Note: Descriptions are shown in the official language in which they were submitted.
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`. 1
TITLE
~n apparatus for reducing the amount of water in
a moist and wa*ery material web.
TECNICAL FIELD
Thc present invention relates to an apparatus
for reducinc3 the amount o water in a moist and wa-tery
material web, by means of one or more press nips, each
being provided between a press roller and a roller-
formed body, which at least to a certain part being
deformable Eor controlling of the length of said press
nip.
THE STATE OF THE ART
In, for example, a paper or cellulose machine, ~
dewatering or demoisturizing of a moist and watery fibre
web, which-in such an event aonsists of a paper web, is
ca.rried out in the press section of the machine, after
transfer of the web from the forming section of the
machine. In the transfer from the formincJ section to the
press section, the paper web has a relat ~ely low dry
solids content. It is desirable to remove as much water
as possible from the paper web in the press section,
since subsequent dewaterinc~ by~drylng in a subse`quent dry
in~ section in~the~machine is ~onserably more~expensive.
n the press section, ~a plurality of~press ni~ps
are normally provided which~are formed of two coope~ra-
ting rollers. It is~also passible~that~the one of the
rollers is provided~with a~suction ~one~for facili-
tating the remo~al o~water from the fibre web. The
moist fi.bre;web is -transported and moved through the
press nip by means of one or more press felts and possib-
:~
Iy also a press wire. The press nip formed between thetwo press xollers has, because of the contact between the
rollers, theoretically the form of a line in the axial
direction of the rolle~s and, because of a certain
compression as a resu]t of the compression pressure,
the line has a certain width. Thereby, the press nip
may be considered as having a certain lenqth in a direc-
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tion at ri~lht an~Jles to the axial direction of the rollersand a narrow press zone is thereby formed. The compression
pressure in the zone runs from zero rapidly up to a maxi-
mum level and thereafter rapidly fa]ls off to zero. ~i
Because of the rapidly increasing compression pressure,hydraulic counter-pressure can be built up in the felt
because this is not capable of storing and conveying off
the amount of water which, during a very short time, is
pressed out from the fibre web. When this hydraulic coun-
ter-pressure reaches a certain level, so-called crushing
occurs in the paper web, and, consequently, the compres-
sion pressure and/or the machine speed must be reduced
with a consequential reduction of production. The pro-
duction capacity of a paper machine is, thus, dependent
- 15 upon the size of the hydraulic counter-pressure in the
felt which, in its turn, is dependent upon the compres-
sion pressure and the machine speed.
Consequently, several methods ha~e been deve]oped
for reducing the hydraulic counter-pressure. The felt-
wire press with an incompressible wire gauze is one method;
another method is the application of a combination felt in
which the base portion proper is incompressible and is
open in order to allow for storage and removal of the
pressed-out water.
A further method is to extend the press nip or press
nip period, that is to say that period during which the
fibre web is subjected to compression pressure. According
to this method, it is attempted to exercise compression
pressure for a longer period of time than in normal press
nips. This methodology has also been developed for making
possible the application of one-step pressing, that is
to say a reduction of the number of press units to a sole
unit as a result of the extended pressing period.
ln one of the prior art apparatuses, the extended
press nip is realised in that one or more press belts co~
operate with a press roller. The moist and watery paper web
is introduced betwcen the press belt and the press roller
together with a press felt and possibly also a press wire.
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The compre.;,sion pressure between the press belt and the
press roller must a~ount to approxlmately
2-3MPa for attaining the desired dewatering effect. For
attaining such a high compression pressure, the specific
tensile force in the press belt will be very high and
great difficulties have been experienced in being able
to manufac-ture a press belt wh:ich permits of such high
compression pressure. If the diameter of the press roller is
1,5 m, the press belt must, Eor attaining the above-
mentioned compression pressure, be able to tolerate atensile force of 1,5-2,3 MN/m. This has entailed that
such apparatuses for realising extended press nip have
not come into practical utilisation. The great tensile
force in the press belt also entails a risk for bending
the pivot rollers of the press belt, which in its turn
entails an uneven distribution of the compression pressure
in the press nip.
U S Patent Specification No 3 808 096 describes an
arrangement with an extended press nip which consists of
a press roller and an endless belt. The endless belt
forms an enclosed compartment for-accommodating a liquid
under excess pressure. The pivot rollers are disposed
` within the belt for retaining it in operative position.
The position on the rollers determines the length of
the press nip and this cannot be changed without a re-
placement of the press belt. This entails a great in-
convenience in being able to regulate the length of the
press nip. Since the press nip is of great length, there
is a risk for permanent compression of the paper web,
whereby this obtains a resultant poor bulk. When the press
nip is of slight length, the spedific compression pressure
must be raised for obtaining the same dewatering capacity,
Which entails a risk for crushing both the paper web and
the press felt.
