In the process of lost foam casting pouring, vacuum the sealed sand box to generate negative pressure in the mold, which can well improve the mold filling capacity of liquid metal. Especially for the alloy with poor fluidity, the vacuum degree directly determines whether the alloy can be used in lost foam casting technology. Vacuuming not only can greatly inhibit the production of gaseous products in foam pattern, but also speed up the gaseous and liquid decomposition products of foam pattern and the speed of mold and coating.
Under the combined action of these two aspects, the air gap pressure at the front of metal filling in lost foam casting has been greatly reduced, and the filling ability of liquid metal in lost foam casting has been greatly improved. In addition, the timely discharge of liquid decomposition products can prevent its further gasification and increase the heat loss at the front of liquid metal filling, avoid the further reduction of liquid metal temperature at the front of filling, and improve the filling capacity to a certain extent.
Vacuum suction will make the liquid metal flow preferentially along the interface between the pattern and the mold, resulting in wall attachment effect and concave filling front. When the negative pressure reaches a certain value, the excessive concave shape increases the moving distance in the escape process of gas and liquid decomposition products in the center, and reduces the escape speed of decomposition products. Further increasing the vacuum degree will not only enhance the filling ability of the molten metal, but will make the foam pattern encapsulated by the metal liquid to form a closed thin shell, resulting in the decomposition product of the mold not rapidly escaping from the cavity.