EP0349779B1 - Double-layer fabric for use in the wet end section of a papermachine - Google Patents

Abstract

The invention relates to a double-layer fabric as the wire screen for the wet end of a paper machine. The advantages of the double-layer fabrics which are provided with only one longitudinal thread system and the advantages of multi-layer fabrics which have at least two longitudinal thread systems are combined in one fabric without having to accept the disadvantages of the prior fabrics. The double-layer fabric according to the invention consists of two sets of longitudinal threads and at least one upper ply and one lower ply of transverse threads, the first set of longitudinal threads being woven only with the upper ply of transverse threads and the second set of longitudinal threads being woven both with the lower ply of transverse threads 50 to 53 and at least partially with the upper ply of transverse threads 40 to 47, the two sets of longitudinal threads forming, with the upper ply of transverse threads, a recurring weaving pattern in which at least some of the upper transverse threads 41, 43, 45, 47 are traversed underneath by at least three successive longitudinal threads and then traversed above by at least three successive longitudinal threads, of the last mentioned at least three successive longitudinal threads at least two belonging to the first set and one belonging to the second set, and the last mentioned longitudinal thread of the second set traversing only above one upper transverse thread of the weaving pattern (repeat), while the longitudinal threads of the first set traverse at least once above two successive upper transverse threads within the weaving pattern. <IMAGE>

Description

The invention relates to a double fabric as a screen fabric for the wet end of a paper machine according to the preamble of claim 1.

As is known, sieve fabrics are known for stability, uniformity of water permeability, surface smoothness, number of stitches / cm and the like. The like. Made extraordinarily high demands. The highest possible number of wearing points on the paper side of the fabric is also sought, and the highest possible wear volume on the running side of the fabric, because the surface quality of the paper to be produced u. a. also depends on the number of wearing points and the lifespan of the fabric on the wear volume. The greater the volume of wear, the longer the sieve service life.

In order to meet these partly conflicting requirements for such screen fabrics, US Pat. No. 3,127,308 proposes a fine upper fabric in a single weave (linen weave) to combine with a lower fabric in a three-twill weave so that the longitudinal threads of the lower fabric also cross individual transverse threads of the fine, simple upper fabric at certain points. Such fabrics are called double or multiple fabrics with a connection in the technical language. The production of suitable double fabrics of this type as forming fabrics has encountered difficulties, however, because the connection of the thick longitudinal threads of the lower fabric in the fine upper fabric causes such severe disruptions that faultless paper production has not been possible. Separate thin binding threads have therefore been used for the connection of double fabrics, but the disadvantage has been observed that the thin binding threads are ground relatively quickly and thus destroyed due to the relative movements occurring between the layers of fabric. These movements are at least partly due to the rather large thickness of the double fabric as a whole.

From DE-PS 30 36 409 a double-layer screen fabric is known, which is shown in the attached drawing figure 1 and in which only a part of the longitudinal threads I, II, and preferably every second longitudinal thread II not only in the upper layer III, but also integrates into the lower layer IV of the cross threads. Since each longitudinal thread I and II is involved in the binding of the surface, i.e. the paper side of the sieve, in these sieve fabrics, the longitudinal threads II, which bind in both transverse thread layers, have to be woven from a separate warp thread roller because of their greater length. Despite this effort, the longitudinal threads I, which are only bound in the upper transverse thread layer, take a higher position after fixing on the paper side than those longitudinal threads which are also bound in the lower transverse thread layer, since the latter longitudinal threads because during their lower binding during of the fixing process be pulled down. However, this affects the paper side so that such double fabrics can only be used for mark-insensitive types of paper.

The object of the invention is therefore to combine the advantages of the double-layer fabrics, which are provided with only one longitudinal thread system, and the advantages of multiple fabrics, which have at least two longitudinal thread systems, without having to take over the disadvantages shown.

