美式复合聚合物异型材挤出成型关键技术

美式复合聚合物异型材(以下简称美式异型材)挤出成型设计包括挤出模头成型设计、定型模冷却成型设计以及水箱冷却定型块设计。挤出模头成型设计关键是挤出流道应平滑过渡,熔体流出模头时流速应均匀一致;定型模冷却成型设计关键是美式异型材冷却均匀、真空吸附压力均衡;水箱冷却定型设计关键是美式异型材局部功能区挤出阻力减小。通过有限元数值模拟和结合并行工程的CAD/CAE/CAM网络系统专家数据库,进一步优化设计,结果表明,熔体从模头出口处均匀挤出,经定型模、水箱冷却成型,美式异型材结构尺寸及性能完全符合要求。     

PMMA/PVC表面复合异型材共挤出成型设计优化

聚甲基丙烯酸甲酯(PMMA)/聚氯乙烯(PVC)表面复合异型材(以下简称复合异型材)是通过共挤出模头成型,以共挤出模头出口处复合异型材截面上各子区域的流速相等为优化目标,以对流动均匀性有较大影响的压缩段间隙为设计变量,有限元数值分析模拟并和ERP系统及并行工程的CAD/CAE网络系统挤出模头专家数据库相结合,通过实例设计优化证明,优化后共挤出模头出口处复合异型材熔体各区域流速均匀性显著提高,复合异型材的型胚质量显著提高,其结构尺寸、性能完全符合要求。     

气辅共挤出流道中聚合物流动过程的数值分析

建立了气辅条件下两种聚合物在矩形流道中共挤出流动的三维非等温数值分析模型。用粘弹性流体模型(PTT模型)描述熔融聚合物的特性,Arrhenius方程表示流动对温度的依赖性,并且考虑聚合物相对于流道壁面的滑移以及不相容聚合物熔体间滑移的边界条件。用有限元方法数值模拟了聚合物成型过程,将计算结果与普通共挤出成型流动进行了对比分析。结果表明,气垫层的加入,将使聚合物熔体的压力降减低20%～40%;使流道出口处的速度场分布均匀,速度场的最大值下降约50%;气垫区聚合物的自由流动还将对共挤出界面的形状和位置有一定的影响。     

PET薄膜挤出成型有限元模拟和阻流分析

设计了厚度为0.12mm的聚对苯二甲酸乙二醇酯(PET)薄膜衣架式挤出流道,使用有限元软件模拟了聚合物熔体的流动规律,获得了流道内部的压力场、速度场和温度场的分布,分析了阻流设计对流场的影响。研究表明,流道结构对压力分布影响显著,对速度、温度分布影响不明显;流道阻流部分尺寸较小的改变,会引起流道内部熔体压力较大的变化,易导致挤出成型过程的不稳定,从而显著影响产品质量。此外,挤出流量对流场压力分布影响很小。     

气体辅助工艺对曲线型异型材共挤成型的影响

基于流变学基本方程和PTT本构方程,建立了三维粘弹曲线型塑料异型材包覆共挤成型数值模型,运用有限元方法对数值模型进行了模拟计算,分析研究了气体辅助工艺对曲线型异型材共挤成型过程中挤出胀大、扭曲变形及口模内流场分布的影响。研究结果表明,传统共挤成型时,共挤制品的挤出胀大及变形、口模内熔体速度场、压力场、剪切速率及应力场等的分布均随着壳层熔体黏度的变化而变化,而气辅共挤成型时,共挤制品的挤出胀大和变形现象以及口模内熔体流场的分布均与芯壳层熔体的物性无关,能实现制品截面形状和尺寸与口模截面形状和尺寸保持一致的精密共挤。     

聚合物熔体复合挤出胀大过程的数值模拟及可恢复弹性形变分析

建立了两种聚合物熔体流经矩形流道共挤出的三维数值计算模型,采用有限元方法数值模拟了共挤出成型过程及胀大过程,得到了速度场、压力场、应力场,并利用数值计算方法得到了共挤出流动过程的可恢复弹性形变场,分析了挤出胀大率以及可恢复弹性形变的变化过程。结果表明,在共挤出流动的胀大段,共挤出界面的形状和位置发生了改变;经矩形流道共挤出得到的挤出胀大末端截面形状为不对称的鼓形;在共挤出界面附近可恢复弹性形变值存在极值,运用数值方法计算可恢复弹性形变可以对流动过程中可能存在的缺陷进行预测。     

等温准热压印中聚合物微结构成型的分析

在传统平板微热压印中,模具需要反复的加热和冷却,工艺循环时间长,存在微结构成型效率低的缺点。文中创新性地提出一种等温准热压印工艺,可有效解决这一问题。首先在研究此工艺原理的基础上,采用有限元模拟的手段探究聚合物微结构的成型过程。模拟分析可知,聚合物微结构的成型是边冷却边压印的过程,模具温度显著影响微结构的复制精度;而聚合物基片预热温度过高不会提高微结构的复制精度,却增加了脱模缺陷的可能性。模拟得到的规律可为等温准热压印实验工艺参数的选取提供依据。最后通过实验验证了模拟规律的正确性及工艺的可行性。     

