Immersion nozzle for twin-roll continuous casting apparatus, twin-roll continuous casting apparatus, and method for manufacturing thin slab

Abstract

To provide a submerged nozzle for a twin-roll continuous caster that allows for stabilizing casting and suppressing slab and material qualities from deteriorating, by further homogenizing the outflow distribution in a width direction of molten metal outflowing from a submerged nozzle to a molten-metal pool unit at a start of casting and stably supplying molten metal from a tundish to the molten-metal pool unit.SOLUTION: A submerged nozzle for a twin-roll continuous caster includes an outer nozzle 30 and an inner nozzle 21. The outer nozzle 30, when arranged on a molten-metal pool unit, comprises a sidewall portion 31 extending along a direction parallel with an axis of a cooling roll, an end wall portion 32 and a bottom surface portion 33. In the vicinity of the bottom surface portion 33 of the outer nozzle 30, a molten-metal outlet port 36 is formed. Within the outer nozzle 30, a pressure-loss member 27 is arranged above the outlet port 36. In an upper position of an inner surface of the sidewall portion 31 of the outer nozzle 30 than the pressure-loss member 27, a plurality of guide protrusions 38 are formed extending along a vertical direction.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a dipping nozzle for a twin-roll continuous casting apparatus used when pouring molten metal into a molten metal pool portion formed by a pair of cooling rolls and a pair of side dams, a twin-roll continuous casting apparatus provided with the dipping nozzle for the twin-roll continuous casting apparatus, and a method for manufacturing a thin slab using the dipping nozzle for the twin-roll continuous casting apparatus. In the twin-roll continuous casting apparatus, molten metal is supplied to a molten metal pool portion formed by a pair of cooling rolls and a pair of side dams, and a solidification shell is formed and grown on the peripheral surface of the cooling roll to manufacture a thin slab.

Background Art

[0002] As a method for manufacturing a thin slab of metal, there is provided a twin-roll continuous casting apparatus having a water-cooling structure inside, including a pair of cooling rolls rotating in opposite directions to each other, supplying molten metal from a tundish to a molten metal pool portion formed by the pair of rotating cooling rolls and a pair of side dams, forming and growing a solidification shell on the outer peripheral surface of the cooling roll, and pressing the solidification shells formed on the outer peripheral surfaces of the pair of cooling rolls against each other at a roll kiss point to manufacture a thin slab having a predetermined thickness. Such a twin-roll continuous casting apparatus is applied to various metals.

[0003] In the above twin-roll continuous casting apparatus, the molten metal pool portion formed between the pair of cooling rolls has a shape extending in the longitudinal direction (width direction of the molten metal pool portion) parallel to the axis of the cooling roll. When supplying molten metal to this molten metal pool portion using a pouring nozzle, if the flow of molten metal becomes non-uniform in the longitudinal direction (width direction of the molten metal pool portion) parallel to the axis of the cooling roll, the surface level of the molten metal pool portion fluctuates in the longitudinal direction parallel to the axis of the cooling roll, and non-uniformity in the plate thickness occurs in the width direction of the thin slab. The pouring nozzle has a structure including an outer nozzle and an inner nozzle inserted inside the outer nozzle, and molten metal is supplied from the inner nozzle to the outer nozzle and then supplied from the discharge port of the outer nozzle to the molten metal pool portion.

[0004] Here, when molten metal is fed into a mold from the submerged entry nozzle, if the discharge flow from the submerged entry nozzle fluctuates or becomes uneven, rippling may occur in the molten metal pool, causing abnormal solidification that may be entrained and destabilizing the casting, or uneven solidification in the mold may cause wrinkles or cracks on the surface of the slab, compromising the quality and material properties of the slab. In particular, in a thin-wall casting process, it is necessary to more precisely adjust the stability and uniformity of the nozzle discharge flow.

