Shell molding . Sand or core sand with a layer of solid resin film on the surface of the sand before molding. There are two coating processes: cold method and hot method: the cold method dissolves the resin, and urotropine is added during the sand mixing process, so that the two are coated on the surface of the sand grains to obtain coated sand; the hot method preheats the sand When the temperature is reached, add resin to melt it, stir to coat the resin on the surface of sand grains, add urotropine aqueous solution and lubricant, cool, crush and sieve to obtain coated sand. For steel castings, iron castings.

Shell molding mainly uses quartz sand as raw sand, thermoplastic phenolic resin, urotropine and reinforcing agent as raw materials. According to the different needs of users, the ratio is properly adjusted in terms of curing speed, release, fluidity, collapsibility, surface finish of castings, and storage. It is one of the modeling materials for automobiles, tractors, hydraulic parts, etc.

Resin sand molding refers to molding sand or core sand that uses synthetic resin as a binder for sand particles. After resin sand is used to make a mold or core, through the action of a solidifying (hardening) agent, the resin undergoes an irreversible cross-linking reaction and is cured, thereby giving strength to the mold or core.

Resin sand molding is used as mold (core) sand in modern foundry production. The molding (core) sand with resin as the binder mainly includes thermal coated resin sand, hot core box resin sand, cold core box resin sand, furan resin sand, I furan resin self-hardening sand, etc. Resin sand has high strength after hardening, which is suitable for machine modeling and can produce complex and thin-walled castings.

The disadvantage of resin sand is that the binder is expensive and pollutes the air. In order to save the amount of resin, the raw sand of pure round sand that has been washed or scrubbed is generally used.