Plastics Revison

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  • Plastics
    • Thermosettings
      • Thermosettings contain interlocking monomers to form very strong bonds.
        • Once heated and moulded, the plastic can't be reheated or reformed. Therefore, they can't be recycled.
      • High boiling point; resist heat and fire
      • Highly flexible design
      • Cost-effective
      • Long-lasting
      • Cannot be recycled
      • More difficult to surface finish
      • Can't be reshaped, remoulded etc.
      • EPOXY RESIN: Good electrical insulator, hard, brittle unless reinforced, resists chemicals well
        • USES: Casting and encapsulation, adhesives, bonding of other materials
      • MELAMINE FORMALDEHYDEl Stiff, hard, strong, resists some chemicals and stains
        • USES: Laminates for work surfaces, electrical insulation, tableware
      • UREA FORMALDEHYDE: Hard, brittle and a good electrical insulator
      • GLASS REINFORCED PLASTIC: mixed with glass strings to make it really strong
        • USES: Racing car bodies and light aeroplanes
    • Mostly synthetic (made from crude oil, sometimes gas and oil) but some are natural
      • Oil extracted from underground by drilling
        • Heated in a refinery and seperated into different chemicals (FRACTIONAL DISTILLATION)
          • Chemicals  linked to make plastics = Monomers
            • Joined  up monomers are called polymers in a process called polymerisation
    • Chemicals added
      • PLASTICISERS help the plastic flow better when melted and makes it less brittle
      • FILLERS make plastics stronger, harder or more rigid
      • BLOWING AGENTS turn plastic into foam = lighter and better insulator
    • Shapes and Sizes
      • FILMS AND ROLLS: Vacuum forming and packaging with wondows
      • FOAM: Protective packaging and making models and mock-ups
      • SHEETS, RODS AND TUBES: Cut to size and bent
      • GRANULES (Manufacture): Melted down and used in injection moulding and extrusion
    • Processes
        • Granules of plastic are poured into a hopper that stores them until needed
          • When the tube reaches a high temp. the motor turns a thread which pushed granules along the heater section, liquidising.
            • Forced into the mould, the liquid cools into shape and the plastic is removed
        • Plastic granules are fed in a hopper and a large thread feeds the granules through a heated section. The granules melt and become liquid as it's fed into the mould
          • Air is forced into the mould which forces the plsstic to its sides, giving the shape of the bottle
            • The bottle takes its shape as it cools and is removed
        • The mould is placed centrally in the vacuum former. A sheet is placed and clamped in position above the mould.
          • It would take approx. 5 minutes for the sheet to be heated and soften when heater is turned on.
            • When the sheet is flexible, the mould is raised towards the sheet and the air underneath the former is pumped out.
              • The air pressure forces the plastic over the mould, taking its form where it cools and hardens. The mould is then lowered.
        • A motor turns a thread, feeding granules of plastic through a heater. The granules melt into a liquid which is forced through a die, forming a long 'tube like' shape.
          • The extrusion is then cooled and forms a solid shape. The shape of the die determines the shape of the tube.
        • Strip heater is turned on. The position of the fold is marked with a pencil. The plastic is placed across the rests, above heating element.
          • Sheet is turned over every 30 seconds to stop damage to the surface. Plastic becomes malleable and placed against a 'jig' or a surface at 90 degrees to hold it into position as it cools.
    • Don't need protective surface finishes because very resistant to corrosion and decay
      • Use wet and dry to remove scratches with mild abrasive polish or anti-static cream
      • Uae a buffing machine
    • Joining acrylic
      • Two piecces are keyed down with abrasive paper. Liquid solvent is placed along sides of the surfaces via. capillary action using a syringe/ paintbrush. The top of the two surfaces dissolve and are fixed together.


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