Pouring nozzle for twin-roll type continuous casting machine, twin-roll type continuous casting machine, and method for producing thin-walled cast strip

Abstract

To provide a poring nozzle for a twin-roll continuous caster that can uniformly deliver molten metal from a poring nozzle to a molten-metal pool with respect to one pair of cooling rolls at a start of casting, thereby stabilizing casting and inhibiting the deterioration of slab quality.SOLUTION: A poring nozzle for a twin-roll continuous caster comprises an outer nozzle 30 and an inner nozzle 40 for feeding molten metal into the outer nozzle 30. The outer nozzle 30, when arranged in a molten-metal pool, has one pair of sidewall portions 31, 31 that are oppositely arranged respectively to one pair of cooling rolls, end-wall portions 32, 32 that are oppositely arranged respectively to one pair of side weirs, and a bottom-surface portion 33 that is formed at a lower end of the sidewall portion 31 and end-wall portion 32. The outer nozzle 30 is formed with at least one slit delivery port 35 made open continuously in one sidewall portion 31A, the bottom-surface portion 33 and the other sidewall portion 31B.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a twin-roll continuous casting apparatus that produces thin slabs by supplying molten metal to a molten metal pool formed by a pair of chill rolls and a pair of side weirs, and forming and growing a solidified shell on the peripheral surface of the chill rolls. The present invention relates to a twin-roll continuous casting apparatus having a pouring nozzle for pouring molten metal into the molten metal pool, a twin-roll continuous casting apparatus equipped with this pouring nozzle for a twin-roll continuous casting apparatus, and a method for producing thin slabs using this pouring nozzle for a twin-roll continuous casting apparatus. [Background technology]

[0002] As a method for producing a thin metal slab, a twin-roll continuous casting machine is provided which has an internal water-cooling structure, is equipped with a pair of chill rolls which rotate in opposite directions, supplies molten metal from a tundish to a molten metal pool formed by the pair of rotating chill rolls and a pair of side weirs, forms and grows a solidified shell on the outer circumferential surface of the chill roll, and presses the solidified shells formed on the outer circumferential surfaces of the pair of chill rolls together at a roll kiss point to produce a thin metal slab of a predetermined thickness. Such twin-roll continuous casting machines are applied to various metals.

[0003] In the above-mentioned twin-roll continuous casting apparatus, the molten metal pool portion formed between the pair of chill rolls has a shape that extends in the longitudinal direction (the width direction of the molten metal pool portion) parallel to the axis of the chill rolls. A twin-roll continuous casting apparatus using a molten metal pouring nozzle (hereinafter, sometimes referred to as a molten metal pouring nozzle) has a structure including an outer nozzle and an inner nozzle inserted inside the outer nozzle, as described in, for example, Patent Documents 1 to 3.

[0004] Here, the outer nozzle has a pair of side wall portions disposed opposite the axial centers of the pair of cooling rolls, and each of the side wall portions is provided with an ejection hole. The molten metal is supplied from the inner nozzle to the outer nozzle, and then from the outlet of the outer nozzle to the molten metal pool portion. At this time, the molten metal is discharged from the outlet of the outer nozzle toward the pair of cooling rolls. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 183752 / 1983 [Patent Document 2] Japanese Patent Application Publication No. 64-005650 [Patent Document 3] JP 2017-131920 A Summary of the Invention [Problem to be solved by the invention]

