SECONDARY COOLING DEVICE AND SECONDARY COOLING METHOD FOR CONTINUOUS CASTING

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a secondary cooling device and a secondary cooling method for continuous casting.

RELATED ART

Conventionally, secondary cooling methods for continuous casting are known (for example, refer to Patent Documents 1 to 3).

In the secondary cooling method of Patent Document 1, a slab is cooled with a cooling mechanism as shown in FIG. 9. FIG. 9 shows a schematic diagram (A) of a part of a secondary cooling device for continuous casting, a graph (B) showing the relationship between the casting distance and the sprayed water density, and a graph (C) showing the relationship between the casting distance and the slab surface temperature.

As shown in FIG. 9(A), the secondary cooling device for continuous casting in Patent Document 1 includes a plurality of rolls 2a and 2b disposed side by side in the vertical direction and a spray nozzle 9 configured to spray cooling water W from between the rolls 2a and 2b to the slab surface 41 of a slab 4.

As shown in FIG. 9(A), the spray nozzle 9 is provided such that the cooling water spray axis J1, which is the central axis of the cooling water W that is sprayed from a nozzle head 31, becomes parallel to the horizontal plane (a plane perpendicular to the vertical direction) P. In addition, the spray nozzle 9 is provided such that the intersection position Q9 between the slab surface 41 and the cooling water spray axis J1 coincides with the middle position 44 between a contact position 42 and a contact position 43. Here, the contact position 42 is a contact position between the roll 2a that is present above the spray nozzle 9 and the slab surface 41, and the contact position 43 is a contact position between the roll 2b that is present below the spray nozzle 9 and the slab surface 41.

With such a configuration, the cooling water W is sprayed to a spray range 45 on the slab surface 41. The spray range has a transversely long elliptical shape, which includes the middle position 44 in the center in the vertical direction.

When the cooling water W is sprayed to the spray range 45, the sprayed water density on the slab surface 41 is maximized at the middle position 44 as indicated by the broken line in FIG. 9(B). In addition, the cooling water W sprayed to the spray range 45 flows downward due to the influence of the force of gravity and gathers between a part of the slab surface 41 on the lower side of the spray range 45 and the outer circumferential surface of the lower roll 2b as dripping water W1.

In the cooling of the slab 4, when a predetermined position on the slab surface 41 moves downward and approaches the contact position 42 with the roll 2a, with which the predetermined position first comes into contact, as indicated by the broken line in FIG. 9(C), the temperature of the slab surface 41 begins to decrease due to the contact with the roll 2a and the consequent roll cooling, and continuously decreases until the predetermined position moves downward a predetermined distance or longer apart from the contact position 42.

After that, until the predetermined position on the slab surface 41 enters the spray range 45 of the cooling water W, the temperature of the slab surface 41 increases due to reheating (hereinafter, reheating occurring between the spray range and the roll 2a that is present above the spray range will be referred to as “first reheating”). Once the predetermined position enters the spray range 45, the temperature of the slab surface continuously decreases due to spray cooling until the predetermined position passes through the spray range.

In addition, once the predetermined position on the slab surface 41 passes through the spray range 45, the temperature of the slab surface 41 increases due to reheating (hereinafter, reheating occurring between the spray range 45 and the roll 2b that is present below the spray range will be referred to as “second reheating”) until the predetermined portion approaches the contact position 43 with the roll 2b, with which the predetermined position second comes into contact. Once the predetermined position approaches the contact position 43, the temperature of the slab surface continuously decreases due to the contact with the roll 2b and the consequent roll cooling until the predetermined position moves a predetermined distance or longer apart from the contact position 43.

After that, the cycle of the first reheating, the spray cooling, the second reheating, and the roll cooling is repeated on the slab surface 41, whereby the entire slab 4 is cooled, and the temperature of the slab gradually decreases.

In Patent Document 1, the cooling water is sprayed to the slab surface at a water pressure higher than an ordinary water pressure using the secondary cooling device as described above, whereby the enhancement of the slab cooling power and the reduction of the bulging amount are achieved.

Patent Document 2 discloses a secondary cooling method for continuous casting in which the major axis direction of the surface of cooling water sprayed to a slab is inclined such that the cooling water is sprayed from the upstream side toward the downstream side of continuous casting by inclining the central axis line of the spray direction of a spray nozzle with respect to the central axis line of the spray nozzle and rotating the spraying direction of the spray nozzle in the in-plane direction of the slab.

