JP5228653B2 - Control apparatus for molten metal bath and method for producing hot-dip metal strip - Google Patents

Description

  The present invention relates to a control device for controlling the flow of a molten metal and movement of foreign matters such as dross in a molten metal bath and a method for producing a hot-dip metal strip using the control device.

As a method for continuously plating a metal band, a hot dipping method in which the metal band is plated by immersing the metal band in a molten metal such as zinc or aluminum is known.
This hot-dip plating method will be described with reference to a case where hot-dip galvanizing is applied to a steel strip. For example, a steel strip that has been cold-rolled or a steel strip that has been hot-rolled and whose surface scale has been removed can be made non-oxidizing or Introduced into an annealing furnace maintained in a reducing atmosphere, and after performing an annealing process that also serves to remove the surface oxide film, it was cooled to a temperature approximately the same as the temperature of the molten zinc, and the steel strip was subsequently heated to a molten zinc bath. It is introduced into a (plating tank), wound around a sink roll provided in the bath, passed through a molten zinc bath through a substantially V-shaped path, and molten zinc is adhered to the surface. Then, a wiping gas is blown from the gas wiping nozzle onto both surfaces of the steel strip immediately after being drawn out from the molten zinc bath, and excess molten metal is wiped off to adjust the amount of plating adhesion.

  The hot dipping method has many advantages over the electroplating method, such as the ability to produce a plated steel strip at a low cost and the ability to easily produce a thick-plated steel strip. In particular, alloyed hot-dip galvanized steel strip manufactured by hot-dip galvanizing and then alloying the plated layer has characteristics of excellent corrosion resistance, weldability and workability. Although it is widely used as a belt, particularly when it is used as a steel strip for exteriors, demands for quality are becoming increasingly severe, such as high definition after painting. In addition, increased production is strongly required to meet the current needs.

  In the manufacturing process of the hot dip galvanized steel strip, when the line speed is increased to improve productivity, when the steel strip is pulled out from the hot dip bath, the amount of lift of the hot zinc that adheres to the steel strip increases. At this time, in order to make the plating adhesion amount equal to that before the acceleration, the molten zinc to be wiped off by gas wiping must be increased, that is, the wiping ability must be increased. In order to increase the wiping capability, it is necessary to increase the gas pressure of wiping. However, if the gas pressure is increased, the splash of molten zinc called splash increases. When the splash increases, it adheres to the steel strip and causes surface quality defects, or enters the slit gap of the gas wiping nozzle and induces nozzle clogging, resulting in streaky surface quality defects due to defective wiping. For this reason, it is not easy to increase the speed while maintaining the quality level, which is a big problem in the hot dip galvanized steel strip manufacturing process.

The root of this problem is an increase in the amount of zinc lift accompanying the increase in speed, and several proposals have been made to suppress this. For example, when the steel strip is pulled up from the molten zinc bath, the temperature of the molten zinc decreases, and from this viewpoint, the increase in the viscosity of the molten zinc reduces the natural flow of molten zinc from the molten zinc bath surface. A technique for reducing the amount of zinc lifted to the wiping part by heating the steel strip at the rising part of the steel and suppressing the decrease in fluidity of the molten zinc has been proposed (Patent Document 1).
In addition, a technique for increasing the apparent gravity and reducing the amount of zinc lift by compressing the molten zinc bath surface at the rising portion downward by the Lorentz force using an alternating magnetic field has been proposed (Patent Document 2). ).

On the other hand, in the hot dip galvanizing plating tank, Fe and Zn eluted from the steel strip react to produce dross containing FeZn ₇ as a main component, and this dross floats in the plating tank or at the bottom of the tank. accumulate. In the plating tank, the molten zinc bath flows along with the rotation of the steel strip passing plate and the sink roll, and the bottom dross deposited on the bottom of the plating tank is wound up in the bath and may adhere to the steel strip. When the plated steel strip to which the bottom dross is attached is pressed, a non-uniform portion is generated on the surface of the plated steel strip, and the sharpness is impaired. Further, the attached dross may damage the mold. Winding up the bottom dross becomes more severe as the plate passing speed of the steel strip increases, and this is a particularly serious problem in the situation where speedup for increased production is required as described above.

As a means for preventing the adhesion of dross, there is a method in which Al is added to the bath, and the bottom dross is floated by changing to Fe ₂ Al ₅ by the reaction of the following formula (1), and recovered as a top dross.
2FeZn ₇ + 5Al → Fe ₂ Al ₅ + 14Zn (1)
However, this top dross may adhere to the steel strip and cause quality defects, so it is not a fundamental solution. Furthermore, since Al has a function of suppressing alloying, there is also a problem of causing alloying failure when producing an alloyed hot-dip galvanized steel strip.

