Dampening device for offset printing machine

Abstract

A dampening device for an offset lithographic printing machine of the type having a pickup roll having radially spaced fluid retaining means thereon rotatable in a bath of a dampening fluid where the fluid is transferred from the pickup roll to any one of a transfer roll, drum or form roll which together comprise part of a fluid distribution system radially spaced from the pickup roll for subsequent movement to a printing plate on a plate cylinder. The dampening device includes a gaseous blow means for directing a current of gas towards the pickup roll near the gap between the pickup roll and transfer roll, drum or form roll whereby fluid is blown from the fluid retaining means onto the surface of the pickup roll from where it rebounds across the gap to impinge on the transfer roll, drum or form roll as a finely dispersed spray. The fluid retaining means comprises bristles, screen material or individual closed loops which carry droplets or a thin film of fluid when the pickup roll is rotated in a bath of dampening fluid.