Vacuum casting mold can be roughly divided into three types: vacuum suction casting, vacuum low-pressure casting, and vacuum differential pressure casting.
1. Vacuum suction casting.
The mold is placed in a sealed container and the air in the mold is drawn out, which causes a certain negative pressure in the mold and causes the liquid metal to suck into the cavity. When the inner runner of the casting solidifies, the negative pressure is removed and the solidified metal liquid in the vertical runner flows back into the melting pool. Its advantage is to improve the filling capacity of alloy liquid, the minimum wall thickness of suction casting can reach 0.2mm, and the casting area is 300mm2 while reducing the defects such as blowhole and slag inclusion. It is suitable for producing thin and fine small precision castings, especially for cast steel (including stainless steel).
2. Vacuum low-pressure casting.
Vacuum low-pressure casting is to vacuum the casting mold in the process of pressure filling. After filling, holding pressure makes the casting crystallize and solidify under constant pressure, and the casting is fully compensated, so the structure of the casting is compact and the mechanical properties are improved. This method is used for precision casting of Al and Mg alloy castings.
3. Vacuum differential casting.
Vacuum differential pressure casting is mainly to seal the resistance holding furnace and the casting mold. The pressure of 500 kPa compressed air is introduced into the sealing cover. At this time, because the pressure of the casting mold is equal to that of the crucible, the liquid metal will not rise, and then the liquid metal will rise to fill the cavity when the pressure of 50 kPa is added to the liquid metal surface. Especially suitable for the production of complex thin-walled castings, but the equipment is large and the operation is troublesome. Only when special requirements are applied.
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