Covering the multi-compartment body with a skin of thermoplastic material

Abstract

The present invention proposes a method for manufacturing a panel (100), which comprises a plurality of partitions (121) defining compartments (150) covered by at least one skin (110, 130), wherein a fiber structure (210) impregnated with thermoplastic material is covered on the upper edge (121a) of the partition (121) by automatically arranging the fibers to form the skin (110, 130), the upper edge (121a) of the partition (121) and the fiber structure (210) being connected together by means of a local heating device (30) when they are placed in contact, the method being characterized in that the fiber structure (210) is covered with a covering tension (T) at the interface between each edge (121a) of the partition (121) and the deposited fiber structure (210), and a shear stress between 50% and 80% of the maximum shear stress is applied before the interface ruptures.

Description

Technical Field

[0001] The present invention relates to the general field of covering methods by automated placement of fibres, in particular for the manufacture of acoustic attenuation panels. Background Art

[0002] Acoustic attenuation panels usually consist of an acoustic skin permeable to the sound waves to be attenuated, a fully reflective skin called "closing skin" and a multi-compartment body arranged between the two skins. The compartment body can take the form of a plurality of partitions defining compartments, for example having a honeycomb shape. In a well-known manner, such panels form Helmholtz-type resonators that allow attenuation of sound waves within a specific frequency range. Acoustic attenuation panels of this type are described in detail in documents US 5 912 442 and GB 2 314526.

[0003] It is known to produce the skin of such an acoustic panel by covering an impregnated fiber structure on a multi-compartment body, using an automated fiber placement technique (also called "AFP"). In particular, when the fiber structure is impregnated with a thermoplastic material and the multi-compartment body is also made of a thermoplastic material, this technique allows a strong bond to be created between the multi-compartment body and the fiber structure during deposition. In fact, the compaction pressure associated with the temperature rise at the contact points between the multi-compartment body and the fiber structure allows a solid bond to be created that meets aeronautical requirements. Such a method for covering on a multi-compartment body is described, for example, in document US2018 / 0018952.

[0004] However, if the technique of automatic fiber placement is particularly suitable for covering fiber structures on smooth and continuous surfaces, its implementation on discontinuous surfaces is more sophisticated. Therefore, when the fiber structure is covered on a multi-compartment body to form a skin, it is observed that the skin sags in the area located above the "voids", that is to say, in the area farthest from the partitions of the multi-compartment body. This phenomenon, known as "telegraphing", reduces the aerodynamic performance of the panel manufactured thereby and reduces its mechanical strength. Summary of the invention

[0005] The main purpose of the present invention is to enable the manufacture of multi-compartment panels comprising at least one skin by overcoming the above mentioned drawbacks.

[0006] To this end, the present invention proposes a method for manufacturing a panel, which comprises a plurality of partitions defining compartments, the compartments being covered by at least one skin of thermoplastic material, the surface being formed by covering a fiber structure impregnated with thermoplastic material on the upper edge of the partition by automatic placement of the fibers, the upper edge of the partition and the fiber structure being joined together by means of a local heating device when they are placed in contact, the method being characterized in that the fiber structure is covered with a covering tension at the interface between each edge of the partition and the deposited fiber structure, a shear stress between 50% and 80% of the maximum shear stress being applied before the interface ruptures.

[0007] The invention thus allows to exert a sufficiently high tension on the fiber structures when covering them, so as to stretch them in a satisfactory manner from one partition to another, while limiting the risk of damaging the connection between the fiber structure and the multiple partitions. Thus, while maintaining a strong connection between the multi-compartment body and the skin, the sagging of the skin in the spaces between the partitions is reduced. The mechanical strength of the final panel is thus improved, and its aerodynamic characteristics are enhanced.

[0008] In case the upper edge of the partition is made of thermoplastic material, the term "connected" may be replaced by "welded".

[0009] It is clearly understood that the upper edges of the partitions define a continuous covering surface on which the fiber structure is covered. Therefore, preferably, the covering fiber structure covers both the upper edges of the partitions and the space belonging to the compartments between the upper edges of the partitions.

[0010] According to a particular embodiment of the invention, the covering tension is at least partially generated by a rotationally controlled tensioner.

[0011] According to another particular embodiment of the invention, the covering tension is at least partially generated by a roller for depositing the rotationally controlled fiber structure.

