JP2008073765A - Cooler and cooling method of hot rolled steel band - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cooler and a cooling method in which a steel band can be cooled uniformly from the tip to the tail end by achieving a high cooling capacity and a stabilized cooling region appropriately when a hot rolled steel band is cooled with cooling water. <P>SOLUTION: On the upper surface side of the steel band 12, circular tube nozzles 14 jetting rod-like cooling water are disposed oppositely while inclining toward immediately above a table roll 9 from the downstream side and the upstream side of the table roll 9, respectively. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a cooling device and a cooling method for cooling a hot-rolled high-temperature steel strip.

  In general, in order to manufacture a hot-rolled steel strip, a slab is heated to a predetermined temperature in a heating furnace, and the heated slab is rolled to a predetermined thickness with a roughing mill to form a rough bar. In a continuous hot finishing rolling mill comprising a rolling stand, a steel strip having a predetermined thickness is formed. And after cooling this hot-rolled steel strip with the cooling device on a run-out table, it manufactures by winding up with a winder.

  At that time, in the run-out table cooling device that continuously cools the hot-rolled hot steel strip, in order to cool the upper surface of the steel strip, a circular laminar cooling nozzle is placed on the steel roller transport table roller. A plurality of laminar cooling water is poured in a straight line over the width direction. On the other hand, in order to cool the lower surface of the steel strip, a spray nozzle is provided between the table rollers, and a method of injecting cooling water therefrom is generally used.

  However, in such a conventional cooling device, the cooling water poured into the upper surface side of the steel strip stays on the upper surface of the steel strip after cooling, and causes overcooling on the upper surface side. The supercooled state was not uniform in the longitudinal direction of the steel strip, and thus the cooling stop temperature in this direction varied. Furthermore, since the cooling water from the circular tube laminar nozzle used for cooling the upper surface of the steel strip is a free-falling flow, if there is a water film of retained water on the upper surface of the steel strip, it is difficult for the cooling water to reach the steel strip. The problem is that there is a difference in cooling capacity with and without stagnant water on the upper surface of the steel strip, and the cooling water that falls on the steel strip freely spreads back and forth and left and right, so the cooling zone (cooling zone) changes. There is a problem that the cooling capacity is not stable. As a result of such fluctuations in cooling capacity, the material of the steel strip tends to be uneven.

Therefore, in order to drain the cooling water (stagnant water) on the steel strip and obtain a stable cooling capacity, a method of ejecting the stagnant water by injecting a fluid obliquely across the steel strip top surface (for example, , Patent Document 1), and a method of making the cooling region constant by blocking the stagnant water using a constraining roll for constraining the vertical movement of the steel strip as a draining roll (for example, refer to Patent Document 2) has been proposed. Yes. In addition, as a cooling system that keeps the cooling region constant by confining the cooling water on the steel strip, as shown in FIG. 4, a system that injects the cooling water by inclining the slit-shaped nozzles so as to face each other. (See, for example, Patent Document 3).
JP-A-9-141322 JP-A-10-166023 JP 59-144513 A

  However, according to the method described in Patent Document 1, since a large amount of cooling water stays on the steel strip as it goes downstream, the draining effect becomes less effective toward the downstream side.

  Moreover, in the method of patent document 2, since the steel strip front-end | tip part from a rolling mill to a winding machine is conveyed in the state which is not restrained by a restraint roll, by a restraint roll (draining roll) The draining effect cannot be obtained. Moreover, since the steel strip tip passes over the run-out table in a state where it swells while moving up and down, if cooling water is supplied to the top surface of this steel strip tip, the bottom of the bottom where waves are struck Cooling water is likely to stay selectively, and the hunting phenomenon of the cooling temperature occurs until the end of the steel strip is taken up by a winder and tension is applied, and the steel strip is stretched to eliminate the up-and-down wave. This cooling temperature hunting phenomenon also caused variations in the mechanical properties of the steel strip.

  On the other hand, in the cooling method in which the slit-shaped nozzles described in Patent Document 3 are inclined and opposed to each other in a direction facing each other and the cooling water is jetted to confine the cooling water on the steel strip, the cooling water flow is slitless. Cooling water cannot be blocked unless it is cooling water, but in order to keep the cooling water flow in a continuous slit shape, the distance between the nozzle and the steel strip cannot be separated, and in this method, the cooling water is filled. Therefore, since the partition plate is provided in the vicinity of the tip of the nozzle, the distance between the steel strip and the nozzle and the partition plate must be reduced, and there is a high risk of the steel strip colliding with the nozzle and the partition plate. In particular, in a corrugated steel strip having a bad shape, contact with a nozzle or a partition plate is unavoidable, and the steel strip is scratched. Therefore, it is difficult to apply to actual operation.

