Manufacturing in Plastics

Thermoplastic Processes

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Extrusion

The plastic is heated and when molten forced under pressure through a die

As the plastic leaves the die in its determined shape it is instantly cooled in water troughs and the hardened extrusion is either coiled or cut into sections

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Extrusion (cont’d)

Thermoplastics such as PVC, and nylon are used in the extrusion process

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EXTRUSION BLOW- MOULDING

The cycle1. A tube of plastic called

a parison is extruded into an open two-part mould

2. Mould closes to pinch the mould and air is blown into the tube forcing the plastic against the insides of the mould

3. The mould is opened to release the plastic shape and the cycle begins again.

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EXTRUSION BLOW- MOULDING (cont’d)

Process for making bottles, milk containers, engine oil containers and hollow toys

PVC, Polythene and polypropylene are common blow moulding materials

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Injection moulding

Making products by injecting molten plastic into a split mould

Polythene, polystyrene, polypropylene and nylon are typical injection moulding materials

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Injection moulding (cont’d)

The cycle

1. Granules are fed into the heating barrel via a hopper whilst the die is also being warmed to 60 degrees. The die is empty at this stage

2. Molten plastic is injected into the mould to fill the cavity via a sprue. The die is water cooled to enable the plastic to harden in the mould

3. The component is the ejected and the cycle is repeated

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Injection moulding (cont’d)

Portable power tool casings

Domestic powered utensils

Air fix model kits Vacuum cleaners Bottle caps Fixtures and snap

fittings

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Vacuum forming cont’d

Polystyrene, ABS, acrylic and PVC are typical vacuum forming materials

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Vacuum forming

Packaging –egg boxes, chocolate liners, point of sale packaging

Seed trays Shop signs and fittings Motor car dash boards

and bumpers Wash basins, shower

trays and baths

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Rotational casting

Litter bins Traffic cones Liquid self-feeding

system for cattle Cooling and breather

pipes for car engines

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Line bending

Jigs and formers are used to make accuratebends in the acrylic

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Plastic coating

In industry the plastic powder and the component is electro statically charged

The powder is sprayed onto the component before entering a temperature controlled oven in the case of thermoplastics and a kiln in the case of enamel or thermosetting materials

(Note that this process is sometimes referred to as fluidizing)

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Plug and yoke forming

Softened sheet plastic is sandwiched betweenA male and female mould and left to cool

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Blow moulding