| With the development of steelmaking and secondary refining technology,the cleanliness of the molten steel has been greatly improved,at present,the T[O] in the molten steel can be less than 5ppm.So the protection casting after refining is an important method of the cleanliness control of the molten steel.There are two critical parts,the first one is the key parameter “height of the vortex at ladle final teeming”,which is to control the residual steel volume and prevent the slag slipping into the tundish,the other one is designing some reasonable tundish flow control devices,which can improve removal of large-size inclusions(>100 ?m)in tundish caused mainly by flaking of refractory material in impact zone.This paper mainly focuses on the problems of high vortex height causing large resudial steel at final ladle teeming process in a certain steel mill,and unreasonable flow pattern of molten steel in the tundish.Taking the ladle and tundish as research objects,and using the method of hydraulics simulation,based on the analysis of the influencing factors of ladle vortex height and the flow pattern of tundish under current working conditions,control methods of height of vortex at ladle final teeming should be proposed.At the same time,some reasonable tundish flow control devices should be designed.The experimental results of ladle show that the key to reducing the vortex height is to slow down the tangential and radial velocity of the fluid before the vortex is formed.The height of the vortex first increase,and then decrease with increasing resting time,accelerating turnover of ladle under permissible conditions appropriately will help reduce the height of the vortex.The change of the flow field due to the diameter of the slag stopping balls and the way there are added is not enough to slow down the formation of the circulation.After the slag stopping balls are sucked into the nozzle,the vortex can be almost completely eliminated.Whether the slag stopping balls can be sucked by the nozzle before the vortex is generated depends on the drop point of the slag stopping balls,and the adding height(from the height of the liquid surface).Slag stopping balls' groove depth is a key parameter to control export flow,when the depth of the model slag stopping balls groove is 8mm,the studied ladle can reach the setting flow requirement of the nozzle(1200L/h)within the allowable opening degree of the nozzle.With the increase of argon flow,the vortex height decreases,and the starting and penetration height decrease by 59.1% and 58.6% respectively when the argon flow reaches 0.8NL/min.The tundish experiment results show that under the working condition,the flow pattern of the molten steel in the tundish is unreasonable,the second-stream has a short flow,and the floatation rate of inclusions is low,only has 77.0%.The size of the diversion hole and the jet angle are the key parameters affecting the flow pattern of molten steel.The y6 scheme(circular turbulence inhibitor+U2-1-75 baffle+single dam height 300mm)not only eliminates the short flow but also prolongs the response time of each stream,and improved the removal rate of inclusions.The average response time increased by 37.9% compared with the working condition,the dead volume fraction is only 6%.The inclusion removal rate is 92.5%,which is 15.5% higher than that of in working condition.The industrial experiment show that the flow pattern of molten steel in the optimized tundish is more reasonable,and the removal rate of inclusions is improved.Among the 21 tested samples,only one inclusion with a size greater than 40 ?m was found.The maximum size of inclusions in the remaining specimens was less than 40 ?m.So the experimental results met the target requirement that the ratio of non-metallic inclusions in continuous casting largerer than 40 ?m does not exceed 5%. |
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