JPH0830407B2 - Ceramic honeycomb structure - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an exhaust gas purifying catalyst for an internal combustion engine, a fine particle purifying filter, a carrier for purifying and / or deodorizing a combustion gas using various gases or petroleum as fuel. The present invention relates to a ceramic honeycomb structure used as.

(Prior Art) A conventional catalytic converter mounted on an automobile is generally used in a direction perpendicular to a through hole 11-1 through which exhaust gas passes (hereinafter referred to as “diameter”) as shown in FIG. 4 so as to withstand severe vibration during use. Direction)) through the cushion materials 12-1 and 12-2 and the seal material, and in the direction of the through hole, the plate material 13 is pressed through the cushion material 12-1 and fixed and held. It has a structure.

However, in the case of the above structure, the honeycomb structure through hole 11-2 in the portion of the cushion material 12-1 that is abutted in the through hole direction is formed.
Since the exhaust gas cannot pass through and the catalyst in that part is wasted, the method of using only the sealing material on all sides and holding it only in the radial direction has also been put into practical use for the purpose of saving the catalyst precious metal ( (Fig. 5) In addition, various methods have been proposed in which the catalyst noble metal is not supported on the outer peripheral annular portion of the ceramic honeycomb structure.

As one example thereof, Japanese Patent Laid-Open No. 51-87482 discloses a method in which a film is formed on the outer peripheral portion of a ceramic honeycomb structure with a non-water-absorbing resin-based glue and γ-alumina is not supported. Further, Japanese Patent Application Laid-Open No. 60-12136 discloses a method in which the outer peripheral portion of the end face of the ceramic honeycomb structure is covered with a water impermeable coating and γ-alumina is not carried.
Further, Japanese Patent Application Laid-Open No. 54-110189 discloses a method in which the through holes in the outer peripheral portion of the end surface of the ceramic honeycomb structure are closed with γ-alumina and γ-alumina is not supported on the inner surfaces of the through holes.

On the other hand, Japanese Utility Model Laid-Open No. 53-152012 discloses a technique in which a protrusion is provided on the outer peripheral portion of a ceramic honeycomb structure so that the honeycomb structure does not rotate when assembled as a catalytic converter.

(Problems to be Solved by the Invention) As described above, the structure of a generally used catalytic converter has a problem that the catalytic precious metal is wasted.

In addition, the method of holding only in the radial direction, which has been practically used in some parts, requires increasing the pressure applied in the radial direction to withstand severe vibration during use. For example, when the thickness is relatively thick such as 0.3 mm and the external pressure strength is high, it can be held only in the radial direction, but when the thickness of the partition wall is relatively thin such as 0.15 mm, the external pressure strength is low and cannot be applied. There is a problem.

Further, in the technologies disclosed in JP-A-51-87482, JP-A-60-12136, JP-A-54-110189, and JP-A-53-152012, the number of manufacturing steps is increased and complicated, There is a disadvantage that the cost also increases in proportion to it. Further, the technique disclosed in Japanese Utility Model Laid-Open No. 53-152012 has a disadvantage that it cannot be manufactured substantially because there is a difference in thickness between the central portion and the outer peripheral portion.

An object of the present invention is to solve the above-mentioned problems and to provide a ceramic honeycomb structure capable of reducing the amount of catalytic precious metal at a low cost and enabling a reliable holding method.

(Means for Solving the Problem) The ceramic honeycomb structure of the present invention has a shape in which at least two positions of the outer peripheral portion of the cross section perpendicular to the through hole are annularly cut out, and the outer peripheral wall has a substantially constant thickness. It is characterized by being.

