JPH07126824A - Production of hot dip metal coated steel sheet - Google Patents

Abstract

PURPOSE:To make the plating deposition in the width direction of a steel strip uniform by changing the positions of supporting rolls in the method for controlling the plating deposition by introducing the steel strip into a plating bath and carrying the steel strip out of this bath through the supporting rolls. CONSTITUTION:The steel strip 1 is introduced from a pretreating furnace 2 via a guide roll 3 into the molten metal bath 4, is turned over by a sink roll 5 and is carried out of the bath through the supporting rolls 6a, 6b. Gas is blown from gas throttling nozzles 7 to both surfaces of the steel strip 1 to adjust the plating deposition to a desired value. The plating deposition is detected by a deposition meter 8. The distribution of the plating deposition in the width direction of the steel strip is determined by a line speed, the spacing between the front ends of the nozzles 7 and the steel strip 1 and the pressure of the gas blown out of the nozzles 7. The distribution is nonuniform if the steel strip 1 is curved in the position of the nozzles 7. The detection data of the deposition meter 8 is sent to an arithmetic section 9 by which the indenting amt. of the supporting rolls 6 is calculated. The plating deposition is then so adjusted as to be made uniform by moving the positions of the supporting rolls 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing continuous hot-dip metal plating of a steel strip, and more specifically, to control the amount of pushing of a support roll to make the coating amount of the steel strip uniform in the width direction. The present invention relates to a method for producing continuous hot dip metal plating of a steel strip.

[0002]

2. Description of the Related Art Plating is roughly divided into electroplating, electroless plating, hot dipping, mechanical plating, vacuum plating, etc., and an appropriate plating method has been adopted according to its characteristics and application. Among them, electroplating has a wide range of uses and has been used for various purposes such as decoration and rust prevention, but hot dipping is intended for large structures and steel sheets with a large area, and is low cost. The hot dipping method has been widely used for plating such objects. But,
The hot-dip galvanizing method uses the front and back surfaces of the treated steel strip,
Alternatively, there is a problem in that there is a large variation in the coating amount in the width direction. Such variations in the coating amount in the width direction, that is, non-uniform distribution of the coating amount is caused by the widthwise warpage of the steel strip when adjusting the coating amount, This is because the distance between the steel strip and the gas throttle nozzle is not constant.

As a method for preventing the uneven distribution of the coating amount of the steel strip in the width direction, a method of preventing the warp of the steel strip to eliminate the variation has been already proposed. It is disclosed in JP-A-57-32359 and JP-A-62-30865. These methods will be described with reference to FIG. FIG. 5 shows a conventional method for producing a hot-dip metal-plated steel sheet of steel strip. The steel strip 1 passes through the pretreatment furnace 2, is introduced into the molten metal bath 4 for plating by the guide rolls 3, is vertically inverted by the sink rolls 5, is discharged from the molten metal bath 4, and is then gas. The adhering amount of molten metal is controlled by the squeezing nozzle 7, and after passing through the top roll 11, it is sent to the next step.

In such a method for producing a continuous metal hot-dip galvanized steel sheet, tension (about 1.0 kg / mm ² ) is applied to the steel strip. The steel strip introduced into the molten metal bath 4 is wound around the sink roll 5 and inverted. However, due to the above tension, the steel strip in contact with the lower portion of the sink roll 5 is sucked by the sink roll 5 at the center. It deforms elastically like a neck. As the sink roll 5 is wound around, the central portion of the sink roll 5 is separated from the surface of the sink roll 5 and is deformed in the reverse direction of the constricted deformation.
"War" occurs.

In the plating method in which the amount of molten metal plating adhered is controlled by the gas blown from the gas throttle nozzle 7, when such bending (C warpage) of the steel strip 1 occurs, the amount of coating adherence of the steel strip is There are adverse effects such as non-uniformity in the width direction. That is, in the case of controlling the coating amount by using a gas throttle, the distance r between the tip of the gas throttle nozzle 7 and the surface of the steel strip 1 controls the coating amount to a constant value. This is a very important factor, but when the steel strip 1 is bent in the direction perpendicular to the width direction, this distance becomes non-uniform in the width direction, so the gas pressure on the steel strip 1 is different for each nozzle. However, the amount of plating adhered becomes uneven in the width direction of the steel strip.

