Method and device for melt-impregnating fibres with thermoplastic matrix

Abstract

In order to provide a method and a device for saturating dry fibres with high-viscosity, thermoplastic matrix, the invention proposes that the fibres are guided over a curved, perforated metal sheet as an impregnation section, while applying a contact pressure, wherein the high-viscosity, thermoplastic matrix passes through the perforations of the metal sheet, in order to then impregnate the fibres. The metal sheet is not flat, but rather integrated into the impregnation unit in a curved shape. By redirecting the fibres, which can be present as a fibre bundle or individual fibres, around the curved metal sheet, the necessary contact pressure can be generated between the fibres and the plastic feed. The fibres therefore move over the perforated metal sheet under longitudinal tension, wherein a sinusoidal contact pressure distribution arises between the fibres and the metal sheet. The high-viscosity thermoplastic matrix emerges through the perforations and coats the fibres evenly.

Description

[0001] DESCRIPTION

[0002] Method and device for melt impregnation of fibers with thermoplastic matrix

[0003] The invention relates to a method and a device for melt impregnation of fibers with a thermoplastic matrix.

[0004] Numerous processes are known for impregnating fibers with a thermoplastic matrix. These can be divided into the following groups:

[0005] • Powder impregnation: The fanned-out fibers are brought into contact with a powder (e.g., using a fluidized bed or electrostatic dispersion). The powdered fibers are then passed through a heating section and consolidated into the fiber-matrix semi-finished product using downstream cooling rollers. The main problem with this process is that the grain size of the powder must roughly correspond to the fiber diameter (e.g., approximately 6 μm for carbon fibers) to achieve good impregnation. Obtaining polymers of such fineness is usually associated with high costs and is sometimes technically impossible.

[0006] • Solvent impregnation: Impregnation occurs by reducing the polymer viscosity with solvents that diffuse out of the finished semi-finished product after the impregnation process. This process only works for thermoplastics such as PC, PSU, PES, or PEI.

[0007] • Film impregnation: Fibers and plastic films are pressed together under temperature and pressure. The fiber volume content can be adjusted by varying the number and thickness of the films. This process enables very high-quality fiber impregnation. However, not every plastic is commercially available or producible as a film in any thickness, so this process has limitations regarding its applicability.

[0008] • Hybrid fiber technology: The reinforcing fibers are spun together with plastic fibers into a mixed roving (also known as mixed yarn or commingled yarn). During processing of the roving, the plastic fiber is melted, thus ensuring the impregnation of the reinforcing fibers. Here, too, as with film impregnation, it is necessary for the plastic fibers to have approximately the same diameter as the reinforcing fibers, otherwise complete impregnation is not possible. • Melt impregnation: The rovings are pulled from a spool holder, spread out, and then impregnated with a molten matrix. There are a variety of design solutions for liquefying the thermoplastic matrix and ultimately feeding it into the dry fibers. The most important process parameters for producing high-quality fiber-matrix semi-finished products are the viscosity of the melt and the effective impregnation pressure.To ensure this functionality, very large systems with corresponding peripherals are usually necessary, which increases the dimensions of the entire system. As a result, current systems for impregnating fibers with thermoplastics can only be combined to a limited extent with other machines (e.g.

[0009] manufacturing plants for component production), which limits their area of ​​application.

[0010] All these known melt impregnation solutions have the following disadvantages:

[0011] • Process control: The fiber impregnation process becomes more complex with increasing matrix viscosity. Precise temperature and pressure control throughout the impregnation process is crucial. Existing systems do not allow for fine-tuned temperature and pressure control throughout the impregnation process, which negatively impacts the quality of the final product (impregnated semi-finished fiber product, also known as tape).

[0012] • Waste: The existing processes generally result in process-related waste, as impregnation cannot be achieved consistently across the entire strip width. A semi-finished fiber product is impregnated over a large area in a continuous process. Edge areas with different cavity conditions and thus different impregnation qualities are usually trimmed off afterward.

