JP2011515225A - Modulated electromagnetic stirring of metals in the advanced stage of solidification - Google Patents

Abstract

A method and apparatus for electromagnetic stirring of molten metal at an advanced stage of solidification is disclosed. This method and apparatus can be used, for example, in continuous casting of steel billets and blooms. At least a first stirrer and a second stirrer are provided to create a first rotating magnetic field and a second rotating magnetic field of different frequencies about the axis of the molten metal being solidified. These agitators are placed around the molten metal sufficiently close to each other so that the respective magnetic fields overlap to create a modulated magnetic field. The magnetic field of each stirrer may have either a common rotation direction or an opposite rotation direction. The modulated agitation created by these magnetic fields creates oscillating primary and secondary flows in the bulk of the melt, and therefore in the region where the temperature of the melt at its central axis is below the liquidus level, and thus A material is produced that produces turbulence and is at least 10% substantially solidified. The turbulence created by this agitation method disrupts the formation of the crystalline structure in the bulk of the melt and mixes the melt enriched in the central region with the bulk volume, which is associated with the casting product. Provides improved solidification structure and overall internal quality.
[Selection] Figure 1

Description

  The present invention relates to electromagnetic stirring, and more particularly to electromagnetic stirring of liquid metal when the liquid metal solidifies. The present invention may be used in continuous casting of steel, alloys or other molten metal, and in other solidification processes of these materials.

  Electromagnetic stirring (EMS) is widely used in the manufacture of continuous cast steel billets, blooms, etc., the casting of different alloys, and the casting and processing of other liquid metals. Typically, alternating current is supplied to an induction coil that surrounds the melt. The alternating current excites a continuously rotating alternating electromagnetic field, which stirs the metal, such as during the production of steel billets and blooms by continuous casting. For example, the AC field may stir the molten metal in the continuous casting mold at the initial stage of solidification.

  Agitation by the rotation of the melt in the mold creates turbulence and shear forces at the solid-liquid interface. This results in dendritic fracture at the solidification front and the formation of an equiaxed solidified structure, which is the most important purpose of agitation in the mold.

  EMS may be used for the agitation of the later or advanced solidification stage of the unsolidified portion of the continuously cast strand below the casting mold.

  However, conventional stirring by rotation is not effective at the stage where solidification of the molten metal has progressed. The reason is that the turbulence created by agitation by rotation is essentially limited to the solid-liquid interface.

  In an effort to improve the effectiveness of stirring by rotation, Japanese Patent Application Publication Nos. 52-4495 and 53-6932, and Kojima et al., Application of Advanced Mild Stirring to a Bloom Caster (The Latest Kosmostir-Magnetogyr Process Technique) describes intermittent and alternating stirring. Intermittent stirring is realized by supplying current intermittently to excite the stirring coil. Alternating agitation is created by generating a magnetic field that alternates its direction of rotation. However, it has been found that the effectiveness of intermittent and alternating stirring is limited. The reason is that such agitation does not create large turbulence in the melt beyond the solid-liquid interface. In addition, the total stirring time available for continuous casting billet and bloom stirring is limited by a 10 to 40 second period, which depends on the cross-sectional size of the cast product and the associated casting speed. . This relatively short period will limit both the duration and the number of intermittent or alternating stirring cycles. The alternating stirring can also be performed without a pause.

  Other methods of EMS rely on magnetic field modulation provided by using a programmable power supply to provide currents of varying frequency and / or intensity. Such an EMS method is described, for example, in US Pat. No. 4,852,632. As disclosed therein, this method is more “gentle” due to the slowly changing stirring flow direction to avoid or reduce the formation of negative segregation at the stirring pool boundary in the continuous casting bloom. May create “stirring”.

  A similar method of magnetic field modulation is described in (Ref. H. Branover et al., The U.S. Patent Application No. US2007 / 0157996A1, J. Pal et al., The German Patent DE 102004017443). These modulation methods have been found to be effective with a modulation period of about 10 seconds, which also limits their usefulness in the continuous casting of billets and blooms.

  Accordingly, there is a need for new EMS methods and apparatus that generate greater turbulence.

JP-A 52-004495 JP-A-53-006932 U.S. Pat. No. 4,852,632 US Patent Application Publication No. US2007 / 0157996 German Patent No. 102004017443

Kojima et al., Application of Advanced Mild Stirring to a Bloom Caster (The Latest Kosmostir-Magnetogyr Process Technique)

  According to the present invention, there is provided an EMS method and apparatus for generating a larger turbulent flow in a molten metal volume to be solidified. In particular, the applied magnetic field is formed by juxtaposing and modulating at least two independent fields of different frequencies, creating a turbulent velocity EMS. The method and apparatus are particularly suitable for agitation at advanced stages of solidification.

