JPH10291018A - Method for cooling high-temperature steel sheet and device for cooling high-temperature steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a stream of cooling water having high relative velocity to a steel sheet and to execute highly efficient and uniform cooling without generating lack of a liquid and disturbance of stream even when the flow rate of the cooling water is less. SOLUTION: The steel sheet 1 is transported on lower rolls 3 and restrained with upper rolls 2. Two slit nozzles 4, 6 are provided in two upper and lower stages between the upper rolls 2 and the slit stream (The laminar flow whose cross section is approximately rectangular.) of cooling water is flowed from the upstream side in the transporting direction of the steel sheet 1 toward the upper roll 2 on the downstream side. The flow velocity of the slit stream which is flowed out of a lower slit nozzle 6 is set so as to be faster than the flow velocity of the slit stream which is flowed out of an upper slit nozzle 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for efficiently cooling a hot-rolled hot steel sheet.

[0002]

2. Description of the Related Art In recent years, hot-rolled high-temperature steel sheets are often subjected to strong cooling immediately after rolling, with the aim of increasing strength by quenching heat treatment and reducing costs by reducing alloys.
This cooling is generally performed while a hot steel sheet after rolling is passed online, and the steel sheet is cooled by pouring cooling water from above and below while being transported in a horizontal state.

[0003] At this time, it is important to adjust and control the amount of water so that the cooling in the plate width direction and the plate longitudinal direction is performed equally on average.

Normally, cooling of a steel sheet immediately after rolling is performed by flowing a continuous flow of cooling water having a substantially rectangular cross section in the conveying direction of the steel sheet from a laminar nozzle having a slit shape. Since the steel plate cooling device cools steel plates of various widths, the width of the slit nozzle is set to a wide nozzle according to the maximum width of the steel plate.

[0005] In order to perform strong cooling and uniform cooling, it is important to increase the relative speed of the steel sheet and the cooling water. However, it is not economical to increase the flow rate by increasing the amount of cooling water. Therefore, it is intended to obtain a high flow rate with a small flow rate by narrowing the gap (slit gap) of the slit-shaped nozzle.

[0006]

However, if the slit gap does not have the desired shape due to poor processing of the slit or deterioration over time due to long-term use, the cooling water flow may be disturbed or the liquid may run out. This causes uniform cooling. As the slit gap is reduced, these effects increase accordingly.

Therefore, there is a limit even if the slit gap is reduced, and the slit gap is usually 8 to 10 mm.
It is necessary to do above. Therefore, there is a problem that there is a natural limit in performing high-efficiency cooling with a small amount of cooling water.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and a cooling water flow having a high relative speed between a steel plate and a steel sheet can be achieved without causing a liquid shortage or a water flow disturbance even with a small flow rate of the cooling water. It is an object of the present invention to provide a cooling method and a cooling device for a high-temperature steel sheet that can achieve high efficiency and uniform cooling.

[0009]

The object of the present invention is to provide a method for cooling a high-temperature steel sheet by flowing cooling water along a top surface of the high-temperature steel sheet from a slit nozzle provided near and above the high-temperature steel sheet. The two slit nozzles are provided in the upper and lower stages in close proximity to each other, and the flow rate of the cooling water flowing out of the lower slit nozzle is made faster than the flow rate of the cooling water flowing out of the upper slit nozzle. The problem is solved by a method for cooling a high-temperature steel sheet (claim 1).

[0010] Since the flow rate of the cooling water flowing out of the lower slit nozzle is high, the relative speed with respect to the steel plate is large, and therefore, uniform cooling with good heat transfer efficiency is realized. Further, the cooling water having a low flow rate is supplied from the upper slit nozzle, and the cooling water merges with the water flow immediately after flowing out, so that cooling is performed on the downstream side without occurrence of liquid shortage and disturbance of the water flow.

The reason is considered as follows.

In the case where the liquid film thickness is small, if the flow velocity of the liquid is increased, the liquid is likely to run out even with a small disturbance. On the other hand, the laminar flow jetted from the double slit nozzle is a liquid film flow with a low flow velocity at the upper part of the laminar flow. Less likely to occur. Note that the small disturbance referred to here is, for example, a disturbance in the velocity of the liquid starting from unevenness or dust attached to the slit nozzle outlet with time.

Therefore, according to the present invention, uniform cooling without unevenness in the sheet width direction and the sheet longitudinal direction can be obtained with a small amount of cooling water at a high relative speed to the steel sheet.

