Twin drum continuous casting device and method for producing thin-walled cast strips

Abstract

To provide a twin-drum type continuous caster capable of advantageously avoiding molten-metal leakage and casting-fin occurrence due to insufficient sealing at slide surfaces between end faces of a cooling drum and side weirs in a duration from a start to end of casting without using abrasives or the like, and a method of producing a thin-walled slab.SOLUTION: There are provided a twin-drum type continuous caster comprising, on slide surfaces of a cooling drum with side weirs, projections having an out-of-surface height of over 0.20 mm and 0.50 mm or smaller, a width in a circumferential direction of the cooling drum of 0.50 mm or smaller, a length in a radial direction of the cooling drum of equal to or smaller than a width of the slide surface, and an arrangement pitch along the slide surface of 0.50 mm or greater and 150 mm or smaller, in which the width in the circumferential direction of the cooling drum of and the arrangement pitch along the slide surface of the projections are set up in a manner that entire side surfaces of the projections are exposed so that, even when unsteady damages are caused to ceramics slide surfaces of the side weirs, the ceramics slide surfaces can be swiftly polished to restore seal-ability, and a method of producing a thin-walled slab using the caster.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a twin-drum continuous casting machine and a method for producing a thin-walled cast strip, and more particularly to a seal between a side dam and an end face of a cooling drum in a twin-drum continuous casting machine. [Background technology]

[0002] As shown in Fig. 1, the twin-drum continuous casting technique forms a basin 30 using a pair of cooling drums 10 that rotate in opposite directions and a pair of side weirs 20 that are pressed against and in sliding contact with sliding surfaces 12 at both ends of the cooling drum 10. Furthermore, molten metal 31 continuously supplied to the basin 30 is cooled by the peripheral surface 11 of the cooling drum 10 to form a solidified shell (not shown). This solidified shell is then pressed together at the closest point (drum kiss point) of the pair of cooling drums 10 to form a thin-walled cast slab 35.

[0003] The side weir 20 that implements this technology is composed of a monolithic refractory housed in a side weir case, a base member embedded in the monolithic refractory, and ceramics embedded on the surface of the base member that faces the sliding surface 12 on the end face side of the cooling drum. During continuous casting, the ceramics of the side weir 20 are brought into close sliding contact with the sliding surface 12 on the end face side of the cooling drum, forming uniform wear grooves and preventing leakage of molten steel.

[0004] However, near the triple junctions where the side weirs 20, the cooling drum 10, and the molten metal 31 meet—more precisely, near the areas where such triple junctions are connected along the circumferential surface of the cooling drum (also referred to simply as triple junctions)—results in the formation of ingots. If this ingot breaks off and gets caught in the drum kissing points, the relative positions of the cooling drum 10 and the side weirs 20 change, often damaging the uniform wear grooves on the ceramic sliding surfaces of the side weirs 20 and creating new linear grooves. These new linear grooves can lead to molten metal leakage due to insufficient sealing between the sliding surfaces of the cooling drum 10 and the side weirs 20, potentially resulting in casting stoppage. Even if casting does not stop, these new linear grooves are undesirable because they can form protrusions called casting burrs (also referred to simply as burrs) on the ends of the thin-walled cast slab 35, adversely affecting rolling and transportation in subsequent processes.

[0005] As a technology for preventing molten metal leakage due to insufficient sealing of the sliding surface between the cooling drum 10 and the side weir 20, for example, a twin-drum continuous casting apparatus 1 is disclosed in Patent Document 1 and Patent Document 2. In the twin-drum continuous casting apparatus 1 disclosed in Patent Document 1, an abrasive supply device (not shown) is disposed on the sliding surface 12 on the end face side of the cooling drum, which is the sliding surface with the side weir 20. The abrasive supply device supplies abrasive, which is then sent to the ceramic sliding surface of the side weir 20 as the cooling drum 10 rotates. As a result, the ceramic is quickly polished and smoothed, preventing molten metal leakage from the gap between the sliding surface on the ceramic side and the sliding surface 12 on the end face side of the cooling drum.

