JPWO2013105670A1 - Slab reduction device - Google Patents

Abstract

The present invention is capable of reliably reducing the center segregation and porosity by reducing the slab drawn from the mold with a sufficient reduction force and suppressing the occurrence of internal cracks, thereby producing a high-quality slab. It is a possible slab pressing device, a pair of slab pressing rolls that sandwich and press the slab, a backup roll that supports this slab pressing roll, and a pair of frames that are arranged to face each other, 3 or more sets of slab pressing rolls and backup rolls are arranged in each of the frames in the slab drawing direction, and the pair of frames have a rolling-down means for moving the distance between the frames close to each other. Are provided at two or more locations.

Description

The present invention relates to a slab reduction device that squeezes a slab drawn from a mold in the thickness direction of the slab.
This application claims priority based on Japanese Patent Application No. 2012-4101 filed in Japan on January 12, 2012, and Japanese Patent Application No. 2012-137020 filed in Japan on June 18, 2012, These contents are incorporated herein.

  For example, in continuous casting of steel, the molten steel injected into the mold is cooled by the cooling means, so that the solidified shell grows and the slab is pulled out from below the mold. Here, the slab pulled out from the mold is not completely solidified when it comes out of the mold, and has an unsolidified portion inside. For this reason, there exists a possibility of causing what is called a bulging deformation which deform | transforms so that a slab may swell by the static pressure of the molten steel in a casting_mold | template. It is known that center segregation occurs in a region where bulging deformation has occurred.

In order to suppress this bulging deformation, for example, Patent Documents 1 and 2 propose a continuous casting facility provided with a slab support roll that contacts the long side surface of the slab drawn from the mold and receives the above-mentioned static pressure. Has been.
Here, in order to reliably support the long side surface of the slab, it is effective to reduce the roll diameter and narrow the interval between the slab support rolls. However, if the roll diameter is reduced, the slab support roll lacks rigidity and deforms so as to bend by static pressure, and the slab cannot be reliably supported.
Therefore, in Patent Documents 1 and 2, a backup roll for supporting the slab support roll is disposed so that the above-described slab support roll is not deformed by static pressure.

In addition, porosity may occur in the slab due to solidification shrinkage or the like. It is possible to reduce the porosity by hot rolling the slab, but in the case of a product with a large thickness, the amount of reduction during hot rolling cannot be ensured sufficiently. Porosity cannot be reduced.
Then, in order to suppress generation | occurrence | production of a porosity at the stage of a slab, the roll segment apparatus which rolls down a slab is proposed by patent document 3, for example. This roll segment device is provided with a rolling-down means for bringing the lower frame and the upper frame close to each other, so that the slab can be rolled down.

  Here, in the roll segment device described in Patent Document 3, the roll contacting the slab is a divided roll divided in the roll axial direction, and between the divided rolls adjacent in the axial direction, A bearing portion that pivotally supports the split roll is disposed. By setting it as such a structure, the load loaded on a roll can be received by a some bearing part disperse | distributing, and it becomes possible to reduce a porosity by squeezing a slab with a big reduction force.

JP-A-10-328799 JP 11-291007 A JP 2000-312956 A

However, when the roll contacting the slab is divided in the roll axial direction, the slab cannot be reduced in the bearing portion disposed between the axially adjacent divided rolls. There is a risk that bulging deformation may occur in the portion. Even if the portion where the bulging deformation occurred was subsequently pressed with another split roll, the bulging deformation could not be sufficiently corrected. For this reason, center segregation and porosity occur, and the quality of the slab deteriorates.
On the other hand, when the split roll is not adopted, the load applied to the roll is received by the two bearing portions, and the slab cannot be reduced with a large reduction force, and the porosity can be sufficiently reduced. could not.
Moreover, in the slab support device in which the backup roll is disposed on the slab support roll, bulging deformation can be reduced and center segregation can be reduced, but the slab is not squeezed, so the porosity can be sufficiently reduced. could not.
Further, when the roll diameter is increased by increasing the roll diameter of the roll in contact with the slab, it is necessary to dispose the roll at a distance in the slab drawing direction. As a result, bulging deformation becomes large, and there is a possibility that center segregation occurs. In addition, the slab is locally pressed, and internal cracks may occur in the slab.
Thus, conventionally, center segregation and porosity of a slab could not be reduced at the same time.

  The present invention has been made in view of the above-described situation, and by reducing the slab drawn from the mold with a sufficient reduction force, the center segregation and porosity can be reliably reduced, and the occurrence of internal cracks can be prevented. An object of the present invention is to provide a slab reduction device that can suppress and can manufacture a high-quality slab.

  In order to solve the above-mentioned problems, a slab pressing device according to the present invention is a slab pressing device for pressing a slab drawn from a mold, and a pair of slab pressing rolls that sandwich and press the slab. And a backup roll that supports the slab pressing roll, and a pair of frames arranged so as to face each other, each of the frames, a set of the slab pressing roll and the backup roll, Three or more sets are provided in the slab drawing direction, and the pair of frames are provided with two or more rolling-down means for bringing the distance between the pair of frames close to or away from each other.

According to the slab pressing device having this configuration, since the slab pressing roll and the backup roll supporting the slab pressing roll are provided, the load applied when the slab is reduced is reduced. It can be received by the bearing portion of the pressing roll and the bearing portion of the backup roll. Therefore, the slab can be reduced with a relatively large reduction force, and the porosity can be sufficiently reduced.
Moreover, the whole width direction of a slab can be fully pressed, without using a slab pressing roll as a division | segmentation roll, and generation | occurrence | production of center segregation can be suppressed.

Furthermore, it is not necessary to increase the rigidity by increasing the roll diameter of the slab pressing roll, the slab pressing roll can be arranged at a narrow pitch in the slab drawing direction, and the slab can be rolled down relatively uniformly. Internal cracking of the slab can be suppressed.
Further, each of the frames is provided with three or more sets of the slab pressing roll and the backup roll in the slab drawing direction, and two or more reduction means are provided on the frame. The slab can be uniformly reduced by three or more sets of the slab pressing roll and the backup roll.

