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
Steel is placed in a ceramic box which is packed with carbon.
Box is heated to around 950
Carbon atoms diffuse into the materials structure
The depth of the carbon layer is determined by the length of time of exposure
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