APPARATUS AND METHOD FOR HYDRODYNAMIC ENTANGLEMENT OF NON-WOVENS, WOVENS AND KNITS

Abstract

The invention relates to an apparatus and method for hydrodynamic entanglement of non-wovens, wovens and knits, comprising an entanglement system having at least one water bar and a drum or endless belt, between which a fibre web is transported and entangled. The invention is characterised in that before the water bar, seen in the running direction of the fibre web, there is arranged a compacting device, which compresses the fibre web on the drum or endless belt.

Description

The invention relates to an apparatus and method for hydrodynamic entanglement of non-wovens, wovens and knits, comprising an entanglement system having at least one water bar and a drum or endless belt, between which a fibre web is transported and entangled.

In systems for the hydrodynamic entanglement of fibre webs, the fibre web is compacted before entanglement by moistening and compressing the fibre web between two belts or between a belt and a drum. As a result, the non-woven web is slightly pre-entangled so that it is less fragile for subsequent needling. Intertwining of the fibres is then carried out by twisting them with one another by means of high-pressure water jets.

Intertwining of the fibres is carried out using bars of nozzles, from which high-pressure water jets strike the fibre web. The drum located underneath the fibre web has a multiplicity of apertures, into which on the one hand some of the fibres can extend and become intertwined and by way of which on the other hand the water of the water jets can be drawn off under suction and drained off. Usually, 2-3 water bars are arranged one after another. Without compacting, the fibre web is very fragile in respect of the water jets and the suction drainage; the fibres would become displaced, which would negatively impact on the appearance of the fibre web and also on its strength and stretching. Without compacting, hydroentanglement of synthetic fibres such as polyester or polypropylene is possible only to a limited degree. In that case great care and attention has to be paid to the correct pressure, to the spacing of the water bar from the fibre web and to the associated suction drainage. As soon as variations are found in the composition of the fibre web, all the parameters have to be modified again and again. Reliable production is not possible in the long term as a result. The known systems in the prior art comprise, for example, spunlace drums or hydroentanglement drums. Alternatively, a corresponding endless belt is referred to as a spunlace belt or hydroentanglement belt.

It is disadvantageous that compaction of the fibre web causes the size of the system to increase and that the bars of nozzles with the associated suction drainage arrangements are expensive.

The problem of the invention is to provide an apparatus and method for hydrodynamic entanglement of non-wovens, wovens and knits which is economical in terms of its construction and which ensures reliable compaction before hydroentanglement by water jets.

The invention solves the addressed problem by means of the teaching according to claims 1 and 20; further advantageous embodying features of the invention are characterised by the subordinate claims.

In accordance with the technical teaching according to claim 1, the apparatus for hydrodynamic entanglement of non-wovens, wovens and knits comprises an entanglement system having at least one water bar and a drum or an endless belt, between which a fibre web is transported and entangled.

In accordance with the invention, provision is made so that before the water bar, seen in the running direction of the fibre web, there is arranged a compacting device, which compresses the fibre web on the drum or endless belt.

Using the features of the invention it is possible to make the existing system substantially shorter, by integrating the compacting device on or into the entanglement system, which is to say the water bar and the drum.

Advantageously, the compacting device has at least one compacting plate, which presses the fibre web onto the drum or endless belt. As a result, by the simplest of technical means, the same effect is achieved as in the case of a compacting system installed upstream, in which the fibre web is pre-compressed between endless belts or drums. It is possible to dispense with an entire system section, giving rise to a considerable price advantage.

As a result of the fact that the compacting plate is arranged to be fixed to the water bar, a very compact unit is obtained, by means of which the fibre web is first compressed and then entangled by means of high-pressure water jets. The short time between compression and entanglement gives rise to advantages in terms of the strength of the fibre web and, at the same time, floating of the individual fibres is avoided, which results in a better non-woven product.

The water jet can have a pressure of from 10 to 100 bar. Optimum values are achieved using a pressure of from 20 to 40 bar.

Fixing the compacting plate to a carrier on the one hand makes possible a solution which is capable of being retro-fitted and which can be fixed, before the water bar, on the machine frame. On the other hand, the spacing of the compacting device to the fibre web can be adjusted independently of the spacing of the water bar to the fibre web. The compacting device can, by means of a pivoting apparatus on the carrier, be adjusted in terms of angle and position so that the compression force of the compacting plate on the non-woven web can be varied. Using the pivoting apparatus, the spacing from the trailing edge of the compacting plate to the row of water jets of the water bar can also be adjusted.

