EP0114656B1 - Compound fabric as a machine clothing for the sheet forming part of a paper machine - Google Patents

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.

Fabrics 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 surface (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 longest possible 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. Only the warp wires are common to both sides. 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 possible with the so-called two-layer. Seven reached. 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-A-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 binding points, which causes defects in the uniformity of the surface.

A certain remedy in this regard is the joining of the two layers with a binding weft, as is known from DE-A-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 e.g. B. in an openly woven and sewn sieve, the connection of the two layers takes place both during weaving and during fixing 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 tensile stress in the binding weft wire already arises during weaving, when the binding wire, which the shooter initially laid out stretched, is bent when changing the position of the harness. 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, unyielding warp and weft wires, the entire tension of the binding weft wire is also transferred to the binding point of the upper layer. Only the finer upper layer can yield in its structure. This means that the structure of the top layer changes at every setting 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 in the production of some types of paper the unevenness of the surface at the binding points of the top wire is not disturbing, certain types of paper that are highly sensitive to wire marking - such as e.g. B. gravure papers, offset and natural art paper in such places to errors in printing, which are then repeated according to the weave repeat in the given law over the entire area of the paper web.

From GB-A-451,752 a felt for the press section and the dryer section of a paper machine is known, which consists of two fabric layers which are connected by binding threads which run partly in the warp direction and partly in the weft direction. Each binding thread is bound in both fabric layers, which results in a very firm connection of the fabric layers. With a corresponding integration of the binding threads in a two-layer covering for the sheet-forming part of a paper machine, the aforementioned difficulties would arise, in particular with regard to the marking of the paper web.

The invention has for its object to provide a composite fabric as a covering for the sheet-forming part of a paper machine, which consists of at least two layers of fabric bound together by binding threads and in which the uniformity of the surface structure of the paper side is improved.

This object is achieved in that the binding threads form an elastic intermediate layer and each individual binding thread is bound in at most 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 therefore 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 chain or only the binding weft is partly bound into the upper and partly into the lower fabric layer, while the other binding threads, i.e. H. the binding weft or the binding chain only act as warp or weft threads of the intermediate fabric, 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 connects the fabric layers elastically 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 binding threads bound into the upper layer are even thinner than the structural warp and weft wires of the upper layer. The structure of the binding threads can that of the running side, i.e. H. absorb stresses from the lower layer and keep them largely away 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.

• Figuren 1 und 2 ein Verbund-Gewebe, bei dem die Lagen durch Bindefäden miteinander verbunden sind ;
• Figur 3 eine Darstellung ähnlich der von Figur 2, wobei der Bindeschuss über eine Strecke von drei Kettfäden in die obere Lage eingewoben ist ;
• Figur 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;
• Figur 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
• Figuren 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 :

• Figures 1 and 2, a composite fabric in which the layers are connected to each other by binding threads;
• FIG. 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 not bound into either the lower or the upper layer, and
• Figures 11 and 12, a composite fabric, in which the warp threads of the intermediate layer are bound neither in the upper layer nor in the lower layer.

Fig. 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. Your density is only one 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 transferred to the upper layer 1 or only in a very weakened form. Tension and distortion 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 bandage 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.

FIGS. 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 weft 5 is bound into the upper layer 1 and, accordingly, the binding weft 5 is bound into the lower layer 2 at the points where 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 exemplary embodiment shown in FIGS. 7 to 10, only every second binding weft 5 is bound into the upper layer 1, while the binding weft 5 in between is not bound into either of the two layers 1, 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. Because only every second binding weft 5 is actually also incorporated into the upper layer 1, a very loose, elastic connection of the two layers 1, 2 is obtained. FIGS. 11 and 12 show an embodiment in which the binding weft 5 alternates into the upper layer 1 (FIG. 11) and in the lower layer 2 (FIG. 12), while the binding chain 4 is not integrated 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.

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 with 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 integrated into the upper fabric layer 1 (FIGS. 7 and 9), in which case these connecting weft wires tie in 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.

Binding weft wires 5 which bind into the upper fabric layer 1 (FIGS. 7 and 9) can be monofilament or multifilament plastic threads made 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.

Binding weft wires 5, which only bind in the intermediate layer 3 (FIG. 8), are expediently monofilaments with a medium to high modulus of elasticity, 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 in the lower fabric _. topping 2.

Claims (6)

1. Composite fabric as clothing for the paper- forming section of a papermaking machine, consisting of at least two fabric layers (1, 2) interconnected by binder threads (4, 5), characterized in that the binder threads (4, 5) extend partly in the warp direction and partly in the weft direction and form an elastic interlayer (3), and in that each single binder thread (4, 5) is woven into not more than one of the at least two fabric layers (1, 2).

2. Composite fabric according to claim 1 characterized in that the binder threads extending in the warp direction (binder warp 4) are woven into one fabric layer (1 or 2) and the binder threads extending in the weft direction (binder weft 5) are woven into the another fabric layer (2 or, resp., 1).

3. Composite fabric according to claims 1 or 2 characterized in that the binder threads (4 or 5) woven into the upper layer (1) are passed underneath all of the binder threads (5 or, resp., 4) woven into the lower layer (2).

4. Composite fabric according to claims 1 or 2 characterized in that the binder warp (4) and the binder weft (5) are interwoven with one another.

5. Composite fabric according to claim 4 characterized in that a number of the binder threads of the binder warp (4) or, resp., of the binder weft (5) are woven into the upper layer (1) and the other binder threads of the respective binder warp (4) or, resp., the binder weft (5) into the lower layer (2), while the non-interwoven binder weft (5) or, resp., the non-interwoven binder warp (4) participate only in the formation of the interlayer (3).

6. Composite fabric according to any one of claims 1 to 5 characterized in that the binder threads (4, 5) are so interwoven into one of the two fabric layers (1, 2) that they are interwoven with a plurality of warp or weft threads, respectively, of these fabric layers (1 or, resp. 2).

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