JP4372760B2 - Ceramic filter assembly and manufacturing method thereof - Google Patents

Description

  The present invention relates to a ceramic filter assembly having a structure in which a plurality of filters made of a ceramic sintered body are bonded and integrated, and a method for manufacturing the same.

  The number of automobiles has increased dramatically since the beginning of this century, and the amount of exhaust gas emitted from the automobile's internal combustion engine has been increasing rapidly. In particular, various substances contained in exhaust gas emitted from a diesel engine cause pollution, and are now having a serious impact on the world environment. Recently, research results have reported that particulates (diesel particulates) in exhaust gas sometimes cause allergic disorders and a decrease in the number of sperm. In other words, taking measures to remove particulates in exhaust gas is considered an urgent issue for humanity.

  Under such circumstances, various types of exhaust gas purification apparatuses have been proposed. A general exhaust gas purifying apparatus has a structure in which a casing is provided in the middle of an exhaust pipe connected to an exhaust manifold of an engine, and a filter having fine holes is disposed therein. As a material for forming the filter, there are ceramics in addition to metals and alloys. As a typical example of a filter made of ceramic, a honeycomb filter made of cordierite is known. Recently, there are advantages such as high heat resistance, mechanical strength, high collection efficiency, chemical stability, low pressure loss, etc., so use porous silicon carbide sintered body as a filter forming material. There are many.

  The honeycomb filter has a large number of cells extending along its own axial direction. As the exhaust gas passes through the filter, particulates are trapped by the cell walls. As a result, fine particles are removed from the exhaust gas.

  However, a honeycomb filter made of a porous silicon carbide sintered body is vulnerable to thermal shock. Therefore, the larger the size is, the easier the cracks are generated in the filter. Therefore, as a means for avoiding breakage due to cracks, a technique has recently been proposed in which a plurality of small filter pieces are integrated to produce one large ceramic filter assembly.

  A general method for manufacturing the above-described assembly will be briefly introduced. First, a rectangular column-shaped honeycomb formed body is formed by continuously extruding a ceramic raw material through a mold of an extruder. After the honeycomb formed body is cut into equal lengths, the cut piece is fired to obtain a filter. After the firing step, the plurality of filters are bundled and integrated by bonding the outer peripheral surfaces of the filters through a ceramic sealing material layer. As a result, a desired ceramic filter assembly is completed.

  A mat-like heat insulating material made of ceramic fiber or the like is wound around the outer peripheral surface of the ceramic filter assembly. In this state, the assembly is accommodated in a casing provided in the middle of the exhaust pipe.

  By the way, the conventional ceramic filter aggregate has a rectangular cross section as a whole. On the other hand, the present applicant has proposed a technique (unpublished) prior to the present application to cut the outer shape of the aggregate so as to make the cross section approximately circular or cross section approximately oval as a whole.

  However, in the above-mentioned prior proposed technique, the filter has a large number of cells. Therefore, when the outer shape of the aggregate is cut, the cell wall is exposed on the outer peripheral surface of the newly exposed aggregate, resulting in the outer peripheral surface. Concavities and convexities are formed on the surface. Therefore, even if the aggregate is accommodated in the casing with the heat insulating material provided on the outer peripheral surface, it is inevitable that a gap is generated along the filter longitudinal direction. For this reason, the exhaust gas easily leaks through the gap, and there has been a problem that the processing efficiency of the exhaust gas is lowered.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a ceramic filter assembly in which leakage of fluid on the outer peripheral surface hardly occurs.

  In order to solve the above-described problems, in the present invention, the respective filters are integrated by bonding the outer peripheral surfaces of a plurality of filters made of a porous ceramic sintered body through a ceramic sealing material layer. It is an aggregate, and the cell wall is partially exposed by being externally cut into a substantially circular cross section or a substantially elliptical cross section as a whole, and from the ridges and grooves extending along the axial direction of the aggregate An uneven surface layer made of a ceramic material is formed on the outer peripheral surface that has the uneven surface, and the uneven surface is filled with the uneven surface layer, and the end of the uneven surface layer in the filter axial direction is A ceramic filter assembly having a curved surface shape with a curvature radius R = 0.1 mm to 10 mm is proposed.

  In the present invention, the unevenness eliminating layer has a thickness of 0.1 mm to 10 mm, the sealing material layer is formed to be thinner than the unevenness eliminating layer, and the unevenness eliminating layer is formed of the sealing material layer. It can be a more effective means that the filter is formed using the same material as that of the filter, and the filters are arranged in a state of being shifted from each other along a direction orthogonal to the filter axial direction.

  In order to solve the above-mentioned problem, in the present invention, a ceramic filter formed by integrating the outer peripheral surfaces of a plurality of filters made of a porous ceramic sintered body by bonding them through the ceramic sealing material layer. The assembly is manufactured, and the outer shape of the ceramic filter assembly is cut into a substantially circular cross section or a substantially elliptical cross section as a whole, and the cell wall of the filter exposed by the outer shape cut is partially exposed on the filter outer peripheral surface. The unevenness-resolving layer forming paste made of ceramic is applied to the outer peripheral surface of the ceramic filter assembly that has unevenness composed of protrusions and grooves extending along the axial direction of the assembly. Then, a method for manufacturing a ceramic honeycomb filter assembly is proposed in which an unevenness eliminating layer is formed.

  In the method of the present invention, the unevenness eliminating layer has an end portion in the filter axial direction having a curved shape with a curvature radius R = 0.1 mm to 10 mm, and the thickness of the unevenness eliminating layer is 1 mm to 10 mm, the unevenness eliminating layer is formed using the same material as the sealing material layer, and the filter is disposed in a state of being shifted from each other along a direction orthogonal to the filter axial direction. It is preferable.

