Method and apparatus for making perforations continuously

An apparatus for forming perforations along a long strip of sheet material while continuously conveying said sheet material in a longitudinal direction thereof, said apparatus comprising:

• circulating means having a peripheral surface which moves in a first direction;
• a plurality of die sets, each having a punch and a die, arranged at regular intervals around said peripheral surface which move in said first direction along with said peripheral surface, each of said die sets having said die secured to a die holder which is mounted to said peripheral surface, and said punch secured to a punch holder which is linearly movable in opposite directions perpendicular to said peripheral surface between a punch position, where said punch is fitted in said die, and a retracted position, where said punch is retracted away from said die;
• roller means, disposed outside said peripheral surface, for bringing a portion of said sheet material into contact with said peripheral surface so as to convey said sheet material on said peripheral surface in said first direction at the same speed as said die sets;
• punch drive means coupled to said punch holder for driving said punch holder relative to said die holder to move in one of said opposite directions perpendicular to said peripheral surface, said punch drive means keeping said punch in said punch position for a predetermined circulating period of said die sets so as to nip said sheet material between said dies and said punches through said perforations;
• and
• shift means for pivoting said die sets relative to said sheet material in a transverse direction with respect to said peripheral surface into a relief position where said punch cannot interfere with said sheet material when said sheet material is approaching or leaving said peripheral surface, a relative position between said punch holder and said die holder remaining constant while said shift means pivots said die sets.