JP2010227991A - Equipment for cooling hot steel plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for uniformly cooling upper and lower surfaces at high cooling rate. <P>SOLUTION: In the equipment for cooling a hot steel plate which is installed on the hot-rolling line of a steel plate, an upper header for supplying cooling water and upper cooling water jetting nozzles for jetting bar-like cooling water, which are hung from the upper header, are provided on the side of the upper surface of the steel plate, a lower header for supplying the cooling water and lower cooling water jetting nozzles for jetting bar-like cooling water upward in the vertical direction from the lower header are provided on the side of the lower surface of the hot steel plate and it is good to make a pitch W2 of collision points 14 of the cooling water for the lower surface of the steel plate with the lower cooling water jetting nozzles 4 in the width direction of the steel plate into a half of a pitch W1 of the collision points 13 of the cooling water onto the upper surface of the steel plate with the upper cooling water jetting nozzles 3 in the width direction. The installation density of the lower cooling water jetting nozzles is taken as 1.5-4 times the installation density of the upper cooling water jetting nozzles. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a thermal steel sheet cooling facility.

  In the process of manufacturing steel plates such as thick plates and thin plates by hot rolling, for example, in equipment as shown in FIG. 9, after hot rough rolling and finish rolling, the structure is controlled by water cooling or air cooling. Yes. When cooling to a relatively low temperature, for example, about 450 to 650 ° C. by water cooling, fine ferrite and bainite structure can be obtained and the strength of the steel sheet can be secured. Therefore, there is a technology for cooling the steel sheet with spray cooling water, laminar cooling water, etc. It is common. In recent years, the development of techniques for increasing the strength of steel sheets by obtaining a high cooling rate and making the structure finer is increasing.

  For example, there are technologies in Patent Document 1 and Patent Document 2 as a technology for cooling a hot steel sheet by supplying a large amount of rod-shaped laminar cooling water. This is one in which cooling water is jetted at high speed from nozzles installed on the upper and lower surfaces of a steel plate, and a very high cooling rate can be obtained and a product excellent in material characteristics can be manufactured.

JP 2001-246612 A JP 2004-66308 A

  However, the conventional technique has a problem in securing the cooling capacity and the cooling uniformity.

  The technology of Patent Document 1 is a cooling device for a hot-rolled steel strip after finish rolling, in which columnar laminar water is jetted symmetrically with respect to the steel strip from the nozzle holes of the upper and lower surface cooling boxes. It is said that the cooling conditions on the lower surface can be made exactly the same, and a uniform hot-rolled steel strip can be produced. Further, by making the fluid pressure applied to the upper and lower surfaces of the steel strip substantially equal, it is said that stable passage can be achieved even in a non-tensioned state.

  However, since the technology of Patent Document 1 has a structure in which only a nozzle hole is formed in the cooling box, when the cooling water sprayed from the lower surface cooling box to the lower surface of the steel strip naturally falls, the accumulated water on the upper end surface of the lower surface cooling box. Thus, it becomes an obstacle to the cooling water jetted later. In addition, in the upper surface cooling, the retained water after colliding with the steel strip surface has a certain cooling capacity, whereas in the lower surface cooling, the water after colliding with the steel strip surface falls naturally and does not participate in cooling. Cooling capacity is inferior for the bottom surface cooling. Therefore, it is difficult to cool the upper and lower surfaces uniformly if the cooling water is jetted symmetrically.

  Moreover, the technique of patent document 2 is provided with a cooling water jet nozzle protruding from the upper and lower cooling water headers, and a plurality of holes or slits in a protective plate provided between the cooling water header and the hot-rolled steel strip. The cooling water sprayed from the cooling nozzle passes through and the cooling water supplied to the steel strip is discharged from the same hole or slit. That is, since the functions of the injection port and the drain port coexist in the holes and slits of the protective plate, the flow of the cooling drainage is reverse to the rod-shaped cooling water sprayed from the nozzle tip as shown in FIG. It was. Also, the discharged water after reaching the steel plate rises by colliding with each other, and the flow path is bent until it reaches the drain outlet that is also used as the nozzle port, so this part becomes a stagnation and the discharged water Smooth flow was hindered.

  Thus, it has been found that the technique of Patent Document 2 has some difficulty in smooth discharge of the cooling water supplied to the steel strip surface. Therefore, it is difficult to cool the steel strip uniformly in the vertical and width directions, and in order to ensure that the cooling water reaches the steel plate, the cooling water must be sprayed at a high speed by applying a high jet pressure to the header. Therefore, there is a problem that equipment costs are required.

