JP6243389B2 - Heating furnace and heating method - Google Patents

Description

  The present invention relates to a heating furnace and a heating method.

  A firing method using a microwave gas complex furnace using an inflammable gas furnace as a basic structure and combined with microwave heating has been put into practical use for ceramics (see, for example, Patent Document 1). By this method, the firing process can be shortened and energy can be saved as compared with the case where the firing is performed in the flame type gas furnace.

JP 2003-246679 A

  However, the conventional microwave gas composite furnace is not suitable for firing ceramic electronic parts.

  The quality of products is judged by the appearance of ceramics, but ceramic electronic parts must satisfy not only the appearance but also strict standards such as electrical performance. When firing in a conventional microwave gas composite furnace, the electrical characteristics of the ceramic electronic component vary greatly depending on the arrangement position in the furnace body. This is considered to be because the temperature distribution in the furnace body is non-uniform, and the fine structure after firing is non-uniform.

  An object of this invention is to provide the heating furnace and the heating method which can aim at the improvement of the temperature uniformity in a furnace main body in view of the above point.

  The heating furnace of the present invention includes a furnace main body in which an object to be heated is disposed at a central portion, a barrier installed between an inner wall surface of the furnace main body and a central portion of the furnace main body, and an inner wall surface of the furnace main body. And a gas burner that forms a flame upward from the hearth of the furnace body, a discharge port for discharging the gas in the furnace body from the furnace floor side to the outside, and the furnace body A microwave oscillator for irradiating microwaves, and a low-temperature gas supply device for supplying a gas having a temperature lower than the temperature in the furnace body from above into a space surrounded by the barrier.

  The heating furnace of the present invention is a microwave gas complex furnace using a microwave oscillator combined with a flame retardant gas furnace, and a gas surrounded by a barrier and having a temperature lower than the temperature in the furnace body in a space where an object to be heated is disposed. It is the structure which added the low-temperature gas supply apparatus which supplies this from the upper direction.

  In the conventional microwave gas complex furnace, the temperature is lowered from the upper side to the lower side in the furnace body due to the nature of the flame retardant gas furnace. However, since the low-temperature gas supply device supplies a gas having a temperature lower than the temperature of the space from above to the space surrounded by the barrier, it is possible to improve the temperature uniformity in the vertical direction of the space. Thereby, regardless of the arrangement of the object to be heated, it can be fired at a uniform temperature, and variations in the characteristics of the fired product can be eliminated.

  In addition, for example, when a plurality of mortars are stacked in a heating furnace, and an object to be heated is arranged in each mortar, the side walls on the furnace inner wall side of the mortars serve as a barrier. Thus, the barrier may not be formed of a single wall but may be formed of a plurality of walls.

  In the heating furnace of the present invention, at least one of the gas burner and the microwave oscillator is plane-symmetric with respect to a vertical plane including a vertical axis at the center of the furnace body, or with respect to a vertical axis at the center of the furnace body. It is preferable to arrange them rotationally symmetrical.

  For example, at least one of the gas burner and the microwave oscillator may be arranged symmetrically with respect to a vertical plane in the horizontal direction including the vertical axis at the center of the furnace body. Alternatively, a plurality of gas burners and / or microwave oscillators may be equally arranged in rotational symmetry with respect to the vertical axis at the center of the furnace body.

  In this case, it is possible to achieve temperature uniformity not only in the vertical direction but also in the horizontal direction in the space surrounded by the barrier. This makes it possible to further eliminate variations in the characteristics of the fired product.

  In the conventional microwave gas complex furnace, the gas pressure decreases from the upper side to the lower side in the furnace main body due to the nature of the flame retardant gas furnace.

  Therefore, in the heating furnace of the present invention, it is preferable that the low temperature gas supply device supplies a gas for controlling the oxygen concentration as the low temperature gas. Note that the gas for controlling the oxygen concentration is a gas capable of changing the concentration of oxygen gas and is oxygen gas or a gas containing oxygen gas, for example, hydrogen gas and reaction with this. Thus, it may be a gas such as a mixed gas with carbon dioxide gas that generates oxygen gas.

  In this case, since the gas containing the gas for controlling the oxygen concentration is supplied from above into the space surrounded by the barrier by the low-temperature gas supply device, the gas can be smoothly moved from above the inside of the furnace having a high gas pressure toward the bottom of the furnace. A gas can be introduced into the gas, and the oxygen concentration in the vertical direction of the space can be made uniform by thermal diffusion. Thereby, regardless of the arrangement of the object to be heated, it can be fired at a uniform oxygen concentration, and it becomes possible to further eliminate variations in the characteristics of the fired product.

The heating method of the present invention includes an arrangement step of arranging an object to be heated in a space surrounded by the barrier in the inner wall surface of the furnace body, and the space between the inner wall surface of the furnace body and the barrier. While forming a flame upward from the hearth of the furnace body and irradiating the inside of the furnace body with microwaves, a gas lower than the temperature in the space is supplied from above into the space surrounded by the barrier And a firing step of firing the object to be heated.

  The heating method of the present invention is a microwave gas composite heating method using a microwave gas composite furnace using a microwave oscillator in combination with a flame retardant gas furnace, surrounded by a barrier, and in a space where an object to be heated is arranged, This is a firing method in which a gas having a temperature lower than that in the furnace body is supplied from above.

  In the conventional microwave gas combined heating method, due to the nature of the flame-extinguishing gas furnace, the temperature falls from the top to the bottom in the furnace body. However, since a gas having a temperature lower than the temperature of the space surrounded by the barrier is supplied from above the space, it is possible to improve temperature uniformity in the vertical direction of the space. Thereby, regardless of the arrangement of the object to be heated, it can be fired at a uniform temperature, and variations in the characteristics of the fired product can be eliminated.

  In the conventional microwave gas combined heating method, the gas pressure decreases from the upper side to the lower side in the furnace body due to the nature of the flame-type gas furnace.

