JP4833740B2 - Metal strip heating device with excellent temperature uniformity in the plate width direction - Google Patents

Description

  The present invention relates to a heating device for a metal strip having excellent temperature uniformity in the plate width direction, which heats the metal strip at an equal temperature with respect to the width direction when induction heating is performed above the Curie point.

  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 apparatus using a solenoid type single-turn induction heating coil, when the metal strip is, for example, a magnetic steel strip, it is difficult to heat above the Curie point (about 750 ° C.), and is less than 750 ° C. There is a problem that it can be applied only to heating in a low temperature region. Furthermore, when the metal strip is a non-magnetic material such as aluminum or SUS, it is difficult to heat itself.

  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.

  The inventors have provided a magnetic field diffusion prevention coil for flowing current in a direction opposite to the current of the single-turn induction heating coil in an apparatus for induction heating of the metal band above the Curie point, and the position of the induction heating coil sandwiching the metal band is elongated. By developing the heating device, a heating device is developed in which the gap between the heating coils is about 40 mm and the temperature deviation in the width direction of the metal strip can be within ± 30 ° C., Japanese Patent Laid-Open No. 2003-187951 (Patent Document 1) Filed a patent application.

  However, in the example described in Patent Document 1, by improving the heating efficiency by concentrating the magnetic field by installing a ferrite core on the outer periphery excluding the surface facing the metal strip of the single-turn induction heating coil, There was no problem when the width of the metal band was 70 mm, but when the width of the metal band was increased to 300 mm, a phenomenon was observed in which the temperature of the metal band edge 20-30 mm decreased by about 50 ° C. from the center during heating. When the temperature of the metal band edge portion is lower than that of the center portion, the thermal expansion of the center portion is constrained, and there is a problem that the metal band shape is easily deformed into a wrinkle shape in the width direction.

  Also, the ferrite core loses its function as a magnetic material when a magnetic field equal to or higher than the saturation magnetic flux density is concentrated on the ferrite core, but the saturation magnetic flux density itself decreases when the core itself rises in temperature. For example, the saturation magnetic flux density is 0.4T at 90 ° C, but 0.3T at 140 ° C. Therefore, the speed of the metal strip is increased, and for example, in order to ensure the required magnetic flux density of 0.4 T, the temperature of the ferrite core needs to be 90 ° C. or lower.

  However, since the gap between the heating coils is 40mm (distance between the heating coil and the metal strip is 20mm), considering the variation in the pass line and the shape of the metal strip, radiant heat from the metal strip of about 900 ° C is used for materials with a thickness of 10mm or less. Although heat insulation must be performed to 90 ° C or less, commercially available heat insulation alone was not sufficient.

    Therefore, in the above-mentioned conventional single-turn induction heating coil, when the width of the metal band is increased to 300 mm, the metal band is likely to deteriorate into a wrinkle shape due to a temperature drop of the metal band edge of 20 to 30 mm during heating. From the point of saturation, the upper limit of the line speed could not be increased and was not practical.

    In addition, when heating a metal strip at room temperature to 850 ° C. with only a single-turn induction heating coil, uniform heating in the width direction cannot be performed. Therefore, as shown in FIG. By providing any one of the induction heating coil 1, the contact-type energization heating roll, and the combustion heating furnace, heating was performed from 650 ° C. to less than 750 ° C., for example, 700 ° C., using these conventional heating methods. Later, it is preferable to heat to 850 ° C. by a single turn induction heating coil used in the present invention, which is economical.

  In addition, JP 2004-296368 A (Patent Document 2 below) discloses that when a steel strip having a thickness of 0.15 mm and a width of 70 mm is heated from 600 ° C. to a Curie point or more, a temperature deviation in the width direction ± 30 ° C. (coil width) W: 40 mm, core thickness h: 20 mm, gap G: 40 mm) is described.

