COLD CRUCIBLE FOR THIN SLAB CONTINUOUS CASTING OF LIGHT METAL WITH HIGH-PURITY

Info

Publication number: 20170291217
Type: Application
Filed: Aug 25, 2015
Publication Date: Oct 12, 2017
Inventors: Byung-Moon MOON (Seoul), Je-Sik SHIN (Bucheon), Hoi-Soo YOO (Incheon)
Application Number: 15/517,302

Abstract

The present invention provides a cold crucible for continuously casting high-purity light metal thin slab, which can control the electromagnetic force applied from the inner wall surface of a cold crucible to the surface of molten metal in order to change the shape of the cold crucible to various shapes during electromagnetic casting, while stabilizing the molten metal inside the cold crucible and casting an ingot having uniform particles.

Description

Description

TECHNICAL FIELD

The present disclosure relates to a cold crucible used during electromagnetic casting, and, in more detail, to a cold crucible for electromagnetic continuous casting for manufacturing a material having poor workability to form an ingot having a shape similar to that of a panel, using a relatively small amount of energy. In particular, the cold crucible proposed in the present disclosure provides an effective technique for manufacturing an ingot of a light metal required to have high purity.

BACKGROUND ART

Electromagnetic casting (EMC) is the most common process used in melting and casting metals using electromagnetic fields. In the technique described above, alternating current (AC) electricity is applied to a cold crucible to generate changes in magnetic fields, thereby forming an induced current on a surface of a metal to be melted. A metal may be melted due to Joule heating generated by the induced current. Such a direct melting method, by electromagnetic induction, may allow a material, such as a metal, to be melted in a short period of time, thereby providing relatively high productivity.

The induced current may interact with a magnetic field to generate electromagnetic force (Lorentz force) in molten metal. Even if a direction of a coil current is changed, the generated electromagnetic force may always be directed toward a center of an interior of a cold crucible, according to Fleming's left-hand rule. Due to a pinch effect, such as electromagnetic pressure, contact between molten metal and an internal wall of a cold crucible may be prevented. Thus, with molten metal not in contact with a cold crucible, molten metal may be melted, and casting without a mold is possible. Contamination of a material is suppressed, quality of an ingot is improved, and a mold is neither consumed nor replaced, thereby reducing equipment costs and improving productivity.

However, in terms of EMC through electromagnetic induction, in a case in which a distance between an internal wall surface of a cold crucible and a center thereof is not uniform, electromagnetic force is not applied to a surface of molten metal in a uniform manner, thereby causing the molten metal to be unstable . In a case in which the molten metal is unstable, the molten metal may slop and come into contact with an internal wall of a cold crucible, and the manufacturing of ingots having a desired shape may be difficult.

However, in order to manufacture ingots having various forms, cold crucibles are required to be altered to have various forms besides a circular shape. In order to facilitate molding, such as forging, rolling, or the like, of a material having poor workability, cold crucibles are required to be changed to have various forms similar to a flat form, so that ingots similar to a panel shape can be manufactured from the time at which ingots are cast using EMC. Thus, the distance between the internal wall surface of cold crucibles and the center thereof may not be maintained to be uniform.

Thin ingots may be cast using a nozzle having a flat shape, while the form of the cold crucibles is not changed, and cold crucibles are maintained in a conventional form during EMC of the related art. However, due to problems such as the excessive consumption of energy required in order to maintain a greater volume of molten metal than is necessary in a molten state, the need for a design of a nozzle that is excellent in terms of form, material and the like, while having durability, excessive costs may be incurred. Thus, cold crucibles for electromagnetic casting having a form the same as that of an ingot are still required.

In detail, in a case in which ingots of light metals having high purity are manufactured using a continuous electromagnetic casting method, a large amount of effort is required to prevent contact between molten metal and the internal wall surface of cold crucibles. For example, in the case of continuous electromagnetic casting of steel having a relatively greater specific gravity and not demanding high purity, a melting operation is performed in a separate furnace, and only a solidification process is performed in a cold crucible for electromagnetic casting. In this case, the function of cold crucibles for electromagnetic casting is used to prevent defects, such as oscillation marks, on the surface of ingots, from being generated, by allowing for light contact between a cold crucible and molten metal. However, in order to produce ingots of a light metal having high purity, melting and solidification of a raw material may be performed simultaneously in a cold crucible for electromagnetic casting. Ina case in which a molten metal pool is in contact with the wall surface of a water-cooling cold crucible, a continuous melting operation is impossible. In particular, since light metals have relatively low specific heat and heat capacity, and ease of the solidification thereof is facilitated, a continuous casting process maybe more difficult. Ina case in which the supply of excessive power allows continuous melting to occur, an inflow of impurities into the molten metal from a cold crucible may not be prevented, so that an ingot of a metal having high purity may not be manufactured. Thus, in order to manufacture light metals continuously to have a flat, thin, slab shape, having high purity without included impurities, specially designed cold crucibles for electromagnetic casting are required.

