OT commutator wear

"Robert Nichols" wrote in message news:f5ppq3$i87$ snipped-for-privacy@omega-3a.local...

How in hell has that bit of information escaped me? It was shocking to read it----and rewarding to explore the reason(s). I'd say it makes sense now that we've kicked it around a little. Thanks to all for the enlightenment.

Harold

Reply to
Harold and Susan Vordos
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One of my clients has a big double sided 24" disk sander. I installed the 3ph plug inside a guard cover, which..got removed for some stupid idea they had, about a week later.

3 weeks later they called me and asked me to come check the sander and the outlet..the outlet seems to have Exploded off the wall.

Found the burned remains of the 3ph Hubble outlet filled with sanding debis (they use it to round and deburr the ends of stainless steel bars)

I commented to the Viet who was running it at the time..it must have made a pretty good flash. He blushed and said he shit his pants when it happened. Seems they had been doing some aluminum too..so the fines mixed with the stainless steel fines and when it all built up and shorted....FLASH!/BLAM!!

I moved the box and outlet about 8 feet down from the sander, put new guts in it and replaced the guard cover. A year later..the cover is still there......

Gunner

"Abortion is self defense" Bob Kolker

Reply to
Gunner

Aluminum oxide does not? Bob

Reply to
Bob Engelhardt

On Tue, 26 Jun 2007 05:38:34 GMT, with neither quill nor qualm, Gunner quickly quoth:

Is the brown stain on the floor still there, too? Great story.

The last outlet I saw go up like that was a 50A 240v circuit in Engineering at Southcom, Int'l. back in the 70s. I was testing power supplies and forgot to kill the feed once. As the second lead came loose, it hit the first one via the screwdriver and I had an instant arc welder. Before I could react, the whole Engineering Dept was down. I blushed in my shipping/receiving dept for two weeks after that one. I think it was about the 25th one I'd done that morning and I got careless. I regained my sight a few minutes after they restored the breaker.

- Metaphors Be With You -

Reply to
Larry Jaques

Hey Bill,

Not quite sure what your application would be for one of these that a solid-state inverter would not do as well.

What you have shown in the bottom 80% of the photo is a set of copper slip-ring commutators, although no brush gear is shown. Slip rings are associated with AC applications.

In the top 20% of the photo you can see just a small part of a copper-bar segmented commutator, normally associated with being used in a DC circuit, although fairly common in AC use too when operated as a "universal" motor such as a drill-motor.

It is hard to determine physical sizes in the pix, but I don't understand why they would use copper slip-rings rather the industry standard of a brass composition. Looks more costly to me, but hey!!!

In any event, the slip-rings can be worked with the proper Ideal commutator stones ( not any kind of "paper"!! ), available at any good electrical wholesaler, or electric motor shop.

and specifically see

Take my word for it that with some effort quite a deep surface flaw can be removed with these stones in a graded-step fashion. The slip-rings are not as "fussy" as the segmented type, and really just need to be round and smooth, so you may be lucky there and able to stone them back to shape.

I'd be more wondering as to why it has happened. You say that there are two brushes per holder per slip-ring (totals 2 pair????), but although I see the white plastic, I can't see how they assemble or mount. But I do see that there is quite a good looking part of the slip-ring where they could (should??) track. In fact, I wonder that the assembly didn't put the brushes tracking in the centre of the ring face. It is also interesting that BOTH the slip-rings have a similar poor commutation wear pattern visible as a dis-coloration. I wonder why that is? If I am correct in what I read in your note, I assume that the brushes are in parallel (physically). I wonder if you could mount them in tandem somehow?

Is there much "end-play" allowing the rotating element to move back and forth under dynamic loading. I don't think there should be more a that a few thousandths, as the Redline specs say the units can be mounted in any position.

Take care.

Brian Lawson, Bothwell, Ontario.

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Reply to
Brian Lawson

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