JP6940059B2 - Heating element, manufacturing method of heating element and microwave heating device - Google Patents

Description

The present invention relates to a heating element that absorbs microwaves and generates heat, and a microwave heating device including the heating element, and more particularly to a configuration of the heating element.

As a furnace for firing metals, ceramics, etc., a firing furnace using microwaves is known. There, a heating element that absorbs microwaves and generates heat is applied to the inner wall of the container made of a heat insulating material. Then, an object to be heated containing metal powder or ceramic powder is placed in the container, and the container is placed in a microwave oven for a predetermined time and fired (see Patent Document 1). As the heating element, a mixture of two types of silicon carbide powder having high heat resistance and a heat resistant material such as water glass or a clay substance is used.

Japanese Unexamined Patent Publication No. 2001-284039

Microwave heating has been used or attracted attention in various fields in recent years because of its stable heat generation and easy control of heat generation rate. Since shortening the heat treatment time of the heating element brings about high-speed firing of the object to be heated in a short time, it is important to raise the temperature of the heating element as a heat source as high as possible.

However, in the above-mentioned microwave heating device in which the heating element is applied to the inner wall of the container, it is difficult to realize a higher-speed temperature rise than before because the heating element contains silicon having a large electric resistance.

Therefore, there is a need for a heating element capable of achieving high-speed temperature rise and a microwave heating device provided with the heating element.

The heating element of the present invention includes a heating member (also referred to as an exothermic material) containing carbon that absorbs microwaves to generate heat, and a container that transmits microwaves. Then, the heat-generating member is arranged in the container, and the container is filled with a fluid that is inert to the heat-generating member. As the container, for example, a tubular container or a tubular container can be applied. Further, the heat generating member can be composed of a heat generating member made of carbon or a heat generating member obtained by adding another substance to carbon.

As the fluid, a fluid that is inert to the heat generating member (particularly carbon) is applied. For example, the container can be filled with a noble gas containing at least one of helium, neon, argon, and xenon. At this time, the pressure of the gas filled in the container can be set to 1 kPa to 10 kPa.

When a heating element composed of the heating member and a container for accommodating a fluid is irradiated with microwaves, the carbon of the heating member absorbs the microwaves and generates heat. On the other hand, the fluid filled in the container does not cause carbon to react with oxygen in the atmosphere, and weight loss due to carbon dioxide in a high temperature state does not occur. By maintaining the amount of carbon, it is possible to raise the temperature in a short time. Therefore, as one aspect of the present invention, a microwave provided with such a heat generating member, a microwave oscillator for irradiating the heating element with microwaves, and a microwave reflecting container for accommodating the heating element and the object to be heated. It is possible to provide a heating device.

There are various arrangement configurations of the object to be heated in the microwave heating device. For example, when the container is a single-tube container, the object to be heated can be arranged outside the container (near the container, etc.). Further, the container can be composed of a double-tube container having an outer tube and an inner tube, a heat generating member is arranged between the outer tube and the inner tube, and the object to be heated is placed inside the inner tube. It should be placed in.

The heat generating member can be either granular or lumpy. For example, the heat generating member can be composed of powder or granular material containing carbon. In this case, at least one of the total thickness of the heat generating member and the particle size of the powder or granular material can be determined so that the temperature rise due to microwave absorption becomes dominant over the temperature rise due to heat conduction between the particles. For example, the powder or granular material can be configured to have a particle size in the range of 1 μm to 1.5 mm. When the heat-generating member is composed of powder or granular material, the space area between the heat-generating member and the upper end surface of the inner surface of the container along the vertical direction and the inside of the introduction pipe for introducing the heat-generating member into the container are filled with fluid. Is possible to form.

On the other hand, when the heat generating member is configured in a lump shape, the heat generating member can be a structure in which a plurality of gaps that open toward the outside of the container are formed. For example, the heat generating member is composed of a structure in which a plurality of carbon-containing plates are arranged at predetermined intervals with respect to the rod-shaped carbon material. In this case, at least one of the size of the gap along the axial direction of the container and the thickness of the carbon-containing plate is dominated by the temperature rise due to the absorption of microwaves that have entered the gap, rather than the temperature rise due to heat conduction in the heat generating body. It can be determined to be the target.

