3. Vacuum differential pressure casting
Vacuum differential pressure casting, mainly to seal the electric resistance holding furnace and the mold, and to introduce compressed air with a pressure of 500 kPa in the sealed cover. At this time, the molten metal does not rise because the pressure inside the mold and the crucible is equal. Then, the pressure of 50 kPa is added to the molten metal surface, and the molten metal rises to fill the cavity. It is especially suitable for the production of complex thin-walled castings, but the equipment is large and the operation is troublesome. It is only applied when there are special requirements. The advantages are as follows:
(1) Compared with conventional gravity casting and vacuum suction casting, vacuum differential pressure casting has a good filling ability on a 1 mm thick sheet sample.
(2) The casting has a dense crystal structure and mechanical properties. In terms of strength properties of the casting, it is about 20% to 25% higher than vacuum suction casting and gravity casting, and the elongation is increased by about 50%.
(3) Vacuum die casting can effectively reduce the pores of the die-casting parts and increase the density of the castings by more than 1%.