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238 Advances in Productive, Safe, and Responsible Coal Mining

(A)

73 74 75 76 77 78 72 73 74 75 76 77
(B) (C)

Fig. 12.22 Secondary sources at the flexplate area (red box in (A)) covered by acoustic
maps at: (B) 1600Hz and (C) 2000Hz.

the coal being conveyed as the CMM tail section is swung from side to side during
loading of haulage units. It is suspected that chain flight tips impacting flexplates
cause them to vibrate and rattle against their guides. Since the clearance between flex-
plate and flight tips is only approximately 1cm, a small transverse displacement of the
chain causes impacting to shift from side to side. A similar phenomenon was observed
in previous studies when the vibration of the left flexplate was greater than that of the
right flexplate [32].
Other noise sources were found at the front of the machine; however, since these
sources were located farther away from the operator location, they were deemed to be
of lesser priority in terms of operator and helper noise exposure reduction [33].

12.4.3.2 Potential noise controls
Conveyor noise has been the subject of previous research [32,34]. From these studies,
three noise controls were proposed: [1] a urethane-coated tail roller [2], a jacketed tail
roller (i.e., a resilient material between an inner and an outer steel shell), and [3]
urethane-coated chain flights. Fig. 12.23 shows prototypes of these noise controls.
Impact forces exerted on the tail shaft by the conveyor chain are transmitted as
vibrations through the rest of the structure. Resilient materials have been placed
between the chain and roller in an attempt to reduce these forces. Studies conducted