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。     

动态成型注塑螺杆熔体输送能力的研究

根据动态注射成型时螺杆的工作特点，采用自行修正的Tanner本构方程研究了聚合物熔体在螺槽中的等温流动。同时，近似地给出了振动力场下注塑螺杆熔体输送能力的表达式，理论分析了振动参数对沿程压力降及动态成型熔体输送能力的影响。结果表明，振动力场使塑化过程中聚合物的粘度降低，流动阻力减小。沿螺槽方向的平均压力降减小，在保持成型条件不变的情况下，施加振动可以提高熔体输送能力。     

塑料电磁动态塑化挤出机的挤出功率研究与模拟

本文采用自行修正的Tanner本构方程研究了塑料电磁动态塑化挤出机中熔体输送挤出功率对振动力场的响应。建立了振动力场作用下熔体输送挤出功率的理论模型,以此为基础模拟塑料电磁动态塑化挤出机的挤出功率,并进行了实验研究,结果表明理论模拟能够在一定范围内反映实际情况,为塑料电磁动态塑化挤出设备的设计和生产应用提供重要的理论指导依据。     

脉动压力诱导注射成型充模过程熔体表观黏度的实时测量

以脉动压力诱导注射成型充模过程浇口流道中熔体壁面表观剪切黏度的数学模型为基础,通过实时测量记录螺杆位置变化以及浇口流道两端熔体压力变化,表征脉动压力诱导注射成型充模过程熔体实时表现剪切黏度的方法,通过实验研究发现,脉动压力的引入使充模过程、熔体的剪切应力和表观剪切黏度降低,同时加剧了熔体的剪切速率变化,在强烈的振动条件下会引起动态充模过程中某些时刻出现断流现象.     

Simulation of nonisothermal flow of melt during melting process of vibration‐induced polymer extruder

A simplified 2D melt film model was established to simulate the nonisothermal melt flow during the melting process of the vibration‐induced polymer extruder of which the screw can vibrate axially. Since polymer has time‐dependent nonlinear viscoelastic characteristic with vibration force filed (VFF), a self‐amended nonisothermal Maxwell constitutive equation that can reflect the relaxation time spectrum of polymer was adopted. Using the 2D melt film model, melt films of two kinds of thickness representing different melting stages were simulated to investigate the influence tendency of the same VFF on the different melting stage. Special flow patterns and temperature distribution of melt in the melt film between the driving wall and the solid/melt interface with various vibration force fields were systematically simulated. It is found out that within a certain range of vibration strength, the application of vibration can optimize the time‐averaged shear‐rate distribution, improve the utilization efficiency of energy, and promote melting process; and the thinner the melt film is, the more intense the nonlinear viscoelastic response becomes with the same VFF; moreover, there exists optimum vibration strength to make the melting process fastest, which is in accord with the visualization experimental results. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5825–5840, 2006     

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.     

Numerical simulation of fluid flow and heat transfer in a single-screw extruder with different dies

In a plasticating screw extruder, a polymer melt forms in the melting zone of the extruder. Pressurization of the molten polymer takes place in the melting and the metering sections so that the melt can flow through the restricted passage of the die and assume a desired shape. In a melt fed extruder, the throughput is governed by the pressure rise over the entire length of the extruder. The pressure developed in the screw channel may also be employed in rapid filling of molds, such as those in injection molding. When the geometry of the screw, the barrel temperature, and the die are selected, a unique set of operating parameters arise for a particular flow rate or screw speed. In the present study, numerical and analytical methods are used to calculate the transport in the extruder and the pressure drop in the die. An iterative numerical method based on solving the equations of motion and energy in the screw channel and a correction scheme to couple the die with the screw channel is discussed. The numerical algorithm is capable of handling an arbitrary variation of the viscosity of the polymeric fluid with the shear rate and temperature. The results obtained by simulating the fluid flow in the screw channel are compared with available numerical and experimental results in the literature, indicating good agreement. The performance characteristics of the extruder, for chosen thermal boundary conditions and screw geometry, are presented for different die geometries and different fluids. The important considerations that arise in the numerical simulation of the extrusion process are also discussed.     

