Note: Descriptions are shown in the official language in which they were submitted.
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Paper machine fabric
The invention relates to a paper machine fabric consisting of two lay-
ers, a paper-side layer and a wear-side layer; the paper-side layer consists
of the
top warps and at least the binding top wefts, which have been adjusted to form
a
part of the paper-side surface, and the wear-side layer consists of the bottom
warps and bottom wefts, where the binding top wefts have been adjusted to bind
the paper-side layer and the wear-side layer together.
The formation of the paper web starts at the wire section, where most
of the water is removed. When spread on the wet wire, the pulp consists of ap-
proximately 99% water, with the remainder consisting of fibres and possible
fill-
ers and additives. The quality of the paper is largely determined at the wire
sec-
tion of the paper machine. For example, the small-scale variations in the
basis
weight of the paper, i.e. the formation, the distribution of fines and fillers
and the
orientation of fibres, are mainly determined at the wire section.
Two-layer paper machine fabric structures, or double-layer wires, are
widely known in the field. These structures have one warp system and two weft
systems. The technology of a double-layer paper machine fabric has been de-
scribed in the US patent publication 4 041 989, for instance. Owing to the
single
warp system, the wires are thin, but also susceptible to breaking. As the
dewater-
ing elements of the paper machine wear down the fabric on the wear side, all
yarns in the warp direction also wear down, and the risk of the fabric
breaking in-
creases. In addition, the wear on the yarns makes the fabric unstable, which
de-
grades the paper profiles.
SSB structures are also known in the field. SSB is an acronym for sheet
support binding. These structures have two warp systems and three weft sys-
tems. One of the weft systems consists of binding yarn pairs that bind the
paper-
side and wear-side layers together and also participate in forming the paper-
side
layer. The art of SSB structures is described in the US patent publications 4
501
303, 5 967 195 and 5 826 627, for instance. Due to the two warp systems, SSB
structures achieve greater wear resistance and improved stability, compared to
double-layer structures.
In SSB structures, the top weft, on both sides of the intersection of the
binding yarns, presses down the top warp yarns at the intersection; at the
same
time, both yarns in the binding yarn pair descend inside the fabric and do not
support the top warp yarns from below. As a result, the intersections remain
un-
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der the surface of the wire, which may cause markings. This has been described
in
the US patent publication 5 967 195, for instance.
Internal wear occurs in SSB structures. Internal wear occurs when the
paper-side and the wear-side layers are not connected to each other closely
enough, which results in the layers rubbing against each other. In SSB
structures,
internal wear especially occurs in the intersections of the binding yarns. The
movement of the paper side and wear side against each other causes wear on the
warp or weft yarns above and below the intersection of the binding yarns. The
wear changes the overlap of the layers in the direction of the warp and the
per-
il) meability of the paper machine fabric deteriorates considerably. The
wear may be
uneven, which means that the overlap of warp threads may vary over the width
of
the machine, causing profile issues in the paper.
In SSB structures, the layers are bound together with binding yarn
pairs. This means that two binding weft threads are required to form one
contin-
uous weft path. For this reason, the weft density becomes quite high in denser
structures. As a result, more material is needed to manufacture the product
and it
becomes more expensive to manufacture.
Passing between the top and bottom warps, the binding yarn pairs in
SSB structures also increase the thickness of the wire. The thickness of the
paper
machine fabric becomes a problem for certain types of fast paper machines.
The purpose of the invention is to create a paper machine fabric that
can eliminate the disadvantages of the prior art. This has been accomplished
by
the paper machine fabric of the invention. The paper machine fabric of the
inven-
tion is known for each binding top weft being adjusted to form a continuous
inde-
pendent yarn path.
One of the advantages of the invention is that all yarns on the paper
side are independent and form the paper side surface. In the prior SSB
structures,
two binding yarns form a continuous yarn path together. In order to achieve
this,
the weaving machine must beat two more wefts in between the warps or, in other
words, two beats of the reed are needed when weaving. In the structure of the
in-
vention, each weft forms an independent weft path. Consequently, all yarns on
the
paper side are counted in the density. Therefore, only one beat of the reed
per
yarn path is needed in the weaving machine. This means that each beat of the
reed advances the formation of the fabric, speeds up the weaving and improves
the production efficiency at the weaving mill. As a further advantage, the
bottom
warp, bound by the binding top weft, rises up inside the fabric to an extent,
which
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creates a good binding. It is also advantageous that the bottom warp, bound by
the binding top weft, does not quite reach the surface of the paper side,
which
means that the paper-side surface will not be blocked. In addition, the
straighter
the warps are in the final structure, the less the structure of the invention
will
stretch due to the tightness of the paper machine.
