Patent Publication Number: US-10327287-B2

Title: Transverse flux induction heating device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional of copending application Ser. No. 13/577,967 filed on Aug. 9, 2012, which is a national stage application of International Application No. PCT/JP2011/053526, filed Feb. 18, 2011, which claims priority to Japanese Patent Application No. 2010-35198, filed on Feb. 19, 2010, the contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a transverse flux induction heating device. In particular, the transverse flux induction heating device is suitably used to inductively heat a conductive sheet by making an alternating magnetic field approximately perpendicularly intersect the conductive sheet. 
     DESCRIPTION OF RELATED ART 
     In the past, heating a conductive sheet such as a steel sheet, using an induction heating device has been performed. The induction heating device generates Joule heat based on an eddy current which is induced in the conductive sheet by an alternating magnetic field (an alternating-current magnetic field) generated from a coil, in the conductive sheet, and heats the conductive sheet by the Joule heat. A transverse flux induction heating device is one type of such an induction heating device. The transverse flux induction heating device heats a conductive sheet of a heating target by making an alternating magnetic field approximately perpendicularly intersect the conductive sheet. 
     In the case of using such a transverse flux induction heating device, unlike the case of using a solenoid-type induction heating device, there is a problem in that both ends (both side ends) in the width direction of the conductive sheet of the heating target become overheated. 
     The techniques described in Patent Citation 1 and Patent Citation 2 are techniques related to such a problem. 
     In the technique described in Patent Citation 1, a movable plain shielding plate made of a non-magnetic metal is provided between a coil and each of both side ends of a conductive sheet of a heating target. 
     Further, in the technique described in Patent Citation 2, a rhombic coil and an oval coil which have different heating patterns are disposed along the conveyance direction of a conductive sheet of a heating target, thereby heating the conductive sheet in a desired heating pattern with respect to the width direction of the conductive sheet. 
     PATENT CITATION 
     [Patent Citation 1] Japanese Unexamined Patent Application, First Publication No. S62-35490 
     [Patent Citation 2] Japanese Unexamined Patent Application, First Publication No. 2003-133037 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, by only providing a simple plate-shaped shielding plate between the coil and each of both side ends of the conductive sheet of the heating target, as in the technique described in Patent Citation 1, since the eddy current spreads in an area slightly to the inside of both side ends of the conductive sheet, eddy current density is small, and since eddy currents flowing in both side ends of the conductive sheet cannot flow out of the conductive sheet, eddy current density becomes large at both side ends. Therefore, it is difficult to lower the temperatures of both side ends of the conductive sheet and the smoothness of the temperature distribution in the width direction of the conductive sheet is also significantly lowered (in particular, the slope of the temperature distribution at each of both side ends of the conductive sheet becomes large). 
     Further, in the technique described in Patent Citation 2, it is possible to suppress lowering of the smoothness of the temperature distribution in the width direction of a specific conductive sheet. However, if the sheet width of the conductive sheet is changed, the coil has to be reset depending on the sheet width. Therefore, a mechanism for moving the coil is required and it is difficult to easily and quickly respond to a change in sheet width. 
     In addition, in the techniques described in Patent Citation 1 and Patent Citation 2, if the conductive sheet moves in a meandering manner, the smoothness of the temperature distribution in the width direction of the conductive sheet is lowered. 
     The present invention has been made in view of such problems and has an object of providing a transverse flux induction heating device which allows unevenness of a temperature distribution in the width direction of a conductive sheet of a heating target to be reduced and allows variations in temperature distribution in the width direction of the conductive sheet of the heating target due to meandering of the conductive sheet to be reduced. 
     Methods for Solving the Problem 
     (1) A transverse flux induction heating device according to an aspect of the present invention allows an alternating magnetic field to intersect the sheet face of a conductive sheet which is conveyed in one direction, thereby inductively heating the conductive sheet. The transverse flux induction heating device includes: a heating coil disposed such that a coil face faces the sheet face of the conductive sheet; a core around which the heating coil is coiled; a shielding plate formed of a conductor and disposed between the core and a side end portion in a direction perpendicular to the conveyance direction of the conductive sheet; and a non-conductive soft magnetic material which is attached to the shielding plate, wherein the shielding plate is interposed between the core and the non-conductive soft magnetic material. 
     (2) The transverse flux induction heating device according to the above (1) may further include a heat-resistant plate which is attached to the non-conductive soft magnetic material, wherein the heat-resistant plate is disposed closer to the conductive sheet than the non-conductive soft magnetic material. 
     (3) In the transverse flux induction heating device according to the above (1), the shielding plate may have a cross section parallel to the coil face, and the cross section may include the non-conductive soft magnetic material. 
     (4) In the transverse flux induction heating device according to the above (1), a depressed portion which faces the side end portion in the direction perpendicular to the conveyance direction of the conductive sheet may be formed in the surface facing the conductive sheet of the shielding plate and the non-conductive soft magnetic material may be housed in the depressed portion. 
     (5) In the transverse flux induction heating device according to the above (4), a portion which is tapered off toward a side close to a central portion in a direction perpendicular to the conveyance direction of the conductive sheet from a side away from the central portion in the direction perpendicular to the conveyance direction of the conductive sheet may be included in the depressed portion. 
     (6) In the transverse flux induction heating device according to the above (4), a first portion which is tapered off toward the downstream side from the upstream side in the conveyance direction of the conductive sheet and a second portion which is tapered off toward the upstream side from the downstream side in the conveyance direction of the conductive sheet may be included in the depressed portion, and the first portion and the second portion may face each other in the conveyance direction of the conductive sheet. 
     (7) In the transverse flux induction heating device according to the above (6), the first portion may be rounded toward the downstream side and the second portion may be rounded toward the upstream side. 
     Effects of the Invention 
     According to the present invention, the non-conductive soft magnetic material is mounted on the shielding plate which is disposed between the core around which the coil is coiled and an end portion in the width direction of the conductive sheet. Through the non-conductive soft magnetic material, the magnitude of an eddy current in the shielding plate, which flows in the vicinity of the non-conductive soft magnetic material, can be made large. Therefore, unevenness of the temperature distribution in the width direction of the conductive sheet of a heating target can be reduced and variations in the temperature distribution in the width direction of the conductive sheet of the heating target due to meandering of the conductive sheet can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view showing one example of the schematic configuration of a continuous annealing line for a steel sheet according to an embodiment of the present invention. 
         FIG. 2A  is a vertical cross-sectional view showing one example of the configuration of an induction heating device according to this embodiment. 
         FIG. 2B  is a vertical cross-sectional view showing one example of the configuration of the induction heating device according to this embodiment. 
         FIG. 2C  is a fragmentary perspective view showing one example of the configuration of the induction heating device according to this embodiment. 
         FIG. 3  is a diagram showing one example of the configurations of an upper side heating coil and a lower side heating coil according to this embodiment. 
