PET systems from Netstal –
more attractive than ever before

Netstal has been one of the plastic industry’s leading providers of premium, precise and fast-running injection moulding machines up to clamping forces of around 8000 kN for decades. Our machines meet the highest requirements in terms of process execution, moulded part quality and production output. This applies above all for applications in the packaging sector.

As demonstrated by its product range and system solutions, Netstal is oriented towards the requirements of users in the packaging industry. Focal points here include making production more cost-efficient for the client while both minimising cycle times and maximising output at lower costs.

The PET-Line production system is established on the market and offers users the best manufacturing capabilities, particularly when it comes to high production volumes. Based on the innovative platform strategy, the client is able to configure each system according to his requirements and capacity utilisation.

Further developments have been made to the Calitec© technology already available on the market in order to increase process efficiency. These developments were brought about by the introduction of different base geometries for the preform to improve the blow-out behaviour of bottle bases. The aim of the modified base geometries for these preforms is to optimise their surfaces for the subsequent heating process in the blowing machine in such a way that they are better able to absorb the thermal energy from the UV lamps. This means that the base can be heated to an optimum temperature in the blowing process later on and blown out to produce the thinnest walls possible. It is not only the weight of the base that is reduced thanks to improved material distribution – a build-up of material, and consequently a high level of crystallisation, is also prevented because the base cannot crack as easily. Conversely, this means that material savings can also be accompanied by improved bottle strength. Unlike the “EcoBase” and the “Cappello”, we are now reliably able to completely remove any unnecessary base material. This may be due to the fact that although the contour was adjusted to improve the blowing process, it was not possible to affect much more important parameters, namely wall strength and hence material build-up, asthe wall strength for an optimal injection moulding process can virtually not be changed.

This innovation, i.e. the patented “preblow” process in which the preform is blown out in the base area immediately after the injection moulding process, brings new possibilities to this sector. For the first time it is possible to adjust not only the base outline and hence the surface dimensions.– Enlarging the base outline also reduces wall thickness in the critical base area as a result of the blowing process. This effect makes it possible to heat the base area in a more specific and efficient manner in the subsequent blowing process, as a larger surface with a lower wall thickness requires less heating from the UV lamps in the blowing machine.

The result: LightBase.
At first glance, a wall thickness curve can be seen after cutting apart the 1 litre juice bottles that no longer shows any material build-ups in the base area. With LightBase, the cut surface runs evenly over the sprue point, while an identical bottle with a modified "Cappello Design" preform manufactured in the comparison still clearly shows material build-ups. The weight of the bottom section on the test bottle, for which the preform was not designed, was 0.6 g. For the original bottle, it was even possible to achieve a weight reduction of more than 1 g relative to the preform.

The LightBase test bottle also stands out not only due to its reduced weight – it boasts other improved properties that are a result of better material distribution. It was possible to increase the overall wall thickness as shown in graph xyz. By measuring the LightBase bottle and using 16 wall measurement points positioned axially on top of each other, it was possible to determine that the material that was taken from the base area during the blowing process distributed itself over the entire bottle. This enables this material to be used to increase bottle strength – or this material can also be saved. This led to an improved top load value.

The test for the examination of the maximum burst pressure also showed improved results. Up until now, the bottles would crack – as far as could be expected – in the sprue area. This occurred at an average pressure of approximately 10 to 11 bar. The crystallisation of material build-ups in the base area that was previously mentioned is accountable for this. The LightBase bottles reached pressures of 11.5 to 12.5 bar before cracking, but the sprue was no longer the weakest point: the LightBase bottles cracked in the body section.