EP0114656A1 - Compound fabric as a machine clothing for the sheet forming part of a paper machine - Google Patents

Abstract

A composite fabric as covering for the sheet forming part of a paper machine consists of at least two fabric layers (1, 2) bound together by binding threads (4, 5). The binding threads (4, 5) form an elastic intermediate layer (3), and each binding thread (4, 5) is bound in at most one of the at least two fabric layers (1, 2). The binding threads run partly in the warp direction and partly in the weft direction, and the binding threads (binding chain 4) running in the warp direction are bound in one fabric layer (1 or 2), and the binding threads running in the weft direction (binding weft 5) are in the other fabric layer (2 or 1) involved. This type of connection largely prevents the transfer of tension from the lower fabric layer to the upper fabric layer and reduces the risk of marking.

Description

The invention relates to a composite fabric as covering for the sheet-forming part of a paper machine with at least two fabric layers bound together by binding threads.

Coverings for the sheet-forming part of a paper machine, so-called sheet-forming screens or paper machine screens, should on the one hand have the smoothest possible top side (paper side) so that no markings occur in the paper. On the other hand, the underside (running side) should be designed in such a way that the sheet forming screen has a long running time: by using cheaper and more abrasive fillers and increasing the working speed, the running side is exposed to high abrasion.

Even with single-layer paper machine screens, the two sides of the fabric are different in most weaves; a smoother paper side, in which mostly warp and weft wires are intertwined monoplane, and a rough running side, which consists of transverse weft bendings (weft screen).

With double-layer paper machine screens, the separation in the design of both sides of the fabric is even clearer. Both sides have only one thing in common

Warp wires. Since the weft wires are divided into two separate weft layers, they can be adapted to the requirements of the corresponding sieve side in terms of both material and wire diameter. In addition, each surface can be given any surface structure that is independent of the other side.

However, a complete separation of both sides of the sieve is only achieved with the so-called two-layer sieves. These are two completely independent layers of fabric, which are connected by an additional binding wire.

Such a fabric as a sheet forming screen is known from DE-OSes 24, -55 184 and 24 55 185. These are round-woven sieves with a binding chain. This means that in the finished sieve, both layers are connected to each other by transverse binding wires.

The binding of both layers of fabric with a binding chain has the disadvantage that the chain is already under tension during weaving (weaving tension) and therefore influences the structure of the paper side.

If a two-layer fabric with a binding chain is woven open and made endless by means of a woven seam, the binding chain runs lengthways in the finished sieve. Since the fabric is lengthened in the heating zone during heat setting, the warp wires are again under a high working tension. Since the weft wires in the lower layer are much thicker and stiffer, the tension of the binding chain affects almost exclusively the finer upper layer. The binding chain pulls the fine weft wires of the upper layer deep down at the tying points, which causes defects in the uniformity of the surface.

A certain remedy in this regard is connecting the two layers with a binding weft, as is known from _D E-OS 29 17 694. Although both types of fabric are identical in the finished state - in both the two layers are connected to each other by the additional cross wire - the production is somewhat easier, since, for example, with an openly woven and sewn sieve, the connection of the two layers is both during weaving and during Fixing is done by a cross wire (weft wire). However, a uniform surface structure of the upper layer is not achieved either. At the tying points, the additional binding weft pulls the upper chain downwards and causes unwanted indentations in the tissue at the tying points.

The tension in the binding weft wire already arises during weaving, when the binding wire, which was first stretched by the shooter, is bent when changing the position of the harness frame. The originally straight binding weft is now cranked and runs in a zigzag pattern alternating between the two relatively far apart upper and lower layers of the composite fabric. Due to this enlargement of its path, the binding wire is stretched during weaving. Since the lower layer consists of relatively thick, resilient warp and weft wires, the entire tension of the binding wire is also transferred to the binding point of the upper layer. Only the finer upper layer can yield in its structure. This changes the structure the upper layer at each tying point during weaving.

