Note: Descriptions are shown in the official language in which they were submitted.
7l~2
PAPERMAKERS FABRIC HAVING A SINGLE LAYER OF CROSS MACHINE
DIRECTION YARNS
The present invention relates to papermakers fabrics and
in particular to fabrics comprised of flat monofilament yarns.
BACKGROUND OF THE INVENTION
Papermaking machines generally are comprised of three
sections: forming, pressing, and drying. Papermakers fabrics
are employed to transport a continuous paper sheet through the
papermaking equipment as the paper is being manufactured. The
requirements and desirable characteristics of papermakers
fabrics vary in accordance with the particular section of the
machine where the respective fabrics are utilized.
With the development of synthetic yarns, shaped
monofilament yarns have been employed in the construction of
papermakers fabrics. For example, U.S. Patent No. 4,290,209
discloses a fabric woven of flat monofilament warp yarns; U.S.
Patent No. 4,755,420 discloses a non-woven construction where
the papermakers fabric is comprised of spirals made from flat
monofilament yarns.
Numerous weaves are known in the art which are
~i~ 74~2
employed to achieve different results. For example, U.S.
Patent No. 4,438,788 discloses a dryer fabric having three
layers of cross machine direction yarns interwoven with a
system of flat monofilament machine direction yarns such that
floats are created on both the top and bottom surfaces of the
fabric. The floats tend to provide a smooth surface for the
fabric.
Permeability is an important criteria in the design of
papermakers fabrics. In particular, with respect to fabrics
made for running at high speeds on modern drying equipment, it
is desirable to provide dryer fabrics with relatively low
permeability.
U.S. Patent No. 4,290,209 discloses the use of flat
monofilament warp yarns woven contiguous with each other to
provide a fabric with reduced permeability. However, even where
flat warp yarns are woven contiguous with each other,
additional means, such as stuffer yarns, are required to reduce
the permeability of the fabric. As pointed out in that patent,
it is desirable to avoid the use of fluffy, bulky stuffer yarns
to reduce permeability which make the fabric susceptible to
picking up foreign substances or retaining water.
U.S. Patent No. 4,290,209 and U.S. Patent No. 4,755,420
note practical limitations in the aspect ratio (cross-sectional
width to height ratio) of machine direction warp yarns defining
the structural weave of a fabric. The highest practical aspect
2~002
ratio disclosed in those patents is 3:1, and the aspect ratio
is preferably, less than 2:1. U.S. Patent No. 4,621,663,
assigned to the assignee of the present invention, discloses
one attempt to utilize high aspect ratio yarns ton the order of
5:1 and above) to define the surface of a papermakers dryer
fabric. As disclosed in that patent, a woven base fabric is
provided to support the high aspect ratio surface yarns. The
woven base fabric is comprised of conventional round yarns and
provides structural support and stability to the fabric
disclosed in that patent.
U.S. Patent No. 4,815,499 discloses the use of flat yarns
in the context of a forming fabric. That patent discloses a
composite fabric comprised of an upper fabric and a lower
fabric tied together by binder yarns. The aspect ratio employed
for the flat machine directi~n yarns in both the upper and
lower fabrics are well under 3:1.
In use, papermakers fabrics are configured as endless
belts. Weaving techniques are available to initially weave
fabrics endless. However, there are practical limitations on
the overall size of endless woven fabrics as well as inherent
installation difficulties. Moreover, not all papermaking
equipment is designed to accept the installation of an endless
fabric.
Flat woven fabrics are often supplied having
opposing ends which are seamed together during installation of
~7~ 002
the fabric on papermaking equipment. Usually one end of the
fabric is threaded through the serpentine path defined by the
papermaking equipment and is then joined to its opposing end to
form a continuous belt.
A variety of seaming techniques are well known in the art.
One conventional method of seaming is to form the machine
direction yarns on each end of the fabric into a series of
loops. The loops of the respective fabric ends are then
intermeshed during fabric installation to define a channel
through which a pintle is inserted to lock the ends together.
For example, U.S. Patent Nos. 4,026,331; 4,438,789;
4,469,142; 4,846,231; 4,824,525 and 4,883,096 disclose a
variety of pin seams wherein the machine direction yarns are
utilized to form the end loops. In each of those patents,
however, t-he machine direction yarn projects from the end of
the fabric and weaves back into the fabric adjacent to itself.
Accordingly, the loops inherently have a twist or torque factor
and are not entirely orthogonal to the plane of the fabric.
U.S. Patent 4,883,096 specifically addresses this problem.
It would be desirable to provide a papermakers fabric with
machine direction seaming loops which do not have torque and/or
twist.
