There are two types of timber, called hardwood and softwood.
Softwoods come from coniferous trees which are evergreen, needle-leaved, cone-bearing trees, such as cedar, fir and pine.
Hardwoods come from broad-leaved, deciduous trees. The main hardwood timbers are ash, beech, birch, cherry, elm, iroko, mahogany, meranti, oak, obeche, sapele and teak.
Most metals are extracted from their ores using a chemical reaction. Metals are rarely used in their pure form, and are usually mixed with other metals to improve their properties. This is called an alloy. Most metals are good conductors and can be recycled.
Ferrous metals contain iron. Examples are cast iron, mild steel, medium carbon steel, high carbon steel, stainless steel and high speed steel.
Cast iron 1200°C Hard skin, softer underneath, but brittle, corrodes by rusting Parts with complex shapes which can be made by casting Mild steel 1600°C Tough, ductile, malleable, good tensile strength, poor resistance to corrosion General purpose engineering material High carbon steel 1800°C Even harder than medium carbon steel and more brittle, can be heat-treated to make it harder and tougher Cutting tools, ball bearings Stainless steel 1400°C Hard and tough, resistant to wear and corrosion Cutlery, kitchen equipment
Non-ferrous metals do not contain iron. Some common non-ferrous metals are aluminium, Duralumin, copper, zinc, brass, gilding metal and tin.
Aluminium 660°C Pure aluminium Good strength-to-weight ratio, light, soft, ductile, good conductor of heat and electricity Kitchen equipment, window frames, general cast components Copper 1080°C Pure copper Malleable and ductile, good conductor of heat and electricity, resistant to corrosion Water pipes, electrical wire, decorative goods Brass 900-1000°C Alloy Resistant to corrosion, fairly hard, good conductor of heat and electricity Ornaments, cast items such as water taps Tin 230°C Pure tin Soft, weak, malleable, ductile and resistant to corrosion Usually used for coating steel to form tin-plate, soft solder
Sources of Plastics:
Natural sources of plastics include:
- plants - from which cellulose can be extracted
- trees - from which latex, amber and resin can be extracted
- animals - from which horn and milk (used to make glues) are obtained
- insects - from which shellac (used to make polish) is obtained
Synthetic plastics are chemically manufactured from:
- crude oil
- natural gas
Polyamide (Nylon) Creamy colour, tough, fairly hard, resists wear, self-lubricating, good resistance to chemicals and machines Bearings, gear wheels, casings for power tools, hinges for small cupboards, curtain rail fittings and clothing Polymethyl methacrylate (Acrylic) Stiff, hard but scratches easily, durable, brittle in small sections, good electrical insulator, machines and polishes well Signs, covers of storage boxes, aircraft canopies and windows, covers for car lights, wash basins and baths Polypropylene Light, hard but scratches easily, tough, good resistance to chemicals, resists work fatigue Medical equipment, laboratory equipment, containers with built-in hinges, 'plastic' seats, string, rope, kitchen equipment Polystyrene Light, hard, stiff, transparent, brittle, with good water resistance Toys, especially model kits, packaging, 'plastic' boxes and containers Low density polythene (LDPE) Tough, good resistance to chemicals, flexible, fairly soft, good electrical insulator Packaging, especially bottles, toys, packaging film and bags High density polythene (HDPE) Hard, stiff, able to be sterilised Plastic bottles, tubing, household equipment
Epoxy resin Good electrical insulator, hard, brittle unless reinforced, resists chemicals well Casting and encapsulation, adhesives, bonding of other materials Melamine formaldehyde Stiff, hard, strong, resists some chemicals and stains Laminates for work surfaces, electrical insulation, tableware Polyester resin Stiff, hard, brittle unless laminated, good electrical insulator, resists chemicals well Casting and encapsulation, bonding of other materials Urea formaldehyde Stiff, hard, strong, brittle, good electrical insulator Electrical fittings, handles and control knobs, adhesives
Composite materials are formed by combining a reinforcing material such as wood pulp, and a bonding agent, such as glue. The wood pulp is made from the waste from cutting solid wood. MDF and GRP are examples of composite materials
Smart materials are reactive materials. Their properties can be changed by exposure to stimuli, such as electric and magnetic fields, stress, moisture and temperature.
- thermochromic pigments react to changes in temperature
- photochromic pigments react to changes in light levels
Photochromatic materials are used in the manufacture of sunglasses. Exposure to sunlight causes the lens of the glasses to darken to protect the eye.