JP2804430B2 - Control method for hot metal coating weight - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a continuous hot-dip coated steel sheet by controlling the amount of plating in a stepwise manner so that the actual value of the amount of plating can be a target value of the amount of plating. The present invention relates to a control method for preventing the range from being exceeded.

[0002]

2. Description of the Related Art There are a feedback control system and a feedforward control system as a method for controlling the amount of deposition of continuous hot-dip galvanizing. Conventionally, a plating control system has a wiping nozzle on a zinc bath, and feedback control that adjusts the wiping pressure of the wiping nozzle or the distance between the wiping nozzle and the steel strip according to the measured coating amount. Feedforward control that determines the relationship between the method and the coating weight and the factors that govern it, sets a model formula that adjusts the controlling factor to achieve the target plating weight, and controls the model according to this model formula. Is controlled by controlling the amount of plating.

For example, (1) Japanese Patent Application Laid-Open No. 49-32821 discloses that, while keeping the distance between a wiping nozzle and a steel strip at an appropriate value, a target plating amount and an actually measured plating amount are determined. A feedback control method that adjusts the wiping pressure according to the deviation, and a control method that combines feedforward control that adjusts the wiping pressure with a change in the basis weight of the plating and a change in the sheet passing speed are disclosed.
(2) In Japanese Patent Application Laid-Open No. 3-173756, the stability of a gas wiping control system is determined based on the fluctuation state of the system.
When the system is stable, feedback-correct the plating weight model using the measured values obtained in the system,
A control method of performing feedforward control based on a model equation when the system is unstable is disclosed.

[0004]

As described above, conventionally, feedforward control has been adopted as control for changing the amount of plating applied. But with this method,
In order to set the plating conditions using a model formula for predicting the coating weight, there are the following problems when changing the coating weight.

[0005] Standards are set for plated products so as to be within a certain range with respect to a target set value of coating weight, and products outside this range are out of specification. The amount of plating varies depending on the controlling factor, but since there are a plurality of controlling factors, the control becomes very complicated. In addition, there are few model formulas created by fully understanding the behavior of those factors. For this reason, in the feedforward control method that directly uses the model formula, the fluctuation of these factors may deviate from the target allowable range of the coating weight. In such a case, even if the coating coefficient can be corrected to some extent automatically by incorporating a correction coefficient into the model formula, if the behavior of the factor controlling the coating weight is not sufficiently understood, the correction coefficient can be set to a certain value. Therefore, since the accuracy of the value obtained from the model equation does not increase, it has been meaningless to make a correction.

[0006] However, the plating adhesion amount falls within a desired allowable range (for example, ±
(About 20%) is required in terms of product quality. If the set value of the coating weight is not changed, this control can be performed with sufficient accuracy.
Change the coating weight setting without stopping the line,
It has been difficult to control the target set value within the above-mentioned allowable range. In particular, when the current set value of the coating weight is changed in one step from the set value to the desired value, if the accuracy of the model formula is poor, the changed plating weight result is within the allowable range by the feedback control. Therefore, these products are out of the allowable range until they are controlled, so that these products are defective products, and the portions must be cut, which causes a decrease in the yield during product manufacturing.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems. When the amount of plating is changed, the amount of plating is controlled in a stepwise manner. It is an object of the present invention to provide a control method for preventing the value of the actual coating amount from deviating from a target upper limit of the allowable range of the coating amount.

That is, according to the present invention, a gas is blown from a wiping nozzle onto the surface of a strip passed through a hot-dip metal plating bath to control the coating weight of the continuous hot-dip metal plating to control the coating weight to a desired set value. In the controlling device, a feedback control for controlling an interval between the wiping nozzle and the strip and / or a wiping pressure of the wiping nozzle based on a result detected by a plating weight meter provided on the line at a plating weight detection position. This is a method for controlling the amount of plating when changing to a target value of plating at a desired position on the strip. The present invention relates to a method in which a desired position of a strip on a line passes a plating adhesion amount detecting position a predetermined time before a predetermined time passes.
At least once, the set value of the coating weight is changed to a value obtained by subtracting a certain value from the target value, and immediately after the desired position of the strip has passed the plating weight detection position, the plating It is characterized in that the set value of the amount is changed to a target value.

Further, according to the present invention, a value obtained by subtracting a predetermined value from the target value is a target value of the plating adhesion amount ±
It is preferable that the value is the value of the overlapping part of the allowable range and the current value of the attached amount ± the allowable range.

[0010]

In the apparatus used in the present invention, a certain amount of plating adheres to the surface of the strip that has passed through the molten metal plating bath, and the plating amount is measured by a plating amount meter provided on the line. Based on the value detected at the amount detection position, the pressure of the gas blown from the wiping nozzle and the distance between the wiping nozzle and the strip and / or the line speed are maintained within an allowable range by appropriate adjustment.

In the present invention, when an attempt is made to change the coating weight of a certain strip flowing at the above-mentioned line speed to a desired value, a certain desired position of the strip is set and this position is used as a reference. The plating amount is changed in the following procedure. This position is set arbitrarily. The strip used here may be continuous or may be a plate of a certain length. When a plate having a certain length flows at a certain interval, a plate flowing first is called a preceding plate, and a plate flowing later is called a following plate.