         FIG. 4A  is a top view showing one example of the configuration of a shielding plate according to this embodiment. 
         FIG. 4B  is a vertical cross-sectional view showing one example of the configuration of the shielding plate according to this embodiment. 
         FIG. 4C  is a vertical cross-sectional view showing one example of the configuration of the shielding plate according to this embodiment. 
         FIG. 4D  is a fragmentary view when an area including a shielding plate  31   d  according to this embodiment is viewed from directly above a steel strip  10 . 
         FIG. 4E  is a transverse cross-sectional view showing one example of the configuration of the shielding plate according to this embodiment. 
         FIG. 5  is a diagram showing one example of the relationship between the amount of insertion of the shielding plate and a width temperature deviation ratio in an example using this embodiment. 
         FIG. 6A  is a top view showing one example of the configuration of a shielding plate according to the first modified example of this embodiment. 
         FIG. 6B  is a top view showing one example of the configuration of a shielding plate according to the second modified example of this embodiment. 
         FIG. 6C  is a vertical cross-sectional view showing one example of the configuration of a shielding plate according to the third modified example of this embodiment. 
         FIG. 7A  is a vertical cross-sectional view showing one example of the configuration of a shielding plate according to the fourth modified example of this embodiment. 
         FIG. 7B  is a vertical cross-sectional view showing one example of the configuration of a shielding plate according to the fifth modified example of this embodiment. 
         FIG. 7C  is a vertical cross-sectional view showing one example of the configuration of a shielding plate according to the sixth modified example of this embodiment. 
         FIG. 8A  is a perspective view showing one example of the configuration of a shielding plate according to the seventh modified example of this embodiment. 
         FIG. 8B  is a perspective view showing one example of the configuration of a shielding plate according to the eighth modified example of this embodiment. 
         FIG. 8C  is a perspective view showing one example of the configuration of a shielding plate according to the ninth modified example of this embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, an embodiment of the present invention will be described referring to the drawings. In this embodiment, a case where a transverse flux induction heating device is applied to a continuous annealing line for a steel sheet is described as an example. In addition, in the following description, the “transverse flux induction heating device” is referred to as an “induction heating device” for brevity, as necessary. 
     [Configuration of Continuous Annealing Line] 
       FIG. 1  is a side view showing one example of the schematic configuration of a continuous annealing line for a steel sheet. In addition, in each drawing, for convenience of explanation, only the necessary configuration is simplified and shown. 
     In  FIG. 1 , a continuous annealing line  1  includes a first container  11 , a second container  12 , a third container  13 , a first sealing roller assembly  14 , a conveyance unit  15 , a second sealing roller assembly  16 , a gas supply unit  17 , an alternating-current power supply unit  18 , rollers  19   a  to  19   u  ( 19 ), and an induction heating device  20 . 
     The first sealing roller assembly  14  transports a steel strip (a strip-shaped sheet, a conductive sheet)  10  into the first container  11  while shielding the first container  11  from the external air. The steel strip  10  conveyed into the first container  11  by the first sealing roller assembly  14  is conveyed into the second container  12  by the rollers  19   a  and  19   b  in the first container  11 . The steel strip  10  conveyed into the second container  12  is conveyed into the first container  11  again by the rollers  19   g  and  19   h  while being heated by the induction heating device  20  disposed above and below the horizontal portion of the second container  12  (the steel strip  10  which is conveyed). Here, the induction heating device  20  is electrically connected to the alternating-current power supply unit  18  and receives alternating-current power from the alternating-current power supply unit  18 , thereby generating an alternating magnetic field which intersects approximately perpendicularly to the sheet face of the steel strip  10 , and inductively heating the steel strip  10 . In addition, the details of the configuration of the induction heating device  20  will be described later. Further, in the following explanation, “electrical connection” is referred to as “connection” for brevity, as necessary. 
     The steel strip  10  returned into the first container  11  is conveyed to the conveyance unit  15  by way of a soaking and slow cooling stage by the rollers  19   c  to  19   f . The steel strip  10  conveyed to the conveyance unit  15  is conveyed into the third container  13  by the rollers  19   i  and  19   j . The steel strip  10  conveyed into the third container  13  is conveyed while being moving in a vertically up and down manner by the rollers  19   k  to  19   u  and rapidly cooled in the third container  13 . 
     The second sealing roller assembly  16  sends the steel strip  10  rapidly cooled in this way to a post-process while blocking the third container  13  from external air. 
     Into “the first container  11 , the second container  12 , the third container  13 , and the conveyance unit  15 ” which become a “transport pathway of the steel strip  10 ” as described above, non-oxidizing gas is supplied by the gas supply unit  17 . Then, by “the first sealing roller assembly  14  and the second sealing roller assembly  16 ” which block the inside (the inside of the continuous annealing line  1 ) from the outside (external air), a non-oxidizing gaseous atmosphere is maintained in the first container  11 , the second container  12 , the third container  13 , and the conveyance unit  15 . 
     [Configuration of Induction Heating Device] 
       FIGS. 2A to 2C  are diagrams showing one example of the configuration of the induction heating device. 
     Specifically,  FIG. 2A  is a diagram showing one example of the induction heating device  20  in this embodiment, as viewed from a side of the continuous annealing line, and is a vertical cross-sectional view cut (in the up-and-down direction in  FIG. 1 ) along the longitudinal direction of the steel strip  10 . In  FIG. 2A , the steel strip  10  is conveyed in the left direction (refer to an arrow pointing from the right to the left in  FIG. 2A ). Further,  FIG. 2B  is a vertical cross-sectional view showing one example of the induction heating device  20  in this embodiment, as viewed in a direction of A-A′ in  FIG. 1  (that is, a diagram as viewed from the downstream in a sheet conveyance direction). In  FIG. 2B , the steel strip  10  is conveyed in a direction from the back of the drawing to the front. Further,  FIG. 2C  is a fragmentary perspective view partially showing one example of the induction heating device  20  in this embodiment. In  FIG. 2C , a lower right area shown in  FIG. 2B  is looked down from above the steel strip  10 . 
     In  FIGS. 2A to 2C , the induction heating device  20  includes an upper side inductor  21  and a lower side inductor  22 . 
     The upper side inductor  21  includes a core  23 , an upper side heating coil (a heating coil)  24 , and shielding plates  31   a  and  31   c.    
     The upper side heating coil  24  is a conductor coiled around the core  23  through a slot of the core  23  (here, a depressed portion of the core  23 ) and is a coil (a so-called single turn) in which the number of turns is “1”. Further, as shown in  FIG. 2A , the upper side heating coil  24  has a portion, the vertical cross-sectional shape of which is a hollow rectangle. A water-cooling pipe is connected to the end face of a hollow portion of the hollow rectangle. Cooling water which is supplied from the water-cooling pipe flows in the hollow portion (the inside of the upper side heating coil  24 ) of the hollow rectangle, so that the upper side inductor  21  is cooled. Further, the shielding plates  31   a  and  31   c  are mounted on the bottom surface (the slot side) of the core  23 . 
