JP2799407B2 - Dielectric heating method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for heating a dielectric, and particularly to a method for heating a dielectric having a high melting point such as a new ceramic, a glass material, or a semiconductor material by using both dielectric heating and induction heating. The present invention relates to a dielectric heating method capable of melting.

[Background of the Invention]

The heating of the dielectric by microwaves can be performed in a short time and with high efficiency due to the extremely high electric field strength generated in the tuning type applicator (high-frequency melting furnace). However, the ultimate heating temperature is limited for the following reasons.

In dielectric heating of the dielectric, the penetration depth L of the microwave
(The depth at which the electric field intensity becomes 1 / e, e... The base of the natural logarithm) is given by the following equation, and is proportional to the wavelength λ.

ε _r is the relative permittivity of the dielectric, and tan δ is the dielectric loss angular rate.

On the other hand, the amount of generated heat Q is given by: Q = (AE ² / λ) × ε _r × tan δ (2), and the shorter the wavelength λ, the higher the efficiency. A is a proportional constant, and E is an electric field strength.

In other words, L and Q have an opposite relationship when the wavelength λ is changed. Therefore, in order to obtain optimum heating, it is necessary to select the wavelength λ in consideration of both.

However, in most dielectrics, the mobility of ions inside increases with an increase in temperature, and the dielectric constant σ tends to increase.

Also, the values of ε _r and tan δ generally increase as the temperature increases, and as a result, the depth L at which microwaves penetrate decreases.

L in the above equation (1) is σ = 0, that is, in the case of a derivative. When this σ increases, the current flows almost only in the so-called skin depth δ depth range due to the microwave electric field. This δ is Given by Thus, when λ is small and σ is large, δ becomes small. In this case, only the surface is heated. c is the speed of light and μ is the magnetic permeability.

Further, when the temperature of the object to be heated becomes high, radiation is given by the next Planck radiation method. That is, the wavelengths are λ and λ +
The radiation energy density ρ _λ dλ between dλ is given by the following equation.

Here, h is Planck's constant, k is Boltzmann's constant, and T is the absolute temperature.

Here, when T exceeds 1500 ° C. in Celsius, the object to be heated emits light having a wavelength in the ultraviolet region. At this time, among the ultraviolet rays, those having short wavelengths ionize the gas to generate ions, so that discharge occurs due to the microwave electric field being irradiated at that time. Therefore, microwave power is consumed by this discharge, and the temperature of the object to be heated can be prevented from further increasing.

[Problems to be solved by the invention]

However, actually, there is a demand in various fields to melt a high-melting-point object to be heated. If this is performed by a conventional microwave dielectric heating method, as described above, heating proceeds and the temperature rises, and due to an increase in conductivity and generation of discharge,
When the temperature rises from a certain temperature or higher, the temperature rise does not progress and reaches a limit, so that not only the above-mentioned demand cannot be met but also power consumption increases.

SUMMARY OF THE INVENTION An object of the present invention is to provide a dielectric heating method in which a dielectric heating method is applied to a low-temperature region and an induction heating method is applied to a high-temperature region, thereby enabling a high-melting dielectric to be heated and melted.

[Means for solving the problem]

For this purpose, the present invention provides a method of performing dielectric heating on a heated object made of a dielectric material by microwave irradiation, and when the conductivity of the heated object becomes a value that can be regarded as a conductor, and / or When a discharge occurs, the microwave irradiation is stopped or cut off, and the object to be heated is induction-heated by applying a high-frequency magnetic field.

〔Example〕

Hereinafter, a heating method according to an embodiment of the present invention will be described.
FIG. 1 is a block diagram of a heating apparatus A for performing the heating method according to the embodiment. 1 is a microwave generator for generating microwaves of about 3 GHz, 2 is an isolator for preventing reflected waves, 3 is a power monitor, 4 is an impedance, a regulator, 5 is a discharge detector, and these are cascades of waveguides. To form a dielectric heating system line 20.

