JPH0760737B2 - Microwave heating device and microwave heating method - 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 means for sintering, calcination, melting, joining, fiber drawing of ceramics and fine ceramics, or a series of drying, calcination, resin removal and sintering. Related to the heating means in the heating process,
Specifically, by repeatedly reflecting the incident microwaves back and forth, a heated object arranged at a position where the microwaves reflected back and forth (that is, microwaves having a frequency range of about 300 GHz as an upper limit) uniformly passes therethrough is heated. The present invention relates to a microwave heating device and a microwave heating method.

[0002]

2. Description of the Related Art Conventionally, for example, as heating means used in a heating process for manufacturing ceramics and fine ceramics, there are combustion heating of fuel, conduction and radiant heating by an electric heater, radiant heating by infrared rays and the like. This is adopted, and in any heating means, the object to be heated is heated from the outside and gradually heated to the inside by heat conduction.

[0003]

All of the above-mentioned conventional heating means heat the object to be heated from the outside and gradually heat it to the inside by heat conduction. Therefore, the object to be heated is constantly heated. Since the temperature of the outside is higher than that of the inside, a temperature gradient occurs in the object to be heated. Therefore, there is a problem that thermal stress due to non-uniformity of temperature is generated in the object to be heated, and firing strain and cracks are generated. Therefore, it is not easy to fire large-sized parts such as those with complicated shapes such as ceramic blades, and in order to prevent the occurrence of firing strain and cracks, the heating rate should be limited to a low temperature gradient. Heating time is longer because
There is a problem that the production cost becomes high. Therefore, in the present invention, the parallel line-shaped microwave output from the microwave output means is continuously reflected back and forth between two reflectors having parabolic reflectors having different focal lengths, and the two reflections are reflected. Microwaves are evenly passed through the heated object placed at the focal point of the parabolic reflector of the body to uniformly heat the heated object from the inside and suppress the occurrence of temperature gradient in the heated object. In addition to enabling rapid heating, it is a technical subject to be solved to improve productivity and quality.

[0004]

The technical means for solving the above-mentioned problems are a microwave heating device for outputting a microwave of a required electric power in parallel with the axis and a microwave heating device for injecting the microwave heating device in parallel with the axis. And a first reflector having a parabolic reflector having a focal length fa formed so that the reflected microwave passes through the focal point, and a parabolic reflection of the first reflector A parabolic reflector that faces the mirror on the same axis, and the focal length fb of the parabolic reflector is smaller than the focal length fa of the parabolic reflector of the first reflector, and A parabolic reflector of the first reflector, and a second reflector disposed so that a focal point is located at a focal position of the parabolic reflector of the first reflector. The object to be heated is arranged in the common focus zone of the parabolic reflector of the reflector.

Further, the first reflector having a parabolic reflector having a focal length fa and the focal length fb smaller than the focal length fa.
And a second reflector having a parabolic reflector of
In addition, the parabolic reflectors are arranged so as to face each other so that their focal points coincide with each other, and the object to be heated is placed in the shared focal zone.
Heating the object to be heated by continuously reflecting the microwave output from the microwave output means parallel to the axis between the two parabolic reflectors and passing the object back and forth. Is.

[0006]

In the above microwave heating apparatus and microwave heating method, when a heated object such as ceramics and fine ceramics formed of a dielectric is placed in a microwave electric field, the unit of the heated object The power P absorbed per volume is P = 2πfε ₀ ε _r tan δ | E | ² where f is the frequency (GHz) ε ₀ is the dielectric constant of the vacuum (8.86 × 10 ⁻¹² F / m) ε _r is the relative permittivity of the object to be heated tan δ is the dielectric loss E (V / m) is the magnitude of the internal electric field. As is clear from the above equation, the relative permittivity ε _{r of} the object to be heated,
And the temperature characteristic of the dielectric loss tan δ are important for the control of the microwave heating process. Relative permittivity ε of heated object
_r and the dielectric loss tan δ with respect to temperature characteristics, the dielectric loss
The effect of tan δ near room temperature is smaller than that of relative permittivity ε _r , and the degree of effect gradually increases as the temperature of the object to be heated increases, and when it reaches a certain critical temperature, it rapidly increases and exceeds that critical temperature. Then, the microwave energy is absorbed more efficiently in the object to be heated, whereby the temperature of the object to be heated exponentially rises. When the temperature of the heated object is increased in this way,
The temperature that reaches the maximum temperature is determined by the balance between the amount of heat generated from the object to be heated and the amount of heat diffused by conduction and radiation, so it is easy to control the temperature of the object to be heated by the microwave output intensity. Therefore, by adjusting the output of the microwave, the upper limit temperature can be made higher than that of the conventional high temperature furnace.

