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How to ruin 3 crucibles


#1
  1. tell your friend how nice his small sculptured heads will
    look in copper, instead of the bronze he’s been using. These are
    "large" melts- up to 400 grams. He uses propane/oxygen with a
    torch the size of Texas and a large rosebud tip.

There goes the first crucible. A bunch of granules fused
together nice and tight.

  1. Tell your friend that Propane/oxygen is just not hot enough
    and to use acetylene/oxygen instead.

There goes the second crucible. Also the little remaining hair
on the top of his head is singed and his broom caught fire.

  1. Tell your friend he must be doing something wrong. Either his
    flame is improperly adjusted or his torch just isn’t hot enough.
    Suggest that he bring his copper and already twice heated flask
    over to your studio where you will demonstrate the superiority of
    your hydrogen/oxygen torch, not to mention your expertise.

There goes the third crucible(and your pride). Only 240 grams
of copper granules and 4000 lbs. of hydrogen later and the copper
still just sat there laughing in my face.

Your friend thinks the copper was impure- me thinks there must
be some metallurgical explanation; There must be some limit of
how much copper one can melt using X torch, with X amount of heat
etc. I recall melting about 150 grams of copper awhile back and
don’t remember any difficulties other than that it took longer
to melt than say gold or silver. Now I’m reluctant to make any
more experiments until consulting Orchid.

Anyone out there with an explanation?

Thanks, Peter Slone


#2

A suggestion or 2:

Pure copper is a very difficult metal to cast, dirty, oxides,
“sticky”, etc. If copper color is what is needed, one type of
coppery alloy to try would be “contact copper” (an alloy used to
cast electrical contact points). Or contact your metals supplier
and ask them what they have for casting that is VERY hig copper
content.

Preheat the metal and the crucible in a burnout kiln before melting.

Be sure to use a rosebud (the bigger the better) for the tip.

Copper melts at around 2000 F (higher or lower depending on the
alloy) so oxy act is definately hot enough, just a question of
the total BTU output of the torch (for 400 grams you need a good
sized one).

Did you use any flux? Again, pure copper is a problem and flux
might be a help (I just do not know what material to suggest).

Laastly, from the descriptions about the granules remaining in
the crucible, I would think there was a lack of heat. I melt 80
lbs of bronze with a forced air, propane burner in about 40
minutes. BUT to melt 4-5 lbs in a crucible with a hand tourch
is very difficult. Try making a kalwoll “furnace” to help retain
the heat and to heat the crucible 360 deg . Pretty easy to make
the “furnace”, a bit of wire, few sq ft. kalwool and the burner
(also home made if necessary from pipe and a hair dryer/blower).
If more instruction is needed/wanted, let me know.

Hope these thought help anyone interested.

John Dach

Maiden Metals Foundry


#3

Peter, I got into jewelry making from the back door. I had been
hobby casting in copper and brass and welding steel for some
years and decided I wanted to make smaller things. So I have some
experiance. Here is the problem. A torch nicely heats, but only a
small area. Since copper alloys melt at a higher temp than gold
and silver. So with all the uneven heating there is a good chance
of frozen crucibles and half poured metal. Or worse, cracked
crucibles and burned feet. I would be lying to you if I told
you this never happened to me. In fact my last copper pour was a
miserable failure due to the mold being too cool (I had been
trying to reconstruct an ancient way of making baked clay molds
and this was a first effort with this technique.

But several things really help. If a sand mold is used I don’t
use greensand. I use either oil based sand or sand plus 20%
plaster of paris then heat them up above 200 degrees to drive out
the free water. If I use an investment mold I pour at 1100
degrees. The big thing I do is use a crucible in a propane
foundry. The foundry will heat up the whole crucible, up to an
eight pound pour, to a yellow heat. It retains the heat better
than if one tries to just heat up the metal. If the crucible
cools to where it is below orange I put it back into the heat and
warm it up before the pour. I always heat about 50% more metal
than I need then pour the extra into a tin can buried in the dry
ground. That way if there is too much dross on top, skimming it
won’t result in a short pour.

Disclaimer: Best bet is to ignore online advice and go to an art
foundry course. I took a short course many years ago at “The
Mother Earth Village” in North Carolina. Without the actual hands
on training there are a lot of ways a person can get burned,
scalded or otherwise hurt. I think that this cannot be learned
from a book or from other people on the internet.

Geo.


#4

John, I have found that old pre 1981 pennies make an acceptable
high copper brass which looks like copper. Also preheating pure
copper to a yellow heat then adding about 6 ounces of zinc per 8
pound pour (can be in the form of new pennies which are copper
plated zinc if none else is available) and a dab of boric acid,
stirring very carefully then skimming with a pinewood spatula
(throwaway item made for the occasion whose burning keeps away
the oxygen) just before the pour works for me. Another coppery
alloy I’ve used is copper with a single one inch cube of American
pewter added to the copper.

If you own a commercial foundry perhaps you could offer
workshops to jewelers who want to learn this craft. Being just a
hobbiest I have no credentials myself except for a scattering of
little burns scars here and there.

Geo.


#5

George,

If this was directed towards me, here goes… I own/operate
a one “man” foundry (going on my 7th year) which is my main
source of income (I used to be an organic apple/etc. farmer for
20 years). I do most all the work myself, requiring at least 1
person (better with 2 or 3 others) for pouring. I primarily use
the ceramic shell system but I also do some sand (oil) casting.
We (wife and I) also do investment casting (jewelry).

In the foundry, I buy all of my bronze in “new metal form” in
ingots (about 20-25 lbs) as the metal is relatively cheap
compaired to pouring teh wax, prpraring it, spruing it, chelling
it burnour and prep prior to casting and casting. New metal can
also be obtained in small pieces (sort of like cut 1" bar) for
smaller users.

I do make my foundry available to those capable (my feelings)
and wishing to do/learn what I know about casting and the entire
process or any part of it. I also do some custom work for those
interested in getting stuff cast but not interested in doing it
themselves. We also offer the same for jewelers as Cynthia is a
longtime jeweler and designer (a carver).

I have only had one case of injury casting, in the first year,
and hope that most would feel adequate procautions are observed
as 2000+F is HOT. If anyone in interested in what is available
here, please feel free to contact us.

John Dach

MidLife Crisis Enterprises

C.T. Designs

Cynthias sculptures are at:

http://www.pacific.net/~mlce/ctdesigns/

Maiden Metals,

A small bronze foundry, not web site yet!!


#6

John, Yes, I was replying to your post, but didn’t know the n.g.
would strip the quoted material from my post. It sounds like you
have more experiance than me. Although I learned to cast in 1981
I have had to continue my day job, casting only as a hobby,
taking up to a year between starting the wax and polishing the
object. Your use of ceramic molds sounds interesting to say the
least. Although I have read of ceramic mold techniques I am only
familiar with oil-sand and plaster-sand for bronze and brass for
simple pieces up to 8 pounds and investment molding for
statuettes small enough to fit in my largest flask, a recycled 2
gallon steel miniature beer keg. Also cast a variety of silver
and brass objects in the more traditional 2 inch to 4 inch flasks
and a few in 6 inch flasks. Needless to say one can’t vacuum a 6
inch flask or a beer keg so those are set into the ground after
burnout just like one would do with sandcasting.

It would be nice to hear more about your ceramic mold technique,
particularly how you overcame the technical problems related to
learning mold burnout and cure. The sizes I like to cast are
right on the transition point between jeweler’s and foundryman’s
technique.

Geo.