JPH0754745B2 - Microwave heating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to heating means for sintering, calcination, melting, joining, fiber drawing, etc. of ceramics and fine ceramics, or drying, calcination, resin removal, It relates to heating means in a series of heating steps such as sintering. Specifically, by repeatedly reflecting the incident microwave back and forth, the microwave reflected back and forth (that is, a frequency range of 300 GHz
The microwave heating device is capable of heating an object to be heated, which is arranged at a position where microwaves whose upper limit is about the degree) converges and passes, under a preset temperature condition.

(Prior Art) Conventionally, for example, as a heating means used in a heating step when manufacturing ceramics and fine ceramics,
Combustion heating of fuel, conduction and radiant heating by electric heater,
Radiant heating by infrared rays or the like 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.

(Problems to be Solved by the Invention) In all of the above conventional heating means, the object to be heated is heated from the outside and gradually heated to the inside by heat conduction. 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 is generated in the object to be heated due to the nonuniformity of temperature, 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. Is required to be small,
There is a problem that the heating time becomes long and the production cost becomes high.

Alternatively, since it is extremely difficult to finely control the temperature of the object to be heated due to the heat storage of the heating furnace, there is a limit in producing fine ceramic products with high quality.

Therefore, in the present invention, the beam-shaped microwave output from the microwave output means is continuously reciprocally reflected between two reflectors having a curved reflecting surface, and is arranged between the two reflectors. By focusing and passing the microwave to the heated body, the specific heating body is uniformly heated from the inside, and the generation of the temperature gradient in the heated body is suppressed, and the output from the microwave output means is changed to, for example, a duty cycle. It is a technical problem to be solved to control the heating of the object to be heated in accordance with the set temperature condition to improve the quality of the object to be heated.

(Means for Solving the Problem) A technical means for solving the above-mentioned problems is to provide a microwave heating device for outputting a microwave of a required electric power for heating an object to be heated in a beam form. Means and
A box body that allows the beam-shaped microwaves to enter through an entrance opening that is opened at the end, and a beam-shaped microwave that is disposed inside the box body and that enters through the entrance port at the outer edge of the curved reflecting surface. A first reflector that reflects the light, and a first reflector that is disposed at a position facing the first reflector and that receives the beam-shaped microwave reflected by the outer edge of the first reflector and then reflects the beam-shaped microwave. Second reflection having a curved reflection surface that continuously reflects the beam-shaped microwave between the first reflection member and the curved reflection surface and gradually converges the beam-shaped microwave to the position where the object to be heated is arranged. Body, temperature detecting means for detecting the temperature of the object to be heated and outputting a signal corresponding to the detected temperature, output control means for duty-controlling the output power from the microwave output means, and the object to be heated The temperature of
Setting means for setting a temperature condition such as a temperature rising time or a temperature falling time, and the object to be heated according to the setting condition based on the temperature condition set by the setting device and a signal from the temperature detecting means. And a temperature control means for outputting a temperature control signal for controlling the temperature to the output control means.

(Operation) According to the microwave heating device having the above configuration, when the object to be heated is placed in the microwave electric field, the electric power P absorbed per unit volume of the object to be heated is P = 2πfε ₀ ε _r tan δ | E | ² where f is the frequency (GHz) ε ₀ is the dielectric constant of vacuum (8.86 × 10 ^-12 F / m) ε _r is the relative permittivity of the heated object tan δ is the microwave electric field and induced current The tangent E (V / m) of the angle of deviation of the phase from and 90 degrees indicates 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,
The temperature characteristics of tan δ and tan δ are important for controlling the microwave heating process. Relative permittivity ε _r of heated object, and t
Regarding the temperature characteristic of an δ, tan δ generally increases as the temperature rises, so that microwave energy is absorbed more efficiently, and thereby the temperature of the heated object rises.

When the temperature of the object to be heated rises in this way, the maximum temperature reached 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. By controlling the duty, the temperature of the object to be heated can be easily controlled. Therefore, by controlling the duty of the microwave output, the object to be heated can be heated according to the set temperature condition, and the productivity and the quality of the object to be heated can be improved.

