BOTTLE MAKING PETplanet Insider Vol. 24 No. 05/23 www.petpla.net 25 Stretch Blow Molding, part 15 Injection 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 third edition under the Elsevier Imprint. PETplanet Insider is publishing extracts from successive chapters in a serie of articles. As the name implies this process involves injection of preforms as well as blowing of bottles in the same machine. Preforms are not cooled down completely after injection; instead residual heat inside the preform allows blowing without reheating. Obviously, this makes it inherently more complex than the two-stage process. Processors must know both parts of the process and, as we will see, there is also some interaction present between injection and blow adding to the overall complexity. Machines of this type are commonly (but by no means exclusively) used in the cosmetics, personal care, and household markets. They are hardly used in the water and carbonated soft drinks (CSD) market as their outputs are limited. There are actually two different types of machines that can be summarised under injection stretch blow moulding (ISBM): Indexing with three or four stations where the preform stays in the neck insert, going through injection (conditioning with four-station machines), blow, and ejection. Various designs where the preform is completely removed from the injection tool, put on mandrels, heatconditioned, and then blown. This process may be called integrated two-stretch blow moulding (ITSBM) (Fig. 8.1) Fig. 8.1 8.1 Four-Station machines Preforms and bottles are oriented vertically and in rows, typically one row only but there are also machines with two rows of up to 16 cavities making 32 cavities the current maximum number. They are spaced not with respect to the preform dimension but to the maximum bottle dimension as the pitch between the cavities does not change within the machine. A 90mm wide or round bottle requires spacing of about 100mm in both preform and blow tooling to allow some metal between the blow cavities. A particular machine can produce a 300ml bottle in 16 cavities or a 15 l bottle in single cavity with various bottle sizes and respective cavitation in between (Fig. 8.2). Fig. 8.2 In order to engage the injection tooling vertically, the following two movements are required: Either the cavities move down and the cores move up with the neck inserts staying in place before rotating. This requires the cavity block with the hot runner underneath it to disengage from the extruder that is moved back. One issue with this arrangement is that air or pollutants can enter the melt stream when extruder and hot runner are not connected. Or both cavities and neck inserts move up leaving the cavities in place. This is a superior solution as the aforementioned problem is not an issue (Fig. 8.3). Fig. 8.3 Amachine with four stations rotates 90 degrees moving preforms and bottles around every cycle, whereas a threestation machine rotates 120 degrees. Orientation of each station is vertical allowing a very compact footprint. Other advantages of this system besides the ability to make both preforms and bottles in one machine are as follows: Flexibility to make bottles of different shapes with good wall distribution. Production of blemish-free bottles. Since preforms are not touched, bottles have no marks when they leave the machine. Important feature for cosmetic bottles. Zero contamination between preform and bottle stage. This may decrease sterilisation measures in the filling plant. A neck support ring is not necessary, also interesting for cosmetic bottles. Thermal efficiency; preforms are cooled down only to blowing temperature of about 100°C (212°F), saving energy needed to cool them to about 60°C (140°F) necessary for twostage moulding. Automatic neck orientation; some caps require the neck to start in a Please order your copy at: info@petpla.net Stretch Blow Molding Third Edition by Ottmar Brandau € 130,00 374 pages © Copyright Elsevier 2017, 2012
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