JP5228720B2 - Thick steel plate cooling equipment - Google Patents

Description

  The present invention relates to a cooling facility for thick steel plates.

  In the process of manufacturing a thick steel plate by hot rolling, for example, in the equipment as shown in FIG. 13, after hot rough rolling and finish rolling, the structure is controlled by water cooling or air cooling. 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 is a technique of Patent Document 1 as a technique for rapidly cooling a hot steel sheet by supplying a large amount of cooling water. This is because many cooling banks are installed on the upper and lower surfaces of the hot-rolled steel strip, each cooling bank is separated by a draining roll, and the number of cooling water discharge banks is increased or decreased depending on the transport speed and finishing temperature of the steel strip. It is said that even at a very high cooling rate, it is possible to produce a product having excellent material properties that are homogeneous in the longitudinal direction of the steel strip.

Moreover, there exists a technique of patent document 2 as another technique which cools a hot-steel plate by supplying cooling water. This makes it possible to supply a large flow rate of spray cooling water between draining rolls, and it is said that a wide range of cooling rates can be secured and cooling uniformity can be improved in a wide temperature range.
JP 2003-145214 A JP 2006-35311 A

However, in order to rapidly cool a thick steel plate, the conventional technique has a problem in securing cooling capacity and cooling uniformity.
The technique of Patent Document 1 is to supply a large amount of cooling water in order to obtain a high cooling rate, and the cooling water film staying on the upper surface of the steel sheet becomes thicker as the amount of cooling water is increased. When a large amount of cooling water is supplied, the accumulated water may get over the draining roll and overflow into the adjacent cooling zone. If the stagnant water overflows into the non-cooling zone, that is, the air cooling zone, the steel plate is overcooled and temperature unevenness occurs, making it impossible to produce a steel plate with uniform quality. In particular, in the case of a thick steel plate, since the plate width is wide and the cooling water supplied near the center of the plate width is difficult to drain from the end portion of the plate width, the water level of the water film tends to be high. Therefore, it was necessary to suppress the amount of cooling water to such an extent that stagnant water does not overflow from the draining roll.

Since the technique of Patent Document 2 uses a spray nozzle, cooling water must be injected at a high pressure. In spray cooling, since cooling water is sprayed from a nozzle in a spray form, if the staying water film is thick as described above, the momentum of the cooling water is greatly attenuated by the staying water film and cannot reach the steel plate. Therefore, it can be applied only in the range where the water density is about 2.0 m ³ / m ² · min, and even if more cooling water is supplied, the cooling capacity is not increased.

  Furthermore, when cooling water is supplied by a spray nozzle, the pressure loss at the spray nozzle is larger than that of a laminar nozzle. Therefore, the pressure of the cooling water supply header must be much higher in spray cooling than in laminar cooling, and there is a problem that the cost of equipment for pumps and piping becomes enormous.

  In view of the above, an object of the present invention is to provide a technique for supplying a large amount of cooling water to the upper surface of the steel sheet and uniformly cooling it at a high cooling rate when supplying the cooling water to the upper surface of the thick steel sheet. .

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

  1st invention is the cooling equipment installed in the hot rolling line of a thick steel plate, Comprising: The header which supplies a cooling water to the upper surface of a thick steel plate, The cooling water injection which injects the rod-shaped cooling water suspended from this header A nozzle and a draining roll disposed on the upstream side and the downstream side of the header in the conveying direction of the thick steel plate and facing the table roll with the thick steel plate sandwiched therebetween, and the wetting height of the staying water film by the draining roll is 300 mm or more It is the cooling equipment of the thick steel plate characterized by these.

  The second invention comprises a plurality of the header and the draining rolls arranged upstream and downstream of the header in the steel plate conveying direction, and at least by the draining rolls on the most upstream side and the most downstream side in the steel plate conveying direction. The thick steel plate cooling facility according to the first aspect of the present invention is characterized in that the dam height of the staying water film is 300 mm or more.

According to a third aspect of the present invention, there is provided a cooling water jet nozzle having a water volume density of 2.0 m ³ / m ² · min or more, a nozzle length of the cooling water jet nozzle of 100 mm or more, The distance from the lower end to the surface of the thick steel plate is 30 to 120 mm. The cooling facility for the thick steel plate according to the first or second invention.

  According to a fourth aspect of the present invention, a large-diameter draining roll having a diameter of 300 mm or more and 450 mm or less is used as a draining roll having a retaining water film damming height of 300 mm or more. It is the cooling equipment of the thick steel plate in any one.

