Bow variation in kiln-dried boxed-heart square timber of sugi (Cryptomeria japonica) cultivars

Abstract

To evaluate the bow variation in boxed-heart square timber of sugi (Cryptomeria japonica), bows from kiln-dried timber for fi ve sugi cultivars with different longitudinal shrinkage trends were compared for two stem heights. Two general trends were observed, depending on the cultivar: (1) either the bow was larger at the lower than at the upper part of the stem, or (2) the bows at the lower and the upper parts of the stem were similar. In timber that had larger bow values, the gradients of longitudinal shrinkage were large across the radius and along the length of the timber. There was a positive relationship between the bow and longitudinal shrinkage. These results suggest that the bow variation between the timbers was caused by a variation in longitudinal shrinkage, which was affected by the microfi bril angle. Furthermore, the bow was inversely proportional to the modulus of elasticity, which suggests that timber with a low modulus of elasticity is susceptible to a large bow due to large longitudinal shrinkage.

Surface-check variation in boxed-heart square timber of sugi (Cryptomeria japonica) cultivars dried by the conventional kiln drying

“…For ryuunohige and kumotooshi (R, K), MC GT was higher in timber 1 than in timber 4, since the moisture contents of their heartwood were high (R1 94%, K1 152%) as shown in our previous study [8]. The MC DT was higher in timber 1 than in timber 4 for boka-sugi, ryuunohige, and kumotooshi (B, R, K), since timber 1 contained a larger percentage of heartwood.…”

“…The sample trees were used in our previous studies on shrinkage [6,7] and bow [8]. The trees of each cultivar were taken from the same stands (boka-sugi: Takaoka, Toyama; aya-sugi and yabukururi: Kahoku, Kumamoto; ryuunohige and kumotooshi: Kikuchi, Kumamoto).…”

“…Tangential and radial shrinkages from the green to oven-dry conditions (a T ii, a R ii) at 60 mm from the pith (suffix ii indicates the distance from the pith [8]) were measured using small clear samples of dimensions 30 (T) 9 30 (R) 9 5 (L) mm for boka-sugi, aya-sugi, and ryuunohige, and 20 (T) 9 20 (R) 9 5 (L) mm for yabukuguri and kumotooshi. Basic density (BD) was measured using small blocks cut at 20 mm intervals from the pith to the edge of the timber, and then averaged.…”

“…The surface checks extending from the end of the timber (end-surface check) and the surface checks not extending from the end of the timber (center-surface check) were also separated. The bow distortion of the timber was calculated as the sum of the maximum deflections of all planes divided by the length at the point of green condition [8]. The moisture contents of the green timber (MC GT ) and dried timber (MC DT ) were obtained as a fraction of the oven-dry wood weight.…”

“…In this study, the surface-check variation of sugi boxedheart square timber was evaluated using conventional kilndried timber taken at different heights along the stem for five cultivars with different wood properties [6][7][8]. The relationships between surface checks and moisture gradient, shrinkage, and bow were investigated.…”