Green Sand Casting or Resin Sand Casting
Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material. The term “sand casting” can also refer to an object produced via the sand casting process. Sand castings are produced in specialized factories called foundries. Over 60% of all metal castings are produced via sand casting process.
Sand casting is one of the earliest forms of casting practiced due to the simplicity of materials involved. It still remains one of the cheapest ways to cast metals because of that same simplicity. Other methods of casting, such as those using coquille, boast higher quality of surface finish, but have higher cost.
Green Sand Casting
Green sand is an aggregate of sand, bentonite clay, pulverized coal and water. Its principal use is in making molds for metal casting. The largest portion of the aggregate is always sand, which can be either silica. There are many recipes for the proportion of clay, but they all strike different balances between moldability, surface finish, and ability of the hot molten metal to degas. The coal, typically referred to in as sea-coal, which is present at a ratio of less than 5%, partially combusts in the surface of the molten metal leading to off gassing of organic vapors.
Green sand is usually housed in what foundry workers refer to as “flask”, which are nothing other than boxes without a bottom or lid. The box is split into two halves which are stacked together in use. The halves are referred to as the cope and drag flask respectively.
The ability to quickly make molds through automated machines makes green sand casting economical and popular for making medium to high volume castings since the automated processes allows for a lot of molds to be quickly made at an affordable cost.
Resin Sand Casting
Forming process where a sand mold made of resin-bonded sand used to create a molded product. Resin binders are natural or synthetic high melting point gums. The two common types used are urea formaldehyde (UF) and phenol formaldehyde (PF) resins. PF resins have a higher heat resistance than UF resins and cost less. There are also cold-set resins, which use a catalyst instead of a heat to cure the binder.
Resin binders are quite popular because different properties can be achieved by mixing with various additives. Other advantages include good collapsibility, low gassing, and they leave a good surface finish on the casting.
MDI (methylene diphenyl diisocyanate) is also a commonly used binder resin in the foundry core process.
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Sources from WIKIPEDIA:
https://en.wikipedia.org/wiki/Sand_casting
https://en.m.wikipedia.org/wiki/Molding_sand#Green_sand