JPH10176224A - Cooling method and cooling device for steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cooling method of a steel plate which can cool even in the low cooling capacity range besides the conventional high cooling capacity by enlarging the flow rate range capable of obtaining plate like flattened water film to a low flow rate side, and a device therefor. SOLUTION: This cooling method executes cooling by using a slit-laminar type cooling device to use the plate like flattened water film flowed out from a nozzle having partitioned plates parallel with the flow-out direction of the cooling water, near the end parts in the width directions of the nozzle outlet. The cooling device has the partitioned plates of >=10mm length and <=4mm thickness, which are parallel with the flow-out direction of the cooling water at a position of 2-50mm from the inner wall surface at the end parts in the width direction of the nozzle outlet of the slit-laminar type cooling device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for cooling a steel sheet, and more particularly, to a method and apparatus for uniformly cooling the upper surface of a steel sheet with a small amount of cooling water.

[0002]

2. Description of the Related Art A laminar flow cooling device is widely used as a device for cooling an upper surface of a steel plate in a runout table of a hot rolling mill in a steel mill, a control cooling facility of a plate mill, and the like. Among them, there is a slit laminar type cooling device that cools a steel plate with a plate-shaped smooth water film. FIG. 5 (A)
FIG. 5B is an explanatory view of a method of cooling the steel plate 4 by the slit laminar type cooling device, and FIG. 5B is a sectional view taken along the line YY. The cooling water supplied to the nozzle header 1 through the water supply pipe 5 flows out from the outlet of the nozzle 2 as a plate-shaped smooth water film, and forms a rectified water film on the surface of the steel plate 4 to cool the steel plate. I do. The method of cooling using this cooling device can provide uniform cooling in the width direction of the steel sheet, has a high cooling capacity,
Since the distance between the nozzle and the steel plate can be increased, there is an advantage that the degree of freedom of equipment arrangement is increased.

However, despite these advantages, the slit laminar type cooling device cannot be said to be particularly popular as compared with other cooling methods. In order to utilize the cooling control, it is desirable that the cooling rate can be freely controlled. However, in this cooling method, the lower limit of the amount of cooling water determined by the slit interval t at the outlet of the nozzle 2 is large, and it is difficult to obtain a low cooling capacity. Obstacles.

[0004] The range of the amount of water in which a plate-like smooth water film can be obtained by the slit laminar type cooling device is substantially determined by the slit interval t at both upper and lower limits. When the amount of water exceeds the upper limit, the water film becomes turbulent. When the amount of water exceeds the lower limit, the water film is sucked from the nozzle outlet to break the water film (hereinafter, simply referred to as “water film breakage”), and a smooth water film flow is generated. No longer available. When the water film breaks, the uniformity and stability of cooling are significantly impaired, and the mechanical performance and shape of the product are greatly affected. The slit laminar type cooling device has one of the attractive features that the number of nozzles can be reduced and the equipment cost and operation cost can be reduced because the cooling capacity per nozzle is high. A small number will hinder stable operation. For this reason, when a slit laminar type cooling device is used, it must be used only in a flow rate range in which a plate-like smooth water film can be stably obtained (this is a high cooling capacity region). The narrow selection range of functions is a major reason why the application of this device is forgotten.

Japanese Patent Application Laid-Open No. 60-133911 discloses that a plate-shaped smooth water film flow is obtained by narrowing the cross-sectional shape of a slit laminar nozzle toward an outlet (t ₀ > t). The lower limit flow rate that can be obtained (hereinafter simply referred to as “water film lower limit flow rate”
) Is disclosed. According to this method, the lower limit of the water film flow rate can be reduced by about 30% as compared with the case where a conventional nozzle having no taper is used, but it is still not sufficient for a demand for expanding the cooling control range.

[0006]

The problem to be solved by the present invention is to increase the flow rate range in which a plate-shaped smooth water film can be obtained to the low flow rate side, and to provide a low cooling capacity in addition to the conventional high cooling capacity. It is an object of the present invention to provide a method of cooling a steel sheet that can be cooled even in a region and a device therefor.

[0007]

The gist of the present invention resides in a method of cooling a steel sheet described in the following item (1) and a cooling device thereof described in the item (2).

(1) A cooling method using a slit laminar type cooling device, wherein a plate-shaped smooth surface is discharged from a nozzle provided with a partition plate near an end in a width direction of an outlet in parallel with a flow direction of cooling water. A cooling method characterized by cooling using a water film.

(2) In the slit laminar type cooling device, a length of 10 mm or more and a thickness of 4 mm or less are provided at a position of 2 to 50 mm from the inner wall surface at the width direction end of the nozzle outlet, in parallel with the outflow direction of the cooling water. A cooling device comprising a partition plate.

Hereinafter, the concept based on the present invention will be described with reference to the drawings.

FIG. 6 is a view for explaining a mechanism when a water film break occurs in the slit laminar type cooling device. As shown in FIG. 6, when the flow rate is gradually reduced in the slit laminar apparatus, the contraction of the end of the water film flow becomes large under the influence of the surface tension. Finally, the air is sucked in from the end and the water film breaks. Considering the conditions under which the water film breaks from the balance of the forces, the interface pulling force S by the surface tension is larger than the interface pulling force I by the inertia force of the water film flow as shown in FIG.

