Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1045433
The present invention concerns a wet press
in a tissue paper machine.
As known in prior art, the press section of a
tissue paper machine consists either of a conventional wet press
and/or two press rolls, which are urged against a large diameter,
so-called Yankee cylinder constructed for evaporation drying.
The drying section, again, consists either of said Yankee cylinder
alone or of this cylinder together with the so-called after-dryer
following thereafter. In both cases the drying of the web takes
place by effect of evaporation when the wet web is brought into
contact with the surfaces, heated by means of internal pressurized
steam, of the Yankee cylinder and of the after-dryer, if any.
From the smooth surface of the Yankee cylinder the web that has
become adherent thereto is detached at the end of the drying zone
with the aid of a doctor blade, which produces in the web the
creping obtained by the upsetting effect. The paper that has
been creped in this manner is then transferred to the after-dryer
and to potential marking prior to reeling. The after-dryer con-
sists of a number of normal steam-heated paper machine drying
cylinders. Especially in the case of the thinnest tissue paper
brands the after-drying may be omitted.
In tissue paper machines of prior art the thin
paper brands are usually dry-creped when the moisture content of
the web is about 5 to 10%, while thicker brands from 25 g/cm base
weight upwards are more commonly subjected to wet creping in which
procedure the moisture content of the web is approximately 40 to
50%, whereby the above-mentioned separate after-dryer is needed
to remove the residual moisture. Its absence restricts the use
of the dry crepe machine to the nominal purpose only. The wet
crepe machine, in contrast, may also be used to turn out dry crepe
paper if the wet press, which mostly has to be used in the
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manufacturing of wet crepe, can be conveniently bypassed. The
after-dryer remains unnecessary, of course.
In the tissue paper machine wet presses of prior
art certain drawbacks have presented themselves, such as the fact
that after the press nip the web no longer follows reliably along
with the Yankee felt (the top felt), and these drawbacks have
constituted part of the motivation for the present invention.
An object of the present invention is to provide in
a tissue paper machine a wet press wherein the conduction of the
web can be improved from what it was before, e.g. so that the
web follows more positively along with the Yankee felt.
It is a further object to enhance the dewatering
in the wet press and to achieve a two-sided, and as symmetrical as
possiblej dewatering action.
Since in tissue paper machines a wet press is
required which could be taken into operation and out of operation
by simple means and preferably even while the machine is running
(by-pass possibility), it is one of the objects of the present
invention to arrange for the said by-pass possibility. In this
connection reference is made to the same applicant's Finnish
patent 51976 of May 10, 1977, the wet press of which is mainly
characterized in that the lower roll of the wet press and at least
one of the adjacent felt guiding rolls are mounted on a movable
base, which can, when desired, by means of a suitable power means
be moved away from the paper web to such a distance that the web
may pass freely through between the press rolls without touching
the felt lapping the lower roll.
Therefore, according to the present invention, in
a tissue paper machine provided with a Yankee cylinder there is
provided a wet press wherein a paper web is conducted to pass.
The wet press comprises an upper suction roll,
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a lower recessed surface roll, arranged to be urged against the
upper suction roll for defining a first press nip therewith, a
second nip defined between the upper suction roll and the Yankee
cylinder, and a third nip defined between the Yankee cylinder
and a further recessed surface roll. Two felts sandwishes the
wet during its passage through the first nip.
In the following the invention is described in
detail with reference to certain embodiment examples of the inven-
tion, presented in the figures of the attached drawing, but to
which the inventionisnottobe exclusively confined.
Fig. 1 shows a wet press according to the invention,
in schematic elevational view.
Fig. 2 shows another wet press design according
to the invention, in schematic elevational view.
As shown in Fig. 1, the web W formed on the wire
10 is transferred with the aid of a pick-up roll 12 onto the
Yankee felt 13. The web W is inaicated in Fig. 1 with a dot-
and~dash line, and the return roll of the forming wire 10 is
indicated by the reference numeral 11~
The tissue paper machine wet press of Figure 1
comprises a lower roll 14, and an upper roll 16, which rolls are
rotatably carried in a manner known in itself in prior art, in
the frame 30 of the machine. The web to be treated, W, arrives,
adherent to the lower face of the Yankee felt 13, to the nip N
defined by the rolls 14, 16. In the said nip Nl the web W is
interposed between two felts, namely, the said Yankee or pick-up
felt 13 and the lower felt 20, the guiding rolls of which are
denoted with 18 and 19. After leaving the said nip Nl the web
follows positively along with the Yankee felt 13, going to the
roll 24, which defines the nip N2 together with the Yankee cylinder
26. In association with the Yankee cylinder 26 even another nip
N3 is formed in connec~ion with the roll 25, and after the said
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nip N3 the course of the Yankee felt ]3 and that of the web W
separate, the web W continuing its travel on the surface of the
Yankee cylinder 26.
In order to obtain a symmetrical and efficient
dewatering action and to make sure that the web W follows reliably
along with the Yankee felt 13, the roll used as lower roll is a
recessed surface roll 14, and the upper roll is a suction roll 16.
A recessed surface roll is understood to mean any such drilled
or grooved roll the cavities of which serve transiently as a place
of storage for the water escaping in the press nip and from which
the water may be removed e.g. by means of the doctor blade 27.
