Die filling is a critical process step in many industries. The majority of powders or powder mixtures utilised in these industries are fine powders. Powder properties dictate the die filling rate. Die filling may cause segregation in a powder blend, which can, for example, have the detrimental effect of changing the concentration of an API in a medicinal tablet.
Using a wide range of powders, the effect of die size and die orifice shape, were investigated, as well as die orientation and aspect ratio of non-axis symmetrical dies. Passive and active die filling were compared, and the effect of varying shoe length during active die filling was also studied. Hopper flow and die filling were modelled using physical equations. The predictions of these equations were compared to the Beverloo Equations. Furthermore, size and density induced segregation of binary powder mixtures during die filling was studied.
The mass flow rate of the small die was lower than the large die even when normalised by die orifice surface area due to the trapped air dampening the flow rate more for orifices with small surface area. Higher critical filling speeds were achieved with all powders when using broad non-axis symmetrical dies in the parallel orientation. For die filling in a rotary die filling system, an empirical correlation for the prediction of the weight in the die at a given shoe speed and the critical filling speeds of any powder was developed. For hopper flow and passive die filling, physical equations were developed that were able to predict the mass flow rate of a wide range of powder more accurately than the Beverloo Equation. Finally, two segregation mechanisms were identified (sieving segregation and fluidization segregation) to occur during die filling and the speed of the shoe affected the balance between the two mechanisms.