WO2004003249A1

WO2004003249A1 - Molten metal plated steel sheet production method and apparatus

Info

Publication number: WO2004003249A1
Application number: PCT/JP2003/007924
Authority: WO
Inventors: Kenji Yamauchi; Yoichi Miyakawa
Original assignee: Jfe Steel Corporation
Priority date: 2002-06-27
Filing date: 2003-06-23
Publication date: 2004-01-08
Also published as: CN1659301A; EP1516939A1; KR20050014836A; KR100758240B1; JP2004027315A

Abstract

A molten metal plated steel sheet production method comprising the steps of dipping a steel sheet in a molten metal plating bath continuously to cause a molten metal to adhere to the steel sheet, changing the orientation of the steel sheet in the molten metal plating bath by means of an orientation changing device to pull it out of the molten metal plating bath, adjusting the amount of molten metal adhering to the steel sheet by means of a gas wiping device, correcting the warp of the steel sheet in a contactless manner by a magnetic force acting perpendicularly to the steel sheet and produced by an electromagnet disposed upstream and/or downstream from the gas wiping device, wherein the value of the current flowing through the electromagnet is set at a predetermined value according to information on the steel sheet. The warp of the steel sheet over the full length is prevented, the amount of plating coating is uniform, and the surface properties are excellent

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a molten metal-plated steel sheet, and more particularly, to a method for correcting the shape of a steel sheet in a non-contact manner using an electromagnet, and an apparatus for manufacturing the same. About. BACKGROUND ART Molten metal plating methods, such as hot-dip galvanizing, have been in practical use for a long time. In particular, the demand for hot-dip galvanized steel sheet as an anti-reflection steel sheet for automobiles, home appliances, and building materials is increasing, and there is a need for higher quality such as uniform coating weight and suppression of surface defects. I have.

At present, as a method of depositing molten metal on a continuous steel sheet, for example, a method of producing a hot-dip galvanized steel sheet, a gas drawing method using an apparatus as shown in Fig. 1 is generally used. Has been adopted. In this method, a steel sheet S continuously penetrated into a molten metal plating bath 2 is vertically pulled up from the plating bath, and a high-pressure gas injected from a gas throttle device 4 provided on both sides of the steel sheet S is provided. Excess molten metal adhering to the steel sheet S is wiped off by the gas, and a desired plating adhesion amount is adjusted.

When an apparatus as shown in Fig. 1 is used, the steel sheet pulled up from the plating bath vibrates or warps in the width direction of the steel sheet. In addition, poor flatness of the steel sheet may occur. Such an interval between the gas expansion device and the steel plate changes, and the amount of coating in the longitudinal direction or the width direction of the steel plate becomes uneven. Therefore, a pair of support rolls are provided in the plating bath and a similar pair of support ports are provided above the gas squeezing device to restrain the steel plate, thereby preventing the steel plate from vibrating and correcting the warpage. This is commonly done. However, in such a method using a support roll, The effects of vibration prevention and shape correction may not be sufficient.

As a countermeasure, a method has been proposed in which an electromagnet is used to suppress the vibration of the steel sheet by magnetic force. For example, in Japanese Patent Application Laid-Open No. 2001-38412, in order to control a running steel sheet, an electromagnet pair for applying a magnetic force to the steel sheet and a position sensor are provided, and the driving current of the electromagnet pair is controlled based on the measured distance. At the same time, there is described a device for determining a control gain in current control based on information on a steel plate such as a plate thickness, a speed, a seam position, a plate width, and a tension. However, the above-described conventional vibration damping devices and vibration damping methods using electromagnets have the following problems.

First, the method using an electromagnet requires a position sensor to measure the position of the steel sheet (distance from the electromagnet) in order to prevent contact and attraction between the steel sheet and the electromagnet. Therefore, not only is it costly, but also it becomes difficult to install an electromagnet near the gas throttle device because the device becomes large and disturbs the gas flow of the gas throttle device.

