JPS63181289A - Induction heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for induction heating an object to be heated using a plurality of induction coils having different resonance frequencies.

[Conventional technology]

When a metal object is placed in an alternating magnetic field, eddy currents flow through the metal object due to electromagnetic induction, causing eddy current loss. An induction heating device is a device that heats the metal object using the heat generated by the loss of eddy current f@, and its principle is well known.

In order to generate an alternating magnetic field, an induction coil is generally provided and an alternating current is passed through the induction coil, but the eddy current generated in the metal object to be heated is caused by the skin effect on the surface of the metal object. The closer it is, the higher the current density. It is also known that the depth to which eddy currents penetrate becomes shallower as the value of the alternating current flowing through the induction coil increases and as the frequency of the alternating current increases. It is also well known that the above-mentioned eddy current loss increases as the frequency of the alternating current increases.

Therefore, when you want to change the heating conditions between the surface and the inside of a metal object, for example, when you want to heat a bar-shaped steel material as a whole and heat the surface part to a particularly high temperature for quenching.

A plurality of induction heating devices were provided to separately inductively heat the surface portion and the inside.

FIG. 3 is a main circuit connection diagram showing a conventional example in which the surface and interior of a heated object are separately heated by induction.

In FIG. 3, AC power supplied from an AC power supply 2 is converted into DC power by a gg1 rectifier 3, and is applied to a first inverter I5 via a first smoothing capacitor 14, and from this 8g1 inverter 15, Single-phase AC power with the desired frequency and voltage is output.

This AC power is supplied to a series circuit composed of a first capacitor 16 as a capacitance and a first induction coil 17 as a sine inductance, and induces a steel bar 9 as an object to be heated in the first induction coil 17. It is designed to heat up.

The second rectifier n also converts the alternating current power from the alternating current power source 2 into direct current power, and this direct current power is input to the second inverter 5 via the second smoothing capacitor 6, so that it is output from the second inverter 5. The alternating current power is applied to the series circuit of the second capacitor (capacitance) and the second induction coil (inductance), so that the steel bar 9 is induction heated by the second induction coil 27 in the same manner as described above. .

At this time, if the steel bar 9 is moved in the direction of the arrow and the first inverter 15 is configured to output alternating current at a relatively low frequency, the deep part of the steel bar 9 will be moved by the first induction coil 17. It will be heated. Next, when this steel bar 9 comes to the position of the second induction coil n, the second inverter 5 outputs a relatively high frequency alternating current.
The surface portion of the steel bar 9 becomes high temperature and is hardened.

[Problem that the invention seeks to solve]

As is clear from Figure 3, in the past, different inverters and induction coils were prepared in order to obtain alternating current with a frequency corresponding to the area to be heated, such as the deep part or the surface part of the object to be heated. However, since a DC power source for supplying DC power to each of these inverters must be prepared separately, this method has the disadvantage that the cost required for the device increases.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide, at a low cost, a power supply device capable of outputting alternating current at a frequency corresponding to a heating site, such as the surface or inside of a heated object.

[Means for solving problems]

In order to achieve the above object, the induction heating device of the present invention utilizes an alternating magnetic field generated by the inductance by supplying alternating current output from an inverter to a series circuit of an inductance and a capacitance. A device for induction heating of heated objects? At t, the MIIa is composed of multiple sets of series circuits of inductance and capacitance, an impark that separately outputs alternating current at a frequency suitable for each series circuit, and a direct current power supply common to these multiple inverters. In addition, in this induction heating device, the primary winding of the matching transformer that connects the induction heating coil to the secondary winding is connected to each inductance that constitutes the plurality of series circuits. do.

[Effect]

The present invention provides a series circuit consisting of an induction coil and a power factor correction capacitor connected in series to the induction coil, by giving a frequency that causes series resonance or a frequency in the vicinity thereof. The object to be heated is effectively heated by electromagnetic induction by absorbing a large amount of electric power.However, when installing multiple such series circuits to heat any part of the object to be heated, it is necessary to By using a common DC power source for inverters that separately supply AC power to circuits, the cost of the device can be reduced.

Furthermore, each induction coil that constitutes a plurality of series circuits is replaced with the primary winding of a common matching transformer, and the induction coil is connected to the secondary winding of this matching transformer. This makes it possible to heat any part of the body without moving the heated object.

〔Example〕

FIG. 1 is a main circuit connection diagram showing an embodiment of the present invention,
Two inverters each supply AC power to separate series circuits.

In FIG. 1, AC power from an AC power supply 2 is converted into DC power by a rectifier 3, and the pull component included in this DC power is absorbed and removed by a smoothing capacitor 4. The DC power smoothed in this way is given to the first inverter 15 and the second inverter δ, and these inverters convert the input DC power into AC power of a desired voltage and frequency by, for example, pulse width modulation control. can.

The first inverter 15 has a first inverter as a capacitance.
A first series circuit consisting of a capacitor 16 and a first induction coil 17 as an inductance is connected to the second inverter 6, and a second capacitor as a capacitance and a second inductance as an inductance are connected to the second inverter 6.
A second series circuit configured with a visiting coil n is connected.

