Apparatus for making butt-welded tube from a strip includes a pair of grooved weld rolls for aligning the longitudinal edges of the strip bent into a tubular shape. To insure that the inside seam of the tube is flush regardless of variations in thickness between strip edges, each roll is made in two...http://www.google.es/patents/US4025749?utm_source=gb-gplus-sharePatente US4025749 - Apparatus for making butt-welded tubes
