Particleboard screening

From the dryer, the strands are screened to remove fines and small particles, which would detract from board quaHty and economy. These fines are burned for fuel or possibly sold to a nearby particleboard mill as raw material. The larger strands are used as surface material and the smaller strands are core material. 

In the production of particleboards, mixtures of particles are often used as raw material. The particles differ in size and shape. A particle size distribution can be done by screening, and two of the three dimensions of the particle must be smaller than the standard measure of the screen to be passed. An exact screening of the particles to their size is only possible for rather similar shapes. Particles, however, can widely differ in shape. For a simplifying description, the shape is assumed as a flat square of length I, width b and thickness d for medium and coarse particles and cubic for the fines. The mechanical screens are graded in... 

Chippers and flakers are the most widely used knife reduction systems. Chippers produce coarse particles from roundwood, slabs, plywood trim, and other residues from the primary wood industry. Chippers are the initial reduction step in particle preparation and further size reduction is necessary to produce a satisfactory particle. The chipping operation may be located at the particleboard plant or the chips may be delivered to the plant from an in-woods chipping operation, a chip-n-saw mill, or from another primary wood industry. Screening after the chipper removes all fines and oversize chips before they enter the secondary reduction step. Oversize chips are recycled to the chipper and fines are normally sent to the boiler for fuel. 

The enthusiasm in this field is explained by the number of potential applications. For example wood-polymer composites (WPC), mostly manufactured through extmsion and injection moulding processes are used in automotive (dashboards or screen-doors of the vehicles) and construction applications (interior floor coverings, profiles for doors and windows, ornamental panels, external shutters, pavements, garage, or entrance doors). Replacement of wood products for building applications such as particleboard and fiberboard materials or injection mouldable wood is another area where natural fibers are generating increased interest. 

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