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Continuous Casting of Billet with High Frequency Electromagnetic Field.
Abstract
In order to develop the high frequency electromagnetic continuous casting technology for applying to steel, numerical analysis of the magnetic field and casting experiments using various parameters have been conducted. The method of using cold inserts was well established to lead to a reliable numerical model. According to this numerical model, it was predicted that while casting, the magnetic field would be concentrated on the common region occupied by the coil and the melt and further its maximum value would be seen just below the melt level, Casting experiments have been carried out using tin as a simulating material for steel, No oscillation mark was observed on the billets because the solidification started without hook. Under an optimum condition, billet surface roughness was improved to 1/10 of the conventionally cast billets. The surface quality of the billet was heavily dependent on the melt level, the casting speed, and the coil current. In case of the excessive coil current, wave marks other than the oscillation mark appeared on the billet surface. The billet with proper electromagnetic conditions showed a thinner solid shell at the early stage of the solidification and a thicker shell at the mold bottom in comparison with the conventional cast billet. It has been concluded that the Joule heat is a more dominant factor than the magnetic pressure in determining the surface quality of cast products in the high frequency electromagnetic continuous casting process.
... Due to electromagnetic force, curvature of the meniscus becomes smaller, solidified shell contact pressure decreases, and flux channel gap increases. It results in a decrease of dynamic pressure arising due to the relative movement of mold oscillation and solidified shell [9,10]. Flow turbulent intensity is found to be maximum at the edge of force field, and the circulation rate remains constant in the stirrer zone [11]. ...
... Therefore, high frequency is adopted to improve the surface quality. Dynamic pressure in mold shell gap and meniscus shape is crucial in controlling the initial solidification [10,[16][17][18]. Detailed investigations into the effect of EMS position on solidification are carried out in billet caster mold, and it is found that disturbance regions become wider on moving the stirrer away from SEN. ...
Electromagnetic stirring (EMS) is a technique that has the potential to improve steel quality with fine microstructure by fragmentation of dendrites and enhancing the inclusion removal. The success of implementing the EMS lies in the selection of key input parameters such as position, frequency, and current density of the stirrer. In the present study, an integrated mathematical model consisting of liquid steel solidification and two phase interface is numerically developed with the use of EMS. The enthalpy porosity and volume of fluid (VOF) model are adopted for numerical modeling analysis of solidification and interface level fluctuation, respectively. The results reveal that on moving EMS downwards decreases the maximum magnetic field value, widens the mushy zone, and promotes the stability of the interface. Current intensity and frequency are seen to have the opposite effect on stirring intensity and interface fluctuation. With an increase in frequency, both stirring intensity and interface level fluctuations decrease while the high liquid fraction region increases. Moreover, current density enhances the swirling flow intensity and homogenizes the liquid fraction, thereby promoting equiaxed grain formation. Interface fluctuation is seen to increase with current density.
... In the presence of high frequency M-EMS, significant improvement in surface quality of billet is seen due to the elimination of oscillation marks and surface defects. 11 Due to high buoyancy force, big size nonmetallic inclusion floats to slag layer and therefore removed easily 12 while the small size inclusion has a high chance of coming into the mold. Few studies on inclusion distribution and transport in continuous casting mold have been carried out. ...
The present study deals with the development of a multiphase numerical model of the continuous casting process of steel bloom. Two SEN configurations that differ in port angles are considered for the study of flow pattern, temperature distribution, solidification thickness, interface fluctuation and inclusion behavior during the process. The influence of mold electromagnetic stirring (M-EMS) on the various output parameters is examined. The results show that the upper circulation loop formed in the 15° port angle case is responsible for higher inclusion removal, high interface level, and low solidification thickness in the meniscus region compared to that of the 30° case. The presence of M-EMS completely changes the flow pattern below SEN. Strong rotational flow coupled with oppositely directed swirl flow provides high tangential velocity near the solidification front and high axial velocity in the core region. It results in fluctuation in shell thickness along the casting direction and decreasing the superheated steam penetration. However, flow patterns remain unaffected above the SEN as upwards swirl flow is not able to reach this region. On applying the M-EMS, inclusion entrapment in solidifying shell increases for both 15° and 30° cases. In contrast, inclusion removal at the interface decreases for 15° case and increases for 30° case.
