Simulation of Air Entrainment during Mold Filling: Comparison with Water Modeling Experiments
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Simulation of Air Entrainment during Mold Filling: Comparison with Water Modeling Experiments SEYYED HOJJAT MAJIDI, JOHN GRIFFIN, and CHRISTOPH BECKERMANN Oxide inclusions form during pouring of metal castings as a result of air entrainment. Recently, a model was developed by the authors to predict the volumetric air entrainment during pouring. It was found that the velocity, diameter, and turbulence intensity of the liquid stream affect the air entrainment rate during pouring. In this study, the developed air entrainment model is validated with water modeling experiments. In the water modeling studies, water was poured using a bottom pour ladle. The effects of nozzle opening, head height, nozzle diameter, and nozzle extension are simulated. The predictions compare favorably with the experimental measurements. Results indicate that low head height and short pouring time have a beneficial effect on reducing the air entrainment during pouring. In addition, a fully open nozzle and the use of a nozzle extension further reduce the amount of entrained air. https://doi.org/10.1007/s11663-018-1334-4 The Minerals, Metals & Materials Society and ASM International 2018
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INTRODUCTION
OXIDE inclusions are among the most commonly reported causes of repair in ferrous and non-ferrous castings.[1,2] These inclusions affect the fatigue strength, fracture toughness, and machinability of a casting and may cause rejection of the cast part.[1,3] Oxide inclusions form when the liquid metal comes into contact with oxygen during mold filling. In aluminum alloy castings, the exposure of liquid aluminum to the oxygen results in an extremely thin solid oxide film covering the liquid metal surface during mold filling. As the liquid metal experiences free surface turbulence, the dry side of an oxide covering the melt can come in contact with the dry side of another oxide, and form double oxide films or bifilms.[1,4,5] In carbon and low alloy steel castings, steel reacts with oxygen to form oxide inclusions composed of the most reactive elements in the steel.[2] These inclusions are typically called reoxidation inclusions. In ductile iron castings, magnesium oxide forms when the magnesium and oxygen react during magnesium treatment and filling. The subsequent reaction between the magnesium oxide and silicon oxide (silica) is responsible
SEYYED HOJJAT MAJIDI and CHRISTOPH BECKERMANN are with the Department of Mechanical and Industrial Engineering, University of Iowa, Iowa City, IA 52242. Contact e-mail: [email protected] JOHN GRIFFIN is with the Department of Material Science and Engineering, University of Alabama at Birmingham, Birmingham, AL 35294. Manuscript submitted March 2, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
for the formation of dross inclusions.[3] Therefore, limiting the exposure of liquid metal to oxygen is necessary to minimize oxide inclusions. Air entrainment is the major source of oxide inclusion formation during pouring of metal castings. In free surface flows, air is entrained once the liquid experiences surf
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