JP2008110896A - Method of manufacturing ceramic honeycomb structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a ceramic honeycomb structure suppressing deformation of a honeycomb formed article caused by combustion of a carbon constituent contained in a work piece of the honeycomb formed article. <P>SOLUTION: The method of manufacturing the ceramic honeycomb structure 1 obtaining the ceramic honeycomb structure by calcinating the honeycomb formed article 10 comprises a honeycomb formed article forming process of mixing a cordierite molding compound containing talc with a binder, kneading, and forming the honeycomb formed article 10 by forming honeycomb-like, and a calcinating process of calcinating the honeycomb formed article by heating the honeycomb formed article 10 at a temperature region (B) not higher than a temperature region (C) easy to deform the honeycomb formed article 10 so as to lose not less than 99% of a total carbon amount contained in the honeycomb formed article 10. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a ceramic honeycomb structure, and is suitable for application to, for example, a method for firing a ceramic honeycomb structure used for a catalyst carrier or a filter in an exhaust gas purification device of an internal combustion engine.

  Conventionally, a ceramic honeycomb structure has been used as a catalyst carrier and a filter in an exhaust gas purification device of an internal combustion engine. This ceramic honeycomb structure is formed by extrusion molding a raw material mixture prepared from a cordierite forming raw material such as talc and a binder as a forming auxiliary material into a honeycomb shape, and then drying the honeycomb formed body. It can be obtained by firing in a molding furnace such as a gas furnace.

  At the time of firing, deformation and cracking may occur in the honeycomb formed body, and therefore various firing methods have been proposed (Patent Document 1, etc.).

  In the technique disclosed in Patent Document 1, the temperature inside the furnace is controlled to prevent cracks and deformation during firing. Specifically, in this technique, in a debinding step of degreasing and degreasing the binder from the honeycomb formed body containing the binder, and a main firing step of firing the degreased honeycomb formed body, respectively, predetermined furnace temperatures Schedule (hereinafter referred to as firing conditions) is set.

In the above technique, a gas furnace is used, and a burner that is supplied with fuel and air and injects combustion gas (flame) into the furnace is provided. In the gas furnace, the temperature inside the furnace is locally different between the area where the combustion gas is directed and the area where it is not, and there is a possibility that the oxygen concentration may be different, so an oxygen supply port is provided to enrich the oxygen concentration. Yes.
JP-A-6-9276

  However, as in the prior art, the method of simply controlling the temperature by controlling the temperature in the furnace has not been sufficient in suppressing the deformation and cracking of the honeycomb formed body during firing.

  Therefore, the inventors diligently studied the deformation and cracking mechanisms of the honeycomb formed body during firing, and as a result, found the following matters.

  At the time of firing, the carbon component contained in the honeycomb molded body burns. The inventors have found a reason why the honeycomb formed body is easily deformed when the carbon burns in the predetermined temperature range of the honeycomb formed body.

  That is, there is a possibility that the honeycomb molded body locally becomes a temperature of 1000 ° C. or more by locally burning carbon in the honeycomb molded body. At this time, it has been found that when the temperature of the honeycomb formed body itself is easily deformed (for example, about 850 ° C.), the honeycomb formed body is greatly affected by the local combustion of carbon and promotes deformation of the honeycomb formed body.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for manufacturing a ceramic honeycomb structure that suppresses deformation of the honeycomb molded body due to combustion of carbon components contained in the honeycomb molded body. There is to do.

  In order to achieve the above object, the present invention comprises the following technical means.

That is, in the invention according to any one of claims 1 to 6, in a method for manufacturing a ceramic honeycomb structure in which a honeycomb formed body is obtained by firing the honeycomb formed body, a cordierite forming material containing talc and a binder are mixed. Kneaded to form a honeycomb formed body, a honeycomb formed body forming step for forming a honeycomb formed body, and a firing step for firing the honeycomb formed body,
The firing step is characterized in that the honeycomb formed body is heated so that 99% or more of the total amount of carbon contained in the honeycomb formed body disappears below the temperature range in which the honeycomb formed body is easily deformed.

  According to this, the disappearance of carbon contained in the honeycomb molded body can be almost completed in a temperature state (temperature condition) below the temperature range in which the temperature of the honeycomb molded body itself is easily deformed. This can suppress local combustion of carbon, which is a factor that promotes deformation in a temperature range in which the honeycomb formed body is easily deformed, so that deformation of the honeycomb formed body due to combustion of the carbon component contained in the honeycomb formed body is prevented. Can be suppressed.

