U.S. patent application number 11/498275 was filed with the patent office on 2007-02-08 for forming fabric for use in a paper machine, and method and apparatus for manufacturing such a forming fabric.
Invention is credited to Walter Best, Christian Molls, Paul Wales.
Application Number | 20070028997 11/498275 |
Document ID | / |
Family ID | 34980045 |
Filed Date | 2007-02-08 |
United States Patent
Application |
20070028997 |
Kind Code |
A1 |
Best; Walter ; et
al. |
February 8, 2007 |
Forming fabric for use in a paper machine, and method and apparatus
for manufacturing such a forming fabric
Abstract
The present invention relates to a forming fabric (2), for use
in the sheet-forming section of a paper machine, having or
comprising a textile planar structure in which, in order to enhance
inherent stability, crossing yarns (5, 6, 7) are engaged into one
another at crossing points (14) and in which yarns (5, 7)
additionally are fused to one another, which is characterized in
that the planar structure comprises crossing first and second yarns
(5, 7), the first yarns (7) having the property that they absorb
laser energy and can be brought, by absorbed laser energy, to
melting temperature at least at the surface; and that first and
second yarns (5, 7) are fused to one another at at least some of
their crossing points (14).
Inventors: |
Best; Walter; (Duron,
DE) ; Molls; Christian; (Aachen, DE) ; Wales;
Paul; (Fermoy Co. Cork, IE) |
Correspondence
Address: |
BERENATO, WHITE & STAVISH, LLC
6550 ROCK SPRING DRIVE
SUITE 240
BETHESDA
MD
20817
US
|
Family ID: |
34980045 |
Appl. No.: |
11/498275 |
Filed: |
August 3, 2006 |
Current U.S.
Class: |
139/383R |
Current CPC
Class: |
B29C 66/721 20130101;
B29K 2313/00 20130101; B29L 2031/14 20130101; B29C 65/1683
20130101; B29C 66/69 20130101; D21F 1/0027 20130101; B29C 65/1654
20130101; B29C 66/729 20130101; B29C 66/344 20130101; B29C
2035/0822 20130101; B29C 65/1616 20130101; D21F 1/0054 20130101;
B29C 66/836 20130101; B29C 66/7392 20130101; B29C 66/73921
20130101; B29K 2101/12 20130101 |
Class at
Publication: |
139/383.00R |
International
Class: |
D03D 23/00 20060101
D03D023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 4, 2005 |
EP |
05 017 006 7 |
Claims
1. A forming fabric (2), for use in the sheet-forming section of a
paper machine, having or comprising a textile planar structure in
which, in order to enhance inherent stability, crossing yarns (5,
6, 7) are engaged into one another at crossing points (14) and in
which yarns (5, 7) additionally are fused to one another, wherein
the planar structure comprises crossing first and second yarns (5,
7), the first yarns (7) having the property that they absorb laser
energy and can be brought, by absorbed laser energy, to melting
temperature at least at the surface; and first and second yarns (5,
7) are fused to one another at at least some of their crossing
points (14).
2. The forming fabric according to claim 1, wherein the first and
second yarns (5, 7) are fused to one another at all their crossing
points.
3. The forming fabric according to claim 1, wherein the second
yarns (5, 6) absorb less laser energy than the first yarns (7) or
none at all.
4. The forming fabric according to claim 1, wherein the yarns (5,
6, 7) are otherwise not joined to one another.
5. The forming fabric according to claim 1, wherein the first yarns
(7) contain an additive that imparts the ability to absorb laser
light.
6. The forming fabric according to claim 5, wherein the additive is
an NIR-active substance or an NIR-light-absorbing substance.
7. The forming fabric according to claim 5, wherein the additive is
incorporated into the first yarns (7) and/or applied onto the
surface of the first yarns (7) and/or introduced at the crossing
points between the first and second yarns (5, 7).
8. The forming fabric according to claim 5, wherein the first yarns
are bicomponent yarns, only one of the two components containing
the additive.
