Method and apparatus for manufacturing a composite material from multifilament fibers

Abstract

A method of manufacturing an elongated composite element comprising a bundle (20) of multifilament fibers embedded in a composition made of a polymerizable material is disclosed, the method comprising the steps of: - producing an arrangement of multifilament fibers in the form of several individual strands, so that a first strand (20a) is located at the center of the bundle and the other strands are arranged around the first strand, - moving the arrangement of multifilament fibers so that it is subjected, in the direction of movement, to the following processes: - degassing the arrangement of fibers by vacuum, - impregnating the arrangement of fibers with the composition, - passing the first impregnated strand through a first die (10a) which subjects it to partial polymerization, - passing all the strands through a second die (10f) which subjects them to gathering into a single strand (20f), - exposing the single strand (20f) to a source of radiation for additional polymerization, thus obtaining the elongated composite element.

Description

Technical Field

[0001] This invention relates to a continuous manufacturing method of elongated composite materials produced by impregnating multifilament fibers with a polymerizable composition, and more particularly to a method of manufacturing composite materials in the form of single strands, such as GRC (glass-resin composite) types comprising continuous unidirectional multifilament glass fibers embedded in a polymerizable resin. Background Technology

[0002] Document EP 1 174 250 describes a method and apparatus for manufacturing ultra-long composite components using continuous resin impregnation of ultra-long fibers, the composites comprising reinforcing fibers embedded in a cured resin matrix. The described method includes the steps of: carrying a bundle of reinforcing fibers from a fiber storage reel through a vacuum chamber and then through an impregnation chamber, in which the fibers are impregnated with resin; and then, after the shape of the prepreg material has been stabilized prior by at least partial polymerization of the resin in the prepreg material, the impregnated fibers are passed through a calibration mold. A calibration mold of predetermined shape and size is also present at the entrance of the vacuum chamber and before the impregnation chamber. The apparatus includes a traction roller for carrying the fibers from the fiber storage reel and a reel for receiving the prepreg material.

[0003] While the functionality was satisfactory, it proved difficult to increase the diameter of composite materials manufactured using this facility beyond a certain limit. Therefore, the need for manufacturing composite materials with larger diameters emerged.

[0004] One solution to this problem is to place resin-impregnated fiber bundles (obtained from facilities that continuously manufacture fibers of the aforementioned type) in an oven to allow polymerization to occur at the core of the bundle. However, this method is time-consuming and labor-intensive.

[0005] Documents EP 1 506 085 A1 and US 2015 / 318080 A1 describe different methods for manufacturing composite materials in the form of cords.

[0006] Another solution to this problem is described in document EP 0 290 849. According to this document, resin-impregnated fiber bundles are produced by pultrusion, in which the fiber bundle is passed through a resin bath, then through a die and exposed to UV radiation. When the bundle travels along the length of the transparent die or through a liquid medium defined by two leak-proof nozzles while simultaneously exposed to UV radiation, polymerization of the bundle proceeds progressively from the outside to the inside. While it is acknowledged that better polymerization can occur at the core of the bundle, this process has proven to be quite slow and unsuitable for the manufacturing speeds of industrial processes. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the above-mentioned literature and provide an original solution for a method and apparatus for the polymerization of multifilament fibers in a facility for the continuous production of slender composite materials, enabling the production of composite materials with large cross-sectional dimensions at high productivity.

[0008] This invention achieves this objective by providing a method for continuously manufacturing elongated composite elements comprising bundles of multifilament fibers embedded in a composition based on a polymerizable material. The method includes the following steps:

[0009] - The multifilament fibers of the bundle are arranged in the form of several individual strands, each strand comprising several multifilament fibers, such that the first strand is located at the center of the bundle and the other strands are located around the first strand.

[0010] - The arrangement of the multifilament fibers is such that, in the direction of travel, it undergoes:

[0011] - The arrangement of fibers is degassed by vacuum action;

[0012] - Impregnate the fiber arrangement with the composition to obtain impregnated strands.

[0013] - The first impregnated strand of yarn is passed through a first die, which performs partial polymerization of the composition.

[0014] - Pass all the strands through the final die, which binds them together into a single strand;

[0015] - The single strand is exposed to a radiation source for further polymerization to obtain the elongated composite element.

[0016] An elongated composite element comprising a bundle of multifilament fibers (the multifilament fibers being embedded in a composition based on a polymerizable material) is understood to mean a composite element of extremely long length, which is continuously manufactured from one or more spools supplied with multifilament fibers to form a bundle, the bundle being carried to continuously impregnate the fibers with a polymerizable organic material and polymerize the material as the bundle moves through.

