成型方法对SCF微孔发泡制品泡孔结构及力学性能的影响

发布时间：2018-12-23 11:21

【摘要】：当今社会正面临着全球能源危机和环境污染问题。超临界流体(Supercritical Fluids,SCF)微孔发泡材料中大量微小泡孔的存在能够减少产品使用的原材料和消耗的能源,同时微孔发泡制品的一些性能更加优异。凭借其独特的优势,微孔发泡技术一度成为研究热点,但是也面临着诸多问题和挑战。其中如何成型具有高密度且规则排列的微孔结构以获得更加优异的机械性能正是一个亟待解决的问题。本文分别采用了常规发泡、高压发泡和注压发泡方法制备出SCF微孔发泡制品,探究了不同成型方法和不同工艺条件对制品泡孔结构的影响。主要工作如下:(1)设计并制造出适应三种不同成型方法的多功能试验模具,应用模流分析软件Moldflow模拟仿真材料聚苯乙烯(PS)的热塑性注射成型和微孔发泡注射成型充填过程,评价模具和材料PS的成型性能。结果表明:带有弹簧结构的压缩框和活动型腔板是该实验模具设计的关键;相较于热塑性注射成型,微孔发泡注射成型的充填时间更短,熔体前沿温度更低,充填完成瞬时的型腔压力低且在型腔内分布更加均匀。(2)研究SCF含量、螺杆背压和预充填量对常规发泡制品泡孔结构的影响。结果表明:常规发泡制品垂直流动方向断面上的泡孔为圆形或者椭圆形,而在沿着流动方向上的泡孔为长条状。泡孔的排布保留着明显的泉涌流动痕迹,沿着流动方向上的泡孔形态、尺寸和密度均具有明显的不均一性。(3)研究保压压力和保压时间对高压发泡制品泡孔结构的影响。结果表明:当保压压力为600bar,保压时间为5s时,泡孔密度最高(6.6×105cells/cm3),泡孔尺寸最小(45μm);在优化后的工艺条件下,高压发泡制品垂直于流动方向和沿着流动方向断面上的泡孔均为圆形。(4)研究压缩压力和压缩时间对注压发泡制品泡孔结构的影响。结果表明:当压缩压力为400bar,压缩时间为5s时,泡孔密度最高(4.3×106cells/cm3),泡孔尺寸最小(10μm);在优化后的工艺条件下,注压发泡制品垂直于流动方向和沿着流动方向断面上的泡孔均为圆形。(5)在常规发泡、高压发泡及注压发泡制品不同泡孔结构的基础上对比分析了成型过程的型腔压力及力学性能。结果表明:常规发泡过程中压力较低,制品的力学性能最差;高压发泡过程中压力较高,形成了二次泡孔,力学性能较高;而注压发泡过程中压力最高,形成的二次泡孔能有效提过制品的力学性能。
[Abstract]:Nowadays, the society is facing the global energy crisis and environmental pollution. In supercritical fluid (Supercritical Fluids,SCF) microcellular foaming materials, the existence of a large number of microbubble pores can reduce the raw materials and energy consumption of the products, at the same time, some properties of microcellular foamed products are more excellent. With its unique advantages, microcellular foaming technology has become a research hotspot, but it also faces many problems and challenges. How to fabricate microporous structures with high density and regular arrangement to obtain better mechanical properties is an urgent problem to be solved. In this paper, SCF microcellular foaming products were prepared by conventional foaming, high pressure foaming and injection pressure foaming, respectively. The effects of different molding methods and different processing conditions on the foam structure of the products were investigated. The main work is as follows: (1) designing and manufacturing multi-function test mould suitable for three different molding methods. The mold flow analysis software Moldflow was used to simulate the filling process of thermoplastic injection molding and microcellular foaming injection molding of polystyrene (PS), and the molding properties of mould and material PS were evaluated. The results show that the compression frame with spring structure and the movable cavity plate are the key to the design of the experimental die. Compared with thermoplastic injection molding, the filling time of microcellular foaming injection molding is shorter, the temperature of melt front is lower, the instantaneous cavity pressure of filling is lower and the distribution of SCF in the cavity is more uniform. (2) the content of SCF is studied. Effect of screw back pressure and pre-filling on foam structure of conventional foamed products. The results show that the bubble pores in the vertical flow direction of conventional foamed products are circular or elliptical, while those along the flow direction are long. The arrangement of the bubble pore retains obvious spring flow trace, and the shape, size and density of the bubble pore along the flow direction are obviously uneven. (3) the influence of the pressure holding pressure and the pressure holding time on the bubble pore structure of the high-pressure foaming products is studied. The results show that when the pressure holding pressure is 600barand the holding time is 5s, the bubble density is the highest (6.6 脳 105cells/cm3) and the bubble size is the smallest (45 渭 m);). Under the optimized process conditions, the foam pores perpendicular to the flow direction and along the section along the flow direction are circular. (4) the effects of compression pressure and compression time on the foam structure of injection-pressure foamed products are studied. The results show that when the compression pressure is 400barand the compression time is 5s, the bubble density is the highest (4.3 脳 106cells/cm3) and the bubble size is the smallest (10 渭 m);). Under the optimized technological conditions, the foam pores perpendicular to the flow direction and along the flow direction are circular. (5) in the conventional foaming, The cavity pressure and mechanical properties of high pressure foaming and injection pressure foaming products were compared and analyzed on the basis of different foam pore structures. The results show that the mechanical properties of the products are the worst when the pressure is low in the conventional foaming process, and the secondary foam pores are formed in the high pressure foaming process, and the mechanical properties are higher. However, the pressure is the highest in the foaming process of injection pressure, and the mechanical properties of the products can be effectively extracted by the formation of secondary foam pores.
【学位授予单位】：郑州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ328

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