DIFFERENTIAL PRESSURE, COUNTERGRAVITY CASTING A method and apparatus for the differential pressure, countergravity casting of a melt involves a casting mold which includes an ingate for engaging an underlying source of the melt, an upstanding, alloyant-containing reaction chamber having an upper region communicated to the ingate, and an exit gate communicating a lower region of the reaction chamber to a mold cavity. The mold and the source are relatively moved to engage the ingate and the source. A sufficient relative vacuum is applied to the mold cavity to draw the melt from the source upwardly through the ingate and into the reaction chamber where the melt reacts with alloyant therein. The melt is drawn upwardly to leave at least a portion of the volume of the mold cavity unfilled with melt and to provide a sufficient volume of melt in the reaction chamber to fill the unfilled volume of the mold cavity after disengagement of the mold and the source. The mold and the source are then relatively moved by suitable means to disengage the ingate and the source while a relative vacuum is applied to the mold cavity sufficient to draw the volume of melt in the reaction chamber into the mold cavity such that the unfilled volume thereof is filled after the mold and the source are disengaged. The reaction chamber is thereby essentially emptied of melt as required to fill the unfilled volume of the mold cavity. The melt in the ingate is drained back to the underlying source when the mold and the source are disengaged. The melt is treated with the alloyant (e.g., nodularized) while melt usage for gating to the castings is substantially reduced.
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