EP0048962A2 - Two-layered sieve for the sheet forming zone of a paper machine - Google Patents

Abstract

A double-layer sieve for the sheet-forming part of a paper machine contains weft threads (3, 4) and warp threads arranged in pairs one above the other, all the warp threads being bound into the upper layer (5) of the sieve. However, only part of the warp threads (construction chain 1) is also integrated in the lower layer (6) of the sieve. The warp number of the upper fabric layer (5) used to form the paper web is preferably at least twice as high as that of the lower layer (6). Furthermore, the lower weft threads (4) are preferably at least 30% thicker than the warp threads.

Description

The invention relates to a double-layer sieve for the sheet-forming part of a paper machine, which consists of weft threads arranged in pairs one above the other and of warp threads, all of the warp threads being integrated in the upper layer of the sieve.

Such screens are known from DE-OSes 2 263 476 and 25 40 490. With these screens, all warp wires bind under the weft wires on the running side and are therefore exposed to abrasion. Since double-layer sieves tear open immediately when grinding through the warp wires - the warp wires transmit the entire driving force that acts on the sieve - the wear of the warp wires is the usual cause for the failure of a sieve. This applies in particular to the screens according to DE-OS 2 263 476, in which the warp wires are looped through long before the weft wires on the running side are used up. According to DE-OS 25 40 490, this difficulty is partially solved in that the warp wires run on the running side only under one weft wire. As a result, the warp bows on the barrel side become significantly shorter, the weft bows become longer and, as a result, the warping of the weft wires can be increased to such an extent that the warp wires on the barrel side are embedded within the weft wires be looped through before the warp wires. As a disadvantage, however, it must be accepted that the weft wires may only be a few hundredths of a millimeter thicker than the warp wires, since otherwise the warp wires are pressed downwards by the stronger and stiffer weft wires and are therefore more exposed to abrasion. It is therefore not possible with such a sieve to use thicker weft wires to increase the abrasion volume.

There has been no shortage of attempts to increase the life of multi-layer paper machine screens. Thus, according to DE-OS 24 55 185, a paper machine screen is constructed from two self-contained fabric webs which are connected by a special binding chain. However, the binding chain runs partly on the barrel side under the weft wires and is therefore exposed to grinding. The thinner the binding chain, the more it is looped through. Such a sieve made up of two self-contained fabric webs is very expensive and complex.

Finally, it is known from European patent application publication 0 010 311 to greatly reduce the number of weft wires on the running side of a double-layer paper machine screen in order to make the screen more permeable. To extend the running time, some of the warp wires are only integrated in the lower layer of the screen, which is intended to increase the volume of abrasion. These warp wires in the lower layer also determine the distance between the warp wires in the upper layer. The small number of warp wires on the paper side leads to a strong screen marking in the paper. A disadvantage of this sieve is in particular the small number of weft wires on the running side and the high number of warp wires on the running side. Both features have the result that on the barrel side each weft wire is looped around by three or four warp wires per repeat and thus has no free length for bulging in the direction of the barrel side. This sieve is therefore a pure warp runner and tears open after a relatively short runtime, namely as soon as the unprotected arches of the warp wires are sanded through. In Fig. 5A of this document, a screen is shown in which a part of the warp wires is not bent down, that is, is not integrated into the lower layer. The wire ratio on the running side still remains un Favorable, since more warp wires are integrated in the few weft wires on the running side than on the paper side.

Starting from DE-OS 25 40 490, the invention has for its object to provide a double-layer, intended for the sheet forming part of a paper machine, which has a longer running time with low screen marking in the paper and high stability in the transverse and longitudinal directions.

This object is achieved in a sieve of the type mentioned in the introduction in that only a part of the warp threads is also integrated in the lower layer of the sieve.

In the embodiment of the invention specified in claim 3, the running time is additionally extended by the larger abrasion volume of the lower weft threads.

The sieve according to the invention is easiest to manufacture if the number of warps on the paper side is twice as high as on the running side, since then every second warp wire is not woven into the lower layer. However, it is also possible to weave only every third, fourth, etc. warp wire into the lower layer, so that the ratio of the warp numbers in the upper and lower layers is 3: 1, 4: 1, etc. The warp number of the upper layer used to form the paper web is preferably at least twice as high as that of the lower layer. Due to the small number of warps in the lower layer, a so-called weft runner screen and very long weft floats are obtained. H. large unbound lengths of the weft threads, so that the abrasion is distributed over a large thread volume.

