JP5741165B2 - Thermal steel sheet bottom surface cooling device - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a lower surface cooling device for a hot steel plate, and more specifically, when cooling hot-rolled hot rolled steel plate and thick steel plate, a spray nozzle (cooling water spreads from the nozzle injection port) for cooling the lower surface side of the steel plate. In the case of using a spray nozzle, the cooling water from the spray nozzle falls on the upper surface of the hot-rolled steel sheet and prevents the width end portion of the hot-rolled steel sheet from being overcooled. The present invention relates to a lower surface cooling device for a hot-rolled steel sheet that can be cooled at a uniform temperature in the width direction.

  In a production line for a hot steel sheet, for example, a hot rolled steel sheet, the slab heated at a high temperature is rolled so as to become a steel sheet of a desired size, and then the steel sheet is cooled on a runout table from the viewpoint of material adjustment. The purpose of the cooling performed here is to adjust the material such as the intended strength and elongation mainly by controlling the precipitates and transformation structure of the steel sheet. As the cooling medium for the cooling, water with low cost is often used. Here, unless the temperature distribution in the width direction after cooling of the steel sheet is not uniform, mechanical test values such as strength and elongation change in the width direction of the steel sheet, and a predetermined material cannot be obtained locally.

In hot-rolled steel sheets, the upper surface is often cooled by a laminar flow, and the lower surface is often cooled by a spray, but in general, there is a non-uniform temperature distribution in the width direction of the steel sheet, especially due to cooling by the laminar flow of the upper surface. It is said to occur.
That is, when cooling the upper surface of the steel sheet by laminar flow, a plurality of headers are provided in the traveling direction of the steel sheet so that the header longitudinal direction is orthogonal to the traveling direction of the steel sheet, and a plurality of nozzles are provided in each header in the header longitudinal direction. (In other words, the cooling water is sprayed from the nozzles all at once, but the cooling water that has reached the upper surface of the steel sheet forms a water flow in the width direction of the steel sheet. Part)), the amount of water passing through increases, and cooling is increased. For this reason, the portion near the edge in the width direction has a higher cooling capacity than the center portion, and often has a temperature distribution in which both edge portions of the steel sheet are at a low temperature.

On the other hand, a non-uniform temperature distribution may occur in the width direction of the steel sheet due to cooling by spraying the lower surface.
That is, since the thickness of the steel plate through which the run-out table is passed after finish rolling is as thin as about 2 to 4 mm and has low rigidity, the table rollers are densely arranged in order to pass the run-out table stably. For example, in many run-out tables, table rollers having a diameter of about 250 to 300 mmφ are arranged at a pitch of 300 to 400 mm, so that the space between the table rollers is narrow. Therefore, when cooling the lower surface of a steel plate, there exists a problem that it is difficult to arrange | position a nozzle between table rollers. Therefore, when cooling the bottom surface of a hot-rolled steel sheet on the run-out table, spray nozzles (nozzles that spread and spray cooling water from nozzle nozzles) can be installed in a narrow space and widened in the pass line width direction. In many cases, a plurality of them are arranged. Cooling using a spray nozzle is called spray cooling. Since there are various plate widths of the steel plate passing through the pass line, there are many cases where a steel plate having a plate width narrower than the full width of the pass line passes. In that case, in the lower surface cooling using the spray type nozzle, the cooling water sprayed from the spray nozzle arranged at the width direction position (width direction end) where the steel plate does not pass above is several hundred mm from the pass line. After a few m blows up, it falls, but a part of the cooling water falls on the upper surface of the steel plate. This falling water also causes overcooling particularly at the end of the steel plate. Such a problem also occurs in the controlled cooling of thick steel plates and has the same problem.

Various proposals have been made so far to prevent overcooling of the width end of the hot steel sheet.
For example, Patent Document 1 describes a method in which a ridge for adjusting the amount of cooling water falling at the steel plate width end portion to be less than that of the steel plate width center portion is provided below the nozzle for the upper surface nozzle. A plurality of this technique are disclosed in addition to this Patent Document 1, and a technique of providing a shielding plate so that the cooling water does not fall at the width end of the steel sheet is also proposed as an application. In addition, there is an example in which the present technique is applied not only to the upper surface of the steel plate but also to the lower surface of the steel plate.