[0005] As a measure to stabilize and uniformize the nozzle discharge flow, for example, Patent Documents 1 and 2 disclose a technique for adjusting the discharge flow by providing an obstacle inside the submerged entry nozzle to prevent the molten metal from flowing downward. However, the flow of the molten metal may be so hindered by adhesion or accumulation of inclusions in the molten metal or solidification of the molten metal itself that the desired discharge flow may not be obtained.

[0006] Moreover, Patent Documents 3 to 5 disclose a method of controlling the flow direction by providing a pressure loss member inside the outer nozzle. Here, Patent Document 3 proposes using a porous refractory material as the pressure loss member. Patent Documents 4 and 5 propose a pressure drop member in which a porous refractory material is formed with through holes. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 61-165257 [Patent Document 2] Japanese Patent Application Publication No. 10-113752 [Patent Document 3] Japanese Patent Application Publication No. 11-342455 [Patent Document 4] Japanese Patent Application Publication No. 61-289953 [Patent Document 5] Japanese Patent Application Publication No. 07-068357 Summary of the Invention

Problems to be Solved by the Invention

[0008] By the way, during the steady state of casting, molten metal is stored inside the outer nozzle, and the discharge holes of the inner nozzle are immersed in the molten metal. On the other hand, at the start of casting, molten metal is not stored inside the outer nozzle, and the discharge holes of the inner nozzle are exposed to the internal space of the outer nozzle. When molten metal is discharged from the discharge holes of the inner nozzle in this state, depending on the opening position and direction of the discharge holes, the outflow distribution in the width direction from the outer nozzle to the molten metal pool part becomes non-uniform due to the influence of the discharge flow from the inner nozzle, and there is a possibility that the flow of molten metal in the molten metal pool part may be disturbed.

[0009] More specifically, the inner nozzles are usually provided with discharge holes respectively facing the width direction of the outer nozzle (the direction parallel to the axis of the cooling roll when installed in the molten metal pool part). The flow of molten metal becomes stronger on the width direction end side of the molten metal pool part, and the flow of molten metal tends to become weaker at the center of the width direction end of the molten metal pool part. As a result, remelting of the solidification shell occurs on the width direction end side of the molten metal pool part, and solidification defects occur at the center of the width direction end of the molten metal pool part, and there is a possibility that casting cannot be started stably.

[0010] The present invention has been made in view of the above-described situation, and aims to make the outflow distribution in the width direction of the molten metal flowing out from the immersion nozzle to the molten metal pool part more uniform at the start of casting, and to stably supply the molten metal from the tundish to the molten metal pool part, thereby stabilizing casting, improving the quality of the cast slab, and suppressing deterioration of the material. An immersion nozzle for a twin-roll continuous casting apparatus, a twin-roll continuous casting apparatus, and a method for manufacturing a thin slab are provided.

Means for Solving the Problems

[0011] In order to solve the above problems, in the immersion nozzle for a twin-roll continuous casting apparatus according to the present invention, molten metal is supplied to a molten metal pool portion formed by a pair of rotating cooling rolls and a pair of side dams, and a solidified shell is formed and grown on the peripheral surface of the cooling roll to produce a thin slab. The immersion nozzle for a twin-roll continuous casting apparatus used in a twin-roll continuous casting apparatus, which has an outer nozzle and an inner nozzle for supplying molten metal into the outer nozzle. When the outer nozzle is disposed in the molten metal pool portion, it has a side wall portion extending along a direction parallel to the axis of the cooling roll, an end wall portion intersecting the axis of the cooling roll, and a bottom surface portion formed at the lower ends of the side wall portion and the end wall portion. A discharge port for the molten metal is formed near the bottom surface portion of the outer nozzle, a pressure loss member is disposed inside the outer nozzle above the discharge port, and a plurality of guide protrusion portions extending in the vertical direction are formed at a position above the pressure loss member on the inner surface of the side wall portion of the outer nozzle. and the guide rib portion is formed up to a position above the discharge hole of the inner nozzle It is characterized by being like this.

