Bricks manufacturing: Composition of good brick earth
Following are the constituents of good brick earth:
(1)Alumina: It is the chief constituent of every kind of clay. A good brick earth should contain about 20% to 30% of alumina. This constituent imparts plasticity to the earth so that it can be moulded. If alumina is present in excess, with inadequate quantity of sand, the raw brick shrink and warp during drying and burning and become too hard when burnt.
(2)Silica: It exists in clay either as free or combined. As free sand, it is mechanically mixed with clay and in combined form, it exists in chemical composition with alumina. A good brick earth should contain about 50% to 60 % of silica. The presence of this constituent prevents cracking, shrinking and warping of raw bricks. It thus imparts uniform shape to the bricks. The durability of bricks depends on the proper proportion of silica in brick earth. The excess of silica destroys the cohesion between particles and the bricks become brittle.
(3)Lime: A small quantity of lime not exceeding 5% is desirable in good brick earth. It should be present in a very finely powdered state. Lime prevents shrinkage of raw bricks.
(4)Iron: A small quantity of oxide of of iron to the extent of about 5% to 6% is desirable in good brick earth. It imparts red colour to the bricks. The excess of oxide of iron makes the bricks dark blue and blackish. If the quality of iron oxide is comparatively less, the bricks will be yellowish in colour.
(5)Magnesia: A small quantity of magnesia in brick earth imparts yellow tint to the bricks and decreases shrinkage. But excess of magnesia leads to the decay of bricks.
In the process of manufacturing bricks, the following four distinct operations are involved:
- Preparation of clay
- Moulding
- Drying
- Burning.
