双螺杆磨浆机螺纹元件三维流场分析

建立了双螺杆磨浆机中螺纹元件流道的三维几何模型,利用FLUENT有限元软件对悬浮液纸浆在流道内的流动状态进行了模拟分析,得出了速度场和压力场.在此基础上,对剪切速率及剪切粘度进行了模拟计算.结果表明,纤维物料通过正向螺纹段时,受到较大的挤压和剪切,促使纤维分离并帚化分丝;纤维物料通过反向螺纹时,同样受到剪切,并能使物料匀整化.     

啮合同向双螺杆挤出机不同螺杆构型对其流场的影响

目的：探究啮合同向双螺杆挤出机不同螺杆构型对流场的影响,改善聚乳酸的材料性能。方法：应用Solidworks软件建立双头螺纹元件的几何模型,在Polyflow中进行数值模拟,借助Fieldview软件对仿真结果进行后处理分析,并对比剪切速率场、压力场、速度场、黏度场以及停留时间分布曲线RTD,得出螺槽深度对流场的影响。结果：在中心距相同的情况下,通过改变螺纹元件的外径和内径之比改变螺槽深度,在相同的工艺条件下,同向双螺杆流道内各物理场以及混合性能均存在较大差异;与构型二相比,构型一的剪切作用更强,但构型二的建压能力更好;挤出过程中,构型二轴向混合能力较好但自清洁能力较差,而构型一轴向混合能力较差、自清洁能力较好。结论：螺槽深度的改变对流道混合性能有着一定影响且存在规律性,可有效指导双螺杆挤出机螺纹元件的设计。     

同向全啮合双螺杆植物蛋白挤出机不同螺杆元件的仿真分析

为了明确和量化同向全啮合双螺杆挤出机各螺杆元件的功能,增加配置用于生产植物基肉双螺杆挤出机螺杆的合理性,以低温脱脂花生蛋白粉的物性参数为条件,对SLZ36型挤出机的3种元件长度为32 mm的螺杆元件双头螺旋元件、5啮合盘啮合元件及3齿形盘齿形元件的剪切速率、混合指数、物料停留时间、最大剪切应力分布进行仿真分析。采用Solidworks软件建立元件的几何模型,应用Gambit软件进行模型的网格划分及网格质量分析,在Polyflow软件中进行数值模拟,通过Fieldview软件对仿真结果进行后处理分析。结果表明：通过混合指数分析得到3种螺杆元件对物料的混合性能大小为齿形元件>啮合元件>螺旋元件;通过物料停留时间分析得到3种螺杆元件的轴向混合性能大小为齿形元件>螺旋元件>啮合元件;通过剪切速率及平均最大剪切应力分析得到对物料的剪切性能大小为啮合元件>螺旋元件>齿形元件。进行植物基肉双螺杆挤出机螺杆组合时,针对目前整个螺杆配置螺旋元件最多的情况,在进行物料更换时可以合理地配置啮合元件以增加螺杆剪切能力,配置齿形元件以增加螺杆的混合能力。     

单螺杆挤出机计量段模拟研究

针对3种不同类型聚乳酸(PLA)专用螺杆的计量段结构,运用Polyflow软件进行三维流场模拟3种不同类型混炼结构,分析聚乳酸挤出过程的三维等温流场。结果表明:在相同的工艺条件下,不同的单螺杆结构,流道内聚乳酸各物理量的值存在较大差异性;普通型单螺杆的熔体的轴向速度和压力较大,利于螺杆挤出过程,但熔体剪切速率小、熔体黏度大,从而导致挤出熔体质量较差;菠萝型单螺杆的熔体的轴向速度和剪切速率较大且黏度值较小,因此具有较好的塑化能力;菠萝型和销钉型单螺杆在流道内会出现环流的情况,不利于熔体输送。     

螺棱间隙对单螺杆食品挤压膨化机熔体输送影响数值模拟

采用POLYFLOW软件对单螺杆挤压膨化机中食品熔体的三维等温流场进行数值模拟,结合粒子示踪技术,探索不同螺棱间隙(0.4,0.8,1.2mm)对食品熔体流场和混合性能的影响。研究表明:随着螺棱间隙的减小,螺棱顶端的剪切速率增大,食品熔体平均黏度变小,螺杆的轴向输送能力变差;随着螺棱间隙的增大,食品熔体的停留时间先增后减,分散混合能力变差。当螺棱间隙增至1.2mm时,物料停留时间反而比间隙值为0.4 mm时长,说明螺棱间隙过大,食品物料的停留时间将难以控制,同时对各物料组分的混合效果也较差。螺棱间隙对熔体流场和混合特性均有一定的影响,螺棱间隙为0.8mm时,既能保证对熔体的输送能力,又能保证良好的流场分布和混合效果,为比较理想的螺棱间隙。     

带捏合块的渐加速型单螺杆三维流场分析

目的:提高单螺杆挤出机的混合性能和工作效率.方法:设计了一种利用行星轮组件和混合元件的同轴渐加速单螺杆,利用Ansys/cfx对其流道进行了三维流场分析,得到了宏观压力场、速度矢量图、速度流线图以及轴向速度变化曲线并与传统单螺杆进行了对比,结果:随着螺杆转速的不断变大,物料在机筒内停留时间变短,渐加速螺杆的挤出效率得以提高20%～25%,使得耗能大大减少,由于捏合块的存在,物料在捏合块处被反复挤压,使得渐加速型单螺杆在增加产能的同时混合性能又可以得到保证.结论:同轴渐加速单螺杆高速旋转的捏合块可使物料混合更充分,且能缩短物料在螺杆中的停留时间,提高产量.     

