Heating device and heating method for heating a heating element

Abstract

To heat and raise temperature of an object to be heated in a short time while precisely controlling the temperature of a heat generator, in a microwave heating device.SOLUTION: A microwave heating device 100 includes a microwave oscillator 150 for oscillating a microwave in a reflector vessel 40. An inside of a heat generating tube 20 is filled with a carbon heating material 70 made of carbon particulate matter 70M, and a noble gas is encapsulated therein. By controlling power of the microwave oscillator 150, the heat generator is heated up at a heating rate of 30 (°C / sec) or more.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a heating device using microwaves, and more particularly to temperature adjustment of a heating element that absorbs microwaves and generates heat. [Background technology]

[0002] As a furnace for firing metals, ceramics, etc., a firing furnace that uses microwaves is known. In this furnace, a heating element that absorbs microwaves and generates heat is applied to the inner wall of a 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 to be fired (see Patent Document 1). For example, a mixture of two types of silicon carbide powder with high heat resistance and a heat-resistant material such as water glass or clay material is used as the heating element. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-284039 A Summary of the Invention [Problem to be solved by the invention]

[0004] Since shortening the heating process time of the heating element results in rapid firing of the heated object in a short time, it is necessary to use microwaves to heat the heating element as a heat source as quickly as possible. However, in the above microwave heating device in which the heating element is applied to the inner wall of the container, it is difficult to achieve a faster temperature rise than ever before because the heating element contains silicon, which has a high electrical resistance. In addition, in order to achieve rapid firing in a short time, it is also necessary to rapidly heat the heating element and ensure that the temperature of the heating element reaches the desired temperature without temperature disturbance.

[0005] Therefore, there is a demand for a heating device and a heating method that can realize rapid temperature rise of a heating element while precisely controlling the temperature. [Means for solving the problem]

[0006] The heating device of the present invention includes a heating element having a heating material containing carbon that absorbs microwaves to generate heat, a container that transmits microwaves and in which the heating material is placed, and a temperature measuring unit that measures the temperature of the heating element. For example, the container can be filled with a heating material of carbon powder. In this case, at least one of the total thickness of the heating material and the packing rate of the powder is determined so that the temperature rise due to microwave absorption is dominant over the temperature rise due to thermal conduction between particles. Also, a fluid that is inactive to the heating material can be sealed in the container.

[0007] In the present invention, the heating device heats the heating element at a heating rate of 30 (°C / sec) or more, and irradiates the heating element with microwaves based on the measured temperature so as to maintain the temperature of the heating element at a target temperature. The heating rate of 30 (°C / sec) or more here refers to a heating rate measured temporarily during the temperature rise process, and represents the heating rate during the period when the temperature rises at a nearly constant heating rate.

[0008] For example, the heating device can heat the heating element to a temperature near the target temperature at a heating rate of 30° C. / sec or more, and then heat the heating element so that the temperature gradually approaches the target temperature. On the other hand, the heating device can also cool the heating element at a cooling rate of 30° C. / sec or more.

[0009] The heating device can be configured to include a magnetron that irradiates microwaves to the heating element, and a control unit that controls the power of the magnetron. The control unit controls the power of the magnetron, so that the heating element can be heated at a heating rate of 30 (°C / sec) or more. For example, the power to the magnetron is set to 100 W or more, and the target temperature is set to 800°C or more.

[0010] The control unit can gradually increase the power of the magnetron from the start of driving until the target temperature is reached. Then, the power can be reduced as the heating element reaches the target temperature, and temperature control can be performed by repeatedly increasing and decreasing the power multiple times. On the other hand, the control unit can gradually reduce the power when the heating element is cooled at a temperature reduction rate of 30 (°C / sec) or more.