Therefore, a method of providing a pair of support rolls 6a and 6b in the bath surface on the sink roll and in the vicinity of the bath surface, or changing the diameter of the support roll has been adopted. When a pair of support rolls 6a and 6b are provided as shown in FIG. 1, the center heights of the respective support rolls are mutually displaced as shown in FIG. 4, and the steel strip 1 is placed between these support rolls. Hold it. Generally, one support roll 6b is fixed and the other support roll 6a is moved as shown in FIG. 4 to prevent the steel strip 1 from being bent at the position of the gas throttle nozzle 7. The method has been adopted. In particular, in JP-A-62-30865, a widthwise warp detection means is provided at a position close to a wiping gas spraying position to constantly monitor the warp and always set the pushing distance of the support roll in a direction to prevent warpage. A method of adjusting and correcting the warp of the steel strip to make the coating amount uniform is adopted.

[0007]

However, even in this method, the following problems are encountered in determining the accuracy of the widthwise warp detecting means, the installation position thereof, and the warp amount detected based on the detected warp amount. There is. The first problem is that the accuracy of the warp detection means has a great influence on the control of the plating adhesion amount.
The warp detection means is installed in a severe environment on the hot dip metal plating bath. For this reason, there is a problem that the accuracy of the warp detection means is deteriorated by heat, the durability is deteriorated, and accompanying maintenance, it is difficult to reset the gain and the like after the maintenance.

The second problem is the installation position of the warp detection means. In order to make the amount of hot-dip galvanized coating uniform in the width direction of the steel strip, it is desirable that the warpage of the steel strip at the nozzle tip position is offset as much as possible.
In order to perform the detection with high accuracy, the position of the nozzle tip and the position of the sensor of the warp detection means must be as close as possible. On the other hand, if the two are placed too close to each other, there is a problem that the plating scattered by the gas adheres to the sensor portion of the warp detection means, and the detection accuracy may decrease.

A third problem is that the pushing amount of the support roll 6a must be adjusted with time. As shown in FIG. 4, the optimum pushing amount d of the support roll 6a for preventing the bending of the steel strip 1 is theoretically calculated under the stationary condition. But,
Actually, when equipment conditions such as a change in operating conditions such as line speed, a change in roll diameter due to wear of the sink roll 5 or the support rolls 6a and 6b, and the like change,
Alternatively, if the value of d is not changed, there is a case where the curvature cannot be sufficiently canceled out. Therefore, it is not necessary to keep the calculated value as it is, and it is necessary to adjust it over time.

[0010]

On the other hand, in order to make the amount of plating adhered on the front surface and the back surface of the steel strip uniform, in addition to the above method of detecting the warp of the steel strip and correcting the warp, There is a method of measuring the distribution of the amount of plating adhered on the steel strip and using this value. Since the steel strip is curved as described above, the amount of coating adhered on the steel strip shows a non-uniform distribution in which it is thin at a portion close to the nozzle tip and thick at a portion far from the nozzle tip. An object of the present invention is to make the coating amount uniform by paying attention to the characteristic distribution of the plating thickness deposited on such a steel strip.

That is, according to the present invention, a steel strip is introduced into a molten metal bath through a guide roll to be plated, is carried out of the bath via a support roll, and is gas-extracted on the surface of the steel strip carried out of the bath. A continuous molten metal plating apparatus is used, in which gas is blown from a nozzle to set the coating amount to a desired value and the coating amount is detected by a coating amount meter. At this time, by changing the position of the support roll from the coating amount distribution in the steel strip width direction detected by the coating amount meter, the continuous molten metal-plated steel sheet is characterized by uniformly controlling the coating amount. It is a manufacturing method. In addition, the support rolls are provided in a pair in contact with the front and back surfaces of the steel strip, and one of them is fixed, and the other position is moved in the direction perpendicular to the longitudinal direction of the steel strip to move the steel strip. It is characterized by controlling the warpage and uniformly controlling the coating amount of the steel strip in the width direction. Here, the support roll 6 has an upper side (6b),
Lower (6a) consists of a pair of rolls, upper roll 6b
Is fixed in order to keep the passing position constant, and the pushing amount of the lower roll 6a is adjusted. The structure of the support roll 6 is not particularly limited, but a structure that allows a quick response is preferable because the plate passing speed is considerably high.