  Further, in Patent Document 2, in laminar flow cooling on the upper surface of the steel plate, the function is divided into a header that selectively cools the steel plate width end portion and a header that selectively cools the steel plate width center portion, and from each header, A technique for controlling the temperature distribution in the width direction of the steel sheet by providing a flow rate distribution in the width direction of the steel sheet by controlling the water injection ON-OFF is disclosed. As a similar technique, there is a method of adjusting the flow rate of the cooling water in the width direction by sequentially changing the diameter of the nozzles attached in the width direction in the width direction. In addition, there is an example in which the present technique is applied not only to the upper surface of the steel plate but also to the lower surface of the steel plate.

JP 2005-238283 A JP-A-1-284419

However, although the methods described in Patent Documents 1 and 2 are effective means for the upper surface of the hot-rolled steel sheet, they are not practically sufficient for cooling the lower surface of the hot-rolled steel sheet.
First, as described in Patent Document 1 and the like, the method of adjusting the amount of cooling water at the width end of the steel sheet by means of scissors or a shielding plate is mainly intended for cooling the upper surface of the steel sheet. Nozzle arrangement in the case of wide roll intervals is described. As the drive mechanism of the shielding plate, wire or screw is used. Especially in the case of a line with a plate width exceeding 5000 mm such as a thick steel plate, the minimum plate width (1500 mm to 2000 mm) and the maximum plate width (4000 to 5500 mm) The difference is large, and the driving distance of the shielding plate is large because it drives a long distance of 1000 to 2000 mm on one side. On the lower surface side of the steel plate, the cooling water sprayed from the nozzle falls after colliding with the steel plate, so that the drive mechanism such as a screw or a wire gets wet, and there are very many failures due to rust and the like. Therefore, as a matter of fact, the masking device using the shielding on the lower surface has not been stably operated.

  Moreover, in the method of dividing the nozzle in the width direction as described in Patent Document 2, it is necessary to have a plurality of water supply pipes to the header, but the normal runout table is a table roller considering drainage after cooling. A sluice is installed underneath and a table roller is placed on it, and large-scale civil engineering work is necessary to secure a space for piping, and it can be handled during line construction. It is difficult to adopt. In addition, as the number of divisions in the width direction is increased, the number of pipes increases, which incurs a large equipment cost.

From the above, in Patent Documents 1 and 2, there is a problem that occurs when spray cooling is employed for cooling the lower surface of the steel sheet, and the cooling water sprayed from the nozzle disposed at the end in the width direction where there is no steel sheet above the nozzle. As a means for preventing the problem that the steel sheet is blown up from below and falls to the upper surface of the steel sheet and the steel sheet width end portion is overcooled, it is not a practical technique.
The present invention has been made in view of the above circumstances, and in a hot steel plate production line, it is sprayed to spread on the lower surface side of the steel plate, particularly like a spray nozzle, to some extent with a single nozzle. When using a nozzle that can cool a large area, it is possible to prevent the cooling water from the nozzle from dropping on the upper surface of the hot steel plate and overcooling the width end, and the hot steel plate It is an object of the present invention to provide a lower surface cooling device for a hot-steel plate that can be cooled at a uniform temperature in the direction and that can operate stably at a low cost as a simple mechanism.

The present invention made to solve the above problems is as follows.
[1]
A thermal steel plate lower surface cooling device in which cooling nozzles for spray cooling the lower surface of the steel plate are arranged in a row in the pass line width direction and a plurality of the rows are arranged in the longitudinal direction of the pass line under the pass line of the hot steel plate. A fluid is jetted outward in the line width direction, and the shut-off water, which is the jetted fluid, is caused to collide with the cooling water from the cooling nozzle at a position 10 to 50 mm above the cooling nozzle jet port, thereby A hot steel plate characterized in that a shut-off nozzle is installed that shuts off the cooling water from the cooling nozzle by bending the main direction at an angle θ of 45 degrees or less obliquely upward from the horizontal in front of the steel plate path. Underside cooling device.
[2]
The blocking nozzle satisfies the following equation (1) when blocking one to one with respect to the cooling nozzle, and satisfies the following equation (2) when blocking one to many. The apparatus for cooling the lower surface of a hot-steel plate according to [1] above.

