This tour was conducted on November 24, 2003, at Conbraco Industries, Conway, SC plant. The people in these photos were classmates of mine as an undergraduate in Materials Science and Engineering at Virginia Tech.
Conbraco did sand casting and ceramic shell (investment) casting. Of most interest to us was the investment casting, as this process is used throughout the world as a way to make a lot of parts with little cost.
Sturm Ruger was the first company to cast handguns this way, and the nay-sayers said that the handguns will be garbage. As it turns out, Ruger handguns have separate instructions for handloading (making your own ammunition), as they are STRONGER than other handguns.
The steps of investment casting are shown below:
First, wax molds are created. They had a machine that made theirs, and we made ours by hand. Once made, they were attached to a wax tree by means of slightly melting the wax.
After treeing the molds were ready to be dipped in ceramic. Here are our molds:
The trees were carried by overhead conveyor belt to the slurry machines. The object was to coat the trees in a ceramic that would be thin enough to capture detail, but thick enough to hold the hot metal.
The ceramic molds were fired to burn out the wax (hence the name ‘Lost Wax’ or ‘Investment’ casting) and to harden the ceramic shell. The preheat furnace takes the ceramic shell to around 1900F.
The metal is poured in at around 2800oF. Some of these pictures are from the sand casting line, but others are from the ceramic shell line. The ceramic shells are placed in a bed of sand and after the metal is poured, a chunk of hexane is tossed in and a hood lowered over the sand and shell. The hexane consumes the oxygen and reduces oxidation.
The shells are allowed to cool and then hit with a sledge hammer to remove the ceramic material. The pieces are separated from the tree and finished with a grinding wheel.
*Note: I originally made fun of the above photo, not realizing how serious of an issue this was. Now that I know a little more about inert gas and confined spaces than I did when I was a junior in college, I see how serious this is!!!
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