A further improvement is obtained as a result of the fact that the compacting plate compresses the fibre web with biasing. The biasing can be produced by the resilience of the compacting plate and/or by means of a contact pressure application apparatus. Construction of the compacting plate from resilient metal or plastics especially produces an economical and very effective compacting device because in the event of irregularities in the material the readily bent metal or plastic strip springs back. Furthermore, by utilising the resilience of the curved compacting plate, a certain run-in region is created, which is very onerous to produce in the prior art by means of endless belts arranged at an angle. By means of this run-in region, the fibres are compacted and are afterwards compressed in the region of the trailing edge of the compacting plate.

A crucial advantage of the invention over the prior art is that a trailing edge of the compacting plate is positioned directly at the water jet. By that means, the drawing-in of regions of the fibre web into the suction region of the aperture or suction slits in the drum or beneath the endless belt is prevented. The fibre web is better fixed to the drum or endless belt whilst the individual fibres are being intertwined with one another. The prior disadvantageous longitudinal stripes which occur when there is no compaction can be effectively prevented as a result.

In accordance with an advantageous embodiment, the trailing edge of the compacting plate is positioned so close to the water jet that at least part of the suction region of the aperture or suction slits is covered over. Only the fibres which are arranged in the region between the trailing edge of the compacting plate and the row of water jets are intertwined with one another. The regions of the fibre web underneath the compacting plate are held by the compacting plate on the drum. At the same time, only small regions of the fibre web between the trailing edge of the compacting plate and the row of water jets are subject to the negative pressure. This too reduces the undesirable longitudinal stripes.

In a preferred embodiment, the spacing of the forward edge to the water jet can be reduced to 0.1 mm, so that partial hydroentanglement is very purposely carried out without stretching the fibre web in the region before the rows of water jets.

A further improvement can be obtained by constructing the trailing edge of the compacting plate to slide over the fibre web. By this means, orientation of the fibres on the surface of the fibre web is obtained, as a result of which increased longitudinal strength is achieved, but without any reduction in transverse strength.

Alternatively, the trailing edge of the compacting plate can be constructed to roll over the fibre web. By that means, a linear pressure is exerted on the fibre web, with the impact on the MD/CD ratio being as small as is possible.

An economical embodiment can be achieved by means of a compacting plate of metal, plastics or a composite material. It is then advantageous if the materials have a certain resilience or spring action and bend readily. As a result, a run-in or compacting region is produced in which the fibres are compressed.

Advantageously, the compacting plate has a thickness of from 0.1 to 3 mm, preferably of from 0.15 to 0.5 mm. Thin plates provide the necessary resilience on bending. Especially in the case of thin spring steel or resilient materials the compacting plates can adapt to irregularities in the material. Especially in the case of thin compacting plates, the spring action is sufficient so that the force on the fibre web is limited and does not tear off the fibre web.

In order to reduce friction and, as a result, to limit the influence on the MD/CD ratio, the compacting plate can be provided with teflon or a nano-coating.

By providing the trailing edge of the compacting plate with a wavy shape or toothed arrangement, the fibre web can be better held on the drum when the drum is subject to a high degree of suction. Especially in the case of thin plates, the wavy shape results in greater stability, because the trailing edge does not become partially bent or deformed as a result of the suction.

Alternatively, the trailing edge of the compacting plate can have apertures or a perforated arrangement through which air can flow so that the compacting plate does not deform in the case of suction drainage by way of the suction slits of the drum or endless belt.

Irrespective of whether the compacting plate is fixed to a separate carrier or to the water bar, it is advantageous that the spacing of the compacting plate to the drum or endless belt is adjustable. As a result, on the one hand, the spacing from the water jet can be adjusted; on the other hand, the biasing of the resilient plate can also be defined.

The method according to the invention for hydrodynamic entanglement of non-wovens, wovens and knits, wherein a fibre web is transported between a water bar and a drum or endless belt and entangled is characterised in that the fibre web is, before the water bar, compressed on the drum or endless belt by means of a compacting device. As a result, a system is provided which is shorter in overall length, which at the same time has significant advantages for the fibre web because compaction shortly before hydroentanglement prevents the fibres from floating.

