KR20240072788A - Electromagnetic control apparatus and method for continuous slab casting of aluminum alloy - Google Patents

Abstract

An electromagnetic wave control device for continuous slab casting of aluminum alloy includes a mold containing liquid metal; a horizontal casting table disposed horizontally above the mold and covering the mold; an injection groove installed on the upper part of the horizontal casting table and extending long for supplying liquid metal; a supply nozzle extending downward from the bottom of the injection groove to supply the liquid metal to the mold; a liquid sump disposed from the horizontal casting table toward the inside of the mold; and a pair of inductors respectively disposed on both sides of the liquid sump.

Description

Electromagnetic control apparatus and method for continuous slab casting of aluminum alloy}

The present invention relates to continuous casting technology, producing ingots, billets, round rods and slabs with high quality, reduced inclusions, low center line porosity and segregation due to microstructure and chemical composition. and methods and equipment for the melting and solidification of non-ferrous alloys by electromagnetic processing, in the production of other products.

7xxx -series aluminum alloys can be used as important aircraft structural materials with high strength, low density and high fracture toughness, fatigue crack growth and stress corrosion resistance. These aircraft structures are widely used for critical power components such as machine body beams, horizontal solid rear walls, upper wing skins, keel booms, ejection seats and rails, etc. It also has great potential in small aircraft missiles, anti-tank missiles, and other large military pontoon bridges.

In general, in series 3 to 7 high-strength aluminum alloys for subsequent deformation processing such as extrusion, rolling, stamping (cold or hot), the most common processes are circular cross-section, slabs or blooms, which are most suitable for extrusion, rolling or It is a billet with a rectangular or square cross section specialized for stamping. Regarding the casting of rectangular melts, slabs or blooms, the most common method is carried out in short water-cooled sliding molds, and oil is supplied to the interface area between the mold and the ingot at the top of the mold along the circumference of the meniscus. The oil prevents the ingot from sliding along the mold body and acts as a non-stick coating.

In the case of 7xxx-series alloys with a wide range of crystallization temperatures, strong temperature segregation across the cross-section of the billet-shaped circular ingot leads to the formation of central porosity and heterogeneity between macro and microstructure. In the latter case, severe residual post-casting stresses occur and annealing is necessary after homogenization casting.

In particular, strong thermal stresses occur in high-alloy alloys with a zinc content of more than 5-7%, such as 7068 (more than 8%).

In the case of slabs, when supplying melt by flotation, a cooling and heat unit is formed according to the uniform cooling of the ingot at the position where the melt is supplied into the mold and at the mold exit position by jet method, so that a serious temperature is generated in the slab separation area. Deterioration occurs. This creates thermal stresses that are orders of magnitude greater and can lead to longitudinal cracks during the casting process and post-cast storage.

In the field of continuous casting of slabs, blooms or billets, there are major challenges that researchers must solve. This reduces thermal heterogeneity in the crystallization zone and ensures the effect of thermal stress on the crystal growth process at the crystal front, along with intensive forced heat and mass transfer in the liquid sump of the ingot.

To solve the problem of controlling heat and mass transfer in the liquid core of the ingot, several methods can be used, including direct internal immersion or external impact, ultrasonic or pulsed direct exposure. However, direct local contact with the melt has many disadvantages, such as causing wear and metal accumulation of the actuator body and waveguide and making it difficult to ensure uniform impact.

From this point of view, the most suitable method for external forcing is to use electromagnetic fields and electromagnetic stirrers.

Electro-Magnetic Casting (EMC) technology applies Lorentz force at a frequency of 2.0 to 20 kHz in an alternating magnetic field generated by the surface area of aluminum melt, and presses the molten liquid metal into the mold, thereby directly cooling it. Effects such as solidification of the second molding, smooth surface of the slab, and prevention of segregation are achieved. However, although high stability is required for the operation of the casting machine, establishment of the casting process is very difficult due to residual vibration of the casting machine, corrugated slab surface, etc., so the application of this technology in industry is limited.

However, although the use of high-frequency magnetic fields is effective in retaining liquid metal on the crystallizer walls, the concentration of the high-frequency magnetic fields causes severe surface overheating. At the same time, the high voltage used in the high-frequency power supply of the winding is dangerous to the human body, and the high-frequency inverter not only produces sounds that are unpleasant to human hearing, but also may have a negative impact on the electrical plant network due to the harmonics of the high frequency, and other industrial equipment in the workshop. It's harmful.

