Study of Noise Transmission from an Electric Impact Wrench

This paper shows how studies have shown that over six million construction workers are exposed to noise that is harmful to hearing, and currently about 50% of these workers have some hearing impairment. In order to address the growing concern of hearing impairment amongst construction workers, the National Institute of Occupational Safety and Health (NIOSH) sponsors undergraduate student projects that deal with the reduction of noise from various power tools and construction equipment. This paper is a part of that study on the radiation, transmission and reduction of noise from an electric impact wrench typically used in the construction industry. Previous projects involved studies on a table saw, pneumatic nail gun, and other tools that are described on the NIOSH’s web page. This paper investigates an Ingersoll-Rand 8049 electric impact wrench. The objectives of this paper were to identify and rank all possible noise sources, and develop possible treatments to attenuate the operating noise levels from the tool. In order to achieve these objectives, the mechanics of impact wrench operation were examined first to gain an understanding of noise sources. A motor inside the wrench spins the hammer/output shaft through a planetary gear system. When the bolt begins to tighten, a resisting torque is generated. When the torque becomes sufficiently high, the hammer is allowed to slip over the ears of the shaft by the ball and cam mechanism causing an impact. The series of impacts generated by this system provides the additional energy necessary to tighten or loosen a bolt. Additionally, there are ball bearings in the ball and cam mechanism, and there is a roller bearing that supports the hammer. The interaction between the balls and runners contribute some structure borne noise from the impact wrench. Gear noise occurs due to the interaction between teeth of interlocking gears. Because of the forces and impacts between the mating teeth, and the fact that in most applications, such as this, metal gears are used, ringing often occurs. When the teeth hit each other it is like a hammer hitting a bell, which sends noise and vibrations throughout the gear train. Another component of gear noise is the design of the surrounding housing. Depending on the material that it is made of and the method of isolating the gear train, the housing may have as much contribution to gear noise as the gears themselves. Motor noise can also be caused by rotor unbalance. This noise is usually due to poor workmanship or damage to the rotor. When an unbalanced rotor is rotating, the movement of the rotor causes vibrations, which will often be manifested as sound. For smaller motors such as those used in impact wrenches, unbalance is less of a noise issue than with larger motors.

Language

  • English

Media Info

  • Media Type: CD-ROM
  • Features: Figures; Photos; References; Tables;
  • Pagination: pp 154-160
  • Monograph Title: Noise-Con 04. The 2004 National Conference on Noise Control Engineering

Subject/Index Terms

Filing Info

  • Accession Number: 01053793
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Jul 13 2007 1:09PM