JP4730285B2 - Method for firing honeycomb formed body - Google Patents

Description

  The present invention relates to a method for firing a honeycomb formed body formed by extruding a ceramic material.

Conventionally, a honeycomb structure made of a ceramic such as cordierite has been used as an exhaust gas purification filter for purifying exhaust gas discharged from an internal combustion engine.
The honeycomb structure is manufactured by extruding a clay-like ceramic material to prepare a honeycomb formed body, drying the honeycomb formed body, and firing the honeycomb formed body (see Patent Document 1).

  In addition, when the honeycomb structure is applied as an exhaust gas purification filter (DPF) for a diesel engine, for example, a high porosity is required to collect particulates in the exhaust gas. Therefore, a ceramic material added with carbon as a pore forming material is extruded to produce a honeycomb formed body, and high porosity is obtained by burning out carbon during firing.

  However, when the honeycomb formed body is fired, if the temperature is raised to the firing temperature all at once, carbon contained in the honeycomb formed body burns rapidly, causing cracks in the honeycomb formed body. That is, since combustion heat is suddenly generated by the combustion of carbon, a large temperature difference is generated between the central portion and the outer peripheral portion of the honeycomb formed body. Thereby, thermal stress was generated in the honeycomb formed body, and cracks were generated.

  Therefore, conventionally, the temperature inside the furnace is maintained at a temperature at which carbon is once burned, and the carbon is burned slowly instead of raising the temperature to the firing temperature all at once. Then, after the combustion of carbon was completed and the temperature of the entire honeycomb molded body and the furnace temperature became substantially the same temperature, the temperature was raised again. However, in such a baking method, the total baking time becomes long, and the productivity is lowered.

  Therefore, there is a demand for a method for firing a honeycomb formed body that can shorten the firing time, improve productivity, and suppress cracking during firing.

JP-A-8-73274

  The present invention has been made in view of such conventional problems, and is capable of reducing the firing time, improving the productivity, and suppressing the cracking during firing. An object is to provide a method for firing a body.

The present invention is a method for firing a honeycomb formed body formed by extruding a ceramic material in which carbon is added to a cordierite raw material, the partition walls being arranged in a honeycomb shape and providing a large number of cells.
When the honeycomb formed body is housed in a furnace and the furnace temperature is raised to the firing temperature, and then fired by holding the honeycomb formed body at the firing temperature,
In the middle of raising the furnace temperature to the firing temperature, the furnace temperature is temporarily held at a carbon combustion temperature that is a temperature at which the carbon can be burned, and the carbon contained in the honeycomb formed body is burned. Let
Due to the combustion of the carbon, the temperature at the outer peripheral portion of the honeycomb formed body rises to be higher than the furnace temperature, reaches a maximum, and then decreases in the outer peripheral peak where the temperature at the outer peripheral portion becomes maximum in the process of descending. When the temperature difference between the temperature of the outer peripheral portion and the furnace temperature at the time is A, the time difference between the time when the temperature difference becomes 0.5 A after the outer peripheral peak and before it becomes 0 The method for firing a honeycomb formed body is characterized in that the temperature rise in the furnace is started again (Claim 1).

  In the firing method of the honeycomb formed body of the present invention, the furnace temperature is temporarily maintained at the carbon combustion temperature in the course of raising the furnace temperature to the firing temperature, and the carbon contained in the honeycomb formed body is reduced. Burn. And, due to the combustion of the carbon, the temperature of the outer peripheral portion of the honeycomb molded body is increased and maximized, and in the process of descending thereafter, the temperature of the outer peripheral portion at the time of the outer peripheral peak at which the temperature of the outer peripheral portion becomes maximum and the above When the temperature difference from the furnace temperature is A, the temperature inside the furnace is increased at a timing between the time when the temperature difference becomes 0.5 A after the outer peripheral peak and before it becomes 0. Start again.

  That is, in the present invention, the furnace temperature that has been held at the carbon combustion temperature is raised again at the timing before the combustion of the carbon contained in the honeycomb formed body is completed. Therefore, compared with the case where the combustion of carbon is completed as in the prior art, and the temperature rise in the furnace temperature is restarted after the temperature of the entire honeycomb formed body and the furnace temperature are substantially the same, The time from when the furnace temperature is maintained at the above-mentioned carbon combustion temperature to when the temperature is raised again can be shortened. Thereby, the total firing time required for firing the honeycomb formed body can be shortened, and productivity can be improved.

