Title of invention: Method for manufacturing slabs
Technical field
[0001]
　The present invention relates to a method for producing a slab in which a molten metal is supplied to a molten metal reservoir formed by a pair of cooling drums and a pair of side weirs to produce a slab.
Background technology
[0002]
　As a method for producing a thin-walled metal slab (hereinafter, may be referred to as a cast strip), for example, as shown in Patent Documents 1 and 2, a twin drum provided with a cooling drum having a water-cooled structure inside. A manufacturing method using a type continuous casting apparatus is provided. In such a manufacturing method, molten metal is supplied to a molten metal reservoir formed between a pair of rotating cooling drums, and solidified shells formed and grown on the peripheral surfaces of the pair of cooling drums are formed and grown at a drum kiss point. It is joined and reduced to produce a slab of a predetermined thickness. The manufacturing method using such a twin drum type continuous casting apparatus is applied to various metals.
[0003]
　Here, in the above-mentioned twin drum type continuous casting apparatus, in order to produce a slab having a uniform thickness in the plate width direction, the pressure is set so that the rotation axes of the pair of cooling drums are held in parallel with each other. Control is done.
　Therefore, in Patent Document 1, the pressing forces at both ends of one cooling drum are detected and added, and the sum of the pressing forces at both ends of one cooling drum is set to a predetermined value by a signal based on the detection and addition. A method has been proposed in which both ends of the cooling drum are moved in parallel by a hydraulic cylinder.
[0004]
　When starting casting in the above-mentioned twin drum type continuous casting apparatus, a dummy sheet is sandwiched between the cooling drums, and the molten metal is placed in the molten metal reservoir formed by the pair of cooling drums and the pair of side dams. Supply. Then, when a certain amount of molten metal is accumulated in the molten metal pool, the cooling drum is rotated to form a slab so as to be connected to the dummy sheet, and the dummy sheet and the dummy sheet are connected from between the cooling drums. The slab is pulled out.
[0005]
　Therefore, in the unsteady state immediately after the start of casting, the deviation of the thickness of the solidified shell is large, and when the pressure is controlled as in Patent Document 1, the solidified shell may not be sufficiently reduced at the drum kiss point. .. In that case, an unsolidified portion is formed in the central portion of the thickness of the slab, the surface temperature of the slab becomes relatively high, the strength is insufficient, the slab is broken, and the casting cannot be started stably. In particular, as the solidified shell grows with the cooling drum stopped, a hump-shaped thickened portion (hereinafter, may be referred to as a thickened portion) is formed on the slab immediately after the start of casting. When this thick portion passes through the drum kiss point, the casting becomes unstable.
[0006]
　Therefore, Patent Document 2 proposes a method of switching the pressure control between the pair of cooling drums immediately after the start of casting and in the steady state.
　Specifically, in the first step from when the cooling drum is rotated and started until the thick part of the slab passes through the latest contact (drum kiss point) of the cooling drum, a pair of cooling is performed without parallel control of the cooling drum. Press at a relatively low pressure in the direction in which the drum approaches. Then, in the second step from after the first step until the influence of shell washing by the discharge flow of molten steel from the nozzle disappears, the cooling drum is pressed at a higher pressure than in the first step without parallel control. Further, in the third step after the second step, parallel control is performed so that the rotation axes of the pair of cooling drums are parallel to each other.
[0007]
　In Patent Document 2, since the pair of cooling drums are simply pressed in the non-stationary state immediately after the start of casting in which the deviation in the thickness of the solidified shells is large, the solidified shells are sufficiently pressed down at the drum kiss point. It is possible to prevent the formation of an unsolidified portion in the central portion of the thickness of the slab. The second step until the effect of shell washing due to the discharge flow of molten steel from the nozzle disappears is the period until the molten metal level rises sufficiently, and in this period, the cooling drum rotates about 0.4 times. To do.
Prior art literature
Patent documents
[0008]
Patent Document 1: Japanese Patent Application Laid-Open No. 01-166863
Patent Document 2: Japanese Patent No. 2957040
Outline of the invention
Problems to be solved by the invention
[0009]
　However, even when the pressure of the pair of cooling drums is controlled by the method described in Patent Document 2, the metal formed on the surface of the side weir is caught between the cooling drums at the start of casting. At the drum kiss point, the solidified shells could not be sufficiently pressed down, and the slabs sometimes broke.
