JP2004059971A - Method for controlling cooling of steel strip - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for controlling cooling of a steel strip in a vertical pass of a continuous annealing facility with which the development of meandering and rolling flaw of the steel strip can be prevented by performing the uniform cooling in the width direction of the steel strip. <P>SOLUTION: In the cooling control method of the steel strip in the vertical pass in the continuous annealing facility, a process for setting divided patterns in the width direction of coolant supplying headers, based on the strip width and kind of steel in the steel strip and number of the coolant supplying headers, a process for calculating the difference between the actual measured temperature distribution and the target temperature distribution and a process, in which in the case the difference between the target temperature distribution and the actual measured temperature distribution in the width direction of the steel strip is out of the permissible range, the number of the coolant supplying headers for starting (ON) or stopping (OFF) the coolant-supply, is calculated, are provided. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for controlling cooling of a steel strip in a vertical pass of a continuous annealing facility.
Specifically, the present invention relates to a method for controlling the cooling of a steel strip that performs uniform cooling in the width direction of the steel strip in a continuous annealing facility.
[0002]
[Prior art]
Various proposals have hitherto been made and put into practice regarding a method of cooling a steel strip in a continuous annealing facility.
FIG. 1 is a diagram showing the entire configuration of the continuous annealing equipment.
In FIG. 1, a steel strip subjected to tension control by dancer rolls and bridle rolls (furnace entrance side BR, furnace exit side BR) is heated by a heating zone (HF) and retained by a soaking zone (SF). It is cooled by the primary cooling zone (1CF).
Next, after the overaging treatment is performed in the overaging zone (OAF), it is cooled to room temperature by the secondary cooling zone (2CF) and the water cooling tank (WQ).
[0003]
FIG. 2 is a diagram illustrating a method of cooling a steel strip in a vertical pass of a primary cooling zone of a continuous annealing facility.
In FIG. 2, the steel strip 1 bent vertically by the direction change roll 2 is cooled by the refrigerant injected from the refrigerant supply header 4.
The bending back by the direction change roll 2 causes a warp (C warp) in the width direction of the steel strip 1, and dripping water due to cooling water is generated in a central part of the steel strip 1. If the steel strip 1 meanders in the width direction due to overcooling or a temperature deviation in the width direction, roll flaws may be generated in the steel strip, which causes problems in operation and quality. I was
Further, when the line speed is increased, the supply amount of the refrigerant is increased, and it is easy to meander. Therefore, it is necessary to perform the operation at a reduced line speed.
[0004]
FIG. 3 is a diagram showing a temperature distribution in a sheet width direction when a steel strip is cooled by a conventional cooling device.
In FIG. 3, the horizontal axis indicates the position in the sheet width direction, and the vertical axis indicates the deviation (° C.) from the center target sheet temperature.
In the example of FIG. 3, the temperature of the steel strip center is low due to the effect of the dripping water generated in the center of the steel strip, and the temperature of the steel strip edge is also low due to the heat removal from the steel strip edge end face.
In addition, the temperature of the left side (DS) is lower than that of the right side (WS) in FIG. 3, and the shape of the left side (DS) of the steel strip is deteriorated. Was.
[0005]
FIG. 4 is a diagram showing a shape of a steel strip cooled by a conventional cooling device.
In FIG. 4, middle elongation occurs due to supercooling of the steel strip center part, ear waves occur due to supercooling of the edge part, and the shape is deteriorated because the temperature on the left side (DS) of the steel strip is low.
As a conventional technique aiming at uniform cooling in the width direction of the steel strip, for example, WO97 / 44498 discloses a technique in which a cooling nozzle is inclined toward both ends in the width direction of the steel strip to generate the cooling nozzle in the center of the steel strip. A method for preventing dripping water is disclosed.
However, in this prior art, the structure of the inclined cooling nozzle and the structure of the width direction divided header are disclosed, but the specific control method of the width direction divided header is not disclosed.
[0006]
[Problems to be solved by the invention]
The present invention solves the problems of the prior art as described above, performs uniform cooling in the width direction of the steel strip, and prevents the meandering of the steel strip and the occurrence of roll flaws in the vertical pass of the continuous annealing equipment. It is an object to provide a cooling control method for a steel strip.
[0007]
[Means for Solving the Problems]
The present invention has been made by studying a specific control method of the width direction divided header in order to solve the above-described problem, and the gist of the invention is as described in the claims. The contents are as follows.
