Controlled-Air Seasoning of Wood for Preservative Treatment

A description is given of a “controlled-air” seasoning process which fills the need for an accelerated drying technique for wood members to be treated. Simple air-drying depends on atmospheric heat to remove moisture, and climatic conditions in many areas are such that extremely large inventories must be carried in stocks being air-dried. The control available in conventional kiln-drying is not required for this operation, since for treatment purposes it is not usually necessary to dry the material below 20 to 40 percent moisture content. The controlled-air seasoning process (U.S. Patent 2,706,344) is carried out in an insulated shed, with heat supplied at one end. The wood moves counter current to the heat input on trams or conveyors, and both heat input and air, velocity are regulated manually or automatically. Typical schedules are: Southern pine poles and timbers — 8 to 10 days to 40 percent M.C.; gum crossties and switchties– 16 to 20 days to 50 percent M.C.; southern pine lumber 3 to 5 inches thick– 16 to 18 days to 20 percent M.C. Economical size units will produce, on a monthly basis, 60,000 to 75,000 cu. ft. of southern pine poles; 320,000 to 500,000 board feet of lumber; or 12,000 to 18,000 gum crossties.

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