Effect of drying temperature on warp and downgrade of 2 by 4's from small-diameter ponderosa pine

Abstract

Kiln drying at high temperature may reduce warp in dimension lumber sawn from small-diameter trees. In this study, we examined the effect on warp of high drying temperatures in conjunction with top loading immediately after drying and after storage in typical conditions that result in further moisture loss. Eight-foot-long 2- by 4-in. (2 by 4) boards sawn from open-grown, 30- to 35-year-old, 9-in.-diameter at breast height ponderosa pine trees were kiln dried at three temperatures, 160°F, 230°F, and 280°F. Crook, bow, and twist were measured and compared. Total grade loss from exceeding Structural Light Framing grade warp limits was also measured. Crook, bow, and twist measured after boards had equilibrated to 14% moisture content decreased by 12%, 29%, and 20%, respectively, with increase in kiln drying temperature from 160°F to 280°F. Total grade loss caused by all forms of warp was 24% lower in boards dried at 230°F than at 160°F and 39% lower in boards dried at 280°F than at 160°F. When boards were equilibrated to 4% to 5% moisture content, warp and grade loss from warp increased significantly.

Citation

Simpson, William T. 2004. Effect of drying temperature on warp and downgrade of 2 by 4''s from small-diameter ponderosa pine. Res. Pap. FPL-RP-624. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory: 8 pages