Dummy sheet for twin-drum continuous casting and method for manufacturing thin-walled cast slabs

Abstract

To provide a twin drum type continuous casting dummy sheet capable of removing a bullion before the bullion is coarsened and starting stable casting, and to provide a manufacturing method of a thin slab.SOLUTION: A twin drum type continuous casting dummy sheet includes: a sheet body held between a pair of cooling drums; and a reinforcing member extending from one end of the sheet body and inserted into molten steel, wherein the reinforcing member is configured to: (a) form one or two plates or a strip group equivalent to a width of the plate which are arranged on a peripheral surface of one or both of the pair of cooling drums, (b2) has a front end surface in a casting direction consisting of one or both of an inclined surface that is inclined in a direction where a distance d from a tangent plane of a cooling drum end face decreases with casting and a vertical surface perpendicular to the casting direction and facing a front side in the casting direction (b1) within 10 mm or less of the tangent plane of the cooling drum end face (b) on an outer end part of the reinforcing member at both end positions of the width of the sheet body, and (b3) has one or more front end surfaces in the casting direction in any range of 200 mm in the casting direction.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a twin-drum continuous casting dummy sheet used at the start of casting in a twin-drum continuous casting apparatus that produces thin-walled slabs by supplying molten metal to a molten metal reservoir formed by a pair of cooling drums and a pair of side weirs, and to a method for producing thin-walled slabs. [Background technology]

[0002] A method for producing thin-walled cast steel slabs has been proposed, which uses a twin-drum continuous casting machine equipped with cooling drums having an internal water-cooling structure, in which molten steel is supplied to a molten steel reservoir formed between a pair of rotating cooling drums, solidified shells are formed and grown on the circumferential surfaces of the cooling drums, the solidified shells formed on the respective circumferential surfaces of the pair of cooling drums are joined at drum kiss points, and the resulting mixture is pressed down to produce thin-walled cast slabs of a predetermined thickness.

[0003] When starting casting in such a twin-drum continuous casting method, as shown in Patent Documents 1 and 2, for example, a dummy sheet is sandwiched between the cooling drums, and the cooling drums are rotated while molten steel is supplied to a molten steel reservoir formed by the pair of cooling drums and the pair of side weirs, to form a thin cast piece connected to the dummy sheet, and the dummy sheet and the thin cast piece connected to the dummy sheet are then pulled out from between the cooling drums.

[0004] At the start of casting, because casting conditions such as the amount of molten steel supplied to the molten steel reservoir and the temperature of the cooling drum are unstable, the strength of the thin billet connected to the dummy sheet may be insufficient, causing problems such as breakage of the thin billet when the dummy sheet is withdrawn, preventing the start of casting. For this reason, Patent Documents 1 and 2 above propose techniques for securing the strength of the thin billet at the start of casting by arranging a reinforcing member connected to the dummy sheet and encasing this reinforcing member in molten metal. For example, Patent Document 2 proposes a dummy sheet 30 for twin-drum continuous casting, as shown in FIG. 8, in which a thin or thick reinforcing member 38 made of a high-melting-point material is attached to the leading end of the sheet body.

[0005] Here, the solidified shell is assumed to form on the circumferential surface of the cooling drum. However, in actual operation, molten steel may also solidify on the surface of the side gates, forming a base metal. As this base metal grows and fuses with the solidified shell on the circumferential surface of the rotating cooling drum at the end of the cooling drum, it is peeled off from the side gate surface and, together with the solidified shell, is caught in the drum kissing point and sent downward through the casting machine. In this case, the drum gap temporarily expands beyond the actual thickness of the slab in an attempt to pass the thick base metal. As a result, the areas not containing the base metal (e.g., the center of the width direction) contain a large amount of unsolidified, high-temperature molten steel. This is called a hot band. Because this hot band is hotter and more fragile than the sound areas before and after it in the casting direction, it may break under the weight of the thin-walled slab.

[0006] To prevent breakage caused by hot bands and ensure stable casting, it is important to prevent the formation and coarsening of ingots on the side dams. Hot bands are often caused by the separation of ingots that form on the side gates when the molten metal level is unstable. They also tend to form during the initial stage of casting, when the molten metal level rises. This is because the molten metal is first brought into contact with the side gate surface, which had not previously been in contact with molten metal, and is then cooled, making it easy for ingots to form.

[0007] As a method for preventing breakage of thin-walled cast slabs due to hot bands, for example, Patent Document 3 proposes a means for suppressing the generation of metal on the surface of the side dam at the start of casting by sufficiently preheating the side dam. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 57-058957 [Patent Document 2] Japanese Patent Application Publication No. 63-224847 [Patent Document 3] Japanese Patent Application Publication No. 62-124051 Summary of the Invention [Problem to be solved by the invention]

[0009] However, even when the side weirs are preheated as in Patent Document 3, the temperature of the side weirs inevitably drops because the side weirs are brought into close contact with the end surface of the cooling drum to form a molten steel reservoir. In particular, when the molten steel level rises to a steady level in the early stages of casting, the molten steel first comes into contact with the side weirs, whose temperature has been reduced by being pressed against the end surface of the cooling drum. This increases the likelihood of ingot formation and increases the risk of breakage due to hot bands. Furthermore, the higher the melting point of the steel, the more the side weirs must be preheated to a high temperature. Therefore, in the case of carbon steels, which have a relatively higher melting point than stainless steels, the side weirs are often not preheated sufficiently, which increases the likelihood of hot bands occurring.

[0010] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a twin-drum continuous casting dummy sheet that, even if metal is generated and grows on the surface of a side dam at the start of casting, can remove the metal at an early stage before it coarsens, thereby suppressing breakage of thin-walled cast strips caused by hot bands and enabling a stable start of casting, and a method for manufacturing thin-walled cast strips using this twin-drum continuous casting dummy sheet. [Means for solving the problem]

[0011] [1] A twin-drum continuous casting dummy seat used in a twin-drum continuous casting apparatus that supplies molten steel to a molten steel reservoir formed by a pair of rotating cooling drums and a pair of side weirs, and produces thin-walled slabs by forming and growing a solidified shell on the circumferential surface of the cooling drums, the dummy seat comprising: a seat body sandwiched between the pair of cooling drums; and a reinforcing member extending from one end of the seat body in the longitudinal direction on the slab connection side and inserted into the molten steel, the reinforcing member comprising: (a) one or two plate-shaped members disposed along the circumferential surface of one or both of the pair of cooling drums; (b) at each end on both sides in the width direction, (b1) Within a range of 10 mm or less from a plane in contact with the end surface of the cooling drum, (b2) A front end surface in the casting direction is formed by either or both of an inclined surface inclined in a direction in which the distance d from the plane tangent to the end surface of the cooling drum decreases as casting progresses, and a vertical surface that is perpendicular to the casting direction and faces forward in the casting direction, (b3) The casting direction front end surface is located at one or more locations within any 200 mm range in the casting direction. A dummy seat for twin-drum continuous casting, characterized in that

[0012] [2] The dummy seat for twin-drum continuous casting according to [1], characterized in that the shape of the inclined surface satisfies formula (1). Δd / ΔL≦-5 / 100 (1) Here, Δd is the change in the distance d of the inclined surface from the plane that is in contact with the end surface of the cooling drum, and a decrease in d is considered negative, and ΔL is the movement distance of the reinforcing member in the casting direction corresponding to Δd.

