EP0000734A1 - Method for making rods or tubes having a constant profile of fibre reinforced material - Google Patents

Abstract

Process for the production of profiles from fiber composite materials, characterized in that strands of fiber materials continuously impregnated with liquid reactive resins immediately after impregnation or in the area of a pre-curing section with stretched and / or pre-oriented and / or textured organic fibers or monofilaments or mixtures of organic and inorganic fibers or monofilaments are wrapped or braided and cured in a subsequent curing section.

Description

A number of processes are known for the continuous production of profiles from fiber composite materials. All of these processes have in common that semi-finished products made of organic, inorganic or metallic fibers in the form of fiber strands, fiber mats or fabrics are drawn off from a storage rack, impregnated with liquid reactive resin and cured into profiles in a curing section with simultaneous shaping in nozzle tools.

In particular, the processes differ in the type of impregnation, the shape and the hardening. For the shaping, nozzle constructions made of high-quality tool steels are customary, which are heated with steam, oil or electrically and whose sliding surfaces to reduce friction and wear are often coated surface layers, e.g. B. hard chrome plating. With such shaping tools, relatively difficult profiles can be produced. It has been shown in practice that the use of such complex tools requires a very precise coordination of all system components. A number of reactive resins can e.g. B. because of their reactivity or due to the frictional conditions, despite the use of release agents, the large nozzle lengths required for precise shaping are not to be used.

The high friction forces that occur in the nozzles limit the fiber content of the fiber composite materials, they disrupt the fiber orientation and cause high pulling forces. The reduction in friction z. B. by the use of Teflon tools brings next to the advantages of low friction and the possibility of microwave curing of the reactive resins, however, serious disadvantages due to mold life, which are very low compared to those of the steel tools.

In order to reduce the disadvantages mentioned when using steel tools, at least in the case of simple circular or elliptical cross sections, it has also been proposed to wrap the impregnated fiber material with a release film. This enables hardening without further shaping in a subsequent simple hardening section. Disadvantages of this method are the costs and the outlay for the winding and unwinding of the separating films, which generally cannot be used repeatedly, and the surfaces which are not perfect and which often require reworking.

Wrapping the impregnated strands with glass fiber products also enables the production of simple profiles without additional shaping. The disadvantage of these processes is the poor surface of the profiles and the occurrence of hardening cracks even with relatively small cross sections.

The invention relates to a method for producing profiles from fiber composite materials, which is characterized in that strands of fiber materials impregnated continuously with liquid reactive resins immediately after impregnation or in the area of a pre curing section with stretched and / or pre-oriented and / or textured organic fibers or monofilaments or mixtures of organic and inorganic fibers or monofilaments wrapped or braided and cured in a subsequent curing section.

II. Description of the procedure

In the claimed method, fiber materials are used in a conventional manner, e.g. B. impregnated in a drinking bath with a liquid reactive resin, the resin content being adjusted by means of nozzles, rollers or similar devices which correspond to the prior art.

The wrapping of the impregnated fiber material according to the invention with the suitable fiber materials after the impregnation can be carried out immediately after the fiber strands have left the impregnation bath. In some cases it is also advantageous to carry out the wrapping only after a pre-curing process - but always in the liquid phase of the reactive resin.

The actual hardening takes place in the usual way, for. B. by convective heat transfer, heat radiation or by microwaves in a heating channel.

For the winding of the impregnated fiber materials with stretched or pre-oriented or textured organic fibers, conventional winding machines are suitable, e.g. B. diagonal winding machines such as those used for the production of reinforced hoses, or machines which are used for the production of insulation in the winding or braiding process. As well

machines for wrapping wires (e.g. guitar strings) are suitable.

The impregnated fiber material can be wrapped in the form of circumferential windings with a small pitch. Screw windings with gradients that can be set within wide limits are also possible. Another type of wrapping is the application of diagonal (cross) windings. Common braiding processes are also suitable for applying the organic fibers to the impregnated fiber strands.

