Extruded honeycomb body of ceramic and/or metallic material with increased flexibility

An extruded honeycomb body of a ceramic or metallic material includes a plurality of conduits being separated from each other by partitions and extending approximately parallel to each other. The partitions are disposed and shaped in at least an outer region in such a way that as seen in a cross section through the honeycomb body they do not form structures which are rigid in the radial direction and/or rigid support structures extending in the circumferential direction. Separating walls extending spirally or involute particularly increase the elasticity of a honeycomb body. Such shapes are particularly suited for electrically conductive extruded honeycomb bodies which can be used, for example, in connection with electrically heatable catalytic converters of motor vehicles.

CROSS-REFERENCE TO RELATED APPLICATION 
This application is a Continuation of International Application Serial No. 
PCT/EP94/00044 filed Jan. 10, 1994. 
BACKGROUND OF THE INVENTION 
Field of the Invention 
The present invention relates to an extruded honeycomb body of a ceramic or 
metallic material with a multiplicity of conduits being separated from 
each other by partitions and extending approximately parallel to each 
other. Such honeycomb bodies, which are used in catalytic converters of 
internal combustion engines in particular, have been described in U.S. 
Pat. No. 3,853,485, for example. 
Such bodies are usually extruded from a powdery or granulate-like ceramic 
material, dried and subsequently baked. 
Of late, that method of production has also been employed for producing 
electrically conductive honeycomb bodies which can be electrically heated, 
wherein a metallic material or a mixture of ceramic and metallic materials 
is used. Such honeycomb bodies have been described, for example, in 
European Patent Application 0 465 184 A1. In order to affect the 
electrical resistance and the course of an electric current in such a 
honeycomb body, slits are additionally provided which generally extend 
parallel to the extruded structures. 
Either squares, rectangles or other polygons are typical cross-sectional 
shapes of conduits in extruded honeycomb bodies. Various polygonal 
progressions have been described as cross-sectional shapes in particular 
in U.S. Pat. No. 3,853,485, in which varied numbers of conduits per 
cross-sectional surface are provided in the various cross-sectional 
regions. 
However, it is common for all heretofore-known extruded honeycomb bodies to 
have preferred orientations of the conduit or channel walls, wherein the 
preferred orientation of the conduit walls leads to reduced elasticity in 
the direction of the preferred orientation. With square conduits, the 
bodies have practically no elasticity in the direction of the webs, and 
elasticity is also very low in typical hexagonal honeycomb shapes. That 
does not even change if additional walls are disposed in various 
directions, as is disclosed in U.S. Pat. No. 3,853,485. 
Besides the extruded honeycomb bodies which have been known for many years, 
honeycomb bodies made of sheet metal are employed in increasing numbers, 
wherein suitable honeycomb bodies are produced by suitable structuring and 
disposition of the sheet metal in layers. Besides the initially used 
honeycomb bodies wound spirally or helically from sheet metal, a plurality 
of shapes with considerably increased elasticity have become known in the 
meantime. In that connection a principal structure which is very important 
for elasticity has been described in European Patent 0 245 736 B1, in 
which the individual sheet metal layers extend in an approximately 
involute shape from a center outward. Honeycomb bodies produced in 
accordance with that principle have also been described in International 
Patent Application WO 90/03220, corresponding to U.S. Pat. Nos. 5,105,539; 
5,135,794; and 5,139,844, and, in a somewhat changed shape, also in 
International Patent Application WO 92/02717, corresponding to U.S. 
application Ser. No. 08/016,041, filed Feb. 10, 1993. Similar properties 
also result in connection with bodies being formed of sheet metal wound in 
an S-shape, wherein the elastic properties and the oscillating behavior 
can be affected by additional reinforced layers, such as is described in 
International Patent Application Wo 89/07488, corresponding to U.S. Pat. 
No. 5,102,743. Those and similar structures have been shown to be 
particularly suited for electrically heatable honeycomb bodies, especially 
because of their elasticity, such as is recited in International Patent 
Application WO 92/02714, corresponding to U.S. Pat. No. 5,411,711. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the invention to provide an extruded 
honeycomb body of ceramic and/or metallic material with increased 
flexibility, which overcomes the hereinafore-mentioned disadvantages of 
the heretofore-known devices of this general type and which increases the 
elasticity of extruded honeycomb bodies, wherein the elastic properties in 
different directions are particularly intended not to be different. The 
increased elasticity of such honeycomb bodies increases their useful life 
under thermally changing loads and permits increased flexibility in the 
structure, particularly with heatable honeycomb bodies. 
With the foregoing and other objects in view there is provided, in 
accordance with the invention, an extruded honeycomb body formed of at 
least one of ceramic and metallic material, comprising a multiplicity of 
conduits; and partitions separating the conduits from one another, some of 
the partitions extending curved from the inside outward at least in an 
outer cross-sectional region of the honeycomb body. 
Structures which are rigid in the radial direction lead to rigidity of the 
body in this direction and to the danger of breaking in case of forces 
attacking at an angle. Structures extending rigidly in the circumferential 
direction, i.e. circular structures, also increase the rigidity of the 
entire body. It is therefore important for the flexibility of a body to 
avoid such structures. In spite of this, regular symmetrical 
configurations in which there are always preferred directions of 
partitions have been used heretofore for extruded honeycomb bodies. This 
is not of decisive importance in the interior of a honeycomb body, 
although a more flexible structure should at least be selected in an 
exterior region of at least 30%, and preferably more than 50%, of the 
radius. Since present-day molds for extruders are mainly produced by 
electric corrosion, the practically arbitrary shaping of conduit walls 
does not present a technical problem, even though no attempts had been 
made to provide other conduit shapes of polygonal cross section because of 
various prejudices in the technical field. One reason for that may be that 
following extrusion the bodies are at first relatively soft, so that a 
certain amount of rigidity is quite desirable, at least in the direction 
in which gravity acts. In spite of that an almost arbitrary shaping of the 
conduit walls is possible with modern production techniques even from that 
point of view. 
