聚合物振动诱导单螺杆熔融塑化过程(Ⅰ)熔融机理及熔融速率

在振动诱导单螺杆挤出机中,通过螺杆的轴向振动使聚合物的熔融塑化过程在周期性的振动状态下进行,而经典熔融塑化理论无法描述处于周期性振动状态的熔融塑化过程。通过可视化和剖分料筒实验,观察了振动诱导单螺杆挤出机的熔融过程,深入分析了振动诱导熔融机理,建立了熔融过程动态物理模型,提出了振动场作用下熔融过程的质量平衡方程、动量平衡方程、能量平衡方程及本构方程,并运用复杂的数学方法求得近似解析解,最后得到了熔融速率方程和熔膜厚度方程,从公式中可以看出：熔融速率与熔膜厚度都是与振动参数相关的,且具有时间依赖性,振动场的引入可以加快熔融速率,减少熔膜厚度。理论研究与前面的实验结果符合得很好.     

聚合物振动诱导单螺杆熔融塑化过程(Ⅱ)轴向振动对熔融过程的影响

在本文（Ⅰ）报所建立的物理模型以及解析模型的基础上,推导出振动诱导单螺杆挤出机的熔融段长度和固体床分布方程.使用低密度聚乙烯（LDPE）进行实例计算,得出：熔融速率随振动频率和振幅的增加而增加,熔膜厚度和熔融段长度随振动频率和振幅的增加而减少.当振动强度达到某一极限值后,熔融速率、熔膜厚度和熔融段长度不再随振动参数的变化而变化.最后运用剖分料筒实验验证了上述结论的正确性,理论计算值与实验结果符合得很好.     

沟槽机筒单螺杆挤出机塑化特性的实验研究

采用剖分式机筒单螺杆挤出机实验平台,对熔融段沟槽机筒单螺杆挤出机塑化过程中熔融起始点、熔融长度、熔体温度/压力等塑化性能及产量进行了实验研究,比较了不同物料在不同工艺条件下对沟槽机筒单螺杆挤出机塑化特性的影响。结果表明,增大螺杆转速或提高机筒温度,塑化过程实际所需熔融长度增加,但对熔融起始点影响不大;熔融段机筒沟槽内熔体温度和熔体压力随螺杆转速增大无明显变化;随螺杆转速增大,沟槽机筒单螺杆挤出机挤出产量呈线性增加,表现出良好的挤出特性。     

沟槽机筒单螺杆挤出机耦合双槽熔融理论研究

利用自制的液压剖分式沟槽机筒单螺杆挤出机实验平台,研究了沟槽机筒单螺杆挤出机的熔融长度和螺杆转速的关系,实验验证了单螺杆挤出机固体输送段和熔融段机筒均开设沟槽的耦合双槽熔融理论。结果表明,与传统光滑机筒单螺杆挤出机和IKV单螺杆挤出机相比,在熔融段机筒开设沟槽的单螺杆挤出机的熔融长度较短且熔融过程比较稳定,熔融效率得到较大提高。     

开槽机筒单螺杆挤出机的研究进展

分析了轴向直槽机筒单螺杆挤出机和螺旋开槽机筒单螺杆挤出机在基本结构、物料输送机理及工业应用领域等方面的不同。随着开槽机筒单螺杆挤出机产量的提高,常规的熔融方式无法实现高产量下物料的高效彻底熔融,因而开槽机筒单螺杆挤出机存在产量与熔融能力无法匹配的问题,通过分析现有解决途径,指明了其未来的发展趋势。     

沟槽机简单螺杆挤出机塑化性能的模拟研究

对传统光滑机筒单螺杆挤出机、固体输送段沟槽机筒单螺杆挤出机和熔融段沟槽机筒单螺杆挤出机的结构特点、输送机理、熔融热源以及熔融模型进行了对比分析,并对其熔融过程中熔融速率、熔融长度和熔融起始点进行了数值模拟,根据模拟结果分析了机筒结构形式对单螺杆挤出机熔融性能的影响。结果表明,机筒内壁开设沟槽的单螺杆挤出机在结构、机理和性能等方面均优于传统光滑机筒单螺杆挤出机,且将机筒沟槽由固体输送段延伸至熔融段对单螺杆挤出机的熔融性能有显著的提高。     

振动力场作用下的单螺杆挤出机固体输送理论

在单螺杆挤出机中,通过螺杆的轴向振动将振动力场引入聚合物固体输送过程,提出振动力场强化固体输送过程的新概念.以螺槽中运动的物料为对象建立了振动力场强化固体输送过程的数学模型,并获得了物料沿螺槽方向输送的压力（密度）、速度的近似解析解.传统固体输送过程就是当螺杆轴向振动的振幅为零时的特例,此时的压力降与Darnell and Mol 理论一致,但不同的是物料速度及密度沿螺槽方向是变化的,从而修正了Darnell and Mol 固体输送理论.螺杆的轴向振动提高了固体输送平均压力,缩短了固体输送的长度,增加了固体输送角.透明料筒全程可视化实验挤出机证明了螺杆轴向振动确实缩短了物料固体压实输送所需的螺槽长度.     

