12/11/2013 Industrial Equipment
Lost wax casting is the process where a metal or metal alloy is cast from a design prototype.Called cire perdue by the French and cera perduta by the Romans, lost wax casting has been around since the time of the Egyptians.Today it is more often called precision casting or investment casting. The process may vary by foundry, but the lost wax casting techniques havent changed much in 4000 years.
Here is a list of the steps involved in the investment or lost-wax casting technique process.There are actually two different ways of creating the casts;the direct method and the indirect method.These are the steps followed when creating a casting by the indirect process.
1.Model-making a copy of the original piece is created out of wax or other substance.
2.Mold making a mold is created using the model to create an outer two-piece shell.
3.Wax:Melted wax is poured into the mold and rolled around in the mold,coating all the nicks and crannies with an even coating.More melted wax is poured in until the desired thickness 3 mm or 1/8 inch is reached.
4.Wax Removal:Next remove the hollow wax model copy from the mold,which can be reused to create multiple copies.
5.Chasing:A metal tool is heated to rub out all mold marks and any imperfections.This is called chasing.
6.Spruing:Wax cylinders are attached to strategic points around the wax copy creating pathways for the molten metal or alloy to flow into the mold and for air to escape.
7.Slurry:The wax copy with its sprued branches is dipped into a silica slurry. Next it is dipped into sand or a sand-like stucco.The combination of slurry and grit creates a ceramic shell.The dipping process is repeated until a minimum ½ inch thickness coats the wax copy.
8.Burnout:Next the piece is placed in a kiln.There the high temperature hardens the shell around the copy and then melts the wax to the point where it runs out of the shell. While the wax can often be recovered and reused,it is often lost, leading to the process being named:lost wax casting technique.
9.Testing:Once the ceramic shell has cooled sufficiently water is run through it to ensure there are no leaks or cracks.Any imperfections in the shell can be fixed after which it is reheated to harden any patches.
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