In the conventional method using an electromagnet, feedback control is performed based on the position information from the position sensor. After vibration or warpage occurs in the steel sheet, the position sensor recognizes the vibration and warpage, and then detects the current value of the electromagnet. Is changed. However, the state of warpage may change abruptly at the seam between the preceding steel sheet and the succeeding steel sheet, which cannot be controlled by the feed pack control, and the warp at the leading end of the succeeding steel sheet cannot be corrected.

Further, since the warp cannot be partially corrected as described above, the interval between the gas expansion device and the steel plate must be set widely so that there is little danger of contact even if the warp occurs. However, if the distance between the gas expansion device and the steel sheet is large, gas expansion must be performed at a high gas pressure and a high gas flow rate, and it is difficult to adjust the coating weight to a desired value. In addition, a defect (splash defect) in which a splash of molten metal generated due to a gas flow near the gas expansion device adheres to the steel sheet is likely to occur.

As described above, the conventional method using electromagnets is not only expensive, but also has an insufficient effect of correcting warpage, and cannot produce high-quality plated steel sheets. There's a problem. DISCLOSURE OF THE INVENTION An object of the present invention is to provide a method for producing a steel sheet with a molten metal, in which the occurrence of warpage is suppressed over the entire length of the steel sheet, the coating amount is uniform, and the surface properties are excellent. » The purpose of this is to continuously infiltrate the steel sheet into the molten metal plating bath and attach the molten metal to the surface of the steel sheet, and to change the direction of the steel sheet by using a direction change device provided in the molten metal plating bath. After the conversion, the process of drawing the molten metal out of the molten metal bath, the process of adjusting the amount of molten metal deposited on the steel sheet by a gas expansion device, and the warpage of the steel plate are performed on the upstream and / or downstream side of the gas expansion device. A step of correcting non-contact by a magnetic force using an electromagnet that applies a magnetic force in a direction intersecting with the surface of the steel sheet, and the current value of the electromagnet is determined in advance based on information on the steel sheet. This is achieved by a method of manufacturing a steel plate with molten metal set to a value. This method comprises: a bath for applying a molten metal to the surface of a steel sheet; a turning device installed in the bath for the molten metal; and a turning device for turning the steel sheet; A gas expansion device installed on the steel plate to adjust the amount of molten metal attached to the steel plate, and a gas expansion device installed upstream and / or downstream of the gas expansion device to apply magnetic force in a direction that intersects the surface of the steel plate Production of a steel plate with a molten metal provided with an electromagnet that corrects the warpage of the electromagnet in a non-contact manner, and a current value preset control device that sets the current value of the electromagnet to a predetermined current value based on information about the steel plate It can be realized by the device. BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a diagram showing an example of a conventional apparatus for manufacturing a hot-dip galvanized steel sheet.

Figure 2 is a conceptual diagram of the amount of displacement of the steel sheet and the force acting on the steel sheet during straightening of the steel sheet.

FIG. 3 is a diagram illustrating an example of a relationship between a displacement amount of a steel sheet and a force acting on the steel sheet. FIG. 4 is a diagram showing an example of the apparatus for producing a molten metal-plated steel sheet according to the present invention. FIG. 5 is a diagram showing an example of the arrangement of electromagnets in the width direction of the steel sheet according to the present invention.

FIG. 6 is a diagram showing an example of a preset control flow according to the present invention.

FIG. 7 is a diagram showing another example of the apparatus for manufacturing a steel sheet with molten metal according to the present invention. FIG. 8 is a diagram showing an example of a feed pack control port according to the present invention.

FIG. 9 is a diagram comparing the shape controllability between the present invention and the conventional technology. MODES FOR CARRYING OUT THE INVENTION As described above, in the conventional method of suppressing the vibration and warpage of a steel sheet by using an electromagnet, so-called feedback control is considered to be indispensable for controlling the current of the electromagnet. I have. This is because the magnetic force of the electromagnet is inversely proportional to the square of the distance from the steel sheet, so when the steel sheet is drawn to the electromagnet by the magnetic force, the magnetic force becomes stronger, and the steel sheet is further drawn to contact or attract the electromagnet. This is to prevent equipment trouble. The attraction of the steel sheet by the electromagnet is thus "unstable" and feedback control by position sensing is considered to be essential.