[0006] Furthermore, in the twin-drum continuous casting apparatus 1 disclosed in Patent Document 2, the ceramic sliding surfaces (not shown) of the pair of side weirs 20 that come into contact with the sliding surfaces 12 on the end faces of the cooling drum have a surface roughness of 12.5 S to 200 S in maximum height (Rmax) as specified in JIS B 0601. This allows the sliding surfaces of the side weirs 20 to wear flat quickly, preventing leakage of molten metal from the gap between the sliding surfaces 12 on the end faces of the cooling drum. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-314945 [Patent Document 2] Japanese Patent Application Publication No. 09-220641 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the technology described in Patent Document 1, the abrasive is applied to the sliding surface 12 on the end face side of the cooling drum, and therefore, there is a concern that the abrasive may also adhere to the peripheral surface 11 of the cooling drum, causing surface defects and material deterioration of the thin-walled cast slab 35.

[0009] Furthermore, the technology described in Patent Document 2 can prevent molten metal leakage from the gap between the ceramic sliding surface of the side weir 20 and the sliding surface on the end face of the cooling drum by quickly wearing it flat, but this can only be done once. Therefore, once the ceramic sliding surface has been flattened, there is a problem that it is not possible to deal with molten metal leakage due to insufficient sealing that may occur throughout the entire casting period, from the start to the end of casting.

[0010] The present invention has been made in view of the above-mentioned circumstances, and has as its object to provide a twin-drum continuous casting apparatus and a method for producing thin slabs, which are capable of advantageously avoiding molten metal leakage and the resulting generation of burrs at the ends of thin slabs due to insufficient sealing of the sliding surfaces between the end faces of the cooling drums and the side weirs throughout the entire period from the start to the end of casting, without using abrasives that may cause quality problems such as surface defects. [Means for solving the problem]

[0011] [1] 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 cast strips by forming and growing a solidified shell on the circumferential surface of the cooling drums, The sliding surface of the cooling drum with the side weir, (a) The height in the out-of-plane direction is more than 0.20 mm and 0.50 mm or less, (b) The width of the cooling drum in the circumferential direction is 0.50 mm or less; (c) The length of the cooling drum in the radial direction is equal to or less than the width of the sliding surface. (d) The pitch along the sliding surface is 0.50 mm or more and 150 mm or less. and a protrusion portion having a shape such that The arrangement pitch of the protrusions is set so that the entire side surfaces of the protrusions are exposed. [2] The twin-drum continuous casting apparatus according to [1], wherein the shape of the protrusion portion is either a triangle, a rectangle, or a protruding shape having a curved portion in a cross section perpendicular to the radial direction of the cooling drum. [3] The twin-drum continuous casting apparatus according to [1] or [2], wherein the protrusion is divided into a plurality of parts in the radial direction of the cooling drum, and further, the divided protrusions adjacent to each other in the radial direction of the cooling drum are misaligned with each other and arranged in a staggered pattern along the sliding surface. [4] A method for producing thin slabs, in which molten steel is supplied to a molten steel reservoir formed by a pair of rotating cooling drums and a pair of side weirs, and a solidified shell is formed and grown on the circumferential surface of the cooling drums, thereby producing thin slabs, using the twin-drum continuous casting apparatus described in [1] or [2]. [5] A method for producing thin slabs, in which molten steel is supplied to a molten steel reservoir formed by a pair of rotating cooling drums and a pair of side weirs, and a solidified shell is formed and grown on the circumferential surface of the cooling drums, thereby producing thin slabs, using the twin-drum continuous casting apparatus described in [3]. [Effects of the Invention]

[0012] As described above, the present invention provides a twin-drum continuous casting apparatus and a method for producing thin slabs, which can advantageously avoid molten metal leakage and the resulting generation of burrs on the ends of thin slabs due to insufficient sealing of the sliding surfaces between the end faces of the cooling drums and the side weirs throughout the entire period from the start to the end of casting, without using abrasives that may cause quality problems such as surface defects. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a perspective view illustrating an example of a twin-drum continuous casting apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram illustrating a partial cross-sectional view of a protrusion having a triangular cross section in one embodiment of the present invention, as viewed from the radial direction of the cooling drum. [Figure 3] FIG. 10 is a partial side view schematically illustrating an example of the arrangement of a protrusion having a triangular cross section on the sliding surface on the end face side of a cooling drum in one embodiment of the present invention, as viewed from a direction perpendicular to the sliding surface on the end face side of the cooling drum. DETAILED DESCRIPTION OF THE INVENTION

[0014] A twin-drum continuous casting apparatus and a method for producing a thin-walled cast strip using the twin-drum continuous casting apparatus according to an embodiment of the present invention will be described below with reference to the accompanying drawings. However, the present invention is not limited to the following embodiment.

