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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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