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ISSUE 04-05 / 2001 |
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| Preform Production | BACK to contents |
GETTING MORE FROM LESS
Increased demand for PET bottles means increased
output requirements for bottle blowers and preform manufacturers – and ultimately
more machines. But what if there isn’t room for more machinery? One answer,
of course, is higher output from the same sized machine.
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A 96-cavity mould of the
new Premax 96 requiring the same space as a standard 72-cavity mould |
The new Premax also includes an improved 4-station robot |
SIG Plastics have recently announced the launch of their new Premax 96 preform
machine which they claim has 15% higher output than its predecessor, with
reduced floor space requirements and lower energy consumption. 133 Please use PETplanet's
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New tool concept
An important contribution to the reduced space requirement is made by the
new tooling concept. The compact mould provides 96 cavities in the same space
as a standard 72-cavity mould. The primary aim in developing such a mould
was the installation of a smaller clamping unit with less mass, and a reduced
clamping force. Other objectives were better preform quality and increased
cooling efficiency with consequently lower cycle times.
More intensive cooling is achieved in all segments thanks to the new design
concepts in the cavity area. These include cooling channel geometry, different
materials and a new coating technology, all helping to ensure that neck ring
and cores as well as cavity and bottom plates are subjected to optimum cooling.
A special feature of the hot runner system, which was developed and manufactured
by SIG, is a 25 % reduction in melt volume resulting in a shorter melting
time in the hot runner. In addition, the new mould design provides improved,
easier maintenance by offering only one service position.
Improved plasticiser
The high-capacity plasticising unit operates at up to 400 g/s with a very
gentle plasticising being achieved by a PET screw developed specifically for
this purpose. The reduced screw speed and the peripheral velocity mean that
the raw material is exposed to less shear forces thus leading to reduced temperature.
This in turn causes less degradation of the molecular weight and lower acetaldehyde
(AA) contents. The improved clamping unit has been reduced to a clamping force
of 5000 kN. In addition to reduced floor space requirements and a higher process
speed, the smaller clamping unit also leads to lower energy consumption. Cycle
time reductions of approx. 0.5 seconds are claimed by SIG for this clamping
unit alone.
To improve the quality of the finished preform SIG have modified the thermal
separation near the gate. A higher gate quality is achieved by the new design,
new material pairing and an improved bottom plate geometry, which also means
lower crystallinity and a neat, clean separation, avoiding bad gates nubs.
Bottles blown from these preforms should have a better quality base thanks
to better material distribution, bringing with it better stress cracking and
burst pressure characteristics.
Better cooling
The new machine also incorporates improvements to the 4-station take-out/cooling
robot – a combination of water and air cooling – in which the preforms are
intensively post-cooled for approximately 4 cycles. This is said to lead to
a reduced preform output temperature and therefore to an improved dimensional
stability. In addition a mechanical ejection system rather than a pure compressed
air systems provides higher production efficiency by ensuring totally safe
ejection of the preforms.
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