     In addition, in  FIG. 2A , a length l 1  in the upper side inductor  21  is 45 [mm], a length l 2  is 180 [mm], a length l 3  is 80 [mm], a length l 4  is 180 [mm], a length l 5  is 45 [mm], a length l 6  is 45 [mm], and a length l 7  is 45 [mm]. Further, a width W of the steel strip  10  is 900 [mm] and a thickness d s  is 0.3 [mm]. However, these dimensions are not limited to the values described above. 
     The lower side inductor  22  includes a core  27 , a lower side heating coil (a heating coil)  28 , and shielding plates  31   b  and  31   d , similarly to the upper side inductor  21 . 
     The lower side heating coil  28  is also a conductor coiled around the core  27  through a slot of the core  27  and is a coil (a so-called single turn) in which the number of turns is “1”, similarly to the upper side heating coil  24 . Further, the lower side heating coil  28  has a portion, the vertical cross-sectional shape of which is a hollow rectangle, similarly to the upper side heating coil  24 . A water-cooling pipe is connected to the end face of a hollow portion of the hollow rectangle and can flow cooling water into the hollow portion of the hollow rectangle. 
     Further, a coil face (a face in which a loop is formed; a face in which a line of magnetic force penetrates) of the upper side heating coil  24  of the upper side inductor  21  and a coil face of the lower side heating coil  28  of the lower side inductor  22  face each other with the steel strip  10  interposed therebetween. In addition, the plate faces of the shielding plates  31   a  to  31   d  ( 31 ) face side end portions (edges) in the sheet width direction of the steel strip  10 . In order to satisfy such a positional relationship, the upper side inductor  21  is provided further on the upper side (in the vicinity of the upper surface of the horizontal portion of the second container  12 ) than the steel strip  10  and the lower side inductor  22  is provided further on the lower side (in the vicinity of the lower surface of the horizontal portion of the second container  12 ) than the steel strip  10 . 
     As described above, the upper side inductor  21  and the lower side inductor  22  are different in the position to be disposed, but have the same configuration. 
     Further, in this embodiment, the shielding plates  31   a  to  31   d  can be individually moved in the width direction (a direction of a double-headed arrow shown in  FIG. 2B ) of the steel strip  10  based on an operation of a driving device (not shown). 
     Further, in this embodiment, a distance d between the upper side heating coil  24  and the lower side heating coil  28 , the heating coil widths  12  and  14  in the upper side heating coil  24 , and the heating coil widths  12  and  14  in the lower side heating coil  28  are the same. Further, a position where an “overlap length R in the width direction of the steel strip  10 ” between each of both side end portions of the steel strip  10  and each of the shielding plates  31   a  to  31   d  is 90 [mm] is defined as the reference position. 
     Here, the heating coil width is the length in the width direction of the upper side heating coil  24  (the lower side heating coil  28 ) that is in the slot. In the example shown in  FIG. 2A , the heating coil width is equal to the length in the width direction of each of the copper pipes  41   a  to  41   d  shown in  FIG. 3 , which will be described later, and is approximately the same length as the width of the slot of each of the cores  23  and  27 . 
     In addition, in the following explanation, each of the heating coil width of the upper side heating coil  24  and the heating coil width of the lower side heating coil  28  is simply referred to as a heating coil width, as necessary, and the distance between the upper side heating coil  24  and the lower side heating coil  28  is referred to as a gap, as necessary. 
     [Configuration of Heating Coil] 
       FIG. 3  is a diagram showing one example of the configurations of the upper side heating coil  24  and the lower side heating coil  28 . In addition, an arrow shown in  FIG. 3  represents one example of a direction in which an electric current flows at a certain time. 
     As shown in  FIG. 3 , the upper side heating coil  24  has the copper pipes  41   a  and  41   b , and a copper bus bar (a connection plate)  42   b  which is connected to the base end sides of the copper pipes  41   a  and  41   b . Further, the lower side heating coil  28  has the copper pipes  41   c  and  41   d , and a copper bus bar  42   f  which is connected to the base end sides of the copper pipes  41   c  and  41   d.    
     One end (the front end side of the copper pipe  41   a ) of the upper side heating coil  24  and an output terminal on one side of the alternating-current power supply unit  18  are mutually connected through a copper bus bar  42   a . On the other hand, the other end (the front end side of the copper pipe  41   b ) of the upper side heating coil  24  and one end (the front end side of the copper pipe  41   c ) of the lower side heating coil  28  are mutually connected through copper bus bars  42   c  to  42   e . Further, the other end (the front end side of the copper pipe  41   d ) of the lower side heating coil  28  is mutually connected to an output terminal on the other side of the alternating-current power supply unit  18  through copper bus bars  42   i ,  42   h , and  42   g.    
     As described above, the upper side heating coil  24  and the lower side heating coil  28  are connected in series with respect to the alternating-current power supply unit  18  by the combination of the copper pipes  41   a  to  41   d  ( 41 ) and the copper bus bars  42   a  to  42   i  ( 42 ) and form coils each of which the number of turns is “1”. In  FIG. 3 , a large magnetic flux is generated toward the bottom from the top of a central portion surrounded by the copper pipes  41  and the copper bus bars  42 , and the magnetic flux passes through the steel strip  10 , whereby Joule heat is generated in the steel strip  10 , so that the steel strip  10  is heated. 
     In addition, here, in order to clearly illustrate the configurations of the upper side heating coil  24  and the lower side heating coil  28 , as shown in  FIG. 3 , the copper pipes  41   a  to  41   d  and the copper bus bars  42   a  to  42   g  are connected to each other. However, when the upper side heating coil  24  and the lower side heating coil  28  are coiled around the cores  23  and  27 , there is a need to pass (attach) the copper pipes  41   a  to  41   d  through the slots of the cores  23  and  27 . Therefore, in fact, the copper bus bars  42  are attached to the copper pipes  41   a  to  41   d  to avoid portions where the copper pipes  41  are installed to the cores  23  and  27 . 
     &lt;Configuration of Shielding Plate&gt; 
       FIGS. 4A to 4E  are diagrams showing one example of the configuration of the shielding plate  31 . 
     Specifically,  FIG. 4A  is a top view of the shielding plate  31  when viewed from directly above (the steel strip  10  side). Further,  FIG. 4B  is a vertical cross-sectional view as viewed from the direction of A-A′ in  FIG. 4A .  FIG. 4C  is a vertical cross-sectional view as viewed from the direction of B-B′ in  FIG. 4A .  FIG. 4D  is a view when an area including the shielding plate  31   d  shown in  FIG. 2C  is viewed from directly above the steel strip  10 .  FIG. 4E  is a transverse cross-sectional view as viewed from the direction of C-C′ in  FIG. 4B . In addition, in  FIG. 4D , only a portion which is required to explain the positional relationship between the steel strip  10  and the shielding plate  31   d  is shown. Further, in  FIG. 4D , eddy currents I e , I h1 , and I h2  which flow in the shielding plate  31   d  are conceptually shown. In addition, the steel strip  10  is conveyed in the direction of an arrow shown in the right end in  FIGS. 4A and 4D . 
