From the idea to the bottle

They’re required to look great, feel good, to be light and nonetheless stable, and also possess a high recognition value into the bargain. We’re talking about PET beverage bottles. A successful design for a beer, water or soft-drinks bottle is always preceded by a process of exciting complexity.

The challenge involved here is to create a product that functions properly and looks appealing. The creative part and the technical part have to complement each other - form and function have to match. The container shapes have to satisfy the requirements of a high-speed line in all respects, a stipulation that is met by the team at Krones.

Because of Krones’ principle of always thinking in terms of holistics, the handling qualities of a container in a complete bottling and packaging line must be covered, and above and beyond this all the way to the consumer’s refrigerator. The entire process demands a lot of experience and intuitive know-how from everyone involved.

From a hand-drawn sketch to the first model

The product development work carried out at Krones is tasked with combining the client’s ideas with the technically feasible possibilities in order to create a viable product. For this purpose, the container design team is able to formulate proposals that already meet the technical requirements involved and also incorporate the structural elements desired, like a recessed grip, or visual upgrading like waves, structures or engravings. There are various elements available as modules for designing a new PET container, like the base, the neck finish and the sidewalls. Starting with an initial hand-drawn sketch, the bottle progressively takes shape until it becomes an actual product amenable to industrial manufacture. From this hand-drawn sketch, the next step is to produce a 2D drawing, in which the specified volumes and fill levels have already been incorporated. Krones is now able to provide 3D models in a PDF document, which can be turned, shifted and magnified so that the thinking behind the container design can be more readily explained. If the 2D and 3D drawings of the bottle match the client’s ideas, they will be converted into a binding template for designing the bottle mould. If so desired, 3D acrylic-glass or plastic models of the subsequent bottle can be produced as demonstration samples.

One vital step after the bottle has been designed is to firm up the dimensioning of the PET preform. In order to find out whether the preform supplied by the client actually fits the mould, a temperature profile is applied to the preform concerned. In the case of conventional bottle designs, standard preforms can be used. For a very offbeat design, it may be necessary to consider a special PET preform that is optimally matched to the bottle design involved. Once the preform and the bottle geometry have been finalised, a sample or experimental mould is produced for the laboratory’s Contiform blow-moulding machine, on which the first test bottles are blow moulded, and then measured by the Plastics Technology Laboratory and rigorously tested.

The sample bottles are subjected to a meticulous program of testing. The Krones laboratory is equipped with state-of-the-art metrological instruments, and is thus able to carry out bottle sampling routines against all the customary specifications. For example, the stackability is examined by testing the behaviour under top load, and the containers’ geometry and the weight of the individual sections are measured. The container is subjected to a steadily rising pressure stress (fill ramp), while the brimful and filling-point volume, the minimum pressure the bottle has to withstand, the thermal stability and the wall thickness distribution are also verified. The test results are now incorporated in a further process of optimisation. After the test bottles have been approved, production is commenced on the series moulds for the Contiform blow-moulding machine.

Producing the moulds

Mould design work begins with a dimensioned drawing of the container concerned. The blow-moulding process triggers a re-shrinking effect, which has to be factored into these dimensions. Using this design, the individual parts are then built up as a 3D model, a negative of the mould shell or the base produced, and the requisite modifications incorporated like vent boreholes or length adjustment.

The production operation for the moulds uses program-controlled high-speed, fully automated milling machines that image the desired bottle contour in the mould with maximised accuracy. The aluminium shells are milled in a tolerance range of plus/minus one 500th of a millimetre. By way of comparison: a human hair measures about two-tenths of a millimetre in diameter. Final testing and inspection puts the individual parts together to form a complete mould, so as to provide the requisite quality assurance.

Ready for the supermarket

The series moulds are meticulously laser tested before bottles are made under realistic conditions on the client’s own production machine prior to delivery. Only when all the stipulations involved have been met can an approval be issued. Only then is the new container ready for the bottling line and the supermarket. Mission accomplished.