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Mechanism of HDPE Thermal Expansion Coefficient Distributions during Blow-up Process
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Terada, Kousuke / Yamabe, Masashi / Shimbo, Minoru / Miyano, Yasushi / Kajiwara, Toshihisa / Funatsu, Kazumori
The shrinkage degree Ė of polymer products must be considered when the molds are at the stage of designing. On the calculation of Ė, the descending temperature ĒT of polymer products after molding process and ŋ (thermal expansion coefficient in polymer products) are necessary. It was found that ŋ has the typical distributions at the various layers along the machine direction (MD) and the transverse direction (TD), especially HDPE products. Consequently, ŋ distributions should be prodicted for estimation of accurate Ė of HDPE products.
The blow molding process is divided into the following two processes.
(a) Parison extrusion process (b) Blow-up process
We reported the previous paper that ŋp (thermal expansion coefficient in parison) distributions correspond to the strain distributions under extrusion process. In this study, we have investigated the experimental data of ŋ distributions after blow-up process and calculated the elongational strain in deforming parison by analysis using finite element method. The following results were obtained.
(1) The measured data of ŋ in products correspond to that of ŋp which gets the reduction by the elongational strain during blow-up process
(2) We proposed the model equation of relationship between ŋp and ŋ. The model equation expressed the characteristic of measured data of a in this study.
Key words: HDPE / Blow-up process / Finite element method / Thermal expansion coefficient / Shrinkage degree