BENEFICIATION
with different hole sizes for the clay to fall
through. It thereafter goes through a mixer
where water is added, and the extrusion
process.
The plant uses brick-making equipment
from French company Ceric; the handling
equipment from Australian firm JC Smale;
while the extrusion equipment for the
shaping of the clay is supplied by JC Steele
and German firm Keller.
After the clay is mined on site at
Corobrik’s adjacent quarry, it is crushed,
reduced to fines, mixed with water, shaped
into a solid rectangular slug and cut into
bricks. Von Wielligh explains how the wet
bricks cannot be placed into the furnace, as
they would explode – hence, they are placed
in the tunnel dryer for about three days to
remove the moisture.
Corobrik Midrand factory manager Heinrich von Wielligh.
“The bricks ideally have
a fairly high quantity of
carbonaceous material
in them as these
give face bricks their
characteristic spots.”
The bricks ideally have a fairly high
quantity of carbonaceous material in
them as these give face bricks their
characteristic spots. Von Wielligh
explains that bricks are packed one on top
of the other on the kiln car as they move
through the kiln tunnel at a consistent
firing rate. The outsides of the bricks are
exposed to adequate oxygen to burn off
the black carbonaceous material, giving
an unblemished surface, but where the
bricks are touching the carbon cannot
burn off, leaving the characteristic and
aesthetic black spots and marks. “The
black spots are the iron that has been
reduced but not completely burned off. It
is only on the surface because the holes
in the brick structure allow the heat to
penetrate right through.
The bricks travel on the cars through the
130m kiln and are exposed to progressively
higher temperatures within the firing zone
until they reach the soaking zone, which can
reach up to 1 100°C – the kiln’s maximum
temperature. After being in the soaking zone
for about eight hours, the bricks gradually
cool down for another day before they reach
34_QUARRY SA| JULY/AUGUST 2019
Wet cut bricks being machine loaded onto kiln cars.
the exit mouth of the kiln. Von Wielligh
says manufacturing these bricks from raw
material takes about seven days.
Von Wielligh notes that energy apart,
another possibility for improving efficiency
is to improve the clay bricks’ receptiveness
to heat, which can be achieved by amending
the clay recipes.
Corobrik has also improved its brick-
drying capabilities, as improving the
efficiency of a dryer essentially means that
water is removed from the clay as efficiently
as possible. Von Wielligh explains that the
drying process is made more efficient by
increasing the amount of air-flow in the
dryer, making the air warmer and enabling
the dryer to accommodate air that is slightly
more humid.
Another efficiency is using gas to fire
the kiln. A number of brick manufacturers
are located in the area precisely to take
advantage of Sasol’s natural gas pipe from
Mozambique, which is more effective than
electricity or other forms of hydrogen-rich
gas. Corobrik manufacturing changed
some years ago to include more holes,
thereby increasing the surface area of
the brick, resulting in more even heat-
distribution and airflow in the kiln, as well
as a lighter brick.
Challenges
“Today, our challenge is to persuade
specifiers of the vastly lower long-
term maintenance costs of face bricks.
Architectural and quantity surveyor
courses unfortunately teach little about
bricks, and we try to educate them as
much as possible. Face bricks are also the
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