  According to an aspect of the present invention, a method for electromagnetic stirring of a molten metal material is provided. The method includes providing at least two agitators for creating independent rotating magnetic fields about an axis extending through the molten material. At least the first stirrer and the second stirrer of the at least two stirrers create independent first and second rotating magnetic fields having different angular frequencies. These agitators are placed around the molten metal material sufficiently close to each other so that independent rotating magnetic fields overlap to create a modulated magnetic field, and this magnetic field is along the central axis of the molten metal material. Creating a turbulent flow of the molten metal material in the transition region of the molten metal material having a temperature below the liquidus, in which the molten metal material is at least about 10% substantially solidified Mixed with.

  According to another aspect of the invention, a casting apparatus is provided. The casting apparatus includes: a mold for casting molten metal; a first stirrer disposed downstream of the mold and creating a first rotating magnetic field about an axis extending through the molten metal; A second stirrer disposed downstream of the first stirrer to create a second rotating magnetic field; at least one for creating the first and second magnetic fields at different rotational frequencies; And a first stirrer and a second stirrer are disposed in close proximity to each other such that the first rotating magnetic field and the second rotating magnetic field create a modulated magnetic field. Creates a turbulent flow of the molten metal material in the region between the first stirrer and the second stirrer.

  According to another aspect of the present invention, a method for electromagnetic stirring of molten metal is provided. The method comprises a first stirrer for creating a first rotating magnetic field that rotates at an angular frequency ω1 about an axis extending through the melt; a second rotating magnetic field that rotates at an angular frequency ω2. A second agitator is provided to produce The first stirrer and the second stirrer are provided with a frequency (ω1-ω2) in the molten metal, in the region between the first stirrer and the second stirrer, the first and second rotating magnetic fields. Arranged sufficiently close together to create a magnetic force having a frequency component, (ω1-ω2) is small enough to allow the magnetic force to overcome the inertia of the melt.

  According to yet another aspect of the invention, a method for electromagnetic stirring of molten metal material is provided. The method includes providing a first stirrer for creating a first rotating magnetic field about an axis extending through the molten material; a second rotating magnetic field having a frequency of rotation different from the first rotating magnetic field A first stirrer and a second stirrer, the first rotating magnetic field and the second rotating magnetic field overlap between the first stirrer and the second stirrer. Placed around the molten metal material, sufficiently close to each other, to create a modulated magnetic field, within the transition region of the molten metal material that has a temperature below the liquidus along the axis And creating a turbulent flow of the molten metal material in which the molten metal material is mixed with the molten metal material that is at least about 10% substantially solidified.

  Other aspects and features of the present invention will become apparent to those skilled in the art from the following description of specific embodiments of the invention with reference to the accompanying drawings. These figures show embodiments of the present invention only as examples.

FIG. 1 is a schematic cross-sectional view of an EMS apparatus of a continuous casting machine according to an example of an embodiment of the present invention. FIG. 2 is a schematic cross section of an example of the stirrer of the EMS apparatus of FIG. FIG. 3 is a simplified perspective view of the agitator of FIG. FIG. 4 is a schematic solidification profile showing the solid fraction isolines in the liquid-solid transition zone (“Massy Zone”) of the portion of the cast strand formed by the caster of FIG. It is. FIG. 5 is a graph of an example axial profile of magnetic flux density produced by two adjacent agitators of the EMS device of FIG. FIG. 6 is a graph of the modulated magnetic force resulting from the overlap of two magnetic field examples in the same rotational direction. FIG. 7 is a graph of the low frequency component of the magnetic force resulting from the force filtering of FIG. 6 due to melt inertia. FIG. 8 is a graph of the angular velocity produced by modulated agitation resulting from the overlap of two magnetic fields in the same rotational direction in an example melt (eg, of mercury). FIG. 9 is a graph of the axial profile of the angular stirring speed produced by the different stirring modes in the molten metal example. FIG. 10 is a graph of an example of the angular velocity created by the modulated reverse rotating agitation in the example melt. FIG. 11 is a graph of a stirring speed profile at a location along the central axis of an example of a molten steel. FIG. 12 is a schematic view of the location of the molten metal in which the axial stirring speed and turbulent viscosity in FIG. 11 are determined by three-dimensional numerical simulation. FIG. 13 is a graph of example turbulent viscosities at different locations on the central axis of the stirring pool created by the modulated reverse rotational stirring. FIG. 14 is a graph of examples of turbulent viscosities at different locations on the central axis of the stirring pool, created by conventional one-way stirring.