During fixation, an offset change also occurs between the warp and the weft wires of both layers. The chain of the lower layer is stretched and loses its offset height. The distance between the lower tie and the upper layer of tissue increases. Since the lower chain is stiff and unyielding, the upper layer is pulled even lower at the tying point.

Due to the effect of the temperature when fixing, own shrinking forces are released in the binding weft. They act as additional tensile force on the thin, upper chain at the binding point and contribute to the deterioration of the uniformity of the surface structure.

While the unevenness of the surface at the binding points of the top wire is not a nuisance in the production of some types of paper, certain types of paper that are highly sensitive to wire marking - such as e.g. Rotogravure papers, offset and nature art paper at such points to errors in the print, which then repeat according to the weave repeat in the given law over the entire area of the paper web.

The invention has for its object to provide a composite fabric as clothing for the sheet forming section of a paper machine, there is at least two indefäden by _B bonded together fabric layers and in which the uniformity of the surface structure is improved the paper side.

This object is achieved in that the _B indefäden form an elastic intermediate layer and each binder thread is at most involved in one of the at least two fabric layers.

Preferred embodiments of the invention are the subject of the dependent claims.

The binding threads of the intermediate fabric run partly in the warp direction and partly in the weft direction and are accordingly referred to as "binding chain" or "binding weft". In a preferred embodiment of the invention, the binding chain is interwoven with the one fabric layer, for example the upper fabric layer, at certain intervals, and the binding weft is interwoven with the other fabric layer, here the lower fabric layer.

In another embodiment of the invention, only the binding warp or only the binder weft is embedded partly in the upper and partly in the lower fabric layer, while the other binding yarns, that is, the binder weft or binding chain, only as a warp or weft threads of the _Z wipe tissue act, and are not integrated into one of the two fabric layers.

The basic idea in each case is that one and the same binding thread is not bound in both fabric layers, as a result of which the intermediate layer formed by the binding threads elastically connects the fabric layers to one another.

The individual layers of the composite fabric consist in the usual way of plastic monofilament, in particular of polyester wire. The binding threads are also monofilament or multifilament plastic threads. In particular, the in the upper layer of bound binding threads is even thinner than the structural warp and weft wires of the upper layer. The structure of the binding threads can absorb the tensions emanating from the running side, ie from the lower layer, and largely keep them from the upper layer. The uniformity of the surface structure of the paper side is therefore not affected by tensions emanating from the lower layer during weaving or fixing.

The intermediate fabric formed from the binding threads thus not only serves to connect the upper fabric layer and the lower fabric layer, but at the same time absorbs the stresses that occur during the production of the composite fabric.

• Fig. 1 und 2 ein Verbund-Gewebe, bei dem die Lagen durch Bindefäden miteinander verbunden sind;
• Fig. 3 eine Darstellung ähnlich der von Figur 2, wobei der Bindeschuss über eine Strecke von drei Kettfäden in die obere Lage eingewoben ist;
• Fig. 4 bis 6 ein Verbund-Gewebe,' bei dem die Bindekette ausschliesslich in die obere Lage und der Bindeschuss ausschliesslich in die untere Lage eingebunden ist;
• Fig. 7 bis 10 ein Verbund-Gewebe, bei dem ein Teil der Schussfäden der Zwischenlage weder in die untere noch in die obere Lage eingebunden ist, und
• _Fig. 11 und 12 ein Verbund-Gewebe, bei dem die Kettfäden der _Zwischenlage.weder in die obere Lage noch in die untere Lage eingebunden sind.

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

• 1 and 2 a composite fabric in which the layers are connected to one another by binding threads;
• 3 shows a representation similar to that of FIG. 2, the binding weft being woven into the upper layer over a distance of three warp threads;
• 4 to 6 a composite fabric, in which the binding chain is bound exclusively in the upper layer and the binding weft is bound exclusively in the lower layer;
• 7 to 10, a composite fabric, in which a part of the weft threads of the intermediate layer is bound neither in the lower nor in the upper layer, and
• _F ig. 11 and 12, a composite fabric in which the warp yarns of _Z are wischenlage.weder incorporated into the upper layer even in the lower layer.

