Note: Descriptions are shown in the official language in which they were submitted.
I
SPIRAL FABRIC PAPER MAKERS FELT FORMED
FROM NON-CIRCULAR CROSS SECTION YARNS
BACKGROUND OF THE INVEN'rlON
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Field of the Invention
The present invention relates to a paper makers
fabric, in general, and -to a dryer felt constructed as a low
permeability spiral coil fabric formed from non-circular
cross section yarns.
BACKGROUND OF THE PRIOR ART
A conventional dryer felt or fabric consists of an
endless conveyor belt, typically made from a 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 a-e variously called, are
united by a plurality of machine direction yarns.
The yarns used to weave the most up-to-date dryer
fabrics are generally made from synthetic monofilaments or
synthetic multi filaments, from materials such as polyester,
polyamide, acrylic and fiberglass. Dryer felts made predom-
irately from monofilament yarns have certain drawbacks.
Because the monofilament yarns are relatively stiff, they are
not easily bent around each other during the weaving process.
Thus, the fabric that results has a relatively open struck
lure. There are several positions on the paper making machine
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: that do not run or cannot run effectively when employing a
very open fabric because of numerous problems with the paper
sheet, such as thread up, blowing, flutter which causes sheet
breaks, and fooling problems.
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A number of attempts to reduce the openness or
permeability of dryer fabrics made predominantly of moo-
filaments have been tried. The major approach has been to
use a bulky spun yarn as a stuffer pick in the middle of the
weave pattern. These stuffer picks are, in effect, sun-
rounded by the original monofilament cross-machine direction
picks that are positioned in both the face and back surfaces
ox the fabric. This approach has been successful in reducing
permeability, but has added little or nothing to the stabile
fly of the fabric. It has also created the disadvantage that
the spun stuffer pick is prone to collect dirt. Also, the
stuffer picks have a tendency to retain and carry moisture, a
condition which is usually undesirable.
A second approach was been to modify the woven
structure in such a way that the top, or face, cross-machine
direction picks are offset in relation to the bottom, or
back, cross-machine direction picks. Although this approach
has produced relatively low permeability in an all moo-
filament fabric, there is no easy way to change permeability.
The weave design does not permit the use of stuffer picks.
Changes in yarn diameter are, of course, possible, but such
changes can only be made within the limitations of the loom.
Yet another example of a way to control permeably-
fly in a dryer felt is the incorporation of warp yarns of
rectangular cross section into a weave pattern that does not
include provision for stuffer picks. In such a weave pat-
tern, the warp or weft yarn typically floats on the paper-
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receiving surface of the fabric over a number of weft peccary warp ends. The longer the float, i.e., the more picks the
warp yarn crosses, or the more ends the weft yarn crosses,
before weaving back into the fabric, the less stable the
fabric becomes. In this way, there is a tradeoff between
permeability and fabric stability.
In addition to woven fabrics, certain types of
non-woven fabrics have been employed as dryer felts or
fabrics. Of particular interest to the present invention are
those made from cross-machine direction spiral coils that are
inter meshed and joined together by cross machine direction
hinge yarns to create the machine direction of a dryer fabric
of desired length.
As is presently known, the predominant approach to
reducing permeability in spiral fabrics involves filling the
gap within a given spiral coil created when that spiral coil
is secured by hinge yarns to two adjacent spiral coils.
Typically the gap is filled with a stuffer-type yarn.
Another approach uses smaller spirals in an attempt to reduce
the size of the space within a given coil.
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In the first approach, the stuffer yarns are
usually inserted as an extra production step after the basic
fabric has been manufactured and finished. Although Perle-
ability is reduced, fabric processing time is increased and,
therefore, this approach is less economical. At the
same time, the use of stuffer yarns tends to reduce the clean
running of the fabric and also reduces its ease of cleaning
as dirt will rapidly adhere to the stuffer yarn.
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The use of smaller spirals, on the other hand,
necessitates increasing the number of filling yarns (which
act as hinge yarns) per unit length. This again reduces
productivity and increases costs. In addition, it has been
observed that the reduction in permeability is relatively
i small, such fabrics, at best, having 800 aim or more.
