JP4076971B2 - Steel plate cooling method - Google Patents

Description

  The present invention relates to a method for cooling a steel plate, and more particularly to a technique for obtaining a steel plate having a good shape by online cooling of a thick steel plate.

As an accelerated cooling method for thick steel plates that sequentially cools a steel plate immediately after hot rolling from the front end to the rear end in the sheet passing direction (a method of air cooling after cooling a specific temperature region at a certain cooling rate), for example, The thing of "patent document 1" is well-known.
In this conventional one, the steel sheet is passed through the front cooling section that is the upper and lower surface slit jet cooling and the rear cooling section that is the upper and lower surface cooling other than the slit jet cooling, from the front end in the sheet passing direction toward the rear end. In order to cool sequentially, when passing the steel plate, the ratio of the amount of water in the upper and lower water (the ratio of the amount of jet water ejected from the slit jet nozzles on the upper and lower surfaces) in the pre-cooling section is set to a predetermined constant value. One-way threading was performed under

Further, in the controlled cooling, the temperature of the upper and lower surfaces of the region immediately before the region where the steel sheet is cooled enters the cooling zone of the cooling device, and the upper and lower surfaces of the cooling zone are measured based on the temperature difference between the upper and lower surfaces of the measurement result. There has also been proposed a technique for changing the water amount ratio to prevent shape defects such as warping and bending (see Patent Document 2).
JP-A-62-289316 JP 2003-293030 A

In the facility described in “Patent Document 1”, it is difficult to obtain a uniform shape (flatness) over the entire length in the sheet passing direction of the steel sheet after cooling by the method of cooling with the upper and lower water amount ratio of the front cooling unit being constant. There was a problem of being.
On the other hand, the thing of the said "patent document 2" measures the upper and lower surface temperature of a steel plate in each cooling zone entrance side, and corrects the upper and lower water volume ratio of the said cooling zone based on the difference of this upper and lower surface temperature. Therefore, there is a problem that the feedforward control is performed, and the control becomes complicated such that high-speed processing is required.

  Then, an object of this invention is to provide the cooling method of the steel plate which can obtain a uniform shape over the full length of a steel plate by simple control, without performing complicated control.

In order to achieve the above object, the present invention takes the following measures. That is, the feature of the present invention is that the hot-rolled steel sheet is passed through a front cooling part that is upper and lower slit jet cooling and a rear cooling part that is upper and lower surface cooling other than the slit jet cooling, In the method of cooling a steel sheet that sequentially cools from the front end to the rear end of the steel sheet, the vertical water ratio of the upper and lower surface slit jet cooling is preset from a preset initial value while the steel sheet passes through the front cooling section. The point is to change to another value.
According to the present invention, since the water / water ratio of the upstream cooling unit is controlled based on a predetermined value, simple control can be performed without performing complicated feedforward control as described in "Patent Document 2".

Further, in the present invention, the relationship between the vertical water amount ratio of the upper and lower surface slit jet cooling and the warpage amount of the front end portion and the rear end portion of the steel sheet is quantified in advance by changing the vertical water amount ratio in various ways. Based on the converted data, the water / water ratio that makes the front end flat is the initial value, and the water / water ratio that makes the rear end flat is the other value.
By adopting such values, a uniform shape can be obtained over the entire length of the steel sheet.

  According to the present invention, since the water / water ratio is controlled so as to have a preset value, a flat steel plate can be manufactured over the entire length of the steel plate by a simple method without complicated control.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
What is shown in FIG. 1 is a rolling cooling facility used for carrying out the method of the present invention.
This cooling facility is connected to the downstream side of a hot rolling facility (not shown), and has a front cooling unit 1 and a rear cooling unit 2. The hot-rolled steel sheet 3 is transported in the direction of arrow a on a pass line 5 formed by transport rolls 4 arranged at a predetermined pitch in the same horizontal plane. By passing, controlled cooling or accelerated cooling is performed so that a predetermined tissue is obtained.

