Copper is not generally a recommended metal to cast in an
unalloyed state. Not by me because I have no direct experience
doing this on a small scale. The reason given is that it picks
up too much oxygen and gets a lot of porosity. A friend who
tried it won't do it any more. Hydrogen is also a problem.
In industrial scrap recovery operations that I am familiar
with, high grade scrap with a high copper content is recovered
in fairly large revebatory furnaces but the product ends up as
alloy ingots. Low grade stuff can be recovered in a coke fired
copula. The results then go to a revebatory furnace for
alloying. Industrial shops can control a proper atmosphere.
At Santa Clara de Cobre in Mexico copper ware is made in an
old traditional way. Haven't been there yet.
My understanding is that they put the copper directly in a
coke or possible charcoal bed with a bellows pumped air blast. I
understand the bed is basically a hole in the ground with an
ingot sized depression in the bottom.
Molten copper ends up in the bottom. The bed is allowed to
cool and a solidified pan shaped ingot is recovered from the
bottom. The ingots are then drawn out into absolutely
beautiful vase and bowl shaped objects.by traditional hand
techniques. I have posted stuff on this before further down
this list.
Jesse
I found this but my other file is missing. Basically you gotta keep the oxy away from the copper. Be it flux or an intense charcoal fire.
Forgeing hot copper is kewl.
Thanks Bruce for your input. You useing Borax for flux?
Here's another option
Microwave blommery
----- Original Message ----- From: <> To: <> Sent: Friday, January 02, 2004 7:46 AM Subject:
Re: [hobbicast] Microwave Melting Update > Ray, > > I don't wish to burst your bubble, but, the
best you can hope for in a 1000 > watt microwave is to melt about 5 lb. of Iron in one hour. > >
Technically speaking, it takes about 0.2 kWh to melt 1 lb. of Iron. That is > with 100% efficiency.
Induction melting is only about 65% efficient, so that > would use about 0.3 kWh to melt 1 lb. of
Iron. We believe that microwave energy > can be substantially more efficient, because we don't
need to heat up the > refractory and we don't need to have cooling water running through a coil. >
> Now, if you really want to melt a lot of Iron at home, let's say 100 lb., you > would need to
have a 20 kilowatt microwave oven, and you would need to run it > for one hour. Anything over
about 2 kW is rare for a home microwave. BUT, > there are lots of industrial units out there with
20 kW or more. > > Now, if I want to melt 2000 lb. of Iron in one hour, I will need to build a >
400 kW microwave. That's getting quite large. We have the notion that we can > build this
furnace quite inexpensively by ganging 400, 1 kW magnetrons into a > series of wave guides that
are mounted tangentially around a cylindrical > "melting zone." A 1 kW magnetron costs less than
$10.00. If we spend $4,000 on > magnetrons and then maybe another $10,000 on the power
supplies and controllers, and > maybe $10,000 on the structure and refractories, we should be able
to have a > furnace that will melt one ton per hour for less than $25,000. This is at > least
one-fifth the cost of an induction melter that will do the same thing. AND, > we will be more
energy efficient. > > Or, maybe it won't quite work that way and we will have blown a few
hundred > thousand dollars to prove that it doesn't work. If we don't try, we will never > know
what is possible. > > More to follow.... > > Tom Cobett > Cleveland, OH > > "In Pyro Veritas" >
----- Original Message ----- From: <> To: <> Sent: Thursday, January 01, 2004 3:12 PM 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" [Non-text
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well it contains melted bronze 