There is thus a need for a dryer felt of spiral
coil construction that may be easily and economically produced
to provide a wide permeability range that is stable and also
dirt resistant, and that exhibits reduced moisture carrying
properties. The present invention is directed toward filling
the need.
SUMMARY OF THE INVENTION
The present invention is directed primarily to a
dryer felt although potential applications include forming
wires, press fabrics and other industrial belting applications
in the form of a spiral fabric that exhibits a marked reduction
in permeability and flatter upper and lower surfaces. This
it accomplished by using non-circular cross section manful-
mints to form a plurality of individual spiral coils which
are held together by hinge yarns which can be of circular or
non-circular cross section. The typical permeability for
known circular cross section spiral fabrics is about 800-plus
i aim, at 1/2" water gauge whereas for a dryer felt produced
i according to the teachings of the present invention, the
- permeability ranges from abut 50 to about 500 aim. The
range is controlled by using differently dimensioned coil
and hinge yarns.
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The dryer felt of the present invention takes the
form of a spiral fabric that consists of lengths of spiral
monofilament or monofilament like coils arranged so that
I they span in a cross-machine direction and lie in a common
plane. An example of a monofilament-like coy is a coil made
from a bundle of multi filaments or monofilaments that have
been resin treated in a conventional manner so that the
bundle acts as a monofilament.
In production, a first spiral coil is usually laid
tout -to -the required width of the fabric. A second spiral is
then inter meshed (single coil to single coil) with the first
spiral and a monofilament hinge yarn is inserted between the
inter meshed coils to hold them together. In order to reduce
torque in the fabric, the spiral lengths of the individual
coils are alternately S-twist and Z-twist coils. The spiral
coils are preferably formed from yarns having non-circular
cross sections, which can be elliptical or rectangular.
The hinge yarns can also have a non circular cross
Saxon and are sized and shaped relative to the spiral
coils so that, when the hinge yarns join adjacent coils
together, they do so in such a manner that they fill the
opening defined when the coils are inter meshed.
After the hinge yarns are inserted, the resultant
fabric is then subjected to heat treatment and controlled
tensioning Under those conditions, the various coils are
flattened and lie against the sides of the hinge yarns.
- I This structural arrangement creates a greater contact area
jlbetween the fabric and paper sheet with an increase in
drying efficiency resulting in higher productivity of the
paper machine and reduced energy costs.
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It is an object of the present invention to provide
I a dryer fabric of spiral construction having low Perle-
ability, good stability, good resistance to dirt, and which
can be easily cleaned.
It is another object of the present invention to
provide a dryer fabric made of monofilament or monofilament-
like spiral coils, each of which is of non-circular cross
section.
! It is still another object of the present invention
to provide a dryer fabric of spiral construction having
flattened paper-receiving and machine-roll contacting
surfaces for improved paper web support and for improved
guiding.
It is a further object of the present invention to
provide a dryer fabric having a reduced thickness to minimize
stretching the paper sheet as the fabric passes around the
machine rolls and to improve the heat transfer through the
fabric by minimizing air pockets.
These and other objects will become apparent from
the following drawings and detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a top plan view of a portion of a
spiral fabric embodying the subject invention.
Figure 2 is a machine direction section of a
portion of the spiral fabric of Figure 1.
i Figure 3 is a diagrammatic sketch of a yarn having
an elliptical cross section
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Figure 4 is a diagrammatic sketch of a yarn having
` a rectangular cross section.
¦ Figure S is a diagrammatic sketch of a yarn having
I a Shaped cross section.
¦ Figure 6 is a diagrammatic sketch of a yarn having
a dog bone shaped cross section.
¦ Figure 7 is a diagrammatic sketch of the cross
section of a hinge yarn made up of three yarns placed side-
by-side in a common plane.
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Figure 8 is a fragmentary cross sectional view
showing a fabric having coils formed from monofilament yarns
of generally rectangular cross section and taken along the
line 8-8 of Figure 1.
DETAILED DESCRIPTION OF THE DRAWINGS
With reference to Figures 1 and 2, a portion of a
dryer fabric produced according to the teachings of the
subject invention is shown and generally identified as 10.
It is to be understood that the figures are in the nature of
schematic representations and do not illustrate the elements
of the fabric to any precise scale.
