Porosity in poured copper ingots may be getting the best of me. The
ingot appears just fine until I try to forge it out, then a cavity
appears. I’ve tried different torch tips and also tried heating the
ingot mold. The ingot needed ingot is about 3/4" wide by 2 1/2" or
so.
Any words of advice would be most welcome.
Thanks
Jerry
I am sure you’ll get wiser advice or observations than mine, but here
goes… copper is a weird creature. It does not flow or “slump” as
some metals do. It seems, from my experience, that enough heat may
not be the only factor, but some kind of inert gas environment? I
know that in a “regular” atmosphere it does not “flow”.
Porosity in poured copper ingots may be getting the best of me. The ingot appears just fine until I try to forge it out, then a cavity appears. I've tried different torch tips and also tried heating the ingot mold. The ingot needed ingot is about 3/4" wide by 2 1/2" or so..
Copper absorbs huge amounts of oxygen and is very difficult to cast
in a non porous form with studio equipment. You need to add some
active deoxidizing material to the copper just before pouring.
Phosphorous is one of the common ones. It is added as copper
phosphorus alloy shot. The problem is you want to add just enough but
not too much as it causes brittle metal if there is too much. It will
take some experimenting to get the right amount for your process.
James Binnion
James Binnion Metal Arts
I've tried different torch tips and also tried heating the ingot mold.
Jerry, Pour it like a beer! Tip the mold and pour it down the side.
After evacuating the water from the mold by preheating I like to
cover the interior surface with acetylene soot (lamp black).
Regards,
Kevin
It is added as copper phosphorus alloy shot. The problem is you want to add just enough but not too much as it causes brittle metal if there is too much. It will take some experimenting to get the right amount for your process.
Is it not as simple as knowing what percentage of copper phosphorus
is right to be effective, whilst not causing a brittle casting? If
you know the correct percentage then the metals can simply be weighed
before melting. Or have I missed something? There may be members who
have experimented and arrived at the optimum proportions, who might
be willing to share such
Helen
UK
Is it not as simple as knowing what percentage of copper phosphorus is right to be effective, whilst not causing a brittle casting? If you know the correct percentage then the metals can simply be weighed before melting. Or have I missed something? There may be members who have experimented and arrived at the optimum proportions, who might be willing to share such
Yes, however you need to know the exact amount of oxygen absorbed
into the molten metal at the time of pouring. This varies depending
on several factors (residual oxygen in the metal, melting time,
oxygen content in crucible atmosphere, surface area of metal being
melted, etc.) so you cannot easily calculate it in advance In modern
state of the art large scale foundry work they actually do ladle
analysis to get the oxygen content and correct on the fly. But the
more common practice is to do post casting analysis and adjust for
the next pour. This works if your process is fairly well controlled
and repeatable. As for jewelry scale work most people give up on
casting copper as it is such a difficult metal to cast. It is viscous
and prone to large amounts of porosity. Using an inert gas shielded
induction melt casting machine would allow you to deal with the gas
issues but molten copper is not very fluid so it will still be
difficult to cast. Even industrially it is rarely cast as a pure
metal for anything other than ingot for wrought stock production. You
can cast copper as an alloy by adding zinc, silicon, tin etc. and all
these make it more fluid and reduce the porosity problems. But then
it is brass or bronze 
Jim
James Binnion
James Binnion Metal Arts
Ok, I don’t have the text handy, and I have no time to find it either
(I fly out to the US Wednesday and have obviously put it into
storage), but from (rather dim memory) the amount for brass/bronze
casting is 15-30g/100kgs of phosphor copper. This depends on how
clean the material for ingots use less and for scrap use more, so in
any case it’s not much.
The text I’m referring to is C.W. Ammen’s “The Complete Sand Casting
Bible” and I think the amount was given in oz/100lbs, so my memory is
based on a figure I derived, and it’s been ages since I last looked
in the book, so I’m not 100% certain…
That said for a #6 crucible (would hold 8.6kgs of bronze) I use 3-5
granules, 3 if the bronze is clean ingot, 5 if scrap/remelt, no
brittle casts nor any bubbles/porosity so I must be pretty close!