  As described above, the methods described in Patent Documents 1 to 3 cannot appropriately obtain a high cooling capacity and a stable cooling capacity.

  In the production of hot-rolled steel strip, the surface temperature may be, for example, 550 ° C. or less in the region close to the run-out table winder, and there are the following problems.

  That is, in such a region, from the heat transfer state in which a vapor film exists between the steel strip whose cooling is mainly film boiling and the cooling water, the steel strip and the cooling water are brought into direct contact and boil. It shifts to an area mainly composed of nucleate boiling. This boiling phenomenon in which the boiling state transitions is called transition boiling, and cooling is rapidly accelerated. As a result of such accelerated cooling, only the surface layer of the steel strip may be quenched and a structure different from the target may be formed. For example, when the vicinity of the surface layer is 400 ° C. or less, the structure becomes martensite, and then the surface layer is reheated and the surface layer has a structure different from the inside such as tempered martensite even if the winding ends at 500 ° C. May be formed.

  Furthermore, in the transition boiling to nucleate boiling region, the cooling water is attached to the steel strip, so the cooling water remains in the air cooling zone after exiting the cooling device (zone), and so-called drainage is poor. It is easy to become a state of. In such a part, it becomes overcooled and the quality of the steel strip varies.

  Conventionally, when increasing the cooling rate from the viewpoint of material, it is possible to simply increase the amount of laminar cooling water in a circular tubular shape, but if a large amount of water is injected perpendicularly to the steel strip, Patent Document In the method described in No. 1 and Patent Document 2, water cannot be dammed, and a large amount of stagnant water is generated on the steel strip, resulting in extremely severe temperature unevenness.

  The present invention has been made in consideration of the above-mentioned circumstances, and the purpose of the present invention is to appropriately provide a high cooling capacity and a stable cooling region when cooling a hot-rolled steel strip with cooling water. By realizing the above, an object of the present invention is to provide a cooling apparatus and a cooling method for a hot-rolled steel strip that can uniformly cool the steel strip from the tip to the tail.

  In order to solve the above problems, the present invention has the following features.

[1] A cooling device for a hot-rolled steel strip for cooling a hot-rolled steel strip after finish rolling conveyed on a run-out table,
A cooling nozzle for injecting a rod-shaped cooling water inclined from the upstream side of the table roll toward directly above the table roll on the upper surface side of the steel strip, and a rod-shaped cooling inclined from the downstream side of the table roll toward immediately above the table roll. A cooling device for a hot-rolled steel strip, wherein the cooling nozzle for jetting water is arranged so as to face the cooling nozzle.

  [2] A plurality of the cooling nozzles are arranged in the width direction of the steel strip, and an angle formed between the rod-shaped cooling water sprayed by the cooling nozzle and the steel strip is 60 ° or less. ] The cooling apparatus of the hot-rolled steel strip described in the above.

  [3] The cooling nozzles on the upper surface side and the lower surface side of the steel strip are arranged so that the cooling amount by the cooling water on the upper surface side of the steel strip is equal to the cooling amount by the cooling water on the lower surface side of the steel strip. The cooling apparatus for hot-rolled steel strips according to [1] or [2].

  [4] The cooling nozzle for injecting rod-shaped cooling water from between the table rolls toward the lower surface of the steel strip is disposed on the lower surface side of the steel strip, according to any one of the above [1] to [3] Cooling device for hot-rolled steel strip.

  [5] The hot-rolled steel strip cooling device according to any one of [1] to [4] is a single cooling device unit, and a plurality of the cooling device units are arranged in the traveling direction of the steel strip. To cool the hot-rolled steel strip.

  [6] The hot-rolled steel strip according to any one of [1] to [5], wherein draining means for draining the cooling water on the upper surface of the steel strip is disposed downstream of the cooling device. Cooling system.

