The BMC Foundry is staffed by volunteers Bill Koch, Henry Scmidtt, Zachary Pritchard and Maryrose Fridey. Together the crew has over 80 years of fabricating and metal casting experience. Not only have they put the BMC Foundry together, they’ve fabricated many unique pieces of equipment, put together events, workshops, and educational classes, and cast bronze and aluminum objects for various projects. They are open to casting boat parts, decorative maritime elements, or artwork.
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The first step to taking on any metal casting project comes with a consultation with a customer, application, opportunity or request for proposal. It can involve custom hand drawings, computer graphic designs, to life scale drawings, or models, but most often a combination of all.
During the modeling phase the sculpture is hand modeled over an armature. We most often use oil based clay over a combination of welded steel and foam.
The drawings and models created during the design step are closely studied while modeling. Each step of the casting process after the modeling is intended to re-create this form in metal.
After the sculpture is modeled in clay or wax a foundry mold is needed to be made. Every sculpture will have different requirements for the molding stage which is entirely dependent on its form. We focus on two different types of foundry molds; resin bonded sand molds and ceramic shell molds.
Resin bonded sand molds (sand molds) are molds that are made by mixing a fine grain sand with a foundry grade resin. Sand has high heat refractory properties. The resins we mix with the sand make the mold sections set up rock hard. When the metal enters the mold the sand doesn’t start to break down until the metal has cooled to a proper temperature. The mold sections are then pulled or broken off and the castings are retrieved.
Ceramic shell molds start off with a wax pattern. The wax pattern is dipped in a slurry mixture and layers of sand are added. These layers are built up until a proper thickness is achieved. The wax is then burned out and the metal is poured in to the mold.
Each molding process has its own benefits and disadvantages, including price of materials, time it takes to make the mold, desired surface quality, and numerous other factors. Each sculpture is unique. We decide which process will be undertaken from the start of the project. Often a plaster or silicone mold is needed to be made from the clay model in order to make a ceramic shell mold. Many larger or more complicated sculptures require a combination of both sand and ceramic shell molds.
The metal casting step is what it is all about. Bronze is poured at 2150 degrees Fahrenheit. That is hot.
The metal is melted inside of a crucible, which is essentially a pot made of a mixture of clay and graphite. The furnace houses the crucible. We use a furnace powered by natural gas and forced air. The gas and air mixture enter the furnace at an angle in order to spin around the crucible in a circle to create a maximum amount of heat.
Once the pot is full of metal and at the right temperature it is lifted out of the furnace. It is placed into a long handled pouring instrument called a shank. The impurities in the metal float to the top of the crucible and are skimmed off. The metal is then hand poured into each mold as swiftly as possible in order to keep the pot at the correct temperature and to properly fill the mold.
The casting process is exciting, fun, dangerous, and often nerve racking to watch. It’s the most fun part of the metal casting process and what many metal casters live for.
Welding and Chasing
Once the molds are poured with metal the castings are broken out, cleaned up and often welded together.
We weld over any imperfections in the castings and blend in all welds to make the sculpture complete. The process of grinding down any extra metal from the gating system or welds is called chasing.
Patination is the final step. During this step various chemicals are sprayed over often heated bronze to create an array of color. Aluminum is anodized or oftentimes powder coated. After the patina is applied layers of a protective coating are sprayed on and a thin coat of wax is rubbed over the surface.