JP3184877B2 - Electromagnetic composite heating furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating furnace for heating and melting a high-melting dielectric material such as a powdery substance or a lump, and uses an electromagnetic wave combining dielectric heating by microwave and induction heating by high frequency. It relates to a combined heating furnace.

[0002]

2. Description of the Related Art Conventionally, when an object to be heated such as a powdery substance or a lump is heated and melted, dielectric heating by microwaves is used to heat the inside of the substance. In order to efficiently heat and bring about melting, dielectric heating using microwaves is used for heating the dielectric. The dielectric heating by microwaves is performed in an oven-type furnace such as a microwave oven, or when heating is performed to an extent that melting is possible, the electric field is concentrated in a heating furnace having a resonator structure to locally concentrate the electric field. It is carried out by a method in which the mixture is heated and melted.

[0003] On the other hand, when a certain degree of melting occurs, electrical conductivity is generated by ionic current or the like. In particular, when heating materials that are considerably conductive at high temperatures, such as glass, for example, eddy currents generated by Joule heating or electromagnetic induction due to resistance loss of current flowing by applying voltage to both ends Heating is also performed.

As a recent new method of induction heating by electromagnetic induction, a cold crucible (cold crucible) method has been proposed. The heating method by the cold crucible method will be described with reference to FIG. The configuration of this heating furnace is, for example, a cylindrical container 11 formed of a material having good electrical conductivity such as copper or brass and having a bottom or a bottom penetrated therethrough. Numeral 11 is divided into a number of strips 13 and connected only at the bottom or upper portion or both up and down, and the strips are cooled by flowing cooling water inside. An induction coil 7 is arranged on the outer periphery of the cylindrical container 11 so that a high-frequency current flows. With this configuration, when a high-frequency current flows through the induction coil 7, an eddy current is induced in the object to be heated by electromagnetic induction, and the object to be heated is heated by the current loss. Moreover, a cylindrical container
Since the object to be heated is separated from the cylindrical container 11 which is a furnace body due to the repulsive force of the magnetic field caused by the current flowing through the belt-shaped portion 11 and the magnetic field caused by the current flowing through the object to be heated, the temperature of the object to be heated rises , The temperature of the object to be heated can be maintained at a high temperature, and the melting and heating can be performed in a cold furnace body.

[0005]

However, in dielectric heating using microwaves, when an object to be heated is heated to a high temperature and becomes molten, the electrical conductivity due to ionic conduction or the like increases, and microwave heating increases. Waves are less likely to enter the object to be heated, and the penetration depth is reduced. As a result, there is a problem that the microwave is reflected in the vicinity of the surface of the object to be heated and heating is not sufficiently performed inside, so that the whole cannot be melted.

When the temperature exceeds 1500 ° C., the gas in the oven is ionized by the radiated ultraviolet rays to generate electric discharge, so that high-temperature heating by microwaves in the gas becomes difficult.

On the other hand, in the cold crucible method using induction heating,
Heating is performed by directly generating an eddy current in the object to be heated by electromagnetic induction.If the object to be heated does not have electrical conductivity, it cannot be heated, and in the case of dielectrics such as powders and lumps, There is a problem that heating cannot be performed by flowing an eddy current directly.

[0008] It is an object of the present invention to provide a heating furnace for efficiently heating and melting even a dielectric substance such as a granular material or a lump.

[0009]

According to one aspect of the present invention, there is provided an electromagnetic wave composite heating furnace having a microwave inlet, and a plurality of axially extending side walls of a cylindrical or rectangular microwave cavity operating in a TM mode. Is formed, the side wall is divided into strips, and an induction heating coil is arranged on the outer periphery of the microwave cavity.

[0010] Further, according to another aspect of the present invention, there is provided an electromagnetic wave combined heating furnace, wherein a coaxial line portion on which an inner shaft is disposed and a remaining portion are formed in the cavity portion up to the middle of the cylindrical cavity resonator. An axial slit is formed in the side wall of the cavity portion of the semi-coaxial resonator, the side wall of the cavity portion is divided into a band shape, and an induction heating coil is provided on the outer periphery of the cavity portion. Are arranged.