[0010]
　The present invention has been made in view of the above-mentioned situation, and is a method for producing a slab capable of suppressing breakage of a slab and stably starting casting in a twin-drum type continuous casting apparatus. The purpose is to provide.
Means to solve problems
[0011]
　The gist of the present invention is as follows.
[0012]
(1) In the first aspect of the present invention, molten metal is supplied to a molten metal pool formed by a pair of rotating cooling drums and a pair of side dams, and a solidified shell is provided on the peripheral surfaces of the pair of cooling drums. Is a method for producing a slab by forming and growing a slab, which is formed when the molten metal is supplied to the molten metal reservoir with the pair of cooling drums stopped at the start of casting. In the first step until the thick portion of the slab passes through the recent contact point of the pair of cooling drums after the rotation of the cooling drums is started, one end side of the pair of cooling drums in the rotation axis direction and the other In the second step from after the first step until the pair of cooling drums make one or more rotations, the pair of cooling drums are pressed toward each other with the same first pressure on the end sides. The pair of cooling drums press the one end side and the other end side of the pair of cooling drums in the rotation axis direction in the same direction and at a second pressure higher than the first pressure in a direction close to each other. In the third step after the second step, the total value of the reaction forces on one end side and the other end side in the rotation axis direction of the pair of cooling drums is set to a predetermined value, and the pair of cooling drums Pressure is controlled so that the axes of rotation are held in parallel with each other.
(2) In the method for producing a slab according to the above (1), the second step may be a period from after the first step until the pair of cooling drums make two or more rotations.
Effect of the invention
[0013]
　According to the slab manufacturing method described in (1) and (2) above, parallel control is not performed during the period when the thermal expansion portion of the cooling drum formed at the start of casting comes into contact with the side weir. One end side and the other end side of the pair of cooling drums in the rotation axis direction are pressed with the same pressure. Therefore, even if the bullion is caught between the cooling drums, the solidified shells can be sufficiently pressed down at the drum kiss point, and the formation of an unsolidified portion in the central portion of the thickness of the slab is suppressed. As a result, breakage of the slab is suppressed, and casting can be started stably.
　Further, in the first step, one end side and the other end side of the pair of cooling drums in the rotation axis direction are pressed by the same first pressure with each other in the direction in which the pair of cooling drums are close to each other. The thick part can be passed between the cooling drums relatively stably.
　Further, in the second step, since the cooling drum is pressed with a second pressure higher than the first pressure, the solidified shells can be sufficiently pressed down at the drum kiss point, and the solidified shells cannot be solidified in the central portion of the thickness of the slab. It is possible to suppress the formation of a portion.
[0014]
　In particular, according to the slab manufacturing method described in (2) above, the above-mentioned thermal expansion portion remains up to the second rotation by setting the period until the cooling drum rotates twice or more as the second step. Even in this case, the one end side and the other end side in the rotation axis direction of the pair of cooling drums are pressed with the same pressure. Therefore, the solidified shells can be sufficiently pressed down at the drum kiss point, and the formation of an unsolidified portion in the central portion of the thickness of the slab can be suppressed. As a result, breakage of the slab can be suppressed and casting can be started stably.
[0015]
　As described above, according to the present invention, in the twin-drum type continuous casting apparatus, it is possible to provide a slab manufacturing method capable of suppressing the breakage of the slab and stably starting the casting. ..
A brief description of the drawing
[0016]
FIG. 1 is an explanatory diagram showing an example of a twin-drum type continuous casting apparatus used in the method for producing a slab according to an embodiment of the present invention.
FIG. 2 is a partially enlarged explanatory view of the twin drum type continuous casting apparatus shown in FIG.
FIG. 3 is an enlarged explanatory view of a side weir of the twin drum type continuous casting apparatus shown in FIG.
FIG. 4 is a cross-sectional explanatory view of FIG.
FIG. 5 is an explanatory view of a cooling drum and a side weir at the start of casting.
