Gas leak inspection method and manufacturing method for columnar honeycomb structure filter

Abstract

To provide a gas leakage inspection method preceding implementation of a film forming process for a columnar honeycomb structure.SOLUTION: An inspection method is provided, including the steps of: preparing a mounting jig having a first O-ring and a second O-ring; preparing a holder having a chuck mechanism capable of gripping a honeycomb structure, a gas inlet, a gas outlet provided in a lower surface, and a gas passage communicating the gas inlet with the gas outlet; gripping the columnar honeycomb structure using the chuck mechanism of the holder; pushing the lower surface of the holder gripping the columnar honeycomb structure, to the first O-ring and the second O-ring of the mounting jig, on the condition that the gas outlet is positioned between the first O-ring and the second O-ring; supplying gas from the gas inlet of the holder while the step of pressing is maintained, and measuring a flow rate of the gas using a flow meter; and determining whether or not the flow rate measured by the flow meter exceeds a predetermined threshold.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a gas leak inspection method for a columnar honeycomb structure prior to a film forming process, and also to a method for manufacturing a columnar honeycomb structure filter. [Background technology]

[0002] Exhaust gas emitted from internal combustion engines such as diesel and gasoline engines contains particulate matter (PM) such as soot. Soot is harmful to the human body, so its emission is regulated. Currently, in order to comply with exhaust gas regulations, filters such as DPFs and GPFs are widely used, which filter out soot and other PM by passing exhaust gas through porous partition walls.

[0003] A known filter for capturing PM is a wall-flow type columnar honeycomb structure filter that includes a plurality of first cells extending in the height direction from the inlet side bottom surface to the outlet side bottom surface, with the inlet side bottom surface being open and the outlet side bottom surface being plugged, and a plurality of second cells that are arranged adjacent to the first cells with partition walls in between, extending in the height direction from the inlet side bottom surface to the outlet side bottom surface, with plugged portions on the inlet side bottom surface and the outlet side bottom surface being open.

[0004] In recent years, with the strengthening of exhaust gas regulations, stricter PM emission standards (PN regulations: particle matter number regulations) have been introduced, and filters are required to have high PM capture performance (high PN capture efficiency). Therefore, it has been proposed to form a layer for capturing PM on the surface of the cells (hereinafter also referred to as a "porous film" or "capture layer"). One known method for forming a porous film is to supply an aerosol containing ceramic particles toward the bottom surface on the inlet side of a columnar honeycomb structure, allow the particles to adhere to the surface of the first cells, and then perform a heat treatment.

[0005] Patent Document 1 describes a particle deposition device for supplying an aerosol containing ceramic particles toward the inlet-side bottom surface of a cylindrical honeycomb structure. Specifically, the particle deposition device includes a holder for holding the cylindrical honeycomb structure, a blower for applying suction to the outlet-side bottom surface of the cylindrical honeycomb structure, an aerosol generator for spraying the aerosol containing ceramic particles toward the inlet-side bottom surface from a direction perpendicular to the inlet-side bottom surface to deposit the ceramic particles on the surfaces of the first cells, and a chamber disposed between the nozzle of the aerosol generator and the inlet-side bottom surface for guiding the aerosol through its interior. According to Patent Document 1, the holder is connected to the downstream end of the side wall of the chamber. Patent Document 1 also describes that the holder has a chucking mechanism, such as a balloon chuck, for gripping the outer peripheral side wall of the cylindrical honeycomb structure.

[0006] According to Patent Document 1, the aerosol sprayed from the aerosol generator of the particle attachment device passes through the inside of a chamber by the suction force of a blower, and is then sucked into the first cells of the columnar honeycomb structure from the bottom surface of the inlet side of the columnar honeycomb structure held by a holder. The ceramic particles in the aerosol sucked into the first cells adhere to the surfaces of the first cells.

[0007] Meanwhile, Patent Document 2, which is a technology related to nuclear reactors, describes an opening and closing device for a reactor vessel access section, characterized in that the cover is provided with a leak detection mechanism that detects the occurrence of a leak between a ring member and a cover. According to the leak detection mechanism, when air is supplied from a pump to a pipe while the cover is pressed against the ring member, the air is supplied through a detection port into the space between a large-diameter O-ring and a small-diameter O-ring attached to one end face of the ring member. If the sealing effectiveness of at least one of the large-diameter O-ring and the small-diameter O-ring attached to one end face of the ring member is reduced due to the adhesion of foreign matter, a liquid level sensor detects the intrusion of water into the detection port, thereby detecting the occurrence of a leak between the cover and the ring member. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2022-157612 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-145479 Summary of the Invention [Problem to be solved by the invention]

[0009] Considering the production efficiency of columnar honeycomb structure filters and the maintainability of particle attachment devices, it is desirable that the holder in a particle attachment device for supplying an aerosol containing ceramic particles be detachable from the chamber. However, if the holder is detachable from the chamber, a gap may occur between the two due to foreign matter getting caught between them. Furthermore, a gap may also occur between the two due to scratches or distortion on the holder or chamber.

[0010] When a gap occurs between the holder and the chamber, the air that seeps in through the gap disrupts the aerosol flow. The air that seeps in through the gap also flows into the bottom of the inlet side of the columnar honeycomb structure. These phenomena cause uneven adhesion of ceramic particles to the surface of the first cell, and the ceramic particles do not adhere sufficiently to the desired locations, which has a negative impact on the collection efficiency of the columnar honeycomb structure filter.

[0011] Since the collection efficiency of the columnar honeycomb structure filter can be inspected only after the columnar honeycomb structure filter is completed, if a large number of columnar honeycomb structure filters are manufactured without noticing the existence of gaps between the holder and the chamber, many defective products may be produced. Therefore, it is thought that being able to inspect for the existence of such gaps in advance will contribute to improving the yield.

[0012] In view of the above circumstances, an object of the present invention is to provide, in one embodiment, a gas leak inspection method for a columnar honeycomb structure before a film forming process is performed on the columnar honeycomb structure, and, in another embodiment, a method for manufacturing a columnar honeycomb structure filter using the gas leak inspection method. [Means for solving the problem]

[0013] The inventors have conducted extensive research to solve the above problems and have found that a method of inspecting for gas leaks by installing a predetermined mounting jig with two O-rings embedded between a chamber and a holder is effective. The present invention was completed based on this finding and is exemplified below.