In the method for producing a heating element in another aspect of the present invention, a material that transmits microwaves is heated to form a container, and a heat generating member containing carbon that absorbs the microwaves to generate heat is arranged in the container to generate heat. A fluid inert to the member is introduced into the container and the container is sealed.

According to the present invention, the object to be heated can be heated and heated in a short time.

It is a schematic block diagram of a microwave heating apparatus. It is a schematic cross-sectional view of the heating tube which is 1st Embodiment. It is the schematic sectional drawing of the heating tube which is 2nd Embodiment. It is a schematic cross-sectional view of the heating tube which is a 3rd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a microwave heating device according to a first embodiment. FIG. 2 is a schematic cross-sectional view of the heating tube.

The microwave multiple reflection type heating device (also referred to as a microwave firing furnace; hereinafter referred to as a "microwave heating device") 10 is a device that heats, fires, or dries an object to be heated by using microwaves. A heat-resistant rectangular microwave reflecting container (hereinafter referred to as a reflecting container) 40 is provided. Microwave oscillators 50 and 60 are mounted on different side surfaces of the reflection container 40, and microwaves are oscillated from two different directions toward the heating tube 20 in the reflection container.

A heating tube 20 is installed by a support member (not shown) in the central portion of the space region 40M of the reflection container 40, and a heated object 30 is held by a holding member (not shown) beside the heating tube 20. ing. Examples of the object to be heated include ceramics, semiconductors, and organic substances. Further, the microwave heating device 10 includes a power supply circuit (not shown) capable of controlling the microwave oscillators 50 and 60, and a thermometer (radiation thermometer) (not shown) for measuring the temperature of the heating tube 20. The power supply circuit controls the microwave oscillators 50 and 60 based on the temperature of the heating tube 20 detected by the thermometer.

As shown in FIG. 2, the heating tube 20 is a container in which a heating member is arranged, and here, the heating tube 20 is composed of a closed bottomed tubular container having an introduction tube 22 formed at one end thereof, and is composed of microwaves. It is heat-molded by a quartz material that is transparent to the material. However, a disk-shaped container having an inner diameter larger than the shaft length may be used. The heating tube 20 is filled with a carbon heating member 70 so as to substantially fill the entire inside of the heating tube 20.

The carbon heat generating member 70 is composed of a flowable carbon powder or granular material 70M here. The carbon powder or granular material 70M is obtained by crushing a lumpy carbon material, and by so-called coarse crushing or medium crushing, carbon powder or granular material 70M which is an aggregate of particles having the above particle size is produced.

Since each particle of the carbon powder or granular material 70M has an irregular uneven surface, when the carbon powder or granular material 70M is put into the heating tube 20, a gap is generated between the particles. The gaps between the particles exist in the entire carbon heating member 70. The inner diameter of the heating tube 20, the particle size of the carbon powder or granular material 70M, and the filling rate are determined so that heat generation due to microwave absorption becomes dominant, as will be described later.

As shown in FIG. 2, a space region S filled with a rare gas is formed over the entire pipe axis direction between the carbon heating member 70 and the upper end surface of the heating pipe inner surface 20U along the vertical direction. .. However, since the size of the space region S is exaggerated in FIG. 2, the total thickness of the carbon heating member 70 composed of the carbon powder particles 70M is substantially equal to the inner diameter of the heating tube 20. Further, the inside of the introduction pipe 22 formed at the end of the heating pipe 20 is not filled with the carbon powder or granular material 70M, and a space region filled with a rare gas is formed.

The remaining space area in the heating tube 20 excluding the carbon heating member 70 is filled with the rare gas. Here, any gas of helium, neon, argon, xenon, or two or more kinds of these gases are sealed. The noble gas is also inactive with respect to the carbon heating member 70 and is also inactive with respect to the heating tube 20 made of quartz glass.

When the carbon powder particles 70M having gaps between the particles and the heating tube 20 in which the rare gas is air-sealed are irradiated with microwaves, the microwaves reach the entire carbon powder particles 70M. In particular, it also reaches the carbon powder particles near the center (axis) of the heating tube 20.