Further, the step of determining the moving amount (pushing amount) of the other support roll is based on a calculation process, and a function is set in advance, and the widthwise plating of the steel strip obtained during the operation is performed. It is characterized by including a so-called learning step of automatically correcting a function set by using the relationship between the measurement of the distribution of the amount of adhesion and the pushing amount of the support roll by a calculation process. Set some function in advance and perform a preliminary test to enable rough control of the coating weight, and use the measured value of the coating weight distribution in the width direction of the steel strip obtained during operation. The pushing amount of the support roll is obtained, and the function fitting is enhanced by repeating this.

[0013]

First, an example of the structure of the present invention will be described with reference to FIG. As shown in FIG. 1, the apparatus used in the present invention is a molten metal in which a pretreatment furnace 2 having a guide roll 2, a sink roll 5 and a pair of support rolls 6a and 6b are provided in the bath near the bath surface. The bath 4 and the pair of gas throttle nozzles 7a and 7b provided on the bath surface, the plating deposition amount meters 8 provided on both sides of the steel strip above the bath 4, and these plating deposition amounts were obtained. Support roll 6 based on data
The calculation unit 9 calculates the pushing amount of a and the operation unit 10 that moves the position of the support roll 6a based on the pushing amount calculated by the calculation unit 9.

The steel strip 1 is guided from the pretreatment furnace 2 into the molten metal bath 4 via the guide rolls 3, plated, inverted by the sink rolls 5 and discharged from the bath through the support rolls 6a and 6b. Gas is blown from both sides of the steel strip carried out of the bath from the gas throttle nozzle 7 to set the coating amount to a desired value, and the coating amount meter 8 detects the coating amount.

At this time, the distribution of the coating amount in the width direction of the steel strip is determined by the line speed, the distance between the tip of the gas throttle nozzle and the steel strip, and the pressure of the gas blown from the gas throttle nozzle. Is not curved at the position of the gas throttle nozzle 7, a uniform distribution is obtained. However, when the steel strip 1 is curved at the position of the gas throttle nozzle 7, the distribution of the amount of plating adhered in the width direction of the steel strip differs depending on the distance between the tip of the gas throttle nozzle and the steel strip. It becomes non-uniform as shown. That is, the coating amount of steel strip is
The part where the distance between the nozzle 7 and the steel strip 2 is long is thick, and the part where the distance is short is thin. The amount of plating on the front surface and the back surface is thin on the back surface as indicated by the dotted line, and thicker on the back surface as indicated by the dotted line. The thick part and the thin part have the opposite relationship.

On the other hand, the relationship between the coating weight and the curvature of the steel strip is shown in FIGS. Since the gas restricting nozzles 7 are provided in a pair on both surface sides of the steel strip 1, the nozzles provided on the right side (pretreatment furnace side) in FIG. The left side is called the front surface nozzle 7a. FIG. 6 shows the positional relationship between the gas throttle nozzle 7 and the steel strip 1. Here, a case is shown in which the center of the surface of the steel strip 1 is curved between the front surface nozzle 7a and the back surface nozzle 7b so as to be close to the front surface nozzle 7a. The distances between the front surface and the back surface of the steel strip 1 and the nozzle 7 at this time are as shown in FIG. Looking at the amount of plating adhered, since the pressure of the gas blown from the nozzle is maintained at a certain set value, it becomes thinner at the portion near the nozzle and thicker at the portion far from it, as shown in FIG. Further, regarding the relationship between the coating deposition amount and the gas pressure, the coating deposition amount becomes thin when the gas pressure becomes high, and the plating deposition amount becomes thick when the gas pressure becomes low.

As shown in FIG. 1, the plating adhesion amount is detected by the plating adhesion amount meter 8 and the data is sent to the arithmetic unit 9. A certain function selected in advance is set in the calculation unit 9, and the value of the amount of deposited plating obtained from the preliminary test is substituted into this function to determine the value of the pushing amount of the support roll 6a. Here, the function set in advance may be one that can uniquely relate the plating adhesion amount in the width direction and the pressing amount of the support roll.

The value obtained by the plating amount meter 8 is substituted into the function selected here, so that the deviation amount of the plating amount of Δw in FIG. 2 becomes zero.
The pushing amount d of a is calculated. Calculated push amount d
The position of the support roll 6a is moved by and adjusted so that the coating amount of the steel strip becomes uniform. As described above, the relationship between the plating deposition amount and the support roll indentation is roughly determined by the function set in advance, but the parameters are corrected from the data obtained during the operation, and By changing the parameters through learning, it is possible to accurately and uniformly control the plating adhesion amount so as to reduce the deviation between the formula and the actual value.

