DE2538613C2 - Ceramic body with a large number of parallel, elongated cells in a honeycomb-like structure - Google Patents

Description

The invention relates to a ceramic body with a plurality of parallel elongated cells in a honeycomb-like structure. It indicates an improved design and arrangement of the cells in the ceramic body of honeycomb-like structure (hereinafter also simply referred to as honeycomb body), so that a greater resistance to compressive and tensile forces is achieved, such as occur at unevenly high temperatures, for example when a such a honeycomb body is used as a carrier for an oxidation catalyst coating.

In particular, the invention provides improved forms of honeycomb structures with special cell structures

events in which all cells consist exclusively of curved walls between common Seam lines are formed. This ensures that in particular tensile stresses without breaking Walls of the monolithic ceramic body can be better received.

One of the main problems with the use of monolithic ceramic bodies honeycomb-like Structures as a carrier for catalyst coatings is based on the fact that a catalyst body, even a bed of catalyst particles, not over its entire length or its entire cross-section constant temperature works. There are usually significant temperature differences between the inlet and outlet ends of the catalyst body and between the central region and the to the Catalyst chamber walls in front of adjacent areas. As a result, the stretch at higher Temperature areas of the catalyst body more than those at lower temperatures located areas, and there are also different sections of the monolithic body, that are exposed to either tensile stresses or compressive stresses. Usually they are Ceramic body of conventional designs relatively resistant to compressive forces, at least in comparison to tensile strength; accordingly, cracks and fractures often occur quickly in the tensile stressed Parting of a ceramic body due to excessive stress.

Honeycomb-like structures with different cross-sectional shapes of the cells are known and in particular for absorption elements and catalyst carriers in the field of air pollution control been used. The individual cells of the honeycomb can be square, rectangular, triangular, hexagonal, round, oval or similar in shape and of various sizes and diameters. If the ceramic honeycomb body is to be used as a catalyst carrier, normally a body with cells as small as possible is chosen, provided that this is done without creating an excessive pressure drop in the exhaust gas flow to provide the largest possible catalytic surface. The smaller the cells are,

however, the greater the rigidity and the less flexibility in a given structure.

Although it is also a feature of the invention to form the connecting walls, which extend between the seam lines and the division into adjacent parallel cells in the monolithic ceramic body , curved, it should be noted that this feature alone is not sufficient and that conventional , circular or oval cell designs do not provide the flexibility and deformability to be striven for in order to avoid tensile stress fractures. Also the cell configurations with curved walls, which result at points of contact from node to node when using manufacturing processes working with adjoining corrugated plates, e.g. B. according to US-PS 34 44 925, do not lead to shapes or patterns of really satisfactory stress relief. For example, in connection with ceramic bodies, the cells of which have a circular or oval cross-section, tensile forces occur without the available wall parts being able to give in and elongate easily. In other words, in curved wall designs formed by circular or oval cells, when tensile forces are applied, seam lines tend to contract closer together in a direction transverse to the tensile force, and there is no real elimination of the problems of breakage due to uneven temperature conditions achieved.

It is therefore a main feature of the invention that cell walls are curved rather than straight to connect the suture lines between a plurality of adjacent cells and the other to arrange the curved walls in a special way to each other, so that the seam lines at Application of tensile forces does not cause them to move closer together in a direction transverse to the Walls that experience elongation and stretching as a result of tensile forces tend to be.

The ceramic body of the invention can, for example, have a cell formation in which the straight Walls of imaginary square cells are all replaced by arched walls and thereby the The curvature of the walls alternates between a concave inward curvature and a convex outward curvature, so that tich "dumbbell" -shaped cells result. Alternatively, the straight walls can be an imaginary one hexagonal cell can all be replaced by arched walls, again alternating one concave inwardly curved wall follows a convex outwardly curved wall so that each cell is one "Kleblatt" -shaped shape.

The invention is therefore based on the object of providing a ceramic body of the type specified at the beginning create, which does not have the above-discussed and similar shortcomings of known ceramic bodies and in particular better absorption of pressure and tensile forces due to uneven temperature conditions guaranteed and thus has improved resistance to cracking and fracture formation. It should the ceramic body can nevertheless be manufactured easily, safely and cheaply.

