JP2003342633A - Method for adjusting heating depth in high-frequency induction heating - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To arbitrarily adjust a heating depth from the surface of a body to be heated, by simultaneously supplying two high-frequency heating electric powers of low and high frequencies, to one high-frequency heating coil. <P>SOLUTION: This method is to adjust the heating depth from the surface of the body to be heated 2, when induction-heating the body to be heated 2 with a high-frequency power. The method comprises induction-heating the above body to be heated 2 with the high-frequency power, by simultaneously supplying the two high-frequency heating electric powers of the low and high frequencies to the one high-frequency heating coil 3 used for heating the above body 2; and arbitrarily or continuously adjusting the heating depth from the surface of the above body 2, by changing an allotment of one high-frequency power and the other high-frequency power to an arbitrary allotment ratio or allotment proportion, or by independently and arbitrarily changing each heating time by each high-frequency power of the above two powers. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting the heating depth from the surface of the object to be heated arbitrarily or continuously when the object to be heated made of a metal material is subjected to high frequency induction heating.

[0002]

2. Description of the Related Art Conventionally, a method of adjusting a heating depth in this type of high frequency induction heating is an induction heating method of supplying high frequency electric power of one frequency to one high frequency heating coil. In order to obtain a certain heating depth from the surface of the heating body, it was necessary to select a frequency that was a high frequency current penetration depth corresponding to the heating depth. FIG. 8 shows the relationship between the frequency and the high-frequency current penetration depth (hereinafter simply referred to as penetration depth) in the austenite region of the steel material.

In FIG. 8, for example, when the required heating depth is 7.0 mm, 5 kHz is set as the frequency at which the penetration depth is 7.0 mm, and the required heating depth is 3.5 mm.
In the case of mm, the penetration depth is about 3.5 mm and the frequency is 20 kHz, and the required heating depth is 1.5 mm.
In this case, 125 kHz is selected, and when the required heating depth is 1.0 mm, 200 kHz is selected as the frequency at which the penetration depth is about 1.0 mm. Therefore, prepare a dedicated high-frequency oscillator according to the required heating depth, or use a high-frequency oscillator that can switch and output multiple frequencies with a single unit, and adjust the frequency according to the required heating depth. The method of selection is customary.

When the heating depth is increased, the heating time may be extended to utilize heat conduction in the body to be heated.

[0005]

However, in the above-mentioned conventional technique, when a plurality of frequencies are switched and output by one high-frequency oscillator, at most three kinds of frequencies are limited, and the obtained heating depth is limited. There is a problem that it becomes gradual.

Alternatively, when the required heating depth range is wide (for example, 7.0 mm to 1.0 mm), the frequency bands corresponding to the required heating depth range are far apart (for example, 5 kHz). To 200 kHz), it is difficult to adopt a structure that switches the frequency with one high-frequency oscillator.
A dedicated oscillator is required for each frequency, but the installation space is required for the number of oscillators, which is not realistic.

Further, when heating is performed by extending the heating time at a high frequency with a small penetration depth (shallow depth) with respect to the required heating depth, even if the heating depth can be obtained, it flows to the object to be heated. Since the high frequency induction current is concentrated on the surface of the object to be heated, there is a problem that the vicinity of the surface is overheated.

On the other hand, when heating is performed at a low frequency with a large (deep) penetration depth with respect to the required heating depth and the heating time is shortened, the region to be heated is not sufficiently heated, and In the case of inclusion, there is a problem that the required hardness cannot be obtained.

The present invention has been made in view of the above points,
The purpose is to solve the above-mentioned problems, and to supply one high-frequency heating coil to be used, simultaneously supplying or supplying two-frequency high-frequency heating power of a low frequency and a high frequency, while the surface of the object to be heated. Another object of the present invention is to propose a heating depth adjusting method in high-frequency induction heating, which can easily and arbitrarily adjust the heating depth from the above.

Another object of the present invention is to propose a heating depth adjusting method in high frequency induction heating which can reduce the cost of the high frequency power supply equipment and reduce the installation space.

[0011]

The structure of the present invention for achieving the above-mentioned object is a method for adjusting the heating depth from the surface of the object to be heated when the object to be heated is subjected to high frequency induction heating. Is like.