  In view of the above, an object of the present invention is to provide a technique for uniformly cooling upper and lower surfaces at a high cooling rate when supplying cooling water to the upper and lower surfaces of a hot steel sheet.

In order to solve the above problems, the present invention has the following features.
1st invention is the cooling equipment of the hot-steel plate installed in the hot rolling line of a steel plate, Comprising: On the upper surface side of a hot-steel plate, the upper header which supplies cooling water, and the rod-shaped cooling water suspended from the upper header An upper cooling water injection nozzle that injects cooling water, and a lower header that supplies cooling water and a lower cooling water injection nozzle that injects rod-shaped cooling water vertically upward from the lower header on the lower surface side of the thermal steel plate. And a thermal steel sheet cooling facility characterized in that the installation density of the lower cooling water injection nozzle is 1.5 to 4 times the installation density of the upper cooling water injection nozzle.

In the second aspect of the invention, the upper surface side cooling water amount density of the hot steel sheet is 1.5 to 4.0 m ³ / m ² · min, and the lower surface side cooling water amount density is 2.0 to 8.0 m ³ / m ^2. -It is set to min, and the water volume density of the lower surface side cooling water is 1.3 to 2.0 times the water volume density of the upper surface side cooling water. is there.

  3rd invention sets the inner diameter of the upper cooling water injection nozzle installed in the upper surface side of a hot-steel plate to 3-8 mm, the distance from the lower end part of the said upper cooling-water injection nozzle to a hot-steel plate upper surface, 30-120 mm, said upper part The flow rate of the cooling water injected from the cooling water injection nozzle is 8 m / s or more, the inner diameter of the lower cooling water injection nozzle installed on the lower surface side of the thermal steel plate is 3 to 10 mm, and the lower cooling water injection nozzle is injected from the lower cooling water injection nozzle. The cooling water flow rate of 2 m / s or more and 90% or less of the flow rate of the cooling water jetted from the upper cooling water jet nozzle. Equipment.

  The fourth invention further comprises a partition wall between the thermal steel plate and the upper header on the upper surface side of the thermal steel plate, and the partition wall includes a water supply port for interpolating a lower end portion of the upper cooling water spray nozzle, The cooling facility for a hot steel sheet according to any one of the first to third inventions, wherein a plurality of drain outlets for draining the cooling water supplied to the upper surface of the hot steel sheet are provided on the partition wall. is there.

  By using the hot steel sheet cooling equipment of the present invention, a high cooling rate can be obtained for both the upper and lower surfaces of the steel sheet, and the steel sheet can be cooled quickly and uniformly to the target temperature, contributing to productivity improvement and material properties such as high strength. An excellent steel sheet can be manufactured. Moreover, since the upper surface of the steel sheet can be cooled uniformly in the width direction of the steel sheet without any temperature unevenness, a high-quality steel sheet can be manufactured.

It is a figure explaining the cooling equipment which concerns on one Embodiment of this invention. It is a figure explaining the cooling water collision point in the steel plate upper and lower surfaces of this invention. It is a figure explaining the cooling installation which concerns on other embodiment of this invention. It is a figure explaining the example of nozzle arrangement | positioning in a partition. It is a figure explaining the flow of the cooling waste water on a partition. It is a figure which shows an example of the relationship between the nozzle installation density ratio of the upper and lower surfaces, and the cooling capacity ratio of an upper and lower surface. It is a figure explaining the steel plate width direction temperature distribution by a prior art example. It is a figure explaining the steel plate width direction temperature distribution by this invention. It is a figure explaining the outline of a thick plate rolling line. It is a figure explaining the flow of the cooling water by a prior art example. It is a figure explaining the flow of the cooling water of this invention. It is a figure explaining non-interference with the cooling drainage on the partition of the present invention.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. Here, the case where the present invention is used for cooling a steel plate in a thick plate rolling process will be described as an example.

  FIG. 9 is a schematic view showing an example of a thick plate rolling line used for carrying out the present invention. The slab extracted from the heating furnace is subjected to rough rolling and finish rolling by a rolling mill to a predetermined finishing temperature and finishing plate thickness, and then conveyed to an accelerated cooling facility online. It is suitable for the steel plate shape after cooling to perform accelerated cooling after adjusting the shape of the steel plate through a pre-leveler before cooling. In the accelerated cooling facility, the steel sheet is cooled to a predetermined temperature by the cooling water sprayed from the upper surface cooling facility and the lower surface cooling facility.