Extrusion Characteristics of Round-Section Dies with VFF

A vibration force field was applied to the whole process of polymer plasticating extrusion by periodical vibration of the screw. It observably affected both the extruder screw extrusion characteristics and the round-section die extrusion characteristics. It also affected the polymer plasticating extrusion process and the quality of the extrudates. An analytical model of typical dynamic extrusion of round-section dies was created. The results showed that a vibration force field can improve extrusion output.     

短圆管挤出模头中熔体取向行为对螺杆轴向振动响应的光散射研究

利用光散射测量方法研究了短圆管挤出模头中聚合物熔体取向行为对螺杆轴向振动的响应。研究结果表明,螺杆轴向振动使聚合物熔体的流动状态和大分子的取向发生了显著的变化,振动力场中振幅或频率的增加都会引起熔体中大分子取向程度的增大。     

Dependence of solids conveying on screw axial vibration in single screw extruders

In the single‐screw extruder, the vibration force field is applied to the solids conveying process by the axial vibration of the screw and the novel concept on the solids conveying process being strengthened with the vibration force field has been brought forward in this study. We establish the mathematical model that describes the solids conveying process with the vibration force field and obtain the approximative analytical solutions of the pressure and velocity of the solids conveying in the down‐channel. In the new theory, if the screw has no axial vibration the solids conveying pressure is the same as that of the Darnell and Mol theory, but the density and velocity of solids conveying along the screw channel is variable, which has modified the Darnell and Mol theory in which the density and velocity of the solids conveying along the screw channel was considered invariable. The results reveal that the axial vibration of the screw can increase the average pressure of solids conveying, decrease the channel length of the solids conveying section and increase the solids conveying angle. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2998–3007, 2006     

中心浇口圆盘模腔正弦脉动充模分析

聚合物动态注射成型通过螺杆的轴向振动实现熔体脉动充模。利用Tanner本构模型建立了中心浇口圆盘模腔正弦脉动充模过程的数学模型,分析了振动参数对注射压力及熔体输送功率的影响。当充模过程的平均注射速率不变时,在一定频率与振幅范围内,模腔入口处的压力随振动源振幅(频率)的增大而增大,但其平均值降低;充模过程中输送熔体所需要的功率降低。     

Pressure profiles in plasticating extruders

The pressure distribution through the melting and melt zones of a plasticating extruder is discussed, and an analysis is described for predicting the pressure profile. In the stable melting zone, the pressure profile is calculated based on flow in the melt pool, and the pressure is strongly influenced by the flow of the solid bed of plastic. The solid bed flow is primarily determined by the polymer rigidity in the screw compression section. If the size (through a melting analysis) and the velocity (through a solid bed acceleration parameter) of the solid bed along the screw channel are reasonably approximated, the pressure profile is reasonably approximated by this analysis. Inaccurate representations of the size or velocity of the solid bed can yield inaccurate pressure profile prediction. In the unstable melting region, the assumption of a complete melt yields reasonable pressure predictions. The introduction of these concepts into an extrusion model permits a more accurate prediction of the operating RPM of a given screw design in a given machine.     

基于电磁动态塑化挤出的模头挤出特性的研究

本文以塑料电磁动态塑化挤出机上的圆截面模头为对象,研究了将振动力场引入聚合物塑化挤出全过程条件下圆截面模头的挤出特性,建立了圆截面模头脉动挤出特性的数学模型,并进行了实验研究,理论分析与实验结果趋向一致,从而揭示了振动力场引入聚合物塑化挤出全过程对圆截面模头挤出特性的影响规律。     

Screw design in injection molding

The performance of screws of advanced design in injection molding has been investigated with respect to four different objectives: (1) improvement of distributive mixing; (2) improvement of dispersive mixing; (3) increase of plasticating capacity; and (4) reduction of inhomogeneity of melt temperature. The screws used are three zone screws with different compression ratios, screws with pineapple or Maddock/Egan mixing elements, with one or two channel barrier sections, with static mixers mounted in the valve or in the nozzle, or with combinations of these different elements. The best mixing quality is obtained with multi-channel Maddock sections. The highest plasticating capacity and, consequently, the shortest cycle times are achieved with the barrier screws. Temperature measurements show that these screws improve melt homogeneity considerably with a relatively small loss of plasticating time. In all cases, increasing the back pressure gives inferior results compared with improvement of the screw design.     