     In addition, a conveyance direction of the steel strip  10  approximately corresponds to the depth direction of the shielding plate  31 , and a direction (the width direction of the steel strip  10 ) perpendicular to the conveyance direction of the steel strip  10  on the sheet face approximately corresponds to the width direction of the shielding plate. Further, the plate thickness (the thickness) direction of the shielding plate  31  approximately corresponds to a direction (the sheet thickness direction of the steel strip  10 ) perpendicular to the coil face of the heating coil (for example, the upper side heating coil  24 ). 
     In  FIGS. 4A to 4C , the shielding plate  31  is made of copper and has depressed portions  51   a  and  51   b  ( 51 ) having the same size and shape. The depressed portions  51   a  and  51   b  are disposed to have a distance therebetween in the conveyance direction of the steel strip  10 . 
     As shown in  FIG. 4A , the shape (the opening shape) in the plate face direction (the plate thickness direction of the shielding plate  31 ) of each of the depressed portions  51   a  and  51   b  is a rhombus in which each of the corner portions  54   a  to  54   h  ( 54 ) is rounded. 
     In  FIG. 4A , a distance P between a corner portion which is an end portion of the depressed portion  51   a  and is on the upstream side in the conveyance direction of the steel strip  10  and a corner portion which is an end portion of the depressed portion  51   b  and is on the downstream side in the conveyance direction of the steel strip  10  is 150 [mm]. Further, a distance Q between a corner portion which is an end portion of the depressed portion  51   a  and is located in the center in the conveyance direction of the steel strip  10  and a corner portion which is an end portion of the depressed portion  51   b  and is located in the center in the conveyance direction of the steel strip  10  is 310 [mm]. 
     As shown in  FIG. 4D , in this embodiment, the shielding plate  31  is moved in the width direction of the steel strip  10  such that a side end  10   a  of the steel strip  10  and the depressed portions  51   a  and  51   b  overlap each other when viewed from the up-and-down direction. As a specific example thereof, the side end  10   a  of the steel strip  10  and the longest portions on the plate face of the depressed portions  51   a  and  51   b  (diagonal line portions of the rounded rhombuses parallel to the conveyance direction of the steel strip  10 ) overlap each other when viewed from the up-and-down direction (a direction perpendicular to the sheet face of the steel strip  10 ). 
     By disposing the shielding plate  31  so as to be in such a positional relationship, a main magnetic flux, which is generated by operating the induction heating device  20 , and thereby flowing an alternating current in the upper side heating coil  24  and the lower side heating coil  28 , can be shielded by the shielding plate  31 . However, eddy currents are generated in both side end portions of the steel strip  10  by the main magnetic flux, and the eddy current touches the side end of the steel strip, so that a current density in the side end becomes high and a difference in temperature occurs between the side end and the vicinity thereof. Therefore, the inventors have found from the results of extensive studies that the difference in temperature can be reduced by housing non-conductive soft magnetic plates  52   a  and  52   b  ( 52 ), each of which is composed of a soft magnetic ferrite (for example, a Mn—Zn-based ferrite or a Ni—Zn-based ferrite) or the like, into the above-mentioned depressed portions  51   a  and  51   b . Here, the non-conductive soft magnetic plates  52   a  and  52   b  can be fixed to the depressed portions  51   a  and  51   b  of the shielding plate  31  using, for example, an adhesive. 
     That is, as shown in  FIG. 4D , if a portion of the eddy current I e  which flows so as to go around the end portion of the shielding plate  31  is branched so that the eddy currents I h1  and I h2  flow along the edges of the depressed portions  51   a  and  51   b , an eddy current of the steel strip  10  which is generated by magnetic fields that are created by the eddy currents I h1  and I h2  cancels out and weakens an eddy current (an eddy current due to the main magnetic flux) which flows in the side end portion of the steel strip  10 . As a result, the effect of pushing the eddy current which flows in the side end portion of the steel strip  10  into the inside in the width direction of the steel strip  10  can be produced, so that homogenization of eddy current density in the vicinity of the side end  10   a  of the steel strip  10  progresses and a difference in temperature between the side end portion (a high-temperature portion) of the steel strip  10  and a portion (a low-temperature portion) further inside than the side end portion is reduced. 
     Therefore, large eddy currents I h1  and I h2  need to flow along the edges of the depressed portions formed in the shielding plate. The inventors have obtained knowledge that in the shielding plate with only a depressed portion simply formed therein, there is a possibility that the effect of reducing the above-mentioned difference in temperature cannot be reliably obtained. This is considered to be because an eddy current continuously flows through the bottom surface of the depressed portion. Therefore, the inventors have found that by housing the non-conductive soft magnetic plates  52   a  and  52   b  in the depressed portions  51   a  and  51   b  of the shielding plate  31 , as described above, it is possible to strengthen a magnetic field which is generated by the eddy current flowing in the shielding plate  31  due to the main magnetic flux. By the strengthening of the magnetic field, it is possible to make the magnitude of the eddy current which is branched from a pathway going around the end portion of the shielding plate  31  larger. As a result, it is possible to make the magnitudes of the eddy currents I h1  and I h2  which flow along the edges of the depressed portions  51   a  and  51   b  larger (than where are the non-conductive soft magnetic plates  52   a  and  52   b  not being housed). 
     For the reason as described above, in this embodiment, the non-conductive soft magnetic plates (non-conductive soft magnetic materials)  52   a  and  52   b  are housed in the depressed portions  51   a  and  51   b  formed in the shielding plate  31 . In the case of using conductive materials in place of the non-conductive soft magnetic plates  52   a  and  52   b , since the shielding plate itself is conductive, the conductive material and the shielding plate act as an integrated conductive member, so that it is not possible to strongly limit the distribution of the eddy current to the edges of the depressed portions  51   a  and  51   b.    
     In addition, in this embodiment, heat-resistant plates  53   a  and  53   b  ( 53 ) which protect the non-conductive soft magnetic plates  52   a  and  52   b  from heat from the outside are disposed on the top (the steel strip  10  side) of the non-conductive soft magnetic plates  52   a  and  52   b  in the depressed portions  51   a  and  51   b  and fixed thereto by, for example, an adhesive. 