Since the flow of water in the width direction is free in the nozzle, once the contraction occurs, a component in the width direction is generated in the flow velocity inside the nozzle, and as a result, the interface lowering force I due to inertia decreases. It is conceivable to further increase the contraction. That is, the contraction and the increase in the width component of the flow velocity (that is, the decrease in the flow velocity component in the vertical direction) interact with each other to decrease I, increase S relatively, and raise the interface. It is presumed that the inhalation of air causes the water film to break.

Conversely, if the flow velocity component in the width direction is not generated near the nozzle end, the contraction of the flow is suppressed and the water film formation is stabilized, and even if the cooling water amount is reduced, the flow from the end is reduced. Water film breakage is less likely to occur, and cooling with a plate-like smooth water film having a low water amount becomes possible. The present invention has been completed based on the above concept.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to examples. FIG. 1 is an enlarged sectional view of one end 2a of an outlet of a nozzle 2 of a slit laminar type cooling apparatus according to an embodiment of the present invention. In the present invention, the partition plate 6a is provided near the end of the nozzle outlet to suppress the generation of the flow velocity component in the width direction.

The distance A between the surface of the partition plate 6a and the inner wall surface of the nozzle end 2a is 2 to 50 mm. If the distance A exceeds 50 mm, a flow component in the width direction occurs between the partition plate 6a and the inner wall surface, and the effect of providing the partition plate is impaired. When the distance A is less than 2 mm, the function as a flow path between the partition plate and the inner wall surface is reduced, and the effect of the present invention is reduced. Distance A is preferably between 3 and 20 mm. These partition plates are desirably installed near the left and right ends of the nozzle 2 in the width direction. However, when the flow rate is uneven in the width direction of the nozzle or the like, the effect can be sufficiently exerted by installing only near the end on the low flow rate side.

The length B of the partition plate 6a is preferably at least 10 mm or more in the nozzle. If the partition plate is shorter than this, a flow contraction is likely to occur due to insufficient suppression of the flow velocity component in the width direction near the nozzle end. Any length is acceptable as long as it is 10 mm or more. The thickness C of the partition plate 6a is preferably thin so as not to disturb the flow of water. If this is too thick, the water film is divided by the partition plate, and the water film formation is more likely to be impaired. Therefore, it is desirable that the upper limit of the thickness C of the partition plate is 4 mm.

The vertical positional relationship between the partition plate 6a and the lower end of the nozzle is basically based on the fact that the lower end of the partition plate is positioned at the same height as the lower end of the nozzle 2. However, FIG.
The lower end of the partition plate 6a is higher than the lower end of the nozzle as shown in FIG. 4A (the distance between them is defined as Da), or protrudes from the lower end of the nozzle as shown in FIG. (A protruding margin is assumed to be Db) or the like. If the distance Da in the case of FIG. 4A is 5 mm or less, the effect of lowering the water film lower limit flow rate can be obtained.
If it exceeds 5 mm, the effect of suppressing the flow velocity component in the width direction at the nozzle outlet end is weakened, which is not preferable. FIG. 4 (B)
In the case of (1), it is preferable to increase the protrusion allowance Db unless the water film is divided by the partition plate. The reason is that the protruding portion produces an effect of suppressing the contraction. Db is 10
If it is not less than mm, the lower limit of the water film flow rate is further improved by about 5% as compared with the case of Db: 0. If Db is excessively large, the water film may be broken, so that Db is preferably set to 50 mm or less. The length B of the partition plate when the partition plate protrudes from the lower end of the nozzle is, for example, 25 mm or more when Db is 15 mm.

The sectional shape of the partition plate may be any shape which does not disturb the water flow, and may be a rectangular cross section like the partition plate 6a shown in FIG. However, as shown in FIG. 3A, a partition plate 6b having upper and lower ends formed into an acute angle, and a partition plate 6c having a streamlined cross section as shown in FIG. A shape is more preferable.

The partition plate according to the present invention is disclosed in JP-A-60-13391.
By providing the tapered nozzle disclosed in Japanese Patent Publication No. 1, the lower limit of the water film volume can be further reduced.

[0020]

【Example】

(Example 1) the width W is used 1400 mm, the length L is 500 mm, 7 to 12 mm slit interval t of the nozzle outlet, the slit laminar type cooling device and the slit interval t ₀ = t of the nozzle inlet, a nozzle end portions Distance A from each inner wall surface is 5
At the position of mm, a metal partition plate 6a having a length B of 100 mm, a thickness C of 2 mm, and a rectangular cross section at the upper and lower ends is installed, and water is passed through the metal partition plate 6a to obtain a water film lower limit flow rate. Was. The position of the lower end of the partition plate was the same as the lower end of the nozzle (Da = 0). The lower limit flow rate of the water film was also examined using an apparatus having the same dimensions as above except that the cross-sectional shape of the nozzle was tapered at t ₀ = 4t.