  Therefore, in the heating method of the present invention, the low temperature gas is preferably a gas for controlling the oxygen concentration.

  In this case, since the gas for controlling the oxygen concentration is supplied from above into the space surrounded by the barrier, it is possible to smoothly introduce the gas from the inside of the furnace having a high gas pressure toward the bottom of the furnace, Diffusion makes it possible to achieve a uniform oxygen concentration in the vertical direction of the space. Thereby, regardless of the arrangement of the object to be heated, it can be fired at a uniform oxygen concentration, and it becomes possible to further eliminate variations in the characteristics of the fired product.

  In the heating method of the present invention, between the inner wall surface of the furnace main body and the barrier, a flame is formed from the hearth of the furnace main body toward the upper part, and at the same time the microwave is irradiated into the furnace main body, A gas having a temperature lower than the temperature in the furnace body is supplied from above into the space surrounded by the barrier, and includes a degreasing process for degreasing the heated object, and after the degreasing process, at least one of the flame and the microwave It is preferable to perform the firing step by increasing one side and raising the temperature in the main furnace.

  In this case, the degreasing process and the baking process of the object to be heated can be performed continuously and consistently, and the processing time can be shortened. Furthermore, as shown in Example 8 to be described later, the exhaust gas discharged in the degreasing step can be exhausted to the atmosphere without being deodorized, and there is no need to install a deodorizing device.

The typical longitudinal section of the heating furnace concerning the embodiment of the present invention. The II-II line | wire schematic sectional drawing of FIG. FIG. 3A is a schematic longitudinal sectional view showing a case where a plurality of shelves are installed in the space S. FIG. FIG. 3B is a schematic longitudinal sectional view showing a case where a plurality of stages of mortars are housed in the furnace. The graph which shows the relationship between the temperature which the thermocouple measured, and the varistor voltage _V1mA per unit thickness.

  A heating furnace 100 according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIGS. 1 and 2, the heating furnace 100 is a microwave composite gas furnace in which a microwave oscillator 10 is added to a flame-extinguishing gas furnace, and an object to be heated A in the furnace body 20 (FIGS. 3A and 3B). 3B) is a firing furnace for mainly firing.

The object to be heated A is, for example, a molded body mainly composed of ceramics, and is obtained by bonding ceramic powder with an organic binder or the like. The object A to be heated is fired (sintered) in the heating furnace 100 or the like, and becomes, for example, a ceramic electronic component or a powder metallurgy component. The ceramic is not limited, but is, for example, ZnO, BaTiO ₃ , ferrite, or transition metal oxide. Furthermore, the object A to be heated may be other than a molded body mainly composed of ceramics, such as a powder metallurgy material.

  The heating furnace 100 includes a furnace body 20 in which the article A to be heated is disposed in the center, a barrier (muffle) 30 installed between the inner wall surface 20a of the furnace body 20 and the center of the furnace body 20, a furnace Between the inner wall surface 20a of the main body 20 and the barrier 30, a gas burner 40 that forms a flame directed upward from the hearth 21 of the furnace main body 20 and a gas that discharges the gas in the main body 20 from the hearth 21 side to the outside. A low-temperature gas supply device 60 that supplies a gas having a temperature lower than the temperature in the furnace body 20 to the space S surrounded by the barrier 30 from above, the outlet 50, the microwave oscillator 10 that irradiates the furnace body 20 with microwaves With.

  The furnace body 20 is composed of a furnace outer shell 22 made of a material that reflects microwaves, such as stainless steel, and an insulating material that is disposed on the inner surface of the furnace outer shell 22 and that allows microwaves to pass through such as alumina board and fire-resistant heat-insulating brick. And a furnace wall 23.

  The furnace body 20 is provided with a door 24 for taking the article A to be heated in and out of the furnace body 20. Although not shown, the door 24 is provided with an observation window for observing the inside of the furnace body 20.

  The barrier 30 is configured by stacking wall materials mainly composed of a material such as alumina having excellent thermal conductivity. The barrier 30 has a gas inflow hole 30a in the upper part, and an opening 30b is formed on the rear side of the lower part.

  In the space S surrounded by the barrier 30, a configuration for arranging the object to be heated A is provided. The configuration may be any known one. For example, as shown in FIG. 3A, a plurality of shelves 71 may be installed. In this case, the support 72 is provided from the hearth 21, the shelf 71 is placed on the support 72, and the article A to be heated is placed on the shelf 71 via the laying plate 74. The shelf board 71 may be provided with a column 73 between them to stack a plurality of stages.

  Further, as shown in FIG. 3B, a plurality of box-shaped saggers 82 made of a refractory material such as mullite, cordierite, and alumina whose upper surfaces are opened are stacked on a support column 81. The object A may be placed in the sheath 82 via the laying plate 83 and a box-shaped mortar 82 having an open upper surface may be placed on the uppermost stage. The uppermost bowl 82 may be covered with a shelf plate 84 provided with gas inflow holes. The mortar 82 is, for example, a rectangular parallelepiped or short cylindrical box, but any commercially available product may be used.

  Further, a thermocouple thermometer 25 is provided in the space S, and the temperature in the space S is always detected.

  The gas burner 40 is a forced combustion gas burner such as a Bunsen forced combustion gas burner. It is preferable that the gas burner 40 is disposed in plane symmetry with respect to a vertical plane including the vertical axis at the center of the furnace body 20 or rotationally symmetrical with respect to the vertical axis at the center of the furnace body 20.

  Here, an even number, in this case, eight, are arranged on the hearth 21 in a symmetrical manner with respect to a vertical plane located at the center in the left-right direction of the furnace body 20. Further, a plurality of, for example, five, six, etc., may be equally arranged in rotational symmetry with respect to the vertical axis at the center of the furnace body 20. Each gas burner 40 is preferably the same type of product having the same output.