[0013] [3] The reinforcing member is (a') Instead of the one or two plate shapes, a plurality of band-shaped plates extending in the casting direction are arranged without any gaps in the width direction or with a predetermined gap, so that the sum of the widths of the plurality of band-shaped plates, including the width of the gaps, is the same as the width of the one or two plate shapes, forming an aggregate of band-shaped reinforcing members; (b') Among the belt-shaped reinforcing members, the belt-shaped reinforcing members located at both ends in the width direction of the seat body have outer end surfaces in the width direction, each having the casting direction front end surface. The twin-drum continuous casting dummy seat according to [1] or [2],

[0014] [4] The reinforcing member is (a'') Instead of the two plate shapes, a plurality of strip-shaped plates extending in the casting direction are arranged without any gaps in the width direction or with a predetermined gap between them, to form an assembly of strip-shaped reinforcing members in which the sum of the widths of the plurality of strip-shaped plates, including the width of the gaps, is the same as the width of the two plate shapes, and further, excluding the strip-shaped reinforcing members located at both ends in the width direction of the sheet body or including the strip-shaped reinforcing members located at both ends in the width direction of the sheet body, the strip-shaped reinforcing members arranged in the width direction are arranged alternately, with one strip-shaped reinforcing member for one cooling drum and one strip-shaped reinforcing member for the other cooling drum being omitted, (b') Among the belt-shaped reinforcing members, the belt-shaped reinforcing members located at both ends in the width direction of the seat body have outer end surfaces in the width direction, each having the casting direction front end surface. The twin-drum continuous casting dummy seat according to [1] or [2],

[0015] [5] A method for producing thin slabs, which comprises supplying molten steel to a molten steel reservoir formed by a pair of rotating cooling drums and a pair of side weirs, and forming and growing a solidified shell on the circumferential surface of the cooling drums to produce thin slabs, characterized in that a twin-drum continuous casting dummy seat according to any one of [1] to [4] is used at the start of casting. [Effects of the Invention]

[0016] As described above, according to the present invention, even if metal is generated and grows on the surface of the side dam at the start of casting, by removing the metal at an early stage before it coarsens, it is possible to suppress breakage of thin-walled cast strips caused by hot bands and to start casting stably, and it is possible to provide a twin-drum continuous casting dummy sheet and a method for manufacturing thin-walled cast strips using this twin-drum continuous casting dummy sheet. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is an explanatory diagram illustrating an example of a twin-drum continuous casting apparatus according to an embodiment of the present invention. [Figure 2] 1A and 1B are explanatory views of a dummy seat for twin-drum continuous casting according to one embodiment of the present invention, in which (a) is a side view and (b) is a view taken along the arrow XX. [Figure 3] 1 is an explanatory view of a twin-drum continuous casting dummy seat having a plate-shaped reinforcing member according to a first embodiment of the present invention.

[0022] FIG. [Figure 4] FIG. 4 is an explanatory view of a twin-drum continuous casting dummy seat having a strip-shaped reinforcing member according to a second embodiment of the present invention. [Figure 5] FIG. 10 is a plan view illustrating a twin-drum continuous casting dummy sheet having strip-shaped reinforcing members alternately arranged in the width direction, according to a third embodiment of the present invention, attached to a twin-drum continuous casting machine before the start of casting. [Figure 6] 1 is an explanatory diagram of the dimensional relationship between different examples of end boundary shapes at the width direction end of a reinforcing member provided in a twin-drum continuous casting dummy seat according to one embodiment of the present invention. FIG. [Figure 7] 1 is an explanatory diagram of the dimensional relationship of an example in which the end boundary shape at the width direction end of a reinforcing member provided in a twin-drum continuous casting dummy seat according to one embodiment of the present invention includes a partial circle. FIG. [Figure 8] FIG. 10 is an explanatory view of a linear reinforcing member provided in a twin-drum continuous casting dummy seat according to the prior art. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, a twin-drum continuous casting dummy sheet (hereinafter simply referred to as a dummy sheet) and a method for producing a thin-walled cast slab using the dummy sheet 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 embodiment.

[0019] Here, the thin-walled cast slab 1 produced in this embodiment is made of steel of various compositions, and has a width in the range of 100 mm to 2000 mm, and a thickness in the range of 1 mm to 6 mm.

[0020] As shown in FIG. 1 , the twin-drum continuous casting apparatus 10 of this embodiment includes a pair of cooling drums 11, 11, bender rolls 12, 12 for bending the thin cast slab 1, pinch rolls 13, 13 for supporting the thin cast slab 1, side weirs 15 disposed at the widthwise ends of the pair of cooling drums 11, 11, a tundish 18 for holding molten steel 3 to be supplied to a molten steel reservoir 16 defined by the pair of cooling drums 11, 11 and the side weirs 15, and an immersion nozzle 20 for supplying molten steel 3 from the tundish 18 to the molten steel reservoir 16.

[0021] In this twin-drum continuous casting apparatus 10, the molten steel 3 comes into contact with the rotating cooling drums 11, 11 and is cooled, causing solidified shells 5, 5 to grow on the peripheral surfaces of the cooling drums 11, 11, and the solidified shells 5, 5 formed on the pair of cooling drums 11, 11 are pressed together at a drum kiss point K (see Figure 2), thereby casting a thin-walled cast 1 of a predetermined thickness.

[0022] In the twin-drum continuous casting apparatus 10 of this embodiment, at the start of casting, a twin-drum continuous casting dummy seat 30 of this embodiment is placed between a pair of cooling drums 11, 11 as shown in FIG. As shown in FIG. 2, this twin-drum continuous casting dummy seat 30 includes a seat body 31 arranged from below the pair of cooling drums 11, 11 to the drum kiss point K, and a reinforcing member 32 arranged to extend from one longitudinal end of the seat body 31 on the slab connection side into the molten steel reservoir 16.