(First embodiment)
FIG. 1 is a view showing an upper and lower surface cooling facility according to an embodiment of the present invention, and is a side view showing an arrangement of the cooling facility.

  The upper surface cooling facility includes an upper header 1 for supplying cooling water to the upper surface of the hot steel plate 12, and an upper cooling water injection nozzle 3 suspended from the upper header 1. The upper cooling water injection nozzle 3 is a rod-shaped cooling water. It consists of the circular tube nozzle 3 which injects. The lower surface cooling facility also includes a lower header 2 for supplying cooling water to the lower surface of the hot steel plate 12, and a lower cooling water injection nozzle 4 for injecting cooling water from the lower header 2 in the vertical direction, similar to the upper surface cooling facility. The lower cooling water injection nozzle 4 also includes a circular pipe nozzle 4 for injecting rod-shaped cooling water. In the cooling on the lower surface side of the steel sheet, the injected cooling water naturally falls after colliding with the steel sheet, so that even if there is no partition wall 5 for discharging cooling drainage such as cooling on the upper surface side in the width direction of the steel sheet, it is uniform. High cooling can be performed.

  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 2 m / s or more, and it refers to cooling water of continuous and straight water flow in which the cross section of the water flow injected from the nozzle outlet 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.

  By the way, in general, lower surface cooling is inferior in cooling capacity to upper surface cooling, and in order to perform uniform cooling on the upper and lower surfaces, a little more cooling water must be supplied to lower surface cooling than upper surface cooling. Don't be. As described above, in the upper surface cooling, the retained water after colliding with the steel sheet surface has some cooling capacity, whereas in the lower surface cooling, the water after colliding with the steel sheet surface falls naturally and does not participate in the cooling. Because.

  On the other hand, in the prior art, as described above with respect to Patent Document 1, the number of cooling nozzles on the upper and lower surfaces is the same, and the flow velocity is made equal on the upper and lower surfaces, or the upper surface side is used to solve the lack of cooling capacity on the lower surface side. However, in this case, the pressure of the lower surface cooling pump must be increased. For example, if the number of nozzles and the number of nozzles installed are the same on the top and bottom surfaces, and the water density of the bottom surface cooling is 1.5 times that of the top surface cooling and the top and bottom uniform cooling is attempted, the bottom surface cooling will have a flow rate 1.5 times that of the top surface cooling Since this is necessary, the equipment cost and running cost increase. Therefore, in the present invention, the cooling capacity is increased by increasing the number of nozzles for lower surface cooling and increasing the area of the direct injection portion.

  Further, the upper surface cooling water needs to break a staying water film on the hot steel plate, and therefore requires a certain high flow rate. On the other hand, the bottom surface cooling water does not have a stagnant water film, so it only needs to reach the hot steel plate, and a high flow rate is not required, so when using the same flow rate density, increase the number of nozzles and slow down the flow rate. Can do.

  Therefore, in the present invention, the number of nozzles for lower surface cooling that is inferior in cooling capacity is made larger than that for nozzles for upper surface cooling. Thereby, although the cost of the nozzle itself is high, the cost of equipment such as a pump for cooling the bottom surface and the running cost can be kept low.

  The above principle will be described in detail. FIG. 6 is a diagram illustrating an example of the relationship between the nozzle installation density ratio of the upper and lower surfaces and the cooling capacity ratio of the upper and lower surfaces. As shown by point A in the figure, in the conventional case where the nozzle installation density on the upper and lower surfaces is the same, in order to make the cooling capacity on the upper and lower surfaces equal (the cooling capacity ratio is 1), the flow rate density of the lower surface cooling Required 1.5 times the top cooling. However, even with the same flow density, if the nozzle installation density on the lower surface side is increased and the total area of the portion directly exposed to the cooling water is increased, the cooling capacity is improved (for example, the nozzle installation density on the lower surface is 1.5 times higher). (See point B in the figure).

  Therefore, if the nozzle installation density on the lower surface side is increased by 1.5 times, the flow rate of the lower surface cooling water is about 0.9 times that of the upper surface cooling and the flow rate density of the lower surface cooling is increased to the upper surface as shown by point C in the figure. Even if the cooling capacity is reduced to 1.3 times that of cooling, the cooling capacity ratio becomes 1, and uniform cooling can be realized. Therefore, the flow rate density and the injection pressure of the lower surface cooling can be lowered as compared with the conventional case. Thus, if the optimal nozzle installation density that maximizes the bottom surface cooling capacity is selected, the flow density necessary for bottom surface cooling is minimized, and the equipment cost can be reduced.

