JPH0812792B2 - High frequency heating equipment - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a new high-frequency heating device in which a microwave oven using high-frequency induction heating and an electromagnetic cooker using high-frequency induction heating are integrated.

2. Description of the Related Art A high-frequency heating device in which high-frequency induction heating and high-frequency induction heating are integrated can be realized by adopting a circuit configuration as shown in FIG. 5, for example. In FIG. 5, a commercial frequency power source 12, a rectifier 17, an inductance 13, and a capacitor 14
The smoothing circuit 18 consisting of, the switching element 16 and the inverter circuit 19 consisting of the capacitor 15, the switching element 16
A high frequency voltage of several tens KHz generated by the control drive circuit 20 for ON / OFF control is applied to either the exciting coil 8 for induction heating or the step-up transformer 10 of the magnetron 1 which is a microwave source for dielectric heating. The switching is performed by the switch 11.

For this type of high-frequency heating apparatus, it is most desirable that an induction coil for induction heating is provided in a heating chamber for dielectric heating, and the heating chamber can be used for both induction heating and dielectric heating. However, if the exciting coil is placed in the heating chamber as it is, the exciting coil winding is heated by the microwave during the dielectric heating, and the insulating film is damaged by radiating between the wires of the coil. The ferrite core used for the purpose of preventing magnetic leakage to the core also absorbs microwaves and generates heat, and is not practical.

As shown in FIG. 6, the excitation coil winding 8a and the ferrite core 23 are made of aluminum plate or the like as a method for preventing the heat generation by microwaves and the damage by discharge even if the excitation coil is arranged in the heating chamber. The shield cover 26 and the shield cover 28 made of a non-magnetic metal are covered, and the shield cover 26 has a direction substantially perpendicular to the generated induced current in order to prevent Joule loss due to the induced current generated by the exciting coil winding. Therefore, a configuration in which a large number of radial slit holes 29 are provided can be considered.

Problems to be Solved by the Invention However, in the case of the configuration shown in FIG. 6, the shield cover A26 is made of a metal plate,
Even if the slit hole 29 is provided, there is a limit to the reduction of Joule loss and heat generation accompanying the generation of the induced current.

The present invention solves such a conventional problem, and at the same time shields the exciting coil from microwaves, it makes it possible to realize a shield cover for the exciting coil that causes almost no loss due to an induced current and heat generated thereby. This is the goal.

Means for Solving the Problems In order to solve the above problems, the high-frequency heating device of the present invention comprises an exciting coil for induction heating provided in a heating chamber for dielectric heating, made of a non-magnetic metal foil such as aluminum. The honeycomb core is covered with a shield cover which is a part or all of the honeycomb core.

Effect The present invention uses the aluminum honeycomb core for the shield cover of the exciting coil, so that a high frequency magnetic field for induction heating of several tens KHz is almost transmitted, while a high frequency electromagnetic field (microwave) for dielectric heating of 2450 MHz is almost Since it does not permeate, the excitation coil winding and the ferrite core are protected from heating and discharge by microwaves, and Joule loss due to induced current hardly occurs during induction heating, so that efficiency and reliability can be greatly improved.

EXAMPLES Examples of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a sectional view of an embodiment of the present invention, and FIG. 2 is a detailed view of a main part of the embodiment, that is, an exciting coil. First
In the figure, the microwave (high frequency electromagnetic field) generated in the magnetron 1 is radiated into the heating chamber 5 through the waveguide 2 and the rotating antenna 3. The rotating antenna 3 is disclosed in JP-A-60-13.
It has a substantially fan shape as described in Japanese Patent Laid-Open Publication No. 2004-242242, and by rotating by the motor 4, uniform heating of dielectric heating is realized.

On the other hand, the exciting coil 8 is arranged immediately above the rotating antenna 3, and a partition plate 9 made of a dielectric material such as a heat-resistant ceramic plate is arranged at a position almost in contact with the exciting coil 8. The partition plate 9 protects the rotating antenna 3 and the exciting coil 8 provided at the bottom of the heating chamber 5 and also functions as a mounting table for the object 7 to be heated.

Here, the method of supplying high-frequency power to the step-up transformer for driving the magnetron 1 and the exciting coil 8 is basically the same as the circuit configuration of the prior art described with reference to FIG. Uses a common number.