 However, the apparatus of Patent Document 2 has a problem that the ferrite core provided to prevent overheating of the edge portion is heated and the edge overheating preventing function is lost in a short period of time.

 JP 2006-068788 (Patent Document 3 below) describes a temperature deviation in the width direction of ± 30 ° C. (coil width) when a steel strip having a thickness of 0.30 mm and a width of 300 mm is heated from 700 ° C. to a Curie point or higher. W: 40 mm, core thickness h: 20 mm, gap G: 40 mm) is described as a heating method.

 However, in the method of Patent Document 3, since the ferrite core coating is not formed on the magnetic field diffusion preventing coil as in the present application, a temperature drop at the edge of the steel strip cannot be avoided.

 Japanese Patent Laid-Open No. 2003-187950 (Patent Document 4 below) discloses that the temperature deviation in the width direction ± 14 ° C. (coil width W) of the steel strip having a thickness of 0.23 mm and a width of 70 mm is heated from room temperature to the Curie point or higher. 6 mm, core thickness h; 3.5 mm, gap G; 6 mm) is described.

However, in the heating coil of Patent Document 4, the ferrite cores that cover the coils are basically in contact with each other, and the adjacent coils are not in direct contact with the ferrite core that covers the coils. The coated ferrite cores were in contact with each other, and there was no technical idea of preventing magnetic field diffusion in adjacent coils.
JP 2003-187951 A JP 2004-296368 A Japanese Unexamined Patent Publication No. 2006-068788 JP 2003-187950 A

  The present invention solves the problems of the prior art as described above, and even if the width of the metal band is widened, the temperature drop width of the metal band edge 20-30 mm is reduced during heating, and the wrinkle shape of the metal band is deteriorated. An object of the present invention is to provide a heating device for a metal strip that can be relaxed and that can relax the upper limit of the line speed that is restricted by magnetic saturation of the ferrite core and has excellent temperature-uniformity in the width direction of the plate that can widen the practicality. And

The present invention has been made as a result of intensive studies in order to solve the problems of the prior art as described above, and the gist of the present invention is as follows.
(1) A single-turn induction heating coil in which induction heating coils arranged with a metal strip sandwiched between them are shifted in the longitudinal direction of the metal strip by the coil width, and in the vicinity of the single-turn induction heating coil. A heating device for a metal strip having a magnetic field diffusion prevention coil arranged to prevent diffusion of a magnetic field by flowing a current in a direction opposite to a current flowing through the single turn induction heating coil, the single turn induction heating A first ferrite core is installed on the outer periphery excluding the surface facing the metal strip of the coil, and the outer periphery excluding the surface facing the metal strip of the magnetic field diffusion prevention coil installed on one surface of the metal strip In addition, the second ferrite core is placed in contact with the first ferrite core,
One of the solenoid-type induction heating coil, the contact-type energization heating roll, and the combustion heating furnace is provided in front of the single-turn induction heating coil. Heating device.
(2) A water cooling jacket for cooling is installed on the side surfaces of the first ferrite core and the second ferrite core, and the first ferrite core, the second ferrite core, the induction heating coil, and the water cooling jacket are opposed to the metal strip. A heating device for a metal strip having excellent temperature uniformity in the plate width direction according to (1), wherein a heat insulating material is provided on the surface.

  According to the present invention, even if the width of the metal band is widened, the temperature drop width of the metal band edge 20 to 30 mm can be reduced during heating, and the deterioration of the wrinkle shape of the metal band can be alleviated and restricted by the magnetic saturation of the ferrite core. Therefore, it is possible to provide an apparatus for heating a metal strip excellent in temperature uniformity in the plate width direction, which can relax the upper limit of the line speed to be received and can expand the practicality, and has a remarkable industrially useful effect.

  Embodiments of the present invention will be described in detail with reference to FIGS.

  FIG. 1 is a diagram for explaining steel plate eddy current and temperature distribution, where the solid line current indicates the surface side of the metal strip and the dotted line current indicates the current on the back side of the metal strip.

