Experimental Investigation Of Biaxial Oriented PEX Pipes Prepared By Quasi-dynamic Continuous Expansion Method

Along with the increasing of requirement of plastic pipes, the widening of the application field of plastic pipes and increasing of the request for using plastic pipes, most of counties wish the higher performance of plastic pipe. The research direction of plastic pipe is aim at how to enhance the performance of all aspects of the pipe as well as saving the material of pipe. The biaxial orientation enhancement technology of plastic pipe is a new production technology in the plastic pipe field, which means stretching the pipe in axial direction and expanding the pipe in hoop direction in production process so that the axial and hoop properties are self-reinforced. This self-reinforcement technology is applied to both of crystalline and amorphous material.After cross-linking, the cross-linked polyethylene gets the three-dimen-sional network structure which improves the performance of polyethylene. What's more, after cross-linking, the heat resistance, thermal strength, heat aging resistance, environmental stress cracking resistance, electrical insulation, barrier resistance, oil resistance of cross-linking polyethylene are all improved significantly. This paper studied on the quasi-dynamic expansion mechanism of PEX pipe. The so-called quasi-dynamic expansion is not the traditional dynamic expansion. The continuous expansion of the pipe is broken down to some repeat static expansion of pieces of pipe, then the all static expansion are combined and achieve the quasi-dynamic after controlling the expanding condition. After each piece is expanded, the shape is determined by cooling before it shrinking, then the length of the piece and the diameter is increased and the wall of the pipe gets thinner. In this paper, the optimal experimental parameters of the expansion of PEX pipe are provided, which include of the heating temperature, heating time, the expansion pressure, the expansion time and so on.After controlling the parameter in expanding process of quasi-dynamic continuous expansion equipment, the oriented PEX pipe with increased properties is gotten. The result reveals that the biaxial oriented PEX pipe can increase the tensile strength by 32.29% at most, while the modulus of elasticity increasing 13.06% and the elongation at break reducing 5.88%.