Here, it is preferable that at least one of the slab pressing rolls that are paired with the slab interposed therebetween has a large-diameter portion that protrudes radially outward at a central portion in the axial direction.
As a result, the central region in the width direction of the slab where the unsolidified portion exists can be reduced by the large-diameter portion, and the end portion in the width direction of the completely solidified slab can be prevented from being reduced. Therefore, the rolling load can be reduced.
Moreover, since the slab pressing roll is supported by the backup roll, even if the rigidity of the slab pressing roll is low, the slab pressing roll is restrained from being deformed in the down direction. Therefore, even a slab having a relatively wide width such as a slab can be applied to a slab pressing roll having a large-diameter portion projecting radially outward in the axial center portion.
Further, as described above, since the slab pressing roll is not pressed against the end portion in the width direction of the completely solidified slab, it is possible to suppress the deflection deformation in the drawing direction of the slab pressing roll. .

Here, it is preferable that the backup roll is divided into a plurality of parts in the axial direction of the slab pressing roll.
In this case, since the backup roll is divided into a plurality of parts in the roll axial direction, a bearing portion is disposed between the divided backup rolls. Therefore, the load applied to the backup roll via the slab pressing roll can be received by a plurality of bearing portions, and the slab can be squeezed with a larger rolling force, so that the porosity can be reliably reduced. It becomes possible.
Furthermore, it is preferable that the said backup roll is arrange | positioned in the width direction inner side of the said large diameter part of a slab press roll. Since the slab pressing roll and the backup roll are in uniform contact, the wear of the backup roll can be made uniform.

Furthermore, it is preferable that the backup roll is disposed on the downstream side in the drawing direction of the slab with respect to the slab pressing roll.
In this case, the pulling resistance can be received by the backup roll disposed on the downstream side in the drawing direction with respect to the slab pressing roll, and the bending deformation of the slab pressing roll in the drawing direction can be suppressed. In addition, when the backup roll is divided | segmented, at least 1 of the divided | segmented backup roll should just be arrange | positioned with respect to the said slab pressing roll in the drawing direction downstream.

Further, the backup roll is divided in the axial direction of the slab pressing roll, at least one backup roll is disposed downstream in the drawing direction of the slab, and at least one backup roll is provided on the slab. It may be arranged upstream in the drawing direction.
When the casting speed (slab drawing speed) is changed depending on the operating conditions, the drawing resistance acting on the slab pressing roll also varies. Therefore, the amount of deflection in the drawing direction of the slab pressing roll varies, and the slab pressing roll shakes.
In this regard, as described above, by providing a plurality of divided backup rolls, the slab pressing roll can be supported from the upstream side and the downstream side in the drawing direction. Can be suppressed.

Furthermore, when it is set as thickness t of the slab, the width direction edge part area | region of the said slab not rolled down by the said large diameter part of the said slab pressing roll is 60 mm or more from the width direction edge part of a slab. And it is preferable that it is set as the area | region of 1.5 * t or less from the width direction edge part of a slab.
In this case, since the end in the width direction of the completely solidified slab is not reduced, the reduction load can be reduced. Further, it is possible to suppress the deformation of the slab pressing roll in the down direction and the deformation of the slab pressing roll in the drawing direction.
If the width direction end region of the slab that is not rolled down by the large diameter portion is less than 60 mm from the width direction end of the slab, the rolling load cannot be reduced sufficiently regardless of the thickness of the slab, Experimental knowledge has shown that it is difficult to suppress the deformation of the slab pressing roll in the rolling direction and the deformation in the drawing direction.
On the other hand, it has been found from experimental knowledge that the width of the solidified portion region at the end portion in the width direction of the slab is 1.5 × t at the maximum in the vicinity of the solidified end portion in the casting direction that requires reduction. Therefore, when the width direction end region of the slab that is not rolled down by the large diameter portion exceeds 1.5 × t from the width direction end of the slab, it becomes difficult to reduce the entire width direction of the unsolidified portion. Bulging deformation occurs in the piece, which tends to lead to internal defects such as center segregation and porosity.

  As described above, according to the present invention, the center segregation and porosity can be reliably reduced by reducing the slab drawn from the mold with a sufficient reduction force, and the occurrence of internal cracks can be suppressed. It is possible to provide a slab reduction device capable of producing a slab.

It is a schematic explanatory drawing of the continuous casting installation by which the slab reduction apparatus which is embodiment of this invention is arrange | positioned. It is front explanatory drawing of the slab reduction apparatus which is embodiment of this invention. It is a partial section explanatory view of the slab reduction device which is an embodiment of the present invention. It is explanatory drawing of the other rolling-down means employable for the slab rolling-down apparatus which is embodiment of this invention. It is front explanatory drawing of the slab reduction apparatus which is other embodiment of this invention. It is upper surface explanatory drawing which shows the example of arrangement | positioning with respect to the cast piece press roll of the divided | segmented backup roll. It is side surface explanatory drawing of the example of arrangement | positioning shown in FIG. It is front explanatory drawing of the slab reduction apparatus of the prior art example compared with the Example. It is front explanatory drawing of the slab reduction apparatus of the example 1 of this invention in an Example. It is front explanatory drawing of the slab reduction apparatus of the example 2 of this invention in an Example. It is front explanatory drawing of the slab reduction apparatus of the example 3 of this invention in an Example. It is front explanatory drawing of the slab reduction apparatus of the example 4 of this invention in an Example. It is a graph which shows the evaluation result of an Example. It is a schematic sectional explanatory drawing of the slab press roll unit of case (1) evaluated in the reference example. It is a schematic sectional explanatory drawing of the slab press roll unit of case (2) evaluated in the reference example. It is a schematic sectional explanatory drawing of the slab press roll unit of case (3) evaluated in the reference example. It is a graph which shows the amount of deflection of the rolling direction of the slab pressing roll calculated in the reference example. It is a schematic upper surface explanatory drawing of the slab press roll unit of case (4) evaluated in the reference example. It is a schematic upper surface explanatory drawing of the slab press roll unit of case (5) evaluated in the reference example. It is a schematic upper surface explanatory drawing of the slab press roll unit of case (6) evaluated in the reference example. It is a graph which shows the drawing direction deflection | deviation amount of the slab press roll calculated in the reference example. It is a schematic upper surface explanatory drawing of the slab press roll unit of case (7) evaluated in the reference example. It is a schematic upper surface explanatory drawing of the slab press roll unit of case (8) evaluated in the reference example.

  Hereinafter, a slab reduction device according to an embodiment of the present invention will be described with reference to the accompanying drawings. In addition, this invention is not limited to the following embodiment.

