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United States Patent Application 20180133785
Kind Code A1
BAE; Il-Sin ;   et al. May 17, 2018

SOLIDIFICATION APPARATUS

Abstract

Provided is a solidification apparatus that makes variations in the surface height of a molten metal relatively non-affected by the proceeding speed of a metal sheet to significantly increase the proceeding speed of the metal sheet and to increase the productivity of the metal sheet. The solidification apparatus for producing a metal sheet by solidifying molten metal includes rows of rollers arranged in a proceeding direction of the metal sheet, wherein when the rows of rollers are grouped into a plurality of sections, an average of roller pitches each being a distance between centers of rollers adjacent in the proceeding direction of the metal sheet is smaller in a given section than in a preceding section.


Inventors: BAE; Il-Sin; (Gwangyang-si, KR) ; LEE; Sang-Hyeon; (Pohang-si, KR) ; KIM; Seong-Yeon; (Gwangyang-si, KR) ; JEONG; Hee-Tae; (Gwangyang-si, KR) ; HAN; Byeong-Ha; (Gwangyang-si, KR) ; HWANG; Jong-Yeon; (Gwangyang-si, KR) ; SHIN; Min-Chul; (Gwangyang-si, KR)
Applicant:
Name City State Country Type

POSCO

Pohang-si

KR
Family ID: 1000003138550
Appl. No.: 15/578974
Filed: June 7, 2016
PCT Filed: June 7, 2016
PCT NO: PCT/KR2016/006000
371 Date: December 1, 2017


Current U.S. Class: 1/1
Current CPC Class: B22D 11/1287 20130101; B22D 11/1282 20130101
International Class: B22D 11/128 20060101 B22D011/128

Foreign Application Data

DateCodeApplication Number
Jun 4, 2015KR10-2015-0079173

Claims



1. A solidification apparatus for producing a metal sheet by solidifying molten metal, the solidification apparatus comprising rows of rollers arranged in a proceeding direction of the metal sheet, wherein when the rows of rollers are grouped into a plurality of sections, an average of roller pitches each being a distance between centers of rollers adjacent in the proceeding direction of the metal sheet is smaller in a given section than in a preceding section.

2. The solidification apparatus of claim 1, wherein the average of roller pitches is smaller in the given section than in a subsequent section.

3. The solidification apparatus of claim 1, wherein each of the sections is a space comprising at least four roller pitches.

4. The solidification apparatus of claim 1, wherein each of the sections is a space comprising rollers arranged within a length of 1 m or greater.

5. The solidification apparatus of claim 1, wherein the sections are physically defined.

6. The solidification apparatus of claim 5, wherein the sections are physically defined on a segment basis.

7. The solidification apparatus of claim 1, wherein each of the sections is a space between a driving roll and a next driving roll.

8. The solidification apparatus of claim 1, wherein a difference between the average of roller pitches in the given section and the average of roller pitches in the preceding section is 10 mm or greater.

9. The solidification apparatus of claim 8, wherein the difference in the average of roller pitches is 20 mm or greater.

10. The solidification apparatus of claim 8, wherein a proceeding speed of the metal sheet is 4 m/min or greater.

11. The solidification apparatus of claim 8, wherein the sections comprise: a horizontal section transferring the metal sheet horizontally; a curved section having a predetermined curvature and located between an exit through which the molten metal is discharged and the horizontal section; and a curvature variation section provided in at least one of a region between the exit and the curved section and a region between the curved section and the horizontal section, the curvature variation section having a different curvature.

12. The solidification apparatus of claim 11, further comprising a vertical section connected to the exit perpendicularly so as to transfer the metal sheet vertically, the vertical section also being connected to the curved section.

13. The solidification apparatus of claim 1, wherein the average of roller pitches in each of the sections is defined by Equation 1 below: Pa(k)=.SIGMA..sub.iP(k,i)/N Equation 1 where N is the number of roller pitches in a given section, k is a section number, and i is a serial number of a roller pitch in a section k.

14. The solidification apparatus of claim 1, wherein the given section having the average of roller pitches smaller than that of the preceding section is within a solidification length in which the metal sheet solidifies, and the solidification length of the metal sheet is defined by Equation 2 below: L = V .times. ( H 2 .times. K ) 2 Equation 2 ##EQU00003## where L is a length in millimeters (mm) required to complete solidification of the metal sheet, V is a proceeding speed of the metal sheet in mm/min, H is the thickness of the metal sheet in mm, and K is a solidification constant ranging from 20 mm/min.sup.1/2 to 30 mm/min.sup.1/2.

