METHOD FOR REDUCING SLAB WIDTH, METHOD FOR MANUFACTURING STEEL PLATE AND APPARATUS FOR REDUCING SLAB WIDTH

Abstract

To provide a slab width rolling method capable of keeping a slab currently rolled in width on a path line, a steel plate manufacturing method using the same, and a slab width rolling device.SOLUTION: The slab width rolling method for rolling a slab by using a pair of molds for rolling the slab and at least two sets of pairs of vertical buckling prevention rolls installed by vertically holding a slab path line therebetween comprises: position-controlling a lower roll of the buckling prevention roll positioned on the entrance side of the slab in an advancing direction so as to fix the upper end position of the lower roll at a path line position; and pressing-force controlling the other buckling prevention rolls so as to apply a predetermined pressing force to the slab currently rolled in width from each of the other buckling prevention rolls.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for width reducing a slab, a method for manufacturing a steel plate, and an apparatus for width reducing a slab, which are capable of maintaining the slab at a pass line position. [Background technology]

[0002] The slab transported from the continuous casting facility is heated to a desired temperature in a heating furnace, descaled if necessary, and then sent to a slab width reduction device. In the slab width reduction device, the slab is transported between a pair of dies installed opposite to each other in the width direction of the slab by pinch rolls, and is pressed by the oscillating dies to be reduced in width. When the slab is reduced in width and its width is narrowed, the slab increases in thickness. After the width reduction, the dies are opened, and the slab is transported by the inlet pinch rolls and the outlet pinch rolls. After the unreduced portion of the slab is transported to the die position, it is reduced in width again. In this way, the slab is repeatedly reduced in width and transported, thereby reducing the entire length of the slab in width.

[0003] Generally, when the leading edge of a slab is reduced in width, the slab is supported by the inlet pinch rolls but not by the outlet pinch rolls, resulting in a cantilevered state. In a cantilevered state, the slab sags under its own weight and deviates from the pass line. Here, deviation of the slab from the pass line means that the slab neutral line deviates from the equipment center line. The slab neutral line is the line connecting the midpoints of the top and bottom surfaces of the slab at the center cross section of the slab's width, i.e., the center line of the slab thickness, and the equipment center line is the horizontal line passing through the center of the mold height.

[0004] If the slab deviates from the pass line, the slab is more likely to buckle. Also, if the slab deviates from the pass line, a moment is generated to rotate the die, causing the press surface to tilt. If the width reduction is performed with the press surface tilted, the slab is more likely to buckle. Furthermore, if the moment to rotate the die becomes large, a large force acts on the width reduction device, causing damage to the equipment. In addition, inclined surfaces called calibers are sometimes provided on the top and bottom of the press surface of the die to prevent edge seam defects. However, if the slab deviates from the pass line, the position of the center of the slab thickness and the center of the die are shifted, and the contact area between the caliber and the slab becomes asymmetrical from top to bottom, which not only causes edge seam defects, but also causes uneven wear of the die and increases the number of die replacements. For this reason, when the slab is width reduced, the top and bottom surfaces of the slab are restrained and supported by buckling prevention rolls installed in the vertical direction between the dies that perform width reduction. This suppresses buckling of the slab and keeps the tip of the slab, which is about to bend under its own weight, on the pass line.

[0005] As a width reduction method and device equipped with buckling prevention rolls that can prevent slab buckling and hold the slab at the pass line position, Patent Document 1 discloses a slab width reduction method in which at least two pairs of buckling prevention rolls, upper and lower, are supported by hydraulic cylinders and pressure is controlled so that a constant pressure is applied to the slab from the lower roll and the upper roll of the buckling prevention rolls. According to Patent Document 1, by using buckling prevention rolls with pressure control, the slab can be maintained on the pass line even if the plate thickness increases after slab width reduction or even if the cantilevered slab tries to bend under its own weight, and thus buckling of the slab can be prevented.

[0006] Patent Document 2 discloses a method for reducing the width of a slab in which at least two pairs of buckling prevention rolls are each supported by a hydraulic cylinder, the amount of thickness increase of the target slab before and after width reduction is calculated before performing width reduction of the slab, and when reducing the width of the slab, the lower buckling prevention roll is lowered from the pass line by half the amount of increase and fixed, and the upper buckling prevention roll is subjected to pressure control. According to Patent Document 2, by lowering the lower buckling prevention roll by half the amount of increase from the pass line and fixing it, and controlling the pressure of the upper buckling prevention roll, it is possible to prevent buckling of the slab and to maintain the slab on the pass line.

[0007] Patent Document 3 discloses a method for reducing the width of a slab in which the slab is supported by an entry-side bottom buckling prevention roll near the pass line, and the exit-side bottom buckling prevention roll is lowered at a preset lowering speed by a distance corresponding to the increase in thickness of the slab. According to Patent Document 3, the lowering speed of the exit-side bottom buckling prevention roll is set to a value corresponding to the slab thickness increase rate that is calculated in advance according to the material and size of the slab. In this way, it is said that by supporting the slab by the bottom buckling prevention roll near the pass line and lowering the exit-side bottom buckling prevention roll at a preset lowering speed, the slab can be accurately held on the pass line. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2001-252704 A [Patent Document 2] JP 2017-30031 A [Patent Document 3] JP 2015-123486 A Summary of the Invention [Problem to be solved by the invention]

[0009] Generally, as the leading edge of a slab is pressed down in width and the slab is transported to the exit side, the weight of the slab in a cantilevered state, i.e., the weight of the slab from the part contacting the entry pinch roll to the leading edge of the slab, gradually increases. Even in a configuration in which a constant pressing force is applied to the slab from the lower roll and upper roll of the buckling prevention roll using the method for pressing down the slab in width disclosed in Patent Document 1, the lower roll on the entry side gradually drops due to the increased slab weight. As a result, there was a problem that the slab shifts downward from the regular pass line, making it impossible to maintain the slab on the pass line.

