JPS6218797B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a ceramic honeycomb structure having the required mechanical strength, a large surface area per unit volume, and a small amount of material. In general, ceramic honeycomb structures have attracted particular attention as catalyst carriers for exhaust gas purification in internal combustion engines and various industrial combustion furnaces, as heat storage bodies in heat exchangers, and as rectifying elements for hot gas flowing in pipes, and are widely used in various fields. It started to be done. However, in recent years, environmental demands for exhaust gas treatment from automobiles and other vehicles have become increasingly severe. 3) Improvements such as shortening the time it takes to reach a predetermined temperature are urgent issues. In order to solve this problem, the thickness of the walls (hereinafter referred to as partition walls) that separate the many through holes provided in the axial direction of the ceramic honeycomb structure from each other should be made as thin as possible to increase the surface area per unit volume. However, it is necessary to reduce the amount of material that makes up the structure.
However, in the case of this type of honeycomb structure, the materials that make up the structure are brittle and have very low breaking strength, so if the partition walls are made too thin beyond the limit without considering the structure, the inside of the structure will be damaged. If the temperature distribution is not uniform, thermal stress may be generated inside the structure due to thermal shock such as rapid heating and cooling, and it may be easily destroyed by vibration or unexpected external force during handling. be. Conventionally, as shown in FIG. 1, for example, the thickness of the partition walls 2, 2' of the through hole 1 has been reduced to a uniform thickness to the limit that can withstand external forces, or in order to make them strong against mechanical external pressure, for example, As shown in Figure 2, only the outer peripheral wall 3 is reinforced with a wall that is at least twice as thick as the partition walls 2, 2' forming the through hole 1. It was something. However, in the case of the former structure in which all the partition walls 2 and 2' are formed with uniformly thin walls, the strength and rigidity of the partition walls 2 and 2' are extremely low. It is weak against external pressure perpendicular to the axial direction of the partition wall 1, and if a mechanical shock is applied to the end face of the structure, this part will easily break off, so to prevent this, each partition wall 2, The thickness of 2' needed to be at least 0.3 mm. Furthermore, even in the latter case where only the outer peripheral wall 3 is thick, in order to satisfy the desired mechanical strength, the wall thickness of the outer peripheral wall 3 needs to be approximately 1 to 5 mm, and the thickness of the outer peripheral wall 3 must be approximately 1 to 5 mm. In order to prevent cracks caused by the difference in thickness between the outer peripheral wall 3 and the partition walls 2, 2' of the through hole 1 during the drying of the molded product or the firing process, the thickness of the partition walls 2, 2' of the through hole 1 is set to 0.25 mm to 0.3 mm. The extent was the limit. In this way, the thickness of conventional partition walls is inevitably determined from the viewpoint of mechanical and thermal shock strength, so it is extremely difficult to simultaneously reduce the surface area per unit volume within this range. It was difficult. That is, although thinner walls are possible in terms of manufacturing technology, it is difficult to further improve the characteristics in terms of application technology. The ceramic honeycomb structure of the present invention was developed to eliminate such drawbacks found in conventional structures. The present invention relates to a ceramic honeycomb structure in which the thickness of partition walls of adjacent through holes is regularly thinned toward the centroid of the honeycomb structure. A more detailed explanation will be given below based on the illustrated embodiment. In the embodiment shown in FIGS. 3 and 4, the cross-sectional shape of the through hole 1 is any shape such as a polygon such as a lattice shape or a hexagonal shape, a circle, an oval shape, etc., and the cross-sectional shape of the through hole 1 is axially The thickness of the partition walls 2, 2' forming the through hole 1 is continuously reduced from the parallel outer circumferential wall 3 toward the cross-sectional centroid O direction of the structure. Further, FIGS. 5 and 6 show other embodiments of the present invention, in which the shape of the through hole 1 in the portion not in contact with the outer peripheral wall 3 is square or rectangular, and the cross section of the structure is circular. When a plurality of regions A, B, and C that include the centroid O and do not intersect are provided, and the directions of the through holes 1 and the partition walls 2 and 2' are the X and Y axes,
The thickness of the partition walls 2 and 2' accommodated in each region A, B, and C, respectively, is equal in both the X and Y directions, and if the thickness of the partition walls in the X and Y axis directions is X ₁ and X, respectively. ₂ , _{X 3} and Y ₁ , _{Y 2} , _{Y 3 , the} partition wall is formed in such _a relationship that all of In this case, X ₁ = Y ₁ , X ₂ = Y ₂ , X ₃ =
Y ₃ is preferable in terms of strength and manufacturing. That is, the preferred structure in this example is as follows:
In each region indicated by A, B, and C in the figure, the thickness of the partition walls 2 and 2' is uniform, and each region A,
Between B and C, the thickness should be gradually reduced toward the centroid O direction. Note that it is preferable to provide as many regions as possible. Further, in the embodiment, the cross section of the honeycomb structure is circular;
Although a case has been described in which the shape of a large number of through holes arranged in the axial direction is square, the present invention is not limited to this, for example,
The outer circumferential shape of the structure may be oval, and
The cross-sectional shape of the through-holes may also be circular, oval, or polygonal such as hexagonal, and in short, it includes anything that can be used as a catalyst carrier. Next, in order to confirm the effects of the present invention, the results of a comparative experiment between the conventional product shown in FIGS. 1 and 2 and the honeycomb structure of the present invention shown in FIG. 3 will be explained. The product of the present invention used this time has an outer peripheral wall thickness of 0.3 mm using an extrusion method, the maximum thickness of the partition wall is 0.2 mm at the part closest to the outer peripheral wall, and the minimum thickness is 0.07 mm at the part closest to the centroid. The surface area and material volume per unit volume of a product manufactured and fired to a diameter of Put the temperature into the electric furnace at the specified temperature.
After heating for 15 minutes, they were taken out into the air, measured, and compared with conventional products. In addition, as for the conventional product, in the embodiment shown in FIG. 1 in which the thickness of the partition wall is formed uniformly, the thickness of the outer peripheral wall is 0.3 mm, the thickness of the partition wall is 0.3 mm, and the outer peripheral wall,
A comparison is made between a partition wall with a thickness of 0.07 mm, which can be manufactured, and an example shown in Fig. 2, in which only the outermost peripheral wall is particularly thick, with an outer peripheral wall thickness of 3.0 mm and a partition wall thickness of 0.25 mm. It was used as a material. It should be noted that the above samples used the same raw material and had the same cross-sectional external shape of the structures. The results are shown in the table below.

