JP2000301303A - Method for continuously casting thin slab and continuous caster - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a further thinner cast slab and a stable operation by executing simultaneously unsolidified rolling reduction while bending in a bending zone after drawing out a cast slab from a mold. SOLUTION: The bending zone B and a rolling reduction zone C are overlapped in a vertical-bending type continuous caster. The bending zone B is disposed of 6-10 pairs of rolls in the upper and lower direction and about 5 pairs of the rolls 2 at the upper part of the bending zone are the rolls for a vertical zone A. At the lower part thereof, a rolling reduction segment 4 assembling about 6 pairs of the rolling reduction rolls 3 into a frame is set and about 5 pairs of the rolling reduction rolls 3 at the upstream side thereof are used for both the rolling reduction action and the bending action. Therefore, these rolling reduction rolls 3 whose radiuses of carvature are set to gradually smaller so as to apply gradually the bending to the cast slab at each fixed position in the segment 4, constitute multi-point bending parts. Then, about 2 pairs of the rolls 3 at the downstream side of the segment 4 are execlusively used for the rolling reduction and the position of the rolls 3 at the lowmost stream side is the completing point P of the rolling reduction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting method for thin slab cast pieces and a continuous casting machine used therefor.

[0002]

2. Description of the Related Art The thinner the slab cast, the thinner the slab can be cast, the later the rolling process can be simplified, which can greatly contribute to a reduction in equipment costs. In continuous casting of thin slabs, reducing the thickness of the mold at the outlet side has a direct effect on the thinner slab thickness, but for mold thickness, pouring from a tundish Since it is necessary to ensure only the thickness for inserting the pouring nozzle used when performing the pouring, there is a limit in reducing the thickness. Therefore, the mold outlet side thickness has been set to 90 mm or more so far, and the slab having a thickness of 90 mm or more is subjected to unsolidification reduction.

[0003] The basic configuration of a continuous casting machine that performs such unsolidification rolling is as shown in FIG. 1 is a mold,
A vertical zone A, a bending zone B, and a rolling zone C continue in this order from immediately below. Below the rolling reduction zone C is the rolling reduction completion point P, and from there downstream are the guiding zones D and E. In the above continuous caster, while cooling the slab in the vertical zone A, a solidified shell is developed somewhat, and the slab is gradually curved in the bending zone B. In order to minimize the strain applied to the slab, The radii of curvature r1 to r5 of the rolls constituting the bending zone B gradually become smaller. For this reason, the bending zone in which the curvature radii r1 to r5 are gradually reduced is also referred to as a multipoint bending portion. The slab that has passed through the bending zone B and entered the reduction zone C gradually develops a solidified shell, but an unsolidified portion still remains in the center of the slab. Depress. Each roll in the rolling zone C has a constant radius of curvature, and is therefore also referred to as a constant arc portion. In this way, if the rolling is performed while the unsolidified portion remains, the rolling pressure can be reduced, the rolling roll can be small in diameter, and the structure around the rolling roll can be simplified.

As described above, the configuration in which the bending zone B and the reduction zone C are separated and the bending and reduction of the slab slab are performed separately is to prevent vertical cracks and breakout on the slab surface. That's why. In other words, bending the slab is also a cause of applying stress to the slab, and pressing down the slab is also a cause of applying stress to the slab. Until now, it has been considered as an absolute contraindication that internal cracking will occur. In other words, it has been common technical knowledge that bending and reduction are always performed separately.

[0005]

In the vertical-bending type continuous casting machine as described above, when unsolidification rolling is performed in a fixed arc portion (rolling zone C), the molten steel surface (meniscus) in the mold is reduced. When the distance is long, and when the distance is long, a solidified shell develops and the unsolidified portion is reduced to make it difficult to reduce the rolling. Therefore, in order to prevent this, the bottom casting speed must be increased. The solidified shell thickness is generally expressed as D = K (L / Vc) ^1/2 solidified shell thickness: D (mm) Casting speed: Vc (m / min) Distance from the meniscus: L (m) Solidification coefficient: K It is known that K = about 28. Therefore, in order to perform unsolidification reduction, it is necessary to complete the reduction before the slab thickness becomes twice the thickness of the solidified shell. For example, if the rolling completion point P is about 4 m from the meniscus and the slab thickness is to be made 50 mm, the steady pouring speed becomes about 5 mm.
If the casting speed is required to be higher than m / min and the casting speed must be exceeded for all types of steel, the operational flexibility is reduced and the operation becomes extremely difficult.

