JP2005209608A - Induction heating device of metal strip and induction heating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a solenoid coil type induction heating device capable of heating even a thin metal strip regardless of magnetic or non-magnetic one. <P>SOLUTION: In the induction heating device, magnetic flux is penetrated aslant through a metal strip and eddy current generated on both sides of the metal strip is made not to be overlapped, and a solenoid coil is arranged so as not to be overlapped on both sides of the metal strip so that the circulating current may flow in the longitudinal direction of the metal strip and heating is carried out. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an induction heating apparatus and induction heating method for a metal strip such as iron or aluminum. In particular, the present invention relates to an induction heating apparatus and an induction heating method for heating uniformly and efficiently regardless of whether the metal strip is thin or magnetic.

  Induction heating by high frequency current of metals is widely used for heat treatment including quenching. Iron and non-ferrous thin plates such as steel plates and aluminum plates are also used for the purpose of controlling the material during the manufacturing process, increasing the heating rate, and improving the productivity and freely adjusting the production volume. It has been used as a heating method that replaces indirect heating by conventional gas heating or electric heating.

  There are two main methods for induction heating a metal strip. One is a so-called heating, in which a high-frequency current is passed through a solenoid coil that surrounds the periphery of the metal strip, and the generated magnetic flux penetrates the longitudinal direction of the metal strip to generate an induction current in the cross section of the metal strip. This is a heating method called LF (longitudinal magnetic flux heating) method.

  The other is that the magnetic flux generated by the primary coil placed on the front and back of the metal strip is passed between the good magnetic bodies called inductors placed at a certain distance on the front and back of the metal strip. This is a TF (transverse heating) method in which a metal strip is passed so as to cross the magnetic flux flowing through the plate, and an eddy current is generated on the plane of the metal strip and heated.

  The LF method has good uniformity of temperature distribution, but the frequency must be increased when the plate thickness is reduced. Furthermore, non-magnetic materials or magnetic materials that exceed the Curie point temperature are infiltrated with current. As the depth increases, the induced currents flowing on the front and back surfaces of the induced current generated in the cross section of the plate flow in opposite directions on the front and back sides and erase each other.

  On the other hand, the TF heating method has the feature that the magnetic flux penetrates the plane of the metal strip and can be heated without distinction between plate thickness, magnetic and non-magnetic, and the magnetic flux can be concentrated so that the heating efficiency is high. is there. However, there is a problem that the magnetic flux tends to be concentrated and concentrated, and the temperature distribution is likely to be non-uniform.

  In order to solve these problems, Patent Document 1 discloses that the single-turn coils on the front and back surfaces in the traveling direction of the strip are shifted and arranged.

JP 2002-43042 A

  FIG. 1 is a schematic view showing conventional LF induction heating. Surrounding the metal strip 1 to be heated with the solenoid coil 2 connected to the high frequency power source 3 and passing the primary current 5, the magnetic flux 4 penetrates the inside of the metal strip 1, and the magnetic flux 4 An eddy current is generated around, and the metal strip 1 is heated by the generated eddy current. FIG. 2 is a schematic diagram showing how eddy currents are generated in the cross section of the metal strip 1.

Due to the magnetic flux 4 penetrating the metal strip 1, an eddy current 6 flows in the direction opposite to the primary current 5 flowing through the solenoid coil 2 in the cross section of the metal strip 1. The eddy current 6 flows from the surface of the metal strip 1 in a concentrated manner within the range of the current penetration depth δ expressed by the following equation (1).
δ [mm] = 5.03 × 10 ⁻⁵ (ρ / μrf) ^0.5 (1)
Here, ρ: specific resistance [Ωm], μr: relative permeability [−], f: heating frequency [Hz]

  As shown in FIG. 2, the generated eddy currents 6 flow in opposite directions on the front and back sides of the plate cross section. Therefore, when the current penetration depth δ increases, the eddy currents on the front and back sides of the plate cancel each other. The current will stop flowing.

  Since ρ increases with increasing temperature, δ becomes deeper with increasing temperature. Further, in the case of a ferromagnetic or paramagnetic magnetic material, μr decreases as the temperature rises and approaches the Curie point, and μr becomes 1 when the temperature exceeds the Curie point. Further, the nonmagnetic material also has a μr of 1.

  When μr is reduced, from the above formula (1), in the case of a non-magnetic material or a magnetic material, the current penetration depth δ becomes deep in the temperature range exceeding the Curie point immediately before the Curie point, and the material to be heated having a thin plate thickness Then, it becomes impossible to heat.

