All efforts for optimising tissue production focus on the improvement of product
quality and the increase in machine efficiency. The new HybriFlex roll cover
for pressure and suction pressure rolls significantly increases the
profitability of the production process and simultaneously contributes to
improved tissue quality.
Pressure roll covers in fast-running tissue machines are subject to very
demanding operating conditions: To compensate the somewhat imperfect shape of
the Yankee cylinder caused by thermal and mechanical loads, a soft mating
pressure roll is required. At the same time it is essential to have a high open
area for maximum de-watering of the web. This is a conflicting situation: a
soft cover to adapt the shape of the cylinder – and a stiff cover to support the structure of a high open area.
Wear resistance and structural stability doesn’t combine with good resilience and shape adaptability. The result is often a
compromise leading to insufficient de-watering.
Figure 1:
Properties and advantages of hard and soft press roll covers in tissue machines
With the patent pending HybriFlex two-layer cover, SchaeferRolls now combines
the advantages of soft and hard materials in the same roll cover. The split of
the functional part of the cover into two different layers enables the specific
optimisation of the properties of the two layers with respect to their
functions:
• a softer polymeric material inside (inner layer)
• a harder polymeric shell (top layer)
The material of the soft inner layer (35-50 P&J) is selected with the best possible resilience, since wear resistance is not a
concern. The harder top layer (10-25 P&J) is designed for the highest-possible wear resistance and high surface
stability, since dynamic properties of the material is less important. The two
layers are structurally bonded to ensure functional reliability. The apparent
hardness of the roll cover is almost equivalent to the average of the two
layers. The bonding to the shell is the system proven with the standard
SchaeferRolls covers in hundreds of positions.
Figure 2:
Design of HybriFlex two-layer cover
