I just have to ask this, If fluting is caused by electrical discharge why are there no burn marks in the bearing...

Mike,
This is just my opinion and I could be wrong but electrical fluting is a steady flow of current and not a arc like static discharge. It occurs in the load zone where the shaft, rollers, and outer race are in contact. I think the lack of an arc is why there are no burn marks and the steady flow acts like electrical plating on the outer race causing the ripple effect as the balls roll through the load zone.
I hope someone will either confirm my thinking or give us a correct answer.

Just my thoughts,
Ronnie

that was kind of my thinking ronnie. as the balls never lose contact there should be no arc.
thanks
Mike

Electrical fluting is sometimes called "electrcial discharge machining".

I don't know for sure what is really going on, but I associate the word "discharge" with something similar to an arc although perhaps on a smaller scale.

I imagine that the discharge does form intense localized high temperatures which I believe may be involved in melting the metal in very small areas for very small periods of time. I picture that is what leads to the visible patterns that we see.

But if that were true, then what about Mike's question - why isn't there black/brown from decomposition of oil products in the area? Hmmm. Beats me. Maybe you guys are right and it's not arcing - but then why do the call it EDM and what causes the pattern? More questions than answers.

I always believed the diference btw. the patterns found in DC drive related fluting, black bar code like marks and the matte finish and weak patterns on the surface found in VFD related fluting was connected to the frequency of the current / arcing. VFD "arcing" would then be at hi or very hi frequency and then mimic the procedure used in arcing machines that produce moulds and tools. I have never worked with such machines so it´s just my view of it. Olov

Mike,

Fluting is caused by very small electrical arcs. Before the fluting occurs, the bearing surface (usually in the load zone) gets a "frosted" look. This is caused by millions of tiny arcs. If you look at the bearing surfaces with a microscope, you will see tiny arc pits that do have burned areas around the pits.

John J

The fluted bearings that I've seen from VDF motors have 'machined' marks that run across the outer race, i.e., "normal" to the bearing track, and spaced very evenly. Why is that?

Rusty,

I don’t know, but have heard that as the arcing process continues to etch the bearing surfaces, the internal clearances increase allowing the balls or rollers to bounce. As the rolling elements bounce, they arc causing the ripple pattern. The more consistent the speed of the motor, the more pronounced the ripple pattern is. If the motor speed constantly changes, the ripple pattern is less likely to occur. Makes sense to me, but doesn’t mean it is true. I have seen bearings on DC motors with extreme etching and excessive clearance in the bearing with no ripple pattern.

John J

I'd like to add my opinion to all of those others who are not really sure

The way I understand it (very little knowledge of electricity here, be warned) the current actually must pass through the oil film which created a gap in the path that must be arced over. Normally, this oil film is very thin so it takes a low potential to make the arc, so the damage is small, like the frosting described. If the distance across the oil film were greatly exaggerated, it would require a much larger potential, the arcs would be much bigger and bluing, pitting and other evidence of arcing would be large enough for us to see. I also think that the evidence on the smaller scale that we see normally is machined away by the normal action of the rollers in the races.

We have some motor designers around here, I wonder if Marko Leo is listening.

This paper on CSI's website may help to explain some of the questions.

http://www.compsys.com/drknow/aplpapr.nsf/06b6f5a4de2ea...062f412?OpenDocument

If there is no arc, why is the grease burnt?