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Bronze Art Casting Process
The bronze art casting process starts with creating a mold of the master model. The original sculpture is covered with a thixotropic rubber which hardens to create a reusable mold. This mold is reinforced so that it is stationary for the creation of a wax replica of the original model.
Wax is poured into the mold, taking care to fill all of the mold cavities in order to get a complete reproduction of the original artwork. Once hardened, the wax pattern is altered to include wax runners or gates that will allow metal to eventually flow into the hollow pattern cavity. The arrangement of gates and sprues (which form the primary metal pathway) varies depending on the pattern.
The next step involves coating the wax tree in a slurry. Slurry is a mixture of liquid binder and flour refractory materials. Depending on the alloy being cast, drying time requirements, and number of coats desired, the binder and flour materials used may vary. If you are new to the process, we recommend reviewing the Introduction to Ceramic Shell Investment Casting for detailed recommendations.
Once the tree is dipped in the slurry material, and excess material is drained from the tree, it is then coated with sand, commonly referred to as stucco. This can be done in a variety of ways 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 take place again. This continues 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, it is time to remove the wax from the mold. This is accomplished by use of an autoclave or a FlashFire dewax oven. The wax will melt out of the shell leaving a hollow cavity.
The shell is then placed into an oven where it is fired for a given period of time. This assists in strengthening the shell and removing any remaining wax residue from 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.