The powder blasting operation involves delivery of a very high temperature and velocity charge of powder at the work-piece. The metal powder mixture forms a sintered coating as it cools instantly on striking the workpiece. The enclosures in which this operation is performed, traditionally of masonry construction, need to contain internal sound pressure levels of over 145dB, with operator workstations nearby.
Acoustic absorption cannot be fitted to the inner surfaces of the enclosure, due to the high temperatures. The traditional enclosures have been found to inadequately control noise break-out, resulting in potentially damaging noise exposure levels in their vicinity.
It was found that the sound insulation performance of the masonry enclosures did not adequately address the non-linear impulsive noise source generated by the blasting operation due to a lack of structural damping provided by the masonry.
An alternative enclosure design was developed using modular acoustic panelling which enabled both damping and low frequency absorption to be introduced using damped steel surfaces. Noise levels were reduced, both within the enclosure and immediately adjacent to it, enabling safe working conditions, albeit with hearing protection in some cases.
The enclosure design also made the considerable cross-flow ventilation requirements more readily achievable than the traditional enclosure.
No additional cost. The total installed cost of the noise control enclosure was estimated to be no more than a traditional masonry alternative, after consideration of lesser structural support requirements for the considerably reduced mass.
Praxair Surface Technologies Ltd. & Alan Saunders Associates.