Vacuum casting can be roughly divided into three types: vacuum suction casting, vacuum low pressure casting, and vacuum differential pressure casting.
1.Vacuum suction casting
Vacuum suction molding refers to placing the mold in a closed container and extracting the air inside the mold to cause a certain negative pressure in the mold, which causes the molten metal to be sucked into the mold cavity. When the inner runner of the casting solidifies, the negative pressure is removed, and the unsolidified molten metal in the vertical runner flows back into the molten pool. The utility model has the advantages that the filling ability of the alloy liquid is improved, the minimum wall thickness of the suction casting is up to 0.2 mm, and the casting area is 300 mm 2 , and the defects such as pores and slag inclusion are reduced. Suitable for the production of small and fine small precision castings, cast steel (including stainless steel) parts are particularly suitable. Its advantages are:
(1) Vacuum suction casting is beneficial to the elimination of gas in the mold, inhibits the generation of turbulent flow and gas generation, overcomes the disadvantages of low pressure casting and differential pressure casting, and significantly improves the filling ability of the molten metal.
(2) Due to the increase in filling ability during vacuum suction casting, the casting temperature of the molten metal can be 20 to 30 ° C lower than that during gravity casting.
(3) Castings with large wall thickness, thin wall and high quality requirements can be cast.
(4) By selecting an appropriate degree of vacuum change rate and controlling the speed at which the molten metal enters the cavity, a smooth filling effect can be obtained.