To provide a manufacturing method of a specially shaped pipe having a wall, cross section of which is incurvated in a convexo-concave shape around a central axis.
This method is to weld the end faces of longitudinal direction of a plate material in which plural identical angular or corrugated shapes in cross-section are formed in the longitudinal direction to obtain a pipe element in which the cross-section meeting a pipe axis at right angles is convexo- concave, and to reduce a distance between respective tip ends of the parts convexed toward the inside of the pipe by a die and/or forming roll to form a pipe wall wherein the cross-section perpendicular to the pipe axis direction is incurvated like pleat. According to this method, manufacturing of a specially shaped pipe 6 can easily be carried out, a tool is hard to abrade and dimentional accuracy is also improved.
NISHIYAMA OSAMU
KOMAI TATSUYA
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