Extrusion mold producing honeycomb molding for honeycomb segment constituting carbonized honeycomb filter and production method of honeycomb molding using the same

Abstract

To provide a production method for a mold suppressing generation of crack or melting defect generated in a honeycomb filter through heat impact by partial exothermic heat and acute temperature change in exhaust gas without increasing pressure loss and for a honeycomb molding.SOLUTION: A mold to form a honeycomb molding for a honeycomb segment with an outer peripheral wall thicker than a partition wall through extrusion is provided with a mold body and a guide ring attached on an outer peripheral side of the mold body. The mold body comprises: a first surface where a cray supply hole opens; a second surface placed opposite to the first surface, where grate slits in communication with the cray supply hole opens; and a third surface positioned at an opposite side of the first surface and at an outer periphery of the second surface, the second surface constitutes an area forming a grid-like partition wall in a honeycomb body, the third surface constitutes an outer peripheral area forming the outer peripheral wall, the second surface is higher than the third surface by a step part H, and the guide ring has a gap between the third surface and itself and an opening with an enough size to cover the outer peripheral side part of the outer peripheral area.SELECTED DRAWING: Figure 7(b)

Description

Technical Field

[0001] The present invention relates to an extrusion mold for manufacturing a honeycomb molded body for a honeycomb segment that constitutes a silicon carbide-based honeycomb filter for removing particulate matter [Particulate Matter (PM)] and the like in exhaust gas discharged from an internal combustion engine such as a diesel engine and purifying the exhaust gas, and a method for manufacturing a honeycomb molded body using the same.

Background Art

[0002] When NOx and PM contained in the exhaust gas of a diesel engine are released into the atmosphere, they may have an adverse effect on the human body and the environment. Therefore, conventionally, a honeycomb structure carrying a NOx catalyst and a ceramic honeycomb filter for collecting PM have been installed in the middle of the exhaust pipe of a diesel engine. An example of a ceramic honeycomb filter for collecting PM in exhaust gas is shown in FIGS. 10(a) and 10(b). The ceramic honeycomb filter 500 includes a ceramic honeycomb structure 510 composed of a porous partition wall 52 forming a large number of flow paths 53a, 53b and an outer peripheral wall 51, and an inflow-side plugging portion 56a and an outflow-side plugging portion 56b that alternately seal the exhaust gas inflow-side end faces 55a and the outflow-side end faces 55b of the flow paths 53a, 53b in a checkerboard pattern. The exhaust gas flows in from the outflow-side sealing flow path 53b that opens to the exhaust gas inflow-side end face 55a as shown by the dotted arrow in FIG. 10(b), passes through the communication holes existing on the surface and inside of the partition wall 52, and flows into the adjacent inflow-side sealing flow path 53a, and then flows out from the exhaust gas outflow-side end face 55b. When passing through the communication holes existing on the surface and inside of the partition wall 52, the PM in the exhaust gas is collected and the exhaust gas is purified. When the collected PM reaches a predetermined deposition amount, it is burned and the ceramic honeycomb structure is regenerated. The usage environment of such a ceramic honeycomb structure has become severe, and refractory ceramics such as silicon carbide (SiC) having excellent thermal shock resistance have come to be used as its constituent material.

[0003] Due to thermal shock caused by uneven combustion of PM during regeneration or rapid temperature changes in exhaust gas, thermal stress due to uneven temperature distribution acts inside the ceramic honeycomb structure, resulting in problems such as cracks, fractures, and melting damage. To address such problems, a ceramic honeycomb filter 400 with a function of dispersing and relaxing thermal stress has been proposed by integrally joining a plurality of honeycomb segments 411 with a rectangular outer shape as shown in Fig. 9 via a bonding material layer 49 as shown in Fig. 8.

[0004] As a honeycomb filter that suppresses crack generation during regeneration by burning the collected PM, Patent Document 1 discloses a columnar honeycomb filter in which a plurality of columnar honeycomb segments are joined via a bonding material layer. Each honeycomb segment has a partition wall that forms a plurality of cells extending from one end face to the other end face. At least one honeycomb segment is composed of a central portion and an outer peripheral portion. The thickness of the partition wall in the outer peripheral portion is 101 to 150% of the average thickness of the partition wall in the central portion. In a cross-section perpendicular to the extending direction of the cells, the total area of the partition walls in the outer peripheral portion is 5 to 35% of the total area of the partition walls of the honeycomb segment.

[0005] In the honeycomb filter of Patent Document 1, the partition walls are made thin to suppress the pressure loss when PM is collected and to increase the PM collection amount until regeneration is started. However, depending on the deposition state of PM, local heat generation may occur due to uneven heating or abnormal combustion during regeneration, but the honeycomb filter of Patent Document 1 cannot suppress cracks and melting damage caused by such heat generation.

[0006] Patent Document 2 discloses a honeycomb structure including a plurality of prismatic honeycomb segments arranged in a lattice pattern, a bonding material layer that joins the side surfaces of the honeycomb segments to each other, and an outer peripheral wall disposed so as to surround the honeycomb segments. Each honeycomb segment has a porous partition wall that surrounds a plurality of cells extending in the axial direction from an inflow end face to an outflow end face, and an outer wall that surrounds the partition wall. One end of each cell, either on the inflow end face side or the outflow end face side, is sealed by a plugging portion. A bottomed hollow void portion extending in the axial direction is formed in part or all of the intersection portions of the lattice-shaped bonding material layer. The ratio of the axial depth of the void portion to the axial length of the honeycomb segment is 5% or more, and the ratio of the opening diameter of the void portion to the thickness of the bonding material layer is 10 to 140%. Patent Document 2 describes that the propagation of cracks generated in the bonding material layer can be suppressed by this structure.

