Manufacture of thermoplastic elastomer tubes by water assisted injection molding technology

The objective of this study was to manufacture thermoplastic elastomer tubes by a novel water assisted injection molding technology and to experimentally investigate the effects of various processing parameters on the molded parts quality. Styrene-ethylene/butylene-styrene (SEBS) compounds based thermoplastic elastomers were used for all the experiments. Experiments were carried out on a lab-developed water assisted injection-molding system, which included a water pump, a water injection pin, a water tank equipped with a temperature regulator, a pressure accumulator, and a control circuit. A porous type water injection pin was designed and made to mold the parts. After molding, the lengths of water penetration as well as the hollowed core ratios in molded tubes were measured. The effects of different processing parameters on the hollowed core ratios were determined. It was found that the melt temperature and water injection delay time were the principal factors influencing the water penetration behaviors. In addition, a comparison has been made between the parts molded by water assisted injection molding and gas assisted injection molding. The results suggest that water assisted injection molded parts mold parts with less residual wall thickness distributions along the channel. However, thermoplastic elastomers molded by water exhibited higher wall thickness difference at curve sections than those molded by gas.