... Kolesnichenko et al. [9] reported that an increase in Joule heating led to a move down the initial solidification point. Kim et al. [10] reported that when Joule heat is high then it may dominate the quality of the cast than the magnetic force applied. Song et al. [11] considered the Joule heating during modelling of electromagnetic stirring in secondary cooling zone and reported to have very limited influence of Joule heating. ...
"It has been developed a 3-D transient model of in-mold electromagnetic stirring in a continuous casting mold. The magnetohydrodynamics model was used to couple the time-varying electromagnetic field with fluid flow, and the solidification of liquid steel was analyzed using the enthalpy-porosity technique. The fluid flow was modelled with turbulence using a realizable k-ε turbulence model. The effect of Joule heat in steel at different frequencies of the electromagnetic stirrer has been predicted using Joule heating caused by induced current inside the mold. Preliminary research indicates that electromagnetic stirring retards the initial start of solid shell formation at the mold wall and transforms the liquid core present at the strand's center into the mush of the liquid-solid interface. Joule heating is observed to be limited in the stirring zone, with a maximum value observed close to the mold wall. The total Joule heat in the strand is found to be less than 1% of the total heat loss from the strand during the solidification process. An increase in frequency though increases the Joule heat in the strand, it is found to be dominant near the wall in the stirrer zone. The liquid core present above the stirrer position is found to expand marginally along the horizontal direction because of Joule heating.
... Currently, soft-contact electromagnetic continuous casting technology research focuses mainly on the softcontact mold, the electromagnetic field imposition method, the electromagnetic field distribution, meniscus shape control, and mechanisms for improving billet surface quality aspects [4][5][6][7][8][9][10]. However, there has been little research on the mold flux. ...
Soft-contact of molten steel can be achieved by applying a high-frequency electromagnetic field above the mold of continuous casting, which can effectively eliminate surface defects and achieve billets with no cracks and no oscillation marks. It also has some influence on the mold flux. In this study, the effect of a high-frequency electromagnetic field (20 kHz) on a mold flux flow field was simulated using a finite element software, and the slag film was extracted using a slag film simulator. The effect of the high-frequency magnetic field on the microstructure of the mold flux was analyzed using X-ray diffraction, Raman spectroscopy, and mineral phase testing. The results show that the high-frequency electromagnetic field disrupts the orderly movement and increases the movement rate of the liquid flux. The precipitate phase of the slag film did not change, but the silicate dimer Q
1 decreased, the chain Q
2 increased, and the network degree was increased. The slag film structure changed from the original two-layer form of crystalline layer–glass layer into a three-layer form of crystal layer–glass layer–crystal, and the crystallization ratio increased by 35% on average. The grain-size melilite granularity was reduced from the original 0.12 to 0.005 mm.
... [2−5] . . Kageyama [6] Cha [7] Cho [2] Kim [8] [9] mm [10] . ...
The distribution of magnetic field in electromagnetic soft-contact mold with different slit parameters was analyzed through 3-D FEM numerical simulation method. The results show that the cover placed on the top of the mold has little influence on the distribution of magnetic field with or without closed slit. With increment of slit number, the permeability of magnetic field and the maximum value of magnetic flux density become larger. The magnetic flux density becomes more uniform along the circumference. The width of slit has little effect on the distribution of magnetic field. The longer the slit length is, the larger the maximum value of magnetic field is, and the effective acting range of magnetic field becomes larger.
... As industry development is moving toward casting thin steel plates, these problems, especially the problem of molten steel breakouts, are expected to become more and more critical to the success of the process. Over the last few decades, extensive studies have been carried out to model various aspects of the continuous casting process, in particular the heat transfer and steel solidification process Wu et al., 1994;Wu and Wiwatanapataphee, 2004), the electromagnetic stirring (Archapitak et al., 2004;Jenkins and Hoog, 1996;Kim et al., 2002;Li and Tsukihashi, 2001;Sivesson et al., 1998), the flow phenomena (Thomas, 1990, Wiwatanapataphee, 1998 and the formation of oscillation marks (Hill et al., 1999). However, as analyzed by Thomas (2001), the continuous casting process involves a staggering complexity of at least eighteen interacting phenomena at the mechanistic level. ...
