Throw-off system for rotary offset printing press

Abstract

A system for facilitating throw-off and re-engagement of a blanket cylinder with respect to cooperating plate and impression cylinders and which minimizes wastage of copies incident to reestablishing equilibrium in the inking and dampening systems following an interruption of the normal printing process. Two separate control means are provided for controlling the rate of water flow, the first being an automatic control at the water fountain and the second being in the form of means for controllably disengaging the water form roller from the printing plate. Means are provided for switching from the first control means to the second when the blanket is disengaged for promptly cutting off the flow and thereafter maintaining a water film of predetermined thickness on the plate. Simultaneously with disengagement of the blanket cylinder the ink feed rolls are declutched and the ink form rollers are disengaged for promptly cutting off flow of ink to the plate while preserving the film thickness gradient which exists in the ink feed system. A blanket cleaner is incorporated together with means for spraying solvent on the ink feed rolls. The throw-off mechanism is so arranged that, upon resumption of normal printing, the blanket is brought into engagement with the plate for a predetermined interval before it is engaged with the impression cylinder, thereby insuring that the blanket is re-inked to optimum degree before contact is made with the impression cylinder. As the blanket is brought into engagement with the plate, the inking system, with its pre-existing gradient, is reactivated and the control of water flow, after a delay interval, is restored to the water fountain, permitting the immediate printing of perfect copies.