  Further, in the invention according to claim 2, the temperature range in which the honeycomb formed body is easily deformed is a temperature range in which 20% or more of talc causes a dehydration reaction with respect to the entire talc contained in the honeycomb formed body. It is characterized by.

Talc is represented by a composition formula of Mg ₃ Si ₄ O ₁₀ (OH) ₂ , and dehydration or the like occurs due to thermal decomposition. In the process of continuing the dehydration reaction, the cordierite molding material shrinks, so that the honeycomb molded body is more likely to be deformed than in the temperature region where there is no dehydration reaction process. This dehydration reaction of talc generally occurs at a temperature stage included in the range of 800 ° C to 1000 ° C.

  On the other hand, as described in claim 2, the temperature range in which the honeycomb formed body is easily deformed is set as a temperature range in which 20% or more of talc causes a dehydration reaction with respect to the entire talc contained in the honeycomb formed body. In the talc dehydration reaction process, carbon contained in the honeycomb formed body can be completely lost in a temperature state (temperature condition) that is equal to or lower than the dehydration start stage temperature.

  In particular, the invention according to claim 3 is characterized in that the temperature range in which the honeycomb formed body is easily deformed is 850 ° C. or more.

  According to this, the temperature range in which the honeycomb formed body is easily deformed can be set to a temperature range equal to or higher than the temperature at which the dehydration reaction starts (around 850 ° C.) among various reactions such as the dehydration reaction by thermal decomposition of talc. .

  The invention according to claim 4 is characterized in that an oxidizing gas is caused to flow into the honeycomb molded body in a temperature region where carbon contained in the honeycomb molded body disappears.

  In general, since a large number of cells extending in the axial direction partitioned by partition walls provided in a honeycomb shape are provided inside the honeycomb formed body, for example, the cells on the center side of the honeycomb formed body are on the surface portion side. There is a risk that the amount of atmosphere (air) in the furnace that can be led into the cell will be insufficient compared to the cell. If the amount is insufficient, the carbon in the central part of the honeycomb formed body may remain undisappeared, resulting in residual carbon.

  On the other hand, in the invention according to claim 4, since an oxidizing gas such as air or oxygen is allowed to flow into the honeycomb formed body, gas exchange inside the cell can be promoted and the oxidizing gas is used. Therefore, carbon disappearance, that is, combustion can be promoted. Therefore, carbon remaining in the honeycomb molded body can be prevented in a temperature range where carbon contained in the honeycomb molded body disappears.

  Here, the inflow amount of the oxidizing gas to be introduced into the honeycomb formed body is preferably 5 m / sec or less as in the invention described in claim 5. This facilitates gas exchange inside the cell and promotes carbon loss without burning carbon more than necessary by the enriched oxidizing gas.

  The invention described in claim 6 is characterized in that the flow rate of the oxidizing gas is 2 m / sec or more.

  Thereby, the combustion of carbon is appropriately promoted, and the carbon can be almost burned under a temperature condition below the temperature range in which the temperature of the honeycomb formed body itself is easily deformed.

  The inventor devised a manufacturing method for obtaining the ceramic honeycomb structure 1 by firing the honeycomb formed body 10 as a workpiece. First, the honeycomb formed body 10 is heated by simply controlling the furnace temperature Tk. In the case of firing, it is possible to suppress a significant deformation that causes cracking or the like, but the reason why the remarkable deformation cannot be sufficiently suppressed was investigated.

  Here, (1) at the time of firing, a plurality of honeycomb formed bodies 10 are placed in a furnace, for example, in a three-stage, six-row arrangement, etc., so that the temperature of each individual honeycomb formed body itself is directly controlled. In comparison, as in the prior art, controlling the firing conditions (sintering schedule) by the furnace temperature Tk is superior in productivity, and (2) to prevent deformations such as cracks, If the method of simply reducing the temperature rate is used, the firing time is wasted, and as a result, it becomes difficult to achieve both excellent productivity and (3) the honeycomb formed body 10 is configured during firing. Since the forming raw material such as cordierite forming raw material, the forming auxiliary material (binder), the pore forming material, etc. are thermally decomposed and contracted (or disappeared) by heating, if the thermal stress is not concentrated, the honeycomb formed body as a whole Shrinkage ratio Regardless, it cracks that can be excessive stress occurs avoid lead to, was repeated intensive studies by focusing on the equal.

