METHOD FOR REDUCING EDGE WAVES IN A LEAF FORMATION SYSTEM AND LEAF FORMATION SYSTEM

Description

[0001] The present invention relates to a method for reducing edge waviness in a sheet forming system of a Fourdrinier paper or Fourdrinier board machine in the area of ​​feeding a stock suspension jet supplied by a headbox onto a rotating wire. It further relates to a sheet forming system of a Fourdrinier paper or Fourdrinier board machine, particularly suitable for carrying out the method, comprising a headbox, a rotating wire onto which a stock suspension jet supplied by the headbox is fed, and a respective jet edge limiter on both sides of the wire.

[0002] In leaf formation systems of the type mentioned above, a marginal wave can occur in the area where the jet of stock suspension supplied by the headbox is directed onto the circulating screen, which adversely affects leaf formation.

[0003] To avoid this adverse effect on sheet formation, document EP0899376 A2 proposes to provide adjustable format markers in the edge areas of the fabric jet and the screen section, relative to the machine direction and the screen of the screen section.

[0004] Based on the Fig. 1 bis 3 The attached drawing explains in more detail the formation of such an edge wave in an exemplary sheet formation system of a Fourdrinier paper or Fourdrinier board machine.

[0005] This shows Fig. 1 A sectioned partial view of the exemplary sheet-forming system 8 of a Fourdrinier paper or Fourdrinier board machine with a headbox 1 that provides a free jet of stock suspension 2 which strikes a rotating screen 3 in the region of a jet impact point 4. The free jet 2 formed by the headbox 1 is deflected at the screen 3 in the region of the jet impact point 4 at an angle β of less than 10° in the screen direction MD. This deflection creates a pressure field 5 with a length F1.

[0006] The point of impact of the jet 4 on the sieve 3 is provided at a distance A in the lower lip 6 of the headbox 1, measured in the direction of sieve travel MD.

[0007] The extent or length F1 of the pressure field 5, measured in the direction of flow MD in the sieve, is, for example, 1 to 1.5 times the jet thickness S1. Due to the backpressure against the flow direction in the free jet 2, the pressure field 5 begins at a distance F2 from the jet impact point 4, which can be approximately 0.1 to 0.3 times the jet thickness S1.

[0008] As shown by the Fig. 1 As can be seen, the substance suspension free jet 2 experiences a kink in the area of ​​the jet impact point 4.

[0009] Fig. 2 schematically shows the momentum effect and the friction-induced decrease in velocity profile of the substance suspension free jet 2 in the transverse direction CD of the exemplary leaf formation system 8 according to Fig. 1 .

[0010] This creates pressure field 5 (see Fig. 1 The pressure profile of the free jet of the substance suspension 2 is three-dimensional due to the momentum effect and the friction-induced decrease in velocity in the transverse direction CD (i.e., perpendicular to the screen direction MD) and in the vertical direction z. The planes closest to the screen, such as plane E1, exhibit a different pressure profile in the transverse direction CD than plane E3 directly below the jet surface. The pressure profile in the middle plane E2 is intermediate.

[0011] In Fig. 2 In addition, one of two lateral beam edge boundaries EM of the leaf formation system 8 can be seen.

[0012] As can be seen in particular from the Fig. 3 As can be seen, due to the relevant pressure gradients and their different characteristics in the z-direction, it begins in the area of ​​pressure field 5 (see Fig. 1 A different flow process occurs in the transverse direction CD outwards, which is intensified on the underside of the jet facing the sieve 3. This flow process comes to a halt in and after the pressure field 5 at a respective lateral jet edge boundary EM of the exemplary blade formation system 8, thereby creating a pressure surge and causing a flow deflection upwards in the z-direction. This hydraulic mechanism results in a steepening of the jet edge and a marginal wave R.

[0013] By placing a jet edge boundary EM at the correct location and radius, space can be provided for the flow, so that the pressure pulse and the corresponding deflection occur preferentially in the direction of the screen belt travel MD and less in the z-direction. The edge wave R can thus be minimized.

[0014] If the contour of a respective jet edge boundary EM is now extended outwards in the sieve direction MD before the jet impact point 4, the pressure in the three-dimensional pressure field 5 drops extremely on the outside. This increases the pressure gradient towards the outside, and the material suspension movement in the transverse direction CD is intensified, causing massive edge wave effects.

