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spesso uno stampo che sulla carta dovrebbe essere bilanciato nella pratica non lo e' - conosci i motivi?

bilanciamento dello stampo

(MOULD Fill Balancing)

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I MATERIALI E LA TECNOLOGIA "

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In the rubber industry, it is difficult to balance the filling of multiple cavities during injection molding, which can result in problems such as excess flash, porosity issues, and non-cured characteristics. This problem becomes more challenging with complex cavity shapes and increasing numbers of cavities, as well as with higher molding temperatures and quicker cure cycles. Despite these challenges, modern injection molding tends to favor higher temperatures and more cavities for economic reasons. Mould designers have limited options for overcoming or minimizing cavity filling imbalance conditions. Balancing the fill sequence of multiple cavities in a rubber injection mould is desirable for efficient cure rates, optimized cure times, and consistent quality of all moulded parts. The reality is that most rubber injection mould do not provide a consistent uniform balanced fill sequence for all the cavities in the mould - even if the runner and cavity layout is geometrically balanced. Tipically, efforts are made during mould design and building to balance cavity layouts so as to encourage simultaneous cavity filling of the mould during injection. The problem is that the injection time must be long enough to completely fill all of the cavities, which is potentially longer than necessary due to some cavities filling entirely while other cavities are barely filled. A further problem is that the cavities that fill first may experience over packing while the last cavities to fill may experience under packing. Over packed cavities may exhibit excess flash at parting lines while under packed cavities may exhibit porosity issues and/or short fills. Over packed cavities may tend to be scorched in very thin cross sections while the very thin cross sections of under packed cavities may exhibit non-cured characteristics [1,2,3,4]. At present, it is established that the imbalance results from the rubber flow shear gradients developed in the runner system, which in turn lead to non-symmetrical temperature and viscosity distributions. This is influenced and complicated by the runner’s geometry, thermo-rheological material characteristics, and injection molding process parameters.The experiments indicated that the process parameters: injection rate, mold and melt temperature as well as the runners’ layout geometry significantly affect the filling imbalance.

Bibliography

[1] "Cavity Fill Balancing Technique for Rubber Injection Molding", Chapin, T. and Walworth, V., SAE Technical Paper 2015-01-0715, 2015

[2] "A Strategy for Problem Solving of Filling Imbalance in Geometrically Balanced Injection Molds", Krzysztof Wilczy ´nski, Polymers, Polymers 2020, 12, 805

[3] "Rubber Molding: A Practical Guide" di John A. Lindsay, Hanser Publications, 2005

[4] "Rubber Technology Handbook" di Werner Hofmann, Hanser Publications, 2001

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