  The gas burner 40 is configured to form a flame upward from the hearth 21 between the inner wall surface 20 a of the furnace body 20 and the barrier 30. Thereby, the combustion gas released by the gas burner 40 rises in the space between the inner wall surface 20a of the furnace body 20 and the barrier 30, then descends in the space S, and is then formed behind the hearth 21. It is discharged from the outlet 50.

  The gas burners 40 are arranged symmetrically on the hearth 21 so that the combustion gas is distributed in the space S without being unevenly distributed. When the combustion gas descends in the space S, the article A to be heated disposed in the space S is heated.

  A fuel gas which is a mixed gas of propane gas or city gas and air is supplied to the gas burner 40 through one gas pipe 41. An original valve 42, two electromagnetic valves 43, and a control valve 44 are connected to the gas pipe 41 in series. A control means (not shown) is connected to these valves 43 and 44, and based on the temperature in the space S detected by the thermocouple thermometer 25, the two fuel valves 43 cut off the fuel gas flow path. Alternatively, the fuel gas amount supplied to the gas burner 40 can be automatically controlled by opening and controlling the gas pressure by the control valve 44.

  Combustion gas passes from the discharge port 50 through the horizontal flue 51 that communicates with the discharge port 50 and extends horizontally to the back side, and the vertical flue 52 that extends vertically upward from the back side end of the horizontal flue 51 to the outside air. The exhaust pipe 53 communicated with the exhaust pipe 53 is discharged outside the heating furnace 100.

  Outside the furnace wall 23, a microwave oscillator 10 and a waveguide 11 extending from the microwave oscillator 10 are provided. The waveguide 11 irradiates microwaves, and its end is fitted into an opening formed in the furnace shell 22.

  The microwave oscillator 10 is preferably arranged in plane symmetry with respect to a vertical plane including the vertical axis at the center of the furnace body 20 or rotationally symmetrical with respect to the vertical axis at the center of the furnace body 20.

  Here, the even number, here four, of the microwave oscillators 10 are arranged symmetrically with respect to a vertical plane located at the center in the left-right direction of the furnace body 20. Further, a plurality of, for example, five, six, etc., may be equally arranged in rotational symmetry with respect to the vertical axis at the center of the furnace body 20. Each microwave oscillator 10 is preferably the same type of product having the same output.

  The microwave passes through the furnace wall 23 made of a heat insulating material having a low microwave absorption rate in the furnace body 20 and is irradiated to the object A to be heated. Then, the microwave is diffused by the diffusion fan 12 and irradiated into the furnace body 20 in a uniform manner. The microwave oscillator 10 is connected to a control means (not shown) so that the irradiation intensity of the microwave can be adjusted.

  The low-temperature gas supply device 60 communicates the space S with the outside of the furnace body 20 through a gas path hole 20b formed in the upper part of the furnace body 20, and includes a gas path 61 made of stainless steel pipe and the like, A gas supply unit 62 that supplies gas into the gas 61, a heating unit 63 that heats the gas in the gas supply unit 62 or the gas path 61, and an adjustment that can adjust the amount of gas supplied from the gas path 61 into the space S And a valve 64.

  Here, the low temperature gas is preferably a gas for controlling the oxygen concentration. Note that the gas for controlling the oxygen concentration is a gas capable of changing the concentration of oxygen gas and is oxygen gas or a gas containing oxygen gas, for example, hydrogen gas and reaction with this. Thus, it may be a gas such as a mixed gas with carbon dioxide gas that generates oxygen gas.

  And the heating part 63 and the adjustment valve 64 are connected to the control means which is not shown in figure, and can adjust the quantity and temperature of the gas supplied to the space S from the gas path 61. FIG.

  Hereinafter, a heating method using the heating furnace 100 according to the embodiment of the present invention will be described.

  First, the arrangement | positioning process which arranges the to-be-heated material A in the space S is performed. For example, as described above, the heated object A is arranged as shown in FIG. 3A or 3B. Here, the article to be heated A is obtained by performing a degreasing process on a molded body in which ceramic powder is bonded with an organic binder or the like.

  Next, while forming a flame with the gas burner 40 and irradiating the microwave with the microwave oscillator 10, a gas having a temperature lower than the temperature in the space S is supplied from above into the space S by the low temperature gas supply device 60. A firing step of firing the article to be heated A is performed. Here, the low temperature gas is a gas for controlling the oxygen concentration.

  In the conventional microwave gas combined heating method, due to the nature of the flame-extinguishing gas furnace, the temperature of the space S decreases from the top to the bottom. In the present embodiment, the low-temperature gas supply device 60 supplies the gas having a temperature lower than the temperature of the space S from above into the space S, so that the temperature uniformity in the vertical direction of the space S can be achieved by thermal diffusion. It becomes. Thereby, regardless of the arrangement of the object to be heated A, it can be fired at a temperature with good uniformity, and it becomes possible to eliminate variations in characteristics of the fired object obtained by firing the object to be heated A.

  Furthermore, in the conventional microwave gas combined heating method, the gas pressure decreases from the upper side to the lower side in the space S due to the nature of the flame-extinguishing gas furnace. In the present embodiment, the low-temperature gas supply device 60 supplies, as a low-temperature gas, a gas for controlling the oxygen concentration from above to the space S, so that the gas pressure is increased from the upper inside of the furnace toward the lower furnace bottom. Gas can be introduced smoothly, and the oxygen concentration in the vertical direction of the space S can be made uniform. Thereby, regardless of the arrangement of the object A to be heated, it can be fired at a uniform oxygen concentration, and it becomes possible to further eliminate variations in the characteristics of the fired product.