The dryer felt 10 basically comprises a plurality
of spiral S-coils 12 joined together with a plurality of
spiral Z-coils 14 through the use of hinge yarns 16 of
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non-circular cross section to create the fabric. The letters
I "S`' and "Z" indicate the direction of twist of the spiral
coils. A spring coil has an S-twist if, when it is held
vertically, the spirals or convolutions around its central
axis slope in ale same direction as the middle portion of
the letter S, and Z-twist if the spirals slope in the same
direction as the central portion of the letter Z.
With reference to Figures 1 and 2, the details of
the fabric structure will now be described. The spiral
coils 12 and 14 each consist of lengths ox spiral monofilament,
i.e., a monofilament with the appearance of a spring coil.
The monofilament. is synthetic in nature and is typically
made from polyester, although other materials, such as,
polyamide, polyolefin, polyetheretherketone and the like are
contemplated.
In constructing a spiral fabric, a spiral coil (in
this case S-coil 12) is first selected and laid out in what
will eventually become the cross-machine direction, as
indicated by arrow 11. Thus it can be appreciated that the
width of the dryer fabric is thereby determined by the
length of the coil. A second spiral (in this case Z-coil
14) is then inter meshed with the first spiral coil 12 to
define a hinge yarn receiving opening 18. The opening 1
receives a hinge yarn 16 which is typically a synthetic
monofilament, and like the spiral coils, may be of polyester,
polyamide, polyolefin, polyetheretherketone and the like.
_ the insertion of the hinge yarns, which also span in the
cross-machine direction, into adjacent inter meshed spiral
coils act as a pivotal hinge between the adjacent coils.
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The laying down of additional spiral coils in an
alternating 'So coil and 'Z' coil relationship with the
subsequent insertion of a hinge yarn is continued until a
fabric of desired length is produced. The spiral coils are
alternately S-twist and Z-twist coils so as to reduce torque
in the fabric.
With reference to Figures through 7 it can be
j seen that the hinge yarns 16 are of non-circular cross
section. It is of particular importance that the yarns be of
non-circular cross section because such yarns close the
spaces or air voids between spiral coils to markedly reduce
permeability, while at the same time increasing the contact
area of the paper-receiving surface of the fabric.
Figure 3 shows one embodiment for a non-circular
hinge yarn. As can be seen, the cross section of the yarn
AYE is approximately elliptical. As viewed in cross-section,
the contemplated height of the yarn measured along the short
axis A is within the range of about 0.1 to 2.0 mm., with the
preferred range being from about 0.3 to 0.9 mm. The contem-
plated width of the yarn as measured along the long axis B is
within the range of about 0.2 to 4.0 mm. with the preferred
range being from about 0.33 to 2.25 mm. The ratio of the
height-to-width of the yarn can be from 1:1.1 to 1;6, while
the preferred range is 1:1.1 to 1:2.5. As used herein the
long axis B is substantially parallel to the plane of the
fabric and the short axis A is substantially perpendicular to
the plane of the fabric.
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i Figure 4 illustrates the cross section of yet
another embodiment of the hinge yarn and bears the number
16B. As can be seen from the illustration, this yarn is
generally rectangular in cross section with rounded corners
31. The height limitations, when measured along the axis A,
I and the width limitations, when measured along the axis B are
I similar to those of the elliptical yarn AYE. The ratio of
~eight-to-width for yarn 16B also is similar to that of the
elliptical yarn.
, Figures 5 and 6 show two additional embodiments for
the hinge yarns. Yarn 16C is a synthetic monofilament having
a cross section resembling a "D" whereas yarn 16D is a
synthetic monofilament having a cross section resembling a
dog zone or dumbbell. The height and width dimensional
limitations for yarns 16C and 16~ are similar to those of the
elliptical yarn AYE. In the case of yarn 16C, the height is
`; measured along axis A at the thickest portion 35 of the "D"
- cross section whereas the width is measured along the base 37
1, (which is essentially parallel with axis B) of the "D". In
Jo the case of yarn 16D, the height is measured along the
direction of short axis A and at the thickest portion of
If either of the two bulbous portions 39 of the dog bone cross
Jo section, whereas the width is measured along long axis B
between the extreme ends 41 of the bulbous portion 39.
