This paper develops a theoretical model of the two-chamber pressure casting process. In this process, the cast mold’s porous exterior is exposed to a low pressure chamber while the mold’s interior is exposed to a high pressure chamber. An inert process gas, typically argon, fills the high-pressure upper chamber, mold interior, and low-pressure lower chamber; due to the pressure difference between the mold’s interior and exterior, gas flows through the mold’s porous bottom wall into the lower chamber. Casting is initiated when a molten metal drop falls into a conical crucible that feeds the cast mold. Process gas, trapped within the mold cavity, leaks through the mold’s bottom, typically reducing gas pressure within the mold and setting up a downward-acting pressure force across the drop. An energy-based model of the mold-filling process is developed which focuses on the drop’s motion within the crucible and mold cavity and on pressure evolution within the mold cavity. The model shows that drop acceleration into the mold depends on three dimensionless parameters, the Euler number, Eu, the Froude number, Fr, and the pressure loss coefficient, K, across the crucible exit. These parameters are in turn determined by the mold’s permeability to the process gas, the pressure difference between upper and lower chambers, the mold thickness, the process gas viscosity, and the metal density. Drop acceleration both compresses trapped gas and determines mold fill time. Under most conditions, leakage-induced pressure decay within the mold occurs at a faster rate than compression.
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