TW202407109A - Induction heating device of metal sheet, metal sheet processing equipment, and induction heating method of metal sheet - Google Patents

Abstract

An induction heating device for a metal sheet comprises: a first conductor component, facing at least one side of the front and the back of the metal sheet, and spanning across the metal sheet in the width direction; a second conductor component, separated from the first conductor component in an over-sheet direction of the metal sheet by a first distance, and facing at least one side of the front and the back of the metal sheet and spanning across the metal sheet in the width direction; a connecting component, connecting the first conductor component and the second conductor component to each other to form a first secondary closed loop at a position where the ends of the metal sheet in the width direction are separated; and an AC power source connected to the first secondary closed loop, wherein the first distance is greater than the sum of the sizes of the first conductor component and the second conductor component in the over-sheet direction of the metal sheet. According to the present disclosure, even if the width of the metal sheet changes or the metal sheet is conveyed in a serpentine manner, the end temperature of the metal sheet can be raised by efficiently heating only at a specific range of the end of the width direction of the metal sheet, thereby stabilizing the quality of the end, preventing end cracking of the metal sheet, improving the dimensional accuracy of the rolling, or avoiding poor alloying caused by the decrease in temperature at the end of the sheet.

Description

Induction heating device for metal plates, processing equipment for metal plates, and induction heating methods for metal plates

The present disclosure relates to an induction heating device for metal plates, metal plate processing equipment and an induction heating method for metal plates.

In the cold rolling of relatively hard steel materials such as stainless steel and high-tensile steel, end cracks may occur at the ends in the width direction because the brittleness of the steel materials is higher than conventional steel materials. For example, Japanese Patent Application Laid-Open No. 2010-221224 describes a technology for dealing with such end cracks. More specifically, Japanese Patent Application Laid-Open No. 2010-221224 describes a technique in which a C-shaped inductor arranged in a C-shape sandwiching the widthwise end of a steel plate from above and below is used to inductively heat the end portion to cause the end portion to be inductively heated. The deformation resistance of the steel plate in the end is reduced, thereby preventing end cracks. In addition, in the case of thick steel materials such as hot-rolled slabs, the ends of the steel materials become cold before being taken out from the heating furnace and subjected to rough rolling and before finishing rolling. Therefore, in order to improve the rolling dimensional accuracy and stabilize the quality of hot-rolled materials, a transverse induction heating device such as the aforementioned C-shaped inductor is usually installed in front of the finishing rolling mill. Furthermore, in order to prevent the end temperature from lowering and causing alloying defects during alloying of molten zinc plating, for example, Japanese Patent Application Laid-Open No. 2009-149970 describes an end detection mechanism and a moving mechanism. Temperature compensation device using flame.

The problem to be solved by the invention

The above-mentioned Japanese Patent Application Laid-Open No. 2010-221224 also describes a method of providing a trolley that moves the inductor in the width direction of the steel plate and a position controller that controls the movement of the trolley, thereby corresponding to the steel plate. The width changes or the meandering during transportation are used to maintain the appropriate overlap length between the inductor and the steel plate. However, as a previous problem, in the case of a C-shaped inductor, due to magnetic flux leaking to the outside of the inductor, a wide range other than the portion sandwiched by the inductor is inductively heated. On the other hand, in order to prevent the edge portion of the metal plate from cracking, it is sufficient to heat a narrow range near the end portion in the width direction of the metal plate. Therefore, the technology described in Japanese Patent Application Laid-Open No. 2010-221224 is at least It cannot be said to be efficient in terms of power consumption. In addition, there is a problem that effective heating cannot be achieved unless the inductor gap is narrowed, and there is a concern that the device may be damaged due to contact with the inductor on poorly shaped materials to be heated, such as hot-rolled steel plates. . In addition, auxiliary equipment such as a detection mechanism and a moving mechanism control device for handling snaking are indispensable, which also has a cost disadvantage. Furthermore, when the edge of the steel plate is heated by a flame as shown in Japanese Patent Application Laid-Open No. 2009-149970, there is a problem that the heating ability of the flame is not large and the heating efficiency is also low. Disadvantages include the need for additional equipment such as end detection mechanisms/moving mechanisms.

Therefore, an object of this disclosure is to provide a technology that efficiently heats only a specific range of the ends of the metal plate in the width direction, even if the width of the metal plate is changed or the metal plate is meandering, so that the ends of the metal plate can be heated. The end temperature rises to stabilize the quality of the end, prevent cracks at the end of the metal plate, improve rolling dimensional accuracy or avoid alloying defects, etc., and solve problems caused by the temperature drop at the end of the plate. means to solve problems

One aspect of the present disclosure is an induction heating device for a metal plate, including: a first conductor member facing at least one of the front and back surfaces of the metal plate and disposed across the metal plate in the width direction; The conductor member is spaced apart from the first conductor member by a first distance in the direction across the metal plate, faces at least one of the front and back surfaces of the metal plate, and spans the metal plate in the width direction. Arrangement; a connecting member that connects the first conductor member and the second conductor member to each other at a position separated from the width direction end of the metal plate to form a primary closed circuit; and an AC power supply, and the primary closed circuit loop connection, The first distance is larger than the sum of the dimensions of the first conductor member and the second conductor member in the direction of the metal plate passing through the metal plate.

Another aspect of the present disclosure is an induction heating method of metal plates, including the following steps: An alternating current flows through a primary closed circuit, and the primary closed circuit is formed by a first conductor member, a second conductor member, and the first conductor member and the aforementioned conductor member at a position separated from the width direction end of the metal plate. The first conductor member is formed by a connecting member connecting the second conductor members to each other. The first conductor member faces at least one of the front and back surfaces of the metal plate and is arranged across the metal plate in the width direction. The second conductor member and At least one of the front and back surfaces of the metal plate faces each other, is separated by a first distance from the first conductor member in a direction across the metal plate, and is arranged across the metal plate in the width direction; and The width direction end of the metal plate is inductively heated by a secondary closed circuit passing through the width direction end of the metal plate, and the secondary closed circuit is connected to the first conductor member and the first conductor member in the metal plate respectively. It is formed by the induced current generated in the areas where the 2 conductive members face each other. Invention effect

According to the present disclosure, even if the width of the metal plate is changed or the metal plate is meandering, the temperature of the end portion of the metal plate can be increased by efficiently heating only a specific range of the end portion in the width direction of the metal plate. It stabilizes the quality of the end and prevents cracks at the end of the metal plate, improves rolling dimensional accuracy, avoids alloying defects, etc., and solves problems caused by the temperature drop at the end of the plate.