In this specification, when there is no need to distinguish the TMmnp mode, it is simply referred to as the TM mode.

[0012]

According to the electromagnetic composite heating furnace in which a number of axial slits are formed in the side wall of the microwave cavity operating in the TM mode according to the present invention, the microwave resonates in the TM mode in the heating furnace. The electric field is parallel to the axial direction of the cylinder or prism, and microwaves hardly leak from the slits formed on the side wall of the heating furnace. Then, the temperature of the object to be heated rises, and the object becomes a semi-molten state. If the microwave becomes difficult to penetrate into the heated object to some extent,
The microwave heating is stopped, and a high-frequency current is applied to the induction coil to switch to the induction heating of the cold crucible method. The heating by the eddy current is continued, and the object to be heated can be efficiently heated and melted.

In this case, a cylindrical conductor is removably disposed as a shield on the outer periphery of the portion where the slit of the microwave resonator is formed, and if the outer periphery of the slit is closed during microwave heating, the microwave is removed. Leakage from the slit is more reliably prevented.

In the heating furnace according to the present invention in which a slit is formed in the cavity portion of the semi-coaxial resonator, the object to be heated is first dielectrically heated by the microwave while tuning in the coaxial portion. After the electrical conductivity is improved in the molten state, the object is further heated by induction by the induction coil. As a result, the object to be heated is heated to the molten state by the eddy current as described above. During microwave heating, an electric field is generated in the cavity from the tip of the inner shaft toward the bottom of the cavity, so that microwaves leak from the slits provided on the side walls of the cavity. Is almost none. However, a cylindrical conductor is removably arranged around the slit formed in the cavity resonator, and the microwave leakage is completely prevented by closing the slit with a cylindrical conductor during microwave heating In the case of induction heating, by removing this cylindrical conductor, the induction heating can be made effective.

[0015]

1 is a schematic perspective view of a combined heating furnace according to one embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a cylindrical cavity formed of a metal such as copper or brass, which has a size such that microwaves introduced from a waveguide 3 through a microwave introduction port 2 resonate in a TM mode. In addition, a matching device 4 formed of a stub or the like is provided so that resonance can be achieved with perfect matching. The matching unit 4 may not be formed on the cylindrical cavity 1 but may be formed on the waveguide 3 side. A large number of slits 5 are formed in the lower side wall of the cylindrical cavity 1 along the axis of the cylinder in the vertical direction, and the side wall is divided into strip-shaped portions 6. An induction coil 7 is arranged on the outer periphery of the portion of the cylindrical cavity 1 where the slit 5 is formed. If the above-mentioned slit 5 is filled with a low-loss electrical insulator such as alumina or mica (not shown), the gas and pressure in the furnace can be arbitrarily adjusted. A crucible made of alumina, mica, or the like, which has low loss with respect to microwaves, is placed in a furnace, and an object to be heated can be supplied to the crucible and melted.

Next, the resonance of the TM mode according to the present invention will be described. FIG. 3 shows the distribution of the electric field and the magnetic field of the _TM01 mode in the circular waveguide. FIG. 3A shows an electric field distribution (magnetic field distribution is omitted) in a side view of the circular waveguide, and FIG.
Is the electromagnetic field distribution in the cross section of the circular waveguide. As can be seen from the figure, the electric field is distributed along the axial direction of the circular waveguide, with the distribution being strongest at the center and weakest at the waveguide wall. When resonating in the _TM01 mode, the electric field distribution becomes a standing wave as shown in a schematic diagram of an electric field in FIG. 4, and places where the electric field is strong are concentrated in certain places (A, B, and C in FIG. 4). Part of the object to be heated is particularly heated and the temperature rises, leading to melting.
Since TM is a ₀₁ mode has become such an electromagnetic field distribution, strong portions of the electric field is concentrated in the center of the resonator, weak electric field at the side wall portion of the cavity, flows the surface currents in the axial direction.
Therefore, even if a slit is formed in the side wall of the resonator in the axial direction (parallel to the direction of the surface current), a large amount of microwave does not leak from the slit. The above example is T
Has been described in M ₀₁ mode, for example, an electric field schematic diagram of a resonant state in the TM ₁₁ mode as shown in FIG. 5, occurs yet another electric field mode in the center, weak electric field is formed in the central portion In the middle part in the radial direction, a strong part of the electric field is formed, but the side wall is the weakest part of the electric field, as in the previous case, and the part where the surface current in the axial direction flows. Leakage is minimized. The TM mode has the same electromagnetic field distribution even in other higher-order modes. Even if a slit is formed on the side wall of the resonator, microwaves are hardly leaked. Can be concentrated in a certain place, and the temperature can be easily raised to a molten state.