  Further, a flame is formed by the gas burner 40 and a microwave is irradiated by the microwave oscillator 10, and at the same time, a gas having a temperature lower than the temperature in the space S is supplied from above into the space S by the low temperature gas supply device 60. You may perform the degreasing process which degreases the to-be-heated material A before a process. In this case, after the degreasing step, the firing step is performed by increasing the output of at least one of the gas burner 40 and the microwave oscillator 10 to increase the temperature in the space S.

  Thereby, it becomes possible to perform the degreasing process and baking process of to-be-heated material A continuously and consistently, and can shorten processing time. Furthermore, as shown in Example 8 to be described later, the exhaust gas discharged in the degreasing step can be exhausted to the atmosphere without being deodorized, and there is no need to install a deodorizing device.

  In the heating furnace 100, the degreasing treatment can be performed by heating by microwave, gas combustion, or a combination of both. However, at least the degreasing treatment is performed by heating accompanied by gas combustion. The malodorous component concentration decreases. Thereby, it becomes possible to discharge | emission exhaust gas directly in air | atmosphere, without installing a deodorizing apparatus. This is thought to be due to the decomposition and combustion of malodorous components in the exhaust gas being advanced by the flame of gas combustion, in addition to the effect of promoting the decomposition of the binder by microwaves, compared to the case where hot air is blown into the furnace body 20. In addition, in the furnace body 20 after the degreasing treatment, residual components generated due to degreasing such as tar components are not detected, and no cleaning work is required.

(Evaluation method of uniformity)
The non-uniformity of the shape, mechanical strength, electrical characteristics and other characteristics of the fired product is based on the non-uniformity of the microstructure of the fired product, and the microstructure of the fired product depends on the temperature and gas atmosphere during firing. Dependent. In order to achieve uniform characteristics of the fired product, it is essential to make the temperature and gas atmosphere in the furnace body 20 uniform. However, it is very difficult to comprehensively measure temperatures and gas atmospheres at various locations in the furnace body 20, and it is necessary to find out an evaluation method thereof.

  For example, the temperature in the furnace main body 20 is generally obtained by determining the temperature after firing shrinkage by placing a molded piece for temperature measurement such as a female ring or a reference thermometer in the furnace main body 20. However, in the case of a microwave gas complex furnace, the microwave absorption efficiency differs between the individual piece for temperature measurement and the article to be heated A for producing the ceramic electronic component. Deviation occurs between the temperature measured by the piece and the actual temperature of the object A to be heated. Moreover, it is extremely difficult to grasp the actual temperature of each object A to be heated contained in the mortar 82 (see FIG. 3B).

  Furthermore, since the gas atmosphere in the furnace body 20 has a flame retardant gas furnace as a basic structure, the gas flow is made uniform and stabilized, but the oxygen concentration is measured over the details in the furnace body 20. Is also very difficult.

  Therefore, the inventor of the present application evaluates variations such as temperature and oxygen concentration distribution in the furnace body 20 based on the measurement results of the electrical characteristics of the ceramic electronic component obtained by firing the object A to be heated. Found that is possible.

(Evaluation method for furnace uniformity)
First, we focused on ZnO varistors, which are mainly composed of a material with high microwave absorption efficiency, and whose electrical characteristics vary greatly depending on the firing temperature and oxygen concentration. Among the electrical characteristics of ZnO varistors, the varistor voltage V _{1 mA} (voltage when a current of ₁ mA is passed) is proportional to the number of grain boundaries, the number of grain boundaries is inversely proportional to the grain size, and grain growth is an increase in firing temperature. Therefore, if the distribution of V _{1 mA} per unit thickness of the ZnO varistor elements arranged in the furnace body 20 is examined, it can be said that substantial variation in the temperature in the furnace body 20 can be evaluated.

Further, the non-ohmic property of the ZnO varistor element is simply expressed as V _{10 μA} / V _{1 mA} (the ratio of the voltages when a current of 10 μA and 1 mA is passed, and the closer to 1, the better the non-ohmic property). This V _{10 μA} / V _{1 mA} shows a high value if the oxygen concentration during firing is equivalent to that in the atmosphere, and decreases as the oxygen concentration decreases. Therefore, the distribution of the oxygen concentration in the furnace body 20 can be evaluated by _obtaining V _{10 μA} / V _{1 mA} .

  That is, the material A to be heated, which is the material of the ZnO varistor element, is placed and fired in each part in the furnace body 20, and the electrical characteristics are evaluated, so that the substantial distribution of temperature and oxygen concentration in the furnace body 20 is achieved. Can be evaluated.

(Reference Example 1)
In ZnO as a main component, Bi ₂ O ₃ : 0.5 mol%, Sb ₂ O ₃ : 1.0 mol%, Co ₂ O ₃ : 0.5 mol%, MnO ₂ : 0.5 mol%, Al (NO ₃ )・ 9H ₂ O: Add 0.01 mol%, add water and dispersant and mix, then add binder to make slurry, spray this with spray dryer to make granulated powder, mold It shape | molded and the disk-shaped molded object was obtained.

  In this evaluation method, it is premised that each object to be heated A is uniform. Therefore, the raw materials were sufficiently mixed, and the shape of the molded body was a small disk having a diameter of about 10 mm and a thickness of about 3 mm, thereby ensuring uniformity in composition and molding density.

  The molded body described above was degreased using a hot air circulating drier at 400 ° C. for 2 hours to obtain an object A to be heated.

  The furnace main body 20 of the heating furnace 100 is composed of a furnace outer shell 22 made of stainless steel and a furnace wall 23 made of alumina board, and the inner dimensions thereof are a height of 600 mm, a width of 550 mm, and a depth of 600 mm. . In the heating furnace 100, eight Bunsen forced combustion gas burners as gas burners 40 are arranged symmetrically on the left and right furnace bottoms, and a total of four magnetrons with a maximum output of 1.5 kW as microwave oscillators 10 are arranged on the left and right furnace walls. The units were placed symmetrically. Here, no barrier 30 is provided in the heating furnace 100.

