聚乙烯护套料的双螺杆造粒工艺研究

Study on Twin Screw Granulation Process of Polyethylene Sheath Material

从分散相分裂模型解释了双螺杆挤出机制备聚乙烯护套料时熔融段和混合段的螺杆设计原则,研究了螺杆组合、螺杆转速、喂料量对聚乙烯护套料的性能影响;用哈克转矩流变仪模拟线缆挤出,评估工艺参数的变化对成缆外观的影响。研究发现:双螺杆挤出机生产聚乙烯护套料时,螺杆的熔融段应该以强剪切为主,如45°厚剪切块和90°剪切块,配合反向输送块进行组合设计;混合段以分散、分布组合为主,如45°的薄、厚剪切块组合设计。当螺杆转速不变,喂料量增加时,熔体流动速率、熔体流动速率比、力学性能均呈下降趋势;聚乙烯护套料属于挤出类产品,为了确保挤出过程的稳定性,应该减少生产工艺的变更。不同分子链长度的黏弹性不一样,短链分子链集中在口模壁一侧,长链分子链集中在中间层。当其离开口模后,表层的短链分子链回弹大,中间层的长链分子回弹小,从而引起竹节缺陷。

The design principle of the screw in the melting section and mixing section of the twin-screw extruder was explained from the dispersed phase splitting model.The effects of screw combination,screw rotation speed and feeding amount on the properties of polyethylene sheath material were studied.Haake torque rheometer was used to simulate cable extrusion and evaluate the influence of process parameters on the appearance of finished cable.The results show that in the production of polyethylene sheath material by twin-screw extruder,the melting section of the screw should be dominated by strong shearing,such as 45°thick shearing block and 90°thick shearing block,which should be designed in combination with reverse conveying block.The mixing section is mainly composed of dispersion and distribution,such as 45°thin and thick shearing block combination design.The melt flow rate,melt flow rate ratio and mechanical properties show a downward trend when the screw speed is constant and the feeding amount increases.Polyethylene sheath material belongs to extrusion products.In order to ensure the stability of extrusion process,the change of production process should be reduced.The viscoelasticity of different molecular chain lengths is different.The short chain is concentrated on one side of the die wall,and the long chain is concentrated on the middle layer.The rebound of short chain is large.When it leaves the die,the short chain molecules in the surface layer rebounds more and the long chain in the middle layer rebounds less,which leads to the defects of bamboo joint.