DISCLOSURE Technical Problem

An aspect of the present disclosure may provide a cold crucible for electromagnetic casting, controlling electromagnetic force applied to a surface of molten metal from an internal wall surface of a cold crucible and, in detail, controlling electromagnetic force applied to a surface of molten metal formed using a light metal, in order to stabilize the molten metal in the cold crucible and to cast an ingot having a uniform-size particle, as well as to change a form of the cold crucible into various forms during electromagnetic casting.

Technical Solution

According to an aspect of the present disclosure, a cold crucible for thin slab continuous casting of light metal with high-purity, in which an alternating current (AC) electricity is applied to a coil wound around an outer circumferential surface of a cold crucible; an edge of the cold crucible is formed of a plurality of segments, in order for a portion of the AC electricity, which is applied, to be applied to the cold crucible; and a plurality of slits are disposed between the plurality of segments. In the cold crucible for thin slab continuous casting of light metal with high-purity, a horizontal, cross-sectional shape of the cold crucible is non-circular; and a ratio (d2/d1) of a width d2 of a segment in a central side portion of the cold crucible disposed closest to a center of the cold crucible, to a width dl of a segment in an end portion of the cold crucible, disposed farthest from the center of the cold crucible, based on the center of the cold crucible, toward which electromagnetic force applied to a surface of molten metal in the cold crucible from an internal wall surface of the cold crucible is directed, is 1.5 or more to 2.0 or less.

A width of the plurality of segments may be 20 mm or more to 50 mm or less.

A ratio (d2/T) of the width d2 of the segment in the central side portion of the cold crucible, to a thickness T of the plurality of segments, may be less than or equal to 1.8.

The molten metal may be formed using a light metal having a specific gravity of less than or equal to 5.

The horizontal, cross-sectional shape of the cold crucible may be oval, rectangular, or polygonal.

The horizontal, cross-sectional shape of the cold crucible maintains a uniform shape from an uppermost portion to a lowermost portion of the cold crucible, thereby minimizing an amount of the molten metal remaining in a molten state in the cold crucible.

Advantageous Effects

According to an aspect of the present disclosure, electromagnetic force applied to a surface of molten metal from an internal wall surface of a cold crucible may be controlled by designating a ratio of a width of a segment in an end portion of a cold crucible to that of a segment in a central side portion thereof as a critical ratio, so that, during EMC, even though a form of the cold crucible may be changed to have various forms, and the form of the cold crucible may be the same as that of the molten metal. In addition, since the molten metal may be stabilized, the molten metal in the cold crucible may be prevented from slopping, thereby removing a risk of the molten metal coming into contact with an internal wall surface of the cold crucible. Furthermore, since the minimum amount of molten metal may be formed, energy may be saved. In detail, a flat, thin slab may be continuously manufactured to have a high purity, without impurity contamination, by using molten metal of a light metal.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic horizontal, cross-sectional view of a cold crucible in which an interval between slits of a cold crucible is maintained to be uniform in the same manner as in the related art and having a non-circular, horizontal cross section.

FIG. 2 is a schematic horizontal, cross-sectional view of a cold crucible having a non-circular, horizontal cross section, illustrating an actual form of molten metal in a case in which the interval between slits of a cold crucible is maintained to be uniform in the same manner as in the related art, and only the shape of a horizontal cross section is non-circular.

FIG. 3 is an image illustrating a form of molten metal generated by actual electromagnetic casting of titanium (Ti) while the interval between slits of a cold crucible is maintained in a uniform manner, and only the shape of a horizontal cross section of a cold crucible is non-circular.

FIG. 4 is a schematic view of a portion of a cold crucible including a relatively wide segment and a relatively narrow segment.