9. The forming fabric according to claim 8, wherein the bicomponent
yarns comprise a core and a casing surrounding it, the additive
being contained only in the casing.
10. The forming fabric according to claim 1, wherein the planar
structure comprises longitudinal and transverse yarns, and the
first yarns extend in the longitudinal and/or the transverse
direction.
11. The forming fabric according to claim 10, wherein the only some
of the longitudinal and/or transverse yarns are first yarns.
12. The forming fabric according to claim 1, wherein the first
yarns are part of the weave of the yarns in the planar
structure.
13. The forming fabric according to claim 1, wherein the first
yarns are distributed in the planar structure in a consistently
regular pattern.
14. The forming fabric according to claim 1, wherein the first
yarns are engaged in such a way that they do not reach as far as
the paper side of the forming fabric.
15. The forming fabric according to claim 14, wherein the planar
structure is embodied with multiple plies; and the first yarns are
engaged only in an internally located layer and/or a roller-side
layer.
16. The forming fabric according to claim 1, wherein the forming
fabric (2) has a finite length with ends joinable via a seam,
transverse yarns that are embodied as first yarns (7) being present
in the region of both ends.
17. The forming fabric according to claim 16, wherein the forming
fabric (2) comprises longitudinal yarns (5) that extend into the
region of the ends and that in the region of the ends are fused to
first yarns (7) that extend in the transverse direction.
18. A method for manufacturing a forming fabric (2) for use in the
sheet-forming section of a paper machine, in which method a textile
planar structure is manufactured from yarns (5, 6, 7) that
intersect one another and are engaged into one another, and in
which yarns (5, 7) are fused to one another at crossing points by
heating to melting temperature, wherein first and second yarns (5,
6, 7) are used in the manufacture of the planar structure, in which
context the first yarns (7) can absorb laser energy; and first and
second yarns (5, 7) are fused by means of laser energy at at least
some of their crossing points (14).
Description
CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM TO PRIORITY
[0001] This application is related to application number 05 017
006.7, filed Aug. 4, 2005 with the European Patent Office, which is
incorporated herein by reference, and to which priority is
claimed.
FIELD OF THE INVENTION
[0002] The invention relates to a forming fabric, for use in the
sheet-forming section of a paper machine, having or comprising a
textile planar structure in which crossing yarns are engaged into
one another at crossing points and in which, in order to enhance
inherent stability, yarns are fused to one another at crossing
points. The invention further relates to a method for manufacturing
such forming fabrics, in which method a textile planar structure is
manufactured from yarns that intersect one another and are engaged
into one another at crossing points, and in which yarns are then
fused to one another at crossing points by heating to melting
temperature. Lastly, the invention also refers to an apparatus for
manufacturing a forming fabric of this kind.
BACKGROUND OF THE INVENTION
[0003] Forming fabrics are long, wide belts that circulate in the
first part of a paper machine, called the sheet-forming section,
forming a flat upper run. At the beginning of the upper run, the
previously prepared fiber pulp is applied onto the forming fabric
and dewatered through the forming fabric, so that a paper web still
having a high liquid content is gradually formed. In subsequent
sections of the paper machine, the paper web is further dewatered
mechanically and thermally.
[0004] Single- or multiple-layer woven fabrics are generally used
as forming fabrics. A woven fabric (or even a knitted fabric)
obtains its inherent stability or diagonal stability from the fact
that crossing yarns are engaged into one another, forming a weave
pattern. Particularly in the context of large stresses such as
those that occur in a paper machine, the inherent stability of the
textile planar structure is not sufficient to ensure stable and
problem-free circulation of the forming fabric through the
sheet-forming section. Additional measures have therefore been
taken in order to improve the dimensional stability, in particular
the diagonal stiffness, of such textile planar structures.
[0005] One of these measures consists in adhesively bonding the
yarns to one another at the crossing points, by the fact that the
fabric structure is equipped with adhesive polymers. This method is
cost-intensive because the dispersion must be applied very evenly,
and because drying consumes a great deal of time and energy.
