The high level of noise from this 115T Bliss power press meant that the whole area was designated a noise hazard zone with mandatory PPE. The previously quoted solution was to fit a full enclosure at a cost of some £30k. This would have introduced both operational and maintenance issues as regular operator access was required.
We were approached to determine if there could be a more practical alternative.
A few hours on site for detailed noise and vibration analysis revealed that the noise was dominated by resonant tones radiated by the flywheel.
Impact tests were used to determine the mode shapes and small steel blocks mounted on gasket springs (dynamic vibration absorbers) were designed to be fitted at specific points on the flywheel to damp the flywheel tones.
Once installed by a fitter (a few hours in total), these £15 absorbers cut the press noise by 90% (10dB). As they fitted inside the existing guards, there was no effect on operation or maintenance.
The remaining pneumatic ejection secondary noise source was then treated by fitting a quieter, more efficient nozzle to not only cut the noise by a further 5dB, but also to cut air consumption by 20%.
Wire drawbench
Similar dynamic vibration dampers fitted to the main gear wheels on a wire draw bench reduced the overall noise by 5dB(A) – again with no effect on normal operation, access or maintenance and at a cost saving of c £13000.