  For example, when the heating frequency is 10 [KHz], the current penetration depth δ of various metals at room temperature is about 1 [mm] for nonmagnetic aluminum, about 4.4 [mm] for SUS304, and for steel of magnetic material Whereas it is about 0.2 [mm], the current penetration depth δ is about 5 [mm] at 750 ° C. when the steel as the magnetic material exceeds the Curie point.

  In order that the front and back currents generated in the plate do not cancel each other, the plate thickness must be at least 10 [mm], and in order to efficiently turn on the power, a thickness of about 15 [mm] is required. . Metal strips that require heat treatment are usually thinner than about 3 [mm] after cold rolling, and are often 2 [mm] or less.

  In order to heat these materials with the LF method, it is necessary to increase the heating frequency to several hundreds [KHz] or more, but there are hardware limitations in the production of large-capacity and high-frequency power supplies, which are realized on an industrial scale. It is often difficult to do.

  The method of Patent Document 1 is considered to be a kind of TF system in which induction coils are arranged above and below the plate, and the magnetic flux generated in the traveling direction of the metal strip is alternately generated in the opposite direction, but the upper and lower coils are shifted. Therefore, it can be considered that the regions where the magnetic fluxes generated by the upper and lower coils cancel each other and the regions where the magnetic flux crosses the strips obliquely can be alternated to prevent the magnetic flux from concentrating.

  Therefore, in the conventional TF method, it is considered that the magnetic flux concentrates on the edge part and the effect of alleviating the problem of overheating of the edge appears. However, since the magnetic flux cancels out an area, it is a single turn. In order to increase power and increase the electric field strength, it is necessary to increase the value of the current that flows to the coil, which increases the copper loss of the coil, and thus has a problem that the efficiency tends to decrease.

  In order to increase the efficiency, as disclosed in the embodiment of Patent Document 1, it is necessary to bring the upper and lower single turn coils close to the strip, but the shape of the strip that passes through is deformed. Or vibrate, it is difficult to heat while passing through a wide and long section.

  The present invention solves the problem of induction heating of the metal strips of these conventional LF methods and TF methods, and uses a solenoid coil method with good temperature uniformity, not limited to magnetic materials, Induction that can be efficiently heated even in a non-magnetic region or in a metal strip having a thickness of 10 mm or less, with excellent temperature uniformity and temperature controllability, while maintaining a sufficient gap between the metal strip and the solenoid coil. A heating device and an induction heating method are provided.

  The gist of the present invention is as follows.

  (1) In an apparatus for inductively heating a metal strip passing through the inside of a solenoid coil, the overlap of areas obtained by vertically projecting the solenoid coils on the front and back sides of the metal strip on the metal strip is 0 to 80%. The induction heating device for a metal strip, wherein the solenoid coils on the front side and the back side are arranged so as to be shifted in the longitudinal direction of the metal strip.

  (2) The induction of the metal strip according to (1), wherein the lengths in the longitudinal direction when the solenoid coils on the front side and the back side are vertically projected onto the metal strip are each 20 mm or more. Heating device.

  (3) In an apparatus for inductively heating a metal strip passing through the inside of a solenoid coil, the overlap of the areas obtained by vertically projecting the solenoid coils on the front and back sides of the metal strip on the metal strip is more than 80% 100 % Or less of the induction heating device of the metal strip according to the above (1) or (2) is disposed downstream of the induction heating device.

  (4) A roll for changing a sheet plate line angle of a metal strip that can be operated at least in the vertical direction is installed before and after the solenoid coil, according to any one of (1) to (3), Induction heating device for metal strip.

  (5) A radiation furnace using a gas combustion or an electric heater or a gas direct flame heating furnace in at least one of the former stage and the latter stage of the induction heating apparatus for a metal strip according to any one of (1) to (4) An induction heating device for metal strips, characterized in that is installed.

  (6) Using the induction heating apparatus for a metal strip according to any one of (1) to (5), a high-frequency current is passed through the solenoid coil, and the metal strip is passed through the solenoid coil to heat it. An induction heating method for a metal strip.

  (7) The induction heating method for a metal strip according to (6), wherein the thickness of the metal strip is 10 μm or more and 10 mm or less.

  (8) The induction heating method for a metal strip according to (5) or (6), wherein the metal strip is heated beyond a Curie point.

  (9) The induction heating method for a metal strip according to any one of (6) to (8), wherein a heating end point temperature is controlled by adjusting a heating frequency of the high-frequency current.

  (10) The heating end point temperature is controlled by adjusting the overlapping amount of the areas obtained by vertically projecting the solenoid coils on the front side and the back side of the metal strip to the metal strip, respectively (6) The induction heating method according to any one of to (9).

