WOUND CLOTHING

Abstract

A clothing for a machine for producing a fibrous web, in particular a paper, board or tissue web, includes a first layer of first strips which are oriented parallel to one another, and a second layer of second strips which are oriented parallel to one another. The second layer is disposed on the first layer and is connected to the first layer. The adjacent first strips are spaced apart from one another and the adjacent second strips are also spaced apart from one another, so that a composite including the first layer and the second layer has a plurality of through openings for dewatering the fibrous web. A production method for producing a clothing of this type is also provided.

Description

The invention relates to clothing for a machine for producing a fibrous web, in particular a paper, board or tissue web, comprising a first layer of first strips which are oriented parallel to one another, and a second layer of second strips which are oriented parallel to one another, which second layer is arranged on the first layer and is connected to the first layer. Furthermore, the invention relates to a production method for producing clothing of this type.

In machines for producing a fibrous web, in particular a paper, board or tissue web, firstly a fibrous suspension is applied to a forming fabric in a forming section. The actual fibrous web is formed on the forming fabric by water being extracted from the suspension, which initially very predominantly contains water. In the machine, the forming section is followed by further sections, specifically as a rule at least one press section and a drying section, in which further moisture is extracted from the fibrous web by mechanical pressure and/or heat, before the finished product can be wound up at the end of the machine. In all these sections, endlessly circulating clothing is provided, which transports the fibrous web and is permeable for the purpose of drying the same.

Normally, the clothing is currently produced by weaving thermoplastic monofilaments, but other production methods are also known. Thus, the clothing can, for example, also be formed as spiral fabrics or as perforated, in particular laser-drilled, films. Furthermore, the clothing can also be produced by threads or strips being wound helically over two rolls having parallel longitudinal axes, the side edges of the threads or strips being firmly connected to one another to stabilize the structure and/or at least one further layer of threads or strips wound helically being applied over the first layer and connected thereto. Such clothing is known, for example from EP 1 354 094 B1.

The disadvantage with such clothing is that the production process is relatively complicated, since a large quantity of perforations finally still have to be introduced into the clothing in order to impart the necessary permeability to the clothing.

It is therefore an object of the present invention to provide clothing which solves or at least reduces the disadvantages of the prior art. In particular, the production of appropriate clothing is to be more simply possible.

This object is achieved by the features of the independent claims. Advantageous developments of the invention are the subject matter of the dependent claims.

According to a first aspect of the invention, this object is thus achieved by a clothing of the generic type described at the beginning which, in particular, is distinguished by the fact that both adjacent first strips are spaced apart from one another and also adjacent second strips are spaced apart from one another, so that the composite comprising the first layer and the second layer has a plurality of through openings for dewatering the fibrous web.

In this way, it is no longer necessary to introduce perforations into the clothing as a separate method step in order to impart the necessary permeability to the clothing, since through openings are already produced during the winding. Even if perforations are subsequently also introduced, these do not have to be as numerous as in the prior art in order to achieve the same permeability. Thus, the outlay on manufacture can be reduced in a simple way. Likewise, the quantity of starting material needed for producing the clothing decreases.

In principle, it is conceivable that the clothing according to the invention is also used as a forming fabric or as a press felt in the machine. However, the advantages of the present invention come into play particularly well if the clothing according to the invention is used as a dryer fabric. In this case, provision can be made for the dryer fabric to be formed substantially exclusively from the first layer and the second layer, that is to say has no further layers or plies. As a result of the winding process, seam elements are also dispensed with, since the clothing already has an endless form during production. If necessary, however, the wound clothing can also be severed and provided retrospectively with a seam element, for example to permit easier insertion of the clothing into the machine. Under certain circumstances, reinforcements are also further necessary in the edge region of the clothing. During use as a press felt, however, the wound structure must necessarily further be provided with at least one further layer or ply, in particular a felt layer, in order that the press felt can fulfil its intended function. Further precautions should also be taken in a forming fabric, since the wound structure on its own otherwise entails the danger of forming undesired markings in the fibrous web.

