A casting method in which molding sand and core sand are used as molding materials to make a mold, and liquid metal is filled with the mold under gravity to produce a casting. Steel, iron and most non-ferrous alloy castings can be obtained by sand casting methods. Because the molding materials used in sand casting are cheap and easy to obtain, and the molds are easy to manufacture, they can adapt to single-piece production, batch production and mass production of castings. For a long time, it has been the basic process in casting production. The mold used in sand casting is generally composed of a combination of an outer sand mold and a core. In order to improve the surface quality of castings, a layer of paint is often applied to the surface of the sand mold and core. The main components of the coating are powdery materials and binders with high refractoriness and good chemical stability at high temperatures. In addition, a carrier (water or other solvents) and various additives are added for easy application.