Bearing Failure due to Elctrical frosting

[williamoh]

I recently examined the bearing races in motors run by a variable frequency drive. The motors ran about 8 months at 1800 rpm. When I opened up the bearing, a big ring of frosting was visible. I took SEM picture of the frosted area and observed thousands of "pits and pot holes" caused by electrical arcing. The sizes of the pits are less than 2-4 microns. I know that this "pits and pot holes" will eventually lead to fluting and catastropic bearing failure. However, I have no idea of how long it will take to get to the point. Is there anyone with some data?

 

[Skogsgurra]

There was a discussion about this kind of problems in thread237-102205 only a week ago. I think that you should check that one.

The time it takes to go from frosted to fluting (which also increases vibration level and evemtually will kill your bearing) is hard to say anything about. If your motor is running slowly, it may run for a long time without developing fluting.

Fast running motors are more prone to fluting and that is a natural consequence of the balls (or rollers) having more kinetic energy. It is this energy that "hammers" the race surface and makes the balls jump - somewhat like car wheels on a dirt road.

If this is an important drive that you cannot allow to stop unscheduled, you should change the bearings and put a shaft grounding brush, or motor filter to get rid of the EDM that is occurring in the bearing.

But, as I said, read thread237-102205 first.

 

[Tmoose]

"fluting and catastropic bearing failure"
I'm not sure how close those 2 are together. I was around a couple of pretty big motors (few hundred HP). They got real noisy, and I think they ran months before being changed. Low speed and well greased is a nice place to be if the wish is to avoid catastrophe.

A nice use for Ceramic balls, I'd say, unless that method forces a discharge problem elsewhere