[0011] Another aspect of the heating method of the present invention is a heating method in which microwaves are irradiated to a heating element that includes a heat generating material containing carbon that absorbs microwaves and generates heat, and a container that is transparent to microwaves and contains the heat generating material, the method measuring the temperature of the heating element, raising the temperature of the heating element at a heating rate of 30 (°C / sec) or more, matching the temperature of the heating element to a target temperature, and irradiating the heating element with microwaves based on the measured temperature so as to maintain the temperature of the heating element at the target temperature. Effect of the Invention

[0012] According to the present invention, it is possible to heat the heating element to a desired temperature in a short period of time and to heat the object to be heated. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram of a microwave heating device. [Diagram 2] 1 is a schematic cross-sectional view of a heating tube according to a first embodiment. [Diagram 3] FIG. 4 is a schematic configuration diagram of a microwave heating device according to a second embodiment. [Figure 4] 1 is a graph showing the power of a microwave generator associated with microwave heating over time. [Diagram 5] 1 is a graph showing the temperature of a heating element over time due to microwave heating. [Figure 6] FIG. 4 is a control block diagram relating to temperature control of a heating element. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0015] Fig. 1 is a schematic diagram of a microwave heating device according to a first embodiment of the present invention, and Fig. 2 is a schematic cross-sectional view of a heating tube.

[0016] The microwave multiple reflection type heating device (also called a microwave baking furnace, hereinafter referred to as the "microwave heating device") 10 is a device that uses microwaves to heat, bake or dry an object to be heated, and is equipped with a heat-resistant rectangular microwave reflecting container (hereinafter referred to as the reflecting container) 40. Microwave oscillators (magnetrons) 50 are attached to different sides of the reflecting container 40, and microwaves are oscillated toward the heating tube 20 inside the reflecting container.

[0017] The heating tube 20 is installed in the center of the spatial region 40M of the reflecting container 40 by a support member (not shown), and the object to be heated 30 is held beside it by a holding member (not shown). The object to be heated may be, for example, ceramics, semiconductors, or organic matter. Furthermore, the microwave heating device 10 includes a power supply circuit (not shown) capable of controlling the microwave oscillator 50, and a thermometer (radiation thermometer) (not shown) that measures the temperature of the heating tube 20, and the power supply circuit controls the microwave oscillator 50 based on the temperature of the heating tube 20 detected by the thermometer.

[0018] As shown in Fig. 2, the heating tube (hereinafter also referred to as heating element) 20 is a container in which a heating material is placed, and here, it is configured as a sealed bottomed tubular container with an introduction tube 22 formed at one end, and is heat-formed from a quartz material that transmits microwaves. However, the container configuration is not limited to this, and it may be, for example, a disk-shaped container with an inner diameter large relative to its axial length. Carbon heating material 70 is filled in the heating tube 20 so as to almost fill the entire inside of the heating tube 20.

[0019] The carbon heating material 70 is composed of flowable carbon powder 70M. The carbon powder 70M is obtained by crushing a lump of carbon material, and the carbon powder 70M, which is an aggregate of particles having a predetermined particle size, is generated by so-called coarse crushing or medium crushing.

[0020] Since each particle of the carbon powder granules 70M has an irregularly uneven surface, gaps are generated between the particles when the carbon powder granules 70M are placed inside the heating tube 20. The gaps between the particles are present throughout the carbon heating material 70. The inner diameter of the heating tube 20 and the filling rate of the carbon powder granules 70M are determined so that heat generation due to microwave absorption is dominant, as described below.

[0021] As shown in Fig. 2, a spatial region S filled with a rare gas is formed over the entire tube axial direction between the carbon heating material 70 and the upper end surface along the vertical direction of the heating tube inner surface 20U. However, since the size of the spatial region S is exaggerated in Fig. 2, the overall thickness of the carbon heating material 70 made of carbon powder particles 70M is approximately equal to the inner diameter of the heating tube 20. Also, the inside of the introduction tube 22 formed at the end of the heating tube 20 is not filled with carbon powder particles 70M, and a spatial region filled with a rare gas is formed.

[0022] The remaining space in the heating tube 20, excluding the carbon heating material 70, is filled with a rare gas. Here, one of helium, neon, argon, and xenon gases, or two or more of these gases, is sealed in. The rare gas is inactive with respect to the carbon heating material 70 and also with respect to the heating tube 20 made of quartz glass.

