Sampling and Classification of Powders^[1]

This article summarizes sampling of powders, which includes the sampling of stored material and flowing streams, sample reduction and evaluation, and weight of sample required. It also summarizes the classification of powders. Classifiers are divided into two categories: counterflow equilibrium and crossflow separation. Classification methods are used to exclude certain powder sizes from a powder distribution and to obtain particular powder distributions. For example, sieving methods are used to obtain particular powder distributions and to obtain narrow size ranges of a powder. The article summarizes the sieving methods for powders. The sieving methods include hand sieving, machine sieving, manual wet sieving, air jet sieving, sonic sifter, wet sieving by machine, the Seishin robot sifter, automated systems, and ultrasonic machine sieving. The article outlines the sieve types and the process variables of the sieving process. An appendix reviews dispersion of powders in liquids.