Form used to implement the invention

Hereinafter, one embodiment of the present disclosure will be described in detail with reference to the attached drawings. In addition, in this specification and the drawings, components having substantially the same functional configuration will be assigned the same reference numerals, and repeated descriptions will be omitted.

(First Embodiment) FIG. 1 is a plan view of a metal plate induction heating device according to the first embodiment of the present disclosure, and FIG. 2A is a side view corresponding to the arrow view along line 2A-2A of the induction heating device shown in FIG. 1 . As shown in FIGS. 1 and 2 , the induction heating device 100 of this embodiment is a device that uses electromagnetic induction to heat a metal strip S which is a metal plate. Here, the metal strip plate S used in this embodiment is, for example, a strip-shaped thin plate, but the present disclosure is not limited to this.

The induction heating device 100 of this embodiment includes conductive members 110 and 120, connecting members 131 and 132, and an AC power supply 140. The conductive member 110 faces at least one of the front surface and the back surface of the metal strip plate S, and is arranged across the metal strip plate S in the width direction. Like the conductor member 110 , the conductor member 120 faces at least one of the front surface and the back surface of the metal strip plate S and is arranged across the metal strip plate S in the width direction. The conductor member 120 is separated by a distance L from the conductor member 110 in the direction across the metal strip S (the direction indicated by arrow PD in FIG. 1 ). Here, the distance L is the distance between the inner sides of the conductor members 110 and 120 . The distance L (distance between inner sides) is larger than the sum of the dimensions B1 and B2 of the conductor members 110 and 120 in the passing direction of the metal strip plate S (L>B1+B2). In addition, the distance L in this embodiment is an example of the first distance in this disclosure.

The connection members 131 and 132 connect the conductor members 110 and 120 to each other at positions separated from the width direction ends of the metal strip plate S in a plan view, forming the primary closed circuit 101, and the primary closed circuit 101 Connect AC power 140. The connecting members 131 and 132 only need to be separable from the width direction end SE of the maximum plate width of the metal strip plate S. Specifically, the distance E from the connecting members 131 and 132 to the width direction end SE of the metal strip plate S is preferably 3% or more and 12% or less of the maximum width Wmax of the metal strip plate S, more preferably 5%. Above and below 10%. It is expected that the relationship between the distance E and the maximum width Wmax will take into account the meandering amount of the conveying line for conveying the metal strip plate S. In addition, when the distance E is less than 3% of the maximum width Wmax, the width direction end SE of the metal strip S may come into contact with the connecting member 131 or 132 due to meandering. On the other hand, when the distance E exceeds 12% of the maximum width Wmax, there are concerns about an increase in the size of the device and an increase in the impedance of the primary closed circuit 101 .

In addition, the conductor members 110 and 120 face at least one of the front surface and the back surface of the metal strip plate S. Therefore, when the AC power supply 140 causes an AC current to flow through the primary closed circuit 101, the magnetic field generated around the conductor members 110 and 120 causes the metal strip S to generate an induced current described below.

Here, as shown in FIG. 2A , the conductor members 110 and 120 of this embodiment include two plate portions 111 and 112 and plate portions 121 and 122 respectively facing the front and back surfaces of the metal strip plate S. In other words, the plate portions 111 and 112 of the conductor member 110 are arranged to face the front and back surfaces of the metal strip plate S, and the plate portions 121 and 122 of the conductor member 120 are arranged to face the front and back faces of the metal strip plate S. Furthermore, the present disclosure is not limited to this. For example, as shown in FIG. 2B , the plate portion 111 of the conductor member 110 and the front surface of the metal strip plate S may face each other and the plate portion 122 of the conductor member 120 and the metal strip plate S may be aligned. Alternatively, the plate portion 112 of the conductor member 110 and the back surface of the metal strip plate S may face each other, and the plate portion 121 of the conductor member 120 and the front face of the metal strip plate S may face each other. Alternatively, as shown in FIG. 2C , both the plate portion 111 of the conductor member 110 and the plate portion 121 of the conductor member 120 may face only the front surface of the metal strip plate S, or the plate portion of the conductor member 110 may be 112 and the plate portion 122 of the conductor member 120 both face only the back surface of the metal strip plate S. In other words, the conductor member 110 and the conductor member 120 are respectively arranged to face the same side surface of the metal strip plate S.

In this embodiment, as shown in FIGS. 1 and 2A , an air-core coil is configured by conductor members 110 and 120 and connection members 131 and 132 . The primary closed loop 101 formed by this air-core coil is connected to the AC power supply 140.

FIG. 3 is a diagram conceptually showing the induced current I generated in the metal strip S in the example of FIGS. 1 and 2A . The secondary closed circuit 102 formed by the induced current I generated in the metal strip S in the area facing the conductor members 110 and 120 of the induction heating device 100 is It flows in the width direction of the metal strip S and passes through the width direction end SE of the metal strip S between both ends of these areas. In this way, the induced current of the secondary closed loop 102 circulates within the metal strip plate S. The induced current I flowing in the secondary closed circuit 102 can suppress the amount of heat generated in the central part of the metal strip plate S because the current density is small, but at the ends SE in the width direction, the high-frequency current is concentrated at the ends. The skin effect causes the current density in a limited range from the end to become higher. Thereby, the width direction end SE of the metal strip plate S can be heated efficiently. As is clear from FIG. 3 , in the present disclosure, the problem of being unable to heat a non-magnetic material due to the penetration depth of the electric current, which is a problem in the so-called LF heating method in which a solenoid coil is used to heat a thin plate, is addressed because the conductor is They are staggered without overlapping in the direction of travel so that the surrounding currents do not overlap, so both non-magnetic materials and magnetic materials can be heated.

In addition, by separating the conductor members 110 and 120 by a distance L in the direction across the metal strip S, the heating duration of the widthwise end SE of the metal strip S becomes longer. Specifically, when the speed of the metal strip S is v, because the width direction end SE of the metal strip S passes below (or above) the conductor member 120 until it passes below the conductor 110 ( or above) will continue to heat, so the heating duration is L/v. On the other hand, since the center portion in the width direction of the metal strip S is heated only while passing under (or over) the conductor member 120 and while passing under (or over) the conductor member 110, the heating duration is: (B1+B2)/v. Therefore, by setting L>B1+B2, the heating duration can be made longer at the width direction end SE than at the width direction center part of the metal strip plate S. In this way, the calorific value Qc of the widthwise central portion of the metal strip plate S and the calorific value Qe of the widthwise end portion SE can be adjusted by the distance L between the conductor members 110 and 120 and the respective dimensions B1 and B2. In addition, the calorific value Qc and Qe can also be adjusted by the frequency f of the alternating current.

