Method for predicting whether or not to acquire post-fired columnar honeycomb molding with prescribed specifications

Abstract

To provide a method for predicting whether to acquire a post-fired columnar honeycomb molding with prescribed design specifications on the basis of a pre-fired columnar honeycomb molding.SOLUTION: A method for predicting whether to acquire a post-fired columnar honeycomb molding with prescribed design specifications, includes a step 1: measuring, for the number of 90% or more of polygonal cells, excluding partial cells on an outermost periphery, one or more types of parameters selected from a structural coefficient characterizing a shape of an opening, a cell direction and a long side / short side ratio, and an area of a partition wall defining a corner by observing at least one of a first bottom surface and a second bottom surface of a pre-fired columnar honeycomb molding; a step 2 of calculating one or more types of statistics according to the parameters measured in the step 1, based on the result of the step 1; and a step 3 of comparing the one or more types of statistics calculated in the step 2 with predetermined criteria according to the prescribed design specifications and the types of the statistics.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] In one embodiment, the present invention relates to a method for searching for a statistical quantity correlated with the strength of a fired columnar honeycomb formed body, and in another embodiment, the present invention relates to a method for predicting whether or not a fired columnar honeycomb formed body meeting predetermined design specifications can be obtained. [Background technology]

[0002] In various fields such as automobiles, chemicals, electricity, and steel, a ceramic columnar honeycomb structure having excellent heat resistance and corrosion resistance is used as a catalyst carrier or filter used for environmental measures and recovery of specific materials. The columnar honeycomb structure has an outer peripheral side wall and partition walls disposed on the inner peripheral side of the outer peripheral side wall and defining a plurality of cells extending from a first bottom surface to a second bottom surface. In general, the columnar honeycomb structure is manufactured by mixing and kneading a ceramic raw material powder, a dispersion medium, a binder, a pore-forming agent, etc. to prepare a clay, which is then molded into a predetermined shape to form a columnar honeycomb molded body, which is then fired.

[0003] Pillared honeycomb structures require sufficient mechanical strength to withstand impact and thermal loads, and in particular those used as vehicle filters or catalyst supports must have sufficient mechanical strength to allow them to be placed into metal housings during a process called "canning."

[0004] One measure of the mechanical strength of a columnar honeycomb structure is its isostatic fracture strength. In measuring the isostatic fracture strength of a columnar honeycomb structure, a test is conducted in which the columnar honeycomb structure is submerged in water in a pressure vessel, and the water pressure is gradually increased to apply isotropic pressure to the columnar honeycomb structure. The gradual increase in water pressure in the pressure vessel eventually causes destruction in the partition walls and outer peripheral side walls of the columnar honeycomb structure. The pressure value (fracture strength) at which destruction occurs is the isostatic fracture strength.

[0005] However, when measuring the isostatic fracture strength, it is time-consuming to set a test specimen in a pressure vessel and apply pressure. In addition, the measurement of the isostatic fracture strength causes damage to the columnar honeycomb structure. For this reason, it is unrealistic to directly measure the isostatic fracture strength for quality inspection of the columnar honeycomb structure. For these reasons, methods for easily performing strength inspection of the columnar honeycomb structure have been proposed.

[0006] For example, JP 2017-96879 A (Patent Document 1) and JP 2001-41867 A (Patent Document 2) propose a simple breaking strength testing method that uses an elastic body and can shorten the measurement time.

[0007] JP2019-512079A (Patent Document 3) discloses a non-contact method for characterizing the isostatic fracture strength of a ceramic article having a web, the method including the steps of recording a digital image of the web, forming a 2D representation of the ceramic article based on the digital image, simulating a selected amount of isostatic pressure applied to the 2D representation to identify a maximum stress value in the 2D representation of the web, and identifying the isostatic fracture strength of the ceramic article using the maximum stress value.

[0008] In addition, although not an invention intended to inspect the strength of a columnar honeycomb structure, JP 2015-161543 A (Patent Document 4) proposes using an image analysis device to measure the size of the inscribed circle inscribed in the partition wall for only a specified portion of cells, for the purpose of inspecting cell deformation defects in a ceramic honeycomb structure in a short period of time.

[0009] Patent Publication No. 2021-139856 (Patent Document 5) discloses an inspection method for a columnar honeycomb formed body before or after firing that can be performed non-destructively and can replace strength testing, based on the finding that the number of cells having openings of abnormal size among the multiple cells held by a columnar ceramic formed body before or after firing shows a significant correlation with the strength of the columnar honeycomb formed body after firing. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2017-96879 A [Patent Document 2] JP 2001-41867 A [Patent Document 3] Special Publication No. 2019-512079 [Patent Document 4] JP 2015-161543 A [Patent Document 5] JP 2021-139856 A Summary of the Invention [Problem to be solved by the invention]

[0011] Although the test methods described in Patent Documents 1 and 2 do not result in destruction, they still require a large amount of work and a long inspection time because they actually apply pressure to the columnar honeycomb structure to inspect its strength. There is also a risk of damaging the product. Patent Document 3 discloses a method for predicting isostatic destruction strength without contact, but this requires complex simulations and the accuracy of the prediction is unclear.

[0012] In Patent Document 4, the presence or absence of deformation defects in some of the cells of a columnar honeycomb structure is inspected using an image analyzer, and the ratio of cells having cell deformation defects among the measured cells is calculated. However, it is unclear what relationship the deformation defects of some of the cells have with the strength of the columnar honeycomb structure.

[0013] In Patent Document 5, the size of the openings of a plurality of cells of a columnar honeycomb formed body before firing is measured, and based on the measurement results, abnormal cells having openings with sizes that deviate from a predetermined allowable range are identified from among the plurality of cells, and the number of abnormal cells is counted. However, the inspection method described in Patent Document 5 requires setting a criterion for determining whether each cell is abnormal or not, and it is possible that the inspection of the columnar honeycomb formed body can be performed by a method other than the method of individually determining the presence or absence of abnormal cells. In addition, depending on the design specifications of the columnar honeycomb formed body, such as size, shape, cell structure, material, etc., there is still a possibility that a method better than the inspection method described in Patent Document 5 will be found.

[0014] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a method for searching for statistics of a columnar honeycomb formed body before firing that can be measured non-destructively and that correlates with the strength of the columnar honeycomb formed body after firing. Also, an object of the present invention is to provide a method for predicting, based on the columnar honeycomb formed body before firing, whether or not a columnar honeycomb formed body of predetermined design specifications can be obtained after firing. [Means for solving the problem]

[0015] [1] A method for searching for a statistical quantity correlated with the strength of a fired columnar honeycomb formed body having a predetermined design specification, the columnar honeycomb structure portion having an outer peripheral side wall and partition walls disposed on the inner peripheral side of the outer peripheral side wall and partitioning a plurality of polygonal cells forming a flow path from a first bottom surface to a second bottom surface, the method comprising: A process A of producing a plurality of unfired columnar honeycomb formed bodies for producing fired columnar honeycomb formed bodies having predetermined design specifications; A process B for measuring two or more measurable parameters by observing at least one of the first bottom surface or the second bottom surface of each of the plurality of unfired columnar honeycomb molded bodies produced in the process A for 90% or more of the polygonal cells excluding the partial cells in the outermost periphery, and calculating two or more statistics for each of the measured parameters; A process C of firing each of the plurality of unfired columnar honeycomb formed bodies produced in the process A under predetermined conditions to produce a plurality of fired columnar honeycomb formed bodies; A process D for evaluating the correlation between two or more statistical quantities calculated in the process B for each parameter and the strength of the plurality of fired columnar honeycomb formed bodies produced in the process C; A step E of determining, based on the result of the step D, a statistical quantity having a highest correlation with the strength of a columnar honeycomb formed body after firing having a predetermined design specification from among the two or more statistical quantities; The method includes: [2] The method according to [1], wherein the two or more parameters are two or more parameters selected from one or more parameters characterizing the shape or size of the opening of each polygonal cell, one or more parameters characterizing the shape or size of the partition portions defining each side of each polygonal cell, and one or more parameters characterizing the shape or size of the partition portions defining each corner of each polygonal cell. [3] the one or more parameters characterizing the shape or size of the opening portion of each polygonal cell include one or more selected from an opening area, an inscribed circle radius, an approximate rectangular short side, an approximate rectangular long side, rectangularity, circularity, compactness, a contour length, a convexity, a major axis / minor axis ratio, an ellipticity, a structure coefficient, a center distance deviation, a roundness, a circumscribed circle radius, an approximate ellipse major axis, an approximate ellipse minor axis, a cell direction, and a major axis / minor axis ratio; The one or more parameters characterizing the shape or size of the partition wall portion defining each side of each polygonal cell include one or more selected from a partition wall curvature, a partition wall thickness, and a partition wall direction; One or more parameters characterizing the shape or size of the partition portion defining each corner of each polygonal cell include an area of ​​the partition portion defining the corner; The method described in [2]. [4] The method according to any one of [1] to [3], wherein the two or more parameters are ten or more parameters. [5] The method according to any one of [1] to [4], wherein the two or more types of statistics are five or more types of statistics. [6] The method according to any one of [1] to [5], wherein the two or more types of statistical quantities include two or more types selected from arithmetic mean, standard deviation, kurtosis, skewness, minimum value, median, and maximum value. [7] The method according to any one of [1] to [6], wherein the strength is an isostatic fracture strength. [8] A method for predicting whether or not a fired columnar honeycomb formed body having a predetermined design specification can be obtained when fired under predetermined firing conditions, based on a measurement result of a columnar honeycomb formed body before firing, the columnar honeycomb formed body having a columnar honeycomb structure portion including an outer peripheral side wall and partition walls disposed on the inner peripheral side of the outer peripheral side wall and partitioning a plurality of polygonal cells that form a flow path from a first bottom surface to a second bottom surface, the method comprising: A step 1 of measuring one or more parameters selected from a structural coefficient characterizing the shape of an opening, a cell direction and a long side / short side ratio, and an area of ​​a partition wall portion defining a corner, for 90% or more of polygonal cells excluding partial cells at the outermost periphery, by observing at least one of a first bottom surface or a second bottom surface of the columnar honeycomb formed body before firing; If the parameter measured in step 1 is a structure coefficient, one or more statistics selected from an arithmetic mean and a median; If the parameter measured in step 1 is a cell direction, one or more statistics selected from standard deviation and kurtosis; When the parameter measured in step 1 is a long side / short side ratio, one or more statistical quantities selected from an arithmetic mean, a standard deviation, and a maximum value; When the parameter measured in step 1 is the area of ​​a partition portion defining a corner, one or more statistical quantities selected from kurtosis and skewness; A step 2 of calculating based on the result of the step 1; A step 3 of comparing one or more types of statistics calculated in the step 2 with a judgment criterion that is predetermined according to the predetermined design specifications and the types of the statistics; The method includes: [9] The method according to [8], which includes a step 4 of estimating the strength of a columnar honeycomb formed body after firing the pre-fired columnar honeycomb formed body under the specified firing conditions based on the one or more statistical quantities calculated in step 2, utilizing a correlation between the one or more statistical quantities for the pre-fired columnar honeycomb formed body and the strength of the other multiple columnar honeycomb formed bodies after firing under the specified firing conditions, which correlation was previously obtained for a plurality of other columnar honeycomb formed bodies having the same design specifications as the columnar honeycomb formed body.

