To speed production several identical moulds may be

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Unformatted text preview: nto a 'hopper' that stores it. 2. A large thread is turned by a motor which feeds the granules through a heated section. 3. In this heated section the granules melt and become a liquid and the liquid is fed into a accumulator. From accumulator melt is pushed to form parison throuh the die in to the mould. 4. Air is forced into the mould which forces the plastic to the sides, giving the shape of the bottle. 5. The mould is then cooled and is removed. Injection blow moulding In injection blow moulding two moulds are used. A mandrel or blowing stick is placed in the first mould, and the thermoplastics material is then injected into the mould flowing around the mandrel to create a tube. This is then transferred to the second mould where air is introduced to expand it to the shape of the mould. A variation on this method is stretch blow moulding whereby the material is biaxially oriented to produce stronger products. This method is particularly used for the manufacture of PET bottles. Applications • • • • • Bottles and containers Automotive fuel tanks Venting ducts Watering cans Boat fenders etc Rotational Rotational Moulding Rotational moulding is a process used for producing hollow plastic products. Rotational moulding differs from other processing methods in that the heating, melting, shaping, and cooling stages all occur after the polymer is placed in the mould, therefore no external pressure is applied during forming. Rotational Rotational Moulding This provides the following advantages: • Economically produced large products • Minimum design constraints • Stress-free products • No polymer weld lines • Comparatively low mould costs The The Process – 4 Stages Charging Mould A pre-determined amount of polymer powder is placed in the mould. With the powder loaded, the mould is closed, locked and loaded into the oven. The powder can be pre-compounded to the desired colour. Heating & Fusion Once inside the oven, the mould is rotated around two axis, tumbling the powder – the process is not a centrifugal one. The speed of rotation is relatively slow, less than 20 rev/min. The ovens are heated by convection, conduction and, in some cases, radiation. As the mould becomes hotter the powder begins to melt and stick to the inner walls of the mould. As the powder melts, it gradually builds up an even coating over the entire surface. Cooling When the melt has been consolidated to the desired level, the mould is cooled either by air, water or a combination of both. The polymer solidifies to the desired shape. Unloading/Demoulding When the polymer has cooled sufficiently to retain its shape and be easily handled, the mould is opened and the product removed. At this point powder can once again be placed in the mould and the cycle repeated....
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This document was uploaded on 03/14/2014.

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