Metal working – Method of mechanical manufacture – Catalytic device making
Reexamination Certificate
2002-08-06
2004-03-09
Cuda-Rosenbaum, I (Department: 3726)
Metal working
Method of mechanical manufacture
Catalytic device making
C029S407050, C029S418000, C029S422000, C029S520000, C072S083000, C072S121000
Reexamination Certificate
active
06701617
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to a method for manufacturing a catalytic converter by spin-forming a metal tube about a catalyst substrate to form a housing. More particularly, this invention relates to a spin-forming method wherein the catalyst substrate has a noncircular circumference and wherein the metal-forming tool is positioned during spin-forming to form a housing shaped similar to the catalyst substrate and sized greater than the catalyst substrate by a uniform distance.
BACKGROUND OF THE INVENTION
Automotive vehicles are equipped with a catalytic converter for treating exhaust gases to reduce noxious compounds prior to emission into the atmosphere. A typical catalytic converter comprises a catalyst substrate that is formed by extruding and firing a ceramic material and defines a plurality of passages that are coated with catalyst agents for treating exhaust gases caused to flow therethrough. The catalyst substrate is generally cylindrical and is enclosed in a metal housing. A thermally insulative material is interposed between the catalyst substrate and the metal housing to maintain the substrate at an elevated temperature effective for treatment and prevent overheating of the housing.
It has been proposed to manufacture a catalytic converter by spin-forming a metal tube about the catalyst substrate to form the housing. During spin-forming, the catalyst substrate is positioned in the metal tube, and the substrate and tube are rotated about a central axis. The metal forming tool is radially urged against the metal, while advancing axially, to reduce the circumference of the tube. Multiple passes are typically required in order to achieve the desired product size and shape. For each pass, the tool is radially advanced a small distance, so that the diameter is reduced incrementally.
In conventional spin-forming processes, the metal-forming tool is positioned a fixed distance from the axis, and produces a housing having a circular cross section. Thus the process is suited for producing a housing about a cylindrical substrate with a circular cross-section uniformly spaced from the housing. It is desired to produce a catalytic converter having other shapes, which would need to be based upon a substrate having a noncircular cross-section; for example, an oval circumference. Moreover, even for catalyst substrates that are designed to be cylindrical, the radial dimensions of the substrate tends to vary as a result of the extruding and firing of the ceramic material, so that the circumference of the catalyst substrate is not a true circle, but tends to have a radius that varies with direction, a condition referred to as out-of-round. During spin-forming, regions of the substrate having a greater radius than specified may experience higher pressure from the metal-forming tool, which may cause breakage of the fragile substrate. Furthermore, variations in the radius may result in a non-uniform thickness of insulation between the substrate and the housing.
Therefore, a need exists for a method of forming a catalytic converter by spin-forming that is suited for forming a metal housing about a catalyst substrate having a noncircular circumference, either by design or as a result of deviations that occur during processing of the ceramic. It is desired that the housing formed by spin-forming be spaced apart form the noncircular substrate by a uniform radial distance, such that a uniform layer of insulative material is disposed between the housing and substrate.
BRIEF SUMMARY OF THE INVENTION
In accordance with this invention, a method is provided for forming a catalytic converter that includes a catalyst substrate having a noncircular circumference. The catalyst substrate is measured to determine the radial dimension of the noncircular circumference relative to an axis. The catalyst substrate is wrapped in a compressible mat and arranged in a metal tube. The arrangement is subjected to a spin-forming process that forms the metal tube about the catalyst substrate into a metal housing. The spin-forming process includes rotating the metal tube about the substrate axis and concurrently radially urging a metal-forming tool against the tube. In accordance with this invention, the metal-forming tool is programmed to follow a metal-forming path corresponding to the substrate circumference plus a predetermined radial distance. In this manner, a metal housing for the catalytic converter is produced having a noncircular circumference that corresponds in shape to the substrate and is spaced apart therefrom by an insulative layer.
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Lanzesira Joseph Michael
Li Houliang
Nelson Earl T.
Brinks Hofer Gilson & Lione
Cuda-Rosenbaum I
Visteon Global Technologies Inc.
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