[10] The method according to claim 9, wherein the strength is the isostatic fracture strength. Effect of the Invention

[0016] According to one embodiment of the present invention, there is provided a method for searching for statistics of a columnar honeycomb formed body before firing that can be measured non-destructively and that are correlated with the strength of the columnar honeycomb formed body after firing. The searching method according to this embodiment targets two or more types of parameters (feature quantities) that can be measured by observing at least one of the first bottom surface or the second bottom surface. Since bottom surface observation can be performed non-destructively and easily, the searching method according to this embodiment is highly convenient.

[0017] In addition, parameters highly correlated with post-fired strength may vary depending on the design specifications of the columnar honeycomb formed body, such as size, shape, cell structure, material, etc., but by employing the search method according to the embodiment, it is possible to find optimal parameters and statistics according to the design specifications of the columnar honeycomb formed body. Therefore, according to the search method according to the embodiment, it is possible to find an optimal non-destructive inspection method according to the type and product number of the honeycomb formed body.

[0018] When the statistics of the unfired columnar honeycomb formed body that are correlated with the strength of the fired columnar honeycomb formed body are found, it becomes possible to provide a method for predicting whether or not a fired columnar honeycomb formed body having a predetermined design specification can be obtained based on the unfired columnar honeycomb formed body. This prediction method can also be used for estimating the strength and inspecting the quality of the fired columnar honeycomb formed body.

[0019] By carrying out the prediction method on a columnar honeycomb formed body before firing, formed bodies that are predicted not to produce a columnar honeycomb formed body of a predetermined design specification after firing can be excluded from firing as rejected products. This has the advantage of not wasting the cost and time required for firing. If rejected products can be selected before firing, they can be easily reused as forming raw materials, which is preferable. [Brief description of the drawings]

[0020] [Figure 1] FIG. 2 is a perspective view showing a typical wall-through type columnar honeycomb formed body. [Diagram 2] FIG. 2 is a schematic cross-sectional view of a wall-through type columnar honeycomb formed body observed from a direction perpendicular to the cell extension direction. [Diagram 3] FIG. 2 is a perspective view showing a schematic view of a wall-flow type columnar honeycomb formed body. [Figure 4] FIG. 2 is a schematic cross-sectional view of a wall-flow type columnar honeycomb formed body observed from a direction perpendicular to the cell extension direction. [Diagram 5] FIG. 2 is a schematic diagram showing an example of an opening shape of a cell. [Figure 6] 1 is a schematic diagram showing straight partition portions that define straight portions of polygonal cells, and partition portions that define corners of polygonal cells. FIG. [Figure 7] 10A and 10B are schematic diagrams illustrating an example of a partition wall in which bending has occurred. [Figure 8] FIG. 1 shows an example of a functional block diagram of an image analyzing device. [Figure 9]1 shows the results of plotting the standard deviation of the long side / short side ratio on a two-dimensional coordinate system with the horizontal axis representing the standard deviation and the vertical axis representing the isostatic fracture strength of the honeycomb formed body according to Test Example 1. [Figure 10] For the honeycomb formed body according to Test Example 2, the standard deviation of the approximate rectangular short side is plotted on a two-dimensional coordinate system with the horizontal axis representing the standard deviation and the vertical axis representing the isostatic fracture strength. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Next, an embodiment 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 embodiment, and that appropriate changes and improvements in the design may be made based on the ordinary knowledge of a person skilled in the art without departing from the spirit of the present invention.

[0022] <1. Columnar honeycomb formed body> The statistical quantity search method according to the present invention can observe a columnar honeycomb molded body before firing. In general, the columnar honeycomb molded body has a columnar honeycomb structure portion including an outer peripheral side wall and partition walls disposed on the inner peripheral side of the outer peripheral side wall and partitioning a plurality of cells that form a flow path from a first bottom surface to a second bottom surface.

[0023] 1 and 2 are schematic perspective and cross-sectional views, respectively, of a columnar honeycomb formed body 100 applicable as a wall-through type exhaust gas filter and / or catalyst carrier for an automobile. This columnar honeycomb formed body 100 has a columnar honeycomb structure portion provided with an outer peripheral side wall 102 and partition walls 112 disposed on the inner peripheral side of the outer peripheral side wall 102 and partitioning a plurality of cells 108 forming a fluid flow path from a first bottom surface 104 to a second bottom surface 106. In this columnar honeycomb formed body 100, both ends of each cell 108 are open, and exhaust gas flowing into one cell 108 from the first bottom surface 104 is purified while passing through the cell, and flows out from the second bottom surface 106.

[0024] 3 and 4 are schematic perspective and cross-sectional views, respectively, of a columnar honeycomb formed body 200 applicable as a wall-flow type exhaust gas filter for automobiles and / or a catalyst carrier. This columnar honeycomb formed body 200 has a columnar honeycomb structure portion provided with an outer peripheral side wall 202 and partition walls 212 disposed on the inner peripheral side of the outer peripheral side wall 202 and partitioning a plurality of cells 208a, 208b that form a fluid flow path from a first bottom surface 204 to a second bottom surface 206.

[0025] In the columnar honeycomb formed body 200, the multiple cells 208a, 208b can be classified into multiple first cells 208a arranged inside the outer peripheral side wall 202, extending from the first bottom surface 204 to the second bottom surface 206, with the first bottom surface 204 open and with plugging portions 209 on the second bottom surface 206, and multiple second cells 208b arranged inside the outer peripheral side wall 202, extending from the first bottom surface 204 to the second bottom surface 206, with plugging portions 209 on the first bottom surface 204, and with the second bottom surface 206 open. In this columnar honeycomb formed body 200, the first cells 208a and the second cells 208b are arranged alternately adjacent to each other with the partition wall 212 in between.

[0026] When exhaust gas containing particulate matter (PM) such as soot is supplied to the first bottom surface 204 on the upstream side of the fired columnar honeycomb molded body 200, the exhaust gas is introduced into the first cells 208a and proceeds downstream inside the first cells 208a. Since the first cells 208a have plugged portions 209 on the second bottom surface 206 on the downstream side, the exhaust gas passes through the porous partition walls 212 that separate the first cells 208a and the second cells 208b and flows into the second cells 208b. Since the particulate matter (PM) cannot pass through the partition walls 212, it is collected and accumulated inside the first cells 208a. After the particulate matter (PM) is removed, the clean exhaust gas that has flowed into the second cells 208b proceeds downstream inside the second cells 208b and flows out from the second bottom surface 206 on the downstream side.

