Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1281~15
FAaRIC FOR THE SHEET FORMING SECTION
OF A PAPERMAKING MACHINE
The invention relates to a fabric for the sheet forming
sectiion of a papermaking machine which is made up of a double
layer fabric within upper and a lower layer directly there-
below of transverse threads interwoven with longitudinal
threads. The transverse threads of the upper layer and the
longitudinal threads form crimps oriented towards the paper
side with their highest points disposed in the plane of the
paper. Within each weave repeat the longitudinal threads are
interwoven two times into the upper layer of transverse
threads, and the number of transverse threads in the upper
layer is twice as high as in the lower layer.
Such double layer sheet forming fabrics are disclosed in
German Auslegeschrifts No. 2,263,476; No. 2,540,490; and
No. 2,706,235, and in European Patent Publication No.
30,490. In the fabric shown in Figure 2F of German
Auslegeschrift No. 2,706,235, the density of transverse
threads in the upper layer is likewise twice as high as in
the lower layer. Although such sheet forming wires exhibit
better marking characteristics than single layer sheet
forming wires, they are nevertheless unsuited for the
production of paper of the type extremely sensitive to
marklng.
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According to German Auslegeschrift No. 2,706,235, the
marking characteristics are improved by extremely long weft
floatings, i.e., transverse thread floatings. European
Patent Publication No. 30,490, and U.S. Patent No.
4,333,502, attempt to reach the same goal with long warp
floatings.
The object of the present invention is to provide a
fabric for the sheet forming section of a papermaking machine
which leaves a minimum of marks on the paper.
According to the invention, this object is achieved
by having first transverse threads of the upper layer form
crimps reaching up to the paper plane while being supported
in a crimp saddle of a longitudinal thread and by having
second transverse threads of the upper layer alternating with
the first transverxe threads to form crimps reaching up to
the paper plane while being supported by two adjacent
longitudinal threads one of which ascends from the fabric
interior to the paper plane, while the other one descends
from the paper plane into the fabric interior.
When a transverse thread is supported by the crimp
saddle of a longitudinal thread, the longitudinal thread
passes underneath the respective transverse thread, while it
passes over the preceding and over the next following
transverse thread. The transverse thread is affected by a
resulting force which is directed upwardly. In the fabric of
the invention the first transverse threads of the upper layer
are supported in this way. The first transverse threads
alternate with second transverse threads in the upper layer.
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The second transverse threads are supported by adjacent
lonyitudinal threads extending in shear-like fashion, i.e., one of
the two longitudinal threads ascends from the fabric interior to
the paper plane, while the other one descends from the paper plane
into the fabric interior. A longitudinal thread is said to run in
the fabric interior if it runs below at least two consecutive
transverse threads of the upper layer. With such a mode of support
a transverse thread is subject not only to a force directed
upwardly toward the paper plane, but at the same time to a torque
turning it away from the transverse direction in the paper plane.
As a result of these two different types of support of the
transverse threads, the transverse thread floats are not all
oriented in parallel, and there exist two types of transverse
thread floats extending at an angle relative to each other. This
eliminates the uniformity of paper marking so that it becomes
indistinct and le~s noticeable.
According to a preferred embodiment of the invention the
longitudinal threads directly before and behind each crimp saddle
pass over two transverse threadæ of the upper layer and adjacent
longitudinal threads are longitudinally offset relative to one
another by six transverse threads in the upper layer. This results
in numerous and short longitudinal and transverse thread floats,
and thus in a great number of paper sheet supporting points. It
has been found that the short longitudinal and transverse floats
further improve the freedom from wire marks.
The longitudinal and the transverse threads suitably consist
of synthetic resin monofilaments, especially polyester
monofilaments. The transverse threads of the lower layer are
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stronyer than those of the upper layer to improve the
abrasion resistance. The latter can be further improved by
making a number of transverse threads in the lower layer from
especially abrasion resistant material, e.g., polyamide.
