单螺杆挤出机压力闭环控制系统的稳定性分析

稳定性是控制系统的重要性能,也是系统正常工作的首要条件.应用已知定理及计算方法对单螺杆挤出机压力闭环控制系统进行稳定性分析,推导出系统处于稳定状态的充分条件是:Tl>Tm(Td=0)或者K1TiTd>Tb(Tm-Ti)/K5K(Td≠0),并计算得出此单螺杆挤出机压力闭环控制系统稳态误差为零,最后通过实验验证理论推导的正确性.     

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。     

单螺杆挤出机螺旋沟槽固体段压力的实验研究

在自制的压力测试仪上对单螺杆挤出机螺旋沟槽固体输送段的压力进行了实验研究,探讨了螺杆转速,沟槽衬套、螺杆的主要结构参数以及物料的粒径大小对挤出机固体输送段压力的影响,同时将螺旋沟槽单螺杆挤出机与IKV挤出机固体输送段的建压能力做了对比.实验研究表明:螺杆转速、沟槽宽度对固体输送段压力影响较小;粒径越小,螺杆螺距越大,挤...     

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。     

耦合双槽单螺杆挤出机停留时间研究

提供了一种全新的分析挤出机停留时间的方法。在相同螺杆转速下,耦合双槽单螺杆挤出机物料的停留时间低于传统光滑机筒单螺杆挤出机和螺旋沟槽IKV单螺杆挤出机;耦合双槽单螺杆挤出机可以有效提高挤出机的熔融效率,实现高固体输送产量下的熔融效率与固体输送效率的匹配。     

单螺杆挤出固体输送段非塞流的三层模型法

依据单螺杆挤出机固体输送段的非塞流现象，把固体塞分成上、中、下三层，通过应力—速度方程，推导出产量与压力降的三次方程；详细讨论了摩擦系数对最大产量的影响，并深入地分析了单螺杆挤出机固体输送段产量与末端压力的关系，通过这些分析计算，三层模型法能很好地预示单螺杆挤出机固体输送段的压力与产量，该方法不仅简单明晰而且精度高，是一个可使用的方法     

德Troester推出高速挤出机

工程师们在提高单螺杆挤出机的经济效益并保持稳定的高塑化质量时，一般都尝试着优化螺杆和驱动装置。Troester公司开发出了一种高速单螺杆挤出机——Rotospeed PXS 45／25D。这种直径为45mm的挤出机转速高达800rpm，产量与直径60mm的挤出机一样高。     

单螺杆挤出机螺旋沟槽固体段产量的实验研究

在自制的测试仪上对单螺杆挤出机螺旋沟槽固体输送段的产量进行了实验研究,探讨了沟槽衬套、螺杆的结构参数,物料粒径大小及螺杆转速对单螺杆挤出机固体输送段产量的影响,同时将螺旋沟槽单螺杆挤出机与IKV挤出机固体输送段的产量进行了对比。实验研究表明：粒径越小,螺旋衬套沟槽越宽,固体输送段产量越高;螺杆螺距变化对挤出机固体输送段产量的影响很小;IKV直槽挤出机固体输送段的产量明显小于螺旋沟槽衬套挤出机的固体输送产量,而且随着转速的增加,趋势越明显。     

艺条件对单螺杆挤出机产量稳定化的影响

通过数学推导,定量研究了单螺杆挤出机各段温度及螺杆转速等工艺条件对产量的影响。     

PET熔融挤出后的特性黏数变化

分别使用单螺杆挤出机、双螺杆挤出机、反应型挤出机挤出聚对苯二甲酸乙二酯(PET),研究其在不同挤出温度、不同螺杆转速下熔融挤出后PET的特性黏数变化情况。使用双螺杆挤出机时,PET降解最严重,特性黏数平均降低23.5%。使用单螺杆挤出机:在较低挤出温度时挤出产物基本不降解;在高温时挤出产物降解明显,挤出温度每提高10℃,产物特性黏数平均降低5.8%;较高的螺杆转速有利于防止PET的降解;原料含水量越低,PET分子越不易降解。使用反应型挤出机时,PET热降解程度大于使用单螺杆挤出机。PET最适合使用单螺杆挤出机,在较低挤出温度、较高螺杆转速、物料经过烘干的情况下进行熔融挤出加工。     

Multivariable fuzzy decoupling control of the polymer electromagnetism dynamic extrusion process

The plastic electromagnetism dynamic extruder has gained wide applications because of its novel structure and fine engineering performance. In the polymer processing, melt temperature and melt pressure control is crucial to the quality of the extruded product. A new multivariable fuzzy decoupling control algorithm of melt temperature and melt pressure for the novel extruder is introduced in the transfer function matrix system, which is obtained through the experimental data with system identification. To verify the application of the proposed control algorithm, the multivariable closed‐loop fuzzy decoupling system is implemented on programmable computer controller. Experimental results show melt temperature and melt pressure can be successful individually controlled by the heater power and the screw speed. The good system performance verifies the control strategy's validity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Theoretical model for intermeshing twin screw extruders: Axial velocity profile for shallow channels

Positive displacement intermeshing twin screw extruders have been analyzed by a simple model for flow in the channel formed by the screw root and screw flights. The model considers the down channel flow to be a combination of drage flow resulting from the relative motion of the barrel and screw and pressure flow resulting from the positive displacement action of the device. The pressure flow in this situation is distinguished from pressure flow in a single screw extruder in that the pressure forces induce flow toward the die for the twin screw model rather than away from the die as in a single screw extruder. Comparison of the down channel shear rate profile of apositive displacement twin screw extruder with that of a single screw extruder with no net flow reveals that they are identical but inverted with respect to channel depth. The model presented does not consider leakage between the twin screws or the rotational motion of the second screw.     

