JP2833474B2 - Method and apparatus for cooling steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel sheet which is continuously conveyed in continuous hot rolling, and which is uniformly cooled to a predetermined winding temperature between a finishing mill at the final stage and a winding machine. Method and apparatus.

[0002]

2. Description of the Related Art A steel sheet finish-rolled in a hot rolling step is cooled by bringing it into contact with cooling water. When the steel sheet is cooled, a uniform temperature distribution is applied to the entire steel sheet from the viewpoint of quality. Cooling is desired.

As an apparatus for performing this type of cooling, there is an apparatus disclosed in, for example, Japanese Patent Application Laid-Open No. 59-197313. In this apparatus, a hairpin-shaped laminar flow nozzle row is disposed above the steel sheet in the width direction thereof in opposition to the steel sheet, and is movable in the steel sheet width direction between the laminar flow nozzle row and the conveyed steel sheet. The water receiving plate is provided, and the water receiving plate is moved to receive a part of the cooling water by the water receiving plate, and a receiving gutter for draining the cooling water received by the water receiving plate is provided near the water receiving plate. It is. According to such an apparatus, since the steel sheet can be uniformly cooled in the width direction, by continuously conveying the steel sheet at a constant speed, it is possible to uniformly cool the entire steel sheet. Have been.

[0004] On the other hand, the present applicant has disclosed Japanese Utility Model Laid-Open No. 6-23607.
In the official gazette, an upper header having both ends closed, and a lower header having one end closed and the other end serving as a water supply port, the upper and lower headers are communicated by a plurality of communication pipes, A cooling nozzle header having a number of nozzles on an upper header is disclosed. The communicating pipe of the cooling nozzle header is provided with a resistance means as appropriate, a rectifying plate is appropriately provided in the upper header, and an air supply pipe is provided above the upper header as appropriate.

[0005]

However, in the case of the apparatuses disclosed in the above publications, laminar flow cooling is performed to cool the steel sheet, so that the thickness of the steel sheet to be cooled is small. When the thickness is 1.6 mm or less, when laminar flow cooling is performed from the beginning, rapid cooling is performed due to high heat transfer, and the shape of the leading end portion of the steel sheet collapses, and the flow through the run-out table is reduced. The plate becomes poor.

Therefore, in order to avoid this, conventionally, cooling water has not been projected onto the tip end portion of the steel sheet and cooling has not been performed. After the tip of the steel sheet bites into the winder, laminar flow cooling was started because there was no problem with the sheet passing property.

[0007] For this reason, the leading end portion of the steel sheet, which is not cooled, cannot obtain the desired mechanical properties and must be treated as a cut-down product, resulting in a reduction in yield.

Accordingly, an object of the present invention is to provide a continuous hot rolling method that prevents the shape of a leading end portion of a steel sheet from collapsing, improves the sheet passing property, and increases the yield.

[0009]

According to a cooling method of the present invention for solving the above-mentioned problems, a continuously conveyed steel sheet is provided.
When the steel sheet is cooled in a continuous hot rolling in which the steel sheet is rolled to a sheet thickness of 1.6 mm or less, then cooled by flowing down cooling water, and then wound up, the tip portion of the steel sheet is cooled only by spray cooling. And performing cooling by only laminar flow cooling or by both laminar flow cooling and spray cooling on a portion of the steel plate other than the front end portion.

The cooling device of the present invention is a cooling device in continuous hot rolling in which a continuously conveyed steel sheet is rolled, then cooled by flowing down cooling water, and then wound.
Above the position where the steel sheet is conveyed, a laminar flow nozzle row in which a number of laminar flow nozzles are arranged in parallel in the width direction of the steel sheet is provided, and a plurality of spray nozzles are arranged in parallel in the width direction of the steel sheet. The laminar flow nozzle row and the plurality of spray nozzles can be configured so that cooling water can flow down independently.

Further, a cylindrical lower header having a structure in which the axis is arranged substantially horizontally, one end of which is liquid-tightly closed, and cooling water is supplied from the other end, An upper header having both ends closed, a plurality of communicating pipes spaced in the axial direction communicating the upper header and the lower header, and the upper header is spaced in the axial direction. It has a number of laminar flow nozzles, the base side of each of these nozzles is rising from the upper header, the discharge port is turned downward from the middle, and the communication part by each of the communication pipes has flow resistance means. The resistance of the flow between the water supply side and the closed side of the cooling water may be configured to increase toward the water supply side.

