Alnico field re-aligning question

[MR COFFEE]

Hi all,
I've got some narrow alnico magnets 3/8" x 1/8" x 4" that are magnetized along the length that I'd like to re-align and magnetize across the width for use in some pickup experiments.

I have tried putting them in between pretty powerful and large 1-1/4" square by 5" long in a vise, and they do seem to at least partly re-align, although when I open the vise the ends tend to stick to opposite sides of the magnets on the jaws which I assume indicates the magnets are only partially re-oriented magnetically.

So does that mean I probably need to heat them up to the curie temperature and put them in a magnetic field oriented across the width as they cool down? Or will getting them hot enough alone make them non-grain-oriented and I can just magnetize them with my vise and magnets after they cool down?

My wife is a potter so I have access to a kiln. Is that the way to go, or just use a propane or map gas torch?

Will the alnico surface oxidize enough to cause a problem. I suppose I could put them in clay if that would be a problem.

I think the magnets are alnico 2 or 3, but they might be 5. I got them surplus and really don't have a way I know of to determine what they the composition is. (Maybe somebody knows a way to tell?)

As you can probably tell, I'm a babe in the woods about this, so any help and education, experience you may have, etc., would be greatly appreciated.

Thanks,

mr coffee

[David King]

I know I've read about this somewhere on line but I can't remember if it's the molten billets that are hit with a strong field to reorient the actual crystals or if that all happens as it gets down to the Curie point which IIRC is around 1600ºF. It might need to happen twice.
There's a little bit about it on the Duramag website:
Alnico Magnets- Technical Information - Dura Magnetics, Inc.

Wikipedia has more detail:
Alnico - Wikipedia, the free encyclopedia
It looks like the field has to be applied as it cools between 900 and 800º C.

[dor baruch]

yes you need to heat the magnets to between 800 and 900 C.
and applying an external magnetic field + Leave the permanent magnetic field Until the alnico is cool
good luck

[MR COFFEE]

Has anybody ever done this?

Any ideas on heating the alnico and how to set up the external magnetic field for it to cool down in? Torch? Kiln? Spacers to keep it in between the big permanent magnets?

[J M Fahey]

Sorry to rain over your picnic but I guess such stuff can be only made in the very specialized ovens used by magnet factories.

[Steve Conner]

I see a problem getting the Alnico magnet hot enough while keeping the neo magnets below their Curie temperature which is about 300 deg.C. You can't just whack the whole assembly into a furnace, you'll have to get the red-hot magnet out and hold it between your neo magnets while it cools.

[the great waldo]

A couple of ceramic tiles covering the neo faces should be enough to dissipate the heat, methinks ! But you'll have to be quick with getting the alnico between the neos.

Cheers
Andrew

I see a problem getting the Alnico magnet hot enough while keeping the neo magnets below their Curie temperature which is about 300 deg.C. You can't just whack the whole assembly into a furnace, you'll have to get the red-hot magnet out and hold it between your neo magnets while it cools.

[David King]

You'll also want the alnico to cool very slowly, I'm sure they use electromagnets to align the field since they won't be affected by the heat. Neos are very sensitive to heat, they'll loose their charge well below 300ºC -more like 80ºC. You would need to cool them with water jackets while keeping the alnicos hot with a controlled flame. One of those IR laser temp guns would be handy and then a PID controller for the heating/cooling of the alnicos. I'll bet they use an induction furnace.

Read all about neos and heat here http://www.kjmagnetics.com/blog.asp?...dymium-magnets

[MR COFFEE]

Thanks for replies, all.
Looks like my big magnets, which are ceramic (not neos, AFAIK), definitely can't go in the kiln either. The putting ceramic tile in between the big ceramic mags and the target magnet idea makes sense to me. I can magnetize them further after they have cooled down, right?

Has anybody tried heating alnico mags with a torch to curie temp? Or am I in unexplored terrritory here?

Thanks for sharing any experience here. Rain on my parade is OK, too. Just trying to find out what is possible.

[Joe Gwinn]

The final bit of rain is to observe that alnico magnets cannot abide too short a magnet, so going across the bar (versus along the bar) may yield a magnet that cannot hold its charge.

[MR COFFEE]

Joe,
So a narrow alnico won't be stable even if I get there??

Has anyone tried heating alnico with a torch or am I on my own here?

[David King]

Isn't a minibucker magnet about 1/8 x 3/8"? I wouldn't think the overall length would make much difference but if it does it could be segmented.
Meanwhile Mr C could just go out and procure some minibucker magnets and save the mapp gas in the short term.
I think we would all have a morbid curiosity in seeing what happens when a red-hot magnet is cooled in a strong field, so video tape it if you do try.

[MR COFFEE]

Nice idea David!
Maybe I can get a friend to video it.

Sounds like nobody around here has fooled around much with the curie temp. My wife's going to do a pottery firing, I may just stick a couple in her kiln and see what happens - no magnetic field to cool down in except the earths, and the heating elements will act like a de-guasser. Wish me luck talking her into letting me stick them in. <grin>

[David King]

You may end up with un-oriented magnets which should work better than ones that are oriented incorrectly.

[MR COFFEE]

Is unoriented bad in terms of pickup magnets? About holding a charge? I don't need maximum strength.