Electromagnetic coupling reduces the low-frequency magnetic field (e.g. 15-60 Hz) generated by the contact pressure with the mold, thereby reducing the primary cooling intensity, removing segregated lumps from the surface and improving surface quality (see Chinese patent CN1425520A) ).

Focusing intensively on melts with a rectangular or square transverse cross-section, heat and mass transfer processes can reasonably be organized in the form of a transverse uniform movement of the melt along the perimeter, with respect to the sides of the crystal front, in both unidirectional and reverse directions. You can.

Systems in the form of radial electromagnetic stators, most often used as electromagnetic stirrers, are most suitable for the construction of rotating and traveling magnetic fields, since, unlike billets of circular cross section, three-phase currents are used in slabs.

The traveling magnetic field system is configured to be arranged in one direction by the stator of a three-phase asynchronous motor, in order to close the internal magnetic flux by means of vertical poles located in the form of steps with their own windings, in which the main longitudinal magnetic circuit is formed into one They are arranged alternately within the plane.

When three-phase currents are applied to alternately energized windings, a shifting condition is created. In other words, as the magnetic field moves in time due to the step between the windings, a wave movement of the magnetic field peak is formed in space along the inductor axis, thereby forming a run/travel magnetic field effect.

An inductor of a traveling magnetic field is installed along the long side of the slab, usually perpendicular to the drawing axis, and creates a magnetic circuit and a mixed melt in a liquid sump along the slab wall. In addition, current is supplied to the inductor on the opposite side of the traveling magnetic field to create the moving direction of the magnetic field and the moving direction of the metal flow, respectively, thereby forming a closed circuit of the melt flow in the liquid sump.

Additionally, to optimize heat and mass transfer processes, various experts use a mode that reverses the flow direction at given intervals.

The known patent US 2008/0164004 A1 discloses a method of electromagnetically stirring molten metal in the unsolidified portion of a continuously cast ingot, bloom or slab. In particular, in order to form a fine and homogeneous microstructure of the ingot and to improve heat and mass transfer processes, a current carrier with a frequency range of 13 - 20 Hz and a modulation range of 3.0 - 6.5 Hz is used in the power winding of the electromagnetic stirrer. We propose the use of multi-harmonic currents with at least two frequency characteristics.

This approach uses a pulse mixing mode of the melt in the unhardened part of the ingot and a different design of a three-phase system to generate an alternating magnetic field when used in various systems for continuous casting of billets, blooms and slabs. In particular, this is illustrated in patent US 4,852,635, which describes an electromagnetic melt mixing method during continuous casting.

In this way, the singular formation of a pulse mode of a magnetic field with at least two frequency components was based on the principle of overlapping two currents with different but similar frequencies, such as 60 Hz and 60+(0.03~0.25) Hz.

At the same time, using the mixed pulse mode at a pulse frequency of 0.5 Hz, the negative segregation can be greatly reduced by making the equiaxed crystals of the clusters at least three times larger.

At the same time, dedicated to tangential electromagnetic wave stirrer systems, it is necessary to strengthen the hydrodynamic stabilization of heat and mass transfer processes in the melt in the horizontal plane. A pulsed mixing mode must be used to create a hydrodynamic vortex flow that provides microturbulence of the entire volume of the melt in the liquid core of the ingot, and sometimes a more efficient homogenization mode may be required, usually in terms of temperature and chemical composition.

Therefore, according to patent US 6,443,219 (Method for casting molten metal) it is proposed to change the parameters of the advancing magnetic field to create an oscillating effect in the melt in the liquid sump of the solidifying ingot. That is, it changes the intensity of time from zero to a nominal value using a given time adjustment parameter, or provides a reverse action of the moving electromagnetic force. At the same time, the patent focuses on the process of crushing the particle size and homogenizing the microstructure in all ingot cross-sections, such as bloom.

On the other hand, according to patent US 5,722,480, a development concept is used that uses a pulse mode of electromagnetic agitation by a traveling magnetic field, where, on the continuous principle of amplitude modulation, it has mainly one carrier frequency, but with a controlled and time-varying amplitude.

The prior art closest to the present invention is Korean patent KR20190071146A, which applies a method of electromagnetically controlling the crystallization process of billets in 7xxx-series alloys. For extensive control of the melt mixing process in the liquid sump of the ingot, pulse action on the semi-solid phase by amplitude-modulated magnetic fields and hydrodynamic impulses is used, contributing to the refinement of the microstructure and homogenization of the structure over the entire cross-section of the ingot. .

