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Heat transfer characterization of secondary cooling in the horizontal direct chill casting process for aluminum alloy re-melt ingot Xue, Boran


Horizontal direct chill (HDC) casting is a continuous process used to produce extrusion billet and re-melt aluminum ingot. As in vertical DC casting, secondary cooling, where water directly impinges on the cast surface, is an important process that can affect cast quality and production rates. During HDC casting, secondary cooling is further complicated by horizontal water flow and the water spray conditions. Characterizing the heat transfer during the secondary cooling process is necessary for improved understanding of the process. Since the accessibility of the HDC casting machine is limited and the direct measurement of heat transfer in secondary cooling are difficult, numerical modeling thus becomes a good approach for process development. In this research, the heat transfer occurring in secondary cooling of an HDC ingot has been studied. Water spray conditions on three different casting surface were simulated separately by quenching the blocks of HDC cast A356 aluminum alloy which was cut from a T-ingot. The temperature history during the cooling within the blocks was recorded by sub-surface thermocouples. An inverse heat transfer model was developed and used to calculate the heat fluxes on the casting surfaces using measured temperature data. The heat fluxes were characterized via boiling curves, which are the functions of surface temperatures, in each spray configuration. The effects of operational parameters, including the casting speed and the water cooling rate, were investigated by comparing the characteristic features of the calculated boiling curves. The spray configuration effect was also studied with the calculated results from the stationary tests in a qualitative fashion. Then a fitting technique was developed to idealize the calculated boiling curves. The idealized boiling curves were summarized into the functions, which provide practical database for application of the results in this research. All in all, the simulation apparatus and the IHC model provide the ability of characterizing the heat transfer occurring in secondary cooling region of HDC casting with lab-scale experiments. Consequently, the expensive and risky plant trials can be avoided.

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