[0012] According to another specific embodiment of the invention, at a given moment, the fiber structure is covered with a compression pressure applied by a pressure applying element on the upper edge of the partition, which compression pressure corresponds to 60% to 85% of the maximum pressure supported by the upper edge of the partition multiplied by the number of partitions covered by the applying element at a given moment.

[0013] The pressure applying element may be a deposition roller or a compaction shoe.

[0014] The compaction pressure applied by the application element at a given moment is therefore adapted according to the number of spacers which are located below said application element at a given moment. The compaction pressure is therefore always sufficient to produce a solid interface between the deposited fiber structure and the upper edge of the spacers, without becoming too great in areas where the spaces between the spacers are larger. This further limits the risk of "print-through", the compaction pressure applied on the "hollow" spaces between the spacers being reduced.

[0015] According to another particular embodiment of the invention, the sensor measures the amount of the web covered by the application element.

[0016] According to another particular embodiment of the invention, the application element is controlled by a device which adapts the compaction pressure applied by the application element as a function of its position and of the overall geometrical pattern formed by the upper edges of the plurality of partitions.

[0017] According to another particular embodiment of the invention, at least the upper edge of the partition is made of thermoplastic material.

[0018] The connection between the multi-compartment body and the fiber structure is therefore made by welding two thermoplastic materials: the connection is therefore very strong.

[0019] The present invention also proposes a device for covering a fiber structure impregnated with a thermoplastic material on the upper edges of a plurality of partitions defining a compartment, the device comprising at least:

[0020] - means for supplying a fiber structure impregnated with a thermoplastic material,

[0021] - means for depositing a fiber structure on the upper edges of a plurality of separators,

[0022] - Local heating means for heating portions of the upper edge of the separator and portions of the fiber structure immediately before they are brought into contact with them by the deposition means.

[0023] The apparatus is characterized in that the deposition means are configured to generate a covering tension at the interface between each edge of the separator and the deposited fiber structure, the covering tension applying a shear stress between 50% and 80% of the maximum shear stress before said interface ruptures.

[0024] According to a specific embodiment of the present invention, the deposition device includes at least one pressure-applying element, which is controlled to rotate on the one hand to achieve covering tension, and is controlled to translate on the other hand to achieve a clamping pressure on the upper edge of the partition at a given moment, which corresponds to 60% to 85% of the maximum pressure supported by the upper edge of the partition multiplied by the number of partitions covered by the applying element at a given moment.

[0025] According to a particular embodiment of the invention, the pressure applying elements are controlled by control means which determine the compacting pressure to be applied to each applying element as a function of the position of said applying element and the overall geometric pattern formed by the upper edges of the plurality of partitions. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] [ Figure 1 ] Figure 1 is a schematic diagram of an apparatus according to the present invention.

[0027] [ Figure 2 ] Figure 2 yes Figure 1 Schematic cross-sectional view of a device.

[0028] [ Figure 3 ] Figure 3 yes Figure 1 Schematic diagram of the position of the pressure applying element of the device on the covering surface.

[0029] [ Figure 4 ] Figure 4 yes Figure 1 Schematic diagram of a first position of a pressure-applying element of a device.

[0030] [ Figure 5 ] Figure 5 yes Figure 1 Schematic diagram of a second position of the pressure-applying element of the device.

[0031] [ Figure 6 ] Figure 6 yes Figure 1 Schematic diagram of a third position of the pressure-applying element of the device.

[0032] [ Figure 7 ] Figure 7 is a schematic cross-sectional view of a panel produced according to the method of the present invention. DETAILED DESCRIPTION

[0033] Figure 1 Schematically and partially shown is a device 1 according to the invention for covering a fiber structure 210 on a multi-compartment body 120 by automated fiber placement. The fiber structure 210 impregnated with a thermoplastic material is thus intended to form a composite skin 110 or 130 with a thermoplastic matrix on the multi-compartment body 120, such as Figure 7 shown.

[0034] The multi-compartment body 120 comprises at least a plurality of partitions 121 forming a network of ribs defining compartments 150. The upper edges 121a of the partitions define a first covering surface 120a which is therefore located at one end of each compartment 150 of the multi-compartment body 120.

[0035] The multi-compartment body may be in a stacked form. For example, the multi-compartment body may include a stack of multiple partitions, each partition defining a compartment sub-body. These stacked compartment sub-bodies may themselves be separated by a skin.

[0036] Additionally, the compartments 150 of the multi-compartment body 120 may include one or more internal structures 122, such as complex hollow acoustic elements in the shape of a frustoconical or pyramidal structure, such as Figure 7 shown.

