Study On Coupled Turbulent Flow Heat Transfer And Solidification During Twin-roll Strip Casting

The twin-roll strip casting process is known as the next generation of near net shapematerials processing technology. During the past two decades, it has been attractedconsiderable attention from researchers around. However, several key issues still needbreakthroughs.The present thesis focuses on the development of a more sophisticated researchmethod to study the process in a limited space. Firstly, a comprehensive coupledmathematical model is developed to study the coupled phenomena of turbulent flow, heattransfer and solidification in the molten pool during the process. Secondly, a more realisticand accurate thermal boundary condition to obtain exact solution is proposed andvalidated through experiment measurement. Then, the heat transfer boundary condition isrevised accordingly when casting parameters varies, and the relationship between thecasting parameters is obtained. Finally, an optimized nozzle structure is obtained byrevising the heat transfer boundary condition accordingly and through studying the effectof nozzle structure on the turbulent flow, heat transfer and solidification in the moltenpool.In the course of study, several conclusions have been drawn:The turbulent flow, heat flux distribution at the roller interface and the formation ofsolidified shells all has impact on each other, during the study they should be consideredsimultaneously.A maximum heat flux value is reached at the initial contact between liquid steel androller interface, the super heat and part of latent heat the liquid metal contained is removedand transferred to the roller surface by the vortexes in the upper region of molten pool.The formation of gap causes the heat flux drops rapidly after the initial contact, then, theexistence of rolling force slightly raise the heat flux near the exit, and the remaining latentheat was extracted by the back flow of mushy metal. The calculated results agrees wellwith the experimental data and the kissing point position where the two solidified shellmeets can be obtained through numerical calculation. Based on timely corrections of the thermal boundary condition, the narrow matchingrange between the various process parameters is obtained, including the casting speed, thebath height, the thickness of the strip, the diameter of the roll diameter.Based on timely corrections of the thermal boundary condition, an optimized nozzlestructure to provide stable and uniform metal flow is obtained.A set of research method is provided in the present work, and further understandingof the process is provided.