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FACE TO FACE WITH
ASPASA
MODERN QUARRYING
July - August 2015
31
a guaranteed method of boosting pro-
duction with benefits that extend from
the extraction of material to the stock-
pile, and the sale of graded products. The
workshop was addressed by none other
than Metso’s crushing specialist Alan
Fletcher.
Depending on the type of material
available at the quarry, the process of
sizing and shaping stone and aggregate
is usually undertaken with the use of a
series of crushers to break rocks into man-
ageable sizes until they confirm to the
required specification. Bottlenecks at any
of the steps along the process can have a
dramatic effect on overall production and
a negative effect on the profitability of the
quarry.
“The single most important aspect of
rock processing is safety and training of
all staff in the correct operation and pro-
cedures when operating heavy process-
ing equipment,” Fletcher says. “Thereafter
it is important to understand the types of
crushing processes required to manufac-
ture the products needed and procure the
right equipment to deliver the required
tonnages.
“Once we have established the type of
product and tonnages, we can build the
processing plant around those principals
and work out what type and how many
crushers are required. The typical plant
will have primary crushers at the first
stage (usually a jaw crusher), and then
materials will go to secondary crushing
(typically cone crushers) and on to tertiary
crushers if finer materials are required.
Quatenary crushing is sometimes used to
make materials finer still.”
He says that as a rule, it takes com-
paratively little energy to break big lumps
and considerably more for small stones
each time the particle is reduced further.
“That is precisely why plants need to be
designed for efficiency to work out the
correct pinch point to break the material
quickly and efficiently. It is also impor-
tant to keep running the plant efficiently
thereafter.”
Regular checks and clearing need to
be done especially on feeders, screens
and scalping screens. Even a 10% buildup
of materials on a screen can have a big
effect on efficiency as it will block 10%
of the material; in addition, it will recircu-
late missed material
and cause a buildup
that will further com-
pound the problem.
Screen size and strati-
fication also deter-
mines the amount of
material that is deliv-
ered to the crusher
and it is therefore
important that the
screen is correctly
specified to deliver
the correct tonnages.
“Users must know
that crushers need to
Aspasa believes the time has come for the
aggregate and sand industry to defineits
own sector with rules designed to protect
and promote companies and individuals
within the smaller mining sector.”
Specialist crushing guru Alan Fletcher.