[0027] The bottom shape of the columnar honeycomb molded bodies 100, 200 after firing is not limited, and may be, for example, a circular shape, an elliptical shape, a racetrack shape, an oval shape, or other round shape, a triangular shape, a rectangular shape, or other polygonal shape, or other irregular shape. The columnar honeycomb molded bodies 100, 200 shown in the figures have a circular bottom shape and are cylindrical as a whole.

[0028] The height of the columnar honeycomb molded body (the length from the first bottom surface to the second bottom surface) is not particularly limited, and may be set appropriately depending on the application and required performance. There is also no particular limit to the relationship between the height of the columnar honeycomb molded body and the maximum diameter of each bottom surface (referring to the maximum length of the diameters passing through the center of gravity of each bottom surface of the columnar honeycomb molded body). Therefore, the height of the columnar honeycomb molded body may be longer than the maximum diameter of each bottom surface, or the height of the columnar honeycomb molded body may be shorter than the maximum diameter of each bottom surface.

[0029] In the statistical quantity search method according to the present invention, from the viewpoint of easily finding parameters that are highly correlated with strength, a columnar honeycomb molded body having a plurality of cells, the opening shape of which is polygonal in a cross section perpendicular to the flow direction of the cells, is targeted. There are no particular limitations on the cell opening shape as long as it is polygonal, but a square, hexagon, octagon, or a combination of these is preferable. Of these, a square and a hexagon are preferable. By setting the cell opening shape in this way, the pressure loss when a fluid is passed through the columnar honeycomb molded body is reduced, and the purification performance of the catalyst is improved.

[0030] Here, the opening shape of a cell being "polygonal" does not necessarily mean that the opening shape of the actual cell is a strict mathematical polygon, but means that the opening shape of the cell in the design specifications is polygonal. Also, even if each corner (near the vertex) of a polygonal cell is curved by rounding or the like, it is considered to be polygonal. Referring to FIG. 5, each side of a polygonal cell 500 has a straight line portion 503 and curved corner portions 502 that are rounded or the like provided at both ends of the straight line portion 503. In this case, the ratio (L2 / L1) of the length (L2) of one curved corner portion 502 along one side to the length (L1) of one side of the polygonal cell 500 when it is assumed that the curved corner portion 502 does not exist can be, for example, 0.005 to 0.020. From the viewpoint of emphasizing suppression of cell deformation and maintaining low pressure loss as an exhaust gas filter, L2 / L1 is preferably set to 0.005 to 0.008, and from the viewpoint of emphasizing strength, it is preferably set to 0.011 to 0.017. Note that L1 and L2 here refer to values ​​in the design specifications of the columnar honeycomb formed body after firing.

[0031] The columnar honeycomb formed body may have cells whose cross-sectional shape is not polygonal, but from the viewpoint of making it easier to find parameters that are highly correlated with strength, it is preferable that the proportion of cells whose opening shape is polygonal among the total number of cells (including partial cells) contained in the columnar honeycomb formed body is 90% or more, more preferably 95% or more, and even more preferably 98% or more.

[0032] A "partial cell" refers to a cell located at the outermost periphery, at least a portion of which is defined by the outer peripheral sidewall. Since a partial cell has a portion of its outline defined by the outer peripheral sidewall, it has a different shape from cells other than partial cells (hereinafter also referred to as "normal cells") and has a smaller area than normal cells. Partial cells are provided as appropriate in consideration of the balance between the outer peripheral sidewall of the columnar honeycomb formed body and the cell arrangement, and are not defects but cells that exist due to the design specifications.

[0033] There is no particular restriction on the cell density (the number of cells per unit cross-sectional area) of the columnar honeycomb formed body after firing, and it is, for example, 6 to 2000 cells / square inch (0.9 to 311 cells / cm 2 ), more preferably 50 to 1000 cells / in2 (7.8 to 155 cells / cm2). 2 ), and particularly preferably 100 to 600 cells / square inch (15.5 to 92.0 cells / cm 2 Here, the cell density is calculated by dividing the number of cells in the columnar honeycomb formed bodies 100, 200 by the bottom area of ​​one side of the columnar honeycomb formed bodies 100, 200 excluding the outer peripheral side wall.

[0034] In the fired columnar honeycomb molded body, the partition walls can be porous. The porosity of the partition walls can be adjusted appropriately depending on the application, but from the viewpoint of keeping the pressure loss of the fluid low, it is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more. In addition, from the viewpoint of ensuring the strength of the fired columnar honeycomb molded body, the porosity of the partition walls is preferably 80% or less, more preferably 75% or less, and even more preferably 70% or less. The porosity is measured by mercury intrusion method using a mercury porosimeter in accordance with JIS R1655:2003.

[0035] The partition wall thickness in the fired columnar honeycomb molded body is preferably 150 μm or more, more preferably 170 μm or more, and even more preferably 190 μm or more from the viewpoints of ensuring strength and increasing collection efficiency in the case of filter applications. Also, the partition wall thickness is preferably 260 μm or less, more preferably 240 μm or less, and even more preferably 220 μm or less from the viewpoints of suppressing pressure loss.

[0036] When the fired columnar honeycomb molded body 100, 200 is used as a catalyst carrier, the surface of the partition wall 112, 212 can be coated with a catalyst according to the purpose. Examples of the catalyst include, but are not limited to, an oxidation catalyst (DOC) for increasing the exhaust gas temperature by oxidizing and burning hydrocarbons (HC) and carbon monoxide (CO), a PM combustion catalyst for assisting the combustion of PM such as soot, an SCR catalyst and an NSR catalyst for removing nitrogen oxides (NOx), and a three-way catalyst capable of simultaneously removing hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). The catalyst can appropriately contain, for example, precious metals (Pt, Pd, Rh, etc.), alkali metals (Li, Na, K, Cs, etc.), alkaline earth metals (Mg, Ca, Ba, Sr, etc.), rare earths (Ce, Sm, Gd, Nd, Y, La, Pr, etc.), transition metals (Mn, Fe, Co, Ni, Cu, Zn, Sc, Ti, Zr, V, Cr, etc.), etc.

[0037] <2. Manufacturing method of columnar honeycomb formed body> The columnar honeycomb molded body can be produced by known production methods, which are described below as examples. First, a raw material composition containing ceramic raw materials, a dispersion medium, a pore-forming agent, and a binder is kneaded to produce a clay, which is then extruded and dried to produce a columnar honeycomb molded body before firing. Additives such as a dispersant can be blended into the raw material composition as necessary. When extruding, a die having the desired overall shape, cell shape, partition wall thickness, cell density, etc. can be used.

[0038] In the drying step, for example, a conventionally known drying method such as hot air drying, microwave drying, dielectric drying, reduced pressure drying, vacuum drying, freeze drying, etc. Among them, a drying method combining hot air drying with microwave drying or dielectric drying is preferred because it can quickly and uniformly dry the entire formed body. The plugging portions can be formed by forming plugging portions at predetermined positions on both bottom surfaces of the dried honeycomb formed body and then drying the plugging portions.

[0039] The ceramic raw material is a raw material of a part that remains after firing of metal oxides and metals, etc., and constitutes the skeleton of a columnar honeycomb formed body (columnar honeycomb structure) after firing as a ceramic. The ceramic raw material can be provided in the form of, for example, 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 alone or in combination of two or more types.

[0040] 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 by firing. 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).

[0041] The dispersion medium may be water or a mixed solvent of water and an organic solvent such as alcohol, with water being particularly preferred.

[0042] The pore-forming agent is not particularly limited as long as it becomes pores after firing, and examples thereof include wheat flour, starch, foamed resin, water-absorbent resin, silica gel, carbon (e.g., graphite, coke), ceramic balloons, polyethylene, polystyrene, polypropylene, nylon, polyester, acrylic, and phenol. The pore-forming agent may be used alone or in combination of two or more. The content of the pore-forming agent 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, relative to 100 parts by mass of the ceramic raw material, from the viewpoint of increasing the porosity of the honeycomb formed body after firing. The content of the pore-forming agent 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, relative to 100 parts by mass of the ceramic raw material, from the viewpoint of ensuring the strength of the honeycomb formed body after firing.

[0043] Examples of the binder include organic binders such as methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol. In particular, it is preferable to use methyl cellulose and hydroxypropyl methyl cellulose in combination. In addition, the content of the binder 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, relative to 100 parts by mass of the ceramic raw material, from the viewpoint of increasing the strength of the honeycomb molded body before firing. The content of the binder 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, relative to 100 parts by mass of the ceramic raw material, from the viewpoint of suppressing the occurrence of cracks due to abnormal heat generation in the firing process. The binder may be used alone or in combination of two or more types.

[0044] The dispersant may be ethylene glycol, dextrin, fatty acid soap, polyether polyol, etc. The dispersant may be used alone or in combination of two or more. The content of the dispersant is preferably 0 to 2 parts by mass per 100 parts by mass of the ceramic raw material.

[0045] The columnar honeycomb formed body may have both ends of all cells open, as in the columnar honeycomb formed body 100 shown in Figures 1 and 2. The columnar honeycomb formed body may also have a cell structure in which one end of the cells is alternately plugged, as in the columnar honeycomb formed body 200 shown in Figures 3 and 4. The method for plugging the bottom surface of the columnar honeycomb formed body is not particularly limited, and known methods can be adopted.

