EP0080686A1 - Double layer fabric as a Fourdrinier wire for paper machines - Google Patents

Abstract

A double-layer woven fabric comprising longitudinally extending warp wires and two layers of transversely extending weft wires, at least part of the warp wires being interwoven with weft wires of both weft layers and warp wires, separated by not more than one intermediate warp wire, extending pair-wise in parallel at least over part of their length on the paper side and/or on the running side of the fabric.

Description

The invention relates to a double-layer fabric as a covering for paper machines, both for the sheet forming part and for the dryer section. The fabric contains two layers of transverse weft wires and longitudinal warp wires, at least some of which are interwoven with the weft wires of both layers.

The synthetic sieve has been in constant development since the start of the conversion of paper machines from operation with metal cloths to synthetic sieves. Synthetic fabrics are also used in the dryer section. First, single-layer bindings were used. The switch to double-layer bindings has improved longitudinal stability and retention. However, the fabric marking of the paper web and the high abrasion still cause difficulties, particularly when used in the sheet-forming part of the wet end.

From DE-OS 22 63 4.76 it is known to guide the warp wire at least twice over a cross wire of the upper weft position for the production of a monoplan sieve, in which the warp and weft cranks lie in one plane in the fixed state. In practice, however, this goal was only partially achieved, because the marking remained very large due to the recesses in the diagonal direction between the groupings of the warp and weft crooks and could not be removed even by sanding the paper side. Because of the warp arch on the running side under two pairs of shots, it was also subjected to very rapid abrasion.

To avoid these disadvantages, in DE-OS 25 40 490 the chain on the running side is only passed under a single weft wire. This lengthened the free weft arc and the warp wire could be embedded deeper into the interior of the fabric with high fixing tension. However, the improvement in the runtime was limited by the fact that only relatively thin weft wires can be woven into the running side, since otherwise the warp wire could not sufficiently deform the thicker, more rigid weft wire and would remain on the outside of the sieve.

From DE-OS 27 06 235 and SE-AS 77 02 520-3 it is known for a double-layer paper machine screen to have the warp wires only tie a single weft wire on the paper side. The screen has a symmetrical weave on the paper side and on the running side and is characterized by a high permeability. However, the long weft arches cause a strong marking, so that the sieve cannot be used with marking-sensitive papers.

While in the aforementioned paper machine screens the paper side is mainly formed by the weft wires, it is known from DE-GM 76 30 822 to form the paper side predominantly from warp wires. With this sieve, the warp wires lie over the weft wires of the upper layer. Since the paper fiber flow is also length-oriented, this leads to difficulties in removing the sheet.

The invention has for its object to provide a double-layer fabric as a covering for paper machines, which is also suitable for the production of marking-sensitive papers, has a good review and a long term.

This object is achieved in that adjacent warp threads or warp threads separated by at most one further warp thread on the paper side and / or on the. Running side are at least partially parallel in sections.

The fact that only a slight marking is caused by the double-layer fabric according to the invention can be attributed to the fact that the fibers of the paper web are supported instead of by individual sheets of the wires by a surface structure which is formed by the adjacent warp wires guided in parallel, in particular if these have two or more weft wires of the upper sieve layer are running. The fact that the warp threads are parallel at least in places means that they rise to the top of the screen in front of the same weft wire and also leave it together _ behind the same weft wire. In the known double-layer fabrics, the marking is stronger because the surface consists of numerous individual offsets of the warp or weft wires, which leave relatively deep impressions in the easily deformable paper fiber flow. According to the weaving pattern, these impressions have a legal arrangement that stands out as a fabric marking, although the individual impression is barely perceptible. By the warp _- caused or Schussabkröpfungen impressions are especially strong when the offsets are surrounded by open mesh.

The flat support of the paper pulp is preferably formed by immediately adjacent warp wires and not by weft wires, because the density of the warp wires in a double-layer wire is normally three times as high as the density of the weft wires. It It is therefore very difficult to bring two successive weft wires so close together that they form an almost closed area for the pulp. -With the warp wires, this problem does not exist, since the filling level of the double-wire screen is usually over 100% percent. The filling degree is defined as follows: filling ratio = number of warp threads / cm x _K ettdrahtdurchmesser (in cm) x 100. Because of the very high degree of filling of a double-screen, it is even possible not only to immediately adjacent current warp, but only to the next warp wire to form the support surface.

