Abstract: Procedure for the fabrication of a blank for a structural product, such as a blank for a structural board, from material (1) comprising longer (L) and shorter (S) particles and possibly also particles (F) smaller than these. The particles are mixed with a binding agent and possible additives and then passed into at least one blank former, from where the particles are brought onto a base (10). Longer particles (L) are brought onto the base (10) to form a first surface layer, onto which is brought at least one layer of smaller particles (F, S), and onto this layer is again brought a layer of longer particles (L) to form a second surface layer, the smallest particles (F) being so brought onto the base that they mainly end up in at least one middle layer in the cross-section of the blank while the amount of the smallest particles (F) diminishes towards the surface layers as seen in the cross-section of the blank.

Abstract: The invention relates to a method and apparatus for screening pulverized or chip material, such as fibers or wood chips, free from impurities. The material to be screened is fed onto a roll set formed by a number of adjacent, essentially parallel rolls (1) and is brought to an advantageous movement with the help of the rolls (1), whereby material particles of highest density drift downward closest to the surfaces of the rolls and that the material fraction closest to the roll surfaces can escape the rolls via a gap (B) a width essentially larger than the gap width (A) of the preceding roll pairs.