JP4120129B2 - Hot-rolled steel strip cooling device and cooling method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cooling device for cooling a hot-rolled high-temperature steel strip and a cooling method thereof.
[0002]
[Prior art]
Generally, a hot-rolled steel strip is obtained by heating a slab to a predetermined temperature in a heating furnace, rolling the heated slab to a predetermined thickness with a roughing mill to form a rough bar, and then forming the rough bar with a plurality of stands. In a continuous hot finish rolling mill, the steel strip has a predetermined thickness. And after cooling this hot-rolled steel strip in the cooling stand on a run-out table, it manufactures by winding up with a winder.
[0003]
In such a run-out cooling device for continuously cooling a rolled high-temperature steel strip, firstly, the plate-passability of the steel strip is taken into consideration.
For example, in order to cool the upper surface of the steel strip, a plurality of laminar cooling waters are injected linearly across the width direction from a circular laminar cooling nozzle directly above the roller table for transporting the steel strip. On the other hand, as a method for cooling the bottom surface of the steel strip, a spray nozzle is provided between the roller tables, and a method of injecting cooling water therefrom is generally used.
[0004]
Therefore, in such a cooling mode, the cooling of the upper and lower surfaces of the steel strip is not strictly symmetrical, and the cooling of the steel strip is intermittent cooling particularly on the upper surface side, and rapid cooling (for example, with a plate thickness of 3 mm) A cooling rate of 200 ° C./s or more) is almost impossible.
[0005]
[Problems to be solved by the invention]
However, in recent years, hot-rolled steel strips with a small crystal grain size have been demanded for their excellent workability and high strength even at low Cep, and rapid cooling (strong cooling) is required for that purpose. Yes.
[0006]
Thus, when performing rapid cooling with respect to a hot-rolled steel strip, the conventional cooling device has the following problems.
That is, since the cooling start positions where the cooling water is applied do not coincide on the upper and lower surfaces of the steel strip, there is a possibility that the material may become non-uniform. Further, after cooling, cooling water stays on the upper surface of the steel strip, causing overcooling on the upper surface side. This supercooling is not uniform in the longitudinal direction, and therefore the cooling stop temperature varies in this direction. Further, in the width direction, the cooling water flows out from the end of the steel strip to both sides of the line, so that the end is likely to be overcooled compared to the central portion of the steel strip, and the temperature stop time varies. As a result, the material was not uniform.
[0007]
Therefore, a method of discharging fluid in an oblique direction so as to cross the steel strip and discharging the cooling water on the upper surface of the steel strip (Japanese Patent Laid-Open No. 9-141322), or a method of damming the cooling water using a constraining roll as a draining roll ( A draining method such as that disclosed in Japanese Patent Laid-Open No. 10-166023 has been proposed.
[0008]
However, according to the former method, when strong cooling is performed, a large amount of cooling water stays on the steel strip and there is almost no draining effect. In the latter method, since the steel strip tip from the rolling mill to the winder is transported in a free state, the steel strip is in an unconstrained state as if it struck waves while moving up and down. Pass by. Therefore, providing the restraining roll on the roller table hinders the stable passage plate, and it has been difficult to apply the restraining roll to the runout cooling device. In addition, if it is attempted to strongly cool the vicinity of the tip of the steel strip that vibrates without restraint, the vibration at the tip is further deteriorated and a stable threading plate cannot be secured.
[0009]
On the other hand, Japanese Patent Laid-Open No. 6-328117 proposes a method of effectively cooling the upper and lower water amount ratio of the cooling water at the tip of the steel strip by increasing the amount of water on the lower surface. However, when the cooling water amount ratio is changed, the cooling with respect to the upper and lower surfaces becomes unbalanced, and in particular when the rapid cooling is required, the material non-uniformity cannot be avoided. And since lower surface cooling becomes weak, it was difficult to implement | achieve strong cooling required for material.