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SUMMARY AND OBJECTS INVENTION
The present invention provides a papermakers fabric having
a system of flat monofilament machine direction yarns
(hereinafter MD yarns) which are stacked to control the
permeability of the fabric. The present weave also provides for
usage of high aspect ratio yarns as structural weave
components. The system of MD yarns comprises upper and lower
yarns which are vertically stacked. Preferably, the upper MD
yarns define floats on the upper surface of the fabric and each
upper MD yarn is paired in a vertically stacked orientation
with a lower MD yarn. The lower MD yarns may weave in an
inverted image of the upper MD yarns to provide floats on the
bottom fabric surface or may weave with a different repeat to
provide a different surface on the bottom of the fabric.
- 15 At least the upper MD yarns are flat monofilament yarns
woven contiguous with each other to reduce the permeability of
the fabric and to lock in the machine direction alignment of
the stacking pairs of MD yarns. In the preferred embodiment,
the same type and size yarns are used throughout the machine
direction yarn system and both the top and the bottom MD yarns
weave contiguously with adjacent top and bottom MD yarns,
respectively. The stacked, contiguous woven machine direction
system provides stability and permits the MD yarns to have a
relatively high aspect ratio, cross-sectional width to
height, of greater than 3:1.; the aspect ratio preferably
~17~0~
ranging from about 2:1 to 6:1. Machine direction yarns further
define a series of orthogonal seaming loops on the opposing
fabric ends. End segments of the lower MD yarns are removed and
the upper MD yarn ends are looped back upon themselves and
rewoven into the fabric end in the space vacated by the trimmed
lower MD yarn end segments. The lower MD yarns may weave in an
inverted image of the upper MD yarns such that the crimp of the
upper MD yarn conforms with the lower MD yarn weave pattern
space into which the upper MD yarn ends are backwoven. This
improves the strength of the seam.
Non-loop forming upper MD yarns are also preferably
backwoven into the space vacated by trimming the respective
lower MD yarns. Preferably, at least the upper MD yarns are
woven contiguous with each other to lock in the machine
direction alignment of the stacking pairs of MD yarns and the
orthogonal orientation of the end loops. In the preferred
embodiment, the same type of material and the same geometric
shape and size yarns are used throughout the machine direction
yarn system and both the top and the bottom MD yarns weave
contiguously with adjacent top and bottom MD yarns,
respectively.
It is an object of the invention to provide a papermakers
fabrics having permeability controlled with woven flat machine
direction yarns.
2174~2
It is a further object of the invention to provide a low
permeability fabric constructed of all monofilament yarns
without the use of bulky stuffer yarns and without sacrificing
strength or stability.
Other objects and advantages will become apparent from the
following description of presently preferred embodiments.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1 is a schematic diagram of a papermakers fabric
made in accordance with the teachings of the present invention;
Figure 2 is a cross-sectional view of the fabric depicted
in Figure 1 along line 2-2;
Figure 3a is a cross-sectional view of the fabric depicted
in Figure 1 along line 3-3;
Figure 3b is a cross-sectional view of a prior art weave
construction;
Figure 4a illustrates the yarn orientation in the fabric
depicted in Figure 1 after the fabric is finished showing only
two representative stacked MD yarns;
Figures 4b, 4c, and 4d are a series of illustrations
showing the formation of a seaming loop for the papermakers
fabric depicted in Figure 1;
Figure Sa is a perspective view of a prior art MD yarn
seaming loop;
~17~0~
Figure 5b is a perspective view of an orthogonal MD yarn
seaming loop made in accordance with the present invention;
Figure 6 is a schematic view of a second embodiment of a
fabric made in accordance with the present invention;
Figure 7 is a cross-sectional view of the fabric depicted
in Figure 6 along line 7-7;
Figure 8 is a cross-sectional view of the fabric depicted
in Figure 6 along line 8-8;
Figure 9 is a perspective view of a portion of the fabric
illustrated in Figures 6-8;
Figure 10 illustrates the yarn orientation in the finished
fabric depicted in Figure 6 showing the end loop formed by one
of the MD yarns;
Figure 11 is a top view of the opposing ends of a fabric
constructed in accordance with Figure 6 just prior to-
pin-seaming the ends together;
Figure 12 is a schematic view of a third alternate
embodiment of a fabric made in accordance with the teachings of
the present invention showing only one pair of stacked MD
yarns;
Figure 13 is a schematic view of a fourth alternate
embodiment of a fabric made in accordance with the teachings of
the present invention showing only one pair of stacked MD
yarns;
%l74~a2
Figure 14 is a schematic view of a fifth alternate
embodiment of a fabric made in accordance with the teachings of
the present invention showing only one pair of stacked MD
yarns;
Figure 15 is a schematic view of a sixth alternate
embodiment of a fabric made in accordance with the teachings of
the present invention showing only one pair of stacked MD
yarns;
Figure 16 is a schematic view of a seventh alternate
embodiment of a fabric made in accordance with the teachings of
the present invention showing only one pair of stacked MD
yarns; and
Figure 17 is a schematic view of a eighth alternate
embodiment of a fabric made in accordance with the teachings of
the present invention showing only one pair of stacked MD
yarns.
DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS
Referring to Figures 1, 2, and 3a, there is shown a
papermakers dryer fabric 10 comprising upper, middle and lower
layers of cross machine direction (hereinafter CMD) yarns 11,
12, 13, respectively, interwoven with a system of MD yarns
14-19 which sequentially weave in a selected repeat pattern.
The MD yarn system comprises upper MD yarns 14, 16, 18 which
interweave with CMD yarns 11, 12 and lower MD yarns 15, 17, 19
217~0 iO2
which interweave with CMD yarns 12, 13.
The upper MD yarns 14, 16, 18 define floats on the top
surface of the fabric 10 by weaving over two upper layer CMD
yarns 11 dropping into the fabric to weave in an interior
knuckle under one middle layer CMD yarn 12 and under one CMD
yarn 11 and thereafter rising to the surface of the fabric to
continue the repeat of the yarn. The floats over upper layer
CMD yarns 11 of upper MD yarns 14, 16, 18 are staggered so that
all of the upper and middle layer CMD yarns 11, 12 are
maintained in the weave.
As will be recognized by those skilled in the art, the
disclosed weave pattern with respect to Figures 1, 2, and 3a,
results in the top surface of the fabric having a twill
pattern. Although the two-float twill pattern represented in
Figures 1, 2, and 3a is a preferred embodiment, it will be
recognized by those of ordinary skill in the art that the
length of the float, the number of MD yarns in the repeat, and
the ordering of the MD yarns may be selected as desired so that
other patterns, twill or non-twill, are produced.
As best seen in Figures 2 and 3a, lower MD yarns 15, 17,
19, weave directly beneath upper MD yarns 14, 16, 18,
respectively, in a vertically stacked relationship. The lower
yarns weave in an inverted image of their respective upper
2174~
., .
yarns. Each lower MD yarn 15, 17, 19 floats under two lower
layer CMD yarns 13, rises into the fabric over one CMD yarn 13
and forms a knuckle around one middle layer CMD yarn 12
whereafter the yarn returns to the lower fabric surface
to continue its repeat floating under the next two lower layer
CMD yarns 13.
With respect to each pair of stacked yarns, the interior
knuckle, formed around the middle layer CMD yarns 12 by one MD
yarn, is hidden by the float of the other MD yarn.
For example, in Figures 1 and 3a, lower MD yarn 15 is
depicted weaving a knuckle over CMD yarn 12 while MD yarn 14 is
weaving its float over CMD yarns 11, thereby hiding the
interior knuckle of lower MD yarn 15. Likewise, with respect to
Figures 1 and 3a, upper MD yarn 18 is depicted weaving a
knuckle under yarn CMD yarn 12 while it is hidden by lower MD
yarn 19 as it floats under CMD yarns 13.
The upper MD yarns 14, 16, 18, are woven contiguous with
respect to each other. This maintains their respective parallel
machine direction alignment and reduces permeability. Such
close weaving of machine direction yarns is known in the art
as 100% warp fill as explained in U.S. Patent No. 4,290,209.
As taught therein (and used herein), actual warp count in a
woven fabric may vary between about 80%-125% in a single layer
and still be considered 100% warp fill.
The crowding of MD yarns 14, 16, and 18 also serves to
11
~1740~2
force MD yarns 15, 17, 19, into their stacked position beneath
respective MD yarns 14, 16, 18. Preferably MD yarns 15, 17,
and 19 are the same size as MD yarns 14, 16, and 18 so that
they are likewise woven 100% warp fill. This results
in the overall fabric of the preferred embodiment having 200%
warp fill of MD yarns.
Since the lower MD yarns 15, 17, 19 are also preferably
woven 100% warp fill, they likewise have the effect of
maint~;n;ng the upper MD yarns 14, 16, 18 in stacked
relationship with the respect to lower MD yarns 15, 17, 19.
Accordingly, the respective MD yarn pairs 14 and 15, 16 and 17,
18 and 19 are doubly locked into position thereby enhancing the
stability of the fabric.
As set forth in the U.S. Patent No. 4,290,209, it has been
recognized that machine direction flat yarns will weave in
closer contact around cross machine direction yarns than round
yarns. However, a 3:1 aspect ratio was viewed as a practical
limit for such woven yarns in order to preserve overall fabric
stability. The present stacked MD yarn system preserves the
stability and machine direction strength of the fabric and
enables the usage of yarns with increased aspect ratio, in a
preferred range of 2:1 to 6:1, to more effectively control
permeability.
