反应注射成型充模过程驻留时间分析

在反应注射成型实际生产过程中，如何选择工艺参数是一个一直使操作者为难的问题。本文利用反应注射成型过程中驻留时间的概念，通过对喷泉流模型进行适当的简化分析，得出在ＲＩＭ充模过程中驻留时间与模腔无量纲纵向ｘ坐标和模腔厚度ｚ坐标之间的关系，并得出最大驻留时间线１＝２ｘ３（１－ｚ２），作出充模过程驻留时间分布曲线。忽略ＲＩＭ充模过程的热传导项，无量纲温度Ｔ与反应进度Φ相同，是流体在模腔内驻留时间线的等值线。将数值计算的反应进度值、温度值与模型计算作比较，基本符合，偏差的出现是由于模型中对前流区的简化处理，恒定粘度假设以及忽略热传导作用。为避免在充模过程中出现过早凝胶现象，在反应进度达到凝胶点时驻留时间不应大于１，这一结论有助于ＲＩＭ加工过程工艺参数的选择     

反应注射成型充模参数的选择

本文在分析聚氨酯反应注射成型反应动力学基本方程的基础上，对影响选择充模过程的主要因素进行了分析，并得出聚氨酯反应注射成型流动阶段充模区域图。     

PUU—RRIM制品中玻璃纤维的取向

通过扫描电子显微镜观察了聚氨酯脲（ＰＵＵ）体系增强反应注射成型（ＲＲＩＭ）制品中玻璃纤维的取向和分布规律。发现在流动横截面上,玻璃纤维非均一分布,其中规则取向区域与杂乱积区域交替存在,呈现多层分布结构,建立了充模过程流体流动方程,应用速度分布方程,对玻璃纤维多层分布结构进行了理论分析。     

增强反应注射成型聚氨酯及其性能研究

以反应注射成型聚氨酯（ＲＩＭ－ＰＵ）为基体树脂，研制了以玻纤增强剂的增强反应注射成型聚氨酯（ＲＲＩＭ－ＰＵ）材料。讨论了原材料及玻纤对ＲＲＩＭ－ＰＵ加工工艺及材料性能的影响。结果表明，以碳化二亚胺改性的异氰酸酯（ＣＭ－ＭＤＩ）和低聚合异氰酸酯改性的异氰酸酯（ＰＡＰＩ）混合物与丙腈－－苯乙烯接枝改性环氧乙烷封端的聚醚二元醇（ＡＰＧ）为主要原料，玻纤长度不大于１．５时，不仅ＲＲＩＭ加工工艺性好，而且Ｒ     

近期国内外聚氨酯工业发展概述

本文叙述世界聚氨酯工业生产概况，包括聚氨酯原材料以及聚氨酯产品的生产和消费情况；聚氨酯泡沫塑料技术进展，如氯氟烃（ＣＦＣｓ）替代技术，阻燃聚氨酯泡沫塑料和聚氨酯反应注射成型（ＰＵ－ＲＩＭ），以及国内聚氨酯工业的发展概况。     

剪切控制取向注射成型概述

对比了剪切控制取向注射成型（ＳＣＯＲＩＭ）与普通注射成型（ＣＩＭ）的基本原理，剪切控制技术（ＳＣＯＴ），可消除制品熔接缝，改善外观质量，还可消除内在应力和空隙等缺陷，提高制品内在质量。     

PA成型收缩率与注射工艺条件的关系

分析了注塑制品的收缩机理及收缩过程，并讨论了聚酰胺（PA）注射成型过程中模腔平均压力、熔体温度、模温、充模速率、成型时间等工艺条件对其收缩率的影响及制品后收缩率的因素，给出了减小制品收缩率，提高制品尺寸稳定性的方法。     

结构反应注射成型(SRIM)—─PU-PI增强塑料的研制及性能研究

在研究结构反应注射成型（ＳＲＩＭ）化学体系的基础上，以玻璃纤维毡片为增强剂，预先配制在模具中，然后进行反应注射成型的新技术－ＳＲＩＭ技术，研究制备了氨酯改性聚异氰脲酸酯（ＰＵ－ＰＩ）增强塑料（ＳＲＩＭＰＵ－ＰＩ）。     

聚氨酯弹性体反应成型混合技术

聚氨酯弹性体产品以其高抗张强度、高伸长率和优异的抗撕裂,耐磨性能等综合特征,得到广泛的应用,同时也带动了反应注射成型技术的运用和发展,但至８０年代末期,反应注射成型（Ｒｅａｃｔｉｏｎ Ｉｎｊｅｃｔｉｏｉｎ Ｍｏｌｄｉｎｇ）混合技术仍未突破旧的混合理论,这导致了它某些难以克服的缺陷,就传统的ＲＩＭ混合技术与新型层流剪切为特征的旋转注射成型混合技术（Ｒｏｔａｒｙ Ｉｎｊｅｃｔｉｏｎ Ｒｅａｃｔｉｏｎ     

矩形腔中反应注射充模过程的数值模拟

<正>1 引言 反应注射充模（RIM）是由聚氨酯工艺发展起来的新型塑料成型方法,它具有模腔压力和进料温度低、节能、模具设备简单和产品性能优良等众多优点,特别适于生产大型塑料制件。近年来国际上已大量开展相关过程的流动和传热的数值模拟研究,以发展此一成型工艺的CAD/CAE工作。本文拟在过去对热注射充模（TIM）过程的流动和传热数值模拟研究的基础上,参考国外近年在RIM数值模拟方面的成就,对典型的端面进料矩形腔内RIM过程进行数值模拟研究。     