When executing screw windings, cross windings or braiding, the impregnated fiber materials are covered depending on the desired properties (effects)

with the stretched or pre-oriented or textured organic fibers possible within wide limits up to multiple overlaps.

An essential feature of the method according to the invention is that by wrapping with stretched or pre-oriented or textured organic fibers, in contrast to wrapping with inorganic fibers, profiles with exact circular cross sections without using a shaping unit, e.g. B. a shaping nozzle can be generated.

Other geometrically simple and exact cross-sectional shapes - e.g. B. ellipses - can be produced by wrapping impregnated fiber materials with organic fibers if the strand emerging from the impregnating bath is e.g. B. has an approximately rectangular cross section.

In addition to the possibility of creating profiles with a geometrically perfect cross-section without shaping nozzles, by wrapping impregnated strands of fiber materials with stretched and / or pre-oriented or textured organic fibers on an inner mold, closed hollow profiles can be produced without an additional outer mold.

Another way of making profiles is. that by wrapping a flat soaked strand of fiber material with stretched and / or pre-oriented or textured organic fibers in a simple manner, flat profiles or angle profiles can only be produced by using a roller calibration.

Due to the lack of shaping nozzles, microwave curing is particularly advantageously possible, since the impregnated fiber strands can absorb the radiation without weakening over relatively long distances.

Particularly interesting possibilities result from the fact that in addition to the wrapping of the impregnated fiber materials. Stretched and / or pre-oriented or textured organic fibers, inorganic fibers can also be applied as additional reinforcements, or fiber mixtures of organic and inorganic fibers for additional reinforcement of the fiber composite materials.

The shaping effect achieved by wrapping the impregnated fiber materials with stretched and / or pre-oriented or textured organic fibers or monofilaments is based, in addition to a uniform application of the winding, in particular on the fact that during the pre-hardening or hardening process, shrinkage forces are released, Degree of stretching and / or pre-orientation and / or texturing and the geometric arrangement of the organic fibers can be determined. The organic fibers are selected so that the shrinkage forces take effect before the gel phase of the reaction resin used is reached. The shrinkage forces occurring depend not only on the type of fiber material used, but also on the proportion (coverage) and on the degree of stretching and / or the pre-orientation as well as on the geometric arrangement of the organic fibers on the profile to be wrapped.

For the aforementioned examples of shaping, it has been shown that a relatively small coverage of approximately 12% is sufficient to produce the effects described.

At the same time, the shrinking forces always create a resin-rich profile surface. With an appropriate selection of the type, quantity and arrangement of the organic fiber material, profiles are obtained with a completely encased pure resin layer, which can only be achieved with an additional manufacturing step in other manufacturing processes.

One of the advantages of such a resin jacket produced in one process step is the improved handling without disruptive reinforcing fibers on the profile surface. This also results in significantly improved weather resistance, which can usually only be achieved by an additional coating with the inherent adhesion problems.

The shrinking forces of the organic fibers can also be used specifically to achieve high fiber contents with an almost ideal longitudinal orientation of the reinforcing fibers and to air-free profiles that have a largely homogeneous fiber distribution. This results in significant increases in module and strength of the profile with significantly improved reproducibility of these values. In processes with external shaping, such fiber contents and strengths and orientations cannot be achieved due to the frictional forces that occur.

By wrapping impregnated fiber materials with organic fibers, the strength transverse to the longitudinal direction of the profile (transverse strength) is particularly significantly improved in the case of predominantly unidirectionally reinforced profiles. Likewise, the notch sensitivity of the profiles produced in this way is significantly reduced by the wrapping with organic fibers.

Targeted and generally considerable improvements in the bending and torsional stiffness of any symmetrical profiles can be achieved by wrapping impregnated fiber materials in such a way that both suitable organic fibers and primarily inorganic fibers are used for wrapping. In this way, the advantage of impregnation of the additionally applied fibers can be combined with the advantage of gaining stiffness without further impregnation bath simply by the shrinking effect of the organic fibers that occurs.

.Wrapping with both types of fibers can take place in separate process steps, particularly advantageously but simultaneously.