  Based on the above knowledge, in the present invention, the conditions of the upper surface cooling and the lower surface cooling are defined as follows.

  In the present invention, the installation density of the lower surface cooling nozzle is increased to 1.5 to 4 times the installation density of the upper surface cooling nozzle. For example, FIG. 2 is a diagram for explaining the collision point of the cooling water with the upper and lower surfaces of the steel sheet. As shown in FIG. 2, the steel sheet width direction pitch W2 of the steel sheet lower surface cooling water collision point 14 by the lower cooling water injection nozzle 4 is shown. Is half the width direction pitch W1 of the steel plate upper surface cooling water collision point 13 by the upper cooling water injection nozzle 3. The upper limit of the installation density of the lower cooling water injection nozzle 4 is four times the installation density of the upper cooling water injection nozzle 3. This is because if the nozzle pitch is too short, there will be no space for inserting the nozzles one by one, and the number of nozzles will increase and the equipment cost will become too high.

  The optimum nozzle installation density varies depending on the inner diameter of the nozzle to be used and the required cooling capacity. For example, if the nozzle diameter is small, the amount of water that can be sprayed from each nozzle is small, so the number of upper surface cooling nozzles is originally large, and there is little room to increase the cooling capacity by further increasing the number of lower surface cooling nozzles. The optimum installation density is about 1.5 times that of the upper surface cooling nozzle. On the other hand, if the nozzle diameter is large, the amount of water that can be sprayed from each nozzle is large, and the nozzle spacing for the top surface cooling is quite large, so even if the installation density of the bottom surface cooling nozzles is increased to about 4.0 times, Cooling capacity continues to increase.

The range of the water density of the top surface cooling that is most effective in the present invention is 1.5 m ³ / m ² · min or more. When the water density is lower than this, the staying water film does not become so thick, and even if the known technology of cooling the steel plate by free-falling the rod-shaped cooling water is applied, the temperature unevenness in the width direction does not become so large There is also. On the other hand, even when the water density is higher than 4.0 m ³ / m ² · min, it is effective to use the technique of the present invention, but there are problems in practical use such as an increase in equipment cost. The most practical water density is 1.5 to 4.0 m ³ / m ² · min.

In addition, as described above, in order to perform uniform cooling on the upper and lower surfaces, the water volume density of the lower surface cooling is 1.3 to 2.0 times that of the upper surface cooling so that the same cooling capacity can be obtained on the upper and lower surfaces. It is preferable to prevent the occurrence of warpage due to thermal strain and the difference in material between the upper and lower surfaces of the steel sheet. That is, the range of the water density of the bottom surface cooling is 2.0 m ³ / m ² · min or more. This is because if the water density is lower than this, the same cooling capacity as that of the upper surface cannot be secured.

On the other hand, even when the water density is higher than 8.0 m ³ / m ² · min, it is effective to use the technology of the present invention, but the capacity of the water pump increases the equipment cost such as the enhancement of drainage equipment. Since there is a problem in practical use, 2.0 to 8.0 m ³ / m ² · min is the most practical water density.

  Furthermore, in order to allow the cooling water to penetrate the staying water film and reach the steel plate, it is necessary to optimize the inner diameter of the circular tube nozzle, the cooling water injection speed and the nozzle distance.

  That is, the inner diameter of the upper cooling water spray nozzle 3 is preferably 3 to 8 mm. If it is smaller than 3 mm, the bundle of water sprayed from the nozzle becomes thin and the momentum becomes weak. On the other hand, when the diameter of the upper cooling water injection nozzle exceeds 8 mm, the flow velocity becomes slow and the force penetrating the staying water film becomes weak. The jetting speed of the cooling water from the upper cooling water jet nozzle needs to be 8 m / s or more. This is because if it is less than 8 m / s, the force that the cooling water penetrates through the staying water film becomes extremely weak.

  The distance from the lower end of the upper cooling water spray nozzle 3 for upper surface cooling to the surface of the steel plate 12 is preferably 30 to 120 mm. If it is less than 30 mm, the frequency with which the steel plate 12 collides with the upper cooling water spray nozzle becomes extremely high, and the equipment maintenance becomes difficult. This is because if the thickness exceeds 120 mm, the force through which the cooling water penetrates the staying water film becomes extremely weak.