Compared to a two-layer or multi-layer sieve, which consists of several self-contained fabric webs, as is known from DE-OS 24 55 185, the inventive sieve has all the advantages of a double-layer sieve. In particular, by avoiding the division of the sieve into individual, complete webs of fabric significantly reduce the tendency to clogging due to contamination during use, and the entire production process is significantly simplified in the production of the sieves: weaving requires a smaller number of pinch rollers; after weaving out a sieve, the change to any conventional bindings takes place without any relocation in the harness system. Seaming in the case of flat-woven sieves is also carried out using conventional apparatus and is considerably easier than with sieves made up of several individual fabric layers, in which each individual fabric layer has to be sewn separately.

The length of the weft float on the barrel side can be shortened if necessary without changing the screen structure of the paper side, by not looping the warp wires that are integrated in the lower layer once or twice, or under two, per repeat Shots of the lower layer are performed.

For example, the free weft float can be shortened from 9 to 7 warp wires without the advantages of this new type of fabric according to the invention being nullified or impaired, because at least half of the warp wires remain hidden inside the screen until the end of the running time at full strength since they do not wear away are exposed.

The warp wires and the weft wires are generally formed by a plastic monofilament; polyester and polyamide monofilaments are particularly suitable. In addition, because of the difficulty of round weaving double-layer screens, the screens are generally flat-woven.

Another advantage of the screen according to the invention is that, because of the higher number of warps in the upper layer, the paper side of the screen has a finer structure and leaves a weaker mark in the paper.

Those warp wires that are only integrated in the upper layer of the wire are referred to below as the "power transmission chain" because they absorb most of the longitudinal tension exerted on the wire. Since the power transmission chain runs largely straight in the sieve, the sieve according to the invention has a small constructional stretch. Those warp wires that are bound in both layers are referred to below as "construction chain". The power transmission chain can be thinner than the construction chain or can be made of less stretchable material than the construction chain. In particular, more elastic material can be used for the construction chain than is usually used for warp wires in a paper machine wire.

• Fig. 1 das Papiermaschinensieb im Längsschnitt, wobei eine Konstruktionskette vor einer Kraftübertragungskette liegend dargestellt ist;
• Fig. 2 den Verlauf der Kraftübertragungskette im Einzelnen,
• Fig. 3 das Sieb im Schnitt in Querrichtung;
• Fig. 4 das Gewebebild der Papierseite eines 10-schäftig gewebten Gewebes;
• Fig. 5 das Gewebebild der Laufseite des Gewebes von Fig. 4;
• Fig. 6 Papiermaschinensieb in abgewandelter Gewebeausführung; bei der die Konstruktionskette unter zwei Schussdrähten der unteren Lage verläuft;
• Fig. 7 Verlauf der Kraftübertragungskette bei dem Papiermaschinensieb nach Fig. 6;
• Fig. 8 das Sieb in abgewandelter Ausführung im Schnitt in Querrichtung;
• Fig. 9 die Ansicht der Papierseite bei abgewandelter Gewebeausführung;
• Fi^g.10 die Ansicht der Laufseite des Gewebes von Fig. 9.

Embodiments of the invention are explained below with reference to the drawing. Show it:

• Figure 1 shows the paper machine screen in longitudinal section, wherein a construction chain is shown lying in front of a power transmission chain.
• 2 shows the course of the power transmission chain in detail,
• Figure 3 shows the screen in cross section.
• 4 shows the fabric image of the paper side of a 10-strand woven fabric;
• 5 shows the fabric image of the running side of the fabric of FIG. 4;
• Fig. 6 paper machine screen in a modified fabric version; in which the construction chain runs under two weft wires of the lower layer;
• 7 shows the course of the power transmission chain in the paper machine screen according to FIG. 6;
• 8 the sieve in a modified version in cross-section;
• 9 shows the view of the paper side with a modified fabric design;
• Fi ^g. 10 shows the view of the running side of the fabric from FIG. 9.

The sieve shown in FIGS. 1 to 3 is woven flat, that is to say the warp threads run in the machine direction and the weft threads run transversely to the machine direction. The sieve contains two layers of weft wires, namely the upper weft wires 3, which form the paper side of the sieve, and the lower weft wires 4, which form the running side of the sieve. An upper weft wire 3 is arranged above a lower weft wire 4, i. H. the weft wires are available in pairs. The screen contains at least two types of warp wires, namely a so-called construction chain 1, which is integrated in the upper layer 5 and the lower layer 6, and a so-called power transmission chain 2, which is only integrated in the upper layer 5.