Bottom dross has a higher specific gravity than molten zinc, so it eventually settles to the bottom, and the top dross has a lower specific gravity, so it floats on the bath surface. In that case, the risk of adhering to the steel strip increases. Thus, various proposals have been made for shortening the dross floating time and preventing the dross from approaching the steel strip.
For example, a technique has been proposed in which bubbles are generated in a molten zinc bath, floating dross in the bath is captured by the bubbles, and the surface is quickly lifted to the bath surface and removed (Patent Document 3). In addition, a technique has been proposed in which a moving magnetic field is generated on the bath at the rising portion of the steel strip from the molten zinc bath, and dross floating on the bath surface is removed from the periphery of the steel strip using electromagnetic force generated by the moving magnetic field. (Patent Document 4). Furthermore, a technique has also been proposed in which a metal flow (molten zinc flow) is generated in the bath at the rising portion of the steel strip from the molten zinc bath, and floating dross in the bath is prevented from adhering to the steel strip (Patent Literature). 5).

JP-A-57-155357 JP-A-4-254564 JP-A-5-320846 Japanese Patent Laid-Open No. 11-6046 JP 2004-169068 A

However, the above prior art for suppressing the amount of zinc lift has the following problems.
First, the method of Patent Document 1 may oxidize the plating surface layer portion to deteriorate the plating quality, or may promote the alloying of zinc and iron. In addition, in order to prevent oxidation of the plating surface layer part, when a device such as a reduction furnace type heating device is used, the heating device is enlarged, so it is installed between the molten zinc bath surface and the gas wiping nozzle. It may not be possible. Moreover, even if it can be installed, the molten zinc wiped off by the gas wiping nozzle will fall on the heating device, causing the device to malfunction, or the deposited zinc will reattach to the steel strip and become a plating surface defect. There are concerns.

Similarly to the above, the method of Patent Document 2 has a problem that the wiped molten zinc accumulates on the magnetic field application device and does not function sufficiently when a top dross (an intermetallic compound of zinc and aluminum or zinc oxide) is generated. There is also a problem. Furthermore, in this method, since an induced current generated by an alternating magnetic field is used as an electric field, a current can flow only on the surface layer of a molten zinc bath, a large current cannot flow, and a magnetic field and an electric field cannot be adjusted independently. There is also a problem.
In order to reduce the amount of zinc lift, it is known that the accompanying flow of molten zinc generated near the steel strip in the bath when the steel strip is pulled upward from the molten zinc should be suppressed. It is desirable if this can be realized by installing a compact device directly under the gas wiping nozzle or in a place not on the surface of the molten zinc bath.

Further, the above-described conventional technique for dealing with dross generated in the molten zinc bath has the following problems.
First, in the method of Patent Document 3, it is impossible to capture all the floating dross in the bath by bubbles, and even if it can be captured, the behavior of the bubbles cannot be controlled. There is a concern.
The method of Patent Document 4 is effective in preventing the floating dross (top dross) on the bath surface from approaching the steel strip, but the electromagnetic force does not sufficiently act in the bath. It is powerless to prevent dross adhesion.
The method of Patent Document 5 is excellent in that it is effective for floating dross in the bath, but the angle of the metal flow with respect to the steel strip, the velocity gradient of the metal flow, or the relationship between the steel strip passage speed and the metal flow velocity. Depending on the case, the effect may be lost. In that case, the floating dross is merely flowing in the vicinity of the steel strip, and there is no effect in preventing the floating dross from adhering.

Accordingly, an object of the present invention is to provide a control device capable of appropriately controlling the flow of molten metal and the movement of foreign matters such as dross while being immersed in a molten metal bath such as a hot dipping bath. It is in.
Another object of the present invention is a method for producing a hot-dip metal strip while controlling the flow of hot metal in the hot-dip plating bath and the movement of foreign matter using such a control device. The molten metal flow accompanying the belt is braked to suppress the amount of molten metal lifted when the metal strip is pulled out of the molten metal bath, or the foreign matter in the molten metal bath is kept away from the metal strip and does not adhere to the metal strip. An object of the present invention is to provide a method of manufacturing a hot-dip metal strip which can be made to be made.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have paid attention to the fact that many molten metals including molten zinc are conductors. The Lorentz force is generated by the electric field and magnetic field created by them, and the Lorentz force is applied to the molten metal to control the flow of the molten metal (damping or accelerating the molten metal flow, melting Because metal such as dross, etc., and foreign matter such as dross have a much lower electrical conductivity than molten metal, electromagnetic Archimedes force acts on the foreign material in the direction opposite to the Lorentz force applied to the molten metal. The electromagnetic Archimedes force has been found to control the movement of foreign matter. According to such a system, the flow of molten metal and the movement of foreign matters such as dross can be controlled by a compact device installed in the molten metal. Brakes the accompanying molten metal flow and appropriately controls and controls the amount of molten metal lifted when the metal strip is pulled out of the molten metal bath, or keeps foreign matter such as dross in the molten metal bath away from the metal strip, It has been found that it can be prevented from adhering to the metal strip.