[0012] A high-frequency heating power of two frequencies, a low frequency and a high frequency, is simultaneously supplied to one high-frequency heating coil used for the object to be heated for high-frequency induction heating of the object to be heated, and one frequency By changing the distribution of the high frequency power and the high frequency power of the other frequency to an arbitrary distribution ratio or distribution ratio, the heating depth from the surface of the object to be heated can be adjusted arbitrarily or continuously. is there.

A high frequency heating power of two frequencies, a low frequency and a high frequency, is simultaneously supplied to one high frequency heating coil used for the object to be heated for high frequency induction heating of the object to be heated, By independently and independently changing the heating time by each high-frequency power, the heating depth from the surface of the heated object is arbitrarily set,
Alternatively, it is a method of continuously adjusting.

A high-frequency heating coil having a low frequency and a high frequency is simultaneously supplied to one high-frequency heating coil used for the object to be heated so that the object to be heated is subjected to high-frequency induction heating. By changing the distribution of the high frequency power of the above and the high frequency power of the other frequency to an arbitrary distribution ratio or distribution ratio, and independently changing the heating time by the high frequency power of each of the two frequencies independently, This is a method of adjusting the heating depth from the surface of the heating body arbitrarily or continuously.

Of the two frequencies, the low frequency is 0.
5 kHz to less than 50 kHz, and the high frequency is 5
The method is 0 kHz to 800 kHz.

In the apparatus used in the above method, one high-frequency heating goyle used for the object to be heated is supplied with high-frequency power having either one of low-frequency and high-frequency two-frequency power. The method is an apparatus capable of heating the object to be heated by supplying the high frequency power of the other frequency at the same time as the high frequency power of the one frequency for an arbitrary time during the high frequency induction heating of the object to be heated.

A high-frequency heating coil used in the object to be heated is simultaneously supplied with high-frequency heating power of three or more frequencies including a low frequency and a high frequency to heat the object to be heated by high-frequency induction. It is a method of adjusting the heating depth from the surface of the object to be heated arbitrarily or continuously by changing the distribution of the high frequency power of each of the three or more frequencies to an arbitrary distribution ratio or distribution ratio. .

A high-frequency heating power of three or more frequencies including a low frequency and a high frequency is simultaneously supplied to one high-frequency heating coil used for the object to be heated for high-frequency induction heating of the object to be heated, and This is a method of arbitrarily or continuously adjusting the heating depth from the surface of the object to be heated by independently and arbitrarily changing the heating time by the high frequency power of each frequency of 3 frequencies or more.

[0019] A high-frequency heating coil used for the object to be heated is simultaneously supplied with high-frequency heating power of three or more frequencies including a low frequency and a high frequency to heat the object to be heated by high-frequency induction. By changing the distribution of the high frequency power of each frequency of 3 frequencies or more into an arbitrary distribution ratio or distribution ratio, and independently changing the heating time by the high frequency power of each frequency of 3 frequencies or more independently, It is a method of adjusting the heating depth from the surface of the object to be heated arbitrarily or continuously.

Since the heating depth adjusting method in the high frequency induction heating of the present invention is configured as described above, the above-mentioned 2
The distribution of the high frequency power of the low frequency and the high frequency power of the high frequency can be changed to an arbitrary distribution ratio, or the heating time by the high frequency power of each of the two frequencies can be changed independently and arbitrarily. Of the two frequencies, the low-frequency heating power and the high-frequency heating power of the two-frequency high-frequency heating device apparatus (proposed by the applicant of the present application in Japanese Patent Application No. 2001-161820) are used. While heating the object to be heated by the heating power of either one of the frequencies, the heating power of the other frequency is supplied at the same time as the heating power of the one frequency at any time.
Alternatively, the heating depth from the surface of the object to be heated can be adjusted arbitrarily or continuously by superposing the heating power of one of the frequencies and performing high-frequency induction heating on the object to be heated.

The heating depth from the surface of the object to be heated is the sum of the penetration depth of the high frequency high frequency current and the depth of the heat conduction component according to the length of the heating time, and the high frequency current of the low frequency. The permeation depth can be adjusted arbitrarily or continuously within the range of the sum of the depth of the heat conduction component and the depth according to the length of heating time.

