| The control of flow pattern of molten steel in mold is one of the important means to increase casting efficiency and improve billet quality in continuous casting of steel. The swirling flow in submerged entry nozzle (SEN) has great effect on improving the uniformity and stability of the outlet flow of the nozzle. It can effectively reduce the meniscus fluctuation, homogenize the distributions of flow and temperature in the mold. A new method for swirling flow generation in the nozzle, which is easy for controlling swirling velocity, has been proposed. In this method, a rotating electromagnetic field is set up around the SEN to induce swirling flow in it by the Lorentz force. No clogging will occur since the swirling flow is induced without contact with the steel. And the swirling flow strength is adjustable for more optimum swirling effect on continuous casting process.The magnetic field is simulated with commercial software ANSYS. The effect of different structures of the electromagnetic swirling flow generator (EMSFG) on the magnetic field of steel in the SEN is examined. The flow field is simulated with commercial software FLUENT. The Lorentz force is firstly calculated in ANSYS EMAG, and applied as a source with UDF to calculate the flow field. The node force of the element is interpolated to the center of the cell with linear interpolation method. The swirling flow in the SEN in round, square and slab continuous casting is numerically analyzed.The result shows that, the magnetic field distribution is the largest and most uniform with round EMSFG For modified U-shape EMSFG, the magnetic flux density and Lorentz force is closer with that of round EMSFG The Lorentz force of U-shape is about 80% of the round one. Therefore, in practical process, the modified U-shape EMSFG is alternative. The effects of coil current intensity and frequency on the magnetic field in molten steel in the SEN are also analyzed. As coil current intensity increases, the magnetic flux density and the Lorentz force in the SEN both increase. While frequency increases, the magnetic flux intensity reduces, but the Lorentz force increases. With coil current intensity 500 A, frequency 50 Hz and round EMSFG, the magnetic flux density in the center of the EMSFG is about 0.6 T.For round billet continuous casting, the effect of the EMSFG structure on the flow field in the SEN and the effect of the divergent angle of the SEN with electromagnetic swirling on the flow and temperature fields in the mold are investigated. The suppression of uneven flow caused by sliding gate is investigated with electromagnetic swirling. It is found that the velocity distribution in the SEN with coil current intensity 500 A, frequency 50 Hz and round EMSFG is the most uniform and the velocity is largest. The largest swirling velocity is about 3 m/s at the center of EMSFG. The results in modified U-shape get the closest situation with that in the round case. In modified U-shape, the velocity is about 2.3 m/s in the left and 2.2 m/s in the right, the rate of deviation is 4.3%. The swirling flow can reduce the impinging depth of outflow, increase the upward flow, this will cause the high temperature zone shift up, the temperature gradient in the mold become less generally, and the meniscus temperature increase. Compared with no swirling flow, with coil current intensity 500 A, frequency 50 Hz, the upward flow velocity increases about 60%, and the meniscus temperature increases about 2?. Compared with conventional nozzle, the swirl effect can be fully exploited with divergent nozzle. The molten steel divergent more widely at the nozzle outlet. The impinging depth of the flow becomes less, and the distribution of the flow and temperature fields are more uniform on each cross section below the nozzle. The upward flow is larger and the meniscus temperature is higher. Compared with conventional nozzle, the upward flow velocity increases about 450%, and the meniscus temperature increases about 10? in case of divergent nozzle with 500 A,50 Hz swirling flow. Uneven flow develops as molten steel passes through an incompletely open sliding gate, and it can be suppressed effectively by swirling flow and divergent nozzle.For square billet continuous casting, the effects of coil current intensity and nozzle structure on the flow and temperature fields in the SEN and mold are numerically simulated and verified by an electromagnetic swirling model experiment of Pb-Sn-Bi alloy. The overall results of the study show that the electromagnetic swirling flow in the SEN can reduce the impinging depth of the flow and increase the upward flow. An impinging flow near the mold corner could be observed. The flow field changes mentioned above result in a uniform temperature field in the mold, increase the meniscus temperature, effectively increase the temperature at the mold corner. Compared with no swirling flow, with coil current intensity 500 A, frequency 50 Hz electromagentic swirling flow, the temperature of mold corner near the nozzle outlet increases about 4?, the temperature of mold corner below the nozzle outlet increases about 8?. The divergent nozzle used in this new process also reduces the impinging depth, increases the upward flow and makes the meniscus temperature increase significantly, about 4?, the temperature of mold corner at the meniscus also increases about 4?.For slab continuous casting, the flow field calculation method and the feasibility of the electromagnetic swirling flow are firstly verified by the simulation of Wakayama mechanical swirling and then the comparation of mechanical swirling wih electromagnetic swirling. The flow and temperature fields in the SEN and mold in slab continuous casting of steel are studied numerically. And the effects of swirling flow on the flow field in the slab mold are analyzed. The relationship between coil current intensity and the outflow is investigated, and the structure of nozzle outlet is optimized to improve the adverse impact caused by electromagnetic swirling. The results of the study show that while the SEN is optimized with the circular arc at the tip of the outlet, the negative pressure is suppressed with coil current intensity 250 A and frequency 50 Hz electromagnetic swirling flow. The molten steel flows into the mold from the central of outlet, which is conductive to obtain a uniform outlet flow. This is helpful to improve the flow and temperature fields in the mold. Clockwise rotation of the nozzle optimization or asymmetric nozzle outlet optimization could reduce the outflow to impact of the wide face of the mold. Changing the inclination of the bottom of nozzle outlet can control the direction of outflow, and the meniscus temperature could be controlled. A new SEN is designed for Laiwu slab continuous casting industrial experiments. With 500 A, 50 Hz swirling flow, it can effectively improve the uniformity and stability of the flow at the outlet of the nozzle. Consequently it can effectively reduce the meniscus fluctuation, homogenize the flow and temperature fields in the mold. |
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