The invention relates to a ceramic body with a large number of parallel elongated cells in a honeycomb structure, which is used to adapt to compressive and tensile forces due to uneven temperature conditions are capable of deformation, which is characterized according to the invention, that all connecting cell walls are curved between the suture lines of adjacent cells formed and arranged spatially to one another in a recurring symmetrical pattern in such a way that in the circumference of each cell the abutting walls curved alternately inwards and outwards are, with each cell of the honeycomb structure of at least two sets of opposite one another curved walls is formed, se that expansion movements in directions transverse to the longitudinal extension The elongated cells deform and stretch a set as a result of temperature differences opposing curved walls without bringing seam lines closer together between ' Cells in a direction transverse to the stretching walls.

In one embodiment, the easiest way to describe the cell formation is to use a conventional square pattern. In each cell there is a pair opposite each other Partition walls are provided which are concave inwardly curved towards one another, and at an angle of 90 ° to this end there is a second pair of partition walls which are curved convexly outwards away from one another. This results in a dumbbell shape for each cell. As the walls in the perimeter of each cell are alternately curved in and out, in the resulting overall pattern each cell is from Surrounding neighboring dumbbell-shaped cells which have a position rotated by 90 °. This arrangement allows for tensile stress in one direction, since the curved walls a noticeable Allow elongation without the risk of breakage, while at the same time practically no reduction in the distance from Seam points between cells in a direction transverse / u the stretch occurs. Indeed, a certain local spreading of seam lines as a result of a rotation of the same and the partial stretching of the Enter transverse walls.

Another advantageous embodiment can be described most simply by talking about a hexagonal cell pattern. There are three sets of opposing curved walls provided here, instead of the three sets of straight walls found in a traditional hexagon. the opposing curved partitions between adjacent cells in each row of the overall pattern are curved in the same sense and each cell has some cell row under consideration the same cross-sectional shape and spatial orientation. In this training too, the curved ones Walls of each cell around the circumference of that cell alternate concave inward and convex outward curved, so that there is a cell which has approximately the shape of a clover leaf. In terms of flexibility This training allows a certain stretching and practically when exposed to tensile forces Extension of two pairs of walls of a cell under consideration occurs, with little or no movement between seam lines in a direction transverse to the tensile forces, so that in turn flexibility of the honeycomb body to adapt to temperature differences is guaranteed. The viewpoints of deformation and flexibility are further illustrated below in connection with the explanation of the drawings.

The desired special cell formation in the

Honeycomb can be produced by extrusion the ceramic material are brought about by appropriately shaped extrusion devices, however, other production methods can also be used. For example, corrugated Sheets or plates of special shape with other specially shaped leaves or plates are joined together so that the end product results in the desired clover-shaped formation of the cells. For example, the working methods for the production of monolithic honeycomb bodies, as described in US Pat. No. 3,444,925 and 3,505,030 are to be applied. Curved or wavy sheets or plates made of ceramic can also be used Material can be slit and then nested, similar to the process of making egg packaging cartons, around the illustrated embodiment from a plurality of dumbbell-shaped cells with consistently to manufacture curved walls. When corrugated sheets, panels or films of green ceramic Material can be nested or combined with other sheets, panels or films fusing and sintering of the contacting areas during curing or firing, resulting in the desired shapes and seams between the elongated cells, as in the above patents is explained.

According to yet another production method, a ceramic mixture can be applied to an appropriately shaped, Applied combustible framework body and the framework body then made of the ceramic material are burned out, so that in turn a honeycomb body with cells of the marked training results. The invention is thus not limited to any particular method of making the ceramic Honeycomb body limited, and the same applies with regard to the Zcllstruktur forming material. For example, high-melting and crystalline materials such as sillimanite, Magnesium silicates, zircon, pctalite, spodumene, cordicrite, Aluminosilicates, mullite and the like. Such materials are advantageous because they are a relative have high porosity over their surface and accordingly as a support for catalyst coatings and ilamil for kalulylischc reactors or converters are particularly suitable.

