JP2009202184A - Method and system for cooling undersurface of hot-rolled steel strip - Google Patents

Abstract

A hot-rolled steel that can cool the lower surface of a hot-rolled steel strip with a large amount of water and a high cooling rate even in a place where the distance between transport table rolls is narrow, such as a run-out table, in a production line for hot-rolled steel strip. A method for cooling a bottom surface of a belt and a bottom surface cooling device are provided.
A plurality of circular tube nozzles 2 for injecting rod-shaped cooling water onto the lower surface of a hot-rolled steel strip are installed in a substantially central position between the table roll 1 and the table roll 1 along the steel strip width direction. The circular tube nozzle 2 is composed of a straight tube nozzle 2a extending vertically upward, and a bent tube nozzle 2b arranged so that only the tip can be bent and sprayed toward the table roll 1.
[Selection] Figure 1

Description

  The present invention smoothly drains the cooling water when cooling a hot-rolled steel strip that has been hot-rolled, particularly when the spray is placed and a large amount of water is jetted for cooling the lower surface side of the hot-rolled steel strip. The present invention relates to a method and an apparatus for cooling a hot-rolled steel strip that can finish cooling at a uniform temperature in the width direction and the longitudinal direction.

  In a hot-rolled steel strip production line, a slab heated at high temperature is rolled to a desired size, and then cooled on a run-out table from the viewpoint of material adjustment. The purpose of the cooling performed here is mainly to adjust the material such as the intended strength and elongation by controlling the precipitates and transformation structure of the steel strip. As the cooling medium for the cooling, water with low cost is often used.

  In recent years, there is a high need for high-strength steel sheets, and in order to achieve this, there are increasing cases in which a high cooling rate is necessary from the viewpoint of transformation structure control. In order to achieve a high cooling rate, it is necessary to increase the amount of cooling water. On the other hand, since the steel strip thickness is thin and low in rigidity after finish rolling of the hot-rolled steel strip, the table rolls are densely arranged in order to stably pass the plate on the runout table. In many facilities, since the table rolls having a diameter of about 250 to 300φ are arranged at a pitch of 300 to 400 mm, there is a problem that the space between the table rolls is narrow and it is difficult to arrange the nozzles between the table rolls. Therefore, in the lower surface cooling of the hot-rolled steel strip at the run-out table, a spray nozzle is often disposed for the purpose of being installed in a narrow space and increasing the cooling area.

  When spraying a large amount of water by cooling with this spray nozzle, the cooling water sprayed upward due to the gravity relation falls down after colliding with the steel strip, so the cooling water is efficiently discharged from the narrow space between the table rolls. Inability to drain, spraying with cooling water with the spray nozzle submerged causes insufficient striking force, non-uniformity in the distribution of the amount of water sprayed, resulting in reduced cooling capacity and temperature unevenness. There was a problem.

For this reason, a general run-out table lower surface cooling facility is often used with the input water amount limited to 1000 L / min · m ² or less, which is an obstacle to increasing the cooling rate.

  Conventionally, various studies have been made on the arrangement of nozzles in the case of cooling a hot-rolled steel strip, and some examples will be described.

  For example, in Patent Document 1, a plurality of headers each having a flat spray attached thereto are arranged at right angles to the plate passing direction, and the spreading direction of the flat spray nozzle is symmetrical with respect to the central axis between the headers for each header. And a cooling method in which the swing angle of the flat spray is tilted in the range of 5 to 45 °, and the gas / liquid weight mixing ratio is 1/50 to 1/1 from the flat spray. (FIG. 6).

  Further, in Patent Document 2, when cooling on a roller table by a columnar jet group, a plurality of nozzles provided at right angles to the steel material are provided with nozzle pitches S and S1 in the steel material width direction and transfer direction between adjacent nozzles. Is 3 to 10 times the nozzle diameter, arranged at regular intervals so that S1 <S, and the flow of fluid after colliding with the steel surface collides with fluid from the adjacent nozzle. A cooling method is described in which a honeycomb cell-shaped cooling surface group having the same shape and surrounded by is regarded as a cell nucleus (FIG. 7).