[0015] If, on the other hand, the contour of a respective beam edge boundary EM is led too far outwards in the sieve direction MD behind the beam impact point 4, the edge wave R is formed, which, once it has started, can no longer be influenced.

[0016] The invention is based on the objective of providing a method and a sheet formation system of the type mentioned above, with which the aforementioned problems can be overcome in the simplest and most effective way possible, and the edge wave can be controlled as optimally as possible. In particular, the contour of a respective beam edge boundary or lateral format plate should be optimally adaptable to the respective beam path geometry, and the edge wave should thus be at least significantly reduced.

[0017] According to the invention, this problem is solved by a method with the features of claim 1 or a leaf formation system with the features of claim 4. Preferred embodiments of the method according to the invention and preferred embodiments of the leaf formation system according to the invention are described in the dependent claims, the present description, and the drawing.

[0018] In the inventive method for reducing edge waves in a sheet forming system of a Fourdrinier paper or Fourdrinier board machine in the area of ​​feeding a stock suspension jet supplied by a headbox onto a rotating screen, a jet edge boundary is used on each of the two screen sides for the forming sheet, the contour of which is adjustable by one or more variably adjustable fold points, in the area of ​​which the contour of the jet edge boundary can generally be deflected transversely to the screen direction, wherein each variably adjustable fold point is variably adjustable with respect to its position in the transverse direction (CD) and / or with respect to its fold radius and / or with respect to its position in the screen direction.The essential aspect of the invention is that the position, viewed in the direction of the screen travel, of a variably adjustable bending point provided in the area where the stock suspension jet hits the rotating screen lies within the pressure field occurring in the stock suspension jet in the direction of the screen travel, up to a maximum of 50 mm after the screen section of the paper machine concerned, which is caused by the deflection of the stock suspension jet at the point of impact on the rotating screen.

[0019] This method allows for optimal control of the edge wave. The edge jet boundary can thus be positioned not only beyond the outlet width of the headbox, perpendicular to the screen direction, but the kink or inflection point of the outward flow can also be positioned very precisely at a defined location. Furthermore, the stock suspension flow after the headbox outlet and before the subsequent kink can be guided, at least essentially, in a straight line. The edge wave is therefore optimally controlled.

[0020] Preferably, each variably adjustable folding point can be adjusted during operation of the paper machine with regard to its position in the transverse direction and / or its folding radius and / or its position in the wire direction. The contour of each steel edge boundary can thus be quickly and precisely adapted to changing conditions.

[0021] Advantageously, each variably adjustable bending point is continuously adjustable or variably adjustable in increments with respect to its position in the transverse direction and / or with respect to its bending radius and / or with respect to its position in the sieve direction. In particular, each variably adjustable bending point is preferably variably adjustable with respect to its position in the transverse direction in increments smaller than 100 mm, preferably in increments smaller than 20 mm.

[0022] A key advantage for optimally controlling or reducing edge waves is the stepless or incrementally variable adjustability of the position of a bend at the beam impact point, which eliminates the aforementioned problems of positioning such a bend too far in front of or too far behind the beam impact point. The bend can now be positioned precisely at the desired location.

[0023] The sheet-forming system according to the invention, particularly suitable for carrying out the process, comprises a headbox, a circulating screen onto which a jet of stock suspension supplied by the headbox is applied, and a jet edge boundary on each of the two screen sides, the contour of which is adjustable by one or more variably adjustable bends, in the area of ​​which the contour of the jet edge boundary can generally be deflected transversely to the screen direction. Each variably adjustable bend is variably adjustable with respect to its position in the transverse direction and / or with respect to its bend radius and / or with respect to its position in the screen direction. It is essential to the invention that the position, viewed in the screen direction, of a variably adjustable bend provided in the area where the jet of stock suspension strikes the circulating screen is...The adjustable bending point lies within the pressure field occurring in the direction of travel of the fabric suspension jet in the fabric suspension jet in the direction of travel of the fabric suspension jet and on the screen section of the paper machine in question, up to a maximum of 50 mm after the point of impact of the jet.

[0024] Each variably adjustable folding point is advantageously also variably adjustable during the operation of the paper machine in question with regard to its position in the transverse direction and / or with regard to its folding radius and / or with regard to its position in the wire direction.

