Wood chip screening and processing method and apparatus

A method of separating and classifying chipped whole trees comprising essentially a mixture of wood and bark overs, chips including some with adhering bark material, and bark and other fines, the overs being in the neighborhood of ten percent by volume and the fines in the neighborhood of twenty-five percent by volume, comprising:

• a. receiving the mixture in a large capacity bin having a first stationary screen trough system with rotating thin blade helical auger conveyors therein extending across the bottom of the bin and forwardly beyond the bin in a longitudinal direction;
• b. augering the mixture in a forward direction longitudinally across the bottom of the bin and variably restricting the opening out of the bin to control the outflow of material in the trough system;
• c. continuing to auger the mixture forwardly in a monitored flow while passing it across a stationary screen portion of the trough system having openings of a size to pass everything but the overs;
• d. moving the mixture forwardly at a rate such as to spread the material along the trough system in a rolling bed which covers approximately thirty percent of the trough by volume and leaves exposed screen surfaces on the rotary downstream side of the auger conveyors;
• e. tumbling the said rolling bed, propelling chips through the openings in the exposed screen surface, and hooking out elongate overs from said openings as the mixture is moved forwardly;
• f. contacting the chips with adhering bark with the helical flight edges to rub the bark off in the form of bark fines, and without damaging the chips;
• g. continuing to auger the overs forwardly to an overs discharge station;
• h. rechipping the overs and blowing them back to the rear portion of the first trough system in an air stream;
• i. centrifugally separating the rechipped overs from the air stream in which they are entrained so that the air stream does not disturb the separating operation, and depositing them by gravity on the first trough system;
• j. collecting the material passed through the first trough system and augering it forwardly, while rubbing bark from said chips across a second stationary screen trough system having openings of a size to pass the fines while retaining acceptable chips;
• k. continuing to auger the acceptable chips forwardly to a chip discharge station and collecting them in a pile;
• and
• l. transporting the fines passed through the second screen trough system and collecting them in a pile.