[0023] In this state, molten steel 3 is poured from the tundish 18 into the molten steel reservoir 16 via the submerged nozzle 20. When the surface of the molten steel 3 in the molten steel reservoir 16 reaches a predetermined position, the cooling drums 11, 11 are rotated in the R direction (see FIG. 1 ). Then, the molten steel 3 moves between the cooling drums 11, 11 together with the reinforcing member 32, and as the molten steel 3 solidifies, the reinforcing member 32 and the thin billet 1 are joined together, and the thin billet 1 is then pulled out following the dummy sheet 30.

[0024] The reinforcing member 32 is formed from a plate of a high melting point metal, for example, Mo, and the plate thickness can be 0.2 mm or more, preferably 0.5 mm or more and 2 mm or less, taking into consideration strength and workability.

[0025] Here, when the molten steel 3 is poured into the molten steel reservoir 16, ingots may be generated and grow on the surface of the side weir 15. In particular, at the triple junction where the side weir 15, the cooling drum 11, and the molten steel 3 come into contact, or more precisely, at the region where such triple junctions are connected along the circumferential surface of the cooling drum (also simply referred to as the triple junction region), the molten steel 3 is cooled from two directions, that is, the cooling drum 11 and the side weir 15. Therefore, ingots are likely to be deposited on the surface of the side weir 15 in the vicinity. This ingots coarsen and become caught in the drum kiss point K, causing severe hot bands and resulting in fractures of the thin-walled cast slab 1.

[0026] In order to remove the base metal that is likely to be generated at the triple junction area before it becomes coarse, in the dummy sheet 30 of this embodiment, after generation, the attached base metal in the early growth stage is removed by applying an external force from the thick part of the solidified shell 5 formed by the boundary shapes of each end part on both sides in the width direction of the reinforcing member 32 disposed nearby.

[0027] Here, we will explain the thickened portion of the solidified shell 5 near the reinforcing member 32 on the cooling drum 11, which is created by the boundary shape of both widthwise ends of the reinforcing member 32. When the reinforcing member 32 is present nearby, the reinforcing member 32, made of a high-melting-point metal, acts as a coolant by itself. Therefore, the thickness of the solidified shell 5 is the total thickness resulting from the cooling action of the reinforcing member 32 in addition to the thickness resulting from the cooling action of the cooling drum 11. By utilizing this phenomenon, for example, near the reinforcing member 32 having an end boundary shape that is inclined so that the distance d to the plane tangent to the end face of the cooling drum (i.e., the surface of the side weir 15 at the beginning of casting) decreases as casting progresses, a thickened portion can be formed in which the thickness of the solidified shell 5 is thicker than before and after the casting direction due to the increased cooling action of the reinforcing member 32 as the distance d decreases. By applying an external force from the thickened portion of the solidified shell 5 to the deposited metal, the deposited metal can be removed from the surface of the side weir 15.

[0028] However, considering the relationship between the immobile metal adhering to the surface of the side weir 15 and the solidified shell 5 formed on the circumferential surface of the rotating cooling drum 11 and moving in the casting direction, the boundary shape of the reinforcing member end must have a portion where the distance d to the surface of the side weir 15 decreases in the casting direction. If the distance d were constant in the casting direction, the increase in thickness of the solidified shell 5 due to the cooling action of the reinforcing member 32 would also remain constant in the casting direction. Since the distance between the reinforcing member and the solidified shell 5 would not change, new external forces would not be applied to the metal adhering to the surface of the side weir 15. Furthermore, if the boundary shape of the reinforcing member end were sloped so that the distance d to the surface of the side weir 15 increases as casting progresses, the cooling effect of the reinforcing member would decrease in the vicinity of the reinforcing member end, preventing the formation of a thick portion where the solidified shell 5 is thicker than before and after the casting direction. Consequently, the distance between the metal adhering to the surface of the side weir 15 and the solidified shell 5 would increase, preventing the application of new external forces to the adhering metal.

[0029] Therefore, in the twin-drum continuous casting dummy seat 30 according to the first embodiment of the present invention, as shown in FIGS. 3 and 6, the reinforcing member 32 is (a) One or two plate-shaped reinforcing members 32a are arranged along the circumferential surface of one or both of the pair of cooling drums 11, (b) At each end of both sides in the width direction of the reinforcing member 32 (32a), (b1) Within a range of 10 mm or less from a plane in contact with the end surface of the cooling drum 11, (b2) a casting direction front end surface 35 including either or both of an inclined surface 35a inclined in a direction in which the distance d from the plane tangent to the end surface of the cooling drum 11 decreases as casting proceeds, and a vertical surface 35b perpendicular to the casting direction and facing forward in the casting direction; (b3) The casting direction front end surface 35 is located at one or more points within any 200 mm range in the casting direction. Do so.

[0030] The thick-walled portions at the widthwise ends of the solidified shell 5 formed as described above are relatively thicker than the portion of the solidified shell 5 ahead in the casting direction. Therefore, after contacting the metal adhering to the surface of the side weir 15 near the triple junction, they penetrate between the cooling drum 11 and the adhering metal, pushing the adhering metal radially outward from the cooling drum 11. As a result, the adhering metal separates from the side weir surface, moving parallel to the surface of the side weir 15 and being pushed radially outward from the cooling drum 11. Before this separation, the metal and the solidified shell are fused together by the pressing force generated between the thick-walled portions and the adhering metal. As a result, the metal moves along with the solidified shell 5 and is caught up in the drum kiss point K. Because the metal caught up in the drum kiss point K is not yet coarsened, it is ultimately discharged from the molten metal pool without generating a severe hot band.

[0031] Here, the plane of the dummy sheet 30 that contacts the end face of the cooling drum 11 is assumed to be the plane that contacts the end face of the cooling drum 11 at the start of casting after the dummy sheet 30 is attached to the twin-drum continuous casting apparatus 10. Therefore, for the dummy sheet 30 before attachment to the twin-drum continuous casting apparatus 10, the plane that contacts the end face of the cooling drum 11 corresponds to the plane that contacts the widthwise end of the slab, and the distance d is specified based on this plane. In practice, the dummy sheet 30 for twin-drum continuous casting of this embodiment is attached to the twin-drum continuous casting apparatus 10 before the start of casting so that the plane that contacts the end face of the cooling drum 11, as defined by the dummy sheet 30, coincides with the plane that contacts the end face of the cooling drum 11 before the start of casting. Furthermore, for the dummy sheet 30 before attachment to the twin-drum continuous casting apparatus 10, the reinforcing member 32 may be attached to the sheet body 31 so as to ensure the distance d from the plane that contacts the end face of the cooling drum 11 after aligning the center line of the sheet body 31 in the width direction with the center line of the cooling drum 11. The reinforcing member 32 can be attached to the sheet body 31 by, for example, passing a thin metal wire through holes 36 provided in the reinforcing member 32 and the sheet body 31 .