  As shown in FIG. 1, for example, the eddy current flowing in the steel plate originally has an edge of 20 to 30 mm, and the eddy current branches. The outermost edge is overheated due to current concentration.

  In addition, when the plate width is 70mm, there is only 35mm on one side, and overheating due to current concentration at the edge is dominant with almost no temperature drop, so it was sufficient to consider only suppression of edge overheating. When the width is increased to 300 mm, it has been found that it is necessary to consider that the temperature is lower than the center portion due to the current density reduction of the edge portion of 20 to 30 mm as shown in FIG.

  FIG. 2 is a side view illustrating an embodiment of a metal band heating device according to the present invention, and FIG. 3 is a perspective view thereof.

  As shown in FIGS. 2 and 3, the heating device of the present embodiment forms a closed loop by single-turn induction heating coils 2 and 2 ′ after heating to a certain temperature with a solenoid type induction heating coil. By flowing a current supplied from a power source in the width direction of the metal strip, an eddy current is generated in the metal strip and heated.

  The metal strip heating apparatus excellent in temperature uniformity in the width direction of the present invention shifts the induction heating coils arranged with the metal strip sandwiched in the longitudinal direction of the metal strip by the coil width. A single-turn induction heating coil 2, 2 ′ is arranged in parallel with the single-turn induction heating coil 2, 2 ′, and a magnetic field is generated by passing a current in a direction opposite to that flowing through the single-turn induction heating coil. A heating apparatus for a metal strip having magnetic field diffusion preventing coils 3 and 3 'for preventing diffusion, wherein the first turn induction heating coils 2 and 2' have a first outer periphery excluding a surface facing the metal strip. A ferrite core 4 ′ is installed, and a second ferrite core 4 is disposed on the outer periphery excluding a surface facing the metal strip of the magnetic field diffusion prevention coil 3 installed on one surface of the metal strip. To touch 4 ' Characterized in that the installation was.

  As shown in FIG. 2, the single-turn induction heating coils 2, 2 ′ arranged with the metal strip sandwiched therebetween are shifted in the longitudinal direction of the metal strip by the coil width (W), so that the plate width direction While the heating efficiency can be improved by preventing the eddy current that goes around the surface layer portion of the cross section from being reversed, the shift amount exceeds the coil width W. Minutes.

  In the present invention, there is no limitation on the method of shifting the single-turn induction heating coils 2, 2 'in the longitudinal direction of the metal strip. For example, as shown in FIG. By bending the coil into an L shape, it is possible to shift in the longitudinal direction of the metal strip while maintaining a closed loop.

  Further, the magnetic field diffusion preventing coils 3 and 3 ′ arranged in parallel in the vicinity of the single-turn induction heating coils 2 and 2 ′ cause a curie point by flowing a current in a direction opposite to the current of the single-turn induction heating coil 2. By preventing diffusion of the magnetic field in heating near (750 ° C.), 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.

  Further, the second ferrite core 4 is installed on the outer periphery excluding the surface facing the metal strip of the magnetic field diffusion preventing coil 3 installed on one surface of the metal strip so as to be in contact with the first ferrite core 4 '. Thereby, the magnetic field diffusion preventing effect of the ferrite core can be enhanced.

  As shown in FIGS. 2 and 4, a first ferrite core 4 ′ is installed on the outer periphery of the single-turn induction heating coil 2, 2 ′ excluding the surface facing the metal strip, and the metal strip The magnetic field is concentrated by placing the second ferrite core 4 in contact with the first ferrite core 4 ′ on the outer periphery excluding the surface facing the metal strip of the magnetic field diffusion preventing coil 3 installed on one surface of Thus, the magnetic flux density can be increased, so that the current density of the metal band center portion is increased as shown in FIGS. Therefore, the current density can be increased even at an edge of 20 to 30 mm where the eddy current at the center is branched and the current density is lowered, and the temperature deviation of this portion can be suppressed within ± 20 ° C. except for the edge of 6 mm.