[Table] As is clear from the above results, the ceramic honeycomb structure of the present invention in which the thickness of the partition walls is regularly reduced toward the centroid of the honeycomb structure,
Compared to conventional products with a uniform outer wall and partition wall thickness (0.3 mm) or a conventional product with only a thicker outer wall, the strength against external pressure and thermal shock resistance are almost the same or slightly higher, and the surface area per unit volume is lower. Excellent values were obtained, with the ratio increasing by 17% and the material volume decreasing by 66%. In addition, by forming both the outer peripheral wall and the partition wall to be extremely thin (0.07 mm), we were able to improve the surface area per unit volume and the material volume ratio, but on the other hand, the breaking load due to external pressure was extremely low, making it difficult to use. I can't stand it. Thus, it can be said that in the conventional structure, it was not possible to simultaneously satisfy mechanical and thermal strength and surface area ratio per unit volume. As mentioned above, the ceramic honeycomb structure of the present invention is a honeycomb structure in which the thickness of the partition walls of a large number of through holes is regularly thinned toward the centroid of the structure, so the thickness of each partition wall is The closer it gets to the centroid, the thinner it can be made regardless of external force. Therefore, according to the present invention, when viewed as a whole, it has become possible to make the average thickness of the partition walls significantly thinner than in the past. In other words, by increasing the surface area per unit volume, we were not only able to increase the contact reaction area and through-hole area, but also shorten the time to reach the specified temperature by reducing the amount of material. did it. Since it has such excellent performance, it can be applied to catalyst carriers for automobile exhaust gas purification, heat storage bodies for heat exchangers, etc., and its industrial value is great, and the present invention will greatly contribute to the development of industry.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views of a conventional ceramic honeycomb structure according to the present invention, and FIGS. 3 to 6 are explanatory diagrams showing a typical example of the present invention, and FIG. Figure 4 is a cross-sectional view of the structure in which the thickness of the partition wall forming the through hole is gradually reduced toward the centroid of the cross-sectional area of the structure.
Fig. 5 is a cross-sectional view of the partition wall in which the thickness of the partition wall is gradually reduced in certain areas;
FIG. 6 is a partially cutaway vertical cross-sectional view taken along line bb' in FIG. 1...Through hole, 2, 2'...Partition wall, 3...Outer peripheral wall, O
...Centroid, A, B, C...A region with equal thickness of the partition wall.

Claims (1)

[Claims] 1. A ceramic honeycomb structure comprising a large number of through holes adjacent to each other in the axial direction with a thin partition wall in between,
A ceramic honeycomb structure characterized in that the thickness of partition walls of adjacent through holes is regularly thinned toward the centroid of the honeycomb structure. 2. Claim 1, characterized in that the thickness of the partition wall of the through hole is oriented in the direction of the centroid of the honeycomb structure, and is gradually thinned by dividing a certain region.
Ceramic honeycomb structure described in section.