There is less internal wear in the structure of the invention than in
prior art solutions. The benefit is due to the weft floats of the top wefts
binding
the structure being shorter than in normal SSB structures. The binding method
of
the invention also reduces internal wear and increases stability.
In one of the embodiments of the invention, the binding top weft binds
to the bottom warp that rises between the top wefts, which makes the structure
substantially thinner. In some embodiments with a warp ratio of 1:2, the warp
density is lower than in conventional SSB paper machine fabrics, which means
that the weft density may be increased, so that the long edge of the openings
on
the paper-side surface is in the cross-machine direction to the paper machine;
that is, perpendicular to the direction in which the paper fibres mainly
orient
when the paper web is formed. This shape of the opening provides optimal fibre
support and dewatering. In addition, the weft floats of the invention on the
paper
side facilitate the detachment of the web at the paper machine; the thin
structure
also results in a better formation compared to prior art solutions.
The structure of the invention creates a dense structure, whose thick-
ness corresponds to the thickness of a double-layer wire, but whose stability
cor-
responds to that of SSB structures. The invention makes it possible to combine
the benefits of a double-layer wire and the SSB structure, while eliminating
their
drawbacks.
The structure of the invention is thinner than the current SSB struc-
tures, which is a benefit, since a thin wire at the wet wire section improves
the ef-
fect of low pressure and dewatering elements compared to SSB structures. Water
removal can be accomplished more effectively at the paper machine, which re-
duces the load of the paper machine. Reducing the paper machine load makes it
possible to increase its speed. This in turn increases productivity.
A thin structure is also an advantage when the aim is to improve the
dry matter content of the paper web. The reason for a poor dry content in
thick
fabric structures is a large water space that increases the rewetting
phenomenon.
Rewetting refers to water drained from the paper web to the wire being
absorbed
back to the paper web in the wire section, after the dewatering elements. When
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the paper web is drier as it enters the press section, there are fewer breaks
and
the consumption of steam at the press section is reduced. This saves energy.
The
increase of dry content by one per cent at the wet wire section may already
make
it possible to raise the speed of the paper machine to a new level.
Unlike in SSB structures, where the bottom warp is thicker than the
top warp, the structures of the invention usually use warp yarns of the same
thickness. This property directly affects the stiffness of the paper machine
fabric
in the direction of the warp. The stiffness of the structure of the invention
is low
in the warp direction, i.e. in the running direction of the paper machine
fabric,
which allows the structure to conform to the dewatering elements of the paper
machine. This means that water is removed evenly over the fabric width at the
different elements which results in a good formation.
It has been found, in the structure of the invention, that it is advanta-
geous to use polyester in all binding top wefts and all top wefts, which
improves
stability and in turn reduces e.g. internal wear.
An essential factor affecting the mechanical life of the fabric on the pa-
per machine is the structure of the bottom side of the fabric, such as the
length of
the weft float, the number of weft yarns and their thickness. In one of the
struc-
tures of the invention, the floats on the bottom side form a 12-shaft
structure.
This embodiment of the invention enables the necessary longer mechanical life
of
the fabric on a paper machine.
In the following, the invention is described in greater detail by means
of the application examples presented in the attached figures, where:
Figure 1 presents the first embodiment of the invention, as a view
from the paper side,
Figure 2 presents the embodiment of the invention, according to Fig-
ure 1, as a view from the wear side,
Figure 3 presents the second embodiment of the invention as a view
from the paper side,
Figure 4 presents the embodiment of the invention, according to Fig-
ure 3, as a view from the wear side,
Figure 5 presents the third embodiment of the invention as a view
from the paper side,
Figure 6 presents the embodiment of the invention, according to Fig-
ure 5, as a view from the wear side,
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Figure 7 presents the fourth embodiment of the invention as a view
from the paper side,
Figure 8 presents the embodiment of the invention, according to Fig-
ure 7, as a view from the wear side,
5 Figures
9a-9d present the fifth embodiment of the invention as views
in the direction of warp threads, and
Figure 10 presents the sixth embodiment of the invention as a view
from the paper side
Figures 1 and 2 show the first embodiment of the invention. Each top
weft forms an independent yarn path. The paper side of the structure consists
of
the top warps (1) and the binding top wefts (2). The binding top wefts (2)
bind to
the top warps (1) under two top warps (1) and over two top warps (1). Each of
the binding top wefts (2) binds to a bottom warp (3), and every bottom warp
(3)
is bound. The wear side of the structure consists of the bottom warps (3) and
the
bottom wefts (4). The wear-side weave is an 8-shaft weave, meaning that the
bot-
tom wefts (4) pass over two bottom warps (3) and under six bottom warps (3).