     In  FIGS. 4A to 4C , a thickness D of the shielding plate  31  is 25 [mm] and a depth D m  of each of the depressed portions  51   a  and  51   b  is 15 [mm]. Each of the non-conductive soft magnetic plates  52   a  and  52   b  has a shape corresponding with the shape (the shape of a cross-section perpendicular to the thickness direction of the shielding plate  31 ) in the plate face direction of the bottom portion of each of the depressed portions  51   a  and  51   b , and a thickness D F  thereof is 5 [mm]. However, these dimensions are not limited to the values described above. The inventors have confirmed that in a frequency range (5 [kHz] to 10 [kHz]) which is used in the induction heating device  20 , if the thickness D F  is equal to or more than 1 [mm] (and is equal to or less than the depth of each of the depressed portions  51   a  and  51   b ), in a case where the non-conductive soft magnetic plates  52   a  and  52   b  are housed and a case where the non-conductive soft magnetic plates  52   a  and  52   b  are not housed, a sufficient difference occurs in the effect of reducing the above-mentioned difference in temperature. Further, each of the heat-resistant plates  53   a  and  53   b  has a shape corresponding with the shape (the shape of a cross-section perpendicular to the thickness direction of the shielding plate  31 ) in the plate face direction of the bottom portion of each of the depressed portions  51   a  and  51   b  of the shielding plate  31 , and a thickness D D  thereof is 10 [mm]. 
     As described above, by housing the non-conductive soft magnetic plates  52   a  and  52   b  in the depressed portions  51   a  and  51   b , a magnetic field which is generated by an eddy current flowing in the shielding plate  31  due to the main magnetic flux is strengthened. By the strengthening of the magnetic field, the magnitudes of the eddy currents I h1  and I h2  flowing along the edges of the depressed portions  51   a  and  51   b  also become larger. Therefore, magnetic fields which are generated by these large eddy currents also become large, so that a larger eddy current which cancels out the eddy current flowing in the side end portion of the steel strip  10  can be produced in the vicinity of the side end portion. As a result, the effect of sufficiently pushing the eddy current of the side end portion of the steel strip  10  which is produced by the main magnetic flux into the inside in the width direction of the steel strip  10  is produced. 
     Further, as described above, in this embodiment, the corner portions  54   a  to  54   h  of the depressed portions  51   a  and  51   b  are rounded. However, it is acceptable if at least the corner portions  54   a  and  54   e  which are the “corner portions on the downstream side in the conveyance direction of the steel strip  10 ” of the depressed portions  51   a  and  51   b  are rounded so as to protrude in the downstream side direction and the corner portions  54   b  and  54   f  which are the “corner portions on the upstream side in the conveyance direction of the steel strip  10 ” of the depressed portions  51   a  and  51   b  are rounded so as to protrude in the upstream side direction. If doing so, even if the steel strip  10  moves in a meandering manner, it is possible to reduce the amount of change in the “overlap length in the conveyance direction of the steel strip  10 ” between the side end  10   a  of the steel strip and each of the depressed portions  51   a  and  51   b ″ when viewed from the up-and-down direction, and it is also possible to reduce the amount of change in the effect of pushing the eddy current of the side end portion of the steel strip  10  further toward the inside than the side end portion. Further, as described above, since the eddy currents I h1  and I h2  flowing along the edges of the depressed portions  51   a  and  51   b  become large due to the non-conductive soft magnetic plates  52   a  and  52   b , even if the steel strip  10  moves in a meandering manner, the magnitudes of the eddy currents I h1  and I h2  and the effect of pushing the eddy current flowing in the side end portion of the steel strip  10  further toward the inside than the side end portion can be maintained to some extent. Therefore, even if the steel strip  10  moves in a meandering manner, a change in temperature distribution in the width direction of the steel strip  10  can be reduced. 
     EXAMPLE 
       FIG. 5  is a diagram showing one example of the relationship between the amount of insertion of the shielding plate and a width temperature deviation ratio. 
     The amount of insertion of the shielding plate corresponds to the “overlap length R in the width direction of the steel strip  10 ” between each of both side end portions of the steel strip  10  and each shielding plate (refer to  FIG. 2B ). Further, the width temperature deviation ratio is a value (=sheet width central portion temperature/sheet end portion temperature) obtained by dividing the temperature of the central portion in a temperature distribution in the width direction of the steel strip  10  (the sheet width central portion temperature) by the temperature of the end portion (the sheet end portion temperature). 
     In  FIG. 5 , in a graph A 1 , a plain shielding plate in which no depressed portion is formed is used. In a graph A 2 , a shielding plate having the depressed portions in which the non-conductive soft magnetic plates are housed, as in this embodiment, is used. 
     Here, the graphs shown in  FIG. 5  are based on the results of experiments performed under the following conditions. 
     Heating coil width: 1300 [mm] 
     Material of core: ferrite 
     Material to be heated: stainless steel sheet (width of 900 [mm], and thickness of 0.3 [mm]) 
     Gap between coils: 180 [mm] 
     Sheet conveyance speed: 50 [mpm (m/min.)] 
     Heating temperature: 400 to 730 [° C.] (the temperature increase of the center is set to be 330 [° C.]) 
     Power-supply frequency: 8.5 [kHz] 
     Current: 3650 [AT] 
     Material of shielding plate: copper 
     External dimensions of shielding plate: width of 230 [mm], depth of 600 [mm], and thickness of 25 [mm] 
     Shape of depressed portion of shielding plate:  FIG. 4A  (graph A 2 ) 
     Material of non-conductive soft magnetic plate: Ni—Zn ferrite 
     Thickness of non-conductive soft magnetic plate: 5 [mm] 
     Standard of amount of insertion of shielding plate: 90 [mm] 
     In  FIG. 5 , it can be found that the smaller the width temperature deviation ratio (the closer to 1 the width temperature deviation ratio), the more uniform a temperature distribution in the width direction of the steel strip  10  can be. Further, it can be found that the smaller the slope of the graph, the greater the change in temperature distribution in the width direction of the steel strip  10  can be reduced even if the steel strip  10  moves in a meandering manner. 
     In  FIG. 5 , it can be found that if the shielding plate having the depressed portions in which the non-conductive soft magnetic plates are housed is used, as in this embodiment, both the smoothing of a temperature distribution in the width direction of the steel strip  10  and reduction of a change in the temperature distribution in the width direction of the steel strip  10  at the time of meandering of the steel strip  10  can be realized. 
     SUMMARY 
     As described, in this embodiment, the shielding plate  31  is disposed between the side end portion of the steel strip  10  and each of the cores  23  and  27  (the upper side heating coil  24  and the lower side heating coil  28 ). In the shielding plate  31 , two depressed portions  51   a  and  51   b  are formed so as to have a distance therebetween in the conveyance direction of the steel strip  10 . In addition, the non-conductive soft magnetic plates  52   a  and  52   b  are housed in the depressed portions  51   a  and  51   b . Therefore, it is possible to strengthen a magnetic field which is generated by the eddy current flowing in the shielding plate  31   d  due to the main magnetic flux and make the magnitudes of the eddy currents I h1  and I h2  flowing along the edges of the depressed portions  51   a  and  51   b  larger. As a result, the smoothing of a temperature distribution in the width direction of the steel strip  10  can be realized. Further, by flowing the large eddy currents I h1  and I h2  along the edges of the depressed portions  51   a  and  51   b  in this manner, even if the steel strip  10  moves in a meandering manner, the effect in which the eddy currents I h1  and I h2  push the eddy current flowing in the side end portion of the steel strip  10  further toward the inside than the side end portion can be maintained to some extent. Accordingly, even if the steel strip  10  moves in a meandering manner, a change in temperature distribution in the width direction of the steel strip  10  can be reduced. In addition, even in a case where the steel strip  10  moves in a meandering manner, a magnetic field which is generated by the eddy current flowing in the shielding plate  31   d  pushes the side end of the steel strip  10  back to the center in the width direction of the steel strip  10 , so that meandering of the steel strip  10  can be suppressed. 
