Offset Printing Press

Overview

A sheet-fed offset press is the workhorse of commercial print: it lays four process colors onto cut sheets to produce brochures, packaging, books, and folding-carton blanks at thousands of sheets an hour. It is lithographic, the image and non-image areas sit on the same plate plane and separate chemically by oil and water, and offset, because the inked image transfers first to a rubber blanket and only then to the paper. This machine has four printing units, one each for cyan, magenta, yellow, and black, mounted on a rigid cast-iron Main Frame.

How it works

The Feeder Unit lifts and separates sheets from the pile with a pneumatic suction head, then forwards each one down the feed board to front and side lays that square it precisely before it enters the first unit. The Main Drive turns a line shaft that keeps all four units in register through the run.

Each printing unit, Printing Unit (Cyan) and the magenta, yellow, and black units behind it, carries three cylinders: a plate cylinder, a blanket cylinder, and an impression cylinder. The inking unit's roller train meters ink through motorised zonal keys and applies it to the plate, while the dampening unit wets the non-image areas so they reject ink. The plate transfers its image to the blanket, and the impression cylinder presses the sheet against the blanket to print it.

Printed sheets pass to the Delivery Unit, where a gripper chain carries them over an IR dryer, an anti-set-off powder spray dusts the wet ink, and joggers square the stack. The Registration & Control reads register marks and color-bar density inline and corrects color register, while the operator runs ink keys and the job from the Operator Console.