The ratio of top wefts (2) to bottom wefts (4) is 2:1.
Figures 3 and 4 show the second embodiment of the invention. The
same reference numbers are used in Figures 3 and 4 as in Figures 1 and 2 to
refer
to the corresponding parts. In this embodiment, too, each top weft forms an
inde-
pendent yarn path. The paper side of the structure consists of the top warps
(1)
and the binding top wefts (2), in addition to the top wefts (2a). The top
wefts (2a)
are non-binding top wefts, meaning that the top wefts (2a) are not bound to
the
wear-side warps. The binding top wefts (2) bind to the top warps (1) under two
top warps (1) and over two top warps (1). Each of the binding top wefts (2)
binds
to a bottom warp (3), and every other bottom warp (3) is bound. Between each
pair of adjacent binding top wefts (2) is one non-binding top weft (2a), which
binds to the top warps (1) under one top warp (1) and over three top warps
(1).
The wear side of the structure consists of the bottom warps (3) and the bottom
wefts (4). The wear-side weave is an 8-shaft weave, meaning that the bottom
wefts (4) pass over two bottom warps (3) and under six bottom warps (3). The
ratio of top wefts to bottom wefts is 2:1.
Figures 5 and 6 show the third embodiment of the invention. The same
reference numbers are used in Figures 5 and 6 as in Figures 4 and 5 to refer
to the
corresponding parts. In this embodiment, too, each top weft forms an independ-
ent yarn path. The paper side of the structure consists of the top warps (1)
and
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the binding top wefts (2), as well as the top wefts (2a). The top wefts (2a)
are
non-binding top wefts, which are not bound to the wear-side warps. The binding
top wefts (2) bind to the top warps (1) under two top warps (1) and over two
top
warps (1). Each of the binding top wefts (2) binds to a bottom warp (3), and
every
other bottom warp (3) is bound. Between each pair of adjacent binding top
wefts
(2) is one top weft (2a), which binds to the top warps (1) under one top warp
(1)
and over one top warp (1). The wear side of the structure consists of the
bottom
warps (3) and the bottom wefts (4). The wear-side weave is an 8-shaft weave,
meaning that the bottom wefts (4) pass over two bottom warps (3) and under six
bottom warps (3). In this embodiment, the ratio of top wefts to bottom wefts
is
2:1 and the ratio of top warps to bottom warps is 1:2.
Figures 7 and 8 show the fourth embodiment of the invention. The
same reference numbers are used in Figures 7 and 8 as in e.g. Figures 5 and 6
to
refer to the corresponding parts. In this embodiment, too, each top weft forms
an
independent yarn path. The paper side of the structure consists of the top
warps
(1) and the binding top wefts (2), as well as the top wefts (2a). The top
wefts (2a)
are non-binding top wefts, which are not bound to the wear-side warps. The
bind-
ing top wefts (2) bind to the top warps under one top warp (1) and over two
top
warps (1). Each of the binding top wefts (2) binds to a bottom warp (3), and
every
other bottom warp (3) is bound. Between each pair of adjacent binding top
wefts
(2) is one non-binding top weft (2a), which binds to the top warps (1) under
one
top warp (1) and over two top warps (1). The wear side of the structure
consists
of the bottom warps (3) and the bottom wefts (4). The wear-side weave is a 6-
shaft weave, meaning that the bottom wefts (4) pass over two bottom warps (3)
and under four bottom warps (3). The ratio of top wefts to bottom wefts is
2:1.