数值研究槽深对单螺杆螺筒挤出机性能的影响

通过数值模拟技术,研究了机筒内壁开螺槽的螺筒结构形成单螺杆螺筒挤出机的性能.使用POLYFLOW软件,数值模拟了硬质聚氯乙烯(PVC-R)熔体在不同螺筒槽深的单螺杆螺筒挤出机中的三维等温流场及混合过程;重点研究了螺筒深度对单螺杆螺筒挤出机的影响.研究表明:在螺筒与螺杆之间间隙不变的情况下,大的螺筒槽深更有利于单螺杆螺筒挤出机混合性能的提高.     

机筒沟槽和螺杆螺槽耦合作用下的熔融理论研究

对固体输送段和熔融段机筒开设螺旋沟槽的单螺杆挤出机,构建了基于反压缩比分离型螺杆和正压缩比沟槽机筒的耦合双槽熔融模型,并通过液压剖分式单螺杆挤出机实验平台对耦合双槽熔融模型进行了验证。结果表明:对于沟槽机筒单螺杆挤出机,利用熔融段沟槽固体塞和螺杆螺槽固体塞在机筒沟槽和螺杆螺槽界面处发生层间剪切产生的大量内摩擦热来实现物料的高效熔融是可行的;实验结果和理论模型相一致;螺杆转速对熔融长度影响不大,而螺杆结构参数则对其影响较大。     

挤出工艺条件对β成核剂改性PPR的影响

使用差示扫描量热仪、广角X射线衍射仪和偏光显微镜研究了不同挤出工艺条件下N,N′-二环己基对苯二甲酰胺(DCHT)对无规共聚聚丙烯(PPR)β成核效果的影响。结果表明:加入质量分数0.15%的DCHT会诱导PPR中部分α晶转变成β晶,使原来粗大的球晶转变成"花心"状晶,出现β晶(300)晶面的特征衍射峰;提高单螺杆挤出机螺筒温度或螺杆转速都会明显增强DCHT对PPR的β成核效果;使用双螺杆挤出机在螺杆转速较高时,挤出改性PPR的β晶相对含量较高;最优工艺条件为单螺杆挤出机料筒温度250℃、螺杆转速120 r/min,或双螺杆挤出机料筒温度230℃、螺杆转速170 r/min,此时改性PPR的β晶相对含量达45.0%以上,DCHT对PPR有较好的β成核作用。     

Melting process and mechanism for vibration induced single‐screw extruder

The effect of a vibration force field on the melting process of an extruder is studied. It is shown that the mechanism for melting differs from conventional theory. Experimental studies of melting of low‐density polyethylene (LDPE) pellets in a vibration‐induced single‐screw (VISS) extruder show that melting is initiated on the inside of the barrel and the surface of screw. Models were developed that explain the melting mechanism in those regions. The melting at the surface of the screw is mainly initiated by frictional work on the pellets by the vibration and rotation of the screw. The melting action at the barrel is induced by a barrel temperature higher than the melting point and propagated by viscous dissipation heating of the melt film produced. The theory is supplemented by a calculation sample, which shows good agreement with experimental data obtained on a transparent barrel VISS (T‐VISS) extruder and a half‐open barrel VISS (H‐VISS) extruder with LDPE. The results of the experiment and calculation sample indicate that the introduction of vibration‐induced field can improve the melting capacity of extruder to a great extent. The present model enables the prediction of processing parameters for VISS extruders, from which the optimum operating conditions can be obtained. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2504–2514, 2007     

Effect of screw axial vibration on polymer melting process in single‐screw extruders

A model for investigating the melting process of polymer in a vibration‐induced single‐screw (VISS) extruder is presented. The key feature of this model is as follows: vibration force field is introduced into the overall course of extrusion by the axial vibration of the screw, and the velocity distribution in the polymer melt behaves strongly nonlinear and time‐dependent. To analyze this model, half‐open barrel visible experimental method and low‐density polyethylene material are adopted to investigate the effect of the vibration parameters on the melting process, which goes into further details of study and research on the melting mechanism, and thus, a novel physical melting model is derived. Combining the conservation equations of mass, movement, energy, and constitutive, analytical expressions of the melting rate, the energy consumption, the length of melting section, and the distribution of solid bed are obtained. This model enables the prediction of the processing and design parameters in the VISS extruders from which the optimum conditions for designing VISS extruder and polymer processing are obtained. The theory is supplemented by a calculation sample and experiment, which shows that the introduction of vibration force field can improve the melting capacity and decrease the power consumption of extruder greatly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3860–3876, 2006     

