The Southern African Institute of Mining and Metallurgy Narrow Vein and Reef 2008 P Marcotte, S Ouellette, G LeBlanc, J Boutin, B Quesnel and R Oddo

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1 DEVELOPMENT OF AN ANTIVIBRATION HANDLE FOR PNEUMATIC JACKLEG ROCK DRILLS Pierre Marcotte (1), Sylvain Ouellette (2), Gilles LeBlanc (2), Jérôme Boutin (1), Bill Quesnel (3), Rémy Oddo (4) (1) Institut de recherche Robert-Sauvé en santé et en sécurité d u travail (Canada) (2) Natural Ressources Canada, CANMET Mining and Mineral Sciences Laboratories, Experimental Mine P.O. Box 1300, 1 Peter Ferderber, Road Val-d'Or, QC, J9P 4P8 (Canada) syouelle@nrcan.gc.ca (3) Parts HeadQuarters Inc, Burlington, ON (Canada) (4) Groupe d Acoustique de l Université de Sherbrooke (GAUS), Sherbrooke, QC (Canada) Abstract Jackleg rock drills expose their operators to high hand-arm vibration levels. To address this problem, an antivibration handle has been developed. The antivibration properties of the handle were achieved through a suspension based on a hinge design, achieved with a torsion spring and o-rings. To provide some bench marking for this new handle and to follow the evolution of its performance over time, a test bench was developed to characterize the vibration emission values of jackleg drills under controlled operating conditions. Testing of four antivibration handles on the test bench have shown reductions of the overall weighted acceleration level in the order of 54 % to 60 %, with most of the attenuation occurring in the z h -axis at the rock drill percussion frequency. 1. Introduction Pneumatic jackleg rock drills are commonly used in underground mining operations. These tools are known to expose the ir operators to hand-arm vibration levels in the order of m/s 2 weighted (W h, ISO 5349). Thus, the majority of the workers who have cumulated several years of jackleg rock drill operation are affected by related health problems such as Raynaud's syndrome or carpal tunnel syndrome [1-2]. Up to now, no efficient personal safety device was available to protect pneumatic rock drill operators against hand-arm vibration (HAV). To address this problem, an antivibration handle prototype for jackleg drills has been developed in a previous study [3]. Then, a multi-partner project was launched to refine the prototype and commercialize an effective antivibration handle for pneumatic rock drills. A picture of the antivibration handle is shown in Figure 1. Page 1

2 Figure 1 for pneumatic jackleg rock drills To provide some bench marking for this new handle and to follow the evolution of its performance over time, a test bench was needed to characterize the vibration emission values of jackleg drills under controlled operating conditions. As the current ISO 8662 series of standards could not apply directly to this type of tool, a test was designed and validated to evaluate the vibration emission values of jackleg drills, while taking into account the conditions specific to the operation of this type of tool (push force, jackleg angle, pneumatic pressure). 2. Materials and methods Pneumatic jackleg rock drills are extremely robust tools. Over the years, several unsuccessful attempts have been made to develop an antivibration handle for pneumatic rock drills. No commercial success was ever achieved because of either poor efficiency or lack of robustness. Among the design criteria for the handle, robustness and simplicity came first. Even though vibration is present in the three axes, a hinge type design, which is efficient in one axis (percussion), has been chosen. The hinge is positioned at a relative angle of 90 degrees with the dominant vibration axis and is held in place by a torsion spring. The pivot is simply formed of a steel shaft with o-ring grooves which seal the air ports for the pneumatic controls. A rubber stopper limits the travel of the handle. The friction of the o-rings is sufficient to prevent the handle from resonating and therefore no viscous material is needed for that purpose. In order to evaluate the performances of the handle and to follow the evolution of its performances according to its wear, a test bench for characterizing the vibratory emission values of jackleg drills under controlled conditions has been developed [4]. The test bench was adapted for jackleg drills from the ISO standard for rock drills and rotary hammers. The vibration emission values of the antivibration handles were compared with that of a conventional handle using a triaxial accelerometer (PCB 356B20) rigidly attached to the handles. The accelerometer has been validated on a jackleg rock drill to ensure that there was no signal saturation and DC shift. Pictures of the test bench and instrumented handle with the accelerometer are shown in Figure 2. For validation purposes, acceleration measurements at the handle of a conventional jackleg drill were taken along the three axes (x h, y h and z h ) in an underground rock drilling operation as well as on the test bench. The handle accelerations were measured for three different jackleg angles (13º, 28º and 43º) determined with respect to the floor. It was also verified that the test bench Page 2