  On the other hand, the inner diameter of the nozzle for cooling the lower surface is preferably 3 to 10 mm. If it is smaller than 3 mm, the nozzle is likely to be clogged. On the other hand, if the inner diameter of the nozzle exceeds 10 mm, the nozzle pitch must be set longer as the cross-sectional area of the water bundle increases. If the number of points where the cooling water directly hits the lower surface of the steel sheet is decreased, the cooling capacity is lowered. Therefore, it is possible to obtain a higher cooling capacity by shortening the nozzle pitch than by increasing the nozzle inner diameter to exceed 10 mm.

  Moreover, the injection speed of the lower surface cooling water needs to be 2 m / s or more. If the speed is less than 2 m / s, the height of the fountain becomes 200 mm or less, and the cooling water just hits the lower surface of the steel sheet.

  Furthermore, the distance from the upper end of the cooling water spray nozzle 4 for lower surface cooling to the lower surface of the steel plate 12 is preferably 30 to 180 mm. If it is less than 30 mm, the frequency with which the steel plate 12 collides with the circular tube nozzle 4 becomes extremely high, and equipment maintenance becomes difficult. This is because if it exceeds 180 mm, there is a high probability that the cooling water falling after colliding with the steel plate 12 will break the water bundle of cooling water newly injected.

  The flow rate of the lower surface cooling water may be 90% or less of the upper surface cooling. If the nozzle installation density of the bottom surface cooling is 1.5 times that of the top surface cooling, the water density of the bottom surface cooling is about 1.3 times that of the top surface cooling, so that uniform cooling can be achieved up and down, so the bottom surface cooling flow rate is 90%. This is because the water density can be achieved sufficiently.

  In addition, it is particularly effective to install the draining roll 10 before and after the cooling header 1 so that the cooling water is not scattered widely in the cooling of the upper surface of the steel sheet when the cooling technique of the present invention is applied. It is possible to apply even when there is no draining roll. For example, the header is relatively long in the longitudinal direction (when it is about 2 to 4 m), and is applied to a cooling facility that sprays a water spray for purging before and after the header to prevent water leakage to the non-water cooling zone. Is also possible.

(Second Embodiment)
FIG. 3 is a view showing an upper and lower surface cooling facility according to another embodiment of the present invention, and is a side view showing an arrangement of the cooling facility.

  The top surface cooling facility is horizontally disposed across the steel plate width direction between the header 1 for supplying cooling water to the top surface of the hot steel plate 12, the cooling water injection nozzle 3 suspended from the header 1, and the header 1 and the hot steel plate 12. A partition wall 5 having a large number of through holes (water supply port 6 and drain port 7) is provided. The cooling water injection nozzle 3 is composed of a circular pipe nozzle 3 for injecting rod-shaped cooling water, and the tip thereof is inserted into a through hole (water supply port 6) provided in the partition wall 5 so that the lower end portion of the partition wall 5 It is installed to be on the top.

  The circular tube nozzle 3 is installed so that the tip of the circular tube nozzle 3 is inserted into the through-hole and above the lower end of the partition wall 5 even if a steel plate whose tip is warped upward enters. This is to prevent the tube nozzle 3 from being damaged. Thereby, since the circular tube nozzle 3 can be cooled over a long period of time in a good state, it is possible to prevent the occurrence of temperature unevenness in the steel sheet without performing equipment repair or the like.

  Further, since the tip of the circular tube nozzle 3 is inserted into the through-hole, as shown in FIG. 12, there is no interference with the flow in the width direction of the drained water indicated by the dotted arrow flowing through the upper surface of the partition wall 5. Therefore, the cooling water sprayed from the circular tube nozzle 3 can reach the upper surface of the steel plate equally regardless of the position in the width direction, and uniform cooling in the width direction can be performed.

  As an example, as shown in FIG. 4, a large number of through holes having a diameter of 10 mm are formed in the partition wall 5 in the grid. A circular tube nozzle 3 having an outer diameter of 8 mm, an inner diameter of 3 mm, and a length of 140 mm is inserted into the water supply port 6. The circular tube nozzles 3 are arranged in a staggered pattern, and the through holes through which the circular tube nozzles 3 do not pass serve as cooling water drains 7. As described above, the large number of through holes provided in the partition wall 5 of the cooling facility of the present invention are composed of substantially the same number of water supply ports 6 and drain ports 7, and share their roles and functions.

