Development of low-noise chisel with ring-shaped dynamic damper

Hydraulic breakers, which are used to demolish concrete structures or rocks etc., make a loud noise. It is considered that one of the major noise sources of the breaker is the longitudinal vibration resonance of the breaker's chisel. Hence, in order to suppress the noise, a chisel in which a dynamic damper is integrated is proposed in this paper. The proposed dynamic damper consists of ring-shaped weight and ring-shaped plastic spacers. To install it on the chisel, a portion of the chisel must be made slender because the diameter of the chisel is limited by size of the chisel holder of the breaker. Because of this structure, the resonance frequencies of longitudinal vibration modes of the chisel are changed with parameters of the dynamic damper, such as the sizes and the position, etc. Therefore, it is difficult to design the dynamic damper with conventional ways. First, vibration response of the proposed chisel is derived with the transfer matrix method theoretically. Second, experimental results of the frequency response are shown and confirm the validity of the theoretical model. Then, effects of the parameters of the dynamic damper are investigated with the model. Finally, the experimental results of the impact noise during demolishing work are shown. These results show that the proposed chisel is valid and feasible for reducing the noise from hydraulic breakers.