FIG. 6 is an explanatory diagram showing a pressure control method of a cooling drum in the first step, the second step, and the third step.
[Fig. 7] Fig. 7 is a graph showing the relationship between the drum reaction force and the drum gap in the comparative example.
FIG. 8 is a graph showing the relationship between the drum reaction force and the drum gap in Example 1 of the present invention.
Mode for carrying out the invention
[0017]
　As a result of diligent studies by the present inventors in order to solve the above problems, the following findings were obtained.
　In the twin-drum type continuous casting apparatus, as described above, since the molten metal is supplied to the molten metal reservoir with the cooling drum stopped, the molten metal is used at the recent contact point (drum kiss point) of the cooling drum. The contact time with the metal is long, and it is locally heated and thermally expanded to form a thermally expanded portion. On the other hand, since the front side in the drum rotation direction from the drum kiss point is not in contact with the molten metal, it is not thermally expanded, and a large step is generated between the thermal expansion portion and the thermal expansion portion.
[0018]
　Then, when the cooling drum rotates and the above-mentioned thermal expansion portion comes into contact with the side weir, a gap is formed between the side weir and the cooling drum. The molten metal is inserted into this gap, and the inserted molten metal is solidified and integrated with the bare metal on the surface of the side weir, which is caught between the cooling drums. At this time, when the cooling drums are controlled in parallel, there is a region where the solidified shells cannot be sufficiently pressed down at the drum kiss point, an unsolidified portion is formed in the central portion of the thickness of the slab, and the slab may be broken. There is.
　With the passage of time, local thermal expansion is suppressed, and the influence of the above-mentioned thermal expansion portion disappears.
[0019]
　Hereinafter, a method for producing a slab according to an embodiment of the present invention made based on the above findings will be described with reference to the attached drawings. The present invention is not limited to the following embodiments.
　Here, in the present embodiment, molten steel is used as the molten metal, and the slab 1 made of a steel material is manufactured. Further, in the present embodiment, the width of the manufactured slab 1 is within the range of 200 mm or more and 1800 mm or less, and the thickness is within the range of 0.8 mm or more and 5 mm or less.
[0020]
　First, the twin-drum type continuous casting apparatus 10 used in the method for producing a slab according to the present embodiment will be described.
　The twin drum type continuous casting apparatus 10 shown in FIG. 1 is arranged at both ends of a pair of cooling drums 11 and 11, pinch rolls 13 and 13 for supporting the slab 1, and a pair of cooling drums 11 and 11 in the width direction. A tundish 18 holding the molten steel 3 supplied to the molten steel pool portion 16 defined by the pair of side weirs 15 and 15 and the pair of cooling drums 11 and 11 and the pair of side weirs 15 and 15. A dipping nozzle 19 for supplying the molten steel 3 from the tundish 18 to the molten steel pool portion 16 is provided.
[0021]
　In the twin drum type continuous casting apparatus 10, the solidified shells 5 and 5 grow on the peripheral surfaces of the cooling drums 11 and 11 when the molten steel 3 comes into contact with the rotating cooling drums 11 and 11 and is cooled. .. Then, the solidified shells 5 and 5 formed on the pair of cooling drums 11 and 11 are pressure-bonded to each other at the drum kiss point, whereby the slab 1 having a predetermined thickness is cast.
[0022]
　Here, as shown in FIG. 2, the molten steel pool portion 16 is defined by disposing the side weir 15 on the end surface of the cooling drum 11.
　As shown in FIG. 2, the molten metal surface of the molten steel pool portion 16 has a rectangular shape surrounded on all sides by the peripheral surfaces of the pair of cooling drums 11 and 11 and the pair of side weirs 15 and 15. A dipping nozzle 19 is arranged at the center of the surface of the hot water forming the water.
[0023]
　Further, as shown in FIG. 3, the contact portion of the side weir 15 with the molten steel 3 has a substantially inverted triangular shape. At the start of casting, the temperature of the side weir 15 is relatively low, so that the metal M is generated at this contact portion.