  Further, even if the temperature rise in the furnace is started again at the above timing, there is no possibility that a defect such as a crack occurs in the honeycomb formed body. That is, since the carbon contained in the honeycomb molded body has burned to some extent at the time of the timing, there is no risk of sudden combustion heat being generated even when the temperature rise is started. The temperature difference between the portion and the outer peripheral portion (hereinafter, appropriately referred to as “internal / external temperature difference”) does not increase rapidly. Therefore, it is possible to reliably shorten the firing time and improve the productivity without causing defects such as cracks.

  Further, as described above, in order to burn the carbon contained in the honeycomb formed body, the furnace temperature is temporarily held at the carbon combustion temperature in the course of raising the furnace temperature to the firing temperature. . Therefore, carbon contained in the honeycomb formed body can be burned slowly, and generation of rapid combustion heat can be suppressed. Thereby, it is possible to prevent a sudden increase in the temperature difference between the inside and outside of the honeycomb formed body, and to suppress the occurrence of cracks.

  Thus, according to the method for firing a honeycomb formed body of the present invention, the firing time can be shortened, productivity can be improved, and cracking during firing can be suppressed.

  In the present invention, when the temperature rise in the furnace temperature is restarted before the temperature difference after the outer peripheral peak reaches 0.5 A, the carbon contained in the honeycomb formed body is sufficiently burned. There is a risk of not. For this reason, when the temperature rise is started at such a point, the difference in temperature between the inside and outside of the honeycomb formed body suddenly increases due to the combustion of carbon, and there is a possibility that cracking may occur. On the other hand, when the temperature rise in the furnace is restarted after the temperature difference becomes 0, the firing time cannot be shortened and the productivity cannot be improved.

Further, it is preferable that the temperature increase in the furnace is started again between the time when the temperature difference after the outer peripheral peak is 0.5 A and the time when the temperature difference is 0.25 A. (Claim 2) .
In this case, it is possible to reliably reduce the firing time and improve the productivity without causing defects such as cracks.

Moreover, after the temperature rise in the furnace is started again, the furnace temperature is preferably raised so that the temperature difference between the central portion and the outer peripheral portion of the honeycomb formed body is within 100 ° C. (Claim 3).
In this case, the thermal stress caused by the temperature difference between the inside and outside of the honeycomb formed body can be reduced, and cracking of the honeycomb formed body during firing can be suppressed.

Moreover, it is preferable that the said carbon combustion temperature is 500 degreeC or more (Claim 4).
In this case, the carbon contained in the honeycomb formed body can be burned sufficiently and reliably.

An embodiment of the present invention will be described with reference to FIGS.
In this example, as shown in FIGS. 1 and 2, a honeycomb formed body 1 having a large number of cells 12 surrounded by a honeycomb-shaped partition wall 11 and a cylindrical outer peripheral wall 13 covering the outer peripheral side surface was fired.
The honeycomb formed body 1 is made of a ceramic mainly composed of cordierite, and has a cylindrical shape. The cell 12 has a quadrangular cross-sectional shape.

  The honeycomb formed body of this example is manufactured by extruding a clay-like ceramic material with an extruder, cutting it to a desired length, and then drying it. The size of the honeycomb formed body is a diameter of 160 mm, a length of 100 mm, a partition wall thickness of 0.3 mm, an outer peripheral wall thickness of 0.5 mm, and a cell count of 300 cpi mesh. This size is just an example, and other sizes can be adopted depending on the application.

  In addition, the above ceramic material contains kaolin, fused silica, aluminum hydroxide, alumina, talc, etc., and the cordierite is adjusted so that the chemical composition is finally composed mainly of cordierite. The raw material was mixed with water, and an organic binder, carbon as a pore former, etc. were added and kneaded. In addition, the ceramic material can also change the material contained according to a use.

Next, a specific firing method of the honeycomb formed body will be described.
In this example, a thermocouple is mounted in the honeycomb formed body and the firing furnace, the temperature of the central portion of the honeycomb formed body (center temperature T ₁ ), the temperature of the outer peripheral wall (outer peripheral temperature T ₂ ), and the temperature of the furnace atmosphere (furnace Firing was carried out while measuring the internal temperature T ₃ ).

