In view of this knowledge we should understand that the priority is to use sand mold precision casting. According to statistics, in China or internationally, 60 ~ 70% of the total casting output 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, the sand mold casting cost is low, the production process is simple, the production cycle is short. So like the car engine cylinder block, cylinder head, crankshaft and other castings are produced by the clay wet sand process. When the wet type can not meet the requirements to consider the use of clay sand table dry sand, dry sand or other sand. The weight of the castings cast by clay wet sand can range from a few kilograms to dozens of kilograms, while the castings produced by clay dry mold can weigh dozens of tons. Generally speaking, for medium and large castings, cast iron parts can be produced by resin self-hardening sand mold, casting steel parts can be produced by water glass sand mold, can obtain precise size, smooth surface of the casting, but the cost is higher. Of course, the casting precision, surface finish, material density, metallographic structure, mechanical properties and other aspects produced by sand casting are often poor, so when these properties of castings are required to be higher, other casting methods should be used, such as investment (loss of wax) casting, die casting, low pressure casting, etc.