共查询到20条相似文献,搜索用时 125 毫秒
1.
2.
结晶型塑料注塑平板冷却模型的研究 总被引:6,自引:3,他引:6
本文从注塑的实际出发,针对注塑塑料平板的冷却凝固本质,提出了有限厚度区域内注塑平板的冷却模型,用精确分析解法与积分近似解法相结合,进行了理论推导,求得了固液两相内的温度分布和平板中心层温度冷却至熔点所需的冷却时间。 相似文献
3.
结晶性注塑平板制品冷却时间的确定 总被引:1,自引:1,他引:1
从传热学基本原理出发,推导出结晶性平板状注塑制品冷却时间的几种计算方法。对于PP,在相同条件下,利用分离变量法对简化的一维传热模型进行求解,得冷却时间τ为7 5s;对一维相变移动边界模型,解析解法采用固相精确求解与液相近似求解相结合的方法,得τ为23s;数值解法采用了焓法,得τ等于23 05s。最后举例讨论了数学模型与实际注塑加工的差距。这些对结晶性聚合物注塑加工具有一定的指导作用。 相似文献
4.
介绍结晶性塑料在注塑过程中的塑化特点、取向与结晶的关系及其对制品性能的影响,注塑参数对结晶性塑料塑化、取向、结晶的影响。讨论了在实际工作中如何利用这些特性进行注塑机塑化系统、模具的设计并确定注塑工艺,从而得到品质优良的制品。 相似文献
5.
为了优化注塑成型工艺,研究了注塑成型的数学模型,以及产生翘曲形变的原因,在此基础上利用Moldflow软件对薄壁件塑料注塑成型过程中的宽浇口平板进行了仿真实验,并采用了无定型塑料丙烯腈-丁二烯-苯乙烯共聚物+聚碳酸酯(ABS+PC)对其进行注射、保压、冷却等流程模拟,选定了保压压力、熔体温度、冷却时间、模具温度、注射时间、保压时间等主要工艺参数,并通过方差比较的方法对这些工艺参数进行了评价,最终确定了注塑成型的优化方案。通过实验得出了ABS+PC的最优工艺参数组合,有效降低薄壳制件的翘曲量并优化了其制品性能。 相似文献
6.
7.
考虑变比热的平板注塑件非对称冷却瞬态温度场数值模拟 总被引:1,自引:0,他引:1
对注塑平板制件非对称冷却过程进行了分析,通过近似假设,建立一维非稳态传热模型。考虑无定形聚合物和结晶型聚合物的比热对温度的依赖性,利用分段线性函数拟合聚合物的比热-温度曲线,通过对空间域和时间域的离散化,运用有限差分数值方法,模拟了无定形聚合物和结晶型聚合物注塑平板制件在模具中非对称冷却的一维瞬态温度场。 相似文献
8.
<正>众所周知,注塑是一种工业产品生产造型的方法。塑料注塑成型是受热融化的材料由高压射入模腔,经冷却固化后,得到成形制品的方法。注射成型机(简称注射机或注塑机)是将热塑性塑料或热固性料利用塑料成型模具制成各种形状的塑料制品的主要成型设备,注射成型是通过注塑机和模具来实现的,产品通常使用橡胶注塑和塑料注塑,注塑还可分注塑成型模压法和压铸法,该方法适用于形状复杂部件的批量生产,是重要的加工方法之一。 相似文献
9.
平板塑件瞬态传热解析解及其在冷却分析中的应用 总被引:4,自引:0,他引:4
简要介绍了建立冷却分析数学模型的两种方法,指出了循环迭代模型的不足,推导了平板塑件瞬态传热解析解,找出循环平均热流与边界温度的线性关系表达式,并将它应用于注塑冷却分析,建立了冷却分析的迭代模型,取代原来的循环迭代模型,从而取消了原冷却分析中的中间迭代计算,有效地减少了冷却分析的迭代次数,提高了运算效率。另外,循环迭代求解平板塑件温度场采用的是有限差分法,即近似数值解,而迭代模型采用的是解析解,从理论上讲结果更精确,所以对提高计算结果的精度有一定的改善作用。 相似文献
10.
11.
Mathematical models were developed to predict the various microstructural properties, including birefringece, residual stress, and density distributions, in the freely quenched compression molded samples as well as in the injection molded samples. To model the birefringence distribution in the injection molded samples, the BKZ type integral constitutive equation was employed to account for the nonisothermal stress relaxation, which takes place during the cooling stage of the molding cycle. The predicted birefringence agreed well with the experimental data near the mold walls. The residual stress distribution was modeled by the existing thermoelastic theory. The residual thermal stress distribution in the freely quenched samples was predicted very well by the model. However, the predicted residual thermal stresses in the injection molded samples were much larger than the measured ones. A phenomenological model to predict the density distribution in injection molded sample is proposed by including the effects of both cooling rate and the pressure on the density development. The predicted results agreed well with the experimental data. 相似文献
12.
