SIEVE CASCADOGRAPHY FOR CHARACTERIZING PARTICLE SHAPE MIXES OF POWDERS

Particle shape has a profound influence on the behavior of the particles present in powders, controlling the manner in which they react, segregate, flow, and agglomerate. The currently available technique of Fourier transformation to characterize particle shape is cumbersome and can be used only by a skilled operator. Recently developed, the Sieve Cascadograph is able to characterize the shape of particles in the 0.1 to 1.0 mm size range. Employing the principle that the residence time of a particle on a sieve is a function of the particle shape, the Cascadograph consists of a stack of sieves of identical size in a shaking device. An essentially monosize powder sample (closely sized on a regular sieve stack) of about 2 grams is placed in the topmost sieve, and shaking commenced. The weight of powder leaving the lowest sieve is measured as a function of time, and is used to produce a signature representative of the particle shape distribution in the powder sample. Theoretical analysis demonstrates that monosize, monoshape samples leave the lowest sieve at a rate given by the gamma function with respect to time. Preliminary experimental results prove that the Cascadograph results are reproducible, and that a 20-sieve Cascadograph has high resolving power.