Alnico field re-aligning question

[David King]

Folks here use unoriented magnets from time to time. I haven't tried them yet but I hope someone here can speak to their attributes.

[Joe Gwinn]

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

Could be. But there is no harm in trying.

The issue is the ratio of length in the direction of magnitization to the length of the full flux path (including a little iron and a lot of air).

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

It will greatly change the magnetic properties. For the better or for the worse is hard to say. But alnico is cheap enough, so just try it.

[SonnyW]

Folks here use unoriented magnets from time to time. I haven't tried them yet but I hope someone here can speak to their attributes.

I use unoriented (iso) A5 humbucker magnets in my bridge pickups, and they are nice IMO. I think they are a little less edgy than regular A5 but not as much so as A2. I sometimes use regular A5 and the other alloys too. Dennis has UOA5 from time to time at Addiction-FX, but I have had these that I use made in a special run by Allstar. It must not be too common, they had to create a part number for them when I ordered them. Also I am not sure, but from some of the information I have read that some companies A2 is also iso. For example here Technical Details » BuyMagnets - Buy Magnets Online - Neodymium, Alnico, and much more By the way this reference has some good technical info. I don't think everyone's A2 is iso though.

On the subject of the shorter magnet's stability, from reading the above technical info, the recommendation varies according to the coercivity (if I have that right) and one recommendation for A5 is that the optimum magnetic length needs to be 5x the equivalent diameter of the pole area. I am assuming that this rule is for rods, but I would think that the equivalent for bars would be roughly similar so that on a regular humbucker magnet you would want the magnetized width to be at least 5x 1/8 inch or 5/8 inch or so to comply with this rule. Regular humbucker magnets are only 4/8 inch wide, and they seem stable enough though. But I do guess that they are getting close to the limit.

[J M Fahey]

I'll bet they use an induction furnace.

I think David King makes a very good point here.
High Frequency AC heats metal in a very clean way, no contamination, it can even be heated in vacuum or in a neutral atmosphere, such as nitrogen, and then another big coil around the melting pot can apply a strong "DC" magnetic field.

As of Curie point experience, I went as fas as to demagnetize ferrite rings in a friend's glassworks oven; in fact was experimenting on disassembling shifted speaker magnets for realignment
Successful, sort of, but not practical at all, heat burnt epoxy adhesive and paint, demagnetized ferrite, but the full cycle took too long.
Never tried that on Alnicos. They self-demagnetize on their own anyway

[David Schwab]

The Curie point for Alnico is pretty high... 1,470 °F/800 °C !

[MR COFFEE]

Thanks for all the helpful replies including the link to the Technical properties tutorial.

I agree with you Joe - cheap enough to be worth a try. If I accomplish anything besides burning my fingers, I'll post results.

Wife's kiln goes to 2000 F routinely.

[David King]

Your wife might end up with some lovely new metallic colors flashed onto her pots.

[Joe Gwinn]

I agree with you Joe - cheap enough to be worth a try. If I accomplish anything besides burning my fingers, I'll post results.

Wife's kiln goes to 2000 F routinely.

Need to put the alnico in a closed container with some carbon, so the alnico doesn't become heavily scaled from oxygen in the kiln atmosphere.

For heat treating, people use stainless steel foil, but pottery sealed with clay will also work.

McMaster-Carr - Heat Treating Foil

[MR COFFEE]

@David - If I tell her that she might get some interesting colors flashed on her pots, she might actually dig it.

But I hadn't really thought much about what the atmosphere in the kiln might do to the magnets.

@Joe -

Need to put the alnico in a closed container with some carbon, so the alnico doesn't become heavily scaled from oxygen in the kiln atmosphere.

For heat treating, people use stainless steel foil, but pottery sealed with clay will also work.

McMaster-Carr - Heat Treating Foil

Good point, Joe. It is an electric kiln, which has an envirovent system that draws air (as in oxygen) through the kiln very slowly and exhausts it to the outside. It is an oxidizing atmosphere, and I hadn't thought much about how that would affect the surface of the alnico bars.

I'm not much at heat-treating, but I'm a bit afraid of putting the Alnico in carbon powder - wouldn't that do something like case-hardening to the alnico bars? That alnico is really hard stuff to grind to start with.

Do you think just wrapping the magnets in scrap clay tightly, letting it dry, putting it through a bisque fire with the wife's pots, and then putting it through the high firing cycle would keep the scaling (and the metal flashing the pots as well) to a minimum? The alnico magnets I've got are rough castings, and already have a little bit of scale on them which I was planning on grinding off after the demagnetizing soak to clean them up.

Thanks for all the really good input.

[Joe Gwinn]

Good point, Joe. It is an electric kiln, which has an envirovent system that draws air (as in oxygen) through the kiln very slowly and exhausts it to the outside. It is an oxidizing atmosphere, and I hadn't thought much about how that would affect the surface of the alnico bars.

I'm not much at heat-treating, but I'm a bit afraid of putting the Alnico in carbon powder - wouldn't that do something like case-hardening to the alnico bars? That alnico is really hard stuff to grind to start with.

Do you think just wrapping the magnets in scrap clay tightly, letting it dry, putting it through a bisque fire with the wife's pots, and then putting it through the high firing cycle would keep the scaling (and the metal flashing the pots as well) to a minimum? The alnico magnets I've got are rough castings, and already have a little bit of scale on them which I was planning on grinding off after the demagnetizing soak to clean them up.

The traditional approach is a scrap of paper in the stainless-steel pouch, with just enough carbon to use up all the oxygen in the pouch.

You are right that if there is lots of carbon, the item will be case hardened. Dose makes the poison.

[MR COFFEE]

Joe,
Thanks for the explanation on the carbon, that makes sense.

What do you think about the idea of putting the magnets in a pot not much bigger than the magnets with a scrap of paper, using scrap clay to seal it tightly, letting it dry, putting it through a bisque fire with the wife's pots, and then putting it through the high firing cycle ?

Does that sound like a reasonable approach? I could make the pot without any glaze on the inside so the magnets wouldn't melt into the glaze.

[Joe Gwinn]

Joe,
Thanks for the explanation on the carbon, that makes sense.

What do you think about the idea of putting the magnets in a pot not much bigger than the magnets with a scrap of paper, using scrap clay to seal it tightly, letting it dry, putting it through a bisque fire with the wife's pots, and then putting it through the high firing cycle ?

Does that sound like a reasonable approach? I could make the pot without any glaze on the inside so the magnets wouldn't melt into the glaze.

I would fire the pot and lid empty, the put everything in the pot and seal the lid to the pot with wet clay, then fire, initially slowly. Yes, the pot should not be glazed, at least not the inside.

I've seen this done for the making of crucible steel in a reverse engineering of how the Ulfberht swords were made circa AD 1000: NOVA | Secrets of the Viking Sword.

Less dramatically, at the bottom of the page from McMaster I posted earlier (posting #23), there are stainless steel pouches listed for small dollars.