PETpla.net Insider 11 / 2019

BOTTLE MAKING 29 PET planet Insider Vol. 20 No. 11/19 www.petpla.net BOTTLE MAKING 29 surface of the rod cools the area it touches on the preform. Light- weight water bottles, for example, need the base totally stretched and a large rod diameter may prevent that from happening. On the other side, making a rod too thin would lend it to easy bending. As a consequence, rods are made to keep the larger diameter in the upper portion to prevent bending but are reduced in diameter in the area of the preform (Fig. 5.5). Figure 5.5 For lightweight water bottles and some soft drinks bottles stretch rods are slimmed down to prevent a cooling effect on the pre- form bottom. In single-stage moulding, stretch rods often have tips screwed on at the end. These could be made from aluminium or nylon. On machines without conditioning, they can also be used to cool the bottom of the preform, just the opposite function they have in two-stage moulding. This is useful because the bottom of the preform is often the hottest part and may lead to thin bottoms. A large tip made from aluminium can be placed into the preform a few seconds before the mould is closing. This does not lead to a cycle time increase as the blow cycle is always faster than the injection cycle. The timer “delay mould close” is used to achieve this effect (Fig. 5.6). Figure 5.6 In single-stage moulding a large stretch rod tip can help in cooling the bottom of the preform down to increase wall thickness in the bottom of the bottle. Please order your copy at the PETplanet Insider book shop: www.petpla.net/book3 Stretch Blow Molding Third Edition by Ottmar Brandau € 130,00 374 pages © Copyright Elsevier 2017, 2012 For more information about BERICAP TetheredCaps: BERICAP TetheredCap Easy handling Safe application No change to • Neck finish • Capper • Filling line Meet us at BrauBeviale Hall 4 / 4-515