The pre-cooling unit 1 has slit jet nozzles 6 and 6 above and below the pass line 5. On the upper side of the pass line 5, the front and rear of the slit jet nozzle 6 (note that the front and rear in the equipment are referred to as “front” on the upstream side in the plate passing direction (arrow a direction), and “rear” on the downstream side, Before and after the steel plate 3, the draining rolls 7 and 7 are provided so as to be able to contact with and separate from the upper surface of the steel plate 3, with the downstream side in the sheet passing direction as “front” and the upstream side as “rear”.
The transport roll 4 is disposed below and facing the front and rear draining rolls 7. Since the transport roll 4 also functions as the draining roll 7, the transport roll 4 below the draining roll 7 is referred to as a draining roll.

The rear stage cooling unit 2 is an upper and lower surface cooling other than the slit jet cooling. In this embodiment, a pipe lamina nozzle 8 is provided on the upper side of the pass line 5, and a spray nozzle 9 is provided on the lower side.
The amount of water and the ratio of the amount of water in the upper and lower nozzles 6, 8, and 9 of the upstream cooling device 1 and the downstream cooling device 2 can be controlled.
FIG. 2 shows details of the pre-cooling unit 1.
The outlets of the upper and lower slit jet nozzles 6 are inclined at a predetermined angle (θ) with respect to the horizontal so that the cooling water ejected from the nozzles 6 flows along the conveying direction (arrow a direction) of the steel plate 3. Are arranged.

On the lower side of the pass line 5, a rectifying plate 10 is disposed between the slit jet nozzle 6 and a transport roll (draining roll) 4 on the downstream side thereof. Further, on the upper side of the pass line 5, a rectifying plate 10 is disposed between the slit jet nozzle 6 and the draining roll 7 on the downstream side thereof.
The front end of the upper and lower rectifying plate 10 and the slit jet nozzle 6 are in close contact with each other, and a gap through which cooling water can be discharged is provided between the rear end of the rectifying plate 10 and the draining roll 7 or the transporting roll (draining roll) 4. Is formed.

Between the upper rectifying plate 10 and the upper surface of the steel plate 3 and between the lower rectifying plate 10 and the lower surface of the steel plate 3, gaps are formed at predetermined intervals in the vertical direction.
The cooling water ejected from the slit jet nozzle 6 collides with the steel plate 3 to form a collision zone A where the heat of the steel plate 3 is taken away. After the collision, the cooling water flows along the gap between the steel plate 3 and the current plate 10. A flow region B is formed along which the heat of the steel plate 3 is taken while flowing, and then the flow of the cooling water is interrupted by the draining roll 7 or the conveying roll (draining roll) 4 to be in a turbulent state and take the heat of the steel plate 3. A stirring zone C is formed. The current plate 10 has a function of separating the flow area B and the stirring area C from each other.

The cooling method of the steel plate 3 of the present invention using the above-mentioned equipment is the upper and lower sides of the upper and lower slit jet cooling (referred to as cooling by the cooling water from the slit jet nozzle 6) while the steel plate 3 passes through the preceding cooling unit 1. The water amount ratio is changed from a preset initial value to another preset value.
The inventors of the present application conducted various experiments until reaching the present invention.
First, the water amount ratio (up / down water amount ratio) of the slit jet nozzles 6 on the upper and lower surfaces of the pre-stage cooling apparatus 1 was set to a predetermined constant value, and a one-way plate cooling experiment was performed.

Table 1 shows the shape of the steel plate 3 after the one-way plate cooling is performed by variously changing the ratio of the amount of water in the upper and lower water of the pre-stage cooling device 1 of the cooling facility shown in FIG.
The experimental conditions are as follows.
Plate size: Thickness 50mm x width 3000mm x length 15000mm,
Length of front end and rear end: 1000-2000mm
Plate speed: 0.22 m / sec,
Cooling start temperature: 800 ° C.