[0017] In other words, in the method of the present invention, the bundle to be impregnated is composed of strands of several multifilament fibers, with different strands selectively and sequentially polymerized so that polymerization of the impregnated multifilament fibers begins at the core of the bundle and is completed at its periphery. This allows for the production of elongated composite elements based on multifilament fibers, whose shape and size are well controlled and whose mechanical properties are uniform throughout their entire length. Preferably, additional polymerization results in the final polymerization of the composition.

[0018] Therefore, the method of the present invention can obtain composite components with large cross-sectional dimensions, which is accomplished at a high manufacturing rate. For example, for GRC (glass-resin composite) composites, the method of the present invention can obtain cross-sections with diameters between 10 mm and 30 mm at a rate of approximately 50 m / min.

[0019] The method of the present invention can also be used to produce composite elements with cross-sectional diameters between 0.5 mm and 10 mm, with the aim of achieving higher shape accuracy in a single operation than the method described in the cited document EP 1 174 250.

[0020] Therefore, it has been observed that by creating a partially polymerized core in the bundle's core, subsequent layers adhere well to this core, allowing for the acquisition of a final composite material with well-controlled cross-section and high production rates. This is because, in laboratory tests, it was found that the resin no longer flows under gravity through the impregnated bundle of fibers as in prior art facilities; in fact, quite the opposite, different successive fiber layers adhere well to the prepolymerized core until the final shape stabilizes after passing through the final mold and undergoing final polymerization of the composite material. For example, with GRC (glass-resin composite) composites, the method of this invention can yield elongated composite elements of extremely large (or continuous) lengths with a circular cross-section diameter between 0.5 mm and 2.5 mm, a tolerance of 0.05 mm, and a rate between 100 m / min and 200 m / min.

[0021] Partially polymerized or prepolymerized cores are understood to refer to composite cores embedded in multifilament fibers within a polymerizable composition. The degree of polymerization of the core ceases when it reaches at most a few percent of full polymerization, typically between 0.5% and 5%. The degree of polymerization can be assessed using a DSC (Differential Scanning Calorimetry) type of measuring instrument.

[0022] When measuring composite materials with a DSC-type device, the composite material is considered fully polymerized when the degree of polymerization of the resin is close to 100%, typically greater than 95%.

[0023] The arrangement of the strands and their sequential passing through at least a first die and a final die is performed such that the strands converge from the impregnation chamber toward the final die, maximally expanding at the outlet of the impregnation chamber, and contracting at the final die to form the single strand. This allows the bundle to be divided into several strands at the beginning of the method, with at least the central strand passing through a die that can act on the core of the bundle. Thus, the bundle is polymerized in stages, with the first polymerization stage occurring at the core of the bundle, and the final stage occurring when all the strands are combined into a final single strand for further polymerization.

[0024] The arrangement of multifilament fibers may include a central strand and several intermediate strands, the intermediate strands being configured to form at least one intermediate layer surrounding the central strand and at least one outer layer surrounding the peripheral strands, wherein each intermediate layer of the intermediate strand passes through an intermediate die, the intermediate die being used for partial polymerization of the composition.

[0025] This allows for staged polymerization with several phases, resulting in composite materials with larger cross-sections.

[0026] The cross-section of the composite element can be circular. However, the cross-section can take any other shape: polygonal, oval, elliptical, tubular, etc., especially by appropriately selecting the shape of the mold.

[0027] Multifilament fiber is understood to mean a fiber comprising several basic fibers arranged side by side to form a bundle, wherein the basic fibers of the bundle are unidirectional and substantially parallel to each other.

[0028] Multifilament fibers can be selected from glass fibers, carbon fibers, silicon fibers, ceramic fibers, and mixtures of such fibers, preferably from glass fibers, carbon fibers, and mixtures of such fibers, and even more preferably from glass fibers. These fibers are used to produce elongated composite materials by impregnating multifilament fibers with a polymerizable composition.

[0029] The polymerizable material can be thermosetting, preferably thermally crosslinkable, and even more preferably vinyl ester. Polymerizable material is understood to mean a substance containing more than 50% by weight, preferably more than 75% by weight, and even more preferably more than 90% by weight of organic matter. Therefore, such a substance can be a thermally polymerizable material, such as one based on unsaturated polyesters, polyepoxides, phenol derivatives, or amino plastics. Preferably, the polymerizable material is crosslinkable. For example, it can be a resin that can be crosslinked by ionizing radiation, and the final polymerization can be easily triggered and controlled by ionization treatment (e.g., UV or UV-visible light type ionization treatment). As a crosslinkable polymerizable material, polyester resins (based on unsaturated polyesters) are preferred, or even more preferably vinyl ester resins.