[0012] According to the immersion nozzle for a twin-roll continuous casting apparatus having this configuration, since a pressure loss member is disposed inside the outer nozzle above the discharge port, and a plurality of guide protrusion portions extending in the vertical direction are formed at a position above the pressure loss member on the inner surface of the side wall portion of the outer nozzle, at the start of casting, when a part of the molten metal discharged from the inner nozzle collides with the inner surface of the side wall portion of the outer nozzle in a state where the discharge hole of the inner nozzle is exposed to the internal space of the outer nozzle, a downward flow of the molten metal is formed along the guide protrusion portions, and the molten metal falls onto the pressure loss member before reaching the end portion in the width direction of the outer nozzle. Also, a part of the molten metal discharged from the inner nozzle reaches the end portion in the width direction of the outer nozzle. Thereby, it becomes possible to make the outflow distribution in the width direction of the molten metal flowing out from the immersion nozzle to the molten metal pool portion more uniform at the start of casting.

[0013] Here, in the immersion nozzle for a twin-roll continuous casting apparatus according to the present invention, it is preferable that the pressure loss member has a plurality of through-holes formed therethrough in the vertical direction. In this case, since the pressure loss member is provided with a plurality of through-holes, the occurrence of clogging of the pressure loss member can be suppressed, and casting can be performed more stably. In addition, when the pressure loss member is provided with a plurality of through-holes, the outflow distribution of the molten metal from the outer nozzle is strongly affected by the discharge flow from the inner nozzle. However, by forming a plurality of guide protrusion portions extending along the vertical direction on the inner surface of the side wall portion of the outer nozzle, it is possible to make the outflow distribution in the width direction of the molten metal flowing out from the immersion nozzle to the molten metal pool portion more uniform at the start of casting.

[0014] Further, in the immersion nozzle for a twin-roll continuous casting apparatus according to the present invention, it is preferable that the width W of the guide protrusion portion is in the range of 5 mm or more and 30 mm or less, the protruding height H of the guide protrusion portion is in the range of 3 mm or more and 20 mm or less, and the pitch P of the plurality of guide protrusion portions is in the range of 5 mm or more and 60 mm or less. In this case, since the width W, protruding height H, and pitch P of the guide protrusion portion are within the above-described ranges, a downward flow of the molten metal directed vertically downward can be surely formed by the guide protrusion portion, and the outflow distribution in the width direction of the molten metal flowing out from the immersion nozzle to the molten metal pool portion at the start of casting can be further made uniform.

[0015] The twin-roll continuous casting apparatus of the present invention is a twin-roll continuous casting apparatus that supplies molten metal to a molten metal pool portion formed by a pair of rotating cooling rolls and a pair of side dams, and forms and grows a solidified shell on the peripheral surface of the cooling rolls to produce a thin slab, and is characterized in that it includes the above-described immersion nozzle for a twin-roll continuous casting apparatus for pouring the molten metal into the molten metal pool portion.

[0016] According to the twin-roll continuous casting apparatus having this configuration, since it is provided with the immersion nozzle for the twin-roll continuous casting apparatus described above, it becomes possible to further uniformize the outflow distribution in the width direction of the molten metal flowing out from the immersion nozzle to the molten metal pool portion at the start of casting, and it is possible to stabilize casting, suppress deterioration of the slab quality and material quality.

[0017] The method for manufacturing a thin slab of the present invention is a method for manufacturing a thin slab in which molten metal is supplied to a molten metal pool portion formed by a pair of rotating cooling rolls and a pair of side dams, and a solidification shell is formed and grown on the peripheral surface of the cooling roll to manufacture a thin slab, characterized in that the molten metal is poured into the molten metal pool portion using the immersion nozzle for the twin-roll continuous casting apparatus described above.

