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Injection and extrusion blow moulding

Injection and extrusion blow moulding are similar to standard injection and extrusion and many of the actions listed for injection moulding and extrusion should be carried out.

All-electric machines
All-electric machines are now available for both injection and extrusion blow moulding. These have all the benefits of all-electric injection moulding machines and can reduce energy use significantly.

Barrel insulation
Shear heating in blow moulding does not contribute greatly to the heat input to the melt and barrel insulation can be very profitable for both injection and extrusion blow moulding.

Melt temperature
Cooling is a major part of the cycle time for both types of blow moulding and a major energy use (at the chillers). Minimising the melt temperature to the minimum needed will reduce the cooling demand and will improve both cycle times and energy use.

Parison control
Good parison control in extrusion blow moulding will improve product quality, process efficiency and reduce energy use. Investment in improved parison control will have a good payback.

Compressed air
The blowing step is a large user of compressed air in both injection and extrusion blow moulding and good compressed air management is vital, particularly for injection blow moulding of PET pre-forms where the compressed air pressure is generally much higher (40 bar).

Actions to take are:

Minimise the blowing pressure to just enough to get full blowing.
Reduce compressed air pressures when holding after initial blowing.
Use compressed air recovery systems to recover the high-pressure air (40 bar) for use in the low-pressure (7 bar) system.

Tops and tails
Tops and tails management is a key energy issue in extrusion blow moulding. The material from the tops and tails may be recycled but the energy and production capacity is lost forever. Setters should be given targets for tops and tails (< 20% by weight) and machines should not be released for production until this target is achieved.

Recrystallization
Recrystallization of regrind from PET pre-forms or mouldings can be combined with drying through the use of infra-red drying to give good energy savings.

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