EP0396036A1 - Belt for paper making machines - Google Patents

Abstract

A belt for use in paper machines, in particular in wet presses with an extended press nip, has a flexible, liquid-impermeable belt layer which is smooth on the back and in the front of which there is only partially embedded a carrier web. So that the bond between the band layer and the carrier web is not endangered under pressure and flexing stress, at least one additional thread (12) is inserted into the band layer (2), which extends progressively in a zigzag shape over the running direction of the band (1) and in which thread sections (13) which run outside the carrier web (5) alternate with thread sections (14) which pass through the carrier web (5).

Description

The invention relates to a belt for use in paper machines, in particular in wet presses with an extended press nip, which has a flexible, liquid-impermeable belt layer which is smooth on the back and in the front of which there is a carrier web which has cavities, for example a fabric, knitted fabric or a wire link belt is partially embedded.

In wet presses of paper machines, a substantial part of the liquid still in the paper web is pressed out between pressure rollers which form a press nip. The paper web is guided through the press nip by means of a rotating wet felt, the liquid in the press nip being pressed out of the paper web into the wet felt and removed.

More recently, wet presses with an extended press nip, so-called "shoe presses", have been developed in which the paper web is exposed to high press pressure over a longer distance and thus for a correspondingly longer time, so that it runs out of the wet press with a higher dry content. For guiding the paper web and at least one wet felt through such an extended press nip, special tapes are used, one have flexible, liquid-impermeable band layer, which is smooth on the back. With this smooth back, they run over a press shoe that is hydraulically loaded and presses the belt in the direction of an opposite pressure roller. The paper web to be dewatered is passed between this pressure roller and the belt, the paper web being accompanied on at least one side by a running wet felt which removes the squeezed out water.

Such belts are subjected to high stresses in the longitudinal and transverse directions in the press nip and are subject to considerable wear on both sides. To solve the first problem, it has been proposed to completely let a fabric as a carrier web into the strip layer (cf. DE-OS 32 31 039, DE-OS 33 18 984; US Pat. No. 4,559,258). However, these embodiments of tapes have not proven successful.

In order to improve the water drainage on the front of the tapes, that is to say the side that faces the paper web and is in contact with one with a surrounding wet felt, the front was structured. For this purpose, tapes were developed, on the front of which carrier webs were only partially embedded, that is to say partially protruding from the tape layer. In this way, cavities and channels for water drainage were created. Multi-layer fabrics (DE-PS 32 35 468, EP-PS 0 098 502; EP-US 0 138 797; DE-GM 83 19 684.6; EP-OS 0 185 108) have been proposed as carrier webs. Instead of fabric as a carrier web, wire link belts (EP-PS 0 098 502) or warp-knitted fabrics (EP OS 0 290 653) were also possible. In the embodiment with a wire link belt as the carrier web, it was proposed that the wire coils coupled together in the longitudinal direction Let run and in this wire coils additionally insert multi and / or monofilaments to absorb the longitudinal forces (EP-PS 0 098 502). They should expediently be embedded in the strip layer in order to improve the stability of the strip and also the retention of the wire coils in the strip layer.

Insofar as the tapes had partially embedded fabrics as carrier webs, it has additionally been proposed to design the outwardly projecting parts of the fabric as a wear layer and the part of the fabric embedded within the tape layer as a tensile base layer (DE-GM 83 19 684.6). Furthermore, it is part of the prior art for such tapes to produce part of the longitudinal threads of the fabric forming the carrier web from very longitudinally stable material and the other part of the longitudinal threads and also of the transverse threads from highly wear-resistant material (EP-PS 0 185 108). This is intended to achieve better wear resistance, pressure distribution, longitudinal stability and resistance to flexing.

Experiments have shown that the bond between the carrier web and the strip layer is at great risk due to the large pressure and flexing stresses with different forces acting in the area of the front and rear if the carrier web protrudes too deep into the strip layer. On the other hand, the carrier web tears very easily out of the strip layer if it is only let into it with a small depth. A satisfactory compromise has so far not been achieved or has not been achieved with sufficient reproducibility.

