At XelaTeco, an affiliate of the Guatemalan NGO where I'm working on a D-Lab project, an "appropriate technology" process is used for casting metal machine parts. Used motor oil, much cheaper than propane or other potential fuels, flows down a hose to fire up a foundry, where scrap metal is melted. The machine part to be cast is pressed into a box of sand and removed to leave an impression. The molten metal is then poured into the mold, creating an exact replica of the original machine part. Though not the cleanest process, this particular sand casting method makes use of motor oil that would otherwise be discarded. XelaTeco uses the process to make parts for micro-hydroelectric turbines, one of the sustainable energy technologies it's promoting, and for other commissioned machinery.
The whole set-up: the black barrel of motor oil is elevated on the empty green barrel to create pressure for the oil flow. A fan between the barrel and crucible chamber creates a convection effect to increase the heat in the chamber.
The crucible where the aluminum will be melted.
Scrap aluminum is cut with a hacksaw into pieces that will fit into the crucible. Any rubber or plastic is removed.
The machine part to be duplicated is pressed into barely moistened sand in a wooden box. Once the sand is well compressed, the piece is removed and the impression remains.
The process is repeated with the top half of the sandbox, but in this case plastic pieces (sawn off legs of a bed frame!) are used to create holes into which the molten metal will be poured. Due to their conical shape, they are easily tapped out with a hammer, leaving channels in the sand.
The aluminum is heated in the foundry to a temperature of about 1300° F.
The red hot crucible is carefully lifted from the foundry.
Debris and contaminants are skimmed from the surface of the molten metal.
The aluminum is carefully poured into the holes left by the bed frame legs.
Once the metal starts to overflow out of the holes, the pouring is stopped.
15 minutes later, the box and sand are removed, leaving the cast piece, which will need much sawing and grinding.
Here's a video of part of the casting process.
-Larisa Jacobson, D-Lab I and II alum, M.S. candidate in International Agricultural Development