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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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