_{^{ρ W Q W P W 0.5 ≦}} ρ S Q S P S 0.5 ‥‥ (1)
Σρ _W Q _W P _W ^0.5 ≦ ρ _S Q _S P _S ^0.5 (2)
ρ: fluid density, Q: fluid ejection flow rate, P: fluid ejection pressure, Σ: total subscript for a plurality of cooling nozzles corresponding to one shutoff nozzle W: fluid ejected from the cooling nozzle Some cooling water, subscript S: shut-off water that is a jet fluid from the shut-off nozzle
[3]
The shut-off nozzles are arranged one by one in part or all between the individual nozzles in each row of cooling nozzles, and the lower surface cooling of the hot steel sheet according to the above [1] or [2] apparatus.
[Four]
The apparatus for cooling a lower surface of a hot-steel plate according to any one of [1] to [3], wherein an on / off valve for individually opening and closing the blocking nozzle is provided.
[Five]
The apparatus for cooling a lower surface of a hot-steel plate according to any one of [1] to [4], wherein the blocking nozzle is a flat spray nozzle having a spread angle of 30 ° or less.

  In the present invention, when a nozzle that spreads like a spray nozzle and sprays cooling water is used for cooling the lower surface side of the hot steel plate, the cooling water from that nozzle blows up and falls onto the upper surface of the hot rolled steel plate. Further, it is possible to accurately prevent the width end portion of the hot steel plate from being overcooled. As a result, the hot steel plate can be cooled at a uniform temperature in the width direction, and a high-strength steel plate can be produced without variations in mechanical properties.

It is a front sectional view which illustrates an embodiment of the present invention. It is a front sectional view which illustrates an embodiment of the present invention. It is a front sectional view which illustrates an embodiment of the present invention. It is a front sectional view which illustrates an embodiment of the present invention. It is front sectional drawing which shows an experimental apparatus. It is a graph which shows an experimental result. It is definition explanatory drawing of the bending angle of the cooling water after a collision. It is a front sectional view which illustrates an embodiment of the present invention. It is a side view which shows the hot rolled sheet steel production line used in the Example. It is front sectional drawing which shows the prior art example (it is an example used as the premise of this invention) of the lower surface cooling apparatus of a hot-steel plate. It is a top view which shows the injection pattern of the nozzle for cooling of FIG. It is side surface sectional drawing which shows the arrangement | positioning form of the cooling nozzle of FIG.

Embodiments of the present invention will be described with reference to the drawings.
In the hot steel sheet production line, when the lower surface side of the hot steel sheet is spray-cooled, the cooling water from the nozzle used for spray cooling falls on the upper surface of the hot-rolled steel sheet, and the width end of the hot steel sheet is By preventing overcooling, cooling is performed so that the temperature distribution in the plate width direction after cooling becomes uniform.

Therefore, in the present invention, below the pass line of the hot steel plate, the cooling nozzle for spray cooling the lower surface of the steel plate is arranged in one row in the pass line width direction, and the lower surface of the hot steel plate formed by arranging a plurality of these rows in the pass line longitudinal direction. A cooling device is assumed. This premise itself is the same as before. Conventional examples are shown in FIGS.
As shown in FIGS. 10 to 12, the hot steel plate pass line is a conveyance line of a steel plate (for example, hot-rolled steel plate) 10 by a table roller 4 forming a run-out table. Below the pass line, there is provided a thermal steel sheet lower surface cooling device in which cooling nozzles 2 for spray-cooling the lower surface of the steel sheet are arranged in a line in the pass line width direction, and a plurality of these rows are arranged in the longitudinal direction of the pass line. Yes. As the cooling nozzle 2, a flat spray nozzle that spreads and sprays the cooling water 3 in a fan shape from the nozzle injection port is suitable, and is frequently used.