[0007] In the embodiment of Patent Document 2, when the ratio of the depth of the void portion to the length of the honeycomb segment is as small as 5 to 20%, the void portions are provided in all of the intersection portions. However, when the ratio of the depth of the void portion is as large as 50 to 80%, the void portions are provided only in part of the intersection portions. Thus, there is no example in which deep void portions are provided in all of the intersection portions.

[0008] Further, the cross-sectional shape of the void portion described in Patent Document 2 is only circular, and in the embodiment, the void portion is formed using cylindrical wood. When arranging cylindrical wood at the intersection portions of the lattice-shaped gaps between the honeycomb segments, the upper limit of the diameter of the cylindrical wood is √2 times the thickness of the bonding material layer, which is approximately 140%. However, since there are tolerances on the side surfaces of the honeycomb segments, it is practically impossible to arrange cylindrical wood with a diameter of √2 times the thickness of the bonding material layer at the intersection portions of the lattice-shaped gaps, and the upper limit of the diameter of the cylindrical wood has to be considerably smaller than 140%. Moreover, even if the diameter of the cylindrical wood is 140% of the thickness of the bonding material layer, the cross-sectional area of the void portion formed by the cylindrical wood is too small to sufficiently suppress cracks.

[0009] From the above structural problems, it was found that in the honeycomb structure of Patent Document 2, the function of dispersing and relaxing thermal stress is insufficient, and cracks cannot be sufficiently suppressed.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0011] Therefore, an object of the present invention is to provide an extrusion die for manufacturing a honeycomb molded body for a honeycomb segment that constitutes a silicon carbide-based honeycomb filter capable of suppressing the occurrence of cracks and melting damage in the honeycomb filter due to thermal shock caused by local heat generation or rapid temperature changes in exhaust gas without increasing the pressure loss, and a method for manufacturing a honeycomb molded body using the same.

Means for Solving the Problems

[0012] As a result of intensive studies to achieve the above object, the present inventor has found that (1) by paying attention to the relationship between the thickness of the outer peripheral wall and the thickness of the partition wall of each honeycomb segment constituting the silicon carbide-based honeycomb filter, it is possible to suppress the occurrence of cracks and melting damage in the honeycomb filter due to thermal shock caused by local heat generation or rapid temperature changes in exhaust gas without increasing the pressure loss, and (2) the deformation of the partition wall that may occur when extruding the raw material for the honeycomb molded body to form an outer peripheral wall thicker than the partition wall can be prevented by attaching a guide ring with a desired structure to the outer peripheral side of the die body of the extrusion die, and thus the present invention has been conceived.

[0013] That is, a mold of the present invention for extrusion-molding a honeycomb molded body for a honeycomb segment, which has a lattice-shaped partition wall and an outer peripheral wall that form a plurality of flow paths extending in the axial direction between both end faces, and the outer peripheral wall is thicker than the partition wall, comprises a mold body and a guide ring attached to the outer peripheral side of the mold body, The mold body has a first surface where the clay supply hole opens, a second surface on the opposite side of the first surface where a lattice-shaped slit communicating with the clay supply hole opens, and a third surface on the opposite side of the first surface and located on the outer periphery of the second surface, where a lattice-shaped slit communicating with the clay supply hole opens, The second surface constitutes a region for forming the lattice-shaped partition wall of the honeycomb molded body, The third surface constitutes an outer peripheral region for forming the outer peripheral wall, The second surface is higher than the third surface by the amount of the step portion, The guide ring has a gap with the third surface and has an opening sized to cover the outer peripheral side portion of the outer peripheral region.

[0014] Preferably, the contour of the second surface is square.

[0015] Preferably, a mask is fixed to the outer peripheral side of the first surface, and the mask has a structure having a gap with the first surface and covering the outer peripheral side portion of the first surface.

[0016] Preferably, the second surface is located at a position higher than the opening of the guide ring.

[0017] Preferably, the four corners of the second surface are at the same height as the outer peripheral region, and the opening of the guide ring is square and provided with triangular closing portions at the four corners.

[0018] A method of the present invention for manufacturing a honeycomb molded body for a honeycomb segment, which has a lattice-shaped partition wall and an outer peripheral wall that form a plurality of flow paths extending in the axial direction between both end faces, and the outer peripheral wall is thicker than the partition wall, using the above extrusion mold, When causing the clay that has flowed into the clay supply hole of the extrusion mold to flow out from the slit, the flow direction of the clay flowing out from the outer peripheral region is changed by the guide ring in the direction of the partition wall forming region, and then changed in the extrusion direction by the stepped portion, thereby manufacturing a honeycomb molded body with a thick outer peripheral wall while preventing deformation of the partition wall caused by the clay flowing from the outer peripheral region.

Effect of the Invention

[0019] The extrusion mold of the present invention has a guide ring attached to the outer peripheral side of the mold body. The guide ring has a gap with a third surface constituting an outer peripheral region that forms an outer peripheral wall, and has an opening sized to cover the outer peripheral side portion of the outer peripheral region. Also, the second surface constituting the region for forming the lattice-like partition walls of the honeycomb molded body is higher than the third surface by the amount of the stepped portion. Therefore, the flow direction of the clay flowing out from the outer peripheral region is changed by the guide ring in the direction of the partition wall forming region, and then changed in the extrusion direction by the stepped portion, thereby being able to manufacture a honeycomb molded body with a thick outer peripheral wall while preventing deformation of the partition wall caused by the clay flowing from the outer peripheral region.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4(a)

Figure 4(b)

Figure 4(c)

Figure 4(d)

Figure 5

Figure 6(a)

Figure 6(b)

Figure 6(c)

Figure 7(a)

Figure 7(b)

Figure 7(c)

Figure 7(d)

Figure 8

Figure 9(a)

Figure 9(b)

Figure 10(a)

Figure 10(b)

Figure 11

MODE FOR CARRYING OUT THE INVENTION

[0021] Embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to these embodiments, and modifications, corrections, or improvements can be made without departing from the scope of the invention.

