WO2004072368A1

WO2004072368A1 - Fabric belt

Info

Publication number: WO2004072368A1
Application number: PCT/AT2004/000009
Authority: WO
Inventors: Harald Reiterer; Raphael Gruber; Klaus Haiden
Original assignee: Huyck Austria Ges.M.B.H.
Priority date: 2003-02-12
Filing date: 2004-01-15
Publication date: 2004-08-26

Abstract

The invention relates to a fabric belt for dewatering machines, comprising a base woven fabric consisting of longitudinal (2, 3, 4) and transversal threads (1). Said base woven fabric contains elastic transversal and/or longitudinal threads, which are at least partly produced from an elastic material.

Description

GEWEBEBAND

The invention relates to a fabric tape for drainage machines, consisting of a base fabric made of longitudinal and transverse threads.

Such fabric belts are used, for example, as sieve belts, as are described in the applicant's EP 0 864 775 A1. In particular, these fabric tapes are used in drainage technology, in particular for pulp dewatering machines or very generally for sludge dewatering. Although water is dewatered in most cases, the term "dewatering" should not be interpreted restrictively, since other liquids can also be the subject of "dewatering".

Fabric belts in the form of such sieve belts and dewatering or press felts are mainly used in continuously running pulp drainage systems and paper machines. The main task of these felts is to absorb water that escapes from the pulp or paper web during a pressing process.

This pressing process takes place in a gap, the so-called (press) nip, which is created by pressing two or more pairs of rollers together or a roller and a press shoe. These systems can be single or double felted, i.e. H. the pulp or paper web either runs between two felts (top and bottom felt) or between a felt and a roller in the press nip and is compressed and pressed out there. The pressed water is absorbed by the felts and later released on a suction device.

Good dewatering cannot be achieved simply by increasing the contact pressure, since too high a pressure on the structure of the fabric has a detrimental effect due to the resulting compression and the service life is reduced accordingly. Furthermore, a rewetting effect occurs in that after leaving the nip, the compressed cellulose web partially opens again - comparable to a sponge - and thereby absorbs water from the felt.

An object of the invention is to provide a fabric tape with which effective dewatering while reducing the rewetting effect is possible. This object is achieved with a fabric tape mentioned at the outset in that, according to the invention, it contains highly elastic transverse and / or longitudinal threads which are at least partially formed from an elastic material.

The amount of water squeezed out and absorbed by the felt is, in addition to many other influences, very much influenced by the felt itself, its structure and construction, and represents a decisive criterion for the efficiency of the pulp or paper drainage system. By using highly elastic components in the base fabric of the Felts result in an elastic-dynamic behavior of the felt construction during the pressing and relief process, which has a positive influence on the dewatering of the cellulose or paper web. Among other things, the elastic components result in a stronger compacting of the felt in the press ip, an increase in the contact area in the press nip (wider nip) and an increase in the drainage speed due to the lower internal volume and reduction of the open pores in the base fabric during the press phase. In the relief phase, the recovery of the elastic components creates a vacuum on the product side, which causes an additional suction effect of the felts and thus an improvement in the drainage performance when leaving the press nip.

Furthermore, these elastic components in the felt cause pressure and vibration damping properties which have a positive influence on the running behavior of the felt, especially at high line speeds.

Highly elastic properties, which allow the elastic components to return to their original shape immediately after relief and thus reinforce the desired effect, are achieved if the elastic material is a thermoplastic elastomer.

These elastic properties are particularly good if the elastic threads consist entirely of the elastic material.

The elastic threads can also consist of a mixture of the elastic material with non-elastic materials, whereby the strength of the fabric can be increased and the elastic threads themselves also become absorbent.

The fabric tape can be produced easily if the longitudinal and / or transverse threads are monofilaments and / or monofilament threads. Easy processing in terms of weaving technology is ensured if the elastic threads have a round cross section.

The diameter of the elastic threads is typically between 0.2 m and 0.9 mm.

However, other cross sections and dimensions are also possible.

In order to offer good mechanical properties of the fabric tape, the non-elastic threads are made of polyamide.

In a specific embodiment of the fabric tape, which has good elastic properties and additionally has a sufficiently high strength, at least one layer of longitudinal threads is formed in the fabric from elastic threads.