6 is a high frequency generator for generating a high frequency of about 400 K to 5 MHz, 7 is a matching monitoring device, 8 is a matching adjusting device, which are also connected in tandem and have an induction heating system line 30.
Is configured.

These two heating system lines 20, 30 are selectively applied to an applicator 10 as a high-frequency melting furnace by a switching operation of a switching device 9. That is, the heating device A of the present embodiment can be set to any of the dielectric heating mode and the induction heating mode by the switching operation. Reference numeral 11 denotes an object to be heated housed in the applicator 10.

The isolator 2 is for preventing the reflected wave of the microwave from returning to the generator 1 from the applicator 10.

The power monitor 3 is a device for monitoring the matching of the object to be heated 11 arranged in the applicator 10, and detects and displays the power incident on the applicator 10 and the power reflected therefrom. Things. If the above matching is not achieved, the reflected power increases.

The impedance adjuster 4 is a device for adjusting the power reflected from the applicator 10 to be minimized.

The discharge detector 5 is a detector for detecting a discharge of the object 11 to be heated.

The matching monitoring device 7 and the matching adjusting device 8 are devices for performing matching adjustment according to the properties (electrical conductivity and the like) of the object 11 to be heated. These devices are the power monitor 3 and the impedance adjuster 4 of the dielectric heating system line 20. And each operates similarly.

Now, the applicator 10 is heated by the heating device A of this embodiment.
In order to heat the object 11 to be heated, the switching device 9 is first operated to select the dielectric heating mode, and the microwave generator 1 is operated.

As a result, the microwave generated by the microwave generator 1 enters the applicator 10 via the reflected wave preventing isolator 2, the power monitor 3, the impedance adjuster 4, the discharge detector 5, and the switching device 9, and the object to be heated 11 To perform dielectric heating.

At this time, if the reflected power from the applicator 10 is displayed large on the power monitor 3 and it is notified that the matching is mismatched, the impedance adjuster is adjusted so that the power is minimized by reflection while looking at the power monitor 3. Adjust 4 With this adjustment, efficient dielectric heating is performed.

Then, when the temperature of the object 11 to be heated rises and its conductivity increases (to the extent that it can be regarded as a conductor) and the heating state becomes only the surface current, matching becomes extremely difficult. At the same time, since the temperature of the object to be heated 11 is increased, ultraviolet rays are emitted to easily generate discharge, and the discharge detector 5 detects the discharge.

When such a state is reached, the dielectric heating system line 20
Is stopped, and the heating device A is switched from the dielectric heating mode to the induction heating mode by the switching device 9, and the induction heating system line
Start the operation of 30. That is, the high-frequency generator 6 is operated to apply a high-frequency magnetic field to the object 11 to be heated, and
11 directly induces a dielectric current. At this time, the matching is adjusted by the matching adjusting device 8 while looking at the matching monitoring device 7. As a result, the object to be heated 11 is heated and melted by induction heating to a temperature higher than the temperature that could not be raised in the dielectric heating mode.

FIG. 2 is a block diagram of a heating device B of another embodiment. In this example, two types of applicators 10, 10 'are provided, an applicator 10 for dielectric heating and an applicator 10' for induction heating, each of which is independently applied to the dielectric heating system line 20 and the induction heating system line 30. doing. Further, a switching device 9 'is connected to the power supply 12, and the microwave generator 1 and the high-frequency generator 6 are connected to the switching device 9' to enable switching.

That is, in this example, by switching the switching device 9 ', the heating device B can be selectively set to one of the dielectric heating mode and the induction heating mode. In this case, it is necessary to exchange the object to be heated 11 between the applicators 10 and 10 'according to the switching of the heating mode.

FIGS. 3 (a), 3 (b) and 3 (c) are diagrams showing specific examples of the method of switching the heating system in each of the above embodiments.

FIG. 3 (a) is a switching method applicable to the heating apparatus A of the embodiment of FIG. 1, and the heating mode in the applicator 10 can be changed by moving the coil 13 into and out of the applicator 10.

