Reference Manual

17−8
Figure 17-15. Modern Straight-Through Press
Drawing is from TAPPI’s Making Pulp and
Paper Series and is used with permission.
Figure 17-14. Shoe Press Nip
Drawing is from TAPPI’s Making Pulp and
Paper Series and is used with permission.
fabric by passing over a suction box on the return
run.
D Extended Nip — This type of press features
a wide nip to give the sheet a long dwell time at
high pressure. When used as the last nip, this
press provides not only a much drier sheet, but
also a stronger sheet due to improved
consolidation of the web structure.
Mechanically pressing the water from the sheet is
eight times cheaper than trying to dry the sheet.
Because less drying would be needed, faster
machine speeds and production can also be
achieved.
One of the most important things on the press is
the press felts. In the past, these were woven
woolen blankets. Now, these are commonly
composted of a woven synthetic base fabric and
fiber matt, attached by a sewing punching
process. These must be strong enough to
withstand the compression of the rolls while still
providing void volume for the water that is
removed from the sheet in the press nip.
Press Arrangements
Below are the typical press arrangements that can
typically be seen in pulp and paper mills.
D Straight-Through — The oldest and
simplest of the press arrangements, this type can
still be found on paper and board machines. Each
press within this design has a smooth top roll and
a bottom felted roll so only the top surface of the
sheet received smooth roll contact. Later, an
inverse second press allowed the bottom of the
sheet to be in contact with the smooth roll.
D Modern Straight-Through — This unit has
two, double felted presses, which is common in
new paper machines (figure 17-15). In this design,
the sheet is fully supported off the couch, between
the individual presses, and into the dryer section.
Depending on the weight of paper, the more shoe
presses are necessary for water removal.