Lost foam casting (LFC) is an economical type of metal casting in the long run. It was patented by H.F. Shroyer in 1958. Unlike other methods, it does not require very expensive equipment. The only drawback is that for metals that can be poured at low temperature, the size of the piece is limited. But it can be used for just about any type of metal, ferrous or nonferrous. Spin casting is another method of low-temperature metal casting. It is good for pewter and zinc alloys.
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Things you need
- For evaporative pattern or lost form casting:
- Polystyrene foam
- Casting sand
- Ceramic mixture
- Vibrating table
- For spin casting:
- Mold parting compound
- Acorn nuts
- Spin casting machine
- Vulcanising compound
- Vulcanising frame
Make a polystyrene foam pattern of the part to be cast. Polystyrene foam is the same material that foam coffee cups are made of. It can be carved or moulded. A gate, which is the opening the metal will be poured through, and feeders, which are reservoirs of extra molten metal that will enter the mould to replace any of the metal that is lost because of shrinkage, must also be added.
Dip the pattern into a semi-liquid ceramic mix. The mix can also be poured over or sprayed on the form.
Let the mixture dry. This will form a shell around the pattern. Support the mould on a bed of unbonded casting sand on a vibration table. A vibration table ensures that the mould will compact evenly.
Pour in the molten metal, which will make the form compact. The metal will replace the form and make a copy of the form down to the smallest details.
Finish the piece by cutting off, grinding, heat-treating (which involves heating and cooling until it is satisfactory), straightening and then blasting.
Evaporative Pattern or Lost Form Casting
Make a mould out of uncured silicone rubber by placing the pieces to be cast on top and cutting the shape into the silicone. Cut the mould in half horizontally to form two halves. The mould must be sprayed with mould parting compound and joined together with acorn nuts.
Make sure the rubber is vulcanised so it will have the necessary strength to survive the process. It sets the shape of the mould, cures the silicone and forces it into all the crevices of the pieces.
Grate and vent the mould to prevent the build-up of gases.
Put the mould into the machine. Start the machine and pour in the molten metal, and it will be forced into the mould by centrifugal force.
Remove the parts from the mould by breaking the gates, runners and vents by hand. The pieces will come out clean and be ready to finish.
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