The method according to the invention also makes it possible to impregnate several individual strands with different impregnation properties, to combine them by wrapping them, and to harden them into a uniform fiber composite material. A uniform fiber composite material is obtained in that the shrinkage forces released during the hardening process combine the individual fiber strands into a profile with a homogeneous fiber distribution, but different mstrix work.

The resin excess generated on the profile surface by the shrinking forces of the stretched or pre-oriented and / or textured organic fibers can serve, as already described, for the complete impregnation of further fiber materials. This means, for example, that decorative profiles can be created by using differently colored fiber materials as well as profiled surfaces.

In addition, the type, proportion, degree of stretch and geometric orientation of the organic fibers can be used to adjust the excess resin such that additionally applied fiber materials are only partially impregnated.

When the profiles are additionally wrapped with organic fibers, the result is that on the profile surface

lying not or only incompletely impregnated fibers oath possibilities, an improved bond adhesion z. B. when embedding the profiles in thermoplastics. For this purpose, the wrapping material is selected as similar as possible to the thermoplastic used. When additionally wrapping the profiles with inorganic fibers such. B. glass fibers result from the effects described particularly favorable conditions when introducing tensile forces z. B. in force introduction elements through the increased profile surface, which is obtained both with a profile and with incompletely impregnated fibers.

III. Materials

The claimed method is suitable for fiber composites made of glass fibers, organic fibers, carbon fibers and metal fibers. The fibers can e.g. B. in the form of fiber strands such as yarns, filament yarns, twists, rovings and spun threads etc. or as a textile fabric and / or as a fiber mat.

Suitable matrix materials are e.g. B. reactive resins such as unsaturated polyester resins, epoxy resins, methacrylate resins, polyurethane resins, novolak resins, polybismaleinimides or cyanate resins, the heat of which in the curing process or the curing temperatures exceed values at which the organic fibers used shrink.

Stretched and / or pre-oriented .and / or textured organic fibers or monofilaments made of polyamides, thermoplastic polyesters, polycarbonates, polyacrylonitrile, modacrylic, polyolefins, polyvinylchloride, polytetrafluoroethylene, cellulose and regenerated cellulose, cellulose esters or polyvinyl alcohol as well as are suitable as materials for wrapping the impregnated fiber materials Polyurethane fibers.

The shrinking temperature of the organic fibers depends on the starting polymer and the conditions during fiber production and stretching or texturing. A suitable organic fiber must be selected according to the curing conditions of the matrix material used, as already described.

Profiles which are produced by the method according to the invention are suitable with their homogeneous fiber arrangement, the high fiber contents and their freedom from Cavities and similar imperfections as well as with their resin-rich or their pure resin surfaces due to their strengths for the reinforcement of concrete as tension wires or tensioning ropes, whereby the improved possibilities for force application, the reduced notch sensitivity and the increased transverse strength mainly benefit from unidirectionally reinforced profiles.

A particular advantage when used outdoors is the high weather resistance of the profiles thanks to their pure resin surface.

High strengths and associated favorable electrical properties allow the use of the profiles produced by the method according to the invention also in the electrical sector, for. B. as strength members in insulators or for contact wire tensioning and in electrical engineering.

example 1

When producing a round rod from glass rovings and polyester resin, which was only drawn through a perfect round outlet nozzle of 10 mm φ at the end of the impregnating bath to adjust the resin content and which was then cured in an electrically heated tube furnace without any further shaping, it was found that the Rod was irregularly shaped and had a rough surface with partially exposed glass fibers. The deviations from the ideal circular shape were up to 10%. The glass content of this rod was 76.4% by weight.

Example 2

In the same way impregnated glass fiber strands, which after leaving the exit nozzle of the impregnating bath of 10 mm φ and a length of 5 mm with Perlon filament yarn, consisting of 140 individual filaments with a total titer of 940 dtex and an aspect ratio of 1: 3.2 in a screw winding up to an overlap of approx. 20% were wrapped in a winding layer, after hardening with temperatures between 140 and 180 ° C gave round profiles without longitudinal and transverse giant with less than 1% deviation from the circular shape. The glass content of the rod after grinding the organic fiber was 81.5% by weight. The surface of the rod thus produced is smooth and high-gloss. The thickness of the pure resin layer on the surface is approx. 100 µm.

