现有的部分企业在模内热切注塑技术规范中,规定了与切刀运动方向垂直的切刀横截面面积须小于注塑机喷嘴截面积,但在多切刀模内热切注塑模中,这一规定并不适用.针对此问题,首先介绍了典型模内热切注塑模的主要结构,以这种结构为案例,结合熔融塑料的体积弹性模量估算,通过熔融塑料在受切刀挤压时熔融塑料体积变化与压力增量的关系分析,得出若在注塑结束、塑料熔体尚未凝固时启动切刀,则压力变化很小,因此切刀的截面积小于注塑机喷嘴截面积不是必要条件;若切刀启动时间较迟,则流道和浇口处的塑料熔体已经凝固,被挤出的半熔融塑料并不是被挤回到注塑机中,而是被容纳于切刀附近的溢料槽.由此明确了切刀动作在注塑行程过程中时机优化的指导思想,以及溢料槽设计的补充思想.%In technical specifications of hot-cutting in-mould technology of some companies,the cross-sectional area of the cutter perpendicular to the direction of cutter motion shall be less than that of the injection molding machine nozzle,but in the injec-tion mould with muti-cutter,the specification is not applicable. According to the problem,the main structure of typical injection mould with hot-cutting in-mould was first introduced. Then taking the structure as an example,and combining with estimating the bulk modulus of molten plastic,the relationship between molten plastic volume change and its pressure increment when the cutter extrudes was analyzed. The conclusion is obtained that,if starting the cutter when the injection is finished and the melt is not yet solidified,the pressure increment is little,so it is not necessary for limiting cross-sectional area of the cutter being smaller than that of injection molding machine nozzle,if starting the cutter later,the melt in the runner and gate is solidified,the half molten plastic is not pushed back into the injection molding machine,instead,is mainly accommodated by the material overflow trough nearby cutter . Thus the guiding ideology of the timing optimization of the cutting action in the process of injection molding and a supplementary thought for the design of overflow trough are confirmed.
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