John and I cut up some scrap bronze and then loaded these clean pieces into the electric melting furnace that I have. We could have easily melted some metal in a crucible with an torch, but I thought it would be easy to keep restocking the furnace with fresh bronze and we would have molten bronze available each time we were ready to pour a mold.
The crucible on this furnace is made of graphite that can be replaced as it wears down from repetitive melting sessions.
The temperature can also be digitally controlled.
Once the metal is up to temperature, we are able to pour molten metal into the mold. Once poured the metal solidifies fairly quickly. I wait for the button to stop glowing and then I am able to split the mold.
Care must be taken as the heat from the metal has transferred through the sand and to the metal flask. Usually I would wait a bit longer to open the mold, but we were looking to produce these quickly, so we opened the mold right away. You will notice a dark shell of carbon like sand surrounding the part.
I tap the button of the piece against the concrete floor and this shell crumbles. It is actually good to lift the piece and shell out of the mold intact as that keeps the sand mold free of the chunks of black hardened sand. The sand in the mold flask can then be put back with the excess sand from in the molding pan and chopped up to be used on the next mold. Just make sure to discard any of the hardened and black sand as this will contaminate your good sand.
The final cast piece can have the button and sprue cut off and then that material can be remelted and used to cast the next piece. The cast piece can be pickled in avery diluted sulphuric acid solution to clean any impurities that are on the surface of the piece. Now it's time to finish the piece....