~l74a32
-
The high aspect ratio of the MD yarns translates into reduced
permeability. High aspect ratio yarns are wider and thinner
than conventional flat yarns which have aspect ratios less than
3:1 and the same cross-sectional area. Equal cross-sectional
area means that comparable yarns have substantially the same
linear strength. The greater width of the high aspect ratio
yarns translates into fewer interstices over the width of the
fabric than with conventional yarns so that fewer openings
exist in the fabric through which fluids may flow. The relative
thinness of the high aspect ratio yarns enables the flat MD
yarns to more efficiently cradle, i.e. brace, the cross machine
direction yarns to reduce the size of the interstices between
machine direction and cross machine direction yarns. F o r
example, as illustrated in Figure 3b, a fabric woven with a
single layer system of a flat machine direction warp having a
cross-sectional width of 1.5 units and a cross-sectional height
of 1 unit, i.e. an aspect ratio of 1.5:1, is shown. Such fabric
could be replaced by a fabric having the present dual stacked
MD yarn system with MD yarns which are twice the width, i.e. 3
units, and half the height, i.e. 0.5 units. Such MD yarns
thusly having a fourfold greater aspect ratio of 6:1, as
illustrated in Figure 3a.
The thinner, wider MD yarns more efficiently control
~174~2
permeability while the machine direction strength of the fabric
r~m~i n~ essentially unaltered since the cross-sectional area of
the MD yarns over the width of the fabric remains the same. For
the above example, illustrated by Figures 3a and 3b, the
conventional single MD yarn system fabric has six conventional
contiguous flat yarns over 9 units of the fabric width having
a cross-sectional area of 9 square units, i.e. 6*(1u.*1.5u.).
The thinner, wider high aspect ratio yarns, woven as contiguous
stacked MD yarns, define a fabric which has three stacked pairs
of MD yarns over 9 units of fabric width. Thus such fabric also
has a cross-sectional area of 9 square units, i.e.
(3*(0.5u.*3u.))+ (3*(0.5u.*3u.)), over 9 units of fabric width.
In one example, a fabric was woven in accordance with
Figures 1, 2 and 3, wherein the CMD yarns 11, 12, 13 were
polyester monofilament yarns 0.6mm in diameter interwoven with
MD yarns 14-19 which were flat polyester monofilament yarns
having a width of 1.12mm and a height of 0.2mm. Accordingly,
the aspect ratio of the flat MD yarns was 5.6:1. The fabric was
woven at 48 warp ends per inch with a loom tension of 40 PLI
(pounds per linear inch) and 12.5 CMD pick yarns per inch per
layer (three layers).
The fabric was heat set in a conventional heat setting
apparatus under conditions of temperature, tension and time
within known ranges for polyester monofilament yarns. For
example, conventional polyester fabrics are heat set within
14
2174~2
parameters of 340F - 380F temperature, 6-15 PLI (pounds per
linear inch) tension, and 3-4 minutes time. However, due to
their stable structure, the fabrics of the present invention
are more tolerant to variations in heat setting parameters.
The fabric exhibited a warp modulus of 6000 PSI (pounds
per square inch) measured by the ASTM D-1682-64 standard of the
American Society for Testing and Materials. The fabric
stretched less than 0.2% in length during heat setting. This
result renders the manufacture of fabrics in accordance with
the teachings of the present invention very reliable in
achieving desired dimensional characteristic as compared to
conventional fabrics. The resultant heat set fabric had 12.5
CMD yarns per inch per layer with 106% MD warp fill with
respect to both upper and lower MD yarns resulting in 212%
actual warp fill for the fabric. The finished fabric has a
permeability of 83CFM as measured by the ASTM D-737-75
standard.
As illustrated in Figure 4a, when the fabric 10 is woven
the three layers of CMD yarns 11, 12, 13 become compressed.
This compression along with the relatively thin dimension of
the MD yarns reduces the caliper of the fabric. Accordingly,
the overall caliper of the fabric can be maintained relatively
low and not significantly greater than conventional fabrics
woven without stacked MD yarn pairs. In the above example, the
caliper of the finished fabric was 0.050 inches.
2174~2
-
It will be recognized by those of ordinary skill in the
art that if either top MD yarns 14, 16, 18 or bottom MD yarns
15, 17, 19 are woven at 100% warp fill, the overall warp fill
for the stacked fabric will be significantly greater than 100%
which will contribute to the reduction of permeability of the
fabric. The instant fabric having stacked MD yarns will be
recognized as having a significantly greater percentage of a
warp fill than fabrics which have an actual warp fill of 125%
of non-stacked MD yarns brought about by crowding and lateral
undulation of the warp strands. Although the 200% warp fill is
preferred, a fabric may be woven having 100% fill for either
the upper or lower MD yarns with a lesser degree of fill for
the other MD yarns by utilizing yarns which are not as wide as
those MD yarns woven at 100% warp fill. For example, upper
yarns 14, 16, 18 could be 1 unit wide with lower layer yarns
15, 17, 19 being .75 units wide which would result in a fabric
having approximately 175% warp fill.
Such variations can be used to achieve a selected degree
of permeability. Alternatively, such variations could be
employed to make a forming fabric. In such a case, the lower MD
yarns would be woven 100% warp fill to define the machine side
of the fabric and the upper ND yarns would be woven at a
substantially lower percentage of fill to provide a more open
paper forming surface.
