铝制两半模轮胎模口错位和凹陷原因分析及解决措施

针对铝制两半模由于设计缺陷及使用不当等原因,成品轮胎出现模口错位及凹陷等问题,提出相应解决措施.通过改变铝制两半模的分型面位置、降低钢制模壳的铝制花纹高度和修整模口面,将成品轮胎因模口错位和凹陷而造成的废次品率由原来的3%降至0.5%.     

如何解决挤出模头渗料难题

模头咬模现象也称为口模泄料、模头渗料、积垢,是挤出加工过程中一种常见的故障问题。这种故障会引起多种产品缺陷,如可见挤出产品表面缺料、加工流程中断和产品完全开     

热收缩套管挤出过程中口模漏料的原因探析及解决途径

口模漏料是热收缩套管挤出过程中经常遇上的一个问题。它引起许多问题,从挤出管材上可见的表面缺陷到工艺紊乱,乃至热收缩套管产品报废。文章分析了口模漏料产生的原因,从优化热缩管挤出物料配方、调整优化挤出设备和模头设计优化及工艺调整三方面对预防口模漏料的发生进行了探析。     

圆环和锥形口模挤出吹塑的数值研究

用Polyflow软件的Carreau本构模型,数值模拟了用于管材挤出吹塑和型坯成型的圆环口模和锥形口模内熔体及其型坯的三维等温流场,考虑了挤出胀大和垂伸效应的综合影响,分析了两种口模的差异.数值计算结果表明,对于同一直径和口模间隙的环形口模和锥形口模,在相同入口流量下,环形口模内熔体的压力梯度大于锥形口模,环形口模成型型坯的厚度小于锥形口模,环形口模成型型坯的直径大于锥形口模;环形和锥形口模内熔体的压力梯度随着入口流量的增加而增加,在环形和锥形口模成型型坯的底端,型坯的厚度和外半径随着入口流量的增加而增加;锥形口模成型型坯厚度较环形口模对流量更敏感.     

衣架式口模设计计算的一种改进

采用表征值方法，根据等压线平行于模唇的流动模式，并考虑歧管斜率的影响，对衣架式口模圆形截面歧管系统的设计公式进行了改进，不但使口模结构设计与材料的性能与流率无关，而且修正了以前文献中对歧管斜率影响的忽略而造成的流率分配的误差，从而使流动均匀性指数提高到１，并对两种流动模式的等效性给予了证明     

标准口模与小口模测试的超高MFR聚丙烯的MFR结果转换关系

分别用标准口模、半口模、小口模1和小口模2测试超高熔体流动速率(MFR)聚丙烯的MFR。结果表明,MFR为700~2600 g/10 min时,标准口模与半口模、小口模1、小口模2的MFR换算关系:标准口模测试结果为半口模测试结果的7.5倍,为小口模1测试结果的15.7倍,为小口模2测试结果的10.0倍。所得倍数关系仅限于本实验室标准口模与小口模的测试结果。各实验室在换算标准口模与小口模测试结果的倍数关系时,需先采用各口模测量超高MFR聚丙烯的MFR,然后根据测量结果换算各口模间的倍数关系。     

PVC异型材挤出模具的使用和保养

本文着重论述了PVC异型材挤出模具(口模、真空定型模)在生产过程中的使用,以及模具的清理、保养等方面的注意事项,其对挤出生产的稳定,挤出制品的质量,减少和延缓模具质量缺陷的发生,延长模具的使用寿命均有一定现实意义。     

不同角度圆锥口模对聚合物熔体挤出胀大的影响

从理论上和实验上研究了圆锥挤出口模的几何结构对挤出胀大的影响,引入口模入口角、流动自然收敛角来计算圆锥型口模的挤出胀大比,从理论上和实验上指出聚合物熔体在圆锥口模的挤出胀大受到挤出口模入口角影响的一些规律.结果表明,不同角度圆锥口模挤出过程中,熔体在收敛流道受到拉伸流变,导致强烈的入口弹性效应,表现出熔体在不同角度圆锥口模挤出时有不同的挤出胀大比.当L/D较小时,挤出胀大与口模入口角有关,口模入口角θ为15°、30°时,挤出胀大较小,当口模入口角θ=45°～120°时,挤出胀大较大,但在这个圆锥口模入口角范围内,口模入口角的变化对挤出胀大影响很小;当L/D较大时,口模入口角对挤出胀大影响较小.     

