US20070000633A1

US20070000633A1 - Papermachine fabric

Info

Publication number: US20070000633A1
Application number: US11/475,503
Authority: US
Inventors: Arved Westerkamp; Hubert Walkenhaus
Original assignee: Voith Paper Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2005-07-01
Filing date: 2006-06-27
Publication date: 2007-01-04
Also published as: EP1739227A1; DE102005030773A1

Abstract

A papermachine fabric for dewatering a fibrous web in a machine producing a fibrous web. The fabric including a laid scrim having at least one layer of longitudinal threads and at least one layer of transverse threads crossing the layer of longitudinal threads. At least a selection of the longitudinal threads being laid at different distances both symmetrically and asymmetrically in relation to one another, the distance between two adjacent threads changing in the course of a laying pattern.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to a papermachine fabric for dewatering a fibrous web in a machine producing a fibrous web, having a laid scrim.
2. Description of the Related Art
A papermachine fabric is known, for example, from European patent application EP 1 357 223 A1, having longitudinal threads running parallel to one another and transverse threads running parallel to one another. The threads are adhesively bonded to one another at crossing points using an adhesive. The adhesive can be, for example, a hot-melt adhesive, a diffusion adhesive, a contact adhesive and/or a reactive adhesive. The use of the adhesive opens up the possibility of effecting a direct connection between the longitudinal and transverse threads at the crossing points.
Apart from the not inconsiderable production costs of the papermachine fabric because of the use of an adhesive together with its properties and peculiarities, the load distribution of the papermachine fabric, which is predefined by the production and not optimal for every application on account of the mutually parallel alignment of the threads, is disadvantageous.