U S Patent Specification No 3 293 121 describes an
arrangement with a deformable roller-like body positi~ned
between t~o rollers. The deformable roller-like body pro-
vides together with one of the rollers an extended press
nip controll1ng in length and pressure. The roller-like
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body ~ S to be jollrnal]ec1 :in the frame of the machine in
order to be posit:Loned and the momerlts provided during
the opcration of the roller-like hody has to be transfered
from the envelope surface of the body to the shat of
the body. secause of the deformable na-ture of the roller-
like body the only possib]e connection between the enve-
lope surface and the shaft is via the gables. These gables
has to be f1exiblc in order that thelr form has to follow
the form of the roller-like body. This is one of the main
problems with the arrangement described in the above men-
tioned patent.
TECHNICAL PROsLEM
It is desirable to rcduce the inconven:ienses inherent
in prior art methods and arrangements for realizing an
extended press nip and, in general terms, to improve the
pressing-out of moisture and water from a fiber web
without any resultant deterrioriation of its quality.
Particulaly it is desirable to cancel the use of
press bands because of the high demands on the ~tension
strength of the press band creatinq both manufacturing
problems and problems with the stiftness of the rollers
carrying the band in operation.
Furthermore, it is desirable to use a deformable
roller-like body without the practical inconvenienses
with the tranfering of driving moment from the envenlope
surface to a journalled shaft.
SOLUTION
According to the present invention the above-
outlined tenchical problem frame work is solved in that
the apparatus discosed by way of introduction is characte-
rized in that said roller-formed body being a central
roller in cooreration with at least three satelite rollers
positioned around the central roller for positioning said
roller in a balanced condition, i.n that said press nip
being provided between at least one of said satelite
rollers and said rollèr-formed central roller and in that
the pressure b h~een said satelite roller and said roller-
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formcd centra] rol]er being controllable almost independent-
ly of the lencJth of the press nip, provided by the defor-
matlon, by a change of the pressure inside said roller-
formed body.
ADVANT~G~S
In an apparatus according to the present invention,
the roller-lilce body needs no pivo-t rollers which, as a
result o~ bending, may give rise to uneven compression
prcssure.
According to the present :invention, the roller-
like body is constructed such that an increase in pressure
at normal excess pressure merely entails a very slight
change of the size of the press nip. Completely independently
of the pressure the length of the press nip is adjustable
by a regulation of the distance between the fixed press
rollers.
The arrangement according to the present invention
permits that the roller-like body need not be fixedly dis-
posed between ~he press rollers, by which is meant fixedly
journalled. Merely side blocks need be disposed at the
ends of the roller-like body in order to prevent it from
"wandering" in an axial direction.
With several press rollers and one roller-like
- body, the press nip may optionally be divided up into
several small press zones or one single long press zone.
The different press zones may be individually felted, that
is to say different felts run through the different zones,
whereby the dewatering capacity is increased.
The arrangement according to the present invention
permits also substantially vibration-free operation and
places low requirements on space.
When three press rollers are placed with equal angular
spacing, three press nips will be obtained of the same length
and compression pressure. By means of extra support rollers
on the roller-]ike body, the length and pressure in the
different press nip.s may be rcgulated separately. Thls can
be appropriate for reducing or lowering the length and
pressure in the Eirst press nip.
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In that t:he rol]er-like body .is deformable, the risk
of burning the fe]t ~ecause of the collection of wadding
ahead of tlle press nip will be reduced, since the passage
of wadding is allowed because of the deformation capacity
of the roller-]ike body. The press nip may also be considered
as fle~ible to a cer-tain degree, whereby -the felt is not
broken up by pulp waste which, in conventional apparatuses,
often penetrate into the felt.
The roller-like body according to the invention may
be divided into different compartments and these may con-
tain different media. The division of the interior of the
roller-like body into different compartments results in spa-
ces of small volume, whereby the risks in possible leakage
are to a great extent obviated.
DESCRIPTION OF TIIE ACCOMPANYING DRAWINGS
Fig 1 schematically shows a side elevation of an
embodiment of an apparatus according to the present inven-
tion. Fig 2 schematically shows a side elevation of a
further embodiment of an apparatus according to~the
present invention. Fig 3 shows, on a larger scale, a
schematic part side elevation of the embodiment of the
present invention shown in fig 1. Fig 4 shows, on a larger
scale, a schematic side elevation o yet another embodi-
ment of the apparatus according to the present invention.
Fig 5 shows, on a larger scale, a schematic side elevation
of still a further embodiment of the apparatus according
to the present invention. Fig 6 shows, on a larger scale,
a schematic side elevation of a further embodiment of the
apparatus according to the present invention. Fig 7 shows,
on a larger scale, a schematic side elevation of a further
embodiment of the apparatus according to the present
invention.
