Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
v
Case 5807
20~0~~3
Dr. Eberhard Janssen
A BELT FOR PAPERMAKING MACHINES
The invention concerns a belt for papermaking machine, in
particular for wet-presses with extended press nips, said belt
comprising a flexible, liquid-impermeable layer smooth on its back
and receiving only in part on its top side a textile so as to form
open cavities.
In wet-presses of papermaking machines, a substantial part of
the liquid still in the paper web is forced out between loaded
rolls subtending a pressing nip. The paper web is guided through
the press nip by a revolving wet felt, the liquid being expelled
from the paper web in the press nip into the wet felt and then
being transported away.
Recently wet presses with extended press nips, the so-called
"shoe presses" have been developed, wherein the paper web is
subjected over a longer path, and hence during a longer time, to
high compression, whereby it exits the wet press with greater dry-
ness. Belts evincing a flexible, liquid-impermea~~~~~t~~ayer
and smooth on their bank side are used in particular to guide the
paper web and at least one wet felt passes through such an extended
press nip. Such belts move by their smooth backside inside the
press nip over a hydraulically loaded shoe forcing the belt against
an opposite press roll.
The paper web to be dewatered is guided between this press
roll and the belt and is accompanied at least on one side by an
additional wet felt moving synchronously and transported the
pressed-out water.
Such belts when in the press nip undergo high longitudinal and
transverse stresses and incur on both sides significant abrasion.
It has been suggested to solve the former problem by wholly
incorporating a woven textile into the belt layer (see German
Offenlegungsschriften 32 31 039 and 33 18 984 and US patent
4,559,258). Where palled for, a web may be needled into the woven
textile (German Offenlegungsschrift 32 31 039). However these belt
embodiments have been found unsatisfactory.
In order to improve the water removal from the top side of the
belts, that is the side facing the paper web and resting against a
synchronous wet felt, the suggestion already has been made to
structure the top side. In this respect belts have been developed
into the top side of which textiles were incorporated only in part,
that is, they exceed in part above the belt layer. In this manner
cavities and ducts are created in the parts of the textile
exceeding the belt layer that serve in the removal of the water.
Multi-ply weaves have been suggested as these textiles (German
patent 32 35 468; European patent 0,098,502; European disclosure
0,138,796; German Gebrauchsmuster 83 19 684.6; European
disclosure 0,185,108). The weaves may also be replaced by spiral
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fabrics (European patent 0,098,502) or warp knit fabrics
(European disclosure 0,290,653).
As regards the species of the last cited belts, a
problem arises in permanently securing the bonding between
the belt layer and the textile absorbing the tensile forces.
Such a belt is subjected to high pressures and fulling
stresses with different forces applied at the front and
back, especially inside the press nip. If the textile is
deeply incorporated into the belt layer, it must be
extraordinarily thick in order that, in spite of deeply
penetrating the cross-section of the belt layer, it can
project so much from it that adequate cavity volume is
achieved to evacuate the water. However such a thick
textile entails the belt becoming stiff and therefore
adapting only poorly to the shape of the shoe and to
curvatures when passing over guide rolls. If the textile is
incorporated in more shallow manner into the belt layer, it
will more easily be torn out.
Accordingly the object of the invention is to so
design a belt of the initially cited kind that on one hand
it evinces high flexibility and a large cavity volume for
water removal while on the other hand it also achieves
improved bonding between the textile and the belt layer.
The invention provides a belt for use in
papermaking machines, especially in wet presses having an
extended press nip, which belt has a flexible, liquid-
impervious layer which is smooth at its rear side and in the
front side of which a textile product is embedded only
partially, forming open hollow spaces, the textile product
(5) having a support web (6) and also a fiber layer (9)
which is secured to said support web and which is arranged
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at the side adjacent tc the belt layer (2), characterised in
that the textile product (5) is embedded only by the fiber
layer (9) in the belt layer (2), and the support web (6) is
situated outside of the belt layer (2).
