Paper Technology Journal - Voith

2
4
5
Density kg/m 3
1300
1200
1100
1000
900
800
700
600
800
1000 1200 1400
Rewind diameter
Nip force kN/m
12
10
8
6
4
2
150
Finishing
Newsprint 680 kg/m 3
a single drum winder had to be used. The
reason for this were the nip forces resulting
from the great roll weights which,
with the two drum winder, could lead to
winding faults, such as crepe wrinkles,
breakages, excessive stretch etc. Fig. 3
shows an example of 2 types of paper on
this subject.
Assuming therefore, that nip forces of
4 or 5 kN/m are critical for the paper
selected, a roll diameter of approx.
1070 mm would be required for
newsprint. This roll diameter would be
considerably smaller for SC paper
(approx. 980 mm). A standard two drum
winder could therefore not be used with
present-day typical rewind diameters
of 1100-1250 mm – and particularly not
for the diameters of 1500 mm required
in the future. It was for this reason that
in the past compressed air systems
(Fig. 4) were used with two drum
winders, so that the depositing forces
resulting from the roll weight could be
reduced.
These requirements have been fully satisfied
by the compressed air systems pro-
SB-B/SC 1100 kg/m 3
Fig. 1: Time table for taking over the
responsibility for winders.
Fig. 2: Field of activities for standard two
drum winders and single drum winders.
Fig. 3: Nip forces at two drum winders.
Fig. 4: Conventional two drum winder roll
with compressed air load relief.
Fig. 5: TORO TD with compressed air load relief.
Critical area
Critical area
300 450 600 750 900 1050 1200 1350 1500
Rewind diameter
51
vided that the paper was air-permeable.
However, as shown in Fig. 4, these standard
installations have a technological
disadvantage: The relieving air gets
wound into the paper roll. With more
dense types of paper, such as, for
instance, improved newsprint and/or
SC-B paper, the wound-in air causes
layer displacements leading to crepe
wrinkles even if the paper roll weights
and the nip forces are low. The situation
is still worse with high-finished or coated
papers, as these types are almost impermeable
to air, e.g. the included air really
has no chance to escape.
This, of course, leads to the question as
to which modified winder concept we
should adopt in the future. With this in
mind, solutions such as belt supports
and application of a soft cover on the
winder drum etc. were discussed. It
became clear, however, that these ideas
were linked in part with other disadvantages.
The best concept, in our opinion,
is illustrated in Fig. 5.
The solution is characterized by the following
features:
3