An-yuan Deng

Effects of vertical electromagnetic stirring on grain refinement and macrosegregation control of bearing steel billet in continuous casting

The grain refinement and macrosegregation control of GCr15 bearing steel were investigated under a type of rarely-used electromagnetic stirring, vertical electromagnetic stirring (V-EMS), in continuous casting. V-EMS can create an upward electromagnetic force and generate longitudinal loop convection, which enables the better mixing of the upper part with the lower part of the liquid steel. The results showed that applying V-EMS can enlarge the region of the equiaxed grain, decrease the secondary dendrite arm spacing (SDAS) and reduce the segregation of both carbon and sulfur. After applying V-EMS, liquid steel with a high solute concentration is brought to the dendrite tips, making the dendrite arms partially melt. The length of the dendrite fragment is approximately 1.8 mm, 10 to 12 times the SDAS. Upon increasing the amount of cooling water from 2.0 to 3.5 m3/h, the dendrite fragments exhibit an obvious aggregation following V-EMS. Finally, a criterion for dendrite fragmentation under V-EMS was derived based on the dendrite fragmentation theory of Campanella et al.

Oscillation Characteristics of Molten Metal Free Surface Under Compound Magnetic Field

The free surface waves of a molten low-melting point Sn-32% Pb-52% Bi alloy under the imposition of an AC and a static magnetic field were visualized and recorded by use of a laser displacement sensor and a high speed video camera. The Fourier analysis method was used to analyze the oscillation characteristics. The results show that at the center of the free surface, the azimuthal and radial oscillation mode can be found simultaneously owing to AC magnetic field. With increasing coil current intensity, the amplitude and the main frequencies of the oscillations increase, and the azimuthal fluctuation at the center of the free surface is also enhanced. The fluctuation characteristics are closely related to the turbulent flow induced by the alternating electromagnetic force. A series of regular traveling waves can be observed on free surface, and the main frequencies of oscillations at three-phase points decrease owing to superposing AC and static magnetic field. The static magnetic field can remarkably control the unstable swinging behavior of free surface. With increasing static magnetic flux density, the amplitude of oscillations at the center of free surface decreases firstly, and then increases, but the fluctuation amplitude at the triple-phase point always reduces and keeps within 1 mm, and the azimuthal waves at the center of free surface are weakened. Especially at 1. 44 T, the radial waves are dominant. The static magnetic flux density should be controlled in an appropriate range to obtain more stable free surface. With compound magnetic field, even if the static magnetic flux density is above 1. 0 T, the free surface still vibrates with lower amplitude and dominant frequency.

Meniscus Behavior in Electromagnetic Soft-Contact Continuous Casting Round Billet Mold

Using molten Pb-Sn-Bi alloy, the meniscus shape under high frequency magnetic field of ø100 mm round billet caster was investigated. The effect of some parameters on meniscus shape was studied. The results show that for a mold with 12 segments, the meniscus shape is relatively stable. With increasing power input, the meniscus height increases with intensification of fluctuation. For the given caster, the reasonable power input is about 70 kW. The coil should be near to the top of mold and/or the initial meniscus should be near to the center of the coil. The lower the frequency, the higher is the meniscus height. With increasing frequency, the free surface is more flattened and meniscus becomes more stable. In practice, the power input should be increased simultaneously with frequency. The optimal frequency is about 20 kHz.

Numerical Analysis of Fluctuation Behavior of Steel/Slag Interface in Continuous Casting Mold with Static Magnetic Field

Utilizing ANSYS CFX commercial software and volume fraction of fluid (VOF) model, fluctuation behavior of steel/slag interface was numerically simulated in continuous casting mold with static magnetic field, and the influence of metal jet characteristics on the behavior of steel/slag interface was investigated. The results indicated that the behavior of steel/slag interface is similar at different process parameters, which is closely related to the characteristic of the flow field. The steel/slag interface has an obvious trough characteristic, which can be divided into three zones: frontal valley zone, back valley zone and horizontal zone; as the magnetic flux density increases, the fluctuation of liquid level increases firstly and then decreases, and a reasonable magnetic flux density can make steel/slag interface obtain a relatively flat interface, which can prevent slag from being entrapped into liquid steel. For a thin slab continuous casting process, when the casting speed is 4 m/min, a reasonable magnetic flux density is about 0. 5 T, and the interfacial fluctuation is weaker. No matter the position of magnetic field is horizontal or vertical, for different operating parameters, there is a corresponding reasonable magnetic field position where the steel/slag interface fluctuation can be properly controlled and slag entrapment can be prevented.