  However, as a result, the outermost edge is also overheated more than before, and the temperature rises by about 100 ° C from the center, which may cause a problem in the quality of the metal band, but the width and shape of the outermost edge deteriorate. Because it tends to be trimmed and not used as a product, it is rarely a problem for practical use.

  The material of the ferrite core 4 used in the present invention is preferably a material having a high relative resistivity of about 2500 and a high resistivity.

    The ferrite core 4 is preferably installed at the outer periphery of the magnetic field diffusion prevention coil 3 on the upper surface of the metal band as shown in FIGS. Even if installed on the outer periphery, there is an effect.

  Here, the solenoid-type induction heating coil is a heating coil that is arranged so that an object to be heated is wound around the coil and applies an alternating magnetic field in parallel to the object to be heated. The roll is in 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. A combustion heating furnace is a furnace that burns fuel such as gas. A heating furnace that heats the metal strip by raising the internal atmosphere temperature.

  FIG. 7 is a side view of a single turn induction heating coil illustrating a preferred embodiment of the present invention.

  As shown in FIG. 7, it is preferable to install a water cooling jacket 5 for cooling on the side surface of the ferrite core 4 used in the present invention.

  The temperature rise of the ferrite core 4 is converted into a rise in water temperature by the water cooling jacket, and the temperature of the ferrite core 4 can be suppressed to, for example, 90 ° C. or less by continuously removing heat. Even if the current of the induction heating coil is about 3000A, the ferrite core 4 is magnetic It becomes possible not to saturate, and it is possible to continuously heat up to, for example, 850 ° C. without lowering the upper limit value of the sheet feeding speed of the metal strip.

  For the same reason, it is preferable to provide a water cooling jacket 5 ′ also on the ferrite core 4 ′ installed on the outer periphery of the single turn induction heating coil 2.

  The water-cooling jacket may be, for example, a water-contained container or a water-cooled pipe, and the material is preferably a non-magnetic material having high thermal conductivity, such as copper or SUS.

    In addition, water supply to the water cooling jackets 5 and 5 'can be suppressed by independently supplying water to each of the plurality of installed ferrite cores 4 and 4'. Water supply can be continued through other water supply lines even when the water supply stops.

  Further, as shown in FIG. 7, by passing water with the inside of the induction heating coil and magnetic field diffusion prevention coil being hollow, it is possible to prevent overheating of the coil itself, and the above-described water-cooling jacket and the inside of the coil. By cooling from both, the cooling effect of the ferrite core can be enhanced.

  In addition, although embodiment of this invention demonstrated above illustrated the heating apparatus installed horizontally, this invention is applicable also to the heating apparatus installed in the line in which a metal strip is conveyed vertically.

FIG. 6 shows the results of carrying out the metal band heating apparatus of the present invention under the following conditions.
<Conditions for implementation>
Steel plate thickness: 0.3mm, Steel plate width: 300mm, Steel plate speed: 300mm / s
Use coils shown in Fig. 2 to Fig. 4 <Heating coil configuration>
Solenoid induction heating coil 1: Power frequency: 20kHz, Power output: 130kW
Single-turn induction heating coil 2, 2 ': Power frequency: 30kHz, Power output: 30kW, Heating coil width W: 40mm, Core thickness h: 20mm, Gap G: 40mm
The solenoid induction heating coil 1 was heated uniformly to 700 ° C. in the width direction, and the single turn induction heating coil 2 was heated to about 850 ° C.

  FIG. 6 is a diagram showing a change in temperature distribution in the plate width direction when the steel strip is heated using the embodiment of FIGS. 2 to 4 in the metal strip heating apparatus of the present invention.