[0022] [1] Silicon carbide honeycomb filter The silicon carbide honeycomb filter 100 shown in FIG. 1 has a honeycomb segment 111 shown in FIG. 2 and a bonding material layer 19 filled in the lattice-like gaps between them for bonding the honeycomb segments 111. The honeycomb segment 111 has an outer peripheral wall 17 and a partition wall 12 that forms cells 13a, 13b defining a plurality of flow paths extending from one end face 15a to the other end face 15b. The inflow-side and outflow-side end faces 15a, 15b of the cells 13a, 13b are alternately plugged in a checkerboard pattern by plugging portions 16a, 16b, respectively.

[0023] The silicon carbide honeycomb filter 100 is characterized in that the thickness of the outer peripheral wall 17 of the honeycomb segment 111 exceeds 1.5 times and is 9 times or less the thickness of the partition wall 12. With such a thick outer peripheral wall 17, even if the partition wall 12 is thin, the heat capacity of the honeycomb segment 111 can be ensured. Therefore, even if local temperature rise occurs due to the combustion of unevenly deposited PM during the regeneration of the honeycomb filter 100, cracks and melting can be suppressed.

[0024] When the thickness of the outer peripheral wall 17 of the honeycomb segment 111 is 1.5 times or less the thickness of the partition wall 12, the heat capacity of the honeycomb segment 111 may be insufficient, and cracks and melting may occur in the honeycomb filter due to thermal shock or the like. On the other hand, when the thickness of the outer peripheral wall 17 of the honeycomb segment 111 exceeds 9 times the thickness of the partition wall 12, the pressure loss of the honeycomb filter becomes too large. The lower limit of the thickness ratio of the outer peripheral wall 17 to the partition wall 12 is preferably 1.6 times, more preferably 1.7 times. Also, the upper limit is preferably 8 times, more preferably 7 times.

[0025] The thickness of the partition wall 12 of the honeycomb segment 111 is preferably 0.17 to 0.31 mm. When the thickness of the partition wall 12 is less than 0.17 mm, not only is the strength of the thermal honeycomb segment 111 too low, but there is also a risk of cracks and melting damage occurring in the honeycomb filter due to impacts or the like. On the other hand, when the thickness of the partition wall 12 exceeds 0.31 mm, the pressure loss of the honeycomb filter becomes too large.

[0026] As shown in FIGS. 3 and 4(c), in a cross-section perpendicular to the flow path direction of the cells of the honeycomb segment 211, the cross-sectional area of the cell (exhaust gas inflow cell) 23b with the outflow side end face sealed may be made larger than the cross-sectional area of the cell (exhaust gas outflow cell) 23a with the inflow side end face sealed. Thereby, it is possible to increase the amount of PM collected until regeneration is started and to obtain a honeycomb filter in which the pressure loss when PM is collected is less likely to increase. The cross-sectional area of the inflow cell 23b is preferably 1.1 to 2.0 times, more preferably 1.2 to 1.9 times, the cross-sectional area of the outflow cell 23a.

[0027] The outer shape of the honeycomb segment in a cross-section perpendicular to the flow path direction is generally rectangular, but it is preferably a rectangle with all angles being 90°, and more preferably a square with all angles being 90° and all sides being equal. Also, as shown in FIGS. 2 and 3, it may not only be a rectangular shape (square shape) without chamfers, but also a rectangular shape having a curved chamfered portion R at the corners as shown in FIG. 4(a), or a rectangular shape having a linear chamfered portion C as shown in FIGS. 4(b) and 4(c).

[0028] In a preferred embodiment of the present invention, the silicon carbide honeycomb filter 200 has: (a) an outer shape of a cross-section perpendicular to the flow path direction of each honeycomb segment 111 being an octagonal shape provided with linear chamfered portions C at each corner of a quadrilateral, the octagonal shape being alternately composed of a first outer peripheral wall 17a corresponding to the sides of the quadrilateral and a second outer peripheral wall 17b corresponding to the linear chamfered portions C; (b) the thickness of the first outer peripheral wall 17a of the honeycomb segment 111 being more than 1.5 times and not more than 9 times the thickness of the partition wall 12; (c) among the lattice-like gaps between the bonded honeycomb segments 111, an intersection hole portion 20 without a bonding material is formed at the intersection formed by the second outer peripheral wall 17b; and (d) a pore ratio (t2 / t1) defined by the ratio of the pore diameter t2 of the intersection hole portion 20 to the thickness t1 of the bonding material layer 19 between the first outer peripheral walls 17a being more than 1.4.

[0029] When forming a hole portion of sufficient size at the intersection of the lattice-like gaps between the honeycomb segments, as shown in FIG. 4(b), the cross-sectional shape of the honeycomb segment is preferably an octagonal shape provided with chamfered portions having an inclination angle of 45° at each corner of a quadrilateral. In the example shown in FIG. 4(b), the honeycomb segment 111 has an octagonal outer wall having linear chamfered portions C with an inclination of 45° at each corner of a square, and the octagonal outer wall is composed of a long first outer peripheral wall 17a corresponding to the sides of the square and a short second outer peripheral wall 17b corresponding to the linear chamfered portions C.