As a result, the high temperature state can be reached in a short time. In particular, by encapsulating the rare gas in the heating tube 20, it is possible to prevent the carbon powder or granular material 70M from being converted into carbon dioxide by the reaction with oxygen in the atmosphere to reduce the amount and reduce the filling amount.

When the carbon powder or granular material 70M generates heat, the heat generated by the carbon powder or granular material 70M near the center is released to the outside of the heating tube 20. As a result, the heat radiation of the heating tube 20 as a whole is increased, and the object to be heated can reach a high temperature state in a short time.

The inner diameter of the heating tube 20, the particle size and the filling rate of the carbon powder or granular material 70M are set so as to realize a temperature rise in a short time by increasing the surface area of the carbon heating member 70 irradiated with microwaves. .. If the inner diameter of the heating tube 20 is too small, the amount of carbon powder or granular material 70M will be small, and the heat generating effect will be small. On the other hand, if the inner diameter of the heating tube 20 (the total thickness of the carbon heating member 70) is too large, the microwave does not reach the vicinity of the center of the heating tube 20, and the temperature rise due to heat conduction becomes dominant and the temperature rises in a short time. It does not become a state. For example, the inner diameter of the heating tube 20 can be set to 1 mm to 100 mm.

If the particle size of the carbon powder or granular material 70M is too small, the particle gap becomes small, and as a result, the reach of the microwave to the carbon powder or granular material 70M is limited to the outside, and the temperature is raised to a high temperature in a short time. Is difficult. On the other hand, if the particle size is too large, the microwave does not reach the vicinity of the center of the heating tube 20, and in the carbon powder granules 70M near the center, the temperature rise due to heat conduction between the particles becomes dominant, and the entire heating tube 20 becomes The high temperature state cannot be reached in a short time.

The particle size of the carbon powder or granular material 70M here is composed of carbon particles having a particle size in the range of 1 μm to 1.5 mm. The carbon powder or granular material 70M having such a particle size can be obtained by performing so-called "fine pulverization" or "medium pulverization" as a pulverization operation.

If the filling rate of the carbon powder or granular material 70M is too small, the heat radiation is reduced due to the small filling amount, and the high temperature is uneven due to the radial or axial bias of the carbon powder or granular material 70M in the heating tube 20. In this state, the load on the heating tube 20 becomes large. On the other hand, if the filling rate is too large, it becomes difficult for microwaves to reach the vicinity of the center of the heating tube 20, and it is difficult to reach a high temperature state in a short time. The filling factor is defined here in the range of 0.05 to 0.2. However, the filling rate represents the volume ratio of the carbon powder or granular material 70M to the space volume in the heating tube 20.

The heating tube 20 in which the rare gas and carbon heating member 70 is sealed can be manufactured as follows. A bottomed cylindrical container that heats a quartz material that transmits microwaves and has an introduction pipe at one end is filled with a carbon material (carbon powder or granular material) that absorbs microwaves and generates heat from the introduction pipe into the container. do. Then, the noble gas, which is inert to the carbon material, is sealed from the introduction pipe so as to be within a predetermined range. For example, it is defined in the range of 1 kPa to 20 kPa. Then, the container is sealed by heating and softening the introduction pipe and sealing it.

The filled gas pressure of the noble gas can be determined from the relationship between the pressure resistance characteristics of the container and the atmospheric pressure in proportion to the absolute temperature of the gas. For example, if the design conditions are such that the heating tube at room temperature of 300K is first microwave-heated to a high temperature of 2000K, and the pressure inside the heating tube at that time is the same as the atmospheric pressure, the gas pressure of the heating tube at room temperature is It becomes 15.195 kPa. If the design conditions are such that the heating tube at room temperature of 300K is heated by microwave to a medium temperature of 800K and the pressure inside the heating tube at that time is the same as the atmospheric pressure, the gas pressure of the heating tube at room temperature is 37. It can be as large as .988 kPa.

As described above, the microwave heating device of the present embodiment includes the airtight quartz heating tube 20, the reflecting container 40 for storing the heating tube 20, and the microwave oscillating device 50 for oscillating microwaves in the reflecting container. , 60, and the inside of the heating tube 20 is filled with a carbon heating member 70 made of carbon powder or granular material 70M, and a rare gas is sealed therein.

