TWO-LAYER SHELL MOLD AND MANUFACTURE THEREOF

PROBLEM TO BE SOLVED: To provide a two-layer shell mold which can obtain good cast surface of a cast product without accompanying with troubles of the development of a gas defect and the aggravation of collapsibility of the mold, etc. SOLUTION: The two-layer shell mold has an integral constitution of an outer layer 8 and an inner layer 7 formed with thermosetting coated sands having different grain size indexes at a part of the shell mold, and the outer layer 8 is formed with larger grain size index that of the inner layer 7. After filling up the thermosetting resin coated sand for outer layer in a pattern space 2 of a heated forming metallic mold, unhardened part is discharged to form the outer layer 8 on the pattern surface. Successively, the thermosetting resin sand for inner layer 7 is filled up in the formed outer layer 8 and both layers are integrated and the unhardened part is discharged.