Figure 7 shows yet another embodiment for the hinge
yarns. In this case, the hinge yarn EYE is actually three
synthetic monofilament yarns 33 of similar cross section
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positioned alongside each other to create an elongated con-
figuration when viewed in cross section r The height and
width limitations of this composite yarn EYE are similar to
those of the elliptical yarn AYE. In the case of composite
yarn EYE, the height is measured along axis A at the thickest
portion of any of the similar yarns 33, whereas the width is
measured along axis B between the extreme ends of the outer-
most yarns 33, with all three yarns lying in a plane Essex-
tidally parallel to axis B.
Thus it will be appreciated that the hinge yarns
may take on essentially any configuration that has a long and
short axis cross section. As already pointed out, this
includes rectangular, elliptical, D-shaped, dog bone and even
two or more circular or non-circular yarns of the same or
different cross sections inserted simultaneously side-by-
side. The choice of cross section is affected by the flex-
ability required in the finished fabric, rectangular and
elliptical yarns giving less flexibility than dog bone and
side-by-side yarns.
The overall size and shape of the hinge yarn
depends on the size and shape of the spiral coils and the
yarn-receiving openings that the coils define when they are
inter meshed.
After the dryer fabric has been formed through the
inter meshing of the S-twist and Z-twist coils and the insert
lion of the hinge yarns, the fabric is then subjected to heat
treatment and controlled tensioning. The tension control is
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placed in what will become the machine direction. Under
these circumstances, the spiral coils 12, 14 which were
originally circular or elliptical in transverse section now
flatten to press up against the long sides 20 of the hinge
yarns. At the same time, the controlled tensioning and
resultant flattening of the spiral coils causes necessary
crimping to occur in the hinge yarns. The crimp resulting
from the heat treatment is desirable to stabilize the fabric
and to ensure good renewability on the paper machine, i.e.,
no distortion or stretching. The crimping also ensures that
the hinge yarns do not move laterally so as to leave an
opening on either edge of the fabric. Thus, upon completion
of the heating and controlled tensioning operations, a
fabric is created in which the hinge yarns all lie in a
common plane. In like manner, the spiral coils are flattened
and also lie in the same common plane of the fabric.
Because of the non-circular cross-sectional shape
of the hinge yarns, it is possible to control the flatness
of the paper-receiving and machine roll contacting surfaces
of the dryer fabric. By the appropriate use of temperature,
time and tension, the spiral may be flattened out so that it
can be pulled down flat against the flat section or long
sides of the hinge yarn. The flatter the surfaces of the
dryer fabric, the greater is the contact area between the
fabric and the paper sheet, as well as the contact area between
the hot cylinder surface and the same paper sheet. This
increases drying efficiency and results in higher productivity
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of the leaper machine thereby reducing energy costs. In
addition, by increasing the contact area, the air void areas
22 (Figure 2) are reduced and, therefore, there is less
chance of the fabric marking the paper sheet, particularly
on critical paper grades.
Increasing the mass of the monofilament hinge yarn
16 in a given area within the fabric causes a reduction in
air voids. In this way, the fabric maintains a higher
operating temperature so that dryer efficiency is enhanced.
Additionally, the dimensional stability of the dryer fabric
is increased by the use of the large hinge yarns 16, because
there is less vowed' area available for the coils to move
into.
The improved fabric flatness on the surfaces of
the fabric improves calendering effects by imparting
increased smoothness to the paper sheet. Also, the
increased flat contact area decreases the picking effect of
the fabric on the paper sheet on after-size and -
after-coating positions, since there are no weave
imperfections that size or coating can adhere to.
It has been found that the desirable flatter upper
and lower surfaces of the fabric can be obtained by using
coils formed from yarns having non-circular cross sections,
and particularly yarns having generally rectangular cross
sections. Specifically, when coils formed from generally
rectangular cross sections are employed, the flatter, end
therefore greater, surface area of the resulting fabric
provides increased contact area with the paper web, for
increased web support, and it also provides increased
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contact area with the respective guide rolls which are
commonly found in paper making machines and about which the
fabric passes. By virtue of the increased guide roll contact,
the guiding of the fabric around the several rolls is sub Stan-
tidally improved, and it also has been found that -the resistance
to surface abrasion of the resulting fabric is also improved
by virtue of the greater contact area.
