Metal mold for width reduction of hot slab and width reduction method

Abstract

To provide a metal mold for width reduction of a hot slab and a width reduction method which can suppress, when performing width reduction of the hot slab by use of the metal mold for width reduction, occurrence of slip to be capable of stably performing width reduction through designing the metal mold for width reduction in consideration of friction force between the hot slab and the metal mold for width reduction and backward moving power.SOLUTION: A metal mold 6 for width reduction of a hot slab comprises: parallel parts 7, 9, 11; and inclined parts 8, 10. When the parallel parts 7, 9, 11 and the inclined parts 8, 10 are pushed into the hot slab 2, a value obtained by multiplying the total value (L0+L1S+L1+L2S+L2) of length (L0+L1+L2) of the parallel parts 7, 9, 11 in a transportation direction and length (L1S+L2S) of the inclined parts 8, 10 in the transportation direction by fiction coefficient (μ) between the hot slab 2 and the parallel parts 7, 9, 11 or the inclined parts 8, 10 is more than the height of the inclined parts 8, 10 in the width direction.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a mold for width reduction of a hot slab and a width reduction method.

Background Art

[0002] As an example of a means for changing the plate width of a hot slab, a plate width press device that intermittently performs width reduction on both sides of the hot slab in the width direction of the hot slab by a pair of molds installed while the temperature of the hot slab produced in the continuous casting process does not drop below a predetermined temperature is conventionally known. Note that the hot slab may be a hot slab that has been put into a heating furnace and heated to a temperature equal to or higher than a predetermined temperature after the temperature has dropped below the predetermined temperature.

[0003] In the above-described plate width press device, the hot slab is conveyed by table rolls and pinch rolls between a pair of molds installed opposite to each other in the width direction of the hot slab. Each mold is configured to move back and forth or swing toward the hot slab. The hot slab is pressed by the mold that moves back and forth or swings, and its width is reduced. That is, the width is reduced.

[0004] In a plate width press device, usually, width reduction for narrowing the plate width by up to about 300 to 350 mm is performed on a hot slab having a plate width of about 900 to 2000 mm. By doing so, it is possible to manufacture a steel plate product having a plate width different from that of the hot slab cast in continuous casting. In addition, the plate width press device greatly contributes to improving the productivity and rationalizing the steel plate manufacturing process, such as reducing the number of times of changing the plate width of the hot slab manufactured in the continuous casting process, expanding schedule-free rolling in the hot rolling process, and increasing the coil single weight. Such advantages expand as the width reduction ability of the plate width press device increases.

[0005] The width reduction ability of the plate width press device means the function of the plate width press device that narrows the plate width of the hot slab. Also, the greater the difference between the plate width of the hot slab before width reduction by the plate width press device and the plate width of the hot slab after width reduction by the plate width press device, the greater the width reduction ability of the plate width press device. Therefore, if it is a plate width press device with a large width reduction ability, hot slabs with various plate widths can be manufactured, and the above-mentioned merits are expanded.

[0006] The above-mentioned mold used in the plate width press device has a flat portion extending along the conveying direction of the hot slab and an inclined portion continuously formed upstream of the flat portion in the conveying direction of the hot slab. The inclined portion is configured such that the distance from the downstream side to the upstream side in the conveying direction gradually increases with respect to the hot slab. When the width of the hot slab is reduced by the plate width press device using the mold of the above-mentioned shape, a flat surface corresponding to the flat portion of the mold and an inclined surface corresponding to the inclined portion of the mold are formed on the hot slab. Thereafter, in the plate width press device, the pair of molds are separated from the hot slab, and the hot slab is conveyed at a predetermined feed pitch.

[0007] Consider the case where the width of the hot slab is reduced using a mold (hereinafter referred to as a flat mold) in which only one stage of the above-mentioned inclined portion is formed. When the width of the hot slab that has not yet been width-reduced is width-reduced using the flat mold, the flat mold is pressed against the hot slab, and a flat surface and an inclined surface corresponding to the flat portion and the inclined portion of the flat mold are formed on the hot slab. After conveying the hot slab at a predetermined feed pitch, the width is reduced again using the flat mold. In that case, if the width reduction amount by the flat mold is gradually increased, the inclined portion of the flat mold for width reduction at the current time contacts the inclined surface formed on the hot slab by the width reduction one time before compared to the current time. If the friction coefficient between the inclined surface of the hot slab and the inclined portion of the flat mold is small, there may be a case where the hot slab is not width-reduced and a slip occurs in which the hot slab moves from the downstream side to the upstream side in the conveying direction.

[0008] When such slip occurs, the passing property of the hot slab in the plate width press device deteriorates. Therefore, in the conventional mold and width reduction method, in order to suppress the occurrence of slip, it was necessary to limit the amount of width reduction of the hot slab in the plate width press device. On the other hand, the friction coefficient between the mold and the hot slab varies greatly depending on the steel type of the hot slab, the state of the oxide scale on the surface of the hot slab due to the heating temperature of the hot slab, and the state of the mold surface. Therefore, it is difficult to always maintain a high value for the friction coefficient between the mold and the hot slab in order to suppress slip. Note that the passing property means the ease with which the hot slab passes through the plate width press device.