[0006] Here, at the start of casting, no molten metal is stored in the molten metal pool, and the pouring nozzle is not immersed in the molten metal (called an open state). In this open state, when molten metal is supplied from the pouring nozzle to the molten metal pool, if the molten metal is discharged unevenly from one chill roll side to the other chill roll side, the solidification may be delayed on the side where the molten metal is strongly discharged, or the heat shock to the chill roll may become larger, causing the chill roll to expand unevenly, and the symmetry of solidification of the cast piece may be lost. This may cause defects such as surface cracks of the cast piece, and in severe cases, the cast piece may break. In particular, in thin-wall casting, the adverse effect of the uneven flow of the nozzle discharge flow at the beginning is significant. In order to prevent this, it is necessary to sufficiently equalize the nozzle discharge at the start of casting.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a pouring nozzle for a twin-roll type continuous casting apparatus, which is capable of uniformly pouring molten metal from the pouring nozzle into a molten metal pool on a pair of chill rolls at the start of casting, thereby stabilizing casting and suppressing deterioration of the quality of the cast strip, as well as a twin-roll type continuous casting apparatus and a method for manufacturing a thin-walled cast strip. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the inventors of the present invention have conducted extensive research and have found that, in the outer nozzle, as described above, a pair of side wall portions each have a discharge hole, and the molten metal supplied from the inner nozzle to the inside of the outer nozzle is distributed to each side wall portion at the bottom portion and discharged from each discharge hole. At this time, if the molten metal is discharged more strongly from one side, the dynamic pressure on that side decreases and the molten metal is discharged even more strongly, resulting in a difference in the discharge flow rate (discharge flow velocity) of the molten metal between one chill roll side and the other chill roll side.

[0009] The present invention has been made based on the above-mentioned findings, and the molten metal pouring nozzle for a twin-roll continuous casting apparatus according to the present invention is a molten metal pouring nozzle for use in a twin-roll continuous casting apparatus which supplies molten metal to a molten metal pool portion formed by a pair of rotating chill rolls and a pair of side weirs, and produces a thin-walled cast strip by forming and growing a solidified shell on the circumferential surface of the chill rolls, the molten metal pouring nozzle for use in a twin-roll continuous casting apparatus which supplies molten metal to the inside of the outer nozzle, the outer nozzle having a pair of side wall portions opposed to the axes of the pair of chill rolls when the outer nozzle is disposed in the molten metal pool portion, an end wall portion opposed to the pair of side weirs, and a bottom surface portion formed at lower ends of the side wall portions and the end wall portions, and the outer nozzle is characterized in that at least one slit discharge hole is formed which opens continuously into one of the side wall portions, the bottom surface portion, and the other side wall portion.

[0010] According to the molten metal pouring nozzle for a twin-roll continuous casting apparatus of this configuration, the outer nozzle is formed with at least one slit discharge hole that opens continuously to one of the side wall portions, the bottom portion, and the other of the side wall portions. This eliminates the difference in dynamic pressure between one of the side wall portions and the other of the side wall portions, making it possible to uniformly discharge molten metal toward a pair of cooling rolls and to carry out stable casting.

[0011] In the molten metal pouring nozzle for a twin-roll continuous casting machine according to the present invention, it is preferable that a side wall discharge hole is formed in the side wall portion of the outer nozzle. In this case, since side wall discharge holes are formed in the side wall portions of the outer nozzle, it is possible to stably supply molten metal to the molten metal pool portion even if the amount of molten metal supplied per unit time is large.

[0012] In the molten metal pouring nozzle for a twin-roll type continuous casting apparatus according to the present invention, it is preferable that the slit discharge hole is formed so as to connect the side wall discharge hole formed in one of the side wall portions with the side wall discharge hole formed in the other side wall portion. In this case, the slit discharge hole is formed so as to connect the side wall discharge hole formed in one of the side wall portions with the side wall discharge hole formed in the other of the side wall portions, so that the dynamic pressure difference between the side wall discharge hole formed in one side wall portion and the side wall discharge hole formed in the other side wall portion can be eliminated, making it possible to discharge molten metal in a balanced manner.

[0013] Furthermore, in the molten metal pouring nozzle for a twin-roll continuous casting machine according to the present invention, it is preferable that the inner nozzle is formed with a slit discharge port extending from a bottom of the inner nozzle to a side wall portion of the inner nozzle along the extension direction of the side wall portion of the outer nozzle. In this case, the inner nozzle is formed with a slit discharge port extending from the bottom of the inner nozzle to the side wall portion of the inner nozzle along the extension direction of the side wall portion of the outer nozzle, so that molten metal can be supplied in a balanced manner from the inner nozzle to a pair of end wall portions of the outer nozzle, and molten metal can be supplied uniformly along the extension direction of the side wall portion of the outer nozzle.

