WHENEVER POWDER is analyzed, whether for physical or chemical assay, the quality of the measurement depends upon how representative the sample is of the bulk from which it is drawn. The measurement may be made on a few milligrams taken from a bulk of many tons, so the chances of measuring a nonrepresentative sample are considerable. Therefore, sampling regimes and/or methods are needed to obtain representative samples for analysis.

In addition, classification methods are used to exclude certain powder sizes from a powder distribution, or to obtain particular powder distributions. Sieving methods, for example, are used to obtain particular powder distributions, or to obtain narrow size ranges of a powder.

This article briefly summarizes sampling, classification, and sieving methods for powders. The properties of metal powders are statistical in nature, so the material to be tested should be properly blended or mixed. An ideal mix is one in which all particles and constituents are distributed uniformly throughout the mixture. This condition is accomplished only through proper application of the variables involved in the mixing process, such as type of blender, volume of metal powder, rotational speed of the blender, and blending time (see the articles "Blending and Premixing of Metal Powders and Binders" and "Effect of Blending Techniques on Properties of Metal Powder Mixes" in this Volume).

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