new motor getting overheating

[Al-Wazeery]

Hi expert engineer,, could you please help me for my issue below :
We commissioned a new pump with new electric motor (315 kw, 546 A, 2985 RPM, 50 Hz), but we have get rising in temperature (overheating) in the MTR DE bearing crazily during first four hours reach to 107 °C, so we stop the motor immediately and the problem still come after run the motor (for two days), so we have decided for opening its shield bearing housing cover (single type) to inspect bearing greasing (proper initial quantity , proper distributed, over greasing or lack of greasing), but we found the bearing greasing well also the initial quantity of grease good also,, for satisfying we have greased the bearing by hand in the some gaps between the balls, after that we run the motor again ,, but the rising of temperature problem @ bearing still (same as before). We have check motor vibration and bearing shock pulse by spatial device we found the motor in perfect condition (max vibration reading reached to 1.8 mm/s and Carpet value -5 & max value 4)

So your help required plz to solve this issue and my questions:
1. Is this rising in the temperature normal for new motor? (Bearing type TKN 6317 C3).
2. Are there other reasons than those related to greasing?
3. Are there any related to motor Hz in bearing overheating ( max. Hz reached 46 Hz )?
4. Practical solution for solving the problem

 

[Al-Wazeery]

I mean by shield bearing housing = housing cover
and spacer rim = bearing stopper ring side face

 

[Al-Wazeery]

Are the motor Bearing Clearance Class caused bearing overheating in sometime Or Not?


In other words, If I have bearing C3 ,then I want to change its clearance class to C4 ,, Is this effective to reduce the bearing temp. If I know that the cause of overheating is due to this class???

 

[JJPellin]

No. I would not expect the bearing class (C3 or C4) to explain the overheating. The note about removing some material from the spacer ring seems to me to be the key. I would suspect one of two potential causes:

The bearing which is overheating is being crushed axially within the housing. The fixed bearing needs to be constrained from axial movement. But, it should not be axially crushed. I am not a motor expert. But, we would normally want this bearing to have 0.002 to 0.004 inch axial clearance between the outer races and the housing.

Both drive and and non-drive-end bearings are fixed axially. Thermal growth of the rotor in service is overloading the bearings in thrust.

Johnny Pellin

 

[Al-Wazeery]

Regarding to axial gap/movement there is enough gap available for free movement,,, we have run motor solo, but the problem still ??!!

 

[Al-Wazeery]

if we run motor solo, no way to say there is thermal expansion there .. is it right?

 

[JJPellin]

Even running solo, the motor is pulling amps and generating heat. As I understand it, the bearings heated up more slowly running solo and did not get as hot. But, they still heated up. Is that not correct?

Johnny Pellin

 

[Al-Wazeery]

Yes,, that was our wondering,, you know motor ampere was 15A during solo test

 

[32c4]

Hi
What I understand ,I think the problem reside in many points that you have to verify.
- quality & ORIGINALTY of the bearing.
- seals shaft contact .
- grease quantity and type and if it is not mixed.
- type of cooling fan of the motor
- alignement

 

[Al-Wazeery]

Many Thanks (32c4) for your replied,,

Regards To :
(1)& (2) We have replace the old bearing by new one (SKF) & New shaft contact seal before a few days,, Problem Still.
(3) First we have working with recommended grease Mobilux EP 3, problem still ,,, then we use Mobilith SHC 100 spatial for higher speed bearing applications, such as electric motors,but problem still,,
(4) built in cooling fan (fixed with shaft)
(5) Alignment is perfect , no high level vibration (all readings under 1 mm/s),, also we have run motor in each time with solo (uncoupled), but still the problem !!!!!

wondering issue!!

 

[Tmoose]

"New shaft contact seal"\
Is the contact seal part of the OEM motor design?
What is the OEM seal number, and what is the number of the replacement seal?
Is the cavity between the seal lips being well greased at installation?

Do you have special requirements making a contact seal necessary?
Typical Contact seals have a service life measured in 1000s of hours.

I am assuming the shaft diameter under the seal is about 2.375" or 60 mm.
3000 would result in a surface speed of around 1900 fpm (15 m/s), which is below the very general limit of 3000 fpm for A typical seal design in NBR material.

I'd remove the contact seal and run the motor solo to see what temperature results.
I'm expecting the temperature to stay low.
If so, I'd work with the OEM to reconsider the true sealing requirements, fully expecting to go back to a non-contact seal design, perhaps with an additional flinger. Options also exist like removing the garter spring from the well lubricated contact seal, substituting a Forsheda V-ring , or even ( grrr ) bearing isolators.

 

[Al-Wazeery]

Hi Tmoose,, thank you for your help & reply,,

1- Is the contact seal part of the OEM motor design?
Yes the contact seal part of the OEM motor design , its number (H218 ID 85, OD 110, TH 12 )
2- Is the cavity between the seal lips being well greased at installation?
I'm not sure I contact my partner, He was there that time.
3- Do you have special requirements making a contact seal necessary?
No

4- shaft diameter 85 mm

So, now we will check the cavity between the seal lips being well greased at installation OR NOT!!
And we will remove the contact seal and run the motor solo to see what temperature results!!

We will see ,, hope good result
thank you again

 

[Al-Wazeery]

ear All,,
Hi Tmoose,,
First of all we inspect the shafts for both direction after dismounting the bearing shield housings,, we found some marks on the shafts under due to lip seal friction,, (see pic attached)
we have run the motor solo w/out motor cooling fan & bearing shield housings with its seals. It is clear from the all readings of temp. (max. reading was 50 C for one an hour),, the temp. of both DE & NDE bearing is NORMAL..with it without cooling fan..

@ Tmoose,,,
you suggest to us :
1- To reconsider the true sealing requirements
2- OR go back to a non-contact seal design
3- OR removing the garter spring from the well lubricated contact seal and we see the result
But what do think ?

Our lip seal (H218 ID 85, OD 110, TH 12 ) contact type

thanking you all