[0009] Under such circumstances, width reduction molds and width reduction methods for suppressing the occurrence of slip during width reduction of hot slabs have been conventionally studied, and an example thereof is described in Patent Document 1.

[0010] Patent Document 1 describes a width reduction mold having a mold parallel part, a first inclined part, a first intermediate parallel part, a second inclined part, a second intermediate parallel part, and a third inclined part. In the width reduction mold, the above-described parts are continuously provided in the above-described order from the outlet side to the inlet side in the conveying direction of the hot slab. Each parallel part is set parallel to the side surface of the hot slab. Each inclined part is inclined such that the distance from the hot slab gradually increases from the downstream side to the upstream side in the conveying direction. And the mold of Patent Document 1 can start width reduction by bringing the flat part generated in the hot slab by the width reduction one time before the current time point into contact with any one of the parallel parts of the mold for width reduction that performs width reduction on the hot slab at the current time point, even when the feed pitch of the hot slab changes. For example, when the hot slab is conveyed at a preset feed pitch, contact is started from the region width-reduced by the second intermediate parallel part in the hot slab when width reduction was performed one time before the current time point and the mold parallel part of the width reduction mold that performs width reduction at the current time point. By doing so, it is said that when width reduction of the hot slab is being performed, the occurrence of slip can be prevented and stable width reduction can be performed.

Prior Art Documents

Patent Document

[0011]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] However, the width reduction die described in Patent Document 1 was insufficient as a countermeasure against slip. That is, in the width reduction die described in Patent Document 1, when the width reduction amount gradually increases, at least one of the three inclined portions comes into contact with the hot slab among the three inclined portions. And, a backward force that moves the hot slab upstream in the conveying direction is generated at those contact portions. Therefore, slip may occur depending on the friction coefficient between the hot slab and the width reduction die, and there was still room for improvement in this regard.

[0013] The present invention has been made to solve the above-described problems, and by designing the width reduction die in consideration of the frictional force and the backward force between the hot slab and the width reduction die, when performing width reduction of the hot slab using the width reduction die, it is an object of the present invention to provide a width reduction die and a width reduction method for a hot slab that can suppress the occurrence of slip and perform width reduction stably.

Means for Solving the Problems

[0014] In order to achieve the above object, the present invention [1]A hot slab width reduction die for hot slab width reduction used for pressing both sides of the hot slab in the width direction of the hot slab to narrow the slab width of the hot slab. The die has a parallel portion parallel to the side surface of the hot slab in the width direction, and an inclined portion continuously formed at the upstream end of the parallel portion in the conveying direction of the hot slab, and the interval between the inclined portion and the side surface increases from the downstream side to the upstream side in the conveying direction. When the parallel portion and the inclined portion are pushed into the hot slab, the value obtained by multiplying the sum of the length of the parallel portion in the conveying direction and the length of the inclined portion in the conveying direction by the friction coefficient between the hot slab, the parallel portion, and the inclined portion is not less than the height of the inclined portion in the width direction. [2]The parallel portion includes a die parallel portion located on the hot slab side in the width direction, a first intermediate parallel portion located outside the hot slab than the die parallel portion in the width direction, and a second intermediate parallel portion located outside the hot slab than the first intermediate parallel portion in the width direction. The inclined portion includes a first inclined portion formed between the upstream end of the die parallel portion in the conveying direction and the downstream end of the first intermediate parallel portion in the conveying direction, a second inclined portion formed between the upstream end of the first intermediate parallel portion in the conveying direction and the downstream end of the second intermediate parallel portion in the conveying direction, and a third inclined portion continuously formed at the upstream end of the second intermediate parallel portion in the conveying direction. Let the length of the first intermediate parallel portion in the conveying direction be L1, the length of the second intermediate parallel portion in the conveying direction be L2, the height of the first inclined portion in the width direction be W1, the length of the first inclined portion in the conveying direction be L 1S , the height of the second inclined portion in the width direction be W2, the length of the second inclined portion in the conveying direction be L 2S , when the portion from the first inclined portion to the second intermediate parallel portion in the conveying direction is pushed into the hot slab, let the contact length between the die parallel portion and the hot slab be L0, the friction coefficient be μ, and the width reduction amount of the hot slab be dw. The hot slab width reduction die according to [1] satisfies the following formulas (1) and (2). (W1 + W2) ≦ dw / 2 ··· (1) μ(L0 + L 1S + L1 + L 2S + L2) ≧ (W1 + W2) ··· (2) [3][1] Or arrange the hot slab width reduction die described in [2] on each of both sides of the hot slab in the width direction of the hot slab, and press the hot slab from both sides of the hot slab in the width direction by the width reduction die to narrow the plate width of the hot slab. A width reduction method for performing width reduction.

Effect of the Invention

[0015] In the present invention, the width reduction die is designed in consideration of the frictional force and the backward force between the hot slab and the width reduction die. Therefore, according to the present invention, when performing width reduction of the hot slab using the width reduction die, the occurrence of slip can be suppressed, and stable width reduction of the hot slab can be performed.