A cylindrical lower header having a structure in which the axis is substantially horizontal, one end of which is closed in a liquid-tight manner, and cooling water is supplied from the other end, is provided in parallel with the lower header. An upper header having both ends closed, a plurality of communicating pipes spaced in the axial direction communicating the upper header and the lower header, and the upper header is spaced in the axial direction. It has a number of laminar flow nozzles, the base side of each of these nozzles rises from the upper header, and the discharge port faces downward from the middle, and a number of through holes are formed in the upper header, dividing the upper and lower sides. Is formed, and the diameter of the through-hole of this straightening plate is reduced toward one end between the one end forming the water supply side and the other end forming the closed side. Configurations can also be employed.

In this aspect, the current plate is a first current plate, and a space between the top end of the upper header and the first current plate is located above the first current plate in the upper header. By partitioning, a substantially horizontal second straightening vane having a large number of through-holes having a uniform diameter can be provided.

A plurality of air supply ports may be formed in the longitudinal direction so as to communicate with the upper header, and a common air supply pipe may be connected to the air supply ports.

Further, a plurality of air vent pipes are arranged at intervals in the longitudinal direction so as to communicate with the upper header, and a common exhaust pipe is provided which communicates with each of the air vent pipes and is higher than the water supply column. Configuration.

Below and in parallel with the lower header,
One end side is liquid-tightly closed, and a cylindrical second upper header to which cooling water for spray cooling is supplied from the other end side is formed,
A second lower header, both ends of which are liquid-tightly closed, is provided below and in parallel with the second lower header.
The lower header is connected to the lower header by a communication pipe, and the spray nozzles may be provided downward in the second lower header.

The second lower header contains the second lower header.
A substantially horizontal current plate having a large number of through-holes can be provided in the lower header by dividing the upper and lower portions.

[0018]

[Function] As a method of cooling a steel sheet continuously conveyed in continuous hot rolling to a target winding temperature between a finishing mill and a winder at the final stage, a laminar flow method is currently used. Cooling methods are the mainstream.

When a water jet is formed by pressurizing water and flowing down from a nozzle, a smooth laminar jet is formed when the outlet flow velocity of the jet is relatively low. When this jet falls a certain distance, it produces an axially symmetric vibration and breaks or becomes a droplet flow. This method of cooling by laminar jet is called laminar flow cooling. On the other hand, when the water is pressurized and flows down from the nozzle, the liquid flow breaks at a flow velocity higher than the continuous jet, and collides with the solid surface as a group of droplets. The cooling by the droplet group is called spray cooling.

In the method for cooling a steel sheet according to the present invention,
When the thickness of the steel sheet is as thin as 1.6 mm or less, the tip part is also cooled to improve the yield, and only the spray cooling is performed at the tip part in order to avoid deterioration of the sheet passing property. Is used alone or in combination with spray cooling.

It has been found that when spray cooling is used, even if the thickness of the steel sheet is as thin as 1.6 mm or less, it is possible to prevent the steel sheet from being deformed. After the leading end of the steel sheet is caught in the winder, sufficient tension is generated in the steel sheet, so that there is no problem of the sheet passing property due to the deformation of the steel sheet shape. Therefore, laminar flow cooling which has excellent cooling capacity is adopted.
On the other hand, if the thickness of the steel sheet exceeds 1.6 mm, laminar flow cooling can be adopted from the beginning also for the tip portion.

Further, in the cooling device according to the present invention, a laminar flow nozzle row and a plurality of spray nozzles are arranged above the conveyed steel plate. This laminar flow nozzle row is formed by a large number of laminar flow nozzles juxtaposed at intervals in the width direction of the steel sheet. On the other hand, according to the present invention, a plurality of spray nozzles are provided in the width direction of the steel plate. Since the laminar flow nozzle row and the spray nozzle group can independently flow the cooling water, the laminar flow cooling and the spray cooling are performed in the transport direction position (in other words, timing) of the steel sheet and the steel sheet. The steel sheet can be cooled while being appropriately changed in accordance with the thickness of the steel sheet, so that the steel sheet can be cooled by the above-described method for cooling a steel sheet according to the present invention.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a steel plate cooling apparatus according to the present invention will be specifically described below with reference to the drawings. FIG.
FIG. 2 is a partially cutaway front view of a cooling device as a first example according to the present invention, FIG. 2 is a side view thereof, and FIG. In this cooling device for steel plates, the left-right direction in FIG. 1 corresponds to the width direction of the steel plates, and a number of unit cooling devices shown in the drawing are provided in the transport direction.

