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Hot runner technology catapults productivity

Manufacturers of hot runner systems set great store by ease of assembly and energy efficiency. New product ranges meet these aims well. It is true that any technological change comes at a price, yet innovative sprue systems are catapulting productivity forwards and are relatively trouble-free to service. That is exactly what injection moulding specialists need for moulded parts in medical equipment.
At first sight, it looks like witchcraft. The machine delivers its shot and soon after that, eight components fall into the catch tray. There are two housings, each with three inner rings, for a plastic needle dispenser. The machine is a sprue system with hot runner technology and the application is a customer-specific design with an externally heated 7-fold manifold system and several nozzles fitted onto it. Synventive developers are particularly proud of the three different nozzle size formats which they have housed in the manifold, with the biggest nozzle feeding two mould nests with liquid plastic.
Injection moulding tools for medical technology are in common use and the range of applications for hot runner technology is very wide, ranging from sealing caps, insulin pens to infusion pumps or needle holders. Manufacturers are producing innovations at a furious rate in response to the huge demand for plastic moulded parts for medical technology applications. Engineers developing sprue systems are fully occupied with work on many fronts, with the most important being reducing energy consumption during the heating stage, improving gate concepts for component optimisation and increasing productivity by shortening throughput times.

Synventive’s main current preoccupations are installation times during tooling and overhauling its hot runner product line for small and medium shot weights which meet the requirement profiles of plastic parts for medical technology appllications. This has resulted in systems known as ‘plug and play systems’ which, according the manufacturer’s information, cut the time needed for installation and adjustment work for hot runner systems to a minimum.

The crucial developmental twist is fully assembled hot runner systems for specific applications and immediate installation. The nozzles are already screwed in place and, depending on the component specification, have different geometries such as an open gate or torpedo or needle valve gate. In addition to this, the system is fully cabled, including even a plug and socket for connection to the mains. Customers needing a needle valve system also have the option of fully assembled pneumatic or hydraulic actuation cylinders.
The recently developed and ingenious concept from Synventive wins hands down, not only with its fully assembled hot runner system but also with the design of its heating and temperature control system. Manifolds and nozzles form a single sealed and leak-proof unit within the tool. Low tool contact with compatible heating design ensures better temperature control all the way to the gate. Whereas in conventional machines, heat is exchanged between the injection tool and the sprue unit, there is now hardly any contact between the tool and manifold. This results in an improved temperature profile with only very slight temperature differences in the hot runner and heat provision tailored to the application. This cuts the unnecessary costs caused by the provision of excess heat and increases process reliability.

The switch to fully assembled hot runner systems and the associated assembly advantages are certainly seductive prospects, but it is not a simple matter to accomplish this. The tool must be equipped with the appropriate acceptance devices for the sprue unit and, equally important, the hot runners must be designed to match the mould exactly. Numerous components play their parts in the configuration of the whole system and manufacturers are hinting at various solutions.

One solution is a particularly slim, low-diameter nozzle construction, which Günther, for example, is currently addressing with its Blue Flow hot runner technology. According to the manufacturer’s information, a new type of thick film heating gives users great scope for system design. Particularly small distances between cavities (5.5 mm) is the advantage offered by Heitec’s flat line series, notable for its flat design and also its thermal flexibility, which is greater than other production series so far. The UltraSync family from Husky Injection Molding Systems has grown by three new needle valve nozzles which attract attention because of the precise control they have of the drive equipment. The technology makes for a high degree of reproducibility precision for each shot and thereby renders the system especially suitable for medical technology applications. Synventive, too, has updated its screwed in manifold nozzles with its 06E series. The 06E plug’n’play manifold nozzle, has a six-millimetre runner diameter and is designed for shot weights of up to 100 g per nozzle. As these nozzles of differing lengths are screwed into the manifold, this produces a leak-free system, dispensing with the need to match parts up to each other precisely. The nozzles are heated externally and are supplied in lengths ranging between 60 and 200 mm.

Nozzle geometry flexibility included
A further advantage of plug’n’play functions is the servicing. The nozzle heating units are easy to exchange and have an integrated, easily demountable thermosensor. The clamping plate is designed such that it can be removed complete with the valve needle. If only the valve pin is to be removed, the clamping plate should be left in the tool and the needle removed simply by hand. Additional modules, such as online flow pressure control, can be easily screwed on or off for particular needle valve nozzles. Hot runner systems with plug’n’play functions come with nozzle geometry flexibility. There are compact nozzle series for shot weights of up to 10 g or 250 g, which are prepared as ready-to-use modules for rapid use. The manufacturer also supplies other pneumatic actuation cylinders with position enquiry and electrically driven cylinders with plug’n’play design.
Andreas Beuthner

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German Summary
Montagefreundlichkeit und Energieeffizenz heißen die Zielgrößen der Heißkanalhersteller und neue Produktreihen kommen diesen Vorgaben näher. Zwar hat jeder Technikwechsel seinen Preis, dafür katapultieren innovative Angießsysteme die Produktivität nach vorn und sorgen für weniger Ärger bei der Wartung. Das genau brauchen die Spritzgußspezialisten für medizinische Formbauteile. Der deutschsprachige Beitrag ist nachzulesen auf www.meditec-international.com/medi0611hot