Press section audit, Janek Schiefer, Head of TASK, Heimbach

PAPERTECHNOLOGYINTERNATIONAL
Figure 6: Correctly positioned deckles on the suction press roll.
Critical point: Sheet release from the centre roll
The centre press roll generally has a ceramic cover with
well-defined roughness and hydrophilic properties. The third
press tends to be designed as a shoe press with grooves in the
belt providing the storage volumes necessary for water to be
successfully discharged. With the aid of a shoe press it is possible to
create an enormous impulse, which in turn allows the sheet to have
the highest possible dry content on leaving the press section.
Of great importance in the context of sheet transfer into the
dryer section is the double doctor system installed on the centre roll.
On the one hand this acts as a dynamic seal that prevents fibres
from passing through and thus causing breaks. On the other hand,
the interaction of the lubrication and cleaning spray pipes, and first
and second blades ensures a constant Ra (roughness) value of the
roll surface – usually with Ra values between 0,6 and 1,0. If these
conditions are respected, there is nothing standing in the way of
reliable sheet transfer with minimum web tension and subsequently
low break frequency.
Single 4th press – with bottom felt only
The bottom roll has a hard, grooved cover. This creates high
maximum pressures in the nip with the aim of achieving an even
greater dry content after the shoe press. This construction, with its
hard nip and design, means that vibration can occur. The vibration
can be dampened by re-tensioning the felt.
Tandem shoe press with transfer belt
Two successive shoe presses are able to generate a very
high press impulse which can create the necessary conditions for
high dry content at the exit of the press section with a closed run.
As there is no longer any free sheet tension during transfer into the
dryer section, higher production speeds can be reached.
In the run-up to a section audit, the Heimbach TASK team
defines tasks and objectives together with the customer. Some
of the aspects that are important in the press section have been
explained in this article. Other issues such as cleanliness and
maintenance of dewatering elements also play a key role in terms of
efficiency in the press section.
Do you have any questions regarding this article, or would
you like to optimise your processes? Please send an e-mail to
task@heimbach.com.
Tri-Nip with 3rd shoe press.
Single 4th press – with bottom felt only
Tandem shoe press with transfer belt
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