_F ig. 1 shows a section in the warp direction through a composite fabric which consists of an upper layer 1 and a lower layer 2. The top layer has a plain weave and is made of relatively fine plastic monofilaments. The lower layer 2 consists of much coarser plastic monofilaments and has a four-shaft binding. The number of weft wires and warp wires per unit length is only half as high as in the top layer 1. Figure 2 shows the same fabric in a section parallel to the weft direction. ^:

The upper layer 1 and the lower layer 2 are connected by binding wires, namely by a binding chain 4 and a binding weft 5. The binding chain 4 is tied with every eighth weft wire of the lower layer 2, ie runs under this weft wire. The binding weft 5 is guided from below over every eighth warp wire of the upper layer 1. Binding chain 4 and binding weft 5 are not interwoven and form an intermediate layer 3, which is located in the space between the upper layer 1 and the lower layer 2. Because the binding chain 4 runs between the binding locations with the lower layer 2 above the binding weft 5, however, cohesion results similar to that in a fabric. The intermediate layer 3 is very wide-meshed and therefore has only a very loose cohesion. Their density is only a quarter of that of the lower layer 2 or an eighth of that of the upper layer 1. Because of the wide meshing of the intermediate layer 3, tensions and distortions of the lower layer 2 are not or only in a very weakened form on the upper layer 1 transfer. Tensions and distortions of the lower layer 2 can largely be absorbed by the intermediate layer 3 in that the binding chain 4 moves relative to the binding weft 5 within the loose bond of the intermediate layer 3. The intermediate layer 3 therefore has great elasticity.

As can be seen in FIG. 1, the binding chain 4 is only integrated into the lower layer 2 after every second binding weft 5.

FIG. 3 shows a section similar to that of FIG. 2, but the binding weft 5 is more firmly integrated in the upper layer 1. The binding weft 5 is bound in each case over a distance of three warp threads of the upper layer 1 by being guided over one warp thread, under the next warp thread and again over the next warp thread. A force exerted by the binding weft 5 on the upper layer 1 is thus distributed over a larger area and less disturbs the uniformity of the surface structure of the upper layer 1.

Figures 4 to 6 show an embodiment in which the binding chain 4 is connected to the upper layer 1 and the binding weft 5 to the lower layer 2. The density of the intermediate layer 3 is twice as high as in the above exemplary embodiment in FIG. 3.

In the exemplary embodiment in FIGS. 4 to 6, the binding chain 4 and the binding weft 5 form a weave, since the binding chain 4 runs alternately above and below a binding weft 5 and, accordingly, the binding weft 5 runs alternately above and below a binding chain 4, the binding chain 4 starting at the places where it runs over a binding section 5 in the upper layer 1 is integrated and, accordingly, the binding weft 5 is integrated into the lower layer 2 at the points at which it runs under a binding chain 4.

FIGS. 4 and 5 show the course of two successive binding chains 4, while FIG. 6 shows the course of a binding weft 5.

In the example shown in the figures 7 to 10 embodiment, only every second binder weft 5 is incorporated into the upper layer 1, while the intermediate _B indeschuss 5 in neither of the two layers 1, is integrated 2 and is only involved in the formation of the intermediate layer 3 , s. Figure 8. Figures 7, 8 and 9 show a section parallel to the weft direction, while Figure 10 shows a section parallel to the warp direction and accordingly the course of the binding chain 4. The fact that only every second binding section 5 is actually also incorporated into the upper layer 1 gives a very loose, elastic connection between the two layers 1, 2.

FIGS. 11 and 1.2 show an embodiment in which the binding weft 5 is alternately bound in the upper layer 1 (FIG. 11) and in the lower layer 2 (FIG. 12), while the binding chain 4 is not bound in either of the two layers 1, 2 and is only involved in the formation of the intermediate layer 3. This type of connection of the layers, in particular, does not transmit tensions and distortions in the warp direction from the lower layer 2 to the upper layer 1.

