【作者】 陈开源；

【导师】 周南桥；

【作者基本信息】 华南理工大学 ， 机械设计及理论， 2010， 博士

【摘要】 塑料管材在建筑、市政建设、水利工程、燃气输送等领域有着广泛和重要的应用。与传统管材(铸铁管、混凝土管等)相比,具有重量轻、流动阻力小、耐腐蚀性好、密封性好、安装方便、节省能耗、寿命长等优点。因而塑料管材已成为重要的工业材料,年消耗量非常巨大。但塑料管材强度比传统管材低得多,因此提高塑料管材的强度以适应工程应用的高要求就具有重大的现实意义。除了外增强塑料管材,出于可持续发展等各方面的考虑,自增强塑料管材已成为国内外研究热点之一。聚合物电磁动态塑化成型加工技术和设备,通过螺杆的轴向振动,将振动力场引入到聚合物成型的整个过程,为聚合物成型加工理论和加工技术提出了新的研究方向。这一独特的加工方法深刻地影响了聚合物塑化挤出过程,使得聚合物的加工应用和理论都发生了巨大的变化。前期研究表明,振动力场的引入,可以提高制品的力学性能和外观质量。目前对于电磁动态塑化挤出成型未见有研究振动力场对塑料管材性能影响的报道。而系统地研究振动力场下管材性能与聚集态结构的变化,解释脉动挤出实现管材自增强的机理,从理论上和实验上深刻地揭示脉动挤出对聚合物产生的影响,可以为聚合物动态挤出成型提供理论指导,具有重要的科学意义和实际意义。本文利用电磁动态塑化挤出机,并自行设计了一个螺旋芯棒式管材机头。首先采用数值模拟方法,揭示了螺旋芯棒式管材机头流道中的聚合物熔体的流动特性,并通过实验验证了数值模拟的可靠性。结合正交试验,以螺旋分配系统出口截面处速度分布均匀性为目标,实现了螺旋芯棒式管材机头的优化设计。根据工业化生产实际情况,搭建起整个挤管实验装置。在工业化生产条件下,将振动力场引入到聚烯烃管材挤出成型的全过程,系统研究了振动参数对管材力学性能、热性能和聚集态结构的影响。研究结果表明,脉动挤出实现了管材的双向自增强,特别是管材周向强度得到明显提高,这对于承受内压力管材的使用具有重要意义。力学性能测试表明,对HDPE管材,与稳态相比,管材爆破压力最大提高了34.2%,轴向拉伸屈服强度最大提高了5.3%,轴向冲击强度最大提高了20.2%;对PP管材,与稳态相比,管材爆破压力最大提高了27.03%,轴向拉伸屈服强度最大提高了7.3%,轴向冲击强度最大提高了16.2%。脉动挤出提高了HDPE管材的耐热性能。当振动频率为6Hz,振幅为200μm时,HDPE管材维卡软化温度比稳态挤出时提高了3.1℃。DSC、WAXD、SEM分析测试表明,脉动挤出的聚烯烃管材熔点向高温漂移,结晶度也有所提高,结晶更加完善,晶面取向度得到提高,但晶型没有发生改变。耐慢速裂纹增长性是提高塑料管道耐用性的关键因素。塑料管材需具有良好的耐慢速裂纹增长性能,以确保管材的使用寿命。对脉动挤出的聚烯烃管材进行了耐慢速裂纹增长性能测试,研究了脉动挤出对HDPE管材耐慢速裂纹增长性能的影响及机理。研究发现,与稳态挤出的HDPE管材相比,脉动挤出的HDPE管材裂纹增长速率更小,脉动挤出可以提高HDPE管材的耐慢速裂纹增长性能,这对于管材的使用具有重要的现实意义。通过螺杆轴向振动引入振动力场后,有利于HDPE的成核和晶粒的长大。脉动挤出的HDPE管材结晶度提高,熔点升高,晶片变厚,晶粒尺寸变大,结晶完善,同时管材制品分子链形成了一种拟网结构,这些均有利于管材耐慢速裂纹增长性能的提高。基于合理的假设,考虑非定常流动,建立起数学模型。根据修正的Ostwald幂律本构方程,加载合适的动态边界条件,首次对脉动挤出条件下螺旋芯棒式管材机头流道中聚合物熔体的流动进行了全三维非牛顿等温数值模拟,同时数值模拟结果与实验结果具有较好的一致性。这为振动力场作用下机头流道内聚合物熔体流动特性的数值模拟提供了新方法和新思路。研究发现,随振动力场的引入,流道内熔体的剪切速率、粘度、剪切应力、压力和速度等呈周期性规律变化。另一方面,随着振动频率或振幅的增加,流场的剪切速率平均值有一定程度的增加,而流场的粘度平均值、剪切应力平均值和压力平均值均有一定程度的下降。最后本文从脉动挤出加工—聚集态结构—性能三者之间的关系出发,对聚集态结构测试结果、数值模拟得到的熔体流变性能进行分析和总结,分析了脉动挤出聚烯烃管材的自增强机理。聚烯烃管材力学性能的改善是振动力场提高结晶度、改善分子链的取向以及改善晶体形态等共同作用的结果。其中管材周向强度明显提高主要是由于螺杆轴向振动增强了管材分子链在周向的取向程度。上述这些研究成果丰富了聚合物动态成型加工理论和内容,加深了对脉动挤出过程中振动影响熔体流变行为、制品结构和性能的规律的认识,同时,为优化振动参数和模具设计,提供了实验数据与理论依据,对聚合物动态成型加工技术的进一步研究和推广,制备高性能的聚合物制品,具有重要的理论与现实意义。更多还原