The present invention has been made on the basis of such findings and has the following gist.
[1] An electric field generating means and a magnetic field generating means arranged in a state immersed in a molten metal bath, and the electric field generating means and the magnetic field generating means are generated by them. A molten metal bath, wherein the Lorentz force is arranged so as to be generated, and the Lorentz force is applied to the molten metal to control the following (1) and / or (2): Control device.
(1) The flow of molten metal is controlled by Lorentz force.
(2) The movement of a foreign substance present in the molten metal and having a lower electrical conductivity than the molten metal is controlled by an electromagnetic Archimedes force acting on the foreign substance as a force opposite to the Lorentz force.
[2] A control apparatus for a molten metal bath according to the control apparatus of [1], wherein the electric field generating means includes a pair of electrodes facing each other for flowing a current in the molten metal.
[3] In the control device of [2] above, the electric field generating means can adjust the amount of current flowing in the molten metal, and the amount of Lorentz force acting on the molten metal can be adjusted by adjusting the amount of current. A control apparatus for a molten metal bath, characterized by being made possible.

[4] The control apparatus for a molten metal bath according to any one of the above [1] to [3], wherein the magnetic field generating means is composed of a permanent magnet.
[5] A control apparatus for a molten metal bath according to any one of the above [1] to [3], wherein the magnetic field generating means is composed of an electromagnet.
[6] In the control device of [5] above, the magnetic field generating means can adjust the amount of current flowing through the electromagnet, and the amount of Lorentz force acting on the molten metal can be adjusted by adjusting the amount of current. An apparatus for controlling a molten metal bath, characterized in that:
[7] In the control device according to any one of [1] to [6], the control device includes a support for supporting the electric field generating means and the magnetic field generating means, and extends in a direction penetrating the empty portion inside the support. An apparatus for controlling a molten metal bath, wherein an electric field generating means and a magnetic field generating means are provided on a support so that Lorentz force acts.

[8] In the control device according to [7], the support is formed of a frame, and a pair of electrodes constituting the electric field generating means are provided on the opposing portions (p1) and (p2) of the frame, A pair of magnets constituting the magnetic field generating means are different from each other in the portions (p3) and (p4) which are the opposing portions of the frame and have a positional relationship of 90 ° with the portions (p1) and (p2). The melting is characterized in that magnetic poles are provided so as to face each other, and an electric field is created between the pair of electrodes, and a magnetic field perpendicular to the electric field is created between the pair of magnets. Metal bath control device.
[9] Control of the molten metal bath according to any one of the above [1] to [8] in a method of manufacturing a hot-dip metal strip in which hot-plating is performed by immersing a continuous metal strip in a hot-metal bath. The apparatus (X) is installed at one or more places in the molten metal bath, and the molten metal is hot-plated while controlling the flow of molten metal and / or the movement of foreign matter by the control apparatus (X). A method for producing a hot dipped metal strip characterized by the following.

[10] The manufacturing method of [9], wherein the metal strip that has entered the molten metal bath from above is redirected upward in the bath and is then drawn from the molten metal bath. Then, the molten metal flow accompanying the moving metal band is redirected upward in the bath by the Lorentz force generated by the control device (X), and the molten metal flow is braked.
[11] In the manufacturing method according to [9] or [10] above, the metal strip that has entered the molten metal bath from above is redirected upward in the bath, and then the molten metal strip is drawn from the molten metal bath. A method for producing a hot-dip metal strip, wherein the molten metal flow flowing toward the bottom of the molten metal bath is braked by a Lorentz force generated by the control device (X).

[12] In the manufacturing method according to any one of [9] to [11] above, the metal strip that has entered the molten metal bath from above is redirected upward in the bath and then drawn from the molten metal bath. A method of manufacturing a metal strip, characterized by causing an electromagnetic Archimedes force to act on the foreign matter in the molten metal bath in a direction away from the metal strip by Lorentz force generated by the control device (X). A method for producing a plated metal strip.
[13] In the manufacturing method according to any one of [9] to [12] above, the molten metal that has entered the molten metal bath from above is redirected upward in the bath and then drawn from the molten metal bath. A method for manufacturing a metal strip, characterized in that an electromagnetic Archimedes force is applied to foreign matter in a molten metal bath in the direction of the foreign matter accumulation portion in the molten metal bath by Lorentz force generated by a control device (X). A method for producing a hot-dip metal strip.

According to the apparatus for controlling a molten metal bath according to the present invention, the movement of foreign matter such as molten metal flow and dross can be freely controlled by a compact means installed in the molten metal (as control of molten metal flow, For example, braking or acceleration of the molten metal flow, fluidization of the molten metal, etc. For controlling the movement of the foreign material, for example, suppressing the approach of the foreign material to the metal band side, moving or accumulating the foreign material to a specific location) be able to.
Further, according to the method of manufacturing a hot-dip metal strip according to the present invention, using such a control device, for example, (a) the molten metal flow accompanying the metal belt is braked, and the metal strip is drawn out of the hot metal bath. (B) Brakes the molten metal flow that flows in the direction of the bottom of the molten metal bath, and suppresses the hoisting of foreign matter existing at or near the bottom of the molten metal bath. (C) Do not allow foreign substances such as dross in the molten metal bath to approach the metal band side (keep foreign objects away from the metal band) and do not adhere to the metal band. (D) Dross in the molten metal bath, etc. The movement of molten metal in the molten metal bath and the movement of foreign substances such as dross are appropriately controlled to be suitable for the hot dipping process. Can High quality hot-dip galvanized metal strip can be manufactured with high productivity.