[0032] Furthermore, the end faces of both widthwise ends of the reinforcing member 32 (32a) are not limited to flat surfaces perpendicular to the plate surface of the reinforcing member 32 (32a), but also include inclined surfaces, rounded curved surfaces, etc. When this end face is an inclined surface or a curved surface, the distance d is defined as the shortest distance to a plane that is in contact with the end face of the cooling drum 11.

[0033] In this embodiment, the reinforcing member 32 (32a) has, at each end on both sides in the width direction, a casting direction front end face 35, which is composed of either or both of: (b1) an inclined surface 35a within a range of 10 mm or less from a plane tangent to the end face of the cooling drum 11, (b2) an inclined surface 35a that slopes in a direction in which the distance d from the plane tangent to the end face of the cooling drum 11 decreases as casting progresses, and a vertical surface 35b that is perpendicular to the casting direction and faces forward in the casting direction. The casting direction front end face 35 is the front end face in the casting direction of a width protruding portion 34 that is disposed so as to protrude outward in the width direction as an end boundary shape of both width direction ends of the reinforcing member 32 (32a). (b1) is a condition for the widthwise range of the thick-walled portion of the solidified shell 5 for applying an external force, since the metal to which an external force is applied in this embodiment is located near the triple junction. It is also a condition for the widthwise range of the front end face 35 of the width-protruding portion 34 in the casting direction, which is required to achieve a thickness change in the solidified shell 5 in the casting direction that fully demonstrates the effects of this embodiment. (b2) is a condition for forming a thick-walled portion of the solidified shell that is relatively thicker than those before and after the casting direction. Even if the distance d is within a range of 10 mm or less, if the distance d is constant, the thickness of the solidified shell 5 at the widthwise end will be constant except for a limited region in the casting direction behind the vertical surface 35b (front end face 35 in the casting direction) of the width-protruding portion 34, which has a vertical surface perpendicular to the casting direction (see "Converted Line Fraction Ratio (%) of Region (A)" described later). Therefore, no pressing force is generated even when the adhering metal and the solidified shell come into contact with each other, and the adhering metal removal effect of this embodiment will not be achieved. Furthermore, if the distance d exceeds 10 mm, the thickness of the solidified shell 5 at the widthwise end portion will decrease, so no pressing force will be generated and the effect of removing the deposited base metal of this embodiment will not be obtained.

[0034] The above (b1) and (b2) must be satisfied simultaneously for the removal of the base metal. In the following explanation, the region where (b1) and (b2) are satisfied will be referred to as region (A). In region (A), the thickness of the solidified shell 5 at the width direction end changes depending on the distance d. The thick portion of the solidified shell 5 at region (A) directly removes the base metal. On the other hand, in a region where either (b1) or (b2) is not satisfied, a solidified shell 5 that has the effect of removing the base metal cannot be formed. In the following explanation, this region will be referred to as region (B). A region where the distance d exceeds 10 mm does not satisfy (b1). A region where the distance d is constant or increases does not satisfy (b2).

[0035] The preferred range of the distance d from the casting direction front end face 35, which forms portion (A) of the reinforcing member 32 (32a), is 5 mm or less, because the shorter the distance d, the stronger the pressing force when the solidified shell 5 at the widthwise end portion contacts the adhering ingot, thereby improving the ingot removal effect. However, if the distance d is too short, the widthwise protruding portion 34 forming the boundary shape of the widthwise end portion of the reinforcing member 32 (32a) may scrape the surface of the side weir 15, possibly destroying the side weir 15. Therefore, it is sufficient that the end of the reinforcing member 32 (32a) is close enough to the side weir 15 so as not to come into contact with it. On the other hand, the distance d from portion (B) of the reinforcing member 32 (32a) may exceed 10 mm.

[0036] The shape of the inclined surface 35a of (b2) is preferably such that it satisfies the formula (1). Δd / ΔL≦-5 / 100 (1) Here, Δd is the change in the distance d from the plane that contacts the end surface of the cooling drum 11 to the inclined surface 35a (front end surface 35 in the casting direction) of the widthwise protrusion 34, and is considered negative when d decreases, and ΔL is the movement distance in the casting direction of the reinforcing member 32 (32a) that corresponds to Δd (ΔL is an absolute value and takes a positive value). Note that when the front end surface 35 in the casting direction of the widthwise protrusion 34 is a vertical surface 35b that is perpendicular to the casting direction, ΔL can be considered to be 0, and the value of the left side of equation (1) becomes negative infinity, so equation (1) is also valid in this case.

[0037] An effective means for changing the distance d is to change the shape of the outer end boundary of the reinforcing member 32 (32a) in the width direction to a shape other than a straight line parallel to the plane tangent to the end surface of the cooling drum 11. For example, any shape, such as a rectangle, triangle, or curve, may be used. Furthermore, even if the shape is straight, the distance d can be changed by tilting it relative to the plane tangent to the end surface of the cooling drum 11. The shape of the outer end boundary of the reinforcing member 32 (32a) in the width direction may be determined based on factors such as ease of processing. Furthermore, as long as the distance d changes in the casting direction, the change in the distance d in the casting direction and the length and interval in the casting direction corresponding to that change are not particularly limited. Furthermore, the shape of the end boundary may be periodic or aperiodic.

[0038] In this embodiment, the reinforcing member 32 (32a) has the casting direction front end surface 35 of the width-protruding portion 34 of the portion (A) that satisfies (b1) and (b2) at least one location within any 200 mm range in the casting direction (b3). If the casting direction front end surface 35 of the reinforcing member 32 (32a) has a portion (B) that does not satisfy either (b1) or (b2) for a continuous length of 200 mm or more in the casting direction, metal deposits will form and grow coarsely in the portion. If this coarse metal deposit is then removed in the subsequent portion (A), severe hot bands will occur, increasing the risk of slab fracture. Therefore, the continuous length of the portion (B) in the casting longitudinal direction must be kept less than 200 mm. As long as the continuous length per portion (B) is less than 200 mm, the reinforcing member 32 (32a) may have multiple portions (B) throughout its entire length. That is, wherever a continuous 200 mm section is selected along the longitudinal direction of casting, it is necessary that at least one portion (A) is included.

