Longitudinal growth strain effect on lumber warp from small yellow -poplar logs

Jose Rafael Serrano Montero, Purdue University

Abstract

Growth stresses are stresses that develop in woody plants. The release of growth stresses generates splits and distortions in both logs and lumber. Therefore, high levels of growth stress in the tree may reduce lumber quality and cause processing problems. This study investigated the effect of surface longitudinal growth strains (GS), sawing patterns and stud position in the tree on warp of yellow poplar 2 by 4's. A sample of trees was harvested during August and processed by the SDR process and the CANT sawing pattern. All the sawn pieces were exposed to the same drying conditions. After air drying, the flitches produced by the SDR process were ripped using a straight-line ripsaw to produce the 2 by 4 studs. Top logs were used to assess the idea that drying stresses can offset growth stresses resulting in straighter lumber. The level of GS increased significantly from May to September. Therefore, harvesting and processing the trees before the dormant period should result in lower levels of GS and perhaps less warping. GS averages for the butt logs were significantly lower than the second logs. Trees with large GS differences between the butt and the second log generated a higher level of green warping with minor increases following drying. After ripping, the studs from the SDR process presented lower levels of warping; however no significant differences were detected after the planing process. Studs with a flat grain pattern presented a higher level of bow and a lower level of crook than those with a quarter grain pattern. However, crook, twist and long checks in quarter sawn studs from the juvenile zone were critical for the market. By acting against each other, growth and drying stresses may help to produce straighter/split free glued pieces from the juvenile core. Log end splits generated in upper crosscuts of the tree bole were found to be good predictors of GS levels in trees and logs and of subsequent warping of the lumber produced from them. It is likely that genotypes of yellow poplar presenting low level of end splitting will reduce growth stress associated problems.

Degree

Ph.D.

Advisors

Cassens, Purdue University.

Subject Area

Wood|Technology|Forestry

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