THE COMPACTION OF METAL POWDERS BY ROLLING. II.–AN EXAMINATION OF THE COMPACTION PROCESS

Abstract

The compaction process is examined in detail. It is shown that, where particle deformation is concerned, compaction by rolling is similar to compaction by static pressing, with the addition of elongation of the particles in the rolling direction when the rolling pressure is sufficiently high. A method for determining the average roll pressure is described. A comparison of the rolling of a metal powder with the rolling of a solid bar, and the determination of the effect of particle shape and mean size, indicates that not only roll/powder friction but also the slip between particles plays an important role in the compaction process. This leads to an examination of the flow properties of powders, which are measured in terms of a “powder-viscosity factor” that indicates whether and at what order of rolling speed a powder can be coherently compacted. Finally, a mechanism of compaction is proposed on the basis of the present findings and on the authors’ earlier work.