Since the heating depth adjusting method of the present invention is as described above, it can be applied to a wide range of fields utilizing high frequency induction heating and has a wide range of applications. In particular, the heating depth is continuously changed by appropriately distributing the heating power of the high frequency and the heating power of the low frequency among the two frequencies and appropriately adjusting the heating time of each of the heating power of the two frequencies. Or, since it can be adjusted, the required heating depth can be heated without overheating or insufficient temperature of the heating portion. Further, since only one heating high-frequency oscillator for two frequencies is required as a high-frequency power source, the facility cost can be kept low, and the installation space can be reduced to one oscillator.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will now be exemplarily described in detail with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a heating depth adjusting method in high frequency induction heating according to the present invention, and is an explanatory configuration diagram of a high frequency induction heating apparatus used for carrying out the heating depth adjusting method.

In FIG. 1, a high frequency induction heating apparatus 1 used for performing the heating depth adjusting method is a metal material,
For example, a two-frequency high-frequency heating power is supplied from a two-frequency oscillator 4 as a two-frequency high-frequency power source to one high-frequency heating goyle 3 mounted on a columnar object 2 made of steel material. Immediately after heating the outer peripheral portion of the object to be heated 2 to a predetermined quenching temperature, a cooling liquid injection unit (not shown) injects a cooling liquid, for example, cooling water toward the heated outer peripheral surface, Induction hardening of the outer peripheral portion is performed.

The two-frequency oscillator 4 adjusts the output of the first high-frequency power supply 11 and the first high-frequency power supply 11 that outputs high-frequency heating power of a low frequency, for example, 5.5 kHz. A control unit 12 that arbitrarily controls (turns on and off) the heating time for outputting the high-frequency power; a second high-frequency power supply unit 12 that outputs high-frequency heating power with a high frequency, for example, 200 kHz; The control unit 22 adjusts the output of the high frequency power from the high frequency power supply unit 12 and arbitrarily controls (turns on and off) the heating time for outputting the high frequency power.

Then, with respect to the high-frequency heating goyle 3 mounted on the object to be heated 2, the low-frequency high-frequency power output from the first high-frequency power supply unit 11 of the dual-frequency oscillator 4 is applied. , The distribution of the high frequency high frequency power output from the second high frequency power supply unit 21,
An arbitrary distribution ratio or distribution ratio (for example,% of the total high-frequency power required for heating is controlled by the control units 12 and 22).
Distribution) or by changing the heating time by the high frequency power of each of the two frequencies independently and independently by the control units 21 and 22, respectively, from the surface of the object 2 to be heated. The heating depth of can be arbitrarily adjusted or can be continuously adjusted.

Further, with respect to the high frequency heating goyle 3,
While changing the distribution of the low-frequency high-frequency power and the high-frequency high-frequency power output from the dual-frequency oscillator 4 to any distribution ratio or distribution ratio by the control units 21 and 22, respectively, The heating time by the high frequency power of each of the two frequencies is independently and arbitrarily changed by each of the control units 21 and 22 to arbitrarily adjust the heating depth from the surface of the heated body 1. Or, it can be adjusted continuously.

Specific examples are shown below. The dual frequency oscillator 4
The respective distributed outputs of the heating high-frequency power having a lower frequency of 5.5 kHz and the heating high-frequency power having a higher frequency of 200 kHz, and the heating time at each of the frequencies are set to the respective control units 21. , 2
2, the material is appropriately adjusted and supplied to the high-frequency heating coil 3, and the object to be heated 2 is heated to the quenching temperature. Immediately after that, the body to be heated 2 was cooled with cooling water and quenched, and the depth of the hardened layer from the surface of the body to be heated 2 was taken as the heating depth. At this time, about 1.0 mm to about 7.0 mm was obtained as the heating depth from the surface of the heated body 2 made of steel.

In this specific example, the heated body 2 and the dual-frequency oscillator 4 are as follows. Metal heated object ... Material: S45C Normalized product Dimension: Diameter φ76 mm x Height 50 mm Dual frequency oscillator Output: 80 kW Frequency: 5.5 kHz 200 kHz

FIG. 2 shows that the heating output at a low frequency of 5.5 kHz is 80 kW (100%) and the heating output at a high frequency of 200 kHz is 0 kW (0%), and the quench hardening layer is heated for 7.70 seconds. Indicates. The depth of the hardened layer at this time is 6.8 mm.

In FIG. 3, the heating output of the low frequency 5.5 kHz is 40 kW (50%), and the heating output of the high frequency 200 kHz is 40 kW (50%), and at the same time 5.6.
The quench hardening layer when heated for 0 seconds is shown. The depth of the hardened layer at this time is 3.9 mm.