[0037] exist Figures 1 to 7 In the example shown, the multi-compartment body 120 has identical hexagonal cells 150, thereby forming a regular structure known as a "honeycomb" structure. Of course, if the cells of the multi-compartment body have square, rectangular, circular, etc. or even any shape, it does not depart from the scope of the present invention. If the cells of the multi-compartment body have variable and / or irregular shapes, it does not depart from the scope of the present invention.

[0038] The manufacture of the multi-compartment body 120 is well known. For example, the multi-compartment body 120 can be manufactured by polymer, composite material or metal additive manufacturing in a well-known manner. The multi-compartment body 120 can also be made of polymer, composite material, metal material or paperboard according to conventional manufacturing methods.

[0039] Preferably, the multi-compartment body 120 is made of a thermoplastic material. Preferably, the upper edge 121a of the multi-compartment body 120 belonging to the covering surface 120a is made of a thermoplastic material, and the rest of the multi-compartment body 120 can be made of another material. In fact, the use of a thermoplastic material on the upper edge 121a of the multi-compartment body 120 intended to be in contact with the epidermis 110 or 130 allows a strong bond with the deposited fiber structure 210 made of a thermoplastic material to be easily and quickly produced. This preferred connection mode is based on thermoplastic / thermoplastic welding, which allows the fiber structure 210 to be easily welded to the upper edge 121a of the partition 121 due to the increase in temperature, and without the need to add additional material. During melting or softening, the properties of thermoplastics, depending on whether they are semi-crystalline or amorphous, allow their surface layers to interpenetrate each other at high temperatures during covering. Therefore, the connection formed between the fiber structure 210 and the upper edge 121a of the partition 121 is mechanically strong and durable. In particular, this type of thermoplastic / thermoplastic joining allows the creation of connections that comply with aerospace standards.

[0040] Thus, the multi-compartment body 120 may be made of a thermoplastic material in a known manner by injection or stamping. The thermoplastic material may be filled with short fibers, or filled with continuous fibers. The thermoplastic material may be unfilled.

[0041] The multi-compartment body 120 can also be produced in a well-known manner by injection compression of filled or unfilled thermoplastic material. Injection compression involves injecting the material into a half-open mold. Therefore, even if the material freezes, the passage becomes less blocked. When the material is distributed throughout the mold, it is completely closed by a closing force to return to the correct size. This allows obtaining the thickness of the partition 121 of the compartment 150 or the wall of the internal structure 122, which is thinner than the thickness obtained by conventional injection methods.

[0042] The multi-compartment body 120 can also be produced in a well-known manner by injection and controlling the temperature of the tool filled or unfilled with thermoplastic material. Injection with tool temperature control comprises controlling the temperature of the tool or mold by means of a system for servo-controlling the tool temperature, for example with a heat transfer fluid or with air.

[0043] Thermoplastic materials that can be used to manufacture the multi-compartment body 120 and the partitions 121 are specifically polyaryletherketone (PAEK), such as polyetheretherketone (PEEK) and polyetherketoneketone (PEKK), polyetherimide (PEI), polyphenylene sulfide (PPS) and polysulfone (PSU).

[0044] The apparatus according to the invention comprises a device 10 for supplying a fiber structure 210 impregnated with a thermoplastic material. The fibers of the fiber structure 210 may be ceramic or carbon fibers. The ceramic fibers may be fibers made of a non-oxide material, such as silicon carbide (SiC), or fibers made of an oxide material, such as aluminum oxide.

[0045] The fiber structure 210 can be in the form of a fiber core (wick) or a fabric layer. "Core" refers to a group of fibers or filaments that are substantially parallel to each other and combined into a non-woven strip. The fiber structure can be woven or non-woven. Preferably, the fiber structure 210 is a roving of pre-impregnated continuous unidirectional fibers.

[0046] The fiber structure 210 is impregnated with a thermoplastic material, which may include a solid filler. The fiber structure 210 may also be impregnated with a thermoplastic material that does not include a solid filler. The fiber structure 210 may be impregnated only with an organic phase consisting of a thermoplastic material. The fiber structure 210 may have a mass content of thermoplastic polymer greater than or equal to 30%.

[0047] The thermoplastic material with which the fiber structure 210 is impregnated may be selected from: polyaryletherketone (PAEK), such as polyetheretherketone (PEEK) and polyetherketoneketone (PEKK), polyetherimide (PEI), polyphenylene sulfide (PPS) and polysulfone (PSU).