A monoplanar surface on the paper supporting side is not
achieved by the weaving process. Only after thermosetting of
the fabric with longitudinal stretching are the uppermost
points of the crimps of the longitudinal threads and
transverse threads on the paper side disposed in one plane,
as is generally known. In a fabric woven from end-to-end, a
monoplanar surface generally can be attained more readily
than in endless woven fabrics.
The foregoing and other objects, features and advantages
of the invention will be apparent from the following more
particular description of a preferred embodiment of the
invention as illustrated in the accompanying drawings , in
which:
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Figure l is a sectional view in longitudinal direction
demonstrating the course of two longitudinal threads in a
seven harness weave.
Figure 2 is a plan view of the fabric shown in Figure 1.
Figure 3 is a schematic diagram showing the weave design
for the fabric shown in Figures 1 and 2.
Figures 4-6 are views analogous to those shown in
Figures 1 to 3, but for an eight harness weave.
Figure 7 is a longitudinal sectional view of an embodi-
ment of the papermaking machine fabric in which a number of
the longitudinal threads are interwoven only with the upper
layer.
Figure 8 is a plan view of the fabric in Figure 7 as
viewed from the bottom or running side.
Figure 9 is a longitudinal sectional view of another
embodiment Yimilar to that of Figure~ 7 and 8 but for a
higher harness weave.
Figure 10 is a plan view of the fabric shown in Figure
: 9.
Figure 11 is a plan view of a papermaking machine fabric
with mirror symmetrical weave pattern in the two fabric
halves.
Figure 12 is a longitudinal sectional view of a paper-
making machine fabric comprising three layers of transverse
threads.
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As is apparent from the longitudinal fabric section
illustrated in Figure 1 the double layer fabric has an upper
layer 1 of first transverse threads 3 and second transverse
threads 4 in alternating sequence and a lower layer 2 of
transverse threads 5. Longitudinal threads 6 are interwoven
with the transverse threads 3, 4 of the upper layer 1 and
transverse threads 5 of the lower layer 2 and connect the two
layers. The density of the transverse threads in the upper
layer 1 is twice that in the lower layer 2 and the fabric is
woven in such a way that the second transverse threads 4 of
the upper layer 1 come to lie as exactly as possible above
the transverse threads 5 of the lower layer 2.
Within each weave repeat each longitudinal thread 6 is
interwoven twice into the upper layer 1 in that it passes in
succession over two transverse threads 3, 4 under a first
transver~e thread 3 and again over two transverse threads 3,
4. Within the upper layer 1 the longitudinal thread 6 thus
forms a saddle which supports a first transverse thread 3 on
which substantially only an upwardly directed force is
exerted. Thereafter the longitudinal thread 6 passes between
the two layers 1, 2 a distance of four transverse threads 3,
4 in the upper layer 1 and two transverse threads 5 in the
lower layer 2 so that it is interwoven also with the lower
layer 2. Then it passes once more between the two layers 1,
~25 2 until it again ascends to the top side within the next
following weave repeat.
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Thermosetting of the fabric under longitlldinal tension
causes ~he ~opmost points of the crimps 7 of~the first transverse
threads 3, the crimps 8 of the second transverse threads 4 and the
crimps 9 of the longitudinal threads 6 to be disposed in the paper
S plane 10. The longitudinal tension exerted during thermosetting of
the fabric also somewhat lifts the transverse thread 5 of the lower
layer 2 under which the longitudinal thread 6 passes, so that the
lowermost point of the crimp formed by the longitudinal thread 6 in
the lower layer 2 is disposed somewhat above the running side
formed by the other transverse threads S of the lower layer 2 and
is thus largely protected against abrasion. Hence the fabric
represents a so-called transverse thread runner ~weft runner with
open end weave).
