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Re: Magnets
---------- Forwarded message ----------
Date: Fri, 3 Oct 1997 19:49:57 -0700 (PDT)
From: "Edward V. Phillips" <ed-at-alumni.caltech.edu>
To: tesla-at-pupman-dot-com
Subject: Re: Magnets
"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)."
Can't emphasize the last point enough. I have an 8" three-jaw
chuck which I don't seem to be able to demagnetize!!!!!!!
By the way, I have had good luck separating ferrite speaker
magnets by the following method (after most of the speaker is removed
by drilling out the spot welds):
1. Clamp the speaker assembly to a firm base.
2. Get a stiff spring, a loop of wire, and something to hook the
spring to.
3. Arrange the loop of wire and the spring to pull sideways on the
magnet. Takes a little care but can be done.
4. Set the above arrangement on a flat surface.
5. Heat a 500 watt electric soldering iron and tin the "top" side
of the pole face over the magnet.
6. Set the soldering iron (suitable held so it can't slip away"
on top of the tinned spot on the pole piece, and wait.
7. In a few minutes the pole face will get hot enough for the
spring to pull things apart. Since the spring exerts continuous
force, it will cause the separation to occur at the lowest possible
temperature.
I have disassembled a number of speakears, large and small,
this way and haven't damaged a magnet yet.
Ed