Huang Po-Wei, Peng Hsin-Shu, Hwang Sheng-Jye, Huang Chao-Tsai
Program of Mechanical and Aeronautical Engineering, Feng Chia University of Engineering and Science, Taichung 407102, Taiwan.
Department of Mechanical and Computer Aided Engineering, Feng Chia University of Engineering and Science, Taichung 407102, Taiwan.
Polymers (Basel). 2023 Apr 28;15(9):2116. doi: 10.3390/polym15092116.
Plastic foam molding methods include thermoforming, extrusion and injection molding. Injection foam molding is a one-time molding method with high production efficiency and good product quality. It is suitable for foamed plastic products with complex shapes and strict size requirements. It is also the main method for producing structural bubbles. In this investigation, we developed a structural foam injection molding technology using the gas supply equipment connected to the unique plasticizing mechanism of the injection machine and studied its influence on the specimens' melt rheology quality and foam structures. In the experiment, the forming material was polypropylene (PP), and the gas for mixing/forming foaming characteristics was nitrogen (N). Additionally, in order to observe the rheological properties of N/melt mixing, a melt flow specimen mold cavity was designed and the change in the melt viscosity index was observed using a melt pressure sensing element installed at the nozzle position. With the nitrogen supply equipment connected to a unique plasticizing mechanism, the mixing of gas and molten plastic can be achieved at the screw plasticizing stage, where the foaming effect is realized during the melt-filling process due to the thermodynamic instability of the gas. It was also found that an increase in N fill content increased melt fluidity, and the trend of melt pressure and melt viscosity index showed that the higher the gas content, the lower the trend. The foaming characteristic depends on the gas thermodynamic instability and the pressure release, so it can be seen from the melt fill path that, the greater the pressure near the gate, the lower the foaming amount and the internal structure (SEM) after molding; the farther from the gate, the greater the relative increase in the foaming growth/amount. This phenomenon will be more obvious when the N fill content is increased.
泡沫塑料成型方法包括热成型、挤出成型和注射成型。注射泡沫成型是一种一次性成型方法，生产效率高，产品质量好。它适用于形状复杂、尺寸要求严格的泡沫塑料制品。它也是生产结构泡沫的主要方法。在本研究中，我们开发了一种结构泡沫注射成型技术，该技术使用与注塑机独特塑化机构相连的气体供应设备，并研究了其对试样熔体流变质量和泡沫结构的影响。在实验中，成型材料为聚丙烯（PP），用于混合/成型发泡特性的气体为氮气（N）。此外，为了观察N/熔体混合的流变特性，设计了熔体流动试样模腔，并使用安装在喷嘴位置的熔体压力传感元件观察熔体粘度指数的变化。通过将氮气供应设备连接到独特的塑化机构，可以在螺杆塑化阶段实现气体与熔融塑料的混合，由于气体的热力学不稳定性，在熔体填充过程中实现发泡效果。还发现，N填充量的增加会提高熔体流动性，熔体压力和熔体粘度指数的趋势表明，气体含量越高，趋势越低。发泡特性取决于气体的热力学不稳定性和压力释放，因此从熔体填充路径可以看出，浇口附近的压力越大，成型后的发泡量和内部结构（SEM）越低；离浇口越远，发泡增长/量的相对增加越大。当N填充量增加时，这种现象会更加明显。