The slab reduction device according to the present embodiment is used by being disposed in a continuous casting facility 10 shown in FIG. First, the continuous casting equipment 10 will be described.
The continuous casting equipment 10 includes a water-cooled mold 11 and a slab support roll group 20 positioned below the water-cooled mold 11, and is a vertical for pulling the slab 1 drawn out from the water-cooled mold 11 downward. Vertical bending type continuous casting having a band 14, a bending band 15 for bending the slab 1, a correction band 16 for bending back the bent slab 1, and a horizontal band 17 for conveying the slab 1 in the horizontal direction. It is supposed to be a machine.

The water-cooled mold 11 has a cylindrical shape having a rectangular hole, and the slab 1 having a cross section matching the shape of the rectangular hole is drawn out. For example, the long side length of the rectangular hole (corresponding to the width of the cast piece 1) is 700 to 2300 mm, and the short side length of the rectangular hole (corresponding to the thickness of the cast piece 1) is 150 to 400 mm. However, the present invention is not limited to this.
In addition, the water-cooled mold 11 is provided with a primary cooling means (not shown) for cooling the molten steel in the rectangular hole.

The slab support roll group 20 is located in the pinch roll part 24 located in the vertical band 14, the bending roll part 25 located in the curved band 15, the straightening roll part 26 located in the straightening band 16, and the horizontal band 17. A horizontal roll unit 27.
Here, the slab support roll group 20 is configured to support the long side surface of the slab 1.
In addition, a spray nozzle (not shown) that ejects cooling water toward the long side surface of the slab 1 is disposed in the continuous casting facility 10 as secondary cooling means.

  And the slab reduction apparatus which is this embodiment is to squeeze the slab 1 drawn out from the water-cooled mold 11 in the thickness direction of the slab 1, and the center solid phase ratio of the slab 1 is 0.2 or more. It is arrange | positioned at the horizontal belt | band | zone 17 so that the slab 1 may be rolled down in the area | region. However, it is not limited to this.

  As shown in FIGS. 2 and 3, the slab pressing device 30 is in contact with the long side surface of the slab 1, and slab pressing rolls 31 and 32 that are paired with the slab 1 interposed therebetween, and the slab A backup roll 40 that supports the pressing rolls 31, 32, a first frame 51 disposed on one surface side of the slab 1, and a second frame 52 disposed on the other surface side of the slab 1. I have.

In the first frame 51 and the second frame 52, three or more slab pressing rolls 31 and 32 are juxtaposed in the slab drawing direction Z. In this embodiment, seven sets of slab pressing rolls 31, 32 is disposed.
As shown in FIG. 2, the slab pressing rolls 31 and 32 are set so that the length in the roll axial direction is longer than the long side width of the slab 1. Further, both ends of the slab pressing rolls 31 and 32 are axially supported by the bearing portions 35, and are rotatable about the central axis. Further, the roll interval between the slab pressing roll 31 of the first frame 51 and the slab pressing roll 32 of the second frame 52 is adjusted so as to become narrower toward the downstream side in the slab drawing direction Z.
Here, in this embodiment, it is preferable that the roll diameter of the slab pressing rolls 31 and 32 is 320 mm or less and the roll pitch in the slab drawing direction Z is 340 mm or less.

The first frame 51 and the second frame 52 are provided with backup rolls 40 that support the slab pressing rolls 31 and 32, respectively. That is, the first frame 51 includes three or more sets of the slab pressing roll 31 and the backup roll 40, and the second frame 52 includes three or more sets of the slab pressing roll 32 and the backup roll 40 in the slab drawing direction. In this embodiment, seven sets of slab pressing rolls 31 and 32 are provided.
As shown in FIG. 2, the backup roll 40 is divided into a plurality of pieces in the axial direction of the slab pressing rolls 31 and 32 (the width direction of the slab 1). In this embodiment, the first backup roll 41, The second backup roll 42 and the third backup roll 43 are divided into three. Both ends of the first backup roll 41, the second backup roll 42, and the third backup roll 43 are supported by bearings 45, respectively, and are rotatable about the central axis.

The first frame 51 and the second frame 52 are connected by a plurality of reduction means 54. In this embodiment, as shown in FIGS. 2 and 3, four rolling-down means 54 are provided, and by these rolling-down means 54, the distance between the first frame 51 and the second frame 52 is close and separated. The rolling force to the slab 1 can be adjusted.
The reduction means 54 is constituted by a hydraulic cylinder with a servo, for example, and one end of a cylinder rod 56 is fixed to the first frame 51 so that the second frame 52 is moved closer to and away from the first frame 51. It is configured.

In the continuous casting equipment 10 having such a configuration, molten steel is injected into the water-cooled mold 11 through the immersion nozzle 12 inserted into the water-cooled mold 11, and this molten steel is cooled by the primary cooling means of the water-cooled mold 11. As a result, the solidified shell 2 grows and the slab 1 is pulled out from below the water-cooled mold 11. At this time, as shown in FIGS. 1 and 2, an unsolidified portion 3 exists inside the slab 1.
As shown in FIG. 1, the slab 1 is pulled downward by a pinch roll portion 24 and is bent by a bending roll portion 25. And it is bent back by the correction | amendment roll part 26, and is conveyed in the horizontal direction by the horizontal roll part 27. FIG.

At this time, cooling water is sprayed toward the slab 1 from spray nozzles provided between rolls such as the pinch roll part 24, the bending roll part 25, and the straightening roll part 26, and the slab 1 is cooled and the solidified shell 2 is cooled. Will grow further. The slab 1 is completely solidified on the rear stage side of the horizontal strip 17 from which the slab 1 is drawn out in the horizontal direction.
At this time, the slab 1 drawn out from the water-cooled mold 11 is squeezed by the slab squeezing device 30 according to this embodiment in a region where the central solid phase ratio is 0.2 or more.
By the way, it has been experimentally found that when the slab has a central solid fraction of 0.2 or more, problems of central segregation and porosity occur experimentally. Since the effect of the present invention becomes remarkable, it is preferable to reduce in the region where the central solid phase ratio of the slab is 0.2 or more.
On the other hand, the upper limit of the center solid phase ratio of the slab is 1.0 because it is a region where problems of center segregation and porosity occur.