[7] A method for cooling a hot-rolled steel strip after finish rolling conveyed on a run-out table,
The upper surface of the steel strip is opposed to the rod-shaped cooling water inclined from the upstream side of the table roll toward directly above the table roll and the rod-shaped cooling water inclined from the downstream side of the table roll toward directly above the table roll. A method of cooling a hot-rolled steel strip.

  [8] The method for cooling a hot-rolled steel strip according to [7], wherein an angle formed between the rod-shaped cooling water and the steel strip is 60 ° or less.

  [9] The cooling water is jetted to the upper surface side and the lower surface side of the steel strip so that the cooling amount by the cooling water on the upper surface side of the steel strip is equal to the cooling amount by the cooling water on the lower surface side of the steel strip. The method for cooling a hot-rolled steel strip according to [7] or [8].

  [10] The hot-rolled steel strip according to any one of [7] to [9], wherein bar-like cooling water is sprayed on the lower surface side of the steel strip from between the table rolls toward the lower surface of the steel strip. Cooling method.

  [11] Intermittent injection of rod-shaped cooling water inclined right above the table roll on the upper surface side of the steel strip at a plurality of locations at intervals in the traveling direction of the steel strip, thereby repeating intermittent water cooling and air cooling The method for cooling a hot-rolled steel strip according to any one of [7] to [10], wherein cooling is performed.

  [12] In the above [7] to [11], the cooling water is drained by draining means provided on the downstream side of the steel strip position where the inclined rod-shaped cooling water is jetted oppositely. The method for cooling a hot-rolled steel strip according to any one of the above.

  According to the present invention, cooling can be performed uniformly from the front end to the tail end of the steel strip, and the quality of the steel strip is stabilized. Along with this, the cutting margin of the steel strip is reduced and the yield is increased.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a hot-rolled steel strip manufacturing facility in one embodiment of the present invention.

  The coarse bar 2 rolled by the coarse rolling mill 1 is conveyed on the table roller 3 and continuously rolled to a predetermined thickness by seven continuous finish rolling mill groups 4 to form a steel strip 12, and then the final finish. It is led to the run-out table 5 constituting the steel strip conveyance path behind the rolling mill 4E. The runout table 5 has a total length of about 100 m, and a cooling device is provided in a part or most of the runout table 5. After the steel strip 12 is cooled here, the runout table 5 is wound by the downstream winder 6 and heated. It becomes the extension coil.

  In this embodiment, as an example, as a cooling device for cooling the steel strip upper surface provided on the run-out table 5, a conventional cooling device 7 and the cooling device 11 of the present invention are arranged in this order.

  The conventional cooling device 7 includes a plurality of circular laminar nozzles 8 that are arranged at a predetermined pitch on the upper surface side of the run-out table 5 and supply cooling water as a free fall flow to the steel strip.

  As a cooling device for cooling the steel strip lower surface, a plurality of spray nozzles 10 are arranged in a row in the width direction between the table rollers 9 for transporting the steel strip. These spray nozzles 10 can adjust the ejection pressure and the water density.

  And an example of the cooling device 11 of this invention is described based on the partial enlarged view shown in FIG. On the run-out table 5, for example, a rotating steel strip conveying table roller 9 having a diameter of 330 mm is arranged at a pitch of about 400 mm in the longitudinal direction, and the steel strip 12 advances on these table rollers 9. In the cooling device 11 of the present invention, the bar-shaped cooling water inclined to the upper surface side of the steel strip 12 from the upstream side and the downstream side of the same table roll 9 toward the table roll is directly injected. A plurality of upper surface cooling units 17 are provided in the traveling direction of the steel strip.

  Each upper surface cooling unit 17 is divided into an upstream side and a downstream side in the traveling direction, and includes a predetermined number (four in each case) of cooling nozzle headers 13. Each cooling nozzle header 13 is connected to a supply pipe 15, and each supply pipe 15 can be independently controlled on and off by an injection valve 16, and each cooling nozzle header 13 has a traveling direction. The circular tube nozzles 14 having a predetermined injection angle θ (for example, 50 °) are arranged in a line at a predetermined pitch in the width direction.