The apparatus for controlling a molten metal bath according to the present invention comprises an electric field creation (formation) means A and a magnetic field creation (formation) means B immersed in the molten metal, and these electric field creation means A and magnetic field creation means. B is arranged so that a Lorentz force is generated by an electric field and a magnetic field created (formed) by them, and the Lorentz force acts on the molten metal, thereby controlling the following (1) and / or (2) It is comprised so that it may perform.
(1) Control (brake or accelerate) the flow of molten metal with Lorentz force.
(2) The movement of a foreign substance present in the molten metal and having a lower electrical conductivity than the molten metal is controlled by an electromagnetic Archimedes force acting on the foreign substance as a force opposite to the Lorentz force.

  The electric field generating means A (electric field generating part) usually comprises a pair of electrodes arranged to face each other in order to pass an electric current in the molten metal, and an electric field is generated by passing an electric current between the electrodes. It is formed. The magnetic field creation means B (magnetic field creation part) is composed of a permanent magnet or an electromagnet, and generates a Lorentz force by forming a magnetic field in a direction orthogonal to the current flow. That is, when an electric field and a magnetic field are created so as to be orthogonal, Lorentz force is generated in a direction orthogonal to each other according to the Fleming left-hand rule. By applying this Lorentz force to the molten metal, the flow of the molten metal can be controlled.

  Further, since foreign matter such as dross has a much lower electrical conductivity than molten metal, when the Lorentz force is generated as described above, the Lorentz force on the foreign matter is much smaller than that of the molten metal. For this reason, a force relative to the Lorentz force applied to the molten metal, that is, an electromagnetic Archimedes force, acts on the foreign material, and this force is used to control the movement of the foreign material such as dross in the molten metal. be able to. Here, the foreign matter present in the molten metal is mainly dross.

Each pair of electrodes (anode, cathode) constituting the electric field generating means A may be composed of a plurality of electrodes. In general, since molten metal is often a conductor, if an electrode is provided and a voltage is applied, a current flows and an electric field can be created. Basically, it is possible to create an electric field at an arbitrary place in the molten metal. Depending on the type of molten metal such as molten zinc, the metal immersed in the molten metal may elute, but there is no particular problem if a device such as gold plating is applied to the electrode.
It is preferable that the electric field generating means A can adjust the amount of current flowing in the molten metal. The intensity of the electric field can be adjusted by changing the amount of current flowing between the electrodes. Since the magnitude of the Lorentz force is proportional to the strength of the electric field, the magnitude of the Lorentz force acting on the molten metal can be adjusted, and the flow of the molten metal can be controlled more appropriately. Moreover, since the magnitude of the electromagnetic Archimedes force acting on the foreign matter can be adjusted by adjusting the magnitude of such Lorentz force, the movement of the foreign matter can be controlled more appropriately.

The magnetic field generating means B is composed of a permanent magnet or an electromagnet. Usually, a pair of magnets are arranged so that different magnetic poles (N pole and S pole) face each other, and a magnetic field is generated between the magnets (magnetic poles). Create.
When the magnetic field generating means B is composed of permanent magnets, a magnetic field can be generated with a particularly compact device configuration by arranging a pair of permanent magnets so that different magnetic poles face each other as described above. The molten zinc bath is usually as high as about 460 ° C., but there is no problem if a permanent magnet having a heat resistant temperature of 500 ° C. or higher such as an alnico magnet is used.

On the other hand, when the magnetic field generating means B is composed of an electromagnet, for example, if a heat-resistant electric wire such as a nickel wire is used for the coil, an electromagnet that functions even in a temperature environment in a molten zinc bath can be obtained. With proper casing, there is no problem in use.
Further, when the magnetic field generating means B is composed of an electromagnet, it is preferable that the amount of current flowing through the electromagnet can be adjusted. By changing the current passed through the electromagnet, the strength of the magnetic field can be adjusted. Since the magnitude of the Lorentz force is proportional to the strength of the magnetic field, the magnitude of the Lorentz force acting on the molten metal can be adjusted, and the flow of the molten metal can be controlled more appropriately. is there. Moreover, since the magnitude of the electromagnetic Archimedes force acting on the foreign matter can be adjusted by adjusting the magnitude of such Lorentz force, the movement of the foreign matter can be controlled more appropriately.

FIG. 1 schematically shows an embodiment of a control apparatus for a molten metal bath according to the present invention. The apparatus of this embodiment is a support for supporting an electric field generating means A and a magnetic field generating means B. And the electric field generating means A and the magnetic field generating means B are provided on the support so that Lorentz force is generated in a direction penetrating the void inside the support.
In this embodiment, the said support body is comprised by the frame 1 (frame structure) which has the cavity 100 (window hole) inside. The frame 1 has a rectangular shape, and a pair of electrodes 2a and 2b (anode and cathode) constituting the electric field generating means A are provided on two opposing sides (parts p1 and p2) of the rectangular frame 1. In addition, a pair of magnets 3a and 3b constituting the magnetic field generating means B are provided on different two opposite sides (portions p3 and p4 having a positional relationship of 90 ° with the portions p1 and p2). Poles and S poles) are opposed to create an electric field between the pair of electrodes 2a and 2b, and create a magnetic field perpendicular to the electric field between the pair of magnets 3a and 3b. I have to do it.