The central solid fraction can be defined as the solid fraction of the molten portion in the center of the slab thickness direction and in the slab width direction.
The central solid fraction can be obtained by heat transfer / solidification calculation. As the heat transfer / solidification calculation, an enthalpy method or an equivalent specific heat method is widely known, and any method may be used. For simplicity, the following equation is widely known, and this equation may be used.
Central solid fraction = (liquidus temperature-melt temperature) / (liquidus temperature-solidus temperature)
Here, the melting part temperature means the temperature of the melting part in the center part in the slab thickness direction and in the slab width direction, and can be obtained by heat transfer / solidification calculation. For the liquidus temperature, refer to, for example, “Akane and Steel, Nippon Steel Association, Vol. 55, No. 3 (19690227) S85, Japan Iron and Steel Institute”. The temperature can be calculated with reference to, for example, “Hirai, Kanamaru, Mori; Gakken 19 Committee, Fifth Solidification Phenomenon Council Material, Solidification 46 (December 1968)”.

In the slab pressing device 30 according to the present embodiment configured as described above, slab pressing rolls 31 and 32 and backup rolls 40 that respectively support the slab pressing rolls 31 and 32 are provided. Therefore, the load applied when the slab 1 is crushed can be received by the bearing portion 35 of the slab pressing rolls 31 and 32 and the bearing portion 45 of the backup roll 40. Therefore, the slab 1 can be reduced with a relatively large reduction force, and the porosity can be reliably reduced.
Moreover, since the slab pressing rolls 31 and 32 are not divided in the roll axis direction, the entire width direction of the slab 1 can be pressed, and the occurrence of center segregation due to bulging deformation can be suppressed.

Furthermore, according to the slab pressing device 30 of this embodiment, in order to ensure the rigidity of the slab pressing rolls 31 and 32, it is not necessary to increase the roll diameter, and the slab pressing rolls 31 and 32 are drawn out. It can arrange in the direction Z closely, can prevent a reduction force from acting locally, and can suppress an internal crack of a slab. Specifically, since the slab pressing rolls 31 and 32 are set to 320 mm or less and the roll pitch in the slab drawing direction Z is set to 340 mm or less, the slab 1 can be squeezed in small increments at a small pitch. 1 can be sufficiently suppressed.
In addition, the size of the slab pressing rolls 31 and 32 and the lower limit value of the roll pitch in the slab drawing direction Z are not particularly limited, and may be set within a range where actual operation is possible.

  In addition, the first frame 51 and the second frame 52 have slab pressing rolls 31 and 32 and backup rolls 40 each having three or more sets in the slab drawing direction Z (in this embodiment, as shown in FIG. A set of slab pressing rolls 31 and 32 and a backup roll 40) are provided, and the first frame 51 and the second frame 52 are provided with two or more rolling-down means 54 (four in this embodiment). Therefore, the slab 1 can be uniformly reduced by the plurality of slab pressing rolls 31 and 32. Further, a rolling load can be received by the bearing portion 35 disposed on the slab pressing rolls 31 and 32.

  Here, the slab pressing rolls 31 and 32 and the backup roll 40 arranged in each frame have three or more sets in the slab drawing direction Z because the size of the slab pressing rolls 31 and 32 This is because when the roll pitch in the slab drawing direction Z is set within a range in which actual operation is possible, the two sets have a large interval in the slab drawing direction and cannot be uniformly reduced.

Further, it is necessary to provide the pressing means 54 for the pair of frames at two or more locations. Here, two places mean both sides in the width direction of the slab, and the slab is made uniform by providing the pressing means 54 of the pair of frames on both sides in the width direction of the slab in this way. Can be rolled down.
By the way, in this embodiment, in addition to two places on both sides in the width direction of the slab, each of the four places in the slab drawing direction Z is provided in a total of four places. It is also possible to grant.
Also, since the reduction force can be increased by simply increasing the device (for example, cylinder diameter) that constitutes the reduction means provided in the frame, the reduction force can be increased without increasing the size of the slab reduction device in the casting direction. Can be given.

Further, since the backup roll 40 is divided into a plurality of parts in the roll axial direction, not only the bearing part 35 but also a plurality of bearing parts 45 arranged between the divided backup rolls 41, 42, 43. Therefore, the slab 1 can be squeezed with a larger squeezing force and the porosity can be sufficiently reduced.
Incidentally, the number of divisions in the roll axis direction of the backup roll 40 may be plural (two or more), and three cases are shown in the present embodiment. The upper limit of the number of divisions is not particularly limited, and may be set within a range where actual operation is possible. Thus, according to the slab reduction device 30 of this embodiment, it is possible to manufacture a high-quality slab 1 in which the occurrence of porosity, center segregation, and internal cracks is suppressed.

As mentioned above, although the slab reduction apparatus which is embodiment of this invention was demonstrated, this invention is not limited to this, In the range which does not deviate from the technical idea of the invention, it can change suitably.
For example, although the present embodiment has been described as including a plurality of backup rolls, the present invention is not limited to this, and one backup roll that is not divided may be provided. However, by dividing the backup roll into a plurality of parts, it is possible to receive the reduction load in a distributed manner and to reduce the cast piece with a large reduction force. Therefore, it is preferable to divide the backup roll into a plurality of parts.
Moreover, there is no restriction | limiting in the division | segmentation number of a backup roll, and what divided | segmented into two or four or more may be sufficient.

In addition, although a hydraulic cylinder is used as the lowering means, the present invention is not limited to this. For example, as shown in FIG. 4, a disc spring 155 is provided between the first frame 151 and the second frame 152. And a mechanical reduction means 154 using a screw jack 156 may be provided.
Furthermore, although it demonstrated as arrange | positioning to a vertical bending type continuous casting machine, you may apply to a curved type continuous casting machine, a vertical type continuous casting machine, and a horizontal type continuous casting machine.

  The slab reducing device of the present invention is preferably arranged in a continuous casting device at a position where no bending distortion or straightening distortion occurs in the slab.

The position where bending distortion or straightening distortion does not occur in the slab means the position of the vertical part, bending part, bending part, straightening part, and horizontal part constituting the continuous casting equipment, excluding the bending part and straightening part. In the case where the slab is squeezed down, the internal crack of the slab can be suppressed by disposing the slab reducing device at the position.
Specifically, in the case of a vertical bending type continuous casting facility, it may be arranged at any position of a vertical part, a curved part, and a horizontal part. In the case of a curved type continuous casting facility, it may be arranged at any position of the curved part and the horizontal part. In the case of a horizontal continuous casting facility or a vertical continuous casting facility that does not have a bending portion or a straightening portion, it may be arranged at any position.

