KR950000007B1 - Method of controlling coating weight on a hot-dipping steel strip - Google Patents

Abstract

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Description

Method for controlling coating weight on steel object of hot dip plating

1 is a representative diagram showing the relationship between magnetic field strength (H) and magnetic flux density (B) of steel strip;

2 is a side view showing an example of an apparatus for implementing the method of the present invention,

3 is a front view of the device shown in FIG. 2,

4A and 4B are side views showing another example of the apparatus implemented by the method of the present invention.

FIG. 5a is a front view of the device shown in FIG. 4a,

5b is a front view of the device shown in FIG. 4b,

6A and 6B are side views showing another example implemented by the method of the present invention;

7 is a side view showing another example implemented by the method of the present invention,

8 is a front view showing still another example carried out by the method of the present invention,

9 is a front view showing still another example carried out by the method of the present invention,

10 is a side view of the device shown in FIG.

FIG. 11 is a schematic explanatory diagram showing an example in which the portion of the high frequency current conductive path facing the steel strip in the age of the steel sheet is inclined in the width direction of the steel strip;

12 is a representative drawing showing an analytical model,

FIG. 13 is a representative diagram showing an example of analysis of one period of maximum magnetic pressure in the analysis model shown in FIG. 12;

14a, 14b and 14c are representative views showing the distribution of magnetic pressure,

15 is a side view showing an example of an apparatus for implementing the method of the present invention,

FIG. 16 is a front view of the apparatus shown in FIG. 15;

17 is a side view showing an example of an apparatus for implementing the method of the present invention,

FIG. 18 is a front view showing the apparatus shown in FIG. 17;

19 is a side view showing an example of an apparatus for implementing the method of the present invention,

20 is a front view of the apparatus shown in FIG. 19,

21 is a side view showing an example of an apparatus for implementing the method of the present invention,

22 is a front view of the device shown in FIG. 21,

23 is a view showing an analysis model,

24 is a schematic explanatory diagram showing the distribution of a magnetic field obtained by analysis;

25 is a side view showing an example of an apparatus for implementing the method of the present invention,

28 is a front view of the device shown in FIG. 27,

29 is a side view showing another example of an apparatus for implementing the method of the present invention.

* Explanation of symbols for main parts of the drawings

1a, 1b: High frequency current path 52, S: Steel band

2: electromagnetic material 3: water-cooled box

4: application bath 5: magnet

6: yoke 51,7: coil

8 wiping nozzle 21 bend

30: excess molten metal

The present invention relates to a method for continuously plating steel strips with molten metal, and more particularly, to a method for controlling coating weight on a steel object.

Sink rolls, pinch rolls and wiping nozzles are used in the prior art methods to continuously plate steel strips with molten metal. The sink roll is located in the application bath, and the steel strip is moved by the sink roll and taken out over the application bath. The pinch roll is used to straighten the bent steel strip by pressing the steel strip downward, and the plating thickness is uniformly obtained by removing excess plating by the spraying gas from the wiping nozzle in the steel object taken out of the coating bath.

In the prior art method, the coating weight of the steel object also increases when the moving speed of the steel sheet is increased to improve the productivity of the steel sheet. It is necessary to increase the gas pressure from the wiping nozzle to lower the coating weight of the steel strip. When the pressure of the gas from the wiping nozzle is increased, the gas injection hits the highway strip, wiping down the excess molten metal downwards. A gas jet hit the steel strip creates a stream of incident gas. A part of the molten metal is splashed by the flow of the accompanying gas, and a part of the molten metal from the splashing is attached to the wiping nozzle, thereby clogging the nozzle. As a result, the gas is not evenly sprayed on the steel object from the wiping nozzle, so that the coating weight of the steel object is not uniform.

If the coating weight of the steel object is not uniform, not only the appearance of the steel strip will be poor, but the non-uniform coating weight of the steel object will cause the steel band to be disturbed during winding and the alloying after plating becomes uneven. Some of the molten metal from the frying is attached to the steel strip again, causing the steel sheet to bond. Increasing the amount of gas from the wiping nozzle will result in increased cost and noise. In order to cope with an increase in the plating rate, various methods for removing excess molten metal of steel are proposed.

According to the method disclosed in Japanese Patent Publication No. 7444/69, an eddy current is generated in the steel strip by applying a high frequency magnetic field to the steel strip, and the molten metal is removed by the Lorentz force generated by the eddy current.

In this case, wiping the molten metal by the gas blowing means and applying a high frequency magnetic field to the steel strip are used together.

According to the method disclosed by Japanese Patent Application Laid-Open No. 227158/86, the steady current flows in the steel strip and the Lorentz force caused by the static magnetic field and the steady current removes the excess molten metal of the steel object. After the excess molten metal is removed from the strip, the strip is wiped off by gas.

According to the method disclosed in Japanese Patent Application Laid-Open No. 204363/86, a static magnetic field is generated on the surface of the steel sheet in the outward direction from the surface of the steel sheet, and excess molten metal is induced in the molten metal by the movement of the steel sheet and the magnetic field. It is removed by the Lorentz force generated by the current and the magnetic field. The strip is also wiped with gas.

