射出成形品の「ひけ」発生位置に対する金型壁の冷却条件の影響
Influence of Cooling Conditions at the Cavity Walls on the Sink Location in Injection Molded Polymers
黒崎晏夫・龍腰健太郎・佐藤 勲
Kurosaki, Yasuo / Tatsukoshi, Kentaro / Satoh, Isao
This paper deals with an experimental study on the influence of cooling conditions at the cavity walls on the sink generation appearing in an injection molded l product. By employing a test mold which has two transparent windows, the processes of skin generation and solidification of the injection molded polymer were observed under various molding conditions. The observed results showed that sinks appear on the surface just before the whole polymer solidifies. This means that the development of sinks must be influenced by the rigidity of the solidified layer generated at the beginning of the cooling stage. This Implies that the sink generation can be controlled by the temperature of the cavity walls. In order to confirm whether the sink location can be controlled by the cooling rate of the cavity walls, sink generation was examined in tests using asymmetrical cooling of the cavity walls. The results are summarized as follows :
(1) When the temperature of one cavity wall is l0-20 K higher than that of opposite wall, sinks appear only on the surface adjacent to the hotter wall.
(2) On the contrary, if the hot wall temperature exceeds the glass-transition temperature of the polymer, the sinks appear on the opposite cold surface.
It was thus concluded that the location of sink can be controlled by the cooling rate of the cavity walls.
Key words: Injection molding / sink / solidified layer / Cooling Rate