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Ceramic Shell Casting Process
The ceramic shell casting process starts with wax injection. A die, or tool, is filled with wax, injected in a liquid or a paste form, so it flows into the detail of the mold. Once cooled, the wax piece, or pattern, is removed from the die.
Several wax patterns are attached to a wax pole, or sprue. Each pattern is attached to the sprue by smaller pieces of wax runners, typically referred to as gates. Gates allow for the eventual creation of a space where molten metal can flow into the hollow pattern cavity. The complete assembly is referred to as a tree.
Next, the wax tree is coated in a slurry, a mixture of liquid binder and flour refractory materials. Binder and flour materials used vary depending upon the alloy being cast, drying time requirements and the number of coats desired.
Once the tree is dipped in the slurry material and excess material is drained from the tree, it is then coated with sand, or stucco. This can be completed in a variety of methods including rainfall sanding, use of a fluidized bed or by hand covering (the cat box method).
After each layer dries, the dipping and stuccoing steps are repeated and continue until the shell is completed. The number of coats will vary depending in part on the pattern configuration and the binder used in the slurry.
Once the dipping sequence is completed and each coat has air dried sufficiently, the wax is removed from the mold with either an autoclave or a FlashFire dewax system; which will melt the wax out of the shell leaving a hollow cavity.
The shell is then placed into an oven where it is fired for a predetermined time period. This assists in strengthening the shell and removing any remaining wax residue from inside the shell.
Finally, the fired shell is placed in a bed of sand with the pour cup opening facing up. Molten metal is poured into the shell. The shell takes on the orange glow of the metal and eventually turns white as the metal cools. The shell is then removed, the parts are cut off of the tree and the finishing area takes care of grinding away any sign of metal from the gating.