  According to the present invention, the unevenness is filled with the unevenness eliminating layer, so that the outer peripheral surface of the aggregate becomes flat. Accordingly, it becomes difficult to form a gap on the outer peripheral surface when the assembly is accommodated. Moreover, since this uneven | corrugated elimination layer consists of ceramics, it is excellent in adhesiveness and heat resistance with the filter which consists of a porous ceramic sintered compact.

  According to the present invention, since the end portion in the filter axis direction of the unevenness eliminating layer has a curved surface shape with a predetermined radius of curvature, the concentration of stress generated by the heat cycle during use is alleviated. Therefore, it is possible to avoid stress concentration at one point, and it is possible to prevent the occurrence of cracks in the unevenness eliminating layer. That is, when the radius of curvature R is less than 0.1 mm, the stress generated by the heat cycle during use tends to concentrate on one end of the unevenness eliminating layer, and in some cases, cracks occur at the end of the unevenness eliminating layer. May occur. On the other hand, when the curvature radius R exceeds 10 mm, the thickness of the end portion of the unevenness eliminating layer is reduced, and as a result, the original function of preventing fluid leakage may be impaired.

  According to the present invention, it is possible to reliably prevent fluid leakage as long as it is not difficult to manufacture the assembly. If the unevenness eliminating layer is too thin, the unevenness on the outer peripheral surface of the aggregate cannot be completely filled, and a gap still tends to remain there. On the other hand, if the unevenness eliminating layer is made thick, it may be difficult to form the same layer or the entire assembly may be increased in diameter.

  According to the present invention, by forming the sealing material layer so as to be thinner than the unevenness eliminating layer, it is possible to prevent a decrease in filtration capacity and thermal conductivity. In addition, since the unevenness eliminating layer is formed using the same material as the sealing material layer, cracks are unlikely to occur at the boundary between the unevenness eliminating layer and the sealing material layer. In addition, since it is not necessary to prepare a different material from the material for forming the sealing material layer, the assembly can be easily manufactured and the cost can be avoided.

  Furthermore, according to the present invention, by disposing the filters in a state of being shifted from each other in advance, it is difficult for the filters to be displaced during use, so that the breaking strength of the aggregate is improved. Moreover, as a result of improving the thermal conductivity along the radial direction of the aggregate, it becomes difficult to produce a temperature difference between the outer peripheral portion and the central portion of the aggregate.

  As described in detail above, (1) according to the present invention, it is possible to provide a ceramic filter assembly in which fluid leakage hardly occurs on the outer peripheral surface.

(2) According to the present invention, fluid leakage can be reliably prevented within a range in which the assembly is not difficult to manufacture.

(3) According to the present invention, it is possible to prevent generation of cracks and fluid leakage in the unevenness eliminating layer and fluid leakage.

(4) According to the present invention, it is possible to prevent a decrease in filtration capacity and thermal conductivity.

(5) According to the present invention, it is possible to prevent fluid leakage at the boundary portion between the unevenness eliminating layer and the sealing material layer, facilitate manufacture of the assembly, and prevent cost increase of the assembly.

(6) According to the present invention, it is possible to improve the breaking strength of the aggregate and to equalize the heat.

  DESCRIPTION OF EMBODIMENTS Hereinafter, an exhaust gas purification device 1 for a diesel engine according to an embodiment of the present invention will be described in detail with reference to FIGS.

  As shown in FIG. 1, this exhaust gas purification device 1 is a device for purifying exhaust gas discharged from a diesel engine 2 as an internal combustion engine. The diesel engine 2 includes a plurality of cylinders (not shown). Each cylinder is connected with a branch portion 4 of an exhaust manifold 3 made of a metal material. Each branch portion 4 is connected to one manifold body 5. Therefore, the exhaust gas discharged from each cylinder is concentrated in one place.

  A first exhaust pipe 6 and a second exhaust pipe 7 made of a metal material are disposed on the downstream side of the exhaust manifold 3. The upstream end of the first exhaust pipe 6 is connected to the manifold body 5. Between the 1st exhaust pipe 6 and the 2nd exhaust pipe 7, the cylindrical casing 8 which consists of a metal material is arrange | positioned. The upstream end of the casing 8 is connected to the downstream end of the first exhaust pipe 6, and the downstream end of the casing 8 is connected to the upstream end of the second exhaust pipe 7. It can also be understood that the casing 8 is disposed in the middle of the exhaust pipes 6 and 7. As a result, the internal regions of the first exhaust pipe 6, the casing 8, and the second exhaust pipe 7 communicate with each other, and the exhaust gas flows therethrough.

  As shown in FIG. 1, the casing 8 is formed so that the central portion thereof has a larger diameter than the exhaust pipes 6 and 7. Therefore, the inner area of the casing 8 is wider than the inner areas of the exhaust pipes 6 and 7. A ceramic filter assembly 9 is accommodated in the casing 8.

  A heat insulating material 10 is disposed between the outer peripheral surface of the assembly 9 and the inner peripheral surface of the casing 8. The heat insulating material 10 is a mat-like material formed including ceramic fibers, and the thickness thereof is several mm to several tens mm. The heat insulating material 10 preferably has a thermal expansibility. The term “thermal expansibility” as used herein means that it has a function of releasing thermal stress because it has an elastic structure. The reason is to minimize energy loss during regeneration by preventing heat from escaping from the outermost periphery of the assembly 9. In addition, the ceramic fiber is expanded by heat at the time of regeneration, thereby preventing the displacement of the ceramic filter assembly 9 caused by exhaust gas pressure or vibration due to running.