On the other hand, the present inventors have conducted a detailed investigation on the relationship between the attractive force of the steel sheet by the electromagnet and the force acting on the warped steel sheet, and as a result, the following has become clear.

1) A steel sheet bent in the longitudinal direction by a contacting roll or the like warps in the width direction on the roll exit side. For example, in the conventional apparatus for manufacturing a hot-dip galvanized steel sheet as shown in Fig. 1, the steel sheet S is warped in the width direction by being bent in the longitudinal direction by the sink roll 3 and the support roll 7 in the mounting bath 2. . The magnitude of this warpage depends on the bending of the roll, the angle of wrapping around the roll, the frictional force with the roll, the tension, the plate thickness, the plate width, and the type of steel. Depends on etc. In addition, the force required to correct warpage depends on these various factors.

2) Correcting the warpage of the steel sheet with an electromagnet ^ As shown in Fig. 2, the steel sheet S warped in the width direction indicated by the dotted line in the figure is opposed to the vicinity of the width direction end of the steel sheet S. When a certain current is applied to the electromagnet 5 and the magnetic force acts on the steel sheet S, a force in a direction approaching the electromagnet 5, that is, an attractive force acts on the steel sheet S. Then, the end in the width direction of the steel sheet S is displaced by the distance X, and the steel sheet S becomes a state shown by a solid line in the figure. At this time, a force to return to the original state (the state indicated by the dotted line), that is, a restoring force acts on the steel sheet S. Therefore, the steel sheet S settles in a state where the suction force and the restoring force are balanced. Figure 3 shows the relationship between the displacement of the steel sheet and the force acting on the steel sheet, based on data collected by a test device simulating an actual line. The displacement of the steel sheet on the horizontal axis in FIG. 3 corresponds to the displacement X in FIG.

Thus, the attractive force of the electromagnet 5 is inversely proportional to the square of the distance between the steel sheet S and the electromagnet 5, and the restoring force of the steel sheet S is proportional to the displacement X. Now, if the value of the current flowing through the electromagnet 5 is appropriately selected, the curve indicating the attractive force of the electromagnet 5 and the straight line indicating the restoring force of the steel sheet S intersect at two points as shown in FIG. One of these two points is a stable neutral point and the other is an unstable neutral point, considering the direction of the resultant force. When the steel sheet S approaches the electromagnet 5 from the unstable neutral point, the attractive force always acts stronger than the restoring force, so the steel sheet S is attracted to the electromagnet 5. If the steel sheet S is located farther away from the electromagnet 5 than the unstable neutral point, the steel sheet S always returns to the stable neutral point. From this, it can be seen that by applying an appropriate current to the electromagnet 5 and generating an appropriate attraction force, the warpage of the steel sheet S settles down to a stable state. Further, the stable neutral point is a point where the suction force and the restoring force balance each other, and is not necessarily a point where the warpage of the steel sheet S is corrected and the steel sheet S is flattened. However, by optimizing the current value of the electromagnet 5, the steel sheet S can be flattened at the stable neutral point.

As described above, there is a stable neutral point between the restoring force and the attraction force, and the shape correction by the magnetic force of the electromagnet 5 can be made not a "unstable system" but a "stable system". For the current control of the electromagnet 5, the feed pack control by the position sensor This means that preset control for setting an appropriate current value in advance is possible. Based on the above findings, the process of continuously infiltrating the steel sheet into the molten metal plating bath and attaching the molten metal to the surface of the steel sheet, and the direction changing device provided in the molten metal plating bath After the conversion, the process of drawing the molten metal out of the molten metal bath, the process of adjusting the amount of molten metal deposited on the steel plate by a gas expansion device, and the warping of the steel plate are performed on the upstream and / or downstream side of the gas expansion device. A step of correcting non-contact by magnetic force using an electromagnet that applies a magnetic force in a direction intersecting with the surface of the steel sheet, and the current value of the electromagnet is predetermined based on information on the steel sheet. By setting the current value, it is possible to suppress the occurrence of warpage over the entire length of the steel sheet, to produce a coated steel sheet with a uniform plating coating amount and excellent surface properties.