[0030] The object of the present invention is also achieved by an apparatus for the continuous manufacture of elongated composite elements comprising bundles of multifilament fibers embedded in a composition based on a polymerizable organic material, the apparatus comprising: means for generating an arrangement of the bundles of multifilament fibers in the form of several individual strands, each strand comprising several fibers such that a first strand is located at the center of the bundle; means for degassing the arrangement and means for impregnating the arrangement with a composition based on a polymerizable material; a first mold capable of receiving the first strand to partially polymerize it and at least one final mold capable of receiving all strands to form a single strand; and means for polymerizing the single strand using a radiation device to obtain the elongated composite element.

[0031] The device according to the invention may include at least one intermediate mold located between the first mold and the last mold.

[0032] The first mold and the intermediate mold may include an annular UV radiation lamp, with a guide tube for the strands included in the central portion of the annular UV radiation lamp.

[0033] The ring lamp may include a disk for supporting several light-emitting diodes (LEDs) and having a central opening through which the guide tube passes, a reflector for directing radiation emitted by the LEDs toward the outlet of the guide tube, a device for cooling the lamp, and a device for supplying power to the lamp.

[0034] The cooling device may include a water cooling circuit and / or a device for generating an airflow or nitrogen flow. A water cooling circuit ensures rapid and effective cooling of the lamp. Cooling using an airflow or nitrogen flow is easier to implement because it does not require sealing elements like a water cooling circuit. Furthermore, the presence of nitrogen promotes surface polymerization of the organic material coating the fibers because the presence of oxygen in the atmosphere acts as an inhibitor of the polymerization reaction.

[0035] The internal cross-section of each guide tube can gradually increase from upstream to downstream between the first and last molds. This allows for the gradual polymerization of the impregnated fibers in each layer around the centerline strand, starting from the core of the bundle. Attached Figure Description

[0036] The invention will be better understood through the following description based on the accompanying drawings:

[0037] Figure 1 This is a perspective view showing components of an apparatus for manufacturing elongated composite elements according to a preferred embodiment of the present invention;

[0038] Figure 2 This is a schematic perspective view showing the main components of another embodiment of the device of the present invention;

[0039] Figure 3 yes Figure 2 Enlarged cross-sectional view of feature A;

[0040] Figure 4 Show Figure 1 Enlarged 3D view of the equipment.

[0041] Figure 5 Shown at magnification Figure 4 The right side of the equipment;

[0042] Figure 6 This is a cross-sectional view of the mold that constitutes part of the equipment of the present invention;

[0043] Figure 7 The enlarged 3D view shows the components that form part of the cooling circuit of the lamp, which constitutes... Figure 6 Part of the mold.

[0044] In the various figures, the same or similar elements are marked with the same reference numerals. Therefore, they are not described systematically again. Detailed Implementation

[0045] Figure 1 An apparatus 1 for manufacturing long, slender composite elements is schematically shown. In the example shown, the composite material comprises a single strand of GRC consisting of glass filaments embedded in a thermosetting resin. The single strand can take any known shape; for example, it can be a cylindrical single strand with a large diameter (e.g., ranging from 10 mm to 30 mm), thus having a circular cross-section. Of course, the apparatus of the present invention can also manufacture single strands with rectangular, elliptical, or other cross-sections. The glass filaments are present in the form of substantially unidirectional multifilament fibers, each multifilament fiber being formed from multiple unit glass filaments, each unit glass filament having an average diameter of about 5 μm to 30 μm. The resin is of a thermosetting or crosslinkable type, understood to mean that the resin is based on a polymerizable or curable (photocurable and / or thermosetting) thermosetting polymer. The glass transition temperature Tg of the resin is preferably greater than 160°C, more preferably greater than 170°C, and particularly greater than 180°C.

