JP3869711B2 - Metal strip heating device with excellent temperature uniformity in the plate width direction - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a metal strip heating apparatus having excellent temperature uniformity in the plate width direction.
[0002]
[Prior art]
Induction heating is a method in which a coil connected to an AC power source is arranged around an object to be heated, and an object is heated by Joule heat of eddy current induced by an alternating magnetic field. There are two types of induction heating: a transverse method in which an alternating magnetic field intersects the object to be heated vertically and a solenoid method in which the object to be heated is wound around a coil and an alternating magnetic field is applied in parallel to the object to be heated. Is selected according to purpose.
In the case of heating a metal strip, a solenoid system is suitable because uniform heating is required in the plate width direction. The solenoid system includes a multi-turn system in which a coil is wound a plurality of times and a single-turn system in which the coil is wound only once.
In a conventional induction heating device using a solenoid type single-turn coil, when the metal strip is a magnetic steel strip, for example, it is difficult to heat above the Curie point (about 750 ° C.), and the low temperature is 650 ° C. or below. There is a problem that it can be applied only to heating in the region. Furthermore, when the metal strip is a non-magnetic material such as aluminum or SUS, it is difficult to heat itself.
[0003]
The reason why it is difficult to heat the magnetic strip above the Curie point is that when the temperature near the Curie point is reached, the current penetration depth of the eddy current increases, and the front and back of the eddy current that goes around the surface layer of the cross section in the plate width direction This is because cancellation occurs and eddy current does not flow.
The reason why heating the non-magnetic strip itself is difficult is that the current penetration depth of the eddy current is large from the normal temperature level, and the front / back offset of the eddy current that goes around the surface layer part of the cross section in the plate width direction is cancelled. This is because eddy current does not flow.
As a method for solving this problem, the inventors previously used a single-turn induction heating coil 2 on the upper surface of the metal strip 1 and a single-turn induction heating coil 3 on the lower surface of the metal strip 1 as shown in FIG. A patent application of Japanese Patent Application No. 2000-289145 was filed by finding a method of eliminating front and back cancellation of eddy currents that make a round in the surface layer portion of the cross section in the plate width direction by shifting each other in the longitudinal direction.
[0004]
With this method, the steel sheet can be heated to the Curie point (750 ° C.) or higher, and non-magnetic materials can be heated. However, the coil size for induction heating is increased, and the upper and lower coils sandwiching the steel sheet are used. The gap between them was expanded from 6 mm to 30 mm, and the temperature distribution in the width direction of the steel strip during heating was measured. As shown in FIG. 2, the following problems were revealed.
In addition, the horizontal axis | shaft of FIG. 2 is heating time (second), and a vertical axis | shaft is heating temperature (degreeC).
(Problem 1) Even in a low temperature heating region of 600 ° C. or lower, a temperature deviation in the width direction of the steel strip occurred.
(Problem 2) In the vicinity of the Curie point (750 ° C.), it was difficult to heat the central portion (4) of the steel strip, and the heating temperature did not reach the Curie point.
(Problem 3) The temperature of the steel strip edge portion (1) exceeded 800 ° C., and overheating of the edge portion became large.
[0005]
[Problems to be solved by the invention]
The present invention solves the problems of the prior art as described above, can heat a steel strip to a Curie point (750 ° C.) or higher, can also heat a non-magnetic material, and is excellent in temperature uniformity in the plate width direction. It is an object to provide a heating device for a metal strip.
[0006]
[Means for Solving the Problems]
As a result of intensive studies on the cause of the temperature deviation in the width direction of the metal strip, the inventors have found the following.
When the coil size is increased, the core thickness h is increased, so that the contraction length of the eddy current is increased at the edge portion and the amount of heat generation is increased.
On the other hand, since the magnetic field diffuses in the central portion, the magnetic flux density becomes small at the same input power, so the eddy current density decreases and the amount of heat generation decreases. The temperature deviation of the part increases.
As a result, the temperature of the edge part tends to overheat from around the low temperature, and when the temperature rises, the resistance of that part further rises. Therefore, the overheating of the edge part occurs extremely near the high temperature due to its synergistic effect. I understood it.
[0007]
Therefore, the inventors have adopted a heating method with good temperature uniformity near the low temperature to prevent overheating of the edge portion from near the low temperature and opposite to the current direction of the single-turn coil. By installing a magnetic field diffusion prevention coil through which current flows in the direction, increasing the magnetic flux density in the center to increase the heat generation at the center, and installing an edge overheating prevention device, the front and back of the metal strip The present inventors have found a method for reducing the amount of heat generated at the edge by diverting the eddy current at the edge flowing around the edge. The gist of the present invention is the following contents as described in the scope of claims.