In the methods disclosed in Japanese Patent Laid-Open Nos. 266560/86 and 103353/87, the strip is cleaned by gas after generating a moving magnetic field in the downward direction of the strip to remove excess molten metal downward.

However, in the above conventional method, when the magnetic field acts on a ferromagnetic material such as a steel band, the steel band is attracted to a stronger magnetic field. As a result, the entire system becomes unstable and proper control of the system becomes difficult. In order to solve this difficulty, it is necessary to leave a gap between the magnetic field generator and the coil. However, when there is a gap between the magnetic field generator and the strong band, the effect of the magnetic field is limited and the desired effect cannot be obtained.

In addition, the vibration of the steel strip and the bending of the steel strip in the width direction may cause the coating weight of the steel strip to be uneven. None of the conventional methods described above have any effect on correcting vibration attenuation and bending of the steel strip. Japanese Patent Laid-Open No. 7444/69 discloses that a steel strip passing between coils is in the center of the coil by magnetic repulsive force. However, when a high frequency magnetic field is simply applied to the steel strip, the magnetic attraction force is strongly operated in the steel object, which is a ferromagnetic material, and the steel band passing between the coils is attracted to the coil. As a result, unstable vibration of the steel strip occurs. Therefore, attenuation of the vibration of the steel strip cannot be obtained in this method.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for controlling the coating weight of a steel object to reduce the vibration of the steel sheet during the plating of the steel sheet with the metal and at the same time to prevent bending of the steel sheet, and to uniformly apply the metal to the steel sheet at high speed. have.

In order to achieve the above object, the present invention is a method for controlling the coating weight on a steel object of hot-dip plating, at least one pair disposed in parallel and parallel to the front side and the rear side of the steel strip taken out from the coating bath above the coating bath. Positioning a high frequency current conduction path of the; A high frequency current flowing strong enough to magnetically saturate the steel band through the at least one pair of high frequency current conduction paths to induce a high frequency current of opposite phase in the steel band, and the magnetic pressure acting on the surface of the steel band And causing the high frequency current to be generated by the interaction of the induced high frequency current.

Even if a magnetic field is simply applied to a ferromagnetic material such as a steel strip in order to control the weight applied to the steel object and to attenuate the vibration of the steel sheet, magnetic attraction force is applied to the steel object to cause an unstable state of the steel strip. In FIG. 1, as shown by the BH curve indicating the relationship between the magnetic flux density (B) and the magnetic field strength (H) in FIG. 1, the region showing the ferromagneticity of the steel band is limited to the unsaturated region, and the steel band is saturated. The present invention has been made by paying attention to the fact that it does not have ferromagnetic properties. When sufficient high frequency current is applied to the steel strip to reach the saturation region, the magnetic repulsive force of the steel band becomes larger than the magnetic attraction force. Repulsive force is generated between the current flowing through the high frequency current conduction path and the current induced in the steel strip. Therefore, the instability created by the magnetic attraction force is eliminated. Preferably, the high frequency current has a range of 500-10,000 Hz. When the high frequency current has a frequency less than 500Hz, it has no effect, and when it has a frequency above 10,000Hz, the electricity consumption becomes extremely large.

In the present invention, high frequency current conduction paths respectively parallel to both sides of the steel strip are disposed close to the steel strip on one side of the steel strip taken out from the coating bath on the surface of the molten metal in the coating bath and on the other side of the steel strip. The high frequency current flows through the high frequency current conduction path sufficient to magnetically saturate the steel band to induce the high frequency current of the opposite phase in the steel band. The high frequency current conduction path generates magnetic pressure acting on the surface of the steel strip through the interaction between the high frequency current and the induced high frequency current. The molten metal attached to the steel strip is wiped off by the magnetic pressure applied to the steel strip on both sides of the steel strip to control the coating weight of the steel object. In addition to controlling the coating weight of the steel strip, the bending of the steel strip in the width direction and the vibration of the steel strip are prevented.

In the present invention, two pairs of high frequency current conduction paths or more are arranged at regular intervals in the moving direction of the steel strip.

Close to one side of the steel strip and the other side of the steel strip, the high frequency current conduction paths are substantially opposite to each other, and the steel bands between the high frequency current conduction paths are positioned. High frequency currents of the same phase flow through opposite high frequency current conduction paths.

In the case where a plurality of high frequency current conduction paths are disposed close to one side and the other side of the steel strip, respectively, the high frequency current conduction paths may be located opposite or not facing each other, and the steel strip is located between the high frequency current conduction paths. Will be. If the high frequency current conduction paths are not opposed to each other, the high frequency current conduction paths are positioned to deviate from the moving direction of the steel strip.

If the high frequency current conduction paths are located to be offset from the moving direction of the steel strip, there is no restriction on the current phase as in the case where the high frequency current conduction paths are located opposite to each other, and the high bands are also located between the passages.

