Note: Descriptions are shown in the official language in which they were submitted.
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PRESS SECTION FOR A PAPER MACHINE
The present invention pertains to a press section for a
paper machine with at least one pressing unit and to a section
downline from the press section.
In ~ost cases, the "downline section" would be another press section.
This can be a simple roll press with two rotatably supported press rolls. In
addition, a so-called "shoe" press could be considered, which has a rotatably
supported roll; a pressing shoe, which can be brought to bear against this
roll; and a sliding belt, which is conducted through the nip between the
pressing shoe and the roll. Finally, the "downline section" could also be the
drying section of the paper machine.
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A prior art press section is known from U.S. Patent No. a ::
4,561,939. This is known device comprises a first press unit :~
with two press rolls and a shoe press downline from that.
Each of these two press units has an upper felt and a lower
felt.
~ orld Patent No. 88/8,051 also describes two press units, both of which
are shoe presses. A suction roll is used to transfer the web between the two
press units. In the transfer region, the paper web travels along an S-shaped
paeh. Here, too, the two press units are double-felted.
In general, the transfer region between the press unit (which can be the
only press unit or one of several press units) presents a number of problems.
First, the transfer region shoult be designed in such a way that the upline
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press unit can remove the water from the pap ~ n~ ~ optimum manner. This
is, of course, the most important function of a press section. After the
paper machine has been shut down and is then to be started up again, it should
also be possible, however, to feed the transfer strip from the first press
unit to the downline section in an easy and reliable manner.
In the prior art, it has been impossible to satisfy these two
demands at the same time. In the case of a double-felted
press section, the paper web travels jointly with the upper
felt and the lower felt through the nip of the pressing unit.
The paper web is enclosed like a sandwich between these two
felts. The two felts absorb
water from the paper web in the nip. At this location there is the danger
that water can flow back from the two fel~s into the paper web, which there-
~ fore becomes wet again. To prevent this, ehe two felts should be sepsrated
¦ fro~ the paper web as soon a~ possible after they have passed through the nip.
Accordingly, at least one of the two felts should be guided in such a way
after leaving~the nip that an angle of divergence is created between the paper
web and the felt. After the paper machine has been turned off or after a tear
in the web, it is necessary to "feed" the web through again, that is, to
threading a narrow strip of the paper or the entire width of the paper web
through the sections in question again. To accomplLsh this successfully, the
initial section of the web must be guided as straight as possible through the
transfer region. It is therefore undesirable for the paths along which the
' beginning section of the web the felt are guided to diverge from one another.
Wire screens are sometimes used in place of the press felts mentioned.It is an object of the present invention to provide a
novel press section for a paper machine which obviates or
mitigates at least one of the above-mentioned di~advantages of
the prior art.
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According to a first aspect of the present invention,
there is provided a press section for a paper machine with at
least one press unit and another unit downline from the press
section, comprising:
at least two belts;
two pressing elements forming a nip therebetween, each
pressing element being partially wrapped by one of said belts;
a pair of guide rolls guiding each of said belts, a first ~ -
guide roll of each pair being a deflection roll located
downline from the nip and being movable toward and away from a
paper web to msve its associated belt away from a paper web,
one of said deflection rolls being spaced farther from the nip
than the other of said deflection rolls, the belt associated
with said one of said deflection rolls operable as a transfer
belt to transfer said paper web to said unit downline;
a suction box located at the nip between said one of said
deflection rolls and the transfer belt, the trailing edge of
the suction box being rounded and the box being movable
between operating and non-operating positions;
a third belt associated with said unit downline and
overlapping said transfer belt.
The invention is based on the task o~ designin8 a press section with a
downline unit for a paper machine in such a way that the problems of the
transfer region are avoided. The machine is therefore to be designed in such
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a way that optimum pressing work is ensured during standard operation, with as
little rewetting of the paper web as possible, and also so that satisfactory
eransfer of the transfer strip can be achieved when the strip has to be
threaded back through again after the machine has been stopped.
Accordingly, the two deflection rolls which deflect the upper and lower felts
of the first (and possibly the only) pressing unit after the nip are supported
in a displaceable or movabl2 fashion 90 that they can be taken out of the
plane in which the paper web tra~els during normal operation.
In particular, the following advantages are thus derived:
After the paper machine has been idle or after the web has torn, the two
units, namely, the first press unit and thc downline unit, can run in complete
independence of each other. For example, the first pres3 unit (possibly the
only pressing unit) can be started and brought up to normal speed, while the
downline unit remains idle at firse. This can be advisable in an initial
phase, e.g., to allow the felts to be threaded through. During an inieial
phase, the paper web itself still travels through the flrst press unit and
possibly through the second press unit and is then contucted into a vat
located in the machine ba~ement underneath the press. ThLs downward deflec-
tion of the web is facilitated or made possible in the first place by the
capacity of the two deflection rolls to be displaced in accordance with the
invention.
Because of the ability of the deflection rolls accorting to the invention
to be moved to a different position, it is possible to direct the web along an
essentially straight line. This ~akes it possible to guide both the transi-
tion strip and also the complete web easily and accurately. In addition, itis also ensured that the paper web remains on the transfer felt (upper felt)
both during the transfer process and later, after the complete wab has been
fed through.
