Metal casting

A method of casting a plurality of parts in a multiple cavity, gas permeable, shell mold, comprising the steps of

• providing a mold with a central vertical riser passage having an open lower end and having a plurality of mold cavities with gas permeable walls connected to said riser passage by gate passages having screen means extending thereacross, said screen means being heat insulating and extending across said gate passages in a slanted plane with the bottom portion thereof nearer to said mold cavities and at an angle of about 45.degree. to 60.degree. to the horizontal, and said mold cavities being positioned above their connecting gate passages
• lowering the open lower end of said mold beneath the surface of molten metal,
• providing a differential pressure to said cavities through said walls of said cavities, causing molten metal to fill said riser passage and said mold cavities through said gate passages and said stabilizing screen means therein and to filter out impurities, while gas in said mold cavities escapes through their walls and
• maintaining said differential pressure, while at least in part solidifying said molten metal around the periphery of said mold cavities and the portion of said gate passages between said stabilizing screen means and said mold cavities, while maintaining said molten metal as a liquid in said riser passage and in the portion of said gate passages between said stabilizing screen means and said riser passage, and
• releasing said differential pressure, causing draining of molten metal from said riser passage and from the portion of said gate passages between said stabilizing screen means and said riser passage, before complete solidification of said molten metal in said mold cavities, said stabilizing screen means stabilizing molten metal in said mold cavities and in the portion of said gate passages between said stabilizing screen means and said mold cavities during and subsequent to said drainage of molten metal from said riser passage and from the portion of said gate passages between said stabilizing screen means and said riser passage.