Acoustic analysis of warp potential of green ponderosa pine lumber

This study evaluated the potential of acoustic analysis as presorting criteria to identify warp-prone boards before kiln drying. Dimension lumber, 38 by 89 mm (nominal 2 by 4 in.) and 2.44 m (8 ft) long, sawn from open-grown small-diameter ponderosa pine trees, was acoustically tested lengthwise at green condition. Three acoustic properties (acoustic speed, rate of wave attenuation, and acoustic modulus of elasticity (MOE)) were then determined through waveform analysis. Boards were then kiln dried, and warp was measured immediately after drying and after equilibrating to about 13 percent equilibrium moisture content. Crook and bow measured after drying decreased as acoustic speed and acoustic MOE of green boards increased and rate of wave attenuation of green boards decreased Twist was found to have no relationship with any acoustic propelties of green 2 by 4’s. The results also show a statistically significant correlation between acoustic properties of green 2 by 4’s and the grade loss caused by exceeding warp limits. As the number of Structural Light Framing grade losses from the green grade increased, the acoustic speed and acoustic MOE decreased significantly, whereas rate of wave attenuation increased significantly. However, no relationship was found between green board density and warp and grades lost.