FIG. 4 shows that the heating output at a low frequency of 5.5 kHz is 0 kW (0%) and the heating output at a high frequency of 200 kHz is 80 kW (100%), and the quench hardening layer is heated for 1.98 seconds. Indicates. At this time, the depth of the hardened layer is 1.2 mm.

FIG. 5 is a graph of the results of FIGS. 2 to 4. Compared to the graph of FIG. 8 showing the relationship between the frequency and the high frequency current penetration depth, according to the heating depth adjusting method of the present invention, the current penetration depth in the frequency range of 5.5 kHz to 200 kHz, that is, the metal coating. It can be confirmed that the heating depth from the surface of the heating element 2 can be continuously and arbitrarily adjusted.

In FIG. 6, the heating time in FIG. 5 is 7.0.
As in the case of FIG. 2 to FIG. 4, the heating output of the low frequency of 5.5 kHz and the high frequency of 200 k are kept constant for 0 seconds.
It is a figure which shows the change of the heating depth from the surface of the said metal-made to-be-heated body 2 at the time of simultaneously heating, changing only the distribution of the heating output of Hz. As described above, according to the heating depth adjusting method by distributing the heating high-frequency outputs of the two frequencies, the current penetration depth in the frequency range of 5.5 kHz to 200 kHz, that is, from the surface of the metal heated body 2 It can be confirmed that the heating depth can be continuously and arbitrarily adjusted.

As the two frequencies in the above embodiment, the low frequency is 0.5 kHz to less than 50 kHz, and the high frequency is 50 kHz to 800 kHz.
Particularly, at the high frequency, 50 kHz to 400 kHz
Is more preferable, and 50 kHz to 300 kHz is most preferable.

In the above-mentioned embodiment, the case where two high frequency heating powers of low frequency and high frequency are simultaneously supplied to one high frequency heating coil 3 used for the object to be heated 2 has been described. Not limited to the two frequencies, if necessary, it is possible to simultaneously supply high-frequency heating power of three, four, or five or more frequencies included in the low frequency and the high frequency. Alternatively, it is applied to frequencies of 5 or more. In this case, as the high-frequency oscillator 4 that heats the object to be heated 2 at a high frequency, an oscillator that can output high-frequency power of three or more frequencies is used, or the high-frequency oscillator 4 is provided side by side with another oscillator. A required number of oscillators capable of outputting high frequency power of 1 or 2 frequencies may be used.

Next, a 2-frequency high-frequency power source used in the heating depth adjusting method in the high-frequency induction heating is used.
An example of the frequency oscillator 4 will be described. (As for this device, the present applicant has already filed Japanese Patent Application No. 2001-1618.
Proposed in No. 20. ) FIG. 7 shows a configuration diagram including a circuit diagram of the dual-frequency oscillator 4.

In FIG. 7, the high frequency induction heating device 1 is used.
Uses one high-frequency heating coil 3 to heat the body 2 to be heated, and outputs two frequencies having different frequencies, for example, 5.5 kHz and 200 kHz.
This is a device for high-frequency induction heating with the high-frequency power of.

The two-frequency oscillator 4 includes a first high-frequency power supply section 11 for outputting heating power having a low frequency of 5.5 kHz among the two frequencies, and the first high-frequency power supply section 1.
Resonant capacitor C1 connected in parallel between the output terminals of 1
And a first transformer T1 for supplying the output from the first high frequency power supply unit 11 to the high frequency heating coil 3.
A second high frequency power supply section 21 for outputting the high frequency heating power of 200 kHz, and the second high frequency power supply section 2
The output from 1 is the resonance capacitor C2 connected in series.
A second transformer T2 for supplying the high-frequency heating coil 3 via the power supply unit 11 and the second high-frequency power supply units 11 and 21, respectively.
The controller 12 that adjusts the distribution of the output of 1 and controls (turns on and off) each heating time,
And 22.

Further, the secondary winding of the second transformer T2 is connected between the first transformer T1 and the high frequency heating coil 3 so as to be connected in series, and A high-frequency bypass capacitor C3 for bypassing the high-frequency component from the second high-frequency power supply unit 21 is connected in parallel to the secondary side of the first transformer T1.

The main function of the circuit of FIG. 7 is to prevent the electric power from the low frequency first high frequency power supply section 11 from leaking to the high frequency second high frequency power supply section 21 while preventing the high frequency heating. The high-frequency heating coil 3 is provided while supplying heating power to the coil 3 and preventing the power from the second high-frequency power supply unit 21 having a high frequency from leaking to the first high-frequency power supply unit 11 having a low frequency. To supply the heating power to.