Further, in Patent Document 3, on the lower surface side of the steel plate traveling on the runout table, a plurality of columnar coolant injection nozzle rows are drilled in a nozzle header having an upper surface parallel to the steel plate lower surface in the space between the table rolls, In addition, a method of cooling the lower surface of the steel sheet is described in which each nozzle row extending in the longitudinal direction has a different angle toward the lower surface of the steel sheet (FIG. 8).
JP-A-2005-21951 JP-A-10-263669 Japanese Patent Laid-Open No. 62-259610

  However, none of the above-described conventional techniques (Patent Documents 1 to 3) is practically sufficient.

  In the technique described in Patent Document 1, a plurality of headers are arranged at right angles to the sheet passing direction, and a flat spray nozzle is arranged symmetrically with respect to the central axis between the headers for each adjacent header. However, when the table roll interval is only about 50 to 100 mm as in a run-out table of a hot-rolled steel strip, there is only a space for arranging the nozzles in the width direction, and nozzles are arranged in the longitudinal direction as described in Patent Document 1. Cannot be placed. Further, Patent Document 1 is limited to upper surface cooling, and there is no description about lower surface cooling. In addition, when flat spray is used, since the liquid is sprayed in the form of liquid droplets from the nozzle, the speed of the cooling water is easily reduced, and the cooling water speed is slow when the cooling water reaches the steel plate. , Exercise power is low. Especially when cooling at a large flow rate, the bottom surface of the steel sheet is surrounded by the steel sheet and the table roll, so water tends to collect. There is a problem that the cooling capacity does not increase so much.

  In the technique described in Patent Document 2, as in Patent Document 1, when the table roll interval is only about 50 to 100 mm like a run-out table of a hot-rolled steel strip, at most two to three rows in the longitudinal direction. There is only space to arrange the nozzles. For this reason, even if, for example, three rows can be installed in the longitudinal direction, honeycomb cells can be formed only around the nozzle in the center in the longitudinal direction, and high cooling ability due to the interference region as described in Patent Document 2 cannot be expected. In addition, since the hot roll steel strip runout table has a large table roll, it becomes an obstacle and cannot bring water directly under the nozzle during the table roll, and cooling during the table roll by cooling water or honeycomb cells is not possible. It will be enough.

  In the technique described in the prior art 3, the case where the table roll interval is only about 50 to 100 mm like a run-out table of a hot-rolled steel strip is considered, and the rod-like nozzles are arranged radially when viewed in the longitudinal direction. ing. In order to reduce the distance between the hot-rolled steel strip (steel plate) and the nozzle, the nozzle tip is arranged in parallel with the steel plate, and the protector and nozzle for preventing the collision between the steel plate and the nozzle are integrated. However, the cooling water that collided with the steel sheet only falls downward, and since such a plate-shaped protector is installed, it becomes an obstacle and there is little space for cooling water to be drained between the table rolls. turn into. Therefore, a thick liquid film is formed between the nozzle and the steel plate, and unless the cooling water is sprayed from the nozzle at a considerably high pressure, this liquid film cannot be broken, and the cooling water can directly collide with the steel plate. There is a problem that it is difficult and the cooling capacity does not increase so much.

  The present invention has been made in view of the above circumstances, and in a hot-rolled steel strip production line, the lower surface of the hot-rolled steel strip can be used even in places where the distance between the transport table rolls is narrow, such as a run-out table. An object of the present invention is to provide a lower surface cooling method and a lower surface cooling device for a hot-rolled steel strip that can be cooled with a large amount of water at a high cooling rate.

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

  [1] When cooling the lower surface of the hot-rolled steel strip, a plurality of circular pipe nozzles for injecting rod-shaped cooling water to the surface to be cooled are arranged between the conveying table rolls in the width direction, and the plurality of circular pipe nozzles Is composed of a straight pipe nozzle and a bent pipe nozzle whose tip is bent so that the table roll can be cooled, and the bent portion of the bent pipe nozzle has a height position above the rotational axis of the table roll. The ratio d / P between the outer diameter d of the circular tube nozzle and the mounting pitch P in the width direction of the adjacent circular tube nozzle is 0.5 or less, and the distance from the tip of the circular tube nozzle to the hot-rolled steel strip is from 50 mm A method for cooling the lower surface of a hot-rolled steel strip, wherein the radius is less than the radius of the table roll.

