JP2003277155A - Ceramic honeycomb structure and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a honeycomb structure which eliminates the boundary segments between partitions and an outer peripheral wall and prevents the occurrence of cracks by the thermal impact of high-temperature exhaust gas, and to provide a ceramic honeycomb structure having excellent dimensional accuracy at a low cost without forming an external wall section, after fabricating and removing the outer edge of the honeycomb structure. <P>SOLUTION: The ceramic honeycomb structure having a number of cells enclosed by partitions obtained by extrusion molding a ceramic body and firing the molding is fabricated in such a manner that the diameter of at least portions of the outer peripheral wall after the firing decreases. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic honeycomb structure, and more particularly to a ceramic honeycomb structure used for purifying exhaust gas of a diesel engine and a method for manufacturing the same.

[0002]

2. Description of the Related Art Reduction of harmful substances contained in exhaust gas emitted from engines such as automobiles is required from the viewpoint of protection of local environment and global environment. A ceramic honeycomb structure is used for a filter for collecting fine particles contained in exhaust gas of a diesel engine. In particular, a filter for collecting fine graphite particles contained in exhaust gas of a diesel engine is required to have a large honeycomb structure having an outer peripheral wall having an outer diameter of at least 125 mm or more. But,
Large-sized honeycomb structure, when extruding the ceramic kneaded material into a molded body, the molded body cannot support its own weight because its own weight is too large or the strength of the molded body is insufficient, or The outer peripheral wall of the molded body is deformed at the time of handling of transfer and movement until the drying of the molded body is completed, or along with this, the partition wall near the outer peripheral wall is deformed or crushed,
There is a problem that a predetermined dimensional accuracy after firing cannot be obtained. Also, it deforms due to expansion and contraction associated with drying and firing,
There is a problem that the dimensional accuracy is deteriorated and a predetermined dimensional accuracy after firing cannot be obtained.

In order to solve this, Japanese Patent Laid-Open No. 3-2753
No. 09 discloses that after the ceramic clay is extruded, dried and fired to obtain a fired body having a honeycomb structure, an outer peripheral wall of the fired body having the honeycomb structure and its peripheral portion (hereinafter referred to as “outer edge portion”) are predetermined. Grinding process to make the diameter smaller than
Disclosed is a method for manufacturing a honeycomb structure in which a coating material is applied to a ground portion, dried, and cured. According to this Japanese Patent Laid-Open No. 3-275309, the partition walls which are deformed at the peripheral edge of the outer peripheral wall by grinding are removed, and when the roundness of the outer periphery is low, this is increased to improve the dimensional accuracy. It is said that a honeycomb structure having high dynamic strength can be manufactured.

[0004]

However, the invention described in the above-mentioned Japanese Patent Laid-Open No. 3-275309 is shown in FIG.
The front view is shown in (b), and the coating material is applied, dried, and cured in a separate process on the outer peripheral surface of the honeycomb fired body extruded into a honeycomb structure, as shown in the enlarged view of part B in (a). Since the material properties of the partition wall 23 and the outer peripheral wall 21 are different from each other, such as thermal expansion coefficient, thermal conductivity, strength, Young's modulus, etc., the interface 25 between them is accompanied by coating, drying and curing of the coating material. Residual stress is generated.
In this phenomenon, even if the same material is used for the partition wall 23 and the outer peripheral wall 21, since the partition wall 23 is formed by extrusion molding and the outer peripheral wall 21 is formed by coating, the material characteristics of both are completely matched. It is difficult to do so, and residual stress occurs due to coating, drying and curing of the coating material. Therefore, when it is used as a carrier for a catalytic converter or as an exhaust gas purification filter for a diesel engine and a thermal shock due to high temperature exhaust gas occurs, the stress at the interface 25 between the partition wall 23 and the outer peripheral wall 21 becomes excessive, and the stress is increased between the two or both. There is a risk that cracks may occur through the holes and propagate to the partition walls. When this crack progresses, the exhaust gas purification efficiency is lowered by passing the exhaust gas through the crack without being purified, or the honeycomb structure gripped by the gripping member in the metal container is damaged or falls off, It has the drawback that it may not be able to be purified. Further, after the peripheral portion of the ceramic honeycomb fired body is processed and removed, the outer peripheral wall portion 21 is formed on the outer peripheral surface, and after that, a drying step, a curing step or a firing step is required. Because it occurs
It has the drawback that the dimensional accuracy cannot be strictly increased, the number of steps is increased, and the manufacturing cost becomes huge.