[0014] [Aspect 1] A gas leak inspection method before a film forming process is performed on a columnar honeycomb structure, The columnar honeycomb structure includes an outer peripheral side wall, a plurality of first cells that are arranged on the inner peripheral side of the outer peripheral side wall, extend from the inlet side bottom surface to the outlet side bottom surface, have open inlet side bottom surfaces and have plugging portions on the outlet side bottom surface, and a plurality of second cells that are arranged on the inner peripheral side of the outer peripheral side wall, extend from the inlet side bottom surface to the outlet side bottom surface, have plugging portions on the inlet side bottom surface and have open outlet side bottom surfaces, and the plurality of first cells and the plurality of second cells are arranged alternately adjacent to each other with porous partition walls sandwiched therebetween, a step of preparing a mounting jig that is installed at the upper end of a chamber and has a mounting surface having an opening, a first O-ring that is embedded in the mounting surface so that a portion of the first O-ring protrudes upward and surrounds the outer periphery of the opening, and a second O-ring that is embedded in the mounting surface so that a portion of the second O-ring protrudes upward and surrounds the outer periphery of the first O-ring at a distance; a step of preparing a holder having a through hole extending in the vertical direction and a chuck mechanism capable of gripping a columnar honeycomb structure inserted into the through hole from the outer peripheral side wall side, a gas inlet, a gas outlet provided on the lower surface, and a gas passage communicating the gas inlet and the gas outlet; a step of holding the pillar-shaped honeycomb structure by a chuck mechanism of the holder; a step of pressing a lower surface of a holder holding the columnar honeycomb structure against the first O-ring and the second O-ring of the mounting jig, on the condition that the gas outlet is positioned between the first O-ring and the second O-ring; supplying gas from a gas inlet of the holder while maintaining the pressing step, and measuring the flow rate of the gas with a flow meter; determining whether a flow rate measured by the flow meter exceeds a predetermined threshold; A method comprising: [Aspect 2] The method according to aspect 1, wherein the gas pressure at the gas inlet of the holder when gas is supplied from the gas inlet is 0.01 to 0.05 MPaG. [Aspect 3] The method according to aspect 1 or 2, wherein the predetermined threshold is set to any value in the range of 0 to 0.10 L / min when converted to a state of 1 atmosphere and 20°C. [Aspect 4] A method according to any one of aspects 1 to 3, wherein the gas is air. [Aspect 5] The method according to any one of Aspects 1 to 4, wherein the opening in the mounting surface and the through-hole in the chuck mechanism are coaxial. [Aspect 6] The method according to any one of Aspects 1 to 5, wherein the wire diameter of the first O-ring and the second O-ring is 5.57 to 5.83 mm. [Aspect 7] The method according to any one of Aspects 1 to 6, wherein the first O-ring and the second O-ring are embedded so as to protrude upward from the mounting surface by 1.27 to 1.58 mm. [Aspect 8] A method according to any one of Aspects 1 to 7, wherein the first O-ring and the second O-ring are crushed by 0.3 mm or more in the pressing step. [Aspect 9] A method according to any one of Aspects 1 to 8, wherein the first O-ring and the second O-ring have a Type A durometer hardness of 65 to 75 as measured in accordance with JIS K6253-3:2012. [Aspect 10] Aspects 1 to 9: The method according to any one of Aspects 1 to 9, wherein the first O-ring and the second O-ring are made of nitrile rubber. [Aspect 11] 11. The method according to any one of aspects 1 to 10, wherein the distance between the first O-ring and the second O-ring is 3 mm or more. [Aspect 12] In the method for manufacturing a columnar honeycomb structure filter according to any one of aspects 1 to 11, if a step of determining whether the flow rate measured by a flow meter exceeds a predetermined threshold is carried out and it is determined that the flow rate does not exceed the threshold, a film-forming step is included in which, while maintaining the pressing step, an aerosol containing ceramic particles is sprayed from the nozzle of an aerosol generator into the chamber in a direction perpendicular to the inlet bottom surface of the columnar honeycomb structure toward the inlet bottom surface, while applying suction force to the outlet bottom surface, thereby sucking the sprayed aerosol from the inlet bottom surface and adhering the ceramic particles to the surface of the first cells. [Effects of the Invention]

[0015] According to the gas leak inspection method of one embodiment of the present invention, it is possible to determine in advance whether or not a film-forming process should be performed on a columnar honeycomb structure. Therefore, by performing the film-forming process on the columnar honeycomb structure only if it passes the inspection, it is possible to expect an improvement in the yield of columnar honeycomb structure filters. In particular, this inspection method is useful when a particle deposition device for supplying an aerosol containing ceramic particles has a holder that can be attached and detached to a chamber. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a perspective view schematically showing an example of a columnar honeycomb structure filter. [Figure 2] 1 is a schematic cross-sectional view of an example of a columnar honeycomb structure filter, observed from a cross section parallel to the cell extension direction. [Figure 3] FIG. 2 is a schematic enlarged partial view of the columnar honeycomb structure filter when observed from a cross section perpendicular to the cell extension direction. [Figure 4]FIG. 1 is a diagram schematically illustrating an example of the structure of an aerosol generator. [Figure 5] FIG. 2 is a schematic diagram illustrating an example of the configuration of a particle adhering device. [Figure 6] FIG. 2 is a schematic plan view of a mounting jig. [Figure 7] FIG. 2 is a schematic cross-sectional view for explaining the positional relationship and structure of a holder, a mounting jig, and a chamber. [Figure 8] FIG. 10 is a schematic diagram for explaining a method for replacing a workpiece (a columnar honeycomb structure) to be placed in a particle attachment device. DETAILED DESCRIPTION OF THE INVENTION

[0017] Next, embodiments of the present invention will be described in detail with reference to the drawings. It should be understood that the present invention is not limited to the following embodiments, and that appropriate design changes and improvements may be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0018] <1. Pillar honeycomb structure filter> A columnar honeycomb structure filter according to one embodiment of the present invention will be described. The columnar honeycomb structure filter can be used as a DPF (Diesel Particulate Filter) or a GPF (Gasoline Particulate Filter) that collects soot and is attached to an exhaust gas line from a combustion device, typically an engine, mounted on a vehicle. The columnar honeycomb structure filter according to the present invention can be installed, for example, in an exhaust pipe.

[0019] 1 and 2 are a schematic perspective view and a cross-sectional view, respectively, of a pillar-shaped honeycomb structure filter 100. The pillar-shaped honeycomb structure filter 100 includes an outer peripheral side wall 102, a plurality of first cells 108 disposed on the inner peripheral side of the outer peripheral side wall 102, extending parallel to each other from an inlet-side bottom surface 104 to an outlet-side bottom surface 106, opening at the inlet-side bottom surface 104 and having plugging portions 109 at the outlet-side bottom surface 106, and a plurality of second cells 110 disposed on the inner peripheral side of the outer peripheral side wall 102, extending parallel to each other from the inlet-side bottom surface 104 to the outlet-side bottom surface 106, having plugging portions 109 at the inlet-side bottom surface 104 and opening at the outlet-side bottom surface 106. In this columnar honeycomb structure filter 100, the first cells 108 and the second cells 110 are arranged alternately adjacent to each other with porous partition walls 112 sandwiched therebetween, so that the inlet side bottom surface 104 and the outlet side bottom surface 106 each have a honeycomb shape.

[0020] When exhaust gas containing particulate matter (PM) such as soot is supplied to the upstream inlet-side bottom surface 104 of the columnar honeycomb structure filter 100, the exhaust gas is introduced into the first cells 108 and travels downstream within the first cells 108. Because the first cells 108 have plugging portions 109 on the downstream outlet-side bottom surface 106, the exhaust gas passes through porous partition walls 112 that separate the first cells 108 from the second cells 110 and flows into the second cells 110. Since the particulate matter cannot pass through the partition walls 112, it is captured and deposited within the first cells 108. After the particulate matter is removed, the clean exhaust gas that has flowed into the second cells 110 travels downstream within the second cells 110 and flows out from the downstream outlet-side bottom surface 106.