[0010] In addition, in the method for reducing the width of a slab disclosed in Patent Document 2, the lower roll is fixed at a height lowered by half the thickness increase amount from the pass line before the slab is transported. Therefore, the lower roll does not contact the slab until the width reduction is completed, so a gap is generated between the lower roll and the slab before the width reduction and immediately after the start of the width reduction. Furthermore, a pressing force is applied to the slab from the upper roll to prevent buckling, so the slab in a cantilevered state bends downward. This downward bending of the slab causes the slab to deviate from the pass line, which can cause uneven wear of the die that reduces the width of the slab.

[0011] In addition, in the slab width reduction method disclosed in Patent Document 3, the pressure of the entry-side bottom buckling prevention roll is controlled, so even if a constant pressure is applied to the slab, the entry-side bottom buckling prevention roll gradually drops due to the increased slab weight. As a result, the slab shifts downward from the regular pass line, and there is a problem that the slab cannot be maintained on the pass line.

[0012] The present invention has been made in consideration of the problems of the conventional technology, and an object of the present invention is to provide a method for width reducing a slab, which can maintain the slab on the pass line during width reduction, a method for manufacturing a steel plate using the width reduction method, and an apparatus for width reducing a slab. [Means for solving the problem]

[0013] The means for solving the above problems are as follows. (1) A method for reducing the width of a slab using a pair of dies for reducing the width of the slab and at least two pairs of upper and lower buckling prevention rolls installed vertically on either side of the pass line of the slab, wherein the lower roll of the buckling prevention rolls located on the entry side of the slab's traveling direction is position-controlled so that the upper end position of the lower roll is fixed at the pass line position, and the other buckling prevention rolls are pressure-controlled so that a predetermined pressure force is applied from each of the other buckling prevention rolls to the slab being width-reduced. (2) A method for reducing the width of a slab described in (1), in which the pressing force of the upper roll of the buckling prevention roll located at the exit side in the traveling direction of the slab and the weight of the slab are controlled so as to be balanced with the pressing force of the lower roll of the buckling prevention roll located at the exit side in the traveling direction of the slab. (3) A method for reducing the width of a slab described in (1) or (2), in which, after the tail end of the slab passes through a buckling prevention roll located on the entry side of the slab's traveling direction, the position of a lower roll of the buckling prevention roll located on the exit side of the slab's traveling direction is controlled so that the upper end position of the lower roll is fixed at a position determined based on the amount of thickness increase of the slab due to the width reduction. (4) A method for reducing the width of a slab as described in (3), wherein the position determined based on the amount of thickness increase of the slab is a position vertically downward from the pass line position by half the amount of thickness increase of the slab due to width reduction. (5) A method for producing a steel plate, comprising the steps of: width-reducing a slab using the method for width-reducing a slab according to any one of (1) to (4) to produce a steel plate. (6) A slab width reduction device comprising a pair of dies for reducing the width of a slab, at least two pairs of upper and lower buckling prevention rolls installed vertically on either side of the pass line of the slab, and a control device for controlling the operation of each of the buckling prevention rolls, wherein the control device controls the position of the lower roll of the buckling prevention roll located on the entry side of the slab's traveling direction so that the upper end position of the lower roll is fixed at the pass line position, and controls the pressure of each of the other buckling prevention rolls so that a predetermined pressing force is applied from each of the other buckling prevention rolls to the slab during width reduction. (7) The control device controls the pressure so that the pressure of the upper roll of the buckling prevention roll located at the exit side in the traveling direction of the slab and the weight of the slab are balanced with the pressure of the lower roll of the buckling prevention roll located at the exit side in the traveling direction of the slab. (8) A slab width reduction device as described in (6) or (7), further comprising a detection means for detecting that the tail end of the slab has passed through a buckling prevention roll located on the entry side of the traveling direction and outputting a detection signal, and when the control device acquires the detection signal, it controls the position of the lower roll of the buckling prevention roll located on the exit side of the traveling direction of the slab so that the upper end position of the lower roll is fixed at a position determined based on the amount of thickness increase of the slab due to the width reduction. (9) A slab width reduction device as described in (8), wherein the position determined based on the amount of thickness increase of the slab is a position vertically downward from the pass line position by half the amount of thickness increase of the slab due to width reduction. Effect of the Invention

[0014] By implementing the present invention, even if a cantilevered slab is deflected by its own weight, the slab can be maintained at the pass line position. This allows the slab to be width-reduced within the caliber of the width-reducing die, suppressing uneven wear of the die. As a result, it is possible to reduce the number of die changes and improve the yield by improving the quality of the slab. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic perspective view showing a slab width reduction device capable of carrying out the slab reduction method according to this embodiment. [Diagram 2] FIG. 2 is a schematic side view illustrating the control of the buckling prevention roll. [Diagram 3] FIG. 3 is a schematic cross-sectional view of a slab showing the dimensions used in calculating the amount of buckling ΔC of the slab. [Figure 4] FIG. 4 is a graph showing the striking position deviation of slabs width-reduced using the width reduction devices of Comparative Examples 1 and 2 and Invention Examples 1 and 2. [Diagram 5] FIG. 5 is a graph showing the standard deviation of the striking position deviation of all slabs width-reduced using the width reduction devices of Comparative Examples 1, 2, and 3 and Invention Examples 1 and 2. [Figure 6] FIG. 6 is a graph showing the amount of tail-end buckling of slabs width-reduced using the width reduction devices of Comparative Examples 1, 2, and 3 and Invention Examples 1 and 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The inventors have thoroughly studied how to deal with deviations of the slab from the pass line during width reduction. The inventors have noted that, since the width of the slab after width reduction is completed becomes narrower toward the exit side of the machine, the amount of thickness increase of the slab is small at the longitudinal position of the buckling prevention roll on the entry side of the machine, and large at the longitudinal position of the buckling prevention roll on the exit side of the machine. Based on this difference in thickness increase, the lower roll on the entry side, where the amount of thickness increase of the slab due to width reduction is small, is positioned to fix the slab at the pass line position, and a configuration has been created in which the slab is in a cantilevered state and the leading end of the slab tends to bend under its own weight, but is kept on the pass line.

