MOULD MAKING PETplanet Insider Vol. 24 No. 12/23 www.petpla.net 28 From the idea to cooperation on material savings Let’s move to lose weight 3% less PET per preform, less energy for reheating, less shear and lower injection pressure: movable cores in preform moulds bring many benefits. Mould specialist MHT Mold & Hotrunner Technology AG is cooperating with GR8 and is using the Active Flow Molding technology to produce preforms with thinner bases. Have you ever made the effort to open a bottle with an extremely short thread? Then you will know that the possibilities for saving material in this area are practically exhausted. But there is still potential in the preform bases, which are often thicker than they need to be for the stability of the bottle and use more PET material than necessary. Active Flow Moulding (AFM) offers the possibility of reducing the wall thickness in the first moulding phase by using movable cores in the mould. Mould manufacturer MHT, based in Hochheim, Germany, and R&D company GR8 from Arundel, UK, are working together to bring this technology to market. They have produced several different preform designs and supplied them to customers for blow moulding tests. There have already been successful tests with Pepsi in Geneva and Moscow, but further tests in Russia have been prevented for the time being due to the war with Ukraine. AFM technology is particularly interesting for large beverage brands with their own PET production, as they can benefit from the material savings directly in the preforming process. If the weight of the preforms in a mould with 96 cavities can be reduced from 41 to 40.5 g and 1,000,000 cycles are carried out, that is 48 t of PET! Normally, a weight reduction of up to 3% is possible. Comparison: conventional round base (left) and Antiflex base (right) The main feature of AFM is that the cores are movable, which results in a similar mechanism to injection compression moulding. The whole thing works as follows: Firstly, the molten plastic pushes the core back during the injection process and the available sprue opening increases. The plastic flows in more easily, the flow path ratio is more favourable, the injection pressure drops (by around 9% in current tests) and the shear is reduced. Once the preform is almost completely filled, the core moves forward (up to 6mm) through the still liquid plastic melt into the end position. Excess material at the base is pressed into the wall and the thread is completely filled to the top. The thin base is achieved during the primary moulding process and therefore bears little stress. Another advantage compared to classically moulded preforms: a high wall thickness at the base can sometimes have a detrimental effect on the subsequent blow moulding process, especially if the blow moulding machines run at high speeds. The output per blow mould is therefore significantly higher for preforms produced using AFM technology. In addition, less energy is required to reheat the preform. The core contour has a cone at the tip, the Antiflex base. This prevents so-called core displacement, which can lead to problems, particularly with thin-walled applications. 1. Valve stem open during injection (the jagged contour lines in the core represent the cooling tube) 6. Core in its end position: the base is thin, the preform, including thread, is completely filled 2. The molten plastic pushes the core backwards, resulting in a larger opening, reducing injection pressure. 7. Valve stem is closed and the preform removed 4. The preform is almost filled. 3. Injection takes place 5. The core travels forwards. Active flow moulding 40.5 g Classic moulding 41.0 g
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