Metals

Metals

1. metal is mined or quarried

   • metal ore
   • lots of energy
     • all metals can be recycled
       • less energy
       • lower environmental impact
   • pollution

2. pure metals are made from a single refined element

   • or alloy- mixture of metals

3. two main families

   • ferrous-contain iron
     • small proportion of carbon
       • medium carbon steel
         • as carbon increases up to 0.4%, steel becomes harder and stronger but less ductile tough and malleable
         • garden tools, springs
       • high carbon steel
         • 'tool' steel- hammers
       • stainless steel
         • alloy of steel with chrome and nickel
         • hard and tough, much better corrosion resistance- but much more expensive and difficult to work
     • cast iron
       • hard skin
       • good compressive strength
       • does not bend
       • not very malleable
     • mild steel
       • less than 0.3% carbon
       • nails, screws
       • high tensile strength
       • ductile
       • tough
       • fairly malleable
       • fairly cheap
       • poor resistance to corrosion
     • some ferrous metals are magnetic
       • magnets can sort retrieve them from landfill recycling
   • non-ferrous- no iron
     • aluminium, copper, zinc
       • ductile + malleable+ low density + corrosion resistance
       • alloyed to improve strength- airoplanes
       • malleable, tough + v good elec conductor
       • water pipes + electrical wires coated with plastic
       • common alloys: brass (copper +zinc), bronze (copper + tin)
       • often used as pure- less strong, but low melting point- easily moulded- car door handle
       • excellent corrosion resistance
       • galvanising- covering steel

4. treating metals

   • hardening
     • ferrous- heating +then plunging into cold water
       • cooling quickly- hard but brittle
     • tempering
       • then makes the material tougher and less likely to break
         • heating to between 230-300C then cooling quickly
   • heat treatment- heating and cooling a metal in a controlled way, to change its properties
   • annealing: ferrous and non-ferrous
     • softer, less brittle, more ductile
     • heat- leave to cool slowly

5. most metals available in standard range shapes and sizes

   • standard forms save time and effort of machining metal parts
   • like pipes and bars