Permanent mold is also called metal mold,and it can be poured hundreds to tens of thousands of times.Low-pressure permanent mold (LPPM) casting uses a gas at low pressure, usually between 0.05 and 0.1Mpa to push the molten metal into the mold cavity. The pressure is applied to the top of the pool of liquid, which forces the molten metal up a refractory pouring tube and finally into mold. The pouring tube extends to the bottom of the mold so that the material being pushed into the mold is exceptionally clean. No risers are required,because the applied pressure forces molten metal in to compensate for shrinkage. Yields are usually over 85%,because there is no riser and any metal in the pouring tube,after release pressure,just falls back into the holding furnace.