[0008]
(1) energizing the heating roll of the induction heating coil or contact type solenoid type, are arranged in parallel and a single-turn induction heating coil, in the vicinity of the single-turn induction heating coil, common to the current of the single-turn induction heating coil A heating device for a metal strip provided with a magnetic field diffusion prevention coil that prevents diffusion of the magnetic field by flowing a current in the reverse direction using a power source of a single-turn induction heating coil on the surface of the metal strip, and A magnetic field diffusion prevention coil, a single-turn induction heating coil and a magnetic field diffusion prevention coil on the back surface of the metal strip are arranged at positions shifted from each other by a coil width W in the longitudinal direction of the metal strip; and
The outer circumference of the single-turn induction heating coil on the front and back surfaces, except for the surface opposite to the front and back surfaces of the metal strip, is covered with a ferrite core, and the magnetic field diffusion prevention coil not covered with the ferrite core is in contact with the ferrite core excellent heating device of the metal strip evenly temperature of the plate width direction, characterized in that cause.
[0009]
(2) Further, the edge portion of the metal strip is arranged in parallel in the vicinity of the single turn induction heating coil, and a current is supplied in the same direction using a power source common to the current of the single turn induction heating coil. An apparatus for heating a metal strip having excellent temperature uniformity in the plate width direction according to (1), wherein an edge portion overheating preventing coil is provided to prevent overheating.
(3) The edge portion overheating prevention coil on the front surface of the metal strip and the edge portion overheating prevention coil on the back surface of the metal strip are shifted to each other by the coil width W in the longitudinal direction of the metal strip. The apparatus for heating a metal strip having excellent temperature uniformity in the plate width direction according to (2), wherein the heating device is provided.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described in detail with reference to FIGS.
(First embodiment)
As a first embodiment of the present invention, an example in which magnetic field diffusion preventing coils 4 and 5 are provided is shown in FIGS.
FIG. 3 is a diagram illustrating an embodiment of a heating device for a metal strip in the present invention. The metal steel strip 1 is heated to about 600 ° C. by the solenoid induction heating coil 6 that is excellent in uniform heating in the plate width direction because eddy current flows in the cross section in the plate width direction. Similarly to this, a contact-type energization heating roll excellent in uniform heating property in the plate width direction may be used. Here, the energization heating roll is a roll that comes into contact with the metal strip, and a current is passed directly from the roll to the metal strip and the metal strip is heated by the Joule heat.
[0011]
Single-turn induction heating coils 2 and 3 are installed at the subsequent stage of the solenoid type induction heating coil 6, and a magnetic field is generated by flowing a current in the opposite direction to the single-turn induction heating coils 2 and 3, respectively. Magnetic field diffusion preventing coils 4 and 5 for preventing diffusion are provided. By preventing the diffusion of the magnetic field in the heating near the Curie point (750 ° C.) by the magnetic field diffusion preventing coils 4 and 5,
It is possible to prevent a decrease in magnetic flux density in the central portion in the plate width direction and increase the heating temperature in the central portion in the plate width direction.
FIG. 4 is a cross-sectional view in the longitudinal direction of the steel strip of the first embodiment in the metal strip heating apparatus of the present invention.
[0012]
The single-turn induction heating coil 2 and magnetic field diffusion prevention coil 4 on the upper surface of the steel strip 1 and the single-turn induction heating coil 3 and magnetic field diffusion prevention coil 5 on the lower surface of the steel strip 1 are mutually shifted in the longitudinal direction of the steel strip 1. Since the eddy currents that circulate around the surface layer portion of the cross section in the plate width direction do not cancel each other, heating to the Curie point (750 ° C.) or higher is possible. Further, a non-magnetic material such as aluminum or SUS can be heated.
Moreover, in order to concentrate the magnetic field (increase the magnetic flux density) and improve the heating efficiency, the relative magnetic permeability of the outer peripheral three surfaces excluding the surface facing the steel strip of the single-turn induction heating coils 2 and 3 is as high as 2500, It is preferable to directly coat with a high resistivity ferrite core 9.
[0013]
FIG. 5 is a diagram showing a change in temperature distribution in the plate width direction when the steel strip is heated using the first embodiment of the metal strip heating apparatus of the present invention.
A steel plate having a plate width of 70 mm and a thickness of 0.35 mm was used, and heating was performed at a plate speed of 70 mm / second, a frequency of 20 KHz, a power output of 50 KW, a coil width of W: 40 mm, a core thickness of h: 20 mm, and a gap G of 30 mm.