  FIG. 1 is a schematic cross-sectional view of a continuous casting machine 10 including an EMS system 12 according to an example embodiment of the present invention. The casting machine 10 includes a tundish 14 from which molten metal, such as liquid steel, is injected into a casting mold 18 through a submerged entry nozzle 20. A cast strand 12 having an outer shell surrounding the molten metal 41 is formed in the mold 18. The cast strand 12 exits from the bottom of the mold 18.

  The example EMS system 12 typically includes at least one electromagnetic stirrer 24 disposed around the mold 18. The agitator 24 can be placed in a mold housing or it can be sealed in a housing (not shown) that surrounds the mold. As will become apparent later, the stirrer 24 is arranged to induce a stirring motion in the melt inside the mold 18 at an early stage of solidification. In the embodiment represented here, a single stirrer 24 is arranged around the mold 18 and causes stirring by rotation of the melt in the mold 18. The agitator 24 may be replaced with a plurality (eg, two) of electromagnetic agitators disposed around the mold 18.

  Additional at least two electromagnetic stirrers 26, 28 are disposed around the cast strand 12 at selected locations downstream of the mold 18 (described in detail below). Again, the agitators 26, 28 are typically sealed in a housing (not shown) and placed together in this housing.

  At a location remote from the mold 18 and downstream thereof, the solidification of the cast strand 12 proceeds, resulting in an increase in shell thickness, during which the central core of the cast strand 12 is shown in FIGS. As shown, it is left in a substantially uncoagulated state. The temperature of the melt 41 in the cast strand 12 gradually decreases with time and distance from the mold 18, and at some point the temperature at the centerline of the cast strand 12 is the specific melt being cast. Lower than the liquidus temperature for the material. This point on the centerline of the cast strand 12 is indicated by reference numeral 48 in FIG.

  When the temperature of the molten metal 41 is lowered to below the liquidus temperature, a solid phase of both shapes, a free floating crystal and a network in which the crystals are combined, is formed over the entire volume of the molten metal 41. Start to be. The mixed state portion of the liquid and solid phase is widely referred to as the “Massy zone” of the melt 41 and is shown as zone 30 in the figure. The region of the cast strand 12 that includes the solidified shell and the melty 41 massey zone is referred to as the transition region of the cast strand 12. The formation of a crystal network in zone 30 typically results in shrinkage cavities, cracks, elemental macrosegregation, etc. in the cast product, thereby affecting the quality of the cast product.

  An example of liquid and solid distribution along the length of the cast strand 12 is shown in FIG. This graph shows the solid ratio of the molten metal 41 and is graphed with respect to the thickness of the shell. Massy zone 30 occupies the area between the liquid and the solid. As shown here, the proportion of solids increases along the radial direction as the distance from the central axis of the cast strand 41 increases, and increases in the length direction of the cast strand 12 as the distance from the meniscus of the molten metal 41 increases. Increase along.

  Conveniently, turbulence in the transition region will disrupt the formation of the crystal network, break the dendrites into smaller pieces, and homogenize the melt 41 in the massey zone 30, at least in part. Resulting in a denser, less porous and more uniform solidification structure, thereby improving the quality of the cast product. However, while conventional rotational agitation essentially creates turbulent flow at the solid-liquid interface, it had only a minor effect on mixing throughout the melt 41.

  As such, in the embodiment represented here, a further first stirrer 26 and a second stirrer 28 are arranged along the cast strand 12 in a position corresponding to the massey zone 30. . In particular, the agitators 26, 28 may be arranged to disrupt crystals and crystal structures within the massy zone 30. For this purpose, the stirrers 26, 28 may be arranged at specific positions along the length of the cast strand 12, where the temperature along the central axis of the molten metal 41 is below the liquidus temperature. And 10 to 20 volume percent of the molten metal 41 is substantially solidified, and at the same time, the remaining 80 to 90 volume percent remains in a substantially liquid state, in which substantially solidified material is present. It is mixed. The volume percentage of the massy zone 30 and its spatial distribution in a particular solidifying melt 41 along the strand 12 may be determined by numerical simulation using a computer using a solidification model. good. Such simulation may be combined in some examples with real-time measurement of key casting variables, such as casting speed, primary and secondary cooling strength, etc. They may be fed into the data to improve model accuracy.

