Plastics Revison
- Created by: leilanah
- Created on: 09-02-15 16:15
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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
- Thermosettings contain interlocking monomers to form very strong bonds.
- 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 linked to make plastics = Monomers
- Heated in a refinery and seperated into different chemicals (FRACTIONAL DISTILLATION)
- Oil extracted from underground by drilling
- 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
- INJECTION MOULDING
- 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
- When the tube reaches a high temp. the motor turns a thread which pushed granules along the heater section, liquidising.
- Granules of plastic are poured into a hopper that stores them until needed
- BLOW MOULDING
- 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
- Air is forced into the mould which forces the plsstic to its sides, giving the shape of the bottle
- 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
- VACUUM FORMING
- 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.
- When the sheet is flexible, the mould is raised towards the sheet and the air underneath the former is pumped out.
- It would take approx. 5 minutes for the sheet to be heated and soften when heater is turned on.
- The mould is placed centrally in the vacuum former. A sheet is placed and clamped in position above the mould.
- EXTRUSION
- 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.
- 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.
- ***** HEATING
- ***** 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.
- ***** heater is turned on. The position of the fold is marked with a pencil. The plastic is placed across the rests, above heating element.
- DOME BLOWING
- INJECTION MOULDING
- 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.
- Thermosettings
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