PETpla.net Insider 07+08 / 2013

PREFORM PRODUCTION 21 PET planet insider Vol. 14 No. 07+08/13 www.petpla.net contents, base shape, etc. (see Sec- tions 1.1 and 1.2 of the book). The output of the preform design is usually a 2D drawing that includes all required dimensions and designations accord- ing to international standards. This ideal preform geometry is then the benchmark for the real pre- form. Here, two fundamentally differ- ent approaches can be taken. Standard preform In most cases, the ideal preform is used as a reference to select a standard preform from the cata- logues of PET converters. Although this will always involve a certain degree of give-and-take, the techni- cal advice from the manufacturers or external consultants can help reduce the inevitable compromise to a minimum. Purpose-made preform Depending on the bottle design and its performance requirements, it may be necessary to create a special preform with the ideal geometry for the bottle to be produced. This may, for instance, be considered if particularly a lightweight container is required or if the container is to be produced in large numbers for a very long period such that the investment in injection moulds permitting an optimum preform geometry will be economically viable. In Chapter 2, this will be discussed in greater detail. At this stage, the real preform geometry for the subse- quent design steps has been defined. The bottle geometry and the preform geometry, and in particular the preform weight, now permit a direct calculation of the average wall thickness. Bottle design for a dependable process Making the bottle design totally suitable for the process requires its adaptation to possible constraints by the downstream equipment, which may even result in a deviation from the initial ideal shape. Aspects to be considered and clarified include: The transport of the bottle downstream of the blow moulding machine may require special design features. If an air conveyor system is used, a certain neck height below the neck ring may have to be provided. Please order your copy at the PETplanet insider book shop: https://www.petpla.net/books Bottles, Preforms and Closures A Design Guide for PET Packaging Second Edition by Ottmar Brandau 115,00 € 180 pages © Copyright Elsevier 2012 The contents as well as the type of filler may have an influence on the design of the shoulder geometry and in particular on the shoulder profile and the diameter in the transition area between the neck and the shoulder. For example, if a spreader or rotating filler head is used, it must be ensured that the flow of the contents is not interrupted during filling and that no excessive foaming occurs. After filling, the bottles are trans- ported on conveyor belts. This requires an examination of the behaviour in bot- tle-to bottle contact. It must be ensured that the bottles do not tip over if jams occur. Also the “bouquet effect,” which may be produced by strongly club- shaped bottles, should be avoided. It should also be remembered that filled bottles should have as few friction points as possible. Ideally, just one such point or line of contact (contact ring) is specifically arranged above and below the labelling zone. When roller conveyors are used, the feet of petaloid bases must be designed such that the bottles do not become stuck between the roll- ers, preventing rotation. Unsuitably designed petaloid bases will also pro- mote tipping over of the bottle when negotiating curves. The feet should not be too narrow or sharply angled. In this context, the tipping angle of the filled bottle as a function of base geometry and conveyor speed must be determined and optimised by modi- fying the bottle geometry to ensure that the bottles do not tip over during transport. The tipping angle should not fall below the minimum values indicated below for the stated base geometries and conveyor speeds. The design of the bottle geometry should also ensure that the required filling level for the volume is reached. In particular for aseptically filled contents, this filling level should be as high as possible to minimise the remaining headspace. It may be zero for hot-filled bottles. For the labelling zone, it is impor- tant that the bottle is designed such that major variations in diameter are avoided. This is particularly impor- tant for wraparound labels, which in many cases are no longer glued in an overlapping fashion but with a butt joint. In particular, for bottles filled with carbonated products, which generate an internal pressure, certain minimum wall thicknesses must be observed, and/or the bottle has to have a high orientation (see Chapter 2). These are just some of the aspects that must be considered when designing the bottle for a reli- able production and filling process. Depending on the contents and other details of the respective line, a large number of other aspects will have to be taken into account. Further input on the wall thick- ness distribution will be available to the bottle designer from the expert knowledge of the process engineers. Such knowledge can either be based on experience or, ideally, can be retrieved from the databases of expert systems during the CAD phase. *This article was published in Bottles, Preforms and Closures, Ottmar Brandau, Chapter 1.4., Copyright Elsevier 2012