Evaluation and Damping of High-Frequency Vibrations on a Percussive Tool

: Percussive tools can generate high-frequency vibrations that are not taken into account in currently applicable standards. In various publications, it has been suggested that those high-frequency vibrations may cause health issues. In the present study, high-frequency vibrations produced by a chipping hammer are evaluated and used to assess the potential damping effect provided by a thin layer of soft rubber.

Measurement Procedure • Vibration levels were measured by using three accelerometers located on the handle of the RRF31 Tool run in the Dynaload Energy Absorber described in ISO TR 20571.
• The measurements were conducted according to the guidelines given in ISO 28927-10.However, the procedure was simplified by using only one machine run by two operators that each performed five runs of 10 s.
• Three accelerometer B&K 4393 were mounted with mechanical filters on a block attached to the tool handle by means of double-sided tape and a cable tie.
• The time signals were acquired with a sampling frequency of 65.536 Hz and in addition to a digital low-pass filter at 20 kHz, the signals were subjected to the effects of the mechanical filters that provided a low-pass filter at 10 kHz.• The acceleration amplitudes can vary significantly on a run of 10 s.
• The acceleration amplitudes are clearly reduced by using a soft layer of damping material in the X, Y and Z-directions.
• The max-min peaks measured for the Regular Handle are above 2000 m/s 2 whereas the max-min amplitudes recorded on the Damped Handle do not exceed 500 m/s 2 , as shown in the plots by the red triangles for max values and the red circles for min values.
• The acceleration spectra obtained by averaging the vibration data from 10 runs are shown for Regular and Damped Handle in 1/24th octave bands in X, Y and Z-directions.
• A large reduction in the acceleration amplitudes can be observed at frequencies above 1 kHz when a soft layer of damping material is used to cover partly the tool handle.
• The data from the three accelerometers were used to evaluate the declared vibration emission value a hw for the chipping hammer and the Vibration Peak Magnitude (VPM) defined as • The value produced by the VPM calculation can be used to quantify the high-frequency content of the vibrations generated, for example, by repeated shocks.
• The VPM value is used in the present study to characterize the effect of vibration damping.
• The damping effects of a thin layer of soft rubber on high frequency vibrations are demonstrated by using time signals, acceleration spectra and VPM values.
• The soft rubber has no impact on the declared vibration emission value measured at 5,3 m/s 2 and the official declaration value for the tool is 5 m/s 2 with an uncertainty K = 1,6 m/s 2 .
• The damping effects of the soft layer shown by the time signals and the acceleration spectra are clearly indicated by the VPM values.This tends to prove that the VPM value can be used as a suitable parameter to quantify high-frequency vibrations.
• The soft layer gives a substantial damping effect on high-frequency vibrations and provides extra insulation against the cold surfaces generated by the pneumatic tool.
• For further development, a suitable damped handle has to be designed and the material durability has to be studied in industrial applications.
A V 6 / 9 J U N E 2 0 2 3 -N A N C Y -F R A N C E Background • Percussive tools for chipping and scaling are used for material removal in foundries, metal workshop and shipyards • The percussive mechanism may generate high vibration levels • A damping system is thus required to reduce vibration transmission to tool handle • Chipping hammer damped with soft spring => Atlas Copco RRF31 • Relatively low vibration emissions according to ISO 28927-10 • Significant accelerations at high frequencies in the tool handle due to piston-chisel impacts • Experimental study for evaluation and damping of high frequency vibrations I C H A V 6 / 9 J U N E 2 0 2 3 -N A N C Y -F R A N C E A V 6 / 9 J U N E 2 0 2 3 -N A N C Y -F R A N C E • Theacceleration signals recorded by the three accelerometers are shown in X, Y and Z-directions for one run performed with the Regular Handle and the other run with the Damped Handle.

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C H A V 6 / 9 J U N E 2 0 2 3 -N A N C Y -F R A N C E