15. The solidification apparatus of claim 1, wherein the given section having the average of roller pitches smaller than that of the preceding section is repeated at least twice.
Description



TECHNICAL FIELD

[0001] The present disclosure relates to a solidification apparatus for producing a metal sheet by continuously solidifying molten metal.

BACKGROUND ART

[0002] In general, apparatuses for continuously solidifying molten metal are made up of a mold into which molten metal enters and a plurality of rows of rollers arranged in series on an exit side of the mold. Usually, the plurality of rows of rollers are provided in segment units.

[0003] In addition, molten metal exits the mold in a half solid state in which the molten metal has solidified on the surface thereof but has not yet solidified in the inside thereof, and the inside of the molten metal gradually solidifies as the molten metal passes through the rows of rollers, thereby leaving the solidification apparatus in a fully solidified state.

[0004] At this time, when a metal sheet formed as the molten metal solidifies passes through the rows of rollers, the metal sheet is in a half solid state for a considerable period of time, and thus molten metal remains intact inside the metal sheet. Therefore, a considerably large amount of pressure is applied to the inside of the metal sheet because of a height difference between the inside of the metal sheet and the surface of molten metal contained in the mold, and thus rollers, roller bearings, and roller support structures are designed to support this load.

[0005] In addition, as the metal sheet proceeds downwardly, the pressure caused by the height difference from the surface of molten metal increases, and thus it is common to design lower rollers to have a relatively large diameter. In addition, large-diameter rollers also have a large roller pitch, the distance between the centers of rollers adjacent to each other in the proceeding direction of the metal sheet.

[0006] In addition, outward swelling of the metal sheet caused by the pressure of molten metal present inside the metal sheet is suppressed by rollers making contact with the surface of the metal sheet. Thus, if the roller pitch of the rollers is large, sections of the metal sheet located between the rollers, and thus not making contact with the rollers, are large, and thus the metal sheet swells to some extent.

[0007] That is, referring to FIG. 1, in the process of passing a metal sheet between rollers, swelling slightly occurs in regions of solidified layers of the metal sheet that do not make contact with the rollers.

[0008] Therefore, it is necessary to arrange rollers as closely together as possible to minimize the pitch of the rollers and thus to prevent swelling of solidified layers.

[0009] In addition, when the solidified layers swell, the amount of swelling may periodically vary, and it is considered that this phenomenon causes variations in the surface height of molten metal. In addition, this phenomenon also causes variations in the volume of the half-solidified inside of the metal sheet, and since the metal sheet passes between the rollers in this state, periodic variations occur in the surface height of molten metal contained in the mold.

[0010] It is observed that the period of variations in the surface height of the molten metal closely relates to the pitch of rollers. Although it is experientially known that variations in the surface height of molten metal tend to increase in proportion to the proceeding speed of a metal sheet and the pitch of rollers, the mechanism thereof has not yet been clearly found.

[0011] Meanwhile, if variations in the surface height of molten metal exceed an allowable limit, non-uniform solidification occurs, which has a negative effect on quality. Furthermore, in severe cases, weak portions of solidified layers may be ruptured, and molten metal that has not yet solidified may leak to the outside, thereby causing considerable damage such as suspension of production or damage to production equipment.

[0012] Therefore, in general, work is performed while limiting the proceeding speed of a metal sheet according to an allowable range of variations in the surface height of molten metal. However, this serves as a factor decreasing the productivity of metal sheets.

DISCLOSURE

Technical Problem

[0013] An aspect of the present disclosure may provide a solidification apparatus in which the repeatability of roller pitches is removed, in addition to changing the arrangement of rollers so as to reduce periodic variations in the surface of molten metal and to make variations in the surface height of molten metal relatively non-affected by the proceeding speed of a metal sheet. Therefore, the proceeding speed of metal sheets may be significantly increased, and thus the productivity of metal sheets may be increased.

Technical Solution

[0014] According to an aspect of the present disclosure, a solidification apparatus for producing a metal sheet by solidifying molten metal may include rows of rollers arranged in a proceeding direction of the metal sheet, wherein when the rows of rollers are grouped into a plurality of sections, an average of roller pitches each being a distance between centers of rollers adjacent in the proceeding direction of the metal sheet may be smaller in a given section than in a preceding section.

