Note: Descriptions are shown in the official language in which they were submitted.
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PRESS FELT AND BASE FABRIC
FIELD OF THE INVENTION
[0001] The invention relates to a press felt comprising: at least one
base fabric, which includes a bottom side and a side facing the web to be
dried
and several longitudinal yarns and transverse yarns and where at least some
of the longitudinal yarns are arranged to form several seam loops at a first
transverse joining edge of the press felt and at a second transverse joining
edge, the joining edges of the base fabric being arrangeable edge on edge to
form a seam, where the seam loops of the first joining edge and the second
joining edge intermesh and form a seam loop channel, into which a seam yarn
connecting the joining edges can be inserted; a seam flap, which is arranged
to cover the seam on the press felt surface facing the web, and at least one
batt fibre layer arranged at least on the base fabric surface facing the web.
[0002] The invention further relates to a base fabric intended for a
press felt, the base fabric consisting of a base side and a web side and com
prising: several longitudinal yarns arranged to form seam loops at a first and
a
second transverse edge of the base fabric; and several transverse yarns ar
ranged to attach to the longitudinal yarns.
BACKGROUND OF THE INVENTION
[0003] Depending on the press structure, the press section of the
paper machine employs a press felt on one or both sides of the web to be
dried, into which the water in the web is absorbed in the pressing phase. The
purpose is to transport the water away in the structure of the press felt
without
letting it back into the web. The press felt comprises a base fabric which,
for
example, provides the felt with a necessary space for water. To obtain a
smooth surface, batt fibre is needled at least onto a base fabric surface
facing
the paper web, the batt fibre preventing markings from being produced on the
web. Also, the water retention capacity of the felt can be adjusted by means
of
the batt fibre. To facilitate the installation of press felts, it is known to
provide
them with seams. The transverse edges of such felts comprise seam loops. It
is not until in the paper machine that the felt is connected into a closed
loop by
intermeshing the seam loops on the opposite edges and inserting a seam yarn
into a seam loop channel thus formed. A problem associated with felts pro-
vided with seams is that the seam loops form a discontinuity in the felt base
fabric where the felt thickness is different, which causes markings on the
web.
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Furthermore, in the seam area, the yarn density differs from that in the rest
of
the structure, in which case the felt permeability is different at the seam.
The
difference in permeability may also cause markings on the web. In addition,
since the number of yarns is lower in the seam area, adherence of the batt fi-
bre may also pose a problem.
BRIEF DESCRIPTION OF THE INVENTION
[0004] The object of the invention is to provide a novel and im-
proved press felt and base fabric for a press felt.
[0005] The press felt according to the invention is characterized in
that the base fabric has at least a three-layer structure which comprises, in
addition to the longitudinal yarns forming seam loops, at least one layer of
lon-
gitudinal surface yarns on the web-side surface of the base fabric, the yarns
being arranged to attach to at least some of the transverse yarns, that the
lon-
gitudinal surface yarns are arranged to continuously extend over the seam
when the base fabric is manufactured, that several additional transverse yarns
are provided at the seam, the yarns being attached at least to the
longitudinal
surface yarns, and that the longitudinal surface yarns have been cut after the
attachment of batt fibre to form a seam flap.
[0006] The base fabric according to the invention is characterized in
that in addition to the longitudinal yarns forming seam loops, there is at
least
one layer of longitudinal surface yarns on the web-side surface of the base
fabric, that the longitudinal surface yarns are attached to at least some of
the
transverse yarns, that the longitudinal surface yarns extend continuously over
a seam formed by seam loops on the first and the second edge, and that the
area where the seam is to be formed is provided with several additional trans-
verse yarns, which are attached at least to the longitudinal surface yarns.
[0007] The invention is based on the idea that the web-side surface
of the base fabric is provided with at least one layer of longitudinal yarns,
which are attached to the transverse yarns of the base fabric and further ar
ranged to extend over the seam when the base fabric is manufactured. Fur
thermore, additional transverse yarns excessive to the rest of the structure
are
brought to the seam area during manufacture. These yarns join at least the
surface yarns that travel over the seam. After the base fabric has been
formed,
one or more batt fibre layers are attached at least to its web-side surface.
It is
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not until after this that the longitudinal surface yarns travelling over the
seam
are cut, whereby a seam flap which protects the seam is formed.
[0008] An advantage of the invention is that the seam flap protects
the seam from mechanical wear. Furthermore, since the seam flap comprises
both longitudinal and transverse yarns, its structure is durable and firm. The
number and quality of longitudinal surface yarns as well as those of the addi-
tional transverse yarns can be easily varied to obtain a desirable base fabric
without having to substantially alter the structure of the basic weave. A
further
advantage is that batt fibre can be attached well to the seam area since the
seam flap comprises both transverse and longitudinal yarns. Thus the perme-
ability and thickness may be substantially the same at the seam as in the
other
press felt sections.