More specifically, the calorific value Qc of the center portion in the width direction of the metal strip plate S, in addition to the above-mentioned quantities, can also be used is the plate width W, plate thickness t, and the portion of the metal strip plate S facing the conductor member 110. The specific impedance ρ1 and the specific impedance ρ2 of the portion facing the conductive member 120 are calculated using the following equation (1).

[Formula 1]

On the other hand, the calorific value Qe (sum of both sides) of the width direction end SE of the metal strip plate S can be calculated by using, in addition to the above-mentioned quantities, the specific impedance ρe of the width direction end SE of the metal strip plate S. Calculate using the following equation (2).

[Formula 2]

The ratio of the calorific value Qc of the widthwise center portion of the metal strip plate S to the calorific value Qe of the widthwise end portion SE becomes the following formula (3) based on the above-mentioned formulas (1) and (2).

[Formula 3]

The conditions for suppressing the temperature rise in the widthwise central portion of the metal strip S and intensively heating the widthwise end SE will be discussed based on the above equation (3). When formula (3) is set to: ρ1=ρ2=ρc, it becomes the following formula (4).

[Formula 4]

Here, the specific gravity γ of the metal strip S, the respective specific heats Cpc and Cpe of the widthwise central portion and the widthwise end SE, the respective temperature rise amounts ΔTc and ΔTe, and the average size of the conductor member B = (B1 + B2 )/2, the calorific values Qc and Qe can be expressed as the following formulas (5) and (6). If equations (5) and (6) are substituted into equation (4) and sorted, they become equations (7) and (8).

[Formula 5]

In the above formula (8), it is assumed that B=0.1m and D=0.07m, and the temperature rise amount ΔTc of the widthwise central portion of the metal strip plate S is suppressed to 10°C, and the widthwise end SE is When ΔTe is set to 500°C, by substituting the specific heats Cpc and Cpe and the specific impedances ρc and ρe corresponding to the respective temperature rise amounts, the appropriate distance L can be obtained as follows. Furthermore, in order to set the appropriate distance L according to the conditions, the connecting members 131 and 132 of the induction heating device 100 may also include a device that allows at least one of the conductive members 110 and 120 to move in the passing direction of the metal strip plate S. The movable part. As an example of the movable part of the present disclosure, the movable part 150 shown in FIGS. 12 and 13 may also be used. This movable part 150 is a plurality of bolt holes provided in the connecting members 131 and 132 respectively connecting the conductor members 110 and 120 (only the connecting member 131 is shown in FIGS. 12 and 13 ). A plurality of bolt holes are provided in the connecting members 131 and 132 at intervals in the plate-passing direction. The distance between the conductor members 110 and 120 can be changed by changing the installation position of the conductor members 110 and 120, specifically, changing the installation position of the conductor members 110 and 120 formed by the bolts 152. For example, when the conductive members 110 and 120 are moved from the position shown in FIG. 12 to the position shown in FIG. 13 , the distance between the conductive members 110 and 120 is lengthened from the distance L1 to the distance L2. Furthermore, when the installation positions of the conductor members 110 and 120 are changed, a roller (a member represented by a two-dot chain line in FIG. 12 ) or the like is arranged under the conductor members 110 and 120 . Moving 120 becomes easy. In addition, as another example of the movable part of the present disclosure, the movable part 160 shown in FIG. 14A and FIG. 15 can also be used. This movable part 160 is an expansion and contraction part constituting the connection members 131 and 132 (only the connection member 131 is shown in FIGS. 12 and 13 ) that connect the conductor members 110 and 120 respectively. This elastic part is made of, for example, a flexible conductor such as a braided metal wire. Moreover, as shown in FIG. 15 , the telescopic portion constitutes the center portion of each of the connecting members 131 and 132 in the plate-passing direction. Specifically, the plate portions 131A and 132A of the connection members 131 and 132 connected to the conductor members 110 and 120 are connected. Furthermore, as shown in FIG. 14B , the telescopic portion is bent into a mountain shape toward the side opposite to the S side of the metal strip plate. As shown in FIG. 15 , when the bent telescopic portion expands and contracts, the positions of the conductor members 110 and 120 in the plate-crossing direction move. Furthermore, when changing the positions of the conductor members 110 and 120 in the board-passing direction, the movement of the conductor members 110 and 120 becomes simple by arranging rollers and the like under the conductor members 110 and 120 . Furthermore, the flexible conductor constituting the telescopic portion can also be used as a water-cooled cable.

[Formula 6]

Furthermore, regarding the frequency f [kHz] of the alternating current, according to the results of the analysis carried out by the inventors of the present disclosure, the range D [mm] from the edge that contributes 70% of the input power to the temperature rise is equal to the induced current I The relationship is expressed as, for example, the following formula (9).

[Formula 7]

According to the structure of the first embodiment disclosed above, the entire width direction of the metal strip S is heated only while passing under (or above) the conductor members 110 and 120 of the induction heating device 100 . Furthermore, the heating range is limited to the width direction end SE of the metal strip S between the conductor members 110 and 120 . In this way, the input power can be saved and unnecessary impact on the metal structure can be avoided. That is, in this embodiment, it is possible to efficiently heat the width direction end SE of the metal strip S and prevent the end portion SE of the metal strip S from being cracked during cold rolling or the like. Furthermore, in the above-mentioned structure, there is no member that must be disposed close to the width direction end SE, which is the heating portion of the metal strip plate S, and because it is generated while passing under (or above) the conductor members 110 and 120 Because of the surrounding current formed by the induced current, it is possible to cope with meandering in the width direction of the metal strip plate S or changes in plate width and thickness without changing the arrangement of the components. In addition, even if the metal strip plate S occurs It can still be heated even if the shape is bad.