This object is achieved in that the two sets of longitudinal threads or the three sets of longitudinal threads with the upper layer of transverse threads form a repeating weaving pattern in which at least some of the upper transverse threads are traversed by at least three successive longitudinal threads and then crossed by at least three successive longitudinal threads at least two of the last at least three successive longitudinal threads if two sets of longitudinal threads are used, at least two belong to the first set and one to the second set and if three sets of longitudinal threads are used, at least two belong to the first set and one to the second set of longitudinal threads and in the case of the use of two as well as three sets of longitudinal threads, this last-mentioned longitudinal thread of the second set only crosses an upper transverse thread within the weaving pattern (repeat), while the longitudinal threads of the first set do at least ns cross two consecutive upper cross threads once within the weaving pattern.

This construction ensures that the thickness of the overall fabric, that of the known double fabrics is often more than 50% larger than in double-layer fabrics, is significantly reduced so that it corresponds to the thickness of comparable double-layer fabrics. The clear separation and spacing of the lower and upper fabric layer as an inevitable consequence of the use of separate binding threads is eliminated in the double fabric according to the invention, which also avoids the disadvantages of too high a fabric thickness, namely the dragging of water as well as strong relative movements in the fabric body due to an excessively large water storage volume when passing through the roller system of the wet end due to constant bending alternating stresses.

In the event that the double fabric as a screen fabric for the wet end of a paper machine for dewatering and forming a paper web consists of three sets of longitudinal threads and at least one upper and one lower layer of transverse threads, the first set of longitudinal threads only with the upper layer of transverse threads, the second set Longitudinal threads with two layers of transverse threads and the third set of longitudinal threads only woven with the lower layer of transverse threads, the solution to the above object is achieved in that the three sets of longitudinal threads with the upper layer of transverse threads form a repeating weaving pattern in which at least one part the upper transverse threads are traversed by at least three successive longitudinal threads and then crossed by at least three successive longitudinal threads, at least two of the latter longitudinal threads belonging to the first set and one to the second set of longitudinal threads and this longitudinal thread of the second set being only one upper thread n Cross thread crosses within the weave pattern (repeat), while the longitudinal threads of the first set cross at least once within the weave pattern two successive upper cross threads.

Advantageous embodiments of the invention are characterized in the subclaims.

It has proven to be expedient to have the first set of longitudinal threads with the upper layer of transverse threads form a weaving pattern in which at least some of the upper transverse threads alternately pass underneath and across the longitudinal threads of the first set in pairs.

The last-mentioned embodiment can be further developed in that in the weaving pattern another part of the upper transverse threads alternately passes underneath and crosses the longitudinal threads of the first set, or in that those upper transverse threads which alternately pass under and cross the longitudinal threads of the first set in order one or two longitudinal threads of the first set are offset with respect to each other.

Another advantageous fabric construction variant follows the one in which in the weave pattern another part of the upper transverse threads alternately passes underneath and crosses the longitudinal threads of the first set, in that those upper transverse threads which alternately pass underneath and separately the longitudinal threads of the first set cross, in each case one longitudinal thread of the first set are offset with respect to one another.

According to a further advantageous embodiment, the lower transverse threads can span three successive longitudinal threads of the second set and all the longitudinal threads of the first set downwards, as seen from the underside of the fabric.

There is also the advantageous possibility that the lower transverse threads seven consecutive longitudinal threads of the second set and all longitudinal threads of the first set span down.

If three sets of longitudinal threads are used, two successive ones, one belonging to the second set of longitudinal threads and the other to the third set of longitudinal threads, can be bound in such a way that they are not bound in the same transverse threads of the lower layer.

Regardless of whether two or three sets of longitudinal threads are used in the double fabric according to the invention, the fabric can be designed according to a further embodiment so that the longitudinal threads of the second set at the points where they cross an upper transverse thread, a plane that lies below the plane which is affected by the longitudinal threads of the first set at those points at which these longitudinal threads of the first set cross the upper transverse threads. The two planes can be spaced apart by at least 15% of the largest diameter of the longitudinal threads of the first or second set.

It is generally true for all variations of the double fabric of the type explained above that the longitudinal threads can have different diameters and can consist of different materials.

