| 摘要 |
<p>An apparatus and method for distributing wear over a plurality of blades on a rotating roll (12). Retractable cutoff or perforation blades (18) can be actuated to be extended or retracted to selectively cut or perforate a web. To hold the web during web cutting or perforating operations, the roll is provided with vacuum apertures (16) to which is supplied vacuum via vacuum lines (16a), vacuum valves, and a vacuum source, creating suction through the vacuum apertures. The valves preferably have disks (30, 32, 34), each with a pattern of apertures (36, 37, 38) therethrough. When the disks are rotated to selected positions with respect to one another and to the roll, certain vacuum lines are opened to vacuum while others are closed. Vacuum can thus be selectively applied to only those vacuum apertures which are necessary to hold the web in place during cutting or perforating operations. <IMAGE></p> |