[0015] FIG. 1 is a perspective view illustrating an example of a twin-drum continuous casting apparatus according to one embodiment of the present invention, and FIG. 2 is a schematic partial cross-sectional view of a protrusion having a triangular cross section according to one embodiment of the present invention, as viewed from the radial direction of the cooling drum.

[0016] 3A and 3B are partial side views schematically illustrating an example of the arrangement of protrusions having a triangular cross section on the sliding surface of the end face of the cooling drum according to one embodiment of the present invention, viewed from a direction perpendicular to the sliding surface of the end face of the cooling drum. Fig. 3A shows an example of the arrangement of protrusions across the entire width of the sliding surface in the sliding direction. Fig. 3B shows an example of the arrangement of protrusions divided into two in the width direction of the sliding surface, and further arranged in a staggered pattern with mutual displacement along the sliding surface.

[0017] In continuous casting using the twin-drum continuous casting apparatus 1 of this embodiment, as shown in FIG. 1, the sliding surface 12 on the end face of the cooling drum 10 is in close sliding contact with the ceramic of the side weir 20 under steady-state conditions. This forms uniform wear grooves in the ceramic of the side weir 20, ensuring sealing and preventing molten metal leakage. However, due to the aforementioned jamming of the bare metal into the drum kissing points, the relative positions of the cooling drum 10 and the side weir 20 may fluctuate, damaging the uniform wear grooves on the ceramic sliding surface and resulting in a non-steady-state condition, resulting in a sealing failure. To prevent such a situation, as shown in FIGS. 2 and 3, the sliding surface 12 on the end face of the cooling drum 10 of this embodiment is provided with a predetermined protrusion 15. This allows the ceramic sliding surface of the side weir 20 to be quickly polished and a uniform wear groove to be re-formed. Therefore, in this embodiment, molten metal leakage due to a sealing failure does not occur even under non-steady-state conditions.

[0018] That is, in the twin-drum continuous casting apparatus 1 of this embodiment shown in Fig. 1, predetermined protrusions 15 are provided on the sliding surface 12 of the cooling drum 10 that contacts the side weir 20 as shown in Fig. 2 and Fig. 3. Therefore, regardless of whether the casting is in a steady state or an unsteady state as described above, the ceramic sliding surface of the side weir 20 is constantly worn, thereby ensuring sealing performance and preventing leakage of molten metal.

[0019] Next, specific conditions for the protrusions 15 disposed on the sliding surface 12 of the cooling drum 10 with the side weir 20 of this embodiment will be described with reference to FIGS.

[0020] The out-of-plane height h of the protrusions 15 is set to be greater than 0.20 mm and less than or equal to 0.50 mm. If the out-of-plane height h of the protrusions 15 is less than 0.20 mm, the wear on the ceramic sliding surface of the side weir 20 does not progress sufficiently during the unsteady state of casting described above, making it difficult to quickly reform uniform wear grooves. Furthermore, if the out-of-plane height h of the protrusions 15 is greater than 0.50 mm, the wear on the ceramic sliding surface of the side weir 20 progresses, creating a gap between the end face of the cooling drum and the sliding surface of the side weir 20, which could result in steel leakage.

[0021] The width w of the protrusion 15 in the circumferential direction of the cooling drum is 0.50 mm or less. If the width w of the protrusion 15 in the circumferential direction of the cooling drum exceeds 0.50 mm, the contact area between the end face of the cooling drum and the sliding surface of the side weir 20 becomes too large, resulting in surface contact. In such a case, a gap is likely to form between the sliding surface of the end face of the cooling drum and the side weir 20, which may cause steel leakage.

[0022] The length of the protrusions 15 in the radial direction of the cooling drum is equal to or less than the width of the sliding surface 12. Figure 3(a) shows an example in which the length of the protrusions 15 in the radial direction of the cooling drum is the same as the width of the sliding surface 12. It is impossible to make the length of the protrusions 15 in the radial direction of the cooling drum longer than the width of the sliding surface 12 because there is no installation surface, and the length can be equal to or less than the sliding surface 12 as long as the protrusions 15 can achieve the polishing effect on the ceramic sliding surface of the side weir 20. The width of the sliding surface 12 is generally about 10 mm ± 5 mm.