That is, in the case of the dielectric heating mode, the coil 13 is taken out of the applicator 10 and microwaves are made incident from the dielectric heating system line 20. Next, in the case of the induction heating mode,
A coil 13 is fitted around an outer peripheral portion of an alumina crucible 14 for storing an object to be heated 11 installed in an applicator 10, and the coil 13
A high-frequency current is supplied from the induction heating system line 30 to the apparatus.

FIGS. 3 (b) and 3 (c) show a switching method applicable to the heating apparatus B of the embodiment of FIG. 2. In the example of FIG. 3 (b), the coil 13 is connected to the applicator 10 'in the lower adjacent room of the applicator 10. The crucible 14 is mounted on a vertically movable pedestal 15
It was moved between 10 and the coil 13 so that both the dielectric heating mode and the induction heating mode could be set.

In the case of the dielectric heating mode, the crucible 14 is pushed up and held in the applicator 10 by the pedestal 15, and an object to be heated in the crucible 14 is dielectrically heated by the supplied microwave. At this time, the pedestal 15 is fitted in the crucible through hole 10b formed in the partition wall 10a of the applicator 10, 10 'to prevent the microwave from leaking from the applicator 10.

In the case of the induction heating mode, the crucible 14 is pulled down into the applicator 10 ′ by the pedestal 15 and fitted inside the coil 13, and the object to be heated in the crucible 14 receives a high-frequency magnetic field from the coil 13 and is induction-heated. .

Further, in the example of (c), for example, a crucible 14 around which a coil 13 is wound is provided below the applicator 10, and the heated object 11 dielectrically heated by the applicator 10 flows into the crucible 14,
Induction heating is used.

In the above embodiment, the switching from the induction heating to the induction heating is performed by detecting the discharge generated in the object to be heated.
Of course, the detection can be performed by detecting the conductivity of the object to be heated. In this case, for example, the electric conductivity (resistance) of plural times
The detection timing may be set, and the microwave irradiation may be cut off only at this time.

〔The invention's effect〕

As described above, according to the present invention, dielectric heating is applied in a low temperature range of an object to be heated, and induction heating is applied in a high temperature range. Even when the temperature of the object becomes high and the conductivity increases or discharge occurs and it becomes difficult to raise the temperature further, switch to induction heating and heat the object to be heated to a higher temperature efficiently. Has the advantage that it can be melted.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a heating device for carrying out the dielectric heating method of the present invention, FIG. 2 is a block diagram of a heating device of another embodiment, and FIG. (B) (c) is explanatory drawing which shows the switching method between the dielectric heating method and the induction heating method. DESCRIPTION OF SYMBOLS 1 ... Microwave generator, 2 ... Reflected wave prevention isolator, 3 ... Power monitor, 4 ... Impedance adjuster, 5 ... Discharge detector, 6 ... High frequency generator, 7 ...
... Matching monitoring device, 8 ... Matching adjustment device,
9, 9 '... switching device, 10, 10' ... applicator, 11
... Heated object, 12 power supply, 13 coil, 14 crucible, 15 pedestal, 20 dielectric heating system line, 30 induction heating system line, A, B heating device.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroe Aoki 20 in Kitakanyama, Odaka-cho, Midori-ku, Nagoya-shi, Aichi, Japan 1 Within Chubu Electric Power Co., Inc. Electricity Utilization Research Institute (72) Inventor Shunichi Yamada Saitama 2-1-1, Fukuoka, Fukuoka City New Japan Radio Co., Ltd. Kawagoe Works (58) Field surveyed (Int. Cl. ⁶ , DB name) H05B 11/00

Claims (1)

(57) [Claims] 1. An object to be heated made of a dielectric material is dielectrically heated by microwave irradiation, and when the conductivity of the object to be heated becomes a value that can be regarded as a conductor, and / or discharge to the object to be heated is performed. A dielectric heating method comprising: stopping or shutting off the microwave irradiation when generated; and inductively heating the object to be heated by applying a high-frequency magnetic field.