DE8412768U1 - High-temperature resistant exhaust catalyst carrier body made of sheet steel with a high aluminum content - Google Patents

Description

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Interatom GmbH VPA 84 H 6712 DE

D-5060 Bergisch Gladbach 1 G 84 12 768.6

High-temperature resistant exhaust catalyst carrier body made of sheet steel with a high aluminum content

The present invention relates to an exhaust catalyst carrier body according to the preamble of the first claim, as described for example in DE-OS-29 24 592.9. Such exhaust catalyst carrier bodies are used with a catalytically active coating to clean exhaust gases in motor vehicles and are exposed to high mechanical and thermal loads. It is therefore very difficult to produce carrier bodies that are mechanically strong enough and durable over a long period of time. For various reasons, in particular because of corrosion resistance, it is desirable for the steel sheets used to contain a high proportion of aluminum, but this leads to technical problems due to the poor rollability of steel with a high aluminum content and the resulting costs. Furthermore, the joining of the contact points between the individual sheets is problematic because these highly stressed points can be weak points due to thermal loads or erosion, depending on the type of connection.

The object of the present invention is an exhaust catalyst carrier body that is wound from inexpensively available steel sheet without any significant aluminum content, but which in the finished state has a large aluminum content in the base material and mainly at the joining points. In addition, such an exhaust catalyst carrier body should have permanent joining points that are easy to produce.

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To solve these problems, an exhaust catalyst carrier body according to the main claim is proposed. For this purpose, an exhaust catalyst carrier body is first layered or wound up from thin sheets in one of the known ways, whereby the sheets can be corrugated, smooth or structured in some other way. In this way, gas-permeable bodies with a large surface and many contact points between the layered or wound sheets are created. It is previously known that these connection points are all or partially connected by joining technology, for example soldered using a suitable solder. According to the invention, it is now proposed that the connection points and the base material, at least near the surface, have a large proportion of aluminum as additional material, which creates a special type of connection. An advantageous embodiment of the invention is specified in claim 2.

To clarify the invention, some details of the manufacturing process for such catalyst carrier bodies are given below. The exhaust catalyst carrier body is first wound or layered in a manner known per se from suitably structured sheets, with a commercially available steel sheet containing chromium, for example, with no or a small proportion of aluminum being used as the starting material. The fully wound or layered exhaust catalyst carrier body is coated with aluminum powder, with as much aluminum powder as possible being introduced into the gaps near the contact points of the sheets, either using an adhesive, binder, pressure-sensitive adhesive or in another way. The method for applying aluminum powder corresponds to the measures known for applying solder. The exhaust catalyst carrier body coated with aluminum powder is then heated for some time in a vacuum furnace above the melting point of aluminum. In this way, the aluminium melts, wets the surfaces and runs into the gaps near the contact points, forming, as is the case with

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Connecting bridges are formed, as would be the case with a solder. In addition, the aluminium begins to diffuse into the steel everywhere, which means that the aluminium content of the steel can subsequently be significantly increased.

The exhaust catalyst carrier body can be heated to such a high temperature that the reduced melting point of the locally aluminum-rich aluminum-steel alloy created by aluminum diffusing into the steel is reached and joints that melt together are formed at the contact points. This is possible because the melting point of an aluminum-steel alloy is lower than that of pure steel. Since the aluminum tends to diffuse into the steel, an alloy with a high aluminum content and a low melting point is quickly created near the gaps where there is enough aluminum. If the temperature is set high enough, a much more intimate connection can be created in this way than is the case with soldering.

The high temperature is maintained until the aluminum has diffused into the steel everywhere and until so much aluminum has diffused away from the locally aluminum-rich alloys that the melting point of these areas is again above the prevailing temperature and they solidify. The aluminum naturally strives to diffuse into the steel everywhere from its original location. The locally aluminum-rich alloy therefore becomes less aluminum-containing over time due to the high aluminum diffusion rate, which increases the melting point. Even after the joints have solidified, aluminum continues to diffuse into the steel. The melting point of the joints can therefore be raised considerably again by maintaining a high temperature for a correspondingly long time, while at the same time the rest of the steel is used to stabilize its high-temperature properties.

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Corrosion resistance is enhanced with aluminum.

In principle, the high temperature can be maintained until the applied aluminum is distributed essentially evenly throughout the steel. An exhaust catalyst carrier body treated in this way has significantly improved properties with regard to high-temperature corrosion, since this process can increase the aluminum content of the base material, at least near the surface, to values greater than 6%, for example to 10 % to 20 % or even more. Steel materials with similarly high aluminum content can no longer be processed due to their susceptibility to cracking and thus cannot be used directly to manufacture catalyst carrier bodies.

Finally, it is also possible that the aluminum grains used for the coating contain proportions of other elements that contribute to improving high-temperature resistance, such as yttrium, zirconium or cerium. This can lead to additional improvements in corrosion resistance.

The present invention will be explained in more detail with reference to the drawing.

Figure 1 shows a chemical cross-section through a typical contact point between two sheets before heating and Figure 2 shows the same point after melting.

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Fig. 1 shows a cross section through a contact point between a smooth sheet metal strip 1 and a corrugated sheet metal strip 2. Such a contact point 57 usually has narrow gaps 3 on the sides, into which an additional material must be introduced using a suitable method in order to produce a joining connection. In this case, aluminum grains 4 have been introduced using a suitable method onto the sheet metal surfaces 10 and into the gaps 3, so that sufficient alloying material is present in the vicinity of the contact point 7.

I As shown schematically in Fig. 2, when the

ij 15 heat approximately as follows:

&xgr; The aluminium grains 4 on the sheets 1,2 and in particular

% melt in columns 3, wet the surface and flow into each other.

I der. The aluminium immediately begins to diffuse into the steel.

«! so that zones 5, 6, 8 in the sheets 1,2

3 20, which have a high aluminium content.

These locally aluminum-rich aluminum-steel alloys have a much lower melting point than

¹ steel, so that these zones 5, 6 temporarily

' liquefy. This creates a very intimate connection

j 25 near the contact point 7, which in the ideal case l· has almost the properties of a welded joint.

f- . The aluminium diffuses at high temperatures

&eeacgr; of course, as indicated by arrows, in the

I steel, whereby the melting point of zones 5, 6

I 30 increases again and the connection point solidifies. § The connection created in this way is extremely stable

and the joining method has the additional advantage that the steel can be enriched with aluminium, which

for the corrosion properties is advantageous. It should be noted that the drawing is only schematic

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and is by no means to scale in terms of the penetration depth of the aluminium.

With the help of the present invention, a long-lasting and particularly stable exhaust gas catalyst carrier body can be produced.

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Claims (2)

Protection claims VPA 84 H 6712 DE 1. Exhaust gas catalyst carrier body, in particular made of spirally wound or layered thin corrugated (2) and/or substantially smooth (1) sheets of high temperature resistant steel, the contact points (7) of the sheets being connected by joining technology, characterized in that the base material, at least near the surface, and the joining points (3, 5, 6) have an aluminum content of more than 6 %, e.g. 10 to 25 % . 2. Exhaust gas catalyst carrier body according to claim 1, characterized in that at least the contact points (7) of the sheets locally consist of an aluminum-rich aluminum-steel alloy and are fused together (3, 5, 6). 02 01