[0039] The proportion of the length of the reinforcing member 32 (32a) occupied by the portion (A) (hereinafter also referred to as the linear fraction (%) of the portion (A)) in the casting direction is preferably 20% or more, and more preferably 50% or more, taking into consideration the processing load of the end boundary shape of the reinforcing member 32 (32a) and the effect of suppressing hot bands. When the reinforcing member 32 (32a) has portions (A) and (B), the proportion of the portion (A) in the casting direction is preferably 20% or more, and more preferably 50% or more. Note that when the widthwise end boundary shape of the reinforcing member 32 (32a) has a rectangular width-protruding portion 34 that protrudes outward in the width direction and has a vertical surface 35b (casting-direction front end face 35) perpendicular to the casting direction, the casting-direction length of the casting-direction front end face 35 of the width-protruding portion 34 may be extremely short. For example, considering the case where ΔL in Equation (1) is 0, the proportion of the portion (A) in the casting direction may be calculated as 0. However, as mentioned in the explanation of Equation (1) above, if the surface perpendicular to the casting direction rises instantaneously, the left side of Equation (1) becomes negative infinity, which indicates that the effect of removing ingots adhering to the side weir is very large. Therefore, the effect of removing ingots adhering to the side weir is maintained within a certain range in the casting direction behind the vertical surface 35b, which is the front end surface 35 of the widthwise protrusion 34 in the casting direction. Furthermore, because the front end surface 35 of the widthwise protrusion 34 in the casting direction is not an inclined surface whose distance d changes as casting progresses, the removed ingots are deposited in front of the vertical surface 35b, which is the front end surface 35 of the widthwise protrusion 34 in the casting direction, thereby providing the effect of artificially increasing the thickness of the solidified shell 5 ahead in the casting direction. Based on the results of tests conducted by the inventors, it was estimated that a 1 mm change in the height of the rectangle (in the width direction of the reinforcing member), i.e., a 1 mm change in the distance d of the vertical surface 35b (the front end surface 35 in the casting direction) perpendicular to the casting direction (limited to a range of d≦10 mm), would result in an effect of approximately 2.5 mm in the casting direction. In other words, a 1 mm change in the height of the rectangle would have an effect equivalent to ΔL = 2.5 mm in equation (1).In this way, when the widthwise end boundary shape includes the width-protruding portion 34 having the casting direction front end face 35 which is the vertical surface 35b perpendicular to the casting direction, ΔL of this vertical surface 35b is zero. Therefore, the change in the distance d of the vertical surface 35b (casting direction front end face 35) perpendicular to the casting direction (limited to the range of d≦10 mm) of 1 mm may be set to ΔL=2.5 mm, and the “converted line fraction rate (%) of portion (A)” may be used, which is the ratio of portion (A) to the length of the reinforcing member 32 (32 a).

[0040] Furthermore, in this embodiment, the above conditions (b1) to (b3) must be satisfied at both widthwise ends of the reinforcing member 32 (32a). If the above conditions (b1) to (b3) are not satisfied at either widthwise end of the reinforcing member 32 (32a), the coarsened metal formed on the surface of the side weir 15 will be caught in the drum kiss point K, causing severe hot bands and resulting in fracture of the thin-walled cast slab 1. However, the portion (A) does not need to be located at the same position in the casting direction at both widthwise ends of the reinforcing member 32 (32a), and the distance d may vary independently on the left and right. Therefore, the same shape pattern may be repeated on the left and right with a shifted period, or the shape itself may be different on the left and right.

[0041] Next, a preferred number of reinforcing members 32 (32a) provided on the dummy sheet 30 according to this embodiment will be described. The side weirs 15 contact both ends of the pair of cooling drums 11, and the area in contact with the molten metal pool 16 expands to the left and right of the surface of the side weirs 15 as it moves upward from the drum kiss point K, forming a shape similar to an inverted triangle or a wedge. The triple junction where the side weirs 15, the cooling drum 11, and the molten steel 3 come into contact, or more precisely, the triple junctions (triple junction regions) where the triple junctions are connected along the circumferential surface of the cooling drum, are located at two positions at each end in the casting width direction, corresponding to the front and back of the slab in the thickness direction, and approach the thickness of the slab at the drum kiss point K.

[0042] As described above, because the molten steel 3 is cooled from two directions, the cooling drum 11 and the side weir 15, at the triple junction, ingots are likely to form. Removing the ingots formed near each of the two triple junctions at one widthwise end of the pair of cooling drums (i.e., one side weir 15) is effective in preventing hot bands. Therefore, in this embodiment, it is preferable that two reinforcing members 32 (32a), the end boundary shapes of which vary in the casting direction at both ends in the casting width direction, be attached, one on each side, along the circumferential surfaces of the pair of cooling drums 11. Since these two reinforcing members are attached to the sheet body 31 in a stacked manner, the connection between the sheet body 31 and the reinforcing member 32 (32a) is structured such that one sheet body 31 and two reinforcing members 32 (32a) overlap. When the overlapping joints pass through the drum kiss point K, they are discharged overlapping each other, sandwiching the solidified shells 5 formed around the reinforcing members 32 (32a) of the two cooling drums 11.

[0043] On the other hand, the area where the formation of ingots is particularly likely is the narrow area near the drum kiss point K. This is because the gap between the two cooling drums 11 narrows, bringing the triple junctions closer, and thus the molten steel 3 is more easily cooled. Even if only one reinforcing member 32 (32a) of this embodiment is used for the two cooling drums 11, the ingots formed in this narrow area can be sufficiently removed. Therefore, the effect of the reinforcing member 32 (32a) of this embodiment can be sufficiently obtained even with only one member. The number of reinforcing members 32 (32a) can be selected by comparing the manufacturing cost and the effort required to deform and shape the two overlapping reinforcing members 32 (32a) so that they fit the circumferential surfaces of the cooling drums 11 before the start of casting, and the hot band suppression effect.

[0044] Next, a preferred length of the reinforcing member 32 (32a) provided on the dummy sheet 30 according to this embodiment will be described. In order to reinforce the area including the joint between the sheet body 31 and the leading edge of the slab, which has unstable strength due to high temperatures in the early stages of casting, the length is preferably about 1 / 4 of the circumference of the cooling drum 11 or more. Since the diameter of the cooling drum 11 is generally several hundred mm, the length of the reinforcing member 32 may also be several hundred mm or more.