[0046] exist Figure 1In the diagram, a bundle 20 of multifilament fibers is observed entering device 1. This bundle is schematically represented by arrow E in other figures, the direction of which indicates the direction of travel of the bundle relative to device 1, which is stationary. Bundle 20 enters vacuum chamber 2 through inlet plate 4, entering the device as several strands of multifilament fibers continuously unwound from different spools 9 of feed device 8. Typically, the fibers are fed in the form of rovings, i.e., groups of fibers wound in parallel on spools, and identified by their Tex codes. The bundle originating from feed device 8 passes through device 1 by traveling in the direction of arrow E, and is moved by a drive located at the outlet of device 1 (understood as after the outlet of radiation device 50, and actually even in the direction of arrow S, as will be explained later). For example, this type of drive (not shown) includes an electrically driven traction roller that allows the composite element to be wound around its axis, or includes two mutually facing electrically driven rollers spaced apart by a distance at least equal to the thickness of the composite element and rotating in opposite directions, carrying the composite element by frictional translational movement through the space between the two rollers. The apparatus 1 comprises, in sequence: a vacuum chamber 2, an impregnation chamber 3, and two molds 10a and 10b, referred to as polymerization molds, a final mold 10f, referred to as a calibration mold (through which the final single strand 20f passes), and a radiation device 50 for the single strand. The radiation device 50 is understood to mean a UV and / or IR radiation device that performs additional (preferably final) polymerization on the single strand emerging from the final mold 10f.

[0047] exist Figure 2 It was observed that the main components of the device 1 according to another embodiment of the present invention sequentially include: a vacuum chamber 2, an impregnation chamber 3, and several molds 10a to 10e called polymerization molds. Figure 4The final mold 10f, referred to as the calibration mold, and the radiation device 50 located before the outlet of the device can be seen. The vacuum chamber 2 is axially defined by a rigid inlet plate 4 (with through holes) and a rigid separation plate 5 (also with through holes, these through holes being axially opposite to the through holes of plate 4). Fibers, divided into several strands, are introduced into the vacuum chamber by passing through the various orifices of plate 4 and exit the vacuum chamber through the orifices of the rigid separation plate 5, such that the path traveled by the strands from one plate to another is linear, parallel to each other, and parallel to the longitudinal axis X-X' of the device. The vacuum chamber is connected to a vacuum pump (not shown), which maintains the pressure level within the vacuum chamber 2 at approximately 0.1 bar, although the diameter of the openings through which the fibers pass is larger than the diameter of the strands passing through them. The impregnation chamber 3 is a sealed housing defined by the rigid separation plate 5 and a rigid outlet plate 6, which also has through holes 7, these through holes 7 being axially opposite to the through holes of the rigid separation plate 5. The number of through holes 7 corresponds to the number of strands constituting the bundle 20. The impregnation chamber receives resin from an external tank (not shown) through an inlet pipe (not shown) at the top, and also includes a pipe (not shown) at the bottom for discharging resin. The impregnation chamber 3 is completely filled with resin, such that the fibers exiting the vacuum chamber 2 follow linear and parallel paths through the impregnation chamber 3 and are completely impregnated with resin.

[0048] Of course, before putting the device 1 of the present invention into use, it is necessary to start from the storage reel 9 and pass through all the molds and radiation devices 50 while passing through the orifices of the plate 4, rigid separation plate 5 and plate 6, until the drive device, to ensure that all the strands of the bundle are tightened in accordance with the predetermined arrangement of the multifilament fibers.

[0049] For example, if you want to obtain a cylindrical composite component with an outer diameter of 19 mm, use Figure 1 , Figure 4 and Figure 5 The apparatus shown uses an arrangement of approximately 80 basic bundles of multifilament fibers, each of which arrives at the apparatus from a spool 9 of 4800 Tex roving. The 80 basic bundles are arranged as follows: a center strand with a diameter of 5.6 mm, which itself comprises an assembly of 8 basic bundles of multifilament fibers from 8 spools of 4800 Tex; and two additional rows concentric with the first row, each row having a radial thickness of approximately 3 mm, each row comprising several concentric strands. The first additional row comprises 3 strands that are themselves composed of 8 basic bundles from 8 spools of 4800 Tex, and the second additional row comprises 6 strands that are themselves composed of 8 basic bundles from 8 spools of 4800 Tex. Clearly, the total number is 8 + 3 × 8 + 6 × 8 = 80 spools of 4800 Tex.

[0050] Downstream of impregnation chamber 3 are polymerization molds 10a to 10e and a final calibration mold 10f, all molds arranged along the same axis (i.e., the longitudinal axis of the equipment, X-X'). Bundle 20 consists of multiple strands from reel 9, arranged to ensure that these strands pass continuously through the various molds of the equipment. The arrangement of the strands is such that the central strand passes through the first mold 10a, which is essentially arranged along the axis of the equipment, and the individual intermediate strands are organized into several consecutive rows around the central strand, coaxial with the axis of the central strand, gradually converging as they pass through molds 10b to 10e until all the strands are combined and pass through the final mold 10f. Figure 4 And form a single line stock 20f.