In a secondary cooling device of Patent Document 2, as shown in FIG. 10A and FIG. 10B, the cooling water spray axis J1 is rotated around the perpendicular line to the slab surface and inclined toward the upstream side in the casting direction DC (the movement direction of the slab), and then the spray range 45 is inclined obliquely downward. In FIG. 10A and FIG. 10B, an element having a corresponding element in FIG. 9 is denoted by the same reference numeral.

Specifically, in the line of sight of FIG. 10A, first, the cooling water spray axis J1 is inclined in the lateral direction of the slab 4 at an inclination angle α with respect to the perpendicular line. At this time, the center 450-1 of the spray range 45-1 moves to the center 450-2 of the spray range 45-2. Subsequently, as shown in FIG. 10B, the cooling water spray axis J1 is rotated at a rotation angle β such that the major axis LB-1 of the spray range 45-1 is directed obliquely downward. As a result, the major axis LB-1 of the spray range 45-1 moves to the position of the reference numeral LB-3, and the spray range moves from the reference numeral 45-2 to the position of the reference numeral 45-3. However, when the rotation angle β is large, the obliquely lower part of the cooling range indicated by the reference numeral 45-3 is blocked by the lower roll. Therefore, in Patent Document 2, the cooling water spray axis J1 is further inclined by an inclination angle γ in a direction opposite to the movement direction of the slab. As a result, the major axis LB-3 moves to the position of the reference numeral LB-4, and the spray range moves from the reference numeral 45-3 to the position of the reference numeral 45-4.

As described above, the cooling water spray axis J1 is inclined obliquely downward on the slab surface in the line of sight of FIG. 10B, and as a result, the center 450-4 of the spray range 45-4 is further inclined obliquely downward than the original state (reference numeral 450-1). With such a configuration, it is possible to spray the cooling water in the lower right direction in which the cooling water scrapes out the dripping water W1 without being blocked by the lower roll even when the rotation angle β is increased (in FIG. 10B, the cooling water is sprayed in the lower right direction in the figure). As a result, the dripping water W1 is discharged toward the lateral sides of the slab in the width direction, and it is possible to decrease the cooling unevenness of the slab in the width direction.

Patent Document 3 discloses that, as shown in FIG. 2, the spray nozzle main body between the plurality of rolls disposed side by side in the vertical direction is inclined upward with respect to the horizontal plane, and the cooling water is sprayed obliquely upward.

PRIOR ART DOCUMENT
Patent Document

[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2003-285147

[Patent Document 2] Japanese Patent No. 5741874

[Patent Document 3] Japanese Unexamined Patent Application, First Publication No. 2018-1208

DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention

Meanwhile, in continuous casting, there is a desire for an improvement not only in the quality of slabs but also in productivity. As one of measures therefor, it is possible to consider an increase in the heat transfer coefficient between cooling water and the slab surface during spray cooling. For example, as disclosed in Patent Document 1, spraying cooling water to the slab surface at a high pressure increases the amount of the cooling water that comes into contact with the slab surface per unit time, and thus the heat transfer coefficient increases, and the productivity also improves.

However, the method of Patent Document 1 requires the extension of pumps or a new facility such as a high-pressure-compatible pipe, which leads to an increase in costs.

The method of Patent Document 2 is intended to reduce the cooling unevenness of the slab by spraying the cooling water from the upstream side toward the downstream side of continuous casting, but pays no attention to an increase in the heat transfer coefficient between cooling water and the slab surface.

In the apparatus and the method of Patent Document 3, the spraying position is adjusted by inclining the spray nozzle main body with respect to the horizontal plane. However, generally, the interval between the rolls is preferably as narrow as possible, and thus the interval between the outer circumferential surface of the upper roll above the spray nozzle and the outer circumferential surface of the lower roll below the spray nozzle can be, for example, a maximum of approximately 30 mm to 40 mm. It is not easy to insert the spray nozzle main body into such a narrow gap, and furthermore, vertically incline the spray nozzle main body.

The present invention has been made in consideration of the above-described circumstances, and an object of the present invention is to provide a secondary cooling device and a secondary cooling method for continuous casting that improve productivity without causing an increase in costs.

Means for Solving the Problem

In order to solve the above-described problems, the present invention employs the following measures.

