The basic concept of brick kiln technology in developing countries has changed little over the past thousands of years. Brick making is an ancient technology.
Bricks are made, dried, fired and cooled.
Kilns first started in pits, walls were then added. The addition of a chimney stack, improved the air flow or draught of the kiln, thus burning the fuel more completely. Several variations have been invented over the years with varying degrees of efficiency and cost.
Brick kilns fall into one, or both, of the following categories: Intermittent or Continuous
Intermittent: Kilns are sealed and the internal temperature is increased according to a schedule. After the firing process is complete, both the kiln and bricks are cooled. The kiln is left to cool sufficiently before the bricks can be removed. Due to the relative ease of this method of firing and these are the kiln types primarily used in developing countries.
Continuous: two types of continuous kilns: The bricks are moved through a stationary fire zone, like a train in a tunnel (Tunnel kiln), or the bricks remain stationary and the fire moves through the kiln with the assistance or help of a chimney or suction fan (Habla Zig-Zag Kiln, Hoffman, FCBTK, Metal Chimney and Bulls Trench).
The main difference is that the tunnel kiln is vastly more expensive to build however, it saves on labour costs and can be highly automated, bricks can be made and fired without being touched by human hands. The kiln requires highly skilled labour and a guaranteed electricity supply.
Brick making consists of the following processes:
|Winning||Digging for clay|
|Preparation||Preparing the clay for shaping|
|Shaping||Moulded using various mould types and methods, by hand or by machine|
|Drying||Open air, hot floor, chamber, tunnel, etc|
|Firing||Various kiln methods, including Bull’s Trench, Clamp, Habla, Hoffman, Tunnel etc.|
|Quality Control||Sorted into grades, e.g. firsts, seconds, soft (re-fire)|
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