When the joint between the preceding steel sheet and the succeeding steel sheet passes through the installation position of the electromagnet, the current value of the electromagnet may be changed to a predetermined current value based on information on the following steel sheet.

More effective if a steel sheet shape measuring device and / or a measuring device for the amount of coating deposited on the steel plate is installed downstream of the gas throttle device, and the current value of the electromagnet is corrected based on the information measured by such a device. The occurrence of warpage can be suppressed over the entire length of the steel sheet, and the coating weight can be made uniform.

The only equipment that supports the steel sheet in the bath with the molten metal is a direction change device for the steel sheet. Except for the supporting rolls, flaws and defects of the steel sheet caused by dross in the plating bath can be reduced.

Such a method of manufacturing a steel plate with a molten metal includes a bath for the molten metal to attach the molten metal to the surface of the steel plate, a turning device installed in the bath for the molten metal, and a turning device for turning the steel plate. A gas throttle device installed above the plating bath surface of the metal plating bath to adjust the amount of molten metal attached to the steel plate; and a gas throttle device installed upstream and / or downstream of the gas throttle device to Apply magnetic force in the direction of intersection The present invention can be realized by a device including an electromagnet that corrects a warp of a steel sheet in a non-contact manner, and a current value preset control device that sets a current value of the electromagnet to a predetermined current value based on information about the steel sheet. In addition, if a device for measuring the shape of the steel sheet and / or a device for measuring the amount of plating applied to the steel plate is provided downstream of the gas expansion device, the occurrence of warpage can be suppressed, and the uniformity of the applied amount of plating is more effective. is there. Embodiment 1

FIG. 4 shows an example of the apparatus for producing a steel sheet with molten metal according to the present invention.

The apparatus for producing a steel sheet with molten metal includes a molten metal plating bath 1 for holding a molten metal plating bath 2 for drawing in the steel sheet S and attaching the molten metal thereto, and a steel sheet S pulled up from the plating bath 2. A gas squeezing device 4 for adjusting the amount of molten metal adhered to the steel plate, an electromagnet 5, a support roll 6 outside the bath, and a force.The current control device 8, a preset control computer 9 as a control device for the electromagnet 5. A line control device 10 is provided.

The molten metal plating tank 1 is provided with a sink roll 3 as a turning device for turning the steel sheet S in the plating bath 2. Further, a supporting roll 7 for supporting the direction-changed steel sheet S in the plating bath 2 may be provided. However, although the support roll 7 is effective in suppressing vibration of the steel sheet S and correcting warpage, dross in the plating bath may be wound and cause dross defects in the steel sheet S. In the present invention, since the vibration can be sufficiently suppressed and the warpage corrected by the electromagnet 5, the support roll 7 is not always necessary, and it is preferable that the support roll 7 is not installed from the viewpoint of preventing the surface defects of the steel sheet S.

The gas expansion device 4 and the electromagnet 5 are provided between the plating surface of the plating bath 2 and the support port 6. The electromagnet 5 is installed above and / or below the gas throttle device 4. Since zinc is scattered and deposited below the gas throttle device 4, it is desirable that the electromagnet 5 be installed above the gas throttle device 4. Masire,

The distance between the tip of the gas ejection port (wiving nozzle) of the gas throttle device 4 and the steel plate S was conventionally set to about 15 mm. This is the case where the warp state of the steel sheet changes abruptly at the seam between the preceding steel sheet and the succeeding steel sheet unless this interval is left. In addition, the wiving nozzle and the steel plate may be fine. However, in the present invention, since the warp can be corrected over the entire length of the steel sheet, the distance between the tip of the wiping nozzle and the steel sheet S can be made smaller than that of the conventional 15-thigh.

The electromagnet 5 is provided to face the steel sheet so as to generate a magnetic force in a direction crossing the steel sheet surface. The electromagnet 5 has a function of suppressing the vibration of the steel sheet S and correcting a warp of the steel sheet S caused by the bending and return deformation received from the sink roll 3 and the support port 7 in the bath. Further, as shown in FIG. 5, for example, a large number of electromagnets 5 are provided in the width direction, and these electromagnets 5 are selectively used according to the degree of warpage in the width direction.