[0021] 3 shows a schematic enlarged partial view of the columnar honeycomb structure filter 100 when observed at a cross section perpendicular to the extending direction of the cells 108 and 110. A porous film 114 is formed on the surface of each first cell 108 of the columnar honeycomb structure filter 100 (the same as the surface of the partition walls 112 that define the first cells 108).

[0022] The porous film can be made of ceramics. For example, the porous film can contain one or more ceramics selected from cordierite, silicon carbide (SiC), talc, mica, mullite, cerium, aluminum titanate, alumina, silicon nitride, sialon, zirconium phosphate, zirconia, titania, and silica. The main component of the porous film is preferably silicon carbide, alumina, silica, cordierite, or mullite. Among these, the main component of the porous film is preferably silicon carbide, since the presence of a surface oxide film (SiO) provides a porous film that is strongly bonded to each other and is difficult to peel off. The main component of the porous film refers to a component that accounts for 50% or more by mass of the porous film. SiC preferably accounts for 50% or more by mass, more preferably 70% or more by mass, and even more preferably 90% or more by mass of the porous film. The shape of the ceramics constituting the porous film is not particularly limited, but examples include granular and fibrous forms.

[0023] The materials constituting the partition walls and outer peripheral side walls of the columnar honeycomb structure filter according to this embodiment include, but are not limited to, porous ceramics. Examples of ceramics include cordierite, mullite, zirconium phosphate, aluminum titanate, silicon carbide (SiC), silicon-silicon carbide composites (e.g., Si-bonded SiC), cordierite-silicon carbide composites, zirconia, spinel, indialite, sapphirine, corundum, titania, and silicon nitride. These ceramics may be used alone or in combination.

[0024] The columnar honeycomb structure filter may support a PM combustion catalyst that assists in the combustion of PM such as soot, an oxidation catalyst (DOC), an SCR catalyst and an NSR catalyst for removing nitrogen oxides (NOx), and a three-way catalyst that can simultaneously remove hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx).The columnar honeycomb structure filter according to this embodiment may also support various catalysts.

[0025] The bottom shape of the columnar honeycomb structure filter is not limited, and may be, for example, a round shape such as a circle, an ellipse, a racetrack shape, or an oval shape, or a polygonal shape such as a triangle or a rectangle. The columnar honeycomb structure filter 100 in Fig. 1 has a circular bottom shape and is cylindrical as a whole.

[0026] There is no particular limitation on the height of the columnar honeycomb structure filter (the length from the bottom surface on the inlet side to the bottom surface on the outlet side) and it may be set appropriately depending on the application and required performance. There is also no particular limitation on the relationship between the height of the columnar honeycomb structure filter and the maximum diameter of each bottom surface (the maximum length of the diameters passing through the center of gravity of each bottom surface of the columnar honeycomb structure filter). Therefore, the height of the columnar honeycomb structure filter may be longer than the maximum diameter of each bottom surface, or the height of the columnar honeycomb structure filter may be shorter than the maximum diameter of each bottom surface.

[0027] Although there is no limitation on the shape of the cells in a cross section perpendicular to the cell extension direction, a quadrangle, a hexagon, an octagon, or a combination thereof is preferred. Among these, a square and a hexagon are preferred. By using such a cell shape, it is possible to reduce the pressure loss when a fluid flows through the columnar honeycomb structure filter.

[0028] The columnar honeycomb structure filter can be provided as an integrally molded product. Alternatively, the columnar honeycomb structure filter can be provided as a segment assembly, which is formed by joining together a plurality of columnar honeycomb structure filter segments, each having an outer peripheral side wall. Providing the columnar honeycomb structure filter as a segment assembly can enhance thermal shock resistance.

[0029] <2. Manufacturing method of columnar honeycomb structure filter> A method for manufacturing a columnar honeycomb structure filter is described below by way of example. First, a raw material composition containing ceramic raw materials, a dispersion medium, a pore-forming material, and a binder is kneaded to form a clay, and then the clay is extruded to form a desired columnar honeycomb molded body. Additives such as a dispersant can be blended into the raw material composition as needed. During extrusion molding, a die having the desired overall shape, cell shape, partition wall thickness, cell density, etc. can be used.

[0030] After drying the columnar honeycomb formed body, plugging portions are formed at predetermined positions on both bottom surfaces of the columnar honeycomb formed body, and the plugging portions are then dried to obtain a columnar honeycomb formed body with plugging portions. The columnar honeycomb formed body is then degreased and fired to obtain a columnar honeycomb structure. A porous film is then formed on the surfaces of the first cells of the columnar honeycomb structure to obtain a columnar honeycomb structure filter.

[0031] The ceramic raw material remains after firing and is the raw material for the portion that constitutes the skeleton of the honeycomb structure as ceramic. As the ceramic raw material, raw materials that can form the above-mentioned ceramics after firing can be used. The ceramic raw material can be provided, for example, in the form of powder. Examples of the ceramic raw material include raw materials for obtaining ceramics such as cordierite, mullite, zircon, aluminum titanate, silicon carbide, silicon nitride, zirconia, spinel, indialite, sapphirine, corundum, and titania. Specific examples include, but are not limited to, silica, talc, alumina, kaolin, serpentine, pyroferrite, brucite, boehmite, mullite, magnesite, and aluminum hydroxide. The ceramic raw material may be used singly or in combination of two or more types.

[0032] In the case of filter applications such as DPF and GPF, cordierite can be suitably used as the ceramic. In this case, a cordierite-forming raw material can be used as the ceramic raw material. The cordierite-forming raw material is a raw material that becomes cordierite when fired. The cordierite-forming raw material preferably has a chemical composition of 30 to 45 mass% alumina (Al2O3) (including aluminum hydroxide converted to alumina), 11 to 17 mass% magnesia (MgO), and 42 to 57 mass% silica (SiO2).

[0033] Examples of the dispersion medium include water and a mixed solvent of water and an organic solvent such as alcohol, with water being particularly preferred.

[0034] The pore-forming material is not particularly limited as long as it forms pores after firing, and examples thereof include wheat flour, starch, foamed resin, water-absorbent resin, porous silica, carbon (e.g., graphite), ceramic balloons, polyethylene, polystyrene, polypropylene, nylon, polyester, acrylic, and phenol. One type of pore-forming material may be used alone, or two or more types may be used in combination. From the viewpoint of increasing the porosity of the fired body, the content of the pore-forming material is preferably 0.5 parts by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, per 100 parts by mass of the ceramic raw material. From the viewpoint of ensuring the strength of the fired body, the content of the pore-forming material is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 4 parts by mass or less, per 100 parts by mass of the ceramic raw material.