Therefore, an object of the present invention is to obtain a honeycomb structure which eliminates the interface portion 25 between the partition wall and the outer peripheral wall and prevents cracks from being generated by thermal shock due to high temperature exhaust gas. Another object is to obtain a low-cost honeycomb structure having good dimensional accuracy without forming an outer peripheral wall portion by applying a coating material after processing and removing the outer edge portion of the ceramic honeycomb fired body.

[0006]

In order to solve the above problems, a ceramic honeycomb structure of the present invention is a ceramic honeycomb structure having a large number of cells surrounded by partition walls obtained by extruding a ceramic kneaded material and firing it. In the body
It is characterized in that it is processed so that the diameter of at least part of the outer peripheral wall after firing is reduced. Here, in order to reduce the diameter of at least a part of the outer peripheral wall after firing, it is necessary to form the outer peripheral wall thickness of the honeycomb formed body and / or the honeycomb fired body to be thicker than the outer peripheral wall thickness of the honeycomb structure. There is. By forming the honeycomb structure thicker than the outer peripheral wall thickness, the strength of the honeycomb formed body is increased, and the honeycomb formed body is deformed by its own weight, or is deformed during the transfer or movement handling until the drying of the formed body is completed. Can be reduced. Therefore, it is possible to reduce the phenomenon that the partition wall is deformed or crushed due to the deformation of the outer peripheral wall. In addition, since the outer peripheral wall thickness of the honeycomb formed body and / or the honeycomb fired body is formed thicker than the outer peripheral wall thickness of the honeycomb structure and processed and removed, the deformation caused by expansion or contraction during molding, drying, or firing is corrected by the processing. can do. At this time, if the outer peripheral wall thickness of the honeycomb formed body and / or the honeycomb fired body is 110% or more of the outer peripheral wall thickness of the honeycomb structure, deformation due to expansion or contraction that occurs during forming, drying, or firing is reduced. In addition to being able to perform, even if deformation occurs, it can be corrected by processing. The thickness is preferably 120% or more. Further, by integrally forming the outer peripheral wall and the partition wall, since the interface portion between the outer peripheral wall and the partition wall is eliminated and the discontinuous portion of the material characteristics is eliminated, cracks due to thermal shock during use as an exhaust gas purification filter are eliminated. Occurrence can be reduced. Further, since the outer peripheral finishing is performed after firing, the dimensional accuracy is particularly excellent in both diameter and length. Further, it is not necessary to form the outer peripheral wall portion after processing and removing the outer edge portion of the ceramic honeycomb fired body, and all the steps relating to this can be shortened, and a low-cost honeycomb structure can be obtained. Here, the honeycomb formed body is a honeycomb structure before being dried by extruding a ceramic kneaded material, and the honeycomb fired body is obtained by drying and firing the honeycomb formed body,
The honeycomb structure is defined as a honeycomb fired body having a desired product outer diameter dimension as necessary.

Next, a second aspect of the present invention is a method for producing a ceramic honeycomb structure having a large number of cells surrounded by partition walls obtained by extruding a ceramic kneaded material and firing it. Alternatively, in the method for manufacturing a ceramic honeycomb structure, the outer peripheral wall of the fired body is formed thicker than the outer peripheral wall of the structure, and at least a part of the outer peripheral wall is processed and removed after firing. Here, if the outer peripheral wall thickness of the honeycomb formed body and / or the honeycomb fired body is formed to be 110% or more of the outer peripheral wall thickness of the honeycomb structure, deformation due to expansion or contraction that occurs during forming, drying, or firing can be reduced. In addition to being able to do, it can be corrected by processing. The thickness is preferably 120% or more.
Incidentally, the extrusion molding is generally performed in a lateral or downward direction of the molded body, but when extruded downward, particularly in the direction of gravity, the partition wall and the outer peripheral wall are continuous in the direction of gravity. This is preferable because the influence of the weight of the outer peripheral wall on the deformation of the partition wall can be further reduced. Furthermore, as the ceramic material constituting the ceramic honeycomb structure of the present invention, the present invention is mainly used as a carrier of an exhaust gas purifying catalyst for an automobile engine or for removing fine particles in an exhaust gas of a diesel engine. It is preferable to use a material having excellent heat resistance because it is used as a filter of, and at least one selected from the group consisting of cordierite, alumina, mullite, silicon nitride, silicon carbide and LAS is the main crystal. It is preferable to use a ceramic material. Among them, the ceramic honeycomb structure having cordierite as a main crystal is most preferable because it is inexpensive, has excellent heat resistance and corrosion resistance, and has low thermal expansion.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. FIG. 1 shows a honeycomb structure 10 according to an embodiment of the present invention, where (a) is a front view, (b) is a sectional view taken along line BB in (a), and (c) is A in (a). FIG.
In FIG. 1, the honeycomb structure 10 has an outer peripheral wall 11 and a large number of cells 14 surrounded by partition walls 13 on the inner peripheral side of the outer peripheral wall 11.

