9th ECCC European Continuous Casting Conference – ECCC 2017

A major contributor to the quality of continuous cast steel is the flow structure in the mold. In case of slab casting, only the double-roll flow structure is expected to result in optimum quality steel, while other flow structures, like the single-roll or the unstable flow-structure, are generally associated with defects like slag entrainment or non-metallic inclusions. As countermeasures, two kinds of actuators, electromagnetic brakes (EMBr) and electromagnetic stirrers (EMS), are available. It is widely assumed that EMBr can calm an unsteady flow and suppress jet oscillations, whereas EMS ensure better mixing of the melt, even distribution of superheat and avoidance of segregation. Because of the opaqueness and temperature of molten steel, flow measurements inside the mold are hardly possible and often limited to very few points either within the volume or at the surface of the mold [1]. Without detailed information about the melt flow, tailored real-time process control is almost impossible. The contactless inductive flow tomography (CIFT) [2, 3] could help give insight into the transient flow structures in the mold. It operates by applying a magnetic field to the melt and measuring the flow-induced perturbations outside the mold. From those magnetic field measurements the flow inside the mold can be calculated by solving the underlying linear inverse problem. It was already demonstrated that CIFT can give quite accurate results (compared with UDV measurements) when applied to the flow of GaInSn in a model slab mold, in the case of a two-phase flow [4] or an EMS around the SEN with a downward-directed nozzle outlet [5]. Recent publications [6] dealt with a possible application of CIFT in the presence of an EMBr, with promising results. In our paper we will show first flow reconstructions using CIFT when the flow in a model slab mold is influenced by an EMBr and validate those reconstructions with reference UDV measurements. Additionally we will show preliminary measurement results for a model round billet caster with downward-directed SEN outlet, where an EMS is applied to the SEN. [1] B. G. Thomas et al., “Comparison of four methods to evaluate fluid velocities in a continuous slab casting mold,” ISIJ International, vol. 41, no. 10, pp. 1262–1271, 2001. [2] F. Stefani et al., “Contactless inductive flow tomography,” Physical Review E, vol. 70, 056306, 2004. [3] T. Wondrak, et al., “Contactless inductive flow tomography for a model of continuous steel casting,” Measurement Science & Technology, vol. 21, no. 4, 045402, 2010. [4] T. Wondrak et al., “Combined electromagnetic tomography for determining two-phase flow characteristics in the submerged entry nozzle and in the mold of a continuous casting model,” Metallurgical and Materials Transactions B, vol. 42, pp. 1202–1210, 2011. [5] T. Wondrak et al., “Liquid metal experiments with swirling flow submerged entry nozzle,” Ironmaking & Steelmaking, vol. 39, pp. 1–9, 2012. [6] M. Ratajczak, et al., “A gradiometric version of contactless inductive flow tomography: theory and first applications,” Philosophical Transactions of the Royal Society A, vol. 374, no. 2070, 20150330, 2016.