An improvement in the fabric marking also results from the fact that the top of the fabric has two types of markings, firstly the surface markings which are formed by the warp wires which are guided in parallel in places, and secondly the individual wire markings which result from the offset of individual weft wires. These two types of markings alternate, thereby breaking the regularity of the marking arrangement, which is tantamount to reducing the marking.

• Fig. 1 ein doppellagiges Gewebe, bei dem die Kettdrähte in beiden Lagen paarweise parallel geführt sind;
• Fig. 2 ein doppellagiges Sieb, bei dem zwei benachbarte Kettdrähte jeweils nur auf der Oberseite parallel geführt sind und von jedem Kettdrahtpaar nur ein Kettdraht auch in die untere Lage eingebunden ist, wobei der Verlauf beider Kettdrähte dargestellt ist;
• _Fig. 3 die Oberseite einer weiteren Ausführungsform des doppellagigen Gewebes;
• Fig. 4 die untere Lage eines doppellagigen Gewebes (von oben betrachtet);
• Fig. 5 die einzelnen auf einen Schussd.raht in der unteren Lage ausgeübten Kräfte, die zu seiner Abkröpfung führen;
• Fig. 6 den Kettdrahtverlauf und den Schussdrahtverlauf in der unteren Lage eines doppellagigen Gewebes und
• Fig. 7 bis 10 jeweils mit Darstellungen a bis c, das Webbild der Oberseite, das Webbild der Unterseite bzw. den Verlauf der Längsdrähte bei den doppellagigen Geweben nach den Beispielen.

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

• 1 shows a double-layer fabric in which the warp wires are guided in pairs in parallel in both layers;
• Fig. 2 shows a double-layer sieve, in which two adjacent warp wires are guided in parallel only on the top side and only one warp wire of each warp wire pair is also integrated in the lower layer is, the course of both warp wires is shown;
• _F ig. 3 shows the top of a further embodiment of the double-layer fabric;
• 4 shows the lower layer of a double-layer fabric (viewed from above);
• 5 shows the individual forces exerted on a weft wire in the lower position, which lead to its bend;
• Fig. 6 the warp wire course and the weft wire course in the lower layer of a double-layer fabric and
• 7 to 10 each with representations a to c, the weave of the top, the weave of the bottom or the course of the longitudinal wires in the double-layer fabrics according to the examples.

The drawing relates to open woven fabrics, so that the warp wires run in the machine direction and the weft wires run transversely to them. However, the invention is also applicable to endless or round woven screens, the terms "warp wires" and "weft wires" to be interchanged. In the following, "warp wires" are always understood to mean those in the machine direction and "weft wires" are always the wires running transversely thereto.

1 shows a double-layer fabric in which the warp wires 1 are guided twice over their entire course, so that the warp wires run in parallel next to one another in pairs both on the paper side and on the running side.

The desired planar support of the pulp is obtained by running the warp wire pair over at least two weft wires 2 of the upper layer.

On the bottom or barrel side, the pair of guiding of the warp wires results in a doubling of the free floatation of the weft wire 2 for a given warp wire density without the number of shafts of the weaving machine having to be doubled.

In the embodiment shown in FIG. 1, the weft wire 2 can also be bent more strongly, because by arranging the warp wires 1 in pairs, much thicker weft wires 2 can be used in the lower layer next to one another.

With single-layer paper machine screens, the double warp wire guide has no advantages. The distribution of the warp wire cross-section over several wires results in an overall thinner and more flexible paper machine wire, but at the same time the open area decreases due to the widening of the wire cross-section in the transverse direction. By reducing the warp wire diameter, the sieves became very sensitive to abrasion, although the overall cross-section of the chain remained unchanged. In the double-layer fabric shown in Fig. 1, however, not one warp wire is divided into two warp wires, but the warp wire thickness remains unchanged compared to a fabric of otherwise the same construction and only the warp wire guide is changed so that a double chain results.

