A probalistic screen with electrically heated decks has been used to produce narrow size fractions of magnetite and olivine below 1 mm. The results indicate that the major limiting production factor is the amount of too fine materials in the desired size fraction. This can be corrected by re-screening the narrow size fraction in various ways, but the best result is had with an air classifier.

The probalistic screen may be evaluated in the same way as a classifier with a cut point and sharpness of separation for each screen deck, and as a total for combinations of screen decks. However, the best way to evaluate the screening results is to plot the proportion of finished product, and the loss of the correct fraction as a function of feed rate and moisture content. These being quantity results, they need to be supplemented with quality parameters, and the best seem to be the percentage of too coarse and too fine particles in the finished product.