Lumber Drying Stresses and Mitigation of Cross-Sectional Deformation
Keywords:Southern red oak, <i>Quercus falcata</i>, shrinkage, cupping, drying stresses, modeling
AbstractLumber drying is a time-consuming and energy-intensive operation that is complicated by shrinkage, which occurs when wood moisture content falls below FSP. Differential shrinkage between radial and tangential directions results in cross-sectional strains that cost the wood industry a substantial amount of money. A novel approach that uses the concept of drying stresses has the potential to mitigate this problem. This study investigated the feasibility of applying an impervious coating to lumber surfaces to induce stresses that minimize a drying distortion called cupping. Flatsawn and quartersawn southern red oak (Quercus falcata) lumber samples from 10 trees were analyzed. Specimens from the same lumber were randomly assigned to three treatments: uncoated, pith-side coated, and bark-side coated for flatsawn specimens; and uncoated, upper-side coated, and bottom-side coated for quartersawn specimens. Quartersawn specimens showed very limited distortion for all three treatments. Cupping was minimized in pith-side-coated flatsawn specimens but exacerbated in bark-sidecoated flatsawn specimens. Experimental strains for flatsawn uncoated specimens agreed with those predicted using a numerical model.
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