[0018] According to the method for manufacturing a thin slab having this configuration, since it is configured to pour the molten metal into the molten metal pool portion using the immersion nozzle for the twin-roll continuous casting apparatus described above, it becomes possible to further uniformize the outflow distribution in the width direction of the molten metal flowing out from the immersion nozzle to the molten metal pool portion at the start of casting, and it is possible to stably manufacture a high-quality thin slab.

Effect of the Invention

[0019] According to the present invention, it is possible to provide an immersion nozzle for a twin-roll continuous casting apparatus, a twin-roll continuous casting apparatus, and a method for manufacturing a thin slab, which can further uniformize the outflow distribution in the width direction of the molten metal flowing out from the immersion nozzle to the molten metal pool portion at the start of casting, and stably supply the molten metal from the tundish to the molten metal pool portion, thereby stabilizing casting, suppressing deterioration of the slab quality and material quality.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0021] Hereinafter, an immersion nozzle for a twin-roll continuous casting apparatus (hereinafter referred to as the immersion nozzle), a twin-roll continuous casting apparatus, and a method for manufacturing a thin slab according to an embodiment 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.

[0022] In the present embodiment, molten steel is used as the molten metal, and a thin slab 1 made of steel is to be manufactured. Examples of the steel grade include extra-low carbon steel with 0.001 to 0.01% C, low carbon steel with 0.02 to 0.05% C, medium carbon steel with 0.06 to 0.4% C, high carbon steel with 0.5 to 1.2% C, austenitic stainless steel typified by SUS304 steel, ferritic stainless steel typified by SUS430 steel, grain-oriented electrical steel with 3.0 to 3.5% Si, non-grain-oriented electrical steel with 0.1 to 6.5% Si, etc. (Note that % is by mass). Further, in the present embodiment, the width of the manufactured thin slab 1 is in the range of 300 mm or more and 2000 mm or less, and the thickness is in the range of 1 mm or more and 5 mm or less.

[0023] As shown in FIG. 1, the twin-roll continuous casting apparatus 10 according to the present embodiment includes a pair of cooling rolls 11, 11, bender rolls 12, 12 for bending the thin slab 1, pinch rolls 13, 13 for supporting the thin slab 1, side dams 15 disposed at the widthwise ends of the pair of cooling rolls 11, 11, and a tundish 18 for holding the molten steel 3 supplied to the molten steel pool portion 16 defined by the pair of cooling rolls 11, 11 and the side dams 15, and a submerged nozzle 20 for supplying the molten steel 3 from the tundish 18 to the molten steel pool portion 16.

[0024] As shown in FIG. 2, the molten steel surface of the molten steel pool portion 16 has a rectangular shape surrounded by the circumferential surfaces of the pair of cooling rolls 11, 11 and the pair of side dams 15, 15, and the submerged nozzle 20 is disposed at the central portion of the molten steel surface having this rectangular shape. In the present embodiment, as shown in FIG. 2, in the molten steel pool portion 16 and the submerged nozzle 20 disposed in the molten steel pool portion 16, the direction along the axial direction of the cooling roll 11 is defined as the "width direction", and the direction orthogonal to the axial direction of the cooling roll 11 is defined as the "thickness direction".

[0025] In this twin-roll continuous casting apparatus 10, as shown in FIG. 1, the molten steel 3 contacts the cooling rolls 11, 11 rotating in the R direction and is cooled, so that the solidification shells 5, 5 grow on the circumferential surfaces of the cooling rolls 11, 11, and the solidification shells 5, 5 formed on the pair of cooling rolls 11, 11 are pressed against each other at the drum kiss point, thereby casting a thin slab 1 having a predetermined thickness.

[0026] Here, as the above-described submerged nozzle 20, a submerged nozzle for a twin-roll continuous casting apparatus according to the present embodiment is used. As shown in FIG. 3, this submerged nozzle 20 includes an outer nozzle 30 and an inner nozzle 21 inserted inside the outer nozzle 30.

