1. Design and Manufacture
Plastics
Design and Manufacture

2. Plastics the basics Natural plastics: fossilised tree resin and latex
Form of rubber
Synthetic plastics: Chemically manufactured from carbon based materials such as crude oil, coal and gas
Basic chemicals used in creating plastics are from coal and crude oil.
Obtained by using heat and chemical catalysts

3. Plastic properties Ideal for mass production of quality products
Light in weight
Resistance to corrosion
Low thermal conductivity
Translucent, transparent and opaque
Electrically resistant
Easily formed
Recyclable

4. Forms plastic comes in Profiled sheets, rods, tubes and bars
Moulding compounds
Thin layers of films and sheets
Foam
Casting compounds such as ingots
Paint, varnish and lacquer used for finishing
Filaments and fibres
Composites that contain reinforcing material

5. Thermosetting plastics
Heated
Softens
Shaped
Permanently hard
Formed by chemical reactions that leave them in a relatively fixed state.
They cannot be softened or reformed when reheated.
Can withstand high temperature, excess heat will cause material to decompose.
Used when products needs resistance to extremes in temperature, electrical current, chemicals and wear.

6. Thermosetting plastics
Some examples of thermosetting plastics are:
Epoxy Resin ER(Araldite) – good adhesive, low shrinkage, strong when reinforced. Used in bonding, laminating, surface coating, printed circuit boards
Polyester Resin PR(Orel Beetle) – stiff, hard, brittle, resilient as laminated GPR, formed without heat or pressure. Used in panels for car bodies and boat hulls, casting and embedding
Melamine formaldehyde MF(Formica Melaware) – waterproof, tasteless, odourless, mark and scratch resistant. Used in worktops, tableware, buttons, electrical insulation.
Urea Formaldehyde UF(Aerolyte Cascamite) – good adhesive, stiff, hard, brittle, good electrical insulator. Used in electrical fittings, paper and textile coating, wood adhesive.
Phenol Formaldehyde PF (phenol methanal) – Hard, brittle plastic with dark colour, glossy finish. Resists heat. Used in parts for domestic appliances, bottles tops, kettle/iron/saucepan handles.

7. Thermoplastics Softens when heated, hardens when cooled down
Shaped
Hardens
Thermoplastics
Softens when heated, hardens when cooled down
Can be repeated indefinitely
When soft they are easily formed under pressure.
PLASTIC MEMORY – this is the property of the thermoplastic returning to its original shape when softened after being shaped.

8. thermoplastic
Polyethene HDPE – High density, tough, resists chemicals, feels waxy. Used for rigid objects: buckets, bowls, sterilised containers.
Polyethene LDPE – Low density, soft and pliable, electrical insulator. Used for flexible objects: bags, bottles, cable, sheathing, toys.
Polypropene PP – rigid, light, good chemical resistance, resistance to fatigue, bending. Used for crates, seats, string, rope, medical equipment, hinges, kitchenware, film.
Polystyrene PS – light, buoyant, stiff, water/weather resistant. Used for packaging, containers, insulation and toys.
Polyvinyl chloride UPVC – rigid, abrasive resistance, water/weather resistant. Used for piped, gutters, bottles, roofing, window frames.
Poly-methacrylate PMMA (Acrylic/Perspex) – Stiff, hard, clear, durable, scratches easily, easily machined and polished. Used for signs, lighting, reflectors/lenses cases, jewellery.
Nylon – Hard material, good resistance to wear and tear. Solid nylon has low friction qualities and high melting point. Used in curtain rail fittings, combs, clothes and gear wheels.

9. elastomers Particular branch of thermoplastics Has elastic properties
Similar to rubber in how it reacts to pressure and their texture
Withstands large amounts of deformation
Can be stretched several times to their length.
Uses:
Waterproof seals
Diaphragms for mechanical purposes
Flexible handles
Sportswear
Foam padding

10. Composite materials Consists of two or more substances
Combines to produce properties that no single substance can achieve.
One component forms the matrix (base) while the other provides reinforcement
Properties are controlled by size and distribution of reinforcing substance.

11. Example of composite material
Using carbon fibres embedded in Resin
Carbon-fibre reinforced plastic CFRP
Properties are:
Low in density
Light in wieght
High tensile strength
Better corrosion resistance and fatigue performance than most metal alloys
Used in aerospace industry and car frameworks.

12. Plastic processing
Plastics part 2

13. Injection moulding
Allows large quantities of plastic components to be made quickly
Most important industrial process in mass production of plastic goods.
Costs of machining original moulds are very high therefore necessary to sell large numbers of products to recover costs.
There are a few features which help identify this process:
Sprue marks
Draw angles
Mould split lines
Ejection pin marks
Webs used for strength
Variation of finishing techniques from high quality shine to texture

14. Injection Moulding
Granules of plastic powder are poured or fed into a hopper which stores it until it is needed.
2. A heater heats up the tube and when it reaches a high temperature a screw thread starts turning.
3. A motor turns a thread which pushes the granules along the heater section which melts then into a liquid.
4. The liquid is forced into a mould where it cools into the shape (in this case a sphere).
5. The mould then opens and the sphere is removed.

