Suppression of the whistling noise in circular saws using “Silentalloy”

Summary

To suppress the so-called whistling noise in idling circular saws, a circular saw with slots in the peripheral area of the blade has been widely used. However, the effect of the slots is uncertain because the natural frequencies of saws vary, even among saws even if they were designed to suppress the whistling noise. Therefore, we made two types of tungsten carbidetipped circular saws; one with the sawblade made of a high-damping alloy named Silentalloy (SIA) and one with the blade made of the common alloy tool steel (SKS5). The noise levels and the power spectra of these saws during idling and cutting were measured at rotational speeds from 1,000 rpm to 6,000 rpm. The minimum damping capacity required to suppress the whistling noise in an idling circular saw was measured using the characteristic of SIA that the damping capacity can be changed depending on the temperature of the heat-treatment. The circular saws made of SIA generated neither the whistling noise nor the low discrete noise caused by the sawblade resonance. Slots are not necessary in a SIA saw because the coefficient of thermal expansion of SIA is relatively small. In fact, the slots raised the noise level of the SIA saw slightly. The degree of scatter in the noise levels of SIA saws was low unlike that of the SKS 5 saws. The noise level of the SIA saw during cutting was reduced a few decibels at the operator's position. It was demonstrated that the minimum damping capacity required to suppress the whistling noise is in the vicinity of 0.07 in logarithmic decrement. In conclusion, the whistling noise can be suppressed completely if a sawblade is made of a high-damping metal such as Silentalloy.