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Bottles,
Preforms, Closures PETplanet
Print Volume 4 a design guide for PET Packaging The
next book in our successful print series concentrates on design of PET beverage
containers. Up to today there is
very little material out that explains design criteria every package developer
should know. This book, slated for
publication in time for PETpoint 2005 will open the doors to some of the
industry’s best-kept secrets. Bottle In
the first part of the book the reader is guided from the first idea for a new
container to the finished set of moulds ready for installation to a mass
production machine. Since the blowing of a bottle is a complex subject and –
in addition – depending on many factors down the line like filling, labelling,
capping etc. the first step is to make the reader “think process not
product”. Before a container design is taken into CAD and finally machined
into aluminum or steel a lot of questions have to be answered. Among these are
questions as to what filling good is to be filled, such as water, still or
carbonized, fruit juice, CSD or beer. What life cycle has the bottle to expect,
is it a short runner, a seasonal product or a long term premium product. How is
the bottle transferred into the downstream equipment? What kind of filling line
is going to be used? And so on. The
next step is to determine the containers properties such as top load, CO2 retention
etc.. After finding the bottles target weight and wall thickness the design
features of the bottle can be translated into mouldable bottle shapes in a CAD
system. The 3D-design of the bottles can be evaluated as to its mechanical
properties via FE analysis. The
ideal and finally the real preform design is subject of the second chapter of
the book. The
first part of the book is continued with the choice of the general mould
concept, be it a compact mould, a shell mould or a special concept such as a
mould concept for heat resistant bottles. Finally the machine cutting data for
the machining of the cavity is generated and the first mould is being
manufactured. Test
runs on lab machines are followed by a comprehensive series of testing of the
first bottle samples. After optimizing the bottle design the complete series of
moulds can be made and the production can start. Preform Once
a bottle has been specified in shape and wall thickness, a proper preform has to
be designed or selected from the pool of available preforms. As many companies
had the misfortune to find out, not every preform with the right weight will
yield an acceptable container. Preform design has so far eluded purely
scientific development and trial and error are commonplace even in companies
with a large database of preform/bottle combinations. Our
section on preform design starts with a thorough review of all pertinent
material parameters. Production of PET, Intrinsic Viscosity and its effect on
the Natural Stretch Ratio of the resin, inflation behaviour, and injection of
preforms are all explained in an easy-to-understand format. Recognizing the
specific characteristics of PET is paramount to being able to use the
opportunities the material affords and avoid its pitfalls. This is especially
important for engineers with a background in injection or extrusion blow molding
because the stretch blow molding process of PET is so very different from these
industries. Next is
a discussion of the various approaches to stretch ratios. As there is no
standard in the industry we outline the different ways in which designers
calculate hoop, axial, and blow-up ratio and their specific advantages and
disadvantages. More than one method may lead to the desired outcome and the
reader can choose which one he/she finds most suitable. The
book then takes the reader through a generic design process where all stretch
ratios are factored in. A step-by-step guide with extensive drawings for each
explains the iterative process a preform designer has to undertake. Often
designers have to compromise between the optimal design and what is available or
practical. The drive to thinner preform walls in order to shorten injection
molding cycle times and save money
is one such factor. Lightweighing containers for overall material savings is
another. We
conclude the section with a discussion on the difference between preforms for
the single-stage and two-stage process. Preforms for these two processes are
very different and we explain why this is necessary and what particular
challenges preforms for the single-process pose. Caps Our
third section deals exclusively with closures. Often overlooked in the initial
stages of package development, proper neck and closure selection is crucial in
producing a functional and cost-effective PET package. We
start with a discussion of the various bottle necks that are tailored to the
bottle contents such as CSD or water. Modern necks are highly engineered bottle
parts that end-users need to understand as designers have achieved significant
material savings without jeopardizing closure functionality. Next is
a discussion of one-piece and two-piece closures, i.e. closures without and with
a liner respectively. This is organized by the different sealing methods, many
of them application-specific. However, for every application there are choices
to make and this section will enable the reader to make informed decisions.
Detailed drawings show the various one-piece seal designs and list their
advantages and disadvantages. Tamper-evident bands with their methods of
manufacturing and desired functionality are discussed next. The book is available now here
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