3 provided comparable values of overall acceleration as well as frequency distribution of the acceleration for all three axes, with much lower coefficients of variation (COV) for the test bench, suggesting a higher measurement repeatability, when compared to underground drilling. Figure 2 - Jackleg rock drill with test bench (left) and instrumented handle (right) 3. Results The vibration emission values of four different antivibration handles were characterized with the test bench. Five acquisitions of 30 seconds were performed for each handle, while an operator was applying zero push force on the handle, for a jackleg angle of 28 degrees. To provide benchmarking, the vibration level of a conventional handle was also measured before and after the testing with the antivibration handles. A summary of the weighted accelerations for each axis is shown in Table 1, while a summary of the attenuations obtained with the four antivibration handles is given in Table 2. The spectrum of one of the antivibration handle, along with the spectrum of the conventional handle, are shown in Figure 3 for all three axes. The results show that the antivibration handles reduce the vibration emission value from 55 % to 61 % when compared with a conventional one. In addition, the attenuation in the z h -axis, where most of vibration occurs, is in the range of 70 % to 77 %. Figure 3 also suggests that most of the attenuation occurs in the z h -axis at the jackleg drill percussion frequency (around 40 Hz). It is shown that the antivibration handle also contributes to significant vibration reduction above the percussion frequency in the z h - axis. Table 1 Vibration emission values (m/s 2, Wh, bold) and coefficient of variation (%) of four antivibration handles and a conventional one Handle x h -axis y h -axis z h -axis total 7,69 4,43 19,46 21,39 Conventional COV (%) 0,80 3,59 0,65 0,67 Antivib. # 1 5,99 4,19 5,26 9,01 COV (%) 1,74 4,08 1,20 1,15 Antivib. # 2 5,64 4,37 5,91 9,27 COV (%) 2,84 4,70 0,75 0,20 Antivib. # 3 5,62 5,70 5,67 9,87 COV (%) 1,79 12,94 17,14 1,88 Antivib. # 4 5,95 4,22 4,56 8,60 COV (%) 1,03 2,59 2,44 0,63 Conventional 7,60 4,92 20,36 22,29 Page 3

4 COV (%) 1,56 5,67 1,00 0,91 Table 2 Summary of antivibration handle attenuations x h -axis y h -axis z h -axis total Antivib. # 1 21,7 % 10,5 % 73,6 % 58,7 % Antivib. # 2 26,3 % 6,6 % 70,3 % 57,6 % Antivib. # 3 26,5 % -21,8 % 71,5 % 54,8 % Antivib. # 4 22,2 % 9,8 % 77,1 % 60,6 % One-third octave band (Hz) (a) x h -axis 0.0 One-thirdoctave band (Hz) (b) y h -axis One-third octave band (Hz) (c) z h -axis Figure 3 - Example of an antivibration handle spectra along with a conventional one for all three axes 4. Conclusion An antivibration handle for jackleg rock drills has been developed in a multi-partner project. Testing of the handles on a test bench shows reductions of hand-arm vibration in the order of 54 % to 60 %, with most of the attenuation occurring in the z h -axis at the rock drill percussion frequency. Prior to their commercialization, ten handle prototypes have been tested into five Canadian mines. During this five month period, more than 7000 meters of drilling have been performed with the handles. The handles have been commercialized by the Canadian manufacturer Parts HeadQuarters in early Page 4

5 5. References [1] H. Iwata, Effects of rock drills on operators. Part 2. Survey and examination on Raynaud s phenomenon, Industrial Health 6, (1968) [2] P.L. Pelmear, J. Roos, D. Leong, L. Wong, Cold provocation test results from a 1985 survey of hard-rock miners in Ontario, Scandinavian Journal of Work, Environment & Health 13, (1987) [3] R.Oddo, T. Loyau, P.-É. Boileau, Y. Champoux, Design of a suspended handle to attenuate rock drill hand-arm vibration: model development and validation, Journal of Sound and Vibration 275, (2004) [4] P. Marcotte, S. Ouellette, J. Boutin, P.-É. Boileau, G. LeBlanc, R. Oddo, Design of a test bench to evaluate the vibration emission values of jackleg drills, in Proceedings of the 1 st American Conference on Human Vibration, Morgantown, WV, USA (2006) Page 5