The cooling nozzles 2 are attached to the header 1, which is a cooling water supply source pipe, in a form in which a plurality of cooling water injection nozzles 2 are arranged in a line at a predetermined pitch (for example, 100 mm pitch) in the header longitudinal direction. . The header 1 is installed between the table rollers 4 and 4 such that the header longitudinal direction is parallel to the pass line width direction and the nozzle mounting portion is on the upper side.
The cooling water 3 sprayed from the cooling nozzles 2 in the pass line width direction cools the lower surface of the steel plate 10 not only immediately above the cooling nozzles 2 but also between the adjacent cooling nozzles 2. . In the case of a hot-rolled steel runout table, the table rollers 4 having a diameter of about 250 to 300 mmφ are arranged at a pitch of 300 to 400 mm, so that one header 1 is provided between the table rollers 4 and 4 from the viewpoint of space. Only installed.

  When the cooling water 3 is injected from the cooling nozzle 2 in this state, the cooling water 3 injected from directly below the steel plate 10 collides with the steel plate 10 and falls downward, as shown in FIG. Since the cooling water 3 sprayed from the outside spreads and is sprayed, a part of the coolant enters the inside of the steel plate 10 width after passing through the outside of the steel plate 10 width and falls onto the upper surface of the steel plate 10. The falling water 9 falling on the upper surface of the steel plate 10 induces supercooling at the width end portion of the steel plate 10.

Accordingly, in the present invention, based on the above premise, as shown in FIG. 1, a fluid is ejected outward in the width direction of a pass line (hereinafter also referred to as a cooling line), and the coolant 3 from the cooling nozzle 2 is ejected by the ejected fluid. A blocking nozzle 21 was installed to block
Thereby, the cooling water 3 injected from the cooling nozzle 2 is caused to collide with the blocking water 22 injected from the blocking nozzle 21, and the injection direction of the cooling water 3 is changed so as not to fall on the steel plate 10. That is, the cooling water 3 can be shut off.

The blocking nozzles 21 are preferably arranged one by one in part or all between each individual in each row of the cooling nozzles 2. In addition, in FIG. 1, the example at the time of arrange | positioning one each of the nozzles 21 for interruption | blocking between the cooling nozzles 2 and 2 of the steel plate 10 width both ends passage position (2 places in total) was shown.
FIG. 2 shows an example in which one blocking nozzle 21 is arranged between each of the cooling nozzles 2 in each row. In this example, only the left half of the full width of the cooling line is shown, but the right half is a left-right inverted view of FIG. Each shut-off nozzle 21 is provided with an on / off valve 23 and can be opened and closed individually. As shown in FIG. 2 (a), when cooling a wide steel plate, all the on / off valves 23 are closed so that the cooling water 3 injected from the cooling nozzle 2 collides with the lower surface of the steel plate 10 and cools it. Is made.

When cooling the narrow steel plate 10 as shown in FIG. 2 (b), the on / off valve 23 of the shut-off nozzle 21 outside the plate width of the steel plate 10 is opened and the shut-off water 22 is sprayed, so The direction in which the cooling water 3 is jetted from the cooling nozzle 2 is changed to the outside in the cooling line width direction, thereby avoiding falling to the upper surface of the steel plate 10.
Here, the condition of the blocking nozzle 21 necessary for changing the injection direction of the cooling water 3 is examined, and the necessary condition is the balance of the jet force of the cooling water 3 and the blocking water 22 as described below. I found that I could organize it well.

The jet force F of the fluid can be expressed by the following equation (3).
F = ρQV (3)
ρ: fluid density [kg / m ³ ]
Q: Fluid flow rate [m ³ / s]
V: Fluid velocity [m / s]
F: Fluid jet force [N]
From equation (1), the cooling water trajectory will bend if the cutoff water jet force is made larger than the cooling water jet force.

Also, since the fluid velocity V is proportional to the pressure P of the fluid and becomes V∝ (P) ^0.5 , using this relationship, assuming that the proportionality constant is 1, converting the above equation (3) The following equation (4) is obtained.
F = ρQP ^0.5 (4)
Therefore, the relationship between the jet force between the cooling water 3 and the cutoff water 22 was investigated using the experimental apparatus shown in FIG.

  In this experimental apparatus, a plurality of flat spray nozzles for spreading and injecting the cooling water 3 in a fan shape with an angle of 75 degrees as a cooling water nozzle 2 on one header 1 extending in the course width direction of the steel plate 10, They were attached side by side in the longitudinal direction of the header at predetermined intervals. At this time, each nozzle is arranged so that the main direction of injection (injection direction at the center of the spread width) is vertically upward, and the spread width direction of injection in the horizontal plane is inclined by 45 degrees with respect to the steel plate traveling direction. .