[0010]
The present invention has been made in consideration of the above circumstances, and the object of the present invention is to stabilize a steel strip that is not subjected to tension in the run-out table from the final finishing rolling mill to the winding machine. The present invention is to provide a hot-rolled steel strip cooling device that strongly cools and a cooling method therefor.
[0011]
[Means for Solving the Problems]
Accordingly, the present invention has been made to solve such a problem, and on the runout where the steel strip is conveyed on a plurality of rotating roller tables, the cooling water is injected between the roller tables at a position closest to the steel strip. The nozzle group that forms the lower surface cooling means is installed, and the nozzle group that forms the upper surface cooling means that can be raised and lowered from the line at a position facing the lower surface cooling nozzle group, and the upper surface cooling nozzle group can be raised and lowered integrally. In addition, a plurality of upper cooling blocks each having one set of restraining rolls that rotate synchronously so as to have the same peripheral speed as the table roll are arranged, and at the same time as the steel strip tip passes through the cooling device, The steel sheet is lowered from the upper cooling block on the upstream side, and simultaneously, cooling water is jetted from the upper and lower surface cooling nozzle groups, and cooling of the upper and lower surfaces of the steel strip is sequentially started simultaneously with the passage of the steel strip.
[0012]
By adopting the cooling device and the cooling method as described above, cooling is started each time the steel strip tip passes through the upper and lower surface cooling nozzle groups, and the non-cooled portion at the steel strip tip is reduced and stable cooling is achieved. The steel strip portion to which is applied becomes longer and the yield is improved. Since the steel strip is tensioned by the restraining roll, the steel strip pass line in the cooling device is stabilized, the cooling state in the longitudinal direction becomes uniform, and the quality is stabilized.
[0013]
Since the restraint roll is provided, the cooling water taken out by the steel strip from the cooling device is blocked, and the cooling water does not remain on the steel strip on the downstream side of the cooling device, thereby preventing overcooling. The cooling stop temperature is constant in the width direction and longitudinal direction of the steel strip, and the cooling conditions on the upper and lower surfaces during cooling are exactly the same, reducing the occurrence of bending during cooling and residual stress after cooling. It is possible to stably manufacture a homogeneous hot-rolled steel strip having a uniform crystal grain size in the longitudinal direction, the width direction, and the thickness direction.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 schematically shows a production facility for a hot-rolled steel strip, and FIG. 2 schematically shows a cooling device.
[0015]
The rough bar 1 rolled by the roughing mill is transported on a roller table forming a steel strip transporting path, continuously rolled to a predetermined thickness by seven continuous finish rolling mills 2, and then the final finish rolling mill 2E. To the run-out table 3 behind. Most of the run-out table 3 constitutes a cooling device 5, and after cooling here, the run-out table 3 is wound up by a rear winder 4 to form a hot rolled coil.
[0016]
Between the final finishing rolling mill 2E and the cooling device 5 in the runout table 3, a steel strip thermometer 6 and a γ-ray thickness gauge 7 are installed.
As shown in FIG. 2, the cooling device 5 is provided from a position about 10 m behind the final finish rolling mill 2E to a position about 25 m. In the arrangement space of the cooling device 5, a rotating steel strip roller table 8 having a diameter of about 350 mm is arranged at a pitch of about 800 mm in the longitudinal direction, thereby constituting a steel strip transport path. That is, these roller tables 8 are located on the lower surface side of the steel strip 11.
[0017]
A lower surface cooling nozzle group 9 having a width of about 1860 mm is provided between the roller tables 8 to form a lower surface cooling means, and a slat-like guide 10 is further provided. The lower surface cooling nozzle group 9 is installed at equal intervals in the width direction below the slat guide 10 in order to avoid contact with the steel strip. The distance between the slat guide 10 and the lower surface of the steel strip 11 is set to about 30 mm.
[0018]
On the other hand, an upper surface cooling nozzle group 12 that forms upper surface cooling means is provided on the upper surface side of the conveying steel strip 11 in the cooling device 5 at a position symmetrical to the lower surface cooling nozzle group 9 via the steel strip conveying path. These upper surface cooling nozzle groups 12 are also provided with a slat-like guide 10 so as not to come into contact with the steel strip 11 to be conveyed.