In the continuous steel casting, an electromagnetic field, generated from the source current through the coil, is imposed to the system to control the fluid flow pattern and the steel solidification process. In this paper, we develop a mathematical model and numerical technique to study the coupled turbulent flow and heat transfer process in continuous steel casting under electromagnetic force. The complete set of field equations are established and solved numerically within the framework of the Galerkin finite element method. The influences of electromagnetic field on flow pattern of molten steel and temperature field as well as steel solidification are presented in the paper. It is found that the introduction of an electromagnetic field affects the flow field and temperature filed. In terms of the thickness of the solidified steel shell, the influence of electromagnetic field is very significant.
... To achieve high production rate and ensure high quality of the casting products, intensive studies have been carried out worldwide over the last few decades to model various aspects of the continuous casting process, in particular the heat transfer -solidification process [10,27], the flow phenomena [22,25], the electromagnetic stirring [12,14,15,21] and formation of oscillation marks [11]. However, as analyzed by Thomas [23], the continuous casting process involves a staggering complexity of at least 18 interacting phenomena at the mechanic level, and due to the complexity, previous work mainly focus on each individual phenomena or interaction of two or three phenomena only. ...
This paper presents a mathematical model and numerical technique for simulating the two-fluid flow and the meniscus interface movement in the electromagnetic continuous steel casting process. The governing equations include the continuity equation, the momentum equations, the energy equation, the level set equation and two transport equations for the electromagnetic field derived from the Maxwell’s equations. The level set finite element method is applied to trace the movement of the interface between different fluids. In an attempt to optimize the casting process, the technique is then applied to study the influences of the imposed electromagnetic field and the mould oscillation pattern on the fluid flow, the meniscus shape and temperature distribution.
Aiming at the process of electromagnetic soft-contact continuous casting, a three dimensional finite element model of electromagnetic field and temperature field was developed to research the effects of high frequency electromagnetic field on the process of billet initial solidification in soft contact mold under various conditions of casting speeds and mold structural parameters. The results show that the Joule heat induced by the high frequency electromagnetic field in molten steel has significant effects on the initial solidification process, which appear as lowering the starting point of the initial solidification, thinning the initial solidified shell and increasing the billet surface temperature. These effects of high frequency electromagnetic field can be greatly weakened by increasing the casting speed, whereas these effects are remarkably enhanced by increasing the slit width and slit number on mold wall.
State-of-art in Electromagnetic Processing of Materials (EPM) is described. The recent topic of EPM in a steel making field is introduced. The application of a high magnetic field in EPM is classified and then the two topics of 1) quantitative evaluation of phase transformation and 2) crystal orientation of ceramics are introduced, which are the recent works on EPM relating with a high magnetic field.
History of Electromagnetic Processing of Materials (EPM) is described. The recent topic of EPM in a steelmaking field is introduced. The application of a high magnetic field in EPM is classified and then the four topics of 1) electromagnetic braking of a molten metal flow, 2) engineering application of spin chemistry, 3) quantitative evaluation of phase transformation and 4) crystal orientation of ceramics are introduced on the basis of our recent works on EPM with the application of the high magnetic field.
Continuously from part I, three dimensional distributions of magnetic field in soft-contacting electromagnetic continuous casting (EMCC) mold are systematically investigated numerically. Influences of structural parameters such as slit length/width, number of slit and wall thickness of mold, and the operating parameters such as free surface heights of liquid steel, electrical current densities, on magnetic flux density in mold were investigated separately. The max magnetic induction increases from 0.056T to 0.071T when slit length goes up to 220 mm from 130 mm; and increases from 0.058T to 0.089T when slit width goes up to 1.1 mm from 0.3 mm. The magnetic induction increases remarkably when the number of slit increases from 8 to 32, and the increase trend becomes smooth after 32. The max magnetic induction decreases about 50% when the mold wall thickness increases from 10 mm to 19 mm. The free surface of liquid steel should locate at the center position of inductor coil to obtain the largest magnetic induction. The max magnetic induction increases linearly against electrical density.
