Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PIN SEAMED PAPERMAKER'S PRESS FELT WITH LOW MELT
MATERIAL BAND IN LAMINATED BASE FABRIC
The present invention relates generally to papermaking, and more
particularly to fabrics used in papermaking.
Background of the Invention
In the conventional fourdrinier papermaking process, a water slurry,
or suspension, of cellulosic fibers (known as the paper "stock") is fed onto
the top
of the upper run of an endless belt of woven wire and/or synthetic material
that
travels between two or more rollers. The belt, often referred to as a "forming
fabric," provides a papermaking surface on the upper surface of its upper run
which
operates as a filter to separate the cellulosic fibers of the paper stock from
the
aqueous medium, thereby forming a wet paper web. The aqueous medium drains
through mesh openings of the forming fabric, known as drainage holes, by
gravity
alone or with assistance from one or more suction boxes located on the lower
surface (1~, the "machine side") of the upper run of the fabric.
After leaving the forming section, the paper web is transferred to a
press section of the paper machine, in which it is passed through the nips of
one or
more pairs of pressure rollers covered with another fabric, typically referred
to as a
"press felt." Pressure from the rollers removes additional moisture from the
web;
the moisture removal is often enhanced by the presence of a "batt" layer on
the
press felt. The paper is then conveyed to a drier section for further moisture
removal. After drying, the paper is ready for secondary processing and
packaging.
Press felts typically include one or more base fabric layers; these
can be "flat-woven" and formed after weaving into an endless belt, or can be
woven in endless form. Generally, the flat-woven process is preferred, as it
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typically less expensive and more versatile than the endless weaving process.
Also, in many instances the felt is cut widthwise and reattached to simplify
installation on a paper machine, in which case some of the advantages of
endless
weaving (such as the absence of a seam in the fabric) are lost.
Of course, flat weaving a fabric of a base layer requires that
provision be made for joining it into endless belts. Such joints should be
constructed in such a manner that they are sufficiently strong to withstand
the
extreme load, temperature, and wear conditions the press felt experiences, yet
do
not cause the surface of the press felt above the seam to unduly mark the
paper.
One popular method of joining the base fabric of a press felt is to form loops
with
machine direction yarns on each end of the base fabric. To form the flat-woven
base fabric into an endless belt, the ends of the fabric are placed adjacent
to each
other, with each of the loops on one end positioned between two loops on the
other
end in interdigitating fashion. A "pin" (usually formed of mutilfilament
polymeric
fiber strands) is then inserted into all of the loops to join the ends. After
the batt
layers) are needled or otherwise attached to the base layer, the batt layers)
are cut
at the seam location, the pin is removed, and the finished press felt is
shipped to a
paper mill. Once at the paper mill, the press felt can be installed by placing
it onto
a paper machine, then inserting another (usually more flexible) multifilament
pin
into the loops. Examples of this type of seam are described in U.S. Patent
Nos. 4,
764,417 and 4,737,241 to Gulya and 4,601,785 to Lilja et al., the disclosures
of
which are hereby incorporated herein by reference in their entireties.
In some press felts, the base fabric layer itself contains multiple
fabric layers (~,g., is a "laminated" base layer). For example, a felt may
contain a
"duplex" fabric (i:g., a fabric having upper and lower sets of machine
direction
yarns interwoven with at least one set of cross machine direction yarns - also
known as a "double layer" fabric) as well as a finer mesh single layer fabric
(j,g" a
fabric having only one set each of machine direction yarns and cross machine
direction yarns). This combination provides a good balance of strength and
durability to the felt with relatively little marking. Typically, the felt is
constructed
by flat weaving the duplex fabric, endless weaving the single layer fabric,
joining
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the duplex fabric with a pin as described above, overlaying the single layer
fabric
over the duplex fabric, needling both fabric layers with batt to form machine
side
and paper side batt layers, removing the pin from the double layer fabric and
cutting the batt layers ~ the single layer fabric at the seam to form a flat
structure. Once at the paper mill, the felt is installed on the papermaking
machine
by inserting a new, more flexible pin into the duplex fabric layer.
This press felt construction has at least one significant shortcoming.
When the single layer fabric is cut, its yarns, particularly its cross machine
direction yarns, tend to fray somewhat at the cut. Thus, when the felt is
installed
and operated on the paper machine, the frayed ends of the finer mesh single
layer
fabric can interfere with the manner in which the cut portion of the batt
layer
(which is often a flap of batt layer material) overlays the base fabric. As
such,
paper formed with such a felt can have an inconsistent appearance and be more
susceptible to breaking on the paper machine due to the presence of the seam
of the
felt.
Summa~r of the Invention
In view of the foregoing, it is an object of the present invention to
provide a press felt having a laminated base fabric with a reduced tendency
for the
fraying of yams at the base fabric seam.