The stacked pair MD weave permits the formation of
16
2174~2
-
orthogonal seaming loops within MD yarns. With reference to
Figures 4a-d, after the fabric has been woven and heat set
(Figure 4a), CMD yarns are removed leaving the crimped MD yarns
14, 15 exposed (Figure 4b). One of the yarns, for example, MD
lower yarn 15, of the stacked pair is trimmed back a selected
distance leaving the other exposed MD yarn 14 of the MD yarn
pair and vacated space between the CMD yarns, as illustrated in
Figure 4c. Upper MD yarn 14 is then backwoven into the space
vacated in the weave pattern by lower MD yarn 15 such that a
loop L is formed on the end of the fabric, as illustrated in
Figure 4d. Preferably, between 0.5 - 5.0 inches of upper layer
yarn 14 is backwoven into the fabric to provide sufficient
strength for the end loop and assure retention of the free end
of MD yarn 14 within the weave of the fabric. The inverted
image weave permits the crimp of the upper MD yarn 14 to match
the space vacated by the lower MD yarn 15 which further
enhances the strength of the end loop.
As shown in phantom in Figure 4d, adjacent yarn pair 16,
17 is processed in a similar manner. However, when upper yarn
16 is looped back and backwoven in the fabric, it is pulled
against the CMD yarns. In the preferred embodiment, wherein the
upper MD yarns are woven 100% fill, the crowding of the yarns
secure the orthogonal orientation of the seaming loops.
To achieve a uniform seam for a fabric woven in accordance
2174~32
-
with the weave pattern depicted in Figure 1, each upper MD yarn
14 forms a loop and the other upper MD yarns 16, 18 are
backwoven against the endmost CMD yarn of the fabric. Thus
every third upper MD yarn defines a loop such that an array of
loops is created on each end of the fabric. The seam is
assembled by intermeshing the opposing arrays of loops and
inserting a pintle yarn between the intermeshed loops.
Preferably, loop forming yarns 14 would all be backwoven
approximately the same distance within the fabric to provide
sufficient strength to prevent the loops from being pulled
apart during normal usage. Non-loop forming yarns 16, 18,
would preferably be backwoven a somewhat shorter distance
since during usage no load is imparted to those yarns. For
example, upper MD yarns 14 would be backwoven approximately 3
- inches, MD yarns 16 would be backwoven approximately 2 inches,
and MD yarns 18 would be backwoven approximately 1 inch.
Respective lower layer yarns 15, 17, 19 would be trimmed to
complement the backweaving of their respective MD yarn pair
yarns 14, 16, 18.
Figures 5a and 5b, respectively, illustrate a
conventional seaming loop 50 in comparison with an orthogonal
seaming loop L of the present invention. In conventional loop
forming techniques, the MD yarn S1 is backwoven into the fabric
adjacent to itself thereby inherently imparting twist and/or
18
2 1 ~ 2
torque to the loop structure 50. In the present invention, the
MD yarn is looped directly beneath itself and does not have
any lateral offset which would impart such twist or torque to
the seaming loop.
s Referring to Figures 6, 7 and 8, there is shown a second
preferred embodiment of a fabric 20 made in accordance with the
teachings of the present invention. Papermakers fabric 20 is
comprised of a single layer of CMD yarns 21a, 21b interwoven
with a system of stacked MD yarns 22-25 which weave in a
selected repeat pattern. The MD yarn system comprises upper MD
yarns 22, 24 which define floats on the top surface of the
fabric 20 by weaving over three CMD yarns, under the next one
CMD yarn 21a to form a knuckle, and thereafter returning to
float over the next three CMD yarns in a continuation of the
repeat.
Lower MD yarns 23, 25, weave directly beneath respective
upper MD yarns 22, 24 in a vertically stacked relationship. The
lower MD yarns weave in an inverted image of their respective
upper MD yarns. Each lower MD yarn 23, 25 floats under three
CMD yarns, weaves upwardly around the next one CMD yarn 21a
forming a knuckle and thereafter continues in the repeat to
float under the next three CMD yarns.
As can be seen with respect to Figures 6 and 8, the
knuckles formed by the lower MD yarns 23, 25 are hidden by the
floats defined by the upper MD yarns 22, 24 respectively.
19
217~û~2
Likewise the knuckles formed by the upper MD yarns 22, 24 are
hidden by the floats of the lower MD yarns 23, 25 respectively.
The caliper of the fabric proximate the knuckle area shown
in Figure 8, has a tendency to be somewhat greater than the
5caliper of the fabric at non-knuckle CMD yarns 21b, shown in
Figure 7. However, the CMD yarns 21a around which the knuckles
are formed become crimped which reduces the caliper of the
fabric in that area as illustrated in Figure 8. Additionally,
slightly larger diameter CMD yarns are preferably used for CMD
10yarns 21b, shown in Figure 7, which are not woven around as
knuckles by the MD yarns to eliminate any difference in fabric
caliber. Preferably the diameter of the larger CMD yarn 21b
equals the diameter d of the smaller CMD yarns 21a plus the
thickness t of the MD yarns.
