BRICKS

BY::

BHATT HETALIJARIWALA DEVANSHI

KELAWALA SHREYAKHANDELWAL AARTI

MASHRUWALA KALYANISHAH YASHRAJ

COMPOSITION OF GOOD BRICKS EARTH

HARMFULL INGREDIENTS IN BRICK EARTH

CLASSIFICATION OF BRICK EARTH

MANUFACTURE OF BRICKS

KILNS

Alumina:  A good brick earth should contain

20–30 per cent of alumina. It imparts the property of plasticity

to the earth. An excess of alumina causes

shrinkage and warping of bricks during drying and burning and it becomes too hard when burnt.

COMPOSITION OF GOOD BRICKS EARTH

Silica: 

Silica forms 50–60 per cent of good brick earth.

It is seen either in the free or combined state. In the free state, it is mechanically mixed with clay

and in the combined form it exists in a chemical composition with alumina.

The cracking, shrinking and warping of raw bricks are being prevented by the presence of silica.

The durability of bricks depends upon the proportion of silica.

An excess of silica destroys the cohesion between particles and the bricks become brittle. 

lime• A small quantity of lime not exceeding 5% is

desirable in good brick .lime prevents shrinkage of raw brick.

• the sand is infusible .but is slightly fuses at kiln temperature in presence of lime .the excess of lime cause the brick to melt and hence its shape is lost.

• the lumps of lime are converted into quick lime after burning this quick lime slakes and expand in presence of moisture such an action results in splitting of brick into pieces

OXIED OF IRON • A small quantity of oxide of iron

to the extent of about 5 to 6% is desirable in good bricks earth.

• It helps as lime to fuse sand .it also imparts red colour to bricks.

• the excess of oxide of iron makes the brick comparatively less, the brick will be yellowish in colour

MAGNESIA A small quantity of magnesia in brick

earth imparts yellow tint to the bricks and decreases shrinkage.

But excess of mangnesia leads to the decay of bricks.

ALKALIS: Alkalis present in the brick earth lower

the fusion temperature abnormally making the brick deform and twist. In addition, alkalis have hygroscopic properties.

They absorb water from atmosphere and make the walls damp resulting into unhealthy atmosphere and weaker structure.

HARMFULL INGREDIENTS IN BRICK EARTH

LIME : If these are present, as explained earlier,

on heating get converted into quick lime. This quick lime in the presence of water

is highly brittle and the brick crumbles.

IRON PYRITES If iron pyrites are present in bricks

earth ,the bricks are crystallized and disintegrated during burning because of the oxidation of the iron pyrites.

PEBBLES In the presence of these, there is

hindrance in molding the brick. In addition, the bricks cannot be cut to the

required size, if needed, while erecting the wall.

 

VEGETATION AND ORGANIC MATTER: Organic matters like roots, leaves etc.

burn while the brick is burnt producing CO2. This Carbon dioxide creates porosity in

bricks affecting the strength of bricks. Hence, organic matter should be avoided

in brick-earth.

The Brick Earth is Classified In Following 3 categories

Loamy, mild or sandy clay

Marls, chalky or Calcareous clay

Plastic, Strong or Pure clay

CLASSIFICATION OF BRICK EARTH

LOMAY, MILD OR SANDY CLAY

• The type of earth consist of considerable amount of free silica adding to alumina . The presence of sand helps in such clay helps to fuse sand and thereby to increase hardness of brick .

METRLS ,CHALLKY OR CALCAREOUS CLAY

• This clay consists of considerable amount of chalk in addition to aluminum and silica .such clay generally makes good bricks .but to avoid undesirable effects of excess lime, the sand is sometimes added to such clay.

Plastic ,strong or pure clay

• This clay consists of alumina and silica and it is sometimes refereed to as strong clay or fat clay. The raw bricks will crack, shrink and wrap during drying if pure clay alone is used I n making of bricks .hence such clay is corrected by the addition of sand and ash. the sand prevents shrinkage and the ash provides lime to act as flux.

As a practice suitable deposits of clay are first located and thouraly tested for the quality of brick making. Clay for bricks are made in following order :

MANUFACTURE OF BRICKS

PREPRATION OF CLAY

MODULING

DRYING

BURNING

MANUFACTURE OF BRICKS

UNSPOLING

DIGGING

CLEANING

PREPARTION OF CLAY

WEATHERING

BLENDING

TEMPERING

A. UNSOILING: the top layer of the soil is taken out. This is

because the clay in the top layer is full of impurities and hence is tob rejected for the purpose of preparing bricks.

B. DIGGING : The clay which is dug out is spread on a

ground level, just little dipper than general ground

level. The height of the heap of the clay is about

60-120cm C. CLEANING: The clay should be made clean from pebbles,

stones and vegetable matter. if these particles are in access the clay should be washed and screneed, which is considered to be uneconomical.