Brief Explanation of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0017] Hereinafter, an example of an embodiment of the present invention (hereinafter referred to as "this embodiment") will be described. FIG. 1 is a perspective view showing an example of a plate width press apparatus to which a die for width reduction according to this embodiment can be applied. The plate width press apparatus 1 shown in FIG. 1 includes pinch rolls 3, 4 and table roll 5 for conveying the hot slab 2, and a die for width reduction (hereinafter simply referred to as "die") 6 that presses both side surfaces of the hot slab 2 in the width direction of the hot slab 2 to change the plate width of the hot slab 2. The pinch rolls 3, 4 are configured to sandwich the hot slab 2 from both sides in the vertical direction of the plate width press apparatus 1. Further, the pinch rolls 3, 4 are connected to a power source such as a motor, and are configured to rotate intermittently by receiving the torque generated by the power source. By doing so, the pinch rolls 3, 4 intermittently convey the hot slab 2 in a predetermined direction. The table roll 5 is a roll called a free roll, on which the hot slab 2 is placed and is rotated by the hot slab 2 conveyed by the pinch rolls 3, 4. Note that the above-described die 6 corresponds to the die for width reduction according to this embodiment.

[0018] Specifically, a pair of inlet-side pinch rolls 3 are arranged on the upstream side, i.e., the inlet side, of the plate width press apparatus 1 in the conveying direction of the hot slab 2. Also, a pair of outlet-side pinch rolls 4 are arranged on the downstream side, i.e., the outlet side, of the plate width press apparatus 1 in the conveying direction. In the example shown in FIG. 1, the inlet-side pinch rolls 3 are arranged to face each other while sandwiching the hot slab 2 above and below the hot slab 2 in the vertical direction. In the following description, the inlet-side pinch roll 3 located above the hot slab 2 in the vertical direction is referred to as the inlet-side upper pinch roll 3a, and the inlet-side pinch roll 3 located below the hot slab 2 in the vertical direction is referred to as the inlet-side lower pinch roll 3b.

[0019] Those pinch rolls 3a and 3b are configured to sandwich the hot slab 2 and convey the hot slab 2 in a predetermined direction at a predetermined feed pitch. Therefore, each of the pinch rolls 3a and 3b rotates in the opposite direction to the other. Also, each of the pinch rolls 3a and 3b is intermittently rotated to convey the hot slab 2 at a predetermined feed pitch after the width reduction of the hot slab 2 by the die 6 described later. That is, each of the pinch rolls 3a and 3b is rotated and stopped by the above-described power source in synchronization with the width reduction of the hot slab 2 by the die 6. The rotation and stop of those pinch rolls 3a and 3b may be performed by an operator or may be performed by a control device (not shown). Note that the above-described feed pitch means the length for conveying the hot slab 2 in the plate width press device 1. In other words, the feed pitch means the length in the conveyance direction of the portion of the hot slab 2 that is width-reduced by the die 6. The conveyance length will be described later.

[0020] The outlet pinch rolls 4 are arranged to sandwich the hot slab 2 from above and below in the vertical direction so as to face each other. In the following description, the outlet pinch roll 4 located above the hot slab 2 in the vertical direction is denoted as the outlet upper pinch roll 4a, and the outlet pinch roll 4 located below the hot slab 2 in the vertical direction is denoted as the outlet lower pinch roll 4b. These pinch rolls 4a, 4b sandwich the hot slab 2 and are adapted to convey the hot slab 2 at a predetermined feed pitch in a predetermined direction. That is, the respective pinch rolls 4a, 4b rotate in opposite directions to each other. Also, similar to the above-described respective pinch rolls 3a, 3b, after the width reduction of the hot slab 2 by the mold 6, the respective pinch rolls 4a, 4b are intermittently rotated to convey the hot slab 2 at a predetermined feed pitch. That is, the respective pinch rolls 4a, 4b are rotated and stopped by the above-described power source in synchronization with the width reduction of the hot slab 2 by the mold 6. The rotation and stop of these pinch rolls 4a, 4b may be performed by an operator or may be performed by a control device (not shown). In the example shown in FIG. 1, the hot slab 2 is conveyed from the left side to the right side in FIG. 1 by the inlet pinch rolls 3 and the outlet pinch rolls 4.

[0021] Note that examples of the hot slab 2 in the present embodiment include slabs that are manufactured by a continuous casting machine (not shown) and have a temperature equal to or higher than a predetermined temperature. Examples of the above-described slab may be, for example, a slab immediately after being manufactured by a continuous casting machine and before its temperature drops below a predetermined temperature. Alternatively, examples of the above-described slab may be a slab that becomes lower than a predetermined temperature after being manufactured by a continuous casting machine and is then heated in a heating furnace (not shown) to a temperature equal to or higher than the predetermined temperature. Examples of the heating furnace include conventionally known heating furnaces installed in the production line of a steelworks for heating slabs.

[0022] In the example shown in FIG. 1, the die 6 is disposed between the inlet pinch roll 3 and the outlet pinch roll 4 in the conveying direction of the hot slab 2, and is respectively arranged so as to face both side surfaces of the hot slab 2 in the width direction of the hot slab 2. Further, the plate width press device 1 has actuators (not shown) on both sides in the width direction. Then, each die 6 is pressed against the hot slab 2 by these actuators to perform width reduction for narrowing the plate width of the hot slab 2 to a predetermined plate width. Further, after the width reduction of the hot slab 2 is performed, the die 6 is separated from the hot slab 2 by an actuator.

