Centrifugal Casting

In preparation for the fall semester I spent a good portion of last week working on learning a Centrifugal Casting process to translate a 3D scan into Bronze. The form I produced in metal is the now familiar Barbe Ornament by Louis H Sullivan that we captured in 3D almost two years or so ago.

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Louis Sullivan “Barbe House” relief milled at CDFS

I milled the positive for the process from modeling wax on a Roland Modelo bench top CNC in the Columbus Digital Fabrication Studio at SAIC. The wax form was milled in two passes and took the best part of a day to do each operation.

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Sprued up and connected to the button the wax model is ready for investment

Once the wax positive was milled and the excess material removed it was sprued up, weighed and fixed to the “button” ready for investment. It is important to weigh the positive plus the sprues to determine the amount of metal needed for the cast. The final weight of the workpiece is multiplied by the specific gravity of the metal which results in the actual amount of metal used.

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On the left a flask holds the wax model and is partially filled with investment material. The bucket on the right holds the remainder of the mixture. Both are “bubbled” in a vacuum to remove the air.

The next step was investing the flask with a silica / plaster combination. The plaster mixture was “bubbled” in a vacuum chamber to remove air trapped in the mixture. The following day the flask was placed in the burnout kiln and the wax was incinerated leaving a void for the metal to occupy.

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Grains of “Ancient Bronze” prior to casting

For the final step, casting, grains of “Ancient Bronze” were placed in the cupola and heated to their melting temperature with a torch. The flask was retrieved from the kiln and placed inside the centrifugal casting apparatus. One the count of the three the pin was dropped and the tightly wound spring quickly rotated the flask and cupola in one swift motion, expelling all the molten bronze into the mold.

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Centrifuge at work. Slowing down.

Once the apparatus had stopped spinning the flask was removed and placed to one side to cool. Once the pour spout had stopped “glowing” the flask was quenched in a bucket of water and divested. The bronze workpiece was cleaned and set to one side. I elected to keep the sprues on in this instance to better show the process later on. Plus i quite like that it stands up. Massive thank you to SAIC Materials Lab Manager Erika Uzmann for demonstrating the process, setting up the kiln and running the casting process.