Working in conjunction with Depro-Electronic of Switzerland, Huntsman Advanced Materials has developed tooling materials for the construction of high quality, lightweight, heatable composite moulds. The moulds can be used for wet lay-up, resin infusion and low temperature prepreg applications.

During the development process, Huntsman and Depro-Electronic produced a 1:9scale model of a yacht hull mould, simulating the exact procedures that a full size marine mould would require using this new system.

CAD data for an original full sized sailing boat was adapted to produce a 1:9 scale model and then used to construct a master model, made from RenShapeBM5460 modelling boards. The board model was milled to size using a CAD-controlled CNC milling machine. RenShapeBM5460 was specifically chosen for this model because it can be easily worked and has good dimensional stability and edge strength (Fig.1).

RenShapeBM5460’s surface quality also give as flawless, high gloss finish, after pre-treatments. After finishing, the master model was then surrounded with shuttering and pre-treated with sealer and releasing agents.

The construction of the mould takes place over a four day schedule, with pre-curing done at room temperature, so no autoclave cure is required.

Day One: a multi-purpose gelcoat system (RenGel XD4615/hardener RenHY5159) is applied to the model and left until the surface is ‘tack-free’ – approximately one hour (Fig.2.) A coupling coat (RenGel P99/HY5159 hardener) is then applied and left to stand for a further hour. Following this, the backing reinforcement is built up using a lo w viscosity, room temperature cure laminating system (RenLam LY113/HY97-1).

This is made up of a first layer of light weight glass fibre fleece (Fig.3), followed by a second layer of non-woven fabric and finally layers of trappable glass fibre fabric.

Each of these layers is impregnated with RenLamLY113/HY97-1 resin. The backing reinforcement is then completely covered with a peel ply, before the vacuum bagging materials are applied.

The whole mould is then cured under vacuum at room temperature (23°C) over night.

Day Two: The vacuum bag and the peel ply are removed. Technicians then assemble an electrical heating element made of a special hybrid carbon fabric covered with a layer of light weight glass fibre fleece, which is impregnated with RenLamLY113/HY97-1 laminating resin (Fig.4). An electric current is passed through the carbon rovings – or threads – and due to the conductivity of the carbon filaments heat is generated, which warms up the mould. If any short circuits are detected through visible sparking across the system, these can be repaired by simply cutting the faulty current-transferring carbon filament.

Once the heating element is in place and operating cleanly, two further layers of tough, trappable glass fibre fabric are added to the backing reinforcement, all impregnated with the RenLam laminating resin. This is topped with a peel ply and left to cure, again at room temperature, over night.

Day Three: The peel ply is removed and further layers of the RenLam laminating system are added, mirroring those already laid down. The mould is then left for a final overnight cure, at room temperature.

Day Four: A post-curing cycle is then undertaken in an oven where the heat of the mould is raised in 20°C stages over a period of several hours, up to a maximum of 100°C. It is then slowly cooled down in equivalent stages. This is done in order to ensure the optimum mechanical and thermal properties for the mould are achieved. The post-cure cycle enables the mould to reach a Glass Transition Temperature (Tg) of about 120°C.

System benefits

The combination of Huntsman tooling materials and the direct heating within the mould results in a light weight, high mechanical and thermally resistant (120°C) construction. The build up of the mould is fast and easy without any major materials investment for the customer. The entire production process from CAD data to finished mould is completed in one week.

The mould has a particularly high quality, smooth and shiny surface finish which can be polished (Fig.5). The scale model of the yacht hull mould produced by Huntsman has been used for successful customer demonstrations and displays, training exercises and for public display at exhibitions.

Subsequent to the production of the scale marine model, this new technology from Huntsman has now been used to produce a large, full size mould for an application in the international marine industry.

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Peter Waldmeier is with Huntsman Advanced Materials (Switzerland) GmbH, Basel, Switzerland. www.huntsman.com/advanced_materials