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Casting copper?


#1

Aloha,

A customer of mine is working on some designs for combining cast
components with blanked-and-fabricated parts, and since the blanked
parts are copper, they want to cast the other parts in Cu as well.
So, since I have never cast copper, and none of the places I used to
work at did either, and I can’t recall any of the casters I knew or
know doing it either, I have to ask. Obviously pure Cu castings are
going to be weak, and will tarnish quickly, so I understand why
they’re not widely used for structural jewelry components, but these
of my customer’s will be decorative, not ‘functional’, so if they
find someone to do it, it should be ok.

I do, however, want to learn more about the possibility from the
people here; what do we/they need to look out for ?. Tips and/or
tricks, etc. ?. Any input is welcome, since, as I said, I’ve got
basically nothing right now.

Thanks,
Dar
http://www.sheltech.net


#2

Hi Dar,

Pure copper is not normally cast in small scale. It is not terribly
fluid when molten and is a major gas sponge. It will absorb oxygen,
hydrogen, carbon monoxide, acetylene so melting it with a flame will
result in is picking up a lot of gas. The oxygen will remain in
solution as copper oxide and result in brittle castings, if you try
to counter this with a reducing atmosphere the fuel gas / combustion
products mentioned above will be absorbed by the molten copper and
released as the copper cools resulting in gross porosity. The trick
is to get a balance of just enough oxygen to react with all the fuel
gasses to make carbon dioxide and or water vapor neither of which
are soluble in molten copper so they will bubble out of the melt. But
you don’t want enough oxygen to cause excessive copper oxide
formation. There are several ways to do this but they are not too
appropriate to small scale casting mostly because you will not have
the real time analysis of the molten metal to know what the gas
status is. However if you have access to one of the fancy inert
atmosphere pressure over vacuum induction casting machines and sprue
to allow for coppers viscous nature you can cast it cleanly.

James Binnion
James Binnion Metal Arts


#3

Hi James,

Pure copper is not normally cast in small scale. 

The addition of another metal into the melt makes a lot of
difference, bung in some gold or silver and the problem or porosity
is lessened if not removed altogether.

I remember in the Ford Hallam video, not only did he make his ingot
under water, he also tapped the bucket, wonder if that could help?
Just postulating, never poured metal into water.

Regards Charles A.


#4

Pure copper is not normally cast in small scale.

The addition of another metal into the melt makes a lot of
difference, bung in some gold or silver and the problem or
porosity is lessened if not removed altogether. 

Well it depends on the metal you add, some like zinc act as a
deoxidizer so they will reduce problems with oxygen but you can
still get in trouble with hydrogen and hydrocarbons. And porosity is
a problem with any casting that is not done in inert or vacuum
atmospheres. The trick or art is to limit its presence or force it
to be in places where you don’t care about it. But you cannot get
rid of it totally.

I remember in the Ford Hallam video, not only did he make his
ingot under water, he also tapped the bucket, wonder if that could
help? Just postulating, never poured metal into water. 

Pouring into water works well to keep the surface oxides down but it
can be very dangerous if not done properly. I have done it several
times and was quite pleased with the results but once I participated
in a pour where a small amount of water splashed back into the
crucible that still had molten metal in it. There was a significant
detonation as the water flashed to steam and spread the molten metal
across the room as a fine powder. Luckily no one was hurt but my
ears were ringing for quite a while afterwards. You must keep the
crucible well clear of the water as there are droplets that splash
up from the surface of the water.

James Binnion
James Binnion Metal Arts


#5
he also tapped the bucket, wonder if that could help? Just
postulating, never poured metal into water. 

Pouring into water works well to keep the surface oxides down but it
can be very dangerous if not done properly.

I’ll point out that this thread has taken a tangent, too. Pouring
copper into water is only casting in the loosest sense. The OP wanted
to do lost-wax casting with copper, not just pour ingots. I did it
once, long ago, for pieces to be enameled. I got some pieces that
were OK, I guess (I ~mean~ long ago). It was a struggle and I really
wouldn’t do it for production, expecting consistent, clean results.


#6
Well it depends on the metal you add, some like zinc act as a
deoxidizer so they will reduce problems with oxygen but you can
still get in trouble with hydrogen and hydrocarbons. 

Jim, I’ve used copper-phosphorus shot (phos premixed in Cu) as a way
to remove oxygen from molten metal when gravity casting into sand
with high copper alloys, including pure copper. I add a couple of
balls (less than 1%) to the molten metal. The pour is to happen
within 15-20 secs after that, as I understand.

What’s your opinion of copper-phos as a deox for copper castings?
Same trouble with hydrogen and hydrocarbons?

Thanks

Brian
Auckland
New Zealand
www.adam.co.nz


#7
What's your opinion of copper-phos as a deox for copper castings?
Same trouble with hydrogen and hydrocarbons? 

Phosphorous is a common deoxidizer for copper, copper alloys and
even sterling. The problem comes in that what you are shooting for is
all the phosphorous to react with the oxygen in the copper or alloy
as the residual phosphorous forms a low melting point brittle
compound called copper phosphide with copper. This material is the
last to solidify and fills grain boundaries of the metal and makes it
brittle and hot short. So to know how much phosphorous is needed you
need to be able to check the crucible chemistry. This is routinely
done in modern foundries but not so practical on the scale we work at
:slight_smile: So it is a guessing game, too much and you end up with oxide free
brittle hot short metal too little and you end up with brittle
oxides in your metal. And yes you need to add it at the last moment
as the molten metal will be continuously be absorbing more oxygen and
deplete the phosphorous if you dawdle.

Jim

James Binnion
James Binnion Metal Arts


#8

Thanks for the input; what % silver or other metal --no gold, as this
is for low priced copper jewelry-- is suggested as an additive?. This
customer of mine got 25% silver in her head, from I’m not sure where,
and I had to say that that sounded like it would be way too costly
but that I didn’t know how much the minimum would be.

Dar


#9

Yes, this is intended to assist someone wanting production lost wax
casting. Their work is a bit funky or rustic, so some roughness or
whatever might be acceptable, but certainly, so much porosity that
would cause structural problems is not, though the pieces probably
won’t need to actually function structurally . I doubt that the
eventual caster, if they end up using copper, will go to the trouble
of water- pouring casting grain to make the alloy.

Dar
http://www.sheltech.net


#10

So, how much silver is added to help cast copper?. The customer in
question appreciates all the input so far but really would like to
know more about adding silver as opposed to other metals.

thanks,
Dar
http://www.sheltech.net