The cooling device is connected to the first upper header 1 in the form of a horizontal cylinder having both ends closed and a plurality of first communication pipes 2,... For cooling the laminar flow. A first upper header 1 and a first lower header 3 in the shape of a long cylinder parallel to the first upper header 1. In addition, independently of the first upper header 1 and the first lower header 3, for spray cooling, below the lower header 3,
A second upper header 4 and a second lower header 5 are provided, and the second upper header 4 and the second lower header 5 are
Are connected in communication by a plurality of second communication pipes 6,.

A hairpin-shaped (inverted J-shaped) laminar flow nozzles 10a,... Are provided on the upper side of the first upper header 1 so as to symmetrically protrude on both sides in a communicating state, and these laminar flow nozzles 10a,. The laminar flow nozzle rows 10 are arranged side by side in the width direction of the steel sheet.

On the other hand, below the second lower header 5, a plurality of, for example, seven spray nozzles 40,... Are provided at regular intervals, for example, at 200 mm intervals. The laminar flow cooling water Wf flowing down from the laminar flow nozzle row 10 is supplied only from one side (the direction of the arrow in FIG. 1) of the first lower header 3, and the laminar flow nozzles 10,.
The spray cooling water Ws is supplied only from one side of the second upper header 4 (in the direction of the arrow in FIG. 1) and flows down from the spray nozzles 40.

With this configuration, the laminar flow cooling water Wf flowing down from the laminar flow nozzle row 10 and the spray cooling water Ws flowing down from the spray nozzles 40,... Can flow down independently. For this reason, when the steel plate to be cooled is a thin plate having a thickness of 1.6 mm or less, spray cooling is performed at the leading end portion, and laminar flow cooling is performed on the subsequent portion, thereby facilitating the passing of the steel plate. Cooling can be performed over the entire length while preventing deterioration of performance.

In the following second and third embodiments or other examples, the description thereof is omitted, but basically, there is a configuration in which laminar flow cooling and spray cooling can be performed independently. doing.

At one end of the first lower header 3, a closing plate 30 is closed in a liquid-tight manner by bolting. With such a configuration, the closing plate 30 is removed so that the inside of the first lower header 3 can be easily cleaned. The other end of the first lower header 3 is connected to a water supply pipe (not shown), from which cooling water Wf is supplied.

First lower header 3 and first upper header 1
Are connected at intervals in the axial direction by a plurality of, for example, six communication pipes 2,.
The cooling water Wf supplied to the inside can be supplied to the first upper header 1. Each of the communication pipes 2 has a connecting portion formed by fastening two opposed flanges 20 at an intermediate portion thereof by bolts, and a resistance means, for example, an orifice plate 21 is inserted into the flange portion. .

The orifice plate 21 is configured such that, as it is closer to the water supply side in the longitudinal direction of the first lower header 3, the orifice diameter becomes smaller so that the throttle amount becomes larger. The reason is that the water pressure is higher near the water supply side, and unless the orifice plate 21 is installed, the supply amount of the cooling water Wf to the first upper header 1 increases nearer the water supply side, and the laminar flow nozzle row 10 This is because the amount of water flowing down varies, and uniform cooling cannot be performed in the width direction of the steel sheet.

Next, the structure of the first upper header 1 will be described. Both ends of the first upper header 1 are similar to the ends of the first lower header 3 on the side where the closing plate 30 is provided. A flange is provided, and a closing plate 31 is bolted to the flange to be liquid-tightly closed. The rising point of each laminar flow nozzle 10a,... Is, for example, about 10 to 20 mm higher than the top end of the first upper header 1, and a straight pipe section of about 300 mm is provided below to improve laminar flow formation. preferable.