[0019]
The upper surface cooling nozzle group 12 is supported by a frame 14, and a restraining roll 13 is attached to the downstream side of the upper surface cooling nozzle group 12 of the frame 14. An air cylinder 15 is connected to the frame 14, and an upper cooling block 20 is constituted by these.
[0020]
By the action of the air cylinder 15, the distance between the upper surface of the hot-rolled steel strip 11 and the end of the upper surface cooling nozzle group 12 is equal to the distance between the end of the lower surface cooling nozzle group 9 and the lower surface of the steel strip 11. The installation height of the upper cooling block 20 can be adjusted.
[0021]
In addition, when the cooling device 5 is not operated and the cooling is not performed, the air cylinder 15 is operated at the timing when the tip of the steel strip 11 passes, and the upper surface cooling nozzle group 12 and the restraining roll 13 are positioned at a position approximately 500 mm above the line. And retreat them from the steel strip 11. The lowering of the upper cooling block 20 is set so that the distance between the tips of the cooling nozzle groups 12 and 9 on both the upper and lower surfaces at the time of normal cooling action on the steel strip 11 is the steel plate thickness +60 mm.
[0022]
The restraining roll 13 is a roll that is rotationally driven with a diameter of 200 mm at a position facing the roller table 8, and its rotation is controlled to be the same as the peripheral speed of the roller table 8.
[0023]
For example, 20 upper cooling blocks 20 are arranged at predetermined intervals along the longitudinal direction of the cooling device 5, and the air cylinders 15 are connected to the respective frames 14. Are driven up and down independently of each other.
[0024]
The cooling nozzles constituting the upper and lower surface cooling nozzle groups 12 and 9 employ columnar circular laminar nozzles in order to perform rapid cooling of the steel strip. Moreover, it is not limited to this, For example, you may combine a flat laminar nozzle and a spray nozzle up and down as another type of nozzle.
[0025]
As a condition for selecting such a cooling nozzle, the type of the cooling nozzle, the water density, and the like so that the fluid pressure that the steel strip receives from the cooling water at the upper surface side and the lower surface side of at least the steel strip 11 are substantially the same up and down. The injection pressure is adjusted, or the distance between the tip of the lower surface cooling nozzle group 9 and the lower surface of the steel strip is adjusted with respect to the distance between the tip of the upper surface cooling nozzle group 12 and the upper surface of the steel strip.
[0026]
This is so that the pass line of the steel strip 11 comes to the point of contact between the restraining roll 13 and the roller table 8 during cooling. Unnecessary tension and the vibrations and meandering generated thereby, or the roller table 8 This is to avoid wrinkling by the restraining roll 13. In addition, even if the fluid pressure of the cooling water with respect to the upper surface and the lower surface of the steel strip 11 is adjusted in this way, the tension necessary for winding on the winder 4 side does not increase.
[0027]
As described above, the distance between the tips of the upper and lower surface cooling nozzle groups 12 and 9 and the upper and lower surfaces of the steel strip 11 is set to about 30 mm, for the following reason.
That is, if the distance between the cooling nozzle tip and the steel strip is further increased, the momentum of the cooling water is absorbed by the fluid (cooling water) existing between the nozzle tip and the steel strip and weakens. Conversely, if the distance between the cooling nozzle and the steel strip is made closer, the momentum of the cooling water increases, and the steel strip balances the surface pressure received from the cooling water sprayed from the upper surface and the surface pressure received from the lower surface. The effect of correcting and centering the vibration of the steel strip and the offset running is achieved by passing through the position where it moves.
[0028]
Therefore, in order to ensure that the cooling water reaches the steel strip and cools the steel strip efficiently, the distance between the cooling nozzle and the steel strip cannot be so great. This distance is preferably 30 to 100 mm if the cooling nozzle is a circular laminar nozzle and the diameter of the laminar flow is about 2 to 5 mm.
