| The flow behavior of liquid steel in the mold has a major impact of inclusion removal, mold powder entrapment, breakout, cracks and sticking defects. Statistics show that nearly80%of the surface defects originated in the mold. Free surface is not active under the conditions of low casting speed. This should lead to mold fiux crust and defects of continuously cast slab.A vertical slab mold of Bao Steel is the object for investigation in the dissertation. The size of bloom cross-section is200×1300mm2.The extent of casting speed is0.45-0.65m-min-1. In order to study the flow field in slab continuous casting mold in a low casting speed, a1:1physical model and a mathematical model of the slab mold are established. The effect of SEN structure (port size and angle) and process parameters (SEN submerged depth and casting speed) on mold flow field has been studied. The flow characteristics (velocity field distribution, surface fluctuation, impacting depth), temperature field distribution and the state of flux in the mold are studied. The SEN is optimized by the above methods. In addition, the influence of mold flow control device on mold flow field has been studied by the same methods. The applicability of the MFCD under the condition of low casting speed is studied.The results of nozzle optimizing show that SEN structure has great influence on flow characteristics and free surface temperature distribution. With SEN submerged depth increases, the level fluctuation decreases slightly. The flow characteristics doesn’t vary much while the SEN submerged depth range from100millimeters to130millimeters. The effect of process parameters on the level fluctuation is related with SEN structure, and that the descending order of sensitivity of nozzles to casting speed is nozzle2, nozzle5, nozzle4, nozzle3, nozzle1. Descending of the area of free surface high temperature followed by nozzle5, nozzle3, nozzle2, nozzle1, nozzle4. So, nozzle5has the best service performance of the five designed nozzles. The range of third of the big wave is0.8mm to2.8mm.The level fluctuation doesn’t vary much while the SEN submerged depth range from100millimeters to130millimeters, the efflux from nozzle is more dispersive, the impact depth is shallower, the powder is active, widely distributed and steady when casting speed ranges from0.45-0.65m/min.Some conclusions can be drawn according to the study on the influence of mold flow control device on flow characteristics. The MFCD creates two recirculation regions for upper recirculation region:one located in between MFCD and SEN, the other one located in between MFCD and narrow side. MFCD has obvious effect on the surface fluctuation, velocity field distribution and temperature field distribution. The influence of MFCD position is more significant than MFCD immersion depth on mold level fluctuation. The turbulent kinetic energy of the the free surface near the mold narrow side increase significantly when adding the MFCD. The effect of MFCD on the velocity field distribution and the temperature field distribution of the mold narrow side is not particularly obvious. MFCD has obvious effect on the flow behavior of liquid steel in the mold under the condition of4SEN, The fluctuations of partial free surface increase obviously. MFCD has no obvious effect on the flow behavior of liquid steel in the mold under the condition of5SEN, The fluctuations of free surface increase slightly. The MFCD can not control the flow behavior of molten steel in low casting speed conditions. The MFCD is not Applicable in low casting speed conditions. |
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