[0017] On the other hand, since the thickness increase of the slab due to the width reduction is large, the upper and lower rolls on the exit side, which are likely to have a large prediction error in the model for setting the thickness increase, are pressure-controlled so that a predetermined pressure is applied. Furthermore, the upper roll on the entry side is also pressure-controlled so that a predetermined pressure is applied. This allows each buckling prevention roll to maintain contact with the slab until the end of the width reduction, and the slab can be kept on the pass line. Furthermore, since the lower roll on the entry side is position-controlled and the remaining rolls are pressure-controlled, even if the pressure of the remaining rolls differs from the set value and there is a slight difference in the pressure of the rolls, the slab is supported by the lower roll on the entry side, which is position-controlled, so that the slab does not deviate significantly from the pass line. Hereinafter, a slab width reduction method, a slab width reduction device, and a steel plate manufacturing method according to an embodiment of the present invention will be described with reference to the drawings.

[0018] 1 is a perspective schematic diagram showing a slab width reduction device that can implement the slab reduction method according to the present embodiment. The slab width reduction device 10 has a pair of dies 12a, 12b that reduce the width of a slab 100 from both sides, namely the Op side and the Dr side, a buckling prevention roll 14 having an upper roll 14a and a lower roll 14b, a buckling prevention roll 16 having an upper roll 16a and a lower roll 16b, a control device 18 that controls the operation of these rolls, and a sensor 20. The upper rolls 14a, 16a and the lower rolls 14b, 16b are each provided so as to be independently movable up and down.

[0019] In this embodiment, an example of a slab width reduction device 10 having two sets of buckling prevention rolls 14, 16 will be described, but the number of sets of buckling prevention rolls may be two or more. That is, the slab width reduction device 10 may have at least two sets of buckling prevention rolls, and when three or more sets of buckling prevention rolls are provided, a buckling prevention roll may be added between the buckling prevention roll 14 and the buckling prevention roll 16. When three or more sets of buckling prevention rolls are provided, the upper roll provided on the entry side from the center of the mold may be controlled in the same manner as the upper roll 14a, and the upper roll provided on the exit side from the center of the mold may be controlled in the same manner as the upper roll 16a. Moreover, the upper roll provided on the entry side from the center of the mold may be controlled in the same manner as the upper roll 14a, and the lower roll provided on the exit side from the center of the mold may be controlled in the same manner as the lower roll 16b.

[0020] The dies 12a and 12b that compress the width of the slab 100 are installed along the traveling direction of the slab 100. The dies 12a and 12b have a tapered section formed so that the distance therebetween narrows from the inlet side to the outlet side in the traveling direction of the slab 100, and a parallel section in which a surface parallel to the traveling direction of the slab 100 is formed following the tapered section.

[0021] After leaving the heating furnace (not shown), the slab 100 is descaled as necessary and transported from the entry side A to between the dies 12a and 12b where it is reduced in width. After the width reduction, the slab 100 is transported to the exit side B where it is subjected to a rolling process such as hot rolling. The shape of the slab 100 is preferably a plate shape with each surface formed by a rectangle, but is not limited to this shape.

[0022] The slab 100 is width-reduced by the dies 12a, 12b. The width reduction by reducing and opening the dies 12a, 12b is performed multiple times while the slab 100 is being transported. As a result, the entire length of the slab 100 becomes a steel plate with the desired plate width. The example shown in FIG. 1 shows a state in which only the front end (side B) of the slab 100 has been width-reduced. After this, the slab 100 is transported to the exit side B, and width reduction is sequentially performed on the central and tail ends of the slab 100 following the front end, to produce a steel plate with the desired plate width. The slab 100 is transported by pinch rolls 40, 42.

[0023] The upper rolls 14a, 16a are disposed on the upper surface side of the slab 100 and press the widthwise center portion of the upper surface of the slab 100. The lower rolls 14b, 16b are disposed on the lower surface side of the slab 100 and press the widthwise center portion of the lower surface of the slab 100. The upper and lower rolls of these buckling prevention rolls 14, 16 are usually provided at upper and lower positions corresponding to the tapered portions of the dies 12a, 12b and parallel portions provided on the exit side of the tapered portions.

[0024] The control device 18 controls the operation of the upper rolls 14a, 16a and the lower rolls 14b, 16b by position control or pressure control. In this embodiment, the position control means control for fixing the position of each roll so that the lower end position of the upper rolls 14a, 16a and the upper end position of the lower rolls 14b, 16b are at a predetermined position. Moreover, the pressure control means control for applying a predetermined pressure force to the slab 100 from each roll. For example, when the lower roll 16b is subjected to pressure control, the lower roll 16b rises and a predetermined pressure force is applied to the lower surface of the slab 100. On the other hand, in the pressure control, since the roll position is not fixed, if a downward load larger than the predetermined pressure force is generated on the lower roll 16b, the lower roll 16b will descend due to the load.

