Note: Descriptions are shown in the official language in which they were submitted.
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PROCEDURE TO BOND A LAYER OF PERMEABLE MATERIAL
TO A BASE FABRIC MA~E OF INTERLACED YARNS; AND FELTS
FOR PAPER MACHINES AND FILTER FABRICS MANUFACTURED ACCORDINGLY
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention refers to the production of a
dewatering felt through a process of bonding a layer of permeable
material on a base fabric of interlaced yarns.
Description of the Prior Art
In ~he manufacture of felts for paper machines, it is a
known procedure to bond a layer of permeable material, made up of
fibers interlaced such as through the needling process, on a base
fabric structure of woven yarns.
The p~ior art felt thus manufactured presents several
disadvantages. First, its permeability is decreased because
fibers have been inserted in the base fabric structure. In
addition, the layer of permeable material becomes compacted and
holds numerous little funnels caused by the needle penetration.
Therefore, the needles injure the base fabric which
decreases the life of the felt and adds to its deformation.
Furthermore, when the base fabric is equipped with
joining means lloops, spirals, etc., intended to be joined by a
pintle wire for forming an endless belt) prior to the needling
process, the needling damages the joining means. Additionally,
the presence of fibers, from the needling process, in the joining
means renders the insertion of the wire more difficult at the
time of the joining process.
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SUMMARY OF THE INVENTION
.
The procedure, according to the invention, eliminating
these disadvantages is characterized by the fact that at the time
the base fabric is manufactured, provisions have been made to
place on its face special yarns, the external part of. which is
made of thermoplastic having a fusion point lower than that of
the other yarns, said face can be heated up to cause fusion to
the external part of said special yarns, and then the layer is
applied on the face. According to a special development of the
invention, the special yarns are core yarns or coextruded yarns
which have a core portion and an e~ternal portion, the fusion
temperature of the external portion is lower than that of the
core portion.
Through the procedure, according to the invention, the
base fabric can be selected for certain characteristics, for
example, by using yarns resistant to chemical degradation; and
even if their resistance is rather low, ~t is not subjected to
being further decreased below an acceptable level by the needling
process. For other applications, highly-resistant bases can be
selected to avoid deformation when the felt rotates, or abrasion
at the time of contact with the rolls, without the fear of their
partial destruction through the needling process.
In the procedure, according to the invention, the
special yarns provide the bonding process, and the other yarns
provide the desired characteristics ~tenaciousness, resistance to
chemical degradation, watertightness, etc...~.
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In a preferred embodiment the present invention
is directed to an improved method for producing a
papermaker's dewatering felt having a permeable layer and
a woven papermaker's base fabric which are secured
together as a single papermaker's fabric, the improved
method characterized by: (a) providing in said woven base
fabric selected yarns having a fusion point less than the
fusion point of the remaining non-selected yarns of said
woven base fabric; (b) weaving said selected yarns into
said base fabric with the remaining non-selected yarns so
that the selected yarns predominate the weave on at least
on~ face of the woven base fabric; (c) providing a source
of permeable layer material; (d) providing a heat source
for elevating the temperature of said at least one face of
the selected yarns to at least their fusion point; (e)
providing press means positioned after said heat source
and pro~imate to said source of permeable layer material;
(f) passing said base fabric beyond said heat source to
elevate the temperature of the selected yarns to at least
their fusion temperature; and (g) presenting said heated
base fabric and said permeable layer material to said
press means with said permeable layer material adjacent
said at least one face, whereby said woven base fabric and
said permeable layer material are united and cooled as a
single fabric.
The present invention is particularly advantageous
in the manufacture of felts for the paper industry because
the permeable layer among other other, eliminates paper
marking under pressure and also carries the water
0 extracted from the sheet in process.
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It is also advantageou~ in the manufacture of filterfabrics where the permeable layer serves to filter a liquid or
gas and to retain impurities, especially when the base fabric,
which gives the mechanical characteristics, is equipped with
joining means.
It must be emphasized that the invention does not
require needling machines, which are relatively expensive.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described in greater
detail while referring to a preferred embodiment and the attached
drawings.
Figure 1 represents a base fabric and a permeable layer
used in the procedure, according to the invention.
Figure 2 is a section through the line II-II of Figure
1.
Figure 3 schematically represents a device for the
application of the procedure, according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
.
With reference to Figure 2, the woven base fabric 20
20comprises warp yarns 1', 2', 3', 4', 5', 6', 7', 8' and special
weft yarns 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12.
On the upper fabric face 21, of base fabric 20, the
weft yarns 1, 3, 4, 6, 7, 9, 10, 12 (i.e., two yarns over three)
are predominate, as seen on cut view II-II (Figure 2).
