JPH07328512A - Baking method and oven for surface coating metal sheet - Google Patents

Abstract

PURPOSE:To provide a baking method or a baking oven or an alloying method or an alloying oven wherein a surface coated metal sheet with good surface properties can be obtd. inexpensively, with a fast baking speed and in a short time in preparing the surface coated metal sheet. CONSTITUTION:A baking method or a baking oven for a coated metal sheet or an alloying method or an alloying oven for a molten plating metal wherein magnetic strain of a metal belt-like body is measured and the max. supplying electric current (strength of a magnetic field) is controlled in accordance with the value is provided in baking of the coated metal sheet or alloying of a molten plating metal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for baking a surface-coated metal sheet or an alloying method, and more particularly to a method for baking a surface-coated metal sheet or an alloying method using a high frequency induction heating method.

[0002]

2. Description of the Related Art In recent years, prepainted steel plates (painted steel plates) have been widely used in various fields such as home appliances. Along with this, high quality is required for the coating film of this steel sheet. Further, there is a demand for coated steel sheets obtained by coating a wide variety of paints with various thicknesses using steel sheets of various thicknesses and baking them. Therefore, it is possible to perform the temperature control suitable for the material and thickness of the metal plate and the paint to be baked, and to increase the baking speed to provide a coated metal plate with good surface performance in a short time. Development of an obtainable baking furnace is expected.

On the other hand, conventionally, a coated metal plate (for example, a coated steel plate) is subjected to paint baking treatment by using a hot air oven of a gas heating system. Recently, a high-frequency induction heating method has been put into practical use, which enables rapid heating, has no thermal inertia, and provides a coated metal plate with a clean atmosphere and few coating defects. Specifically, there are two methods, a method of performing a baking process in an induction heating furnace using a high frequency induction heating method (for example, see JP-A-1-139178), and evaporation of most of the solvent in the induction heating furnace. (Volatilization), and then baking in a hot air oven (see, for example, Japanese Patent Laid-Open No. Sho 6
2-99479, JP-A-62-133083, JP-A-62-133084). The same applies to an alloying furnace for hot-dip galvanized metal in which a metal strip is passed through a bath of molten metal, the surface of the strip is coated with the molten metal, and an alloy of the coating and the strip is produced.

[0004]

As described above, as a conventional coated metal sheet baking oven, a hot air oven is used, an induction heating oven is used, and an induction heating oven is used in the first half of the heating. It is known to apply a hot stove. However, these conventional coated metal plate baking furnaces have the following problems. First of all, in the case of using a hot stove, it is required to coat a wide variety of paints with various thicknesses using metal plates of various thicknesses and then bake it, but the thermal inertia of the hot stove is Since it is large, it takes a lot of time to change the conditions, and the heating time has to be long.

Further, the one using the induction heating furnace has a problem that a streak pattern is formed in the sheet passing direction when the current (magnetic field) applied to the metal strip is too large. The occurrence of streak patterns differed depending on the material of the metal plate, the plate thickness, and the type of paint, and the cause of occurrence was not clear, and it was difficult to use the induction heating furnace except for limited materials. Further, even in a furnace in which an induction heating furnace is applied in the first half of the heating and a hot air stove is applied in the latter half of the heating, the generation of the streak pattern could not be suppressed. This streak pattern generation phenomenon is the same in the molten metal alloying furnace. In recent years, it has been speculated that the streak pattern generation phenomenon is a resonance vibration of the metal strip in the plate width direction due to induction heating, but the true cause remains unclear. As a countermeasure for preventing this resonance, Japanese Patent Laid-Open No. 64-6
Although a method of modulating the power source of the induction heating device has been proposed as seen in Japanese Patent No. 8455, it is necessary to modulate the power source, and the equipment cost is unavoidably high.

In view of the problems of the conventional baking or alloying process for a surface-coated metal sheet described above, the present invention performs temperature control suitable for the material and thickness of the coating material and achieves a high baking speed in a short time. An object of the present invention is to provide a baking method, a baking furnace, an alloying method, or an alloying furnace capable of obtaining a surface-coated metal sheet having good surface performance.