It should be noted that a conventional apparatus using an electromagnet requires a position sensor for measuring the position of a steel sheet, but in the present invention, so-called preset control is performed, and such a position sensor is not necessarily required. From the viewpoint of cost increase and large equipment size, it is preferable that there is no position sensor.

The steel sheet S that has entered the plating bath 2 is turned by the sink roll 3, pulled up from the plating bath 2, and adjusted by the gas squeezing device 4 to adjust the adhesion amount. At this time, the steel sheet S that has passed through the sink roll 3 is supported by the support roll 7 in the bath and the support roll 6 outside the bath, and the magnetic force from the electromagnet 5 provided between these support rolls causes the steel sheet S to move. Vibration is suppressed and warpage is corrected.

The current control of the electromagnet 5 is performed as follows. First, various operation condition data are sent from the line control device 10 to the preset control computer 9. The preset control computer 9 determines the current value in the preset control based on these operation condition data. As a determination method, a table value prepared in advance may be used, or a model formula may be constructed and calculated. In the method using table values, an appropriate current value (current value at which the steel sheet becomes flat at a stable neutral point) is obtained in advance for each operating condition, and that value is used for each operating condition. The operating conditions should take into account the thickness of the steel sheet, the width, the type of steel, the tension, the roll diameter of the upstream roll, the winding angle, the frictional force, the pushing amount, and the like. The model formula may be constructed from a physical model representing the occurrence of warpage or the attractive force of the electromagnet, but may be constructed by multiple regression of operating conditions. And this The optimum current value calculated as described above is sent to the current control device 8, and the output of the electromagnet 5 is controlled by a command from the current control device 8. Also, the current value of the electromagnet 5 may be changed to a predetermined current value based on the information of the succeeding steel sheet when the seam between the preceding steel sheet and the succeeding steel sheet passes through the installation position of the electromagnet. .

FIG. 6 shows an example of a preset control flow according to the present invention.

The flow indicated by the solid line is the flow of the preset control for the preceding steel sheet currently being processed as described above.

For the succeeding steel sheet, as shown by the dotted line, the preset control computer 9 calculates the optimum current value by a table value or a model formula using the operating conditions of the succeeding steel sheet sent from the line controller 10. Is done. Then, a signal is received from the line controller 10 at which the joint between the preceding steel sheet and the succeeding steel sheet passes through the position of the gas expansion device 4 or the electromagnet 5, and the optimum current value of the electromagnet 5 is sent to the current control device 8. . In this way, the current value of the electromagnet 5 is set to the optimum value from the time when the leading end portion of the succeeding steel sheet passes.

As described above, by performing the preset control as the current control of the electromagnet 5, it is possible to correct the warp over the entire length of the steel sheet including the vicinity of the joint between the preceding steel sheet and the succeeding steel sheet. In addition, since the use of the support roll 7 in the bath is not required, the preset model can be further simplified. In addition, it is possible to prevent the occurrence of surface defects caused by rolls in the bath and to reduce the cost of mouth maintenance. Further, since the distance between the tip of the wiping nozzle of the gas expansion device 4 and the steel plate S can be reduced, operation at a low gas pressure becomes possible, and generation of splash defects can be suppressed. Embodiment 2

FIG. 7 shows another example of the apparatus for producing a steel sheet with molten metal according to the present invention.

In this apparatus for manufacturing a steel plate with molten metal, the apparatus shown in Fig. 4 was installed downstream of the steel roll shape measuring device 11 and the out-of-bath support roll 6 provided near the gas expansion device 4. A plating adhesion amount measuring device 12 and a feedback control computer 13 as a control device for the electromagnet 5 are added. According to this device, it is described in Embodiment 1. In addition to the preset control, based on the information measured by the shape measuring device 11 and / or the adhesion measuring device 12, the warpage of the steel sheet is recognized and the current value of the electromagnet 5 is corrected. Control can be performed.

Since the shape measuring device 11 and the attached adhesion amount measuring device 12 are installed to recognize the state of vibration and warpage of the steel sheet S, it is not always necessary to provide both measuring devices.