With such a configuration, the heating tube 20 raises the temperature in a short time, and the object to be heated 30 can be heated and fired at high speed. In addition, it brings about a reduction in power consumption as compared with a conventional electric furnace or the like. In addition, the heating tube 20 that serves as a heat source can be easily replaced, which simplifies maintenance.

In the microwave heating device (microwave firing furnace) described above, the reflection container has a rectangular shape, but it may be cylindrical or substantially spherical. Further, in the reflection container, the object to be heated is arranged near the heating tube 20 which is a heating element, but the object to be heated may be installed while being surrounded by the heating tube 20. For example, it can be configured as a muffle furnace surrounded by a plurality of heating tubes 20. Alternatively, it can also be used as a heat source for other heat treatment equipment.

Next, the heating tube according to the second embodiment will be described with reference to FIG. In the second embodiment, the fluid (noble gas) that has flowed into the heating tube is heated by the carbon heating member, and the heated fluid is released.

FIG. 3 is a schematic cross-sectional view of the heating tube according to the second embodiment.

A lumpy carbon heating member 700 is arranged inside a bottomed cylindrical heating tube 200 provided with an inflow port 200A and an outflow port 200B at both ends using a quartz material. The fluid that has flowed into the heating tube 200 as an object to be heated is heated to raise the temperature. The carbon heating member 700 has a structure in which a plurality of disc-shaped carbon plates 720 are pivotally supported by support rods 710 made of the same carbon material, and has a three-dimensional structure functionally equivalent to a so-called porous structure (multi-pore structure). It has become. The plurality of carbon plates 720 are arranged along the axial direction of the heating tube 200 at predetermined distance intervals.

The diameter of the carbon plate 720 is substantially equal to the inner diameter of the heating tube 200, and the carbon plate 720 is in contact with the inner surface 200I of the heating tube. Therefore, between the adjacent carbon plates 720, the support rod 710 and the heating tube inner surface 200I form a gap facing each other, and the heat generating tube 200 is opened toward the outside. Cylindrical (doughnut-shaped) gaps along a plurality of radial directions are formed intermittently along the pipe axis direction, and the inflow port 200A and the outflow port 200B are spatially connected through the heating tube 200. The structure is such that the fluid flows.

The inner diameter of the heating tube 200, the thickness W of the carbon plate 720 along the axial direction of the heating tube 200, and the distance interval (gap size) D between the carbon plates 720 are the values of the carbon heating member irradiated with microwaves. By increasing the surface area, the temperature of the carbon heat generating member 700 is set to rise in a short time. If the inner diameter of the heating tube 200 is too small, the size of the carbon heating member 700 itself becomes small, and the heat generating effect becomes small. On the contrary, if the inner diameter of the heating tube 200 is too large, it is difficult for microwaves to reach the central portion of the heating tube 200. For example, the inner diameter of the heating tube 200 can be set in the range of 1 mm to 100 mm.

If the carbon plate 720 is too thin, it becomes difficult for the carbon heat generating member 700 to maintain the shape of the structure due to vibration, temperature change, or the like, and the carbon plate 720 is easily damaged. On the other hand, if the carbon plate 720 is too thick, the temperature rise due to axial heat conduction in the carbon plate 720 becomes dominant. For example, the thickness W of the carbon plate 720 can be set to 1 mm to 20 mm.

If the distance interval D (the gap opened toward the outside of the heating tube 20) between the adjacent carbon plates 720 is too large, the heat generating effect becomes small. On the other hand, if the distance interval D of the carbon plate 720 is too small, the reachable range of the microwave is limited, and it becomes difficult for the heating tube 200 as a whole to reach the high temperature state in a short time. For example, the distance interval D of the carbon plate 720 can be set to 1 mm to 20 mm.

Similar to the first embodiment, when microwaves are oscillated from the microwave oscillator, the carbon heating member 700 generates heat. Since the carbon heating member 700 adopts the above three-dimensional structure, microwaves reach the center of the heating tube 200. As a result, the temperature rise due to the absorption of microwaves in the entire carbon plate 720 becomes dominant rather than the temperature rise due to the radial heat conduction in the carbon plate 720, and the carbon heat generating member 700 becomes a high temperature state in a short time. Further, the microwave reaches the vicinity of the support rod 710 through the gap, and the heat radiation from the vicinity of the center of the heating tube 200 reaches the outside of the heating tube. As a result, the heat radiation of the heating tube 200 as a whole becomes high.