塑料异型材挤出口模设计

主要对塑料熔体在圆环形口模及扁形口模中的流动机理进行分析，给出了由圆环口模及扁口模组成的口模的长度设计方法。     

聚合物口模挤出计算机模拟中的高We数问题研究

讨论了聚合物口模挤出计算机模拟中高Weissenberg(We)数问题 (HWNP)产生的可能的原因 ,指出本构方程本身固有的缺陷、流变方程的双曲线型、局部高应力梯度都有可能导致HWNP。从本构方程的选择、应力求解方法的改进和网格离散的精细化等方面详细分析了现有研究成果中提高临界We数所采取的措施。为今后解决聚合物口模挤出计算机模拟中的HWNP提供了借鉴。     

衣架式挤出模的流动模型分析及其简化设计的容许条件

从理论上分析了衣架式挤出模的两个流动模型,即熔体在扇形区内等压线平行于模唇(PIPDO)模型和任一流动路径上熔体的压力损失均相等(PLFPE)模型,并证明了这两个流动模型的等效关系。考虑到"蛤壳现象"对挤出模流动均匀性的影响,提出了挤出模简化设计的容许条件。     

C形口模共挤出胀大的三维黏弹数值研究

运用有限元方法,采用PTT本构方程和Arrhenius黏度对温度依赖方程,对C形共挤口模中的聚丙烯(PP)和聚苯乙烯(PS)两熔体进行了三维非等温黏弹数值研究,主要研究了口模入口端熔体层间界面位置（r）对挤出胀大率和界面位置稳定性的影响,研究表明,随着r的增大,口模出口处熔体的二次流动程度减弱,挤出胀大率减小;在两熔体入口流率相等的情况下,取使得两熔体入口面面积近似相等的r值,能保证口模内及口模出口端熔体层间界面位置稳定性较好。     

线性锥形衣架机头流率分布数值模拟

给出了预测线性锥形歧管衣架机头出口流率分布的计算程序,研究了影响出口流率分布的相关因素。模拟结果表明:衣架机头的出口流率分布与机头的几何参数和材料的物性参数都有关系,其中调节块区的缝隙高对出口流率分布的影响最大;基于流动指数n为常数而设计的衣架机头,如果没有调节块的调节作用是很难满足实际生产需要的。     

Effect of sloped die lip geometry on the operability window in slot coating flows using viscocapillary and two-dimensional models

As an indicator for determining the operability window in slot coating flow, the viscocapillary model considering various configurations of upstream and downstream slot die lips was tested and compared with Navier–Stokes two-dimensional model. Bead pressure and sloped lip angle conditions for uniform coating operation demarcated from leaking and bead break-up defects were quantitatively predicted from the position of upstream meniscus from both models. By comparing the results, it is confirmed that the viscocapillary model for many kinds of sloped die lips could predict the operability window accurately. It is also found that there exists vortex or recirculation regimes inside upstream and downstream coating bead regions, depending on the angles of sloped die lips, even for the stable coating flow. The flow control by die lip structure will be usefully applied to design the strategy for the reliable and optimal coating process, including vortex-free windows.     

Pressure drop of polymeric melts in conical converging flow: Experiments and predictions

It is of importance to estimate the pressure drop of polymeric materials in a converging die with an abrupt change in geometry for many polymer processes. In the present study, experiments have been conducted with an extruder and conical dies of four different converging angles for two different polymeric melts under various processing conditions. As part of the analysis, numerical calculations have been carried out using a finite element method (FEM) for a power-law fluid model, A simple formula for estimating pressure drops has also been derived based on a power-law fluid model with normal-stress effects incorporated. In particular, the formula with the normal-stress term excluded underpredicts pressure drops systematically at high flow rates, giving very similar results to those by the FEM calculation. When the normal-stress term is included, the formula is in bettor agreement with the experimental data, confirming that the normal stress effect is important at high flow rates. Other formulae in the literature have been also compared with the present experimental data.     

