Health and Safety Executive Vibration measurements on torque multipliers Prepared by the Health and Safety Laboratory for the Health and Safety Executive 2010 RR794 Research Report Health and Safety Executive Vibration measurements on torque multipliers Richard Heaton MPhys(Hons) Sue Hewitt BA(Hons) MSc Health and Safety Laboratory Harpur Hill Buxton Derbyshire SK17 9JN It was brought to HSE’s attention that torque multipliers were being used instead of impact wrenches in some instances in the workplace. Given that torque multipliers are purely rotary machines, the vibration level is likely to be much lower than that on an impact wrench. HSL had not previously measured the vibration magnitudes associated with the use of torque multipliers and so were asked by HSE to see whether they are a practicable alternative to impact wrenches and to investigate the differences in vibration exposure associated with their use. When comparing HSL measured emission values with field measurements, the emission values are lower than the field measurements, indicating that the risk is underestimated by the emission values. However the risk from vibration exposure associated with the use of the machines is very low. The number of vibration exposure points incurred from use of a torque multiplier when processing 100 nuts is approximately ten times lower than would be incurred with an impact wrench, however it would take three times longer. A torque multiplier may be the preferred choice of tool if an operator is subject to vibration exposure from using other machines, as very few vibration exposure points will be incurred from its use. This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy. HSE Books © Crown copyright 2010 First published 2010 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means (electronic, mechanical, photocopying, recording or otherwise) without the prior written permission of the copyright owner. Applications for reproduction should be made in writing to: Licensing Division, Her Majesty’s Stationery Office, St Clements House, 2-16 Colegate, Norwich NR3 1BQ or by e-mail to [email protected] ACKNOWLEDGEMENTS The authors gratefully acknowledge those who assisted in this project, in particular the tool manufacturers who supplied the tools and the site used for the field measurements. ii CONTENTS 1 INTRODUCTION......................................................................................... 1 1.1 Outline of work......................................................................................... 2 2 TOOLS TESTED......................................................................................... 3 3 LABORATORY TESTING OF VIBRATION EMISSION ............................. 4 3.1 Emission test procedure for torque multipliers......................................... 4 3.2 Transducer mounting locations................................................................ 5 3.3 Data acquisition and analysis .................................................................. 5 3.4 Emission test results................................................................................ 7 4 FIELD MEASUREMENTS .......................................................................... 8 4.1 Measurement protocol ............................................................................. 8 4.2 Data acquisition and analysis .................................................................. 8 4.3 Results of field measurements ................................................................ 9 5 DISCUSSION............................................................................................ 10 5.1 Comparison of declared and measured emission.................................. 10 5.2 Comparison of measured emission and field measurements ................ 10 5.3 Comparison of a torque multiplier and an impact wrench ...................... 11 6 CONCLUSIONS........................................................................................ 12 7 REFERENCES.......................................................................................... 13 APPENDICES .................................................................................................. 14 Appendix A – Emission and field measurement equipment ............................. 14 Appendix B – Emission and field measurement data ....................................... 15 iii iv EXECUTIVE SUMMARY Objectives Torque multipliers are handheld, air driven, non-impacting torque delivery tools intended to tighten and loosen nuts, bolts and threaded fasteners. It was brought to HSE’s attention that torque multipliers were being used instead of impact wrenches in some instances in the workplace. Given that torque multipliers are purely rotary tools, the vibration level is likely to be much lower than that on an impact wrench. HSL had not previously measured the vibration magnitudes associated with the use of torque multipliers and so were asked by HSE to investigate two tools as part of the current work programme on the comparison of emission data and in-use magnitudes, to see whether torque multipliers are a practicable alternative to impact wrenches and to investigate the differences in vibration exposure associated with their use. Main Findings Using the standard test outlined in ISO/FDIS 28927-2:2008, manufacturers’ declared emission values were verified according to the criteria in BS EN 12096:1997 for torque multipliers using the values from both brake device and free running tests. When comparing HSL measured emission values with field measurements, the emission values are lower than the field measurements, indicating that the risk is underestimated by the emission values. However the risk from vibration exposure associated with the use of the machines is very low. The number of vibration exposure points incurred from use of a torque multiplier when processing 100 nuts is approximately ten times lower than would be incurred with an impact wrench. A torque multiplier may be the preferred choice of tool if an operator is subject to vibration exposure from using other machines, as very few vibration exposure points will be incurred from its use. It may also be advantageous if a specific torque is required, as changing the pressure on the external regulator can easily vary and set the torque. Torque multipliers are however slower than impact wrenches and there is also increased potential for trapping injuries to occur, due to the movement of the reaction bar. An impulse nutrunner may also be a suitable alternative to an impact wrench as it is likely to lie somewhere between a torque multiplier and an impact wrench in terms of vibration exposure and speed of use. v vi 1 INTRODUCTION Torque multipliers are handheld, air driven, non-impacting torque delivery tools intended to tighten and loosen nuts, bolts and threaded fasteners. Two examples are shown in Figure 1. Every tool is supplied with an individual air pressure calibration graph, which relates torque output to air pressure. The pressure is controlled using an external air pressure regulator. Figure 1 Torque multipliers; Left – Tool A, Right – Tool B Whilst in operation the reaction arm on a torque multiplier rotates in the opposite direction to the output square drive and must be allowed to rest squarely against a solid object or surface adjacent to the bolt to be tightened or loosened as shown in Figure 2. This reaction allows the torque to be applied. Once the required torque is achieved the tool stalls and no further tightening is possible. Figure 2 Torque reaction for clockwise operation 1 1.1 OUTLINE OF WORK It was brought to HSE’s attention that torque multipliers were being used instead of impact wrenches in some instances in the workplace. Given that torque multipliers are purely rotary tools, the vibration level is likely to be much lower than that on an impact wrench. HSL had not previously measured the vibration magnitudes associated with the use of torque multipliers and so we investigated two tools as part of the current work programme on the comparison of emission data and in use magnitudes, to see whether torque multipliers are a practicable alternative to impact wrenches and to investigate the differences in vibration exposure associated with their use. The work involved: 1. Measuring the vibration emission according to the provisions in the most relevant standard. There is no standardised vibration emission test for torque multipliers, the most suitable existing standard is that for impact wrenches which is BS EN ISO 28662-7:1997. This standard is currently under revision and the replacement standard is in its final draft stage of approval, so the torque multipliers were tested according to the latest draft of this standard, ISO/FDIS 28927-2:2008. 2. Comparing vibration emission values with vibration magnitudes measured under real operating conditions. 3. Providing HSE with information regarding (1) and (2) above, and any other information on machine use and vibration risk. The vibration exposures reported here are very low and so in order to differentiate between them they have been given in terms of exposure points. Exposure points can be converted to partial exposures using Table 1. Table 1 Conversion from exposure