For this knowledge we should know that the preferred use of sand mold precision casting. According to statistics, in our country or the international, in the total casting output, 60 ~ 70% of the casting is produced by sand mold, and about 70% of it is produced by clay sand mold. The main reason is that compared with other casting methods, sand mold casting has low cost, simple production technology and short production cycle. So the engine block, cylinder head, crankshaft and other castings, such as automobile, are produced by wet sand clay process. When the wet type can not meet the requirements to consider the use of clay sand table dry sand type, dry sand type or other sand type. The castings of wet sand can weigh from a few kilograms to dozens of kilograms, while those of dry sand can weigh tens of tons. Generally speaking, for medium and large castings, cast iron can be produced by resin self-hardening sand mold, and steel castings can be produced by water glass sand mold. Casting with accurate size and smooth surface can be obtained, but the cost is high. Of course, sand mold casting production of casting precision, surface finish, material density and metallographic structure, mechanical properties and other aspects are often poor, so when these properties of the casting requirements are higher, should use other casting methods, such as investment (lost wax) casting, die casting, low pressure casting and so on.