微孔塑料连续挤出成型快速降压口模的数值模拟

摘要

利用Polyflow有限元软件对聚苯乙烯(PS)/CO2均相体系在连续挤出成型圆形快速降压口模中的流动进行数值模拟,考察快速降压口模入口角、长径比及口模温度对PS微孔塑料熔体沿轴线方向的压力降速率和剪切速率的影响.结果表明,当入口角大于30°时,改变入口角对压力降速率和剪切速率无明显影响,即对微孔塑料的气泡成核影响微小,但当入口角为0°时,与其它各入口角相比,其熔体压力降速率最大,气泡成核时间最早；在毛细管段口模直径不变的情况下,改变其长径比对熔体气泡成核亦无明显影响,但压力降随口模长度缩短而变小；口模温度对剪切速率影响不大,但降低口模温度,压力降速率明显提高,从而有利于微孔塑料的气泡成核.%Numerical simulation of polystyrene (PS)/CO2 homogeneous phase system flowing in circular rapid decompressive die of continuous extrusion molding was done through finite element analysis software Polyflow,moreover,effects of inlet angle and aspect ratio (L/D) of the rapid decompressive die and die temperature on pressure drop rate and shearing rate of the PS microcellular plastic melt along the direction of axis were analyzed.The results show that when the inlet angle is more than 30°,changing inlet angle has no obvious effect on the pressure drop rate and shearing rate,in other words,it has little influence on bubble nucleation of microcellular plastic,but when the inlet angle is 0°,the pressure drop rate is highest and the bubble nucleation time is earliest comparing with other inlet angles.Changing L/D has also no obvious influence on bubble nucleation of microcellular plastic under the conditions of die diameter in capillary section being constant,but pressure drop decreases with the die length shortening.The effect of die temperature on shearing rate is slight,but the die temperature decreases,the pressure drop rate increases obviously,which is benefit for bubble nucleation of microcellular plastic.