Here, end cracks of the metal strip occur, for example, in the pickling step after the hot rolling step or in the cold rolling step. Therefore, the above-mentioned induction heating device 100 can also be arranged in the front stage of the pickling device 500 (see FIG. 20 ) including the metal strip plate S, for example, or in the cold processing equipment including the metal strip plate S. The rolling device 510 (see FIG. 21 ) is disposed in the front stage of the cold rolling device 510 in the processing equipment. In addition, cracks at the end portions of the metal strip may occur, for example, during the molten metal plating step. Therefore, the above-mentioned induction heating device 100 can also be disposed between the wiping device 522 and the alloying heating device 524 in a processing equipment including a plating tank 520, a wiping device 522 and an alloying heating device 524 as shown in FIG. 22 . The aforementioned plating tank 520 stores molten metal M (for example, molten zinc), the aforementioned wiping device 522 sprays gas (for example, air) toward the metal strip S attached to the molten metal M, and the aforementioned alloying heating device 524 The molten metal M attached to the metal strip S is heated to an alloying temperature and maintained at the temperature to alloy it.

(Second Embodiment) 4 is a plan view of an induction heating device for a metal strip according to a second embodiment of the present disclosure. As shown in the figure, the induction heating device 200 of this embodiment is composed of a parallel circuit. The parallel circuit includes: conductor members 110A and 120A and connecting members 131A and 232A forming a primary closed circuit 101A; and a conductor member forming a primary closed circuit 101B. 110B, 120B and connecting members 131B, 232B; and AC power supply 240. The primary closed circuits 101A, 101B are adjacently arranged in the direction of the metal strip plate S (the direction shown by arrow PD in FIG. 4). In each of the primary closed circuits 101A and 101B, the conductor members 110A and 110B and the conductor members 120A and 120B have the same configurations as the conductor members 110 and 120 in the first embodiment, respectively. The conductor member 120A constituting the primary closed circuit 101A and the conductor member 110B constituting the primary closed circuit 101B are arranged adjacent to each other in the passing direction of the metal strip plate S, and currents in the same phase flow therethrough.

The connection members 131A and 131B connect the conductor members 110A and 120A and the conductor members 110B and 120B to each other at positions separated from the width direction end SE of the metal strip plate S in a plan view to form a primary closed circuit 101A. ,101B. The connection members 232A and 232B connect the conductor members 110A and 120A and the conductor members 110B and 120B to each other at positions separated by a distance E from the width direction end SE of the metal strip plate S to form primary closed circuits 101A and 101B. , and the primary closed circuits 101A and 101B are connected in parallel to the AC power supply 240 . The AC power supply 240 is connected to the primary closed circuits 101A and 101B so that the same-phase AC current flows through the conductor members 120A and 110B that are adjacent conductor members in the sheet-passing direction of the metal strip plate S.

According to the structure of the second embodiment disclosed above, not only the same effect as the first embodiment can be obtained, but also an appropriate distance L can be set as the sum of the primary closed loops 101A and 101B. Therefore, when the primary closed circuits 101A and 101B are connected in parallel, the inductance of each primary closed circuit can be reduced to about half compared to the case where the distance L is set with a single primary closed circuit. In addition, by causing the same-phase alternating current to flow through the mutually adjacent conductor members 120A and 110B, the magnetic flux generated around each conductor member becomes the same direction, and the magnetic flux becomes easier to concentrate on the metal strip plate S. Specifically, primary closed circuit 101A (inductor L1, impedance Z1) composed of one set of conductor members 110A and 120A, and primary closed circuit 101B (inductor L2) composed of another set of conductor members 110B, 120B. , impedance Z2) are connected in parallel, the parallel combined inductance L can be obtained using the following equation (10). L=L1×L2/L1+L2…(10)

Usually, if connected in parallel, the inductance and impedance can be reduced. If the inductance L1 and the inductance L2 are almost equal, according to the above equation (10), the inductance will be about half. Especially when the metal strip plate S (usually a thin material) passes through the plate at a high speed and the heating time cannot be fully obtained, making the separation distance of a set of conductor members longer will cause the inductance and impedance to change. Larger and higher voltages will increase the burden on the power supply, resulting in increased equipment costs or safety issues. By connecting them in parallel, the inductance can be made smaller even if the separation length is long. Therefore, the power supply load can be reduced and safety issues associated with higher voltages can be solved. Even if a large amount of electric power is input without extending the separation distance, the current can be divided, so the heat generation of one set of conductor members can be reduced and the efficiency can be improved. Furthermore, the resonance frequency f of the current can be increased as shown below.

[Formula 8] Furthermore, L is the inductance [H], and C is the capacitance [F]. When the resonant frequency increases, the heating range of the width-direction end SE of the metal strip plate S can be narrowed, and a limited range of the width-direction end SE can be effectively heated.

5 is a plan view of an induction heating device for a metal strip according to another example of the second embodiment of the present disclosure. As a difference from the above-described example, in the illustrated example, the connection members 232C and 232D connect the primary closed circuits 101A and 101B in series to the AC power supply 240 . The same-phase alternating current flows through the conductor member 120A and the conductor member 110B adjacent to each other in the sheet-passing direction of the metal strip plate S at the same point. By connecting primary closed circuits 101A and 101B in series, the magnitude of the current flowing in each primary closed circuit can be made equal. In addition, the oscillation conditions can be changed by increasing the inductance. Specifically, when connected in series, the combined inductance L is the following equation. L=L1+L2…(12) Series connection makes the inductor larger, which reduces the frequency. If the frequency is reduced, the current penetration depth δ can be made deeper, so especially in the case of thicker materials, the heating range in the thickness direction can be expanded, and the width of the metal strip S can also be expanded. The heating range from the direction end SE.

[Formula 9] Furthermore, ρ is specific impedance [μΩcm], μr is relative magnetic permeability, and f is frequency [Hz]. In addition, since the currents flowing through the conductive members are all the same, even if the impedances are different, the edge heating amount of each closed loop can still be formed to be the same. As mentioned above, as long as the parallel/series connection can be freely performed, it has the following advantages: the required frequency, current/power distribution, and width direction ends of the metal strip can be changed in a relatively free manner according to the load. It does not matter if you do not prepare multiple individual devices for the heating range. Generally speaking, when the plate thickness is thin, the plate passing speed is fast, and the temperature change of the specific impedance is small (SUS304, etc.), since the change in impedance is small and the amount of power/current is large before and after heating, so What is desired is a parallel connection that can reduce the heat generation of the conductor. In the case of ordinary steel, which has a large temperature change in specific impedance, and there is a difference in impedance before and after heating, or in the case of thick steel with a slow passing speed, What is desired is a series connection in which the current amount between the circuits is the same, the inductance is large, and heating on the low-frequency side is easier.

