Method for producing a device for muffling sound or catalytic treatment of exhaust

A method of manufacturing an apparatus for muffling sound or catalytic treatment of exhaust and including a casing formed of two substantially identical metallic shells each of which consists of an outer wall part and an imperforated inner wall part, with both wall parts having a curved section and flanges projecting outwardly from the curved section, said method comprising the steps of:

• forming each of the two shells by connecting the outer and inner wall parts with each other at their flanges;
• connecting the two shells with each other at least at the flanges of respective inner wall parts;
• and
• thereafter, generating a pressure between the outer and inner wall parts of each shell by a substance for indenting the inner wall part, at least in some places, toward an interior of the casing thereby to produce an interior space between the two wall parts.

A method of manufacturing an apparatus for muffling sound or catalytic treatment of exhaust and including a casing having an elongate longitudinal wall formed of an outer wall part and an imperforated inner wall part, and two opposite closing walls, said method comprising the steps of:

• producing two sheet metal pieces for forming the outer and inner wall parts;
• applying a foamable expanding agent to at least one of two surfaces facing each other of the two sheet metal pieces;
• placing the two sheet metal pieces one upon another;
• bending the two sheet metal pieces to form the longitudinal wall, said bending step including the step of pressing longitudinal end portions of the two wall parts extending along a surface line together and turning them up to form a longitudinal flange;
• connecting the two wall parts, at opposite axial ends of the casing, to each other and to respective closing walls;
• thereafter, generating a pressure between the outer and inner wall parts by heating the expanding agent for indenting the inner wall part, at least in some places, toward an interior of the casing thereby to produce an intermediate space between the two wall parts;
• and
• thereafter, burning the foamed expanding agent at a temperature of at least 300.degree. C.

A method of manufacturing an apparatus for muffling sound or catalytic treatment of exhaust and including a casing having an outer wall part and an inner all part spaced from each other at least in some places, and two opposite ends, said method comprising the steps of:

• applying a foamable expanding agent between the inner and outer wall parts;
• connecting the inner and outer wall parts to each other at least at the two opposite ends of the casing;
• generating a pressure between the inner and outer wall parts by heating the expanding agent for indenting the inner wall part toward an interior of the casing, at least in some places, thereby to produce an intermediate space between the two wall parts;
• and
• thereafter, burning the foamed expanding agent at a temperature of at least 300.degree. C.

A method of manufacturing an apparatus for muffling sound of exhaust, including a casing having an elongated longitudinal wall formed of an outer wall part and an imperforated inner wall part and two closing walls at opposite ends thereof;

• and
• an interior which is divided into three regions by two intermediate walls wherein the middle interior region is constructed as a hollow chamber and is connected with the inlet and the outlet of the casing via exhaust pipes which are enveloped in the outer region of the interior by a sound absorbing material;
• said method comprising the steps of:
• placing two sheet metal pieces for forming the two wall parts, respectively, one upon the other;
• bending the two sheet metal pieces to form the longitudinal wall;
• inserting the two intermediate walls, the exhaust pipes and the sound absorbing material during or after bending;
• placing the two closing walls on the exhaust pipes which partially project out;
• connecting the two wall parts to each other and to a closing wall at the two opposite ends of the casing;
• and
• generating a pressure between the outer wall part and the inner wall part by a substance for indenting the inner wall part between a closing wall and an intermediate wall and between the two intermediate walls toward an interior of the casing thereby to produce an intermediate space between the inner and outer wall parts.