  Referring to FIG. 3A, a shelf 71 made of SiC is installed at a distance of 150 mm from the hearth 21 using a support 72 in the furnace body 20, and the total is added at a distance of 70 mm using a support 73. A three-stage SiC shelf 71 was provided, and the SiC shelf 71 was also placed on the third shelf 71 to form a ceiling cover. Each of the SiC shelf plates 71 was a square plate having a side of 300 mm and a thickness of 10 mm. And on each shelf board 71, three to-be-heated articles A are arranged side by side in the front-rear direction on each stage via a magnesium-spinel-based laying board 74, and a thermocouple and a beside each molded body. An oxygen analyzer was placed.

The fired bodies after firing were taken out, and the varistor voltages V _{1 mA} and V _{10 μA} of each fired body were measured. During firing, the temperature was measured with each thermocouple, and the oxygen concentration was measured with each oxygen concentration meter. These measurement results are shown in Table 1.

From the measurement results in Table 1, within each stage, the maximum difference in varistor voltage V _{1 mA} per unit thickness is 6 V / mm or less, the maximum difference in temperature measured by the thermocouple is as small as 7 ° C., and excellent temperature uniformity. I found out. However, it was found that the temperature decreased from the upper stage toward the lower stage, and the difference increased to 14 ° C. throughout the furnace. This is because the heating furnace 100 has a flame-extinguishing gas furnace as its basic structure, so that the gas flow becomes high at the top of the furnace body 20 and the exhaust gas is cooled toward the discharge port 50 at the bottom. Conceivable.

Furthermore, from the measurement results in Table 1, as shown in the graph of FIG. 4, a clear correlation was confirmed between the temperature measured by the thermocouple and the varistor voltage V _{1 mA} per unit thickness. Therefore, if the distribution of the varistor voltage V _{1 mA} per unit thickness of the molded body arranged in the furnace body 20 can be obtained, it is understood that the substantial temperature variation in the furnace body 20 can be evaluated. .

Also. The measured values of the oxygen concentration of each oximeter were all close to the oxygen concentration in the atmosphere, and the maximum difference of V _{10 μA} / V _{1 mA} was 0.01, indicating that the variation was small. . Therefore, it is considered that the oxygen concentration in the furnace body 20 is substantially uniform.

(Comparative Examples 1 to 3)
In order to confirm whether or not the large-sized object to be heated A can be uniformly fired in the heating furnace 100, the granulated powder produced in the same manner as in Reference Example 1 was used, and the mold was molded to have a diameter of 50 mm and a height of 50 mm. It was manufactured as a cylindrical shaped body.

  This molded body was degreased by maintaining it at 400 ° C. for 2 hours using a hot air circulating dryer to obtain an object A to be heated.

  The same heating furnace 100 as in Reference Example 1 was used, and the configuration of the shelf 71 was also the same.

  Nine pieces to be heated A in each stage were placed on a shelf board 71 made of SiC via a magnesium-based laying plate 74, arranged three in the left-right direction and three in the front-rear direction.

  And in the comparative example 1, the to-be-heated material A was baked for 2 hours in the state which maintained the furnace main body 20 inside at 1200 degreeC. In Comparative Example 2, firing was performed at 1100 ° C., and in Comparative Example 3 maintained at 1000 ° C. for 2 hours.

The fired bodies after firing were taken out, and the varistor voltages V _{1 mA} and V _{10 μA} of each fired body were measured. The measurement results of Comparative Example 1 are shown in Table 2, the measurement results of Comparative Example 2 are shown in Table 3, and the measurement results of Comparative Example 3 are shown in Table 4, respectively.

From the measurement results of Table 2, it was found that when the firing temperature was 1200 ° C., the varistor voltage V _{1 mA} per unit thickness was 6 V / mm or less in each stage, and the heat uniformity was excellent. As in Reference Example 1, the varistor voltage per unit thickness increased from the upper stage toward the lower stage, and the maximum difference was 9 V, indicating that the temperature difference was large.

On the other hand, from the results of Tables 3 and 4, when the firing temperature is 1100 ° C. and 1000 ° C., the maximum difference of varistor voltage V _{1 mA} per unit thickness in each stage increases from 11 V / mm to 17 V / mm. It was found that the heat uniformity was slightly inferior. The standard deviation / average value of the varistor voltage per unit thickness is as small as 1.65% at 1200 ° C, but 2.48% at 1100 ° C and 3.42% at 1000 ° C. It was found to increase.

From the measurement results shown in Table 2, when the firing temperature is 1200 ° C., the value of V _{10 μA} / V _{1 mA} shows an excellent non-ohmic property of 0.926, the maximum difference is 0.02, and the variation is small. It was found that the oxygen concentration in 20 was almost uniform.

On the other hand, from the measurement results in Table 3 and Table 4, when the firing temperature is 1100 ° C. and 1000 ° C., the value of V _{10 μA} / V _{1 mA} is as low as 0.89 to 0.84, and the non-ohmicity is significantly reduced. I found out.

This is because the oxygen concentration in the furnace body 20 decreases and is not uniform, but gas such as carbon dioxide or water vapor is contained in the air flow by gas combustion, so the interior of the furnace body 20 tends to be in a reducing atmosphere. The combustion of residual carbon in the object to be heated A is suppressed, and the non-ohmicity is extremely reduced because the residual carbon of the object to be heated A is not completely combusted especially at a firing temperature of 1000 ° C. This is presumably because the variation in the varistor voltage V _{1 mA} per unit thickness increased due to the variation in the amount.

(Example 1 to Example 3)
In the furnace main body 20 of the heating furnace 100, a barrier 30 that is mainly composed of alumina, has a gas inflow hole 30a in the upper part, has an opening 30b in the lower part, and is divided into four stages in the height direction is used as a comparative example. It was installed so as to cover the entire three-tiered shelf 71 arranged in the same manner as in Examples 1 to 3.

