frequent failure of motor thrust bearing
frequent failure of motor thrust bearing
(OP)
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
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





RE: frequent failure of motor thrust bearing
Muthu
www.edison.co.in
RE: frequent failure of motor thrust bearing
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
RE: frequent failure of motor thrust bearing
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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(2B)+(2B)' ?
RE: frequent failure of motor thrust bearing
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.
RE: frequent failure of motor thrust bearing
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
RE: frequent failure of motor thrust bearing
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 . "
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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.."
RE: frequent failure of motor thrust bearing
Meanwhile, op seems to have disappeared.
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(2B)+(2B)' ?
RE: frequent failure of motor thrust bearing
some of the pictures and vibration details are attached pl refer. this motor bearing dismantling is under progress
RE: frequent failure of motor thrust bearing
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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(2B)+(2B)' ?
RE: frequent failure of motor thrust bearing
Selection of Housing Tolerances for Thrust Bearings
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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(2B)+(2B)' ?
RE: frequent failure of motor thrust bearing
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). 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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(2B)+(2B)' ?
RE: frequent failure of motor thrust bearing
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:
- Outer zone 4 - flange face bolts to housing?
- next inward zone 3 - presses on the thrust ring
- next inward zone 2 - should not be contacting anything... yet this is the one with damage marked by arrows?
- last inner most zone 1- clamps against innter ring
If I have labeled things right, I really don't understand what is creating contact in zone 2.=====================================
(2B)+(2B)' ?
RE: frequent failure of motor thrust bearing
It still leaves the question what is creating contact in zone 2.
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(2B)+(2B)' ?
RE: frequent failure of motor thrust bearing
RE: frequent failure of motor thrust bearing
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: frequent failure of motor thrust bearing
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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(2B)+(2B)' ?
RE: frequent failure of motor thrust bearing
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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(2B)+(2B)' ?
RE: frequent failure of motor thrust bearing
RE: frequent failure of motor thrust bearing
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
www.edison.co.in
RE: frequent failure of motor thrust bearing
It would be much easier to tilt/cock the outer ring in a very loose housing than a tight one, wouldn't you agree?
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(2B)+(2B)' ?
RE: frequent failure of motor thrust bearing
Muthu
www.edison.co.in
RE: frequent failure of motor thrust bearing
We can tilt the outer ring a limited amount with respect to inner ring before the internal clearnance is used up.
After that further tilting stresses the internal parts.
Assume we are assembling a machine where shaft is straight and true to housing bore...
For bearing with standard fit, the ability of bearing to tilt is limited by the housing. We cannot possibly tilt the bearing enough to stress the bearing within that standard fit.
But for bearing with loose fit, you no longer have that benefit. The bearing can tilt near its full limit of travel without being stopped by the housing. What would cause it to tilt I picture would be an assembly process pushing housing axially relative to bearing and the bearing (maybe slightly off-center at that stage of assembly) sees more friction on one side and tilts. The tilting reduces the clearance. In order to remain cocked it would have to tilt far enough to reduce the clearance to zero. For 6044 bearing D=340mm, B=56mm, it requires less than 1 degree tilt to use up the 0.7mm diametral clearance if my trigonometry is correct. I neglected the rounded bearing corners which would have helped the situation somewhat. Assuming the bearing is capable of tilting 1 degree (under stress), the way to avoid preclude cocking thru design (if cannot be precluded by assembly method) would either be either A - reduce clearance to standard clearance or B - increase clearance even further so that bearing will tilt to its limit without ever contacting the housing.
I agree that if the outer ring face is clamped tightly and squarely on each side of the bearing, there cannot be a skew or tilt. I think maybe the photos show damage over only portion of the bearing outer ring face and portion of the thrust plate face as if there is not a firm square contact between bearing and thrust plate (although I’m still confused about that zone 2). And it suggests to me bearing cocked in the housing. Is that what you see? If not what kind of skew do you see or envision is going on here... inner ring cocked on shaft?
op - can you tell us more specifically what kind of skew you saw?
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(2B)+(2B)' ?
RE: frequent failure of motor thrust bearing
most of your assumptions are matching with mine.
last year I have raised a modification proposal that too enclosed with this post please find the attachment.