热压罐成型工艺所用框架式模具的变形分析

模具在使用过程中的变形会影响到复合材料制件的固化变形,为了控制复合材料制件的成型质量,就要了解框架式模具在热压罐固化成型工艺过程中的变形情况。建立了模具变形的数值模拟预报方法,将计算结果与实际模具测量结果进行对比,本文中所提供的有限元分析计算模型可对实际情况进行较为精确的模拟。考察了平板型框架式模具在整个固化工艺过程中的变形情况,数值计算结果表明：型面翘曲变形量与模具温度的分布有关,而与模具温度的大小无关;模具翘曲变形量的峰值出现在降温阶段的中间时刻,且该变形量能够保持一段时间;最大变形时刻整个模具型面与进入热压罐前相比中心位置的变形最大,周边位置的变形最小。     

聚合物共挤出过程的挤出胀大有限元分析

采用有限元方法模拟了非牛顿流体在共挤出过程中的挤出胀大现象,分析了模具流道收敛角、模具内壁的表面质量以及平直段长度对共挤出聚合物挤出胀大的影响。结果表明:当流道收敛角α在0°~30°区间变化时,角度的大小对两种熔体的挤出胀大率均有一定的影响;当30°≤α≤90°时,角度的变化对熔体挤出胀大率几乎没有影响。模具内壁的表面质量对挤出胀大率影响较大,改善模具壁面质量可以有效地减小挤出胀大率。适当增加流道出口平直段长度可以显著减小挤出胀大率。     

基于三维有限元模拟的聚合物复合型材共挤出过程分析

建立了两种聚合物熔体在圆柱形流道中共挤出流动的三维数值计算模型,采用有限元方法数值模拟了复合棒材(LDPE/PS)的共挤出成形过程,并对共挤出界面的形状、入口与出口的速度、流动过程的压力降以及入口流量对界面的影响等进行了分析。结果表明,在对接棒材的共挤出过程中,当入口流量相同时,共挤出界面偏向低黏度熔体一侧;入口流量较小的变化即引起共挤出界面的形状与位置较大的变动,在对接棒材的成形过程中为获得稳定的流动,须严格控制入口流量的变化。最后将数值计算得到的界面与实验结果进行了对比,表明数值计算的结果与实验结果是一致的。     

Effect of extrusion stem speed on extrusion process for a hollow aluminum profile

Extrusion stem speed is one of important process parameters during aluminum profile extrusion, which directly influences the profile quality and choice of extrusion equipments. In this paper, the extrusion process of a thin-walled hollow aluminum profile was simulated by means of the HyperXtrude commercial software. Through a serial of numerical simulation, the effects of stem speed on extrusion process, such as metal flow behavior at die exit, temperature distribution, extrusion force, and welding pressure, have been investigated. The numerical results showed that there existed an optimum value of stem speed for flow velocity distribution. With the increasing stem speed, the temperature of the extrudate and required extrusion force increased, and the welding quality of extrudate would be improved. Through comprehensive comparison and analysis, the appropriate stem speed could be determined for practical extrusion production. Thus, the research results could give effective guideline for determining initial billet and die temperature and choosing the proper extrusion press in aluminum profile industry.     

振动力场对聚合物挤出胀大的影响

为了改善聚合物材料的挤出胀大现象,将振动力场引入聚合物的挤出过程.采用动态毛细管流变仪对不同振动参数下的挤出胀大进行研究,建立了相应的物理模型和数学模型,并借鉴前人的工作成果,运用数学推导得到了挤出胀大与振动参数间关系的解析式.研究表明:随着振动频率和振幅的增加,挤出胀大呈非线性减少,并最后趋于稳定.     

L-alpha-glycerophosphate and L-lactate electrodes based on the electrochemical "wiring" of oxidases.

The title electrodes were constructed by coimmobilizing the respective FAD oxidases on solid electrode surfaces with a poly(vinyl pyridine) polymer which was N-derivatized with bromoethylamine and Os(bpy)2Cl2. The redox-polymer-enzyme hydrogels were cross-linked on the electrode surface using poly(ethylene glycol) diglycidyl ether. As in the case of glucose oxidase, the redox polymer acts as an electron relaying "wire" transferring electrons directly from the enzymes' FADH2 centers to the electrode. This transfer competes with the natural process of reoxidation of FADH2 by molecular oxygen. The variation of the response of these electrodes with the atmosphere (N2 or air), pH, and substrate concentration was determined. The pH profile of the electrocatalytic current differs from that of the activity of the free enzymes, exhibiting a broader maximum, shifted to higher pH values. The observed sensitivities and linear ranges are respectively 2 x 10(-2) A M-1 cm-2 and 2.7 mM for L-alpha-glycerophosphate, and 0.3 A M-1 cm-2 and 0.2 mM for L-lactate that may be compared to 2 x 10(-2) A M-1 cm-2 and 10 mM for glucose. The 0-90% response time for all electrodes is 1 s or less.     