The resonance capacitor C1 is connected in parallel between the output terminals of the first high frequency power supply section 11 and has an inductance component including the first transformer T1, the high frequency heating coil 3 and the body 2 to be heated. A capacitance value that resonates with is selected.

The resonance capacitor C2 is connected in series from the output side of the second high frequency power supply unit 21, and
The capacitance value that resonates with the inductance component including the transformer T2, the high frequency heating coil 3 and the object to be heated 2 is selected.

The high-frequency bypass capacitor C3 bypasses the high-frequency current component from the second high-frequency power supply unit 21 having a high frequency so as not to flow into the resonance capacitor C1 of the first high-frequency power supply unit 11 having a low frequency. The resonant capacitor C1 is attached when the frequency characteristic of the resonant capacitor C1 is large and the loss is large.

Next, the operation of the high frequency heating device 1 will be described. One of the first or second high-frequency power supply units 11 and 21 is the high-frequency power supply unit 11 (or 21,
Hereinafter, the description in this paragraph number is the same order in the parentheses), during the high-frequency heating of the object 2 to be heated through the high-frequency heating coil 3 through the high-frequency heating coil 3, at any time, the other high-frequency power supply unit The heating power from 21 (or 11) is supplied by the other control unit 22 (or 12) at the same time as the heating power output from the one high frequency power supply unit 11 (or 21), or the one high frequency power. Power supply unit 11 (or 2
1) The heating target 2 is superposed on the heating power output from 1), and the object 2 to be heated is subjected to high frequency heating via the high frequency heating coil 3.

Although one embodiment of the present invention has been described above, the present invention is not limited to this embodiment, and various modifications and changes can be made based on the technical idea of the present invention. is there.

[0047]

As is apparent from the above description, according to the heating depth adjusting method in the high frequency induction heating of the present invention, one high frequency heating coil used for the object to be heated has a low frequency and a high frequency. By simultaneously supplying two-frequency high-frequency heating power to perform high-frequency induction heating on the object to be heated, and changing the distribution of the high-frequency power of one frequency and the high-frequency power of the other frequency to an arbitrary distribution ratio, Since the heating depth from the surface of the object to be heated is adjusted arbitrarily or continuously, high-frequency heating power of two frequencies of low frequency and high frequency supplied to one used high-frequency heating coil at the same time is simultaneously supplied. The heating depth from the surface of the object to be heated can be adjusted over a wide range, arbitrarily or continuously while being supplied or while supplying, and it is possible to prevent overheating or insufficient temperature. It without an excellent effect that it is possible to improve the workability can be heated to the required heating depth.

Further, according to the present invention, since only one high-frequency oscillator is required as a high-frequency power supply facility for high-frequency induction heating, the cost can be reduced and the installation space can be reduced. Therefore, it can be said that there is an excellent effect that the method is industrially useful.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a heating depth adjusting method in high frequency induction heating according to the present invention, and is an explanatory configuration diagram of a high frequency induction heating apparatus used for carrying out the heating depth adjusting method.

FIG. 2 is a cross-sectional view of a metal heating target object showing a quench-hardened layer when a low-frequency heating output is 100% and a high-frequency heating output is 0%.

FIG. 3 is a cross-sectional view of a metal heating target object showing a quench-hardened layer when a low-frequency heating output is 50% and a high-frequency heating output is 50%.

FIG. 4 is a cross-sectional view of a metal heated object showing a quench-hardened layer when the low frequency heating output is 0% and the high frequency heating output is 100%.

FIG. 5 is a diagram showing changes in the heating depth when both the distribution of the low-frequency heating output and the high-frequency heating output and the heating time are changed.

FIG. 6 is a diagram showing a change in heating depth when only the distribution of low-frequency heating output and high-frequency heating output is changed while the heating time is kept constant.

FIG. 7 is a configuration diagram including a circuit diagram of a two-frequency oscillator 4 that simultaneously outputs two-frequency high-frequency heating power as a two-frequency high-frequency power source of the high-frequency induction heating device used in the method of the present invention.

FIG. 8 is a diagram showing a relationship between a frequency and a high frequency current penetration depth in an austenite region of a steel material.