[0023] The feed pitch described above is preferably set slightly shorter than the length of the portion of the hot slab 2 that is pressed by the die 6 in the conveying direction. This is to perform width reduction over the entire length of the hot slab 2 by slightly overlapping the portion of the hot slab 2 where width reduction was performed one time before the current time point and the portion where width reduction is performed at the current time point.

[0024] FIG. 2 is a top view showing an example of the die 6 according to the present embodiment. FIG. 3 is a view showing an enlarged part of the die 6 shown in FIG. 2. The die 6 shown in FIGS. 2 and 3 is a die called a three-stage die, and among the outer peripheral surfaces of the die 6, the side surface on the hot slab 2 side in the width direction is a pressing surface. Among the pressing surfaces, a die parallel portion 7 substantially parallel to the side surface in the width direction of the hot slab 2 before pressing is formed on the downstream pressing surface in the conveying direction of the hot slab 2. Note that the die parallel portion 7 is located on the side closest to the hot slab 2 in the width direction among the die 6, as will be described below.

[0025] On the pressing surface of the mold 6, a first inclined portion 8 is formed which is continuous with the upstream end of the mold parallel portion 7 in the conveying direction and extends at a first inclination angle α1 toward the upstream side in the conveying direction. As shown in FIGS. 2 and 3, the first inclined portion 8 extends inclined from the mold parallel portion 7 to the side opposite to the hot slab 2 in the width direction. That is, the distance between the plane (not shown) parallel to the mold parallel portion 7 and the first inclined portion 8 gradually increases from the downstream side to the inflow side in the conveying direction. Note that the angle formed by the plane parallel to the mold parallel portion 7 and the first inclined portion 8 is the first inclination angle α1 of the first inclined portion 8 as shown in FIG. 3. The length L of the first inclined portion 8 in the conveying direction 1S The setting of the height W1 of the first inclined portion 8 in the width direction will be described later. The height W1 of the first inclined portion 8 is equal to the height between the mold parallel portion 7 and a first intermediate parallel portion 9 (to be described later) in the width direction.

[0026] A first intermediate parallel portion 9 is formed continuously with the upstream end of the first inclined portion 8 in the conveying direction within the first inclined portion 8. That is, the first intermediate parallel portion 9 is located outside the hot slab 2 with respect to the mold parallel portion 7 in the width direction. The first intermediate parallel portion 9 is substantially parallel to the mold parallel portion 7. The length L1 of the first intermediate parallel portion 9 in the conveying direction is shorter than the total length of the mold parallel portion 7. The setting of the length L1 of the first intermediate parallel portion 9 in the conveying direction will be described later.

[0027] A second inclined portion 10 is formed continuously with the upstream end of the first intermediate parallel portion 9 in the conveying direction within the first intermediate parallel portion 9 and extends at a second inclination angle α2 toward the upstream side in the conveying direction. As shown in FIGS. 2 and 3, the second inclined portion 10 extends inclined from the first intermediate parallel portion 9 to the side opposite to the hot slab 2 in the width direction. That is, the distance between the plane parallel to the mold parallel portion 7 and the second inclined portion 10 gradually increases from the downstream side to the inflow side in the conveying direction. Note that the angle formed by the plane parallel to the mold parallel portion 7 and the second inclined portion 10 is the second inclination angle α2 of the second inclined portion as shown in FIG. 3. The length L of the second inclined portion 10 in the conveying direction 2S The setting of the height W2 of the second inclined portion 10 in the width direction will be described later. The height W2 of the second inclined portion 10 is equal to the length between the first intermediate parallel portion 9 and a second intermediate parallel portion 11 (to be described later) in the width direction.

[0028] Of the second inclined portion 10, a second intermediate parallel portion 11 is formed continuously at the upstream end of the second inclined portion 10 in the conveying direction. That is, in the width direction, the second intermediate parallel portion 11 is located outside the hot slab 2 compared to the first intermediate parallel portion 9. The second intermediate parallel portion 11 is substantially parallel to the mold parallel portion 7 and the first intermediate parallel portion 9 described above. The length L2 of the second intermediate parallel portion 11 in the conveying direction is shorter than the total length of the mold parallel portion 7. The setting of the length L2 of the second intermediate parallel portion 11 in the conveying direction will be described later.

[0029] Of the second intermediate parallel portion 11, a third inclined portion 12 extending at a third inclination angle α3 toward the upstream in the conveying direction is formed continuously at the upstream end of the second intermediate parallel portion 11 in the conveying direction. As shown in FIGS. 2 and 3, the third inclined portion 12 extends inclined from the second intermediate parallel portion 11 to the side opposite to the hot slab 2 in the width direction. That is, the distance between the plane parallel to the mold parallel portion 7 and the third inclined portion 12 gradually increases from the upstream side to the downstream side in the conveying direction. The angle formed by the plane parallel to the mold parallel portion 7 and the third inclined portion 12 is the third inclination angle α3 of the third inclined portion 12. When the mold 6 and the hot slab 2 collide during the conveyance of the hot slab 2, the conveyance of the hot slab 2 may stop. Therefore, in the present embodiment, in order to prevent the mold 6 and the hot slab 2 from accidentally colliding during the conveyance of the hot slab 2, the third inclination angle α3 is set to be smaller than the first inclination angle α1 and the second inclination angle α2.