When the capacitance of the first capacitor 16 is C1 and the inductance of the first induction coil 17 is Ll, the current 11 flowing through the first series circuit is expressed by equation (1). Here, E is the voltage, ωl is the angular frequency, and R is the resistance of the first series circuit.

The current It shown in equation (11) becomes maximum under the condition that the denominator on the right side becomes the minimum, that is, when equation +21 holds true.

ω1・Ll・C□=1 ・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
...(2) If the frequency at this time is Fl, ω1=
From the relationship 2π·Fl, the following equation (31) can be obtained.

This (frequency F shown in equation 31) is the resonant frequency of the first series circuit, and when the frequency of the alternating current output from the inverter 5 is Ft, the first series circuit absorbs the maximum power and the object to be heated is heated. The steel bar 9 as shown in FIG.

If the capacitance of the @2 capacitor constituting the second series circuit is 02) the inductance of the second induction coil τ is L2, and the frequency at which this second series circuit resonates in series is F2, then the above-mentioned Similar to equation (3), between these (
The relationship shown in equation 41 is established.

Therefore, the first inverter 15 outputs an alternating current with a frequency near the resonance frequency of the first series circuit, and the steel bar 9 is heated by the induction coil 17, and then the steel bar is moved in the direction of the arrow to generate the second induction. By outputting alternating current of different frequencies from the second inverter δ using the coil n, different parts of the steel bar 9 can be heated.

At this time, since the first inverter 15 and the second inverter 5 will operate at different times, it is sufficient for the rectifier 3 to have the capacity to operate one of the inverters.

FIG. 2 is a main circuit connection diagram showing a second embodiment of the present invention, in which two sets of inverters supply AC power to separate series circuits, as in the embodiment shown in FIG. It's raining when it happens.

In this FIG. 2, the first coil 81 of the matching transformer 8 is an inductance, and this first coil 81
and a first capacitor 16 as a capacitance.
The second coil 8 of the matching transformer 8 forms a series circuit.
2 and a second capacitor as a capacitance, a second series circuit is formed.An induction coil 7 is connected to the secondary winding of this matching transformer 8, and a steel bar 9 as a heated object is induced. I'm trying to heat it up. Note that the AC power supply 2) rectifier 3, smoothing capacitor 4, first inverter 15, and second inverter 5 in FIG.
Since these are just functions, their explanations will be omitted.

In FIG. 2, the first inverter 15 outputs alternating current at a frequency near F1 to induction heat a steel bar 9 as an object to be heated via a matching transformer 8, and then inverts the operating inverter to a frequency near F2. By switching to the second inverter B which outputs alternating current at the same frequency and applying this alternating current to the induction coil 7 via the matching transformer 8, $
Heat 849. That is, even if the steel bar 9 is not moved, the surface portion and the deep portion thereof will be heated by the alternating current of two types of frequencies, Fl and F2.

Note that the first inverter 15 and the second inverter 5 have a resonance frequency of F, which is the resonant frequency of the series circuit connected to each.
If the value l or F2 is used, the impedance of the series circuit will be minimum and there is a risk that the inverter 5 will overcurrent, so select a value that is appropriately shifted from the above resonance frequency to adjust the absorbed power. Of course, such consideration is necessary.

〔Effect of the invention〕

According to this invention, a plurality of series circuits of capacitance and inductance are prepared so as to generate series resonance at the optimal frequency for U conduction heating of different parts such as the surface part or the deep part of the object to be heated. , an inverter is connected to each separately, and AC of the desired frequency is supplied from this inverter. However, since these inverters operate at different times, only one set of DC power supply is required for these inverters, which reduces the cost of the device. can be reduced.

Furthermore, if the primary coil of a matching transformer is used as the inductance for these multiple inductances, the object to be heated can receive induction heating by alternating current of different frequencies while remaining stationary, so when changing the heating area, Since the movement of the object to be heated can be omitted, a drop in temperature during movement of the object to be heated can be avoided, and an energy saving effect can also be obtained.

[Brief explanation of the drawing]

Fig. 1 is a main circuit connection diagram showing an embodiment of the present invention, Fig. 2 is a main circuit connection diagram showing a second embodiment of the invention, and Fig. 3 is a main circuit connection diagram showing a second embodiment of the invention.
The figure is a main circuit connection diagram showing a conventional example in which the surface and interior of a heated object are separately heated by induction. 2... AC power supply, 3... Rectifier, 4... Smoothing capacitor, 7... Induction coil, 8... Matching transformer, 9... Bar casting, 15... First inverter, 16.
...first capacitor, 17...first cast conduction coil, 5.
...Second inverter. Death...Second capacitor, γ...Second'#s conductive coil, 81...First coil, 82...Second coil.

Claims (1)

[Scope of Claims] 1) An apparatus for inductively heating an object to be heated using an alternating magnetic field generated by the inductance by supplying alternating current output from an inverter to a series circuit of an inductance and a capacitance. An induction device characterized by being composed of a plurality of series circuits of inductance and capacitance, an inverter that separately outputs alternating current at a frequency suitable for each series circuit, and a direct current power supply common to these plurality of inverters. heating device. 2) In the induction heating device according to claim 1, a plurality of primary windings of a matching transformer having an induction heating coil connected to a secondary winding constitute a plurality of series circuits. An induction heating device characterized in that each inductance is