Moreover, because the fabric is thinner, the unit
mass of yarns is greater and therefore the amount of air
acting as insulation is diminished. This permits the fabric
It Hun hotter which, with increased contact area increases
Thea drying efficiency on the paper sheet. Additionally, by
providing coils formed from yarns having rectangular or
other non-circular cross sections, the thickness of the
resulting fabric is reduced, thereby increasing its flexibility
and minimizing the presence of moisture laden air there within,
which avoids resetting of the paper sheet. Thinner fabrics
also involve less machine direction stretching of the paper
sheet as it is carried around the various rolls on the
outside surface of the fabric. Additionally, the reduced
air space within the fabric allows the use of a wider range
of stuffer picks without the danger of the fabric running
wet. For example, monofilament, continuous filament slit or
split film, tape, and spun yarns can be utilized to form the
l hinge yarns. Additionally, by the use of different types of
hinge yarns, fabrics having controlled variations in Perle- ¦
- I ability across the fabric width can be produced.
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Structurally the preferred coils having the
attributes described above can be formed prom monofilaments
as illustrated in cross section in Figures 3 and 4. The
longer sides 20 are substantially flat and parallel and are
so oriented that they lie generally parallel with the upper
and lower surfaces of the resulting fabric. The spacing
between the respective surfaces 20 defines the thickness of
the coil yarn and the distance between the respective end
portions aye defines the width of the coil yarn. The width
to thickness ratio of the coil yarns can range from about
1:1.1 to about 1:6, and preferably lies within the range
from about 1:1.5 to about 1:2Ø
Pyre 8 is a fragmentary cross sectional view of
a fabric formed from spiral coils wherein the coils are of
monofilament having a generally rectangular cross section.
As shown, hinge yarn 16' passes between inter engaging coils
12', the coil yarns having their major axes generally
parallel to the upper and lower surfaces of the fabric to
provide the benefits of the present invention.
In the course of the formation of the fabric as
hereinabove described, it is intended that the respective
coil yarns and hinge yarns are substantially non-deformed,
so that their respective cross sections remain constant
throughout their respective lengths, and so that they are
substantially free of surface discontinuities. Although it
is virtually impossible to completely eliminate surface
deformation at points of contact between the coil yarns and
the hinge yarns, particularly when flexible synthetic
monofilaments are employed, the improved fabric of the
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I present invention does not require that her- be such
deformation to provide a coherent fabric, as has been
suggested in the prior art. Thus, reference to the
substantially uniform cross sections of the yarns in the
present invention and that such yarns are substantially free
of surface discontinuities is intended to reflect the fact
i that such non-uniformities and discontents are not
¦ intended, although they may be present to a very slight
degree, and are not necessary for the proper functioning of
the present invention.
The spiral coils of non-circular cross section
yarns provide a further advantage over such coils formed
from yarns having a circular cross section in that the
corners that result when coils formed from the latter are
flattened are prone to fibrillate, or split into fibrils
across the thickness of the monofilament at the points of
greatest stress, whereas the former are less prone to such
I fibrillation. The fibrillation, is a particular problem with
I the circular cross section yarns when incorrect heat
treating conditions are employed to heat stabilize the
spiral fabric. Such incorrectly heat stabilized fabrics can
fail quickly on the paperma~ing machine, even though there
Al is no outwardly visible sign of fibrillation in the finished
¦ fabric. However, the use of non-circular cross section
yarns to form such spiral coils has been found to reduce
substantially the tendency to fibrillate.
Although the present invention has been shown and
described in terms of specific preferred embodiments, it
I will be appreciated by those skulk in the art that changes
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or modifications are possible which do not depart from the
inventive concepts described and taught herein.
Further, it is contemplated that the coil yarns
need not be monofilament, the only requirement being that
the coil yarns behave like monofilaments. An example of a
yarn that behaves like a monofilament is one made from a
bundle of synthetic multifilam~nts or monofilaments, such as
polyester, that have been resin treated in a conventional
manner so that the bundle acts as a monofilament. Typically
the resin is applied by moving the bundle and resin through
a sizing die. In this way a cross section of desired con-
figuration can be made. Such changes and modifications are
deemed to fall within the purview of these inventive concepts.
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