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Jomar
Continuous Extrusion Blow Moulding
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In
the simplest form of continuous extrusion blow moulding (EBM),
parisons are extruded from the core and die of the extrusion
head. When the parisons reach the correct, predetermined length,
in Station 1, the moulds are closed around them and simultaneously
a cutting unit cuts the parisons.
The moulds have the external shape of the finished container
and immediately move still closed from Station 1 to Station
2. Here the blow pins are inserted into the centre of the
hot parison calibrating the container necks through the pinch-off
bushings. Air at 4 -10 bar then enters through the blow pin
to blow the parison to form the shape of the container
inside the moulds.
The moulds are made usually of an Aluminum alloy or Stainless
Steel and cooled to 5-10°C, which will cool the bottle.
Excess material at the top and bottom (flash) is also compacted
and cooled at Station 2. Now the moulds open and return
to Station 1 to collect new parisons.
Meanwhile the existing blow mouldings (still attached
to the blow pins) are collected by a holding unit attached
to the moulds. The blow pins are then removed, and the bottles
transported to Station 3 by the holding unit,
where the flash is removed automatically.
In the next capture, the finished mouldings are transported to
Station 4 for optional additional cooling or optional
leak testing.
From here the finished bottles can be transported for packing,
filling, decorating or labelling downstream. In the example
above, the neck of the bottle is compression moulded (calibrated)
between the blow pin and the mould neck finish.
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Handleware
(any bottle with a solid or blown handle) can be considered
a more complex form of extrusion blow moulding where the process
excels. In this case the parison needs low pressure air preblow
through the extrusion head as the moulds close around the parison
in Station 1 to increase the parison diameter. At Station
2, the parisons are blown to the final shape.
By careful balancing of the depth of the flash pockets inside
the handle and at the top and bottom of the mould, the flash
is compacted to a solid mass and cooled by the mould. Knife edges
around the cavity, where the flash is attached to the bottle
are designed to allow for the removal of the flash by mechanical
knock outs in Station 3. Some handleware containers need
other supports at Station 2 to stabilise the bottle during
mould open and transfer.
All of the flash (scrap) is allowed to fall onto a lower conveyor,
where it can be taken away for recycling back into the process.
Double
head - single sided shown.
Double station replicates Stations 2-4 on left hand side of
the machine.
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