Surface-oriented melt/substrate heat-transfer model in aluminum strip casting
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3/4/04
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Surface-Oriented Melt/Substrate Heat-Transfer Model in Aluminum Strip Casting A.G. GERBER, C. NG, and M. GALLERNEAULT A coupled heat- and fluid-flow model to study the initial contact between a melt and a water-cooled substrate (belt) is presented. The key elements of the model are the fluid flow and heat transfer of the molten metal (including phase change), waterside cooling, intervening moving metal substrate, and a gas layer generated by an active interfacial “contact” layer. A unique aspect of this article is the introduction of a subgrid model for the description of the contact-layer heat transfer in the initial melt/substrate contact region. The subgrid model, developed around multiphase conservation equations and an Arrhenius reaction model, is incorporated within the framework of macroscopic equations for heat and fluid flow applied to a computational grid much larger than the scale of the contact layer. The model results are compared against experimental casting data, and the predictions are assessed with a view to understanding surface cooling conditions and the impact on surface metallurgy in strip casting of thin-gage product.
I. INTRODUCTION
OVER the past decade, computational fluid dynamics (CFD) has become a mature discipline applied extensively to a wide range of manufacturing processes. Excellent examples where CFD has been used successfully to improve manufacturing processes are those applied to flows in ladles, tundishes, and various continuous casting configurations.[1–4] Within the latter application, CFD modeling has been conducted to support the extensive university and industry research into near-net-shape continuous casting. Strip casting using configurations such as the twin-belt caster, twin roll, and single roll have been, to a large degree, successfully deployed for low-melting-point nonferrous materials. However, the potential of near-net-shape casting of light metals has yet to be fully realized due to the control of cast quality at high casting speeds and cooling rates. Mathematical models for the macroscopic behavior of the process have been developed;[5–11] however, success lies in understanding the micro/macroscale interactions, and it is in this area that mathematical models still need extensive development. In the present article, a finite-volume–based CFD model has been developed to examine the very early cooling conditions, and subsequent solidification, along the surface of a moving substrate. This configuration, at a reduced scale, corresponds to a variety of continuous-casting scenarios including both strip and conventional direct-chill (DC) casting. Since the outer “skin” of the casting is formed in this dynamic region, understanding the interactions between melt flow, waterside cooling, substrate/mold coatings, and solidification is critical to controlling the quality of the as-cast surface. Eventual coupling of this macrobehavior with the microstructural development of the alloy provides the basis for including all of the key variables in u
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