In view of the above circumstances, an object of the present invention is to provide a continuous casting method and a continuous casting machine for a thin slab slab which can obtain a thinner slab slab and can operate stably.

[0007]

The continuous casting method of a thin slab cast according to claim 1 is a method of casting a thin slab cast by a vertical-curved continuous casting machine, wherein the cast slab is drawn from the mold. Thereafter, the unsolidification reduction is simultaneously performed while bending in the bending zone. According to a second aspect of the present invention, in the continuous casting machine for thin slab slabs, the unsolidification reduction is performed by pressing the slabs from the inside to the outside of the curved portion. The continuous casting machine for thin slab casts according to claim 3 is the vertical-curved continuous caster for casting thin slab casts, wherein a roll in a bending zone below a mold is constituted by a roll-down roll segment. . The continuous casting machine for thin slab slab of claim 4 is
The pressing roll segment is composed of a fixed roll group outside the curved portion and a tilting roll group inside the curved portion, and the tilting roll group is supported by a tilting frame. It is characterized by being constituted.

According to the first aspect of the present invention, the distance between the meniscus and the reduction completion point is reduced by starting the reduction together with the bending without waiting for the completion of the bending of the slab and performing the unsolidification reduction early. Can be. When the rolling completion point moves to the upstream side in this way, the rolling is reduced while the solidified shell is still thin and many unsolidified portions remain, so that the required rolling reduction can be reduced even if the casting speed is reduced. For this reason, the lowest bottom casting speed can be reduced, the operational flexibility increases, and stable operation is facilitated. Moreover, although the rolling is performed while bending the slab, it has been surprisingly found that unsolidification rolling can be performed without causing internal cracks of the slab, contrary to the conventional technical knowledge. Although the reason has not been fully elucidated yet, in the state where the solidified shell is still thin and the unsolidified portion remains inside the slab, even if the strain caused by bending and the strain caused by rolling are combined, they are mutually distorted. It is presumed that the behavior of overlapping or expanding is unlikely to occur. According to the invention of claim 2, by performing the unsolidification reduction inside the curved portion, it is possible to prevent the occurrence of internal cracks well. Although the reason for this has not yet been sufficiently elucidated, it is presumed that it acts to crush the crack at the portion facing the unsolidified portion in the solidified shell inside the curved portion where cracks are likely to occur. According to the invention of claim 3, since the reduction roll segment is arranged in the bending zone, the reduction can be performed while bending the slab,
Uncoagulation reduction at a position closer to the upstream can be performed. Therefore, it is suitable for carrying out the casting method of claim 1. According to the fourth aspect of the present invention, since the amount of reduction can be adjusted by changing the distance of the tilting roll group to the fixed roll group, a thin slab slab having an arbitrary thickness can be cast. Further, since the rolling is performed by pressing the tilting roll group inside the bending portion toward the fixed roll group outside the bending portion, bending distortion can be reduced. Therefore, it is suitable for carrying out the casting method of claim 2.

[0009]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a continuous casting machine according to an embodiment of the present invention, and FIG. 2 is a side view of a reduction roll segment. In FIG. 1, reference numeral 1 denotes a mold, in which a vertical zone A, a bending zone B, a rolling zone C, and guide zones D, E, F are provided in this order from immediately below. The drawing path of the slab is curved as shown in the figure,
The following "inside the curved portion" refers to the center point side of the curved path,
“Outside the curved portion” refers to the side opposite to the center point.

The present invention is characterized in that the bending zone B and the pressing zone C overlap. That is, the bending zone B is configured by arranging rolls of 6 to 10 pairs (a pair refers to a set of rolls inside the curved portion and rolls outside the curved portion) in the vertical direction. Rolls 2 in the vertical zone A are rolls in the vertical zone A.
Below this, a roll roll segment 4 in which six pairs of rolls 3 are assembled into a frame is installed. The upstream and downstream 5 pairs of the reduction rolls 3 in the reduction roll segment 4 serve both a reduction operation and a bending operation. Therefore, the five pairs of the reduction rolls 3 on the upstream side are located at fixed positions of the reduction roll segments 4.
The radius of curvature is set to be gradually smaller so as to gradually bend the slab, thereby forming a multipoint bent portion. The two pairs of rolls 3 on the downstream side of the rolling roll segment 4 are dedicated to rolling, and the position of the most downstream rolling roll 3 is the rolling completion point P.

