Also known simply as shell molding, shell mold casting is a casting process that involves the use of resin-covered sand for the mold. Molten metal is poured into the mold’s cavity, at which point the mold vaporizes to create a hard shell. Although it sounds complex, shell mold casting is a relatively simple process that’s comprised of just six steps.
#1) Creating the Pattern
The first step in shell mold casting is to create the pattern. The patterns used in this molding process typically consist of two pieces of metal, such as iron or steel, in a custom shape as desired for the finished casting.
#2) Creating the Mold
After the pattern has been created, a mold is created. During this step, both of the pattern parts are heated and then treated with a lubricant. The pattern parts are then inserted into a large container, known as a dump box, that contains the resin-covered sand. Once inserted into the dump box, the pattern parts themselves will become covered in the sand.
#3) Assembly of Pattern Parts
Now it’s time to assemble the pattern parts. During this step, the top and bottom pieces of the pattern are joined together. Depending on the type of pattern, it may feature a locking mechanism that holds the two pieces together. Once fully secured, they are then inserted into a flask. Here, they’ll be exposed to molten metal, which is the proceeding step after the pattern parts have been assembled.
#4) Exposure to Molten Metal
The fourth step in the shell mold casting process pouring molten metal into the mold’s cavity. Different types of metals and alloys can be used in this molding process, including steel and iron. Regardless, the metal or alloy is heated until it turns to a liquid state, after which the molten metal is poured into the mold’s cavity to form of a hardened shell.
#5) Wait to Cool
The molten metal must cool before it will create a hardened shell and, thus, the casting. Typically, the pattern parts are allowed to cool at room temperature. As the pattern parts cool, the molten metal will harden to create a shell.
#6) Ejecting the Casting
The sixth and final step in the shell mold casting process is ejecting the casting from the mold’s cavity. Because this casting process uses a two-pieced pattern, castings are easily ejected by “opening” the pattern. The top and bottom pattern parts are separated from each other, at which point the newly created casting can be safely ejected.