  In the depicted embodiment, only two agitators 26, 28 are shown downstream of the mold 14. However, those skilled in the art will appreciate that more than two agitators can be placed downstream of the mold 14 to disrupt the crystals and crystal structure in the massy zone 30. .

  FIG. 2 shows an enlarged schematic view of the cast strand 12 of FIG. 1 in the vicinity of the first and second stirrers 26,28. As shown here, the agitators 26 and 28 are disposed adjacent to each other around the zone 30 along a longitudinal extent of the cast strand 12 at a predetermined distance “L”. Also good. This distance “L” may be, for example, in the decimeter to meter range, for example, about 0.2 m.

  Each of the agitators 24, 26, 28 may be formed, for example, as an inductor, and includes a stator 32 made of a ferromagnetic material or similar material, as shown in FIG. Is excited by a plurality of winding coils 36 wound around. One or more controlled AC power sources (not shown) may be coupled together by windings 36 to supply current to each winding 36. The current supplied to the winding 36 is multiphase, and the currents supplied to the opposite magnetic poles 34 are in the same phase. The supplied current provides a rotating magnetic field in the volume surrounded by the stator 32.

  Conveniently, the exact structure of the agitators 24, 26, and 28 may be the same or different, and each agitator 24, 26, 28 has its own number of pole pairs, windings. , Size, and power. For example, the agitators 26 and 28 may each have three magnetic pole pairs; alternatively, one may have two magnetic pole pairs and the other have three magnetic pole pairs. is there. Other combinations will be apparent to those skilled in the art. Similarly, the longitudinal extent along the cast strand 12 of each of the agitators 26 and 28 may be different from the other longitudinal extent.

  During operation, the stirrer 24 is energized to stir the molten material in the mold 18 (FIG. 1). The agitators 26 and 28 are also excited to generate rotating magnetic fields each having a common axis of magnetic field rotation. The axis of this magnetic field rotation may be parallel, but does not necessarily coincide with the central axis of the cast strand 12. In particular, each of the windings 36 (FIG. 3) of the agitators 26, 28 is an alternating multiphase, single frequency current supplied from one or more independent power sources (not shown). And is controlled by the controller. This electrical arrangement provides independent control of the magnetic field produced by each respective stirrer 26, 28 and thus provides an independent rotating magnetic field. As a result, the magnetic flux densities produced by the first stirrer 26 and the second stirrer 28 may be the same or different. The difference in magnetic flux density may be a constant or may change with time.

  The direction of rotation of the magnetic fields of the agitators 26 and 28 may be coincident as indicated by arrows “B” and “C” in FIG. 2, or alternatively by arrows “A” and “C”. As shown, they may be in opposite directions. The direction of rotation and angular velocity may be selected by the operator.

  The alternating current supplied to the windings 36 of the stirrers 26, 28 generates a rotating electromagnetic field, which has a frequency in the range of about 1 to about 60 Hz, depending on the application of the stirring. . For many common applications, such as steel billets and bloom continuous casting, frequencies between 5 and 30 Hz may be used. In the illustrated embodiment, the field frequency of one stirrer 26 differs from the frequency of the other stirrer 28 by a predetermined value to create a modulated magnetic field. The frequency difference may change with time, or may be a constant independent of time. The range of frequency variation may be between about 0.1 and 3.0 Hz (ie less than 3.0 Hz).

  The modulated magnetic field resulting from the overlap of the original magnetic field produced by each adjacent stirrer is dominant, but adjacent stirrers 26, indicated by “L” in FIG. There is no restriction within the region between 28. The magnetic force created by these overlapping magnetic fields is the result of the interaction between the magnetic fields of the stirrers 26 and 28 and the currents induced in the melt 41 by these magnetic fields, respectively. This magnetic force will have multiple terms and may create turbulence in the melt 41 in the massey zone 30.

  In particular, the magnetic flux density and current induced in the melt 41 are largely confined between adjacent inductors, and as a result of their respective magnetic field overlap shown in FIG. Vector sum of contributions of The magnetic force created in the molten metal 41 is a vector product of the total magnetic flux density and the total current density. Since the magnetic flux and current density are composed of two contributions from two adjacent stirrers 26, 28, the magnetic force will have multiple terms.