Korean Patent Publication No. 2019-0071146 (published on June 24, 2019)

The technical problem to be achieved by the present invention is to not only change the influence vector of electromagnetic waves over time, but also control the direction and form magnetic force lines over time. Specifically, providing two types of electromagnetic pulses to the liquid core of the ingot, from the "tangential" component, producing rotational motion of the melt as the "normal" component, providing pulsed hydroacoustic and electromagnetic action in the direction of the central billet. intend

The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the description below.

An electromagnetic wave control device for continuous slab casting of aluminum alloy according to an embodiment of the present invention for achieving the above technical problem includes a mold (4) containing liquid metal; A horizontal casting table (1) disposed horizontally above the mold (4) and covering the mold (4); an injection groove (2) installed on the upper part of the horizontal casting table (1) and extending long to supply liquid metal; a supply nozzle (3) extending downward from the bottom of the injection groove (2) to supply the liquid metal to the mold (4); a liquid sump (5) disposed from the horizontal casting table (1) toward the inside of the mold (4); and a pair of inductors 10 and 7 respectively disposed on both sides of the liquid sump 5.

The electromagnetic wave control device for continuous slab casting of the aluminum alloy includes a lubrication device that supplies lubricant to the cavity of the mold (4); And it further includes a water cooling device for cooling the mold (4).

The pair of inductors 10, 7 generates a unidirectional pulsating alternating magnetic field for unidirectional electromagnetic agitation of the liquid metal.

The single-phase current of the unidirectional pulsating alternating magnetic field is generated by the following equation,

Where Uc is a constant amplitude of carrier frequency oscillation, M is the modulation ratio (M≤1), ωm and ωc are the modulation frequency and carrier frequency, respectively, and ϕm and ϕC are the initial phase shift for the modulation frequency and the initial phase for the carrier frequency, respectively. It's better.

The three-phase current of the unidirectional pulsating alternating magnetic field is generated by the following equation,

Where Uc is the constant amplitude of the carrier frequency oscillation, M is the modulation ratio, ωm and ωc are the modulation frequency and carrier frequency, respectively, and ϕm is the initial phase shift with respect to the modulation frequency.

The pair of inductors 10, 7 generate a reversible pulsating alternating magnetic field for reversible electromagnetic agitation of the liquid metal.

The three-phase current of the reversible pulsating alternating magnetic field is generated by the following equation,

Where Uc is a constant amplitude of carrier frequency oscillation, M is the modulation ratio, ωm and ωc are the modulation frequency and carrier frequency, respectively, ϕm is the initial phase shift with respect to the modulation frequency, and ϕC is the initial phase shift with respect to the carrier frequency.

The pair of inductors 10 and 7 has a magnetic core in the form of a stator having multiple poles, and a winding installed on the multiple poles.

The pair of inductors 10 and 7 has a plurality of winding sections installed alternately with each winding mixed at a predetermined step, through which control and phase shift change by carrier frequency or amplitude are possible.

According to the invention, it is possible to implement an electromagnetic method for controlling the bloom and solidification process of slabs from 7xxx-series aluminum alloy in half-continuous casting or continuous casting.

According to the invention, a pulsed unidirectional or reversibly traveling magnetic field impulse can be applied to equalize the solidification front in the mushy zone of the melt.

According to the present invention, a homogeneous grain size of the microstructure can be provided in all ingot cross-sections, and a non-dendritic type microstructure with improved properties, especially in the case of production of forged alloy cases for extrusion and rolling forging. may be provided.

In addition, it is possible to prevent defects such as thermal stress, casting defects, or internal/external cracks after casting.

