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.

 

[edison123]

How do you define premature failure ? What is the MTBF ? 208 deg F (= 98 deg C) is not that high for anti-friction bearings if you use high temp grease. Mobil makes such high temp greases.

 

[eyec]

did you happen to notice and scoring or pitting in the bearing races?

Steven C
Senior Member
ThirdPartyInspections.com

 

[rmw]

It looks like you have the right grade of grease but is it the type and grade that the bearing mfg (not the motor mfg) recommends? If they recommend a lithium based NLGL #2, it looks like the Mobilith SHC 220 might be suitable for your use too.

Bearing grease has to flow into and out of and around the bearing in order to lubricate and cool it and be able to be displaced by new grease once the oils separate from the soaps. Is there a place for the displaced grease to be pushed from the bearing cavity other than through the seals?

Many make the mistake of putting "high temperature" greases, meaning greases that are designed to be tacky and stay in or on high temperature surfaces like furnace parts; I am talking about temperatures much higher than the range you are describing into their bearings and wondering why they blue the bearings while still having lots of fresh grease in the cavity. Been there had that pulled on me; had to deny the warranty claim.

Overfilling the grease cavity can cause overheating too. Does the pump have its own thrust bearing? Is the coupling solid or gear type? (I am trying to rule out pump thrust being imposed on the motor DE bearing.)

Is the pump service hot such that heat is transferred along the shaft to the motor through the coupling, or radiated to the motor or could the pump operating temperature be causing the cold alignment to be right but wrong at temperature? (I suspect hot and I would look for the pump to be aligned low to the motor cold-am I right?) Are the pump bearings roller or sleeve type? What is the normal operating ambient?

rmw

 

[migueldiazch]

The grease that we used was recommended by the project engineering company. The place that grease can be pushed away beside the seals is inside the motor, we have had some experiences due to over lubrication, but the issue was corrected and in the last inspection there were no signs of over lubrication.
The pumps have thrust bearing and the coupling is Rexnord No 300 Series 71. We have check the coupling hud distance and inspected coupling shims for deformation.
The fluid temperature is 110°F and the pump is roller bearing type.

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

Regards.