Muffler or other hollow article and fabrication of same

Claim 1

A SEAMLESS HOLLOW STRUCTURE COMPRISING: (A) A SEAMLESS METAL SHEET HAVING OPPOSED FACES, (1) SAID SHEET HAVING A PORTION OF THE THICKNESS THEREOF BULGED OUTWARDLY BEYOND AT LEAST ONE OF SAID OPPOSING FACES OVER A MAJOR PORTION OF THE AREA OF SAID SHEET THEREBY DEFINING A PAIR OF OPPOSED SPACED APART WALLS EXTENDING OVER SAID MAJOR AREA PORTION, (2) SAID SHEET FURTHER HAVING AN INTEGRAL, SEAMLESS, PERIPHERALLY EXTENDING FLANGE PORTION SURROUNDING SAID BULGED PORTION WHEREBY SAID SHEET DEFINES, BETWEEN SAID WALLS AN EXPANDED CHAMBER DISPOSED INTERNALLY WITHIN SAID SHEET AND PERIPHERALLY SEALED THEREIN, (3) SAID PORTION OF THE THICKNESS OF SAID SHEET BEING CORRESPONDINGLY BULGED OUTWARDLY ACROSS SAID FLANGE PORTION AND FORMING AN EXTENSION OF SAID SPACED APART WALLS THEREBY DEFINING A FIRST OPENING THROUGH SAID SHEET ADJACENT THE MARGINAL EDGE THEREOF AND EXTENDING INTO SAID CHAMBER TO PROVIDE A PORT IN COMMUNICATING RELATIONSHIP EXTERNALLY OF SAID SHEET, (4) SAID SHEET HAVING OTHER OPPOSED PORTIONS OF ITS THICKNESS BULGED OUTWARDLY OVER AN ELONGATED TORTUOUS PATH TO DEFINE A SYSTEM OF CONINUOUS TUBULAR PASSAGEWAYS DISPOSED AND EXTENDING INTERNALLY WITHIN SAID OTHER PORTIONS OF SAID SHEET, (A) SAID SYSTEM OF PASSAGEWAYS HAVING AN OPENING IN A FIRST TERMINAL END THEREOF TO PLACE SAID SYSTEM OF PASSAGEWAYS IN COMMUNICATING RELATIONSHIP WITH SAID CHAMBER, (5) A PORTION OF THE THICKNESS OF SAID SHEET BEING BULGED OUTWARDLY ACROSS SAID FLANGE PORTION THEREBY FORMING A SECOND TERMINAL END OF SAID SYSTEM OF PASSAGEWAYS WHICH IS DISPOSED INTERNALLY WITHIN SAID FLANGE PORTION AND IN SEALED RELATIONSHIP WITH SAID CHAMBER, AND DEFINING A SECOND OPENING ADJACENT THE MARGINAL EDGE OF SAID SHEET TO PLACE SAID SYSTEM OF PASSAGEWAYS IN COMMUNICATING RELATIONSHIP EXTERNALLY OF SAID SHEET.