Analytical testing of powders used or produced in industrial applications is based on the characteristics of the particle size distribution of the material. Fractions of the same product with different distributions have different physical properties, so for authentic and reproducible measurements, a particle analysis test must be performed.

1. Sampling

One of the most difficult and uncertain parts of particle analysis is sampling. Examining the same product, we can get different results if our sampling is not appropriate. For the sake of repeatability, it is therefore important that the particle size distribution of the tested sample approximates the particle size distribution of the product set as closely as possible. This task is particularly difficult if we have a large quantity (up to several tons of product) available for sampling. In such a case, the product must be sampled in several different places, and then it is advisable to continue working with a mixture of these. In such a case, it is advisable to use trial dividers operating on different principles to divide the samples received in our laboratory into equal fractions.

2. Test

The number and hole size of the sieves used is determined by the distribution spectrum of the sample. Before starting the process, the sieves used, the delivery quantity and other parameters of the sieve, such as frequency and amplitude, must be selected accordingly. Sifting is carried out according to the DIN 66165 standard.

3. Evaluation, protocol

After the software evaluation of the sifted quantities, the parameters determining the sifting and the obtained results, diagrams, and conclusions are recorded in a report. Contents of the report issued as a result of the investigation:

particle distribution curve

frequency curve

crossover and residual curve

average particle size

median grain size

Explosion protection aspect

In the field of explosion protection, the guiding value is 500 µm, because above this particle size, the combustion speed is not fast enough to speak of an explosion. So if a product does not contain a significant fraction below 500 µm, it is not dangerous from an explosion protection point of view.

The smaller and lighter a dust particle is, the easier it remains in the floating state, so from the point of view of explosion protection, this fraction is more dangerous. According to the standard describing the determination of explosion parameters, before each test, the dust sample must be sieved to a specific particle size in order for the obtained results to approximate the explosion properties from a safety perspective.