  First, the characteristic diagram shown in FIG. 6 shows the relationship between the temperature of the honeycomb formed body itself and the shrinkage rate (hereinafter referred to as the firing shrinkage rate) when the honeycomb formed body 10 is heated during firing.

  According to this characteristic diagram, when the temperature of the honeycomb molded body 10 rises as the honeycomb molded body 10 is heated, the honeycomb molded body 10 contracts at any temperature point that is higher than the heating start temperature.

  Further, the temperature increased by heating is a low temperature region (region of 450 ° C. or less in FIG. 6) A, and a high temperature region (850 ° C. or more of FIG. In the region (C), the change behavior of the firing shrinkage rate is relatively large. On the other hand, in the intermediate temperature region B (region in the range of 450 ° C. to 850 ° C. in FIG. 6) B corresponding to the predetermined temperature increase interval, the firing shrinkage rate does not change even if the temperature is increased during this time.

  In other words, in these low temperature region A and high temperature region C, if the temperature rises due to, for example, combustion due to thermal decomposition of the material constituting the honeycomb formed body 10, shrinkage may be significantly advanced.

  In the case where the temperature rise due to this thermal decomposition occurs locally in the honeycomb formed body 10, thermal stress is concentrated between the local portion and the surrounding portions, and there is a possibility that excessive stress is generated. is there.

  Further, in the intermediate temperature region B, even if the temperature of the honeycomb formed body 10 is increased by thermal decomposition, if the increased temperature is in the intermediate temperature region B, the firing shrinkage rate due to the temperature increase does not change. Therefore, even if the temperature rise due to thermal decomposition occurs locally, the thermal stress does not concentrate.

  From the knowledge obtained from the firing shrinkage-temperature characteristic diagram, by increasing the ratio of firing time in the intermediate temperature region B under firing conditions, the thermal decomposition of the material constituting the honeycomb formed body 10 is performed. It is expected that stress concentration of thermal stress during the process can be avoided.

  Here, from the above knowledge, as a method of setting the firing conditions in the intermediate temperature region B, a method of setting the furnace temperature on the upper limit temperature side (for example, 800 ° C.) in the intermediate temperature region B can be easily considered. . Since this method seems to be able to suppress deformation while activating thermal decomposition, there seems to be no other optimal countermeasure.

  However, as a result of intensive studies by the inventor, the in-furnace temperature is set to a temperature other than the upper limit temperature side in the intermediate temperature region B by paying attention to the combustion of the carbon component thermally decomposed in the intermediate temperature region B. Surprisingly, the present inventors have found that this is the best countermeasure method for suppressing deformation such as cracking due to combustion of the carbon component.

  That is, at the time of firing, the carbon component contained in the honeycomb formed body 10 is ignited and burned by thermal decomposition. When the carbon component burns locally in the honeycomb formed body 10, the honeycomb formed body 10 at the local portion may be 1000 ° C. or more. At this time, when the honeycomb formed body itself is in a temperature region where it is easily deformed, that is, in the high temperature region C, the stress concentration of the thermal stress is likely to occur due to the large influence of local combustion of the carbon component, causing cracks and the like. It has been found that the honeycomb formed body 10 having a fear of being urged to be deformed.

  Specifically, the firing condition in the intermediate temperature region B is set to the lowest ignition temperature (hereinafter, ignition temperature) at which the carbon component can continue to burn (in this embodiment, 600 ° C.). By setting the firing conditions in this way, the furnace temperature is set to the lowest temperature at which the combustion of the carbon component can be continued, and therefore, this is the case where local combustion of the carbon component occurs in the honeycomb formed body 10. However, since it is possible to suppress the temperature of the local portion due to the combustion from exceeding the intermediate region B, the honeycomb molded body 10 that may cause cracking due to the combustion of the carbon component as compared with the conventional case. It is possible to suppress deformation.

  Hereinafter, the manufacturing method of the ceramic honeycomb structure of the present invention will be specifically described with reference to FIGS.

  The honeycomb formed body 10 to which the manufacturing method of the present invention is applied is an unfired honeycomb formed body for obtaining a ceramic honeycomb structure. The honeycomb formed body is not limited to all of the green body, but may be a part of the green body. That is, a honeycomb molded body that is partitioned by partition walls (hereinafter referred to as cell walls) 3 provided in a honeycomb shape and in which the plug material 4 is sealed in a part of the cell 11 is all unfired, or the plug material 4 is sealed. An object is that the honeycomb formed body before firing is fired (hereinafter referred to as first firing) and then the unfired plug material 4 is packed in the honeycomb formed body.