[0015] In addition, the average of roller pitches may be smaller in the given section than in a subsequent section.

[0016] In addition, each of the sections may be a space including at least four roller pitches.

[0017] In addition, each of the sections may be a space including rollers arranged within a length of 1 m or greater.

[0018] In addition, the sections may be physically defined spaces.

[0019] In addition, the sections may be physically defined on a segment basis.

[0020] In addition, each of the sections may be a space between a driving roll and a next driving roll.

[0021] In addition, a difference between the average of roller pitches in the given section and the average of roller pitches in the preceding section may be 10 mm or greater.

[0022] In addition, the difference in the average of roller pitches may be 20 mm or greater.

[0023] In addition, a proceeding speed of the metal sheet may be 4 m/min or greater.

[0024] The sections may include: a horizontal section transferring the metal sheet horizontally; a curved section having a predetermined curvature and located between an exit of a mold through which the molten metal is discharged and the horizontal section; and a curvature variation section provided in at least one of a region between the exit and the curved section and a region between the curved section and the horizontal section, the curvature variation section having a different curvature.

[0025] In addition, the solidification apparatus may further include a vertical section connected to the exit perpendicularly so as to transfer the metal sheet vertically, the vertical section also being connected to the curved section.

[0026] In addition, the average of roller pitches in each of the sections may be defined by Equation 1 below:

Pa(k)=.SIGMA..sub.iP(k,i)/N Equation 1

[0027] where N is the number of roller pitches in a given section, k is a section number, and i is a serial number of a roller pitch in a section k.

[0028] In addition, the given section having the average of roller pitches smaller than that of the preceding section may be within a solidification length in which the metal sheet solidifies, and the solidification length of the metal sheet may be defined by Equation 2 below:

L = V .times. ( H 2 .times. K ) 2 Equation 2 ##EQU00001##

[0029] where L is a length in millimeters (mm) required to complete solidification of the metal sheet, V is a proceeding speed of the metal sheet in mm/min, H is the thickness of the metal sheet in mm, and K is a solidification constant ranging from 20 mm/min.sup.1/2 to 30 mm/min.sup.1/2.

[0030] In addition, the given section having the average of roller pitches smaller than that of the preceding section may be repeated at least twice.

Advantageous Effects

[0031] According to an embodiment of the present disclosure, the proceeding speed of a metal sheet may have a less influence on variations in the surface height of molten metal contained in a mold, and thus the proceeding speed of the metal sheet may be markedly increased.

DESCRIPTION OF DRAWINGS

[0032] FIG. 1 is a schematic view illustrating a proceeding state of a metal sheet.

[0033] FIG. 2 is a schematic view illustrating a solidification apparatus according to the embodiment of the present disclosure.

[0034] FIGS. 3A to 3C are schematic views illustrating rows of rollers of the solidification apparatus according to the embodiment of the present disclosure.

[0035] FIG. 4 is a graph illustrating the average of roller pitches in each section of the solidification apparatus in inventive examples of the present disclosure in comparison with the average of roller pitches in each section in the related art.

[0036] FIG. 5 is a view illustrating a relationship between the solidification length, rate, and thickness of a metal sheet according to an embodiment of the present disclosure.

[0037] FIG. 6 is a graph showing the average of roller pitches in each section of the solidification apparatus in an inventive example.

BEST MODE

[0038] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. However, the embodiments of the present disclosure may be modified in various forms, and the scope of the present disclosure is not limited to the embodiments. In the drawings, the shapes and dimensions of elements may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or like elements.

[0039] FIG. 2 is a schematic view illustrating a solidification apparatus according to an embodiment of the present disclosure, and FIG. 3 is a schematic view illustrating rows of rollers of the solidification apparatus according to the embodiment of the present disclosure.

[0040] Referring to FIGS. 2 and 3, according to the present embodiment, the solidification apparatus 10 may include a mold 20 configured to produce an initially-solidified molten sheet B by cooling molten metal Y supplied from a tundish 1.

[0041] The mold 20 includes a cooling device therein, and thus molten metal making contact with the mold 20 is cooled from the surface thereof and is discharged from the mold 20 in the form of a metal sheet B with the inside of the metal sheet B being not yet solidified.