  The fifth invention is characterized in that the sum of the diameters of the backup roll and draining roll is set to 300 mm or more by using a draining roll having a backup roll as the draining roll having a retaining water film damming height of 300 mm or more. The thick steel plate cooling equipment according to any one of the first to third aspects of the invention.

  By using the thick steel plate cooling equipment of the present invention, a large flow rate of cooling water can be supplied to the upper surface of the steel plate, a high cooling rate can be obtained, and a high strength steel plate can be produced. Moreover, since cooling of the upper surface of a steel plate can be performed uniformly over the entire surface, a high-quality steel plate can be produced.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings.

FIG. 13 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 to obtain a uniform material by performing accelerated cooling after adjusting the shape of the steel sheet 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.

FIG. 1 is a side view showing an arrangement of a top surface cooling facility according to an embodiment of the present invention.
The upper surface cooling equipment of the present invention includes an upper header 1 for supplying cooling water to the upper surface of the thick steel plate 12, an upper cooling water injection nozzle 3 suspended from the upper header 1, and a draining roll 10 installed before and after the upper header 1. Has been. The upper cooling water spray nozzle 3 is composed of a circular tube nozzle 3 for spraying rod-shaped cooling water, and is installed at a constant pitch in the width direction and the longitudinal direction of the thick steel plate. In addition, although the guide 14 makes the front-end | tip of the thick steel plate 12 enter smoothly between the draining roll 10 and the table roll 11, it is not an essential structure in this invention.

  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 8 m / s or more, and the water flow jetted from the nozzle jet outlet is a continuous and straight water flow cooling water in which the cross section of the water flow 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.

  In the upper surface cooling facility shown in FIG. 1, large-diameter draining rolls 10a are installed above and below the upper header 1 above the table roll 11 so that the cooling water does not spread in the longitudinal direction of the thick steel plate. The cooling zone length by the header 1 becomes constant, and the cooling temperature control becomes easy. Further, the flow of the cooling water in the conveying direction of the thick steel plate is blocked by the draining roll 10a, and the cooling water staying water 31 supplied from the upper header 1 flows outward in the width direction of the thick steel plate.

  FIG. 2 is a side view showing the arrangement of the upper surface cooling equipment according to another embodiment, and by supporting the draining roll 10b having a smaller diameter by the backup roll 13 as compared with the large diameter draining roll 10a shown in FIG. The stagnant water 31 in the cooling zone can be prevented from flowing into the other cooling zones in the same manner as when the large-diameter draining roll 10a is installed.

  In the present invention, in order to allow the cooling water to penetrate the staying water film and reach the thick steel plate, and to smoothly drain the staying water to the outside in the width direction of the thick steel plate, the following conditions are preferably satisfied It is.

  As shown in FIG. 9, when the height of the upper header 1 from the upper surface of the steel plate is high, the flow of stagnant water in the width direction of the steel plate is relatively smooth, but the cooling water injection distance is long. The force through which water penetrates the staying water film is weakened. On the other hand, as shown in FIG. 10, when the height of the upper header 1 from the upper surface of the steel plate is low, the header 1 becomes an obstacle and the drainage flow passage area in the width direction of the steel plate becomes narrow. It becomes difficult to discharge the water and the water level of the accumulated water becomes high.

  Accordingly, in the present invention, as shown in FIG. 11, the height position of the upper header 1 from the upper surface of the steel sheet is increased, and the leg length of the cooling water injection nozzle is increased, thereby increasing the drainage flow passage area in the steel sheet width direction. The cooling water can penetrate the staying water film and reach the thick steel plate.

  In addition, in FIG. 11, the example which provided the partition 5 so that the thick steel plate 12 may not collide with the upper cooling water injection nozzle 3 is shown, and it is preferable in terms of equipment maintenance, but the present invention includes the partition 5. It is not limited to. However, when the partition wall 5 is provided, a number of through holes are provided in the partition wall 5, and a part of the partition wall 5 serves as a water supply port 6 for inserting the tip of the cooling water injection nozzle 3, and the rest serves as a cooling water drain port 7. It is preferable because both high cooling capacity and drainage can be achieved.

  The length of the cooling water injection nozzle 3 is preferably 100 to 200 mm. When the nozzle length is shorter than 100 mm, the drainage space between the upper header 1 and the steel plate 12 becomes narrow as shown in FIG. 10, and the cooling drainage cannot be smoothly discharged in the width direction of the thick steel plate. On the other hand, if the length is longer than 200 mm, the pressure loss of the circular tube nozzle increases, and the force for the cooling water to penetrate the staying water film becomes weak.

