VACUUM CYLINDER FOR PRINTING PRESSES

摘要

19.01 The invention relates to an improved form of vacuumoperated printing cylinder for a printing press, providing a practical means for holding the printing plate on the cylinder by vacuum alone, without requiring separate adhesive means and/or supplementary mechanical devices for clamping the plate. The cylinder includes a supporting shaft mounting, between its bearing portions, a plurality of cylinder supporting rings. A cylinder sleeve is supported by the rings and forms, together with the rings and the supporting shaft, a hollow cylinder structure having a plurality of vacuum chambers. The interior of the cylinder can be evacuated from one end of the shaft, and independently controllable valve means are built into the cylinder, to enable the several chambers thereof to be independently evacuated. The cylinder sleeve is provided with a large number of radial passages, providing communication to the outside surface of the cylinder. In another form, the sleeve is provided with a plurality of axially spaced, continuous annular grooves, which communicate at one or more places with the interior of the cylinder. The continuous grooves are blocked off at one or more places around the circumference of the cylinder to avoid leakage at the end-to-end discontinuity in a printing plate supported on the cylinder. A relatively continuous media may be used around the exterior of the printing cylinder and about which the printing plate is wrapped and secured by vacuum. In some cases, the porous media is a filter paper material, which may be of various thicknesses to accommodate printing plates of different thicknesses. In other cases, the porous media may be a sintered metal coating, permanently bonded about the exterior of the cylinder. In either case, the porous media serves to diffuse and render more uniform the application, of vacuum to the underside of the printing plate.