Further, it is preferable to learn the relationship between the support roll pushing amount d and the plating adhesion amount deviation amount Δw for each layer, if necessary. Here, stratification refers to stratification for each steel type. The reason why it is preferable to learn by layer is that the relationship between d and Δw differs depending on the steel type.

The function of the arithmetic unit 9 shown in FIG. 1 will be described in detail below. In the calculation unit 9, the pushing amount of the support roll is calculated from the plating adhesion amount by the following theory. A) The degree of curvature of the steel strip 1 is obtained from the distribution of the amount of deposit detected by the plating amount detector, and B) The support roll required to correct the curvature of the steel strip 1 is obtained from the obtained degree of curvature. The pushing amount d is obtained, and C) these values are taken into consideration by taking into consideration factors such as the pushing amount d of the support roll and the distribution of the coating deposition amount, the line speed, the variation of the width or thickness of the steel strip, and the variation of the roll diameter. Is calculated, and the support roll pushing amount d when such a factor fluctuates is calculated.

First, the process A) for obtaining the degree of curvature of the steel strip will be described with reference to FIG. Two points at both ends and three points at the center (OP, CE, DR) are set in the width direction of the steel strip, and the measured values of the plating adhesion amount at these points are w _OP , w _CE , w _DR (g /
m ² ). The relationship between the amount W of coating adhered and the wiping condition (nozzle pressure p (kg / m ² ), nozzle-steel strip distance x (m), line speed ls (m / sec)) w _OP = f (p, x _OP , ls) _wCE = f (p, _xCE , ls) ... _wDR = f (p, _xDR , ls), the nozzle-steel strip distance x in the width direction is _xOP = f ' (P, w _OP , ls) x _CE = f '(p, w _CE , ls) ... x _DR = f' (p, w _DR , ls). Here, x _CE − (x _OP + x _DR ) / 2 is defined as the bending amount of the steel strip.

Next, the process of B) for obtaining the amount of pushing of the support roll required for straightening from the bending amount obtained in A) will be described. Here, the curvature of the steel strip [Delta] x = x _CE - and _{(x OP + x DR) /} 2. When the thickness of the steel strip is t, the width of the steel strip is W, and the tension is T _S , when these values are determined, the relationship between the support roll pushing amount Δp and the bending amount Δx is uniquely determined, and Δx = S (T, W, T _S , Δp) ... An example of the formula is shown in FIG. Where Δ
The relationship between x and Δp is obtained as a downwardly convex quadratic curve, and when the point at which the bending amount Δx is made zero is obtained, it is found that the support roll pushing amount Δp at this time is 9 mm.

The relation of this equation is input into the arithmetic unit 9 in advance, and the proper pushing amount Δp is obtained. As is clear from the above description, in principle, the amount of deviation Δw of the coating adhesion amount uniquely determines the bending amount Δx of the steel strip, and the bending amount Δx of the steel strip and the pushing amount d of the support roll are also unique. To be determined. Therefore, when the thickness t of the steel strip, the width W of the steel strip, and the tension T _S are determined, the pushing amount d of the support roll can be obtained from the deviation amount Δw of the plating deposition amount without calculating the bending amount Δx.

Finally, the process of C) in which the arithmetic unit 9 learns based on the operation results will be described. The equation has parameters set in advance by a preliminary test, but the parameters are further modified using the actual values obtained during the operation (actual plating deposit amount value and actual push amount amount value). In this way, the arithmetic unit 9 learns and corrects the coefficient of the parameter used for control, thereby improving the control accuracy.

[0025]

【Example】

(Manufacturing Example) A galvanized steel strip was manufactured using the apparatus shown in FIG. Steel strip 1.2 mm thick and 1000 mm wide,
A steel strip having a thickness of 1.0 mm and a width of 980 mm was used. At this time, the line speed is 100 m / sec, the pressure of the gas throttle nozzle is 0.6 kg / m ² , and the target amount of coating is 40 g / m ² .
It was fixed at m ² and plated.

