EP0120337A1 - Paper machine fabric in a texture weave which does not show a longitudinal symmetric axis - Google Patents

Abstract

The paper machine clothing consists of a fabric whose weave repeat does not have an axis of symmetry extending in the longitudinal direction and that at least in one part of the one half of the sieve (1) can have a mirror-symmetrical weave to that in at least a part of the second half of the sieve (2). At the joint where the areas are woven with correction longitudinal wires (5) that prevent the cross wires (4) from floating too long on the running side.

Description

The invention relates to a paper machine clothing comprising interwoven longitudinal and transverse threads, the weave not having an axis of symmetry running in the longitudinal direction and the weave in a first area being mirror-symmetrical to that in a second area.

With the exception of a few bonds, almost all of the bonds used in the manufacture of paper machine clothing have an asymmetrical structure, i. H. the binding points of the longitudinal wires with the cross wires are strung together in the diagonal direction. As a result, a fabric with an asymmetrical structure in the direction of the diagonal has greater extensibility than perpendicular to it. The stress-strain behavior of the fabric is therefore dependent on the direction.

In all twill weaves, this diagonal structure is particularly pronounced as a so-called twill ridge.

In the case of fabrics in satin weave, the tying points are evenly distributed over the fabric surface and do not touch each other. This creates two, three or more diagonals running parallel to each other in each weave repeat instead of the single diagonal of a twill weave. This makes the fabric image of an atlas weave refined and the one left in the paper web

Marking is less noticeable, but the asymmetrical binding structure is retained and has a greater impact the more asymmetrical the binding points of successive wires are.

When loaded in the longitudinal direction, the stress is distributed symmetrically from row of rows to row of rows in the case of symmetrical bindings. H. the force components to the right and to the left cancel each other out. In the case of asymmetrical bonds, on the other hand, a force component predominates and a distortion of the fabric arises, since the binding points located directly behind or close to one another make the deformability of the fabric direction-dependent. This is strongest in twill weaves. For this reason, these fabrics can only be used as paper machine screens up to a 4-strand diagonal twill, and moreover only on machines with very low specific power consumption, e.g. B. Tissue machines. Even in these cases, screens in pure twill weave are quickly warped.

Atlas bindings are slightly better in this regard, since the asymmetry is less. Single-layer, 5-strand atlas sieves can be operated without any problems, and sieves with 7 to 12-strand weave are used for double-layer fabrics, which are known to have a high degree of filling of 100 - 115% of the warp wires. However, even with double-layer screens, 7-binding bindings occur on high-speed paper machines with a working speed of 900 m / min. and more regulation problems because the screen moves sideways in the direction the diagonal is pointing.

Lateral distortion makes the work even stronger of the tissue. It sometimes happens that a tissue is unusable and is cut out because it warps too much in one side direction in the tensioned zone. While the screen on the breast roller, where the paper mass is transferred from the headbox onto the screen, is still completely centered, it comes e.g. B. at the other end of the wire section with a lateral distortion of 7-10 cm. Since the paper web formed moves to the side with the sieve, it can get outside the working width of the egoutteur, so that further work with the sieve becomes impossible.

If one changes the diagonal of the sieve during weaving, i. H. e.g. B. Instead of a screen with a left diagonal, the fabric is woven with a right diagonal, so the screen warps in the opposite direction with all the related problems for the papermaker. The construction of the paper machine in the upper sieve strand is so unfavorable that no mechanical action can be taken to counteract this warping of the sieve. The screen guide rollers can only be offset on one side in the return line so that the screen is brought back to the center.

_' Warping in the diagonal direction of a paper machine screen with an asymmetrical weave is known. Use has already been made of this in order to prevent the suction pad surface from grooving (groove-shaped removal of the support surface) in the case of a chain runner screen. By weaving the sieve alternately with the left diagonal and the right diagonal, a zigzag-shaped course of the warp wires has been achieved, whereby the aforementioned grooving of the suction pad was avoided (DE-AS 1 710 373).

From DE-OS 30 44 762 a papermaker's fabric is known in which the binding alternates in the edge strips from repeat to repeat in mirror symmetry. This measure is intended to achieve shot floatings of different lengths in the edge regions, in order to delay the occurrence of longitudinal cracks.

The invention has for its object to provide a paper machine clothing from a fabric, the binding on the one hand does not have a longitudinal axis of symmetry, but on the other hand does not distort or distort in use.

This object is achieved in that the weave is mirror-symmetrical at least in parts of the two fabric halves of the paper machine clothing.