[0045] As described above, Fig. 3 shows an example of a dummy sheet 30 of this embodiment, in which plate-shaped reinforcing members 32 (32a) are attached to the sheet body 31. The reinforcing members 32 (32a) have widthwise protruding portions 34 at both widthwise ends, each having a front end face 35 in the casting direction where the distance d changes. The reinforcing members 32 (32a) in this example have widthwise protruding portions 34 whose end boundaries facing the surfaces of the side weirs 15 change into rectangular shapes. The distance d becomes smaller at the front end faces 35 in the casting direction of the widthwise protruding portions 34, and the thickness of the solidified shell 5 at the widthwise ends is relatively thicker than at the front and rear portions in the casting direction. Therefore, even if ingots are formed and grow on the surfaces of the side weirs at the start of casting, they can be removed at an early stage before they become coarse. This prevents breakage of the thin-walled slab due to hot bands and allows for a stable start of casting. The example of the reinforcing member 32 (32a) shown in FIG. 3 has the same rectangular pattern at both ends in the width direction, but the period of the pattern is shifted in the casting direction.

[0046] 4 is a diagram illustrating a twin-drum continuous casting dummy seat 30 including strip-shaped reinforcing members 32 (32b, 32bc, 32be) according to a second embodiment of the present invention. Up to this point, the embodiment in which the reinforcing member 32 (32a) according to the first embodiment is plate-shaped has been described. In the second embodiment of the present invention, the reinforcing members 32 (32b, 32bc, 32be) are (a') A plurality of strip-shaped plates extending in the casting direction are arranged without any gaps in the width direction or with a predetermined gap between them, so that the sum of the widths of the plurality of strip-shaped plates, including the width of the gaps, is the same as the width of one or two plate shapes, forming an assembly of strip-shaped reinforcing members 32b (32bc, 32be); (b') Of the belt-shaped reinforcing members 32b (32bc, 32be), the belt-shaped reinforcing members 32be located at both ends in the width direction of the seat body 31 have the casting direction front end faces 35 at their outer end faces in the width direction. A dummy seat 30 for twin-drum continuous casting.

[0047] In the second embodiment, it is preferable to arrange a plurality of reinforcing members 32b (32bc, 32be) in the width direction at predetermined intervals in the width direction. This is because the solidified shell 5 is formed so as to wrap around each divided strip-shaped reinforcing member 32b (32bc, 32be), thereby enhancing the reinforcing effect of the solidified shell 5.

[0048] Furthermore, of the strip-shaped reinforcing members 32b (32bc, 32be) of the second embodiment, the outer widthwise ends of the reinforcing members 32be at both widthwise ends have widthwise protruding portions 34 having the same configuration as in the first embodiment as the casting direction front end faces 35. Therefore, by changing the distance d in the casting direction, it is possible to obtain the same effect as in the first embodiment. Of the multiple reinforcing members 32b (32bc, 32be) in the width direction, the strip-shaped reinforcing members 32bc arranged on the inside other than the both end portions may be straight strip-shaped reinforcing members with a constant width and widthwise side surfaces parallel to the casting direction.

[0049] In the example of the reinforcing member 32b (32bc, 32be) shown in FIG. 4, all the strip-shaped plates have the same length, but the lengths of the respective plates may be changed. In addition, the example of the reinforcing member 32b (32bc, 32be) shown in Figure 4 is an example in which the same rectangular pattern is formed on the outside of each of the widthwise end band-shaped reinforcing members 32be at both ends in the width direction, but the period of the pattern is shifted in the casting direction.

[0050] FIG. 5 is a plan view illustrating a twin-drum continuous casting dummy sheet 30 according to a third embodiment of the present invention, which includes strip-shaped reinforcing members 32 (32b, 32bc, 32be) arranged alternately in the width direction, attached to a twin-drum continuous casting apparatus 10 before the start of casting. The third embodiment of the present invention is different from the second embodiment of the present invention in that the reinforcing members 32b (32bc, 32be) are (a'') The difference is that, excluding the band-shaped reinforcing members 32be located at both ends of the width direction of the sheet main body 31, or including the band-shaped reinforcing members 32be located at both ends of the width direction of the sheet main body 31, the band-shaped reinforcing members 32bc, 32be arranged in the width direction are arranged alternately, with one band-shaped reinforcing member 32bc, 32be for one cooling drum 11 and one band-shaped reinforcing member 32bc, 32be for the other cooling drum 11 being omitted from each other.

[0051] In the third embodiment, the strip-shaped reinforcing members 32bc, 32be are alternately arranged in the width direction with one reinforcing member removed from each other, and therefore the solidified shell 5 is formed to wrap around each of the strip-shaped reinforcing members 32bc, 32be, thereby further enhancing the reinforcing effect of the solidified shell 5.

[0052] Furthermore, of the strip-shaped reinforcing members 32b (32bc, 32be) of the third embodiment, the outer widthwise ends of the reinforcing members 32be at both widthwise ends have widthwise protruding portions 34 having the same configuration as the first and second embodiments' front end faces 35 in the casting direction, so that by changing the distance d in the casting direction, it is possible to obtain the same effects as the first and second embodiments. Of the multiple reinforcing members 32b (32bc, 32be) in the width direction, the strip-shaped reinforcing members 32bc arranged on the inside other than the both end portions may be straight strip-shaped reinforcing members with a constant width and widthwise side surfaces parallel to the casting direction.

[0053] In the example of the reinforcing member 32b (32bc, 32be) shown in FIG. 5, all the strip-shaped plates have the same length, but the lengths of the respective plates may be changed. In addition, the example of the reinforcing member 32b (32bc, 32be) shown in Figure 5 is an example in which the same rectangular pattern is formed on the outside of each of the widthwise end band-shaped reinforcing members 32be at both ends in the width direction, but the period of the pattern is shifted in the casting direction. [Example]

[0054] The following describes the results of experiments conducted in Examples 1 to 3 to confirm the effects of the present invention. Note that the present invention includes the various forms described above as embodiments, and is not limited to the forms of the examples described below.

[0055] The common experimental conditions for the thin-walled cast slab manufacturing methods of Examples 1 to 3 are as follows. Cooling drum diameter: 1200mm Casting width: 1300mm Casting thickness: average 2.0mm Casting speed: Average 60m / min Casting atmosphere: Ar Casting volume: 10 tons Casting steel type: low carbon steel

[0056] The following dummy seats were used: Seat body: Mild steel sheet material, width 1290mm Shape of reinforcing member: Strip-shaped (multiple pieces arranged across the casting width) Reinforcement material: Mo Reinforcement material thickness: 0.5 mm Reinforcement member length: 400~800mm Reinforcing member width: The reinforcing member width is 15 mm (except at both ends) (the boundary shape at the width end is a straight line) The reinforcing members at both ends are given a predetermined boundary shape on the outer side of the width of the 15 mm wide strip material.

