Study On Formation And Suppression Of Votex In Ladle During Steel Teeming Process

With the developments of science and technology,the performance of steel is required strictly and the quality of steel needs to improve continuously.Reducing inclusions and further implementing some improvements in steel quality are the important objectives of the steel industry.In continuous casting process,there is an important flow phenomenon when the molten steel flows from ladle to tundish.It is that the rapidly rotating free surface vortex will form as the liquid level descending continuously.The free surface vortex occurs not only in steel teemingof ladle but it also occurs in steel teeming of converter and tundish.The surface vortex can cause the slag entrainment.Especially in the end of steel teeming process,the slag entrainment becomes serious and even the air is entrained when the liquid level is lower than the critical height of vortex(the critical height is the distance from the liquid level to the edge of nozzle when the tip of vortex arrives to the nozzle).The vortex can also results in inhibiting inclusion floating,causing nozzle corrosion and clogging,and increasing molten steel reoxidation.At present the existing prevention methods of vortex have the disadvantages of low metal yield and large ladle structural changing.Therefore,how to improve the metal yield and effectively prevent the vortex is the important issue for clean steel production.In order to effectively suppress or eliminate vortex formation in ladle during steel teeming,a lot of studies have been done in this paper.Firstly,the formation mechanism and influence factors of vortex are examined.And the flow field in ladle during steel teeming process is analyzed.Thus the movement law and suppression mechanism of vortex are obtained.Then according to the suppression mechanism of vortex two methods of vortex prevention are proposed.And the feasibility of two methods is predicted using the numerical simulation.Finally,it is studied and verified further about the movement law and suppression mechanism of vortex using the water modle experiment.And the same conclusions are obtained as that of numerical simulation results.Meanwhile,in the actural production the equipment of blowing gas has exsited because the blowing gas at the bolttom of ladle is necessary in the refining process.Thus the method of blowing gas to prevent vortex is easy to realize in practice.So in this paper the method of blowing gas is also futher verified using the water modle experiment.And the better effect on the vortex suppression and the optimal parameter of blowing gas are got in the experiment.Through the above study of numerical simulation and water modle experiment,the main conclusions are as follows:(1)The Coriolis force has little effect on vortex formation during steel teeming process.And the initial tangential disturbance in ladle at the beginning of steel teeming plays the key role in vortex formation.When the nozzle is opened,there is the static pressure difference caused by gravity of fluid in the ladle.The static pressure difference is the energy source of vortex formation and development.Then under the law of angular momentum conservation,the vortex will rotate faster and faster.Finally when liquid level descends to a certain height,the gravity force can not provide enough energy.Thus the liquid surface begans to dimple and extends to the nozzle.And the vortex begins to form from the bottom of the nozzle.(2)The Critical height of vortex obviously increases with the increasing eccentricity(the ratio between the distance from nozzle to center of ladle and the radius of ladle).When the position of nozzle is centeral,critical height of vortex increases with the increasing initial tangential velocity and slightly decreases with the increasing nozzle diameter.When the position of nozzle is eccentric,critical height of vortex firstly increases and then almost no longer changes with the increasing initial tangential velocity.And it increases with the increasing nozzle diameter.The physical property of fluid has a little effect on the ciritical height of vortex regardless of the position of nozzle is central or eccentric.The fomula of critical height of vortex is deduced using dimensional analysis method.(3)The vortex can be effectively suppressed by changing the distribution of flow field and decreasing the values of tangential velocity.Two methods of vortex suppression are designed according to the mechanism of vortex suppression.When the force with the opposite direction of vortex is applied,the tangential velocity in ladle is decreased.And during steel teeming process blowing gas at the bottom of ladle can disturb the distribution of flow field.Thus both of the methods can decrease the critical height of vortex and suppress the vortex effectively.(4)The movement law and suppression mechanism of vortex are verified futher though the water modle experiments.And by the experiments,the feasibility of blowing gas to suppress vortex is also verified futher.In the experiment,it is found that blowing gas can disturb the flow field during steel teeming to decrese the critical height of vortex indeed.And the critical height of vortex firstly decreases a lot and then almost no longer change with the increasing gas flow rate.The suppression effect is best for the ladle with centeral nozzle when the gas nozzle is closed to the nozzle of ladle.The suppression effect is the best for the ladle with eccentric nozzle when the gas nozzle is closed to the center of ladle.