Compressing the fibre web can alternatively be brought about by means of a sliding or rolling compacting device, depending on whether a modification of the MD/CD ratio is desired. The trailing edge of the compacting plate is then constructed accordingly.

In the case of a sliding compacting device, the strength of the fibre web in the longitudinal direction can be increased. Direct entanglement by the water bar immediately after the compacting plate is more effective and therefore more efficient than entanglement with prior moistening in a compacting unit located upstream.

In accordance with the invention, a compacting device is integrated into an entanglement system using the smallest space, with compacting taking place just before entanglement. As a result, floating of the fibres is avoided, as a result of which the quality of the nonwoven increases and the undesirable longitudinal stripes are avoided. In addition, as a result of sliding compaction, the longitudinal strength can be increased without this having an impact on the transverse strength.

The invention is explained in greater detail hereinbelow with reference to a possible example of an embodiment shown in diagrammatic form, wherein:

FIG. 1: is a side view, in diagrammatic form, of an entanglement system;

FIG. 1 a: shows, to an enlarged scale, the entanglement region together with a drum having suction drainage;

FIGS. 2 a-2h: show various embodiments of the compacting plate;

FIG. 3: shows a further embodiment of an entanglement system;

FIG. 4: shows a further embodiment of an entanglement system.

FIG. 1 shows an entanglement system 1 which substantially comprises a drum 3 or, alternatively, an endless belt, having at least one water bar 4. The drum 3 can be constructed in the form of a so-called screen drum, comprising a perforated plate drum, which is covered with a support fabric and a fine screen or, alternatively, with a microporous shell. Alternatively, the drum can be in the form of a structured drum, the surface of which is perforated in order to provide the fibre web 2 with a structure or pattern.

The drum 3 has a multiplicity of apertures 3a, by way of which the water from the water bar 4 is drained off. Within the drum 3 there is arranged a suction tube 3c having a multiplicity of suction drainage slits 3d, by way of which the water is drained off under negative pressure. Above the drum 3 there is arranged the water bar 4, which sprays a series of water jets 6 under high pressure onto the fibre web 2 by means of a multiplicity of nozzles 5. In accordance with the invention, the water bar 4 is operated using a pressure of from 10 to 100 bar, preferably using a pressure of from 20 to 40 bar. The nozzle bar 4 can be operated using one or more rows of water jets 6. The nozzles 5 are arranged along the longitudinal axis of the water bar 4. For reasons of clarity, only one row of water jets 6 is shown. In this example of an embodiment, the fibre web 2 runs over the drum 3 in the direction of the arrow from left to right and is struck continuously by the water jets 6. The water bar 4 therein is arranged so as to be adjustable in its spacing from the drum 3 or endless web.

In the case of a structured drum, individual fibres extend into the apertures 3a and intertwine with one another until they are pulled out from the aperture 3a. When the drum 3 is provided with a suction tube, the fibre web 2 is at least partially sucked into the suction drainage slit 3d, which can result in undesirable stripes on the entangled non-woven.

In accordance with the invention, a compacting device 10 is arranged before the water bar 4, seen in the running direction of the fibre web 2, which compacting device 10 applies a pressure to the fibre web 2 along the longitudinal axis of the drum 3. In this example of an embodiment, the compacting device 10 includes a suspension arrangement 13 having an articulation 12 to which a carrier 11 is rotatably fixed. The suspension arrangement 13 is fixed to a machine frame (not shown) or stand. Beneath the carrier 11 there is arranged a compacting plate 14, which can be seen in side view. In its longitudinal extension, which is to say over the working width, the compacting plate 13 extends over substantially the entire length of the drum 3. In the region of a rear edge or run-in edge 14b, the compacting plate 14 is fixed to the carrier 11, whereas the forward or trailing edge 14a presses the fibre web 2 onto the drum 3 with biasing.

The compacting device 10 can be pivoted by means of the articulation 12, as a result of which the position of the contact-making surface or contact-making line of the compacting plate 14 on the fibre web 2 is adjustable. At the same time, as a result of rotation of the compacting device 10 about the articulation 12, the pressure of the compacting plate 14 on the fibre web 2 can be modified. For that purpose it is advantageous if, in addition to the articulated arrangement of the compacting device 10, the latter is constructed so that its height is adjustable. For that purpose, the suspension arrangement 13 can be of adjustable construction. As a result the pressure or force applied to the fibre web 2 can be adjusted in dependence on the fibres being processed. The compacting plate 14 can be made, for example, from a strip of metal or plastics which can be readily bent by the pressure of the compacting device 10 and so press resiliently on the fibre web 2. The free end or trailing edge 14a of the compacting plate 14 herein points in the running direction of the fibre web 2.

