Residence time distribution in a twin screw extruder

The residence time distribution (RTD) in a fully intermeshing, corotating twin screw extruder was determined with a stimulus-response technique. In addition to varying three process parameters (i.e. throughput, screw rotational speed, and barrel temperature), two screw configurations were also studied: one containing four kneading block mixing sections, and the other consisting only of regular screw bushings. Although screw configuration was an important variable, it was found that for both configurations the throughput had the largest effect on RTD. The screw rotational speed was second in importance, and the barrel temperature change produced no effect. A fluid mechanical model based on the fluid flow in a partially-filled rectangular channel was used to explain the experimentally observed dependence of RTD on the process parameters. Reaction engineering approaches were adopted to compare the RTD results of two screw configurations with two idealized flows.     

Residence time distribution in a commercial twin-screw extruder

The residence time distribution of poly(vinyl chloride) (PVC) polymers in a counterrotating twin screw commercial extruder was determined and analyzed. The experimental technique involved the use of manganese dioxide as a tracer after being neutron activated and was injected into the extruder during normal operation without interrupting the poly(vinyl chloride) compound production. The experimental results enabled us to better understand the flow and mixing conditions in the extruder.     

Residence time in a single screw free helix extruder using a new solution to the biharmonic equation

A new analytical solution for the biharmonic equation was developed for single screw extrusion cross-channel fluid mechanical flow. This analysis led to a quantitative model for residence time distribution when combined with the historic solutions of the drag and pressure flow in the rectangular channel in the single-screw extruder. The focus of the theoretical and experimental investigation here was to examine how closely the new analytical solution correlated with experimental residence time data for a free-helix extruder. This new extrusion device was operated as both a conventional extruder and a more positive displacement device by using only helix rotation as the pump. The Moffatt eddies that occur in the quiescent corners of the rectangular channel with screw rotation were found to have a strong effect on the residence time of the extruder. Because there were no quiescent corners for the free-helix flow there was essentially no residence time tail for this mode of extruder displacement. The theoretical results for a sheet of dye spanning the screw channel width and dye “blobs” were compared with experimental results for both modes of operation. In all cases, the experiments and the theory predictions were essentially consistent.     

单螺杆挤出机中聚合物熔体停留时间分布预测

基于有限差分数值模拟技术 ,提出了预测聚合物熔体在单螺杆挤出机内停留时间分布半解析模拟方法 ,得到了不同操作参数下的停留时间及其函数的分布曲线。结果表明 ,无因次挤出流量越小 ,聚合物熔体在单螺杆挤出机内的停留时间就越长 ,而且分布越宽。所提出的方法能够反映耦合流场及压力反流对停留时间分布的影响 ,能更真实地反映聚合物熔体在单螺杆挤出机内的停留时间分布     

Residence time distribution of a pharmaceutical grade polymer melt in a single screw extrusion process

The residence time distribution (RTD) of a flowing polymer through a single screw extruder was studied. This extruder allows injecting supercritical carbon dioxide (scCO₂) used as physical foaming agent. The tested material is Eudragit E100, a pharmaceutical polymer. RTD was measured at various operating conditions and a model describing RTD has been developed. High screw speed or high temperature implies short residence time, but these parameters do not have the same effect on polymer flow. In the flow rate range studied, scCO₂ has no significant influence. A mathematical model consisting of a plug flow reactor in series with a continuous stirred tank reactor (CSTR) cross-flowing with a dead volume fitted well the experimental data.     

一种往复运动的单螺杆挤出机

本文介绍的是一种螺杆往复运动的单螺杆挤出机,具有剪切均匀、高分散、高填充、拉伸熔体等特点。尤其是螺杆与机筒结构布局,齿轮箱往复运动的结构设计具有一定的特点。     

注塑螺杆计量段物料的停留时间分布

根据注塑螺杆的工作特点,计算了计量段的停留时间分布函数及表征计量段纵向混合能力的优化目标函数停留时间分布函数的方差。通过对无量纲最短停留时间的分析,得到了计量段物料的停留时间分布函数及其方差的影响参数。     

Mixing studies in the single screw extruder

Laminar mixing in a single screw extruder between two miscible liquids is considered. Studies are presented which examine the mixing performance in single screw extruders with mixing sections, variable geometry screws, and multi-viscosity mixtures. Model extruders, set up on engine lathes, were used to mix colored silicone rubber which eventually cured in the screw channel. The cured silicone was then removed and sliced to measure the mixing. Results show mixing as a function of both down channel location and total average strain. For the mixing section study, results support the theory of interfacial area reorientation as the key mechanism in mixing section performance. Increasing viscosity ratio for the multi-viscosity study showed a decrease in mixing rate.     

Randcastle develops single screw compounding extruder

Randcastle Extrusion Systems, Inc. has developed a new compounding extruder. The company says that the Taskmaster is a single screw extruder that can compound and devolitilize. The Taskmaster is claimed to take single screw extruders into applications that were previously only possible with twin screw extruders. The prototype is a marked departure from Randcastle's vertical line of extruders with its first entry into the traditional horizontal extruder market.This is a short news story only. Visit www.addcomp.com for the latest additives and compounding industry news     

Reactive processing of polyethylenes on a single screw extruder

The modification of low density polyethylene, linear low density polyethylene, and their blend by dicumyl peroxide at the time of the extrusion on a single screw extruder is reported. The study shows that the optimum conditions of modification can be determined on a torque rheometer and these can then be applied for actual extrusion. A low level of crosslinking can be introduced by reactive extrusion for improving the heat stability without adversely affecting the processing behavior. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2545–2549, 2001     

