Pouring Gold and Silver Bars
Pg. 20 - 21
Here are some inside Diameter Specs. for graphite ingot molds I just used a bench drill press to cut them out. I think a router could get messy and create to much dust with the high speed.
Once you have added the alloy to the 24 karat gold you then
melt, flux, and stir the molten alloy using the procedure
mentioned previously. then pour the molten alloy into shot.
When you are ready to pour bars make sure the bar molds
are very clean. If you are going to pour into a graphite ingot
mold be sure to preheat the mold to drive off any moisture
it contains or the metal will explode when it contacts the mold.
Graphite molds will absorb water from the air so they have
to be heated prior to pouring molten metal into them. Be
sure not to pour any boric acid or borax slag into the graphite
molds or it will stick to the mold and you will damage the
mold chipping it out. Heat the graphite molds enough to
drive off the moisture but not to red heat because this will
will make the mold weak and porous. No oil or lubricant
should ever be used in a graphite mold like you can do with
an iron mold. Iron molds should never be too hot when
pouring gold or silver into them or the metal will fuse to
the mold. Warm the iron mold just to hot to the touch and
it is ready to pour into. Slag can be poured into iron molds
with no damage being done to the mold. It's important to
keep a different mold for each metal or alloy that you pour.
For instance don't use a mold that you have been pouring
silver into for pouring 999.9 gold bars . It's okay to pour
any alloy of scrap into the same bars prior to refining but
if you are producing 999 silver, 999 gold or karat alloys
for sale them you should have a separate mold for each.
The torch flame should be feather like and completely cover the surface
of the metal. The oxygen should not be turned down far enough to allow
the metal to cool below the desired pouring temperature of the metal when
you are pouring. When you have completed the pour, turn off the oxygen
and play the hydrogen flame on the bars surface as it cools and solidifies.
You should be able to develop some skill handling the oxygen - gas
controls with the hand you hold the torch with because you will be holding
the crucible with your other hand. I like using hydrogen gas better than
other gasses because it produces a very hot flame with no contaminating
properties and you can use an oxygen regulator fit with an adaptor to fit
the hydrogen cylinder.
When pouring from a blast furnace the air should be reduced or the
gas increased to produce a flame extending 6' to 8' above the hole of the
furnace for approximately 3 to 5 minutes before pouring. You should have
an assistant stand by with a torch fitted with a rosebud tip and play a
hydrogen flame on the bars as you pour them. If you are pouring 500oz.
or 1000oz. bars you will be using 2 man tongs and you'll need a third
person to handle the torch and bars.
When the oxygen in the heat source is enough to form oxides on the
metals surface you have an oxidizing flame and it is creating an
oxidizing atmosphere. When the oxygen is reduced or eliminated
in the heat source and is low enough to reduce oxides on the molten
metals surface back to metal it is called a reducing flame or reducing
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