RTM tool for injecting a low-viscosity resin reaction mixture into a pre-formed component, as well as the use of a high-temperature resistant, high-performance thermoplastic for a sealing element.

Abstract

RTM tool (10; 10') for injecting a low viscosity resin reaction mixture into a preformed component (20), comprising at least: - two metallic tool halves (10; 10') which are to be placed against each other in at least one contact zone (14) and which enclose at least one mold cavity (12; 12') between them in which the component (20) is to be arranged, and - at least one continuous sealing element (15; 15', 16') enclosing the mold cavity (12; 12'), which consists of a high-temperature resistant high-performance thermoplastic and is assembled from several partial sealing elements (15.1,..., 15.18) joined together in a row, which are inserted into a sealing groove which is provided in at least one of the tool halves (10; 10').

Description

[0001] The invention relates to an RTM tool for injecting a low-viscosity resin reaction mixture into a long-fiber preform with the features of the preamble of claim 1, an RTM tool for injecting a low-viscosity resin reaction mixture into a preformed component, and the use of a high-temperature-resistant high-performance thermoplastic for a sealing element.

[0002] The resin injection molding process (RTM = Resin Transfer Molding) is used for the fully automated production of three-dimensional, fiber-reinforced plastic components. First, a core is manufactured that defines the shape of the component and around which the long fibers are wound. If necessary, the core is designed so that it can be washed out later to create a hollow body. The preform made from the fiber-wrapped core is roughly trimmed and placed in a special, two-part RTM mold reminiscent of an injection molding tool. The tool is then closed hydraulically. Highly reactive, low-viscosity resin reaction mixtures, such as mixtures of polyols with polyisocyanates, are injected into the tool under high pressure. In addition, other types of components can be coated with a thermoset, for example, wood-coated decorative parts for use in automotive interiors.To increase scratch resistance and dimensional and chemical resistance, it can be provided with a high-gloss thermosetting layer.

[0003] The reaction between the resin components, which leads to curing, takes place within the closed mold. This is an exothermic reaction and thus increases the pressure and temperature within the mold. The reaction resin mixtures used in the resin injection process are significantly less fluid than, for example, injected thermoplastics in conventional injection molding. For this reason, the mold halves in the closed mold must be carefully sealed against each other, and the sealing elements must withstand higher surface pressure. Conventional sealing materials such as seals made of elastomer rubbers, e.g., SBR, EPDM, or NBR; silicone-based rubbers, e.g., FPM; and even fluoroplastic materials, e.g., PTFE, fail in this process.

[0004] EP 1 721 719 B1 describes an RTM mold that features an O-ring seal at the parting line and a relief channel inside it, into which excess reaction mixture can flow. While this generally prevents normal influences on the seal, damage to the seal cannot be ruled out in the event of overdosage. Furthermore, a burr is created that must be mechanically removed.

[0005] During this process, it can also happen that fibers from the preform "wander around" within the mold or that loose fibers settle on the sealing surface. This destroys any form of inelastic, rigid seal, because the carbon or glass fibers are so hard compared to all other materials used in the mold that if they were to get caught between the sealing surfaces of a rigid (metallic) seal, they would cause irreversible damage. The seal must be able to deform elastically under these environmental conditions and must not be destroyed by the fibers.

[0006] The high pressures of up to 250 bar and the equally high temperatures that occur during the RTM process due to the exothermic reaction of the components in the mold cavity also place special demands on the seal. Elastomer seals cannot withstand the stresses of pressure and temperature. Silicone seals, on the other hand, stick to the reaction resin mixture and thus become unusable.

[0007] DE 199 11 655 A1 discloses the production of shaft seal rings from high-performance materials such as PEEK. US 2010 / 0 116 422 A1 describes the production of large-diameter ring seals from high-temperature-resistant high-performance thermoplastics. An application in connection with mold cavities in multi-part injection molds is not disclosed. The object of the present invention is to improve a two-part mold of the type mentioned above with regard to the seal, which must withstand the special conditions in an RTM mold, such as the stickiness of the resin and the hardness of the preform, as well as pressure and temperature, and the other general conditions of the applied high-pressure RTM process.

[0008] To solve this problem, the invention proposes an RTM tool for injecting a low-viscosity resin reaction mixture into a preform having the features of claim 1 or the use of a high-temperature-resistant high-performance thermoplastic for a sealing element for an RTM tool having the features of claim 12.

[0009] Further state of the art can be found in DD 17 943 A1.

[0010] The use of high-temperature-resistant high-performance thermoplastic enables the resulting sealing element to withstand the high base temperatures in the RTM process of approximately 140°C to 200°C and high injection pressures of the resin reaction mixtures into the tool of typically approximately 100 bar to 200 bar.

