Learn : Hand moulding,ground moulding and machine moulding of bricks
MOULDING OF BRICKS
Hand moulding,ground moulding and machine moulding of bricks
Giving the required shape to the prepared brick-earth is known as moulding of bricks. There are two different ways of doing it: (i) Hand moulding, and (ii) Machine moulding.
1. Hand moulding .
Hand moulding of bricks is extensively used in India and the neighbouring countries. This could be done on ground or on table known respectively as Ground moulding and as Table moulding.
(a) Ground moulding.
This method is adopted when a large and level area of land is available for the purpose. The area of land on which moulding is to be done is levelled, plastered smooth and sprinkled over with sand.
(i) To prevent the moulded bricks from sticking to the moulds either sand is sprinkled on the inner sides of the mould or the mould is dipped in water each time before moulding is done. When sand is used to prevent the sticking of earth to moulds the moulded bricks are known as sand moulded and if the mould is dipped in water each time before moulding a brick then the bricks are known as slop moulded bricks. Sand moulded bricks have better finish sharper edges.
(ii) After either sprinkling sand on the inside of the mould or dipping the mould in water take a lump of well prepared earth, the volume of which is a little more than that of the brick. This lump is shaped in hands to the size and shape of the brick.
(iii) Now it is rolled in sand and with a jerk the lump is dashed into the mould rn such a manner that the mould is completely filled with earth. The moulder then gives blows with his fists and presses in the corners and edges with the thumbs.
(iv) The surplus soil is then scrapped off and the top surface levelled. A metal plate with a sharp edge, known as strike is used for removing the surplus soil. Generally a thin wire stretched on a frame is used for this purpose.
(v) After the brick has been moulded the mould is given a gentle stroke with something hard and the mould lifted leaving the brick to dry on the ground. The mould is placed nearby to mould another brick and the process is repeated.
Bricks moulded directly on the ground have their lower faces objectionably rough and can have no frog*. To avoid it bricks ear (*Frog is an indentation provided in a face of the brick. It may carry the trade mark of the manufacturer. Bricks are laid in masonry with frog up. Frog provides a key for the mortar and holds the bricks on top firmly in place) moulded on a block of wood known as the moulding block, having a projection 0.5 cm thick and of same length and breadth as the inside of the mould (Fig. 2.4).
In this case the mould should be made 0.5 cm deeper than the thickness of brick. The mould is so placed on the moulding block that it closely fits round the projection. The projected portion is protected by means of metallic strips. To provide frog or any other impression on the finished brick a corresponding raised projection is provided on the projection itself as is clear from the figure. The clay is then filled in the mould as explained before and the brick is moulded. Then a thin fiat board a little larger than the mould, known as the pallet, is placed on the mould containing the brick.
The moulder then lifts the mould containing the brick and sandwiched between the pallet and the moulding board, inverts it bringing the pallet below. He then removes the moulding board and the mould, leaving the brick on the pallet. Another pallet is then placed on the brick which is then carried between the two pallets to the drying site and laid on side. The next moulded brick is placed by its side and the process repeated. As the bricks in this method are not laid fiat for drying, as in moulding directly on the ground, but on sides so lesser space is required for drying in this method. The bricks dry better and quicker, and also the faces are all smooth.
In it the moulder carries out the moulding of bricks on a table. He does so while standing by the side of the table (Fig. 2.5).
He moulds bricks on boards known as stock boards; Stock boards are of the same size as the moulds and have a projection for the frog. Sand is sprinkled inside the mould and on the stock board. The mould is placed to fit the stock board and then filled with earth. Sufficient quantity of earth is dashed into the mould, pressed hard and the surplus earth is removed with a strike or a thin wire. A pallet is then placed on the mould. The mould containing the brick is then smartly lifted off the stock board and inverted so that the whole rests on the pallet. The mould is then given a gentle blow and lifted leaving the brick on the pallet. One more pallet is placed on the brick and it is carried to drying site between the two pallets. It is allowed to dry on side.
A moulder can mould between 500 to 1000 bricks per day.
2. Machine moulding.
There are a variety of moulding machines is used in the “West”. Description of even the simplest of them is beyond the scope of this book. However, Central Building Research Institute, Roorkee has developed a hand-operated brick moulding machine. Operational principle of these machines in brief is that after these have thoroughly pugged the soil and made a plastic mass of it then it is pushed under pressure through an opening whose length and breadth is equal to the length and breadth of the brick. This pushed out plastic band is cut to the desired thickness of bricks by wires fitted in a frame at distances equal to the brick’s thickness.
Such machines are common in “West” but are rarely used in India because of their initial high cost, cheap and plentiful availability of labour. These machines are capable of manufacturing large number of bricks quickly. Frog cannot the provided on machine moulded bricks.
3. Pressed bricks.
These bricks are used when they are required for brickwork of a high quality or for positions where they will be subjected to great pressures. There are made by subjecting most powdered clay to a great pressure of about 40 kg/sq cm. These bricks are stronger and are more compact than ordinary bricks. They do not require drying and can be burnt directly. They need careful burning otherwise they are likely to crack. These are heavier, stronger, more impervious, have sharp edges, regular and smooth external surfaces. These can be provided with clean and distinct frogs.