  At this time, the total cross-sectional area of the drain port 7 is ensured to be about 11 times the total cross-sectional area of the inner diameter of the circular tube nozzle 3, and the cooling water supplied to the upper surface of the steel plate as shown in FIG. Through the partition wall 5. FIG. 5 is a front view for explaining the flow of cooling drainage near the end in the width direction of the steel plate on the partition wall. The drainage direction of the drain port 7 is upward opposite to the cooling water injection direction, and the upper side of the partition wall 5 The cooling drainage that has passed through is turned to the outside in the width direction of the steel sheet and flows through the drainage flow path between the header 1 and the partition wall 5 and is drained.

  Here, as shown in FIG. 10, when the drainage port and the water supply port are installed in the same through hole, the cooling water is difficult to come out above the partition wall 5 after colliding with the steel plate, and the steel plate 12 and the partition wall. 5 flows toward the end in the steel sheet width direction. Then, since the flow rate of the cooling drainage between the steel plate 12 and the partition wall 5 increases as it approaches the end in the plate width direction, the force that the injected cooling water reaches the steel plate through the staying water film is the end in the plate width direction. It will be hindered.

  In the case of a thin plate, since the plate width is about 2 m at most, the influence is limited. However, in the case of a thick plate having a plate width of 3 m or more, the influence cannot be ignored. Accordingly, the cooling at the end in the width direction of the steel sheet becomes weak, and the temperature distribution in the width direction of the steel sheet in this case becomes a non-uniform temperature distribution having a concave shape as shown in FIG.

  On the other hand, in the cooling facility of this embodiment, as shown in FIG. 11, the water supply port 6 and the water discharge port 7 are provided separately and share the roles of water supply and water discharge. And smoothly flows above the partition wall 5. Accordingly, since the drainage after cooling is quickly removed from the upper surface of the steel sheet, the cooling water supplied subsequently can easily penetrate the staying water film, and a sufficient cooling capacity can be obtained. In this case, the temperature distribution in the width direction of the steel sheet can obtain a uniform temperature distribution in the width direction as shown in FIG.

  The upper surface cooling facility and the lower surface cooling facility in the present embodiment are the same as those in the first embodiment except that the partition wall 5 is provided in the upper surface cooling facility. That is, the nozzle installation density of the upper surface cooling and the lower surface cooling, the nozzle inner diameter, the distance from the nozzle to the hot steel plate, the water amount density, and the cooling water flow rate may be the conditions described in the first embodiment.

  According to the present embodiment, as in the first embodiment, a high cooling rate can be obtained uniformly on both the upper and lower surfaces of the steel plate, and uniform cooling can be performed particularly in the steel plate width direction. Can be manufactured.

  Hereinafter, as an embodiment of the present invention, a case of cooling a steel plate having a tensile strength of 590 MPa class in a thick plate rolling process will be described with reference to the drawings.

  In the thick plate rolling facility schematically shown in FIG. 9, the slab extracted from the heating furnace is formed by a rolling mill, subjected to tenter rolling, then rough rolled, and further subjected to finish rolling to obtain a plate thickness of 25 mm, The plate width was 4.5 m. The steel sheet surface temperature measured immediately after finish rolling, that is, the finish temperature was 820 ° C. Thereafter, accelerated cooling was performed in an accelerated cooling facility through a hot leveler. Cooling was performed from a cooling start temperature of 780 ° C. to a cooling end temperature of 560 ° C. (a value obtained by measuring the temperature after reheating on the accelerated cooling equipment exit side).

As the cooling equipment of Example 1 of the present invention, the upper and lower surface cooling equipment according to the first embodiment of the present invention shown in FIG. 1 was used. For both the upper and lower surfaces, cooling water spray nozzles having an inner diameter of 5 mm and an outer diameter of 9 mm were used, and the nozzles were arranged in nine rows at a 100 mm pitch in the transport direction in a zone with a distance between table rollers of 0.9 m. Further, the top surface cooling was performed at a water density of 1.50 m ³ / m ² · min with a width direction nozzle pitch of 90 mm and a cooling water injection speed of 11.45 m / s.

On the other hand, in the lower surface cooling, the nozzle pitch density in the width direction was set to 60 mm, 1.5 times the nozzle installation density of the upper surface cooling, and the cooling water injection speed was set to 10.19 m / s. The water density on the lower surface side at this time is 2.00 m ³ / m ² · min.