[0030] The honeycomb segment having a chamfered portion at each corner preferably has no flow path in the second outer peripheral wall at the corner. For example, the honeycomb segment 111 shown in Fig. 4(b) has no flow path at the corner where the second outer peripheral wall 17b is located, and the second outer peripheral wall 17b preferably has a shape of a triangle 171 having a vertex P on the center side of the honeycomb segment 111 as shown in Fig. 4(d). In this case, the maximum thickness L (the distance between the outer peripheral surface 17b’ of the second outer peripheral wall 17b and the vertex P) in the central direction of each second outer peripheral wall 17b is thicker than the thickness of the first outer peripheral wall 17a. In particular, when the honeycomb segment 111 is an octagonal shape having a linear chamfered portion with an inclination of 45° at each corner, the triangle 171 is a right isosceles triangle having the outer peripheral surface 17b’ as the base, and the maximum thickness L is half of the length of the outer peripheral surface 17b’ of the second outer peripheral wall 17b. With such a shape, the heat capacity of the honeycomb segment 111 increases, and even if a local temperature rise occurs in the honeycomb segment 111 due to the combustion of PM deposited unevenly, the occurrence of cracks can be suppressed.

[0031] When a plurality of honeycomb segments 111 having such an octagonal outer wall are bonded vertically and horizontally, a lattice-like gap is formed between the honeycomb segments 111, and an intersection is formed by four facing second outer peripheral walls 17b. This is the same when the honeycomb segment 211 shown in Fig. 4(c) is bonded, so the case where the honeycomb segment 111 is bonded will be described below, and the description also applies to the case where the honeycomb segment 211 is bonded as it is.

[0032] Since the adjacent second outer peripheral walls 27b are separated by the width of the lattice-like gap, the cross section of the intersection can have various shapes in the portion other than the contour of the second outer peripheral wall 27b. However, as will be described later, the cross-sectional shape of the hole portion formed at the intersection is determined by the cross-sectional shape of the rod-shaped spacer placed at the intersection. Therefore, it is not necessary to define the contour of the intersection as a space for forming the hole portion up to the lattice-like gap portion, and here it is only defined as "the shape formed by the four facing second outer peripheral walls 27b constituting the contour".

[0033] When joining the honeycomb segments 111 as shown in Fig. 5 to form the honeycomb filter 200, it is preferable to form the intersection hole portion 20 without the bonding material at the intersection formed by the four second outer peripheral walls 17b. As described above, the cross-sectional shape of the intersection hole portion 20 is determined by the cross-sectional shape of the rod-shaped spacer that can be accommodated in the intersection where the second outer peripheral wall 17b constitutes the contour. For example, when the cross-sectional shape of the rod-shaped spacer is a square or a circle in contact with the second outer peripheral wall 17b, the cross-sectional shape of the obtained intersection hole portion 20 is a square or a circle. In any case, it is preferable that each intersection hole portion 20 extends in the axial direction from one end face 15a to the other end face 15b. Due to the intersection hole portion 20, the thermal stress is dispersed and relaxed without impairing the heat conduction between adjacent honeycomb segments 111, and even if there is local heat generation due to the combustion of PM accumulated unevenly, cracks and melting damage can be suppressed.

[0034] The rod-shaped spacer is in contact with the two second outer peripheral walls 17b located on the lower side during production, but it is not necessarily in contact with the two second outer peripheral walls 17b on the upper side. However, in order to maximize the cross-sectional area of the intersection hole portion 20 so that cracks can be sufficiently suppressed, it is preferable that the contour of the intersection hole portion 20 is in contact with all the second outer peripheral walls 17b. However, since a gap of the order of error is allowed, in this specification, it is said that "it is preferable that the contour of the intersection hole portion 20 is substantially in contact with the second outer peripheral wall 17b".

[0035] Figs. 6(a), 6(b) and 6(c) show an intersection hole portion 20a having a square cross-section, an intersection hole portion 20b having an octagonal cross-section, and an intersection hole portion 20c having a circular cross-section, respectively.

[0036] In the intersection hole portion 20a with a square cross-section shown in Fig. 6(a), all the sides in contact with the second outer peripheral wall 17b are connected within the bonding material layer 19, and among the above three types of intersection hole portions 20a, 20b, 20c, t2 2has the largest cross-sectional area. The ratio of the interval (aperture diameter) t2 between two facing second outer peripheral walls 17b to the thickness t1 of the bonding material layer 19 (void ratio t2 / t1) is preferably greater than 1.4. When the void ratio t2 / t1 is 1.4 or less, the effect of suppressing the propagation of the generated cracks is insufficient. The void ratio t2 / t1 is preferably 1.5 or more, more preferably 2 or more. On the other hand, if the void ratio t2 / t1 is too large, the strength of the honeycomb filter decreases, which is not preferable. The void ratio t2 / t1 is preferably 7 or less, more preferably 5 or less, and most preferably 4 or less. Therefore, the range of the void ratio t2 / t1 in the cross-sectional intersection void portion 20a with a square cross-section is generally greater than 1.4 to 7, preferably 1.5 to 5, and more preferably 2 to 4. Since the void ratio t2 / t1 is greater than 1.4, the cross-sectional area of the cross-sectional intersection void portion 20a is greater than 1.4t1×1.4t1 = 1.96t1 2 exceeds.

[0037] The cross-sectional intersection void portion 20b with an octagonal cross-section shown in FIG. 6(b) is composed of four sides of the length in contact with the second outer peripheral wall 17b and the side in the width direction of the bonding material layer 19, and has a cross-sectional area of (t2 2 -t1 2 ). From the formula of the cross-sectional area, it can be seen that if t2 is not sufficiently larger than t1, the cross-sectional intersection void portion 20b cannot secure a sufficient cross-sectional area. Therefore, the void ratio t2 / t1 is preferably 1.7 or more, more preferably 2 or more, and most preferably 2.5 or more. Also, regarding the upper limit of the void ratio t2 / t1, as in the case of the square cross-section, it is preferably 7, more preferably 5, and most preferably 4. Therefore, the range of the void ratio t2 / t1 in the cross-sectional intersection void portion 20b with an octagonal cross-section is preferably 1.7 to 7, more preferably 2 to 5, and most preferably 2.5 to 4. When the void ratio t2 / t1 is within the above range, the cross-sectional intersection void portion 20b with an octagonal cross-section has a sufficiently large cross-sectional area and does not penetrate into the bonding material layer 19, so that it is possible to achieve both the securing of a cross-sectional area sufficient to sufficiently suppress cracks and the bonding strength.