(1) A first aspect of the present invention is a secondary cooling device for continuous casting that is configured to cool a slab, which is sent in a casting direction, by spraying cooling water to a slab surface, the secondary cooling device including a plurality of rolls disposed side by side in a vertical direction along the casting direction and a spray nozzle configured to spray the cooling water to the slab surface from between the plurality of rolls, in which the spray nozzle is provided such that a cooling water spray axis of the spray nozzle is inclined with respect to a major axis direction of a spray range of the cooling water on the slab surface, a major axis of the spray range is rotated upward around an axis line that is a perpendicular line to the slab surface from the spray nozzle, and a center of the spray range is positioned above a middle position between a contact position between the roll that is present above the spray nozzle and the slab surface and a contact position between the roll that is present below the spray nozzle and the slab surface.

According to the aspect according to (1), since the center of the spray range is positioned above the middle position, and the cooling water spray axis is inclined obliquely upward with respect to the perpendicular line to the slab surface, it is possible to bring the spraying point of the cooling water close to the contact position between the roll that is present above the spray nozzle and the slab surface. As a result, it is possible to cool the slab surface, which passes through the same contact position and moves downward, before the temperature of the slab surface is significantly increased due to reheating. Therefore, it is possible to enhance the cooling effect on the slab compared with the cooling effect in the related art and to improve productivity. Furthermore, since the cooling effect on the slab can be enhanced without providing a new facility, the cost does not increase.

(2) In the aspect according to (1), the spray nozzle may be provided such that the cooling water spray axis is inclined at 30° to 40° with respect to the major axis direction of the spray range of the cooling water on the slab surface, and the major axis of the spray range rotated 5° to 15° upward around the axis line that is the perpendicular line to the slab surface from the spray nozzle.

(3) A second aspect of the present invention is a secondary cooling method for continuous casting, the secondary cooling method including a step of cooling a slab by spraying cooling water to a slab surface from a spray nozzle disposed between a plurality of rolls disposed side by side in a vertical direction along a casting direction, in which a cooling water spray axis of the spray nozzle is inclined with respect to a major axis direction of a spray range of the cooling water on the slab surface, a major axis of the spray range is rotated upward around an axis line that is a perpendicular line to the slab surface from the spray nozzle, and a center of the spray range is positioned above a middle position between a contact position between the roll that is present above the spray nozzle and the slab surface and a contact position between the roll that is present below the spray nozzle and the slab surface.

According to the aspect according to (3), it is possible to obtain the same action effect as the action effect of (1).

Effects of the Invention

According to each of the above-described aspects of the present invention, it is possible to provide a secondary cooling device and a secondary cooling method for continuous casting that improve productivity without causing an increase in costs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing a part of a secondary cooling device for continuous casting according to an embodiment of the present invention, and an enlarged view of a main part of the side view.

FIG. 2 is a front view showing a disposition state of rolls and spray nozzles in the same embodiment, and an enlarged view of a main part of the front view.

FIG. 3 is a schematic perspective view of the spray nozzle in the same embodiment.

FIG. 4A is a view showing a state in which the cooling water spray axis of the spray nozzle in the same embodiment is inclined with respect to the major axis direction of a spray range and is a top view of the slab surface.

FIG. 4B is a perspective view of FIG. 4A.

FIG. 5A is a view showing a state in which the cooling water spray axis of the spray nozzle in the same embodiment is inclined obliquely upward with respect to a perpendicular line to the slab surface and is a top view of the slab surface.

FIG. 5B is a perspective view of FIG. 5A.

FIG. 6 is an explanatory view showing a cooling mechanism in the secondary cooling device for continuous casting of the same embodiment and shows a schematic diagram (A) of a part of a secondary cooling device for continuous casting, a graph (B) showing the relationship between the casting distance and the sprayed water density, and a graph (C) showing the relationship between the casting distance and the slab surface temperature.

FIG. 7 is a view showing a comparative example for confirming the effect of the present invention and is a front view showing a disposition state of rolls and spray nozzles.

FIG. 8 is a graph showing the simulation results of secondary cooling for continuous casting in an example of the same embodiment and the comparative example.

FIG. 9 is an explanatory view showing a cooling mechanism in a conventional secondary cooling device for continuous casting and shows a schematic diagram (A) of a part of a secondary cooling device for continuous casting, a graph (B) showing the relationship between the casting distance and the sprayed water density, and a graph (C) showing the relationship between the casting distance and the slab surface temperature.

FIG. 10A is a view for showing a secondary cooling method using a conventional secondary cooling device for continuous casting and is a top view of a slab surface.

FIG. 10B is a view showing a state in which a spray range is further moved in FIG. 10A.