The honeycomb bodies of the invention are advantageously useful without a catalyst, e.g. B. as absorption or heat exchange elements. However, they are particularly advantageous with synthetic film coatings for use in catalytic! Converters for the passage of exhaust gases, in particular motor vehicle exhaust gases, in order to bring about a conversion and removal of undesired components such as carbon monoxide, hydrocarbons and nitrogen oxides. The invention, of course, is not limited to any particular catalyst terms. It should be noted, however, that such coatings usually contain an oxidation catalyst and metals of groups I, V, VI and VIII of the periodic table, especially copper, silver, vanadium, chromium, iron, cobalt, nickel, platinum or palladium, using only one component or a combination of several active components. Furthermore, the ceramic honeycomb body is usually coated with a high-melting inorganic oxide, e.g. B. aluminum oxide or a combination of aluminum oxide with one or more other high-melting inorganic oxides. Normally, the oxidic carrier layer is applied to the wall surfaces before coating with the active catalytic component, but it can also be a

S Mixture of the high-melting metal oxide carrier material with the active catalytic component and the mixture by spraying, dipping or in any other way onto the walls of the Cell body are applied. For example, reference is made to US-PS 35 65 830 in which various methods of coating a high-melting honeycomb body with an aluminum oxide base layer and an active catalytic coating.

Preferred embodiments of the flexible cell formation for the ceramic honeycomb body and Procedures for making the particular cell designs are discussed below in conjunction with the drawings further explained. Aspects are also illustrated in which way according to In our view, temperature differences in conventional ceramic honeycombs lead to damage and lead to breakage, in the case of the ceramic honeycomb bodies of the invention, on the other hand, without disadvantageous Effects remain.

F i g. 1 shows schematically the way in which different temperature conditions over the cross-section of a conventional honeycomb body can generate tensile forces that cause the cell walls to break Honeycomb lead;

F i g. 2 and 3 schematically show two different embodiments of the cell design according to FIGS Regulations of the invention, whereby in both cases only curved cell walls are provided so that tensile stresses due to different temperatures are better absorbed be able;

F i g. 2A schematically illustrates how an in / .clzcllc can deform and stretch without Rupture occurs;

F i g. 4 and 5 illustrate schematically how specially shaped sheets or plates of ceramic Material can be nested or bonded together to form ceramic honeycombs

Invention to manufacture with curved cell walls.

According to FIG. I is located in a reactor or

Converter 1 (hereinafter usually referred to simply as converter) with a cylindrical housing 2 Honeycomb body 3, the parts shown in section

are. When the converter serves as an exhaust gas purification device, e.g. B. for the detoxification of hydrocarbon-containing exhaust gases from a motor vehicle engine, and the cellular honeycomb body 3 is coated with an active oxidation analyzer, occur inside

of the reactor at high temperatures. for example in the region of about 650 to 87O ⁰ C (1200 to 1600 ⁰ F). In some operating states and perhaps during most of the operating periods, however, there is a substantial amount in the central core area 3 'of the honeycomb body

higher temperature than in the circumferential areas 3 " of the honeycomb body. The hot interior therefore becomes considerably stronger because of the higher temperatures expand as the edge areas 3 ", so that - as indicated by the arrows - the outward thrust as a result of the

Expansion of the inner areas necessarily stresses and tensile stresses in the outer ring-shaped area 3 ″ of the cell structure, which leads to wall breaks. As at the beginning

noted, common ceramic materials can be relatively resistant to compressive stresses be, but they have very little resistance to tensile loads and splinter, jump or break easily, especially if the cells of the honeycomb are straight Walls are formed as shown in FIG. 1 is indicated.

FIG. 2 shows a cell construction according to the invention, which consists exclusively of curved walls and gives the honeycomb body flexibility. As already noted, this embodiment can best be described starting from a normal square pattern, as indicated by the dashed lines 4. All the walls of the square pattern in all cells of the entire honeycomb body are replaced by curved walls, the curved walls being curved alternately inward and outward in the circumference of each cell. Looking at a single cell, such as cell C of Fig. 2, it can be seen that the cell is separated from one another by opposing walls 5, which are concave inwardly towards one another, and, in principle, opposing walls 6 running at right angles thereto, which are away from one another are convex outwardly, is formed. As a result of the constricted area in the middle section, the overall dumbbell-shaped shape of cell C results. From FIG adjoining neighboring cell C has the same dumbbell-shaped shape, but a position rotated by 90 " with respect to cell C.

