Metal treatment – Process of modifying or maintaining internal physical... – Producing or treating layered – bonded – welded – or...
Reexamination Certificate
1998-02-23
2001-05-01
Wyszomierski, George (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Producing or treating layered, bonded, welded, or...
C148S534000, C148S535000
Reexamination Certificate
active
06224691
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the manufacture of honeycomb bodies, and more specifically to a method of producing a honeycomb body comprising metal sheets which are stacked and/or wound in a layer configuration.
2. Description of the Related Art
Honeycomb bodies are used in particular as catalyst carrier bodies for the conversion of exhaust gases of internal combustion engines. Such honeycomb bodies are known for example from international publication WO 89/07488. Catalyst carrier bodies of this type are exposed to high levels of mechanical and thermal loading. Besides the thermal and mechanical loading of the honeycomb body it is exposed to the aggressive gas components which are present in the exhaust gas. The aggressive gas components can result in corrosion of the honeycomb body. It is therefore desirable to produce honeycomb bodies from metal sheets which are resistant to corrosion.
It has become known from European patent EP 0 159 468 B1 to produce honeycomb bodies from steel sheets with a high aluminum content. The production of a honeycomb body from such materials, however, gives rise to problems and involves high costs due to the poor rollability of steel with a high proportion of aluminum.
U.S. Pat. No. 5,366,139 proposes a metal sheet for the production of a honeycomb body which comprises an aluminum-plated steel. The processing of such sheets in the production of the honeycomb body is less expensive as such sheets can be more easily subjected to cold working.
After aluminum-plated metal sheets have been stacked and/or wound in a layered configuration, they are subjected to a subsequent heat treatment. The heat treatment provides for substantial homogenization of metal sheets which have at least a layer of chromium-bearing steel and at least one primarily aluminum-bearing layer. It has been found that, in the production of honeycomb bodies, in particular those with a relatively large cross-section, which have metal sheets with a laminate structure, it is not always possible to guarantee that the metal sheets are connected together and/or to a casing which encloses the honeycomb body. However, a sound connection of the sheet metal layers to each other and/or to a tubular casing enclosing the honeycomb body is a matter of great significance in terms of the mechanical strength of the honeycomb body. It is now known that, when the honeycomb body is subjected to a heat treatment, there may be a reduction in the volume of the sheet metal layers of laminate structure. The reduction in volume of the sheets of a laminate structure is attributed to the fact that the aluminum which forms an outer layer of the metal sheet diffuses into the first layer of chromium-bearing steel, during a heat treatment. The aluminum which diffuses into the layer of chromium-bearing steel however does not increase the volume of that layer, to the extent to which there is the reduction in volume of the aluminum layer. In addition, layered or laminate sheets have only a low degree of elasticity during the homogenization procedure.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method of producing a honeycomb body whose sheet layers at least in part initially comprise a layered or laminate material which has at least one layer of chromium-bearing steel and at least one primarily aluminum-bearing layer which are substantially homogenized in a subsequent heat treatment by diffusion, which overcomes the above-mentioned disadvantages of the prior art devices and methods of this general type and which compensates for the reduction in volume which occurs due to homogenization of the sheets so that nonetheless connections which can carry a high loading are produced between the sheets.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of producing a honeycomb body assembly, which comprises:
providing sheet metal at least partially formed of a laminate material with a layer of chromium-containing steel and a layer primarily containing aluminum;
forming a layered sheet metal honeycomb body with structured sheet metal layers defining passages through which a fluid can flow;
fitting the honeycomb body into a tubular casing with a defined degree of prestressing; and
subjecting the honeycomb body to heat treatment and substantially homogenizing the laminate material by diffusion;
wherein at least a portion of the sheet layers has a structure which increases a degree of elasticity of the honeycomb body prior to and in the heat treatment and wherein the degree of prestressing is defined such that contact locations between adjacent sheet metal layers remain in contact in the heat treatment.
In accordance with an added feature of the invention, the sheet metal is formed with additional microstructures reducing a total surface area of the contact locations between the adjacent sheet layers and for reducing the degree of prestressing necessary to maintain the contact locations in contact during the heat treatment.
In accordance with an additional feature of the invention, the additional microstructures are formed transversely, obliquely, or parallel to the direction along which the fluid passages extend.
In accordance with another feature of the invention, the micro-structures are formed such that the microstructures in adjacent sheets are substantially or entirely prevented from engaging one another in a form-lock.
In accordance with a further feature of the invention, the sheet layers are formed with structures interlocking adjacent sheet layers such that the sheet layers are prevented from relative movement even where the degree of prestressing is substantially reduced or virtually eliminated during the heat treatment.
In accordance with again a further feature of the invention, an elastic intermediate layer is inserted between the tubular casing and the honeycomb body for maintaining a degree of prestressing in the honeycomb body during the heat treatment.
In accordance with a concomitant feature of the invention, the tubular casing has a lower coefficient of thermal expansion than the honeycomb body material.
To avoid large areas in which the sheet layers are not connected to one other and/or to the casing, or only weakly connected, when the heat treatment causes a change in volume of the metal sheets which are stacked and/or wound in layers, the invention proposes that at least a part of the sheet layers is of a structure which increases the elasticity of the honeycomb body prior to and in the heat treatment. In that respect the honeycomb body is fitted into a tubular casing with such a prestressing effect that, in the heat treatment, the locations of contact between the sheet layers remain in contact. That operating procedure provides a honeycomb body which is resistant to corrosion by virtue of the choice of the material for the sheet layers and which also has a high level of thermal and mechanical stability. The contact in respect of the contact locations between the sheet layers is always guaranteed during the heat treatment, by virtue of the structure which enhances the elasticity of the honeycomb body prior to and in the heat treatment and the fact that the honeycomb body is introduced into a tubular casing in a prestressed condition, in spite of possibly only slight elasticity of the materials used. Ensuring contact at the contact locations between the sheet layers is also an aspect of significance in terms of forming the connections between the sheet layers. The sheets are connected together at their contact locations, by the heat treatment. The sheets are connected together for example by virtue of the fact that aluminum-steel alloys have a substantially lower melting point than steel so that the inner layer of the metal sheets of layered or laminate structure temporarily liquefies and an intimate connection is produced in the region around the contact locations, such connection virtually enjoying the property of a welded connection. By virtue of the conce
Maus Wolfgang
Wieres Ludwig
Emitec Gesellschaft fuer Emissions-technologie mbH
Greenberg Laurence A.
Lerner Herbert L.
Stemer Werner H.
Wyszomierski George
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