  (11) Using the induction heating device for a metal strip described in (4) above, a high-frequency current is passed through the solenoid coil, and the solenoid coils on the front side and the back side of the metal strip are each vertically projected onto the metal strip. An induction heating method for a metal strip, characterized in that heating is performed by adjusting an angle of a sheet passing line of the metal strip with a roll so that the overlap of the areas is 0 to 80%.

  (12) The induction heating method for a metal strip according to (11), wherein the heating end point temperature is controlled by adjusting the sheet passing line angle.

  Here, the longitudinal direction described in (2) above refers to the longitudinal direction of the metal strip. The radiation furnace refers to a heating furnace using radiation and a soaking furnace using radiation.

  The heating method according to the present invention makes it possible to heat a thin plate in the magnetic region and has a small specific resistance, which is impossible with the conventional induction heating method of a solenoid coil, and a non-ferrous metal band such as non-magnetic aluminum or copper. Heating of a plate and further heating in a nonmagnetic region above the Curie point temperature of a magnetic material such as iron are possible.

  The frequency of the high-frequency heating power source to be used is also several kilohertz to several tens of kilohertz, which is easy to handle, and may be as high as about 100 kilohertz. Therefore, there is an insulation problem associated with the increase in coil voltage, which is a problem with high-frequency heating, It is easy to cope with heating by surrounding leakage magnetic flux, and hardware restrictions are greatly eased.

  In addition, since the heating end point temperature can be accurately controlled, it is possible to prevent overheating and the temperature distribution in the plate width direction can be made uniform, enabling precise heating with extremely high temperature controllability. There is an excellent effect that metallurgical control can be freely performed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 3 is a schematic diagram illustrating the induction heating device of the present invention, and FIG. 4 is a schematic diagram illustrating a side surface of the induction heating device of the present invention and an induction heating method.

  The solenoid coil used in the following description of the present invention is a general term for an induction coil in which a material to be heated is wound by one or more turns with a pipe, wire, plate, or the like of a good conductor such as copper. Neither circular nor circular is particularly specified.

  In the present invention, the solenoid coil on the front side and the back side is connected to the metal strip so that the overlap of the areas obtained by vertically projecting the solenoid coils on the front and back sides of the metal strip to the metal strip is 0 to 80%. Are shifted in the longitudinal direction. That is, as shown in FIG. 3 and FIG. 4, the solenoid coil 2 facing the metal strip 1 in the width direction is shifted in the longitudinal direction of the metal strip with the metal strip 1 interposed therebetween.

  The amount of displacement of the front and back side solenoid coils 2 is more than 80% in the area when each of the front and back side solenoid coils 2 is vertically projected onto the metal strip, and is separated from the position. And

  As shown in FIGS. 4 (a) and 4 (b), the area when perpendicularly projected onto the metal strip in the present invention means that the coil with the solenoid coil 2 at the end of the metal strip is made of metal. An area surrounded by a line when vertically projected on the band plate is shown, and includes not only the area of the solenoid coil alone but also a space portion sandwiched between the solenoid coils.

  FIG. 4 (a) shows a case where the areas of the front surface side solenoid coil and the back side solenoid coil of the metal band plate that are projected perpendicularly to the metal band plate do not overlap at all (overlap 0%). ) Indicates a case of partial overlap, and the area ratio of the overlapping portion is defined as Sx / Sy × 100%.

  To prevent 80% or more of the area when the solenoid coils 2 on the front and back sides of the metal strip are projected vertically on the metal strip, the solenoid coils on the front and back sides are shifted so that the sides of the metal strip The solenoid coil on the side is arranged obliquely with respect to the longitudinal direction of the metal strip.

  There are two reasons for this. The first reason is that by shifting the coils on the front and back sides of the solenoid coil 2 facing the metal strip in the longitudinal direction, the rate of interference of the magnetic flux generated by the front and back solenoid coils is reduced, and the right-handed screw law Thus, as shown in the side view of the metal strip in FIG. 5 (the solenoid coil is not shown), the magnetic flux 4 generated by each solenoid coil 2 facing the front and back surfaces of the metal strip is strengthened. This is because the strip 1 penetrates diagonally, and a path 7 of eddy current is generated by the magnetic flux 4 and spreads in an oblique direction of the plate thickness at right angles to the magnetic flux 4.

  In the conventional LF induction heating, the magnetic flux generated by the solenoid coil on the front and back surfaces of the metal strip is generated almost symmetrically across the metal strip, so the magnetic flux generated in the direction perpendicular to the metal strip interferes. The magnetic flux is canceled and only the longitudinal component of the metal strip, that is, the traveling direction component is strengthened and remains, and penetrates the cross section of the metal strip.

