緊張時の帯鋸の応力分布

Abstract

腰入れ・背盛りや上部鋸車の傾斜の応力分布に及ぼす影響を知るため, 腰入れや背盛り量の異なる4本の帯鋸の緊張時に生じる応力の鋸幅方向の分布を, 上下鋸車軸間の自由部分の中央から鋸車上にわたりひずみゲージを用いて測定し, また鋸と鋸車の接触圧力分布を感圧紙を用いて測定した。その結果, 自由部分での応力は腰入れ・背盛りされていない鋸L, 背盛りのみの鋸B, 腰入れ・背盛りの鋸Fでは鋸前縁から後縁に向かつて直線的に増加または減少し, 腰入れのみの鋸Tでは放物線状に分布した。上部鋸車の傾斜角度を大きくすると, 応力分布の直線部分の傾きや放物線の形状は, 鋸前縁での応力が低下し, 後縁では上昇するように変化した。自由部分の応力は鋸の緊張によって発生する鋸幅方向に一定の引張応力と直線的に分布する曲げ応力からなると予測されたが, 実験結果からこの曲げ応力は上部鋸車の傾斜によって変化するだけでなく, 腰入れ・背盛りによる鋸断面の変形の結果, 鋸と鋸車の接触状態が変化し, それによって生じる鋸幅方向の面内曲げの影響も受けると推定された。また鋸Tの放物線状の応力分布は鋸が幅方向の中央で長さ方向に特に強く圧延されたためと考えられる。鋸車上での応力は鋸T, Fでは鋸車前縁と鋸後縁付近で, 鋸Bでは鋸車前縁で, 鋸Lでは鋸幅の中央部で大きくなった。この分布にほぼ対応して鋸と鋸車の接触圧力は鋸Lでは概ね鋸幅の全域にわたり比較的低く分布し, 鋸T, B, Fでは鋸車前縁部で鋭いピークが見られ, さらに鋸Tでは鋸後縁付近にもやや高いピークが見られた。また応力分布は鋸と鋸車の接触開始点の近傍では急激に変化することもわかった。

The distribution of longitudinal stress in a cross section of a band saw and the contact pressure distribution between the saw and the wheel of the machine was measured for four kinds of saws with strain gauges and pressure measuring film, respectively. The influence of tensioning and back stretching in the saws as well as the inclination of the wheel on the stress distribution was investigated. The stresses in the cutting span of the saws, L (neither tensioned nor back stretched), B(back stretched), F(both tensioned and back stretched), changed linearly along the width of the saw blade, except that the distribution for saw T (tensioned) was parabolic. When the inclination angle of the upper wheel was increased, the gradient or the form of the stress distribbtion changed so that the stress in the front part of the saw was decreased. It is considered that the stress in the cutting span consists of the tensile stress, distributing uniformly along the saw blade width, and the bending stress in the plane of blade width. It was revealed that this bending stress is influenced not only by the inclination of the wheel but also by another bending, that is caused by the tensiling of the saws tensioned or back stretched and influenced by the contact state of the saw with the wheel. It is considered that the parabolic stress distribution for saw T is due to the strong roll stretching in the middle of blade width. The stress on the wheel for saws T and F was large at the front rim of the wheel and the rear edge of the saw, for saw B at the wheel rim, and for saw L in the middle of the blade width. According to these stress distributions, the contact pressure distribution for saws T, B and F had a discrete peak at the front wheel rim, for saw T also a low broad peak near the rear edge of the saw. On the other hand, the contact pressure for saw L was low almost over the saw blade width. It was also revealed that the stress distribution changed near the end of the cutting span.