| In the continuous casting process of steel,the electromagnetic stirrer agitate the molten steel of solidification process to improve the internal structure of the cast slab by stimulating the alternating magnetic field.It has been widely used in the continuous casting production of steel because of the advantages of high efficiency,no contact,no pollution,etc.For a long time,the external control current of the electromagnetic stirrer is mainly sinusoidal wave current.In recent years,due to the large magnetic field change rate and intermittent characteristics of the pulsed magnetic field,it has received extensive attention in the field of advanced material preparation.The practical effect of pulsed magnetic field on the solidification structure of metal has been verified by many scholars.For the influence mechanism of pulsed magnetic field on the solidification structure of metal,a large number of scholars believe that the electromagnetic oscillation of the metal melt during solidification breaks the dendrite or the pulsed magnetic field inducing effect reduces the energy of nucleation to achieve the effect of solidification structure's grain refinement.Therefore,considering the special effect of the pulsed magnetic field on the solidification of the metal,the external control current waveform of the electromagnetic stirrer is changed to the pulse square wave current.In this case,the stirrer has multiple effects on the electromagnetic shock of the molten steel inside the cast billet and the form of pulsed magnetic fields without changing the stirring effect of the existing stirrer.This study was based on the three-phase six-pole electromagnetic stirrer model,and the electromagnetic field-flow field coupling mathematical model was established by ANSYS finite element software.The numerical simulation calculation was respectively carried out under electromagnetic stirring process of sinusoidal current and square wave current,and the distribution law of electromagnetic field and flow field inside the slab was analyzed to determine the stirring effect of the agitator.This study found that the radial magnetic induction cross-direction of the inner billet and the electromagnetic force coupling direction rotate when the electromagnetic stirrer is connected to the three-phasesinusoidal current,in the meantime,it promotes the rotary flow of molten steel,and the flow field is relatively stable,which is consistent with the actual effect.When the electromagnetic stirrer is connected to the three-phase square wave current,it also promotes the rotary flow of molten steel,and magnetic induction,electromagnetic force peak,electromagnetic force peak penetration depth and flow velocity of the inner billet are larger than the case which three-phase sinusoidal wave current is connected,electromagnetic force and flow rate show a strong oscillating effect.The current intensity ranges from 100 A to 500 A.Connecting the three-phase sinusoidal current and the three-phase square wave current respectively,and with the increase of the current intensity,the internal magnetic induction,electromagnetic force and flow velocity of the cast slab are increased;The current frequency ranges from 1Hz to 10 Hz.Connecting the three-phase sinusoidal current,and with the increase of the current frequency,the internal magnetic induction intensity of the cast slab is reduced.When the three-phase square wave current is connected,the internal magnetic induction of the cast slab increases,but the basic change is small after 6 Hz;in the flow field comparison,this study found that as the frequency increases and the number of impacts increases,the impact effect and the node flow velocity fluctuation decreases.Therefore,it is considered that a stronger stirring effect and multiple effects of flow field oscillation and pulse magnetic field treatment are achieved when the agitator is supplied with a three-phase square wave current.At the same time,under different duty ratio parameters,the internal flow field oscillating amplitude of the cast slab under the three-phase square wave current of the duty ratio of 66.66% and 100% is basically the same,the flow rate is relatively reduced by 7%,but the current power is only2/3 of the original.Therefore,we consider that it has batter practical application value when the duty ratio is 66.66%. |
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