[0009] In respect of weaving technique, the length of the seam flap
can be implemented such that stretching of the seam loops during use is com-
pensated for and the seam flap always provides sufficient protection for the
seam.
[0010] An embodiment of the invention is based on the idea that the
longitudinal yarns to be extended over the seam on the base fabric surface
differ from the monofilaments that form seam loops in the base fabric. For ex-
ample, plied yarns can be used as longitudinal surface yarns. Thanks to the
structure according to the invention, the longitudinal surface yarns can be se-
lected so as to obtain a good surface smoothness and batt fibre adherence.
[0011] An embodiment of the invention is based on the idea that the
additional transverse yarns in the seam flap are attached to the longitudinal
surface yarns by weaving.
[0012] An embodiment of the invention is based on the idea that the
additional longitudinal yarns and longitudinal surface yarns are attached to
one
another by weaving, and after weaving, the attachment of the yarns is secured
by melting or welding the yarns into one another. The result is a very firm
and
durable seam flap.
[0013] An embodiment of the invention is based on the idea that the
additional transverse yarns attach only to the longitudinal yarns that travel
over
the seam.
[0014] The basic idea of an embodiment according to the invention
is that the longitudinal yarns in the base fabric do not cross one another.
Thus
the longitudinal surface yarns form a layer which is independent of the rest
of
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the structure and whose yarns can be selected relatively freely. In addition,
since the longitudinal surface yarns do not cross the yarns forming seam
loops, they do not take room between adjacent seam loops. The longitudinal
surface yarns have no effect on the density of the seam loops, and thus the
loop density can be selected according to the need.
[0015] An embodiment of the invention is based on the idea that the
seam flap area is provided with a special reinforced layer, such as a layer
made of resin or adhesive which reinforces the structure of the seam flap.
BRIEF DESCRIPTION OF FIGURES
[0016] The invention will be described in greater detail in the ac-
companying drawings, in which
Figure 1 is a schematic perspective view of a press felt according to
the invention which is provided with a seam and connected into a closed loop,
Figure 2 schematically illustrates the structure of an edge of a press
felt according to the invention seen in the direction of transverse yarns,
Figure 3 schematically illustrates the structure of a base fabric ac-
cording to the invention seen in the direction of transverse yarns, and
Figure 4 schematically illustrates a method of manufacturing a base
fabric according to the invention.
[0017] For the sake of clarity, the figures illustrate the invention in a
simplified manner. Like reference numbers refer to like parts in the figures.
DETAILED DESCRIPTION OF THE INVENTION
[0018] It appears from Figure 1 how the press felt can be formed
into a closed loop by connecting the joining edges at its transverse edges to-
gether by a seam 1. The press felt may also consist of several press felt
pieces
joined together, in which case there are naturally several seams. The press
felt
is run on the paper machine in the machine direction A marked in the figure.
In
addition, in the transverse direction B, the width of the press felt
corresponds
to that of the paper machine.
[0019] Figure 2 illustrates a transverse B joining edge of a press felt
according to the invention. For the sake of clarity, the figure illustrates
only a
few of the transverse yarns. The base fabric of the press felt shown in the
fig-
ure has been manufactured by weaving longitudinal yarns and transverse
yarns together using a suitable weave. The structure comprises at least three
layers, i.e. it contains three superimposed longitudinal yarns. The
longitudinal
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yarn 2 on the bottom side C of the press felt and the longitudinal yarn 3 in
the
middle form a seam loop 4 at the joining edge. Usually, all yarns 2 and 3 at
the
bottom and in the middle form seam loops but in some cases some of the lon-
gitudinal yarns may not form seam loops. The longitudinal yarns 2 and 3 at the
5 bottom and in the middle bind to transverse yarns 5. In addition, on the web-
side surface D, there is a longitudinal surface yarn 6, which also binds to
the
transverse yarns 5 in the weave. The longitudinal surface yarn 6 clearly ex-
tends further than the seam loops in direction A in the embodiment shown in
Figure 2. In some cases, the longitudinal surface yarns 6 may be cut approxi-
mately at the seam loops. In addition, the seam 1 area is provided with a
suffi-
cient number of additional transverse yarns 7, which attach to the
longitudinal
surface yarns 6. The materials, cross sections and yarn types of the
additional
yarns 7 and longitudinal surface yarns 6 can be selected independently of the
rest of the base fabric structure. The longitudinal yarns 2 and 3 that form
seam
loops 4 are typically made of monofilaments but the longitudinal surface yarns
6 as well as the additional yarns 7 may also be made of plied fibre, for exam-
ple. Batt fibre is much easier to attach to yarns made of plied fibre and to a
weave structure formed from them. The longitudinal surface yarns 6 and addi-
tional yarns 7 form together a seam flap 8, which protects the seam 1. The
seam flap 8 is a press felt part which has substantially the same width as the
press felt and whose one transverse edge is attached to the rest of the press
felt structure when the other transverse edge is free. In addition, on the web-
side surface D of the press felt, there is at least one layer of batt fibre
11. Usu-
ally, the batt fibre is attached to the base fabric 10 by needling. There may
also
be batt fibre on the bottom-side surface C. Furthermore, the seam flap 8 may
be provided with one or more reinforcing layers 12, which makes the seam flap
firm and affects its permeability. The reinforcing layer 12 may be a
perforated
film, a resin layer, an adhesive layer or another material layer applied by
spreading, spraying, injecting or by means of a roller, for example. On the
other hand, after weaving, the base fabric may be treated with an ultrasonic
device or heated at least in the seam area, in which case the longitudinal sur-
face yarns 6 and additional yarns 7 join one another. A suitable material can
be selected for the yarns 6 and 7 by taking the treatment in question into ac-
count. Thus the yarns 6 and 7 may be 'fusible yarns', for instance.