  Since the ceramic filter assembly 9 used in the present embodiment removes diesel particulates as described above, it is generally called a diesel particulate filter (DPF). As shown in FIGS. 2 and 3, the assembly 9 of the present embodiment is formed by bundling and integrating a plurality of filters F1. The filter F1 located in the central portion of the assembly 9 has a quadrangular prism shape, and its outer dimensions are 33 mm × 33 mm × 167 mm. Around the square columnar filter F1, a plurality of non-square columnar filters F1 are arranged. As a result, a cylindrical ceramic filter assembly 9 (diameter around 135 mm) is configured as a whole.

  These filters F1 are made of a porous silicon carbide sintered body which is a kind of ceramic sintered body. The reason for adopting the silicon carbide sintered body is that it has an advantage of being particularly excellent in heat resistance and thermal conductivity as compared with other ceramics. As a sintered body other than silicon carbide, for example, a sintered body such as silicon nitride, sialon, alumina, cordierite, and mullite can be selected.

  As shown in FIG. 3 and the like, these filters F1 are so-called honeycomb structures. The reason for adopting the honeycomb structure is that there is an advantage that the pressure loss is small even when the amount of collected fine particles is increased. In each filter F1, a plurality of through holes 12 having a substantially square cross section are regularly formed along the axial direction. Each through hole 12 is partitioned from each other by a thin cell wall 13. On the outer surface of the cell wall 13, an oxidation catalyst composed of a platinum group element (for example, Pt or the like), other metal elements and oxides thereof is supported. The opening of each through-hole 12 is sealed with a sealing body 14 (here, a porous silicon carbide sintered body) on either one of the end faces 9a and 9b side. Accordingly, the end faces 9a and 9b as a whole have a checkered pattern. As a result, a large number of cells having a square cross section are formed in the filter F1. The cell density is set to about 200 cells / inch, the thickness of the cell wall 13 is set to about 0.3 mm, and the cell pitch is set to about 1.8 mm. Of the many cells, about half of the cells open at the upstream end surface 9a, and the remaining cells open at the downstream end surface 9b.

  The average pore diameter of the filter F1 is preferably 1 μm to 50 μm, more preferably 5 μm to 20 μm. When the average pore diameter is less than 1 μm, clogging of the filter F1 due to accumulation of fine particles becomes significant. On the other hand, if the average pore diameter exceeds 50 μm, fine particles cannot be collected, and the collection efficiency is lowered.

  The porosity of the filter F1 is preferably 30% to 70%, more preferably 40% to 60%. If the porosity is less than 30%, the filter F1 becomes too dense, and there is a possibility that the exhaust gas cannot be circulated inside. On the other hand, if the porosity exceeds 70%, the filter F1 has too many voids, so that the strength becomes weak and the collection efficiency of fine particles may be reduced.

  As shown in FIGS. 2 and 3, the outer peripheral surfaces of a total of 16 filters F <b> 1 are bonded to each other via a ceramic sealing material layer 15. Here, the ceramic sealing material layer 15 of the present embodiment will be described in detail.

  The sealing material layer 15 is composed of at least an inorganic fiber, an inorganic binder, an organic binder, and inorganic particles, and binds the inorganic fibers and the inorganic particles that are three-dimensionally crossed to each other via the inorganic binder and the organic binder. It is desirable to form using a sealing material made of an elastic material.

  Examples of the inorganic fiber contained in the sealing material include at least one ceramic fiber selected from silica-alumina fiber, mullite fiber, alumina fiber, and silica fiber. Among these, it is particularly desirable to select a silica-alumina ceramic fiber. This is because the silica-alumina ceramic fiber is excellent in elasticity and absorbs thermal stress.

  In this case, the content of the silica-alumina ceramic fiber in the sealing material is 10% by weight to 70% by weight, preferably 10% by weight to 40% by weight, and more preferably 20% by weight to 30% by weight. It is because the effect as an elastic body will fall that content is less than 10 weight%. On the other hand, if the content exceeds 70% by weight, the thermal conductivity is lowered and the elasticity is lowered.

  The shot content in the silica-alumina ceramic fiber is 1 wt% to 10 wt%, preferably 1 wt% to 5 wt%, more preferably 1 wt% to 3 wt%. This is because it is difficult to make the shot content less than 1% by weight. On the other hand, if the shot content exceeds 50% by weight, the outer peripheral surface of the filter F1 is damaged.

  The fiber length of the silica-alumina ceramic fiber is 1 mm to 100 mm, preferably 1 mm to 50 mm, more preferably 1 mm to 20 mm. This is because the elastic structure cannot be formed when the fiber length is less than 1 mm. This is because if the fiber length exceeds 100 mm, the fiber becomes like a pill and the dispersibility of the inorganic fine particles deteriorates. Moreover, it becomes impossible to make the sealing material layer 15 thin, resulting in a decrease in thermal conductivity between the filters F1.

The inorganic binder contained in the sealing material is preferably at least one colloidal sol selected from silica sol and alumina sol. Among these, it is desirable to select silica sol. This is because silica sol is easy to obtain and easily becomes SiO ₂ by firing, and is therefore suitable as an adhesive in a high temperature region. Moreover, silica sol is excellent in insulation.

  In this case, the content of the silica sol in the sealing material is 1 to 30% by weight, preferably 1 to 15% by weight, more preferably 5 to 9% by weight in terms of solid content. This is because if the content is less than 1% by weight, the adhesive strength is lowered. Conversely, if the content exceeds 30% by weight, the thermal conductivity is reduced.

