Build the walls and floor of your refactory furnace with a heat-resistant brick. Gypsum block, cement and chamotte bricks or a high melting point ceramic of silica or alumina are the best choices. The furnace should have a cylindrical shape about 1.5 times the diameter of your crucible. The opening should be at the top with a hole in the center the same size as the torch hole. Leave a hole at the bottom of the wall at a tangential entry for the torch. Make sure it fits exactly.
Weigh the metal and fill the crucible. The crucibles that work best with cast iron DO NOT include graphite. A crucible made with Hessian clay works the best. Put the crucible in the furnace.
Light the fire using newspaper as kindling between the wall and the crucible. Turn on the gas (torch) slowly and once the paper catches you can turn the torch to full power. If the torch roars loudly, it's fine.
Inhale a whiff as the fire burns. If there is a bad smell, then the combustion isn't complete because the walls are too cold. Take the lid off the furnace for a few minutes and put it back on to fix this problem.
Use a thermocouple to watch the heat. You want to heat the cast iron to 1300ªC / 2500ªF for fifteen minutes. You will know you have reached this temperature when the crucible's bottom is light yellow, nearly blinding in color.
Remove the crucible from the furnace and heat. Add a teaspoon of borax to dissolve all oxides.
Pour the molten cast iron metal into the molds you have purchase. Let cool.
Things You Will Need
- Dark welding goggles
- Optional face shield
- Oven gloves
- Large flat iron pan to put the mold on
- Molds (your personal preference to size and shape)
- Running cold water or five gallon bucket full of cold water
- Optional heat resistant bricks
- Gypsum blocks
- Optional chamotte blocks with optional alumina based concrete
- Propane gas torch with shorten nozzle
- Propane gas
- Optional steel pipe for shortened nozzle
- Non-graphite crucible
- Optional Hessian crucible
- Crucible tongs
- Preheat meltal molds above 100ªC / 212ª F to remove moisture.
- The sand in sand molds shouldn't be too wet.
- Hot cooling objects should not be near tools.
- Wear shoes you can easily kick off if any molten metal falls on them.