[0025] According to an advantageous embodiment of the sheet-forming system according to the invention, each variably adjustable folding point is continuously adjustable or variably adjustable in increments with respect to its position in the transverse direction and / or with respect to its folding radius and / or with respect to its position in the sieve direction. Advantageously, each variably adjustable folding point is variably adjustable, particularly with respect to its position in the transverse direction, in increments smaller than 100 mm, preferably in increments smaller than 20 mm.

[0026] Advantageously, the bending radius of at least one bending point provided in the area of ​​the point of impact of the substance suspension jet on the circumferential sieve is variably adjustable in a range of 2 to 50 mm, preferably in a range of 5 to 20 mm.

[0027] Each beam edge boundary preferably consists at least partially of a compliant and / or elastic material, and preferably at least partially of a compliant and / or elastic plastic material. Such a partially compliant or elastic beam edge boundary is particularly suitable for creating variably adjustable bending points.

[0028] Each jet edge limiter can advantageously be attached to the headbox and preferably be pivotable. According to an alternative embodiment of the sheet-forming system according to the invention, however, each jet edge limiter can also be attached to the wire section of the paper machine in question.

[0029] It is particularly advantageous if, viewed in the direction of sieve movement, a respective beam edge boundary only begins at a predetermined or predetermined distance from the headbox.

[0030] According to a further advantageous embodiment of the sheet formation system according to the invention, a respective beam edge limit is adjustable in the z-direction for the variable setting of a gap between the circumferential sieve and the beam edge limit.

[0031] The contour of each beam edge boundary is preferably adaptable to the respective beam impact geometry via at least one variably adjustable bending point.

[0032] The distance between the two lateral beam edge boundaries is advantageously greater than the outlet width of the material headbox.

[0033] According to a further advantageous embodiment of the sheet formation system according to the invention, the flow guidance through a respective jet edge limitation in the sieve direction after the headbox and before the first variably adjustable kink point is at least essentially straight.

[0034] In addition, at least one further variably adjustable bend point following the first variably adjustable bend point in the sieve direction of each edge jet boundary can be provided in combination with at least an essentially straight section of the edge jet boundary contour.

[0035] The deflection of the contour of a respective jet edge boundary in the area of ​​the first bend in the sieve direction, generally transverse to the sieve direction and beyond the outlet width of the material outlet, is expediently less than 2 mm.

[0036] It is particularly advantageous if each beam edge boundary includes at least one format plate, which preferably consists at least partially of a compliant and / or elastic material, preferably at least partially of a compliant and / or elastic plastic material.

[0037] The contour of a respective beam edge boundary or a respective bending point is expediently adjustable by means of, in particular, linear adjustment devices, which may be attached to a holder or the like, in particular to a flange of the headbox.

[0038] The length of each variably adjustable bending point, which is measured particularly in the direction of sieve movement, is expediently adjustable by means of filler pieces.

[0039] The bending radius of each variably adjustable bending point is advantageously adjustable by stiffening a section of a weakening or recess of the respective beam edge boundary using different filler pieces.

[0040] The position of each variably adjustable bending point in the sieve direction can advantageously be variably adjustable via different filling pieces between, in particular, a flange of the stock head and the respective jet edge boundary.

[0041] Another preferred practical embodiment of the sheet formation system according to the invention is characterized in that a respective beam edge boundary is weakened over its entire length or section by a plurality of incisions generally extending in the z-direction, and the position of a respective variably adjustable kink point in the transverse direction and / or in the sieve direction is variably adjustable by stiffening certain areas of the wall beam boundary by means of clamping pieces of different lengths and / or the kink radius of the respective variably adjustable kink point over the length of the non-stiffened areas of the edge beam boundary.

[0042] According to the invention, the position of a variably adjustable bending point, viewed in the direction of the screen travel, is located within the pressure field occurring in the screen travel direction in front of and on the screen section of the paper machine in question, up to a maximum of 50 mm after the point of impact of the jet of the stock suspension, within the area of ​​the impact of the stock suspension jet on the rotating screen, which is caused by the deflection of the stock suspension jet at the point of impact on the rotating screen.

[0043] It is also advantageous if, viewed in the direction of sieve rotation, the first suspension jet guidance is achieved by a respective jet edge limitation at a distance from the headbox or a flange associated with it that is smaller than the distance of the jet impact point on the rotating sieve from the headbox or the flange associated with it.

[0044] After the jet impact point, further variable bending points can be positioned to align or shape the contour of the stock suspension jet. This allows for the creation of additional contours in combination with straight sections after the initial bending point at the jet impact point. With the inventive method and sheet forming system, each bending point can be easily and reliably adapted to the specific conditions of different paper machines, such as varying lengths and thicknesses of the stock suspension jet, with regard to its position and / or bending radius, thus improving control of the edge wave.