[0035] Examples of binders include organic binders such as methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol. It is particularly preferable to use a combination of methyl cellulose and hydroxypropyl methyl cellulose. Furthermore, from the viewpoint of increasing the strength of the honeycomb formed body, the binder content is preferably 4 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 6 parts by mass or more, per 100 parts by mass of the ceramic raw materials. From the viewpoint of suppressing cracks due to abnormal heat generation during the firing process, the binder content is preferably 9 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 7 parts by mass or less, per 100 parts by mass of the ceramic raw materials. One type of binder may be used alone, or two or more types may be used in combination.

[0036] The dispersant may be ethylene glycol, dextrin, fatty acid soap, polyether polyol, etc. One type of dispersant may be used alone, or two or more types may be used in combination. The content of the dispersant is preferably 0 to 2 parts by mass per 100 parts by mass of the ceramic raw material.

[0037] The method for plugging the bottom surface of the columnar honeycomb formed body is not particularly limited, and known methods can be used. The material for the plugging portions is not particularly limited, but ceramics are preferred from the viewpoints of strength and heat resistance. The ceramic is preferably a ceramic material containing at least one selected from the group consisting of cordierite, mullite, zircon, aluminum titanate, silicon carbide, silicon nitride, zirconia, spinel, indialite, sapphirine, corundum, and titania. It is even more preferred that the plugging portions have the same material composition as the main body of the honeycomb formed body, as this allows the expansion coefficients during firing to be the same, leading to improved durability.

[0038] After drying the honeycomb formed body, degreasing and firing are performed to manufacture a columnar honeycomb structure. The conditions for the drying, degreasing and firing processes may be well known conditions depending on the material composition of the honeycomb formed body, and no particular explanation is required, but examples of specific conditions are given below.

[0039] In the drying step, a conventionally known drying method can be used, for example, hot air drying, microwave drying, dielectric drying, reduced pressure drying, vacuum drying, freeze drying, etc. Among them, a drying method that combines hot air drying with microwave drying or dielectric drying is preferred, since it can dry the entire molded body quickly and uniformly.

[0040] When forming plugging portions, it is preferable to form plugging portions on both bottom surfaces of the dried honeycomb formed body and then dry the plugging portions. The plugging portions are formed at predetermined positions so that a plurality of first cells extending from the inlet-side bottom surface to the outlet-side bottom surface, having an open inlet-side bottom surface and a plugging portion on the outlet-side bottom surface, and a plurality of second cells extending from the inlet-side bottom surface to the outlet-side bottom surface, having a plugging portion on the inlet-side bottom surface and an open outlet-side bottom surface, are alternately arranged adjacent to each other with the porous partition wall interposed therebetween.

[0041] Next, the degreasing process will be described. The combustion temperature of the binder is about 200°C, and the combustion temperature of the pore-forming material is about 300 to 1000°C. Therefore, the degreasing process can be carried out by heating the honeycomb formed body to a temperature in the range of about 200 to 1000°C. The heating time is not particularly limited, but is usually about 10 to 100 hours. The honeycomb formed body after the degreasing process is called a calcined body.

[0042] The firing step depends on the material composition of the honeycomb formed body, but can be carried out, for example, by heating the calcined body to 1350 to 1600°C and holding it for 3 to 10 hours. In this way, a pillar-shaped honeycomb structure is produced, which includes a plurality of first cells extending from the inlet-side bottom face to the outlet-side bottom face, which are open at the inlet-side bottom face and have plugging portions at the outlet-side bottom face, and a plurality of second cells extending from the inlet-side bottom face to the outlet-side bottom face, which have plugging portions at the inlet-side bottom face and are open at the outlet-side bottom face, and in which the plurality of first cells and the plurality of second cells are alternately arranged adjacent to each other with porous partition walls sandwiched therebetween.

[0043] Next, a porous film is formed on the surfaces of the first cells of the columnar honeycomb structure that has undergone the firing process. First, a film-forming process is carried out in which an aerosol containing ceramic particles is sprayed in a direction perpendicular to the inlet-side bottom surface of the columnar honeycomb structure, preferably toward the center of the inlet-side bottom surface, while a suction force is applied to the outlet-side bottom surface to suck the sprayed aerosol from the inlet-side bottom surface, thereby adhering the ceramic particles to the surfaces of the first cells. Illustratively, the distance between the aerosol spray nozzle and the inlet-side bottom surface can be 500 mm to 2000 mm, and the aerosol spray speed can be 2 to 80 m / s.

[0044] The ceramic particles in the aerosol preferably have a median diameter (D50) of 1.0 to 6.0 μm, more preferably 2.0 to 5.0 μm, in the volume-based cumulative particle size distribution measured by laser diffraction / scattering. By spraying extremely fine ceramic particles, it is possible to increase the porosity while minimizing the average pore diameter of the resulting porous film.

[0045] The ceramic particles used are the same as those used to form the porous film. For example, ceramic particles containing one or more selected from cordierite, silicon carbide (SiC), talc, mica, mullite, cerium, aluminum titanate, alumina, silicon nitride, sialon, zirconium phosphate, zirconia, titania, and silica can be used. The main component of the ceramic particles is preferably silicon carbide, alumina, silica, cordierite, or mullite. The main component of the ceramic particles refers to a component that accounts for 50% or more by mass of the ceramic particles. Preferably, SiC accounts for 50% or more by mass of the ceramic particles, more preferably 70% or more by mass, and even more preferably 90% or more by mass.

[0046] In order to prevent aggregation of the ceramic particles, it is advantageous to spray the aerosol using an aerosol generator that includes a drive gas flow path for flowing a pressurized drive gas, a supply port located midway through the drive gas flow path that can draw ceramic particles from the outer periphery of the drive gas flow path toward the inside of the drive gas flow path, and a nozzle attached to the tip of the drive gas flow path that can spray the aerosol. In one embodiment, the supply port can be configured so that the ceramic particles are introduced into the drive gas flow path from a direction approximately perpendicular to the flow direction of the drive gas through the drive gas flow path.

[0047] When ceramic particles are introduced into the drive gas flow path, they may be agglomerated. Fine ceramic particles are particularly prone to agglomeration. However, when ceramic particles are supplied from the outer periphery of the drive gas flow path toward the inside of the drive gas flow path, the drive gas has a greater effect of crushing the ceramic particles. This is thought to result in ceramic particles with reduced agglomeration being sprayed from the nozzle of the aerosol generator.

[0048] (aerosol generator) FIG. 4 shows a schematic example of the structure of an aerosol generator 420 suitable for spraying ceramic particles with reduced aggregation. The aerosol generator 400 is a drive gas flow path 407 for flowing a pressurized drive gas; a supply port 407i provided in the driving gas flow path 407 and capable of sucking ceramic particles 402 from the outer periphery of the driving gas flow path 407 toward the inside of the driving gas flow path 407; a nozzle 401 attached to the tip of the driving gas flow path 407 and capable of injecting an aerosol; a flow path 403 for sucking and transporting ceramic particles 402, the flow path 403 having an outlet 403e communicating with a supply port 407i; a container 409 for containing ceramic particles 402 and supplying the ceramic particles 402 to a flow path 403 for suction and transport; It has.

