Numerical Analysis Of The Electromagnetic Continuous Casting Process In The Thin Slab Funnel Shape Mold

With the tendency of steel fierce competition and raw material shortage in the world, the near—net—shape continuous casting and rolling technology with high efficiency and short process has been developed dominantly in the steel industry nowadays. During the past twenty years, the thin slab casting and rolling technology has been used more and more widely. At the same time, a new environmental protection technique named the electromagnetic metallurgy, which can improve the slab quality significantly, has been developed rapidly. Using the thin slab funnel shape mold, the casting speed is much higher than normal slab casting even more than 6m/min, and the mold has a large ratio of wide to narrow sides, hence the fluid flow in the mold is much more difficult to control to prevent non uniform of initial very thin solidification shell even breakout. All above can improve the slab quality and shorten the casting equipment serving life. Therefore, Electromagnetic Brake (EMBr) technology is developed to control and redistribute the melt steel flows in a mold region using a transverse static magnetic field. Lorentz force generated by the static electromagnetic field is used to control the moving slab indirectly.This research is to do numerical simulation of the EMBr effects on steel behaviors in the thin slab continuous casting funnel shape mold. Based on the results, the optimized structure and operating parameters are determined. The data obtained can be remarkable contributions in industry production.There are two parts in this work, the development of the new type magnet and the numerical simulations of the steel behaviors in the mold. Details are described as following:Based on the conventional magnet, a new type magnet is designed in order to fit the complex, irregular funnel structure of the compact strip production (CSP) thin slab mold. Compared with the conventional one, the new type magnet can provide more significant EMBr effects and higher quality; improve production efficiency. This fact implies lots of electrical energy and cost.Numerical simulations have been made step by step. Three—dimensional (3D) mathematical models of steel flow, heat transfer, solidification and electromagnetic field have been built successfully. In the lack of experimental data for validation, classical examples are adopted for each model. The comparisons show that, the numerical results of the models used in this research are reliable.Software CFD—ACE based on the finite volume method (FVM) is used to do the simulation research of the steel flow. In this study, the scales and geometrical structures of mold and nozzle are fixed. Two main operational parameters, the casting speed and depth of submerged entry nozzle (SEN), are considered in the computations. Based on the distributions of steel vector and turbulent kinetic energy, and the maximum velocity beneath the meniscus, the effects of two parameters on the flow field are analyzed. The results can do contributions for further researches.In the numerical simulation of the electromagnetic field, the software ANSYS based on finite element method (FEM) is adopted to do the simulation of the magnetic field in the funnel shape mold region produced by the new type EMBr equipment. Compared with the conventional magnet, the new type magnet can induce more stronger and irregular magnetic fields. The maximum intensity appears in the region closed to the narrow wall of the mold, and this is just the region where the melt steel may impinge on the narrow wall. Moreover, the influence law of the magnetomotive force and the height of the magnet on the distribution of the magnetic field are studied. The results show that, as the magnetomotive force increases, the magnitude of the magnetic field density becomes bigger while the trend of the magnetic field remains the same; the main magnetic field in the funnel shape mold becomes lower as the height of the magnet decreases, while the distribution remains the same.In the simulation of the EMBr effect on the steel flow, for computing the fluid field coupled with the magnetic field, software ANSYS with FEM is used and software FLUENT with FVM is adopted. Magnetohydrodynamics (MHD) model is activated to couple the applied magnetic field and flow field. The FORTRAN programs of linear interpolation of magnetic field, B, are developed to impose the magnetic field into the flow field. Steel turbulent flow is controlled by the EMBr. The results show that, the turbulent flow is significantly controlled with the help of EMBr. Further, the magnet structure, the height of the magnet and the magnetomotive force are considered in the analysis. The results show that, the new type EMBr offers more uniform downstream velocity profile than a conventional system for the same conditions, and has a cost of almost 40% less in magnetomotive force and corresponding electrical energy. With the decreasing of magnet height, the EMBr can make the flow field much more reasonable and the velocity beneath the meniscus becomes much lower. As the casting speed increases by 0.5m/min, 1000a·n more of magnetomotive force is needed correspondingly.As an expansion of the former work, not only the flow fields and electromagnetic fields are considered, but also the resultant macrosolidification is taken into account. Thus, the phenomena become much more realistic. The specific heat method is used to treat the latent heat of solidification, and the Darcy's Law—type porous media treatment is used to account for the effect of phase change on convection. Thermal buoyancy force is considered. Both the narrow and the wide walls are treated as cooling walls and the Neumann boundary condition is applied. The User—Defined Functions (UDFs) are written in FLUENT for Darcy source term and thermal conductivity in mushy zones. The results show that: the temperature field distribution and trend are similar to the flow field. This is attributed to the effect of turbulent flow on the heat transfer mechanism. The new type magnet is superior to the conventional one on the EMBr effects with lower cost. In the case of SEN depth 300mm with the casting speed of 5.5m/min, the effects in the condition of magnet height 250mm is the most significant among the three heights. The magnetomotive force 8000a·n can offers better effects on flow and temperature fields as well as the solidified shell.