand:
1 - I agree with you that a little bit of drag is normal. The grease friction is high when the bearing is stationary and cool... goes way down during running condiitons.
2 - I have seen bearings with lots of damage that "felt good" when rolling by hand but a different story when cut open.

Tough to draw any conclusions but my guess on the two biggest suspects would be: bearing defect and skidding. If bearing defect you can pick it up easily on vibration spectrum or by disassembling the bearing., If skidding, perhaps you will notice the bearing running hot.

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[edison123]

I would say bearing. Since it is sealed, you can't see the rolling elements. The wavy washer is to accomodate the axial thermal expansion.

Muthu

http://www.edison.co.in

 

[MikeHalloran]

Spin the bearings with an axial load applied, as if the wave spring were present.

Or just replace them.
Motor manufacturers typically use inexpensive bearings.



Mike Halloran
Pembroke Pines, FL, USA

 

[waross]

Do you mean that the noise continues after the motor is de-energized? Any time I have heard bearing noise n a small coasting motor, it has been bearings failing.
How long in service? I had a bearing fail catastrophically the first day of service. The retainer that keeps the balls spaced was faulty and the balls bunched up and jammed the shaft.
The discussion went something like this:
Me; "The bearing seems to be shot."
Mechanical; "It can't be, it's brand new."
"Is it normal for there to be this much play and flop?"
"No but it's brand new."
"You guys have been working on this for hours now. Why not try removing the bearing?"
"But it's brand new."
Eventually a new bearing solved all the problems.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

Another thought. After ten years of inverter duty the bearings may be damaged by bearing currents.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Thanks for all the suggestions!

I'm assuming it makes noise during running and coasting, right?

Yes pretty much exactly the same noise. There is ZERO pwm noise at the 12kHz modulation I am using.

Does it make noise consistently during coasting, or only certain speeds?

Very consistently.

Regarding rolling a bearing in your hand:
1 - I agree with you that a little bit of drag is normal. The grease friction is high when the bearing is stationary and cool... goes way down during running condiitons.
2 - I have seen bearings with lots of damage that "felt good" when rolling by hand but a different story when cut open.

Tough to draw any conclusions but my guess on the two biggest suspects would be: bearing defect and skidding. If bearing defect you can pick it up easily on vibration spectrum or by disassembling the bearing., If skidding, perhaps you will notice the bearing running hot.

OK, for bearings this small it probably suggests to just change them out.

I would say bearing. Since it is sealed, you can't see the rolling elements. The wavy washer is to accommodate the axial thermal expansion.

Ah, Another vote to replace! Thanks for the spring explanation.

Spin the bearings with an axial load applied, as if the wave spring were present.

Or just replace them.
Motor manufacturers typically use inexpensive bearings.

Yet another!

Do you mean that the noise continues after the motor is de-energized?

Yes... most definitely.

Any time I have heard bearing noise n a small coasting motor, it has been bearings failing.

And yet another thumbs-down..

As you mention it I think that has always been my finding too. It's just that this motor doesn't make a lot of noise, just more than I would expect. So I was looking for confirmation that it's normal to make some noise. Except, I think I've seen large TEFC units that made less noise than this one.

How long in service? I had a bearing fail catastrophically the first day of service. The retainer that keeps the balls spaced was faulty and the balls bunched up and jammed the shaft.
The discussion went something like this:
Me; "The bearing seems to be shot."
Mechanical; "It can't be, it's brand new."
"Is it normal for there to be this much play and flop?"
"No but it's brand new."
"You guys have been working on this for hours now. Why not try removing the bearing?"
"But it's brand new."
Eventually a new bearing solved all the problems.

Another thought. After ten years of inverter duty the bearings may be damaged by bearing currents.

Yes, but as I said only 400 hrs of operation - TOTAL. Are bearing currents that damaging in factional hp motors? On the other hand, touching this motor under excitation with it ungrounded will give you a real thrill...

Alright folks, I will order some new bearings. I take it there are no special "quiet" bearing types. I'd hate to go to all the bother this represents, if this motor just likes being noisy.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ccjersey]

I was under the impression that there are indeed high grade bearings that should be quieter than the common grades.