[0007]

The present invention advantageously solves the problems of the prior art, and as a result of the inventors' ingenuity to achieve the above object, the method is inexpensive and It is possible to obtain a surface-coated metal sheet having good surface performance in a short time by increasing the baking speed, and the gist of the invention is (1) a liquid or powder in a metal strip. Apply body-shaped paint,
In the baking method of a coated metal plate in which the solvent is evaporated or the powder is melted and baked, the magnetostriction of the metal strip is measured, and the maximum input current of the induction heating device is controlled according to that value. A characteristic method for baking painted metal sheets.

(2) The method for baking a coated metal sheet according to (1), wherein the magnetostriction of the metal strip is measured, and the maximum input current of the induction heating device is controlled by a magnetostriction function α satisfying the following equation. . α = {πhf _n √ (Eγ / 3g) − (ν · σ _tL )} /
_{(-Σ mC + σ sC)>} 3 × 10 3 ^{_{where, σ mC = μJH-μH 2}} /2 σ sC = E × (ΔW / Wo) However, [pi is circle ratio, h is the plate thickness of the steel sheet, f _n is the frequency of the induction heating device, γ is the density of the steel plate, E is the Young's modulus of the steel plate, g
Is the acceleration of gravity, σ _tL is the unit tension of the steel sheet in the sheet passing direction, ν is the Poisson's ratio of the steel sheet, and σ _mC is the M acting on the steel sheet.
axwell stress (tensile stress in the plate width direction), μ is magnetic permeability,
H is the external magnetic field strength (proportional to the input current of the induction heating device),
J is the eddy current density induced by the external magnetic field H, and σ _sC is the magnetostrictive stress of the steel sheet (compressive stress in the sheet width direction). In addition, ΔW
/ Wo is the magnetostriction when Wo is the material width when there is no external magnetic field and ΔW is the width shrinkage allowance when there is an external magnetic field.

(3) The baking furnace is divided into a plurality of regions, the magnetostriction of the metal strip is measured for each region, and the maximum amount of each region is applied according to the measured magnetostriction and the viscosity of the coating material at the temperature of the region. (1) or (2) characterized by controlling current
Baking method of the coated metal plate described (4) Apply liquid or powder paint to the metal strip,
In the baking method of the coated metal plate in which the solvent is evaporated or the powder is melted and baked, the magnetostriction of the metal strip is measured, and the solvent is evaporated or the powder is melted in a material having a large value, A method for baking a coated metal sheet, which comprises heating with hot air or far infrared rays until the viscosity of the coating becomes high, and then induction heating. (5) In a method of alloying a hot-dip plated metal, which comprises passing a metal strip through a molten metal bath, coating the surface with the molten metal, and forming an alloy between the coating and the strip, the metal strip Is measured, and the maximum input current of the induction heating device is controlled according to the measured value.

(6) The magnetostriction of the metal strip is measured, and the maximum input current of the induction heating device is controlled by a magnetostriction function α satisfying the following formula: alloying of the hot-dip metal according to (5). Method. α = {πhf _n √ (Eγ / 3g) − (ν · σ _tL )} /
_{(-Σ mC + σ sC)>} 3 × 10 3 ^{_{where, σ mC = μJH-μH 2}} /2 σ sC = E × (ΔW / Wo) However, [pi is circle ratio, h is the plate thickness of the steel sheet, f _n is the frequency of the induction heating device, γ is the density of the steel plate, E is the Young's modulus of the steel plate, g
Is the acceleration of gravity, σ _tL is the unit tension of the steel sheet in the sheet passing direction, ν is the Poisson's ratio of the steel sheet, and σ _mC is the M acting on the steel sheet.
axwell stress (tensile stress in the plate width direction), μ is magnetic permeability,
H is the external magnetic field strength (proportional to the input current of the induction heating device),
J is the eddy current density induced by the external magnetic field H, and σ _sC is the magnetostrictive stress of the steel sheet (compressive stress in the sheet width direction). In addition, ΔW
/ Wo is the magnetostriction when Wo is the material width when there is no external magnetic field and ΔW is the width shrinkage allowance when there is an external magnetic field.

