Metals

Metals

metal is mined or quarried
1. metal ore
2. lots of energy
  1. all metals can be recycled
    1. less energy
    2. lower environmental impact
3. pollution
pure metals are made from a single refined element
1. or alloy- mixture of metals
two main families
1. ferrous-contain iron
  1. small proportion of carbon
    1. medium carbon steel
      1. as carbon increases up to 0.4%, steel becomes harder and stronger but less ductile tough and malleable
      2. garden tools, springs
    2. high carbon steel
      1. 'tool' steel- hammers
    3. stainless steel
      1. alloy of steel with chrome and nickel
      2. hard and tough, much better corrosion resistance- but much more expensive and difficult to work
  2. cast iron
    1. hard skin
    2. good compressive strength
    3. does not bend
    4. not very malleable
  3. mild steel
    1. less than 0.3% carbon
    2. nails, screws
    3. high tensile strength
    4. ductile
    5. tough
    6. fairly malleable
    7. fairly cheap
    8. poor resistance to corrosion
  4. some ferrous metals are magnetic
    1. magnets can sort retrieve them from landfill recycling
2. non-ferrous- no iron
  1. aluminium, copper, zinc
    1. ductile + malleable+ low density + corrosion resistance
    2. alloyed to improve strength- airoplanes
    3. malleable, tough + v good elec conductor
    4. water pipes + electrical wires coated with plastic
    5. common alloys: brass (copper +zinc), bronze (copper + tin)
    6. often used as pure- less strong, but low melting point- easily moulded- car door handle
    7. excellent corrosion resistance
    8. galvanising- covering steel
treating metals
1. hardening
  1. ferrous- heating +then plunging into cold water
    1. cooling quickly- hard but brittle
  2. tempering
    1. then makes the material tougher and less likely to break
      1. heating to between 230-300C then cooling quickly
2. heat treatment- heating and cooling a metal in a controlled way, to change its properties
3. annealing: ferrous and non-ferrous
  1. softer, less brittle, more ductile
  2. heat- leave to cool slowly
most metals available in standard range shapes and sizes
1. standard forms save time and effort of machining metal parts
2. like pipes and bars

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