A bench-mounted pneumatic impact press used for riveting small switch components was found to be generating excessive noise levels. The main peak noise emissions were from the release of compressed air at the actuator exhaust and from the impact of the metal actuator ram as it struck the metal tool ram.
The compressed air exhaust noise was reduced after a proprietary lightweight silencer had been fitted. The flow was passed through a porous polythene cap of the type indicated in the figure.
The impact noise was reduced by cushioning the contact between metal surfaces with an insert of damping compound, again as indicated in the diagram. The most effective acoustic performance was by an insert of 8 mm thick nitride rubber. However, this showed early signs of wear and some loss of force transmission to the workpiece. The best compromise between impact force transmissions, wear and noise reduction was obtained by 8 mm thick Betathene, a proprietary urethane elastomer.
About £50. (1995)
The compressed air exhaust silencer reduced peak noise levels at each operating position by some 7 dB, with a corresponding reduction of some 5 dB over about five cycles of the machine during continuous operations.
The cushioning of the impact noise gave a further reduction in peak noise levels of 5 dB and about 4 dB while the machine was running continuously.
Overall, there was a 9 dB reduction from the two modifications, achieved with no significant effect on the overall working efficiency of the machine.
Information supplied by Lucas Industries Noise Centre.