In the above description, a circular waveguide or a circular cavity is described as an example of a resonator. However, even if the cross section is not circular, the same shape as a circular cylinder can be used as long as it is a square tube or more. An electric field distribution is formed, and a similar melting furnace can be formed.

Next, the configuration of induction heating will be described. The induction heating according to the present invention is based on the cold crucible concept described above, and has a structure in which a vertical slit is formed in a side wall of a heating furnace and the side wall is divided into a band shape. From the standpoint of induction heating only, it is only necessary to generate an eddy current in the belt-shaped portion, so the width of the slit can be set appropriately, but in the present invention, in order to combine microwave heating with this heating furnace, From the viewpoint of reducing microwave leakage, the slit width is preferably 2 to 5 mm (in the case of a microwave of 2450 MHz). However, if the slit portion is shielded by a conductor described later, the slit width is not necessarily limited to the above-described slit width.

It is desirable that the width of the strip portion divided by the above-mentioned slit is 10 to 20 mm in order to easily generate an eddy current. From the viewpoint of generating the eddy current, the side wall of the heating furnace is preferably formed to have a thickness of about 10 to 15 mm, and is formed of copper, brass, or the like having good electric conductivity, and the inside is water-cooled. When a high-frequency current is applied to the induction coil 7 in this configuration, an eddy current is generated in the object to be heated by electromagnetic induction, and the object is heated by resistance loss of the object to be heated. The repulsive force works with the eddy current, the object to be heated is separated from the melting furnace, and the temperature of the melting furnace can be prevented from rising.

In the present invention, the microwave heating and the induction heating are used in a single heating furnace, and the microwaves are resonated in the TM mode as microwaves. Therefore, the microwaves leak from the axial slits formed on the side walls. Although it is unlikely, at the time of microwave heating, insert a conductor tube having an inner diameter matching the outer periphery of the heating furnace to block the slit portion,
If the conductor tube is removed during induction heating, microwave leakage can be completely prevented.

FIG. 2 shows an example of a semi-coaxial cylindrical cavity resonator according to another embodiment of the present invention. In this structure, a metal rod 9 is disposed at the center of the cylindrical cavity 8 above the cylindrical cavity 8,
A coaxial line portion P is formed between the cylindrical cavity 8 and the metal rod 9, and a lower portion of the coaxial line portion P serves as a cavity resonator portion Q. Is formed, and is divided into a band-shaped portion 6, and an induction coil 7 is arranged around the band-shaped portion 6 to perform the same induction heating as described above. By doing so, microwave heating and induction heating can be used together as described above.

In this semi-coaxial cavity resonator, an electric field is applied to the metal rod 9 in the upper coaxial line portion P as shown by E in FIG.
From the inner axis of the cylindrical cavity 8 to the outer axis of the cylindrical cavity 8, and from the tip of the metal rod 9, along the axial direction of the cylindrical cavity 8, similarly to the above-described TM mode resonance. It is directed toward the bottom surface, and has a structure in which microwaves are unlikely to leak from the slit as described above.