  [2] In the lower surface cooling method of the hot-rolled steel strip according to [1], a collision portion of the rod-shaped cooling water sprayed from the circular tube nozzles arranged side by side in the width direction on the hot-rolled steel strip is transported in the steel strip. A method for cooling the lower surface of a hot-rolled steel strip, wherein a ratio LL / Pw between a length LL projected on a side surface and a distance Pw between the table rolls is 0.6 or more.

[3] The method for cooling the bottom surface of the hot-rolled steel strip according to [1] or [2], wherein a cooling water density based on a distance between the table rolls is 1500 L / min · mm ² or more. The lower surface cooling method of a hot-rolled steel strip.

  [4] The lower surface cooling of a hot-rolled steel strip according to any one of [1] to [3], wherein a plurality of rows of circular tube nozzles are arranged in the transport direction. Method.

  [5] A lower surface cooling device for a hot-rolled steel strip, wherein a plurality of circular tube nozzles for injecting rod-shaped cooling water to the surface to be cooled are arranged between the conveying table rolls in the width direction, and the plurality of circular tubes The nozzle is composed of a straight pipe nozzle and a bent pipe nozzle whose tip is bent so that the table roll can be cooled, and the height position of the bent portion of the bent pipe nozzle is above the rotational axis of the table roll. The ratio d / P between the outer diameter d of the circular tube nozzle and the mounting pitch P in the width direction of the adjacent circular tube nozzle is 0.5 or less, and the distance from the tip of the circular tube nozzle to the hot-rolled steel strip The lower surface cooling device for a hot-rolled steel strip, characterized in that is less than the radius of the table roll from 50 mm.

  [6] In the lower surface cooling device for a hot-rolled steel strip according to [5], a steel strip transporting a collision portion of the rod-shaped cooling water sprayed from a circular pipe nozzle arranged in the width direction to the hot-rolled steel strip. A lower surface cooling device for a hot-rolled steel strip, wherein a ratio LL / Pw between a length LL projected on a side surface in a direction and a distance Pw between the table rolls is 0.6 or more.

[7] The hot-rolled steel strip lower surface cooling device according to [5] or [6], wherein a cooling water density based on a distance between the table rolls is 1500 L / min · mm ² or more. A bottom surface cooling device for hot rolled steel strip.

  [8] The hot-rolled steel strip lower surface cooling apparatus according to any one of [5] to [7], wherein a plurality of circular tube nozzles are arranged in the longitudinal direction. Bottom cooling device.

  In the present invention, with regard to the cooling of the bottom surface of the hot-rolled steel strip, it is possible to cool a large flow rate particularly on a run-out table where the interval between the conveying table rolls is narrow and it is difficult to install a conventional cooling nozzle. A high cooling rate can be obtained while securing the properties. As a result, a high-strength steel strip can be manufactured without variations in mechanical properties.

  As an embodiment of the present invention, the nozzle configuration of a lower surface cooling device in a run-out table having a narrow table roll interval, particularly a hot-rolled steel strip will be described here. In particular, a large amount of water injection is assumed, and it is important to efficiently drain cooling water from a narrow space between table rolls.

  FIG. 1 shows a specific nozzle configuration for ensuring drainage and cooling the lower surface of the steel strip uniformly across the width and the longitudinal direction as the nozzle configuration in this embodiment. Here, FIG. 1A is a side view, and FIG. 1B is a plan view.

  As shown in FIG. 1, the nozzle 2 employs a circular nozzle (circular tube nozzle) capable of injecting a rod-shaped cooling water with high straightness. A plurality of nozzles 2 are installed along the steel strip width direction at substantially the center between the table roll 1 and the table roll 1. The plurality of circular tube nozzles 2 are a straight tube nozzle (straight advance nozzle) 2a extending vertically upward, and a bent tube nozzle 2b arranged so that only the tip portion is bent and sprayed toward the table roll 1 can be performed. Consists of. With such a configuration, the cooling water can collide with the steel strip in a wide range between the table rolls 1. At that time, the distal end portion (bent portion) of the bent tube nozzle is located above the rotation center axis O of the table roll 1.

