Method of making perforated tubular member for perforating thermoplastic film

Abstract From the Canadian patent

Abstract A method is described for making a relatively thin wall perforated tubular member having a wall which is perforated by an array of radially inwardly tapered apertures. A pattern cylinder is formed with radially outwardly extending protruberances, these being tapered to radially outwardly disposed free ends and comprising an inside-out negative pattern for the desired array of perforations. Metal is then applied between the protruberances to form an inside-out perforated tubular member, which is longitudinally slitted reverse rolled, and longitudinally seamed along the slitted edges.