Compared with FIG. 2 showing the temperature distribution in the plate width direction of the prior application, there is no temperature deviation in the plate width direction in the low temperature portion of 600 ° C. or less, and the heating temperature in the center portion in the plate width direction near the Curie point (750 ° C.). Is significantly higher.
In addition, although the heating temperature of the edge part in FIG. 5 is high and the overheating phenomenon of the edge part remains, this is because a copper plate is installed on the upper and lower surfaces of the edge part of the steel strip. This can be prevented by shielding.
[0014]
(Second Embodiment)
As a second embodiment of the present invention, an example in which magnetic field diffusion preventing coils 4 and 5 and edge portion overheating preventing coils 7 and 8 are provided is shown in FIGS.
FIG. 6 is a diagram illustrating a second embodiment of the metal strip heating apparatus according to the present invention.
The metal steel strip 1 is heated to about 600 ° C. by the solenoid induction heating coil 6 that is excellent in uniform heating in the plate width direction because eddy current flows in the cross section in the plate width direction. Similarly to this, a contact-type energization heating roll excellent in uniform heating property in the plate width direction may be used.
[0015]
Single-turn induction heating coils 2 and 3 are installed at the subsequent stage of the solenoid type induction heating coil 6, and a magnetic field is generated by flowing a current in the opposite direction to the single-turn induction heating coils 2 and 3, respectively. Magnetic field diffusion preventing coils 4 and 5 for preventing diffusion are provided. By preventing the diffusion of the magnetic field in the heating near the Curie point (750 ° C.) by the magnetic field diffusion preventing coils 4 and 5,
It is possible to prevent a decrease in magnetic flux density at the central portion in the plate width direction and increase the heating temperature at the central portion in the plate width direction.
Between the solenoid-type induction heating coil 6 and the single-turn induction heating coils 2 and 3, eddy currents at the edges of the metal strip are caused to flow in the same direction as the current of the single-turn induction heating coils 2 and 3. Edge part overheating prevention coils 7 and 8 are provided to shunt and prevent overheating of the edge part. By diverting the eddy current at the edge portion by the edge portion overheating preventing coils 7 and 8, the phenomenon of contraction of the eddy current at the edge portion can be alleviated and the overheating of the edge portion can be remarkably suppressed.
[0016]
FIG. 7 is a diagram illustrating a second embodiment of the metal strip heating apparatus according to the present invention, where the single-turn induction heating coils 2 and 3 and the edge portion overheating preventing coils 7 and 8 are commonly used. This is an example. Thereby, the installation cost can be reduced by reducing the number of installed power supply devices.
FIG. 8 is a diagram illustrating a second embodiment of the metal strip heating apparatus according to the present invention, which is a single-turn induction heating coil 2, 3, edge portion overheating prevention coils 7, 8, solenoid type induction heating. This is an example in which all the power sources of the coil 6 are shared. Thereby, the installation cost can be further reduced by reducing the number of installed power supply devices.
[0017]
FIG. 9 is a longitudinal sectional view of the steel strip of the second embodiment in the metal strip heating apparatus of the present invention.
Single turn induction heating coil 2, magnetic field diffusion prevention coil 4, and edge portion overheating prevention coil 7 on the upper surface of steel strip 1, and single turn induction heating coil 3, magnetic field diffusion prevention coil 5 and edge portion on the lower surface of steel strip 1 Since the overheating prevention coils 7 are arranged at positions shifted from each other in the longitudinal direction of the steel strip 1, there is no cancellation of the front and back of the eddy current that goes around the surface layer portion of the cross section in the plate width direction. It can be heated to a point (750 ° C.) or higher. Further, a non-magnetic material such as aluminum or SUS can be heated.
[0018]
Between the solenoid type induction heating coil 6 and the single turn induction heating coils 2 and 3, edge overheating prevention coils 7 and 8 for supplying current in the same direction as the current of the single turn induction heating coils 2 and 3 are provided. ing.
For example, 70% of the current flows through the single-turn induction heating coils 2 and 3 and the remaining 30% of the current is installed at positions shifted in the longitudinal direction of the metal strips 7 and 8. Since the edge overheating due to the contraction of the eddy current generated at the edge portion of the strip plate works by the square of the current, the edge overheating can be reduced to about 50% (0.7 * 0.7 = 0.49). .
Further, in order to concentrate the magnetic field (increase the magnetic flux density) and improve the heating efficiency, the three outer peripheral surfaces excluding the surface facing the steel strip of the single-turn induction heating coils 2 and 3 have a high relative permeability of 2500. It is preferable to directly coat with a high resistivity ferrite core 9.