[0014] In the molten metal pouring nozzle for a twin-roll continuous casting machine according to the present invention, it is preferable that the inner nozzle is formed with a pair of discharge ports which open respectively toward the pair of end wall portions of the outer nozzle. In this case, the inner nozzle is formed with a pair of discharge ports that respectively open toward a pair of end wall portions of the outer nozzle, so that molten metal can be steadily supplied to the inside of the outer nozzle even if the amount of molten metal supplied per unit time is large.

[0015] Furthermore, in the molten metal pouring nozzle for a twin-roll continuous casting machine according to the present invention, it is preferable that the slit discharge port is formed so as to connect one of the discharge ports to the other discharge port. In this case, the slit discharge port is formed so as to connect one of the discharge ports to the other discharge port, so that the molten metal is discharged in a well-balanced manner from one of the discharge ports to the other discharge port.

[0016] The twin-roll continuous casting apparatus of the present invention is a twin-roll continuous casting apparatus which supplies molten metal to a molten metal pool portion formed by a pair of rotating chill rolls and a pair of side weirs, and produces a thin-walled cast strip by forming and growing a solidified shell on the circumferential surface of the chill rolls, and is characterized in that it comprises the above-mentioned molten metal pouring nozzle for a twin-roll continuous casting apparatus as a molten metal pouring nozzle for pouring the molten metal into the molten metal pool portion.

[0017]

[0013] According to a twin-roll continuous casting apparatus having this configuration, since the twin-roll continuous casting apparatus is equipped with the above-mentioned molten metal pouring nozzle, at the start of casting, molten metal can be uniformly poured from the pouring nozzle into the molten metal pool of the pair of chill rolls, thereby stabilizing casting and suppressing deterioration of the quality of the cast piece.

[0018] The method for producing a thin slab of the present invention comprises supplying molten metal to a molten metal pool portion formed by a pair of rotating chill rolls and a pair of side weirs, and forming and growing a solidified shell on the peripheral surface of the chill rolls to produce a thin slab, and is characterized in that the molten metal is poured into the molten metal pool portion using the above-mentioned pouring nozzle for a twin-roll continuous casting apparatus.

[0019] According to the thin-walled cast slab manufacturing method having this configuration, the molten metal is poured into the molten metal pool portion using the above-mentioned pouring nozzle for a twin-roll continuous casting apparatus. Therefore, at the start of casting, the molten metal can be uniformly discharged from the pouring nozzle into the molten metal pool portion on the pair of chill rolls, thereby stabilizing casting and suppressing deterioration of the cast slab quality. Effect of the Invention

[0020] According to the present invention, it is possible to provide a pouring nozzle for a twin-roll continuous casting apparatus, a twin-roll continuous casting apparatus, and a method for manufacturing a thin-walled cast strip, which are capable of uniformly pouring molten metal from the pouring nozzle into a molten metal pool portion of a pair of chill rolls at the start of casting, thereby stabilizing casting and suppressing deterioration of cast strip quality. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic explanatory diagram showing an example of a twin-roll continuous casting apparatus using a molten metal pouring nozzle for a twin-roll continuous casting apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic explanatory view of a molten steel pool portion of the twin-roll continuous casting apparatus shown in FIG. [Diagram 3] FIG. 1 is a schematic explanatory diagram of a molten metal pouring nozzle for a twin-roll continuous casting machine according to an embodiment of the present invention. [Figure 4] FIG. 2 is an enlarged explanatory view of a discharge port of an inner nozzle in the molten metal pouring nozzle for a twin-roll continuous casting machine according to the embodiment of the present invention. [Diagram 5] FIG. 2 is a schematic explanatory view of a molten metal pouring nozzle for a twin-roll continuous casting machine according to another embodiment of the present invention. [Figure 6] FIG. 4 is an enlarged explanatory view of a discharge port of an inner nozzle in a molten metal pouring nozzle for a twin-roll continuous casting machine according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, a pouring nozzle for a twin-roll continuous casting apparatus (hereinafter referred to as a pouring nozzle), a twin-roll continuous casting apparatus, and a method for producing a thin-walled cast strip according to embodiments of the present invention will be described with reference to the accompanying drawings. Note that the present invention is not limited to the following embodiments.