[0038] The intersecting portion hole 20c with a circular cross-section shown in Fig. 6(c) has a diameter in contact with the second outer peripheral wall 17b, so it has a cross-sectional area of (π / 4)t2 2 In order for the intersecting portion hole 20c to secure a sufficient cross-sectional area, the hole ratio t2 / t1 is preferably 1.5 or more, more preferably 2 or more, and most preferably 2.5 or more. Also, regarding the upper limit of the hole ratio t2 / t1, as in the case of a square cross-section, it is preferably 7, more preferably 5, and most preferably 4. Therefore, regarding the range of the hole ratio t2 / t1 in the intersecting portion hole 20c with a circular cross-section, it is preferably 1.5 to 7, more preferably 2 to 5, and most preferably 2.5 to 4. When the hole ratio t2 / t1 is within the above range, the intersecting portion hole 20c with a circular cross-section has a sufficiently large cross-sectional area and hardly penetrates into the bonding material layer 19, so it is possible to achieve both ensuring a cross-sectional area sufficient to sufficiently suppress cracks and the bonding strength.

[0039] Summarizing the range of the hole ratio t2 / t1 of the intersecting portion holes for all cross-sectional shapes, generally it is more than 1.4 to 7, preferably 1.5 to 5, and more preferably 2 to 4.

[0040] In order to suppress the occurrence of cracks regardless of where local temperature rise due to combustion of unevenly deposited PM occurs in each honeycomb segment 111, the ratio of the intersecting portion holes 20 in each honeycomb segment 111 to all intersecting portions is preferably 30% or more, more preferably 50% or more, and most preferably 70% or more. The upper limit of the ratio of the intersecting portion holes 20 is preferably 100% of all intersecting portions, but 95% or less is also acceptable.

[0041] [2] Method for manufacturing a silicon carbide honeycomb filter (1) Manufacture of honeycomb segments To 100% by mass of the molding raw material composed of silicon carbide particles, alumina particles, and magnesium hydroxide particles, 5 to 15% by mass of an organic binder is mixed. The silicon carbide particles preferably have an average particle size of 30 to 50 μm. Also, with respect to 100% by mass of the silicon carbide particles, the total of the alumina particles and the magnesium hydroxide particles is preferably 8 to 15% by mass.

[0042] Examples of the organic binder include methyl cellulose, ethyl cellulose, ethyl methyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, hydroxyethyl ethyl cellulose, etc. Among these, methyl cellulose or hydroxypropyl methyl cellulose is preferable.

[0043] Water is added to the obtained mixture and kneaded to form a plastic clay. In order to obtain a clay with a moldable hardness, the amount of water added is preferably 20 to 50% by mass with respect to 100% by mass of the molding raw material.

[0044] The clay is extrusion-molded using the mold 30 of the present invention shown in FIGS. 7(a) and 7(b). The mold 30 has a first surface 31a, a second surface 32a on the opposite side of the first surface 31a, a third surface 32b on the opposite side of the first surface 31a and located on the outer periphery of the second surface 32a, a clay supply hole 31 opening in the first surface 31a, and a slit 32 having a square cross-section that communicates with the clay supply hole 31 and opens in a grid pattern in the second and third surfaces 32a, 32b. The slits 32 are connected in a grid pattern within the mold body. The second surface 32a constitutes a region 33a for forming the grid-like partition walls of the honeycomb molded body, and the third surface 32b located outside the partition wall forming region 33a constitutes a region 33b for forming the outer peripheral wall. The second surface 32a is higher than the third surface 32b by the amount of the step H. A guide ring 35 having an opening for regulating the outer peripheral surface shape of the honeycomb molded body is arranged so as to surround the partition wall forming region 33a. The opening of the guide ring 35 is sized to cover the outer peripheral side portion of the outer peripheral region 33b. A mask 36 for controlling the inflow amount of the clay is arranged on the first surface 31a.

[0045] As shown by the arrow in FIG. 7(c), in the outer peripheral region 33b, the flow direction of the green compact discharged from the slit 32 of the third surface 32b changes to the direction of the partition forming region 33a by the guide ring 35, and then changes to the extrusion direction by the stepped portion H. Thereby, since it becomes difficult for the force of the green compact flowing from the outer peripheral region 33b to act on the partition wall extruded from the second surface 32a, a honeycomb molded body with a thick outer peripheral wall can be obtained without the partition wall being deformed. The thickness of the outer peripheral wall can be adjusted by changing the distance between the inner end of the guide ring 35 and the stepped portion H and the position of the inner end of the mask 36.

[0046] A honeycomb molded body in which the maximum thickness L of the second outer peripheral wall 17b is thicker than the thickness of the first outer peripheral wall 17a can be molded using, for example, the mold shown in FIG. 7(d). This mold is the same as the mold shown in FIG. 7(a) except that the four corner portions 32a1, 32a2, 32a3, 32a4 of the second surface 32a are at the same height as the outer peripheral region 33b, and the guide ring 35 has triangular closing portions 35a1, 35a2, 35a3, 35a4 at the four corners of the opening. In FIG. 7(d), the region (outer peripheral region 33b and four corner portions 32a1, 32a2, 32a3, 32a4) that is lower than the stepped portion H by the amount of the stepped portion H from the partition forming region 33a is hatched.