In the invent:icn, the belt manufacture resorts to
a textile which in known manner comprises a support web
adequate for the tensile forces b:zt additionally comprising
a fiber layer .~ffi;ted t~:~ t:: he sup~c;rt web at least on one
side, the textile being :i_n~~crporated into the belt layer
only by the fiber layer, wuereby the :~uzppor~ web lies
entirely outside the belt:..Layer. Thi~a design
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oLiers the advantage ~n the first place that even a ~~~t~~e~~ thin
support web, for instance a single-layer weave or kni[~t, Ucabn form a
comparatively high cavity volume -- because being entirely outside
the belt layer. In commensurate manner the support web little
hampers the belt flexibility. Surprisingly it was found that the
boncting between the textile and the belt layer is better than in
the known solutions in which a support web is partly incorporated
into the belt layer, even though the bonding is implemented by the
fiber layer alone. Shear strength also is improved.
In addition, the fiber layer is able to absorb some dif-
ferential changes in lengths on one hand of the belt layer and on
the other of the support web such as might arise from differing
materials for these components. Accordingly the particular optimal
materials can be used for the belt layer and the support web in a
manner substantially independent of their physical properties. As
a result this belt offers significantly improved properties rela-
tive to all belts of this kind known to-date.
The invention provides that the textile side which is away
from the belt layer also bears a fiber layer. As a result
additional cushioning of the paper side is achieved. When such
fiber layer is suitably designed, even the heretofore obligatory
wet felt, synchronously moving with and between the belt and the
paper web, can be dropped. Substantial savings are possible there-
by.
Appropriately the fiber layers) is (are) needled fiber webs,
especially with longitudinally arrayed fibers. Each fiber layer
may consist of several needled fiber webs. Single-layer or multi
layer weaves, knits or sheets of unwoven filaments or combinations
thereof may form the support web, however other textile lengths
provided they can absorb tensile forces, are suitable.
Another feature of the invention provides reinforcing
filaments being inserted longitudinally and/or transversely into
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the fiber layer(s). Moreover, the support web may consist
of two or more superposed weaves or knits joined to each
other by needling the fiber layer(s).
The drawing elucidates the invention by means of
an illustrative embodiment shown in longitudinal section.
This drawing shows a belt 1 comprising a belt layer 2 with a
top side 3 and a back side 4. The back side 4 is ground
smooth. In the application of the invention, namely in the
wet press of a papermaking machine with extended press nip,
this back side 4 slides past the pressure shoe in the press
nip.
A textile 5 is present at the top side 3 of the
belt layer 2 and comprises a support web 6 in the form of a
double-stratum weave with longitudinal and transverse
filaments illustratively denoted by 7 and 8 resp., a fiber
layer 9 and 10 being needled into the top and bottom side
resp. of said weave. The fiber layer 9, 10 forms the
particular outermost layers of the textile 5. The top fiber
layer 9 is partly incorporated into the belt layer 2 in such
manner that the support web 6 remains completely outside the
belt layer 2. In this manner the connection between the
support web 6 and the belt layer 2 is implemented solely by
the fiber layer 9. Nevertheless an extraordinarily shear-
resistant connection between textile 5 and belt layer 2 is
achieved thereby. The support web itself 6 absorbs the
tensile forces acting on the belt 1.
The lower fiber layer 10 serves as a cushion
against a synchronous wet felt pressing against it and in
turn bearing the paper web. Provided the fiber layer 10 be
suitably designed, the wet felt will not be needed, whereby
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the paper web can directly rest against the belt 1, that is
against the fiber layer 10.
Suitable longitudinal and transverse filaments 7,
8 are all PEK, PEEK, PPS all polyester mixtures, PBT and all
conceivable polyamide variations, in particular PA6.6, PA6,
PA6.10, PA6.12 and
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PA10 and PAll . Polyams ~f= , polye~~t:er, PPS and PAN may be
used for the fiber layer: 9, 10.
Preferably at least one of 1=he fiber layers 9, 10
has fibers that point in 'the direction. of advance of the
belt.
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