Understanding and minimizing variation sources in dry sieving tests
Accurately determining the particle size distribution of a dry powder or granular material can help you improve processing efficiency and product quality. A dry sieving test, also called sieve analysis, is the most widely accepted method for determining particle size distribution. However, variation among results for different sieving tests of the same material is common. To use a sieving test effectively, you need to understand and minimize the sources contributing to variation in particle size distribution results. This article's first two sections describe an example sieving test series and how variation sources affected the test results. The final sections describe how to minimize variation sources in your sieving tests and how to account for inherent variation in your test results.
In a dry sieving test, a material sample is separated into various size fractions by running it through a nested set of woven wire mesh sieves [screens] of different mesh sizes, called a sieve stuck. The sieves in each stack are arranged with the largest, or coarsest, mesh size on top and succeedingly smaller, or finer, mesh sizes toward the bottom; a pan for collecting fines is located below the bottom sieve. After a sample is placed into the top sieve, a sieving machine agitates the sieve stack to sieve the sample. Weighing the material retained on each sieve and the collecting pan after the test determines the material's particle size distribution. The distribution can be recorded in percentage of sample weight passing each sieve, percentage of sample weight retained on each sieve, or cumulative percentage of sample weight retained [the weight retained on a particular sieve and on all preceding sieves].