As a rule

K belin Formenbau GmbH, in D-79 56 Eichstetten near Freiburg/Germany are manufacturers of high-precision injection moulds, specialising in clean room applications, in particular for medical engineering and pharmaceutical packagings. The company also has the necessary expertise in tool and mould technology when it comes to the demanding PEEK base material, expertise which is of crucial importance for process stability.

The shot weight of these PEEK applications is often just a few grams or well below one gram. As a rule, parts such as these are made on injection moulding machines with clamping forces between 150 kN and 200 kN. Seen in proportion to the very small cavities, the moulds must therefore be made in unnecessarily large dimensions, with cold runners to be used. A higher shot weight is needed to ensure that the maximum allowed dwell time of the melt in the relatively large screw barrels is not exceeded. These drawbacks account for a high material throughput. Also, the high energy consumption of over-dimensioned machines and the energy required to control the temperature of the relatively large moulds is unsatisfactory and calls for new solutions.

The perfect alternative is the fully electric Micro Moulder 12/90 miniature injection moulding machine made by the British MTT and marketed by Hewaco GmbH in 7918 Waldkirch/Germany. This machine with its mould clamping force of 90 kN has been developed specially for thermoplastic parts with shot weights between 0.02 g and 12 g. The power-assisted screw has excellent mixing properties and an extremely precise plastification.

Matching this fully electric injection mould, K belin Formenbau have now developed a special metering block with integrated hot runner nozzle. The hot runner nozzle specially designed for processing PEEK has been supplied by Günther of Frankenberg/Germany. A metering block was necessary because the injection moulding tool with its outside dimensions of approx. 100 by 120 mm did not offer enough installation space for a hot runner nozzle.

The metering block and the injection moulding tool also made by K belin Formenbau are optimised in terms of thermal insulation, and the contact surface between mould and machine has been minimised to ensure that as little heat as possible is transferred to the machine. In spite of this insulation technique, the moving platens are fitted with additional temperature control elements.

The first requirement for a stable process when working with PEEK is an optimised thermal balance inside the mould. This, in turn, requires high melt temperatures of as much as 400°C and mould temperatures of up to 200°C. Connector plugs for surgical instruments with a shot weight of 2.8 grams are made with this mould.

After a successful test run lasting several weeks at the Berger Spritzgie - Technikum, D-79 41 Kenzingen, a sister company of K belin Formenbau GmbH, the unit was presented in October at the Fakuma in Friedrichshafen where it met with great interest by the expert public. This extraordinarily energy-efficient and accurate system offers the ideal features for PEEK processing - an opinion shared by the expert visitors.

The attractiveness of this solution, says K belin Formenbau GmbH's managing director Joachim K belin, is that it is significantly more economical than the conventional methods due to its enhanced reproducibility, better process stability and in spite of its highly sophisticated engineering features.

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