  The distance from the lower end of the upper cooling water injection nozzle 3 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 thick steel plate 12 collides with the upper cooling water jet nozzle 3 is extremely increased, and equipment maintenance becomes difficult. If it exceeds 120 mm, the injection distance of the cooling water becomes long as shown in FIG. 9, and the force of the cooling water penetrating the staying water film becomes extremely weak.

The range of the water density that is most effective in the present invention is 2.0 m ³ / m ² · min or more. When the water density is lower than this, the staying water film is not so thick, and even when a conventional draining roll is used, there is no possibility that the staying water gets over the draining roll and leaks to the adjacent cooling zone.

On the other hand, even when the water density is higher than 5.0 m ³ / m ² · min, it is effective to use the technology of the present invention, but the accumulated water film becomes too thick to get over the draining roll, and the adjacent cooling zone There is a problem in practical use, such as an increase in the risk of leakage to the plant and an increase in equipment costs. A water density of about 3.0 m ³ / m ² · min or less is a practical range as a cooling device.

  Furthermore, the inner diameter of the circular tube nozzle 3 is preferably 3 to 8 mm. If the inner diameter of the nozzle is smaller than 3 mm, the bundle of water ejected from the nozzle becomes thin and the momentum becomes weak. On the other hand, if the nozzle diameter is larger than 8 mm, the flow velocity becomes slow, and it is impossible to secure the penetration force of the cooling water.

  The injection speed of the cooling water from the circular tube nozzle is preferably 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.

  By the way, as shown in FIG. 11, if the height position of the upper header 1 from the upper surface of the steel plate is increased and the leg length of the upper cooling water injection nozzle 3 is increased, the drain passage area in the steel plate width direction can be increased. However, since there are many nozzles with long legs in the drainage flow path, and a bundle of rod-shaped cooling water jetted from these nozzles at high speed, the flow of stagnant water flows in the width direction of the steel plate. It becomes resistance and the flow of cooling drainage is suppressed. Therefore, the water level in this case is lower than in the case of FIG. 10, but higher than in the case of FIG.

  Therefore, when the upper header 1 and the upper cooling water injection nozzle 3 of the present invention are used and cooling is performed at a high water density, particularly on a wide steel plate having a width of 3 m or more, the staying water film becomes too thick. Thus, there is an increased risk that the cooling wastewater will get over the draining roll 10 and leak into the cooling zone adjacent in the steel plate conveyance direction.

  FIG. 7 schematically shows a steel plate width direction water level distribution of stagnant water when a large amount of cooling water is supplied to the upper surface of the steel plate. The cooling water supplied to the upper surface of the steel plate 12 with a uniform water amount density becomes the staying water 31 to form a water film. The water level has the highest distribution at the center portion of the plate width and the lowest distribution at the left and right end portions of the plate width.

  And when the highest water level shown in FIG. 7 becomes higher than the upper end of the draining roll 10, a staying water will overflow into the cooling zone adjacent to a steel plate conveyance direction. When the cooling zone is an air cooling zone, the steel sheet is supercooled by the overflowing cooling water, resulting in large temperature unevenness.

  FIG. 8 shows the relationship between the water density and the maximum water level of the accumulated water. This maximum water level is a value simulated for a thick steel plate having a plate width of 4.5 m on the assumption that the upper end of the draining roll is sufficiently high (the stay water does not overflow).

  The maximum water level varies depending on the drainage determined by the table roll diameter, the distance between the table rolls, the structure of the cooling header on the lower surface of the steel plate, etc., but it tends to increase as the water density increases and the plate width increases. is there.

For example, when a wide steel plate having a width of 4.5 m is cooled at a water density of 3.0 m ³ / m ² · min, the maximum water level is 300 mm and the diameter of the draining roll is less than 300 mm. In this case, the accumulated water overflows.

  Therefore, as described above, even if a large amount of cooling water is supplied to the upper surface of the steel sheet, the high-strength steel sheet can be obtained by giving a uniform and high cooling rate without overflowing the remaining water in the air cooling zone adjacent to the steel sheet conveying direction. In order to produce, it is necessary to maintain the damming height of the accumulated water film by the draining roll higher than the maximum water level of the accumulated water by increasing the diameter of the draining roll to some extent. Therefore, in the present invention, the retaining height of the staying water film by the draining roll is set to 300 mm or more.

