Electromagnetic Stirring In Continuous Casting Research Articles

Numerical method to depict the time-varying Lorentz force field under harmonic magnetic field

The time-varying Lorentz force field(tvLFf), induced by harmonic magnetic field, is widely used in materials pocessing, one of its typical applications is electromagnetic stirring in continuous casting. However, knowledge about the tvLFf is quite limited, only its time-averaged component is studied, and the profile of its time-varying component is unknown up to now. In this paper, the author develops a method to depict the tvLFf using 11 features, which are classified into 3 categories: Strength features, Morphology features and Tide features. All 11 features are created or extracted based on an analysis of the time-varying force ellipse, ruled by the amplitudes and initial phase angles of the induced eletromagnetic field. The elliptical characteristics of the time-varying Lorentz force are derived mathematically and via necessary numerical calculations, by which the effect of stirring or driving is clarified. The author finds that, the amplitudes of the induced eletromagnetic field are proportional to the magnitude of the exciting current, and that Strength features are proportional to the square of the magnitude of the exciting current, while the initial phase angles, Morphology features, and Tide features do not change with the magnitude of the exciting current, when frequency is fixed and the physical properties are constant. Finally, the author presents a model to illustrate the analyzing process, and a detailed visualization of the tvLFf is presented, with revealed features in conformity to the published results.

On an Anomaly in the Modeling of Electromagnetic Stirring in Continuous Casting

Early, yet still often-cited, mathematical models for electromagnetic stirring (EMS) in continuous casting are re-examined and found to contain a surprising anomaly: the solutions obtained were not unique. Analysis for the case of a round billet under rotary EMS shows how to avoid this behavior, whilst still making use of the experimental data that motivated the original models. The relevance of this result for current-day modeling of EMS is highlighted, particularly in the context of modulated EMS.

Numerical simulation of electromagnetic stirring in continuous casting of wires

PurposeThe purpose of this paper is to describe how electromagnetic stirring during continuous casting of ferrous and non‐ferrous metals is applied in order to increase the homogeneity and the material properties by improving the grain refinement in the solidification process. The fluid flow and thermal modeling was performed for studying the metal wire pulling process, where melt is being stirred at the solidification front (SF) by electromagnetic forces. Transient simulation has been carried out in order to investigate the periodical character of the process.Design/methodology/approachThe numerical analysis was performed in 2D utilizing the rotational symmetry of the problem. First the electromagnetic fields were estimated using FEM and were subsequently exported as source terms in a coupled thermal and flow simulation with FVM.FindingsThe presented numerical model estimated the most suitable position between the stirring coil and the SF to achieve high flow velocities which improve the grain refinement process.Originality/valueThis work enables estimation of the melt solidification in an electromagnetic stirred continuous casting process with oscillating pull velocities.

Improvement of In-mold Electromagnetic Stirrer by Feeding of Magnetic System with Polyharmonic Current

The elaboration relates to a method of electromagnetic stirring in continuous casting of carbon steels, when the surface quality and entrapping of nonmetallic inclusions still remain as the major problems concerning of ingot quality and success on the steel market.The improvement of surface quality of ingot means a decreasing or elimination of oscillating mark, corner cracking, and pinholes. Intensity of nonmetallic particles entrapping depends on meniscus disturbance: inclusions do not penetrate into liquid portion of ingot through quiet meniscus. Based on the phenomenon of electromagnetic edge effect, which exists in each of asynchronous stirrer, by condition of feeding of magnetic system by polyharmonic currents the new method of in-mold electromagnetic stirring has been developed. Thanks to that the depth of oscillating marks decreases, the flow on the meniscus is suppressed, and the meniscus disturbance and inclusions entrapping is prevented.

Electromagnetic stirring for continuous casting - Part 2

The multiple versions of electromagnetic stirring in continuous casting are described. For long products, linear or rotational stirring appears confusing, but is clarified based on liquid steel flow pattern and metallurgical results. Rotational mould stirring is the predominant application. For slabs, butterfly type single and double strand stirring and rotational mould stirring coexist with different metallurgical purposes. Also, the evolution to higher casting speeds has required a new type of mould stirring that combines accelerating and braking functions. The trend goes to multi-mode systems.

Finite element analysis of electromagnetic and fluid flow phenomena in rotary electromagnetic stirring of steel

This paper describes a fixed-grid methodology for the numerical simulation of electromagnetically driven flow in three-dimensional inductively stirred systems. It is based on a hybrid differential–integral formulation of the electromagnetic field to limit the finite difference/element solution of the electromagnetic field problem to the fluid flow domain. The electromagnetic field in the system was described using current vector potential ( T) and reduced magnetic scalar potential ( ψ) formulation of the field. The fluid flow problem was represented by turbulent Navier–Stokes equation. The governing equations were discretized using Galerkin method of weighted residual, and the discretized electromagnetic and fluid flow equations were solved simultaneously using an efficient finite element segregated algorithm. This new method was used to simulate sub-mold rotary electromagnetic stirring in continuous casting of steel. The computed results have shown that the electromagnetic force field generates a strong rotational flow within the vertical section covered by the stirrer, and a relatively strong secondary flow beyond the stirrer. It has also been shown that the rotational and secondary flows were driven primarily by the vorticity of the force field at the billet corners. The induced flow in the molten pool was found to be turbulent and the effective mixing region in the molten pool was about three times the length of the stirrer. The principal conclusion emerging form this work is that the secondary flow promotes mixing beyond the region confined by the stirrer, and the extent of mixing depends on the frequency of the applied rotating magnetic field.

