Techtextil: High-tech fibres for cars, aeroplanes and wind turbines
Manufacturers of cars, aeroplanes and wind energy plants are fervently committed to the use of fibre-reinforced plastics. For some it is to reduce the energy consumption of their products, while for others it is to increase energy generation with ever larger rotor blades. Although they start out from very different positions, they find a common denominator in technical textiles, all the more so because it is fibres made from carbon, aramid, glass and sustainable raw materials that provide the backbone for many duroplastic and thermoplastic materials. Filaments, fibre bundles and all intermediate products that are made from them are a science in themselves, a point proven by Techtextil which takes place in Frankfurt am Main from 11 to 13 June 2013.
Composites reinforced with carbon fibres are often superior to steel or aluminium components in terms of tear strength, modulus of elasticity and fatigue strength. The fact that carbon-based fibres continue to play much less of a role in the automotive industry than they do in aviation is down to price and the fact that it has only today become possible to produce fibre-reinforced components on a large scale. What is more it will be some time before all the recycling requirements of the automotive industry have been met.
Nevertheless technical innovations have been the catalyst in both fields for unprecedented change. The Airbus A380 and Boeing 787 have been the 'technology ice-breakers' to clear the path through which the automotive industry is now pushing - no longer with racing cars and concept vehicles but with large series 'bread and butter' models.
Everything points to the fact that textile reinforced plastic components will now break through into large scale production. Whilst on the one hand new production processes such as reactive resin transfer moulding enable the cycle times for duroplastic carbon fibre reinforced plastic components to be reduced to a few minutes, on the other the market is looking to fibre-reinforced thermoplastics, since in addition to cycle times of only one to two minutes, these also offer many other advantages. Not only are they suitable for production on injection moulding machines eliminating the need for post-processing, but they also enable structural components to be welded together for assembly or repair. Last but not least, new recycling processes have emerged that enable production waste and end-of-life components containing carbon fibres to be recycled with 100% of the carbon fibre content being reclaimed.
Carbon fibres can also be made from sustainable raw materials
Nevertheless, in the view of material scientist Professor Hans-Josef Endres from the University of Hanover Institute for Bioplastics recycling on its own is not enough to improve the ecological balance of composites. According to Professor Endres "Neither is the attempt to replace carbon fibres 1:1 by natural fibres going to get us where we want. Natural fibres have a different characteristic profile: they are based on a sustainable raw material, are more cost-effective, provide better acoustic properties and do not tend to splinter. Ultimately the objective must be to offer an alternative where the characteristic profile of the manufactured composite components as a whole is superior to that of carbon-based composites." As part of the 'Bio-concept Car' research project, managed by the University of Hanover and sponsored by the German Federal Ministry of Food, Agriculture and Consumer Protection (BMELV) and the Fachagentur Nachwachsende Rohstoffe e.V. (Agency for Renewable Resources - FNR), a VW Scirocco rally vehicle has been built that incorporates numerous components made from bio plastics in addition to a biobased, fibre-reinforced tailgate.
The automotive industry needs composites with fibres whose longterm availability does not depend on mineral oil. These can be lignin or cellulose based fibres or also fibres from thermoplastic polyolefins enabling components to be produced from composite materials with identical fibre / matrix properties, capable of 100% recycling in terms of material content.
Techtextil 2013 demonstrates graphically the high complexity of fibre-based composite technology. Important research establishments in the field of composite technologies are present along with the manufacturers of weaving, knitting and embroidery machines amongst many others. One of the innovations in terms of machine construction is an embroidery machine from Tajima with which it is possible to manufacture prepregs that are optimised for load force. The University of Bremen Fibre Institute has played a significant role in this development, focussing on the processing of high-grade carbon fibres. These fibres are embroidered onto an inexpensive substrate to create pre-forms close to the final shape required with hardly any production-related carbon fibre waste. What is more: the carbon, high tensile strength fibres, follow precisely the lines of load force flowing through the component, while a second, more cost-effective type of fibre reinforcement provides sufficient strength in areas that are subjected to a lesser mechanical load.
Eliminating fibre waste
The technology of the hybrid pre-form may still be very young, yet its further development is now already in the offing: tow placement technology in which the carbon fibres act as 'tow ropes', while thermoplastic PEEK fibres with an iron-ore based nano-coating act as binder yarn and stabilise the 2D or 3D form without any need at all for tacking threads. In addition, the PEEK fibres are laid by a robotic arm in two or three dimensions and heated by an induction unit just before they are dispensed. So the nano-sized iron ore particles indirectly heat the PEEK rovings which can then be freely formed. This results in pre-forms that are close to the final shape required and which can be processed next by thermoforming or as a structural insert on injection moulding machines. This technology even enables localised thickening at points subjected to a high mechanical load force - without any limitation in terms of the number of layers.
Essential to increase knowledge about fibres and composites
Unfortunately knowledge about fibre and structural reinforcement is increasing at as fast a pace as the multiplicity of market-ready technologies. This is a view shared by Professor Lothar Kroll, director of the Technical University of Chemnitz Institute for Lightweight Structural Construction. It is explained in part, he believes, by the massive amount of money invested in research over the last few years, necessary at the same time to get lightweight wide-bodied jets like the Airbus A380 and the Boeing 787 'Dreamliner' off the ground. Professor Kroll: "The wide scope of the research has found many new ways of manufacturing composite components which are now ready to be put into practice. The automotive industry is profiting from the experience of technical applications in aviation and often is even able to follow a valuebased approach - away from very expensive components towards cost-optimised designs on a large-scale production basis, that nevertheless offer outstanding mechanical strength and a very good ecological balance."
However, to break new ground in lightweight construction will require you to look for the optimum solution to your own specific problems, which is far from easy. Having said that, many opportunities are provided by the multiplicity of mineral or vegetable oil based fibres and the even greater number of matrix materials made through synthesis or equally from sustainable resources. An example of this is the possibility of manufacturing carbon fibres both from upstream, mineral oil dependent components and also from natural fibres by way of pyrolysis. What is more, alongside isotropic carbon fibres, anisotropic fibres are also available, that modify their properties according to the direction of load force. This makes it possible to design functions into components such as load dependent deformations for example. This technological approach can be significant for development of smart blades, i.e. ‘intelligent’ rotorblades for wind energy turbines, that modify their shape to optimise airflow, the stronger the wind blows, the greater the deformation.
Market open for duroplastic and thermoplastic composites
It is hard to keep track of the many and varied processing
technologies used to manufacture new lightweight structures. They pose additional challenge that already requires consideration, of course, in investment terms even as the ‘foundation-stone’ of the new composite component is laid. With respect to scaling up production the manufacturers of plastics processing machines have succeeded in reducing the cycle times of fibre-reinforced components made from duroplastic reactive materials to a few minutes. At the same time the manufacturers of plastics processing machines are preparing for a future increase in the use of thermoplastic composites capable of being produced by thermoforming or on injection moulding machines. Since each production process places its own requirements on the reinforcement fibres, the fibre lengths and / or the non-woven / woven, knitted, embroidered or braided materials made from the rovings, it is essential that those with specialist know-how are consulted at an early stage.
Techtextil exhibitor breaks fundamental new ground
Teijin Aramid, an exhibitor at Techtextil, is breaking new ground with carbon nanotube fibres, that offer thermal and electrical conductive properties similar to those of metals, whilst at the same time being as flexible, strong and as easy to use as textile fibres. In aviation and space flight, automotive construction, medical technolo
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