Each of the electrodes 2a and 2b may be one large electrode or a plurality of small electrodes arranged side by side. The magnets 3a and 3b may be composed of permanent magnets or electromagnets, and the magnets 3a and 3b may be one large magnet or a plurality of small magnets arranged side by side.
The electrodes 2a, 2b (anode and cathode) and magnets 3a, 3b (N pole and S pole) are arranged so that the electric field and magnetic field created by them are perpendicular to each other. A Lorentz force is generated in a direction orthogonal to the inside, that is, in a direction penetrating through the hollow portion 100 (window hole) inside the frame 1, and the flow of the molten metal is controlled by this Lorentz force (breaking or accelerating the molten metal flow, melting Metal fluidization). In addition, when Lorentz force acts on the molten metal, the electromagnetic Archimedes force acts on the foreign material such as dross in the opposite direction to the Lorentz force applied to the molten metal, and this electromagnetic Archimedes force controls the movement of the foreign material. It is possible to suppress the approach to the metal band side.

When such a control device is used in molten metal, the device should be arranged or controlled in such a position that the molten metal flow to be controlled (for example, braking) flows in the void 100 (window hole). If the device is arranged at a position where the foreign material passes through the void 100 (window hole), the Lorentz force is most efficiently applied to the molten metal flow to be controlled, or the electromagnetic Archimedes force is most efficient. It can be made to act on the foreign object that is the control target.
Further, as required, by changing the amount of current passed between the electrodes 2a and 2b of the electric field generating means A, or by changing the amount of current supplied to the electromagnet when the magnetic field generating means B is an electromagnet. By changing the magnitude of the Lorentz force or electromagnetic Archimedes force, it is possible to adjust the force acting on the molten metal or foreign matter.

The control apparatus of the molten metal bath of this invention can take various forms other than the form of FIG. For example, in the case of an apparatus including the frame 1, the frame 1 can be configured in a circular shape, an elliptical shape, an arbitrary polygonal shape, or the like. Further, the electric field generating means A and the magnetic field generating means B can be supported in the molten metal by an arbitrary support (structure) other than the frame 1.
Moreover, the control apparatus of the molten metal bath of this invention can be applied to the various methods and equipment which handle a molten metal besides the manufacturing method of the hot dip metal strip which is demonstrated below.

Next, the manufacturing method of the hot dip metal strip using the molten metal bath control device X of the present invention as described above will be described.
This method for manufacturing a hot-dip metal strip is a hot-dip metal strip manufacturing method in which hot-dip plating is performed by immersing a metal strip in a continuous plate in a hot metal bath, and the control device X is placed in the hot metal bath. The metal strip is subjected to hot dip plating while controlling the flow of molten metal and / or the movement of foreign matter with this control device X. As a form of controlling the flow of the molten metal, for the reason described above, there is a form in which the molten metal flow accompanying the metal strip is braked and the amount of the molten metal lifted when the metal strip is drawn out of the molten metal bath is suppressed. Most useful. In addition, a mode is also useful in which the molten metal flow flowing toward the bottom of the molten metal bath is braked to suppress the rolling-up of foreign matters such as dross existing at or near the bottom of the molten metal bath. Further, as a form of controlling the movement of the foreign matter, for the reason described above, a form in which the foreign matter such as dross in the molten metal bath is kept away from the metal strip and is not attached to the metal strip is most useful. Further, a form in which foreign matter such as dross in the molten metal bath is moved and accumulated in the foreign matter accumulation portion in the molten metal bath is also useful.

Here, in the generally performed hot dip plating process of the metal band, the metal band that has entered the molten metal bath from above is redirected upward in the bath and is then drawn out of the molten metal bath to be melted into the metal band. Plating is applied. Therefore, in the manufacturing method of the hot dip metal strip of the present invention using the control device X, it is preferable that one or more of the following (a) to (d) are realized.
(A) The Lorentz force generated by the control device X brakes the molten metal flow accompanying the moving metal band that is redirected upward in the bath, and the molten metal when the metal band is drawn out of the molten metal bath. Reduce lifting.
(B) The Lorentz force generated by the control device X brakes the molten metal flow that flows in the direction of the bottom of the molten metal bath and suppresses the winding of foreign matter (for example, bottom dross) existing at or near the bottom of the molten metal bath. .
(C) The Lorentz force generated by the control device X causes the electromagnetic Archimedes force to act on the foreign matter in the molten metal bath in a direction away from the metal strip, thereby moving the foreign matter away from the metal strip.
(D) By the Lorentz force generated by the control device X, the electromagnetic Archimedes force is applied to the foreign matter in the molten metal bath in the direction of the foreign matter accumulation portion in the molten metal bath, and the foreign matter is moved and accumulated in the foreign matter accumulation portion.