The elasticity can be increased if two layers of elastic cross threads are separated by a layer of non-elastic cross threads.

In order to further reduce the rewetting effect that occurs after leaving the nip, since the compressed cellulose web partially opens again - comparable to a sponge - and thereby absorbs water from the sieve again, the fabric band is needled with hydrophilic fibers and points in the area of its product side Surface at least a hydrophobic fine fiber layer.

Because of the hydrophobic fine fiber layer, the water from the cell web is pressed through the hydrophobic fiber layer into the fabric band at the comparatively high pressures in the press nip, where it is absorbed. After leaving the press nip, the water then "flows back" out of the felt prevented by the water-repellent fiber layer or at least reduced, since the pressures in the felt are not high enough to push the water through the fine fiber layer again in large quantities.

A firm, mechanically stable connection results when the hydrophobic fine fiber layer is needled to the base fabric / hydrophilic fibers.

Particularly good water-repellent properties and thus a strong reduction in rewetting is achieved if the hydrophobic fibers are made of polypropylene. It is particularly advantageous if the fine fiber layer is a fiber fabric. A non-woven fabric is required for an even fiber layer in the felt and results in a homogeneous felt structure. In contrast to foils or the like, an anti-rewetting barrier made of non-woven fabric basically does not represent a foreign body in the felt and can be produced using existing needle technology.

Usually, all the fibers in a felt are laid on the base fabric as a non-woven fabric and then needled, i.e. H. mechanically anchored.

Furthermore, it is advantageous if the hydrophobic fine fiber layer is arranged directly on the surface or immediately below one or a few product-side layers of hydrophilic fibers. This ensures that the fine fiber layer is as close as possible to the cellulose web. In addition, a lot of free felt volume is available for water storage under the fine fiber layer, and such a cover with a polyamide fiber layer also protects the fine fiber layer from mechanical wear.

Very good water-absorbing properties of the felt are achieved if the hydrophilic fibers consist of polyamide.

The invention is explained in more detail below with reference to the drawing. In this show

1 shows a fabric tape according to the invention with the cellulose web placed thereon in the unloaded state,

2 shows the fabric tape according to the invention with the cellulose web from FIG. 1 placed thereon in the loaded state,

3 shows the fabric tape according to the invention with the cellulose web according to FIG. 1 placed on it in a relaxed state,

4 shows another fabric tape according to the invention with the cellulose web placed thereon in the unloaded state,

5 shows the fabric tape according to the invention with the cellulose web from FIG. 5 placed on it in the loaded state, 6 shows the fabric tape according to the invention with the cellulose web placed thereon according to FIG. 4 in a relaxed state,

7 an inventive fabric tape with an additional water-repellent fine fiber layer in the unloaded state,

8 shows the fabric tape according to the invention with the cellulose web from FIG. 7 placed thereon in the loaded state,

9 shows the fabric tape according to the invention with the cellulose web from FIG. 7 in a relaxing state, and

FIG. 10 shows the fabric tape according to the invention with the cellulose web placed thereon according to FIG. 7 in the unloaded state.

Fig. 1 shows a cross section of a felt (needled fabric tape) according to the invention, which can be used in dewatering machines. Usually an upper, endless and a lower, endless felt circulate in a dewatering machine, with a layer of the mass to be dewatered (cellulose) being located between the upper and lower felt. This three-layer structure, namely upper sieve belt - pulp - lower sieve belt, runs on the dewatering machine in the viewing direction, i.e. H. towards normal in the drawing, through the gap of one or more pairs of rollers.

The sieve belt consists of a basic fabric, which like every fabric has weft and warp threads. The screen belt 100 shown consists of a fabric belt 101, which is composed of a base fabric, which is formed from transverse threads 1 and as weft threads from longitudinal threads 2, 3, 4. This base fabric is needled with fine fibers 102, which are preferably made of polyamide or a similar water-absorbing material. Furthermore, such fine fibers are still connected to this base fabric 101 on the side facing the product 200 to be dewatered in the form of a non-woven fabric 103.