[0023] When microwaves are applied to carbon powder granules 70M having gaps between particles and heat generating tube 20 containing rare gas sealed therein, the microwaves reach the entire carbon powder granules 70M. In particular, the microwaves reach the carbon powder granules near the center (axis) of heat generating tube 20.

[0024] As a result, a high temperature state can be reached in a short time. In particular, by sealing the rare gas inside the heating tube 20, it is possible to prevent the carbon powder 70M from reacting with oxygen in the air to become carbon dioxide, which reduces the weight and reduces the filling amount.

[0025] When the carbon powder granules 70M generate heat, the heat generated in the carbon powder granules 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 in a short time.

[0026] The inner diameter of the heat generating tube 20 and the filling rate of the carbon powder granules 70M are determined so as to increase the surface area of ​​the carbon heat generating material 70 irradiated with microwaves, thereby realizing a temperature rise in a short time. If the inner diameter of the heat generating tube 20 is too small, the amount of carbon powder granules 70M will be small, and the heat generation effect will be small. On the other hand, if the inner diameter of the heat generating tube 20 (total thickness of the carbon heat generating material 70) is too large, the microwaves will not reach the center of the heat generating tube 20, and the temperature rise due to thermal conduction will become dominant, and a high temperature state will not be reached in a short time. For example, the inner diameter of the heat generating tube 20 can be set to 1 mm to 100 mm.

[0027] If the filling rate of the carbon powder granules 70M is too small, the thermal radiation decreases due to the small filling amount, and the carbon powder granules 70M in the heat generating tube 20 are misaligned in the radial or axial direction, resulting in an uneven high temperature state, which increases the load on the heat generating tube 20. On the other hand, if the filling rate is too large, it becomes difficult for microwaves to reach the center of the heat generating tube 20, making it difficult to reach a high temperature state in a short time. The filling rate is set in the range of 0.05 to 0.2 here. However, the filling rate represents the volume ratio of the carbon powder granules 70M to the spatial volume inside the heat generating tube 20.

[0028] The heating tube 20 filled with rare gas and carbon heating material 70 can be manufactured as follows. A microwave-transparent quartz material is heated to form a bottomed cylindrical container with an introduction tube at one end, and carbon material (carbon powder) that absorbs microwaves and generates heat is filled into the container through the introduction tube. Then, a rare gas that is inactive to the carbon material is filled through the introduction tube so that the pressure is within a predetermined range. For example, the range is set to 1 kPa to 40 kPa. The introduction tube is then heated and softened to seal the container, thereby sealing it.

[0029] The pressure of the rare gas can be determined from the pressure resistance of the container and the relationship that the air pressure is proportional to the absolute temperature of the gas. For example, if a heating tube with a room temperature of 300K is heated by microwaves to a high temperature of 2000K, and the pressure inside the heating tube is designed to be the same as atmospheric pressure, the gas pressure in the heating tube at room temperature will be 15.195kPa. Also, if a heating tube with a room temperature of 300K is heated by microwaves to a medium temperature of 800K, and the pressure inside the heating tube is designed to be the same as atmospheric pressure, the gas pressure in the heating tube at room temperature can be increased to 37.988kPa.

[0030] As described above, the microwave heating device of this embodiment comprises an airtight quartz heating tube 20, a reflecting container 40 that houses the heating tube 20, and a microwave oscillator 50 that generates microwaves inside the reflecting container 40. The inside of the heating tube 20 is filled with carbon heating material 70 made of carbon powder and granular material 70M, and a rare gas is sealed inside.

[0031] With this configuration, the heating tube 20 can heat up in a short time, and the object 30 can be heated and baked at high speed. This also reduces power consumption compared to conventional electric furnaces. In addition, the heating tube 20, which is the heat source, can be easily replaced, simplifying maintenance.

[0032] In the microwave heating device (microwave baking furnace) described above, a rectangular reflecting vessel is used, but it may be cylindrical or approximately spherical. In addition, in the reflecting vessel, the object to be heated is placed next to the heating tube 20, which is a heating element, but the object to be heated may be placed surrounded by the heating tube 20. For example, it can be configured as a muffle furnace surrounded by multiple heating tubes 20. Alternatively, it can be used as a heat source for other heat treatment devices.