[0045] The invention is described in more detail below with reference to exemplary embodiments and the drawing; in this drawing: Fig. 1 a schematic partial representation of the sheet formation system of an exemplary Fourdrinier paper or Fourdrinier board machine, Fig. 2 a schematic cross-sectional representation of the area of ​​the beam impact point of the exemplary sheet formation system according to Fig. 1 forming three-dimensional pressure field with different pressure gradients in the various, successive planes in the z-direction, Fig. 3 a schematic representation of the area of ​​the exemplary leaf formation system according to Fig. 1 The resulting pressure field produces flow processes that differ in the z-direction. Fig. 4a shows a schematic partial representation of an exemplary embodiment of the sheet formation system according to the invention with adjustment devices attached to a holder, via which the contour of a respective jet edge boundary can be adjusted. Fig. 4b shows a schematic partial representation of another exemplary embodiment of the sheet formation system according to the invention, in which the first suspension jet guidance takes place at a distance from the headbox. Figs. 5 and 6 show a schematic partial representation of another exemplary embodiment of a sheet formation system according to the invention, in which the variable length of the kinks can be achieved by means of filler pieces FS1 and the kink radii by stiffening a respective jet edge boundary with filler pieces FS2.Figures 7 and 8 show a schematic partial representation of a further exemplary embodiment of the leaf-forming system according to the invention, in which the respective folding position and folding radius are variably adjustable.

[0046] The based on the Fig. 4a bis 8 The exemplary embodiments of the leaf formation system 10 according to the invention described include, as in Fig. 1 The exemplary sheet formation system 8 shown each comprises a headbox 12, a circulating sieve 3 onto which a jet of stock suspension 2 supplied by the headbox 12 is fed (see also Fig. 1 ), and a respective beam edge boundary 14 on both sides of the screen. According to the invention, the contour of a respective beam edge boundary 14 is adjustable by one or more variably adjustable bending points 16, in the area of ​​which the contour of the steel edge boundary 14 is generally transverse to the screen running direction MD (see also Fig. 1 ) is deflectable. In this case, each variably adjustable bending point 16 is variably adjustable with respect to its position in the transverse direction CD, i.e. transverse to the screen running direction MD, and / or with respect to its bending radius (R i ) and / or with respect to its position in the screen running direction MD.

[0047] Each variably adjustable bending point 16 can be continuously or variably adjustable with respect to its position in the transverse direction CD and / or with respect to its bending radius (R i ) and / or with respect to its position in the sieve direction MD.

[0048] Furthermore, each beam edge limit 14 or format plate can consist at least partially of a flexible and / or elastic material and, for example, at least partially of a flexible and / or elastic plastic material.

[0049] In the embodiment of the leaf formation system 10 according to the invention Fig. 4a The contour of a respective jet edge boundary 14 or a respective bend 16 is variably adjustable via linear adjustment devices VE, which are attached to a holder H that can, for example, be mounted on a flange SF of the headbox 12. The first bend 16 is positioned here at the jet impact point 4. However, further bends 16 can also be provided or created. In the present case, the jet edge boundary 14 experiences a deflection Al in the transverse direction CD starting from the bend 16 at the jet impact point 4.

[0050] During the Fig. 4b In the exemplary embodiment of the sheet-forming system 10 according to the invention, viewed in the sieve direction MD, the first suspension jet guidance is achieved by a respective jet edge boundary 14 at a distance B from the headbox 12 or an associated flange SF. The first kink 16 is again positioned in the region of the jet impact point 4. Further kinks can also be provided or created.

[0051] As shown by the Fig. 4b As can be seen, the distance B between the first suspension jet guide and the headbox 12 is smaller than the distance A of the jet impact point 4 on the rotating screen to the headbox 12 or the flange SF associated with it. In this case, a gap can therefore exist between the start of the jet guide and the format plate of the headbox 12, in which the suspension jet is laterally free or unguided as a free jet FS. A phase or radius RS can assist in capturing the flow, which facilitates adjustment in the transverse direction CD.