Hereinafter, the manufacturing method of the hot dip galvanized metal strip of the present invention will be described by taking as an example the case of manufacturing a hot dip galvanized steel strip. 2 to 9 described below, 4 is a molten zinc bath (plating bath), 5 is a steel strip, 6 is a sink roll, 7 is a gas wiping nozzle, and 8 is a plating tank for holding a molten zinc bath.
FIG. 2 shows the flow state of molten zinc in a molten zinc bath (plating bath). The steel strip 5 entering the molten zinc bath 4 from above is turned upward (vertical direction) by the sink roll 6 and then pulled up from the molten zinc bath 4, but the direction is changed by the sink roll 6 and moved upward. In the vicinity of the steel strip 5, there is a molten metal flow f1 (associated flow) that rises accompanying the steel strip. This accompanying flow is an important flow that determines the lift amount of the molten zinc. If this flow is large, the lift amount increases.

  In addition, the molten metal flow f1 (associated flow) changes direction in the direction away from the steel strip 5 (rightward in the drawing) in the vicinity of the bath surface of the molten zinc bath 4, and further collides with the front wall 80. Then, a molten metal flow f2 (downward flow) directed toward the bottom of the molten zinc bath 4 is obtained. Further, due to the rotation of the sink roll 6, a molten metal flow f <b> 3 (downflow) toward the bottom of the molten zinc bath 4 is also generated on the steel strip entrance side (left side in the drawing) of the sink roll 6. These molten metal flows f2 and f3 (downflow) cause foreign matter existing at or near the bottom of the molten zinc bath 4, particularly iron and zinc intermetallic compounds called bottom dross accumulated on the bottom. In particular, as the line speed increases, the downward flow also increases and the bottom dross winding amount tends to increase. Since the rolled-up bottom dross may adhere to the steel strip 5 and become surface quality defects (dross defects), it is important to suppress this downward flow in order to increase the speed while maintaining high quality.

FIG. 3 shows an embodiment of a manufacturing method mainly aimed at realizing the action (a) above. After the direction is changed upward (vertical direction) by the sink roll 6, the molten zinc bath 4 is used. A control device X as shown in FIG. 1 is arranged on both the front and back sides of the steel strip portion 50 (hereinafter referred to as “bath rising portion 50”) immediately before being pulled up and immediately below the bath surface, and the Lorentz force Thus, the molten metal flow f <b> 1 accompanying the steel strip 5 is braked to suppress the lift amount of the molten zinc when the steel strip 5 is drawn out from the molten zinc bath 4.
Each of the control devices X is disposed obliquely so that the Lorentz force L is generated obliquely downward toward the rising part 50 in the bath. By generating the Lorentz force L in such a form, it is possible to brake the molten metal flow f1 (associated flow) even from the control device X arranged slightly away from the steel strip 5, and the steel strip 5 It is possible to reduce the amount of zinc lift by. Moreover, if the magnitude of the Lorentz force is adjusted by adjusting the amount of current flowing between the electrodes 2a and 2b of the control device X, for example, the zinc lifting amount may be controlled to an appropriate amount according to the line speed. it can. In addition, the control apparatus X may have the width | variety which covers the full width of the steel strip 5 with one apparatus, and may arrange | position several apparatus to the board width direction.

FIG. 4 shows an embodiment of a manufacturing method whose main purpose is to realize the action (b) above. In the portion where the molten metal flows f2 and f3 flowing toward the bottom of the molten zinc bath 4 are generated. 1, the control device X as shown in FIG. 1 is arranged to brake the molten metal flows f2 and f3 by the Lorentz force, and to wind up foreign matter existing at or near the bottom of the molten metal bath, particularly bottom dross accumulated at the bottom. It is intended to suppress. The control device X is configured so that a Lorentz force L is generated upward at a position in the vicinity of the wall surface 80 of the plating tank 8 facing the rising portion 50 in the bath and a position below the steel strip entrance side of the sink crawl 6. It arrange | positions and it is made to brake the molten metal flow f2, f3 (downflow) in each position. Such braking of the molten metal flows f2 and f3 makes it possible to reduce the amount of winding up such as bottom dross. The adjustment of the Lorentz force generated by the control device X and the arrangement of the device in the steel strip width direction are the same as described in FIG.
FIG. 5 is an embodiment in which all the control devices X installed in FIGS. 3 and 4 are arranged. By installing the control device X in such a form, hot-dip galvanized steel having high quality and high productivity. The band can be manufactured.