[0025] The sensor 20 detects that the tail end of the slab 100 has passed the entry-side buckling prevention roll 14 and outputs a detection signal to the control device 18. The sensor 20 is an example of a detection means for detecting that the tail end of the slab 100 has passed the entry-side buckling prevention roll 14, and for example, an optical sensor having a light emitting section, a light receiving section, and a light receiving section for receiving light reflected by the slab 100 is used. Note that the tail end of the slab 100 may be detected to have passed the buckling prevention roll 14 from the position of the upper roll 14a, in which case the upper roll 14a serves as the detection means for detecting that the tail end of the slab 100 has passed the entry-side buckling prevention roll 14.

[0026] FIG. 2 is a schematic side view illustrating the control of the buckling prevention roll. As shown in FIG. 2, the upper rolls 14a, 16a and the lower rolls 14b, 16b are installed on either side of the pass line in the vertical direction. The upper rolls 14a, 16a and the lower rolls 14b, 16b are connected to hydraulic cylinders 22, 24, 26, 28, respectively. The hydraulic cylinders 26, 28 are set to have maximum strokes so that the upper end positions of the lower rolls 14b, 16b coincide with the pass lines. The hydraulic cylinders 22, 24 are set to have maximum strokes so that the lower limit positions of the upper rolls 14a, 16a are lower than the upper surface of the slab 100 with the minimum plate thickness. Each hydraulic cylinder is provided with a relief valve, and by adjusting the set pressure of this relief valve, each of the buckling prevention rolls can apply a predetermined pressing force to the upper and lower surfaces of the slab 100. In addition, servo valves 30, 32 are connected to the hydraulic cylinders 26, 28, and the buckling prevention rolls are fixed in position by these servo valves 30, 32. Here, the pass line refers to a line formed by a horizontal plane corresponding to the height of the upper end faces of the table rolls and transport rolls that transport the slab 100. In Fig. 2, the line (dashed line) formed by the height of the upper end of the lower roll of the pinch roll 40 and the horizontal plane is the pass line.

[0027] The control device 18 is, for example, a general-purpose computer such as a workstation or a personal computer. The control device 18 outputs control signals for controlling the hydraulic cylinders 22, 24, 26, 28 and the servo valves 30, 32, and acquires pressure information and position information from these hydraulic cylinders. By outputting the control signals and acquiring the pressure information and position information, the control device 18 controls the upper rolls 14a, 16a and the lower rolls 14b, 16b to position control or pressing control via the hydraulic cylinders 22, 24, 26, 28 and the servo valves 30, 32. Similarly, the control device 18 can switch the lower rolls 14b, 16b from pressing control to position control, or from position control to pressing control, by outputting a control signal.

[0028] In this embodiment, the control device 18 controls the upper rolls 14a, 16a and the lower roll 16b under pressure control. On the other hand, the control device 18 controls the position of the lower roll 14b, fixing the position of the lower roll 14b so that the upper end position of the roll is the pass line position. In this state, when the slab 100 increases in thickness due to width reduction, the upper rolls 14a, 16a and the lower roll 16b, which are under pressure control, rise and fall so as to move away from the center of the slab 100 in the vertical direction in response to the increase in thickness of the slab 100. In other words, the upper rolls 14a, 16a rise and the lower roll 16b falls.

[0029] The width reduction by the width reduction device 10 configured as described above will be explained below with respect to the width reduction of the leading end of the slab 100, and the width reduction when the tail end of the slab 100 passes through the buckling prevention roll 14 located on the entry side and the slab 100 is restrained by the buckling prevention roll 16.

[0030] First, we will explain the width reduction of the leading end of the slab 100. Before the width reduction of the leading end of the slab 100, the upstream side of the slab 100 in the traveling direction is restrained by the pinch roll 40 and the buckling prevention roll 14, but the leading end side of the slab 100 is not restrained and is transported between the dies 12a and 12b by the pinch roll 40 located on the inlet side.

[0031] When the slab 100 is transported, the height direction position of the slab 100 is set by the lower roll 14b located on the inlet side. That is, the lower surface of the unpressed part at the tip side of the slab 100 is supported by the lower roll 14b, which is fixed at the pass line position by position control. This maintains the slab neutral line on the equipment center line. That is, since the slab 100 is maintained on the pass line, the slab 100 is maintained within the caliber of the dies 12a and 12b. Here, the slab neutral line is a line connecting the middle positions of the upper and lower surfaces of the slab 100 in the width center cross section of the slab 100, that is, the slab thickness center line. Also, the equipment center line is a horizontal line passing through the center of the dies.

[0032] When the slab 100 is transported and the leading end of the slab 100 reaches between the upper and lower rolls 16a and 16b located on the exit side, the lower roll 16b located on the exit side assists the lower roll 14b and is changed to a pressing force control in which the slab 100 is pressed down by the slab 100, that is, the sum of the weight of the slab 100 and the pressing force of the upper roll 16a, and the pressing force control is changed to a pressing force control in which the slab 100 is pressed down against the lower surface of the slab 100. In addition, the upper roll 14a and the upper roll 16a are changed to a pressing force control in which the buckling prevention rolls touch the slab 100 with their own weights. The lower roll 14b is maintained in the position control fixed at the pass line position. With the above settings, the lower surface of the slab 100 is set to the pass line, and the width reduction of the slab 100 is started while the slab 100 is maintained on the pass line.

[0033] At the start of width reduction, the pressure settings of the upper roll 14a, the upper roll 16a, and the lower roll 16b are changed to prevent buckling during width reduction. Specifically, the upper rolls 14a, 16a, and the lower roll 16b support the buckling load of the slab 100 during width reduction, and apply a pressure force to the slab 100 that causes it to retreat in the vertical direction when a further reverse load is applied due to an increase in the thickness of the slab 100 caused by width reduction. At this time, in order to support the slab 100 with the upper roll 16a and the lower roll 16b located on the exit side, the pressure of the lower roll 16b is controlled so that the pressure of the upper roll 16a acting on the slab 100 and the weight of the slab 100 and the pressure of the lower roll 16b are balanced. The pressure at this time may be set to an appropriate pressure within a range in which the slab 100 does not buckle and does not cause an indentation on the slab 100 due to the increase in thickness of the slab 100. The lower roll 14b is maintained under the position control fixed at the pass line position, so that the upper end position of the lower roll 14b is fixed at the pass line position.

