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A method of casting a metal article comprising the steps of forming a mold having a mold cavity with a height, a thinwall portion and a base wall portion. The thinwall portion may be less than 0.05 inches thick and free of gating. The method comprises the steps of: positioning the mold in a preheate

A method of casting a metal article comprising the steps of forming a mold having a mold cavity with a height, a thinwall portion and a base wall portion. The thinwall portion may be less than 0.05 inches thick and free of gating. The method comprises the steps of: positioning the mold in a preheated furnace so that the furnace substantially surrounds the mold and so that a longitudinal axis of the long thin portion of the mold cavity is in an upright orientation; heating the mold in the furnace to a temperature between 1045° C. and 1055° C.; and drawing a vacuum in the furnace. The metal is heated until it is molten and is then poured at a temperature between 1560° land 1570° C. into the mold cavity. The vacuum is then broken and the mold cavity withdrawn from the furnace. The molten metal is allowed to solidify in the mold cavity so that it will solidify with a equiaxed grain structure.

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A method of casting a metal article comprising the steps of forming a mold having a mold cavity with a height, a thinwall portion and a base wall portion. The thinwall portion may be less than 0.05 inches thick and free of gating. The method comprises the steps of: positioning the mold in a preheate

A method of casting a metal article comprising the steps of forming a mold having a mold cavity with a height, a thinwall portion and a base wall portion. The thinwall portion may be less than 0.05 inches thick and free of gating. The method comprises the steps of: positioning the mold in a preheated furnace so that the furnace substantially surrounds the mold and so that a longitudinal axis of the long thin portion of the mold cavity is in an upright orientation; heating the mold in the furnace to a temperature between 1045° C. and 1055° C.; and drawing a vacuum in the furnace. The metal is heated until it is molten and is then poured at a temperature between 1560° land 1570° C. into the mold cavity. The vacuum is then broken and the mold cavity withdrawn from the furnace. The molten metal is allowed to solidify in the mold cavity so that it will solidify with a equiaxed grain structure. 3. An accordion fire door as in claim 1 wherein said obtuse angle is 114 degrees. 4. An accordion fire door as in claim 1 wherein each said guide assembly comprises a pair of horizontal rollers and a vertical roller. 5. An accordion fire door as in claim 1 further comprising a self extinguishing neoprene seal on at least one of said top and bottom edges of said panels. 6. An accordion fire door as in claim 1 wherein said actuator comprises a pulley, a cable coupled with the pulley, and a counterweight fixed to the cable. 7. An accordion fire door as in claim 1 wherein said panels are formed of steel. 8. An accordion fire door as in claim 7 wherein said panels are formed of one of galvanized steel and stainless steel. 9. An accordion fire door comprising an accordion member comprising a plurality of panels each having a first vertical edge, a second vertical edge, a top horizontal edge, and a bottom horizontal edge, the first vertical edge of each panel being provided with a female hook member having a hook shank formed at an acute angle to said panel and a female hook portion formed on said hook shank away from said panel, said female hook portion having a semicircular cross-section with an inside radius, the second vertical edge being provided with a male hook member having a hook shank formed at an acute angle to said panel and a male hook portion which is received in the female hook portion of an adjacent one of said panels to form a pivotable connection between adjacent panels, said male hook portion being formed on said hook shank toward said panel, said male hook portion having a semicircular cross-section with an outside radius which is slightly smaller than said inside radius of said female hook portion, and a plurality of guide assemblies attached to the top edges of respective panels for suspending said panels from a guide track and for guiding said panels from an open position to a closed position wherein adjacent said panels extend transversely to each other in a zig-zag pattern at an obtuse angle, one of said guide assemblies being fixed to every other one of said panels substantially centrally between the vertical edges, said hook members being designed so that a predetermined obtuse angle between adjacent said panels cannot be exceeded, said predetermined obtuse angle corresponding to the sum of the acute angles of said male and female hook shanks with respect to said panels. 10. An accordion fire door as in claim 9 wherein said panels are formed of steel. 11. An accordion fire door as in claim 10 wherein said panels are formed of one of galvanized steel and stainless steel. 12. An accordion fire door installation comprising an overhead guide track, an accordion member comprising a plurality of panels each having a first vertical edge, a second vertical edge, a top horizontal edge, and a bottom horizontal edge, the first vertical edge of each panel being pivotably connected to the second vertical edge of an adjacent one of said panels, wherein said first vertical edge of each said panel has a female hook member having a hook shank formed at an acute angle to said panel and a female hook portion formed on said hook shank away from said panel, said female hook portion having a semicircular cross-section with an inside radius, and said second vertical edge has a male hook member having a hook shank formed at an acute angle to said panel and a male hook portion which is received in said female hook portion of an adjacent panel to pivotably connect said first and second vertical edges of adjacent panels, said male hook portion being formed on said hook shank toward said panel, said male hook portion having a semicircular cross-section with an outside radius which is slightly smaller than said inside radius of said female hook portion, and wherein adjacent said panels form an obtuse angle to each other when said accordion member is in the closed position, said hook portions being designed so that a predeterm