EP0000734B1 - Method for making rods or tubes having a constant profile of fibre reinforced material - Google Patents

Abstract

1. A process for the production of profiles from composite fibrous materials, wherein strands of fibrous materials continuously impregnated with liquid reaction resins are wrapped or braided immediately after impregnation or in the vicinity of a prehardening zone with drawn and/or preoriented and/or textured fibres or monofils and are hardened in a following hardening zone, characterised in that the fibres or monofils consist of polyamides, thermoplastic polyesters, polycarbonates, polyacrylonitrile, modacrylics, polyolefins, polyvinyl chloride, polytetrafluoro-ethylene, cellulose, regenerated cellulose, cellulose esters, polyvinyl alcohol or polyurethane.

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 their sliding surfaces to reduce friction and wear, often tempered 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 in the large nozzle lengths required for exact shaping not 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 e.g. By using Teflon tools, besides the advantages of low friction and the possibility of microwave curing of the reactive resins, there are serious disadvantages due to mold life, which are very short 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.

According to DE-OS 1 504 197, a method for producing rods, profiles and tubes made of fiber composite materials is known, in which fibers from a slip tree 1, FIG. 1, are continuously combined by guide plates 2. The fibers are then introduced into a heatable impregnation trough 4 filled with synthetic resin and simultaneously shaped by nozzles 5 and 6. Immediately after the impregnation, helical fiber material is wound onto the impregnated fiber material with the aid of a winding device 7. Then the material runs into a dielectric field 9 to the hardening furnace 10. On page 6, lines 9 to 11 it is described that the threads are braked by special tensioning devices so that they are applied to the impregnated fiber material with a certain tension.

In contrast, the method according to the invention differs in that the helical fibers are organic fibers or monofilaments or mixtures of organic and inorganic fibers or monofilaments.

The invention relates to a process for the production of profiles from fiber composite materials, wherein strands of fiber materials impregnated continuously with liquid reactive resins immediately after impregnation or in the area of a pre-curing section are wrapped or braided with stretched and / or pre-oriented and / or textured fibers or monofilaments and in one subsequent hardening section can be hardened, which is characterized in that the fibers or monofilaments consist of polyamide, thermoplastic polyesters, polycarbonates, polyacrylonitrile, modacrylic, polyolefins, polyvinyl chloride, polytetrafluoroethylene, cellulose, regenerated cellulose, cellulose esters, polyvinyl alcohol or polyurethane.

11. Description of the procedure

In the claimed process, fiber materials are used in the usual way, e.g. impregnated with a liquid reaction resin in an impregnation bath, the resin content being determined by nozzles, rollers or the like. Devices which correspond to the prior art are set.

The impregnation of the impregnated fiber material with the appropriate fiber materials after impregnation according to the invention 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 curing takes place in the usual way, for example by convective heat transfer wear, heat radiation or by microwaves in a heating duct.

For the wrapping of the impregnated or impregnated fiber materials with the stretched or pre-oriented or textured organic fibers according to the invention, conventional winding machines are suitable, e.g. Diagonal winding machines, such as those used for the production of reinforced hoses, or machines used for the production of insulation in the winding or braiding process. Machines for wrapping wires (e.g. guitar strings) are also 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, depending on the desired properties (effects), it is possible to cover the impregnated fiber materials with the stretched or pre-oriented or textured organic fibers 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, the impregnated strands can be wrapped with fibers or monofilaments on an inner mold and hardened into closed hollow profiles without any further outer mold.

Another possibility of profile production is that by wrapping a flat impregnated strand of fiber material with stretched and / or pre-oriented or textured organic fibers, flat profiles or angle profiles can be produced in a simple manner only by using a roll 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 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, for wrapping the impregnated fiber materials.

The effect of the shaping achieved with the wrapping of 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 which are caused by proportion, type, degree of stretch and / or pre-orientation and / or texturing and the geometric arrangement of the organic fibers are determined. The organic fibers are selected in such a way that the shrinkage peaks become effective 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 about 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. Berte processes with an external shape cannot achieve such fiber contents and strengths and orientations 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 rigidity 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 be done 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 impregnating resins, 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 hardening combine the individual fiber strands into a profile with a homogeneous fiber distribution but different matrix materials.