According to these configuration examples, the cavity resonator section Q
If the object to be heated is not in a semi-molten state at high temperature, it is heated by the microwave electric field by the dielectric, and if the temperature rises to some extent and conductivity occurs, it is heated by the eddy current of induction heating and Because the light is reflected, appropriate heating is performed according to the state of the object to be heated, and the melting operation can be continuously performed.

[0024]

According to the present invention, since the dielectric heating by microwave and the induction heating by high frequency current are used together,
When the temperature is low, it is heated from the inside by microwaves and heats up efficiently.If the temperature rises to the semi-molten state and microwaves do not penetrate, the temperature is further raised by eddy current due to induction heating and melting And efficient heating can be achieved.

Further, since the induction heating according to the present invention employs the cold crucible method, the magnetic fields generated by the induction current generated in the strip on the side wall of the heating furnace and the induction current generated between the objects to be heated are mutually different. Then, the side wall and the object to be heated are separated from each other, and the melting operation can be performed without increasing the temperature of the heating furnace so much.

As a result, even at a high temperature, a dielectric material in which an ion current easily flows can be melted most efficiently and in a short time, and can be heated and melted with clean and energy saving, and a material having a high melting point and high hardness can be easily processed. This has the effect of contributing to the development of fields such as semiconductor materials and new ceramics in the future.

[Brief description of the drawings]

FIG. 1 is an explanatory perspective view of a combined heating furnace according to one embodiment of the present invention.

FIG. 2 is an explanatory sectional view of a combined heating furnace according to another embodiment of the present invention.

FIG. 3 is an electromagnetic field distribution diagram of _TM01 mode in a circular waveguide.

4 is a field schematic view when resonated TM ₀₁ mode in the cylindrical cavity resonator.

5 is a field schematic view when resonated TM ₁₁ mode in the cylindrical cavity resonator.

FIG. 6 is a diagram illustrating induction heating in cold crucible.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylindrical cavity 2 Microwave introduction port 5 Slit 7 Induction coil 8 Cylindrical cavity 9 Metal rod

──────────────────────────────────────────────────続 き Continuing from the front page (73) Patent holder 000208695 Dai-ichi High Frequency Industrial Co., Ltd. 1-6-2, Nihonbashi Bakurocho, Chuo-ku, Tokyo (72) Inventor Chokichiro Shibata 1-7-7, Gakuen Higashicho, Kodaira City, Tokyo No. 34 (72) Inventor Hiroe Aoki 20-1, Kita-Sekiyama, Odaka-cho, Midori-ku, Nagoya-shi, Aichi, Japan Chubu Electric Power Co., Inc. Electricity Research Institute (56) References JP-A-3-184296 (JP, A) Actual opening 48-72042 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) H05B 11/00 F27D 11/06

Claims (4)

(57) [Claims] 1. A side wall of a cylindrical or rectangular cylindrical microwave cavity having a microwave inlet and operating in a TM mode, a number of axial slits are formed, and the side wall is divided into strips, An electromagnetic combined heating furnace in which an induction heating coil is arranged on the outer periphery of a wave cavity. 2. A conductor which is detachably mounted on the outer periphery of a side wall of the microwave cavity, the conductor being adapted to the outer shape of the side wall of the cavity.
2. The combined electromagnetic heating furnace according to claim 1, wherein a slit formed in the side wall is closed by the conductor during microwave heating, and the conductor is removed during induction heating to expose the slit. 3. A side wall of the cavity portion of a microwave semi-coaxial resonator in which a coaxial line portion on which an inner axis is disposed and a remainder are formed in the cavity portion up to halfway of the cylindrical cavity. An electromagnetic wave combined heating furnace, wherein an axial slit is formed in the cavity, a side wall of the cavity resonator is divided into a band shape, and an induction heating coil is arranged on an outer periphery of the cavity. 4. A conductor conforming to the outer shape of the side wall of the resonator is disposed on the outer periphery of the side wall of the cavity resonator portion of the microwave semi-coaxial resonator, and is formed on the side wall during microwave heating. 4. The electromagnetic wave combined heating furnace according to claim 3, wherein the slit is closed by the conductor, and the conductor is removed during induction heating to expose the slit.