Note: Descriptions are shown in the official language in which they were submitted.
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MU~TILAYER FORNING FABRIC
BACKGROUND OF THE INVENTION
This invention relates to papermakers' fabrics and
especially to papermakers' fabrics for the forming section of a
papermaking machine.
In the conventional papermaking process, a water slurry or
suspension of cellulose fibers, known as the paper "stock", is
fed onto the top of the upper run of a traveling endless forming
belt. The forming belt provides a papermaking surface and
operates as a filter to separate the cellulosic fibers from the
aqueous medium to form a wet paper web. In forming the paper
web, the forming belt serves as a filter element to separate the
aqueous medium from the cellulosic fibers by providing for the
drainage of the aqueous medium through its mesh openings, also
known as drainage holes, by vacuum means or the like located on
the drainage side of the fabric.
After leaving the forming medium, the somewhat self-
supporting paper web is transferred to the press section of the
machine and onto a press felt, where still more of its water
content is removed by passing it through a series of pressure
nips formed by cooperating press rolls, these press rolls serving
to compact the web as well.
Subsequently, the paper web is transferred to a dryer
section where it is passed about and held in heat transfer
relation with a series of heated, generally cylindrical rolls to
remove still further amounts of water therefrom.
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Over the years, papermakers have sought improvements in the
forming fabric, not only with respect to the operating life of
the fabric, but also with respect to the quality of the paper
sheet produced on it. Triple layer fabrics were introduced for
this purpose. The triple layer fabric has two generally distinct t
surfaces. The top surface is one integral fabric structure
designed specifically for papermaking to achieve the best
possible sheet quality and machine efficiency. This top fabric
is manufactured as an integral part of a woven structure with a
completely separate bottom fabric designed specifically for
mechanical stability and fabric life. The purpose of triple
layer fabric development is to eliminate the compromises which
exist with both single and double layer forming fabrics so that
papermakers can produce the best possible paper sheet for top
quality at reduced cost without sacrificing the wear
characteristics of the papermakers' fabric.
References known in the art have described these so called
triple layer fabrics with additional binder yarns in the warp
direction and in the weft direction. Interconnection of the two
fabric layers by a binder warp, however, has the drawback that
during weaving the warp yarn is under tension so that it
influences the structure on the paper side. Additionally, when
a triple layer fabric is woven flat and made endless by means of
a woven seam, the binder warp in the final screen extends in the
longitudinal direction. Since the fabric is lengthened during
thermosetting in the heating zone, the warp threads are again
subject to high working tension. Owing to the fact that the weft
threads of the lower layer are substantially thicker and stiffer,
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the tension of the binder warp affects nearly exclusively the
finer threads of the upper layer. Thus, the binder warp pulls
the fine weft threads of the upper layer deep into the fabric at
the binding points, thereby causing distortions in the uniformity
of the surface.
Accordingly, triple layer fabrics are in practice joined
together by weft binder yarns. This solution is less than ideal,
however, because the movement of the individual fabric layers
relative to each other is unrestrained with the binder weft
yarns. Delamination of these triple layer fabrics becomes a
problem, reducing the fabric's life.
OBJECTS OF THE INVENTION
Accordingly, it is an object of the present invention to
provide a novel triple layer fabric for use in a papermakers'
machine.
It is another object of the present invention to provide a
triple layer fabric in which the fabric layers are joined
together by additional warp binder yarns.
Another object of the present invention is to provide such
a fabric that has increased stability of the papermakers' fabric,
resulting in a longer service life.
Still another object of the present invention is to provide
a novel triple layer papermakers' fabric for a papermakers'
machine that has an improved joining arrangement for the fabric
layers.
A further object of the present invention is to provide such
a papermakers' fabric with a superior papermaking surface, good
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wear life, abrasion resistance and good drainage.