(1) A method for controlling cooling of a steel strip in a vertical pass of a continuous annealing facility,
Based on the plate width of the steel strip, steel type and the number of refrigerant supply headers to be used, a step of setting a width direction division pattern of the refrigerant supply header,
Measuring the actual temperature distribution in the width direction of the steel strip, and calculating the difference between the actual temperature distribution and the target temperature distribution;
Calculating a refrigerant supply header number for starting (ON) or stopping (OFF) the refrigerant supply when a difference between the target temperature distribution and the actual temperature distribution in the width direction of the steel strip is out of an allowable range. A method for controlling the cooling of a steel strip.
[0008]
(2) The widthwise division pattern of the coolant supply header always starts (ON) the coolant supply to the center portion (center) in the width direction of the steel strip, and other than the middle portion in the width direction of the steel strip (middle). Or (1) starting or stopping (OFF) the supply of the refrigerant to the steel strip.
(3) A target temperature distribution in the width direction of the steel strip is defined as a sine curve, actual temperatures at a plurality of points in the width direction of the steel strip are measured, and a difference from the target temperature distribution is calculated. ) Or (2).
(4) The coolant supply header that starts (ON) or stops (OFF) coolant supply based on the difference between the actual temperature distribution in the width direction of the steel strip and the target temperature distribution in the vertical path of the continuous annealing equipment. The method for controlling cooling of a steel strip according to any one of (1) to (3), wherein the refrigerant supply header on the upper side is preferentially selected.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 5 is a diagram showing an embodiment of a steel strip cooling control method according to the present invention.
In FIG. 5, the steel strip 1 is bent back vertically by the direction change roll 2 and transported to a vertical path.
This vertical path is provided with a coolant supply header 4 for spraying and cooling a coolant from both sides of the steel strip 1. In the present embodiment, a coolant supply header group divided into N blocks on one side on both sides of the steel strip 1. Are installed in each block, and three blocks are provided on each block, and there are a total of 6N refrigerant supply headers on one side, 3N stages.
[0010]
In the upper unit of the vertical path (one unit in FIG. 5), radiant cooling nozzles inclined toward both ends in the width direction of the steel strip are installed on the lower surface side (−surface side) of the descending steel strip in the horizontal path. Thereby, dripping water generated at the center of the steel strip can be eliminated in the direction of both ends in the width direction of the steel strip, and as a result, supercooling of the steel strip center can be reduced.
In addition, in FIG. 5, the block of a lattice pattern is a place where a radiation cooling nozzle is installed.
[0011]
On the other hand, the lower unit (two units in FIG. 5) of the vertical path is provided with six refrigerant supply headers from the lower part of the upper surface side (+ side shown in FIG. 5) in the horizontal path of the descending steel strip. By installing radiant cooling nozzles inclined toward both ends in the width direction, dripping water generated in the center of the steel strip can be eliminated in the direction of both ends in the width direction of the steel strip. The supercooling of the section can be reduced.
[0012]
Next, the installation location of the width-wise divided header in the present embodiment will be described.
In FIG. 5, the width direction divided headers were installed in the # 2 to #N blocks on the minus side of one unit of the steel strip indicated by oblique lines.
By installing the width direction division header, supply of the refrigerant to both ends of the steel strip can be selectively started and stopped, and overcooling of the steel strip edge can be prevented.
[0013]
The number of headers to be installed in the width direction is determined by the temperature difference between the steel strip center and the edge to prevent plastic deformation of IF steel, which is a soft steel type that is apt to undergo plastic deformation due to the temperature difference between the steel strip center and the edge. In order to reduce the temperature to 20 ° C. or lower, the temperature was set by determining the number of refrigerant supply headers at which the injection of the refrigerant to the steel strip edge should be stopped.
In the present embodiment, the width direction division header is installed in only one unit, but the width direction division header may be installed in two units.
[0014]
The size (steel width) of the steel strip, the steel type, and the number of refrigerant supply headers to be used are transmitted from the process computer shown in FIG. 5 to the control device.
The control device sets a width direction division pattern of the steel strip in accordance with the width of the steel strip, the steel type, and the number of refrigerant supply headers to be used, and starts (ON) and stops (OFF) the refrigerant supply to the divided headers and the refrigerant. Controls the amount of refrigerant supplied to the supply header.
A width direction sheet thermometer is installed on the outlet side of the steel strip cooling device in FIG. 5, and can measure the temperature distribution in the width direction of the steel strip. This sheet thermometer is preferably a scanning-type sheet thermometer, and it is preferable that nine points among the actual temperatures of the entire width of the steel strip be transmitted to the control device as representative values.
[0015]
In this control device, based on the difference between the target temperature distribution and the actual temperature distribution in the width direction of the steel strip set according to the width of the steel strip, the steel type and the number of refrigerant supply headers to be used, the supply of the refrigerant to the refrigerant supply header is performed. By setting a division header to be started (ON) and stopped (OFF) and opening and closing the valve of the division part, the actual temperature distribution can be made closer to the target temperature distribution.