[0034] In the slab width reduction device 10 according to this embodiment, the lower roll 14b located on the entry side is fixed at the pass line position during width reduction, so that the lower roll 14b does not descend even if the weight of the slab 100 increases as the slab 100 is transported to the exit side and becomes cantilevered. As a result, the leading end of the slab 100, which becomes cantilevered and tends to bend under its own weight, can be maintained at the pass line position.

[0035] Moreover, the upper roll 14a only moves back in the vertical direction by the amount of thickness increase caused by the width reduction of the slab 100. As described above, the pressing forces of the upper roll 16a and the lower roll 16b are controlled to balance each other, so that the upper roll 16a and the lower roll 16b on the exit side, which are prone to large prediction errors in the model for setting the thickness increase due to the large amount of thickness increase of the slab 100, are also kept in contact with the slab 100 until the end of the width reduction. In other words, even if the amount of thickness increase of the slab 100 is different from the set value, no gap is generated between the lower roll 16b on the exit side and the lower surface of the slab 100 during the width reduction, and the lower roll 16b on the exit side does not push up the slab 100. In other words, even if the amount of thickness increase of the slab 100 is different from the set value, the slab 100 can be maintained at the pass line position.

[0036] Furthermore, even if the actual pressing force of the rolls differs from the set value and a difference occurs in the pressing forces of the upper and lower rolls, which is the pressing force control, the slab 100 is maintained on the pass line. First, when the pressing force of the lower roll 16b becomes larger than the pressing force of the upper roll 16a on the exit side, the weight of the slab 100 supported by the lower roll 14b on the entry side acts on the lower roll 16b on the exit side, and the difference in the pressing forces of the upper roll 16a on the exit side and the lower roll 16b on the exit side acting on the slab 100 is eliminated. At this time, since the lower roll 14b on the entry side is fixed in position, the slab 100 does not move significantly upward. Also, when the pressing force of the lower roll 16b becomes smaller than the pressing force of the upper roll 16a on the exit side, the pressing force difference between the upper roll 16a and the lower roll 16b on the exit side acting on the slab 100 is supported by the lower roll 14b on the entry side. Therefore, the slab 100 does not deviate significantly downward from the pass line. Furthermore, if the actual pressing force of the inlet upper roll 14a differs from the set value, the pressing force error is supported by the inlet lower roll 14b, which is fixed in position, so that the slab 100 is maintained on the pass line. Therefore, even if the actual pressing force of the roll differs from the set value, the slab 100 is maintained on the pass line and the leading edge of the slab 100 can be transported to the pinch roll 42 without being significantly shifted.

[0037] Next, the width reduction of the slab 100 will be described in a state where the tail end of the slab 100 passes through the buckling prevention roll 14 located on the entry side and the slab 100 is restrained by the buckling prevention roll 16. When the tail end of the slab 100 passes through the buckling prevention roll 14 located on the entry side, the tail end of the slab 100 becomes a free end, so that buckling of the slab 100 is likely to occur. Even when the tail end of the slab 100 becomes a free end, if the buckling prevention roll is controlled in the same manner as when the tail end is restrained by the buckling prevention roll 14, the pressing forces of the upper roll 16a and the lower roll 16b on the delivery side are set to be balanced with the weight of the slab 100, so that a restraining load required to suppress buckling is not generated when the tail end of the slab 100 is width reduced. Therefore, when the slab 100 is restrained only by the buckling prevention roll 16 on the delivery side, the effect of suppressing buckling of the slab 100 is hardly obtained.

[0038] Therefore, when the tail end of the slab 100 is width-reduced, it is preferable that the control device 18 switches the pressure control of the lower roll 16b on the exit side from the previous pressure control to a position control in which the upper end position of the lower roll 16b is fixed at a position determined based on the thickness increase of the slab 100 due to the width reduction. That is, when it detects that the tail end of the slab 100 has passed the buckling prevention roll 14 located on the entry side, the sensor 20 outputs a detection signal to the control device 18. When the control device 18 receives the detection signal, it switches the control of the lower roll 16b from pressure control to position control. The position determined based on the thickness increase of the slab 100 is a position vertically lowered from the pass line position by half the thickness increase. The thickness increase of the slab 100 can be calculated using conditions such as the steel type of the slab, the temperature of the slab, the width of the slab, and the width reduction amount.

[0039] The control device 18 switches the lower roll 16b to position control, and the position of the lower roll 16b located on the exit side is fixed. Since the upper roll is pressure controlled, by fixing the position of the lower roll 16b, the upper roll 16a can support the buckling load, and the expansion of buckling can be suppressed. In addition, the position of the lower roll 16b is fixed at a position lower than the pass line position by half the amount of thickness increase of the slab 100. Therefore, even if the slab 100 is reduced in width and increased in thickness, a defect such as deviation from the pass line position due to the increase in thickness does not occur. When three or more sets of buckling prevention rolls are used, the lower rolls of the buckling prevention rolls installed one step further to the exit side from the buckling prevention roll from which the tail end of the slab 100 has fallen can be switched from pressure control to position control in sequence. After the width reduction of the slab 100 is completed, the settings of each buckling prevention roll are returned to the settings at the time of transporting the slab 100, and the next slab 100 is transported between the dies 12a and 12b. EXAMPLES

[0040] Next, an example will be described in which the slab width reduction method according to the present embodiment and the effect of the slab width reduction device 10 shown in FIG. 1 were verified. In this example, rolls with a roll diameter of 580 mm and a barrel width of 200 mm were used as the upper and lower rolls constituting the buckling prevention roll. The slab subjected to width reduction was a mild steel slab with a thickness of 260 mm, a width of 1280 mm, a length of 8000 mm, and an average temperature inside the slab of 1100°C, and 25 such slabs were prepared in total. In addition, the above mild steel slab was width-reduced with a width reduction amount of 350 mm (slab width after width reduction was 930 mm), a feed amount of 350 mm, and a width reduction load of 2400 tonf.