On the other hand, as a comparative example, a cooling device in which the nozzle pitch in the width direction of the bottom surface cooling was 90 mm in Example 1 of the present invention, that is, a cooling device having the same nozzle installation density on the top and bottom surfaces was used. And in the comparative example 1, the injection of the cooling water which made the water amount density of the lower surface side the same 2.00 m < ³ > / m < ² > * min as the upper surface side was performed. On the other hand, in Comparative Example 2, the water amount density on the lower surface side was set to 2.25 m ³ / m ² · min, 1.5 times that on the upper surface side, so that the cooling capacity was equal on the upper and lower surfaces.

  Table 1 shows the nozzle specifications and cooling conditions in this example, along with the occurrence of warpage of the steel sheet after cooling.

  In Comparative Example 1, since the water density of the upper and lower surfaces was equal and the upper surface cooling was stronger than the lower surface cooling, the steel plate was warped. In Comparative Example 2, since the same cooling capacity as that of the upper and lower sides was obtained on the lower surface side, the warpage of the steel plate did not occur, but an injection speed as high as 17.18 m / s was required as the lower surface cooling water injection speed. .

  On the other hand, in Example 1 of the present invention, equal cooling ability was obtained on the upper and lower surfaces, and not only the warpage of the steel sheet did not occur, but also the cooling water injection speed and the water amount density on the lower surface side were smaller than those in Comparative Example 2. As a result, it can be seen that the cost of equipment such as pumps and piping can be reduced, the amount of cooling water used can be reduced, and the running cost can be reduced.

  As Example 2 of the present invention, instead of the upper and lower surface cooling facilities used in Inventive Example 1 of Example 1, the upper and lower surface cooling described in FIG. 3 has a partition wall in the upper cooling facility according to another embodiment of the present invention. The same thick plate rolling as in Example 1 was performed using the equipment.

  This cooling equipment is an equipment provided with a flow path that allows the cooling water supplied to the upper surface of the steel plate to flow above the partition as shown in FIG. 3 and further drains from the side of the steel plate width direction as shown in FIG. is there. In the partition wall, holes with a diameter of 12 mm were formed like a grid, and as shown in FIG. 4, circular nozzles were passed through nozzle ports arranged in a staggered pattern, and the remaining holes were used as drain ports. The lower end of the nozzle for cooling the upper surface was installed so as to be at an intermediate position between the upper and lower surfaces of the partition wall having a thickness of 25 mm, and the distance to the steel plate surface was 80 mm. The distance between the header lower surface and the partition upper surface was 100 mm.

For the cooling water injection nozzle, the upper surface side has an inner diameter of 8 mm and an outer diameter of 12 mm, and the lower surface side has an inner diameter of 10 mm and an outer diameter of 14 mm. Nine rows were arranged. The top surface cooling was performed at a water density of 4.00 m ³ / m ² · min with a width direction nozzle pitch of 90 mm and a cooling water injection speed of 11.94 m / s.

On the other hand, in the lower surface cooling, the nozzle pitch density in the width direction was set to 45 mm, 2.0 times the nozzle installation density of the upper surface cooling, and the cooling water injection speed was set to 7.64 m / s. The water density on the lower surface side at this time is 8.00 m ³ / m ² · min.

  On the other hand, as Comparative Example 3, the nozzle specifications and cooling water injection conditions are the same as in Example 2 of the present invention, but instead of the partition wall of the present invention in which the water inlet and the drain port are separately provided, Patent Document 2 A partition wall provided with the slit-like holes described was used.

  Table 1 shows the nozzle specifications and cooling conditions in this example, together with the occurrence of temperature unevenness in the steel plate width direction after cooling.

  In the cooling facility of Example 2 of the present invention, the jet cooling water hitting the upper surface of the steel plate flowed upward and was quickly discharged. Furthermore, the drainage to the edge of the board was very good. Since the drainage after cooling is quickly eliminated, the cooling water supplied subsequently can easily penetrate the staying water film, and a higher upper surface cooling capacity than before can be obtained.

  In the lower surface cooling, since the nozzle installation density was doubled that of the upper surface cooling, the number of points where the cooling water directly hits the lower surface of the steel sheet doubled. And since the flow rate density was doubled that of the top surface cooling, the cooling capacity could be increased efficiently. As a result, even with bottom cooling that does not contribute to cooling of stagnant water, the same cooling capacity can be secured on the top and bottom surfaces, so that warpage due to thermal strain can be prevented and the difference in material between the top and bottom surfaces of the steel plate does not occur. I was able to.