[Explanation of symbols]

1 High frequency induction heating device 2 heated object 3 high frequency heating coil 4 2 frequency oscillator (2 frequency high frequency power supply) 11 First high frequency power supply 12,22 Control unit 21 Second high frequency power supply section

Claims (8)

[Claims] 1. When high-frequency induction heating of an object to be heated,
In the method for adjusting the heating depth from the surface of the object to be heated, high-frequency heating power of two frequencies of low frequency and high frequency is simultaneously supplied to one high-frequency heating coil used for the object to be heated. While heating the object to be heated by high frequency induction, by changing the distribution of the high frequency power of one frequency and the high frequency power of the other frequency to an arbitrary distribution ratio, the heating depth from the surface of the object to be heated is A heating depth adjusting method in high-frequency induction heating, which is adjusted arbitrarily or continuously. 2. When heating an object to be heated by high frequency induction heating,
In the method for adjusting the heating depth from the surface of the object to be heated, high-frequency heating power of two frequencies of low frequency and high frequency is simultaneously supplied to one high-frequency heating coil used for the object to be heated. The heating depth from the surface of the object to be heated is arbitrarily, or continuously, by heating the object to be heated by high frequency induction and independently changing the heating time by the high frequency power of each of the two frequencies. The method for adjusting the heating depth in high-frequency induction heating is characterized in that the heating depth is adjusted. 3. When heating the object to be heated by high frequency induction heating,
In the method for adjusting the heating depth from the surface of the object to be heated, high-frequency heating power of two frequencies of low frequency and high frequency is simultaneously supplied to one high-frequency heating coil used for the object to be heated. The object to be heated is subjected to high frequency induction heating, the distribution of the high frequency power of one frequency and the high frequency power of the other frequency is changed to an arbitrary distribution ratio, and the heating time by each high frequency power of the two frequencies is respectively set. A heating depth adjusting method in high frequency induction heating, wherein the heating depth from the surface of the object to be heated is adjusted arbitrarily or continuously by independently changing the heating depth. 4. The method according to claim 1, wherein the low frequency is 0.5 kHz to less than 50 kHz and the high frequency is 50 kHz to 800 kHz among the two frequencies. Method for adjusting the heating depth in high frequency induction heating. 5. The apparatus used in the method comprises a high-frequency heating goyle used for the object to be heated, a high-frequency power of one of two frequencies of low frequency and high frequency. An apparatus capable of heating the object to be heated by supplying the high frequency power of the other frequency at the same time as the high frequency power of the one frequency during the high frequency induction heating of the object to be heated by the electric power. The heating depth adjusting method in the high frequency induction heating according to any one of claims 1 to 3. 6. When heating an object to be heated by high frequency induction heating,
In the method of adjusting the heating depth from the surface of the object to be heated, one high frequency heating coil used for the object to be heated is simultaneously supplied with high-frequency heating power of three or more frequencies including a low frequency and a high frequency. Then, the object to be heated is subjected to high-frequency induction heating, and the distribution of the high-frequency power of each of the three or more frequencies is changed to an arbitrary distribution ratio, whereby the heating depth from the surface of the object to be heated is arbitrarily set. The method for adjusting the heating depth in high-frequency induction heating is characterized by performing continuous or continuous adjustment. 7. When heating an object to be heated by high frequency induction heating,
In the method of adjusting the heating depth from the surface of the object to be heated, one high frequency heating coil used for the object to be heated is simultaneously supplied with high frequency heating power of three or more frequencies including a low frequency and a high frequency. And heating the object to be heated by high frequency induction, and independently changing the heating time by the high frequency power of each of the three or more frequencies, the heating depth from the surface of the object to be heated is changed. A heating depth adjusting method in high-frequency induction heating, which is adjusted arbitrarily or continuously. 8. When the object to be heated is subjected to high frequency induction heating,
In the method of adjusting the heating depth from the surface of the object to be heated, one high frequency heating coil used for the object to be heated is simultaneously supplied with high-frequency heating power of three or more frequencies including a low frequency and a high frequency. Then, the object to be heated is subjected to high-frequency induction heating, and the distribution of the high-frequency power of each of the three or more frequencies is changed to an arbitrary distribution ratio, and the heating time by the high-frequency power of each of the three or more frequencies is used. The heating depth adjustment method in high-frequency induction heating is characterized in that the heating depth from the surface of the object to be heated is adjusted arbitrarily or continuously by independently changing the above.