JP2004327375A - High-frequency induction heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-frequency induction heating device capable of temperature control with high accuracy even if the number of division of heating coils is increased in high-frequency induction heating of a comparatively large area. <P>SOLUTION: The high-frequency induction heating device is provided with a plurality of high-frequency induction heating coils 1 consisting of magnetic substance cores and coil conductors, a plurality of high-frequency power supply device 4 fitted in correspondence with each high-frequency heating coil for feeding high-frequency power to each heating coil, a temperature distribution measuring device 14 measuring temperature distribution of a heated plate, and a temperature distribution control device 13 having a function of individually controlling output power of the high-frequency power supply device by operating in comparison temperature distribution data from the temperature distribution measuring device and a preset temperature table. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high-frequency induction heating technique for metal.
[0002]
[Prior art]
Conventionally, there has been a need to heat metal in various technical situations.For example, in the field of brakes, after a metal brake plate is heated to a predetermined temperature, a non-metal brake pad for a friction surface is required. Joining and bonding are performed. Further, when performing insulation coating on the surface of the band-shaped metal as rust prevention treatment, the target metal is heated to a predetermined temperature, and then an insulation coating agent is applied.
[0003]
When raising the temperature of metals for bonding and bonding between these metals and non-metals, the temperature unevenness affects the bonding and bonding unevenness, but when heating by high frequency induction heating, the temperature distribution is not uniform. There were drawbacks. In addition, even in applications where a relatively large disc-shaped or band-shaped metal is heated in a stationary state, when high-frequency induction heating is used, there is a problem that the temperature distribution is not uniform. For this reason, conventionally, in the heating of these metals, heating by an atmosphere furnace has been mainly employed, although the working efficiency is lower than that of the high frequency induction heating. In addition, even when high-frequency induction heating is used, it is necessary to repeat heating for a short time or soak by heat conduction while heating is stopped, to gradually raise the temperature, and there is a problem in that the working efficiency is poor.
[0004]
In view of such a problem, there is a uniform heating method using a large-area crucible for vacuum evaporation disclosed in Japanese Patent Application Laid-Open No. 5-299163. FIG. 7 shows a circuit configuration of the heating device disclosed in this publication. That is, this device has the following advantages.
[0005]
First, by dividing the high-frequency heating coils 15a, 15b, and 15c into a plurality of parts and individually controlling the variable inductances 16a, 16b, and 16c attached to the heating coils, the heat generation distribution of the metal to be heated in which the heating coils are arranged is determined. It could be adjusted, and uniform heating of the large area metal to be heated was possible.
In addition, since the resonance frequency as an operation requirement of the high-frequency power supply changes with the control of the variable inductance attached to the individual heating coils, one common variable inductance is installed to correct this. It was possible to control at the same time.
Furthermore, there is an advantage that it is economical because only one power supply 17 is required, and there is no need to consider magnetic interference between the heating coils.
[0006]
[Patent Document 1]
JP-A-5-299163
[Problems to be solved by the invention]
However, when the technology described in the above-mentioned publication is applied to a device that requires more precise control of the temperature distribution, there are the following problems.
First, since the power factor of the heating coil in the high-frequency heating is extremely small, assuming that the inductance of the heating coil is Lc and the value of the variable inductance of the circuit is Li, the heating amount of the heating coil is approximately [Lc / (Lc + Li)] ² Is proportional to Of the plurality of heating coils, individual variable inductances Li attached to one heating coil are controlled, and the amount of control when increasing (or decreasing) the amount of heating at that portion is determined by the variable inductance change range and the heating coil. Is limited to a certain ratio determined by the inductance of the control, and control close to zero is impossible.
[0008]
Further, when the number of divisions of the heating coil is increased and the heating area of one heating coil is narrowed to improve the controllability of the temperature distribution, the impedance of the heating coil becomes small and the loss of the variable inductance cannot be ignored.
[0009]
Furthermore, as the number of divisions of the heating coil increases, the required change range of one variable inductance commonly installed for tracking the resonance frequency increases, which may become impossible.
[0010]
Accordingly, an object of the present invention is to provide a high-frequency induction heating apparatus that can perform high-precision temperature control even when the number of divisions of a heating coil is increased in a relatively large-area high-frequency induction heating.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a high-frequency induction heating apparatus according to the present invention includes a plurality of high-frequency induction heating coils, each of which is arranged to face a plate to be heated and includes a magnetic iron core and a coil conductor, and A plurality of high-frequency power supply devices are provided for each coil and supply high-frequency power to each heating coil.