(7) Magnetostriction of a metal strip in a baking furnace for a coated metal plate in which a liquid or powder coating material is applied to the metal strip and the solvent is evaporated or the powder is melted for baking. B. A baking furnace for coated metal sheets, characterized in that the measuring device is installed, and an induction heating device having a maximum input current control device is installed behind it. (8) An induction heating device including a plurality of regions is provided, and a device for controlling the maximum input current of the induction heating device is provided for each region according to the magnetostriction of the metal strip and the viscosity of the paint. A baking furnace for coated metal plates according to (7).

(9) In a baking furnace for a coated metal plate, in which a liquid or powder coating material is applied to a metal strip, and the solvent is evaporated or the powder is baked, the first half region of the furnace is A baking furnace for coated metal sheets, characterized in that a magnetostriction measuring device for a metal strip and a hot-air heating device or a far-infrared heating device are provided, and an induction heating device is provided in the latter half of the furnace. (10) An induction heating device in an alloying furnace for hot-dip plated metal, in which a metal strip is passed through a molten metal bath, the surface is coated with molten metal, and an alloy of the coating and the strip is produced. In front of the above, there is provided an apparatus for measuring the magnetostriction of the metal strip, and an induction heating apparatus having a maximum input current control apparatus.

[0013]

The present invention will be described in detail below. The present inventors, while investigating the resonance vibration of the steel sheet in the width direction, paying attention to the magnetic properties, and investigating this in detail, found that the resonance vibration of the steel sheet in the width direction due to magnetostriction and induction heating. Found that there is a strong relationship between. The survey is
The procedure was as follows. FIG. 1 shows an example of a baking furnace for coated metal plates. As shown in the figure, in the baking furnace 1 of this example, the baking furnace is divided into four regions I, II, III, and IV, and the coil 31 connected to the power supply device 21 is divided into region I.
The coil 32 connected to the power supply device 22 in the area
II, the coil 33 connected to the power supply device 23 is arranged in the region III, and the coil 34 connected to the power supply device 24 is arranged in the region IV. Inner atmosphere and ventilation conditions are not stated.)

The present inventors have made various steel plates (plate thickness / material)
Regarding, about the change of the applied current (the strength of the magnetic field) of the induction heating device to investigate the occurrence of streak pattern, and the change of various magnetic properties of the steel plate against the applied current (the strength of the magnetic field) of the induction heating device. Was measured. As a result, there is a strong correlation between the magnetostriction and the resonance vibration in the width direction of the steel plate via the applied magnetic field of the induction heating device, and in addition, when the resonance vibration in the width direction of the steel plate occurs, It was found that streak patterns occur when the viscosity of the coating is low.

Further detailed analysis revealed that the magnetostrictive function α
It was found that there is a strong correlation between α and the resonance vibration of the steel sheet in the sheet width direction when is defined by the following equation. α = {πhf _n √ (Eγ / 3g) − (ν · σ _tL )} /
(-Σ _mC + σ _{sC) ^{where, σ mC = μJH-μH 2}} /2 σ sC = E × (ΔW / Wo) However, [pi is circle ratio, h is the plate thickness of the steel sheet, f _n is an induction heating device , Γ is the density of the steel plate, E is the Young's modulus of the steel plate, g
Is the acceleration of gravity, σ _tL is the unit tension of the steel sheet in the sheet passing direction, ν is the Poisson's ratio of the steel sheet, and σ _mC is the M acting on the steel sheet.
axwell stress (tensile stress in the plate width direction), μ is magnetic permeability,
H is the external magnetic field strength (proportional to the input current of the induction heating device),
J is the eddy current density induced by the external magnetic field H, and σ _sC is the magnetostrictive stress of the steel sheet (compressive stress in the sheet width direction). In addition, ΔW
/ Wo is the magnetostriction when Wo is the material width when there is no external magnetic field and ΔW is the width shrinkage allowance when there is an external magnetic field.