  However, if the slab is greatly reduced immediately after exiting the mold, not only does it not lead to center segregation and improvement of porosity, but the strength of the solidified shell is small and internal cracking occurs. For the range below, it is highly likely that the central solid phase ratio is usually 0, so it is desirable not to arrange the slab reduction device. Therefore, the effect of improving center segregation or the like can be obtained by arranging the filter at a position 2 m or more from the lower end of the mold and cooling the center solid phase ratio to be larger than 0. The range of the central solid phase ratio is not particularly limited, but the effect can be obtained even if the solidification is somewhat reduced after the solidification has progressed. Therefore, as described above, the range may be 0.2 to 1.0. Furthermore, it is good also as the range of 0.6-1.0.

  Further, as shown in FIG. 5, either one or both of the slab pressing rolls 31 and 32 that are paired with the slab 1 interposed therebetween, has a large diameter that protrudes radially outward at the axial center portion thereof. You may make it provide the part 201 and the small diameter part 202 located in the both ends of this large diameter part 201, respectively.

In this example, the width W of the slab 1 is set to 900 mm or more, and one slab pressing roll 31 presses the central region S1 in the width direction of the slab 1 where the large-diameter portion 201 is located, and the small-diameter portion. It is set as the structure which does not press the width direction edge part area | region S2 of the slab 1 in which 202 is located.
In addition, the width direction edge part area | region S2 of the slab 1 is 60 mm or more from the width direction edge part of the slab 1 as thickness t of the slab 1, and 1. mm from the width direction edge part of the slab 1 is 1. FIG. The area is 5 × t or less. In this example, the area is 60 mm or more from the width direction end of the slab 1 and 360 mm or less from the width direction end of the slab 1.

The backup roll 40 that supports one slab pressing roll 32 is divided in the axial direction of the slab pressing roll 32 (the width direction of the slab 1). In this example, as in the above-described embodiment, The first backup roll 41, the second backup roll 42, and the third backup roll 43 are divided into three.
Here, these backup rolls 40 are arranged so as to support the large-diameter portion 201 of the slab pressing roll 32.
Further, both ends of the first backup roll 41, the second backup roll 42, and the third backup roll 43 are pivotally supported by the shaft support portions 45, and the center axes O _b1 , O _b2 , and O _b3 are respectively centered. It is supposed to be rotatable.

Here, as shown in FIGS. 6 and 7, the first backup roll 41 and the third backup roll 43 are arranged on the downstream side in the drawing direction Z of the slab 1 with respect to the slab pressing rolls 31 and 32. May be. In this case, the second backup roll 42 is disposed on the upstream side in the drawing direction Z of the slab 1 with respect to the slab pressing rolls 31 and 32.
That is, the slab pressing rolls 31 and 32 may be sandwiched in the drawing direction Z by the first backup roll 41 and the third backup roll 43 and the second backup roll 42.

In this case, as illustrated in FIG. 7, the slab pressing roll 32 will be described as an example. In the cross section orthogonal to the central axis O _w of the slab pressing roll 32, the central axis O _w of the slab pressing roll 32 and the first axis The angle θ formed by the straight line connecting the central axes O _b1 and O _{b3 of the} backup roll 41 and the third backup roll 43 and the reduction direction (vertical direction) is 5 ° or less.
Further, the deviation amount X in the drawing direction Z between the center axis O _w of the slab pressing roll 32 and the center axes O _b1 and O _{b3 of} the first backup roll 41 and the third backup roll 43 is sin 0.23 ° × (R _w + R _b ) ≦ X ≦ sin 5 ° × (R _w + R _b ). Incidentally, _{R w} is the radius of the large diameter portion 201 of the slab pressing roll 32, the _{R b} is the radius of the backup roll 40.

When the rolling load F acts on the slab support roll in the vertical direction, the bearing portion of the backup roll disposed on the downstream side in the drawing direction of the slab with respect to the slab support roll has a vertical direction. A load of F / cos θ, which is a resultant force of the rolling load F acting on the horizontal axis and the load in the horizontal direction, acts. Here, since the angle θ is set to θ ≦ 5 °, it is possible to suppress an excessive load applied to the bearing portion of the backup roll and to extend the life of the bearing portion of the backup roll. Become.
Further, since the angle θ is θ ≧ 0.23 °, it is possible to reliably receive the drawing resistance by the backup roll, and it is possible to suppress the bending deformation of the slab support roll in the drawing direction. .

In this example, for the second backup roll 42 which is disposed in the pull-out direction Z upstream side of the slab press roll 32, in a cross section perpendicular to the central axis O _w of the slab press roll 32, the billet pressing roll 32 the center axis of the O _w and the straight line connecting the center axis O _b2 of the second backup roll 42, a pressing direction (vertical direction), the angle θ'formed by is 5 ° or less, the slab pressing roll The displacement amount X ′ in the drawing direction Z between the central axis O _{w of} 32 and the central axis O _b2 of the second backup roll 42 is sin 0.23 ° × (R _w + R _b ) ≦ X ′ ≦ sin 5 ° × (R _w + R _b ).

  In the continuous casting apparatus 10 provided with the slab pressing device 30 having the configuration having the large-diameter portion 201 projecting radially outward in the axially central portion of the slab pressing roll 32, the above embodiment is described. As described above, the slab 1 is completely solidified on the rear stage side of the horizontal strip 17 from which the slab 1 is drawn out in the horizontal direction, and the horizontal roll portion 27 of the horizontal strip 17 is compared with the slab 1. The reduction is performed.

  At this time, a force in the reduction direction (vertical direction in the present embodiment) acts on the slab pressing rolls 31 and 32 by the reduction reaction force. Moreover, the force to the drawing direction Z (horizontal direction in this embodiment) acts on the slab pressing rolls 31 and 32 by the drawing resistance when the slab 1 moves to the drawing direction Z side.

  Here, in the embodiment having the above-described configuration, the slab pressing roll 32 has a large-diameter portion 201 projecting radially outward at the axial center portion thereof, and a small-diameter positioned at both ends of the large-diameter portion 201. The slab pressing roll 32 presses the center region S1 in the width direction of the slab 1 where the large diameter portion 201 is located, and the width direction end portion of the slab 1 where the small diameter portion 202 is located. Since it is set as the structure which does not press area | region S2, it becomes possible to reduce only the width direction center area | region S1 of the slab 1 in which the unsolidified part 3 exists. Therefore, the rolling load can be greatly reduced.