In this honeycomb structure 10, the outer peripheral wall 11 and the partition wall 13 are integrally formed, the interface portion between the outer peripheral wall 11 and the partition wall 13 is eliminated, and cracks are generated by thermal shock when used as an exhaust gas purification filter. To prevent it from happening.

Next, a method for manufacturing the above-mentioned honeycomb structure 10 will be described with reference to the process chart of FIG. In FIG.
(1) to (5) show manufacturing steps, and (2a), (4)
Reference symbols a) and (5a) show a honeycomb formed body, a honeycomb fired body, and a honeycomb structure formed in the immediately preceding manufacturing process. (1) First, powders of kaolin, talc, alumina, silica, etc. are prepared to obtain cordierite-forming raw material powder. In addition, the cordierite-forming raw material powder contains a molding aid,
Add an appropriate amount of pore-forming agent and mix well by dry method. Next, a specified amount of water is poured and kneading is further performed to refine the ceramic kneaded clay.

(2) Next, the ceramic kneaded material is extruded in the direction of gravity with an extrusion die. In extrusion molding,
The formed body or the honeycomb dried body that has been dried and fired thereafter is formed so that the outer peripheral wall is thicker than the outer wall thickness of the ceramic honeycomb structure. In FIG. 3, (a) is a cross-sectional view of a main part of the extrusion molding die 50, and (b) is a front view of a part of the molded body 10 ′. Further, (c) is a front view of a part of the fired body 10 ″ after the molded body shown in (b) is dried and fired.

As shown in FIG. 3 (a), the extrusion molding die 50 has a large number of supply passages 51a and discharge passages 51 for collecting kneaded clay from the supply passages 51a and forming a lattice shape.
The die 51 having b, the masking plate 52 for adjusting the amount of kneaded material with the inner diameter Dm, the amount of discharged kneaded material, and the thickness t, the inner diameter Ds, and the protruding amount w are adjusted to form The outer peripheral wall 11 ′ of the body 10 ′ is composed of a pressing frame 53 and the like that is thickly formed in a predetermined shape. It should be noted that the extrusion molding die 50 includes the supply passage 51a to the discharge passage 5 in FIG.
The direction toward 1b is the extrusion direction. Passage 5 for supplying clay
By extruding from 1a to the discharge passage 51b, a molded body 1 having an outer peripheral wall 11 'and a large number of cells 14 surrounded by partition walls 13 in the outer peripheral wall 11' as shown in FIG. 3 (b).
0'is obtained ((2a) in FIG. 2). Note that FIG. 3 (b)
11a indicates the outer diameter of the completed honeycomb structure, 11t ′ indicates the outer peripheral wall thickness of the honeycomb formed body, and 11t indicates the outer peripheral wall thickness of the completed honeycomb structure. Then, the molded body 10 'is extruded and the molded body is extruded in the direction of gravity through the molding die 50,
A cutting device (not shown) cuts to a predetermined length.

(3) Then, the molded body 10 'is put in a microwave dryer and heated to be dried, so that the water content in the molded body 10' is evaporated. (4) Next, the molded body 10 'is put in a firing furnace and gradually heated to be fired, and as shown in FIG.
As a result, a honeycomb fired body 10 ″ having a thick outer peripheral wall having a large number of cells 14 ″ surrounded by partition walls 13 ″ in the outer peripheral wall 11 ″ can be obtained (4a in FIG. 2). Note that FIG. 3 (c)
11a indicates the outer diameter of the completed honeycomb structure, 11t indicates the outer peripheral wall thickness of the completed honeycomb structure, and 11t ″ indicates the outer peripheral wall thickness of the honeycomb fired body.

(5) Next, the honeycomb fired body is gripped and rotated by a processing jig on a cylindrical grinder, and the honeycomb fired body is cut and fed by a grinding wheel to form a honeycomb outer peripheral wall 11a "after firing. The outer diameter of the structure is processed to obtain a ceramic honeycomb structure ((5a) in Fig. 2.) Through the above steps, the outer peripheral wall thickness 11t 'of the ceramic honeycomb molded body 10' and / or the fired body 10 ", Since 11t ″ is formed to be thicker than the desired outer peripheral wall thickness 11t of the ceramic honeycomb structure 10, the outer peripheral wall and the partition walls near the outer peripheral wall are not deformed between the extrusion molding and the drying step, and further, the outer peripheral wall is not deformed. Since the outer peripheral wall surface of the honeycomb fired body having a thick wall is processed, the ceramic honeycomb structure 10 having excellent dimensional accuracy can be obtained, and the outer edge of the ceramic honeycomb fired body can be obtained. The after processing removed, there is no need to form the outer peripheral wall portion 21 by applying a coating material, it is possible to form a ceramic honeycomb structure at a low cost.

