Metal fusion bonding – Process – Plural joints
Reexamination Certificate
2002-10-18
2004-11-02
Edmondson, L. (Department: 1725)
Metal fusion bonding
Process
Plural joints
C228S181000, C228S183000, C427S207100, C118S300000
Reexamination Certificate
active
06811071
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a method for the manufacture of a metal structure that includes separate walls, which form channels through which a fluid can flow. The walls inside the channels are at least partially wetted with an adhesive. The metal structure is, then, brought into contact with a solder, which adheres to the adhesive, a heat treatment then being carried out to form soldered connections between the separate walls. A device for wetting a metal structure with an adhesive is furthermore described with the device including an adhesive reservoir that is connected to at least one dosing element through which the adhesive can flow.
Such metal structures are preferably used as catalyst carrier substrate in exhaust systems of mobile internal combustion engines. For such use and in order to obtain a highly efficient catalytic conversion of pollutants in the exhaust gas, it is necessary to provide the metal structure with the largest possible catalytically active contact surface. For this reason, a development trend toward high channel densities and very thin channel walls has emerged in recent years. The use of very thin channel walls, especially ones of high temperature and corrosion-resistant metal foils, means, however, that the joining technology used to connect the channels walls together must take account of the high thermal and dynamic stresses occurring in the exhaust system of an automobile. Thus, to ensure a compensatory expansion due to the heat, for example, it is necessary to connect at least some of the channel walls together only in a predefinable axial section so that continuous joining over the entire length of the channels is avoided. At the same time, the limits of such a joined section are to be adhered to as precisely as possible.
A further increase in the catalytically active surface is achieved by coating the relatively smooth channel walls with a so-called washcoat, which has a highly fissured surface. The fissured surface, on one hand, ensures a sufficiently large area for the fixing of catalytically active constituents (platinum, rhodium, etc., are used as catalysts, for example), and, on the other hand, serves to swirl the exhaust gas flowing through, thereby producing an especially intensive contact with the catalyst. Application of the washcoat results in a further reduction of the free-flow cross section, however, which, particularly in the case of high channel densities, can lead to an undesirable pressure drop over the catalyst carrier substrate. In this respect, it is quite important to place solder material only at the contact points of each of the channel walls, in order not to increase the height of the coating (solder plus washcoat) on top of the channel wall unnecessarily.
The washcoat is generally composed of a mixture of an aluminum oxide of the transition series and at least one promoter oxide, such as a rare earth oxide, zirconium oxide, nickel oxide, iron oxide, germanium oxide, and barium oxide, for example. The catalytic top-surface washcoat layer is applied in a conventional manner by dipping the honeycomb monolith in a liquid washcoat dispersion or spraying it therewith. The excess washcoat dispersion is, then, removed, and the washcoat in the, preferably, honeycomb catalyst substrate is dried and then calcined at temperatures usually in excess of 450° C. During the calcining, the volatile constituents of the washcoat dispersion and constituents of any bonding agent or adhesive are expelled to produce a temperature-resistant and catalytic layer with high specific surface. If necessary, such a process is repeated several times to achieve a desired layer thickness.
A method for the manufacture of such a catalyst carrier substrate is disclosed, for example, by U.S. Pat. No. 5,082,167 to Sadano et al., and U.S. Pat. Reexamination No. RE35,063 to Sadano et al. These documents describe, in particular, the technical problems relating to the dosing and application of a solder to a honeycomb monolith structure. It is explained, for example, that excessive use of solder with inaccurate application of adhesive leads to corrosion in the metal foil, care needing to be taken to ensure that the adhesive or the bonding agent is placed only at the contact points of the metal foils. It is also stated that any application of the solder prior to a sheet metal foil winding or layering operation is unsuitable because, on one hand, the final diameter of the honeycomb monolith cannot be precisely set due to the grains of solder between the sheet metal foils, and gas can sometimes occur between adjacent sheet metal foils due to subsequent fluidization of the grains of solder. Spraying the catalyst carrier substrate with a bonding agent has also proved ineffective because it is very difficult to get a nozzle close to the corresponding joining areas inside the channels.
U.S. Pat. No. 5,082,167 to Sadano et al., and U.S. Pat. Reexamination No. RE35,063 to Sadano et al. propose to manufacture a catalyst carrier substrate with a honeycomb structure by layering and winding flat and corrugated sheet metal foils. Such a honeycomb structure is, then, brought into contact at the end face with a suction sponge. The suction sponge is disposed in a vessel containing a bonding agent or an adhesive and is saturated thereby. When the honeycomb structure is placed on the suction sponge, the bonding agent from inside the suction sponge penetrates into the interior of the channels through capillary action. After reaching the required height of capillary rise, the end face of the honeycomb structure is removed from the suction sponge. If necessary, such a process can be repeated from the other end face of the honeycomb structure.
It is stated with regard to the suction sponge, that this ensures a continuous supply of sufficient bonding agent because the suction sponge can always absorb bonding agent from one side of the bonding agent reservoir and can deliver it to another surface. However, the suction sponge does have a multiplicity of pores and passages, which, in each case, have greatly varying flow cross sections. This means that a very even supply of bonding agent to the surface on which the metal structure is placed cannot be ensured. Moreover impurities that occur in the production of such metal structures and are deposited on the suction sponge or in the bonding agent reservoir mean that the quality of the dosing may increasingly deteriorate. This would result, for example, in frequent interruptions to production because the suction sponge has to be frequently cleaned or replaced. If this is not done, catalyst carrier substrates of highly variable quality, in terms of their joining technology and hence, their durability, will be produced, which cannot be tolerated in automobile manufacturing or exhaust systems.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for the manufacture of a metal structure and device for wetting a metal structure with an adhesive that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that specify a device, in which a precisely dosed and highly uniform delivery of adhesive to a metal structure is guaranteed. In so doing particular account must be taken of the technical production problems involved in the manufacture of such a catalyst carrier substrate for automobile manufacturing so that the method and the device are at least suitable for mass production with regard to production quality, production costs and product quality.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for manufacturing a metal structure having separate walls forming channels through which a fluid can flow, including the steps of at least partially wetting walls inside the channels with an adhesive by performing a dosed delivery of the adhesive with at least one honeycomb configured dosing element having an inlet side and an outlet side and bei
Caspar Hans-Peter
Kurth Ferdi
Müller Christoph
Scholz Alexander
Voit Michael
Edmondson L.
EMITEC Gesellschaft fuer Emissionstechnologie mbH
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