     Further, in this embodiment, the corner portions  54   a  and  54   e  which are the “corner portions on the downstream side in the conveyance direction of the steel strip  10 ” of the depressed portions  51   a  and  51   b  are rounded so as to protrude in the downstream side direction and the corner portions  54   b  and  54   f  which are the “corner portions on the upstream side in the conveyance direction of the steel strip  10 ” of the depressed portions  51   a  and  51   b  are rounded so as to protrude in the upstream side direction. Therefore, even if the steel strip  10  moves in a meandering manner, it is possible to reduce the amount of change in the “overlap length in the conveyance direction of the steel strip  10 ” between the side end  10   a  of the steel strip and each of the depressed portions  51   a  and  51   b ″ when viewed from the up-and-down direction, so that the amount of change in the push-in effect of the eddy current flowing in the side end portion of the steel strip  10  can also be reduced. Accordingly, a change in temperature distribution in the width direction of the steel strip  10  when the steel strip  10  moves in a meandering manner can be even further reduced. 
     Further, in this embodiment, since the heat-resistant plates  53   a  and  53   b  are disposed on the top (the steel strip  10  side) of the non-conductive soft magnetic plates  52   a  and  52   b , even if the induction heating device is used under high temperature, degradation of the characteristics of the non-conductive soft magnetic plates  52   a  and  52   b  can be prevented. However, in a case where the induction heating device is not used under high temperature, there is no need to necessarily use the heat-resistant plates  53   a  and  53   b . In a case where the heat-resistant plates  53   a  and  53   b  are not used in this manner, the thickness of the non-conductive soft magnetic plate which is housed in the depressed portion of the shielding plate may also be set to be the same as the depth of the depressed portion. In this manner, the thickness of the non-conductive soft magnetic plate may also be the same as the depth of the depressed portion and may also be less than the depth of the depressed portion. 
     MODIFIED EXAMPLES 
     &lt;Shielding Plate&gt; 
       FIGS. 6A to 6C  are diagrams showing modified examples of the configuration of the shielding plate.  FIGS. 6A and 6B  respectively show the first and the second modified examples of the shielding plate and are diagrams showing the shielding plate when viewed from directly above (from the steel strip  10  side). These drawings correspond to  FIG. 4A . 
     In  FIG. 6A , a shielding plate  61  is made of copper and has depressed portions  62   a  and  62   b  ( 62 ) disposed to have a distance therebetween in the conveyance direction of the steel strip  10  and having the same size and shape. In these points, the shielding plate  61  is the same as the shielding plate  31  shown in  FIGS. 4A to 4C . However, as shown in  FIG. 6A , the shape (the opening shape) in the plate face direction of the depressed portion  62   a  is a triangle which is tapered off toward the upstream side from the downstream side in the conveyance direction (a direction of an arrow shown in  FIGS. 6A and 6B ) of the steel strip  10  and in which the corner portions  64   a  to  64   c  ( 64 ) are rounded. In such a case, it is preferable that at least the corner portion  64   a  which is a “corner portion on the upstream side in the conveyance direction of the steel strip  10 ” of the depressed portion  62   a  be rounded so as to protrude in the upstream side direction. 
     Further, the shape (the opening shape) in the plate face direction of the depressed portion  62   b  is a triangle which is tapered off toward the downstream side from the upstream side in the conveyance direction of the steel strip  10  and in which the corner portions  64   d  to  64   f  ( 64 ) are rounded. In such a case, it is preferable that at least the corner portion  64   d  which is a “corner portion on the downstream side in the conveyance direction of the steel strip  10 ” of the depressed portion  62   b  be rounded so as to protrude in the downstream side direction. 
     Further, the non-conductive soft magnetic plates and the heat resistant plates  63   a  and  63   b  ( 63 ), each of which has a shape corresponding with the shape (the shape of a cross-section perpendicular to the thickness direction of the shielding plate  61 ) in the plate face direction of the bottom portion of each of the depressed portions  62   a  and  62   b , are housed in the depressed portions  62   a  and  62   b  and fixed thereto using an adhesive or the like. 
     Further, in  FIG. 6B , a shielding plate  71  is made of copper. As shown in  FIG. 6B , the number of depressed portions  72  which are formed in the shielding plate  71  is one. As shown in  FIG. 6B , the shape in the plate face direction of the depressed portion  72  is a shape in which the “corner portion (the corner portion  54   b ) on the upstream side in the conveyance direction of the steel strip  10 ” of the depressed portion  51   a  shown in  FIGS. 4A to 4C  and the “corner portion (the corner portion  54   e ) on the downstream side in the conveyance direction of the steel strip  10 ” of the depressed portion  51   b  are connected to each other, and the corner portions  74   a  to  74   f  ( 74 ) are rounded. Further, a non-conductive soft magnetic plate and a heat resistant plate  73 , each of which has a shape corresponding with the shape (the shape of a cross-section perpendicular to the thickness direction of the shielding plate  71 ) in the plate face direction of the bottom portion of the depressed portion  72 , are housed in the depressed portion  72  and fixed thereto using an adhesive or the like. 
     As described above, it is preferable that a portion (a second portion) which is tapered off toward the upstream side from the downstream side in the conveyance direction of the steel strip  10  and a portion (a first portion) which is tapered off toward the downstream side from the upstream side in the conveyance direction of the steel strip  10  be included in the depressed portion which is formed in the shielding plate. The first portion and the second portion may also be formed individually ( FIGS. 4A and 6A ) and may also be formed integrally ( FIG. 6B ). In addition, it is preferable that the tapered first and second portions face each other in the conveyance direction of the steel strip  10 . If the shape in the plate face direction of the depressed portion is such a shape, it becomes possible to form the edge of the depressed portion of the shielding plate according to a pathway of an eddy current flowing through the steel strip  10 . Further, in this case, it is preferable that at least the tapered end portion (the tapered portion) among the “corner portions on the upstream side and the downstream side in the conveyance direction of the steel strip  10 ” of the depressed portion be rounded. 
     In addition, the shape (the opening shape) in the plate face direction of the depressed portion which is formed in the shielding plate may also be any shape and the number thereof may also be 1 and may also be 2 or more. 