  Basically, this force will have two constant terms (ie DC terms) and two double frequency terms. In addition, there are two time-varying terms that include the sum of the initial angular frequencies of the magnetic field (ω1 + ω2) and two time-varying terms that include the difference in angular frequency, ie, (ω1-ω2). Due to the inertial effect of the melt 41, the double frequency and frequency sum components of the magnetic force or torque typically have only a minor effect on the flow in the melt 41. The magnetic force or torque of the component having the frequency (ω1-ω2) changes sufficiently slowly with respect to time, and overcomes the inertia of the molten metal 41.

  Since the current induced in the molten metal 41 is proportional to the relatively large angular frequency of the initial magnetic field, the strength of the magnetic force and torque also increases. At the same time, the low frequency time variation resulting from the frequency difference between the two magnetic fields will create a large intensity vibration of the modulated force, which in turn will cause a variation in angular velocity. . The effect of modulation on the stirring speed increases as the modulation frequency decreases.

  As can be seen, if more than two stirrers are placed around the massey zone 30, the overlap of multiple independent rotating fields of the multiple stirrers may create the desired turbulence.

  The magnetic force has a high frequency component and a low frequency component, but due to the inertia of the molten metal 41 (also called inertia filtering by the molten metal 41), only the low frequency component typically affects the molten metal 41. It will be. 6 and 7 show the magnetic force resulting from the overlap of two magnetic fields in the same rotational direction. As shown here, the intensity per unit of the modulated magnetic force oscillates between 0 and 4, where “1” is the intensity of the steady state force without modulation, It is an intensity related to one of the magnetic fields.

  After the high frequency component of the modulated force is filtered by the inertia of the molten metal 41, the low frequency force variation is, for example, the average force intensity as shown in the example in FIG. Vibrates within a range of +/− 20 percent. Agitation created by this force may be characterized by large vibrations of the primary and secondary flows. An example of the angular velocity vibration of stirring is shown in FIG.

  FIG. 9 is a graph showing the angular stirring speed produced by the different modes of stirring. The velocity profile indicated by “A” is created by agitation with two identical magnetic fields in the same rotational direction. The velocity profile indicated by “B” is created under the same stirring conditions as in “A”, except that the frequency of each magnetic field differs by 0.5 Hz. That is, f1 = 18.0 Hz and f2 = 17.5 Hz. The velocity profile shown here is created by two magnetic fields with opposite directions of rotation. The frequencies of the rotating magnetic fields in the opposite directions are f1 = 18.0 Hz and f2 = 17.5 Hz. The arrow below the speed profile “C” indicates the reverse rotational agitation motion in the agitation pool.

  As shown in FIG. 9, when a reverse rotation field is applied, the angular velocity of the reverse rotation stirring indicated by “C” is the same frequency magnetic field (“A”). May be substantially reduced compared to the rate of unidirectional stirring flow created by a different frequency (as indicated by “B”). Convenient, reduced agitation speed has no negative effect on agitation. The reason is that the kinetic energy of the flow is converted into turbulent flow. The reverse rotating stirring flow impinges in the region between the stirrers 26 and 28, resulting in a steep slope of angular velocity caused by a decrease in speed in one direction, as shown in FIG. Leading to a similar rapid recovery in the opposite direction of speed. This oscillating nature of angular and axial / radial velocity components is an indicator of turbulence strength.

  FIG. 10 further illustrates an example of angular velocity vibration measured in a mercury column using induced reverse rotation agitation. The large changes in vibration result from the combined action of the modulated magnetic field and the opposite direction of the stirring flow, which are created by the reverse rotating magnetic field of the adjacent stirrers 26,28.

  FIG. 11 shows the speed of vibration in the direction of the central axis obtained by three-dimensional numerical simulation in an example of a molten steel. The speed profile shown here corresponds to a location in the molten metal 41 shown in FIG. Large velocity oscillations are known to be indicative of large turbulence induced by EMS in the melt 41. The strength of turbulence may be qualitatively characterized by turbulent viscosity.

Figures 13 and 14 further show examples of turbulent velocity viscosities at different locations in the agitation pool. FIG. 13 shows the turbulent viscosity at the center of the stirring pool at each location in FIG. As shown in FIG. 13, the strongest turbulence occurs at an intermediate distance between adjacent inductors (location III in FIG. 12). For comparison, the turbulence intensity at the same location of the stirring pool created by conventional one-way rotary stirring is shown in FIG. As shown here, in the melt example, the turbulence created by the reverse rotating agitation is up to 5 times greater than ² Ns / m ² and often more than 2.5 Ns / m ^2. It has a peak characterized by a large turbulent viscosity.

