Critical Phenomena of Rheodynamic Origin in the Process of One-Sided Cold Pressing of Powder Materials

Abstract

In this paper, a comparative analysis is carried out of the kinetics of compaction of a powder material in the process of one-sided cold pressing for different modes depending on the externally set conditions for the movement of the press plunger: the modes of constant specified force or speed. It is shown that in the constant speed mode, a critical phenomenon is realized on the press plunger, which is accompanied by a progressive increase in pressure over time, ensuring a sharp increase in the compaction speed. As a result, after a certain period of induction, the compaction process begins to accelerate automatically over time. The described situation has a physical analogue of combustion and explosion. This circumstance allows us to introduce new ideas into the theory of powder material pressing processes. Based on numerical calculations, it is established that the dependence of the press plunger speed on the voltage on it has a non-monotonic nature, which is due to the competitive influence of the dynamic factor: the loads and dependence of the bulk viscosity on density. It is shown that in the given force mode, a “harmful effect” occurs: progressive auto-braking of the compaction process over time. The conducted analysis allows us to develop specific recommendations for predicting rational modes of one-sided pressing of powder materials.