Patent ID: 8549747

Claim:
A method for producing a tubular catalytic converter a housing for enclosing a monolith wrapped in a mat, the method comprising the steps of: cutting a housing blank to a dimension commensurate with an average diameter of the monolith and a thickness of the mat, bending the cut housing blank into a shape of the tubular housing with longitudinal sides providing an overlap, forming a stepped longitudinal fold on one of the longitudinal sides by: arranging on an inner side of the longitudinal side an inner electrode pair with a first positive electrode arranged on a first side of the stepped fold to be formed and a first negative electrode on a second side of the stepped fold to be formed with a first distance between the first positive electrode and the first negative electrode; arranging on an outer side of the longitudinal side an outer electrode pair with a second positive electrode arranged on the first side of the stepped fold to be formed and a second negative electrode on the second side of the stepped fold to be formed with a second distance between the second positive electrode and the second negative electrode, wherein the second distance is identical to the first distance, wherein the outer electrode pair has an offset relative to the inner electrode pair in a circumferential direction of the tubular housing corresponding to at least a thickness of the housing blank; applying a voltage to both the inner and the outer electrode pairs to produce a current flow between the first and second sides of the stepped fold to be formed, thereby heating to a yield point a region of the longitudinal side proximate to the stepped fold to be formed; and moving the first positive electrode relative to the first negative electrode and the second positive electrode relative to the second negative electrode, so that the first distance between the positive and negative electrodes of the corresponding first and second electrode pair is steadily reduced, while simultaneously moving the first and second positive electrodes and the first and second negative electrodes in a radial direction of the tubular housing, thereby forming the stepped longitudinal fold, and materially joining opposing longitudinal sides of the tubular housing along the stepped longitudinal fold with the overlap.