SUMMARY OF THE INVENTION

The present invention is based on the object of developing a papermachine fabric of the type mentioned at the beginning in such a way that, in addition to an optimal load distribution, a beneficial pore size for each application is also ensured.
According to the present invention, this object is achieved in that at least a selection of threads of a layer are laid at different distances both symmetrically and asymmetrically in relation to one another, the distance between two adjacent threads is preferably changed in the course of their laying pattern. The change in the respective distance is carried out continuously, abruptly, periodically, in some regions and the like. In addition, the preferable change in the distance between two adjacent threads in the course of their laying pattern preferably assumes a value ≧1%, preferably ≧3%, in particular ≧5%, based on the length of a respective thread.
This individual laying of at least a selection of threads of a layer provides for the first time a papermachine fabric having a laid scrim which, in addition to the advantage of an optimal load distribution, also provides the advantage of determinable and beneficial pore sizes as a result of the resulting “meshes” in the vertical arrangement of different layers.
The term “thread” is used here as broadly as possible. The thread can, for example, have been produced by way of an additive and also reductive fabrication method. Furthermore, its material can include a Polyethylene Terephthalate (PET), Polyamide (PA) in all modifications, Polypeptide (PP), Polyphenylene Sulfide (PPS), Polyetherketone (PEK), Polyetherketoneketone (PEKK), elastic Polyethylene (PE), Polybutylene Terephtalate (PBT), Poly Trimethylene or Poly Terephthalate (PTT) or combinations thereof. It can also be reinforced, for example fiber-reinforced with glass fibers, carbon fibers and/or ceramic fibers. In addition, it can also be a multi-component thread, such as a sheath-core thread, a side-by-side thread and the like. Its properties, in particular tensile strength, stretch and the like, are in general not subject to any restrictions.
In an advantageous refinement of the present invention, a selection of threads of the two layers are laid at different distances both symmetrically and asymmetrically in relation to one another. This permits, amongst other things, improved load distributions with individual pore sizes of the laid scrim.
For example, the threads of a layer can be laid symmetrically or asymmetrically in relation to one another in a plurality of groups, and the groups of threads of a layer can in turn be laid symmetrically or asymmetrically in relation to one another.
In order that the marking, of the fibrous material to be dewatered by the fabric, is kept as diffuse as possible, in particular also over a plurality of layers, the different distances are selected in accordance with a pattern, randomly or in combination.
In another embodiment of the present invention, at least two adjacent layers of threads with the same or approximately the same alignment, at least in some regions, which have a complementary position of threads in relation to one another is provided. In this case, interspaces can be provided between the threads of a layer, at least in some regions, which are filled with a permeable material. The permeable material is preferably at least one polyurethane foam. Such an arrangement has the substantial advantage that the complementary layers are able to distribute optimally the pressure pulses acting in a press of a paper or board machine and, at the same time, always have adequate permeability. The filling polyurethane foam is generally applied only when the scrim is arranged on a two-dimensional carrier medium, such as a nonwoven carrier medium. This is necessary since the foam would otherwise flow through the holes present in the scrim and thus not result in a homogeneous surface. The pores depend, inter alia, on the viscosity of the polyurethane foam and the existing pore size.
In order to be able to influence this permeability further, a layer that is preferably permeable over its entire area is introduced, at least between the two adjacent layers of threads, at least in some regions. Furthermore, the threads arranged above one another of two adjacent layers can have at least one different property, at least in some regions. They can therefore complement one another in their function. The threads of one layer have the at least one different property alternately and offset with respect to the threads of the adjacent layer. Therefore, overall, a constant feature is obtained with, at the same time, optimized permeability and/or pressure behavior.
The different property is preferably at least the thread thickness, the thread hardness, the thread structure, the thread material or the like. Of course, further characteristics of the thread can also form the different property. The thread can also be a nonwoven strip or a material ribbon, it being conceivable for these to perform other functions as well, such as the production of internal volume or rebound capacity, in addition to the load-absorbing function.
Furthermore, the common factor in all the configurations described is that two adjacent layers of threads can run at an angle α, at least in some regions. The angle α can assume a value in the range from 0°≦α≦90°. The threads can therefore, run in a longitudinal, transverse and/or diagonally oriented alignment in relation to one another. Of course, the threads of an individual layer can also run at the aforementioned angle α in relation to one another.
In addition, the papermachine fabric can have at least two, preferably a plurality of, layers of laid scrims according to the invention, it preferably being possible for at least two, preferably all, of the layers of laid scrims to be separated from one another by a separating layer in each case. However, in the final stage of the production of the fabric, the separating layers must enter into an intimate connection with the laid scrims.
In one embodiment of the present invention, the papermachine fabric is a press felt for dewatering a fibrous web in a machine producing a fibrous web, having a laid scrim including at least one layer of longitudinal threads and at least one layer of transverse threads crossing the longitudinal threads. The fabric has at least one fine fiber batt on the side of the fibrous web, at least one coarse fiber batt on the carrier side and a central layer having a described laid scrim between the two fiber batts. In this case, the fine fiber batt preferably has a fiber weight ≦5 dtex, whereas the coarse fiber batt preferably has a fiber weight ≧50 dtex. The fiber batt can also consist of a mixture of different fibers, in this case the fibers having the greatest proportion by weight preferably defining the criterion “fine” versus “coarse”.
The threads of the central layer can be filled with a permeable material, in particular polyurethane foam, in their two lateral regions. As already mentioned, the filling polyurethane foam is normally applied only when the scrim is arranged on a two-dimensional carrier medium, such as a nonwoven carrier medium.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