[0057] The ends of the sheet body and the reinforcing member in the casting direction were overlapped, and holes were drilled in the overlapping area, through which wires were passed to join them.

[0058] In the present invention examples No. 1-6 and No. 1-7, two reinforcing members 32b (32be) are attached at both ends (see width end band-shaped reinforcing member 32be in Figure 5). In the other examples, the reinforcing members 32b (32be) at both ends are attached one by one without overlapping (see Figure 4). In addition, in examples No. 1-6 and No. 1-7, the reinforcing members 32b (32bc) at other than both ends are attached one by one without overlapping.

[0059] Each of the multiple reinforcing members 32b (32bc, 32be) located in the casting width direction was deformed to fit the circumferential surface of the cooling drum before being attached. More specifically, since there was a pair of cooling drums, the direction of deformation of the reinforcing members 32b (32bc, 32be) was alternated, and the reinforcing members 32b (32bc, 32be) were attached to each cooling drum with every other reinforcing member 32b (32bc, 32be) spaced apart and in a shape that fit the circumferential surface (as shown in Figure 5, the reinforcing members 32be were also attached to both ends in the width direction, one at a time). However, since two reinforcing members 32be with modified end boundary shapes were attached to the dummy sheet body at both ends of No. 1-6 and No. 1-7 as shown in Figure 5, one reinforcing member was attached to each cooling drum so that it fit the circumferential surface.

[0060] The boundary shapes given to the widthwise outer portions of the reinforcing members 32be at the widthwise ends are all shown in Fig. 6. Fig. 6(a) shows the end boundary shape of Example 1, which is rectangular and includes a vertical surface 35b on the front end face 35 in the casting direction, Fig. 6(b) shows the end boundary shape of Example 2, which is triangular and includes an inclined surface 35a on the front end face 35 in the casting direction, and Fig. 6(c) shows the end boundary shape of Example 3, which is curved and includes an inclined surface 35a on the front end face 35 in the casting direction.

[0061] Casting was carried out under the above conditions, and the number of hot bands that occurred within one minute from the start of casting and the presence or absence of breakage in the thin-walled cast slab were visually observed and evaluated. The number of hot bands was evaluated in descending order of quality, with ○ being 1 or less, △ being 2 to 3, and × being 4 or more. The overall evaluation was ○ for no breakage and the number of hot bands occurring 1 or less, △ for no breakage and the number of hot bands occurring 2 to 3, and × for breakage. The evaluation results for Examples 1 to 3 are shown in Tables 1 to 3, respectively. [Example]

[0062] Example 1 is an example in which the end boundary shape includes a rectangle, and a schematic diagram of the end boundary shape is shown in Figure 6(a). Casting was carried out by repeating one cycle shown in the figure. Circles indicate the start and end points of a cycle. In other words, the end point of the previous cycle overlaps with the start point of the next cycle. When the end boundary shape includes a rectangle, as in Example 1, the end boundary shape is easy to process. As shown in (a) and (b) of Figure 6(a) at the front end surface 35 in the casting direction, the distance d decreases vertically, so the gradient defined by equation (1) is minus infinity, which is very large. The line fraction of the portion (A) relative to the total length of the reinforcing member 32 is expressed as the converted line fraction defined above. The evaluation results are summarized in Table 1.

[0063] Inventive Examples No. 1-1 to No. 1-7 satisfied all of the requirements of the present invention, and no slab fracture occurred, resulting in an overall rating of ○ or △. Among these, when comparing No. 1-1 and No. 1-2, which had a higher converted linear fraction ratio of the portion (A), with No. 1-3 to No. 1-5, which had a lower converted linear fraction ratio of the portion (A), it can be seen that No. 1-1 and No. 1-2, which had a higher converted linear fraction ratio of the portion (A), were able to limit the number of hot bands to one or less. In addition, No. 1-1 to No. 1-5 are examples in which there is one reinforcing member 32be at both ends, but No. 1-6 and No. 1-7 are examples in which two reinforcing members 32be are stacked on top of each other at both ends, and one reinforcing member 32be is attached to each of the peripheral end portions of the two cooling drums so that it fits along the edge.Since the reinforcing member 32be of the present invention is attached to the peripheral end portion of each cooling drum, hot bands were further reduced compared to No. 1-2 and No. 1-5.

[0064] On the other hand, in Comparative Example No. 1-11, the distance d3 was constant and did not change, L3, exceeded 200 mm, and in Comparative Example No. 1-12, the distances d1 to d4 at each part all exceeded 10 mm, so the metal removal effect was not achieved and the cast piece broke, resulting in an overall rating of ×.

[0065] [Table 1] [Example]

[0066] Example 2 is an example in which the end boundary shape includes a triangle, and a schematic diagram of the end boundary shape is shown in Figure 6(b). In the figure, the section between L1 and L4 is the area (A) where the bare metal removal effect is achieved. The evaluation results are shown in Table 2. The line segment ratio (%) of area (A) to the total length can be defined as (L1 + L4) / (ΣLi) × 100 (i = 1 to 6). Also, for example, in the section L1 in the figure, the distance d from the plane tangent to the end surface of the cooling drum decreases from d1 to d2, so Δd=d2-d1 and ΔL=L1.

[0067] Inventive examples No. 2-1 and No. 2-2 have a shape that changes into a mountain shape, and Nos. 2-3 to 2-5 have a sawtooth shape in which the distance d of the inclined surface changes vertically. Inventive Examples No. 2-1 to No. 2-5 satisfied all of the requirements of the present invention, and no slab fracture occurred. The overall evaluation was ○ or △. Among these, comparing No. 2-1 with No. 2-2, No. 2-2, which had a relatively small absolute value of the negative gradient of the region (A), had an increased number of hot bands, although within the allowable range. Furthermore, comparing No. 2-2, No. 2-3, and No. 2-5, the absolute value of the negative gradient of the region (A) was low and comparable, and the linear fraction of the region (A) was also high and comparable. However, No. 2-3 had a relatively short cycle of repetition of the end boundary shape, which increased the frequency of occurrence of the region (A) and reduced the number of hot bands. In addition, in No. 2-4, the line fraction (%) of the entire length accounted for by the portion (A) was 0%, but since the end boundary shape had a casting direction front end face 35 which was a vertical surface 35b perpendicular to the casting direction, the converted line fraction (%) of the portion (A) used for evaluation in Example 1 showed a value equivalent to the line fraction (%) of the portion (A) in No. 2-1.Furthermore, in No. 2-1 and No. 2-4, the absolute value of the negative gradient of the portion (A) was relatively larger than in the other examples, so no hot bands occurred.