Fig. 1

eine Schnittansicht entlang der Längsfäden eines bekannten doppellagigen Gewebes,bei welchem nur ein Teil der Längsfäden II in der unteren Lage von Querfäden einbindet, alle Längsfäden I und II jedoch an der Bindung der papierseitigen Oberflächenstruktur beteiligt sind;

Fig. 2

eine Schnittansicht längs der Längsfäden des erfindungsgemäßen Doppelgewebes, entsprechend den in den Fig. 4 und 5 dargestellten Ausführungsformen;

Fig. 3

eine Schnittansicht längs der Längsfäden des erfindungsgemäßen Doppelgewebes, entsprechend den in den Fig. 7 und 8 dargestellten Ausführungsformen;

Fig. 4

eine Draufsicht auf die Oberlage bzw. Papierseite eines erfindungsgemäßen Doppelgewebes, wobei die schraffierten Stellen zeigen, wie und wo die Längsfäden des zweiten Satzes gemäß der Ausführung nach Fig. 5 eingebunden sind;

Fig. 5

eine Draufsicht auf die untere Lage bzw. Laufseite eines erfindungsgemäßen Doppelgewebes der in den Fig. 2 und 4 dargestellten Art, wobei die schraffierten Stellen der Längsfäden des zweiten Satzes die Querfäden der oberen Lage an den in Fig. 4 schraffierten Stellen überqueren und die Kreise a) und b) in den Fig. 4 und 5 die Zuordnung bzw. Position der beiden Lagen zueinander markieren;

Fig. 6

eine Draufsicht auf die untere Lage bzw. Laufseite eines erfindungsgemäßen Doppelgewbes, dessen obere Lage bzw. Papierseite in Fig. 4 dargestellt ist, wobei die Kreise a) und c) wiederum die Position der beiden Lagen zueinander markieren;

Fig. 7

die Draufsicht der papierseitigen Lage einer weiteren Ausführungsform des erfindungsgemäßen Doppelgewebes, und

Fig. 8

die Draufsicht der laufseitigen Lage der weiteren Ausführungsform des erfindungsgemäßen Doppelgewebes von Fig. 7, wobei die Kreise d) und e) wiederum die Position der beiden Lagen zueinander markieren.

The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawing. The drawing shows:

Fig. 1

a sectional view along the longitudinal threads of a known double-layer fabric, in which only a part of the longitudinal threads II binds in the lower layer of transverse threads, but all the longitudinal threads I and II are involved in the binding of the paper-side surface structure;

Fig. 2

a sectional view along the longitudinal threads of the double fabric according to the invention, corresponding to the embodiments shown in Figures 4 and 5;

Fig. 3

a sectional view along the longitudinal threads of the double fabric according to the invention, corresponding to the embodiments shown in Figures 7 and 8;

Fig. 4

a plan view of the top layer or paper side of a double fabric according to the invention, the hatched areas showing how and where the longitudinal threads of the second set are incorporated according to the embodiment of FIG. 5;

Fig. 5

a plan view of the lower layer or running side of a double fabric according to the invention of the type shown in Figs. 2 and 4, the hatched locations of the longitudinal threads of the second set cross the transverse threads of the upper layer at the hatched locations in Fig. 4 and the circles a ) and b) mark the assignment or position of the two layers to one another in FIGS. 4 and 5;

Fig. 6

a plan view of the lower layer or running side of a double fabric according to the invention, the upper layer or paper side is shown in Fig. 4, the circles a) and c) again marking the position of the two layers to each other;

Fig. 7

the top view of the paper-side layer of a further embodiment of the double fabric according to the invention, and

Fig. 8

the top view of the running-side layer of the further embodiment of the double fabric according to the invention from FIG. 7, the circles d) and e) again marking the position of the two layers relative to one another.

The double fabric or screen fabric shown in FIG. 1 is known and was mentioned at the beginning. It is therefore not explained in more detail here.