Figure 1 is a diagram showing an external perspective view and a two-plane cross-sectional view of a pilot plant for continuous slab casting.
Figure 2a is a general view of a four zone inductor in a traveling magnetic field with three layer coils shifted 25 mm per layer, and Figure 2b is a general view of a four zone inductor with corner stacking in stepped layers of windings.
Figure 3 shows a schematic diagram of forced pulsation unidirectional electromagnetic melt agitation in a liquid sump inside a slab crystallization crust in the horizontal plane using two pulsating traveling magnetic fields generated by a left inductor and a right inductor; am.
FIG. 4A is a timing diagram showing the pulsating unidirectional electromagnetic force of the 5 Hz pulsating magnetic field generated by the left inductor, and FIG. 4B is a timing diagram showing the pulsating unidirectional electromagnetic force of the 5 Hz pulsating magnetic field generated by the right inductor 7. It's a diagram.
Figure 5 shows a schematic diagram of reversible electromagnetic stirring of a melt in a liquid sump inside the crystallization crust of a slab in the horizontal plane using a two pulse mode reversible traveling magnetic field generated by the left inductor and the right inductor. am.
Figure 6a is a timing diagram showing the pulsating reversible electromagnetic force of a 5 Hz pulsating magnetic field generated by the left inductor, and Figure 6b is a timing diagram showing the pulsating reversible electromagnetic force of a 5 Hz pulsating magnetic field generated by the right inductor. am.
Figure 7a is a diagram showing the microstructure of a 350*150mm slab of the conventional 7075 alloy without applying 5Hz unidirectional pulse EMS, and Figure 7b is a diagram showing the microstructure of the 7075 alloy according to the present invention with 5Hz unidirectional pulse EMS applied. *Drawing showing the microstructure of a 150mm slab.

The advantages and features of the present invention and methods for achieving them will become clear by referring to the embodiments described in detail below along with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and will be implemented in various different forms. The present embodiments only serve to ensure that the disclosure of the present invention is complete and that common knowledge in the technical field to which the present invention pertains is not limited. It is provided to fully inform those who have the scope of the invention, and the present invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

Unless otherwise defined, all terms (including technical and scientific terms) used in this specification may be used with meanings that can be commonly understood by those skilled in the art to which the present invention pertains. Additionally, terms defined in commonly used dictionaries are not interpreted ideally or excessively unless clearly specifically defined.

The terminology used herein is for describing embodiments and is not intended to limit the invention. As used herein, singular forms also include plural forms, unless specifically stated otherwise in the context. As used in the specification, “comprises” and/or “comprising” does not exclude the presence or addition of one or more other elements in addition to the mentioned elements.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the attached drawings.

The invention is based on an electromagnetic method of controlling the process for crystallizing blooms and slabs from 7xxx-series aluminum alloys in the process of continuous casting method, using two different methods for electromagnetic processing.

The key application of pulse travel electromagnetic stirring control is to provide equalization of the crystal front in the mushy region, uniform grain size of the microstructure at the center, middle and surface of the slab cross section, and to produce high quality slabs. The goal is to provide a non-dendritic type microstructure for this purpose. This improves quality, reduces thermal stress after casting and eliminates casting defects or internal/external cracks.

Figure 1 shows an external perspective view and a two-plane sectional view of a pilot plant for continuous slab casting (9). In the slip mold (4) and floating system (3), the casting process of slab size 350*150 mm by vertical drawing method is demonstrated. Traveling magnetic field inductors (10, 7) are located on both long sides of the slab on both sides and provide electromagnetic melt agitation into the liquid sump (5) by means of a horizontally pulsating traveling magnetic field. The electromagnetic process is implemented with primary solidification of the slab skin at the outlet of the crystallizer (4). Also shown are floatation systems 3, 4 for maintaining a predetermined melt level in the mold (open meniscus) (flotation valves not shown).

For electromagnetic control, bifacial (located on both long sides of the slab) electromagnetic stirring of the melt in the liquid sump (5) of the slab (9) by means of a pulsating traveling magnetic field directed horizontally below the primary solidification formation zone of the slab skin. Systems (7, 10) exist.

Implementation The proposed method is carried out in a continuous casting device 50 of the sliding type, consisting of a horizontal casting table 1, on which there is an injection groove 2 for supplying liquid metal (e.g. 7xxx-series alloy). . During the casting process of feeding into the water-cooled casting mold (4) through the supply nozzle (3), a fixed melt level is maintained inside the mold (4) by means of a floating melt level control valve. Also shown is a starting head 8 that starts the pulling of the slab.

The sliding type casting mold (4) is installed inside the casting table (1), and is connected to the water supply chamber inside the casting table and the lubricating oil supply system to supply lubricating oil to the casting mold inlet, and the inner mold wall by a thin oil layer. Cover.

The electromagnetic stirring device for the liquid sump (bloom, etc.) of the slab 9 is installed at the bottom of the casting table 1, and is closest to the output of the sliding casting mold 4 from the two long sides of the slab in a plane. connected.