[0047] After drying the obtained honeycomb molded body, processing such as end face and outer periphery is performed as necessary. Then, it is fired in an oxidizing atmosphere at a temperature of 1100 to 1350 ° C. to obtain a silicon carbide-based honeycomb segment. The drying method is not particularly limited, and examples thereof include methods such as hot air drying, microwave heating drying, and high frequency heating drying.

[0048] (2) Manufacture of honeycomb filter The material for bonding the honeycomb segments (bonding material) contains a bonding material raw material composed of silicon carbide aggregate particles and binder particles, an organic binder, and, if necessary, an inorganic binder and a pore-forming material. The binder particles are composed of at least one selected from the group consisting of an aluminum source, a magnesium source, a silica source, and their compounds. Examples of the alumina source include alumina or aluminum hydroxide, and examples of the magnesium source include magnesium oxide or magnesium hydroxide. The total of the alumina source particles and the magnesium source particles is preferably 5 to 25% by mass based on 100% by mass of the silicon carbide particles.

[0049] The organic binder may be the same as that used in the production of the honeycomb segments. The addition amount of the organic binder is preferably 5 to 15% by mass based on 100% by mass of the bonding material raw material.

[0050] Examples of the inorganic binder include colloidal silica, colloidal alumina, etc. The addition amount of the inorganic binder is preferably 40% by mass or less based on 100% by mass of the bonding material raw material.

[0051] Examples of the pore-forming material include foaming resin, foamed resin, carbon, water-absorbing resin, fly ash balloon, etc. Among these, a foaming resin or a foamed resin with a small variation in particle diameter is preferable. The addition amount of the pore-forming material is preferably 2 to 20% by mass based on 100% by mass of the bonding material raw material.

[0052] Water is added to the obtained mixture and kneaded to produce a bonding material slurry. The addition amount of water is preferably 20 to 50% by mass based on 100% by mass of the bonding material raw material.

[0053] After applying the bonding material slurry to the outer peripheral wall 17 of the honeycomb segment 111, as shown in FIG. 1, the honeycomb segments 111 are pressure-bonded and joined via the bonding material. At this time, the bonding material layer 19 formed between the honeycomb segments 111 becomes lattice-shaped.

[0054] When manufacturing the honeycomb filter 200 having the intersection hole portion 20 shown in FIG. 5, when bonding the honeycomb segments 111, a rod-shaped spacer having the same dimensions as the intersection portion and the same length as the honeycomb segment 111 is arranged so that the bonding material does not enter the intersection portion formed by the four second outer peripheral walls 27b. The rod-shaped spacer is preferably made of wood, paper, resin, etc. that are easily burned out. The rod-shaped spacer preferably has a length extending between both end faces 25a and 25b.

[0055] After drying the bonding material layer 19 between the honeycomb segments 111, when firing in an oxidizing atmosphere at a temperature of 1100 to 1350°C, the rod-shaped spacer burns out and a sintered body (precursor of the honeycomb filter) having the intersection hole portion 20 is formed.

[0056] After machining the outer periphery of the obtained sintered body into a circular shape with a lathe, an outer skin material containing silicon carbide particles and an inorganic binder is applied to the circular outer periphery to form the outer skin 11, dried, and a silicon carbide-based honeycomb filter 200 is obtained.

[0057] The present invention will be described in more detail by the following examples, but the present invention is not limited to these examples.

[0058] Example 1 A molding raw material composed of 100% by mass of silicon carbide particles, 5.9% by mass of alumina particles, and 4.1% by mass of magnesium hydroxide particles, and 10% by mass of hydroxypropylmethylcellulose as an organic binder were mixed, and water was added to the obtained mixture at a ratio of 35% by mass per 100% by mass of the molding raw material and kneaded. The obtained plastic clay was extruded from the mold of a screw molding machine to form a honeycomb segment molded body having a square cross-section shown in FIG. 2, and dried at 120°C for 2 hours by a hot air dryer. Then, the end faces 15a and 15b of the cells 13 of the honeycomb segment molded body were alternately sealed in a checkerboard pattern with a sealing material having the same composition as the clay, and dried to form an inflow-side sealing portion 16a and an outflow-side sealing portion (not shown).

[0059] With respect to 100% by mass of silicon carbide particles, 5.9% by mass of alumina particles, 4.1% by mass of magnesium hydroxide particles, 4.0% by mass of foamed resin as a pore former, 8.0% by mass of colloidal silica, 10% by mass of hydroxypropyl methylcellulose as an organic binder, and 30% by mass of water were mixed and kneaded to produce a bonding material slurry. After applying this bonding material slurry to the outer peripheral wall 17 of the honeycomb segment molded body, 6×6 honeycomb segment molded bodies were pressure-bonded and joined as shown in FIG. 1.

[0060] After drying the bonding material, it was fired in an oxidizing atmosphere at a temperature of 1300°C, and the outer periphery of the obtained sintered body was machined circumferentially with a lathe. An outer skin material containing silicon carbide particles and colloidal silica was applied to the circumferential outer periphery and dried to obtain a silicon carbide honeycomb filter 100 with an outer diameter of 190 mm and a total length of 203 mm. The honeycomb segments 111 constituting the honeycomb filter 100 have a square cross-section with a side length of 35 mm, the thickness of the outer peripheral wall 17 is 0.7 mm, the thickness of the partition wall is 8 mil (0.20 mm), and the cell density is 300 cpsi (46.5 cells / cm 2 ). Also, the thickness of the bonding material layer 19 between the honeycomb segments 111 was 2 mm.

