微小切削法による射出成形品のウエルドラインおよびスキン・コア構造の評価
A Micro-cutting Test for Checking Weld-line and Skin-core Structure of Injection Molded Materials
成澤郁夫・栗山 卓・木嶋芳雄
Narisawa, Ikuo / kuriyama, Takashi / Kishima, Yoshio
The formation of weld-line or skin-core structure in injection molded materials reduces their strength. A new technique which is called "micro-cutting test" has been performed on injection molded specimens of crystalline polymers. This method can give quantitative information on shear yield strength in the region near weld-line or in the subsurface layer so that inhomogenous mechanical properties of the weld-line and the skin-core structure can be evaluated. The following results have been obtained :
(1) There is a significant difference in shear yield strength between the flow and transverse directions in a liquid crystalline polymer (LCP) specimen. This difference attained a minimum value at the weld-line.
(2) The shear yield strength obtained from cutting along the weld-interface decreased with approach to the weld-line. The region which was affected by the presence of the weld-line was within 6-8 mm from the center of the weld line.
(3) The fracture toughness of the LCP weld specimen was about 25% of that of the non-weld material. The reduction of fracture toughness has also been observed for the other crystalline polymers.
(4) The skin-core structure of HDPE consisted of three different layers. The shear yield strength of the skin-layer increased with increasing mold temperature.
Key words: Weld-line / Skin-core structure / Micro-cutting / Shear yield strength / Fracture toughness