  The organic binder contained in the sealing material is preferably a hydrophilic organic polymer, and more preferably at least one polysaccharide selected from polyvinyl alcohol, methylcellulose, ethylcellulose, and carbomethoxycellulose. Among these, it is desirable to select carboxymethyl cellulose in particular. The reason for this is that carboxymethylcellulose exhibits excellent adhesiveness in the normal temperature region in order to impart suitable fluidity to the sealing material.

  In this case, the content of carboxymethyl cellulose in the sealing material is 0.1 wt% to 5.0 wt%, preferably 0.2 wt% to 1.0 wt%, more preferably 0.4 wt% in terms of solid content. ~ 0.6% by weight. This is because if the content is less than 0.1% by weight, migration cannot be sufficiently suppressed. “Migration” refers to a phenomenon in which the binder in the sealing material moves as the solvent is dried and removed when the sealing material filled between the objects to be sealed is cured. On the other hand, when the content exceeds 5.0% by weight, the organic binder is burned away at a high temperature, and the strength of the sealing material layer 15 is lowered.

  The inorganic particles contained in the sealing material are preferably elastic materials using at least one inorganic powder or whisker selected from silicon carbide, silicon nitride, and boron nitride. This is because such carbides and nitrides have a very high thermal conductivity and contribute to the improvement of the thermal conductivity by interposing on the surface of the ceramic fiber and the surface of the colloidal sol and the inside thereof.

  Among the carbide and nitride inorganic particles, it is particularly preferable to select silicon carbide powder. The reason is that silicon carbide has a property of being easily compatible with ceramic fibers in addition to extremely high thermal conductivity. In addition, in the present embodiment, the filter F1, which is a sealed object, is the same type, that is, made of porous silicon carbide.

  In this case, the content of the silicon carbide powder is 3% by weight to 80% by weight, preferably 10% by weight to 60% by weight, and more preferably 20% by weight to 40% by weight in terms of solid content. This is because if the content is less than 3% by weight, the thermal conductivity of the sealing material layer 15 is reduced. On the other hand, if the content exceeds 80% by weight, the adhesive strength decreases at high temperatures.

  The particle size of the silicon carbide powder is 0.01 μm to 100 μm, preferably 0.1 μm to 15 μm, more preferably 0.1 μm to 10 μm. This is because if the particle size exceeds 100 μm, the adhesive force and the thermal conductivity are reduced. On the other hand, when the particle size is less than 0.01 μm, the cost of the sealing material is increased.

  As shown in FIG. 2 and the like, an unevenness eliminating layer 16 made of a ceramic material is formed on the outer peripheral surface 9c of the ceramic filter assembly 9 of the present embodiment. The unevenness eliminating layer 16 is formed using a ceramic material containing at least ceramic fibers and a binder as its components. The ceramic material preferably contains inorganic particles such as silicon carbide, silicon nitride, boron nitride and the like. As the binder, an inorganic binder such as silica sol or alumina sol may be used, and an organic binder typified by polysaccharides may be used. The ceramic material is preferably one in which ceramic fibers and inorganic particles that cross three-dimensionally are bonded to each other through a binder. The unevenness eliminating layer 16 is preferably formed using the same material as that of the sealing material layer 15, and particularly preferably formed using exactly the same material.

  The thickness of the unevenness eliminating layer 16 is preferably 0.1 mm to 10 mm, more preferably 0.3 mm to 2 mm, and particularly preferably 0.5 mm to 1 mm. This is because if the unevenness eliminating layer 16 is too thin, the unevenness 17 on the outer peripheral surface 9c of the ceramic filter assembly 9 cannot be completely filled, and a gap is likely to remain there. On the contrary, if the unevenness eliminating layer 16 is to be thickened, it is difficult to form the layer or the entire assembly 9 may be increased in diameter.

  In addition, it is preferable that the sealing material layer 15 is formed so as to be thinner than the unevenness eliminating layer 16, and specifically, it is desirable that the sealing material layer 15 be formed in a range of 0.3 mm to 3 mm. This is because, by forming the sealing material layer 15 so as to be thinner than the unevenness eliminating layer 16, it is possible to prevent a decrease in filtration capacity and thermal conductivity.

  By the way, it is preferable that the edge part in the filter axial direction of the uneven | corrugated elimination layer 16 is a curved surface shape (refer the curved surface part 18 shown by FIG. 4). More specifically, it is preferable that the end portion has a curved surface shape with a radius of curvature R = 0.1 mm to 10 mm, and further has a curved surface shape of 0.5 mm to 2 mm.

  When the radius of curvature R is less than 0.1 mm, the stress generated by the heat cycle during use tends to concentrate on one end of the unevenness eliminating layer 16, and in some cases, cracks occur at the end of the unevenness eliminating layer 16. This is because there is a possibility of chipping.

  On the other hand, if the radius of curvature R exceeds 10 mm, the thickness of the end portion of the unevenness eliminating layer 16 is reduced, and as a result, the original function of preventing leakage of exhaust gas may be impaired in some cases.

In addition, the value of the curvature radius R in the curved surface portion 18 is preferably set to be larger as the thickness of the unevenness eliminating layer 16 is larger.
Next, a procedure for manufacturing the ceramic filter assembly 9 will be described with reference to FIG.

  First, ceramic raw material slurry used in the extrusion molding process, sealing paste used in the end face sealing process, sealing material layer forming paste used in the filter bonding process, and unevenness eliminating layer forming used in the unevenness eliminating layer forming process A paste is prepared in advance. When the sealing material layer forming paste is also used for forming the unevenness eliminating layer, the unevenness eliminating layer forming paste need not be prepared.