[0041] In Comparative Example 1, during the transport of the slab, the upper roll on the entry side and the upper roll on the exit side were subjected to pressure control such that each roll touched the top surface of the slab with its own weight. In addition, the lower roll on the entry side and the lower roll on the exit side were subjected to pressure control such that each roll applied a pressure of 6 tonf to the slab. During the width reduction of the slab, the upper roll on the entry side and the upper roll on the exit side were subjected to pressure control such that each roll applied a pressure of 20 tonf to the slab, and the lower roll on the entry side and the lower roll on the exit side were subjected to pressure control such that each roll applied a pressure of 25 tonf to the slab, which was greater by the weight of the slab than the pressure of the upper roll, in order to support the weight of the slab. That is, in Comparative Example 1, the width reduction of the slab was performed with all the upper rolls and lower rolls subjected to pressure control.

[0042] In Comparative Example 2, during the transport of the slab, the upper roll on the entry side and the upper roll on the exit side were subjected to pressure control such that each roll touched the upper surface of the slab under its own weight. In addition, the lower roll on the entry side and the lower roll on the exit side were subjected to position control such that the upper end position of the roll was a position lowered by half the amount of thickness increase due to width reduction predicted in advance from the pass line. During the width reduction of the slab, the upper roll on the entry side and the upper roll on the exit side were subjected to pressure control such that each roll applied a pressure of 20 tonf to the slab. In addition, the lower roll on the entry side and the lower roll on the exit side were subjected to position control such that the lower roll position was fixed to the same position as during the transport of the slab. That is, in Comparative Example 2, the pressure control of all the upper rolls was performed, and the lower roll position was fixed so that the upper end position of all the lower rolls was a position lowered by half the amount of thickness increase due to width reduction.

[0043] In Example 1 of the present invention, the upper rolls on the entry side and the exit side were subjected to pressure control so that each roll touched the top surface of the slab under its own weight while the slab was being transported. The lower roll on the entry side was subjected to position control so that the pass line position was fixed at the position where the upper end of the roll was located, and the lower roll on the exit side was subjected to pressure control so that the roll applied a pressure of 6 tonf to the slab. During the width reduction of the slab, the lower roll on the entry side was subjected to position control so that the roll applied a pressure of 20 tonf to the slab, and the lower roll on the exit side was subjected to pressure control so that the roll applied a pressure of 25 tonf to the slab, which is larger than the pressure of the upper rolls by the weight of the slab, in order to support the weight of the slab. That is, in Example 1 of the present invention, all the upper rolls and the lower roll on the exit side were subjected to pressure control, and the lower roll on the entry side was subjected to position control so that the lower roll position was fixed so that the pass line position was located at the upper end of the roll, and the width reduction of the slab was performed.

[0044] In Inventive Example 2, width reduction was performed in the same manner as Inventive Example 1 until the tail end of the progressively fed slab passed the entry roll. After the tail end of the slab passed the entry buckling prevention roll, the exit lower roll was switched to position control, and width reduction was performed under position control in which the position of the exit lower roll was fixed so that the position lowered from the pass line by 22 mm, which corresponds to half the amount of thickness increase due to width reduction, became the upper end position of the lower roll.

[0045] Under the conditions of Comparative Examples 1 and 2 and Invention Examples 1 and 2, the mild steel slabs were width-reduced one by one, and the striking position shift δy and the buckling amount δC of the slab end were measured. The striking position shift δy is a value defined by the following formula (1). The striking position shift δy is positive when the slab is shifted upward from the center of the die, and negative when it is shifted downward.

[0046] δy = (yOp + yDr) / 2 (1) In the above formula (1), yOp and yDr are the heights (mm) of the grooves transferred to both ends of the slab. yOp and yDr are values ​​obtained by measuring the heights of the grooves transferred to the slab by the protrusions provided at the center of the thickness of the dies 12a and 12b on the Op and Dr sides shown in Figure 1. In this example, the striking position deviation δy of the slabs that were width-reduced under each of the conditions of Comparative Examples 1 and 2 and Invention Examples 1 and 2 was measured from the tip of the slab at a pitch of 350 mm, which is equal to the feed amount.

[0047] The buckling amount ΔC is a value defined by the following formula (2). The buckling amount ΔC is positive in the case of an upward warp (concave shape) and is negative in the case of a downward warp (convex shape).

[0048] δC=(y'Op+y'Dr) / 2-y'Cr····(2) In the above formula (2), y'Cr is the height (mm) of the slab thickness center at the width center, and y'Op and y'Dr are the heights (mm) of the slab thickness center at both ends of the slab width.

[0049] FIG. 3 is a schematic cross-sectional view of a slab showing the dimensions used to calculate the buckling amount δC of the slab. FIG. 3(a) shows the buckling amount δC of the downward camber (convex shape), and FIG. 3(b) shows the buckling amount δC of the upward camber (concave shape). In this example, y'Op, y'Dr, and y'Cr were measured for a longitudinal cross section 100 mm from the tail end of the slab to calculate the buckling amount δC. The height y'Cr of the center of the slab thickness was obtained by measuring the slab shape in the width direction of the top and bottom surfaces of the slab after width reduction using a laser displacement meter.