13.
Means of reducing the flow-induced residual stresses in injection molded parts through optimization of the thermal history of the process are presented. An approach through the use of a passive insulation layer with low thermal inertia on the cavity surface was investigated. The passive insulation layer prevents the polymer melt from freezing during mold filling and allows the flow-induced stresses to relax after the filling. The criteria for the optimal thermal properties and the required thickness of the layer are presented. A numerical simulation model of non-isothermal filling and cooling of viscoelastic materials was also used to understand the molding process and to evaluate this approach. This model predicts the stress development and relaxation in the molding cycle. Both simulation and experimental results show that the final stresses in the molded parts can be reduced significantly with the use of an insulation layer. This technique can also be applied to other molding or forming processes in order to decouple the material flow and cooling process for minimum residual stresses in the molded parts. 相似文献
14.
15.
16.
Shui‐Po Liang Bin Yang Xiao‐Rong Fu Wei Yang Nan Sun Sheng Hu Ming‐Bo Yang 《应用聚合物科学杂志》2010,117(2):729-735
Gas‐assisted injection molding (GAIM) is an innovative plastic processing technology, which was developed from the conventional injection molding, and has currently found wide industrial applications. About 70% of the whole gas‐assisted injection molding cycle is actually occupied by the cooling stage. The quality and production efficiency of molded parts are considerably affected by the cooling stage. Hence, it is necessary to study the solidification behaviors during the cooling stage. In this work, a simple experimental method was designed to simulate the solidification behaviors of high‐density polyethylene during cooling stage of GAIM. The enthalpy transformation approach, coupled with the control‐volume/finite difference techniques, was adopted to deal with the transient heat transfer problems with phase change effects. In situ measurements of the temperature decreases in the cavity were also carried out. Reasonable agreements between the experimental values and the simulated results such as cooling time, cooling rates, and temperature curves were obtained, which proved that this simple experimental method was effective. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
17.
This paper presents an analytical approach to predict in-mold constrained shrinkage of injection molded semi-crystalline plastic parts. Existence of mold constraints exerts a noticeable effect on the final dimensions of molded parts due to the viscoelastic characteristics of polymeric materials. Variation of in-mold cooling time introduces variations in final part dimensions in relation with the constraints. Although this inter-relationship is well applied, few investigations have been reported to analyze the effect. In the present study, an analytical approach is introduced to predict constrained shrinkage of semi-crystalline thermoplastics and experimentally examined using a case study. Essential to this analytical solution, innovative mathematical expressions of elastic modulus and relaxation time constant with respect to temperature have been introduced. A mold was constructed to produce a plate featured by holes and injected to produce experimental data. The results indicated that there is a good agreement between the prediction and the experimental data, especially at longer cooling times. It can also be shown that the material relaxation time has the most dominant influence on the final shrinkage. 相似文献
18.
运用Moldflow软件进行某后盖产品的翘曲变形分析,结合Moldflow软件的翘曲变形分析理论,将影响注塑件的翘曲变形因素分为3类:冷却不均、收缩不均及取向因素。然后针对翘曲变形不同的影响因素提出冷却优化、结构优化、保压优化及反变形设计等优化方案。分析结果表明:提出的这几种优化方案能极大地改善注塑件的翘曲变形,为注塑制品企业在控制产品尺寸、满足装配质量要求、改善翘曲变形等方面提供优化思路及工艺参考。 相似文献
19.
Specimens of two engineerig plastics i.e., poly(ether imide), PEI, and poly(2,6-dimethyl- 1,4-phenylene ether), PPE, were injection molded employing a 40t Van Dorn injection molding machine and industrial practices. The mold and melt temperatures and the injection speed were varied in a limited range which furnished acceptable samples. The density, birefringence, residual stress distributions, flexure and tensile properties, and crack development of the injection molded specimens were studied. Vacuum compression molded samples were also prepared to investigate the role played by the cooling rate in shaping microstructural distributions. The results revealed significant differences in the development of microstructure of the molded specimens of the two resins, which was related to rheology and molding conditions on one hand and to development of cracks and ultimate properties on the other hand. 相似文献
20.
以电视机透明支柱实体塑料件为例,在三维模流分析理论研究的基础上确定塑料件质量评价指标为体积收缩率。影响质量的工艺参数为模具温度、熔体温度、注射时间、保压压力、保压时间和冷却时间。结合正交实验法、CAE分析及数据处理技术,确定各工艺参数对塑料件质量的影响及最优工艺方案。 相似文献