High frequency vibrations in chipping hammers

Abstract: Percussive tools such as chipping hammers, riveting hammers and concrete breakers produce shock-type (impact) vibrations with large amount of vibration energy in the high frequency region (kHz). Reported injuries from shock-type and high frequency vibrations are higher  occurrence of vascular disorders, myelin disruption, edema and reduced motor performance. An Atlas Copco Tools customer has reported an increase of VWF (vibration induced white finger) during the last decade and the chipping hammers have been identified as the main cause. A mean of 1.8 workers/year has been injured with VWF and the cost of one injured worker has been estimate to 0.5 million SEK. One way to eliminate the injuries could be to replace the tools from Atlas Copco with better tools from another manufacturer. A protective handle was designed for the chipping hammers by Atlas Copco, to prevent operators from holding directly on the vibrating parts. However, the protective handle was not vibration isolated and a follow up project, this thesis, was started to redesign and vibration isolate the handle. An isolated protective handle with two rubber bushings was finally developed from theory of vibration isolation together with a subjective evaluation by experienced personnel and with low and high frequency vibration measurements. The final protective handle significantly reduced both the harmful low frequency vibrations (measured according to ISO 5349) and the potentially harmful high frequency vibrations (not measured according to any ISO standard), compared to the non-isolated original handle  developed by Atlas Copco.