Each of the high frequency current conduction paths is disposed across the steel strip in the width direction. However, it is unnecessary to arrange the steel strips in parallel to the width direction of the steel strips. Each total length of the high frequency current conduction path can be inclined with respect to the width direction of the steel strip. Since current flows near both ends of the steel strip at an angle of 90 ° to the direction of current flow through the high frequency current conduction path, the magnetic pressure adjacent to both ends of the steel strip tends to be weak. In order to prevent the magnetic pressure from weakening near both ends of the steel strip, the total length of each of the high frequency current conduction paths may be inclined with respect to the width direction of the steel strip, or may be inclined near both ends of the steel strip.

FIG. 2 is a side view showing an example of a device for implementing the method of the present invention, and FIG. 3 is a front view showing the device as shown in FIG. Symbol I in the figure represents current.

The steel strip S is continuously taken out from the application bath 4. The high frequency current conduction paths 1a and 1b are disposed in parallel with one side of the steel strip S and the other side of the steel strip. When the high frequency current I of the same phase flows through the high frequency current conduction paths 1a and 1b, a current having a phase opposite to that of the high frequency current I flows through the steel strip S. The symbol ⊙ of the high frequency current conduction path 1a and the high frequency current conduction path 1b indicates that both currents of the high frequency current conduction path have the same phase. Since the current flowing through the steel strip flows in the direction opposite to the direction of current flow through the high frequency current conduction path, the magnetic repulsive force, or magnetic pressure, acts on the surface of the steel strip. However, ferromagnetic materials such as steel strips have a high permeability, so when the current simply flows through the high frequency current conduction paths 1a and 1b, the magnetic attraction force of the steel strip exceeds the magnetic repulsive force of the steel strip, causing the steel strip to become unstable. When the current flowing through the high frequency current conduction paths 1a and 1b is increased, as shown in FIG. 1, the strength of the magnetic field is increased in the steel strip, and the holding time while the steel strip maintains the saturation region is longer. You lose. As a result, when the strength of the magnetic field in the steel band exceeds the predetermined magnetic field strength, the magnetic repulsive force of the steel band becomes larger than the magnetic attraction force of the steel band. In the present invention, a high frequency current sufficient to magnetically saturate the steel strip flows through the high frequency current conduction paths 1a and 1b, thereby obtaining the necessary magnetic repulsion force. The magnetic repulsive force of the steel strip acts on the steel object just as it operates a non-contact spring on the steel object on both sides of the steel strip. The magnetic repulsion force attenuates the vibration of the steel strip and corrects it. Under the condition that the bending of the steel sheet is straightened by the magnetic repulsion force and the molten metal attached to the steel sheet is removed from the steel sheet under the condition that the vibration of the steel sheet is attenuated, molten metal is uniformly applied to the surface of the steel sheet.

In the example shown in FIGS. 2 and 3, the pair of high frequency current conduction paths 1a and 1b are located near the steel band S, and face the steel band S, and the steel bands are the high frequency current conduction paths 1a and 1b. Will be located between). The high frequency current I of the same phase flows through the current conduction paths 1a and 1b.

4 (a) is a side view showing another example of an apparatus for implementing the method of the present invention.

FIG. 5 (a) is a front view showing the apparatus shown in FIG. 4 (a). Two pairs of structural wave current conduction paths 1a and 1b face the steel strips, respectively, and are disposed above and below the steel strips located between the high frequency current conduction paths 1a and 1b. In this example, the current phase of the upper current path is opposite to the current phase of the lower current path. In the examples shown in FIGS. 4 (b) and 5 (b), the current phase of the upper current path is the same as the current phase of the lower current path. Therefore, the current phases of the upper and lower current conduction paths may be the same or opposite.

6 (a) is a side view showing still another example of the apparatus according to the embodiment of the present invention. The high frequency current conduction paths are arranged in close proximity to both sides of the steel strip, and the steel strips are located between the high frequency current conduction paths 1 which are not opposed to each other but are shifted up and down. It is arranged in a zigzag. When a plurality of high frequency current conduction paths are arranged in proximity to one side and the other side of the steel strip, the high frequency current conduction paths are arranged in the manner shown in Fig. 6 (a). Corresponding to each high frequency current of the high frequency current conduction path, a current having a phase opposite to that of the high frequency current of the high frequency current conduction path flows through the steel strip S. FIG. Opposite magnetic pressure alternates on both sides of the strip S perpendicularly to the direction of movement of the strip. In the example of FIG. 6 (a), the phases of the currents flowing through the current conduction paths close to both sides of the steel strips are opposite to each other. In the example of FIG. 6 (b), the current flows through the high frequency current conduction paths near the both sides of the steel strips. The phases of the currents are the same. That is, the phase of the current flowing through the current conduction path is optional.

7 is a side view showing another example of an apparatus for implementing the method of the present invention. The high frequency current conduction paths 1a and 1b are enclosed with the electromagnetic material 2 having a high permeability and a high saturation magnetic flux density except for both sides facing the steel strip. The water cooling box 3 is installed inside the electromagnetic material 2. Because of the small magnetoresistance of the electromagnetic material 2, a magnetic field sufficient to saturate the strip can be effectively applied to the strip by means of a relatively low current and a high magnetic pressure can be generated in comparison thereto.

