With foundry sands, the sediments (VDG bulletin P 36) must be removed by a wet process and the remaining samples dried before the screen analysis is performed. The proportions of the individual minus fractions indicate the grain distribution based on which the relative grain fineness can be determined. The test procedure is described in VDG bulletin P34.
It is important that foundries periodically check the grain size and the fines in the sand, in particular. Major changes in the sand grain affect the strength of the molds and cores. In green molding sands (s. Green sand casting, Green sand molding process), an increase of the fines may lead to a dramatic reduction of the mold strength.