[0049] The container 409 may be, for example, a funnel. Ceramic particles 402 adjusted to a predetermined particle size distribution are contained in the container 409. The ceramic particles 402 contained in the container 409 are transported by suction from an outlet 409e at the bottom of the container 409 through the flow path 403 to an outlet 403e by the suction force of the drive gas flow path 407, and then introduced into the drive gas flow path 407 through the supply port 407i. At this time, ambient gas (typically air) sucked through the inlet 409i of the container 409 is also introduced into the drive gas flow path 407 along with the ceramic particles 402 through the flow path 403. In this embodiment, the outlet 403e and the supply port 407i are common. Furthermore, in this embodiment, the ceramic particles 402 are introduced into the drive gas flow path 407 from a direction approximately perpendicular to the flow direction of the drive gas flowing through the drive gas flow path 407.

[0050] Ceramic particles 402 supplied into drive gas flow channel 407 collide with the drive gas flowing through drive gas flow channel 407, and are crushed and mixed to form an aerosol, which is then sprayed from nozzle 401. Nozzle 401 is preferably installed at a position and oriented so that the aerosol is sprayed in a direction perpendicular to the inlet-side bottom surface of the columnar honeycomb structure. More preferably, nozzle 401 is installed at a position and oriented so that the aerosol is sprayed in a direction perpendicular to the inlet-side bottom surface toward the center of the inlet-side bottom surface.

[0051] The ceramic particles 402 are preferably supplied to the container 409 using, but not limited to, a powder quantitative feeder 411 such as a screw feeder or a belt conveyor. The ceramic particles 402 discharged from the powder quantitative feeder 411 can fall into the container 409 by gravity.

[0052] In a preferred embodiment, the drive gas flow path 407 includes a venturi section 407v with a narrowed flow path, and the supply port 407i is located downstream of the most narrowed point of the venturi section 407v. The venturi section 407v in the drive gas flow path 407 increases the velocity of the drive gas passing through the venturi section 407v, allowing the drive gas to collide with the ceramic particles 402 supplied downstream of the venturi section 407v at a higher velocity, thereby improving the disintegration force. To enhance the disintegration force of the drive gas, the supply port 407i is preferably located downstream of and adjacent to the most narrowed point of the venturi section 407v. This configuration can be achieved, for example, by connecting the drive gas flow path 407 and the suction-transport flow path 403 using a venturi ejector 410.

[0053] From the viewpoint of increasing the crushing force of ceramic particles, the lower limit of the flow velocity of the driving gas immediately before passing through the venturi section 407v is preferably 13 m / s or more, more preferably 20 m / s or more, and even more preferably 26 m / s or more. There is no particular upper limit to the flow velocity of the driving gas immediately before passing through the venturi section 407v, but it is usually 50 m / s or less, typically 40 m / s or less.

[0054] From the viewpoint of increasing the disintegration force, the lower limit of the ratio of the flow path cross-sectional area immediately before the venturi section to the flow path cross-sectional area of ​​the venturi section is preferably 8 or more, and more preferably 16 or more. There is no particular upper limit to the ratio of the flow path cross-sectional area immediately before the venturi section to the flow path cross-sectional area of ​​the venturi section, but if it is too large, the pressure loss in the venturi section increases, so it is preferably 64 or less, and more preferably 32 or less. Here, the flow path cross-sectional area of ​​the venturi section means the flow path cross-sectional area at the narrowest point in the venturi section. Furthermore, the flow path cross-sectional area immediately before the venturi section means the flow path cross-sectional area immediately before the flow path narrows upstream of the venturi section.

[0055] By using the venturi ejector 410, for example, when the drive gas is flowed through the drive gas flow path 407, a large suction force can be applied to the flow path 403 for suction and transport, and the flow path 403 for suction and transport can be prevented from being clogged with the ceramic particles 402. The venturi ejector 410 is also effective as a means for removing the ceramic particles 402 when the flow path 403 for suction and transport is clogged with the ceramic particles 402.

[0056] The flow rate of the aerosol sprayed from the nozzle 401 can be controlled by using a compressed gas such as pressure-adjusted compressed air as the driving gas. Dry air (e.g., with a dew point of 10°C or less) is preferably used as the driving gas to suppress aggregation of the ceramic particles. In this specification, the "dew point" refers to a value measured using a polymer-type capacitance dew point meter conforming to JIS Z8806:2001.

[0057] Fine ceramic particles have a tendency to agglomerate, but by using the aerosol generator 400 according to this embodiment, it is possible to spray ceramic particles with a targeted particle size distribution in which agglomeration is suppressed.

[0058] (Particle attachment device) FIG. 5 shows a schematic configuration example of a particle attachment device 510 suitable for carrying out a film forming step of attaching ceramic particles to the surfaces of the first cells of a pillar-shaped honeycomb structure. The particle deposition device 510 includes: a holder 514 for holding the columnar honeycomb structure 500; a blower 512 for applying suction force to the outlet side bottom surface 506 of the columnar honeycomb structure 500; an aerosol generator 511 for spraying an aerosol containing ceramic particles toward the inlet side bottom surface 504 in a direction perpendicular to the inlet side bottom surface 504 to cause the ceramic particles to adhere to the surface of the first cell; a chamber 513 provided between the nozzle 511a of the aerosol generator 511 and the inlet-side bottom surface 504 for guiding the aerosol through its interior; Equipped with.

[0059] The holder 514 is configured so as to be able to hold the columnar honeycomb structure 500 at a position facing the nozzle 511a of the aerosol generator 511 with the inlet-side bottom surface 504 of the columnar honeycomb structure 500 exposed. For example, the holder 514 has a main body portion 514a. The main body portion 514a has a through hole 514c extending in the vertical direction, and may have a chuck mechanism 514b for holding the columnar honeycomb structure 500 inserted into the through hole 514c from the outer peripheral side wall 502 side. There is no particular limitation on the chuck mechanism 514b, but a balloon chuck is an example. There is no particular limitation on the material of the main body portion 514a of the holder 514, but it may be made of plastic such as nylon, for example.

[0060] The holder 514 holding the columnar honeycomb structure 500 is preferably enclosed by a housing 520 in order to rectify the aerosol that has passed through the columnar honeycomb structure 500 in one direction without diffusing during the film-forming process. The housing 520 may be attached and detached manually, but the up and down movement of the housing can also be automated by connecting the housing 520 to an electric cylinder 570 such as a Robocylinder, a single-axis actuator, or a single-axis robot. The pressing force from the electric cylinder 570 can also be used to press the lower surface 514f of the holder 514 holding the columnar honeycomb structure 500 against a first O-ring 533 and a second O-ring 534 of a mounting jig 530, which will be described later, via the housing 520.

[0061] Side wall 513d of chamber 513 can be formed in a tubular shape such as a cylindrical or square tube. Chamber 513 has surface 513a facing inlet side bottom surface 504. Surface 513a facing inlet side bottom surface 504 has insertion port 513b for nozzle 511a of aerosol generator 511. With this configuration, aerosol sprayed from aerosol generator 511 can be directly introduced into chamber 513.