FIG. 5 is a graph illustrating a value of electromagnetic force measured in a horizontal direction in Experimental Examples 1 to 4 of the present disclosure.

FIG. 6 is a schematic horizontal, cross-sectional view of a cold crucible in Experimental Example 5 of the present disclosure.

FIG. 7 is a graph illustrating a value of electromagnetic force measured in the horizontal direction in Experimental Example 5 of the present disclosure.

FIG. 8 is a graph illustrating a relation between a ratio of a perimeter of a segment of a cold crucible to a cross-sectional area of a segment thereof and electromagnetic pressure generated on a surface of the molten metal.

FIG. 9 is a graph illustrating a relation between a width of a segment of a cold crucible and a ratio of a perimeter of a segment thereof to a cross-sectional area of a segment.

FIG. 10 is a schematic horizontal, cross-sectional view of a portion of a cold crucible, illustrating a concave portion on a molten metal surface generated by a difference in electromagnetic pressure between a central portion of a segment and a slit portion of a cold crucible.

FIG. 11 is a graph illustrating the difference in electromagnetic pressure between the central portion of a segment and the slit portion according to a change in a width of a segment of a cold crucible, as well as a change in Laplace pressure generated according to a curvature of a concave molten metal surface by the difference in electromagnetic pressure.

FIG. 12 is a schematic horizontal, cross-sectional view of a cold crucible setting a ratio of a width of a segment in an end portion of a cold crucible to that of a segment of a central side portion thereof as a critical ratio and having a non-circular, horizontal cross section.

BEST MODE FOR INVENTION

Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The disclosure may, however, be exemplified in many different forms and should not be construed as being limited to the specific embodiments set forth herein, and those skilled in the art and understanding the present disclosure can easily accomplish retrogressive inventions or other embodiments included in the scope of the present disclosure by the addition, modification, and removal of components within the same scope, but those are construed as being included in the scope of the present disclosure. Like reference numerals will be used to designate like components having similar functions throughout the drawings within the scope of the present disclosure.

All terms, including technical and scientific terms, to be used hereinafter have the same meaning as that commonly understood by those skilled in the art. Terms defined in advance are additionally construed as having a meaning conforming to relevant technical documents and the contents presently disclosed and are not construed as an ideal or official meaning, as long as they are not defined as such.

FIG. 1 illustrates a structure of a horizontal cross section of a cold crucible 1 maintaining an interval between slits (a width of a segment) 3 in a uniform manner, as in related art, and having a non-circular, horizontal cross section (in more detail, a form of a long side and a short side having a predetermined curvature).

Here, in order to apply AC electricity to the cold crucible 1, AC electricity is applied thereto in such a manner that a coil is wound around an outer surface of the cold crucible 1. A magnetic field penetrates through a slit by the AC electricity, thereby directly applying a primary induced current to molten metal 4. In addition, a secondary induced current is formed in each segment 6. AC electricity is also applied to a surface of the molten metal 4 by AC electricity applied to the segment 6, thereby forming electromagnetic force between the segment 6 and the molten metal 4.

In FIG. 1, a slit 7, formed using an insulating material, is formed between segments 6 in a manner the same as a cold crucible for electromagnetic casting of the related art, and a segment perimeter portion is formed using a conductor, such as copper (Cu), which is electrified. In addition, a cooling device 5 using water or the like is designed to be disposed in a segment surrounded by a conductor.

However, in a case in which all structures are maintained in a manner the same as that of a related art cold crucible, and only a shape of a horizontal cross section of a cold crucible is formed to be non-circular, molten metal assumes a form for maintaining linear balance, in order to minimize surface energy of the molten metal moving in a manner the same as a fluid in the cold crucible, and to minimize internal energy due to a volume of a fluid of molten metal. Plateau-Rayleigh instability is a theory describing the case above. In a case in which molten metal having an elongated form is present, as illustrated in FIG. 2, if a pressure Pc (Formula 1) in a concave central portion is higher than a pressure Pe (Formula 2) in a convex edge portion, molten metal in a central portion flows spontaneously toward the edge portion. Plateau-Rayleigh instability reaches the highest level in a case in which a ratio (l/d) of a length of molten metal to a diameter thereof is 4.5. In general, Plateau-Rayleigh instability is known to be generated in a case in which the ratio thereof is in a range of 3.5 to 7. (For reference, the ratio is applied to a considerable number of thin slab shapes.) In Formula 1 and Formula 2, P₀, P_c, P_e, γ, Rm, 1, and δ refer to external pressure of molten metal (a constant), pressure in the concave central portion thereof, pressure in the convex edge portion thereof, surface energy thereof, an average radius thereof, a length, and an amplitude of a radius, respectively.

