HOW BRICKS ARE MANUFACTURED? – ProCivilEngineer.com

brick building

Bricks are one of the oldest and most enduring building materials of mankind. Bricks are made by shaping a plastic mass of clay and water, which is then dried and hardened by fire. Till relatively recent times, clay was dug, bricks were made and kilns were set up or pulled by manual labor with the help of animal power. About 100 years ago, the first effective machines for brick production appeared, and the trend of mechanization of the tasks of conquering, forming and handling clay continues at an increasing pace today.

Brick is the simplest and most ancient of all building materials. Few other fabricated building units have enjoyed such widespread and continued popularity. This permanent public acceptance is based on the unique combination of the proper relationship bestowed by brick to owner and builder. This single material can be used to enclose a structure with a decorative, load-bearing wall that is exceptionally durable and, if built properly in the first place, requires practically no maintenance. is not needed.

Due to the versatility of the raw material, which can be easily molded into a large range of shapes and sizes, and the flexibility it gives to design and construction, construction in brick has been cost-effective.

Secondary clay materials are compounds of alumina, silica with minor amounts of lime, magnesia, soda or potash. Iron compounds, usually oxides, hydroxides or carbonates, are almost always present as impurities in brick clay, and they are responsible for the wide range of colors found in the finished product. Soils containing up to 3% iron oxide give a white to cream or buff color, which changes to pink and red as the iron oxide content increases between 8 and 10%. A range of brown and gray can be produced by adding manganese dioxide in a ratio of 1 to 4%.

More important than their chemical structure is the fact that:

  • When mixed with water, clay minerals give a plastic mass that can be shaped by pressure to form bricks;
  • At an economically practical temperature between 1,000° to 1 200° C, clay particles can be combined into a cohesive mass of great compressive strength;
  • Controlled evaporation of free water around the particles in plastic clay minimizes excessive shrinkage and defects in the brick structure.

Modern brick manufacturing involves high speed processing at extrusion rates of 25 000 bricks per hour. Conventional sized concrete bricks weigh 3 to 4 kg.

Steps Involved in Brick Manufacturing Process

1. Removal

Heavy earth-moving equipment such as bulldozers, scrapers and mechanical shovels are used to remove soil and shale.

2. Crushing and Blending

After being transported from the pit by truck or endless conveyor, the materials are stored to enable the blending of different types of soil.

Clay is fed separately to the primary crusher by hopper or conveyor. These reduce the particle size to 3 – 5 mm or less. The soil mix is ​​as follows to provide the desired proper bonding such as color and strength.

3. Grinding

Conveyors move the mixed soil away for secondary crushing, which is usually done through a pan mill. The pan mill consists of two heavy steel wheels mounted on a spindle that are connected to a central vertical axis around which they rotate, crushing the soil against the base of the pan.

The base is perforated to allow the crushed material to fall through. This process, when done with dry clay, breaks the brittle particles into smaller pieces. When a pan mill is used with wet clay, the plastic material is squeezed through the pores and then dropped between high-speed rollers that complete the grinding process.

4. Screening – Dry Processing

Before shaping, the soil is tested and the larger sized pieces are returned to the pan mill for further crushing.

5. Shaping

Bricks are made by hand, pressed or extruded to their final shape. The method used to shape bricks affects their final appearance and texture, and places some limitations on the operating methods employed during construction.

6. Extruded bricks (common method in South Africa)

Soil with a water content of 18-25% is pumped by an auger into a horizontal cone-shaped tube that dies down. Two compaction steps are usually involved, with a vacuum chamber between them to remove any air in the soil that would reduce the strength of the final product.

The extruded clay column is cut into brick-sized pieces by a wiring arrangement. Extruded bricks, although often smooth, can be mechanically patterned or textured. Most bricks of this type have anything from 3-12 pores, which increases the surface area, reducing the required drying, firing and cooling times. Any internal stress is released from the holes and prevents deformation of the bricks during firing.

