plastics and their_properties
TRANSCRIPT
Take a few minutes to look around the room and identify some everyday plastics.
Everyday plastics
Chairs
Jumper
Comb
Carrier bag
Pencil case
Polypropene
Acrylic
Nylon
Polyethene
Neoprene
Plastics can be broken down into two categories: thermoplastics and thermosetttings.
Categories of plastics
ThermoplasticsSoften when heatedCan be reshapedMore commonly used in schools
ThermosettingsInitially set by heatCannot be reshaped once setExtremely strong and durable
Plastics have an extremely wide range of uses. Here are some common products made from thermoplastics.
Uses of plastics (thermoplastics)
Acrylic
High DensityPolyethene
Polystyrene
ABS
Low DensityPolyethenePolypropene
Thermosets have different qualities to thermoplastics. Here are some uses for thermosets.
Uses of plastics (thermosets)
Melamine formaldehyde
Ureaformaldehyde
GRP
Phenol formaldehyde
Epoxyresin
Common plast ics applications
.Thermoplastics : Nylons :handels , bearing , cams.
Vinyls : phonograph records. Polyethylene : toys , ice cream trays
.Thermosets: Phenolics : telephones , motor housing
Epoxis : adhesives , sinks Polysters : fans , helmets ,chairs
Properties of plastic
• Light weight• High toughness
• Feels waxy• Low thermal conductivity
• Resistance to flow of current
• A wide range of colours
Working with plastics – other processes
Buffer
Oven
Scroll Saw
Drill
Hot wire strip heater
Working with plastics – industrial processes
Injection moulded polyethene wheel
The injection moulding process involves heating plastic granules to their melting point and then injecting them at high pressure through a nozzle into a mould. When the plastic cools the mould is opened and the newly formed plastic part can be removed.
What similarities and differences can you identify between the vacuum forming and injection moulding processes?
Materials can be joined temporarily or permanently. Three methods of joining plastic are shown below.
Joining plastics
Nut, bolt and washer
Riveting Adhesive
MASTER QUESTIONS?
Which method is permanent?
Which method is most quick?
Which is the strongest method to join plastic?
Which method is most expensive method?
Which is the least expensive method?
Working with plastics – finishing techniques
Plastics have excellent surface qualities. As they are self-finishing, plastics require little or no surface finish. However, when designers want a specific colour or texture, spray paints can be used.