  When the large-diameter draining roll 10a described with reference to FIG. 1 is used, if the draining roll diameter is too large, the space for installing the upper header 1 becomes narrow, and the amount of cooling water that can be supplied to the thick steel plate decreases. The diameter of the water draining roll 10a is preferably 300 to 450 mm.

  Furthermore, when there are a plurality of upper headers 1 and there are a plurality of cooling zones, if all the draining roll diameters are increased, the space for installing the upper surface cooling header 1 in each cooling zone is reduced, and the amount of water that can be supplied to the steel plate is reduced. Therefore, it is only necessary to increase the diameter of at least the drainage roll 10 on the most upstream side and the most downstream side, and the diameter of the draining roll in that case is also preferably 300 mm or more and 450 mm or less.

  For example, as shown in FIG. 1 draining roll before the cooling zone; The large-diameter draining roll 10a is installed in the draining roll between 3 to 4 zones. No. 1-2 draining roll and No. 1 What is necessary is just to let the draining roll between 2-3 be the normal draining roll 10. FIG.

  When the draining roll 10b described with reference to FIG. 2 is supported by the backup roll 13, the sum of the diameters of the backup roll 13 and the draining roll 10b may be 300 mm or more.

  Further, when a plurality of upper headers 1 are provided and there are a plurality of cooling zones, backup drains 13 may be provided along all draining rolls 10b as shown in FIG. 5, but at least the most upstream side and the most downstream side of the cooling zone. The backup roll 13 may be provided on the side draining roll 10b. In this case as well, the sum of the diameters of the backup roll 13 and the draining roll 10b is preferably 300 mm or more.

  In the present invention, the cooling device on the lower surface side of the steel plate is not particularly limited. In the embodiment shown in FIG. 1 and the like, the example of the cooling header 2 provided with the circular tube nozzle 4 similar to the cooling device on the upper surface side is shown. A known technique may be used as long as the same level of cooling capability is provided so that warpage during cooling of the steel sheet is unlikely to occur.

  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. 13, 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).

  The upper surface cooling equipment used in this example includes three upper headers 1 as shown in FIGS. 4 to 6, and has three cooling zones each partitioned by a draining roll 10 (one zone corresponds to one zone). Have. FIG. 4 shows the cooling equipment of Example 1 of the present invention. 1 draining roll before the cooling zone; A φ320 mm large-diameter draining roll 10 a is installed in the draining roll between 3 and 4 zones. No. 1-2 draining roll and No. 1 A draining roll 10 having a normal diameter of 270 mm was used as a 2-3 draining roll.

  FIG. 5 shows the cooling equipment of Example 2 of the present invention. The diameter of the draining roll on the entry / exit side of each cooling zone is 220 mm. However, by supporting the draining roll 10b with the backup roll 13 having a diameter of 150 mm, This is an example in which it does not overflow until it reaches 370 mm.

  FIG. 6 shows a case where the diameter of the draining roll on the entry / exit side of each cooling zone is constant at 270 mm in the cooling equipment of the comparative example.

Moreover, since a cooling rate of 25 ° C./s or more is necessary to obtain a high-strength steel plate, the water density is 3.0 m ³ / m ² · min (excluding Comparative Example 2), and the steel plate conveyance speed is 1 m / s. As the upper cooling water spray nozzle 3, a circular pipe nozzle having an inner diameter of 5 mm was arranged as shown in FIG.

  The length of the circular tube nozzle was 160 mm, and the injection distance (distance from the lower end of the circular tube nozzle to the surface of the thick steel plate) was 80 mm. In the present embodiment, the partition wall 5 as shown in FIG. 12 is used, a number of through holes are provided in the partition wall 5, and a part of the partition wall 5 serves as a water supply port 6 for inserting the tip of the upper cooling water spray nozzle 3. The remainder was used as the cooling water outlet 7.

  Table 1 shows the implementation conditions and results.

  In Comparative Example 1, since a high water density was set, the staying water film on the upper surface of the steel sheet became too thick, and the staying water exceeded the draining roll 10 having a diameter of 270 mm as shown in FIG. No. 1 zone or no. It overflowed from between 3 and 4 zones. Since the overflowing water stayed locally in the steel sheet, partial cooling occurred and temperature irregularities of ± 40 ° C. occurred. As a result of taking out a part of the product and conducting a material test, the acceptance rate was as low as 60% and the yield was also poor.

