Damping device for rotary offset press

Claim 1

In a rotary press of the offset type having a rotating inking roll, a trough for a dampening liquid, a rotating transfer roll having a hydrophilic surface, part of said surface being disposed in said trough to pick up said dampening liquid from said trough as the transfer roll rotates, a third roll with a flexible peripheral layer in rolling contact with said inking roll and said transfer roll, and a wiping roll having a flexible peripheral layer pressed firmly against the transfer roll so as to compress said flexible peripheral layer of the wiping roll in the zone of contact with the transfer roll, means for rotating said transfer roll in a direction to engage said wiping roll after picking up dampening liquid from said trough and before engaging said third roll, the improvement comprising means for maintaining said wiping roll almost stationary so as to collect on the inlet side of the zone of contact between the transfer roll and the wiping roll any sludge comprising an ink-dampening liquid emulsion formed on the transfer roll while rotating said wiping roll in a direction opposite to the transfer roll at a very low speed ranging from a hundredth to a tenth of the speed of rotation of the transfer roll to remove any such collection of said sludge on to the wiping roll and thereby avoid its accumulation.