The invention has for its object a tape of the type mentioned at the outset in such a way that the bond between the strip layer and the carrier web is not endangered under pressure and flexing stress and nevertheless there is a high resistance to tearing the carrier web out of the strip layer.

• (a) in die Bandschicht ist wenigstens ein Zusatzfaden eingelassen;
• (b) der Zusatzfaden bzw. die Zusatzfäden erstrecken sich zick-zack-förmig fortschreitend über die Laufrichtung des Bandes;
• (c) bei dem Zusatzfaden bzw. den Zusatzfäden wechseln sich Fadenstrecken, die außerhalb der Trägerbahn verlaufen, mit Fadenstrecken ab, die durch die Trägerbahn hindurchgehen.

This object is achieved according to the invention by the following features:

• (a) at least one additional thread is embedded in the strip layer;
• (b) the additional thread or the additional threads extend in a zigzag shape progressively over the running direction of the belt;
• (c) in the case of the additional thread or threads, thread sections which run outside the carrier web alternate with thread sections which pass through the carrier web.

According to the invention, the band additionally contains at least one additional thread in its band layer, which progresses in the running direction over the entire length of the band, but not straight, but zigzag-shaped, so that its individual thread paths between the reversal points are essentially transverse to the running direction of the Tape. The additional thread runs partly in the area between the carrier web and the back of the belt and partly through the carrier web, so it is integrated with it. In this way, an enormous pull-out strength of the carrier web is achieved without it having to be inserted deep into the strip layer. This opens up the possibility of depth of penetration Align the carrier web in the strip layer optimally according to the pressure and flexing stress, without having to take the tear resistance into account. In addition, the tape has a higher resistance in the transverse direction, in particular an improved resistance to tensile and flexing stress. Such stresses occur in particular at the lateral boundaries of the pressure shoe and can lead to bulging of the band.

In an embodiment of the invention it is provided that the thread sections located outside the carrier web are at a distance from the carrier web, since this promotes the pull-out strength.

It is further provided that the additional thread or at least one of the additional threads has a helical course with a reversal of direction between two thread sections. This means that a thread section runs outside the carrier web and, after a reversal of direction, passes through the carrier web and comes to lie outside the carrier web again after another reversal of direction.

It is expedient that the additional thread or at least one of the additional threads extends between the edges of the band. However, it should be ensured that the additional thread in question does not protrude beyond the edge of the carrier web, but rather that the direction is reversed within the lateral boundaries of the carrier web.

As is known from the prior art, fabrics, in particular multi-layer fabrics, knitted fabrics and in particular wire link belts, are suitable as the carrier web. In the latter The preferred case are those wire link belts which are composed of wire helices extending transversely to the running direction of the belt, since they can easily be connected at the seam with the help of a coupling wire when the belt is finally formed. When using such a wire link belt, it is advisable that the additional thread or the additional threads each run or run with one thread section through a wire coil and with the following thread section after a reversal of direction over the next wire coil.

The tear-out strength of the carrier web can also be improved in that longitudinal threads extending outside the carrier web are embedded in the band layer and extend between the carrier web and thread sections of the additional threads running outside the carrier web. In this way, a crossing layer of thread is created outside the carrier web, but within the band layer, which is connected to the carrier web via the additional thread or the additional threads and therefore further improves the hold of the carrier web in the band layer. In addition, it is achieved that the longitudinal threads improve the longitudinal stability and the flex resistance in this direction, in particular if - as is also proposed - the longitudinal threads are connected to one another at their ends in a tensile manner, that is to say they run all around in the running direction of the belt. The result is a tape that can cope particularly well with the stresses in wet presses with an extended press nip, above all in terms of longitudinal and transverse tensile strength, resistance to flexing and tear resistance.