8 is a front view showing yet another example of an apparatus for implementing the method of the present invention. In order to apply a particularly strong magnetic pressure to both ends of the steel strip, a bent portion 11 is formed in the part of the high frequency current conduction path 1 which is opposed to both ends of the steel strip in the moving direction of the steel strip.

Each of the examples shown in FIGS. 1 to 7 can be applied to forming a bent portion in a portion of the high frequency current conduction path 1. In the vicinity of the end of the steel strip, since the direction of current flow through the steel strip is formed at an angle of 90 ° with respect to the current flowing through the high frequency current conduction path, the magnetic pressure becomes weak near the end of the steel strip.

In order to prevent the magnetic pressure near the end of the steel strip from weakening, the high frequency current conduction path may be inclined with respect to the entire length of the high frequency current conduction path in the width direction of the steel strip or inclined near the end of the steel strip.

9 is a front view showing another example of an apparatus for implementing the method of the present invention. 10 is a side view of the device shown in FIG. The overall length of the high frequency current conduction paths 1a and 1b close to both sides of the steel strip is inclined in the width direction of the steel strip. 11 shows an example in which the respective portions of the high frequency current conduction paths 1a and 1b are inclined in the width direction of the steel strip near the ends of the steel strip. Inclination of a part of the high frequency current conduction path in the vicinity of both ends can be applied to each of the examples shown in FIGS. 2 to 7.

The inventors conducted simulation analysis to calculate the magnetic pressure in which the high frequency current flowing through the high frequency current conduction path is effective. This analysis was performed with the apparatus shown in FIG. 4 (a). Coils 30 mm thick and 50 mm wide were used. A current of 3 × 10 ₄ [A] flowed through the coil. A 2.3 mm thick strip with a specific permeability (at saturation) of 1 was used. 12 is a diagram showing an analysis model. The relative position of the coil 51 and the steel strip 52 is shown in FIG.

The center strip between the high frequency current paths was located at the following level. (a) In the case of a steel strip located centrally between high frequency current-carrying paths, the steel strip is located 15 mm from each of the two high-frequency current-carrying paths. The position of this steel strip corresponds to the position of the steel strip 52 of FIG. (b) the band is shifted by 5 mm from the center as described above toward one high frequency current path, (c) the band is shifted by 10 mm from the center as described above towards one high frequency current path as a result of analysis. Under the above-described conditions, it was confirmed that the strip amplitude of the magnetic field strength was 160,000 A / m, and the steel strip having the representative BH curve shown in FIG. 1 and Table 1 was completely saturated.

TABLE 1

FIG. 13 is a diagram representatively showing an example in which one period of the maximum magnetic pressure is interpreted by the analysis model shown in FIG. Symbol A in the figure shows the state of magnetic pressure in the saturation region, symbol B shows the state of magnetic pressure in the saturation region, and symbol C is the average value of the magnetic pressure. The time during which the magnetic attraction force exceeds the magnetic pressure is 6% or less. The maximum magnetic pressure is five times greater than the magnetic attraction force. Therefore, irrespective of whether the steel strip is a ferromagnetic material, it can be applied very stably to the magnetic steel strip.

Next, an example of analyzing the distribution of the average magnetic pressure averaged over time in a steel object is shown. FIG. 14 (a) shows the distribution of magnetic pressure when the steel strip is in the center between two high frequency current conduction paths. 14 (b) and 14 (c) are representative views of the distribution of magnetic pressure in the case where the steel bands are shifted by 5 mm and 10 mm, respectively, from the center between the two high frequency current conductive paths toward the high frequency current conductive path on one side. to be. According to the distribution of the magnetic pressures in Figs. 14 (b) and 14 (c), it can be seen that a force pushing toward the center as a whole is applied when the steel band is shifted from the center position. This magnetic pressure is increased when the strip approaches the high frequency current path. As a result, the magnetic pressure acts effectively to center the strip, and is effective in damping the vibration of the strip. This magnetic pressure is also effective in extending the bending of the steel strip. The total amount of warpage of the steel strip may be limited to 0.5 mm or less by the magnetic pressure. The magnetic pressure shown in Figure 14 (a) has a maximum of 13452 Pa, which is understood to be sufficient pressure to wipe off the molten metal on the surface of the steel strip. The apparatus corresponding to the example of FIG. 4 and FIG. 5 is installed in 40 mm on the surface of a coating bath, and steel strip application weight is controlled based on the result mentioned above. The conditions of the width and the current of the steel strip are the same as in the case of the simulation analysis. The linear velocity was 150 m / min.

The bending of the steel strip in the position of wiping is completely straight, and the vibration of the steel strip is limited to 5 mm or less according to the invention. No splashing or noise as in the case of gas wiping nozzles. The coating weight of the steel object is controlled so that the metal is very uniformly attached to the steel strip. Although the galvanizing of the steel strip whose coating weight of steel object reaches 35 g / m <_2> is difficult to achieve by the conventional wiping method, it was confirmed that it can be easily performed by the method of this invention.

The method for controlling the coating weight on the steel object by using the gas wiping nozzle of the prior art can be applied to the above-described method of the present invention.