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As soon as stable operation has been achieved, one of the two deflection
rolls is moved in such a way that the paper web and the felt in question div-
erge from each other at a certain angle.
A preferred embodiment of the invention will now be
', described, by way of example only, with reference to the
attached Figures, wherein:
Figure 1 shows a press section in accordance with thepresent invention in its configuration prior to the start of
the paper making machine;
Figure 2 shows the press section of Figure 1 in its
configuration to effect transfer o~ a web; and
Figure 3 shows the press section of Figure 1 in its
normal operating position.
The press section comprises two press units, each of which is designed as
a shoe press. The press which comes first in the direction of travel of the
paper web (see arrow A) comprises a press roll 1. This operates together with
a pressing element, which consists essentially of a pressing shoe 2 and an
impermeable press belt 3, which wraps around the shoe. These two form
together a press nip, which extends for a considerable distance in the travel
direction of the paper web. Two felts 4, 5 pass through the nip. These two
press belts pass around not only pressing elements l, 2, and 3 but also around
a series of other components. For example, lower felt 4 wraps around guide
¦ rolls 6, 7, and upper felt 5 wraps around a suction takeoff roll 8, a suction
box 9, and a guid- roll 10. Additional guide rolls are present, but they are
not shown here. Suction guide roll 8 receives the approaching paper web from
I the wire ~ection, namely, from wire 11.
I The second press unit also has a press roll 1.1 and a pressing element
¦ cooperating with it, co~prising a pressing shoe 2.1 and a press belt 3.1,
which wraps around the shoe. In contrast to the first press unit, which is
double-felted, the second pressing unit has only a single felt, namely, lower
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felt 12.
After the second press unit comes the drying section, of which only a
guide roll 20 and a drying screen 21 are visible. The paper web is trans-
ferred from press roll 1.1 to drying screen 21.
Especially important for the implementation of the invention is the fact
tkat at least the two last (seen in the direction of travel of tha paper web)
guide rolls 7, 10, referred to in this application as "transfer rolls", are
movable in tha direction of arrows B and C. The capacity for movement can be
achieved in practice by the use of guide rails, which extend in the direction
of arrows B, C, and on which the bearings of the two transfer rolls can be
pushed. The two rolls can also be moved by means of pivoting levers. To
facilitate the transfer, a transfer blade 1.5 is provided on press roll 1.1.
The three figures represent specifically the following phases of oper-
ation:
Figure 1 shows the phase before the paper machine ls started, e.g., the
first phase after the shutdown of the paper machine, such as after a preceding
maintenance process, after the replacement of the wire, or after a change of
felts.
One of the ewo deflection rolls of this first press unit, namely, deflec-
tion roll 10, has been backed off in the direction of arrow C, so that there
is no longer any connsction between the two press units by way of the felts.
Suction box 9 has a erailing edge, which is rounded. For this resson, deflec-
tion roll 10 can be moved a considerable distance in the upward direc~ion, and
uppar felt 5 can make a small bend there. The two press units can now be
operated independently of each other. This situation can be necessary for a
certain period of ti~e after new felts have been pulled through, but it can
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also be useful when it is necessary to clean ~he felts.
At a certain point, the pulp suspension begins to be deposited on wire 11
from a headbox, not shown here, and the web starts to travel onward. At this
point either only a narrow transfer strip or the entire paper web is threaded
through. Then the transfer strip or the paper web runs automatically eo the
un$t downline from the first press unit, i.e., to a second pressing unit, for
example.
Before the transfer strip or web is transferred from the first press unit
to the second press unit, the two deflection rolls 7, 10 are moved into posi-
tions which allow the two felts 4, 5 to travel parallel to each for as long as
possible. This is the plane in which later the paper web will run during nor-
mal operation. This phase ls shown in Figure 2. As can be seen, roll 7 is in
its upper position (as already seen in Figure 1), whereas roll 10 has been
lowered. It has been lowered to such an extent that felt 5 now touches lower
felt 12 of the second press unit. This is in the area of a guide roll 13 of
lower felt 12. Guider roll 13 has a suction zone 14. In this phace1 the
vacuum to the suction box is on; suction box 9 is therefore operating, and the
transfer strip or the web is held agsinst upper felt 5.
As can be seen, the transfer of the transfer strip and the paper web pro-
ceed~ with almost no change of direction. In any casa, there are no abrupt
changes of direction with small radii of curvature. In no case whatever is
there an S-~haped deflection. The transfer proceeds essentially along a
straight line.
Figure 3 illustrates the phase of normal operation. The transfer strip ~ ;
spreads out at a certain point to assume the full wldth of the web, so that
ths web now travels in its full width through the first press unit, across the
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~ransfer section, and through the second press unie. Now, while the suction
box vacuum is still operating, roll 7 is lowered in the direction of arrow B.
The suction box reduces the rewetting of the paper web after the web has
passed through the first nip, but it also prevents the web from adhering to
lower felt 4 and from continuing to travel with it. Upper felt 5 and the web
therefore emerge from the first nip together.
During normal operation, the vacuum at suction box 9 is off, so that the
web can stretch out after the first, double-felted pressing unit.
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