According to Figure 2, adjacent longitudinal threads are
longitudinally offset by six transverse threads 3, 4 each in the
upper layer 1. As is apparent in Figure 1, adjacent longitudinal
threads 6 therefore cross beneath a second transverse thread 4 of
the upper layer 1. This results in a shear-like support of said
second transverse thread 4 whereby the second transverse thread 4
is not only urged upwardly but is at the same time twisted in the
transverse direction in the fabric plane. The crimps 8 of the
second transverse threads therefore are not disposed parallel to
the crimps 7 of the first transverse threads 3 in the upper layer
1.
The fabric weave of Figures 1-3 is a seven harness weave as it
repeats after seven transverse threads 5 in the lower layer 2 and
: seven longitudinal threads 6. Hence a weave repeat comprises ~even
transverse threads 5 in the lower layer 2 and
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seven Longitudinal threads 6 and fourteen transverse threads 3 and
4 in tl~e upper layer 1. The first transverse threads 3 and the
second transverse threads 4 can be made of the same material and
can have equal dimensions. For the second transverse threads 4
preferably a softer material is selecte~, suitable in connection
with a l arger diameter, in order that the crimps 8 of said
transverse threads 4 extend at a wider angle -to the transverse
direction which may be beneficial to freedom from wiremarks.
Figures 4-6 show an example analogous to that of Figures 13,
but for an eight harness weave. Each longitudinal thread again
forms two crimps 9 in the upper layer 1 separated by a first
transverse thread 3 which in this place forms crimp 7 extending in
the transverse direction.
The crimps 8 of the second transverse threads 4 again extend
at an angle to the transverse direction since the second transverse
threads 4 are supported shear-like by adjacent longitudinal threads
6 offset relative to each other by six transverse threads. A
comparison or Figures 2 and 5 demonstrates that the crimps 9 of the
longitudinal threads 6 are very uniformly distributed. On the
other hand, the crimps 7 and 8 extending obliquely relative to each
other to counteract the monotony of pattern and especially do not
form any diagonally extending lines which leave a mark on the
; paper.
It is also possible to separate the two crimps 9 of each
~; 25 longitudinal thread 6 by three or five transverse threads 3 in the
upper layer 1 rather than by one transverse thread 3. In case of
separation by three transverse threads the two
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different types of crimps extending obliquely to each ~ther are
for~ed in each transverse thread of the upper layer 1. In case of
separation of the crimps 9 by five transverse threads of the upper
layer the transverse threads float over four longitudinal threads
and there is only one type of crimp so that this does not lead to a
further improvement in the reduction of marks on the paper.
Figures 3 and 6 show the weave designs for the examples
illustrated by Figures 1, 2 and 4, 5, respectively. The numbers 1
to 7 in Figure 3, and 1 to 8 in Figure 6 along the lower margin
designate the longitudinal threads, and the numbers 1 to 21 and 1
to 24, respectively, along the lateral margin designate the
transverse threads of one weave repeat.
In Figure 3 the transverse threads 1, 4, 7, 10, etc., relate
to the first transverse threads 3 supported by a crimp saddle of
one longitudinal thread, while the transverse threads 2, 5, 8,
etc., relate to the second tranxverse threads 4 are ~upported in
shear fashion by longitudinal threads. The transverse threads 3,
6, 9, etc., represent transverse threads 5 of the lower layer 2.
In Figure 6 the transverse threads 2, 5, 8, 11 r etc., belong to the
lower layer, while the first transverse threads 3 ~1, 4, 7, etc.),
are supported by crimp saddles and second transverse threads 4
supported in a shear-like manner are 3, 6, 9, etc.
Each individual square of the weave design represents a
crossing point between a longitudinal and a transverse thread.
~25 Black squares indicate that the longitudinal thread passes over the
t~ransverse thread while white squares indicate that the
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transverse threads of the upper layer 1 pass over the longitudinal
thread 6. The squares marked with a black dot indicate that the
transverse threads of the lower layer 2 are disposed above the
longitudinal threads 6, when viewed from the paper side. These are
the points of interweaving between the lower layer 2 and the
longitudinal threads 6.