[0029]
If it is 100 mm or more, the momentum of the cooling water flow weakens and strong cooling becomes impossible. On the other hand, if it is too close to 30 mm or less, there is no place for the cooling water and it becomes difficult to obtain a good water flow. Therefore, rapid cooling becomes impossible, or the flow of cooling water is greatly different between the central portion and the end portion of the steel strip, resulting in uneven cooling. Since this differs depending on the cooling nozzle type, the condition is not limited to the above.
[0030]
Below, the cooling process with respect to the hot-rolled steel strip 11 is demonstrated.
The upper surface cooling nozzle group is aligned with the timing when the tip of the hot-rolled steel strip 11 carried out from the final finish rolling mill 2E passes through the facing position between the uppermost surface cooling nozzle group 12 and the lower surface cooling nozzle group 9 on the closest side. 12 and the frame 14 supporting the restraining roller 13 are lowered, and jetting of cooling water is simultaneously started from the upper surface cooling nozzle group 12 and the lower surface cooling nozzle group 9 at the symmetrical position.
[0031]
The setting of such a process is that if cooling water is jetted from the upper and lower surface cooling nozzle groups 12 and 9 before the tip of the steel strip passes, the cooling water becomes resistance to passage with respect to the tip of the steel strip, so This is because there is a risk of obstruction.
[0032]
After the tip of the steel strip 11 has passed once, the path of the steel strip 11 depends on the balance between the pressure of the cooling water injected from the upper surface cooling nozzle group 12 and the pressure of the cooling water injected from the lower surface cooling nozzle group 9. The line is kept constant. Therefore, even if no tension is applied to the steel strip 11, the plate passing property of the steel strip is stabilized, and uniform strong cooling is applied to the steel strip.
[0033]
With the conveyance of the steel strip, after the first upper cooling block 20 descends from the entrance side of the cooling device 5, the second upper cooling block 20 descends downstream, and further the third upper cooling block. 20 and the subsequent upper cooling block 20 descend in order. The timing of the lowering of each upper cooling block 20 is such that the tip of the steel strip 11 is detected by a sensor provided in the line, the operation of the air cylinder 15 connected to each frame 14 is controlled according to the signal, and the frame is lowered. Start.
[0034]
Since the steel strip 11 is tensioned by the restraining roll 13, the steel strip pass line in the cooling device 5 is stabilized, the cooling state in the longitudinal direction becomes uniform, and the quality is stabilized.
[0035]
In the above equipment, a steel strip having a finished sheet width of 1500 mm and a finished sheet thickness of 3 mm is accelerated at a threading speed of 650 mpm and an acceleration rate of 9 mpm / s, accelerated to a maximum of 1200 mpm, decelerated, and the steel band rear end is moved at 650 mpm. I missed my butt.
[0036]
At the time of acceleration of the steel strip, the coiling temperature was controlled to be constant by increasing the number of cooling nozzles to turn on the cooling water by turning on / off the cooling device 5 and increasing the amount of water in each nozzle. At that time, the steel strip 11 passed through the cooling device 5 stably from the front end to the rear end, and predetermined cooling was performed.
[0037]
Moreover, by providing the restraining roll 13, the cooling water taken out from the cooling device 5 by the steel strip 11 is blocked, there is no leakage of the cooling water before and after the cooling device, and no flaws are generated. As a result, it is possible to stably produce a hot-rolled steel strip having a uniform crystal grain size from the front end to the rear end of the steel strip 11 and a stable fluctuation of the coiling temperature from the front end to the rear end within 15 ° C. Cooling was achieved.
[0038]
【The invention's effect】
As described above, according to the present invention, the following effects can be obtained.
[0039]
(1) Since the cooling is started each time the tip of the steel strip passes through each cooling block, the number of uncooled portions at the tip of the steel strip is reduced, and the steel strip that is stably cooled is lengthened. Yield is improved. Moreover, since tension | tensile_strength is applied by a restraint roll, the pass line in a cooling device is stabilized, the cooling state of the longitudinal direction of a steel strip becomes uniform, and quality is stabilized.