In the first upper header 1, a current plate, for example, a punching metal 11 having a large number of holes is mounted horizontally over the entire length in the longitudinal direction. The punching metal 11 has a form as shown in FIG.
By the action of the punching metal 11, the pressure of the cooling water Wf supplied from the first lower header 3 becomes more uniform and is supplied to the laminar flow nozzles 10a,. Therefore, there is no difference in the flow rate of each laminar flow nozzle 10a,.
The flow rate distribution is made uniform, and in combination with the installation of the orifice 21 described above, more uniform cooling in the width direction of the steel plate becomes possible.

Further, at the upper end of the first upper header 1, a plurality of, for example, 10 to 12 air supply ports 13 are provided.
It is preferable to connect an air supply pipe 12 for sending compressed air to each air supply port. A valve (not shown) is attached to the other end of the air supply pipe 12. It is preferable that the valve be simultaneously opened in conjunction with the closing of the header water supply valve. In this way, the supply of water to the first lower header 3 is stopped, and at the same time, the compressed air is sent from the punching metal 11 in the first upper header 1 into the upper half space. At this time, the first
Since the punching metal 11 is mounted on the upper header 1, the compressed air collides with the upper surface of the punching metal 11, and the reaction causes the air pressure to force the residual water in the hairpin type laminar flow nozzle 10a. Since it works in the discharge direction, drainage responsiveness can be improved. At this time, each laminar flow nozzle 10a,.
The air consumption can be reduced by lowering the rising portion or by setting the mounting position of the punching metal 11 at a higher position.

In the above example, the flow resistance is adjusted by providing the orifice plate 21 as resistance means in the first communication pipe 2. For example, by providing a flow control valve, the opening degree of each flow control valve is set in advance. Alternatively, it may be adjusted each time.

On the other hand, the second upper header 4 and the second lower header 5 will be described. The second upper header 4
Like the first lower header 3, one end thereof is liquid-tightly closed by a closing plate 32 attached by bolting, so that the closing plate 32 is removed so that the inside of the first upper header 4 can be easily cleaned. Have been. The other end to which the closing plate 32 is not attached is connected to a water supply pipe (not shown), from which the cooling water Ws is supplied. On the other hand, the second lower header, like the first upper header 1,
Closing plate 33 attached at both ends by bolts
Fluid tight. And the second communication pipe 6
Through the second upper header 4 to the second lower header 5
The cooling water Ws is supplied to the spray nozzle 40, and spray cooling can be performed by spray nozzles 40,. In addition, the first
Since the upper header 1, the first lower header 3, the second upper header, and the second lower header 4 are arranged vertically, a large space is not required for installation.

The cooling water Ws supplied from the pipe to the second upper header 4 is sprayed from each of the spray nozzles 40 as spray cooling water. This spray nozzle 40,
... can be appropriately selected from a flat type and a full cone type. The injection angle from the nozzle is not limited to the downward direction, and may be inclined at an appropriate angle in the front-rear direction, for example, 45 degrees.

Further, in order to equalize the flow rate of the cooling water Ws from each of the spray nozzles 40,..., A rectifying plate, for example, a punching metal 11S can be provided on the second lower header 5. .. Are preferable in that uniform cooling water flows down.

Next, a second example which is effective for a nozzle header having a small number of first communication pipes 2 communicating the first upper header 1 and the first lower header 3 will be described. FIG.
FIG. 5 is a front view of a second example according to the present invention, FIG. 5 is a side view thereof, and FIG. 6 is a view thereof taken along line 6-6. A substantially horizontal punching metal 11A having a large number of through holes is provided in the first upper header 1 so as to partition the upper and lower portions. More specifically, a first punching metal 11A for adjusting the water amount distribution is horizontally mounted over the entire length in the longitudinal direction, for example, at a quarter position below the first upper header 1, and further attached to the first punching metal 11A. A second punching metal 11 for rectification is provided in parallel with, for example, a central position above it.
B is attached.

