Àú¾ÐÁÖÁ¶¹ý(î¸äâñÑðãÛö; low pressure casting, pressure pouring casting, pressure casting)

In contrast to the gravity pouring of conventional permanent-mold casting, low-pressure permanent-mold casting forces the molten metal up through a vertical tube by applying low pressure of 5 ~ 15psi to a molten bath below. The figure provides an illustration of this process, which can be applied to a wide variety of metals, including steel and cast iron.
Clean metal from the center is drawn into a graphitte or metal mold, never passing the atmosphere. Thus, the low-pressure process becomes particularly attractive for rapidly oxidizing metals, such as aluminum. By control of the pressure, the mold can be filled from the bottom in a controlled, nonturbulent manner, and the pressure is maintained until the metal has completely solidified in the mold. Mold cooling is designed in such a way as to promote directional solidification from the top down. Cycle times may be somewhat slow, but the applied pressure continually feeds molten metal to compensate for shrinkage, and the unused metal in the feed tube simply drops back into the crucible after the pressure is released. Since no risers are used(the pressurized feed tube acts as a riser) and the molten metal in the feed tube can be immediately reused, yields are generally greater than 85%. Gas porosity and dross are thus minimized and mechanical properties are typically 5% superior to those in conventional permanent-mold castings.

In low pressure die casting, molten metal is displaced vertically upwards into a die by means of low pressure on the liquid metal. The die cavity is filled slowly upwards which ensures no entrained air and high soundness. Castings, therefore, have better metallurgical integrity than die castings, and they can be heat-treated. The process, thus, has the benefits of die casting without the disadvantages. Tooling may be made in permanent or semi-permanent configurations. Tooling costs are about half those for pressure die casting.