Conversion of Illinois clays and shales into useful products is an
interesting process and is exemplified by the making of building bricks.
Mechanical shovels dig the clay or shale and load it into trucks or
small railroad cars that take it to the brick plant. There, machines
grind the raw material and mix water with it until it has the
consistency of stiff mud.
Next, a machine, which operates somewhat like a meat grinder, extrudes a
brick-sized column of clay. As the column moves forward, it is
automatically cut into bricks by wires. The bricks are then dried in
large heated rooms.
[Illustration: Figure 21—Beehive brick kiln.]
From the driers, the bricks go to huge ovens (kilns) and are heated
until they are hard and have attained the desired color. This is known
as firing or burning the bricks. Temperatures employed are rarely lower
than 1800° F.
Three kinds of kilns are used in Illinois for burning bricks—beehive,
tunnel, and scove. A beehive kiln (fig. 21) has a round base and a
dome-shaped top and somewhat resembles an oversized beehive. Unfired
bricks are stacked in the kiln and the doors are sealed with burned
bricks and clay. Fires are started in hearths or fire boxes in the wall
of the kiln and the heat is circulated into and through the kiln. It
usually takes several days to fire the bricks adequately and let the
kiln cool so that the bricks can be removed.
Tunnel kilns, made from heat-resistant bricks, are actually tunnels big
enough for a man to stand in. The unburned bricks are loaded on flat
steel cars on top of a layer of refractory blocks that protect the steel
from the heat. The cars enter the kiln and heating begins. As they move
through the kiln, they carry the bricks through a firing area, then
through a cooling zone, and finally out into the air.
In some brickyards in the Chicago area, dried unburned bricks are
carefully stacked by machines into piles about 17 feet high, 35 feet
wide, and 115 feet long, which are known as scoves or scove kilns. A
layer of burned bricks that is plastered with clay covers the sides of
the scove. A jet of flame is directed through small tunnels at the base
of the scove, and the heat fires the bricks.
During 1963, more than 325,000,000 bricks were produced by Illinois
brick plants. In the same year, the value of all the clay and clay
products produced in Illinois was nearly $54,000,000. Besides brick and
drain tile, the products of the clay and shale industry of Illinois
include refractory brick, building block and tile, fire-proofing, sewer
pipe, flue liners, stoneware, lightweight bloated burned clay aggregate
for concrete, and a variety of unburned clays for special purposes,
including bonding clay, refractory fireclays, absorbent for use on
garage floors, and litter for animal cages.