[0027] In the example shown in FIG. 3, the inner nozzle 21 has a tubular shape with a closed lower end and is disposed facing the inner space of the outer nozzle 30. In this inner nozzle 21, when it is disposed in the molten steel pool portion 16, discharge holes 22, 22 are provided toward both axial sides of the cooling rolls 11, 11. The shape of the inner nozzle 21 may be any shape that can discharge without bias with respect to the inner space of the outer nozzle 30, and is not limited to the above shape.

[0028] When the outer nozzle 30 is disposed in the molten steel pool portion 16, it has a side wall portion 31 extending along a direction parallel to the axis of the cooling roll 11, an end wall portion 32 intersecting the axis of the cooling roll 11, and a bottom surface portion 33 formed at the lower ends of the side wall portion 31 and the end wall portion 32, and has an inner space along the molten steel pool portion 16. Note that, as shown in FIG. 3(b), the lower region of the outer nozzle 30 is shaped such that its thickness gradually decreases downward. And at the lower end portion of the lower region of the outer nozzle 30, a discharge port 36 that opens in the direction facing the cooling roll 11 side is opened. Here, the widthwise length of the lower region of the outer nozzle 30 is within the range of 40 to 80% of the width of the thin slab 1 to be cast.

[0029] Inside the lower region of the outer nozzle 30, a pressure loss member 27 is disposed above the discharge port 36. By disposing the pressure loss member 27, in the steady state, the molten steel 3 is stored inside the outer nozzle 30. In this embodiment, it is preferable that the pressure loss member 27 has a plurality of through holes formed therethrough in the thickness direction.

[0030] And at a position above the pressure loss member 27 on the inner surface of the side wall portion 31 of the outer nozzle 30, a plurality of guide protrusion portions 38 extending in the vertical direction are formed. In this embodiment, the lower region of the outer nozzle 30 is shaped such that its thickness gradually decreases downward as shown in Fig. 3(b). Therefore, the guide rib 38 is formed to extend in the vertical direction and gradually toward the center in the thickness direction downward.

[0031] In this embodiment, as shown in Fig. 4(c), the guide rib 38 is configured such that the cross-section orthogonal to the extending direction is rectangular. Here, it is preferable that the width W of the guide rib 38 is in the range of 5 mm or more and 30 mm or less. Also, it is preferable that the protruding height H of the guide rib 38 is in the range of 3 mm or more and 20 mm or less. Furthermore, it is preferable that the pitch P of the plurality of guide ribs is in the range of 5 mm or more and 60 mm or less.

[0032] In this embodiment, as shown in Figs. 4(a) and (b), the guide rib 38 is uniformly formed in the width direction on the inner surface of the side wall portion 31. Also, the protruding height H is constant in the extending direction. Also, in this embodiment, as shown in Fig. 3, the guide rib 38 is formed above the discharge holes 22, 22 of the inner nozzle 21.

[0033] Next, a method for manufacturing a thin slab according to this embodiment using the above-described immersion nozzle 20 and twin-roll continuous casting apparatus 10 will be described.

[0034] Molten steel 3 is supplied from the tundish 18 through the immersion nozzle 20 to the molten steel pool portion 16 formed by the pair of cooling rolls 11, 11 and the side weir 15, and the pair of cooling rolls 11, 11 are rotated in the rotational direction R, that is, so that the region where the pair of cooling rolls 11, 11 are close to each other faces the drawing direction of the thin slab 1 (downward in Fig. 1).

[0035] Then, a solidified shell 5 is formed on the peripheral surface of the cooling roll 11. And the solidified shell 5 grows on the peripheral surface of the cooling roll 11, and the solidified shells 5, 5 formed on the pair of cooling rolls 11, 11 are pressed against each other at the roll kiss point, whereby a thin slab 1 with a predetermined thickness is cast.

