Recently, KraussMaffei, together with Covestro and the Institute of Plastics Processing at RWTH Aachen University, has won 2017 FSK Innovation Award for Polyurethanes issued by the Specialist Association of Foamed Plastics and Polyurethanes (FSK), which elected to honor the partners’ achievements in promoting the wider industrial use of pultrusion with polyurethane resins.
Tremendous potential of polyurethane composite sections
Polyurethane resins offer significant advantages over established pultrusion materials, such as epoxy, unsaturated polyester and vinyl ester resins. Their low viscosity, good fiber wetting and high reactivity support faster processing speeds than epoxies, which reduces manufacturing costs. Another advantage is their considerable flexibility: The reaction time and viscosity of polyurethane resins can be varied widely, permitting the reproduction of even very thin component geometries.
Pultruded composite sections have already proven successful in thermally insulating window frames and in reinforcing rotor blades for wind turbines, however, more widespread use was prevented until now by the inadequate degree of industrialization.
KraussMaffei is working closely with Covestro and the Institute of Plastics Processing (IKV) at RWTH Aachen University on pultrusion process development using polyurethanes. The IKV with its long-term experience is supporting Covestro in the fields of polyurethane processing and pultrusion with reactive resin systems in case of development issues regarding pultrusion processes.
Flexible turnkey systems with high automation
The new iPul machines from KraussMaffei are the first turnkey systems to incorporate system, process and die technology all from a single supplier. Critical processing parameters, such as output rate and haul-off rate, are controlled centrally.
In the new systems, the fibers are no longer impregnated in an open process, but rather by a metering machine in a closed injection chamber. Apart from eliminating odor problems for a pultruder’s employees, the new technology supports precision temperature management during curing and thus increasing production speeds. The systems are sensor-assisted and highly automated.
Another advantage of the iPul machines is their extensive flexibility and precision. Thanks to the injection chamber and metering device with newly engineered mixing head, a wide variety of resins can now be processed, including highly reactive polyurethane systems. The matrix material is injected at low pressure to additionally cut costs.
How pultrusion works
In pultrusion, glass, carbon or other fibers are fed continuously from rovings into an injection chamber, where they are impregnated with a liquid, thermoset resin system. The fiber composite cures on exposure to heat in a die. The hardened section is pulled continuously in the process, hence its name. After cooling, the strand is trimmed by an integrated saw. The resulting, straight sections display low weight, paired with very high strength and stiffness in the fiber direction.
(Source: PU world)