Moreover, since the slab pressing roll 32 is supported by the backup roll 40, the bending deformation of the slab pressing roll 32 in the reduction direction can be suppressed.
Further, since the small-diameter portion 202 of the slab pressing roll 32 is located in the width direction end region S2 of the slab 1 that has been completely solidified, it is drawn only in the width direction central region S1 where the unsolidified portion 3 exists. Resistance acts, and it becomes possible to prevent the bending deformation of the slab pressing roll 32 in the drawing direction.

  Here, in this embodiment, the width direction edge part area | region S2 of the slab 1 in which the small diameter part 202 is located is 60 mm or more from the width direction edge part of the slab 1 as thickness t of the slab 1, and The region of 1.5 × t or less from the width direction end of the slab 1 to the center side, specifically, 60 mm or more from the width direction end of the slab 1 and the slab 1 The area | region of 360 mm or less can be illustrated from the width direction edge part. Thereby, it is possible to avoid rolling down the completely solidified region, and it is possible to reliably reduce the rolling load. Moreover, the bending deformation of the slab pressing roll 31 in the reduction direction and the bending deformation of the drawing direction can be suppressed.

  Further, since the backup roll 40 is divided into the first backup roll 41, the second backup roll 42, and the third backup roll 43 in the axial direction of the slab pressing roll 32, the axial lengths of these backup rolls 40 are determined. The rigidity can be ensured even when the roll diameter is small.

  Here, since the first backup roll 41 and the third backup roll 43 are disposed on the downstream side in the drawing direction Z of the slab 1 with respect to the slab pressing rolls 31 and 32, the drawing resistance is reduced to the first backup roll. 41 and the 3rd backup roll 43, and the bending deformation | transformation to the extraction direction of the slab press rolls 31 and 32 can be suppressed.

  Furthermore, the 2nd backup roll 42 is arrange | positioned with respect to the slab press rolls 31 and 32 in the drawing direction Z upstream side of the slab 1, and the 1st backup roll 41, the 3rd backup roll 43, and 2nd Since the slab pressing rolls 31 and 32 are sandwiched by the backup roll 42 in the drawing direction Z, even if the casting speed (slab drawing speed) is changed depending on the operation status, the slab pressing It is possible to prevent the rolls 31 and 32 from shaking.

Furthermore, as described above, the displacement amount X in the drawing direction Z between the central axis O _w of the slab pressing roll 32 and the central axes O _b1 and O _{b3 of} the first backup roll 41 and the third backup roll 43 is set to sin 0. It is preferable that 23 ° × (R _w + R _b ) ≦ X. Thereby, the drawing resistance applied to the slab pressing roll 32 can be reliably transmitted to the first backup roll 41 and the third backup roll 43, and the bending deformation of the slab pressing roll 32 in the drawing direction Z is prevented. be able to.

Further, the deviation X is preferably X ≦ sin 5 ° × (R _w + R _b ), and in the cross section orthogonal to the central axis O _w of the slab pressing roll 32, the central axis O of the slab pressing roll 32 _The angle θ formed by the straight line connecting _w and the central axes O _b1 and O _{b3 of} the first backup roll 41 and the third backup roll 43 and the reduction direction (vertical direction in this embodiment) is 45 ° or less. Therefore, the load in the reduction direction can be transmitted to the first backup roll 41 and the third backup roll 43, and the deformation of the slab pressing roll 32 in the reduction direction can be suppressed.

Further, for the second backup roll 42 which is disposed in the pull-out direction Z upstream side of the slab press roll 32, extraction of the center axis O _w and the center axis O _b2 of the second backup roll 42 of the slab pressing roll 31 The displacement amount X ′ in the direction Z is set within the range of sin 0.23 ° × (R _w + R _b ) ≦ X ′ ≦ sin 5 ° × (R _w + R _b ), and is orthogonal to the center axis O _w of the slab pressing roll 32. in a cross section, a straight line connecting the center axis O _w and the center axis O _b2 of the second backup roll 42 of the slab press roll 32, (in the present embodiment vertically) reduction direction and forms an angle [theta] & apos 5 It is preferable that the slab pressing roll 32 is prevented from swinging in the drawing direction Z, and the second backup roll 42 can receive a load in the reduction direction.

In the above-described example, the backup roll is described as being disposed on the downstream side and upstream side of the slab pressing roll in the drawing direction. However, the present invention is not limited to this, and the backup roll is downstream in the drawing direction of the slab pressing roll. The central axis of the slab pressing roll and the central axis of the backup roll may be arranged at the same position in the drawing direction.
Furthermore, in the above-described example, it has been described that one slab pressing roll 32 of the slab pressing rolls 31 and 32 that are paired with the slab interposed therebetween has the large-diameter portion 201, but the present invention is limited to this. However, both of the slab pressing rolls 31 and 32 that are paired with the slab interposed therebetween may have a large diameter portion.

In the present invention, the width of the target slab is preferably 900 mm or more.
Even in the case of a wide slab of 900 mm or more, since the slab pressing rolls 31 and 32 are supported by the backup roll, it is possible to suppress the slab pressing rolls 31 and 32 from being bent and deformed in the reduction direction. Become. Further, bending deformation of the slab pressing rolls 31 and 32 in the drawing direction is also suppressed. Therefore, the center part in the width direction of the slab 1 can be surely reduced, and the occurrence of internal defects such as center segregation and porosity due to bulging deformation can be suppressed.

Below, the result of the experiment conducted in order to confirm the effect of this invention is demonstrated.
In this experiment, two slab reduction devices shown in FIGS. 8 to 12 were installed in the horizontal direction of the vertical bending type continuous casting machine shown in FIG. The rolling force index, bulging index, central segregation index, and porosity index were evaluated.
The size of the slab is 300 mm in thickness x 2200 mm in width, the casting speed is 0.9 m / min, and the slab center solid phase ratio where the slab reduction device is arranged is in the range of 0.2 to 1.0. Two slab reduction devices were installed continuously in the direction of drawing the slab from the position 22 m below the mold.
Moreover, the roll diameter of the slab pressing roll and the backup roll was 270 mm, and seven sets of slab pressing rolls were arranged in the slab drawing direction of the frame. Further, the first frame and the second frame are connected by four reduction means (hydraulic cylinders).