Preferably, provision is made for the first strips to have a first angle relative to the cross-machine direction of the clothing which is greater than 0° and less than 90° and preferably lies between 45° and 80°, and for the second strips to have a second angle relative to the cross-machine direction of the clothing which is greater than 90° and less than 180° and preferably lies between 100° and 135°. The machine direction of clothing corresponds to its longitudinal direction, i.e. the direction in which the clothing moves in the machine during intended use. The cross-machine direction, on the other hand, is the direction which is oriented orthogonally to the machine direction in the plane of the clothing.

Provision can be made for the second angle to correspond substantially to 180° minus the first angle. In other words, with respect to the machine direction, the first strips run mirror-symmetrically to the second strips in the plane of the clothing. In this way, the first strips and the second strips can absorb to the same extent the tensile forces which act on the clothing in the machine direction.

Furthermore, it is preferred for the first strips to have a substantially rectangular cross-sectional shape with a first thickness and a first width, and for the second strips to have a substantially rectangular cross-sectional shape with a second thickness and a second width. The width is measured in the plane of the clothing and the thickness is measured orthogonally thereto. As a result of this flat cross-sectional shape, firstly a good contact area between the first strips and the second strips can be provided, so that a stable connection of the two layers can be ensured. Secondly—if the clothing is used as a dryer fabric—good heat transfer can be ensured by the large contact area with the fibrous web, on the one hand, and with the heated drying cylinders, on the other hand. The term “substantially rectangular” means that the cross-sectional shape can also deviate slightly, for example can have rounded corners or a slight convexity on the side surfaces.

The first thickness can differ from the second thickness. In particular in order to avoid undesired markings, it is advantageous if the layer of the first layer and second layer which faces the fibrous web during intended use has strips with a lower thickness than the layer which faces away from the fibrous web during intended use. Thus, the layer which faces away from the fibrous web can primarily ensure the structural stability as a result of its greater thickness, while the layer which faces the fibrous web provides only a low level of unevenness for the contact area with the fibrous web as a result of its lower thickness.

Provision can be made for the first width to correspond substantially to the second width, wherein the first width and the second width preferably have a value between 1 mm and 30 mm, further preferably between 1 mm and 15 mm. These widths have proven to be particularly advantageous during the use of the clothing according to the invention as a dryer fabric.

The through openings can have a substantially rectangular, preferably diamond-like shape, wherein, preferably, all the through openings formed in this way substantially have the identical shape. “The shape of the through openings” is to be understood as the shape which appears when the clothing is looked at orthogonally relative to the plane of the same.

The first strips and the second strips can be connected integrally to one another, in particular welded to one another. This results in a secure hold between the strips of the two layers. For example, a welded connection can be achieved by means of hot air, a hot wedge, ultrasound or hot pressing. An integral connection can additionally or alternatively also be produced by means of an adhesive.

In particular, the first strips and the second strips can be connected to one another by laser welding, for example by means of an NIR laser. For this purpose, it is advantageous if the first strips have a property absorbing the radiation from a laser, in particular an NIR laser, which differs from the second strips. Thus, the laser light can shine through one of the two layers without being absorbed noticeably, while the other layer absorbs the laser light, begins to melt and, as it cools under appropriate pressure, produces the integral welded connection. Alternatively or additionally, of course an auxiliary material, such as for example ClearWeld®, can also be introduced between the first strips and the second strips at the crossing points of the same before the irradiation with the laser light, in order to specifically produce the laser-absorbing action locally there. If the laser beam is aimed directly into a gap between the first strips and the second strips to be connected thereto, both strips can also have an equally high laser light-absorbing property, in particular be colored black.

