Long slats with outstanding surface finish and optimum dimensional stability
Key Plastics Löhne supplies complete assemblies to the automotive industry. For the VW Touran, the company developed a new air vent with longer slats than in any other vehicle type. The Hamburg-based plastics distributor K.D. Feddersen provided support in the product selection.
The material for the new slats had to have a good surface finish yet still possess a high degree of stiffness, while also offering good value for money. For all other models, Key Plastics already used a 50% glass fibre reinforced PA 6 compound with reduced moisture absorption from AKRO-PLASTIC. In this case, however, the stiffness was inadequate. Christoph Gerling, Business Development Manager at K.D. Feddersen consequently recommended increasing the level of reinforcement to 60 %, and the very first test using AKROMID® B3 GF 60 4 RM-M satisfied the customer's requirements.
AKROMID® RM-M (mechanical types) is suitable as a design material for components subject to high mechanical stress. This product range offers only reinforced compounds with varying glass fibre content in three designs: standard, surface-modified ("9") and with increased chemical resistance ("4"). The material is a blend of polyamide and PBT, combining the favourable properties of both polymers: the high degree of stiffness and low water absorption of PBT and the large processing window and excellent surface finish of the polyamide. Precisely these properties were of key importance for the implementation of the new design with significantly longer slats. The reduced moisture absorption (1 %) is on par with partially aromatic blends and thus enables a design with low tolerances. A further advantage of the material is that the tensile modulus is only slightly reduced and the slat therefore exhibits a consistently high degree of stiffness under a wide range of climatic conditions (see Table 1), thereby enhancing the value of the design.
As a number of injection moulders have already discovered, an excellent surface finish with a high glass fibre content of 60 % is not easy to realise. Quite often the glass fibres are clearly identifiable on the surface. In this compound, the glass fibres are optimally bonded to the matrix and are scarcely perceptible on the surface, thanks to the blend technology. The article and mould design also play an important role in ensuring that the ensuing component has a good surface finish despite the high degree of reinforcement.
The material meets Volkswagen's requirement of producing the component without additional paintwork and at a mould temperature below 100° C. The blend is thus a cost-effective alternative to partially aromatic polyamides.