  Therefore, since an eddy current is generated in the cross section of the metal strip, when the current penetration depth is increased, the currents on the front and back surfaces of the metal strip interfere with each other and no current flows.

  On the other hand, in the present invention, the solenoid coil 2 on the front and back surfaces is shifted with respect to the longitudinal direction of the metal strip so that the magnetic flux is inclined, so that the current flows even when the current penetration depth δ is deep. Can be secured independently in the longitudinal direction of the metal strip.

  However, if the amount of displacement of the coil on the front side and the back side of the solenoid coil 2 facing the metal strip is small, the density of magnetic flux generated by the solenoid coil on the front side and back side of the metal strip is small. Since the direction is the same and the direction is opposite, the other than the magnetic flux in the longitudinal direction of the metal strip cancel each other, and it becomes close to the conventional LF induction heating.

  Therefore, as a result of various investigations by electromagnetic field analysis regarding the amount of shift in which magnetic flux that obliquely penetrates the metal strip works effectively, if the metal strip and the solenoid coil are close, the front side solenoid coil and the back side solenoid coil Effective induction current is generated in the metal strip even if the coil displacement is relatively small or non-magnetic, but if the metal strip is separated from the solenoid coil, the front side solenoid coil and the back side solenoid coil It has been found that effective induced current cannot be generated in the metal strip unless the amount of deviation is increased.

  In the present invention, in consideration of the distance between the metal strip and the solenoid coil that can be realized at the production site, the area when the front and back solenoid coils of the metal strip are vertically projected onto the through-line of the metal strip. In this case, the oblique magnetic flux 4 can be effectively expressed by disposing the metal strips at positions that do not overlap each other in the traveling direction of the metal strips, that is, by setting the overlap to 0 to 80%.

  Preferably, when the overlap is 0 to 60%, it is more effective, and heating can be performed more effectively even in the non-magnetic region.

  The second reason is to prevent the above-described eddy current path 7 from canceling out on the front and back of the plate. When the solenoid coils 2 on the front and back surfaces of the metal strip are projected vertically onto the metal strip, the metal By shifting with respect to the longitudinal direction of the strip, as shown in the side view of the metal strip in FIG. 6A (solenoid coil is omitted), an eddy current path 7a independent in the traveling direction of the metal strip 1 is shown. And 7b can be made.

  The current paths 7a and 7b are connected by a path 7c on the side surface to form a circulating current path as shown in FIG. 6B, and induction heating can be performed. 6 (c) and 6 (d) show the case where the overlap of the solenoid coils on the front and back surfaces becomes large, but a certain amount of current can flow if the current paths do not completely overlap. .

  If the path of the eddy current can be provided independently in the longitudinal direction of the metal strip as described above, an eddy current having a current penetration depth equal to or greater than the plate thickness can be generated in the metal strip 1. Alternatively, the metal thin plate can be induction-heated by a solenoid coil method even with a non-magnetic material.

  The method of winding the solenoid coil on the front and back sides of the metal strip does not necessarily have to be horizontal with respect to the metal strip line, as shown in FIG. The same effect can be obtained.

  Therefore, in general, when there is a solenoid coil having a rectangular cross section used for heating the strip material, the through plate line is modified so that the solenoid coils on the front side and the back side of the metal strip are respectively connected to the metal coil. It is also possible to apply the present invention by inclining the through-plate line with respect to the solenoid coil so that the overlap with the area vertically projected onto the band plate is 0 to 80%.

  That is, as shown in FIG. 10, before and after the existing solenoid coil 2, roll plate line changing rolls 11 and 12 are provided so as to freely control the feed plate line of the metal strip, and the solenoid coil 2. If the approach angle is freely changed, induction heating can be freely performed in accordance with the thickness of the metal strip and the end point temperature described above.

  The rolls 11 and 12 placed before and after the solenoid coil 2 are preferably made of a non-magnetic material so that they are not easily heated by induction, and may be made of insulating ceramics or non-magnetic stainless steel, and are affected by the solenoid coil. It is desirable that the surface is made of an insulating material so that it is installed at a sufficiently distant position and no spark is generated between the metal strip and the metal strip.

  Rolling line angle changing rolls 11 and 12 can be easily moved up and down like 11 → 11 ′ and 12 → 12 ′ if they are moved together with the roll bearing using a hydraulic cylinder, air cylinder, motor, etc. Thus, the relative angle with respect to the solenoid coil can be changed.