The transverse threads 1 consist of polyamide monofilaments or polyamide threads, whereby mixtures of monofilaments and threads can also form the base fabric. According to Figure 1, longitudinal threads 2, 4 are now also formed from such polyamide threads, as shown from a 6-ply thread. Of course, monofilaments or other threads can also be used here. According to the invention, the base fabric, as can be seen in the drawing, now contains threads 3 which are at least partially formed from an elastic material. It is particularly advantageous if this elastic material is a thermoplastic elastomer which has highly elastic properties and is therefore particularly suitable for the invention.

Of particular importance in the context of the invention is that the elastic threads 3 in the transverse direction, ie. H. normal to their longitudinal axis, are elastic. In particular, it is advantageous if the threads are only elastic in the transverse direction, since the threads then have high stability in the longitudinal direction.

The modulus of elasticity E of the highly elastic threads used is in a range E <1000 N / mm ² , typical values are in a range of E = 250 N / mm ² - 470 N / mm ² . In contrast to this, the value for non-highly elastic polyamides used in felts is also given, this is approximately E = 1800 N / mm ² - 3200 N / mm ² .

According to FIG. 1, the middle layer of longitudinal threads 3 in the 3-layer base fabric consists of such elastic threads. According to the drawing, these are elastic monofilaments, for example made of a thermoplastic elastomer. In principle, however, as an alternative or in addition to the elastic monofilaments, threads can also be used that either contain elastic components (for example a 6-fold thread made of 2 elastomer and 4 polyamide threads), or are made entirely of elastomer (for example a 4-fold Thread made of 4 elastomer threads).

According to FIG. 1, the entire middle layer consists of such elastic threads 3. In principle, however, it is also conceivable that only every second thread is elastic, while the other threads of the layer are not elastic. It can also be provided that, for example, only the uppermost, product-side layer of longitudinal threads is formed from elastic threads.

In principle, the arrangement of the elastic threads, ie which of the threads is elastic, can be selected relatively freely depending on the field of application, the contact pressures used, etc. It is also conceivable that the entire base fabric is formed from such elastic threads. It can also be provided that only transverse threads or also longitudinal and transverse threads are formed from elastic threads. As a rule, however, sieve belts with a relatively high tensile force are applied in the dewatering machines. In order to be able to absorb these tensile forces without excessive deformation of the bath, an arrangement as in the drawing, in which non-elastic threads are also provided in the fabric, is advantageous, since these non-elastic threads can absorb the tensile forces and so on there is no undesired deformation of the fabric tape in the direction of the tensile forces.

It should also be noted that the non-elastic transverse and longitudinal threads 1, 2, 4 of the screen belt are made of polyamide, for example, as already mentioned, but also polyester or mixtures of these materials, and can be monofilaments or threads.

Due to the elastic components, i.e. H. the elastic threads in the fabric are achieved so that during the pressing process, as is shown schematically in FIG. 2, the felt is more compacted, i. H. the felt is compressed more, and there is an increase (broadening) of the contact area of the felt with the cellulose web. Furthermore, the open areas or pores of the base fabric 101 are reduced in size, which leads to a reduction in the inner volume of the felt 201 fabric. These effects mean that the drainage rate is increased, which means that the cell web is better drained.

If the sieve belt with the cellulose web leaves the press nip, re-moistening usually occurs by the cellulose web, which has much better water absorption properties than the felt, sucking in again from this water. With the felt according to the invention, this effect can be weakened, since - as is clearly shown in FIG. 3 - the use of highly elastic threads in the base fabric immediately takes on its original shape again after relieving the pressure of the felt, before it was inserted into the press nip the original shape as it were "bounces".

This creates a kind of "vacuum" in the felt, which - since the underside of the sieve belt is initially covered by the press roller - is filled by sucking in water from the cellulose web, which can reduce the rewetting effect.

It should also be mentioned that the elastic components in the felt give it pressure and vibration damping properties, which gives the felt better running behavior, especially at high running speeds of the drainage system. In the specific embodiment, the elastic threads have a round cross section, the diameter is generally between 0.2 mm and 0.9 mm.

In principle, however, other cross sections and dimensions are also possible.

In the case of monofilaments, the non-elastic threads have diameters of, for example, 0.5 or 1.5 mm; in the case of a twisted thread, the dimensions are also in this range, the individual monofilaments of the threads typically having a diameter of 0.1 to 0 , 4 mm. Basically, however, cross sections other than circular are also possible, although the circular shape enables simple processing in terms of weaving technology.