FIG. 6 shows an embodiment of a manufacturing method mainly intended to realize the action (c) above, on both the front and back sides of the rising part 50 in the bath, and at a predetermined depth position from the bath surface. 1 is arranged, and foreign matter such as dross (hereinafter referred to as “dross” for convenience) in the molten zinc bath 4 is moved away from the steel strip 5 by the electromagnetic Archimedes force and attached to the steel strip 5. This is what I did not.
Each of the control devices X generates a Lorentz force L obliquely downward toward the rising portion 50 in the bath, and therefore the electromagnetic Archimedes force E acting on the dross is obliquely upward in the anti-steel strip direction (direction away from the steel strip 5). It is arranged to act toward. Since this embodiment is mainly intended to realize the above action (c), the control device X is arranged at a deeper position below the bath surface than in the embodiment of FIG. 3 and the Lorentz force L is applied in the bath in the action direction. The inclination with respect to the rising portion 50 is larger than that in the embodiment of FIG. In this embodiment, when the electromagnetic Archimedes force E acts on the dross, the approach of the foreign matter to the steel strip 5 is suppressed, and the dross adhesion to the steel strip 5 is prevented. The adjustment of the Lorentz force generated by the control device X and the arrangement of the device in the steel strip width direction are the same as described in FIG.

Further, in this embodiment, Lorentz force L is generated obliquely downward toward the rising part 50 in the bath, so as a secondary action, the molten metal flow accompanying the steel strip 5 is the same as in the embodiment of FIG. (The molten metal flow f1 in FIG. 3) is braked, and the lift amount of the molten zinc when the steel strip 5 is drawn out from the molten zinc bath 4 is suppressed.
In addition, in this embodiment, although the control apparatus X is installed so that dross may be distanced to the out-of-plane direction of the steel strip 5 by electromagnetic Archimedes force, in the in-plane direction (direction along the steel strip surface) of the steel strip 5 The electromagnetic Archimedes force may be applied in the direction so as to keep the dross away, that is, so as to keep the dross away from both edges in the plate width direction.

  FIG. 7 shows an embodiment of a manufacturing method mainly aimed at realizing the action (d) above. A foreign matter accumulating portion Sa (accumulating location) is set at a specific location in the molten metal bath, A control device X as shown in FIG. 1 is arranged at a position where the electromagnetic Archimedes force to the dross acts in the direction of the foreign material accumulating portion, and the dross is moved and accumulated in the foreign material accumulating portion Sa by the electromagnetic Archimedes force. It is a thing. In the present embodiment, a foreign matter accumulation portion Sa is set at the corner of the plating bath bottom, and in each foreign matter accumulation portion Sa, a position where the electromagnetic Archimedes force to the dross acts in the bath bottom direction (vertically downward), and the bath The control devices X are arranged at positions where the electromagnetic Archimedes force to the dross acts in the side wall direction (horizontal direction). The adjustment of the Lorentz force generated by the control device X is the same as described in FIG.

In the present embodiment, the specific location (corner) at the bottom of the plating tank is only set as the foreign matter accumulation portion Sa, but the foreign matter accumulation portion is a means for accumulating or accumulating and holding dross. It may be provided with means for recovering dross.
Further, in the present embodiment, since the upward Lorentz force L is generated for the control device X arranged at a position where the electromagnetic Archimedes force acts on the foreign matter in the tank bottom direction (vertically downward), the secondary Lorentz force L is generated. As a function, the descending molten metal flow (molten metal flow f2 in FIG. 4) is braked in the same manner as in the embodiment of FIG. 4, and the rolling up of the bottom dross accumulated at the bottom is suppressed.

FIG. 8 shows another embodiment of the manufacturing method whose main purpose is to realize the action (d), and a saw-like member with an appropriate interval between the bottom of the plating tank and the tank bottom 81. 9 is set as a foreign material accumulating portion Sb for accumulating and allowing dross to accumulate between the saw-like member 9 and the bottom of the tank. A control device X as shown in FIG. 1 is arranged between the saw plate 90 constituting the saw-like member 9 so that the electromagnetic Archimedes force to the dross acts in the direction of the foreign matter accumulation portion (vertically downward), and the dross Is moved and accumulated in the foreign matter accumulation portion Sb. Each slatted plate 90 has a mountain shape in cross section so that dross does not accumulate on the upper surface. The adjustment of the Lorentz force generated by the control device X is the same as described in FIG.
Also in the present embodiment, since an upward Lorentz force L is generated, the descending molten metal flow (molten metal flow f2 in FIG. 4) is braked as a secondary action, as in the embodiment of FIG. Rolling up of the bottom dross accumulated on the bottom is suppressed.

FIG. 9 is an embodiment in which all the control devices X installed in FIGS. 6 and 7 are arranged. By installing the control device X in such a form, it is possible to more appropriately attach dross to the steel strip. This makes it possible to manufacture hot-dip galvanized steel strip that can be prevented and that has both high quality and high productivity.
The manufacturing method of the hot-dip metal strip of the present invention described above can be applied to the manufacture of any hot-dip metal strip such as hot-dip galvanized steel strip, hot-dip zinc-aluminum alloy-plated steel strip, and aluminum-plated steel strip.

