8th December 2016, Düsseldorf
At the recent Composites Europe 2016 exhibition in Düsseldorf, Saertex exhibited a prototype motor shell made with its multiaxial fabrics for the new Carbon Azipull 65C propulsion system built by Rolls-Royce.
The propulsion system has been specifically constructed for the Benetti F125 superyacht of the Azimut Benetti Group and is a mechanical steerable propulsion thruster with a pulling propeller, for powering leisure craft and commercial vessels at speeds of up to 30 knots. Similar components are currently comprised mostly of steel, but for a high power-to-weight ratio and to achieve the hydrodynamic shape, Rolls-Royce requested a composite solution from Saertex.
Due to the geometrically challenging shape, especially for the inner shells, particular attention had to be paid to the manual draping of the fabrics.
The prototype moulds were made using a special polyurethane formula, CNC-milled from the block. This provided a cost-effective solution that could be easily adapted. The layout and all vacuum-infusion requirements were worked out in close contact with the mould builder,
For the outboard unit, a combination custom-made Saertex unidirectional carbon PES and bi-diagonal glass fabric were produced at the company’s headquarters in Saerbeck, Germany.
The infusion concept for each part was developed based on experience and prior trials with the respective fabrics. Using epoxy resin and vacuum infusion also guaranteed no emissions of curing gases, particularly when compared to an open mould application. The primary reason for using a vacuum infusion was its inherently controllable process, with a specific resin-fibre ratio. Due to the optimized material consumption, the component exhibits high strength. Detailed documentation of every process and challenge has left Saertex well prepared for any future serial production.
All in all, two prototype sets and several preliminary articles were produced, consisting of 42 individual parts.
“It is still amazing to see components of such size in this quality,” said Dariusz Dorochowicz, a mechanical engineer at Rolls-Royce. “I really like what Saertex did with the outer shells – using just two pieces of fabric joined right at the edge where the shape totally changes, so that it is not visible.”