Graphic Design & Printing Technologyor more paper rolls and feed each in turn with consistent and controlled tension
into the printing unit of the press. When the roll begings to run out a new roll
can be spliced on to the old, using and automatic splicer. Splicer is a machine
that joints the end of two webs of paper to make a continuous roll without
stoping the press.
The paper is threaded into the press while the press continues to run at full
speed. Large festoons are used to unwind the paper. Festoon is a paper storage
device that unwinds paper to keep the press running at the same speed while
the splice is made and the new roll accelerates to press speed. This device also
gives the web a long lead time into the press.
To run a continuous web of paper at high speed between numerous rollers and
cylinders, it is necessary to control the tension of the web precisely. Tension
control device regulates the amount of pull needed to keep the paper from
having slack.
Web guide control the side-to-side register of the web as it passes through the
press, just as a side guide exercise this control on sheet fed presses.
Drier and Chill rollers:- Modern web offset printing uses heat set inks, inks
that require the application of high temperatures to dry. As a result, web presses
that utilize such inks need a dryer and chill rolls attached after the last printing
section.
Most of the web offset printing machines have a drying chamber as an extra
attachment. Some machines have a device for blowing hot air on the printed
web for setting and drying the ink.
After passing the printed web through the heating chamber it is necessary to
cool it. The surface of the web, structure of the fibres and the newly prined ink
density are affected when it passess through the heating chamber. All these
factors of the web become normal when it pass through the chilling unit.
There are two large cylinders for chilling the web which are kept away from
each other. One side of the web passes in contact with one cylinder and the
other side with the other cylinder. Droplets of water are formed on the surface
of chilling cylinders. Chilled droplets of water vapour normalizes the heated
web by this process.
Flying pasters(Splicers):- A unique mechanism for bringing a new roll of paper
into the feed cycle without stoping the press is called a flying paster or a splicer.
As the main feeding roll nears its end, the roll stand is rotated to bring the next
full roll of paper into running position without slowing the running speed of
the press. Double sided tape is applied on the leading edge of the new role.
The full roll is then moved into contact with the running roll of paper and the
taped edge of full roll is pressed against and immediately adhers to the running