Manufacturing process of Bricks.

Manufacturing of clay bricks:

The following four distinct operations are involved in the process of manufacturing of bricks,:

Preparation of clay / Brick earth
Moulding
Drying
Burnin 1. Preparation of clay l brickcarth

1. Preparation of clay l brickcarth :

It consists of the following operations:

a) Un- soiling:

Un-soiling: The soil used for making building bricks should be processed and to be made free from gravel, sand (> 2 mm ); lime and kankar particles, organic matter, etc.
About 200 mm of the top layerof the earth, normally containing stones. pebbles, gravels, plant roots are removedafter clearing the trees and vegetation etc.

b) Digging

* After removing, the top layer of, the earth,proportions of additives:such as fly ash, sandy loam, rice husk ash, stone dust, etc. should be spread over the plane ground surface on volume basis.

* The soil mass is then manually excavated, puddled, watered and left over for veathering and subsequent processing. The digging operation should be done beforerains.

c)Weathering:

Stones, gravels, pebbles, roots, etc. are removed from the dug earth and the soil is heaped on level ground in layers of 60-120cm.
The soil is left in heaps and exposed to weather. This is done to develop homogeneity in the mass of soil;particularly if they are from dierent sources, and also to eliminate the impurities which get oxidized.
Soluble salts in the clay would also be eroded by rain to some extent, which othenwise could have caused scumming at the time of burning of the bricks in the kiln. The soil should be turned over at ieast twice and it should be ensurcd that the entire soil is wet throughout the period of weathering
In order to keep it wet, water may be sprayed as often as necessary. The plasticity and strength �f the clay 2re improved by exposing the clay to weather.

d) Blending :

After weathering the eath is ten smiud with sandy-earth and calcareous-carth in suitable proportions to modity ihe cemposition of soil.
Moderate amount of watc: is mixed so as to obtain the right consistency for moulding. The mass is then mixed unifoaiy with spades.
Addition of water to the soil at the dumps is necessary for the easy mixing and workability, but the addition of water should be controlled in such a way that it may not create a problem in moulding and drying. Excessive moisture content may affect the size and shape of the finished brick.

e) Plugging:

Tempering consists of kne�ding the earth with feet so as to make the mass stiff and plastic without cracking .
It should preferably b� carried out by storing the soil in a cool place in layers of about 30 cm thickness for not less than 36 hours. This will ensure homogeneity in the mass of clay for subsequent processing.
For manufacturing good brick, tempering is. done in pugmills and the operation is called puigging.

f) Moulding :

It is a process of giving a required, shape to the brick from the prepared brick earth and moulding may be carried out by, hand or by machines.
The process of moulding of bricks may be eitherby hand moulding in case of soft clays, machine moulding if it is the stif-miud or the dry pressprocess (moulding using maximum-10 per cent water and forming bricks at highet pressures).
In hand moulding process, the bricks are mouldedby hand manually. It is adoptedwhere man poweris cheapand for producing a amall quantityof bricks. A typical wooden mould should b� prepared from well seasoned wood for making bricks. The longer sides are kept slightly. pr�jecting to serve as handles. The strips of brass or steel are sometimes fixed on the edges of wooden ioulds to make them more durable.
The steel mould can also be prepar�dfrom steel angles and plates. The thickriess of steel mould is generally 6.mm.
The machine moulding may be achieved by machines: It proves to be economical when bricks in huge quantity are to be manufactured at the same spot in a short time.
Hand moulding is f�rther cla_sified as ground moulding and table moulding.
In ground moulding proces, the ground is leveled and sand is sprinkled on it: The moulded bricks are left on the� ground for drying. Such bricka do not have frog and the. lower brick surface becomes too rough, To overcome these defects, moulding blocks or boards are used at the base of tie mould.
In case of table moulded bricks, the bYicks �re moulded on stock boards nailed on the moulding table Stock boards h�ve the projection for forming the frog. The process of filling clay in the mould is the same as explained above. After this, a thin board called pallet is placed over the mould:The mould containing the brick is then smartly lifted off the stock bord and inverted so that the moulded clay al�ng with the mould rests on the pallet. The mould is then removed as explained before and the brick is carried to the drying site.

g) Drying :

→ The damp bricks, if burnt, are likely to be cracked and distorted. Hence moulded bricks are dried before they are taken for the next operation of burning. Bricks are laid along and across the stock in alternate layers.

The drying of brick is by the following means (i) ArtificiaBdrying-

drying by tunnels usually 1200C about 1, to 3 days .

(ii) Circulation of air- Stacks are arranged in such a way that sufficient air space is left i. between them free circulation of air.

(iii) Drying yard- special yards should be preparedslightlyhigher level prevent the accumulation of rain water.

(iv) Period for drying- usually about 3 to 10 daysto bricks to becomedry .

(v) Screens-screens are necessary, may be provided tg avoid direct exposure to wind or sun.

* For drying, the briks are laid longitudinally in stacks. The brieks in stacks should .be arranged in such a way that sufficient air space is left between then. The bricks should be allowed to dry till they become hard,or the moisture content is brought down to about 3% under exposed conditions within 3 to 4 days.

* For the drying purpose, Drying yards should b� prepared: The Drying yards should be. slightly on a higher level and it is desirable to cover it with sand. Such an arrang�ment would prevent the accumulation of rain water.

h) Burning:

This is a veiy important operation in the manufacture of bricks.

→ The burning of clay may be divided under three main stages.

1. Dehydration

2. Oxidation Period

3. Vitrification

Burning of bricks is done either in clamps or in kilns.

- Clamps �re temporary structures and they ar� adopted to manufacture bricks on small scale.

- Kilns are permanent structures, and they are adopted to manufacture bricks on a large scale.