  As the ceramic raw material slurry, a mixture obtained by kneading a silicon carbide powder with an organic binder and water in predetermined amounts and kneading them is used. As the sealing paste, a silicon carbide powder blended with an organic binder, a lubricant, a plasticizer and water and kneaded is used. As the sealing material layer forming paste (the same applies to the unevenness eliminating layer forming paste), a mixture of inorganic fibers, an inorganic binder, an organic binder, inorganic particles, and water each in a predetermined amount and kneaded is used.

  Next, the ceramic raw material slurry is put into an extruder and continuously extruded through a mold. Thereafter, the extruded honeycomb formed body is cut into equal lengths to obtain a rectangular pillar-shaped honeycomb formed body cut piece. Further, a predetermined amount of sealing paste is filled into one side opening of each cell of the cut piece, and both end faces of each cut piece are sealed.

  Subsequently, the main firing is performed by setting the temperature, time, and the like to predetermined conditions, and the honeycomb formed body cut piece and the sealing body 14 are completely sintered. All of the filters F1 made of a porous silicon carbide sintered body thus obtained are still in the shape of a quadrangular prism at this point.

  In this embodiment, the firing temperature is set to 2100 ° C. to 2300 ° C. in order to set the average pore diameter to 6 μm to 15 μm and the porosity to 35% to 50%. Moreover, the firing time is set to 0.1 hours to 5 hours. Moreover, the atmosphere in the furnace at the time of baking is made into an inert atmosphere, and the pressure of the atmosphere at that time is made into a normal pressure.

  Next, after forming a ceramic base layer on the outer peripheral surface of the filter F1 as necessary, a sealing material layer forming paste is further applied thereon. Then, 16 such filters F1 are used and their outer peripheral surfaces are bonded together to be integrated. At this time, as shown in FIG. 5A, the ceramic filter aggregate 9A has a square cross section as a whole.

  In the subsequent outer shape cutting step, the aggregate 9A having a square cross section obtained through the filter adhering step is ground, and unnecessary portions on the outer peripheral portion are removed to adjust the outer shape. As a result, as shown in FIG. 5B, a ceramic filter assembly 9 having a circular cross section is obtained. Note that the cell wall 13 is partially exposed on the surface newly exposed by the outer shape cut, and as a result, irregularities 17 are formed on the outer peripheral surface 9c. The unevenness 17 that can be formed in the present embodiment is about 0.5 mm to 1 mm, and includes protrusions and grooves extending along the axial direction of the assembly 9 (that is, the longitudinal direction of the filter F1).

  In the subsequent unevenness eliminating layer forming step, the sealing material layer forming paste is used as the unevenness eliminating layer forming paste, and the paste is uniformly applied on the outer peripheral surface 9 c of the assembly 9. Thereafter, a curved surface portion forming step is performed as necessary, and the curved surface portions 18 are formed at both ends of the unevenness eliminating layer 16 in the filter axial direction. Specifically, for example, there is a method in which both ends of the unevenness eliminating layer 16 are brushed slightly by using a brush or the like to remove the portions. Through such a process, not only the curved surface portion 18 having a suitable shape is formed, but also the excess paste protruding from the end surfaces 9a and 9b is removed.

As a result, the ceramic filter assembly 9 shown in FIG. 5C is completed.
Next, the particulate trap action by the ceramic filter assembly 9 will be briefly described.

  Exhaust gas is supplied to the ceramic filter assembly 9 housed in the casing 8 from the upstream end face 9a side. The exhaust gas supplied through the first exhaust pipe 6 first flows into the cell opened at the upstream end face 9a. Next, the exhaust gas passes through the cell wall 13 and reaches the inside of the cell adjacent to the cell wall 13, that is, the cell opened at the downstream end face 9b. Then, the exhaust gas flows out from the downstream end face 9b of the filter F1 through the opening of the cell. However, the fine particles contained in the exhaust gas cannot pass through the cell wall 13 and are trapped there. As a result, the purified exhaust gas is discharged from the downstream end face 9b of the filter F1. The purified exhaust gas further passes through the second exhaust pipe 7 and is finally released into the atmosphere.

Example 1
(1) Wet-mixing 51.5% by weight of α-type silicon carbide powder and 22% by weight of β-type silicon carbide powder, and adding 6.5% by weight and 20% of organic binder (methyl cellulose) and water to the resulting mixture, respectively. It added and knead | mixed by weight%. Next, by adding a small amount of a plasticizer and a lubricant to the kneaded product and further kneading, extrusion-molding was performed to obtain a honeycomb-shaped formed shape.

(2) Next, this generated shaped body was dried using a microwave dryer, and then the through hole 12 of the molded body was sealed with a sealing paste made of a porous silicon carbide sintered body. Next, the sealing paste was dried again using a dryer. Following the end face sealing step, the dried body was degreased at 400 ° C., and then further baked at 2200 ° C. for about 3 hours in an atmospheric argon atmosphere. As a result, a porous and honeycomb-like silicon carbide filter F1 was obtained.

(3) Ceramic fiber (alumina silicate ceramic fiber, shot content 3%, fiber length 0.1 mm to 100 mm) 23.3% by weight, silicon carbide powder 30.3% by weight with an average particle size of 0.3 μm, inorganic binder 7% by weight of silica sol (the equivalent amount of SiO _{2 in} the sol was 30%), 0.5% by weight of carboxymethyl cellulose as an organic binder and 39% by weight of water were mixed and kneaded. By adjusting the kneaded product to an appropriate viscosity, a dual-purpose paste used for both the formation of the sealing material layer 15 and the formation of the unevenness eliminating layer 16 was produced.

