Vacuum assisted roll apparatus and method

Abstract

An apparatus and method for distributing wear over a plurality of elements on a rotating member. In the case of a cutoff or perforation roll, a plurality of retractable cutoff or perforation blades can be actuated to be extended or retracted to selectively cut or perforate a web. To distribute blade wear, extended blades are occasionally retracted while other blades are extended. Where it is desired to continue producing cuts or perforations of a desired length through such blade indexing, the spacing and number of blades before and after indexing are preferably the same. Most preferably, each blade retracted during indexing is replaced by a blade on the same side of and at the same distance from the blade being retracted. To hold the web during web cutting or perforating operations, the roll is preferably provided with vacuum apertures to which is supplied vacuum via vacuum lines, vacuum valves, and a vacuum source, thereby creating suction through the vacuum apertures. The valves preferably have disks each with a pattern of apertures therethrough. When the disks are rotated to selected positions with respect to one another and to the roll, certain vacuum lines are opened to the vacuum source while others are closed therefrom. In this manner, vacuum can be selectively applied to only those vacuum apertures which are necessary to hold the web in place during cutting or perforating operations. By rotating the disks, the application of vacuum can be adjusted as desired (e.g., when the blades are indexed).