The basic idea of the invention is not to produce the entire fabric in a single weave, but to achieve by varying the weave that those forces which try to distort the paper machine screen in one direction compensate each other. For this purpose, the left half of the sieve or at least part of it is made with a binding that allows the sieve to run to the left, while the right half of the sieve or at least part of it is made with a binding that pulls the sieve to the right. Since the forces pulling to the right and to the left then cancel each other out, the paper machine clothing is running. A positive side effect is that the paper machine clothing is simultaneously stretched somewhat in width by these forces.

This counteracts the formation of central longitudinal folds, which are not infrequent as a result of sagging weak guide rollers or in unfavorable drive conditions in the middle of the screen and would make the screen unusable.

Symmetrical weaves are in particular plain weave and four-twill cross twill weave. Unsymmetrical bindings are all basic twill weaves and satin weaves. In the present case, a bond would also be referred to as symmetrical if the symmetry only arises after a displacement in the longitudinal direction, as is the case with the four-twill cross-twill weave.

The paper machine clothing according to the invention may only be used in a certain running direction, since the opposite effect would also occur in the opposite running direction, ie. H. the sieve would converge towards the middle.

At the location of the paper machine clothing at which the diagonal direction is changed - generally this is the middle of the screen - there are deviations in the length of the weft floats both on the paper side and on the running side. The longer weft floats have the consequence that the weft wires are particularly exposed to abrasion at these points and are the first to be ground through. This difficulty cannot be solved simply by changing the diagonal direction, with or without additional displacement by a few wires in the longitudinal direction. However, it has been shown that only the wire floats protruding from the tissue level interfere. Flotations that protrude beyond the screen level on the paper side mark the paper web. However, if the difference in float length is not too great, they can be leveled by sanding the screen surface on the paper side. This would create greater difficulties cause too long floats on the barrel side, since the protrusion of the weft wire due to hydrodynamic pressure waves can mark the paper web and even tear it. In addition, an outstanding weft wire grinds through early.

However, it has been shown that, on the contrary, threads hardly cause difficulties that lie deeper in the fabric than is customary with the respective weave. With the conventional warp wire density of e.g. B. 60 or 70 threads / cm, the absence of the support surface by a single somewhat recessed running wire float is not at all recognizable. Likewise, a single, shortened shot bath is harmless on the barrel side. According to claim 3, longitudinal correction threads are therefore woven in along the butt joint where the areas with different weave meet so that each weft thread on the paper or barrel side does not have a substantially longer float. Too long shot floats along the joint of both diagonals are shortened by one or more correction warp wires, which are guided in a repeat that is completely independent of the rest of the fabric. These correction warp wires are driven by additional harness frames. Since there are only 1 to 3 individual threads, the elaborate frame can also be dispensed with, and the actuation of these threads can be achieved using individual, individually driven, special strands. Since the correction warp threads have a course that is independent of the rest of the weave, they can tie off any weft threads that have a float that is too long on the running side, thereby preventing the weft floats from protruding from the sieve level on the running side. The inventive paper machine clothing, in the preferred embodiment with mutually mirror-image _G ewebehälften in the manner made that the warp wires are drawn into the strands of the shaft frame in the usual half of a sieve. In order to avoid an excessively high number of shafts, the sieve feed is carried out in reverse order from the middle of the fabric. In a four-shaft fabric, for. B. on the left with the sequence 1, 2, 3 and 4 and from the middle on the right in the sequence 4, 3, 2, 1. In this way, the bonding points a V pattern in the fabric form, with breaking in the middle fabric _B indungsdiagonale without additional shafts.

The basic idea of the invention is applicable to single-layer as well as double-layer and two-layer or multi-layer composite fabrics. In the case of two-layer or multi-layer composite fabrics, all or only some of the layers can be designed according to the invention. Is z. B. to weave a two-ply composite fabric with a fine top layer in plain weave and with a coarser bottom layer in four-twill weave, only the bottom layer needs to be equipped with a V-shaped diagonal and with correction wires, since the top layer already has a lengthwise weave Has axis of symmetry.

The invention is applicable to both the _F laughing weave arrears seam forming paper machine clothing as well as the circular weaving applicable. When circular weaving, the embodiment of the invention is simplified in that the first half of the screen z. B. can be woven in right-hand diagonal weave, if the corrective longitudinal wires (weft wires) are pulled through, the weave is changed accordingly, so that the long floats of the transverse wires (warp wires) are shortened and then the weaving of the second half of the sieve with the woven cartridge with the opposite Diagonal direction, here left diagonal, is woven.

