Shellmoulding

Shellmoulding, also called shell mold casting, is a metal casting process in which a thin, rigid shell is formed from a mixture of silica sand and a thermosetting resin. The shell, about 0.8 to 1.2 mm thick, reproduces the pattern surface with high fidelity and serves as the mold insert.

To form the shell, resin-coated sand is applied around a heated pattern. The heat causes the binder to cure rapidly, creating a hard shell on each side of the pattern. The shells are removed, joined as a cope and drag mold, and trimmed to accept gates and runners. Cores may be placed before assembly.

Shell molds yield excellent surface finish and dimensional accuracy, with good repeatability and relatively short cycle times. The thin walls reduce metal consumption and permit complex geometries not easily produced by traditional sand molds. The process is well suited for small- to medium-sized castings in a range of alloys, including iron, steel, aluminum, and copper alloys.

Limitations include the need for specialized equipment and handling of hot shells, binder fumes, and higher tooling costs. Shells are delicate and can be damaged if mishandled, and the technique is less economical for very large parts or simple geometries.

Developed in the mid-20th century as an improvement on conventional sand casting, shell molding has become a standard method for producing precise, near-net-shape castings with good surface quality and repeatable tolerances.