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ENGINEERING, PPT 2023 HSC 11 MC

Which manufacturing process is used to make soft drink bottles out of polyethylene terephthalate (PET)?

  1. Stamping
  2. Extrusion
  3. Blow moulding
  4. Rotational moulding
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\( C \)

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Making soft drink bottles out of PET:

  • PET is first polymerized to create long molecular chains then processed into plastic pellets, which serve as the raw material for making bottles.
  • The plastic pellets are melted into preforms and heated and stretched in a process known as “blow moulding” to create the final bottle shape.

\(\Rightarrow C \)

ENGINEERING, PPT 2016 HSC 24c

Truck tyres are made using vulcanised synthetic rubber combined with high tensile steel wire.

Explain why this combination of materials has been chosen.   (3 marks)

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Vulcanised synthetic rubber construction:

  • High coefficient of friction.
  • Resilience, formability and wear resistant.
  • Elastic and highly flexible.
  • High tensile steel bands ensure distortion properties of rubber are managed.
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Vulcanised synthetic rubber construction:

  • High coefficient of friction.
  • Resilience, formability and wear resistant.
  • Elastic and highly flexible.
  • High tensile steel bands ensure distortion properties of rubber are managed.

ENGINEERING, PPT 2017 HSC 24a

Sleds are used to slide loads over soft surfaces such as grass, sand and snow. They can be made using polypropylene.

  1. Explain how the properties of polypropylene make it a suitable material for this application.   (3 marks)
  1. Describe a suitable manufacturing method to make a sled from polypropylene.   (3 marks)
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i.   Polypropylene properties

  • Low coefficient of friction, lightweight and durable with excellent flexural strength.
  • In the manufacturing process, polypropylene is a good material for injection moulding which makes it easy to produce. 

ii.  Manufacturing method:

  • Polymer pellets are introduced into an injection moulding machine.
  • A heating unit surrounding the exterior of the machine and internal friction heat the pellets.
  • They are forced into a steel mould under pressure.
  • After solidifying, the mould halves are separated and removed using injector pins.
  • Cooling, removal of surplus flash and polishing complete the process.
Show Worked Solution

i.   Polypropylene properties

  • Low coefficient of friction, lightweight and durable with excellent flexural strength.
  • In the manufacturing process, polypropylene is a good material for injection moulding which makes it easy to produce.

ii.  Manufacturing method:

  • Polymer pellets are introduced into an injection moulding machine.
  • A heating unit surrounding the exterior of the machine and internal friction heat the pellets.
  • They are forced into a steel mould under pressure.
  • After solidifying, the mould halves are separated and removed using injector pins.
  • Cooling, removal of surplus flash and polishing complete the process.

♦ Mean mark (ii) 53%.

ENGINEERING, PPT 2022 HSC 21a

The following images show an older bus and a contemporary bus.
 

  1. Older buses had flat, toughened glass windscreen panels.
  2. How is toughened glass manufactured?   (2 marks)
  1. Contemporary buses have windscreens which curve around the front of the bus.
  2. Describe the manufacturing process used to make these windscreens.   (3 marks)
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i.    Toughened glass is formed by:-

  • heating the glass to annealing temperature (approximately 600 degrees) and quenching/rapidly cooling the outside layers using a jet of water.
  • Alternatively toughened glass can be created by soaking the glass in potassium nitrate for an extended period.

ii.    Production of curved glass panels:

  • Windscreens are produced by placing a flat sheet of glass above a metal mould.
  • The glass is then evenly heated until it falls and takes the shape of the mould, and then allowed to cool.
  • Once cooled, the glass is then laminated.
  • Laminating involves placing a layer of polymer between two identically shaped sheets of glass, in this case curved windshields.
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i.    Toughened glass is formed by:-

  • heating the glass to annealing temperature (approximately 600 degrees) and quenching/rapidly cooling the outside layers using a jet of water.
  • Alternatively toughened glass can be created by soaking the glass in potassium nitrate for an extended period.

♦ Mean mark (i) 43%.

ii.    Production of curved glass panels:

  • Windscreens are produced by placing a flat sheet of glass above a metal mould.
  • The glass is then evenly heated until it falls and takes the shape of the mould, and then allowed to cool.
  • Once cooled, the glass is then laminated.
  • Laminating involves placing a layer of polymer between two identically shaped sheets of glass, in this case curved windshields.

♦ Mean mark (ii) 39%.

ENGINEERING, PPT 2020 HSC 3 MC

Which of the following manufacturing methods can be used to produce complex polymer components?

  1. Sand casting
  2. Blow moulding
  3. Lost wax casting
  4. Injection moulding
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`D`

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By Elimination:

  • Sand casting and lost wax casting are for metals, so not `A` or `C`.
  • Blow moulding can only make simple hollow shapes (eliminate `B`).

`=>D`