[0023] The arrangement pitch p of the protrusions 15 along the sliding surface 12 is set to 0.50 mm or more and 150 mm or less. If the arrangement pitch p is smaller than 0.50 mm, wear debris from the ceramic sliding surface of the side weir 20 will clog the gaps between the protrusions 15 arranged at a small arrangement pitch during long-term casting, preventing wear on the ceramic sliding surface of the side weir 20. On the other hand, if the arrangement pitch p is larger than 150 mm, the number of protrusions 15 per unit area will be extremely small, preventing sufficient wear on the ceramic sliding surface of the side weir 20.

[0024] Furthermore, the arrangement pitch of the protrusions along the sliding surface must be set so that the entire side surface of the protrusions is exposed. For example, if the width w of the protrusions 15 is 0.50 mm, the pitch p is the same as the width w of the protrusions 15, 0.50 mm, and the cross-sectional shape of the protrusions is typically rectangular, the following problem occurs. In such a case, the entire side surface of the protrusions 15 is not exposed, which is the same as when the protrusions 15 are not arranged, and the protrusions 15 cannot fulfill their function of polishing the ceramic sliding surface of the side weir 20.

[0025] If the cross-sectional shape of the protrusions 15 has vertices, the pitch p of the protrusions 15 is defined as the distance p between the vertices, as shown in Fig. 2. If no such vertices exist, the pitch p is similarly defined by regarding the center position of the upper part of the cross-sectional shape of the protrusions 15 as the vertex.

[0026] The cross-sectional shape of the protrusion 15 is preferably triangular, rectangular, or a protruding shape with a curved portion. A triangular cross-sectional shape is preferable because, as shown in FIG. 2, the apex 16 of the protrusion 15 efficiently increases the pressing force per unit area against the ceramic sliding surface, thereby promoting wear of the ceramic sliding surface. On the other hand, a triangular cross-sectional shape makes the apex 16 more likely to wear in response to high pressing forces. Therefore, a rectangular cross-sectional shape or a protruding shape with a curved portion can be used to mitigate the tendency of the protrusion 15 itself to promote wear. Typical examples of a protruding shape with a curvature include, but are not limited to, a semicircular or semi-elliptical shape. Furthermore, when the cross-sectional shape of the protrusion 15 is triangular or rectangular, the corners may be chamfered.

[0027] The arrangement of the protrusions 15 on the sliding surface 12 is not limited to the case shown in FIG. 3( a), in which the length of the protrusions 15 in the radial direction of the cooling drum is equal to the width of the sliding surface 12. As shown in FIG. 3( b), the protrusions 15 may be divided into multiple parts in the radial direction of the cooling drum, and adjacent divided protrusions in the radial direction of the cooling drum may be arranged in a staggered pattern along the sliding surface 12. This staggered arrangement of the protrusions 15 is preferable because it allows wear debris from the ceramic sliding surface of the side weir 20 to be more efficiently removed from the gaps between the protrusions 15. The division of the protrusions 15 in the radial direction of the cooling drum may be equal or unequal.

[0028] Since the protrusions 15 are formed on the sliding surface 12 on the end face side of the cooling drum, they are required to have the same thermal shock resistance as the plating layer on the sliding surface 12 on the end face side of the cooling drum. Therefore, the material for the protrusions 15 is preferably nickel or a nickel-based alloy that has the same thermal shock resistance as the plating layer on the sliding surface 12 on the end face side of the cooling drum. Furthermore, when improving wear resistance, the material for the protrusions 15, together with the plating layer on the sliding surface 12 on the end face side of the cooling drum, can be a tungsten-containing nickel-based alloy.

[0029] The method for forming the protrusions 15 involves first forming a normal plating layer about 2 to 3 mm thick on the sliding surface 12 on the end face side of the cooling drum, and then cutting the surface of the plating layer by machining such as cutting. Note that the cutting depth in this case is at most about 0.50 mm in the out-of-plane direction height of the protrusions 15 of the present invention, and does not impair the function of the conventional plating layer on the sliding surface 12 on the end face side of the cooling drum. Note that, if necessary, the thickness of the plating layer formed before cutting may be increased to a thickness that takes this cutting depth into consideration.

[0030] Here, the thin-walled cast slab 35 produced in this embodiment can be, for example, steel having various component compositions, and may have a width in the range of 100 mm to 2000 mm and a thickness in the range of 0.5 mm to 6 mm. [Example]

[0031] The following describes the results of experiments conducted 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.