[0023] In this embodiment, molten steel is used as the molten metal, and a thin-walled cast slab 1 made of a steel material is manufactured. Examples of steel types include 0.001-0.01%C extra-low carbon steel, 0.02-0.05%C low carbon steel, 0.06-0.4%C medium carbon steel, 0.5-1.2%C high carbon steel, austenitic stainless steel such as SUS304 steel, ferritic stainless steel such as SUS430 steel, 3.0-3.5%Si grain-oriented electrical steel, 0.1-6.5%Si non-oriented electrical steel, etc. (% is by mass). In this embodiment, the width of the thin-walled cast strip 1 to be produced is within a range of 300 mm or more and 2000 mm or less, and the thickness is within a range of 1 mm or more and 5 mm or less.

[0024] As shown in FIG. 1 , the twin-roll continuous casting apparatus 10 of this embodiment comprises a pair of cooling rolls 11, 11, bender rolls 12, 12 for bending the thin cast strip 1, pinch rolls 13, 13 for supporting the thin cast strip 1, side dams 15 arranged at the widthwise ends of the pair of cooling rolls 11, 11, a tundish 18 for holding molten steel 3 to be supplied to a molten steel pool portion 16 defined by the pair of cooling rolls 11, 11 and the side dam 15, and a molten steel pouring nozzle 20 for supplying molten steel 3 from the tundish 18 to the molten steel pool portion 16.

[0025] As shown in FIG. 2, the molten steel surface in the molten steel pool 16 is rectangular in shape and surrounded on all four sides by the peripheral surfaces of a pair of cooling rolls 11, 11 and a pair of side weirs 15, 15, and a pouring nozzle 20 is disposed in the center of this rectangular molten steel surface. In this embodiment, as shown in FIG. 2, in the molten steel pool section 16 and the molten steel pouring nozzle 20 arranged in the molten steel pool section 16, the direction along the axial direction of the chill roll 11 is defined as the "width direction", and the direction perpendicular to the axial direction of the chill roll 11 is defined as the "thickness direction".

[0026] In this twin-roll continuous casting apparatus 10, as shown in FIG. 1, molten steel 3 comes into contact with and is cooled by cooling rolls 11, 11 rotating in the R direction, whereby solidified shells 5, 5 grow on the peripheral surfaces of the cooling rolls 11, 11, and the solidified shells 5, 5 formed on the pair of cooling rolls 11, 11 are pressed against each other at the drum kiss points, thereby casting a thin-walled slab 1 of a predetermined thickness.

[0027] Here, as the above-mentioned molten metal pouring nozzle 20, a molten metal pouring nozzle for a twin-roll continuous casting apparatus according to this embodiment is used. As shown in FIG. 3, the molten metal pouring nozzle 20 includes an outer nozzle 30 and an inner nozzle 40 that is inserted into the outer nozzle 30.

[0028] The outer nozzle 30 has a pair of side wall portions 31, 31 arranged opposite the pair of cooling rolls 11, 1, respectively, end wall portions 32, 32 arranged opposite the pair of side weirs 15, 15, respectively, and a bottom surface portion 33 formed at the lower ends of the side wall portions 31 and the end wall portions 32, when placed in the molten steel pool portion 16. Also, the lower region of the outer nozzle 30 is shaped so that its thickness gradually decreases downward, as shown in Fig. 3. Here, the width direction length of the lower region of the outer nozzle 30 is set within a range of 40 to 80% of the width of the thin-walled cast strip 1 to be cast.

[0029] The outer nozzle 30 is formed with at least one slit discharge hole 35 that opens continuously to one side wall portion 31A, the bottom surface portion 33, and the other side wall portion 31B. In this embodiment, as shown in Fig. 3, three slit discharge holes 35 are formed in parallel in the extension direction of the side wall portion 31 (direction along the axis of the cooling roll 11). Note that this slit discharge hole 35 is formed to extend in a direction perpendicular to the extension direction of the side wall portion 31 (direction along the axis of the cooling roll 11) when viewed from above.

[0030] Further, in a lower region of the side wall portion 31 of the outer nozzle 30, a side wall discharge hole 36 that opens toward the cooling roll 11 is formed. In this embodiment, as shown in Fig. 2, each side wall portion 31 has three side wall discharge holes 36 formed in the extending direction of the side wall portion 31 (direction along the axis of the cooling roll 11). In this embodiment, as shown in FIG. 3, a slit discharge hole 35 is formed to connect a side wall discharge hole 36 formed in one side wall portion 31A and a side wall discharge hole 36 formed in the other side wall portion 31B.

