Note: Descriptions are shown in the official language in which they were submitted.
CA 02290558 1999-11-16
Calender arrangement
s The invention relates to a calender arrangement.
In vertical calenders having a plurality of rolls, one of the intermediate
rolls is provided with a main drive and transmits the torques to all the other
rolls
frictionally, by means of tangential forces, from one roll to the next and via
the web
to be treated and the roll covers. This leads to undesired horizontal
deflections,
to that is to say to deformations of the intermediate rolls. In addition, the
web
structure and the roll covers are impaired. Fig. 1 shows a schematic side view
of a
known off-line calender, in which an intermediate roll 2, that is the drive
roll with a
main drive, is driven.
In an on-line calender, before the paper web is threaded, and with the
15 nips open, all the rolls in contact with the paper web are accelerated by
their
auxiliary drives, and the drive roll with the main drive is accelerated to a
rotational
speed at which the respective circumferential speed corresponds to the web
speed of the paper, which can be 1000 m per minute and much higher. After the
nips have been closed, power is introduced only by the main drive of a single
2 o drive roll. This is illustrated schematically in Fig. 2, in which the main
drive 4 is
represented by a large drive symbol and the auxiliary drives 6 are represented
by
a small drive symbol. In Figs. 1 and 2, the horizontal deflections at the
centre of
the roll are drawn schematically as a centre offset.
In modern calenders, the top roll and the bottom roll of the roll stack are
2 s designed as controllable-deflection rolls. Because of their internal
frictional losses,
necessitated by their functioning, these two rolls need a greater drive force
than
the remaining calender rolls. In addition, the most extreme deformation of the
paper web takes place in the first nip. In conventional calenders having a
main
drive, these two power components have to be dragged through the entire roll
3 o stack and, in so doing, stress the paper web and the roll covers in a
damaging
way as a result of frictional transmission of the tangential forces. This
results in
increased wear of the roll surfaces and a reduction in the service life of the
rolls.
According to an earlier proposal in DE-196 50 576.3, all the rolls are
provided with their own (power) drives, and the powers of the individual
drives are
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coordinated with one another in such a way that the horizontal roll
deformations
are minimized.
The object of the invention is to provide a calender whose roll drive is
designed such that the outlined disadvantages of the prior art are avoided
cost
s effectively.
The achievement of this object in accordance with the invention is
defined in Patent Claim 1.
According to the invention, the controllable-deflection rolls are each
provided with their own power drive. In one configuration of the invention, a
i o controllable-deflection top roll and bottom roll can be driven with drive
powers
matched to each other. It is preferred to register the horizontal deformation
of an
intermediate roll and to control or regulate the power distribution to the two
drives
in such a way that this deformation at least remains below an amount which is
still
permissible. It has been shown that this requirement can be met if the top
roll and
15 bottom roll are driven with essentially the same power.
Two embodiments of the calender arrangement according to the
invention are reproduced schematically in side view in the appended Figures 3
and 4. Here, Fig. 3 shows a calender arrangement analogous to Fig. 1, while
Fig.
4 represents a calender arrangement analogous to Fig. 2. The symbols for the
2 o power drive and auxiliary drive in Fig. 3 and Fig. 4 correspond to the
symbols for
the main drive and auxiliary drive in Figs. 1 and 2.
After the nips have been closed, the calender rolls have the predefined
line load applied to them, at which predefined pressure stresses are developed
in
the nips. At the same time, the calendering forces corresponding to the
loading
2 s are provided by the two power drives of the top and bottom rolls. An
intermediate
roll is expediently provided with sensors for the horizontal deformations, and
the
distribution of the drive power to the top and bottom roll is carried out in
such a
way that these horizontal deformations are minimized. Alternatively, it is
also
possible for the horizontal forces acting on an intermediate roll to be
measured
3 o and minimized.
In the embodiments according to the invention according to Figs. 3 and
4, the paper web 10 runs firstly into the nip formed between the upper
controllable-deflection roll 12 and the first intermediate roll 14, which is a
heatable
hard roll. After this, the paper web passes into the nip formed between the
latter
3 s roll and a central intermediate roll 16; roll 16 is provided with a
resilient cover. On
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the side facing away from roll 14, roll 16 forms, with a second heatable hard
roll
18, the next nip through which the paper web 10 passes. A last nip is formed
between roll 18 and the bottom controllable-deflection roll 20. The rolls 12
and 20
are equipped with power drives. The intermediate rolls 14, 16 and 18 are
mounted
s in a manner known per se in lever arms 22, via which forces from operating
cylinders 24 can be introduced, in particular in order to compensate for the
so-
called overhung loads. Hydraulic units 26 are used to close the nips; instead
of
this, the inner stroke of the roll 20 could also be used for this purpose,
while the
upper controllable-deflection roll 12 is mounted in a fixed location in the
frame.
1 o On one of the intermediate rolls 14, 16, 18, transverse forces which
occur can be measured via sensing elements (not illustrated) and, depending on
the measurement result, the power distribution of the drives for the top roll
12 and
the bottom roll 20 can be adjusted, in order that these transverse forces do
not
exceed a predefined value. Alternatively, possible deformations of the
15 intermediate rolls 14, 16, 18, in particular at their roll centre, can be
measured by
means of measuring elements. This measurement result can be included in the
power distribution of the drives for the top roll 12 and the bottom roll 20,
in order
also to minimize these deformations.
It should further be noted that the concept according to the invention is
2 o particularly suitable for re-equipping existing calenders, in which there
is often a
lack of space, or for narrower machines having a relatively low drive power
and
relatively stiff intermediate rolls.