  In the following description of this example, it is assumed that the honeycomb formed body 10 is all unfired.

  In manufacturing the honeycomb formed body 10, a cordierite forming raw material, a binder as a forming auxiliary material, a combustible substance such as carbon, and the like are prepared. Next, a cordierite-forming raw material, a binder, a combustible substance, and the like are mixed, and an appropriate amount of water is added and kneaded. Next, the kneaded raw material is extruded into a honeycomb shape with a known honeycomb extruder and dried to obtain the honeycomb formed body 10.

  The cordierite forming raw material (hereinafter referred to as forming raw material) contains talc as an essential component, and for other raw materials, the blending raw materials and blending ratios described in JP-A-9-77573 filed by the applicant can be applied. . For example, a specific talc, aluminum hydroxide or the like is used as a basic raw material so as to be in the region of cordierite SiO2: 45 to 55 wt%, Al2O3: 33 to 42 wt%, MgO: 12 to 18 wt%. Blend. In addition, a binder and the flammable substance are added to the basic raw material within a predetermined range.

  Here, the carbon component contained in the honeycomb formed body 10 may be carbon such as graphite or an organic substance containing carbon. Carbon such as graphite is a flammable substance and is added as a pore forming agent (pore forming agent) that disappears and forms pores when the honeycomb formed body 10 is fired.

  Further, the honeycomb shape of the honeycomb formed body 10 in the present embodiment is a cell that becomes a flow path extending in the axial direction by being partitioned by the extremely thin cell walls 3 as in the honeycomb formed body 10 shown in FIG. 11 is a shape formed. The overall shape of the honeycomb formed body is not particularly limited, and for example, as shown in FIG. 4, a cylindrical shape, a quadrangular prism shape, a triangular prism shape, or the like may be used. The cell shape of the honeycomb formed body is not particularly limited, and may be a cell shape such as a square shape, a triangular shape, or a hexagonal shape as shown in FIG.

  Further, the honeycomb formed body 10 of the present embodiment is arranged by sealing the plug member 4 at the end of the cell 11 in a so-called checkered pattern on both end faces 12 in the axial direction. The honeycomb formed body 10 is obtained by integrally molding the outer peripheral skin portion 2 and the cell wall 3.

  Such a honeycomb formed body 10 is cut into a predetermined length and dried using a microwave or the like. Next, the plug 4 is filled into the end portions of the predetermined cells 11 on both end faces 12 of the honeycomb formed body 10. Thereafter, the firing shown in the flowchart of the firing step in FIG. 2 and the firing schedule in FIG. 1 is performed to obtain the ceramic honeycomb structure 1.

  FIG. 1 shows the temperature Tk in the furnace on the vertical axis, and the firing time from the start of heating to the end of cooling on the horizontal axis. The firing stages I, II, and III for dividing the firing period shown in FIG. This corresponds to the binder removal process, the decarburization process, and the main firing process shown in FIG.

  As shown in FIG. 2, the firing step includes a binder removal step (I), a decarburization step (II), and a main firing step (III).

  The binder removal step (I) is a step of removing the binder, which was necessary at the time of forming included in the honeycomb formed body, by heating before performing the main firing step (III). In the binder removal process, as shown in the firing schedule of FIG. 1, the temperature is raised from room temperature to 200 ° C. at a temperature rising rate of 50 ° C./hr, and then in the range of 200 ° C. to 450 ° C. (hereinafter referred to as the binder). (Thermal decomposition range) is heated at a heating rate of 25 ° C./hr.

  The decarburization step (II) is a step in which the carbon component of the combustible material contained in the honeycomb formed body is thermally decomposed and removed before the main firing step (III) is performed. In the decarburization step (II), as shown in FIG. 1, a range of 450 ° C. to 600 ° C. (hereinafter, an ignition temperature preparation range) is heated at a heating rate of 75 ° C./hr, and then 600 ° C. For 20 hours (hereinafter, the continuation range of 600 ° C. is called the ignition temperature range). After the end of this ignition temperature range, the range up to 800 ° C. is heated at a heating rate of 75 ° C./hr.

  In the ignition temperature range, almost all of the entire carbon component contained in the honeycomb formed body disappears due to combustion. In addition, it is defined that almost all disappears by combustion because carbon remains partially in the honeycomb formed body 10 as the ash content of the final sintered body when the carbon burns.

  Therefore, it can be paraphrased that 99% or more of all the carbon components are lost when all the carbon amount excluding ash is lost by combustion.