(4) Next, the paste is applied uniformly to the outer peripheral surface of the filter F1, and the filter F1 is dried and dried under conditions of 50 ° C. to 100 ° C. × 1 hour with the outer peripheral surfaces of the filter F1 being in close contact with each other. Harden. As a result, the filters F1 are bonded to each other through the sealing material layer 15. Here, the thickness of the sealing material layer 15 was set to 1.0 mm.

(5) Next, an external shape cut was performed to prepare the external shape by preparing the ceramic filter assembly 9 having a circular cross section, and then the above-mentioned combined paste was uniformly applied to the exposed outer peripheral surface 9c. And it dried and hardened on the conditions of 50 to 100 degreeC x 1 hour, the 0.6 mm-thick unevenness elimination layer 16 was formed, and the assembly 9 was completed.

Thereafter, the end portion of the unevenness eliminating layer 16 was uniformly brushed to slightly scrape the portion, thereby forming a curved surface portion 18 having a curvature radius R of about 1 mm.
When each part of the assembly 9 obtained as described above was observed with the naked eye, the unevenness 17 of the outer peripheral surface 9c was almost completely filled with the unevenness eliminating layer 16, and the outer peripheral surface 9c was in a flat state. It was. In addition, no cracks occurred in any of the boundary portion between the unevenness eliminating layer 16 and the filter F1 and the boundary portion between the unevenness eliminating layer 16 and the sealing material layer 15. Therefore, it was suggested that high adhesion and sealability were secured at these boundary portions. Of course, no cracks or chips were observed in the unevenness eliminating layer 16 itself.

Therefore, when the aggregate 9 was accommodated in the casing 8 with the heat insulating material 10 wound, no gap was formed on the outer peripheral surface 9c of the aggregate 9. Further, when exhaust gas was actually supplied, it was found that the exhaust gas did not leak to the downstream side through the gap on the outer peripheral surface 9c. Therefore, according to the present Example, it became clear that exhaust gas can be processed efficiently.
(Example 2)
In Example 2, ceramic fiber (mullite fiber, shot content 5% by weight, fiber length 0.1 mm to 100 mm) 25% by weight, silicon nitride powder 30% by weight with an average particle diameter of 1.0 μm, alumina sol as an inorganic binder (Conversion amount of alumina sol was 20%) 7% by weight, 0.5% by weight of polyvinyl alcohol as an organic binder and 37.5% by weight of alcohol were mixed and kneaded, and the combined paste was used. Otherwise, the ceramic filter assembly 9 was produced in the same manner as in Example 1. The thickness of the unevenness eliminating layer 16 was set to 0.6 mm, and the curvature radius R of the curved surface portion 18 was set to about 1 mm.

  When the same visual observation as in Example 1 was performed, the unevenness 17 on the outer peripheral surface 9 c was almost completely filled with the unevenness eliminating layer 16. In addition, no cracks occurred in any of the boundary portion between the unevenness eliminating layer 16 and the filter F1 and the boundary portion between the unevenness eliminating layer 16 and the sealing material layer 15. Therefore, it was suggested that high adhesion and sealability were secured at these boundary portions. Of course, no cracks or chips were observed in the unevenness eliminating layer 16 itself.

Further, it was found that when the assembly 9 is used, there is no gap on the outer peripheral surface 9c, and no exhaust gas leaks through the gap. Therefore, it became clear that Example 2 can treat exhaust gas efficiently as well as Example 1.
(Example 3)
Example 3 is a ceramic fiber (alumina fiber, shot content 4% by weight,
(Fiber length 0.1 mm to 100 mm) 23% by weight, boron nitride powder 35% by weight with an average particle diameter of 1 μm, alumina sol as an inorganic binder (equivalent amount of alumina sol is 20%) 8% by weight, ethyl cellulose as an organic binder 0. What mixed and kneaded 5 weight% and 35.5 weight% of acetone was used as the said combined paste. Otherwise, the ceramic filter assembly 9 was produced in the same manner as in Example 1. The thickness of the unevenness eliminating layer 16 was set to 0.6 mm, and the curvature radius R of the curved surface portion 18 was set to about 1 mm.

  When the same visual observation as in Example 1 was performed, the unevenness 17 on the outer peripheral surface 9 c was almost completely filled with the unevenness eliminating layer 16. In addition, no cracks occurred in any of the boundary portion between the unevenness eliminating layer 16 and the filter F1 and the boundary portion between the unevenness eliminating layer 16 and the sealing material layer 15. Therefore, it was suggested that high adhesion and sealability were secured at these boundary portions. Of course, no cracks or chips were observed in the unevenness eliminating layer 16 itself.

Further, it was found that when the assembly 9 is used, there is no gap on the outer peripheral surface 9c, and no exhaust gas leaks through the gap. Therefore, it became clear that Example 3 can treat exhaust gas efficiently as well as Example 1.
(Examples 4 and 5)
In Example 4, the thickness of the unevenness eliminating layer 16 was set to 0.4 mm, and the curvature radius R of the curved surface portion 18 was set to about 0.2 mm. Otherwise, the ceramic filter assembly 9 was produced in the same manner as in Example 1.

  In Example 5, the thickness of the unevenness eliminating layer 16 was set to 7 mm, and the curvature radius R of the curved surface portion 18 was set to about 8 mm. Otherwise, the ceramic filter assembly 9 was produced in the same manner as in Example 1.

When these were observed with the same naked eye as in Example 1, no cracks or chips were observed. Further, it was found that when the assembly 9 is used, there is no gap on the outer peripheral surface 9c, and no exhaust gas leaks through the gap. Therefore, it became clear that Examples 4 and 5 can treat exhaust gas efficiently as in Example 1.
(Comparative example)
In the comparative example, the unevenness eliminating layer 16 was not provided on the outer peripheral surface 9c, and the other matters were basically applied to Example 1 to produce a ceramic filter assembly.