In accordance with another feature of the invention, if a portion of the 
partitions extends curved in cross section from the inside to the outside, 
in at least an outer region, the partitions extend spirally and in 
particular approximately involutely from the inside to the outside. Such 
shapes are particularly elastic and yet allow the even filling of a cross 
section with partitions. 
There are many possibilities for dividing the intervals between the curved 
partitions into conduits through the use of further partitions. It is 
again important in this case that the partitions between the curved 
partitions do not form rigid webs between each other in the radial 
direction. The direction of the transverse webs between the curved 
partitions should therefore be adapted to their course. 
In accordance with a further feature of the invention, there are provided 
transverse webs disposed between the curved partitions, the transverse 
webs including radially adjacent transverse webs being located in 
different radial planes. 
The present invention is particularly suitable for honeycomb bodies 
extruded from metallic materials which are sintered. The present invention 
is also particularly important for honeycomb bodies made from an extruded 
mixture of metal and ceramic powders, in which the intention is to cut 
slits for their electrically insulated separation. Since such slits 
usually divide the body in such a way that a current can flow through it 
in a meander shape, the regions adjoining the slits are particularly 
stressed mechanically, so that elastic structures result in great 
advantages in this case. 
Therefore, in accordance with an added feature of the invention, the 
partitions are formed of electrically conductive material, in particular 
an extruded mixture of metal powder and ceramic powder and define slits 
for an electrically insulating subdivision. 
In accordance with an additional feature of the invention, the course of 
the slits in the honeycomb bodies is parallel to the curved partitions, 
and in particular parallel with partitions which extend spirally or 
involute. 
In accordance with yet another feature of the invention, some of the 
partitions are thicker than others of the partitions. 
In accordance with yet a further feature of the invention, since linearly 
extending wall sections always have a different flexibility in different 
directions, the partitions in the extruded honeycomb bodies also 
essentially are formed of curved sections. Such a shape results 
automatically with honeycomb bodies being wound from variously corrugated 
sheet metal layers, while so far it had not been considered for extruded 
honeycomb bodies. 
However, increased elasticity can also be achieved with polygonal cross 
sections if the conduits themselves are not disposed along straight lines, 
but along lines which are curved from the inside to the outside, 
preferably along approximately involute lines. The elasticity of bodies 
constructed in this manner is also clearly increased in comparison with 
bodies having conduits disposed along straight lines. 
With the objects of the invention in view, there is also provided an 
extruded honeycomb body formed of at least one of ceramic and metallic 
material, comprising a multiplicity of individual flow conduits having a 
substantially polygonal cross section; and partitions separating the flow 
conduits from one another; the flow conduits being disposed along lines 
being curved and preferably involute from the inside outward, and the flow 
conduits being spaced apart from one another along the lines, having walls 
not being parallel to one another. 
Other features which are considered as characteristic for the invention are 
set forth in the appended claims. 
Although the invention is illustrated and described herein as embodied in 
an extruded honeycomb body of ceramic and/or metallic material with 
increased flexibility, it is nevertheless not intended to be limited to 
the details shown, since various modifications and structural changes may 
be made therein without departing from the spirit of the invention and 
within the scope and range of equivalents of the claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the single FIGURE of the drawing in detail, there is seen 
a honeycomb body 1 which is generally distinguished by the fact that there 
are no structures extending in the radial direction as well as no 
approximately circular rigid structures. Channels or conduits are disposed 
along lines 3 extending in an involute shape from a center 2 toward the 
exterior. These lines themselves can be constructed as partitions or 
separating walls. It is possible in this case to create flow conduits 4 
which are only edged by curved surfaces, for example by additional 
partitions 8 disposed in wave shapes. In another embodiment transverse 
webs which are provided between the involutely extending partitions 3 can 
be straight webs 9, so that rectangular or rhomboid cross sections of flow 
conduits 5 are created. As is indicated by webs 11, the direction of such 
transverse webs can be adapted to the course of the curved partitions 3, 
because of which cross-sectional surfaces of conduits 7 that are created 
in this way can be kept approximately constant. However, polygonal 
conduits 6 can also be utilized in a honeycomb body in accordance with the 
invention, although walls 10 of the polygonal conduits 6 are disposed in 
such a way that the conduits are not disposed along straight lines but 
instead follow curved lines 3. Finally, as is diagrammatically indicated, 
it is also possible to provide slits 12 parallel to the curved lines 3 in 
such a honeycomb body, in particular for the electrical separation of the 
honeycomb body. It is additionally possible to provide reinforced 
partitions 13 for a directed introduction of forces or for affecting an 
oscillating behavior of the honeycomb body. 
In accordance with International Patent Application WO 92/02717, 
corresponding to U.S. application Ser. No. 08/016,041, filed Feb. 10, 
1993, it is of course also possible for the curved lines not to follow 
exactly an involute course but to open more in the outer area or the inner 
area, through which it is possible to provide different conduit cross 
sections in the outer or inner areas. 
The invention is particularly suitable for extruded honeycomb bodies which 
are capable of conducting electricity and for areas of use in which large 
changing thermal loads and therefore large mechanical stresses must be 
managed.