Vertical Blanket-to-Blanket Unit

Nowadays virtually all printing units on commercial web offset presses are designed in such a way that two blanket cylinders are arranged on top of one another with the web guided between them in a horizontal direction. The plate cylinders, the inking units, and the dampening units belonging to each printing unit are arranged at the top and bottom respectively.

This printing unit configuration is referred to as a vertical blanket-to-blanket unit with horizontal web travel. Four-color printing on both sides is produced by arranging four such blanket-to-blanket units in sequence.

There are various options for installing and coupling presses for multi-web production. It is, for example, possible to install an identical but inverted production line on the other side of the folder. Another variant is to choose a two-level hot air dryer where both print lines are arranged behind each other and reroute the web via the second section.

Double-deck configurations can also be found, as can parallel configurations with cross transfer of the second web to the common folder via turner bars. Of course it might be necessary to arrange more than four printing units in a row, for instance, when using spot colors or coatings. In addition the press can be equipped with “in-line finishing units”, for example, for

plow folding, punching, perforating, and applying adhesive.

Horizontal Blanket-to-Blanket Unit (Arch-Type Printing Unit and Four-High Unit)

In newspaper printing multiple web operation is usually required.With the vertical blanket-to-blanket unit configuration described above this is very difficult to achieve. This led to the development of another basic design – the arch-type printing unit. Here, both blanket cylinders are brought into contact with each other in a horizontal direction and the web runs between

them in a vertical direction. The plate cylinders, inking units, and dampening units are arranged to the sides of each blanket cylinder in a downward slanting direction. This results in an arch shape, giving the design its name.

Single-color printing on both sides in multi-web operation can be achieved by arranging several such archtype printing units (printing towers) alongside eachother with the reel stands in the basement of the building and the webs being fed through slits in the floor.

For multicolor printing the arch-type printing units need to be stacked in a vertical direction. This means that for four-color prints on both sides of the web, four arch-type printing units are arranged on top of each other, producing the so-called four-high unit or tower.

To save on overall height, the vertical U-type printing unit was designed. This is arranged inverted to the arch-type printing unit, and placed on top of an arch type unit to form an H-type unit. Two of these stacked on top of each other will form a four-high unit.The majority of applications now utilize this compact four-high design (fig. 1.6-13).The web has to travel the short-

est distance between printing nips through this four-high configuration to produce a 4/4 print. Cylinders and web are easily accessible for the operator.

Initially, it was sufficient in newspaper printing to introduce individual spot colors and not to have them on all pages. So-called “Y-shaped printing units”were quite adequate for this application,using blanket-to-blanket printing twice on one side to manage without a separate impression cylinder. There were also attempts to let two plate cylinders run in contact with one

blanket cylinder. However, this only produced satisfactory results if the spot color was used completely separately and no overprinting of two colors was required.