  Further, it is preferable to move the metal strip 1 horizontally as well, since it is possible to move 11 ′ → 11 ″, and the relative position of the metal strip 1 with respect to the induction coil 2 can be freely controlled. Thereby, free heating regardless of magnetism or non-magnetism becomes possible.

  In addition, the solenoid coil is not limited to the existing one, and the projection when the solenoid coil on the front side and the back side of the metal strip according to the present invention is vertically projected onto the plate line (the plate line before the line change). A solenoid coil having an area overlap of 0 to 80% may be used.

  The form of the solenoid coil used in the present invention is not particularly specified, but it is easy to make a rectangular shape when viewed from the front. A circular or semi-elliptical shape may be used.

  Since the width of the solenoid coil increases the magnetic flux density, it does not work effectively without a certain width.

  As a result of various experiments, as shown in the schematic side sectional view of FIG. 7 (the side coil is omitted), the width of the solenoid coil is 20 mm even in the case of one turn (a) using the simplest copper pipe. The above is preferable, and even when a plurality of thin copper pipes are used (by a plurality of turns or parallel connection) (b), it has been found that 20 mm or more is effective. (C) shows a case using a bus bar, but a width of 20 mm or more is also effective.

  In this heating method, in order to increase the magnetic flux density, it is more efficient to wind the induction coil multiple turns. By winding multiple turns, a large ampere turn is obtained at a low current, and the copper loss is small and the electric field strength is large. Efficient heating (high magnetic flux density) can be performed, and as a result, the heating length can be reduced and the power source capacity can be reduced.

  As described above, the present invention has a problem in the current penetration depth, and in particular, since the effect in the nonmagnetic region and the nonmagnetic material, which is impossible by the induction heating by the conventional solenoid coil, is remarkable, The effect on a metal strip having a thickness of 10 μm or more and 10 mm or less, which cannot be effectively heated by induction heating with a coil, is remarkable.

  Next, with regard to temperature control, which is a problem with induction heating, the heating end point temperature may be adjusted by adjusting the total amount of power. When control is required, this heating method can freely control the path of the current generated in the metal strip 1 by controlling the interference between the magnetic fluxes generated by the front and back induction coils as described above. The end point temperature can be accurately controlled.

  That is, the current penetration depth δ represented by the above equation (1) and the range of the eddy current path to be generated are the angle at which the heating frequency f and the magnetic flux 4 penetrate the metal strip 1, that is, the metal of the solenoid coil 2 on the front and back surfaces. By controlling the amount of shift in the strip travel direction, the path of eddy current that can flow in the metal strip 1 is changed as shown in the change from FIG. 6A to FIG. Can be controlled.

  The frequency control of the power source can be realized by changing the matching condition with a matching device installed between the solenoid coil and the power source. Further, the control of the overlapping of magnetic fluxes can be realized by the device as shown in FIG. 10 described above, or by the devices as shown in FIGS. 8A and 8B.

  FIGS. 8A and 8B are schematic views of the solenoid coil as viewed from the side. First, the connection state shown in FIG. 8A, for example, 8C → 9A → 8D → 9B → 8E → 9C. → 8F → 9D → 8G → 9E, as shown in Fig. 8 (b), 8D → 9A → 8E → 9B → 8F → 9C → 8G → 9D → 8H → 9E If it connects to, the interference amount of magnetic flux can be changed.

  For example, the connection can be changed by changing the connection positions of the coils above and below the metal strip 1 with a water-cooled copper cable. In this way, if the amount of overlap of the current paths can be changed, even if the output of the power supply is increased, power does not enter above a certain temperature, and the heating end point temperature can be accurately controlled.

  In addition, although this heating method generates a magnetic flux by a solenoid coil, the efficiency is somewhat lowered. However, unlike the TF heating method, the magnetic flux does not concentrate on the edge and tends to be distributed on the average. Very good temperature uniformity.

  As described above, this heating method is an excellent induction heating method for a metal strip that enables induction heating in a non-magnetic region, which was impossible with conventional solenoid induction heating, but as described above, Since the magnetic flux 4 generated in the solenoid coil 2 penetrates the metal strip 1 diagonally, the solenoid coil 2 facing the front and back surfaces of the metal strip must be arranged so as not to overlap in the metal strip travel direction. A large space must be taken in the direction of travel of the metal strip.

  Therefore, when there is a space restriction, as shown in FIG. 11, the overlap of the area where the front and back solenoid coils of the metal strip are vertically projected onto the metal strip is more than 80% and less than 100%. If the solenoid coil 15 of this heating system is arranged at the subsequent stage of the LF induction heating device 14, it is effective because minimal expansion is sufficient.