It is also an object of the present invention to provide such a press
felt at a relatively low cost.
It is a further object of the present invention to provide a method for
constructing such a press felt.
These and other objects are satisfied by the present invention, which
is directed to a press felt having a laminated base fabric layer wherein one
of the
fabrics of the base fabric layer is joined via a pin seam as described
hereinabove,
and another of the fabrics of the base fabric layer includes a band of "low
melt"
material positioned over the pin seam. The papermaker's press felt of the
present
invention includes a base fabric layer (preferably sandwiched between a paper
side
batt layer and a machine side batt layer) comprising a first fabric and a
second
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fabric. The first fabric includes machine direction yarns and cross machine
direction yarns interwoven with the machine direction yarns, wherein the first
fabric has first and second ends with loops. The loops of the first end are
interdigitated with the loops of the second end and receive a pin to form the
first
fabric into an endless belt having a seam. The second fabric is formed into an
endless belt overlying the first fabric and includes machine direction yarns
and
cross machine direction yarns interwoven with the machine direction yarns. A
set
of the cross machine direction yarns is formed of a low melt material and
forms a
low melt band that traverses the fabric. The low melt band is positioned to
overlie
the seam of the first fabric. The low melt yarns, particularly after a
finishing heat
treatment, have a lower tendency to fray after cutting; thus, they are less
likely to
interfere with a cut seam in adjacent portions of attached batt layers.
Such a fabric can be constructed by a method of the present invention,
which comprises the following steps. The machine direction yarns and cross
machine direction yarns of the first fabric are interwoven such that the ends
of the
fabric have the aforementioned loops. The loops are then positioned in
interdigitated relationship, and a pin is inserted into the loops to form a
seam that
joins the first and second ends of the first fabric, thereby forming the first
fabric
into an endless belt. The machine direction yarns and cross machine direction
yarns of the second fabric are then interwoven (preferably through a flat
weaving
process) such that cross machine direction yarns formed of a low melt material
forms a low melt band that traverses said fabric. The second fabric is
attached to
the first fabric such that the low melt band of the second fabric overlies the
seam of
the first fabric to form a laminated base fabric layer. After any batt layers
are
attached, the low melt band is heated to cause the low melt material to
soften. A
seam is then cut through the low melt band and any batt layers that correspond
to
the seam of the first fabric.
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Figure 1 is a schematic illustration of the press section of a paper
machine employing a press felt of the present invention.
Figure 2 is an enlarged partial cutaway perspective view of the
press felt of Figure 1.
Figure 3 is a greatly enlarged side section view of the press felt of
Figure 1.
Figure 4A is a greatly enlarged partial perspective view of the pin
seam of the press felt of Figure 1 in a joined condition.
Figure 4B is an enlarged partial perspective view of the pin seam of
Figure 4A in an unjoined position.
Figure 5 is a schematic representation of a process for constructing
the press felt of Figure 1.
Detailed Description of the Invention
The present invention now will be described more fully hereinafter
with reference to the accompanying drawings, in which preferred embodiments of
the invention are shown and described. This invention may, however, be
embodied in many different forms and should not be construed as limited to the
embodiments set forth herein; rather, these embodiments are provided so that
this
disclosure will be thorough and complete, and will fully convey the scope of
the
invention to those skilled in the art. Like numbers refer to like components
throughout. Components and layers may be exaggerated for clarity.
As used herein, the teens "machine direction" (MD) and "cross
machine direction" (CMD) refer, respectively, to a direction aligned with the
direction of travel of the papermakers' fabric on a papermaking machine, and a
direction parallel to the fabric surface and transverse to the direction of
travel.
Also, both the flat weaving and endless weaving methods described hereinabove
are well known in the art, and the term "endless belt" as used herein refers
to belts
made by either method.
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Referring now to the drawings, a papermaking machine press
section, designated broadly at 10, is illustrated in Figure 1. The press
section 10
includes a press felt I4 that is installed upon and conveyed by a set of
rollers 12.
In its travel, the felt 14 travels over a press roll 15. An opposed press roll
17 is
positioned to, in conjunction with the felt 14 and press roll 15, form a nip
~1
between the press rolls 15.
In operation, a paper web ~ is conveyed from a forming section 16
through the nip ~ formed by the press rollers 15, 17, wherein pressure is
applied to
the paper web ~ by the press rolls 15, 17. The pressure forces moisture from
the
paper web ~ that is absorbed by the feh 14. As the felt 14 is conveyed around
its
roller set 12, moisture is removed therefrom, and the felt 14 is conditioned
by one
or more suction boxes 20.