The induction heating device 200 can manually switch between the series connection and the parallel connection of the primary closed circuits 101A and 101B, but may also include a switching circuit that switches between each other automatically. The switching circuit includes, for example, a switch that selectively connects the AC power supply 240 to any one of the connecting members 232A, 232B shown in FIG. 4 or the connecting members 232C, 232D shown in FIG. 5 . As an example, switches 201A and 201B shown in FIGS. 18 and 19 may be used to switch between parallel connection (the connection in FIG. 18 ) and series connection (the connection in FIG. 19 ). In FIG. 18 , the contact point A of the switch 201A connected to the conductor member 120A and the contact point B of the conductor member 110B are short-circuited. Furthermore, the contact point D of the switch 201B connected to the connection member 232A and the contact point E connected to the connection member 232B are short-circuited. Thereby, the primary closed circuit 101A and the primary closed circuit 101B are connected in parallel. On the other hand, in FIG. 19 , the contact point A of the switch 201A connected to the conductive member 120A is released from the contact point B of the conductive member 110B. Then, the primary closed circuit 101A and the primary closed circuit 101B are connected in series by short-circuiting the contact point D of the switch 201B connected to the connection member 232A and the contact point C connected to the conductive member 110B.

(Third Embodiment) 6A and 6B are cross-sectional views for explaining the third embodiment of the present disclosure. As shown in FIG. 6A , in this embodiment, magnetic core materials 351 , 352 , 361 , and 362 can be disposed on the opposite side to the metal strip plate S of the plate portions 111 , 112 , 121 , and 122 constituting the conductive member. . Thereby, compared with the case where the magnetic core material is not arranged as shown in FIG. 6B , the plate portions 111 , 112 , 121 , and 122 that originally constitute the conductor member are freely surrounding the side opposite to the metal strip plate S. The magnetic flux concentrates through the magnetic core materials 351, 352, 361, 362 with high magnetic permeability, so that the magnetic flux becomes easy to concentrate into the metal strip plate S directly below the conductor members 111, 112, 121, 122, and The metal strip plate S can be induction heated more efficiently. In this embodiment, by arranging the magnetic core material as described above, the magnetic flux generated by the current flowing in the conductor can be concentrated on the plate portions 111, 112, 121, and 122 of the conductor member. The gap between the metal strip S and the metal strip S can be increased, and it can correspond to the corrugated shape of the metal strip S in the thickness direction, for example. Furthermore, in this embodiment, the leakage magnetic flux toward the back side of the conductor member (the side not facing the metal strip plate S) can be reduced by the arrangement of the magnetic core material. Therefore, for example, it is possible to prevent the conductor member from supporting the conductor member. Components or peripheral machines are heated. The magnetic core material only needs to ensure an appropriate cross-sectional area that does not cause magnetic saturation. For example, when using high frequencies, it is sufficient to use a ferrite core material that has a small cross-sectional area even if the saturation magnetic flux density is small. , and if the frequency is relatively low, it is enough to use a laminated electromagnetic steel plate with a large saturation magnetic flux density or a ferromagnetic material such as amorphous (amorphous). Furthermore, if heat generation is a concern, it is advisable to appropriately install a cooling device such as a water-cooled copper plate to cool the magnetic core material.

7A and 7B are cross-sectional views illustrating another example of the third embodiment of the present disclosure. Although FIG. 7B is composed only of the plate portions 111A, 111B, 112A, 112B, 121A, 121B, 122A, and 122B that constitute the conductor member, in the case of FIG. The traveling direction of S (same as the direction through the plate) radiates freely in the front and rear directions, so the magnetic flux will be difficult to concentrate. On the other hand, in another example of the third embodiment, when the same-phase current flows to the plate portions 111A, 111B, 112A, and 112B in the center portions of the two closed circuits, the plate portions 111A, 111B, 112A, The magnetic flux generated by 112B will not fly forward and backward in the longitudinal direction of the metal strip plate S (the same as the plate passing direction) due to the reverse magnetic flux generated in the plate portions 111A, 112A, 121B, and 122B. Narrow, the magnetic flux is confined near the plate portions 111A, 111B, 112A, and 112B. As a result, the induced current can be efficiently concentrated. As shown in FIG. 7A , in this embodiment, a magnetic core is disposed on the opposite side to the metal strip plate S of the plate portions 111A, 111B, 112A, 112B, 121A, 121B, 122A, 122B constituting the conductor member. Materials 351, 352, 361, 362, 371, and 372 can concentrate the induced current more efficiently. Here, as long as the magnetic core materials 371 and 372 are close to each other, it does not matter even if they are divided midway in the longitudinal direction/width direction. However, it is preferable that they be two plates of conductive members adjacent to each other in the passing direction of the metal strip plate S. The portions 121A and 111B and the plate portions 122A and 122B are each arranged in common. That is, the magnetic core material 371 covers the back sides of both the plate portions 121A and 111B of the conductor member, and the magnetic core material 372 covers the back sides of both the plate portions 122A and 112B of the conductor member. Therefore, even in the case where a plurality of primary closed circuits are arranged adjacent to each other in the passing direction of the metal strip plate S, as in the examples of FIGS. 4 and 5 described above, compared to the case where no primary closed loops are arranged as shown in FIG. 7B In the case of a magnetic core material, magnetic flux will also become easier to enter the metal strip S. Thereby, the metal strip plate S can be induction heated more effectively. It is also the same as the above example in that the gap between the conductor member and the metal strip plate S can be increased and the leakage magnetic flux can be reduced.

(Fourth Embodiment) 8A is a plan view of an induction heating device for a metal strip according to a fourth embodiment of the present disclosure, and FIG. 9 is a side view corresponding to the arrow 9-9 view of the induction heating device shown in FIG. 8A . As shown in the figure, the induction heating device 400 of this embodiment includes conductor members 110 and 120 and connection members 132 and 431 forming a primary closed circuit 101, and an AC power supply 140. As a difference from the above-described first embodiment, in this embodiment, the connecting members 431 and 132 are on the end side of the metal strip plate S so as not to interfere with the metal strip plate S in the thickness direction of the metal strip plate S. configured on the upper or lower surface. Specifically, as shown in the example of FIG. 9 , the plate portions 111 and 121 of the conductor member are connected to the front side of the metal strip plate S by the connecting member 431 , and the plate portions 112 and 122 of the conductor member are connected to the back side. No conductive member is connected between the front side and the back side of the metal strip plate S.