[0030] (Relationship between frictional force and backward force) When the width reduction of the hot slab 2 is performed by the plate width press device 1, the relationship between the frictional force Ff and the backward force Fb generated between the hot slab 2 and the mold 6 will be described. The backward force Fb means the force that retreats the hot slab 2 to the upstream side of the plate width press device 1 in the conveying direction when the side surface of the hot slab 2 is pressed by the mold 6.

[0031] Specifically, when the mold 6 is moved to both sides of the hot slab 2 by the above-described actuator, first, the mold parallel portion 7 of the mold 6 contacts the side surface of the hot slab 2. When the moving amount of the mold 6 toward the hot slab 2, that is, the width reduction amount, is increased, the mold 6 is pushed into the hot slab 2, and the width of the hot slab 2 decreases. In addition to the mold parallel portion 7, the first inclined portion 8 contacts the hot slab 2. When the width reduction amount is further increased, the mold 6 is further pushed into the hot slab 2, and the width of the hot slab 2 further decreases. When the width reduction amount is gradually increased in this way, the mold 6 contacts the hot slab 2 in the order of the mold parallel portion 7, the first inclined portion 8, the first intermediate parallel portion 9, the second inclined portion 10, the second intermediate parallel portion 11, and the third inclined portion 12. Further, while the width of the hot slab 2 is being reduced in this way, a frictional force Ff is generated at the contact portion between the hot slab 2 and the mold 6. Furthermore, the above-described backward force Fb is generated between the hot slab 2 and the first inclined portion 8, and between the hot slab 2 and the second inclined portion 10.

[0032] Since the acting line direction of the frictional force Ff and the acting line direction of the backward force Fb are opposite to each other, the value obtained by subtracting the backward force Fb from the frictional force Ff is the force with which the mold 6 grips the hot slab 2 (hereinafter referred to as the grip resultant force G0. G0 = Ff - Fb). For example, when the mold parallel portion 7 of the mold 6 contacts the hot slab 2, the grip resultant force G0 can be expressed as follows, where L0 is the contact length between the mold parallel portion 7 and the hot slab 2, p is the surface pressure, and μ is the friction coefficient between the hot slab 2 and the mold 6. Since the mold parallel portion 7 is substantially parallel to the side surface of the hot slab 2, no backward force Fb is generated at their contact portion (Fb = 0). G0 = μpL0

[0033] When width reduction is first performed on the hot slab 2 that has not undergone width reduction, the contact length L0 is equal to the entire length of the mold parallel portion 7 in the conveying direction and remains constant regardless of the progress of width reduction.

[0034] As described above, when width reduction is performed on the hot slab 2, the mold 6 is pressed against the hot slab 2, and unevenness corresponding to the shape of the mold 6 is generated on the hot slab 2. When the mold 6 is separated from the hot slab 2, the hot slab 2 is conveyed downstream of the plate width press device 1 in the conveying direction at a predetermined feed pitch. Therefore, when width reduction is performed on the hot slab 2 that had width reduction performed on it one time before the current time, the mold 6 comes into contact with the above-described unevenness. FIG. 4 shows an example thereof. In the following description, the width reduction at the current time is referred to as the current reduction pass, and the width reduction one time before the current reduction pass is referred to as the previous reduction pass.

[0035] In the example shown in FIG. 4, a part of the mold parallel portion 7 in the current reduction pass comes into contact with a part of the plane 13 corresponding to the second parallel portion 11 of the mold 6 generated on the hot slab 2 by the previous reduction pass. The contact length L0 between the hot slab 2 and the mold 6 at the time when they come into contact can be expressed as follows, where the feed pitch is f. As described above, the feed pitch f is the length by which the hot slab 2 is conveyed. The length of the feed pitch f is shorter than the sum of the lengths L1, L2 of the respective intermediate parallel portions 9, 11 of the mold 6 in the conveying direction and the lengths L 1S , L 2S of the respective inclined portions 8, 10 of the mold 6 in the conveying direction. L0 = f - (L 1S + L1 + L 2S )

[0036] When the width reduction amount is increased from the state where a part of the mold parallel portion 7 is in contact with a part of the plane 13 corresponding to the second parallel portion 11 of the mold 6 generated on the hot slab 2 by the above-described previous reduction pass, the hot slab 2 is pressed and deformed by the mold parallel portion 7. Then, a shape corresponding to the shape of the mold parallel portion 7 is generated on the hot slab 2. Thus, the contact length L0 increases as the width reduction progresses. Also, the time when the mold parallel portion 7 comes into contact with the plane 14 corresponding to the mold parallel portion 7 of the mold 6 generated on the hot slab 2 by the previous reduction pass is the end point of the width reduction. Therefore, immediately before the end point of the width reduction, the contact length L0 becomes almost equal to the feed pitch f (L0 ≈ f).

[0037] In addition, when approximating the shape generated in the hot slab 2 by the width reduction of the hot slab 2 using the mold 6 as shown by the dotted line in Fig. 4, the contact length L0 that changes as the width reduction progresses can be simply obtained.

