Polymer Processes

Question 1

Vacuum forming

Answer 1

Polymer is heated to its glass transitional temperature, the polymer is then forced onto the mould by a vacuum pump

Mould is placed on the platen

Can be used for polymer sheets up to 6mm thick

Moulds require a draft angle and rounded corners

Used for small scale batch and mass production

Not cost effective for one-off manufacture

Used for:

Trays
Takeaway coffee cups
Yoghurt pots
Blister packaging

Question 2

Thermoforming

Answer 2

Polymer sheet is clamped between two mould halves (positive and negative) and heated. The mounds are then forced together

Approx 6mm thick polymer sheets

Similar to vacuum forming but there is a negative mould when the vacuum is applied

Good for fine detail
Slow process
Used in industrial production

Used for:

food packaging
Sandwich boxes
Cake boxes

Question 3

Calendaring

Answer 3

A series of heated rollers squash and stretch the polymer to make it thinner

Industrial method used by specialist manufacturers for continuous production

The required stock form is thermoplastic pellets

Used for thin polymer sheet and film such as cling film food wrap

Question 4

Line bending

Answer 4

An electrically heated element heats a thin line along the polymer sheet, along which the polymer can then be bent

Slow and labour intensive - used in school workshops

Suitable for one-off or limited batch production

Uses:

Acrylic boxes
Shelves

Question 5

Lamination (lay-up)

Answer 5

Used for composites - CFRP and GRP

Layers of fibre are arranged on the mould on top of a release agent/catalyst, polyester resin is then added followed by another layer of fibre then resin etc

The product must then cure/dry - CRP requires an autoclave for this

A top gel coat is applied which contains pigment

Used for:

Boat hulls
Kayaks
Theme park rides
Train carriages

Question 6

Injection moulding

Answer 6

Thermoplastic granules are heated and melted whilst travelling along an Archimedean screw which forces the molten polymer into a mould

Complex 3D shapes can be made easily
Fast industrial production method
High initial tooling cost
Used for large scale mass or continuous production

Used for electric product casings, vacuum cleaner components and toys

Question 7

Blow moulding

Answer 7

Air is used to force the molten parison into the shape of the mould cavity

Produces hollow, thin walled products
High initial tooling costs
Used for continuous production

Products:

Drinks bottles
Shampoo bottles
Detergent bottles

Question 8

Rotational moulding

Answer 8

Mould is heated and rotated rapidly to ensure even layer of polymer

Produces seamless, hollow components with a large wall thickness

Large scale batch or mass production

Products:

Traffic cones
Kayaks
Water tanks
Children’s play equipment

Question 9

Extrusion

Answer 9

Similar to injection moulding except the polymer is forced through a die to produce lengths of the same cross section (extrusions)

Industrial method for continuous production

Products:

Solid rods
Tubing
Angle sections
Curtain track

Question 10

Compression moulding

Answer 10

Uses a pre weighed ‘slug’ of polymer which is heated and places in the negative half of the mould. The positive half hydraulically presses the slug into shape

Polymer is removed from the mould whilst still warm

Large scale batch production

Products:

Electrical light fittings 
Switches 
Plugs 
Picnic plates 
Cups