The connection between the longitudinal threads and carrier web can also be improved in that the longitudinal threads with the Carriers are periodically connected or inserted into them. Furthermore, there is also the possibility of connecting the longitudinal threads with the additional thread or the additional threads at crossing points.

The additional arrangement of longitudinal threads also gives greater freedom with regard to the choice of material for the carrier web. Thus, the longitudinal threads can be made from a particularly tensile material, for example polyester or aramid fibers or threads, and the carrier web can be made from a particularly wear-resistant material, such as polyamide. In this way, the part of the carrier web protruding from the strip layer is particularly protected against wear. Since such highly wear-resistant plastic materials are often not particularly tensile or have a high elongation, their use for carrier webs was limited or not possible at all. The particularly tension-resistant longitudinal threads relieve the load on the carrier web, so that less tensile material that has other advantages can also be used for the carrier web.

• Figur (1) einen Längsschnitt durch ein erfindungsgemäßes Band;
• Figur (2) einen Längsschnitt durch ein anderes erfindungsgemäßes Band;
• Figur (3) eine Draufsicht auf die Trägerbahn ohne Bandschicht des Bandes gemäß Figur (1).

In the drawing, the invention is illustrated in more detail using exemplary embodiments. Show it:

• Figure (1) shows a longitudinal section through a band according to the invention;
• Figure (2) shows a longitudinal section through another band according to the invention;
• Figure (3) is a plan view of the carrier web without the band layer of the band according to Figure (1).

The tape (1) shown in Figure (1) has a tape layer (2) with the front (3) and back (4). The back (4) is ground smooth. When used as intended in the wet press of a paper machine, this rear side (4) runs past the pressure shoe there in the press nip.

A wire link belt (5) serving as a carrier web is partially embedded in the front (3) of the belt layer (2). Such wire link belts (5) are particularly known for use as drying belts in the dryer section of paper machines. They consist of a multiplicity of wire helices extending transversely to the running direction of the band (1) - denoted by (6) for example - which are arranged next to one another in the running direction and overlap with their head arches - denoted by (7) for example. In the area of the overlap of the head bends (7), they are articulated to one another with the aid of a coupling wire extending over the width of the wire helix (6) - designated by (8) for example. Your winding legs - designated by way of example with (9) - between two head bends (7) run essentially straight, so that there is an essentially flat support surface (10) on the free side of the wire link belt (5). When the tape (1) is used as intended, a wet felt cloth lies against this support surface (10). The paper web to be dewatered is carried on the other side of the wet felt cloth.

As can be seen from Figure (1), only about a third of the wire link belt (5) is embedded in the belt layer (2), that is to say only up to the coupling wires (8). In this way, they are created inside the external parts the wire helices (6) have large cavities (11), which can absorb water when the water is squeezed out of the paper web and ensure that this water is quickly removed. So that the wire link belt (5) does not tear out of the belt layer (2) too easily, an additional thread (12) runs within the belt layer (2), alternately once with a thread section - designated by (13) for example - outside a wire helix, that is between the wire link belt (5) and the rear side (4), and once with a thread section - designated by way of example (14) - within an adjacent wire coil (6).

The course of the additional thread (12) can better be seen from FIG. (3), which shows the wire link belt (5) with the additional thread (12) before the band layer (2) is applied, that is without it. It can be seen that the additional thread (12) runs back and forth between the edges of the wire link belt (5) in a zigzag shape or, in this special case, even helically, once by a wire helix (6) and after a reversal of direction over the adjacent wire coil (6). The reversal points - denoted by way of example (15) - of the additional thread (12) are chosen such that the additional thread (12) exits or enters the wire helix (6) before the last turn of the latter. It goes without saying that a plurality of additional threads (12) can also be connected to the wire link belt (5) in the manner shown, for example also in such a way that a second additional thread always runs within the wire helices (6) where the first additional thread ( 12) extends outside the wire coil (6) in question, and vice versa.

