Sand casting — or by its real name Green Sand Casting — has been around for a long time. Green sand is not green in color but is tan like what you see on the beach. The term green sand means that the sand is not cured before the molten metal is poured into the mold. In the 1700 and 1800s sand casting made it possible to mass produce tools, cooking pots and stoves at low cost. Everything from frying pans to steam locomotives were cast in gray iron in Green Sand Molds. (Gray iron is poured at a temperature of 2500 degrees F.) These large foundries of the late 1800s became the steel industry that was so dominant in the east all through the first half of this century. The old methods of Green Sand Casting of the turn of the century that fell aside to more cost efficient methods and automation are well suited to use in homebuilt aircraft as most of the parts needed are small and need only a small amount of molten metal to cast them. Thanks to a very good book by David J. Gingery, 'The Charcoal Foundry", I discovered that you can save a lot of time and money on odd shaped fittings if you cast them in aluminum rather than having them made at a machine shop. The small foundry that I made from Gingery's book is a 5 gal. paint can with a 2 inch thick refractory lining inside that's made of sand and fire clay like you use for the bricks in a fireplace. At the refractory bottom lining there is a 1-1/4" pipe for the air blast from a hair dryer to enter. The top is cast of the same refractory materials with a 3" hole in the center and wires running through it to the outside ring which is made of sheet metal with ears on each side that can be removed to add metal to the pot. The pipe at the bottom of the furnace is called the tuyere (tweer). This is where you connect the output of the hair dryer to produce the blast and to get the 40

heat to the point that will melt aluminum (about 1500 degrees F). I used a one quart cast iron sauce pan with the handle cut off for my crucible to melt the aluminum in my "back yard foundry". I made a pair of tongs (about 3 ft. long) to fit the pan so I could remove it from the furnace and pour it in the mold. These simple tools work just fine as you will note in the photos of a wing mount being cast out of aluminum from a piston. The most important part of your back yard foundry is the molding sand. Without good sand, you can't make a good part! Molding sand is simple to make — I used a mix of 100 Ibs. silica sandblasting sand of 75 mish, 25 Ibs. of fire clay and 1 Ib. of corn flour — you can use just about any kind of flour, wheat, cornstarch or even wood sanding dust. You can substitute bentonite clay for the fire clay but you will only need a small

amount. I made a box out of 2" x 6" lumber with a plywood bottom and hinged cover in which to mix and store the sand. It is 2' x 4' and has a sturdy support under it. That little box will gross out at about 150 plus Ibs. Temper of the sand is when it is moistened properly. The sand must be damp but not wet; too little water and it will not hold the form — too much water and you can have a steam bomb! A good test for the proper temper is to take a handful and squeeze it into a sausage shape — you should see the distinct imprint of your fingers. Then break it in half and it should break cleanly without crumbling. If the sand passes this test, it should be just about right to use. Before we can start to cast parts, we need a few more tools to make the molds. You need a riddle to sift the sand — a 16" x 16" box made of 1" x 4" lumber with a 1/2" square wire mesh for

the bottom. You simply scoop the sand into it with an empty coffee can to break up the lumps. Next you will need a rammer — a large wooden hammer handle. It is used to pack the sand down over the pattern. Next are the sprue pins .. . they are a short length of pipe, dowel or broomstick. They provide the entrance for the molten metal. Then we come to the flasks. To make a mold you need a top and bottom flask called the cope and drag. The flasks are made like a box with no top or bottom. To use the flasks you need a molding board and a bottom board. The two boards are cut from plywood a little larger than the flasks. To make a mold you lay the lower half of the pattern on the molding board, set the drag over the molding board and then ram the drag full of the molding sand, strike it off level and rub the bottom board down onto it. Now roll the drag over and remove the molding board. You will have exposed the parting surface of the drag and the bedded pattern. To finish the mold, put the cope in place over the drag, put the top half of the pattern in place and set one or more sprue pins in place, then ram in the molding sand to the top of the cope and strike it off level. Vent the mold with a vent wire made from a 1/16" diameter stiff wire, pressing it into the mold over the pattern. Now open the mold, remove the sprue pins and cut a gate from the pins to the pattern. Cut a funnel at the top of the sprue holes and then remove any loose sand. Close up the mold and set it down by the furnace and it is ready to pour. Fill the furnace with charcoal so the lid will close with the pot or crucible inside, fill the crucible with aluminum, light the fire and turn on the blast. CAUTION! Charcoal is essentially carbon. When you burn it at high temperatures it produces CARBON

MONOXIDE at DANGEROUSLY HIGH QUANTITIES so use it outside in well ventilated areas only. Melting of the metal is really very simple — the furnace does all the work. When the temperature gets high enough, the metal will melt. The DANGEROUS part is transferring the molten metal from the furnace to the mold. Make a sand bed for your work area and never carry the pot of molten metal outside of it. MOLTEN METAL SPILLED ON CONCRETE CAN BE EXTREMELY DANGEROUS. When the metal is ready, remove the pot from the furnace with the tongs and pour it into the sprue hole in the top of the sand mold. Pour steadily until the mold is full to the top of the sprue. There should be lots of steam and maybe a sound like frying eggs. If the mold is not too wet, nothing violent — like boiling and bubbling in the sprue as it nears the top — will happen. Now pour any extra metal in an ingot mold. I use a 41

cupcake pan. You can now take a rest and clean up — it will take about 1/2 hour for the metal in the mold to cool to the point that you can open it. If all goes well, you will have a good part that, with a little finishing, is ready to use. If not, all you have to do is put it back in the pot, melt it and try the mold again. The only loss is some time and a little charcoal. Everytime you try a casting you will learn more about it and become a better SAND CRAB. Look back to WW-II and how they mass produced all the great aircraft. Almost all the fittings from the control stick and rudder pedals to the flap hinges were aluminum castings. As you can see by now there is no real trick to it. Like any other skill it takes practice to get it right but so does setting a rivet or welding 4130 tubing. Remember the steps — you make the part you need out of wood, then you press your wood pattern into the sand. Take out the pattern and pour in the molten aluminum. Take the part out of the sand, clean it up and put it in your airplane. Education about how an aircraft is built is what the EAA is all about... the more you know about the way it has been done in the past will help you make safer homebuilts in the future. Recommended Reading Charcoal Foundry by Dave Gingery. Green Sand Casting, Lindsay Publications Reprint. Patternmaking 1905, Lindsay Publications Reprint Casting Aluminum by C. W. Ammen All of the above are available from Lindsay Publications, Inc., PO Box 12, Bradley, IL 60915-0012.

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