  The reason for the nozzle configuration as described above will be described below.

  In cooling the steel strip underneath, it is necessary to inject cooling water from below the steel strip, but there is a steel strip bottom above the nozzle, and there are table rolls before and after the nozzle in the direction of steel strip travel. Therefore, the cooling water flows along the steel strip after colliding with the steel strip, and a part of the coolant flows in the traveling direction of the steel strip and collides with the table roll, and then falls along the table roll. Moreover, after the remaining cooling water collides with the steel strip, it flows along the steel strip in the width direction of the steel strip, collides with cooling water jetted from nozzles adjacent in the width direction, and falls downward. Since there is a table roll, the gap becomes the narrowest at the rotation axis of the table roll, and particularly when a large amount of water is injected, a puddle occurs. Since there is such falling water and a puddle, if a spray nozzle with low rectilinearity is arranged, the flow of spray water is hindered by the falling water or the puddle, and the momentum of the cooling water is reduced. In this embodiment, a large amount of water is cooled to obtain a high cooling capacity on the lower surface side of the steel strip, but in a region where the steel strip temperature is as high as 600 to 900 ° C., a vapor film is generated between the steel strip and the cooling water. It is easy to be in a so-called film boiling state. In this film boiling, the heat exchange between the steel strip and the cooling water is performed through the vapor film, so the cooling capacity cannot be increased, so it is necessary to give the cooling water a high momentum. It becomes.

  Therefore, in this embodiment, the lower surface of the steel strip is cooled using a circular pipe nozzle that injects rod-shaped cooling water. This is because a high momentum that breaks down the falling water and the puddle can be obtained before the collision with the steel strip from the nozzle tip. Further, by bending some of the nozzle tips, it is possible to cool stably until the table rolls.

  On the other hand, when sprayed in the form of droplets and sprayed from the nozzle tip like spray cooling, the air resistance increases, so the cooling water is greatly decelerated and a high flow rate cannot be obtained. In addition, it is conceivable to arrange slit-shaped nozzles that are long in the width direction in a rectangular cross section. Since it is impossible to obtain a high flow rate unless it is narrowed to a minimum, it is necessary to narrow the gap between the nozzles to about several hundreds μm to 1 mm. On the other hand, the cooling water on the run-out table uses cooling water of about several thousand tons, so it is difficult to increase and manage the cooling water, and the scale generated during rolling is several mm or more. It is inevitable that foreign matter having a thickness is mixed, and it is inevitable that the foreign matter is clogged in the gap between the nozzles of about several hundred μm to 1 mm.

  However, since rod-shaped cooling water is used, the effects of falling water and water pools are relatively small, but they are not without them. Therefore, it is necessary to eliminate the influence of falling water and stagnant water as much as possible.

  For this reason, the tip of the nozzle for cooling the table roll is bent. As described above, this makes it possible to cause the cooling water to collide with the steel strip in a wide range, but in addition, there are the following reasons. As described above, since the falling water falls along the table roll, it is preferable that the tip of the nozzle is located as far as possible from the table roll. For example, when a straight nozzle is arranged as in Patent Document 3, the tip of the nozzle is close to the table roll, so that cooling water passes through the falling water, and a reduction in momentum is inevitable. Furthermore, when a nozzle protector is arranged as in Patent Document 3, this protector becomes an obstacle, and the falling water does not fall smoothly and tends to accumulate between table rolls, so it is preferable that it is not present.

  As for the arrangement of the bent tube nozzles for cooling the table roll, there are three nozzles as shown in a side view in FIG. 1A and a plan view in FIG. As an example, one straight pipe nozzle 2a and one bent pipe nozzle 2b on the downstream side and the upstream side thereof are arranged, a side view in FIG. 2 (a), and a side view in FIG. 2 (b). As shown in the plan view, an example in which one straight pipe nozzle 2a and two bent pipe nozzles 2b with different bending angles are arranged on each of the downstream side and the upstream side in units of five can be considered. .

