Study On Rolling Of UHMWPE Pipe Based On Dynamic Extension

Due to its excellent comprehensive properties,particularly impact resistance and tribological properties,ultra-high molecular weight polyethylene(UHMWPE)can be used in various fields such as aerospace,national defense and biomedicine.The wide applications of UHMWPE can accelerate the realization of the goal of "replacing steel with plastic".However,the processing technology based on shear deformation is difficult to realize the transportation and processing of UHMWPE,and the traditional pipe processing methods always have these disadvantages of high energy consumption and low efficiency,which severely restrict the production and application of UHMWPE pipes.The novel polymer processing method dominated by volume elongational deformation,innovatively realizing the subversive transformation of polymer processing from shear deformation to elongational deformation,which has the advantages of high efficiency in mass and heat transfer,short thermal mechanical process and low energy consumption.This paper innovatively combined the processing technology of polymer materials dominated by elongational deformation with the rolling theory,put forward the dynamic rolling technology of UHMWPE pipes,and successfully developed the equipment of rolling of pipe based on dynamic extension.The structure,principle and characteristics of the equipment were described in detail.The equipment can realize the processing of pure UHMWPE pipe using a novel processing method without the restriction of processing difficulties of UHMWPE.The theoretical output and leakage of the eccentric rotor extruder(ERE)were analyzed,and the actual output of ERE was proportional to the rotor speed.The physical and mathematical model of dynamic rolling process were established.The velocity distribution and elongational deformation rate distribution of melt and the elongational deformation action index were obtained.The rolling speed was in direct proportion to the rotor speed,indicating that dynamic rolling process had the characteristics of positive displacement transportation.The dynamic rolling process was the extension process of the melt along both the circumferential and axial directions,which was dominated by elongational deformation.The proportion of area dominated by elongational deformation in the inner wall of pipe of forming stage reached 80%,the proportion of area dominated by elongational deformation in the convergent stage was about70%.The extrusion characteristics of ERE and the dynamic rolling characteristics of UHMWPE pipes were studied through experiments.The extruded UHMWPE by ERE was highly compacted,the extrusion output of UHMWPE was proportional to the rotor speed,and the processing residence time was inversely proportional to the rotor speed.The rolling output and rolling speed of UHMWPE pipes formed by dynamic rolling were in direct proportion to the rotor speed.When the rotor speed was 40 rpm,the maximum output weight and output speed of UHMWPE pipes reached 26.3 kg/h and 45.1 m/h,respectively.The influence law between processing process,structure and performance of UHMWPE pipe formed by dynamic rolling was obtained.The elongational deformation can effectively realize the disentanglement of UHMWPE,reducing the degree of entanglement and the fracture of molecular chain and increasing the crystallite size.Dynamic rolling can promote the extension and fusion of melt and improve the forming of pipe.The tensile and flexural properties of UHMWPE improved significantly by dynamic rolling process.The optimum values of the average tensile modulus,yield strength,tensile strength,elongation at break,flexural modulus and flexural strength of the pipes were 17.9%,8.3%,18.5%,20.8%,18.6%and 8.8% higher than those of the corresponding molded samples.The development of the equipment of rolling of pipe based on dynamic extension realized the rapid and stable processing of pure UHMWPE pipe and the improvement of mechanical properties of UHMWPE pipe,which was of great significance to promote the wide application of UHMWPE pipes.