On the dynamics and control of a plasticating extruder

In recent years, there have been many papers published on the application of process control to plasticating extruders. Much of the literature concentrates on the more classical control techniques. However, recent research has studied the application of stochastic identification techniques for building transfer function models for the extruder. In particular, the relationship of screw speed to die pressure and temperature has been studied. In the present work, both step tests and pseudorandom binary sequence tests were used to study the process dynamics of a 38 mm Killion extruder having a Iength-to-diameter ratio of 24:1. This study concentrates on the regulation of the extruder pressure in the face of its inherent surging characteristics. Variations in the quality of the feed plastic were studied through pulse and step changes in input polymer composition. Significant control problems resulted from measurement noise, which appeared at the same frequency as the screw rotation speed. Various mathematical filters to reduce the effect of this noise on the control variables were studied.     

单螺杆挤出机螺杆计算机辅助设计软件的研究与开发

主要介绍了基于VisualBasic的单螺杆挤出机螺杆计算机辅助设计软件,绘图软件选用Solid works,阐述了Solidworks相对于二维CAD软件的优点,该软件能与仿真系统接口,得到挤出过程的温度、速度、压力等曲线,分析这些曲线,进而指导螺杆的设计。最后给出了普通三段式螺杆的设计实例。     

涤锦复合超细纤维螺杆挤压机变频调速系统抗干扰改造

阐述了涤锦复合超细纤维螺杆挤压机变频调速系统抗干扰改造的实例,分析了电磁干扰对变频器调速系统的干扰途径及改造措施,解决了螺杆压力控制中干扰的问题,提高了系统的控制精度,满足生产工艺的要求。     

新型PVC粉料直接成型单螺杆挤出机及应用

从硬质聚氯乙烯(UPVC)型材、管材的特殊成型规律入手讨论了单螺杆挤出机在UPVC粉料直接成型时所面临的各种问题,提出了特殊设计的IKV系统、功能螺杆、可控的排气机筒、计量喂料、螺杆控温等五个有关UPVC干混粉料直接成型的关键。同时介绍了这种单螺杆挤出机在生产中的应用情况。     

A die rotating system for moderations of extrusion load and pressure drop profiles for molten PP and wood/polypropylene composites in extrusion processes

A die‐rotating system was proposed in this work for moderations of extrusion forces and entrance pressure drop for molten polypropylene (PP) and wood/polypropylene (WPP) composites in a capillary rheometer and a single screw extruder. The effects of processing conditions and wood loading in PP were of our interests. The extrusion force and entrance pressure drop with and without the die rotating system were monitored in real‐time. This was the first time that the die‐rotating system was used for processing of highly viscous wood/polymer composite materials. It was found that the flow properties of the molten PP and WPP composites obeyed pseudoplastic non‐Newtonian behavior. The behavior was more obvious at wood contents of above 6 wt % and in the capillary rheometer. The rotation of the die could moderate the extrusion load by 60% and entrance pressure drop by 20% in the capillary rheometer, and the entrance pressure drop by 30% in the single screw extruder, especially at the conditions where the viscosities of the WPP and the extrusion rate were high. Greater fluctuations in entrance pressure drop caused by die rotation were observed in the single screw extruder. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120:1006–1016, 2011     

Steady and transient flow of a non‐Newtonian chemically reactive fluid in a twin‐screw extruder

The flow of chemically reactive non‐Newtonian materials, such as bio‐polymers and acrylates, in a fully intermeshing, co‐rotating twin‐screw extruder is numerically investigated. A detailed study of the system transient behavior is carried out. The main transient aspects, including response time, variation of system variables, and instability of operation, are studied for both single‐ and twin‐screw extruders, since single‐screw extruder modeling closely approximates the region away from the intermeshing zone in a twin‐screw extruder. The effect of a time‐dependent variation in the boundary conditions is studied. The coupling due to conduction heat transfer in the screw barrel is found to be very important and is taken into account for single‐screw extruders. In the absence of this conjugate coupling, the response time is much shorter. Several other interesting trends are obtained with respect to the dependence of the transient response on the materials and operating conditions. Steady state results are obtained at large time. The calculated velocity distributions in the screw channel are compared with experimental results in the literature for steady state flow and good agreement has been obtained. The calculated results for transient transport agree with the few experimental observations available on this system. Chemical reaction, leading to chemical conversion of the material, is also considered and the resulting effects on the flow and transport determined. These results will be useful in the design, control and optimization of polymer extrusion processes.     

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.     

Transport in a twin-screw extruder for the processing of polymers

The fluid flow and heat transfer in polymer extrusion in a twin-screw extruder was studied numerically by using the finite volume method. In the mathematical model, the coordinate system is fixed to the screw so that it is held stationary and the barrel is moved to simplify the complicated geometry. The screw channel of a twin-screw extruder is approximated as two regions: translation and intermeshing. The flow in the translation region is similar to that in a shallow single screw extruder and is treated by the numerical methods given in the literature. In the nip or intermeshing region, strong mixing effects are expected, along with the diffusion of energy and momentum. The full governing equations are solved in this region to determine the velocity components in all the three coordinate directions. The energy equation is coupled with the equations of motion through viscosity, since the viscosity of the polymeric, non-Newtonian, fluids considered here is dependent upon the shear rate and temperature. There is no clear physical demarcation between the nip region and the translation region. Therefore, a domain matching was employed at an arbitrary location that was varied numerically to ensure that the results were independent of this location. The variation of pressure and bulk temperature along the helical channel of the twin-screw extruder is obtained, along with the shear rate. An experimental investigation of the velocity profiles in the translation region of a self-wiping twin-screw extruder, which is often used in practical applications, was carried out using a Laser Doppler Anemometer. The numerically predicted velocity profiles are compared with those from the experiments, yielding fairly close agreement.