三螺杆分散混合数值模拟及实验分析

Numerical Simulation and Experimental Analysis of Tri-screw Dispersion Mixing

为了研究平行同向啮合三螺杆挤出机的分散混合效果,采用离散元法对三螺杆挤出机中聚丙烯(PP)/低密度聚乙烯(PE-LD)两种塑料颗粒在加料段的混合情况进行数值模拟。首先建立了三螺杆挤出机的三维模型,在EDEM软件中仿真出不同螺杆转速下挤出机的混合效果,通过对收集盒分层处理计算得出混合过程中混合均匀度的变化趋势。分析结果表明,当转速为200 r/min时,三螺杆挤出机有最高均匀度稳态值,此时分散混合效果最好。在转速低于200 r/min时,表现为螺杆的转速越高,塑料颗粒混合均匀度稳态值越高,所用最佳混合时间越少;当转速高于200 r/min时,物料颗粒所用最佳混合时间继续减少,但均匀度稳态值下降。同时捏合块对挤出机的混合效果影响较大,最优是单根螺杆轴上安装2个捏合块。最后通过自行设计的小型三螺杆挤出机做验证实验,结果表明,此次实验与仿真模拟表现一致,200 r/min转速下两种塑料的分散混合效果最佳。

In order to study the dispersing and mixing effect of the parallel co-rotating tri-screw extruder,and the numerical simulation was performed on the mixing of polypropylene(PP)/low-density polyethylene(PE-LD)plastic particles in the feeding section by using discrete element method.Firstly,a three-dimensional model of the tri-screw extruder was established,and the mixing effects of the extruder under different screw speeds were simulated in EDEM software.The layered processing of the collection box was calculated to obtain the change of the mixing uniformity during the mixing process.The analysis results show that,when the rotation speed is 200 r/min,the tri-screw extruder has the highest steady-state value of uniformity,and the dispersion and mixing effect is the best at this time.When the rotation speed is lower than 200 r/min,the higher the rotation speed of the screw,the higher the steady-state value of the plastic particle mixing uniformity and the shorter the optimal mixing time;when the rotation speed is higher than 200 r/min,the optimal mixing time of the plastic particle continues to reduce,but the steady-state value of uniformity decreases.At the same time,the kneading block has a greater influence on the mixing effect of the extruder.The best is to install two kneading blocks on a single screw shaft.Finally,a self-designed small tri-screw extruder was used for verification experiments.The results show that this experiment is consistent with the simulation performance,and the dispersion and mixing effect of the two plastics at 200 r/min is the best.