15In one example, a fabric was woven in accordance with
Figures 6-9, wherein the CMD yarns 21a, 21b were polyester
monofilament yarns 0.6mm and 0.8mm, respectively, in diameter
interwoven with MD yarns 22-25 which were flat polyester
monofilament yarns having a width of 1.12mm and a height of
200.2mm. Accordingly, the aspect ratio of the flat MD yarns was
5.6:1. The fabric was woven at 48 total warp ends per inch
with a loom tension of 40 PLI (pounds per linear inch) and 20
CMD total pick yarns per inch. The permeability averaged 90 CFM
in the resultant fabric.
25In another example, fabric was woven in accordance with
~171û~2
Figures 6, 7 and 8, wherein the CMD yarns 2la, 2lb were
polyester monofilament yarns 0.7mm in diameter interwoven with
MD yarns 22-25 which were flat polyester monofilament yarns
having a width of 1.12mm and a height of 0.2mm. Accordingly,
s the aspect ratio of the flat MD yarns was 5.6:1. The fabric was
woven at 22 CMD pick yarns per inch. The fabric was heat set
using conventional methods. The fabric exhibited a modules of
6000 PSI. The fabric stretched less than 0.2% in length during
heat setting. The resultant fabric had 22 CMD yarns per inch
with 106% MD warp fill with respect to both upper and lower MD
yarns resulting in 212% actual warp fill for the fabric. The
finished fabric had a caliper of .048 inches and an air
permeability of 60CFM.
As best shown in Figure 9, the high aspect ratio yarns
22-24 effectively brace the CMD yarns 21a in the weave
construction. This bracing effect can be quantified in terms of
the degree of contact arc ~ and contact bracing area, CBA, as
follows:
CBA = II d ( o~ w
360
where d = diameter of the CMD yarn
= the degree of arc over which there is
contact between the MD and CMD yarns
w = width of the MD yarn
~ = the constant pi.
217~02
The degrees of arc over which MD yarns 22-25 are in
contact with CMD yarns 2la is dependent upon the spacing of the
CMD yarns within the weave. For the above example, employing
alternating 0.6mm and 0.8mm diameter CMD yarns with 0.2mm thick
MD yarns, the degree of contact arc can be maintained in a
preferred range of between 60 to 180 by varying the pick
count of the CMD yarns from 14 picks per inch to a maximum of
28.22 picks per inch.
In the preferred embodiment where the pick count is 20
picks per inch, the degree of contact arc ~ is approximately
101. This results in a bracing contact area of approximately
0.79mm2at each knuckle in the fabric.
Applicant's use of high ratio aspect yarns, i.e. yarns
having a width:thickness ratio of at least 3:1, provides for
increased bracing contact of the flat MD yarns with the CMD
yarns 21a. This is comparatively exemplified by modifying the
equation for contact bracing area, CBA, to be defined in terms
of the thickness of the MD yarns.
Since the MD yarn width w equals the thickness t of the MD
yarn multiplied by the aspect ratio, w > 3t for yarns having an
aspect ratio greater than 3:1. Accordingly, fabrics made in
accordance with the teachings of the present invention
utilizing high aspect ratio MD yarns exhibit enhanced bracing
of the CMD yarns by the MD yarns such that:
~17~Q~2
CBA > ~ d ¦ O~ 3t.
360
As best seen in Figure 10, seaming loops are formed by
upper MD yarns 22. The respective lower MD yarns 23 are trimmed
a selected distance from the fabric end and the upper MD yarns
22 are backwoven into the space vacated by the trimmed lower MD
yarns 23.
Upper MD yarns 24 are similarly backwoven into the space
vacated by trimming back lower MD yarns 25. However, as best
seen in Figure 10, upper MD yarns 24 are backwoven against the
madness CMD yarn 21b.
As illustrated in Figure 11, a series of seaming loops is
formed on each of the opposing fabric ends 27, 28. When the
fabric is installed on paperm~king equipment, the respective
end loops formed by MD yarns 22 are intermeshed and a pintle 30
is inserted therethrough to lock the intermeshed series of
loops together.
Since the seaming loops L are formed by backweaving MD
yarns 22 directly beneath themselves, no lateral twist or
torque is imparted on the loop and the loops are orthogonal
with the plane of the fabric. This facilitates the intermeshing
of the loop series of the opposing fabric ends 27, 28. The
orthogonal loops are particularly advantageous where, as shown
in Figure 10, the MD yarns 22, 24 are 100% warp fill and
adjacent loops are separated by individual MD yarns of the same
23
217'1~2
,
width as the loop MD yarns 22. Lateral torque or twist on the
seaming loops make the seaming process more difficult
particularly where the loop-receiving gaps between the loops of
one fabric end are essentially the same width as the loops on
the opposing fabric end and vice versa.
