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Materials such as polystyrene, nylon, polypropylene and polythene can be used in a process called injection moulding. These are thermoplastics - this means when they are heated and then pressured in a mould they can be formed into different shapes. A simple diagram of an injection moulding machine is shown below. |
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The mould on this machine has been made to form plastic into a sphere. |
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Click here for a more detailed example of injection moulding |
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Granules of plastic powder (note the plastics listed above) 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. |
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| List products that have
been manufactured through injection moulding.
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EXTRUSION |
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A machine used to extrude materials is very similar to the injection moulding machine above. 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. |
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(Only the left- hand side of the machine is shown - the right-hand side is the same as the injection moulding machine) |
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Opposite are examples of the type of shapes (sections) that can be extruded using an extrusion machine. |
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| Describe items you have
seen that have been formed through extrusion.
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