(Example) A molding aid was added to a raw material powder of cordierite-based ceramics, thoroughly mixed in a dry system, and a prescribed amount of water was injected to perform sufficient mixing. Next, using the extrusion molding die 50 shown in FIG. 3, extrusion molding is performed in the vertical direction in a known extrusion molding apparatus, and further cut to obtain the outer peripheral wall 11 ′.
Various molded bodies 10 'in which a large number of cells 14' were integrally formed by partition walls 13 'were manufactured by changing the thickness of the outer peripheral wall 11'. Next, the molded body 10 'is dried to about 1
The temperature was raised to about 400 ° C. and firing was performed to obtain a fired body having an outer peripheral wall thickness as shown in Table 1. The outer peripheral wall 11t "after firing was removed by a cylindrical grinder to obtain a diameter φ267 of Examples 1 to 4 of the present invention.
The honeycomb structure 10 having a size of 10 mm is used. The partition wall thickness 13t of the obtained honeycomb structure was 0.3 mm, the cell pitch 13p was 1.5 mm, and the total length L was 300 mm.

On the other hand, the outer peripheral wall and the partition wall are integrally molded to form the outer peripheral wall of the molded body so that the outer peripheral wall thickness after firing is 1.0 mm, and then the outer peripheral wall is dried and fired. Unprocessed diameter φ267 mm, total length L 300 mm,
Partition thickness 13t 0.3 mm, cell pitch 13p 1.5
Comparative Example 1 was manufactured by manufacturing a honeycomb fired body having an outer peripheral wall thickness of 11 mm. Further, the above-mentioned Japanese Patent Laid-Open No. 3-2
According to the method for manufacturing a honeycomb structure described in Japanese Patent No. 75309, a ceramic kneaded material is extruded, dried and fired to obtain a honeycomb fired body, and an outer edge portion thereof is ground to 3 m.
The coating material is applied to the part that has been removed and ground.
A honeycomb structure having a diameter of 267 mm, an overall length L of 300 mm, a partition wall thickness of 13 t of 0.3 mm, and a cell pitch of 13 p of 1.5 mm, which was dried and cured to form an outer peripheral wall, was prepared and used as Comparative Example 2. And the invention examples 1-4 and the comparative example 1,
Regarding No. 2, the outer peripheral wall thickness of the honeycomb fired body was “outer wall thickness of the fired body”, the outer peripheral wall thickness of the honeycomb structure was “structure outer peripheral wall thickness”, and the diameters of 12 locations in the circumferential direction on the outer peripheral surface of the honeycomb structure were measured. The variation is "roundness", the number of steps from the honeycomb fired body to the honeycomb structure is "the number of steps after firing", and the thermal shock test result is "thermal shock temperature (Δt ° C)".
Are shown in Table 1. However, regarding the outer peripheral wall thickness of the structure, Comparative Example 1 is the outer peripheral wall thickness of the honeycomb fired body, and Comparative Example 2 is the outer peripheral wall thickness after grinding the outer edge portion of the honeycomb fired body and applying and drying the coating material, that is, coating. The thickness, Examples 1 to 4 of the present invention refer to the outer peripheral wall thickness after the outer peripheral wall of the honeycomb fired body is processed and removed. Regarding the roundness evaluation, the roundness was less than 0.2 mm and was good (○), and the roundness was 0.2 to 0.5 mm and there was no problem in practical use (△), 0.
Those that exceed 5 mm and cannot be actually used are indicated by (x). Further, the number of steps after firing is 0 because Comparative Example 1 does not have a processing step after the fired body, and Comparative Example 2 has the steps of processing the outer edge of the fired body, coating the outer periphery, and drying the outer periphery. Therefore, the number of processes is 3, and the number of processes is set to 1 in Examples 1 to 4 because a process removing process of the outer peripheral portion of the fired body is added. The thermal shock temperature was determined by holding the ceramic honeycomb structure in an electric furnace heated to a constant temperature for 30 minutes, then rapidly cooling it to room temperature, and measuring the temperature difference between the heating temperature and the room temperature when cracks were visually detected. It was evaluated as a thermal shock temperature. When no crack was found, the temperature was raised to 25 ° C. and the same test was conducted, and the process was repeated until a crack was generated. The number of tests is 3 each
The average value is shown.

