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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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