Note: Descriptions are shown in the official language in which they were submitted.
CA 02752532 2011-09-14
INDICATION OF THE WEAR LEVEL OF A FABRIC BY THE USE OF FILAMENTS
-5 Field of the Invention
The present invention is directed towards means
for detecting the wear level of, and creating
guidelines on, papermaking and other industrial
fabrics, particularly towards multilayered and
conductive filaments used as such a means.
Background of the Invention
During the papermaking process, a cellulosic
fibrous web is formed by depositing a fibrous slurry,.
that is, an aqueous dispersion of cellulose fibers,
onto a moving forming fabric in the forming section
of a paper machine. A large amount of water is
drained from the slurry through the forming fabric,
leaving the cellulosic fibrous web on the surface of
the forming fabric.
The newly formed cellulosic fibrous web proceeds
from the forming section to a press section, which
includes a series of press nips. The cellulosic
fibrous web passes through the press nips supported
by a press fabric, or, as is often the case, between
two such press fabrics. In the press nips, the
cellulosic fibrous web is subjected to compressive
forces which squeeze water therefrom, and which
adhere the cellulosic fibers in the web to one
another to turn the cellulosic fibrous web into a
paper sheet. The water is accepted by the press
fabric or fabrics and, ideally, does not return to
the paper sheet.
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The paper sheet finally proceeds to a dryer
section, which includes at least one series of
rotatable dryer drums or cylinders, which are
internally heated by steam. The newly formed paper
sheet is directed in a serpentine path sequentially
around each in the series of drums by a dryer fabric,
which holds the paper sheet closely against the
surfaces of the drums. The heated drums reduce the
water content of the paper sheet to a desirable level
through evaporation.
It should be appreciated that the forming, press
and dryer fabrics all take the form of endless loops
on the paper machine and function in the manner of
conveyors. It should further be appreciated that
paper manufacture is a continuous process which
proceeds at considerable speeds. That is to say, the
fibrous slurry is continuously deposited onto the
forming fabric in the forming section, while a newly
manufactured paper sheet is continuously wound onto
rolls after it exits from the dryer section.
Operating, as they do, in the form of endless
loops on paper machines, papermaker's fabrics, and
particularly their inner surfaces, are susceptible to
abrasive wear. PMuch of this woar results from
contact with stationery components of the paper
machine. Ultimately, many fabrics must be removed
from paper machines when the wear caused by such
moving contact has reduced the thickness of the
fabric, at least in some locations, to the point
where it is weakened or has lost some quality or
characteristic desired by papermakers in its
particular application.
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Normally, wear is monitored using a thickness
gauge. However, it is difficult to measure the
thickness of a papermaker's fabric more than a foot
or two in from its edges with such a gauge,
especially when the fabric is running on a paper
machine.
Clearly, a means for monitoring wear on a
papermaker's fabric, and particularly at any point on
its inner and outer surfaces, even when the paper
machine is operating, would be very helpful to those
in the papermaking industry. The present invention
provides such a means to the industry.
Summary of the Invention
It is therefore a principal object of the
invention to provide for an industrial fabric having
a built-in mechanism that enables wear of the fabric
to be monitored.
It is a further object of the invention to
provide for a fabric which has a detectable
guideline.
This and other objects and advantages are
provided by. the present invention. In this regard,
the present in.-entirn is d.i-ected towards a fabric
which includes multilayer filaments comprising a core
yarn surrounded by one or more outside layers. The
core and the layers are visibly distinguishable from
one another by, for example, their contrasting color,
or reflectivity. This enables fabric wear to be
monitored as abrasion gradually wears away successive
layers of the filaments, eventually revealing the
core yarns.
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In a second aspect of the invention, conductive
monofilaments are woven into the wear side of a
fabric to create another type of wear detection
system. By measuring, for' example, the resistance in
the cross direction of the fabric, it is possible to
determine the level of wear.
In a third aspect of the invention, the
multilayer filaments are used to create a visible
guideline on the fabric in CD and/or MD directions.
The guideline is not removable by high-pressure
showers or chemical cleaning, and is used for
determining-belt alignment, speed. measurements, or as
a trigger for an electronic guiding system.
In a fourth aspect of the invention, a
conductive filament having a` contrasting color is
used to create a permanent guideline on a fabric.
The color contrast or the electrical properties of
the filaments can be used as a trigger for on-line
speed measurements or as a trigger for an electronic
guiding system.
Brief Description of the Drawings
Thus by the present invention, its objects and
advantages will be realized the description of which
should be taken in conjunction with the drawings
wherein:
Figure 1 is a cross sectional view of the an
example of a multilayered filament according to the
- present invention;
Figure 2 is side and top views of the
multilayered filament in Figure 1 exhibiting wear,
incorporating the teachings of the present invention;
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Figure 3 is a cross sectional view of the an
example of a multilayered optical filament according
to another aspect of the invention;
Figure 4 is a top view of an example of a fabric
comprising the multilayered filaments of Figures 1,-2
and 3;
Figure 5 is a top view of the fabric in Figure
4, exhibiting wear;
Figures 6 and 7 illustrate examples of fabrics
with, respectively, CD and MD guidelines, incorp-
orating the teachings of 'the present invention.
