METHOD FOR MAKING THIN-WALL TUBES WITH INNER FOLDED SEAM Russian patent published in 2006 - IPC B21D39/02 

FIELD: plastic metal working, possibly manufacture of thin-wall tubes with folded seam.

SUBSTANCE: at first transitions flanged portions are bent beginning from imparting to flanged portions of folded seam final curvilinear shape of ready tube. It allows form complex butt of folded seam without after-shaping of flanged portions in range of bending angle 80 - 100°. Remaining portions of complex butt of folded seam are shaped till their final shape. Other butt of folded seam is shaped while keeping equal height of butt walls and bending portion of round part of tube near butt along radius of ready tube. At further transitions flanged portions near edges of angles are after-shaped in order to provide joining of butts of folded seam. Portions of round part of tube are bent by lowering radius and simultaneously portions adjoined to portions of folded seam are bent by ready tube radius. Then stages of coupling and seaming are realized by means of rotating roller tool without final after-shaping of portions of folded seam adjoined to round part of tube.

EFFECT: enhanced quality of surface, improved seam strength of tube.

21 dwg