[0050] [Effect of the tip of the slab bending under its own weight when it is in a cantilevered position] In order to prevent damage to the width reduction device 10, quality defects in the slab such as edge seams when a caliber is provided on the press surface of the die, and uneven wear of the dies 12a and 12b, it is preferable to keep the striking position deviation within 0 mm ± 10 mm over the entire length. Figure 4 is a graph showing the striking position deviation at the start of width reduction for each of the slabs width-reduced using the width reduction devices of Comparative Examples 1 and 2 and Invention Examples 1 and 2.

[0051] In Comparative Example 1, the striking position shift gradually shifted downward after the third press, and exceeded -10 mm at the 11th press. In Comparative Example 1, the pressure setting of the lower roll on the inlet side was constant both during slab transportation and width reduction. Therefore, as the slab was transported to the outlet side while undergoing width reduction, the weight of the slab in a cantilevered state increased, and the lower roll was pushed down by the slab, causing the slab to shift downward and resulting in a striking position shift.

[0052] In Comparative Example 2, the striking position deviation was negative overall, and exceeded -10 mm in the ninth press. In Comparative Example 2, the lower roll was lowered in advance before width reduction. As a result, a gap was generated between the lower roll and the slab before width reduction and immediately after the start of width reduction. This gap caused the cantilevered slab to bend downward due to the pressing force of the upper roll, and when width reduction was performed in this state, striking position deviation occurred.

[0053] In the present invention examples 1 and 2, the positional deviation of the slab during conveying and the slab during width reduction were smaller than those in the comparative examples 1 and 2, and the positional deviation of the slab during width reduction were within the target range of 0 mm ± 10 mm. In the present invention examples 1 and 2, the position of the lower roll on the inlet side was controlled, so that the slab during conveying and the slab during width reduction could be maintained on the pass line. Furthermore, by controlling the pressing force of the other rolls and bringing these rolls into contact with the slab, it was possible to assist in maintaining the slab during width reduction on the pass line. Due to these effects, the positional deviation of the slab during width reduction was smaller than that in the comparative examples 1 and 2, and the positional deviation of the slab during width reduction could be kept within the target range. From this result, it was confirmed that the slab can be maintained on the pass line by width reduction of the slab using the slab width reduction device and the slab width reduction method according to the present embodiment. If the slab can be maintained on the pass line, the slab can be width reduced in the die caliber, so that uneven wear of the die is suppressed, and as a result, the number of die replacements can be reduced and the yield can be improved by improving the slab quality.

[0054] [Effect of actual slab thickness increase differing from the set value] In order to prevent damage to the width reduction device 10, quality defects in the slab such as edge seams when a caliber is provided on the press surface of the die, and uneven wear of the dies 12a and 12b, it is preferable that the variation in the striking position deviation is small. Fig. 5 is a graph showing the standard deviation of the striking position deviation at the start of width reduction for all slabs width-reduced using the width reduction devices of Comparative Examples 1, 2, and 3 and Invention Examples 1 and 2.

[0055] In Comparative Example 3, during the transport of the slab, the upper roll on the entry side and the upper roll on the exit side were subjected to pressure control such that each roll touched the top surface of the slab with its own weight. In addition, the lower roll on the entry side and the lower roll on the exit side were subjected to position control such that the pass line position was fixed at the position where the upper end of the roll was located. During the width reduction of the slab, the upper roll on the entry side and the upper roll on the exit side were subjected to pressure control such that each roll applied a pressure of 20 tonf to the slab. The lower roll on the entry side was subjected to position control such that it was fixed at the same position as during the transport of the slab, and the lower roll on the exit side was subjected to position control such that it was lowered at a lowering speed corresponding to the slab thickness increase speed calculated in advance according to the type of slab. That is, in Comparative Example 3, all the upper rolls were subjected to pressure control, and the lower roll on the entry side was subjected to position control such that the lower roll position was fixed so that the pass line position was the upper end position of the roll. In addition, the lower roll on the exit side was position-controlled to fix the position of the lower roll at the upper end position of the roll during transport of the slab, and the slab was reduced in width by position control to lower it at a predetermined lowering speed during width reduction of the slab.

[0056] In Comparative Example 1, since all rolls are pressure controlled, the tapping position deviation becomes large as shown in FIG. 4, but the standard deviation of the tapping position deviation becomes relatively small. In Comparative Example 2, the lower roll on the entry side and the lower roll on the exit side are controlled in position so that the upper end position of the roll is fixed at a position lowered by half the amount of thickness increase due to width reduction. Therefore, the fluctuation of the tapping position deviation becomes large due to the fluctuation of the thickness increase on the exit side where the slab thickness increase due to width reduction is large, and the standard deviation of the tapping position deviation in Comparative Example 2 becomes large. In Comparative Example 3, the lower roll on the exit side is controlled in position so that the lower roll is lowered at a preset lowering speed. Therefore, the fluctuation of the tapping position deviation becomes large due to the fluctuation of the thickness increase on the exit side where the slab thickness increase due to width reduction is large, and the standard deviation of the tapping position deviation in Comparative Example 6 becomes large.

[0057] In Examples 1 and 2 of the present invention, the fluctuation in the overall length average value of the striking position deviation was smaller than in Comparative Examples 2 and 3, and the amount of fluctuation was within the range of ±1 mm. In Examples 1 and 2 of the present invention, the rolls on the exit side, where the amount of slab thickness increase due to width reduction is large, are subjected to pressure force control. Therefore, even if the amount of pressure increase on the exit side, where the amount of slab thickness increase due to width reduction is large, fluctuates, the fluctuation is absorbed by the pressure force control, so the effect of fluctuations in the amount of thickness increase is reduced, and the standard deviation of the striking position deviation in Examples 1 and 2 of the present invention is small. These results are shown in Table 1 below.

