Distortions of Wood: Drying with and Without Restraint

Distortions of wood deduced from pure geometrical considerations were compared with those obtained experimentally. The samples used were turned wood cylinders (1/4-inch thick and 6-1/4-inches long) from Sitka spruce grown in England. In addition, distortion reduction methods were studied using end-matched 2-ply strips and solid samples from both quarter-sawn and slash-cut boards of three hardwood species. It was found for spruce that twist increased with increased angle of spirality, and decreased with increased distance from pith, during drying at 77?F and 90 percent relative humidity. It was concluded that slash-cut material from near the outside of a tree or wide quarter-sawn material from larger trees, twists less in seasoning than does material from smaller trees. Restraint imposed during drying at 77?F and 45 percent relative humidity, minimized distortion more in beech than in African mahogany. It was more effective in reducing cross-grain distortion (cup) than longitudinal distortion (bow), while a combination of restraint and drying from the green condition at a temperature of 140?F and a relative short high temperature treatment for 12 hours at 212?F when almost dried brought more effective minimizing with Keruing (Diterocarpus spp.). Green wood behaved better than did partially dried wood. A method of limiting twist by mechanical restraint was investigated. For green Sitka spruce planks (4- by 2-inch and 5- by 2-inch), dried at 120?F and 80 percent relative humidity with induced mechanical counteracting twist, average twist was only 1.43 degrees, whereas controls developed 5.04 degrees.

You must be logged in to download any documents. Please login (login accounts are free) or learn how to Become a Member