I have zero foundry experience. I want to melt a few pounds of Copper and
cast it into backup plates for welding. What should I make the crucible and
moulds out of? OR, is it possible to buy a crucible somewhere?
Thanks.

Roger in Vegas
Worlds Greatest Impulse Buyer

"Roger Hull" wrote in message
s.net...
I have zero foundry experience. I want to melt a few pounds of Copper and
cast it into backup plates for welding. What should I make the crucible
and
moulds out of? OR, is it possible to buy a crucible somewhere?
Thanks.

Roger in Vegas
Worlds Greatest Impulse Buyer

[Nobody casts pure copper. It takes a lot of heat, and oxidizes badly. If
you want back-up plates for welding, why not just get some copper plate and
cut it up?]

Andrew Werby
www.unitedartworks.com

Hi Roger - There's also a lot of information about how to build your
own foundry
on the web. Google for "home foundry" - a lot of hobby machinist types
have made really nice tutorial web pages about how to build a furnace,
sand cast, etc.
You can get a small foundry set up for about $200 (propane). You
might try starting with Aluminum for casting. Cheap, melts easily.

- Jud
www.judturner.com

"Andrew Werby" wrote in message
...
|
| "Roger Hull" wrote in message
| s.net...
| I have zero foundry experience. I want to melt a few pounds of Copper and
| cast it into backup plates for welding. What should I make the crucible
| and
| moulds out of? OR, is it possible to buy a crucible somewhere?
| Thanks.
|
| Roger in Vegas
| Worlds Greatest Impulse Buyer
|
| [Nobody casts pure copper. It takes a lot of heat, and oxidizes badly. If
| you want back-up plates for welding, why not just get some copper plate
and
| cut it up?]
|
| Andrew Werby
| www.unitedartworks.com

So that reminds me of a question I've had for awhile. What's the best
places to get copper plate, and what are the sizes and shapes we should be
looking for? Are there sizes that are more versatile than others? What is
the common ways of securing them in place while welding? Obviously magnets
won't work, so what's best?

On Wed, 24 Aug 2005 14:56:48 -0700, Roger Hull
wrote:

I have zero foundry experience. I want to melt a few pounds of Copper and
cast it into backup plates for welding. What should I make the crucible and
moulds out of? OR, is it possible to buy a crucible somewhere?
Thanks.

Roger in Vegas
Worlds Greatest Impulse Buyer

Ping Tim Williams.

"Roger Hull" wrote in message
s.net...
I have zero foundry experience. I want to melt a few pounds of Copper and
cast it into backup plates for welding. What should I make the crucible
and
moulds out of? OR, is it possible to buy a crucible somewhere?
Thanks.

Roger in Vegas
Worlds Greatest Impulse Buyer


I'm not convinced your plan is well conceived. If you've never worked with
molten copper, you're in for some unpleasant surprises, one of which is the
casting temperature is relatively high, over 2,000 F. It's a bitch to
work with in that it often comes out quite porous. It loves to solder
to almost anything it contacts, to add insult to injury. I can't help
but think you'll spend a lot more money trying to make your copper pieces
than you'd pay for some scrap buss bar at your local recycling place, but if
you're hell bent on melting copper, you'll need a decent furnace, fuel to
fire it, a proper handling tool, as well as a reasonable crucible. One
made of steel won't do well unless you cover it with a wash, otherwise the
copper will dissolve a percentage of the steel and ruin the copper to some
degree. You also risk dissolving through your container if it's very thin.
I'd suggest a graphite clay crucible, or even better, a silicon carbide
model. Bottom line, unless you'd like to do some casting in the future,
you'd be far better off not trying to cast your own plates. The cost of
getting set up is prohibitive if that's your only purpose.

Assuming you get so far as to actually melt your copper, you could probably
use a heavy channel with plates welded on the ends for a mold, but it will
need some mold dressing so the copper won't solder to it. You won't achieve
flat castings, but they'll be close.

Foundry supply houses sell a mold dressing, and would be the source for a
decent crucible and a handling tool. You'd probably have to build your own
furnace, although they sell them, too.