The shape measuring device 11 measures the magnitude of the warpage of the steel sheet S, and does not necessarily need to be able to measure the entire width of the steel sheet S in the width direction. For example, it may be a position sensor that can measure only the center and the end in the width direction of the steel sheet S. In order to measure the shape at the position of the gas throttle device 4, it is desirable to install the gas throttle device 4 as close to the gas throttle device 4 as possible. Furthermore, it is desirable to install above the gas expansion device 4 in order to avoid the scattering of zinc.

The coating weight measuring device 12 measures the coating weight attached to the steel sheet S, and obtains the plating weight distribution in the width direction. The distance between the gas expansion device 4 and the steel plate S, that is, the warpage of the steel plate S can be estimated from the adhesion distribution.

First, the shape of the steel sheet S is measured by the shape measuring device 11, or the distribution in the width direction of the plating amount on the steel sheet surface is measured by the plating amount measuring device 12. These pieces of information are sent to the feedback control computer 13, where the amount of warpage of the steel sheet S is obtained. Then, based on various operation condition data sent from the line control device 10, a correction amount of the current value set in the feedback control is determined. As in the case of the preset control, this correction amount may be determined from table values prepared in advance, or may be determined by constructing a model formula. Then, the correction amount of the current value calculated in this way is sent to the current control device 8, and the output of the electromagnet 5 is controlled by a command of the current control device 8. FIG. 7 shows an example of a feedback control port according to the present invention.

The flow indicated by the solid line is the preset control flow described in the first embodiment. In the feedback control, as shown by the dotted line, data on the shape measured by the shape measuring device 11 or data on the widthwise distribution of the sticking amount measured by the plating amount measuring device 12 is sent to the feed pack control computer 13. Sent. With plating In order to use the coating amount measuring device 12, the relationship between the distribution of coating weight in the width direction and the shape of the steel sheet is determined in advance, and the shape of the steel sheet is determined based on the relationship. The warpage of the steel sheet is calculated from the data of these shapes, and the amount of correction of the current value of the electromagnet 5 is calculated using a table value or a model formula in the feed pack control computer 13 using various operating conditions sent from the line control device 10. Is calculated. Then, the correction amount of the current value is sent to the current control device 8.

With the preset control described in the first embodiment, an almost flat steel plate can be realized. There is an error in the preset accuracy due to uncertain factors such as a force model error and roll wear. If such ^^ is further subjected to this feedback control to measure the actual warpage of the steel sheet and to correct the output of the electromagnet, a flatter steel sheet can be obtained. In addition, it is more preferable to consider such a preset error and perform error learning that reflects the error at the next and subsequent presets. FIG. 9 is a diagram comparing the shape controllability between the present invention and the conventional technology.

In the prior art, since only the feedback control is performed, it is not possible to correct the warp of the leading end of the succeeding steel sheet at the joint between the preceding steel sheet and the succeeding steel sheet.

In the first embodiment of the present invention, since the preset control is performed, the amount of warpage can be suppressed to a certain range over the entire length of the steel sheet.

In the second embodiment of the present invention, since feedback control is performed in addition to the preset control, an error generated by the preset control can be corrected, and the flat shape can be controlled substantially over the entire length of the steel sheet.

In the first and second embodiments, the method of controlling the current of the electromagnet 5 has been described. However, the adjustment of the magnetic force by the electromagnet 5 can also be achieved by adjusting the distance between the electromagnet 5 and the steel plate. Therefore, the same effect can be obtained by adjusting the distance between the electromagnet 5 and the steel sheet instead of controlling the current of the electromagnet 5 of the present invention.

In Embodiments 1 and 2, warpage can be corrected over the entire length of the steel sheet, and the occurrence of surface defects caused by rolls in the bath can be eliminated without using the support rolls in the bath. Since the distance between the tip of the wiving nozzle of the gas expansion device and the steel plate can be reduced to suppress the occurrence of the splash defect, it is possible to manufacture a high quality hot-dip galvanized steel plate.

