Manufacturing Of Clay Bricks(Part 1)





Manufacturing Of Clay Bricks | Part 1 | Selection And Preparation Of Clay And Moulding | Bricks | Construction Materials | By Ashutosh Nautiyal
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 

  • Moulding

  • Drying 

  • Burning 




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:-


Unsoiling:-




  • 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.


Digging:-




  • 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.



Weathering:-




  • 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.



Blending:-




  • 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:-




  • 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.






Manufacturing Of Clay Bricks(Part 1) | Selection And Preparation Of Clay | Bricks | Construction Materials | By Ashutosh Nautiyal
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.





Moulding:-




  • 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.




Manufacturing Of Clay Bricks(Part 1) | Selection And Preparation Of Clay And Moulding | Bricks | Construction Materials | By Ashutosh Nautiyal
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:-



Hand moulding is further divided into two types:-


Ground moulding:-




  • 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.




Manufacturing Of Clay Bricks(Part 1) | Selection And Preparation Of Clay | Bricks | Construction Materials | By Ashutosh Nautiyal
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.



Table moulding



  • The bricks are moulded on stock boards nailed on the moulding table.




Manufacturing Of Clay Bricks(Part 1) | Selection And Preparation Of Clay | Bricks | Construction Materials | By Ashutosh Nautiyal
Moulding Table(Image From Book By S.K. Duggal)





  • Stock boards have the projection for forming the frog.




Manufacturing Of Clay Bricks(Part 1) | Selection And Preparation Of Clay | Bricks | Construction Materials | By Ashutosh Nautiyal
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:-



Machine moulding is further divided into two types:-


Plastic Method:-




  • 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.





Manufacturing Of Clay Bricks(Part 1) | Selection And Preparation Of Clay | Bricks | Construction Materials | By Ashutosh Nautiyal
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.



Dry-press Method:-

  


  • 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.









*Self Typed
*Source- Internet, Books, Self-Analysis