[0017]

[Table 1]

From Table 1, in the honeycomb structures of Examples 1 to 4 of the present invention, the outer peripheral wall and the partition wall are integrally formed, and since there is no interface portion between the outer peripheral wall and the partition wall, cracks due to thermal shock are generated. We were able to reduce the occurrence. In addition, the circularity of Examples 1 to 4 of the present invention is extremely good, and the honeycomb structures of Examples 1 to 4 of the present invention have the outer peripheral wall portion after processing and removing the outer edge portion of the ceramic honeycomb fired body as in Comparative Example 2. Because there is no need to form
The number of steps after firing is only one step for processing the outer peripheral wall, and it can be manufactured at a lower cost than in Comparative Example 2. On the other hand, in the honeycomb structure of Comparative Example 1, since the outer peripheral wall of the fired ceramic honeycomb body was not processed, it was not possible to obtain a ceramic honeycomb structure having poor roundness and good dimensional accuracy. Further, in the honeycomb structure of Comparative Example 2, it is necessary to form the outer peripheral wall portion after processing and removing the outer edge portion of the ceramic honeycomb fired body, and the number of steps after firing increases,
Generation of cracks due to thermal shock could not be prevented, and a ceramic honeycomb structure with good dimensional accuracy could not be obtained.

[0019]

As described above in detail, according to the honeycomb structure of the present invention, since the partition wall and the outer peripheral wall are integrally formed of the same material, there is no interface portion between the partition wall and the outer peripheral wall, and the material characteristics are improved. Since there is no discontinuous portion, it is possible to prevent cracks from occurring due to thermal shock due to high temperature exhaust gas. Further, according to the method for manufacturing a honeycomb structure of the present invention, there is no need to form the outer peripheral wall portion after processing and removing the outer edge portion of the ceramic honeycomb fired body, and a honeycomb structure excellent in dimensional accuracy is obtained at low cost. You can

[Brief description of drawings]

FIG. 1 is a honeycomb structure 10 of an embodiment,
(A) is a front view, (b) is a BB sectional view of (a),
(C) is an enlarged view of part A in (a).

FIG. 2 is a process drawing showing the method for manufacturing the honeycomb structure 10 of the example.

3A is a cross-sectional view of a main part of an extrusion molding die 50, and FIG. 3B is a front view of a part of a molded body (10).
(C) is a front view of a part of the fired body (100) after drying and firing the molded body shown in (b).

FIG. 4 shows an example of a conventional honeycomb structure, (a) is a front view thereof, and (b) is an enlarged view of a B part in (a).

[Explanation of symbols]

10: Honeycomb structure (ceramic honeycomb structure) 10 ': molded body 10 ": fired body 11, 21: Outer peripheral wall 11 ': outer peripheral wall of the molded body 11 ": outer peripheral wall of the fired body 11a, 21a: outer diameter 11a ': outer diameter of molded body 11a ": outer diameter of fired body 11t: Outer wall thickness 11t ': outer peripheral wall thickness of the molded body 11t ": outer peripheral wall thickness of the fired body 12, 22: End face 13, 23: partition wall 13 ': Partition wall of molded body 13 ": Partition of the fired body 13t: Partition thickness 13p: Cell pitch 14, 24: Cell 14 ': Cell of molded body 14 ": fired cell 20: Conventional honeycomb structure 25: Interface part 50: Mold for extrusion molding 51: Die 51a: Supply passage 51b: discharge passage 52: Masking plate 53: Holding frame Dm: Inner diameter Ds: Inner diameter L: Total length t: thickness of the holding frame w: amount of protrusion

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Claims (2)

[Claims] 1. A ceramic honeycomb structure having a large number of cells surrounded by partition walls, which is obtained by extruding a ceramic kneaded material and firing it, and processing it so that at least a part of the outer peripheral wall after firing has a reduced diameter. A ceramic honeycomb structure characterized by comprising: 2. In a method for producing a ceramic honeycomb structure having a large number of cells surrounded by partition walls, which is obtained by extruding a ceramic kneaded clay and firing it, the outer wall thickness of the formed body and / or the fired body is A method for manufacturing a ceramic honeycomb structure, which is characterized in that it is formed thicker than a desired outer peripheral wall thickness, and after firing, at least a part of the outer peripheral wall portion is processed and removed.