Permeability is furthermore considerably decreased, which has a
negative effect on the sheet-forming process. A further
disadvantage is the fact that the adhesion at all crossing points
resulting from this method causes a stiffening that is often not
desired.
[0006] U.S. Pat. No. 5,888,915 A proposes, in order to improve the
dimensional stability of such textile planar structures, to use
bicomponent yarns in which the melting temperature of the outer
casing is lower than that of the core. A woven or knitted fabric or
yarn layer equipped with bicomponent yarns of this kind is then
heated, in a continuous furnace, to a temperature that is above the
melting temperature of the outer casing of the bicomponent yarns,
but below the melting temperature of the core of those yarns, so
that the casing melts and a fused or adhesive bond to other yarns
is produced in this fashion at the crossing points.
[0007] Forming fabrics having good dimensional stability can be
manufactured using this method. Manufacture is costly, however,
since the bicomponent yarns are expensive, and heating of the
entire forming fabric in a continuous furnace is
energy-intensive.
[0008] Also known are forming fabrics having or comprising a
textile planar structure that is formed from a yarn layer in which
the yarns are not engaged with one another, i.e. not woven or
interlinked with one another. Instead, transverse yarns that extend
parallel to and at a distance from one another are laid onto a
layer of longitudinal yarns that are likewise parallel to and at a
distance from one another, and the longitudinal yarns are then
joined to the transverse ones. Only thereby does the yarn layer
acquire inherent stability. Joining can occur according to the
method according to U.S. Pat. No. 5,888,915 A, using bicomponent
yarns.
[0009] The disadvantages of the aforementioned method are
eliminated by a method that is evident from EP 1 359 251 A1. In
this method, the longitudinal and transverse yarns are fused to one
another at crossing points as a consequence of a heating to melting
temperature that is confined to those crossing points. The heating
can be applied in single-point fashion by means of high-frequency,
inductive, and/or laser energy. As an alternative thereto, however,
the energy can also be applied in planar fashion if the crossing
points are first equipped with an additive that promotes absorption
of the energy and that concentrates energy uptake at the crossing
points despite the planar application, so that only those points
are heated to melting temperature and consequently fused to one
another. When a laser is used, the additive should be a
light-absorbing dye, e.g. black dye, or a photoactive substance.
The additive can be applied between the yarns or onto the yarns. It
is also proposed instead to add the additive to the yarn material
during the extrusion operation.
SUMMARY OF THE INVENTION
[0010] It is the object of the invention to manufacture a forming
fabric of the kind cited initially more economically, preferably
without producing structural changes. A further object is to make
available a method suitable for manufacture, and an apparatus
therefor.
[0011] The first object is achieved, according to the present
invention, by a forming fabric in which the planar structure
comprises crossing first and second yarns, the first yarns having
the property that they absorb laser energy and can be brought, by
absorbed laser energy, to melting temperature at least at the
surface; and in which first and second yarns are fused to one
another at at least some of their crossing points. For many
situations it is sufficient if only some of the first and second
yarns are welded to one another, and those only at some of their
crossing points.
[0012] The basic idea of the invention is therefore to use for some
of the yarns, in the context of a forming fabric, particular yarns
which are distinguished by the fact that they absorb laser light.
In this fashion, the textile planar structure can be additionally
stabilized by the fact that the first yarns are heated by means of
a laser to melting temperature, and at at least some of the
crossing points (if not at all) a fused join is thus produced with
the second yarns, which absorb only little or no laser light. This
manner of producing the fused join is substantially less
time-consuming and energy-intensive than the known methods,
especially since the first yarns themselves require little
additional cost. A further advantage consists in the fact that the
dimensional stability can be individually adapted to particular
requirements by correspondingly varying the number of first yarns
as well as the number of crossing points at which welding or fusing
is performed. This is because in many cases, a forming fabric that
is too stiff and therefore insufficiently adaptable is also
disadvantageous.