Developments in the analysis of steady screw extrusion of polymers

A review is undertaken of theoretical and experimental work which has advanced the understanding of the single screw extrusion process for polymers. Detailed consideration is given to the many published theoretical models of solids conveying, melting and melt flow in the channel of a plasticating extruder. Development of such models is traced in terms of the gradual relaxation of simplifying assumptions to provide methods of analysis which give realistic predictions of machine performance. Comparisons between the results of such analyses and observed machine behaviour are also discussed.     

动态充模过程熔体表观黏度的实时测量与研究

修正了脉动压力诱导注射成型充模过程浇口流道中熔体壁面表观剪切黏度的数学模型,并介绍了建立在此基础上的通过实时测量并记录螺杆位置变化以及浇口流道两端熔体压力变化来表征脉动压力诱导注射成型充模过程熔体实时表观剪切黏度的方法,通过实验研究发现,脉动压力的引入对熔体的实时表观剪切黏度产生了深刻的影响,且降低了充模过程单振动周期内壁面熔体的平均表观剪切黏度及受到的平均剪切应力。在此过程中,还提出了特定振动参数下熔体剪切应力与剪切速率之间相位角的计算方法。     

Study on the Effect of Axial Vibration of Screw in Plasticating Process (Extrusion Part)

To improve the conformation of polymers, axial vibration is offered in the entire polymer process. Two sections, the axial shearing section and the axial pressing section, exert the effects of vibration on the melt. In the axial shearing section, with the effect of vibration, molecular chain orientations in the direction of flow and vibration produce the network frame, which ameliorates the mechanical properties, especially in the transverse direction, of the polymer product. The vibration can promote the disentanglement of molecular chains, which leads to a decrease in the viscosity and an increase in the flowability of melt. At the same time, it can ameliorate the blend quality of the filling system. Some experiments on extruded film, sheet, pipe, foam, and filling systems prove that the analyses are correct.     

振动参数对动态注射螺杆塑化能力的影响

根据动态成型注射螺杆塑化时的工作特点,采用自行修正的Tanner本构方程,建立了螺杆动态塑化理论模型,并近似地给出动态注射螺杆塑化能力的表达式,研究了振动参数对注射螺杆塑化能力的影响。结果表明:注射螺杆的塑化能力随着螺杆直径、计量段螺槽深度、计量段长度的增加而提高;注射螺杆的塑化能力与螺杆转速成正比,与螺杆的背压成反比;保持其他加工参数不变的情况下,螺杆的塑化能力随着振幅和振动频率的增加而增强。     

A plasticating model for single-screw extruders

By measuring the solid-bed transfer velocity, width and thickness under various conditions, die following results are obtained. As the result of melting, the solid bed decreases in width and thickness almost with the same rate, and the solid-bed transfer velocity is constant, while a melt layer exists between the solid bed and the screw root; also, when the phenomenon of dam-up occurs, caused by the combined effect of decreasing depth of the screw channel with tin insufficient decrease of solid-bed thickness, the transfer velocity increases proportional to the rate of decrease of channel depth. Consequently, the solid bed is considered to behave us loosely packed particles. A new plasticating model is developed by making the above results an assumption and adopting finite differential calculus with the Newton-Raphson method to obtain accurately the melting velocity, melt profile, and solid-bed temperature. Calculated values are in remarkably good agreement with the experimental values Solid-bed softening point, pressure, and screw torque are also successfully estimated.     

A Computer Model for Single-Screw Plasticating Extrusion

A fully predictive computer model has been developed for a single-screw plasticating extrusion (with conventional screws). The model takes into account five zones of the extruder (hopper, solids conveying, delay zone, melting zone, melt conveying) and the die, and describes an operation of the extruder-die system, making it possible to predict a mass flow rate of the polymer, pressure and temperature profiles along the screw channel and in the die, solid bed profile, and power consumption. Moreover, mixing degree, temperature fluctuation and viscoelastic properties of the polymer are estimated. The simulation parameters are the material and rheological properties of the polymer, the screw, hopper and die geometry, and the operating conditions (screw speed and barrel temperature profile). Such a comprehensive approach to the modeling of extrusion creates the possibility of optimizing the process, for example, from the point of view of the quality of extrusion. The model has been verified experimentally for a low-density polyethylene on a 45 mm diameter single-screw extruder.