The technical effect of the compacting device 10 lies in the fibre web 2 being compressed within a very small space before entanglement by the water bar 4 occurs. The system can be of substantially shorter construction than a compacting device having rolls or belts according to the prior art. A further advantage lies in the fact that the compacting produces compression of the fibres shortly before entanglement by the water jets, as a result of which floating of the individual fibres is prevented, which ultimately results in a better non-woven product.

Compacting just before the water jet 6 is essential to the invention, as a result of which the fibre web 2 is prevented, in relatively large regions before the row of water jets 6 and/or as a result of the negative pressure in the suction tube 3c, from being sucked into the drum 3 in the direction of production, with the non-woven undergoing deformation. If the suction is uneven, transverse corrugations can be produced in the non-woven, and also longitudinal stripes. At the same time, the strength of the fibre web 2 in the longitudinal direction can increase whereas the strength of the fibre web 2 in the transverse direction remains the same. Conventionally, when fibre webs stretch, there is a change in the MD/CD ratio in both directions, that is to say, for example, the strength increases in the longitudinal direction but decreases in the transverse direction or vice-versa. The compacting plate 14 on the other hand can, as a result of the compacting action shortly before entanglement by the water jets, increase the strength in the longitudinal direction of the fibre web 2, because the trailing edge 14a only slides over the surface of the fibre web 2. In contrast, over the cross-section of the fibre web 2 as a whole, no change in the orientation of the fibres takes place. A further advantage arises out of the fact that the disadvantageous longitudinal stripes or longitudinal structures are prevented by means of the compacting plate, because the fibre web 2 is pressed onto the drum 3 in the longitudinal direction of the drum 3 and only the partial region or strip between the compacting plate 14 and the water jets is stretched and the fibres intertwined with one another.

FIG. 1 a shows, to an enlarged scale, a view of the entanglement region without the suction tube 3c arranged within the drum. In contrast to the embodiment according to FIG. 1, the aperture 3a has a run-in region 3b arranged before the water jet 6, seen in the running direction of the fibre web 2. The aperture 3b of the suction drainage slit 3a is of wedge-shaped construction so that the suction force caused by the negative pressure in the suction slit increases only slowly and the non-entangled non-woven is compressed slowly without displacement of the fibres due to suction air.

In this example of an embodiment, the trailing edge 14a of the compacting plate 14 is arranged close up to the water jet 6 and, in so doing, covers over the run-in region 3b at least in part. As a result, the fibre web 2 is pushed onto the drum 3 along the longitudinal axis of the drum 3 by the compacting plate 14. Only the fibres which are arranged in the region of the aperture 3a and the run-in region 3b are intertwined with one another.

Only small regions of the fibre web 2 which are located in the region of the run-in region 3b are pulled into the aperture 3a by the negative pressure of the suction drainage.

The spacing of the trailing edge 14a of the compacting plate 14 from the water jet 6 can be reduced to 0.1 mm so that partial hydroentanglement can be very purposely achieved without stretching the fibre web 2 in the region of the suction drainage slit 3a. The trailing edge 14a of the compacting plate 14 can, however, also be arranged on the drum 3 or belt with a larger spacing from the water jet 6. The advantage then lies in the space-saving arrangement of the compacting device according to the invention, with its being possible for the strength of the web to become greater as a result of the construction with the compacting plate.

FIGS. 2 a to 2f show various arrangements of a compacting plate 14, wherein in the simplest embodiment according to FIG. 2f the compacting plate 14 has a straight trailing edge 14a.

In FIG. 2a, the trailing edge 14a of the compacting plate 14 is provided with a rotatable roller 20, which although applying a linear pressure to the fibre web rolls on the surface of the fibre web so that the impact on the MD/CD ratio is as small as possible.

In the subsequent FIGS. 2b to 2e, the compacting plate 14 with its trailing edge 14a is so constructed that it slides over the fibre web and, in so doing, orientates the fibres on the surface as desired—in dependence on the pressure—in the longitudinal direction or, that is, the running direction.

