Abstract

Atmospheric humidity is introduced into powders during handling, transportation, and storage. High moisture content can increase cohesive forces between particles and make it difficult to spread a powder into thin layers in powder bed processes or to fill a mold in processes such as press-and-sinter. Furthermore, water can cause porosity and uptake of oxygen in the final component, damaging its mechanical properties. In this study, a Freeman FT4 powder rheometer was placed inside a climate chamber. Both flowability and shear tests were performed on four steel powders under a range of humidity and temperatures. Basic flowability energy and specific energy were both found to increase significantly with humidity (typically increase by 50% for 80% of relative humidity compared to dry conditions) and were insensitive to temperature change (10–30 °C). Conversely, the behavior of the powders under shear was neither sensitive to relative humidity nor temperature. Measurements of moisture content revealed that finer powders contained more moisture than coarser ones, but the moisture content was not correlated with humidity, probably due to shortcomings with the measurement method. This knowledge can be used to optimize powder processing conditions.

摘要

在处理、运输和储存过程中，大气湿度会被引入粉末中。高水分含量会增加颗粒之间的内聚力，并且难以在粉末床工艺中将粉末分散成薄层或在压制和烧结等工艺中填充模具。此外，水会导致最终组件中的孔隙率和氧气吸收，从而损害其机械性能。在这项研究中，Freeman FT4 粉末流变仪被放置在气候室内。在一定湿度和温度范围内对四种钢粉进行流动性和剪切试验。发现基本流动能和比能都随湿度显着增加（与干燥条件相比，80% 的相对湿度通常增加 50%），并且对温度变化不敏感（10-30°C）。相反，粉末在剪切下的行为对相对湿度和温度都不敏感。水分含量的测量表明，较细的粉末比粗粉含有更多的水分，但水分含量与湿度无关，可能是由于测量方法存在缺陷。该知识可用于优化粉末加工条件。