　As shown in FIG. 4, the side weir 15 has a base plate 15a and a ceramic plate 15b arranged in a region in sliding contact with the cooling drum 11, and the ceramic plate 15b is formed from the base plate 15a. Is also made of hard refractory material. FIG. 4 is a horizontal cross section of the contact portion between the end face of the cooling drum 11 and the ceramic plate 15b (point E in FIG. 5D).
[0024]
　Here, at the start of casting in the above-mentioned twin drum type continuous casting apparatus 10, a dummy sheet (not shown) is inserted between the cooling drums 11 and 11 with the pair of cooling drums 11 and 11 stopped, and a molten steel pool is used. The molten steel 3 is supplied toward the portion 16.
　Then, the cooling drums 11 and 11 are rotationally activated, and the slab 1 is pulled out from the lower side of the cooling drums 11 and 11.
[0025]
　At this time, immediately after the start of casting, the molten steel 3 in the molten steel pool portion 16 solidifies and the thickness of the slab 1 becomes thicker, and the hump-shaped thick portion, that is, the plate thickness of the slab 1 locally increases. The site is formed.
　Further, in the molten steel pool portion 16, shell washing occurs in which the discharge flow of the molten steel 3 from the immersion nozzle 19 flushes the solidified shell 5. This shell washing does not occur when the height of the molten metal in the molten steel pool portion 16 becomes high.
[0026]
　Here, the relationship between the cooling drum 11 and the side weir 15 immediately after the start of casting will be described with reference to FIG.
　First, as shown in FIG. 5A, the cooling drum 11 and the side weir 15 are in close contact with each other before the molten steel 3 is supplied.
[0027]
　Then, the molten steel 3 is supplied with the cooling drums 11 and 11 stopped. Then, as shown in FIG. 5B, the cooling drum 11 thermally expands due to the contact with the molten steel 3 in the vicinity of the recent contact P (drum kiss point) of the cooling drums 11 and 11, and the thermal expansion portion E is formed. To. Since the region of the cooling drums 11 and 11 on the front side of the drum rotation direction R with respect to the recent contact P is not in contact with the molten steel 3, it is not thermally expanded and is large between the cooling drums 11 and 11 and the thermal expansion portion E. There is a step.
　On the other hand, since the region of the cooling drums 11 and 11 on the rear side of the drum rotation direction R with respect to the recent contact P is located in the molten steel pool portion 16, it is thermally expanded by contact with the molten steel 3, but with the molten steel 3. The amount of thermal expansion gradually decreases with the contact time toward the rear side of the drum rotation direction R. Therefore, the side weir 15 is in contact with the cooling drums 11 and 11 in an inclined state, but a large gap is not generated.
[0028]
　In this state, the rotation of the cooling drums 11 and 11 is started. Also at this time, as shown in FIG. 5 (c), the region of the cooling drums 11 and 11 on the rear side of the drum rotation direction R with respect to the recent contact P is thermally expanded, but the amount of thermal expansion is the drum rotation. Since the side weir 15 gradually becomes smaller toward the rear side in the direction R, the side weir 15 is in contact with the cooling drums 11 and 11 in an inclined state, but a large gap is not formed.
[0029]
　Then, the cooling drum 11 further rotates, and the thermal expansion portion E (the portion located at the latest contact P (drum kiss point) of the cooling drums 11 and 11 when the cooling drum 11 is stopped at the start of casting) becomes the side weir 15. When located in the sliding contact area, a gap is formed between the side weir 15 and the cooling drum 11 as shown in FIG. 5 (d). Here, when the size of the gap is, for example, 0.2 mm or more, the molten steel 3 is inserted into this gap.
[0030]
　Here, at the start of casting, as shown in FIG. 4, a bullion M is formed on the surface of the side weir 15, and the molten steel 3 inserted into the gap between the side weir 15 and the cooling drum 11 solidifies. Then, it is integrated with the above-mentioned bullion M and is bitten between the cooling drums 11 and 11.
　In the portion where the metal M is bitten between the cooling drums 11 and 11, the plate thickness of the slab becomes locally thicker in the width direction and the longitudinal direction.
