Manufacturing Of Clay Bricks(Part 1)
The manufacturing of clay bricks is carried out in a number of stages which are as follows:-
- Selection And Preparation Of Clay
Selection And Preparation Of Clay:-
First of all, suitable deposits of clay are first located and thoroughly tested for the quality of brick making. Then, the clay for bricks is prepared in the following order:-
- About 20 cm of the top layer of the soil is removed after clearing the trees and vegetation as it generally contains stones, pebbles, gravel, roots, etc.
- The soil used for making building bricks should be free of gravel, coarse sand( having particle size more than 2 mm), lime and kankar particles, organic matter, etc.
- After unsoiling, the proportion of additives such as fly ash, sandy loam, rice husk ash, stone dust, etc. should be spread over the plane ground surface on a volume basis.
- The soil mass is then dug out, puddled, watered and leftover for weathering and further processing.
- The digging operation should be done before rains.
- Stones, gravels, pebbles, roots, etc. are removed from the dug soil and it is heaped on level ground in layers of 60-120 cm.
- This soil is left in heaps and for at least one month it is exposed to the weather if weathering is considered necessary for the soil.
- It is done to develop homogeneity in the mass of soil, particularly if they are from different sources.
- It is also done to eliminate the impurities which get oxidized.
- To some extent, soluble salts in the clay also get eroded by rain which may otherwise cause scumming at the time of burning of the bricks in the kiln.
- The soil should be turned over at least twice and it should be ensured that the entire soil is wet throughout the period of weathering.
- Water may be sprayed in order to keep the soil wet as often as necessary.
- By exposing the soil to weather, the strength and plasticity of the clay are improved.
- To modify the composition of the soil, it is mixed with sandy-earth and calcareous-earth in suitable proportions.
- To obtain the right consistency for moulding, a moderate amount of water is mixed to the clay.
- The mass is mixed uniformly with spades.
- For easy mixing and workability, the addition of water to the soil at the dumps is necessary.
- The addition of water to the clay should be controlled in such a way that it may not create a problem in moulding and drying.
- The size and shape of the finished brick may get affected by excessive moisture.
- Tempering consists of kneading the earth with feet so as to make the mass stiff and plastic.
- In this stage, the clay is brought to a proper degree of hardness and it is made fit for moulding.
- It should preferably be carried out by storing the soil in a cool place in layers of about 30 cm thickness for not less than 36 hours as it will ensure the homogeneity in the mass of clay for further processing.
- For manufacturing good brick, tempering is done in pug mills and the operation is called pugging.
|Pug Mill(Image From Book By S.K. Duggal)|
- Steam, diesel or electric power may be used for the pugging operation in a pug mill.
- Blended clay along with required water, is fed into the pug from the top.
- The knives cut through the clay and break all the lumps of clay when the shaft rotates.
- The thoroughly pugged clay is then taken out from the opening which is provided in the side near the bottom.
- The yield from the pug mill is about 1500 bricks.
- It is a process of giving a required shape to the brick from the prepared clay.
- Moulding may be carried out by hand or by machines.
|Details Of A Mould(Image From Book By S.K. Duggal)|
- The process of moulding of bricks may be the hand moulding(soft-mud), the stiff-mud(machine moulding) or the dry-press process(moulding using a maximum of 10% water and forming bricks at higher pressure).
- The Soft-mud process is used to make fire bricks.
- The Dry-press method is used for making roofing, floor and wall tiles.
- The Stiff-mud process is used for making all the structural clay products.
Types of Moulding:-
Hand moulding is further divided into two types:-
- This method is adopted when a large and level land is available.
- The ground is levelled and sand is sprinkled on it.
- The bricks obtained from this moulding don't have a frog and their surface becomes too rough.
- Moulding blocks or boards are used at the base of the mould to overcome these defects.
- The process consists of shaping in hands a lump of well-pugged clay, slightly more than the size of the brick volume.
- It is then rolled into the sand and with a jerk, it is dashed into the mould.
- The moulder then gives blows with his fists and presses the clay properly in the corners of the mould with his thumb.
- The extra clay on the top surface is removed with a strike(sharp edge metal plate) or with a thin wire stretched over the mould which has to be dipped in water every time it is used.
|Wire Strike And WoodenStrike(Image From Book By S.K. Duggal)|
- After this, the mould is given a gentle slope and is lifted leaving the brick on the ground to dry.
- If the mould is dipped in water every time after use, such preparation of bricks is known as slope moulded bricks.
- If fine sand or ash is sprinkled on the inside surface of the mould every time after use, such preparation of bricks is called sand moulded bricks.
- The bricks are moulded on stock boards nailed on the moulding table.
|Moulding Table(Image From Book By S.K. Duggal)|
- Stock boards have the projection for forming the frog.
|Stock Board(Image From Book By S.K. Duggal)|
- The process of filling clay in the mould is the same as in the ground moulding process.
- After this, a thin board called pallet is placed over the mould.
- The mould containing the brick is then smartly lifted off the stock board and inverted so that the moulded clay along with the mould rests on the pallet.
- The mould is then removed in the same way as in the ground moulding and the brick is carried to the drying site.
- The cost of brick moulding increases when table moulding is adopted.
Machine moulding is further divided into two types:-
- It is a quick and economical method.
- The pugged, stiffer clay is forced through a rectangular opening of a brick size by means of an auger.
|Plastic Moulding(Image From Book By S.K. Duggal)|
- Clay comes out of the opening in the form of a bar.
- The bricks are cut by a frame which consists of several wires at a distance of brick size.
- These bricks are also known as wire-cut bricks.
- The moist and powdered clay is fed into the mould on a mechanically operated press.
- This clay in the mould is subjected to high pressure and takes the shape of bricks.
- The bricks obtained from this process are denser, smoother and uniform than the ordinary bricks.
- They are burnt carefully as they are likely to crack.
- These bricks are also known as pressed bricks.
For Manufacturing of Bricks (Part 2) kindly visit- https://www.akhandduttaengineering.in/2020/08/manufacturing-of-bricks-part-2.html
*Source- Internet, Books, Self-Analysis