Melting performance of single screw extruders with a grooved melting zone

A novel melting model for single screw extruders with a grooved melting zone was established. The whole solid plug, which came from the grooved feed zone, was ruptured and melted mainly by continuously changing the volume of the barrel grooves and the screw channel in the grooved melting zone. A new single screw extruder platform with hydraulic clamshell barrels was constructed to investigate the melting of solid polymer with different combinations of barrels and screws. The melting model was verified by experiments. The results showed that the melting started earlier and finished in a shorter length for single screw extruders with a grooved melting zone than that for conventional single screw extruders and the melting efficiency was improved by introducing a grooved melting zone to a single screw extruder. The theoretical values are consistent with experimental results. The novel single screw extruder with grooved melting zone can dramatically increase the plasticizing efficiency and the throughput.     

Infrared melt temperature measurement of single screw extrusion

An infrared temperature sensor has been used to provide real time quantification of the thermal homogeneity of polymer extrusion. The non‐intrusive sensor was located in the barrel of a single screw extruder, positioned such that it provided a measurement of melt temperature in the channel of the metering section of the extruder screw. The rapid response of the technique enabled melt temperature within the extruder screw channel to be monitored in real time, allowing quantification of the thermal stability of the extrusion process. Two polyethylenes were used in experiments with three extruder screw geometries at a range of screw speeds. Data generated by the infrared sensor was found to be highly sensitive to thermal fluctuations relating to the melting performance of the extruder screw. Comparisons made with an intrusive thermocouple grid sensor located in the extruder die suggested that the infrared technique was able to provide a similar level of information without disturbing the process flow. This application on infrared thermometry could prove highly useful for industrial extrusion process monitoring and optimization. POLYM. ENG. SCI., 55:1059–1066, 2015. © 2014 The Authors. Polymer Engineering & Science published by Wiley Periodicals, Inc. on behalf of Society of Plastics Engineers     

数值模拟研究螺筒结构对单螺杆挤出机性能的影响

通过数值模拟研究了机筒内壁开螺槽的螺筒结构对单螺杆挤出机性能的影响。采用POLYFLOW软件模拟了硬质聚氯乙烯(PVC-R)熔体在单螺杆螺筒挤出机以及传统单螺杆挤出机中的三维等温流场及混合过程,并对二者的混合挤出性能进行了比较。结果表明:机筒内壁为螺旋沟槽结构的单螺杆螺筒挤出机,其混合性能相对于传统单螺杆挤出机有所提高。     

振动力场作用下聚合物熔体单螺杆挤出过程数值模拟

根据塑料电磁动态塑化挤出过程中熔体输送的实际情况，对三维模型进行简化，利用大型有限元软件ANSYS模拟了叠加轴向振动力场作用下聚合物熔体在螺槽中的流动情况，求解出周期性变化的速度，压力场分布，结果表明，与稳态挤出过程相比，振动力场的引入在进出口压力差恒定的情况下，可以提高熔全输送流率。采用有限元模拟方法可以为确定和优化工艺参数，产品质量控制提供指导。     

Contribution of the melting stage to the evolution of the morphology and chemical conversion of immiscible polyamide/polyethylene blends in twin‐screw extruders

This study investigates the effects of processing conditions (the screw speed, throughput, barrel temperature, and screw configuration) on the chemical conversion and morphology evolution of polyamide/polyolefin blends along a twin‐screw extruder. Polymer samples were collected rapidly at specific barrel locations with a special sampling device for subsequent chemical and morphological characterization. Increasing the screw speed or using more restrictive screw modules at the beginning of the melting zone promoted a faster reaction and better dispersion along the extruder. Increasing the throughput or decreasing the barrel temperature slowed the evolution of the morphology and chemical conversion along the extruder because of the lower melting rate. As soon as melting started, the chemical reaction took place. However, high chemical conversion rates required extensive melting, that is, significant interface generation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

电磁动态塑化挤出机熔体混合性能的研究

在不同振动频率下，利用剖分式料筒电磁动态塑化挤出机，对碳酸钙填充聚乙烯体系进行了螺杆沿程混合性能的研究。通过对不同位置处物料的SEM图的分散相作粒径统计分析。发现振动力场对CaCO3在LDPE熔体中的分散有促进作用。改善了混合物料的混合程度；相同振幅下，振动频率高则分散效果越好。