Further, in the situation where the resonance vibration of the steel sheet in the width direction is generated, the value of the Maxwell stress σ _mC is generally less than 1/10 of the value of the magnetostrictive stress σ _sC of the steel sheet. I found it. It should be noted that in the molecular term of α, the first
It was also confirmed that the value of the term is more than 10 times the value of the second term.
From this, the magnetostrictive function α is simplified as a simple magnetostrictive function α ′, that is, α ′ = {πhf _n √ (Eγ / 3g)} / σ _sC, and α ′ and the resonance vibration of the steel sheet in the width direction are reduced. A strong correlation also holds between them.

FIG. 2 shows an example of the relationship between the strength of the magnetic field and the resonance vibration of the steel plate in the plate width direction. The frequency of the induction heating device is
6 kHz. The product type A has a steel plate material of SUS400 series and a plate thickness of 0.5 mm, and the product type B has a steel plate material of ordinary steel and a plate thickness of 0.4 mm. Although the value of magnetostriction (indicated here as a magnetostriction function) at the same magnetic field strength is significantly different depending on the steel plate material (in this example, the SUS400 series is about 10 times that of ordinary steel), but the magnetostriction is different for all steel plate materials. Function α
However, it was found that when the value exceeds 3 × 10 ³ , the resonance vibration of the steel sheet in the width direction does not occur. The same arrangement can be made with the simple magnetostrictive function α ′.

Further, the inventors of the present invention used a plurality of induction heating devices as shown in FIG. 1 to increase and decrease the strength of the magnetic field of each coil, and conducted repeated research, and as a result, even if the resonance vibration of the steel sheet occurred. It was found that a streak pattern does not always occur. When the surface coating material was changed and examined in detail, it was also found that the higher the viscosity of the surface coating material, the less streaky pattern does not occur even if resonance vibration of the steel sheet occurs.

The present invention is constructed on the basis of the above findings, and operates as described below. In the invention according to any one of claims 1, 2 and 7, liquid or powder coating material is applied to the metal strip, and the solvent is evaporated, or the powder is melted and baked. In the baking of the coated metal plate, first, the magnetostriction of the metal strip is measured prior to induction heating. Then, according to the value, desirably, the maximum input current of the induction heating device is controlled so that the value of the following magnetostrictive function α exceeds 3 × 10 ^3, and induction heating is performed to bake the coated metal sheet. α = {πhf _n √ (Eγ / 3g) − (ν · σ _tL )} /
(-Σ _mC + σ _{sC) ^{where, σ mC = μJH-μH 2}} /2 σ sC = E × (ΔW / Wo) Thus, the magnetostriction of the in baking of the coated metal plate, through the turned magnetic field of the induction heating device Is suppressed and the generation of resonance vibration of the metal strip in the plate width direction is suppressed, so that it is possible to advantageously suppress the generation of streak patterns on the coating on the metal surface with an inexpensive standard induction heating device. .

In the invention according to claim 3 or claim 8, a coated metal plate in which a liquid or powdery coating material is applied to the metal strip, and the solvent is evaporated or the powder is melted and baked. In baking, first, the magnetostriction of the metal strip is measured prior to induction heating for each of the divided regions. Then, depending on the value of the magnetostriction and the viscosity of the coating material at the temperature in that region, it is desirable to control the maximum input current of the induction heating device so that the value of the following magnetostrictive function α exceeds 3 × 10 ^3. Heat and bake the painted metal plate. α = {πhf _n √ (Eγ / 3g) − (ν · σ _tL )} /
(-Σ _mC + σ _{sC) ^{where, σ mC = μJH-μH 2}} /2 σ sC = E × (ΔW / Wo)

Therefore, in the baking of the coated metal plate, the magnetostriction via the applied magnetic field of the induction heating device is suppressed to be small in each of the divided regions, and the resonance vibration of the metal strip in the plate width direction is generated. In addition, since the temperature can be controlled in accordance with the material and thickness of the coating material, it is possible to advantageously suppress the generation of streak patterns in the coating on the metal surface with a standard inexpensive induction heating device. Also, since the baking oven is divided into multiple areas, more detailed control is possible,
Productivity can be improved.