[0032] First, we will explain the common conditions for the thin-walled cast slab production experiments. Using a twin-drum continuous casting machine, we cast thin-walled cast slabs made of steel with a composition (by mass): 0.05% C, 0.6% Si, 1.5% Mn, 0.03% Al, with the remainder being Fe and impurities. The cooling drum of the twin-drum continuous casting machine was 600 mm in diameter and 600 mm wide. It consisted of an internally water-cooled drum body and a copper sleeve attached to its outer periphery, with the peripheral surface of the copper sleeve plated with Ni. The sliding surfaces on the end faces of the cooling drum were Ni-plated and provided with protrusions as shown in Table 1. The ceramic material for the sliding surfaces of the side weirs was boron nitride (BN). The side weirs were pressed against the cooling drum with loads of 3.9 to 14.7 kN during casting. The depth of the molten steel in the molten steel pool was 212 mm, and a circumferential speed of the cooling drum was 50 m / min. Thin-walled billets with a thickness of 2 mm were cast. After the casting experiment, the presence or absence of casting burrs in the thin-walled billets was confirmed, and the appearance of the side dams was observed to check for linear grooves that occur in an unsteady state in addition to uniform wear grooves on the ceramic sliding surface, and for defects at the bottom ends of the side dams. In this example, the presence or absence of casting burrs was used to determine whether the product was acceptable or not.

[0033] Table 1 summarizes the protrusion conditions and evaluation results for the invention examples and comparative examples. In invention examples 1 to 12 and comparative examples 2 to 6, protrusions with a triangular cross section were provided on the sliding surface on the end face side of the cooling drum. Comparative example 1 was an example where no such protrusions were provided. In invention examples 13 and 14, the cross section of the protrusions was square, and in invention example 15, the cross section of the protrusions was a protruding shape with a curved section, where the upper half of a square with sides of 0.3 mm was replaced with a semicircle with a curvature radius of 0.15 mm. In invention examples 11 and 12, the protrusions were divided into multiple sections in the radial direction of the cooling drum, and further, adjacent divided protrusions in the radial direction of the cooling drum were arranged in a staggered pattern along the sliding surface. In invention example 11, the protrusions were divided into two equal sections, and in invention example 12, the protrusions were divided into three equal sections. In the invention examples and comparative examples other than invention examples 11 and 12 and comparative example 1 in which no protrusions were provided, the protrusions were not divided in the radial direction of the cooling drum.

[0034] As shown in Table 1, in Examples 1 to 15, which satisfied all the requirements of the present invention, no casting burrs were observed on the thin-walled cast slabs, and no abnormalities were observed on the side dams after casting, such as linear grooves that occur in an unsteady state or chipped areas at the bottom ends of the side dams. On the other hand, in Comparative Examples 1 to 6, either linear grooves that occur in an unsteady state on the side dams or chipped areas at the bottom ends of the side dams were observed, and casting burrs were observed on the ends of the thin-walled cast slabs.

[0035] [Table 1] [Explanation of symbols]

[0036] 1. Twin drum continuous casting equipment 10 Cooling drum 11 Cooling drum peripheral surface 12 Sliding surface on the end face side of the cooling drum 15 Projection part 16 Top 20 Side Weir 30 Bathtub 31 Molten Metal 35 Thin-walled billets

Claims

1. 1. A twin-drum continuous casting apparatus for producing thin-walled slabs 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, The sliding surface of the cooling drum with the side weir, (a) The height in the out-of-plane direction is more than 0.20 mm and 0.50 mm or less; (b) the width in the circumferential direction of the cooling drum is 0.50 mm or less; (c) the length of the cooling drum in the radial direction is equal to or less than the width of the sliding surface; (d) the arrangement pitch along the sliding surface is 0.50 mm or more and 150 mm or less and a protrusion portion having a shape such that The arrangement pitch is set so that the entire side surface of the protrusion portion is exposed. Twin drum continuous casting equipment.

2. 2. The twin-drum continuous casting apparatus according to claim 1, wherein the shape of the protrusions is any one of a triangular, a rectangular, and a protruding shape having a curved portion in a cross section perpendicular to the radial direction of the cooling drum.

3. 3. The twin-drum continuous casting device according to claim 1, wherein the protrusion is divided into a plurality of parts in the radial direction of the cooling drum, and further, the divided protrusions adjacent to each other in the radial direction of the cooling drum are misaligned with each other and arranged in a staggered pattern along the sliding surface.

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, using the twin-drum continuous casting apparatus according to claim 1 or 2.

5. 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, using the twin-drum continuous casting apparatus according to claim 3.

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