Not real sure how one would go about ordering some as opposed to just picking some of the correct number/size.

 

[electricpete]

Do you happen to know if noise was there from day one or just appeared.

For noise reduction, get higher precision bearings. i.e. look for a higher ABEC tolerance class (1 is the lowest.. 9 is the highest). I think typical industrial bearings are ABEC 1. There is also an ISO precision rating for overseas.

Just to expand on good earlier discussion about wavey washer - thermal expansion is accomodated by providing room for bearing movement in the housing. Therefore you can't impose preload without a wavey washer. The wavey washer provides preload which helps prevent skidding. If the outboard bearing sticks in its housing then you might lose preload and skid.




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[ccjersey]

I have a new 56J single phase motor that is the noisiest motor I have ever seen or heard.

I guess I'll wait to bearing failure which probably won't be long now before removing it from the intermittent duty pump it is installed on, but it sure is irritating to have a new motor with this problem.

The previous old motor failed from water (not moisture, WATER!)collecting inside the housing after many years, but it still wasn't anywhere this noisy.

 

[MikeHalloran]

>>>On the other hand, touching this motor under excitation with it ungrounded will give you a real thrill... <<<

The bearings are toast.



Mike Halloran
Pembroke Pines, FL, USA

 

[waross]

Given the billions of bearing hours accumulated by standard bearings in motors, I would just go with standard bearings.
Assuming that the bearing(s) are failing from VFD induced shaft currents, you may go with another set of standard bearings for another 400hrs/10years. Bearing currents may fail an expensive high quality bearing as soon as a standard bearing.
If you want to do better than original, how about rereading Gurra's posts re: "Bearing current detection and abatement".
Concerning a "Resilient mounted bearing; The wavy washer provides axial resilience. A radially resilient bearing may produce a resilient air gap. Grin.
Getting a "tingle" from the motor housing may be an indication of possible bearing currents.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[electricpete]

Tracking the discussion of noise:

I was under the impression that there are indeed high grade bearings that should be quieter than the common grades.

Not real sure how one would go about ordering some as opposed to just picking some of the correct number/size.

For noise reduction, get higher precision bearings. i.e. look for a higher ABEC tolerance class (1 is the lowest.. 9 is the highest). I think typical industrial bearings are ABEC 1. There is also an ISO precision rating for overseas.

Given the billions of bearing hours accumulated by standard bearings in motors, I would just go with standard bearings. Assuming that the bearing(s) are failing from VFD induced shaft currents, you may go with another set of standard bearings for another 400hrs/10years. Bearing currents may fail an expensive high quality bearing as soon as a standard bearing.

No-one here suggested to install high precision bearings as means to prevent bearing degradation. I responded to a simple question from ccjersey.

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[electricpete]

However, in the unlikely event that itsmoked responded:
1 - noise was there from day 1
2 - the noise is the problem, not the concern for beairng reliability
then we should talk some more about precision bearings.

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[edison123]

pete - why do you need an axial preload in a bearing in a horizontal motor ? I have seen many small motors with no wavy washers for the non-locating ball bearing i.e. bearing free to move axially in the end bell. Only few OEM's use wavy springs presumably to prevent the outer race from spinning while at the same time allowing the thermal expansion.



Muthu

http://www.edison.co.in

 

[itsmoked]

electricpete;

1 - I can't say the noise was there from day one. No data.

2 - Noise is the only problem..


BTW: I've pulled the bearings and pried one open. Still packed with functional looking grease but I couldn't see any obvious issues. I'm not willing to tear them all apart, clean them, and look at them with a microscope at this point.

If I was, I'm not actually sure how you get them apart? Do you have to mangle the carrier?

I'm proceeding with bearing replacement and will report on the results.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

Keith,
Given the "thrill" factor from touching the case and the apparent bearing noise, I would highly suspect fluting of your bearing races from VFD operation. The fact that it was only 400hrs of operation is a reason for immediate dismissal, there are other factors involved that can accelerate the damage. This article does a decent job of summarizing.

http://64.211.107.26/technical/tech_detail.php?display=files/Product_guide/fa117_03

If you plan on running from a VFD again, I would consider using an insulated bearing system like Aegis.



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