[0046] The material of the plugging portion is not particularly limited, but is preferably ceramics from the viewpoint of strength and heat resistance. The ceramic is preferably ceramics 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. The plugging portion is preferably formed of a material containing 50 mass% or more of these ceramics in total, and more preferably formed of a material containing 80 mass% or more. It is even more preferable that the plugging portion has the same material composition as the main body of the honeycomb formed body, since the expansion coefficient during firing can be made the same, which leads to improved durability.

[0047] A method for forming plugging portions will be described by way of example. Plugging slurry is stored in a storage container. Next, a mask having openings at locations corresponding to the cells in which plugging portions are to be formed is attached to one of the bottom surfaces. The bottom surface with the mask attached is immersed in the storage container, and the plugging slurry is filled into the openings to form plugging portions. Plugging portions can also be formed on the other bottom surface in the same manner.

[0048] A degreasing process and a firing process are carried out on the pre-fired columnar honeycomb formed body to manufacture a fired columnar honeycomb formed body (columnar honeycomb structure). The conditions for the degreasing process and the firing process may be any known condition depending on the material composition of the honeycomb formed body, and no particular explanation is required, but specific examples of the conditions are given below.

[0049] The degreasing step will now be described. The combustion temperature of the binder is about 200°C, and the combustion temperature of the pore-forming agent is about 300 to 1000°C. Therefore, the degreasing step may be carried out by heating the honeycomb molded body to a temperature range of about 200 to 1000°C. The heating time is not particularly limited, but is usually about 10 to 100 hours. The honeycomb molded body after the degreasing step is called a calcined body.

[0050] The firing step may vary depending on the material composition of the honeycomb formed body, but may be carried out, for example, by heating the calcined body to 1350 to 1600° C. in an air atmosphere and holding the body for 3 to 10 hours.

[0051] <3. Methods for searching for statistics that are correlated with strength> According to one embodiment of the present invention, A method for searching for a statistical quantity correlated with the strength of a fired columnar honeycomb formed body having a predetermined design specification, the columnar honeycomb structure portion having an outer peripheral side wall and partition walls disposed on the inner peripheral side of the outer peripheral side wall and partitioning a plurality of polygonal cells forming a flow path from a first bottom surface to a second bottom surface, the method comprising: A process A of producing a plurality of unfired columnar honeycomb formed bodies for producing fired columnar honeycomb formed bodies having predetermined design specifications; A process B for measuring two or more measurable parameters by observing at least one of the first bottom surface or the second bottom surface of each of the plurality of unfired columnar honeycomb molded bodies produced in the process A for 90% or more of the polygonal cells excluding the partial cells in the outermost periphery, and calculating two or more statistics for each of the measured parameters; A process C of firing each of the plurality of unfired columnar honeycomb formed bodies produced in the process A under predetermined conditions to produce a plurality of fired columnar honeycomb formed bodies; A process D for evaluating the correlation between two or more statistical quantities calculated in the process B for each parameter and the strength of the plurality of fired columnar honeycomb formed bodies produced in the process C; A step E of determining, based on the result of the step D, a statistical quantity having a highest correlation with the strength of a columnar honeycomb formed body after firing having a predetermined design specification from among the two or more statistical quantities; A method is provided that includes:

[0052] According to the search method of this embodiment, a statistical quantity having the highest correlation with the strength of a columnar honeycomb molded body after firing of a predetermined design specification is determined from statistical quantities related to two or more types of parameters that can be measured by observing at least one of the first bottom surface or the second bottom surface of the columnar honeycomb molded body before firing. Since bottom surface observation can be performed easily and non-destructively, the search method of this embodiment is highly convenient. In addition, the parameters that are highly correlated with the strength after firing may vary depending on the design specifications of the columnar honeycomb molded body, such as size, shape, cell structure, and material, but by employing the search method of this embodiment, it is possible to find optimal parameters and statistical quantities according to the type and product number of the columnar honeycomb molded body.

[0053] (Process A) In step A, a plurality of pre-fired columnar honeycomb molded bodies are produced in order to produce a fired columnar honeycomb molded body of a predetermined design specification. The method for producing the pre-fired columnar honeycomb molded body is as described above, and the target dimensions of the pre-fired columnar honeycomb molded body are usually determined taking into account shrinkage during firing. It is desirable to determine the die shape, extrusion molding conditions, drying conditions, etc. according to the raw material composition so that the pre-fired columnar honeycomb molded body to be produced approaches the target dimensions.

[0054] (Process B) In step B, for each of the multiple unfired columnar honeycomb molded bodies produced in step A, two or more parameters that can be measured by observing at least one of the first bottom surface or the second bottom surface are measured for at least 90%, preferably at least 95%, and more preferably all of the polygonal cells excluding the partial cells at the outermost periphery (hereinafter also referred to as "normal cells"), and two or more statistics are calculated for each measured parameter. The reason for measuring two or more parameters for the polygonal cells excluding the partial cells at the outermost periphery is to obtain highly reliable statistics. Partial cells are excluded from the parameter measurement targets because they are few in number and their correlation with strength is negligible.

[0055] In order to obtain highly reliable statistics, the number of pre-fired columnar honeycomb molded bodies to be measured in step B is preferably 10 or more, more preferably 20 or more, and even more preferably 50 or more. On the other hand, if the number of pre-fired columnar honeycomb molded bodies to be measured is too large, the workload increases. Furthermore, as the number of data increases, the statistics also converge. For this reason, the number of pre-fired columnar honeycomb molded bodies to be measured in step B is preferably 500 or less, more preferably 300 or less, and even more preferably 100 or less.

[0056] Among the parameters that can be measured by observing at least one of the first bottom face or the second bottom face, it is preferable to measure parameters that are predicted to have a high correlation with the strength of the fired columnar honeycomb molded body. Therefore, in a preferred embodiment, the measurement targets are two or more parameters selected from one or more parameters that characterize the shape or size of the openings of each polygonal cell, one or more parameters that characterize the shape or size of the partition wall portions that define each side of each polygonal cell, and one or more parameters that characterize the shape or size of the partition wall portions that define each corner of each polygonal cell.

[0057] The one or more parameters characterizing the shape or size of the opening of each polygonal cell are not limited to, but preferably include one or more selected from opening area, inscribed circle radius, approximate rectangular short side, approximate rectangular long side, rectangularity, circularity, compactness, contour length, convexity, long axis / short axis ratio, ellipticity, structure coefficient, center distance deviation, roundness, circumscribed circle radius, approximate ellipse long axis, approximate ellipse short axis, cell direction, and long axis / short axis ratio, and more preferably include at least the structure coefficient, cell direction, and long axis / short axis ratio.

[0058] The opening area refers to the area of ​​one cell opening. The inscribed circle radius refers to the radius of the largest circle inscribed in one cell opening. The approximate short side of a rectangle refers to the short side of the smallest rectangle that circumscribes the opening of one cell, taking into account rotation. The approximate long side of a rectangle refers to the long side of the smallest rectangle that circumscribes the opening of one cell, taking into account rotation. Rectangularity refers to the area of ​​the symmetric difference between the area of ​​a cell opening and the area of ​​an approximate rectangle when that cell opening is approximated by a rectangle. An approximate rectangle is a rectangle that has the same center of gravity, the same second moment, and the same area as that cell opening. The second moment is the same as the second moment used to calculate an approximate ellipse, which will be described later. Circularity refers to the ratio of the area of ​​a cell opening to the area of ​​an approximation of a perfect circle with the same center of gravity as the cell opening and the same area. Either ratio may be used as the denominator in the calculation. Compactness is the ratio of the area of ​​a cell opening to the contour length of the cell opening. Either denominator can be used to calculate the ratio. The contour length refers to the contour length of one cell opening. Convexity refers to the ratio of the area of ​​a cell opening to the area of ​​the approximate convex hull when the cell opening is approximated by a convex hull. The approximate convex hull is defined as the smallest convex set that contains the cell opening. The ratio can be calculated using either denominator. The long axis to short axis ratio refers to the ratio of the long axis to the short axis of an ellipse when approximating the opening of a cell with an ellipse. Either of these can be used as the denominator in the calculation of this ratio. For example, the equation of the approximating ellipse can be found by determining the coordinate values ​​of each pixel included in the area that constitutes the opening of a cell, finding the centroid coordinates from the image moment of that area, and then calculating the second moment from the centroid coordinates. The degree of ellipticity refers to the ratio of the area of ​​one cell opening to the area of ​​an ellipse when that cell opening is approximated by an ellipse. Either denominator can be used to calculate this ratio. The structural coefficient is calculated using the formula: (structural coefficient) = (ratio of major axis to minor axis) x (degree of ellipticity) - 1. The center distance deviation refers to the standard deviation of the length of multiple lines drawn connecting the outline of one cell opening to the center of gravity. It is preferable to draw 360 or more lines at equal angular intervals. Roundness refers to the ratio of the standard deviation of the length of the lines (center distance deviation) to the average length of the lines when multiple lines are drawn connecting the outline of one cell opening to the center of gravity. Either denominator can be used to calculate the ratio. The circumscribing circle radius refers to the radius of the smallest circle that circumscribes the opening of one cell. The approximate major axis of an ellipse refers to the major axis of an ellipse when the opening of a cell is approximated by an ellipse. The approximate minor axis of an ellipse refers to the minor axis of an ellipse when the opening of one cell is approximated by an ellipse. The cell direction refers to the degree of inclination of an ellipse when the opening of a cell is approximated by an ellipse. The degree of inclination can be expressed in radians (rad) or degrees (°). The long side to short side ratio refers to the ratio of the long side to the short side of the smallest rectangle that circumscribes the opening of one cell, taking into account rotation. Either side may be used as the denominator in the calculation.