EMBODIMENTS OF THE INVENTION

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

In the case of expressing directions in the present embodiment, the +X direction, −X direction, +Y direction, −Y direction, +Z direction, and −Z direction of the coordinate axes shown in FIG. 1 will be respectively referred to as “left”, “right”, “front”, “back”, “up”, and “down”.

[Configuration of Secondary Cooling Device for Continuous Casting]

First, the configuration of a secondary cooling device for continuous casting will be described.

As shown in the upper diagram of FIG. 1, a secondary cooling device 1 for continuous casting includes a plurality of rolls 2 (in the lower diagram of FIG. 1, rolls 2a and 2b) disposed side by side in the vertical direction along a casting direction DC and spray nozzles 3 configured to spray cooling water W to a slab surface 41 from between the plurality of rolls 2. As shown in FIG. 2, the rolls 2 and the spray nozzles 3 are also disposed side by side in the front-back direction.

The diameter R of the roll 2 is preferably 100 mm or more and 400 mm or less. The pitch L1 between the rolls 2 that are vertically adjacent to each other (the distance between the centers C of the rolls 2 vertically adjacent to each other) is 100 mm or more and 450 mm or less. In addition, it is preferable that the tip end portion of the spray nozzle 3 can be inserted into the gap between the outer circumferential surfaces of the rolls 2 that are vertically adjacent to each other. Specifically, the gap is 30 mm to 40 mm.

As shown in the lower diagram of FIG. 1, the spray nozzle 3 includes a nozzle head 31 having, for example, a columnar shape or a prismatic shape. In addition, a spray range 46 of the cooling water W that is sprayed to the slab surface 41 from the nozzle 3 forms an elliptical shape as shown in the lower diagram of FIG. 2. The direction of the major axis LA of this elliptical shape (hereinafter, simply referred to as the major axis direction in some cases) is inclined with respect to the horizontal direction (Y direction), and the center 460 (reference numeral 460-3) of the spray range 46 is positioned above the middle position 44 between a contact position 42 and a contact position 43. Here, the contact position 42 is a contact position between the roll 2a that is present above the spray nozzle 3 and the slab surface 41, and the contact position 43 is a contact position between the roll 2b that is present below the spray nozzle 3 and the slab surface 41. Furthermore, a cooling water spray axis J1 of the spray nozzle 3 is provided so as to be inclined obliquely upward with respect to the perpendicular line to the slab surface 41. The spray nozzles 3 may be provided such that the end portions in the major axis direction of the spray ranges 46 that are adjacent to each other in the front-back direction (Y direction) vertically overlap each other as shown in FIG. 2 or do not overlap each other.

Such a configuration can be realized as described below.

First, as the spray nozzle 3, which is used in the secondary cooling device of the present embodiment, for example, a two-fluid nozzle having the following configuration as shown in FIG. 3 can be preferably used.

That is, as the spray nozzle 3, as shown in FIG. 3, it is possible to employ a configuration including a nozzle main body 11 having a prismatic nozzle head, a plurality of (one pair in the figure) groove parts 12 and 12′ formed at the tip end portion of the nozzle main body 11, a pair of ejection ports 13 and 13′ that is open in an elongated shape in the groove parts 12 and 12′, and a plurality of flow paths 14, 15, and 16 that continues into the ejection ports 13 and 13′. Second end portions of the groove parts 12 and 12′ are formed deeper than first end portions. Furthermore, the positions of the centers of the ejection parts 13 and 13′ in the groove parts 12 and 12′ deviate from the axial core of the nozzle main body 11 and are positioned on the second end portion side of the groove parts 12 and 12′.

In the spray nozzle 3, a fluid sprayed from the ejection ports 13 and 13′ flows along ejection walls that form the groove parts 12 and 12′. Furthermore, since the centers of the ejection ports 13 and 13′ are positioned on the second end portion (deep groove part) side of the groove parts 12 and 12′, a larger amount of the fluid from the ejection ports 13 and 13′ flows into the deep groove part side. Therefore, it is possible to increase the amount of the fluid sprayed from the second end portion (the thick portion of the ejection wall or the deep groove part) side while controlling the amount of the fluid sprayed from the first end portion (the thin portion of the ejection wall or the shallow groove part) side. As a result, the cooling water (gas-liquid mixed mist) is mainly sprayed to a region obliquely forward of the nozzle tip end. Therefore, with this spray nozzle 3, it is possible to make the shape of the spray range 46 on the slab surface 41 an eccentric elliptical shape as shown in the lower diagram of FIG. 2. More specifically, since the cooling water is mainly sprayed to the region obliquely forward of the nozzle tip end, the center 460-1 of the spray range 46-1 moves to the reference numeral 460-3. That is, as indicated by the solid line in the lower diagram of FIG. 2, the spray range 46-3 of the cooling water that is sprayed from the nozzle tip end forms an eccentric elliptical shape.