  In addition to the above, the order of arrangement in the width direction may be any way such as the upstream side bent tube nozzle and the downstream side bent tube nozzle are interchanged. In this case, it is not preferable to arrange two straight pipe nozzles 1a in the width direction from the viewpoint of uniform cooling. It should be arranged periodically for each unit number of nozzles.

  In addition, the height position of the tip of the circular tube nozzle is specifically set to 50 mm or more and less than the table roll radius with respect to the distance from the steel strip lower surface. If the nozzle tip is arranged farther away from the steel strip than the table roll radius, the table roll interferes and cooling water cannot be sprayed toward the table roll. Also, if the nozzle tip is separated from the steel strip by the same distance as the center axis of the table roll, the nozzle tip comes to the narrowest part of the gap between the table rolls. Risk of jetting resistance. Therefore, it is necessary to bring the nozzle tip as close to the steel strip as possible. However, if the distance is shorter than 50 mm, the hot-rolled steel strip is manufactured to an extremely thin steel strip of about 1 mm. Is low and there is a risk that the steel strip will bend and collide with the nozzle. As described above, if this is prevented with a protector or the like, a drainage problem will occur, so it must be carried out within the above range.

  Moreover, although a part of falling water falls along a table roll, the remainder flows into the width direction after colliding with a steel strip, collides with the cooling water injected from the adjacent nozzle, and falls. For this reason, if the distance between the nozzles is not larger than a certain distance, the falling water scatters and falls directly above the nozzles, resulting in a decrease in momentum. Specifically, if the ratio d / P between the nozzle diameter (outer diameter) d and the nozzle mounting pitch P in the width direction is smaller than 0.5, the falling water can be stably passed between the nozzles. Can do.

  Furthermore, from the viewpoint of the cooling capacity, the cooling capacity can be increased by cooling in a wider range on the lower surface of the steel strip. Therefore, as shown in FIG. 1, the nozzle collision point interval (the length projected on the side surface in the steel strip conveying direction of the collision portion of the rod-shaped cooling water on the hot-rolled steel strip) LL is projected on the table. It is preferable to arrange so that LL / Pw> 0.6 with respect to the mounting pitch Pw in the steel strip traveling direction of the roll.

  Incidentally, the rod-shaped cooling water of the present invention refers to cooling water ejected from a circular (including elliptical or polygonal) nozzle outlet. In addition, the rod-shaped cooling water of the present invention is not a spray-like jet, but a film-like laminar flow. It refers to cooling water with a characteristic water flow.

Moreover, in this invention, it applies when the water quantity density computed on the basis of the amount of large water quantities, especially the distance between table rolls is 1500 L / min * m < ² > or more. In the case where a low cooling capacity is sufficient, the amount of cooling water can be reduced, so that the amount of falling water is originally small and water is not collected between the table rolls.

  And although this invention is applied to the lower surface cooling of a hot-rolled steel strip, if it is a place where table rolls are narrow, it is also possible to apply to various facilities, such as a thick plate and a shape steel.

  Examples of the present invention will be specifically described below.

  FIG. 3 shows a layout of a production facility for hot-rolled steel strip in the embodiment of the present invention. A 250 mm thick slap is heated to about 1200 ° C. by the heating furnace 60, then rolled to a thickness of 40 mm by the rough rolling mill group 61, and rolled to 2.6 mm by the finish rolling mill group 62. After rolling, the sheet is cooled to a predetermined temperature by the runout table 63 and then wound by the coiler 64.

  In the runout table 63, the upper surface of the steel strip is cooled by the upper surface cooling device 51 (upper surface cooling device group 52) of the hairpin laminator, and the lower surface of the steel strip is cooled by the lower surface cooling device 55 (lower surface cooling device group 56). Here, the upper surface cooling device 51 is installed in a pair with the lower surface cooling device 55 so that the cooling water falls on each table roll. The temperature distribution of the steel strip before and after cooling on the runout table 63 can be measured by a radiation thermometer 65.

(Example of the present invention)
As an example of the present invention, the run-out table 63 was cooled based on the above-described embodiment of the present invention. That is, as the lower surface cooling device 55, the lower surface cooling device in which the circular tube nozzle 2 capable of ejecting rod-shaped cooling water as shown in FIG. 1 is used.