The strips are preferably substantially formed from a plastic, in particular from a meltable thermoplastic. In principle, unstretched material can of course be used. However, in order to achieve the necessary strength of the strips, according to a development of the invention the first strips and/or the second strips consist either of monoaxially stretched plastic or of biaxially stretched plastic, wherein preferably a biaxially stretched film is cut into the shape of the strips, or consist of a plastic which is provided with fillers and/or reinforcing fibers to increase the strength. “Monoaxially stretched” means that the polymer chains of the plastic already contain a preferential direction as a result of tensile forces, in the extreme case are all oriented in the same direction. The more highly the material is stretched monoaxially, the greater is its modulus of elasticity in the stretching direction and the less the material can stretch still further in this direction under the action of force. Monoaxial stretching is generally carried out as early as when the material is forced through a die in the heated state during an extrusion process. The shear forces acting on the material in the die cause preferential alignment of the polymer chains in the material. “Biaxially stretched” means that the material has been stretched substantially equally highly in two mutually orthogonal directions, so that there are no unique preferential alignments of the polymer chains. Instead, the material has a substantially identical modulus of elasticity, which is increased with respect to an unstretched material, in the two directions in which it has been stretched. Additionally or alternatively to stretching, the strips can be provided with fillers and/or reinforcing fibers to increase the strength. These can be introduced into the strips, for example as early as during the extrusion, or co-extruded with the material. Aramid or glass fibers, for example, are conceivable here.

As already mentioned above, to increase the permeability of the clothing further, it may be advantageous if the first strips and/or the second strips additionally have perforations, in particular laser-drilled perforations, the perforations preferably being smaller than the through openings.

According to a further aspect, the present invention also relates to a method for producing previously described clothing according to the invention, comprising the following steps: a) producing the first layer by a first strip being wound helically over two rolls having parallel longitudinal axes, wherein an interspace is formed between the windings of the first layer, so that the side edges of the first strip do not touch one another, and b) producing the second layer on the first layer, by a second strip being wound helically over the two rolls, wherein an interspace is formed between the windings of the second layer, so that the side edges of the second strip do not touch one another, wherein the strips of the two layers cross in such a way that the composite comprising the first layer and second layer has a plurality of through openings for dewatering the fibrous web. Since the finished clothing needs two defined side edges extending in the machine direction, re-treatment of the clothing formed in this way is necessary at the end, such as, for example, trimming and possibly reinforcing the side edges. As a result of the trimming, depending on the length of the clothing and the selected winding angle, each layer has a structure which consists of a plurality of separate strips, even though the production of each layer can be carried out by only a single strip.

In this method, provision can be made for the first layer to be connected integrally to the second layer, preferably welded, further preferably laser-welded, wherein the connection is optionally carried out during the production of the second layer in step b) or else as a separate step c) following step b). In the first case, for example, a robot arm which winds the second strips over the first strips can simultaneously irradiate the crossing points with laser light in order to produce the welded connection. The welding is preferably carried out on a base such as, for example, a large drum or roll. Similar techniques are known from the production of large pressure tank containers.

As already described further above, provision can be made for the side edges of the clothing to be subsequently re-treated, in particular trimmed and/or reinforced.

An exemplary embodiment of the clothing according to the invention and the production method according to the invention for such clothing will be described in more detail below with reference to FIGS. 1 to 3. In the drawing:

FIG. 1 shows a top view in the viewing direction orthogonal to the plane of the clothing of an imaginary detail of the same, which illustrates the structural design;

FIG. 2 shows a cross-sectional view of a first strip;

FIG. 3 shows a cross-sectional view of a second strip;

FIG. 4 shows a schematic view to illustrate the production method, wherein the production of the first layer by winding helically over two rolls is illustrated here; and

FIG. 5 shows a schematic view like FIG. 4 but from another viewing angle.