$\begin{matrix} P_{c} = P_{0} + γ (\frac{1}{R_{m} - δ} - \frac{{δ (2 π)}^{2}}{l^{2}}) & [Formula 1] \\ P_{e} = P_{0} + γ (\frac{1}{R_{m} + δ} + \frac{{δ (2 π)}^{2}}{l^{2}}) & [Formula 2] \end{matrix}$

Furthermore, a small difference in distribution of an induced current generated and flowing in molten metal causes a difference in electromagnetic force applied to molten metal, so that a form of molten metal may be changed. Since a change in the form of molten metal allows a difference in distribution of the induced current to be greater, the change tends to make the form of the molten metal different from that of the cold crucible. In more detail, the induced current generated in molten metal has a relatively high current density in a long side, rather than a corner or a short side, in a rectangular conductor, due to characteristics in which the induced current is intensively concentrated on a surface of molten metal by a skin effect, and the induced current flows to minimize electrical resistance. The small difference in distribution of a current causes the difference in electromagnetic force to be greater; the difference in electromagnetic force makes the change in the form of molten metal greater; and the change in the form of molten metal makes a difference in distribution of a current greater. Ultimately, the molten metal results in having a polyhedral form significantly different from that of an interior of the cold crucible. Thus, the form of molten metal in the cold crucible having a non-circular, horizontal cross section is not formed to be the same as that of the cold crucible in a manner the same as the molten metal 4 of FIG. 1, but has a form similar to that of a janggu, a double-headed Korean drum with a narrow waist section in the middle, in a manner the same as molten metal of FIG. 2. Thus, the molten metal is unstable, and an ingot having a desired form and quality may not be manufactured.

FIG. 3 illustrates a case in which in a case in which Ti, a type of light metal, is continuously cast, while an interval between slits of a cold crucible is maintained in a uniform manner, and only a shape of a horizontal cross section thereof is non-circular, a form of molten metal is changed to have a form of a janggu, and the molten metal comes into contact with a cold wall surface of the cold crucible, thereby freezing the molten metal and stopping an operation of casting.

EXPERIMENTAL EXAMPLE

Hereinafter, the present disclosure will be described in detail through a specific experimental example, but the scope of rights of the present disclosure is not limited by the experimental example.

Example of Analytic Design Based on Theory

An analytic process of designing a cold crucible using theories related to electromagnetics and electricity, in order to implement the present disclosure, is described as follows. FIG. 4 is a schematic view illustrating a relatively wide segment and a relatively narrow segment of a cold crucible. In FIG. 4, an induced current 13 applied to a small segment 11 and an induced current 14 applied to a relatively large segment 12 by a coil wound around an outer surface of the cold crucible are expressed using Formula 3.

=V/R [Formula 3]

In Formula 3, I is an induced current applied to a segment, while Vis induced electromotive force applied to a segment. Since resistance R is proportional to a distance which an electric current flows, while induced electromotive force V is proportional to a cross-sectional area through which magnetic flux penetrates, based on Formula 3, a primary induced current I in the small segment 11 is expressed using Formula 4

I=V/RD²/4D=D/4, [Formula 4]

while, based on Formula 3, a primary induced current I in the large segment 12 is also expressed using Formula 5

I=V/R=ND²/2D(1+N)=ND/2(1+N). [Formula 5]

TABLE 1 Path (length) and cross-sectional area of primary induced current flowing into each horizontal cross section of cold crucible Cross Section of Cold Crucible Small Segment 31 Large Segment 32 Path 4D 2D (1 + N) Area D² ND²

Thus, in molten metal of a conductive metal in the cold crucible, a secondary induced current is generated by the primary induced current generated in the cold crucible.

In the meantime, since electromagnetic force F, generated on a surface of molten metal, is proportional to J×B, the electromagnetic force F may be expressed as below:

FJ×B [Formula 6]

In Formula 6, J is a primary current applied by the cold crucible, while B is magnetic flux density generated by the primary current.

