Finishes

Finishes

1. Why apply a finish?

   • Protect against corrosion
   • Make it water repellent
   • Improving resistance to wear and fatigue
   • Make it reflect or absorb heat
   • Make it insulate heat or current

2. Plastics

   • Texture can be added to the mould to make it grippy or smooth
     • Adds expense to mould production
   • Pigment powder/granules can be added to the hopper to colour the product
   • Polymer Coating
     • Plastic is coated with a different polymer
       • Glasses lenses are Acrylic coated with CR39 to make them more scratch reisistant
         • Antireflective coatings can also be applied
     • Physical vapour deposition
       • In a vacuum chamber the coating plastic is evaporated
         • The atoms are deposited on the plastic to be coated
           • Doesn't need high temperatures and doesn't distort product
   • Overmoulding
     • Second polymer is injected over targeted areas
       • For an acrylic toothbrush a thermoplastic elastomer iis overmoulded as a grip
   • Twinshot Injection Moulding
     • Same outcome as overmoulding however uses a signle mould with double barrled injection moulder
       • Much reduced cycle time and fewer moulds

3. Metals

   • Blueing
     • Heating steel to 300 degrees and quenching in oil
     • Leaves a fine oxide layer
   • Electroplating
     • This is how stainless steel is made, used for taps, cutlery
     • Chromium ions coat the steel
     • Electrolysis process to leave a coat of gold, silver, copper, tin...
   • Anodising
     • Similar to electroplating but for aluminium
     • More durable, scratch resistant and can be coloured
   • Dipping
     • Steel can be galvanised by dipping it in molten zinc
       • Car bodies
     • Steel can be plated with tin in the same way, used for food cans
     • Steel has to be cleaned and fluxed
   • Enamelling
     • Finely ground glass in a slurry is sprayed onto metal and then fired
     • Creates a heat and scratch resistant surface, can be coloured
     • Used in jewellery and cooker components
   • Titanium Coatings
     • Titanium is extremely hard wearing, this make it ideal as a cutting edge
     • Can be applied by physical vapour deposition or plasma spraying
   • Painting
     • Metal needs to be clean and degreased
       • Layers of primer and undercoat are applied
         • Top coats of acrylic paint is applied
           • A layer of clear lacquer can also be applied
     • Electrostatic painting gives the paint a +ve charge and the metal a -ve charge
     • Powder coating is a dry process using +ve powder sprayed through a air gun
       • The product is then baked which gives a very hard and tough finish
       • Used for domestic white goods and gates
       • No solvents are used and any excess powered can be recovered, better for the enviroment
   • Plastic Coating
     • Metal is heated to 230 degrees and passed through plastic powder and air
       • Heat from the metal melts the plastic and creates a protective layer

4. A burr is a rough edge created from a cutting process

5. Woods

   • Paints
     • Primers and undercoats are applied with light sanding in between
       • Top coat is then applied
     • Yacht varnish
       • Used for products that are for outdoor use
       • Not affected by sunlight or expanding timber as much
     • Polyurethane paint
       • Hardwearing, tough and scratch resistant
       • Used for children's toys
     • Oil based
     • Tanalising
       • Vacuum created in chamber and then preservative is added
         • Pressure is increased to force it into the wood and then dried
       • Helps timber last a long time