[0019]
Furthermore, in order to adjust the partial flow rate of the eddy current passing through the edge portion, the outer peripheral three surfaces excluding the surface facing the steel strip of the edge portion overheating preventing coil 8 have a high relative permeability of 2500 and high resistivity. It is preferable to directly coat with the ferrite core 9.
FIG. 10 is a diagram showing changes in the temperature distribution in the plate width direction when the steel strip is heated using the metal strip heating apparatus of the present invention.
A steel plate having a plate width of 70 mm and a thickness of 0.35 mm was used, and heating was performed at a plate speed of 70 mm / second, a frequency of 20 KHz, a power output of 50 KW, a coil width W of 40 mm, a core thickness h of 20 mm, and a gap G of 30 mm.
[0020]
As a result, the central portion could be heated to the Curie point or higher, and the temperature deviation in the plate width direction was about + -30 ° C., which is a practical target, and a uniform temperature distribution in the plate width direction could be realized.
Compared to FIG. 5 showing the temperature distribution in the plate width direction in the first embodiment, it can be seen that the overheating phenomenon at the edge portion is eliminated.
[0021]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the steel strip can be heated more than a Curie point, a non-magnetic material can be heated, and a metal strip heating device excellent in temperature uniformity in the plate width direction can be provided. Useful and significant effect.
[Brief description of the drawings]
FIG. 1 is a sectional view showing a heating device for a metal strip of a prior application.
FIG. 2 is a diagram showing a temperature distribution in the plate width direction when heated using a metal band plate heating device of a prior application.
FIG. 3 is a view showing a first embodiment of the metal strip heating apparatus of the present invention.
FIG. 4 is a cross-sectional view in the longitudinal direction of the steel strip of the first embodiment in the metal strip heating apparatus of the present invention.
FIG. 5 is a view showing a temperature distribution in the plate width direction when heated by using the first embodiment of the metal strip heating apparatus of the present invention.
FIG. 6 is a view showing a second embodiment of the heating apparatus for the metal strip of the present invention.
FIG. 7 is a view showing a second embodiment of the heating device for the metal strip of the present invention.
FIG. 8 is a view showing a second embodiment of the metal strip heating apparatus of the present invention.
FIG. 9 is a longitudinal sectional view of a steel strip according to a second embodiment of the metal strip heating apparatus of the present invention.
FIG. 10 is a diagram showing a temperature distribution in the plate width direction when heated by using the second embodiment of the metal strip heating apparatus of the present invention.
[Explanation of symbols]
1: Metal strip 2: Single-turn induction heating coil (upper surface of strip)
3: Single-turn induction heating coil (underside of strip)
4: Magnetic field diffusion prevention coil (upper surface of strip)
5: Magnetic field diffusion prevention coil (bottom surface of strip)
6: Solenoid induction heating coil 7: Edge overheating prevention coil (upper surface of strip)
8: Edge part overheating prevention coil (lower surface of strip)
9: Ferrite core

Claims (3)

A solenoid-type induction heating coil or contact-type energization heating roll, a single-turn induction heating coil, and a single-turn induction heating coil are arranged in parallel in the vicinity of the single-turn induction heating coil, and a common power source is shared with the current of the single-turn induction heating coil. A metal strip heating device provided with a magnetic field diffusion prevention coil that prevents diffusion of a magnetic field by flowing a current in the reverse direction using the single turn induction heating coil and magnetic field diffusion prevention on the surface of the metal strip A coil, a single-turn induction heating coil and a magnetic field diffusion prevention coil on the back side of the metal strip are arranged at positions shifted from each other by a coil width W in the longitudinal direction of the metal strip, and
The outer circumference of the single-turn induction heating coil on the front and back surfaces, except for the surface opposite to the front and back surfaces of the metal strip, is covered with a ferrite core, and the magnetic field diffusion prevention coil not covered with the ferrite core is in contact with the ferrite core excellent heating device of the metal strip evenly temperature of the plate width direction, characterized in that cause. Furthermore, it is arranged in parallel in the vicinity of the single-turn induction heating coil and overheats the edge portion of the metal strip by flowing a current in the same direction using a power source common to the current of the single-turn induction heating coil. 2. An apparatus for heating a metal strip having excellent temperature uniformity in the plate width direction according to claim 1, wherein an edge overheating preventing coil is provided. The edge overheating prevention coil on the front surface of the metal strip and the edge overheating prevention coil on the back surface of the metal strip are arranged at positions shifted from each other by the coil width W in the longitudinal direction of the metal strip. The apparatus for heating a metal strip having excellent temperature uniformity in the plate width direction according to claim 2.

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