According to the microwave heating device for heating the object to be heated based on the heating principle as described above, the microwave of the required power output in the beam form from the microwave output means is incident on the box body. When entering through the mouth, the incident beam-like microwave is continuously reflected back and forth between the first reflector and the second reflector. By focusing and passing the beam-shaped microwaves to the heated object placed between the two reflectors, the heated object is uniformly heated from the inside, and the generation of the temperature gradient in the heated object is suppressed. You can

Further, the temperature control means outputs to the output control means a temperature control signal for controlling the temperature of the object to be heated to a temperature in accordance with the temperature condition set by the setting means and the signal from the temperature detection means. Then, the output control means outputs the output power according to the temperature control signal from the microwave output means. As a result, when the output control means recognizes the actual temperature of the object to be heated based on the signal from the temperature detection means, and the actual temperature has a difference from the temperature condition set by the setting means, , It is automatically controlled so as to correct it, and the object to be heated is made to match the temperature according to a preset temperature condition.

(Example) Next, the Example of this invention is described, referring drawings.

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

In this embodiment, the microwave generator 1 has a maximum output of 20
A gyrotron that outputs a microwave of 0KW and 53GHz into a beam is used. The controller 2 controls the electric power of the microwave output from the microwave generator 1. This control device 2 is the microwave generator 1
It outputs a duty signal for controlling the power of the microwave output from. The duty signal output from the controller 2 is manually set in the output setter 2A, for example, 0.01%.
The temperature setter 2B is provided to set temperature conditions such as the temperature of the object to be heated M, the temperature raising time and the temperature lowering time, which can be arbitrarily set within a duty percentage range of 100% to 100%. A duty signal for automatic control having a cycle T as shown in FIG. 2 corresponding to the temperature condition set in 2B is output.

The duty signal output from the controller 2 is input to the gate circuit 3 and drives the gate circuit 3. The gate circuit 3 uses the DC signal 4 based on the duty signal.
The DC power supplied from the microwave generator 1 to the microwave generator 1 is turned on / off. The microwave generator 1 outputs the microwave of 53 GHz in the state where the DC voltage from the DC power source 4 is applied, while the microwave output is stopped when the application of the DC voltage is cut off. That is, the microwave generator 1
The average power corresponding to the duty percentage of the duty signal is output.

The beam-shaped microwave 10 output from the microwave generation device 1 is incident on the microwave heating body 6 via the microwave injection device 5. The microwave injection device 5 allows the beam-shaped microwaves 10 output from the microwave generation device 1 to pass through in the microwave heating body 6 direction without attenuation, while reflecting microwaves reflected from the microwave heating body 6 in the microwave direction. The microwave generation device 1 is configured to be protected from irradiation of reflected microwaves without being transmitted in the direction of the generation device 1.

The beam-shaped microwave 10 output from the microwave generation device 1 and passed through the microwave injection device 5 is incident on the box-shaped microwave heating body 6 formed of a metal material. The microwave heating body 6 is configured as shown in FIG.
That is, a first reflector 11 having a concave mirror-shaped reflecting surface 11A is provided inside the microwave heating body 6, and the microwave beam 10 incident from the entrance 12 is reflected on the reflecting surface 11A. Is fixed as. The second reflector 13
Has a concave mirror-shaped reflecting surface 13A, and the reflecting surfaces 11A and 13A
A has a parabolic shape in which parallel beams are focused on one point. The focusing points of the first reflector 11 and the second reflector 13 are set near the heated object M. That is, the second reflector 13 is arranged at a position facing the first reflector 11 with the central optical axis being the same as that of the first reflector 11 with a required space therebetween. At the center of the space between the reflector 11 and the second reflector 13, a heated object M such as ceramics or fine ceramics is arranged.

In the microwave heating body 6 configured as described above,
When the pulsed microwave beam 2 incident from the entrance 12 is reflected on the reflecting surface 11A, as shown in FIG. 3, the reflecting surface 11A of the first reflector 11 and the second reflecting body 11A are reflected. The first reflector 11 is continuously reciprocally reflected between the 13 reflecting surfaces 13A.
Since the light passes through the center of the space between the second reflector 13 and the second reflector 13, the electromagnetic field strength in the center of the space is increased by a factor of 5 to 10. Then, the continuous reflected wave is generated by the first reflector 11
Since the microwave converges and passes through the object M to be heated placed in the central portion of the space between the second reflector 13 and the second reflector 13, the object M to be heated is rapidly heated.