As shown in FIG. 10, the first punching metal 11A has a large number of through-holes 11a, and the diameter of the through-hole 11a is reduced as it approaches the water supply side (to the right in FIGS. 4 and 10). ing. The reason is that the water pressure of the cooling water Wf supplied becomes higher as the water supply side is closer to the water supply side. Therefore, assuming that the diameter of the through-hole 11a is uniform in the longitudinal direction, the laminar flow nozzle 10a closer to the water supply side flows down from there. The amount of water to be discharged increases, and each laminar flow nozzle 10
This is because the amount of water flowing down from a,... varies, and uniform cooling in the width direction of the steel sheet cannot be performed.

In this regard, as shown in FIG.
By reducing the diameter of the hole closer to the water supply side, the resistance is large and the permeation flow rate is small in the case of a small perforation diameter, and the resistance is small and the permeation flow rate is large in the case of a large perforation diameter. Furthermore, the higher the water pressure is, the closer the water pressure is to the water supply side, so that the amount of water flowing down from each laminar flow nozzle 10a,.

On the other hand, as shown in FIG. 11, the second punching metal 11B has a large number of through holes 11b having a uniform diameter. This second punching metal 11B can be attached together with the first punching metal 11A by sandwiching it between the mounting seats 31a on the inner surfaces of the closing plates 31, 31 at both ends. By providing the second punching metal 11B, the pressure of the cooling water supplied from the first lower header 3 is further uniformed, so that the difference in the flow rate between the hairpin type laminar flow nozzles 10 is reduced, and the flow rate is reduced. The distribution is made uniform. This, combined with the effect of the first punching metal 11A, enables cooling with a more uniform temperature distribution.

At this time, the punching metals 11A and 11B can be easily removed by removing the closing plates 31, 31 provided at both ends of the first upper header 1 by bolting.
Cleaning of 1B can be easily performed.

Next, a third example according to the present invention will be described. 7 is a front view of an example of the third cooling device according to the present invention, FIG. 8 is a side view thereof, and FIG. 9 is a view taken in the direction of arrows 9-9. In order to obtain the stability of the water flow, which is also a problem in the first and second examples, the laminar flow nozzle 1
The rising position of Oa was set to be about 200 to 300 mm above the top end of the first upper header 1. In order to improve drainage at this time, in the third example, air bleeding pipes 14, 14,... Are provided in the first upper header 1, communicate with these air bleeding pipes, and are higher than the water supply column. Is provided with an exhaust pipe 15 that is open to the atmosphere, thereby improving drainage.

The laminar flow nozzle 10a is preferably of a hairpin type, but if the nozzle is partially raised from the first upper header 1 and the cooling water discharge port faces downward, the hairpin type is used. Not limited. In addition, each header may have a cylindrical shape, and is not limited to a cylindrical shape.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above-described configuration. For example, a spray nozzle group may be provided between adjacent laminar flow nozzle rows. You may. Further, in the above embodiment, the second upper header 4 and the second lower header 5 are provided. However, the spray cooling does not have a large variation in the amount of water. The spray nozzle may be directly attached to the header. Similarly, for a laminar flow cooling system, only a single header can be used. In short, if it has a laminar flow nozzle and a spray nozzle, if the laminar flow cooling water flowing down from the laminar flow nozzle and the spray cooling water flowing down from the spray nozzle are configured to flow down independently, respectively. Good. The number of spray nozzles and laminar flow nozzles, the amount of water, and the like can be appropriately selected according to conditions such as the thickness of the steel sheet to be cooled and the target temperature.

In actual operation, for example, FIG.
As shown in the figure, the steel sheet M rolled by the finishing mill 57 at the final stage in the hot rolling mill is then conveyed to the proximity cooling zone 61 and is particularly thin (for example, 1.2 mm).
mm or less), it is wound up by the proximity winder 66. Otherwise, it is further conveyed to the remote cooling zone 62 and wound up by the remote winder 67. The steel plate cooling device according to the present invention is disposed in each of the near cooling zone 61 and the far cooling zone 62, and in each cooling zone, the steel sheet M is cooled by the cooling method and device according to the present invention.

In this case, the tip portion for performing spray cooling can be specifically a portion where the steel sheet M is bitten by the winder. After being bitten, laminar flow cooling is promptly changed in relation to the cooling capacity. During the laminar flow cooling, spray cooling may be used together.

