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On 29 Oct 97, Greg Merritt wrote:
> At 8:52 PM -0500 10/29/97, Jake Kooser wrote:
> >Sometimes, when I would weld a magnet holder assembly together, it would
> >kill the magnets and I'd have to scrap the whole part.
>
> If the temperature reaches the material's Curie temperature, the
> magnetic domains will have sufficient thermal energy to be able to
> orient themselves in any direction & you can loose the net
> macroscopic magnetization of the bulk. Right?
The Curie effect is reversible; as the temperature drops the magnetic
field returns. This fact is beautifully used in the old Weller WTCP
soldering stations to maintain tip temp at the Curie point. They
have a magnet crimped to the back of the tip. When the temp rises
above the Curie point the magnetic field releases a steel plunger
that is normally attracted to it and this allows the switch which
provides power to the heater to open. When the temp drops below the
Curie point the magnet "comes back on" and turns the heater on again.
Since the Curie effect is very sharp, this gives good temp control.
You can hear a light click from across the room as these units cycle.
Weller sells tips with magnets that have different Curie temps so
you can choose your operating temp: either 600, 700, or 800 deg C.
Cheap, effective, beautiful, nothing to drift out of calibration.
I believe higher temps bring out different phenomena which
permanently kill the magnetism.
Jim
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Melissa Kepner Jim Adney
Laura Kepner-Adney
jadney@vwtype3.org
Madison, Wisconsin
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