In the present invention, each of the high-frequency current conduction path is disposed in close proximity to one side and the other side of the steel strip taken out of the coating bath.

Each of the high frequency current conduction paths is disposed parallel to the strip on the surface of the molten metal in the coating bath. One high frequency current conductive path adjacent to one side of the steel strip faces the other high frequency current conductive path, and the steel band is positioned between the high frequency current conductive paths.

The north pole (N pole) and south pole (S) poles of the magnet are disposed outside the ends of the steel strip adjacent to the high frequency current conduction path, and actually face each other, and the width direction of the steel band is located between the north pole and the south pole of the magnet. The strip is magnetically saturated by a magnet. The high frequency current of the same phase flows through the high frequency current conduction path, and the high frequency current of the opposite phase is induced in the steel strip. The magnetic pressure acting on the surface of the steel strip is generated by the interaction of the high frequency current of the high frequency current conduction path with the induced high frequency current. The bending of the steel strip and the vibration of the steel strip in the width direction of the steel strip are prevented by the magnetic pressure acting on both sides of the steel strip to the steel object, and the applied weight of the steel object is controlled by wiping the molten metal attached to the steel strip. Two pairs of high frequency current conduction paths or more are arranged at regular intervals in the moving direction of the steel strip. Any magnet and permanent magnet made of electromagnet can be used. The magnets are actually arranged opposite each other, with the strip placed between the magnets. The magnets are arranged in two positions or more in the direction of movement of the steel strip.

15 is a side view showing an example of an apparatus for implementing the method of the present invention. FIG. 16 is a front view showing the apparatus shown in FIG. The steel strip S is continuously taken out from the application bath 4. Each of the high frequency current conduction paths 1a and 1b is disposed in parallel to both sides of the steel strip S in close proximity to the steel strip on the surface of the molten metal in the table bath. The north and south poles of the magnet 5 are located in close proximity to the high frequency current conduction paths 1a and 1b and actually face each other, and the width direction of the steel strip is located between the south pole and the north pole of the magnet 5 outside both ends of the steel strip. do. Both the high frequency current conduction paths 1a and 1b adjacent to both sides of the steel strip are arranged in the lower side (or lower side) and the upper side (or upper side) in the height direction. The magnets are disposed above and below the high frequency current conduction paths 1a and 1b, respectively. When a high frequency current of the same phase flows through the high frequency current conduction paths 1a and 1b, a current having a phase opposite to that of the high frequency current flows through the steel strip S. The symbol ⊙ of the high frequency current conduction path 1a on the upper side and the symbol ⊙ of the high frequency current conduction path 1b indicate that they are in phase. The symbol of the lower high frequency current conduction path 1a and the symbol of the high frequency current conduction path 1b indicate that the two phases are the same. In this example, the phase of the high frequency current conduction path 1a on the upper side and the phase of the high frequency current conduction path 1a on the lower side may be opposite to each other or may be the same. Since the current flowing through the steel strip S is opposite to the flow of current flowing through the high frequency current conduction path, the magnetic repulsive force of the steel strip mainly acts on the surface of the steel strip. However, ferromagnetic materials such as steel strips have a high permeability, so when the current flows simply, the magnetic attraction force exceeds the magnetic repulsion force, causing the steel strip to become unstable. Magnets 5 disposed outside both ends of the steel strip self-saturate the steel strip to eliminate the instability described above. That is, the magnetic field in the steel band appears in the magnetically saturated region by the operation of the magnetic field 5.

In addition, various ranges of the magnetic field generated by the high frequency current appear in the magnetic saturation region. As the steel strip magnetically saturates the ferromagnetic material and becomes paramagnetic, the steel strip receives only a repulsive force from the high-frequency current path. As a result, the instability caused by the magnetic attraction force is eliminated. This repulsive force acts like a noncontact spring. The vibration of the steel strip is suppressed by the magnetic repulsive force, and the bending of the steel strip is also held straight. The excess molten metal attached under the condition that the vibration of the steel strip is suppressed by the magnetic repulsion force and the bending of the steel strip is straightened is removed by the magnetic pressure acting on the steel object on both sides of the steel strip, and the molten metal is uniformly applied to the surface of the steel strip.

17 is a side view showing an example of an apparatus for implementing the method of the present invention. FIG. 18 is a front view showing the apparatus of FIG. 17. FIG. In the example shown in FIGS. 17 and 18, the north and south poles of the magnet are located between two pairs of high frequency current paths, one of which is above the magnet and the other below. Current flows through the two pairs of high frequency current flow paths as in the examples of FIGS. 15 and 16.

19 is a side view showing an example of an apparatus for implementing the method of the present invention. FIG. 20 is a front view showing the apparatus shown in FIG. 19. FIG. In the example shown in FIGS. 19 and 20, the high frequency current conduction path and the magnet are arranged in the manner shown in FIGS. 15 and 16, but the magnet 5 is composed of an electromagnet. Each of the electromagnets consists of a yoke 6 and a coil 7.