With reference to the fabric depicted in Figures 6-11, the
loop forming MD yarns 22 are preferably backwoven approximately
2 inches while the non-loop forming MD yarns 24 are preferably
backwoven 1 inch.
With reference to Figure 12, a third embodiment of a
papermakers fabric 30 is shown. Fabric 30 comprises a single
layer of CMD yarns 31 interwoven with stacked pairs of flat
monofilament yarns in a selected repeat pattern. For clarity,
only one pair of stacked MD yarns is shown comprising upper MD
yarn 32 and lower MD yarn 33. The upper MD yarns weave in a
float over two CMD yarns 31, form a single knuckle under the
next CMD yarn 31 and thereafter repeat. Similarly the lower MD
yarns weave in an inverted image of the upper MD yarns weaving
under two CMD yarns 31, forming a knuckle over the next CMD
yarn 31 and then returning to the bottom surface of the fabric
in the repeat. Since the repeat of both the upper and lower MD
yarns is with respect to three CMD yarns 31, a total of three
different stacked pairs of yarns comprise the weave pattern of
the MD yarn system.
A fabric was woven in accordance with Figure 12 wherein
the CMD yarns 31 were polyester monofilament yarns 0.7mm in
24
21 ~ t~
diameter interwoven with MD yarns which were flat polyester
monofilament yarns having a width of 1.12mm and a height of
0.2mm. Accordingly, the aspect ratio of the flat MD yarns was
5.6:1. The fabric was woven 48 warp ends per inch under a loom
tension of 60 PLI and 18 CMD pick yarns per inch. The fabric
was heat set using conventional methods. The fabric exhibited
amodulus of 6000 PSI. The fabric stretched less than 0.2% in
length during heat setting. The resultant fabric had 18 CMD
yarns per inch with 106% MD warp fill with respect to both
upper and lower MD yarns resulting in 212% actual warp fill for
the fabric. The finished fabric having a caliper of 0.046
inches and an air permeability of 66CFM.
With reference to Figure 13, a fourth embodiment of a
papermakers fabric 40 is shown. Fabric 40 comprises upper,
-15 middle and lower layers of CMD yarns 41, 42, 43, respectively,
interwoven with stacked pairs of flat monofilament yarns in a
selected repeat pattern. For clarity, only one pair of stacked
MD yarns is shown comprising upper MD yarn 44 and lower MD yarn
45. The upper MD yarns weave in a float over two upper layer
CMD yarns 41, under the next yarn 41 and a middle layer yarn 42
to form a single knuckle, under the next CMD yarn 41 and
thereafter rise to the top surface to continue to repeat.
Similarly, the lower MD yarns weave in an inverted image of the
upper MD yarns weaving under two lower layer CMD yarns 43 over
the next CMD yarn 43 and a middle CMD yarn 42 forming a
knuckle, over the next CMD yarn 43 then returning to the bottom
2~7 10~2
surface of the fabric to repeat. Since the repeat of both the
upper and lower MD yarns is with respect to four upper and
lower CMD yarns 41, 43, respectively, a total of four different
stacked pairs of yarns comprise the weave pattern of the MD
yarn system.
A fabric was woven in accordance with Figure 13, wherein
the upper and lower layer CMD yarns 41, 43 were nylon-sheathed,
multifilament polyester yarns 0.62mm in diameter and the middle
layer CMD yarns 42 were polyester monofilament yarns O.Smm in
diameter interwoven with MD yarns 22-25 which were flat
polyester monofilament yarns having a width of 0.60mm and a
height of 0.38mm. Accordingly, the aspect ratio of the flat MD
yarns was 1.58:1. The fabric was woven with 96 warp ends per
inch under a loom tension of 40PLI and 15 CMD pick yarns per
inch per layer. The fabric was heat set using conventional
methods. The resultant fabric had 15 CMD yarns per inch per
layer with 113% MD warp fill with respect to both upper and
lower MD yarns resulting in 226% actual warp fill for the
fabric. The finished fabric had a caliper of .075 inches and an
air permeability of 60CFM.
Figures 14, 15 and 16 illustrate the fifth, sixth and
seventh embodiments of the present invention. Figure 14
illustrates the weave of a relatively long float on both sides
of the fabric; Figure 15 illustrates how a stacked pair MD
26
2~ 7~3~2
-
yarn weave can define floats of different lengths on opposite
sides of the fabric; and Figure 16 illustrates how a stacked
pair MD yarn weave can be used to construct fabrics having MD
knuckles on one side of the fabric.
Relatively long floats predominating the surfaces of a
dryer fabric are beneficial for both the paper-carrying side as
well as the machine side of the fabric. On the paper-carrying
side, long floats provide greater contact area with the paper
sheet for increased heat transfer. On the machine side, long
floats provide increased wear surface and contact area to
reduce bounce and flutter. The stacked pair MD yarn weave is
versatile in allowing different surfaces to be defined on the
top and bottom sides of the fabric. Accordingly, fabrics made
in accordance with the teachings of the present invention may
be used for other industrial purposes such as in the drying of
sludge.