In the meantime, according to a change in a level of an induced current generated in the small segment 11 and the large segment 12, based on Formula 4 and Formula 5, strength of a magnetic field generated on the surface of molten metal in the cold crucible varies, as expressed in Formula 7, below.

B=−L·dI/dt [Formula 7]

In Formula 7, Lisa constant value, dI is an amount of change of an electric current, and dt is a change in time.

In other words, a relative ratio of a magnetic field strength between a magnetic field strength B(α), generated at a position α of FIG. 4 and a magnetic field strength B(β), generated at a position β of FIG. 3, based on Formula 7, may be expressed using Formula 8, below, based on Formula 4 and Formula 5.

B(β)/B(α)ND/2(1+N)/D/4=2N/1+N [Formula 8]

Thus, in a case in which Formula 8 is inserted into Formula 6 to calculate a relative ratio between the electromagnetic force at the position α and that at the position β, J applied to molten metal in the cold crucible are equal, so that the relative ratio between electromagnetic force at the position α and that at the position β may be 2N/(1+N), equal to a relative ratio between a magnetic field at the position α and that at the position β. In other words, in a case in which N is a number greater than 1, those skilled in the art could expect that electromagnetic force generated in the large segment 12 would be relatively greater than that generated in the small segment 11 of the cold crucible. Thus, the inventors may control electromagnetic force applied in a direction from the surface of molten metal toward the central portion in the cold crucible in such a manner that an interval between slits, that is, a width of a segment, is controlled to be a non-uniform interval, in order to solve problems in which molten metal is unstable in a non-circular cold crucible, and the ingot having a desired form and quality cannot be manufactured. In other words, in order to prevent a slab form from being changed into a janggu form during continuous casting of a light metal having a form of a thin slab, the interval between slits disposed adjacent to the central side portion of the cold crucible should be wider than that in an end portion.

Example of Experimental Design Based on Numerical Analysis

Electromagnetic force according to the actual number of slits and an interval of segments of a cold crucible has been measured.

Table 2 provides conditions related to the cold crucible of Experimental Examples 1 to 5.

TABLE 2 Diameter Form of Cross Interval of (inch) Section No. of Slits Segments Experimental 12 Circular 16 Uniform Example 1 Experimental 12 Circular 32 Uniform Example 2 Experimental 12 Circular 48 Uniform Example 3 Experimental 12 Circular 64 Uniform Example 4 Experimental 9 Circular 24 Non-uniform Example 5

1. Melting material: Ti and Ti alloy

2. Cold crucible form: FIG. 2

3. Cold crucible material: Cu

4. Melting method: non-contact type electromagnetic induction melting of cold crucible

5. Condition of melting operation

1) Input power of induction coil: 10 to 75 kW

2) Frequency: less than or equal to 15 kHz

3) Condition in melting chamber: maintaining an argon (Ar) gas atmosphere (Ar purging) at one atmospheric pressure after vacuum decompression (10⁻³torr or less)

4) Melting time: 5 to 10 minutes

6. Thickness of segment: 20 mm

FIG. 5 illustrates a value of electromagnetic force measured in a horizontal direction in Experimental Examples 1 to 4, while FIG. 7 illustrates a value of electromagnetic force measured in the horizontal direction in Experimental Example 5.

With reference to FIG. 5, Experimental Example 1, in which the number of slits is 16, has a relatively low level of electromagnetic force, while Experimental Example 4, in which the number of slits is 64, has a relatively high level of electromagnetic force. With reference to FIGS. 6 and 7, it can be confirmed that a portion in which the number of slits is relatively high has a relatively high level of electromagnetic force, while a portion in which the number of slits is relatively low has a relatively low level of electromagnetic force, which is a tendency opposite to that of an analytic design performed based on a theory. Table 3 provides the number of slits, a width D of a segment, a cross-sectional area A of a segment, a perimeter L of a segment, electromagnetic pressure, a difference in electromagnetic pressure between a central portion of a segment and a slit portion, and the like, in Experimental Examples 1 to 4.