  The main firing step (III) is a step of determining the characteristics of the ceramic honeycomb structure 1 obtained by firing. The product size, porosity, heat resistance, and other characteristics of the ceramic honeycomb structure 1 are determined by the rate of temperature rise, the maximum temperature, and the retention time at the maximum temperature in the main firing step (III). In the main firing step (III), a range of 800 ° C. to 1430 ° C. (hereinafter referred to as a main firing temperature increase range) is heated at a temperature increase rate of 75 ° C./hr, and then at a maximum temperature of 1430 ° C. for 15 hours. Hold (hereinafter referred to as the maximum temperature holding range). After completion of this maximum temperature holding range, cooling is performed at a temperature drop rate of 75 ° C./hr.

  In the main firing step (III), in the range of 800 ° C. to 1000 ° C., a temperature range in which the raw material talc undergoes a dehydration reaction by thermal decomposition (hereinafter referred to as a talc dehydration reaction stage). In this talc dehydration reaction stage, structural water containing OH groups in the talc composition formula (hereinafter referred to as crystal structure) is released from the honeycomb formed body 10, and the crystal structure changes and contracts significantly. In addition, the contraction rate change of the honeycomb formed body 10 is relatively large.

  For this reason, when the furnace temperature is set in the talc dehydration reaction stage, the honeycomb formed body 10 itself becomes a temperature region in which the honeycomb formed body 10 is easily deformed (hereinafter, easily deformable temperature region by thermal decomposition). The easily deformable temperature range by the thermal decomposition can be substantially defined as a temperature range equal to or higher than the temperature at which the talc dehydration reaction has started (hereinafter referred to as the talc dehydration start temperature). The talc dehydration reaction start temperature was set to a temperature at which 20% of talc was dehydrated with respect to the entire talc contained in the honeycomb formed body 10.

  Therefore, the easily deformable temperature region by the thermal decomposition is a temperature region that is equal to or higher than the talc dehydration reaction start temperature, and a temperature region in which 20% or more of talc undergoes a dehydration reaction with respect to the entire talc contained in the honeycomb formed body 10. In other words.

  In addition, since the talc dehydration reaction start temperature is approximately 850 ° C., it can be rephrased that the easily deformable temperature region by the thermal decomposition is 850 ° C. or higher.

  In the firing step, the dried honeycomb formed body 10 is fired in a single firing furnace such as a shuttle kiln or a continuous furnace such as a tunnel furnace.

  Moreover, in the said furnace, there exist a gas furnace and an electric furnace from the classification of a heating system, and any furnace may be used in the furnace of this embodiment. When a honeycomb furnace is fired by heating with a combustion gas such as LPG gas heating, the gas furnace is not a natural atmosphere air but an oxygen concentration of the atmosphere in order to control the combustion of the combustion gas. Enrichment, or control of poverty is made. In the electric furnace, in order to heat the honeycomb formed body, unlike the gas furnace, combustion for controlling the temperature in the furnace is not necessary.

  In the case where it is assumed that an oxidizing gas (air) is introduced into the honeycomb formed body 10 as in a modification described later, as shown in FIG. 2, the binder removal step (I) and the decarburization step ( It is preferable to set the firing conditions for the temperature II) at the furnace temperature in the electric furnace. Note that the main firing step (III) is not limited to setting the firing conditions in a gas furnace as shown in FIG. 2, but may be one in which the firing conditions are set in an electric furnace.

  Here, the binder removal step (I), the decarburization step (II), and the main firing step (III) are performed in a first firing step, a second firing step, and a second firing step, as shown in FIGS. Also called 3 firing stage.

  In the present embodiment described above, the firing step eliminates 99% or more of the total amount of carbon contained in the honeycomb formed body 10 below the easily deformable temperature region due to thermal decomposition. As a result, it is possible to suppress the local combustion of carbon, which is a factor for promoting the deformation in an easily deformable temperature range due to thermal decomposition, and thus suppress the deformation of the honeycomb molded body due to the combustion of the carbon component contained in the honeycomb molded body. be able to.

  Further, in the present embodiment described above, the easily deformable temperature region by the thermal decomposition is a temperature region equal to or higher than the temperature at which the talc dehydration reaction starts, and is 20 with respect to the entire talc contained in the honeycomb formed body 10. It was set as the temperature range in which more than% of talc dehydrates. Therefore, the carbon component contained in the honeycomb formed body can be completely eliminated in a temperature range equal to or lower than the talc dehydration reaction start stage temperature.