A rare gas as an object to be heated flows into the heating tube 200 from the gas inflow port 200A with respect to the carbon heating member 700 that has become hot due to microwave irradiation. The inflowing rare gas is heated by passing through the gaps between the carbon heating members 700 in the high temperature state, and the noble gas in the high temperature state flows out from the outlet 200B. Naturally generated heat convection may be used for the inflow and outflow of the rare gas to be heated, or the inflow and outflow may be forcibly carried out by a propeller, a piston, or the like.

As described above, according to the second embodiment, in the microwave heating device, the massive carbon heating member 700 in which the carbon plates 720 are arranged in the axial direction is arranged in the heating tube 200, and the rare gas flows in and out. As a result, the fluid to be heated can be heated and heated at high speed.

The heating pipe 200 may be tubular with the same inner diameter as the inlet 200A or the outlet 200B, and the carbon heating member 700 may be arranged in a partial space region of the pipe through which the fluid to be heated flows.

Next, the heating tube according to the third embodiment will be described with reference to FIG. In the third embodiment, a heat-generating tube having a hollow cylindrical shape (double tube structure) is heated by arranging an object to be heated in the hollow portion.

FIG. 4 is a schematic cross-sectional view of the heating tube according to the third embodiment.

The heating tube 2000 is heat-molded into a hollow cylindrical shape (doughnut-shaped double tube structure) by integrally sealing the inner tube 2100 and the outer tube 2200 made of quartz material at both ends, and the inner tube 2100 and the outer tube 2000 are heat-molded. The carbon heating member 7000 is arranged in the internal space formed between the pipe 2200 and the pipe 2. The space area of this internal space residue is filled with a rare gas. As the carbon heat generating member 7000, the three-dimensional structure made of the carbon powder or granular material 70M described in the first embodiment or the carbon material described in the second embodiment can be applied. The description of the introduction pipe, the space area S, and the gap is omitted.

The object to be heated 3000 is arranged in a hollow portion formed along the central axis of the heating tube 2000. The overall thickness of the carbon heating member 7000, which is within the reachable range of microwaves, is substantially equal to the difference between the inner diameter of the outer tube 2200 and the outer diameter of the inner tube 2100. By setting the total thickness to a thickness at which the microwave hardly reaches the hollow portion, the microwave propagating to the object to be heated 3000 may be shielded.

When microwaves are oscillated from the microwave oscillator by the microwave heating device similar to the first embodiment, the carbon heating member 7000 generates heat. When the heating tube 2000 becomes a high temperature state, the object to be heated 3000 arranged in the hollow portion of the heating tube 2000 is heated at high speed.

When the object to be heated 3000 is longer in the axial direction than the hollow portion of the heating tube 2000, a mechanism for moving the object to be heated 3000 or the heating tube 2000 in the axial direction may be provided. Further, the object to be heated may be a fluid, and since the carbon heating member and the object to be heated are separated by an inner pipe, there is no reaction.

The material of the heating tube may be other than quartz, and it is sufficient that it transmits microwaves and does not react with a fluid such as a rare gas. Further, a fluid other than the noble gas, which is inert to microwaves, may be applied.

Hereinafter, examples corresponding to the first embodiment will be described.

An embodiment is a microwave heating device corresponding to the first embodiment, in which a heating tube having an outer diameter of 8 mm and an inner diameter of 6 mm is filled with carbon powders having a particle size of about 2 μm and filled with argon at 5 kPa. bottom. Then, a heat generation experiment was conducted by irradiating a 2.45 GHz microwave in a spherical reflection container. A radiation thermometer (measurement wavelength 900 nm) was used for measuring the carbon surface temperature. Further, a carbon powder having a particle size of about 1 mm was filled instead, and the same experiment was performed.