The groove parts 12 and 12′ may be inclined by 3° to 40° with respect to the direction orthogonal to the axial core of the nozzle main body 11.

That is, in at least one of the groove parts 12 and 12′, the line connecting the lower end of the bottom part of the first end portion (shallow groove part) and the lower end of the bottom part of the second end portion (deep groove part) may be inclined by approximately 3° to 40° with respect to the direction orthogonal to the axial core of the nozzle main body 11. With this inclination angle, it is possible to adjust the distribution of the flow rates toward the respective end portions of the groove parts 12 and 12′ (the distribution of the amounts sprayed from the respective end portion).

As described above, in this spray nozzle 3, since the first end portions of the groove parts 12 and 12′ (spraying ports) configured to spray the cooling water W are formed deeper than the second end portions, as shown in FIG. 4A and FIG. 4B, the cooling water spray axis J1, which is indicated by the solid line, is inclined at an inclination angle α1 with respect to an axis line 310 of the nozzle head 31.

Specifically, the cooling water spray axis J1 of the spray nozzle 3 is inclined at the inclination angle α1 with respect to the major axis direction of the spray range 46 of the cooling water W on the slab surface 41. The axis line 310 is a perpendicular line to the slab surface 41 from the nozzle head 31. In a case where the cooling water spray axis J1 is not inclined with respect to the major axis direction of the spray range 46, and the major axis direction of the spray range 46 is rotated around the axis line 310 with respect to the horizontal direction, as indicated by the dashed-two dotted line in the lower diagram of FIG. 2, the intersection position of the axis line 310 of the nozzle head 31 and the slab surface 41 coincides with the center 460-1 of the spray range 46-1, and the cooling water W is sprayed in a symmetrical pattern with respect to the axis line 310. In contrast, in a case where the cooling water spray axis J1 is inclined with respect to the major axis direction of the spray range 46, as indicated by the solid line in FIG. 4B, since the intersection position of the axis line 310 and the slab surface 41 does not coincide with the center 460-2 of the spray range 46-2, the cooling water W is sprayed in an asymmetric pattern with respect to the axis line 310. In the present embodiment, the cooling water W is sprayed onto the slab surface 41 in an asymmetric pattern as described above.

As shown in FIG. 4B, the inclination angle α1 of the cooling water spray axis J1 in the major axis direction of the spray range 46 is preferably 30° to 40°. Regarding the spread angle in the major axis direction of the cooling water W that is sprayed from the spray nozzle 3, it is preferable that the narrow angle-side angle α2 is more than −90° and less than 90°, and the wide angle-side angle α3 is the inclination angle α1 or more and 95° or less. The narrow angle-side angle α2 is the angle of the cooling water W that spreads toward the narrow angle side of the axis line 310 (in FIG. 4B, the left side of the axis line 310 in the figure), and the wide angle-side angle α3 is the angle of the cooling water W that spreads toward the wide angle side of the axis line 310 (in FIG. 4B, the right side of the axis line 310 in the figure).

In addition, when the major axis of the spray range 46-2 of the cooling water W on the slab surface 41 is rotated upward around the axis line 310 at a rotation angle β from a state in which the axis line 310 is parallel to the perpendicular line to the slab surface 41 and the nozzle head 31 of the spray nozzle 3 is positioned in the middle between the upper and lower rolls 2a and 2b, as indicated by the solid line in FIG. 5A and FIG. 5B, the major axis LA of the spray range 46-2 is directed obliquely upward as indicated by the reference numeral LA-1. As a result, the cooling water spray axis J1 is inclined obliquely upward with respect to the perpendicular line to the slab surface 41, and the spray range moves from the reference numeral 46-2 to the position of the reference numeral 46-3. With such a configuration, it is possible to incline the wide angle side of the spray range 46 in the major axis direction obliquely upward with respect to the horizontal direction as shown in FIG. 2. In addition, it is possible to position the center 460-3 of the spray range 46-3 above the middle position 44, and furthermore, to incline the cooling water spray axis J1 of the spray nozzle 3 obliquely upward with respect to the perpendicular line to the slab surface 41.

