Shape Changes in Hornbeam (Carpinus betulus L.) Lumber Induced by Spiral Grain

Abstract

Hornbeam (Carpinus betulus L.) wood often has a spiral grain character, which contributes to shape instability in the resulting products. Spiral grain refers to the deviation of wood fibers from the longitudinal axis. This study identified and quantified specific shape changes caused by spiral grain in hornbeam samples. Differences between samples were analyzed with varying degrees of spiral grain and their impact on the shape stability of hornbeam lumber. Changes in the warp cup and the warp twist were monitored during three months of an air-drying process. Moisture loss was found to have a significant influence on the increase in the observed types of warps. An average rise in warp cup from 0 mm to 0.61 mm was recorded in specimens lacking spiral grain, whereas in specimens exhibiting spiral grain, it was raised from 0 mm to 0.92 mm over the same period. Warp twist was increased from a mean value of 7.2 mm in non-spiral-grain specimens to 19.6 mm in spiral-grain specimens. Moreover, the original position of the lumber pieces within the logs whether adjacent to the pith or the bark was determined to be a significant factor in the final type and size of the warp (curvature). This study highlights the critical role of spiral grain and log positioning in shaping the dimensional stability of hornbeam lumber during drying.