Section 3

• polymers


  plastics, usually made from synthetic materials
• thermoplastics, thermoforming plastics


  can be remoulded after heating, recyclable, good surface finish possible, damaged by high temperatures and UV liight

  
• thermosets, thermosetting plastics


  cannot be reformed once set into shape, strong chemical bonds between polymer chains, hard and durable, can withstand higher temperatures, good electrical insulators, often used with other materials for paints and adhesives

  
• vacuum forming


  softened sheet plastic formed over mould, used for yoghurt pots etc.

  
• polyethylene


  most common thermoplastic, rigid with good strength to weight ratio
• polyethylene terephthalate


  thermoplastic used for soft drink bottles

  
• high-density polyethylene


  thermoplastic used for plastic milk bottles and detergent bottles

  
• low-density polyethylene


  thermoplastic used for plastic bags

  
• polyvinyl chloride


  thermoplastic: uses include packaging, pipes, toys and electrical insulation; rigid and tough

  
• UPVC


  PVC with chemical added to prevent UV damage
• polypropylene


  thermoplastic; very versatile; used for solid plastics, film and fibres; lightweight, low-density and ductile; chemically resistant

  
• high-impact polystyrene (HIPS)


  thermoplastic: flexible, light weight, impact resistant, suitable for vacuum forming

  
• acrylic


  "Polymethyl Methacrylate" - versatile and hardwearing thermoplastic, can be spun into threads, brittle when thin
• epoxy resin


  class of reactive thermosets; supplied as two liquids, resin + hardener; used for adhesives; good strength compared to weight; gives off nasty fumes
• polyester resin


  viscous pale solution; hardened with a catalyst; often used in composite materials such as fibreglass; often used for flooring and anatomical models
• fibreglass


  lightweight, strong, waterproof, uses include boat hulls and vehicle parts
• formaldehydes


  old plastic, all that was available 100 years ago
• melamine formaldehyde


  heavy and good heat resistance, often used for worktops and plastic utensils
• urea formaldehyde


  good heat resistance and good electrical insulator; used as glue in MDF, for easy care textiles, and for electrical sockets
• Ferrous Metal


  Contains iron

  - Magnetic

  - Will rust unless treated

  eg. cast iron, low-carbon steel, high-carbon steel
• Non-ferrous metal


  Does not contain iron

  - Not magnetic

  - More resistant to corrosion

  - More expensive

  eg. aluminium, copper, tin, zinc
• Alloys


  Metals mixed with other metals to improve and combine their physical properties.

  eg. stainless steel, brass, high-speed steel
• Low-carbon steel


  - Malleable and reasonably tough

  - Cannot be hardened and tempered

  - Inexpensive but rusts easily

  Uses: car bodies, nails and screws
• High-carbon (tool) steel


  - Very hard but brittle

  - Difficult to cut and work

  - Can be hardened and tempered

  - Prone to rust

  Uses: drill bits, tools, springs
• Cast Iron


  - Hard but brittle, cannot be bent or forged

  - Resistant to deformation, wear and rust

  - Strong under compression

  - Weak under tension

  Uses: manhole covers, car brake discs
• Aluminium


  - Durable, lightweight, resistant to corrosion

  - A good conductor of heat and electricity

  Uses: drinks cans, aircraft, foil
• Copper


  - Relatively soft, malleable and ductile

  - Great thermal and electrical conductor

  Uses: electrical wiring, central heating pipes
• Tin


  - Soft, malleable, ductile

  - High resistance to corrosion

  - Low melting point

  Uses: tin can coating, solder
• Zinc


  - Weak but malleable once heated

  - High resistance to corrosion

  - Low melting point

  Uses: galvanising (coating steel)
• Brass


  Copper and zinc

  - Increased hardness

  - Good conductor

  - Resistant to corrosion

  Uses: musical instruments, taps, keys
• Stainless steel


  Iron, carbon and a minimum of 10.5% chromium

  - Tough, hard, strong, difficult to cut

  - High resistance to corrosion if chromium and nickel are added

  Uses: cutlery, surgical equipment, sinks
• High-speed steel


  Various elements such as carbon, tungsten and chromium

  - Strong and remains hard even when heated

  - Can cut at high speeds and high temperatures

  Uses: cutting tools, power saw blades, drill bits
• State the 3 classes of wood

  -soft

  -hard

  -manufactured

  
• Define timber


  - SAWN chunks of solid WOOD that are used as BUILDING MATERIALS

  
• Softwoods


  -grow in COLDER climates

  -FAST GROWING

  -CHEAP

  -readily ACCESSIBLE

  -they have leaves like NEEDLES + cones

  -EVERGREEN (coniferous)

  
• Name 3 softwoods

  -pine

  -larch

  -spruce
• Pine

  -YELLOW with brown STREAKS

  -STRONG + CHEAP

  -KNOTTY-> hard to work with

  
  

  USES: telegraph poles, fences + cheap furniture

  
• Larch

  - attractive yellow to REDDISH-BROWN colour

  - HARDER + TOUGHER + more DURABLE than other softwoods

  -RESISTANT to ROTTING

  
  

  USES: decking, cladding + fence posts

  
• Spruce

  - REDDISH-BROWN colour

  - HARD

  - good strength-to-weight ratio

  - KNOTTY + NOT very DURABLE

  
  

  USES: structural purposes e.g. aircraft, crates + ship masts

  
• Hardwoods

  -grow in WARM climates

  -SLOW GROWING

  -more EXPENSIVE

  -broad, flat leaves

  -deciduous -> LOSE LEAVES in autumn

  -TIGHTER GRAIN

  -DENSER + HARDER than softwood except balsa