  Further, the induction heating device of the present invention can be installed in at least one of a front stage and a rear stage of a gas combustion or electric heater-based radiation furnace or a gas direct flame heating furnace. For example, a case in which an induction heating device is provided in the middle or on the exit side of a general annealing furnace is shown below.

  Here, the radiation furnace refers to a so-called preheating furnace, a heating furnace, or a soaking furnace that equalizes the temperature of the material to be heated, which raises the temperature of the material to be heated by radiation. In addition, the gas direct flame heating furnace refers to a furnace that directly heats the material to be heated and heats it, a furnace that heats the material on the surface of the material to be heated by applying a reducing flame, and the like.

  In continuous heat treatment furnaces for steel sheets (also called continuous heat treatment equipment or continuous annealing furnaces), after heating, soaking, and cooling, reheating between the cooling zone and the overaging zone (also called overaging oven) However, only the magnetic region can be heated.

  In contrast, the induction heating apparatus of the present invention can heat a thin metal strip regardless of whether it is magnetic or non-magnetic, so that no curie is generated from the temperature range near the Curie point where the heating efficiency drops sharply. Heating is possible even in a temperature range exceeding the point.

  Therefore, in the induction heating apparatus of the present invention, in the preheating furnace and the heating furnace using gas heating, such as a radiation furnace that is a conventional indirect heating method or a flame combustion furnace that is a direct heating, the thickness of the metal strip Even if it is not possible to heat to the specified temperature without slowing down the line speed because it becomes thicker, it is possible not only to heat to the specified temperature without reducing the line speed, but also to increase the line speed and increase the production volume However, if the power supply is sufficient, it will be possible to cope with it, and the freedom of operation will increase dramatically.

  In addition, in radiant heating, as the temperature of the material to be heated increases, the amount of radiant heat transfer from the furnace decreases, and the heating efficiency decreases, whereas the induction heating device of the present invention forcibly supplies power. Since it can be directly put into the material to be heated, there is also an advantage that the heating efficiency can be increased.

  However, heating by electricity has a higher energy unit price per calorific value than heating by gas, and heating all of them with electricity is disadvantageous because the energy cost increases.

  Therefore, the present invention is capable of reliably raising the temperature to the non-magnetic region above the Curie point on the high temperature side where the heating efficiency is high and the energy unit price is low and the indirect heating by the conventional gas is used and the heating efficiency is reduced by radiation. By using the induction heating apparatus, a low-cost true schedule-free operation that cannot be realized by a conventional continuous heat treatment apparatus is realized.

  As shown in FIG. 12A, the induction heating device of the present invention may be installed between a radiation furnace or a direct flame heating furnace 16a and a radiation furnace or a direct flame heating furnace 16b, or most effectively. As shown in FIG. 12 (b), it is preferable to install it at the rear stage of the radiation furnace or the direct flame heating furnace 16. The installation is a horizontal path in the figure, but the vertical path or the diagonal is not particularly concerned with the form.

  Although the above description assumes a moving metal strip, the same effect can be obtained when applied to heating in a stationary state.

  As described above, this heating method enables heating of the magnetic region as well as heating of the non-magnetic region, which is impossible with the conventional induction heating method of the solenoid coil.

  The heating power supply frequency to be used can be a relatively low frequency that is easy to handle and inexpensive, and it is easy to adjust the coil voltage, which is a problem with high frequency heating, and there are hardware limitations. It is greatly eased.

  Unlike single-turn heating, by making a plurality of coils, a large ampere turn can be obtained with a relatively low current, so that the heating efficiency can be increased.

  In addition, since the end point temperature control is reliable, it is possible to prevent overheating, and the present invention is an excellent induction heating method for a metal strip having characteristics that have not existed in the past.

  The effect of the present invention was confirmed by experiments. In the experiment, a cold rolled steel sheet having a thickness of 0.23 mm and a width of 80 mm was used. The power source was 25 KHz, 25 KW, and a solenoid coil (3T (turn)) having a width of 120 mm and a height of 250 mm was manufactured and heated with a water-cooled copper pipe having an outer diameter of 10 mm and an inner diameter of 8 mm.