The flexibility and deformability properties of the cells are given in IMg. 2A further illustrates. The cell C ″ is delimited by the walls 5 and 6 with the seam lines 7. When tensile forces Tin act on the cell walls in the direction indicated by the arrows, the walls 5 can stretch into the partially flattened position indicated by 5 'and the seam lines 7 into the position indicated by T without moving the seam lines 7 closer to one another. The curved or arched walls 5 will thus stretch into a somewhat straightened position and the seam lines will shift somewhat without breaking, which is the case for the roller body as a whole gives good flexibility. practically probably occurs a certain amount of rotation of the seam lines 7 during the displacement T may cause as a result of stiffness and strength moments that a certain stretching of the β Wllndc and low Sprci / .ung the Nahtlinicn 7 and T me.

The embodiment of FIG. 3, as already explained, can best be found on the basis of a hexagonal pattern. which is indicated by the dashed lines 8 describe. All cells are made up exclusively of alternatingly curved walls, so that each cell has an approximately glutinous shape. Each cell H comprises a pair of opposing wounds 9 which are arched in the same direction in each cell, another set of opposing walls 10 which are also arched in the same direction in their row, and a third puttr opposite one another lying walls 11. which in turn are curved in their row in the same direction. Here, too, in the circumference of each cell // the abutting walls are alternately curved outward and inward; one wall 9 is outward and the two adjoining walls 10 and 11 are arched inward, conversely in the case of the inwardly arched wall 9 the two adjoining walls 10 and ί 1 are arched outward. In this cloverleaf-shaped design, all cells - in all three rows indicated by the arrows and lying at an angle of 120 ° to one another - have the same shape and spatial position.

In connection with the F i g. 3 is compared to that Training according to Figure 2 should also be noted that the three sets of opposing walls each cell tensile forces allow an attack at the same time in more than one direction and that normally four walls will flatten and stretch under tensile forces and that four Seam lines for each cell can be moved in the direction of the tensile forces. There are also seam lines in the transverse direction to the tensile forces do not tend to move closer together and due to the effects of rotation on the seam lines and due to the compressive strength the opposing walls, which are generally transverse to the direction of the tensile forces, kept apart. Again it follows that the curved walls can withstand tensile forces, by deforming and flattening themselves slightly while simultaneously moving seam lines and in the honeycomb can move in a way that no breakage of individual walls and thus no Damage and no uselessness of the ceramic body entry.

Figure 4 illustrates a manufacturing wcisc in which corrugated sheets of green ceramic are nested at right angles to one another to form the intersecting and abutting walls of the cells. The nesting of a large number of such plates leads to a cell structure as shown in FIG. As can be seen from Fig. 4, a plurality of corrugated plates 12 with slits 13 are nested at right angles in a similar manner to the manufacture of egg-packing cartons with a plurality of corrugated plates 14 with slits 15 to form the honeycomb structure. Overall, to manufacture the honeycomb body, the required number of wall panels 12 is arranged parallel to one another in the desired spacing according to the spacing of the slots 15 and the required number of wall panels 14 in corresponding spacings parallel to one another and at right angles to the panels 12, aligning the slots 15 with the Slits 13 inserted so that the plates intermesh and form a honeycomb body with the desired cell size in the embodiment according to FIG. 2 results. Heating and hardening after the sheets have been bonded together leads to sintering and welding with the formation of firmly welded seam lines between the resulting parallel lines. Incidental cells throughout the honeycomb body.

In the case of the in FIG. 5 illustrated manufacturing process is a correspondingly shaped plate 16 made of green ceramic material with a corresponding! shaped plate 17 joined together, so that the curved areas 18 nncncllake, whereby slcl the cells H 'of the embodiment according to FIG. By joining a corresponding number of panels, a wall body with the target structure of FIG. 3 received. The heating and welding of the seam strips 18 leads to sintering

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and welding all of the plates together to form the solid honeycomb body.

