Time to Dry 2-, 3-, and 4-Inch S4S Southern Pine At 240 F. as Related to Board Width

Southern pine dried at a dry-bulb temperature of 240?F and a wet-bulb temperature of 160?F with air cross-circulated at 1,000 f.p.m, attained 10 percent moisture content when kilned 11 or 12 hours per inch of thickness. This generalization is true for medium-width lumber (e.g., 8 inches) in thicknesses from 1 through 4 inches. The data confirms and extends conclusions from prior work. In 3- and 4-inch thicknesses, 4-inch-wide lumber required less time to dry than that 8 or 12 inches wide. Surface checks were moderate or absent in lumber of all thicknesses so dried. End checks were minimal in lumber 2 inches thick or less. In 3- and 4-inch-thick lumber, however, end checks penetrating several inches were usual. A high-temperature resistant end coating would likely reduce severity of such end checks. Only rarely did internal checks develop; they were observed only in 4 by 4’s dried to 10 percent MC or less. Internal checks in 2- and 3-inch-thick lumber were not observed. Case hardening in 4 by 8’s was relieved by 4 hours of steaming at 195?F dry-bulb temperature and 185?F wet-bulb temperature. Prior experience indicates that 3 hours of conditioning is sufficient to relieve case hardening in 2-inch-thick lumber. Crook and bow in this experiment averaged 0.20 inch, while twist averaged 0.23 inch. Width shrinkage to 10 percent moisture content averaged about 0.03 inch per inch of green width. Thickness shrinkage was somewhat less in 4-inch-wide boards than in wider boards; with width data pooled, thickness shrinkage averaged 0.09, 0.15, and 0.17 inch for 2-, 34, and 4-inchthick lumber dried to 10 percent moisture content. Considerable resin exuded to the surface of a few pieces, but most remained clear. Where such exudations would be objectionable, they could be removed by a light planing.

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