挤出过程停留时间分布影响因素之间的交互作用

应用全析因设计方法,研究了捏合块角度、比产率(喂料速率/螺杆转速)和螺杆转速对双螺杆挤出机机筒不同位置的延迟时间和平均停留时间的影响,考察了各因素之间的交互作用。结果表明,在所选取的操作条件下,螺杆转速对延迟时间和平均停留时间的影响最大,捏合块角度与比产率的影响程度相近。3因素两两交互作用对延迟时间的影响程度由大到小依次为捏合块角度与比产率、螺杆转速与比产率、捏合块角度与螺杆转速;对平均停留时间的影响由大到小依次为比产率与螺杆转速、捏合块角度与比产率、捏合块角度与螺杆转速。3因素3阶交互作用对平均停留时间的影响比较显著。     

Optimisation of silane grafting in single screw extruder

Abstract

Reactive extrusion is an attractive means of polymer processing since the shaping and reaction takes place in a single operation. Silane grafting of low density polyethylene has been achieved in a single screw extruder. The optimum conditions for silane grafting, i.e. temperature, shear rate, and silane and dicumyl peroxide concentrations, were determined on a torque rheometer and extrusion was then performed under optimum conditions. The study shows that an optimum low level of grafting/crosslinking can be introduced into polyethylene during extrusion for better mechanical behaviour and/or thermal stability without aecting the processability.     

An ultraviolet method for the determination of the residence time distribution in a twin screw extruder

The stereoselective substitution of chlorine atoms was used to graft anthracene and phenyl groups onto the poly(vinyl chloride) (PVC) backbone as ultraviolet (UV) tracers for the assessment of the residence time distribution (R.T.D) of PVC chains during the extrusion of rigid and plasticized PVC. The residence time distribution obtained using these-grafted tracers was compared with that obtained using a free UV tracer (anthracene). The polymeric tracer had a narrower R.T.D and a shorter mean residence time. This difference of behavior between a free and grafted tracers was attributed to the compatibility of these tracers with the PVC.     

Study of mixing of liquid/polymer in twin screw extruder by residence time distribution

The present investigation is an experimental study of the mixing of two phases of strongly different viscosity in a co‐rotating twin‐screw extruder (TSE). Two cases were considered: a miscible (copolymer of ethylene and vinyl acetate/bis(2‐ethylhexyl)phtalate [EVA/DOP]) and an immiscible (EVA/ethylene‐glycol [EVA/EG]) binary system. The residence time distribution (RTD) has been determined for each phase of both systems for different screw profiles and different operating conditions. The behavior of the first system is simple: the type of flow is basically the same. However, in the case of nonmiscibility, when the flow rate is high, the shape of the RTD of both phases may be different. We interpret this result with the appearance of a lubrication phenomenon. POLYM. ENG. SCI., 45:926–934, 2005. © 2005 Society of Plastics Engineers     

Temperature-induced pressure gradient in the clearance between screw flight and barrel of a single screw extruder

The effect of temperature-induced pressure gradients occurring in drag flow in a narrow gap between parallel walls, when a viscosity gradient in flow direction is present is described and analyzed. The effect dominates the technologically important clearance flow problem, where the viscosity gradient originates from temperature changes. The polymer layer in the clearance between screw flight and barrel of a single screw extruder supposedly has to separate the metallic surfaces from each other. In certain operating conditions this bearing function breaks down and dry friction between metallic surfaces occurs. This failure, which has not yet been explained, is reasoned to be caused by the temperature-induced pressure flow in the clearance.     

Measuring the residence time distribution in a twin screw extruder with the use of NIR‐spectroscopy

The mean residence time (MRT) and the residence time distribution (RTD) of polypropylene in a twin‐screw extruder was determined directly in‐line with the help of near infrared (NIR) spectroscopy and the use of an UV‐absorber as tracer. Different experiment alignments such as screw speed, mass throughput, back pressure as well as tracer content and their influence on MRT and RTD have been investigated. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39919.     

单螺杆挤出机加工条件对橡胶返原的影响

近年来,聚合物材料的回收利用受到关注。对于热塑性材料,只要将材料加热和熔融就可以实现回收利用;对于热固型材料如橡胶,可供选择的回收利用方法就受到较大限制。但从经济和环境方面考虑,橡胶应该被回收利用。对通用单螺杆挤出方法作为连续橡胶回收工艺使天然橡胶屑粒返原进行了研究。研究发现,挤出机温度所起的作用似乎比螺杆速度重要得多。     

Residence time distribution in continuous crystallisers

The theory of continuous crystallisation (especially of sucrose) in crystallisers connected in series, in which a suspension of growing crystals is fed forward through the system without backmixing, is presented, and the calculation of the minimum coefficient of variation that can be attained under stated conditions is described. Two cases specifically considered are: (1) stirred reactors of equal mean residence times connected in series, and (2) tubular reactors in which the residence time distribution is given by a Gaussian error function. Reduction of coefficients of variation either by connecting reactors in series or by extending a tubular reactor in the axial direction is considered. Series connexion is always superior to extension because it prevents backmixing at the points of connexion.     

Residence time distribution in twin-screw extruders

Twin screw extruders are finding increased usage in reacting and devolatilizing applications. Using self-wiping profiles, the twin screws fulfill the requirement that there be no “dead” or “unmixed” zones. Agitator design must be chosen with care so that a reasonable balance can be obtained between forwarding rate, surface-generation rate, vapor passageway, power, and axial mixing. Techniques have been developed for measuring residence time distributions and characterizing axial flow behavior. The method also permits direct determination of the holdup in starved barrel applications. Data on residence time distribution are presented for 4-in. diameter twin screw equipment with a variety of rotor configurations.