SAND CORE

PROBLEM TO BE SOLVED: To provide the sand core which is smooth in surface, and free from metal penetration during the high-pressure casting. SOLUTION: In a sand core 1, a coating layer 7 is coated on a core body 6 comprising a core part 3 formed of core sand 2 of small grain size and an outer shell part 5 which is formed of core sand 4 of large grain size and covers the core part 3 to form a mold. The coating layer 7 formed on the surface of the core body 6 is filled in a space 8 between adjacent core sands 4 of large grain size on the surface of the core body 6, and covers the core body 6.