DISTRIBUIÇÃO DE GÁS INERTE DENTRO DO SISTEMA DE REFRATÁRIO DURANTE O LINGOTAMENTO CONTÍNUO DE PLACAS: MODELO FÍSICO E MATEMÁTICO

Abstract

Inert gas is usually injected in the nozzles through the refractories during continuous casting of slabs. Although the main objective is to avoid deposition of inclusions on the ceramic parts there are some unavoidable consequences. Too much gas disturbs the metal-slag interface improving slag entrapment. The flow field inside the mold is affected since the gas shows a lift effect on the metal leaving the submerged entry nozzle. For a given geometry the net effects are defined by gas flow rate, number and location of injection points, metal throughput and refractories characteristics. In this study gas distribution inside the Submerged Entry Nozzle (SEN) and inside the mold is analysed using mathematical modelling (computational fluid dynamics - CFD) and physical modelling. The late was done in an actual size mold, with an acrylic replica of the submerged entry nozzle (SEN) and two upper nozzles for gas distribution: double inlet porous material with different configuration. The consequences of gas distribution in the flow field and metallurgical aspects are discussed. For low and intermediate flow rates of water and high rates of gas injection was observed an occurrence of bubble’s coalescence with large diameters, from the bottom and the exit port of the SEN, leading to an upward flow next to the exit SEN. That situation interferes with the structure of superior double roll, causing a region of low velocity in the meniscus and foamy layer on the surface. Though, for high water flow rates that situation was not observed for any injection rates used in this study. About the mathematical modelling a critical factor for adjust it to the physical model is the set of bubble diameter, which reinforce the importance of consider the coalescence-breakup phenomena in the SEN. For low flow rates of liquid phase a large bubble diameter fits better, while for high flow rates of liquid a minor diameter is more adequate to represent the condition inside and near the SEN, however it is not represented satisfactorily the flux behavior inside the mold.