单螺杆挤压破裂植物细胞力学模型的研究

单螺杆挤压可以破裂植物细胞,用于辅助植物有效成分的提取.通过选取单螺杆中物料运动方向上的一段微元进行受力分析,分别求得螺杆、机筒、背压对物料的作用力和物料由于自身形变而产生的作用力,得到单螺杆中压力分布的数学模型;并针对截面为正六边形的柱状植物细胞模型,得到植物细胞受力的数学模型.模型表明细胞的受力情况和螺杆自身的结构参数、螺杆转速和挤出速率有关系,在螺杆结构参数确定的前提下,可以通过调整螺杆的转速和挤出速率来改变物料的受力情况,从而达到理想的破壁效果.     

啮合异向双螺杆挤出机中螺杆端面结构参数对聚乳酸流场的影响

目的:探究啮合异向双螺杆挤出机中螺杆构型的改变对聚乳酸流场的影响。方法:通过Solidworks软件建立异向双头螺纹元件的理论模型和经两种不同方式调整结构参数后的螺纹元件几何模型，将建立的三维模型导入Gambit软件进行网格划分，再应用Polyflow软件进行流场模拟计算，最终借助Fieldview软件提取流场分布结果，对比分析修正时螺纹元件端面上结构参数的调整对剪切速率场、黏度场和速度场的影响。结果:修正时螺纹元件的结构参数经两种方式调整后均会对聚乳酸流场造成影响；两种对结构参数的调整方式均在不同程度上减小了流道内的剪切速率梯度，方式一还造成了流道内聚乳酸的黏度降低。结论:从对剪切速率场、黏度场和速度场的影响上看，经方式一调整后的螺纹元件更有利于挤出，而经方式二调整后的螺纹元件实体构型更贴近螺纹元件理论构型。     

挤压膨化对玉米豆粕混合物糊化度及脲酶活性的影响

以玉米豆粕为原料,研究了不同挤压膨化条件对挤出物的糊化度及脲酶活性的影响。通过单因素结果得知:随着出口段温度、物料含水量、螺杆转速、喂料速度的增加,挤出物的糊化度均呈现先增大后减小的趋势;随着物料配比(豆粕∶玉米)的增大,挤出物的糊化度逐渐减小。通过脲酶活性正交试验结果得知,4个因素对脲酶活性的影响顺序为出口段温度螺杆转速喂料速度物料含水量。     

挤压技术(续)

（接上期）反向旋转式双螺杆挤出机一般采用两根尺寸完全相同但螺纹方向相反的螺杆。向内反向旋转和向外反向旋转两种型式的主要区别在于压力区的位置不同。向内反向旋转式双螺杆在上部进人啮合建立高压区,在下部双螺杆脱离啮合变为低压区。物料在通过双螺杆时,会受到类似于碾轮产生的挤压作用,但因螺杆啮合紧密,势必形成极高的人口压力造成进料困难,因此,目前这种向内反向旋转的双螺杆挤出机很少被采用。向外反向旋转式曾是一种被广为采用的形式,特别适用于干粉料的加工。这种旋转所建立的高压区在下部,低压区在上部,因此有利于喂人物料。与同向旋转不同的是,物料在螺杆内形成的C型段内,因两根螺杆旋向相反而不可能从一根螺杆移向另一     

注塑螺杆熔体输送过程的工艺参数分析

运用注塑机螺杆熔体输送过程的相关理论，借助较为成熟的数学模型和几何模型，利用有限元分析软件ANSYS对注塑螺杆的熔体输送过程进行了模拟，讨论了螺杆转速和熔体压力对熔体输送过程的影响。根据讨论的结果选取了较为合理的工艺方案，并把该工艺方案的运用状况与模拟的结果作了对比。利用这种方法对塑化过程中的相应工艺参数的选取提供了一定的理论依据。     

TWIN SCREW EXTRUSION OF PINK SALMON MUSCLE: EFFECT OF MIXING ELEMENTS AND FEED COMPOSITION

The effects of type of mixing element in the screw configuration and feed composition on specific mechanical energy input and product attributes during twin-screw extrusion were investigated. The mixing elements studied were kneading, reverse screw and combination of kneading and reverse screw elements. The feed composition was changed by altering the ratio of rice flour to pink salmon muscle. Incorporation of mixing elements increased the specific mechanical energy, and water solubility index; but decreased apparent density and Warner-Bratzler shear stress. Expansion ratio was maximum with kneading elements. However, reverse screw and combination produced extrudates with lesser expansion than that obtained using conveying screws with no mixing element. Increasing the fish solids content in the feed decreased specific mechanical energy, expansion ratio, and water solubility index; but increased the shear stress and apparent density. The shear stress for 0% and 30% fish solids blends were not affected in the expansion ratio range of 3 to 10. Water solubility index and shear stress were linearly related to specific mechanical energy and apparent density respectively.     