  In Comparative Example 2, the water density was suppressed more than that in Comparative Example 1 so that the accumulated water did not exceed the draining roll 10, so No. 1 zone or no. The cooling water did not overflow from 3 to 4 zones. However, since the water density is low, the cooling rate is lowered, the target 25 ° C./s or higher cannot be obtained, and the target strength cannot be obtained. The temperature unevenness was ± 20 ° C., which was smaller than Comparative Example 1, but because the cooling rate was low, the strength was often insufficient, the pass rate of the material test was as low as 40%, and the yield was also poor.

On the other hand, this invention example 1 is No.1. No. 1 draining roll before the cooling zone and No. 1 Since the large-diameter draining roll 10a having a diameter of 320 mm is installed in the draining roll between the 3 and 4 cooling zones, even if the cooling water having a water amount density of 3.0 m ³ / m ² min is supplied, as shown in FIG. Beyond this roll, No. One zone before or no. There was no overflow from between 3 and 4 zones.

  In Example 2 of the present invention, the retained water is prevented from overflowing until the water level reaches 370 mm in each cooling zone by supporting the draining roll 10b of φ220 mm with the backup roll 13 of φ150 mm, as shown in FIG. The stagnant water did not overflow beyond the backup roll. In any of the inventive examples, the temperature unevenness was as small as ± 10 ° C., a high cooling rate was obtained, and the target strength was obtained with a margin. For this reason, the pass rate of the material test was as high as 99%, and the yield was also sufficiently high.

  By using the cooling equipment of the present invention for a hot-rolled sheet, a high flow rate of cooling water can be supplied to the upper surface of the steel sheet, a high cooling rate can be obtained, and a high-strength steel sheet can be manufactured. Moreover, since cooling of the upper surface of a steel plate can be performed uniformly over the entire surface, a high-quality steel plate can be produced.

It is a side view which shows the cooling equipment of this invention. It is a side view which shows the cooling equipment of this invention. It is a side view which shows the conventional cooling equipment. It is a side view which shows the cooling equipment (multiple installation) of this invention. It is a side view which shows the cooling equipment (multiple installation) of this invention. It is a side view which shows the conventional cooling equipment (plural installation). It is a figure which shows the steel plate width direction distribution of stagnant water. It is a figure which shows the relationship between a water quantity density and the highest water level of stagnant water. It is a figure which shows the steel plate width direction flow of cooling waste water. It is a figure which shows the steel plate width direction flow of cooling waste water. It is a figure which shows the steel plate width direction flow of cooling waste water. It is a side view which shows the cooling equipment of this invention. It is a figure which shows the rolling equipment of a thick steel plate.

Explanation of symbols

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 Drainage port 8 Injection cooling water 9 Drained water 10 Draining roll 10a Large diameter draining roll 10b Draining roll (having a backup roll)
11 Table roll 12 Thick steel plate 13 Backup roll 14 Guide 31 Stagnant water 32 Leaked water

Claims (5)

  A cooling facility installed in a hot rolling line for a thick steel plate, a header for supplying cooling water to the upper surface of the thick steel plate, a cooling water injection nozzle for injecting rod-shaped cooling water suspended from the header, It is arranged on the upstream side and the downstream side in the thick steel plate conveyance direction, and includes a draining roll facing the table roll with the thick steel plate interposed therebetween, and the weir height of the staying water film by the draining roll is 300 mm or more. To cool thick steel plates.   The header and a plurality of the draining rolls arranged on the upstream side and the downstream side in the transport direction of the thick steel plate of the header are provided, and at least a staying water film is blocked by the draining rolls on the most upstream side and the downstream side in the thick steel plate transport direction. The cooling equipment for thick steel plates according to claim 1, wherein the height is 300 mm or more. From the cooling water injection nozzle to the thick steel plate surface, the cooling water injection density from the cooling water injection nozzle is 2.0 m ³ / m ² min or more, the nozzle length of the cooling water injection nozzle is 100 mm or more. The cooling equipment for thick steel plates according to claim 1 or 2, wherein the distance is 30 to 120 mm.   The thick steel plate according to any one of claims 1 to 3, wherein a large-diameter water draining roll having a diameter of 300 mm or more and 450 mm or less is used as the draining roll having a retaining water film blocking height of 300 mm or more. Cooling equipment.   The sum of the diameter of a backup roll and a draining roll is made into 300 mm or more using the draining roll which has a backup roll as a draining roll which makes the blocking height of a stagnant water film 300 mm or more. The thick steel plate cooling equipment according to any one of 3 above.

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