The screen fabric shown in section in FIG. 2 is woven with 8 strands and is shown in FIG. 4 in a top view of the paper side and in FIG. 5 in a top view of the running side.

This screen fabric has a total of approximately 75 longitudinal threads of the first set 10 to 13; 10 'to 13', and the second set 20 to 23; 20 'to 23', per cm of polyester with a diameter of 0.15 mm. Its upper cross threads 40 to 47 are also made of polyester and have a diameter of 0.13 to 0.15 mm, while the diameter of the lower cross threads 50 to 53 is 0.20 mm or 0.22 mm and every second cross thread is made of polyamide can.

Since the connection of the longitudinal threads 20 to 23; 20 'to 23' of the second set with the upper fabric on inward floating of the upper transverse threads 41, 43, 45, 47; 41 ', 43', 45 ', 47' occurs, there are no surface defects in the upper tissue and thus no conspicuous marking. The longitudinal threads 20 to 23; 20 'to 23' of the second set tangent at those points 7 where they cross an upper transverse thread, a plane which is at least 10% of the diameter of a longitudinal thread of the first set lower than the plane from the upward floats 8 of the longitudinal threads 10 to 13, 10 'to 13' of the first Set is affected, measured on the uncut sieve.

The distance between the two planes is essentially generated by the type of weave and not by the formation of so-called "wells", as they occur in known double fabrics.

When ground, this screen fabric has a thickness of approx. 0.63 to 0.56 mm and is therefore not significantly thicker than the known double-layer fabrics of corresponding fineness. The change from longer to shorter floats of the transverse threads 40 to 47 on the paper side results in a low-marking surface which enables very favorable fiber placement and fiber distribution of the paper stock. Despite the relatively high longitudinal thread density and the relatively high number of transverse threads on the paper side of approx. 34 / cm, this screen fabric still has a good air permeability of approx. 2,200 l / m². s.

In this screen fabric, as can be seen from FIGS. 4 and 5, a construction is realized which is characterized in that the two sets of longitudinal threads 10 to 13 and 20 to 23 designated with 1 and 2 with the upper layer of transverse threads 40 to 47 form a repeating weave pattern in which at least a portion of the upper transverse threads 41, 43, 45, 47 are traversed by five successive longitudinal threads and then crossed by three successive longitudinal threads, two of the last three successive longitudinal threads being the first set 1 and one the belong to the second set 2 and the latter longitudinal thread of the second set only crosses an upper transverse thread within the weaving pattern or repeat, while the longitudinal threads of the first set twice within cross two consecutive upper cross threads of the weaving pattern.

The hatched areas in FIG. 4 show how and where the longitudinal threads 20 to 23 of the second set 2 are incorporated with reference to FIG. 5. Here, the special embodiment is realized that those upper transverse threads 41, 43, 45, 47, which alternately pass underneath and cross the longitudinal threads of the first set 1 in pairs, are offset with respect to one another by one longitudinal thread of the first set 1. It can also be seen that there is also the possibility of those upper transverse threads 40, 42, 44, 46 which alternately pass underneath and cross the longitudinal threads of the first set 1 in order to offset one longitudinal thread of the first set 1 in relation to one another.

In the plan view of the underside or running side of the screen fabric, which can be seen from Fig. 5, the hatched locations of the longitudinal threads 20 to 23 of the second set are arranged so that they the transverse threads 41, 43, 45, 47 of the upper layer on the Cross hatched points in FIG. 4, the circles a and b drawn in FIGS. 4 and 5 being intended to indicate the assignment or position of the two layers to one another.

4 shows the special embodiment of the fabric, in which the lower transverse threads 50 to 53 span three successive longitudinal threads of the second set 2 and span all the longitudinal threads of the first set 1, seen from the underside of the fabric, downward.

