|Title of Invention||
A HONEYCOMB BODY IN PERTICULAR A CATALYST BODY FOR EXHAUST CLEANING SYSTEMS OF MOTORCYCLES OR DIESEL APPLICATION
|Abstract||A honeycomb catalyst carrier body for exhaust gas-cleaning systems of motorcycles, comprising: layered or wound sheet-metal layers at feast partially structured to form passage through which exhaust gas can flow, said sheet-metal layers formed of a stainless steel, having a thickness of more than 0.08 mm and having an aluminum content in percent by weight of between 6 and 12% multiplied by 0.02 mm divided by said thickness of said sheet-metal layers.|
|Full Text||Catalyst support body for motorcycle or diesel applications
The present invention relates to a honeycomb body which is produced from stacked or wound sheet-metal layers, as is used in particular as a catalyst support body for exhaust-cleaning systems. Honeycomb bodies of this type are typically produced from alternating layers of smooth and. corrugated sheets or from alternating layers of differently structured metal sheets, by winding or stacking. Honeycomb bodies of this type are described, for example, in WO 94/13939.
Since high temperatures and a corrosive environment typically prevail in exhaust systems of internal-combustion engines, hitherto alloys which are resistant to high-temperature corrosion, i.e. steel alloys with a high chromium and aluminum content, have substantially been used as materials for honeycomb bodies of this type.
Although it is generally known that stainless steels with an increasing aluminum content become more and more difficult to process, with the result that the material has to be constantly reannealed during the rolling process, a trend toward higher aluminum contents in metallic honeycomb bodies has nevertheless started to emerge. This can be established, for example, from US 4,602,001, in which it is attempted to compensate for the difficulty of processing steel with a high aluminum content by only adding the aluminum subsequently by using additional aluminum layers and diffusion.
DE 44 10 744 has also revealed a trend toward high aluminum contents, although the electrical properties are to the fore in this case.
At the same time, there is a discernible trend toward thinner sheet-metal layers, since a lower mass in a catalyst support body has a beneficial effect on the cold-starting performance, and thin walls cause a lower pressure loss. However, the thinner the sheet-metal layers become, the less favorable the ratio of aluminum to surface area, which is the decisive criterion for the long-term corrosion resistance of the sheet-metal layers. This explains the trend toward increasing aluminum contents with relatively thin foils, even though this makes the rolling processes considerably more difficult.
The trend toward increasingly thin metal sheets in honeycomb bodies can also be established, for example, from DE 44 18 630.
In the meantime, however, it has emerged that there are special applications for metallic honeycomb bodies in which the above considerations do not apply. These are, in particular, applications for the exhaust systems of motorcycles, in which the mechanical loads are so great that thicker foils have to be used. Moreover, there are applications for metallic honeycomb bodies in exhaust-cleaning systems of diesel engines, in which the temperatures which prevail are much lower than in the exhaust systems of spark-ignition engines. For both applications, therefore, the general considerations relating to other applications of honeycomb bodies do not necessarily apply.
It is an object of the present invention to provide suitable honeycomb bodies, which can be produced at particularly low cost, for precisely these applications.
This object is achieved by a honeycomb body in accordance with claim 1 or 2, in particular for exhaust cleaning systems of motorcycles, and by a honeycomb body in accordance with claim 5 for exhaust-cleaning systems of diesel engines. Advantageous configurations are given in the respective dependent claims.
Recent developments in the production of metal sheets with high aluminum contents are based on multistage processes, in which first of all steel sheet with a relatively low aluminum content is rolled down to a defined thickness, and then in a second part of the process, the aluminum content is increased and the final thickness is achieved. The aluminum content can be increased by rolling on aluminum foil or by hot-dip aluminizing or by aluminum dipping processes. Over the course of production processes of this type, rolling processes have been developed which enable steels with an aluminum content of at most 4.5% to be rolled at relatively low cost, in particular without frequent intermediate annealing.
The present invention makes use of the discovery that materials of this type, despite having an aluminum content of below 4.5 or even below 4%, are sufficiently resistant to high-temperature corrosion if they are used in honeycomb bodies with a thickness of the sheet-metal layers of more than 0.06 mm, preferably more than 0.08 mm. With sheet-metal layers of a thickness of this nature, the ratio of the total aluminum present to the surface area, for an aluminum content of 3 or 4%, is in fact better than for sheet-metal layers with a thickness of, for example, 0.03 mm and an aluminum content of 6%. Since aluminum diffuses very rapidly in steel at high temperatures, sufficient aluminum reaches the surface, even with relatively low aluminum contents in thick sheet-metal layers, to compensate for any damage to the protective oxide layer by forming further aluminum oxide.
For sheet-metal layers with a thickness of over 0.06 mm, there is an approximation formula, according to which the aluminum content (in percent by weight) should be between 6 and 12%, in particular between 8 and 10%, multiplied by 0.02 mm divided by the thickness of the sheet-metal layers. In this way, the ratio of total aluminum present to the surface area in these metal sheets is always better than in a metal sheet with a thickness of 0.02 mm and an aluminum content of 6%.