  These circular tube nozzles 14 are straight tube nozzles having an inner diameter of 3 to 10 mmφ and a smooth inner surface, and the cooling water sprayed is rod-shaped cooling water. The rod-shaped cooling water forms a predetermined angle θ with the steel strip 12 in a certain direction, that is, in the traveling direction of the steel strip 12. Further, the steel strip 12 may be parallel to the steel strip 12 in the width direction. However, in order to cause the injected cooling water to quickly flow outward from both width end portions of the steel strip 12, the steel strip 12 is used. It is desirable to incline toward the outside by 1 ° to 30 °, preferably 5 ° to 15 ° from the center in the width direction. The height of the outlet of the circular tube nozzle 14 is set a predetermined height (for example, 1000 mm) away from the upper surface of the steel strip 12 so that it does not contact the circular tube nozzle 14 even if the steel strip 12 moves up and down. ing.

  Here, the rod-shaped cooling water in the present invention is cooling water injected in a state of being pressurized to some extent from a circular (including elliptical or polygonal) nozzle outlet, and is cooled from the nozzle outlet. The water jet velocity is 7 m / s or more, and the water flow has a continuous and straight running cooling water in which the cross section of the water flow from the nozzle outlet to the steel strip is maintained in a substantially circular shape. That is, it is different from a free fall flow from a circular tube laminar nozzle or a liquid ejected in a droplet state such as a spray.

  Further, regarding the arrangement of the circular tube nozzles 14, the width direction of the circular tube nozzles 14 for each column is such that the collision position of the rod-shaped cooling water of the next column comes approximately in the middle of the collision position of the rod-shaped cooling water of the previous column. It is preferable to shift the positions. As a result, the rod-shaped cooling water in the next row collides with a portion where the cooling becomes weak between the rod-shaped cooling waters adjacent in the width direction, and the cooling is supplemented to achieve uniform cooling in the width direction.

  Then, from each of the four rows of circular tube nozzles 14 toward substantially the same position of the steel strip 12 (for example, toward the same table roller 9), the cooling water is opposed from the upstream side and the downstream side in the steel strip traveling direction. Is injected.

  Thus, when rod-shaped cooling water is ejected from the circular tube nozzles 14 arranged in a row, the rod-shaped cooling water flow group flows intermittently as each rod-shaped cooling water runs in parallel, but flows in a quasi-planar shape. On top of that, since each of the four rows of circular tube nozzles 14 is jetted oppositely from the upstream side and the downstream side in the traveling direction of the steel strip, the cooling waters that collide with the steel strip 12 are dammed together and collide with each other. In this position, the steel strip 12 flows outward from both width ends of the steel strip 12, so that the cooling water is prevented from flowing out on the steel strip to the upstream side and the downstream side.

  At that time, if the injection angle θ exceeds 60 °, depending on the speed of the steel strip 12, cooling water may flow out upstream and downstream on the steel strip, so the injection angle θ is 60 ° or less. It is preferable to do this. If the injection angle θ is set to 60 ° or less, the cooling water does not flow out upstream and downstream on the steel strip regardless of the speed of the steel strip 12. More preferably, the injection angle θ is 50 ° or less. However, if the injection angle θ is smaller than 45 °, the height of the circular tube nozzle 14 from the steel strip 12 is set to a desired value (for example, 1000 mm) in order to avoid collision between the steel strip 12 and the circular tube nozzle 14. Then, the distance until the rod-shaped cooling water sprayed from the circular tube nozzle 14 collides with the steel strip 12 is too long, and there is a risk that the rod-shaped cooling water is dispersed on the way and the cooling characteristics are deteriorated. Therefore, the injection angle θ is preferably 45 ° to 60 °, and more preferably about 45 ° to 50 °.

  Incidentally, in the cooling device 11 of the present invention, the circular pipe nozzle 14 that forms rod-shaped cooling water is adopted as the cooling water nozzle on the upper surface of the steel strip 12 for the following reason.

  That is, in order to surely perform the cooling, it is necessary to reliably make the cooling water reach the steel strip 12 and collide with it. For this purpose, the water film on the upper surface of the steel strip 12 must be broken to allow fresh cooling water to reach the steel strip 12, and cooling with a weak penetrating force such as a group of droplets ejected from the spray nozzle. It should be a rod-shaped cooling water that is not a water droplet flow but a water flow with high continuity and straightness. Furthermore, since the laminar flow by the conventionally used circular tube laminar nozzle is a free-falling flow, if there is a stagnant water film, it is difficult for the cooling water to reach the steel strip 12, and when there is no stagnant water. Thus, there are problems such as a difference in cooling capacity, and water falling on the steel strip 12 spreads back and forth and right and left, so that the cooling capacity changes when the speed of the steel strip changes. Therefore, in the present invention, the circular pipe nozzle 14 (which may be an ellipse or a polygon) may be used, the cooling water injection speed from the nozzle outlet is 7 m / s or more, and the steel outlet to the steel strip. The rod-shaped cooling water having continuity and straightness in which the cross section of the water flow until the collision is maintained in a substantially circular shape is jetted. According to the rod-shaped cooling water having a cooling water injection speed of 7 m / s or more from the nozzle outlet, the water film on the upper surface of the steel strip is stably formed even when the cooling water is inclined and injected. Because it can break through.