[0059] The one or more parameters characterizing the shape or size of the partition wall portion defining each side of each polygonal cell are not limited to, but preferably include one or more selected from partition wall curvature, partition wall thickness, and partition wall direction, and more preferably include two or more selected from the group consisting of partition wall curvature, partition wall thickness, and partition wall direction.

[0060] The partition curvature means the length of the short side of the smallest rectangle that can surround the center line extending in the longitudinal direction of the partition portion that defines the linear portion of the polygonal cell in design. Since the linear partition portion 504 that defines the linear portion 503 of the polygonal cell 500 in design extends linearly in the longitudinal direction, the length of the short side of the smallest rectangle 507 that surrounds the center line 505 is equal to the width of the center line 505 extending in the longitudinal direction (FIG. 6). In contrast, when the linear partition portion 504 is curved in the manufacturing process, the center line 505 is also curved according to the degree of the curvature, and the length of the short side of the smallest rectangle 507 that can surround the center line 505 becomes longer (FIG. 7). The width of the center line 505 may be set appropriately, and may be, for example, 1 to 3 pixels, and may be preferably 1 pixel. In addition, the statistics of the partition bending may be calculated using straight partition portions 504 that are parallel to each other in design as a unit, or the statistics may be calculated collectively for the straight partition portions 504 of all the partitions. The partition wall thickness means the radius of a maximum circle 508 inscribed in a straight partition wall portion 504 that defines a straight portion 503 of a polygonal cell 500 (FIG. 6). The partition wall thickness may be calculated as the diameter of the maximum circle 508. Furthermore, the partition wall thickness statistics may be calculated for each straight partition wall portion 504 that is parallel to one another in design, or the statistics may be calculated collectively for the straight partition wall portions 504 of all partition walls. The partition direction means the degree of inclination of the direction in which the linear partition portions 504, which are parallel to each other in design, extend in the longitudinal direction.

[0061] The one or more parameters characterizing the shape or size of the partition portion defining each corner of each polygonal cell preferably include, but are not limited to, the area of ​​the partition portion defining the corner. A partition portion 506 defining a corner 502 of a polygonal cell 500 refers to a portion of the partition surrounded by a straight partition portion 504 defining a straight line portion 503 in the design of the polygonal cell 500 (FIG. 6).

[0062] The above parameters and statistics can be automatically measured and calculated from images generated by capturing the first and / or second bottom surfaces with a camera using an image processing library, for example, HALCON (Ver. 18.11 or later version) from MVTec.

[0063] In order to obtain highly reliable statistics, it is preferable to observe both the first and second bottom faces. In particular, in the case of a columnar honeycomb formed body having plugged portions, there are cells having plugged portions whose opening sizes cannot be measured even if one of the bottom faces is imaged, so it is preferable to observe both bottom faces.

[0064] The more types of parameters to be measured, the easier it is to find parameters that have a high correlation with intensity. For this reason, the number of types of parameters to be measured is preferably 10 or more, more preferably 15 or more, and even more preferably 20 or more. On the other hand, the number of types of parameters to be measured is limited, and the more types there are, the more labor required for data processing increases. For this reason, the number of types of parameters to be measured is preferably 30 or less, more preferably 28 or less, and even more preferably 25 or less.

[0065] Many kinds of statistics can be derived from one parameter. The more types of statistics to be considered, the easier it is to find a combination of parameters and statistics that have a high correlation with strength. For this reason, the number of types of statistics calculated for one parameter is preferably two or more, more preferably five or more, and even more preferably seven or more. On the other hand, there is a limit to the number of types of statistics to be measured, and the more types there are, the more labor required for data processing will increase. For this reason, the number of types of statistics calculated for one parameter is preferably 15 or less, more preferably 13 or less, and even more preferably 10 or less.

[0066] The types of statistics include, but are not limited to, representative values ​​such as arithmetic mean, standard deviation, kurtosis, skewness, minimum value, median value, maximum value, first quartile, third quartile, and range (maximum-minimum). Among these, it is preferable to include two or more types selected from arithmetic mean, standard deviation, kurtosis, skewness, minimum value, median value, and maximum value, which are statistical quantities empirically predicted to have a high correlation with the strength of the columnar honeycomb molded body after firing, and it is more preferable to include five or more types. In particular, it is preferable to include two or more types selected from arithmetic mean, standard deviation, minimum value, median value, and maximum value, and it is more preferable to include all five types.

[0067] When the structural coefficient of polygonal cells is to be measured, it is predicted that there is a particularly high correlation with the strength of the columnar honeycomb formed body after firing, so it is preferable to calculate one or more statistical quantities selected from the arithmetic mean and the median, and it is more preferable to calculate both the arithmetic mean and the median.

[0068] When the cell direction of polygonal cells is the object of measurement, it is predicted that there is a particularly high correlation with the strength of the columnar honeycomb formed body after firing, so it is preferable to calculate one or more statistical quantities selected from standard deviation and kurtosis, and it is more preferable to calculate both standard deviation and kurtosis.

[0069] When the long side / short side ratio of a polygonal cell is the object of measurement, it is predicted that there is a particularly high correlation with the strength of the columnar honeycomb formed body after firing, so it is preferable to calculate one or more statistical quantities selected from the arithmetic mean, standard deviation, and maximum value, it is more preferable to calculate two or more statistical quantities, and it is even more preferable to calculate all three statistical quantities.

[0070] When the area of ​​the partition wall portion defining the corners of a polygonal cell is to be measured, it is predicted that there is a particularly high correlation with the strength of the columnar honeycomb formed body after firing, so it is preferable to calculate one or more statistical quantities selected from kurtosis and skewness, and it is more preferable to calculate both kurtosis and skewness.

[0071] There is no particular limitation on the method for observing the first or second bottom surface of each columnar honeycomb molded body before firing, but an example is a method of imaging the first or second bottom surface with a camera. It is preferable to perform imaging with a camera from a direction perpendicular to the first or second bottom surface in order to improve inspection accuracy. The camera may be an area camera or a line camera, but an area camera is preferable because it has a fast imaging tact time, a wide illumination width, and can reduce the size of the equipment. From the viewpoint of improving inspection accuracy, it is preferable to use a camera with high pixel resolution. Specifically, taking into account the general opening area of ​​a cell, the camera preferably has a pixel resolution of 40 μm / pixel or less in both the vertical and horizontal directions, preferably 25 μm / pixel or less, and can be, for example, 1 to 40 μm / pixel.

[0072] The above-mentioned two or more parameters are measured in an image generated by capturing an image with a camera. Although the various parameters may be measured by an inspector based on the image, since there are a large number of cells to be inspected, it is preferable to perform the measurements automatically using an image analyzer. An example of the measurement procedure using an image analyzer will be described later.

[0073] (Process C) In step C, each of the multiple unfired columnar honeycomb molded bodies produced in step A is fired under a predetermined condition to produce multiple fired columnar honeycomb molded bodies. The firing conditions are appropriately set according to the design specifications of the columnar honeycomb molded bodies. In order to properly evaluate the correlation between various statistics measured before firing and the strength of the fired columnar honeycomb molded body, when firing the multiple unfired columnar honeycomb molded bodies, it is preferable to match the design firing conditions such as the furnace atmosphere, heat curve, and firing time in addition to the degreasing conditions before firing. Note that since the actual firing conditions can inevitably vary due to disturbances, "matching the design firing conditions" means that the firing conditions are not intentionally changed.

[0074] (Process D) In step D, the correlation between two or more statistical quantities calculated for each parameter in step B and the strength of the multiple fired columnar honeycomb molded bodies produced in step C is evaluated. The correlation between the two can be evaluated, for example, by calculating a correlation coefficient. It can be said that the larger the absolute value of the correlation coefficient, the higher the correlation between the two. If the absolute value of the correlation coefficient is 0.4 or more, it can be said that there is a significant correlation, and it is preferable that the absolute value of the correlation coefficient is 0.5 or more, and more preferably 0.6 or more. In addition to the correlation coefficient, the coefficient of determination, which is the value obtained by squaring the correlation coefficient, can also be used to evaluate the correlation.

