A strip-fed, 115 tonne power press, installed to stamp oil filter base plates, generated A-weighted noise levels of 99 dB, principally in 'bell-like' tones radiated by the flywheel.
The vibration response of the flywheel was checked to confirm that its natural frequencies corresponded to the dominant tones in the radiated noise. A small electrodynamic vibrator was used to excite each resonant frequency of the flywheel to determine how the system worked and where the maximum vibration could be found.
The level of acoustic radiation was determined from the mechanical vibration in the flywheel. It was concluded that this could be reduced by using dynamic vibration absorbers fixed to the flywheel where the vibration was at its highest. The absorbers consisted of mass on a spring, tuned to a specific frequency. When attached to the flywheel, it transferred its vibratory motion into vibration of the small masses.
In this case, small mild steel discs and plates, mounted on rubber-bonded cork, were used as absorbers. They were bolted on to the flywheel at positions of maximum vibration and then tuned to the resonant frequencies. The flywheel itself needed no modification.
£15 per absorber. (1995)
An overall noise reduction of 10 dB and virtual elimination of the flywheel tones.
Consultants were Industrial Noise and Vibration Centre.