TRADE SHOW REVIEW PETplanet Insider Vol. 24 No. 06/23 www.petpla.net 28 tion, engineers can effectively design a network of hot runner distribution channels to optimise flow characteristics. The ISO technology makes use of a state-of-the-art diffusion bonding process. Put simply, diffusion bonding is a process where the atoms of separate surfaces intersperse to become one, resulting in the formation of a single inseparable object. A distinctive characteristic of diffusion bonding is that it does not use any form of brazing, soldering, or welding. There are no pastes, no flux or bonding elements used at all. Adjoining plates are simply in direct contact with each other during the entire process. The next phase involves applying a high pressure and heat to the adjoining plates. This is maintained for a defined period of time, depending upon the plate size used. During this time a molecular exchange takes place across the plates, and just as gases and liquids diffuse, solids do as well under the right conditions. Once the process is completed the result is the creation of a single piece manifold which is robust, accurate and has no risk of separation. Rick explained that they do this because traditional manifolds are manufactured using gun drilled linear channels that interconnect within a steel block. Lines are drilled from the sides that intersect each other, then plugged, to form a series of melt channels directed to each drop. By contrast, diffusion bonding allows the entire channel arrangement to be simplified without the complications of using end plugs so there is no risk of leaks. The melt channels can be contoured and shaped to provide an optimised flow path to each cavity. As an example, Rick showed a 96 cavity ISO hot runner layout as manufactured by diffusion bonding. The process permits smooth level transitions and eliminates any sharp corners and edges with no dead spots. This helps to enhance flow characteristics and minimise pressure drop throughout the entire channel layout. It is a characteristic that benefits PET and other heat sensitive materials. Rick asked: “How does this impact performance and part quality?” In a back-to-back comparison of a short shot test with a conventional hot runner and the ISO hot runner from a 96 cavity 28 g preform mould, StackTeck stopped the injection when the preforms were filled to 50 per cent. The resulting fill pattern showed the weight distribution of the plastic injected into each cavity, helping to highlight imbalances in the hot runner. In this example the weight variation was reduced from 46 per cent to 19 per cent when comparing conventional to ISO. The improved uniformity with ISO translates into a larger processing window for moulding, minimising the need to adjust and tweak parameters for the outlier preforms that may be on the edge of acceptable quality. This makes setting up the process conditions easier and quicker such as when speeding up cycle times or when starting up a new mould. There is less need to make adjustments to fix quality problems on the outlier preforms. As a downstream benefit the customer in this example reported fewer bottle-to-bottle quality variations at the blow moulder. Rick also presented a back-toback comparison showing a reduction in pressure drop using the ISO hot runner. In the same 96 cavity 28 g preform mould two injection rates were set up with the conventional hot runner at 10 and 13 g per second per cavity, resulting in a 680 and 780 bar peak injection pressure respectively. The ISO hot runner achieved a 16.9 g per second per cavity injection rate yet still registered a slightly lower peak pressure than the slowest injection rate using the conventional hot runner. The preforms made in each case were checked under a polarised light to confirm that no changes in stress pattern were visible. The end result was a significant injection time reduction which reduced the overall cycle. These two characteristics; improved balance and reduced pressure drop enable technologies such as over-moulding and thin wall preforms to be accurately and consistently moulded. Over-moulded preforms tend to have very thin layers with high L/T ratios and this requires both a tight cavity to cavity balance and a low pressure drop throughout the hot runner to ensure the layers are accurately and consistently formed with no risk of short shooting the very thin layers. This also benefits monolayer preforms, most notably with flat water applications especially as they become thinner and thinner due to light weighting programs. In another example, a 144 cavity application with a conventional hot runner was compared with an ISO hot runner. The comparison revealed the peak injection pressure was reduced by 19 per cent, the preform weight variation halved, and the average acetaldehyde level reduced by 24 per cent. Finally, Rick introduced KoolTrack, another way to take advantage of the diffusion bonding technology which also helps to improve product quality and cycle time but now on the cold half side. The KoolTrack can simply be described as conformal cooling similar to how ISO diffusion bonding changes the way hot runners are designed and manufactured. KoolTrack is currently being successfully used in a variety of PET and non-PET applications. We thank all speakers and participants and point out that a video and the presentations can be found on our homepage! Sponsored by https://petpla.net/2023/03/10/petinar-2023-opening-debate/
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