A very close to realistic production soft-contact EMCC (electromagnetic continuous casting) round billet mold was introduced, and the corresponding three dimensional mathematical model for electromagnetic fields was developed. The mathematical model was numerically solved using finite element method under well-posed conditions. After the validation of numerical results by experiments, the three dimensional distributions of magnetic flux density in the soft-contacting EMCC mold were systematically investigated. The errors between numerical and experimental values are less than 5 percent. The relations between magnetic flux density and all structural and operational parameters are obtained quantitatively, which will provide a theoretical quidance to the design and operation of soft-contacting EMCC round billet mold.
The application of high magnetic field in the electromagnetic processing (EMP) and continuous casting without mold oscillation in the steelmaking field is presented. The electromagnetic force enlarges enlarges the meniscus channel between the metal and the mold and improves the inflow of inflow of a mold flux along with reducing the contact pressure between a solidified shell and the mold. In addition to this, the Joule heat accompanied by the induced current retards solidification of the flux existing in the channel between the shell and the mold and accelerates the heat transfer between the shell and the mold. Besides this, the suppression of molten metal flow, a function of a static magnetic field, had been applied on a Czochralski method in the silicon industry and on a magnetic brake in a continuous casting process for use in the metal industry.
Based on electromagnetism theory, a physical and mathematical model of electromagnetic continuous casting was developed through ANSYS software. The distribution of magnetic induction density (B) in the coil was measured through the little coil method. By comparing the measured value with the calculated results, the validity of calculating the electromagnetic field through the model was proved. The ununiformity of B distribution in slit mould was analyzed. The results show that the effect of slit on the B distribution in the area with radius smaller than 25 mm is unconspicuous, and the ununiformity of B distribution in the area close to the mould wall is much remarkable. The effect of distance between coil circles on the B distribution was also studied. The results show that the magnetic induction density increases by decreasing the distance between coil circles, and the better distance between cow circles is 5-10 mm.
A three dimensional finite element mathematical model of electromagnetic field and temperature field was developed to investigate the effect of high frequency amplitude-modulated magnetic field on the billet surface temperature. The results show that the induction heat power of magnetic field amplitude-modulated with sine wave and square wave is unrelated to the frequency of modulating wave. The induction heat power of magnetic field modulated with square wave is between the induction heat powers of the two constant amplitude magnetic fields employed to modulate. If the induction heat powers of the two constant amplitude magnetic fields are determined, the induction heat power of magnetic fields modulated with square wave is determined by the relative scale of the acting time of the two constant amplitude magnetic fields. The induction heat power of magnetic field modulated with sine wave is about 62-64% of that of the high frequency magnetic field before modulation.
A three-dimensional mathematical model to present the electromagnetic force of molten steel in soft-contact mold was established by means of the finite element method. The effect of molten steel level variation on the electromagnetic force distribution was investigated through the simulation method. The results show that the maximum of electromagnetic force, which is imposed on the side surface of molten steel column along the height direction, can be found at 5-6 mm below the molten steel level. When the molten steel level is higher than the height of coil center by 5 mm, the electromagnetic force comes to the maximum. Moreover, the maximum values of electromagnetic force along the height direction are almost equal when the molten steel level is between the center and three-quarter of the coil. Whereas when the molten steel level is higher than the height of the three-quarter of coil, the electromagnetic force falls sharply with the increase of molten steel level. As a result, the molten steel level should be controlled between the center and three-quarter of coil so as to assure that the electromagnetic force is strong enough, especially, the electromagnetic force has little fluctuation.
Three-dimensional numerical simulations on the magnetic field in an electromagnetic soft-contact continuous casting mold were carried out through the finite element software ANSYS. The effects of molten steel level in mold on the distributions of magnetic field and electromagnetic force were analyzed. The results show that the magnetic induction density, B, is mainly distributed at the profile-surface of molten steel. If the molten steel level is below the coil top, the maximum value of B is near the top surface of molten steel and falls gradually along the withdrawing direction. If the molten steel level is above the coil top, the maximum value of B is moving toward the centre of the coil as the molten steel level is rising. The distributing character of electromagnetic force is mostly consistent with that of B.
