| To solve the problem of the floatation and removal of small size inclusions in liquid steel is of great practical significance for stabilizing the production of continuous casting,preventing nozzle from clogging and improving the slab quality.Argon blowing is widely used in the removal of inclusions by incorporating three mechanisms:（1）changing the flow behavior of fluid;（2）bubbles collide with and adhere to inclusions;（3）the wake flow of bubble promotes the floatation of inclusions.Another way is to enhance the intensity of turbulent flow to promote the collision,aggregation and growth of inclusions.In this paper,based on the metallurgical effects of argon blowing and swirl flow,the effect of process of annular argon blowing and swirl flow at tundish upper nozzle on the gas-liquid two phase flow was investigated.The main conclusions can be concluded as follows:（1）The research results of the bubble formation behaviour and the pore activation mechanism of the porous permeable brick used for the tundish upper nozzle（TUN）showed that the pores inside the porous permeable brick had different sizes and irregular shapes,and the formed bubbles had different sizes.As the gas flow rate increased,the pressure gradient inside the porous permeable brick and the number of activated pores increased.Simultaneously,the size range of the bubbles increased and changed to a normal distribution.Among the parameters considered,the gas permeability directly affected the pressure gradient inside the porous permeable bricks and had the maximum correlation coefficient with the number of activated pores.The pore size distribution was the key factor affecting the size distribution and Sauter mean diameter（SMD）of bubbles.（2）The research results of the influence of the process parameters of the annular argon blowing at the TUN on the flow behaviour of the liquid steel and the migration behavior of bubbles showed that a frustum cone shaped bubble plume centered on the stopper rod was formed.Due to the wall-attached effect,the bubble plume flowed towards the wall of stopper rod.Some small bubbles were wrapped into the nozzle and the mold with liquid steel.The flow of liquid steel near the liquid level of the tundish was activated around the stopper rod.The flow path of liquid steel was extended,but the change of average residence time of liquid steel was not significantly.With increasing the argon flow rate,the bubble number of the annular bubble plume and the vertical velocity of liquid steel near the liquid level of the tundish increased significantly.With increasing the casting speed,the width and the bubble number of the annular bubble plume gradually decreased,which lead to the decrease of the vertical velocity of liquid steel near the liquid level in tundish.Increasing the distance between the annular gas permeable brick and the center of TUN can increase the dispersion of bubble plume,expanded the width of bubble plume and weaken the impact of bubbles on the liquid level in tundish.As the argon flow rate and casting speed increased,and the distance between the gas permeable brick and the center of tundish upper nozzle decreased,the argon flow rate and bubble dimension in mold increased.（3）The research results of the formation and evolution of the slag eye with the annular argon blowing at the TUN showed that a strong upwelling flow was formed around the stopper rod,and there were multiple vortex flows in the vicinity of the upper part of the stopper rod.Under the influence of the vortex flow,the lower layer of liquid slag moved away from the stopper rod and the upper layer flows from the periphery to the stopper rod.With increased argon flow rate,the average turbulent kinetic energy and velocity of liquid steel around stopper rod increased gradually,and the liquid steel velocity at the interface of steel-slag increased first and then decreased.The liquid steel velocity at the edge of slag eye increased initially,followed by a decrease,but then again increases,accompanied by the decrease of velocity angle with the vertical direction.With the further increase of the argon flow rate,a donut-shaped slag eye centered on stopper rod was formed on the tundish liquid level,and the area of slag eye gradually increase.The critical argon flow rate of slag-eye-free was 4.2 L·min-1 in this paper,at which the liquid steel velocity of steel-slag interface reached 0.247 m·s-1,and the dip angle with vertical direction was 70°.（4）The results of the study on the migration behavior of inclusions with the annular argon blowing at the TUN in tundish showed the removal of inclusions by bubbles included two mechanisms in the microscopic system:collision and adhesion by bubbles,and floatation by the wake flow of bubbles.The rising bubble plume formed by the annular argon blowing at the TUN could effectively promote the floating and the removal of inclusions in tundish.As increasing argon flow rate,the driving effect of annular bubble plume on the rise of liquid steel flow increases,leading an increase of removal of inclusions.Industrial tests showed that the number of inclusions in steel slab with argon blowing was significantly reduced.The maximum sizes of different types of inclusions basically showed a trend of decrease.（5）The research results of the flow behavior of gas-liquid two phase under the coupled process of annular argon blowing and swirl flow at the TUN showed that a complete annular gas curtain was formed above the TUN and around the stopper rod.Meanwhile,part of bubbles entried the nozzle and the mold through the swirl slots.With the cooperation of stopper rod and swirl slots,the argon bubbles entering the nozzle gradually converged to the center of the nozzle under the centrifugal force of the swirl flow liquid steel.In the height direction of the nozzle,the maximum concentration of bubbles increased first and then decreased,and the tangential velocity of liquid steel in nozzle gradually decreased under the action of wall shear force.With increasing the argon flow rate,the casting speed,the height and the number of swirl slots increase,the tangential velocity of liquid steel in the nozzle increased,and the gas flow distribution and average size of bubbles in mold also showed a trend of increase. |
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