As Mr Muthu comments I agree that with cylindrical and ball bearing combinations are working well without any problem. these all motors are driving which has anti friction bearings
the problem which has friction bearing with larger radial clearances, also when the motor is in operation motor and the blower shaft runout was measured blower side 0.15 to 0.20mm motor side 0.15mm the peak raise looks both shaft moving with the same timing
a sectional drawing also attached it may help to get more details
grease: SHC 100 mobile
intervals : 1000 hrs/ 40g
RE: frequent failure of motor thrust bearing
I can see why you would be concerned about tigher radial clearance of thrust bearing than radial bearing. Even if thrust bearing does not contact housing radially, it is still clamped so it can still either see radial load or have relative motion at the axial clamping surfaces.
Did you happen to see if the outer ring move as the shaft was manually rotated with thrust plate removed? (that would rule out cocked bearing to my mind).
Can you explain some more the pattern shown in the middle and bottom row of photos? It looks to me as if the damage is preferentially on the upper half of the outer ring and thrust plate. If the only problem is deep groove ball bearing internal clearance tighter than cylindrical beairng internal clearance, we'd expect to see wear 360 around those surfaces, wouldnt' we? (if not cocked bearing maybe it suggests shaft at permanent angle to the housing)
If you implement the proposed solution the spherical bearing is wider than the ball bearing. I gather you will machine the thrust plate or the housing to accommodate that.
Still thinking about the grease. My experience has been bad reliability (low life) with high D*N greased bearings. It seems the motor OEM's routinely go beyond the recommendations of the grease and bearing OEMs. I'll see if I can dig up some bearing manufacturer guidelines on D*N
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(2B)+(2B)' ?
RE: frequent failure of motor thrust bearing
The thrust bearing wear pattern studied most of the housing and thrust bearing end cover step bearing seating area found worn out around the bearing outer ring.
After installation the thrust bearing alignment was inspected there is no scew found.
one more experiment done while operation in rated load and RPM motor thrust bearing end cover loosen found that motor vibration came down 3.6mm/sec to 1.9mm/sec same time two dial indicators on drive and driven shafts measured 0.15mm in both shaft no difference in runout readings after loosening the thrust bearing end cover its conforming that thrust bearing is oscillating
greasing we under discussing with the mobile to select suitable one
now I collecting all the damage bearings once dismantle bearings and ensure the wear pattern indications
modification till not started looking for more information
RE: frequent failure of motor thrust bearing
RE: frequent failure of motor thrust bearing
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(2B)+(2B)' ?
RE: frequent failure of motor thrust bearing
Photo showing the partially dismantled bearing, and bearing bracket conflicts with the bearing installation arrangement drawing provided by the OP.
The engineering drawing shows the cylindrical roller bearing shouldered on shaft journal first, and held enclosed by a bracket labeled at “A” on my attached photo.
A spacer with dust fin labeled “B” secures the separable NU 1044 inner race and rides with the shaft on the outside of bracket A.
These two components would visibly shroud, hide, or prohibit the NU bearing from even being seen during the dismantling process.
The OP’s picture showing the NU bearing surrounded by a bracket and completely exposed doesn’t “jive” with the engineering drawing.
Are we looking at a scenario where the bearings are not or (were not) in their proper locations to begin with?
John
RE: frequent failure of motor thrust bearing
...That's what it looks like to me but I've been wrong before or maybe I misunderstood John's comment. Hopefully op (or John) can clarify.
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(2B)+(2B)' ?
RE: frequent failure of motor thrust bearing
What I'm seeing is a brass cage cylindrical roller bearing fully exposed, sticking out of the bearing bracket that's in the process of being pulled off
using long rods threaded into the bracket. That bearing we can all see in the photo is a cylindrical roller bearing with a separable inner race.
Behind that bracket (not yet removed during the dismantling phase) is another bearing that according to the drawing supplied by the OP, should be the cylindrical roller bearing.
There's a LOT going on with this failure. And the placement/location of the bearings may explain the frequent failures the OP mentions earlier in the conversation.
It's not uncommon for an expert repair person to follow someones earlier mistake.
Couple this bearing placement question with the PowerPoint slideshow that's suggesting a proposed engineering design change in the whole arrangement makes the situation more complicated.
There's a "To be continued" here we may never get to read about.
