| Electromagnetic stirring has become the primary means to solve the quality problems of steel products by virtue of its characteristics of transferring heat energy and kinetic energy without direct contact with molten steel.But with the continuous development of modernization,the demand of large section and high alloy steel products also increases,and the quality of the billet is more difficult to control.These factors also put forward great challenges to electromagnetic stirring.Therefore,it is particularly important to understand the characteristics of electromagnetic stirring and its applicability in the production process.In this thesis,for the continuous casting of Φ800mm round blooms with strand electromagnetic stirring,the excitation mechanism and function characteristics of traditional electromagnetic stirrers are deeply studied.Based on this,a structural design idea of a single-winding spiral electromagnetic stirrer and side-spiral electromagnetic stirrer is proposed,To improve the limitations of the traditional electromagnetic stirrer in the production process of casting billet.The electromagnetic,flow,and heat transfer coupling mathematical models of rotating,traveling wave,combined spiral,single-winding spiral,and side-spiral electromagnetic stirring were constructed by finite element software and finite volume software,and the reliability and rationality of the models were verified.The electromagnetic field,molten steel flow,and heat transfer solidification behavior of each type of electromagnetic stirring in a round billet were studied by numerical simulation.Taking the rotating magnetic field as the standard,the advantages of the magnetic field of various forms of electromagnetic stirring were verified,and the cross-section size and installation position of various stirrers were put forward.The main contents and research results of this thesis are as follows:(1)With the rotating magnetic field,the molten steel flows steadily along the casting direction in a spiral shape,the stirring energy is mainly concentrated in the center of the stirrer,and the effective range of the molten steel flow accounts for13.7% of the whole flow field area.Under the influence of stirring,the tangential velocity of molten steel reaches its peak at the solidification front,but the magnetic field attenuates seriously inside the billet,the velocity of molten steel at the core does not increase significantly,and the temperature drop at the core of the billet is only higher than the traveling wave magnetic field.This kind of stirring is suitable for the mold or casting flow stirring of small cross-section round and square billet.(2)The combined spiral magnetic field can further improve the action range of the rotating magnetic field.The effective action range of the molten steel flow accounts for 32.4% of the whole flow field area.Compared with the rotating magnetic field,the flow rate at the center of the casting billet increased by 123.1%,and the temperature at the center of the billet decreased by 0.34 K.However,the flow field is unevenly distributed on both sides of the billet,showing the characteristics of "one side is strong,one side is weak".This stirring method is more suitable for the casting flow with a larger section or the end stirring.When the traveling wave magnetic field is excited alone,the flow rate of molten steel under the same parameters is one order of magnitude lower than that of other magnetic fields,the temperature drop of molten steel in the core is the smallest,and the magnetic energy loss is serious,so it is not suitable for a single application in the process of circular billet continuous casting.(3)The single-winding spiral magnetic field improves the non-uniformity of the combined spiral magnetic field in the billet,and the effective range of the magnetic field is further expanded,accounting for 49.1% of the whole flow field area.Compared with the rotating magnetic field,the velocity at the core of the billet is reduced by 32.9%,and the temperature at the core is reduced by 0.30 K.The range of steel applicable to the magnetic field and the area where the stirrer can be installed can also be further expanded,but it is more suitable for the electromagnetic stirring of cast flow with small and medium section.(4)The side-spiral magnetic field can make the molten steel present a state of inclined centripetal stirring,the effective range of molten steel flow is 14.2%.Moreover,the velocity of molten steel at the core of the casting billet is significantly enhanced,which is 2.5 times that of the rotating magnetic field.The temperature drop of molten steel at the core of the casting billet is significantly higher than other magnetic fields,which is very suitable for the application of large section round and square billet end stirring. |
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