In FIG. 1, an imaginary detail of clothing 10 according to the invention, in particular a dryer fabric, is illustrated schematically, wherein the viewing direction is aligned orthogonally relative to the plane in which the clothing 10 lies. The machine direction MD of the clothing 10 points upward in FIG. 1 and extends in the vertical direction, whereas the cross-machine direction CD of the clothing 10 points to the right in FIG. 1 and is oriented in the horizontal direction. The clothing 10 is substantially formed from a first layer 12 which, during the intended use of the clothing 10 in the paper machine, can face away from the fibrous web, and a second layer 22, which is arranged on the first layer 12 and is firmly connected to the latter and which, during the intended use of the clothing 10 in the paper machine, can face the fibrous web. The first layer 12 comprises a plurality of first strips 14, which are all oriented parallel to one another, wherein immediately adjacent first strips 14 are spaced apart from one another, so that their side edges 16, 18 do not touch one another. Relative to the cross-machine direction CD, the first strips 14 are oriented at an angle α which, here, can be 70°, for example. The second layer 22 comprises a plurality of second strips 24, which are likewise all oriented parallel to one another, wherein immediately adjacent second strips 24 are spaced apart from one another so that their side edges 26, 28 do not touch one another. Relative to the cross-machine direction CD, the second strips 24 are oriented at an angle of 180°−α, here, therefore, at an angle of 180°−70°=110°, for example, so that the first strips 14 and the second strips 24 extend mirror-symmetrically relative to one another in relation to an imaginary plane aligned orthogonally to the plane of the image or fabric, which is oriented in the MD direction.

As can be seen in FIG. 2, the first strips 14 have a substantially rectangular cross-sectional shape, with a first thickness d1 and a first width b1. Likewise, the second strips 24 have a substantially rectangular cross-sectional shape, with a second thickness d2 and a second width b2, as can be seen in FIG. 3. In the present example, the first width b1, which, for example, can be 2.2 mm, corresponds to the second width b2. However, the first thickness d1, which, for example, can be 0.5 mm, is somewhat larger than the second thickness b2, which, for example, can be 0.3 mm. The first width b1 and the second width b2 are smaller than a spacing a between two adjacent first strips 14 and two adjacent second strips 24 (see FIG. 1). The gap or spacing a which thus results between two immediately adjacent strips 14, 24 of a corresponding layer 12, 22 can be 1 mm, for example.

In FIG. 1 it is possible to see clearly the diamond-shaped through openings 20 in the clothing 10 which are given by the two layers 12, 22. These through openings 20 are used to dry the fibrous web transported on the clothing 10. At the same time, during intended use, the clothing 10 according to the invention provides a large, largely flat, contact area both on the side facing away from the fibrous web and facing the drying cylinders and also the sides facing away from the fibrous web, which permits good heat transfer and thus efficient drying of the fibrous web.

The first strips 14 and the second strips 24 can be produced from a thermoplastic as monoaxially highly stretched monofilaments by means of an extrusion process, wherein the die of the extruder has a corresponding rectangular shape. Furthermore, the first strips 14 and the second strips 24 have been welded to one another at their respective crossing points, preferably with an NIR laser. To this end, the first strips 14 and/or the second strips 24 can have a laser light-absorbing property, in particular be colored black.

FIGS. 4 and 5 illustrate schematically from two different viewing angles a possible production process for the clothing 10 according to the invention, only the first layer 12 of the clothing 10 being shown in these two figures. Here, a first strip 14 is wound helically over two mutually spaced rolls 30, 32 having parallel longitudinal axes. The winding is carried out in such a way that the side edges 16, 18 of two immediately adjacent windings of the first strip 14 do not touch but have a spacing a from one another. Thus, even in the wrapped region of the two rolls 30, 32, their respective outer surface O can easily be seen.

Next, a second strip 24 would be wound helically over the two rolls 30, 32 and over the first strips 14 of the first layer 12 to form the second layer 22. The winding angle would be chosen such that the diamond-shaped through openings 20 illustrated in FIG. 1 would result. At the end, the side edges of the clothing 10 would be trimmed along the machine direction MD and reinforced to fix the free ends of the first strips 14 and the second strips 24. Optionally, the first strips 14 and/or the second strips 24 can additionally also be perforated, preferably by means of an appropriately powerful laser light source.

