Product Design (Plastics)

Overview of Various Plastics. 

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Advantage over other materials

Advantages –

- Replaced other materials.

- Lightweight.

- Self coloured.

- Self finished.

- Thermal insulation.

- Electric insulation.

- More user friendly.

- More complex shapes can be manufactured.

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Plastics Originality

Natural

Animal & vegetable by-products cellulose & casein. 

Manmade

Coal – Oil – Gas for purely synthetic plastics.

Made by “Thermal Cracking” process.

Account for majority of plastic materials.

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Polymers - Plastics

The 3 types of plastic materials

Thermoplastics - can be repeatedly heated and moulded

Thermosets – undergo a chemical change making them permanently rigid & cannot be reheated and changed

Elastomers – have good elasticity, under pressure they change shape but return to their original shape when the pressure is removed

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The Structure of Plastic Materials

 

 

Loose linked – more relaxed making moulding easier.

 

 

Rigid cross links - making the material stiffer.

 

 

Elastomers - Springy flexible links.

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Properties of Plastics

- Good electrical & thermal insulators

- Good strength to weight ratio

- Generally good resistance to atmospheric & chemical corrosion

- Thermoplastics have low melting temperatures ranging from 70° to 185°C

- Generally they are lightweight

- Generally they are self colored - opaque, translucent or transparent - and don’t require a finish (woods & metals need painting/varnishing/polishing)

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Types of Plastics

ABS

Cellulose Acetate

Nylon

Acrylic

Polypropylene

HIPS

Polyester resin – fibre glass – GRP

Melamine formaldehyde

Epoxy resin – Araldite adhesive

Neoprene - Elastomer

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Process to make Products

 3 basic processes

Moulding – heating/melting & pressurising into a mould (think of making a jelly / Playdoh factory)

Forming – heating flat sheets and shaping over a former

Joining - Mechanical – screws/bolts etc.

             - Adhesives – using special glues

             - Welding – melting along a seam/join

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Processing Plastics

- Moulding processes

- Injection moulding

- Blow moulding

- Rotational moulding

- Extrusion

- Calendaring

- Compression moulding

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Injection Moulding

Injection Moulding -

Used for making:

- Complex 3D shapes

- Bowls

- Buckets

- Combs

- Chair seats

- Dashboards

- Computer casings

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Blow Moulding

Blow moulding –

Used to produce:

- Hollow shapes with narrow necks

- Tubes

- Bottles for

Drinks

Detergents

Cosmetics

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Rotational Moulding

- Used to manufacture hollow 3-D shapes like footballs, road cones & storage tanks

- Can produce rigid, tough shapes as well as flexible ones

- Large and small shapes are possible

- Surfaces can be textured

- Moulds are cheaper to make so smaller production runs are possible

- Only hollow shapes can be produced

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Vacuum Forming

- A former is placed in the bottom of the air tight chamber

- A sheet of a thermoplastic material is heated

- This softens the plastic sheet

- The mould is raised up to the soft plastic sheet

- A vacuum removes the air so sucking the sheet onto the mould

- The sheet is removed & trimmed

- Deep moulds thin the walls of the plastic sheet

- Limited to simple designs

- Sheets must be trimmed

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Thermo Forming

- Similar to vacuum forming but has an outer mould to help form the shape

- A vacuum is also applied

- It’s a low cost method

- Good for smooth shapes with finer detail

- Deep moulds thin the walls of the plastic sheet

- Limited to simple designs

- Sheets must be trimmed

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Extrusion

Used to make

Long shapes with the same cross - section

- Curtain rails

- Drain pipes

- Conduit

- Rods

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Calendering

Used to make:

- Thermoplastic film

- Sheet material

- Plastic bags

- Embossing patterns

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***** Heating

- Line/strip heating is used to form straight bends with small curves.

- Accurate bends can be achieved using bending jigs of the required angles.

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Compression Moulding

- Thermo setting plastics only

- Complex shapes can be manufactured

- Long production runs

- Moulds are relatively cheap to make

- Little material waste

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Enhancing Plastic Properties

Fillers reduce bulk giving improved qualities – reduced costs, stronger & harder, less brittle

Flame retardants reduce the risk of combustion – agents stifle combustion – eg foam cushions

Anti – static agents reduce static charges that can build up  - eg walking on carpets

Plasticisers – improved the flow of plastics when being moulded – less brittle

Stabilisers – reduce the effects of ultraviolet light so they are not broken down easily – windows, doors conservatory fittings

 

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Biodegradable Plastics

- Conventional oil based plastics do not break down easily – may last 100 years

- Bad environmental effects

- BIODEGRADABLE plastics degrade in the right conditions – biologically rich environments

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Sources

Plant based

- Biodegradable plastics come from renewable raw materials


Starch based polymers derived from wheat, corn & potatoes

PLA’s  - Polylactides

- Similar properties to polythene & polypropylene and can be processed like them 

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Applications

- Packaging – bottles, bags, food trays, cutlery, disposable pots, gardening products

- Medical implants and sutures.

- Disposable nappies

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Biopol

- Harvested from bacterial cultures

- Used in packaging because it is similar to polypropylene

- Also in medical fixatives - films, screws, bone plates

- Will break down when in contact with microorganisms in the soil

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Water Soluble Polymers

- Water soluble polymers

- Lactel & Ecofilm

- Liquid detergent sachets dissolve in contact with warm water

- Laundry bags containing soiled clothes can be put in to washing machines, so clothes do not have to be handled, and is more hygienic

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Thermoplastic Elastomers

Thermoplastic Elastomers

- Used in insulating wires, cables & fibre optics

- Over moulding grips on power tools, kitchen utensils, pens & tooth brushes

- Seals & hoses on cars

- Can be injection or blow moulded

- Quick production time

- Scrap & waste can be recycled

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Thermosetting Elastomers

Liquid Silicone Rubber -

- Two components, one a catalyst are mixed and injected into a heated mould where they are hardened

- Used for moulds, teats for baby bottles, seals & covers, baking trays & spatulas

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Advantages of Silicone

- It is very resistant to outside influences like heat, cold and abrasion due to daily use.

Therefore products made of silicone rubber maintain their quality longer than many other materials such as gum rubber.

- Silicone products are available in different grades of hardness as well as in different colours.

- Besides the classic transparent look every other colouring is possible.

- Silicone offers nearly unlimited options of application. With the appropriate know-how almost everything is possible.

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Comments

Sam

Not all plastics are thermally insulating, most of them melt under extremes of heat. Helpful though :)

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