Here, the force S described for the application to the production of a general hot-dip galvanized steel sheet is not limited to this, and the present invention is applicable to the production of other hot-dip galvanized steel sheets. it can. Example

Using the apparatus for producing a molten metal-plated steel sheet according to the present invention shown in FIGS. 4 and 7, a cold-rolled steel sheet having a thickness of 0.7 mm and a width of 1500 mm was used as an original plate for plating, and the electromagnets and Hot-dip galvanized steel coil was manufactured under four conditions for the sensor.

Under the conditions of Invention Example 1, electromagnet preset control is performed using the manufacturing apparatus of FIG. The electromagnet is located 250 mm above the wiping nozzle and close to the wiping nozzle because it does not require a special sensor and has a simple device configuration. The distance between the wiving nozzle and the steel plate is 7 mm, which is narrow. Regarding the support rolls in the bath, whether they were used or not were examined.

Under the conditions of Invention Examples 2 and 3, electromagnet preset control and feedback control are performed using the manufacturing apparatus of FIG. As a sensor, a shape measuring device is provided in Invention Example 2, and a plating adhesion amount measuring device is provided in Invention Example 3. The electromagnet is located 500 mm above the wiping nozzle because the shape measuring device is installed near the upper part of the wiping nozzle in Invention Example 2, whereas it is located 250 mm above the wiping nozzle in Invention Example 2. The distance between the wiving nozzle and the steel plate is 7 mm, which is narrow. Regarding the supporting roll in the bath, both used and non-used ^^ were examined in the same manner as in Invention Example 1.

Under the conditions of the comparative example, feedback control of the conventional electromagnet is performed using the conventional manufacturing apparatus of FIG. 9 in which the electromagnet and the shape measuring device are provided in the vicinity thereof. The electromagnet is located 500mm above the wiping nozzle because the shape measuring device is also installed. The distance between the wiving nozzle and the steel plate is 15 minutes. The support roll in the bath As for, only the case where it is used was considered.

Then, with respect to the manufactured hot-dip galvanized steel sheet, the occurrence of splash defects and the width direction distribution of the adhesion amount were investigated. The occurrence of splash defects was evaluated based on the total number of splash defects over the entire length of the steel sheet coil using a surface defect meter installed in the hot-dip galvanizing line. The distribution of the coating weight in the width direction was evaluated by measuring the distribution of the coating weight in the width direction by using a coating weight meter provided in the hot-dip galvanizing line.

As a result, with regard to the occurrence of splash defects, the number of splashes generated in one steel sheet coil was about 10 in the comparative example, whereas the number of splashes in Invention Example 1-3 was 1-2 in all conditions. This was significantly reduced as compared with the comparative example. This is because the distance between the wiping nose and the steel plate was 15 mm in the comparative example, but could be reduced to 7 thighs in the invention example, and gas wiping at a low gas pressure became possible. In Inventive Examples 1-3, no difference was observed between the use and non-use of the support roll 7 in the bath.

Regarding the distribution of the coating weight in the width direction at the tip of the steel coil, the coating weight in the comparative example was non-uniform at about ± 10 g / m ² , whereas the coating weight in Invention Example 1-3 was not uniform. It was almost uniform at about ± 3 g / m ² . This is because, in the comparative example in which the electromagnet feedback control was performed, the change in the warp of the leading end of the succeeding steel sheet at the seam between the preceding steel sheet and the succeeding steel sheet could not be dealt with, but the invention example 1 in which the electromagnet preset control was performed. In the case of -3, the warpage can be properly corrected from the leading end of the succeeding steel sheet. Regarding the distribution of coating weight in the width direction at the center in the longitudinal direction of the steel coil, in Example 1, the coating weight was ±

Inventive Examples 2 and 3 showed that the adhesion amount was improved to about ± 1 to ² g / m ² . This is because in Invention Example 1 in which only the electromagnet preset control was performed, the warpage of the steel sheet could be made substantially flat, but a slight warp might remain due to an error in the preset control, and in addition to the electromagnet preset control, In the invention examples 2 and 3 in which the feed pack control is performed, even if an error occurs in the preset control, the error can be appropriately corrected by the feedback control to correct the shape. Table 1 Invention example 1 Invention example 2 Invention example 3 Comparative example Electromagnet Yes Yes Yes Yes Preset + Preset +