[0062] The opposing surface 513a is provided at a lower end 513f of the chamber 513 (typically, at the upstream end of the side wall 513d). An opening 513c for taking in ambient gas can be provided in the side wall 513d and / or the surface 513a facing the inlet-side bottom surface 504. This makes it possible to adjust the flow rate of gas flowing into the chamber 513 according to the suction force from the blower 512. However, as shown in FIG. 5, it is preferable that the side wall 513d of the chamber 513 does not have an opening 513c for taking in ambient gas, and that the ambient gas flowing into the chamber 513 is taken in only through the opening 513c provided in the surface 513a facing the inlet-side bottom surface 504.

[0063] Taking in ambient gas only from surface 513a facing inlet-side bottom surface 504 has the advantage that the ambient gas flows in in the same direction as the flow of the sprayed aerosol, eliminating any disturbances to the aerosol and stabilizing the aerosol. Conversely, having openings 513c in sidewall 513d of chamber 513 is disadvantageous because the ambient gas flowing in from these openings is likely to cause disturbances and destabilize the flow of the aerosol. Therefore, in a preferred embodiment, surface 513a facing inlet-side bottom surface 504 has one or more openings 513c for taking in ambient gas into chamber 513, and no openings for taking in ambient gas into chamber 513 exist other than on surface 513a.

[0064] In one embodiment, a punched plate and / or nonwoven fabric can be used on the opposing surface 513a. Furthermore, a filter 513g may be installed in the opening 513c to prevent the inclusion of agglomerated powder, honeycomb fragments, and dust.

[0065] A mounting jig 530 is installed at an upper end 513e of the chamber 513 (typically, at the downstream end of the side wall 513d). The mounting jig 530 may be configured to be able to fit onto the inner circumferential surface of the side wall 513d of the chamber 513. The mounting jig 530 may also have a flange portion 535 that can come into contact with the upper end 513e of the chamber 513. FIG. 6 is a schematic plan view of the mounting jig 530. Referring to FIG. 6, the mounting jig 530 is installed on the inner circumferential side of the side wall 513d of the chamber 513 and includes a mounting surface 532 having an opening 531, a first O-ring 533 embedded in the mounting surface 532 so as to partially protrude upward and surrounding the outer circumferential side of the opening 531, and a second O-ring 534 embedded in the mounting surface 532 so as to partially protrude upward and surrounding the first O-ring 533 at a distance S on the outer circumferential side. There are no particular restrictions on the material of the mounting jig 530, but it can be made of plastic such as nylon, for example.

[0066] It is preferable that the opening 531 of the mounting surface 532 and the through-hole 514c of the chuck mechanism 514b are coaxial, because this allows the aerosol to flow in a balanced manner into the inlet-side bottom surface 504 of the columnar honeycomb structure 500. For example, when the outer shape of the columnar honeycomb structure 500 is cylindrical, it is preferable that the opening 531 of the mounting surface 532 and the through-hole 514c of the holder 514 are concentrically arranged.

[0067] The shape and size of the opening 531 of the mounting surface 532 preferably correspond to the shape and size of the bottom surface of the columnar honeycomb structure 500. This makes it possible to stabilize the flow of aerosol flowing into the inlet-side bottom surface 504 of the columnar honeycomb structure 500.

[0068] 7, holder 514 has gas inlet 514d, gas outlet 514e provided on bottom surface 514f, and gas passage 514g connecting gas inlet 514d and gas outlet 514e. Gas passage 514g can be provided, for example, inside main body 514a of holder 514. Gas pipe 561 can be connected to gas inlet 514d of holder 514 so as to supply gas for testing. A flow meter 562 can be installed midway along gas pipe 561 to measure the flow rate of the gas.

[0069] There are no particular limitations on the location where gas inlet 514d is installed, and it may be installed on any of the outer peripheral side surface, inner peripheral side surface, top surface, or bottom surface of holder 514, as long as gas piping 561 can be connected to it. In the embodiment shown in Fig. 7, gas inlet 514d is installed on the outer peripheral side surface of holder 514. Installing gas inlet 514d on the outer peripheral side surface of holder 514 is preferable because gas piping 561 can be easily connected to it.

[0070] Gas outlet 514e provided on lower surface 514f of holder 514 is positioned between first O-ring 533 and second O-ring 534. With this configuration, when an inspection method described later is performed, it can be determined whether or not a predetermined level of airtightness is present in the space between first O-ring 533 and second O-ring 534, which is sandwiched between lower surface 514f of holder 514 and mounting surface 532 of mounting jig 530.

[0071] If first O-ring 533 and second O-ring 534 are embedded so that portions thereof protrude upward from mounting surface 532, then when performing the step of pressing lower surface 514f of holder 514 toward mounting surface 532 of mounting jig 530, lower surface 514f of holder 514 comes into contact with first O-ring 533 and second O-ring 534. At this time, first O-ring 533 and second O-ring 534 are crushed by the pressing pressure, and therefore a certain amount of airtight space is created between first O-ring 533 and second O-ring 534 unless there is a defect.

[0072] For example, the first O-ring 533 and the second O-ring 534 can be embedded so as to protrude 1.27 to 1.58 mm above the mounting surface 532. Furthermore, in the pressing step, from the viewpoint of improving airtightness, the first O-ring 533 and the second O-ring 534 are preferably compressed by 0.3 mm or more, more preferably by 0.5 mm or more, and even more preferably by 0.7 mm or more. The same conditions for the pressing step can be used when carrying out the film-forming step and when carrying out the gas leak test described below. Therefore, the film-forming step can be carried out subsequently while maintaining the pressing conditions used in the gas leak test method.

[0073] The specifications of the first O-ring 533 and the second O-ring 534 are not particularly limited and may be selected appropriately taking into account the purpose of the inspection. However, in order to enhance the airtightness of the space between the first O-ring 533 and the second O-ring 534, it is desirable that the specifications of the first O-ring 533 and the second O-ring 534 be the same except for the difference in opening area (diameter), such as the wire diameter (meaning the equivalent diameter of a circle in a cross section perpendicular to the circumferential direction), the height protruding upward from the mounting surface 532, and the material. For example, the wire diameter of the first O-ring 533 and the second O-ring 534 may be 5.57 to 5.83 mm. Furthermore, the type A durometer hardness of the first O-ring 533 and the second O-ring 534 measured in accordance with JIS K6253-3:2012 may be 65 to 75. The material of the first O-ring 533 and the second O-ring 534 may be rubber, such as nitrile rubber.

[0074] The distance S between the first O-ring 533 and the second O-ring 534 is not particularly limited, and it is sufficient if the distance S is large enough to perform the gas leak inspection method while taking into account the dimensions of the gas outlet 514e (e.g., 2 to 4 mm in equivalent circle diameter). However, if the distance S is too large, the gas leak inspection will take a long time. Therefore, the distance S may be, for example, 3 mm or more, typically 3 to 10 mm, and more typically 4.5 to 8.5 mm. The distance S refers to the length of a line segment extending from a point on the outer periphery of the first O-ring 533 to a point on the inner periphery of the second O-ring 534, the line segment being perpendicular to the tangent line that connects the tangent point, when the line segment is extended toward the inner periphery of the second O-ring 534. The distance S being within the range of X to Y means that the distance S is within the range of X to Y regardless of the point on the outer periphery of the first O-ring 533 from which the distance S is measured.

