The effect of injection mold gate construction on selected properties of polyethylene moldings
Polimery 2000, No 2, 89
SummaryResults of property measurements of test specimens are considerably affected by the method and by the conditions under which the material is injected into the mold. Mold design is of particular importance. The molded piece produced is reliable only when the mold is filled with a material introduced in the laminar flow mode. The mode of flow is affected by the way a molten polymer is conveyed into the mold and particularly by the shape, size and location of mold runners and gates (Figs. 1–7). Selected mechanical and thermal properties were examined for Borealis' HDPE injection molding specimens in relation to gate size. Test specimens were prepared by using an injection mold designed to meet the ISO 294-1:1996 requirements (Fig. 8) provided with interchangeable cavity plates to be mounted in the mold frame to produce test specimens varying in type. The gate inserts used with the line gates differed in thickness. The gate inserts used were 16 mm in width, 1 mm in length and 0.2, 0.7, 1.2, 1.7,2.2,2.7 or 3.2 mm in thickness. Gate thickness was found to affect considerably the mechanical and thermal properties of polyethylene (Figs. 9–15). As the gate thickness was increased, the tensile strength, yield stress, Young modulus, hardness and softening temperature decreased, whereas the impact strength and the unit strain at maximum tensile stress rose (Figs. 9–15).