With respect to Figure 14, a fabric 50 is illustrated
comprising three layers of yarns 51, 52, and 53 respectively.
In this construction, the MD yarn pairs, such as the pair
formed by upper layer yarn 54 and lower layer yarn 55, define
relatively long floats on both the top and bottom surfaces of
the fabric. Upper yarn 54 weaves over five upper layer CMD
yarns 51, drops into the fabric to form a knuckle under one
middle layer CMD yarn 52, weaves under the next upper layer
~1 7/1~2
yarn 51 and thereafter repeats. Lower MD yarn 55 weaves in an
inverted image under five lower layer CMD yarns 53, rising into
the fabric over the next CMD 53 to weave a knuckle over one
middle layer CMD yarn 52 thereafter dropping to the bottom
surface of the fabric to continue its repeat. In such a
construction, six pairs of stacked MD yarns are utilized in the
repeat of the fabric and are sequentially woven in a selected
sequence to produce a desired pattern on the surfaces of the
fabric which will be predominated by the MD yarn floats.
The embodiment shown in Figure 15 depicts a fabric 60 in
which the MD yarns weave with a five-float repeat on the top
fabric surface and a two-float repeat on the bottom fabric
surface. For example, upper MD yarn 64 interweaves with upper
and middle CMD yarns 61, 62 in the same manner that upper MD
yarn 54 weaves with respective CMD yarns 51, 52 with respect to
fabric 50 in Figure 14. However, lower MD yarn 65, which forms
a stacked pair with upper MD yarn 64, weaves in a two-float
bottom repeat with respect lower and middle CMD yarns 63, 62.
For example, lower MD yarn 65 floats under two lower layer CMD
yarns 63, rises above the next CMD yarn 63 to form a knuckle
over one middle layer CMD yarn 62 and thereafter drops to the
bottom surface of the fabric 60 to continue to repeat. As with
the other embodiments discussed above, the interior knuckles
formed by the lower MD yarns are hidden by the upper MD yarn of
28
417~ ~ 2
the respective stacked pair and vice-versa.
The construction shown in Figure 15 permits different
surfaces to be defined on the top and bottom of the fabric
while utilizing the benefits of the stacked MD yarn pairing.
5The embodiment shown in Figure 16 discloses another
example of a fabric 70 having five-float MD yarns predominating
the upper surface of the fabric, but with MD knuckles on the
lower surface of the fabric. This type of construction may be
advantageously used to construct a forming fabric where the
10upper fabric surface, having relatively long floats, would be
used as the machine side of the fabric and the knuckled lower
surface of the fabric would be used as the paper forming side.
Fabric 70 includes three layers of CMD yarns 71, 72,73
respectively which interweave with stacked pairs of MD yarns to
15define this construction. Only one pair of stacked pair of MD
yarns 74, 75 is depicted for clarity. Upper MD yarn 74 weaves
in a five-float pattern with respect to upper and middle layer
CMD yarns 71, 72 in the same manner as upper MD yarn 54 with
respect to fabric 50 shown in Figure 14. Lower MD yarn 75
20weaves three interior knuckles and three lower surface knuckles
with respect to middle and lower layer CMD yarns 72, 73 under
each upper surface float of its respective MD yarn pair yarn
74. The repeat of the upper MD yarns is defined with respect to
29
~ ~ 7 ~ 2
-
six upper layer CMD yarns 71 and the repeat of the lower MD
yarns is defined with respect to only two lower layer CMD yarns
73. Accordingly, there are six different pairs of stacked MD
yarns which constitute the MD yarn system which, as noted
above, can be arranged such that a desired pattern is formed on
the upper surface of The fabric.
Generally for stacked pair weaves, the repeat of the upper
MD yarns will be equally divisible by, or an equal multiple of,
the repeat of the lower MD yarns in defining the stacking pair
relationship. For example, with respect to Figure 12 the repeat
of the upper MD yarns is six upper layer CMD yarns which is
equally divisible by the repeat of the lower MD yarns which is
three lower layer CMD yarns.
With respect to the eighth alternate embodiment shown in
Figure 17, a fabric 80 is-illustrated having a single layer of
CMD yarns 81 and a representative stacked pair of MD yarns 82,
83. Upper MD yarn 82 waves with two floats over CMD yarns 81
with a repeat occurring with respect to three CMD yarns 81.
Lower MD yarn 83 weaves with five floats under CMD yarns 81
with a repeat of six CMD yarns 81. Thus, in fabric 80, the
repeat of the upper MD yarns, which is three, is an equal
multiple of the repeat of lower MD yarns, which is six.
A variety of other weave patterns employing the paired
stacked weave construction of the instant invention may be
,~74a~2
constructed within the scope of the present invention. For
example, in some applications it may be desirable to have MD
yarn surface floats over six or more CMD yarns. Such fabrics
are readily constructed in accordance with the teachings of the
present invention.
