Spalls on Outer Race of Deep Groove Ball Bearing (NSK 6226)

[oss39347]

Hello everyone!

I'm seeking assistance and confirmation about the bearing damage we encountered two months ago.

Last April, the inboard bearing (drive-end) of one of our motors driving an air fan experienced high enveloped acceleration (as high as 9.2 gE). The problem actually started on January, when the enveloped acceleration began to increase. We already replaced the old bearing and had it disassembled for further inspection. It was found that the outer race surface had a 4 to 5 cm coarse spall, as shown in the image. I am suspecting that this was caused by Rolling Contact Fatigue.

As background, the fan is delivering combustion air for one of our Circulating Fluidized Bed boiler (coal or petcoke fired). That being said, the fan is operating in an environment full of suspended particles (ash) and moisture. I suspect that these contaminants somehow shortened the fatigue life of the bearing.

 

[Tmoose]

Accurate root cause analysis requires much more information than a good picture of the bearing outer ring damage.

How many hours on the fan?

I'd be interested in the repair and maintenance history, which might provide clues that the problem actually started way before January.
What is the coupling type, what was the condition of the coupling, and when was the last time the motor>fan alignment was checked ?

I'm guessing the fan is direct drive/coupled, not belt driven, but only you know the answer to that. Drawings and pictures of the fan general arrangement are required.

Were the spalls on the "bottom" of the race, which would be subjected to the weight of the motor rotor, half the coupling, etc if direct drive.

Oil or grease lube?
What was the condition of the lubrication in the bearing?
Please provide pictures and drawings of the motor seal design, and OEM's seal IP rating.
Had someone substituted sealed or shielded bearings for open bearings?

Is the motor subjected to wash down either directly, or from equipment on the mezzanine above?

Please post pictures of the rest of the race, and the other components.

This is a nice example of how detailed Vibration Analysis can provide usefully advanced warning of some kinds of bearing failure.