[0036] Here, at the start of casting, the molten steel 3 is not stored inside the outer nozzle 30, and the discharge hole 22 of the inner nozzle 21 is exposed to the inner space of the outer nozzle 30. In this state, the molten steel 3 is discharged from the discharge hole 22 of the inner nozzle 21. Then, when the discharged molten steel 3 collides with the inner surface of the side wall portion 31 of the outer nozzle 30, it flows downward along the guide ridge portion 38 extending in the vertical direction, and a downward flow of the molten steel 3 is generated. As a result, a part of the molten steel 3 discharged from the inner nozzle 21 falls to the pressure loss member 27 before reaching the widthwise end of the outer nozzle 30. Also, a part of the molten steel 3 discharged from the inner nozzle 21 reaches the widthwise end of the outer nozzle 30. Thereby, the molten steel 3 is uniformly supplied in the width direction from the discharge port 36 of the outer nozzle 30 to the molten steel pool portion 16.

[0037] Note that, during the steady state of casting, since the pressure loss member 27 is disposed inside the outer nozzle 30, the molten steel 3 is stored inside the outer nozzle 30, and the discharge hole 22 of the inner nozzle 21 is immersed in the molten steel 3. In this state, the molten steel 3 is supplied from the inner nozzle 21 into the outer nozzle 30. Thereby, the molten steel 3 is uniformly supplied in the width direction from the discharge port 36 of the outer nozzle 30 to the molten steel pool portion 16.

[0038] According to the immersion nozzle 20 for a twin-roll continuous casting apparatus configured as described above, a pressure loss member 27 is disposed inside the outer nozzle 30 above the discharge port 36, and a plurality of guide protrusion portions 38 extending along the vertical direction are formed at a position above the pressure loss member 27 on the inner surface of the side wall portion 31 of the outer nozzle 30. Therefore, at the start of casting, when the molten steel 3 is discharged from the inner nozzle 21 with the discharge hole 22 of the inner nozzle 21 exposed to the inner space of the outer nozzle 30, when a part of the discharged molten steel 3 collides with the inner surface of the side wall portion 31 of the outer nozzle 30, a downward flow of the molten steel 3 is formed along the guide protrusion portion 38, and the molten steel 3 falls onto the pressure loss member 27 before reaching the widthwise end of the outer nozzle 30. Also, a part of the molten steel 3 discharged from the inner nozzle 21 reaches the widthwise end of the outer nozzle 30. Thereby, at the start of casting, it becomes possible to make the outflow distribution in the width direction of the molten steel 3 supplied from the immersion nozzle 20 to the molten steel pool portion 16 more uniform.

[0039] Further, in the present embodiment, when a plurality of through holes are provided in the pressure loss member 27, the occurrence of clogging of the pressure loss member 27 can be suppressed, and casting can be performed more stably. And as described above, by forming a plurality of guide protrusion portions 38 extending along the vertical direction on the inner surface of the side wall portion 31 of the outer nozzle 30, even when a plurality of through holes are provided in the pressure loss member 27, it becomes possible to make the outflow distribution in the width direction of the molten steel 3 supplied from the immersion nozzle 20 to the molten steel pool portion 16 more uniform.

[0040] Further, in the present embodiment, when the width W of the guide protrusion portion 38 is in the range of 5 mm or more and 30 mm or less, the molten steel 3 that has collided with the guide protrusion portion 38 can be reliably guided downward. Here, the lower limit of the width W of the guide protrusion portion 38 is more preferably 10 mm or more, and even more preferably 15 mm or more. On the other hand, the upper limit of the width W of the guide protrusion portion 38 is more preferably 25 mm or less, and even more preferably 20 mm or less.

