Influence Study Of Ladle Shroud Structure And Electromagnetism On Molten Steel Flow In Tundish Impact Zone

The molten steel injected into the tundish from the ladle through the shroud has great impingement on the steel in the tundish impact zone.Especially in the process of ladle change,the liquid level fluctuates greatly,which can easily cause the slag entrapment and the exposure of liquid steel.Consequently the reoxidation of molten steel and entrapment of the slag inclusions may happen,which can reduce steel cleanliness and deteriorate the inner quality of the billets.Therefore,the way to restrain the molten steel turbulence in tundish during the casting process has become of concern.In this paper,a simple expansion ladle shroud and an electromagnetic swirling flow technique are proposed to control the turbulent flow in tundish.Firstly,a multiphase Volume of Fluid(VOF)model including steel,slag and air phases is developed and verified by water model experiment to investigate the effects of ladle shroud structure on the flow behavior of liquid steel in the impact zone,and specially emphasize on the unsteady casting process during ladle change.Moreover,the calculated electromagnetic force is loaded on the ladle shroud by User Defined Functions(UDF)to study the influence of the in-shroud electromagnetic swirling flow on the fluid flow behavior of the three phases in the tundish impact zone based on the above model.The results are shown as follows:(1)During the steady state casting,a large buffer effect on the high speed injection can be obtained,which can restrain the impact on the flow in the tundish,effectively reduce the turbulent kinetic energy and flow velocity at free surface in the tundish impact zone,and decrease the chance of liquid steel exposure and steel slag mixing.During transient casting,the exposed area of the steel decreases gradually with the increase of the internal diameter of the expansion ladle shroud.However,as the internal diameter of the expansion ladle shroud expands to 2 times of its original value,the molten steel will continue to be exposed to about 25 s due to the large amount of excluded gas.The proper value of the ladle shroud internal diameter is about 1.5 times than the original one.(2)The of the expansion ladle shroud and the turbulence controller are two kinds of flow control devices in the tundish that can reduce the turbulent kinetic energy and the steel flow velocity in tundish impact zone.By combining these two method,the turbulent kinetic energy of the molten steel in the tundish impact zone can be reduced by 71%,and the liquid steel velocity can be decreased by a factor of 65%.The combination of expansion ladle shroud and turbulence controller is more effective on metallurgical effects.(3)When operating the rotating magnetic field in the ladle shroud zone,the molten steel in the ladle shroud rotates obviously,and the swirling flow can be observed near the outlet of ladle shroud,the circulation range of the molten steel in the impact zone enlarged and the path becomes elongated.However,the swirling flow has no enough time to spread and is affected by steel backflow due to the short distance from the ladle shroud outlet to the tundish bottom,and the high flow velocity of the steel.Eventually,the electromagnetic swirling flow technology to reduce the impingement effects on the steel flow in tundish impact zone is not prominent.