The effect of mold temperature and injection velocity on selected properties of polyethylene moldings
Polimery 2000, No 11-12, 830
SummaryA literature review shows how injection molding conditions affect process capacity, energy consumption and molding structure and properties. Mechanical and thermal properties of HDPE moldings were studied in relation to mold temperature (20°C–80°C) and injection velocity (0.015–0.12 m/s). As the mold temperature was raised, the tensile strength, yield stress, tensile modulus, hardness and Vicat softening temperature were found to increase; the strain at maximum tensile stress and impact strength decreased (Figs. 1–3). At higher temperatures, the mold cavity is easier to fill. At low polymer/mold wall temperature gradients, internal stresses and molecular orientation are lesser and moldings exhibit smaller sink marks and better mechanical properties. Economically, higher temperatures, are unfavorable because then the injection molding cycle is longer. Higher injection velocities gave rise to reduced tensile strength, stress at break and hardness and to lowered softening point and to increased plastic properties (strain at break, impact strength) (Figs. 4–6). The time to fill the mold cavity is shorter and thermal losses along melt flow path are smaller. At velocities that are too high, defective moldings are likely to form containing voids and having inferior mechanical properties.