[0041] Further, in the present embodiment, when the protrusion height H is 3 mm or more, the molten steel 3 that has collided with the guide protrusion 38 can be reliably guided downward. On the other hand, when the protrusion height H is 20 mm or less, the generation of scale on the guide protrusion 38 can be suppressed. Here, the lower limit of the protrusion height H of the guide protrusion 38 is more preferably 5 mm or more, and even more preferably 8 mm or more. On the other hand, the upper limit of the protrusion height H of the guide protrusion 38 is more preferably 15 mm or less, and even more preferably 12 mm or less.

[0042] Also, in the present embodiment, when the pitch P of the guide protrusions 38 is 5 mm or more, the generation of scale between the guide protrusions 38 can be suppressed. On the other hand, when the pitch P of the guide protrusions 38 is 60 mm or less, the molten steel 3 that has collided with the guide protrusion 38 can be reliably guided downward. Here, the lower limit of the pitch P of the guide protrusions 38 is more preferably 10 mm or more, and even more preferably 25 mm or more. On the other hand, the upper limit of the pitch P of the guide protrusions 38 is more preferably 50 mm or less, and even more preferably 40 mm or less.

[0043] Furthermore, according to the twin-roll continuous casting apparatus 10 and the method for manufacturing a thin slab in the present embodiment, since the above-described immersion nozzle 20 is used, it is possible to further uniformize the outflow distribution in the width direction of the molten steel 3 flowing out from the immersion nozzle 20 into the molten steel pool 16 at the start of casting, and to stabilize casting and suppress deterioration of the slab quality and material.

[0044] As described above, the immersion nozzle for a twin-roll continuous casting apparatus, the twin-roll continuous casting apparatus, and the method for manufacturing a thin slab according to the embodiments of the present invention have been specifically described. However, the present invention is not limited thereto, and can be appropriately modified without departing from the technical idea of the invention.

[0045] In this embodiment, as shown in FIG. 3(c), although the description has been made assuming that the cross-section orthogonal to the extending direction is rectangular, the present invention is not limited thereto. For example, as shown in FIGS. 5(a) and 5(b), the cross-section orthogonal to the extending direction may be triangular. Also, as shown in FIGS. 5(c) and 5(d), the cross-section orthogonal to the extending direction may be arcuate. Furthermore, there is no particular limitation on the shape of the portion between the guide ridge portions.

Example

[0046] Hereinafter, the experimental results carried out to confirm the effects of the present invention will be described.

[0047] Using the twin-roll type continuous casting apparatus described in the embodiment, a thin slab of low-carbon aluminum-killed steel (containing 0.01 mass% C, 0.24 mass% Si, 0.5 mass% Mn, 0.036 mass% Al, and the balance being Fe and inevitable impurities) was cast under the following conditions and with the immersion nozzle.

[0048] (Casting conditions) Diameter of the cooling roll: 1200 mm Width of the cooling roll: 1300 mm Thickness of the thin slab: 3.0 mm Casting speed: 50 mpm

[0049] (Immersion nozzle) It has an outer nozzle and an inner nozzle. Inner dimensions: long side 510 mm × short side (upper end 300 mm, lower end 60 mm) Material of the nozzle: Al2O3-C Pressure loss member: maximum thickness 36 mm, with through holes (diameter 12 mm × 20 pieces, evenly arranged in the long side direction) Material of the pressure loss member: ZrO2-CaO-C

[0050] In the example of the present invention, the guide ridge portion described in the embodiment was formed on the inner surface of the side wall portion of the outer nozzle. The width W of the guide ridge portion was 17 mm, the pitch P was 34 mm, and the protruding height H was 10 mm. In the comparative example, a guide ridge portion was not formed on the inner surface of the side wall portion of the outer nozzle.

[0051] Using the above immersion nozzle, casting of 100 channels was carried out and the casting situation was confirmed.

[0052] In the comparative example, in 45 channels out of 100 channels, at the start of casting, the cast slab broke due to solidification failure caused by uneven flow, and casting could not be started stably. Also, the deviation of the molten steel pool surface height during steady state was up to 15 mm at maximum. And longitudinal cracks occurred on the surface of the cast slab in the portion where the deviation of the molten steel pool surface height was large.