  As shown in FIG. 6, when the ferrite core is provided in the magnetic field diffusion preventing coil used in the present invention, the steel strip outermost portion is overheated by about 100 ° C. from the center portion, but it is about 50% higher than the conventional center portion. The edge 20-30 mm, which had decreased in temperature, could be suppressed to a temperature decrease of about 20 ° C. from the center, and the risk that the shape of the metal strip deteriorated into wrinkles could be reduced.

  In addition, the most edge part is trimmed finally and is not used as a product, and there are few practical problems.

  FIG. 6 shows an example of the present invention in which the upper magnetic field diffusion prevention coil is provided with a ferrite core, but when the upper and lower magnetic field diffusion prevention coils are provided with a ferrite core, the overheating at the outermost edge is very large. Therefore, it is not practical.

Table 1 shows the results of carrying out a preferred embodiment in which the water cooling jacket is installed on the side surface of the ferrite core in the metal band heating device of the present invention under the following conditions.
<Conditions for implementation>
Steel plate thickness: 0.3 mm, steel plate width: 300 mm, steel plate temperature: 900 ° C
Heat insulation material is installed on the coil and core facing surface of Fig. 4 as shown in Fig. 7 Heat insulation material thickness: 8mm, thermal conductivity 0.2W / m · K
The single-turn induction heating coil was provided with a magnetic field diffusion prevention coil, the upper surface magnetic field diffusion prevention coil was provided with a ferrite core, and the temperature of the ferrite core surface was measured with and without a water cooling jacket.

  As a result, when there is no water cooling jacket as shown in Table 1, the temperature of the ferrite core surface is 141 ° C and the saturation magnetic flux density of the ferrite core is 0.3T, but when there is a water cooling jacket, the temperature of the ferrite core surface is 89 ° C. The saturation magnetic flux density can be increased up to 0.4T, and the upper limit of the plate feed speed was 833mm / s, but it was confirmed that it could be continuously heated to 1333mm / s.

It is a figure explaining a steel plate eddy current and temperature distribution. It is a side view which illustrates embodiment of the heating apparatus of the metal strip in this invention. It is a perspective view which illustrates embodiment of the heating apparatus of the metal strip in this invention. It is a side view which illustrates embodiment of the single turn induction heating coil used for this invention. It is a figure explaining the eddy current in embodiment of this invention. It is a figure which shows the effect of the width direction temperature uniformity in this invention. 1 is a side view of a single turn induction heating coil illustrating a preferred embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solenoid induction heating coil 2, 2 'Single turn induction heating coil 3, 3' Magnetic field diffusion prevention coil 4 '1st ferrite core 4 2nd ferrite core 5, 5' Water-cooling jacket 6 Thermal insulation W Heating coil width h Core thickness G gap

Claims (2)

A single-turn induction heating coil in which the induction heating coils arranged with the metal strip sandwiched between them are shifted in the longitudinal direction of the metal strip by the coil width, and arranged in parallel in the vicinity of the single-turn induction heating coil. A metal strip heating device having a magnetic field diffusion prevention coil for preventing magnetic field diffusion by flowing a current in a direction opposite to the current flowing through the single turn induction heating coil, wherein the metal of the single turn induction heating coil A first ferrite core is installed on the outer periphery excluding the surface facing the band plate, and the outer periphery excluding the surface facing the metal band plate of the magnetic field diffusion prevention coil installed on one surface of the metal band plate, 2 Install the ferrite core in contact with the first ferrite core,
One of the solenoid-type induction heating coil, the contact-type energization heating roll, and the combustion heating furnace is provided in front of the single-turn induction heating coil. Heating device.   Water cooling jackets for cooling are installed on the side surfaces of the first ferrite core and the second ferrite core, and the first ferrite core, the second ferrite core, the induction heating coil, and the water cooling jacket are insulated from the surfaces facing the metal strip. The apparatus for heating a metal strip having excellent temperature uniformity in the plate width direction according to claim 1, wherein a material is provided.

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