manufacturing of bricks

Manufacture of bricks:

In the manufacturing of bricks, the following operations are involved.

Operations involved in manufacturing of clay bricks

The processes involved in the manufacturing of bricks are as follows

1.   Preparation of clay

2.   Moulding

3.   Drying

4.   Burning

1.   Preparation of clay: The clay for bricks is prepared in the following order

(i)                         Unsoiling: The top layer of soil, about 200mm in depth, is taken out and thrown away. The clay in top soil is full of impurities and hence it is to be rejected for the purpose of preparation bricks.

(ii)                           Digging: The clay is then dug out from the ground. It is spread on the leveled ground. The height of heaps of clay is about 600 to 1200mm.

(iii)                      Cleaning: The clay obtained in the process of digging should be cleaned of stones, pebbles, vegetable matter etc. I f these particles are in excess then the clay is to be washed and screened. The lumps of clay should be converted into the powder form in the earth crushing roller.

(iv)                    Weathering: The clay is then exposed to atmosphere for softening. The period of exposure varies from few weeks to full season.

   

(v)                          Blending: The clay is made loose and any ingredient to be added to it, is spread out its top. It is carried out by taking small portion of clay every time and turning it up and down in vertical direction.

(vi)                       Tempering: In the process of tempering, the clay is brought to a proper degree of hardness and it is made fit for the next operation of moulding. The water in required quantity is added to clay and the whole mass is pressed under two feet of men or cattle. The tempering should be done to obtain homogeneous mass of clay of uniform character. For manufacturing good bricks on a large scale the tempering usually done in a pug mill.

2.   Moulding:

There are two types of moulding

(i)                  Hand moulding

(ii)                Machine moulding

(i)   Hand moulding: In hand moulding the bricks are moulded by hand i.e. manually. It is adopted where manpower is cheap and is readily available for the manufacturing process of bricks on a small scale.

The moulds are rectangular boxes which are open at top and bottom and it is made of may be wood or steel.

The bricks prepared by hand moulding are of two types:

(a)  Ground-moulded bricks

(b)  Table-moulded bricks

(a)   Ground-moulded bricks

The ground on which the bricks are to be moulded is cleaned & leveled. Over the leveled surface dry sand is sprinkled. Then the mould is dipped in water and placed over the ground. The clay is pressed in the mould in such a way that it fills all the corners of the mould. Any surplus earth from the top of the mould is removed using a cutting wire or with a metal with sharp edge, which has to be dipped in water every time it is used. The mould is then lifted up and the brick is left on the ground. If the mould is dipped in water every time, such preparation of bricks is known as slope moulded bricks. If fine sand or ash is sprinkled on the inside surface of the mould instead of dipping the mould in water, such bricks are called sand moulded bricks.

(b)    Table moulded bricks

The process of moulding operations is carried out on a specially designed moulding table. The clay, mould, water pots, stock board etc. are placed on the table. The bricks are moulded similar to the ground moulding on the table.

(ii)   Machine moulding

The moulding can also be achieved by using machines. It is quite economical when bricks are produced in huge amounts. The machine moulding is broadly classified into two categories:

(a)     Plastic clay machines

(b)    Dry clay machines

(a)    Plastic clay machines

The machines contain rectangular openings of size equal to the length and width of a brick. The pugged clay is placed in the machine and as it comes out through the openings it is cut into strips by wires fixed in frames. Hence, it is known as wire cut bricks.

(b)    Dry clay machines

In this machine, the strong clay is first converted to powder form. A small quantity of water is added to the stiff plastic paste. Such paste is placed in the mould and pressed by machines to form well shaped hard bricks. These bricks are known as pressed bricks. The machine moulded bricks have regular shape, sharp edges and corners; they are heavier and stronger than hand moulded bricks.

3.   Drying:

The drying of bricks is necessary, firstly to make them strong enough for rough handling during subsequent stages and secondly to save fuel during burning. It can be achieved by either natural or artificial methods. The bricks are generally dried by natural process. But when bricks are to be rapidly dried, artificial drying may be adopted. The bricks in stocks should be arranged in such a way that sufficient air space is left between them for circulation of air.

4.   Burning:

Burning of dried bricks is essential to develop the desired engineering properties like hardness, durability and resistance to decay. Three chemical changes are known to takes place in the brick earth during burning, namely dehydration, oxidation and vitrification.

Dehydration is completed within 425-750^oC temperature range and it results expulsion of most of the water from bricks.

During oxidation carbon and sulphur are eliminated as oxides, whereas the fluxes are also oxidized. Oxidation starts at the range of dehydration temperature and is completed at about 900°C.

Vitrification is the extreme reaction and occurs when heating is carried out beyond 900°C. This is commonly not required in building bricks but it is necessary in sewer pipes.

Burning of bricks is either done in clamps and kilns. Clamps are temporary structures while kilns are permanent structures. Clamps are adopted to manufacture bricks on a small scale while kilns  are adopted to manufacture bricks on a large scale.

** basic civil engineering notes for bput students.