  As an alternative to applying an electromagnetic field in the same rotational direction, a rotating magnetic field in the opposite direction may be created by the agitators 26 and 28. The reverse rotating magnetic field created by the adjacent agitators 26, 28 will cause a reverse rotating flow in the melt 41 in the zone 30, which flows adjacent to the agitators 26, 28. Collide in the space between. As a result of this flow collision, a steep slope of decreasing angular velocity in one direction of rotation will result in a similar gradient due to the increasing speed in the opposite direction of rotation. In addition, the angular velocity will also exhibit large vibrations.

  Both of these primary flow properties, namely velocity gradients and vibrations, contribute to the generation of a strong and circulating flow in the axial and radial planes. By the numerical simulation, the existence of the flow in the molten metal 41, particularly the existence of the flow at the position in FIG. 12, is confirmed. High strength turbulence and shear stress develops in the volume of the melt 41, especially in the direction and radial direction along the axis of the cast strand 12, especially in the region between the adjacent stirrers 26,28. become.

  Further turbulence in the region between the stirrers 26, 28 may result from electromagnetic forces created by the overlapping of opposite rotating magnetic fields of different frequencies. As described above, the low-frequency oscillating magnetic force from the magnetic field modulation will cause perturbations in the molten metal 41, and if those frequencies are the natural frequency of the molten metal (for example, the effect of the parametric resonance of the molten metal). These perturbations may be particularly important.

  In addition, other modulation parameters, such as variations in current intensity and phase angle, can further enhance the modulated force compared to the unmodulated, time-averaged magnetic force. Yes, as a result, increasing its effect on turbulence strength and improvement in solidified tissue. Adjacent stirrers 26, 28 provide a strongly modulated magnetic force, such a magnetic force being created by a conventionally designed device (ie, inductor and power supply), overlapping in either the common or opposite rotational direction. Resulting from a magnetic field.

  Conveniently, the increased turbulence in the melt 41 results in effective collapse of the crystal network and mixing of the crystal with the central region enriched in the solute of the melt and the remainder of the bulk. It will be. As a result, the solidification structure and overall quality of the cast product is improved.

  As can be readily appreciated, although the EMS system 12 is represented as including two EMS agitators 26 and 28 arranged to create a modulated magnetic field, such a field is an overlapping rotating magnetic field. It is also possible to produce using three or more stirrers that generate

  As now becomes apparent, the modulated electromagnetic agitation of the example embodiment of the present invention allows the size and shape of the cast product to create a rotating flow in the solidifying melt. It may be used in most castings and casting processes. For example, in the case of static casting, a modulated electromagnetic stirring system initially creates a unidirectional magnetic field, and therefore a unidirectional rotating vortex flow is created in the early solidification stage. Well. At a predetermined time, the agitation system may be switched to the operation in the reverse rotation agitation mode, and turbulence may be generated when solidification has progressed. Similarly, some fluid casting processes can benefit from such modulated agitation.

  Of course, the above-described embodiments are intended for illustrative purposes and are not intended to limit the scope of the invention in any way. The embodiments described herein for carrying out the invention may be subject to many changes with regard to part placement, details and order of operation. The present invention is intended to encompass within its scope all such modifications as defined by the following claims.

According to an aspect of the present invention, a method for electromagnetic stirring of a molten metal material is provided. The method includes providing at least two agitators for creating independent rotating magnetic fields about an axis extending through the molten material. Here, at least the first stirrer and the second stirrer of the at least two stirrers create independent rotating magnetic fields having different angular frequencies. Here, these agitators are placed around the molten metal material in close proximity to each other so that independent rotating magnetic fields overlap to create a modulated magnetic field, which is the center of the molten metal material. Create a turbulent flow of molten metal material in the region of the molten metal material having a temperature below the liquidus along the axis, wherein the molten metal material is substantially solidified by at least about 10% by volume . Mixed with molten metal material.

According to another aspect of the invention, a casting apparatus is provided. The casting apparatus includes: a mold for casting molten metal; a first stirrer disposed downstream of the mold and creating a first rotating magnetic field about an axis extending through the molten metal; A second stirrer disposed downstream of the first stirrer to create a second rotating magnetic field; at least one for creating the first and second magnetic fields at different rotational frequencies; And a first stirrer and a second stirrer are disposed in close proximity to each other such that the first rotating magnetic field and the second rotating magnetic field create a modulated magnetic field. However, in order to disrupt the formation of the crystal network in the region, a turbulent flow of molten metal material is created in the region between the first stirrer and the second stirrer.