Figures 2 and 3 illustrate an enlarged section of the felt 14. As can
be seen in Figure 2, the felt 14 includes a laminated base fabric layer 22
which
comprises two separate fabrics: namely, a lower fabric layer comprising a
duplex
fabric 24 and an upper fabric layer comprising a single layer fabric 36. The
duplex
fabric 24 includes two sets of machine direction yams 26 and one set of cross
machine direction yarns 28 interwoven with the machine direction yarns 26. The
duplex fabric 24 is woven in a flat weave process; thus, in a flat condition,
the
duplex fabric 24 has two free ends 29a, 29b, one of which (29a) includes loops
30
(formed by machine direction yarns 26), and the other of which (29b) includes
loops 32 formed by machine direction yarns 26. When the duplex fabric 24 is in
an endless condition such as that illustrated in Figures 2 and 3, the loops
30, 32 are
positioned in interdigitated fashion, and a pin 34 is inserted through the
loops 30,
32 to join the ends 29a, 29b of the duplex fabric 24 (see Figures 4A and 4B).
Those skilled in this art will recognize that other types of fabrics can be
employed as the lower fabric layer of the base fabric layer 22 in the manner
of the
duplex fabric 24, including single layer fabrics, other duplex fabrics, and
triplex
fabrics (~, those having two sets of machine direction yarns and two sets of
cross
machine direction yarns). Virtually any weave pattern known to those skilled
in
this art, such as the illustrated plain weave, twills, satins, and the like,
can be used
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for this fabric layer. The lower fabric layer will typically, but not always,
have a
mesh that is somewhat more coarse than that of the upper fabric layer; it is
preferred that the mesh of the lower fabric layer be between about 30 to 50
machine direction yarns and 50 to 100 cross machine direction yarns per inch.
The
lower fabric layer should have the aforementioned loops 30, 32 at its ends
29a, 29b
to enable it to be joined into an endless belt with the pin. The construction
of the
loops 30, 32 and pin 34 are known to those skilled in this art and need not be
described in detail herein; exemplary loop and pin constructions are described
in
U.S. Patent Nos. 4,737,241 and 4,764,417 to Gulya.
Still referring to Figures 2 and 3, the single layer fabric 36
comprises machine direction yarns 38 interwoven with cross machine direction
yarns 40 in a plain weave pattern. The single layer fabric 36 includes a low
melt
band 42 that traverses the width of the single layer fabric 36 over an area
approximately six inches in length. The low melt band 42 includes low melt
cross
machine direction yarns 44 that differ in material composition from the
remaining
cross machine direction yarns. As used herein, the term "low melt" means that
the
yarns have a lower melting point than at least the machine direction yarns of
the
lower fabric layer, and in many instances than the other yarns of both the
upper and
lower fabric layers. The melting point of the low melt yarns should be at
least
25°C lower than that of the machine direction yarns of the lower fabric
layer.
Exemplary low melt materials to be employed as cross machine direction yarns
44
in the low melt band 42 include nylons (including nylon 6, nylon 66, nylon
610,
nylon 612 and nylon 12, and blends and copolymers thereof), polyesters and
copolymers thereof and polypropylene and copolymers thereof.
Those skilled in this art will recognize that other types of fabrics can be
employed as the upper fabric layer of the base fabric layer 22 in the manner
of the
single layer fabric 36, including other single layer fabrics, duplex fabrics,
and
triplex fabrics. Virtually any weave pattern known to those skilled in this
art, such
as the illustrated plain weave, twills, satins, and the like, can be used for
this fabric
layer. The mesh of the upper fabric layer may vary from between about 16 to
100
machine direction yarns and 16 to 100 cross machine direction yarns per inch,
but
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typically the mesh will be somewhat finer than that of the lower fabric layer.
Those skilled in this art will also recognize that, although it is preferred
for cost
reasons to employ low melt yarns 44 as cross machine direction yarns in the
low
melt band 42 only, low melt yarns can also be used as the machine direction
yarns
and/or the remaining cross machine direction yarns of the upper fabric layer,
or
even as the cross machine direction yarns of the lower fabric layer.
Preferably, the single layer fabric 36 is woven in a flat weaving
process that produces a fabric with two free ends. The single layer 36 is
formed
into an endless belt through a joining process such as heat welding, which
forms a
weld line 46, although other methods of joining known in the art may also be
employed.
The form of the yarns employed in the lower and upper fabric layers
of the base fabric layer 24 can vary, depending upon the desired properties of
the
final press felt. For example, the yarns may be multif lament yarns,
monofilament
yarns, twisted or cabled multifilament or monofilament yarns, spun yarns, or
any
combination thereof. Also, the materials from which the yarns employed in the
fabric layers are formed may be those commonly used in press felts, such as
nylon,
cotton, wool, polypropylene, polyester, aramid, polyamide, or the like, and
blends
and combinations thereof.
