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

PAPERTECHNOLOGYINTERNATIONAL
Press section audit
Janek Schiefer, Head of TASK, Heimbach
INTRODUCTION:
Paper machines are sensitive giants. As complex as the various machine configurations are, the parameters that influence
productivity are just as varied. It is often the small details that make the difference or can decide the quality on the reel. Heimbach offers
section or machine audits, which can be carried out for a specific section or for the entire paper machine, depending on the task at hand.
The following article provides a general overview and recommendations for the press section.
Figure 1: Format setting suction box.
Mode of operation and characteristics
As the paper web passes through the press section, water
removal is essentially generated by means of mechanical pressure.
In the course of this process the water is stored temporarily within
the press felts or in the open area of roll covers. This water is then
removed via one of the assembly types described below.
There is no single or blanket answer to the question of
whether nip or Uhle box dewatering is more suitable. In the case of
high speed machines the laws of physics speak against the use of
felt suction boxes as there is simply not enough time available. In
machines with lower speeds felt suction boxes can prove to be more
efficient. As a rule, the two modes of action complement each other.
It is important to know that the method of dewatering will
have an effect on the service life of the felts, energy consumption
and paper quality.
Assemblies
The machine frame usually has a cantilever system, so that
endless felts can be installed relatively easily. The roll arrangement
in the press section usually comprises several positions, each
consisting of one or more presses and various lead rolls.
A single guiding roll and single tension roll is used for each
felt position; an additional spreader roll tends to be used when
machine working width exceeds six metres.
Figure 2: Adjustment mechanism for suction box.
Pick-up and suction press rolls have a format setting (Fig.1)
as well as an adjustment option for the angular position of the
suction box (Fig.2).
Press Nips
A loading mechanism (usually hydraulic or pneumatic) can
be used to control the contact pressure of the individual press nips.
If crowned rolls are not sufficient to cover the load range, deflection
compensated rolls are employed. Soft covers of press rolls, when
running with the felt, can cause an increased dwell time in the nip
and store the water to be discharged as it passes through.
Doctors and savealls drain the water expressed from the
nip out of the press. The water volumes exiting the felts is drained
through the vacuum system by suction boxes. Low pressure
showers and edge spray nozzles create a lubricating film between
the felt and the suction box. High pressure showers help to maintain
the permeability of the press felts. The vacuums of the different
suction elements can be controlled by an appropriate system.
Transmitters are used to monitor dewatering flows online ( Ecoflows,
for example).
123

Paperturn flipbook viewer