Timbers, metals and polymers
Design & Technology · GCSE · The School
Timbers
HARDWOOD comes from broadleaved deciduous trees — oak, ash, beech, mahogany, balsa — grows slowly and costs more. SOFTWOOD comes from conifers — pine, spruce, larch, yew — grows fast and is cheaper, which is why construction uses it. MANUFACTURED BOARDS — MDF, plywood, chipboard — come in large flat sheets with no grain direction and no warping, which solid timber cannot offer.
Metals
FERROUS metals contain iron and rust: mild steel, cast iron. NON-FERROUS do not: aluminium, copper, zinc, tin. ALLOYS mix metals to get properties neither has alone — brass from copper and zinc is harder than either, stainless steel adds chromium and stops rusting. Ask "does it contain iron?" first; the rest follows from it.
Polymers
THERMOFORMING polymers soften every time they are heated and can be reshaped and recycled repeatedly — acrylic, polythene, polypropylene, PVC. THERMOSETTING polymers set once, permanently, and char rather than soften — epoxy resin, urea formaldehyde, melamine. That is why a saucepan handle is thermosetting and a drinks bottle is not.
PRODUCT: an outdoor bench for a park. THE FRAME. Mild steel is strong and cheap but ferrous, so it rusts — which is fine only if it is galvanised or powder-coated, and that is a real cost. Aluminium is non-ferrous and will not rust, is lighter, and costs more. Cast iron is traditional, extremely rigid, and brittle under a sharp impact — a vandalised cast-iron bench cracks rather than bends. THE SLATS. Softwood is cheap but needs treating and replacing. A hardwood such as oak weathers to grey and lasts decades untreated, which is why park benches use it despite the price. Manufactured board is out immediately: MDF disintegrates when wet. THE FIXINGS. Stainless steel, because ordinary steel bolts would rust and stain the timber, and the staining shows years before the bolt fails. Notice that every choice was decided by the OUTDOORS, not by which material is best.