  In the present embodiment described above, the firing step includes a debinding step, a decarburization step, and a main firing step. In the decarburization step, the furnace temperature is used as a firing condition for heating the honeycomb formed body. Is set to the ignition temperature of carbon. Since the carbon can be continuously burned at such an ignition temperature, the carbon contained in the honeycomb formed body 10 is completely disappeared, and the temperature in the honeycomb formed body 10 is set within the easily deformable temperature range due to the thermal decomposition. The following can be suppressed.

(Modification)
The inventor further examined the shortening of the time required for the decarburization step in the firing step. First, when the decarburization process time is shortened, a method of shortening the holding time in the ignition temperature range and, for example, increasing the heating rate at 50 ° C./hr after the end of the ignition temperature range can be considered. When this technique is applied, carbon (hereinafter referred to as “residual carbon”) remains undisappeared in the central portion of the honeycomb formed body 10, and anomalies occur along the boundary between the residual carbon and the disappeared portion of the carbon. Since cracking occurs due to heat generation, there seems to be no countermeasure other than suppressing the rate of temperature rise.

  However, as a result of intensive studies by the inventors, it has been found that by promoting gas exchange inside the cells 11 of the honeycomb formed body 10, it is possible to prevent the generation of residual carbon and to prevent cracking due to abnormal heat generation. First, the inside / outside temperature difference ΔTw of the honeycomb formed body 10 shown in FIG. 9A is the temperature at the center of the honeycomb formed body 10 (measurement point 101 in FIG. 5) and the temperature at the outer periphery (measurement point 102 in FIG. 5). The temperature difference ΔTw between the inside and outside is shown in relation to the firing schedule. As shown in FIG. 9A, in the decarburization step, when the furnace temperature Tk reaches the ignition temperature of carbon, the carbon contained in the honeycomb formed body 10 burns and the combustion diffuses in the honeycomb formed body 10. To do. As the combustion diffuses, the temperature on the central portion side becomes higher on the outer peripheral portion side, so that the internal / external temperature difference ΔTw increases temporarily abruptly. Further, when the furnace temperature is further raised in the main firing step, a part of the residual carbon is rapidly burned at the high furnace temperature.

  On the other hand, when an oxidizing gas (air) is introduced into the honeycomb molded body 10 to promote gas exchange in the cell interior 11, as shown in FIG. 9 (b), an abrupt internal / external temperature difference ΔTw in the decarburization process. The temperature rise due to carbon combustion can be made uniform in the honeycomb formed body 10. As a result, residual carbon in the decarburization process can be eliminated, and cracks due to abnormal heat generation caused by residual carbon in the main firing process can be prevented.

  Further, as shown in FIG. 9B, the inventor has the effect that the supply of the oxidizing gas reduces the internal / external temperature difference ΔTw in the honeycomb formed body 10 and makes the temperature in the honeycomb formed body 10 substantially uniform. Focusing on the fact, the relationship between the supply amount of the oxidizing gas (air flow rate) and the maximum temperature of the honeycomb formed body 10 made uniform by the supply of the oxidizing gas was verified.

  Hereinafter, the firing process according to the modification will be specifically described with reference to FIGS. 7 and 8. As shown in FIG. 7, in the firing step, when the honeycomb formed body 10 is placed in a furnace and heated under predetermined firing conditions, an oxidizing gas such as atmospheric air (air) or oxygen is introduced into the honeycomb formed body 10. (In this embodiment, air) is introduced. A firing jig 9 on which the honeycomb formed body 10 is placed is provided in the furnace, and the honeycomb formed body 10 is disposed on the shelf board 91 with the firing table 92 interposed therebetween.

  In the present embodiment, it is preferable that the oxidizing gas (air) can be supplied into the honeycomb formed body 10 in a predetermined flow rate range. The characteristic diagram of FIG. 8 shows the supply amount of the oxidizing gas and the maximum temperature in the honeycomb formed body 10. The maximum temperature of the honeycomb formed body 10 indicates the maximum temperature in the decarburization process, and when the total amount of carbon disappears during the decarburization process, the temperature of the honeycomb formed body 10 approaches the furnace temperature. The time during which the temperature in the furnace is maintained at the ignition temperature and the honeycomb formed body 10 reaches the ignition temperature again due to the disappearance of the total amount of carbon is defined as the carbon disappearance time.

