Page 256 - Advances In Productive, Safe, and Responsible Coal Mining

Engineered noise controls for miner safety and environmental responsibility 235

Fig. 12.18 Details of the DBI: (A) diagram of the prototype detailing various components,
(B) close-up of inner and outer members showing the location of the isolating rubber layer, and
(C) an actual DBI equipped with a 35-mm drill bit and installed on a hexagonal drill steel.

Fig. 12.18. The rubber layer between the inner and outer cylinders isolates vibrations
at the drill bit from the drill steel, thereby reducing the noise radiated from the drill
steel. This layer is chemically bonded to the steel components to limit torsional travel
and produce consistent stiffness. Fig. 12.18B is a close-up view of the inner and outer
members and the rubber layer that separates them. The DBI has a drill steel coupling
on one end and a bit coupling on the other. These couplings are welded to the ends of
the inner and outer cylinders. There is a 0.4-in. (10-mm) gap at the end of the outer
cylinder, which is designed to allow for a small amount of relative movement between
the layers as axial thrust loads are applied and removed. The gap acts as a safety fea-
ture, preventing axial overload by partially closing when thrust is applied and
rebounding to the original position when thrust is removed. Fig. 12.18C shows the
device installed on a drill steel with a drill bit attached to the end. Minor modifications
based on field study results detailed here were incorporated into the final production
version of the device.

12.4.3 Noise controls for continuous mining machines
Continuous mining machines (CMMs) are used to extract approximately half of the
US underground coal production in room-and-pillar operations, and to develop entries
in longwall mines. Unlike longwall operations where the roof collapses after coal is
extracted, in room-and-pillar operations coal pillars are left behind for roof support
purposes. CMMs are usually operated via a wireless remote control device by a miner
who may or may not have a helper. The three main CMM components that radiate
noise are the cutting head, the conveyor, and the dust scrubber fan, which are shown
in Fig. 12.19. Of these three components, it was determined that conveyor noise is the
most important contributor to the total radiated sound [31].