Optimization Of Nozzle In CSP Continuous Casting Mold Based On Liquid Level Fluctuation F Value

The quality of slab is closely related to the flow behavior of molten steel in the mold.For CSP thin slab continuous casting technology,due to its production characteristics of high drawing speed and thin specification,the flow field in the mold is more affected by the submerged nozzle parameters.Therefore,it is of great significance to study the influence of CSP submerged nozzle parameters on the flow field in the mold to improve the quality of CSP thin slab.The CSP submerged nozzle with a section size of 1200mm×70mm in a factory is optimized.Combined with the structural characteristics of CSP submerged nozzle and according to the fluid submerged jet theory,the derivation process of F value analytical formula is given.The relationship surfaces between F value and mold size,nozzle immersion depth,nozzle inner diameter,nozzle inclination,nozzle outlet area ratio and blank drawing speed are obtained.The correlation between each nozzle parameter and F value is analyzed,and a method for optimizing the design of CSP submerged nozzle based on the expression of F value is proposed.According to this method,a group of ideal nozzle parameter combination surfaces are obtained.According to the combination surface of the ideal nozzle parameters,the numerical calculation model of the flow field of liquid steel in the mold is established,and the nine groups of schemes on the surface are numerically simulated.The flow field in the mold,the fluctuation amplitude of the steel slag interface and the cloud diagram of its surface velocity corresponding to each scheme are obtained.After comparative analysis,a group of optimal schemes are determined.According to the obtained optimal scheme,the drawing speed range when the F value is between 3～5 is solved by programming,and the drawing speed range is 3.506m/min～4.526m/min,which meets the production requirements of the plant of 3.6m/min～4.5m/min.The simulation calculation is carried out under the conditions of blank drawing speed of 3.6m/min and 4.5m/min respectively.The results show that the nozzle parameters under the optimal scheme can meet the requirements that it is not easy to cause slab quality defects.Finally,through physical simulation,the mathematical model and physical model of molten steel flow in the mold are consistent,which proves that the method of reverse design to solve the nozzle parameter combination according to the analytical formula of F value theory is feasible.