  Although it is conceivable to use a laminar flow on a continuous curtain instead of a rod-shaped cooling water flow group, a slit-like nozzle having a gap (practically 3 mm or more is required) that does not clog the nozzle. In this case, the nozzle cross-sectional area becomes extremely large as compared with the case where the circular tube nozzles 15 are installed at intervals in the width direction. For this reason, in order to inject cooling water at an injection speed of 7 m / s or more from the nozzle outlet in order to have a penetrating force to the staying water film, an extremely large amount of water is required, and the equipment cost is enormous and difficult to realize. It is. Further, in the laminar flow on the curtain, the cooling water that collides with the steel strip 12 in the first row is layered to prevent the collision of the cooling water in the second and subsequent rows, so the cooling capacity in the second and subsequent rows decreases or the width direction However, there are problems such as differences in cooling capacity. On the other hand, if it is rod-shaped cooling water, the laminar staying water is partially pushed away and the rod-shaped cooling water reaches the steel strip 12. The pushed-off cooling water flows through between the intermittent rod-shaped cooling water flows, so that the remaining cooling water after cooling is unlikely to hinder subsequent cooling.

  On the other hand, in the cooling device 11 of the present invention, the cooling nozzle on the lower surface side of the steel strip is not particularly limited, but a liquid film is formed when water is easily placed in a narrow space such as between table rolls and a large amount of water is ejected. It is preferable to use a circular pipe nozzle that injects rod-shaped cooling water having a high ability to penetrate. That is, in this embodiment, the cooling nozzle header 18 is arrange | positioned between the adjacent table rollers 9, and the circular pipe nozzle 19 which injects rod-shaped cooling water to each cooling nozzle header 18 at a predetermined pitch in the width direction. A predetermined number of columns (here, two columns) are arranged. Each cooling nozzle header 18 is connected to a supply pipe 20, and each supply pipe 20 can be independently controlled on and off by an injection valve 21. Thus, as a cooling nozzle on the lower surface side of the steel strip, by using a circular tube nozzle that injects rod-shaped cooling water having a high cooling capacity, the cooling zone length can be shortened and a compact apparatus can be obtained.

  At that time, the cooling amount by the cooling water on the upper surface side of the steel strip (bar-shaped cooling water from the circular tube nozzle 14) is equal to the cooling amount by the cooling water on the lower surface side of the steel strip (bar-shaped cooling water from the circular tube nozzle 19). As described above, it is preferable to adjust the arrangement of the cooling nozzles on the upper surface side and the lower surface side of the steel strip 12, the water density, the arrival speed, and the like of the cooling water.

  And in the cooling device 11 of this invention, since the bar-shaped cooling water inclined from the upper surface cooling unit 17 toward right above the same table roll 9 is jetted oppositely, the steel strip 12 is bar-shaped cooling. The steel strip 12 passes through the run-out table 5 while being pressed against the table roll 9 by water, and the plate of the steel strip 12 is stable even in a no-tension state until the tip of the steel strip 12 is taken up by the winder 6. To do.

  Moreover, in the cooling device 11 of the present invention, since a plurality of cooling units 17 are arranged in the traveling direction of the steel strip, the counter injection of the rod-shaped cooling water on the upper surface side of the steel strip 12 is spaced in the traveling direction of the steel strip 12. It is possible to perform intermittent cooling (intermittent cooling) in which water cooling and air cooling are repeated by performing the cooling at a plurality of locations. Therefore, especially in the case of steel strip cooling where the surface is supercooled and a hard layer such as martensite is likely to be generated, even if the surface layer temperature falls, the next air cooling will recuperate the heat. Therefore, there is an effect of suppressing supercooling of the surface layer and reducing not only temperature variation but also micro structure microstructure variation in the steel strip thickness direction.