According to the fourth embodiment disclosed above, in addition to obtaining the same effects as the first embodiment, when it is necessary to remove the induction heating device 400 from the conveyance line of the metal strip plate S for maintenance, Just pull it out from the bottom (power supply side) in the figure, and there is no need to stop/cut off the metal strip S being transported even during operation, making maintenance easy.

In the aforementioned embodiment, the connection members 131 and 132 are separated from the width direction end SE of the metal strip plate S, but the present disclosure is not limited to this structure. As shown in FIG. 8B , the connecting member may overlap the width direction end SE of the metal strip plate S in a plan view (as an example, the connection member may overlap by about tens of mm). Specifically, the connection members are arranged above and below the conductor members 110 and 120 so that, in a plan view, a portion overlaps the width direction end SE of the metal strip plate S with respect to the maximum plate width of the heated material to be processed. . By having this structure, it is possible to avoid contact between the connecting member and the end portion in the width direction of the metal strip plate S. In addition, the width dimension of the connecting member may be larger than the width dimension of the conductor members 110 and 120 . By adopting this structure, even if the metal strip plate S meanders, current can be caused to flow uniformly in the width direction end SE of the metal strip plate S.

Furthermore, in the aforementioned embodiment, the metal strip S which is a thin plate is used as the metal plate, but the present disclosure is not limited thereto. Thick metals such as thick plates or flat blanks can also be used as metal plates. In this case, the effects of the present disclosure can be obtained similarly to the first embodiment. In addition, although the material to be heated is exemplified in a moving state, it can also be applied in a stationary state. FIG. 17 illustrates the flow of electric current on the side of the thick metal in a state where the electric current flows through the thick metal using the induction heating device of the present disclosure (see FIG. 16 ).

(Verification of heating effect) 10 and 11 are graphs showing analysis results for verifying the effect of heating the width direction end portion of the metal strip in the embodiment of the present disclosure. Regarding the induction heating device described above with reference to FIGS. 1 to 3 , electromagnetic field analysis based on the finite element method was carried out under the following conditions, and the temperature Tc of the widthwise center portion of the metal strip plate and the temperature of the widthwise end portion were calculated. Te ratio, and the temperature at the end in the width direction (edge temperature).

・The plate width of the metal strip plate W=1200mm ・The plate thickness of the metal strip plate t=2mm ・The width of the conductor member B=200mm ・The frequency of the alternating current f=10kHz ・The magnitude of the alternating current=10kA ・The distance between the conductor members L = Can be changed between 200mm~600mm・The temperature of the metal strip before heating T ₀ =0℃

In the above analysis, when the distance L between conductor members is set to the minimum (100 mm), the ratio L/B of the width B of the conductor members to the distance L is 1. As shown in the graph of FIG. 10 , when the ratio L/B is in a range of 1 or more, the temperature Te at the widthwise ends of the metal strip is much higher than the temperature Tc at the center. On the other hand, as shown in the graph of Fig. 11, when the ratio L/B is 1 or more and 2 or less, the edge temperature is low. However, when the ratio L/B exceeds 2, the edge temperature exceeds 50°C, and As the ratio L/B becomes larger, the edge temperature will increase. The case where the ratio L/B exceeds 2 (L/B>2) is equivalent to the case where the distance L exceeds the sum of the widths of two conductive members (L>2B). Under such conditions, the induction heating device can efficiently heat the widthwise ends of the metal strip.

As mentioned above, the preferred embodiments of the present disclosure have been described in detail with reference to the accompanying drawings, but the present disclosure is not limited to these examples. As long as a person skilled in the art in the technical field to which the present disclosure belongs, it is obvious that various modifications or modifications can be conceived within the scope of the technical ideas described in the patent application scope, and these modifications or modifications should of course also be considered. It is understood that it belongs to the technical scope of this disclosure.

Regarding the above embodiment, the following supplementary remarks are further disclosed.

(Note 1) An induction heating device for metal plates, equipped with: The first conductor member faces at least one of the front and back surfaces of the metal plate and is disposed across the metal plate in the width direction; The second conductor member is spaced apart from the first conductor member by a first distance in the direction across the metal plate, faces at least one of the front and back surfaces of the metal plate, and spans the metal plate in the width direction. board and configuration; A connecting member that connects the first conductor member and the second conductor member to each other to form a primary closed circuit; and AC power supply, connected to the aforementioned primary closed loop, The first distance is larger than the sum of the dimensions of the first conductor member and the second conductor member in the direction of the metal plate passing through the metal plate.

(Note 2) The induction heating device according to appendix 1, wherein the first conductor member and the second conductor member are arranged facing each other with the same side surfaces of the metal plate.

(Note 3) The induction heating device according to Appendix 2, wherein the first conductor member and the second conductor member are respectively arranged on the front side and the back side of the metal plate.

(Note 4) The induction heating device for a metal plate as described in any one of Supplementary Notes 1 to 3, wherein the first and second primary closures are each formed by the first conductor member, the second conductor member and the connecting member. The circuits are arranged adjacent to each other in the direction of passing the metal plate, The AC power supply causes the same-phase AC current to flow through the conductor members adjacent to each other in the direction of passing the metal plate in the first and second closed circuits.

(Note 5) For example, the induction heating device for metal plates described in Appendix 4 further includes a switching circuit, and the switching circuit can mutually switch between the series connection and the parallel connection of the first and second closed circuits.

(Note 6) The induction heating device for a metal plate according to any one of Supplementary Notes 1 to Supplementary Notes 5, further comprising a magnetic core material arranged on at least one of the first conductor member and the second conductor member. The side is opposite to the aforementioned metal plate.

(Note 7) The induction heating device for a metal plate as described in any one of Supplementary Notes 1 to 6, wherein the connecting member is on at least one side of the metal plate in the width direction so as not to interfere with the metal plate in the thickness direction of the metal plate. mode configuration.

(Note 8) The induction heating device for metal plates as described in any one of Appendix 1 to Appendix 7, wherein the connecting member includes a movable part, and the movable part can make at least one of the first conductor member and the second conductor member in the The metal plate moves upward in the direction of the plate.

(Note 9) A metal plate processing equipment, including: Pickling plants for metal plates; and The induction heating device for a metal plate as described in any one of Supplementary Notes 1 to 8 is arranged in the front stage of the aforementioned pickling device.