  The same molded body as the molded body produced in Comparative Example 1 to Comparative Example 3 was degreased using a hot air circulating dryer and maintained at 400 ° C. for 2 hours to obtain an object A to be heated. And this to-be-heated material A was arrange | positioned on the shelf 71 similarly to Comparative Examples 1-3.

  And in Example 1, the to-be-heated material A was baked for 2 hours in the state which maintained the furnace main body 20 inside at 1200 degreeC. In Example 2, baking was performed at 1100 ° C. and in Example 3 while maintaining at 1000 ° C. for 2 hours.

  In Examples 1 to 3, oxygen gas of 300 ° C. is supplied from outside the furnace at a rate of 2 L / min into the space S through the gas path 61 during firing, and from the upper part to the lower part of the barrier 30. Washed away.

The fired bodies after firing were taken out, and the varistor voltages V _{1 mA} and V _{10 μA} of each fired body were measured. The measurement results of Example 1 are shown in Table 5, the measurement results of Example 2 are shown in Table 6, and the measurement results of Example 3 are shown in Table 7, respectively.

From the measurement results in Tables 5 to 7, the maximum difference in the varistor voltage V _{1 mA} per unit thickness is 6 V / mm to 11 V / mm in each stage when the firing temperature is 1200 ° C., 1100 ° C., or 1000 ° C. It was found that there was little variation in mm and excellent heat uniformity.

Unlike the cases of Comparative Examples 1 to 3, the varistor voltage V _{1 mA} per unit thickness decreases from the upper stage to the lower stage, and the maximum difference is 9 V / mm to 16 V / mm, and the standard deviation thereof. The average value is 1.52 to 1.62%, and the maximum difference is 9 to 34 V in Comparative Examples 1 to 3, and the standard deviation / average value is 1.65% to 3.42%. I found it small. This is presumably because the temperature distribution in the vertical direction of the space S was reversed and the temperature difference was reduced by supplying a gas having a temperature lower than the temperature in the space S into the space S from above.

  Thereby, it is presumed that by making the flow rate and temperature of the gas supplied to the space S appropriate, the temperature in the vertical direction in the space S can be made more uniform. It is considered that the gas flow rate and temperature that can be appropriately uniform can be obtained by performing a plurality of experiments while changing the set values.

In addition, from the results of Tables 5 to 7, the value of V _{10 μA} / V _{1 mA} is 0.91 or more and exhibits excellent non- _ohmicity when the firing temperature is 1200 ° C., 1100 ° C., or 1000 ° C. It was found that the oxygen concentration in the space S was almost uniform. This is because the oxygen concentration is increased by supplying oxygen gas into the space S, and even if the firing temperature is as low as 1000 ° C., the combustion of residual carbon in the heated object A proceeds and the non-ohmic property is restored. It is thought that.

When the gas flow direction was set upward from the furnace bottom, the value of V _{10 μA} / V _{1 mA} was not improved even when the gas flow rate was increased to 30 L / min.

(Example 4, Example 5 and Comparative Example 4)
A heating furnace having the same structure as that of the heating furnace 100 but having a larger size was used. The inner dimensions of the furnace body 20 were 1200 mm in height, 1100 mm in width, and 1000 mm in depth. In the heating furnace 100, 12 Bunsen forced combustion gas burners as gas burners 40 are arranged symmetrically on the left and right furnace bottoms, and 12 magnetron meters with a maximum output of 1.2 kW as microwave oscillators 10 are placed on the left and right furnace walls. They are arranged symmetrically.

  Referring to FIG. 3A, SiC shelf plates 71 are installed in space S with a space of 150 mm from hearth 21, and a total of 10 shelf plates 71 of SiC are arranged on it at intervals of 70 mm. The shelf board 71 made of SiC was also placed on the shelf board 71 of the 10th stage to form a ceiling cover. Each SiC shelf 71 was a rectangular plate having a long side of 300 mm, a short side of 250 mm, and a thickness of 10 mm.

  Further, in the furnace body 20 of the heating furnace 100, alumina is the main component, the gas inlet hole 30a is formed in the upper part, the opening 30b is formed in the lower part, and the barrier 30 is divided into five stages in the height direction. A unit was installed to cover the entire stacking shelf 71. A total of four sets of the same units as those in the left and right sides were arranged in the furnace.

  The same molded body as the molded body produced in Comparative Example 1 to Comparative Example 3 was degreased using a hot air circulating dryer and maintained at 400 ° C. for 2 hours to obtain an object A to be heated. And this to-be-heated material A was arrange | positioned on the shelf 71 through the laying board 74 similarly to the comparative example 1 thru | or the comparative example 3. FIG.

  And the to-be-heated material A was baked for 2 hours in the state which maintained the furnace main body 20 inside at 1000 degreeC.

  However, in Example 4, during firing, oxygen gas at 500 ° C. was supplied from outside the furnace into the space S through the gas path 61 at 2 L / min, and flowed from the upper part to the lower part of the space S. In Example 5, air at 500 ° C. was supplied from the outside of the furnace through the gas path 61 at a rate of 2 L / min during firing, and flowed from the upper part to the lower part of the space S. In Comparative Example 4, no gas was supplied into the space S from outside the furnace during firing.

The fired bodies after firing were taken out, and the varistor voltages V _{1 mA} and V _{10 μA} of each fired body were measured. The measurement results of Example 4 are shown in Table 8, the measurement results of Example 5 are shown in Table 9, and the measurement results of Comparative Example 4 are shown in Table 10, respectively.

From the measurement results in Tables 8 to 9, in each case, the maximum difference in varistor voltage V _{1 mA} per unit thickness is 10 V / mm to 15 V / mm in each stage, and the varistor voltage per unit thickness of the entire furnace. It was found that the standard deviation / average value of A was 1.42% to 1.63% and the variation was small and the heat uniformity was excellent.