Enjoying the forum,
John
RE: frequent failure of motor thrust bearing
I m not sure that motor shaft slides towards driven machine. if there is axial movement on the motor shaft and it creates excessive axial load on the ball bearing then the bearing failure should lead to damage to the balls runway or bearing internal parts. the ball bearing axial face should not get damage because the ball bearing don't have space to move along with the shaft. the motor shaft axil movement limited as the ball bearing axial clearance.
the motor bearings are removed and the damage bearings are in analysis soon I will upload the photos
the intension of the modification is to avoid radial load sharing between ball bearing and cylindrical roller bearing. the spherical bearing selected because it can work well with both loads radial and axial.
what are the complications in spherical roller bearing design kindly write more about this
RE: frequent failure of motor thrust bearing
Another question either from position as devil's advocate or maybe from a position of ignorance… As you mentioned many bearings operate reliably with deep groove thrust bearing adjacent to cylindrical roller radial bearing (and with large housing clearance at the deep groove). You're blaming the problem here on lower internal clearance for the deep grooves than for the cylindrical rollers, but doesn't that same factor apply to other motors with similar configuration with same bore diameter DGBB and CRB? How is this one different? Maybe others use something other than C3?
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(2B)+(2B)' ?
RE: frequent failure of motor thrust bearing
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(2B)+(2B)' ?
RE: frequent failure of motor thrust bearing
Look forward to seeing, and reading what you've found.
I'm still confident the bearings were originally installed in the wrong place. Hence, the continued failures.
Staying tuned,
John
RE: frequent failure of motor thrust bearing
Pl check the attached video I have check the radial clearance of the rotor till 0.05mm rotor move with minimum pressure then rotor stops the movement then the hydraulic pressure was raised then we can see jumping movement from 0.05 to 0.10 and then 0.23mm
Mr John
Can you pl explain your view
As you said the bearing installed in wrong place what do you mean is themagnetic Centre not positioned properly ?
Most of the readings are taken I didn't found any abnormal issues rotor run out 0.01mm
Ball bearing housing concentric to the cylindrical roller bearing housing 0.01mm bearing alignment is good
RE: frequent failure of motor thrust bearing
Pl comments and the wear pattern
RE: frequent failure of motor thrust bearing
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(2B)+(2B)' ?
RE: frequent failure of motor thrust bearing
1 - it looks like a track right down the center, which would correspond to zero axial load.
2 - there are many whitish marks on each side of that center load track. Not sure what to make of that. Either frosting from severely degraded lubrication or perhaps denting from many particles in the lubricant. Speculation: if lubricant severely degraded it may be result of overheating but if foreign particles present they would be result of rubbing/movement of the clamping faces against the outer ring
3 - brown stains generally signs of lubricant overheating although doesn't look that sever. Would like to look at all signs of possible overheating together (the whole bearing).
It's tough to tell from this angle whether we're looking at a segment of inner ring or outer ring.
Any other views available?
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(2B)+(2B)' ?
RE: frequent failure of motor thrust bearing
Study the attached photo screen shots. Tell me I'm not going insane.
John
RE: frequent failure of motor thrust bearing
Because the motor has a cylindrical roller bearing on each end of the motor, it requires an additional ball bearing to hold the rotor in place during its operation.
It’s a bearing basically going for a ride.
The cylindrical roller bearings support the mass of the rotor. The ball bearing holds/controls shaft thrust forces.
About the failure, the outer race of the cylindrical roller bearing “hammered” around inside the bearing pocket/bracket (that it does not belong in)
because the fit was too loose. And also because it was free to slide back-n-forth on its inner race.
One other point: The manufacturer of the motor came up with a shaft journal dimension tolerance that’s acceptable for both styles of bearings.
For typically, a cylindrical roller bearing has a slightly tighter shaft fit requirement than a deep groove radial ball bearing.
Bearing housing fit tolerances for both styles of bearings are normally identical.
I'm going for a bike ride. Have a nice evening,
John
RE: frequent failure of motor thrust bearing
The bearing which you have pointed it's ball bearing please check section drawing
RE: frequent failure of motor thrust bearing
RE: frequent failure of motor thrust bearing
Thanks again.
Bill
--------------------
"Why not the best?"
Jimmy Carter