The below is dangerous info, moderator may choose to edit or remove
it:
BTW if you like to live dangerously 1.5% to 7% arsenic (DEADLY fumes
given off when heated) can be added to make it pour a bit better (not
a huge improvement), and with no real change to the appearance and
workability of the metal. Please DO NOT DO THIS, it’s just some
trivia I’ve picked up from studying the history of metal usage by
man, and I only mention it as by the by thing seeing as there are
many metals that can be added in quite small amounts to make copper
more “foundry friendly”, arsenic is just one extreme example. Some
other metals aRe: lead, antimony, tin, zinc, iron, aluminium,
silicon (1.5% tops IIRC), beryllium, oxygen (increases the
conductivity when added at up to 1%, don’t ask me how they do that!)
well you get the idea the list is just as long as the periodic table,
within reason anyway.
Cheers, Thomas Janstrom.
Little Gems.
http://tjlittlegems.com
Yes, however you need to know the exact amount of oxygen absorbed into the molten metal at the time of pouring.
Ah, I knew I must be missing something vital to the whole equation,
so thanks for the elucidation James. Things are usually more complex
than they at first appear.
Helen
UK
lead, antimony, tin, zinc, iron, aluminium, silicon (1.5% tops IIRC),
Generally speaking… Iron and carbon, silver and copper, gold
and silver - those are alloys, and the two (or more) metals form
solid solutions or intermetallics. Silicon and phosphorus are used
as “getters” - they don’t actually alloy, they “go and get it”,
usually gasses and other impurities. Generally speaking…
Jim,
As for jewelry scale work most people give up on casting copper as it is such a difficult metal to cast. It is viscous and prone to large amounts of porosity.
Having said this, am I wasting my time trying to cast copper ingots?
I’ve cast smaller copper ingots without issue but want larger as
well. Possibly I should simply purchase copper bar for the forgings.
Melting the copper has proven very interesting in itself. In all,
this process has been an interesting learning experience.
To explain the overall goal. I’ve been pouring silver ingots,
forging those into cuff bracelets in various widths, some of which
are set with various types of stones. Simply want to expand on the
silver with copper.
All this is a result of acquiring an old anvil last summer. A good
friend purchased a small house, outside on the well was an old rusty
anvil. It’d sat in the rain for several years. She and another
friend managed to drag it off the well, intending toss it or use it
as a table. My ears burned when I heard about it. I’d looked for an
affordable anvil for a long time. She told me if I could lift and
haul it off it was mine. I loaded in my truck and carried it home
where I brought it back to life. The logo is almost gone however I
believe it to be 75 - 100 years old and must weigh 175 - 200 pounds
with a beautiful ring.
Jerry
Having said this, am I wasting my time trying to cast copper ingots? I've cast smaller copper ingots without issue but want larger as well. Possibly I should simply purchase copper bar for the forgings. Melting the copper has proven very interesting in itself. In all, this process has been an interesting learning experience.
It all depends on whether you are more interested in the process or
the result If what you want to do is forge copper bracelets then
you are better off buying the copper and getting on with it. If you
are more interested in the process then there is lots to learn in the
casting of your own ingots of copper. You can buy copper-phosphorous
alloy solder at the welding supply to provide a source of alloy
addition for your experiments.
James Binnion
James Binnion Metal Arts
Generally speaking....... Iron and carbon, silver and copper, gold and silver - those are alloys, and the two (or more) metals form solid solutions or intermetallics. Silicon and phosphorus are used as "getters" - they don't actually alloy, they "go and get it", usually gasses and other impurities. Generally speaking...
Well yes and no if you look at its place in the periodic table
silicon is almost a metal. Silicon in small amounts (0.1% or less)
will alloy with several metals copper, gold iron etc. too much and
you end up with brittle silicides. It acts a deoxidizer and increases
fluidity in low karat golds but will ruin higher (18k and above)
karat alloys. Phosphorous is similar in that very tiny amounts are
tolerated by some alloys but get too much and you end up with brittle
phosphides in the matrix and cracking will result when you work the
metal. Phosphorous is used to deoxidize sterling silver in large
scale ingot casting. Both silicon and phosphorous are alloyed with
copper to make silicon and phosphor bronzes but both require very
precise control of tiny amounts to get the desired properties.
James Binnion
James Binnion Metal Arts
Jerry,
How nice that you are having a good time forging on your new old
anvil! By all means, buy copper bar to do your forged designs. You
will like it! This is one case where it is so much better not to DIY
(do it yourself). Try some square bar; it’s easier to keep the
forging direction changes crisp-looking. Plus it is fun to twist.
Have fun hammering!
M’lou