Figures 11 and 12 each show a section parallel to the weft wires.

• Die obere Gewebelage 1 eines Verbund-Gewebes aus zwei Gewebelagen wird mit 32 Längsfäden (Kette) pro Zentimeter und 36 Querfäden (Schuss) pro Zentimeter offen in Leinwandbindung gewebt.

Example:

• The upper fabric layer 1 of a composite fabric consisting of two fabric layers is openly woven with 32 longitudinal threads (warp) per centimeter and 36 transverse threads (weft) per centimeter in plain weave.

The longitudinal threads 6 have a diameter of 0.17 mm and consist of a polyester monofilament of medium to low longitudinal stability and medium modulus of elasticity (Trevira 930).

The transverse threads 7 also have a diameter of 0.17 mm and consist of a polyester monofilament with a very low modulus of elasticity and low thermal shrinkage (Trevira 900).

The lower fabric layer 2 is a four-strand, four-twill weave of weave No. 0401 with long floats of the cross threads on the running side and short floats on the top. The lower fabric layer 2 is open-woven with 16 longitudinal threads per centimeter and 18 transverse threads per centimeter at the same time as the top layer 1. The longitudinal threads 8 have a diameter of 0.32 mm and consist of polyester monofilament with a high modulus of elasticity. The transverse threads 9 of the lower fabric layer 2 are made of a particularly abrasion-resistant material and consist alternately of polyester monofilament and polyamide monofilament with a diameter of 0.35 mm.

The active, outer fabric layers 1 and 2 are connected by an elastic, tension-compensating intermediate layer 3.

Only the weft wires of the intermediate layer 3 are in the upper fabric layer 1 integrated (Figures 7 and 9), then these tie weft wires bind three successive warp wires 6 of the upper fabric layer 1. Additional connecting weft wires 5 of the intermediate layer 3 do not bind the upper fabric layer 1, but only run inside the intermediate layer 3.

_B indeschussdrähte 5 which embed in the upper fabric layer 1 (figure 7 and 9) may be monofilament or multifilament synthetic threads of polyester or polyamide. In the present example, a polyester monofilament with a diameter of 0.15 mm with a low modulus of elasticity was used.

_B indeschussdrähte 5, which incorporate only in the intermediate layer 3 (Figure 8), are functional monofilaments with medium to higher elastic modulus, and also have a diameter of 0.15 mm.

Monofilament or multifilament polyester or polyamide threads can be used as binding warp wires 4 of the intermediate layer 3. In the present example, monofilament polyester threads with a diameter of 0.18 mm were used. The binding warp wires 4 bind only into the lower fabric layer 2.

Claims (6)

1. Composite fabric as covering for the sheet forming part of a paper machine from at least two fabric layers bound together by binding threads, characterized in that the binding threads (4, 5) run partly in the warp direction and partly in the weft direction and form an elastic intermediate layer (3) and that each The binding thread (4, 5) is at most bound in one of the at least two fabric layers (1, 2). 2. Composite fabric according to claim 1, characterized in that the binding threads running in the warp direction (binding chain 4) are integrated into the one fabric layer (L or 2) and the binding threads running in the weft direction (binding weft 5) into the other fabric layer (2 or 1) are involved. 3. Composite fabric according to claim 1 or 2, characterized in that the binding threads (4 or 5) bound in the upper layer (1) are passed under all binding threads (5 or 4) bound in the lower layer (2). 4. Composite fabric according to claim 1 or 2, characterized in that the binding chain (4) and the binding weft (5) are interwoven. 5. Composite fabric according to claim 4, characterized in that the binding chain (4) or the binding weft (5) partly in the upper layer (1) and partly in the lower layer (2) are connected, while the binder weft (5) and the _B is indekette (4) only involved in the formation of the intermediate layer (3). 6. Composite fabric according to one of claims 1 to 5, characterized in that the binding threads (4, 5) are integrated into one of the two fabric layers (1, 2) in such a way that they have several warp or weft threads Fabric layers (1 or 2) are woven.

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