It is thus understood that the lower roll 14, is e.g. a grooved
roll, a blinddrilled roll, a roll coated with a plastic wire, or
another equivalent recessed surface roll. As can be seen from
Fig. 1, the upper roll 16 is a roll provided with a suction zone
17. The said suction zone 17 commences at the nip Nl and continues
forward in the direction of travel of the web W through the angle
indicated in the figure. This suction zone 17 causes the
reliable transfer of the web W along with the Yankee felt 13.
Moreover, by action of the suction zone 17 water is also removed
upward, whereby a two sided and substantially symmetrical dewatering
action is obtained. In Fig. 1 the recessed surface of the lower
roll 14 has been indicated with 15.
In the manufacturing of dry crepe with the tissue
paper machine just described, the wet press may be disconnected
from operation by turning the frame 22 of the lower roll 14 about
its pivot 21 into its lower position. This can be accomplished
e.g. with the aid of the power means 23, which have been schemati-
cally showninFig. 1. As regards the conversion of the wet crepe
machine just described to be appropriate for the manufacturing of
dry crepe and the by-passing of the wet press, reference is made
to the same applicant's earlier Finnish patent 51976 of May 10, 1977;
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the structurespresented therein may also be applied in connection
with the wet press of Fig. 1. This is accomplished in the manner
just described, in that the upper roll I6 is a fixedly installed
suction roll and the lower roll 14 is a recessed surface roll that
can be displaced from its position by means of a pivot 21 or
equivalent.
As regards the mutual positioning of the rolls 14,
16 it is advantageous if the centre of the upper roll 16 lies
slightly forward in the direction of travel of the web W from the
vertical plane passing through thecentre of the lower roll 14.
The roll 14 may, if required, be fitted with compensation for its
deflection, but this is by no means always necessary.
Referring to Fig. 2, wherein an advantageous
embodiment of the tissue paper machine wet press according to
the invention is presented. For greater ease of understanding
the description, those structural components which correspond to
components occurring also in Fig. 1 have been indicated with
identical reference numerals. The web W formed upon the wire 10-
is transferred with the aid of the pick-up roll 12 onto the
Yankee felt 13. As in Fig. 1, the web has been indicated by a
dot-and-dash line, and the return roll of the forming wire 10
has been denoted with 11. The reference numeral 31 indicate the
guiding roll of the felt 13 and web W.
It has been understood in the embodiment of Fig. 2
to make use of the roll 24 of Fig. 1, which already exists, and
which thus in the present embodiment is the equivalement of the
suction roll 16 of Fig. 1. Hereby one suction roll is saved,
and part of the frame structure. It is thus now understood that
the wet press comprises the lower roll 14 and the upper roll 24,
which rolls arerotatably carried in a manner previously known in
itself. The web W to be treated arrives, adherent to the lower
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face of the Yankee or pick-up felt 13, to the nip Nl defined by
the rolls 14, 24, where, as in the preceding embodiment, the web
W is interposed between the Yankee felt 13 and the lower felt 20.
The rolls 18 and 19 serve as guiding rolls of the lower felt 20.
After leaving the said nip Nl, the web W arrives, following along
with the Yankee felt 13, at the nip N2 defined by the suction roll
24 and the Yankee cylinder 26. It is thus observed that in this
embodiment, differing from the preceding embodiment, the suction
roll 24 has two suction zones, 17 and 17'. The web passes, after
leaving the nip N2, adherent to the surface of the Yankee cylinder
26, and the Yankee felt 13 travels over the guiding rolls 32 and
33 to the roll 25, which is a blind drilled roll. The Yankee felt
13 may, of course, also be carried as-in Fig. 1 directly from
the suction roll 24 to the said roll 25, but the arrangement of
Fig. 2 enables the water absorbed by the felt 13 from the web W
to be removed in a manner previously known in itself (not depicted)
prior to conduction of the felt 13 to the roll 25. The Yankee
cylinder 26 and the said roll 25 define a nip N3, and after leaving
said nip N3 the courses of the Yankee felt 13 and the web W go
apart, the web W continuing its travel upon the surface of the
- Yankee cylinder 26.
In this embodiment, too, a symmetrical and efficient
dewatering action is obtained at the nip Nl defined by the suction
roll 24 and the roll 14 with recessed surface 15, and in addition
it is ensured that the web W follows reliably along with the Yankee
felt 13 after the nip Nl. The angular width of the suction zone
17 of the suction roll 24 is denoted with a in Fig. 2. The
suction roll has furthermore a second suction zone 17' substantially
opposite to the nip N2! and its angular width is denoted with
a'. Of course, water escapes in one direction only at the suction
zone 17', whereas, as has been said, the dewatering is in two
directions at the suction zone 17.
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It is also possible in the embodiment of Fig, 2
to take the wet press out of operation when dry crepe is being
manufactured on the tissue paper machine, and this is done by
turning the frame of the lower roll 14 about its pivot into the
lower position. In Fig. 2 the frame structure of the lower roll
14 has not been depicted, because it may be completely the same
structure as in Fig. 1.
In the foregoing only two advantageous embodiments
have been presented, and it is obvious to one skilled in the art
that numerous modifications of these embodiments are possible,
without digression from the protective scope of the invention.
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