Förfarande för tillverkning av ett böjt rör

摘要

A bent pipe (1) is made of a metal strip (2) having one edge in a straight line and the other edge in a curved line by winding it helically. A double fold (5) and a single fold (6) are formed along the straight edge and the curved edge, respectively. Then the metal strip (2) is wound helically so that the narrow portions will be in juxtaposition with one another.