FIG. 2 is a detailed view of an essential part of the embodiment described with reference to FIG. 1, showing a detailed configuration of one embodiment of the exciting coil 8 which is the basic part of the present invention. 2A is a plan view corresponding to FIG. 2A. In FIG. 2, the exciting coil 8 is composed of a flat winding formed by flatly winding the winding, an exciting coil winding 8a, a ferrite core 23 for magnetic shielding provided on the lower surface of the exciting coil winding 8a, and the above-mentioned exciting coil. Disc-shaped aluminum honeycomb cores 21a and 21b provided so as to be sandwiched from the upper and lower surfaces of both the coil 8a and the ferrite core 23, and further provided on both inner and outer peripheral sides of these aluminum honeycomb cores 21a and 21b, The shield rings 24a and 24b are made of a non-magnetic metal plate such as aluminum. Here, the shield rings 24a, 24b radially have a large number of slit holes 25a, 25b, which prevent the flow of the induced current in the circumferential direction generated on the shield rings 24a, 24b, and cause loss due to heat generation. This is to prevent temperature rise.

FIG. 3 is for explaining the details of the structure of the aluminum honeycomb core 21. FIG. 3 (a) is a perspective view of a part of the aluminum honeycomb core cut out into a substantially rectangular shape, and FIG. 3 (b). FIG. 3 is an enlarged view of one cell (unit structure) forming an aluminum honeycomb core. The honeycomb core is shown in Fig. 3 (b).
As can be seen from the enlarged view of Fig. 3, the aluminum foil is laminated to form a hexagonal cell, which is continuously formed in a large number. Despite being extremely lightweight, it can be given a considerable amount of mechanical strength, so it can be used as a structure of an aircraft. In addition, it can obtain electromagnetic wave shielding performance while maintaining breathability. It is widely used for ventilation holes in rooms. In the case of this example, the foil thickness S of the aluminum foil used for the honeycomb cores 21a and 21b is 1/10 or less of the high-frequency used for induction heating, for example, the penetration depth of aluminum at 20 KHz of 0.6 mm. I'm using one.
Cell size D and core height T of the honeycomb cores 21a and 21b
Is determined in consideration of the core height T such that the 2450 MHz radio wave used for dielectric heating can be sufficiently shielded and the distance between the exciting coil winding 28a and the object 7 to be heated is within a range in which induction heating can be performed. However, in this embodiment, the core height T is 21
Both a and 21b have a value of 1.5 mm, and the cell size D has a value of about 3 mm.

Next, the operation of the above embodiment will be described with reference to FIG. FIG. 4 (a) shows an exciting coil winding 8a and a magnetic field line 3 showing a high-frequency magnetic field generated by the exciting coil winding 8a.
1. A metallic object 7 to be heated by an induction current generated by this high frequency magnetic field, a ferrite core 23 for shielding the leakage of the high frequency magnetic field to the lower surface, and a high frequency for induction heating, that is, 2450 MHz. 3 shows the mutual positional relationship of the aluminum honeycomb cores 21a for preventing heating by the microwave and generation of electric discharge. Since the cell size D of the honeycomb core 21a interposed between the exciting coil winding 8a and the object 7 to be heated is sufficiently smaller than the wavelength of the high frequency electromagnetic field (microwave) of 2450 MHz used for dielectric heating. Since each cell can be regarded as a waveguide, a high shielding effect (for 2450MHz) can be obtained by the same effect as the waveguide cut-off phenomenon. On the other hand, the relationship between the 20 KHz high-frequency magnetic field 31 used for induction heating and the aluminum honeycomb 21a is shown in FIG. 4 (a), and FIG. 4 (b) shows the aluminum honeycomb 21a and magnetic field lines 31.
It is an enlarged view of the relationship with
Reference numeral 31 is substantially parallel to the tube axis direction of the cells forming the honeycomb core 21.

In general, a conductor represented by a metal generates an induced current when an alternating magnetic field is applied regardless of whether it is a magnetic substance or a non-magnetic substance, but the depth of penetration of the induced current from the surface is finite,
The depth at which the current density I becomes 1 / e of the surface current density I ₀ is called the penetration depth δ (m), and the specific resistance of the conductor is ρ
(Ω.m), frequency (Hz), relative permeability μr, Becomes Using this penetration depth δ, the current density I in the conductor at the position x from the surface is expressed by I = I ₀ e ^{−x / δ} (1) where I ₀ is the current density on the surface. . For example, if the conductor is aluminum, the penetration depth at 20 KHz is about 0.6 mm. The direction of the induced current is perpendicular to the direction of the magnetic field (the magnetic force line 31).