Figure 2a is a general view of a four zone (25-28) inductor of traveling magnetic fields (7, 10) with three layer coils (22-24) shifted 25 mm per layer. Meanwhile, Figure 2b is a four zone inductor with corner stacking in stepped layers of windings.

The electromagnetic stirring device 7, 10 is a system of electromagnetic stirring of a liquid-metal conductive medium in the horizontal plane, as shown in Figure 2, and is implemented as a multi-zone propagating magnetic field inductor. The inductor consists of a magnetic core 20 in the form of a common magnetic circuit with windings 22-23, etc. and a developed stator of an asynchronous motor with multi-pole 21.

Windings 22 to 23 are installed on poles in at least three layers by mixing each winding with respect to each other with a step equal to 1/3 of the winding width, and the three windings installed alternately have two to six layers. It has areas (25-28). The winding can be driven with a three-phase current that controls the carrier frequency and amplitude and changes the phase shift.

1 and 2A, multi-zone propagating magnetic field inductors (7, 10) are mounted on a waterproof stainless steel case (11, 6), which is a load-bearing frame for fixing the electromagnet system.

2A and 2B, the main W-shaped multi-zone magnetic core 20, together with the common solid magnetic core 20, has a length of 725 mm and a height of 100 mm. Additionally, the space and width of the inner pole are perpendicular to it for the 15 poles 21 of 25 mm.

Depending on the width of the slab, from 2 to 6 zones (25-28) can be installed on the magnetic core 21, which consists of three windings 22 installed on the poles of the magnetic core via shifts. , 23, 24). The three windings 22, 23, 24 are installed on the poles of the magnetic core with one phase shift relative to each other, as shown in Figure 2a.

Each winding layer includes a series connection to each of the three phase supplies, for example, the upper layer is phase R, the middle layer is phase S, and the lower layer is phase T. In some cases, the structure for disposing the windings in the space between the poles may be a single layer with a uniform slope, as shown in FIG. 2B.

Figure 2a shows a general view of a four-zone (25-28) inductor of traveling magnetic fields (7, 10), with a three-tier arrangement of coils (22-24) with a layer shift of 25 mm per layer. Figure 2b also shows a four-zone inductor with a single layer edge stack of windings.

Figure 3 shows a forced pulsation unidirectional flow within a liquid sump (5) inside a slab crystallization crust (9) in the horizontal plane, using two pulsating traveling magnetic fields generated by the left inductor (10) and the right inductor (7). (Counterclockwise) This is a diagram showing a schematic of the electromagnetic melt stirring (15). Here, the blue arrow 15 indicates the direction of the melt flow in the form of solid and dotted arrows showing pulsating characteristics with time, and the red arrow 14 indicates the direction of the electromagnetic pulse generated by the pulsating magnetic field.

To illustrate the essence of the invention, Figure 3 shows a crystallized crust of the slab 9 in the horizontal plane, using two pulsating traveling magnetic fields generated by the left inductor 10 and the right inductor 7. ) of the liquid sump (5), a scheme is presented for carrying out pulsating unidirectional (counterclockwise) electromagnetic stirring of the melt (15).

By applying pulsed mode in melt agitation, hydrodynamic mass transfer processes for volumetric micro-vortices can also be generated by the melt. Additionally, the agitation method must create the effect of “compression/rarefaction” waves, called acoustic impulses, in the liquid sump of the slab.

In order to generate a pulsed unidirectional moving pulsating alternating magnetic field, the amplitude modulated electromagnetic force impulse proposed in the present invention can be expressed as Equation 1 below.

[Equation 1]

Here, Uc is the constant amplitude of the carrier frequency oscillation, M is the modulation ratio (M≤1), ωm, ωc are the modulation frequency and carrier frequency, respectively, and ϕm and ϕC are the initial phase shift with respect to the modulation frequency and the initial phase shift with respect to the carrier frequency, respectively. It is a phase shift.

Additionally, in embodiments that generate a unidirectional pulsed traveling magnetic field, the 1st, 2nd, and 3rd coils (Figure 2a) in one coil group 25 or in a series coil group (25, 26, 27, and 28 in Figure 2a or Figure 2b) Alternatively, the equation of the three-phase current for supplying power to 22, 23, and 24) in FIG. 2B can be defined in general terms as Equation 2. Here, the pulsating magnetic field is a three-phase current ( ), which is formed by at least two control frequencies, i.e. corresponding phase-to-phase shifts ( ) and an amplitude modulation envelope frequency ωm along with a carrier frequency ωc.