The high mechanical loads in exhaust-cleaning systems of motorcycles and some applications require the use of metal sheets with a thickness of between 0.08 and 0.12 mm. Therefore, metal sheets with an aluminum content of from 1 to 4.5% are suitable for these applications. Steel sheets of this type typically have a chromium content of from 15 to 25% and a certain level of rare earths; the known conditions for these and other fractions in stainless steels also apply in the present case.
Naturally, relatively thick sheet-metal layers cannot be used to produce extremely fine structures, and consequently the honeycomb bodies according to the invention typically have between 200 and 600 cpsi (cells per square inch).
A particular economic benefit of the present invention is that the material for catalyst support bodies for motorcycles can be derived from another production process. This means that it can be made available very economically even if relatively small quantities of the material are required. Separate production of specific melts and the rolling of special foils for relatively small numbers of exhaust-cleaning systems of motorcycles could not be carried out similarly economically. However, since stainless steels with an aluminum content of 1
to 4.5% are in any case required for the abovementioned multistage processes with a subsequent increase in the aluminum content, it is possible to use part of this material directly for the production of honeycomb bodies, especially since it is in any case produced with a suitable thickness as an intermediate product before the aluminum content is increased.
A similar consideration applies to exhaust-cleaning systems of diesel vehicles. In these systems, the temperatures which prevail are much lower than in the exhaust-cleaning systems of spark-ignition engines, so that for this reason a lower aluminum content and the associated lower resistance to high-temperature corrosion can be tolerated. In this case, although the metal sheets, for mechanical reasons, do not have to be as thick as in motorcycles, there is also no need for the ratio of the total aluminum content to the surface area to be as high. The foils with aluminum contents of between 1 and 4.5% which have been branched off from a production process as described above can therefore be rolled down further to a suitable thickness of, for example, 0.03 to 0.06 mm and can then be used without problems, despite the lower aluminum content, in exhaust-cleaning systems of diesel vehicles. In this case too, the fact that there is no need for separate production processes provides an enormous economic advantage.
To explain the present invention, a typical metallic catalyst support body is illustrated in the drawing.
A honeycomb body 1, which is produced from smooth sheet-metal layers 2 and corrugated sheet-metal layers 3 and the metal sheets of which have a thickness d of from 0.08 to 0.12 mm, is situated inside a tubular jacket 5. The sheet-metal layers 2, 3 form passages 4 through which exhaust gas can flow and which
are preferably ot a size which is such that the honeycomb body has between 200 and 600 cpsi. The sheet-metal layers consist of a stainless steel containing 15 to 25 percent by weight of chromium, preferably 18 to 22%, typical levels of certain rare earths which are known to increase the resistance to corrosion, and an aluminum content of 1 to 4.5%, in particular 2 to 4%.
The present invention allows particularly inexpensive production of catalyst support bodies for exhaust- cleaning systems of motorcycles or diesel vehicles, the quality of which is adapted to the surrounding conditions.
List of reference symbols
1 honeycomb body
2 smooth sheet-metal layer
3 corrugated sheet-metal layer
5 tubular jacket
d thickness of the sheet-metal layers
1. A honeycomb catalyst carrier body for exhaust gas-cleaning systems of
layered or wound sheet-metal layers at least partially structured to form passage through which exhaust gas can flow, said sheet-metal layers formed of a stainless steel, having a thickness of more than 0.08 mm and having an aluminum content in percent by weight of between 6 and 12% multiplied by 0.02 mm divided by said thickness of said sheet-metal layers.
2. The honeycomb body as claimed in claim 1, wherein said thickness of said sheet-metal layers is from 0.08 to 0.12 mm.
3. The honeycomb body as claimed in claim 1, wherein said passages number between 200 and 600 cpsl (cells per square Inch).
4. The honeycomb body as claimed in claim 1, wherein said aluminum has a content of 2 to 4%.
5. The honeycomb body as claimed in claim 1, wherein said sheet-metal layers are rolled.
6. The honeycomb body as claimed In claim 1, wherein said sheet-metal layers are rolled and removed from a production process for producing hot-dip aluminized material before an aluminium content is raised.
7. A honeycomb body, comprising:
Layered or wound sheet-metal layers at least partially structured to form passages through which exhaust gas can flow, said sheet-metal layers formed of a stainless steel, having a thickness of more than 0.08 mm and having an aluminum content In percent by weight of between 6 and 12% multiplied by 0.02 mm divided by said thickness of said sheet-metal layers.
A honeycomb catalyst carrier body for exhaust gas-cleaning systems of motorcycles, comprising: layered or wound sheet-metal layers at feast partially structured to form passage through which exhaust gas can flow, said sheet-metal layers formed of a stainless steel, having a thickness of more than 0.08 mm and having an aluminum content in percent by weight of between 6 and 12% multiplied by 0.02 mm divided by said thickness of said sheet-metal layers.
|Indian Patent Application Number||IN/PCT/2001/01255/KOL|
|PG Journal Number||08/2007|
|Date of Filing||27-Nov-2001|
|Name of Patentee||EMITEC GESELSCHAFT FUR EMISSIONSTECHNOLOGIE MBH|
|Applicant Address||HAUPTSTRASSE 150, D-53797 LOHMAR,|
|PCT International Classification Number||B 01 J 35/04|
|PCT International Application Number||PCT/EP00/04885|
|PCT International Filing date||2000-05-29|