[0075] When the cross-sectional area of ​​the flow path of the aerosol flowing through the chamber 513 is larger than the size of the inlet-side bottom surface 504, a tapered portion 513h may be provided on the side wall 513d so that the cross-sectional area of ​​the flow path gradually decreases toward the inlet-side bottom surface 504. It is preferable that the outline of the flow path cross section formed by the tapered portion 513h at the downstream end of the side wall 513d matches the outer circumferential outline of the inlet-side bottom surface 504. By providing the tapered portion 513h, ceramic particles are more likely to be sucked into the inlet-side bottom surface 504.

[0076] The distance L from the outlet of the nozzle 511a to the inlet side bottom surface 504 of the columnar honeycomb structure 500 is preferably designed in accordance with the area A of the inlet side bottom surface 504 of the columnar honeycomb structure 500. Specifically, the area A (mm 2 ) increases, it is preferable to increase the distance L (mm) because this makes it easier for the aerosol to spread uniformly in the direction perpendicular to the direction of the aerosol flow.

[0077] The aerosol sprayed from the aerosol generator 511 passes through the inside of the chamber 513 by the suction force of the blower 512, and is then sucked into the first cells of the columnar honeycomb structure 500 from the inlet-side bottom surface 504 of the columnar honeycomb structure 500 held by the holder 514. The ceramic particles in the aerosol sucked into the first cells adhere to the surfaces of the first cells.

[0078] The housing 520 has an exhaust port 520e downstream of the outlet-side bottom surface 506 of the columnar honeycomb structure 500. The exhaust port 520e is connected to an exhaust pipe 515, and a blower 512 is provided downstream of the exhaust port 520e. Therefore, when the aerosol from which the ceramic particles have been removed is discharged from the outlet-side bottom surface 506 of the columnar honeycomb structure 500, it passes through the exhaust pipe 515 and is then exhausted through the blower 512. A flow meter 516 is provided in the exhaust pipe 515, so that the gas flow rate measured by the flow meter 516 can be monitored, and the strength of the blower 512 can be controlled according to the gas flow rate.

[0079] As the film-forming process of adhering ceramic particles to the surfaces of the first cells continues, the pressure loss between the inlet-side bottom surface and the outlet-side bottom surface of the columnar honeycomb structure increases as the amount of ceramic particles attached increases. Therefore, by determining the relationship between the amount of ceramic particles attached and the pressure loss in advance, the end point of the film-forming process of adhering ceramic particles to the surfaces of the first cells can be determined based on the pressure loss. Therefore, the particle attachment device 510 can be equipped with a differential pressure gauge 550 to measure the pressure loss between the inlet-side bottom surface 504 and the outlet-side bottom surface 506 of the columnar honeycomb structure 500, and the end point of the process can be determined based on the value of the differential pressure gauge.

[0080] 8 is a schematic diagram illustrating a method for replacing a workpiece (a columnar honeycomb structure 500) to be placed in the particle attachment device. First, the first workpiece 1 is placed in the particle attachment device, and the film forming process is carried out on the workpiece 1 by the method described above (Step 1). Step 1 can be performed in a state where the holder 514 holding the workpiece 1 is pressed against the first O-ring and the second O-ring of the mounting jig 530 via the housing 520 by the pressing force from the electric cylinder 570.

[0081] When the film-forming process is completed, the housing 520 is lifted by the electric cylinder 570 (step 2). This allows access to the holder 514 holding the workpiece 1, and also releases the pressing force, making it possible to easily remove the holder 514 holding the workpiece 1 from the mounting jig 530.

[0082] Next, the workpiece 1 is removed from the particle attachment device together with the holder 514, and the holder 514 holding the second workpiece 2 is installed in the particle attachment device (step 3). By holding the workpiece 2 in the holder 514 in advance, it is possible to shorten the workpiece replacement process. Thereafter, as in step 1, the film formation process is carried out on the workpiece 2 using the method described above (step 4). By repeating this operation, it is possible to efficiently carry out the film formation process on a large number of pillar-shaped honeycomb structures 500.

[0083] After removing the columnar honeycomb structure with ceramic particles attached to the surfaces of the first cells from the holder 514, the columnar honeycomb structure is heat-treated at a maximum temperature of 1000°C or higher for at least 1 hour, e.g., 1 to 6 hours, typically at a maximum temperature of 1100°C to 1400°C for 1 to 6 hours, to complete the columnar honeycomb structure filter. The heat treatment can be performed, for example, by placing the columnar honeycomb structure in an electric furnace or gas furnace. The heat treatment bonds the ceramic particles together and causes them to adhere to the partition walls within the first cells, forming a porous film on the surfaces of the first cells. When the heat treatment is performed under oxygen-containing conditions such as air, a surface oxide film is formed on the ceramic particle surfaces, promoting bonding between the ceramic particles. This results in a porous film that is less likely to peel off.

[0084] <3. Gas leak inspection method> Before carrying out the film-forming process on the columnar honeycomb structure, a gas leak inspection method according to one embodiment of the present invention can be carried out. This gas leak inspection method makes it possible to determine in advance whether or not the film-forming process should be carried out on the columnar honeycomb structure. Therefore, by carrying out the film-forming process on the columnar honeycomb structure only if it passes the inspection, it is possible to expect an improvement in the yield of columnar honeycomb structure filters. Furthermore, if the inspection is not passed, this means that there is some abnormality in the particle attachment device, and therefore, it is possible to immediately carry out the necessary repairs.

[0085] In one embodiment, the gas leak detection method includes: a step of preparing a mounting jig (530) that is installed at an upper end (513e) of the chamber (513) and has a mounting surface (532) having an opening (531), a first O-ring (533) that is embedded in the mounting surface (532) so as to protrude partially upward and that surrounds the outer periphery of the opening (531), and a second O-ring (534) that is embedded in the mounting surface (532) so as to protrude partially upward and that surrounds the outer periphery of the first O-ring (533) at a distance; a step of preparing a holder 514 having a chuck mechanism 514b having through holes 514c extending in the vertical direction and capable of gripping the columnar honeycomb structure 500 inserted into the through holes 514c from the outer peripheral side wall 502 side, a gas inlet 514d, a gas outlet 514e provided on a lower surface 514f, and a gas passage 514g communicating the gas inlet 514d and the gas outlet 514e; a step of holding the columnar honeycomb structure 500 by a chuck mechanism 514b of a holder 514; a step of pressing a lower surface 514f of the holder 514 holding the columnar honeycomb structure 500 against the first O-ring 533 and the second O-ring 534 of the mounting jig 530, on the condition that the gas outlet 514e is positioned between the first O-ring 533 and the second O-ring 534; a step of supplying gas from the gas inlet 514d of the holder 514 while maintaining the pressing step, and measuring the flow rate of the gas with a flow meter 562; determining whether the flow rate measured by the flow meter 562 exceeds a predetermined threshold; Includes:

[0086] There are no particular limitations on the type of gas used in the test. For example, air, nitrogen, argon, etc. can be used. However, air is preferred from the standpoints of simplicity, cost, and safety. Furthermore, if the gas pressure at the gas inlet 514d of the holder 514 is too high when gas is supplied from the gas inlet 514d, gas leakage will occur even when the desired airtightness is achieved, making it difficult to set the threshold. Furthermore, if the gas pressure is too low, gas leakage will not occur even when the airtightness is poor, resulting in reduced test accuracy. Therefore, it is preferable to set the gas pressure so that gas leakage is almost undetectable when the desired airtightness is achieved. From this perspective, the gas pressure is preferably, for example, 0.01 to 0.05 MPaG, and more preferably 0.03 to 0.05 MPaG.