[0013] • Design: Conventional systems do not allow for a compact design and therefore only a limited integration of the technology into existing automation systems (e.g. as an attachment for an industrial robot).

[0014] • System maintenance: Cleaning conventional systems is usually very laborious. For example, with molten bath impregnation, the entire system must be disassembled and cleaned, which is a complex process. Cleaning during the ongoing process (e.g., using a cleaning agent) is not possible.

[0015] A. Lutz and T. Harmia, "Impregnation techniques for fiber bundles or tows," Polypropylene, Vol. 2, J. Karger-Kocsis, Ed. Dordrecht: Springer Netherlands, 1999, pp. 301-306. Doi: 10.1007 / 978-94-011-4421-6_43, describe a melt impregnation system in which the fibers are alternately passed over two impregnation tools made of a metal foam whose pore structure makes it permeable to liquid plastic. With the aid of an extruder, liquid plastic is injected into the core of the metal foam during the ongoing process and transported toward the surface of the metal foam. Impregnation occurs through contact between the dry fibers and the plastic-wetted metal foam. This process has shown promising results in practice. The invention is based on the object of creating a method and a device for impregnating dry fibers with a highly viscous, thermoplastic matrix.

[0016] This object is achieved in a method according to the invention in that the fibers are guided over a bent, perforated metal sheet as an impregnation section while applying a contact pressure, wherein the highly viscous, thermoplastic matrix passes through the perforations of the metal sheet in order to subsequently impregnate the fibers.

[0017] All organic or inorganic fibers suitable for material reinforcement, for example carbon, glass or polyamide fibers, can be used as fibers in the process according to the invention.

[0018] The perforated metal sheet is not flat, but integrated into the impregnation unit in a curved shape. By deflecting the fibers around the perforated, curved metal sheet, the necessary contact pressure between the fibers and the plastic feed is generated. The fibers can be present as fiber bundles or as individual fibers and move across the metal sheet under longitudinal tensile stress. This creates a sinusoidal contact pressure distribution between the fibers and the metal sheet. The highly viscous, thermoplastic matrix emerges through the perforations and evenly envelops the fibers.

[0019] The advantages of the inventions are the following:

[0020] • The material and manufacturing costs are very low (for example, the perforation of the metal sheet can be created by laser drilling).

[0021] • Steel sheets can be obtained inexpensively in very high quality, allowing them to withstand the abrasive effects of the fibers for a long time. Additionally, surface hardening can be performed to extend the service life of the metal sheet. • The surface roughness of the metal sheet can be adapted to the specific fibers and process parameters to protect the fibers.

[0022] • The perforation geometry can be flexibly adapted to the respective fiber-matrix combination depending on the matrix viscosity, for example using numerical flow simulation.

[0023] • The bent metal sheet requires only a small amount of space and thus enables a compact design of the device.

[0024] A preferred embodiment of the invention is that the perforation pattern of the metal sheet is determined by numerical fluid simulation.

[0025] By adjusting the hole size, hole shape and arrangement of the perforations across the width of the metal sheet depending on the contact pressure, a targeted pressure ratio can be set during the impregnation of the fibers.

[0026] The object of the invention is achieved in a device according to the invention in that a bent, perforated metal sheet is provided as an impregnation section, over which the fibers can be guided under application of a contact pressure, wherein the highly viscous, thermoplastic matrix can be guided through the perforations of the metal sheet in order to subsequently impregnate the fibers.

[0027] According to a preferred embodiment of the invention, two or more metal sheets are provided instead of one. These can be arranged either side by side or stacked.

[0028] This makes it possible to create opening contours for the plastic outlet that would otherwise not be possible in terms of manufacturing technology or would only be possible with great effort.

[0029] In a further development of the invention, it is provided that the metal sheets consist of the same material or of different materials and / or have different stiffnesses and / or have different wall thicknesses.

[0030] These can be metal sheets made of the same material or metal sheets made of different materials. By using metal sheets with different stiffnesses, for example, a sealing effect can be created in the contact surfaces with the impregnation tool. The metal sheets can also have different wall thicknesses.