According to another aspect of the present invention, a method for electromagnetic stirring of molten metal is provided. The method comprises a first stirrer for creating a first rotating magnetic field that rotates at an angular frequency ω1 about an axis extending through the melt; a second rotating magnetic field that rotates at an angular frequency ω2. A second agitator is provided to produce Here, in the first stirrer and the second stirrer, the first and second rotating magnetic fields have a frequency (ω1-ω2) in the molten metal in a region between the first stirrer and the second stirrer. ) Placed sufficiently close to each other to create a magnetic force having a frequency component provided, and (ω1-ω2) is small enough to allow the magnetic force to overcome the inertia of the melt.

According to yet another aspect of the invention, a method for electromagnetic stirring of molten metal material is provided. The method includes providing a first stirrer for creating a first rotating magnetic field about an axis extending through the molten material; a second rotating magnetic field having a frequency of rotation different from the first rotating magnetic field A first stirrer and a second stirrer, the first rotating magnetic field and the second rotating magnetic field overlap between the first stirrer and the second stirrer. Molten metal, placed around the molten metal material, close enough to each other to create a modulated magnetic field, the magnetic field having a temperature below the liquidus along the central axis of the molten metal material Within the transition region of the material, a turbulent flow of the molten metal material is created, in which the molten metal material is mixed with the molten metal material that is at least about 10% substantially solidified.
According to yet another aspect of the invention, a method for electromagnetic stirring of molten metal material is provided. The method comprises a first stirrer for creating a first rotating magnetic field about an axis extending through the molten material; one or more having a frequency of rotation different from the first rotating magnetic field Providing at least one further stirrer for generating a further rotating magnetic field of the second stirrer; the first stirrer and the further stirrer are produced by an adjacent stirrer of the first stirrer and at least one further stirrer Of the molten metal material that is placed around the molten metal material so that the rotating magnetic field overlaps to create a modulated magnetic field and that has a temperature below the liquidus along the center of the molten metal material. A turbulent flow of molten metal material is created in the transition region, thereby disrupting the formation of a crystal network in the region.
According to yet another aspect of the present invention, there is provided a method of electromagnetic stirring of a molten metal having at least two stirrers: a first frequency around an axis extending through the molten metal at a frequency f1 of about 60 Hz or less. A first stirrer is provided for creating a rotating magnetic field; a second stirrer is provided for creating a second rotating magnetic field with a frequency f2 that differs from the frequency f1 by 3 Hz or less; a first stirrer and a second stirrer The stirrer of the first and second rotating magnetic fields is disposed between the first stirrer and the second stirrer in order to disrupt the formation of crystals between the first stirrer and the second stirrer. Are arranged around the molten metal sufficiently close to each other so that they overlap.

Claims (29)