Rheological aspects of thermoplastic foam extrusion

Several rheological aspects of thermoplastic foam extrusion are described by a phenomenological model of the flow in an extrusion die. The macroscopic effects of the phase change, from a homogeneous polymer melt that contains a blowing agent, to a foam, are described in terms of two dimensionless parameters. α is defined as the ratio of the pressure gradient in the melt phase to the average pressure gradient in the foam phase. Θ represents the ratio of the pressure drop in the melt phase to the pressure drop in the foam phase. The position at which the phase change initiates, the exit contribution to the Bagley ends pressure correction, and the true wall shear stress in the melt phase are related to α and Θ. The quality of the foam produced is discussed in terms of the extrusion conditions and their effect on the foaming position in the die. It is demonstrated that the ends pressure correction cannot be neglected on the basis of a long die alone. Asymptotic conditions for which the phase change has negligible effect on the melt flow rate are predicted. α is calculated from the data of Han and Villamizar, who measured the pressure distribution in the die and observed the phase change directly. The prediction of α from theory is complicated by the lack of suitable constitutive relations for the foam phase. Since Θ only requires knowledge of the pressure at which the phase change initiates, it is relatively easy to evaluate.     

振荡管最佳隔热位置

就有关因素对振荡管管壁轴向导热最佳热隔阻位置的影响进行了实验研究和理论分析 .提出了一种预测最佳隔热位置的有效方法     

A study of bubble nucleation in a mixture of molten polymer and volatile liquid in a shear flow field

Bubble nucleation in a mixture of volatile liquid and polymer melt under shear flow conditions was investigated, using a light scattering technique. In the study, a mixture of polystyrene and trichlorofluoromethane was extruded through a slit die having glass windows and bubble nucleation in the flow channel was observed optically. A He-Ne laser was used to illuminate the nucleating and growing bubbles. The light flux scattered by the growing bubbles at a fixed angle was detected by a photomultiplier with the aid of a high-voltage power supply. The bubble nucleating site in the flow channel was located using a computer controlled tracking system, which was designed to move the entire optical system automatically in the three dimensional space, and also had the ability to follow the software control command and cooperate with the data acquisition system. When the site of bubble nucleation was located, the coordinates of this site in the flow channel and the experimental conditions were automatically recorded on a floppy diskette by entering a software command. The pressure profile along the flow channel was measured by pressure transducers, with the aid of a microprocessor-based pressure reading system. It has been found that the site of bubble nucleation varies with the position in the direction perpendicular to the flow direction, which is attributed to the nonuniform velocity and stress distributions in the slit flow channel. The present investigation suggests that bubble nucleation can be induced either by flow and/or shear stress; specifically, flow-induced bubble nucleation is the dominant mechanism at positions near the center of the die opening, and shear-induced bubble nucleation is the dominant mechanism at positions near the die wall. It should be mentioned that the bubble near the die wall may also be generated by cavitation brought about by the surface roughness of the wall and also by thermal fluctuations due to the heat transfer between the metal (die wall) and the mixture of polymer and volatile component. The present study indicates that bubble nucleation in a shear flow field can occur at an unsaturated condition. This is in contrast to bubble nucleation under static conditions, where supersaturation is necessary.     

木塑复合材料挤出技术研究

在传统聚氯乙烯(PVC)异型材配方、挤出工艺和模具设计的基础上,对生产木粉填充PVC复合材料的挤出技术进行了研究,归纳出适合木塑复合材料的合理配方和工艺条件;提出了新的口模和干湿定型装置的设计参数,并利用Flow2000软件对口模方案进行分析。     

An integrated analysis for a coextrusion process

An integrated numerical approach is proposed to simulate the polymeric liquid flow in a bicomponent coextrusion die with a feedblock inlet system. The three-dimensional finite element method is applied to determine the fluid motion and the interfacial position of the two polymeric liquids before entering the die body, whereas the two-dimensional Hele-Shaw model is assumed to be applicable for fluid flow in the manifold and the slot section of the die body. An optimal design procedure is incorporated into the simulation and the dimensions of the manifold can be properly selected such that the die can deliver the composite liquid film with acceptable uniformity. A specially designed choker bar can also be inserted to reduce the flow non-uniformities caused by production variations. The contraction of the composite liquid film emanating from the die exit is also predicted under different draw ratios.