  As shown in FIG. 4 (a), the experiment was conducted according to the experiment A and FIG. 9 according to the present invention, in which the overlapping area ratio of the vertical projection areas of the upper and lower solenoid coils facing the steel plate was 0% (hereinafter abbreviated as overlapping area ratio). As shown, Experiment B according to the present invention in which the coil is wound in a rectangular shape and the steel plate is arranged at 30 degrees with the solenoid coil (overlap area ratio 0%) and induction heating is performed according to the present invention, and the overlap area ratio is 30%. C, Experiment D with the same configuration as Experiment C and a heating frequency of 6 KHz, and Experiment E using a conventional heating method with an overlapping area ratio of 90% as a comparative example were compared.

  The steel plate was heated in a state where a thermocouple was welded at the center of the plate width at a pitch of 50 mm, the front and back surfaces of the steel plate were intimately bonded with 50 mm ceramic fibers and insulated, and the temperature was measured. Normally, the material to be heated is heated while traveling, even if there is a current distribution, it is often smoothed as a whole, but this experiment looks at the influence of the current distribution, so the influence of the current distribution is likely to appear. Heating was performed in a stationary state.

  The results are shown in Table 1. The evaluation was evaluated as “◎” when heating exceeding 750 ° C., which is a nonmagnetic region, and “x” when heating was not possible.

  In this experiment, the current penetration depth is 3.2 [mm], and heating of the non-magnetic region exceeding about 730 ° C. with a plate thickness of 0.25 [mm] is not possible with the conventional method. In both heating methods A and B, the heating rate did not decrease even in the temperature range exceeding 730 ° C., and the heating was stopped at 1000 ° C.

  In Experiment C, the temperature rises without any significant change in the heating rate even when the temperature exceeds 750 ° C., the temperature rise stops exactly at 820 ° C., and the end point temperature control is performed in the non-magnetic region by controlling the coil overlap ratio. I confirmed that I was able to.

  Experiment D, in which the frequency was decreased under the same conditions, confirmed that the end point temperature could be controlled by changing the frequency without increasing the temperature beyond 765 ° C, which is a non-magnetic region. did.

  This is presumably because the current penetration depth increases as a result of the increase in current penetration depth by lowering the frequency.

  On the other hand, in Experiment E, which is a conventional method, the heating rate suddenly fell from 650 ° C., and finally, heating could be performed only up to 725 ° C.

  As described above, according to the present invention, heating of a thin plate in a magnetic region, heating of a nonmagnetic nonferrous metal strip having a small specific resistance, and heating in a nonmagnetic region above the Curie point temperature of a magnetic material such as iron. Is possible.

  In the present invention, the frequency of the high-frequency heating power source to be used may be several kilohertz to several tens of kilohertz, and may be as high as around 100 kilohertz, which greatly reduces hardware restrictions.

  Furthermore, according to the present invention, the end point temperature of heating can be controlled with high precision, so that precise heating with extremely high temperature controllability is possible, and metallurgical control of metal can be freely performed.

  Thus, since this invention has the outstanding effect, its industrial applicability is large.

It is a schematic diagram which shows the conventional solenoid type induction heating. It is a schematic diagram explaining the induction current which flows into the cross section of the metal plate of the conventional solenoid type induction heating. It is a schematic diagram which shows the induction heating apparatus of this invention. (A) It is a schematic diagram explaining the induction heating apparatus and induction heating method of this invention, and is a figure which shows the case where the vertical projection area of the solenoid coil in the front and back side of a metal strip is zero. (B) It is a schematic diagram explaining the induction heating apparatus and induction heating method of this invention, and is a figure which shows the case where the vertical projection area of the solenoid coil of a metal strip board front and back side overlaps partially. It is a side cross-sectional schematic diagram explaining the eddy current which generate | occur | produces in a metal strip with the induction heating method of this invention. (A) It is a side cross-sectional schematic diagram explaining the relationship of the eddy current which generate | occur | produces on the front and back of a metal strip by the induction heating method of this invention. (B) It is a plane schematic diagram explaining the relationship of the eddy current which generate | occur | produces on the surface of a metal strip by the induction heating method of this invention. (C) It is a side cross-sectional schematic diagram explaining the condition where the eddy current generated on the front and back surfaces of the metal strip overlaps by the induction heating method of the present invention. (D) It is a plane schematic diagram explaining the condition where the eddy current which generate | occur | produces on the surface of a metal strip by the induction heating method of this invention overlaps. It is a side cross-sectional schematic diagram explaining the width | variety of the solenoid coil of this invention. (A) shows a case where one turn coil is used, (b) shows a case where a plurality of coils are used, and (c) shows a case where a wide plate material such as a bus bar is used. (A), (b) is a side cross-sectional schematic diagram explaining the method to change the vertical projection area to the metal strip of the front and back solenoid coils of this invention. It is a schematic diagram explaining the passage direction of a metal strip with respect to the arrangement | positioning direction of the solenoid coil by the induction heating method of this invention. It is a side cross-sectional schematic diagram explaining the method of changing a path | pass with the roll for angle change of the sheet | seat installed before and behind the solenoid coil by this invention, and changing freely the vertical projection area to the metal strip of the solenoid coil of the front and back. It is a schematic diagram explaining the induction heating apparatus which has arrange | positioned the induction heating apparatus shown in FIG. 3 in the back | latter stage of the conventional LF type induction heating apparatus of this invention. (A) It is a schematic diagram explaining the induction heating apparatus which has arrange | positioned the induction heating apparatus shown in FIG. 3 in the middle of the conventional heating furnace of this invention. (B) It is a schematic diagram explaining the induction heating apparatus which has arrange | positioned the induction heating apparatus shown in FIG. 3 in the back | latter stage of the conventional radiation furnace or direct flame heating furnace of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Metal strip 2 ... Solenoid coil 3 ... High frequency power supply 4 ... Magnetic flux 5 ... Primary current 6a ... Eddy current 6b ... Eddy current direction 7 ... Eddy current path 7a ... Independent eddy current path 7b ... Independent eddy current Current path 8A, 8B, 8C, 8D, 8E, 8F, 8G, 8H ... Table (upper) side coil side surface terminal portions 9A, 9B, 9C flowing between the current paths 7a and 7b , 9D, 9E, 9F, 9G, 9H ... Back (lower) coil side surface terminal part 10 ... Roll 11, 11 ', 11''... Rolling plate line angle changing roll 12, 12' ... Passing plate line angle changing Roll 13 ... Roll 14 ... Conventional LF induction heating device 15 ... Induction heating device 16, 16a, 16b of the present invention ... Radiation furnace or direct flame heating furnace 17 ... Induction heating device 18 of the present invention ... Next treatment zone

