Analytical
notes
Establishing
register seems to be a continuing mystery in many pressrooms.
Let me share some recent horror stories, which
illustrate the extent of the misunderstandings. Possibly you will find that some of the scenarios fit your
situation.
It
is observed that register was is so bad that papers go out on
the first run with registers at least six-mm out. This may be considered normal in some presses.
The first run went to the “wastebin” anyway. What are the root causes?
First, the cylinder plate locating pins have to be
investigated. Have they been loosened by interference with the
plate lockup key ? This
means that plate locating on the cylinder is strictly random.
The plate punch if out of adjustment, leads to the
gross inaccuracy in turn leading to mounting problems.
The vacuum frame needs to be investigated. Does it have
a pin system, which did not allow for stretch or shrink of the
film ? Pins being
used in the frame are high enough to hold the film in the
locked-down position ? The
vacuum system, is it effective ?
The solutions are obvious.
The problems which cost thousands every week and ruined
print quality can be avoided if these matters are looked into
in earnest.
Remedies
Stripping
procedures:
Sloppy stripping and ineffective management includes stripping
in process color without a glass. Sloppy work, which is not challenged, becomes the standard.
Establish accountability in the stripping area, and
provide some training.
Crew
training: All of this effort to align, adjust,
calibrate, and simplify, will fail if crews are not instructed
on the correct procedures for hanging plates.
This must not be left to chance.
A plate not firmly seated on the cylinder can defeat
even the, most perfectly aligned press.
Follow this procedure.
Place
the plate on the cylinder.
With both hands spread, firmly press the plate down
tight to the cylinder. Remove
one hand while still pressing down on the plate with the
other. Take the
lock up wrench and lock the plate.
Critically examine the plate to ensure it is hanging
straight. On the
tail of the plate, thumb the plate down hard.
Again check alignment and laydown of the plate.
If the plate has a gap between the plate and the
cylinder, is must be rehung.
The plate should hug the cylinder across its full
width. A minute
spent in re-hunging a plate is the best guarantee of good
initial register. On
a single-plate press, the procedure is the same with two men
doing it together.
Press
input factors: Register will be poor if there is too
much tension on the web, causing stress wrinkles, or too
little tension, allowing the web to “float”.
If there is too much water, the web will stretch or
spread. Unbalanced
blankets, such as different brands running together, variation
in blanket heights or loose blankets cause faults.
Strictly ink increases blanket pilling.
Good
register procedures
The
register pin system is the primary control for the
entire system. Use
the biggest pins plates can carry.
The ideal would be the 6-7 mm size.
These pins should be used all the way from the
pre-press area to the plate burner.
The pins should be at least three-mm high in the vacuum
frame. Pinholes
in the film should be smaller than the actual pin to make a
tight fit of the film to the pin.
The film should be punched with a round hole on one
side and an oblong hole on the other to allow for stretch and
shrink. Positioning
holes should be on the narrow end of the film.
The
bender must be examined to ensure it provides the
right shape to allow the plate to seat itself on the cylinder.
One African press recently examined had that problem.
If the bend is correct, the next consideration is to
check the vacuum system.
If the plate lifts off the bending bed, it means that
the image may be shifting as the bend is made.
The pin system on the bender is also important.
Plate should lock tightly on the positioning pins.
Essentially the pins hold the plate until the vacuum
system takes over.
Plate
cylinder locating pins must be in line with each
other, cylinder to cylinder.
Any misalignment will result in plate misregister.
One system for aligning locating pins was developed by
the Chicago Tribune.
It is simple. All
that is required is to make a small template, which is notched
to fit over the plate-locating pin.
A very narrow slot is cut in the template and used to
scribe a line directly on the plate.
A proof is made. The locating pin is then moved until the lines print on top
of the other. The
system will even allow for web spread.
Richard Malone of the Tribune has given away a great
many of these templates, complete with instructions.
0
Plate punching must be as accurate as the rest of the system.
The punch should be triggered by electrical contact
rather than by visual response.
One good test: punch is accurate, the original hole
should not grow.
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