As a result, as shown in FIG. 6(A), the cooling water W is sprayed to the spray range 46 having a position above the middle position 44 in the line of sight of FIG. 6 as the center in the vertical direction. That is, as indicated by the solid line in FIG. 6(B), the cooling water W is sprayed to the spray range 46 shifted upward from the conventional spray range 45 in FIG. 9(A) (shown by the broken line in FIG. 6(B)). In addition, the thickness (height) in the vertical direction (Z direction) of the spray range 46 when viewed from the line of sight (+Y direction side) of FIG. 6 becomes thicker than the thickness in the vertical direction (Z direction) of the conventional spray range 45 of FIG. 9(A). Furthermore, when the cooling water spray axis J1 is inclined obliquely upward, as indicated by the dashed-two dotted line in the lower diagram of FIG. 2, it is possible to increase the amount of the cooling water sprayed obliquely upward compared with that in the configuration in which the cooling water spray axis J1 is not inclined with respect to the major axis direction of the spray range 46 and the cooling water W is sprayed in a symmetrical pattern with respect to the axis line 310. Furthermore, it is possible to position the upper end position 461 of the spray range 46 on the slab surface 41 above the upper end position of the spray range 45 on the conventional slab surface 41.

In addition, the rotation angle β of the spray nozzle 3 (spray range 46) that is rotated upward around the axis line 310 is preferably 5° to 15°.

The distance M from the middle position 44 of the pair of rolls 2 to the center 460-3 of the spray range 46 (refer to the lower diagram of FIG. 2) in the vertical direction (Z direction) is more than 0 mm to (L1/2) mm or less.

The distance L2 (X direction) from the tip end of the nozzle head 31 of the spray nozzle 3 to the slab surface 41 (refer to the lower diagram of FIG. 1) is preferably 50 mm or more and 450 mm or less.

The spray range 46 may or may not include the middle position 44 on the slab surface 41. The distance L3 from the upper end position 461 of the spray range 46 to the contact position 42 with the upper roll 2a on the slab surface 41 (refer to the lower diagram of FIG. 1) is preferably 0 mm or more and 200 mm or less. The cooling water W may be sprayed so as to come into contact with the upper roll 2a, but preferably does not come into contact with the upper roll. For example, in a case where the diameter R of the roll 2 is 250 mm, the pitch L1 between the rolls 2 is 290 mm, and the distance L2 from the tip end of the nozzle head 31 to the slab surface 41 is 80 mm, the distance L3 is preferably approximately 45 mm.

The intersection position of the axis line 310 of the spray nozzle 3 and the slab surface 41 may or may not overlap the middle position 44.

As shown in FIG. 2, the inclination directions of the major axis LA of the spray range 46 may be alternately different every row of the slab 4 in the width direction or may be the same. The inclination directions may be symmetrical with respect to the center of the slab 4 in the width direction in a single row.

[Action of Secondary Cooling Device for Continuous Casting]

Next, the action of the secondary cooling device 1 for continuous casting will be described. In a secondary cooling method for continuous casting according to the same embodiment, the slab is cooled with a cooling mechanism as shown in FIG. 6. FIG. 6 shows a schematic diagram (A) of a part of a secondary cooling device for continuous casting, a graph (B) showing the relationship between the casting distance and the sprayed water density, and a graph (C) showing the relationship between the casting distance and the slab surface temperature. Hereinafter, a case where the upper roll 2a in FIG. 6(A) is the first roll 2 of the secondary cooling device 1 will be described.

In the cooling of the slab 4, when a certain predetermined position on the slab surface 41 approaches the contact position 42 with the roll 2a, with which the predetermined position first comes into contact, as indicated by the solid line in FIG. 6(C), the temperature of the slab surface 41 begins to decrease due to the contact with the roll 2a and the consequent roll cooling, and continuously decreases until the certain predetermined position moves downward a predetermined distance or longer apart from the contact position 42.

At this time, the effect margin after the roll cooling by the roll 2a, with which the certain predetermined position first comes contact (the difference in temperature immediately after the roll cooling between the present embodiment and the conventional configuration) ΔTr1 becomes 0° C.

After that, until the certain predetermined position on the slab surface 41 enters the spray range 46, the temperature of the slab surface 41 increases due to the first reheating. Once the certain predetermined position enters the spray range 46, the temperature of the slab surface continuously decreases due to spray cooling until the certain predetermined position passes through the spray range.