Claims (12)

  In the apparatus for induction heating of the metal strip passing through the inside of the solenoid coil, the overlap of the area where the solenoid coils on the front side and the back side of the metal strip are vertically projected onto the metal strip is 0 to 80%. Further, the induction heating device for a metal strip, wherein the solenoid coils on the front surface side and the back surface side are shifted in the longitudinal direction of the metal strip.   2. The induction heating apparatus for a metal strip according to claim 1, wherein the lengths in the longitudinal direction when the front and back solenoid coils are vertically projected onto the metal strip are each 20 mm or more.   In an apparatus for inductively heating a metal strip passing through the inside of a solenoid coil, the overlap of the area where the solenoid coils on the front and back sides of the metal strip are vertically projected on the metal strip is more than 80% and less than 100%. 3. An induction heating apparatus for a metal strip according to claim 1 or 2, wherein the induction heating apparatus for a metal strip according to claim 1 or 2 is disposed after an induction heating apparatus.   The metal strip according to any one of claims 1 to 3, wherein a roll for changing the sheet plate line angle of the metal strip that can be operated at least in the vertical direction is installed before and after the solenoid coil. Induction heating device.   A radiation furnace using gas combustion or an electric heater or a gas direct flame heating furnace is installed in at least one of the former stage and the latter stage of the induction heating apparatus for a metal strip according to any one of claims 1 to 4. An induction heating device for a metal strip.   A high frequency current is passed through a solenoid coil using the induction heating device for a metal strip according to any one of claims 1 to 5, and the metal strip is passed through the solenoid coil to heat it. An induction heating method for a metal strip.   The thickness of the said metal strip is 10 micrometers or more and 10 mm or less, The induction heating method of the metal strip of Claim 6 characterized by the above-mentioned.   The induction heating method for a metal strip according to claim 5 or 6, wherein the metal strip is heated beyond a Curie point.   The induction heating method for a metal strip according to any one of claims 6 to 8, wherein a heating end point temperature is controlled by adjusting a heating frequency of the high-frequency current.   10. The heating end point temperature is controlled by adjusting the overlapping amount of the areas obtained by vertically projecting the solenoid coils on the front side and the back side of the metal strip to the metal strip, respectively. An induction heating method for a metal strip according to claim 1.   A high frequency current is passed through the solenoid coil using the induction heating device for a metal strip according to claim 4, and the surface area and back surface solenoid coils of the metal strip are vertically projected onto the metal strip, respectively. An induction heating method for a metal strip, characterized in that heating is performed by adjusting an angle of a sheet passing line of the metal strip by means of a roll so that is 0 to 80%.   The induction heating method for a metal strip according to claim 11, wherein the heating end point temperature is controlled by adjusting the sheet passing line angle.

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