New Ball bearing in 280 fr motor 2

[Feg]

Hi Guys

Can anyone shed some light on this matter. We replaced both SKF 6317 ball bearings on a 280 frame 90Kw 4pl B3 motor on pump application with flexible coupling drive. This motor has been in service for 5 years and we replaced the bearings during routine service. The bearings were purchased prepacked with grease and heated to give a nice gentle fit. The chamber had the old grease removed and was 2/3 rds filled with new SKF grease. (gap as instructed to allow for expansion)When we put it back into service we gave it a quick run and then put in another 5 grams of grease. It ran fine for a few days but then began to get noisey on both ends. We gave another shot of grease and problem went for another few days and returned. What do you think the problem. Thanks for any replies.

 

[electricpete]

One would think a problem that appears only after a few days (following maintenance) and temporarily resolved by adding grease would be related to the grease somewhow.

Was the greases added compatible with the grease pre-packed into the bearing itself? Do you know both types of grease?

What is the shield configuration?

Possibility of contamination with dirt?

Less likely maybe preload was not established correctly with wavey washer.


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[aolalde]

Antifriction bearings must roll the balls on the race to work properly.
If the bearing does not have enough load force the balls will skid on the races producing noise and overheating.
As Epete say probably you omitted the axial preload spring or wave washer regularly on the non drive end. This preload will allow the balls to roll properly on the races. Check for a few mils of free axial displacement after assembly of the rotor shaft.
In my opinion, the best grease for a regular electric motor with ball bearings is a good Lithium base grease grade NLG2.

 

[Farkel]

Are the bearings getting hot? Have you used a c3 fit bearing for replacement?

 

[Feg]

Hi Farkel

No bearings are not getting hot, running at 22 degs and 19 degs C at NDE. Yes C3 was used.

Regards

 

[Mendit]

Problem to me does not seem to be a lubrication issue. Incompatible greases take a little longer to mainfest themselves. You did check the shaft sizes for the standard size (3.3472-3.3466") the shaft shoulder is equally important to be free of bumps and bruises. A bearing which is not square on the shaft will exhibit the problems you are seeing. Contamination from the housing may be a problem did you wash and flush out all the old crap. When you put in 5 grams of grease, I was surprised the problem went away, usually 5 grams in a big bearing would have no effect unless it was plugged with grease. I have seen it happen where bearings are installed and fitted OK but too much grease has jammed the balls and cage and prevented from them rotating, hence the inner race spins when the motor accelerates and causes minor damages to the inner race. This is where a wavy spring comes in to provide axail preload and ensure the balls turn without skidding.

 

[electricpete]

The reason I thought it was lubrication related is that it didn't appear immediately.

Fits, shoulder, cocked bearing, wavy washer - for none of those do I see any reason for a delay until sound occurs. But you never know.

I may be totally wrong but I just wanted to explain my thought process.

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