著者

亀田 隆夫 高橋 辰宏 小山 清人

出版者

The Japan Society of Polymer Processing

雑誌

成形加工 (ISSN:09154027)

巻号頁・発行日

vol.17, no.8, pp.571-579, 2005-08-20

参考文献数

15

被引用文献数

1

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The precise measurement of three dimensional shrinkage at different locations within molded parts is seldom reported. In this research, we compared the measured shrinkage (relating the difference between the dimensions of the metal mold and the resultant molded plastic parts) with calculations based on PVT measurements for parts made from AS and ABS resins. With increasing packing pressure, the shrinkage was minimized in the normal direction (ND) more than in the melt flow (MF) and transverse (TD) directions. The ND shrinkage was proportional to the volume shrinkage, while those of the other directions were proportional to less than the 1/3 power of volume shrinkage. The TD shrinkage was larger than the MD shrinkage. With increasing packing pressure, the gate seal time increased for ABS, but hardly changed for AS. The molecular orientation, obtained from birefringence measurements, increased with packing pressure.

著者

亀田 隆夫 高橋 辰宏 小山 清人

出版者

The Japan Society of Polymer Processing

雑誌

成形加工 (ISSN:09154027)

巻号頁・発行日

vol.17, no.5, pp.342-348, 2005-05-20

参考文献数

15

被引用文献数

1 1

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The size of the dependence of the shrinkage anisotropy in different locations of injection molded parts is not frequently reported (shrinkage calculated by comparing the actual plastic parts to the metal mold, while anisotropy refers to differences in the melt flow (MD) and the transverse (TD) directions). In this study, the effects of packing pressure (from 20 to 100MPa) in the injection molding process on the shrinkage anisotropy at two positions in a molded part were investigated in two ABS resins. The shrinkage anisotropy decreased as a function of packing pressure at both locations, although at different rates. It was found that the shrinkage anisotropy at these two positions was quite similar at around 60MPa. It was also found that the screw head moved forward (backward) at pressures higher (lower) than 60MPa. At a packing pressure of 60MPa the screw head position was almost constant during the packing process in a plunger type injection molding machine where the polymer melt can hardly flow backwards.<br>In order to get further insight into the causes of the shrinkage anisotropy, birefringence measurements were performed with a transparent ABS resin. The measured birefringence at the two locations of the injection molded part were in good agreement with the respective shrinkage anisotropy values. Moreover, the packing pressure dependence seen in the shrinkage anisotropy was found to be similar for that of birefringence. It was demonstrated that a difference in molecular orientation in the two directions (MD and TD), caused the shrinkage anisotropy, and that the ratio of molecular orientation difference becomes almost identical at the two locations at around 60MPa of packing pressure.