processes, techniques and specialist tools

• Heat treatments: metals are made from metal grains. The grain structure influences properties.

  • Metal properties can be altered by heat treatment
• Hardening

  Medium and high carbon steel are heated then held at certain temps for given time then quenched.

  • Process increases the hardness but also increases brittleness.
• Tempering reduces some of the hardening and brittleness from hardened metals and increases toughness and ductility
• During tempering the metal is heated to below the critical point then air cooled. The exact temperature the metal is heated to will determine the amount of hardness removed.
• Case hardening is a process that hardens the surface of steels which have less than 0.4 % carbon steel.
• Case hardening produces an outer surface which has improved hardness and resistance to surface indentation.
• The case hardening process

  • Carburising : This changes the chemical composition of the surface of low carbon steel of low carbon steel so it can absorb more carbon to increase surface hardness.
• Case hardening process

  1. Steel is placed in a ceramic box which is packed with carbon.
  2. Box is heated to around 950
  3. Carbon atoms diffuse into the materials structure
  4. The depth of the carbon layer is determined by the length of time of exposure
  5. Product is the quenched
• Quenching is when a hot metal is added to a liquid causing to to cool rapidly and seal the surface.
• Annealing

  • The heating and cooling of work hardened metal to make it easier to work, less brittle and more ductile.
• Normalising is used on low carbon steel; to give a metal a uniform, fine grained structure. Material is heated then cooled. Metal is made more ductile, with increased toughness.
• Alloying

  An alloy is a metal made of two or more metals or combing two or more elements but one must be a metal.

  • An Alloy gives enchanced properties
  • Alloys are produced in a furnace or casting process
• Printing

  • Flexography and offset lithography use a four colour process: cyan, magenta, yellow and key (black)
  • The four colours are printed on top of each other in various quantities
  • colours must line up.
• Offset lithography is used for medium to long runs of products
• Advantages of offset lithography

  • High quality images
  • High volume prints
  • long life of printing plate
• This image is of offset lithography

  
• Disadvantages of offset lithography

  • expensive set up
  • expensive running cots
• Flexography uses fast drying water based inks and the ink is transferred to the roller the transferred to the material via pressure.
• Flexography is used to help print newspaper, packaging labels and carrier bags
• Advantages of flexography

  • High print speed
  • Long runs
  • Low cost of equipment
  • low maintenance
• Disadvantages of flexography

  • Cost of printing plates
  • Time consuming
• This is an image of flexography

  
• Screen printing is a process of transferring ink from a mesh screen to a substrate
• Screen printing is used for small print runs such as posters
• Advantages of screen printing is minimal set up costs
• Disadvantages of screen printing is it is a slow process and high cost products being produced.
• Gravure is a rotary printing process. An image is engraved onto a rolling cylinder.
• Gravure printing is good for high volume printing and is used for packaging, labels, and books.
• Advantages of gravure is it has good quality and high speeds
• Disadvantages of gravure

  • It is not economic for small runs
  • Not very fine print
  • Expensive set up costs