China Cast Iron Flange Supplier

Shell casting is a six-step process: 

1. Create All the Pattern Parts

The first step in shell molding is creating a pattern part. This is achieved by first machining a metal pattern tool, usually from iron or steel, in the shape of the part you want. Usually, each pattern represents one-half of the part; a second pattern is required for the other half. If you’re casting reactive metals, the pattern will need to be made of graphite rather than metal. Figure 1 is an example of a pattern tool:

2. Construct the Mold

Molds can be repeatedly made from a single pattern. Lubricate the pattern with calcium stearate and then preheat it to between 175 ºC and 370 ºC. Next, place the pattern atop a “dump box” full of the sand and resin mixture. Flip the box so the resin and sand contact the pattern; the heat will cause the resin to cure.

3. Assemble All the Pattern Parts

After the shell has cooled, it can be ejected from the pattern tool and assembled with the other half of the shell in a flask. The flask is filled with a metal shot that fills in the space between the two-part shell and the flask’s walls. Mold halves must be clamped tightly together.

4. Expose the Pattern to Molten Metal

Next, pour molten metal into the pattern. The metal can be poured in manually or using an automated machine.

5. Allow To Cool

After the molten metal is poured, it must be allowed to cool properly in room-temperature air. Any attempt to cool the casting actively and/or with liquid coolants can lead to changes in the metal’s structure and properties. Total cooling time depends on the volume and specific type of metal involved. 

6. Eject the Casting

Once the metal has cooled, it is ejected from the casting. This may be done by separating the mold halves at their seam or by simply breaking the mold itself. The mold material is easier to remove from the metal if it was properly lubricated before the molten metal was introduced.