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Direct Long Fibre Technology Makes Inroads in the Sky

26 March 2010

Thermoplastic composite parts made by PlastiComp are replacing traditional aluminium materials in a non-structural application for Wipaire, Inc., the largest aircraft float manufacturer in the world.

The parts, inspection hatch covers, provide access to water-tight compartments in seaplane floats for Wipaire’s Wipline 7000 floats as installed on the amphibious version of the Quest Kodiak, a single-engine turboprop, ten-seat, backcountry utility aircraft manufactured in Sand Point, Idaho. The float-equipped Kodiak is scheduled to be certified for service in the spring of 2010. The new long glass reinforced thermoplastic hatch covers were a joint development: PlastiComp provided technical guidance on materials and processes plus the actual part moulding; Wipaire designed the part and made the mould in their in-house machine shop. The project took just under 120 days to complete.

“Our people saw this project with Wipaire as a particularly good partnership with a well-established aviation manufacturer”, said Steve Bowen, president of PlastiComp. He added, “It spotlights our ability to help develop a custom-designed metal replacement part, which, despite its low-volume, still represents an important breakthrough in the aviation field for our Pushtrusion D-GMT (Direct Glass Mat Thermoplastic) process.”

The hatch cover is approximately 14""x16"". The exposed, upper, surface is largely smooth, with a channel for a sealing gasket and thicker sections at the perimeter for threaded fasteners as well as a perimeter wall with ribs radiating to it from a central boss where a standard, snap-in-place, inspection port is installed. The hatch itself is moulded in a self-coloured, black pigmented, UV stabilized, long glass fibre reinforced thermoplastic composite material which is then painted with a black non-skid coating on its exposed surface to match the upper, walked upon deck surface of the float. Foot traffic dictated sufficient load bearing stiffness as a primary criterion in the design.

The new hatch cover replaces earlier machined aluminium versions. Dan Garrett, the Wipaire R&D engineer in charge of the project, said, “The aluminium parts were too heavy while these new ones weigh less than two pounds. Also, they were subject to dents and bending, and they cost too much – approximately five times the cost of the composite parts provided by PlastiComp.” He added, “The composite hatch covers have good corrosion resistance and have the advantage of being easily replaced, which was another benefit we were looking for.”

Steve Bowen explained PlastiComp’s interest: “I have a background that includes aircraft design and modification, so naturally I was attracted to this application, but, more importantly, it seemed like the perfect fit for PlastiComp. It was an opportunity to demonstrate our part moulding capabilities, an area of our business that we are expanding.” He went on to explain how PlastiComp’s proprietary Pushtrusion technology, which they have installed in their Technical Development Center in Winona, allows them to operate small volume production, preproduction or prototype manufacturing for selected customers. Since 2006 PlastiComp has been producing parts for customers who do not want - or need - full-scale, in-house, Pushtrusion technology but do want the benefits of parts produced with the advanced technology. Initially this contract moulding was limited to injection moulding with Pushtrusion Direct In-line Compounding but it is now offered with Pushtrusion D-GMT for compression moulding as well, the technology that produced the hatch covers for Wipaire.

The Pushtrusion D-GMT system produces hot charges of customized, precisely metered, long fiber reinforced compound that are transferred to a compression press and immediately pressed into finished parts, eliminating the typical glass mat technology (GMT) sheet used for compression molding. Pushtrusion units are custom-sized to the job and can be used with a wide variety of polymers (PP, PA, TPU, PBT, etc.) and fibers (E-glass, S-glass, and carbon).

“The Pushtrusion process gives processors the flexibility to customize their specific formula by fiber loading, polymer type, and colour,” Bowen explained. “They are not limited to standard GMT sheet offerings. Our customers see this as a big plus.”