Note: Descriptions are shown in the official language in which they were submitted.
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Background of the Invention
Field of the Invention
This lnvention relates to woven papermakers
fabrics, and more particularly to an improved woven
papermakers fabric that exhibits substantially less
machine direction stretch and shrinkage than other
available fabric structures.
Description of the Prior Art
In papermaking machines, a papermakers belt
in the form of an endless, belt-like fabric struc-ture
is supported on and advanced by a plurality of
metallic rolls rotatably suppor-ted in the papermaking
machin.e. The belt serves to transpor-t paper during
the various stages of its processing during the
papermaking process, as it passes through the
papermaking machine. Papermakers belts have various
names, depending upon the portion of the machine in
which they are
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used. By way of example, papermakers belts can include
so-called forminy fabrics, wet press felts, and dryer felts and
fabrics. In many cases, the belt or ~abric is joined at its
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ends to form an endless belt that is supported on and
controlled by various machine rolls forming part of the
papermaking machine.
A papermakers fabric can be made from a one, two,
three, or more plane fabric, wherein the various planes are
defined by different groups of cross-machine direction yarns.
The planes, plies, or layers, as they are variously called, are
united by a plurality of machine direction yarns that are
interwoven with the cross-machine direction yarns to form a
coherent fabric that has desired surface, stability and
permeability characteristics, depending upon the portion of the
papermaking process in which it is used. In that regard, the
yarns that are used to weave the most modern papermakers
fabrics are often made ~rom synthetic monofilaments, or
synthetic mutilfilaments, and from such materials as polyester
or polyamide.
By virtue of the interwoven structure oE the typical
papermakers fabric, both the cross-machine direction yarns and
the machine direction yarns are crimped, or bent, as they pass
above or below the respective yarns with which they are
in~e~woven. Although after weaving the fabric is subjected to
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heat and tension to se-t the yarns in the desired relative
orientation, regardless of the tightness of the weave, any
crimped machine direction yarn will increase in leny-th as the
fabric is placed under tension. Such a result is undesirable
in that it causes the fabric to stretch and lengthen in the
machine direction. As the fabric tension must be kept constant
during the paper making process, fabric stretch can cause the
fabric to lengthen beyond the take-up capabilitles of the paper
machine in which case tension is lost and the fabric has to be
removed, because it is too long. Furthermore, if the tension
applied to the fabric is relatively low, the fabric may shrink
back, again beyond the adjustment capabilities of the machine.
In this case the tension builds up and can result in damage to
the paper machine. Further complicating the situation is that
the tension in the fabric as it runs is not constant and
uniform along the fabric, which brings about fluctuations as
the fabric travels through the papermaking machine.
; One attempt to overcome stretching of a papermakers
fabric on the papermaking machine involved the techni~ue of
overstretching the fabric by the fabric manufacturer during the
finishing operation. However, it has been found that finishing
a woven fabric by using high stretch forces will result in
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built-in high shrinkage and consequent shrink forces that cause
the fabric to contract on the paper machlne to the point of
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tension build-up and subsequent machine damage. On the other
hand, finishing a fabric by using low stretch forces will
reduce the likelihood of -it contracting on low tension
positions of the machine, but it will increase the likelihood
of it stretching in high tension positions on the machine.
However, because in many cases neither the papermakers fabric
manufacturer nor the paper mill that uses the fabric knows
precisely under what tension the fabric will be operating,
there is always the possibility of either fabric stretching or
fabric shrinking.
It is an object of -the present invention to overcome
the above-described problems associated with the prior art
fabric structures, and to provide a papermakers fabric that has
improved resistance to stretching when under tension after
being finished using low stretch forces, such that it performs
well on a large variety of papermaking machines under a variety
of operating conditions.
Su~nary of the Invention
Briefly stated, in accordance with~ one aspect of the
present invention, a papermakers fabric is provided in the form
of a woven structure that incIudes a plurality of~machine
direction yarns and a plurality of cross~machine direction
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yarns that are interwoven according to a preselec-ted weave
pattern. The interwoven yarns define a woven structure having
a top layer and a bottom layer. A plurality of load control
yarns are positioned between the top and bottom layers of the
fabric and extend in the machine direction and lie between the
cross-machine direction yarns. The load control yarns pass
linearly through the interior of the woven fabric structure and
are substantially uncrimped. The load control yarns are made
from a synthetic material capable of withstanding high tensile
loads without appreciable stretch.