• Fig. 1 einen Ausschnitt aus der Laufseite eines Papiermaschinensiebes einschliesslich der Stosstelle der beiden Bereiche mit spiegelsymmetrischer Bindung;
• Fig. 2 eine Darstellung ähnlich der von Fig. l, jedoch mit geändertem Verlauf der Korrekturkettdrähte;
• Fig. la und Fig. 2a den Verlauf der normalen Kettdrähte und der Korrekturkettdrähte von Fig. 1 bzw. Fig. 2;
• Fig. 3 und 4 die Papierseite eines 7-schäftigen, doppellagigen Gewebes, und zwar in naturgetreuer Darstellung bzw. als schematisches Webbild;
• Fig. 5 und 6 Darstellungen der Laufseite der Gewebe von _Fig. 3 und 4, und zwar ohne bzw. mit Korrektur-kettdrähten;
• Fig. 6a den Verlauf der normalen Kettdrähte und der Korrekturkettdrähte des Gewebes der Fig. 3 bis 6 und
• Fig. 7 und 8 schematische Darstellungen zu den Fig. 5 bzw. 6.

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

• Figure 1 shows a section of the running side of a paper machine screen including the butt joint of the two areas with mirror-symmetrical binding.
• FIG. 2 shows a representation similar to that of FIG. 1, but with a modified course of the correction warp wires;
• Fig. La and 2a, the course of the normal warp wires and the correction warp wires of Fig. 1 and Fig. 2;
• 3 and 4 the paper side of a 7-strand, double-layer fabric, namely in a lifelike representation or as a schematic web image;
• FIGS. 5 and 6 are illustrations of the running side of the fabric of _F ig. 3 and 4, with or without correction warp wires;
• Fig. 6a the course of the normal warp wires and the correction warp wires of the fabric of Figs. 3 to 6 and
• 7 and 8 are schematic representations of FIGS. 5 and 6 respectively.

Fig. 1 is an illustration of a section of the running side of a paper machine screen with four twill weave. The cutout comprises part of the left half 1 and the right halves 2 of the paper machine screen, so that the impact point can be seen. The fabric consists of warp wires 3 and weft wires 4. Between the left half 1 and the right half 2 there is also a correction tur warp wire 5 woven. The paper machine sieve has three weft floats on the running side, so it is a so-called weft runner. While the normal warp wires 3 have only short floats corresponding to a weft wire 4 on the running side, the correction warp wire 5 has longer floats comprising two weft wires 4. Without these longer floats of the correction warp wire 5 on the running side z. B. the weft 7 too long floatation of 5 warp wires. This long float is divided by the correction warp wire 5 into two short floats of two warp wires each.

_F ig. la shows in section in the longitudinal direction the course of the normal warp wires 3 or that of the correction warp wires 5.

_F ig. 2 shows the running side of a paper machine wire, similar to that of FIG. 1, but with two correction wires 5, between which a normal warp wire 3 lies. In addition to the normal binding points, the correction warp wires have 8 additional binding points 9 around the weft wire 10 to be shortened.

3 to 8 relate to a double-layer, 7-shaft fabric, with FIGS. 3 and 4 showing the paper side in a lifelike or schematic representation. On the paper side, the normal length of the weft floats is 4 warp wires. Only the weft wire 11 has a float that is longer by one warp wire. This small irregularity is not disturbing and can be compensated for by slightly grinding the screen, so that additional weaving in of a correction warp wire is not necessary to shorten this weft floatation.

5 and 7 show the running side of the double-layer, 3 and 4, namely without correction warp wires in a true-to-life or schematic representation. The circled numbers in FIG. 5 each indicate the length of the shot floats. Without correction wires, therefore, deviating from the normal float length corresponding to six warp wires, there are also those with a length of up to nine warp wires.

6 and 8 show a representation similar to that of FIGS. 5 and 7, but with correction warp wires 5 to shorten the excessively long weft floats. As can best be seen from a comparison of the schematic representations of FIGS. 7 and 8, the correction warp wires 5 are normal warp wires 3 with additional binding points, which are highlighted in FIG. 8 by a cross in the binding point squares.

The course of the normal warp wires 3 and the correction warp wires 5 is shown in Fig. 6a. It can be seen from this that the correction warp wires 5 on the paper side have the same course as the normal warp wires 3 and only on the running side, instead of only tying a weft wire (binding point 12), are tied with a further weft wire (binding point 13).

Claims (3)

1. Paper machine clothing made of interwoven longitudinal and transverse threads, the weave having no longitudinal axis of symmetry and in a first area of the paper machine clothing the weave being mirror-symmetrical to that in a second area, characterized in that the first and second areas each have at least one comprise part of the two opposite fabric halves of the paper machine clothing. 2. Paper machine clothing according to claim 1, characterized in that the first and the second area are the two fabric halves separated by the longitudinal center line. 3. Paper machine clothing according to claim 2, characterized in that one or more longitudinal threads are woven in along the butt joint of the two areas in such a way that no floatings of the transverse threads are present on the running side, which are substantially longer than the floatings of the fabric weave in question Cross threads.

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