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Ingot casting


#1

thanks for all the great info everyone. i still want to tackle this
problem and not send my scrap for refining because i’d like to be
able to cast small ingots in varying sizes for wire and ring shanks,
as well as sheet. so i guess i need a real torch. i’ve been reading
the torch safety thread and almost have myself talked into
oxy/propane. i live in sitka, southeast ak,… (temperate
rainforest,100% humidity all the time)… no one fills acetylene or
oxygen bottles here, they have to be sent away. it’s expensive just
for the shipping. aside from safety issues, if i only have to send
the oxygen away for refilling, it will be cheaper. so will
oxygen/propane serve me well in the future if i decide to do some
centrifugal lost wax casting? lots of people recommend the little
torch from rio grande, but there is only one tip size available for
oxy/propane. are there other torches with changeable tips for
propane? what about the regulators? is there anything special about
propane? as for technique , just how hot do i need my mold to be?
i’ve been trying to pour 3mm round wire ingots in a vertical mold,
and it won’t flow very far down into the mold before it freezes.
also should the crucible be red hot or should i be able to keep the
silver liquid with only the torch despite the heat sink from the
cold crucible? thanks everyone for answering my previous post so
well… d.


#2

Doug, And I thought things were hard to get in Kodiak! At least we
can get acetyline bottles refilled. You say you just want to be
able to cast small ingots for wire and ring shanks. you can do that
with a Smith torch using the small propane bottles you can get in
the hardware store (providing Sitka at least has one of course). I
wouldn’t go to all the trouble of using a crucible and ingot mold
just for that. You can do very well using the charcoal block
technique I mentioned in my last post. Just cut two parallel lines
about 1/2" to 3/4" long, 1/4" apart and 1/4’ deep into a smooth
section of the block with a small thin sharp blade. Chip out the
charcoal in between the lines and smooth the bottom and sides. I use
the end of a small equalling file for this. Pile small pieces of
scrap sheet and wire that do not contain any solder in the trench
thus created. Sprinkle on some boric acid powder and melt until the
surface is bright and shiny and the little beads of molten borax
swim around on the surface, Take the torch away and immediately
press down on the molten glob with some flat smooth metal object.
That will force the metal pretty much into the shape of the
depression. (I use a roller bearing from the roller path of a 5
inch 38 gun mount… you probably can’t get one of those in Sitka
either, so you’ll have to improvise). When the ingot thus formed is
solidified, pop it out and quench it. I don’t know if it’s
necessary, but at this point I anneal the ingot and then proceed
with the rolling, drawing or whatever.Hope this works for you as it
does for me. Jerry in Kodiak


#3
 Smith=AE Little Torch=99 Propane/Oxygen Outfit Rio Grande now
offers this new kit, which accommodates both propane and oxygen gas
use. The five-pound propane tank easily refills at your local
pro-pane station. The steel carrier holds the tanks secure next to
the bench. The outfit includes: a five-pound propane tank; five
tips (#3-#7); 20-cubic-foot oxygen tank with stainless steel
carrier; Smith=AE propane and oxygen regulators; and the Little
Torch=99 with two six-foot hoses. Jewelers may call (800) 545-6566
from the U.S., (800) 253-9738 from Canada, or (505) 839-3011 from
all other countries. Or, fax (800) 965-2329, e-mail
info@riogrande.com, or visit www.riogrande.com 

Sounds like there’s no ‘specialness’ to it’s propane, also it quotes
five tips as opposed to one. Since many have recommended this
product, how do they find it’s fared in casting? All the casting
I’ve done to date is with pure propane tanks, we tend to have two or
three in use to heat the crucible and melt the silver, so with the
Little Torch=99 is more than one torch required?

The New Brunswick College of Craft and Design under Ken Valen
recommends prepping your crucibles with borax first. You bring it
to a red heat, toss in some borax and repeat until you cover the
inner surface of the crucible (if you contaminate the crucible with
too much solder or what have you bringing it to a heat and scrapping
out the offending pieces and re-prepping is the recommended fix).
We bring the crucible to a good heat, toss in your pieces of
sterling, a bit of borax and swish it about, when sand casting (or
cuttlefish) for example you keep the silver under heat until the
last moment, poor in a fluid motion, and so long as your mold
doesn’t go against the gravity the vertical casting should turn out.
The longer the distance the molten silver has to travel the greater
the chance of it getting caught up and consequently not going
anywhere. Making a few air vents may also help, never had to in
sand casting, always did with cuttlefish bone. Hope this help.

David
Fredericton, New Brunswick, Canada


#4
   thanks for all the great info everyone. i still want to tackle
this problem and not send my scrap for refining because i'd like to
be able to cast small ingots in varying sizes for wire and ring
shanks, as well as sheet. 

G’day Doug; I was going to write directly to you but don’t have
your address.

However, I have been making ingots for many years such as you seem
to require. I reckon that the first thing that you need to do is to
stop trying to use the tall graphite crucible and to buy a flat
alumina dish crucible so that you can play your good torch flame
directly upon the metal. I have always used propane and of course
the heat is greater even with a quite small flame if you have oxygen
boost, but a decent air-propane torch will do the job, provided, as
I said you use the flat dish type crucible and play the flame on the
metal. Just before you pour. add a pinch of borax, and silver will
look and flow like a pool of mercury. Keep playing the flame on
the metal even as you pour. As for heating the mould, well, it
doesn’t need to be much hotter than too hot to touch, certainly not
red heat. but do take care that the mould contains no moisture, or
steam will drive the hot metal straight out again. It is considered
to be unlucky if you put your face in the way of exploding red hot
metal.

I made my own 3 and 5 mm diameter rod moulds from two pieces of flat
1cm thick steel, clamped together and drilled lengthwise where they
meet to make the actual could cavity. You will need to place two
pins, top and bottom of the moulds to allow you to register the half
cavities properly and easily. When you come to pouring the metal,
have the moulds at an angle towards the crucible, not vertical, and
make sure the opening is widened to become a funnel… And don’t
clamp the two halves too tightly together; a tiny gap of a couple of
thous between the plates will allow air to escape as you pour the
metal. This will give a thin “flash” of metal, but you can quickly
file that off . Do anneal the little rod ingot and pickle it before
attempting to roll it. If the first pour doesn’t give a good rod,
then have another go! But stand your loosely clamped moulds in an
old metal plate, so if you miss-pour you won’t lose metal. - I use
an old frying pan that has lost it’s ‘non stick’ .

If you want to cast a small piece of flat metal, use the mould
plates back to back separated by a piece of U shaped heavy gauge
wire - at least 3 mm. thick Questions? Send me a note personally,

Cheers for now,
John Burgess; @John_Burgess2 of Mapua, Nelson NZ