According to Table 1, the warpage of the front end portion of the steel plate 3 and the subsequently cooled portion (center portion / rear end portion) in the one-way plate cooling is from the lower warp to the upper warp as the water-to-water ratio is increased. However, it was found that there is no water / water ratio that can flatten the front end and the center / rear end. That is, when the water / water ratio is made constant, it is impossible to flatten the entire length of the steel plate after cooling.
To consider the reason, the cooling of the steel plate 3 by the jet water flow in the pre-stage cooling apparatus 1 is considered to be composed of three-stage cooling by the collision zone A, the along flow zone B, and the stirring zone C. In the stirring zone C, when the front end of the steel sheet reaches the draining roll, the stirring phenomenon begins to occur for the first time, and when the stirring is in a steady state, the front end of the steel sheet 3 is already at the draining roll. Therefore, it is considered that this region C hardly contributes to the cooling of the front end portion of the steel plate 3.

That is, the cooling method is different between the front end portion and the central portion / rear end portion of the steel plate 3, and it is necessary to set the water amount ratio of the upper and lower jet water according to each cooling method. it was thought.
Therefore, the inventors of the present application made a graph to quantify the data in the experiment shown in Table 1. The graph is shown in FIG.
According to FIG. 3, it is understood that the water / water ratio in which the front end of the steel plate 3 is flat is 0.8, and the water / water ratio in which the center / rear end is flat is 1.3.

  Next, an experiment was conducted as to which timing is optimal for changing the water / water ratio. The results are shown in Table 2 below.

According to Table 2, it can be seen that the optimum timing for changing the water amount ratio is when the steel sheet tip advances 1000 mm to 2000 mm from the downstream draining roll 7.
From the above experiments, the following can be generalized.
That is, when the steel plate 3 is passing through the pre-cooling section 1, when changing the water ratio of the upper and lower surface slit jet cooling from the preset initial value to another preset value, The relationship between the vertical water amount ratio of the upper and lower surface slit jet cooling and the warpage amount of the front end portion and the rear end portion of the steel plate 3 is quantified in advance by changing the vertical water amount ratio in various ways, and based on the quantified data, the front end The steel plate 3 that is flat over the entire length can be obtained by setting the water / water ratio in which the part is flat as the initial value and the water / water ratio in which the rear end part is flat as the other value.

  The best time to switch the water / water ratio is when the front end of the steel plate 3 advances 1500 mm from the downstream draining roll 7.

In order to confirm the effect of the present invention, a comparison experiment with a conventional method was performed under the following conditions.
Accelerated cooling equipment: Front stage upper / lower slit jet cooling, rear upper surface pipe lamina / lower surface spray cooling.
Steel plate size: 50 mm thickness x 3000 mm width x 18000 mm length.
Cooling start temperature: 900 ° C.
Cooling stop temperature: 200 ° C. or less.
Slit jet cooling water flow ratio: Change during feeding (method of the present invention), fixing during feeding (conventional method).
Top / bottom water ratio of upper surface pipe lamina / lower surface spray cooling: fixed in through plate.

  The results are shown in Table 3.

According to Table 3, it can be seen that a flat steel plate can be obtained over the entire length according to the present invention.
In addition, this invention is not limited to what is shown to the said embodiment.

  The present invention can be used for on-line cooling of hot plate rolling.

FIG. 1 is a configuration diagram of a cooling facility used in the method of the present invention. FIG. 2 is a detailed view of the pre-cooling unit shown in FIG. FIG. 3 is a graph showing the relationship between the ratio of the amount of water between the upper and lower water in the slit jet cooling and the amount of warpage of the steel sheet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st stage cooling part 2 2nd stage cooling part 3 Steel plate 6 Slit jet nozzle 7 Draining roll 10 Current plate

Claims (2)

The hot-rolled steel sheet is sequentially cooled from the front end to the rear end of the steel sheet by passing through the front cooling section with upper and lower slit jet cooling and the rear cooling section with upper and lower surface cooling other than the slit jet cooling. In the cooling method of the steel sheet
A method for cooling a steel sheet, wherein the steel sheet is changed from a preset initial value to another preset value while the steel sheet passes through the pre-stage cooling section. The relationship between the water ratio of the upper and lower surface slit jet cooling and the amount of warpage of the front end and the rear end of the steel sheet is preliminarily quantified by changing the water ratio in various ways.
2. The water / water ratio that makes the front end flat based on the quantified data is the initial value, and the water / water ratio that makes the rear end flat is the other value. A method for cooling steel sheets.

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