RIM充模过程数值模拟

用有限元法对RIM充模过程进行数值模拟．采取任意拉格朗日－欧拉法（ALE）处理流动前缘.并以边充模边划分网格的方法,使前缘边界条件得到较充分的满足．对不同操作参数下的RIM充模模拟结果进行了讨论、分析,得出选用薄腔、较快的充模速度以及适当较高的物料初始温度对RIM充模有利的结论,这对工业实践有重要的指导意义．     

Three-dimensional modeling of reaction injection molding. I

In this research a model to simulate both the filling the curing stages of a reaction injection molding (RIM) process in complex three-dimensional molds is developed. This model can be used to predict not only the temperature and conversion changes with time but also the front position during filling. Using given physical and chemical properties of the RIM system, moldability can be determined in advance. The numerical techniques used in this research include adaptation of the SIMPLE algorithm developed by Patankar for a moving-front, two-phase system with non-negligible inertial effects, and exothermic chemical reaction. The model predictions of temperature and conversion compare favorably with available data on simple two-dimensional molds. The ability of the model to predict the dynamics of filling in more complicated molds was verified by comparison to mold filling experiments with water and a polyurethane foam.     

Space-time distribution in filling a mold

The residence time of a fluid particle in mold filling is total time spent in the mold. Displaying curves of constant residence time in the mold gives the space-time distribution during the filling process. A simple method to calculate space-time distributions is presented. Applications to mold filling in reaction injection molding (RIM) are illustrated.     

Three-dimensional modeling of reaction injection molding. II: Application

The objective of this research is to demonstrate the application of a general model of reaction injection molding (RIM) to a complex shaped mold part. Using the fundamental physical and chemical properties of the RIM system, prediction of RIM moldability can be made. The numerical techniques used in this research are presented in a previous paper (1). The rigorous modeling of the transport processes and the dynamics of the filling front for a particular application are described in this work.     

RIM充模过程中流动行为研究

本文采用无化学反应的低粘度流体进行ＲＩＭ充模过程的冷态模拟研究。考察了充模过程中的基本流动行为。对稳定铺展流、失稳流、射流和绕流等各种充模现象进行了描述、分析，并提出了各种流动行为的判别准则。     

Moldability diagrams for the reaction injection molding of a polyurethane crosslinking system

A trial and error approach reflects the state of the art in reaction injection molding. Material and process parameters determine the “moldability” of a specific system in a particular application. The concept of “molding areas” on the critical parameters plane can be extended form thermoplastic injection molding (TIM) to reaction injection molding (RIM). In this work moldability diagrams for the filling and curing stages of a RIM process are obtained based on a simplified engineering approach. The key process parameters chosen for the filling stage are initial material temperature and filling time. In the curing stage, the critical parameters are considered to be mold wall temperature and demold time. Experimental results obtained on a laboratory-scale RIM machine on a Crosslinking polyurethane system are used to check the validity of the predicted molding areas. The agreement obtained is satisfactory considering the broad range of processing parameters used.     

反应注射充模特性及模具浇口结构设计的研究

本文对反应注射充模过程中的铺展流、射流、绕流和气泡的特性进行了分析研究，并讨论了模具浇口结构及位置对充模的影响，给出了制品的设计方法。     

A model of advancing flow front in RIM

A two-dimensional model is developed for mold filling in Reaction Injection Molding using a Petrov-Galerkin finite-element method with free surface parameterization. Dependence of viscosity on the conversion and temperature is represented by the Castro-Macosko function. The model predicts the velocity, pressure, temperature, and conversion distributions with time during the filling stage of a rectangular mold. No a priori assumptions are made regarding the shape of the advancing flow front, or regarding any variables in the flow front region. The accuracy is further improved by using the Petrov-Galerkin formulation, rather than the Galerkin formulation. The results are presented for well-characterized polyurethane systems, for which reliable experimental data is available. The predictions of the model for the pressure rise are in excellent agreement with the experimental data (1) even close to the gel point. These refined predictions are expected to assist in estimating fiber orientation and bubble growth in the final RIM parts, in which the flow front region plays the most important role. Characterization of polyurethane/polyurea and polyurea materials is underway, and will be subsequently incorporated in the model.     

Simulation of reactive injection molding

This paper deals with the computer simulation of those aspects of Reactive Injection Molding (RIM) dealing with the non-isothermal and transient flow of a chemically reacting mixture into a mold cavity, and the in situ polymerization (“curing”) which follows mold filling. Linear polyurethane systems were considered. The purpose of this simulation work is to investigate the effects of the operating, chemical, and rheological variables on the length and the stability of the RIM process, as well as the quality of the resulting product. Since the flowing fluid mixture is reactive, there is a need to know the thermal history of each of the flowing fluid particles. For this reason the “fountain” flow at the fluid-air interface is considered in a heuristic fashion.     

Moldability studies for the reaction injection molding of polydicyclopentadiene

Moldability diagrams for the filling and curing stages of a dicyclopentadiene (DCPD) based reaction injection molding (RIM) system were established based on a simplified engineering approach. Initial monomer temperature and filling time are the critical parameters for the filling stage whereas in the curing stage, mold wall temperature and demold time proved to be the main processing variables. The physical and thermal properties of the molded samples were examined and the results indicate that such simplified moldability diagrams are sufficiently accurate to establish the processing conditions for the system under investigation.