(Evaluation of Control Method) A galvanized steel strip was manufactured using the apparatus shown in FIG. First, the thickness is 1.2m
A steel strip having a width of m and a width of 1000 mm was manufactured. When plating was performed with the pushing amount of the support roll +15 mm, the plating adhesion amount showed the distribution of the plating adhesion amount in the steel strip width direction of FIG. 3A, and Δw was almost zero. Thickness 1.0 mm, width 980
When the steel strip was changed to mm, the deviation amount Δw of coating adhesion amount was 3 g / m ^{2 as shown} in FIG. That is, w _CE = 1 and w
_DR = 4, w _OP = 4, Δw = 1− (4 + 4) / 2 = −3. Here, as the setting function formula, the one shown in FIG. 10 was used. In addition, when the calculation unit 9 corrects the deviation amount of 3 g / m ² , it has already been learned that +2 mm is added to the pushing amount up to that point. From this relationship, the pushing amount of the support roll is +17 mm. As a result of automatic correction, the amount of plating adhered was as shown in FIG. 3C, and it was possible to control Δw to be substantially zero. The pushing amount of the support roll 6a is represented by + in the direction approaching the support roll 6b and − in the direction distant from the support roll 6b.

[0027]

The present invention detects the distribution of the coating amount of steel strip in the width direction, learns the relationship between this value and the pushing amount of the support roll in the bath, obtains the pushing amount of the support roll, and obtains the target value. The amount of indentation is automatically controlled when the hysteresis of the applied amount of plating is exceeded. As a result, the coating amount in the widthwise direction of the steel strip becomes uniform, the amount of deviation is small, and it is possible to control with high accuracy. Further, since the coating amount of the steel strip is detected by using the coating amount meter, it is not necessary to install a steel strip warp detector near the gas restriction nozzle. Since the plating deposition meter can be installed away from the bath, the installation environment is better, damage to the detection sensor is less, and maintenance is easier than when the warpage detector is installed on the bath. .

[Brief description of drawings]

FIG. 1 is a control schematic diagram of the present invention.

FIG. 2 is a graph showing a distribution of coating amount in the width direction of a steel strip when the steel strip is curved at the gas throttle nozzle position.

FIG. 3 is a graph showing an example of the present invention.

FIG. 4 is a diagram showing a support roll pushing amount definition.

FIG. 5 is a diagram showing a general continuous hot-dip galvanizing apparatus.

FIG. 6 is a schematic diagram showing a relationship between a gas throttle nozzle and a steel strip.

FIG. 7 is a schematic diagram showing the relationship between the distance between the gas throttle nozzle and the steel strip.

FIG. 8 is a graph showing a distribution of coating weight in the width direction of the steel strip.

FIG. 9 is a schematic diagram showing how to determine a bending amount.

FIG. 10 is a diagram showing a relationship between a pushing amount of a support roll and a bending amount.

[Explanation of symbols]

 1 Steel Strip 2 Pretreatment Furnace 3 Guide Roll 4 Molten Metal Bath 5 Sink Roll 6a and b Support Roll in Bath 7a and b Gas Squeezing Nozzle 8 Plating Deposition Meter 9 Calculation Unit 10 Operating Unit 11 Top Roll

Claims (3)

[Claims] 1. A steel strip is introduced into a molten metal bath through a guide roll for hot-dip galvanizing, is carried out from the bath via a support roll, and gas is blown from a gas throttle nozzle onto the surface of the steel strip carried out of the bath. Steel strip width detected by the coating weight meter when performing molten metal plating using a continuous molten metal plating device that attaches the desired amount of coating weight and detects the coating weight with a coating weight meter. A method for producing a continuous hot-dip galvanized steel sheet, characterized in that the position of the support roll is changed from the distribution of the coating amount in the direction to uniformly control the coating amount in the width direction of the steel strip. 2. The support rolls are provided in a pair in contact with the front and back surfaces of the steel strip, and one of them is fixed,
The continuous hot-dip galvanized steel sheet according to claim 1, wherein the other position is moved in a direction perpendicular to the longitudinal direction of the steel strip to control the warpage of the steel strip and uniformly control the coating amount in the width direction of the steel strip. Production method. 3. The step of determining the movement amount (pushing amount) of the other support roll is based on arithmetic processing, and a function is set in advance, and the widthwise plating of the steel strip obtained during operation is performed. The continuous hot-dip galvanized steel sheet according to claim 2, further comprising a so-called learning step of automatically correcting a function set by using the relationship between the measurement of the distribution of the amount of deposit and the amount of pushing of the support roll by arithmetic processing. Manufacturing method.