[0052] During the Fig. 5 and 6In the exemplary embodiments of the sheet-forming system 10 shown, the length of each variably adjustable bending point 16, particularly in the sieve direction, is variably adjustable via filler pieces FS1. The bending radius of each variably adjustable bending point 16 is variably adjustable by stiffening a section of a weakening or recess 18 of the respective jet edge boundary 14 using different filler pieces F2. With filler pieces FS1 between the flange SF of the headbox 12 and a respective jet edge boundary 14, a variable bending point can thus be set. With screwed-on filler pieces FS2, a section of the weakening or recess 18 of the, for example, strip-like jet edge boundary 14 can be stiffened, for example, so that the bending area B2 is reduced to a bending area B1 in order to set or reduce the bending radius.

[0053] During the Fig. 7 and 8 In the exemplary embodiment of the sheet-forming system 10 shown, a respective beam edge boundary 14 is weakened over its entire length or section by a plurality of incisions 20, each generally extending in the z-direction, which in this case each have a width b measured in the screen direction MD. The position of a respective variably adjustable bend 16 in the transverse direction CD and / or in the screen direction MD is variably adjustable by stiffening certain areas of the edge beam boundary 14 by means of clamping pieces KS1, KS2 of different lengths L1, L2 and / or by means of the bend radius, R1, R2 of a respective variably adjustable bend 16 over the length of the unstiffened areas of the edge beam boundary 14. Fig. 8 A holder H can also be seen, to which the various adjustment devices VE can be attached.

[0054] As from Fig. 7 As can be seen, each clamping piece KS1, KS2 can comprise two plates 24 that can be connected to each other via connecting element 22, one of which can be inserted into a slot 26 provided in the respective edge beam limiter 14, while the other plate 24, when the opposite plate 24 is inserted into the slot 26, rests on the outside of the edge beam limiter 14. After such a clamping piece KS1, KS2 has been inserted into or attached to the edge beam limiter 14, the limiter is stiffened accordingly in the respective area over the relevant length L1 or L2 of the respective clamping piece KS1, KS2.

[0055] In the representation according to Fig. 8 For example, three stiffened sections of the respective edge beam boundary 14, each reinforced by clamping pieces KS1, KS2, and KS3, can be seen. These sections can have different lengths, at least partially, depending on the length of the clamping pieces. As already explained, the bending radii R1 and R2 can be adjusted via the respective lengths of the unreinforced sections of the edge beam boundary 14. Bezugszeichenliste

[0056] 1 Headbox 2 Sump jet, free jet 3 Circulating screen 4 Jet impact point on the screen 5 Pressure field 6 Lower lip 8 Exemplary sheet formation system 10 Sheet formation system 12 Headbox 14 Jet edge boundary 16 Bend point 18 Weakening, recess 20 Incision 22 Connecting element 24 Plate 26 Inner slot ADistance of the jet impact point from the lower lip of the headbox AlDistance in the transverse direction BDistance between headbox and jet edge boundary CDTransverse direction E1Plane near screen E2Middle plane E3Plane directly below the jet surface EMJ ... bWidth zVertical or vertical direction βAngle

Claims

1. Method for reducing edge waves (R) in a sheet formation system (10) of a Fourdrinier paper machine or Fourdrinier card machine in the region of the application of a material suspension jet (2) which is supplied by a headbox (12) to a rotating screen (3), in which a jet edge limitation (14) is used in each case at both screen sides for the sheet which is being formed, the contour of which can be adjusted by one or more variably adjustable bending locations (16), in the region of which the contour of the jet edge limitation (14) can be redirected in each case generally transversely relative to the screen running direction (MD), wherein a respective variably adjustable bending location (16) can be adjusted in a variable manner with respect to its position in the transverse direction (CD) and / or with respect to the bending radius (Ri) thereof and / or with respect to its position in the screen running direction (MD), characterized in that the position viewed in the screen running direction (MD) of a variably adjustable bending location (16) which is provided in the region of the impact of the material suspension jet (2) on the rotating screen (3) is located within the pressure field (5), which occurs as a result of the redirection of the material suspension jet (2) at the jet impact location (4) on the rotating screen (3) in the material suspension jet (2) in the screen running direction (MD) in front of and on the screen portion of the relevant paper or card machine, up to a maximum of 50 mm after the jet impact location.

2. Method according to Claim 1, characterized in that a respective variably adjustable bending location (16) can also be adjusted in a variable manner during the operation of the respective paper machine with respect to its position in the transverse direction (CD) and / or with respect to its bending radius (Ri) and / or with respect to its position in the screen running direction (MD).