[0042] In addition, rows of rollers may be arranged at an exit side of the mold 20 in the proceeding direction of the metal sheet B so as to guide the metal sheet B discharged in a half-solidified state, and the rows of rollers may form a transfer unit 30 in association with a driving unit.

[0043] The transfer unit 30 cools and solidifies the half-solidified metal sheet B and transfers the metal sheet B to a subsequent process.

[0044] In the present embodiment, the transfer unit 30 may be divided into a plurality of sections according to the average of roller pitches of the rows of rollers.

[0045] Here, referring to FIG. 3A, each section may be a space having at least four roller pitches. That is, each section may be defined as being a space including five rollers and at least four roller pitches each being the distance between the centers of rollers. In the present embodiment, roller pitches are a key factor causing variations in the surface height of molten metal, and thus sections may be defined by roller pitches rather than the number of rollers.

[0046] In addition, the average of roller pitches in each section may be expressed by Equation 1 below.

Pa(k)=.SIGMA..sub.iP(k,i)/N Equation 1

[0047] where N is the number of roller pitches in a given section, k is a section number, and i is a serial number of a roller pitch in a section k.

[0048] In the present embodiment, each section is defined as being a space having at least four roller pitches. However, the same roller arrangement is not required in a section opposite and symmetric to the section, or it is not required to define, in the same manner, a section opposite and symmetric to the section. That is, sections may be defined independently of each other.

[0049] In addition, although each section is defined as being a space having at least four roller pitches in the present embodiment, the definition of each section is not limited thereto. For example, sections may be defined according to the length thereof.

[0050] That is, in the present embodiment, each section may be defined as being a space including rollers arranged within a length of 1 m or greater.

[0051] In the present embodiment, if each section has a length less than 1 m, rollers are quite densely arranged in the section, and thus variations in the surface height of molten metal may not easily occur. Furthermore, in the present embodiment, each section may be defined as being a space including rollers arranged along a sufficient length allowed by equipment conditions.

[0052] In addition, each section may be a physically defined space.

[0053] For example, the physically defined space may be a space defined on a segment basis as shown in FIG. 3B. In each segment, a plurality of rollers for guiding the movement of the metal sheet B may be provide, and rows of the rollers may be physically grouped to be, for example, exchanged or replaced on a segment basis.

[0054] In addition, referring to FIG. 3C, the physically defined space may not be a space defined on a segment basis but may be a space between a driving roll and the subsequent driving roll.

[0055] In general, each segment may have one driving roll, for example, in a center region of the segment. In addition, each segment may include a plurality of rows of rollers in addition to the driving roll. Here, the space between a driving roll and the subsequent driving roll may be a space between a driving roll of a segment and a driving roll of the subsequent segment, or may be a space between driving rolls of structures other than segments. In the space, a plurality of rows of rollers may be arranged.

[0056] In rows of rollers grouped into a plurality of sections as described above, the average of roller pitches, each being the distance between the centers of two rollers adjacent to each other in the proceeding direction of the metal sheet may be greater in a given section than in the preceding section or may be the same in both of the sections.

[0057] In this case, as the metal sheet B proceeds along the sections of the rows of rollers, a load caused by the height difference between the surface of molten metal and the metal sheet B increases, and pressure acting on the rows of rollers increases.

[0058] On the other hand, in a given section of the plurality of sections of the present embodiment, the average of roller pitches each being the distance between the centers of two adjacent rollers in the proceeding direction of the metal sheet B may be smaller than the average of roller pitches in the preceding section. That is, when the rows of rollers are grouped into a plurality of sections, the average of roller pitches each being the distance between the centers of two adjacent rollers in the proceeding direction of the metal sheet B may be smaller in a given section than in the preceding section.

[0059] When the average of roller pitches each being the distance between the centers of two adjacent rollers in the proceeding direction of the metal sheet B is smaller in a given section than in the preceding section, the average of roller pitches in the give section may also be smaller than the average of roller pitches in the subsequent section.

[0060] That is, the average of roller pitches may be reversed in a given section, and thus the average of roller pitches in the given section may be smaller than the average of roller pitches in the preceding section and the average of roller pitches in the subsequent section.

[0061] The average of roller pitches in each section may be as shown in the graph of FIG. 4. FIG. 4 is a graph illustrating the average of roller pitches in each section of the solidification apparatus according to inventive examples of the present disclosure in comparison with the average of roller pitches in each section in the related art. In FIG. 4, the x-axis is sections, and the y-axis is an average of roller pitches.

