Casting is among the oldest manufacturing processes dating back to 4000 B.C. Casting is now more refined, but the basic process has not changed. The metal casting process involves pouring molten metal into a mold cavity where it cools and solidifies into the shape of the cavity. The casting process can produce intricate shapes in a single piece, including parts with internal cavities. Parts can be cast in nearly the final shape desired with only minor machining required, saving time and money.
There are two principle types of molds, expendable and permanent. In permanent-mold casting, the mold is generally made of metallic materials and used over and over. In expendable-mold casting, the mold is made of nonmetallic materials, i.e. sand, plaster or ceramic. The mold is broken to remove the casting, and one mold will make one casting, hence the term expendable.
Clinch River Casting uses expendable sand molds. Sand molds require a bonding agent for the mold to hold its shape. CRC is a 100% Air Set sand foundry. Air Set molding, commonly referred to as No Bake molding, uses a chemically bonded sand. Clinch River Casting employs a Phenolic Urethane resin system. The sand is blended with a three-part resin system in a high-speed sand mixer. The sand leaves the mixer in a “wet” state and cures and hardens around the pattern in a short time. The advantages of No Bake over Green Sand foundries are an improved surface finish, dimensional accuracy, larger castings, and lower tooling costs.
Common Molding Terms
Mold – The sand form that contains the cavity into which molten metal is poured to produce a casting.
Cope – The upper or top section of a mold. (In a horizontally parted mold)
Drag – The lower or bottom section of a mold. (In a horizontally parted mold) See illustration below
Core – A preformed sand shape inserted into a mold to form the interior or undercut of a casting. A core may be as simple as a cylinder to form a hole in a casting or intricate as forming the inside of a volute.