木材の質的生産技術に関する研究 : (II) 枝打ちとボタン材

Abstract

スギ材におけるボタンの発生を主に枝打技術との関連において調査した。1. 材に発生したボタンはその発生場所, 原因に基づいてα_l, α_2, βの3型に分類した。α_1型は生枝打, α_2型は自然落枝, β型はその他の自然, 人為の様々の原因によって, 節に無関係におこる。2. α_1型は生枝打によって幹表面に傷ができたことによって発生し, その発生率は節径の大きいほど高かくなった。また, 枝打季節が関係をもつようで, この場合, 2月枝打が発生率において低かった。3. ボタンはおおむね相似形で発達した。α_1型の発達には節の太さと季節が関係をもっていた。4. α_2型は自然落枝にともなって発生し, 材の中に巻込まれた死節が長いもので発生率が高かった。生枝打ではほとんど発生しなかった。その発達はα_1型に比し, 一般に小さかった。5. ボタン材の部分において|α|値が正常材に比して大きい場合があり, 比引張強度は小さい傾向があった。

Botans are the discoloration of wood originating from mechanical wounds of living tree trunks, and correspond to artificial heartwood formation. In the previous paper, it was mentioned that environmental factors have no effect on the development of Botan, while intensity of pruning is very effective. The present studies which were undertaken on Sugi (Cryptomeria japonica) stands on Kuma-Chyo, Ehime Pref., aimed to clarify the development of Botan in connection with green pruning. 1. Botans developed in Sugi wood were classified into three types: α1, α2 and β. 2. Botan originating from a wound of trunk accompanied by green pruning is classified into α1 type. α2 type develops around the base of a knot of natural pruning, and the one which has no connection with a knot in its origin is classified into β type. 3. The rate of formation of α1 type depends upon diameter of the knot and season of pruning. The rate of formation increases with the increase of diameter of knot, and it was considerably smaller in Feb. pruning compared with Oct. and Dec. pruning. 4. The extent of α1 type is also related to diameter of knot and season of pruning. There was a loose relation between diameter of knot and the extent of α1 type, and the max. longitudinal length became greater with increase of diameter of knot. The extent of α1 type was remarkably small in Feb. pruning compared with other seasons. 5. The rate of formation of α2 type had no connection with diameter of knot, but with the length of loose knot. It was remarkably high in loose knots over 30mm. in length. The extent of α2 type had no relation with diameter of knot and they were generally smaller than the other types. 6. The values of | α | in Botan wood were larger than those in normal wood. These results might show existence of large growth stress in Botan wood. The values of specific tensile strength in Botan wood were smaller than those in normal wood and were almost the same as those in juvenile wood.