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Re: Magnets



---------- Forwarded message ----------
Date: Thu, 2 Oct 1997 12:17:32 -0500
From: Geoff Schecht <geoffs-at-onr-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Magnets

Gary:

Briefly, unless you've got diamond tooling, forget trying to machine magnet
materials like alnico, neodymium-iron-boron or samarium-cobalt. They're
extremely hard and brittle. The one with the highest Hc that I'm aware of
is samarium-cobalt, but it's also the most expensive. NIB's are cheaper and
in more wide use in things like stepping motors. In "the old days", you
used to be able to get decent alnico-5 magnets out of radars, they were the
field magnets for the magnetrons. I have one that came from an installation
that is about a foot long and probably weighs over 10 pounds. It was made
by Indiana General. The gap is about 2" wide and the field strength in the
gap should be around 0.8T although it may need recharging since it's over
50 years old and alnico has a definite half-life.

Loudspeakers typically use barium ferrite magnets these days. They aren't
great magnets but they're pretty common. They're usually bonded to the
speaker shunts with epoxy. Soak the assembly in Methylene chloride for a
while and then see if the glue softens enough to slide the shunts away from
the magnet. You could turn the assembly in a lathe and just shave off the
shunt (they're soft iron, I believe) but avoid striking the magnet; it's
just about as brittle and hard on tooling as alnico, SC or NIB! (You'll
have an interesting accumulation of iron shavings sticking to everything as
you work, too).

Don't use a torch to soften the glue as you're likely to exceed the Curie
point of the magnet and ruin it.

Even small magnetrons like 2J51's have a couple of substantial horseshoe
alnico-5's attached. You could easily adapt one of them by machining a
couple of soft iron shunts to couple the field between the magnet and your
particular gap. That's probably the most practical way to get the field
that you need in a magnetic quencher.

The older mangetron magnets from the dismountable assemblies are
schematically as shown below. "i" stands for iron, "a" for alnico and "g"
is the air gap where the magnetron went. Some of those magnet assemblies
were quite large.


     a i g i a
  a             a
a                 a
iiiiiiiiiiiiiiiiiiiiiiiiiiii

Geoff

----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Magnets
> Date: Tuesday, September 30, 1997 11:45 PM
> 
> 
> 
> ---------- Forwarded message ----------
> Date: Tue, 30 Sep 1997 20:10:47 -0700 (PDT)
> From: gweaver <gweaver-at-earthlink-dot-net>
> To: Tesla-at-pupman-dot-com
> Subject: Magnets
> 
> There has been a lot of talk about magnet quenching the spark gap on the
> list.  This has gotten me interested.
> 
> I have been checking catalogs and have found many companies that sell
> magnets.  Having access to a machine shop I would like to make my own
> magnets the size, shape and design I want.   I have been researching
magnets
> and they are made of iron, aluminum and cobalt.   I checked with a metal
> company but they can't tell me much.  Does anyone know of a metal that
can
> be used to make magnets.
> 
> I built a electro magnet with 2 coils 2000 turns each of #24 wire.  Power
> supply is 170 VDC 7 amps.  I can increase the power to 678 VDC 7 amps. I
> used it to increase the power of several old magnets.  I increased the
> magnetisum of 6 round magnets.  I had no luck and increasing the power of
3
> horse shoe magnets. If I could find the correct metal I could make my own
> magnets.
> 
> Any suggestions
> 
> Gary Weaver
>