Coated sand refers to molding sand or core sand whose surface is covered with a solid resin film before molding. There are two coating processes: cold method and hot method: the cold method uses ethanol to dissolve the resin, and adds methenamine during the sand mixing process, so that the two coat the surface of the sand, and the ethanol evaporates to obtain coated sand; hot method Method: Preheat the sand to a certain temperature, add resin to melt it, stir to coat the surface of the sand with the resin, add methenamine aqueous solution and lubricant, cool, crush and screen to obtain coated sand. Used for steel castings and iron castings.
China’s coated sand technology began in the mid-1950s and was discontinued in the 1960s. In the 1980s, due to the rapid development of the automobile industry and the need for export of mechanical products, higher requirements were placed on the quality of castings, thus promoting the rapid development of coated sand production and application technology. In 1986, Jinan Casting and Forging Technology Research Institute first developed a new coated sand production technology. The amount of resin added dropped from 6 to 10% in the early 1980s to 3 to 4%, which was close to the international advanced level in the same period. In the early 1990s, coated sand factories across the country developed rapidly, and new products and new technologies continued to emerge. By the 21st century, the annual production and sales volume of my country’s coated sand industry had reached more than 900,000 tons, and it was widely used in automobile cylinder blocks and cylinders. Production of various complex castings such as covers, intake manifolds, various pipe fittings, pump bodies, excavator bucket teeth and etc.