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Oh my gosh, we just discovered magnetic aluminum

S

SDConcepts

Stainless
Joined
Mar 1, 2007
Location
warren, mi
and were not even using one of those special aluminum magnets. our scrap guy is complaining and won't take our aluminum milling chips any longer since they are magnetic. is this pretty much the standard for getting aluminum bar in this country? we aren't even using chinese metal, so i'm pretty floored as to whats going on here. my scrap guy told me to pitch it as he doesn't want it, so i know he's not screwing me, plus i've been dealing with him for 3 years now.


whats a guy to do? i can only assume that this wears out tools faster as well and i'm paying more per lb but getting less actual aluminum.
 
Must have been a bad batch, perhaps? Do you have the analysis certificate for what you've been buying? You might have to have a chat with your supplier.
 
I will have to dig through the certs to find out what we got or supposedly got. i am assuming there is no way that using carbide end mills on aluminum could possibly impart a magnetic charge to the particles unless there was metal transfer. but for that to happen i would expect my endmills to eventually disintegrate and my parts to be out of spec.
 
Everything seemed to stick to our metal guys magnet.

They kept it coated in oil so that it would pick up everything, plastic, sawdust, non magnetic stainless, aluminum, brass, copper. And then "sorry, I can only give you 2cents a pound for that, its got steel in it".
 
Mebfab said:
Carbide doesnt stick to a magnet
Click to expand...


Yes it does, quite a lot actually, take a decent rare earth magnet and try it.


As to aluminum sticking to a magnet, haven't yet seen that happen.
Seen small titanium chips stick to magnets but it was mostly just because they seemed to pick up a charge and it would only do it once.

Did you run a good magnet over the chips yourself to see what the deal is?
Never trust a thing any scrapper says, just like they think stainless isn't magnetic...
 
Neodinium magnets can create enough Reverse EMF (electro-motive-force) to pull a piece of aluminum when it's passed by closely. In other words, the magnet can impart a reverse current which develops some polarity in the aluminum making it another magnet. It only lasts until the motion is stopped.

I don't know about a static lift though. If they lift the aluminum quickly it may follow.

I think the Scrappers are trying to get away with something here. Maybe you can find a standard magnet you can use to show them you know what you're talking about. Then you could tell them to go pound sand! And that you will do business with honest people only, and then point them to the door.

Please check this out. :)


YouTube - Magnetic Drag Force,

Regards,

Stan-
 
Eddy currents are one thing, and aluminum isn't the only metal that it does it to but its strength or effect varies with the composition/alloy etc. It does nothing over a straight pull off the face and won't cause actual sticking. The real fun is in trying to eliminate the eddy currents, or managing them so things don't melt/cook themselves. Kinda fun when you're burning around 20-50kw to overcome that alone ;)
 
my scrap guy told me to pitch it as he doesn't want it, so i know he's not screwing me,
Click to expand...

Seems most didn't bother to read this statement?


Carbide doesnt stick to a magnet
Click to expand...

Yeah - well tell my magnet that! Good grief - recently I sorted a bunch of carbide and tossed the inserts in one bucket and the mills/drills in a nother. Then - just to dbl check my werk, I grabbed a mag and ran through it. I never found a tool that didn't stick! :eek: :bawling:

Well so much for THAT quick dbl check. :rolleyes5:


Please check this out. :)


YouTube - Magnetic Drag Force,
Click to expand...

That's pretty kewl! I have a chumm that was working in ND Testing and talked on Eddy Current, and I have browsed past their show on TV (Ed, Ed, and Eddie?) but didn't know much about it. Seems maybe the Cartoon Netwerk actually has some decent stuff on - other than Scoobie Doo eh?


--------------------

Kant wait to hear the end results on this eppisode!
Ox
 
i know we didn't contaminate the chips and even went to check the chips in the pan that we just got done machining. this is not the first time we are getting dinged for it. i figured the first time we contaminated them so let it go. this time i was in disbelief so we checked it and sure enough, the aluminum chips are sticking to the magnet, and yes it was my block magnet that was clean that i use to hold prints to the side of the machine enclosure. i was even able to pull a chip away from the magnet and let go of it and it went right back to the magnet. its clearly magnetic. now its not all the chips but enough of them to cause my scrap guy to complain. oh and btw i'm not going to sort through them that would just be crazy.
 
Ekectro Magnet

The scrapper is using an *electro*magnet on his crane--right? If so, that magnet has a large alternating current running through it. That alternating current causes an alternating magnetic field which could easily induce eddy currents in aluminum scrap that would cause it to stick to the magnet.
If you test the same scrap with a neodymium magnet it will not stick as the magnetic forces are static. The electromagnet is causing a moving magnetic field much like the moving magnet causes eddy currents in the You tube demo. I am guessing that the larger the aluminum chips are the more efficiently eddy currents could be induced. And the cleaner they are the more conductive they are from one chip to another and the more efficiently eddy currents could be induced.
Steel contamination from the cutting tool of sufficient quantity to induce magnetism is most unlikely.
Denis
 
Just to throw some additional considerations into the mix, you might also want to think about having a Geiger counter around the shop these days. If you're getting iron mixed into your aluminum, who knows what else may be in there....
I worked as a research machinist at a major university medical school for a couple of years, and we found having a Geiger counter invaluable to be able to screen equipment that was brought in for repair, especially centrifuges that had been holding samples containing radioactive iodine when there was an "incident". Info was never volunteered by the centrifuge users.... It's also handy for screening items from Harbor Freight.
 
Other than the "peddlers Post" up front, our scrap yard has radiation towers that you pass through at the scales.

Same at any border crossing. (At least they doo in the Soo.)


-----------

Think Snow Eh!
Ox
 
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