The compacting plate 14 according to FIG. 2b has on its trailing edge 14a a beading 14c, in which a sliding element 21 can be accommodated and/or fixed. The sliding element 21 can be in the form of a round bar or strip and be made of, for example, teflon or some other very low-friction plastic. The sliding element 21 can extend preferably over the entire length of the compacting plate 14 but of course also only in sections.

According to FIG. 2c, the compacting plate 14 has a large radius at the round trailing edge 14a, which acts as a rounded contact-making member and which slides especially gently over the fibre web 2. As a result, orientation of the fibres on the surface of the fibre web 2 is reduced.

The opposite is achieved using the arrangement of a compacting plate 14 according to FIG. 2d. The trailing edge 14a acting on the fibre web has been given a very sharp edge so that orientation of the fibres on the surface of the fibre web 2 is maximised.

In the arrangement according to 2e, a compacting plate 14 having a rectangular cross-section at the trailing edge 14a is shown, wherein the edges are only slightly rounded. In this embodiment, the compacting plate is of very thin construction and is straight in the unloaded state, as in FIG. 2f, so that it bends in the region of the contact-making surface. As a result, owing to the curve in the plate, an area, and not a line, is applied to the fibre web 2. Alternatively, the compacting plate 14 can also be pre-bent so that with less pressure a larger area can however be worked.

The compacting plate can be made in a thickness of from 0.1 to 3 mm, preferably in a thickness of from 0.15 to 0.5 mm, it being possible for the pressure to be adjusted in dependence on the spring action. Normal sheet metals, stainless steel sheets, spring steel sheets, flexible or rigid plastics strips can be used as materials. In order to reduce friction with the fibre web and have minimum impact on the MC/CD ratio, the compacting plates 14 can be provided, for example, with teflon or a nano-coating.

In contrast, should it be desired to influence the MD/CD ratio purposely, there is of course also the possibility of structuring and/or roughening the surface of the compacting plates.

FIG. 2 g shows a top view onto a compacting plate 14, in which the trailing edge 14a extends, not in a straight line as in FIGS. 2a to 2e, but rather in a wavy shape. The advantage lies in the fact that the trailing edge 14a attains greater stability because the trailing edge 14a does not undergo partial bending and/or deformation in the region of the aperture 3a and/or run-in region 3b, especially in the case of thin plates. A like effect is achieved by a compacting plate having a roughly toothed arrangement.

Also to be seen in this context is the embodiment according to FIG. 2h, wherein at least the trailing edge 14a of the compacting plate 14 has apertures 14d or a perforated arrangement through which air can flow. This compacting plate too will not undergo substantial deformation in the region of the aperture 3a in the case of strong suction drainage. The apertures 14d can have a diameter in the millimetre range, for example from 0.5 to 3 mm, but they can also be of much finer construction, in which case they are then referred to as micro-perforation. In dependence on the fibre mixture to be processed, it is possible to influence the fibre quality and surface by means of the arrangement and size of the apertures 14d.

In the example of an embodiment according to FIG. 3, the compacting device 10 is provided with a contact pressure application apparatus 16, which presses the carrier 11 with the compacting plate 14 onto the fibre web 2. In this Figure, the contact pressure application apparatus 16 is shown symbolically as a spring. It can consist of a hydraulic or pneumatic cylinder or be of spring-loaded construction. In this example of an embodiment, the rear edge 14b of the compacting plate 14 is arranged underneath the carrier 11 by means of a fixing 15. As in the example of an embodiment according to FIG. 1, it is possible, by means of the articulation 12, for the position of the contact-making surface or contact-making edge of the trailing edge 14a to be adjusted, and also, in addition, the force which is applied to the fibre web 2, by slightly bending the compacting plate 14.