The continuous casting technology appeared almost more than 40 years. The most attractive advantage of continuous casting machines is the shortest process from the melt liquid metal to the near-end-products. Further the energy consuming can be remarkably reduced. With the development of socio-economic, the qualitative requirements of metal products are getting stricter. Thanks to the deep scientific researches of magnetohydrodynamics (MHD), the applications of MHD are enjoying more and more extensions. For example, the electromagnetic continuous casting (EMCC) is the most spotlighted issue during the past double decades. Magnetic fields can provide energy into media without any contact, and the energy supplement can be controlled locally and directionally. According to the types of magnetic fields produced and applied in the continuous casting process, the applications of electromagnetic fields in EMCC can be classified into the following categories (a) Electromagnetic braking (EMBr), (b) Electromagnetic soft contact (EMSC), (c) Electromagnetic stirring (EMS). Based on the latest results of EMCC, a comprehensive review is given. The experiments, numerical simulations, together with some theoretical analysis and industrial applications are presented and discussed in detail.
Based on the numerical simulation, a round soft-contact mold with diameter 100 mm was designed. Using molten Pb-Sn-Bi low-melting alloy, the meniscus behavior in the round billet continuous caster with high frequency magnetic field was investigated. The effects of some parameters, such as frequency, electric power and metal level, on the meniscus deformation were discussed. The 0.22% (wt) C carbon steel was successfully casted in the pilot continuous casting machine. The results show that on the azimuthal direction the magnetic flux density distribution and meniscus deformation are relatively homogeneous when the slit number is 12. With power increasing, meniscus height increases, but the meniscus fluctuation is more intensified, the power should be controlled in an appropriate range. The reasonable power is about 50-60 kW. In practice, the metal level should be controlled between the center and the top of coil. The lower the frequency, the higher the meniscus height, and the optimal frequency is about 20 kHz. The Ø100 mm 0.22%C carbon steel with smooth surface is obtained by applying alternative magnetic. It shows that the oscillation mark of billet surface have three different statuses, annular oscillation, smooth surface and ripple oscillation respectively.
In the steel industry, the continuous casting product is usually a pre-produt before being fed to hot rolling mill, which brings in high cost and pollution and low productivity. So a new technology is demanded urgently to produce surface defect free billets and slabs. The success of electromagnetic casting (EMC) technology utilized in aluminum casting to improve surface quality enlightens the metallurgical researchers to apply this novel technology into production of steel. An experiment using high frequency magnetic field (26 kHz) was carried out on a vertical type caster with a segmented copper mold in our laboratory. Carbon structural steel (0.20% C, mass fraction) was used as experimental material. A special power was used to provide high frequency current to an induction coil surrounding the segmented mold. Moreover, the distribution of magnetic field and meniscus shape of Sn-Pb-Bi alloy in the mold were investigated and used to explain the phenomena happened in the initial solidification area in the case of EMC. The result shows that oscillations marks (OMs) can be totally suppressed and the surface of round billets with EMC technology becomes extremely smooth compared to the billets without EMC technology when the output power comes to an optimal one. According to the conventional mechanism of OM formation, the pressure generated in the flux channel due to the relative movement between solid flux rim and molten steel pool plays an important role in the formation of OMs. In the case of EMC, the solid flux rim becomes smaller as temperatures of mold and liquid steel in the initial solidification area increase because of Joule heat generated by the high frequency magnetic field, and the flux channel turns wider as Lorentz force is imposed on the liquid steel. As a result, the flux pressure becomes smaller, which makes the billets have better surface quality. However, when the powder exceeds the optimal value, the distribution of initial solidification starting point along the mold perimeter behaves in a wavy pattern. Simultaneously, the free surface of molten steel fluctuates more greatly, resulting in formation of OMs. As a conclusion, the formations of wavy OMs on the round billet surface are resulted from non-homogeneity of magnetic field between slit center and segment center as well as fluctuation of liquid steel level.
