Low pressure casting is a casting method that allows liquid metal to complete the filling cavity and solidification process under pressure to obtain castings. Due to the low pressure used (20-60kPa), it is called low-pressure casting. The process is as follows: in a sealed crucible (or sealed jar), dry compressed air is introduced. Under the action of gas pressure, the metal liquid enters the sprue and rises along the riser, smoothly entering the mold cavity through the inner sprue, and maintaining the gas pressure on the liquid surface inside the crucible until the casting is completely solidified. Then release the gas pressure on the liquid surface, allowing the unsealed metal liquid in the riser to flow back into the crucible, then open the mold and remove the casting.
Advantages of Low Pressure Casting
1. Gas and debris are less involved, and the pressurization speed can be changed. The molten soup is filled by laminar flow
2. By using bottom injection molding, the metal liquid filling is smooth and free of splashing, which can avoid gas entrapment and erosion of the mold wall and core, and improve the qualification rate of castings.
3. Castings crystallize under pressure, with a dense microstructure, clear contours, smooth surface, and high mechanical properties, making them particularly advantageous for casting large and thin-walled parts.
4. The pressure rate can be changed, and the molten soup is filled by laminar flow.
5. The range of materials used is wide.
Disadvantages of low-pressure casting
1. Low production efficiency compared to gravity die casting. Die casting>gravity>low pressure
2. Long casting cycle and poor productivity. In order to maintain directional solidification and melt fluidity, the mold temperature is higher and the solidification speed is slower.
3. The structure near the gate is relatively coarse, and the mechanical performance of the lower surface is not high, requiring comprehensive and rigorous management (temperature, pressure, etc.).