Distribution of Magnetic Flux Density in Soft-Contact EMCC Rectangular Mold

The distribution of the magnetic flux density in a soft-contact electromagnetic continuous casting (EMCC) rectangular mold was investigated, The experimental results show that with an increase in electric power, the magnetic flux density increases. The position where the maximum magnetic flux density appears will shift up when the coil moves to the top of the mold. At the same time, the maximum magnetic flux density will increase and the effective acting range of electromagnetic pressure will widen. As a result, in practice, the coil should be placed near the top part of the mold. The meniscus should be controlled near the top part of the coil, as this not only remarkably improves the billet surface quality but also saves energy. With the same electric power input, the higher the frequency, the lower the magnetic flux density.

Influence of Vertical Electromagnetic Brake on the Steel/Slag Interface Behavior in a Slab Mold

The steel/slag interface behavior under a new type of electromagnetic brake (EMBr), vertical electromagnetic brake (V-EMBr), was investigated. The influence of the magnetic induction intensity, the submerged entry nozzle (SEN) immersion depth, and the port angle of the SEN are investigated numerically. The effect of magnetic induction intensity on the meniscus fluctuation of molten alloy is further studied by the experiments. The results show that the meniscus fluctuation is depressed as the magnetic induction intensity is increased, especially for the region in the vicinity of the narrow face of the slab mold. This result is validated by the following experiments. For the influence of the SEN immersion depth and the port angle, the results show that the meniscus fluctuation is suppressed as the values of the immersion depth and the port angle are increased (absolute values for the port angle). However, the influence of the immersion depth and the port angle are not as sensitive as those in the other type of EMBr, e.g., EMBr Ruler. The industrial application of V-EMBr could benefit from this result.

Effect of Structure Parameters on Power and Magnetic Field in Electromagnetic Soft-Contact Continuous Casting System

To design a power source system and mold for electromagnetic soft-contact continuous casting process and to theoretically estimate the heat losses from the charges and the system power, the effect of structure parameters on system power and magnetic flux density distribution was calculated using finite element method. The results show that as for electromagnetic soft-contact continuous casting system with partial-segment type mold, the power consumption is much more than that with a full-segment type mold; about 62% of electric power is dissipated in the mold, and the effective acting range of magnetic field is relatively narrow. Optimizing mold structure is a crucial measure of remarkably reducing mold power consumption and saving electric energy. Increasing slit number, width, and length can remarkably increase the magnetic flux density in the mold and can reduce the electric energy consumption. Among structure parameters, slit number and slit width are relatively more effective to reduce energy consumption. For a round billet electromagnetic continuous casting system with diameter of 178 mm, the reasonable slit number, width, and length are about 24–32, 0. 5–1. 0 mm, and 160 mm, respectively.

Parametric investigation on an industrial electromagnetic continuous casting mould performance

Abstract This research aimed at conducting a quantitative investigation of process parameters on the magnetic field contribution in an electromagnetic continuous casting mould. The Taguchi method (4 factors and 3 factor value levels: L9 orthogonal array) was adopted to design matrix of the simulation runs and the analysis of variance was used to evaluate the contributions of each control factor. The simulations were conducted based on the finite element method and the numerical set-up was validated by the designed experiment. The results showed that the applied alternating current magnitude contributed most (76.64%) to the magnetic field level in the mould, compared to the other control factors. It was followed by the slit length (17.72%), the alternating current frequency (4.17%) and the slit width (1.57%).

Effects of Magnetic Pressure Constraint on Dynamic Deformation and Oscillation Behavior of Metal Free Surface

A new method was presented to constrain deformation and oscillations of liquid metal free surface by using a high frequency magnetic field. A magnetic field generator was designed to investigate its feasibility using numerical simulation and physical simulation. The results indicate the feasibility of controlling bulge deformation of liquid metal surface using magnetic pressure. Sunken deformation with a slight fluctuation occurs on the surface when magnetic pressure acts on the static liquid metal surface. The largest amplitude remains within ±0. 8 mm even if current reaches 1400 A. In case of the bump-type deformation, the magnetic pressure strengthens gravity field by the superposition effect, dissipates the kinetic energy of metal flow impacting on free surface in advance, reduces the velocity of free surface, and decreases the bulge height. On the region without magnetic field, the liquid metal surface rises and tends to be flat because of the significant damping effect on surface fluctuation. The constraint strength of the magnetic pressure increases with the augment of current intensity. However, different heights of bulge deformation should have a corresponding reasonable coil current for achieving the best constraint effect.