Note: Descriptions are shown in the official language in which they were submitted.
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The present invention concerns a pxocedure applied in
the press section of a paper makiny mach~ne, wherein the paper or
paperboard web coming from the wire is conducted through nips
defined by press rolls, in closed conduction, so tha~ the web is
continually supported adherent either to a felt or to the surface
of a roll, and in ~hich procedure the web is detached from the
wire and subsequently conducted through at ]east two press nips
dewatering the web, the first of these dewatering press nips
being defined by two press rolls each provided with its own felt
and the second being defined by a roll with smooth surface and a
suction roll belonging to the first press nip.
The press sections in connection with which it is
intended to apply the invention are known and they operate
substantially as follows. The paper web is detached Erom the
wire with the aid of a pick-up roll, whereby the web becomes
adherent to the lower surface of a felt lapping the pick-up roll,
and this felt conveys the web further to a first dewatering press
nip, a suction roll belonging to this press nip being located
within the same felt loop as the said pick-up roll. The arrange-
ment just described is the most common arrangement of pick-up
transfer known in prior art, and in its operation certain limita-
tions and drawbacks have been observed, which the present
invention aims to eliminate.
In systems of prior art the run of the pick-up felt
between the wire and the first dewatering nip is substantially
horizontal. On this run, the web is adherent to the lower surface
of the pick-up felt merely by effect of surface tension force.
;~ The surface tension force per unit area of the web must exceed
the base weiyht of the wet web, as otherwise the web ~ould be
~,^ 30 separated from the surface of the web and cause a production
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shut-do~ t fol:Lows -that a pick-up transfer of this kind is
only fit for use in the manufacturing of comparatively thin paper
grades, bu-t it is not usable when the paper machine i9 used to
handle a web which is heavy ei-ther due to its inherent base weight
or to its water content.
- In order that the surface tension force might be opera-
tive, it is furthermore necessary that there is a good contact
between the web and the ~elt and that between them is an appro-
priate water interface. ~his implies that the pick-up felt has
; 10 to meet certain requirements of textile technology e.g. A9
regards its surface s-tructure and its porosity. It should be
noted, however, that in the conventional pick-up system one and
the æame felt serves both the -transfer to the press nip and the
dewa-tering pres3ing process itself in the press nip in question.
Those characteristics o~ the felt which are advan-tageous when
the web is detached from the wire and -transported forward thence
are not always required in the pressing process. Owing to the
reasons mentioned, the conventional pick-up transfer is no per-
fect process from the viewpoint of the operation of the paper
machine nor from that of the quality which the paper thus turned
out will ha~e.
~ he object of the invention is to teach a procedure
for application in connection with a press section as defined
I in the introduction, and by the aid of which it is possible to
- improve the efficiency in operation of the paper machine and its
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running reliability on the whole, and particularly in those -
' instances in which paper and paperboard grades with a relatively
~3~ ' great thickness are being made, as well as in cases in which it
; is desired to optimate the operation of the press section with
regard -to its efficiency of dewatering, at the same time observing
~ high quality requirements imposed on the surface of -the paper.
; In order to attain the aims stated, the i~vention is
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mainly characteri%ed in that in -the procedure the web is detached .~
from -the wire by the aid of a pick-up roll which opera-tes within ~ -
a separa-te felt loop of its own, that after its detachment from
the wire the web is adh0rent to the lower surface of the pick-up
felt over a part of same substantially consistent with -the suction
sector of the pick-up roll, that the web is subsequently detached
from the pick-up fe~t by means of a suction trallsfer roll.oper-
ating within a felt loop of its own, in such manner that after
the last-mentioned point of detachment the web will be supported
~0 from below by the felt of the suction transfer roll, and that the
felt of the suction transfer roll con~eys the web to the first
dewatering press nip so that the pick-up fel-t is no longer
invol~ed in the said first press nip.
~ he impro~ement in the operating efficiency of the
paper machine achie~able by the aid.of the invention arises from
the fact that when this invention is practiced -there are more
~ extensire possibili-ties of selection of the pick-up felt as
regards its quality and characteristicsO In prior art, it was -~
necessary in the choice of pick-up felt and in the determination
of the felt ~uality to mind the following factors~ among others:
- the pick-up transfer and the adherence of the web to
the felt,
- the pressing process and dewatering in the first nip,
- the pressing process in -the second nip, and .;
. - the effect of the felt on paper marking and structure
of the paper.
~ hose characteristics which a felt is required to possess
. in view of an optimal pick-up detachment from the wire, or those
j.......... surface characteristics of the felt which are necessary precondi-tions ensuring that the web remains adherent to the lower surface :~
of the fe~t, are quite often greatly different from the characte-
ristics which are desirable from the viewpoint of the dewatering
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action in the press nlp.