The embodiment of the apparatus according to the
present invention shown in fig 1 forms a press section in
a paper machine, par~s of the forming section and a drying
section of the paper machine being also shown.
Or a forming wi--e 2, which comes from the forming
section, a fibre web i is formed. The continuous fibre
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wcb is îemo~ed from the wire 2 hy means oE a pick ~p
roller 3. ~rhe fibre web 1 runs around thc roller 3 into a
first press nip 4 bctween the press roller 3 and a roller-
like body 5. sy means of further press rollers 8 and 9,
furtherpress nips 6 and 7 are arranged against the roller-
like body 5. The fibLe web 1 passes the press nips 4, 6
and 7 and leaves -the press section by the intermediary
of a removal roller 10 and is fcd from the press section
to a drying section, of which but a part is shown. Apart
from the fibre web 1, a press wire 11 and a press 12 pass
through the first press nip 4, these running over return
rollers 13 and 14, respectevely. At the press felt 12,
two suction boxes 15 are provided for dewatering the
felt. The press wire 11 is incompressible and, thereby,
the first press nip 4 may be considered as forming a so-
called felt wire press. The fibre web 1 passes through the
two otherpress nips 6 and 7 together with press felts 16
and 17, respectively which are disposed on return rollers
14 and at whlch ~re provided suction boxes 15.
In fig 2 is shown an embodiment of the present
invention which is arranged in a conventional press
section. The lower press roller has, according to the
present invention, been replaced by a roller-like body
18 which is supported by two support rollers 19 and an
upper press roller 20. The fibre web 1 passes through the
thus formed press nip 22 together with a press felt 21
- which runs over return rollers 14.
In fig 3 is shown the embodiment according to the
present invention shown in a press section in fig 1,
on a larger scale.
In fig 4 is shown a simialar embodiment to that of
fig 3 but with a further small press roller 23 for forming
a further small press nip 24 against the roller-li]ce
body 5. The press nip 24 forms a so-called prepress nip.
It is, naturally, not necessary that all of the con-
tact zones between the roller-like body 5 and the circum-
jacent rollcrs constitute press nips; one or more of the
contact zones may instead constitute support zones. The
pressure rollers 3, 8, 9 may ha~1e dif~erent diameters and
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be pos.i.~ioncd wi.tll di.fferel1t angular spacirlg. The pressure
inside ti1e roller~li.ke body 5, the anyular spacing of
the pressure rollers and -the distance between the pressure
rollers are adju.stable durlng operation in order to cont-
rol the specific compression pressure and the length of
the press n.1p independent]y o:E each o-ther. Furthermore,
the different press nips need not be individually felted.
One and the same felt may pass through several press nips.
Furthermore, several felts may be disposed in one or more
of the press nips, the paper web passing through the press
nip located between, for example, two felts.
In fig 5 is shown a part of an embodiment of an
apparatus according to the present invention, according
to wich a fibre web 1 runs through a press nip 25 between
15 two press felts 26 and 27. The press nip 25 is formed
between a roller-like body 5 and three press rollers 3, 8
and 9.
In fig 5 is shown an arrangement of an apparatus
accordiny to the present invention, which arrangement
is of principally the same type as the arrangement shown
in fig 3 with the only exeption that the angular spacing
between the rollers is different. The angular spacing
between the rollers 3 and 8 is less, while the angular
spacing between the rollers 3 and 9 is larger and largest
between the rollers 8 and 9.
The invention is not limited to the arrangement
of three press rollers or satelite rollers. In fig 7 is
shown an embodiment of the present invention with a central
roller-formed body 28 and for satelite rollers 29, 30, 31,
30 32. There are press nips 33, 34 between the c-entral roller
28 and the satelite rollers 29, 30 and it is possible to
arrange press nips between the central roller 28 and the
other satelite ro]lers 31, 32.
An apparatus according to the present invention may
also be used for other types ol treatment of a fibre web
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tharl dewate.r:i.ncJ. For ev.clmple, the apparatus may he used
in cale]lderincJ, in whi.ch it is not necessary to include the
elts in the ~ystem.
I-t should further be pointed out that it is desi,rable
that the roller-like body 5 be of a construction which
permits expansion to a certain diam~ter, in which a further
pressure increase withi,n the rol].er-l:i.ke body 5 should
no-t r.esult .in any appreciabl.e .increase of the diameter of
the roll.er-like body, but should merely give rise to an
increased spec.ific pressure in the different press nips.
Obviously the roller-like body 5 may be called a
central roller and the pressure rollers 3, 8, 9 may be
called satelite rollers in the different embodiments
described and shown.