  On the other hand, as the blocking nozzle 21, a flat spray nozzle that spreads the blocking water 22 in a fan shape with an angle of 25 degrees and sprays it, one on each of the portions between the plurality of cooling nozzles 2, 2. A plurality of nozzles are arranged so that the spreading width direction is located in a horizontal plane immediately above the cooling nozzle 2 injection port, and the main injection direction is a direction from the center to the end of the steel plate 10 in the width direction.

Using the above experimental apparatus, the cutoff water 22 is caused to collide with the cooling water 3 immediately above the cooling nozzle 2, and at that time, the cooling water 3 after the collision is changed with respect to the jet force at various levels through the injection flow rate and the injection pressure. The injection direction was investigated and it was determined whether or not it was possible to shut off.
Regarding the determination of whether or not to shut off, the main direction of the injection of the cooling water 3 bends at a bend angle θ from the horizontal to the diagonally upward in front of the steel plate path shown in FIG. In the range of degrees, it has been found that the falling water 9 does not come to the shut-off nozzle 21 side, that is, the cooling water 3 does not fall on the upper surface of the steel plate 10, so the jet of shut-off water vs. cooling water satisfying θ ≦ 45 ° The force range was defined as the range that can be shut off.

The result of the experiment is shown in FIG. The figure shows the jet force F _W = ρ _W Q _W P _W ^0.5 calculated by the equation (4) and the jet force F _S = ρ _S Q _{S of} the cutoff water 22 calculated by the equation (4). In the correspondence diagram with P _S ^0.5 , the relationship between the two becomes θ = 45 degrees is entered, and from this figure, the data is arranged using the jet force of both, θ = 45 their relationship to the degree is represented well by F S ₌ F _W becomes linear, F _S ≧ F _W becomes a range, i.e. the range satisfying the above formula (1) it has a cut-off range. Here, the subscript W means cooling water, and the subscript S means shut-off water.

In addition, as shown in FIG. 8, it is possible to block a plurality of cooling nozzles 2 (three in this example) with one blocking nozzle 21. In this case, as shown in the above formula (2), one shutoff nozzle 21 corresponding to the total jet force of cooling water from the plurality of cooling nozzles: Σρ _W Q _W P _W ^0.5 The squirting force of the blocking water 22 from ρ _S Q _S P _S ^0.5 should be equal or larger.

  In FIG. 2, the blocking nozzles 21 are arranged one by one between the cooling nozzles 2 in each row in the cooling line width direction, each of the blocking nozzles 21 is provided with an on / off valve 23, and the passage plate width An example is shown in which the cooling water 3 from the cooling nozzle 2 located on the outer side is blocked by the blocking water 22 injected by opening the on / off valve 23 of the blocking nozzle 21 adjacent to the center side of the plate width. However, it is not limited to this.

  For example, as shown in FIG. 3, the arrangement of the blocking nozzle 21 is the same as in the example of FIG. 2, but the injection of the blocking water 22 is most in the width range of the passage plate and at the end of the passage plate width. It is possible to use only the shut-off nozzle 21 at a close position. In this case, the wider the passage plate width, the smaller the number of cooling nozzles to be shut off. Therefore, according to the change of the passage plate width to the increase side (or decrease side), The injection pressure and the injection flow rate may be adjusted to the decreasing side (or increasing side).

  Further, as shown in FIG. 4, for example, the arrangement of the blocking nozzles 21 is such that one part between each of the cooling nozzles 2 in each row in the cooling line width direction and two sets of the cooling nozzles 2 are set. An arrangement in which one part is mixed between each set may be possible. In this arrangement form, when the number of cooling nozzles 2 that discharge the cooling water 3 toward the lower surface of the steel sheet increases or decreases by two by changing the pitch of the passage plate width by two, each set of the two sets is set. Each of them can be shut off by one shutoff nozzle 21 and is advantageous in that the equipment cost can be reduced because the number of shutoff nozzles can be reduced as compared with the examples of FIGS.