[Equation 2]

Here, Uc is the constant amplitude of the carrier frequency oscillation, M is the modulation ratio (M≤1), ωm and ωc are the modulation frequency and carrier frequency, respectively, and ϕm is the initial phase shift with respect to the modulation frequency.

This method can also be used under conditions for the algebraic superposition of two harmonic currents U1(t) and U2(t) with different frequencies (f1≠f2), or of the inductor of the traveling magnetic field already generated by the amplitude-modulated current. This can be implemented by generating a modulation by an amplitude magnetic field when energizing all series-connected group windings from four zones.

Examples of time diagrams for 5 Hz amplitude modulated pulsed unidirectional traveling electromagnetic forces generated by the left inductor 10 and right inductor 7 inductors and with a 22.5 Hz carrier frequency with a modulation ratio of -0.7 are shown in Figures 4a and 4b. is shown in

FIG. 4A is a timing diagram showing the pulsating unidirectional electromagnetic force of the 5 Hz pulsating traveling magnetic field generated by the left inductor 10. Additionally, Figure 4b is a timing diagram showing the pulsating unidirectional electromagnetic force of the 5 Hz pulsating traveling magnetic field generated by the right inductor 7.

4A and 4B, the blue arrow 15 represents the time diagram of the “tangential” component of the electromagnetic force, which is oriented parallel to the inductors 10, 7 and points downward. As shown in FIG. 3, the component moves downward in the left inductor 10 and moves upward in the right inductor 7. At this time, the unidirectional force vibration generated can vary from a maximum of 20N (Newton) to a minimum of 5N at a modulation rate of 0.7 for 5Hz.

Meanwhile, in Figures 4a and 4b, the red arrow 14 represents the time diagram of the “normal” component of the electromagnetic force, which is directed toward the slab surface and perpendicular to the magnetic core 7, 10. Here, the vibration mode ranges from 5 to 0N. The maximum amplitude of the “normal” component generally has one direction and is located between the pulses of the “tangential” force, and is defined by the natural interaction of two harmonic magnetic fields with different frequencies, especially in the transition period.

Figure 5 shows a liquid sump (5) inside the crystallization crust (9) of a slab (9) in the horizontal plane using a two pulse mode reversible traveling magnetic field generated by the left inductor (10) and the right inductor (7). In the drawing, a schematic diagram of reversible electromagnetic stirring of the melt 15 is shown. Here, the blue arrow 18 indicates the direction of the melt flow in the form of solid and dotted arrows showing pulsating characteristics with time, and the red arrow 19 indicates the direction of the electromagnetic pulse generated by the pulsating magnetic field.

To illustrate the essence of the invention, Figure 5 shows the crystallized crust of the slab 9 in the horizontal plane, using two reversible pulsating traveling magnetic fields generated by the left inductor 10 and the right inductor 7. A scheme is presented for performing forced pulsatile electromagnetic agitation on the melt (15) within the liquid sump (5) of .

The blue arrow 18 represents the flow direction of the melt in the form of solid and dotted arrows, and shows the property of pulsating over time. And, the red arrow 19 indicates the direction of the electromagnetic force pulse generated by the pulsating magnetic field.

This is a reversible method of mixing melt in pulsation mode, that is, unlike the pulsation unidirectional mode, the direction of melt movement is reversed according to a circular harmonic pattern, preventing unidirectional movement of melt along the perimeter of the slab 9 in the horizontal plane.

This ensures that microstructural inhomogeneities are substantially eliminated across the cross-section of the slab 9 and, additionally, the melt flow used in the opposite direction ahead of the crystal front causes the axes of the dendritic branches to run counter to the melt flow. Practically prevents escape. This can lead to the formation of equiaxed spherical microstructures.

From a technical point of view, a fraudulent pulsating reversible traveling magnetic field can produce a three-phase current ( ) can be created by. According to the half frequency of the modulation envelope in Equation 3, the reverse mode ( ), with the corresponding phase shift varying with time, at least two control frequencies, namely the amplitude modulated harmonic type envelope frequency ωm and the carrier frequency ωc.

[Equation 3]

where ϕC is the initial phase shift with respect to the carrier frequency.

