What causes electrical fluting symmetrical pattern

Rick,

I asked a similar question about the mechanism that machines those nice even grooves a couple of years ago.

Try a search and you might find your answer in that dscussion.

I suspect epete will haven the correct explanation. I'll give my best guess. The capacitive effect builds up a charge and when it gets high enough to overcome the insulation, discharges. Velocity is constant and the pattern probably reinforces itself as it progresses.

Thanks for the vote of confidence, but probably not waranted in this case.

We did have a previous discussion here:
http://maintenanceforums.com/e...20929863#77220929863

My contribution was in attaching an excerpt from a book (attachment 24 February 2012 03:22 PM) which provides an explanation that sounds.....well, "technical".. as if the author has studied it a lot. Whether it is correct or not beats me.

There were some other ideas thrown around in the thread as well.

It is a subject that was also discussed recently on eng-tips and if I recall the guy named skogsgurra (whose is quite familiar with vfd and fluting) had some ideas that should carry some weight based on his background.

Here's our earlier discussion:

http://maintenanceforums.com/e...20429863#19320429863

I'd go with Ron Brook. He was there when they invented electricity.

Danny,
Now there you go insulting Ben. Next time I am in center city, I'll go by his grave and tell him you didn't mean it. You know what thin skin us Northeasterners have!
By the way, the thread you have suggested to him is a good one.
ep hit it hard.
I like to think the symmetric pattern on non-VFD applications is primarily due to the tight specification we have for the frequency of our electrical power. The charge cycle is going to be based on that frequency, so it makes sense that non-VFD EDM will be very symmetrical.
Ron

Here's another link to throw into the mix:
http://www.skf.com/binary/12-6...Handbook-6230-EN.pdf

quote:

The fluting results from a mechanical resonance vibration caused by the rolling elements when rolling over micro-craters.

That is similar to ideas mentioned by some in the other linked thread.

I'm not sure I can wrap my head around why the result of microcraters from electrical sources would end up so much different than micro damage from other causes (you don't see fluting from poor lubrication). I'd think there must be a little more to the story like what happens to current flowing through the rolling element which is resonantly vibrating as it rolls over the microcrater.

I'm not disagreeing with anyone, just haven't landed anywhere that makes sense to me yet.

Me neither, Pete.

I still don't understand what does the "machining" for lack of a better word.

What serves as the cuttng tool?

As described to me in the VFD case it is pure electric as the arcing is doing the same thing as in the type of arc machining does, the arc move material, very little at a time but many times not that it explain the sync pattern. In the DC drive case it looks more like welding like "real" arcing action and it get black and dirty, still you have a nice sync pattern like a bar code. Since speed vary in all those cases it must be a rotation synced behaviour? Olov

Had trouble wrapping my head around that one as well until I found a page in a Rockwell/Reliance paper. I have attached the plot to this response.
The phenomena requires a build up of voltage on the rotor/ball until it reaches a potential where it can now jump the capacitance/inductance that is represented by the oil film. Remember, if the ball never lost contact with the races (very low speeds), there would be no potential build up, there would be no EDM. It takes place only after the balls are riding on the oil film.
A ball that is riding on a damaged (spalled) area continues to ride that area regardless of what the voltage and current are doing.
The key to what happened in this data is the very center of the graph. You can see the shaft voltage charge up, then again, without a safe level discharge to ground. The next charging cycle is over 30 volts and this is sufficient to jump the oil barrier and cause a 3 amp current spike. It is this current spike that takes the bite from the outer race. Repeat this process over and over at a fixed frequency and the result is perfectly even grooves. Have this happen with variable speed changes and the grooves are not so symmetrical.
Ron

Oli,

Thanks for clearing that up and including the difference between AC and DC effects.

Ron,

Even clearer. Thanks.