While in single-layer paper machine screens with double warp guides, the warp wires are much thinner than the weft wires and even less than half the way through In the embodiment of the invention shown in FIG. 1, the weft wires 2 and the warp wires 1 have approximately the same diameter, whereby, as is generally customary, the diameter of the warp wires can be approximately 10% smaller.

In the embodiment shown in FIG. 2, the warp wires 1 a, 1 b run in pairs only on the upper side of the fabric. The course of the one warp wire of a pair is shown in the upper illustration of FIG. 2 and the course of the other warp wire of the same pair in the lower illustration of FIG. 2.

It was recognized from this that only one warp wire la of each warp wire pair is also integrated in the lower layer. At this point, the other warp wire 1b continues to run inside the fabric and is therefore not exposed to abrasion. With this fabric construction there is a doubling of the free float length of the weft wires 2 on the running side, but the weaving requires a double number of shafts compared to the weaving of the fabric shown in FIG. 1 and also two warping rollers.

Another embodiment of the principle of the formation of support surfaces is shown in FIG. 3. The warp wires 1 are guided in such a way that they are involved twice in the formation of the supporting surfaces per repeat on the paper side: the first time together with the preceding warp wire, the second time with the subsequent warp wire.

This embodiment has the advantage over the embodiment shown in FIGS. 1 and 2 that adjacent warp wires 1 no longer run parallel to one another in the inside of the sieve, but in the inside of the sieve always run at a considerable angle to each other. This causes an opening in the oblique direction and thus a higher permeability inside the tissue.

In FIG. 4, a view from above of the lower layer of the fabric shows how a better (stronger) cropping of these weft wires can be achieved by twisting the warp wires 1 in pairs around the lower weft wires 2. In Fig. 4, each warp wire 1 is cranked together with the preceding warp wire around a certain weft wire 2, i.e. H. runs under a weft wire. It then runs two warp wires far inside the screen, i. is passed over two weft wires, and is then bent again with the subsequent warp wire under the third weft wire. Of course, the warp wires can also run over a distance of more than two weft wires inside the fabric. Regardless of the binding of the upper layer, this twisting of the warp wires in the lower layer results in a stronger cranking of the weft wires and thus an improvement in the running time.

5 explains the influencing variables which determine the offset of the weft wire on the barrel side. The goal is to bend the weft wires 2 so that they lie lower than the warp wires and loop through in front of the warp wires 1. For a given warp wire thickness, a weft wire is cranked the more, firstly, the longer the free float F is, secondly, the greater the force A with which the outer warp wires A press against the weft wire, and thirdly, the larger the downward force exerted by the internal warp wires B.

The following can be said about these three influencing factors: The length of the free float is determined by the number of shafts in the binding and is therefore predetermined, so that for a specific binding the strength of the offset is influenced by the forces exerted by the external and internal warp wires becomes. The outer warp wires A must be strong enough (large diameter) to form the short weft arc. According to the principle illustrated in FIG. 4, this is achieved in that two adjacent warp wires cooperate in the cranking. The downward force exerted by the inner warp wires B can be increased by cranking each warp wire per repeat by at least two not immediately successive weft wires on the running side. While in conventional bindings the chain is looped upwards to the upper layer on the inside of the wire after looping a weft wire, the warp wire is cropped by another weft wire before it is tied into the upper layer.

Fig. 6 shows in the upper figure this two-time integration of each warp wire per repeat in the lower layer. The lower illustration of FIG. 6 shows the joining together of two warp wires to form a weft arch.

Another advantage is that there are relatively few parallel warp wires inside the screen, i. H. most of the warp wires run at an angle to each other inside the sieve. This prevents blockages in the inside of the sieve and increases the drainage capacity of the sieve. This measure has a greater impact the higher the number of shanks of the binding.

Example 1:

The fabric is double-layered and consists of 62 longitudinal wires / cm (warp wires for flat weaving, weft wires for continuous weaving) made of polyester monofilament with a wire diameter of 0.17 mm.

The cross wires lying one above the other in pairs are also monofilaments. The fabric has a total of 2 x 23 cross wires, 23 in the top layer and 23 in the bottom. The cross wires of the top layer are made of polyester throughout and have a diameter of 0.17 mm. In the lower layer, alternating wires made of polyester and polyamide are woven, both have a diameter of 0.18 mm.