(Note 10) A metal plate processing equipment, including: Cold rolling equipment for metal plates; and The induction heating device for a metal plate as described in any one of Appendix 1 to Appendix 8 is arranged in the front stage of the aforementioned cold rolling device.

(Note 11) A metal plate processing equipment, including: Wiping device sprays gas towards the metal plate with molten metal attached; An alloying heating device that alloys the molten metal attached to the metal plate by heating; and The induction heating device for a metal plate according to any one of Appendix 1 to Appendix 8 is arranged between the wiping device and the alloying heating device.

(Note 12) An induction heating method for metal plates, including the following steps: An alternating current flows through a primary closed circuit, and the primary closed circuit is formed by a first conductor member, a second conductor member, and a connecting member that connects the first conductor member and the second conductor member to each other. 1. The conductive member faces at least one of the front and back surfaces of the metal plate and is arranged across the metal plate in the width direction, and the 2nd conductive member faces at least one of the front and back surfaces of the metal plate, and The first conductor member is spaced apart from the first conductor member by a first distance in the direction across the metal plate and is arranged across the metal plate in the width direction; and The width direction end of the metal plate is inductively heated by a secondary closed circuit passing through the width direction end of the metal plate, and the secondary closed circuit is connected to the first conductor member and the first conductor member in the metal plate respectively. It is formed by the induced current generated in the areas where the 2 conductive members face each other.

(Note 13) An induction heating device for metal strip plates, equipped with: The first conductor member faces the front or back of the metal strip and is arranged across the metal strip in the width direction; The second conductor member is positioned apart from the first conductor member by a first distance in the direction across the metal strip plate, faces the front or back surface of the metal strip plate, and spans the metal strip in the width direction. Configured with boards; A connecting member that connects the first conductor member and the second conductor member to each other at a position separated from the width direction end of the metal strip plate to form a primary closed circuit; and AC power supply, connected to the aforementioned primary closed loop, The first distance is larger than the total size of the first conductor member and the second conductor member in the direction of the metal strip plate passing through the plate.

(Note 14) An induction heating device for a metal strip plate as described in Appendix 13, wherein the first and second primary closed circuits formed by the first conductor member, the second conductor member and the connecting member are in the metal strip plate. are arranged adjacent to each other in the board-passing direction, The AC power supply causes the same-phase AC current to flow through the conductor members adjacent to each other in the passing direction of the metal strip plate in the first and second primary closed circuits.

(Note 15) For example, the induction heating device for metal strip plates described in Appendix 14 further includes a switching circuit, and the switching circuit can mutually switch between the series connection and the parallel connection of the first and second closed circuits.

(Note 16) The induction heating device for a metal strip plate according to any one of Supplementary Notes 13 to 15, further comprising a magnetic core material, and the magnetic core material is arranged on at least one of the first conductor member and the second conductor member. The side is opposite to the aforementioned metal strip plate.

(Note 17) The induction heating device for a metal strip as described in any one of Supplementary Notes 13 to 16, wherein the connecting member is on at least one side of the metal strip in the width direction so as not to interfere with the metal strip in the thickness direction. Metal strip configuration.

(Note 18) The induction heating device for metal strips as described in any one of Supplementary Notes 13 to 17, wherein the connecting member includes a movable part, and the movable part can move at least one of the first conductor member and the second conductor member to The aforementioned metal strip plate moves upward in the plate-passing direction.

(Note 19) A metal strip processing equipment, including: Pickling equipment for metal strips; and The induction heating device for metal strips as described in any one of Supplementary Notes 13 to 18 is arranged at the front stage of the aforementioned pickling device.

(Note 20) A metal strip processing equipment, including: Cold rolling equipment for metal strip; and The induction heating device for the metal strip described in any one of Supplementary Notes 13 to 18 is arranged in the front stage of the cold rolling device.

(Note 21) An induction heating method for metal strip plates, including the following steps: An alternating current flows through a primary closed circuit, and the primary closed circuit is formed by a first conductor member, a second conductor member, and the first conductor member and the second conductor member at a position separated from the width direction end of the metal strip plate. The aforementioned second conductor members are formed by connecting members to each other. The front or back surfaces of the aforementioned first conductor member and the aforementioned metal strip plate face each other and are arranged across the aforementioned metal strip plate in the width direction. The aforementioned second conductor member and the aforementioned The front or back surfaces of the metal strips face each other, are separated by a first distance from the first conductor member in the direction of passing the metal strips, and are arranged across the metal strips in the width direction; and The width direction end portion of the metal strip plate is inductively heated by a secondary closed circuit passing through the width direction end portion of the metal strip plate, and the secondary closed loop is connected to the first conductor member in the metal strip plate respectively. and the induced current generated in the area where the second conductor member faces each other.

According to the above structure, the entire width direction of the metal strip is heated only while passing under (or above) the conductor members, and the heating range can be limited to the width direction ends of the metal strip between the conductor members. department. Thereby, the width-direction end portion of the metal strip plate can be efficiently heated to prevent the end portion of the metal strip plate from cracking. In addition, since the distance between the induction coil and the material to be heated can be ensured to be relatively wide, deformation or meandering of the material to be heated can be easily responded to without additional equipment.

100,200,400: Induction heating device 101,101A,101B: 1st closed loop 102: 2 times closed loop 110,110A,110B,120,120A,120B: Conductor components 111,112,121,122,111A,111B,112A,112B,121A,121B,122A,122B,131A,132A: Board part 131,131A,131B,132,232A,232B,232C,232D,431: connecting components 140,240:AC power supply 14B,PD:arrow 150,160: Movable part 152:Bolt 201A, 201B: switch 351,352,361,362,371,372: Magnetic core material 500: Pickling device 510: Cold rolling device 520:plating tank 522: Wiping device 524:Alloying heating device A,B,C,D,E: contacts 2A-2A,9-9: Line B1,B2: size D: range E,L,L1,L2: distance I: induced current M: molten metal S: Metal strip plate SE: Width direction end W: Board width