In the above-described embodiment, an example in which a flat spray nozzle is employed as the blocking nozzle has been described. However, a nozzle that forms a straight jet flow like a round jet nozzle may be employed depending on the application. .
From the viewpoint of efficiently shutting down the cooling water by increasing the jet force of the shutoff water from the shutoff nozzle, the spread width of the shutoff water at the position where it collides with the cooling water is almost equal to or slightly equal to that of the cooling water at the same position. It is preferable to make it wide (for example, about 100 to 150% of the cooling water spreading width). When a flat spray nozzle is used as the cooling nozzle, the cooling water spreads in a fan shape immediately after jetting, so the position where the blocking water collides with the cooling water is the position directly above the cooling nozzle (for example, 10-50 mm from the cooling nozzle jet port). It is preferable to set the position approximately upward) because the blocking process can be performed in a narrow area.

  As the blocking nozzle, it is preferable to use a flat spray nozzle that is wider than the round jet nozzle. In this case, if the fan-shaped jet has a spreading angle of 30 degrees or less, it can be used for cooling water with a sufficiently high jet force. It can be made to collide, and the interruption | blocking efficiency becomes high and is preferable.

Examples of the present invention will be described.
FIG. 9 shows a layout of a hot-rolled steel sheet production line that is a hot-steel sheet production line used in this example. In this hot-rolled steel sheet production line, a slab having a thickness of 220 mm is heated to about 1200 ° C. by a heating furnace 60, then rolled to a thickness of 35 mm by a rough rolling mill group 61, and rolled to 3.2 mm by a finish rolling mill group 62. The The rolled steel sheet 10 is subsequently cooled to a predetermined temperature by a run-out cooling device 51 provided on the run-out table 63 and then wound by a coiler 64. The runout table 63 has a maximum plate width of 2000 mm and a minimum of 600 mm.

In this example, a steel plate having a plate width of 700 mm and 1200 mm was passed.
The run-out cooling device 51 cools the upper surface of the steel plate by a hairpin laminar type upper surface cooling device 71 and cools the lower surface of the steel plate by a spray type lower surface cooling device 75. Here, the upper surface cooling device 71 is installed in a pair with the lower surface cooling device 75, and both are configured such that the destination of the cooling water sprayed when the plate is not passed is on the table roller in the installation area. The maximum plate width that can be cooled by the run-out cooling device 51 can cover the maximum plate width of 2000 mm. The temperature distribution of the steel sheet before and after cooling by the runout cooling device 51 can be measured by a radiation thermometer 65.

In the lower surface cooling device 75, a flat spray nozzle is used as the cooling nozzle 2 in the arrangement form shown in FIGS. 10 to 12. The nozzle specifications, geometric arrangement conditions, etc. are shown below.
・ Table roller diameter: 280 mm, table roller pitch: 350 mm
・ Injection fluid: water ・ Spreading angle: 75 degrees ・ Injection flow rate: 80 L / min / piece ・ Injection pressure: 0.1 MPa
... Cooling water jet force: 18.64N / piece ・ Distance between nozzle nozzle and underside of steel plate: 150mm
・ Pitch of nozzles in line: 150mm
・ Water density between table rollers: 3000 L / min / mm ²
In the example of the present invention, the cooling nozzle 2 is additionally installed in the lower surface cooling device 75 in the same embodiment as in FIGS. 2 and 3, and the cooling nozzle 2 located outside the plate width of the passing steel plate using this. The cooling nozzle 3 was used to cool the bottom surface while blocking the cooling water 3 from the cooling nozzle 2. In the blocking process here, a flat spray nozzle having a spreading angle of 25 degrees is used as the blocking nozzle 21, the injection fluid is water, the injection pressure is 2 MPa, and the jet force of the cutoff water 22 is changed by changing the injection flow rate. Various levels are set as shown below. The collision position between the blocking water 22 and the cooling water 3 was 30 mm above the cooling nozzle injection port.

On the other hand, in the comparative example, the blocking nozzle 21 was not additionally installed in the lower surface cooling device 75, and the lower surface cooling similar to the conventional one was performed.
The temperature distribution in the plate width direction of the upper surface of the steel plate 10 after cooling is measured by the radiation thermometer 65 on the exit side of the run-out cooling device 51, and the lower surface cooling is evaluated based on the temperature deviation in the plate width direction obtained from the measurement data. It was. In view of the material tolerance, the temperature deviation in the plate width direction needs to be 15 ° C. or less, preferably 10 ° C. or less.

