15 - Polymer processes Flashcards
Vacuum forming
Thermoplastic sheet up to 6mm thick is clamped, heated, and draped on to the mould. A vaccum then sucks the sheet tight to the mould, before the sheet is left to cool and then ejected from the mould
- Mould must have air holes and rounded corners
- Small-scale batch and mass production
Uses: Trays, takeaway coffee cups, yoghurt pots
Thermoforming
Similar to vacuum forming, but an additional ‘positive’ mould is pressed on to the polymer sheet as the vacuum is applied
-Good for fine detail such as moulded in logos
-Slow process, used in industrial production
Uses: Food packaging
Calendering
Thermoplastic pellets
- Heated rollers squash and stretch the polymer to make it thinner
- Industrial production method, carried out by specialist manufacturers
- Used for continuous production
Uses: Thin polymer sheet and film
Line bending
Thermoplastic sheet
- Uses a heating element which provides heat along a straight line, to soften the polymer so it can be bent
- Mainly used in schools and college workshops as it is slow and labout intensive
- Used for one-off or limited batch production
Uses: Acrylic boxes and shelves, or one-off displays for school etc.
Lamination (lay-up)
Fibre-based composite sheets (e.g CRFP)
The bonding of two or more layers of materials using pressure, heat and a polymer adhesive (e.g polyester resin)
- Requires a former to mould around
Injection moulding
Therrmoplastic granules travel down Hopper to the Archimedian Screw
Granules are heated and melted as they are pushed through by the Archimedian screw into a mould
- Complex 3D shapes can be easily made
- Fast industrial production method
- High start-up cost
Used for large scale mass or continuous production
Blow moulding
Parison (tube) of polymer is placed in a mould.
Hot air is then blown into the parison, so that it expands to fill the mould
-It is used to create hollow, thin-walled components
-High start-up cost
-Used for contunuous production
Rotational moulding
Thermoplastic powder or granules placed in a mould
Mould is heated and rotated, spreading a layer of the polymer around the mould
Mould is still spinning whilst it cools
-Large scale mass or batch production
Extrusion
Similar to injection moulding
-Instead of being pushed into a mould the molten plastic is pushed through a die, and carried away on a conveyor belt
-This forms a thin, extended length of plastic
Compression moulding
Preheated ‘slug’ of polymer (block) placed into the lower mould.
Hydraulic press the reverse shape of the mould is lowered on to the slug, to form the polymer into the shape of the mould
Both halves of the mould are heated during the process, and the polymer shape is removed while it is still warm
- Large-scale batch production