The set value of the plating amount is changed stepwise as follows. In the first stage, the current set value (x ₀ ) of the coating weight is subtracted from the final target set value (x ₂ ) by a fixed value (y) (temporary set value = x ₁ ). Set so that That is, x ₁ = x ₂ -y. The provisional set value (x ₁ ) is an overlap between the target set value (x ₂ ) ± permissible range and the current set value (x ₀ ) ± permissible range, that is, an arbitrary part in the target adhesion amount range wrap margin. Select a value. This is because if such a setting is made, the fluctuation range of the plating adhesion amount immediately after the setting change does not exceed the target allowable range of 20%.

[0013] Changes to x ₁ of x ₀ is changed the position of the target value of the coating weight of the strip carried out before a certain time through the coating weight detection position. Here, the fixed time is determined by the accuracy of the model equation corresponding to the actual operation, and the optimum value is determined. For example, according to the present facility, the strip length corresponding to the line speed corresponds to 150 to 200 m, and the time The time is about 90 to 120 seconds. And
Until an arbitrarily determined position on the strip passes the plating adhesion amount detection position, hot-dip plating is performed with the provisional set value (x ₁ ).

In this stage, in the apparatus for controlling the coating weight, the position at which the coating weight of the strip is changed to the target value approaches the coating weight detection position, and the coating weight meter provided on the line is used. , The interval between the wiping nozzle and the strip and / or the wiping nozzle so that the set value of the plating amount becomes the tentative set value (x ₁ ) while continuing the feedback control for controlling the wiping condition based on the detected result. Change the wiping pressure of. That is, at this stage, the target basis weight used for control is set to an apparently tentative set value (x ₁ ), that is, a value within the lap margin of the target adhesion amount range of the preceding plate and the following plate, and this setting is changed. Then, the control system recognizes that a deviation of the changed amount appears in the plating adhesion amount apparently, thereby controlling the adhesion amount by feedback. At this time, if the feedback gain is set so that the coating weight immediately after the setting value change does not overshoot,
The actual plating weight does not fall outside the range. Then, when the strip passes through the wiping nozzle, the plating adhesion amount is stably controlled within the target adhesion amount range lap margin between the preceding plate and the succeeding plate.

[0015] In the second stage, the coating weight is set to a tentative set value.
(X₁) To the target set value (x _Two)
The distance between the wiping nozzle and the strip and / or
Change the wiping pressure of the wiping nozzle. this
Changes in settings target strip coating weight
The position to be changed to the value determines the plating adhesion amount detection position.
Immediately after passing. Also, x₀To x₁Change to
The change need not be performed once. That is, the target adhesion amount range
Two or more different values within the gap may be arbitrarily selected. Selection
Two or more values separated change them from small to large
You. Specifically, x₁₁<X₁₂Two values that are₁₁And x
₁₂And first set x from the current setting₁₁Change the set value to
Then x₁₂Change to In this way, the temporary
By changing the constant value, the coating weight can be more accurately adjusted.
It becomes possible to control.

If the set value of the coating weight is changed in one step to the target coating weight as in the prior art, if the model formula for predicting the coating weight is inaccurate, immediately after the setting value is changed, Overshoot of the coating weight occurred. However, the control method using the stepwise change of the coating amount of the present invention prevents overshooting of the coating amount that occurred immediately after the change of the set value as described above, and a model formula for predicting the coating amount. Regardless of the accuracy of
It has become possible to accurately control the amount of plating applied.

[0017]

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

FIG. 3 is a schematic diagram showing a preferred automatic apparatus for controlling the amount of applied plating in the present invention. This control device comprises a metal melting bath 3, a strip 2, a wiping nozzle 1, and a plating adhesion amount detector 4. In this control device, feedback control and feed forward control are selectively used based on stability determination. . That is, whether or not the control system is stable is determined based on the magnitude of the deviation between the detected plating amount and the target set value.

First, the strip 2 is plated through a metal melting bath 3 and the amount of plating is adjusted by adjusting the distance between the wiping nozzle 1 and the strip 2 provided above the bath and / or the wiping pressure of the wiping nozzle 1. Is adjusted. The coating weight on the strip is detected by a coating weight detection meter 4 provided further above the wiping nozzle 1. The value of the detected amount of plating is input to the feedback control system 9 and is subjected to feedback control. Specifically, the present plating adhesion amount detected at regular intervals is compared with the target adhesion amount setting value, and a correction coefficient is used so that the deviation amount between them becomes zero. The model formula is corrected, the interval between the wiping nozzle 1 and the strip 2 and / or the wiping pressure of the wiping nozzle 1 is adjusted, and the set value is fixed so that the current plating amount becomes the target plating amount. Keep at the value.

