GENERATION OF VOIDS IN FIBER-REINFORCED THERMOPLASTIC INJECTION MOLDINGS

Power-Take-Off covers (PTO) for a truck were injection moulded from va rious grades of glass fibre reinforced polyamide 6,6. Voids were gener ally not visible at areas of uniform cross-section, but were primarily located at areas of diverging flow. No voids were found for unfilled polyamide 6,6, while voids of varying size were produced with the fibr e filled materials. Void size was affected by the average fibre length , where a high number average fibre length led to the generation of a large void size. Increasing fibre content from 50 to 60% w/w caused a reduction in average fibre length by up to 20%, which was reflected by a 20% reduction in the average void size. An inverse relationship exi sted between void size and the number of voids produced. Voiding was a ttributed to the phenomenon of foaming (material opening out by fibre spring-up) which was accentuated with high aspect ratio fibres (1/d > 20).