These and other objects of the present invention will become
apparent from a review of the following detailed description of
the invention, taken together with the drawing, in which like
reference numbers refer to like members throughout the different
views.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. l is a sectional view in the weft direction of a fabric
according to the present invention including additional warp
binder yarns;
FIG. 2 is a sectional view in the warp direction of the
fabric shown in FIG. l;
FIG. 3 is a sectional view in the weft direction of another
embodiment of the present invention including additional weft
binder yarns;
FIG. 4 is a sectional view in the warp direction of the
fabric shown in FIG. 3;
FIG. 5 is a sectional view in the weft direction of another
embodiment of the present invention including both additional
warp and weft binder yarns;
FIG. 6 is a sectional view in the warp direction of the
fabric shown in FIG. 5;
FIG. 7, including FIGS. 7A-7H, show the eight different
positions of the warp direction yarns of another embodiment of
the fabric of the present invention, utilizing an additional warp
binder yarn;
FIG. 8 is a weft direction view of the fabric of FIG. 7;
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FIG. 9 illustrates the papermaking surface of the top fabric
layer of the fabric of FIGS. 7 and 8 and shows the relationship
between the interfacing surfaces of the two fabric layers.
SUMMARY OF THE INVENTION
A triple layer fabric, useful in the forming section of a
papermakers' machine, is provided. The triple layer fabric
includes: a top fabric layer having at least one set of warp
yarns interwoven with at least one set of weft yarns; a bottom
fabric layer having at least two sets of weft yarns forming a top
and bottom layer of the bottom fabric layer, and at least one set
of warp yarns; and at least one binder yarn interweaving and
joining the top fabric layer and the bottom fabric layer. The
top fabric layer is preferably a plain weave fabric while the
bottom fabric layer is preferably a semi-duplex weave. Also, in
one preferred embodiment, the sets of weft yarns in the bottom
fabric layer are generally stacked, as are the warp and weft
yarns of the top and bottom fabric layers.
The binder yarn is preferably a binder warp yarn, but may
be a binder weft. Additionally, the fabric may include both
binder warp and weft yarns. In interweaving the top and bottom
fabric layers, the binder yarns engage only the upper weft yarns
or the warp yarns of the bottom fabric layer. Thus, the binder
yarn is protected by the lower weft yarns of the bottom fabric
layer from normal wear and abrasion thereby increasing fabric
life. Fabric life is further increased in the case of a binder
warp yarn since the friction during use between the fabric layers
and the binder yarns is minimized.
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The binder yarn may stitch the weft or warp yarns of the
fabric layers in any repeating fashion. However, in the one
preferred embodiment the binder warp yarn engages every eighth
weft yarn of the top fabric layer and every eighth weft yarn in
the top layer of the bottom fabric layer. In another embodiment,
the binder weft yarn engages every fourth warp yarn of the top
fabric layer and every fourth warp yarn in the bottom fabric
layer.
DETAILED DESCRIPTION OF THE INVENTION
The fabric of the present invention is a triple layer
fabric, incorporating a top fabric layer and a bottom fabric
layer joined by an additional binder yarn in a particular manner.
For purposes of the present invention, reference will be
made to "warp" and "weft" to define the path of travel of the
yarns making up the fabric of the present invention. Generally,
in a flat woven fabric, warp yarns travel in the warp direction
and weft yarns travel in the weft direction. When the fabric is
woven endless, however, the warp yarns travel in the weft
direction and the weft yarns travel in the warp direction. One
skilled in the relevant art will be aware of the distinction and
can easily translate the concepts of the present invention to
produce a fabric according to these concepts, noting the
distinction above.
The yarns utilized in the fabric of the present invention
will vary depending upon the desired properties of the final
papermaking fabric, and of the papersheet to be formed on that
fabric. For example, the yarns may be multifilament yarns,
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monofilament yarns, twisted multifilament or monofilament yarns,
spun yarns or any combination of the above. It is within the
skill of those practicing in the relevant art to select a yarn
type, depending on the purpose of the desired fabric, to utilize
the concepts of the present invention.
Yarn types selected for use in the fabric of the present
invention may be those commonly used in papermaking fabrics. The
yarns could be cotton, wool, polypropylene, polyester, aramid or
nylon. Again, one skilled in the relevant art will select a yarn
material according to the particular application of the final
fabric.
