Optimization And Application Of Immersion Nozzle Structure For Thick Slab Continuous Casting

The mold take a part of heart in continuous caster,which is the last part of improving the slab quality and the removal of inclusion in steel.Metallurgical effect of submerged entry nozzle on flow field and early solidification become more important.Optimization on the nozzle structure parameters and choice of the appropriate process parameters are of great significance for improving slab quality.Based on the continuous caster mold of a steel mills as the research object,a mold physical model with the scale 1:2 was established and the influence of the nozzle structure parameters(five nozzle)and process parameters(throughput of molten steel,immersion depth and gas flow rate)on flow behavior of liquid steel(liquid level fluctuation,flow field and impact depth),the distribution of liquid slag layer and the bubble distribution was studied.In the meantime numerical simulation the flow and heat transfer of various operating conditions by using commercial application of FLUENT software and researched the influence law of nozzle structure,immersion depth on the the temperature field and velocity field.Combining with the results of physical simulation and numerical simulation,and through field testing procedure,and the optimum nozzle structure and process parameters were reached.The experimental results are as follows:(1)The liquid level fluctuation are varied under N1~N5 nozzle in section of 1800 mm,with the increase of throughput of molten steel,the liquid level fluctuation increased.The sensitive degree of each nozzle to throughput of molten steel change from large to small respectively are N5、N1、N3 、N2 、N4;Along with the increasing of the immersion depth,the liquid level fluctuation showed a trend of decrease as a whole,The sensitive degree of each nozzle to immersion depth change from large to small respectively are N2、N3、N1、N5、N4.(2)The liquid level fluctuation are almost same,while blowing air with straight pipe type and air vent plug type;With the increase of immersion depth,the impact depth also showed a trend of increased;The impact depth of the nozzle from large to small is supposed to be N2、N3、N5、N1、N4 and the nozzle structure comprehensive influence impact depth;The slag layer dynamism under the N1 nozzle in each section are more appropriate,it is reasonable while N4 nozzle in the big cross section and N5 nozzle in the small section,but the slag layer dynamism is less active under N2 nozzle.(3)Structure of nozzle with the width section of 1550~1800mm is N4,and the optimum process parameters are that immersion depth of 110~150mm and gas flow rate of7~9L/min;Structure of nozzle with the width section of 1550~1800mm are N1 and N5,while the the optimum process parameters are that immersion depth of 130~170mm and gas flow rate of5~7L/min.(4)Temperature of liquid steel meniscus is around 1810 k in section of 1050 mm with N1 nozzle and it distributed uniformly,The nozzle of N2~N5 have a similar temperature field and flow field distribution pattern,but influence range of raceway flow with N3 nozzle is greater.(5)The degradation rate of surface defects with two optimized nozzle while on-site verification are less than or equal to 0.2%,and the rate of rolling defects under N1 and N5 nozzle than original nozzle respectively reduced by 33.3% and 22.8%.