Graphic Design & Printing TechnologyDelivery Unit
Delivery unit removes the printed substrate from the printing system of the
press and prepares it for finishing operations. Delivery systems on sheetfed
presses are designed differently from those used on web-fed presses. On a
sheet-fed press, the delivery system removes sheets of paper and places them
into a stack called the delivery pile. On a webfed press, the delivery system
conducts a number of additional operations.
There are two common designs for sheetfed press delivery units: Gravity
delivery and Chain gripper delivery.
Gravity delivery is the simpler and less dependable of the two. As the sheet
leaves the printing unit, it is dropped into a delivery pile. The basic limitation
is that paper cannot be delivered faster than gravity can pull it into place.
Gravity delivery is usually found only on smaller presses.
Chain gripper delivery:-Most presses are equipped with delivery grippers
consisting of a series of small metal fingers attached to a bar extended between
two continuous delivery chains. The delivery chains are belts or chains used
to transfer the printedsheet from the impression cylinder to the delivery pile.
A pair of sprockets guides and drives
the delivery chains. The grippers are
spaced at regular intervals along the
chains so one set of grippers is
receiving a sheet while another set is
delivering the preceding sheet.
Spring pressure usually holds the
grippers closed. As the chains carry
the grippers towards the impression
cylinder, they pass over a cam that
forces the grippers open long enough to receive the sheet. The grippers then
carry the sheet to the end of the press, where a trip cam forces the grippers to
open and release the sheet to the delivery platform. The sheet comes to the
delivery pile faceup, with the gripper edge towards the front of the press.
Parts of delivery unit
The delivery unit of an offset press consists of delivery chain, delivery table,
delivery grippers, delivery cylinder, skeleton wheel, joggers and may contain
some ancillary units like anti-set off spray.