[0051] Figure 4 A preferred embodiment of the device is shown, the device comprising a first mold 10a, an intermediate mold 10b, and a final calibration mold 10f. (Refer to...) Figure 5 To better observe, the bundle 20 of multifilament fibers comprises a central strand 20a and peripheral strands concentrically arranged with the first strand. The central strand 20a is designed to pass through the first die 10a, ensuring its partial polymerization. The strands exiting the first die 10a, together with the peripheral strands 20ae, pass through the intermediate die 10b, ensuring the partial polymerization of the newly formed strand 20b. The strands 20b exiting the intermediate die 10b, together with the remaining peripheral strands 20be, pass through the calibration die 10f, which shapes them to form the final strand 20f before final polymerization in the radiation device 50. The calibration die 10f is a tube with a defined shape and size. In an alternative form, the calibration die is a polymerization die type.

[0052] Reference Figure 3 and Figure 6 The structure of the polymerization mold 10a will be described below. This mold has an elongated shape along a longitudinal axis A-A' and includes a ring lamp 30 and a guide tube 40 for the fiber strands entering the mold. The lamp and guide tube are held together in a mold body 45 consisting of two parts 45a and 45b, the mold body 45 being provided with fins 46 for attachment to device 1. At its exit end, the mold body is extended by a tube 41 that guides the bundle exiting the mold to the next mold. The ring lamp 30 is an assembly comprising several LEDs 31 with UV radiation, which are interconnected by printed circuits on a common support 32 in a ring centered on axis A-A'. The ring lamp 30 includes a reflector 33 capable of directing the radiation emitted by the LEDs toward the exit direction of the guide tube 40. For example, the ring light 30 includes several high-power LEDs that emit wavelengths between 365 nm and 410 nm, preferably 385 nm, with a maximum power consumption between 100 W and 500 W, and requires cooling during operation. Figure 3 The mold shown includes a liquid cooling circuit (e.g., water), while Figure 6 The mold in the mold includes an air cooling circuit or a nitrogen cooling circuit. Figure 6 The mold shown includes a cooling circuit 35 for this purpose, the cooling circuit 35 including an inlet 34 connected to an air or nitrogen supply and a distribution plate 36 in thermal contact with the support member 32. Figure 7 The distribution plate 36 includes a distribution chamber 38, which includes an inner wall forming a baffle for cooling gas. The path of the cooling gas within the distribution chamber and the mold is as follows: Figure 6 and Figure 7 The arrows indicate this. Plate 36 also includes a central aperture 37 through which the guide tube 40 passes and an aperture 39 for accommodating the electrical connections of the lamp 30. Gas used to cool the distribution plate 36 then exits from the plate via conduit 47 so that it is subsequently distributed in the annular chamber 48 and continues in the space provided between components 40 and 45a for this purpose, so that it eventually exits concentrically in the space formed in component 45b in the direction indicated by arrow G. Thus, this airflow serves a dual purpose: firstly, to cool the distribution plate 36, and secondly, to continuously clean any suspended resin solvent or resin micro-jet in the internal volume of component 45b, more specifically ensuring the cleanliness of the reflector 33. The polymerization mold 10a is arranged within the device 1 with its longitudinal axis A-A' coaxial with the axis X-X' of the device.

[0053] Figure 3 The mold shown has two inlets 34 for gas (air or nitrogen) to enter, leading to an annular chamber 48 and then, along the direction of arrow G, to the interior space of the mold body 45, also to ensure the cleanliness of the reflector 33. Figure 3 The mold shown, except Figure 6 In addition to the mold shown, there is a coolant inlet 49 leading to a distribution plate (not shown) and then to a return conduit 51, which is used to circulate and maintain the temperature of the cooling circuit.

[0054] The first step of the method of the present invention involves, upon arrival of the bundle 20 at the device 1, generating an arrangement of multifilament fibers in the form of several individual strands forming the bundle 20, each strand comprising one or more multifilament fibers. The resulting arrangement places the first strand at the center of the device, with several peripheral strands arranged around it along the X-X' axis of the device. For this purpose, the inlet plate 4 in the vacuum chamber 2 includes several orifices for the strands to pass through, including a central orifice and several peripheral orifices. This arrangement then passes through a rigid separation plate 5 with an impregnation chamber 3 and an outlet plate 6 of the impregnation chamber 3. Subsequently, the strands exiting the impregnation chamber pass through various molds 10a, 10b (in fact, even...). Figure 2In the devices 10c, 10d, and 10e, each die ensures that the strands passing through it are partially bonded. The final center strand exiting from the final die 10e passes through the final die 10f. The final die 10f only concentrates all the strands at its center so that the resulting single strand 20f can be passed through the radiating device 50 that ensures the final bonding of the single strands. In an alternative form, the final die 10f is of the same type as the intermediate dies, performing the final bonding of the single strands 20f passing through it.

