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。     

挤出机计量段螺杆的优化设计

通过有限元与正交设计相结合的方法,对单螺杆挤出机计量段内物料的流动过程进行数值模拟,通过多目标优化计算得到的结果探讨螺杆的几何参数对计量段挤出过程的单耗,熔体输送速率及螺杆所受轴向力的影响,得出最优的螺杆参数因子水平组合.用此方法对螺杆的优化设计有一定指导意义,不但可缩短产品设计周期.而且减少设计成本.     

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。     

单螺杆挤出过程固体粒子输送的离散单元法模拟

用离散单元法对单螺杆挤出固体粒子输送运动进行模拟,所得结果与实验和塞流模型对比,进而验证了离散单元法的有效性。速度计算结果显示了螺槽内各粒子的运动情况,此外还研究了物料参数如颗粒大小、摩擦系数以及螺杆转速对固体输送量的影响。     

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...     

挤出机固体输送段物料塑性能量耗散模拟

单螺杆挤出机固体输送段承担着物料输送和提升料温的作用,该段能耗占总能耗的比例较大,为了达到节能降耗、提高产能的目的,明确该段的能量转变方式至关重要。通过构建简化计算模型,在利用Flow2000软件获得相应初始数据的基础上,运用ANAYS软件对单螺杆挤出机固体输送段物料塑性能量耗散进行了模拟,计算出了塑性能量耗散热,明确了该段的能量转变方式。     

开槽机简单螺杆挤出机的对比研究

针对轴向直槽机筒单螺杆挤出机和螺旋沟槽机筒单螺杆挤出机的结构、固体输送机理和优缺点进行了对比分析,并对其比产量和比能耗进行了对比实验研究.结果表明,通过正确的沟槽结构设计,可实现螺旋沟槽机筒单螺杆挤出机固体输送段的正位移输送,螺旋沟槽机筒单螺杆挤出机在比产量、比能耗等挤出性能指标方面均优于轴向直槽机筒单螺杆挤出机.     

螺旋沟槽单螺杆挤出机双螺棱推动理论模型的研究

通过在单螺杆挤出机固体输送段机筒内壁开设螺旋沟槽,建立了将机筒与螺杆视为一个对物料协同作用的整体的新型物理模型——弧板模型;同时将嵌入机筒沟槽与螺杆螺槽中的物料视为固体塞,提出了新型"双螺棱推动理论",弥补了单螺杆挤出机不能实现正位移输送的传统理论缺陷;最后,通过理论分析确定了螺旋沟槽挤出机由摩擦拖曳输送向正位移输送转换的边界条件方程及正位移输送下沟槽结构参数的设计准则。     

单螺杆挤出过程固体输送段的数值模拟

介绍了挤出成型过程数值模拟的现状及现有通用计算流体力学(CFD)软件在模拟聚合物流动时存在的缺陷，指出自主开发CFD程序的必要性。针对单螺杆挤出过程固体输送段的数值模拟方法，讨论了传统塞流固体输送理论的缺陷，介绍了非塞流固体输送理论的优越性及相关的有限元计算方法。并针对有限元方法的复杂性，介绍了简化的三层模型方法。计算结果表明：非塞流固体输送理论的三层模型法与有限元法计算结果接近，且优于塞流固体输送理论，而三层模型法计算方法简单，便于其在工程计算中的应用。     

沟槽机筒单螺杆挤出机固体输送产量的粒径模型研究

在分析机筒衬套沟槽槽深、螺杆螺槽槽深和加工物料粒径关系的基础上,建立了沟槽机筒单螺杆挤出机3种常见的固体输送段产量粒径模型,该模型可用于研究机筒衬套沟槽槽深、螺杆螺槽槽深和颗粒物料粒径对固体输送机理的影响并定量计算沟槽机筒单螺杆挤出机固体输送段产量。此外,通过不同的机筒和螺杆组合及不同粒径的原料在自制的在线模拟试验机上对该模型进行了验证和试验分析。     

啮合同向双螺杆挤出机不同螺杆流场仿真分析

根据啮合同向双螺杆几何学,运用Solid Works三维建模软件建立螺杆的实体模型。采用190℃聚乳酸熔体作为流体,通过ANSYS软件划分网格得出有限元模型,然后在Polyflow里进行仿真,分别得到了两种不同截面的螺纹元件的流场模拟结果。分析对比了压力场,速度矢量场、剪切速率场和黏度场,得出螺棱厚度对流场的影响。结果表明,I型截面螺杆的建压能力强于II型截面螺杆。II型截面的剪切能力强于I型截面的剪切能力,II型截面增强了螺杆的分散混合能力。     

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.     