15. Injection moulding (uses)
High volume, automated industrial manufacturing process.
Golf tees
Spoons
Wash basins
Buckets
Product casings

16. extrusion Used for products with long uniform cross sections.
Variety of metals and thermo-plastics are suited to the extrusion process.
Plastic is easier as it requires less force
Polythene, PVC, polypropylene
Lead, copper, brass, bronze, aluminium, steel
Features that help identify this process;
smooth-walled long sections
Line texturisation

17. Extrusion
A machine is used to extrude materials which is very similar to the injection moulding.
A motor turns a thread which feeds 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.

18. Extrusion (Uses) Curtain rails Drainpipes Electric cable sheathing
Fluorescent light covers
Hose pipes

19. Blow moulding
Several variations to the process, producing various sizes
Finish is not as high a standard as injection moulding
Good mould allows:
Uniform thickness
Complex shape
Good quality of production
Fast process
Little waste
Features that allow for identification:
Mould separation lines
Flash lines
Any shape of bottle or container
Transparent, opaque or coloured

20. Blow moulding
The process is similar to injection moulding and extrusion.
1. The plastic is fed in granular form into a 'hopper' that stores it.
2. A large thread is turned by a motor which feeds the granules through a heated section.
3. In this heated section the granules melt and become a liquid and the liquid is fed into a mould.
4. Air is forced into the mould which forces the plastic to the sides, giving the shape of the bottle.
5.  The mould is then cooled and is removed.

21. Blow moulding (uses)
Variety of mass produced bottles and liquid containers, using variety of polymers and laminates.

22. Compression moulding Used for shaping thermosetting plastics
These are strong and brittle but have poorer impact resistance than thermoplastics
Features that identify compression moulding:
Walls of uniform thickness 3-6mm
Draft 1˚ minimum
Flashes on edges
Quality finish on female mould
Plastic used can resist temperature increases.

23. Mould through compression
The stages are as follows:
1. The mould is heated.
2. A 'slug' or piece of the plastic is placed into the mould and warms up.
3. The hydraulic press begins to move down when the plastic has reached the correct temperature..
4. As the upper and lower mould meet, the plastic is compressed into the shape of the mould.
5. The upper mould moves upwards and the plastic piece (in this case a dish) is removed.

24. Compression moulding (uses)
Automotive distributor caps (cars)
Camera cases
Electrical wall sockets
Handles
Door knobs
Light switches

25. Vacuum forming Widely used in industrial processes to mould plastic.
No need for expensive moulds or dies
Moulds generally used from wood/ steel/ aluminum
Process is over in a few minutes
Thermoplastics are suited for this process
Features that identify this process:
Thin sheets normally used
Patterns and textures are transformed from the mould to the product surface
Venting holes cause ‘pips’ on surface
Tapers are pronounced
Thinning on side surfaces

26. Vacuum forming

27. Vacuum forming (uses) Packaging items that have complex shapes Toys
Trays
Dishes
Margarine tubs
Toys
Light panels

28. Rotational moulding
Produces “closed and seam free” components made from plastic polymers
Products produced are hollow, stress free and come in a wide range of shapes and sizes.
Moulds made from steel
copper coated for better surface detail
Aluminium for better heat transfer
Electroformed nickel for best surface detail.
Moulds rotates several axes with speed dependent on production requirements.
Large moulds have air vents to avoid distorting
Suited to small production runs used for prototypes

29. Rotational moulding (process)
Measured quantity of plastic power is added to mould
Mould is closed and rotated slowly around 2/3 axes. Allows distribution over hot surface
Plastic melts on contact and builds up even coating on inside surface of mould
Mould surface is cooled, plastic retains its shape
Mould opens and product is removed.

30. Rotational moulding (uses)
Plastic toys
Play equipment
Road markers
Buoys
Large tanks (10,000litres)

31. Other processes
Calendering: Thermoplastics are squeezed between hot rollers forming thin sheets or film
Casting: useful for thermosetting plastics. Molten plastic poured into mould
Bending: thermoplastics heated along a line using strip heater, folded to desired angle. Bending jig sometimes used to hold in place.
Fabrication: joining together using a variation of fixings and adhesives
Coating: powered thermoplastic melts on surface of heated product.(dip coating)
Forming: Layers o glass fibre matting and polyester resin formed over a mould. Resin cures it hardens giving rigidity to fibre/resin matrix. Thermoplastic formed by heating whole sheet till soft then pressed between two formers.