Sand casting is a casting method to produce castings in sand mold. Steel, iron and most non-ferrous alloy castings can be obtained by sand casting. Because the molding materials used in sand casting are cheap and easy to obtain, and the mold manufacturing is simple, it can adapt to the single production, batch production and mass production of castings. For a long time, it has been the basic process in casting production.
In order to improve the surface quality of castings, a coating is often applied on the surface of sand mold and core. The main components of the coating are powder materials and binders with high fire resistance and high temperature chemical stability. In addition, carriers (water or other solvents) and various additives are added for easy application.
In order to improve the service life of sand casting die, the die-casting die is preheated before operation, and the die-casting die life can be increased by 1 ~ 2 times by stress relief tempering in the middle. The intermediate stress relief tempering should be carried out before cracks appear, and the tempering temperature should be 30 ~ 50 ℃ lower than the original tempering temperature.
Shot peening treatment of professional sand casting mold can make the surface layer of mold form compressive stress, make the surface crack close and not easy to expand, delay the formation and expansion of thermal fatigue crack, so as to improve the mold life. Nitriding can improve the wear resistance and turbidity resistance of die casting die, and prevent the adhesion of aluminum, copper and other die castings. The cold and hot fatigue resistance of the die can be improved by properly reducing the brittleness of the carburized layer after nitriding.
The working parts of aluminum alloy die casting die made of 40Cr steel can have strong surface strength, good red hardness and oxidation resistance, deep penetration layer and gentle hardness distribution gradient, and the service life of die can be increased by 3-4 times. The rapid homogenization and spheroidization annealing process can effectively solve the dimensional sensitivity of the uneven structure of the die casting die steel.