The above-mentioned method is a cooling device for a hot steel plate, which is provided in the vicinity of an upper portion of the high-temperature steel plate and in which cooling water flows from a slit nozzle along the upper surface of the high-temperature steel plate. The cooling water flowing from each slit nozzle is provided close to each other and the flow rate of the cooling water can be adjusted independently. Is done.

In this device, since the flow rate of the cooling water flowing out of the upper and lower slit nozzles can be adjusted independently, the flow rate of the cooling water flowing out of the lower slit nozzle is made to flow out of the upper slit nozzle. It can be faster than the cooling water flow rate.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing an embodiment of the present invention. In FIG. 1, 1 is a steel plate, 2 is an upper roll, 3
Is a lower roll, 4 is an upper slit nozzle, 5 is a circular nozzle,
6 is a lower slit nozzle.

The lower roll 3 has a role as a transport roll, and the steel sheet 1 is transported on the lower roll 3 and restrained between the lower roll 3 and the upper roll 2. In this embodiment, the pitch of each lower roll is 1000 mm. Also, one upper roll 2 is provided for every two lower rolls.

Between the upper rolls 2, two slit nozzles 4 and 6 are provided in upper and lower stages, and a slit flow (cross section) flows from the upstream side in the conveying direction of the steel sheet 1 to the upper side roll 2 on the downstream side. Is a continuous flow having a substantially rectangular shape).
In this embodiment, the slit gap of the upper slit nozzle 4 is 10 mm, the slit gap of the lower slit nozzle 6 is 5 mm, and the width is 5 m.

The flow velocity of the slit flow flowing out of the lower slit nozzle 6 is set to be faster than the flow velocity of the slit flow flowing out of the upper slit nozzle 4.

The lower surface of the steel plate 2 is sprayed with water from a tube nozzle 5 submerged in water, and is cooled by a liquid flow generated by the accompanying flow.

FIG. 2 shows a detailed view of an example of the slit nozzle. In the following drawings, the same reference numerals are given to the elements described in the preceding drawings, and the description thereof will be omitted. In FIG. 2, 7, 7 'are cooling water supply pipes, 8, 8' are header pipes,
9, 9 'is a skirt portion, and 10 and 10' are outlets.

The cooling water is supplied to the cooling water supply pipes 7 and 7 via two flow control valves (not shown) capable of independently controlling the flow rate and two shut-off valves (not shown) for turning on and off. To each header tube 8, 8 '. From header tubes 8, 8 ', skirt 9, to inject cooling water onto steel plate,
9 'is extended and cooling water is injected through the skirts 9, 9' from the outlets 10, 10 'at an angle of about 15 degrees to the steel plate.

FIG. 3 shows the flow of the cooling water. The cooling water injected from the discharge ports 10 and 10 ′ of the upper and lower slit nozzles collide with the steel sheet 1 while immediately joining,
As shown by the flow velocity distribution (the size of → corresponds to the velocity) shown in FIG.
There is a layer with a high flow velocity injected from 0 ', and strong cooling and uniform cooling are realized.

As described above, in this embodiment, the slit gap of the lower slit nozzle 6 is 5 mm, and if only the lower slit nozzle 6 is used, turbulence of the cooling water flow or liquid shortage occurs, resulting in uneven cooling. This is the area that causes However, in this embodiment, since the slow slit flow is flowing out from the upper slit nozzle 4,
The turbulence of the cooling water flow generated in the lower slit nozzle 6 and running out of liquid can be prevented.

[0026]

【Example】

(Example) Using the apparatus shown in FIGS. 1 and 2, a high-temperature steel plate was cooled.

The exit speed from the upper slit nozzle 4 is 0.2 m /
In s, the cooling water was discharged from the lower slit nozzle 6 at an outlet speed of 5 m / s. The cooling water flow rate is 0.01 m ³ / s per 5 m width with the upper slit nozzle 4 and 5 m width with the lower slit nozzle 6
0.125 m ³ / s, and the total was 0.135 m ³ / s. On the other hand, the lower surface was cooled by supplying cooling water to the lower surface of the steel plate from a circular pipe nozzle 5 provided at a pitch of 100 mm.

