On the surface of the casting, all or part of the surface is covered with a layer of metal (or metal oxide) and sand (or coating) mixture (compound) or a layer of burnt structure molding sand, which makes the surface of the casting rough and difficult to clean. Most of the sand sticking occurs on the surface of mold and core with strong heating effect, which can be divided into mechanical sand sticking and chemical sand sticking. Mechanical sand sticking is formed by the metal liquid penetrating into the micropores on the mold surface. When the penetration depth is less than the sand radius, the casting does not form sand sticking, but the surface is rough. When the penetration depth is greater than the sand radius, mechanical sand sticking is formed. Chemical sand sticking is the product of chemical interaction between metal oxides and molding materials, which is firmly combined with the casting.
Precautions for sand sticking:
- Select the sand with high fire resistance to improve the fire resistance of molding sand and core sand. The SiO2 content of the original sand is above 96% (mass fraction), and the sand should be coarser. The higher the pouring temperature and the thickness of the steel casting, the higher the SiO2 content in the original sand.
- Reduce the pouring temperature and speed properly, reduce the thermodynamics and physicochemical effect of the metal liquid on the sand mold.
- The compactness of the sand mold should be high (usually greater than 85) and even, reducing the sand gap; the mold and core should be repaired in place, without local looseness.
- The coating that does not crack or burn to form a melting hole under high temperature shall be used.