FIG. 1 is a plan view of a metal plate induction heating device according to the first embodiment of the present disclosure. FIG. 2A is a side view corresponding to the arrow view along line 2A-2A of the induction heating device shown in FIG. 1 . FIG. 2B is a side view showing a modification of the induction heating device shown in FIG. 1 (side view corresponding to FIG. 2A ). FIG. 2C is a side view showing another modification of the induction heating device shown in FIG. 1 (side view corresponding to FIG. 2A ). FIG. 3 is a diagram conceptually showing the induced current generated in the metal plate in the example of FIG. 1 and FIGS. 2A to 2C . 4 is a plan view of a metal plate induction heating device according to a second embodiment of the present disclosure. 5 is a plan view of an induction heating device for a metal plate according to another example of the second embodiment of the present disclosure. FIG. 6A is a cross-sectional view for explaining the third embodiment of the present disclosure. FIG. 6B is a cross-sectional view for explaining the third embodiment of the present disclosure. 7A is a cross-sectional view for explaining another example of the third embodiment of the present disclosure. 7B is a cross-sectional view for explaining another example of the third embodiment of the present disclosure. 8A is a plan view of an induction heating device for a metal plate (narrow width) according to the fourth embodiment of the present disclosure. 8B is a plan view of an induction heating device for a metal plate (wider) according to the fourth embodiment of the present disclosure. Fig. 9 is a side view corresponding to the arrow 9-9 view of the induction heating device shown in Fig. 8A. FIG. 10 is a graph showing analysis results for verifying the effect of heating the width direction end portion of the metal plate in the embodiment of the present disclosure. FIG. 11 is a graph showing analysis results for verifying the effect of heating the width direction end portion of the metal plate in the embodiment of the present disclosure. FIG. 12 is a side view illustrating a movable portion usable in the embodiment of the present disclosure. FIG. 13 is a side view showing a state in which the distance between conductor members is changed using the movable part of FIG. 12 . FIG. 14A is a side view illustrating a modification of the movable portion that can be used in the embodiment of the present disclosure. FIG. 14B is a view viewed from the direction of arrow 14B in FIG. 14A. FIG. 15 is a side view showing a state in which the distance between conductor members is changed using the movable part of FIG. 12 . FIG. 16 is a plan view of an induction heating device according to an embodiment of the present disclosure applied to thick metal. FIG. 17 is a side view showing the current flowing at the end portion in the width direction when the side surface of the thick metal shown in FIG. 16 is viewed. 18 is a plan view of another example of the induction heating device of the metal plate according to the second embodiment of the present disclosure. FIG. 19 is a plan view showing a state in which the circuit of the induction heating device of FIG. 18 is switched. 20 is a schematic block diagram showing an example of a processing equipment using an induction heating device for a metal plate according to an embodiment of the present disclosure. 21 is a schematic block diagram showing another example of processing equipment using the induction heating device for metal plates according to the embodiment of the present disclosure. FIG. 22 is a schematic block diagram showing another example of processing equipment using the induction heating device for metal plates according to the embodiment of the present disclosure.

100:Induction heating device

101:1 times closed loop

110,120: Conductor components

131,132: Connecting components

140:AC power supply

2A-2A: Line

B1,B2: size

E,L: distance

PD:arrow

S: Metal strip plate

SE: Width direction end

Claims (12)

An induction heating device for metal plates, equipped with: The first conductor member faces at least one of the front and back surfaces of the metal plate and is arranged across the metal plate in the width direction; The second conductor member is spaced apart from the first conductor member by a first distance in the direction across the metal plate, faces at least one of the front and back surfaces of the metal plate, and spans the metal plate in the width direction. board and configuration; A connecting member that connects the first conductor member and the second conductor member to each other at a position separated from the width direction end of the metal plate to form a primary closed circuit; and AC power supply, connected to the aforementioned primary closed loop, The first distance is larger than the total size of the first conductor member and the second conductor member in the direction of the metal plate passing through the metal plate. The induction heating device according to claim 1, wherein the first conductor member and the second conductor member are arranged facing each other on the same side of the metal plate. The induction heating device according to claim 2, wherein the first conductor member and the second conductor member are respectively arranged on the front side and the back side of the metal plate. The induction heating device for metal plates according to any one of claims 1 to 3, wherein the first and second primary closed loops are respectively formed by the first conductor member, the second conductor member and the connecting member. arranged adjacent to each other in the passing direction of the aforementioned metal plates, The AC power supply causes AC currents of the same phase to flow through the conductor members adjacent in the direction of passing the metal plate in the first and second primary closed circuits. The induction heating device for metal plates according to claim 4 is further provided with a switching circuit, and the switching circuit can mutually switch the series connection and the parallel connection of the first and second closed circuits. The induction heating device for a metal plate according to any one of claims 1 to 5, further comprising a magnetic core material arranged on at least one of the first conductor member and the second conductor member. It is the opposite side to the aforementioned metal plate. The induction heating device for a metal plate according to any one of claims 1 to 6, wherein the connecting member is on at least one side of the metal plate in the width direction so as not to interfere with the metal plate in the thickness direction of the metal plate. configuration. The induction heating device for a metal plate according to any one of claims 1 to 7, wherein the connecting member includes a movable part, and the movable part can make at least one of the first conductor member and the second conductor member connect to the metal plate. The board moves upward in the direction of the board. A metal plate processing equipment, including: Pickling plants for metal plates; and The induction heating device of the metal plate according to any one of claims 1 to 8 is arranged in the front section of the aforementioned pickling device. A metal plate processing equipment, including: Cold rolling equipment for metal plates; and The induction heating device of the metal plate according to any one of claims 1 to 8 is arranged in the front section of the aforementioned cold rolling device. A metal plate processing equipment, including: Wiping device sprays gas towards the metal plate with molten metal attached; An alloying heating device that alloys the molten metal attached to the metal plate by heating; and The induction heating device for a metal plate according to any one of claims 1 to 8 is arranged between the wiping device and the alloying heating device. An induction heating method for metal plates, including the following steps: An alternating current flows through a primary closed circuit, and the primary closed circuit is formed by a first conductor member, a second conductor member, and the first conductor member and the aforementioned conductor member at a position separated from the width direction end of the metal plate. The first conductor member is formed by a connecting member that connects the second conductor members to each other. The first conductor member faces at least one of the front and back surfaces of the metal plate and is arranged across the metal plate in the width direction. The second conductor member and At least one of the front surface and the back surface of the metal plate faces each other, is separated from the first conductor member by a first distance in the direction across the metal plate, and is arranged across the metal plate in the width direction; and The width direction end of the metal plate is inductively heated by a secondary closed circuit passing through the width direction end of the metal plate, and the secondary closed circuit is connected to the first conductor member and the first conductor member in the metal plate respectively. It is formed by the induced current generated in the areas where the 2 conductive members face each other.