Plastics — Injection moulding of test specimens of thermoplastic materials — Part 5: Preparation of standard specimens for investigating anisotropy
ISO 294-5:2011 specifies a two-cavity mould (designated the type F ISO mould) for the injection moulding of 80 mm x 90 mm plates with a preferred thickness of 2 mm for single-point data acquisition because 2 mm has been found to provide the maximum anisotropic properties, with only a slight sensitivity to the rate of injection. For the design of plastic parts, this will provide upper and lower bounds for the tensile properties. Matching the plate thickness to a given part thickness is not a suitable criterion because of the effect of mould filling rate and part geometry on anisotropy. Suitable test specimens [ISO 527‑2 type 1BA tensile test specimens or type 1 (80 mm x 10 mm) bars] are then machined or die-cut from the plates and used to obtain information on the anisotropy of thermoplastic parts.
Investigation of the anisotropy of materials is a special procedure intended to provide guidance in the design of mouldings for end-use applications and is not intended as a quality control tool.
In the injection moulding of thermoplastic materials, the flow of molten polymer may influence the orientation of fillers such as fibreglass or the orientation of polymer chains. This can result in anisotropic behaviour. The knowledge of anisotropic behaviour is valuable in designing plastic parts.
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