From the top view shown in FIG. 6 on the bottom or barrel side of an embodiment of the screen fabric according to the invention, that of the one shown in FIG. 4 A top view of the top or paper side is to be assigned, the circles denoted by a and c marking the positions of the two fabric layers relative to one another, resulting in a further embodiment of the screen fabric construction. This embodiment is characterized in that not only those upper transverse threads 41, 43, 45, 47, which cross the longitudinal threads of the first set 1 alternately under and over, are offset by one longitudinal thread of the first set 1 in relation to each other, but that the lower transverse threads 60 to 67 span seven consecutive longitudinal threads of the second longitudinal thread set 2 and all the longitudinal threads of the first set 1 downwards, as seen from the underside of the fabric. The lower or running transverse threads 60 to 67 form very long floats, which further increases the available wear volume.

3, 7 and 8, a further embodiment of the screen fabric forming double fabric according to the invention is shown, in which a third set of longitudinal threads 3, consisting of the longitudinal threads 30 to 33, is used, the transverse threads 50 'to 53 only with the lower layer 'Is woven. Here, the three sets of longitudinal threads 1, 2, 3 with the upper layer of transverse threads 40 'to 47' also form a repeating weave pattern, in which at least some of the upper transverse threads 41 ', 43', 45 ', 47' are traversed by five successive longitudinal threads and then crossed by three successive longitudinal threads, two of the latter longitudinal threads belonging to the first set 1 and one to the second longitudinal thread set 2, and the longitudinal thread of the second set crossing only one upper transverse thread within the weaving pattern or repeat, while the longitudinal threads of the first Set twice within the weaving pattern or repeat Cross two successive upper cross threads.

Fig. 7 shows a further top view of the upper or paper-side layer of a top view of Fig. 4 comparable embodiment of the screen fabric, in which those upper transverse threads 41 ', 43', 45 ', 47', which alternate the longitudinal threads of the first set 1 Cross underneath and in pairs, in each case two longitudinal threads of the first set 1 are offset with respect to one another, and those upper transverse threads 40, 42, 44, 46; 40 ', 42', 44 ', 46', which alternately pass underneath and cross the longitudinal threads of the first set 1, each offset by a longitudinal thread of the first set 1 with respect to one another.

FIG. 8 shows the lower or running layer of the fabric belonging to the upper or paper-side layer of the screen fabric shown in FIG. 7, the circles denoted by d and e in the last two drawing figures indicating the position of the two layers relative to one another.

It goes without saying that the longitudinal threads can have different diameters and can consist of different materials.

Furthermore, in the cases where, in the screen fabric according to the invention, which is equipped with either two sets of longitudinal threads or with three sets of longitudinal threads, the longitudinal threads of the second set 2 can touch a plane at the points 7 where they cross an upper transverse thread. which lies below the plane which is affected by the longitudinal threads of the first set 1 at those points 8 (FIG. 2) at which these longitudinal threads of the first set the upper transverse threads cross. The two planes can be spaced from each other by at least 15% of the largest diameter of the longitudinal threads 10 to 13, 20 to 23 of the first or second set.

If, in the embodiment of the screen fabric according to the invention, in which the longitudinal threads 20 to 23 of the second set 2 are just as common as the longitudinal threads 10 to 13 of the first set 1, the same diameter is also chosen for all the longitudinal threads, a double fabric is produced, which is of one double-layered fabric is almost indistinguishable insofar as this double-woven fabric has the well-known good properties of a double-layered fabric, but despite a comparable thickness it has a significantly higher volume of wear, since in addition to the lower transverse threads 50 to 53, the longitudinal threads 60 to 67 of the second set 2 can wear out completely.

This results in an extended service life of this screen fabric without the risk of transverse tearing, since the longitudinal threads of the first set 1 are only subjected to wear when the entire lower layer of transverse threads and longitudinal threads is completely worn out. Even then, the longitudinal threads of the first set 1 are still partially protected by the inward floating of the upper transverse threads.

