The latest version of Krauss-Maffei's long-fiber injection (LFI) equipment that simultaneously deposits polyurethane foam and long fibers works with natural fibers. The key difference between this and the original version for glass fibers is the way in which the fibers are cut, since natural fibers do not snap like glass. It is suitable for flax, hemp, and sisal, and the modular nature of the cutter means the equipment can be quickly adapted to use glass. Fibers are cut to lengths of 5, 10, 15, or 20 mm by two intermeshing gear wheels, which also move the roving along. Once the PUR components have been combined in the high-pressure mix head, the fibers are conveyed by compressed air into the center of the flow stream. The expansion of the air helps improve the wetting of the fibers.
Different LFI/NFI units have PUR output rates of around 80 to 300 g/sec and 250 to 500 g/sec; the natural fiber content can be as high as about 40%. Output rates of natural fiber at the present state of development are at around 80 g/sec.
K-M says properties in parts 3- to 4-mm thick with a density range from 700 to 1100 kg/cu m are: tensile strength 32 to 38 N/sq mm; elastic modulus 3000 to 4500 N/sq mm; impact strength 10 to 30 kJ/sq m. Krauss-Maffei Kunststofftechnik GmbH, Munich, Germany; +49 89 88990; www.krauss-maffei.de