The operation of a small small foundry





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Published on Aug 10, 2010

A COMMENTER SUGGESTED USING A REGULATOR FOR THE PROPANE TANK AND YES, PLEASE DO THAT IF YOU ARE USING PROPANE TANKS, ALSO, AVOID TAPING YOUR GAS LINES TOGETHER. I plan to make a couple quick videos on the operation of a small foundry. This is the first video in this series. The best use of a
foundry like this would be for the artisan, or the small job shop. Since natural gas is used which is mostly composed of Methane the upper limit on temperature of this foundry in practical terms is about 1800 degrees, or just hot enough to melt true bronze.

There are two widely used casting techniques to make the molds the molten metal will eventually be poured into. One technique is sand-casting where a refractory sand with a binding agent like dextrin is used with a small amount of water and the sand holds an impression of what is to be cast like a wet dirt ball. The sand can't be too wet as you'll form steam pockets in your casting when you pour in the molten metal, but just wet enough to hold together. This is one of the trickery parts to sand-casting, getting the right moisture content of your sand to make it hold together and get an impression of what is to be cast and not get flashes of steam as molten metal is poured. As molten metal is poured into the mold it will super heat the moist sand and if there is too much moisture it will cause what looks like air bubbles in your finished casting. Sometime the steam generated can cause a min-volcano of sputtering liquid hot metal which is very dangerous to be around. For sand-castings the object being molded should have at least a 3 degree taper so it will pull out of the sand easily. Under-cuts in your mold in sand-casting are always more of a challenge and require that you section your mold into more than just two halves.
For the lost-wax-method you carve your pattern in a block of wax then put refractory plaster around the wax piece and then melt out your wax out of the plaster cast. The beauty of the lost-wax-method is there are no worries about complex mold making for under-cuts and nothing has to be purposely tapered to 3 degrees so it will pull out of the cast like in sand casting. The down side to the lost-wax-method is that you have to generate a new pattern for every new piece to be cast so everything cast is one of a kind. All your bronze statues you see in parks and the like use the lost-wax-method. Naturally, the plaster is cooked for awhile to get all the wax out, as like water, it has a flash point where it will instantly turn to a gas at the temperatures of molten metals. I have used an out door grill to bake out the wax on my smaller projects. Using an indoor oven I think would be a big mistake and very stinky.

The next video will be a quick video on sand casting.
friendly advice from a lawyer/ tinkerer: people are on here looking for how-to and will copy what they see. it's all fun and games to demo a foundry barefoot and in shorts until somebody who sees you spills molten metal all over the neighbor's kid who was standing there in bare feet and legs not realizing that it could spill and hurt, like yours almost did when you set in teetering on the grass. that said, cool setup.

gscatty 8 hours ago

@gscatty definitely wear leather boots. Any moisture in the sand and you get a small volcano sputtering hot aluminum, or brass for some distance from the pour. I took a load of hot molten lead on my arm once after pouring molten lead into a moist plaster mold. I burned my arm good. Leather and nothing plastic (It melts) is going to make the best barrier for a temporary splash of red hot liquid metal. Leather: boots, chaps, apron, gloves, cap, and a plastic face shield are a must!


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