Claims (12)

1. Double fabric as forming wire for the wet end of a paper making machine for dewatering and formation of a paper web, which wire consists of two or three sets of longitudinal threads and at least one upper and one lower layer of cross threads, wherein the first set of longitudinal threads (1) are interwoven only with the upper layer of cross threads, and the second set of longitudinal threads (2) are interwoven with the lower layer of cross threads (50 - 53; 60 - 67) as well as at least partly with the upper layer of cross threads (40 - 47), and eventually the third set of longitudinal threads (3) is interwoven only with the lower layer of the cross threads, characterized therein that the tow sets of longitudinal threads (1, 2) or the three sets of longitudinal threads (1, 2, 3) configure with the upper layer of cross threads (40 - 47) a repeating weave pattern in which at least some of the upper cross threads (41, 43, 45, 47; 41', 43', 45', 47') are undercrossed by at least three subsequently following longitudinal threads and are thereafter overcrossed by at least three subsequently following longitudinal threads, wherein of the last mentioned at least three subsequently following longitudinal threads in case usage of three sets of longitudinal threads at least two belong to the first set (1) and one belongs to the second set (2) and in case of usage of three sets of longitudinal threads at least two of them belong to the first set (1) and one of them to the second set longitudinal threads (2) and in case of usage of two as well as of three sets of longitudinal threads this last mentioned longitudinal thread of the second set (2) overcrosses only one upper cross thread within the weave pattern (repeat), whereas the longitudinal threads of the first set (1) overcross within the weave pattern at least one time two subsequently following upper cross threads.
2. Double fabric according to claim 1, characterized in that the first set longitudinal threads (1) provides with the upper layer of cross threads (40 - 46; 40' - 47') a weave pattern, in which at least a part of the upper cross threads (41, 43, 45, 47; 41', 43', 45', 47') alternately and in pairs undercross and overcross the longitudinal threads of the first set (1).
3. Double fabric according to claim 2, characterized in that within the weave pattern another part of the upper cross threads (40, 42, 44, 46; 40', 42', 44', 46') alternately and solely undercross and overcross the longitudinal threads of the first set (1).
4. Double fabric according to claim 2, characterized in that those upper cross threads (41, 43, 45, 47) undercrossing and overcrossing alternately and in pairs the longitudinal threads of the first set (1) are each offset with respect to one another by one longitudinal thread of the first set (1).
5. Double fabric according to claim 2, characterized in that those upper cross threads (41', 43', 45', 47') undercrossing and overcrossing alternately and in pairs the longitudinal threads of the first set (1) are each offset with respect to one another by two longitudinal threads of the first set (1).
6. Double fabric according to claim 3, characterized in that those upper cross threads (40, 42, 44, 46; 40', 42', 44', 46') which are alternately and solely undercrossing and overcrossing the longitudinal threads of the first set (1) are each offset with respect to one another by one longitudinal thread of the first set.
7. Double fabric according to one of the claims 1 to 6, characterized in that the lower cross threads (50 - 53) overspan downwardly three longitudinal threads of the second set (2) succeeding one another and all longitudinal threads of the first set (1).
8. Double fabric according to one of the claims 1 to 6, characterized in that the lower cross threads (60 - 67) overspan downwardly seven longitudinal threads of the second set of longitudinal threads (2) succeeding one another and all longitudinal threads of the first set (1)(as seen from the underside of the fabric).
9. Double fabric according to one of the claims 1 to 3, characterized in that two subsequently following longitudinal threads, one of which belongs to the second set (2) of longitudinal threads and the other one to the third set of longitudinal threads (3) are not interwoven with the same cross threads (50' - 53') of the lower layer.
10. Double fabric according to claim 1, characterized in that the longitudinal threads of the second set are at those locations in which they overcross one upper cross thread tangent to a level positioned below that level which is tangented by the longitudinal threads of the first set (1) at those locations (8) in which these longitudinal threads of the first set overcross the upper cross threads.
11. Double fabric according to claim 10, characterized in that the two levels are distantly arranged from one another by at least 10% of the greatest diameter of the longitudinal threads (10 - 13; 10' - 13') of the first or second set.
12. Double fabric according to one of the claims 1 to 11, characterized in that the longitudinal threads have different diameters and/or consist of different material.

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