There is a layer of sand particles on the surface of castings that are difficult to remove, which is called bonded sand. Bonded sand of castings can be divided into mechanical bonded sand and chemical bonded sand.
The essence of mechanical sand sticking is the filling and infiltration of liquid metal into the pores between sand particles. This situation is caused by the infiltration pressure of liquid metal exceeding the gas back pressure in the gap between sand particles and the additional pressure caused by the surface tension of liquid metal, which is caused by the infiltration of liquid metal into the gap between sand particles. If a layer of dense coating is coated on the outer surface of shell mold, it can prevent the infiltration of liquid metal, so as to effectively prevent the mechanical sand sticking of castings.
The formation of chemical bonded sand is mostly caused by the low fire resistance and low melting temperature of the mold material. When poured into the high-temperature liquid metal, it is easy to be melted by the liquid metal to form nodules and other defects.
Sand sticking not only affects the appearance of castings, but also increases the workload of casting cleaning and cutting, and even affects the service life of the machine.