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11.4.1 Describe the process of spray-up.
Spray-up is carried out on an open mould, where both the resin and reinforcements are sprayed directly onto the mould. The resin and glass may be applied separately or simultaneously “chopped” in a combined stream from a chopper gun. Workers roll out the spray-up to compact the laminate. Wood, foam or other core material may then be added, and a secondary spray-up layer embeds the core between the laminates (sandwich construction). The part is then cured, cooled and removed from the reusable mould.
11.4.2 Identify products that could be made using spray-up processes.
For example, pleasure boats and swimming pools.
11.4.3 Describe the process of hand lay-up.
In hand lay-up processing, fibreglass continuous strand mat and/or other fabrics such as woven roping are manually placed in the mould. Each ply is sprayed with catalysed resin and the resin is worked into the fibre with brushes and rollers to wet-out and compact the laminate.
11.4.4 Identify products that could be made using hand lay-up processes.
Products of varying sizes that do not need a high accuracy finish, for example, prototypes.
11.4.5 Describe the process of filament winding.
This process is primarily used for hollow, generally circular or oval-sectioned, components, such as pipes and tanks. Fibre tows are passed through a resin bath before being wound on to a mandrel in a variety of orientations, controlled by the fibre feeding mechanism, and rate of rotation of the mandrel. Filament winding machine design varies with part geometry.
11.4.6 Identify products that could be made using filament winding processes.
For example, fishing rods and rowing oars.
11.4.7 Describe the process of vacuum bagging.
This process is basically an extension of the wet lay-up process where pressure is applied to the laminate once laid-up in order to improve its consolidation. This is achieved by sealing a plastic film over the wet laid-up laminate and onto the tool. The air under the bag is extracted by a vacuum pump, and thus up to one atmosphere of pressure can be applied to the laminate to consolidate it.
11.4.8 Outline the benefits of using vacuum bagging when using composite lay-up techniques.
Large products are possible; top-quality products through the use of pre-pregs; clean production method; and low moulding costs.
11.4.9 Identify products that can be made using vacuum bagging processes.
For example, laminated curved furniture.
11.4.10 Explain how a curved shape is produced in timber using lamination.
Thin layers of ply or veneers are laid onto a former, then glued and clamped. To eliminate spring-back on tight curves, a fast drying adhesive should be used. Thicker timber can be steamed and shaped over a former. Some spring-back is likely to occur, but it is possible to reduce this by combining lamination and steaming.
11.4.11 Discuss how lamination can be used to strengthen material.
The structure of a timber is such that all fibres run along its length. Laminating more than one timber together but with fibres running at right angles increases the strength in all directions.
11.4.12 Describe how LVL (Laminated veneered lumber) differs from plywood.
Consider material cross-section and grain direction.
11.4.13 Discuss how forming techniques have enabled designers to be more flexible in the way they approach the design process.
Material choice, environment and cost factors can be more widely addressed.
Bulleted list and italicised paragraphs are excerpted from Design Technology: guide. Cardiff Wales, UK: International Baccalaureate Organization, 2007.
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