Inclusion Behaviour under a Swirl Flow in a Continuous Casting Process

Abstract: A swirl flow generated in a submerged entry nozzle (SEN) can effectively improve a flow pattern and heat transfer in a continuous casting process by using the methods of “swirl blade type” and “electromagnetic type”. In order to obtain a further in-depth understanding with respect to the effect of a swirl flow on a continuous casting process, the inclusion behaviour in a SEN and a mold was studied in the present work. Moreover, the use of electromagnetics was adopted for to generate a rotating electromagnetic field in a continuous casting process of steel. Specifically, an electromagnetic swirl flow generator (EMSFG) was placed around a SEN.First of all, two kinds of a full type EMSFG and a half type EMSFG were designed based on mathematical modeling. Then, distributions of a magnetic flux intensity in an EMSFG as well as distributions of a Lorentz force in molten steel were simulated. It was found that the EMSFG structure and electromagnetic parameters have an important effect on the magnetic flux intensity and Lorentz force distributions. For both a full type and a half type EMSFG, the magnetic flux intensity and Lorentz force increases as the magnetomotive force increases. Especially, for a full type EMSFG, the magnetic flux intensity is distributed evenly in molten steel. Moreover, the Lorentz force increases along a radial direction in the molten steel in the SEN. However, for a half type EMSFG, the magnetic flux intensity and Lorentz force decreases gradually towards the region without an EMSFG. Consequently, a full type EMSFG with a 44000 AT magnetomotive force and a 50 Hz frequency is more suitable to apply in the operation of an EMSFG under actual production conditions.Secondly, the flow field, the temperature field of molten steel and the inclusion behaviour in a SEN and a square bloom mold were simulated under the influence of a rotating electromagnetic field (swirl generator). Also, the influences of different inclusion parameters such as the densities, sizes and boundary conditions, on the inclusion behavior were studied. The results show that a flow pattern in a SEN can be characterized into three distinct flow regions: an accelerating flow of molten steel from an electromagnetic swirl flow generator (EMSFG) inlet to an EMSFG center, a decelerating flow of molten steel from an EMSFG center to an EMSFG outlet, and a recirculation flow of molten steel from an EMSFG outlet to an SEN outlet. In addition, it was found that light Al2O3 inclusion moves towards the rotational center by a centrifugal force, and that a swirl flow prevents nozzle clogging. Moreover, it was also found that the inclusion separation to a mold meniscus increased and that the inclusions trap into a solidified shell wall decreased by using a swirl flow.