[0075] There are various parameters that represent the strength of the columnar honeycomb molded body, and although there are no particular limitations, examples include isostatic fracture strength and compressive strength. Among these, it is preferable to adopt isostatic fracture strength because it is easy to evaluate whether the molded body can withstand the pressure applied during canning.

[0076] (Process E) In step E, a statistical quantity having the highest correlation with the strength of a fired columnar honeycomb molded body having a predetermined design specification is determined from the two or more statistical quantities based on the result of step D. The statistical quantity having the highest correlation with the strength of a fired columnar honeycomb molded body having a predetermined design specification can be determined, for example, by selecting the statistical quantity having the highest absolute value of the correlation coefficient.

[0077] <4. Method for predicting whether a columnar honeycomb formed body having a given design specification can be obtained after firing> When the statistical quantity having the highest correlation with the strength of a fired columnar honeycomb formed body of a specified design specification is determined, it becomes possible to predict whether or not a fired columnar honeycomb formed body of a specified design specification can be obtained based on the fired columnar honeycomb formed body by using the statistical quantity. It is also possible to estimate the strength of the fired columnar honeycomb formed body. Therefore, the statistical quantity can be incorporated as a quality inspection item for the fired columnar honeycomb formed body.

[0078] According to the research results of the present inventors, there are combinations of parameters and statistics that are highly correlated with the strength of the fired columnar honeycomb molded body, regardless of the design specifications such as size, shape, cell structure, material, etc. Specifically, the following combinations (1) to (4) are preferable. (1) A combination of a “structure coefficient” and one or more statistics selected from the arithmetic mean and the median. (2) A combination of “cell direction” and one or more statistics selected from standard deviation and kurtosis. (3) A combination of the “length-to-length ratio” and one or more statistical quantities selected from the arithmetic mean, standard deviation, and maximum value. (4) A combination of the "area of ​​the partition portion defining the corner" and one or more statistics selected from kurtosis and skewness.

[0079] Among the above (1) to (4), a combination of the “long side / short side ratio” and one or more statistical quantities selected from the arithmetic mean and the standard deviation is more preferable, and a combination of the “long side / short side ratio” and the standard deviation is even more preferable.

[0080] Therefore, according to one embodiment of the present invention, A method for predicting whether or not a fired columnar honeycomb formed body having a predetermined design specification can be obtained when fired under predetermined firing conditions, based on a measurement result of a columnar honeycomb formed body before firing, the columnar honeycomb formed body having a columnar honeycomb structure portion including an outer peripheral side wall and partition walls disposed on the inner peripheral side of the outer peripheral side wall and partitioning a plurality of polygonal cells that form a flow path from a first bottom surface to a second bottom surface, the method comprising: A step 1 of measuring one or more parameters selected from a structural coefficient characterizing the shape of an opening, a cell direction and a long side / short side ratio, and an area of ​​a partition wall portion defining a corner, for 90% or more, preferably 95% or more, and more preferably all, of polygonal cells excluding partial cells at the outermost periphery, by observing at least one of a first bottom surface or a second bottom surface of the columnar honeycomb molded body before firing; If the parameter measured in step 1 is a structure coefficient, one or more statistics selected from an arithmetic mean and a median; If the parameter measured in step 1 is a cell direction, one or more statistics selected from standard deviation and kurtosis; When the parameter measured in step 1 is a long side / short side ratio, one or more statistical quantities selected from an arithmetic mean, a standard deviation, and a maximum value; When the parameter measured in step 1 is the area of ​​a partition portion defining a corner, one or more statistical quantities selected from kurtosis and skewness; A step 2 of calculating based on the result of the step 1; A step 3 of comparing one or more types of statistics calculated in the step 2 with a judgment criterion that is predetermined according to the predetermined design specifications and the types of the statistics; A method is provided that includes:

[0081] The judgment criteria used for the comparison in step 3 may be determined in advance as appropriate criteria according to the predetermined design specifications and the type of statistical quantity. As an example, a case will be described in which it is predicted based on the standard deviation of the long side / short side ratio whether or not a columnar honeycomb molded body with a predetermined design specification can be obtained. First, for a plurality of other columnar honeycomb molded bodies with the same design specifications as the columnar honeycomb molded body to be predicted, a correlation is obtained between the standard deviation of the long side / short side ratio for the columnar honeycomb molded body before firing and the strength of the other plurality of columnar honeycomb molded bodies after firing under predetermined firing conditions. Next, based on the obtained correlation, an allowable range of the standard deviation of the long side / short side ratio that is predicted to have the required strength after firing is set for the columnar honeycomb molded body before firing. Therefore, in this case, the allowable range of the standard deviation of the long side / short side ratio can be used as a judgment criterion.

[0082] Based on the above-mentioned criteria, a quality inspection of the columnar honeycomb molded body before firing can be carried out. For example, if the standard deviation of the calculated long side / short side ratio exceeds an allowable range, the columnar honeycomb molded body can be determined as a rejected product, and if the standard deviation of the calculated long side / short side ratio is within an allowable range, the columnar honeycomb molded body can be determined as a pass product.

[0083] Furthermore, by utilizing the above correlation, it is also possible to estimate the strength of the columnar honeycomb molded body after firing. Therefore, according to one embodiment of the prediction method, the method includes a step 4 of estimating the strength of the columnar honeycomb molded body after firing the columnar honeycomb molded body before firing under the predetermined firing conditions based on the one or more statistics calculated in the step 2, by utilizing a correlation between the one or more statistics for the columnar honeycomb molded body before firing and the strength of the other multiple columnar honeycomb molded bodies after firing under the predetermined firing conditions, the correlation being obtained in advance for multiple other columnar honeycomb molded bodies having the same design specifications as the columnar honeycomb molded body to be predicted.

[0084] Based on the strength estimated by the above estimation method, a quality inspection of the columnar honeycomb formed body before firing can be performed. For example, if the estimated strength is lower than the strength required for the columnar honeycomb formed body after firing, the columnar honeycomb formed body being inspected can be judged as a defective product, and if the estimated strength is equal to or higher than the required strength, it can be judged as an acceptable product.

[0085] (Image analysis device) 8 shows an example of a functional block diagram of an image analyzing device 300. The image analyzing device 300 includes a data storage unit 301, a display unit 302, an input unit 303, and a calculation unit 304.

[0086] The data storage unit 301 can be configured, for example, by a semiconductor memory, and can store image data of at least one of the first bottom surface and the second bottom surface of the columnar honeycomb molded body generated by a camera. In addition, the data storage unit 301 can store the judgment criteria used in step 3 of the above prediction method.

[0087] The input unit 303 can be composed of, for example, a keyboard, a touch panel, a numeric keypad and a mouse, and the inspector can use the input unit 303 to give an instruction to start image analysis for a desired image showing the first bottom surface or the second bottom surface of the columnar honeycomb molded body.

[0088] The display unit 302 can be configured with a display device such as a liquid crystal display or an organic EL display, and can display the image data stored in the data storage unit 301. It can also display the results of image analysis.

[0089] The calculation unit 304 can be configured with, for example, a CPU (Central Processing Unit), an MPU (Micro Processing Unit), etc. When the calculation unit 304 receives a command to start image analysis from the input unit 303, it executes image analysis based on image data stored in the data storage unit 301, and can measure predetermined parameters and calculate statistics. As software used for image analysis, the above-mentioned HALCON (Ver.18.11 or later version) by MVTec can be suitably used.

[0090] In one embodiment, the image analysis includes a step of image processing at least one of the images of the first bottom surface or the second bottom surface of the columnar honeycomb molded body captured by a camera, a step of measuring the two or more parameters mentioned above for at least 90%, preferably at least 95%, and more preferably all of the polygonal cells excluding the partial cells at the outermost periphery, based on the image of at least one of the first bottom surface or the second bottom surface obtained by the image processing step, and a step of calculating two or more statistics for each of the measured parameters.

[0091] In order to easily measure various parameters, in the image processing step, the calculation unit 304: A binarization process for dividing an inner peripheral side of an outer peripheral side wall in at least one image of a first bottom surface or a second bottom surface of the columnar honeycomb molded body into two regions, a cell opening region, and a partition wall region and an outer peripheral side wall region, based on a predetermined brightness threshold value; a step of identifying a partition wall region by distinguishing an outer peripheral sidewall region from an area offset inwardly by a predetermined threshold value from a contour line forming an outer surface of the outer peripheral sidewall after the binarization process; It is preferable to carry out image processing including the steps of: When calculating the "partition curvature," it is preferable to perform a skeletonization process for extracting the center line of the partition region from the partition region.

[0092] The threshold value in the binarization process can be set from the viewpoint of distinguishing and recognizing the opening region from the partition region and the outer peripheral side wall region. The binarization process may be performed using a known method, but a dynamic binarization method such as Otsu's binarization method can be preferably used. By performing the binarization process, it is possible to clearly distinguish the partition portion from the opening, which has the advantage of facilitating image analysis.

[0093] In the skeletonization process, for example, circles having a diameter equivalent to the thickness of the partition are arranged in series in the partition region adjacent to each other along the extension direction of the partition, and the center pixels of the circles are connected to each other to extract the center line. Since the skeletonization process makes it possible to recognize the center line of the partition, it is possible to clearly recognize the linearity of the partition, which has the advantage of improving the inspection accuracy.

