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Sheet
fed presses are used in the printing industry
to print jobs that require lower counts. For example,
if a printer was printing a job that required
50,000 impressions they would use a sheetfed press.
On the other hand, if they were printing a wide
distribution magazine, a high speed web would
be used.
It
was said, years ago, that sheetfed printing was
used for quality printing and web for volume.
Today, that is no longer the case. Web and sheetfed
can both give equal print performance. It is more
now a matter of your customer base and the length
of run.
Figure
1 shows a common six color sheetfed press with
a coater and infrared dryers. Each unit prints
a different color. The usual sequence for printing
is to print black, cyan, magenta and then yellow.
The extra two units on the press are used to print
special colors. The coater is used to give gloss
or protection to the printed sheet. Between each
print unit is a transfer cylinder to transfer
the printed sheet from one unit to the other.
As indicated in the picture, the ink is still
wet during this transfer process.
Many
of today's sheetfed presses are configured so
that the sheet can be turned and printed on the
back side. In the above press, it would be common
to have the "turn" cylinder between the 2nd and
3rd print units. This is called a "perfector cylinder."
The cylinder can be configured by the pressmen
so that he can print 2 colors on the top of the
sheet and 2 colors on the bottom or not configure.
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