  When the same visual observation as in Example 1 was performed, the unevenness 17 remained on the outer peripheral surface 9c. Therefore, it was confirmed that a gap is formed in the outer peripheral surface 9c when the assembly is used, and exhaust gas leaks through the gap. Therefore, it was clear that the exhaust gas treatment efficiency was inferior compared with Examples 1-3.

Therefore, according to the example of the present embodiment, the following effects can be obtained.
(1) In each Example, the unevenness | corrugation 17 is filled with the unevenness | corrugation elimination layer 16, and the outer peripheral surface 9c of the aggregate 9 is in the flat state. Therefore, it is difficult to form a gap in the outer peripheral surface 9c when the assembly 9 is accommodated, and leakage of exhaust gas through the gap is prevented. As a result, it is possible to realize the ceramic filter assembly 9 excellent in exhaust gas processing efficiency, and thus the exhaust gas purification device 1 excellent in exhaust gas processing efficiency.

  Moreover, since this unevenness elimination layer 16 consists of ceramics, it is excellent also in adhesiveness with the filter F1 which consists of a porous ceramic sintered compact, and heat resistance. Therefore, even if the aggregate 9 is exposed to a high temperature of several hundred degrees C., the unevenness eliminating layer 16 is not burned out or deteriorated, and a suitable adhesion strength is maintained.

(2) In each example, since the thickness of the unevenness eliminating layer 16 is set within a preferable range of 0.1 mm to 10 mm, the exhaust gas can be surely leaked within a range in which the manufacture of the assembly 9 is not difficult. Can be prevented.

(3) In each Example, the curvature radius R of the curved-surface part 18 in the uneven | corrugated elimination layer 16 is set to the suitable range of 0.1 mm-10 mm. For this reason, even if stress is generated by a heat cycle during use, the concentration of the generated stress on the end portion of the unevenness eliminating layer 16 is alleviated. Therefore, it is possible to avoid the concentration of stress on the portion, and it is possible to prevent the occurrence of cracks and chips in the unevenness elimination layer 16. For this reason, generation | occurrence | production of the crack etc. in the uneven | corrugated elimination layer 16 can be prevented reliably, preventing generation | occurrence | production of exhaust gas leak.

(4) In each Example, since the sealing material layer 15 is formed so as to be thinner than the unevenness eliminating layer 16, it is possible to prevent a decrease in filtration capacity and thermal conductivity.

(5) In each embodiment, the unevenness eliminating layer 16 is formed using the same material as the sealing material layer 15. For this reason, cracks are unlikely to occur at the boundary portion between the unevenness eliminating layer 16 and the sealing material layer 15 because the thermal expansion coefficients are equal. That is, high adhesiveness, sealing performance, and reliability are ensured at the boundary portion.

  In addition, since it is not necessary to prepare the unevenness eliminating layer forming paste separately from the sealing material layer forming paste, the assembly 9 can be easily manufactured, and the overall cost can be avoided.

(6) In each embodiment, the following materials are used as the material for forming the sealing material layer 15 and the unevenness eliminating layer 16. That is, an elastic material comprising at least an inorganic fiber, an inorganic binder, an organic binder, and inorganic particles, and the three-dimensionally intersecting inorganic fibers and inorganic particles bonded to each other via the inorganic binder and the organic binder. Is used.

  Such materials have the following advantages. That is, sufficient adhesive strength can be expected in both the low temperature range and the high temperature range. Moreover, since this material is an elastic material, even when a thermal stress is applied to the assembly 9, the thermal stress can be reliably released. Furthermore, since this material is excellent in thermal conductivity, heat can be easily and uniformly conducted to the entire assembly 9 and efficient exhaust gas treatment can be realized.

In addition, you may change embodiment of this invention as follows.
The number of combinations of the filters F1 does not have to be 16 as in the above embodiment, and can be any number. In this case, it is of course possible to use a combination of filters F1 having different sizes and shapes as appropriate.

As in another example of the ceramic filter assembly 21 shown in FIG. 6, the filters F1 are preliminarily shifted from each other along the direction orthogonal to the filter axial direction, and the filters F1 are bonded and integrated. Also good. In such a case, the filter F1 is less likely to be displaced when accommodated in the casing 8, so that the breaking strength of the aggregate 21 is improved. Unlike the above-described embodiment, in another example, a portion where the sealing material layer 15 intersects in a cross shape cannot be formed, and this is considered to contribute to an improvement in fracture strength. Moreover, as a result of improving the thermal conductivity along the radial direction of the aggregate 21, it becomes difficult to make a temperature difference between the outer peripheral portion and the central portion of the aggregate 21. As a result, the aggregate 21 is heated evenly, and it is difficult for fine particles to remain unburned in the outer peripheral portion.

-The uneven | corrugated elimination layer 16 does not need to be formed using the same kind of ceramic material as the sealing material layer 15, and may be formed using a different kind of ceramic material.
The unevenness eliminating layer 16 may be formed to have the same thickness as the sealing material layer 15, and may be formed to be thicker than the sealing material layer 15.

-As a formation method of the uneven | corrugated elimination layer 16, the application | coating method is employ | adopted in embodiment. The method is not limited to this method. For example, the unevenness eliminating layer 16 may be formed by employing a printing method, a baking method, a dipping method, a curtain coating method, or the like.

The filter F1 is not limited to the one having the honeycomb structure as shown in the above embodiment, and may be a three-dimensional network structure, a foam structure, a noodle structure, a fiber structure, or the like.