[0031]
　Therefore, in the present embodiment, the pressure control of
the cooling drums 11 and 11 is (a) started by rotating the pair of cooling drums 11 and 11 from the state where the pair of cooling drums 11 and 11 are stopped, and the slab 1 The first step until the thick part of the cooling drums 11 and 11 passes through the recent contact P (drum kiss point) of the pair of cooling drums 11 and 11 and
(b) after the first step until the cooling drums 11 and 11 make one or more rotations. The second step of
(c) and the third step after the second step
are carried out separately.
　Each step will be described below with reference to FIG. 6, which is an explanatory diagram showing a pressure control method for the cooling drum.
[0032]
(First Step)
　First, in the first step, as shown in FIG. 6A, the hydraulic cylinders 21A, which are arranged on one end side and the other end side of the pair of cooling drums 11 and 11 in the rotation axis direction, 21B presses the pair of cooling drums 11 and 11 toward each other at a predetermined pressure (first pressure).
　In the present embodiment, as shown in FIG. 6A, the hydraulic cylinders 21A and 21B are arranged on the cooling drum 11a on the moving side, and the cooling drum 11a on the moving side is moved toward the cooling drum 11b on the fixed side. It is configured to press. The hydraulic cylinders 21A and 21B are fixed to the side surfaces of the columns, but the columns are not shown for simplification.
　The first pressure is aimed at a value as high as possible within a range that does not affect the start-up of the cooling drum 11, but the specific values ​​are mainly the width, diameter, molten metal type, and drum maximum of the cooling drum 11. It is determined by the driving force. In reality, it is difficult to obtain an appropriate value by prior calculation, etc., so an appropriate value is obtained and set in an actual test.
[0033]
(Second Step)
　Next, in the second step, as shown in FIG. 6A, the hydraulic cylinders 21A arranged on one end side and the other end side of the pair of cooling drums 11 and 11 in the rotation axis direction. , 21B presses the pair of cooling drums 11, 11 toward each other at a predetermined pressure (second pressure).
　The second pressure is aimed at a value as high as possible within a range that does not cause damage such as deformation to the surface of the cooling drum 11, but mainly the width, diameter, surface shape, surface material, and molten metal of the cooling drum 11. It is determined by the type and maximum drum pressure. In reality, as with the first pressure, an appropriate value is obtained and set in an actual test.
　Here, the second pressure in the second step is set higher than the first pressure in the first step.
[0034]
　That is, in the first step and the second step, the hydraulic cylinders are arranged on one end side and the other end side of the pair of cooling drums 11 and 11 in the direction in which the pair of cooling drums 11 and 11 are close to each other in the rotation axis direction. 21A and 21B press each other with the same pressure. Therefore, as described above, even if the bullion M is bitten, the cooling drums 11 and 11 are pressed in the direction in which they are close to each other.
　In the present application, the "same pressure" allows an error of 10%, but in order to start casting more stably, the error range is allowed to be 5% or less, more preferably 1% or less. It is preferable to manage it.
[0035]
(Third Step)
　Next, in the third step, as shown in FIG. 6B, the total value of the reaction forces on one end side and the other end side of the pair of cooling drums 11 and 11 in the rotation axis direction is predetermined. The pressure is controlled so that the values ​​of are obtained and the rotation axes of the pair of cooling drums 11 and 11 are held in parallel with each other.
　Specifically, as shown in FIG. 6B, the hydraulic cylinders 21A and 21B are arranged on the cooling drum 11a on the moving side, and the load cells 22A and 22B are arranged on the cooling drum 11b on the fixed side. The load cells 22A and 22B are fixed to the side surfaces of the columns, but the columns are not shown for simplification. The reaction force signal measured by the load cells 22A and 22B is transmitted to the reaction force control unit 24 so that the reaction force control unit 24 moves forward and backward in the hydraulic cylinders 21A and 21B so that the sum load becomes a predetermined value. Give a command.
　As a result, the rotation axes of the pair of cooling drums 11 and 11 are held in parallel, and the slab 1 whose plate thickness is controlled is manufactured. The predetermined value of the sum load is mainly determined by the width, diameter, and type of molten metal of the cooling drum 11 while aiming to maintain the stability of operation within the range that satisfies the quality of the slab 1. It is a thing. In reality, as with the first pressure and the second pressure, an appropriate value is obtained and set in an actual test.
