frequent failure of motor thrust bearing 2

[Khader001]

hi ,
the motor has combination of ball bearing and cylindrical roller bearing on the drive end. only cylindrical roller bearing on the non drive end side. The motor running in decouple condition the axial vibration is higher side comparing with horizontal and vertical. The thrust ball bearing failure frequency is every year

Driven machine has sleeve bearing with thrust collar axial float max 0.5mm
flexible coupling with 6.5mm gap between tow hubs

Is this symptom indicating the motor magnetic center not set properly
Motor : 2200HP
RPM :590rpm

 

[edison123]

Is this a vertical or horizontal motor? Since you mention "the axial vibration is higher side comparing with horizontal and vertical", I assume it is a horizontal motor?

Muthu

http://www.edison.co.in

 

[dArsonval]

Electric motors with ball bearings, cylindrical roller bearings, do not call for the setting of their magnetic center.
That's found on sleeve bearing motors.

With all the different bearing arrangements in place with the installation, the spacing and placement of the entire group is suspect.

What happened during the very first thrust bearing failure? That's where 'Ya need to start.

John

 

[electricpete]

Good comments and questions above as usual

Some more thoughts/questions for op:

Magnetic centering would not be high on my list at all. It is a relatively low force.
Loading from the driven machine would be higher on my list.
What type of flexible coupling? What are the endfloat characteristics.
Is the driven machine set up to be centered within the 0.5 mm endplay? Is there evidence (temperature or inspection) of whether the driven machines thrust surfaces are loaded?


Other general question in addition to above
To give a general overview of the machine: What is the horsepower, speed, and voltage. What does this motor drive? Is there elevated temperature?
what type of lubrication does this thrust bearing have?
Do you happen to know the thrust bearing part number or shaft size?

What are the symptoms when "failure" occurs?
Got any pictures of previous failed bearings? (look at the failed bearing is usually more relevant than almost any other analysis you can do)


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[Tmoose]

Soooo much more info is needed.

Please provide the vibration readings of the original motor, each fresh rebuild, each year-old rebuild before replacement, and the readings you asking about now ( I presume is a fresh rebuild).
How long did the first bearing last?
As other asked, how did each of the bearings "fail" ?
Have you been throwing a new bearing in, without a thorough evaluation of the motor shaft's bearing seats?
What are the Motor rpm, bearing part number ( original, and each replacement) and size, and manufacturer's recommended grease ?
Most likely C3 extra clearance bearings are being installed. If standard clearance bearings are being used as replacements there may be problem right there.

If the bearing seat was damaged the inner race can be tipped or not round, both of which bearings hate.
A tipped inner race simulates a bent shaft, which vibration diagnostic charts from as far back as the last millennium have associated with high axial vibration.

 

[panter]

Hello everyone ,
my boss had a habit of mentioning that axially vibrations should be less than half of radial in such situation .
If axial vibration is larger he doubted bad installation and misalignment .
I have not found anywhere in documentation confirm of this attitude so I was wondering if anyone has such knowledge and experience .
Good luck

 

[Tmoose]

" my boss had a habit of mentioning that axially vibrations should be less than half of radial in such situation .
If axial vibration is larger he [highlight #FCE94F]doubted[/highlight] bad installation and misalignment .
I have not found anywhere in documentation confirm of this attitude so I was wondering if anyone has such knowledge and experience . "

============

Did you mean he suspected bad installation and misalignment when axial vibration is higher than radial?

The diagnosis of misalignment or bent shafts when a machine has axial vibration higher than radial vibration at 1X or 2X shaft rotation goes back at least to the old IRD training manuals.
Similar info appears in the useful survey document by HP/Agilent.
Section 4.4 and Table 4.10.2 here.

http://www.hpmemoryproject.org/an/pdf/an_243-1.pdf

I agree higher axial is pretty suspicious, but the diagnosis is rarely that quick and easy.

Recall I posted - "A tipped inner race simulates a bent shaft, which vibration diagnostic charts from as far back as the last millennium have associated with high axial vibration.."

 

[electricpete]

the diagnosis is rarely that quick and easy.

Amen to that. It's a good way to view charts and thumbrules - a starting point but not an answer.

Meanwhile, op seems to have disappeared.

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[Khader001]

Thanks to all nice discussion,
some of the pictures and vibration details are attached pl refer. this motor bearing dismantling is under progress

 

[electricpete]

You wrote "bearing screwed and overheated". I think you're saying the bearing outer ring is turning excessively within the housing causing wear between bearing outer ring faces and thrust plate. I'll assume that's the case.

If you ask me, it looks like you have excess clearance between housing and OD of thrust bearing 0.7mm = 0.028" and that is allowing "spinning" of bearing within housing (I think that's what you meant by "screw").

At least the standard fits would be a lot less for this size bearing. Since it is the thrust bearing it is not required to slide axially and there is not much reason for this clearance. The only thing to prevent bearing from spinning in the housing is the axial clamping force applied on the faces. Perhaps you could prevent it by increasing that axial clamping force but I'm more used to seeing tighter fit at the bearing od.

Obviously you'll want to get some input from OEM or a shop familiar with this setup if possible before making any changes.



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[electricpete]

EDIT - I just looked up in SKF Bearing Installation and Maintenance Handbook
Selection of Housing Tolerances for Thrust Bearings

Axial loads only...
Thrust ball bearings H8
For less accurate bearing arrangements there can be radial clearance of up to 0.001 D...