[0062] Referring to FIG. 4, when the difference between the average of roller pitches in a given section and the average of roller pitches in the preceding section is 10 mm or greater, meaningful results for increasing the rate of casting may be obtained.

[0063] That is, when the average of roller pitches in a given section is less than the average of roller pitches in the preceding section by less than 10 mm, there is no effect on variations in the surface height of molten metal in a mold.

[0064] On the other hand, the average of roller pitches in a given section is less than the average of roller pitches in the preceding section by 10 mm or greater, variations in the surface height of molten metal in a mold may be reduced.

[0065] For example, when the average of roller pitches in a given section is less than the average of roller pitches in the preceding section by about 17 mm, variations in the surface height of molten metal in a mold are reduced, and thus the rate of casting may be increased by about 0.5 m/min compared to the related art. That is, when the rate of casting is 6.5 m/min in the related art, it could be understood that the rate of casting is increased to 7.0 m/min after the average of roller pitches is reduced according to the technique of the present disclosure.

[0066] When the average of roller pitches in a given section is less than the average of roller pitches in the preceding section by about 20 mm or greater, variations in the surface height of molten metal in a mold may be much more reduced.

[0067] For example, when the average of roller pitches in a given section is less than the average of roller pitches in the preceding section by about 38 mm, variations in the surface height of molten metal in a mold are reduced, and thus the rate of casting may be increased by about 1.5 m/min compared to the related art. That is, it could be understood that although the rate of casting is 6.5 m/min in the related art, the rate of casting is 7.0 m/min when a decrease in the average of roller pitches is about 17 mm, and 8.0 m/min when a decrease in the average of roller pitches is about 38 mm.

[0068] Therefore, according to the above-described data, it could be understood that when the average of roller pitches is smaller by 20 mm or greater in a given section than in the preceding section, desired results can be obtained.

[0069] However, the degree to which the average of roller pitches is reduced may have an upper limit according to the allowable load of equipment. In general, if the degree of reduction in the average of roller pitches is increased, a large load may be transmitted to roller supporting structures and driving systems such as bearings, and thus an upper limit to reduction of the average of roller pitches may be determined according to the load that equipment can endure.

[0070] As described above, it will be understood that when the average of roller pitches in a given section is smaller than the average of roller pitches in the preceding section, variations in the surface height of molten metal in a mold may be reduced. In addition, after the average of roller pitches is reduced in the given section compared to the preceding section, the average of roller pitches may be increased in the subsequent section.

[0071] FIG. 5 is a view illustrating a relationship between the solidification length, rate, and thickness of a metal sheet according to an embodiment of the present disclosure.

[0072] Referring to FIG. 5, in the present embodiment, the length required for a metal sheet B to completely solidify may be reduced as the proceeding speed of the metal sheet B is increased.

[0073] The proceeding speed of the metal sheet B may be increased as described above because before the metal sheet B completely solidifies, variations in the surface height of molten metal are relatively non-affected by the proceeding speed of the metal sheet B, owing to a section having the average of roller pitches smaller than that of the preceding section.

[0074] As described above, the section having the average of roller pitches smaller than that of the preceding section may exist within a length in which the metal sheet B is not yet completely solidified, thereby reducing pressure caused by the height difference between the metal sheet B and the surface of molten metal contained in a mold before the metal sheet B is completely solidified, and suppressing outward swelling of the metal sheet B caused by the pressure of molten metal in the metal sheet B while the metal sheet B moves.

[0075] Therefore, in the present embodiment, the maximum length of a reverse section having the average of roller pitches smaller than that of the preceding section is equal to the length required for solidification of the metal sheet B, which may be expressed by Equation 2 as a function of the proceeding speed V of the metal sheet B.

L = V .times. ( H 2 .times. K ) 2 Equation 2 ##EQU00002##

[0076] where L is a length (mm) required to complete solidification of a metal sheet, V is the proceeding speed of the metal sheet in mm/min, H is the thickness of the metal sheet in mm, and K is a solidification constant ranging from 20 mm/min.sup.1/2 to 30 mm/min.sup.1/2.