[0011] Despite the high operating temperatures and the high basic hardness at room temperature during the process, the material still gives the seal such a high level of elasticity that surface irregularities and foreign bodies on the sealing surface can be compensated.

[0012] In addition, the sealing element provided according to the invention is chemically resistant, particularly to almost all organic and inorganic chemicals, and up to about 280 °C also to hydrolysis.

[0013] Semi-finished products made of such high-temperature-resistant, high-performance thermoplastics are available in various dimensions. The sealing element according to the invention is preferably machined from solid material. This allows modern machine tools to produce sealing elements for use in custom-shaped tools without significant manufacturing effort.

[0014] In addition, the sealing elements preferably directly surround the mold cavity with the preform to be inserted therein, thus forming a direct boundary of the outer circumference of the molded part.

[0015] A particular advantage of using a high-temperature-resistant, high-performance thermoplastic is its good elastic formability. When the mold halves are closed and pressed together, this ensures secure contact with the contact zone of the opposing mold half. Geometric changes in the metal parts of the mold are compensated for by the sealing element deforming and maintaining contact at all times, ensuring the tightness of the mold during all phases of the process.

[0016] High-temperature-resistant high-performance thermoplastics are particularly suitable for forming a sealing element or partial sealing element: polyamideimide, polyetheretherketone, polyphenylenesulfone.

[0017] A polyetheretherketone modified by the applicant, marketed under the trade name Murlock®, has proven particularly suitable and is characterized by the following properties: Ball indentation hardness 230 MPa Shore hardness D 87 Melting point 340 °C Glass transition temperature 143 °C Linear thermal expansion coefficient a average value between 23° and 100°C 5,5 × 10 -5 m / (m·K) Linear thermal expansion coefficient a - average value above 150°C 13 × 10 -5 m / (m·K)

[0018] In addition to the choice of material, the structure of the sealing element is essential: Although the result is an endless sealing element that completely encloses the mold cavity, according to the invention it is formed from partial sealing elements that are lined up in the longitudinal extension of the sealing element, i.e. relatively short, rod-shaped parts that are formed in particular from plate blanks that are machined and that are lined up in a seal receiving groove in at least one of the tool halves and in their entirety form the sealing element.

[0019] The division into partial sealing elements brings various advantages: First and foremost, the simple production of relatively small elements from standard plates is worth mentioning. A three-dimensional profile of the sealing element can also be easily created by arranging partial sealing elements at a specific angle to one another. If damaged, a partial sealing element can be easily replaced. By eliminating a fixed connection between the partial sealing elements, local stresses due to pressure and temperature influences cannot arise in the first place, or at least they are not transferred to neighboring elements, thus preventing them from affecting the geometry of the sealing element. The main advantage of subdividing the mold into partial sealing elements, however, is that it compensates for the relatively greater thermal expansion of the sealing material compared to the tool steel, starting from a certain mold cavity size and sealing element length. The partial sealing elements are manufactured in such a way that they are undersized in terms of their longitudinal extension at room temperature. Gaps exist between the adjacent partial sealing elements when cold; these close when the tool heats up. - The joints are preferably geometrically simple, particularly as butt joints, i.e., simply facing each other, without serrations or other form-fitting features. This allows the gap to be most easily determined and manufactured in the cold state, and the geometry is easy to manufacture. - Also because the sealing elements are not all flat but can be three-dimensional, the parting planes were chosen to be as simple as possible from a manufacturing perspective. However, this also resulted in different lengths for the partial sealing elements.

[0020] Therefore, there are preferably no additional connecting elements whatsoever between the partial sealing elements. When using the tool according to the invention in the RTM tool, it is deliberately provided that the reactive resin can penetrate into the remaining gaps between the partial sealing elements and harden there. Thus, the sealing element in the RTM tool according to the invention has a self-sealing function as soon as resin has been injected into the tool mold once. The production of the partial sealing elements is also simple because, based on the relative thermal expansion between the sealing element and the tool half to be expected at the process temperatures, a larger undersize can always be selected in the initial state at room temperature in case of doubt. Even if a gap does not close immediately upon heating due to end-to-end contact of the partial sealing elements, it closes automatically in the first process pass.This is a significant advantage, especially in the case of non-linear sections in the sealing element, because the axial mobility of a partial sealing element within the sealing groove may be restricted, so that the thermal expansion may not have an even effect at both ends, which means that the resulting gap widths cannot be precisely predicted.

[0021] The resin cured in the remaining gaps then forms a precisely fitting seal between the individual partial sealing elements. The only thing that is currently certain is that the RTM tool according to the invention with the sealing elements is absolutely tight and that the resin penetrates between the elements but does not ooze out.

[0022] Preferably, the sealing element, viewed in cross-section, has a block body with which it is inserted into a seal receiving groove, and at least one sealing lip that is significantly narrower and thinner than the block body projects beyond the adjacent surfaces on the tool. Thus, preferably, only the upper edge of the sealing lip on the sealing element rests against the opposite contact zone of the other tool half. The sealing lip faces the cavity in cross-section. The width of the sealing lip is related to the closing force acting on the tool and the resulting surface pressure.

