ディスク型チッパーの騒音分析

Abstract

ディスク径400mmの小型ディスク型チッパーをもちいて騒音分析をおこなった。とりあげた因子のうち, 匁先の出, 投入材木口断面形状, 回転数, 樹種, および樹種と含水状態の交互作用が音圧レベルに影響をおよぼした。匁先の出が大きいほど, 回転数の高いほど音圧レベルは大きい。また断面の扁平な板状材の方が断面の正方形の材より相対的に音圧レベルが大きい。スギ切削よりブナ切削の方が音圧レベルが大きいが, ブナでは気乾状態より飽水状態の方が音圧レベルが小さくなり, スギではこの関係が逆になった。チッパーの空転時の音圧レベルは切削時のそれとくらべて20dB程度低く, 切削時の音響スペクトルは特徴的なピークのない, 全周波数域にまたがる白色騒音的なものである。これは他の木材加工機械にくらべて回転数が低く切削が衝撃的におこなわれるためであり, また切削自体の音にくわえて材とスパウトとの振動による音や生成チップがカバーに衝突する音などが含まれてくるためでもある。

It was studied how several mechanical factors and cut materials influence to the noise of a disk chipper. (disk diameter: 400 mm) It was found that the amount of cutting knife projection, the rotating speed of disk, the kind of the cross section of materials and wood species were significant factors in the sound pressure level. It was also found that the interaction between the variety of wood and the moistening condition of materials was a significant factor. Therefore, with an increase in the amount of cutting knife projection and the rotating speed of disk, the sound pressure level increased, and the chipping of the flatter materials generated a greater noise than square materials per cross section area. The noise generated by chipping beech wood was louder than that by chipping Japanese cedar wood. The noise of chipping an air dried beech wood was louder than that of chipping a wet one, however, the noise of chipping a wet Japanese cedar wood was louder than that of chipping an air dried one. The sound pressure level of idling was lower by about 20 dB than that of chipping. The sound spectra of chipping had comparatively no high peaks over the frequency range, and so it resembled the white noise. This is because the cutting speed of a chipper is lower than that of other wood working machinery, and thus the cutting process of the former is not as smooth as that of the latter, and because the noise of a chipper includes the vibration noise of the materials hitting against a spout and striking noise of chips against a cover.