[0077] In the solidification apparatus of the present embodiment, the average of roller pitches each being the distance between the centers of two rollers adjacent in the proceeding direction of a metal sheet B may be smaller in a given section than in the preceding section, thereby reducing variations in the surface height of molten metal in a mold and maintaining the proceeding speed of the metal sheet B at 4 m/min or greater.

[0078] Furthermore, in the present embodiment, as shown in FIG. 2, the transfer unit 30 may be divided into a vertical section 100 perpendicularly connected to the exit side of the mold 20, a horizontal section 300 connected to a subsequent process section, and a curved section 200 located between the vertical section 100 and the horizontal section 300.

[0079] In this case, a curvature variation section 400 curved with a different slope may be provided in one of a region between the vertical section 100 and the curved section 200 and a region between the curved section 200 and the horizontal section 300.

[0080] In addition, the vertical section 100 of the transfer unit 30 may include at least one segment, and the average of roller pitches each being the distance between the centers of two rollers adjacent in the proceeding direction of the metal sheet B may be smaller in the curvature variation section 400 located between the vertical section 100 and the curved section 200 than in the preceding section.

[0081] After the reverse section, of which the average of roller pitches, each being the distance between the centers of two rollers adjacent in the proceeding direction of the metal sheet B, is smaller than the average of roller pitches in the preceding section, the average of roller pitches may increase again in the subsequent section.

[0082] Although the transfer unit 30 is divided into the vertical section 100, the curved section 200, and the horizontal section 300 in the present embodiment, the transfer unit 30 may include only the vertical section 100, or the transfer unit 30 may include only the curved section 200 and the horizontal section 300 in a state in which the curved section 200 is directly connected to the exit side of the mold 20 without the vertical section 100. In addition, the curvature variation section 400 in which the slope of curve varies may not be provided if the slope of the curved section 200 is constant.

[0083] In addition, a section having the average of roller pitches smaller than that of the preceding section may appear two or more times, and in this case, variations in the surface height of molten metal in a mold may be further reduced.

[0084] Variations in the surface height of molten metal in the mold 20 increase as the proceeding speed of the metal sheet B increases and the arrangement in which the average of roller pitches increases uniformly is repeated many times. Therefore, if the arrangement in which the average of roller pitches increases uniformly is minimally repeated, variations in the surface height of molten metal may be less sensitive to the proceeding speed of the metal sheet B. In this case, if variations in the surface height of molten metal are maintained at the same degree as that in the related art, as a result, the proceeding speed of the metal sheet B may be increased.

[0085] FIG. 6 is a graph showing the average of roller pitches in each section of the solidification apparatus in an inventive example. In FIG. 6, the x-axis is sections, and the y-axis is an average of roller pitches.

[0086] Referring to FIG. 6, according to the embodiment, the degree of reduction in the average of roller pitches in a given section is less than 10 mm compared to the average of roller pitches in the preceding section, and even when the average of roller pitches increases somewhat in the subsequent section, the total decrease in the average of roller pitches in the given section and the second subsequent section is 10 mm or greater. In this case, the degree of reduction of variations in the surface height of molten metal in a mold may be improved.

[0087] That is, even when the average of roller pitches is not sufficiently reduced by 10 mm or greater in a certain section, if the sum of the average of roller pitches in consecutive sections is reduced by 10 mm or greater showing a decreasing trend as a whole, meaningful results for reducing variations in the surface height of molten metal in a mold may be obtained.

[0088] Specifically, the average of roller pitches may be reduced by 8 mm between D1 and D2, increased by 4 mm between D2 and D3, and then decreased by 8 mm between D3 and D4.

[0089] In this case, the degree of reduction in the average of roller pitches is 10 mm or less between sections, and only with this degree of reduction in the average of roller pitches between sections, meaningful results for reducing variations in the surface height of molten metal in a mold may not be obtained.

[0090] However, the sum of decreases in the average of roller pitches may be 12 mm between D1 and D4, and in this case, since the average of roller pitches is reduced by 10 mm or greater as a whole, variations in the surface height of molten metal in a mold may be reduced.

[0091] As described above, after the average of roller pitches is reduced in a preceding section (for example, a section between D1 to D4), the average of roller pitches may be increased again in a following section (for example, a section D5 or a later section).

[0092] The above-described embodiments and the accompanying drawings are not non-limiting examples, and it will be apparent to those skilled in the art that various replacements, modifications, and variations could be made without departing from the scope of the present invention as defined by the appended claims.

* * * * *

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