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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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