The felt 14 also includes two batt layers: a machine side batt layer
50 and a paper side batt layer 52. Illustratively and preferably, these batt
layers 50,
52 are attached to the base fabric layer 22 through a needling process,
although
other attachment techniques, such as heat bonding and adhesives, can also be
used
with the present invention. The machine side and paper side batt layers 50, 52
should be formed of material, such as a synthetic fiber like acrylic, aramid,
polyester, or nylon, or a natural fiber such as wool, that assists in wicking
water
away from the base fabric layer 22. Preferred materials for the batt layers
50, 52
include polyamide, polyester and blends thereof. The weight and thickness of
the
batt layers 50, 52 can vary, although it is preferably that the ratio of batt
weight to
fabric weight is about between about 0.5 and 2.0, with 1.0 being more
preferred.
Also, in some embodiments, it may be desirable to have additional batt layers
or to
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omit either or both of the batt layers 50, 52.
Notably, the felt 14 includes a seam cut 48. The seam cut 48
extends through the paper side batt layer 52, the single layer fabric 36, and
the
machine side batt layer 50. Illustratively and preferably, the seam cut 48 is
made at
an angle of between about 30 and 90 degrees to the plane of the base fabric
layer
22, and a flap 52a is formed by loosening the portion of the paper side batt
layer 5Z
adjacent the seam cut 48. This process is described in detail in the
aforementioned
U.S. Patents to Gulya and Lilja. Of course, no cut is necessary for the duplex
fabric 24, as the pin 34 can simply be removed to enable the ends 29a, 29b of
the
duplex fabric 24 to be separated.
Figure 5 illustrates an exemplary manufacturing process for the felt
I4. Initially, the duplex fabric 24 is flat woven such that machine direction
loops
30, 32 are created on the ends 29a, 29b. A pin 60 (which is typically larger
and
less flexible than the pin 34 described above) is inserted through the loops
30, 32
(as they are interdigitated) to join them and thereby form the duplex fabric
24 into
an endless belt. Separately, the single layer fabric 36 is woven in a flat
weaving
process. The single layer fabric 36 is formed into an endless belt with a heat
welding process, such as one that employs heat or ultrasonic radiation. The
single
layer fabric 36 is then positioned to overlie the duplex fabric 24 such that
the low
melt band 42 overlies the pin 34, and the machine side and paper side batt
layers
50, 52 are needled to the base fabric layer 22.
Once the batt layers 50, 52 have been added, the entire felt 14 is
then heat treated at a temperature sufficient to cause softening of the yarns
44 of
the low melt band 42 without unduly softening the other yarns of the base
fabric
22, and in particular the machine direction yarns 26. Typically, the heat
treatment
is carried out at a temperature of between about 130° to 200° C.
The pin 60 is then
removed, and the seam cut 48 is formed with blades or other cutting devices
through the machine side and paper side batt layers 50, 52 and the single
layer
fabric 36. The felt 14 can then be shipped in its flat form to a paper mill,
where the
pin 34 can be inserted into the machine direction loops 30, 32 as the felt 14
is
installed on the upper rolls 12.
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Importantly, when the seam cut 48 is made, the yarns of the single
layer fabric 36, and in particular the cross machine direction yams 38 have a
far
lower tendency to fray than the fabrics of prior art felts. This reduced
fraying is the
result of the inclusion of the low melt cross machine direction yarns 44 and
the low
melt band 42. As described, during the heat treatment of the felt 14, the
softening
of the low melt cross machine direction yarns 44 causes the agglomeration of
the
cross machine yarns 44, the machine direction yarns 38 and the fibers of the
paper
side batt layer 52. As a result, the flap 52a adjacent to the seam cut 48 lays
much
more uniformly than has been the case in prior art fabrics.
The invention will now be more particularly described in the
following non-limiting example.
A press felt was constructed according to the following parameters
MD yarns CMD Mesh
yarns
Base Fabric Layer Size Material Size Materials
(inches) (inches)
Duplex Layer 0.040 Nylon 0.040 Nylon 40x80
Single Layer 0.08x4 Cabled 0.080 Nylon 32x
nylon 12
Low Belt Band --- --- 0.080 Nylon 32x12
copolymer
Batt Layers Material Weight (glmz}
Machine Side Nylon staple 1 SO
Paper Side Nylon staple 780
Heat Treatment: 3 minutes at 175°C.
The resulting press felt successfully produced linerboard paper.
The foregoing is illustrative of the present invention and is not to be
construed as limiting thereof. Although exemplary embodiments of this
invention
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have been described, those skilled in the art will readily appreciate that
many
modifications are possible in the exemplary embodiments without materially
departing from the novel teachings and advantages of this invention.
Accordingly,
all such modifications are intended to be included within the scope of this
invention as defined in the claims. The invention is defined by the following
claims, with equivalents of the claims to be included therein. In the claims,
means-
plus-function clauses are intended to cover the structures described herein as
performing the recited function and not only structural equivalents but also
equivalent structures.
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