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Engineered noise controls for miner safety and environmental responsibility 227

modification of helical vanes. The third constraint was that noise controls should not
compromise the structural integrity of the drum. Changing a drum between sched-
uled overhauls is not common practice in underground longwall mines. Therefore,
most longwall mines do not have spare cutting drums in stock. The fourth and final
constraint is that noise controls should be durable enough to withstand rough under-
ground mining conditions.

12.4.1.4 Selected solution
Based on these constraints and upon discussion of the potential noise control concepts
with an original equipment manufacturer, it was determined that the most viable solu-
tion complying with all constraints was structural modifications to the outermost
plates of the helical vanes. However, due to manufacturing and maintenance consid-
erations, this was accomplished by replacing stiffener plates connecting bit holders to
outer vane segments with gussets installed behind each bit holder, as shown in
Fig. 12.8A. In addition, 1-in. (2.5-cm)-thick steel plates were welded between each
gusset and the associated outer helical plate to increase the thickness of these plates,
as shown in Fig. 12.8B. A total of eight ribs were used to stiffen the face plate, as seen
in Fig. 12.8C.
To evaluate the performance of these controls in terms of noise reduction, a pair of
standard drums were built and tested in a laboratory setup to collect baseline data.
Then, noise controls were implemented into this pair of drums by making the struc-
tural modifications previously described. The modified drums with the implemented
noise controls were then tested in a laboratory setup. Comparison of the data collected
from the baseline drums and the modified drums confirmed the noise reduction esti-
mated by the numerical models of the cutting drums, and thus validated these models.
The last step of the project involved evaluating the performance of these noise con-
trols in an underground mining environment under actual operating conditions. The
objective was to evaluate their effect on the longwall shearer operator’s noise expo-
sure with all other noise sources present during normal operation, especially noise

(A) (B) (C)

Fig. 12.8 Stiffeners and ribs (shown in green) implemented as cutting-drum noise controls.
(A) Gussets installed behind each bit holder, (B) 1-in. thick plates between each gusset,
and (C) rib stiffeners at face ring.