     Further, it is preferable that a portion (a third portion) which is tapered off toward a side close to the central portion in the width direction (a direction perpendicular to the conveyance direction) of the conductive sheet from a side away from the central portion in the width direction of the conductive sheet be included in the depressed portion. In this case, it is possible to gradually increase the amount of change in the effect in which the magnetic field that is generated by the eddy current flowing in the shielding plate pushes the side end of the steel strip into the center side in the width direction of the steel strip, so that suppression of meandering of the conductive sheet can be more flexibly controlled. For example, in  FIG. 4A , two third portions are included in the two depressed portions  51   a  and  51   b  of the shielding plate  31 . In addition, only a single depressed portion may be formed in the shielding plate and the third portion may be included in the single depressed portion. However, if a plurality of third portions is included in the depressed portion of the shielding plate, it is possible to more uniformly produce the above-mentioned push-in effect. Further, a portion (a fourth portion) which is tapered off toward a side away from the central portion in the width direction of the conductive sheet from a side close to the central portion in the width direction of the conductive sheet may also be included. 
       FIG. 6C  shows the third modified example of the shielding plate and is a vertical cross-sectional views of the shielding plate when cut in the thickness direction of the shielding plate along the conveyance direction of the steel strip  10 .  FIG. 6C  corresponds to  FIG. 4B . 
     In  FIG. 6C , a shielding plate  81  is made of copper and has depressed portions  82   a  and  82   b  ( 82 ) disposed to have a distance therebetween in the conveyance direction of the steel strip  10  and having the same size and shape. Further, the shape (the opening shape) in the plate face direction of each of the depressed portions  82   a  and  82   b  is a rhombus in which each corner portion is rounded. In this manner, the shielding plate  81  shown in  FIG. 6C  and the shielding plate  31  shown in  FIGS. 4A to 4C  are the same in material, shape, and size. However, the shielding plate  81  shown in  FIG. 6C  is formed by superimposing an upper plate  84   a  and a lower plate  84   b  on each other and fixing them to each other. 
     As described above, the shielding plate may also be integrally formed and may also be formed by combining a plurality of members. 
     Moreover, although in this embodiment, the shielding plate is made of copper, the shielding plate is not limited to a copper plate. That is, provided that the shielding plate is a conductor, preferably, a conductor having a relative permeability of 1, the shielding plate may also be formed of any material. For example, the shielding plate can be formed of aluminum. 
     In addition, in this embodiment, by increasing the magnitude of the eddy current in the shielding plate which is generated in the vicinity of the non-conductive soft magnetic plate (the non-conductive soft magnetic material), the magnitude of the eddy current which flows in the side end portion of the steel strip (the conductive sheet)  10  due to the main magnetic flux is reduced. Further, since the conductive shielding plate is interposed between the core (or, the heating coil) and the non-conductive soft magnetic plate, direct passage of the main magnetic flux through the non-conductive soft magnetic plate can be avoided. For this reason, it is acceptable if the induction heating device includes the heating coil, the core, the conductive shielding plate which is disposed between the core and the side end portion in a direction perpendicular to the conveyance direction of the steel strip, and the non-conductive soft magnetic plate which is attached to the shielding plate such that the shielding plate is interposed between the core and the non-conductive soft magnetic plate. 
     For this reason, for example, shielding plates in which the non-conductive soft magnetic plates as shown in  FIGS. 7A to 7C and 8A to 8C  are mounted can be used. In addition,  FIGS. 7A to 7C  are vertical cross-sectional views showing one example of the configuration of each of shielding plates in the fourth to the sixth modified examples of this embodiment. Further,  FIGS. 8A to 8C  are perspective views showing one example of the configuration of each of shielding plates in the seventh to the ninth modified examples of this embodiment. 
     In the fourth modified example of this embodiment shown in  FIG. 7A , non-conductive soft magnetic plates  102   a  and  102   b  ( 102 ) are disposed on a flat shielding plate  101  and the non-conductive soft magnetic plates  102  face the side end portion of the steel strip. In this manner, the non-conductive soft magnetic plates may also be mounted on the shielding plate such that protruded portions are formed on the shielding plate, without forming a depressed portion in the shielding plate. In this case, it is possible to increase an eddy current in the shielding plate in a peripheral portion of the contact surface between the shielding plate and the non-conductive soft magnetic plate. However, since by forming a depressed portion in a shielding plate and disposing a non-conductive soft magnetic plate in the depressed portion, an eddy current can be constrained in an edge of the depressed portion and the distance between an edge of the depressed portion and the non-conductive soft magnetic plate can be reduced, it is possible to secure a larger eddy current at the edge of the depressed portion. For this reason, as shown in  FIG. 7B  (the fifth modified example), it is also acceptable that depressed portions  114   a  and  114   b  ( 114 ) be formed in a shielding plate  111  and non-conductive soft magnetic plates  112   a  and  112   b  ( 112 ) be mounted in the depressed portions  114  of the shielding plate  111  such that protruded portions are formed on the shielding plate  111 . Further, as shown in  FIG. 7C  (the sixth modified example), non-conductive soft magnetic plates  122   a  and  122   b  ( 122 ) in which the shape of the upper surface and the shape of the lower surface are different from each other may also be mounted in depressed portions  124   a  and  124   b  ( 124 ) of a shielding plate  121 . 
     Further, in the seventh modified example shown in  FIG. 8A , a non-conductive soft magnetic plate  202  is mounted on a shielding plate  201  having protruded portions (two rhombic portions)  205   a  and  205   b  ( 205 ). In this case, it is possible to increase eddy currents flowing in edges of the protruded portions  205 . Further, the shape (the outer peripheral shape) of the shielding plate is not particularly limited. In the eighth modified example shown in  FIG. 8B , depressed portions (two rhombic portions)  214   a  and  214   b  ( 214 ) are formed in a shielding plate  211  and the shielding plate  211  has frame portions  216   a  and  216   b  following the outer peripheral shapes (the opening shapes) of the depressed portions  214 . Further, non-conductive soft magnetic plates  212   a  and  212   b  ( 212 ) are housed in the depressed portions  214 . In this case, it is possible to increase eddy currents flowing in edges of the depressed portions  214 . Further, in the ninth modified example shown in  FIG. 8C , protruded portions (two rhombic portions)  225   a  and  225   b  ( 225 ) are formed on a shielding plate  221  and the shielding plate  221  has an outer peripheral shape similar to (following) the outer peripheral shapes (the base end shapes) of the protruded portions  225 . Further, a non-conductive soft magnetic plate  222  is disposed on the shielding plate  221  so as to surround edge portions of the protruded portions  225 . In this case, it is possible to increase eddy currents flowing in edges of the protruded portions  225 . 