A Basic Model for a Twin-Screw Extruder

A model based on solving thermal balance and Stokes equation in a corotating twin-screw extruder with deep screw channels was developed. The present stage of the model described the evolution of temperature in the conveying section and the isothermal evolution of pressure in the melt pumping and reverse screw elements, with a Newtonian viscosity adapted to each part of the screw; residence time distribution in the whole extruder was also computed. Experimental validation was carried out on a pilot scale twin-screw extruder CLEXTRAL BC 45 fed with maize starch. Good agreement was found between the theoretical and actual temperature and pressure profiles, as well as with residence time distribution. In standard operating conditions (30 kg/hr, 200 rpm), the pressure generation in one C-shaped chamber was computed to be about 2.2 MPa, while pressure drops were about 0.3 MPa (intermeshing zone) and 0.5 MPa (reverse screw element) while the major part of the residence time per unit of screw length was spent in the reverse screw element.     

Monitoring the Diameter Changes of Flax Fibre Elements during Twin Screw Extrusion Using X-Ray Computed Micro-Tomography

ABSTRACT

Fiber size aspect ratio is known to impact the mechanical and reinforcement properties of natural fiber-based composites. However, the representation of fiber diameter change occurring during the extrusion process is controversial compared to the length. Fiber elements undergo multidirectional stresses and complex interactions within the extruder, leading to their breakage, which consequently may modulate their reinforcing properties. To better understand these mechanisms, short fiber reinforced polymer composites were prepared from flax fibers and polypropylene matrix (PP) by melt mixing. Five sampling zones were selected along the screws, both in screw conveying elements and inside blocks of kneading discs. X-ray computed micro-tomography, and 3D images analysis were then used for monitoring sample diameter distributions along the screw profile, according to specific twin-screw compounding conditions. The effects of the considered processing condition on fiber bundle diameters decrease along the screw profile are quantified.     

SCREW CONFIGURATION EFFECTS ON STARCH BREAKDOWN DURING TWIN-SCREW EXTRUSION of RICE FLOUR

Screw configuration effects on starch breakdown and ext rudate porosity were investigated during twin-screw extrusion of rice flour. the type, length, position, of mixing elements and spacing between two elements significantly affected molecular breakdown of starch in rice flour and extrudate porosity. Generally, screw profiles with reverse screw element produced more starch breakdown and porous extrudates than those with kneading block. A systematic increase of starch breakdown was observed as the mixing elements were moved fart her from the die, with longer elements, and with increased spacing between elements. Extent of starch breakdown affected porosity of extrudates. Extrudate porosity decreased systematically with increasing distance between die and mixing element, with larger spacing between the elements, and by moving two elements (with same spacing) farther from the die, irrespective of the element type and length. Porosity increased with increasing die temperature.     

MODELING A TWIN SCREW CO-ROTATING EXTRUDER1

This work desribes the simulation of a twin screw co-rotating extruder. Based on a uni-directional analysis, the temperature and pressure profiles within the extruder are predicted from knowledge of feed and extruder characteristics. A non-Newtonian, non-isothermal viscosity model is used to describe the materials rheology. the analysis covers an evaluation of conditions within the solid conveying zone, the melt pumping zone and a melt shearing zone achieved by reverse screw elements. the total energy input (both mechanical and through the barrel) is also evaluated. the simulation work has proved satisfactory in the design and optimization of extruder operation.     

基于CFX的同轴变速双螺杆挤出机三维流场分析

目的：分析物料在改良后的同轴变速优化双螺杆挤出机流道中的工作状态。方法：运用ANSYS/CFX模拟分析双螺杆挤出机流道数值,得到物料的运动情况,并与传统双螺杆进行对比,通过宏观压力场、宏观速度场、速度流线图、速度矢量图对比分析两种螺杆的性能。结果：同轴变速优化双螺杆的建压能力、混合性能明显优于传统双螺杆,通过中段的减速输送可有效延长物料运输时间。结论：新型优化双螺杆在保留传统双螺杆优势的情况下,额外提升了建压能力和混合性能。     

Screw Configuration Effects on Corn Starch Expansion During Extrusion

Normal corn starch was extrusion cooked in a Brabender single-screw extruder. Three screws with no mixing, one mixing or two mixing elements were used to extrude the samples through a 3 mm cylindrical die nozzle at 140°C barrel temperature and 140 rpm screw speed. Dependent variables included overall and radial expansion ratios, bulk density and specific mechanical energy (SME). Extrudates were ground and re-extruded using the same three screws, and the same extrusion conditions. Significant differences (P < 0.05) in bulk density, SME and radial expansion ratio were found on re-extrusion. No changes occurred in overall expansion ratio (P < 0.05).