LIST OF DESIGNATIONS

• 10 Clothing
• 12 First layer
• 14 First strip
• 16 Side edge
• 18 Side edge
• 20 Through opening
• 22 Second layer
• 24 Second strip
• 26 Side edge
• 28 Side edge
• 30 Roll
• 32 Roll
• α Angle
• CD Cross-machine direction
• b1 First width
• b2 Second width
• d1 First thickness
• d2 Second thickness
• MD Machine direction
• O Outer surface

Claims

1-15. (canceled)

16. A clothing for a machine for producing a fibrous, paper, board or tissue web, the clothing comprising:

a first layer of first strips oriented parallel and adjacent to one another, and a second layer of second strips oriented parallel and adjacent to one another, said second layer disposed on said first layer and connected to said first layer;

said adjacent first strips being spaced apart from one another and said adjacent second strips being spaced apart from one another, forming a composite including said first layer and said second layer, said composite having a plurality of through openings for dewatering the fibrous web.

17. The clothing according to claim 16, wherein the clothing is a dryer fabric.

18. The clothing according to claim 17, wherein the dryer fabric is formed exclusively of said first layer and said second layer.

19. The clothing according to claim 16, wherein:

said first strips are oriented at a first angle being greater than 0° and less than 90° relative to a cross-machine direction of the clothing; and

said second strips are oriented at a second angle being greater than 90° and less than 180° relative to the cross-machine direction of the clothing.

20. The clothing according to claim 19, wherein said first angle lies between 45° and 80° relative to the cross-machine direction of the clothing, and said second angle lies between 100° and 135° relative to the cross-machine direction of the clothing.

21. The clothing according to claim 19, wherein said second angle corresponds to 180° minus said first angle.

22. The clothing according to claim 16, wherein said first strips have a substantially rectangular cross-sectional shape with a first thickness and a first width, and said second strips have a substantially rectangular cross-sectional shape with a second thickness and a second width.

23. The clothing according to claim 22, wherein said first thickness differs from said second thickness, and said thickness of said strips of one of said layers facing the fibrous web during an intended use is lower than said thickness of said strips of another of said layers facing away from the fibrous web during the intended use.

24. The clothing according to claim 22, wherein said first width corresponds substantially to said second width, and said first width and said second width have a value between 1 mm and 30 mm.

25. The clothing according to claim 22, wherein said first width corresponds substantially to said second width, and said first width and said second width have a value between 1 mm and 15 mm.

26. The clothing according to claim 16, wherein said through openings have a substantially rectangular or diamond shape.

27. The clothing according to claim 26, wherein all of said through openings have an identical shape.

28. The clothing according to claim 16, wherein said first strips and said second strips are connected integrally or welded to one another.

29. The clothing according to claim 16, wherein said first strips have a property absorbing radiation from a laser or NIR laser, and said second strips have a property differing from said property of said first strips.

30. The clothing according to claim 16, wherein at least one of said first strips or said second strips are formed either of:

monoaxially stretched plastic or of biaxially stretched plastic, or

a plastic provided with at least one of fillers or reinforcing fibers to increase strength.

31. The clothing according to claim 30, wherein said biaxially stretched film is cut into a shape of said strips.

32. The clothing according to claim 16, wherein at least one of said first strips or said second strips have perforations or laser-drilled perforations for increasing a permeability of the clothing.

33. The clothing according to claim 32, wherein said perforations or laser-drilled perforations are smaller than said through openings.

34. A method for producing the clothing according to claim 16, the method comprising:

a) producing said first layer by winding said first strip helically over two rolls having mutually parallel longitudinal axes, and forming an interspace between windings of said first layer preventing side edges of said first strip from touching each other;

b) producing said second layer on said the first layer by winding said second strip helically over the two rolls, and forming an interspace between windings of the second layer preventing side edges of said second strips from touching one another; and

c) orienting said strips of said first and second layers to cross one another and to form a composite including said first layer and said second layer having a plurality of through openings for dewatering the fibrous web.

35. The method according to claim 34, which further comprises connecting said first layer integrally or by welding or by laser-welding to said second layer.

36. The method according to claim 35, which further comprises carrying out the step of connecting said first layer to said second layer during production of said second layer in step b) or as a separate step following step b).

37. The method according to claim 34, which further comprises subsequently at least one of re-treating, trimming or reinforcing side edges of the clothing.