Preferably, the high-frequency induction heating device compares the temperature distribution measurement device for measuring the temperature distribution of the plate to be heated with the temperature distribution data from the temperature distribution measurement device and a preset temperature table. And a temperature distribution control device having a function of individually controlling the output power of the high-frequency power supply device.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating a connection relationship between a plurality of heating coils, a high-frequency power supply that supplies high-frequency power, and a control device according to the present embodiment.
[0013]
In FIG. 1, a small-capacity high-frequency power supply device 4 is individually arranged for each of n heating coils 1. The high frequency power supply 4 converts the commercial frequency (50 Hz or 60 Hz) power supplied from the commercial power supply 12 into DC power by the forward conversion circuit 6 and high frequency power of a frequency suitable for the output power by the next inverse conversion circuit 5.
[0014]
The high-frequency output of the high-frequency power supply 4 is supplied to the heating coil 1 via the output transformer 3, the resonance capacitor 2, and a high-frequency cable 35 described later.
The temperature distribution of the heated plate 40 (see FIG. 2) heated by the n heating coils is measured by the temperature distribution measuring device 14 and sent to the temperature distribution control device 13 as a signal.
[0015]
The temperature distribution control device 13 obtains n from the temperature table, that is, the scheduled heating history (time-temperature) of the heated plate and the allowable temperature difference, and the elapsed time and the temperature distribution signal measured by the temperature distribution measurement device 14. Each heating amount of each heating coil is calculated, and a signal is sent to the corresponding high-frequency power supply device 4 as an output command value. Further, it is preferable that the output of the high-frequency power supply device 4 is controlled by an output history database based on past performance data or the like.
[0016]
The high-frequency power supply 4 feeds back the output of the input power supply current measurement CT (current transformer) 9 and the input power supply voltage measurement PT (instrument transformer) 10 as an input power signal via the power converter 11. This is compared with the output command value from the temperature distribution control device 13 by the comparison operation circuit 8 and the timing of each element of the inverse conversion circuit 5 is controlled, so that the output power of the power supply device can be reduced. It works in the direction to match the command value from.
[0017]
Since the high-frequency power supply device 4 corresponds to one heating coil 1, each heating coil can individually control the output between 0% and 100%, so that it is possible to control the temperature distribution with high accuracy. Become.
[0018]
The above-mentioned feedback and output control targets of the high-frequency power supply device 4 are one example, and there are countless other combinations. In each case, the actual output signal of the high-frequency power supply device 4 and the temperature distribution control device 13 It is not limited to any form as long as it is compared with the output command value from the controller and the deviation is controlled to be small.
[0019]
FIG. 2 schematically shows a state in which a plurality of heating coils are arranged on a plate to be heated. A plurality of heating coils 1 are arranged on a disk-shaped heated plate 40 having a thickness t and a diameter ΦD with a gap g. In the embodiment of FIG. 2, a total of 37 heating coils are arranged, but the number is arbitrary.
[0020]
Further, since the direction in which the heating coil is not disposed is a free space, it can be used as an access to a plate to be heated, a space for installing a temperature distribution measuring device (not shown), and the like.
In FIG. 2, a high-frequency cable 35 is connected to each of the plurality of heating coils 1 arranged, and individually controlled high-frequency power is supplied from individual high-frequency power supplies (not shown).
[0021]
If magnetic interference between the high-frequency cables 35 becomes a problem due to the respective currents and frequencies, the high-frequency cables 35 are respectively covered with magnetic shield tubes (not shown) made of copper or aluminum.
[0022]
3 to 5 show structural diagrams of one heating coil for multiple arrangements according to the present embodiment. 3 to 5, a coil conductor 31 made of a water-cooled copper tube is arranged so as to wind around a coaxial core 32 using a magnetic material such as a ferrite core. A high-frequency current and cooling water are supplied from a water-cooled high-frequency cable 35.
[0023]
The entire heating coil 1 is protected by the insulating cover 33. Depending on the temperature of the metal to be heated, the insulating cover 33 can be made of a heat-insulating and heat-resistant material. In FIGS. 3 to 5, the coil conductor 31 and the high-frequency cable 35 are shown as water-cooled examples. However, when the value of the high-frequency current is small, both the coil conductor 31 and the high-frequency cable 35 are naturally air-cooled high-frequency twists. It is also possible to use a wire (Litz wire).
