Metals

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					                Metals




Brian Russell
                           Exam expectations


Knowledge about the properties of materials is often tested
in the written paper. You are expected to know about
paper/card and at least one other material group.
               General properties of metals

•   Strength
•   Lustre
•   Heat conductivity
•   Electrical conductivity
•   Density (Weight)
•   High melting points
•   Malleability
                                Sources of metals
•   Gold is the only metal that is found in a useable form.

•   All others are found as ores.

•   25% of the Earth’s crust is made up of metal ores.

•   The most abundant ores are aluminium and iron
                                      Ferrous metals

This group of metals contain metals
•   Iron is produced in a blast furnace.
•   The material that is produced is called pig iron.
•   This is converted into steel by adding carbon to its structure
    in an oxygen furnace or an electric arc furnace.
                                        Ferrous metals
•   Iron is soft and ductile, not particularly useful.
•   When carbon is added, it becomes steel and its properties
    are improved.
•   Medium and high carbon steel can be heat treated to make
    them even stronger so that they can be formed into cutting
    tools.
                                                  Ferrous Metals


 BASE      ADDITIONAL     TYPE OF
                                      DUCTILITY    HARDNESS   TOUGHNESS
MATERIAL    CARBON         STEEL



                        LOW CARBON
            <0.3%          STEEL
                          MEDIUM
           0.3-0.6%       CARBON
                           STEEL
IRON
                        HIGH CARBON
           0.6-1.7%        STEEL


            3.5%         CAST IRON                            BRITTLE
                                        Ferrous Metals

     NAME                      COMMON USES

                    Nuts, bolts, washers, car bodies, panels
   Mild Steel             for cookers, appliances etc.

Medium carbon
                       Springs, general gardening tools
    steel
                      Hand tools, scribers, dot punches,
High carbon steel
                           chisels, plane blades.

    Cast iron        Machine parts, brake discs, engines
                             Non-Ferrous metals
•   Do not contain iron
•   Although aluminium ore is the most common on Earth, it is
    not the most processed metal, steel is.
•   This is because aluminium production uses large amounts
    of energy and energy = cost.
                             Non-Ferrous metals
 METAL              COMMON USES AND PROPERTIES

Aluminium   Kitchenware, power cables, drinks cans, aircraft bodies.

 Copper     Electrical contacts, electrical cable and wire, jewellery.

  Gold          Jewellery, electrical contacts (does not oxidise)
  Lead           Soft but heavy metal, used on roofs, durable

Platinum    Precious metal used in jewellery, but also to make wires

  Silver              Cutlery, decorative items, jewellery.
   Tin               Used to coat steel plate in food cans

                 Surgical applications (very clean) such as hip
Titanium
                                 replacements

            Used for coating steel (galvanising), can be die-cast to
  Zinc
                        produce high detail products.
                                                   Alloys
•   Two (or more) metals are combined to produce
    materials with enhanced properties.
•   Example: adding zinc to copper produces a much
    harder and stronger material than pure copper.
•   Benefits can be changes to: colour, strength,
    hardness, ductility, resistance to corrosion/oxidation,
    electrical/thermal properties, flow properties...
                                               Alloys
  NAME      BASE METAL   COMPOSITION      COMMON USES


                            4% copper        Structural
DURALUMIN    Aluminium    1% manganese     components for
                         0.1% magnesium       aircraft
                                           Cast valves and
 BRASS        Copper        35% zinc      taps, boat fittings.
                                             ornaments

                                           Statues, coins,
 BRONZE       Copper        10% tin
                                              bearings
                                       Alloying steels
•   Most metals, including steel, will become less hard and
    more ductile when heated.
•   By alloying with other metals, high speed steels can be
    produced that keep their cutting edge even when they are
    cutting at high temperatures.
                                                    Alloying steels

 ALLOY STEEL           ALLOYED WITH         CHARACTERISTICS          COMMON USES


                                             Tough and wear-
                       Chromium, nickel,
  Stainless steel                           resistant; corrosion    Sinks, cutlery etc.
                         magnesium
                                                  resistant

                      Tungsten, chromium,    Very hard, will cut   Cutting tools, such as
High Speed Steel
                           vanadium          while at red heat              drills

                                                                     Fine press tools,
                                            Very hard and tough,
                          Chromium,                                    extruder dies,
Tool and die-steels                            excellent wear
                          manganese                                  blanking punches
                                                  resistant
                                                                         and dies.
                                                Good tensile
                                                                        Car engine
High tensile steels         Nickel           strength; corrosion
                                                                       components
                                                  resistant
            Work hardening & heat treatment

•   Because metal is made up of crystals, the way they are
    arranged affects the properties (strength) of the metal.
•   There are two categories of hardening, cold-working
    (bending, rolling, hammering, drawing) and heat treating.
                                       Heat treating
•   Heat treatments are process that heat and cool metals in
    a controlled way in order to improve their properties.
    Some common heat treatments are:
•   Annealing
•   Hardening
•   Tempering
•   Normalising
                     Other types of hardening

•   Mild steels do not contain enough carbon to be affected
    by heat treatments.
•   These can be case hardened; i.e. the outer surface is
    hardened, while the centre remains tough and shock
    resistant.
•   Types of case hardening are: carburising and nitriding.
                             Processing metals
There are many ways of processing metals to manufacture
   products.
These can be divided into three categories:
•   Wasting
•   Addition
•   Redistribution
                             Wasting processes
•   These are processes where material is cut away.
    Examples are:
•   Sawing and filing
•   Drilling and milling
•   Turning
•   Grinding and sanding
•   Blanking and piercing
                             Addition processes
•   These are processes where materials are joined
    together.
•   Bolts and screws
•   Welding, brazing and soldering
•   Adhesives
                                        Redistribution
•   These are processes where materials are reshaped
    without loss of material. There are further categories:
•   Casting
•   Forging
•   Pressing
•   Spinning
•   Sintering
                                                Casting
•   Like polymers, metals can be heated to known melting
    temperatures.
•   When they become liquid, they can be poured into moulds
    made of sand, alloy steel, or ceramics.
•   Three main types of casting are sand casting, die-casting
    and investment casting

				
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posted:9/19/2011
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