A temperature sensor 15 of, for example, a radiation type that detects the temperature of the object to be heated M and outputs a signal corresponding to the detected temperature is attached in the vicinity of the microwave heating body 6, and the signal is sent to the control device 2. It is configured for feedback input. Then, the control device 2 recognizes the actual temperature of the object to be heated M by inputting a signal from the temperature sensor 15, and detects the actual temperature between the actual temperature and the temperature set by the temperature setting device 2B. When a difference occurs in the duty ratio, the duty percentage of the duty signal for correcting the difference to zero is automatically corrected.

Next, a sintering experiment when the object to be heated M is sintered using the microwave heating device having the above-described configuration will be described.

In this experiment, as a sample, a Y-Ba-Cu-O-based superconductor, that is, a calcined powder of YBa ₂ Cu ₃ O _y was applied with a pressure of 1 t / cm ² and press-molded to form a pellet of 15φx5t. Various characteristics were compared between one pellet that was normally fired in an electric furnace and 10 pellets that were fired by microwave heating.

FIG. 4 is a firing temperature pattern diagram when one pellet is normally fired in an electric furnace. As shown in this figure, the heating time takes 184 minutes, and after heating up to 920 ° C, 920 ° C
Is held for 5 hours and then cooled in a furnace to be normally fired.

As 11 pellets of 15φ x 5t, a total of 11 pellets YM-1 to YM-10 which are fired by microwave heating and YS-1 which is normally fired according to the temperature characteristics shown in FIG.
Is given.

In this experiment, the size is 50x1 as shown in Fig.5.
Four 00x100 insulation materials 21 are used, and the temperature sensor is on the side.
A hole for temperature detection is made by 15 and pellets YM-1 to YM-5 and pellets YM-6 to YM-1 are provided in the central space.
With 0 and 1 arranged separately,
After the microwave heating element 6 was set to the heating object arrangement position, the group of pellets YM-1 to YM-5 was subjected to microwave heating in the first experiment based on the temperature condition and duty ratio shown in FIG. It is to be fired. Also, pellet YM-6
7 to the YM-10 group is subjected to microwave heating and firing in the second experiment based on the temperature condition and the duty ratio shown in FIG.

Fig. 8 shows 15φ x 5t pellets YM-1 to YM-10 used in the experiment and YS-1 cut into strips.
It shows that a sample number is assigned to each.
As an example, YM-4 is divided into eight, and each strip is given a subnumber from 1 to 8. The reason why each pellet is divided into eight parts and the sub-numbers are assigned to each is to see variations in characteristics of the same pellet.

Fig. 9 shows a sample obtained by cutting each of 15φx5t pellets YM-1 to YM-10 fired by microwave heating into strips, and a sample of normally fired pellets YS-1 cut into strips. 3 shows the results of measuring the superconducting characteristics of the.

According to the measurement results, the critical current density Jc clearly illustrate superconducting properties (A / cm ^2), the sample YM-4-4 is 21A / cm ² and the highest, the the sample YM-6-4 followed this It is 11 A / cm ² .
On the other hand, many samples have a critical current density Jc (A / cm ² ) of 1 or less. This is because when pellets are arranged in groups in the microwave heating body 6 in the state shown in FIG. It is considered that the amount of microwaves transmitted through the pellets varies depending on the arrangement position of the pellets. Therefore, it is considered that the same superconducting characteristics as those of the samples YM-4-4 can be obtained by making the amount of microwaves transmitted through the pellets the same.

Since the critical current density Jc (A / cm ² ) of the sample YS-1-4 of the normally fired pellet YS-1 is 1 A / cm ² or less, compared with the pellet fired by microwave heating, It is clear that the normally fired pellet YS-1 has poor superconducting properties.

FIG. 10 shows the critical current densities of the samples YM-4-2 to YM-4-7 of the pellet YM-4 that showed the highest critical current density in the experiment, and the superconducting properties of the same pellet. This is the result of investigating the variation of.

As shown in this figure, even with the same pellet, there are variations in superconducting characteristics depending on the sample, that is, the location. The cause of this variation seems to be that the microwave transmission amount is different even for the same pellet.

In FIGS. 9 and 10, the critical current density Jc (A /
cm ² ) was 77K and showed a value at zero magnetic field. Moreover, the bulk density showed the approximate value by dimension measurement.

FIGS. 11 (A) and 11 (B) show a sample YS-1-4 of the normally fired pellet YS-1 and a pellet YM fired by microwave heating.
-4 is a diagram illustrating a crystal structure of each of YM-4-2 samples observed with an electron microscope at the same magnification.