[0013] In an embodiment of the invention, provision is made for the
yarns otherwise not to be joined to one another, i.e. for no
further joint to exist beyond the mutual engagement of the yarns
and their single-point welding at crossing points.
[0014] To allow the first yarns to absorb the laser light, they can
contain an additive that imparts the ability to absorb laser light.
Examples of such additives are near-infrared-active (NIR-active)
substances that absorb, for example, in the region of the
wavelengths 808 nm, 940 nm, 980 nm, or 1064 nm. Suitable for this
are, for example, carbon or colorless additives such as Gentex's
Clearweld.RTM. or BASF's Lumogen.RTM. IR. The additive preferably
extends over the entire length of the first yarns and is evenly
distributed over the length and cross section. The additive can be
incorporated into the first yarns and/or applied onto the surface
of the first yarns and/or introduced at the crossing points between
the first and second yarns. If the additive is incorporated, the
proportions by weight should be approximately 0.10% to 2.5%.
[0015] In a further embodiment of the invention, provision is made
for the first yarns to be bicomponent yarns, only one of the two
components containing the additive. The bicomponent yarns should
preferably comprise a core and a casing surrounding it, the
additive then being contained only in the casing.
[0016] Planar structures suitable according to the present
invention are those in which crossing yarns are engaged with one
another, as is the case, for example, with woven and knitted
fabrics. The planar structure should preferably comprise
longitudinal and transverse yarns, in which context the first yarns
can extend only in the longitudinal direction, only in the
transverse direction, or in both directions. Depending on the
dimensional stability requirements, only some of the longitudinal
and/or transverse yarns can then also be embodied as first yarns.
The first yarns should preferably be part of the weave of the yarns
in the planar structure, i.e. should not have been additionally
introduced into the existing woven fabric, knitted fabric, etc., in
order not to disrupt the desired yarn distribution and structure.
It is definitely useful if the first yarns are distributed in the
planar structure in a consistently regular pattern.
[0017] The first yarns are, if possible, advantageously engaged
into the planar structure in such a way that they do not reach as
far as the paper side of the forming fabric. If the planar
structure is embodied with multiple plies, the first yarns should
be engaged only in an internally located layer and/or a roller-side
layer.
[0018] Possible materials for the yarns are any type of
thermoplastic material that is suitable for the respective
application, i.e. that permanently withstands the respective
ambient conditions in the paper machine. For cost reasons, at least
the first yarns, but better yet all the yarns, can be embodied as
single-component yarns that can additionally be fiber-reinforced;
i.e. individual yarns, or all the yarns, can contain a fiber
reinforcement.
[0019] Forming fabrics have a finite length, with ends joinable via
a seam. In the region of the two ends, i.e. in the seam region,
first yarns should be present that extend in the transverse
direction and are welded to second yarns extending in the
longitudinal direction. In order to achieve particularly high
strength there, the first yarns should be present in a higher
concentration in the seam region than in the remaining region of
the forming fabric, and the first and second wires should be welded
to one another at as many crossing points as possible. The
longitudinal yarns inserted in correctly woven fashion into the
respectively opposite end during the stitching process are then
fused to the first yarns. This creates the possibility of
shortening the seam region without thereby impairing the strength
of the seam. In this fashion the seam region can be reduced from a
usual extension of, for example, 100 mm in the longitudinal
direction to, for example, 60 mm, i.e. the seam region can be
shortened by 20-60% in the machine direction.
[0020] A laser beam that has a power output of 20 to 200 W,
preferably 50 to 150 W, should be used for welding.
[0021] The second object is achieved, according to the invention,
by a method in which first and second yarns are used in the
manufacture of the planar structure, in which context the first
yarns can absorb laser energy; and in which first and second yarns
are fused by means of laser energy at at least some of their
crossing points or at all their crossing points.
