Monday, 11 October 2004 - 1:50 PM

This presentation is part of : Metal Forming II

Theoretical model of the two-chamber pressure casting

R. G. Keanini1, K. Watanabe2, Harishandra Cherukuri1, and T. Okabe3. (1) University of North Carolina at Charlotte, Department of Mechanical Engineering & Engineering Science, Charlotte, NC 28223, (2) Niigata University, Division of Dental Biomaterials Science, 5274 Gakkoucho-dori 2, Niigata,, 951-8514, Japan, (3) Texas A&M University System Health Science Center, Department of Biomaterials Science, Baylor College of Dentistry, Dallas,, TX 75246

This paper develops a theoretical model of the two-chamber pressure casting process. In this process, the cast moldís porous exterior is exposed to a low pressure chamber while the moldís 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 moldís interior and exterior, gas flows through the moldís 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 moldís 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 dropís 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 moldís 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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