As a conventional example, as shown in FIG. 8, a slab pressing device having a structure in which there is no backup roll and the slab pressing rolls 31 and 32 are divided into three in the roll axis direction was used.
As Example 1 of the present invention, as shown in FIG. 9, slab pressing rolls 31 and 32 having a length in the roll axial direction longer than the width of the slab are provided, and one slab pressing roll is provided for each slab pressing roll. A slab reduction device having a structure in which a backup roll was provided was used.

As Example 2 of the present invention, as shown in FIG. 10, slab pressing rolls 31 and 32 having a length in the roll axis direction longer than the width of the slab are provided, and a roll shaft is provided for this slab pressing roll. A slab reduction device having a structure in which a backup roll 40 divided into two in the direction was provided was used.
As Example 3 of the present invention, as shown in FIG. 11, slab pressing rolls 31 and 32 having a length in the roll axis direction longer than the width of the slab are provided. A slab reduction device having a structure in which a backup roll 40 divided into three in the direction was disposed was used.
As Example 4 of the present invention, as shown in FIG. 12, it has slab pressing rolls 31 and 32 whose length in the roll axial direction is longer than the width of the slab, and the upper slab pressing roll 32 has an axial center portion. A slab reduction device having a structure in which a backup roll 40 divided into three in the roll axial direction is provided for one slab pressing roll and having a large-diameter portion protruding radially outward. The roll diameter of the large diameter portion for pressing the slab was 270 mm, and the roll diameter of the other portions was 255 mm. The length of the large diameter portion was 1900 mm. The range of the large diameter portion supported by a plurality of backup rolls was 1890 mm.

In addition, the rolling force index when evaluating the experimental results is the distribution load to each bearing (each bearing of the slab pressing roll and each bearing of the backup roll) measured by the load cell arranged at the bottom of the bearing during casting. The rolling force was adjusted so that the largest value satisfied the following formula (1), and the value in the conventional example was normalized.
(Basic static load rating of the bearing) / (Distributed load to the bearing) = 5.0 (1)
Incidentally, the value of 5.0 in the formula (1) is set to 5.0 because it is a value within an appropriate range of the load applied to the bearing from the operation results.
The reduction index is obtained by actually measuring the slab thickness after casting, and calculating the thickness difference between when the reduction is applied and when the reduction is not applied as the reduction applied to the slab. Indicated by relative value.

  The bulging index was evaluated by a finite element method analysis, and the maximum value of the deformation amount in the slab thickness direction was evaluated.

The central segregation index was obtained from the following equation (2).
(Slab Mn Segregation Degree) / ((Slab Mn Segregation Degree in Conventional Example) -1) (2)
Here, the slab Mn segregation degree is (the maximum value of the Mn concentration of the Mn segregation part) / (Mn concentration of the entire slab), and was measured by the following procedure.
A sample of 50 mm × 50 mm is collected from the center of the slab thickness from 10 positions along the width direction of the slab, and the surface of this sample is polished. X-ray line analysis was performed, the peak value of the Mn concentration was measured, and this was taken as the Mn concentration of the Mn segregation part. As the Mn concentration of the entire slab, the value analyzed and measured at the molten steel stage was used.

  The porosity index is a 20 mm thick sample cut out from the slab centered on the thickness center, and by X-ray transmission photography, the total cross-sectional area of the porosity with respect to the cross-sectional area in the slab thickness direction is obtained. Shown as a relative value.

  The evaluation results are shown in Table 1 and FIG.

  In Example 1 of the present invention, the load distributed to each bearing is increased by reducing the number of bearings compared to the conventional example, and the rolling force index is reduced, but the slab pressing roll is not divided. The roll unsupported band disappeared in the width direction of the slab, and the bulging index was reduced. This reduced the porosity index by 15% and the central segregation index by 40%.

  In Example 2 of the present invention, by dividing the backup roll into two parts, the load distributed to each bearing decreased, and the reduction force index could be increased as compared with the conventional example. In addition to the fact that the bulging index was reduced to the same level as Example 1 of the present invention, and the reduction force index was increased, it was considered that a reduction amount that compensated for solidification shrinkage could be imparted to the slab. The index was reduced by 40% and the central segregation index was reduced by 70%.

  In Invention Example 3, the reduction roll index could be further increased by dividing the backup roll into three parts. As a result, the reduction amount of the slab further increased, and the porosity index was reduced by 55% and the central segregation index was reduced by 75%.

  In Invention Example 4, by dividing the backup roll into three parts, compared with Invention Example 2, the load distributed to each bearing was reduced and the rolling force index could be increased, but the narrow range was reduced. As a result, the load distributed to the specific bearing increased and the rolling force index slightly decreased as compared with Invention Example 3. However, since the reduction of the end of the slab with high deformation resistance could be avoided, the amount of reduction increased, the porosity index decreased by 70%, and the central segregation index decreased by 76%.

  Thus, according to Example 1-4 of this invention, it was confirmed that center segregation and a porosity are improved simultaneously compared with a prior art example. Moreover, when a slab pressing roll has a large diameter part, it turned out that a center segregation and a porosity can be reduced most.

  The slab pressing roll 32 described above includes a large diameter portion 201 that protrudes radially outward at an axial center portion thereof, and a small diameter portion 202 that is positioned at each end of the large diameter portion 201. In order to confirm the effect of the slab pressing roll, the result of calculating the deflection amount of the slab pressing roll in the reduction direction and the drawing direction by the finite element method analysis will be described as a reference example (slab pressing roll unit).

The following cases were evaluated for the amount of deflection of the slab pressing roll in the rolling direction.
(1) When only one (upper side) of the slab pressing rolls that are paired with the slab sandwiched has a large-diameter portion in the central portion in the axial direction, and has a backup roll that supports this,
(2) Although the slab pressing roll does not have a large diameter portion in the axial center portion, but has a backup roll that supports this,
(3) When only one (upper side) of the slab pressing rolls that are paired with the slab sandwiched has a large-diameter portion at the axial center, but does not have a backup roll that supports this. Outlines of these cases (1), (2), and (3) are shown in FIG. 14, FIG. 15, and FIG. The reduction load in each case is shown in the figure.