[0087] Even if the airtightness of the space between the first O-ring 533 and the second O-ring 534, sandwiched between the lower surface 514f of the holder 514 and the mounting surface 532 of the mounting jig 530, is the same, the threshold value to be set varies depending on the pressure of the supplied gas. Therefore, the threshold value used as the criterion for determining whether or not there is a gas leak can be set arbitrarily as long as it is possible to determine whether or not there is sufficient airtightness that does not affect the flow of the aerosol during the film formation process. For example, it can be set to any value in the range of 0 to 0.10 L / min, converted to a state of 1 atmosphere and 20°C. In particular, when the gas pressure at the gas inlet 514d is set to 0.01 to 0.05 MPaG, it is preferable to set the threshold value to any value in that range.

[0088] As a result of carrying out a step of determining whether the flow rate measured by the flow meter 562 exceeds a predetermined threshold, if it is determined that the threshold is not exceeded, the film-forming step can be carried out while maintaining the pressing step. This allows the film-forming step to be carried out while maintaining a state in which a predetermined airtightness is ensured, making it possible to reduce the rate of defective products and improve yield. [Explanation of symbols]

[0089] 100: Pillar honeycomb structure filter 102: Outer wall 104: Bottom of the inlet 106: Outlet side bottom surface 108: First cell 109: Plugging part 110: Second cell 112: Bulkhead 114: Porous membrane 400: Aerosol generator 401: Nozzle 402: Ceramic particles 403: Flow path 403e :Exit 407: Drive gas flow path 407i: Supply port 407v: Venturi section 409: Storage unit 409e :Exit 409i :Entrance 410: Venturi ejector 411: Powder quantitative feeder 420: Aerosol generator 500: Pillar honeycomb structure 502: Peripheral side wall 504: Bottom of the inlet 506: Outlet side bottom surface 510: Particle attachment device 511: Aerosol generator 511a: Nozzle 512: Blower 513: Chamber 513a: Opposing surfaces 513b: Insertion port 513c :Aperture 513d: Side wall 513e :Top edge 513f: Bottom end 513g: Filter 513h: Tapered section 514: Holder 514a: Main body part 514b: Chuck mechanism 514c:Through hole 514d: Gas inlet 514e: Gas outlet 514f: Bottom surface 514g: Gas passage 515: Exhaust pipe 516:Flowmeter 520: Housing 520e: Exhaust port 530: Mounting jig 531 :Aperture 532: Placement surface 533: First O-ring 534: Second O-ring 535: Flange part 550: Differential pressure gauge 561: Gas piping 562:Flow meter 570: Electric cylinder

Claims

1. A gas leak inspection method before a film forming process is performed on a columnar honeycomb structure, The columnar honeycomb structure includes an outer peripheral side wall, a plurality of first cells arranged on the inner peripheral side of the outer peripheral side wall, extending from the inlet side bottom surface to the outlet side bottom surface, having an open inlet side bottom surface and having plugging portions on the outlet side bottom surface, and a plurality of second cells arranged on the inner peripheral side of the outer peripheral side wall, extending from the inlet side bottom surface to the outlet side bottom surface, having plugging portions on the inlet side bottom surface and having an open outlet side bottom surface, the plurality of first cells and the plurality of second cells being arranged alternately adjacent to each other with porous partition walls interposed therebetween, a step of preparing a mounting jig that is installed at the upper end of a chamber and has a mounting surface having an opening, a first O-ring that is embedded in the mounting surface so that a portion of the first O-ring protrudes upward and surrounds the outer periphery of the opening, and a second O-ring that is embedded in the mounting surface so that a portion of the second O-ring protrudes upward and surrounds the outer periphery of the first O-ring at a distance; a step of preparing a holder having a through hole extending in the vertical direction and a chuck mechanism capable of gripping a columnar honeycomb structure inserted into the through hole from the outer peripheral side wall side, a gas inlet, a gas outlet provided on the lower surface, and a gas passage communicating the gas inlet and the gas outlet; a step of holding the pillar-shaped honeycomb structure by a chuck mechanism of the holder; a step of pressing a lower surface of a holder holding the columnar honeycomb structure against the first O-ring and the second O-ring of the mounting jig, on the condition that the gas outlet is positioned between the first O-ring and the second O-ring; supplying gas from a gas inlet of the holder while maintaining the pressing step, and measuring the flow rate of the gas with a flow meter; determining whether a flow rate measured by the flow meter exceeds a predetermined threshold; A method comprising:

2. 2. The method according to claim 1, wherein the gas pressure at the gas inlet of the holder when supplying gas from the gas inlet is 0.01 to 0.05 MPaG.

3. 3. The method according to claim 1, wherein the predetermined threshold value is set to any value in the range of 0 to 0.10 L / min when converted to a state of 1 atmosphere and 20°C.

4. 3. The method of claim 1 or 2, wherein the gas is air.

5. The method according to claim 1 or 2, wherein the opening in the mounting surface and the through-hole in the chuck mechanism are coaxial.

6. 3. The method according to claim 1, wherein the wire diameter of the first O-ring and the second O-ring is 5.57 to 5.83 mm.

7. 3. The method according to claim 1, wherein the first O-ring and the second O-ring are embedded so as to protrude upward from the mounting surface by 1.27 to 1.58 mm.

8. 3. The method according to claim 1, wherein the first O-ring and the second O-ring are compressed by 0.3 mm or more in the pressing step.

9. The method according to claim 1 or 2, wherein the first O-ring and the second O-ring have a type A durometer hardness of 65 to 75 measured in accordance with JIS K6253-3:2012.

10. 3. The method according to claim 1, wherein the first O-ring and the second O-ring are made of nitrile rubber.

11. 3. The method according to claim 1, wherein the distance between the first O-ring and the second O-ring is 3 mm or more.

12. In the method described in claim 1 or 2, a method for manufacturing a columnar honeycomb structure filter includes a film-forming process in which, when a step of determining whether the flow rate measured by a flow meter exceeds a predetermined threshold is performed and it is determined that the flow rate does not exceed the threshold, while maintaining the pressing process, an aerosol containing ceramic particles is sprayed into the chamber from the nozzle of an aerosol generator in a direction perpendicular to the inlet bottom surface of the columnar honeycomb structure toward the inlet bottom surface, while applying suction force to the outlet bottom surface, thereby sucking the sprayed aerosol from the inlet bottom surface and adhering the ceramic particles to the surface of the first cells.

Images