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TeXtreme® fabrics and TeXero® UD tapes are ultra lightweight spread-tow reinforcements that enable further weight savings in racing, aerospace and other high-performance application segments of the composite materials market. TeXtreme® fabrics, starting at 80 gsm, are lighter than today’s standard 1k fabrics.
(Published on October 2008 – JEC Magazine #44)
DR NANDAN KHOKAR, CO-FOUNDER & R&D MANAGER, OXEON AB, SWEDEN
During the past 50 years, composite materials have been evolving from low-volume niche items to high-volume commodity products. This clearly reflects the acceptance of tailor-made high-performance materials for a variety of applications, from space to sports.
The role of textile reinforcements in the success of composite materials cannot be over-emphasized. Many different types of textile materials are used as reinforcements. As woven materials constitute a major share of the reinforcements market, it is pertinent to briefly put the spotlight on weaving technology.
Weaving: an extraordinary process
Weaving has been in practice for at least 5,000 years. This is the only technology that still remains in service and works wonders after all these millennia. Today, it is employed for many more applications than its original purpose of manufacturing clothing and furnishing materials.
Weaving technology is historically important because it ushered in the industrial revolution and also formed the basis for the punched-card computing technique (first-generation computers in the 1950s), which was the forerunner of today’s digital technology, through its jacquard programming system.
Notwithstanding the sophistication of today’s weaving machines, the method remains by and large the same in terms of its most elementary working element, the heald (or heddle), which constitutes the foremost shedding operation. The use of healds necessitates processing of yarns and tows (as warps). As a consequence, the use of healds limits the production of woven materials that could otherwise be made better performing for composite materials applications.
Engineering performance in woven materials
The following performance characteristics are generally required in a textile reinforcement for composite applications:
Traditional woven materials inherently cannot realize all these requirements because they comprise yarns or tows.
Realizing that woven materials for composite applications had to be engineered differently to incorporate the performance characteristics listed above, Dr Nandan Khokar developed a completely new weaving technique − the tape-weaving technology − during the 1990s in the course of his doctoral work at the Chalmers University of Technology, Sweden. Oxeon AB, Sweden, is now utilizing and developing tapeweaving technology.
The tape-weaving process
Tape-weaving is an entirely new technology devised to weave tape-like warps and wefts without using healds for shedding and a reed for beating up the weft. Existing weaving machines cannot be modified for this process. The use of tapes, instead of yarns/tows, uniquely enables achievement of all the above-listed performance features at once.
The products of tape-weaving technology are new in their structural architecture and construction because the required performance, aesthetic and functional characteristics can be uniquely combined in a single product. The use of tapes makes the process highly efficient because the setting-up time and effort are reduced. Furthermore, the process is highly suitable for short production runs because neither warp beam preparation nor creeling are needed.
The process incorporates unique warp control mechanisms that ensure proper handling of the warp tapes to avoid deformations caused by excessive tensioning at each stage of the working cycle. Similarly, novel weft insertion mechanisms, together with a weft gripper, positively lay the weft tapes in a flat condition. The tape-like wefts are aligned at the fabric-fell position from outside of the fabric, thus eliminating any risk of deformation to the weft tapes or to the warp tapes. All these arrangements ensure gentle processing of all types of tapes, thereby preserving the tape structure to obtain woven products with the desired properties.
The tape-weaving process can directly produce fabrics comprising tapes of dissimilar materials to create woven materials for engineering performance, aesthetics or other functions. It is a flexible process that can gently handle a variety of materials (delicate to stiff), different widths of warps and wefts, different tape compositions (thermoplastic to wood veneer) and different tape structures (perforated to plain, sandwich, fibrous to non-fibrous) to achieve the desired performance level and functional features, and to design innovative woven products.
Oxeon’s woven spread-tow carbon fabrics are marketed under the TeXtreme® name. These novel materials, which are produced in widths of up to 1,500 mm, have been received favourably in the composites market as they uniquely offer:
The improved performance offered by the Textreme® range stands validated by its use in Nike-Bauer’s latest goaltender sticks, several new products in the racing industry including Formula 1 cars, and certain other high-performance product applications. Oxeon is now recognized as the market leader in the spread-tow reinforcement segment.
The tape-weaving technology is also suitable for ballistic mitigation application as it provides straight (crimpless) paths for the fibres to dissipate impact energy efficiently.
Tapes from spread tows
The production of TeXtreme® woven materials requires carbonfibre tapes. To meet this requirement, Oxeon has developed its own technology to spread carbon tows into thin and wide unidirectional tapes marketed as TeXero®. These tapes are produced in 20-50 mm widths, with an areal weight starting at 40 gsm. The development of tapes up to 300 mm wide is underway.
The tape-spreading technology involves feeding carbon tows under the required tension to a spreading unit that gently separates the constituent filaments. The degree of filament separation is positively controlled. As the filaments separate, the tow changes into a thin and wide tape. To preserve the produced tape for subsequent handling during either the weaving process or shipment, the spread filaments are treated on one face with a suitable chemical formulation that is compatible with the currently available resins. The consolidated Texero® tape is continuously wound into spools in lengths suitable for either a given production run at the weaving machine or customers’ requirements.
The tape-weaving technology has opened up new opportunities in engineering high-performance textile materials and created new markets for its novel woven products. Perhaps this development is an indication of why weaving continues to evolve time and again!