Residence time and conversion in the extrusion of chemically reactive materials

Twin‐screw extruders offer improved control of the residence time distribution (RTD) and mixing in materials such as plastics, rubber and food. Based on the flow and the heat transfer characteristics obtained for a self‐wiping, co‐rotating twinscrew extruder, the residence time and chemical reaction are studied by tracking the particles. For normally starve‐fed twin‐screw extruders, the length of the completely filled section is calculated as function of the process variables using the coupling of the flow with the die. With a model of the solid conveying section, the RTD for the whole extruder is calculated for corn meal at different screw speeds and flow rates. The calculated variation of RTD with the screw speed and the flow rate yields good agreement with observations from many experiments. The variation of the fully filled section length, chemical conversion and mixing effectiveness are also obtained under different operation conditions. Most of the results are in qualitative agreement with experimental results and may be used as guidelines for extruder design and determination of optimal operating conditions.     

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。     

双锥型螺杆挤出机固体输送离散元分析

利用EDEM软件对一种普通锥形和两种双锥型螺杆挤出机固体输送段进行模拟.分析了高密度聚乙烯(PE-HD)颗粒在锥形双螺杆挤出机内的运动状态和分布规律.对比分析了3种锥形螺杆挤出的质量流速率、填充率、平均速度、平均压力、平均剪切应力和力矩等参数,给出了普通型和双锥型螺杆挤出机固体输送机理以及主要影响因素.结果表明,相比于...     

A theoretical melting model for plasticating extruders

A theoretical model for melting in plasticating extruders is described. Compared to previous models, this model introduces more accurate and less restrictive assumptions, adds a mass balance on the entire channel, and replaces certain approximate solutions by exact solutions. Flow of the solid bed is represented by a solid bed acceleration parameter, SBAP, which permits solid bed acceleration in a screw compression section. New experimental melting data for a variety of screw designs, polymers, and extruder sizes are presented and compared to the theoretical predictions. With the optimum SBAP, reasonably accurate model prediction of the melting profiles is observed for a wide variety of cases.     

Twin-screw extrusion technology,an original solution for the extraction of proteins from alfalfa (Medicago sativa)

The aim of this study is to develop a new approach to green plant fractionation using twin-screw extrusion, leading to the production of a green filtrate, rich in proteins and a solid fibrous residue, rich in cellulose. The influence of the screw profile on protein recovery in the liquid extract and on plant dehydration was characterized. Two screw profiles were tested, at different temperatures and liquid/solid ratios. Increasing the shearing action on the plant produces a liquid extract richer in protein; from 25% of dry matter to 31% of dry matter when two additional sections of paddle screw elements are inserted onto the screw profile. However, it leads to higher liquid retention in the alfalfa fibers and thus dehydration of the plant is less efficient. The fibrous residue still contains at least 60% humidity when the alfalfa is highly degraded, whereas less than 47% humidity remain with only one section of bilobe paddle screws on the profile. For the two screw profiles tested, the crucial parameter influencing the fraction quality (protein content of the filtrate, dry matter content of the fibrous residue) is the liquid/solid ratio.     

Analytical expressions for transient melting of polymer pellet sliding against adiabatic wall

The melting of polymer caused by friction before the solid plug is formed is an important phenomenon in the plastic injection process. To analyze the melting process caused by solid particles sliding against the bellow, a method that can simulate behavior of each particle during the calculation should be used. Particle element numerical method is hence adopted in the analysis for this research to take into consideration the behavior of each particle, where the melting of pellets caused by friction against flight and screw are assumed as friction against adiabatic walls. In this paper, analytical expressions of the transient melting process for spherical polymer pellets sliding against adiabatic wall are derived, which is essential for the numerical simulation of melting process in solid conveying section by particle element method.