Since the reversible pulsed traveling magnetic field has a component that changes the initial phase shift to the opposite value, it creates the effect of a reverse action of the traveling magnetic field.

This method is performed under conditions of algebraic superposition of two currents U1(t) and U2(t) with different frequencies (f1≠f2) in the power supply coil, or three-phase currents already modulated by amplitude and phase according to equation (3). When powering the winding groups 25 to 28 from zones 1 to 6 of the traveling magnetic field inductor in FIG. 2, the current can produce a modulation in the reversible direction of the amplitude modulated magnetic field.

Examples of time diagrams for 5 Hz amplitude modulated pulsed reversible traveling electromagnetic forces generated by the left inductor 10 and right inductor 7 inductors, using a 22.5 Hz carrier frequency with a modulation ratio M of 1, are shown in Figures 6a and It is shown in Figure 6b.

Figure 6a is a timing diagram showing the electromagnetic force in the pulsating reversible direction of the 5 Hz pulsating magnetic field generated by the left inductor 10, and Figure 6b is a timing diagram showing the pulsating reversible direction of the 5 Hz pulsating magnetic field generated by the right inductor 7. This is a timing diagram showing electromagnetic force.

6A and 6B, the blue arrow 18 represents the “tangential” component of the electromagnetic force, which is oriented parallel to the inductors 10, 7 and oscillates from bottom to top, reversible in time and direction. As shown in Figure 5, the components oscillate up and down in the left inductor 10 and the right inductor 7 (but the phases are opposite). At this time, the vibration of the reversible force generated is

It is generated at 2.5 Hz (2.5 times per second) in the range of 0 to 20 N.

Meanwhile, in FIGS. 6A and 6B, the red arrow 14 points toward the slab surface and shows the “normal” component of the electromagnetic force perpendicular to the magnetic cores 7 and 10. Here, the vibration mode represents a frequency of 5Hz and 0~15N.

To test the effectiveness of the above-described embodiment using a unidirectional pulsating runner magnetic field, experiments were performed using electromagnetic processing (EMS) rather than DC.

Under the crystallization apparatus of the primary slab crust, to create conditions for a unidirectional pulsating traveling magnetic field as shown in Figure 1, there is a three-layer winding decoupling, with a shift for each by a third part (Figure 2a). Two four-zone traveling magnetic field inductors were used.

Generation of the pulse mode is performed by connecting the windings of the layers to a three-phase power supply. Here, the input of the first inductor winding is connected to a three-phase voltage with a frequency of 20 Hz, the winding input of the second inductor is connected to a three-phase voltage with a frequency of 25 Hz, and the outputs of the two inductors are each connected sequentially.

At a modulation ratio M = 1, an amplitude modulation envelope of 5 Hz, and a carrier frequency of 22.5 Hz, the melt inside a slab liquid sump generates algebraic superposition conditions for the generation conditions for two three-phase harmonic currents of different frequencies but of equal intensity. For a mixture of pulses, a unidirectional (clockwise) traveling magnetic field can be generated, pulsating with a frequency of 5 Hz.

The current in the inductor winding is about 275~315A when supplied with a voltage of 12~14V at a frequency of 20 and 25Hz.

As an alloy, a high-strength aluminum alloy such as 7075 with a chemical composition containing 5.5% Al, 2.5% Zn, 1.6% Mg, 0.2% Cu, and 0.2% Cr and with the addition of 0.1% by weight or less titanium diboride is used. It was used. The alloy was melted in a 700 kg colored resistance crucible, and before casting, residual gas was removed by blow melting argon gas for 20 minutes using a GBF rotary impeller type device at a flow rate of 10 to 15 l/min. .

A slab with dimensions of 350*150 mm and a length of 1.8 m was cast while supplying cooling water to the mold and secondary cooling area at a drawing speed of 62 mm/min, 150 liters/min, and a melt temperature of 710-720°C.

Figure 7a is a diagram showing the microstructure of a 350*150mm slab of conventional 7075 alloy without applying unidirectional pulse EMS of 5 Hz, and Figure 7b is a diagram showing the microstructure of 350*150 mm slab of 7075 alloy according to the present invention to which unidirectional pulse EMS of 5 Hz was applied. *Drawing showing the microstructure of a 150mm slab.