The sieve according to the invention can have any type of weave, ie twill weave, satin weave or a derived weave. The sieve preferably has satin weave, ie the weave points do not touch each other and are evenly distributed. The number of warps on the paper side of the wire is considerably higher than on the running side, since part of the warp wires, namely the power transmission chain 2, is not integrated in the lower layer. The power transmission chain 2 is therefore not ground during operation and does not suffer any abrasion. There are no warp wires that are only integrated in the lower layer 6. All warp wires, that is to say both the construction chain 1 and the force transmission chain 2, are integrated in the upper layer 5. This force transmission chain 2 can also absorb the fabric tension if the warp and weft wires are already completely on the running side (lower layer 6) of the fabric are ground down. This shows the decisive advantage of this sieve shape according to the invention: the sieve has a wire system protected from abrasion, which holds the fabric together long after the wires intended for wear are used up. The power transmission chain 2 should also run as far as possible inside the sieve in order to obtain a sieve that is as free of markings as possible and a good one To achieve web acceptance. In addition, the power transmission chain 2 should have as few bends as possible, ie have a straight course, in order to give the screen a high degree of longitudinal stability and a small constructional stretch.

Figures 4 and 5 show the fabric image of the paper side or the running side of a screen according to the invention. The top view of FIG. 4 shows a 5-volume atlas and that of FIG. 5 shows a 10-volume atlas. In FIG. 4, the binding points 7 correspond to the crankings of the construction chain 1 and the power transmission chain 2, while in FIG. 5 the binding points 8 only originate from the construction chain 1.

A variant of the embodiment according to the invention is shown in FIGS. 6 to 10. The construction chain 1 runs on the running side under two weft wires (FIG. 6). According to the principle of the invention, the force transmission chain 2 runs predominantly inside the sieve and only binds the weft wires 3 of the upper layer 5. The necessary tensile strength of the fabric is retained after the lower layer of the sieve has been destroyed. "The course of the power transmission chain 2 is the same for both bindings, so Figures 2 and 7 are identical.

The structure of the upper layer of the two screen designs is also the same, therefore the fabric image in FIGS. 4 and 9 is identical. Only the lower layer of the sieve (FIG. 10) shows an extension of the warp crooks 8 and a shortening of the crooks 9 of the weft wires. In the cranking 8 on the running side, the two warp wires 1 are always in pairs, which doubles the cranking effect of these warp wires.

In the exemplary embodiments of the invention, a weave with at least 10 shafts and an Atlas distribution was shown. Controlling the length of the shot floats of the bottom Its position is particularly important for fabrics with a higher weave repeat, so that the length of the weft bend on the barrel side can be adapted to the requirements of the respective case.

• Bei einem Gewebe mit Atlasverteilung der Abkröpfungen, gewoben mit 14 Schäften, einer Dichte der Kettdrähte aus Polyester-Monofil von 52 Drähten pro cm und einem Drahtdurchmesser von 0,20 mm ergibt sich auf der oberen Gewebelage 5 ein Gewebebild entsprechend einer 7-schäftigen Rapportlänge. Die Schusszahl beträgt für beide Lagen 24 Drähte pro cm. Der Durchmesser der Schussdrähte 3 der oberen Lage ist 0,18 mm, diese Schussdrähte sind ebenfalls alle aus Polyester-Monofil.

Example:

• In the case of a fabric with an atlas distribution of the offsets, woven with 14 shafts, a density of the warp wires made of polyester monofilament of 52 wires per cm and a wire diameter of 0.20 mm, a fabric image corresponding to a 7-repeat length results on the upper fabric layer 5. The number of shots for both layers is 24 wires per cm. The diameter of the weft wires 3 of the upper layer is 0.18 mm, these weft wires are also all made of polyester monofilament.

The lower fabric layer 6 is woven with much thicker weft wires, namely 0 0.27 mm polyester monofilament, with the possibility of alternately weaving polyester and polyamide monofilaments into this layer to further increase the abrasion resistance. Depending on the strain on the sieve, the alternation can be 1: 1, in extreme cases 2: 1, in which case two polyamide wires and one polyester wire are woven in.

Claims (3)

1.Double-layer sieve for the sheet forming part of a paper machine, with weft threads arranged in pairs one above the other and with warp threads, all of the warp threads being integrated in the upper layer of the sieve, characterized in that only a part of the warp threads (construction chain 1) is also in the lower layer ( 6) the sieve is integrated. 2. Sieve according to claim 1, characterized in that the warp number of the upper fabric layer serving to form the paper web is at least twice as high as in the lower layer. 3. Sieve according to claim 1, characterized in that the lower weft threads (4) are at least 20 and preferably at least 30% thicker than the warp threads.

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