FIG. 1 shows a schematic cross-sectional illustration of an embodiment of a papermachine fabric according to the present invention;
FIGS. 2 and 3 show two partial schematic cross-sectional illustrations of further embodiments of the papermachine fabric according to the present invention; and
FIG. 4 shows a view of exemplary courses of adjacent threads of a layer of the fabrics in FIGS. 1-3.
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1 there is shown a schematic sectional illustration of an embodiment of a papermachine fabric according to the present invention. Papermachine fabric 1 is used for dewatering a fibrous web, not illustrated, in a machine producing a fibrous web. Fabric 1 includes a laid scrim 2, a layer A of longitudinal threads 3.1 to 3.6 and a layer B of transverse threads 4 crossing longitudinal threads 3.1 to 3.6, only one transverse thread 4 being visible.
At least a selection of threads 3.1 to 3.6 of layer A at different distances A₁to A₅are laid both symmetrically and asymmetrically with respect to one another, the distance B₁to B₃between two adjacent threads 3.1, 3.2; 3.3, 3.4; 3.5, 3.6 preferably changing in the course of their laying pattern. The change in the respective distance B₁to B₃can be made continuously, abruptly and/or periodically, in some regions.
Threads 3.1 to 3.6 of layer A are laid symmetrically or asymmetrically in relation to one another in a plurality of groups G₁to G₃. Groups G₁to G₃of threads 3.1 to 3.6 of layer A in turn are laid symmetrically or asymmetrically in relation to one another. In the embodiment of the present invention, illustrated in FIG. 1, the different distances A₁to A₅are selected in accordance with a pattern, but can also be selected randomly or in combination. Longitudinal threads 3.1 to 3.6 of layer A and transverse threads 4 of layer B run at an angle α, at least in some regions, angle α assuming a value in the range from 0°≦α≦90°.
Now, additionally referring to FIG. 2 there is shown a partial and schematic sectional illustration of another embodiment of papermachine fabric 1 according to the present invention. Two adjacent layers C and D of threads 5.1 to 5.6 and 6.1 to 6.6 form a laid scrim 2 having the same or approximately the same alignment, at least in some regions. Layers C and D have at least one different property, at least in some regions, such as a complementary pairwise positioning of threads 5.1, 6.1, 5.2, 6.2, 5.3, 6.3, 5.4, 6.4, 5.5, 6.5, 5.6 and 6.6 in relation to one another. Although for purposes of clarity the different property in the embodiment illustrated is the thread thickness, the different property can also be the thread hardness, the thread structure, the thread material or the like.
Between threads 5.1 to 5.6 and 6.1 to 6.6 of a layer C or D, interspaces 7.1 to 7.5 and 8.1 to 8.5 are provided, at least in some regions, which are filled with a permeable material 9. The permeable material 9 may include at least one polyurethane foam 10.
Between two adjacent layers C and D of threads 5.1 to 5.6 and 6.1 to 6.6, at least in some regions, a layer 11 that is preferably permeable over its entire area is introduced. The two adjacent layers C and D of threads 5.1 to 5.6 and 6.1 to 6.6 run at an angle α, at least in some regions. Angle α assumes a value in the range from 0°≦α≦90°. In the present case, as already mentioned, angle α assumes a value in the region of 0°, that is to say the same or approximately the same alignment.
Now, additionally referring to FIG. 3 there is shown a partial and schematic cross-sectional illustration of yet another embodiment of papermachine fabric 1 according to the present invention. Here again, two adjacent layers E and F of threads 12.1 to 12.5 and 13.1 to 13.5 form a laid scrim 2 and have the same or approximately the same alignment, at least in some regions. Layers E and F having at least one different property, at least in some regions, which have a complementary pairwise positioning of threads 12.1, 13.1, 12.2, 13.2, 12.3, 13.3, 12.4, 13.4, 12.5 and 13.5 in relation to one another. In this case, threads 12.1 to 12.5 of layer E have the at least one different property alternately and offset with respect to threads 13.1 to 13.5 of adjacent layer F. The different property in the embodiment illustrated is the thread thickness. In a further embodiment, (not illustrated) it can also be the thread hardness, the thread structure, the thread material or the like.
For example, thread 12.1 of layer E has a small thread thickness, adjacent thread 13.1 of layer F, by contrast, has a large thread thickness. Adjacent thread 12.2 and 13.2 of respective layers E and F in turn has a contrary thread thickness. These geometries are repeated, so that ultimately a uniform thickness of laid scrim 2 is provided. The same thread thicknesses can of course also extend over a plurality of threads of the same layer and/or with a pattern in the same layer.
The two adjacent layers E and F of threads 12.1 to 12.5 and 13.1 to 13.5 run at an angle α, at least in some regions. Angle α having a value in the range from 0°≦α≦90°. In the present case, as already mentioned, angle α assumes a value in the region of 0°, that is to say the same or approximately the same alignment.
Laid scrim 2, illustrated in FIGS. 1-3 can, for example, be part of a central layer 15 of a press felt 14, which has a fine fiber batt 16 on the fibrous web side and a coarse fiber batt 17 on the carrier side. This structure of press felt 14 is illustrated in FIG. 2. Central layer 15 is arranged between two fiber batts 16 and 17, which can have still further layers of threads. In addition, illustrated threads 5.1 to 5.6 and 6.1 to 6.6 of central layer 15 can be filled with a permeable material 18, in particular polyurethane foam, in lateral regions H and I. Layer 11, which is preferably permeable over its entire area, does not necessarily have to be present in this embodiment.
Now, additionally referring to FIG. 4 there is shown a view of exemplary courses of adjacent threads 3.1 to 3.11 of a layer. In this case, threads 3.1 to 3.11 can be ordered in the longitudinal direction and in the transverse direction and also in combination. It can be seen that the respective distance B₁to B₆between two adjacent threads 3.1 to 3.11 changes in the course of their laying pattern. The change in the respective distance B₁to B₆can take place continuously (threads 3.1, 3.2), abruptly (threads 3.3, 3.4), periodically, in some regions (threads 3.5, 3.6), varying continually (threads 3.7, 3.8; 3.10, 3.11), pseudo-parallel (threads 3.9, 3.10) and the like. The courses illustrated are, as already mentioned, purely exemplary. Of course, it is possible for there to be both further courses, not illustrated, and also combinations of courses.
In summary, it is to be recorded that, by means of the invention, a papermachine fabric of the type mentioned at the beginning is developed in such a way that, in addition to an optimal load distribution, a beneficial pore size for every application is also ensured.
While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