As shown in FIG. 11 (A), normally fired pellets YS-1
While the crystal structure of the sample YS-1-4 of No. 2 is an aggregate of grains, as shown in FIG. 11 (B), the sample YM-of the pellet YM-4 fired by microwave heating is used. Since 4-2 is uniformly heated to the inside at a predetermined temperature, it is single-crystallized and has large grains. Therefore, it is considered that Sample YM-4-2 has less voids between crystals and has improved current-carrying characteristics. On the other hand, since the sample YS-1-4 of the pellet YS-1 is normally heated by the electric furnace, the internal temperature becomes lower than the external temperature, and thus it is presumed that single crystallization is difficult.

In addition, the sample YM-4-2, which is single-crystallized and has large grains,
It has the characteristic of high mechanical hardness.

(Effect of the invention) As described above, according to the present invention, the beam-shaped microwave output from the microwave output means is continuously reflected back and forth between two reflectors having a curved reflecting surface. In a microwave heating device configured to focus and pass a microwave to a heated body disposed between the two reflectors, the heated body is appropriately controlled by duty-controlling the output from the microwave output means. Since the temperature can be controlled so that the quality of the object to be heated can be improved, the quality of the object to be heated can be improved.

[Brief description of drawings]

The drawings relate to an embodiment of the present invention, and FIG. 1 is a structural system diagram schematically showing the overall structure of a microwave heating device, and FIG.
The figure is a waveform diagram of the duty signal, Fig. 3 is a cross-sectional view of the microwave heating body, Fig. 4 is a firing temperature pattern diagram of the normal firing pellets used in the experiment, and Fig. 5 is a sample when firing the pellets used in the experiment. Arrangement diagram, FIG. 6 is a firing temperature pattern diagram in the first experiment, FIG. 7 is a firing temperature pattern diagram in the second experiment, FIG. 8 is a sample number explanatory diagram, and FIG. 9 is microwave heating. Fig. 10 is a characteristic comparison diagram between the fired pellets and the normally fired pellets. Fig. 10 is a diagram showing variations in superconducting properties of each sample of the same pellet fired by microwave heating. Fig. 11 (A) is a graph of the normally fired pellets. The crystal structure diagram of one sample, FIG. 11 (B) is the crystal structure diagram of one sample of pellets fired by microwave heating. 1: Microwave generator 2: Controller 2B: Temperature setting device 3: Gate circuit 4: DC power supply 5: Microwave injection device 6: Microwave heating element M: Heated element 15: Temperature sensor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kei Mutoh 3-2, Kitasenshi, Chikusa-ku, Nagoya, Aichi 14-2 Chikusa Higashi Housing 14-14 (72) Inventor Motoyasu Sato Ono Asahi, Shiga-cho, Shiga-gun 1 ―5-21 (72) Inventor Sakuji Kobayashi 4944, Gotenyamaminami-cho, Hirakata-shi, Osaka (72) Inventor Tsutomu Kadooka 25-8 Dandome, Noda-cho, Kariya-shi (72) Inventor Yutaka Higashida Aichi Komaki City Mitsugaoka 2-chome 18-3 (56) References JP-A-58-186200 (JP, A) JP-B-52-6505 (JP, B2)

Claims (1)

[Claims] 1. A beam-shaped microwave output means for outputting a microwave of a required electric power for heating an object to be heated in a beam shape, and a box body for injecting the beam-shaped microwave from an entrance opening opened at an end thereof. And a first reflector which is disposed inside the box body and reflects the beam-shaped microwaves incident from the entrance through the outer edge portion of the curved reflecting surface, and which opposes the first reflector. The beam-shaped microwaves, which are arranged at a position and receive the beam-shaped microwaves reflected by the outer edge portion of the first reflector, reflect the beam-shaped microwaves, and then generate a beam-shaped microwave between the curved surface of the first reflector. A second reflector having a curved reflecting surface that continuously reflects the beam-like microwaves and gradually converges the beam-shaped microwaves to the position where the object to be heated is placed, and the temperature of the object to be heated is detected, and the detected temperature is responded to. Temperature detection means for outputting the signal Output control means for duty-controlling the output power from the microwave output means, setting means for setting temperature conditions such as temperature of the object to be heated, temperature rising time, or temperature lowering time, and the setting means set by the setting means. Temperature control means for outputting to the output control means a temperature control signal for controlling the object to be heated at a temperature according to the set condition based on a temperature condition and a signal from the temperature detection means. A microwave heating device.