Electromagnetic stirring for continuous casting

The multiple versions of electromagnetic stirring in continuous casting are described. For long products, linear or rotational stirring appears confusing, but is clarified based on liquid steel flow pattern and metallurgical results. Rotational mould stirring is the predominant application in billet casting. For slabs, butterfly type single and double strand stirring and rotational mould stirring coexist with different metallurgical purposes. Also, the evolution to higher casting speeds has required a new type of mould stirring that combines accelerating and braking functions. The trend goes to multimode systems.

In-mold electromagnetic stirring in continuous casting

To get the optimal operation of in-mold electromagnetic stirring through the fundamental characteristics, a three-dimensional magnetohydrodynamic calculation model was used, taking into consideration heat transfer and solidification as well as free surface. Comparison between measured velocity and calculated velocity is in agreement. A shadow method that calculates electromagnetic force in consideration of free surface transition is proposed to reduce computing time and maintain sufficient accuracy. A calculated free surface of mercury under a 200-Hz magnetic field shows an adequate agreement with the experimental one. Calculation results applied to the continuous casting process taking into consideration heat transfer and solidification are in good agreement with operation data. This model shows that electromagnetic stirring makes the solidified shell uniform and dynamic deviation of temperature stable.

Mathematical Modeling of Iron and Steel Making Processes. Evaluation of Multiphase Phenomena in Mold Pool under In-mold Electromagnetic Stirring in Steel Continuous Casting.

Multiphase phenomena in the application of in-mold electromagnetic stirring in continuous casting were discussed through cold experiment using mercury and numerical simulation by using two fluid model. The result revealed the critical flow rate of argon injected in the submerged entry nozzle, which leads to the change in flow pattern in the bulk liquid metal inside the mold pool. This change does not have a large effect on the flow driven by in-mold electromagnetic stirring because the Lorentz force acts mainly in the vicinity of solidifying shell except for the case of large amount of the argon flow rate. The particle behavior under in-mold electromagnetic stirring in the vicinity of the solidifying shell was also discussed by solving near-wall fluid flow and employing the particle tracking method, which showed the important effect of lift force by the increase in velocity inclination near the solidifying shell by electromagnetic field.

Finite Element Analysis of Electromagnetically Driven Flow in Sub-mold Stirring of Steel Billets and Slabs.

This paper describes a new method for solving coupled three-dimensional electromagnetic and fluid flow equations in induction systems and its application to electromagnetic stirring in continuous casting of steel. This method is based on the differential-integral potential formulation of the electromagnetic field, and is capable of computing the field for any given stirrer configuration without solving the magnetic field in free space. The turbulent flow in the melt is represented by time averaged Navier–Stokes equation together with k-e turbulent model. The finite element formulation of the governing equations is also presented. Computed results were presented for the electromagnetic force distribution, velocity and turbulent parameters in rotary stirring of billets and linear stirring of slabs during continuous casting of steel. For rotary stirring, it was found that the electromagnetic forces are confined to the region surrounded by the stirrer, and the effective flow region is about twice the length of the stirrer and the flow exhibits weak axial velocity component. It was also found that the flow is turbulent with a maximum intensity of about 15% of the mean velocity, and decays rapidly above the edges of the inductor. For linear stirring of slabs, the spatial variation of the force field along and across the slab was found to generate a more complex flow pattern than predicted by two-dimensional analysis. The turbulent intensity was found to increase monotonically in the direction of the traveling force field.

Electromagnetic processing of liquid materials in Europe.

Research works concerning electromagnetic processing of liquid materials began very early in Europe. Through active cooperative programs between industrial companies and universities original results were obtained which gave rise to new technologies and innovative processes. Some typical examples are given relating to electromagnetic flow control of liquid metals, manufacturing of materials in cold crucible, electromagnetic stirring in continuous casting and in ladle.

Rotational electromagnetic stirring in continuous casting of round strands

A model is presented to compute the three-dimensional flow field in rotational electromagnetic stirring of round strands. The model involves the solution of the Maxwell equations, the Navier-Stokes equations, and the transport equations for the turbulence characteristicsk ande. For the limiting case of one-dimensional stirring, the computations were checked with experiments using mercury as the fluid. Several sets of computations were carried out to determine the influence of stirrer position, stirrer length, and electromagnetic parameters on the flow field in continuous casting of steel strands.