As shown in Figure 7a, the microstructure of the DC cast slab is severely damaged by micropores at both the surface, center, and central part. Up to 5 mm from the surface, a pronounced columnar inhomogeneous microstructure of the resin with an average size of up to 160 μm is found. At the same time, the microstructure, extending deep into the slab by 10 mm from the surface and up to 45 mm, shows a strong heterogeneity of the resin-spherical hybrid type with an average grain size of up to 150 μm. In addition, the structure of the central part of the slab also contains fine pores with severe heterogeneity in fine particles of 80-125㎛.

Meanwhile, as shown in Figure 7b, when a pulsed magnetic field of 5 Hz is applied unidirectionally, identical to the DС casting conditions up to 5 mm from the surface, it exhibits a hybrid uniform dimension microstructure with a grain size of up to 125 μm. Additionally, in contrast to DC conditions at 10 mm from the surface slab, remarkable comminution and uniformity of compact spherical fine particles with a particle size of 80 to 90 μm can be confirmed. In particular, the micropores of the base were almost eliminated throughout the entire cross section of the slab, and in the central part, there were no spherical micropores with a particle size of 80 to 90 μm, showing a more uniform microstructure.

Although embodiments of the present invention have been described above with reference to the attached drawings, those skilled in the art will understand that the present invention can be implemented in other specific forms without changing its technical idea or essential features. You will be able to understand it. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims (9)

A mold (4) containing liquid metal;
a horizontal casting table (1) disposed horizontally above the mold (4) and covering the mold (4);
an injection groove (2) installed on the upper part of the horizontal casting table (1) and extending long to supply liquid metal;
a supply nozzle (3) extending downward from the bottom of the injection groove (2) to supply the liquid metal to the mold (4);
a liquid sump (5) disposed from the horizontal casting table (1) toward the inside of the mold (4); and
An electromagnetic wave control device for continuous slab casting of aluminum alloy, comprising a pair of inductors (10, 7) respectively disposed on both sides of the liquid sump (5). According to paragraph 1,
a lubrication device that supplies lubricant to the cavity of the mold (4); and
Electromagnetic wave control device for continuous slab casting of aluminum alloy, further comprising a water cooling device for cooling the mold (4). The method of claim 1, wherein the pair of inductors (10, 7)
Electromagnetic wave control device for continuous slab casting of aluminum alloy, generating a unidirectional traveling pulsating alternating magnetic field for unidirectional electromagnetic stirring of the liquid metal. The method of claim 3, wherein the single-phase current of the unidirectional pulsating alternating magnetic field is generated by the following equation,

Where Uc is a constant amplitude of carrier frequency oscillation, M is the modulation ratio (M≤1), ωm and ωc are the modulation frequency and carrier frequency, respectively, and ϕm and ϕC are the initial phase shift for the modulation frequency and the initial phase for the carrier frequency, respectively. Convenient, electromagnetic wave control device for continuous slab casting of aluminum alloy. The method of claim 3, wherein the three-phase current of the unidirectional pulsating alternating magnetic field is generated by the following equation,

Wherein Uc is a constant amplitude of carrier frequency oscillation, M is the modulation ratio, ωm and ωc are the modulation frequency and carrier frequency, respectively, and ϕm is the initial phase shift with respect to the modulation frequency. Electromagnetic wave control device for continuous slab casting of aluminum alloy. The method of claim 1, wherein the pair of inductors (10, 7)
Electromagnetic wave control device for continuous slab casting of aluminum alloy, generating a reversible pulsating alternating magnetic field for reversible electromagnetic agitation of the liquid metal. The method of claim 6, wherein the three-phase current of the reversible pulsating alternating magnetic field is generated by the following equation,

Wherein Uc is a constant amplitude of carrier frequency oscillation, M is the modulation ratio, ωm and ωc are the modulation frequency and carrier frequency, respectively, ϕm is the initial phase shift with respect to the modulation frequency, and ϕC is the initial phase shift with respect to the carrier frequency of the aluminum alloy. Electromagnetic wave control device for continuous slab casting. The method of claim 1, wherein the pair of inductors (10, 7)
An electromagnetic wave control device for continuous slab casting of aluminum alloy, comprising a magnetic core in the form of a stator with multi-poles, and windings installed on the multi-poles. The method of claim 8, wherein the pair of inductors (10, 7)
An electromagnetic wave control device for continuous slab casting of aluminum alloy that has a plurality of winding sections in which each winding is mixed and installed alternately at a predetermined step, through which control and phase shift change are possible by carrier frequency or amplitude.