The most common method used to make metal castings is green sand molding. In this process, granular refractory sand is coated with a mixture of bentonite clay, water and, in some cases, other additives. The additives help to harden and hold the mold shape to withstand the pressures of the molten metal.
The green sand mixture is compacted through mechanical force or by hand around a pattern to create a mold. The mechanical force can be induced by slinging, jolting, squeezing or by impact/impulse.
The following points should be taken into account when considering the green sand molding process:
• for many metal applications, green sand processes are the most cost-effective of all metal forming operations;
• these processes readily lend themselves to automated systems for high-volume work as well as short runs and prototype work;
• in the case of slinging, manual jolt or squeeze molding to form the mold, wood or plastic pattern materials can be used. High-pressure, high-density molding methods almost always require metal pattern equipment;
• high-pressure, high-density molding normally produces a well-compacted mold, which yields better surface finishes, casting dimensions and tolerances;
• the properties of green sand are adjustable within a wide range, making it possible to use this process with all types of green sand molding equipment and for a majority of alloys poured.