[0022] Welding of the first and second yarns at the crossing points
can occur in a consistently regular pattern, but also in
stochastically distributed fashion. The possibility exists of
guiding the laser over the forming fabric in parallel longitudinal
tracks, the laser and forming fabric being moved relative to one
another in the longitudinal direction of the forming fabric by the
fact that either the laser is moved two-dimensionally over the
forming fabric stretched in stationary fashion, or the forming
fabric is moved along in the longitudinal direction below the
laser, in which context the laser can additionally be displaced
laterally. As an alternative thereto, the possibility exists of
guiding the laser over the forming fabric in parallel transverse
tracks along a transverse yarn. For this, the forming fabric can be
alternately moved and then stopped, so that the laser is guided
along every transverse yarn, or even every second, every third, or
every tenth transverse yarn.
[0023] A further possibility is that of guiding the laser over the
forming fabric in a diagonal direction, the angle between the
diagonal direction and the transverse direction being selected so
that the first and second yarns are fused to one another at as many
crossing points as possible. The laser can follow the weave ridges
of the fabric weave. The distances between the laser tracks can be
selected, in the longitudinal direction, depending on the desired
embodiment. Regardless thereof, it is not excluded for the laser to
be guided over the forming fabric in spiral tracks.
[0024] Provision is also made according to the invention for the
laser to be controlled in such a way that it is displaced to those
crossing points of first and second yarns designated for joining.
For joining, the laser first shines through the second yarn before
striking the first yarn. The concentration of the additive in the
first yarns, and the energy of the laser, should be correlated in
such a way that the first yarns are melted only at the surface
facing toward the laser, so that there is only a slight negative
effect on the structure and shape of the yarns.
[0025] The third part of the object is achieved, according to the
present invention, by an apparatus that comprises a tensioning
device with which the forming fabric, rendered endless, is
stretchable; and such that a laser device having at least one laser
head is associated with the tensioning device in such a way that at
least one laser beam is directable onto the forming fabric in the
stretched state; and that the tensioning device and laser device
are embodied in such a way that a relative motion is producible
between the forming fabric and laser beam. With the aid of this
apparatus, first and second yarns can be welded to one another by
means of the at least one laser head.
[0026] Particularly suitable as a tensioning device are two
spaced-apart tensioning rollers with which a longitudinal tension
is impartable to the forming fabric pulled onto the tensioning
rollers, for example by the fact that the spacing of the tensioning
rollers is modifiable. At least one of the tensioning rollers
should be connected to a drive motor in such a way that a forming
fabric pulled onto the tensioning rollers can be caused to
circulate continuously or in steps, in which context the drive
motor can also be embodied reversibly.
[0027] According to a further feature of the invention, provision
is made for the at least one laser head to be movably guided
transversely with respect to the forming fabric pulled onto the
tensioning device, and preferably over the entire width of the
tensioning device. As an alternative thereto, but preferably in
combination therewith, the at least one laser head should also be
movably guided longitudinally with respect to the forming fabric
pulled onto the tensioning device. This can usefully be done in
such a way that the at least one laser head is supported on a guide
rail that extends transversely with respect to the forming fabric
and is displaceable in the longitudinal direction of the forming
fabric, the forming fabric being in each case pulled onto the
tensioning device.