[0023] This sealing lip's geometry, particularly the height at which it protrudes above the adjacent contact zone of the mold half, was also selected so that the seal only deforms in the elastic range when the mold is completely closed and both mold halves are pressed together. Therefore, the ratio of the sealing lip to the overall size of the seal is also important. However, the press applying the closing force must also be capable of deforming the seal. This requires considerable pressing forces, so a narrow sealing lip is preferred.

[0024] It is also possible to manufacture entire sections of one half of the RTM tool from the same material as the sealing element. This material not only serves as a seal within the tool, but also acquires shaping properties within the tool.

[0025] It is also advantageous to provide at least one ejector pin in the mold cavity, which is slidably mounted in a bushing, which is also made of one of the aforementioned high-temperature-resistant, high-performance thermoplastics. This can be the same type of plastic or a different one of the aforementioned types.

[0026] At least one ejector pin is almost always required to enable the workpiece to be removed from the mold cavity. Conventional ejector pins, such as those used in molds for injection molding thermoplastic materials, are not suitable for the RTM process. Due to the significantly higher temperatures involved in the RTM process, larger gaps would have to be provided between the ejector and the metal bushing in which it is guided. The low viscosity of the reactive resins, which is advantageous for self-sealing between the preferred partial sealing elements, would automatically lead to permanent blockage of the ejector pins in their bushings.By using PEEK as a material not only for the sealing element but also for the ejector pin bushings, the thermal expansion behavior of this high-temperature-resistant, high-performance thermoplastic, which differs from steel, can be utilized specifically: At room temperature and at demolding temperature, an annular gap exists between the bushing and the ejector pin, allowing it to move freely. At injection and reaction temperatures, however, the gap closes, clamping the ejector pin tightly and thus preventing the penetration of reaction resin. During cooling for demolding, the bushing shrinks and releases the ejector pin.

[0027] The invention is explained in more detail below with reference to the drawings. The figures show in detail: Fig. 1 a tool half of a first RTM tool in perspective view; Fig.2 a tool half of a second RTM tool in perspective view; Fig. 3 an enlarged detail of the RTM tool after Fig. 2; Fig. 4 a sealing element in plan view from above; Fig. 5 the sealing element from Fig. 5 in side view; and Fig. 6 a cross-section of the sealing element.

[0028] Fig.Figure 1 shows a perspective view of a lower mold half 10' of an RTM mold. This includes a complementary, second, upper mold half, not shown here. Recesses are formed in the mold half 10', which are part of a mold cavity 12' with an injection opening 13'. A contact zone 14' is provided around the mold cavity, in which the corresponding contact zone of the other mold half rests when the mold is closed. A first sealing element 15' is provided on the inner circumference of the contact zone 14', which directly encloses the mold cavity 12'. The width of the first sealing element is approximately 10 mm.

[0029] A second sealing element 16 is arranged at a significant distance from the first sealing element 15' on the outer periphery of the contact zone 14'. Should the resin reaction mixture overcome the sealing line there due to damage to the first sealing element 15', it will be held back by the second sealing element 16'. However, since the finished molded part, once the resin injection has cured, requires edge trimming anyway, this does not pose any disadvantages.

[0030] In Fig. Figure 2 again shows a lower mold half 10 of a second RTM mold. A long-fiber preform 20, which is connected to a metallic insert 21, is located in a mold cavity 12, which is enclosed and delimited by a sealing element 15. The sealing element 15 is located in a contact zone 14 of the mold half 10, onto which an upper mold half is pressed.

[0031] The insert part 21 also lies within the circumference of the sealing element 15. To prevent the insert part 21 from being accidentally encased in resin, an additional sealing element 17 extends from one side of the inner circumference of the sealing element 15 to the opposite side of the inner circumference of the sealing element. The insert part 21 rests on the additional sealing element 17. Although no further endless sealing element is provided in the contact zone on the upper tool half (not shown) to delimit the mold cavity, there is also a corresponding additional sealing element 17 running transversely across the mold cavity. This creates an inner bulkhead that encloses the insert part 21 and separates it from the rest of the mold cavity 12.

[0032] Fig. 3 shows the area with the insert part 21 in an enlarged view. Fig.2, the front area is spared from resin injection due to the additional sealing element 17. The sealing element 15 nevertheless encloses this area and ensures absolute tightness of the entire mold cavity, even if reactive resin should penetrate the joint between the additional sealing element 17 and the insert part 21.