As a result of the experiment, the carbon powder having a particle size of about 2 μm reached 600 ° C. or higher in 5 seconds or less and 1000 ° C. in 10 seconds or less. On the other hand, in the carbon powder granules having a particle size of about 1 mm, the temperature reached 600 ° C. or higher in 30 seconds or less. These have realized a temperature rise in a short time, which has not been obtained in the past.

10 Microwave heating device 20 Heat generating tube 30 Heated object 40 Reflective container (container)
50, 60 Microwave oscillator 70 Carbon heating member (heating member)
70M carbon powder

Claims (11)

A heat-generating material containing carbon that absorbs microwaves and generates heat,
Equipped with a container that allows microwaves to pass through
The heat generating material, such that a space region between an inner surface of the container and the heat generating material is formed, while being filled in the container, the inert fluid is filled into the container to said heat generating material ,
The exothermic material is composed of carbon powder particles in which each particle has an irregular uneven surface having a particle size in the range of 1 μm to 1.5 mm and there are gaps between the particles.
The exothermic material is filled in the container so that the filling rate representing the volume ratio of the exothermic material to the space volume of the container is in the range of 0.05 to 0.2. body. The particle size before Symbol heating material, heating element according to claim 1, characterized in that it manner, defined heating by microwave absorption than Atsushi Nobori due to the thermal conduction between particles is dominant .. A heat-generating material containing carbon that absorbs microwaves and generates heat,
Equipped with a container that allows microwaves to pass through
The exothermic material is housed in the container, and the fluid that is inert to the exothermic material is filled in the container.
A space region filled with the fluid is formed between the heating material and the upper end surface of the inner surface of the container along the vertical direction and inside the introduction pipe into which the heating material is introduced into the container. A heating element characterized by that. A heat-generating material containing carbon that absorbs microwaves and generates heat,
Equipped with a container that allows microwaves to pass through
The exothermic material is housed in the container, and the fluid that is inert to the exothermic material is filled in the container.
A heating element characterized in that the exothermic material is a structure in which a plurality of gaps that open toward the outside of the container are formed. The exothermic material is a structure in which a plurality of carbon-containing plates are arranged at predetermined intervals with respect to the rod-shaped carbon material.
At least one of the size of the gap and the thickness of the carbon-containing plate along the axial direction of the container is dominated by the temperature rise due to the absorption of microwaves entering the gap rather than the temperature rise due to heat conduction in the heating element. The heating element according to claim 4, wherein the heating element is defined so as to be a target. The heating element according to claim 1 to 5, wherein the heating element is housed and the fluid is filled so that the temperature reaches 600 ° C. or higher in 30 seconds or less by irradiating with microwaves. The heat generation according to any one of claims 1 to 6, wherein the fluid contains at least one of helium, neon, argon, and xenon, and the gas pressure enclosed in the container is 1 kPa to 10 kPa. body. The heating element according to any one of claims 1 and 7.
A microwave oscillator that irradiates the heating element with microwaves,
A microwave reflecting container for accommodating the heating element and the object to be heated,
A microwave heating device characterized by being equipped with. The container is a single tube container and
The microwave heating device according to claim 8, wherein the object to be heated is arranged outside the container. An exothermic material containing carbon that absorbs microwaves to generate heat and a container that transmits microwaves are provided, the exothermic material is housed in the container, and a fluid inert to the exothermic material is said. The exothermic body filled in the container and
A microwave oscillator that irradiates the heating element with microwaves,
A microwave reflecting container for accommodating the heating element and the object to be heated is provided.
The container is a double-tube container including an outer tube and an inner tube.
The exothermic material is arranged between the outer tube and the inner tube,
A microwave heating device characterized in that the object to be heated is arranged inside the inner tube. The material that transmits microwaves is heated to form a container,
It is an exothermic material that absorbs microwaves and generates heat. Each particle has an irregular uneven surface with a particle size in the range of 1 μm to 1.5 mm, and heat is generated from carbon powder particles with gaps between the particles. The material is filled in the container so that a space region is formed between the inner surface of the container and the exothermic material.
A fluid that is inert to the carbon is introduced into the container.
A method for producing a heating element, which comprises sealing the container.
Manufacture of a heating element, characterized in that the exothermic material is filled in the container so that the filling rate representing the volume ratio of the exothermic material to the space volume of the container is in the range of 0.05 to 0.2. Method.

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