[0048] The thermoplastic material used to impregnate the fiber structure 210 may have a glass transition temperature greater than or equal to 50° C., and preferably included between 80° C. and 180° C. The thermoplastic material used to impregnate the fiber structure 210 may have a melting temperature greater than or equal to 80° C., and preferably included between 120° C. and 500° C. The glass transition temperature and the melting temperature may be calculated by differential scanning calorimetry.

[0049] Pre-impregnation of the fiber structure 210 with the thermoplastic material can be carried out by any conventional technique, for example by dipping, by roller coating or also by spraying.

[0050] The fiber structure 210 impregnated with the thermoplastic material is then conveyed from the feeding device 10 to a device 20 for depositing the impregnated fiber structure 210. The deposition device 20 comprises at least one pressure applying element 2, which is located on one side of the covering surface 120a of the multi-compartment body 120, that is, on one side of the upper edge 121a of the partition 121 of the multi-compartment body 120. This or these pressure applying elements 2 each exert a compacting pressure, also called covering pressure, on the multi-compartment body 120, so as to achieve the deposition of the impregnated fiber structure 210 on the covering surface 120a defined by the upper edge 121a of the partition 121 of the multi-compartment body 120. Figure 1 As shown, the pressure-exerting element 2 may be in the form of a roller or may be in the form of a compacting shoe.

[0051] During the covering operation, the deposition device 20 is movable in the covering direction D so as to apply the impregnated fiber structure 210 to a first area of ​​the covering surface 120a of the multi-compartment body 120, thereby forming an impregnated fiber strip 211 on at least a portion of the upper edge 121a of the partition 121. Once applied on said first area, a cutting element (not shown) cuts the impregnated fiber strip 121. After this cutting, a deposition of the first fiber strip 121 impregnated with thermoplastic material on the first area of ​​the covering surface 120a is thus obtained. The deposition device 20 can then be moved so as to deposit the impregnated fiber structure 210 on a second area of ​​the covering surface 120a, which second area is different from the first area.

[0052] Preferably, only one layer of impregnated fiber structure 210 is deposited on the cover surface 120a of the multi-compartment body 120. Thus, the material required to produce a skin 110 or 130 made of composite material with a thermoplastic matrix is ​​completely deposited in a single pass of the deposition device 20. This deposition method allows to obtain a skin 110 or 130 made of a material with good microstructural characteristics, consolidation taking place under good conditions.

[0053] The device 1 according to the invention further comprises local heating means 30. The local heating means 30 comprises one or more elements 31 and 32 capable of heating a very small portion 210c of the fiber structure 210 during deposition, or a very small portion 121c of the upper edge 121a of the partition 121 covered by the heated fiber structure 210. Figure 1 In the example shown, the local heating device 30 may be a laser heating system, which allows excellent precision of the heated area. The laser heating system may include a laser diode, a yttrium aluminum garnet (YAG) laser, or a fiber laser.

[0054] like Figure 1 As shown, one or more first heating elements 31 can be used to heat the portion 210c of the fiber structure 210 to be covered. Thus, this or these first heating elements 31 ensure continuous and uniform heating of the deposited fiber structure 210. In addition, one or more second heating elements 32 can be used to heat the portion 121c of the upper edge 121a of the partition 121 to be placed in contact with the fiber structure 210. This or these second heating elements 32 ensure a very limited heating of the upper edge 121a of the partition 121, limiting the risk of undesired deformation of the multi-compartment body 120, and in particular the risk of collapse of the multi-compartment body 120 due to the passage of the deposition device 20. The first and second heating elements 31 and 32 can be different, or at least partially combined.

[0055] In order to limit the risk of sagging of the skin 110 or 130 in the areas not supported by the partitions 121 of the multi-compartment body 120, a sufficient tension T is applied to the impregnated fiber structure 210 during deposition, such as Figure 2 This tension T is referred to herein as "covering tension".

[0056] The covering tension T is high enough to avoid sagging of the fiber structure 210 not supported by the upper edge 121a of the separator 121, but not too high to avoid damaging the connection between the fiber structure 210 and the upper edge 121a of the separator 121. Therefore, the covering tension T applies a shear stress to the interface between the fiber structure 210 and the upper edge 121a of the separator 121, which is 50% to 80% of the maximum shear stress supported by the interface. This maximum shear stress can be characterized by performing a "single lap shear stress" or "double lap shear stress" type test on a thermoplastic or thermosetting interface suitable for this characterization.

