Coated sand casting has a long history in the field of foundry, and the output of castings is quite large; The coated sand has suitable strength performance and good fluidity; The sand mold and sand core made by coated sand have clear outline and compact organization, and can make complex sand core;The surface quality of sand mold (core) is good, the surface roughness can reach Ra = 6.3 ~ 12.5 μ m, and the dimensional accuracy can reach CT7 ~ CT9 grade; The coated sand has good collapsibility and the castings are easy to clean.

The coated sand can be used for making moulds and cores, and the moulds or cores of the coated sand can be used together or together with other moulds (cores); It can be used not only in metal mold gravity casting or low pressure casting, but also in iron mold coated sand casting and hot centrifugal casting; It can be used not only in the production of cast iron, non-ferrous alloy castings, but also in the production of steel castings.

The preparation process of coated sand mainly includes cold method coating, warm method coating and hot method coating. At present, coated sand production almost all uses hot coating method. By hot coating method, the sand is heated to a certain temperature, then mixed with resin, urotropine solution and calcium stearate respectively, cooled, crushed and screened.Due to different formulations, mixing processes are different. At present, there are many kinds of coated sand production lines in China, including about 2000 to 2300 semi-automatic production lines with manual feeding and nearly 50 automatic production lines with computer control, which effectively improves production efficiency and product stability.

However, coated sand casting production of precision steel castings are faced with many problems: bonded sand (scab), cold shut, air holes. The casting expansion defects can be effectively prevented by using part of the precious bead sand in the molding sand and core sand.In recent years, some manufacturers of resin coated sand in China have added some sapphire sand into raw sand, so that the shell mold and shell core can have high temperature resistance, low expansion, easy collapse, high strength and low gas generation.Especially for the complex shape of the core, it can also solve the problem that the sand is not easy to compact. Therefore, in recent years, almost all large-scale coated sand factories use ceramic foundry sand as raw sand to produce coated sand.

Ceramic foundry sand is a kind of ball artificial sand made by high-quality bauxite through electric melting, ball, screening and other processes. It has high refractoriness (> 1820 ℃), small angle coefficient (< 1.06, approximate ball shape), low acid consumption value (neutral material), small binder addition (Binder addition reduced by 30%), high strength, no crushing, no poison, etc. It is more and more widely used in the field of casting, it can be used in lost foam casting (filling sand) and sand casting (Sodium silicate sand, resin sand, coated sand), precision casting and copper, aluminum polishing cleaning.