May 2014
MODERN MINING
47
CRUSHING, SCREENING
AND MILLING
feature
shovel extraction, which – says MMD – proved
to be a significant economic improvement over
the traditional systems previously employed. A
typical three-tooth Series 1500 unit with twin
400 kW drives has an approximate mass of
160 tonnes.
Complementing its Mineral Sizers, MMD
has a range of heavy-duty apron plate feed-
ers to convey raw material to the crushing
plant. Available with an optional in-built
fines retrieval system, the main features of the
apron feeders are the heavy-duty rolled steel
flights, mounted on chains and rollers from the
Caterpillar range. The design of the feeders is
such that impact energy is reduced to a mini-
mum. The impact force is initially absorbed by
the conveyor plates, which, due to the method
of manufacture, can deform within their elastic
limits without damage. The impact rails then
transmit the forces which are dissipated into
the main frame construction.
Four feeders are available, designated the
D4, D7, D9 and D11, offering effective widths
from 1 500 mm to 4 000 mm. The advantage
of the use of rolled steel flights is that it is pos-
sible to ‘dump’ material onto an empty feeder
directly, a feature unique to MMD feeders,
which is an essential requirement for fully
mobile sizing systems.
The full range of MMD Mineral Sizers can
be incorporated into a wide range of mobility
options enabling them to operate as mobile
or semi-mobile units. Specifically, wheeled,
track modular, transportable modular and fully
mobile track-mounted options are offered. One
of MMD’s latest innovations is the 9 000 t/h
‘Low Profile Fully Mobile Sizer Station’ which,
it says, allows the flexibility of a mining shovel
to be matched with the cost effectiveness of
long distance conveyor haulage.
In a typical fully mobile application, the
Sizer Station would be positioned between the
mining bench and face conveyor, with the hop-
per on the Sizer Station being directly fed from
the face with run of mine material by a mining
shovel. Material is then drawn up the variable
speed MMD apron feeder and discharged into
the sizer, reducing the material to a definable
product size suitable for efficient long distance
conveyor haulage. Material is subsequently
discharged from the Sizer Station, via the dis-
charge conveyor and into a hopper car that
travels along the face conveyor. It then moves
onto an overland conveyor to the downstream
processes. The Sizer Station and the shovel
work together along the face length moving
frequently and are relocated to other benches
as the face line progresses.
Where the mining method does not provide
ideal conditions for a fully mobile system to
work efficiently, the use of a semi mobile sys-
tem gives some of the advantages of both a
truck and shovel operation and an in-pit sizing
operation. A modular Sizer Station consisting
of truck bridges, feeder module, sizer module
and sacrificial conveyor can be positioned in
the mine at an optimal position and be loaded
by a truck fleet travelling short distances to
the station. Once the trucking distance gets
beyond a certain point, the Sizer Station can
be relocated in a few days to a new location
closer to the mining area keeping trucking
distance to a minimum and optimising cost
savings while retaining the flexibility of a
truck and shovel operation.
Notable current or recent contracts secured
by MMD Africa include the supply of units
to Exxaro’s Leeuwpan opencast coal mine in
Mpumalanga, South Africa and ARM/Vale’s
new Lubambe underground copper mine on
the Zambian Copperbelt. Its flagship contract,
however, is definitely the supply of three semi-
mobile systems to Exxaro’s huge Grootegeluk
Medupi Expansion Project (GMEP) near
Lephalale in Limpopo Province to provide a
complete in-pit crushing solution. This con-
tract is ongoing with the first system up and
running and the second just installed. An inter-
esting aspect of the second station is that it was
assembled outside the pit and then transported
into the pit over a distance of over 5 km using
a transporter specially developed by MMD for
the purpose utilising several unique features
to enable the sizing station to be moved in the
shortest time.
Of course, the reliability of sizing instal-
lations is critical to mining operations since
the failure of these systems can bring a mine
to a complete halt. MMD recognises this and
prides itself on providing fast, efficient backup
throughout Africa to ensure that any downtime
is reduced to an absolute minimum, which is
why MMD provides a full service backup with
teams available 24 hours a day.
A trailer-mounted unit from
MMD.
MMD’s flagship
contract is the
supply of three
semi-mobile
systems to
Exxaro’s huge
Grootegeluk
Medupi
Expansion Project
(GMEP) near
Lephalale in
Limpopo Province
to provide a
complete in-pit
crushing solution.