A method of electromagnetic stirring of molten metal material comprising:
Providing at least two agitators for creating independent rotating magnetic fields about an axis extending through the molten material;
At least a first stirrer and a second stirrer of the at least two stirrers create independent first and second rotating magnetic fields having different angular frequencies;
The stirrer is placed around the molten metal material sufficiently close to each other so that the independent rotating magnetic fields overlap to create a modulated magnetic field, which magnetic field is the central axis of the molten metal material Creating a turbulent flow of the molten metal material in a transition region of the molten metal material having a temperature below the liquidus along; and
The molten metal material is mixed with at least about 10% of the substantially solidified molten metal material;
A method characterized by. The method of claim 1 having the following characteristics:
The first rotating magnetic field and the second rotating magnetic field rotate in opposite directions. The method of claim 1 having the following characteristics:
The first rotating magnetic field and the second rotating magnetic field rotate in the same direction. The method of claim 1 having the following characteristics:
The longitudinal extent of the first stirrer of the at least two stirrers around the molten metal material is the longitudinal extent of the second stirrer of the at least two stirrers around the molten metal material Is different. The method of claim 2 having the following characteristics:
The difference in frequency between the first rotating magnetic field and the second rotating magnetic field is less than about 3 Hz. The method of claim 2 having the following characteristics:
The difference in frequency between the first rotating magnetic field and the second rotating magnetic field changes with time. The method of claim 1 having the following characteristics:
Each of the agitators has at least two magnetic pole pairs, and each magnetic pole pair is excited by a current from at least one multilayer current source. The method of claim 2 having the following characteristics:
The molten metal material is in the cast strand downstream of the casting mold. The method of claim 1 having the following characteristics:
Each of the first and second agitators of the at least two agitators creates a different magnetic flux density in the molten metal material. The method of claim 1 having the following characteristics:
The magnetic flux density created in the molten metal material <created> by the at least one of the first and second of the at least two stirrers varies with time. The method of claim 1 having the following characteristics:
The turbulent flow has a turbulent viscosity with a peak higher than ² Ns / m ² . The method of claim 1 having the following characteristics:
The region has a substantially liquid molten metal material and a crystalline material surrounded by a solid shell. The method of claim 1 having the following characteristics:
The turbulence disrupts the formation of a crystal network within the region. The method of claim 1 having the following characteristics:
The method further comprises injecting molten metal material through the mold upstream of the region and providing a further stirrer around the mold to generate a rotating magnetic field in the mold. A casting apparatus having a mold for casting molten metal comprising:
A first stirrer for creating a first rotating magnetic field about an axis disposed downstream of the mold and extending through the molten metal;
A second stirrer disposed downstream of the first stirrer to create a second rotating magnetic field;
At least one power source for creating the first and second magnetic fields at different rotational frequencies;
Have
The first stirrer and the second stirrer are disposed in close proximity to each other such that the first rotating magnetic field and the second rotating magnetic field create a modulated magnetic field, the magnetic field being A casting apparatus characterized by creating turbulent flow in the molten metal material in the region between the stirrer and the second stirrer. The apparatus of claim 15 having the following characteristics:
The first rotating magnetic field and the second rotating magnetic field are created to rotate in opposite directions by the at least one power source. The apparatus of claim 15 having the following characteristics:
The first rotating magnetic field and the second rotating magnetic field are created to rotate in the same direction by the at least one power source. The apparatus of claim 15 having the following characteristics:
The longitudinal extent of the first stirrer around the molten metal is different from the longitudinal extent of the second stirrer around the molten metal. The apparatus of claim 16 having the following characteristics:
The difference in frequency between the first rotating magnetic field and the second rotating magnetic field is less than about 3 Hz. The apparatus of claim 16 having the following characteristics:
The difference in frequency between the first rotating magnetic field and the second rotating magnetic field changes with time. The apparatus of claim 15 having the following characteristics:
Each of the first and second stirrers has at least two magnetic pole pairs, and each magnetic pole pair is excited by a current from the at least one power source. The apparatus of claim 15 having the following characteristics:
Each of the first stirrer and the second stirrer creates a different magnetic flux density in the molten metal. The apparatus of claim 15 having the following characteristics:
The magnetic flux density created in the molten metal by at least one of the first stirrer and the second stirrer varies with time. The apparatus of claim 15 having the following characteristics:
The turbulent flow has a turbulent viscosity with a peak higher than ² Ns / m ² . The apparatus of claim 15 having the following characteristics:
The region comprises a substantially liquid molten metal and a crystalline material surrounded by a solid shell. The apparatus of claim 15 having the following characteristics:
The turbulence disrupts the formation of a crystal network within the region. The apparatus of claim 15 having the following characteristics:
A further stirrer is further provided around the mold for generating a rotating magnetic field in the mold. A method of electromagnetic stirring of molten metal:
Providing a first stirrer for creating a first rotating magnetic field that rotates at an angular frequency ω1 about an axis extending through the melt;
Providing a second agitator for creating a second rotating magnetic field rotating at an angular frequency ω2;
In the first stirrer and the second stirrer, the first and second rotating magnetic fields have a frequency (ω1-ω2) in the molten metal in a region between the first and second stirrers. ) Placed close enough to each other to create a magnetic force having a component with
(Ω1-ω2) is small enough to allow the magnetic force to overcome the inertia of the melt,
A method characterized by. A method of electromagnetic stirring of molten metal material comprising:
Providing a first stirrer for creating a first rotating magnetic field about an axis extending through the molten material;
Providing a second stirrer for creating a second rotating magnetic field having a different frequency of rotation than the first rotating magnetic field;
The first stirrer and the second stirrer are configured such that the first rotating magnetic field and the second rotating magnetic field overlap between the first stirrer and the second stirrer to create a modulated magnetic field. In the transition region of the molten metal material disposed around the molten metal material in close proximity to each other and having a temperature below the liquidus along the center of the molten metal material. Creating a turbulent flow of molten metal material; and
The molten metal material is mixed with at least about 10% of the substantially solidified molten metal material;
A method characterized by.

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