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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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