[0031] An advantageous embodiment of the invention is that a lateral limitation of the impregnation section is provided. A further development of the invention is that a hinged bolt clamp is provided to seal the metal sheet against the tool, which presses the metal sheet against a curved support tool.

[0032] This ensures that no plastic can escape radially.

[0033] An advantageous embodiment of the invention is that the hinge pin clamp is milled out in the middle.

[0034] The articulated bolt clamp thus simultaneously represents a lateral demarcation of the impregnation section. This allows for functional integration of the support of the sheet metal holder and the limitation of the impregnation section in one component.

[0035] It is known from toolmaking for injection molding technology that sealing polymer channels is problematic, especially at high operating pressures. The present design solves this problem by applying a preload force perpendicular to each contact surface of the impregnation device through which the plastic could escape. Furthermore, the impregnation device can be quickly disassembled and is easy to clean. There is no waste, as impregnation is possible across the entire width of the impregnation section. This allows simultaneous width calibration of the product. The width of the impregnation section is adjustable depending on the spreading capacity of the rovings to be processed. This creates a novel, cost-effective device for producing fiber thermoplastic semi-finished products with adjustable parameters.

[0036] According to the invention, the carrier tool is designed in two parts.

[0037] This carrier tool serves not only to hold the perforated metal sheet but also to feed the highly viscous, thermoplastic matrix.

[0038] For this purpose, the carrier tool advantageously has a matrix supply and an associated distribution channel on which the bent metal sheet is arranged.

[0039] Preferably, a take-off unit is located at the end of the impregnation section, which serves to calibrate the thickness of the fiber-matrix composite. The thickness of the fiber-matrix composite can thus be variably adjusted. This take-off unit creates a circulation of the matrix before it leaves the impregnation section, which further increases the impregnation performance and surface quality.

[0040] In combination with the aforementioned lateral limitation of the impregnation zone, a closed cavity can be created. An exemplary embodiment of the invention is explained in more detail below with reference to the drawings.

[0041] It shows

[0042] Fig. 1 is a schematic representation of the impregnation process,

[0043] Fig. 2 the production and operation of the bent metal sheet,

[0044] Fig. 3 a sectional view (XY plane) of the impregnation device,

[0045] Fig. 4 a sectional view (ISO view) of the impregnation device,

[0046] Fig. 5 is a sectional view (YZ plane) of the impregnation device,

[0047] Fig. 6 a sectional view (XY plane) of the impregnation device according to Figure 3 with a withdrawal unit.

[0048] Fig. 1a shows a schematic representation of the impregnation process. The dry fibers 1 move continuously in the direction of the image plane (x-direction) on the metal sheet 2 (shown flat here for simplicity), while a highly viscous thermoplastic matrix passes through the perforations 3 of the metal sheet 2, impregnating the fibers 1.

[0049] The perforations shown do not correspond to the actual dimensions. The diameter of the individual perforations is – depending on the viscosity of the plastic matrix – between 10 and 500 pm, preferably between 15 and 300 pm, and most preferably between 20 and 150 pm.

[0050] Instead of a single metal sheet 2, two or more metal sheets 2 can be stacked on top of each other. This allows opening contours for the plastic outlet to be realized that would otherwise be impossible to achieve in terms of manufacturing technology.

[0051] Fig. 2 shows the production and operation of the bent metal sheet 2. First (Fig. 2a), a flat perforated metal sheet 2 is produced, whereby the perforation pattern can be adapted to the respective application.

[0052] The opening contours in the metal sheet can be circular, rectangular or any polygonal contour and - depending on the sinusoidal contact pressure distribution - have different dimensions and arrangements on the metal sheet (Fig. 2b).

