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Numerical simulation of roll compaction of aerated powders

机译：充气粉辊压实的数值模拟

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Permeating air is known to have a negative impact on the roller compaction process, because the feed is destabilized by the flow of escaping gas, causing pressure to build-up and potentially damage compacts at release. Airflow during powder roller compaction and its effect on the rolling process are investigated in the rolling direction (1D), using an extension of the Johanson model for the solid. Fluid transport obeys Darcy's law, with permeability being a function of both material density and particle size, through the Kozeny-Carman relationship. In this modeling, the effect of the air pressure on the solid is neglected in the compaction zone. Assuming air at atmospheric pressure at the feeding angle and ignoring airflow through the gap, predictions of air pressure as a function of the rolling angle for bentonite material powder are presented and discussed. Results suggest the existence of two different stability zones within the operating conditions, where industrial systems could function without being affected by airflow effects. The model highlights the importance of the permeability/rotation speed ratio, which governs the proportion of air trapped in the compacts to the portion evacuated through the feed. We also investigate the effect of particle fragmentation during the rolling process. Finally, we provide guidelines for the scale-up of roller presses subjected to air flow issues, through a study of the effect of the system dimensions and rotation speed on the elimination of air. In spite of the lack of available experimental data, this model allows for a better understanding of how air escapes by diffusing through the material during the rolling process, and opens interesting perspectives for the mitigation of its effect on the process.
机译：众所周知，渗透的空气会对辊压实过程产生负面影响，因为进料会因逸出的气体流而不稳定，从而导致压力积聚并在释放时损坏压坯。使用Johanson模型的扩展，研究了压粉辊压实过程中的气流及其对轧制过程的影响（1D）。流体运输遵循达西定律，通过科泽尼-卡曼关系，渗透率是材料密度和粒径的函数。在此模型中，在压实区中忽略了气压对固体的影响。假设空气在大气压下处于进料角，而忽略了通过间隙的气流，则介绍并讨论了空气压力随膨润土材料粉末的滚动角而变化的预测。结果表明在运行条件下存在两个不同的稳定区，工业系统可以在其中不受气流影响的情况下运行。该模型强调了渗透率/转速比的重要性，它决定了压在压坯中的空气与通过进料排出的部分的比例。我们还研究了轧制过程中颗粒破碎的影响。最后，我们通过研究系统尺寸和转速对消除空气的影响，为遭受气流问题的辊压机的放大提供了指南。尽管缺乏可用的实验数据，该模型仍可以更好地了解空气如何通过在轧制过程中扩散穿过材料而逸出，并为减轻其对工艺的影响开辟了有趣的前景。

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