An induced coil surrounding a segmented mold used in soft-contact electromagnetic casting (soft-contact EMC) was used to produce a high frequency magnetic field for reducing ferrostatic pressure between the mold and melt. The distribution of magnetic field in the mold was examined using a magnetic probe of the induction coil type. Then mathematical model was developed to study the distributions of magnetic field, electromagnetic force and flowing velocity of molten steel in the mold. Finally, continuous casting experiments were conducted with alloy constructional steel 15CrMo in the laboratory caster. The surface morphologies and macrostructure were examined and analyzed. Based on the comprehension of the distributions of magnetic field, electromagnetic force and flowing velocity of molten steel in the mold through measurements and numerical simulation, the effects of electromagnetic field were systematically investigated. The results indicate that when the electromagnetic field was applied in the initially solidified area, the mold flux consumption was increased dramatically. As a result, the surface quality of continuously cast billets is greatly improved, for example, oscillation marks disappeared due to the decrease of flux pressure. Moreover, the growth of columnar grains is suppressed for two main reasons. The first one is that the mold near meniscus is heated by Joule heat generated by the high frequency electromagnetic field. The other one is that the thermal resistance between mold and the solidified shell is increased as the increase of mold flux thickness. Inhomogeneous distributions of magnetic field in the mold along the casting direction were confirmed both by measurement and numerical simulation. And the Lorentz force on the molten steel along the casting direction is uneven likewise. Under the drive of Lorentz force, two counter-rotational vortices are formed below the meniscus. Moreover, the temperature gradient in front of the solid/liquid interface is decreased as a result of the circulation of liquid steel. Therefore, composition supercooling is easily obtained in the liquid core, which is helpful to the growth of equiaxed crystals.
We develop a mathematical model and numerical technique to study the coupled turbulent flow and heat transfer process in continuous steel casting under an electromagnetic force. The complete set of field equations is solved numerically. We examine the influence of the electromagnetic field on flow patterns of molten steel, on the temperature field and on the steel solidification.
A three-dimensional finite element model of electromagnetic field and temperature field was developed to investigate the effects of induction heat of high frequency electromagnetic field on the early solidification process of molten steel. The results show that the increases of exciting current frequency make the effects of induction heat on solidification increase remarkably. Contrarily, the effects of induction heat on solidification process are weakened sharply with the increase of casting speed. Especially, when the casting speed exceeds a certain value, the effects of induction heat on solidification process are nearly negligible.
A level measuring system has been investigated to work with the electromagnetic continuous casting of steel billet, based on the principle of electromagnetic induction. The basic idea of the development is the distinction of the magnetic field measured in the mold into the effect of the applied one and the effect of the level variation. Several candidates of induction type magnetic probes were devised and examined. It was seen that the so-called global sensor was the proper one from the viewpoint of sensing range, resolution of the signal, and robustness to the external perturbation. The level of the melt was successfully calculated from the sensor output by employing the reference voltage for the set current in the power supply as a measure of the applied magnetic field. The use of the global sensor associated with the electronic device and the program showed that the resolution of the measurement was within +/-0.2 mm, the dynamic range of sensing the level was 0-300 mm below the top of the mold under the electromagnetic field at 20 kHz. In its application to commercial scale electromagnetic continuous casting at a billet caster of POSCO works, it worked well with the existing control device in supplying the molten steel to the mold. Particularly, its accuracy and promptness was sufficient to control the level at the initial stage of casting.
A three-dimensional finite element model of the electromagnetic field and temperature field of electromagnetic continuous casting (EMCC) process was developed. The aim was to investigate the effects of induction heat of high frequency electromagnetic field on the early solidification process of molten steel in mould under various conditions of exciting current parameters. The results show that the induction heat has significant effects on the early solidification process, which appear as increasing the billet surface temperature, thinning the initial solidified shell and lowering the starting point of the initial solidification. The increases in exciting current frequency and density make the effects of induction heat on solidification process increase remarkably. Especially, with the exciting current frequency increase, the early solidification process and shell growth become non-uniform in billet circumferential direction. Furthermore, if the exciting current density exceeds a certain value, there occurs a high temperature region in the top of molten steel column, and then the initial solidification rate is greatly decreased. As a conclusion, the effects of induction heat on initial solidification process must be considered when the exciting current frequency and density are adjusted during the electromagnetic continuous casting process.