Numerical investigation of an arc inlet structure extrusion die for large hollow sections

This paper aims to improve the working life of extrusion dies by optimal structure design, which plays an important role in mass production. First, an arc-shaped inlet die structure for an aluminum large-hollow-section profile was developed. Second, a three-dimensional finite-element model of the porthole extrusion process was established using an arbitrary Lagrangian-Eulerian method. Third, the comparison of the formability was analyzed and discussed, including the diversity of extrusion forces and uniformity properties between the proposed design and two traditional design schemes using the same extrusion process. A group of square-profile extrusion dies was used to set up a L16_4_3 orthogonal experimental scheme, considering the side length of profiles, L, with four levels, 110, 100, 90, and 80 mm; inlet angles, α, of the porthole bridge of 0°, 10°, 20°, and 30°; and profile wall thicknesses, t, of 1, 1.5, 2, and 2.5 mm. The results of the orthogonal tests were similar to those of the actual production die model. Two different analysis models reached the same conclusion: the inlet angle or the arc inlet structure has a small effect on the metal flow and the forming distribution, but the arc inlet structure can alleviate the stress load of the dies. The die testing and production validation results indicate that the novel structural design of the arc inlet die will have a long working life.     

超声振动对聚合物挤出过程及制品性能的影响

描述了超声振动技术在聚合物挤出成型过程中的典型应用方式及其研究结果,重点阐述了挤出模头中引入超声振动后,超声振动对聚合物熔体挤出过程及制品结构性能的影响。     

实心边框铝型材挤压数值模拟与模具结构优化

目的针对汽车用某实心边框铝型材出口流速不均匀的现象,改进模具的工作带、阻流块和促流角结构。方法运用专业铝型材挤压成形有限元软件系统,对型材的挤压过程进行分析,模拟稳态挤压成形过程,以速度相对差作为衡量速度均匀程度的指标。结果初始模具结构挤出的型材流速不均匀。通过改变工作带长度、增设阻流块以及增加促流角的方法,使得模具出口处的金属流速变得均匀。结论改进后模具所受的压力更小,可以减小模具的磨损,增加模具寿命,模拟结果与实验吻合。     

聚合物气辅共挤成型中挤出胀大的数值模拟

以一矩形截面共挤型材为例,采用Giesekus本构方程和Navier滑移模型建立数值模型,使用EVSS、SU等有限元方法对气辅共挤和传统共挤时两种聚合物熔体在口模内外的等温粘弹流动做了三维数值模拟,得到了气辅共挤和传统共挤时的挤出胀大率、速度场、应力场及剪切速率分布。对模拟结果进行了分析和对比,结果表明,气辅共挤能消除挤出胀大和模外熔体偏转流动现象;气辅共挤时两相熔体的速度场均匀一致,熔体流动稳定,呈柱塞状挤出;熔体表面的切向和法向应力为零,因而可有效提高挤出速率,并防止制品表面"鲨鱼皮"现象的出现。     

Effects of T5 heat treatment on extrusion welds in AZ80 hollow profile

AZ80 hollow profile was produced by porthole-die extrusion. The mechanical behavior and microstructure characteristic of extrusion welds in AZ80 hollow profile during different T5 heat treatments were investigated. Five kinds of morphologies of β-Mg₁₇Al₁₂ were observed in turn in weld regions under various temperatures. Extrusion weld is not weakest region in AZ80 hollow profile in terms of hardness, the peak hardness of weld regions is roughly equal to the weld-free regions at different aging temperatures, which is attributed to similar volume fraction, morphology, and size of β-Mg₁₇Al₁₂ precipitate in weld regions and weld-free regions. The precipitate-free zones (PFZs) usually form near the welds interface in aging process, and the hardness of PFZs is usually lower than those of weld regions and weld-free regions. Aging at 200°C for 24?h is suitable heat treatment system for AZ80 hollow profile, which can achieve excellent mechanical property and simultaneously reduce the width of PFZs.     

The effect of temperature on the extrusion behavior of a polymer/ceramic refractory paste

The effect of temperature on the extrusion behavior of a polymer/ceramic refractory paste, known as taphole clay, has been investigated. Experiments were performed to determine the extrusion pressure and the viscosity of the pastes phenolic resin binder between 30 and 60°C. The extrusion parameters were determined using the Benbow and Bridgwater method [1]. As the temperature was increased, a decrease in the extrusion pressure was observed. Three of the four Benbow and Bridgwater extrusion parameters were found to be dependent on temperature and the binders viscosity. From this data a model was produced using a modified Benbow and Bridgwater equation that predicts the effect of temperature on the extrusion pressure of the paste.     

IN690合金管热挤压温升与挤压力的研究

温升和挤压力是影响钢管挤压过程的重要指标,利用热模拟实验获得了IN690合金的热加工本构关系,建立了IN690合金钢管热挤压过程的有限元模型.采用正交实验设计的仿真实验系统分析了坯料温度（T b=1000～1200℃）、挤压速度（v=20～200 mm/s）和模具预热温度（T d=300～500℃）对管材成形过程中温升...