[0061] Using this silicon carbide honeycomb filter, a Drop to Idle test consisting of the following steps was performed. First, combustion soot with an average particle size of 0.11 μm was introduced at a rate of 1.57 g / h into the silicon carbide honeycomb filter fixed to the test stand so that the soot adhesion amount per liter of the filter was 6 g at an air flow rate of 4.5 Nm 3 / min. In order to reproduce the state where the vehicle suddenly stops at the top of the uphill road (Drop to Idle), combustion gas was introduced into the honeycomb filter with the temperature control shown in FIG. 11, and combustion was stopped when the honeycomb filter inlet temperature reached 600°C, and the inside of the filter was allowed to reach the maximum temperature. Then, the honeycomb filter was taken out and checked for any damage. As a result, it was confirmed that no cracks or melting damage occurred in the silicon carbide honeycomb filter of Example 1.

[0062] Example 2 The green body produced in the same manner as in Example 1 was extruded from the mold of a screw molding machine to form a honeycomb segment molded body in which the cross-sectional area of the inflow cell was larger than the cross-sectional area of the outflow cell as shown in Fig. 3. After drying the honeycomb segment molded body at 120 °C for 2 hours in a hot air dryer, a plugging material having the same composition as the green body was alternately filled in a checkered pattern at the ends of cells 23a and 23b, respectively, and dried to form an inflow-side plugging portion 26a and an outflow-side plugging portion (not shown).

[0063] The bonding material slurry produced in the same manner as in Example 1 was applied to the outer peripheral wall of the honeycomb segment molded body, and 6×6 honeycomb segment molded bodies were bonded by crimping. After drying the bonding material, it was fired in an oxidizing atmosphere at a temperature of 1300 °C, and the outer periphery of the obtained sintered body was machined circumferentially with a lathe. An outer skin material containing silicon carbide particles and colloidal silica was applied to the circumferential outer periphery and dried to obtain a silicon carbide honeycomb filter having an outer diameter of 190 mm and a total length of 203 mm. The honeycomb segment 211 constituting the honeycomb filter has a square cross-section with a side length of 35 mm, the thickness of the outer peripheral wall 17 is 1.3 mm, the thickness of the partition wall is 8 mil (0.20 mm), and the cell density is 300 cpsi (46.5 cells / cm 2 ). The cross-sectional area of the inflow cell 23b was 1.58 times that of the outflow cell 23a. Also, the thickness of the bonding material layer between the honeycomb segments 211 was 2 mm.

[0064] As a result of conducting the same Drop to Idle test as in Example 1, it was confirmed that the maximum temperature reached by the silicon carbide honeycomb filter of Example 2 was lower than that of Example 1, and no cracks or melting damage occurred.

[0065] Example 3 The green compact produced in the same manner as in Example 1 was extruded from the mold of a screw molding machine and dried at 120°C for 2 hours using a hot air dryer, to form a honeycomb segment molded body having an octagonal cross section with linear chamfered portions having an inclination angle of 45° at each corner of a square as shown in Fig. 4(c), and having a cross-sectional area of the inflow cell larger than that of the outflow cell. The outer periphery of the honeycomb segment molded body was composed of a first outer peripheral wall 27a corresponding to the side of the square and a second outer peripheral wall 27b corresponding to the linear chamfered portion.

[0066] The end faces of the cells 23a and 23b of the honeycomb segment molded body were alternately plugged in a checkered pattern with a plugging material having the same composition as the green compact and dried, and then fired in an oxidizing atmosphere at a temperature of 1300°C to obtain a honeycomb segment 211 having an inflow side plugging portion 26a and an outflow side plugging portion 26b.

[0067] When arranging the honeycomb segments 211 via lattice-like gaps, a wooden rod-shaped spacer having a square cross section and the same length as the total length of the honeycomb segments 211 was previously arranged at the intersection portion formed by the second outer peripheral wall 27b. The length of one side of the square cross section of the rod-shaped spacer was the length of the second outer peripheral wall 47b + the thickness t1 of the lattice-like gap (bonding material layer) × √2.

[0068] The bonding material slurry produced in the same manner as in Example 1 was applied to the outer peripheral walls of the honeycomb segments 211 other than the rod-shaped spacers, and then 6 × 6 honeycomb segments 211 were pressure-bonded via the bonding material slurry. After drying the bonding material layer formed between the honeycomb segments 211, it was fired in an oxidizing atmosphere at a temperature of 1300°C to burn out the wooden rod-shaped spacers, and a cross-sectional hole portion 20 having a square cross section and extending in the axial direction between both end faces 25a and 25b was formed as shown in Fig. 5. The cross-sectional hole portion 20 had a hole diameter t2 of 7 mm.

[0069] A masking material was applied to one end face 25a of the cross-hole part 20 to a depth of 1 mm, and the outer circumference of the honeycomb filter was machined circumferentially with a lathe. An outer skin material containing silicon carbide particles and colloidal silica was applied to the obtained circumferential outer circumference and dried to obtain a silicon carbide-based honeycomb filter 200 having an outer diameter of 190 mm and an overall length of 203 mm. The honeycomb segment 211 constituting the silicon carbide-based honeycomb filter 200 has an octagonal cross-section provided with linear chamfered portions having an inclination angle of 45° at each corner of a square with a side of 35 mm. The length of the first outer peripheral wall 27a is 30 mm, the length of the second outer peripheral wall 27b is 4 mm, the thickness of the first outer peripheral wall is 1.3 mm, the maximum thickness L of the second outer peripheral wall is 2 mm, the thickness of the partition wall 22 is 8 mil (0.20 mm), and the cell density is 300 cpsi (46.5 cells / cm 2 ). The cross-sectional area of the inflow cell 33b was 1.58 times that of the outflow cell 33b. Also, the thickness of the bonding material layer was 2 mm.