[0033] The carbon heating material may be configured with a lump carbon heating element instead, for example, a lump carbon heating element in which carbon plates are arranged in the axial direction. It is also possible to configure the heating tube so that gas (rare gas) is sent into the heating tube, heated by the carbon heating element, and the heated gas is released. Furthermore, it is also possible to heat an object to be heated by placing it in the hollow part of a hollow cylindrical (double tube structure) heating tube.

[0034] The material of the heating tube may be other than quartz as long as it transmits microwaves and does not react with gases such as rare gases. Furthermore, a fluid that is inert to microwaves and is a gas other than rare gas may be used. The gas contained in the container may not be filled with a gas inert to the carbon heating material, but may be configured to contain some active gas.

[0035] Next, a microwave heating device according to a second embodiment will be described with reference to Figures 3 to 5. In the second embodiment, the temperature rise and fall of the heating element is controlled.

[0036] FIG. 3 is a schematic block diagram of a microwave heating device according to the second embodiment.

[0037] As in the first embodiment, in the microwave heating device 100, a reflecting container 40 accommodates a material to be heated 30 and a heating tube (heating element) 20 in which carbon powder granules 70M are enclosed, and a microwave oscillator 150 irradiates microwaves to the heating element 20. The microwave oscillator 150 is driven by a power supply unit 86 and connected to an AC transformer 88.

[0038] The thermometer (temperature measuring unit) 90, a radiation thermometer used here, measures the surface temperature of the heating element 20 at a predetermined time interval (for example, several milliseconds). The thermometer controller 92 converts the measured temperature into a voltage and sends the voltage data to the controller 84. The controller (control unit) 84 controls the microwave output of the microwave oscillator 150 by sending a signal to the power supply unit 86 that controls the drive voltage of the microwave oscillator 150 based on the temperature-voltage conversion data. The heating element 20 is controlled to increase and decrease its temperature by this drive voltage control.

[0039] The operation unit 82 is operated when the operator sets the temperature of the heating element, and an operation signal is sent to the controller 84. Here, it is possible to set a temperature of 800° C. or higher.

[0040] Fig. 4 is a graph showing the drive power of the microwave oscillator 150 with microwave heating over time. Fig. 5 is a graph showing the temperature of the heating element with microwave heating over time. In Fig. 5, the temperature rises first due to the output of several millivolts before the microwave oscillator 150 turns on.

[0041] When a target temperature T0 (here, 1100°C) is set by an operator, a controller 84 according to the target temperature T0 controls the power supply unit 86 to gradually increase the power to the microwave oscillator 150. As shown in Fig. 4, during a predetermined period V1 from the start of driving, the rate of increase in power is approximately constant. During this predetermined period V1, the rate of temperature rise (°C / sec) of the heating element 20 is approximately constant, and the temperature of the heating element 20 rises at a rate of temperature rise of 30 (°C / sec) or more (see L1 in Fig. 5).

[0042] When the temperature of the heating element 20 reaches a temperature T1 (near-target temperature) close to the target temperature T0, the controller 84 reduces the power and performs voltage control by repeatedly increasing and decreasing the power (see period V2 in FIG. 4). As a result, the power at the near-target temperature T1 becomes the maximum power, and thereafter, power control is performed at a power lower than this.

[0043] While the power is being increased or decreased, the temperature of the heating element 20 rises at a slower rate than during period V1, and asymptotically approaches the target temperature T0 (see L2 in FIG. 5). When the temperature of the heating element 20 reaches the target temperature T0, the power is controlled so that the temperature of the heating element 20 is maintained at the target temperature T0.

[0044] When lowering the temperature of the heating element 20, the power is gradually reduced (see period V3 in FIG. 4). As a result, the temperature of the heating element 20 is lowered at a substantially constant temperature drop rate (°C / sec). Here, the power is reduced so that the temperature drops at a rate of 30°C / sec or higher. As the rate at which the power is reduced becomes substantially constant, the temperature drop rate also becomes substantially constant (see L3 in FIG. 5).

