Page 260 - Advances In Productive, Safe, and Responsible Coal Mining

Engineered noise controls for miner safety and environmental responsibility 239

Fig. 12.23 Noise controls for tail section noise: (A) jacketed tail roller, (B) urethane-coated tail
roller, and (C) urethane-coated chain flights.

by the Bureau of Mines investigated an isolated tail roller design where an elastomer
was bonded to the tail shaft and protected with a steel tube [35,36]. This treatment
achieved a 2-dB(A) reduction in sound level at the operator’s position, but was never
tested underground. Recently, a urethane coating, similar to the coating used for the
coated flight bar design, was applied to the outer diameter of the tail roller [37]. In the
aforementioned hemi-anechoic chamber, testing with this design resulted in a 2-dB
reduction in the operator location sound level. This design failed in underground test-
ing, however, due to high point contact loading from material (e.g., coal or overburden
rock) under the chain.
To document the overall noise emission of the CMM during conveying, NIOSH
conducted sound power testing in a large reverberation chamber [38]. This testing
was conducted using the comparison method of sound power calculation per the
requirements of the acoustic standard ISO3743-2 [39]. The same resilient material
used for the urethane tail roller tested underground was used to build a prototype
for testing in the reverberation chamber. During normal operation of the conveyor
(i.e., conveying coal from the cutting end of the CMM to the tail section), the coal
has a damping effect on the noise radiated by the conveyor. From these tests, it
was determined that overall sound power level of the CMM is 116dB(A) with a stan-
dard tail roller, and is 115dB(A) with the urethane-jacketed tail roller. Thus, the
urethane-jacketed tail roller resulted in a 1-dB reduction.
NIOSH also conducted similar ISO 3743-2 based sound power testing in its rever-
beration chamber to determine the effect of coating conveyor flight bars with ure-
thane. Here, testing was conducted without loading the conveyor, both for standard
tail roller tests and for urethane-coated tail roller tests. The overall sound power level
of the CMM with standard chain was 117dB(A) while the overall sound power level
with the urethane-coated flight bars was 112dB(A). This 5-dB reduction in the sound
power emission was considered significant and indicated that the urethane-coated
flights bars might be an effective noise control.