Interparticle Forces and Cohesive Powder Flow

摘要

Powder flow behavior is a manifestation of the interparticle interactions occurring during the transport and handling of materials. A correlation between the interparticle forces and the bulk behavior is required to develop a predictive model for cohesive powder flow behavior. Current methodologies rely on extensive testing and are not scalable to different operating conditions. The current study deals with role of liquid bridges in cohesive powder flow. The adhesion forces between particles due to the liquid bridges are measured using an atomic force microscope (AFM). The flow characteristics of the powder depend on the unconfined yield strength, which were measured using a direct shear tester, the Schulze tester in this study. A model based on the particle size and binder content is developed and shown to reasonably predict the unconfined yield strength of powder samples. The variables involved in the current model are the particle size distribution, co-ordination number and the number of particles per unit area (dictated by the packing), binder content, consolidation pressure, and the width of the shear zone participating in the shear. Results for a bimodal particle size distribution as a function of oil content are compared to theoretical predictions. The final objective is to have a predictive model for the strength of powder samples under different process conditions based on the characteristics of the powder (particle size) and operating conditions (humidity, binder content).