[0031] Here, there is no particular limitation on the width or number of the slit discharge holes 35, but in order to ensure the strength of the outer nozzle 30, it is preferable to set the width or number of the slit discharge holes 35 so that the ratio of the total area occupied by the slit discharge holes 35 to the area of ​​the bottom surface portion 33 is 15% or less. Furthermore, it is more preferable to set the ratio of the total area occupied by the slit discharge holes 35 to the area of ​​the bottom surface portion 33 to 10% or less.

[0032] In the example shown in FIG. 3 and FIG. 4, the inner nozzle 40 has a tubular shape with a closed lower end, and is disposed facing the internal space of the outer nozzle 30. As shown in FIG. 4, in the inner nozzle 40, a slit discharge port 41 is formed extending from the bottom of the inner nozzle 40 to the side wall of the inner nozzle 40 along the extending direction of the side wall 31 of the outer nozzle 30. That is, in this embodiment, the extending direction of the slit discharge port 41 of the inner nozzle 40 and the slit discharge hole 35 of the outer nozzle 30 are arranged so as to be perpendicular to each other when viewed from above.

[0033] In this embodiment, the inner nozzle 40 is provided with a pair of discharge ports 42, 42 that open toward the pair of side weirs 15, 15, respectively, when the inner nozzle 40 is disposed in the molten steel pool portion 16, as shown in FIG. In this embodiment, as shown in FIG. 4, a slit outlet 41 is formed so as to connect the pair of outlets 42, 42.

[0034] Next, a method for producing a thin-walled cast slab according to this embodiment using the above-mentioned molten metal pouring nozzle 20 and twin-roll continuous casting apparatus 10 will be described.

[0035] Molten steel 3 is supplied from a tundish 18 via a pouring nozzle 20 to a molten steel pool 16 formed by a pair of cooling rolls 11, 11 and a side weir 15, and each of the pair of cooling rolls 11, 11 is rotated in the rotation direction R, i.e., so that the area where the pair of cooling rolls 11, 11 are adjacent to each other faces the drawing direction of the thin-walled cast slab 1 (downward in Figure 1).

[0036] As a result, a solidified shell 5 is formed on the peripheral surface of the chill roll 11. The solidified shell 5 grows on the peripheral surface of the chill roll 11, and the solidified shells 5, 5 formed on the pair of chill rolls 11, 11 are pressed against each other at the roll kiss points, thereby casting a thin-walled cast strip 1 having a predetermined thickness.

[0037] Here, at the start of casting, no molten steel 3 is stored in the molten steel pool portion 16, and the slit discharge hole 35 and side wall discharge hole 36 of the outer nozzle 30 are exposed. In this state, molten steel 3 is discharged from the slit discharge hole 35 and side wall discharge hole 36 of the outer nozzle 30. At this time, since the slit discharge hole 35 is provided, the dynamic pressure difference between one side wall portion 31A and the other side wall portion 31B can be eliminated, and the molten steel 3 is discharged uniformly toward the pair of cooling rolls 11, 11.

[0038] Furthermore, at the start of casting, no molten steel 3 is stored inside the outer nozzle 30, and the discharge port 42 of the inner nozzle 40 is exposed to the internal space of the outer nozzle 30. In this state, the molten steel 3 is discharged from the discharge port 42 of the inner nozzle 40. At this time, since the inner nozzle 40 is provided with the slit discharge port 41 , the molten steel 3 is discharged uniformly toward the pair of end wall portions 32 of the outer nozzle 30 .

[0039] During steady-state casting, molten steel 3 is stored in the molten steel pool portion 16, and the slit discharge holes 35 and side wall discharge holes 36 of the outer nozzle 30 are immersed in the molten steel 3. This allows the molten steel 3 to be discharged uniformly toward the pair of cooling rolls 11, 11. During steady casting, the molten steel 3 is stored inside the outer nozzle 30, and the slit discharge port 41 and the discharge port 42 of the inner nozzle 40 are immersed in the molten steel 3. This allows the molten steel 3 to be discharged uniformly toward the pair of end wall portions 32.