TABLE 3 Difference in Electromagnetic Pressure Ratio of Between Perimeter Central Cross- to Cross- Portion of sectional Perimeter sectional Width of Electromagnetic Segment and Area of of Area, No. of Segment, Pressure Slit Portion Segment, Segment, L/A Slits D (mm) (N/m²) (N/m²) A (mm²) L (mm) (mm⁻¹) Experimental 16 60 2,060 288 1,320 164 0.125 Example 1 Experimental 32 30 3,070 145 658 104 0.158 Example 2 Experimental 48 20 3,460 76 439 84 0.191 Example 3 Experimental 64 15 3,810 42 329 74 0.225 Example 4

FIG. 8 is a graph illustrating a relation between a ratio of a perimeter of a segment to a cross-sectional area (L/A) and electromagnetic pressure, based on Table 3. It can be confirmed from FIG. 8 that, in a case in which the number of slits is increased, thereby narrowing a width of a segment (in the case of the experiment, the number of slits is increased to 30 or more, and the width of a segment is 30 mm or less), electromagnetic pressure is proportional to the ratio of the perimeter of a segment to the cross-sectional area (L/A). In other words, it can be understood that, in a case in which the number of slits is sufficiently increased, an effect that a magnetic field generated by an electric current, applied to an external induced coil, directly has on molten metal through a slit is stronger than an effect that a magnetic field generated by a primary induced current, generated in a segment of the cold crucible, has on molten metal. A direction of the magnetic field generated in the external induced coil is opposed to that of the magnetic field generated in a segment of the cold crucible. Thus, as a ratio of a cross-sectional area of a segment to a perimeter becomes higher, the electromagnetic pressure generated in molten metal tends to be relatively reduced. In other words, as illustrated in FIG. 8, in a case in which the number of slits is increased, thereby narrowing the width of the segment, it has been determined that the electromagnetic pressure applied to a surface of molten metal in the cold crucible is proportional to the ratio (L/A) of the perimeter of a segment to the cross-sectional area. In a case in which the relation described above is used, in order for a designer to design a desired difference (ΔP′) in electromagnetic pressure between an end portion of the cold crucible and a central side portion thereof, a difference in the ratio (Δ(L/A)′) of the perimeter of a segment to the cross-sectional area in the central side portion and the end portion of the cold crucible may be set. FIG. 9 illustrates the ratio (L/A) of the perimeter of a segment to the cross-sectional area, according to the width of a segment D.

In a case in which Ti, a type of a light metal, is, in actuality, continuously cast to have a thin slab shape of 20 mm in width, if instability corresponding to about 12.5% of a width of the cold crucible is generated (d=20 mm, 1=7d, δ=d/8), pressure P_cin a concave central side portion of molten metal is higher, by about 410 N/m², than pressure P_ein a convex end portion, based on Formula 1 and Formula 2. Thus, in a case in which an interval between slits in the end portion of the cold crucible is smaller than an interval between slits in the central side portion, thereby causing the difference in electromagnetic pressure to be greater than 410 N/m², the molten metal may initially have a flat shape, conforming to a cavity in the cold crucible. In a case in which a condition satisfying the case described above is expressed, in FIG. 9, if the width of the segment in the central side portion of the cold crucible is 30 mm to 50 mm, the width of a segment in the end portion should be about 20 mm to about 25 mm. In other words, in a case in which the width of a segment in the end portion of the cold crucible, disposed farthest from the central side portion of the cold crucible, is referred to as ‘d1’, and the width of a segment in the central side portion of the cold crucible, disposed closest to a center of the cold crucible, is referred to as ‘d2’, if a ratio (d2/d1) of d2 to d1 is set as a critical ratio (1.5 or more to 2.0 or less), molten metal may be prevented from being changed to have a form of a janggu due to instability caused by surface energy and a curvature of molten metal.

Thus, in order to solve a problem in which molten metal is unstable in the cold crucible having a non-circular shape, and an ingot having a desired form and quality cannot be manufactured, the inventor sets a ratio of the width of a segment in the end portion of the cold crucible to that of a segment of the central side portion thereof as the critical ratio, thereby controlling electromagnetic force applied in a direction from the surface of molten metal toward the center thereof in the cold crucible. In a case in which electromagnetic force applied in a direction from the surface of molten metal toward the center thereof in the cold crucible is controlled, anisotropy of a form may be caused when molten metal is formed in the cold crucible. Thus, a form of molten metal may be properly controlled.