FIGS. 4-6 show a further embodiment, as already briefly mentioned above, in which the uppermost, product-side layer of longitudinal threads consists of elastic threads 3 ', while the layers below contain threads 2', 4 'made of a non-elastic material ,

An advantage of this embodiment consists in a possible intensification of the “suction effect”, since the relaxation of the elastic monofilaments and thus the vacuum that occurs are closer to the cellulose web.

Finally, FIGS. 7-10 also show a fabric tape similar to that from FIG. 1, the fabric tape additionally having at least one hydrophobic fine fiber layer 104 in the area of its surface on the product side, this preferably extending over the extent of the total surface extension.

When compressed in the press nip, as shown in FIG. 8, water from the cell web 200 is pressed through the hydrophobic fiber layer 104 into the fabric band 101, where it is absorbed. After leaving the press nip (FIG. 10), a "backflow" of the water out of the felt through the water-repellent fiber layer is prevented or at least reduced. In addition, of course, there are also the advantages of the highly elastic threads 3 'of the base fabric, as already described above to carry, for example, as indicated in Figure 9, water is still sucked out of the relaxing cellulose web.

A firm, mechanically stable connection results when the hydrophobic fine fiber layer is needled to the base fabric / hydrophilic fibers. Particularly good water-repellent properties and thus a strong reduction in rewetting is achieved if the hydrophobic fibers are made of polypropylene or other polyolefin fibers.

It is particularly advantageous if the fine fiber layer is a non-woven fabric. A non-woven fabric is required for an even fiber layer in the felt and results in a homogeneous felt structure. In contrast to foils or the like, an anti-rewetting barrier made of non-woven fabric basically does not represent a foreign body in the felt and can be produced using existing needle technology.

Furthermore, it is advantageous if the hydrophobic fine fiber layer is arranged directly on the product-side surface or immediately below one or a few product-side layers of hydrophilic fibers. This ensures that the fine fiber layer is as close as possible to the cellulose web. In addition, a lot of free felt volume is available for water storage under the fine fiber layer, and such a cover with a polyamide fiber layer also protects the fine fiber layer from mechanical wear.

Claims

1. Fabric tape for drainage machines, consisting of a base fabric made of longitudinal and transverse threads, characterized in that it contains elastic transverse and / or longitudinal threads, which are at least partially formed from an elastic material.

2. Fabric tape according to claim 1, characterized in that the elastic material is a thermoplastic elastomer.

3. Fabric tape according to claim 1 or 2, characterized in that the elastic threads consist entirely of the elastic material.

4. Fabric tape according to claim 1 or 2, characterized in that the elastic threads are made of a mixture of the elastic material with non-elastic materials.

5. Fabric tape according to one of claims 1 to 4, characterized in that the longitudinal and / or transverse threads are monofilament and / or monofilament threads.

6. Fabric tape according to one of claims 1 to 5, characterized in that the elastic threads have a round cross-section.

7. Fabric tape according to claim 6, characterized in that the diameter of the elastic threads is between 0.2mm and 0.9mm.

8. Fabric tape according to one of claims 1 to 7, characterized in that the non-elastic threads are formed from polyamide.

9. Fabric tape according to one of claims 1 to 8, characterized in that at least one layer of longitudinal threads in the tissue is formed from elastic threads.

10. Fabric tape according to claim 9, characterized in that two layers of non-elastic longitudinal threads are separated by a layer of elastic longitudinal threads.

11. Fabric tape according to one of claims 1 to 10, characterized in that it is needled with hydrophilic fibers and has at least one hydrophobic fine fiber layer in the area of its product-side surface.

12. Fabric tape according to claim 11, characterized in that the hydrophobic fine fiber layer is needled to the base fabric / the hydrophilic fibers.

13. Fabric tape according to claim 11 or 12, characterized in that the hydrophobic fibers are formed from polypropylene.

14. Fabric tape according to one of claims 11 to 13, characterized in that the fine fiber layer is a non-woven fabric.

15. Fabric tape according to one of claims 11 to 14, characterized in that the hydrophobic fine fiber layer is arranged directly on the surface or immediately below one or a few product-side layers of hydrophilic fibers.

16. Fabric tape according to one of claims 11 to 15, characterized in that the hydrophilic fibers consist of polyamide.