In addition, the required cooling rate at the time of cooling a steel strip with the runout table 63 is 200 degrees C / s or more. FIG. 4 shows the relationship between the cooling rate and water density when a 2.6 mm thick material is cooled with rod-shaped cooling water. In order to set the cooling rate to 200 ° C./s, the water density is about 3500 / min.・ M ² is required. Therefore, here, the cooling water amount was set to 4000 / min · m ² .

  The geometric relationship between the table roll 1 and the circular tube nozzle 2 in FIG. 1 is as follows.

Table roll radius R: 150 mm, table roll pitch Pw: 370 mm, distance H from nozzle tip to steel strip H: 100 mm
Nozzle outer diameter d: φ10.9 mm, height L1: 30 mm from the table roll axis to the bent portion of the bent tube nozzle, nozzle width mounting pitch P: 52 mm, d / P = 0.21
Cooling water projection cooling length LL: 124 mm, LL / Pw = 0.67
Flow rate per nozzle Qm: 78 L / min, water volume density between table rolls: 4000 / min · m ² , cooling water pressure Pm: 0.2 MPa
Then, the number of used upper surface cooling devices 51 and lower surface cooling devices 55 (the number of nozzles used) is cooled so that the run-out table inlet side temperature is 870 ° C. and the run-out table outlet side temperature is 640 ° C. at a plate speed of 650 mpm. Went. Specifically, from FIG. 4, when the water density is 4000 / min · m ² , a cooling rate of 210 ° C./s is obtained, so the cooling time is 11 sec and the equipment length (cooling zone length) is 11.9 m. . On the other hand, since the upper surface cooling device 51 and the lower surface cooling device 55 are installed every table roll pitch 370 mm, the cooling water is supplied from 32 units (each 32 headers) for the upper surface cooling device 51 and the lower surface cooling device 55. Jetted.

(Comparative example)
As a comparative example, the runout table 63 was cooled based on Patent Document 3 which is the closest type to the present invention. That is, as the lower surface cooling device 55, a lower surface cooling device having a nozzle configuration simulating Patent Document 3 shown in FIG. 8 was used.

  In addition, about other conditions, it was made equivalent to the example of this invention as follows.

Table roll radius R: 150 mm, table roll pitch Pw: 370 mm, distance H from nozzle tip to steel strip H: 100 mm
Nozzle outer diameter d: φ10.9 mm, nozzle width direction mounting pitch P: 52 mm, d / P = 0.21
Cooling water projection cooling length LL: 124 mm, LL / Pw = 0.67
Flow rate per nozzle Qm: 78 L / min, water volume density between table rolls: 4000 / min · m ² , cooling water pressure Pm: 0.2 MPa
Then, the number of used upper surface cooling devices 51 and lower surface cooling devices 55 (the number of nozzles used) is cooled so that the run-out table inlet side temperature is 870 ° C. and the run-out table outlet side temperature is 640 ° C. Went. Specifically, from FIG. 4, when the water density is 4000 / min · m ² , a cooling rate of 210 ° C./s is obtained, so the cooling time is 11 sec and the equipment length (cooling zone length) is 11.9 m. . On the other hand, since the upper surface cooling device 51 and the lower surface cooling device 55 are installed at every table roll pitch 370 mm, the upper surface cooling device 51 and the lower surface cooling device 55 are supplied with cooling water from 32 units (each 32 headers). Sprayed.

  FIG. 5 shows the temperature distribution in the width direction of the steel strip after cooling in the above inventive examples and comparative examples.

  In the example of the present invention, the temperature distribution is very uniform in the width direction. As a result, tensile strength and elongation were the target mechanical properties.

  On the other hand, in the comparative example, temperature unevenness in the width direction occurs periodically, and the temperature deviation is about 50 ° C. at the maximum. As a result, the tensile strength, elongation, etc. deviated from the target locally, and there were parts that had non-standard mechanical properties, and could not be shipped as a product. As a cause of this, in the comparative example, some of the circular tube nozzles are inclined, and the falling water drops along the table roll and the inclined circular tube nozzle interferes, resulting in a decrease in striking force. Is considered to be the cause.

