JEC COMPOSITES MAGAZINE - Issue #57 - May 2010 - 36

FEATURE
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“Automation”

FCS

g / The layered approach to producing high-quality components

First-generation systems were thus not suitable for producing parts with complex three-dimensional geometries. The company has now completely reengineered the way glass fibres reach the mixing head. These second-generation systems are more flexible and cleaner. The fibres are blown coaxially into the PUR spray jet at the mixing head via venturi nozzles and a closed tube. This system now makes it possible to swing the spray jet as much as 90° from the vertical and spray the PUR/glass fibre mix onto vertical surfaces. This provides considerable design freedom for parts designers. The closed feed system minimizes fly during processing. Another advantage is that the fibres are uniformly wetted with the PUR mix, which is important for product quality. Coaxial fibre feed also means that the cutter unit need not be located directly at the mixing head. This facilitates access to the mixing head and results in a more compact spray head design.
Fig. 3: FCS machine with additional filled Polyol component

trucks. There are also many potential applications in the construction and furniture industries. The reinforcing filaments are cut from endless glass fibre rovings. The endless fibre is fed into a cutter and chopped to the specified length. Simultaneously, the PUR components are mixed in the mixing head and discharged using a special spray nozzle. The chopped glass filaments are blown into the spray jet, where they are wetted with the PUR mixture. The glass-reinforced PUR is applied layer by layer as the mixing head follows a preset spray pattern. Fibre content and fibre length can be varied to suit product specifications. Glass-free layers can also be specified, for example when FCS is combined with in-mould painting. Combining the two processes produces reinforced parts with high-gloss surfaces in one manufacturing step. A glass-free PUR material is sprayed as the first layer on top of the paint layer in the mould. This barrier layer prevents fibres from coming into contact with the paint layer and ensures an impeccable paint surface.

Four-component mixing head opens up new design options
The 4-component mixing head deployed in FCS processes opens up a wide range of material system options. For example, by using up to three different polyol components, compact layers and foam layers can be combined in the same product. The foamed layers reduce the product weight, and can also improve its acoustic properties. Another variant is to process two different polyols and two isocyanates. In other words, two completely different PUR systems can be processed. For example, the outer layer of a product can be a UV-stable coating made of an aliphatic PUR system, while the inner layers can be made of conventional PUR. The tooling technology for fibre spraying can be matched to product specifications. Depending on how and where the part will be installed, it may not be necessary to produce a perfectly contoured reverse side. In these cases, a one-part mould – made of resin, aluminium or steel – will be perfectly adequate. A one-part mould is a cheaper option that substantially reduces manufacturing costs for small and medium-sized production runs. If both the front and reverse sides of the part must meet high optical standards, then fibre spraying is perfectly feasible with two-part moulds. Once spraying is finished, the mould is closed and the part is pressed into shape. More information: www.kraussmaffei.com

Design freedom thanks to coaxial fibre injection
The cutter was located directly at the mixing head in firstgeneration FCS systems. The chopped glass fibres slid from the side, down a chute and into the spray jet. This system, however, had some disadvantages. One was the fly problem caused by the open design of the chute. Another was that the spray jet could only be directed vertically downwards.

jec composites magazine / No57 May 2010

http://www.kraussmaffei.com

JEC COMPOSITES MAGAZINE - Issue #57 - May 2010

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #57 - May 2010