High bearing temperature

[migueldiazch]

Hi;

I am having bearings high temperature problems. The machines are GE electrical motor Model 5KS447SS146D8, Horsepower 200 HP, Frame 447TS, 3 Phases, 3570 RPM, 460 Volt, 60 Hertz, Enclosure TEFC, Insulation Class F, Bearing DE/ODE 6314ZC3, driven two Sulzer 9 stage centrifugal pump size 3x4x8.75A MSE
These motors seems to run since star up (about 6 years ago) with high DE bearing temperature over 200°F and max. 208°F (measured with a infrared thermometer), causing premature bearing failure, we lubricate with Mobilith SHC 100. Running the motor with no load the maximum temperature found was 136°F after 2 hours running.
We have done several test and we have found nothing abnormal.
1.Check current and voltage with no load and load.
2.Check alignment motor-pump, inspect coupling condition, coupling hub distance, motor shaft runout, even tough there were no high vibration condition.
3.Replace bearings, check over/lack lubrication condition, check bearing outer race/motor bearing housing clearances and bearing inner race/shaft clearances.

Could you please tell me if I am missing something?

Regards.

 

[romke]

The temperatures you mention are somewhat high, but not that high that the grease mentioned would run into problems.

To have a clue to what exactly is the problem, i have some additional questions:

what relubrication interval is used?
what bearing life do you get?
are the motors heated by ambient temperature or nearby hot equipment?

as a general rule of thumb you may assume that with each 15 deg C above 70 the relubrication interval should be cut in half. in your case that would mean shortening it to a quarter of the original interval specified. allthough given the type of grease used that seems a bit too short.

another point to watch carefully is the amount of grease that resides in the bearings. if new bearings are mounted, how much of the available space is filled with grease? 50% or less seems to be appropriate - most bearings are overfilled and that can play a big role in overheating. and if relubricating - how much grease is put in and what happens to the amount the bearing is then filled?

 

[Tmoose]

Looks like a boiler feed pump.
Does Sulzer provide hot and cold alignment specs?

what kind of coupling? Is that what came with it OEM?
Is the initial axial setting arranged to provide plenty of axial growth capability in the "right" direction?
Among other things I'm wondering about the axial expansion capabilities, since the uncoupled the DE end bearing ran so much cooler.

Can you get demodulated or Spike energy type readings on the DE bearing housing at running temp?

 

[rmw]

I gave mechanical answers over where you double posted this in the electrical power forum.

rmw

 

[PaulvdH]

- What type of sealing do you use?
- is the radial clearance sufficient?
- what is the failure mode: due to high temp bearing is failing or due to lack of grease, temp is going up, causing bearing failure?

----------------------------------------
Paul van der Heijden
Composite Engineer
Vekoma Rides Manufacturing BV
Internet:

http://www.vekoma.com

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[migueldiazch]

The information that I got was that in the past the motors were running with DE bearing temperature over 200°F. The last maintenance was done because of the temperature and not because a bearing failure.

The relubrication interval used is 6 months.
There is not hot equipment nearby.
The coupling is Rexnord No. 300 Series 71.
IOM Manual do not provide hot alignment specs, but we have ran the motor till operating temperature and then we have checked alignment.
Pump axial clearance were between specs.

My concern is that according with API 541 bearing temperature shall not exceed 200°F.

Thanks for you participation

 

[chief]

Where are you sourcing your bearings. If they are SKF ensure the OEM are USA, Japan or Germany. Other manufacturing areas do not have the same quality in the metallurgy of the races, even if the part no. is similar.

Offshore Engineering&Design

 

[JJPellin]

You list the same bearing for both ends of the motor. One of them must be set up as the fixed bearing and the other one as the floating. We have seen problems with this arrangement with two motors. One of the motors was set up with the fixed bearing on the non-drive end based on the original installation which used a greased gear coupling which had a lot of end play for changes in DBSE. When the coupling was converted to Thomas Disk Pack, the DBSE had to be adjusted for substantial axial growth of the motor shaft. The other motor that gave us problems had been repaired and the repair shop had accidentally fixed both bearings. The bearings ran not (both bearings, I think) because there was no allowance for axial growth of the motor rotor. I would verify the arrangement of both bearings. It would be preferable if the motor manufacture allows for the option to fix the drive end bearing and direct the growth away from the coupling to minimize the required pre-stretch.

The last big Sulzer pump I installed also had an axial growth problem. The inboard was supposed to be fixed, with the outboard keyed for axial growth away from the coupling. The outboard was incorrectly locked down and not allowed to grow properly. If this occurred, there could be problems with DBSE and alignment (internal and across the coupling). Verify that the pump growth is properly arranged.

Depending on the temperature of the BFW product, the alignment offset could be significant. Even if the vibration is not showing clear indication of misalignment, I would verify the predicted thermal growth for vertical cold alignment. Take temperatures of the pump support pedestals in service and calculate the growth from ambient. Compare this to the OEM predicted thermal growth. Adjust the cold alignment targets if necessary. The OEM predicted growth may not be correct for your installation. The growth depends a lot on the presence of any insulation and ambient conditions (in a building versus out in the wind). Look at the coupling under normal operating conditions using a strobe light to check for wavy shims indicating distortion from axial growth or misalignment.

Inspect the coupling carefully. This style of coupling has a thin lip to create a rabbet fit between the center member and the hub. If this lip gets damaged, it can fold over into the joint and produce a potential for vibration or excess forces on the adjacent bearings.


Johnny Pellin

 

[Tmoose]

spec show +/- 0.085" axial capacity

http://www.delzer.com/rex/2000.pdf

I'd use a strobe light to check axial position at full operating temp

 

[NomLaser]

Can you describe the type of premature failure? Could the failures be due to a shaft grounding issue? If your shaft isn't properly grounded, it can cause pitting and premature failure of the bearings.

 

[NomLaser]

I also agree that, while the temperature is high it doesn't appear to be high enough to cause issues with the grease. I have worked in the brushless AC motor/generator side for a couple of years and our heat soaked machines would run in the 135C range. (these weren't the typical brushless motors though)