6044 bearing, D= 340mm. 0.001*D = 0.34mm
H8 = 0 - 0.129mm loose for 340mm housing.

To be honest I don't get why there is such a large clearance even 0.34mm since the bearing is not required to slide axially (it is clamped).
Edit 2 - I guess the clearance helps prevent the thrust bearing from carrying any radial load, so that all its "capacity" is saved for thrust.
If it is "a less accurate bearing arrangement" they need a wider clearance to achieve that goal (0.34mm).
Otherwise they go with H8 0-0.129mm loose.

The clearance you are using (0.7mm) is still twice as high as even the 0.34mm.
I'd certainly prefer lower clearance, even lower than 0.34mm if it were up to me.
If it were up to me I would use H8 which is 0 - 0.129mm loose for this size and minimize the "less accurate bearing arrangement" concern by checking concentricity to make sure the thrust housing is reasonably concentric with the radial housing and also confirming radial bearing clearance below the max listed 0.22mm and thrust bearing clearance above the min listed 0.16mm. Given that the apparent failure mode is bearing spinning in housing, it seems reasonable to push the clearance to the tight end in attempt to help reduce this failure, and minimize radial loading of thrust bearing with the other checks. That is just my thought and I'll admit I don't know how to quantify the degree of radial loading the thrust bearing might see. Obviously it's preferable if you can consult the OEM or at least repair shop that is familiar with this motor design.


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[electricpete]

You wrote "bearing screwed and overheated". I think you're saying the bearing outer ring is turning excessively within the housing causing wear between bearing outer ring faces and thrust plate. I'll assume that's the case.

Can you confirm whether this is what you are seeing? I can't tell from the photos.

Also I'm not exactly familiar with this clamping arrangement. During assembly, how is it assured that the bearing has adequate axial clamping force on the outer ring? (axial clamping force is the other thing that may help prevent spinning along with reduced radial clearance in housing[sup][sub][/sub][/sup]). As far as I can tell it just relies on dimensions of the machined parts... in that case double check the dimensions to make sure you are getting clamping.







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[electricpete]

From the spectrum I'm guessing it is 3600 rpm... is that correct?
In that case it's a high D*N and very sensitive to greasing technique/amounts/intervals imo.
Can you tell us about the greasing.

Looking back at your photos and diagram..., I may have misunderstood which parts are rubbing. Can you talk us through them?

First of all looking at your drawing you have two blue rectangles (large and small) labeled as thrust plate. I'm assuming that this is two separate pieces. The large one I'd call a thrust plate (bolts inward) and the smaller one I'd call a thrust ring that sandwiches between thrust plate and bearing outer ring. Is that correct (two pieces)?

Now the photos:
Upper left - we are seeing part of the thrust ring? Bearing outer ring is further behind not yet visible?
Upper right - thrust ring removed, grease cleaned/removed, and shaft pulled outward?
Middle left/right... these are the thrust plate?
In middle row photos of othe thrust ring we can identify four zones from outer to inner, call them 4,3,2,1:
[ul]
[li]Outer zone 4 - flange face bolts to housing?[/li]
[li]next inward zone 3 - presses on the thrust ring[/li]
[li]next inward zone 2 - should not be contacting anything... yet this is the one with damage marked by arrows?[/li]
[li]last inner most zone 1- clamps against innter ring[/li]
[/ul]
If I have labeled things right, I really don't understand what is creating contact in zone 2.


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[electricpete]

Maybe I was wrong and the thrust plate / thrust ring are one piece... and what we are seeing in upper left photo is outer ring.

It still leaves the question what is creating contact in zone 2.

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[djs]

A possible issue is the non-drive end bearing is not floating. I once had a 1500 hp motor destroy the non-shaft end bearing due to an excessively tight fit between the outer race and the bearing housing. Solution was to take a light cut off of the bearing housing.

 

[waross]

Pete; The bearing is scewd, or tilted, not screwed.

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

 

[electricpete]

Hah, yeah good point - that would well be what was meant.
That large clearance we talked about means outer ring could easily end up cocked in the housing. In that case the cure for that particular problem may be assembly technique or reduced clearance. If careful attention has already been paid during assembly based on previous failures and the problem is continuing, then think about reducing the clearance some.


Lots more questions to ask. I'll just add one:
Middle row, right photo... what type of damage is shown on the thrust plate. Doesn't look like spinning. Doesn't really look like heat. Sort of looks like fretting. Again does anything contact in this area.





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[electricpete]

Is the damaged area on the bearing face and the thrust plate limited to about half the circumference (the top half in the photos)?
It sort of looks that way. Although for photo in lower left I'm not sure if it's just the light.

If it is damage over just half the faces that seems to fit together with the observation of bearing skewed in the housing.

Bearing tilted like that would certainly be bad for the bearing. It could be the cause of the other problems.

How does bearing get tilted to begin with: during installation seems most likely.
The only alternative would be shaft bending movement turned it enough to cock during operation.... seems like an unlikely alternative.



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[BrianE22]

From your assembly drawing at the bottom it appears that, depending on thicknesses, you could be applying an axial preload to the bearing. If it is preloaded check that the preload is within limits.

 

[edison123]

In a three bearing arrangement like yours, the ball bearing is always loose in the housing to prevent skewing. The ball bearing is the locating bearing in this case with no radial loading. In my factory, we always set the housing bore 1 mm greater than the ball bearing OD and the motors have been running without any issues.

Three bearing arrangement is used where the ball bearing capacity for radial load is insufficient and only roller bearings can take up such a radial load.

Muthu

http://www.edison.co.in