In this cooling device, a thick steel plate just after rolling, width 28
00mm, length 28m, thickness 32mm, initial temperature 920 ° C
Was passed through at a speed of 30 mpm for cooling.
The temperature profile in the width direction of the plate at a stage 30 seconds after passing through the cooling device was measured with a thermometer.
The temperature was 0 ° C. and the variation was ± 10 ° C. This steel sheet was cooled to room temperature on the cooling floor, but no distortion such as warpage occurred. After cooling, it was cut into 400 mm strips in the width direction, but no camber was generated. The hardness in the width direction of the sheet was measured. As a result, no unevenness was found and the hardness distribution was uniform.

Comparative Example 1 A high-temperature steel sheet was cooled using the same equipment as that used in the example. However, in this case, the lower slit nozzle 6 was not used. The slit gap of the upper slit nozzle 4 is the sum of the slit gap 10 mm of the upper slit nozzle 4 and the slit gap 5 mm of the lower slit nozzle 6 in the embodiment.
5 mm. At this time, cooling water was allowed to flow out of the slit at a rate of 5 m / s, which is the same as the cooling water flowing speed from the lower slit nozzle 6 of the example. For this, the cooling water flow rate is 0.375
m ³ / s was required.

As a result of cooling the steel sheet, a result equivalent to that of the example was obtained, but a larger amount of cooling water was required as compared with the example.

(Comparative Example 2) Slit of upper slit nozzle 4
Under the same conditions as Comparative Example 1 except that the gap was set to 5 mm.
Cooled high-temperature steel sheet (cooling water from slit nozzle
The outflow velocity is 5m / s, and the cooling water flow rate at this time is 0.125m
^Three/ s). Then, the cooling water flow is disturbed,
I did this. Therefore, the steel plate after this liquid shortage occurred
High temperature cooling is not applied to parts where cooling water did not reach.
There was a foot area.

Comparative Example 3 Cooling of a high-temperature steel sheet was performed under the same conditions as in Comparative Example 1 except that the outflow velocity of the cooling water from the upper slit nozzle 4 was 0.2 m / s (the flow rate of the cooling water was 0.01 m ³ / s). Was done. At this time, cooling unevenness was observed 50 cm downstream of the upper slit nozzle.

The temperature of the steel sheet after passing through the cooling device was 570 ° C. on average and 70 ° C. variation.

The above results are summarized in Table 1. It can be seen that, in this example, excellent cooling in terms of cooling capacity and uniform cooling can be performed with a smaller flow rate than any of the comparative examples. .

[0035]

[Table 1]

[0036]

As described above, in the present invention, since the flow rate of the cooling water flowing out of the lower slit nozzle is high, the relative speed with respect to the steel plate is large, and therefore, the cooling efficiency with good heat transfer efficiency is uniform. Is realized. Further, the cooling water having a low flow rate is supplied from the upper slit nozzle, and the cooling water merges with the water flow immediately after flowing out, so that cooling is performed on the downstream side without occurrence of liquid shortage and disturbance of the water flow. Therefore, the relative velocity with respect to the steel sheet can be increased with a small flow rate of the cooling water, and uniform cooling without unevenness in the sheet width direction and the sheet longitudinal direction can be obtained.

Therefore, no deformation occurs after cooling of the steel sheet, and no correction work such as pressing or leveling is required later. In addition, the material of the steel plate is improved by reducing the unevenness in the baking in the steel plate. Further, there is no distortion remaining in the steel sheet, and no tempering operation is required.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an embodiment of the present invention.

FIG. 2 is a diagram showing details of an example of a slit nozzle.

FIG. 3 is a diagram showing a state of a flow of cooling water flowing out of a slit nozzle.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel plate 2 Upper roll 3 Lower roll 4 Upper slit nozzle 5 Circular pipe nozzle 6 Lower slit nozzle 7, 7 'Cooling water supply pipe 8, 8' Header pipe 9, 9 'Skirt part, 10, 10' Outflow port

Claims (2)

[Claims] 1. A method of cooling a hot steel sheet by flowing cooling water along the upper surface of the hot steel sheet from a slit nozzle provided near and above the high temperature steel sheet. A method for cooling a high-temperature steel sheet, wherein the flow rate of cooling water flowing out of a lower slit nozzle is set to be higher than the flow rate of cooling water flowing out of an upper slit nozzle. 2. A cooling device for a high-temperature steel plate provided near and above a high-temperature steel plate and configured to flow cooling water from a slit nozzle along an upper surface of the high-temperature steel plate, wherein the two slit nozzles are adjacent to each other in two upper and lower stages. A cooling water flowing out of each slit nozzle, the flow rate of the cooling water being independently adjustable.