The binder yarn, which joins the two fabric layers together,
can be of the same diameter as the yarns in the top fabric layer
and/or the bottom fabric layer. In a preferred embodiment, the
binder yarns will be of smaller diameter than the yarns making
up the fabric layers. A typical binder yarn will be a
monofilament or multifilament thread of polypropylene or nylon.
The top fabric layer is designed to present an optimal
surface for papermaking. The top fabric layer may be woven in
any manner, but in a preferred embodiment, this fabric layer will
be a plain weave. A plain weave is preferred because it presents
a higher index of fiber support with greater drainage than most
fabric weaves. With the support and drainage system provided,
better fiber distribution of the forming paper web occurs. The
pattern of a plain weave also presents optimal bicrimp conditions
for papermaking.
The bottom fabric layer of the present invention, however,
is a semi-duplex weave, having two weft yarn systems. The yarns
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in the top fabric layer can be of the same size and type as those
in the bottom fabric layer, or they may be of a smaller diameter,
depending upon the purpose of the final papermakers fabric. In
the preferred embodiment of the present invention, the
combination of a plain weave top fabric layer with a semi-duplex
bottom fabric layer provides "inclined" drainage through the weft
yarns' three systems. Additionally, a semi-duplex fabric is
associated with good drainage due to the warp yarns' low density
and the weft yarn systems' position.
In combination with these fabric layers, binder yarns of the
present invention will preferably run in the warp direction
thereby binding weft yarns from the top and bottom fabric layers.
Binding in the warp direction has been found to have significant
advantages because the direction of movement of the papermaking
fabric and the stresses normally applied to forming fabrics in
the paper machine are longitudinal. Accordingly, using warp
yarns as binders reduces the stresses normally found with weft
binder yarns.
In addition, since the bottom fabric layer is a semi-duplex
weave in the preferred embodiment, the binder yarn in the warp
direction will always engage a weft yarn from the upper set of
weft yarns when it is binding the bottom fabric layer. In doing
so, the binder yarn will form an interlayer in which the
structural weft yarns are interlaced. This interlacing of a
longitudinal binder yarn through the top layer and semi-duplex
bottom fabric layer reduces the friction between the layers as
the fabric works under stress in the longitudinal direction. In
addition, since the binder yarns are subjected to the same
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longitudinal forces as the fabric layers, the friction between
the layers and the binder yarns is significantly reduced thereby
avoiding the rupture of binder yarns causing delamination.
Moreover, the semi-duplex bottom layer has two weft yarn
systems and the top weft yarns of the semi-duplex bottom layer
are interlaced with the weft yarns of the top fabric layer. This
results in increased protection for the binder warp yarns because
they are protected by the bottom weft yarns of the semi-duplex
bottom layer from the fabric's common abrasion wear in the
longitudinal direction. The weft yarns are better able to absorb
the wear and abrasion caused by that contact, and therefore the
papermakers fabric has a longer life.
Even though it is preferred that binder yarns are woven in
the warp direction as discussed above, advantages can still be
achieved when the binder yarn is woven in the weft direction.
This is because binder yarns in either the warp or weft direction
are protected from normal abrasion wear by the bottom weft yarns
of the semi-duplex weave of the bottom fabric layer. Finally,
it is also envisioned that binder yarns will run in both the warp
and weft direction and will bind with both the warp and weft
yarns of the top and bottom fabric layers.
In a papermakers' fabric of the present invention, the yarn
systems are selected to facilitate and optimize the role each
will play in the papermakers fabric. For example, the yarns that
will face the paper to be formed will be finer, and of smaller
diameter, than the remaining yarns. Similarly, the yarns that
will face the machine elements of the papermakers machine will
be coarser, and of larger diameter, than the remaining yarns.
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It is envisioned that one skilled in the art can select the sizes
of yarns to optimize the concepts of the present invention.
