| Continuous casting technique has been widely used in the industrial manufacture because it has the advantages of high efficiency and low cost. However, continuous casting slabs are likely to have problems of segregation and shrinkage porosity which can influence the subsequent processing and the final performance of slabs. For this reason, the development of continuous casting technique is limited to some extent. Electromagnetic stirring can signally improve the quality of casting billets, but people are unable to actually measure some parameters and can’t well know the influence of stirring parameters on slab quality for electromagnetic stirring is a complex time-varying process referring to heat transmission and mass transfer. With the development of numerical simulation technique, it is probable to research the influence of stirring parameters on quality improvements by using numerical calculation method.Aiming at final electromagnetic stirring project of Baosteel, the author of this paper has researched the improvement results of different magnetic field forms by choosing Pb-80%Sn alloy which was used to simulate steel billet. Finite element model was built by ANSYS to simulate the magnetic induction intensity distribution when electromagnetic stirrer was in no-load condition and electromagnetic force distribution in alloy melt when electromagnetic stirrer was under load condition. This paper analyzed the influence law of different electromagnetic parameters(f=4Hz,7Hz, lOHz,13Hz,16Hz, and I=50A,75A,100A,125A,150A). The simulation results were as follows:the space distribution of magnetic induction intensity had such features that magnetic induction intensity mainly distributing in the range of H=-150-150mm reduced from the center to both ends in the axial direction and the magnetic induction intensity mainly distributing in the range of R<60mm increased with the increase of radius in the radial direction. With the increase of current, magnetic induction intensity and electromagnetic force increased. With the increase of frequency, magnetic induction intensity increased and electromagnetic force decreased.To prove the feasibility and the rationality of the simulation results, this paper has tested the distribution of magnetic field and done the replication experiment under corresponding parameters that the influence of electromagnetic stirring on the solidification structure and composition segregation of Pb-80%Sn alloy was studied. Measurement results showed that the real distribution feature of magnetic induction intensity and its changing rule along with current were same as the simulated result. The simulated result had good agreement with the actual result in most cases while there were some differences only in partly numerical cases. Therefore, the simulation results had feasibility and rationality. The experimental results about Pb-80%Sn alloy showed that the solid ratio of ingots was67%at6.5min of the freezing curve and the melt temperature was205℃at the same time which was selected as initial temperature to apply final electromagnetic stirring. There were optimal current and frequency values of electromagnetic stirring in terms of improving solidification structure and composition segregation of the ingots. The optimal current of rotating magnetic field and spiral magnetic field were125A. The grain sizes in those two conditions were140um and133μm and the differences of Sn content were1.95wt.%and1.12wt.%respectively. The optimal frequency values of rotating magnetic field and spiral magnetic field were13Hz and lOHz in terms of improving solidification structure respectively. The grain sizes were142.5μm and140.6μm correspondingly. The optimal frequency values of those two forms of magnetic fields were13Hz in terms of improving composition segregation. The differences of Sn content were1.14wt.%and0.34wt.%correspondingly.The spiral magnetic field can be equivalent to the superposition of rotating magnetic field and traveling magnetic field. In comparison with rotating magnetic field, the spiral magnetic field can form stronger and greater flow in the melt, smash dendritic crystal more thoroughly and better promote the uniform distribution of isometric crystal. So the improvement of spiral magnetic field was better than that of rotating magnetic field, which proved the correctness of simulated results that the electromagnetic force of spiral magnetic field was bigger. |
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