[0038] The feed pitch f generally has a substantially common value for all the hot slabs 2 width-reduced by the plate width press device 1 shown in Fig. 1. That is, the feed pitch f is substantially constant regardless of the steel type and width of the hot slab width-reduced by the plate width press device 1. The contact length L0 during width reduction is the length L1, L2 of each intermediate parallel portion 9, 11 of the mold 6 in the transport direction, the length L 1S 、L 2S 、and the heights W1, W2 of each inclined portion 8, 10 of the mold 6 in the width direction. Therefore, if the shape of the mold 6 is designed such that the frictional force Ff is greater than the backward force Fb (Ff > Fb), the grip resultant force G0 becomes a value of zero or more. And when width reduction of the hot slab 2 is performed using such a mold 6, as will be described later, slip of the hot slab 2 during width reduction can be suppressed, and width reduction can be stably performed. The feed pitch f is set to a value of about 250 to 450 mm according to the production efficiency required for the width reduction device, but is not necessarily limited to this range. The relational expression between the above-described contact length L0 and the feed pitch f, "L0 = f - (L 1S + L1 + L 2S )" may be set within a range that satisfies it.

[0039] The frictional force Ff and the backward force Fb change with the increase in the width reduction amount. Generally, in order to prevent the slip of the hot slab 2 when the feed amount of the slab is less than the feed pitch f and the width reduction is started from the state where the hot slab 2 is in contact with the third inclined portion 12, tanα3 is set to be less than or equal to the friction coefficient μ. Therefore, the grip force acting on the third inclined portion 12 is always zero or more. Thus, the situation where the backward force Fb is maximized and the hot slab 2 is most likely to slip is, in the example shown here, the situation where the range from the first inclined portion 8 to the second intermediate parallel portion 11 of the mold 6 is pushed into and contacts the hot slab 2. Hereinafter, the grip resultant force G0 in that situation will be considered. When the backward force Fb is maximized, the third inclined portion 12 of the mold 6 is not in contact with the hot slab 2. Therefore, it is not necessary to include it in the calculations described below.

[0040] If the width reduction amount of the hot slab 2 is denoted as dw, the above-described situation can be expressed by the following formula. That is, when the following formula is satisfied, it can be said that the range from the first inclined portion 8 to the second intermediate parallel portion 11 of the mold 6 is pushed into and contacts the hot slab 2. (W1 + W2) ≤ dw / 2 ···(1)

[0041] On the other hand, the grip resultant force G1 acting on the first inclined portion 8 and the first intermediate parallel portion 9 of the mold 6 can be expressed by the following formula. Note that tanα1 = W1 / L 1S where μ is the friction coefficient and p is the surface pressure. G1 = L1(μp) + (L 1S / cosα1)(μpcosα1 - psinα1) = μp(L1 + L 1S ) - pL 1S tanα1 = μp(L 1S + L1) - pW1

[0042] FIG. 5 is a diagram for explaining each term of the calculation formula of the grip resultant force G1. As shown in FIG. 5, "psinα1" in the calculation formula of the grip resultant force G1 indicates the backward force generated by the contact of the first inclined portion 8 with the hot slab 2. "μpcosα1" in the calculation formula of the grip resultant force G1 is a component force whose acting line direction is opposite to that of "psinα1", and as shown in FIG. 5, it indicates the frictional force generated between the first inclined portion 8 and the hot slab 2. Further, "μp" in the calculation formula of the grip resultant force G1 indicates the frictional force generated between the first intermediate parallel portion 9 and the hot slab 2. Furthermore, as shown in FIG. 5, in the state where the first inclined portion 8 is pushed into the hot slab 2, the contact length between the mold 6 and the hot slab 2 in the width direction is equal to the height W1 of the first inclined portion 8. The contact length between the mold 6 and the hot slab 2 in the conveying direction is equal to the value obtained by adding the length L 1S of the first inclined portion 8 in the conveying direction and the length L1 of the first intermediate parallel portion 9. Therefore, each of the above lengths L 1S , L1, and the height W1 is used as the contact length between the mold 6 and the hot slab 2 in the conveying direction and the width direction in the calculation formula of the grip resultant force G1.

[0043] The grip resultant force G2 acting on the second inclined portion 10 and the second intermediate parallel portion 11 can also be calculated in the same manner as the above-described grip resultant force G1. Therefore, the grip resultant forces acting on the first inclined portion 8, the first intermediate parallel portion 9, the second inclined portion 10, and the second intermediate parallel portion 11 can be expressed as follows. G1 + G2 = μp(L 1S + L1 + L 2S + L2) - p(W1 + W2)

[0044] The value obtained by adding the grip resultant force G0 acting on the mold parallel portion 7 to the above-described grip resultant force is the grip resultant force G in the situation where the range from the first inclined portion 8 to the second intermediate parallel portion 11 of the mold 6 is in contact with the hot slab 2. The grip resultant force G can be expressed as follows. The value of the contact length L0 used in the following formula is the value at a point immediately before the end of the width reduction of the hot slab 2, and is approximately equal to the feed pitch f as described above. G = G0 + G1 + G2 = μp(L0 + L 1S + L1 + L 2S + L2) - p(W1 + W2)

[0045] In order to prevent the slip of the hot slab 2, it is necessary to make the grip resultant force G zero or more (G ≧ 0). When both sides of the above formula representing the grip resultant force G are divided by the surface pressure p, it can be transformed as follows. G / p = μ(L0 + L 1S + L1 + L 2S + L2) - (W1 + W2)

