Now that the burnout is complete and the molds are sitting in the kiln at 900F, I am ready to vacuum cast. I fill the crucible with bronze. In this case I’ve salvaged silicon bronze from my last casting: these are sprews and sprew caps cut up and sand blasted to get rid of any foreign material. A propane burner provides a constant heat into the fire brick oven.
I heat the bronze with a rose-bud tip on an oxy/acetaline torch until the bronze is molten at around 1900 to 2100 F. I remove any slag from the top of the molten metal with a steel rod and open the kiln to get the mold.
The mold is removed from the kiln and placed in the vacuum caster making sure that the heat resistant rubber seal is snug with the steel flange on the mold. The large part of the mold descends into a vacuum chamber. The steel flange sits on a rubber “o” ring to create a seal so that the vacuum pressure will suck the bronze into the mold.When the bronze is ready, I turn on the vacuum pump on the casting machine and bring the molten bronze to the mold.
I pour it quickly into the sprew cap. Once the pour is complete I turn off the vacuum pump and remove the mold from the rubber seal as soon as the bronze is no longer molten.
Once the bronze sprew cap is at a black heat I quench it in cold water. This blasts off the investment solution and anneals the bronze. It’s an exciting moment when the mold is screaming and bubbling under the water and then you draw out the bronze to see if it filled or not.
A successful casting! Once the bronzes have dried I sand blast them if I’m planning to patina them, or if not I clean them with a fine wire brush.
Here they are sand blasted.
Now I cut the sprews off with a jewelers saw and fit them to the blade.
Here are the castings assembled as part of a finished project. Thanks for reading!by