In general, in a case in which the width of the segment of the cold crucible is significantly wide, efficiency of a process is relatively low, due to a magnetic field blocking effect, and distribution of electromagnetic pressure in the cold crucible is non-uniform, so that the width of the segment of the cold crucible may be less than or equal to 50 mm. In addition, since, in a case in which the width of the segment is significantly narrow, proper strength of the segment as a member is difficult to be secured, and, further, a cooling channel is difficult to be formed in a segment, the cold crucible is difficult to be manufactured at an affordable price. Thus, in general, the width of the segment may be greater than or equal to 20 mm.

In a case in which an interval between slits is relatively wide, as illustrated in FIG. 10, electromagnetic pressure of a slit portion is significantly higher than that in a central portion of a segment, so that molten metal may be concave. Once molten metal becomes concave, an induced current is intensively concentrated in a concave portion thereof, and electromagnetic pressure is increased, so that a tendency for molten metal to be concave is increased. Thus, during design of the cold crucible, a method of preventing the tendency should be considered. In a case in which molten metal is locally concave as illustrated in FIG. 10, Laplace pressure is generated in a direction in which a surface of molten metal is returned to an initial state, due to a curvature and surface tension of the surface of the molten metal, as illustrated in Formula 9.

$\begin{matrix} Δ P = γ (\frac{1}{r_{1}} + \frac{1}{r_{2}}) = \frac{γ}{(D / 2)}, & [Formula 9] \end{matrix}$

where γ refers to surface energy of molten metal, while r1 and r2 refer to principal radii of curvature of a surface of molten metal.

FIG. 11 illustrates Laplace pressure (a restitution force) according to a curvature of a surface of molten metal and a difference in electromagnetic pressure between a central portion of a segment and a slit portion (power to lead to molten metal being concave) according to a width change of a segment, in the case of Ti molten metal. From FIG. 11, it can be determined that, in a case in which the width of a segment is designed to be less than or equal to 35 mm, the restitution force of molten metal may be maintained to be greater than the power that leads to the molten metal becoming concave. In other words, since the width of a segment of the cold crucible is 20 mm, a width D of all segments of the cold crucible should be designed to be less than or equal to 1.8 T (T being a thickness of a segment).

FIG. 12 illustrates a structure of a cross section of a cold crucible 21, setting a ratio of a width of a segment in an end portion of the cold crucible to a width of a segment in a central side portion thereof as a critical ratio and having a non-circular, horizontal cross section, according to characteristics of the present disclosure. Only an interval 23 of slits between the cold crucible is formed in a non-uniform manner. In terms of the remainder of components of the cold crucible, a slit 27, formed using an insulating material, is formed between segments so that an induced current is formed in each segment in a manner the same as a cold crucible for electromagnetic casting of the related art, while a segment perimeter portion 26 is formed using a conductor, such as Cu, which is electrified. In addition, a cooling device 25, using water or the like, is designed to be disposed in a segment surrounded by a conductor. In this case, a width 22 of all slits is uniform. A slit 27 may be formed to have a relatively wide interval in a central side portion of the cold crucible disposed closest to a center of the cold crucible, while a slit 27 is formed to have a relatively small interval in an end portion of the cold crucible disposed farthest from the center thereof, based on the center of the cold crucible, where electromagnetic force is directed in a direction from an internal wall surface of the cold crucible toward a surface of the molten metal 24. In more detail, a ratio of a width of a segment in the central side portion of the cold crucible (segment 26a, disposed closest to the center of the cold crucible) to a width of a segment in the end portion of the cold crucible (segment 26b, disposed farthest from the center of the cold crucible) should be designed to be 1.5 or more to 2.0 or less, and a width of each segment should be designed to be less than or equal to 1.8 times a thickness of a segment. Thus, transformation of a surface of molten metal, caused by instability generated in a case in which a surface of molten metal has a form of an elongated thin slab, and transformation of the surface of molten metal, caused by a difference in electromagnetic pressure between the central portion of a segment and a slit portion, may be effectively prevented.

Thus, according to characteristics of the present disclosure, electromagnetic force applied to the surface of molten metal formed using a light metal such as Ti may be controlled to maintain molten metal to have the same form as that of the cold crucible, while molten metal may be manufactured to have a shape similar to a panel shape, thereby facilitating molding, such as forging, rolling, and the like.