7. Drying of Bricks

In the process of brick making, clay is refined and water is added to mold the brick. Before burning bricks, they must be properly dried: the moisture content must be reduced to 8% for a clamp kiln.


The bricks are sun dried, making full use of this free source of energy by placing the bricks on open hack lines. The disadvantage of this operation is that it can make the process time-consuming, especially during the rainy season.

To reduce the drying cycle, brick manufacturers have introduced some mechanical means of drying. The two most common methods are tunnel or chamber drying. The energy (heat) for drying is generated in a supplementary coal heater or recycled from the furnace and hot air is fed into the dryer. These methods work as follows:


  • tunnel drying machine: Bricks are produced and then offset on flat rail trolleys or kiln cars. Cars are pushed through the tunnel. From green to dry, this operation can take from 40 to 50 hours.
  • Chamber Dryer: Patented Chamber Dryers are large rooms where bricks are packed on pallets. The capacity of the chambers can be from 50,000 to 60,000 bricks. Hot air is filled in the chamber.

Drying times range between 30 and 45 hours – much faster than the 14 to 21 days required for solar drying.

8. Firing

Bricks are fired at temperatures between 1 000° and 1 200° C, depending on the clay. Light colored clays generally require a higher firing temperature than darker colored clays. Of the many known types of ceramic kilns, four common types are used:

1. Down draft kiln,

2. Hoffmann-type transverse arc slit (TVA),

3. tunnel kiln and


4. Clamp Kiln

However, down draft type kilns have been discontinued due to their uneconomical firing process (labour, coal etc.).

Down-draft kilns have a rectangular space with a barrel-vaulted ceiling and a slotted or perforated floor open at the bottom. Green bricks (40,000 to 100,000 at a time) are placed in the kiln. Fire is lit in fireboxes along the sides and hot gases are ignited up the vaulted ceiling, down through the bricks and from there to the chimney stacks. Fire is started by coal, gas or oil. When the desired temperature is reached, the temperature is maintained for a specified period and then the fire is allowed to die. The kiln cools down, the baked bricks are removed and another batch of green bricks are placed in the kiln for firing.

Firing continues in TVA kiln. Each day, the green bricks are placed in the cleaned chambers, in front of the fire and the burnt bricks are removed from behind it, leaving two or three adjacent wickets open for this purpose. When a chamber is full, the wicket is filled with brick and the fuel (coal, oil or gas) between the bricks is fed through a hole in the kiln crown or ceiling.

Every 2 to 4 hours in an average-sized kiln, the fire is made to move forward by dropping a row of fire holes in the front and a row at the back. In this way the fire revolves right around the kiln every 10 to 14 days. Hot gases from the firing zone are drawn forward to preheat and dry the green bricks, while the fired bricks are cooled by an air flow from open crickets behind the firing zone.


Tunnel kiln is also a continuous kiln, but the fire is stationary while the bricks run on the kiln cars. As in the TVA kiln, the unburned bricks are preheated by the spent combustion gases. After a fire, the heat released by the cooling bricks can be extracted for use in the respective dryer. With this exchange of heat, the tunnel kiln uses less fuel than the intermittent type of down-draft kiln. It has many more benefits. For example, cars can be loaded and unloaded in an open factory, and always at the same loading point, to simplify handling problems; And the kiln car acts as a conveyor belt so bricks are fired as they pass through the firing area.

In clamp kilns, some fuel is poured into the body of each brick. The bricks are packed in a pyramid-shaped structure. The clamp consists of a layer of coal, the equivalent of two courses of bricks, packed on the bottom. This layer is set on fire, it ignites the fuel in the base layer of bricks and, progressively, each brick in the pack burns.

Clamp kiln firing can take up to three weeks, and although the bricks may have finished burning in that time, it may take longer for them to cool down enough to be fired. The temperature in the center of the clamp can be as high as 1 400 °C.

Conclusion

Modern clay brick making is a capital intensive ceramic process that requires long-term planning sensitive to the cyclical nature of the building and construction industries.


Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.