[0036]
　Here, in the second step, it is preferable that the period is such that the cooling drum 11 makes two or more rotations after the first step.
　However, if the switching timing from the second step to the third step is delayed, the amount of initial defects until the slab 1 whose plate thickness is controlled increases, so that the third step is performed before the cooling drum 11 rotates three times. It is preferable to switch to.
[0037]
　According to the method for manufacturing the slab 1 according to the present embodiment having the above-described configuration, after the first step, in the second step until the cooling drums 11 and 11 make one or more rotations, a pair of cooling is performed. The hydraulic cylinders 21A and 21B arranged on one end side and the other end side of the drums 11 and 11 in the rotation axis direction direct the pair of cooling drums 11 and 11 toward each other at a predetermined pressure (second pressure). Since the cooling drum 11 is pressed, the thermal expansion portion E of the cooling drum 11 is located in the region where it is in sliding contact with the side dam 15, and a gap is formed between the side dam 15 and the cooling drum 11. Therefore, even when the molten steel 3 is inserted into this gap and the bullion M is involved, the pair of cooling drums 11 and 11 are pressed in a direction close to each other, and the pair of cooling drums 11 and 11 Recently, the solidified shells 5 and 5 can be sufficiently pressed down at the contact point P (drum kiss point). Therefore, the unsolidified portion in the central portion of the thickness of the slab 1 is hardly formed, and the slab strength is maintained. As a result, breakage of the slab 1 can be suppressed, and casting can be started stably.
[0038]
　Further, in the method for manufacturing the slab 1 according to the present embodiment, the pair of cooling drums 11 and 11 are rotated and started from the state where the pair of cooling drums 11 and 11 are stopped, so that the thick portion of the slab 1 is formed. Hydraulic cylinders arranged on one end side and the other end side of the pair of cooling drums 11 and 11 in the rotation axis direction in the first step until the pair of cooling drums 11 and 11 pass the latest contact P (drum kiss point). Since the pair of cooling drums 11 and 11 are pressed by the 21A and 21B toward each other at a relatively low first pressure, the thick parts of the slab 1 formed at the start of casting are compared. It is possible to pass between the cooling drums 11 and 11 in a stable manner, and the influence on casting can be suppressed.
　Further, in the second step, since the cooling drum 11 is pressed with a second pressure higher than the first pressure of the first step, the solidification shell 5 is formed at the recent contact P (drum kiss point) of the pair of cooling drums 11 and 11. , 5 can be sufficiently suppressed. Therefore, the unsolidified portion in the central portion of the thickness of the slab 1 is hardly formed, and the slab strength can be maintained.
[0039]
　In the present embodiment, when the second step is a period until the cooling drum 11 makes two or more rotations after the first step, the above-mentioned thermal expansion portion E remains up to the second rotation and the metal is formed. Even if M bites occur, the solidified shells 5 and 5 can be sufficiently pressed down at the recent contacts P (drum kiss points) of the pair of cooling drums 11 and 11. As a result, breakage of the slab 1 can be suppressed, and casting can be started stably.
[0040]
　Although the method for producing a slab according to the embodiment of the present invention has been specifically described above, the present invention is not limited to this, and can be appropriately changed without departing from the technical idea of ​​the invention. ..
　In the present embodiment, the twin drum type continuous casting apparatus shown in FIG. 1 has been described as an example, but the present invention is not limited thereto.
　Further, the pressing method of the cooling drum is not limited to that shown in FIG. 6, and any configuration may be used as long as the pressure control can be performed as shown in the embodiment.
Example
[0041]
　The results of experiments carried out in order to confirm the effects of the present invention will be described below.
　Using the twin-drum type continuous casting apparatus shown in FIG. 1, a slab made of carbon steel having a carbon content of 0.05 mass% was produced.
　Here, the diameter of the cooling drum was set to 600 mm, and the width of the cooling drum was set to 400 mm. Further, the slab thickness of the steady casting was set to 2.0 mm.
[0042]
　In Example 1 of the present invention, switching from the first step to the second step is performed when the rotation speed of the cooling drum is 0.1 rotation, and the second step is performed when the rotation speed of the cooling drum is 1.3 rotations. To the third step.
