Hot runnings

When injection moulding technology is integrated into complex, automated production cells, for example in the production of parts through the insert moulding process, a stable process is one of the key requirements. Valve gate technology is applied in many cases to increase reliability. This allows for production with short cycle times and perfect gate shape and to exclude from the outset potential causes for rejects, like tailing. Ease of maintenance is another important issue, as long downtimes for maintenance must be avoided.

Armin Kölz, sales manager Hot Runner Systems at Hasco Hasenclever in Lüdenscheid, Germany says that heat balancing was "an issue determined by many factors". In addition to constructive measures in the tool to avoid interferences, using alternative materials like titanium or ceramic for supports and sealing surfaces, but also cross sections and diverters of mass channels, and the location of heaters and thermal sensors play a key role in maintaining a constant heat balance in the entire hot runner system.

Controls should be highly accurate, provide monitoring functionality and also have a user friendly and intuitive interface. The processor must be capable of reliably controlling the ever more rapid and sensitive nozzle heaters in virtually all processing windows.

Clean room requirements particularly concern drives used in valve gate technologies. Electric drives are increasingly used beside well-known drives, like pneumatic and hydraulic drives. Servo motors in particular offer 100% clean room compatibility combined with maximum accuracy. But hydraulic systems that do not necessarily need to be opened for maintenance purposes also meet the requirements thanks to their special construction.

More productive, multi-cavity tools require modular, low-maintenance systems that can be integrated quickly and simply into the tool concept already in the construction stage. So-called modular or compact systems, where nozzles can be clustered in small cavity numbers, not only simplify production of the distributor block, but of the whole system, both from a technical and an economic perspective.

The trend within the trend is cooperation with the system supplier, who in this case not only provides the hot runner system, but also assembly right up to the electrical wiring and the complete "hot part".

Dr. Dominic Friederich, Managing Director of Roko Heißkanaltechnik Friederich GmbH, Pforzheim (Germany) and Xintech Hotrunner AG, Dübendorf (Switzerland) sums it up: "Current trends in hot runner technology reflect the latest developments in plastics processing". Material-wise, hot runner technology increasingly faces the challenge of providing reliable hot runner systems for high performance and high temperature polymers. On the other hand, the number of so-called "precision parts" and items with special surface finishes is still increasing.

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Both developments ask specific questions of hot runner technology, which manifests itself particularly in regard to heat balancing. Required are hot runner systems that ensure optimum heat management for both flowing and stationary plastic melt. Furthermore, it is increasingly important for hot runner manufacturers to not only provide the product itself, but also application-specific support.

In addition to the thermal insulation of the hot runner system, in particular of the hot runner distributor, heaters that ensure maximum efficiency through optimal heat transfer are also needed in order to increase energy efficiency. Apart from the use of highly thermo-conductive materials, this also requires optimum utilisation of the heat conducting surface.

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