[0046] Note that as the width reduction of the hot slab 2 progresses, the work hardening of the hot slab 2 progresses, and accordingly the surface pressure p changes. However, the surface pressure p is always a positive value. Therefore, the value obtained by dividing the grip resultant force G by the surface pressure p is zero or more, and the right side of the above formula is also zero or more. Representing this as an inequality gives the following formula. μ(L0 + L 1S + L1 + L 2S + L2) - (W1 + W2) ≧ 0

[0047] Among the above-mentioned inequalities, when the terms (W1 + W2) of the height W1 of the first inclined portion 8 and the height W2 of the second inclined portion 10 are transposed to the right side, the following formula (2) is obtained. μ(L0 + L 1S + L1 + L 2S + L2) ≧ (W1 + W2) ···(2)

[0048] According to formula (2), when the value on the left side is greater than or equal to the value on the right side, the grip resultant force G is zero or more. The value on the left side of formula (2) is the product of the friction coefficient μ and the total value of the lengths L 1S , L1, L 2S , L2 and the contact length L0 of the die parallel portion 7 immediately before the end of the width reduction of the hot slab 2. The value on the right side of formula (2) is the total value of the heights W1 and W2 of the inclined portions 8 and 10 in the width direction. Therefore, if the dimensions of each part of the die 6 are set so as to satisfy formula (2), the slip of the hot slab 2 can be suppressed when the width reduction of the hot slab 2 is performed by the die 6.

[0049] Further, Equation (2) represents the grip resultant force G in a situation that satisfies Equation (1) where the backward force Fb is maximized. Therefore, when Equation (1) is not satisfied, for example, the grip resultant force within the range where contact occurs between the hot slab 2 and the mold 6 may be calculated, and the dimensions of each part of the mold 6 may be designed so that the grip resultant force becomes a positive value.

[0050] (Coefficient of friction) The coefficient of friction μ between the mold 6 and the hot slab 2 varies depending on the steel type of the hot slab 2, the state of the oxide scale on the surface of the hot slab 2 due to the heating temperature of the hot slab 2, and the state of the surface of the mold 6. Therefore, the relationship between the coefficient of friction μ, the steel type of the hot slab 2, the state of the oxide scale on the surface of the hot slab 2, and the state of the surface of the mold 6 may be obtained in advance by, for example, FEM (finite element method), and the coefficient of friction μ may be calculated based on the previously obtained relationship. Further, the coefficient of friction μ can be obtained by a conventionally known pin-on-disk test. In the pin-on-disk test, a small piece (for example, a pin) made of the same steel type as the hot slab 2 that simulates the hot slab 2 on which width reduction is performed by the plate width press device 1 and having substantially the same state of the oxide scale is prepared. Also, a disk made of the same material as the mold 6 described above is prepared. Then, by bringing the above-described small piece and the disk into contact with each other and relatively moving them, the coefficient of friction between them is measured. Furthermore, since the width reduction load increases as the coefficient of friction μ increases, the width reduction load when the coefficient of friction μ is changed in advance may be calculated by FEM or the like, and the coefficient of friction may be calculated inversely from the load actual results. Note that the method for calculating the coefficient of friction μ is not limited to the method described above.

[0051] According to the present embodiment, the dimensions of each part of the mold 6 are set so as to satisfy the above-described formulas (1) and (2), that is, the dimensions of each part of the mold 6 are set in consideration of the frictional force and the backward force between the mold 6 and the hot slab 2. Therefore, when performing the width reduction of the hot slab 2, the occurrence of slip in which the hot slab 2 retreats can be prevented or suppressed. As a result, the passing property of the hot slab 2 in the plate width press apparatus 1 can be improved. Further, the plate width press apparatus 1 can stably perform the width reduction of the hot slab 2. Note that the method of installing the mold 6 having the above-described configuration in the plate width press apparatus 1 and performing the width reduction of the hot slab 2 using the mold 6 corresponds to the width reduction method according to the present embodiment.

[0052] Note that the present invention is not limited to the above-described embodiment. For example, although the above-described formula (2) is for the case of the three-stage mold shown in FIG. 2, the above-described concept regarding the grip resultant force G is not limited to the three-stage mold, and can be similarly applied to a two-stage mold or a multi-stage mold of four or more stages. That is, the length of each parallel part of the multi-stage mold in the transport direction and the height of each inclined part in the width direction may be set so that the grip resultant force G becomes a positive value. Further, in the embodiment of the present invention, a width reduction apparatus that intermittently transports the slab 2, generally called a stop-and-go method, has been described, but it is also applicable to a flying sizing press that continuously transports the slab 2, and is not limited to the stop-and-go method. Even in such a case, the same operations and effects as those of the above-described embodiment can be obtained.

Example

[0053] Hereinafter, examples performed to confirm the effects of the present embodiment will be described. In this example, a plate width press apparatus having substantially the same configuration as the above-described plate width press apparatus 1 was used, and width reduction was performed on a hot slab of carbon steel having a thickness of 260 mm, a width of 1500 mm, and a length of 9000 mm. Further, a width reduction mold having substantially the same configuration as the above-described width reduction mold 6 was used. Table 1 summarizes the dimensions of the hot slabs in Examples 1 to 4 and Comparative Examples 1 to 4, and the results of width reduction performed on those hot slabs.