The fabric of the invention is generally woven and thermoset
in such a way that the longitudinal thread density ranges between
90 and 110 percent. A typical value for the longitudinal thread
density ranges between 100 and 105 percent. However, for tissue
paper suitably lower values are selected.
The presently described papermaking machine fabric can,
according to European Patent Publication No. 48,962, also be
produced in such a way that only a portion of the longitudinal
thread~ 6 is interwoven with the lower layer 2 of transverse
threads 5 while the other longitudinal threads 16 are interwoven
only with the weft threads 3, 4 of the upper layer 1 so that they
are not subject to abrasion on the running side. Such embodiments
of the papermaking machine fabric of the present invention are
20 shown in section in Figures 7 and 9. The embodiment shown in
Figure 7 is largely identical with that of Figure 1 and the only
difference resldes in the fact that every second longitudinal
thread 16 is not interwoven with the lower layer 2. Also another
ratio of longitudinal threads 6 to longitudinal 16 can be selected.
~25 Within each weave repeat the longitudinal threads 6 are interwoven
twice with the upper layer 1 and once with the lower layer 2.
W1thin each weave repeat the longitudinal threads 16 are interwoven
twice
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wit:h the uppet layer 1 but never with the lower layer 2. This
results in ~-ery long transverse thread floats on the running side
extending over 13 longitudinal threads, as shown in Figure 8. On
the paper side there is no difference from the embodiment of
Figures 1 and 2.
Figures 9 and 10 show an embodiment of the papermaking
machine fabric in which the warp threads 6 are interwoven twice
with the upper layer 1 and twice with the lower layer 2. The
other longitudinal threads 16 are interwoven twice with the upper
layer 1 but never with the lower layer 2. This results in shorter
floats on the running side, viz. over 7 longitudinal threads, as
shown in Figure 10. The paper face of this embodiment corresponds
with that of Figures 4 and 5 since there are no differences with
respect to interweaving into the upper layer 1. According to
European Patent Publication No. 120,337 the paper making machine
fabric of the present invention can be made such that the weave
pattern is mirror-image symmetrical in the two fabric halves on
either side of the longitudinal centre line and the points of
interweaving form a V pattern in the fabric with a weave diagonal
interrupted in the middle of the fabric. This prevents lateral
running or drifting of the travelling papermaking fabric in the
papermaking machine. Additional longitudinal threads 26 in the
fabric centre prevent excessively long floats of the transverse
threads so that along the borderline between the two fabric halves
there are no substantially longer floats of the transverse threads
than in the remaining fabric. Figure 11 shows in plan view a
section of such a papermaking machine fabric including several
additional longitudinal threads 26.
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Fig~lre ~ shows in longitudinal section an embodiment in
whicl~ three layers of transverse threads are provided. The top
laye;r 21 and the layer directly therebelow, i.e. the intermediate
layer 22, of transverse threads are interwoven with the
longitudinal threads 6 as shown in Figure 1 of the upper layer 1
and the lower layer 2.
The further lower, i.e. lowermost Layer 23 of transverse
threads in Figure 12 is an additional layer of transverse threads
25 interwoven by additional longitudinal threads 27 with the
intermediate layer 22 of transverse threads 5. On the whole, each
longitudinal thread is interwoven only with the transverse threads
of two adjacent layers. Suitably the density of the transverse
threads 25 of the lower layer 23 is the same as that of the
transverse threads 5 of the inter- mediate layer 22. Such a
composite fabric is described in detail in German Auslegeschrift
No. 3,225,599. The paper face of this embodiment is the same as
that shown in Figure 2.
Example 1
A fabric with a seven harness weave according to Figures 1
to 3 is made by open end weaving. The longitudinal threads
consist of polyester monofilament having a high elastic modulus
and a diameter of 0.15 mm. After thermosetting the longitudinal
thread density is 71 threads / cm.