<Experimental Example> Hereinafter, the effect of the present invention will be clarified by an experimental example. The steel sheet continuously conveyed was cooled using the steel sheet cooling device shown in FIG. As the conditions, the thickness of the steel sheet is 1.6 mm, and the target winding temperature of the steel sheet to be cooled is 620 ° C. As an example of the present invention, spray cooling was performed on the tip portion of the steel sheet, and laminar flow cooling was performed on the other portions. Further, as a comparative example, laminar flow cooling was performed only on the other portions of the steel plate at the other end portions without cooling in order to prevent the shape of the steel plate from collapsing. FIG. 13 shows a chart of the winding temperature of the steel sheet by the cooling method according to the present invention, and FIG. 14 shows a chart of the winding of the steel sheet by the cooling method of the comparative example. The circled portion in FIG. 14 is a portion where cooling was not performed.

In the cooling method according to the present invention, the winding temperature at the leading end of the steel plate was 640 ° C., whereas in the cooling method according to the comparative example, the winding temperature at the leading end in the latter half was 67 ° C.
It was 0 ° C. As a result, it was found that the steel sheet can be cooled to near the target winding temperature by the cooling method according to the present invention. In this experimental example, when the target winding temperature of the cooled steel sheet is 620 ° C.,
Since the temperature is within the allowable range, the cooling method according to the present invention can be said to be a very excellent cooling method.

Using the cooling device shown in FIG. 4, a steel plate rolled to a thickness of 1.63 mm was conveyed, and cooling experiments were performed with the target winding cooling temperatures set at 620 ° C. and 610 ° C., respectively. . FIGS. 15 and 16 show charts of the temperature on the exit side of the finishing mill and the winding temperature at that time.

As is clear from FIGS. 15 and 16,
According to the cooling method of the present invention, even at the tip of the steel sheet, the temperature can be kept within ± 20 ° C. of the target temperature, and the shape of the tip of the steel sheet does not collapse.

The average temperature of the steel sheet tip cooled by a conventional cooling method with a target winding cooling temperature of 620 ° C., and the steel sheet tip cooled by the cooling method according to the present invention. Are shown in FIG. In the conventional cooling method, the temperature was 656 ° C., whereas in the cooling method according to the present invention, the temperature was 629 ° C., and the difference was improved by about 27 ° C., and as a result, the amount of devaluation of the steel plate due to the high temperature at the tip end was reduced. Is about half of the conventional one.

[0054]

As is apparent from the above description, according to the present invention, in continuous hot rolling, the shape of the leading end portion of a steel sheet is prevented from being deformed, the sheet passing property is improved, and the yield is increased. be able to.

[Brief description of the drawings]

FIG. 1 is a partially cutaway front view of a first example of a cooling device according to the present invention.

FIG. 2 is a side view thereof.

FIG. 3 is a view taken in the direction of arrow 3-3.

FIG. 4 is a partially cutaway front view of a second example of the cooling device according to the present invention.

FIG. 5 is a side view thereof.

FIG. 6 is a view taken in the direction of arrows 6-6.

FIG. 7 is a partially cutaway front view of a third example of the cooling device according to the present invention.

FIG. 8 is a side view thereof.

FIG. 9 is a view taken in the direction of the arrow 9-9.

FIG. 10 is a plan view of a punching metal.

FIG. 11 is a plan view of another punched metal.

FIG. 12 is a diagram showing a model from a cooling step to a winding step in hot rolling.

FIG. 13 is a winding temperature chart of a steel sheet in the cooling method according to the present invention.

FIG. 14 is a winding temperature chart of a steel sheet in a cooling method of a comparative example.

FIG. 15 is another example of a winding temperature chart of a steel sheet in the cooling method according to the present invention.

FIG. 16 is another example.

FIG. 17 is a graph showing the average value of the temperature of the steel plate tip when the steel plate is cooled by the conventional cooling method and the cooling method according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... 1st upper header, 2 ... 1st communicating pipe, 3 ... 1st lower header, 4 ... 2nd upper header, 5 ... 2nd lower header, 6 ... 2nd communicating pipe, 10 ... Laminar flow nozzle, 1
1 ... punching metal, 30, 31, 32, 33 ... closing plate, 40 ... spray nozzle, M ... steel plate, Wf ... laminar flow cooling water, Ws ... spray cooling water.

