MECHANISED COAL_proof 22/08/2016 16:43 Page 8
MECHANISED COAL
The Fletcher six-head bolter has a single
platform and six independent masts and
drillheads; four masts strictly for drilling and
installing roof bolts on the front of the platform
and two masts on the back of the platform for
rib bolts. The feed and rotation controls at each
operator’s station include a latch control for
drilling. The rear of the machine is equipped
with material handling. There are two material
pods with winch controls as well as a mesh rack
that includes mesh lift, mesh tilt and mesh
sump
be designed and built for mine use in the US. The
machine is intended to work in the Illinois Basin.
The mine employs the room and pillar method,
the continuous miner taking 10.67 m cuts. The
entry width is 5.49-6.1 m with a mining height of
2.44-4.27 m, the average working height is 3.05
m. The current bolting process involves installing
roof mesh panels and corner rib bolts with 90°
610 x 610 mm J channel. Initially there were two
steps; a CM would cut and then a dual boom
CHDDR style bolter would install mesh and rib
bolts. The mine has good top and bottom
conditions and uses a 1.22 x 1.22 m bolt pattern.
The objective was to produce a machine
capable of drilling and installing six bolts
simultaneously, with a limited number of
operators. The goal of the mine was to decrease
the time to bolt a cut, improving the safety level
of the current roof bolting method, improve
efficiency and to improve the bottom line cost of
entry development. The customer wanted the
capability to install one rib bolt 305 mm down
from the roof (where bolts did not have to be
aligned with the roof bolts). Thus, the customer’s
request was for a machine with four drillheads at
the front of the machine to install roof bolts and
two separate drillheads dedicated to rib bolts.
With the requirement of a semi-automatic
drilling system, Fletcher was able to utilise the
existing four head roof bolter design and expand
it into a six head roof and rib bolter to meet the
customer’s needs. Some of the main design
concerns were the ability to fit two more drilling
140 International Mining | SEPTEMBER 2016
apparatus along with material handling on the
machine, and the concept of a latched feed and
rotation drilling system. With two more drilling
apparatus for rib drilling, the four head machine
design would have to be enlarged to handle the
additional hydraulic requirements. The first major
obstacle was the need for a new and larger
crawler drive system, to handle a machine of this
size. Therefore a 508 mm wide crawler pad
assembly was developed with a bolt on style
gear case. For the increased hydraulic demand
the chassis had to grow in size to be able to
handle the much larger hydraulic tank and the
addition of another electric motor. The machine
now consisted of two 75 kW electric motors used
on the four-head design and an additional 56 kW
electric motor to power the two new rib drills
attached to the machine.
The final design included mounting the rib
drills at the rear of the lifting platform; mounting
them there to reduce the functions required to
manipulate them as well as the number of hoses
required to come up and down the platform
boom. Thus all six drilling devices are located on
the front lifting and extending platform. The
platform is designed to lift 1,524 mm and each
side platform has the capability of extending 966
mm.
The four roof drills are located at the front of
the platform. All have the ability to tilt 2.5°
forward as well as 2.5° backwards for a total of
5°. The outer roof drills also have the ability of
tilting side to side 10°; 5° in and 5° out. The inner
roof drill rigs only tilt side to side 7.5°; 2.5° in
and 5° out.
The two rib drills are mounted on rotary
actuators on the rear of the lifting platform. The
rotary actuator allows the rib drills to rotate
toward the rib 150° before it would contact the
side of the machine. They are mounted on the
platform’s centre assembly therefore they do not
move when the side platforms are extended. The
drill controls are mounted on the extending
platform to keep the operator under the drill
canopy. The platform is equipped with three
driller canopies; one centre canopy to cover the
two inner roof drill controls and one on each
outer extending platform to cover the outer roof
drill controls and the rib drill controls. The
platform is also equipped with an Automated
Temporary Roof Support (ATRS) and two drill
trays for storage.
The use of multiple drillheads dictated the
requirement for latched controls. This allows the
operator to start drilling one hole and then latch
the controls to be able to move on to the next. To
accomplish this, a unique hydraulic latch circuit
was developed to maintain operator safety and
compliance. The latched drilling system does not
replace the normal drilling controls; however it is
an enhancement to the existing system. This
design allows fewer operators to drill and install
roof and rib bolts, which in turn lowers the
miners’ exposure per cut. It reduces the
operator’s exposure from the inherent pinch
points and rotary hazards once latched drilling is
engaged. Therefore the machine will help to
decrease the time to bolt a cut, improving
productivity while enhancing the ability to
operate the machine safely.
The platform has been equipped with railings
and guards between the operator and drill rig.
Nevertheless, a small opening had to be left to
allow the operator access to install and remove
drill steels and bolts. The openings are small
enough so an operator could not fall through and
adjacent to each opening is a hydraulic
disconnect as well as