Study On Argon Injection Through Long Shroud In Continuous Casting With Cold Experiment And Mathematical Modeling

This thesis focuses on the effects of argon injection through long shroud in continuous casting with cold experiment and mathematical modeling.The influence of gas nozzle diameter,nozzle number,gas flowrate,water flowrate and different long nozzle on the size distribution of bubbles,bubble numbers,flow behavior in tundish was studied in the cold experiment.The flow behavior of different size bubbles and steel in different tundish configurations and the removal degree of inclusions were simulated with mathematical modeling.Experimental study has shown that the diameter of the argon bubble is mainly related to the diameter of gas injection nozzle and the liquid flowrate through the shroud.The diameter of bubbles is decreased and numbers of bubbles are increased when the diameter of the gas nozzle is smaller and the flow rate becomes larger.When the gas flowrate is 24 ml/min and the water flowrate is less than 2.7 m3/h,the proportion of tiny bubbles(0.1～0.5mm diameter)at 0.11,0.25 and 0.58 mm diameter gas nozzle is 55%,45%and 35%,respectively.When the water flow rate reaches 3.3m3/h,the proportion from 0.11 mm diameter gas nozzle is higher than 70%,that from 0.25 mm diameter nozzle is about 65%,and that from 0.58mm gas nozzle is only 45%in the range of 0.1～0.2 mm diameter bubbles.The bubbles flow directly up to the liquid surface because of the constraints of the turbulence inhibitor in tundish,while bubbles move around and upward under the combined action of buoyancy and water drag in the tundish without turbulence inhibitor.The results of the mathematical simulation show that the smaller the bubble diameter is,the larger the motion range of the bubbles is and the longer the residence time of the bubbles in tundish is.Bubbles with 0.1 mm diameter are distributed to most parts of tundish area,ones with 0.3 mm diameter are distributed to about 1/3 area,but the bubbles with 1 mm diameter is only distributed to small area in tundish without any control device.The bubbles of 0.1 mm diameter are mainly distributed to the area between the two weirs,the residence time of bubbles with 0.1 mm diameter is over 200s,and that of 0.5mm diameter bubbles is 20～30s in tundish with dam and weir.It is not benefit to the interaction between the bubbles and the molten steel,because the area of the bubble is smaller in tundish with a turbulence inhibitor.The residence time of 0.1 mm diameter bubbles in such tundish is only about 100s,and that of 0.5mm diameter bubbles is 20～30s.The removal degree of inclusions in tundish with dams,weirs and turbulence inhibitor is significantly increased,being improved by 10%～25%.The removal degree of l0μm inclusions is about 28%without argon injection but the removal degree is 43%in the case with argon injection in tundish with the dams,weirs and turbulent inhibitor.Argon injection can increase the removal degree of inclusions by about 15%,in comparison with the case without argon injection.