According to a further broad aspect of the present
invention there is provided a stretch-and-shrinkage resistant
dryer fabric which comprises a low tension finished woven
structure including a plurality of machine direction yarns and
a plurality of cross-machine direction yarns made from at least
one of polyester and polyamide material interwoven according to
a preselected weave pattern to define the woven structure
having at least a top plane and a bottom plane. A plurality of
load control yarns extend in the machine direction between the
top and bottom planes and between the cross-machine direction
yarns. The load control yarns are essentially straight and
pass linearly and substantially uncrimped through the interior
of the woven fabric structure. The load control yarns are made
from an aramid synthetic material having high strength and low
shrinkage characteriscics capable of withstanding high tensile
loads without appreciable stretch under high heat and high
tension, and being resistant to shrinkage under high heat and
low tension. The plurality of machine and cross-machine
direction yarns are arranged to cover the load control yarns so
as to protect the load control yarns from wear and heat
deterioration and -the plurality of machine and cross-machine
direction yarns have better abrasion characteristics than the
load control yarns so that full advantage is taken of the
strength and resistance to stretch and shrinkage charac-
teristics of the load control yarns.
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Accordi.ng to a s-till further broad aspect of the
present invention, there is provided a pape.rmakers fabric which
comprises a plurality of machine direction yarns and a
plurality of cross-machine direction yarns interwoven according
to a preselected weave pattern to define a woven structure
having at least a top plane and a bottom plane. ~ plurality of
load control yarns extend in the machine direction between the
top and bottom planes and between the cross-machine direction
yarns. The load control yarns are substantially straight and
pass linearly and substantially uncrimped through the interior
of the woven fabric structure. The load control yarns are also
made from a synthetic material which is capable of withstanding
tensile loads without appreciable stretch under high heat and
high tension to control overall fabric stretch as compared to
the plurality of machine direction yarns that are interwoven
with the plurality of cross-machine direction yarns. The load
control yarns are also resistant to shrinkage under hiyh heat
and low tension. The top and bottom planes include respective
portions of the cross-machine direction yarns arranged in
vertically aligned pairs in the machine direction. At least
two machine direction yarns have yarn portions engaging and
passing partially around an outwardly facing portion of every
other top plane and bottom plane cross-machine direction yarn
portion, to increase resistance of the fabric to wear.
Brief Descri tion of the Drawings
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Figure 1 is a fragmentary cross-sectional view taken
along the machine direction, of one type of weave pattern
constructed in accordance with the present invention and having
load control yarns passing through the interior portion of the
fabric in the machine direction.
Figure 2 is a fragmentary cross-sectional view
similar to that of Figure 1, showing another form of weave
structure incorporating load control yarns in accordance with
the present invention.
Figures 3 through 13 show alternative weave struc-
tures that incorporate load control yarns in accordance with
the present invention.
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Description of the Preferred Embodiments
Referring now to the drawinys, and
particularly to Figure 1, there is shown a portion of
a papermakers fabric 10 that includes a plurality of
cross-machine direction yarns 12 through 22 that are
arranged in alterna-ting relationship in a machine
direction and interwoven with a plurality of groups
of machine direction yarns 32, 34 and 36 (only one of
each shown) to provide a substantially two layer, or
duplex fabric. As is clearly apparent from Figure 1.,
the base, or interwoven portion of the fabric is
characterized by a weave pattern hav~ng three ends
and a six pick repeat. In this regard, as is clearly
shown in Figure 1, the groups of machine direction
yarns 32, 34 and 36 pass in identlcal undulating
patterns back and fcrth between portions of the
cross-machine direction yarns 12 through 22 in the
top and bottom planes, and the machine directi.on
yarns in each group engage and pass about every third
cross-machine direction yarn portion in the top and
bottom planes.