In the following description of the firing method, FIG. 3 showing a control pattern (firing pattern) of the furnace temperature T ₃ in the actually set firing furnace, the actually measured center temperature T ₁ , and outer peripheral temperature T _2. and it will be described with reference to FIGS. 4 shows the results of the in-furnace temperature T _3. Further, a time lag or a temperature difference is generated between the firing pattern of FIG. 3 and the actual furnace temperature T _{3 of} FIG.

First, the honeycomb formed body is housed in a firing furnace, and the furnace temperature T ₃ is raised from room temperature to 350 ° C. as shown in FIG. 3 (first temperature raising step S1).
Next, the furnace temperature T ₃ is raised from 350 ° C. to the carbon combustion temperature T _C at which carbon contained in the honeycomb formed body can be burned (second temperature raising step S2). In this example, the carbon combustion temperature T _C was set to 600 ° C.

Next, as shown in FIG. 3, the furnace temperature T ₃ is maintained at 600 ° C., which is the carbon combustion temperature T _C , and the carbon contained in the honeycomb formed body is combusted (carbon combustion step S3). In addition, as shown in FIG. 4, the combustion of carbon actually starts from around 550 ° C. At this time, due to the generation of combustion heat due to the combustion of carbon, the center temperature T ₁ and the outer peripheral temperature T ₂ are starting to rise.

Then, the carbon burning step S3, as shown in FIG. 4, center temperature T ₁ and the outer peripheral temperature T ₂ is increased by the carbon combustion heat is higher than the furnace temperature T _3. Then, the outer peripheral temperature T ₂ becomes maximum at the time the outer peripheral peak P. At this time, the outer peripheral temperature T ₂ is 750 ° C., the furnace temperature T ₃ is 600 ° C., and the temperature difference A between the outer peripheral temperature T ₂ and the furnace temperature T ₃ is 150 ° C.

Further, after the outer peripheral peak P, the outer peripheral temperature T ₂ of the outer peripheral portion where carbon is more easily combusted than the central portion starts to slowly decrease. On the other hand, the center temperature T ₁ reaches a maximum with a slight delay from the outer peripheral temperature T ₂ , and then begins to fall slowly. In this example, the temperature difference between the outer peripheral temperature T ₂ and the furnace temperature T ₃ after the outer peripheral peak P is half of the temperature difference A (150 ° C.) at the outer peripheral peak P, that is, 0.5 A (75 ° C.). The temperature rise timing Q was set, and at this temperature rise timing Q, the temperature rise in the furnace temperature T ₃ was started again.

Next, as shown in FIG. 3, the furnace temperature T ₃ is raised from 600 ° _C. which is the carbon combustion temperature T _C to 1400 ° C. (third temperature raising step S4).
Next, the furnace temperature T ₃ is maintained at 1400 ° C. for 25 hours, and the honeycomb formed body is fired (firing step S5).
Next, the furnace temperature T ₃ is cooled from 1400 ° C. to room temperature (cooling step S6).
Thus, firing of the honeycomb formed body was completed.

Next, as a comparative example, in the carbon burning step S3, firing the honeycomb formed body by conventional baking methods heating time Q to start raising the temperature in the furnace temperature T ₃ again differ.
The actually set firing pattern is shown in FIG. 5, and the results of the actually measured center temperature T ₁ , outer peripheral temperature T ₂ and furnace temperature T ₃ are shown in FIG.

In the comparative example, as shown in FIG. 5, when the center temperature T ₁ , the outer temperature T _2, and the furnace temperature T ₃ after the time of the outer peripheral peak P become the same in the carbon combustion step S ₃ , the temperature rising timing Q is set. . Then, at this temperature rise timing Q, the temperature rise in the furnace temperature T ₃ was started again.
Other steps are the same as above.

Next, the effect of the firing method of the honeycomb formed body of this example will be described in comparison with the comparative example.
As is known from FIG. 6, in the comparative example, in the carbon combustion step S3, the temperature rise in the furnace temperature T ₃ is started after the center temperature T ₁ , the outer peripheral temperature T ₂ and the furnace temperature T ₃ become the same. A conventional firing method is used. Therefore, it takes time until the temperature rise timing Q when the furnace temperature T ₃ is maintained at the carbon combustion temperature T _C and then the temperature is raised again, and the time required for the carbon combustion step S 3 is also increased. The total firing time was 90 hours.

