PET-LINE - high performance manufacturing of lightweight preforms

Netstal already made an impact with its PET-LINE platform 2000 (2000 kN clamping force) at the K 2007 in Dusseldorf. With this highly cost-efficient complete system package, Netstal has ably covered the 24 to 60 cavity range and the system has firmly established itself on the market since its initial presentation three years ago. There has also been much development in the area of "lightweighting" over this period, with the trend moving towards increasingly lighter PET containers. K 2010 in Dusseldorf presents the ideal opportunity to demonstrate these developments, once again using a PET-LINE platform 2000 machine.

Todayʼs standard minimum wall thickness of up to 2 mm means that preforms have long since reached their limit; in other words, in relation to the sub-sequent hollow containers, preform geometry has reached the threshold. Any further reduction in preform weight will only be achievable through specific know-how and a high level of innovation.
A reduction in weight through further minimi-sation of the preform wall thickness is possible; however, undercutting the magic threshold of 2 mm necessarily depends on the flow path length ratio in the cavities. Only a precision-built system with reliable injection moulding process reproducibility and extremely sound mould construction could live up to such a challenge. Given that high-pressure injection can deform the cores (deflection) and result in poor wall thickness distribution on the preform "“ a situation that must be avoided at all costs "“, the most stringent requirements are placed on the system and in particular the mould.
Working in close cooperation with Swiss mould manufacturer Otto Hofstetter, Netstal is now in a position to offer systems that enable the 2 mm threshold to be undercut while nonetheless safeguarding all the requisite quality criteria.

Saving raw materials through weight reduction
In addition to wall thickness reduction, other weight reduction measures have also been achieved: for example, on the screw neck. In this area, the two mould manufacturers, Otto Hofstetter AG of Switzerland and MHT AG from Germany, have succeeded in utilising weight reduction potential without straying from clamping system standards or negatively influencing quality.

Although this involves only a few tenths of a gram per preform, in sum this represents a saving of tons of PET raw material every year.
Another area of the preform that is of interest when it comes to weight reduction is the base. Using special base geometries such as the Cappello Design, an infrared heater can heat the base more effectively, particularly in the case of older blow moulding machines. This ultimately improves the stretching of the base and largely avoids thick spots in the preform sprue area. This benefit not only improves the distribution of tension in what will later become the bottle base, effectively reducing the chance of stress corrosion cracking, but also leads to a reduction in weight.

K 2010 "“ lightweight preforms on the PET-LINE platform 2000
At this yearʼs K trade fair, Netstal-Maschinen AG will be unveiling a production system for manufacturing PET preforms in combination with a mould from Otto Hofstetter AG. In the shortest of cycle times, preforms will be manufactured on the PET-LINE platform 2000 that encompass the weight reduction approaches described in this article "“ preforms that will be increasingly required in the future. A further strength of the PET-LINE series will also be demonstrated, namely the efficient utilisation of energy. As with all PET-LINE systems, the minimum energy consumption of the PET-LINE platform 2000 is still unsurpassed on the world market.