Claims (8)

(57) [Claims] The present invention relates to a method for cooling a steel sheet in continuous hot rolling in which a continuously conveyed steel sheet is rolled to a sheet thickness of 1.6 mm or less, then cooled by flowing down cooling water and then wound up. For the tip portion of the steel plate, perform cooling only by spray cooling, and for portions other than the tip portion of the steel plate, only by laminar flow cooling,
Alternatively, a method for cooling a steel sheet, comprising performing cooling by both laminar flow cooling and spray cooling. 2. A cooling device in continuous hot rolling in which a continuously conveyed steel sheet is rolled, then cooled by flowing down cooling water, and then wound, wherein the cooling device is disposed above a position where the steel sheet is conveyed. A laminar flow nozzle row in which a plurality of spray nozzles are arranged in parallel in the width direction of the steel sheet, and a number of laminar flow nozzles are arranged in parallel in the width direction of the steel sheet; The row is arranged such that the axis is substantially horizontal, one end side is closed in a liquid-tight manner, and a cylindrical lower header having a structure in which cooling water is supplied from the other end side,
An upper header, which is provided in parallel with the both ends and is closed at both ends, comprises a plurality of communication pipes spaced apart in an axial direction for communicating the upper header and the lower header, and the upper header is provided in the axial direction. There are a number of laminar flow nozzles spaced apart from each other, and the base side of each of these nozzles rises from the upper header, and the nozzles are bent from the middle and the discharge ports face downward. Having means,
The cooling device for a steel sheet, wherein the resistance of the flow is increased between the water supply side and the closed side of the cooling water toward the water supply side. 3. A cooling device in continuous hot rolling, in which a continuously conveyed steel sheet is rolled, cooled by flowing down cooling water, and then wound, wherein the cooling device is disposed above a position where the steel sheet is conveyed. A laminar flow nozzle row in which a plurality of spray nozzles are arranged in parallel in the width direction of the steel sheet, and a number of laminar flow nozzles are arranged in parallel in the width direction of the steel sheet; The row is arranged such that the axis is substantially horizontal, one end side is closed in a liquid-tight manner, and a cylindrical lower header having a structure in which cooling water is supplied from the other end side,
An upper header, which is provided in parallel with the both ends and is closed at both ends, comprises a plurality of communication pipes spaced apart in an axial direction for communicating the upper header and the lower header, and the upper header is provided in the axial direction. It has a number of laminar flow nozzles spaced apart from each other, and the base side of each of these nozzles rises from the upper header, and the discharge port is turned downward from the middle, and the upper header is divided into upper and lower parts. A substantially horizontal straightening plate having a large number of through holes is provided, and the through hole diameter of the straightening plate is closer to one end between the one end forming the water supply side and the other end forming the closed side. A cooling device for a steel sheet, which is reduced in size. 4. A rectifying plate, wherein the rectifying plate is a first rectifying plate, and a space between a top end of the upper header and the first rectifying plate is partitioned at a position above the first rectifying plate in the upper header. 4. The cooling apparatus for a steel sheet according to claim 3, further comprising a substantially horizontal second straightening plate having a plurality of through holes having a uniform diameter. 5. The cooling of a steel plate according to claim 3, wherein a plurality of air supply ports are formed in the longitudinal direction in communication with the upper header, and a common air supply pipe is connected to the air supply ports. apparatus. 6. A plurality of air vent pipes are provided at intervals in the longitudinal direction so as to communicate with the upper header, and a common exhaust pipe is provided in communication with each of the air vent pipes and at a higher level than the water supply water column. The cooling device for a steel sheet according to claim 3, 4 or 5. 7. Below and in parallel with the lower header,
One end side is liquid-tightly closed, and a cylindrical second upper header to which cooling water for spray cooling is supplied from the other end side is formed,
A second lower header, both ends of which are liquid-tightly closed, is provided below and in parallel with the second lower header.
The cooling device for a steel sheet according to any one of claims 2 to 6, wherein the spray nozzle is provided in a downward direction in the second lower header, and is communicated with the lower header by a communication pipe. 8. The steel plate according to claim 7, wherein a substantially horizontal straightening plate having a large number of through-holes is provided inside the second lower header, and the upper and lower partitions are formed inside the second lower header. Cooling system.