Ball Bearing Failure 4

[replica]

Dear all,

Any idea what is the possible cause of the failure of this angular contact ball bearing? Attached is the photograph of the ball bearing 14 out of 15 balls have the similar pattern on the ball with the initiation site at the center and propagate radially like fatigue striation. The outer and inner raceway show microcrack and spalling but not as severe as the ball. They are 1 inch ball bearings.

Note: Why I could not upload the file...why doing this ...this statement came out.

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Anybody can help me...

Regards,

Happy New Year...

 

[replica]

Dear all,

Thank you very much for the comments and I am very sorry for a late reply as I was on a long holiday....

Tmoose,

Our bearing type is is 7220 MN MBR SU ,,,Single row angular contact light, 100mm bore, Angular contact low shoulder (both) 40 degree, Machined Bronze retainer , Flush ground, control clearance for duplex mount single package.


Pictures of the races and bearing separator/cage would be helpful.

Please find attached picture of raceways and cage.

Usually angular contact bearings exist in pairs, or even 3s and 4s.

This is with code 72..single row angular contact light that only can handle thrust at one direction..and not duplex.

Please Post pictures of the other bearings, and the housings and shaft as they were disassembled, and after being gently cleaned

How are the bearings >> supposed<< to be lubricated ?

It is lubricated automatically and filtered for any particle as the bearing is no accessible during operation as it a part in RGB.

In the first picture there is debris on the blue towel. If that came from the ball, I'm thinking the lubricant is charred or has turned to varnish.

The debris on the towel is from other part and not from the bearing.

And the ball looks quite dark, like things got pretty hot

It is not dark but due to the reflection. No sign of overheating and corrosion. However it has dark circumference..seemed like propagating from the centre as I mention earlier. When we did EDS analysis on this region we found silica, copper and aluminium, oxygen and carbon....Just I am figuring out from where these has come from...especially copper and aluminum...

What is the machine history?

The bearing is used for one year after replacing new RGB (reduction gear box). The indication after replacing this RGB was high vibration ...The bearing is at the output shaft used at the RGB...used in alternator.

 

[Tmoose]

Hi Replica,

The bearing manufacturer's name is still witheld.
What is operating rpm?
With a 100 mm bore I'm guessing relatively slow.

"Filtered" sounds like some kind of oil lube. Constant flow, air-oil, oil mist. I'd be checking for actual flow delivered to the bearing.
Are there any shut off valves or switches that could accidentally be off/closed while the machine was in operation? Some operators would have a hard time confessing to making such a mistake.

If any of the oil lines are exposed they might be vulnerable to damage that could limit flow.


I'm still not clear about The condition of the other bearing in the duplex pair. Did the pictured bearing suffer alone, or did both bearings die together?
Is the bearing shown in a position to be subjected to primary thrust loads ?

Cage/retainer wear is often a sign of inadequate lubrication.
BARDEN and SKF both list machined brass/bronze cage materials having max levels of Fe as 0.3% and Aluminum just .05% max.
Cage wear could conceivably liberate some iron or aluminum I guess.