Text 2 Processing machinery

Printing presses belong to the group known as processing machinery. Processing machines include the following areas of function:

• materials processing (e. g., inking, printing, substrate transportation),

• drive (motors and transmission elements),

• control system (e. g., sensors, actuators, and control processors),

• support and covering area (frame, bearings, guides, guards).

All but the first of these operational areas ensure the functioning of the active elements that process the paper, ink, varnish, and other materials. Direct imaging presses feature input facilities for text, graphics, and image information.To carry out their function, printing presses comprise the following sub-assemblies or units:

• Equipment for feeding the substrate

– sheet feeder to separate sheets from piles of paper,

– unwinding stands for reels of paper;

• Equipment for conveying the substrate

– alignment, acceleration, and transport elements for sheets,

– draw and idler rollers for webs;

• Equipment for metering, evening out and applying the coating substances

– inking units,

– dampening systems,

– varnish application systems;

• Equipment for transferring the coating substances,

– printing units,

– coating units;

• Equipment for drying the coating substances,

–dryers;

• Equipment for finishing

– folders in web presses,

– cross cutters for open sheets (unfolded sheets from webs),

– slitters for dividing sheets or webs;

• Equipment for storing printed sheets or webs,

– sheet delivery unit (individual sheets to the pile),

– rewind unit (webs to reels),

– winding of folded sheets onto storage reel.

Configured in the printing units are:

• the printing cylinders (printing unit),

• the inking unit,

• the dampening system (only in offset printing),

• the wash-up devices

Each maximum printing format depends on the dimensions of the plate cylinder. Smaller formats are also possible using narrower webs and sheets and for sheet-fed presses by using shorter sheets in a circumferential direction.

Web presses have a constant print length in accordance with the circumference of the cylinder, and this can only be varied by changing the diameter of the cylinder.Variations of format in gravure and flexographic presses are mainly achieved by changing the plate cylinder, but this option is not usually available in offset and letterpress printing. The terms fixed format printing press and variable format printing press always refer to the print length, not to the print width which can always be changed.

Multicolor printing requires a configuration of several printing units in one press. To print the front and reverse side of sheets or webs (perfecting), blanket-to-blanket printing units are often used in web printing, whereas sheet-fed presses (with a few exceptions) have perfecting equipment especially for this purpose.