Hey fellow board members I was playing with magnets today, and decided to heat one up till it's glowing red hot(With a little propane torch). The magnet lost it's magnetic properties even after it cooled down. Why does heating it cause the magnet to lose it's magnetic force?

P.S. Yes I am a bored teenager with too much time on my hands, and an outdoor lab (I mean shed) :wink:

 

Now this is hot subject. The atoms inside the magnet act as a magnetic dipole--each having a N and S pole. Before things got too hot to handle, the dipoles were arranged more or less in one direction, so those millions tiny "N"s and "S"s formed one gaint N-S dipole. The heating caused them to collide and loose alignment. Sounds like the steering on my car. :lol: Heh heh.

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here's a FAQ about magnets: http://www.rare-earth-magnets.com/ma...agnets_FAQ.htm
It does not exactly say *why* but what you have discovered is common knowledge. I think it has somehing to do with heat altering the crystalline matrix of the magnetic material but then I'm not a metallurgist :wink:
What kind of magnet did you heat, a rare earth one or a steel magnet?

have fun,

Klaus

 

Thanks for your replies It was a rare earth magnet.

Btw I love the little disclaimer in their explanations

"Can magnets cure disease?

As far as we know, no one has definitively linked static magnetic field to the cure of any medical ailment. You should seek qualified medical assistance if you have a health problem."

Good stuff, good stuff.

So basically the added heat energy "excites" the dipoles making them attract and combine; since opposites attract. Then basically the dipoles become neutral?

 

It's a little more like a tug of war. If you get all the dipole to cooperate and point in one direction, they can exert a very strong force. When they get misaligned, they pull in any direction they like and (essentially) cancel each other out.

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heating magnets distroys them and yet they still make these useless products

http://store.weldingdepot.com/cgi/we...ot/ECM60R.html

:roll: :roll: :roll:

after a few minutes of welding, the steel heats the magnet making it useless

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Interesting, I would think that if your earth clamp gets hot enough to loose its magnetism you are doing something wrong. Like running far more current through it than it was designed to handle. Like placing it on a painted or poorly conducting surface. Like placing it where not all of its footprint is in contact with the work.

My welder came with a clamp on work lead, like those used on battery jumper cables. It also got hot and made starting the arc tricky, I soldered the crimped wires to the clamp and it worked better. Eventually replaced the clamp with a soldered cable lug which is attached to the work with a C clamp.
No more problems, C clamp runs only barely warm.
Klaus

 

My Weller soldering iron uses the Currie effect that heat causes a magnet to lose magnetism to control its temperature. The magnet "heals" when it cools and is magnetic again, so the soldering iron keps turning on and off controlling its temp. Of course it doesn't get red hot like some noobies' soldering guns. :lol:

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audioguru: I had one of the really old blue one-piece Weller stations years ago, and one new guy I was working with went crazy trying to find the source of the "clicking" sound in the lab. I let him look for quite a while before I told him it was the mag switch in the soldering iron... Was almost as funny as secretly popping a small bubble wrap bubble when someone powered up a new circuit for the first time. You never saw equipment get powered down so fast in your life.

We have several of those "magnetic squares" for welding in the shop at work, they make great grounding points once the paint is removed from them. Very handy when there is no convienent clamping point. Change one of the rivets to a lug, and you can ground anywhere big enough to stick the magnet.

Like these: http://www.magnetics.com/magmate2/magweldandclamp.htm

 

windozeuser, to further your magnetic education, try applying an external magnetic field to your demagnetized magnet while letting it cool down from the same temperatiure you heated it to when you demagnetized the magnet. If you haven't altered the basic properties of the material by overheating, you should regain some magnetism as the magnetic domains freeze into the newly magnetized orientation.

Don't know if this will work with your particular material. Specific heat-treating is part of the magnet production process, and they don't do it with a propane torch.

You will probably never regain the original magnetic strength because the manufacturers have optimal magnetizing procedures, equipment, and magnetic field concentrators for the specific magnet shape. Takes a lot of current, coil cooling, and knowledge of magnetic structure design.

Have fun

awright