[0033] Furthermore, Fig. 3 that the upper side of the sealing element 15 is not smooth, but has an upstand in the form of a sealing lip 18.2 on the inner side facing the mold cavity 12. The dot-dash lines indicate dividing lines between individual partial sealing elements 15.8, 15.9, 15.10, 15.1, 15.12, which are separate parts of the sealing element 15, at least until the first resin injection, which leads to the closing of the joints between the partial sealing elements 15.8, 15.9, 15.10, 15.1, 15.12.

[0034] The entire sealing element 15 is in Fig.4 shown in plan view. It consists of a plurality of partial sealing elements 15.1, ..., 15.10. The partial sealing elements 15.1, 15.10 on the left and right are clip-shaped and each present only once. Because the molded part is symmetrical with respect to the one axis of symmetry in the mold parting plane, the sealing element 15 is also symmetrical. Thus, partial sealing elements 15.2, ..., 15.9, 15.11 ... 15.18 of equal length are present above and below the axis of symmetry, with the respective upper ones being mirror images of the respective lower ones.

[0035] The side view in Fig.Figure 5 illustrates that the sealing element 15 in the illustrated embodiment does not extend in a single plane, but rather—following the mold parting plane—is a three-dimensional structure. Due to the division into partial sealing elements 15.1, ..., 15.18, each of the partial sealing elements has only a small height and can be manufactured, for example, from a plate-shaped semi-finished product.

[0036] A cross section 18 of the sealing element 15 is shown in Fig. 6. On a solid, wide block body 18.1, which is inserted into the seal receiving groove in the respective tool half, a sealing lip 18.2 or sealing edge is formed, which is preferably arranged pointing towards the mold cavity.

[0037] It is also possible to have the seal receiving groove run directly along the contour of the finished part, eliminating any burrs in the mold parting line. The sealing lip 18.2 and, if applicable, parts of the block body 18.1 then directly form part of the mold cavity.

Claims

[1] RTM tool (10; 10') for injecting a low-viscosity resin reaction mixture into a preformed component (20), at least comprising: - two metallic tool halves (10; 10') which are to be placed against one another in at least one contact zone (14) and which enclose between them at least one mold cavity (12; 12') in which the component (20) is to be arranged, and - at least one endless sealing element (15; 15', 16') enclosing the mold cavity (12; 12'), which consists of a high-temperature-resistant high-performance thermoplastic and which is assembled from a plurality of partial sealing elements (15.1,..., 15.18) arranged in a row and inserted into a seal receiving groove which is introduced into at least one of the tool halves (10; 10'). [2] RTM tool (10; 10') according to claim 1, characterized bythat the partial sealing elements (15.1,...,15.18) are individually formed by machining from plate blanks and form a spatial sealing element (15). [3] RTM tool (10; 10') according to claim 1 or 2, characterized by that the profile cross-section (18) of the sealing element (15) has at least one block body (18.1) inserted into the seal receiving groove and a sealing lip (18.2) formed thereon. [4] RTM tool (10; 10') according to claim 3, characterized by that the height of the sealing lip (18.2) is less than 1 / 10 of the height of the block body (18.1) and the width of the sealing lip (18.2) is less than ¼ of the width of the block body (18.1). [5] RTM tool (10; 10') according to claim 4, characterized bythat the sealing element (15, 15') is arranged directly on the outer circumference of the mold cavity (12; 12'), wherein a side edge of the sealing lip (18.2) is flush with a side edge of the block body (18.1) and is arranged facing the mold cavity (12; 12'). [6] RTM tool (10') according to one of the preceding claims, characterized by that a second sealing element (16') extends around the first sealing element (15') and is arranged at a distance therefrom. [7] RTM tool (10) according to one of the preceding claims, characterized by that the partial sealing elements (15.1,...,15.18) are each joined together with a butt joint. [8] RTM tool (10) according to one of the preceding claims, characterized by that an additional sealing element (17) extends from the inner circumference of the sealing element (15) into the mold cavity (12) up to a solid insert part (21). [9] RTM tool (10; 10') according to one of the preceding claims, characterized by that the width of the sealing element (15; 15' 16') is 10 mm to 20 mm. [10] RTM tool (10; 10') according to one of the preceding claims, characterized by that the sealing element (15; 15', 16') protrudes by 0.1 mm to 3 mm above the surface of the adjacent contact zone (14). [11] RTM tool (10; 10') according to one of the preceding claims, characterized by that at least one ejector pin is arranged in the mold cavity (12, 12'), which is displaceably mounted in a bushing made of a high-temperature-resistant high-performance thermoplastic. [12] Use of a high-temperature-resistant high-performance thermoplastic for a sealing element (15; 15', 16') for an RTM tool (10; 10') for injecting a low-viscosity resin reaction mixture into a long-fiber preform (20), wherein the sealing element (15; 15', 16') consists of several partial sealing elements (15.1,...,15.18) arranged in a row, which are arranged in a seal receiving groove in the RTM tool (10; 10').

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