FIG. 6 is a diagram showing a processing flow of a process controller as a control device used in the present invention.
In FIG. 6, the feedforward control based on the strip information including the size and steel type of the steel sheet performs the opening and closing operation of the divided header in advance,
A real-time split header opening / closing pattern is set by performing split header opening / closing calculation by feedback control based on the deviation between the target sheet temperature distribution and the actual sheet temperature distribution.
FIG. 7 is a diagram illustrating a split header in the steel strip width direction.
In FIG. 7, the upper, lower, middle and lower three headers indicate one of the # 2 to #N blocks in FIG.
The upper header and the middle header are each divided into five in the width direction of the steel strip, and a solenoid valve (SOV) is provided under the divided header to selectively start and stop the supply of the refrigerant. be able to.
[0016]
In particular, solenoid valves (SOV) are installed in the left and right refrigerant supply lines of the steel strip in the most frequently used middle section divided header, and the refrigerant can be supplied to only one of the left and right headers. it can.
By using this width direction divided header, by starting and stopping the supply of the refrigerant for each header, it is not necessary to perform complicated flow rate control, and it is possible to easily prevent overcooling of the steel strip edge portion, As a result, it is possible to prevent the meandering of the steel strip and the occurrence of roll flaws.
[0017]
In the example of FIG. 7, the refrigerant is supplied to the white divided header, the upper header supplies the refrigerant only to the center, and the middle header supplies the refrigerant to the center and the right middle part. By stopping (OFF) the supply of the refrigerant to the other divided headers, the temperature distribution in the width direction of the steel strip can be made closer to the target temperature distribution.
Further, the widthwise division pattern of the refrigerant supply header is such that the supply of refrigerant to the central portion (center) in the width direction of the steel strip is always started (ON), and other than the central portion in the width direction of the steel strip (middle or side). ) Is preferably started (ON) or stopped (OFF). Since the center of the steel strip serves as a reference for the temperature of the steel strip, it is possible to approach the target temperature by adjusting the overall coolant supply rate, while the middle and sides of the steel strip are likely to be partially supercooled. This is because it is necessary to approach the target temperature by stopping the supply of the refrigerant to the divided header.
In addition, a shutoff valve (SOV) and a flow control valve (FCV) are provided under each header, so that the supply of the refrigerant to each header can be stopped and the supply amount can be controlled.
[0018]
As the refrigerant, a mixture of an inert gas such as N2 and cooling water is preferable from the viewpoint of cooling capacity and availability, and in particular, a supply port of a gas used for the refrigerant is provided on one side of the refrigerant supply header. In this case, an imbalance in the air flow occurs in the width direction of the steel strip. Therefore, by changing the supply balance between the left and right cooling water, the cooling speed in the width direction of the steel strip can be made uniform.
FIG. 8 is a diagram showing a flow of a cooling control method for a steel strip in the present invention.
In FIG. 8, first, a division pattern in the width direction of the coolant supply header is set based on the plate width of the steel strip, the steel type, and the number of coolant supply headers to be used.
Here, the width of the steel strip is designated as one of three widths, four widths, and five widths depending on the use of the steel strip, and is the basic data for dividing the header in the width direction of the steel strip.
[0019]
In addition, since the meandering behavior of the steel strip and the accuracy of the sheet thermometer differ depending on the steel type, this is an important factor in determining the width direction division pattern of the header in the width direction. For example, IF steel, general Al-K steel, 440 It is preferable to use four categories of high tensile strength of 590 MPa class and high tensile strength of 780 MPa class or higher.
The number of coolant supply headers to be used is set to adjust the cooling capacity according to the thickness of the steel strip and the production amount. Further, when an operation trouble occurs, it is necessary to reduce the line speed. In this case, the number of refrigerant supply headers to be used is also reduced.
[0020]
Next, the temperature distribution in the width direction of the steel strip is measured by a sheet thermometer installed on the outlet side of the cooling device, and nine representative values are extracted to calculate a difference from the target temperature distribution.
The target temperature distribution is preferably a sine curve so that the temperature difference between the middle and high ends and the both ends can be arbitrarily set.
For example, the target temperature distribution is defined by the following equation.
ΔTi = a * (cos (π * i / 3 / w) -√3 / 2)
Here, ΔTi: target temperature a at a distance Xi from the center a: allowable temperature difference between the center and the edge w: plate width Next, the difference between the actual temperature and the target temperature is calculated by the following equation.
