PETpla.net Insider 09 / 2017

BOTTLE MAKING 30 PET planet Insider Vol. 18 No. 09/17 www.petpla.net Stretch Blow Molding, part 6 Reheat Stretch Blow Moulding Machines by Ottmar Brandau Ottmar Brandau has newly revised his book “Stretch Blow Molding”, first published by hbmedia/ PETplanet Publisher, and now re-issued in a second edition under the Elsevier imprint. PETplanet Insider is publishing extracts from successive chapters in a series of articles. Figure 3.5 Linear continuous motion machines increased in popularity, as they combine excellent quality with a lower price tag compared to rotary machines. Diagram courtesy of Siapi. 3.4 Linear continuous motion machines To improve the performance and quality of low-to medium-output machines, companies have developed new type of machine, borrowing some proven concepts from the rotary line of blow-moulding machines (Fig. 3.5). This starts with the in-feed section. On these machines, only a single rail is mounted and preforms flow continu- ously into a star wheel (Fig. 3.6). They are right side up at this point and will stay this way throughout their journey through the machine. Figure 3.6 The in-feed section of these linear continuous motion machines is very similar to rotary machines. Picture courtesy of Sipa. As the star wheel turns, mandrels move down into the neck opening of the preforms and pick them up via a spring-loaded mechanism. Spac- ing of the mandrels is around 38mm or 50mm, allowing necks with maxi- mum transfer rings of 36.5mm and 48.5mm diameter, respectively. There are a few machines for preforms with wider necks that I will describe later. Close preform spacing improves oven efficiency and the continuous motion guarantees even preform heat. Once preforms leave the oven section, they are grouped in the appropriate number of cavities (up to 12 at the time of writing) and shuttled into the blow moulds where they are stretched and blown together (Fig. 3.7). While they travel into the mould area, the pitch is increased to the cavity pitch by a pitch-changing device, which is proprietary to each manufacturer. Each cavity has its own set of blow