FIG. 2 shows the results of these tests. In the present invention example 1 and the comparative example 1 shown in FIG. 2, the nozzle shape is t ₀ = t.
And the results of the present invention example 2 and the comparative example 2 are obtained when the nozzle shape is t ₀ = 4t. As can be seen from this figure, when the partition plate of the present invention is applied to the conventional nozzle in which t ₀ = t, the lower limit of the water film flow rate is about 40%.
Reduced. In addition, when the partition plate of the present invention was provided to the tapered nozzle disclosed in Japanese Patent Application Laid-Open No. 60-133911, the lower limit flow rate of the water film could be reduced by about 50% compared to the conventional apparatus.

In the comparative example, the amount of water near the lower limit of the water film flow rate (for example, the point in FIG. 2, t = 9 mm, and the flow rate is 0.65 m ³ /min.m
In (2), the water film formation becomes unstable if there is a water pressure fluctuation due to the contraction of flow at both ends of the nozzle. However, under the conditions of the present invention example, an extremely stable smooth water film was obtained.

(Embodiment 2) The width W is 1400 mm and the length L is 500
In mm, slit spacing t of the nozzle outlet is 9 mm, the distance A from the respective inner wall surfaces of the left and right ends of the outlet of the nozzle 2 of the slit laminar type cooling device and the slit interval t ₀ = t of the nozzle inlet 1.5 to Length B is 8 to 50 at 55mm
A 0 mm partition plate was installed, and water was passed through the partition plate to determine the water film lower limit flow rate. The position of the lower end of the partition plate was the same as the lower end of the nozzle (Da = 0). Table 1 shows the results of the water film lower limit flow rate investigation when the thickness C of the partition plate was 4 mm.

[0024]

[Table 1]

When the slit interval at the nozzle outlet was 9 mm and there was no partition plate, the minimum flow rate of the water film was 0.63 m ³ /min.m. As shown in Table 1, the use of the cooling device that satisfies the condition described in the second aspect of the present invention significantly reduces the water film lower limit flow rate. The water film minimum flow rate under the same conditions as above except that the thickness C of the partition plate was 2 mm was not different from the case of C = 4 mm. When the thickness C of the partition plate was set to 6 mm, the water film was divided and a good plate-like smooth water film could not be obtained.

(Embodiment 3) The width W is 1400 mm and the length L is 500
mm, the slit interval t at the nozzle outlet was 9 mm, and the slit interval t ₀ = t at the nozzle inlet. The length B was 100 at the left and right ends of the outlet of the nozzle 2 of the slit laminar type cooling device.
mm, a partition plate having a thickness C of 2 mm, a distance A from each inner wall surface of 5 mm, and a lower end portion of the partition plate is provided at a position protruding from a lower end portion of the nozzle, and water is passed through the partition plate so that a water film lower limit flow rate is reduced. I asked. Table 2 shows the results.

[0027]

[Table 2]

When the protrusion amount Db becomes 10 mm or more, Db =
In comparison with the case of 0, the lower limit of water amount at which a smooth water film is obtained is 0.39
To 0.36 m ³ /min.m, and the water film forming flow region is further expanded.

[0029]

By installing a partition plate near the widthwise end of the exit of the slit laminar type cooling device nozzle,
Even if the amount of cooling water is significantly reduced, a stable and smooth water film flow can be obtained. Thereby, cooling can be performed uniformly in the width direction over a wide range from high cooling ability to low cooling ability. In addition, this device can be manufactured in the same size range as before and at low cost.
This can be realized only by modifying the existing slit laminar type cooling device.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of one end of a nozzle outlet showing an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a slit interval at a nozzle outlet and a water film lower limit flow rate.

FIG. 3 is an enlarged sectional view of one end of a nozzle outlet showing another embodiment of the present invention.

FIG. 4 is an enlarged sectional view of one end of a nozzle outlet showing another embodiment of the present invention.

FIG. 5A is an explanatory view of cooling a steel sheet by a slit laminar type cooling device. (B) Sectional drawing of a slit laminar type cooling device.

FIG. 6 is an explanatory diagram of a water film breakage generation mechanism in a slit laminar type cooling device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Nozzle header 2 Nozzle 2a Nozzle outlet end part 3 Smooth water film flow 4 Steel plate 5 Water supply pipe 6 Partition plate L Nozzle length W Nozzle width I Water film flow inertia S Surface tension of water film A the partition plate from the drawing amount Db nozzle lower end portion of the partition plate from the thickness Da nozzle lower end portion of the distance B partition plate length C partition plate between the inner wall surface of the nozzle end protrusion amount t ₀ at the nozzle inlet Slit interval t Slit interval at nozzle exit

Claims (2)

[Claims] 1. A cooling method using a slit laminar type cooling device, wherein a plate-shaped smooth water film is discharged from a nozzle provided with a partition plate near an end in a width direction of an outlet in parallel with a flow direction of cooling water. A method for cooling a steel sheet, wherein the method is characterized by cooling using a steel sheet. 2. In a slit laminar type cooling device, at a position of 2 to 50 mm from an inner wall surface at a width direction end of a nozzle outlet,
A cooling device comprising: a partition plate having a length of 10 mm or more and a thickness of 4 mm or less, which is parallel to a flow direction of cooling water.