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
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
Boat fenders etc Rotational
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
This provides the following
advantages: • Economically produced large
• 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
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
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.
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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- Spring '14
- Plastics industry, Blow molding, injection moulding