FIGS. 1 and 2 show one embodiment of the fabric of the
present invention. In those views, yarns 11 and 12 are the warp
direction and weft direction yarns of the top fabric layer 13.
Reference numbers 14 and 15 are weft direction yarns and 16 is
the warp direction yarns of the bottom fabric layer 17. The top
fabric layer 13 and bottom fabric layer 17 are joined by
additional warp direction binder yarns 18. The binder yarns 18
may join with the weft direction yarns 12 of the top fabric layer
13 and the upper weft direction yarns 14 of the bottom fabric
layer in any repeating pattern thereby forming an interlayer.
In the preferred embodiment of FIGS. 1 and 2, however, the binder
yarns 18 engage every eighth weft direction yarn 12 of the top
fabric layer and every eighth upper weft direction yarn 14 of the
bottom fabric layer 17.
It is evident from FIG. 2 that the configuration achieved
by the weave of the present invention protects both the binder
yarn 18 and most of the load bearing structural warp yarns 16 of
the bottom fabric layer 17 from exposure to the machine elements
on the papermaking machine and therefore from wear and abrasion.
The binder yarns 18 and structural warp yarns 16 will not be
exposed until the weft yarn lS of the bottom fabric layer 17
wears completely through.
FIGS. 3 and 4 illustrate another embodiment of the
papermaking fabric of the present invention, one in which the
additional binder yarn runs parallel to the weft yarns and
therefore travels in the weft direction. This embodiment again
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features a plain weave top fabric layer 21, with a semi-duplex
bottom fabric layer 22. Top fabric layer 21 has warp direction
yarns 23 interwoven with weft direction yarns 24. In the bottom
fabric layer 22, weft direction yarns 25 are generally stacked
over weft direction yarns 26, and are interwoven with warp
direction yarns 27. Additionally, binder yarns 28 run in the
weft direction and engage the warp direction yarns 23 of the top
fabric layer 2l and the warp direction yarns 27 of the bottom
fabric layer 22. As in the embodiment of FIGS l and 2, the
binder yarns 28 may join with the warp direction yarns 23 of the
top fabric layer 2l and the upper warp direction yarns 27 of the
bottom fabric layer 22 in any repeating pattern thereby forming
an interlayer. It is preferred, however, that the binder yarns
28 engage every fourth warp direction yarn 23 of the top fabric
layer and every fourth upper warp direction yarn 27 of the bottom
fabric layer.
Compared to the longitudinal binder yarn structure depicted
in FIGS l and 2, this structure may be manufactured on a loom-
with only two warp cylinders instead of three. In addition, the
binder yarn 28 is protected by the bottom weft yarns 26 of the
bottom semi-duplex fabric layer. Despite these advantages,
however, the fabric of FIGS. 1-2 containing warp direction binder
yarns is preferred since it has been found to be more resistant
to delamination. This is primarily due to the fact that the
forces on the fabric during operation are longitudinal, i.e. in
the warp or warp direction. With binder yarns solely in the weft
direction greater friction between the structural layers is
observed resulting in expedited delamination.
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Nonetheless, warp direction binder yarns may be combined
with weft direction binder yarns to achieve a fabric with an
extremely rigid fabric with high resistance to delamination.
FIGS. 5 and 6 illustrate this construction as a third embodiment
of the fabric of the present invention. In this embodiment,
additional binder yarns are present in the weft direction and in
the warp direction in the weave patterns described above. Top
fabric layer 31 is joined to bottom fabric layer 32 by additional
binder warp yarn 38 and additional binder weft yarn 39. Top
fabric layer 31 incorporates warp yarns 33 interwoven with weft
yarns 34 in a plain weave pattern. In the bottom fabric layer,
weft yarns 35 are generally stacked over warp yarns 36 and they
are interwoven with warp yarns 37. The binder warp yarn 38
engages weft yarns 34 from the top fabric layer and weft yarns
35 from the bottom fabric layer in a predetermined pattern.