[0040] According to the present embodiment of the molten steel pouring nozzle 20 for a twin-roll continuous casting apparatus configured as described above, the outer nozzle 30 is formed with at least one (three in this embodiment) slit discharge hole 35 that opens continuously to one side wall portion 31A, the bottom portion 33, and the other side wall portion 31B, thereby eliminating the difference in dynamic pressure between the one side wall portion 31A side and the other side wall portion 31B side, allowing the molten steel 3 to be discharged uniformly toward the pair of cooling rolls 11, 11, making it possible to carry out stable casting.

[0041] Furthermore, in the molten steel pouring nozzle 20 for a twin-roll continuous casting apparatus according to this embodiment, when the side wall discharge hole 36 is formed in the side wall portion 31 of the outer nozzle 30, it becomes possible to stably supply the molten steel 3 to the molten steel pool portion 16 even if the amount of molten steel 3 supplied per unit time is large.

[0042] Furthermore, in the molten steel pouring nozzle 20 for a twin-roll continuous casting apparatus of this embodiment, when the slit discharge hole 35 is formed so as to connect the side wall discharge hole 36 formed in one side wall portion 31A and the side wall discharge hole 36 formed in the other side wall portion 31B, the dynamic pressure difference between the side wall discharge hole 36 formed in one side wall portion 31A and the side wall discharge hole 36 formed in the other side wall portion 31B can be eliminated, making it possible to discharge the molten steel 3 in a balanced manner.

[0043] Furthermore, in the molten steel pouring nozzle 20 for a twin-roll continuous casting apparatus of this embodiment, when the inner nozzle 40 is formed with a slit discharge port 41 extending along the extension direction of the side wall portion 31 of the outer nozzle 30, the molten steel 3 can be supplied in a balanced manner from the inner nozzle 40 toward the pair of end wall portions 32, 32 of the outer nozzle 30, and the molten steel 3 can be supplied uniformly along the extension direction of the side wall portion 31 of the outer nozzle 30.

[0044] Furthermore, in the present embodiment of the molten steel pouring nozzle 20 for a twin-roll continuous casting apparatus, when the inner nozzle 40 is formed with a pair of discharge ports 42, 42 that respectively open toward a pair of end wall portions 32, 32 of the outer nozzle 30, it is possible to stably supply molten steel 3 into the inside of the outer nozzle 30 even if the amount of molten steel 3 supplied per unit time is large.

[0045] Furthermore, in the molten steel pouring nozzle 20 for a twin-roll continuous casting apparatus of this embodiment, when a slit discharge port 41 is formed so as to connect one discharge port 42 with the other discharge port 42, it becomes possible to discharge the molten steel 3 in a well-balanced manner from one discharge port 42 and the other discharge port 42.

[0046] The twin-roll continuous casting apparatus of this embodiment is equipped with the molten steel pouring nozzle 20 for the twin-roll continuous casting apparatus of this embodiment, so that at the start of casting, molten steel 3 can be uniformly poured from the twin-roll continuous casting apparatus pouring nozzle 20 into the molten steel pool 16 toward the pair of cooling rolls 11, 11, thereby stabilizing casting and suppressing deterioration of the quality of the cast slab.

[0047] The method for producing a thin-walled cast slab of this embodiment is configured to pour molten steel 3 into the molten steel pool 16 using the twin-roll continuous casting apparatus pouring nozzle 20 of this embodiment. Therefore, at the start of casting, the molten steel 3 can be uniformly discharged from the twin-roll continuous casting apparatus pouring nozzle 20 into the molten steel pool 16 toward the pair of cooling rolls 11, 11, thereby stabilizing casting and suppressing deterioration of the cast slab quality.

[0048] The embodiments of the present invention, that is, the molten metal pouring nozzle for a twin-roll continuous casting machine, the twin-roll continuous casting machine, and the method for producing a thin-walled cast strip, have been specifically explained above. However, the present invention is not limited to these embodiments, and appropriate modifications can be made without departing from the technical concept of the invention.