Detailed Description of the Preferred Embodiments
A preferred embodiment of the present invention
will be described in the context of filaments and
fabrics woven therefrom used in papermaking.
However, it should be noted that the invention is
applicable to the fabrics used in other industrial
settings where wear detection and guiding are of
importance.
Fabric constructions include woven, spiral
wound, knitted, extruded mesh, spiral coil, and other
nonwoven fabrics. These fabrics may also include
monofilament, plied monofilament, multifilament or
plied multifilament yarns, and. may he a single-layer
weave, a multi-layer weave or laminated. When the
fabric ist a spiral coil fabric, the filament can be
the coils, the yarns used to connect the coils or the
inserts (stuffers) that may be present in the coil
interior void. The yarns are typically extruded from
any one of the synthetic polymeric resins, such as
polyatnide and polyester -resins, used for this purpose
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by those of ordinary skill in the industrial fabric
arts.
An example of the multilayer filament 10 of the
present invention is illustrated in Figure 1 (cross-
sectional view). The filament 10 can comprise, for
example, a core- yarn 12 surrounded by a plurality of
outside layers 14, 16, 18. Advantageously, the core
12, and the surrounding layers 14, 16, 18 are visibly
distinguishable from 'one another by, for example,
their contrasting color, or reflectivity. This
enables the wear of fabrics comprising such filaments
10 to be monitored as abrasion gradually wears away
successive layers 14, 16, 18 of the filaments 10,
eventually revealing the core yarns 12. An example
of the multilayered filament 10 exhibiting such wear
is shown in Figure 2 (cross-sectional view and plan
view).
In alternative embodiments (not shown) the core
12 and the layers 14, 16, 18 can also be doped with
dyes or other substances that will change their
appearance. The dye would then be detectable by a
sensor when excited with an external energy source,
for example, a light (e.g., laser, or UV) or ultra
sound.
In yet a further embodiment, the filaments 10
can also comprise a light absorbing/transmitting core
12 and several transparent layers 14, 16, 18 having
varying refractions n1, n2, n3. An example of this
multilayer optical filament 10 is shown in Figure 3.
in this case, the transmitted/reflected light from
the filament 10 changes color depending on the wear
level through the layers 14, 16, 18.
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Figure 4 is a plan view of an unused fabric 20
(wear side) comprising at least some of the
multilayered filaments 10, according to the teachings
of the present invention. Fabric 20 can be a
structure woven from yarns 10 lying in the cross-
machine direction (CD) and yarns 22 lying in the
machine direction (MD), although it need not be woven
to fall within the scope of the present invention,
and could be a nonwoven structure. in Figure 4, CD
yarns 10 which are multilayered filaments of the
variety shown in Figures 1, 2 and 3 are depicted as
weaving with MD yarns 22 in a plain weave. - In the
example shown, the knuckles 24 on the surf ace õ of the
fabric 20 are most susceptible to wear because they
are formed where a yarn in one direction of the
fabric 20 passes or crosses over one in the other
direction, and are therefore elevated points on the
surface of the fabric 20.
After the fabric 20 has been used for some
period of time, the same plan view of the fabric 20
will appear as shown in Figure 5. At least one or
more of the outer layers 16, 18 of the CD
multilayered filaments 10 are shown to be worn away
to the point where an inner la!y%er 1d or the core 12
is exposed to view. By virtue of its different color
or reflectivity, for example, compared to that of the
outer layers 16, 18, the inner layer 14 or core 12
gives an indication of the wear of the fabric 20.
Alternatively, the CD yarns 10 can be conductive
monofilaments woven into the wear side of fabric 20
to provide another means of wear detection. Thus, by
measuring the conductivity in the CD direction of the
fabric 20 over a period of use, a corresponding level
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of fabric wear is determined. That is, less cross
sectional area of the conductive monofilaments
corresponds to lower conductivity in the CD direction
of the fabric 20.
In another aspect of the invention, shown in
Figures 6 and 7, the multilayer filaments 10 are used
to create a visible guideline 30 on a fabric in the
CD and/or MD directions. This guideline 30 is used
for determining belt alignment, on-line speed
measurements, or as a trigger for an electronic
guiding system. Advantageously, the guideline 30 is
not removable by high-pressure showers or chemical
cleaning. Alternatively, a conductive monofilament
having a contrasting color can also be used to create
the guideline 30 on the fabric. In this case, the
color contrast and/o:r; the electrical properties of
the monofilaments can be used as the trigger for on-
line speed measurements or as the trigger for the
electronic guiding system. In all cases, the
filament used can be either round or non-round in
cross section. If the yarn is a multifilament, that
is, a yarn that has more than one filament, each
filament can be the inventive filament, or at least
one filament can have inventive (e.g.,
conductive) property. As for all aspects of the
invention recited, however, there should be
sufficient filaments in a multifilament yarn that
have the inventive property so as to achieve the
desired results.
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