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The
delivery unit takes the paper from the printing
unit and places it on the delivery pile. There
are two common designs for sheetfed press delivery
units: gravity and chain gripper systems.

Typeical Press End With a Coater, IR Dryers, spray
Powder system and the chain delivery
The
gravity system is the simpler of the two but less
dependable and functional. As the printed sheet
leaves the printing unit, it is dropped into the
delivery pile by gravity. The basic limitation
is that the paper cannot be delivered faster than
gravity can pull it into place. With light weight
papers this can pose problems. Today this type
of delivery system is found mostly on small inexpensive
offset duplicators.
Most
modern sheetfed presses today utilize the chain
gripper system. With this type of system, the
paper can be either pulled through the printing
and delivery units by the same chain system or
transferred from the paper grippers on the impression
cylinder in the printing unit to a different set
of grippers on the delivery chain.
As
the sheet leaves the printing unit, a set of mechanical
fingers or grippers grabs the leading edge of
the sheet and pulls it out of the printing system.
The gripper bar is attached to a continuous chain
that moves the printed sheet to paper pile, releases
it, and moves the grippers back to receive another
sheet. The chain moves at the same rate and in
synchronization with the feeder, registration,
and printing units.
Like
the feed system, the delivery pile is automatically
controlled for proper height. As sheets are stacked,
the pile table automatically lowers itself to
accommodate new sheets being added. Adjustments
to the pile height can be made by the pressmen
for different types of paper (board to light-weight
paper).
In
the delivery section, most sheetfed presses, today,
have static eliminators, Infrared dryers, decurlers
and a starch powder system. Static eliminators
are used to reduce any static the printed sheets
may have or accumulated during the printing process.
Infrared (IR) dryers Typeical Press End With a
Coater, IR Dryers, spray Powder system and the
chain delivery are equipped on many presses today
to help drive off the solvents in the ink. The
IR dryers don't actually dry the ink but assist
in removing the solvents in the ink allowing for
the exposed varnishes to react quicker with oxygen.
This results in quicker ink drying. IR dyers also
are used to help quickly dry aqueous coatings
that may be applied over the printed ink. Sheetfed
presses can also be equipped with Ultraviolet
(UV) coaters. If these types of coaters are used,
the press must be equipped with a UV light source
to 뱒et?the coating. These type of coating
usually are used to give excellent protection
to the printed sheet as well a develope high gloss.
An example of this type of coating would be on
a magazine glossy cover.
The
use of decurlers is to reduce any curl the sheet
may have which will hinder delivery or post press
performance. The use of starch spray powder is
done to help, on a microscopic level, separate
the printed sheets so that air (oxygen) can reach
the ink and begin setting and drying the ink.
The heavier the paper weight, the larger the particle
size of starch needed. Starch powders come in
a variety of particle sizes.
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