The determination of the stability and instability of the control system is performed as follows. That is, if the operation results other than the plating weight detected by the plating weight detector are measured, for example, when the line speed is changed or when the plating weight change is performed significantly beyond a certain range, the system is It is determined to be unstable. If the operation results are within the desired range, the system is determined to be stable. When it is determined that the system is stable, the above-described feedback control is performed. If it is determined to be unstable, the system is switched to the feedforward system 10 and feedforward control is performed. More specifically, a target set value or a tentative set value is inserted into an appropriate model formula to set a distance between the wiping nozzle 1 and the strip 2 and / or a wiping pressure of the wiping nozzle 1 to set a plating adhesion. Adjust so that the amount becomes the target set value or the temporary set value. By adopting the control device and the control method as described above, the difference in the control of the amount of plating applied between the present invention example and the comparative example was examined.

(Production Example) A steel strip having a width of 1800 mm was used, and the line speed was changed to 100 m / min, the wiping nozzle pressure was changed to 0.5 to 0.3 kg / m ² and the interval between the wiping nozzle and the steel strip was changed to 5 to 20 mm. Hot-dip galvanizing was performed under the conditions. The plating adhesion amount was as follows. Comparative Example 1
Then, set the target set value to 45 g / m
^It was changed from ² to 60 g / m ² in one step. In Example 1 of the present invention, the set value of the plating adhesion amount was changed from 45 g / m ² per side to 60 g / m ² in two steps.

The measurement of the coating weight is performed by scanning measurement 1 in the width direction.
The average value of the scan is shown in FIGS. As is clear from the results of Comparative Example 1 shown in FIG. 2, when the set value of the plating adhesion amount was changed in one step, immediately after the set value was changed,
It was observed that the measured value of the plating adhesion amount exceeded the allowable range (the hatched portion indicated by A in FIG. 2). In the feedforward control system, a change is detected at the process input, and a correction signal is issued in anticipation of the change before the process output is affected. It is considered that the amount of plating decreases at one time, and such an excessive amount of plating adheres.

FIG. 1 shows the results of a similar experiment performed by the control method of the present invention. An arbitrary position for changing the coating weight of the strip passes through the coating weight detection position 120.
Seconds ago, the target set value of the coating weight was 52 g / m2.
Changed to ² . Until the above-mentioned position of the strip for changing the coating weight passes through the plating weight detection position, 52
The set value of the coating weight was maintained at g / m ² , and immediately after passing the coating weight detection position, the setting value of the coating weight was changed to 60 g / m ² . As a result, as shown in FIG. 1, it was shown that the amount of plating applied was accurately controlled within an allowable range at any set value.

[0024]

As described above, according to the present invention, when the amount of plating is changed from the current set value to the target set value, the set value is changed stepwise. The coating amount did not exceed the allowable range, and the control accuracy of the coating amount was improved. In addition, when the set value of the coating weight is changed in a conventional one-step, the coating weight overshoots immediately after the change of the setting value and exceeds the permissible limit. First, it has been a cause of lowering the yield in manufacturing products of a certain standard. However, by adopting the method for controlling the amount of plating applied according to the present invention, such overshoot of the amount of plating applied was eliminated, and the yield of products could be improved.

[Brief description of the drawings]

FIG. 1 is a graph showing measured values and allowable ranges when the control method of the present invention is employed and the amount of plating applied is changed from 45 g / m ² to 60 g / m ² .

FIG. 2 is a graph showing measured values and allowable ranges when a conventional control method is employed and the amount of plating is changed from 45 g / m ² to 60 g / m ² .

FIG. 3 is a flowchart showing an outline of an automatic plating weight control apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Wiping nozzle 2 Strip 3 Metal melting bath 4 Plating weight detector 5 Upper limit of current allowable range of plating weight 6 Lower limit of current allowable range of plating weight 7 Target upper limit of allowable range of plating weight 8 Target The lower limit of the allowable range of the coating weight A The part where the coating weight exceeds the target set value allowable range 9 Feedback control system 10 Feedforward control system

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-171395 (JP, A) JP-A-5-33110 (JP, A) JP-A-3-170653 (JP, A) JP-A-51- 141730 (JP, A) JP-A-51-137626 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 2/00-2/40

Claims (2)

(57) [Claims] 1. An apparatus for controlling the amount of plating of continuous molten metal plating, in which a gas is blown from a wiping nozzle onto a surface of a strip passed through a molten metal plating bath to control the amount of plating to a desired set value. A feedback control method that controls the distance between the wiping nozzle and the strip and / or the wiping pressure of the wiping nozzle based on the result of detection at the plating weight detection position by the plating weight meter provided on the line. When changing to the target plating weight at the desired position of the strip, the set value of the plating weight is set at least once before a certain time before the desired position of the strip passes the plating weight detection position. Is changed to a value obtained by subtracting a certain value from the value to be applied. After passing the exit position, immediately changing the coating weight of the set value so that the target value, the molten metal coating weight control method characterized by. 2. A value obtained by subtracting a predetermined value from the target value is a value of an overlapping portion of the target value of the coating amount ± the allowable range and the current value of the coating amount ± the allowable range. Item 2. The method for controlling the amount of deposited hot metal plating according to Item 1.