[0070] As a result of performing the same Drop to Idle test as in Example 1, it was confirmed that the maximum temperature reached by the silicon carbide-based honeycomb filter of Example 3 was lower than that of Example 2, and no cracks or melting damage occurred.

[0071] Comparative Example 1 The green body produced in the same manner as in Example 1 was extruded from the mold of a screw molding machine to form a honeycomb segment molded body having the shapes shown in FIGS. 9(a) and 9(b), and dried at 120° C. for 2 hours with a hot air dryer.

[0072] The end faces 45a and 45b of the cells 43 of the honeycomb segment 411 were alternately masked in a checkered pattern with a masking material having the same composition as the green body and dried, and then fired in an oxidizing atmosphere at a temperature of 1300° C. to obtain a honeycomb segment 411 having an inflow-side masking portion 46a and an outflow-side masking portion 46b.

[0073] After applying the bonding material slurry prepared in the same manner as in Example 1 to the outer peripheral wall 47 of the honeycomb segment 411, as shown in FIG. 8, 6×6 honeycomb segments 411 were pressure-bonded via the bonding material. After drying the obtained honeycomb filter, it was fired in an oxidizing atmosphere at a temperature of 1300°C, and the outer periphery was machined into a circular shape using a lathe.

[0074] An outer skin material containing silicon carbide particles and colloidal silica was applied to the circumferential outer periphery of the honeycomb filter and dried to obtain a silicon carbide-based honeycomb filter 400 having an outer diameter of 190 mm and an overall length of 203 mm. The honeycomb segment 411 constituting the honeycomb filter 400 has a square cross-section with a side length of 35 mm, the thickness of the outer peripheral wall is 0.2 mm, the thickness of the partition wall 42 is 8 mil (0.20 mm), and the cell density is 300 cpsi (46.5 cells / cm 2 ). Also, the thickness of the bonding material layer 49 was 2 mm.

[0075] As a result of performing the same Drop to Idle test as in Example 1, it was confirmed that the maximum temperature reached by the silicon carbide-based honeycomb filter of Comparative Example 1 was higher than that of Example 1, and cracks and melting damage occurred.

Explanation of Symbols

[0076] 100, 200, 400: Silicon carbide-based honeycomb filter 111, 211, 411: Honeycomb segment 11, 21, 41, 51: Outer skin 12, 22, 42, 52: Partition wall 13a, 23a, 43a, 53a: Inlet side sealed flow path (outlet cell) 13b, 23b, 43b, 53b: Outlet side sealed flow path (inlet cell) 15a, 25a, 45a, 55a: One end face (inlet side end face) 15b, 25b, 45b, 55b: The other end face (outlet side end face) 16a, 26a, 46a, 56a: Inlet side eye seal portion 46b, 56b: Outlet side eye seal portion 17, 27, 47: Outer peripheral wall 17a, 27a: First outer peripheral wall 17b, 27b: Second outer peripheral wall 19, 29, 49: Bonding material layer 20, 20a, 20b, 20c: Intersection hole part 30: Extrusion mold 31: Supply hole 31a: First surface 32: Slit 32a: Second surface 32b: Third surface 32a1, 32a2, 32a3, 32a4: Corners of the second surface 33a: Partition forming region 33b: Outer peripheral region 35: Guide ring 35a1, 35a2, 35a3, 35a4: Closing part 36: Mask H: Step part L: Maximum thickness of the second outer peripheral wall t1: Thickness of the bonding material layer between the first outer peripheral walls t2: Hole diameter of the intersection hole part

Claims

1. A mold for extruding a honeycomb molded body for a honeycomb segment having a lattice-shaped partition wall and an outer peripheral wall that form cells defining a plurality of flow paths extending in the axial direction between both end faces, wherein the outer peripheral wall is thicker than the partition wall, comprising a mold body and a guide ring attached to the outer peripheral side of the mold body, the mold body having a first surface in which a clay supply hole opens, a second surface on the opposite side of the first surface in which a lattice-shaped slit communicating with the clay supply hole opens, and a third surface on the opposite side of the first surface and located on the outer periphery of the second surface in which a lattice-shaped slit communicating with the clay supply hole opens, the second surface constituting a region for forming the lattice-shaped partition wall of the honeycomb molded body, the third surface constituting an outer peripheral region for forming the outer peripheral wall, the second surface being higher than the third surface by a step portion H, the guide ring having a gap with the third surface and having an opening sized to cover an outer peripheral side portion of the outer peripheral region. A mold characterized by this.

2. The extrusion mold according to claim 1, wherein the contour of the second surface is square.

3. The extrusion mold according to claim 1, wherein a mask is fixed to the outer peripheral side of the first surface, and the mask has a structure having a gap with the first surface and covering the outer peripheral side portion of the first surface.

4. The extrusion mold according to claim 1, wherein the second surface is at a position higher than the opening of the guide ring.

5. The extrusion mold according to claim 1, wherein four corners of the second surface are at the same height as the outer peripheral region, and the opening of the guide ring is square and provided with triangular closing portions at four corners.

6. A method for manufacturing a honeycomb molded body for a honeycomb segment having a lattice-shaped partition wall and an outer peripheral wall that form cells defining a plurality of flow paths extending in the axial direction between both end faces, wherein the outer peripheral wall is thicker than the partition wall, using the extrusion mold according to claim 1, When causing the clay that has flowed into the clay supply hole of the extrusion die to flow out from the slit, the flow direction of the clay flowing out from the outer peripheral region is changed by the guide ring in the direction of the partition wall forming region, and then changed in the extrusion direction by the step portion H, thereby manufacturing a honeycomb molded body with a thick outer peripheral wall while preventing deformation of the partition wall caused by the clay flowing from the outer peripheral region. A method characterized by this.

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