The shrinkage degree ξ of polymer products must be considered when the molds are at the stage of designing. On the calculation of ξ, the descending temperature ΔT of polymer products after molding process and α (the coefficient of thermal expansion) are necessary.
It was found that α has the typical distributions at the various layers along the machine direction (MD) and the traverse direction (TD), especially under HDPE melts flow in the dies. Consequently, α distributions should be predicted for estimation of accurate ξ of HDPE products. In this study, we have investigated the experimental data of HDPE α distributions under extrusion process and calculated the strain distributions by polymer melts flow analysis using finite element method. The following results were obtained.
(1) The measured data of α (MD) distributions correspond to the strain distributions which generate along the flow direction within the inner and the outer die.
(2) The measured data of α (TD) distributions correspond to the strain distributions which generate along the θ direction within the inner and the outer die.
(3) The measured data of α distributions in this study showed the correlation between the strain distributions much better than the shear stress distributions.