In the invention according to claim 4 or claim 9, a coated metal plate for applying a liquid or powder coating material to a metal strip, evaporating the solvent thereof, or melting the powder for baking. In the baking, first, the magnetostriction of the metal strip is measured prior to the heating for the baking. And
For a metal material having a large value, hot air heating or far infrared heating is performed until the solvent evaporates or the powder melts and the viscosity of the coating becomes high. After that, induction heating is performed to bake the coated metal plate. Therefore, in the baking of the coated metal plate, in the first half region of the baking in which the resonance vibration in the plate width direction of the metal strip by the induction heating device becomes a problem, hot air heating or the resonance vibration in the plate width direction of the metal strip does not occur. Since far-infrared heating is used, it is possible to advantageously suppress the generation of streak patterns in the coating on the metal surface with a standard inexpensive induction heating device.

In the invention according to claim 5, claim 6 or claim 10, the metal strip is passed through a molten metal bath, the surface is coated with the molten metal, and the coating and the In alloying a hot-dip metal to form an alloy with a strip, first, the magnetostriction of the strip is measured prior to induction heating. Then, according to the value, desirably, the maximum input current of the induction heating device is controlled and induction heating is performed so that the value of the following magnetostrictive function α exceeds 3 × 10 ^3, and the hot dip metal is alloyed. . α = {πhf _n √ (Eγ / 3g) − (ν · σ _tL )} /
(-Σ _mC + σ _{sC) ^{where, σ mC = μJH-μH 2}} /2 σ sC = E × (ΔW / Wo)

Therefore, in the alloying of the hot-dip galvanized metal, the magnetostriction through the applied magnetic field of the induction heating device is suppressed to be small, and the resonance vibration of the metal strip in the plate width direction is suppressed. A standard induction heating device can advantageously suppress the generation of streak patterns in the plated metal layer on the metal surface. As the magnetic field control index, the applied voltage or the applied power may be used instead of the applied current. The magnetostriction measuring method is not limited and may be any method (for example, the differential transformer method or the laser Doppler method). However, the measured value may be different depending on the measuring method. It is necessary to make and calibrate the relationship between the strength of the magnetic field (magnetostriction) and the resonance in the width direction of the steel plate as shown in FIG.

[0025]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an example of a baking furnace for coated metal plates.
As shown in the figure, in the baking furnace 1 of this example, the baking furnace is divided into four regions I, II, III, and IV, and the coil 31 connected to the power supply device 21 is arranged in the region I. The coil 32 connected to the power supply device 22 is disposed in the area II, the coil 33 connected to the power supply device 23 is disposed in the area III, and the coil 34 connected to the power supply device 24 is disposed in the area IV. The inside of the furnace is ventilated (atmosphere and ventilation conditions in the furnace are not stated).

FIG. 2 shows an example of the relationship between the magnetic field strength (magnetostriction) in a plurality of induction heating devices as shown in FIG. 1 and the resonance vibration of the steel plate in the plate width direction. The frequency of the induction heating device is 6
kHz. The product type A has a steel plate material of SUS400 series and a plate thickness of 0.5 mm, and the product type B has a steel plate material of ordinary steel and a plate thickness of 0.4 mm. Although the value of the magnetostriction (magnetostriction function) at the same magnetic field strength varies significantly depending on the steel plate material (in this example, the SUS400 series is about 10 times that of ordinary steel).
Regardless of the material of the steel plate, when α exceeds 3 × 10 ³ , resonance vibration of the steel plate in the plate width direction does not occur.

FIG. 3 shows a baking furnace according to the present invention which is particularly effective in baking a material having a low surface coating material viscosity or a large steel sheet magnetostriction. As shown in the figure, the baking furnace 1 of the present example has four areas I, II, and I.
The far-infrared ray device 51 connected to the power supply device 21 is arranged in the area I, and the far-infrared ray device 52 connected to the power source device 22 is arranged in the area II.
The coil 33 connected to No. 3 is arranged in the region III, the coil 34 connected to the power supply device 24 is arranged in the region IV, and the inside of the furnace is ventilated. (Furnace atmosphere and ventilation conditions are not stated). For example, in the case where a fluororesin-based powder coating material is applied on the surface and baked, in a region where the viscosity of the surface coating material is low (up to the melting stage of the powder coating material), the surface coating material is heated with a far infrared device. In the high viscosity region (fluorine levitation stage), the induction heating device is used for heating, and the final reaching temperature of the steel plate is controlled by the induction heating device, and the effects of size changes, etc., can be made to be similar to those of the induction heating device alone. It was