[0057] This covering tension T can be achieved by various means of tension control. For example, the covering tension T can be generated at least in part by means of a tensioner 3. The control of the tensioner 3 can be performed by selective braking that produces rotation, motorization of the rotation or controlled displacement of the lateral translation of the tensioner.

[0058] The covering tension T can also be generated at least partially by rotating the above-mentioned pressure applying element 2 at a rotation speed ω. For example, the deposition roller 2 can be rotated to generate sufficient covering tension T and it can no longer rotate freely. The pressure applying element 2 is controlled by means of a rotation selection brake or by means of a rotation motor.

[0059] Preferably, the means for generating the covering tension T are controlled in a closed loop so as to ensure the desired tension value in the majority of the fibres.

[0060] In order to further reduce the risk of sagging of the skin 110 or 130 covering the multi-compartment body 120, it is also possible to control the pressure P applied by the aforementioned pressure applying element 2 on the covering surface 210a of the multi-compartment body 120. a , P b , P c The pressure P a , P b , P c The pressure P applied by the pressure applying element 2 can be controlled, for example, by translationally controlling the pressure applying element 2 by means of a cylinder. a , P b , P c .

[0061] For each deposition point 121c of the fiber structure 210 on the upper edge 121a of the multi-compartment body 120, the compaction pressure P a , P b , P c The direction of is therefore perpendicular to the direction of the covering tension T.

[0062] Since the covering surface 120a is not smooth but discontinuous, it is necessary to adapt the pressing pressure P applied by each pressure applying element 2 according to the number of edges 121a of the partition 121 present under said pressure applying element 2. a , P b , P c .like Figures 3 to 6 In the example shown in FIG. 1 , the application element can be Figure 4 The first position a shown passes continuously over three partitions 121, and then according to Figure 5 The second position b shown passes over six baffles 121 and then according to Figure 6 The third position c shown passes over eight partitions 121. Therefore, the first position a of the application element 2 will require the application of a first compaction pressure Pa, and the second position b of the application element 2 will require the application of a second compaction pressure P b , the third position c of the application element 2 will require the application of a third pressing pressure P c, so that the second pressing pressure P b Greater than the first pressing pressure Pa but less than the third pressing pressure P c .

[0063] The number of edges 121a of the partitions 121 present under the pressure applying element 2 may be determined in real time as the applying element 2 moves over the covering surface 120a, or may be predetermined from an overall geometric pattern of the covering surface 120a formed by the upper edges 121a of a plurality of partitions 121.

[0064] The real-time determination of the number of webs 121 present under the application element 2 can be carried out by means of sensors or specific instruments, for example by means of a profilometer.

[0065] The defined reference compression pressure Pref corresponds to the maximum pressure applied by the pressure applying element 2 supported by the diaphragm 121. For a given local force, the reference compression pressure P ref Obtained from the minimum buckling limit of the diaphragm 121 .

[0066] Therefore, the pressing pressure P applied by each application element 2 is selected a , P b , P c , the compaction pressure is included in the reference compaction pressure P ref Multiply by between 60% and 85% the number of webs 121 located below the application element 2 .

[0067] exist Figures 3 to 6 In the context of the example of , the first, second and third pressing pressures P are obtained thereby a , P b and P c The following formula:

[0068] 0.6×P ref ×3≤P a ≤0.85×P ref ×3;

[0069] 0.6×P ref ×6≤P b ≤0.85×P ref ×6;

[0070] 0.6×P ref ×8≤P c ≤0.85×P ref ×8.

[0071] This method for determining the compaction pressure can be adapted to the case where the multi-compartment body has different types of partitions, a different reference compaction pressure Pref being used for each type of partition.

[0072] Thus, it is possible to form a skin 110 or 130 on the upper edge 121a of the multi-compartment body 120, for example by heat treating the fiber structure deposited as described above to form a matrix of the composite material of the skin 110 or 130. The method of the invention can be used to manufacture any type of multi-compartment panel 100, which comprises at least one skin 100 or 130 covering the compartments 150. However, the invention is particularly suitable for the manufacture of acoustic attenuation panels. The invention may in particular allow the production of one or more skins 110, 130 of the same sound attenuation panel 100, including an open acoustic skin 110, a closed acoustic skin 130 or an intermediate acoustic skin located between multiple partitions of the same panel. In the case of an open acoustic skin 110, perforations 111 must be formed in the skin to allow sound waves to enter the acoustic compartments 150 of the panel 100.