  Furthermore, in the cooling device 11 of the present invention, the air injection nozzle 22 is provided on the downstream side of the cooling unit 17 so that the cooling water on the upper surface of the steel strip does not flow out to drain the water. At that time, as a draining method, a draining method in which water is jetted is generally used. However, when the surface temperature of the steel strip is 550 ° C. or less, the draining with water sticks to the surface of the steel plate and the cooling water is stuck. In such a case, it is desirable to drain water by injecting air, since it may cause complete supercooling. The air injection nozzle 22 is desirably provided on the downstream side of all the cooling units 17, but may be provided at least on the downstream side of the cooling unit 17 on the most downstream side.

  And when using the cooling device 11 comprised as mentioned above, cooling control is performed as follows.

  First, the length of the cooling zone of the upper surface and the lower surface to be ejected is determined from the speed of the steel strip, the measured temperature, and the cooling amount up to the target cooling stop temperature. Then, the number of cooling units 17 covering the obtained cooling zone length of the upper surface and the number of rows of cooling nozzle headers 13 to be injected in the cooling unit 17 are determined, the corresponding injection valve 16 is opened, and the obtained lower surface The number of cooling nozzle headers 18 covering the cooling zone length is determined and the corresponding injection valve 21 is opened. At that time, it is desirable that the cooling amount by the cooling water on the upper surface side of the steel strip is equal to the cooling amount by the cooling water on the lower surface side of the steel strip.

  Thereafter, the number of cooling units 17 on the upper surface and the cooling nozzle header to be sprayed are changed so as to change the cooling zone length while considering the change in the steel plate speed (acceleration / deceleration) by looking at the results of the thermometer after cooling. The number of thirteen rows and the number of cooling nozzle headers 18 on the lower surface are adjusted. When changing the number of rows of the cooling nozzle header 13, in order to prevent the cooling water from flowing out to the non-cooling zone (air cooling zone) on the steel strip as much as possible, the number of rows to be injected from the upstream side to the downstream side It is desirable to adjust the number of rows to be ejected from the downstream side toward the upstream side so that the fluid pressure of the cooling water is balanced between the upstream side and the downstream side of the steel strip. For example, it is desirable to turn the upstream and downstream cooling nozzle headers on and off in pairs.

As described above, in this embodiment, the following effects can be obtained.
(1) The steel strip can be uniformly cooled from the tip to the tail, and the quality of the steel strip is stabilized. Along with this, the cutting margin of the steel strip is reduced and the yield is increased.
(2) Since the steel strip travels on the run-out table while being pressed against the table roll by the rod-shaped cooling water, the plate passing through the steel strip is stabilized even in a non-tensioned state until the tip of the steel strip is wound up. As a result, troubles such as clogging of the steel strip and operation stoppage can be reduced.

  In the above embodiment, as shown in FIG. 2, the bar-shaped cooling water inclined from the upstream side and the downstream side of the same table roll toward the upper side of the table roll is opposed to the upper surface side of the steel strip. However, the present invention is not limited to this. For example, as shown in FIG. 3, the rod-shaped cooling water inclined from the upstream side of the table roll toward directly above the table roll, and from the downstream side of the table roll disposed on the downstream side to directly above the table roll. You may inject | pour the inclined rod-shaped cooling water to oppose. However, the cooling water sprayed on the upper surface of the steel strip is allowed to flow down from both width ends of the steel strip to the outside, and in order to stabilize the plate, it is sprayed oppositely directly onto the same table roll. Is preferable.

  Moreover, in the said embodiment, although the conventional cooling device 7 and the cooling device 11 of this invention are arrange | positioned in that order as a cooling device of steel strip upper surface cooling provided in the run-out table 5, it is limited to this. Instead, a part or all of the cooling device provided on the run-out table 5 may be constituted by the cooling device 11 of the present invention. However, as described above, depending on the winding temperature, the cooling may be in an unstable state called transition boiling in a region close to the winder. However, according to the cooling device 11 of the present invention, the entire surface nucleate boiling. Thus, a transition boiling region where cooling becomes unstable can be avoided. Therefore, stable cooling is possible regardless of the winding temperature, and the winding temperature can be accurately controlled. Therefore, it is preferable to dispose the cooling device 11 of the present invention at least immediately before the winder. With such an arrangement, there is no unstable cooling even at a low coiling temperature (500 ° C. or less), and temperature variation is small. As a result, the quality of the steel strip such as strength and elongation is uniform over the entire length of the steel strip.