[0040]
(2) Rapid cooling can be performed symmetrically with respect to the steel strip, and rapid cooling can be performed from the tip of the steel strip, thus stabilizing the cooling effect.
[0041]
(3) Since the cooling water taken out by the steel strip from the cooling device is blocked by the restraining roll, overcooling can be prevented without the cooling water remaining on the steel strip on the downstream side of the cooling device. Moreover, the cooling stop temperature is constant in the width direction and the longitudinal direction of the steel strip, and the cooling conditions for the upper surface and the lower surface of the steel strip being cooled are the same. This makes it possible to reduce the occurrence of bending during cooling and residual stress after cooling, and stably produce a homogeneous hot-rolled steel strip with uniform grain size in the longitudinal direction, width direction and thickness direction of the steel strip. it can.
[0042]
(4) Even in a state where the plate passing until the steel strip tip is wound around the winder is unstable, the plate passing is stabilized by providing the restraining roll in the cooling device, and uniform cooling is obtained. As a result, the material is constant and the yield is high.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of rolling equipment showing an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram of a cooling device according to the embodiment.
[Explanation of symbols]
2E ... Final finish rolling mill,
5 ... Cooling device,
12 ... Upper surface cooling nozzle group,
13: Restraint roll,
8 ... Roller table,
9: Lower surface cooling nozzle group,
20: Upper cooling block.

Claims (6)

A steel strip conveying path comprising a plurality of roller tables provided behind the final finish rolling mill in the hot rolled steel strip manufacturing facility, arranged at a predetermined interval and conveying the hot rolled steel strip;
The upper surface cooling means and the lower surface cooling means disposed between the roller tables of the steel strip conveyance path and in the vertical position via the steel strip conveyance path,
A constraining roll provided at a position facing the roller table on the downstream side of the upper surface cooling means, and driven up and down integrally with the upper surface cooling means;
An apparatus for cooling a hot-rolled steel strip. A steel strip conveying path comprising a plurality of roller tables provided behind the final finish rolling mill in the hot rolled steel strip manufacturing facility, arranged at a predetermined interval and conveying the hot rolled steel strip;
The upper surface cooling means and the lower surface cooling means disposed between the roller tables of the steel strip conveyance path and in the vertical position via the steel strip conveyance path,
A restraint that is provided at a position facing the roller table on the downstream side of the upper surface cooling means, is driven up and down integrally with the upper surface cooling means, and its rotation is set so that the circumferential speed is substantially the same as the roller table Roles,
An apparatus for cooling a hot-rolled steel strip. 3. The cooling condition for the upper surface cooling means and the lower surface cooling means is set so that the fluid pressure received by the upper surface side and the lower surface side of the steel strip is the same. Cooling device for hot rolled steel strip. Using the hot rolled steel strip cooling device of claim 1,
The upper surface cooling means and the pair of restraining rolls are sequentially lowered at the same timing as the end of the hot-rolled steel strip to be conveyed, and the restraining roll is brought into rolling contact with the roller table and the upper surface cooling means and the lower surface cooling at the symmetrical position A method for cooling a hot-rolled steel strip, wherein the steel strip is cooled by spraying cooling water from a means under predetermined conditions. Using the hot-rolled steel strip cooling device of claim 2,
The upper surface cooling means and the pair of restraining rolls are sequentially lowered in time with the passage of the tip of the hot-rolled steel strip being conveyed, and the restraining roll is rotated at the same peripheral speed as the roller table and is brought into rolling contact with the roller table. And simultaneously cooling the steel strip by injecting cooling water from the upper surface cooling means and the lower surface cooling means at the symmetrical position under a predetermined condition. The cooling condition is set for the upper surface cooling means and the lower surface cooling means so that the fluid pressure received by the upper surface side and the lower surface side of the steel strip is the same. Cooling method for hot-rolled steel strip.

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