3. Method according to at least one of the preceding claims, characterized in that a respective variably adjustable bending location (16) can be adjusted in a variable manner with respect to its position in the transverse direction (CD) and / or with respect to its bending radius (Ri) and / or with respect to its position in the screen running direction (MD) in a stepless manner or in rasters.

4. Sheet formation system (10) of a Fourdrinier paper machine or Fourdrinier card machine, in particular for carrying out the method according to any one of the preceding claims, having a headbox (12), a rotating screen (3) to which a material suspension jet (2) which is supplied by the headbox (12) is applied and a respective jet edge limitation (14) at both screen sides, the contour of which can be adjusted by means of one or more variably adjustable bending locations (16), in the region of which the contour of the jet edge limitation (14) can in each case be generally redirected transversely relative to the screen running direction (MD), wherein a respective variably adjustable bending location (16) can be adjusted in a variable manner with respect to its position in the transverse direction (CD) and / or with respect to its bending radius (Ri) and / or with respect to its position in the screen running direction (MD), characterized in that the position viewed in the screen running direction (MD) of a variably adjustable bending location (16) which is provided in the region of the impact of the material suspension jet (2) on the rotating screen (3) is located within the pressure field (5), which occurs as a result of the redirection of the material suspension jet (2) at the jet impact location (4) on the rotating screen (3) in the material suspension jet (2) in the screen running direction (MD) in front of and on the screen portion of the relevant paper or card machine, up to a maximum of 50 mm after the jet impact location.

5. Sheet formation system according to Claim 4, characterized in that a respective variably adjustable bending location (16) can also be adjusted in a variable manner during the operation of the relevant paper machine with respect to its position in the transverse direction (CD) and / or with respect to its bending radius (Ri) and / or with respect to its position in the screen running direction (MD).

6. Sheet formation system according to any one of the preceding Claims 4 and 5, characterized in that a respective variably adjustable bending location (16) can be variably adjusted in a stepless manner or in rasters with respect to its position in the transverse direction (CD) and / or with respect to its bending radius (Ri) and / or with respect to its position in the screen running direction (MD).

7. Sheet formation system according to any one of the preceding Claims 4 to 6, characterized in that a respective jet edge limitation (14) is advantageously secured to the headbox (12) and can preferably be pivoted away.

8. Sheet formation system according to any one of Claims 4 to 6, characterized in that a respective jet edge limitation (14) is secured to the screen portion of the relevant paper machine.

9. Sheet formation system according to at least one of the preceding Claims 4 to 8, characterized in that a respective jet edge limitation (14) when viewed in the screen running direction (MD) begins only with a predetermined or predeterminable spacing (B) with respect to the headbox (12).

10. Sheet formation system according to at least one of the preceding Claims 4 to 9, characterized in that a respective jet edge limitation (14) for variable adjustment of a gap between the rotating screen (3) and the jet edge limitation (14) can be adjusted in the z direction.

11. Sheet formation system according to at least one of the preceding Claims 4 to 10, characterized in that the contour of a respective jet edge limitation (14) can be adapted to the respective jet impact geometry by means of at least one variably adjustable bending location (16).

12. Sheet formation system according to at least one of the preceding Claims 4 to 11, characterized in that the spacing between the two lateral jet edge limitations is greater than the outlet width of the headbox (12).

13. Sheet formation system according to at least one of the preceding Claims 4 to 12, characterized in that the flow guide extends through a respective jet edge limitation in the screen running direction after the headbox and in front of the first variably adjustable bending location at least in a substantially linear manner, and in that at least one additional variably adjustable bending location (16), which follows the first variably adjustable bending location (16) in the screen running direction (MD), of a respective jet edge limitation (14) is provided in combination with an at least substantially linear portion of the jet edge limitation contour.

14. Sheet formation system according to at least one of the preceding Claims 4 to 13, characterized in that a respective jet edge limitation (14) is weakened over the entire length thereof or partially by means of a large number of incisions (20) which generally extend in the z direction and the position of a respective variably adjustable bending location (16) can be variably adjusted in the transverse direction (CD) and / or in the screen running direction (MD) by reinforcing specific regions of the jet edge limitation (14) by means of clamping pieces (KS1, KS2) of different lengths (L1, L2) and / or the bending radius of a respective variably adjustable bending location (16) can be variably adjusted over the length of the non-reinforced regions of the jet edge limitation (14).