The cold crucible 21 of FIG. 12 neither requires a condition in which an interval of slits is formed to be symmetrical, nor requires the interval of the slits to be formed to be gradually reduced or increased. However, the ratio of the width of a segment in the end portion of the cold crucible to the width of a segment in the central side portion thereof should be set as the critical ratio, so that electromagnetic force applied in a direction from an interior of the cold crucible toward a surface of molten metal may be controlled. In this case, a width of the remainder of segments, except for a segment in the end portion of the cold crucible and a segment in the central side portion thereof, may have an arbitrary value within the critical ratio (including a boundary value). The molten metal 24 having a form the same as that of the cold crucible may be formed by controlling electromagnetic force, and the molten metal 24 may be stabilized.

Since a cold crucible for electromagnetic casting has a non-circular, horizontal, cross-sectional shape, an ingot having a desired form may be manufactured from the time of EMC. In particular, in a case in which the ingot is manufactured to have a form similar to a panel shape, molding, such as forging, rolling, and the like, of a material having poor workability may be facilitated. A non-circular shape thereof described above may include one shape among an ellipse, a rectangle, and a polygon.

As described in the Background Art of the present disclosure, the ingot having a form similar to a panel shape may be manufactured in such a manner that a form of the cold crucible is not changed, and only a nozzle in a lower portion of the cold crucible is flattened. However, in a design described above, a greater volume of molten metal is formed than is necessary, so that an amount of molten metal included in the cold crucible is increased. Thus, a relatively large amount of energy to melt the molten metal is required, in order for the cold crucible to melt and store a relatively large amount of molten metal. In addition, since molten metal is required to float, in order not to be in contact with the lower portion of the cold crucible, larger amounts of energy may be required.

In a case in which a relatively narrow nozzle is formed in the lower portion of the cold crucible, and the volume of molten metal is formed to be greater than that of the nozzle in the cold crucible, even if the form of the cold crucible is changed to have any form, a phenomenon in which molten metal is formed to be different from the form of the cold crucible, or molten metal is unstable, does not occur.

Thus, the present disclosure may be valuably used in the cold crucible to maintain a uniform form of molten metal from an uppermost portion to a lowermost portion of the cold crucible, in order to save energy needed to melt and float molten metal in the cold crucible.

While exemplary embodiments have been shown and described above, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope of the present invention as defined by the appended claims.

Claims

1. A cold crucible for thin slab continuous casting of light metal with high-purity, wherein an alternating current (AC) electricity is applied to a coil wound around an outer circumferential surface of a cold crucible; an edge of the cold crucible is formed of a plurality of segments in order for a portion of the AC electricity, which is applied, to be applied to the cold crucible; and a plurality of slits are disposed between the plurality of segments, the cold crucible for thin slab continuous casting of light metal with high-purity characterized in that a horizontal, cross-sectional shape of the cold crucible is non-circular, based on a center of the cold crucible, toward which electromagnetic force applied to a surface of molten metal in the cold crucible from an internal wall surface of the cold crucible is directed, the plurality of slits are formed to have a relatively wide interval on a surface of the cold crucible disposed relatively close to the center of the cold crucible, rather than on a surface of the cold crucible disposed relatively distant from the center of the cold crucible; and a ratio (d2/d1) of a slit interval d2 on an internal side of the cold crucible, on a surface of the cold crucible disposed closest to the center of the cold crucible, to a slit interval dl on the internal side of the cold crucible on a surface of the cold crucible disposed farthest from the center of the cold crucible, is 1.5 or more to 2.0 or less.

2. The cold crucible for thin slab continuous casting of light metal with high-purity of claim 1, wherein a width of the plurality of segments is 20 mm or more to 50 mm or less.

3. The cold crucible for thin slab continuous casting of light metal with high-purity of claim 1, wherein a ratio (d2/T) of the width d2 of the segment in the central side portion of the cold crucible to a thickness T of the plurality of segments is less than or equal to 1.8.

4. The cold crucible for thin slab continuous casting of light metal with high-purity of claim 1, wherein the molten metal is formed using a light metal having a specific gravity of less than or equal to 5.

5. The cold crucible for thin slab continuous casting of light metal with high-purity of claim 1, wherein the horizontal, cross-sectional shape of the cold crucible is an ellipse, a rectangle, or a polygon.

6. The cold crucible for thin slab continuous casting of light metal with high-purity of claim 1, wherein the horizontal, cross-sectional shape of the cold crucible maintains a uniform shape from an uppermost portion to a lowermost portion of the cold crucible, thereby minimizing an amount of the molten metal remaining in a molten state in the cold crucible.