[0073] The panel 100 manufactured according to the method of the invention can be used in the aeronautical field, in particular for manufacturing a multi-compartment panel belonging to an aerospace engine, a nacelle or a nacelle interior.

[0074] The expression “included between… and…” must be understood as including the limits.

Claims

1. A method for manufacturing a panel (100) comprising a plurality of partitions (121) defining compartments (150), the compartments (150) being covered by at least one skin (110, 130) of thermoplastic material, the skin (110, 130) being formed by covering an upper edge (121a) of the partitions (121) with a fiber structure (210) impregnated with thermoplastic material by automated fiber placement, the upper edge (121a) of the partitions (121) and the fiber structure (210) being joined together by means of a local heating device (30) when they are placed in contact, The method is characterized in that the fiber structure (210) is covered with a covering tension (T) at the interface between the upper edge (121a) of the partition (121) and the fiber structure (210), and before the interface ruptures, the covering tension (T) applies a shear stress to the interface, and the applied shear stress is 50% to 80% of the maximum shear stress.

2. The method according to claim 1, characterized in that The covering tension (T) is at least partially generated by a rotationally controlled tensioner (3).

3. The method according to claim 1 or 2, characterized in that: The covering tension (T) is at least partially generated by the rollers used to deposit the fibrous structure (210) whose rotation is controlled.

4. The method according to claim 1, characterized in that: At a given moment, a pressing pressure (P) is applied by a pressure applying element (2) to the upper edge (121a) of the partition (121). a , P b , P c ) covers the fiber structure (210), and the pressing pressure corresponds to 60% to 85% of the maximum pressure supported by the upper edge (121a) of the partition (121) multiplied by the number of partitions (121) covered by the pressure applying element (2) at the given moment.

5. The method according to claim 4, characterized in that The sensor measures the amount of the diaphragm (121) covered by the pressure applying element (2).

6. The method according to claim 4 or 5, characterized in that: The pressure applying element (2) is controlled by a device that adapts the compacting pressure (P) applied by the pressure applying element (2) according to the position (a, b, c) of the pressure applying element (2) and the overall geometric pattern formed by the upper edges (121a) of the plurality of partitions (121). a , P b , P c ).

7. The method according to claim 1, characterized in that At least the upper edge (121a) of the partition (121) is made of thermoplastic material.

8. A device (1) for covering a fiber structure (210) impregnated with a thermoplastic material on the upper edges (121a) of a plurality of partitions (121) defining a compartment (150), the device (1) comprising at least: - a device (10) for supplying a fiber structure (210) impregnated with a thermoplastic material, - means (20) for depositing a fiber structure (210) on said upper edge (121a) of a plurality of separators (121), - a local heating device (30) configured to heat the portion (121c) of the upper edge (121a) of the partition (121) and the portion (210c) of the fiber structure (210) immediately before the portion (121c) of the upper edge (121a) of the partition (121) and the portion (210c) of the fiber structure (210) are placed in contact by the device (20) for depositing the fiber structure (210), The device is characterized in that the device (20) of the fiber structure (210) is configured to cover the fiber structure (210) with a covering tension (T) on the interface between the upper edge (121a) of the partition (121) and the fiber structure (210), and before the interface ruptures, the covering tension (T) applies a shear stress to the interface, and the applied shear stress is 50% to 80% of the maximum shear stress.

9. The device according to claim 8, characterized in that The device (20) for depositing a fiber structure (210) comprises at least one pressure applying element (2), which is controlled to rotate on the one hand to achieve the covering tension (T) and to translate on the other hand to achieve a compacting pressure (P) on the upper edge (121a) of the partition (121) at a given moment. a , P b , P c ), the pressing pressure corresponding to 60% to 85% of the maximum pressure supported by the upper edge of the partition multiplied by the number of partitions (121) covered by the pressure-exerting element (2) at a given moment.

10. The device according to claim 9, characterized in that The pressure applying elements (2) are controlled by a control device, which determines the pressing pressure (P) to be applied to each pressure applying element (2) based on the positions (a, b, c) of the pressure applying elements (2) and the overall geometric pattern formed by the upper edges (121a) of the plurality of partitions (121). a , P b , P c ).

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