[0049] For example, in this embodiment, as shown in FIG. 3, in the outer nozzle 30, the slit discharge hole 35 is formed so as to connect the side wall discharge hole 36 formed in one side wall portion 31A to the side wall discharge hole 36 formed in the other side wall portion 31B. However, this is not limited to this, and for example, as shown in FIG. 5, the slit discharge hole 35 may be formed without being connected to the side wall discharge hole 36. In addition, in this embodiment, the inner nozzle 40 is described as having a pair of outlets 42, 42 as shown in FIG. 4, but this is not limited to this, and it may be formed with only a slit outlet 41 as shown in FIG. 6. EXAMPLES

[0050] The results of experiments carried out to confirm the effects of the present invention will be described below.

[0051] Using the twin-roll continuous casting apparatus described in the embodiment, a thin-walled slab of low carbon steel (C content: 0.05 mass%) was cast under the following conditions and with the following pouring nozzle.

[0052] First, as an example of the present invention, a pouring nozzle having an outer nozzle and an inner nozzle as shown below was prepared. (inner nozzle) Inner diameter: 75mm A pair of outlets: width 30mm x height 42mm Slit outlet: Width 30 mm, pair of outlets connected Material: Alumina graphite (Outer nozzle) Maximum inner dimensions: 630 mm in the width direction of the slab, 250 mm in the thickness direction of the slab A pair of outlet holes: Width 130mm x Height 15mm, 3 on one side wall (total 6) Slit outlet hole: Width 10 mm, connecting the center of the width of opposing outlet holes Material: Alumina graphite

[0053] As a comparative example, a pouring nozzle having an outer nozzle and an inner nozzle as shown below was prepared. (inner nozzle) Inner diameter: 75mm A pair of outlets: width 30mm x height 42mm Slit outlet: None Material: Alumina graphite (Outer nozzle) Maximum inner dimensions: 630 mm in the width direction of the slab, 250 mm in the thickness direction of the slab A pair of outlet holes: Width 130mm x Height 15mm, 3 on one side wall (total 6) Slit outlet hole: None Material: Alumina graphite

[0054] Using a twin-roll continuous casting apparatus equipped with the above-mentioned pouring nozzle, molten steel was poured for 5 minutes at an initial supply rate of 6.8 kg / sec, after which casting was started (the cooling rolls started to rotate). Continuous casting was carried out for 100 channels, with 100 t per channel, under the following conditions.

[0055] (Casting conditions) Cooling roll diameter: 1000mm Cooling roll width: 800mm Thin-walled casting thickness: 2.5mm Casting speed: 50mpm (steady condition) Casting arc angle (angle between the roll kiss point and the contact point between the molten steel pool surface and the chill roll surface, as seen from the center of rotation of the chill roll): 45° (steady condition) Roll pressure: 2 tonf (steady condition) The period from the start of casting until the casting speed, casting arc angle and roll pressure force reach the above-mentioned values ​​is defined as unsteady.

[0056] The obtained thin-walled cast pieces were evaluated for surface cracks and porosity by the following methods. (Surface cracks on cast slab) A 3m long (approximately one rotation of the cooling roll) x full width sample was taken from a position 50m into the casting length. The surface of this slab was pickled and then visually observed. The total length of cracks per unit area of ​​the slab was then evaluated. (Porosity of cast slab) A 3m length (approximately one rotation of the cooling roll) x full width sample was taken from a position 50m into the casting length. X-rays were passed through this slab. The porosity area ratio per unit area of ​​the slab was then evaluated.

[0057] In the comparative example, 84 out of 100 channels were able to continue casting to the end (84% completion rate). In the 16 channels that could not be completed, the slab broke immediately after the mold within 10 seconds of starting casting. At this time, it was observed that the nozzle discharge was significantly biased. In addition, 30 of the completed casts were evaluated for surface cracks. The total length of cracks per unit area of ​​the cast slab was 20 to 2500 mm / mm in the unsteady state. 2 , 0~300mm / mm in steady state 2 Due to the uneven solidification, many cracks with lengths of 1 mm or more appeared on the surface of the slab immediately after the start of casting. The uneven solidification also extended to the steady state area. Furthermore, 30 of the completed casts were evaluated for slab porosity. The porosity area ratio per unit area of ​​the slab was 0.2-3.5% in the non-steady state and 0-0.07% in the steady state. The compression of the solidified shell by the cooling roll was not uniform, causing numerous porosities to form, the effects of which extended to some of the steady state.

