Investigation of the poly(vinyl chloride) extrusion process using a feed throat with a feed pocket

The effectiveness of the extrusion process depends on a number of factors, the most important being barrel design, e.g., longitudinal or helical grooves; screw, feed opening, and polymer hopper designs are significant in this respect, too. The effect of these factors on the extrusion process has been thoroughly discussed in the available literature. This notwithstanding, there is little information providing insight on the effect of a feed pocket made below the feed opening, on the side of the barrel toward which the screw rotates, on the main characteristics of the extrusion process. For the experiments, five special profile inserts with different feed pocket depths were made and then mounted in the extruder barrel equipped with a 25‐mm diameter screw. The extrusion of plasticized poly(vinyl chloride) (PVC) at the screw speed ranging from 30 to 150 rpm was investigated. Presented graphically as charts, the obtained results show the dependences of extrudate temperature, extruder screw torque, polymer output, power supplied to the extruder and conveyed by the polymer, unit energy consumption and energy efficiency on the feed pocket depth, and screw speed. It has been found that the feed pocket made in the extruder barrel has little effect on the course and effectiveness of plasticized PVC extrusion and does not worsen the studied properties of the received extrudate; yet, it should be taken into account to ensure the highest polymer output and lowest energy consumption. POLYM. ENG. SCI., 54:2037–2045, 2014. © 2013 Society of Plastics Engineers     

The effect of the feed section groove taper angle on the performance of a single‐screw extruder

A new mechanism is described that allows adjustment of the groove geometry in grooved feed extruders. This mechanism enables efficient, continuous and independent change of the groove geometry during the extrusion process. The patented solution of the activated grooved feed section enables one to change the number of grooves, taper angle and, connected with it, groove depth. The paper contains the graphical presentation of the selected results of experimental studies of autothermal extrusion of a medium density polyethylene in an extruder with the grooved feed section in which the groove taper angle, and thus groove depth, was changed during the extrusion process. The influence of changing the groove taper angle in the range from 0 to 5.236 × 10^?2 rad and screw speeds ranging from 177 to 279 rev/min on extruder output was studied. The energy efficiency of the extruder was studied as well.     

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.     

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。     

螺杆挤出式3D打印机结构设计与仿真分析

分析了传统桌面级FDM型3D打印机与螺杆挤出式3D打印机的挤出原理,为提升桌面级FDM型3D打印机对打印材料的兼容性并降低打印材料的制作成本,设计了螺杆挤出式3D打印机新结构,具有螺杆与机筒便捷拆换功能。结合设计计算获得了适用于打印丙烯腈-丁二烯-苯乙烯共聚物（ABS）材料的螺杆计量段结构,在螺杆低转速与小型化的要求下,可实现小流率高精度打印并可通过提高转速获得更高的流率。通过仿真实验的方法,分析了计量段熔体的速度场、压力场以及剪切速率场的特征。使用最小二乘法,得出了螺杆转速与出口流率对应的回归方程,验证了计算结果的合理性。结果表明,螺杆挤出机构能够适用于3D打印,可降低打印成本并拓宽可打印物料的选择范围,并可通过对螺杆转速的控制实现对物料挤出流率较为精确的调节。     

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     

The effect of melt viscosity on thermal efficiency for single screw extrusion of HDPE

In this work, a highly instrumented single screw extruder has been used to study the effect of polymer rheology on the thermal efficiency of the extrusion process. Three different molecular weight grades of high density polyethylene (HDPE) were extruded at a range of conditions. Three geometries of extruder screws were used at several set temperatures and screw rotation speeds. The extruder was equipped with real-time quantification of energy consumption; thermal dynamics of the process were examined using thermocouple grid sensors at the entrance to the die. Results showed that polymer rheology had a significant effect on process energy consumption and thermal homogeneity of the melt. Highest specific energy consumption and poorest homogeneity was observed for the highest viscosity grade of HDPE. Extruder screw geometry, set extrusion temperature and screw rotation speed were also found to have a direct effect on energy consumption and melt consistency. In particular, specific energy consumption was lower using a barrier flighted screw compared to single flighted screws at the same set conditions. These results highlight the complex nature of extrusion thermal dynamics and provide evidence that rheological properties of the polymer can significantly influence the thermal efficiency of the process.     

A study of degradation of high density polyethylene in a corotating intermeshing twin screw extruder

A study of the effect of extrusion conditions on the degradation of high density polyethylene was carried out. The extent of degradation was quantified by dynamic viscometry. The effect of barrel temperature profile, screw speed, and feed rate on the degradation of high density polyethylene was determined. The viscosity response of high density polyethylene is complex with respect to extrusion conditions. Residence time studies were carried out to correlate the viscosity data. Simulations of simple theoretical models give an insight into the flow behavior of the polymer in a twin screw extruder.     

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.     

新型螺杆挤出机固体输送理论的研究

介绍了一种嵌套式新型螺杆挤出机。在固体输送段对内螺杆的两种等效情况下固体塞的运动和受力作了深入分析。理论上证明了这两种情况下的固体输送机理与外螺杆的情况相同,均建立在固体摩擦输送机理基础之上;讨论了牵引角、摩擦因数和螺纹升角对上述三种情况固体输送流率的影响。结果表明,螺杆旋转机筒静止和螺杆静止机筒旋转两种情况下固体输送流率相差不大,而螺杆机筒同时旋转情况下的固体输送流率远大于其他两种情况。增大牵引角、降低螺杆表面粗糙度和提高机筒内表面的摩擦因数均有助于提高固体输送流率。螺杆旋转机筒静止和螺杆静止机筒旋转这两种情况下最佳螺旋角均为17°左右,而螺杆机筒同时旋转情况下最佳螺旋角为15°左右。     

