Wall slip of highly filled powder injection moulding compounds in dependence on capillary die geometry

Abstract

The feedstocks used in Powder Injection Moulding (PIM) are formed by solid particles incorporated into a binder with presence of surfactant enabling manufacturing of highly concentrated suspensions. Relatively even distribution of particles is violated in the close vicinity of the walls. A thin layer adjacent to the walls is pre-dominantly occupied by the binder only and at the interface wall-binder so-called wall slip occurs. Success and acceptance of an injection moulding step in PIM process primarily subjects to this wall slip phenomenon. The wall slip was qualitatively and quantitatively measured using a capillary rheometer equipped with the dies of different entrance angles. It was proved that this differentness has a significant impact on an appearance of wall slip (its intensity). Using four PIM feedstocks reliable slip velocity values of highly filled compounds were obtained for conical dies contrasting to the results with flat dies used in the majority of studies. © 2019 Author(s).