The same applies to a galvanizing metal alloying furnace in which a metal strip is passed through a bath of molten metal and the surface is coated with molten metal to form an alloy of the coating and the strip. In addition, by measuring the magnetostriction of the steel sheet and controlling the coil input power (magnetic field) based on that value, it is possible to obtain good surface quality without the occurrence of streak patterns with a standard inexpensive induction heating device. Became.

[0029]

In summary, according to the present invention, the following excellent effects can be obtained. According to the invention described in claim 1, claim 2 or claim 7, the magnetostriction of the induction heating device via the applied magnetic field is suppressed to a small level, and the resonance vibration of the metal strip in the plate width direction is generated. Therefore, it is possible to advantageously suppress the generation of streak patterns on the coating on the metal surface with a standard inexpensive induction heating device. According to the invention as set forth in claim 3 or claim 8, in addition to suppressing generation of resonance vibration of the metal strip in the plate width direction, temperature control suitable for the material and thickness of the coating material is further divided. Since it can be performed for each of a plurality of regions, it is possible to further effectively suppress the generation of the streak pattern on the coating on the metal surface with a standard inexpensive induction heating device, and it is also possible to improve the productivity.

According to the invention described in claim 4 or claim 9, in the first half region of baking in which the resonance vibration in the plate width direction of the metal strip due to the induction heating device becomes a problem, in the plate width direction of the metal strip. Since hot air heating or far-infrared heating that does not generate resonance vibration is used, even if a metal plate with a low surface coating material viscosity or large magnetostriction is baked, a standard induction heating device that is inexpensive is used to coat the metal surface. It is possible to advantageously suppress the generation of the streak pattern in. According to the invention described in claim 5, claim 6, or claim 10, the magnetostriction of the induction heating device via the applied magnetic field is suppressed to a small level, and the resonance vibration of the metal strip in the plate width direction is generated. Therefore, it is possible to suppress the generation of streak patterns in the plated metal layer on the surface of the metal plate with a standard inexpensive induction heating device.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of a baking furnace for coated metal plates,

FIG. 2 is an explanatory diagram showing the relationship between magnetic field strength and resonance in the plate width direction,

FIG. 3 is an explanatory view showing an example of a baking furnace for coated metal plates according to the present invention.

[Explanation of symbols]

 1 Baking Furnace 6 Steel Plate 21-24 Induction Heating Coil Power Supply Device 31-34 Induction Heating Coil 41-42 Far Infrared Power Supply Device 51-52 Far Infrared Device I First Heating Area II Second Heating Area III Third Heating Area IV Fourth heating area

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area F27B 9/40

Claims (10)

