The Role of Submerged Entry Nozzle Port Shape on Fluid Flow Turbulence in a Slab Mold
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generally believed that wide slab molds should be operated at high casting speeds to maintain a stable meniscus and steady casting conditions.[1] However, additional important factors must be considered to achieve a smooth casting operation. For example, discharging ports with cross-section areas larger than the bore cross-section area of the submerged entry nozzle (SEN) will lead to meniscus turbulence and slag entrainment.[2] Large ports make their discharging angle less influential on the angle of the jet.[3] Downward port angles are preferred over upward port angles because the later promote larger turbulence on the melt meniscus.[4,5] Moreover, large port dimensions lead to recirculating flows just in the upper edge of the port, leading to backflow conditions and aggravating clogging problems.[6,7] Most of the SEN designs available in the market observe this characteristic under the reasoning that large ports help to compensate the clogging effects of alumina. Smoothing the angle of the interior upper port edge decreases the clogging and the backflow issues.[8] Circular ports generate more swirls and have a larger spread angle than rectangular ones having the same cross-section area. Opposite to that opinion, Lu et al.[9] claimed that port shape is less important than port size and port angle in controlling the flow inside the mold. It seems that all those factors require additional ISMAEL CALDERO´N-RAMOS, Ph.D. Student, and RODOLFO D. MORALES, Professor, are with the Department of Materials and Engineering and Metallurgy, IPN-ESIQI, Mexico. Contact e-mail: [email protected] Manuscript submitted August 6, 2014. Article published online April 25, 2015. 1314—VOLUME 46B, JUNE 2015
studies aimed at gaining a more complete understanding of steel flow in molds. Turbulent flows at melt meniscus lead to slag entrainment and these slag particles could, eventually, become inclusions in the cast slab.[10] Actually, the flow at the meniscus should permit a continuous infiltration of mold powder between the mold’s hot face and the strand to promote a slab surface free of cracks. To attain that result, the flux properties, casting speed, nozzle design, and the mold oscillation play the most important operating factors. However, one factor that has not been studied completely is the role that the fluid flow plays to get appropriate infiltration of the mold flux. Few studies have also been reported about the steel shell remelting by the effects of momentum and convective energy transport by the discharging jets.[11–13] This leads to the very important question of what criteria a SEN design should fulfill to ensure a stable meniscus, good flux infiltration, a growing shell with no breakouts, and appropriate solidification conditions of steel at the meniscus level. Yet, there is still an unknown field where the SEN design, the flux, and steel chemistries and fluid flow meet to ensure smooth casting operations that must be defined. Specifically regarding the aspects of fluid flow, many researchers have applied physical modeling and mathematical
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