  Since the supply amount of the oxidizing gas (air flow rate) varies depending on the size of the honeycomb formed body, the flow rate for promoting gas exchange was evaluated as a parameter. Specifically, the flow rate of the oxidizing gas (air) was evaluated with parameter values of 0 m / s, 2.5 m / s, 5 m / s, and 7 m / s, and (1) honeycomb formed body 10 It was evaluated as a criterion that the maximum temperature was 850 ° C. or less and (2) the high cam molded body 10 had no cracks.

  By supplying an oxidizing gas (air) into the honeycomb formed body 10, gas exchange at the cell end portion of the honeycomb formed body 10 is promoted, and the inside of the honeycomb formed body 10 in each parameter value except 0 m / S. The inside and outside temperatures on the center side and the outer periphery side of the sheet were made uniform.

  As shown in FIG. 8, the maximum temperature in the honeycomb formed body 10 is 770 ° C. when the flow velocity (air flow) is 0 m / s, 830 ° C. at 2, 5 m / s, and 900 ° C. at 5 m / s. It is. With these air volumes, the honeycomb formed body 10 was not cracked. In addition, when the flow velocity (air volume) is 5 m / s, the temperature in the honeycomb formed body 10 is made uniform, so that cracking does not occur even at a temperature exceeding 850 ° C.

  Further, as shown in FIG. 8, when the flow velocity (air volume) was 7 m / s, the honeycomb formed body 10 was cracked. This is because the carbon component in the honeycomb formed body 10 is burned more than necessary, and a difference in temperature between the inside and outside of the hynicum body is caused due to this combustion, causing deformation that causes cracking of the honeycomb formed body 10. In this case, the honeycomb formed body 10 generates abnormal heat, and the abnormal heat generation exceeds 950 ° C. from the estimated temperature indicated by the one-dot chain line in FIG.

  Here, the carbon disappearance time is 20 hr, 10.5 hr, 10 hr, and 8 hr as the flow velocity (air volume) increases to 0 m / s, 2.5 m / s, 5 m / s, and 7 m / s. And can be shortened. When converted from such a relationship, when the flow velocity (air volume) is 2 m / s and 1 m / s, the carbon disappearance time is 11 hr and 12 hr.

  Further, when the flow velocity (air volume) is 2 m / s and 1 m / s, the maximum temperature is 800 ° C. and 790 ° C. from the estimated temperature by the one-dot chain line in FIG.

  In the present embodiment described above, the oxidizing gas (air) flows into the honeycomb molded body 10 in the decarburization step, that is, in the temperature region where the carbon component contained in the honeycomb molded body 10 disappears. The gas exchange inside the 10 cells 11 can be promoted, and since it is an oxidizing gas, carbon loss, that is, combustion can be promoted. Therefore, carbon remaining in the honeycomb molded body 10 can be prevented in a temperature range where carbon contained in the honeycomb molded body 10 disappears.

  In the present embodiment described above, the flow rate (air volume) of the oxidizing gas is preferably 5 m / s or less. This facilitates gas exchange inside the cell and promotes carbon loss without burning carbon more than necessary by the enriched oxidizing gas.

  In the present embodiment described above, the flow rate (air volume) of the oxidizing gas is preferably 2 m / s or less. The combustion of carbon is appropriately promoted, and the carbon can be substantially burned in a temperature region (II) below the temperature region (III) in which the temperature of the honeycomb formed body itself is easily deformed.

  Further, in the present embodiment described above, in the decarburization step, by setting the flow rate at which the oxidizing gas flows into the honeycomb formed body 10 within the range of 2 m / s to 5 m / s, the oxidizing gas Compared to the case where no carbon is introduced, the holding time in the ignition temperature range for eliminating carbon can be almost halved. Therefore, deformation of the honeycomb molded body due to combustion of the carbon component contained in the honeycomb molded body can be suppressed, and the firing time of the honeycomb molded body can be shortened.

  Moreover, in this embodiment demonstrated above, it is preferable to heat the honeycomb molded object 10 in an electric furnace at least in the decarburization process (II) among the debinding process (I) and the decarburization process (II). This makes it easier to set the firing conditions so that a predetermined amount of oxidizing gas flows into the honeycomb formed body 10 as compared with the case of heating in the gas furnace.

(Other embodiments)
As mentioned above, although one Embodiment of this invention was described, this invention is limited to this embodiment and is not interpreted and can be applied to various embodiment in the range which does not deviate from the summary.

  (1) In the present embodiment described above, 15 hours is set as an example of the maximum temperature holding time in the main baking step. However, the present invention is not limited to this, and any time may be used as long as it is within the range of 10 to 30 hours. May be.