  The cooling time for setting the cooling stop temperature at the center of the plate width to 560 ° C. was 2.5 seconds. Since the cooling rate is increased, it is possible to reduce the steel alloy components (for example, Mn) necessary for obtaining high strength, and to reduce the manufacturing cost.

  The temperature distribution in the width direction of the steel sheet was 550 to 560 ° C., and the distribution was almost uniform as shown in FIG. For this reason, the pass rate of the material test was as high as 99.5%, and the yield was also sufficiently high.

  Since the lower end of the nozzle is set at the middle position between the upper and lower ends of the partition wall, the partition wall served as a protective plate even when the upper warp could not be corrected by the pre-leveler, and the nozzle was not broken.

  On the other hand, in the cooling facility of Comparative Example 3, as shown in FIG. 10, the cooling water after colliding with the steel plate is difficult to escape upward, so that the cooling stop temperature at the center of the plate width is 560 ° C. A water cooling time of 3 seconds was required.

  The distribution of the cooling stop temperature in the plate width direction was concave as shown in FIG. The highest temperature near the edge of the plate was 600 ° C., and the temperature unevenness in the width direction (maximum temperature-minimum temperature) was 40 ° C. As a result of taking out a part of the product and conducting a material test, the acceptance rate was as low as 70% and the yield was also poor.

  Moreover, although the hole was vacant in the slit shape in the partition, the rigidity of this part was weak, and when the warped steel plate collided, the partition and the nozzle were deformed and damaged.

1 Upper header 2 Lower header 3 Upper cooling water injection nozzle (circular tube nozzle)
4 Lower cooling water injection nozzle (circular tube nozzle)
5 Bulkhead 6 Water supply port 7 Drain port 8 Spray cooling water 9 Drained water 10 Draining roll 11 Table roll 12 Steel plate 13 Steel plate upper surface cooling water collision point 14 Steel plate lower surface cooling water collision point W1 Steel plate width direction pitch L1 of upper cooling water injection nozzle Steel sheet conveying direction pitch of cooling water injection nozzle W2 Steel sheet width direction pitch of lower cooling water injection nozzle L2 Steel sheet conveying direction pitch of lower cooling water injection nozzle

Claims (4)

  An apparatus for cooling a hot steel plate installed in a hot rolling line for a steel plate, and an upper header for supplying cooling water to the upper surface side of the hot steel plate, and an upper cooling water for injecting rod-like cooling water suspended from the upper header A lower header for supplying cooling water, and a lower cooling water injection nozzle for injecting rod-shaped cooling water vertically upward from the lower header, and the lower cooling water. A thermal steel sheet cooling facility, characterized in that an installation density of injection nozzles is 1.5 to 4 times an installation density of the upper cooling water injection nozzle. The upper surface side cooling water amount density of the hot steel sheet is 1.5 to 4.0 m ³ / m ² · min, the lower surface side cooling water amount density is 2.0 to 8.0 m ³ / m ² · min, and the lower surface The water density of the side cooling water is 1.3 to 2.0 times the quantity of water density of the upper surface side cooling water.   The inner diameter of the upper cooling water injection nozzle installed on the upper surface side of the hot steel plate is 3 to 8 mm, the distance from the lower end of the upper cooling water injection nozzle to the upper surface of the hot steel plate is 30 to 120 mm, and the upper cooling water injection nozzle is injected from the upper cooling water injection nozzle The cooling water flow rate is 8 m / s or more, the inner diameter of the lower cooling water injection nozzle installed on the lower surface side of the hot steel plate is 3 to 10 mm, and the cooling water flow rate injected from the lower cooling water injection nozzle is 3. The thermal steel sheet cooling equipment according to claim 1, wherein the temperature is set to 2 m / s or more and 90% or less of a flow rate of the cooling water injected from the upper cooling water injection nozzle.   Further, a partition wall is provided between the hot steel plate and the upper header on the upper surface side of the hot steel plate, and a water supply port for inserting a lower end portion of the upper cooling water spray nozzle is provided on the upper surface of the hot steel plate. 4. The hot steel sheet cooling facility according to claim 1, wherein a plurality of drain outlets for draining the supplied cooling water onto the partition walls are provided.

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