[0053] On the other hand, in the example of the present invention, casting could be started stably in all 100 channels, and the planned amount could be completely cast. Also, the deviation of the molten steel pool surface height during steady state was suppressed to 2.5 mm at maximum, and the occurrence of longitudinal cracks on the surface of the cast slab could be suppressed.

[0054] From the above, according to the example of the present invention, it is possible to make the outflow distribution in the width direction of the molten metal flowing out from the immersion nozzle to the molten metal pool portion more uniform at the start of casting, and stably supply the molten metal from the tundish to the molten metal pool portion, thereby providing an immersion nozzle for a twin-roll type continuous casting apparatus capable of stabilizing casting and suppressing deterioration of the quality and material of the cast slab, as well as a twin-roll type continuous casting apparatus and a method for manufacturing a thin slab. It was confirmed that it is possible.

Explanation of reference numerals

[0055] 1 Thin slab 10 Twin-roll type continuous casting apparatus 20 Immersion nozzle for twin-roll type continuous casting apparatus 21 Inner nozzle 22 Discharge hole 27 Pressure loss member 30 Outer nozzle 31 Side wall portion 36 Discharge port 38 Guide ridge portion

Claims

1. A dipping nozzle for a twin-roll continuous casting apparatus used in a twin-roll continuous casting apparatus that supplies molten metal to a molten metal pool formed by a pair of rotating cooling rolls and a pair of side dams, and forms and grows a solidified shell on the circumferential surface of the cooling roll to produce a thin slab, comprising: an outer nozzle and an inner nozzle for supplying molten metal into the outer nozzle; When the outer nozzle is disposed in the molten metal pool portion, the outer nozzle has a side wall portion extending along a direction parallel to the axis of the cooling roll, an end wall portion intersecting the axis of the cooling roll, and a bottom surface portion formed at the lower ends of the side wall portion and the end wall portion; A discharge port for the molten metal is formed near the bottom surface portion of the outer nozzle, and a pressure loss member is disposed above the discharge port inside the outer nozzle; A plurality of guide protrusion portions extending in the vertical direction are formed at a position above the pressure loss member on the inner surface of the side wall portion of the outer nozzle, and the guide protrusion portions are formed up to a position above the discharge holes of the inner nozzle. A dipping nozzle for a twin-roll continuous casting apparatus characterized by this.

2. The dipping nozzle for a twin-roll continuous casting apparatus according to claim 1, wherein the pressure loss member is formed with a plurality of through holes penetrating in the vertical direction.

3. The width W of the guide protrusion portion is in the range of 5 mm or more and 30 mm or less, the protruding height H of the guide protrusion portion is in the range of 3 mm or more and 20 mm or less, and the pitch P of the plurality of guide protrusion portions is in the range of 5 mm or more and 60 mm or less. The dipping nozzle for a twin-roll continuous casting apparatus according to claim 1 or claim 2, characterized by this.

4. A twin-roll continuous casting apparatus that supplies molten metal to a molten metal pool formed by a pair of rotating cooling rolls and a pair of side dams, and forms and grows a solidified shell on the circumferential surface of the cooling roll to produce a thin slab, comprising: A twin-roll type continuous casting apparatus, comprising an immersion nozzle for pouring the molten metal into the molten metal pool portion, the immersion nozzle for a twin-roll type continuous casting apparatus according to any one of claims 1 to 3.

5. A method for manufacturing a thin slab, comprising supplying molten metal to a molten metal pool portion formed by a pair of rotating cooling rolls and a pair of side dams, and forming and growing a solidified shell on the circumferential surface of the cooling rolls to manufacture a thin slab. A method for manufacturing a thin slab, characterized in that the molten metal is poured into the molten metal pool portion by using the immersion nozzle for a twin-roll type continuous casting apparatus according to any one of claims 1 to 3.

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