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 fibers lying on the profile surface do not or only incompletely impregnate them, giving simple options for improved bond adhesion, e.g. B. when embedding the profiles in thermoplastics. For this purpose, the wrapping material is chosen 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.

111. Materials

The claimed method is suitable for fiber composites made of glass fibers, organic fibers, carbon fibers and metal fibers. The fibers can, for example. are in the form of fiber strands such as yarns, filament yarns, twisted yarns, rovings and spinning threads etc. or as textile fabrics and / or as fiber mats.

Suitable matrix materials are e.g. B. reaction resins such as unsaturated polyester resins, epoxy resins, methacrylate resins, polyurethane resins, novolak resins, polybismaleinimides or cyanate resins, the heat of which during the curing process, or whose 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, polyvinyl chloride, polytetrafluoroethylene, cellulose and regenerated cellulose, cellulose esters or polyvinyl alcohol and polyurethane fibers are suitable as materials for wrapping the impregnated fiber materials.

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 that are produced by the method according to the invention are suitable with their homogeneous fiber arrangement, the high fiber contents and their freedom from voids 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 tensioning wires or tensioning ropes, whereby advantageous the improved possibilities for applying force, the reduced notch sensitivity and the increased transverse strength of predominantly unidirectionally reinforced profiles come into play. 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 profiles produced by the method according to the invention to also be used in electrical engineering sector z. B. as a strength member in insulators or for contact wire tensioning and in electrical engineering.

example 1

In preparing a round rod of glass yarns and polyester resin, the mm by a flawless round outlet nozzle 10 only at the end of the impregnating bath _was' 0 pulled to adjust the resin content and was then cured without any further molding in an electrically heated tube furnace was noted that the rod unre ^g el was moderately formed, and having 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 0 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 wound in a winding layer, after hardening with temperatures between 140 and 180 ° C there were round profiles without longitudinal and transverse cracks 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 Example 1, glass fiber strands were impregnated with polyester resin and, after leaving the impregnation bath, were wrapped with an outlet nozzle full of 10 mm 0 with e-glass spun threads of 3100 dtex and polyester (PETP) filament yarn consisting of 34 individual filaments, a total titer of 167 dtex and a (stretch) aspect ratio of 1: 4 in equal proportions. The coverage was chosen to be 100% in one position by means of screw windings with a pitch of 15 °. 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 strength compared to a comparison bar with approx. 1350 MPas with the same cross section 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 were cast in devices made of a synthetic resin mortar. 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 three pairs of rollers calibrated, 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 multiple nozzle in a ring arrangement. After leaving the exit nozzle, the fiber strands were passed over a cylindrical drag core as the inner form and in the area of a pre-curing section still on the tow core with Perlon monofilaments 0.20 mm 0 (≐ 400 dtex) with a stretch ratio of 1: 4 by screw windings with a cover wrapped by about 40%. In the subsequent curing section (tube furnace), the profiles were cured at temperatures between 140 and 160 ° C. By this method is obtained without any further outer shape with the drag core hollow profiles which a geometrically correct inside diameter with wall stärkeschwankun ^g s of ± 0.1 mm at a wall thickness of 2 mm. The surface of the profiles was wavy in the longitudinal direction.

Claims (2)

1. A process for the production of profiles from composite fibrous materials, wherein strands of fibrous materials continuously impregnated with liquid reaction resins are wrapped or braided immediately after impregnation or in the vicinity of a prehardening zone with drawn and/or preoriented and/or textured fibres or monofils and are hardened in a following hardening zone, characterised in that the fibres or monofils consist of polyamides, thermoplastic polyesters, polycarbonates, polyacrylonitrile, modacrylics, polyolefins, polyvinyl chloride, polytetrafluoroethylene, cellulose, regenerated cellulose, cellulose esters, polyvinyl alcohol or polyurethane.

2. A process according to claim 1, characterised in that the impregnated strands are wrapped on an internal former with the fibres or monofils and are hardened in the absence of an external former to form closed hollow profiles.