A Brief Discussion on the Vacuum Exhaust System in Casting Processes

The vacuum exhaust system consists of a vacuum pump, pressure stabilizing tank, dust removal tank, and connecting pipelines.

The selection of the vacuum pump’s vacuum level and pumping capacity is the key factor determining the success or failure of the V-process molding. In actual production, a vacuum level of approximately –66,500 Pa (–500 mmHg) is generally sufficient.

The pressure stabilizing tank is a sealed vessel whose primary function is to stabilize the vacuum pressure of the system and buffer pressure fluctuations that may affect molding quality. At the same time, it also plays a role in filtering dust.

During long-term reuse of sand flasks and repeated pouring of molten iron, the filter screens of the sand flasks are prone to damage. Once damaged, sand may be sucked into the vacuum pump, causing serious wear and failure. To prevent this, a dust collector is installed upstream of the vacuum pump. The system is connected through a dust removal tank before entering the vacuum pump, thereby ensuring the service life of the vacuum pump.

Process Steps

1.Place the sand flask equipped with a filtered exhaust pipe onto the pattern plate that has already been covered with plastic film.

2.Release the vacuum inside the pattern plate and then withdraw the pattern. The mold must continue to be evacuated until the poured metal has fully solidified. The lower mold is produced using the same method.

3.After the metal has solidified, stop vacuum extraction. When the internal mold pressure approaches atmospheric pressure, the mold collapses automatically.

4.Manufacture pattern plates equipped with vacuum boxes and exhaust holes.

5.Set cores, assemble the mold halves, and pour molten metal.

6.Fill the sand flask with dry quartz sand of 100–200 mesh, free of binders and additives. Apply slight vibration to compact the sand, level the surface, then cover it with a sealing plastic film. Open the valve to evacuate the air inside the molding sand, creating a pressure difference between the inside and outside of the mold (approximately 300–400 mmHg).

Under this pressure difference, the mold is formed and achieves high strength, with wet mold hardness readings reaching approximately 95.

7.Heat the plastic film until it becomes plastic and cover it over the pattern plate. The heating temperature is generally controlled between 80°C and 120°C. Simultaneously, the vacuum pump extracts air, causing the film to tightly adhere to the pattern plate and form the mold.