At this time, the spray range 46 indicated by the solid line in FIG. 6(B) is shifted above the conventional spray range 45 indicated by the broken line in the same figure when seen from the line of sight of FIG. 6 and becomes thick in the vertical direction (Z direction). Therefore, the first reheating period indicated by the solid line in FIG. 6(C) becomes shorter than the first reheating period in the conventional configuration indicated by the broken line in the same figure, and the spray cooling begins earlier than the spray cooling in the conventional configuration. That is, it is possible to cool the slab surface 41 before the temperature of the slab surface is significantly increased by reheating. Therefore, compared with the conventional configuration, the amount of reheating is decreased, the temperature of the slab surface 41 at the beginning of the spray cooling becomes low, and the heat transfer coefficient during the spray cooling becomes large. As a result, the cooling efficiency E1 becomes higher than the cooling efficiency E9 of the conventional configuration, and the slab surface 41 is cooled to a lower temperature by the spray cooling. In addition, since the cooling water spray axis J1 is inclined obliquely upward, and the amount of the cooling water sprayed obliquely upward is increased, it is possible to further decrease the amount of reheating in the first reheating period and to further increase the heat transfer coefficient during the spray cooling.

In addition, once the predetermined position on the slab surface 41 passes through the spray range 46, the temperature of the slab surface 41 increases due to the second reheating. However, since the temperature at the beginning of the second reheating is lower than the temperature in the conventional configuration, the temperature at the beginning of the cooling by the roll 2b, with which the predetermined position second comes contact, also becomes low, and the effect margin after the roll cooling by the roll 2b ΔTr2 becomes larger than 0° C. After that, the cycle of the first reheating, the spray cooling, the second reheating, and the roll cooling is repeated, whereby the temperature of the slab 4 gradually decreases, and the slab is cooled.

In this cooling process, since the effect margin after the roll cooling gradually increases as the slab is moved downstream in the casting direction, the cooling time of the slab is shortened compared with the cooling time in the conventional configuration.

Effects of Present Embodiment

With the present embodiment, effects as described below are obtained.

Since the center of the spray range 46 is positioned above the middle position 44, and the cooling water spray axis J1 is inclined obliquely upward with respect to the perpendicular line to the slab surface 41, it is possible to bring the spraying point of the cooling water W close to the contact position 42 between the roll 2a that is present above the spray nozzle 3 and the slab surface 41. As a result, it is possible to cool the slab surface 41, which passes through the same contact position 42 and moves downward, before the temperature of the slab surface is significantly increased due to reheating. Therefore, it is possible to enhance the cooling effect on the slab 4 compared with the cooling effect in the related art and to improve productivity. Furthermore, since the cooling effect on the slab 4 can be enhanced without providing a new facility, the cost does not increase.

Therefore, with the secondary cooling device and the secondary cooling method for continuous casting of the present embodiment, it is possible to improve productivity without causing an increase in costs.

Modification Example

The present invention is not limited to the above-described embodiment, and a variety of improvements and design changes are allowed within the scope of the gist of the present invention. In addition, specific order, structure, or the like at the time of carrying out the present invention may be changed to other structures or the like as long as the object of the present invention can be achieved.

For example, the spray nozzle 3 in which the cooling water spray axis J1 is not inclined with respect to the major axis direction of the spray range 46 may be used. In this case, the tip end portion of the spray nozzle 3 is disposed to be close to the slab surface 41 and above compared with the position of the tip end portion in FIG. 6(A), whereby, as indicated by the dashed-two dotted line in the lower diagram of FIG. 2, the intersection position of the axis line 310 of the nozzle head 31 and the slab surface 41 coincides with the center 460 of the spray range 46. Furthermore, the major axis of the spray range 46 may be rotated around the axis line 310, which is a perpendicular line to the slab surface 41 from the spray nozzle 3, and the center 460 of the spray range 46 may be positioned above the middle position 44.

Even with such a configuration, compared with the conventional configuration, it is possible to shift the spray range 46 of the cooling water W upward and to make the spray range thick in the vertical direction (Z direction), and it is possible to improve productivity without causing an increase in costs.

As the spray nozzle 3A, a one-fluid nozzle may be used.

Example

Next, the present invention will be described in more detail using an example, but the present invention is not limited to this example.

Simulation for verifying the effect of the present invention will be described.

Parameters common to the example and a comparative example were set as described below.

