Diagnosis of Production Facilities of Bandsaw Mills by Sawing Accuracy : Investigative report at Norwegian bandsaw mills

Abstract

ノルウェーの帯鋸製材工場で夏と冬に合計231本の製材について挽材精度と挽道の直線性を測定した。精度測定の基準線として太鼓に落とした材の挽材前後にその上面に墨つぼで直線を引き, 末口から元口までの20等分点で製材の厚さ, 幅, 挽道の直線性をノギスで測定した。さらに製材工場ごとに製材側面の形状の相関分析により製材ラインの診断を試みた。調査した7製材工場間の製材の厚さと幅の標準偏差に差が認められ, 予想に反して数工場で厚さの標準偏差が幅のそれに比べて危険率5％で大きかった。製材側面の形状の相関分析の結果, 厚さや幅のばらつきの少ない製材を生産している工場が必ずしも直線性の良い製材を生産していなかった。送材車式帯鋸盤は自動送材装置付き複式帯鋸盤に比べ材を真っ直ぐに挽けるが, 定められた線上を挽くのは不得手であることが分かった。挽道の直線性が悪かった原因は一工場では送材装置に, 他の工場では帯鋸盤と送付装置の両方にあった。挽材精度や挽道の直線性には夏と冬とで有意な差が認められなかった。挽材精度を低下させている原因を知るために帯鋸と鋸車の間の接触圧力分布を測定した結果, 多くの製材工場で接触幅の中央から後方にかけて接触庄力が高かったので, 鋸身の歯側は十分安定走行していなかったと考えられる。

Sawing accuracy and straightness of cut were studied at seven Norwegian bandsaw mills. Two hundred and thirty one pieces of lumber were measured under both winter and summer conditions. Straight and thin lines were drawn on the upper face of the cants before and after secondary sawing. Thickness, width and profile of cut were measured at twenty one points from top end to bottom using a caliper and these data were analyzed statistically. Furthermore, diagnosis of the quality of production facility was intended by the analysis of correlation among profiles of side faces on boards at each mill. It was recognized that there were differences in the standard deviations of thickness and width among the seven bandsaw mills. Unexpectedly, variation of thickness was found to be significantly (5%) greater than that of width at several mills. According to the analysis of correlation for profiles of cut, mills producing boards with less variations for thickness and width do not always produce straight boards. It can be said that a bandsaw machine with carriage is superior in sawing a board straight but inferior in sawing it along a set line to a set of multiple bandsaw machines with an automatic feeding system. Bad straightness of cut was caused by only a feeding system at one mill and by tangle of sawing and feeding systems at other mills. The sawing accuracy and straightness of cut did not differ significantly (5%) between winter and summer. According to the measured contact pressure distribution between sawblade and wheel of a bandsaw machine, the parts of the highest contact pressure were mostly in the middle or back zone of the contact area at most of mills. Therefore these distributions must have been one of the causes for inaccuracy of sawing.