I used to melt scrap copper to cast bars for silver recovery. It was less
than pleasant, and I had the equipment at hand.

Harold

Roger Hull wrote:
I have zero foundry experience. I want to melt a few pounds of Copper and
cast it into backup plates for welding. What should I make the crucible and
moulds out of? OR, is it possible to buy a crucible somewhere?
Thanks.

Roger in Vegas
Worlds Greatest Impulse Buyer


You'll need a silicon carbide crucible and a furnace capable of about
2100deg. I've melted copper scrap using a propane furnace. It takes a
long heating time and leaves a lot of dross or oxide. The pieces of
scrap (in my case, copper tubing) seem to hold their shape due to the
outer layer of oxide. The copper inside melts away leaving the vague
shape of the original piece until well along in the heating process.
Finally, the oxide crumbles and floats on top of the molten copper. It
then has to be skimmed and the high heat of the copper tends to make my
skimmer less than sturdy. It can be done, but melting aluminum is a
better experience.

Gary Brady
Austin, TX

"Roger Hull" wrote in message
s.net...
I have zero foundry experience. I want to melt a few pounds of Copper
and cast it into backup plates for welding. What should I make the
crucible and moulds out of?

Well first of all, read up on foundry practice obviously... ABYMC.com and
backyardmetalcasting.com are good starts.

You *can* make your own crucibles, but the thing with pottery is it has to
be fired slowly (over at least 5 hours, much longer if you need a more
stable product), and any typical formulation is about as good a conductor as
your average 3000 degree rated castable refractory, not to mention the
expansion is greater. Try this: toss a coffee mug on a fire. Watch it snap
into pieces. Thermal shock in action.

Even Vince Gingery in his crucible book goes only as far as grog and clay
with a little feldspar, as I recall. Something like 77% 20-80 mesh grog,
20% fireclay and 3% spodumene (lithium feldspar, a flux). Now fireclay
alone has a high silica content, which - when not tied up as something
else - tends to form quartz or crystobalite. Both of these have dramatic
changes in density at specific low temperatures; the "quartz inversion"
occurs at 573C (1% change, IIRC) and cristobalite at 180C (0.5 to 1%, I
forget exactly). Not only that, but the high grog content, coarse grog no
less, means high porosity - holes that insulate, just what you don't need!
The only thing it's really got going for it is the high melting point - up
around cone 25, at least (2800-3000°F I'd say).

OR, is it possible to buy a crucible somewhere?

Well, yeah...

LA Graphite is the cheapest, IIRC. Clay-graphite takes more care than SiC
or steel crucibles, but can also handle iron if you desire to try that.
Don't use steel, it'll dissolve and not only will your alloy be askew, but
the crucible might burn through as well.

Once you make a furnace and get a crucible, you need fuel... go with
propane, it's just easier. You can use wood, coal or charcoal (stay away
from briquettes), but melting something hot like copper isn't the easiest
goal with it. Not to mention, the uneven and often all-or-nothing heat
control is sure to crack any but the best crucible.

You asked what for mold, sand mold is fine. Read for yourself, I don't have
to say another word on this!

As for melting and pouring copper... use a slight reducing atmosphere. The
posters above who say pipe just kinda sorta collapses royally screwed
something up. Copper is a noble metal and as such, its oxide is very easy
to reduce to pure metal. Not to say there won't be any trouble: oxygen
(gas, not oxide!) is soluble in copper, just like CO2 in water. When it
freezes, it comes out and gives you trouble. The common fix is borax plus
either soda (baking soda, washing soda, etc.) or boric acid, with crushed
charcoal (any kind) on top to absorb the oxygen. If you don't mind
alloying, you can add 1-5% zinc (pennies) and that'll combine with the
oxygen, keeping it clean. There's still the matter of hydrogen, but oxygen
is probably your #1 concern.

I personally have recast scrap wire as ingots for storage. Works fine,
though it did come out all bubbly!

Beware of shrinkage defects in the casting BTW: copper - being pure - has a
steep melting/solidifying point, so it'll want to suck in metal all at once.
Use big gates and even bigger risers. Pour around 2200°F.

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms