Green molding has also been applied in the production of small steel castings and machine modeling. At this time, the quality of molding sand should be strictly controlled to prevent defects such as sand holes, sand sticking and pores. Because the molding sand produces more gas at high temperature and more water in the green mold, the tendency of steel castings to produce invasive pores and reaction pores is relatively large. Cast steel green sand generally has the following characteristics:

(1) Quartz sand with high fire resistance is used, but the particle size is finer than that of cast steel dry mold. 70 / 140 fine quartz sand is commonly used.

(2) Reduce the dust in the old sand, or increase the amount of new sand. Some or all of the surface sand use new sand, so as to improve the fire resistance of the molding sand and reduce the moisture in the molding sand.

(3) The activated bentonite is used, and syrup and other additives are added to improve the strength of molding sand on the basis of minimizing the amount of clay, which is also conducive to reducing water content and preventing sand sticking, sand inclusion and pore defects.

(4) Add a small amount of coal powder, heavy oil and other additives to the surface sand to prevent sand sticking. However, too many of these additives will cause porosity and carbon penetration in the casting, so the dosage needs to be limited.

(5) Strictly control the moisture content of molding sand and improve the air permeability of molding sand.

(6) Spray slurry lining, pulp waste liquid or water glass on the surface of the sand mold to improve the surface strength of the sand mold. However, after spraying this solution, it must be parked for several hours and dried on the surface.