[0054]

Table 1

[0055] When the condition of Equation (2) was satisfied, a "◯" was entered in the column of "Relationship of Equation (2)" in Table 1, and when the condition of Equation (2) was not satisfied, an "×" was entered in the column of "Relationship of Equation (2)". Also, when width reduction was performed and no slip occurred, a "◯" was entered in the column of "Whether Through-Passing is Possible" in Table 1, and when slip occurred, an "×" was entered in the column of "Whether Through-Passing is Possible".

[0056] Examples 1 to 3 are examples in which a width reduction die was designed to satisfy Equation (2), and the width reduction of a hot slab was performed using the width reduction die. In Examples 1 to 3, as shown in Table 1, no slip of the hot slab occurred when the width reduction of the hot slab was being performed. Therefore, width reduction could be stably performed over the entire length of the hot slab.

[0057] Comparative Examples 1 to 3 are examples in which a width reduction die that does not satisfy Equation (2) was designed while the friction coefficient between the hot slab and the width reduction die is the same as that in Examples 1 to 3, and the width reduction of the hot slab was performed using the width reduction die. In Comparative Examples 1 to 3, as shown in Table 1, slip occurred when width reduction was performed, and stable width reduction could not be performed over their entire lengths.

[0058] Example 4 is an example in which a width reduction die was designed in the same manner as in Example 1 except that the amount of width reduction was reduced compared to Example 1, and the width reduction of the hot slab was performed using the width reduction die. In Example 4, as shown in Table 1, when width reduction was performed, stable width reduction could be performed over its entire length without slip occurring.

[0059] Comparative Example 4 is the same as Example 4 except that a width reduction die that does not satisfy formula (2) was designed, and the width reduction of the hot slab was performed using the width reduction die. In Comparative Example 4, as shown in Table 1, when width reduction was performed, slip occurred, and stable width reduction could not be performed over their entire lengths.

Explanation of Signs

[0060] 1 Plate width press device 2 Hot slab 3 Inlet pinch roll 4 Outlet pinch roll 5 Table roll 6 Width reduction die 7 Die parallel part 8 First inclined part 9 First intermediate parallel part 10 Second inclined part 11 Second intermediate parallel part 12 Third inclined part 13 Plane corresponding to the second intermediate parallel part generated in the hot slab in the pre-reduction pass 14 Plane corresponding to the die parallel part generated in the hot slab in the pre-reduction pass

Claims

1. A hot slab width reduction die for hot slab width reduction used for pressing both sides of the hot slab in the width direction of the hot slab to narrow the slab width of the hot slab, which is arranged on each of both sides of the hot slab in the width direction, and has a parallel portion parallel to the side surface of the hot slab in the width direction, and an inclined portion formed continuously at the upstream end of the parallel portion in the conveying direction of the hot slab, and the distance between the inclined portion and the side surface increases from the downstream side to the upstream side in the conveying direction, wherein a value obtained by multiplying the sum of the length of the parallel portion in the conveying direction and the length of the inclined portion in the conveying direction when the parallel portion and the inclined portion are pushed into the hot slab by the friction coefficient between the hot slab and the parallel portion and the inclined portion is not less than the height of the inclined portion in the width direction. A hot slab width reduction die for hot slab width reduction.

2. The parallel portion has a die parallel portion located on the hot slab side in the width direction, a first intermediate parallel portion located outside the hot slab more than the die parallel portion in the width direction, and a second intermediate parallel portion located outside the hot slab more than the first intermediate parallel portion in the width direction, and the inclined portion has a first inclined portion formed between the upstream end of the die parallel portion in the conveying direction and the downstream end of the first intermediate parallel portion in the conveying direction, a second inclined portion formed between the upstream end of the first intermediate parallel portion in the conveying direction and the downstream end of the second intermediate parallel portion in the conveying direction, and a third inclined portion formed continuously at the upstream end of the second intermediate parallel portion in the conveying direction. Let the length of the first intermediate parallel part in the conveying direction be L １ and the length of the second intermediate parallel part in the conveying direction be L ２ and the height of the first inclined part in the width direction be W １ and the length of the first inclined part in the conveying direction be L １Ｓ and the height of the second inclined part in the width direction be W ２ and the length of the second inclined part in the conveying direction be L ２Ｓ and the contact length between the die parallel part and the hot slab when the part from the first inclined part to the second intermediate parallel part in the conveying direction is pushed into the hot slab be L ０ The hot slab width reduction die according to claim 1, which satisfies the following formulas (1) and (2), where the friction coefficient is μ and the width reduction amount of the hot slab is dw (W １ + W ２ ) ≤ dw / 2...(1) μ(L ０ + L １Ｓ + L １ + L ２Ｓ + L ２ ) ≥ (W １ + W ２ )...(2)

3. A width reduction method for pressing the hot slab with the hot slab width reduction die according to Claim 1 or 2 arranged on each of both sides of the hot slab in the width direction of the hot slab to narrow the slab width of the hot slab by pressing the hot slab from both sides of the hot slab in the width direction with the width reduction die.

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