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.
A systematic study on the electrical load forecasting for large-scale iron and steel companies was made. After analyzing the electrical load's characteristics, an algorithm framework for the load forecasting in iron and steel complex was formulated based on model combination and scheme filtration. The algorithm features data quality self-adaptation, convenient forecasting model extension, easy practical application, etc., and has been successfully applied in Baoshan Iron and Steel Co Ltd, Shanghai, China, resulting in great economic benefit.
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.
In order to improve surface quality of continuously cast steel, the investigation applying alternating magnetic field on initial solidification shell was carried out. The capacity of electric generator is 200kW, and frequency is 20kHz. Mold size is 150mm and 180mm square, and the upper part of mold is divided into 28 segments and surrounded with coil.
0.12% carbon steel which has high crack sensitivity, was cast to verify the effect of alternating magnetic field on the billet surface quality. Casting speed ranges from 0.4 to 1.3m/min. At the casting, a mold flux was used.
Surface roughness caused by mold oscillation and meniscus fluctuation can be remarkably decreased by applying optimum magnetic flux density distribution. In case of no magnetic field, average surface roughness caused mainly by mold oscillation is about 600 to 700μm and the deepest one reaches to 1300μm.
However, when the electric power of 150kW is applied, the average roughness can be improved less than 300μm. When too much power is applied, the surface roughness worsens. It can be also cleared that there must be an optimum condition of the distance between coil and meniscus. The relation between the coil and meniscus position is an important factor to realize a soft contact situation between the solidified shell and mold.
Shell formation in the electromagnetic mold was also examined.
In order to improve surface quality of continuously cast steel, alternating magnetic field was applied through the copper mold to the early solidification zone of round billet. The mold has a number of slits and was specifically designed to achieve the efficient penetration of the field as well as high stiffness. A mold size is 0.18 m in internal diameter and is surrounded with a multi-turn induction coil. Casting velocity is 1.2m/min. The capacity of high frequency generator is 300kW and the frequency is 25kHz.
0.11% carbon steel was cast to investigate the effects of the intensity of magnetic field and the imposing area on the surface quality of billets. Even under the strong magnetic field, the meniscus level was controled precisely by RFLC method (Resonant Frequency Level Control Method) detecting the small shift of resonant frequency of high frequency generator.
Surface marks on the cast billets had three types by the imposition of electromagnetic field. Regular surface marks caused by the mold oscillation have disappeared by selecting the optimum meniscus level under suitable electric power. By the use of developed two fluids model based on VOF code, dynamics of meniscus shape at the early solidification zone during oscillation were studied theoretically. The model shows that the disappearance of oscillation marks is responsible for the stability of interfacial shape between flux and molten steel by the imposition of electromagnetic field.
Simulation experiments using Mould Simulator developed by the authors and plant trials have been carried out to investigate the formation mechanism of oscillation marks and the factors affecting powder consumption rate in continuous casting.
Following results were obtained through the experiments.
1) Oscillation marks are formed as a result of interaction between solidified shell and very viscous layer of mould powder at the circumference of molten steel surface in a mould.
2) Depth of oscillation marks increases as the negative strip time of the mould oscillation cycle increases.
3) Consumption rate of mould powder, q is proportional to the positive strip time.
Low frequency mould oscillation mode with decreased amplitude has been proposed to obtain shallow oscillation marks and high consumption rate of powder for a fixed powder property.
Besides the above stated proposal, several measures which were not well documented have been studied in order to produce slabs without surface defects such as slag spots, transverse corner cracks and longitudinal facial cracks.
The results obtained are listed below.
1) Proposed mould oscillation mode is effective for reducing both slag spots and transverse corner cracks.
2) Stable molten steel level in a mould during casting is very important for decreasing both slag spots and longitudinal facial cracks.