- Diameter R of roll: 150 mm or more and 360 mm or less
- Pitch L1 between rolls: 190 mm or more and 430 mm or less
- Distance L2 from tip end of spray nozzle to slab surface: 80 mm or more and 430 mm or less
- Distance L3 from upper end position of spray range to contact position with upper roll on slab surface: More than 0 mm and (L1/2) mm or less
- Amount of water sprayed: 8 L/min or more and 80 L/min or less per nozzle
- Number of nozzles in width direction between rolls: 1 to 16
- Casting speed: 2.0 m/min
- Amount of carbon in molten steel: 0.04%
- Slab width: 1500 mm
- Slab thickness: 250 mm

In addition, the disposition state of the rolls 2 and the spray nozzle 3 in the example was set as shown in FIG. 2, and the disposition state of the rolls 2 and the spray nozzle 9 in the comparative example was set as shown in FIG. 7. “Inclination angle α1 of cooling water spray axis J1 in major axis direction of spray range 46”, “narrow angle-side angle α2 of cooling water W with respect to axis line 310”, “wide angle-side angle α3 of cooling water W with respect to axis line 310”, “rotation angle β of spray nozzle 3 or 9 (spray range 46) rotated upward around axis line 310”, and “distance M from middle position 44 of pair of rolls 2 to center 460 of spray range 46 in vertical direction” in the example and the comparative example are shown in Table 1 below.

In the comparative example, the cooling water spray axis J1 was not inclined with respect to the major axis direction of the spray range 46, and the spray nozzle 9 for which the intersection position of the axis line 910 of a nozzle head 91 and the slab surface 41 coincided with the center 460 of the spray range 46 was used. Regarding the spread angle in the major axis direction of the cooling water W sprayed from the spray nozzle 9, since the angles on both sides of the axis line 910 in the major axis direction (both right and left sides) were the same as each other, an angle obtained by combining the angles on both sides is shown in Table 1.

TABLE 1

Comparative

Example
Example

Inclination angle α1 of cooling water spray axis J1
30° to 40°
0°

Narrow angle-side angle α2 of cooling water W
5° to 25°
90° to 110°

Wide angle-side angle α3 of cooling water W
75° to 95°

Rotation angle β of spray range 46
5° to 15°
0°

Distance M from middle position 44 to
5 to 15 mm
0 mm

center 460 of spray range 46

In addition, simulation of secondary cooling for continuous casting was carried out. FIG. 8 is an example of the results showing the temperature changes of the slab surfaces in the numerical range shown in Table 1.

As shown in FIG. 8, the effect margin after roll cooling due to the contact with the first roll (the difference in temperature immediately after roll cooling between the example and the comparative example) ΔTr1 was 0° C., but the first reheating period after the roll cooling became shorter in the example indicated by the solid line than in the comparative example indicated by the broken line, and the amount of reheating in the example could be decreased more than the amount of reheating in the comparative example by 7° C. (indicated as “ΔTa” in FIG. 8).

In addition, the temperature drop ΔTsc due to spray cooling in the comparative example was 150° C., the temperature drop ΔTsp in the example was 176° C., and the effect margin immediately after the spray cooling (the difference in temperatures immediately after the spray cooling between the example and the comparative example) ΔTb1 was 33° C.

Furthermore, the effect margins after roll cooling due to the contact with second and third rolls ΔTr2 and ΔTr3 were 14° C. and 25° C., and then the effect margins after roll cooling gradually increased as the slabs were moved downstream in the casting direction. In addition, the effect margins immediately after second and third spray cooling ΔTb2 and ΔTb3 were 49° C. and 59° C., and then the effect margins immediately after the spray cooling gradually increased as the slab was moved downstream in the casting direction.

As a result, it was confirmed that, in the example, the cooling time of the slab was reduced by 0.3 min compared with the cooling time in the comparative example.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to provide a secondary cooling device and a secondary cooling method for continuous casting that improve productivity without causing an increase in costs. Therefore, the present invention is significantly industrially applicable.

BRIEF DESCRIPTION OF THE REFERENCE SYMBOLS

- 1 Secondary cooling device
- 2, 2a, 2b Roll
- 3 Spray nozzles
- 4 Slab
- 41 Slab surface
- 42, 43 Contact position
- 44 Middle position
- 46 Spray range
- 460 Center
- J1 Cooling water spray axis
- W cooling water

SECONDARY COOLING DEVICE AND SECONDARY COOLING METHOD FOR CONTINUOUS CASTING

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