Jetting and fibre degradation in injection moulding of glass-fibre reinforced polyamides

Injection-moulded glass fibre-reinforced polyamides with up to 50% by weight fibre content were examined for processing behaviour such as jetting and fibre degradation. Jetting was found to be a function of the ratio of the gate depth to mould-cavity depth, fibre length, fibre content and injection ram speed. Contrary to expectation, jetting occurred less frequently as the injection ram speed was increased. Major fibre degradation was experienced during the transport of the melt from the injection machine to the mould cavity. Further fibre degradation due to increases in injection back-pressure was comparatively small. Tensile strength was shown to be sensitive to variations in the fibre length distribution, whereas the elastic modulus remained unaffected.