[0053] The impregnation pressure is controlled by the perforation pattern, which is preferably determined by numerical fluid simulation. The metal sheet 2 is then bent into a circular segment (Fig. 2c), for example, by roll bending. Fig. 2d schematically shows the fiber impregnation process. The fibers 1 move across the perforated metal sheet 2 under longitudinal tensile stress, creating a sinusoidal contact pressure distribution between the fibers 1 and the metal sheet 2. The liquid plastic flows out through the perforations 3. By adjusting the dimensions of the perforations 3 depending on the contact pressure, a targeted pressure ratio can be set for the impregnation of the fibers 1.

[0054] Figs. 3 to 5 show an impregnation device according to the invention. To seal the metal sheet 2 against the support tool 4, a specially developed hinged bolt clamp 5 is used. This presses the metal sheet 2 against the support tool 4, thus ensuring that no plastic can escape radially. The special feature of this solution is that the hinged bolt clamp 5 is additionally milled out in the center, thus simultaneously forming the lateral boundary of the impregnation section. This allows for the functional integration of sheet metal support and boundary of the impregnation section in a single component.

[0055] The carrier tool 4 is constructed in two parts and, in addition to holding the perforated metal sheet 2, is responsible for feeding the highly viscous, thermoplastic matrix. Through a stepped contour of the matrix feed 6, the highly viscous, thermoplastic matrix is ​​fed from an extruder to the carrier tool 4 and distributed evenly beneath the perforated metal sheet 2 via a distribution channel 7. In addition, the carrier tool 4 serves as a holder for various sensors (e.g.

[0056] Pressure sensor 10, temperature sensor 11) to control the process. The dry fibers 1 are guided via a deflection roller 8 onto the carrier tool 4, then run in a semicircle over the perforated metal sheet 2, where they are impregnated with the highly viscous, thermoplastic matrix emerging from the perforations 3, and then leave the carrier tool 4 as an impregnated fiber-matrix semi-finished product 9.

[0057] As shown in Fig. 6, a take-off unit 10 is located at the end of the impregnation section. This unit serves to calibrate the thickness of the fiber-matrix composite. The thickness of the fiber-matrix composite can thus be variably adjusted. This take-off unit 10 creates a circulation of the matrix before it leaves the impregnation section, which further increases the impregnation performance and surface quality.

[0058] In combination with lateral limitations of the impregnation section, a closed cavity can be created.

Claims

CLAIMS A method for melt impregnating fibers (1) with a thermoplastic matrix, characterized in that the fibers (1) are guided over a bent, perforated metal sheet (2) as an impregnation section while applying contact pressure, wherein the highly viscous, thermoplastic matrix passes through the perforations (3) of the metal sheet to subsequently impregnate the fibers (1). Method according to claim 1, characterized in that the perforation pattern of the metal sheet (2) is determined by numerical fluid simulation.Device for melt impregnation of fibers (1) with a thermoplastic matrix, characterized in that a bent, perforated metal sheet (2) is provided as the impregnation section, over which the fibers (1) can be guided under the application of a contact pressure, wherein the highly viscous, thermoplastic matrix can be guided through the perforations (3) of the metal sheet (2) in order to subsequently impregnate the fibers (1). Device according to claim 3, characterized in that two or more metal sheets (2) are provided. Device according to claim 3, characterized in that the metal sheets (2) consist of the same material or of different materials and / or have different rigidities and / or have different wall thicknesses.Device according to one of claims 3 to 5, characterized in that a hinge pin clamp (5) is provided to seal the metal sheet (2) against the tool, which clamp presses the metal sheet (2) against a curved support tool (4). Device according to claim 6, characterized in that the hinge pin clamp (5) is milled out centrally. Device according to one of claims 3 to 7, characterized in that the carrier tool (4) is designed in two parts. Device according to one of claims 3 to 8, characterized in that the carrier tool (4) has a matrix feed (6) and a distribution channel (7) connected thereto, on which the bent metal sheet is arranged. Device according to one of claims 3 to 9, characterized in that a lateral limitation of the impregnation section is provided. Device according to one of claims 3 to 10, characterized in that a withdrawal unit (10) is arranged at the end of the impregnation section.

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