Adhesive application tumbling

Primer and adhesive application are generally accomplished by spraying, brushing, tumbling or dipping. Each different application method has its own strengths and weaknesses. The choice of the application method is dependent on the size and shape of the parts, the number of parts to be coated, and whether the part is to be wholly or only partially coated. 

Chips and shavings from scrap logs or from the processing of lumber are screened to the desired size. After drying to a moisture content of about 7 %, the chips are coated with the resin adhesive, usually to about 7-9%, solids basis. The adhesive can be sprayed onto the chips as they tumble in a blender. A wax emulsion may also be applied to reduce the water absorption of the finished board. Total moisture content of the resin coated chips should be in the range of 8-12%. Too much moisture can cause blisters when the cured board is removed from the heated press. After application of the resin, the treated flakes are spread onto trays and formed into a mat which may be prepressed, and then loaded into a multiplaten heated press for curing. Cure time will depend on the thickness of the board and may be in the range of 10-20 minutes at a temperature of 125-175°C. 

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