According to the microwave heating device for heating the object to be heated based on the above heating principle, the first reflector having the parabolic reflector having the focal length fa and the focal length fa A second reflector having a parabolic reflector with a small focal length fb is coaxially opposed to the parabolic reflector so that the focal points of the two parabolic reflectors coincide with each other, and the shared focal zone is covered by the same. When the heating body is arranged, the microwaves parallel to the axis output from the microwave output means are continuously reflected back and forth between the two parabolic reflectors, and when the heated body is passed back and forth, Each time the microwave is repeatedly reflected back and forth, its trajectory gradually approaches the axis from the outer peripheral portion of the parabolic reflector, so that the object to be heated is efficiently and uniformly heated.

[0008]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a structural system diagram schematically showing the structure of a microwave heating device. In FIG. 1, the microwave generator (microwave generating means) 1 is, for example, 53 GH.
The microwave 2 of z is output in parallel and in an annular shape.
The microwave generator 1 can change the microwave output, frequency, duty%, etc. within a predetermined range. The microwave 2 output from the microwave generator 1 is a box 3 made of a metal material.
Is incident on. The box body 3 is internally provided with a first reflector 5 having a parabolic reflector 5A and a second reflector 6 having a parabolic reflector 6A.

As shown in FIG. 1, the parabolic reflection mirror 5A of the first reflector 5 provided inside the box 3 has a focal length fa, and the second reflector 6 has a parabolic reflection. The focal length of the mirror 6A is f
The focal length fa is larger than the focal length fb. The first reflector 5 and the second reflector 6 are on the same optical axis P, and the focus of the parabolic reflector 5A and the parabolic reflector 6A.
Are arranged so as to face each other so that their focal points coincide with each other.
A heated object 7 such as fine ceramics or a ceramic material is placed at the shared focal point position, and is heated by microwaves by the following action.

In FIG. 1, when the microwave 2 generated from the microwave generator 1 is reflected by the lower part of the parabolic reflector 5A of the first reflector 5, the reflected wave 2a is the common focus position. The parabolic surface of the first reflector 5 by heating the object 7 to be heated and reaching the parabolic reflector 6A of the second reflector 6 and being reflected to form a parallel reflected wave 2b. Reflector 5
Reach A. The parallel reflected wave 2b is reflected by the parabolic reflector 5.
The reflected wave 2c reflected by A passes through the common focal point position to heat the object 7 to be heated and the second reflector 6
Reach the parabolic reflector 6A. The parallel reflected wave 2d reflected there reaches the parabolic reflector 5A of the first reflector 5, and the reflected wave 2e reflected there passes through the common focal point position to heat the object 7 to be heated. The reflected waves 2f, 2g, 2h, 2i, 2 are sequentially acquired while following a locus of reaching and being reflected by the parabolic reflector 6A of the second reflector 6.
As the distance becomes j, 2k, 2l, etc., it gradually approaches the optical axis P. Therefore, the object 7 to be heated is
Uniform heating can be performed since ~ 2 liters and the like pass sequentially.