  (2) In the present embodiment described above, all the unfired honeycomb formed bodies have been described as being fired. However, after the honeycomb formed body before sealing the plug material 4 is fired for the first time, What plugged the plug material 4 in the honeycomb formed body may be applied to the honeycomb formed body. In this case, only the maximum temperature holding time of the main baking step is 0 to 6 hours in the first baking, and then the second baking is performed in 10 to 24 hours, which is different from the description of the present embodiment. .

  (3) In the present embodiment described above, the amount of oxidizing gas supplied to the inside of the honeycomb molded body 10 is represented by an index value called a flow velocity. However, the present invention is not limited to this, and the gas inside the cell 11 of the honeycomb molded body 10 Any index value may be used as long as it promotes the exchange.

It is an example of the firing conditions for firing the honeycomb formed body of the embodiment of the present invention, and is an explanatory view showing a firing schedule. 2 is a flowchart showing a firing process corresponding to the firing conditions of FIG. 1 for a method for manufacturing a ceramic honeycomb structure of an embodiment of the present invention. 1 is a perspective view showing an example of a ceramic honeycomb structure to which a method for manufacturing a ceramic honeycomb structure of an embodiment of the present invention is applied. FIG. 4 is a perspective sectional view as seen from VI in FIG. 3. It is a longitudinal cross-sectional view of the ceramic honeycomb structure for demonstrating the measurement point of the temperature of the center part (center part) temperature in the measurement of the internal-external temperature difference (DELTA) Tw of the honeycomb molded body in a baking process, and the temperature of an outer peripheral part. It is a figure explaining the change behavior of the shrinkage rate of the honeycomb formed body in the temperature range of the second firing stage (decarburization step) in FIG. 1, and is a characteristic diagram showing the relationship between the firing shrinkage rate and temperature. FIG. 2 is a diagram for explaining supply of an oxidizing gas (air) into a honeycomb formed body in the second firing stage (decarburization step) in FIG. 1, and shows an example of a mounting state of the honeycomb formed body in a furnace. It is a perspective view. It is explanatory drawing which shows the relationship between the oxidizing gas (air) supply amount supplied into a honeycomb molded body, and the internal-external temperature difference (DELTA) Tw of a honeycomb molded body. FIG. 9A is a diagram for explaining the behavioral characteristics of the inside / outside temperature difference ΔTw of the honeycomb formed body in the firing process (firing schedule), and FIG. 9A is a diagram when oxidizing gas (air) is not supplied into the honeycomb formed body. 9 (b) is a characteristic diagram showing a case where an oxidizing gas (air) is supplied.

Explanation of symbols

1 Ceramic honeycomb structure 10 Honeycomb compact (base material)
101 Base material center (base material center)
102 Base material peripheral part (base material surface part)
11 cell 12 end surface 13 outer peripheral surface 3 cell wall (partition wall)
4 Plug material 9 Firing jig 91 Shelf plate 92 Firing stand

Claims (6)

In the method for manufacturing a ceramic honeycomb structure, the ceramic honeycomb structure is obtained by firing the honeycomb formed body.
A honeycomb molded body forming step of forming a honeycomb molded body by mixing and kneading a cordierite molding material containing talc and a binder to form a honeycomb molded body; and
A firing step of firing the honeycomb formed body,
The firing step is characterized in that the honeycomb formed body is heated so that 99% or more of the total amount of carbon contained in the honeycomb formed body disappears at a temperature range below which the honeycomb formed body is easily deformed. A method for manufacturing a ceramic honeycomb structure.   The temperature range in which the honeycomb formed body is easily deformed is a temperature range in which 20% or more of talc causes a dehydration reaction with respect to the entire talc contained in the honeycomb formed body. A method for manufacturing the ceramic honeycomb structure according to claim.   The method for manufacturing a ceramic honeycomb structure according to claim 1 or 2, wherein the temperature range in which the honeycomb formed body is easily deformed is 850 ° C or higher.   The ceramic according to any one of claims 1 to 3, wherein an oxidizing gas is allowed to flow into the honeycomb molded body in a temperature range where carbon contained in the honeycomb molded body disappears. A method for manufacturing a honeycomb structure.   The method for manufacturing a ceramic honeycomb structure according to claim 4, wherein an inflow amount of the oxidizing gas is 5 m / sec or less.   The method for manufacturing a ceramic honeycomb structure according to claim 4 or 5, wherein an inflow amount of the oxidizing gas is 2 m / sec or more.

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