Fabric 10 includes a plurality of machine
direction yarns 40 (only one of which is visible in
Figure 1) that pass directly through the~ center of
the fabrlc structure, and are arranged in parallel
relationship to define an intermediate plane within
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the fabric, the intermediate plane lying between the
plane defined by upper cross-machine direction yarns
12, 14 and 16, and the plane defined by lower
cross-machine direction yarns 18, 20 and 22. By
passing straight through the ~abric structure, and
without being crimped, the center machine direction
yarns 40, or load control yarns are able to undergo a
higher tensile load without substantial stretch, as
compared with machine direction yarns that are
interwoven with cross-machine direction yarns.
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The types of yarns that can be used to
provide -the base, interwoven fabric s-tructure,
exclusive of the load control yarnsl can be any of a
variety of synthe-tic materials such as polyesters,
polyamides, and -the like. For example, nylon has
excellent resistance to abrasion, althouyh it will
extend or contract in use. Thus, the preferred
machine directon yarns, which can be selected to
provide a standard temperature and hydrolysis
resistant warp structure, preferably include a
combination of polyester, nylon and acrylic yarns so
engineered as to combine the best properties of each
yarn. For example, the polyester and nylon yarns
resist wear, the nylon and acrylic yarns resist
hydrolysis, the polyester and acrylic yarns resist
heat, and the polyester yarns give fabric stability.
Similarly, a high temperature and hydrolysis
resistant warp s-tructure can include a combination of
polyes-ter, nylon,acryLic, Nomex* and Kevlar* yarns.
In that case, the polyester and nylon yarns resist
wear, thé acrylic, nylon and Nomex* yarns resist
hydrolysis, the polyester, acrylic and Nomex* yarns
resist heat, and the polyester and Kevlar* yarns give
fabric stability.
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In the case of the cross-machine direction
yarns, standard cross-machine yarns usually cornbine
glass, polyester, and nylon and are engineered to
give excellent cross-machine stability and medium to
high permeability. However, for smooth
face fabrics at low permeability, the cross-machine direction
yarns are preferably glass and acrylic. Again, the yarns are
engineered to give excellent cross-machine stability.
Alternatively, a design having a machine dixection float face
can be used to produce a smooth face fabric as shown in Fig.
13. This can be produced with standard cross-machine yarns or,
for ultra smoothness, can be produced with glass and acrylic or
similar cross-machine yarns.
In the case of the load control yarns, the preferred
material is Kevlar, which has high strength, but o~fers poor
resistance to plucking-type wear. However, by using Kevlar as
the straight-through load control yarns, advantage can be taken
of its low stretch and high strength characteristics to control
o~erall fabric stretch, and because the Kevlar yarns are in the
interior of the fabric, they are at the same time fully
protected from wear, and hence their relatively poor abrasion
characteristics do not result in loss of ~abric strength during
fabric life on the paper machine. Similarly, when nylon is
employed in the basic weave, hecause the nylon has excellent
~o abrasion resistance, it will exhibit less wear, but the poor
resistance of nylon to stretch and contraction is overcome
because those properties of the fabric are controlled by the
Kevlar yarns in the interior of the fabric. The suitabillty of
Kevlar yarns as load control yarns is an unexpected result in
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view of Kevlar's* known ease of degrada-tion by
exposure to heat and moisture, and because both heat
and moisture are present in the papermaking machine,
the suitability of Kevlar* was questioned. Sur-
prisingly, however, the Kevlar* yarns , when employed
as described above, provided excellent results. In
particular, the Kevlar* straight-through center
machine-direction yarns were not attacked by the heat
and moisture because they were protected by the outer
yarns, and, further, because the Kevlar* yarns were
not crimped, they did not show the expected weakness
at the apex of a crimp. The performance of Kevlar*
was markedly better than anticipated.
Referring now to Figure 2, an alternative
fabric structure is illustrated in which double
machine direction yarn portions 42, 44 and 46, 48,
for example, engage and pass over and partially
around respective ones of each of the outwardly
facing surfaces of each of the cross-machine
direction yarns to further increase the resistance of
the fabric to surface wear. This particular fabric
structure is especially suitable where the fabric is
subjected to a high degree of abrasion, as could
exist, for example, when rusty or rough surface rolls
are present in the papermaking machine.