[0045] FIG. 6 is a control block diagram relating to the temperature control of the heating element 20. As shown in FIG.

[0046] A target temperature (hereinafter, the target temperature is referred to as “TT”), a maintenance time TK of the target temperature TT, a temperature rise rate (temperature rise speed) TI, and a temperature fall rate (temperature fall speed) TD are set by an operator in the operation unit 82. The temperature T measured by the radiation thermometer is converted into a voltage TV in the thermometer controller 92 and sent to the controller 84.

[0047] The controller 84 includes a temperature regulator 84A that executes PID control (not shown) for controlling the relationship between temperature and drive voltage. The temperature regulator 84A determines a power supply control voltage MV, which is a drive voltage control signal, based on the difference between a drive voltage (hereinafter referred to as a target drive voltage) of a temperature (hereinafter referred to as a target temperature) input to the controller 84 and a drive voltage (hereinafter referred to as a measured drive voltage) corresponding to the temperature of the heating element 20 measured at a predetermined time interval. The controller 84 sends the determined power supply control voltage MV to the power supply unit 86. The power supply unit 86 changes the drive voltage QV in microseconds under the control of the controller 84.

[0048] Specifically, PID control uses P (proportional constant) to change the output (drive voltage) according to the difference between the current temperature and the target temperature (the difference between the target drive voltage and the measured drive voltage). Also, I (integral constant) is used together with P (proportional constant) to calculate the heat storage capacity and suppress overshoot and hunting. For sudden temperature changes due to disturbances, the drive voltage is corrected by D (differential constant). Power supply unit 86 outputs power (W) according to drive voltage QV to microwave oscillator 150. Note that in order to perform optimal temperature control, temperature regulator 84A detects the optimal PID constant by prior auto-tuning.

[0049] During the time period when the heating element 20 is heated, the temperature regulator 84A performs PID control based on the target temperature TT and the temperature rise rate TI. The temperature regulator 84A determines a power supply control voltage MV for the power supply unit 86, and the controller 84 changes the drive voltage QV (power) for the microwave oscillator 150. P (proportionality constant) is determined according to the set temperature rise rate TI.

[0050] In a time period during which the increased temperature of the heating element 20 is to be maintained, the temperature regulator 84A performs PID control based on the target temperature TT and the temperature maintenance time TK. In a time period during which the temperature of the heating element 20 is to be decreased, the temperature regulator 84A performs PID control based on the temperature decrease rate TD.

[0051] As described above, according to this embodiment, precise temperature control can be achieved in the temperature increase and decrease processes of the heating element 20 by controlling the power of the microwave oscillator 150. As a result, the object to be heated can also be precisely heated.

[0052] The rate of temperature rise of the heating element depends on the mass of the carbon powder granules 70M, and when the mass is large, precise temperature control is difficult using proportional control alone. On the other hand, the carbon powder granules 70M dissipate heat quickly. In this embodiment, PID control is performed by the temperature regulator 84A according to the characteristics of the carbon powder granules 70M, which is the object to be heated. This makes it possible to suppress overshooting and hunting and to increase the temperature of the heating element 20 asymptotically near the target temperature, so that the target temperature can be efficiently reached without disturbances such as unintended temperature fluctuations, even in the case of a sudden temperature rise.

[0053] Furthermore, by gradually increasing the power of the microwave oscillator 150 after the start of operation, the power reaches maximum after a certain period of time when microwave absorption has stabilized, reducing the generation of reflected waves and preventing damage to the microwave oscillator 150. Conversely, by gradually decreasing the power of the microwave oscillator 150, the temperature of the heating element 20 can be reduced at a rate of 30 (°C / sec) or more. EXAMPLES

[0054] An example corresponding to the second embodiment will be described below.

[0055] The example is a microwave heating device corresponding to the second embodiment, in which a heating tube with an outer diameter of 6 mm, an inner diameter of 4 mm, and a tube length of 60 mm was filled with carbon powder particles at a filling rate of 0.08, and rare gas was sealed in at 1.4 kPa. Then, a heating experiment was performed by irradiating a 2.45 GHz microwave in a spherical reflecting container and setting the target temperature to 1100°C. In the heating experiment, temperature control was performed by a controller as in the embodiment, and a radiation thermometer with a measurement wavelength of 900 nm was used to measure the surface temperature of the heating tube.

