Basic Systems Of Sheetfed Offset Presses
A sheetfed press consists of a feeder, one or more printing units, a sheet register system including transfer devices to move the paper through the press, a delivery, and various auxiliary devices.
The printing unit of a sheetfed offset lithographic press generally consists of three primary cylinders and systems for dampening and inking the plate.
Plate cylinder, a cylinder that carries the printing plate, a flexible image carrier with ink receptive image areas and , when mostened with a water based solution, ink repellent nonimage areas.
Blanket cylinder. A cylinder that carriers the offset blanket, a fabric coated with synthetic rubber that transfers the image from the printing plate to the substrate.
Impression cylinder. A cylinder running in contact with the blanket cylinder that transports the paper or other substrate and forces the paper against the inked blanket.
Damening system. A series of rollers that carry a metered fiml of water mixed with other important chemicals together called dampening solution, dampening the printing plate. The water based dampening solution contains additives such as acid, gum arabic, and isopropyl alcohol or other wetting agents.
Inking system. An ink fountain that functions as an ink reservoir and a series of rollers that tranport and mill the ink, finally depositing a metered film of ink onto the printing plate.
In addition to one or more printing units, a press also includes the following:
Feeder, which lifts and forwards the sheets of paper or other substrate from a pile to the first printing unit.
Sheet register system, which provides alignment guides and devices that enable every sheet to be registered and printed in the exact same location and transsfer devices often auxiliary cylinders with sheet groppers- that facilitate sheet transports through the press.
Delivery, which receives the stacks the printed sheet.
Edit By Vikas
April 10, 2012