(Operation) Since the honeycomb structure catalyst of the present invention has the above-mentioned structure, the structure for holding the honeycomb structure catalyst of the present invention is such that a notched portion in the radial direction is filled with a holding material to have a cylindrical shape and the outer periphery thereof is kept to have a uniform thickness. Can be held with wood. That is, by using a holding material integrated into a shape having an increased thickness by a thickness corresponding to the depth of the cutout portion at a position corresponding to the cutout portion, the holding material can be easily stored by the same method as the conventional one, Since the honeycomb structure has the same outer peripheral extension annular portion as the notched outer peripheral annular portion (hereinafter referred to as "remaining portion"), whether pressure is applied to the remaining portion through the cushion material in the through hole direction. Alternatively, the position can be directly fixed by a plate material, and a reliable holding method that has been generally practically used can be applied. Further, since the thickness of the outer peripheral wall is substantially constant, the notch can be formed at the same time as the honeycomb structure is extruded. Further, by making the outer peripheral wall constant in thickness, the outer peripheral wall can be thickened. As compared with the case where the thickness of the outer peripheral wall is not constant as in the case where the notch is formed on the outer peripheral wall, the ceramic having the notch efficiently does not generate cracks during drying or firing after molding. A honeycomb structure can be obtained.

Further, since the purification performance of the catalyst is proportional to the area where the exhaust gas contacts the catalyst, it is required that the geometric surface area of the through holes of the ceramic honeycomb structure through which the exhaust gas passes is large. However, since the γ-alumina coating amount is also proportional to the geometric surface area, the remaining portion or a portion slightly inside the notched outer peripheral annular portion may have a structure having a small through hole density for the purpose of reducing the geometric surface area. . The reason why the structure may be such that the through hole density is slightly smaller to the inside of the notched outer peripheral annular portion is because the exhaust gas transfer pipe connected to the catalytic converter has a smaller diameter than the cross-sectional diameter of the catalyst, This is because the flow mainly flows through the center of the honeycomb structure and the vicinity of the outer periphery is small, and therefore the purification performance is not affected even if the geometric surface area is small.

The ceramic honeycomb structure carrier is generally manufactured by extrusion molding. The honeycomb structure carrier of the present invention also has a constant radial cross section in the through-hole direction, and therefore can be manufactured by the same extrusion manufacturing method as the conventional method using a predetermined jig and tool.

Since the catalyst supporting method does not carry out any complicated pretreatment, it can be manufactured by the same method as the conventional method without increasing the pretreatment step, and the catalyst noble metal can be reduced.

(Examples) Examples of the present invention will be described below.

Outer diameter 6 of the remaining portion 6 having the cross-sectional shape shown in FIGS. 1 (a) and 1 (b) after the cordierite raw material is extruded and then fired.
A ceramic honeycomb structure 1 of the present invention having a through hole 3 surrounded by partition walls 2 having a length of 0 mm and a total length of 100 mm was obtained. The thickness of the portion other than the remaining portion was 0.19 mm, and the cell density of the through holes was 62 cells / cm ² . That is, in the example of the sectional shape shown in FIG. 1 (a), two notches 4 having a uniform width of 3 mm are provided in the radial direction of the outer peripheral annular portion, and the thickness of the outer peripheral wall 5 is substantially constant. . In the example of the cross-sectional shape shown in FIG. 1 (b), the notch 4 having a width of 3 mm is also provided uniformly at four positions in the radial direction of the outer peripheral annular portion, and the thickness of the outer peripheral wall 5 is substantially constant. . 2 (a) and 2 (b) show another example of the cutout portion of the present invention in an enlarged manner.

Inventive products No. 1 to 6 having the remaining cell structure and the notch shown in Table 1 produced by the above-mentioned method, and the outer diameter of 100 m
Measurement of the weight of the structure for each of two comparative examples Nos. 1 and 2 having a cell structure shown in Table 1 with a circular cross section as shown in FIG. The test, the canning test, and the heating vibration test were performed, and three mechanical external pressure strength tests were performed. The results are shown in Table 1.

Here, the amount of activated alumina adhered is determined by immersing these ceramic honeycomb structures in an aqueous solution in which γ-alumina and a small amount of binder are sufficiently stirred and then taking them out, blowing off an excess coating material, and then drying and firing. To do.
The weight before coating was subtracted from the weight of the ceramic honeycomb structure thus obtained.

