Study On Gas Pressure Balance Process And Stabilization Mechanism Of Biaxially Oriented Polyvinyl Chloride Tube

Traditional PVC pipe can not obtain good comprehensive performance beacause it is uniaxial stretched and uniaxial tension weakens its circumferential performance.Circumferential performance can be improved by biaxially stretching technology.Gas pressure balance process of tube under biaxially tension has an obovious effect on performance of PVC-O pipes.In this paper,using compressed air as the expansion of power,PVC tube is biaxially oriented during gas pressure balance process;mathematical model of pressure balance process of biaxially oriented PVC tube was established to discuss the geometrical and mechanical properties of gas pressure balance process of PVC tube;finally,the geometrical properties of gas pressure balance process of PVC tube and the mechanical properties of PVC-O pipes under different process parameters were tested and the mechanical properties of PVC-O pipes and uniaxial oriented PVC pipes under different process parameters were compared and stabilization mechanism of biaxially oriented PVC tube was discussed.Mathematical model of gas pressure balance process of biaxially oriented PVC tube was established to discuss the geometrical and mechanical properties of gas pressure balance process of PVC tube.Under the action of internal pressure expansion,the radius of the outer wall of the tube increases first and then reduces to the vacuum forming size.When the internal gas pressure increases,the circumferential tension of the tube increases gradually,and the wall thickness of the tube decreases,and the maximum value of the outer wall radius of the tube is larger than the vacuum forming size;internal gas pressure both improve axial and circumferential strain and stress.When the axial stretching ratio increases,the wall thickness of the tube decreases,the degree of circumferential stretching of the tube decreases and the axial stress increases.The distribution of axial stress at the axial distance first increases and then decreases and the maximum axial stress value is obtained at the axial distance corresponding to the maximum radius of the outer wall of the tube.The experimental results show that the diameter of the inner air-conditioning plug improves the degree of circumferential stretching of PVC tube,and maximum circumferential stretching ratio can be obtained in the vicinity of the head of the inner air-conditioning plug.The diameter of the inner air-conditioning plug can improve the axial tensile strength,impact strength and pressure resistance of biaxially oriented PVC tube,but decrease the axial elongation at break.The larger diameter of inner air-conditioning plug can provide a larger circumferential stretching ratio,with the increase of axial stretching ratio,axial stretchingratio and circumferential stretching ratio are closer to provide a better comprehensive performance of axial tensile properties,impact resistance,pressure resistance.The influence of process parameters on the geometrical characteristics of the gas pressure balance process and the performance of the pipe under the corresponding process parameters were dicussed to analyze the stability mechanism of the gas pressure balance process.The axial stretching ratio has a negative effect on the degree of circumferential stretching of the tube during gas pressure balance process.But the inner air cushion between the inner air and the tube hold up the PVC tube so that the maximum diameter and maximum circumferential stretch ratio of the tube is stable and not significantly affected by the axial stretching ratio and the stability of the gas pressure balance process of PVC tube is ensured.