Example 3

Similar to the example, glass fiber strands were impregnated with polyester resin and, after leaving the impregnation bath with an outlet nozzle of 10 mm φ, wrapped with e-glass spun threads of 3100 dtex and polyester (PETP) filament yarn consisting of 34 individual filaments with a total denier of 167 dtex and one (Stretch) aspect ratio of 1: 4 in equal proportions. The cover was made by screw windings with a pitch

selected from 15 ° to 100% in one position. After curing at temperatures between 160 and 195 ° C, a perfect round profile without longitudinal cracks was obtained. To test the notch sensitivity and the load capacity perpendicular to the profile axis as well as the tensile strength of the profiles, notch tests were carried out on approximately 15 mm long profile sections with the stamp of a conventional bending testing machine (tip radius 1 mm) and compression tests between flat plates, the profile axis being arranged perpendicular to the direction of force was. Compared to the non-wrapped comparative bar, the breaking loads were about 35% higher. In the pressure test between flat plates, an average of 15% higher values were achieved compared to the comparison rod. Tensile tests based on DIN, 53455 showed approx. 10% higher strengths with a same cross section compared to a comparison bar with approx. 1350 MPas due to the defect-free surface and the even fiber distribution over the bar cross section in the wrapped round profile. The known difficult clamping in the testing of fiber composites with such high strengths was avoided here in that the round bars in devices from one Resin mortar was poured. It turned out that much longer casting lengths had to be chosen for the unwrapped rods in order to break the glass fibers.

Example 4

In the manner of Example 1, carbon fiber strands were soaked in a resin bath and the fiber content was adjusted in a rectangular nozzle with a cross section of 20 × 2 mm. After the fiber bundle emerged from the nozzle, the fiber strand was wrapped with a cross winding at ± 75 ° to the longitudinal axis of the rod with Perlongarn consisting of 18 individual filaments and a total titer of 67 dtex stretch ratio 1: 2.8 with a coverage of about 30% and after a pre-hardening stretch calibrated by three pairs of rollers, the profile was covered on both sides with siliconized paper, and then hardened. A profile with a smooth surface and rounded edges was obtained. It showed thickness fluctuations of 2% along the length, the profile surfaces were parallel to each other. The profile was completely free of longitudinal cracks.

Example 5

In a manner similar to that in the first example, glass rovings were soaked in a soaking bath and the soaked rovings were adjusted to the desired resin content in a multi-nozzle in a ring arrangement. After leaving the exit nozzle, the fiber strands were guided over a cylindrical drag core as the inner shape and in the area of a pre-curing section still on the tow core with Perlon monofilaments 0, 20 mm0̸ (≙400 dtex) with a stretch ratio of 1: 4 by screw windings with a coverage of wrapped around 40%. In the subsequent curing section (tube furnace), the profiles were cured at temperatures between 140 and 160 ° C. With this method, hollow profiles with a geometrically perfect inner diameter with fluctuations in wall thickness of ± 0.1 mm with a wall thickness of 2 mm can be obtained with the drag core only with the drag core. The surface of the profiles was wavy in the longitudinal direction.

Claims (2)

1. A process for the production of profiles from fiber composite materials, characterized in that strands of fiber materials impregnated continuously with liquid reactive resins immediately after impregnation or in the region of a pre-curing section with stretched and / or pre-oriented and / or textured organic fibers or monofilaments or mixtures organic or inorganic fibers or monofilaments are wrapped or braided and cured in a subsequent curing section. 2. The method, characterized in that impregnated strands of fiber materials according to claim 1 are wrapped on an inner shape with stretched or pre-oriented and / or textured organic fibers or organic and inorganic fibers or mixtures of inorganic and stretched organic fibers and without further outer shape closed hollow profiles are hardened.