ΔTai = (Tsoa + ΔTi) −Tai
Here, ΔTai: the difference between the actual temperature at the i-th representative point and the target temperature Tsoa: the actual temperature value of the center part Tai: the actual temperature at the i-th representative point
When the difference ΔTai between the actual temperature and the target temperature at the i-th representative point is, for example, less than 5 ° C., ΔTai = 0 is set, and the operation of stopping the opening of the refrigerant supply header is not performed.
On the other hand, when the difference ΔTai between the actual temperature and the target temperature at the i-th representative point exceeds, for example, 5 ° C., the number of headers for stopping and opening the refrigerant supply is calculated by the following equation based on ΔTai.
Ui = int (β * Σj (ΔTaj * Cij) +0.5)
Here, Ui: the number of headers to stop opening at the i-th representative point β: constant Cij: influence coefficient of the opening and stopping of the i-th header on the temperature difference at the j-th representative point
As described above, based on the difference between the actual temperature distribution and the target temperature distribution in the width direction of the steel strip, the number of the refrigerant supply headers for starting (ON) or stopping (OFF) the refrigerant supply is calculated and operated. It is preferable that the selection of the header gives priority to the refrigerant supply header on the upper side in the vertical pass of the continuous annealing equipment. This is because the lower header is difficult to operate because the refrigerant supply header to be used changes depending on the line speed and the plate thickness, and the operation of the upstream refrigerant supply header has the effect of stabilizing the plate temperature.
[0023]
FIG. 9 is a diagram showing a change in the temperature distribution in the width direction of the steel strip when the present invention is implemented.
In FIG. 9, as shown by the direction of the arrow, the trace temperature distribution in the width direction of the steel strip approaches the target temperature distribution shown by the sine curve, and the temperature difference between the center and the edge can be suppressed to 20 ° C. or less. .
[0024]
【The invention's effect】
According to the present invention, it is possible to provide a method for controlling cooling of a steel strip in a vertical pass of a continuous annealing facility that can perform uniform cooling in the width direction of the steel strip and prevent the meandering of the steel strip and the occurrence of roll flaws. It has significant industrially useful effects.
[Brief description of the drawings]
FIG. 1 is a diagram showing an entire configuration of a continuous annealing facility.
FIG. 2 is a diagram illustrating a configuration of a cooling device for a steel strip in a vertical path of a primary cooling zone of a continuous annealing facility.
FIG. 3 is a diagram showing a temperature distribution in a sheet width direction when a steel strip is cooled by a conventional cooling device.
FIG. 4 is a view showing a shape of a steel strip cooled by a conventional cooling device.
FIG. 5 is a view showing an embodiment of a steel strip cooling control method according to the present invention.
FIG. 6 is a diagram showing a processing flow of a process controller as a control device used in the present invention.
FIG. 7 is a diagram illustrating an inclined cooling nozzle used in the present invention.
FIG. 8 is a diagram showing a flow of a cooling control method for a steel strip in the present invention.
FIG. 9 is a diagram showing a change in a temperature distribution in a steel strip width direction when the present invention is implemented.
[Explanation of symbols]
1: steel strip,
2, 3: turning roll,
4: Refrigerant supply header
5: radiation cooling nozzle,
6: Split header in width direction

Claims (4)

A method for controlling cooling of a steel strip in a vertical pass of a continuous annealing facility,
Based on the plate width of the steel strip, steel type and the number of refrigerant supply headers to be used, a step of setting a width direction division pattern of the refrigerant supply header,
Measuring the actual temperature distribution in the width direction of the steel strip, and calculating the difference between the actual temperature distribution and the target temperature distribution;
Calculating a refrigerant supply header number for starting (ON) or stopping (OFF) the refrigerant supply when a difference between the target temperature distribution and the actual temperature distribution in the width direction of the steel strip is out of an allowable range. A method for controlling the cooling of a steel strip. The width direction division pattern of the coolant supply header always starts (ON) coolant supply to a center portion (center) in the width direction of the steel strip, and other than the middle portion in the width direction of the steel strip (middle or side). The method for controlling cooling of a steel strip according to claim 1, wherein the supply of the refrigerant to the steel strip is started (ON) or stopped (OFF). The target temperature distribution in the width direction of the steel strip is defined as a sine curve, actual temperatures at a plurality of points in the width direction of the steel strip are measured, and a difference from the target temperature distribution is calculated. Item 3. A method for controlling cooling of a steel strip according to item 2. Based on the difference between the actual temperature distribution and the target temperature distribution in the width direction of the steel strip, the refrigerant supply header that starts (ON) or stops (OFF) the refrigerant supply is connected to the upper side in the vertical path of the continuous annealing equipment. The method for controlling cooling of a steel strip according to any one of claims 1 to 3, wherein the refrigerant supply header is preferentially selected.

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