Hello Folks
I want to cast a tree of about 500 grams of sterling, but I’m not
sure if that it will be possible with a Harris torch with a heating
multi tip using Oxy-propane mix.
Thank you.
Gustavo Suarez
Gustavo,
My largest sterling casting so far was about 26 ounces, this is
really more of a foundry project than a silversmithing one. It is a
1/2 KG melt, so you need to be careful, that is alot of hot melt
flying around
Some pointers:
a) have a clear retreat path, free of trip objects, so you can run
away if you have to, if something goes wrong. make sure no objects,
including people, are in the way.
b) use ‘gates’ for venting your model. if you are using investment,
then you may want to use a vacuum assist, which can also be done in
sand but it is more complicated
c) use a furnace for melting the metal; you can use either a melting
furnace, a casting furnace with a crucible and charcoal blocks, or
you can build a temporary one with bricks and/ or soldering blocks
d) plan your pour path, and do a “dress rehearsal” of the motions
that you are going to do during your pour, when everything is cold;
you may find that you need different tongs, etc to move the large
items, best to discover this when everything is cold.
e) allow for metal shrinkage; on larger pieces, the dimensional
change can be quite dramatic from hot to cold. I have had a 5" wax
model turn into 4.75" of metal after casting; the 0.25" can be quite
dramatic if you are trying to either 1) get parts to fit together, or
2) extract the casting from other objects used to make the pour
mold.
with large amounts of metal, it takes a large amount of heat; in a
2500 watt furnace, going full tilt, it can take a 1/2 hour or more
to melt this amount of material; with a torch, it could take an hour
or longer.
good luck, and let us know how it turns out.
warm regards
Mark Zirinsky
denver
Hello Gustavo;
I doubt you’ll get that to work using a torch. Enough flame and
you’ll melt it, but you’ll be inviting lots of problems with porosity
keeping a torch on it that long. I once worked in a shop where we
cast something like that, I think aroud 400 grams, but we used an
electo-melt. Problem is, even with vacum casting, the pressure from
that amoung of metal blew right through the bottom of the mold and
and filled the vacume machine’s hoses. Nasty mess, had to replace all
the hoses and valves. If you tried to cast in with centrifugal, you’d
have metal sloshing out of the falsk for sure, and what didn’t would,
again, likely blow out the bottom of the flask (if you could fit that
large of a flask in your machine). Personally, as much problem as
silver is to cast, I’d contract that job out to a casting company. It
would be money well spent to avoid the problems.
David L. Huffman
HI Gustavo
if you look again you might be able to cast the item in more than one
mould and join them together afterwards It will need a bit of good
mould designing
Thats gonna be your best bet
Frank
Hi Mark and David
Thank You very much for your advise and warnings
I resolve the issue lowering the amount to 270 gr of sterling in a
vacuum machine and It work pretty well, a little porosity due to no
precise torch control I guess, to much heat. So, I hope next time it
will be better.
Gustavo
I used to do production casting and I melted 350 grams of sterling
to centrifugally cast into a 3"x7" flask with a large oxy-acetylene
welding torch.
Takes about two minutes to melt the metal, 500 grams would not take
much longer.
I used to buy 1000 gram sterling bars and holding the bar with tongs
I would heat the bar holding it 4-5 feet over a 5 gallon bucket full
of water to make shot for casting. The concept of having to heat the
whole piece to get solder to flow is a moot point when you are
trying to melt one end of a bar. Get that flame hot enough and the
bar surrenders, and I talking a few minutes at most. Was it somewhat
dangerous, absolutely, was it fun, absolutely. The metal was so hot
that it would travel the length of a 5 gallon bucket full of water
and stick to the bottom of the bucket and I would have to dig some
of the metal out of the plastic. This method did not contaminate the
sterling, the castings came out fine. I really like fire. I really
like melting metal. One of the most beauti= ful things to me is when
sterling or gold is in a liquid state just before casting it. The
metal glows, the surface is clean and shiny and it is very fluid.
Using two gases that can transform a solid into a molten mass that
can be reformed is quite amazing, and I never am not in awe.
Richard Hart G.G.
Jewelers Gallery
Denver
My largest sterling casting so far was about 26 ounces, this is really more of a foundry project than a silversmithing one.
It’s actually easily done - IF YOU HAVE THE EQUIPMENT. We use a
standard centrifuge, which takes a 12oz crucible, max. That’s about
360gms, and we avoid castings that large, even. I toured a large
casting company long ago - 100 employees, 30 wax pots, a white metal
department. Among other things they had a 6 foot long centrifuge
that took eight inch flasks. But that was custom made, and well
made, by a machine shop and cost about $10k. Comes a time to let the
specialists do the specialties…
I recently cast a part of one of my large pieces of pottery.
The wax with sprues weighted 59 grams. The final casting with sprues
and sprue button weighted 823 grams.
There was only 1/4 inches between the flask and the wax with only 1.5
inches of investment above the wax.
The silver was melted in a large Electro Melt furnace.
I have cast many of these large creations without failures.
Check out my blog on the subject.
http://leessilver.ganoksin.com/blogs/
Lee Epperson
I regularly cast over 500gm sterling in a single casting, although I
use ceramic shell and not the usual jewellery investment. A small
air-propane torch from a 3.9kg bottle heats 500gm sterling from room
temperature to 1000C (the temperature I usually cast at) in just
under 15 mins. You can see the furnace I use on
the furnace is the small cubical white box on the far table in the
centre right of the picture. The lower picture shows the furnace with
the dome replaced with a smaller ceramic fibre ‘hat’, for casting
smaller amounts e.g. 100gm metal.
The same furnace easily heats a kilo of bronze to melt temperature
in something over 30 mins. The furnace is now getting rather worn
out, I have probably cast at least a couple of hundred kilos of
silver, and probably 50 kilos of silicon bronze and ‘art’ bronze, in
it over the past few years. I have a somewhat larger furnace I use
for 1 to 20 kilos.
Paul Jelley
London