[0020] Figure 3 illustrates part of a base fabric 10 according to the
invention. To illustrate the seam 1 structure, a seam yarn 13, which connects
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the joining edges together, has been inserted into the seam loop channel
formed by the seam loops 4. The longitudinal surface yarns 6 are arranged to
extend over the seam 1. A point where the longitudinal surface yarns 6 can be
cut e.g. in the transverse direction to form a seam flap is marked in the
figure
with reference number 14. The cutting is performed after the necessary batt
fibre layers have been attached to the base fabric 10. This is advantageous
since batt fibre makes the structure stable, in which case there is no risk
that
the longitudinal surface yarns 6 will slip inside the weave basic structure
after
cutting and thus shorten the length of the seam flap to be formed. It further
ap-
pears from Figure 3 that there may be additional transverse yarns at the seam
loops 4 as well as at a section before the base fabric section. Thus the
discon-
tinuity caused in the weave structure by the seam loops 4 can be sealed and
supported with additional yarns 7.
(0021] Figure 3 further illustrates an alternative cutting point 14',
which is clearly outside the seam area 1. In that case, a relatively long seam
flap 8 is formed in the base fabric. This flap compensates for the
discontinuity
caused by the seam 1 over a longer section. The free edge of the seam flap
can be, if necessary, attached after insertion of the seam yarn by needling,
stitching, melting, using an adhesive or with suitable form-locking members.
When the cutting point 14' is used, the transverse yarn is in position 5b
instead
of position 5a.
[0022] As further appears from Figure 3, at least some of the addi-
tional transverse yarns 7' may also bind to the yarns 2 and 3 that form seam
loops 4.
[0023] Figure 4 illustrates a method of manufacturing a base fabric
10, where the fabric is manufactured in one step in one weaving machine. For
the sake of clarity, only a few of transverse yarns are shown. The section of
the fabric that forms seam loops 4 is woven into an endless structure using
'horseshoe weaving'. In the figure, seam loops are formed on the upper and
the lower level at the right-hand edge of the fabric. The figure also shows an
edge yarn 15, round which the seam loops 4 are woven. An upper structure is
simultaneously woven into a closed loop on top of the structure forming seam
loops 4. This structure comprises longitudinal surface yarns 6 that extend
over
the seam and additional yarns 7. After weaving, the base fabric 10 is trans-
ferred into a needling machine, where batt fibre is attached. Then the press
felt
can be subjected to a thermal treatment and other necessary post-treatments.
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Finally, before installation in a paper machine, the longitudinal surface
yarns 6
are cut and the seam is opened.
[0024] It further appears from Figure 4 that the longitudinal surface
yarns 6 can be woven into a loop with a desired length around the structure
forming seam loops 4. A suitable filling material can be used as an aid in
weav
ing, such as auxiliary yarns 16, by means of which the longitudinal surface
yarns 6 can be guided in a weaving machine. This way, it is possible to form a
seam flap 8' with a desired length independent of the rest of the base fabric
10
structure. This seam flap is illustrated in the figure with a broken line
[0025] It should be noted that the base fabric 10 can be formed us-
ing weave patterns other than those illustrated in the figures. In addition,
the
longitudinal surface yarns 6 can be arranged in two or more layers and they
form a seam flap 8 with the additional yarns 7.
[0026] It should further be mentioned that instead of the woven
structures described above, the base fabric may be a yarn assembly.
[0027] The drawings and the related description are only intended
to illustrate the inventive concept. The details of the invention may vary
within
the scope of the claims.