Similarly, binder weft yarns engage the warp yarns 33 of the top
fabric layer 31 and the warp yarns 37 of the bottom fabric layer
32. Although this construction has significant advantages in
terms of rigidity and delamination, this is achieved at the cost
of a reduction in the drainage index due to the large number of
binder yarns.
FIG. 7 illustrates a fourth embodiment of a papermakers
fabric according to the concepts of the present invention. FIGS.
7A-7H show eight different positions of the warp direction yarns
73, 77 in the fabric. As described above, the papermakers fabric
includes a plain weave top layer 71, with interwoven warp
direction yarns 73 and weft direction yarns 74. The bottom
~abric layer 72 is a semi-duplex, 8 harness design weave. In
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this embodiment, however, the bottom fabric layer 72 includes
weft direction yarns 75 generally stacked over weft direction
yarns 76 and interwoven by warp direction yarns 77. In addition,
the top fabric layer weft direction yarns are generally stacked
over the weft direction yarns of the bottom fabric layer. FIGS.
7D and 7H show the positions of the binder warp yarn 78 and how
it joins the top and bottom fabric layers 71, 72.
FIG. 8 illustrates the fabric of FIG. 7 in the weft
direction. As can be seen, the warp direction yarns of the top
fabric layer are generally stacked over the warp direction yarns
of the bottom fabric layer. With the both the weft direction
yarns and the machined direction yarns stacked in this manner the
fa~ric exhibits excellent drainage characteristics. Stacking of
the warp direction and weft direction yarns also produces a
fabric which is highly resistant to deformation under compression
forces. This is because the stacked yarns are forced against
each other under compression instead of between each other in the
case of an unstacked fabric. Another advantage of this
configuration that the structure of the top fabric layer is not
significantly influenced by the weaving of a binder warp yarn as
before. Accordingly, the top surface of the fabric layer is more
uniform, resulting in less marking of the paper product.
Although FIGS. 7 and 8 show a perfectly stacked fabric, it
is possible to achieve the above described advantages with the
structural warp and weft direction yarns less than perfectly
stacked. That is, these advantages may be achieved in a fabric
in which the yarns in each direction are stacked with the center
axis of each yarn in less than perfectly alignment. This may be
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advantageous especially in light of the fact that the yarns of
the top fabric layer may be relatively fine compared to the yarns
of the bottom ~abric layer.
Additionally, FIG. 8 clearly shows the advantage of
combining a top fabric layer and semi-duplex bottom fabric layer
with a binder yarn in the warp direction. As is shown, the load
bearing structural warp direction yarns 77 and the additional
binder yarns 78 are protected by the weft direction yarns 76 of
the bottom fabric layer 72 from wear and abrasion until the weft
direction yarn 76 is worn. Moreover, since the binder yarn is
woven in the warp direction it is subjected to the same
longitudinal stresses as the top and bottom fabric layers. The
friction between the layers and the binder yarns is reduced under
this construction compared to a fabric with a transverse binder
yarn. As discussed above in connection with FIGS 5 and 6,
however, it is also possible to combine a transverse binder yarn
with the warp binder yarn in the embodiment of FIGS 7 and 8.
FIG. 9 is a plan view of the fabric shown in FIGS. 7 and 8
showing the top papermaking surface of the papermaking fabric.
The cut-out area in the right lower corner illustrates the
interfacing top surface of the bottom fabric layer. The plain
weave top fabric layer 71 presents an optimal papermaking surface
and provides good pulp support to retain fibers from the pulp and
good release of the forming paper web. The binder warp yarns 78,
as discussed above, may engage the structural weft yarns in any
repeating pattern. In addition, any number of binder warp yarns
may be used to stitch the layers of the fabric. FIG 9, however,
represents a preferred embodiment in which a binder warp yarn is
14
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inserted adjacent every fourth structural warp yarn and stitches
every eighth weft yarn of the top and bottom fabric layers.
The embodiments which have been described herein are but
some of the several which utilize this invention and are set
forth here by way of illustration but not of limitation. It is
obvious that many other embodiments which will be readily
apparent to those skilled in the art may be made without
departing materially from the spirit and scope of this invention.