3) A suitable viscosity range of the powder exists for minimizing the frequency of longitudinal facial cracks.
A new method of mold oscillation for continuous casting termed "horizontal oscillation" was developed to reduce the depth of oscillation marks without increasing the possibility of breakout. In this method, the wide faces of the mold oscillate horizontally in synchronization with conventional vertical oscillation. Oscillation marks on slabs of SUS304 cast with a pilot continuous easter were examined under various conditions of mold oscillation. Horizontal oscillation successfully reduced the depth of oscillation marks and surface segregation at oscillation marks, and was extremely effective when the wide face of the mold was expanded against the solidified shell during positive strip time. Experiments with an actual machine reproduced these effects of horizontal oscillation. A numerical analysis of the deformation of the solidified shell during one cycle of vertical oscillation was performed to study the effect of horizontal oscillation on the control of early solidification near the meniscus. Friction force acting on the shell near meniscus was also discussed to explain the reduction in the surface segregation.
A marked improvement of the surface quality of casts and a break-through in casting speed in conventional continuous casting of steel require the introduction of new technology for initial solidification control. The authors have approached these problems by the use of electromagnetic shaping of the meniscus and demonstrated the possibility using simulation experiments. This paper describes the results of numerical prediction of the effect of electromagnetic field on the initial solidification of steel and the experimental results obtained by continuous casting of round austenite stainless steel billets of 180mm diameter with solenoidal magnetic field with main frequency, 60 Hz. The numerical results concerned with magnetohydrodynamics and heat transfer phenomena predicted improvement of the surface roughness of the cast billet and improvement of mold lubrication by decreasing the dynamic pressure due to the meniscus shaping effect. In the experimental casting, the surface of billets were smoothed and the mold friction force was reduced by imposing the magnetic field, which are in consistent with the numerical predictions.
While many investigators have examined electromagnetic and magnetohydrodynamics phenomena in electromagnetic casting (EMC)
of aluminum, there appears to be no published work on heat transport and solidification in such casters. This two-part series
is an attempt to remedy this deficiency. The first part describes two experimental campaigns, carried out on a pilot-scale
electromagnetic caster at Reynolds Metals Company, in which sacrificial thermocouples were used to obtain many data on temperature
distributions within the aluminum of a pilot-scale caster and thereby to obtain the shape of the liquid metal pool (“sump”).
The data reveal a strong dependence of temperature distribution and sump depth on casting speed but a relatively weak dependence
on the flow rate of the quenching water striking the outside of the ingot.
Surface quality of continuously cast metals can be improved by imposing a continuous high-frequency magnetic field from the
outside of a mold. Newly proposed concepts of “soft contacting solidification” and “slow cooling solidification,” which is
tightly related to the mechanism of improving surface quality, were confirmed in model experiments by using molten gallium
and tin. The meniscus motion of the molten gallium accompanied by a mold oscillation and magnetic pressure was measured by
a laser level sensor. The shape variation of a meniscus and the process of ripple formation in an oscillation cycle were directly
visualized by an optical fiberscope camera. Moreover, molten tin was continuously cast and the relationship between the surface
quality and the meniscus motion was studied. A mechanical model for predicting the space between the oscillation marks is
proposed. The casting process using intermittent highfrequency magnetic field was developed. New functions of this field were
investigated regarding the control of initial solidification. It was found that the surface quality of the continuously cast
metal can be improved by the intermittent high-frequency magnetic field as well as the continuous high-frequency magnetic
field.
In the first part of this paper, the working principle of a new electromagnetic continuous casting process is described. The
main peculiarities of this process are (1) the presence in the sump of a strong electromagnetically driven forced convection,
which promotes the production of a fine equiaxed structure, and (2) the fact that the thickness of the segregation zone tends
toward zero. Local measurement methods are applied to the study of electromagnetic and hydrodynamic phe-nomena inside the
sump of aluminum alloy billets. Further, the evolution of both the grain size and the thickness of the segregated surface
layer with the electric power input is presented. In summary, this new technology presents the advantages of avoiding the
addition of grain refiners and substantially reducing the scalping operation.