[0094] In the above-mentioned method for predicting whether or not a columnar honeycomb formed body of predetermined design specifications will be obtained after firing under predetermined firing conditions, the step 3 of comparing with the judgment criterion can also be performed by the image analysis device 300. In this case, information related to the judgment criterion is stored in the data storage unit 301, and the calculation unit 304 compares the calculated statistics with the judgment criterion. The image analysis device 300 can also be configured so that the result of the comparison, whether or not the judgment criterion is satisfied, is displayed on the display unit 302.

[0095] In addition, in the method for predicting whether or not a columnar honeycomb molded body having a predetermined design specification can be obtained after firing under predetermined firing conditions, it is also possible to have the image analysis device 300 perform step 4 of estimating the strength of the columnar honeycomb molded body after firing under the predetermined firing conditions. In this case, the data storage unit 301 stores information regarding the correlation between one or more types of statistics for the columnar honeycomb molded body before firing and the strength of the other multiple columnar honeycomb molded bodies after firing under the predetermined firing conditions, and the calculation unit 304 estimates the strength based on the calculated statistics. It is also possible to configure the image analysis device 300 so that the estimated strength is displayed on the display unit 302. EXAMPLES

[0096] <Test Example 1> (1. Preparation of honeycomb molded body) For a honeycomb formed body having the following design specifications to be assigned a predetermined product number, a honeycomb formed body before firing was produced by the following procedure. [Design specifications of honeycomb formed body after firing] Overall shape: Cylinder with diameter 118mm x height 114mm Normal cell shape in cross section perpendicular to the flow direction: Square Design dimensions of the opening in the cross section perpendicular to the flow direction of a normal cell: 0.97 mm x 0.97 mm Cell density (number of cells per unit cross-sectional area): 600 cells / in 2 Partition thickness: 64μm

[0097] To 100 parts by mass of the cordierite raw material, 1 part by mass of a pore former, 30 parts by mass of a dispersion medium, 8 parts by mass of an organic binder, and 1 part by mass of a dispersant were added, mixed, and kneaded to prepare a clay. Alumina, aluminum hydroxide, kaolin, talc, and silica were used as the cordierite raw material. Water was used as the dispersion medium, coke with an average particle size of 1 to 10 μm was used as the pore former, hydroxypropyl methylcellulose was used as the organic binder, and ethylene glycol was used as the dispersant.

[0098] The clay was put into an extrusion molding machine and extruded horizontally through a predetermined die to obtain a cylindrical honeycomb molded body. The obtained honeycomb molded body was subjected to dielectric drying and hot air drying, and then both bottom surfaces were cut to a predetermined dimension to obtain a cylindrical honeycomb molded body.

[0099] A total of 306 cylindrical honeycomb molded bodies were produced using the same procedure as above. However, for eight of these, the amount of dispersion medium was intentionally changed to reduce strength and promote distortion of the cell shape. For the remaining 298 honeycomb molded bodies, no intentional changes were made to the manufacturing conditions, but some dimensional variations were unavoidable.

[0100] (2. Measurement of various parameters characterizing the cell and calculation of statistics) For each of the obtained honeycomb molded bodies, various parameters were measured according to the following procedure, and various statistics were calculated for each parameter. One bottom surface of each columnar honeycomb molded body was imaged from a direction perpendicular to the bottom surface with an area camera (vertical pixel resolution 0.01455 mm / pixel, horizontal pixel resolution 0.01453 mm / pixel), and an image of the bottom surface was generated. The generated image was subjected to image processing and image analysis using an image processing library (HALCON, Ver. 18.11, manufactured by MVTec Corporation), and various parameters shown in Table 1 were measured for all cells except for the partial cells, and the following statistics related to the parameters were calculated for each honeycomb molded body. [Parameters that characterize the shape or size of the opening of each polygonal cell] Opening area, inscribed circle radius, approximate short side of rectangle, approximate long side of rectangle, rectangularity, circularity, compactness, contour length, convexity, major axis / minor axis ratio, ellipticity, structure coefficient, center distance deviation, roundness, circumscribed circle radius, approximate major axis of ellipse, approximate minor axis of ellipse, cell direction, and major axis / minor axis ratio [Parameters characterizing the shape or size of the partition portions defining each side of each polygonal cell] Bulkhead bending, bulkhead thickness, and bulkhead direction (In a cross section perpendicular to the extension direction of the cells, a partition wall extending in the vertical direction during extrusion molding is defined as partition wall 1, and a partition wall extending in the horizontal direction during extrusion molding is defined as partition wall 2, and the partition wall bending, partition wall thickness, and partition wall direction were calculated for each of partition wall 1 and partition wall 2.) [Parameters characterizing the shape or size of the partition portions defining each corner of each polygonal cell] Area of ​​the partition wall portion defining the corner

[0101] For image analysis, the following image processing was performed using an image processing library (HALCON, Ver. 18.11, manufactured by MVTec). In the bottom image, a binarization process is performed to divide the inner peripheral side of the outer peripheral side wall into two regions, a cell opening region and a partition wall region, based on a threshold dynamically calculated by Otsu's binarization method. - Only when calculating "partition bend", a skeletonization process is performed to extract the center line (thickness 1 pixel = 0.01453 mm) of the partition area from the partition area after smoothing processing.

[0102] (3. Firing of honeycomb molded body) Then, each honeycomb molded body was degreased under the specified conditions of 200 to 1000°C in the air, and then heated to 1350 to 1600°C and fired under the specified firing conditions for 3 to 10 hours. All honeycomb molded bodies were fired under the same firing conditions (no intentional changes to the firing conditions).

[0103] (4. Measurement of isostatic fracture strength) The isostatic fracture strength of all the fired honeycomb molded bodies was measured based on the automobile standard (JASO M505-87) issued by the Automotive Engineers Association.

[0104] (5. Calculation of correlation coefficient) The correlation coefficient between the two was calculated from various statistics calculated before firing for all the honeycomb molded bodies produced and the results of the isostatic fracture strength measured after firing. The results are shown in Table 1. When the absolute value of the correlation coefficient is 0.4 or more, it is considered that there is a significant correlation between the two. For this reason, in the table, combinations of parameters and statistics with absolute values ​​of correlation coefficients of 0.4 or more are marked "OK," and combinations of parameters and statistics with absolute values ​​of correlation coefficients of less than 0.4 are marked "-."

[0105] <Test Example 2> (1. Preparation of honeycomb molded body) For honeycomb formed bodies with the following design specifications that were to be assigned product numbers different from those of Test Example 1, honeycomb formed bodies before firing were produced in the same manner as in Test Example 1. Test Example 2 differs from Test Example 1 only in the overall design shape. [Design specifications of pillar-shaped honeycomb bodies after firing] Overall shape: Cylinder with diameter 132 mm x height 95 mm Normal cell shape in cross section perpendicular to the flow direction: Square Design dimensions of the opening in the cross section perpendicular to the flow direction of a normal cell: 0.97 mm x 0.97 mm Cell density (number of cells per unit cross-sectional area): 600 cells / in 2 Partition thickness: 64μm

[0106] A total of 135 cylindrical honeycomb molded bodies were produced using the same procedure as above. However, for 13 of these, the amount of dispersion medium was intentionally changed to reduce strength and promote distortion of the cell shape. For the remaining 122 honeycomb molded bodies, no intentional changes were made to the manufacturing conditions, but some dimensional variations were unavoidable.

[0107] (2. Measurement of various parameters characterizing the cell and calculation of statistics) For each of the obtained honeycomb formed bodies, various parameters were measured in the same manner as in Test Example 1, and various statistics were calculated for each parameter.

[0108] (3. Firing of honeycomb molded body) Then, each honeycomb molded body was degreased under the specified conditions of 200 to 1000°C in the air, and then heated to 1350 to 1600°C and fired under the specified firing conditions for 3 to 10 hours. All honeycomb molded bodies were fired under the same firing conditions (no intentional changes to the firing conditions).

[0109] (4. Measurement of isostatic fracture strength) The isostatic fracture strength of all the fired honeycomb molded bodies was measured based on the automobile standard (JASO M505-87) issued by the Automotive Engineers Association.

[0110] (5. Calculation of correlation coefficient) The correlation coefficient between the two was calculated from various statistics calculated before firing for all the honeycomb molded bodies produced and the results of the isostatic fracture strength measured after firing. The results are shown in Table 1. When the absolute value of the correlation coefficient is 0.4 or more, it is considered that there is a significant correlation between the two. For this reason, in the table, combinations of parameters and statistics with absolute values ​​of correlation coefficients of 0.4 or more are marked "OK," and combinations of parameters and statistics with absolute values ​​of correlation coefficients of less than 0.4 are marked "-."

