May 2014
MODERN MINING
45
CRUSHING, SCREENING
AND MILLING
feature
sizing solutions
Top:
The full range of
MMD Mineral Sizers can be
incorporated into a wide
range of mobility options.
Seen here is an MMD semi-
mobile station.
Above:
A fully mobile
tracked MMD station. In the
right applications the fully
mobile system can eliminate
the high cost of running a
truck fleet.
Initially, the material is gripped by the lead-
ing faces of opposed rotor teeth. These subject
the rock to multiple point loading, inducing
stress into the material to exploit any natu-
ral weaknesses. At the second stage, material
is broken in tension by being subjected to a
three-point loading, applied between the front
tooth faces on one rotor, and rear tooth faces
on the other rotor. Any lumps of material that
still remain oversize are broken as the rotors
chop through the fixed teeth of the breaker bar,
thereby achieving a three-dimensional con-
trolled product.
A major advantage of the MMD Mineral
Sizer is its compact size, which has obvious
benefits (particularly in underground mines
where space is often constrained). Based on
a medium/hard feed, a jaw crusher able to
handle 1 000 t/h would typically come in at
around 170 tonnes in weight and a gyratory
crusher at 120 tonnes. By contrast, an equiva-
lent Mineral Sizer would have a mass of just
60 tonnes, says MMD. Also the way a Mineral
Sizer processes minerals means that heavy
foundations are not needed and supporting
structures are substantially less than those
required for gyratory and jaw crushers, result-
ing in reduced capex and faster installation.
Another advantage of the MMD Mineral
Sizer is its ability to process not just hard, dry
rock but also wet, sticky material which tends
to cause problems for traditional crushers,
allowing year round production. In addition,
the breaking principle which takes advantage
of the natural fracture planes by breaking in
tension and shear produces fewer fines than
crushers that work against the compressive
strength of the ore; this principle also requires
much less energy to process material as gen-
erally ore is ten times weaker in tension and
shear than it is in compression.
The original Mineral Sizer developed by
MMD was specifically designed to work in the
confined space of underground coal mines and
was able to handle tonnages of up to approxi-
mately 1 500 t/h. Building on the success of this
original 500 Series machine, MMD developed
a range of sizers from the original 625 Series.
These are the 750, 850, 1000 1150, 1300, 1500
Series all currently in use with a 1650 sizer
available, which is capable of handling material
up to 3 m
3
at a capacity of more than 15 000 t/h.
Depending on the sizer shaft centres, machines
can be configured for primary, secondary or ter-
tiary crushing and all can be customised to the
client’s requirements.
The 1500 Series was first supplied to oper-
ate within the oil sands industry in Canada to
facilitate the switch to short haul truck and
