The influence of particle characteristics on bulk powder properties

2 The influence of particle characteristics on bulk powder properties 

The packing variation in packed products and goods, together with the rate of packing, has to be constantly monitored to maintain production assurance. 

Bulk and pack densities are known to be dependent upon powder feed rates, height of fall and particle morphology when directed into specific volume containment. Thus powder flowability, cohesiveness, impact pressure and powder yield strength together with other physical particle properties such as particle size and particle shape contribute influentially to powder bulk behaviour. 

Kurz and Minz (1975) investigated the flowability of powders in terms of the relationship between the unconfined yield strength, /c, and the major consolidation, tri - the failure function of Jenike — for different-sized limestone powders (3.1-55.0 um) having either a narrow or a wide particle size distribution. The width of the distribution was defined by a variation coefficient, Cv, where Cv = cTstatAi.3, with agtat as the standard deviation of the particle size profile and X1.3 the average particle size of the number-volume diameter distribution of the limestone particles. A narrow distribution was considered to have a Cv 0.5 while a wide distribution had a Cv 0.5. 

It was concluded that average particle size was not the only criterion, which could be used to characterise the cohesiveness of powders, but also the spread of particle sizes in a size distribution was also a significant contributory factor. Limestone powders, with average sizes above 8 pm and a narrow size distribution freely flowed but with the same-sized limestone particles which had a wide distribution, cohesive flow behaviour existed. 

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