结晶型聚合物注塑过程冷却模型的数值模拟

对HDPE平板状注塑件的冷却过程进行了数值模拟 .基于小分子结晶性物质的冷却模型 ,建立了固相、液相及固液相界面的控制方程 ,方程中引入热焓E和参数T 后 ,将带耦合条件的热传导方程转变为非线性抛物型方程 ,按控制容积法将其离散后 ,用数学软件Matlab获得了PE的三维温度场 ,这为探讨带相转变的热传导问题提供了一种有效的数值方法 .通过对制件芯层温度变化的模拟值与实验值的比较 ,比较了不同相变温度下理论结果的准确性 ,结果表明 ,在引入一定过冷度后 ,将相变温度定义在低于平衡熔点以下时 ,该方法的模拟值具有更好的准确性 .同时 ,模型分析了不同工艺条件对制件芯层冷却过程的影响 ,通过相变平台出现的先后以及终止时间的不同 ,说明充模温度主要影响熔体阶段的冷却以及相变出现的先后 ,而模具温度主要影响固体阶段的冷却以及相变平台终止的先后 .

NUMERICAL SIMULATION ON THE COOLING STAGE FOR INJECTION MOLDED PARTS OF CRYSTALLINE PLASTICS

Numerical simulation was applied to calculate temperature changes of injection molded HDPE in the cooling process.Based on the cooling model of low molecular crystalline material,the governing equations were developed to describe the cooling temperature of solid,liquid,and solid-liquid interface,respectively.An enthalpy E and a parameter T* were employed to convert the energy equation into a non-linear equation,which was then discreted by the control volume finite difference approach and solved with mathematical software Matlab.The calculated temperature profile exhibited the existence of thermosphere and phase transformation and required a time period of 2 min for the cooling cycle,which was in agreement with the experimental data for the inner layer of the HDPE sample.Thus it can be applied to the numerical performance of Stefan problems.The effect of molding conditions on the cooling temperature of HDPE was also discussed,which can reflect the change of its crystalline behavior.