25By contrast, on lower fabric face 22, of base fabric
20, the other weft yarns 2, 5, 8, 11 (i.e., one yarn over three)
are placed under the warp yarns which predominate.
In the preferred embodiment, predominate weft yarns 1,
3, 4, 6, 7, 9, 10, 12 are special, bicomposition monofilaments.
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~ith reference to Figure 2, yarn 6, they include a core portion
24 preferably of polyester surrounded by a shield portion 25
made of polyamide. The other warp yarns 1l, 2', 3', 4', 5', 6',
7', 8' and weft yarns 2, 5, 8, 11 are made of polyester, which
will be known to those skilled in the art.
These bicomposition yarns, can be obtained through extru-
sion, through weaving, or even covering by spinning. Suitable
yarns are available through DuPont Company of Wilmington,
Delaware, and Shakespeare Monofilament Division, 6111
Shakespeare Road, Columbia, South Carolina 29240.
By way of example, the fusion temperature of the polyester
is 230C, and that of the polyamide 6 is 180C. Accordingly,
the polyamide may be heated to its fusion point, in order to
achieve an adhesive effect, without adverse effect upon the
polyester.
The base fabric 20 can be made by various techniques, for
example weaving, knitting, or spiral assembly, etc.
When the special yarns are bicomposition yarns, the core
portion may be made of a monofilament or several filaments, or
cut fiber filaments; the external portion around the core, which
can be a shield encapsulating the core or filament surrounding
the core, has a fusion point lower than that of the core portion
of the special yarns and of other non-special yarns making up
the base Eabric. The special yarns can also be made of a
single thermoplastic material having a fusion point lower than
that of the other non-special yarns.
It follows that after fusion of the external portion 25,
the special yarns via the core portion 24 maintain their
mechanical characteristics.
Since there are no limitations, which can be caused by the
needling process, the layer 26 of permeable material is selected
to meet the desired characteristics of the finished product.
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Layer 26 can be constituted of continguous or discontinued
fibers interlaced in themselves through needling, through
fusion, through impregnation with resin, etc. Layer 26 may
be generally referred to as a felt layer, which will be known
to those skilled in the art, both as to composition and
manufacture.
Layer 26 could also be made of an extruded fiber or film,
which is or has been made permeable or fluid passing, such as
a foam.
Base fabric 20 can be finished at each end with seaming
devices 23 (such as loops, spirals, etc.), which will be known
to those skilled in the art of seaming flat fabrics.
A device for assembling the base fabric 20 and layer 26 of
the invention is depicted in Figure 3, and comprises: heating
lS elements 30, for example, infrared; two rolls 31, 32 the first
of which has a fixed axle and where the second is applied like
the first; a heated cylinder 33; take-up rolls 34, 35; as well
as a tension roll or stretcher roll 36.
The permeable layer 26 is mounted or wrapped around
cylinder 37. The base fabric 20 is mounted about rolls 34, 35
and 36; it passes between rolls 31, 32 and around cylinder 33.
Preferably, roller cylinder 31 is driven in a first or counter-
clockwise direction and roller 32 rotates in a second or clock-
wise direction. Roller 31 and 32 are spaced so as to be
separated by less than the combined thickness of the base
fabric 20 and the permeable layer 26.
Face 21 with the special base yarns passes under the heating
elements 30, which heat it to a temperature causing the external
portion 25 of the special yarns to melt (for example, 200C~.
The permeable layer 26 is applied or pressed on to base fabric
20 through the nip of rolls 31 and 32 to face 21 with the yarns
softened in the melting process. At the exit of rolls 31,
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32, the layer adheres to base 21 via the previously described
shield portion 25, and the assembly, 26 and base fabric 20 is
passed around cylinder 33 (layer 26 passing against cylinder 33),
which is heated up at a lower temperature (for example, 120C) to
improve the quality of the surface or face of the resulting
fabric.
As will be appreciated by those skilled in the art,
precautions will have to be taken at the beginning and at the end
of the operation so that the ends of the permeable layer are not
out of alignment and to present the fabric in continuous
alignment.
Furthermore, it will be understood that by providing
the base fabric 20 with two faces 21, 22, of special yarns, it is
possible to apply a layer 26 on both sides. In application of a
second layer 26, the apparatus of Figure 3 may be used with
appropriate adjustment to roller 31 and 32 or an additional heat
source 30 may be provided along with a second source of layer 26.
~y adjustment of the apparatus of Figure 3, the second heat
source 30 may be positioned opposite the first and the second
source of layer 26 may be positioned within the loop of base
fabric 20 opposite the first said source.