[0056] As a result of the experiment, it was possible to confirm the temperature change that drew a curve similar to that of Figure 5, and it was found that the heating tube 20 was heating at a heating rate of 30 (°C / s) or more. It was also confirmed that the temperature rose asymptotically near the target temperature, and that the target temperature was maintained as shown in Figure 5 even after the target temperature was reached. [Explanation of symbols]

[0057] 20 Heating tube (heating element) 30 Heated object 40 Reflective container 70 Carbon heating material (heat generating material) 70M Carbon Powder 84 Controller 90 Thermometer 100 Microwave Heating Device 150 Microwave Oscillator (Magnetron)

Claims

1. A heating device that irradiates microwaves to ceramics, semiconductors, or organic materials other than food as objects to be heated, A reflecting container that reflects microwaves; A heating element including a powder containing carbon that absorbs microwaves and generates heat, and a container that transmits microwaves and is filled with the heating element, the heating element being installed in the reflecting container; A temperature measuring unit for measuring a temperature of the heating element, The object to be heated is placed in the reflecting container at a distance from the container, The heat generated by the heat generating material is transferred to the object to be heated through the spatial region of the reflector container, A heating device characterized in that the temperature of the heating element is increased to a temperature near a target temperature at a heating rate of 30 (°C / sec) or more, and when the temperature near the target temperature is reached, the heating element is increased to asymptotically approach the target temperature, and when the target temperature is reached, the temperature of the heating element is maintained at the target temperature by continuously irradiating the heating element with microwaves from the start of irradiation based on the measured temperature.

2. 2. The heating device according to claim 1, wherein the heating element is cooled at a temperature decreasing rate of 30[deg.] C. / sec or more.

3. A magnetron that irradiates microwaves to the heating element; A control unit for controlling the power of the magnetron, 3. The heating device according to claim 1, wherein the control unit controls the power of the magnetron to raise the temperature of the heating element at a temperature rise rate of 30 (.degree. C. / sec) or more.

4. 4. The heating device according to claim 3, wherein the control unit gradually increases the power of the magnetron from the start of driving until the temperature reaches near the target temperature.

5. 5. The heating device according to claim 4, wherein the control unit reduces the power when the heating element reaches a temperature close to the target temperature, and repeats increasing and decreasing the power a plurality of times.

6. 3. The heating device according to claim 2, wherein the control unit gradually reduces the power when lowering the temperature of the heating element at a temperature lowering rate of 30 (.degree. C. / sec) or more.

7. The power to the magnetron is 100 W or more; 7. The heating device according to claim 3, wherein the target temperature is 800[deg.] C. or higher.

8. The heat generating material is made of flowable carbon powder, 8. The heating device according to claim 1, wherein the packing rate of the powder or granular material is set in the range of 0.05 to 0.

2.

9. 9. The heating device according to claim 1, wherein a fluid inert to the heat generating material is sealed in the container.

10. A heating method for irradiating microwaves to a heating element that is placed in a reflecting container that reflects microwaves, the heating element being made of a powder containing carbon and absorbing microwaves to generate heat, the heating element being made of a powder containing carbon and absorbing microwaves to generate heat, the heating element being placed in a reflecting container that reflects microwaves, the method comprising the steps of: The object to be heated is placed away from the container in the reflecting container, and heat generated by the heat generating material is transferred to the object to be heated through a spatial region of the reflecting container; Measure the temperature of the heating element; A heating method characterized in that the temperature of the heating element is increased to a temperature near a target temperature at a heating rate of 30 (°C / sec) or more, and when the temperature near the target temperature is reached, the heating element is increased to asymptotically approach the target temperature, and when the target temperature is reached, the temperature of the heating element is maintained at the target temperature by continuously irradiating the heating element with microwaves from the start of irradiation based on the measured temperature.

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