Numerical Simulation of Metal Melt Flow in a One-Strand Tundish Regarding Active Filtration and Reactive Cleaning
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ETALLIC inclusions (NMI) such as alumina inclusions in steel melt are generated from several sources.[1] Due to their negative effects on the quality of the final steel product, there is an ongoing research for measures, which enhances NMI removal from the molten steel during the continuous casting process. Among others, steel filtration using ceramic filters (CFs) with different geometries has been frequently considered in this context.[2–7] Uemura et al.[2] tested CF made of loops and foams to remove alumina inclusions in steel. The cleaning efficiency was investigated experimentally in a small-scale tundish. A strong reduction was found for filters with small filter pore diameters. However, the cleaning efficiency decreases with the increasing pore sizes. On inspecting the filters after the filtration experiments, it was found that filtered nonmetallic inclusions were entrapped onto the filter surfaces.
SEBASTIAN NEUMANN, AMJAD ASAD, TOM KASPER, and RU¨DIGER SCHWARZE are with the Institute of Mechanics and Fluid Dynamics, Technische Universita¨t Bergakademie Freiberg, 09599, Freiberg, Germany. Contact e-mail: [email protected] Manuscript submitted August 21, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
In a series of papers, Janiszewski and coworkers[3–5] performed steel filtration experiments with CF in a small-scale tundish. A noticeable, moderate reduction of inclusion content was found in their studies. Scanning microscopy pictures showed that alumina inclusions are deposited at the filter walls, as found in Uemura et al.[2] In this paper, this cleaning technique is termed as ‘active filtration.’ In case of active filtration, NMI are removed from the melt by deposition at the filter surfaces. Aneziris et al.[6] investigated the active filtration of steel melt in a steel casting simulator (SCS). The results indicate a higher cleaning efficiency by collecting NMI on CF surfaces due to alumina-active coatings on nozzles or filters. Schmidt et al.[7] analyzed a time-dependent interaction between alumina-coated carbon-bonded filters and steel. Experiments in the SCS show a reactive cleaning by means of dissolution and reaction resulting in high cleaning efficiencies combined with in situ layer formation on the filter walls. This further cleaning technique is termed as ‘reactive cleaning’ in this paper. In reactive cleaning, carbon (C) gets dissolved from the filter coating into the steel melt. Here, it reacts with oxygen (O) which is present in the melt. This way, the NMI get surrounded by CO bubbles, which lift them up to the melt surface. Similar processes have been described, e.g., in Schlautmann et al.[8] and Rzehak.[9]
With reactive cleaning, Storti et al.[10] found NMI removal rates up 95 pct in small-scale, short-term (10 seconds) batch filtration experiments. In a laboratory-scale induction furnace crucible corresponding numerical study, Asad et al.[11] recently proved that only reactive cleaning gives such high NMI removal rates. On the contrary, active filtration with NMI deposition at the filter surfaces ex
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