D. WEATHERING: The softening of clay is done by exposing it in

the atmosphere. The period of exposure varies from weeks to full seasons.

E. BLENDING: The clay is made losseand any ingredient to be

added is spread out as its top. Blending indicates intimae mixing. A small portion is taken out everytime for mixing.

F. TEMPERING: In this stage the clay is brought to a proper degree

of hardness and is made fit for moulding. Water in required quantity is added and the whole mass is mixed so as to form a mass of unifom character. a large scale tempering is usually done in a pug mill. The process of grinding clay with water and making it plastic is known as pugging.

PUG MILL

Moulding is the process of making rectangular shaped units for properly tempered clay. The 2 types of moulding are:

Hand moulding Machine moulding

Hand moulding: This is presently the most common method for

brick manufacture. this is adopted where man power is cheap and readily available. the moulds used for hand moulding are rectangular boxes made from well seasoned wood or stellopen at the top and bottom.

MOULDING

TYPES OF HAND MOULDING :

1. Ground moulding 2. Table moulding  GROUND MOULDING IN the method the ground is first levelled and fine sand is sprinkled

over it. 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 concerns of the mould. any surplus earth from the top of the mould is removed using cutting wire or metal.

the same mould can b used for othre also so that wastage is avoided.

TABLE MOULDING The process of operations are carried out on a specially designed

moulding tabel. the clay , the mould, water pots, stock board, etc are placed on this tabel. the bricks are moulded similar to the ground moulding on the table. the cost of brick increase when table moulding is adopted.

 

MACHINE MOULDING the moulding can also be achieved by using machines. it is quiet

economical when bricks are produced in huge amount. this moulding is classified into two categories.

1 plastic clay machine 2 dry clay machine

PLASTIC CLAY MACHINE the machines containing regular opening of size equal to the

length and width of brick. the pugged clay is placed in th machine ans as it comes out through the openings it is cut into strips by wires fixed into frames. so it is known as " WIRE CUT BRICK. "

  DRY CLAY MACHINE In this machine , the strong clay is first converted to powder form.

a small quantity of water is added to stiff plastic paste. such paste is placed in mould and pressed by machine to form well shaped hard brick. this bricks are known as " PRESSED BRICK"

  this machine mould bricks have regular size , shape , edges and

corners ; they are heavier and stronger than hand moulded bricks.

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, for drying the bricks are laid to longitudinally in stock of bricks with width equal to two bricks.

The important facts to be remembered while drying bricks are as follow…

DRYING

a) The bricks are generally dried by natural Process, but when bricks are to be rapidly dried, the artificial drying may be adopted. In artificial drying, bricks are made to pass through driers in the form of tunnels or hot channels or floors.

b) The brick in stocks should e arranged in such a way that sufficient air space is left between them for circulation air.

c) The period of drying bricks is depend on the prevailing of weather condition.

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

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

Vitrification is an extreme reaction and occurs when heating is carried out beyond 900 degree Celsius.

BURNING

The shape of he clamp is generally trapezoidal.The brick is constructed on the short end and a layer of fuel is placed on the prepared floor.The fuel genereally used are cow dung,litter,husk of rice,coal,wood,etc.the thickness of the fuel layer varies from 70 to 80cm.The layer consisting of 4 to 5 course of raw bricks is then put up.Sufficient space for air circulation is provided.

the clamp is then allowed to burn for 1 or 2 month and cooling is also done for 2 months and later the burnt bricks are taken out.

CLAMPS

The kilns used for manufacture of bricks are of two types:- Intermittent kilns Continuous kilns

Intermittent kilns

These kilns can be underground or overground in the model.They are classified in two ways:-

• Intermittent up-draught kiln-these kilns are in the form of rectangular structure with thick walls outside.Doors are provided at each end for loading and unloading of kilns.he flues ate channel or passage which are provided to carry flames or hot gases through the body of kiln.

• A roof is prvided to protect the raw bricks from rain.The quality of bricks is not uniform.The brick at the bottom are overburnt and at the top ate underburnt.

KILNS

These kilns are rectangular or circular in shape.They are provided with permanent walls and a closed tight roof.The floor of the kilns have opening which are connected to a common chimney stacked through flues.

Intermittent down-draught kiln

These kilns are continuous in operation where loading,firing,cooling and unloading are simultaneously carried out.

bull’s trench kiln

Continuous kiln

This is a continuous type of kiln.These kilns are circular,rectangular or oval in shape In plan.These kilns are constructed in trench excavated on the ground.It may fully underground or partially projecting above the ground.The outer and the inner walls are to be consructed in bricks

These kiln is constructed underground,is circulaer in plan and consist of number of chambers.A permanent roof is provided so that the kilns can function even in the rainy season.

tunnel kiln

This type of kiln is in the form of tunnel,which is oval,circular or straight in plan.it contains stationary soruce of fire.The raw bricks are placed in trolley which are then moved from one end to another end of the tunnel.

Hoffmann kiln