Help needed - Making Steel Magnets

[Frank Ford]

I'm looking for info on making steel magnets. Not high tech new stuff, with exotic alloys such as alnico, but regular old-fashioned steel ones - you know, early 20th Century horseshoe magnets.

I won't be doing the actual "Gaussing-up" so I don't need to know about that. My end of the deal is to the metal fabrication, and I have that down with no problem.

I understand the steel needs to be hardened for best results, and my local heat treating shop has no better idea of what I'm asking for than I do.

Anybody have any experience, or reference?

The magnets I'm reproducing are carbon steel, pretty close to O-1, so that's what I figured I'd use, at least for a test batch. I did one with O-1 and hardened it in my usual offhand way - heat until nonmagnetic, dunk in oil, clean up mess. Result tested reasonably well, but if I could do a little better, I'd like that. . .

[Bateman147]

Lindsay Books has several books on making magnets from the early 1900s -

http://www.lindsaybks.com/bks8/magn/index.html

Hopefully that link will get to the right place.

I just ordered several machining books from them and I'm quite happy with both the price and quality of reprinting.

Not sure if it'll apply to your situation -

Michael

[Evan]

They need to be work hardened for maximum results. Bang them with a hammer.

[Weston Bye]

A couple of quotes from an Arnold Magnetics App note TN 0205 December 2002:

IRON CHROME COBALT

This material was developed years ago. It has properties
similar to Alnico 5: the Br is quite high, 9,000 - 13,500
gauss and the coercive force (Hc) can be between 50 to
600 oersteds. The material is ductile: it can be rolled,
stamped and bent prior to the final heat treatment, a
property no other magnet material has. It can be rolled
down to very thin strip and still maintain its magnetic
properties.
One use of this material is in EAS (Electronic Article
Surveillance). The thin magnetic strip is attached to the
book, CD, or other store or library item. Upon exiting the
premise, one passes between sensing coils on either side
of the aisle. These are large antenna for sending a signal
to and receiving a response from the magnetic “tag” on the
product. If the tag has been “desensitized” prior to
leaving, there is no response. However, an active tag will
provide a signal to the surveillance system.
In addition to the low coercivity, another shortcoming of
this material is the relatively high cost.
Although mostly iron, which is inexpensive,
there is significant cobalt and chrome
content which is considerably more
expensive.

Alnico is one of the older magnetic materials, engineered
just prior to World War II. There are some great attributes
with this material. It has very high flux output
characteristics, called Br, which ranges anywhere from
6,700 to 13,500 Gauss.
It has a very high Curie temperature (Tc) of approximately
840؛C. It is very temperature stable. The temperature
coefficient of induction, another characteristic of magnetic
materials, is -0.02؛C, lower than any other commonly
available material. The temperature coefficient relates to
how much flux loss will occur when the material is raised
1؛C.
Another attribute of Alnico is that a curved field can be
established through the material. One of the old Alnico
shapes is a horseshoe shape, a curved magnet with the
north and south poles aligned so that they can pick up a
bar of steel.One of the detriments of Alnico is that it is difficult to attach
into the final application. Alnico is very hard and brittle. Tt
cannot be milled or machined other than by grinding or
with EDM.
Alnico has a low coercive force. The Hc of Alnico runs
between 640 and 1,900 oersteds. The coercive force,
another characteristic of magnetic material, relates to the
magnet’s resistance to demagnetization.

I include the quote about Alnico particularly concerning the magnetizing. All the experience I have says that solid material magnets (other than alnico) can only be magnetized in a straight line. This is not true for ceramic and bonded magnets, as these are composite magnets - small magnetic particles suspended in a non-magnetic binder. Still, I know that steel horseshoe magnets exist, in magnetos and old generators.

[Weston Bye]

So the question comes to mind, How would I magnetize a steel horseshoe magnet?

Turns out to be not impossible. I would position a pair of the magnets with the poles facing each other like parenthes () , then the magnetizing coils would be positioned North above and South below. The result would be a ring magnet, magnetized across it's diameter. Both magnets would be magnetized and would immediately repel each other. Handle carefully, as they would want to twist to swap attracted poles. Next time I have access to the magnetizer I may try this.

[Tony Ennis]

They need to be work hardened for maximum results. Bang them with a hammer.

In fact, if you do this while the non-magnetic bars are aligned with magnetic north an south, you'll end up with magnetized bars.

[Evan]

To magnetize just wrap with a single layer of 14 gauge house wire and swipe the wire ends across 12 volt battery terminals.

[Frank Ford]

Thanks for the quick responses, guys!

That Lindsay reprint looks like just the thing - I have a copy on the way now thanks to Michael.

[Bateman147]

No problem Frank -

It was very good timing - I had just ordered some books from them and remembered seeing the magnet books while perusing the catalog. Another couple of weeks and it'd have been all forgotten... :-)

I hope you're as happy with it as I am with the books I ordered. I'm now looking forward to ordering some more soon. I really like reading the older machining books - there's a lot to be learned and most of what I'm doing is really fully "from the era."

Michael