Properties and types of material

Few candidates state the key advantage of a thermoplastic: because it SOFTENS when reheated it can be reshaped and recycled, whereas a thermoset sets permanently on curing and cannot be re-melted. Weak answers only say one is "harder". Thermoplastics have weak inter-chain forces that loosen with heat; thermosets form heat-proof cross-links.

A one-mark definition is often lost. A FERROUS metal CONTAINS IRON and usually rusts — mild steel, cast iron, high-carbon steel. A NON-FERROUS metal contains no iron — aluminium, copper, tin, zinc; naming one of these as "ferrous" scores zero. Learn the term with a one-line meaning and a correct example on each side.

Boards are widely misjudged. Candidates rightly say MDF is cheap, machines cleanly and has no grain, but wrongly add it is LIGHTER than solid wood — MDF is a dense fibre board, usually as heavy or heavier. Plywood is also under-known: it is cheaper than solid wood for large panels and more DIMENSIONALLY STABLE (crossed veneers resist warping), though its edges need lipping.

Only thermoplastics soften with heat, so only they can be vacuum-formed, line-bent or recycled by melting. A thermoset (urea/melamine formaldehyde) forms permanent cross-links on curing: reheating chars or burns it, it does not soften. Never claim a thermoset can be reshaped or melted to recycle — that permanence is why it suits pan handles.

Asked WHY beech suits a turned or steam-bent part, most candidates cannot give the property: beech is CLOSE-GRAINED — a fine, even, dense grain with no large open pores — so it turns cleanly on a lathe and bends without splintering. Weak answers say only that it is "strong" or "cheap". Learn the property word and link it: close-grained → clean turning and a smooth finish.

Most candidates misread "sustainable". A sustainable material can be replenished: a timber like beech can be replanted and regrown, whereas aluminium comes from bauxite, a FINITE ore. Sustainability is about the SOURCE and whether it renews, not how strong the material is. Do not answer with "it is strong" — contrast a replantable timber with a finite ore.

Hardwood/softwood is NOT a hardness scale — it is a BOTANICAL classification. Hardwoods come from broad-leaved (deciduous) trees, softwoods from coniferous trees, whatever the timber's real hardness. Balsa is a HARDWOOD yet one of the softest, lightest woods; yew is a softwood yet fairly hard. So the answer comes from the tree type, not from pressing the sample.