Rheological Studies on the Compression and Shearing Procedures of Some Powder Beds

Abstract

The angle of internal friction is one of the most important properties of powder and is often used to characterize powder in industry. In general, the angle of internal friction is determined from the slope of yield locus. However, it has been reported in many previous works that the shape of yield locus was affected by the preconsolidation or compaction pressure. Thus the significance of this property has been confused considerably. In this paper, the shape of yield locus was studied to establish the rheological significance of angle of internal friction through observations mainly from the view point of microscopic structure of powder beds.For lactose and calcium carbonate powders compacted under various pressures, the yield loci were determined. The results obtained show that the curves of shear index determined from the slope of yield locus can be divided into two characteristic parts at the specific compaction pressure, and that the porosity and strength of compacted powder bed change discontinuously also at this critical point.It can be concluded that the contact mechanisms of particles have been affected by compaction pressure, and also that the shape of yield locus is determined by the contact mechanisms.