【Abstract】 Plastic pipes are widely and importantly used in many fields including building, municipal construction, hydraulic engineering and gas transportation etc.. Compared with traditional pipes (cast iron pipe, concrete pipe etc.), plastic pipes have multiple advantages such as low weight, small flow resistance, excellent corrosion resistance, good sealing performance, convenient installation, low energy consumption and long service life. So plastic pipes play a very important role among industrial materials and the consumptions every year are very tremendous. However, the strength of plastic pipe is much lower than traditional pipe. And in engineering applications, plastic pipes have to be reinforced to meet the high demands on strength. Besides the additive-based reinforcement plastic pipes, the self-reinforcement plastic pipes have become one of the hot topics at home and abroad based on continuous development.The electromagnetic dynamic plasticating processing technology and equipment for polymer provide a new research direction for polymer processing theory and technology, which introduces a vibration force field into the entire polymer process by the axial vibration of the screw. The particular processing technology has a great impact on the polymer plasticating and extrusion processing, which makes the polymer processing technology, application and theory change greatly. The previous research showed that the vibration force field can improve the mechanical properties and apparent quality of the products. But at present, no investigation has been carried out on the effect of the vibration force field on the properties of plastic pipes prepared by the electromagnetic dynamic plasticating processing technology. The detailed research on the relationship between microstructures and mechanical properties, and the self-reinforcement mechanism of plastic pipes obtained by pulsatile extrusion, and study on the impact of pulsatile extrusion on polymer by experiment and theory ways can provide the theory guidance for polymer dynamic extrusion processing, which has an important scientific and realistic significance.An electromagnetic dynamic plasticating extruder equipped with a specially designed spiral mandrel die for pipe was used in this work. The melt flow characteristic of the spiral mandrel die for pipe was studied by numerical simulation, and the reliability of numerical simulation was validated by experiment. Based on the orthogonal experiment, the optimum design of spiral mandrel die for pipe was achieved by aiming at the distribution uniformity of the exit velocity of the spiral distribution system. The whole experiment device for pipe extrusion was builded according to industrial production.The vibration force field was introduced into the whole extrusion process for polyolefins pipe under industrial production condition, and the effect of the vibration parameters on the mechanical properties, thermal properties and microstructure of plastic pipes was studied. The results showed that the circumferential strength of pipes increased significantly, and biaxial self-reinforcement pipes could be obtained by pulsatile extrusion, which has an important significance for the pipe application. When compared with the static extruded pipes, for HDPE pipes, the mechanical properties testing showed that the maximum increase of bursting pressure, tensile yield strength, and impact strength were 34.2%, 5.3%, and 20.2%, respectively. For PP pipes, they were 27.03%, 7.3%, and 16.2%, respectively. The heat resistance of HDPE pipe was also improved. When the vibration frequency is 6Hz and vibration amplitude is 200μm, the Vicat softening temperature of HDPE pipe increased 3.1℃compared with the static extrusion pipe. The DSC, WAXD and SEM analysis showed that the polyolefins pipe prepared by pulsatile extrusion had higher melting temperature, higher crystallinity, more perfect crystals and higher orientation degree of crystalline planes, but no change in the crystalline form.The slow crack growth resistance is the key factor to improve the plastic pipe application. The plastic pipe should have excellent slow crack growth resistance in order to ensure the service life. The slow crack growth resistance of polyolefins pipe obtained by pulsatile extrusion was investigated in this paper, and the effect and mechanism between pulsatile extrusion and slow crack growth resistance of HDPE pipe was studied. The results showed that the HDPE pipes prepared by pulsatile extrusion had lower crack growth rate, namely the slow crack growth resistance was increased by pulsatile extrusion, which has an important realistic significance for the pipe application. The vibration force field introduced by axial vibration of the screw can make the HDPE melt form crystal nuclei more easily to facilitate the growth of HDPE crystals. The HDPE pipes prepared by pulsatile extrusion had higher crystallinity, higher melting temperature, larger lamellar thickness, larger crystal sizes and more perfect crystals, and the molecular chains formed a network structure. All these were favorable for the improvement of slow crack growth resistance of HDPE pipes.The mathematical model was established based on reasonable assumption and time-dependent flow considered. The polymer melt flow of spiral mandrel die for pipe was firstly studied by three-dimensional non-Newtonian and isothermal numerical simulation under pulsatile extrusion, and the numerical simulation result was well consistent with the experiment result, which provided a new method and idea for the numerical simulation of the polymer melt flow characteristic in the dies under vibration force field. The research showed that the melt shear rate, viscosity, shear stress, pressure and velocity had the cycle change when the vibration force field was introduced. On the other hand, The average value of shear rate increased with the increase of the vibration frequency or amplitude, but the average value of the viscosity, shear stress and pressure decreased.Finally, the microstructure results and the melt rheological properties obtained by numerical simulation were discussed and summarized, and the self-reinforcement mechanism of polyolefins pipe was analyzed based on the relationships among the pulsatile extrusion process and microstructure and property. The improvement of mechanical properties of polyolefins pipe using the pulsatile extrusion process was attributed to the higher crystallinity and the improvement of the molecular orientation and of the crystalline morphology under the influence of a vibration force field. Also, the significant increase of the circumferential strength of pipe was mainly assigned to the axial vibration of the screw which improved the circumferential degree of orientation of molecular chains.The above research achievements enrich the theory and content of polymer dynamic processing technology, and the knowledge about the effect of the vibration on the melt rheological behavior, the product structure and properties during pulsatile extrusion. Also, the experimental data and theoretical basis are provided for the optimization of the vibration parameters and mold design. The research has an important scientific and realistic significance for the further research and popularization of the polymer dynamic processing technology and the production of high performance polymer products.更多还原