The external pressure strength test is performed on the upper and lower end faces of the honeycomb structure with a thickness of about
Approximately 20 mm aluminum plate is applied through a 0.5 mm urethane sheet, the side is wrapped with a 0.5 mm-thick urethane tube and sealed, put in a pressure vessel filled with water, the pressure is gradually raised, and a breaking noise is generated. The pressure at which it occurred was measured.

In the canning test, a ceramic mat with a width of 90 mm is wound around the carrier as a holding material on the carrier, and the outlet has an inner diameter almost the same as the steel pipe inlet and the inlet has an inner diameter larger than the outlet. After placing the jig in a tapered jig, hitting the jig outlet to the entrance of the steel pipe and pushing the carrier into the steel pipe with a hydraulic ram, the carrier was pushed out from the steel pipe and the appearance was observed.

In the case of the comparative product, a thickness of 4.9 mm is used as the ceramic mat, and in the case of the present invention, a ceramic mat having a thickness of 4.9 mm is attached to a portion corresponding to the cutout portion of the ceramic mat having a thickness of 4.9 mm. Was used. The inner diameter of the steel pipe is
It is 104 mm long, 100 mm long, and has flanges with an inside diameter of 104 mm on both ends.

In the heating vibration test, the same ceramic mat as in the canning test was wrapped around the carrier, and the honeycomb structure was damaged in the canning test.
After being pressed into a steel pipe having a flange welded, a megaphone-shaped cone in which a flange having an inner diameter of 94 mm on the steel pipe connection side was welded to both ends of the steel pipe was subjected to a bolting test. However, only the comparative example product 2 has a structure in which the inner diameter of the cone on the steel pipe connection side is 106 mm, that is, the cone is not held in the through hole direction.

The test conditions were 80 with a propane gas burner as the heating source.
One cycle consists of heating 0 ° C hot gas for 2 minutes and then heating room temperature air for 2 minutes for cooling, and performing 50 cycles while applying vibration of 200Hz, 0 to 20G. Then remove the cone and remove the carrier from the steel pipe. The extruded appearance was observed.

As can be seen from Table 1 above, the external pressure strength is 20 kgf / cm ²
Even in the following comparatively weak ceramic honeycomb structures, the products 2, 3 and 6 of the present invention can reduce the amount of γ-alumina coating by about 10% by partially cutting out the outer peripheral annular portion, and therefore the catalytic precious metal can be reduced by about 10%. %, And it can endure a heating vibration test simulating actual use conditions and can be sufficiently put to practical use.

The size of the outer peripheral annular portion of the present invention, which is partially cut away, is a design requirement determined by the radial width of the cushion material that abuts in the through-hole direction and the actual use conditions, and is therefore limited to this embodiment. is not. Further, in the present embodiment, the ceramic honeycomb structure having a circular cross-sectional shape in the radial direction is used, but it is not limited to this and may have an elliptical shape, for example.

Further, the shape of the cell is a square in this embodiment, but is not limited to this. As for the material, cordierite is used in this embodiment, but the material is not limited to this.

(Effect of the invention) As is clear from the above description, according to the present invention, by limiting the cross-sectional shape of the honeycomb structure and the thickness of the outer wall, it is possible to save the catalytic precious metal when assembled as a catalytic converter. It is possible to inexpensively and easily obtain a ceramic honeycomb structure that can be reliably held.

[Brief description of drawings]

1 (a) and 1 (b) are cross-sectional views showing an example of the ceramic honeycomb structure of the present invention, and FIGS. 2 (a) and 2 (b) are enlarged views of another example of the notch portion of the present invention. 3 is a perspective view showing a ceramic honeycomb structure of a comparative example, and FIGS. 4 and 5 are cross-sectional views showing an example of a conventional catalytic converter. DESCRIPTION OF SYMBOLS 1 ... Ceramic honeycomb structure 2 ... Partition wall 3 ... Through hole 4 ... Notch part 5 ... Outer peripheral wall 6 ... Remaining part

Claims (1)

[Claims] 1. A ceramic honeycomb structure characterized in that at least two portions of an outer peripheral portion of a cross section perpendicular to a through hole are cut out in an annular shape, and an outer peripheral wall has a substantially constant thickness.