The embodiment of a band (1) shown in FIG. (2) agrees with that of FIG. (1) except for one Exception agree, so that the same parts are provided with the same reference numerals and in this respect reference is also made to the preceding description. The exception is that in the band layer (2) a plurality of parallel threads extending parallel to each other in the running direction - for example, designated (16) - are embedded. These longitudinal threads (16) run in the strip layer (2) between the wire link strip (5) and the thread sections (13) of the additional thread (12) running outside the wire coils (6). In this way, a cross-laid scrim is created, which further improves the pull-out strength of the wire link belt (5).

The longitudinal threads (16) are connected to each other at their ends, not shown here, so that they also absorb longitudinal forces. They are preferably made of a particularly tensile material, for example an aromatic aramid or even steel. This opens up the possibility of using less tensile but highly wear-resistant material, such as polyamide or the like, for the wire coils (6) of the wire link belt (5) and thereby keeping the abrasion on the support surface (10) low.

Depending on the requirements, the longitudinal threads (16) and / or the additional threads (12) and / or the wire helices (6) can be formed as yarns, threads or monofilaments or multifilaments. Polyester, such as polybutylene therapy or polyethylene therapy, and its copolymers, polyamide, polyether ketone, polyether ether ketone, polyphenylene sulfide, polypropylene, polyacrylonitride or also carbon or graphite are suitable as materials.

The wire helices (6) can also be designed in this way be as described in DE-GM 86 23 879.5 and 87 06 893.1.

Claims (11)

1.Band for use in paper machines, in particular in wet presses with an extended press nip, which has a flexible, liquid-impermeable band layer which is smooth on the back and in the front of which there is a carrier web with voids, for example a woven, knitted or wire link belt, only partially embedded is characterized by the following features: (a) at least one additional thread (12) is let into the band layer (2); (b) the additional thread (12) or the additional threads extend in a zigzag shape progressively over the running direction of the belt (1), (c) in the additional thread (12) or the additional threads, thread sections (13) which run outside the carrier web (5) alternate with thread sections (14) which pass through the carrier web (5). 2. Band according to claim 1,
characterized in that the thread sections (13) located outside the carrier web (5) are spaced apart to the carrier web (5). 3. Band according to claim 1 or 2,
characterized in that the additional thread (12) or one of the additional threads has or have a helical course with a reversal of direction (15) between two thread sections (13, 14). 4. Band according to one of claims 1 to 3,
characterized in that the additional thread (12) or at least one of the additional threads extends between the edges of the band (1). 5. Band according to claim 4,
characterized in that the additional thread (12) or the additional threads do not protrude beyond the lateral edge of the carrier web (5). 6. Tape according to one of claims 1 to 5,
characterized in that the carrier web is a wire link belt (5) with wire helices (6) extending transversely to the direction of travel of the belt (1) and in that the additional thread (12) or the additional threads each have a thread section (14) through a wire spiral (6 ) and after a reversal of direction (15) with the following thread section (13) over the next wire helix (6) runs or run. 7. Band according to one of claims 1 to 6,
characterized in that longitudinal threads (16) run in the strip layer (2) outside the carrier web (5), which run between the carrier web (5) and the thread sections (13) of the additional thread (12) or outside the carrier web (5). extend at least one of the additional threads. 8. tape according to claim 7,
characterized in that the longitudinal threads (16) are connected to one another at their ends in a tensile manner. 9. tape according to claim 7 or 8,
characterized in that the longitudinal threads (16) are connected to the carrier web (5) at regular intervals or are inserted therein. 10. Band according to one of claims 7 to 9,
characterized in that the longitudinal threads (16) are connected with the additional thread (12) or at least one of the additional threads at crossing points. 11. Band according to one of claims 7 to 10,
characterized in that the longitudinal threads (16) consist of material with a higher tensile strength than the material of the carrier web (5) and the carrier web (5) consists of more wear-resistant material than that of the longitudinal threads (16).

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