Transient Mold Fluid Flow with Well- and Mountain-Bottom Nozzles in Continuous Casting of Steel
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BOTH the steady-state flow pattern and transient variations in the mold cavity are important to steel quality in continuous casting. Excessive meniscus velocities and surface turbulence lead to inclusion defects due to slag entrainment and level fluctuations in the mold.[1,2] Insufficient surface flows lead to meniscus freezing and other surface defects.[1,2] The mold flow pattern should be optimized to achieve a flat surface profile with stable meniscus velocities of the desired magnitude and minimum turbulence. These important flow parameters are governed by the flow-control system (stopper rod or slide gate), nozzle geometry, Submerged Entry Nozzle (SEN) depth, casting speed, strand cross-sectional dimensions, argon-gas injection rate, slag behavior, and the application of electromagnetics.[1] The most influential and easily changed of these parameters are the nozzle port geometry details (port angle and port area) and the nozzle-bottom shape. In particular, the shape of nozzle bottom has an important influence on flow quality in the mold, including the surface velocity, surface-level profile, and turbulent variations that vary the frequency and magnitude of their fluctuations and asymmetries. This article applies a computational model and water-model R. CHAUDHARY, Graduate Student, is with the Department of Mechanical Science and Engineering, University of Illinois at Urbana– Champaign, Urbana, IL 61801. GO-GI LEE, Graduate Student, is with the Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, Kyungbuk, 790-784, South Korea. B.G. THOMAS, Wilkins Professor of Mechanical Engineering, is with the Department of Mechanical Science and Engineering, University of Illinois at Urbana–Champaign. Contact e-mail: [email protected] SEON-HYO KIM, Professor, is with the Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, Kyungbuk, 790-784, South Korea. Manuscript submitted July 17, 2008. Article published online October 28, 2008. 870—VOLUME 39B, DECEMBER 2008
experiments to analyze and compare the effect of two popular nozzle-bottom shapes on these flows.
II.
PREVIOUS WORK
Owing to the difficulty of plant experiments and the similar kinematic viscosity of water and steel, much previous insight into mold fluid flow has been gained using water models.[1–6] Although most studies have focused on steady-state flow patterns, a few studies have noted transient phenomena.[3–11] Honeyands and Herberton[8] observed surface-level fluctuations in a thin-slab water model with a characteristic frequency that increased with casting speed, according to the time period for flow to circulate around the mold cavity. Gupta and Lahiri[5] observed flow asymmetries in the lower recirculation zones that alternated between sides like large-scale vortex shedding. Lawson and Davidson[9] used Laser Doppler Velocimetry (LDV) to measure oscillatory flow in a 0.33-scale thin-slab water model. Low-frequency oscillation modes had the most oscillatory energy, especially b
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