[0058] [Table 1]

[0059] As shown in Table 1 above, by using the slab width reduction device and slab width reduction method according to the present embodiment to reduce the width of a slab, it was confirmed that the slab can be maintained on the pass line without being affected by the tip of the slab being in a cantilevered state and deflecting under its own weight, and without being affected by the amount of thickness increase of the slab being different from the set value. By maintaining the slab on the pass line in this way, it was confirmed that the moment that rotates the die during width reduction of the slab can be suppressed, and therefore it is possible to suppress a situation in which an excessive force acts on the die and causes damage to the equipment. In addition, when a caliber is provided on the die press surface for width reduction, the slab can be width reduced within the caliber. This suppresses the occurrence of seam defects in the slab, thereby improving the yield. In addition, uneven wear of the die is also reduced, so the number of die replacements is reduced.

[0060] On the other hand, in Comparative Examples 1 and 2, it was confirmed that the slab was in a cantilevered state, and the leading end of the slab was deflected by its own weight, causing a large deviation in the striking position. In Comparative Examples 2 and 3, it was confirmed that the amount of thickness increase of the slab was different from the set value, causing a large fluctuation in the striking position deviation. For this reason, it was confirmed that the configurations of Comparative Examples 1, 2, and 3 could not suppress damage to the width reduction device 10, and could not suppress quality defects of the slab such as edge seams when a caliber is provided on the pressing surface of the die, or uneven wear of the dies 12a and 12b.

[0061] 6 is a graph showing the amount of buckling at the tail end of slabs width-reduced using the width reduction devices of Comparative Examples 1, 2, and 3 and Invention Examples 1 and 2. In Invention Example 2, when reducing the width of the tail end of the slab, control of the lower rolls on the delivery side was switched from pressure control to position control, so that the amount of buckling at the tail end was smaller than that of Invention Example 1. From this result, it was confirmed that when reducing the width of the tail end of a slab, it is preferable to switch the control of the lower rolls on the delivery side from pressure control to position control, and this makes it possible to reduce the amount of buckling at the tail end. [Explanation of symbols]

[0062] 10 Width reduction device 12a Mold 12b Mold 14 Anti-buckling roll 14a Upper roll 14b Lower Roll 16 Anti-buckling roll 16a Upper roll 16b Lower Roll 18 Control device 20 Sensors 22 Hydraulic cylinder 24 Hydraulic Cylinder 26 Hydraulic Cylinder 28 Hydraulic Cylinder 30 Servo valve 32 Servo valve 40 Pinch Roll 42 Pinch Roll 100 Slabs

Claims

1. A pair of dies for reducing the width of the slab; A method for reducing the width of a slab by using at least two pairs of upper and lower buckling prevention rolls installed on either side of a pass line of the slab in the vertical direction, the method comprising: a lower roll of the buckling prevention roll located on the inlet side of the traveling direction of the slab is position-controlled so that the upper end position of the lower roll is fixed at the pass line position, and the other buckling prevention rolls are pressure-controlled so that a predetermined pressure force is applied from each of the other buckling prevention rolls to the slab during width reduction; A method for reducing the width of a slab, comprising controlling the pressure force so that the pressure force of the upper roll of the buckling prevention roll located at the exit side in the traveling direction of the slab and the weight of the slab are balanced with the pressure force of the lower roll of the buckling prevention roll located at the exit side in the traveling direction of the slab.

2. A method for reducing the width of a slab as described in claim 1, wherein, after the tail end of the slab passes through a buckling prevention roll located on the entry side of the slab's traveling direction, a lower roll of the buckling prevention roll located on the exit side of the slab's traveling direction is position-controlled so that the upper end position of the lower roll is fixed at a position determined based on the amount of thickness increase of the slab due to the width reduction.

3. 3. A method for reducing the width of a slab according to claim 2, wherein the position determined based on the amount of thickness increase of the slab is a position vertically downward from the pass line position by half the amount of the thickness increase of the slab due to the width reduction.

4. A method for producing a steel plate, comprising the steps of: width-reducing the slab by the method for width-reducing the slab according to claim 1 or 2 to produce a steel plate.

5. A method for producing a steel plate, comprising the steps of: width-reducing the slab by the method for width-reducing the slab according to claim 3 to produce a steel plate.

6. A pair of dies for reducing the width of the slab; At least two pairs of upper and lower buckling prevention rolls are installed on either side of the pass line of the slab in the vertical direction; A control device for controlling the operation of each of the buckling prevention rolls, The control device controls the position of the lower roll of the buckling prevention roll located on the entry side of the slab's traveling direction so that the upper end position of the lower roll is fixed at the pass line position, and controls the pressure of each of the other buckling prevention rolls so that a predetermined pressure force is applied to the slab during width reduction.

7. The slab width reduction device according to claim 6, wherein the control device controls the pressing force so that the pressing force of the upper roll of the buckling prevention roll located at the exit side in the traveling direction of the slab and the weight of the slab are balanced with the pressing force of the lower roll of the buckling prevention roll located at the exit side in the traveling direction of the slab.

8. The method further comprises a detection means for detecting that the tail end of the slab has passed a buckling prevention roll located on the entry side of the traveling direction and outputting a detection signal, A slab width reduction device as described in claim 6 or claim 7, wherein when the control device acquires the detection signal, it controls the position of the lower roll of the buckling prevention roll located on the exit side in the traveling direction of the slab so that the upper end position of the lower roll is fixed at a position determined based on the amount of thickness increase of the slab due to the width reduction.

9. 9. A slab width reduction device as described in claim 8, wherein the position determined based on the amount of thickness increase of the slab is a position vertically downward from the pass line position by half the amount of thickness increase of the slab due to width reduction.

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