21 is a side view showing another example of an apparatus for implementing the method of the present invention. FIG. 22 is a front view of the device shown in FIG. 21. FIG. Two pairs of high frequency current conduction paths 1a and 1b are arranged with one on the top and the other on the bottom. The magnet 5 is located between the high frequency current conduction path of the high position and the low position. In order to apply a particularly strong magnetic pressure to the end of the steel strip, the bent portion 21 is formed along the moving direction of the steel strip at a position where the high frequency current conduction paths 1a and 1b oppose the ends of the steel strip.

Magnetic pressure is attenuated near the end of the steel strip because the direction of flow of the current flowing through the steel strip in close proximity to the end of the steel strip is formed at an angle of 90 ° to the direction of the current flowing through the high frequency current conduction path. In order to prevent the magnetic pressure from attenuating, the high frequency current path needs to be inclined with respect to the full length of the high frequency current path in the width direction of the steel strip as shown in FIGS. 9 and 10. It can be inclined close to the end.

The inventors conducted a simulation analysis for calculating the magnetic pressure acting on the steel object under the influence of the high frequency current flowing through the high frequency current conduction path. First, in order to confirm that the steel strip is self-saturated by the electromagnet, the steel band is analyzed in the static field of the electromagnet and in the structure of the apparatus shown in FIGS. 19 and 20. 23 is a representative view showing an analysis model. The relative position of the steel strip 52 and the iron core 53 are shown in the same figure.

The analysis conditions are as follows.

Iron core investment ratio: 1,000

Current of coil: 2.6 × 10 ⁵ A

Size of steel strip: width 1800mm

Thickness 2.3mm

The distribution of the magnetic field is obtained by the analysis shown in FIG. The magnetic field strength of ferromagnetic material is more than 6 × 10 ₅ A / m. This means that the steel strip is fully magnetically saturated. That is, the steel strip is in the saturation region.

Based on this result, the apparatus corresponding to the example in FIG. 19 and FIG. 20 is installed on 40 mm on molten metal in a coating bath, and the coating weight of a steel object is controlled. The width and current conditions of the steel strip are determined as in the simulation simulation described above, and the linear velocity is 150 m / min.

The bending of the steel strip is held straight at the position of the wiping and the vibration of the steel strip is suppressed within the range of 1 mm or less by the present invention. There is also no splash or noise as with a gas wiping nozzle. Therefore, the coating weight of the steel object is controlled very uniformly. In the gas wiping method as described above, it was confirmed that galvanizing the steel strip with an application weight of 35 g / m ₂ attached to the steel strip, which was difficult to be carried out at a linear speed of 150 m / min. The method for controlling the coating weight on a steel object by using a conventional gas wiping nozzle can be applied to the above-described method of the present invention.

In the present invention, the wiping nozzle is disposed close to both ends of the steel strip taken out from the application bath. A high frequency current path is located in the wiping nozzle. The gas is blown out of the table bath. High frequency currents sufficient to magnetically saturate the steel bands also flow through the high frequency currents, and high frequency currents of opposite phases are induced in the steel bands. The magnetic pressure acting on the surface of the steel strip is generated by the interaction of the induced high frequency current with the high frequency current flowing through the high frequency current conduction path. The coating weight of the steel object is controlled by the magnetic pressure acting on both the gas and the steel jet injected from the wiping nozzle. In addition, the bending of the steel sheet and the vibration of the steel sheet in the width direction of the steel sheet are prevented by the magnetic pressure acting on both sides of the steel sheet.

In the present invention, two pairs of high frequency current conduction paths or more may be arranged at regular intervals in the moving direction of the steel strip. That is, two pairs of high frequency current conduction paths or more may be located in the nozzle at regular intervals in the moving direction of the steel strip. A high frequency current conduction path may be disposed above and below the nozzle, away from the nozzle.

A pair of wiping nozzles includes a high frequency current conduction path and is positioned opposite each other, and a steel strip is located between the wiping nozzles. High frequency currents of the same phase flow through opposite high frequency current paths. When a plurality of high frequency current conduction paths are arranged in proximity to both sides of the steel strip, the wiping nozzle including the high frequency current conduction path does not have to face the steel strip, and the steel strips are positioned between the wiping nozzles. The high frequency current conduction path may be arranged to be shifted in the moving direction of the steel strip. In this case, there is no limitation on the phase of the current flowing through the high frequency current path.

The high frequency current conduction path included in the nozzle is arranged in the width direction of the steel strip, but is not necessarily arranged parallel to the width direction of the steel strip. The entire length of the high frequency current conduction path may be inclined with respect to the width direction of the steel strip. Since the flow direction of the current flowing through the strip near the end of the strip is formed at an angle of 90 ° with respect to the direction of the current flowing through the high-frequency current path, the magnetic pressure near the edge of the strip tends to be weak. In order to prevent the magnetic pressure from weakening near the end of the steel strip, the entire length of the high frequency current conduction path may be inclined with respect to the width direction of the steel strip or the high frequency current conduction path may be inclined near the end of the steel strip. As described above, when a part of the high frequency current conductive path or the entire length of the high frequency current conductive path is inclined, the nozzle may be inclined, and only the high frequency current conductive path in the nozzle may be inclined.