: When the pre.sen-t inven-tion is appl:ied, it is only
necessary to pay attention to two functions of the felt: first,
to -the detaching of the web l`rom the wire and its transfer onto
a felt belonging to -the first nip~ and secondly -to the influence
of -the pick-up felt on the surface or structure of the paper or
cardboard. This is a circumstance which greatly facilitates the
felt problems encoun-tered by the paper maker.
When the procedure of the present invention is applied, 10 it is po~sible to select for the felt such -thickness and porosity
parameters which are optimal with regard to the suction transfer
process, and it is possible to select a surface structure of the ~.
felt whioh is favourab}e in view of the quality of the paper that
is being turned out. ~he felt may al90 be selected, considering
the longest possible service life.
The inventi.on is described in detail in the following
with reference to certain embodiment examples of the invention,
presented in the figures of the attached drawing, but -to which
the invention is in no way confined.
~ig. 1 shows an embodiment of the invention in connec-tion
with a press section having three nips.
Fig. 2 shows the invention, applied in connection with
a press section in which the third dewatering nip is defined by
~ a separate pair of press rolls.
.; ~he paper web W is detached, between the rolls 5 and 53,
from the wire 52 by the aid of the pick-up roll 3, which operates ~.
within its own felt loop 32. ~he web W is kept adherent to the :
fel-t 32 by the suction prevailing within the roll 3. ~his suction
zo~e has been indicated with the reference numeral 31. ~he roll
3 is opposed at a distance equivalent to about 150-180 degrees
- of arc by the transfer suction roll 4, which operates within the
loop o~ its own felt 1a. ~he suction zone ~ the transfer sucti.on
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roll 4 has been indica-ted with 41 At the nip ~/~ defined by the
pick-up roll 3 together with the suction trans~er roll 4 the web
W is transferred from felt ~2 onto felt 1a. It should be par-ticu-
larly noted that at thls nip 3/4 no appreciable pressure is
exerted on the web W; this circumstance is significant in view
of the retention of porosity in the papex in the process of
manufacturing.
~ he pick-up roll 3 and transfer suction roll 4 are
preferably small-diameter and of light cons-truction, beca~se in
the nip ~/4 defined by them no pressure or loading is applied,
and this nip 3/4 is not intended to be a true dewatering nip.
When the web has been transferred to the felt 1a, this
felt conveys the web W to the first dewatering nip 2a/2b of the
press ~ection, which is defined by the rolls 2a and 2b and in
which nip 2a/2b pressing is accomplished between two felts 1a and
lb Ihe roll 2a is a cavernous surface roll, and 2b is a suction
roll with either a continuous suction zone 21 or with a plurality
of suction compartments, found for instance only opposite to the
nips 2a/2b and 2b/2c. Adherent to the surface of the felt 1b,
the web travels to the second dewatering nip 2b/2c, defined by
the rolls 2b and 2c. The roll 2c is a roll with smooth surface
and without felt, whereby the dewatering in this nip 2b/2c is in
the direction towards the suction roll 2b. At the nip 2b/2c the
web W transfers from the felt 1b to the roll 2c, which conveys
it to the third nip 2c/2d of the press system, where the roll 2d
is a cavernous surface roll and has been pro~ided with a felt 1d
of its own
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~ rom the third nip 2c/2d the web may be conducted in
conventional manner to the drying section. It is possible,
however, to fit additional nips operating against the roll 2c.
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; These may alternatively be provided with felts, if an enhanced
dewatering action is desired, or they may be without felt merely
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in vie~ of a smoothing effect, as is -the roll 2e, which has been
provided ~ith a 90~t coating.
According to Fig. 2, the press section comprises,
instead of the cavernous æurface roll 2d, a separate pair of
rolls 7,8, which de~ines a pxess nip. The roll 7 has a ca~ernous
surface and has been provided with a felt 72 of lts own, '~he roll
8 is a roll with smooth surface. The web W is detached from the
roll 2c in conventional manner and conducted, guided by rolls 63, ?
-to the nip defined by the rolls 7,8.
The felts of the systems depicted in the figures have
been denoted with reference nUmerals 1a, 1b, ld, 32, 72; the
felt guiding rolls, correspondingly, with 23, 33, 73. The suction
æones of the differènt rolls hare been indicated by 21, 31, 41, `
51, and the cleaning doctor of the roll 20 carries the reference
numeral 64.
'~he invention is in no way narrowly confined to the
embodiment examples presented in the foregoing, and a number of `-
modifications are possible wi~hin the compass of the present
invention.
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