Metal treatment – Process of modifying or maintaining internal physical... – Producing or treating layered – bonded – welded – or...
Reexamination Certificate
1998-04-02
2001-02-20
Andrews, Melvyn (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Producing or treating layered, bonded, welded, or...
C148S645000, C428S607000, C428S653000
Reexamination Certificate
active
06190470
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a process and a device for manufacturing a honeycomb body, in particular a supporting body for catalytic converters in exhaust gas cleaning systems, as preferably fitted in motor vehicles.
The general construction of such honeycomb bodies is described, for example, in European Patent 0 454 712 B1, corresponding to U.S. Pat. No. 5,157,010. That document also describes so-called transversal microstructures, which are fitted for influencing the flow and improving the effectiveness of a catalytic converter. Honeycomb bodies are wound, laminated or layered or interlaced from at least partially structured metal sheets, wherein the structure of the metal sheets additionally results in the formation of channels through which an exhaust gas can pass. For that reason, the main structure determines the size of the channels. A microstructure is understood in the description given below, as in the prior art, to be a structure of substantially smaller dimensions than the main structure, wherein the microstructure should preferably be disposed at an angle or perpendicularly with respect to the direction of the channels in the honeycomb body. In order to manufacture a microstructure disposed in that way, it is necessary to structure a metal foil band along its longitudinal direction or at an angle with respect thereto. Considerable cold forming is necessary for such structuring, if it is to result in a continuous passage without a great degree of change in the width of the metal foil band.
Metal foils which are constructed from two or more layers and are intended for the manufacture of metallic honeycomb bodies, are known from European Patent 0 159 468 B1 and U.S. Pat. No. 5,366,139. Metal foils that are constructed in such a layered or laminated manner can be rolled from the desired alloy components, in which steel sheets roll-bonded with aluminum are preferably used. In principle it is possible to homogeneously anneal such foils after rolling, whereby a high-temperature corrosion resistant material, that is suitable in every way for the manufacture of metallic honeycomb bodies, is produced. However, that homogenous annealing is costly in terms of energy and increases the cost of the rolling process which in itself is very inexpensive.
It has also been proposed previously to manufacture honeycomb bodies from roll-bonded metal foils which have not yet been homogeneously annealed and to combine the homogeneous annealing with a brazing process that is in any case subsequently necessary. Although that variation is less expensive in terms of energy consumption, it requires that the steps which are necessary for the structuring of the metal sheets be carried out on a roll-bonded foil that is not heat-treated. It has, however, been shown that certain production steps, in particular the manufacture of microstructures, cannot be carried out without problems because of the poor capability of the roll-bonded material to be cold formed, since roll-bonded metal foils can be cold formed by no more than 1% without tearing.
Lastly, manufacturing methods for honeycomb bodies are also known in which not all of the honeycomb body is brazed at the end and thereby subjected to a heat treatment process. Thus, for example, honeycomb bodies such as are described in International Patent Application WO 89/07488 or other honeycomb bodies with involute or S-shaped metal sheets can also be joined together into a sturdy composite, in such a way that the ends can simply be welded or brazed onto a sheathed pipe, without the need to heat the metals foils in their entirety. With that manufacturing process, if the metal foils are neither homogeneously annealed or otherwise heat treated they lack a sufficiently thick oxide layer, which is desirable for the adhesion of a later catalytically active coating.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a process and a device for manufacturing a honeycomb body from heat-treated two-layered or multi-layered metal foils, which overcome the hereinafore-mentioned disadvantages of the heretofore-known processes and devices of this general type and which make neither annealing at the end of a rolling process nor at the end of a process of manufacturing the honeycomb body necessary, but instead advantageously permit a heat treatment integrated with the actual manufacturing process in terms of processing technology and energy use.
With the foregoing and other objects in view there is provided, in accordance with the invention, a process for manufacturing a honeycomb body, which comprises constructing at least one metal foil from at least two different layers, in particular from steel roll-bonded with aluminum; heat-treating the metal foil by resistance heat generated within the metal foil; subsequently at least partly structuring the metal foil by shaping; and subsequently laminating, layering or winding the metal foil to form a honeycomb body.
It is important for the invention that, on one hand, the heat treatment, which does not necessarily have to be a complete homogeneous annealing, takes place before shaping of the metal foil into the honeycomb structures and where appropriate microstructures, in order to obtain sufficient capability to be cold formed for these steps. In addition, it is important that the metal foil is heated by resistance heat produced in itself. This process is very advantageous in terms of energy, since the heat losses can be kept very small. Resistance heat always occurs when an electrical current flows in the metal foil. This can be obtained by applying a voltage to the metal foil or, in accordance with another mode of the invention, by producing eddy currents through the use of induction coils. Heating through the use of resistance heat is also particularly advantageous because of the rapid heating which can be obtained thereby, which requires only a relatively short heat treatment zone without deflecting apparatus in a continuous process, and permits relatively short cycle times for the heat treatment step in a discontinuous process.
In accordance with a further mode of the invention, heating with induction coils acting on the metal foil being passed through is particularly suitable for a continuous process.
In accordance with an added mode of the invention, the application of an electrical voltage to the sections to produce a sufficiently strong current in the foil is particularly suitable for a discontinuous process on individual sections of the foil.
In accordance with an additional mode of the invention, in order to avoid uncontrolled reactions of the foil surface with the surrounding air, it is useful to carry out the heat treatment in a chamber in which a defined atmosphere is maintained.
In accordance with yet another mode of the invention, the chamber is filled with a defined atmosphere composed of inert gas, in particular of a noble gas such as argon, to which only small proportions of oxygen are added for slow, uniform oxidation of the metal foil. This is done because it is known from the literature that both excessive oxidation and the bonding of nitrides in the oxide surface are disadvantageous for the adhesion of a subsequent coating.
In accordance with yet a further mode of the invention, the partial pressure of oxygen is below that of the standard atmosphere, and preferably only a few millibars. The inert gas can be substituted with nitrogen according to the maximum temperature which the foil reaches during the heat treatment, since up to certain temperatures there is no risk of nitride formation on the surface. As already mentioned, it is not absolutely necessary to completely homogenize the metal foil since this is not necessary for the further production process, and when the honeycomb bodies are used later on, for example as exhaust gas catalytic converters in motor vehicles, homogenizing results from the calcining of a coating because of the prevailing temperatures which in any case are frequently reached, if not already
Caspar Hans-Peter
Faust Günther
Kurth Ferdi
Wieres Ludwig
Andrews Melvyn
Emitec Gesellschaft fuer Emissions-technologie mbH
Greenberg Laurence A.
Lerner Herbert L.
Stemer Werner H.
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