25 is a side view showing an example of an apparatus for implementing the method of the present invention. FIG. 26 is a front view of the device shown in FIG. 25. FIG.

The steel strip is continuously taken out of the coating bath 4. The gas wiping nozzle 8 is disposed on the application bath 4 in close proximity to one side and the other side of the steel strip S. The two gas wiping nozzles 8 face each other, and the steel strip S is located between the gas wiping nozzles 8. Gas wiping nozzles have high frequency current conduction paths 1a and 1b at their ends. Each of the high frequency current conduction paths 1a and 1b is disposed parallel to the surface of the steel strip. In this example, two pairs of high frequency current conduction path nozzles are positioned above and below each nozzle slit. When the high frequency current of the same phase flows through the high frequency current conduction paths 1a and 1b, the current of the phase opposite to the phase of the high frequency current flows through the strip S.

The symbol (⊙) of the high frequency current conduction path 1a and the symbol (⊙) of the high frequency current conduction path 1b represent the same phase. Since the current flowing through the steel strip flows in the opposite direction to the current flowing through the high frequency current conduction path, magnetic repulsive force, mainly magnetic pressure, acts on the surface of the steel strip. However, ferromagnetic materials such as steel strips have a high permeability, so the magnetic attraction force exceeds the repulsive force when the current simply flows, increasing the instability of the steel strip. When the current in the high frequency current conduction paths 1a and 1b is increased, the magnitude of the magnetic field in the steel strip increases as shown in FIG. 1, and the retention period in which the steel strip is maintained in the saturation region becomes long. As a result, the magnetic repulsive force becomes much larger than the magnetic attraction force when the magnitude of the magnetic field exceeds a predetermined size. In the present invention, a high frequency current sufficient to magnetically saturate the steel strip flows through the high frequency current conduction paths 1a and 1b, thereby obtaining the necessary magnetic repulsive force. The vibration of the steel strip is attenuated and the bending of the steel strip is held straight by the magnetic repulsive force of the steel strip. Under the condition that the vibration of the steel sheet is weakened and the bending of the steel sheet is held straight by the magnetic force on the steel sheet, the excess molten metal 30 attached to the steel sheet is removed from the steel sheet by the magnetic pressure acting on the steel object on both sides of the steel sheet and melted. The metal is uniformly applied to the surface of the steel strip. That is, the magnetic pressure acts on the position of the wiping to suppress the vibration and bending of the steel strip, and the surface of the steel strip is cleaned by the magnetic pressure and the pressure of the gas wiping. Even if the pressure of the wiping gas is low, molten metal on the surface of the steel strip is appropriately and effectively removed. In addition, the flatness of the coated surface of the steel strip is properly maintained.

27 is a side view showing yet another example for implementing the method of the present invention. 28 is a front view of the apparatus of FIG. 27.

The high frequency current conduction paths 1a and 1b are included in each tip nozzle in the wiping nozzle 8 facing each other. The other high frequency current conduction paths 1a 'and 1b' are disposed close to both sides of the steel strip. In this example, the phases of the high frequency currents located above and below may be opposite to each other or may have the same phase.

29 is a side view showing another example of an apparatus for implementing the method of the present invention. The high frequency current conduction paths 1a and 1b are included in the wiping nozzle 8. While the wiping nozzles 8 are located adjacent to both sides of the steel strips, the steel strips are positioned between the wiping nozzles 8 without facing each other, but the wiping nozzles 8 are disposed upside down. The other high frequency current conduction paths 1a 'and 1b' are disposed above and below each wiping nozzle 8. As a whole, the high frequency current conduction path is arranged in a zigzag. Current in phase opposite to the high frequency current flows through the steel strip in response to the high frequency current of each high frequency current conduction path. Magnetic pressure acts on the strip S alternately on both sides of the strip's moving direction. In the example of FIG. 29, the phases of the current flowing through the high frequency current conduction path are opposite to each other close to one side of the steel strip and the other side of the steel strip, but the phases of the current may be the same. That is, the phase of the current flowing through the high frequency current path is optional. Since the direction of the current flowing through the steel strip near the end of the steel strip is formed at an angle of 90 ° with the current flowing through the high frequency current conduction path, the magnetic pressure of the steel strip becomes weak near the end of the steel strip. In order to prevent the magnetic pressure near the end of the steel strip from weakening, the high frequency current conduction path may be inclined with respect to the entire length of the high frequency current conduction path in the width direction of the steel strip, or the high frequency current conduction path may be inclined near the end of the steel strip. In order to prevent the magnetic pressure from weakening near the end of the steel strip, the high frequency current path is inclined with respect to the entire length of the high frequency current path as shown in FIGS. 9 and 10, or the high frequency current path is Can be inclined near the end.

The apparatus as shown in Figs. 27 and 28 is installed 400 mm above the application bath based on the results described above and the application weight is controlled in the steel object of the hot dip plating. The conditions of the width of the steel strip and the current are the same as those of the simulation analysis. The linear velocity is 150m / sec and the gas blowing speed is 190m / sec. Coarse bending in the position of the wiping is held straight by the present invention. The vibration of the steel strip is limited in the range of 1 mm or less. When using a gas wiping nozzle, there is no splash and noise, and the coating weight of the steel strip can be controlled very uniformly. In the gas wiping method of the prior art, it was confirmed that steel strip galvanizing can be easily carried out with a coating weight of 35 g / m ^{2 which} is difficult to be practical.