[0111] [Table 1-1]

[0112] [Table 1-2]

[0113] [Table 1-3]

[0114] [Table 1-4]

[0115] <Consideration> In the honeycomb molded body having the design specifications according to Test Example 1, the absolute value of the correlation coefficient between the following parameters and statistical quantities is 0.4 or more, which indicates a significant correlation. The combination with the long side / short side ratio and the standard deviation had the highest correlation coefficient. Combination of structure coefficients and arithmetic averages Combination of structure coefficients and medians · Combination of cell direction and standard deviation · Combination of cell direction and kurtosis Combination of length ratio and arithmetic mean Combination of length ratio and standard deviation -Combination of long side / short side ratio and maximum value -Combination of area and kurtosis of the partition part that defines the corner -Combination of area and skewness of the partition wall that defines the corner

[0116] Fig. 9 shows the results of plotting all the honeycomb molded bodies produced in Test Example 1 on a two-dimensional coordinate system with the standard deviation of the long side / short side ratio on the horizontal axis and the isostatic fracture strength on the vertical axis. From Fig. 9, it can be seen that when the standard deviation of the long side / short side ratio is 0.0162 or less, the isostatic fracture strength is 3 MPa or more. Therefore, when an isostatic fracture strength of 3 MPa or more is the strength required for a fired honeycomb molded body, for example, if the standard deviation of the long side / short side ratio of the honeycomb molded body before firing is 0.0162 or less as a judgment criterion to judge whether or not a fired columnar honeycomb molded body having the design specifications according to Test Example 1 can be obtained, a quality inspection can be performed with high accuracy (overdetection in which a passing product is judged as a failing product = 0, overlooked cases in which a failing product is judged as a passing product = 0).

[0117] In the honeycomb molded body having the design specifications according to Test Example 2, the absolute value of the correlation coefficient between the following parameters and statistical quantities is 0.4 or more, which indicates a significant correlation. In addition, the combination with the rectangular approximation short side and the standard deviation had the highest correlation coefficient. Combination of opening area and arithmetic mean Combination of opening area and standard deviation Combination of opening area and distortion Combination of opening area and maximum value -Combination of inscribed circle radius and standard deviation -Combination of inscribed circle radius and maximum value Combination of rectangular approximation short side and standard deviation Combination of rectangular approximation short side and skewness -Combination of rectangular approximation short side and maximum value Combination of rectangular approximation and arithmetic mean Combination of rectangular approximation long side and standard deviation Combination of rectangular approximation length and skewness Combination of rectangular approximation long side and median -Combination of rectangular approximation long side and maximum value Combination of rectangularity and arithmetic mean Combination of rectangularity and standard deviation Combination of rectangularity and skewness Combination of roundness and arithmetic mean -Combination of circularity and skewness Combination of circularity and median Combination of compactness and arithmetic mean Combination of compactness and median Combination of major axis / minor axis ratio and arithmetic mean Combination of major axis / minor axis ratio and standard deviation Combination of major axis / minor axis ratio and median Combination of structure coefficients and arithmetic averages Combination of structure coefficients and standard deviations Combination of structure coefficients and medians Combination of center distance deviation and arithmetic mean Combination of center distance deviation and standard deviation Combination of center distance deviation and median Combination of roundness and arithmetic mean Combination of roundness and standard deviation Combination of roundness and median Combination of circumscribed circle radius and arithmetic mean -Combination of circumscribed circle radius and standard deviation Combination of circumscribed circle radius and median - Combination of circumscribed circle radius and maximum value Combination of ellipse approximation major axis and arithmetic mean - Combination of ellipse approximation major axis and standard deviation - Combination of ellipse approximate major axis and median - Combination of ellipse approximate major axis and maximum value - Combination of ellipse approximation minor axis and standard deviation - Combination of ellipse approximate minor axis and maximum value Combination of cell direction and arithmetic mean · Combination of cell direction and standard deviation · Combination of cell direction and kurtosis Combination of cell orientation and skewness Combination of cell direction and median Combination of length ratio and arithmetic mean Combination of length ratio and standard deviation -Combination of long side / short side ratio and maximum value Combination of bulkhead bending (bulhead 1) and standard deviation Combination of bulkhead bending (bulhead 2) and standard deviation Combination of partition thickness (partition 1) and arithmetic mean Combination of partition thickness (partition 1) and minimum value Combination of partition thickness (partition 2) and arithmetic mean Combination of bulkhead thickness (bulhead 2) and standard deviation -Combination of the area of ​​the partition wall that defines the corner and the arithmetic mean -Combination of area and kurtosis of the partition part that defines the corner -Combination of area and skewness of the partition wall that defines the corner -Combination of area and minimum value of partition wall portion defining corner -Combination of area and median of partition wall defining corner

[0118] FIG. 10 shows the results of plotting all honeycomb molded bodies produced in Test Example 2 on a two-dimensional coordinate system with the standard deviation of the rectangular approximation short side on the horizontal axis and the isostatic fracture strength on the vertical axis. From FIG. 10, it can be seen that when the standard deviation of the rectangular approximation short side is 0.402 or less, there is an extremely high probability that the isostatic fracture strength is 3 MPa or more. Therefore, when an isostatic fracture strength of 3 MPa or more is the strength required for a fired honeycomb molded body, for example, if the standard deviation of the rectangular approximation short side of the honeycomb molded body before firing is 0.402 or less as a judgment criterion, whether or not a fired columnar honeycomb molded body having the design specifications according to Test Example 2 can be obtained, a quality inspection can be performed with high accuracy (1 over-detection example in which a passing product is judged to be a failing product, 0 oversight examples in which a failing product is judged to be a passing product).

[0119] Furthermore, from the above results, it can be seen that the combinations of the following parameters and statistics have a significant correlation, with the absolute value of the correlation coefficient being 0.4 or more in both Test Example 1 and Test Example 2. In other words, these combinations of parameters and statistics have a high correlation with strength even if the design specifications of the honeycomb molded body change. In particular, the combination of long side / short side ratio and standard deviation has an absolute value of the correlation coefficient being 0.6 or more in both Test Example 1 and Test Example 2, making it highly versatile. Combination of structure coefficients and arithmetic averages Combination of structure coefficients and medians · Combination of cell direction and standard deviation · Combination of cell direction and kurtosis Combination of length ratio and arithmetic mean Combination of length ratio and standard deviation -Combination of long side / short side ratio and maximum value -Combination of area and kurtosis of the partition part that defines the corner -Combination of area and skewness of the partition wall that defines the corner [Explanation of symbols]

[0120] 100, 200 Pillar honeycomb formed body 102, 202 Outer peripheral side wall 104, 204 First bottom surface 106, 206 Second bottom surface 108, 208a, 208b cells 112, 212 bulkhead 209 Plugging part 300 Image analysis device 301 Data storage unit 302 Display section 303 Input section 304 Arithmetic section 500 Polygonal Cells 502 Corner 503 Straight section 504 Straight partition wall portion defining straight line portion of polygonal cell 505 Center line 506 Partition wall portion defining corners of polygonal cells 507 minimum rectangle 508 Maximum yen

Claims

1. A method for predicting whether or not a fired columnar honeycomb formed body having a predetermined design specification can be obtained when fired under predetermined firing conditions, based on a measurement result of a columnar honeycomb formed body before firing, the columnar honeycomb formed body having a columnar honeycomb structure portion including an outer peripheral side wall and partition walls disposed on the inner peripheral side of the outer peripheral side wall and partitioning a plurality of polygonal cells that form a flow path from a first bottom surface to a second bottom surface, the method comprising: A step 1 of measuring one or more parameters selected from a structural coefficient characterizing the shape of an opening, a cell direction and a long side / short side ratio, and an area of ​​a partition wall portion defining a corner, for 90% or more of polygonal cells excluding partial cells at the outermost periphery, by observing at least one of a first bottom surface or a second bottom surface of the columnar honeycomb molded body before firing; If the parameter measured in step 1 is a structure coefficient, one or more statistics selected from an arithmetic mean and a median; If the parameter measured in step 1 is a cell orientation, one or more statistics selected from standard deviation and kurtosis; When the parameter measured in step 1 is a long side / short side ratio, one or more statistical quantities selected from an arithmetic mean, a standard deviation, and a maximum value; When the parameter measured in step 1 is the area of ​​a partition portion defining a corner, one or more statistics selected from kurtosis and skewness; Step 2 of calculating based on the result of step 1; a step 3 of comparing one or more types of statistics calculated in the step 2 with a judgment criterion that is predefined according to the predetermined design specifications and the types of statistics; The method includes:

2. The method according to claim 1, further comprising a step 4 of estimating the strength of the columnar honeycomb formed body after firing the pre-fired columnar honeycomb formed body under the specified firing conditions based on one or more statistical quantities calculated in step 2, by utilizing a correlation between the one or more statistical quantities for the pre-fired columnar honeycomb formed body and the strength of the other multiple columnar honeycomb formed bodies after firing under the specified firing conditions, which correlation was previously determined for a plurality of other columnar honeycomb formed bodies having the same design specifications as the columnar honeycomb formed body.

3. The method of claim 2, wherein said strength is an isostatic fracture strength.

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