Arrangement for spreading sheets evenly on impression cylinder of

Abstract

A device for seating and spreading a conveyed sheet evenly on an impression cylinder of a printing press thereby to prevent fluttering which includes a pair of pipes arranged parallel to one another in axially extending position above the cylinder. The pipes are bridged by a top wall and end walls to enclose the space between them to form a plenum chamber adjacent the surface of the cylinder, the under surfaces of the pipes defining, with the surface of the cylinder, an air gap of constant width. The outer side walls of the pipes each have a flat upper portion and an inwardly curved lower portion smoothly continuous therewith, each flat upper portion having a skirt arranged parallel thereto in overlapping relation to define nozzles in the form of a narrow slit which extends continuously along each pipe and which is in communication therewith so that air supplied to the pipes under pressure is directed radially inward along and parallel to each side wall, the air being diverted by the Coanda effect inwardly into the air gaps for building up a pressure head in the chamber. Such pressure head presses upon and tends to spread a conveyed sheet evenly on the surface of the cylinder. The chamber is vented through a restriction to limit the pressure which is in the chamber and which is applied to the sheet.