In FIG. 4, in contrast to FIG. 1, an endless belt 7 rather than the drum is arranged in the entanglement system 1, on which endless belt 7 the fibre web 2 is entangled by means of water jets 6. The endless belt 7 can be in the form of a screen belt in order to drain off the water rapidly. Underneath the endless belt 7, in the region of the nozzle, there is shown a suction tube 3c in the form of a rectangular box, which likewise has at least one suction drainage slit 3d. In contrast to the previous embodiments, the compacting plate 14 is arranged on and fixed to the water bar 4 directly. The fixing 15 in the region of the rear edge 14b can be made on a side wall of the water bar 4 or also, of course, on the bottom surface in the region of the nozzles 6. This has the advantage that the trailing edge 14a can be oriented very well relative to the water jet 6. It is self-evident that the lateral fixing 15 on the water bar 4 can also have, inter alia, a height adjustment facility so that the pressure on the fibre web 2 is adjustable by means of the spring action of the bent compacting plate. The arrangement directly on the water bar is a space-saving solution, in which all previously mentioned adjustment capabilities, in terms of spacing or height or angle, can likewise be implemented.

REFERENCE NUMERALS

• 1 entanglement system
• 2 fibre web
• 3 drum
• 3 a aperture
• 3 b run-in region
• 3 c suction tube
• 3 d suction drainage slit
• 4 water bar
• 5 nozzle
• 6 water jet
• 7 endless belt
• 10 compacting device
• 11 carrier
• 12 articulation
• 13 suspension arrangement
• 14 compacting plate
• 14 a trailing edge
• 14 b lead-in edge
• 14 c beading
• 14 d aperture
• 15 fixing
• 16 contact pressure application apparatus
• 20 rotatable roller
• 21 sliding element

Claims

1. Apparatus for hydrodynamic entanglement of non-wovens, wovens and knits, comprising an entanglement system having at least one water bar and a drum or endless belt, between which a fibre web is transported and entangled, characterised in that before the water bar, seen in the running direction of the fibre web, there is arranged a compacting device, which is integrated on or into the entanglement system and which compresses the fibre web on the drum or endless belt, the compacting device having at least one compacting plate, which presses the fibre web onto the drum endless belt.

2. (canceled)

3. Apparatus according to claim 1, characterised in that the compacting plate is arranged to be fixed to the water bar.

4. Apparatus according to claim 1, characterised in that the compacting plate is arranged to be fixed to a carrier.

5. Apparatus according to claim 3, characterised in that the carrier is arranged to be pivotable.

6. Apparatus according to claim 1, characterised in that the compacting plate compresses the fibre web with biasing.

7. Apparatus according to claim 6, characterised in that the biasing is produced by means of the resilience of the compacting plate and/or by a contact pressure application apparatus.

8. Apparatus according to claim 1, characterised in that a forward edge or trailing edge of the compacting plate is positioned directly at the water jet.

9. Apparatus according to claim 8, characterised in that the trailing edge of the compacting plate covers over at least part of the suction regions of an aperture and/or run-in regions arranged in the drum.

10. Apparatus according to claim 8, characterised in that the spacing of the trailing edge to the water jet is arranged to be reduced to 0.1 mm.

11. Apparatus according to claim 1, characterised in that the trailing edge of the compacting plate is constructed to slide over the fibre web.

12. Apparatus according to claim 1, characterised in that the trailing edge of the compacting plate is constructed to roll over the fibre web.

13. Apparatus according to claim 1, characterised in that the compacting plate is made of metal, plastics or a composite material.

14. Apparatus according to claim 1, characterised in that the compacting plate has a thickness of from 0.1 to 3 mm, preferably of from 0.15 to 0.5 mm.

15. Apparatus according to claim 1, characterised in that the compacting plate is provided with teflon or a nano-coating.

16. Apparatus according to claim 1, characterised in that the trailing edge of the compacting plate has a wavy shape or toothed arrangement.

17. Apparatus according to claim 1, characterised in that the trailing edge of the compacting plate has apertures or a perforated arrangement.

18. Apparatus according to claim 1, characterised in that the spacing of the compacting plate to the drum or endless belt is adjustable.

19. Apparatus according to claim 1, characterised in that the pressure of the water bar is between 10 and 100 bar, preferably between 20 and 40 bar.

20. Method for hydrodynamic entanglement of non-wovens, wovens and knits, wherein a fibre web is transported between a water bar and a drum or endless belt and entangled, characterised in that the fibre web is, directly before the water bar, compressed on the drum or endless belt by means of a compacting device so that floating of the fibres is prevented.

21. Method according to claim 20, characterised in that compressing is brought about by a compacting device sliding or rolling on the fibre web

22. Method according to claim 20, characterised in that, as a result of the compaction, the strength of the fibre web in the longitudinal direction is arranged to be increased