[TheForge] Microwaving Metals From the Virtual Junkyard

[Rob Fertner]

Over on keenjunk.com this was posted. It sounded so interesting I just had
to share with the rest of you.

Copied from the Virtual Junkyard:
Friend of mine sent me this thought y'all might enjoy it
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Subject: [hobbicast] Microwave Melting Update


Some of you may know that I make a living by developing new products
and
processes for the metal casting and steel making industries. About 6
months ago,
we started looking seriously at using microwave energy for melting
metals.
About $40,000 later, we have done an immense amount of lab work. We
have
successfully melted Aluminum, Bronze, Iron, Steel and even Glass in a
simple 1000 watt
microwave oven. The key points in doing this are as follows.

1. You need do have either a special crucible that absorbs microwaves,
or,
you will need to have microwave absorbing materials nearby to a
microwave
transparent crucible.

So far, we have made all of our own crucibles. I can't tell you what we
are
using, because we fully intend to offer these crucibles for sale to the
public,
sometime this year. What I can tell you is that Silica (fused silica)
is
microwave transparent. Alumina becomes a microwave absorber at elevated
temperatures. Once you get it hot, it will get very hot, very quickly
in microwave
energy. We have developed a mixture of refractories that can be shaped
into a
crucible that will reach over 2,000�F. in less than 5 minutes of
microwave heating.

2. You will need to use some fairly fancy refractory insulation to keep
from
burning up the inside of the microwave. We use a very low density solid
or
fibrous material that is about 70% Alumina and 30% Silica. You can
either build a
box and then put the crucible inside of it, or, you can line the whole
inside
of the microwave. Just remember that the radiant heat from a glowing
crucible
needs to be contained, or you will quickly burn the inside of the oven.
Remove any plastic covers inside the microwave, or they will melt.

3. You really need to keep close tabs on the temperature of the metal
in
order to avoid some serious over heating disasters. Last month, we over
heated
some Iron, which then melted through an Alumina crucible (that takes
3700�F), and
then we vaporized the Iron (that takes about 5000�F). Things can get
really
hot really fast. Be prepared to shut down the power if you get into
runaway
heating. Have some really well insulated gloves or tongs to handle the
crucible.

4. Now, here's the neat part. We know that metals behave as microwave
reflectors. They won't heat up in a microwave. BUT, we have learned
that all metals
will become microwave absorbers at elevated temperatures. We suspect
that the
temperature at which this occurs is about half of the melting point of
the
metal. We will know what the exact temperatures are later in January.

Once you reach this magical temperature, the metals will absorb the
microwaves and you can melt lickety split! Virtually all of the energy
that you put
into the oven is going directly into the metal and causing molecular
vibration
(heating).

DON'T DO ANY OF THIS KIND OF STUFF IN YOUR WIFE'S MICROWAVE!

I have toasted 3 microwaves in the past 3 months, mainly because they
got too
hot from runaway heating. I melted through the bottom of one and the
Iron ran
out onto the table, along with a fair amount of microwave energy, which
can
be quite dangerous. If you are serious about doing this, you need to
constantly
measure for microwave leakage from the unit.

I expect to make a public announcement about the availability of these
special crucibles and the refractory insulation for holding them,
sometime in the
next 3 months. This is no BS. We are quite serious about designing a
microwave
that will have the capability of melting at least one ton per hour, by
the end
of 2004. The eventual goal is to design and build a system that can
melt
several hundred tons a day.

I will keep all of my Hobbicast friends posted on our progress.

Tom Cobett
Cleveland, OH

"In Pyro Veritas"