Next, the features when the object 7 to be heated is heated by microwave are summarized as follows. (1) Since the object to be heated can directly absorb the microwaves to heat the object to be heated uniformly from the inside, it is possible to uniformly heat an object having a complicated shape or a large object. Therefore, since the temperature gradient of the object to be heated is reduced, the internal stress of the object to be heated is reduced, and cracking or destruction can be prevented. (2) Since the place where the object to be heated is heated, that is, the place where the heat is generated, can be spatially separated from the energy supply device,
Heating can be performed in vacuum, in a pressure chamber, in air, or in an oxidizing / reducing atmosphere. (3) When the object to be heated exceeds the critical temperature, microwave absorption is more efficiently performed. Therefore, when heated above the critical temperature, the temperature of the object to be heated rises rapidly, and Since the temperature is raised functionally, rapid heating is possible. Therefore, rapid heating of about 2 to 50 times as much as that of the conventional heating means becomes possible, so that a dense body having the minimum necessary growth grains, that is, accelerated sintering can be performed. (4) Since the heating time is shortened, energy and man-hours can be reduced, so that the production cost can be reduced. (5) Since the temperature of the object to be heated rises in proportion to the product of the relative permittivity ε _{r of the} object to be heated and the dielectric loss tan δ, there is no upper temperature limit in principle, and a large power output device can be used. Since the high temperature electric furnace can be configured, the ceramics and the like can be heated at a high temperature of 2000 ° C. or higher. (6) By using the reflector, the supplied microwaves can be reflected back and forth and the microwaves can uniformly pass through the object to be heated, so that the conversion efficiency from microwaves to heat can be further improved. ..

[0012]

As described above, according to the present invention, the microwave output from the microwave output means is continuously reflected back and forth between two reflectors having parabolic reflectors having different focal lengths. The heating element is placed between the two reflectors so that microwaves can pass through it uniformly, so that the heating element can be heated uniformly from the inside, and the occurrence of temperature gradients in the heating object can be suppressed. In addition, the rapid heating can be enabled, and the productivity in the heating process of the object to be heated can be improved, and the quality of the object to be heated can be improved.

[Brief description of drawings]

FIG. 1 is a system diagram schematically showing the configuration of a microwave heating device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Microwave generator 2 Microwave 3 Box body 5 1st reflector 5A 1st reflector parabolic reflector 6 6 2nd reflector 6A 2nd reflector parabolic reflector 7 Heated Body fa Focal length of parabolic reflector of first reflector fb Focal length of parabolic reflector of second reflector

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Motoyasu Sato 1-5-21 Ono Asahi, Shiga-cho, Shiga-gun, Shiga (72) Inventor Sakuji Kobayashi 4944 Gotenyamaminami-cho, Hirakata-shi, Osaka (72) Invention Tsutomu Tsunooka 25-8 Dandome, Noda-cho, Kariya City, Aichi Prefecture (72) Inventor Yutaka Higashi 2-chome, Mitsugaoka 18-3, Komaki City, Aichi Prefecture (56) Reference JP-A-4-137391 (JP, A) Flat 4-209495 (JP, A)

Claims (2)

[Claims] 1. A microwave output means for outputting a microwave of required power in parallel with an axis, and a microwave for reflecting the microwave incident in parallel with the axis so that a reflected microwave passes through a focal point. A parabolic surface having a first reflector having a parabolic reflector having a focal length fa and a parabolic reflector facing the parabolic reflector of the first reflector on the same axis. The focal length fb of the reflector is smaller than the focal length fa of the parabolic reflector of the first reflector, and the focus is located at the focal position of the parabolic reflector of the first reflector. A parabolic reflector of the first reflector and a paraboloidal reflector of the second reflector, the object to be heated is disposed in the shared focal zone of the parabolic reflector of the second reflector. The microwave heating device characterized in that 2. A first reflector having a parabolic reflector having a focal length fa and a second reflector having a parabolic reflector having a focal length fb smaller than the focal length fa are coaxially arranged. Further, the parabolic reflectors are opposed to each other so that the focal points thereof coincide with each other, and the object to be heated is placed in the shared focal zone, the microwave parallel to the axis output from the microwave output means is A microwave heating method, characterized in that the object to be heated is heated by causing the object to be heated to reciprocate continuously between the two parabolic reflecting mirrors and passing the object to be heated back and forth.