[0058] In contrast, in the example of the present invention, casting was able to continue to the end in all 100 channels (100% completion rate). In addition, 30 of the completed casts were evaluated for surface cracks. Almost no surface cracks were observed in either the non-steady or steady state sections. Furthermore, porosity of slabs was evaluated for 30 of the completed casts. The porosity area ratio per unit area of ​​slabs was low at 0 to 0.05% in the non-steady state and 0% in the steady state.

[0059] From the above, it has been confirmed that the present invention can provide a pouring nozzle for a twin-roll continuous casting apparatus, a twin-roll continuous casting apparatus, and a method for manufacturing thin-walled slabs, which can uniformly pour molten metal from the pouring nozzle into the molten metal pool on a pair of cooling rolls at the start of casting, thereby stabilizing casting and suppressing deterioration of slab quality. [Explanation of symbols]

[0060] 1 Thin-walled cast pieces 10 Twin roll continuous casting equipment 20. Pouring nozzle for twin-roll continuous casting machine 30 Outer nozzle 31 Side wall 32 Bottom part 33 End wall 35 Slit outlet hole 36 Side wall discharge hole 40 Inner nozzle 41 Slit outlet 42 Discharge port

Claims

1. A twin-roll continuous casting machine is provided with a molten metal pouring nozzle for use in a twin-roll continuous casting machine that supplies molten metal to a molten metal pool portion formed by a pair of rotating chill rolls and a pair of side weirs, and produces a thin-walled cast strip by forming and growing a solidified shell on the peripheral surface of the chill rolls, the nozzle comprising: The method includes the steps of: providing an outer nozzle; and providing an inner nozzle for supplying molten metal into the outer nozzle. the outer nozzle has a pair of side wall portions disposed opposite the pair of cooling rolls, respectively, and end wall portions disposed opposite the pair of side dams, respectively, when the outer nozzle is disposed in the molten metal pool portion, and a bottom surface portion formed at lower ends of the side wall portions and the end wall portions, the outer nozzle is provided with at least one slit discharge hole which opens continuously through one of the side wall portions, the bottom surface portion, and the other of the side wall portions.

2. 2. The molten metal pouring nozzle for a twin-roll continuous casting machine according to claim 1, wherein a side wall discharge hole is formed in the side wall of the outer nozzle.

3. 3. The molten metal pouring nozzle for a twin-roll type continuous casting apparatus according to claim 2, wherein the slit discharge hole is formed so as to connect the side wall discharge hole formed in one of the side wall portions with the side wall discharge hole formed in the other side wall portion.

4. 4. The molten metal pouring nozzle for a twin-roll continuous casting apparatus according to claim 1, wherein the inner nozzle is formed with a slit discharge port extending from a bottom portion of the inner nozzle to a side wall portion of the inner nozzle along an extension direction of the side wall portion of the outer nozzle.

5. 5. The molten metal pouring nozzle for a twin-roll continuous casting machine according to claim 4, wherein the inner nozzle is formed with a pair of discharge ports each opening toward the end wall portion of the outer nozzle.

6. 6. The molten metal pouring nozzle for a twin-roll continuous casting machine according to claim 5, wherein the slit discharge port is formed so as to connect one of the discharge ports with the other discharge port.

7. 1. A twin-roll continuous casting apparatus for producing a thin-walled cast strip by supplying molten metal to a molten metal pool portion formed by a pair of rotating chill rolls and a pair of side gates, and forming and growing a solidified shell on a peripheral surface of the chill rolls, 7. A twin-roll continuous casting apparatus comprising the twin-roll continuous casting apparatus according to claim 1 as a pouring nozzle for pouring the molten metal into the molten metal pool portion.

8. A method for producing a thin cast slab by supplying molten metal to a molten metal pool formed by a pair of rotating chill rolls and a pair of side weirs, and forming and growing a solidified shell on a peripheral surface of the chill rolls, comprising the steps of: A method for producing a thin-walled cast strip, comprising pouring the molten metal into the molten metal pool using the pouring nozzle for a twin-roll continuous casting apparatus according to any one of claims 1 to 6.

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