  Examples of the present invention will be described.

  As an example of the present invention, a steel strip having a finished plate thickness of 2.8 mm was manufactured based on the above embodiment using the equipment shown in FIGS. The steel strip speed on the exit side of the finish rolling mill 4 was 700 mpm at the front end of the steel strip, and after the front end of the steel strip reached the winder 6, the speed was gradually increased to a maximum of 1000 mpm. The temperature at the delivery side of the steel strip finisher is 850 ° C., and is cooled to about 650 ° C. using the conventional cooling device 10. Thereafter, the cooling device 11 of the present invention is used up to the target coiling temperature of 400 ° C. And cooled. Here, the injection angle θ of the cooling water from the cooling device 11 is set to 50 °, and the flow rate in the longitudinal direction of the cooling water at the time of collision with the steel strip is equal to or higher than the maximum speed of the steel strip. The jetting speed of the cooling water was 30 m / s. Thereby, the flow velocity in the longitudinal direction of the steel strip is 30 m / s × cos 50 ° ≈1152 mpm.

  And cooling control was performed as follows. First, the length of the cooling zone of the upper surface and the lower surface for injecting the cooling water was determined from the speed of the steel strip, the measured temperature, and the cooling amount up to the target cooling stop temperature. Then, the number of cooling units 17 covering the obtained cooling zone length of the upper surface and the number of rows of cooling nozzle headers 13 to be injected in the cooling unit 17 are determined, the corresponding injection valve 16 is opened, and the obtained lower surface The number of cooling nozzle headers 18 covering the cooling zone length was determined and the corresponding injection valve 21 was opened. At that time, the cooling amount by the cooling water on the upper surface side of the steel strip was made equal to the cooling amount by the cooling water on the lower surface side of the steel strip. Thereafter, the number of cooling units 17 on the upper surface and the cooling nozzle header to be sprayed are changed so as to change the cooling zone length while considering the change in the steel plate speed (acceleration / deceleration) by looking at the results of the thermometer after cooling. The number of thirteen rows and the number of cooling nozzle headers 18 on the bottom surface were adjusted. However, when changing the number of rows of cooling nozzle headers to be injected, the number of rows to be injected from the upstream side and the number of rows to be injected from the downstream side are balanced between the upstream and downstream sides of the steel strip. In this way, the upstream and downstream cooling nozzle headers were turned on and off in pairs.

  In addition, the zone length of the cooling unit 17 is adjusted so that the steel strip upper surface does not become martensite on the exit side of each cooling unit 17, and heat recovery from the inside is sufficiently completed in the next air cooling zone. Thus, the air cooling zone length was determined, and the subsequent use conditions of the cooling unit 17 were determined. Incidentally, since the steel used here produces a martensite structure at 350 ° C. or lower, cooling was controlled so that the surface does not become 350 ° C. or lower.

  As a result, in the present invention example, the steel strip temperature in the winder 6 was within 400 ° C. ± 10 ° C. over the entire length, and very uniform cooling could be realized. In addition, there was no martensite structure tempered on the upper surface of the steel strip. As a result, a stable quality steel strip could be obtained.

  On the other hand, as a comparative example, in the same equipment as the above-described present invention example, the cooling device 11 of the present invention is not used, but the conventional cooling device 7 (the circular tube laminar nozzle 8 on the upper surface and the spray nozzle 10 on the lower surface). ) Only to the target coiling temperature of 400 ° C. Others were the same as the example of the present invention.

  As a result, in the comparative example, the laminar flow by the circular tube laminar nozzle 8 is a free-falling flow. Therefore, if there is a staying water film, it is difficult for the cooling water to reach the steel strip 12 and there is no case where there is any staying water. In some cases, there was a difference in cooling capacity, and temperature hunting was observed in the longitudinal direction of the steel strip. In particular, during the period from the start of winding by the winder 6 until tension is applied to the steel strip, stagnant water stays in the concave portion at the steel strip tip, thereby causing the temperature in the longitudinal direction of the steel strip. Unevenness occurred. Therefore, the dispersion | variation in the temperature in a steel strip was large, and it varied widely with 250-450 degreeC with respect to the target temperature 400 degreeC with the winder 6. FIG. Therefore, the variation in strength in the steel strip was large.