Electromagnet control method Preset feed pack

Feed Pack Feed / Cook

With つ "付

No sensor Shape measurement device Shape measurement device Measurement device

Electromagnet installation position

250mm 500mm 250mm 500mm (above the nozzle)

7mm / 'mm 7mm 15mm distance between nozzle and steel plate

Support roll in bath Used / Not used Used / Not used Used / Not used Used

Claims

The scope of the claims

1. A steel sheet is continuously immersed in a bath for plating a molten metal, and the molten metal is adhered to the surface of the steel sheet;

A step of turning the steel sheet by a turning device provided in the molten metal plating bath, and then drawing the steel sheet to the molten metal;

Adjusting the amount of the molten metal adhered to the steel plate by a gas throttle device;

A step of correcting the warpage of the steel sheet by using an electromagnet provided on the upstream side and / or the downstream side of the gas expansion device and applying a magnetic force in a direction intersecting with the surface of the steel sheet;

Has,

A method of manufacturing a steel sheet with a molten metal, wherein a current value of the electromagnet is set to a current value determined in advance based on information on the steel sheet.

2. Change the current value of the electromagnet to a predetermined current value based on the information about the succeeding steel sheet as the seam between the preceding steel sheet and the succeeding steel sheet passes through the installation position of the electromagnet. 2. The method for producing a molten metal-plated steel sheet according to claim 1.

3. Provide a shape measuring device for steel sheet and / or a coating weight measuring device for steel plate on the downstream side of the gas throttle device, and use an electromagnet based on the information measured by the shape measuring device and / or the adhesion measuring device. 2. The method for producing a molten metal-plated steel sheet according to claim 1, wherein the current value of the steel sheet is corrected.

4. Provide a shape measuring device for steel sheet and / or an adhesion measuring device for steel plate on the downstream side of the gas expansion device, based on the information measured by the shape measuring device and / or the adhesion measuring device for plating. 3. The method for producing a steel sheet with a molten metal according to claim 2, wherein the current value of the electromagnet is corrected.

5. The method for producing a steel sheet with molten metal according to claim 1, wherein the apparatus for supporting the steel sheet in the molten metal plating bath is only the direction change device for the steel sheet.

6. The method for producing a steel sheet with molten metal according to claim 2, wherein the apparatus for supporting the steel sheet in the molten metal plating bath is only the direction change device for the steel sheet.

7. The method for producing a steel sheet with molten metal according to claim 3, wherein the apparatus for supporting the steel sheet in the molten metal plating bath is only the direction change device for the steel sheet.

8. The method for producing a hot-dip metal-plated steel sheet according to claim 4, wherein the apparatus for supporting the steel sheet in the hot-dip metal bath is only the direction change device for the steel sheet.

9. A bathtub for applying molten metal to the surface of the steel plate,

A turning device installed in the molten metal plating bath, for turning the steel plate;

A gas squeezing device installed above a plating bath surface of the molten metal plating bath to adjust a molten metal plating amount attached to the steel plate;

An electromagnet installed upstream and / or downstream of the gas expansion device to apply a magnetic force in a direction intersecting the surface of the steel sheet to correct the warpage of the steel sheet in a non-contact manner; A current value preset control device that sets a current value determined in advance based on information on the steel sheet;

For manufacturing steel sheet with molten metal.

10. Further, a shape measuring device for the steel plate and / or a coating weight measuring device for the steel plate installed downstream of the gas throttle device,

A current value feedback control device that corrects the current value of the electromagnet based on the information measured by the shape measurement device and / or the plating adhesion amount measurement device, 10. The apparatus for producing a molten metal-plated steel sheet according to claim 9, comprising:

11. The apparatus for producing a steel sheet with a molten metal according to claim 9, wherein the apparatus for supporting the steel sheet provided in the bath with the molten metal is only the direction change device for the steel sheet.

12. The apparatus for manufacturing a hot-dip metal-plated steel sheet according to claim 10, wherein the apparatus for supporting the steel sheet provided in the bath with the hot-dip metal plating is only the direction change device for the steel sheet.