Now, FIG. 4 (c) shows the thickness S for forming the honeycomb core.
This is for explaining the state of the aluminum foil, the magnetic force lines 31 of the alternating magnetic field applied in parallel with the aluminum foil, and the induced current induced in the aluminum foil. The current induced in the aluminum foil is
Although it decreases exponentially from the surface as shown by the equation (1), its direction is perpendicular to the magnetic field and has current densities I _a and I _b which are opposite to each other on the front and back of the foil. By the way, the thickness S of the aluminum foil constituting the aluminum honeycomb 21 is sufficiently smaller than the permeation depth δ = 0.6 mm, for example, if 0.02 mm is selected, it is induced in the opposite direction with the front and back of the foil being symmetrical. Current density
I _a, cancel each other I _b are each other, the current actually flowing density I will become the difference I _a and I _b. The current induced in such an aluminum foil placed in parallel with the magnetic field is almost negligible when the thickness is sufficiently small as 1/10 or less of the penetration depth δ as in the example.

Therefore, although the aluminum honeycomb 21 is interposed between the object to be heated 7 and the exciting coil winding 8a, it hardly causes a loss with respect to the high frequency magnetic field of 20 KHz used for induction heating. On the other hand, 2450MH used for dielectric heating
Excitation coil winding 8 from the high frequency electromagnetic field (microwave) of z
It plays the role of shielding (protecting) a from microwaves.

Furthermore, since the aluminum honeycomb core 21b on the lower surface is also covered, including the ferrite core 23, the problem that the ferrite core 23 absorbs microwaves and generates heat can be solved.

In the above description, as the metal foil forming the honeycomb,
Although the explanation has been given on the premise of aluminum foil, it is natural that its function is limited to aluminum. The non-magnetic metal is more preferable for the purpose of forming as few branch channels as possible with respect to the generated high frequency magnetic field.

In the embodiment, the aluminum honeycomb core is used for the upper and lower surfaces of the excitation coil winding, and the inner circumference and the outer circumference are made of non-magnetic metal such as aluminum. However, the range of using the honeycomb core is the present embodiment. Of course, it is not limited.

In addition, the features such as air permeability and lightness of the honeycomb also work effectively, and particularly regarding air permeability, the cooling effect of suppressing the temperature rise of the exciting coil winding 8a is exhibited.

Effects of the Invention As described above, according to the present invention, the following effects are obtained.

(1) Since the exciting coil winding is covered with the honeycomb core made of a metal foil, heat generation and discharge of the exciting coil winding due to microwaves can be prevented, and at the same time, for induction heating generated by the exciting coil winding. Since the high-frequency magnetic field reaches the object to be heated with almost no attenuation, it is possible to suppress the heat generation of the exciting coil during induction heating and also to keep the heating efficiency high.

(2) Further, since the honeycomb core naturally has air permeability, it also has an effect that it effectively works for air cooling of the exciting coil and that heat is effectively radiated from the exciting coil.

(3) Since the honeycomb core covers the ferrite core for magnetic shielding, which is provided below the exciting coil winding, the problem that the ferrite core absorbs microwaves and generates heat can be solved. .

Due to the above effects, it has become possible to realize a high-frequency heating device capable of both induction and induction heating, in which an induction coil for induction heating is provided in a heating chamber for induction heating, which has been considered to be hardly practical in the past. It is a thing.

[Brief description of drawings]

FIG. 1 is a sectional view of a high-frequency heating device according to an embodiment of the present invention, FIGS. 2 (a) and 2 (b) are a partially cutaway side view and a partially cutaway plan view of the same exciting coil, and FIG. 3 (a). ), (B)
Is a perspective view and an enlarged plan view of a main part of an aluminum honeycomb core forming the same exciting coil, FIGS. 4 (a) to 4 (c) are illustrations of the same operation, and FIG. 5 is a heating method of both dielectric heating and induction heating. Circuit diagram of a general high-frequency heating device that can select
1A and 1B are a cross-sectional view and a partially cutaway plan view of an exciting coil arranged in a heating chamber that has been conventionally proposed. 1 ... Magnetron, 3 ... Rotating antenna, 7 ... Object to be heated, 8 ... Excitation coil, 9 ... Partition plate.

Claims (3)

[Claims] 1. A heating chamber which is irradiated with microwaves, a magnetron which generates the microwaves, a step-up transformer which supplies electric power to the magnetron, and an exciting coil for induction heating which is provided in the heating chamber. A high-frequency heating device comprising: a step-up transformer and a high-frequency inverter circuit for supplying electric power to the exciting coil, the exciting coil being partially or entirely covered with a honeycomb core made of a metal foil. 2. The exciting coil has a flat winding formed by winding the winding flatly and is arranged substantially parallel to the bottom surface of the heating chamber.
The high frequency heating device according to claim 1, wherein a ferrite core for magnetic shielding is provided on the lower surface of the exciting coil, and the exciting coil including this ferrite core is partially or entirely covered with a honeycomb core made of metal foil. . 3. The metal foil constituting the honeycomb core is made of a non-magnetic metal such as aluminum and has a thickness of about 1/10 or less of the penetration depth of the metal. The high frequency heating device according to the item.