It is a schematic block diagram of the rolling equipment in one Embodiment of this invention. It is explanatory drawing of the cooling device in one Embodiment of this invention. It is explanatory drawing of the cooling device in other embodiment of this invention. It is explanatory drawing of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Rough rolling mill 2 ... Rough bar 3 ... Table roller 4 ... Continuous finishing rolling mill group 4E ... Final finishing rolling mill 5 ... Run-out table 6 ... Winding machine 7 ... Conventional cooling device 8 ... Round pipe laminar nozzle 9 ... Table roller 10 ... Spray nozzle 11 ... Cooling device of the present invention 12 ... Steel strip 13 ... Cooling nozzle header 14 ... Circular nozzle 15 ... Supply pipe 16 ... Injection valve 17 ... Cooling unit 18 on the upper surface 18 ... Cooling nozzle header 19 ... Circular pipe Nozzle 20 ... Supply pipe 21 ... Injection valve 22 ... Air injection nozzle

Claims (12)

A hot-rolled steel strip cooling device for cooling the hot-rolled steel strip after finish rolling conveyed on the run-out table,
A cooling nozzle for injecting a rod-shaped cooling water inclined from the upstream side of the table roll toward directly above the table roll on the upper surface side of the steel strip, and a rod-shaped cooling inclined from the downstream side of the table roll toward immediately above the table roll. A cooling device for a hot-rolled steel strip, wherein the cooling nozzle for jetting water is arranged so as to face the cooling nozzle.   2. The cooling nozzle according to claim 1, wherein a plurality of the cooling nozzles are arranged in a steel strip width direction, and an angle formed between the rod-shaped cooling water sprayed by the cooling nozzle and the steel strip is 60 ° or less. Cooling device for hot-rolled steel strip.   The cooling nozzles on the upper surface side and the lower surface side of the steel strip are arranged so that the cooling amount by the cooling water on the upper surface side of the steel strip is equal to the cooling amount by the cooling water on the lower surface side of the steel strip. Or the cooling apparatus of the hot-rolled steel strip of 2.   The cooling nozzle for hot-rolled steel strip according to any one of claims 1 to 3, wherein a cooling nozzle for injecting rod-shaped cooling water from between the table rolls toward the lower surface of the steel strip is disposed on the lower surface side of the steel strip. apparatus.   A cooling device for a hot-rolled steel strip according to any one of claims 1 to 4 is used as a single cooling device unit, and a plurality of the cooling device units are arranged in the traveling direction of the steel strip. Cooling system.   The cooling device for a hot-rolled steel strip according to any one of claims 1 to 5, further comprising a draining means for draining the cooling water on the upper surface of the steel strip on the downstream side of the cooling device. A method for cooling a hot-rolled steel strip after finish rolling conveyed on a run-out table,
The upper surface of the steel strip is opposed to the rod-shaped cooling water inclined from the upstream side of the table roll toward directly above the table roll and the rod-shaped cooling water inclined from the downstream side of the table roll toward directly above the table roll. A method of cooling a hot-rolled steel strip.   The method for cooling a hot-rolled steel strip according to claim 7, wherein an angle formed by the rod-shaped cooling water and the steel strip is 60 ° or less.   8. The cooling water is injected to the upper surface side and the lower surface side of the steel strip so that the cooling amount by the cooling water on the upper surface side of the steel strip is equal to the cooling amount by the cooling water on the lower surface side of the steel strip. Or the method for cooling a hot-rolled steel strip according to 8.   The method for cooling a hot-rolled steel strip according to any one of claims 7 to 9, wherein rod-shaped cooling water is sprayed from the table rolls toward the lower surface of the steel strip on the lower surface side of the steel strip.   By performing counter-injection of rod-shaped cooling water inclined to the upper surface side of the steel strip directly above the table roll at a plurality of locations at intervals in the traveling direction of the steel strip, intermittent cooling that repeats water cooling and air cooling is performed. The method for cooling a hot-rolled steel strip according to any one of claims 7 to 10.   The heat according to any one of claims 7 to 11, wherein drainage of the cooling water is performed by a draining means provided downstream of a steel strip position where the inclined rod-shaped cooling water is jetted oppositely. Cooling method for rolled steel strip.

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