• Fig. 7 a zeigt das Webbild der Papierseite,
• Fig. 7 b zeigt das Webbild der Laufseite,
• Fig. 7 c zeigt den Verlauf eines Längsdrahtes.

The weave has 8 strands. The longitudinal wires are guided in such a way that they are passed twice over two cross wires on the paper side. The desired surface structure is created by the parallel running of two consecutive longitudinal wires.

• 7 a shows the web image of the paper page,
• 7 b shows the web image of the running side,
• Fig. 7 c shows the course of a longitudinal wire.

The longitudinal wires are therefore only brought together on the paper side, so that there is a fabric with a flat top and a conventionally designed running side.

Example 2:

• Fig. 8 a zeigt das Webbild der Papierseite dieses Siebes,
• Fig. 8 b zeigt das Webbild der Laufseite und
• Fig. 8 c zeigt den Verlauf der Längsdrähte.

The sieve has the same design of the longitudinal wires as in Example 1, only the guidance of the longitudinal wires was changed. Successive longitudinal wires are joined in sections on the running side by double binding. They are only included once on the paper side. This creates a conventional paper side and an underside with reinforced cross wires. Cross wires with a diameter of 0.17 mm are used on the paper side, alternating polyester and polyamide wires on the running side, both with a diameter of 0.22 mm.

• 8 a shows the weave of the paper side of this screen,
• Fig. 8 b shows the web image of the running page and
• 8 c shows the course of the longitudinal wires.

Example 3:

The successive longitudinal wires are merged in pairs once at the top and once at the bottom, but have the remaining length, i. H. outside of these bend points, a different course.

• Fig. 9 a zeigt das Webbild der Oberseite,
• Fig. 9 b das der Unterseite und
• Fig. 9 c den Verlauf der Längsdrähte.

The selected binding has 11 strands. The design of the longitudinal wires remains unchanged with 62 longitudinal wires / cm with a diameter of 0.17 mm. The cross wires of the top layer have a diameter of 0.17 mm and are all made of polyester. The cross wires of the lower layer have a diameter of 0.24 mm and are alternately made of polyester and polyamide.

• 9 a shows the weave image of the top,
• Fig. 9 b the bottom and
• Fig. 9 c the course of the longitudinal wires.

Example 4:

In contrast to the previous three examples, two longitudinal wires run parallel in pairs over the entire length.

The density of the longitudinal wires is again 62 per cm. They are polyester monofilaments with a diameter of 0.17 mm.

• Fig. 10 a zeigt das Webbild der Oberseite,
• Fig. 10 b das der Unterseite und
• Fig. 10 c den Verlauf eines Längsdrahtes.

The cross wires of the top layer are 0.17 mm thick. In the lower layer, the transverse drains have a diameter of 0.26 mm, the material is alternating between polyester and polyamide.

• 10 a shows the weave image of the top,
• Fig. 10 b the bottom and
• Fig. 10 c the course of a line wire.

Claims (6)

1. Double-layer fabric as a covering for paper machines with longitudinal warp wires (1) and with two layers of transverse weft wires (2), at least some of the warp wires (1) being interwoven with weft wires (2) of both layers, characterized in that successive or by at most one intermediate warp wire separated warp wires (1) on the paper side and / or the running side are guided in pairs at least in sections. 2. Fabric according to claim 1, characterized in that in the upper layer the pair of parallel warp wires (1) are guided over at least two weft wires (2). 3. Fabric according to claim 1 or 2, characterized in that two adjacent warp wires (1) are guided in parallel over the entire repeat length. 4. Fabric according to one of claims 1 to 3, characterized in that only one warp wire (1) is integrated into the lower layer of each warp wire pair. 5. Fabric according to one of claims 1 to 4, characterized in that each warp wire (1) in the upper layer per repeat is guided at least twice over two weft wires (2), for the first time together with the preceding warp wire (1) and the second time together with the subsequent warp wire (1). 5. Fabric according to one of claims 1 to 5, characterized in that in each case two adjacent warp wires (1) are joined together in the lower position when bent by two non-successive weft wires (2).

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