Although honeycomb bodies with the desired cell configurations according to the in connection with the F i g. 4 and 5, it is usually preferred to use body to manufacture the desired cell formation by extrusion. Extrusion methods allow in particular a simple way of creating dimensionally accurate, uniform, thin walls between the multitude of the cells in the honeycomb body designed in the manner indicated.

The size of the cells for a particular honeycomb is usually made by criteria of the pressure drop for the one to be conducted through the honeycomb body or through a series of honeycomb bodies Electricity chosen. Usually the cells have a nominal diameter in the range of about 0.8 mm or even below that, to about 13 mm or more. It is clear that the Honeycomb body different formula depending on the shape of the reactor chamber or the converter housing can have and that in individual cases desired shapes from larger honeycomb bodies, regardless of voi their production method, can be cut.

It is also clear that the honeycomb body of the fiction according to prescribed cell structure with different A coefficient of thermal expansion can be produced, depending on the type of ceramic material that for the production of the honeycomb framework

ίο is used. Normally , the coefficient of thermal expansion of the honeycomb body is small compared to steel or other metal housings, and accordingly: the honeycomb body can be used well in metal housings without the arrangement of a resilient, expansion-absorbing means between the outer wall of the honeycomb body and the inner wall of the housing, that is, a certain amount can be used Mobility in ile housings can be allowed without difficulties due to breakage in the case of uneven temperature

genes occur.

1 sheet of drawings

Claims (7)

Patent claims: 1. Ceramic body with a multitude of parallel elongated cells in a honeycomb-like structure which are capable of deformation to adapt to compressive and tensile forces as a result of uneven temperature conditions, characterized in that all connecting cell walls (5,6; 9,10, II ) between the seam lines (eg 7} of adjacent cells (C;. H) are curved and arranged in recurrent symmetric pattern such spatially to each other, that the extent of each cell (C; H), the abutting walls (5, 6; 9,10, 11) are alternately curved inward and outward, each cell (C; H) of the honeycomb structure of at least two sets of opposing curved walls (5-5, 6-6; 9-9, 10-1 (1 , 11-11) is formed so that expansion movements in directions transverse to the longitudinal extension of the elongated cells (C; H) due to temperature differences cause a deformation and stretching of a set of opposing curved walls (e.g. E.g. 5-5), without bringing suture lines (e.g. 7) closer together between cells in the transverse direction to the stretching walls (e.g. 5-5 '). 2. Ceramic body according to claim 1, characterized in that each of the parallel cells (C, C) is formed by two pairs of opposing curved walls (5-5, 6-6), of which one pair in the overall pattern (F i g . 2) and is arranged at the seam lines (7) approximately at right angles to the other pair, the opposing walls (5) of one pair being curved inward towards one another and the opposing walls (6) of the other pair being curved outwardly away from one another and together give a constricted dumbbell-shaped cell cross-section, and all cells (C) which have a common wall with an adjacent cell (C) have the same shape as this cell (C), but a position rotated by 90 ° with respect to this cell exhibit. 3. Ceramic body according to claim 1, characterized in that each of the parallel cells (H) of three pairs of opposing curved walls (9-9,10-10,11-11) is formed, each pair at an angle of about 120 ° with respect to an adjacent pair, the opposing curved walls between adjacent cells in each row of cells are curved in the same direction and each cell in any given row of cells has the same cross-sectional shape and spatial orientation as the other cells. 4. Ceramic body according to one of claims 1 to 3, characterized in that it uses a catalytically active material for the conversion is covered in pollutants. 5. Ceramic body according to claim 4, characterized in that it is in a housing (2) with Gas inlets and outlets for converting an exhaust gas flow, in particular a motor vehicle exhaust gas flow, is arranged. 6. Ceramic body according to one of claims 1 to 3, characterized in that it is according to a Extrusion process has been produced 7. Ceramic body according to one of claims I to 3, characterized in that it is by joining and sintering or fusing of the curved walls of the cells correspondingly shaped plates (12,14; 16, 17) made of ceramic Material has been manufactured.