短繊維強化ナイロン射出成形品のウェルドライン強度に関する研究
Study on the Weld Strength of Fiber Reinforced Polyamide Injection Moldings
泊 清隆・_田泰以・前川善一郎
Tomari, Kiyotaka / Hamada, Hiroyuki / Maekawa, Zenichiro
Weld lines markedly reduce the strength of FRTP injection moldings, which are often used for structural parts. The effects of weld lines on strength are closely related to molding conditions such as resin temperature, injection rate, injection pressure, etc. They are also related to fiber orientation in FRTP, which results in difficulties in the proper design of moldings. This study aims to clarify the effects of weld lines on the strength of short fiber reinforced polyamide. Dumbbell type tensile specimens with a weld line were molded under several molding conditions. Furthermore, SEM observations of the fracture surface were carried out and the distributions of fiber orientation were measured. The results were obtained as follows.(1) A "back flow" occurred in the weld region when using the multi-cavity mold and led to the re-orientation of fibers in the flow direction.(2) The specimens did not break at the weld lines on the surface because of the back flow. (3) Thedistribution of fiber orientation on the fracture surface were influenced by molding conditions. The number of fibers oriented in the flow direction increased and the distribution became more uniform by increasing holding pressure.(4) The weld strength was improved by the back flow up to a maximum of about 140% with efficient holding times.
Key words: Weldline/ FRTP / Injection molding / Polyamide / Fiber orientation / Tensile strength