Table 1 shows the evaluation results of the temperature deviation in the plate width direction and the lower surface cooling. In Table 1, the temperature deviation ΔT1 is “the temperature of the central portion—the temperature of the portion in the plate 20 mm away from the end of the plate width” in the plate width direction of the steel plate after cooling. When the temperature deviation ΔT1 was 15 ° C. or less, it was evaluated as good (◯), and when it exceeded 15 ° C., it was evaluated as defective (×).
From Table 1, it can be seen that ΔT1 is 15 ° C. or less in all of the examples of the present invention, and that the bottom surface can be cooled satisfactorily. Of the examples of the present invention, those satisfying the formula (1) or the formula (2) all have ΔT1 of 10 ° C. or less, and it can be seen that the lower surface cooling can be performed more satisfactorily. Thus, in the example of this invention, the supercooling of the edge part of a board width could be suppressed effectively, and the predetermined material was obtained also in any of the steel plate after cooling.

  On the other hand, in all the comparative examples, ΔT1 exceeds 15 ° C., and the lower surface cooling evaluation is poor. In Comparative Example 1 and Comparative Example 2, the amount of water falling from the outside of the plate width to the top surface of the plate is larger in Comparative Example 1 having a narrow passage plate width, and the degree of supercooling at the plate width end portion is large. Thus, in the comparative example, it was not possible to suppress overcooling at the end of the plate width, and a predetermined material could not be obtained in the cooled steel plate.

DESCRIPTION OF SYMBOLS 1 Header 2 Cooling nozzle 3 Cooling water 4 Table roller 9 Falling water 10 Steel plate (hot rolled steel plate)
21 Nozzle for blocking
22 Shut-off water 23 On-off valve
25 Collective flow of cooling water and shut-off water 51 Runout cooling device 60 Heating furnace 61 Coarse rolling mill group 62 Finish rolling mill group 63 Runout table 64 Coiler 65 Radiation thermometer 71 Upper surface cooling device 75 Lower surface cooling device

Claims (5)

A thermal steel plate lower surface cooling device in which cooling nozzles for spray cooling the lower surface of the steel plate are arranged in a row in the pass line width direction and a plurality of the rows are arranged in the longitudinal direction of the pass line under the pass line of the hot steel plate. A fluid is jetted outward in the line width direction, and the shut-off water, which is the jetted fluid, is caused to collide with the cooling water from the cooling nozzle at a position 10 to 50 mm above the cooling nozzle jet port, thereby A hot steel plate characterized in that a shut-off nozzle is installed that shuts off the cooling water from the cooling nozzle by bending the main direction at an angle θ of 45 degrees or less obliquely upward from the horizontal in front of the steel plate path. Underside cooling device. The blocking nozzle satisfies the following equation (1) when blocking one to one with respect to the cooling nozzle, and satisfies the following equation (2) when blocking one to many. The lower surface cooling device for a hot-steel plate according to claim 1.
_{^{ρ W Q W P W 0.5 ≦}} ρ S Q S P S 0.5 ‥‥ (1)
Σρ _W Q _W P _W ^0.5 ≦ ρ _S Q _S P _S ^0.5 (2)
ρ: fluid density, Q: fluid ejection flow rate, P: fluid ejection pressure, Σ: total subscript for a plurality of cooling nozzles corresponding to one shutoff nozzle W: fluid ejected from the cooling nozzle A certain cooling water, subscript S: shut-off water which is a jet fluid from the shut-off nozzle   The apparatus for cooling a lower surface of a hot steel sheet according to claim 1 or 2, wherein the blocking nozzles are arranged one by one in a part or all of the individual nozzles in each row of cooling nozzles.   The apparatus for cooling a lower surface of a hot-steel plate according to any one of claims 1 to 3, further comprising an on / off valve that individually opens and closes the blocking nozzle. The apparatus for cooling a lower surface of a hot steel sheet according to any one of claims 1 to 4, wherein the blocking nozzle is a flat spray nozzle having a spread angle of 30 ° or less.

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