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Motor noise reduction.
2

Motor noise reduction.

Motor noise reduction.

(OP)
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

RE: Motor noise reduction.

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

RE: Motor noise reduction.

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.

RE: Motor noise reduction.

(OP)
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

RE: Motor noise reduction.

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.   

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Motor noise reduction.

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
www.edison.co.in

RE: Motor noise reduction.

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

RE: Motor noise reduction.

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

RE: Motor noise reduction.

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

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

RE: Motor noise reduction.

(OP)
Thanks for all the suggestions!


Quote (electricpete):


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.

Quote (electricpete):


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


Quote (electricpete):


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.

Quote (edison123):


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.


Quote (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.
Yet another!

Quote (waross):


Do you mean that the noise continues after the motor is de-energized?
Yes...  most definitely.


Quote (waross):


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.


Quote (waross):


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.

Quote (waross):


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

RE: Motor noise reduction.

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.

RE: Motor noise reduction.

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.


 

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Motor noise reduction.

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.

RE: Motor noise reduction.

>>>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

RE: Motor noise reduction.

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

RE: Motor noise reduction.

Tracking the discussion of noise:

Quote (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.

Quote (electricpete):

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.

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

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Motor noise reduction.

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.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Motor noise reduction.

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
www.edison.co.in

RE: Motor noise reduction.

(OP)
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

RE: Motor noise reduction.

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.
 


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln  
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies  

RE: Motor noise reduction.

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&amp;lang=en

Quote:

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.
=============================
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.
========================

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?
 

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Motor noise reduction.

(OP)
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

RE: Motor noise reduction.

(OP)
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

RE: Motor noise reduction.

(OP)
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

RE: Motor noise reduction.

Kudos returned to you from someone just lurking.

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

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Motor noise reduction.

(OP)
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

RE: Motor noise reduction.

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

Muthu
www.edison.co.in

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