The use of particle image velocimetry in the physical modeling of flow in electromagnetic or direct-chill casting of alu
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PART I of this two-part article has briefly described the two technologies, direct-chill (DC) and electromagnetic (EM) casting, that are widely used for the semicontinuous casting of aluminum. There it is emphasized that the flow of liquid metal into the pool of aluminum (‘‘sump’’) at the head of the caster can affect both the heat transport in this region, and, thereby, the operability of the caster and the microstructure of the solidified ingot. The flow in a typical industrial caster is a function of the flow control devices that are in common use. These devices are a submerged nozzle and various designs of bags. The former is a ceramic tube through which the metal flows vertically downward into the bag. The latter is of woven ceramic fiber and is approximately in the shape of an open-topped rectangle, parallelepiped with its long dimension horizontal and parallel to the wide face of the ingot. Two types of bag in common use are the ‘‘channel bag’’ and the ‘‘combo bag,’’ they are sketched in Figure 1. The former bag is of a uniform weave permeable to aluminum (although an impermeable strip may be sewn inside the bag just below the nozzle exit). It serves to dissipate much of the momentum that the metal inflow has at the nozzle exit. The flow out of this bag is intended to be uniform across its entire surface. In contrast, the combo bag is mostly composed of densely woven material of limited permeability, windows, of a much more open weave, provide exits for the aluminum, and the outflow is, therefore, highly nonuniform. Combo bags can be made in any length, and windows of any size can be placed wherever desired; consequently, DONG XU, Assistant Specialist, W. KINZY JONES, Jr., Graduate Student, and J.W. EVANS, Professor, are with the Department of Materials Science and Mineral Engineering, University of California, Berkeley, CA 94720. Manuscript submitted October 6, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS B
there is a plethora of bag designs in use, with little or no scientific justification for their choice. A further complication is that inclusions/oxidation products can partially block widows (or even completely block some of the windows) during a cast, and little is known of the effect of this blockage on the flow. The submergence of the nozzle, or the distance from the nozzle exit to the bottom of the bag, may also have an influence on the flow. Finally, bags can be placed incorrectly (not centered, tilted, etc.) and the authors are aware of one manufacturing facility where the bag is deliberately placed off center to accommodate a level control device.[1] Part I of this article has also described the water model that was constructed in the authors’ laboratory to simulate the flow of liquid metal in the sump and allow a study of the influence of various bags on the flow. The model was intended to simulate a pilot caster at the Reynolds Metals Company (Richmond, VA). It was constructed of clear Lexan, and a permeable plastic material was used to simulate the solidification front that is the lower b
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