[0068] On the other hand, in Comparative Example No. 2-11, the length of section L5 where the distance d increases exceeded 200 mm, and in Comparative Example No. 2-12, the total length of sections L5 and L6 exceeded 200 mm, so the metal removal effect was not obtained and slab fracture occurred, and the overall evaluation was poor.

[0069] [Table 2] [Example]

[0070] Example 3 is an example in which the end boundary shape includes a curve, such as a semicircle or part of a circle, and schematic diagrams of the end boundary shape are shown in Figures 6(c) and 7. In the figure, the section between L2 and L4 is the area (A) where the bare metal removal effect is achieved. The line segment ratio (%) of area (A) to the total length can be defined as (L2 + L4) / (ΣLi) × 100 (i = 1 to 6). The evaluation results are summarized in Table 3.

[0071] Inventive example No. 3-1, semicircles are arranged in contact with each other without any gaps (see Fig. 7(a)), while No. 3-2 and No. 3-3 are examples in which parts of the circles are arranged with gaps (see Figs. 7(b) and (c)). No. 3-3 has an opening that is larger than the semicircles (see Fig. 7(c)). Inventive Examples No. 3-1 to No. 3-3 satisfied all of the requirements of the present invention, and no slab fracture occurred, resulting in an overall rating of ○ or △. Among these, when comparing No. 3-1, which has a high linear fraction of the portion (A), with Nos. 3-2 and 3-3, which have lower linear fractions of the portion (A), it can be seen that No. 3-1, which has a high linear fraction of the portion (A), was able to limit the number of hot bands to one or less.

[0072] On the other hand, in Comparative Example No. 3-11, the length of the section L5 where the distance d was constant and did not change exceeded 200 mm, so the metal removal effect was not obtained and the slab broke, resulting in an overall rating of ×.

[0073] In the third embodiment, a semicircle or a portion of a circle is described as a typical example of a curve, but the present invention is not limited to a portion of a circle and can use any curve, such as an ellipse or a sine curve.

[0074] [Table 3] [Explanation of symbols]

[0075] 1 Thin-walled cast billets 3 Molten steel (molten metal) 5 Solidified shell 10. Twin drum continuous casting equipment 11 Cooling drum 12 Vendor Roles 13 Pinch Roll 15 Side Weir 16 Molten steel reservoir (molten metal pool) 18 Tundish 20 Submerged Entry Nozzle 30 Dummy seat for twin drum continuous casting 31 Seat body 32 Reinforcement member 32a Plate-shaped reinforcing member 32b Belt-shaped reinforcing member 32bc width center strip reinforcement member 32be Width edge strip reinforcement member 34 Width protruding part 35 Casting direction front end face 35a Inclined surface of front end face in casting direction 35b Vertical plane of the front end face in the casting direction 36 Hole 38 Linear reinforcement member

Claims

1. A twin-drum continuous casting dummy seat used in a twin-drum continuous casting apparatus that supplies molten steel to a molten steel reservoir formed by a pair of rotating cooling drums 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 cooling drums, a sheet body sandwiched between the pair of cooling drums; and a reinforcing member extending from one end of the sheet body in a longitudinal direction on a side where the slab is connected and inserted into the molten steel, The reinforcing member is (a) one or two plate-shaped members disposed along the circumferential surface of one or both of the pair of cooling drums; (b) at each end on both sides in the width direction, (b1) Within a range of 10 mm or less from a plane contacting the end surface of the cooling drum, (b2) A front end surface in the casting direction is formed of either or both of an inclined surface that is inclined in a direction in which the distance d from the plane tangent to the end surface of the cooling drum decreases as casting progresses and whose shape satisfies Δd / ΔL≦−5 / 100, and a vertical surface that is perpendicular to the casting direction and faces forward in the casting direction; (b3) The portion not satisfying either (b1) or (b2) extends continuously for less than 200 mm in the casting direction. A dummy seat for twin-drum continuous casting, characterized in that where: Δd is a change in the distance d of the inclined surface from the plane that is in contact with the end surface of the cooling drum, and a decrease in d is considered negative, ΔL is the moving distance of the reinforcing member in the casting direction corresponding to Δd.

2. The reinforcing member is (a') Instead of the one or two plate shapes, a plurality of strip-shaped plates extending in the casting direction are arranged without any gaps in the width direction or at predetermined intervals, so that the sum of the widths of the plurality of strip-shaped plates, including the width of the predetermined intervals, is the same as the width of the one or two plate shapes, forming an aggregate of strip-shaped reinforcing members; (b') Among the belt-shaped reinforcing members, the belt-shaped reinforcing members located at both ends in the width direction of the seat body have the casting direction front end faces at their widthwise outer ends.

2. The dummy seat for twin-drum continuous casting according to claim 1 , wherein the dummy seat is a dummy seat for twin-drum continuous casting.

3. The reinforcing member is (a'') Instead of the two plate shapes, a plurality of strip-shaped plates extending in the casting direction are arranged without any gaps in the width direction or at predetermined intervals, so that the sum of the widths of the plurality of strip-shaped plates, including the width of the predetermined intervals, is the same as the width of the two plate shapes, forming an aggregate of strip-shaped reinforcing members; Furthermore, the assembly of the belt-shaped reinforcing members excluding the belt-shaped reinforcing members located at both ends in the width direction of the sheet main body, or the assembly of the belt-shaped reinforcing members including the belt-shaped reinforcing members located at both ends in the width direction of the sheet main body, are arranged so that the belt-shaped reinforcing members for one cooling drum and the belt-shaped reinforcing members for the other cooling drum are arranged alternately, (b') Among the belt-shaped reinforcing members, the belt-shaped reinforcing members located at both ends in the width direction of the seat body have the casting direction front end faces at their widthwise outer ends.

2. The dummy seat for twin-drum continuous casting according to claim 1 , wherein the dummy seat is a dummy seat for twin-drum continuous casting.

4. A method for producing a thin cast slab by supplying molten steel to a molten steel reservoir formed by a pair of rotating cooling drums and a pair of side weirs, and forming and growing a solidified shell on a peripheral surface of the cooling drums, comprising: A method for producing a thin-walled cast strip, characterized in that the twin-drum continuous casting dummy seat according to any one of claims 1 to 3 is used at the start of casting.

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