From the measurement results of Table 10, in Comparative Example 4, the varistor voltage V _{1 mA} per unit thickness increases from the upper stage toward the lower stage, and the temperature decreases, whereas in Examples 4 and 5, It was found that the varistor voltage V _{1 mA} per unit thickness decreased from the upper stage to the lower stage, and the temperature increased. This is considered to be because the temperature distribution in the vertical direction in the space S is reversed by supplying a gas having a temperature lower than the temperature in the space S into the space S from above.

  Accordingly, it is presumed that the temperature in the vertical direction in the space S can be made uniform by appropriately adjusting the flow rate and temperature of the gas supplied into the space S. It is considered that the gas flow rate and temperature that can be appropriately uniform can be obtained by performing a plurality of experiments while changing the set values.

Further, in Example 4, the value of V _{10 μA} / V _{1 mA} is 0.91 or more, which shows an excellent non-ohmic property, and the oxygen concentration in the space S is made uniform in an appropriate state. I found out. This is because the oxygen concentration is increased by supplying oxygen gas into the space S, and even if the firing temperature is as low as 1000 ° C., the combustion of residual carbon in the heated object A proceeds and the non-ohmic property is restored. It is thought that.

In Example 5, the value of V _{10 μA} / V _{1 mA} was clearly increased to 0.87 as compared with Comparative Example 4, but it was found that non-ohmicity was improved. . It is considered that this is because non-ohmic properties have been recovered by the combustion of residual carbon in the article A to be heated by supplying air into the space S and increasing the oxygen concentration.

(Example 6)
The same heating furnace as in Example 4 and Example 5 was used.

  However, referring to FIG. 3B, a mullite mortar 82 is installed in the furnace body 20 at a distance of 150 mm from the hearth 21, and a total of five mullite mortars 82 are provided thereon. A ceiling shelf 84 made of SiC having a 30 mm diameter through hole in the center was placed on the uppermost mortar 82 to form a ceiling cover. The mortar 82 had a rectangular bottom surface with a long side of 350 mm and a short side of 300 mm, a thickness of 15 mm, a height of 150 mm, and a box shape with an open top surface. A through hole having a diameter of 30 mm is formed at the center of the mortar 82. Furthermore, a total of 4 sets of the same 5-layered mortars were set in the furnace on the left and right sides.

  The same molded body as the molded body produced in Example 4 and Example 5 was degreased using a hot-air circulating dryer and maintained at 400 ° C. for 2 hours to obtain an object A to be heated. Then, twelve pieces of each of the objects A to be heated were stored in a mullite mortar 82. Then, these mortars 82 are placed in each mortar 82 through a magnesium spinel laying plate 83, three in the front-rear direction and four in the left-right direction, for a total of twelve objects A to be heated. Placed.

  And the to-be-heated material A was baked for 2 hours in the state which maintained the furnace main body 20 inside at 1200 degreeC.

  During firing, oxygen gas at 500 ° C. was supplied from outside the furnace through the gas passage 61 into the space S at 3 L / min, and flowed from the upper part to the lower part of the space S.

The fired bodies after firing were taken out, and the varistor voltages V _{1 mA} and V _{10 μA} of each fired body were measured. Table 11 shows the measurement results.

From the results of Table 11, within each stage, the varistor voltage V _{1 mA} per unit thickness has a maximum difference of 7 V / mm to 8 V / mm, and the maximum difference in the whole furnace is also 9 V / mm, and the standard deviation is small. / The average value was 1.64%, and it was found that the heat uniformity was excellent.

  And it turned out that temperature is rising from the upper stage toward the lower stage. This is considered to be because the temperature distribution in the vertical direction in the space S was reversed by supplying a gas having a temperature lower than that of the space S into the space S from above.

In addition, it was found that the value of V _{10 μA} / V _{1 mA} was 0.93 or more and was very excellent in non-ohmicity, and the oxygen concentration in the space S was made uniform in an appropriate state.

(Example 7)
In the same heating furnace 100 as in Example 6, the heated object A before degreasing treatment was arranged in the same manner as in Example 6.

  And the inside of the furnace main body 20 of the heating furnace 100 was maintained at 400 ° C. for 2 hours for degreasing treatment. Then, the to-be-heated material A was baked for 2 hours in the state which maintained the furnace main body 20 inside at 1200 degreeC.

  During the degreasing process and firing, oxygen gas at 500 ° C. was supplied from outside the furnace into the space S through the gas path 61 at a rate of 2 L / min and flowed from the upper part to the lower part of the space S.

The fired bodies after firing were taken out, and the varistor voltages V _{1 mA} and V _{10 μA} of each fired body were measured. Table 12 shows the measurement results. Further, the exhaust gas discharged from the heating furnace 100 during the degreasing process was evaluated by a three-point comparative odor bag test.

From the measurement results in Table 12, within each stage, the maximum difference of varistor voltage V _{1 mA} per unit thickness is 8 V / mm or less, the maximum difference in the whole furnace is 9 V, and the variation is small, and the standard deviation / average value is also It was found that the variation was as small as 1.56% and the heat uniformity was excellent.

  And it turned out that temperature is rising from the upper stage toward the lower stage. This is considered to be because the temperature distribution in the vertical direction in the space S is reversed by supplying a gas having a temperature lower than the temperature in the space S into the space S from above.

In addition, it was found that the value of V _{10 μA} / V _{1 mA} was 0.93 or more, which was very excellent in non-ohmicity, and that the electrical characteristics were almost the same as in Example 6.

  The exhaust gas discharged from the heating furnace 100 during the degreasing process is lower than the standard value that can be directly discharged into the atmosphere as evaluated by the three-point comparative odor bag test. It was found that the exhaust gas was not brominated. Therefore, it was confirmed that the exhaust gas can be released into the atmosphere without deodorizing, and it is not necessary to install a deodorizing device. Furthermore, the residual component generated by degreasing such as the tar component was not detected in the furnace body 20, and no cleaning work was required.

