| In a twin roll strip casting process, the molten steel is fed through a delivery system intothe special mold formed by the two-counter rotating water-cooled rolls and two side dams.The molten steel is solidified in an extremely short time and exits out from the rolls in theform of strip. Comparing with the traditional casting process, the twin roll strip casting maynot only save energy and manufacturing cost by eliminating some of the intermediate stages,but also meet the requirement of the recycling economy. But during the strip productionprocess, the direct casting of strips poses a new set of challenges since the pool is narrow andthe casting speed and solidification speed are an order of magnitude higher than thoseachieved in conventional casting. This makes the process parameters control even morecritical and are difficult for improving the strip quality, due to the heat transfer andsolidification are completed within a very short period of time for the factors influencing thequality of thin strips are complicated.In this article, the commercial software of ProCAST is conducted to study the tansportphenomena at the pouring stage of twin roll strip casting. The mathematical model for1:1scale twin roll strip caster used two side delivery system and wedge shaped delivery systemrespectively is set up to investigate the flow patterns, temperature distribution andsolidification process at various process parameters, which with60m/min, and80m/min, and100m/min for three different casting speeds and40℃, and50℃, and60℃for threedifferent superheat. The following conclusions are drawn from this study:1. Influence of casting speed:(1) Using two-side delivery system, as casting speed increases, the flow patterns inthe molten pool are similar, but the ascending height of the melt in molten poolalong the side dam significantly increased. When the casting speed is more than60m/min, turbulent kinetic energy increases significantly near the free surface andthe side dam.(2) Using wedge shaped delivery system, compared with two-side delivery system,the flow patterns in a molten metal pool are complex with many small vortexes,and the turbulent kinetic energy on the free surface and near the side dam is smaller.As casting speed increases, the turbulent kinetic energy on the free surface andnear the side dam in the molten pool becomes bigger, but it is only about tenpercent of turbulence kinetic energy using two-side delivery system. 2. Influence of superheat:(1) When using two-side delivery system, with superheat increasing, thetemperature of melt in the molten pool and the areas of higher temperature regiongradually increase. The molten steel in molten pool solidifies from the surface ofthe cooling rolls to the middle of the pool, and from bottom to the upside. Whilethe superheat increasing, solidified shell thickness of the strip decreases.(2) When using wedge shaped delivery system, temperature distribution in the Y-Zcentre section of the molten pool and cooling rolls surface is more uniform andthere are no obvious higher temperature areas. And when the melt flows to thebottom of molten pool through the surface of cooling rollers, which with hightemperature gradient, this will more easily generate the uniform solidified shell ofthe strip. As the superheat increases, the shell thickness gradually reduces in asmall range.In conclusion, it is more desirable using wedge-shaped delivery system to produce thestrip with higher casting speed and superheat in the twin-roll strip casting process. Theresearch results provide a basis for the optimization of process parameters and designing ofthe delivery system. |
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