[0024]
FIG. 6 shows a model of heating of the metal to be heated by the heating coil.
When a high-frequency current 41 as shown flows through the coil conductor 31 of the heating coil 1 which has a gap g in the heated plate 40 and is opposed to the heated coil 1, the coaxial core 32 to the heated plate 40 are surrounded by the illustrated high-frequency current 41. A high-frequency magnetic flux 42 is generated in the loop, and an induced current flows through the plate 40 to be heated so as to prevent the change of the magnetic flux, so that the illustrated heat generation distribution is obtained.
[0025]
At this time, since the high-frequency magnetic flux 42 generated by the high-frequency current 41 flowing through the coil conductor 31 is limited to the closed range of the coaxial core 32, magnetic interference to the outside is also prevented, and the core made of a magnetic material is removed. Utilization increases the magnetic flux generation efficiency, increases the inductance of the heating coil, and reduces the voltage drop rate in the wiring.
[0026]
The heating distribution of the heated plate by one heating coil shown in FIG. 6 is an image diagram, which changes according to the material, the gap, and the frequency of the heated plate. The area served by the heating coil is heated substantially uniformly.
[0027]
As described above, the present invention has a configuration in which a plurality of heating coils including a coaxial iron core and a coil conductor using a magnetic material such as a ferrite core and a small-capacity high-frequency power supply are connected to each heating coil. The present invention solves the problems of the conventional device.
[0028]
In other words, by using a heating coil consisting of a coaxial iron core using a magnetic material such as a ferrite core and a coil conductor, the high-frequency magnetic flux generated by the current flowing in the coil conductor is converged in the iron core, Since only the portion acts on the metal to be heated, unnecessary magnetic interference between the heating coils is prevented.
[0029]
At the same time, the use of the iron core increases the magnetic permeance, increasing the heating efficiency as compared with the case without the iron core, and at the same time, increasing the inductance of the coil and reducing the voltage drop rate in the wiring.
[0030]
By preventing unnecessary magnetic interference among the plurality of heating coils, a high-frequency power supply can be provided for each heating coil, and the heating amount can be individually controlled from 0% to 100%. Distribution control becomes possible.
[0031]
Due to recent advances in power electronics and mass production, high-frequency power supplies of several kW, for example, have become extremely low-cost compared to conventional ones. It can be determined that the disadvantage of installing a plurality of power supplies is eliminated because the cost may be low.
[0032]
【The invention's effect】
As described above, according to the high-frequency induction heating apparatus of the present invention, high-precision temperature control can be performed even when the number of divided heating coils is increased in high-frequency induction heating of a relatively large area.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a connection relationship between a plurality of heating coils, a high-frequency power supply that supplies high-frequency power, and a control device according to the present embodiment.
FIG. 2 is a diagram schematically showing a state in which a plurality of heating coils are arranged on a plate to be heated.
FIG. 3 is a longitudinal sectional view of a heating coil for multiple arrangements according to the present embodiment.
FIG. 4 is a cross-sectional view of the heating coil taken along line IV-IV in FIG. 3;
FIG. 5 is a view of a heating coil as viewed from a direction V in FIG. 3;
FIG. 6 is a diagram showing a model of heating of a metal to be heated by a heating coil.
FIG. 7 is a diagram showing a circuit configuration of a conventional heating device.
[Explanation of symbols]
Reference Signs List 1 heating coil, 4 high-frequency power supply device, 13 temperature distribution control device, 14 temperature distribution measurement device, 31 coil conductor, 32 coaxial core (magnetic iron core), 40 heated plate.

Claims (2)

A plurality of high-frequency induction heating coils comprising a magnetic iron core and a coil conductor, which are arranged to face the plate to be heated,
A high-frequency induction heating device comprising: a plurality of high-frequency power supply devices provided for each of the plurality of high-frequency induction heating coils and supplying high-frequency power to each heating coil. A temperature distribution measuring device that measures the temperature distribution of the heated plate,
A temperature distribution control device having a function of comparing and calculating temperature distribution data from the temperature distribution measurement device with a preset temperature table to individually control output power of the high-frequency power supply device. The high-frequency induction heating device according to claim 1, wherein:

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