Developments in Wood Drying

This article reviews applied and basic research in Canada and U.S. during the preceeding 2 years. Hardwood producers have found that forced or accelerated air-drying has reduced costs. Western softwood mills are automating lumber handling activities with sorters, stackers, and unstackers. Some have reduced costs by as much as 1/2 to 1/3 using repaired rather than new stickers. Some southern mills are using boards, paper, or polyethylene to cover piles of air-drying lumber for reduced degrade and drying time. Certain redwood mills are experimenting with new wax emulsions and sealers. Water. repellent pretreatments are keeping lumber clean and reducing sticker stain. Pre-drying and accelerated air-drying is getting increased attention particularly in the southeast and northern U.S. and eastern Canada, mainly because of advantages in increased capacity, increasing air-dried stock inventory, drying thick hardwoods, and removing high moisture contents in redwood and sweet gum. Several west coast firms using temperatures up to 200?F. for western hemlock and white fir have increased kiln capacity and reduced drying time. New kilns are mostly steam-heated conventional type. Package kilns are popular with small operators especially in the South and Lake states. Prefabricated kilns are widely accepted. Some studies on western softwoods showed improved lumber quality when conventional temperatures were used during initial drying followed by high temperature. In the realm of special drying treatments, the use of solvents has been successful in reducing drying time and degrade for tanoak sapwood and redwood. High frequency drying results have shown costs to be high but a large reduction in drying time is achieved. There is little research on drying chips. Studies of veneer drying have concentrated on improving roller dryers with higher temperatures, uniform air circulations of greater volume and velocity, and improved temperature control resulting in higher quality veneer and shorter drying time. Adverse effects on the wettability of wood surface have been noticed. Studies on predrying by electrical resistance heating followed by conventional drying conclude that this method would probably cost more than current methods. There is a general increase in protecting green and dry lumber during transit and in storage by buildings and various types of physical and chemical surface covers.

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