Machine enclosure and extraction system reduces dust hazard
Note µ represents a micro-metre
For analyses mineral ore samples must be crushed and then milled until 95% are less than 212 µ. (Less than one quarter of a millimetre). The milling task is performed using ‘Raymond’ hammer mills. To avoid contamination this mill must be cleaned with compressed air between samples. The use of compressed air, while being quick and efficient, generates vast amounts of dust and is noisy. The inhalation of this dust is hazardous to the health of workers, though symptoms may take years to appear.
Before an enclosure and extraction system was fixed in place, several prototype capture systems were made for the milling machine (from cardboard) and connected, via a length of flexible ducting, to an old welding exhaust fan. Once a successful prototype had been found, a fixed capture enclosure was manufactured. Fixed ducting and a new exhaust system with an appropriate capture strength were also installed. In addition, a fixed air jet was located inside the enclosure to provide automatic cleaning of the mill between preparation of samples.
Despite enclosure of much of the process, it was found that some dust was still contaminating the workplace environment. The source of the dust was the sample hopper during operation of the mill. Because other mills were present in the workshop it was decided to also install a mobile dust extractor. The capture hood of the mobile extractor can be placed above any of the mills in only 5 seconds.
Hierarchy of Control:
- The mineral sample dust problem has been reduced for this process thereby improving the health and safety of workers.
- A small reduction in noise levels due to the enclosure of the air jet was an additional benefit.