ハンマ腰入れした丸鋸の振動特性

Abstract

丸鋸の振動特性に及ぼすハンマ腰入れの影響について検討するため, 厚さと腰入れ量の異なる数種の円板の静止時および回転時の固有振動数を調べた。円板の固有振動数は節円数0で節直径数1以下の低次のモードでは腰入れ量とともに低下したが, 節直径数2以上のモードでは高くなった。一方, 節直径数が1のモードでは腰入れの影響は認められなかった。回転時の固有振動数は回転数とともに上昇したが, 腰入れとの間に一定の関係を見いだすことはできなかった。加振せずに回転したときに励起される主要な振動の周波数は回転数とともに直線的に上昇し, 空気力学的な振動励起が生じていることが確かめられた。また, 円板の残留応力測定時の応力解放の手段としてレーザ切断を試みたが, 切断時の熱影響層が比較的大きく, 残留応力を評価するまでには至らなかった。

This paper describes preliminary experiments to examine the vibration characteristics of saws tensioned by hammering. Several circular discs, which are to be used as blades for carbide-tip-ped saws, were differently tensioned by hammering (Table 1). Natural frequencies of stationary and rotating discs were determined, and the vibrations excited aerodynamically were also examined (Fig. 1). Increasing the degree of tensioning decreased natural frequencies of modes (0, 0) and (0, 1), where (m, n) means m nodal circles and n nodal diameters, and increased those of mode (0, 2) and higher order modes (Table 2). Tensioning, however, little affected natural frequencies of one nodal circle modes. Natural frequencies of discs increased monotonically with rotation speed due to the effect of centrifugal forces, and three discs of different tensioning states showed a similar increase in frequency (Fig. 3). The frequencies of aerodynamically excited vibrations appeared to be proportional to rotation speed (Fig. 4). Residual stresses in discs measured using laser beam cutting were also discussed (Figs. 2 and 5).