Additionally, -as clearly apparent from the Figure 2
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embodiment, two load control yarns 52, S4 are
provided in the same plane in each repeat of -the
fabric design. As is also clearly shown in Figure 2,
six machine direction yarns 56, 58, 60, 62, 64 and 66
are provided in the disclosed fabric structure, with
the yarns 56, 58, 64 and 66 also having portions
engaging and passing partially around inwardly Eacing
surfaces of respective ones of the cross-machine
direction yarns 12 through 22. Further, the machine
direction yarns are arranged in respective pairs 56
and 66, 58 and 64, and 60 and 62, which are
interwoven with the cross-machine yarns 12 through 22
in respectlve symmetrical patterns.
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Additional possible base fabric weaves that
can be provided -and in which the load control yarn
concept of the present invention can be employed are
illustrated in Figures 3 through 13. In Figures 3,
4, and 6, 11 and 12, three-ply fabrics are
illustrated, each having a pair of planes of load
control yarns 52, 54. The two planes are each
defined by a plurality of machine direction load
control yarns, the planes being symmetrical with a
center plane of the fabric structure and being
equally spaeed on each side of the center plane. In
Figures 5 and 7 through 10, and 13, two-ply fabrics
are illustrated, each having two load control yarns
52, 54 ln the same plane in each repeat of the fabric
design. In each fabric structure illustrated, load
control yarns 52, 54 define either one or more
parallel planes tha-t pass -through the fabrie
strue-ture without being interwoven with the
eross-maehine yarns. The load eontrol yarns are
preferably either at the fabrie eenter plane, or if
plural planes are defined by the load eontrol yarns,
as in the strueture shown in eaeh of Figures 3, 4, 6,
11 and 12, the planes are preferably clisposed at
equal distanees from the fabrle center plane.
However, as illustrated in Figure 5, it is also
possible to arrange the load control yarns so that
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they are disposed in a single plane on a single side
of the fabric center plane, with two load control
yarns 52, 54 being in the same plane in each repeat
of the fabric design. Also, as Figure 8 clearly
shows, six maehine direction yarns 76, 78, 80, 82, 84
and 86 are provided. Yarns 76, 78, 84 and 86 have
portions engaging and passing partially around an
outwardly facing surface portion of every other top
plane and bottom plane cross-machine direction yarn
portion. Additionally, the machine direction yarns
in the fabric structure illustrated in Figure 8 are
arranged in respective pairs 76, 86 and 80, 82. The
respective pairs of machine direction yarns engage
and pass partially around respectlve ones of the
outwardly facing and inwardly facing surfaee portions
of the cross-machine direction yarn portions in
respective symmetrical patterns. Two of the machine
direction yarns, 78 and 84, pass between top and
bottom planes and partially around ou-twardly facing
surface portions of the cross-machine dlrection
yarns.
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The fabrics that are made in accordance wlth the
present invention can have their ends~ joined toge~her to form~
an endless belt by using either metallic or non-metallic seams
such as are well known to those skilled in the art.
In addition to permitting a fabric construction that
has reduced stretch as compared with the prior known fabrics,
the above-described fabric structures having load control yarns
passing therethrough can be designed to provide fabric
permeability in the range of from 0 to 600 cfm, depending upon
the types of yarns and the type of weave that is employed.
Although, as pointed out above, several types of
desired weave patterns can be employed to take advantage of the
low stretch characteristics oE weaves that incorporate load
control yarns as hereinabove described, the preferred fabric
structures for use on papermaking machines are the structures
i}lustrated in Figures 1 and 2 of the drawings.
Although particular embodiments of the present
invention have been illustrated and described, i-t will be
apparent to those skilled in the art that various changes and
modifications can be made without departing from the spirit of
the present invention. It is therefore intended to cover in
the appended claims all such~ changes and modifications that
fall within the scope of the present invention.
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