  Therefore, the degreasing treatment and the firing treatment can be performed consistently in the same heating furnace 100, and the total treatment time can be shortened.

(Other embodiments)
The present invention is not limited to the embodiment described above. For example, in the embodiment, the case where the heating furnace 100 includes a plurality of the microwave oscillators 10 and the gas burners 40 has been described, but the present invention is not limited to this. For example, a heating furnace provided with only one microwave oscillator 10 and one gas burner 40 may be used. In this case, the uniformity of heating in the horizontal direction in the space S is inferior to that of the heating furnace 100, but since the low-temperature gas supply device 60 supplies low-temperature gas from above into the space S, the vertical direction in the space S It is possible to improve the uniformity of heating.

  Moreover, although embodiment demonstrated the case where oxygen gas or the gas containing oxygen gas was supplied from the low temperature gas supply apparatus 60 as low temperature gas, it is not limited to this. For example, the low temperature gas supply device 60 may supply a gas that does not contain oxygen gas as a low temperature gas. In this case, the uniformity of the oxygen concentration in the space S is inferior to that of the heating furnace 100, but it is possible to improve the uniformity of the heating in the vertical direction in the space S.

(Example 8)
In Example 6, when degreased with a hot air circulating dryer, the number of objects to be fired to be processed increased, so that the odor of exhaust gas generated along with degreasing became tight, which could cause environmental problems. Was confirmed. Then, when the evaluation by the three-point comparative odor bag method was carried out, it was confirmed that it exceeded the reference value that can be directly released into the atmosphere.

  Therefore, in the case of degreasing with a hot air circulating dryer, the exhaust gas has to be processed with a deodorizing device, and the problem that the price of manufacturing equipment increases has been revealed. The method to avoid this was examined.

  As a result, it was found that the degassing of the exhaust gas proceeds by degreasing in the microwave gas complex furnace. As in the case of degreasing using a hot-air circulating dryer, the exhaust gas was evaluated by the three-point comparative odor bag method, and as a result, it was confirmed that the level would not cause any problems even if released directly into the atmosphere. It was. Furthermore, when the inside of the microwave gas combined furnace after the degreasing treatment was observed, no deposits such as tar components were observed in the low temperature part of the furnace wall or door, and the same condition as before the degreasing was maintained. It was also confirmed. Therefore, it is possible to make exhaust gas into the atmosphere without deodorizing, and it is not necessary to install a deodorizing device.

  The malodor of the exhaust gas that accompanies degreasing is thought to be generated by the combustion and decomposition of the organic components that are the main components of the binder and plasticizer in the molded body. It is considered that the exhaust gas is made non-brominated as the decomposition is promoted and the exhaust gas is completely combusted by gas combustion.

  DESCRIPTION OF SYMBOLS 10 ... Microwave oscillator, 11 ... Waveguide, 12 ... Diffusion fan, 20 ... Furnace main body, 20a ... Inner wall surface, 20b: Gas passage hole, 21 ... Furnace floor, 22 ... Furnace outer shell, 23 ... Furnace wall, 24: Door, 25 ... Thermocouple thermometer, 30 ... Barrier, 30a ... Gas inlet, 30b ... Opening, 40 ... Gas burner, 50 ... Outlet, 51 ... Horizontal flue, 52 ... Vertical flue, 53 ... Exhaust Cylinder, 60 ... Low-temperature gas supply device, 61 ... Gas passage, 62 ... Gas supply unit, 63 ... Heating unit, 64 ... Adjusting valve, 71 ... Shelf plate, 72, 73: Column 74 ... Base plate, 81: Column, 82 DESCRIPTION OF SYMBOLS ... A bowl, 83 ... Laying board, 84: Shelf board, 100 ... Heating furnace, A ... Object to be heated, S ... Space.

Claims (6)

A furnace body in which an object to be heated is arranged in the center;
A barrier installed between the inner wall surface of the furnace body and the central part of the furnace body;
Between the inner wall surface of the furnace body and the barrier, a gas burner that forms a flame from the hearth of the furnace body toward the upper part,
A discharge port for discharging the gas in the furnace body from the hearth side to the outside;
A microwave oscillator for irradiating microwaves into the furnace body;
A heating furnace comprising: a low-temperature gas supply device that supplies a gas having a temperature lower than a temperature in the furnace body from above into a space surrounded by the barrier.   At least one of the gas burner and the microwave oscillator is arranged in plane symmetry with respect to a vertical plane including a vertical axis at the center of the furnace body, or rotationally symmetrical with respect to the vertical axis at the center of the furnace body. The heating furnace according to claim 1.   The heating furnace according to claim 1 or 2, wherein the low-temperature gas supply device supplies a gas for controlling an oxygen concentration as the low-temperature gas. An arrangement step of arranging an object to be heated in a space surrounded by the barrier in the inner wall surface of the furnace body, front, rear, left and right;
Between the inner wall surface of the furnace body and the barrier, a flame is formed upward from the hearth of the furnace body, and microwaves are irradiated into the furnace body, and at the same time, a space surrounded by the barrier is formed. And a firing step of firing the object to be heated while supplying a gas having a temperature lower than the temperature in the space from above.   The heating method according to claim 4, wherein the low temperature gas is a gas for controlling an oxygen concentration. Between the inner wall surface of the furnace body and the barrier, a flame is formed from the hearth of the furnace body to the upper part, and microwaves are irradiated into the furnace body, and at the same time, the temperature is lower than the temperature in the furnace body. A degreasing step of degreasing the object to be heated, supplying the gas from above into the space surrounded by the barrier,
The said baking process is performed by increasing at least any one of the said flame or the said microwave and raising the temperature in the said main furnace after the said degreasing | defatting process. Heating method.