On the other hand, as is known from FIG. 4, in this example, in the carbon combustion step S3, the temperature difference between the outer peripheral temperature T ₂ and the furnace temperature T ₃ after the outer peripheral peak P is the temperature difference A at the outer peripheral peak P. When the temperature reaches half (0.5 A), that is, before the combustion of the carbon contained in the honeycomb formed body is completed, the temperature rise in the furnace temperature T ₃ is started. Therefore, the time until the temperature raising timing Q is shortened, and the time required for the carbon combustion step S3 is shortened. The total firing time is 80 hours, which is about 10 hours shorter than that of the comparative example.

Further, in this example, the temperature rise in the furnace temperature T ₃ was started before the combustion of the carbon contained in the honeycomb molded body was completed, but no defects such as cracks were found in the honeycomb molded body. . This is because, at the time of the temperature rise timing Q, the carbon contained in the honeycomb molded body is burned to some extent, so that sudden combustion heat is not generated even when the temperature rise is started. In addition, since the temperature rise is started when the outer peripheral temperature T ₂ decreases and the temperature difference from the center temperature T ₁ begins to open, an effect of suppressing an increase in the inner and outer temperature difference of the honeycomb formed body can be obtained. It was.

Further, in the present example, similarly to the comparative example, the furnace temperature T ₃ is temporarily held at the carbon combustion temperature T _C during the course of raising the furnace temperature T ₃ to the firing temperature, and is contained in the honeycomb formed body. A carbon combustion process for burning carbon is performed. Therefore, carbon can be burned slowly, and generation of rapid combustion heat can be suppressed. As a result, it is possible to prevent the temperature difference between the inside and outside of the honeycomb formed body from becoming abruptly large, and to suppress the occurrence of cracks.

  From the above, it can be seen that according to the method for firing a honeycomb formed body of this example, the firing time can be shortened, productivity can be improved, and cracks during firing can be suppressed.

The perspective view which shows the honeycomb molded object in an Example. Cross-sectional explanatory drawing which shows the honeycomb molded object in an Example. Explanatory drawing which shows the baking pattern in an Example. Explanatory drawing which shows the temperature measurement result in a honeycomb molded object and a furnace in an Example. Explanatory drawing which shows the baking pattern in a comparative example. Explanatory drawing which shows the temperature measurement result in a honeycomb molded object and a furnace in a comparative example.

Explanation of symbols

1 honeycomb formed body 11 partition wall 12 cells 13 outer peripheral wall P periphery peak Q heating timing T ₁ center temperature T ₂ outer circumferential temperature T ₃ furnace temperature T _C carbon combustion temperature

Claims (4)

In a method of firing a honeycomb formed body formed by extruding a ceramic material in which carbon is added to a cordierite raw material, in which partition walls are arranged in a honeycomb shape and a large number of cells are provided,
When the honeycomb formed body is housed in a furnace, the temperature of the furnace atmosphere (hereinafter referred to as the furnace temperature) is raised to the firing temperature, and then the honeycomb formed body is held at the firing temperature for firing. ,
In the middle of raising the furnace temperature to the firing temperature, the furnace temperature is temporarily held at a carbon combustion temperature that is a temperature at which the carbon can be burned, and the carbon contained in the honeycomb formed body is burned. Let
Due to the combustion of the carbon, the temperature at the outer peripheral portion of the honeycomb formed body rises to be higher than the furnace temperature, reaches a maximum, and then decreases in the outer peripheral peak where the temperature at the outer peripheral portion becomes maximum in the process of descending. When the temperature difference between the temperature of the outer peripheral portion and the furnace temperature at the time is A, the time difference between the time when the temperature difference becomes 0.5 A after the outer peripheral peak and before it becomes 0 A method for firing a honeycomb formed article, wherein the temperature rise in the furnace is started again.   2. The temperature increase in the furnace is restarted between the time when the temperature difference becomes 0.5A and the time when the temperature difference becomes 0.25A after the peak of the outer circumference. A method for firing a honeycomb formed body.   In Claim 1 or 2, after the temperature rise in the furnace is started again, the furnace temperature is increased so that the temperature difference between the central portion and the outer peripheral portion of the honeycomb formed body is within 100 ° C. A method for firing a honeycomb formed body, characterized by heating.   The method for firing a honeycomb formed body according to any one of claims 1 to 3, wherein the carbon combustion temperature is 500 ° C or higher.

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