The shape of the filter F1 before the outer shape cutting step is not limited to the quadrangular prism shape as in the embodiment, and may be a triangular prism shape, a hexagonal prism shape, or the like. Further, not only the overall shape of the aggregate 9A is processed into a circular cross-section by the outer shape cutting step, but it may be processed into an elliptical cross-section, for example.

The method for forming the curved surface portion 18 is not limited to brushing using a brush as shown in the embodiment. For example, it is also possible to employ a technique such as scraping the unevenness eliminating layer 16 of the part using an instrument other than a brush (for example, a brush, a spatula, etc.). Furthermore, instead of the above-described method using an instrument, a technique that does not use an instrument (specifically, a technique that uses abrasive grains such as sandblasting) may be employed.

-If there is no necessity in particular, you may abbreviate | omit the curved surface part formation process which was performed by embodiment.
In the embodiment, the ceramic filter assembly of the present invention is embodied as a filter for an exhaust gas purification device attached to the diesel engine 2. Of course, the ceramic filter assembly of the present invention can be embodied as other than a filter for an exhaust gas purification device, for example, a heat exchanger member, a filtration filter for high temperature fluid or high temperature steam, or the like. Can.

Next, in addition to the technical ideas described in the claims, the technical ideas grasped by the embodiment described above are listed below.
(1) In the present invention, the aggregate is a diesel particulate filter.

(2) In the present invention, the filter is a honeycomb filter made of a porous silicon carbide sintered body. Therefore, according to the present invention, the pressure loss is small, and the heat resistance and thermal conductivity can be excellent.

(3) In the present invention, the sealing material layer is composed of at least an inorganic fiber, an inorganic binder, an organic binder, and inorganic particles, and the inorganic fibers and the inorganic particles that are three-dimensionally interlaced with each other. It is formed by a sealing material made of an elastic material that is bonded to each other via a gap.

(4) In the present invention, the sealing material is 10 wt% to 70 wt% silica-alumina ceramic fiber, 1 wt% to 30 wt% silica sol, 0.1 wt% to 5.0 wt% in solid content. Of carbomethoxycellulose and 3 to 80% by weight of silicon carbide powder.

(5) According to the exhaust gas purifying apparatus of the present invention, a practical apparatus excellent in strength, reliability and the like can be provided.

1 is an overall schematic diagram of an exhaust gas purifying apparatus according to an embodiment embodying the present invention. The side view of the ceramic filter assembly of embodiment. The principal part expanded sectional view of the said exhaust gas purification apparatus. The principal part expanded sectional view of the ceramic filter assembly which performed the brushing to the uneven | corrugated elimination layer. (A), (b), (c) is a schematic perspective view for demonstrating the manufacturing process of a ceramic filter assembly. The side view of the ceramic filter assembly of another example.

Explanation of symbols

9, 21 Ceramic filter assembly 9c Outer peripheral surface 15 of ceramic filter assembly 15 Ceramic sealing material layer 16 Concavity and convexity elimination layer F1 filter

Claims (10)

An aggregate formed by integrating the respective filters by adhering the outer peripheral surfaces of a plurality of filters made of a porous ceramic sintered body through a ceramic sealing material layer, and has a substantially circular cross-section By cutting the outer shape into a substantially oval cross section, the cell walls are partially exposed, and the outer peripheral surface that has protrusions and grooves extending along the axial direction of the aggregate has ceramic on the outer peripheral surface. An unevenness-resolving layer made of quality is formed, and the unevenness is filled with the unevenness-resolving layer, and the end of the unevenness-resolving layer in the filter axial direction has a curved surface shape with a radius of curvature R = 0.1 mm to 10 mm. A ceramic filter assembly characterized by comprising: The ceramic filter assembly according to claim 1, wherein the unevenness eliminating layer has a thickness of 0.1 mm to 10 mm. The ceramic filter assembly according to claim 1, wherein the sealing material layer is formed to be thinner than the unevenness eliminating layer. The ceramic filter assembly according to any one of claims 1 to 3, wherein the unevenness eliminating layer is formed using the same material as the sealing material layer. The ceramic filter assembly according to any one of claims 1 to 4, wherein the filters are arranged in a state of being shifted from each other along a direction orthogonal to the filter axial direction. A ceramic filter assembly is manufactured by bonding the outer peripheral surfaces of a plurality of porous ceramic sintered bodies through the ceramic sealing material layer, and the outer shape of the ceramic filter assembly is cut. As a whole, the cross-section is substantially circular or the cross-section is substantially oval, and the cell wall of the filter exposed by the outer cut is partially exposed on the outer peripheral surface of the filter, and extends along the axial direction of the aggregate. A ceramic honeycomb characterized in that an unevenness-resolving layer is formed by applying an unevenness-resolving layer forming paste made of a ceramic material to the outer peripheral surface of the ceramic filter assembly having unevenness consisting of stripes and grooves. A method for manufacturing a filter assembly. The ceramic filter assembly according to claim 6, wherein after forming the unevenness eliminating layer, an end portion in the filter axial direction of the layer is formed to have a curved shape with a curvature radius R = 0.1 mm to 10 mm. Body manufacturing method. The method for producing a ceramic filter assembly according to claim 6 or 7, wherein the unevenness eliminating layer has a thickness of 0.1 mm to 10 mm. The method for producing a ceramic filter assembly according to any one of claims 6 to 8, wherein the unevenness eliminating layer is formed using the same material as the sealing material layer. The method for producing a ceramic filter assembly according to any one of claims 6 to 9, wherein the filters are arranged in a state of being shifted from each other along a direction orthogonal to the filter axial direction.

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