Next, the pressing roll segment 4 will be described with reference to FIG. In the figure, 5 is a fixed frame outside the curved portion, 6 is an upper fixed frame inside the curved portion, and 7 is a lower tilting frame inside the curved portion. The fixed frame 5 is fixed to an appropriate machine frame outside the curved portion of the casting machine, and a plurality of rolls 8 are supported on the fixed frame 5 in a vertically arranged manner. The fixed frame 6 is fixed to a fixed frame outside a curved portion of the casting machine.
Are rotatably supported.

The tilting frame 7 is attached to the lower surface of the fixed frame 6 by a fulcrum pin 9 so as to be tiltable. A tilting cylinder 10 is attached to a vertically intermediate portion of the tilting frame 7, and a piston rod 11 of the tilting cylinder 10 is pin-connected to a bracket 12 fixed to the fixed frame 5. The roll 3 is rotatably supported by the tilting frame 7.
Therefore, by expanding and contracting the tilt cylinder 10, the tilt frame 7 can be tilted so as to approach or separate from the fixed frame 5 side.

In FIG. 2, the position shown by the solid line is a reduced state, and the position retracted by a distance d is a non-rolled position. In the non-roll-down position, each pair of rolls 3, 8 constitutes a multipoint bend, which allows the slab to be gradually bent.
When the tilting frame 7 is moved closer to the fixed frame 5 from that state, the interval between the rolls 3 and 8 is reduced, and the cast piece can be pressed down from the inside of the curved portion to the outside. The amount of reduction can be continuously changed by changing the amount of tilt d of the tilting frame 7.

As described above, according to the present embodiment, the unsolidified pressure of the thin slab slab can be carried out on the upstream side almost overlapping with the bending zone B. Can be easily performed. For example, if the rolling completion point P is about 3 m from the meniscus and the target slab is 50 mm, the lowest casting speed is about 3.8 m / min or more. The casting speed is much more flexible than the bottom casting speed. Therefore, stable operation is easily performed.

According to the above embodiment, for example, a slab having a thickness of 150 mm or less on the slab exit side can be unsolidified and reduced to a thickness of 70 to 35 mm. In this case, the rolling completion point P is within 4 m from the meniscus. Thus, stable operation was possible at a casting speed of about 3 m / min under a pressure of 15 mm or less per roll.

[0016]

According to the first aspect of the present invention, unsolidified rolling can be performed without causing vertical cracks or breakout on the surface of the slab, and the rolling completion point moves further upstream, so that the bottommost casting can be performed. Since the speed can be reduced, the range of the steady casting speed is widened and stable operation is possible. According to the second aspect of the invention, the unsolidification reduction is performed inside the curved portion, so that the vertical cracks and breakout of the slab can be further prevented. According to the third aspect of the present invention, the slab can be reduced while bending the slab, and the unsolidification reduction can be performed at a position closer to the upstream. According to the invention of claim 4, a thin slab slab having an arbitrary thickness can be cast, and the reduction is performed by pressing the tilting roll group inside the curved portion toward the fixed roll group outside the curved portion. Can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a continuous casting machine according to an embodiment of the present invention.

FIG. 2 is a side view of a reduction roll segment.

FIG. 3 is a schematic explanatory view of a conventional vertical-curved continuous casting machine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold 4 Roll-down roll segment 7 Tilt frame 10 Tilt cylinder B Bending zone C Roll-down zone

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yuhisa Kikuchi 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd. F-term (reference) 4E004 LA01

Claims (4)

[Claims] 1. A method for casting a thin slab slab by a vertical-bending continuous casting machine, wherein the slab is drawn out of a mold, and simultaneously unsolidified rolling is performed while bending in a bending zone. Continuous casting method of thin slab slab. 2. The continuous casting method for a thin slab slab according to claim 1, wherein the unsolidification reduction is performed by pressing the slab from the inside to the outside of the curved portion. 3. A continuous casting machine for thin slab slabs for casting thin slab slabs, wherein a roll in a bending zone below a mold is constituted by a roll-down roll segment. 4. The rolling roll segment comprises a fixed roll group outside the curved portion and a tilt roll group inside the curved portion, the tilt roll group being supported by a tilt frame,
A continuous casting machine for thin slab slabs, which is configured to approach and separate from a fixed roll group by a rolling cylinder.