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Analysis of strain stress state in roller compaction process

Abstract : The process of drawing and densification of powdered microcrystalline cellulose by roller press in a steady state operation is analyzed using a 2D modeling with the finite element method and the modified Drucker-Prager Cap model as material behavior. Distributions of process variables in contact surface between powder and roller such as pressure, shear stress and relative speed were predicted and used to analyze the basic mechanisms of the transport and the densification of powder between rolls. The results show clearly the existence of three contiguous zones: a phase where the powder is drawn between rolls by a sliding mechanism, a sticking phase where the powder is transported with the same velocity as the roll and where the densification by deforming the powder bed is achieved under the increase of roll pressure that reaches its peak before the neutral angle. The formed compact is then expulsed out of the gap by a slip mechanism resulting from the change of the sign of the shear stress. The predicted density distribution between the rolls, shows a gradual increase. The density reaches its maximum before the neutral point and shows values in agreement with the density of strips prepared with an instrumented roll press. The effect of varying the material parameters on the maximum pressure and the nip angle s also investigated. Beyond the description of the basic mechanisms of roller compaction, this modeling shows a real potential of the optimization of the roller compaction process.
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Abderrahim Michrafy, Harona Diarra, John A. Dodds, M. Michrafy, Luc Penazzi. Analysis of strain stress state in roller compaction process. Powder Technology, Elsevier, 2011, 208 (2, SI), pp.417-422. ⟨10.1016/j.powtec.2010.08.037⟩. ⟨hal-01680752⟩



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