ABSTRACT
I. INTRODUCTION The flow of powders and granular materials, often termed particulate solids and having a solids volume fraction that typically ranges from 0.3 to 0.6. is encountered in many aspects of everyday life. It is also important in several practical applications involving powder metallurgy. soil mechanics. ceramic science, and polymer engineering. Plastic pellets and powders. for example. are stored in bins and hoppers, and these containers have to be designed for emptying in a freeflowing manner. Ln recent years, powder coatings have become important and have replaced liquid surface coatings in many applications. The flow characteristics of such powders are essential to the successful use of these coatings. Another place where the flow of polymer powders is encountered is in rotational molding. Ln addition. granular polymers and polymer pelJets are melted in extruders and are also compounded, either with rubber to form toughened polymers or with glass fibers to give reinforced polymers. The rheological properties of these granular materials before they become melted down to a liquid are important to the proper performance of extruders and injection molding machines. Ln particular, an appreciable fraction of the energy used to operate these machines can go into the polymer while it is in the granular state.