The first transverse threads 3 of the upper layer 1 are
polyester monofilaments of 0.17 mm diameter and have an average
elastic modulus (elongation 19% under a load of 27 cN/tex). The
second transverse threads 4 are polyester monofilaments
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of l).185 mm diameter and have a relatively low elastic modulus
(elongation ~3.~% under a load of 27 cN/tex). After thermoset-
ting the density of transverse threads in the upper layer 1 is
36/cm.
The transverse threads 5 of the lower layer 2 forming the
running side are especially soft polyester monofilaments ~elon-
gation 23.4% under a load of 27 cN/tex) of 0.20 mm diameter
alternating with soft polyamide 6 monofilaments of 0.21 mm
diameter, and after thermosetting the density of transverse
threads in the lower layer 2 is 18/cm.
The fabric is thermoset in such a way -that on the paper
face the crimps 7 and 8 of the first transverse threads 3 and of
the second transverse threads 4 and the crimps 9 of the
longitudinal threads 6 are disposed in one plane so that the
fabric is monoplanar. On the running side there was a mono-.
planity differential between the transverse threads 5 and the
longitudinal threads 6 of 7.5/100 mm so that the fabric is a
weft runner. During weaving and setting care was taken that the
second transverse threads 4 of the upper layer 1 are disposed
exactly above the transverse threads 5 of the lower layer 2.
Example 2
A fabric of an eight harness weave as shown in Figures 4-6
is produced by open end weaving end, after setting, it is made
endless by means of a woven seam. The fabric is woven with a
Iongitudinal thread count of 54/cm. During thermoietting the
longitudinal thread count increased to a value
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of 60~cm due to the transverse contraction of the abric. The
longitudinal threads consist of polyester monofilament of
0.17 mm diameter of a longitudinally stabilized quality with
high elastic modulus.
The transverse threads 3 of the upper layer consist of
polyester monofilament of 0.17 mm diameter of a relatively hard
weft quality Trevira Type 902 with an elastic modulus relatively
high for weft wires corresponding to an elongation of 8.5% under
a load of 27 cN/tex). The second weft threads 4 of the upper
layer 1 are likewise polyester monofilaments, but of the softer
Trevira Type 900 with an elongation of 23.4% at 27 cN/tex and a
diameter of 0.20 mm. This fabric is woven with a transverse
thread density of 35/cm and after thermosetting the transverse
thread count is reduced to 32/cm in the upper layer l and to
16/cm in the lower layer 2. The transver~e thread~ 5 in the
lower layer 2 are polyester monofilaments of 0.22 mm diameter of
the soft Trevira Type 900 corresponding to an elongation of
23.5% at 27 cN/tex alternating with polyamide monofilaments of
the PA Type 6.6 with a diameter of 0.24 mm. The fabric is set
at lgsC and during this operation a maximum longitudinal
tension of 95 N/cm is reached. During setting a crimp reversal
between longitudinal and transverse threads takes place. The
longitudinal warp threads originally disposed on the outside of
the woven fabric stretch under the influence of the setting
~25 tension and heat and, as a result of this crimp reversal, are
embedded in the interior of the fabric. In the final fabric the
longitudinal thread floats
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and the floats of the first transverse threads ~ and the
second transverse ~hreads 4 on the paper side are all
disposed in one plane. On the running side the longitudinal
thread 6 forces the transverse threads S to form distinct
crimE~s so that in the final fabric solely the floats of the
trancsverse threads 5 form the external side, i.e., the
running side, of the fabric in the lower layer 2. On the
running side differences in height between the transverse
threads and the longitudinal threads of 8.5/100 mm are
measured, i.e., only after 8.5/100 mm of the transverse
thread material have been abraded do the longitudinal threads
6 for the first time get in contact with the elements of the
wire section of the papermaking machine.
While the invention has been particularly shown and
described with reference to preferred embodiments thereof it
will be understood by those in the art that the foregoing and
other changes in form and details may be made therein without
departing from the spirit and scope of the invention.
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