It is a figure which shows an example of the lower surface cooling device in one Embodiment of this invention. It is a figure which shows the other example of the lower surface cooling device in one Embodiment of this invention. It is a layout of the hot-rolled steel strip manufacturing equipment in Example 1 of the present invention. It is a figure which shows the relationship between the cooling water amount density and cooling rate of rod-shaped cooling water. It is a figure which shows the steel strip width direction temperature distribution after the cooling in Example 1 of this invention. It is a figure explaining patent document 1. It is a figure explaining patent document 2. FIG. It is a figure explaining patent document 3. FIG.

Explanation of symbols

1 Table roll 2 Circular nozzle (bar-shaped cooling water injection nozzle)
2a Straight pipe nozzle 2b Bend pipe nozzle 51 Upper surface cooling device 52 Upper surface cooling device group 55 Lower surface cooling device 56 Lower surface cooling device group 60 Heating furnace 61 Coarse rolling mill group 62 Finish rolling mill group 63 Runout table 64 Coiler 65 Radiation thermometer

Claims (8)

  When cooling the lower surface of the hot-rolled steel strip, a plurality of circular pipe nozzles for injecting rod-shaped cooling water to the surface to be cooled are arranged between the conveying table rolls in the width direction, and the plurality of circular pipe nozzles are straight pipes. A nozzle tube and a bent tube nozzle whose tip is bent so that the table roll can be cooled, and the height of the bent portion of the bent tube nozzle is above the rotation axis of the table roll, The ratio d / P between the outer diameter d of the nozzle and the mounting pitch P in the width direction of the adjacent circular tube nozzle is 0.5 or less, and the distance from the tip of the circular tube nozzle to the hot-rolled steel strip is from 50 mm to the table roll The lower surface cooling method of the hot-rolled steel strip characterized by being less than the radius of this.   In the lower surface cooling method of the hot-rolled steel strip according to claim 1, a collision portion of the rod-shaped cooling water sprayed from the circular pipe nozzles arranged side by side in the width direction is projected on the side surface of the steel strip conveyance direction. A method for cooling the bottom surface of a hot-rolled steel strip, wherein the ratio LL / Pw between the length LL and the distance Pw between the table rolls is 0.6 or more. The hot-rolled steel strip according to claim 1 or 2, wherein a cooling water density based on a distance between the table rolls is 1500 L / min · mm ² or more. Of cooling the bottom surface of the.   The lower surface cooling method of the hot-rolled steel strip according to any one of claims 1 to 3, wherein a plurality of circular tube nozzles are arranged in the transport direction.   A lower surface cooling device for a hot-rolled steel strip, wherein a plurality of circular tube nozzles for injecting rod-shaped cooling water to a surface to be cooled are arranged between conveyance table rolls in the width direction, and the plurality of circular tube nozzles are directly arranged. A tube nozzle and a bent tube nozzle whose tip is bent so that the table roll can be cooled, and the height position of the bent portion of the bent tube nozzle is above the rotational axis of the table roll, The ratio d / P between the outer diameter d of the circular tube nozzle and the mounting pitch P in the width direction of the adjacent circular tube nozzle is 0.5 or less, and the distance from the tip of the circular tube nozzle to the hot-rolled steel strip is from 50 mm A lower surface cooling device for a hot-rolled steel strip, which is less than a radius of the table roll.   In the lower surface cooling apparatus of the hot-rolled steel strip according to claim 5, a collision portion of the rod-shaped cooling water sprayed from a plurality of circular tube nozzles arranged in the width direction on the hot-rolled steel strip is projected on the side surface in the steel strip conveying direction. The lower surface cooling device for a hot-rolled steel strip, wherein a ratio LL / Pw between the length LL and the distance Pw between the table rolls is 0.6 or more. The hot-rolled steel strip lower surface cooling device according to claim 5 or 6, wherein a cooling water density based on a distance between the table rolls is 1500 L / min · mm ² or more. Underside cooling device.   The lower surface cooling device for a hot-rolled steel strip according to any one of claims 5 to 7, wherein a plurality of circular tube nozzles are arranged in the longitudinal direction.

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