Abstract: this paper describes the design of a self-locked pin for water-assisted inj ection molded polypropylene curved pipes, which meets the demand of high flow rate and preventing being stuck by melt. the wall thickness of parts molded using both self-locked and orifice pins were compared under the same processing parameters. the parts molded using the self-locked pin resulted in more uniform and thinner wall thickness. the effects of the water pressure and injection delay time on the wall thickness and water penetration length of parts were investigated using the self-locked pin.

Key words: water-assisted injection molding, water injection pin, polypropylene, water penetration length;residual wall thickness