Experimental Research On Flow Field In Immersion Nozzle And Mold Under Electromagnetic Swirling Nozzle

In the continuous casting process of molten steel, the occurrence of the deviation of the bulk flow from the center line is unavoidable in the immersion nozzle, which leads to the inhomogeneous distribution of the fluid flow and temperature and to the meniscus fluctuation in the mold. It causes the decrement of the surface and internal quality of the ingots, as well as the casting speed. Research result shows that the swirling flow is effective to control the occurrence of the deviation of the bulk flow from the center line in the immersion nozzle. In the preceding research a new process was proposed, in which a rotating electromagnetic stirrer was set up outside the nozzle to induce swirling flow by Lorentz force in the molten steel. And the experimental and simulating works on magnetic field and fluid flow in the nozzle and mold induced by different types of EMS were done.Since the physical properties of Pb-Sn-Bi alloy are quite similar to that of molten steel, in this study, it is used in the model experiment of continuous casting under the imposition of a new type electromagnetic stirrer around the nozzle. The flow and temperature field of Pb-Sn-Bi alloy in the nozzle (in the case of without mold) and round and square type mold were measured and analyzed with high speed camera, ultrasonic Doppler velocimetry and thermocouple, respectively so as to determine the influence of rotating magnetic field on flow and temperature field of alloy in the nozzle and mold.The following results are obtained.In the hole of the new type electromagnetic stirrer, magnetic flux density measurement was carried out. It is found that the magnetic flux density increases as the coil current intensity increase. The magnetic flux density in the central axis and in the vertical line in the inner wall of the stirrer has largest value at the center of the stirrer. It decreases with the distance from the central axis, and with the distance from the center in height.In the velocity measurement experiment of the swirling flow from the nozzle outlet, the effects of the diameter of the nozzle, the coil current intensity are investigated at different magnetic flux density. It is find that swirling velocity increases parabolicly with the increase of the nozzle diameter. The swirling velocity increases linearly with the increase of the electromagnetic frequency as well.The Doppler ultrasonic velocimetry was used in the measurement of the molten steel velocity distribution in the round and square mold under rotating magnetic field. It is found that in both cases, the swirling velocity in case of no EMS is minor, and the swirling velocity in the extension line of the Doppler transducer central axis increases with the distance from the wall of the nozzle until half length of the measuring line segment, and is centrosymmetry. This tendency is in accordance with the result obtained in proceeding simulation work. The swirling velocity gets less as distance from the outlet of the nozzle.Four thermocouples were set in different position to investigation the temperature distribution in the mold. The result shows with EMS in the upper part of the mold the temperature value improved and the temperature distribution get more homogeneously.