1. A model railway system is remotely controlled using a handheld unit (shown opposite). The unit is manufactured from plastic and inside is an electronic circuit. The unit controls the movement of model trains, barriers, traffic lights etc.....

Name a suitable plastic for the casing:

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2. What are the properties of the plastic you name in the previous question that make it suitable for the manufacture of the handheld control unit?

ANSWERS

PROPERTIES: High density polystyrene has a relatively low melting point. This material is a thermoplastic - which means when heated and then pressured in a mould it can be formed into different shapes

3. It has been decided that the casing is to be manufactured through the process of injection moulding. In the space below draw a suitable diagram representing this process. Include labels and notes explaining the process.

NOTES

Granules of plastic powder are poured or fed into a hopper which stores it until it is needed. A heater heats up the tube and when it reaches a high temperature a screw thread starts turning. A motor turns a thread which pushes the granules along the heater section which melts then into a liquid. The liquid is forced into a mould where it cools into the shape of the casing. The mould then opens and the coupling is removed.