[Claims] 1. A method for baking a coated metal plate, which comprises applying a liquid or powdery coating material to a metal strip, evaporating the solvent thereof, or melting the powder to perform baking, wherein the magnetostriction of the metal strip is reduced. A method for baking a coated metal sheet, which comprises measuring and controlling the maximum input current of the induction heating device according to the measured value. 2. The method for baking a coated metal sheet according to claim 1, wherein the magnetostriction of the metal strip is measured, and the maximum input current of the induction heating device is controlled by a magnetostriction function α satisfying the following equation. α = {πhf _n √ (Eγ / 3g) − (ν · σ _tL )} /
_{(-Σ mC + σ sC)>} 3 × 10 3 ^{_{where, σ mC = μJH-μH 2}} /2 σ sC = E × (ΔW / Wo) However, [pi is circle ratio, h is the plate thickness of the steel sheet, f _n is the frequency of the induction heating device, γ is the density of the steel plate, E is the Young's modulus of the steel plate, g
Is the acceleration of gravity, σ _tL is the unit tension of the steel sheet in the sheet passing direction, ν is the Poisson's ratio of the steel sheet, and σ _mC is the M acting on the steel sheet.
axwell stress (tensile stress in the plate width direction), μ is magnetic permeability,
H is the external magnetic field strength (proportional to the input current of the induction heating device),
J is the eddy current density induced by the external magnetic field H, and σ _sC is the magnetostrictive stress of the steel sheet (compressive stress in the sheet width direction). In addition, ΔW
/ Wo is the magnetostriction when Wo is the material width when there is no external magnetic field and ΔW is the width shrinkage allowance when there is an external magnetic field. 3. The baking furnace is divided into a plurality of regions, the magnetostriction of the metal strip is measured for each region, and the maximum applied current of each region is determined according to the measured magnetostriction value and the viscosity of the paint at the temperature of the region. The control of claim 1 or claim 2
The method for baking a painted metal sheet as described above. 4. A method for baking a coated metal plate, which comprises applying a liquid or powder coating material to a metal strip, evaporating the solvent thereof, or melting the powder to perform baking. Measured.For materials with large values, the solvent evaporates or the powder melts, and hot air heating or far infrared heating is performed until the viscosity of the coating becomes high, and then induction heating is performed. Method. 5. A method of alloying a hot-dipped metal, which comprises passing a metal strip through a bath of molten metal, coating the surface with molten metal, and forming an alloy between the coating and the strip. A method for alloying a hot-dip metal, comprising measuring the magnetostriction of a strip and controlling the maximum input current of an induction heating device according to the value. 6. The method for alloying hot-dip galvanized metal according to claim 5, wherein the magnetostriction of the metal strip is measured and the maximum input current of the induction heating device is controlled by a magnetostriction function α satisfying the following equation. . α = {πhf _n √ (Eγ / 3g) − (ν · σ _tL )} /
_{(-Σ mC + σ sC)>} 3 × 10 3 ^{_{where, σ mC = μJH-μH 2}} /2 σ sC = E × (ΔW / Wo) However, [pi is circle ratio, h is the plate thickness of the steel sheet, f _n is the frequency of the induction heating device, γ is the density of the steel plate, E is the Young's modulus of the steel plate, g
Is the acceleration of gravity, σ _tL is the unit tension of the steel sheet in the sheet passing direction, ν is the Poisson's ratio of the steel sheet, and σ _mC is the M acting on the steel sheet.
axwell stress (tensile stress in the plate width direction), μ is magnetic permeability,
H is the external magnetic field strength (proportional to the input current of the induction heating device),
J is the eddy current density induced by the external magnetic field H, and σ _sC is the magnetostrictive stress of the steel sheet (compressive stress in the sheet width direction). In addition, ΔW
/ Wo is the magnetostriction when Wo is the material width when there is no external magnetic field and ΔW is the width shrinkage allowance when there is an external magnetic field. 7. A magnetostriction of a metal strip is applied in a baking furnace for a coated metal plate, in which a liquid or powder coating material is applied to the metal strip and the solvent is evaporated or the powder is baked. A baking furnace for coated metal sheets, comprising a measuring device and an induction heating device having a maximum input current control device behind the measuring device. 8. An induction heating device comprising a plurality of regions, and a device for controlling the maximum input current of the induction heating device for each region according to the magnetostriction of the metal strip and the viscosity of the paint. A baking furnace for a coated metal sheet according to claim 7, wherein: 9. In a baking furnace for a coated metal plate, which comprises applying a liquid or powder coating material to a metal strip, evaporating the solvent thereof, or melting the powder for baking, in the first half region of the furnace. A baking furnace for coated metal sheets, characterized in that a magnetostriction measuring device for a metal strip and a hot-air heating device or a far-infrared heating device are provided, and an induction heating device is provided in the latter half of the furnace. 10. A galvanizing metal alloying furnace in which a metal strip is passed through a bath of molten metal, the surface is coated with molten metal, and an alloy of the coating and the strip is produced. An alloying furnace for hot-dip galvanized metal, comprising a device for measuring magnetostriction of a metal strip in front of a heating device, and an induction heating device having a maximum input current control device.