Sanetrnik Daniel, Hausnerova Berenika, Pata Vladimir
Dept. of Production Engineering, Faculty of Technology, Tomas Bata University in Zlin, nám. T. G. Masaryka 5555, 760 01 Zlín, Czech Republic.
Centre of Polymer Systems, University Institute, Tomas Bata University in Zlin, Trida T. Bati 5678, 760 01 Zlín, Czech Republic.
Polymers (Basel). 2019 Mar 6;11(3):432. doi: 10.3390/polym11030432.
Wall slip in the flow of powder injection molding (PIM) compounds can be the cause of unrealistically low viscosity values, and can lead to a failure of flow simulation approaches. Regardless of its importance, it has been considered only scarcely in the rheological models applied to PIM materials. In this paper, an online extrusion rheometer equipped with rectangular slit dies was used to evaluate the slip velocity of commercial as well as in-house-prepared PIM feedstocks based on metallic and ceramic powders at close-to-processing conditions. The tested slit dies varied in their dimensions and surface roughness. The wall-slip effect was quantified using the Mooney analysis of slip velocities. The smaller gap height (1 mm) supported the wall-slip effect. It was shown that both the binder composition and the powder characteristic affect slip velocity. Slip velocity can be reduced by tailoring a powder particle size distribution towards smaller particle fractions. The thickness of the polymer layer formed at the channel wall is higher for water-soluble feedstocks, while in the case of the catalytic polyacetal feedstocks the effect of surface roughness was manifested through lower viscosity at smooth surfaces.
粉末注射成型（PIM）复合材料流动过程中的壁面滑移可能是导致粘度值低得不符合实际的原因，并且可能导致流动模拟方法失效。尽管其很重要，但在应用于PIM材料的流变模型中却很少被考虑。本文使用配备矩形狭缝模头的在线挤出流变仪，在接近加工条件下评估基于金属和陶瓷粉末的商用以及自制PIM原料的滑移速度。所测试的狭缝模头尺寸和表面粗糙度各不相同。使用滑移速度的门尼分析来量化壁面滑移效应。较小的间隙高度（1毫米）会助长壁面滑移效应。结果表明，粘结剂组成和粉末特性都会影响滑移速度。通过调整粉末粒度分布使其朝向较小颗粒级分，可以降低滑移速度。对于水溶性原料，在通道壁形成的聚合物层厚度更高，而对于催化聚缩醛原料，表面粗糙度的影响则表现为在光滑表面处粘度较低。
