Metal fusion bonding – Process – Plural joints
Reexamination Certificate
1999-12-13
2001-08-21
Dunn, Tom (Department: 1725)
Metal fusion bonding
Process
Plural joints
C228S184000, C228S190000, C502S439000
Reexamination Certificate
active
06276595
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a process and a brazing foil for the production of a metallic honeycomb body which is wound, stacked or twisted from at least partially structured sheet layers.
Metallic honeycomb bodies are used, for example, as carrier bodies for catalytically active material for use in exhaust gas cleaning in connection with motor vehicles. Other uses in comparably fine sheet metal structures such as, for example, in heat exchangers are also possible.
The honeycomb body is subjected to a brazing operation to form a metallic connection of the sheet metal layers. German Published, Non-Prosecuted Patent Application DE 29 24 592 A1 discloses different possible ways of introducing brazing material into a metallic honeycomb body. The way in which the brazing material is introduced into a honeycomb body is dependent on the brazing material involved. If the material is brazing material in powder form, it can be introduced into the honeycomb body through the use of a brazing powder fluidized bed. In order to ensure that the brazing powder remains in the honeycomb body until a brazing procedure has been carried into effect, it is necessary for the honeycomb body to be at least partially coated with an adhesive so that the brazing powder can cling to the adhesive. Such a brazing procedure is also known from International Publication No. WO 94/06594.
It is also known from German Published, Non-Prosecuted Patent Application DE 29 24 592 A1 that the brazing material is introduced into the honeycomb body in the form of a brazing foil, in particular brazing strips. A brazing strip is introduced between the structured sheet metal layers during an operation of winding or stacking the sheet metal layers. When using a brazing strip it is possible to eliminate the use of an adhesive as is required when using a brazing powder. However, the step of introducing a brazing strip between the sheet metal layers results in losses in a prestressing force in the honeycomb body during the brazing procedure so that in part brazed joints are not formed between the sheet metal layers.
In accordance with German Published, Non-Prosecuted Patent Application DE 29 24 592 A1 a further possible way of introducing a brazing material into a honeycomb body provides for the at least partially structured sheet metal layers to be wound, stacked or twisted to form a cylindrical honeycomb body and then for a brazing foil of given thickness to be pressed into at least one end surface of the honeycomb body. In that operation the brazing foil is pressed into the honeycomb body to such an extent that the brazing material is intended to remain in the individual honeycombs during the brazing procedure.
A problem encountered with such a mode of operation is that the brazing foil may not be severed by the edges of the sheet metal layers since otherwise the brazed portions would fall out of the individual honeycombs of the honeycomb body upon thermal expansion of the honeycomb body in the radial direction. Brazing the honeycomb body in the region of the two end surfaces of the honeycomb body also involves problems since, during the operation of heating the honeycomb body with the brazing material to a brazing temperature, air which is to be found in the honeycomb body expands and that results in an increase in pressure within the honeycomb body. That increase in pressure can cause the brazing material to be urged out of the individual honeycombs.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a process and a gas-permeable brazing foil for the production of a metallic honeycomb body, which overcome the hereinafore-mentioned disadvantages of the heretofore-known processes and devices of this general type, in which the production of the honeycomb body is simplified and in which a good brazed joint is achieved between sheet layers.
With the foregoing and other objects in view there is provided, in accordance with the invention, a process for the production of a metallic honeycomb body wound, stacked or twisted from at least partially structured sheet layers, which comprises placing at least one at least partially gas-permeable brazing foil at least at one end surface of the honeycomb body; bringing the at least one brazing foil into contact at least with at least one partial region of the sheet layers; and subjecting the honeycomb body to a brazing procedure for metallically joining at least the sheet layers.
The fact that the brazing foil is gas-permeable means that the gas in the honeycomb body has very little or no influence on the behavior of the brazing foil during the brazing procedure. That also provides that the brazing foil is sucked into the honeycomb body by virtue of a capillary action. It is therefore not absolutely necessary for the brazing foil to be pressed into the honeycomb body to that extent, for which purpose particular tools would be necessary, as is required from the state of the art.
The process according to the invention also permits the selective formation of metallic joints with at least the sheet layers of the honeycomb body. The sheet layers of the honeycomb body can be joined together in individual regions by virtue of a suitable configuration of the foil, so that it involves an external contour which does not necessarily correspond to the peripheral line of the end surface of the honeycomb body. This operating procedure also means that it is not necessary, as is known according to the state of the art in a brazing operation using powder, to employ masks through which an end surface of a honeycomb body is only selectively brazed. The selective or region-wise formation of metallic joints with the sheet layers can also be effected by a plurality of brazing foils being disposed at the end surface. The process according to the invention also permits a large number of variations in the possible configurations of metallic joints with at least the sheet layers of the honeycomb body.
Therefore, in accordance with another mode of the invention, at least one region of the sheet layers in each end surface of the honeycomb body can be brought into contact with at least one brazing foil.
In accordance with a further mode of the invention, a particularly mechanically stable honeycomb body is achieved if all sheet layers are brought into contact at least at one end surface with at least one brazing foil and subjected to a brazing procedure.
In accordance with an added mode of the invention, a preferred process is one in which at least one end surface of the honeycomb body which is produced from the sheet layers is at least partially brought into contact with a gas-permeable porous brazing foil. In particular, the brazing foil involves a brazing foam foil which has an open-pore, cell structure. A brazing foam foil of that kind has particularly good adhesion to the end surface of a honeycomb body. A further advantage of that operating procedure is also relatively good gas exchange between the ambient atmosphere and the honeycomb body through the brazing foam foil.
In accordance with an additional mode of the invention, in order to provide that the individual sheet layers of a honeycomb body are metallically joined to each other, the entire end surface of the honeycomb body is brought into contact with a brazing foil. Particularly good stability of a metallic honeycomb body is achieved by each end surface of the honeycomb body being brought into contact with a brazing foil and subjected to a brazing procedure. The fact that the brazing foil has a gas-permeable nature means that the sheet layers at each end surface of the honeycomb body can be brazed simultaneously, that is to say during a single brazing procedure.
In accordance with yet another mode of the invention, in order to provide improved adhesion of the brazing foil to an end surface of the honeycomb body it is proposed that the brazing foil be partially pressed into the honeycomb body. It is, however, pressed-in in such a way that gas-permeability of the brazing f
Dunn Tom
Emitec Gesellschaft fuer Emissions-technologie mbH
Greenberg Laurence A.
Johnson Jonathan
Lerner Herbert L.
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