LIST OF DESIGNATIONS

1 Papermachine fabric
2 Laid scrim
3.1 to 3.6 Longitudinal thread
4 Transverse thread
5.1 to 5.6 Thread
6.1 to 6.6 Thread
7.1 to 7.5 Interspace
8.1 to 8.5 Interspace
9 Material
10 Polyurethane foam
11 Layer
12.1 to 12.5 Thread
13.1 to 13.5 Thread
14 Press felt
15 Central layer
16 Fiber batt
17 Fiber batt
18 Material
A Layer
A₁to A₅Distance
B Layer
B₁to B₃Layer
C Layer
D Layer
E Layer
F Layer
G₁to G₃Group
H Lateral region
I Lateral region
α Angle

Claims

1. A papermachine fabric for dewatering a fibrous web in a machine producing a fibrous web, the fabric comprising:

a laid scrim including:

at least one layer of longitudinal threads; and

at least one layer of transverse threads crossing said layer of longitudinal threads, at least a selection of said longitudinal threads being laid at different distances both symmetrically and asymmetrically in relation to one another, the distance between two adjacent threads changing in the course of a laying pattern.

2. The papermachine fabric of claim 1, wherein a selection of threads of said layer of longitudinal threads and said layer of transverse threads are laid at different distances both symmetrically and asymmetrically in relation to one another.

3. The papermachine fabric of claim 1, wherein said longitudinal threads are laid symmetrically or asymmetrically in relation to one another in a plurality of groups.

4. The papermachine fabric of claim 3, wherein said groups of said longitudinal threads are laid symmetrically or asymmetrically in relation to one another.

5. The papermachine fabric of claim 4, wherein said different distances are selected in accordance with at least one of a pattern, randomly and a combination thereof.

6. The papermachine fabric of claim 1, wherein at least two adjacent layers of said at least one layer of longitudinal threads and said at least one layer of transverse threads having approximately the same alignment, in at least some regions have a complementary positioning of threads in relation to one another.

7. The papermachine fabric of claim 6, wherein interspaces are provided between threads of said at least two adjacent layers in at least some regions, said interspaces being filled with a permeable material.

8. The papermachine fabric of claim 7, wherein said permeable material includes at least one polyurethane foam.

9. The papermachine fabric of claim 6, wherein a layer that is permeable is introduced between said at least two adjacent layers of threads at least in some regions.

10. The papermachine fabric of claim 9, wherein threads arranged above one another of said two adjacent layers have at least one different property in at least some regions.

11. The papermachine fabric of claim 10, wherein threads of one of said two adjacent layers have the at least one different property alternately and offset with respect to the threads of another of said two adjacent layers.

12. The papermachine fabric of claim 10, wherein said different property is at least one of thread thickness, thread hardness, thread structure and thread material.

13. The papermachine fabric of claim 10, wherein said at least two adjacent layers of threads run at an angle α in at least some regions, said angle α assuming a value in the range of 0°≦α≦90°.

14. The papermachine fabric of claim 1, further comprising a plurality of layers of laid scrims.

15. The papermachine fabric of claim 14, wherein at least two of said plurality of layers of laid scrims are separated from one another by a separating layer.

16. A press felt for dewatering a fibrous web in a machine producing a fibrous web, the fabric comprising:

at least one fine fiber batt on the side of the fabric facing the fibrous web;

at least one coarse fiber batt on the side of the fabric facing away from the fibrous web; and

a central layer having a laid scrim between said fine fiber batt and said coarse fiber batt, said laid scrim including:

at least one layer of longitudinal threads; and

at least one layer of transverse threads crossing said layer of longitudinal threads.

17. The fabric of claim 16, wherein said longitudinal threads and said transverse threads of said central layer are filled with a permeable material.

18. The fabric of claim 17, wherein said permeable material is polyurethane foam in two lateral regions of the fabric.