　In Example 2 of the present invention, switching from the first step to the second step is performed when the rotation speed of the cooling drum is 0.1 rotation, and the second step is performed when the rotation speed of the cooling drum is 2.3 rotations. To the third step.
　In the comparative example, the switching from the first step to the second step is performed when the rotation speed of the cooling drum is 0.1 rotation, and the second step to the second step is performed when the rotation speed of the cooling drum is 0.4 rotation. Switching to 3 steps was carried out. The switching from the second step to the third step in this case corresponds to the time when the shell washing is completed.
[0043]
　Then, in Examples 1 and 2 of the present invention and Comparative Example, the number of breaks and the number of breaks of the slab at the first and second rotations of the cooling drum were evaluated. The evaluation results are shown in Table 1.
　Further, FIG. 7 shows changes in the drum reaction force and the drum gap in Comparative Example, and FIG. 8 shows changes in the drum reaction force and the drum gap in Example 1 of the present invention.
[0044]
[table 1]

[0045]
　In the comparative example, the breaking rate of the slab at the first and second rotations of the cooling drum was 25%, and the start of casting tended to be unstable.
　On the other hand, in Examples 1 and 2 of the present invention, the breaking rate of the slab at the 1st and 2nd rotations of the cooling drum was 0%.
[0046]
　Further, in the comparative example, as shown in FIG. 7, when the bullion is bitten by the WS (Work Side), the drum gap of the DS (Drive Side) follows the WS, and at this time, the DS Then, the reaction force of the drum is greatly reduced, the contact of the cooling drum with the solidification shell becomes unstable, and the cooling becomes insufficient.
　On the other hand, in Example 1 of the present invention, as shown in FIG. 8, the drum reaction force did not decrease in the DS even when the bullion was bitten by the WS, and the solidified shells were strongly crimped to each other, and the DS The drum gap is getting smaller. Therefore, there is almost no unsolidified portion in the central portion of the thickness of the slab, the surface temperature of the slab is relatively low, and the strength of the slab is maintained. As a result, breakage of the slab is suppressed.
[0047]
　From the above results, according to the slab manufacturing method according to the present invention, in the twin-drum type continuous casting apparatus, the slab breaking can be suppressed and the casting can be started stably. It was confirmed that we can provide.
Industrial applicability
[0048]
　According to the present invention, it is possible to provide a method for producing a slab that can suppress breakage of a slab and can start casting stably in a twin-drum type continuous casting apparatus.
Code description
[0049]
1 Shard
3 Molten steel (molten metal)
5 Solidification shell
10 Twin drum type continuous casting equipment
11 Cooling drum
15 Side weir
16 Molten steel pool part (molten metal pool part)
The scope of the claims
[Claim 1]
　Casting in which molten metal is supplied to a molten metal reservoir formed by a pair of rotating cooling drums and a pair of side dams, and a solidified shell is formed and grown on the peripheral surfaces of the pair of cooling drums to produce slabs. In the method for producing a
　piece, the thick portion of the slab formed when the molten metal is supplied to the molten metal reservoir with the pair of cooling drums stopped at the start of casting is the cooling. In the first step from the start of rotation of the drums to the passage through the recent contacts of the pair of cooling drums, the one end side and the other end side of the pair of cooling drums in the rotation axis direction are subjected to the same first pressure with the same first pressure. In the
　second step from after the first step until the pair of cooling drums make one or more rotations by pressing the pair of cooling drums toward each other , one end of the pair of cooling drums in the rotation axis direction. The pair of cooling drums press the side and the other end side in the same direction as each other and at a second pressure higher than the first pressure in a direction close to each other
　, and in the third step after the second step, the said The total value of the reaction forces on one end side and the other end side in the rotation axis direction of the pair of cooling drums is set to a predetermined value, and the rotation axes of the pair of cooling drums are held in parallel with each other. A
method for producing a slab, which comprises performing pressure control .
[Claim 2]
　The
method for producing a slab according to claim 1, wherein the second step is a period from after the first step until the pair of cooling drums make two or more rotations .