Reducing noise from pneumatic screwdrivers
Pneumatically-driven screwdrivers can produce high A-weighted noise levels of over 80 dB, particularly when used in large numbers and in confined spaces, eg on production lines. In general, there are two noise generating mechanisms:
- exhaust air sound caused both by air flow variation as the air flows past the motor and by aerodynamic sound generation in the exhaust-air channel;
- vibration-radiated sound from the surface of the machine produced by the moving parts of the machine and by the flow of air inside the machine.
To reduce the noise generated by exhaust air, a manufacturer of pneumatic tools modified its range of screwdrivers to incorporate a hose to pipe the air away from users. This also removed any oil fog carried in the exhaust air.
As the exhaust noise was reduced, the vibration-induced noise radiation became more significant. To overcome the problem, the company investigated the precise mechanism of vibration driving, which resulted in a major change of screwdriver design.
The rear section of the tool was screwed into an outer housing of anodised aluminium. An inner housing containing the air motor and gears was carried on axial and radial rubber elements to isolate it from the outer casing. The motor rested on the axially positioned elements but the radial O-rings prevented direct metallic contact between casing and motor.
Cross-section of a screwdriver motor isolation
Negligible difference over traditional screwdrivers. (1995)
In a controlled test on an individual machine, the treatment resulted in noise levels being reduced by up to 7 dB.
Photograph courtesy of Atlas Copco Tools Limited. Equipment designed and manufactured by Atlas Copco Tools Limited.