Figures 9a-9d show the fifth embodiment of the invention. The same
reference numbers are used in Figures 9a-9d as in the previous embodiments to
refer to the corresponding parts. In this embodiment, too, each top weft forms
an
independent yarn path. The paper side of the structure consists of the top
warps
(1) and the binding top wefts (2), as well as the top wefts (2a). The binding
top
wefts (2) bind to the top warps under three top warps (1) and over two top
warps
(1). Between each pair of adjacent binding top wefts (2) is one non-binding
top
weft (2a), which binds to the top warps (1) under two top warps (1) and over
three top warps (1). The wear side of the structure consists of the bottom
warps
(3) and the bottom wefts (4). The wear-side weave is a 6-shaft weave, meaning
that the bottom wefts (4) pass over one bottom warp and under five bottom
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warps (3), in such a way that the adjacent bottom warps are also bound. The
bot-
tom weft could also be bound in a 3-shaft or a 12-shaft structure. In the
embodi-
ment shown in Figures 9a-9d, the warp ratio is 5:3.
Figure 10 shows the fifth embodiment of the invention. The same ref-
erence numbers are used in Figure 10 as in e.g. Figure 5 to refer to the corre-
sponding parts. In this embodiment, too, each top weft forms an independent
yarn path. The paper side of the structure consists of the top warps (1) and
the
binding top wefts (2), as well as the top wefts (2a). The top wefts (2a) are
non-
binding top wefts, which are not bound to the wear-side warps. The binding top
wefts (2) bind to the top warps under one top warp (1) and over three top
warps
(1). Each of the binding top wefts (2) binds to a bottom warp (3), and every
other
bottom warp (3) is bound. Between each pair of adjacent binding top wefts (2)
is
one non-binding top weft (2a), which is bound to the top warps (1) under one
top
warp (1) and over three top warps (1).
A common feature of all of the embodiments described above is that
each top weft forms an independent yarn path. The paper side of the structure
al-
so consists of, at least, the top warps (1) and the binding top wefts (2). The
weave
of the binding top wefts (2) with the top warps (1) can vary, as shown in the
fig-
ures, such as a 3-shaft or 4-shaft weave, twill, satin, etc. In the pattern
repeat, the
binding top weft (2) always binds to at least one bottom warp. The binding top
weft (2) can also bind to the bottom warps (3) in other ways, such as to every
other bottom warp (3) or every third bottom warp (3). In some applications,
there may be non-binding top wefts (2a) in between the binding top wefts (2).
Their weave can vary, meaning that the weave can be a 2-shaft weave, twill,
satin,
etc. The ratio of the binding top wefts (2) to the non-binding top wefts (2a)
may
be 1, >1 or <1. Furthermore, in all embodiments of the invention, the wear
side of
the structure consists of the bottom warps (3) and the bottom wefts (4). The
wear-side weave can be twill or satin, for example, but other weaves are also
pos-
sible. It is advantageous for the bottom weft (4) to bind to two adjacent
bottom
warps (3) and form a bottom weft loop after this, such as two over/3-14 under,
but there are also other options from 2-shaft up to 16-shaft weaves. The ratio
of
top wefts to bottom wefts is 2:1 in many of the embodiments in the figures,
but it
can also be something else, such as 1:1, 1:2, 2:3, etc. The ratio of top warps
to bot-
tom warps is 1:2 in many of the embodiments in the figures, but it can also be
1
(=1), greater than one (>1) or smaller than one (<1). The top warps can be
locat-
ed either on top of the bottom warps or between them; for example, in 1:2 one
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bottom warp can be directly under a top warp, while the other bottom warp does
not have a pair, or a top warp can be in the middle of the bottom warps.
The solutions described above use polyester and polyamide yarns.
Other possible yarn materials include PEN (polyethylene naphthalate) or PPS
(polyphenylene sulphide). The yarns or a part of the yarns may have a round
cross-section or they may be, for example, profile yarns, where the cross-
section
is not round, but rather flat, oval, rectangle, or some other shape. The yarns
may
also be hollow, in which case they can flatten in the fabric and the structure
can
be made even thinner than before. One advantageous form of the invention is
that
all warps are 0.12 mm in diameter. The warp diameter may also be different;
however, top warps 0.08 mm and bottom warps 0.11 mm. The diameter of the
binding top wefts and the non-binding top wefts may be 0.08 mm. Similarly, bi-
component yarns may also be used. The properties of the fabric can be
influenced
by the choice of yarn properties; for example, to achieve a thinner structure
or an
even paper-side surface, etc. The structure of the invention is intended for
use as
a wire in the wet section of a paper machine, but the structure can also be
used
with e.g. tissue, paperboard and non-woven machines. The structure of the
inven-
tion can also be adjusted for use at the press or drying section of a paper
machine.
The invention is described above by means of different embodiments.
However, the invention is in no way restricted to the embodiments of the
figures,
but may naturally be freely modified, within the scope of the accompanying
claims.
