Attenuating sound on this industrial fan, large cyclone and duct
When a company installed a large industrial milling machine, a fan was fitted to extract oil mist and metal swarf from the machine. The system was designed for the fan to blow air and scrap metal through a long duct to a large cyclone from where the scrap metal falls down another duct into a compacter below. The cyclone and much of the duct were installed above the factory roof, and directly in line with the bedroom windows of a row of houses opposite the plant.
Unsurprisingly, the extraction system produced very high sound levels at the nearest houses – the sound was 27 dBA above the night-time background noise, which means that extensive sound attenuating measures were required. These sound measurements were made with air only passing through the cyclone, fan and duct. Once the system becomes fully operational such that metal scrap also passes through the system, it is likely that the sound will be considerably higher.
We presented the company with three different sound attenuating options so they could choose their preference depending on cost and ease of installation. Due to the very high sound levels, all options involved extensive sound attenuating measures. Had noise been considered before the industrial fan, cyclone and duct system were installed, it is likely that noise reduction could have been achieved at considerably lower cost. It would also have been much easier to implement the sound attenuating treatment at the same time as the industrial fan, duct system and cyclone were installed.