  Here, each bearing of the roll is fixed by a plate which is an elastic body. The thickness of the plate was 40 mm and the height was 500 mm. The roll diameter was set to φ300 mm and a 50 mm cooling water hole was formed. The size of the slab was 300 mm thick x 2200 mm wide. When the slab of this cross section is reduced by 0.6 mm per slab pressing roll, the average drawing resistance in the range of 200 mm from the end of the slab width direction is about the drawing resistance due to the molten steel static pressure in the unsolidified part. It is obtained by calculation that it is about 2.3 times. (1), The width direction edge part area | region of the slab which is not reduced by the said large diameter part of the slab press roll in (3) was 200 mm on one side. In cases (1), (2), and (3), the axis of the slab pressing roll and the axis of the backup roll coincide with each other in the drawing direction.

The calculation results are shown in FIG. By comparing (1) and (2), only one (upper side) of the slab pressing roll that is paired across the slab has a large-diameter portion at the center in the axial direction. It has been confirmed that the rolling load acting on both of these can be reduced, and that the deformation deformation of both of the paired slab pressing rolls can be suppressed to about two thirds. Thereby, the lifetime until permanent deformation occurs in the slab pressing roll can be greatly prolonged. Moreover, it is possible to produce a high quality slab having few internal defects such as center segregation and porosity due to bulging deformation caused by deformation of the slab pressing roll.
Further, by comparing (1) and (3), the slab pressing roll is supported by a backup roll disposed on a rigid plate-like frame, so that the deflection deformation of the slab pressing roll can be reduced to about 1/6. It was confirmed that suppression was possible. In the comparison between cases (1) and (2) and the comparison between (1) and (3), even when only the other (lower side) of the paired slab pressing rolls has a large diameter portion, Similar effects can be obtained.

Next, the following cases were evaluated for the amount of deflection of the slab pressing roll in the drawing direction.
(4) Only one (upper side) of the slab pressing roll that is paired with the slab sandwiched has a large-diameter portion at the axial center, and the axis of the backup roll and the axis of the slab pressing roll are in the drawing direction. If it matches,
(5) When the slab pressing roll does not have a large-diameter portion in the axial central portion, and the axis of the backup roll and the axis of the slab pressing roll coincide with each other in the drawing direction,
(6) When only one (upper side) of the slab pressing rolls that are paired with the slab sandwiched has a large-diameter portion in the central portion in the axial direction, and one of the backup rolls is disposed downstream in the drawing direction. Outlines of these cases (4), (5), and (6) are shown in FIG. 18, FIG. 19, and FIG.

The calculation results are shown in FIG. By comparing (4) and (5), only one (upper side) of the slab pressing rolls that are paired with the slab interposed therebetween has a large-diameter portion at the center in the axial direction. As a result, the drawing resistance is proportional to the rolling load, so that the drawing resistance can be reduced and the deflection deformation of the slab pressing roll in the drawing direction is about 30%. It was confirmed that suppression was possible. Thereby, the lifetime until permanent deformation occurs in the slab pressing roll can be greatly prolonged. Moreover, it is possible to produce a high quality slab having few internal defects such as center segregation and porosity due to bulging deformation caused by deformation of the slab pressing roll.
When one of the backup rolls is arranged on the downstream side in the drawing direction as in (6), the number of locations supporting the drawing resistance is increased compared to the case of (4), so that the deflection deformation of the slab pressing roll is 8 minutes. It was confirmed that it can be suppressed to about 1. In addition, in the comparison between cases (4) and (5) and in the comparison between (4) and (6), even when only the other (lower side) of the pair of slab pressing rolls has a large diameter portion, the same applies. The effect is obtained.

Next, (7) a case in which only one (upper side) of the slab pressing rolls paired with the slab sandwiched has a large-diameter portion at the axial center, and (8) a slab paired with the slab sandwiched therebetween. About the case where both of the pressing rolls have a large-diameter portion at the central portion in the axial direction, the rate of occurrence of internal cracks was experimentally evaluated when the slab in progress of solidification was reduced with one roll. Outlines of these cases (7) and (8) are shown in FIGS.
Here, the internal crack occurrence rate indicates the probability that one or more internal cracks were visually confirmed in the etch print of the cross section in the casting direction of the slab extracted at random. Table 2 shows the results of the experimental conditions and the rate of occurrence of internal cracks.

  When the roll having the large diameter portion is only on one side of the slab, it will be reduced by a large reduction amount from one side of the slab, but when the roll having the large diameter portion is arranged on both sides of the slab, It was confirmed that the rate of occurrence of internal cracks was very small because the slab was reduced from both sides with a small reduction amount.

DESCRIPTION OF SYMBOLS 1 Cast slab 10 Continuous casting equipment 11 Water-cooled mold 30 Slab squeezing device 31, 32 Slab pressing roll 40 Backup roll 51, 151 1st frame 52, 152 2nd frame 54, 154 Rolling means

Claims (6)

A slab reduction device for reducing a slab drawn from a mold,
A pair of slab pressing rolls that sandwich and press the slab, a backup roll that supports the slab pressing roll, and a pair of frames arranged to face each other,
In each of the frames, three or more sets of the slab pressing roll and the backup roll are disposed in the slab drawing direction,
The pair of frames are provided with two or more rolling-down means for bringing the distance between the pair of frames close to and away from each other.
Slab reduction device.   2. The slab pressing device according to claim 1, wherein at least one of the slab pressing rolls paired with the slab interposed therebetween has a large-diameter portion protruding radially outward at a central portion in the axial direction.   The slab reduction device according to claim 1, wherein the backup roll is divided into a plurality of pieces in the axial direction of the slab pressing roll.   The slab reduction device according to claim 1, wherein the backup roll is disposed on the downstream side in the drawing direction of the slab with respect to the slab pressing roll.   The backup roll is divided in the axial direction of the slab pressing roll, at least one backup roll is arranged downstream in the drawing direction of the slab, and at least one backup roll is in the drawing direction of the slab. The slab reduction device according to claim 1, which is disposed on the upstream side.   When the thickness of the slab is t, the width direction end region of the slab that is not rolled down by the large diameter portion of the slab pressing roll is 60 mm or more from the width direction end of the slab, And the slab reduction apparatus in any one of Claim 2 to 5 made into the area | region of 1.5 * t or less from the width direction edge part of a slab.

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