Flakes or strands must be divided into different fractions according to their size in order to be able to form the layers of the panel. At the same time, fine material (dust) and coarse material (oversize) are sorted out. This is done by sieving in a drum screen.
In particleboard production, the fractions are still sifted after screening: Any oversized material still contained as well as heavy material and fine material are removed by the pneumatic process of fraction sifting. The entire process is called screening.
The fine wood dust is burned in the hot gas generator and the energy is used for drying. The fine fraction in OSB production can also be used for particleboard production. Oversized particles are re-shredded in a grinder and fed back into the process.