[0055] Within the scope claimed by this invention, other alternative forms and embodiments of the invention are conceivable. The method of this invention can use different types of multifilament fibers, and in fact, can even use different types of fibers within the same bundle.

[0056] Furthermore, it is conceivable to use the splicing method and apparatus of the present invention with thermally polymerizable organic materials.

[0057] Alternatively, the equipment may have a single reel conveying bundle at the inlet, which is separated into several individual strands.

Claims

1. A method for continuously manufacturing an elongated composite element comprising a bundle (20) of multifilament fibers embedded in a composition based on a polymerizable material, the method comprising the following steps: - The multifilament fibers of the bundle are arranged in the form of several individual strands, each strand comprising several multifilament fibers, such that the first strand (20a) is located at the center of the bundle and the other strands are located around the first strand. - The arrangement of the multifilament fibers is such that, in the direction of travel, it undergoes: - The arrangement of fibers is degassed by vacuum action; - Impregnate the fiber arrangement with the composition to obtain impregnated strands. - The first impregnated strand is passed through the first die (10a), which performs partial polymerization of the composition. - Pass all strands through the final die (10f), which gathers all strands into a single strand (20f). - The single strand (20f) is exposed to a radiation source for further polymerization to obtain the elongated composite element. The arrangement of the strands and their continuous passage through at least the first and last dies is performed such that the strands converge from the impregnation chamber (3) toward the last die (10f), the arrangement is most expanded at the outlet of the impregnation chamber (3), and the arrangement contracts at the last die (10f) to form the single strand (20f), and The arrangement of the multifilament fibers includes a central strand and several intermediate strands, the intermediate strands being configured to form at least one intermediate layer surrounding the central strand and at least one outer layer surrounding the peripheral strands, wherein each intermediate layer of the intermediate strands passes through an intermediate die for partial polymerization of the composition.

2. The method according to claim 1, characterized in that, The cross-section of the composite element is circular.

3. The method according to any one of the preceding claims, characterized in that, The multifilament fibers are selected from glass fibers, carbon fibers, silicon fibers, ceramic fibers, and mixtures of such fibers.

4. The method according to claim 1, characterized in that, The polymerizable material is thermosetting.

5. An apparatus (1) for the continuous manufacture of elongated composite elements, the elongated composite elements comprising bundles (20) of multifilament fibers embedded in a composition based on a polymerizable material, the apparatus (1) comprising: The apparatus includes: a device for producing an arrangement of multifilament fibers in the form of several individual strands, each strand comprising several fibers, such that a first strand (20a) is located at the center of the bundle; a device for degassing the arrangement and a device for impregnating the arrangement with a composition based on a polymerizable material; a first die (10a) capable of receiving the first strand (20a) to partially polymerize it and at least one final die (10f) capable of receiving all strands to form a single strand (20f); and a device for polymerizing the single strands using a radiation device (50) to obtain the elongated composite element. The device includes at least one intermediate mold (10b-10e) located between the first mold (10a) and the last mold (10f). The first mold (10a) and the intermediate molds (10b-10e) include an annular UV radiation lamp (30), and the central portion of the annular UV radiation lamp (30) includes a guide tube (40) for the strands. The internal cross-section of each guide tube (40) gradually increases from upstream to downstream between the first mold (10a) and the last mold (10f). The first strand (20a) passes through the first die (10a), the intermediate strands pass through the intermediate dies (10b-10e) and gradually converge until all the strands come together and pass through the final die (10f) to form a single strand (20f).

6. The device according to claim 5, characterized in that, The annular UV radiation lamp (30) includes a disk (32) for supporting several light-emitting diodes and having a central opening through which the guide tube (40) passes, a reflector (33) for sending the radiation emitted by the light-emitting diodes toward the outlet direction of the guide tube, a device for cooling the lamp, and a device for supplying power to the lamp.

7. The device according to claim 6, characterized in that, The device for cooling the lamp includes a water cooling circuit and / or a device for generating an airflow or nitrogen flow.

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