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 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 weight percentage of too coarse (plus material) and too fine (minus material) particles in the finished product. There appears to be some threshold level for the heating effect, but to what extent this is related to the screen deck type, the heat capacity, and density of the material, or the particle size, is still unclear.