Explanatory drawing which shows typically one Embodiment of the control apparatus of the molten metal bath of this invention Explanatory drawing showing the flow state of molten zinc in molten zinc bath (plating bath) Explanatory drawing which shows one Embodiment of the manufacturing method of the hot dip metal strip of this invention Explanatory drawing which shows other embodiment of the manufacturing method of the hot dipped metal strip of this invention. Explanatory drawing which shows other embodiment of the manufacturing method of the hot dipped metal strip of this invention. Explanatory drawing which shows other embodiment of the manufacturing method of the hot dipped metal strip of this invention. Explanatory drawing which shows other embodiment of the manufacturing method of the hot dipped metal strip of this invention. Explanatory drawing which shows other embodiment of the manufacturing method of the hot dipped metal strip of this invention. Explanatory drawing which shows other embodiment of the manufacturing method of the hot dipped metal strip of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Frame 2a, 2b Electrode 3a, 3b Magnet 4 Molten zinc bath 5 Steel strip 6 Sink roll 7 Gas wiping nozzle 8 Plating tank 9 Saw-shaped member 50 Rising part in the bath 80 Wall surface 81 Tank bottom face 90 Slat board 100 Empty part A Electric field Creation means B Magnetic field creation means X Controller p1, p2, p3, p4 part f1, f2, f3 Molten metal flow Sa, Sb Foreign matter accumulation part L Lorentz force E Electromagnetic Archimedes force

Claims (13)

An electric field generating means and a magnetic field generating means arranged in a state of being immersed in a molten metal bath, and the electric field generating means and the magnetic field generating means are provided by Lorentz by an electric field and a magnetic field generated by them. An apparatus for controlling a molten metal bath, which is arranged so as to generate a force, and is configured to control the following (1) and / or (2) by applying the Lorentz force to the molten metal.
(1) The flow of molten metal is controlled by Lorentz force.
(2) The movement of a foreign substance present in the molten metal and having a lower electrical conductivity than the molten metal is controlled by an electromagnetic Archimedes force acting on the foreign substance as a force opposite to the Lorentz force.   2. The apparatus for controlling a molten metal bath according to claim 1, wherein the electric field generating means includes a pair of opposed electrodes for flowing an electric current in the molten metal.   The electric field generating means is capable of adjusting the amount of current flowing in the molten metal, and adjusting the amount of the current to adjust the magnitude of the Lorentz force acting on the molten metal. The control apparatus of molten metal bath of description.   The apparatus for controlling a molten metal bath according to any one of claims 1 to 3, wherein the magnetic field generating means is composed of a permanent magnet.   The apparatus for controlling a molten metal bath according to any one of claims 1 to 3, wherein the magnetic field generating means is composed of an electromagnet.   The magnetic field generating means is capable of adjusting the amount of current flowing through the electromagnet, and adjusting the amount of the current to adjust the magnitude of the Lorentz force acting on the molten metal. Control device for molten metal bath.   A support for supporting the electric field generating means and the magnetic field generating means is provided, and the electric field generating means and the magnetic field generating means are supported so that a Lorentz force acts in a direction penetrating through the void inside the support. The apparatus for controlling a molten metal bath according to claim 1, wherein the apparatus is provided on a body.   The support is made of a frame, and a pair of electrodes constituting the electric field generating means is provided on the opposing portions (p1) and (p2) of the frame, and the opposing portions of the frame and the portion A pair of magnets constituting magnetic field generating means are provided at portions (p3) and (p4) in a positional relationship of 90 ° with (p1) and (p2) so that different magnetic poles face each other. The molten metal bath control device according to claim 7, wherein an electric field is created between the electrodes and a magnetic field perpendicular to the electric field is created between the pair of magnets. In the method for producing a hot-dip metal strip, in which hot-dip plating is performed by immersing a continuous metal strip in a hot metal bath,
The molten metal bath control device (X) according to any one of claims 1 to 8 is installed at one or more locations in the molten metal bath, and the flow of molten metal or / and by the control device (X). A method for producing a hot dipped metal strip, comprising performing hot dipping on a metal strip while controlling the movement of foreign matter. A method for producing a hot dipped metal strip drawn from a hot metal bath after the metal strip that has entered the hot metal bath from above is redirected upward in the bath,
The hot-dip metal strip according to claim 9, wherein a Lorentz force generated by the control device (X) brakes a molten metal flow accompanying the metal strip that is redirected and moved upward in the bath. Production method. A method for producing a hot dipped metal strip drawn from a hot metal bath after the metal strip that has entered the hot metal bath from above is redirected upward in the bath,
The method for producing a hot-dip metal strip according to claim 9 or 10, wherein the molten metal flow flowing toward the bottom of the molten metal bath is braked by the Lorentz force generated by the control device (X). A method for producing a hot dipped metal strip drawn from a hot metal bath after the metal strip that has entered the hot metal bath from above is redirected upward in the bath,
The electromagnetic Archimedes force is applied to foreign matter in the molten metal bath in a direction away from the metal band by Lorentz force generated by the control device (X). Manufacturing method of hot-dip plated metal strip. A method for producing a hot dipped metal strip drawn from a hot metal bath after the metal strip that has entered the hot metal bath from above is redirected upward in the bath,
The electromagnetic Archimedes force acts on the foreign matter in the molten metal bath in the direction of the foreign matter accumulation portion in the molten metal bath by the Lorentz force generated by the control device (X). The manufacturing method of the hot dipped metal strip of description.

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