Claims (16)

Positioning at least one pair of high frequency conduction paths 1a and 1b so as to be in close proximity to one side and the other side of the steel strip S drawn out from the plating bath 4 so that each is parallel to the steel surface in the plating bath. And the at least one pair of high frequency currents such that a high frequency current of an opposite phase is induced in the steel strip and a magnetic pressure acting on the surface of the steel sheet is generated by the interaction between the induced high frequency current and the high frequency current in the high frequency current conduction path. Flowing a high frequency current of sufficient strength to magnetically saturate the strips through a passageway. 2. The method of claim 1, wherein positioning the at least one pair of high frequency current conduction paths comprises: positioning at least one pair of high frequency current conduction paths such that the high frequency current conductive paths can be opposed to each other through the strip. Flowing a high frequency current through at least a pair of high frequency current conduction paths. The method of claim 1, wherein the positioning of the at least one pair of high frequency current conduction paths comprises: arranging at least two pairs of high frequency current conduction paths such that each of the high frequency current conduction paths is shifted upward and downward with respect to a steel band. Characterized in that it comprises a. A method according to claim 1, characterized in that the high frequency current conduction path controls the side facing the steel strip and is surrounded by an electromagnetic material (2). The method according to claim 1, wherein the high frequency current conduction path has a bent portion (11) according to the moving direction of the steel strip at a portion facing the end of the steel strip. The method of claim 1, wherein the high-frequency current conduction path is inclined in the width direction of the opponent at full length. The method according to claim 1, wherein the portion of the high frequency current conductive path which faces the end of the steel strip is inclined in the width direction of the steel strip. 3. The north and south poles of claim 2 wherein the width direction of the steel strip is located between the north and south poles of the magnet outside both ends of the steel band adjacent to at least one pair of high frequency current conduction paths such that the steel pole is magnetically saturated by the magnet. And installing the north and south poles of the at least one magnet (5) opposite each other. 9. The high frequency current conduction path of claim 8, wherein the pair of high frequency current conduction paths are two pairs of high frequency current conduction paths installed in a height direction such that a pair of high frequency current conduction paths is an upper high frequency current conduction path, and the other pair is a lower high frequency current conduction path. And one magnet close to the upper portion of the upper high frequency current path, and the other magnet is two magnets positioned close to the lower portion of the lower high frequency current path. 9. The two high frequency current conductive paths of claim 8, wherein the pair of high frequency current conductive paths are provided in a height direction such that a pair of high frequency current conductive paths is an upper high frequency current conductive path, and the other pair of high frequency current conductive paths is a lower sine wave current conductive path. And a high frequency current conduction path, wherein the magnet is a magnet located between an upper high frequency current conduction path and a lower high frequency current conduction path. 9. The method of claim 8, wherein the magnet is an electromagnet. 9. The method of claim 8, wherein the magnet is a permanent magnet. 2. The method of claim 1, further comprising positioning the wiping nozzles in proximity to both sides of the strip drawn out of the plating bath and dispersing gas at the wiping nozzle with the strip drawn out of the plating bath. How to feature. 2. The method of claim 1, wherein positioning the at least one pair of high frequency current paths comprises positioning the high frequency current paths at a nozzle portion of a wiping nozzle. Close to each of one side and the other side of the steel strip 5 taken out of the plating bath 4, each of the high frequency current conduction paths 1a, 1b is parallel to the surface of the steel strip on the plating bath, Positioning a high frequency current conduction path so that a high frequency current conduction path close to one side of the high frequency current conduction path proximate the other side of the steel strip is positioned between the high frequency current conduction paths, and Magnets (5) on the outside of both ends of the steel strip near the high frequency current path so that the north and south poles face each other such that the width direction of the beam is located between the north and south poles outside the two ends of the steel band near the at least one pair of high frequency current conduction paths (5) Arranging the north and south poles of the polarizer, and flowing a high frequency current of the same phase through the high frequency conductive path so as to induce a high frequency current of a reverse phase, And causing an acting magnetic pressure to be generated by the interaction of the induced high frequency current with the high frequency current of the high frequency current conduction path. Positioning the wiping nozzles 8 in close proximity to both sides of the steel strip S taken out from the plating bath 4, and placing the wiping nozzles so that each of the high frequency conductive paths is parallel to the surface of the steel strip on the plating bath. Positioning high frequency current conduction paths 1a and 1b, injecting a gas from a wiping nozzle to a steel object taken out of the plating bath, and inducing a high frequency current in a reverse phase in the steel strip through the high frequency conduction path Flowing a high frequency current of sufficient strength to magnetically saturate the steel strip such that a magnetic pressure acting on the surface of the steel strip is generated by the interaction of the induced high frequency current with the high frequency current of the high frequency current conduction path. Method for controlling the coating weight on the steel object of the hot dip plating provided.