     In addition, a heat-resistant plate may also be mounted on the non-conductive soft magnetic plate in each modified example shown in  FIGS. 7A to 7C and 8A to 8C . Further, the shape and the number of depressed portions or protruded portions of the shielding plate in the plate face direction are not particularly limited. Further, the shape and the number of non-conductive soft magnetic plates are also not particularly limited. 
     It is preferable to make the magnitude of the eddy current in the shielding plate which flows through the vicinity of the non-conductive soft magnetic plate, as large as possible. In the following, the configuration of making the eddy current larger will be described. 
       FIG. 4E  is a cross-sectional view as viewed from a direction of C-C′ in  FIG. 4B . As shown in  FIG. 4E , the non-conductive soft magnetic plates  52   a  and  52   b  ( 52 ) are included in the cross section, and a boundary portion (a boundary line) between the shielding plate  31  and each of the non-conductive soft magnetic plates  52  describes a closed curve (a total of two closed curves). That is, a case where the shielding plate surrounds the non-conductive soft magnetic plate and a case where the non-conductive soft magnetic plate surrounds the shielding plate are included in the cross section. In this manner, if the shielding plate has a cross section perpendicular to the thickness direction including the non-conductive soft magnetic material (a cross section parallel to the coil face), the distance between the non-conductive soft magnetic plate and the eddy current in the shielding plate, which is strengthened by the non-conductive soft magnetic plate, can be shortened. Further, the above-mentioned boundary portion describes a closed curve (is ring-shaped), whereby an area of an eddy current which is strengthened can increase and the characteristic of the non-conductive soft magnetic plate can be fully utilized. In addition, in order to make the magnitude of the eddy current in the shielding plate which flows through the vicinity of the non-conductive soft magnetic material, as large as possible, it is preferable that the shielding plate and the non-conductive soft magnetic material be in contact with each other. However, a space (a space as a boundary portion) may also be present between the shielding plate and the non-conductive soft magnetic material such that the non-conductive soft magnetic material can be easily attached to the shielding plate. 
     Further, in the case of using the induction heating device under high temperature or the case of rapidly heating the steel strip, the temperature of the shielding plate sometimes becomes high due to an eddy current. In this case, it is preferable to cool the shielding plate and the non-conductive soft magnetic material using a cooler such as a water-cooling pipe. This cooling method is not particularly limited. For example, the shielding plate may also be cooled by integrally forming a water-cooling line in the shielding plate, or the shielding plate may also be cooled by sending a gas to the shielding plate by a blower. 
     &lt;Non-Conductive Soft Magnetic Plate and Heat-Resistant Plate&gt; 
     A material constituting the non-conductive soft magnetic plate is not limited to a soft magnetic ferrite, provided that it is a non-conductive soft magnetic material. Further, the non-conductive soft magnetic material may also be a material in which powder or particles are packed or compacted, or a material in which a plurality of blocks is combined, rather than a plate. Further, the shape of the non-conductive soft magnetic plate is not particularly limited. If it is possible to dispose a non-conductive soft magnetic plate according to the portion (for example, the edge of the depressed portion) of the inside of the shielding plate, in which the eddy current flows, since it is possible to obtain a magnetic field which enhances the eddy current, for example, the non-conductive soft magnetic plate may also have a hollow portion. However, in order to sufficiently use the magnetism of the non-conductive soft magnetic plate, it is preferable that the non-conductive soft magnetic plate be solid. 
     The heat-resistant plate also need not necessarily be a plate and may also be any material, provided that a heat-resistant material is used. 
     Further, a method of fixing the non-conductive soft magnetic plate and the heat-resistant plate which are housed in the depressed portion, to the inside of the depressed portion is not limited to a method using an adhesive. For example, it is possible to fix them to the depressed portion using a screw with insulation secured between the shielding plate and the non-conductive soft magnetic plate and the heat-resistant plate. 
     &lt;Others&gt; 
     In this embodiment, the disposition place of the induction heating device  20  is not limited to the position shown in  FIG. 1 . That is, provided that it is possible to inductively heat a conductive sheet by a transverse method, the induction heating device  20  may also be disposed anywhere. For example, the induction heating device  20  may also be disposed in the second container  12 . Further, the induction heating device  20  may also be applied to places other than the continuous annealing line. 
     Further, in this embodiment, a case where the heating coil width and the gap between the heating coils are equal to each other has been described as an example. However, the heating coil width and the size of the gap are not particularly limited. However, it is preferable that the heating coil width be equal to or greater than the gap (or, the heating coil width be greater than the gap). In this case, a main magnetic field which is generated from the induction heating device  20  becomes more than a leak magnetic field, thereby being able to improve the heating efficiency of the induction heating device  20 . In addition, the upper limit of the heating coil width can be appropriately determined according to the conditions such as a space where the induction heating device  20  is disposed, or the weight or the cost which is required for the induction heating device  20 . Further, the numbers of heating coils and cores disposed are not particularly limited. For example, a plurality of the heating coil and the core can be disposed in the conveyance direction of the steel strip in order to flexibly perform the heating control of the steel strip. 
     In addition, the number of shielding plates disposed is also not particularly limited. For example, a plurality of the shielding plates may also be disposed in the conveyance direction of the steel strip in accordance with the numbers of heating coils and cores disposed. A plurality of shielding plates having a single depressed portion may also be disposed to form a shielding plate unit having a plurality of depressed portions. 
     Further, in this embodiment, a case where the upper side inductor  21  and the lower side inductor  22  are provided has been shown as an example. However, only one of either the upper side inductor  21  or the lower side inductor  22  may also be provided. 
     In addition, all the embodiments of the present invention described above merely show examples embodied in implementation of the present invention and the technical scope of the present invention should not be construed as being limited by these. That is, the present invention can be implemented in various forms without departing from the technical idea thereof or the main features thereof. 
     INDUSTRIAL APPLICABILITY 
     A transverse flux induction heating device is provided which allows unevenness of a temperature distribution in the width direction of a conductive sheet of a heating target to be reduced and allows variation in temperature distribution in the width direction of the conductive sheet of the heating target due to meandering of the conductive sheet to be reduced. 
     REFERENCE SYMBOL LIST 
     
         
         
           
               10 : steel strip (conductive sheet) 
               18 : alternating-current power supply unit 
               20 : induction heating device 
               21 : upper side inductor 
               22 : lower side inductor 
               23 ,  27 : core 
               24 : upper side heating coil (heating coil) 
               28 : lower side heating coil (heating coil) 
               31 ,  61 ,  71 ,  81 ,  101 ,  111 ,  121 ,  201 ,  211 ,  221 : shielding plate 
               51 ,  62 ,  72 ,  82 ,  114 ,  124 ,  214 : depressed portion 
               205 ,  225 : protruded portion 
               52 ,  102 ,  112 ,  122 ,  202 ,  212 ,  222 : non-conductive soft magnetic plate (non-conductive soft magnetic material) 
               53 ,  63 ,  73 : heat-resistant plate (heat-resistant material)