Reducing noise from a glass tempering line
The problem
Glass tempering is achieved by heating glass and then quickly cooling it at a controlled rate to align the molecules in one 3/s.
Traditionally, cooler fans are mounted outside the factory to reduce the impact of the fan noise on the workers. However, in this plant, the fans had to be mounted internally. With fan A-weighted sound power levels in excess of 126 dB, the effective acoustic enclosure of the fans was essential.
The solution
To minimise costs, a masonry enclosure, rather than one with conventional metal acoustic panels, was constructed. The enclosure consisted of 225 mm thick, heavy-density blockwork (2400 kg/m3) walls and a 250 mm deep timber joist roof. The space between the joists was packed with 100 kg/m3mineral wool. A 50 mm thickness of plaster board was fixed to the top and bottom, with staggered and taped joints. Access to the fan room was via two large double door sets (3 m wide x 3 m high).
The very high volume of intake air was brought in through vertically-mounted rectangular duct attenuators (1.2 m wide x 2 m high x 2.4 m long). The thickness of the silencers within the attenuators was tuned specifically to give enhanced low-frequency attenuation without adding excessive pressure drop to the fans.
The cost
About £15 000. The cost of the project was thought to offer a 50% saving over an all-steel acoustic enclosure. (1995)
The result
A noise reduction of about 45 dB.
Source
Information supplied by Preedy Glass Limited. Tempering Line supplied by EFCO Limited.