A combined DEM «amp« FEM approach for modelling roll compaction process

Roll compaction is a continuous manufacturing process aiming to produce particulate granules from powders. A roll press typically consists of a screw feeding system, two rolls and a side sealing. Despite its conceptual simplicity, numerical modelling of the process is challenging due to the complexity involving two different mechanisms: feeding by the screw and powder compaction between the rolls. To represent the materials' behaviour both in the feeding zone and in the compaction area, a combined three-dimensional Discrete Elements Method (DEM) and Finite Elements Method (FEM) is developed in this work. The DEM, which is a more suitable method to describe the flow of granular material, is used to model the motion of particles in the feeding zone. As the granular material deforms under high pressure between rolls, FEM offers a more versatile approach to represent the powder behaviour and frictional conditions. In the proposed approach the DEM and FEM are treated as complementary methods, enabling us to take advantages of the strengths of both. In this proposed approach, the time dependent velocity field of the particles at the end of the screw feeder is evaluated as a continuous field using the coarse graining (CG) framework, which was used as input data for the FEM model. FEM is then used to simulate the powder compaction in between the rolls, and the resultant roll pressure and ribbon relative density are obtained. Our results show a direct correlation between the particle velocity driven by the screw conveyor and the roll pressure, both oscillating with the same period. This translates into an anisotropic ribbon with a density profile varying sinusoidally along its width, with a period equal to the duration of a screw turn.