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The
Manufacturing
Process
Process
The initial step in producing brick
is crushing and grinding the raw materials in a separator and a jaw crusher.
Next, the blend of ingredients desired for each particular batch is selected
and filtered before being sent on to one of three brick shaping
processes—extrusion, molding, or pressing, the first of which is the most
adaptable and thus the most common. Once the bricks are formed and any
subsequent procedures performed, they are dried to remove excess moisture that
might otherwise cause cracking during the ensuing firing process. Next, they
are fired in ovens and then cooled. Finally, they are dehacked—automatically
stacked, wrapped with steel bands, and padded with plastic corner protectors.
Grinding, sizing, and combining
raw materials
- 1 First, each of the ingredients is conveyed to a separator that removes oversize material. A jaw crusher with horizontal steel plates then squeezes the particles, rendering them still smaller. After the raw materials for each batch of bricks have been selected, a scalping screen is often used to separate the different sizes of material. Material of the correct size is sent to storage silos, and over-sized material goes to a hammermill, which pulverizes it with rapidly moving steel hammers. The hammermill uses another screen to control the maximum size of particle leaving the mill, and discharge goes to a number of vibrating screens that separate out material of improper size before it is sent on to the next phase of production.
Extrusion
- 2 With extrusion, the most common method of brick forming, pulverized material and water are fed into one end of a pug mill, which uses knives on a rotating shaft to cut through and fold together material in a shallow chamber. The blend is then fed into an extruder at the far end of the mill. The extruder usually consists of two chambers. The first removes air from the ground clay with a vacuum, thereby preventing cracking and other defects. The second chamber, a high-pressure cylinder, compacts the material so the auger can extrude it through the die. After it is compressed, the plastic material is forced out of the chamber though a specially shaped die orifice. The cross-section of the extruded column, called the "pug," is formed into the shape of the die. Sections of desired length are cut to size with rotating knives or stiff wires.
In molding, soft, wet clay is shaped in a mold,
usually a wooden box. The interior of the box is often coated with sand, which
provides the desired texture and facilitates removing the formed brick from the
mold. Water can also be used to assist release. Pressing, the third type of
brick forming, requires a material with low water content. The material is
placed in a die and then compacted with a steel plunger set at a desired
pressure. More regular in shape and sharper in outline than brick made with the
other two methods, pressed bricks also feature frogs.
Chamfering the brick
- 3 Chamfering machines were developed to produce a furrow in brick for such applications as paving. These machines use rollers to indent the brick as it is being extruded. They are sometimes equipped with wire cutters to do the chamfering and cutting in one step. Such machines can produce as many as 20,000 units per hour.
Coating
- 4 The choice of sand coating, also applied as the brick is extruded, depends on how soft or hard the extruded material is. A continuous, vibrating feeder is used to coat soft material, whereas for textured material the coating may have to be brushed or rolled on. For harder materials a pressure roller or compressed air is used, and, for extremely hard materials, sand blasting is required.
Drying
- 5 Before the brick is fired, it must be dried to remove excess moisture. If this moisture is not removed, the water will burn off too quickly during firing, causing cracking. Two types of dryers are used. Tunnel dryers use cars to move the brick through humidity-controlled zones that prevent cracking. They consist of a long chamber through which the ware is slowly pushed. External sources of fan-circulated hot air are forced into the dryer to speed the process.
- 6 Automatic chamber dryers are also used, especially in Europe. The extruded bricks are automatically placed in rows on two parallel bars. The bricks are then fed onto special racks with finger-like devices that hold several pairs of bars in multiple layers. These racks are then transferred by rail-mounted transfer cars or by lift trucks into the dryers.
Firing
- 7 After drying, the brick is loaded onto cars (usually automatically) and fired to
After forming and coating, the bricks are dried using
either tunnel dryers or automatic chamber dryers. Next, bricks are loaded onto cars
automatically and moved into large furnaces called tunnel kilns. Firing hardens
and strengthens the brick. After cooling, the bricks are set and packaged.
high temperatures in furnaces called kilns. In general, the
cars that moved the bricks through the drying process are also used to convey
them through the tunnel kiln. These cars are pushed through the kiln's
continuously maintained temperature zones at a specific rate that depends on
the material. The majority of kilns in the United States use gas as a fuel
source, though a third of the brick currently produced is fired using solid
fuels such as sawdust and coal. Tunnel kilns have changed in design from
high-load, narrow-width kilns to shorter, lower-set wider kilns that can fire
more brick. This type of design has also led to high-velocity, long-flame, and
low-temperature flame burners, which have improved temperature uniformity and
lowered fuel consumption.
Setting and packaging
- 8 After the brick is fired and cooled, it is unloaded from the kiln car via the dehacking process, which has been automated to the point where almost all manual brickhandling is eliminated. Automated setting machines have been developed that can set brick at rates of over 18,000 per hour and can rotate the brick 180 degrees. Usually set in rows eleven bricks wide, a stack is wrapped with steel bands and fitted with plastic strips that serve as corner protectors. The packaged brick is then shipped to the job site, where it is typically unloaded using boom trucks.