Modeling the solids conveying zone of a novel extruder

On the basis of the theory of relative motions, a novel nested screw extruder was invented in which one rotating outer screw acted as the barrel for an inner screw; the combination of the outer screw and outer barrel was the other extrusion system. It was realized that centrifugal force resulted in the difference between the forces acting on the solids by the screw and by the barrel, which further compacted the solid pellet or powder. These factors benefited the frictional drag of solids and the early melting. This was consistent with the fact that the solids conveying flow rate increased greatly when the barrel and screw rotated oppositely at the same time. Thus, centrifugal force and material compressibility were significant in the feeding zone. A mathematical model was developed to calculate the output, pressure, and velocity of the solids in the screw down‐channel with consideration of the centrifugal force and material compressibility. The predicted pressure distribution and output were better than those by previous models in fitting the experimental data. The simulations revealed that the maximum traction angle was close to 90° ? the helix angle for maximum output in contrast to the maximum traction angle of 90° predicted by the Darnell–Mol theory. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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。     

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.     

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     

Simulation of transient process in melting section of reciprocating extruder

Plastic injection molding machine that can be classified as reciprocating extruders are among the most widely used machines in industry. However, most studies in the injector design were based on steady state models developed for extruders that involved no reciprocation. This over-simplified model leaves out the most important aspect of reciprocation. The authors of this paper have derived a transient melting model that takes care of the change from the conventional steady extrusion to that of a discontinuous transient process. This paper describes simulations conducted on the derived model to explain observation that cannot be explained by the steady extrusion model in practical experiments. The simulation was conducted by using parameters given in Donovan's experiment [Polym Engng, 11 (1971) 353]. The simulation results are found to qualitatively match with the experimental results. It proves the validity of the model. Simulation has also been conducted with the model on materials that their viscosities are temperature and shear rate dependent. The result has shown that screw rotation speed, screw axial movement speed, barrel thickness, barrel heat capacity, temperature of heater and polymer are factors affecting the melting speed and the transient effects.     

橡胶在销钉机筒挤出机中的流动分析

建立了销钉机筒挤出机的非牛顿流体流动模型,并计算出压力场、流动场和螺杆的特性曲线,结果表明,随着流体非牛顿特性的增强,螺杆的生产能力降低;随着螺杆螺槽上切口的增多,逆流增多,挤出产量降低,机筒上的销钉对挤出特性影响很小,销钉式挤出机的挤出特性与螺杆上有切口的挤出机的挤出特性相似。     

Effect of dissolved gas on the viscosity of HIPS in the manufacture of microcellular plastics

The microcellular plastics (MCPs) process is a foaming process that has been developed to reduce the weight of a product without significant changes to the mechanical properties. To apply microcellular plastics to mass production systems such as extrusion, injection molding, and blow molding, research must be done on material properties, such as viscosity, glass transition temperature, and melt index of polymer resin. Among the properties, it is critical to predict the change in viscosity with the amount of inert gas, which can be an index of the injection molding working condition of polymer resin. The purpose of this paper is to study the relationship between the amount of dissolved gas and the viscosity of high impact polystyrene (HIPS) resin in extrusion. The experiment was carried out with newly designed gas supply equipment and with a screw and die modified for MCPs. In addition, a pressure gauge was set up on the end of a barrel for measuring the pressure change. The experiment has shown that the viscosity of polymer decreases with increasing amounts of inert gas. A new model was applied to estimate the viscosity change as a function of the amount of dissolved gas.     

Research on the micro-extrusion characteristic of mini-screw in the screw extruding spray head

Extrusion production capacity is a chief factor of measuring how good the extruding spray head of Fused Deposition Modeling (FDM) is. The main geometrical parameters of screw and barrel (the active length of screw, the diameter of screw, the helix angle, the width of screw arris, the depth of screw channel, the clearance between screw, and barrel, etc.,) and the processing parameters such as screw speed, the pressure of nozzle are closely related to extrusion production capacity. In this article, the spray head is designed to be a special mini-screw extruding spray head and the mini-screw is different from common screw. The characteristics of the mini-screw in the research are that it is small in size, with narrow screw channel and wide screw arris structurally. Based on hydrodynamics and melt conveying theory, the micro-extrusion characteristics of mini-screw used in the screw extruding spray head of FDM were discussed in detail in this article. The relationship between extrusion production capacity and the main geometrical parameters of screw and barrel and the processing parameters is researched. Theoretical analysis was performed to find out the quantitative relationships between production capacity of extrusion and main parameters (the screw speed, main geometrical size of screw, the clearance between screw and barrel, and the pressure of nozzle, etc.,) so that the theoretical guidance on the design of spray head with mini-screw could be provided. The characteristic curves of mini-screw and nozzle are analyzed to find out the jointed work point of spray head. The main factors influencing extrusion capacity of nozzle are discussed in this article. Furthermore, the development of FDM will be promoted and the micro-extrusion theory would be more perfect by the research.     

Dynamic behavior of a single screw plasticating extruder part I: Experimental study

The dynamic responses of a 2–1/2 inch single screw plasticating extruder and extrusion line were investigated. Step changes in screw speed, take-up speed, back pressure, and processing materials were used to determine the transient responses of barrel pressures, die pressure, melt temperature, and extrudate thickness. Dynamic responses of the entire extrusion line can be explained by the flow mechanism of the extruder and the logical properties of the polymer used. A capillary rheometer was also used to determine if it could simulate pressure responses in the extruder for screw speed changes. Results showed that capillary rheometer was helpful in estimating the short term pressure responses in the die.