PETpla.net Insider 12 / 2016

CAPPING / CLOSURES 26 PET planet Insider Vol. 17 No. 12/16 www.petpla.net Different applications, neck finishes for various, last part (10) Closure for PET bottles & Resins PETplanet Insider is publishing extracts from successive chapters of Ottmar Brandau’s “Bottles, Preforms and Clo- sures,” which was published by hbmedia. A newly revised version is reissued under the Elsevier imprint. 4.9.4 Mould closing and opening times In terms of producing closures, the mould opening as well as clos- ing times are nonproductive, which means that during these times noth- ing is produced. However, in order to achieve maximum productivity through the shortest possible cycle time, at least the ejector movements should be timed to happen parallel to the mould opening as well as mould closing movements. 4.9.5 Ejection time and mould opening stroke Ejection time is mould as well as product related. The heavier the prod- uct design, the faster the caps drop to clear the horizontal bottom mould line. In a perfectly timed moulding process, the ejection movement starts early in the beginning of the mould opening stroke. The speed of the ejector for- ward movement has to be adjusted in order to achieve a stable part ejection, without any caps touching one of the mould parting lines. The ejector return position is supposed to be reached before the mould opening stroke end point has been reached. 4.9.6 Plasticising Preferably, plasticising starts with the beginning of cooling time and ends before mould closing is com- pleted. Due to today’s need for higher output and increased efficiency, the mould cavitation increases together with the number of machine cycles per minute. As a direct result of increased number of cavitations, the IM machine plasticising capacity has to become more powerful and be able to provide the required melted plastic resin in a much shorter time than years ago. As a matter of fact, today’s plasticising units limit further cycle time improve- ments in most of the cases. 4.9.7 Delay times Many a times machine setters optimise the moulding process by including delay times at the end of the cycle. These times have to be minimised, if not eliminated, in order to obtain the best possible process providing maximum output. 4.9.8 Air blast Depending on the closure design, air blast systems in the core area help to adjust the closures visual as well as physical properties. Better ejec- tion due to the air blast system will be a second improvement gained. To achieve good-quality products, the airflow as well as pressure has to be adjustable accordingly. Figure 4.40 Relevant injection para- meters on one screen. (Picture courtesy of Corvaglia Ltd). 4.10 Lightweighing of bottles and caps The 50% surge in resin prices in 2008 has further spurned a rush of developments to reduce the weight of bottles and caps. The results have been astonishing:  Water bottles of 500ml as low as 8.9g from a previous average of 16g  CSD bottles of 20 oz. as low as 21g from a previous average of 26g  Water bottle caps from 2.5g to less than 1g  These improvements came from several, unrelated areas.  Lighter neck designs for both water and CSD bottles  Different bottle designs allowing smaller wall thicknesses  Improved preform designs  Machines built specifically for small, lightweight containers