[0028] In order to allow the relative motions between laser beam
and forming fabric, as proposed in accordance with the method
according to the present invention, to proceed automatically, a
programmable control device should be provided for controlling the
tensioning device and laser device and their motors for moving, for
example, the tensioning rollers and/or the laser head. This control
device can additionally be combined with a sensor that is mounted
on the laser device and serves to sense yarns of the forming fabric
that differ from the other yarns of the forming fabric in terms of
a property that can be sensed by the sensor. The sensor can be, for
example, an optoelectronic sensor (photocell) if the first yarns of
the forming fabric according to the present invention have a
different color and/or a different brightness from the second
yarns. It is also possible, however, to use a sensor that responds
to the presence of the additive in the first yarns that imparts the
ability to absorb laser light. In conjunction with the control
device, the sensor allows the first yarns to be located, and allows
the laser to be moved to the locations designated for welding.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The invention is illustrated in more detail in the drawing,
with reference to an exemplifying embodiment. The drawing shows, in
an oblique view, an apparatus for partial manufacture of forming
fabric 2 according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0030] Forming fabric 2 was previously woven in a finite length,
and its ends were then stitched to one another so that an endless
structure was produced. Forming fabric 2 was then stretched between
two rollers 3, 4 arranged at a distance from one another, one of
the rollers being movably guided in such a way that forming fabric
2 acquires a specific longitudinal tension. At least one of rollers
3, 4 is driven clockwise in motorized fashion. Upon activation of
the drive system, forming fabric 2 is moved at a predetermined
speed in the direction of arrow A, while rollers 3, 4 execute a
rotary motion in the direction of arrow B, C. It is understood that
rollers 3, 4 are supported in an apparatus frame (not depicted in
further detail) in which the drive system is also housed.
[0031] Forming fabric 2 was manufactured in a finite length, and
was converted into the endless form shown by way of a seam joining
the ends. Forming fabric 2 is made of a woven fabric that, in this
embodiment, comprises longitudinal yarns (labeled 5 by way of
example) extending in the machine direction (arrow A) and
transverse yarns (labeled 6 by way of example) extending
perpendicular thereto. Longitudinal and transverse yarns 5, 6 are
produced from a thermoplastic that is usual for use in forming
fabrics, and constitute second yarns for purposes of the present
description. Longitudinal and transverse yarns 5, 6 are engaged
into one another in accordance with a specific weave pattern.
[0032] Extending between each two transverse yarns 6 constituting
second yarns is a respective further transverse yarn (labeled 7 by
way of example) that is emphasized in the drawing. Transverse yarns
7 are engaged into longitudinal yarns 5 and are part of the weave
pattern. They constitute first yarns for purposes of the present
description. They contain an additive that makes them capable of
absorbing laser energy, so that they can be brought to melting
temperature with the aid of a laser beam.
[0033] A laser apparatus 8 is arranged above the plane of rollers
3, 4. Laser apparatus 8 has longitudinal rails 9, 10 (depicted only
in shortened fashion here) that extend, parallel to one another,
parallel to the plane of rollers 3, 4 and above them, and are
immovably joined to the apparatus frame. Longitudinal rails 9, 10
have a spacing that is larger than the width of forming fabrics 2
that are to be processed in apparatus 1.
[0034] Mounted displaceably in the directions of double arrow D on
longitudinal rails 9, 10 is a transverse rail 11. It extends
perpendicular to longitudinal rails 9, 10 and thus parallel to the
axes of rollers 3, 4. Mounted on transverse rail 11 via an arm 12
is a laser 13, which can be displaced back and forth on transverse
rail 11 in the directions of double arrow E. It can furthermore be
pivoted about the longitudinal axis of transverse rail 11 in the
directions of double arrow F. The movements of transverse rail 11
relative to longitudinal rails 9, 10, and the movement of laser
head 13 relative to transverse rail 11, are brought about by means
of motors (not depicted here in further detail).
[0035] Apparatus 1 comprises a programmable control device
(likewise not depicted here in further detail), similar to a CNC
controller, with which the individual motors for moving laser head
13 and rollers 3, 4 can be controlled, and laser head 13 can be
activated. In the example shown, laser head 13 is moved only in the
transverse direction via transverse rail 11. Rollers 3, 4 are
halted when a first transverse yarn 7 comes to rest below laser
head 13. Laser head 13 is then guided along transverse yarn 7 over
the width of forming fabric 2, and activated at the positions
designated for welding. As a result of the laser energy, transverse
yarn 7 heats up at the surface to melting temperature, with the
consequence that it fuses to longitudinal yarns 5 at crossing
points 14, so that a welded join is produced there after
cooling.
* * * * *