Department of Pharmaceutical Sciences, Hoshi University.
Department of Physical Chemistry, School of Pharmacy and Pharmaceutical Sciences, Hoshi University.
Chem Pharm Bull (Tokyo). 2024;72(1):86-92. doi: 10.1248/cpb.c23-00721.
For powder compaction, the Kawakita equation has been used to estimate the powder behavior inside the die. The compression pressure exerted on powders is not homogeneous because of the friction on the die wall. However, the yield pressure and porosity estimated using the Kawakita equation are defined based on the assumption that homogeneous voids and compression pressure are distributed throughout the powder bed. In this study, an extended Kawakita equation was derived by considering the variation in the compression pressure as it corresponds to the distance from the loading punch surface. The yield time section estimated from the extended Kawakita equation was wider than that which was estimated via the classical equation. This result is consistent with the assumptions used to derive the extended Kawakita equation. Furthermore, a comparison of the porosity changes before and after the yield pressure was applied indicate that the direct cause of the yield is the spatial constraints of the powder particles. Equivalent stresses were defined to clarify the critical factor that constitutes the extended Kawakita equation. As a result, "taking into account the die wall friction" was considered to be the critical factor in the extended Kawakita equation. As these findings were theoretically determined by the extended Kawakita equation, a useful model was derived for a better understanding of powder compaction in die.
对于粉末压实，川北田方程已被用于估计模具内粉末的行为。由于模具壁的摩擦，作用在粉末上的压缩压力不均匀。然而，使用川北田方程估计的屈服压力和孔隙率是基于假设整个粉末床均匀分布有空隙和压缩压力的情况下定义的。在本研究中，通过考虑与加载冲头表面的距离相对应的压缩压力的变化，导出了扩展的川北田方程。从扩展的川北田方程估计的屈服时间部分比通过经典方程估计的部分宽。这一结果与推导扩展川北田方程所使用的假设一致。此外，对屈服压力施加前后孔隙率变化的比较表明，屈服的直接原因是粉末颗粒的空间约束。定义了等效应力以阐明构成扩展川北田方程的关键因素。结果表明，“考虑到模具壁摩擦”被认为是扩展川北田方程的关键因素。由于这些发现是通过扩展的川北田方程从理论上确定的，因此为更好地理解模具中的粉末压实，推导出了一个有用的模型。
