多型腔注射模充填不平衡试验

多型腔注射模在实际生产中有着广泛应用,充填平衡是保证多型腔模塑制品质量均匀一致的关键.自然平衡流道中也会发生充填不平衡现象,其原因可能是熔体流动产生的剪切热所致,但一直没有试验结果予以证明.基于此,利用可视化注射模具和红外温度传感器,通过直接观测熔体在流道和型腔中的动态流动行为并测量型腔入口处熔体的温度变化,对不同注射速率下不同材料在自然平衡多型腔注射模的充填不平衡进行研究.结果表明,由于剪切热的作用,主流道中不均匀但对称的熔体温度分布在分流道中失去对称性是产生充填不平衡的根本原因;充填不平衡程度不但取决于主流道中熔体的温度分布,还取决于分流道中凝固层的分布及熔体粘度对温度变化的敏感性.解决自然平衡多型腔注射模充填不平衡问题的根本,在于改善或消除分流道中熔体温度分布在流动平面的不对称性.

EXPERIMENTAL STUDY ON FILLING IMBALANCE IN MULTI-CAVITY INJECTION MOLD

Multi-cavity injection mold is used widely in practice, and filling balance is recognized as the most important problem in multi-cavity molding.Filling imbalance can also occur in a multi-cavity mold with a geometrically balanced runner.It may be due to the shear heat produced in melt flow,but it has not been proven by experimental results.Filling imbalance in a multi-cavity mold with a geometrically balanced runner is in- vestigated by using the visualization glass-inserted injection mold and infrared thermometers,through visualizing the flow behavior of the melt in the runner and cavity and measuring the melt temperature near the cavity entrance simultaneously.The results show that the root cause of filling imbalance occurring in naturally balanced runner systems is due to that the symmet- rical but no-uniform temperature distribution of the melt across primary runner section is lost when the flow splits at a branch, and the degree of filling imbalance not only depends on the melt temperature distribution inside the primary runner,but also depends on the frozen layer distribution in the secondary runner and the resin viscosity sensitivity to temperature.It is a radical solution of avoiding filling imbalance in a multi-cavity mold with a geometrically balanced runner to improve or eliminate the asymmetry of the melt temperature distribution in flow plane.